# Patent

## Title
Charge pump for a hydraulic pump

## Abstract

A charge pump design for a hydraulic drive apparatus such as a hydrostatic transmission, integrated hydrostatic transaxle or pump having a rotatable pump cylinder block mounted in a sump and connected to a hydraulic circuit by means of a center section or the like. A fluid gallery for charge fluid is in communication with the hydraulic circuit and the charge pump is mounted adjacent to and is driven by the pump cylinder block to provide hydraulic fluid from the sump to the fluid gallery. The charge pump can be of many different styles such as a gerotor, a centrifugal pump or a flexible impeller style.

## Background
HISTORY OF THE INVENTION
This application claims the benefit of U.S. Provisional App. No. 60/483,375, filed Jun. 27, 2003 which is incorporated herein in its entirety.


BACKGROUND OF THE INVENTION
This invention relates to hydraulic pumps and transmissions having a closed hydraulic circuit and in particular to a charge pump for use with hydraulic pumps, hydrostatic transmissions and the like.
The invention described herein can be used with hydraulic pumps, which may be a stand alone hydraulic unit such as is shown in commonly-owned U.S. Pat. Nos. 6,332,393 and 6,494,686, the terms of which are incorporated herein by reference. It can also be used with a hydrostatic transmission (“HST”) comprising a pump and motor mounted in a common housing on a center block or center section. The invention can also be used with an integrated hydrostatic transmission (“IHT”) wherein the axles and other gearing such as a differential may be included in the same housing as the hydrostatic transmission. Integrated hydrostatic transmission designs are depicted in commonly-owned U.S. Pat. Nos. 5,314,387 and 6,253,637, the terms of which are incorporated herein by reference.
SUMMARY OF THE INVENTION
It is understood by those of skill in the art that hydraulic devices such as those described above use a closed hydraulic circuit to transfer hydraulic fluid to and from the rotating cylinder blocks of the hydraulic pump and motor. The closed circuit has a high pressure side and a low pressure side which is often referred to as the vacuum side. It is preferable in some applications to use a charge pump to provide pressurized fluid to the low pressure side to improve the performance of the unit. Such charge pumps are connected to the hydraulic circuit through porting, hoses or similar means. The invention described herein provides a device for providing pressurized charge fluid to the low pressure side of the hydraulic circuit.
A better understanding of the objects, advantages, features, properties and relationships of the invention will be obtained from the following detailed description and accompanying drawings which set forth illustrative embodiments and are indicative of the various ways in which the principles of the invention may be employed.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of a center section for use in a hydrostatic transmission or integrated hydrostatic transaxle.
FIG. 2 is a perspective view of the center section shown in FIG. 1 including a pump cylinder block and pump input shaft mounted thereon and a gerotor charge pump mounted adjacent to the cylinder block, with certain elements removed for clarity.
FIG. 3 is a side view of an integrated hydrostatic transaxle incorporating the center section assembly of FIG. 2, with one housing element removed to show the internal structure.
FIG. 4 is a side external view of the transaxle of FIG. 3.
FIG. 5 is a top plan view of the transaxle of FIG. 3.
FIG. 6 is a partially exploded view of the center section assembly of FIG. 2.
