Patent Publication Number: US-11661938-B2

Title: Pump system and method for optimized torque requirements and volumetric efficiencies

Description:
INTRODUCTION 
     The present disclosure generally relates to the field of pump systems and more specifically, to pump systems providing desired and tunable performance characteristics by leveraging thermal expansion rates. 
     Pump systems of apparatus such as vehicles and other equipment and machinery, move fluids and/or generate pressures for a variety of purposes. Many types of pumps are available and each generally requires a motive input device (motor), such as one that operates on electric, pneumatic, hydraulic, or mechanical power to drive moving parts of the pump. The design and operating conditions of the pump determine the amounts of torque or force required to drive the moving parts. The amount of torque/force required influences the cost, weight and type of the motive input device that is appropriate for use. Characteristics of pumps include the relationship between the volume, flow and the pressure at different driving speeds, the relationship between the output pressure and flow and the provided input energy (such as torque or force), and the actual amount of fluid flowing through a pump, rather than its theoretical maximum (volumetric efficiency). Volumetric efficiency may also be described as a measure of volumetric losses, such as through internal leakage and fluid compression. 
     The torque/force requirements for driving a pump, determine the size and cost of the motive input device coupled with the pump. The pump&#39;s volumetric efficiency has an impact on the size of the pump that will achieve performance requirements for a given application. In applications such as those for vehicles, size and its impact on weight may have an influence on factors such as fuel economy. As a result, in designing pump systems, the torque/force requirements and the volumetric efficiencies, along with other factors, are taken into consideration. 
     Accordingly, it is desirable to provide a pump system for a given application that results in appropriate 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 subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background. 
     SUMMARY 
     Systems and methods are provided for pump systems that deliver desirable performance characteristics at prescribed conditions. In various embodiments, a pump 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 determinative of target performance characteristics of the pump system. The housing is made of a material selected to have a thermal expansion characteristic and the rotor is made of a second material selected to have another thermal expansion characteristic. The thermal expansion characteristics deliver the target performance characteristics of the pump system. 
     In additional embodiments, the thermal expansion characteristics deliver a greater expansion of the rotor than that of the housing, in response to temperature increases. 
     In additional embodiments, one of the materials is steel and the other material is aluminum. 
     In additional embodiments, the thermal expansion characteristics result in opening the face clearance as temperature decreases and closing the face clearance as temperature increases. 
     In additional embodiments, the thermal expansion characteristics provide a matched expansion of the rotor and with that of the housing in response to temperature increases, maintaining the face clearance at a consistent value. 
     In additional embodiments, a motor is coupled with the rotor. The thermal expansion characteristics deliver a targeted increase of the face clearance as temperature decreases, minimizing torque requirements of the motor. 
     In additional embodiments, the thermal expansion characteristics are selected to target maximization of the volumetric efficiency of the pump system as temperature increases. 
     In additional embodiments, an electric motor is coupled with the rotor, and power electronics are coupled with the electric motor. The thermal expansion characteristics are selected to minimize size of the electric motor. 
     In additional embodiments, the rotor comprises a gerotor, and an idler surrounds the gerotor. 
     In additional embodiments, the housing defines a cavity, with the rotor disposed in the cavity. The cavity is closed by a cover defining another surface, and the rotor includes the face, which faces the surface of the housing and includes another face facing the other surface. Gaps are defined between respective faces and the surfaces of the housing. The face clearance is a sum of the two gaps. 
     In various other embodiments, a method includes constructing a pump with a housing defining a surface. A rotor is assembled in the pump, with the rotor defining a face. A face clearance is defined between the face and the surface, with the face clearance being variable in magnitude. Based on the face clearance, target performance characteristics of the pump system are determined. A material is selected for the housing that has a thermal expansion characteristic. A material is selected for the rotor and also has a thermal expansion characteristic. The two thermal expansion characteristics deliver the target performance characteristics of the pump system. 
     In additional embodiments, the thermal expansion characteristics deliver a greater expansion of the rotor than that of the housing, in response to temperature increases. 
     In additional embodiments, steel is selected as the material for the housing and aluminum is selected as the material for the rotor. 
