Patent Publication Number: US-9850898-B2

Title: Gerotor pump for a vehicle

Description:
TECHNICAL FIELD 
     Various embodiments relate to an oil pump for a powertrain component such as an internal combustion engine or a transmission in a vehicle. 
     BACKGROUND 
     An oil pump is used to circulate oil or lubricant through powertrain components such as an engine or a transmission. The oil pump is often provided as a generated rotor or gerotor pump. Gerotor pumps have a positive displacement characteristic and tight clearances between various components of the pump that result in the formation of pressure ripples or fluctuations of the fluid within the pump and the attached oil galleries during operation of the pump. The pressure ripples of the fluid in the pump may act as a source of excitation to powertrain components, for example, when the pump is mounted to the powertrain components. For example, the pump may be mounted to an engine block, a transmission housing, an oil pan or sump housing, a transmission bell housing, and the like, where the pressure ripples may cause tonal noise or whine from the engine or the transmission. This oil pump-induced powertrain whine or tonal noise is a common noise, vibration, and harshness (NVH) issue, and mitigation techniques may include countermeasures such as damping devices that are added to the powertrain to reduce noise induced by a conventional pump. 
     SUMMARY 
     In an embodiment, a gerotor pump is provided with a body defining a chamber with cylindrical wall sections and having a fluid inlet and a fluid outlet. A cover is configured to mate with the body to enclose the chamber. An internally toothed gear member is supported for rotation within the chamber about a first axis, and the gear has a cylindrical outer wall defining a series of grooves. Each groove has an associated aperture extending through the gear member to an inner surface of the gear member. Each groove and associated aperture is radially positioned between adjacent teeth of the internally toothed gear member. An externally toothed gear member is rotatably supported within the internally toothed gear about a second axis spaced apart from the first axis. A drive shaft is coupled for rotation with the externally toothed gear member. The internally toothed gear member and externally toothed gear member cooperate to form a plurality of variable volume pumping chambers therebetween to pump fluid from the fluid inlet to the fluid outlet. 
     In another embodiment, a gerotor fluid pump for a vehicle component is provided with a housing defining a cylindrical chamber with a fluid inlet and a fluid outlet spaced apart therefrom. An idler rotor is positioned within the chamber and has a cylindrical outer wall adjacent to the cylindrical chamber and defining a series of grooves therein. An inner wall of the idler rotor defines a first series of teeth. Each groove corresponds with an associated tooth of the first series of teeth and has an opening fluidly connecting the groove and the inner wall. An inner rotor is driven by a pump shaft and is positioned within the idler rotor. The inner rotor has an outer wall defining a second series of teeth. The teeth of the inner rotor and the idler rotor cooperate to form a variable volume chamber to provide fluid flow through the pump as the inner rotor drives the idler rotor. An axis of rotation of the inner rotor is offset from an axis of rotation of the idler rotor. The opening and the groove of the idler rotor provide a fluid pathway for pressure relief in the pump thereby reducing tonal noise. 
     In yet another embodiment, an idler rotor for a gerotor pump is provided with a body having a cylindrical outer wall defining a series of longitudinal grooves. The body has an inner wall surrounding a central region and defining a series of teeth. Each tooth is radially aligned with a respective groove. The body defines a series of apertures. Each aperture is associated with a respective groove and extends radially through the body to fluidly connect the central region with the groove. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a schematic of a lubrication system for an internal combustion engine in a vehicle according to an embodiment; 
         FIG. 2  illustrates a perspective sectional view of gerotor pump according to an embodiment; 
         FIG. 3  illustrates a partial perspective view of a portion of the gerotor pump of  FIG. 2 ; 
         FIG. 4  illustrates a top view of the inner and outer rotors of the gerotor pump of  FIG. 2 ; 
         FIG. 5  illustrates a perspective view of the outer rotor of the gerotor pump of  FIG. 2 ; 
         FIG. 6  illustrates a graph of pressure output from the pump of  FIG. 2  compared to a pressure output from a pump with a conventional idler rotor; and 
         FIG. 7  illustrates a frequency domain analysis for the pump of  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION 
     As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention that may be embodied in various and alternative forms. The figures are not necessarily to scale; some features may be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention. 
