Pump system and process for optimized torque requirements and volumetric efficiencies

Abstract

A pump system (20) comprising a gerotor pump, comprising: a housing (34) defining a surface; and an idle wheel (32), a rotor (30) defining a surface, wherein a surface clearance (50) is defined between the surface and the surface (44), wherein the surface clearance (50) is variable in its extent and determines the desired performance characteristics of the pump system (20), wherein the housing (34) comprises a first material selected to have a first thermal expansion property, wherein the rotor (34) comprises a second material selected to have a second thermal expansion property, wherein the first thermal expansion property and the second thermal expansion property provide the desired performance characteristics of the pump system, wherein the first thermal expansion property and the second thermal expansion property comprise a greater expansion of the rotor (30) than that of the housing in response to increasing temperature, wherein the first thermal expansion property and the second thermal expansion property result in the surface clearance (50) being opened when the temperature decreases and the surface clearance (50) being closed when the temperature increases, comprising a motor coupled to the rotor (30), wherein the first thermal expansion property and the second thermal expansion property comprise a targeted increase in the surface clearance (50) with decreasing temperature in order to minimize the torque requirements of the motor, wherein the first thermal expansion property and the second thermal expansion property comprise a targeted maximization of the volumetric efficiency of the pump system (20) with increasing temperature, where: the housing (34) defines a cavity, wherein the rotor (30) is arranged in the cavity, the cavity is closed by a cover (36) defining a second surface, the rotor (30) comprises the surface facing the surface of the housing and a second surface facing the second surface, a first gap is defined between the surface and the surface of the housing (34), a second gap is defined between the second surface and the second surface, and the surface clearance (50) is a sum of the first gap and the second gap, wherein the housing (34) is made of steel and the rotor (30) and the idler wheel (32) are made of aluminum.

Description

INTRODUCTION

[0001] The present disclosure relates generally to the field of pumping systems, and more particularly to pumping systems that provide desired and tunable performance characteristics by utilizing thermal expansion rates.

[0002] Pumping systems of devices such as vehicles and other equipment and machinery move fluids and / or generate pressure for a variety of purposes. There are many types of pumps, and each generally requires a drive device (motor), such as an electric, pneumatic, hydraulic, or mechanical drive, to power the moving parts of the pump. The design and operating conditions of the pump determine the amount of torque or power required to drive the moving parts. The amount of torque or power required affects the cost, weight, and type of drive device suitable for the application. Characteristics of pumps include the relationship between the volume, flow, and pressure at different drive speeds, the relationship between the output pressure and the flow and the supplied energy (e.g.Torque or force) and the actual amount of fluid flowing through a pump, not its theoretical maximum (volumetric efficiency). Volumetric efficiency can also be described as a measure of volumetric losses, e.g., due to internal leakage and fluid compression.

[0003] The torque / power requirements for driving a pump determine the size and cost of the drive device coupled to the pump. The volumetric efficiency of the pump affects the size of the pump that can meet the power requirements for a particular application. In applications such as automotive, size and its impact on weight can affect factors such as fuel consumption. Therefore, torque and power requirements, as well as volumetric efficiency, are considered, among other factors, when designing pump systems.

[0004] Accordingly, it is desirable to provide a pump system for a particular application that results in suitable performance characteristics such as torque / force requirements and volumetric efficiencies. Furthermore, other desirable features and characteristics of the present invention will become apparent from the following detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.

[0005] DE 10 2005 061 880 A1 describes a fuel pump in which pumping elements are mounted in a housing section to transport fuel from a suction to a pressure area. To increase wear resistance, the housing consists of a metallic base material in which a ceramic filler material is embedded. This material is also suitable for die-casting.

[0006] DE 103 56 807 A1 relates to a positive displacement pump, in particular an external gear pump, in which the housing and the displacement elements, in particular gears with external teeth, are made of different materials. It is proposed that the housing material have a lower coefficient of thermal expansion than the material of the displacement elements in order to specifically influence temperature-related tolerance changes during operation.

