Abstract:
A reversible gerotor pump for a machine having a drive shaft is provided, the pump including a housing, an offset ring, and an inner and outer gear. The offset ring is disposed in the housing and includes a tab extending radially from an outer periphery. The outer periphery of the offset ring defines a first axis in common with the axis of a drive shaft. The inner periphery of the offset ring defines a second axis that is slightly offset from the second axis. The axis of the outer gear moves relative to the axis of the inner gear to allow pumping action in both rotational directions using the same suction and line cavities for both directions.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 61/430,526, filed on Jan. 6, 2011. The disclosure of the above application is incorporated herein by reference. 
    
    
     FIELD 
     The invention relates generally to a lubrication pump for providing pressurized hydraulic fluid to a transmission, and more particularly to a gerotor pump for use in a transmission. 
     BACKGROUND 
     The statements in this section merely provide background information related to the present disclosure and may or may not constitute prior art. 
     A typical multiple speed transmission uses various pumps and valves to provide high pressure and high flow hydraulic fluid to the various mechanical devices of the transmission; including clutches, brakes, actuators, etc. These pumps and valves are driven by the torque from a driver such as an engine. In typical cases, the clutches, brakes and actuators require constant pressure from the hydraulic fluid source. The fluid source is commonly a pump coupled with at least one valve body to provide constant fluid pressure and flow even when the pump is fluctuating in pressure output and fluid flow direction. 
     While current hydraulic fluid pumps achieve their intended purpose, the need for new and improved hydraulic pump configurations which exhibit improved performance, unidirectional fluid flow and reduction in accompanying system assemblies is evident. Accordingly, there is a need for an unidirectional, reversible, high pressure and high flow hydraulic fluid pump for a transmission. 
     SUMMARY 
     A reversible pump for a machine having a drive shaft is provided, the reversible pump including a housing, an offset ring, an outer gear, an inner gear, and a cover. The housing has a center hub defining a first axis, an outer hub, a first and second radial surface, and a first and second arcuate cavity. The first cavity is disposed on a first side of the center hub and the second cavity is dispose on a second side of the center hub opposite the first side. The outer hub includes a arcuate portion extending radially from an outer periphery of the outer hub, and the first radial surface is disposed adjacent the outer periphery of the outer hub and an inner periphery of the arcuate portion, and the second radial surface is disposed opposite the first radial surface, adjacent the outer periphery of the outer hub and the inner periphery of the arcuate portion. The offset ring is disposed within the outer hub. The offset ring includes a tab extending radially from an outer periphery of the offset ring. The outer periphery of the offset ring defines a second axis and the inner periphery of the offset ring defines a third axis that is offset from the second axis. The outer gear is disposed on the inner periphery of the offset ring. The inner gear is disposed on an inner periphery of the outer gear. The inner gear is splined to the drive shaft for common rotation. The cover has a third and fourth cavity. The third cavity is disposed opposite the first cavity of the housing and the fourth cavity is disposed opposite the second cavity of the housing. The offset ring is disposed in one of a first and a second position. The first position having the tab of the offset ring disposed in contact with the first radial surface and the second position having the tab of the offset ring disposed in contact with the second radial surface. 
     In another example of the invention, the tab of the offset ring includes a plurality of bores and a first and second surface. The first surface contacts the first radial surface of the housing when the offset ring is in the first position and the second surface contacts the second radial surface of the housing when the offset ring is in the second position and the bores extend from the first surface of the tab to the second surface of the tab. 
     In yet another example of the invention, the drive shaft is capable of rotating in either direction. 
     In yet another example of the invention, the first cavity is a high pressure cavity and the second cavity is a low pressure cavity. 
     In yet another example of the invention, the arcuate portion of the outer hub extends 180° around the first axis. 
     In yet another example of the invention, the outer periphery of the outer gear further includes a circumferential groove and the outer periphery of the offset ring includes a circumferential rib disposed in the groove of the outer gear. 
     In yet another example of the invention, the housing includes a seal disposed in a groove dispose radially outward from the outer periphery of the outer hub. 
     In yet another example of the invention, the offset ring is capable of rotating approximately 180°. 
     Further features and advantages of the present invention will become apparent by reference to the following description and appended drawings wherein like reference numbers refer to the same component, element or feature. 
    
    
     
       DRAWINGS 
       The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way; 
         FIG. 1  is a partial cross-sectional view of an example of a reversible gerotor pump as installed in a transmission; 
         FIG. 2  is an axial view of an example of a reversible gerotor pump rotating in a clockwise or first direction; and 
         FIG. 3  is an axial view of an example of a reversible gerotor pump rotating in a counterclockwise or second direction. 
     
    
    