     A vehicle component  10 , such as an internal combustion engine or transmission in a vehicle, includes a lubrication system  12 . The vehicle component  10  is described herein as an engine, although use with other vehicle components is contemplated. The lubrication system  12  provides a lubricant, commonly referred to as oil, to the engine during operation. The lubricant or oil may include petroleum-based and non-petroleum-synthesized chemical compounds, and may include various additives. The lubrication system  12  circulates oil and delivers the oil under pressure to the engine  10  to lubricate rotating bearings, moving pistons and engine camshaft. The lubrication system  12  may additionally provide cooling of the engine. The lubrication system  12  may also provide the oil to the engine for use as a hydraulic fluid to actuate various tappets, valves, and the like. 
     The lubrication system  12  has a sump  14  for the lubricant. The sump  14  may be a wet sump as shown, or may be a dry sump. The sump  14  acts as a reservoir for the oil. In one example, the sump  14  is provided as an oil pan connected to the engine and positioned below the crankshaft. 
     The lubrication system  12  has an intake  16  providing oil to an inlet of a pump  18 . The intake  16  may include a strainer and is in fluid contact with oil in the sump  14 . 
     The pump  18  receives oil from the intake  16  and pressurizes and drives the oil such that it circulates through the system  12 . The pump  18  is described in greater detail below with reference to  FIGS. 2-4 . In one example, the pump  18  is driven by a rotating component of the engine  10 , such as a belt or mechanical gear train driven by the camshaft. In other examples, the pump  18  may be driven by another device, such as an electric motor. 
     The oil travels from the pump  18 , through an oil filter  20 , and to the vehicle component or engine  10 . The oil travels through various passages within the engine  10  and then leaves or drains out of the engine  10  and into the sump  14 . 
     The lubrication system  12  may also include an oil cooler or heat exchanger to reduce the temperature of the oil or lubricant in the system  12  via heat transfer to a cooling medium such as environmental air. The lubrication system  12  may also include additional components that are not shown including regulators, valves, pressure relief valves, bypasses, pressure and temperature sensors, and the like. 
     In other examples, the pump  18  may be implemented on other vehicle systems, for example, as a fuel pump, and the like. 
       FIGS. 2-5  illustrate a pump  50  and various components thereof. The pump  50  may be used in the lubrication system  12  as pump  18 . The pump  50  has a housing  52  and a cover  54 . The housing  52  and the cover  54  cooperate to form an internal chamber  56 . The cover  54  connects to the housing  52  to enclose the chamber  56 . The cover  54  may attach to the housing  52  using one or more fasteners, such as bolts, or the like. A seal, such as an O-ring or a gasket, may be provided to seal the chamber  56 . 
     The internal chamber  56  may be provided with or defined by a substantially cylindrical support or guide wall  57  as shown in  FIG. 3 . The guide wall  57  may include one or more sections of wall that have a common radius of curvature and center. Various sections of the guide wall  57  may lie about a perimeter of a common cylinder. 
     The pump  50  has a fluid inlet  58  and a fluid outlet  60 . The fluid inlet  58  has an inlet port as shown in  FIG. 3  that is adapted to connect to a conduit such as intake  16  in fluid communication with a supply, such as an oil sump  14 . The fluid inlet  58  is fluidly connected with the chamber  56  and intersects the wall(s)  57  such that fluid within the inlet  58  flows into the chamber  56 . As shown in  FIG. 2 , both the housing  52  and the cover  54  may define portions of the inlet  58  region. The inlet  58  may be shaped to control various fluid flow characteristics. 
