Enhancement of proportional solenoid valve to manage variable displacement oil pump

Universidade do Minho Escola de Engenharia Francisco Manuel Mendes Gomes Enhancement of proportional solenoid valve to manage variable displacement oil pump. Maio de 2024 Universidade do Minho Escola de Engenharia Francisco Manuel Mendes Gomes Enhancement of proportional solenoid valve to manage variable displacement oil pump. Dissertação de Mestrado Integrado em Engenharia Mecânica Trabalho efetuado sob a orientação dos Professor Doutor Jorge José Gomes Martins Professor Doutor Francisco Carrusca Pimenta de Brito Maio de 2024 ii DIREITOS DE AUTOR E CONDIÇÕES DE UTILIZAÇÃO DO TRABALHO POR TERCEIROS Este é um trabalho académico que pode ser utilizado por terceiros desde que respeitadas as regras e boas práticas internacionalmente aceites, no que concerne aos direitos de autor e direitos conexos. Assim, o presente trabalho pode ser utilizado nos termos previstos na licença abaixo indicada. Caso o utilizador necessite de permissão para poder fazer um uso do trabalho em condições não previstas no licenciamento indicado, deverá contactar o autor, através do RepositóriUM da Universidade do Minho. Atribuição-NãoComercial CC BY-NC https://creativecommons.org/licenses/by-nc/4.0/ iii AGRADECIMENTOS Ao professor doutor Jorge Martins e ao professor doutor Francisco Brito pela orientação do trabalho, pelos esclarecimentos e pelas correções necessárias. À Bontaz Portugal pela oportunidade de realizar o estágio e pelas ótimas condições oferecidas para a sua realização. Ao meu orientador na Bontaz, engenheiro André Santos, pela disponibilidade e ajuda valiosas à minha adaptação e ao desenvolvimento das atividades no âmbito do meu estágio. A cada membro da equipa de R&D da BCTP que contribuiu com um enorme apoio ao longo do trabalho, seja em discussão de ideias, ajuda técnica, integração e convívio, e por me transmitirem a vontade de aprender sempre mais. Aos técnicos António Malheiro e Pedro Correia, pela paciência louvável e auxílio na componente prática, imprescindível à realização deste trabalho. Ao engenheiro Tomé Barreiro, pela importante contribuição no âmbito da conceção do modelo de simulação e compreensão do sistema em estudo. Aos meus pais, por me darem as condições para chegar até aqui e me ajudarem desde o princípio. À minha irmã, por me acompanhar e apoiar sempre de perto, independentemente da distância. Ao meu avô, a quem devo grande parte do meu conhecimento prático, e à minha avó, por me apoiarem desde sempre. À minha restante família, pelo apoio em todos os momentos. À Margareida, pela companhia e motivação que tornam o dia a dia mais fácil. Aos meus amigos, pelo companheirismo e interajuda indispensáveis ao longo destes anos, que hoje fazem também parte de quem eu sou. iv STATEMENT OF INTEGRITY I hereby declare having conducted this academic work with integrity. I confirm that I have not used plagiarism or any form of undue use of information or falsification of results along the process leading to its elaboration. I further declare that I have fully acknowledged the Code of Ethical Conduct of the University of Minho. v ABSTRACT The present work was done within BONTAZ – BCTP Equipamento Automóvel with the aim of optimising a solenoid valve used to manage an automotive variable displacement oil pump (VDOP). The system works by using the solenoid valve to hydraulically regulate the pump to provide less oil flow, lowering its engine torque demand, thus reducing fuel consumption and emissions. The product in question has been facing problems during customer end of line (EoL) tests, regarding oscillation in the engine oil pump’s output pressure, resulting in a percentage of the parts being considered not OK (NOK). To avoid reproducing the issue in the newer generation of the solenoid valve, this work serves as a tool to understand the problem faced by the customer and take corrective measures. Firstly, a revision of the literature was carried out, in order to accurately describe the functioning of oil pumps, and more specifically variable displacement types. Additionally, the functions of different types of solenoid valves and their control systems were enumerated. Secondly, the methodology followed in the execution of the work was established, starting from a brief description of the system in study, followed by a product and process analysis, where the documents related to production of the solenoid valve are presented. There is an explanation of the functional tests employed on the solenoid valves, as well as the test benches where these were done, along with the software used to analyse the performance curves. Some changes had to be done to the pump test bench, which are also shown. From a problem-solving point of view, quality tools such as an Ishikawa diagram and the evaluation matrix were applied in order to provide a well-guided approach to the problem and assist in finding the root cause. The tests and analysis done were based on the possibilities presented here, which were gathered from the research and brainstorming within the Bontaz Portugal R&D team. Furthermore, the present work provided Bontaz with the tools to create a simulation model of a solenoid valve operated variable displacement vane oil pump, which can be used to develop new products and foster internal knowledge on VDOP systems. Lastly, the experimental results from the different tests are presented and discussed. KEYWORDS Ishikawa; Proportional hydraulic solenoid valve; Root cause analysis; Variable displacement oil pump. vi RESUMO O presente trabalho foi desenvolvido na BONTAZ – BCTP Equipamento Automóvel, com o objetivo de otimizar uma electroválvula utilizada para gerir uma bomba de óleo de caudal variável para automóvel. O sistema funciona através da utilização duma electroválvula para regular hidraulicamente a bomba para fornecer menos caudal, reduzindo o seu consumo de binário e, por isso, reduzindo consumo de combustível e emissões. O produto em causa tem enfrentado problemas durante os testes End of Line (EoL) do cliente, relacionados com oscilação da pressão de descarga da bomba, o que resulta numa percentagem das peças serem consideradas não OK (NOK). Para evitar reprodução deste problema na nova geração da electroválvula a ser desenvolvida, este trabalho serve de ferramenta para a compreensão do problema encontrado pelo cliente e para tomar ações corretivas. Em primeiro lugar, é feita uma revisão à literatura, de forma a descrever o funcionamento de bombas de óleo e, mais especificamente, dos tipos de caudal variável. Adicionalmente, as funções de diferentes tipos de electroválvulas e os seus sistemas de controlo são enumerados. De seguida, a metodologia seguida na execução do trabalho é estabelecida, começando por uma breve descrição do sistema em estudo, seguida duma análise de produto e projeto, em que os documentos relacionados com a produção da electroválvula são apresentados. São explicados os testes funcionais feitos às electroválvulas, bem como os bancos de ensaio em que estes se realizam e o software em que se analisam as curvas de desempenho. Algumas alterações que tiveram de ser feitas ao banco de ensaios são expostas. Do ponto de vista da resolução do problema, ferramentas de qualidade como um diagrama Ishikawa e a matriz de avaliação foram aplicadas de modo a seguir uma análise cuidada ao problema e dar auxílio na descoberta da causa raiz. Os testes e análises feitas foram baseados nas possibilidades neles apresentadas, que foram recolhidas através de pesquisa e brainstorming no seio da equipa de R&D da Bontaz Portugal. Além disso, o presente trabalho equipa a Bontaz com as ferramentas necessárias à criação de um modelo de simulação de bombas de óleo de caudal variável equipadas com electroválvula, que poderá ser utilizado para o desenvolvimento de novos produtos e para fomentar conhecimento interno sobre bombas de volume variável. Por fim, os resultados experimentais dos diferentes testes são apresentados e discutidos. PALAVRAS-CHAVE Análise de causa raiz; Bomba de óleo de caudal variável; Eletroválvula hidráulica proporcional; Ishikawa. vii TABLE OF CONTENTS Agradecimentos .................................................................................................................................. iii Abstract............................................................................................................................................... v Resumo.............................................................................................................................................. vi Table of Contents .............................................................................................................................. vii List of Figures ...................................................................................................................................... x List of Tables ..................................................................................................................................... xv List of Symbols, Greek Letters, and Acronyms ................................................................................... xvi 1. Introduction ................................................................................................................................ 1 1.1. Framing and Motivation ....................................................................................................... 1 1.2. Objectives ........................................................................................................................... 1 1.3. Company presentation ........................................................................................................ 2 2. Oil Pumps ................................................................................................................................... 4 2.1. Evolution and Components of Lubrication Systems .............................................................. 4 2.2. Concepts Concerning Oil Pumps.......................................................................................... 7 2.2.1. Positive Displacement versus Centrifugal Pumps .......................................................... 7 2.2.2. Reciprocating versus Rotary Oil Pumps ........................................................................ 9 2.2.3. Fixed versus Variable Displacement Oil Pumps ........................................................... 10 2.3. Types of Oil Pumps ........................................................................................................... 11 2.3.1. Reciprocating Positive Displacement Pumps ............................................................... 11 2.3.2. External Gear Pumps ................................................................................................. 14 2.3.3. Lobe Pumps .............................................................................................................. 15 2.3.4. Screw Pumps ............................................................................................................ 16 2.3.5. Internal Gear Pumps .................................................................................................. 16 2.3.6. Gerotor Pumps .......................................................................................................... 17 2.3.7. Vane Pumps .............................................................................................................. 19 3. Solenoid Valves ......................................................................................................................... 23 3.1. Automotive Solenoid Valve Applications .............................................................................. 23 3.1.1. Piston Cooling Jet (PCJ) Control ................................................................................. 23 viii 3.1.2. VDOP Management ................................................................................................... 24 3.2. Working Principle .............................................................................................................. 