     In additional embodiments, the thermal expansion characteristics result in opening the face clearance as temperature decreases, and in closing the face clearance as temperature increases. 
     In additional embodiments, matching, based on the thermal expansion characteristics deliver a matched expansion of the rotor with that of the housing in response to temperature increases, maintaining the face clearance at a consistent value. 
     In additional embodiments, a motor is coupled with the rotor. The thermal expansion characteristics target increase of the face clearance as temperature decreases to minimize torque requirements of the motor. 
     In additional embodiments, the thermal expansion characteristics target maximization of the volumetric efficiency of the pump system as temperature increases. 
     In additional embodiments, an electric motor is coupled with the rotor and power electronics are coupled with the electric motor. The thermal expansion characteristics are selected to minimize size of the electric motor. 
     In additional embodiments, a range of materials are considered to deliver the target performance characteristics. The materials that best deliver minimized torque requirements at lowered temperatures and maximized volumetric efficiency at increased temperatures are selected. The selected materials are tuned by altering their thermal expansion characteristics to deliver a desirable magnitude of the face clearance at select temperatures. 
     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 is determinative of desired target performance characteristics of the pump system. A motor is coupled with 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 another thermal expansion characteristic. The first thermal expansion characteristics deliver a greater expansion of the rotor as compared to that of the housing under increasing temperatures. The expansions deliver minimized torque requirements of the motor at decreasing temperatures and maximized volumetric efficiency of the pump system under increasing temperatures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The exemplary embodiments will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and wherein: 
         FIG.  1    is a schematic illustration of a pump system, in accordance with various embodiments; 
         FIG.  2    is a detail illustration of a part of the pump system of  FIG.  1   , in accordance with various embodiments; 
         FIG.  3    is a schematic, detail illustration of a part of the pump system of  FIG.  1    shown in a first state, in accordance with various embodiments; 
         FIG.  4    is a schematic, detail illustration of the part of the pump system of  FIG.  1    shown in a second state, in accordance with various embodiments; 
         FIG.  5    is a graph of face clearance in millimeters versus temperature in degrees Celsius for the pump system of  FIG.  1   , in accordance with various embodiments; 
         FIG.  6    is a graph of input powers in Watts versus speeds in revolutions per minute for the pump system of  FIG.  1    and for a comparison examples, in accordance with various embodiments; and 
         FIG.  7    illustrates a method of constructing the pump system of  FIG.  1   , in accordance with various embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     The following detailed description is merely exemplary in nature and is not intended to limit the application and uses. Furthermore, there is no intention to be bound by any expressed or implied theory presented in the preceding introduction, brief summary or the following detailed description. 
     As disclosed herein, pump systems are provided that deliver desirable performance characteristics over a substantial range of operating temperatures by leveraging the thermal expansion characteristic of different components of the system. For example, in a system with an internal gear type pump, the stationary housing of the pump is made with one material and the moving rotor of the pump is made from a different material. The two materials are selected and tuned to have specific thermal responses that result in desirable 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 is tailorable such as to achieve low torque requirements at colder temperatures and simultaneously to achieve high volumetric efficiencies at hotter temperatures. In embodiments, the outcomes are a result of managing clearances, such as the running face clearance, over a wide temperature range. 
     In an exemplary application, a pump system may operate under conditions that range widely, such as from negative forty degrees Celsius to one-hundred-twenty-five degrees Celsius. Such applications include vehicle system pumps that are exposed to ambient temperatures in diverse environments and where fluid heating may result from the work being done by the pump system. Managing the running face clearance for cold temperature operation results in minimized input torque requirements, including start-up torque, enabling the use of a relatively small motor. Managing the running face clearance for hot temperature operation results in maximized volumetric efficiency enabling the use of a relatively small pump both physically and in terms of displacement for a given application than would otherwise be possible. The results include minimized energy input and consumption needed to drive the pump system. 
