Abstract:
A dual gerotor pump is used for an automatic transmission. A dual gerotor pump which is driven by a central drive mechanism has a first chamber which continuously provides transmission fluid to the automatic transmission. The pump also has a second pumping chamber which selectively directs fluid to the automatic transmission when necessary. A valve mechanism is provided to divert fluid from the second pumping chamber back to the second pumping chamber so that it can recirculate thereby decreasing fluid pressure to the automatic transmission when it is not required.

Description:
Rotary or gerotor pumps have been used extensively in many different applications including automotive applications. Pumps such as those disclosed in Clark, U.S. Pat. No. 2,490,115, Obrist, U.S. Pat. No. 4,960,370, Brundage, U.S. Pat. No. 3,551,081 and Hill, U.S. Pat. No. 1,496,227 provide good pumping action powered by a central axis. Many of these pumps are specifically designed for automotive purposes. 
     A dual gerotor pump is a rotary pump which has two pumping chambers driven by the same shaft. These can be used in automotive applications with one pump pumping fluid to one vehicle system and a second pump pumping a second fluid to a second vehicle system. 
     In many applications the fluid pressure required is variable. An automatic transmission requires higher pressures under certain conditions such as during acceleration and lower pressures at other times. Driving at constant speed would require less. This is particularly true with continuous variable transmissions which utilize a belt and pulley system to vary the gear ratio. Such transmissions require a 60 to 800 psi difference. 
     SUMMARY OF THE INVENTION 
     The present invention is premised on the realization that a dual gerotor pump can be used to provide a wide range of fluid pressures for automatic transmissions and in particular constant variable transmissions. More particularly the present invention is premised on the realization that a dual gerotor pump having a primary pump constantly connected to the transmission and a secondary pump which can on demand be used to provide additional pressure to the transmission provides a superior range of pumping efficiencies for an automatic transmission of an automobile. By recirculating the fluid in the secondary pump when not needed, one can maintain optimum fluid pressure within the automatic transmission. Further, fluid pressure can be increased instantaneously when needed. 
     The objects and advantages of the present invention will be further appreciated in light of the following detailed descriptions and drawings in which: 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an exploded view of a dual gerotor pump of the present invention. 
     FIG. 2 is a cross-sectional view of the assembled gerotor pump of FIG.  1 . 
     FIG. 3 is a cross-sectional view taken at lines  3 — 3  of FIG.  2 . 
     FIG. 4 is a cross-sectional view taken at lines  4 — 4  of FIG.  2 . 
     FIG. 5 is a cross-sectional view taken at lines  5 — 5  of FIG.  3 . 
     FIG. 6 is a cross-sectional view taken at lines  6 — 6  of FIG.  2 . 
     FIGS. 7,  7 A and  7 B are diagramatic depictions of the present invention. 
    
    
     DETAILED DESCRIPTION 
     As shown in FIGS. 1,  3  and  5 , a pump  22  includes an outer housing  24  which includes an end casing  26 , a central casing  28  and a sealing plate  30 . This is operated by a central drive shaft or torque converter  34 . First pump chamber  36  is within end casing  26  and the second pump chamber  38  is located in the central casing  28 . 
     The first pump chamber  36  is defined by the bottom wall  40  of end casing  26  and the outer wall  42  of end casing  26 . The outer wall  42  is relatively thick and includes an inlet passage  44  and a discharge passage  45 . Bushing  46  rests in the first pump chamber  36  adjacent inner wall  43 . 
     As shown in FIG. 2 the inlet and outlet passages  44  and  45  extend through the outer wall  42  to a bottom portion  47  and  49  of the end casing  26  and connect with the pumping chamber from the bottom section of the casing  26 . Encircling bushing  46  is a stepped drive gear  48 . Further separating the drive shaft  34  from the inner wall  43  of end casing  26  is inner bushing  50 . The inner surface  52  of drive gear  48  rotates about bushing  46 . 
     The first pump chamber  36  includes an internally toothed pump gear  54  having an external smooth surface  58  which mates with the interior surface of wall  42  of end casing  36 . Positioned within the internally toothed gear is an externally toothed gear  60  which has teeth  62  which are designed to engage the internal teeth  56  of gear  54 . Gear  60  has one fewer tooth than gear  54  thereby providing the pumping action as is explained hereinafter. 