[0007] DE 10 2014 107 735 A1 discloses a vane for a vane pump, in particular a vacuum pump, in which the vane body has an opening on at least one end face, in which an insert is mounted for axial displacement. This allows for improved adaptation of the vane to the cover or floor of the pump chamber to reduce leakage and increase pump efficiency.

[0008] DE 10 2005 033 679 A1 shows an oil pump with a cam ring made of a material with a low coefficient of thermal expansion and a pump element rotatably mounted within it. Housing elements made of materials with higher coefficients of thermal expansion are arranged on both sides of the cam ring. The targeted selection of materials achieves a temperature-dependent sealing effect, which optimizes the pump's gap behavior and improves efficiency.

[0009] JP 2001 - 207 974 A provides an oil pump in which the outer rotor is made of a material with a relatively low linear thermal expansion coefficient (e.g., sintered iron alloy), while the inner rotor is made of a material with a higher thermal expansion coefficient (e.g., aluminum alloy). This ensures good pumping performance, especially at high temperatures, in a simple and cost-effective manner and effectively suppresses leakage.

[0010] US 2005 / 0 063 851 A1 relates to improved gerotor pumps in which the outer rotor is laterally offset relative to a preferred eccentricity axis, but can move freely along this axis. This allows it to self-align via the meshing of the gerotors. Higher output pressures can be achieved by reducing operating clearances, particularly by adapting the shape of the rotor tips. DESCRIPTION

[0011] The object of the invention is to optimize the performance and efficiency of a pump system over a wide temperature range without having to resort to complex electronic controls or mechanical adjustment mechanisms.

[0012] This object is achieved by an object according to claim 1. Further developments can be found in the subclaims.

[0013] Systems and methods are provided for pumping systems that deliver desirable performance characteristics under prescribed conditions. In various embodiments, a pumping system includes a housing defining a surface and a rotor defining a face. A face clearance is defined between the face and the surface. The face clearance is variable in magnitude and determines the desired performance characteristics of the pumping system. The housing is made of one material having a selected thermal expansion property, and the rotor is made of a second material having a different selected thermal expansion property. The thermal expansion properties provide the desired performance characteristics of the pumping system.

[0014] In further embodiments, the thermal expansion characteristics cause the rotor to expand more than the housing in response to increasing temperature.

[0015] In other embodiments, one of the materials is steel and the other is aluminum.

[0016] In further embodiments, the thermal expansion properties cause the surface clearance to open as the temperature decreases and the surface clearance to close as the temperature increases.

[0017] In further embodiments, the thermal expansion properties ensure an adjusted expansion of the rotor and the housing in response to increasing temperature, thereby keeping the surface clearance at a constant value.

[0018] In other embodiments, a motor is coupled to the rotor. The thermal expansion properties ensure a targeted increase in the surface clearance as the temperature decreases, thus minimizing the motor's torque requirements.

[0019] In further embodiments, the thermal expansion properties are selected to maximize the volumetric efficiency of the pump system with increasing temperature.

[0020] In further embodiments, an electric motor is coupled to the rotor, and power electronics are coupled to the electric motor. The thermal expansion properties are selected to minimize the size of the electric motor.

[0021] In further embodiments, the rotor comprises a gerotor, and an idler wheel surrounds the gerotor.

[0022] In further embodiments, the housing defines a cavity, with the rotor arranged in the cavity. The cavity is closed by a cover defining another surface, and the rotor comprises the surface facing the surface of the housing and another surface facing the other surface. Gaps are defined between the respective surfaces and the surface of the housing. The surface clearance is the sum of the two gaps.

[0023] In various other embodiments, a method comprises constructing a pump having a housing defining a surface. A rotor is mounted within the pump, the rotor defining a surface. A surface clearance is defined between the surface and the surface, the surface clearance being variable in magnitude. Based on the surface clearance, the desired performance characteristics of the pump system are determined. A material having a thermal expansion property is selected for the housing. A material also having a thermal expansion property is selected for the rotor. The two thermal expansion properties result in the desired performance characteristics of the pump system.

