HYDROSTATIC TRANSAXLE ASSEMBLY

Abstract: A hydrostatic transaxle assembly is disclosed including a pump (13), a manifold portion (15), and left and right axle assemblies (17,19). The manifold portion (15) includes inlet and outlet ports (65,67). Each of the axle assemblies includes a gerotor displacement mechanism (95) including an inter­ nally toothed member (101) which forms a portion of the axle housing which is fixed to the manifold housing (63). A drive shah (121) transmits the low speed high torque rotational movement of the rotor (103) to the axle shaft (21).

Description: HYDROSTATIC TRANSAXLE ASSEMBLY BACKGROUND OF THE DISCLOSURE The present invention relates to hydrostatic transaxle assemblies, and more particularly, to such an assembly having built-in hydraulic gear reduction. Certain vehicles, such as lawn and garden tractors, and smaller farm tractors, have used hydrostatic transaxle assemblies for transmitting engine torque to a pair of ground-engaging drive wheels, to propel the vehicle. A typical transaxle assembly includes a variable displacement hydraulic pump, such that the ratio of pump output flow to pump input speed (engine speed) can be infinitely varied by the vehicle operator. This ability to infinitely vary the output-input ratio, without interruption of torque transmission, makes transaxle assemblies greatly preterred over conventional clutch and gear transmissions, for vehicles of the type described above. It will be understood by those skilled in the art that a primary requirement ot a transaxle assembly is its '1gear reduction capability, i.e., the ratio of engine speed to vehicle wheel speed for any given displacement of the variable pump. In the prior art, there have been two primary types of arrangements for obtaining the necessary gear reduction between the engine and the wheels. One approach involved the use of a light duty hydrostatic transmission, comprising a variable displacement pump hydraulically coupled to a fixed displacement motor to drive a single output shaft, arranged coaxially with the pump input shaft. The motor output shaft would engage the input of a transaxle assembly including a spur and/or beveled gear reduction unit, and an axle arrangement including some sort of device to permit differential action between the left and right axles. Although the performance of this type of transaxle assembly has been generally satisfactory, the excessive size, weight, and cost make this type of transaxle commercially less desirable. In addition, the excessive size makes the overall layout of the vehicle difficult, especially with regard to the operator r s seat and the inclusion of a power take-oft (PTO) capability. In another type of prior art vehicle propel system, a variable displacement pump provides pressurized fluid to a pair of wheel motors, connected in parallel. The wheel motors directly drive the vehicle wheels, and are of the low speed-high torque variety, thus inherently providing the necessary gear reduction. Typically, these motors are of the orbiting rotor type, such that the gear rev ova will be on the order of 25:1 or 30:1. However, in this type of propel system, it is necessary to provide hose connections from the pump to each of the motors, and the presence of exposed hydraulic hoses is considered undesirable on most vehicles of this type. In addition, the use of separate wheel motors means that the vehicle has no true axle assembly to which the vehicle frame can be mounted, or which can provide hitch points for vehicle implements. S#iMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a hydrostatic transaxle assembly which is substantially smaller, lighter, and less expensive that transaxles of the type utilizing spur andlor beveled gear reduction units It is another object of the present invention to provide a transaxle assembly of the type which eliminates the need for exposed hydraulic hoses, and which facilitates mounting of the vehicle frame and vehicle accessories to the transaxle assembly. The above and other objects of the present invention are accomplished by the provision of a transaxle assembly comprising manifold housing means defining an inlet port adapted to be in fluid communication with the pump fluid outlet, and an outlet port adapted to be in fluid communication with the pump fluid inlet. The manifold housing means defines a pair of oppositely disposed, generally symmetrical axle assembly receiving (mounting) portions defining an axis of rotation. The manifold housing means further defines inlet passage means in fluid communication with the inlet port and return passage means in fluid communication with the outlet port. A pair of axle assemblies are received in the axle assembly receiving portions defined by the manifold housing means. Each of the axle assemblies comprises a stationary axle housing means fixedly mounted relative to the manifold housing means, and an axle shaft disposed within the axle housing means and mounted for rotation relative thereto. The axle assembly also includes a fluid pressure actuated rotary displacement mechanism, and means for transmitting the rotary output of the displacement mechanism to the axle shaft. The displacement mechanism defines expanding and contracting fluid chambers, and valve means provide fluid communication between the inlet passage means and the expanding fluid chamber and between the contracting fluid chamber and the return passage means. In accordance with one aspect of the present inven ton, the displacement mechanism comprises an internally toothed member and an