     In various embodiments, a pump system is configured to move a fluid/generate a pressure through at least two components parts that move relative to each other, such as a rotor and a housing. Relative movement of the parts requires clearance, which is sized to account for part build variation within tolerance ranges, to account for the nature of the fluid being worked, and for temperature variations. One component part has a coefficient of thermal expansion tailored to have a first level of expansion and the other component part has a coefficient of thermal expansion tailored to have a second level of expansion, where both levels of expansion are tailored to achieve performance characteristics such as motive power input and volumetric efficiencies desirable for the application over the applicable range of operating temperatures. 
     In the embodiments disclosed herein, certain motor types, pump types and material selections may be described. In other embodiments of the current disclosure as described in the claims, other torque input devices (motors), other fluid drivers (pumps), and other material combinations are contemplated. For example, metal materials may be described for their desired thermal expansion properties, but the current disclosure is not limited to metal materials, and any material appropriate for the components, the applications, and the thermal response desired may be used. As additional examples, plastics, polymers, ceramics, composites, or other materials may be employed. In some embodiments, one or more components may be made of a material that exhibits limited thermal expansion and the other components may be made of a material with thermal expansion characteristics tailored to achieve the desired outcomes. In other embodiments, the thermal expansion characteristics of the various components may be selected and balanced to achieve the outcomes that are desired. In some embodiments, the thermal expansion characteristics may be matched to achieve flat responses. 
     Referring to  FIG.  1   , a pump system  20  generally includes a motor  22  coupled with a pump  24 . The motor  22  is a motive input device that imparts motion to parts of the pump  24  for its operation and in various embodiments, acts using electric power, pneumatic power, hydraulic power, mechanical power, or a combination thereof. The imparted motion may be rotary, linear, or otherwise configured. In the current embodiment, the motor  22  is electric and imparts a rotary torque to drive elements of the pump  24  through a shaft  26 . The motor  22  may be a variety of types of electric motors and is one example is a brushless DC (BLDC) electric motor operated by a controller and power electronics  28 , which may be separately or commonly housed. The size of the motor  22  drives the capacity of the power electronics  28  and therefor drives the cost and weight of the power electronics  28 , Output power of the motor  22  may be specified in Watts, which varies according to speed of the motor, while output torque, such as in newton-meters is generally consistent over the operating speed of the motor. The amount of torque required to spin the pump  24  is a determining factor in the size and cost of the motor  22  and of its associated power electronics  28 . Therefor, minimizing torque requirements of the pump system  20  is beneficial. 
     In general, the pump  24  operates to move fluid and/or to generate fluid pressure for any number of purposes. In the current embodiment, the pump  24  may be an internal gear-type pump and specifically is a gerotor pump. The moving parts include a rotor  30  (gerotor gear), fixed to the shaft  26  and an idler  32  within which the rotor  30  operates and which may also rotate. The moving parts including the idler  32  and the rotor  30  are contained in a housing  34  that includes a cover  36 . The housing  34  defines a cavity  38  that contains 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 fluid being pumped. Faces  40 ,  42  of the rotor  30  comprise running faces and are pointed in opposite directions disposed parallel to the shaft  26 . The face  40  is directed at (faces), a surface  44  in the housing cavity  38  and the face  42  is directed at (faces), a surface  46  of the cover  36 . 
     Spaces or gaps may exist around the rotor  30 , with one between the face  40  and the surface  44  and another between the face  42  and the surface  46 . These two spaces/gaps may vary as the rotor  30  moves closer to the surface  44  or closer to the surface  46  and may be considered together as a datumized sum referred to collectively as a face clearance  50 . The face clearance  50  is causal to various factors (performance characteristics), including torque to turn the rotor  30 , which is provided by the motor  22 , and to volumetric efficiency of the pump  24 . The face clearance  50  may also apply to the idler  32 . In a number of embodiments, the idler  32  may be a design factor in making the thermal expansion property selection, for optimized torque and volumetric efficiency requirements and the desired performance characteristic outcomes. The idler  32  has face clearances (as with rotor  30 ) and additionally an outer diameter face clearance  52  to the housing  34 . The idler  32  thermal expansion relative to housing  34  may be a factor in the optimization. The idler  32  has face clearance properties and independent design freedom for material property and face clearance selection (multiple face clearances) to that of the rotor  30  yielding a possible third material thermal expansion characteristic. Another consideration may be an operating clearance between the rotor  30  and idler  32  as a variable for optimization of torque and volumetric efficiency. 