[0024] In further embodiments, the thermal expansion characteristics cause the rotor to expand more than the housing in response to increasing temperature.

[0025] In other embodiments, steel is chosen as the material for the housing and aluminum as the material for the rotor.

[0026] In further embodiments, the thermal expansion properties cause the surface clearance to open as the temperature decreases and the surface clearance to close as the temperature increases.

[0027] In further embodiments, the adjustment based on thermal expansion properties provides a matched expansion of the rotor with that of the housing in response to increasing temperature, while maintaining the face clearance at a constant value.

[0028] In further embodiments, a motor is coupled to the rotor. The thermal expansion properties aim to increase the surface clearance as temperature decreases to minimize the motor's torque requirements.

[0029] In further embodiments, the thermal expansion properties aim to maximize the volumetric efficiency of the pump system as the temperature increases.

[0030] In further embodiments, an electric motor is coupled to the rotor, and power electronics are coupled to the electric motor. The thermal expansion properties are selected to minimize the size of the electric motor.

[0031] In further embodiments, a range of materials is considered to achieve the desired performance characteristics. Materials are selected that are best suited to minimize torque requirements at lower temperatures and maximize volumetric efficiency at higher temperatures. The selected materials are tuned by altering their thermal expansion properties to exhibit a desired amount of face clearance at specific temperatures.

[0032] In various additional embodiments, a housing defines a surface, a rotor defines a face, and a face clearance is defined between the face and the surface. The face clearance is variable in magnitude and determines the desired performance characteristics of the pumping system. A motor is coupled to the rotor. The housing is made of a material selected to have a desired thermal expansion characteristic, and the rotor is made of a material selected to have a different thermal expansion characteristic. The first thermal expansion characteristic results in a greater expansion of the rotor compared to that of the housing as temperatures increase. The expansions provide for a minimized torque requirement of the motor as temperatures decrease and for maximum volumetric efficiency of the pumping system as temperatures increase. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The exemplary embodiments are described below in conjunction with the following drawings, wherein like numerals indicate like elements and wherein: Fig. 1 is a schematic representation of a pump system according to various embodiments; Fig. 2 a detailed view of part of the pump system of Fig. 1 is in accordance with various embodiments; Fig. 3 a schematic detailed representation of part of the pump system of Fig. 1 in a first state according to various embodiments; Fig. 4 a schematic detailed representation of the part of the pump system of Fig. 1 in a second state according to various embodiments; Fig. 5 a diagram of the surface clearance in millimetres as a function of the temperature in degrees Celsius for the pump system of Fig. 1 is in accordance with various embodiments; Fig. 6 a diagram of the input power in watts versus the speeds in revolutions per minute for the pump system of Fig. 1 and for a comparative example according to various embodiments; and Fig. 7 a method for constructing the pump system of Fig. 1 in accordance with various embodiments. DETAILED DESCRIPTION

[0034] The following detailed description is merely exemplary and is not intended to limit the application and use. Furthermore, there is no intention to be bound by any express or implied theory presented in the preceding introduction, the description, or the following detailed description.

[0035] As disclosed herein, pump systems are provided that exhibit desirable performance characteristics over a significant range of operating temperatures by utilizing the thermal expansion properties of various components of the system. For example, in a system including an internal gear pump, the stationary housing of the pump is made of one material and the moving rotor of the pump is made of a different material. The two materials are selected and matched to exhibit specific thermal behaviors that result in the desired performance characteristics. For example, the housing material is selected to have a relatively low coefficient of thermal expansion, and the rotor material is selected to have a relatively high coefficient of thermal expansion. In one embodiment, the coefficient of thermal expansion of the rotor material is approximately twice that of the housing material.The result can be adjusted to achieve low torque requirements at colder temperatures while maintaining high volumetric efficiency at warmer temperatures. In certain embodiments, the results are the result of controlling clearances, such as face clearance, over a wide temperature range.