25 3.2.1. Definition of Magnetic Field ........................................................................................ 25 3.2.2. Ferromagnetic Materials ............................................................................................ 27 3.3. Construction and Functioning ............................................................................................ 29 3.3.1. Normally Open versus Normally Closed ...................................................................... 31 3.3.2. Nomenclature and Schematic Representations ........................................................... 31 3.3.3. On/off versus Proportional ......................................................................................... 33 3.4. Control System .................................................................................................................. 37 3.4.1. Voltage Adjustment – PWM Signal .............................................................................. 37 3.4.2. PID Controller ............................................................................................................ 38 4. Methodology ............................................................................................................................. 38 4.1. Object of Study .................................................................................................................. 38 4.1.1. Customer’s Pump ...................................................................................................... 39 4.1.2. Bontaz Solenoid Valve – 146320 ............................................................................... 41 4.2. Product and Process ......................................................................................................... 43 4.2.1. Product Overview and Production Register ................................................................. 43 4.2.2. Assembly of the Solenoid Valve .................................................................................. 46 4.3. Test Equipment and Facilities ............................................................................................ 48 4.3.1. Prototype Test Benches ............................................................................................. 48 4.3.2. Pump Test Bench ...................................................................................................... 50 4.4. Functional Tests ................................................................................................................ 54 4.4.1. Test Curve Analysis Software – Bontaz Data Processor ............................................... 55 4.4.2. SLR Calibration .......................................................................................................... 55 4.4.3. P-A Flow .................................................................................................................... 57 4.4.4. A-T Flow .................................................................................................................... 58 4.4.5. Pass-through connector leak test ................................................................................ 58 5. Root Cause Analysis .................................................................................................................. 60 xv LIST OF TABLES Table 1: Key differences between Positive Displacement and Centrifugal (or Dynamic) pumps [15]. ..... 9 Table 2: Bill of Materials of the 146320 Solenoid Valve. .................................................................... 44 Table 3: Assembly Flowchart of the 146320 Solenoid Valve............................................................... 45 Table 4: Problems found during initial pump bench tests. .................................................................. 53 Table 5: Problem description table. ................................................................................................... 60 Table 6: 5-Why method for problem solving applied to the problem in study....................................... 61 Table 7: Scope of the possible root causes that can be included in each category of the Ishikawa diagram. ........................................................................................................................................................ 62 Table 8: Ishikawa diagram with the possible root causes targeted in this study. ................................. 64 Table 9: Evaluation Matrix of the possible root causes present on the Ishikawa diagram. .................... 66 Table 10: Unregulated pump flow per revolution values obtained in bench testing. Cells highlighted in yellow correspond to the pump speeds where oscillation has been found in the EoL test. ................... 82 Table 11: Data gathered in each point specified in Figure 85. ............................................................ 83 Table 12: Comparison between Figure 89 Figure 90 speeds, frequencies, and pressure values. ........ 86 Table 13: Amesim data regarding chamber characteristics from Figure 91 and Figure 92. ................. 88 xvi LIST OF SYMBOLS, GREEK LETTERS, AND ACRONYMS SYMBOL DEFINITION UNIT 𝐴𝑠 Surface area [m2] 𝐴𝑠𝑒𝑐 Cross-sectional area [m2] 𝐵 Magnetic flux density [T] 𝐷 Solenoid valve piston’s large diameter [m] 𝐷𝑃 Pipe diameter [m] 𝑑 Solenoid valve piston’s small diameter [m] 𝐹 Force [N] 𝑓 Discharge frequency [Hz] 𝑓 𝐷 Darcy friction factor 𝑔 Gravitational acceleration [m/s2] 𝐻 Magnetic field strength [A/m] ℎ Height [m] 𝐼 Electric current [A] 𝑙 Wire length [m] 𝑁 Number of coils 𝑝 Pressure [bar] 𝑝𝑋 Pressure at point “X” [bar] 𝑄 Volumetric flow [m3/s] 𝑅 Electrical resistance [Ω] 𝑉 Voltage [V] 𝑣 Velocity [m/s] 𝑍 Rotational speed [rpm] GREEK LETTER DEFINITION UNIT 𝛥𝑝 Pressure differential [bar] 𝜇 Magnetic permeability [N/A2] 𝜇0 Magnetic permeability of the vacuum [N/A2] 𝜌 Density [kg/m3] xvii ACRONYM DEFINITION BCTP BONTAZ Portugal BCUS BONTAZ United States of America BEV Battery Electric Vehicle CAD Computer-Aided Design EGR Exhaust Gas Recirculation EoL End of Line EU European Union FLR First Level Regulation HVAC Heating, Ventilation, and Air Conditioning NOK Not Okay OEM Original Equipment Manufacturer PCJ Piston Cooling Jet PD Positive Displacement PEEK Polyether Ether Ketone PHEV Plug-In Hybrid Electric Vehicle PID Proportional-Integral-Derivative PWM Pulse Width Modulation R&D Research and Development SLR Second Level Regulation SV Solenoid Valve USA United States of America VDOP Variable Displacement Oil Pump VVT Variable Valve Timing Enhancement of proportional solenoid valve to manage variable displacement oil pump 1 1. INTRODUCTION 1.1. Framing and Motivation Although Battery Electric Vehicle (BEV) sales are showing a rapid increase over the last few years, the vast majority of cars on the road still rely on internal combustion engines as a power unit. More specifically, of approximately 1470 million cars on the road worldwide in 2023 [1], only about 26 million of those are electric, and, within these, 18.1 million are BEV (the remaining 7.9 million being Plug-in Hybrid Electric Vehicles, or PHEV). Besides this, 13.8 million of the 26 million total electric vehicles were registered in China, as of 2022 [2] In fact, in 2023, electric vehicle represented only nearly one out of every five new cars sold [3]. Therefore, the internal combustion engine is still very much relevant, representing about 98% of all cars as of today. Internal combustion engines need lubrication and cooling, so oil pumps are employed in order to maintain appropriate pressure and flow levels of engine oil in important points of lubrication. These pumps are moved (directly or indirectly) by the spinning crankshaft of the engine and can draw up to 2.5 % of engine torque. [4] Traditional fixed displacement oil pumps are over dimensioned for most conditions, ensuring that sufficient lubrication is provided, regardless of conditions. To produce this extra power to run the oil pump and other accessory systems, fuel consumption is increased. In line with both the EU’s [5] and the USA’s [6] ambitions to become climate-neutral until 2050, regulations concerning CO2 emissions are becoming ever stricter. As CO2 is a product of the complete combustion of fuels containing carbon, fuel consumption has to be decreased in order to reduce its emissions [7]. One solution in this direction was the creation of Variable Displacement Oil Pumps (VDOPs). These pumps minimise over dimensioning and allow for less power to be drawn from the engine by adapting their flow output to the needs of the engine under different conditions. VDOPs can either have two stages of regulation or be continuously regulated. Two stage pumps can be managed by mechanical valves, thermal actuators, springs, or ON/OFF solenoid valves, whereas continuously regulated VDOPs are controlled via proportional solenoid valves. 1.2. Objectives The present work was done within a project of Bontaz, involving a client’s request for investigation into a problem which is described further ahead, and as a means to acquire internal knowledge. It concerns the study and optimization of a vane VDOP system equipped with a Bontaz solenoid valve. The solenoid Enhancement of proportional solenoid valve to manage variable displacement oil pump 2 valve has 3 ports – an inlet, an outlet, and a draining port – and can open in proportion to the voltage supplied to its coil. In this specific project, Bontaz acts as a tier 2 supplier to the OEM, through the pump manufacturer (tier 1 supplier). The OEM has reported an excessive output pressure oscillation issue with the functioning of the vane VDOP system to the tier 1, who could not eliminate it by changing pump parameters alone, so Bontaz was given the task of looking into the issue. Having said this, the goals of this project are to: ▪ Creation of state of art for oil pumps, fostering internal knowledge concerning oil pump systems; ▪ Equip Bontaz Portugal with the necessary conditions to test VDOP systems with integrated proportional solenoid valve (test fixtures, procedure); ▪ Analyse tests previously done at Bontaz USA; ▪ Replicate the customer’s problem; ▪ Utilise quality tools – Root Cause Analysis – and define corrective measures; ▪ Run tests in order to evaluate possible root causes; ▪ Analyse tests to find the root cause (if possible); ▪ Provide data for creation of a simulation model of solenoid valve controlled VDOP systems; ▪ Serve as a “Lessons Learned” for future problem solving. 