Charge pump for a hydrostatic transmission

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 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.

DETAILED DESCRIPTION OF THE DRAWINGS

FIGS. 1 to 23show several versions of a first embodiment of this invention, namely a pump or transaxle incorporating a gerotor-style charge pump.FIGS. 1 to 14show such a charge pump in connection with a center section for use in a HST or IHT, whileFIGS. 15 to 23show 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.

Hydrostatic transmission64is mounted in a housing consisting of two housing components14A and14B joined along a split line perpendicular to the output axles24, and which form an internal sump66. Hydrostatic transmission64comprises pump cylinder block12and motor cylinder block23mounted on center section32and connected via hydraulic porting30, as seen most clearly inFIG. 8. A swash plate16controls the output of hydrostatic transmission64. Gear train65connects hydrostatic transmission64and output axles24.

Center section32, which would be mounted in sump66, has a pump running surface33with kidneys34A and34B formed thereon to access hydraulic circuit30and a motor running surface35also having similar kidneys (not shown) formed thereon, again to access hydraulic circuit30. Center section32has a charge gallery37mounted thereon to provide fluid to check plugs58, which are used to provide make up fluid to the low pressure (or vacuum) side of hydraulic circuit30. A charge port48is formed in center section32with a first opening52adjacent to pump running surface33and a second opening53into gallery37. As shown inFIG. 6, gallery37comprises a gallery housing57secured to center section32by means of check plugs58and closed by cover59. Other designs to form a charge gallery could readily be used with this invention.FIG. 7shows a bottom view of this assembly with cover59removed.

InFIGS. 2,3,6, and8, one can see pump cylinder block12mounted on center section32and driven by input shaft13. A gerotor charge pump40is mounted on center section32adjacent to cylinder block12.FIGS. 9–12show gerotor charge pump40in differing states of assembly in order to clearly depict the interaction of the various components.

Gerotor charge pump40comprises a rotor plate39mounted to center section32. Filter housing46including mesh filter47snaps onto or interlocks with lower gerotor housing or rotor plate39, which then captures the remaining elements, described further below.

An outer rotor ring42is mounted in rotor plate39about the circumference thereof, and outer rotor ring42and inner rotor ring44are slidingly mounted within rotor plate or housing39. An inner rotor ring44is also mounted in rotor plate39in a manner so that it engages both a portion of outer rotor ring42and rib43formed in rotor plate39so that rotation of inner rotor ring44with respect to outer rotor ring42creates a pumping action. Upper rotor plate45is positioned on top of rotor plate39and cooperates with rotor plate39to constrain inner gerotor ring44and outer gerotor ring42. Wave spring50is compressed between upper rotor plate45and filter housing46, keeping upper rotor plate45in position against the pressure created by gerotor charge pump40as it is driven by pump cylinder block12. Upper rotor plate45may also be kept in a position by a feature formed in filter housing46, by a spacer positioned between upper rotor plate45and filter housing46, or other known means. Pin41is mounted to center section32to prevent rotation of the rotor plates39and45.

For relief of excessive pressure in charge gallery37a charge relief61is provided. However, an alternative charge relief finction may be provided by the components of this embodiment. The compressive force of wave spring50may be chosen to allow upper rotor plate45to move when the pressure created by charge pump40reaches a predetermined level, thus functioning as a charge relief.

As shown inFIGS. 12 and 13, for example, inner rotor ring44has a plurality of projections49formed thereon, which engage corresponding notches51on cylinder block12so that rotation of cylinder block12also drives inner rotor ring44and thus drives gerotor charge pump40. The rotary action of gerotor charge pump40, and in particular the action of inner rotor ring44against outer ring42, pulls fluid through mesh filter47and through opening93formed in upper rotor housing45. The fluid pressurized by charge pump40is then pushed through charge port48to provide pressurized fluid to gallery37.

A variation on this design is shown inFIG. 14, which shows cylinder block12′ having a plurality of engagement projections or ribs54extending outwardly therefrom, and rotor44′ has a plurality of matching openings55to receive ribs54to thereby drive rotor44′.

With regard to the pump unit110shown inFIGS. 15 to 23, a pump cylinder block12is mounted in a sump120created by housing114mounted to an end cap. It will be understood that these figures depict a simplified view of such a pump unit110and 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 pistons119are mounted in cylinder block12and interact against movable swash plate116to push hydraulic fluid through system porting124. In this embodiment, swash plate116is controlled by means of a trunnion (not shown) extending out of the side of housing114; it will be understood that other means of controlling swash plate116, and thus the output of pump unit110are known and could be used with this invention. Input shaft113extends through housing114to drivingly engage cylinder block112.

As shown most clearly in the cross-sectional view ofFIG. 16, end cap115comprises a pair of system ports124which can be connected to a hydraulic motor (not shown) or other apparatus, a pair of check plugs125, and a bypass valve126. Cross-passage126A connects bypass valve126and both system ports124.

A charge passage127is also bored into end cap115. A charge port108connects charge pump121to charge passage127, and pressure relief valve109permits excessive pressure to escape to sump120. A star shaped retaining ring128may be pressed into charge relief109to retain the components of the charge relief and to permit oil to escape around its periphery.