[0036] In an example application, a pumping system may operate under conditions that range widely, such as minus forty degrees Celsius to one hundred and twenty-five degrees Celsius. Such applications include vehicle pumps, which are exposed to ambient temperatures in a variety of environments and where the fluid may be heated by the operation of the pumping system. Controlling the face clearance for cold-temperature operation results in minimal input torque requirements, including starting torque, allowing the use of a relatively small motor. Controlling the face clearance for hot-temperature operation maximizes volumetric efficiency, allowing a relatively smaller pump, both physically and in terms of displacement, to be used for a given application than would otherwise be possible.The result is a minimization of the energy input and energy consumption required to drive the pump system.

[0037] In various embodiments, a pump system is configured to move a fluid / generate pressure through at least two relatively movable parts, such as a rotor and a housing. The relative movement of the parts requires a clearance dimensioned to account for variations in part manufacturing within tolerance ranges, the nature of the pumped fluid, and temperature variations. One component has a coefficient of thermal expansion adjusted to a first expansion level, and the other component has a coefficient of thermal expansion adjusted to a second expansion level, with both expansion levels adjusted to achieve the performance characteristics desired for the application, such as drive power and volumetric efficiency, over the applicable operating temperature range.

[0038] In the embodiments disclosed herein, certain motor types, pump types, and material combinations may be described. In other embodiments of the present disclosure, as described in the claims, other torque input devices (motors), other fluid drivers (pumps), and other material combinations are contemplated. For example, metallic materials may be described based on their desired thermal behavior; however, the present disclosure is not limited to metallic materials; any material suitable for the components, applications, and desired thermal behavior may be used. As further examples, plastics, polymers, ceramics, composites, or other materials may be used.In some embodiments, one or more components may be made from a material that has limited thermal expansion, and the other components may be made from a material whose thermal expansion properties are tailored to the desired results. In other embodiments, the thermal expansion properties of the various components may be selected and matched to achieve the desired results. In some embodiments, the thermal expansion properties may be matched to achieve a consistent response.

[0039] As in Fig. 1, a pumping system 20 generally includes a motor 22 coupled to a pump 24. The motor 22 is a drive device that moves parts of the pump 24 to operate the pump 24 and, in various embodiments, uses electrical energy, pneumatic energy, hydraulic energy, mechanical energy, or a combination thereof. The transmitted motion may be rotary, linear, or otherwise configured. In the present embodiment, the motor 22 is electric and transmits torque to the drive elements of the pump 24 via a shaft 26. The motor 22 may be various types of electric motors; one example is a brushless direct current (BLDC) motor driven by a controller and power electronics 28, which may be housed separately or together.The size of the motor 22 determines the capacity of the power electronics 28 and thus the cost and weight of the power electronics 28. The output power of the motor 22 can be specified in watts, which varies depending on the motor speed, while the output torque, e.g., in Newton meters, generally remains constant throughout the motor's operating speed. The torque required to drive the pump 24 is a determining factor in the size and cost of the motor 22 and the associated power electronics 28. Therefore, it is advantageous to minimize the torque requirements of the pump system 20.

[0040] Generally, the pump 24 is used to move fluids and / or generate fluid pressure for any number of purposes. In the present embodiment, the pump 24 may be an internal gear pump, and more particularly, a gerotor pump. The moving parts include a rotor 30 (gerotor gear) attached to the shaft 26 and an idler 32 in which the rotor 30 runs and which may also rotate. The moving parts, including the idler 32 and the rotor 30, are located in a housing 34 having a cover 36. The housing 34 defines a cavity 38 containing the rotor 30 and the idler 32 and which is closed by the cover 36. The rotor 30 may generally float in a hydraulic film within the housing 34 created by the pumped fluid.The surfaces 40, 42 of the rotor 30 are running surfaces and face in opposite directions, parallel to the shaft 26. Surface 40 faces a surface 44 in the housing cavity 38, and surface 42 faces a surface 46 of the cover 36.