     An objective of the pump system  20  is to provide a combination of minimizing torque requirements, particularly at cold temperatures where the fluid being pumped may be most viscous, and maximizing volumetric efficiency, particularly at hot temperatures where the fluid being pumped may be least viscous. To provide the somewhat inconsistent combination, the pump  24  is designed to provide increased face clearance  50  at cold temperatures and decreased face clearance  50  at hot temperatures. The combination may be tuned with the objective of balancing the performance benefits by delivering a larger gap when less fluid resistance to rotation is desired, such as for lower torque requirements, and delivering a smaller gap when less internal fluid leakage is desired, such as for higher volumetric efficiency. As a result, lower pump, motor, and related costs are delivered along with higher pump system performance. 
     Referring additionally to  FIG.  2   , the moving parts of the pump  24 , and specifically the idler  32  and the rotor  30 , are shown in isolation. As the rotor  30  turns on the shaft  26 , suction and pressure areas are created between the rotor  30  and the idler  32  to pump fluid. During operation, the face clearance  50  may vary as shown in  FIGS.  3  and  4   . For example, at lower temperatures the face clearance  50  may be larger as shown in  FIG.  3    and at higher temperatures the face clearance  50  may be smaller as shown in  FIG.  4   . This response is beneficially accomplished by the selection of materials used to make component parts such as the rotor  30  and the housing  34 . For example, the rotor  30  and the housing  34  may be made of materials having coefficients of thermal expansion selected so that the rotor  30  expands more than the housing  34  to close the face clearance as temperatures increase. In other embodiments, the coefficients of thermal expansion may be tailored, factoring in the physical dimensions of the parts, so that the face clearance  50  remains constant as temperature changes. In other embodiments, various combinations of outcomes may be accomplished by tailoring the thermal expansions of the rotor  30  and of the housing  34  to target the magnitude of the face clearance  50  provided at temperatures of interest for the application. In other embodiments, the face clearance  50  and the outer diameter face clearance  52  of the idler  32  may be designed to tailor the thermal expansions at the temperatures of interest. In a number of embodiments, the thermal expansions may be tailored to achieve desired performance characteristic outcomes. In the current embodiment, the performance outcomes targeted include torque requirements and delivered volumetric efficiency. The two outcomes may be balanced by the selection of materials used and their coefficients of thermal expansion. One choice of materials to accomplish desirable results includes the use of steel to make the housing  34  and aluminum to make the rotor  30 . The coefficient of thermal expansion of the resulting rotor  30  is approximately twice that of the housing  34  and as a result, the face clearance  50  closes as temperatures increase, and opens are temperature decrease. The idler  32  may be made of steel, aluminum, or any material to achieve the desired thermal and performance characteristics. 
     As shown in  FIG.  5   , a graph depicts the face clearance  50  of the pump system  20  on the vertical axis  60  in millimeters versus temperature on the horizontal axis  62  in degrees Celsius. In various embodiments, the temperatures are those to which the pump system  20  is exposed and may be a result of a number of factors. For example, following a cold-soak where the pump system  20  has been idle in cold environmental conditions, the temperature is a result of the ambient temperature. Also for example, where the pump system  20  has been operating in hot environmental conditions the temperature is a result of the ambient temperature and may also be a result of temperature increases due to working of the fluid being pumped. For the current embodiment, the temperatures of interest are those to which the housing  34  and the rotor  30  are exposed. 
     Curve  64  depicts the pump system  20  with a response to achieve low cold temperature torque for minimizing the size of the motor  22  and to achieve high hot temperature volumetric efficiency for minimizing 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 tailored to achieve a face clearance  50  of approximately 0.073 millimeters at the point  66 . At approximately one-hundred-ten degrees Celsius, the relative thermal expansion of the housing  34  and the rotor  30  is tailored to achieve a face clearance  50  of approximately 0.053 millimeters at the point  68 . This outcome may be accomplished, for example, by making the housing  34  of steel and making the rotor  30  of aluminum. In a number of embodiments, the design/material selections of the parts will move the curve  64  vertically, and the materials may be tuned to change the slope of the curve  64 . For example, the size of the face clearance  50  may be increased or decreased across the temperature range by means of the selection of materials for the component parts. 