1.3. Company presentation Bontaz started out in 1965 as a small turning workshop on a family farm in Marnaz (Haute-Savoie, France). Initially manned solely by Yves Bontaz, the company manufactured precision-turned parts on a subcontract basis for local businesses, until it established business relationships with French automakers and parts manufacturers. In a few decades, through production of engine and brake subassemblies, establishing itself as a Tier 1 OEM supplier and opening a total of 24 plants in 11 countries, including 4 R&D centres, Bontaz became and solidified itself as the world leader in automotive hydraulic functions, producing 165 million parts per year. The bulk of the production is based on piston cooling jets and solenoid valves, the latter mainly for oil pump and nozzle control, as well as parking brake and coolant valves. Nowadays, the company is set on keeping up with the changes in mobility and diversifying into highpotential markets such as electric vehicles, fuel cell engines and light mobility. In line with the company’s Enhancement of proportional solenoid valve to manage variable displacement oil pump 3 aim to accompany the changes in mobility, there is a current focus on BEV product development, such as oil cooling and battery pack ventilation. Alongside the will to develop new products for zero emissions means of transportation, Bontaz aims to achieve carbon neutrality by 2050 [8]. BONTAZ – BCTP Equipamento Automóvel is an R&D site which opened in 2018, in Lanheses, Viana do Castelo district, and currently employs a workforce of around 100 people. The subsidiary comprises several departments, such as Industrialisation, Mechanics, Production, Injection, and R&D, among others. In support of the R&D department, BCTP is equipped with prototype assembly lines, containing both manual and electrical presses, a leak testing machine, and hydraulic test benches for oil pumps or solenoid valve/piston cooling jet products and water valves. Alongside these devices, there are basic measurement devices such as callipers, micrometres, comparators, as well as more complex tools - profilometer, vertical measuring columns, tensile and compression testing equipment, 3D coordinate measuring machine, x-ray and tomography scanner, and a profile projector. Enhancement of proportional solenoid valve to manage variable displacement oil pump 4 2. OIL PUMPS 2.1. Evolution and Components of Lubrication Systems Internal combustion engines have several moving parts that require lubrication in order to prevent wear or, at worst, friction welding. In older, simpler engines, usually with side valves (or flathead) in which the camshaft is located in the crankcase, sufficient oil could reach these parts through splash lubrication via a spade in the rotating conrod cap (see Figure 1) which would hit the oil in the sump, causing it to splash, hence the name. This, however, might provoke the formation of excessive foam and overheat the oil in engines that work at higher rotational speeds. As engines evolved to use overhead camshafts and were subjected to greater demands, lubrication systems had to keep up and be able to send the oil upward under pressure, integrating oil pumps, still mixed with splash lubrication. Figure 1: Conrod with spade for splash lubrication. [7] Nowadays, however, most engines, especially in cars, do not resort to splash lubrication whatsoever, using an oil pump (with a filter) to deliver pressurised oil to all the required points, as can be seen in Figure 2. Having said this, the purpose of oil pumps in an internal combustion engine is to force the circulation of the necessary oil for lubrication and cooling of the engine. Additionally, the film formed by oil around the components helps to improve the seal around the pistons, preventing compression leaks [7]. To avoid potentially damaging pressure peaks, the system is equipped with a safety valve downstream of the pump. Such pressure peaks usually occur mainly when the oil is cold and thus at a higher viscosity level than it would be in steady-state conditions [9]. Enhancement of proportional solenoid valve to manage variable displacement oil pump 5 Figure 2: Lubricating oil circuit (without dedicated heat exchanger) [10]. As seen above, the oil stored in the pan, or sump, is sucked by the oil pump, then being forced under pressure through the filter. Downstream of the filter, there is a main gallery, or ramp, from which oil is routed to the different lubrication points, including the crankand camshaft journals, valvetrain, among others; and other functions, such as regulating camshaft position. The oil pump can be moved directly through the movement of the crankshaft, or via chain or belt drive, or even with gears, connected to the camshaft. When a transmission system is used instead of direct drive, the transmission ratio can assume different values, depending on project specifications. Apart from these systems, there are also electric motor driven pumps, but they are still not widely used in internal combustion engines [7]. This is because the energy required to drive such systems would have to be supplied by the alternator, which has an associated energy conversion efficiency, making it less efficient than driving the pump directly, while at the same time raising both system complexity and weight. Another reason is the fact that oil supply to the engine is only necessary when the engine is working, meaning that there is no need for an external source of power to the pump during periods when the engine is off. Although most internal combustion engine vehicles use the the wet sump system depicted in Figure 2, some vehicles may resort to a different solution, known as dry sump. The idea is to have one pump (called the scavenger pump) for moving the oil that drops from the engine onto the sump to an exterior tank, and another to provide oil from the tank to the engine. These two pumps may be connected together in modules, reducing the overall space taken up by this design, constituting what is known as a tandem pump. A diagram of this system can be seen in Figure 3. Enhancement of proportional solenoid valve to manage variable displacement oil pump 6 Figure 3: Dry sump lubrication system diagram [11]. The main reasons why dry sumps are used is because certain applications, such as race cars and offroad vehicles, are subjected to high cornering speeds or road slopes steep enough to cause the oil to slosh around in the sump from the centrifugal force or gravity, respectively, leaving the oil pick-up zone without oil, causing the engine to starve. Additionally, dry sump systems allow manufacturers to reduce oil pan height, making the engine lower, thus permitting a lower centre of gravity, and the oil to be relocated elsewhere to accommodate for any weight imbalances [7]. Besides the drive system, pumps can differ in their working principles and geometry. Enhancement of proportional solenoid valve to manage variable displacement oil pump 7 2.2. Concepts Concerning Oil Pumps Oil pumps can be categorised using several criteria. Having already analysed the way they are driven, one can separate them according to their working principle (positive displacement or centrifugal), and within those, in terms to their mechanism (reciprocating or rotary), and output (fixed or variable displacement). More distinctions can be made, namely relating to their field of application, design complexity, number of moving parts, etc. 2.2.1. Positive Displacement versus Centrifugal Pumps Oil pumps should be chosen in accordance with the desired pressure and flow values, depending on the system and pump curves. Besides that, it is necessary to take into consideration the working fluid, namely its viscosity. There are two big groups of pumps: positive displacement (PD), and centrifugal or dynamic pumps. These two types have different means of working and the distinction is evident upon looking at their typical pressure/flow curves, displayed in Figure 4. Figure 4: Examples of Positive Displacement (PD) vs Centrifugal pump curves [12]. (adapted) Centrifugal pumps are also referred to as dynamic pumps because they use centrifugal force to pump fluids to a higher level of pressure. The fluid enters the pump through the centre of the rotating impeller, which imparts velocity to it. Then, it is discharged through a variable cross-section volute, creating pressure. If a system requires a pressurized network with approximately constant pressure at a given flow rate, this kind of pump tends to be the best option. PD pumps create suction and discharge by displacing a volume of fluid. These pumps suck fluids via an expanding cavity, which creates a pressure drop, sucking in the working fluid to fill the space. Then, the Enhancement of proportional solenoid valve to manage variable displacement oil pump 14 These pumps offer little friction, they can be sensitive to low pressures, and are self-priming [25]. Also, they can pump a variety of fluids, even containing suspended solids, depending on the materials used. However, as they are reciprocating pumps, they require frequent maintenance [26]. 2.3.2. External Gear Pumps External gear pumps contain two gears in mesh inside a case, being a type of multiple-rotor pump. One of the gears, which is driven by the input shaft, moves the other, but each gear has its own shaft. This design is widespread in internal combustion engines, because of the reduced number of components and, consequently, its affordability and reliability. A diagram showing the basic functioning of these pumps is presented in Figure 11. Figure 11: External gear pump diagram [27]. As illustrated, oil is pressurized by the movement of the gears, which drag it along the walls of the pump case and out through the other side, a process that can be reversed simply by changing the direction of rotation. The meshing of the gear teeth impedes the oil from leaking back onto the suction side. Nevertheless, they create a nearly constant loss through running clearances between gear faces, tooth crests, and the housing, meaning that running low speeds and flows may be inefficient and that these pumps should be operating close to their maximum speeds and outputs [28]. Different gear types can be used in this kind of pumps and their design is not normalised, being the individual choice of each manufacturer, according to their own needs [29]. In summary, external gear pumps are compact, well-suited for high viscosity fluids, and easily manufactured in different materials to match fluid properties. [26] They should not be used when dry, having to be primed in order to ensure lubrication to the pump’s own moving parts. This also means that abrasive fluids or entrained solids might damage the pump [14]. Enhancement of proportional solenoid valve to manage variable displacement oil pump 15 2.3.2.1. External Gear VDOP In the case of the external gear pumps, displacement variability is provided by moving the shaft of the driven gear (not powered by the engine), thus reducing the pumped volume, which varies proportionally according to the length of the meshing area of the gears [30]. An example can be seen in Figure 12. Figure 12: External gear VDOP [30]. 2.3.3. Lobe Pumps Lobe pumps are a type of multiple-rotor rotary pump whose operation is quite similar to that of external gear pumps and can also be reversed simply by changing the direction of rotation. In comparison, one big advantage with this design is that the lobes do not come in contact with each other, be it a two, three or more lobe pump, avoiding contamination and fluid shear, as well as reducing wear on the pump. A diagram of this type of pump is represented in Figure 13. Figure 13: Lobe pump diagram [31]. (adapted) Enhancement of proportional solenoid valve to manage variable displacement oil pump 16 These need tight dimensional and geometric tolerances, but not as strict as those with the rotating elements in contact. Rotation timing between the shafts is maintained by gears in the gearbox of the pump, where the support bearings are also located. For this reason, pressure is limited by the bearing location and shaft deflection. Because the lobes do not touch, fluid contamination is kept to a minimum [32]. 2.3.4. Screw Pumps They move the fluid via a rotating, helical threaded shaft (screw), causing it to move axially. For a diagram of a screw pump, see Figure 14. Figure 14: Single screw pump diagram [33]. This kind of pump is typically used for hydraulic lifts and submarines, as well as cutting oils and lubricants, thanks to its low noise and reduced pulsation [33]. 