[0041] There may be gaps or gaps around the rotor 30, one between the face 40 and the surface 44 and another between the face 42 and the surface 46. These two gaps / gaps may change as the rotor 30 approaches the surface 44 or the surface 46 and may be considered together as a sum, collectively referred to as the face clearance 50. The face clearance 50 is causative of various factors (performance characteristics), including the torque to rotate the rotor 30 provided by the motor 22 and the volumetric efficiency of the pump 24. The face clearance 50 may also apply to the idler gear 32. In a number of embodiments, the idler gear 32 may be a design factor in selecting thermal expansion characteristics to optimize torque and volumetric efficiency requirements and achieve the desired performance characteristics.

[0042] The idler 32 has face clearances (like the rotor 30) and an additional face clearance of the outer diameter 52 to the housing 34. The thermal expansion of the idler 32 relative to the housing 34 can be a factor in the optimization. The idler 32 has face clearance characteristics and a design freedom independent of the rotor 30 with regard to the material properties and the selection of face clearances (multiple S face clearances), resulting in a possible third material thermal expansion characteristic. Another consideration can be an operating clearance between the rotor 30 and the idler 32 as a variable for optimizing torque and volumetric efficiency.

[0043] One objective of the pumping system 20 is to achieve a combination of minimizing torque requirements, particularly at cold temperatures where the pumped fluid may be at its most viscous, and maximizing volumetric efficiency, particularly at hot temperatures where the pumped fluid may be at its least viscous. To achieve this somewhat contradictory combination, the pump 24 is designed to have a larger face clearance 50 at cold temperatures and a smaller face clearance 50 at hot temperatures. The combination can be tuned to balance the performance benefits by providing a larger gap when less fluid resistance to rotation is desired, e.g., for lower torque requirements, and a smaller gap when less internal fluid leakage is desired, e.g., for higher volumetric efficiency.The result is lower pump, motor and associated costs while simultaneously increasing the performance of the pump system.

[0044] In Fig. 2, the moving parts of the pump 24, in particular the idler wheel 32 and the rotor 30, are shown in isolation. When the rotor 30 rotates on the shaft 26, suction and pressure areas for pumping liquid are created between the rotor 30 and the idler wheel 32. During operation, the surface clearance 50 can vary, as shown in the Fig. 3 and Fig. 4. For example, the surface clearance 50 may be larger at lower temperatures, as shown in Fig. 3, and at higher temperatures the surface clearance 50 can be smaller, as shown in Fig. 4. This behavior is advantageously achieved by the selection of materials used to manufacture components such as the rotor 30 and the housing 34. For example, the rotor 30 and the housing 34 can be made of materials whose thermal expansion coefficients are selected so that the rotor 30 expands more than the housing 34 to close the face clearance as temperatures increase. In other embodiments, the thermal expansion coefficients can be adjusted, taking into account the physical dimensions of the parts, so that the face clearance 50 remains constant during temperature changes. In other embodiments, various combinations of results can be achieved by adjusting the thermal expansions of the rotor 30 and the housing 34 to achieve the size of the face clearance 50 at temperatures of interest to the application.In other embodiments, the face clearance 50 and the face clearance of the outer diameter 52 of the idler gear 32 can be adjusted to match the thermal expansions at the desired temperatures. In several embodiments, the thermal expansions can be adjusted to achieve the desired performance characteristics. In the present embodiment, the desired performance results include the torque requirement and the achieved volumetric efficiency. The two results can be balanced by the selection of the materials used and their thermal expansion coefficients. One choice of materials to achieve the desired results is the use of steel for the housing 34 and aluminum for the rotor 30.The thermal expansion coefficient of the resulting rotor 30 is approximately twice that of the housing 34, so that the face clearance 50 closes as the temperature rises and opens as the temperature decreases. The idler wheel 32 can be made of steel, aluminum, or another material to achieve the desired thermal and performance characteristics.