     The fluid outlet  60  has an outlet port as shown in  FIG. 2  that is adapted to connect to a conduit in fluid communication with an oil filter, a vehicle component such as an engine, etc. The fluid outlet  60  is fluidly connected with the chamber  56  and intersects the wall(s)  57  such that fluid within the chamber  56  flows into the outlet  60 . As shown in  FIG. 2 , both the housing  52  and the cover  54  may define portions of the outlet  60  region. The outlet  60  may be shaped to control various fluid flow characteristics. The inlet  58  and the outlet  60  are spaced apart from one another by a section of wall  57 , and in one example, may be generally opposed to one another. 
     The pump  50  has a pump shaft  62  or driveshaft. The pump shaft  62  is driven to rotate components of the pump  50  and drive the fluid. In one example, the pump shaft  62  is driven by a mechanical coupling with an engine, such that the pump shaft rotates as an engine component such as a crankshaft rotates, and a gear ratio may be provided to provide a pump speed within a predetermined range. In one example, an end  64  of the pump shaft  62  is splined or otherwise formed to mechanically connect with a rotating vehicle component to drive the pump  50 . 
     The other end  66  of the shaft  62  is supported for rotation within the housing  52  of the pump  50 . The housing may define a support  68  for the end  66  of the shaft to rotate therein. The support  68  may include a bushing, a bearing connection, or the like. The shaft  62  rotates about a longitudinal axis  70  of the shaft  62 . 
     The shaft  62  extends through the cover  54 , and the cover  54  defines an opening  72  for the shaft  62  to pass through. The opening  72  may include a sleeve or a seal to retain fluid within the pump and prevent or reduce leakage from the chamber  56 . The opening  72  may also include additional bushings or bearing assemblies supporting the shaft  62  for rotation therein. 
     An inner rotor  80  or inner gear is connected to the pump shaft  62  for rotation therewith. The inner rotor  80  has an inner surface or wall  82  and an outer surface or wall  84 . The inner wall  82  is formed to couple to the pump shaft  62  for rotation therewith about the axis  70 . In one example, the inner wall is splined to mate with a corresponding splined section of the pump shaft  62 . The outer wall  84  defines a series of external gear teeth  86 . The inner rotor  80  may be defined as an externally toothed gear. 
     An outer rotor  90 , outer gear, or idler gear or rotor surrounds the inner rotor  80  and is supported for rotation within the chamber  56 . The outer rotor  90  has an inner surface or wall  92  and an outer surface or wall  94 . The inner wall  92  defines a series of internal gear teeth  96 . The outer rotor  90  may be defined as an internally toothed gear. The outer wall  94  is cylindrical in shape and is sized to be received by and generally interface with the cylindrical wall sections of the housing for rotation therein about an axis  98 . Axis  98  is the longitudinal or central axis of the cylindrical chamber  56  in the housing. The outer wall  94  may be directly adjacent to and may contact the cylindrical wall sections  57 , as the wall sections  57  act to retain the outer rotor  90  in position during pump  50  operation. 
       FIG. 4  illustrates a top view of the inner rotor  80  and outer rotor  90 . Flow into the pump  50  is generally indicated by arrow  100 . Flow out of the rotor  80  pump is generally illustrated by arrow  102 . 
     The inner rotor  80  is rotated about axis  70  by the pump shaft  62 . The series of teeth  86  on the inner rotor  80  have an addendum region  104  and a dedendum region  106 . The addendum region  104  is adjacent to the top land  108  of each tooth  110 . The dedendum region  106  is adjacent to the bottom land  112  between adjacent teeth  110 . Each of the addendum and dedendum regions  104 ,  106  may be formed by a cycloid shape, or another shape. In the example shown, the dedendum region  106  is formed by a cycloid or a hypocycloid shape such that the dedendum regions  106  are smooth curves. 