2.3.5. Internal Gear Pumps In this kind of pump, the oil is also pressurised due to the rotation of two gears, but in a different layout, with one inside of the other. The outside gear has internal teeth to mesh with the inside gear’s external teeth. Either gear can be the drive gear or the driven gear, depending on the pump. One example is shown in Figure 15. Enhancement of proportional solenoid valve to manage variable displacement oil pump 17 Figure 15: Internal gear pump scheme [34]. Space between the gears increases from the meshing zone towards the direction of rotation, creating a pressure drop which sucks in the oil from the inlet port. This oil is then conducted through either side of a crescent shaped filler piece separating the lowand high-pressure zones. Tolerances in this area must be tight to keep both zones sealed. After passing by the crescent, the oil is pressurised using the opposite effect that initially provided suction, that is, by diminishing the space between gears, forcing the oil out through the outlet port. 2.3.6. Gerotor Pumps Gerotor pumps have a working principle analogous to the one described above, comprising an internal and an external gear in constant contact, with the external gear containing one more tooth than the internal gear – also called gerotor - providing displacement of volume between them. Within vehicle applications, besides internal combustion engines, they can also be placed in some automatic gearboxes, or in hydraulic locking differentials and power steering systems [35]. However, instead of a crescent sealing and separating the highand low-pressure zones, the contact of the teeth of the internal rotor with the external gear is what guarantees the seal. To better understand the concept, a scheme of a gerotor pump is exposed in Figure 16. Enhancement of proportional solenoid valve to manage variable displacement oil pump 18 Figure 16: Gerotor pump scheme [36]. Typically, the teeth of the internal gear have an epitrochoidal, hypotrochoidal, or cycloidal profile, among others, and the outer gear is made to match with circular arc profiles [37]. This way, the space that was otherwise occupied by the crescent (in an internal gear pump) can now be filled with oil, meaning that, when comparing a gerotor pump with an internal gear pump with the same teeth width, outer diameter of the internal gear and root diameter of the external gear, the volume displaced per rotation is bigger in the case of the gerotor pump [38]. 2.3.6.1. Gerotor VDOP Gerotor VDOPs work by moving the minimum area zone shown in Figure 16. In these VDOPs, the outer gear sits inside a stator, which is held in place by a spring. An example of a gerotor VDOP is exhibited in Figure 17. Figure 17: Gerotor VDOP [39]. Enhancement of proportional solenoid valve to manage variable displacement oil pump 19 To reduce displacement, oil pressure is fed to a regulation chamber outside of the stator, pushing it. When the force applied by oil on the stator overcomes the force of the spring, the stator rotates and in turn, the eccentric axis of the outer gear rotates about the central axis of the gerotor, changing the position of the minimum area zone relative to the inlet and outlet ports of the pump. This way, the suction and discharge zones’s alignment with their respective ports is altered, reducing flow [40]. 2.3.7. Vane Pumps Vane pumps are a type of single-rotor pump, composed of an external case containing an outer ring, an eccentric shaft, and two or more sliding vanes, inserted in cavities in the eccentric shaft. An outline of this kind of pump is illustrated in Figure 18. Figure 18: Vane pump diagram [41]. As the eccentric shaft rotates, the vanes slide across it, due to the contact between the tip of the vanes themselves with the outer ring. To guarantee the vanes are always in contact with the outer ring, the system might rely on centrifugal force caused by the rotation, on a centring ring, on springs, or on pressurised oil taken from the discharge port to the inner base of the vanes, pushing them outward [29]. To avoid damaging the inner surface of the ring (usually made of steel), the vanes are normally made from materials with a lower hardness, varying according to their application. Rotor materials can also vary for the same reasons [42], [43]. Because the rotor is eccentric, the distance between a fixed point on its surface and internal perimeter of the outer ring varies as it rotates. Hence, the vanes create several cavities between them, whose volume Enhancement of proportional solenoid valve to manage variable displacement oil pump 20 is shorter near the point where the eccentric’s axis of rotation is closer to the outer ring (left side in Figure 18), and larger on the opposite side (right side in Figure 18). The oil enters the pump through the inlet hole, being sucked by the pressure drop caused by the increase of the cavities’ volumes. Then, it is moved around the pump by the rotating vanes and, at the exit port, the opposite effect occurs: the cavities decrease in volume, pressurizing the oil, which is forced out of the pump. This process can be reversed, changing the direction of pumping [43]. The flow occurring at the exit of vane pumps should be mostly low pulsation flow, but pulsation might be a problem for pumps with a low number of vanes (one or two) at low rotation speeds [43]. There are several design variations for vane pumps, with an important variant being pendulum pumps. The design is very similar to regular vane pumps, except that instead of sliding vanes, the pump contains pendulum-shaped sliders supported on an outer rotor, sliding in grooves located in the internal rotor. One example can be seen in Figure 19. Figure 19: Sliding pendulum type vane pump [44]. (adapted) 2.3.7.1. Vane VDOP When it comes to vane pumps, to regulate the displacement, the eccentricity of the rotor might be reduced through rotation of the external ring around a fixed pivot point. This is the case of the example in Figure 20. Enhancement of proportional solenoid valve to manage variable displacement oil pump 21 Figure 20: Unregulated vane VDOP (solenoid valve not activated) [45]. Between the outer ring and the pump casing is a volume called the regulation chamber. As shown in Figure 20, a spring keeps the external ring in its unregulated position until its force is exceeded by the pressure in the chamber. When the force exerted by the pressure on the outer ring is greater than the opposing spring force, it starts to move, compressing the spring, as seen in Figure 21. This adjusts the pump so that the outer ring’s centre travels closer to the inner ring’s centre. In doing so, the difference in volume between the chambers formed by the rotating vanes becomes smaller, thus creating less suction and less pressure on exit. Enhancement of proportional solenoid valve to manage variable displacement oil pump 22 Figure 21: Regulated vane VDOP (solenoid valve activated) [45]. The necessary pressure to regulate the pump might be approximately constant or increase as the outer ring rotates [16]. Alternatively, vane VDOPs can use a translational mechanism, where the displacement is adjusted through the translation of the outer ring, rather than its rotation, but following the same principles. (Figure 22). Figure 22: Vane translation VDOP model [46]. Enhancement of proportional solenoid valve to manage variable displacement oil pump 23 3. SOLENOID VALVES Solenoid valves (SV), often abbreviated as just “solenoids”, are a type of electromechanical valve with a wide array of possible functions of fluid (either gas or liquid) control, of which on/off and flow regulating valves are examples. Since their first appearance, perhaps the greatest turning point towards solenoid valve sustainability in the market was the introduction of plastic overmouldings in the 1950s, making them more efficient, reliable, and resistant to corrosion and other chemical interactions [47]. Ever since, these valves have proved their usefulness throughout the several different industries, as they control pneumatic and hydraulic circuits which can be used in operating tools, from handheld to large industrial equipment; HVAC systems; domestic applications, such as automated garden watering lines; and automotive systems, among others. Besides this, SV can be used as part of a control circuit to pilot other, larger valves, in a function analogous to that of a relay. Nowadays, solenoid valve applications are proliferating as new mechanisms are developed, and the introduction of new composites and high performance polymers such as PEEK provide a large diversity of possible improvements. 3.1. Automotive Solenoid Valve Applications Focusing on the automotive industry, solenoid valves see a significant range of applications. These applications are spread out across various systems in a car, operating with different working fluids. For example, in a car, there can be solenoid valves controlling the heating and cooling systems - flow of HVAC refrigerant, coolant for cabin heating and cooling systems – emissions reduction systems - Exhaust Gas Recirculation (EGR), Adblue thermal management – braking systems – compression brakes and exhaust brake – and even Variable Valve Timing systems (VVT), among others. However, as the focus of this work is on an oil regulation SV, two important examples of oil valve function provided by Bontaz are explained in more detail - piston cooling jet and VDOP management valves. 3.1.1. Piston Cooling Jet (PCJ) Control The piston cooling jets (example in Figure 23) are a fundamental part when it comes to cooling and lubricating internal combustion engines and play a very significant role in oil consumption, as they can direct around 40 % of the pumped oil flow [48] towards the pistons (see Figure 24) in order to lower their temperature and ensure the proper running conditions are maintained. Enhancement of proportional solenoid valve to manage variable displacement oil pump 30 propagation for the magnetic field lines, which also bridge the air gaps between some of the components. The fixed and mobile cores are in opposite poles of the magnetic field, and, therefore, are subjected to magnetic forces, attracting them to one another. These forces move the mobile core closer to the fixed core, closing the air gap between them, and actuating the valve. Figure 31: Magnetic circuit representation on a cross section of the electronic subassembly of a SV [59] (adapted). Dotted blue lines represent the magnetic circuit. Yellow arrows represent direction of motion of the mobile core. On the other hand, the components in the mechanic subassembly of an SV can vary widely depending on the application, but usually consist of: ▪ Valve body; ▪ Piston; ▪ Spring; ▪ Stopper. The body is responsible for guiding the fluid from and to the desired canals, with the piston regulating flow (and, necessarily, pressure). The spring acts to return the piston, needle, and mobile core to their original position when the valve is not activated and offers resistance to their advance when activated. The stopper is a metal plate whose function is to hold the spring and allow SLR calibration (see 3.3.3.2), according to the required specification. To illustrate an example of how a solenoid valve could function, an SV cross section diagram can be seen in Figure 32. Enhancement of proportional solenoid valve to manage variable displacement oil pump 31 Figure 32: Cross section diagram of a 3/2 on/off solenoid valve. Left – SV off; Right – SV on [60]. (adapted) While the solenoid valve is off (left side), the mobile core is forced downward by the return spring, and in turn holds the needle and piston (green) down. In this state, the SV is closed, so there is no passage from port P to port A. However, there is passage from port A to port T. In this case, imagining that port A leads to a reservoir and knowing that port T leads to atmospheric pressure, flow from port A to T could be called “draining” flow. On the right side, where the solenoid is on, the mobile core is pulled towards the fixed core, which is acting as an electromagnet, beating the force of the return spring, and pulling the mobile core upward. As the piston moves with the core, passage from port P to A is opened and flow from port A to T is stopped. The solenoid valve is, therefore, open when energized. Following the previous line of thought, if fluid flows from the inlet, P, to the reservoir, downstream of port A, this influx can be described as “filling” flow, as it fills the reservoir. Apart from the design shown in Figure 32, there are many different configurations, depending on the valve’s function and the environment in which it operates. Other geometries will be explained further below. 