[0045] As in Fig. 5, a graph shows the face clearance 50 of the pumping system 20 on the vertical axis 60 in millimeters versus the temperature on the horizontal axis 62 in degrees Celsius. In various embodiments, the temperatures are those to which the pumping system 20 is exposed and can be the result of a number of factors. For example, after a cold period in which the pumping system 20 was not operating in cold ambient conditions, the temperature is the result of the ambient temperature. If the pumping system 20 was operating in hot ambient conditions, the temperature is the result of the ambient temperature and can also be the result of rising temperature due to the processing of the pumped fluid. In the present embodiment, the temperatures to which the housing 34 and the rotor 30 are exposed are of interest.

[0046] Curve 64 shows the pump system 20 responding to achieve low torque at cold temperatures to minimize the size of the motor 22, and to achieve high volumetric efficiency at hot temperatures to minimize the capacity / size of the pump 24. Specifically, at approximately minus forty degrees Celsius, the relative thermal expansion of the housing 34 and the rotor 30 is adjusted to achieve a face clearance 50 of approximately 0.073 millimeters at location 66. At approximately one hundred ten degrees Celsius, the relative thermal expansion of the housing 34 and the rotor 30 is adjusted to achieve a face clearance 50 of approximately 0.053 millimeters at location 68. This result can be achieved, for example, by constructing the housing 34 from steel and the rotor 30 from aluminum.In several embodiments, the curve 64 is shifted vertically by the design / material selection, and the materials can be tuned to change the slope of the curve 64. For example, the size of the surface clearance 50 can be increased or decreased across the temperature range by the choice of component materials.

[0047] Curve 70 shows the pump system 20 with a response that achieves a constant face clearance 50 regardless of temperature. In particular, at approximately minus forty degrees Celsius, the relative thermal expansion of the housing 34 and the rotor 30 is adjusted to achieve a face clearance 50 of approximately 0.060 millimeters. At approximately one hundred ten degrees Celsius, the relative thermal expansion of the housing 34 and the rotor 30 is adjusted to achieve a face clearance 50 of approximately 0.60 millimeters. This result can be achieved, for example, by manufacturing the housing 34 from steel and the rotor 30 from steel. In some embodiments, the alloy composition of the steel can be adjusted to achieve this uniform behavior.

[0048] Curve 72 represents the pump system 20 with a response that shows the results of the material selection for comparison purposes. For example, if the rotor 30 is made of steel and the housing 34 is made of aluminum, the temperature change has the opposite effect to curve 64. At minus 40 degrees Celsius, the relative thermal expansion of the housing 34 and the rotor 30 is adjusted to achieve a face clearance 50 of approximately 0.042 millimeters. At 110 degrees Celsius, the relative thermal expansion of the housing 34 and the rotor 30 is adjusted to achieve a face clearance 50 of approximately 0.062 millimeters.

[0049] Curves 64 and 72 intersect at point 74, which is located at approximately 75 degrees Celsius. At point 74, the performance of pump system 20 is the same regardless of whether rotor 30 is made of aluminum and housing 34 of steel, or whether rotor 30 is made of steel and housing 34 of aluminum. Curves 64 and 70 intersect at point 76, which is located at approximately 90 degrees Celsius.

[0050] In Fig. Figure 6 is a graph of power in watts on the vertical axis 78 versus the speed of the rotor 30 in revolutions per minute on the horizontal axis 80. The graph shows an example of the pump system 20 with a steel housing 34 and a steel rotor 30 in curve 82 and the pump system 20 with a steel housing 34 and an aluminum rotor 30 in curve 84. Both curves 82 and 84 show the power requirement at a temperature of twenty degrees Celsius. As shown, curve 84 results in a reduction in power requirement of up to twenty-one percent, which is achieved by adapting the materials used to their thermal behavior.