FIG. 7 is a bottom plan view of the center section of FIG. 2 with the charge gallery cover removed.
FIG. 8 is a cross-sectional view of the center section and motor assembly of FIG. 7 along the lines 8-8.
FIG. 9 is a perspective view of the center section of FIG. 1 with the gerotor charge pump mounted thereon.
FIG. 10 is a perspective view of the center section of FIG. 1 with a portion of the gerotor charge pump mounted thereon.
FIG. 11 is a perspective view of the center section of FIG. 1 with a portion of the gerotor charge pump mounted thereon.
FIG. 12 is a perspective view of the center section of FIG. 1, with a portion of the gerotor charge pump mounted thereon.
FIG. 13 is a bottom view of the cylinder block and portions of the gerotor charge pump of this embodiment.
FIG. 14 is a bottom view of a different embodiment of the cylinder block and gerotor charge pump, similar to that shown in FIG. 13.
FIG. 15 is a cross-sectional side view of a hydraulic pump assembly incorporating a gerotor charge pump.
FIG. 16 is a cross-sectional plan view of the end cap of the pump assembly of FIG. 15, along the lines 16-16.
FIG. 17 is a top plan view of the end cap of the pump assembly shown in FIG. 15.
FIG. 18 is a top plan view of the end cap shown in FIG. 17, with the first gerotor plate of the charge pump added.
FIG. 19 is another top plan view of the end cap shown in FIG. 17, with additional charge pump elements added.
FIG. 20 is another top plan view of the end cap of FIG. 17, with the charge pump and pump cylinder block added.
FIG. 21 is a cross-sectional side view of a further embodiment pump assembly including a gerotor charge pump.
FIG. 22 is a cross-sectional side view of a further embodiment pump assembly including a gerotor charge pump.
FIG. 23 is a cross-sectional side view of a further embodiment pump assembly including a gerotor charge pump.
FIG. 24 is a side view of a portion of an integrated hydrostatic transaxle incorporating a further embodiment of the invention.
FIG. 25 is a perspective view of a center section for use in the integrated hydrostatic transaxle of FIG. 24, with the charge gallery mounted thereon.
FIG. 26 is a perspective view of a centrifugal pump mounted on the center section of FIG. 25.
FIG. 27 is a perspective view of a center section for use in the integrated hydrostatic transaxle of FIG. 24, with a portion of the centrifugal pump mounted thereon.
FIG. 28 is a perspective view of a center section for use in the integrated hydrostatic transaxle of FIG. 24, with a portion of the centrifugal pump mounted thereon.
FIG. 29 is a perspective view of a center section for use in the integrated hydrostatic transaxle of FIG. 24, with a portion of the centrifugal pump mounted thereon.
FIG. 30 is a top plan view of the center section of FIG. 25 with a portion of the centrifugal pump mounted thereon.
FIG. 31 is a perspective view of a center section for use in a hydrostatic transmission with a further alternative embodiment of the present invention.
FIG. 32 is a perspective view of the center section of FIG. 31 with the flex-impeller charge pump and the pump and motor cylinder blocks mounted thereon.
FIG. 33 is a perspective view of the center section of FIG. 31 with a portion of the flex-impeller charge pump mounted thereon.
FIG. 34 is a perspective view of the center section of FIG. 31 with a portion of the flex-impeller charge pump mounted thereon.
FIG. 35 is a perspective view of the center section of FIG. 31 with a portion of the flex-impeller charge pump mounted thereon.
FIG. 36 is a perspective view of the center section of FIG. 31 with a portion of the flex-impeller charge pump mounted thereon.