3.3.1. Normally Open versus Normally Closed In the example represented in Figure 32, it is shown that the SV is closed when the solenoid valve is not energized, which means that it is a normally closed valve. In cases where the solenoid valve stays open when not energized and closes when activated, it is said that the SV is normally open. 3.3.2. Nomenclature and Schematic Representations In a pneumatic or hydraulic scheme, valves are distinguished by: Enhancement of proportional solenoid valve to manage variable displacement oil pump 32 ▪ Number of ports and positions/states they can be in: For a valve with x ports and y positions, the designation is x/y valve. ▪ Normally open or normally closed: As previously explained, a vale whose resting (deactivated) state is open is said to be normally open, and the opposite for normally closed. ▪ Activation and Return Mechanism: Valves can be activated and returned in several different ways. For the case in study, the relevant types are solenoid activated, spring returned valves. Besides this, however, they can be pneumatically/hydraulically, and manually activated and returned. 3.3.2.1. On/off Solenoid Valves Scheme Considering the on/off valve pictured in Figure 32, because it has 3 ports and 2 possible positions, it is called 3/2 solenoid valve. Its representation, obtained using the Fluidsim software, is as depicted in Figure 33. Figure 33: 3/2 on/off SV hydraulic scheme. The valve is shown in its resting position, with the spring forcing it to stay closed. When the solenoid receives current, it moves the valve scheme to the right, compressing the spring. 3.3.2.2. Proportional Solenoid Valves Scheme Considering the same example, but assuming that it has a proportional behaviour as current is gradually applied, the valve is still a 3/2 SV, but there is now a middle ground between the two positions. Such a behaviour is represented through a third position, as seen in Figure 34. Enhancement of proportional solenoid valve to manage variable displacement oil pump 33 Figure 34: Proportional 3/2 SV hydraulic scheme. The middle position represents the state of the SV when it is getting between 0 % and 100 % current, with all the ports being in communication. When full current is achieved, the SV is at the leftmost position. 3.3.3. On/off versus Proportional As was explained before, 2-stage VDOPs can be managed by an on/off SV, whereas continuously variable VDOPs are controlled by proportional SV. On/off and proportional valves are not just different in their hydraulic scheme, but also when it comes to their geometry. Figure 35 presents an example of a Bontaz on/off SV. Figure 35: Cross section view of a 3/2 on/off solenoid valve [61] . (adapted) From an electrical subassembly point of view, this design is analogous to the one presented in Figure 32. The mechanical subassembly, however, differs. The spring separates the mobile core from the fixed core when the SV is off. Instead of a piston, the needle holds a sphere in place, blocking flow between ports P and A. When the solenoid is energized, the mobile core is pulled upward by the magnetic force, compressing the spring. The pressure coming from port P pushes the sphere and needle upward, blocking flow from A to T (and allowing flow from P to A). Enhancement of proportional solenoid valve to manage variable displacement oil pump 34 It is shown in this design that there is no possibility of only partially opening flow from P to A. It is either fully open or fully closed. On the other hand, proportional valves are used when there is the need to create a pressure drop from P to A port, but without fully closing flow. This is made possible by a mechanism such as the one demonstrated Figure 36. Figure 36: Cross section view of a 3/2 proportional solenoid valve [62]. (adapted) This specific design pertains to an SV whose electrical subassembly is located outside of the engine, meaning that there cannot be leaks from the hydraulic circuit to the outside of the valve. Due to this, o-rings are used to contain the oil. If the SV was to be used inside the engine, the sealing would only be necessary on the connection between the interior of the engine and the outside environment – usually the electric connector. In this design, initially, there is a piston blocking flow from ports P to A, but allowing it from ports A to T (normally closed SV). As the solenoid receives current, the mobile core is pulled downward, towards the fixed core, pushing the needle and the piston downward, and compressing the spring against the stopper. If the solenoid is fully energized, the piston will allow for unrestricted flow from ports P to A. If it is partially energized, the piston moves less, and flow from P to A will happen, but will suffer a greater pressure drop than in the first case. This type of system can be applied in any system that benefits from continuous regulation when compared to on/off. In clarification of what has been described, Figure 37 shows the behavioural distinction between on/off and proportional SV. Enhancement of proportional solenoid valve to manage variable displacement oil pump 35 Figure 37: On/off and proportional solenoid valves flow versus current graphs. 3.3.3.1. Underlap, Zero Lap, and Overlap in Proportional Solenoid Valves Following the design shown in Figure 36, there could be different concepts adopted when it comes to deciding piston height in relation to the diameter of the ports, which impacts the way the SV behaves in transient response. The possible scenarios are: ▪ Underlap: height < port opening; ▪ Zero lap: height = port opening; ▪ Overlap: height > port opening. Zero lap is impossible in practice, since there are always tolerances for the machined sizes of the parts and exact measures cannot be obtained, so there is always a slight underor overlap, even if it is unwanted. What this means from a functional point of view is clarified through Figure 38. Figure 38: Underlap versus zero lap versus overlap effects on flow rate through valves in function of valve opening [63]. Enhancement of proportional solenoid valve to manage variable displacement oil pump 36 As shown, with zero lap, flow is directly proportional to the valve opening at a fixed slope. However, with underlap, there is a larger slope in the beginning. During that short period, both P to A and A to T flow can happen. When there is overlap, the opening of the A port is delayed, so flow only begins a while after the piston has passed the port. In this situation, before P to A flow is possible, A to T flow has already been closed (the whole A port is covered by the piston). 3.3.3.2. Proportional Solenoid Valves with Second Level Regulation (SLR) In case a proportional SV fails to activate, there is the possibility of opening it through a failsafe mode, usually called SLR. The SLR calibration takes its name from the Second Level Regulation of two-stage VDOPs, since the pressure at which it limits pump oil is equivalent to that of the traditional SLR, pictured in Figure 7, and consists of opening the passage of oil to the regulation chamber mechanically, rather than electrically. Three ways of going about this mechanical regulation are in the pump itself (direct regulation), the engine, or the SV (indirect regulation), the latter being the object of focus in this study. SLR mode in SVs take advantage of equation 3, where it is obvious that, maintaining pressure, the greater the area, the greater the force applied on it. 𝐹 = 𝑝𝐴𝑠 3 For force to be applied, different diameters are used on the piston (providing different surface areas), and the body of the valve also has to be shaped in order to facilitate this effect. This is the case when pistons such as the one shown in Figure 36 are used. A hand drawn exaggeration of the shape of the body and piston was drawn in Figure 39. Figure 39: Hand drawn scheme of proportional valve body and piston for SLR mode (exaggerated). Piston coloured for clarification. Enhancement of proportional solenoid valve to manage variable displacement oil pump 37 In this case, the body of the SV is narrower on top than at the bottom - 𝑑 < 𝐷 - and the same happens on the piston. This way, the geometry of the latter is simplified. The same principle from equation 3 applies. The calibration of when the valve opens – meaning how much pressure is necessary to cause the failsafe mode to open the valve – is done by pushing the solenoid valve’s stopper against the spring. This compresses the spring, increasing the preload, meaning that a greater force acting on the piston is required to push it down. 3.4. Control System For on/off SV, the current supply is either at the nominal value (on) or zero (off). For proportional solenoid valves, current is applied as necessary, within the range from zero to the nominal current value. As such, there has to be an electronic closed-loop controller which regulates how much current passes through the solenoid, in function of a setpoint (defined by a control unit) and the measured pressure value at the exit of the pump (or at the oil main gallery). At a given temperature, the electrical resistance of the solenoid is constant. Therefore, in order to limit current, the voltage applied on the circuit has to be changed (as per equation 4 – Ohm’s Law), which is how the controller manages the SV. 𝑅 = 𝑉 𝐼 4 3.4.1. Voltage Adjustment – PWM Signal The manner in which the voltage in the circuit is managed is by using Pulse Width Modulation (PWM). PWM is a method of controlling analogue circuits with a microcontroller’s digital outputs [64], by varying the pulse width of a fixed frequency of a rectangular wave [65], with the value of the frequency depending on the application. A typical value for solenoid valve solutions is 250 Hz [48]. The pulse width sent out by the controller over time determines the average voltage “felt” by the load (in this case, a solenoid). An example is shown in Figure 40. Enhancement of proportional solenoid valve to manage variable displacement oil pump 38 Figure 40: Exemplification of PWM output signal at 60 % (single wave represented). In this case, the load would receive an average voltage of 60 %, which corresponds to the portion of the wave’s period during which the output was on. The microcontroller calculates the percentage of time it has to send “on” pulses via a PID system. 3.4.2. PID Controller A PID controller is a system which allows for a better following of the setpoint and better transient response than a typical on/off controller [66]. This type of control system has three adjustable actions: Proportional (P), Integrative (I), and Derivative (D). Each of these terms can be adjusted by attributing a certain value to them (gain), increasing or diminishing their influence on the output value as necessary. Very often only PI controllers are used, usually by setting the derivative term to zero (nullifying its functionality). 4. METHODOLOGY In this chapter is a description of the methodology followed in conducting the study of the system at hand, with description of the object of study, a product and process analysis and depiction of the facilities in which the work has been carried out. 4.1. Object of Study This project exists within Bontaz for one of its direct clients, which is a tier 1 supplier for an OEM. In this instance, Bontaz is a tier 2 supplier to the OEM, meaning the tier 1, Bontaz’s direct customer, supplies Enhancement of proportional solenoid valve to manage variable displacement oil pump 39 the OEM with their product already fitted with a Bontaz solenoid valve. The object of study consists of a vane VDOP system equipped with a Bontaz 3/2 proportional solenoid valve. The assembly is under study following a complaint from the OEM to the tier 1 supplier, who has relayed the problem to Bontaz after failing to solve it within the pump. The problem consists on pressure oscillations which cause alarms in the OEM’s fault detection equipment, possibly masking other potential problems. An investigation into this problem had already been started at Bontaz France and Bontaz USA (BCUS), so a pump and test fixtures were already available for testing the system. In order to provide support from Bontaz Portugal (BCTP), it was requested that the available equipment was sent to Portugal. In the beginning of the development of the present work, communication with the customer was put on hold due to an agreement made between the tier 1 and the OEM, which allowed around 99 % of otherwise NOK parts to be accepted. This was not a solution to the problem, but a walkaround, and so Bontaz decided to keep investigating. 