[0051] A method 100 for designing a pump system to optimize the torque requirements and volumetric efficiencies of the pump system 20 is described in Fig.7 is presented in flowchart form, to which reference is made. The temperatures at which the pumping system 20 is to operate are determined 102. The objectives for the pumping system are established 104. For example, the temperatures at which the required power of the motor 22 is minimized and the temperatures at which the volumetric efficiency of the pump 24 is maximized are determined. In the case of a vehicle application, the temperatures of interest may be between minus forty and one hundred and twenty-five degrees Celsius. A specific temperature of interest may be between minus forty and one hundred and ten degrees Celsius. The size of the face clearance 50 and / or the face clearance of the outer diameter 52 to achieve the determined objectives 102 is calculated 106.The pump system 20 can be modeled, for example, using commercially available fluid dynamics modeling software, or other calculations can be used. Alternatively, physical modeling and testing can also be performed. The materials, e.g., for the housing 34, the rotor 30, and the idler 32, and their thermal expansion coefficients are taken into account 106. For example, various materials can be considered 106, the performance characteristics of which are modeled using software and / or physically. A selection 110 is made from the materials considered 106 in order to achieve the calculated 106 surface clearances 50 and / or 52 at the determined target temperatures 104. Next, the necessary tuning 112 is performed to adapt the performance of the pump system 20, e.g.,to achieve the desired torque requirements and / or volumetric efficiencies at the desired temperatures. The pump system 20 is then constructed 114 using the selected materials for the rotor 30, the idler 32, and the housing 34 that achieve the desired results. In several embodiments, the order of steps in the method 100 may vary from those described herein; other steps may be added, and some steps may be omitted.

[0052] Accordingly, pumping systems and methods are provided in which the torque requirement is minimized at low operating conditions and volumetric efficiency is maximized at high operating conditions. While at least one exemplary embodiment has been presented in the foregoing detailed description, it should be appreciated that a large number of variations exist. It should also be noted that the exemplary embodiment or embodiments are merely examples and are not intended to limit the scope, applicability, or configuration of the disclosure in any way. Rather, the foregoing detailed description is intended to provide those skilled in the art with a practical guide for implementing the exemplary embodiment or embodiments.It is to be understood that various changes in the function and arrangement of elements may be made without departing from the scope of the disclosure as set forth in the appended claims and their legal equivalents.

Claims

[1] A pump system (20) comprising a gerotor pump, comprising: a housing (34) defining a surface; and an idle wheel (32), a rotor (30) defining a surface, wherein a surface clearance (50) is defined between the surface and the surface (44), wherein the surface clearance (50) is variable in its extent and determines the desired performance characteristics of the pump system (20), wherein the housing (34) comprises a first material selected to have a first thermal expansion property, wherein the rotor (34) comprises a second material selected to have a second thermal expansion property, wherein the first thermal expansion property and the second thermal expansion property provide the desired performance characteristics of the pump system, wherein the first thermal expansion property and the second thermal expansion property comprise a greater expansion of the rotor (30) than that of the housing in response to increasing temperature, wherein the first thermal expansion property and the second thermal expansion property result in the surface clearance (50) being opened when the temperature decreases and the surface clearance (50) being closed when the temperature increases, comprising a motor coupled to the rotor (30), wherein the first thermal expansion property and the second thermal expansion property comprise a targeted increase in the surface clearance (50) with decreasing temperature in order to minimize the torque requirements of the motor, wherein the first thermal expansion property and the second thermal expansion property comprise a targeted maximization of the volumetric efficiency of the pump system (20) with increasing temperature, where: the housing (34) defines a cavity, wherein the rotor (30) is arranged in the cavity, the cavity is closed by a cover (36) defining a second surface, the rotor (30) comprises the surface facing the surface of the housing and a second surface facing the second surface, a first gap is defined between the surface and the surface of the housing (34), a second gap is defined between the second surface and the second surface, and the surface clearance (50) is a sum of the first gap and the second gap, wherein the housing (34) is made of steel and the rotor (30) and the idler wheel (32) are made of aluminum.

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