     Curve  70  depicts the pump system  20  with a response to achieve a constant face clearance  50 , regardless of temperature. Specifically, at approximately minus-forty degrees Celsius, the relative thermal expansion of the housing  34  and the rotor  30  is tailored 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 tailored to achieve a face clearance  50  of approximately 0.060 millimeters. This outcome may be accomplished, for example, by making the housing  34  of steel and making the rotor  30  of steel. In some embodiments, the alloy composition of the steel may be tuned to achieve the flat response. 
     Curve  72  depicts the pump system  20  with a response, for comparison purposes, that shows the results of material selection. For example, if the rotor  30  is made of steel and the housing  34  is made of aluminum, the effect of temperature change is opposite that of the curve  64 . Specifically, at minus-forty degrees Celsius, the relative thermal expansion of the housing  34  and the rotor  30  is tailored to achieve a face clearance  50  of approximately 0.042 millimeters. At one-hundred-ten degrees Celsius, the relative thermal expansion of the housing  34  and the rotor  30  is tailored to achieve a face clearance  50  of approximately 0.062 millimeters. 
     The curves  64  and  72  intersect at point  74 , which is at approximately seventy-five degrees Celsius. At point  74  the performance of the pump system  20  is the same regardless of whether the rotor  30  is aluminum and the housing  34  is steel or the rotor  30  is steel and the housing  34  is aluminum. The curves  64 ,  70  intersect at the point  76 , which is at approximately ninety degrees Celsius. 
     Referring to  FIG.  6   , a graph of power in Watts is depicted on the vertical axis  78  versus speed of the rotor  30  in revolutions per minute on the horizontal axis  80 . The graph depicts an example of the pump system  20  with a steel housing  34  and a steel rotor  30  by the curve  82  and the pump system  20  with a steel housing  34  and an aluminum rotor  30  at the curve  84 . Both curves  82  and  84  demonstrate power requirements at twenty degrees Celsius temperature. As shown, the curve  84  results in up to a twenty-one percent reduction in power requirements, achieved by tailoring the materials used for their thermal response characteristics. 
     A process  100  for constructing a pump system, such as to optimize torque requirements and volumetric efficiencies of the pump system  20 , is depicted in  FIG.  7    in flowchart form, to which reference is directed. The temperatures at which the pump system  20  will operate are determined  102 . The targets for the pump system are determined  104 . For example, the temperatures at which minimizing the power required of the motor  22  are determined 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-twenty-five degrees Celsius. Specific temperature of interest may be minus forty and one-hundred-ten degrees Celsius. The size of the face clearance  50  and/or of the outer diameter face clearance  52  to achieve the targets determined  102  are calculated  106 . For example, the pump system  20  may be modeled using commercially available fluid dynamics modeling software, or other calculations may be employed. Alternatively, physical modeling and testing may be conducted. The materials, such as for the housing  34 , the rotor  30 , and the idler  32 , and their coefficients of thermal expansion are considered  106 . For example, various materials may be considered  106 , with their performances modeled via software and/or physically. From the materials considered  106 , a selection  110  is made to achieve the calculated  106  face clearances  50  and/or  52  at the target temperatures that were determined  104 . Next, any needed tuning  112  is undertaken to adjust the performance of the pump system  20 , such as to achieve desired torque requirements and/or volumetric efficiencies at temperatures of interest. 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 a number of embodiments, the order of the steps in the process  100  may differ from those described herein, other steps may be added, and some steps may be omitted. 
     Accordingly, pump systems and methods are provided where torque requirements are minimized at low temperature operating conditions and volumetric efficiency is maximized at high temperature operating conditions. While at least one exemplary embodiment has been presented in the foregoing detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the disclosure in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing the exemplary embodiment or exemplary embodiments. It should be understood that various changes can be made in the function and arrangement of elements without departing from the scope of the disclosure as set forth in the appended claims and the legal equivalents thereof.