4.1.1. Customer’s Pump The pump in study is a vane VDOP. It regulates flow output via rotation of the outer ring and is piloted by a proportional solenoid valve which adjusts the pressure of oil that reaches the regulation chamber. The pump is shown as it arrived in Figure 41. Figure 41: Object of Study: Vane VDOP. It is noticeable from analysing the pump on the outside that it has two different modules, one of them being a gerotor pump (which is visible through its intake port in Figure 41). From this analysis, and according to the previous research, despite no indication from the customer, it is possible to conclude that the pump in question is applied to a dry sump system, and combines a pressure Enhancement of proportional solenoid valve to manage variable displacement oil pump 46 4.2.2. Assembly of the Solenoid Valve Building the 146320 SV involves a series of defined steps, already shown above. On the prototype assembly lines, since production runs are small (usually ≤ 200 prototypes), assembly is done by hand and not automated at all. In Figure 45, components have been laid out on a prototype line table: Figure 45: 146320 SV components lined up for assembly (prototype line). To assemble the SV, the following steps are done: ▪ Electrical subassembly (146313): ▪ Place magnetic washer in the coil overmoulding; ▪ Place overmoulding with magnetic washer inside the shell; ▪ Insert cartridge, mobile core, needle, and fixed core in the overmoulding; At this point, a crimping operation is performed (Figure 46), using an electric press, to secure the components inside the shell during the next steps. Figure 46: Crimping of the electrical subassembly (by pressing on the flaps atop the shell) Enhancement of proportional solenoid valve to manage variable displacement oil pump 47 Following the crimping: ▪ Place the plate at the bottom of the electrical subassembly; ▪ Insert the half-washers on the body; ▪ Mechanical subassembly (146324): ▪ Place the body with half-washers on the plate; ▪ Crimp the shell a second time to secure the body (Figure 47); ▪ Insert piston, spring and stopper in the body; ▪ Crimp the stopper (Figure 48). Figure 47: Solenoid valve after second crimping operation. Figure 48: Crimping of the stopper (by pressing on the edge of the body). After this third and last crimping operation, the valve will be as shown in Figure 49: Enhancement of proportional solenoid valve to manage variable displacement oil pump 48 Figure 49: Solenoid valve after last crimping operation. From here, the only parts left to be assembled are the filters at the P and A ports, however, the A port filter can only be installed after SLR calibration of the valve, explained in 4.4.2. 4.3. Test Equipment and Facilities In order to verify correct functioning of the prototypes produced at BCTP, the site is equipped with test benches designed to accommodate testing, according with the specific requirements of each product. Among this equipment are the prototype test benches, which in this case are used to verify SLR, P-A flow, and A-T flow, and the pump test benches, whose function is to replicate test conditions on the customers’ side and observe oil pump operation. Measured variables can be monitored live and be stored for further analysis, using dedicated software. 4.3.1. Prototype Test Benches The prototype test benches consist of a working area (Figure 50) containing: ▪ Oil reservoir; ▪ Oil supply hose with flow meter; ▪ Electric current supply for solenoid valves; ▪ Oil pressure sensors and temperature probe; Enhancement of proportional solenoid valve to manage variable displacement oil pump 49 Figure 50: Prototype bench working area. For the SLR and flow tests, a fixture in which the SV, supply hose and sensors can be connected is required. In this case, a standard Bontaz fixture was used (Figure 51), which means it was not necessary to develop a new, purpose-made one. Figure 51: Standard fixture used in bench testing. Ports P and A have two possible connection lines each, whose female connectors are closed by default, until connected with a male connection line. Port T is left open, as it represents a tank at atmospheric pressure. Enhancement of proportional solenoid valve to manage variable displacement oil pump 50 The control interface of the benches (Figure 52) provides two different ways to operate the tests – automatic or manual – and allows the user to change parameters such as oil temperature and supply oil pressure control PID values. Figure 52: Prototype test bench interface in automatic testing mode (with loaded test file). 4.3.2. Pump Test Bench In order to use the pump bench, a standalone fixture needs to be made specifically for each project. 4.3.2.1. Fixture As previously explained, the fixture had been made by the team which first worked on this project, but it was necessary to reassemble it and fix the pump. The resulting assembly is shown in Figure 53 (a). Enhancement of proportional solenoid valve to manage variable displacement oil pump 51 (a) (b) Figure 53: Fixture used for pump testing with pump assembled (a) and fixture shaft assembled onto the bench motor’s shaft (b). The fixture has four functions: ▪ Hold the pump in place; ▪ Connect bench hoses to the pump; ▪ Attach drive gear to the bench motor’s shaft and drive the pump; ▪ Allow regulation of chain tension. The pump is attached to the fixture via five bolts, in three locations. There are gaskets in each support point between the pump and the fixture to avoid leaks. The bench hoses connect directly onto the male hydraulic connectors on top of the fixture. The connection to the bench’s shaft is done by tightening the fixture’s shaft around the motor shaft with a bolt (Figure 53 (b)). The drive gear has 40 teeth and the driven gear has 20 teeth, meaning the pump rotates at twice the speed of the bench motor. To regulate chain tension, the six bolts on the regulating arm have to be loosened. Then, the adjustment screw is rotated in the desired direction, pushing or pulling the pump in relation to the fixed drive gear. After this adjustment, the six bolts are tightened once again, securing the pump at the set distance. 4.3.2.2. Pump Bench Setup The intent when using the pump bench is to simulate engine operating conditions, so there have to be restrictions to the flow of oil similar to those present inside the engine. As explained in 2.1, oil flows from the pump to the filter, then to a main gallery, and finally towards the necessary lubrication points, through small channels. To simulate the pressure drop caused by the oil filter, there is a valve which can be partially closed (henceforth called “vanne 1”). To simulate the backpressure caused by the small cross-section of the engine’s lubrication channels, there is another similar valve downstream, henceforth called “vanne 2”. To decide how much each vanne should restrict flow, the customer provides pressure values from their own testing, which can then be correlated to those obtained at Bontaz. Typically, opening values operated are of 80 % for vanne 1, and 60 % for vanne 2 as an internal standard. Having said this, the pump test bench’s working area comprises the following elements: ▪ Oil reservoir; ▪ Built-in pressure sensors (P1 and P2) and temperature probe; ▪ Electric current supply for solenoid valves; Enhancement of proportional solenoid valve to manage variable displacement oil pump 52 ▪ Two pneumatic valves (henceforth called “vannes” for clarity); ▪ Flow meter. The setup can be better understood in the hydraulic diagram provided in Figure 54. Figure 54: Hydraulic diagram of the pump bench - oil pick-up point (channel that leads to the solenoid valve) indicated. Green line represents the zone that simulates engine main oil gallery. The pump is driven by the bench’s electric motor, drawing oil from the reservoir (not shown). The P1 sensor measures output pressure. The line between vannes 1 and 2 (in green) acts as the main gallery, from which there is an oil pick-up to the solenoid valve, in order to regulate the VDOP. Sensor P2 measures pressure in this gallery. The remaining oil passes through a flow meter and is returned to the reservoir. The pump and the solenoid valve are placed in the working area, supported on the pump fixture, shown in Figure 55. Figure 55: Pump bench working area. Pump attached to fixture and mounted in the bench. Pressure at the entrance of the solenoid valve is equal to P2 minus the pressure drop caused by the line that carries the oil towards the valve. Enhancement of proportional solenoid valve to manage variable displacement oil pump 53 The bench where the fixture was made to be attached was slightly different from the one at BCTP. As such, initial testing showed some problems. The problems and the solutions devised to solve each of them are schematised in Table 4. Table 4: Problems found during initial pump bench tests. Problem found Solution devised Fixture grinding against shaft; Placed washers on mounting bolts behind fixture Drive gear not centred on bench shaft Placed a tighter insert in the centre of the gear Drive chain misaligned Designed a washer to bring the drive gear into alignment with the driven gear Driven gear slipping on pump shaft Rebored hole diameter, retightened and applied structural adhesive Sensors’ response time too slow and sensitivity too low Installed quicker, more sensitive sensors Firstly, the fixture ground against the shaft’s (Figure 53 (b)) wider section zone, causing instability. The mark left on the fixture’s bearing can be seen in Figure 56 (a). Placing washers behind the fixture was enough to provide clearance from the spinning shaft, solving the issue. Then, the drive gear had to be properly centred, but its inner diameter was significantly larger than the bolt which fixed it to the shaft, so the diameter was reduced by placing an insert in the centre – see Figure 56 (b). In order to align both gears to ensure correct chain positioning, the drive gear had to be brought away from the shaft 7 mm. By machining a washer with this thickness Figure 56 (c) and placing it between the drive gear and the shaft, the drive gear as attached in the correct position. Lastly, as the driven gear slipped on the pump’s shaft, the surface of the hole suffered some damage. This was corrected by reboring the hole. To ensure slippage would not reoccur, a structural adhesive was added - Figure 56 (d) - which fixed the problem. Enhancement of proportional solenoid valve to manage variable displacement oil pump 54 (a) (b) (c) (d) Figure 56: Problems with the pump bench setup. Ground bearing inner ring (a); Drive gear with added insert (b); Spacing washer to align drive gear with driven gear (c); Rebored driven gear with structural adhesive (glue) (d). Finally, the pump test bench’s control interface setup screen is shown in Figure 57. Figure 57: Pump test bench setup interface. Parameters required to run a pump test are: pump rotation speed, SV voltage, desired current, and vannes’ opening percentages. Each of these parameters is written in steps with an associated duration, in seconds. Vanne openings can be set as a fixed value or vary throughout the test. 4.4. Functional Tests Enhancement of proportional solenoid valve to manage variable displacement oil pump 55 All Bontaz solenoid valves are functionally checked with oil. In the prototype phase, test benches are used to carry out the functional performance checks, which aim to verify correct behaviour of the valve according to customer specifications (hydraulic data specified in 4.1.2). However, in order to analyse the tests, it is necessary to take the data retrieved by the test benches and graph it using an appropriate software. 