     DETAILED DESCRIPTION 
     The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. 
     Referring to the drawings, wherein like reference numbers refer to like components, in  FIG. 1  an example of reversible gerotor pump  10  installed in a transmission  12  is illustrated. The reversible gerotor pump  10  includes a housing  14 , an offset ring  16 , an outer gear  18 , an inner gear  20  and a cover  22 . The gerotor housing  14 , filled with hydraulic fluid  11 , may be formed as a portion of a housing  14  of the transmission  12 . The housing  14  includes an annular shaped center hub  24  defining an axis i, a suction portion  26 , a line portion  28 , an gear portion  30  and an offset ring portion  32 . The hub  24  has an inner periphery  24 A through which passes a shaft  34  of the transmission  12 . The shaft  34  can be an input, output or intermediate shaft without departing from the scope of the invention. The suction portion  26  is a crescent-shaped relief disposed proximate an outer periphery  24 B of the hub  24  that communicates with a hydraulic fluid return port (not shown) of the transmission  12 . The suction portion  26  extends partially around the outer periphery  24 B of the hub  24 . The line portion  28  is a crescent-shaped relief disposed proximate the outer periphery  24 B of the hub  24  that communicates with a hydraulic fluid supply port (not shown) of the transmission  12 . Similar to the suction portion  26 , the line portion  28  extends partially around the outer periphery  24 B of the hub  24 , however, the line portion  28  is disposed opposite the suction portion  26  and there is no overlap between the suction portion  26  and line portion  28 . Further description of the disposition of the suction and line portions  26 ,  28  is found below. The gear portion  30  of the housing  14  overlaps the hub, suction and line portions  24 ,  26 ,  28 . The gear portion  30  is open to an outer surface  34 A of the shaft  34  allowing for interconnection between the shaft  34  and the inner gear  20  for common rotation. The offset ring portion  32  is disposed on an outer periphery  30 A of the gear portion  30 , however, it extends approximately 180° around the outer periphery  30 A of the gear portion  30 . One end of the offset ring portion  32  includes a forward stop  32 A and the opposite end includes a reverse stop  32 B. The stops  32 A,  32 B are radially extending walls that are aligned approximately at a midpoint of the suction and line portions  26 ,  28 , respectively. The cover  22  includes a hub  22 A, a line portion  22 B and suction portion  22 C. The cover  22  is disposed such that the hub  22 A receives the shaft  34  of the transmission  12  and the line portion  22 B and suction portion  22 C align with the line portion  28  and suction portion  26  of the housing  14 , respectively. 
     The inner gear  20  has a splined inner surface  20 A that meshes with a splined outer surface  34 A of the transmission shaft  34  for a solid connection allowing the inner gear  20  to rotate with the shaft  34 . Referring now to  FIGS. 2 and 3 , the gerotor is shown in an axial view with the cover  22  removed. An outer periphery  20 B of the inner gear  20  includes, for example, six teeth  20 C but may have more or less teeth. The outer gear  18  has an inner periphery  18 A that includes, for example, seven teeth  18 B and an outer periphery  18 F that includes a circumferential groove  18 E. In general, the number of teeth on the inner gear  20  is always one less than the number of teeth on the outer gear  18 . The teeth  20 B of the inner gear  20  mesh with the teeth  18 B of the outer gear  18  to create a plurality of pockets  36  of variable volume between the gears  18 ,  20 . As the inner gear  20  rotates relative to the outer gear  18 , the pockets  36  increase in volume as they pass over the suction portion  26  of the housing  14  and decrease in volume as they pass over the line portion  28  of the housing  14 . As the pocket  36  volume increases, decreased pressure in the pocket  36  draws or sucks hydraulic fluid  11  into the pocket  36  from the suction portion  26 . As the pocket  36  volume decreases over the line portion  28 , increased pressure in the pocket  36  forces the hydraulic fluid  11  into the line portion  28  of the housing  14  and therefore the supply line of the transmission  12 . 
     The offset ring  16  is an annular ring having an outer periphery  16 A from which a tab portion  38  extends radially. The tab portion  38  of the offset ring  16  is disposed in the offset ring portion  32  of the housing  14 . The tab portion  38  may also include holes, channels or specified clearances  38 A with the housing  14 . As is explained below, the tab portion  38  moves through the offset portion  32  of the housing  14 . The clearances, holes or channels  38 A in the tab portion  38  can be tailored to vary the damping effect the hydraulic fluid  11  in the offset portion  32  of the housing as the offset ring  16  rotates. Additionally, while the outer periphery  16 A defines a circle that fits within the inner periphery  30 A of the gear portion  30  of the housing  14 , an inner periphery  16 B of the offset ring  16  defines a circle including a center  16 D that is slightly offset from a center  16 C of the circle defined by the outer periphery  16 A of the offset ring  16 . Additionally, the inner periphery  16 B of the offset ring includes a circumferential rib  16 E that is disposed in the circumferential groove  18 E of the outer gear  18 . The two offset centers  16 C,  16 D allow the offset ring  16  to have a variable thickness. The variable thickness forces the outer gear  18  to have the same axis of rotation as the inner periphery  16 B of the offset ring  16 . 
     As stated above, the inner gear  20  is connected to the shaft  34  that passes through the hub  24  of the housing  14 . The outer gear  18  is disposed on the outer periphery  20 B of the inner gear  20  and the offset ring  16  is disposed on the outer periphery  20  of the outer gear  18 C with the tab portion  38  of the offset ring  16  disposed in the offset ring portion  32  of the housing  14 . Further, the outer diameter of the outer gear  18  is the same or slightly smaller than the inner diameter of the offset ring  16 . Therefore, the position of the rotational axis of the outer gear  18  relative to the inner gear  20  is controlled by the rotational position of the offset ring  16 . When the offset ring  16  is in a forward or first position as in  FIG. 2 , the tab  38  of the offset ring  16  is in contact with the forward stop  32 A of the housing  14  and the center  16 D of the outer gear  18  is on a first side of the center  16 C of the inner gear  20 . As the rotation of the shaft  34  changes to a reverse or clockwise direction D 2  as in  FIG. 3 , the offset ring  16  is in a reverse or second position and the center  16 D of the outer gear  18  is on a second side of the center  16 C of the inner gear  20  opposite of the first side. Without the shift in the center  16 D or rotation of the outer gear  20  upon a change in direction of the inner gear  18 , the pockets  36  between the gears  18 ,  20  would increase in volume over the line portion  28  of the housing  14  and decrease in volume over the suction portion  26  of the housing  14  thus reversing flow of hydraulic fluid  11 . However, as the offset ring  16  shifts the center  16 D of rotation of the outer gear  18 , the variable volume pockets  36  maintain the same pressure changes as when the shaft  34  is moving in the first or forward direction D 1 . 
     The description of the invention is merely exemplary in nature and variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.