DETAILED DESCRIPTION OF THE DRAWINGS
FIGS. 1 to 23 show several versions of a first embodiment of this invention, namely a pump or transaxle incorporating a gerotor-style charge pump. FIGS. 1 to 14 show such a charge pump in connection with a center section for use in a HST or IHT, while FIGS. 15 to 23 show this charge pump in connection with a stand-alone pump unit. For consistency, similar features will be given similar reference numerals. The term center section is used herein to mean any structure comprising a hydraulic circuit and at least a running surface for the rotating kit of a hydraulic pump.
An exemplary center section 32 is shown in FIG. 1 and an exemplary transaxle 60 is shown in FIGS. 3, 4 and 5. Most of the elements of the transaxle 60, including center section 32 are depicted in the form similar to that shown in U.S. Pat. No. 6,253,637, as a representative design. It will be understood, however that many different shapes and configurations of transaxles and center sections are known and could be used with this invention. It will also be understood that some elements of the hydrostatic transmission that are not essential to the invention (e.g., the pump and motor pistons and the motor shaft) are not depicted in certain figures for reasons of clarity.
Hydrostatic transmission 64 is mounted in a housing consisting of two housing components 14A and 14B joined along a split line perpendicular to the output axles 24, and which form an internal sump 66. Hydrostatic transmission 64 comprises pump cylinder block 12 and motor cylinder block 23 mounted on center section 32 and connected via hydraulic porting 30, as seen most clearly in FIG. 8. A swash plate 16 controls the output of hydrostatic transmission 64. Gear train 65 connects hydrostatic transmission 64 and output axles 24.
Center section 32, which would be mounted in sump 66, has a pump running surface 33 with kidneys 34A and 34B formed thereon to access hydraulic circuit 30 and a motor running surface 35 also having similar kidneys (not shown) formed thereon, again to access hydraulic circuit 30. Center section 32 has a charge gallery 37 mounted thereon to provide fluid to check plugs 58, which are used to provide make up fluid to the low pressure (or vacuum) side of hydraulic circuit 30. A charge port 48 is formed in center section 32 with a first opening 52 adjacent to pump running surface 33 and a second opening 53 into gallery 37. As shown in FIG. 6, gallery 37 comprises a gallery housing 57 secured to center section 32 by means of check plugs 58 and closed by cover 59. Other designs to form a charge gallery could readily be used with this invention. FIG. 7 shows a bottom view of this assembly with cover 59 removed.
In FIGS. 2, 3, 6, and 8, one can see pump cylinder block 12 mounted on center section 32 and driven by input shaft 13. A gerotor charge pump 40 is mounted on center section 32 adjacent to cylinder block 12. FIGS. 9-12 show gerotor charge pump 40 in differing states of assembly in order to clearly depict the interaction of the various components.
Gerotor charge pump 40 comprises a rotor plate 39 mounted to center section 32. Filter housing 46 including mesh filter 47 snaps onto or interlocks with lower gerotor housing or rotor plate 39, which then captures the remaining elements, described further below.
An outer rotor ring 42 is mounted in rotor plate 39 about the circumference thereof, and outer rotor ring 42 and inner rotor ring 44 are slidingly mounted within rotor plate or housing 39. An inner rotor ring 44 is also mounted in rotor plate 39 in a manner so that it engages both a portion of outer rotor ring 42 and rib 43 formed in rotor plate 39 so that rotation of inner rotor ring 44 with respect to outer rotor ring 42 creates a pumping action. Upper rotor plate 45 is positioned on top of rotor plate 39 and cooperates with rotor plate 39 to constrain inner gerotor ring 44 and outer gerotor ring 42. Wave spring 50 is compressed between upper rotor plate 45 and filter housing 46, keeping upper rotor plate 45 in position against the pressure created by gerotor charge pump 40 as it is driven by pump cylinder block 12. Upper rotor plate 45 may also be kept in a position by a feature formed in filter housing 46, by a spacer positioned between upper rotor plate 45 and filter housing 46, or other known means. Pin 41 is mounted to center section 32 to prevent rotation of the rotor plates 39 and 45.
For relief of excessive pressure in charge gallery 37 a charge relief 61 is provided. However, an alternative charge relief function may be provided by the components of this embodiment. The compressive force of wave spring 50 may be chosen to allow upper rotor plate 45 to move when the pressure created by charge pump 40 reaches a predetermined level, thus functioning as a charge relief.