4.4.1. Test Curve Analysis Software – Bontaz Data Processor Bontaz has developed an in-house data processor in Octave for the purpose of analysing test data, which can be used to read parameters related to any of the required tests. Within this software, the user can change displayed variables, customise axes (displayed variables, scales, gridlines), as well as track values in the curves. Another important feature is the filtering of high frequency noise, which could be created by electromagnetic interference. Presented in Figure 58 are two different graphic representations of the data collected through a disconnected pressure sensor (0 bar): Figure 58: Two different graphics obtained from the same data: On the left - unfiltered signal, showing noise. On the right - filtered signal with minimal noise. Although sensor noise is of a relatively small scale overall, it can reach peaks of up to 0.1 bar, which could hinder analysis. By filtering the noise, it is reduced to insignificant levels. Using this software, any number of curves can be compared at the same time. In the following chapters, several graphics created with this data processor are going to be displayed. 4.4.2. SLR Calibration The first functional test consists of the calibration of the valve in order to provide the correct mechanical regulation pressure. The test procedure is as follows: ▪ close port A; Enhancement of proportional solenoid valve to manage variable displacement oil pump 62 5.2. DFMEA (Design Failure Mode and Effect Analysis) At the time of development, each product has its own DFMEA, which aims to answer the following questions [68]: ▪ How might the product fail and how can failure be prevented? ▪ What are the consequences of a specific type of failure?; ▪ How is the problem detected?; ▪ What are the recommended actions to avoid these problems, if any? For this reason, whenever an issue arises, it is wise to look for the failure mode in this document, as it may have already been considered. The predicted failure types for SLR mode in this product are shown in Annex 3. None of the presented failure modes predict an oscillation in output pressure of the pump, so the problem has to be more deeply investigated. 5.3. Ishikawa Diagram The preceding investigation team from BCUS had already resulted in an Ishikawa diagram, which is exposed in Annex 4. As seen, the diagram is organised into eight different categories. The purpose is to organise the thoughtprocess and help target the source of the problem more efficiently. It is possible that only part of the categories are relevant, so not all of the Ishikawa fields or categories have to be filled out. A brief explanation of the categories present on the Ishikawa diagram is exposed in Table 7: Table 7: Scope of the possible root causes that can be included in each category of the Ishikawa diagram. Category Scope People Direct impact of humans on the tests. Machine Functioning of the system’s mechanisms. Materials Raw materials, components used, part dimensions. Method Methodology followed during production. Management Management decisions that could affect the process. Measurement Techniques followed to measure quality standards. Environment External factors related to the system surroundings. Money Funding of the project. Enhancement of proportional solenoid valve to manage variable displacement oil pump 63 While investigating the root causes numbered on the diagram, they experimented with different changes to SV design. The most important experiments to note include: ▪ Varying underlap/overlap condition; ▪ Testing springs with different spring rates; ▪ Comparing bodies with highest vs lowest surface roughness; Having said this, none of these attempts provided satisfactory results – all of the tested valves still showed occasional oscillation. For this reason, these experiments were not repeated in this study, and focus shifted to other different possibilities. In order to study relevant parameters, a series of possibilities was proposed and placed into an Ishikawa diagram, shown below in Table 8. Enhancement of proportional solenoid valve to manage variable displacement oil pump 64 Table 8: Ishikawa diagram with the possible root causes targeted in this study. Enhancement of proportional solenoid valve to manage variable displacement oil pump 65 A total of nine possible root causes were considered, and the explanation of each is going to be elaborated in chapter 6. 5.4. Evaluation Matrix A systematic approach to the identification of the root cause implied prioritising within the nine possibilities. With the aid of the product development team at BCTP, the items on the Ishikawa diagram were given different levels of priority with the goal of fulfilling the following objectives in order: ▪ Guarantee correct operation of testing equipment to ensure accurate results; ▪ Verify functional parameters of the SV and overall system functionality; ▪ Deeper studies of other alternatives from least to most time consuming. This way, the quicker verifications are made in the beginning, paving the way to attaining a better understanding of the system and the testing facilities, which enables more complex studies. The resulting final order of investigation is shown in Table 9, alongside a brief description of the possible root cause. Nevertheless, each entry will be expanded further in chapter 6. Enhancement of proportional solenoid valve to manage variable displacement oil pump 66 Table 9: Evaluation Matrix of the possible root causes present on the Ishikawa diagram. Enhancement of proportional solenoid valve to manage variable displacement oil pump 67 6. TESTS AND RESULTS ANALYSIS In this chapter, each possible root cause is described in the following structure: ▪ Explanation of why it is a possible root cause; ▪ Description of the tests performed to confirm/rule out the root cause in question; ▪ Analysis of test results. Test viscosity, unless otherwise indicated, is of 4.5 cSt, as per the solenoid valve requirements stated on the customer drawing. Sample size used in each study was of 50 (fifty) parts, unless otherwise stated. For ease of reading, the presented data does not show results for all of the parts when they can be considered analogous. 6.1. Improper Operation of Test Bench Although Bontaz is equipped with pump test benches (Figure 55), these are typically only employed when a customer has a more specific request and ships the development team at Bontaz a pump to test the solenoid valve on. For this reason, as the bench is of less frequent usage than the prototype test benches (Figure 50), the team at BCUS is not as experienced in its operation, and might have been using incorrect parameters or a test configuration file which may, for example, have caused the pump to behave in an unusual manner. To rule out this possibility, the test’s configuration file made by the BCUS team was passed on to BCTP to be verified and remade, matching the slightly distinct test bench program. The time parameter had to be changed from hundredths of seconds to seconds, to match BCTP’s bench software, and the number of steps in the test file was simplified without altering the actual test sequence. The final test file elaborated at BCTP can be interpreted in Figure 66. Enhancement of proportional solenoid valve to manage variable displacement oil pump 68 Figure 66: Graphic of pump speed and solenoid valve current over time using the provided test file. In this test file, the vanne 2 is set to 0% (fully closed), which is unusual, as it is meant to correlate to engine backpressure. Having vanne 2 fully closed represents a completely clogged engine downstream of the main oil gallery. As this is the file with which correlation was established with the customer, this value was respected, nonetheless. Confirmation runs were tested on the pump bench with the final configuration file, which provided the test curves shown in Figure 67: Figure 67: BCTP test curve recreation graph. Previously defined problematic oscillation zone circled, with pump rotation speeds identified. Enhancement of proportional solenoid valve to manage variable displacement oil pump 69 There are clear differences between the data gathered from the test at BCTP and the graph from BCUS (Figure 65). These are mainly a consequence of the different sensors which are used on the test stands. BCTP data acquisition has a 100 Hz frequency (0.01 s period), whereas the BCUS bench only records data every 0.02 s (50 Hz). This means that the BCPT data can record faster fluctuations in the pressure values, capturing the spikes caused by sudden pump acceleration or solenoid valve closing (pump deregulation). Nonetheless, the maximum oscillation magnitude detected in this test was approximately 0.2 bar, as found in the BCUS test, and the mean pressure in this portion of the test is around 7 bar. Additionally, the increase in pressure oscillation which had been previously observed in Figure 65 can be located after the sudden drop at (3350*10-2) s and is much more noticeable in Figure 67. The pressure drop and variation in oscillation frequency was found to be caused by a sudden change in pump rotation speed, which is programmed to decrease from 1000 rpm to 718 rpm at this instant. 6.2. Valve SLR Mode Failure Although every Bontaz solenoid valve is functionally checked with oil at the end of the production line, something might have happened afterward (impacts, mishandling, etc.) which may have caused the SLR regulation to fail. If this is the case, the output pressure of the pump might be limited by the pump’s own pressure relief valve, instead of its regulation mechanism, for example. In order to check the valves’ functional requirements (SLR, P-A flow and A-T flow), the three test procedures explained in 4.4.2, 4.4.3, and 4.4.4 were run on every valve which was tested along the present work. All of the tested valves exhibited good results (within customer requirements), with stable curves analogous to those presented in Figure 61, Figure 62, and Figure 63. For this reason, SLR mode failure is discarded as the root cause of the oscillation. 6.3. Valve Mechanism Seized If contact between mobile components, namely the piston and body, involves any burrs or particle contamination, the movement of the piston along its intended length may be partially or totally impaired, causing it to have a choppy movement or to not move at all. Aditionally, from previous experience at Bontaz, it is known that excessively high surface roughness on the piston could result in an increase in friction to a point where its advance upon activation could be unstable. For this reason, a maximum surface roughness (Ra) is specified on the internal drawing of this part (Figure 68). Enhancement of proportional solenoid valve to manage variable displacement oil pump 70 Figure 68: Specified maximum roughness (Ra) values on the piston's outer surfaces. In order to assess this, a request was made to BCTP’s Mechanics team to make pistons with high roughness. In parallel, a few lower roughness samples were tested for comparison. From the piston’s drawing (Figure 68), it can be seen that the maximum surface roughness specified is 0.6 mm (Ra). Roughness measurements were obtained using the profilometer in Figure 69. Figure 69: Mitutoyo Contracer SV-C-3200 profilometer. Seven valves were then assembled and calibrated using these pistons. To check if this is the cause of instability, one can graph the test data from the P-A flow test and analyse the evolution of the flow as the current increases. If the piston movement is smooth – as intended – the curve will not present any visible steps and, instead, follow a smooth line. Should there be something hindering piston movement, the curve will show that some values of flow might stay constant as the Enhancement of proportional solenoid valve to manage variable displacement oil pump 71 current increases. This means that the solenoid is forcing its movement against an obstacle and opening as the it is cleared. The obtained data graphics can be seen in Figure 70. Figure 70: Flow over Current curves from the P-A Flow tests of valves built using the measured pistons. The smooth evolution of the curve and the absence of any steps shows that piston movement is smooth throughout the whole current range, proving that hindered movement of the piston due to surface roughness is not the cause for the observed instability. As for the other pre-built solenoid valves, the result of this test