     The stepped drive gear  48  has a externally toothed surface  66  which engages the inner surface  64  of gear  60  which mates with surface  66 . Central casing  28  is bolted to end casing  26  with the bottom wall  68  of central casing  28  defining the top portion of the first pump chamber  36 . 
     A portion  90  of stepped gear  48  in turn extends through a central hole  70  through end wall  68  into the second pump chamber  38 . As with end casing  26 , central casing  28  includes a thick exterior wall  72  which has an inlet passage  74  designed to communicate with inlet passage  44  and an outlet passage  76  designed to communicate with outlet passage  45 . 
     Located in the second pump chamber  38  is an outer gear  80  which has a plurality of inwardly positioned teeth  82  and a smooth outer surface  83  which is designed to mate with wall  72 . Likewise there is an inner gear  84  which has outwardly extended teeth  86 . This inner gear  84  has an inner segmented surface  85  which mates with an exterior segmented peripheral surface  90  of step drive gear  48 . Gear  48  likewise includes a small stepped portion  92  separating tooth portion  66  from segmented portion  90 . Stepped portion  92  as shown in FIG. 2 rests against the bottom wall  68  of central casing  28  and seals the second pump chamber  38 . 
     Sealing plate  30  covers the second pump chamber  38 . Sealing plate  30  includes an inlet  94  into the second pump chamber  38  and an outlet  96  from this chamber. Further it includes an inlet  98  which is aligned with passage  74  and inlet  44  into the first pump chamber and likewise includes an opening  100  which aligns with passage  76  to outlet  45  from the first pump chamber. Thus as shown, both the inlet and outlets from the pump extend through the sealing plate  30  and further as shown the inlets and outlets of the respective first and second pump chambers are on opposite sides of the sealing plate to provide better balance for the pump. 
     Plate  30  likewise includes a central opening  102  which allows torque converter  34  to pass through. The end casings, central casings, and sealing plate are all held firmly together with bolts which extend through bolt holes  104 . 
     As shown in FIG. 6, the torque converter  34  has two V-shaped channels  106  which are machined along the axis of the torque converter which are designed to mate with V-shaped raised portions  108  in the central surface of the stepped drive gear  48 . Thus as the shaft  34  rotates the gear  48  rotates causing both pumps to rotate and pump fluid. 
     As shown diagrammatically in FIG. 7, the inlet and outlet passages from the primary pump chamber  98  and  100  are connected directly to the automatic transmission  110  maintaining the fluid pressure. This can be a CVT transmission as represented by FIG. 7A or a conventional transmission as represented by FIG.  7 B. The inlet and discharge openings  96  from the secondary pump chamber communicate through a recirculation valve  112  which permits the fluid from the outlet to be directly passed back to the inlet or alternately to be directed to the automatic transmission, either that represented by FIGS. 7A or  7 B. 
     In operation the shaft  34  is rotated which will in turn cause the stepped gear  48  to rotate. It will engage the toothed gear  60  causing it to rotate in the primary pump chamber and causing the inner toothed gear  54  to rotate. This will pull liquid in through inlet  44 , force it out through discharge passage  58  and eventually through discharge port  100  into the automatic transmission  110 . The gear  48  likewise will engage the inner surface  85  of gear  84  causing it to rotate and in turn rotating outer toothed gear  80 . Likewise this will cause an expansion and contraction pulling fluid in through inlet  94  and forcing it out through discharge opening  96 . 
     As represented in FIGS. 7,  7 A and  7 B, when the transmission  110  detects a need for additional fluid, recirculating valve  112  will cause direct fluid discharged through port  96  into the automatic transmission increasing the pressure as needed to achieve the desired pressure. Valve  112  can be adjusted to direct the fluid to recirculate through the secondary pump chamber. The valve  112  likewise can be opened partially to slightly increase pressure. Preferably it will be able to increase the pressure within the automatic transmission by up to 800 psi. 
     Thus by using the dual gerotor pump, the optimum fluid pressure within the automatic transmission can be maintained to provide for a smooth, efficient change in gear ratio. Further due to the nature of the pump, it is very compact which is particularly important in an automobile engine environment. The inlets and outlets of the two pump chambers being on opposite sides makes the pump more balanced. Thus all in all the pump of the present invention provides a very efficient mechanism to operate an automatic transmission and in particular a continuous variable transmission. 
     This has been a description of the present invention along with the preferred method of practicing the present invention.