As shown in FIGS. 12 and 13, for example, inner rotor ring 44 has a plurality of projections 49 formed thereon, which engage corresponding notches 51 on cylinder block 12 so that rotation of cylinder block 12 also drives inner rotor ring 44 and thus drives gerotor charge pump 40. The rotary action of gerotor charge pump 40, and in particular the action of inner rotor ring 44 against outer ring 42, pulls fluid through mesh filter 47 and through opening 93 formed in upper rotor housing 45. The fluid pressurized by charge pump 40 is then pushed through charge port 48 to provide pressurized fluid to gallery 37.
A variation on this design is shown in FIG. 14, which shows cylinder block 12′ having a plurality of engagement projections or ribs 54 extending outwardly therefrom, and rotor 44′ has a plurality of matching openings 55 to receive ribs 54 to thereby drive rotor 44′.
With regard to the pump unit 110 shown in FIGS. 15 to 23, a pump cylinder block 12 is mounted in a sump 120 created by housing 114 mounted to an end cap. It will be understood that these figures depict a simplified view of such a pump unit 110 and that not all elements of the pump are shown for purposes of clarity. It will also be understood that other alternative pump designs could readily be used with the present invention.
In this design, a plurality of pump pistons 119 are mounted in cylinder block 12 and interact against movable swash plate 116 to push hydraulic fluid through system porting 124. In this embodiment, swash plate 116 is controlled by means of a trunnion (not shown) extending out of the side of housing 114; it will be understood that other means of controlling swash plate 116, and thus the output of pump unit 110 are known and could be used with this invention. Input shaft 113 extends through housing 114 to drivingly engage cylinder block 112.
As shown most-clearly in the cross-sectional view of FIG. 16, end cap 115 comprises a pair of system ports 124 which can be connected to a hydraulic motor (not shown) or other apparatus, a pair of check plugs 125, and a bypass valve 126. Cross-passage 126A connects bypass valve 126 and both system ports 124.
A charge passage 127 is also bored into end cap 115. A charge port 108 connects charge pump 121 to charge passage 127, and pressure relief valve 109 permits excessive pressure to escape to sump 120. A star shaped retaining ring 128 may be pressed into charge relief 109 to retain the components of the charge relief and to permit oil to escape around its periphery.
FIGS. 18 to 20 show end cap 115 with various elements of the charge pump assembly to demonstrate the interaction of these elements. The operation of gerotor charge pump 121 is similar to that of gerotor charge pump 40 described above. Charge pump 121 comprises an upper housing 130 and a lower housing or valve plate 133, and it is secured to end cap 115 by means of a plurality of screws or similar fasteners 135. Lower housing 133 forms a pump running surface 139 and a pair of kidneys 138. Oil is pulled into charge pump 121 through inlet 134, which may be connected to an external sump (not shown). A rib 143 is formed in lower housing 133, and outer rotor ring 142 and inner rotor ring 144 are mounted in a mating relationship as shown most clearly in FIG. 19. A plurality of projections 149 mate the inner rotor ring 144 with cylinder block 12 so that inner rotor ring 144 can rotate with cylinder block 12.
A variation on this design is shown in FIG. 21 as gerotor 221, where the lower gerotor housing 133 has been replaced with two separate pieces, namely a separate, generally circular valve plate 153 on which cylinder block 12 runs, and a gerotor plate 154. A dowel pin 155 or similar device would be used to secure valve plate 153 to end cap 115′. An elastomeric material 156 is mounted under the head of screws 135 to prevent deformation of upper housing 130 due to the clamp force of screws 135.
Similar to the first described embodiment, upper housing 130 in cooperation with elastomeric material 156 may be configured to provide a charge relief function. In this embodiment, the durometer and compression of elastomeric material 156 may be selected to control the pressure at which upper housing 130 compresses elastomeric material 156 to provide charge pressure relief.
Yet another variation on this design is shown in FIG. 22 as gerotor 221′, which is similar to FIG. 21 except that valve plate 153′ is mounted in recess 157 formed in the top face of end cap 115′′, and inner rotor and outer rotor 42 run on end cap 115′′.
FIG. 23 shows a further variation on this design, where a retainer 146 is mounted on top of upper housing 130 to retain a wave spring 150 used to maintain pressure around the periphery of charge pump 121′.