was analogous, as can be seen in Figure 71. Figure 71: Flow over current curves extracted from the P-A Flow tests of valves 1, 2, and 3. Enhancement of proportional solenoid valve to manage variable displacement oil pump 78 Figure 79: Fixture used for vibration test. Figure 80: Fixture with solenoid valves placed on the shaker. Sample - SV being tested; Control and Monitor accelerometers – sensors for fixture and SV acceleration measurement, respectively. The test procedure involves placing a control accelerometer in the fixture, and another, monitoring accelerometer on each valve at a time. The control accelerometer reads the fixed acceleration at the fixture, caused by the shaker. The monitor accelerometer reads the acceleration of the solenoid valve. When a difference between accelerometer readings is found, the valve is vibrating in relation to the fixture. When this vibration rises over a set limit, the valve is considered to be resonating (see Figure 81). Figure 81: Vibration test results from one of the four tested solenoid valves. Green line represents fixture acceleration, blue line shows solenoid valve acceleration. Results were analogous on the remaining three SV. The indicated values are correspondent to the peak relative acceleration between the fixture and the valve, at a frequency of 871.58 Hz and 1721.68 Hz. Both of these values are far above the established 300 Hz for all tested valves, so these do not exhibit resonance below the set limit, meaning that this factor should not be the cause for the oil pressure oscillation. Enhancement of proportional solenoid valve to manage variable displacement oil pump 79 6.9. Pulsating Pump Output Flow From the research done in 2.2.2, it is known that, even though positive displacement rotary pumps cause less pulsation than their reciprocating counterparts, their output flow still pulses due to the manner in which the pump operates. 6.9.1. Reasoning for Possible Root Cause In a viscous flow along a flow path, there is an intrinsic relation between flowrate and pressure drop. The following explanation provides an example of this relationship. According to Bernoulli’s Principle (equation 5), the energy of the fluid flowing between two points in a pipe with fixed characteristics (as represented in Figure 82) will decrease by a certain amount, denominated pressure drop, or ∆𝑃, due to friction losses. Figure 82: Schematic representation of oil flow through a straight pipe with constant cross-sectional area and internal surface roughness. Points 1 and 2 serve as references for equation 5. Point 1 is located upstream of Point 2. 𝑝1+1 2𝜌𝑣1 2+𝜌𝑔ℎ1= 𝑝2+1 2𝜌𝑣2 2+𝜌𝑔ℎ2+ Δp1−2 5 where: ▪ 𝑃 𝑥 is the pressure at point 𝑥; ▪ 𝜌 is the fluid’s density; ▪ 𝑣 is the fluid’s velocity; ▪ 𝑔 is the Earth’s gravity; ▪ ℎ is the height of the fluid. For a pipe like this, ∆𝑃 between points 1 and 2 is provided by the Darcy-Weisbach formula, stated in equation 6: Δ𝑃1−2 = 𝑓 𝐷∗𝐿 𝐷𝑃 ∗𝑣2 2∗ 𝜌 6 The Darcy friction factor, 𝑓 𝐷, is dependent on both fluid and pipe geometry, so it is constant if these are unchanged. 𝐷𝑃 and 𝑔 are maintained for the same pipe as well [69]. Enhancement of proportional solenoid valve to manage variable displacement oil pump 80 It is, then, possible to conclude that for the same pipe and fluid, Δ𝑝1−2 varies only with fluid velocity, which is a function of the flow rate, 𝑄, and cross-sectional area of the pipe, 𝐴, the latter being constant. 𝑣 = 𝑄 𝐴𝑠𝑒𝑐 7 Considering 𝑝2= 0 bar (atmospheric pressure), then 𝑝1= Δ𝑝1−2, meaning that pressure upstream varies in function of the flow rate. From these notions, it is concluded that pulsation in the pump’s output flow rate will theoretically result in a pulsation of the outlet pressure value, therefore, this could be the cause of the pressure oscillation. This in turn implies that pressure must also pulsate with the flow pulsation at the outlet of the pump, which feeds the solenoid valve at port P after passing through vanne 1. An outlet pressure oscillation could, therefore, trigger a cyclic instability, where the outlet pressure oscillation causes the input pressure at the solenoid valve to oscillate as well, thus compromising SLR mode stability. 6.9.2. Investigation through Simulation Model To study this hypothesis, a simulation model of the pump had to be developed using the Amesim software. The goal of this test was to obtain a functioning theoretical system which would help evaluate the oscillation at the outlet of the pump at different speeds and stator eccentricities, and not necessarily to perfectly represent the object of study, as such an investigation would require very extensive know-how on the pump and its simulation. 6.9.2.1. Test bench Hydraulic Characterisation As a tool to aid in setting up the simulation model and test bench if necessary, a more detailed version of the hydraulic diagram represented in Figure 54, now including the solenoid valve, was elaborated using the Fluidsim Hydraulic software (Figure 83): Enhancement of proportional solenoid valve to manage variable displacement oil pump 81 Figure 83: Hydraulic diagram of the pump bench and solenoid valve. From the analysis of this diagram, it is possible to conclude that, in normal operation, the flow meter shown does not receive the entirety of the oil pumped, because a portion of it goes to the solenoid valve and fills the regulation chamber, eventually making its way back to the reservoir. Moreover, when vanne 2 is fully closed, as said in 6.1, no oil reaches the flow meter at all. Instead, all of the oil goes to the solenoid valve, so it is not possible to measure pump output with this setup. 6.9.2.2. Dimensional Characterisation of the Pump The software includes a virtual vane pump model which needs to be parameterised, by providing some important dimensions, which could be retrieved from the CAD model of the pump. ▪ Number of vanes (8); ▪ Vane depth (height of the pump chambers; ▪ Rotor outside diameter; ▪ Stator inside diameter; ▪ Maximum angle of rotation of the stator. 6.9.2.3. Hydraulic Characterisation of the Pump In order to establish a correlation between the simulation model and the real pump, a baseline reference for pump behaviour across a range of speeds is necessary. To guarantee that the stator maintains its position across the different tests, regulation was disabled completely, by closing the shut off valve shown Enhancement of proportional solenoid valve to manage variable displacement oil pump 82 in Figure 83. The pump was then tested at several different speeds with the standard restriction only in vanne 1 (80 %), providing the values shown in Table 10: Table 10: Unregulated pump flow per revolution values obtained in bench testing. Cells highlighted in yellow correspond to the pump speeds where oscillation has been found in the EoL test. As expected, without regulation the flow per revolution remains approximately constant even as pressure increases at the outlet. On the other hand, for measuring output flow during the oscillation test, an additional flow meter was placed between the shut off valve and the SV, such as illustrated in the update hydraulic diagram (Figure 84). Figure 84: Updated hydraulic diagram of the pump bench and solenoid valve with additional flow meter installed. The original oscillation test configuration was followed, with vanne 2 fully closed, meaning that all of the output flow from the pump goes to the solenoid valve. An example of obtained in this test are shown in Figure 85, with the points where flow was measured noted. Enhancement of proportional solenoid valve to manage variable displacement oil pump 83 Figure 85: Example of BCTP sequence pump test curve where flow to the solenoid valve has been measured. Blue line represents pressure, orange line represents current, and yellow line represents flow. Numbers show the points where parameters were monitored. Table 11 contains the flow rates measured during the oscillation portion of the test: Table 11: Data gathered in each point specified in Figure 85. This information shows that the pump is providing the same total output flow at 1000 rpm and at 718 rpm despite the speed difference, implying that the stator is in a distinct regulation angle. This is confirmed by checking the disparity in the values of flow per revolution for points 4 and 5. 6.9.2.4. Simulation Model Obtained Having provided the data for characterisation of the pump, the simulation model was made using Amesim’s vane pump template. Enhancement of proportional solenoid valve to manage variable displacement oil pump 84 Figure 86: Virtual vane pump model hydraulic diagram made with Amesim. Inlet and outlet purely representative. As previously explained, this model allows for a good understanding of the pump but is not 100 % accurate at representing the system. The angle of the stator is perfectly fixed and not regulated by the solenoid valve, and there is only one restriction to the output flow instead of the two vannes in the pump bench. This restriction was defined to match the flow/pressure relationship found in Table 11. Besides this hydraulic scheme representation, Amesim provides a scheme of the pump to allow a better visualisation of the chambers’ volumes throughout their rotation and the eccentricity between rotor and stator (Figure 87). Figure 87: Amesim pump model in fully unregulated position. Inlet represented in blue, outlet shown in red. Shaft rotates counterclockwise. Having defined the pump model, behaviour during the part of the test which exhibits the greatest magnitude of oscillation (point 5 in Figure 85) was mimicked in order to verify whether the flow output from the pump shows this - it was necessary to find the position of the stator during this phase, portrayed in Figure 88. Enhancement of proportional solenoid valve to manage variable displacement oil pump 85 Figure 88: Amesim pump model with stator regulated to 4.8º rotation. Inlet represented in blue, outlet represented in red. Shaft rotates counterclockwise. This angle of 4.8º was defined through an iterative process, applying angles between 0º and 8.4º (maximum angular regulation), until average output flow approximately matched that of point 5 (5.2 L/min). The output of the pump, in this position, provided by the simulation software is presented in Figure 89. Figure 89: Regulated (4.8º) pump output flow and pressure at 718 rpm provided by the Amesim model. It is very clear from the analysis of this graphic that the software is capturing the theoretical output oscillation characteristic of this kind of pump. As a way to comprehend how pulsation might vary according to the stator’s position, another simulation was run. However, this time, the stator was left in its unregulated position (Figure 87), and rotation speed was adjusted until the average output of the pump was approximately that of Figure 89 – 177 rpm. The output of the pump at this speed (with the same restriction applied) is shown in Figure 90. Enhancement of proportional solenoid valve to manage variable displacement oil pump 86 Figure 90: Unregulated pump output flow and pressure at 177 rpm provided by the Amesim model. As the pulsations in these graphics is periodic, their respective frequencies can be estimated by counting the number of peaks during one second. A comparison of the values from Figure 89 and Figure 90 is shown in Table 12. Table 12: Comparison between Figure 89 Figure 90 speeds, frequencies, and pressure values. Since the pump has eight vanes and, therefore, eight chambers in between them, for each rotation of the rotor there are eight discharges of oil. To verify the frequencies counted in these graphics, the number of discharges per second can be calculated using the pump speed in rpm, 𝑍, per equation 8: 𝑓 = 8𝑍 60 𝐻𝑧 8 This equation provides a discharge frequency of 23.6 Hz for 177 rpm, and 95.7 Hz for 718 rpm, confirming the estimates in Table 12. When it comes to pressure, minimum values are approximately equal, however, the maximum and magnitude figures are greater for 177 rpm (unregulated pump) than for 718 rpm (regulated). 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