     The outer rotor  90  has a series of inner gear teeth  96  that have an addendum region  120  and a dedendum region  122 . The addendum region  120  is adjacent to the top land  124  of each tooth  126  and the dedendum region  122  is adjacent to the bottom land  128  between adjacent teeth  126 . Each of the addendum and dedendum regions  120 ,  122  may be formed by a cycloid shape, or another shape. In the example shown, the addendum region  120  is formed by a cycloid or a hypocycloid shape such that the addendum regions  120  are smooth curves. The addendum region  120  is formed with the same curve or shape as the dedendum region  106  of the inner rotor  80  such that the regions  106 ,  120  mate to form a continuous seal as illustrated by arrow  130 . 
     As the inner rotor  80  is rotated by the shaft  62 , the teeth  86  of the inner rotor  80  mesh with the teeth  96  of the outer rotor  90 , and the outer rotor  90  is driven as an idler by the inner rotor  80 . In the present example, the pump shaft  62  rotates the inner rotor  80  in a clockwise direction, and the idler rotor  90  is rotated in a clockwise direction by the inner rotor  80 . As the inner rotor  80  rotates about an axis  70  that is offset relative to the axis of rotation  98  of the outer rotor  90 , the inner rotor  80  is eccentric relative to the outer rotor  90  and the cylindrical housing  56 ,  57 . As can be seen from  FIGS. 3 and 4 , the pump  50  operates without a crescent shaped seal or insert in the chamber  56 . 
     A plurality of chambers  140  are formed between the inner rotor  80  and the outer rotor  90 . Each chamber  140  has a variable volume as the pump  50  operates. Each chamber  140  increases in volume to draw in the fluid from the inlet  58 , and then decreases in volume to push the fluid out of the outlet  60 . A chamber that is increasing in volume is shown at  142 . A chamber that is decreasing in volume is shown at  144 . 
     The cylindrical outer wall  94  defines a series of grooves  150  or depressions therein. Note that a conventional outer rotor typically has a smooth, continuous, cylindrical outer wall without depressions  150 . In one example, the series of grooves  150  are spaced equally about the perimeter of the outer wall  94 . In other examples, the grooves  150  may be spaced alternately or in another order, for example, as groups of three grooves with a spaced apart region, and may be positioned to reduce pump associated noise at the dominant pump orders. 
     Each groove in the series of grooves  150  may extend from a first end  152  of the outer gear to a second end  154  of the outer gear. Each groove in the series of grooves  150  may be generally parallel with the axis  98 , for example, within two degrees, five degrees, or ten degrees of the axis  98 . Each groove in the series of grooves  150  may be uniform along the length of the groove as shown. In alternative examples, the grooves  150  may have sections with increasing and/or decreasing tapered shapes along their length. The grooves  150  are illustrated as having a cross section formed as an arc or section of a circle. In other examples, the grooves  150  may have other cross sectional shapes including triangular, parabolic, other smooth continuous curves and/or linear discontinuous shapes. Each groove  150  is shown as being symmetrical; however, asymmetric grooves are also contemplated. The cross sectional shape of the groove  150  may be constant or may change along the length of the groove. In the present example, each groove  150  has a radius of curvature such that it is formed by a smooth curve or an arc of a circle, and is positioned to be concentric with an associated top land  124  of the inner gear teeth  126 . 
     The grooves  150  are positioned between adjacent bottom lands  128  or between adjacent dedendum regions  122  of the outer rotor  90 . The grooves  150  may be radially aligned with a corresponding addendum region  120  or corresponding top land  124  of the outer rotor  90 . For idler rotors with alternate groove spacing, some of the top lands  124  have an associated groove and aperture, and others are provided without a groove and aperture. For idler rotors with equal groove and aperture spacing, each top land  124  has an associated groove and aperture. 