FIGS. 24 to 30 show another embodiment of this invention using a centrifugal pump. This embodiment is depicted in use in an integrated hydrostatic transaxle 60′ having a hydrostatic transmission 64. Most elements of transaxle 60′ in these figures are identical to those previously described. The alternative embodiment depicted in FIGS. 24 to 30 could also be used in connection with a stand-alone pump such as is shown in FIG. 15 or an HST.
Center section 132, which can be identical to center section 32 except as described herein, includes a charge gallery or sump 137 secured to the bottom thereof. As can be seen, e.g., in FIG. 25, pump running surface 33 has a pair of kidneys 34A and 34B, but it does not have a separate charge port formed therein. Rather, the charge port function is performed by upper chimney 73 formed as part of lower rotor cover 72 and lower chimney 68, which is formed as part of charge sump 137. Charge sump 137 is preferably composed of a plastic material and has a top piece 69 in which chimney 68 is integrally formed therewith and a bottom piece 77 snapped or otherwise secured to top piece 69. Top piece 69 may be secured to center section 132 by means of the check plugs (not shown) such as described previously or other means known in the art.
A centrifugal pump 70 is mounted on center section 132 and comprises lower rotor cover 72, upper rotor cover 78 and rotor 74. As shown in FIGS. 25 and 28, lower rotor cover 72 is located on center section 132 by means of step 75, and rotor 74 is mounted therein. Rotor 74 has a plurality of fins 76 mounted about its outer circumference and a pair of projections 79 formed on its inner circumference to engage corresponding slots (not shown) on cylinder block 112 so that rotation of cylinder block 112 powers centrifugal charge pump 70. Furthermore, the slots on cylinder block 112 maintain the position of rotor 74, thus maintaining lower rotor cover 72 in position. When upper rotor cover 78 is secured to snaps 80 formed on lower cover 72, all the components of centrifugal pump 70 are conveniently captured and retained on center section 132.
Lower rotor cover 72 has a mating portion 73 formed therewith to mate to chimney 68 to provide fluid from centrifugal pump 70 to charge gallery 137. As seen in FIG. 26, openings 81 are created between upper rotor cover 78 and cylinder block 112, whereby hydraulic fluid is pulled therethrough by action of centrifugal pump 70 and pressurized to flow through chimney 68 into charge gallery 137, thus providing pressurized fluid to low pressure side of the hydraulic circuit as described above.
A mesh filter 71 may be mounted in chimney 68 to filter fluid being passed from centrifugal pump 70 to charge gallery 137. It will be understood that filter 71 could be moved adjacent to openings 81 to filter the hydraulic fluid before it is pulled into pump 70.
The charge feature of the present invention could also be provided by a flexible impeller driven by the pump block. In a further embodiment of this invention depicted in FIGS. 31 to 36, flex impeller pump 290 is shown mounted on center section 232 and driven by pump cylinder block 212. Pump cylinder block 212 is mounted on pump running surface 233 and is in communication with kidneys 234A and 234B. Port 208 connects charge pump 290 to gallery 237. Motor cylinder block 223 is also mounted on center section 232.
The specific construction of this embodiment is best shown by a comparison of FIGS. 33, 34, 35 and 36, which show the apparatus in various stages of assembly. Impeller pump 290 comprises an upper impeller plate 296 mounted to lower impeller plate 292, which is mounted to center section 232 adjacent running surface 233 for cylinder block 212. An impeller 294 is mounted in lower impeller plate 292, as shown in FIG. 34, and comprises a generally circular flexible member having a series of fins 295 formed about the outer circumference thereof and a series of projections 299 formed on the inner circumference thereof. Filter housing 297 is mounted to upper impeller plate 296 with snaps 291 that extend below and lock onto lower impeller plate 292, and mesh filter 298 acts to filter out impurities in the hydraulic fluid being pulled into impeller pump 290. Oil is pulled through filter housing 297 and into the opening 293 formed in upper impeller plate 296. The oil is then pushed through port 208 into charge gallery 237, as described previously. An anti-rotation surface 56 may be formed on center section 232 to mate with a corresponding tab (not shown) on lower impeller plate 292, to prevent rotation of the charge pump.
While specific embodiments of the invention have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangement disclosed is meant to be illustrative only and not limiting as to the scope of the invention, which is to be given the full breadth of the appended claims and any equivalents thereof.