FIGS. 18 to 20show end cap115with various elements of the charge pump assembly to demonstrate the interaction of these elements. The operation of gerotor charge pump121is similar to that of gerotor charge pump40described above. Charge pump121comprises an upper housing130and a lower housing or valve plate133, and it is secured to end cap115by means of a plurality of screws or similar fasteners135. Lower housing133forms a pump running surface139and a pair of kidneys138. Oil is pulled into charge pump121through inlet134, which may be connected to an external sump (not shown). A rib143is formed in lower housing133, and outer rotor ring142and inner rotor ring144are mounted in a mating relationship as shown most clearly inFIG. 19. A plurality of projections149mate the inner rotor ring144with cylinder block12so that inner rotor ring144can rotate with cylinder block12.

A variation on this design is shown inFIG. 21as gerotor221, where the lower gerotor housing133has been replaced with two separate pieces, namely a separate, generally circular valve plate153on which cylinder block12runs, and a gerotor plate154. A dowel pin155or similar device would be used to secure valve plate153to end cap115′. An elastomeric material156is mounted under the head of screws135to prevent deformation of upper housing130due to the clamp force of screws135.

Similar to the first described embodiment, upper housing130in cooperation with elastomeric material156may be configured to provide a charge relief finction. In this embodiment, the durometer and compression of elastomeric material156may be selected to control the pressure at which upper housing130compresses elastomeric material156to provide charge pressure relief.

Yet another variation on this design is shown inFIG. 22as gerotor221′, which is similar toFIG. 21except that valve plate153′ is mounted in recess157formed in the top face of end cap115″, and inner rotor and outer rotor42run on end cap115″.

FIG. 23shows a further variation on this design, where a retainer146is mounted on top of upper housing130to retain a wave spring150used to maintain pressure around the periphery of charge pump121′.

FIGS. 24 to 30show another embodiment of this invention using a centrifugal pump. This embodiment is depicted in use in an integrated hydrostatic transaxle60′ having a hydrostatic transmission64. Most elements of transaxle60′ in these figures are identical to those previously described. The alternative embodiment depicted inFIGS. 24 to 30could also be used in connection with a stand-alone pump such as is shown inFIG. 15or an HST.

Center section132, which can be identical to center section32except as described herein, includes a charge gallery or sump137secured to the bottom thereof. As can be seen, e.g., inFIG. 25, pump running surface33has a pair of kidneys34A and34B, but it does not have a separate charge port formed therein. Rather, the charge port function is performed by upper chimney73formed as part of lower rotor cover72and lower chimney68, which is formed as part of charge sump137. Charge sump137is preferably composed of a plastic material and has a top piece69in which chimney68is integrally formed therewith and a bottom piece77snapped or otherwise secured to top piece69. Top piece69may be secured to center section132by means of the check plugs (not shown) such as described previously or other means known in the art.

A centrifugal pump70is mounted on center section132and comprises lower rotor cover72, upper rotor cover78and rotor74. As shown inFIGS. 25 and 28, lower rotor cover72is located on center section132by means of step75, and rotor74is mounted therein. Rotor74has a plurality of fins76mounted about its outer circumference and a pair of projections79formed on its inner circumference to engage corresponding slots (not shown) on cylinder block112so that rotation of cylinder block112powers centrifugal charge pump70. Furthermore, the slots on cylinder block112maintain the position of rotor74, thus maintaining lower rotor cover72in position. When upper rotor cover78is secured to snaps80formed on lower cover72, all the components of centrifugal pump70are conveniently captured and retained on center section132.

Lower rotor cover72has a mating portion73formed therewith to mate to chimney68to provide fluid from centrifugal pump70to charge gallery137. As seen inFIG. 26, openings81are created between upper rotor cover78and cylinder block112, whereby hydraulic fluid is pulled therethrough by action of centrifugal pump70and pressurized to flow through chimney68into charge gallery137, thus providing pressurized fluid to low pressure side of the hydraulic circuit as described above.

A mesh filter71may be mounted in chimney68to filter fluid being passed from centrifugal pump70to charge gallery137. It will be understood that filter71could be moved adjacent to openings81to filter the hydraulic fluid before it is pulled into pump70.

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 inFIGS. 31 to 36, flex impeller pump290is shown mounted on center section232and driven by pump cylinder block212. Pump cylinder block212is mounted on pump running surface233and is in communication with kidneys234A and234B. Port208connects charge pump290to gallery237. Motor cylinder block223is also mounted on center section232.

The specific construction of this embodiment is best shown by a comparison ofFIGS. 33,34,35and36, which show the apparatus in various stages of assembly. Impeller pump290comprises an upper impeller plate296mounted to lower impeller plate292, which is mounted to center section232adjacent running surface233for cylinder block212. An impeller294is mounted in lower impeller plate292, as shown inFIG. 34, and comprises a generally circular flexible member having a series of fins295formed about the outer circumference thereof and a series of projections299formed on the inner circumference thereof. Filter housing297is mounted to upper impeller plate296with snaps291that extend below and lock onto lower impeller plate292, and mesh filter298acts to filter out impurities in the hydraulic fluid being pulled into impeller pump290. Oil is pulled through filter housing297and into the opening293formed in upper impeller plate296. The oil is then pushed through port208into charge gallery237, as described previously. An anti-rotation surface56may be formed on center section232to mate with a corresponding tab (not shown) on lower impeller plate292, to prevent rotation of the charge pump.