     Each groove  150  defines an aperture  160  that extends through the wall  162  of the outer rotor to fluidly connect the groove  150  with the inner wall  92  of the outer rotor  90 , and with a variable volume chamber  140 . The grooves  150  may each have a single aperture  160 , or may have two or more apertures  160 . The apertures  160  may be provided with a circular, elliptical, slotted, or otherwise shaped cross section. The apertures  160  may be substantially circular, for example, with a radius that varies about the aperture by no more than  10  percent. The apertures  160  in each groove  150  may be the same size as shown, or may be different sizes. The apertures  160  may have a constant cross sectional area through the wall  162  of the outer rotor  90 , or may have an increasing or decreasing cross sectional area. The apertures  160  may be equally spaced with respect to one another and the outer rotor  90 , or may be offset relative to one another and/or the outer rotor  90 . 
     As the pump  50  operates, pressure ripples of the fluid in the pump  50  may act as a source of excitation to powertrain components, for example, when the pump  50  is mounted to the powertrain components. For example, the pump  50  may be mounted to an engine block, a transmission housing, an oil pan or sump housing, a transmission bell housing, and the like, where the pressure ripples may cause tonal noise or whine from the engine or the transmission. The outer rotor  90  design of the present disclosure acts to reduce or eliminate the oil pump-induced powertrain whine or tonal noise by providing pressure relief or acting in a bypass capacity. 
     The grooves  150  and the apertures  160  provide pressure relief for the pump  50  and act to reduce the tonal noise or whine. As the pump  50  operates, fluid within one of the variable volume chambers  140  is able to flow from the chamber  140  through an aperture  160 , across the outer rotor  90  and into a groove  150 . The grooves  150  each form an outer chamber  170  with the cylindrical wall  57  of the housing  52 . Modeling and testing of the outer rotor  90  with the grooves  150  and apertures  160  show improved pump operating characteristics compared to a conventional outer rotor. A gerotor pump having the rotor as described herein showed a reduction in pressure ripples or spikes during operation. For example, as shown in  FIG. 6 , a conventional pump while operating may provide fluid at the outlet of the pump with pressure fluctuations or pressure waves as shown by line  200  during a steady state operating condition. These pressure fluctuations are a difference between a maximum fluid pressure or spike and a minimum fluid pressure at the outlet. The pump  50  according to the present disclosure has a pressure fluctuation as shown by line  202  for the same steady state operating condition. In addition to a significant decrease in pressure fluctuation, the pump  50  according to the present disclosure also provides the fluid at the high pressure value for a longer time period, whereas the high pressure from the conventional pump appears as a spiked value and is not sustained. Additionally, an analysis across a frequency domain showed a significant decrease in pressure peaks for the various orders of the pump  50 , with the pressure peaks essentially disappearing for the higher orders as shown in  FIG. 7  with a conventional pump illustrated by line  210 , and a pump  50  according to the present disclosure illustrated by line  212 . 
     The pump  50  according to the present disclosure provides for a comparable or increased fluid pressure at the pump outlet compared to the conventional pump across a range of pump speeds. Therefore, the pump  50  according to the present disclosure does not incur any significant losses based on differences in efficiencies, etc., and is in fact may be said to be more efficient depending on the pump speed. 
     The pump  50  according to the present disclosure additionally provides for decreased noise. For example, when the pump  50  according to the present disclosure is used with a powertrain for a vehicle the tonal noise from the powertrain is reduced. In one example, the pump according to the present disclosure is used with a four cylinder engine for a vehicle and resulted in noise reductions ranging between 2-10 decibels for the various pump orders and across a frequency range compared to a conventional gerotor pump. The tonal noise reduction using the pump  50  may provide for reduced noise, vibration, and harshness (NVH) from the powertrain. Additionally, the powertrain or lubrication system may be simplified using a pump  50  according to the present disclosure. For example, the powertrain or lubrication system with a conventional pump may include noise reduction devices or features, and these features may be eliminated by switching to a pump according to the present disclosure. In one example, the conventional lubrication system includes a damping material such as a mastic located on the oil sump, and this damping material may be removed by switching to a pump  50  as described herein without an increase in tonal noise from the powertrain. 
     While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention. Additionally, the features of various implementing embodiments may be combined to form further embodiments of the invention.