## Claims

1. A hydraulic pump apparatus, comprising:
a housing having an end cap secured to one end thereof to form an internal oil sump and a rotatable cylinder block disposed inside the sump;
an input shaft extending into the housing to drive the rotatable cylinder block; and
a charge pump located in the sump and comprising:
a lower charge housing member mounted to the end cap;
an upper charge housing member secured to the lower charge housing member; and
a plurality of rotors disposed between the upper and lower charge housing members, wherein one of the rotors is engaged to and driven by the rotatable cylinder block.

2. A hydraulic pump apparatus as set forth in claim 1, wherein the rotatable cylinder block is disposed on the lower charge housing member.

3. A hydraulic pump apparatus as set forth in claim 1, further comprising a pressure relief valve located in the end cap.

4. A hydraulic pump apparatus as set forth in claim 1, wherein the charge pump is secured to the end cap by a plurality of fasteners extending through both the upper and lower charge housing members.

5. A hydraulic pump apparatus as set forth in claim 4, further comprising an elastomeric material located between the head of at least one of the fasteners and the upper charge housing member, to permit the upper charge housing member to move with respect to the end cap.

6. A hydraulic pump apparatus, comprising
a housing having an end cap mounted thereto to form an internal sump;
hydraulic porting formed in the end cap;
a valve plate located on the end cap;
a rotatable cylinder block disposed on the valve plate and in fluid communication with the hydraulic porting;
a charge pump disposed on the valve plate adjacent to the outer circumference of the cylinder block, wherein the charge pump is engaged to and driven by the cylinder block.

7. A hydraulic pump apparatus as set forth in claim 6, wherein the charge pump comprises a gerotor.

8. A hydraulic pump apparatus as set forth in claim 6, wherein the hydraulic porting further comprises a pressure relief valve.

9. A hydraulic pump apparatus as set forth in claim 6, wherein the charge pump further comprises an upper charge housing member secured to the valve plate.

10. A hydraulic pump apparatus as set for in claim 9, wherein the charge pump is secured to the end cap by a plurality of fasteners extending through both the upper charge housing member and the valve plate.

11. A hydraulic purop apparatus as set forth in claim 10, further comprising an elastomeric material located between the head of at least one of the fasteners and the upper charge housing member, to permit the upper charge housing member to move with respect to the valve plate.

12. A hydraulic pump apparatus as set forth in claim 10, further comprising a retaining means mounted on the charge pump.

13. A hydraulic pump apparatus as set forth in claim 12, wherein the retaining means further comprises a wave spring.

14. A hydraulic pump apparatus as set forth in claim 6, further comprising means for permitting oil to escape the hydraulic circuit when pressure therein exceeds a selected level.

15. A hydraulic pump apparatus comprising:
a rotatable cylinder block having a generally circular cross section disposed on a porting block;
a valve plate disposed between the cylinder block and the porting block and having a generally circular cross section having a diameter equal to that of the cylinder block; and
a charge pump disposed on the porting block adjacent to and encircling the valve plate, wherein the charge pump is engaged to and driven by the cylinder block.

16. A hydraulic pump apparatus as set forth in claim 15, wherein the charge pump comprises a gerotor.

17. A hydraulic pump apparatus as set forth in claim 16, wherein the charge pump further comprises an upper charge housing member secured to the valve plate.

18. A hydraulic pump apparatus as set forth in claim 17, wherein the charge pump is secured to the porting block by a plurality of fasteners extending through both the upper charge housing member and the valve plate.

19. A hydraulic pump apparatus as set forth in claim 18, further comprising an elastomeric material located between the head of at least one of the fasteners and the upper charge housing member, to permit the upper charge housing member to move with respect to the valve plate.

20. A hydraulic pump apparatus as set forth in claim 15, further comprising a retaining means mounted on the charge pump.

21. A hydraulic pump apparatus as set forth in claim 20, wherein the retaining means further comprises a wave spring.

22. A hydraulic pump apparatus comprising:
a housing;
a port block mounted to the housing and having hydraulic porting formed therein;
a generally circular recess formed in one side of the port block;
a valve plate located in the recess and having a rotatable cylinder block disposed thereon, the valve plate configured to permit fluid communication between the hydraulic porting and the cylinder block; and
a charge pump rotatably disposed on the one side of the port block adjacent to the recess.

23. A hydraulic pump apparatus as set forth in claim 22, wherein the charge pump comprises a gerotor.

24. A hydraulic pump apparatus as set forth in claim 22, wherein the hydraulic porting further comprises a pressure relief valve.

25. A hydraulic pump apparatus as set forth in claim 22, wherein the charge pump further comprises an upper charge housing member secured to the valve plate.

26. A hydraulic pump apparatus as set forth in claim 25, wherein the charge pump is secured to the porting block by a plurality of fasteners extending through both the upper charge housing member and the valve plate.

27. A hydraulic pump apparatus as set forth in claim 26, further comprising an elastomeric material located between the head of at least one of the fasteners and the upper charge housing member, to permit the upper charge housing member to move with respect to the valve plate.

28. A hydraulic pump apparatus as set forth in claim 22, further comprising means for permitting oil to escape the hydraulic circuit when pressure therein exceeds a selected level.

29. A hydraulic pump apparatus as set forth in claim 28, further comprising a retaining means mounted on the charge pump.

30. A hydraulic pump apparatus as set forth in claim 29, wherein the retaining means further comprises a wave spring.