externally toothed member eccentrically disposed in the internally toothed member for relative orbital and rotational movement therein, and the internally toothed member comprises a portion of the stationary axle housing means. In accordance with another aspect of the present invention, the means for transmit ting rotary output of the displacement mechanism to the axle shaft comprises a drive shaft which cooperates with the externally toothed member to define a first universal connection and cooperates with the axle shaft to define a second universal connection. In accordance with another aspect of the present invention, the valve means comprises a rotatable disc valve member cooperating with the manifold housing means to define an inlet fluid chamber and a return fluid chamber, each of the inlet fluid chambers being in open, relatively unrestricted fluid communication with the inlet passage means of the manifold housing. means, and each of the return fluid chambers being in open, relatively unrestricted fluid communication with the outlet port of the manifold housing many. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a rear plan view of a vehicle such as a garden tractor equipped with the bydrostatic transaxle assembly of the present invention. FIG. 2 is an end view of the transaxle assembly of the present invention on a larger scale than FIG. 1, comparing its profile to the profile of a prior art transaxle assembly of the type including spur gear reduction. FIG. 3 is a horizontal, axial cross section of the variable displacement pump associated with the transaxle assembly of the present invention. FIG 4 is a horizontal1 axial cross section, on the same scale as FIG. 3, showing the central portion of the transaxle assembly of the present invention. FIG. 5 is a horizontal, axial cross section, which is axially foreshortened, and on the same scale as FIGS. 3 and 4, showing one of the axle assemblies of the invention DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings, which are not intended to limit the invention, FIG. 1 is a rear plan view showing the transaxle assembly of the present invention, generally designated 11 installed on a typical garden tractor. The tractor includes a vehicle frame F which supports a stamped body and fender assembly B. Disposed above the body assembly B is a seat S for the vehicle operator. The tractor also includes a pair of ground-engaging wheels W which are adapted to be driven by the transaxle assembly of the present invention. The transaxle assembly 11 includes a variable displacem nt hvd#aulic pump, generally designated 13, a central manifold portion, generally designated 15, and left and right axle assemblies, generally designated 17 and 19, respectively. Extending out of the axle assembly 17 is a left axle shaft 21, and extending out of the axle assembly 19 is a right axle shaft 23. Referring now to FIG. 2 which is an end view of the transaxie assembly 11 alone, in conjunction with FIG. 1, it may be seen that each of the axle assemblies 17 and 19 includes a mounting pad 25, to which is attached a portion of the vehicle frame F. In addition, each of the axle assemblies 17 and 19 includes an integral hitch mounting point 27, to permit attachment of a tractor implement lift arms to the transaxle assembly 11. Also shown schematically in FIG. 2 is the vehicle engine, with a schematic representation of the engine output being transmitted to an input shaft 29 of the hydraulic pump 13. Referring now only to FIG. 2, there is shown a comparison of the profile of the transaxle assembly 11 and the profile of the prior art transaxle device (dotted line). The prior art transaxle is positioned in FIG. 2, relative to the transaxle assembly 11, such that the axis of rota tion of the axle shafts of the two assemblies coincide. The prior art transaxle device shown in FIG. 2 comprises a hydraulic pump P (which may be substantially identical to the pump 13, but is rotated at a 90 degree angle relative to the pump 13, for reasons which are not relevant to the present invention). The prior art transaxle device also includes a gear reduction unit G, which is typically of the spur and bevel gear type as described in the background. Mounted below the gear reduction unit G is the axle assembly A. A gear reduction unit G and axle assembly A, having the profile shown in FIG. 2, are produced commercially by Peerless, and are well known in the art. R rrln± now to FIG. 3, the hydraulic pa 53 will be described briefly. It should be understood that the pump 13 may comprise any one of several well known pump configurations, and that the structural details of the pump 13 form no part of the present invention. In the subject embodiment, the pump 13 is a variable displacement, radial ball (piston) pump, which is essentially just the pump portion of a Model 11 hydrostatic transmission sold by Eaton Corporation. The pump 13 includes a housing assembly 31 enclosing a make-up pumping element 33. The input shaft 29 simultan- eously rotates components of the make-up pump 33, and of the radial ball pumping element. The ball pump includes a movable cam ring assembly 35 having a circular concave race 37 which mates with a plurality of pump balls 39 which are located in bores 41 of an annular pump rotor 43. Cam ring assembly 35 is free to pivot about the axis of a cam pivot pin 45 to vary the eccentricity of the race 37 relataive to the longitudinal axis of the pump (which coincides with the axis of the input shaft 29). Rotation of the pump rotor 43 about a boss 47 of a pintle assembly 49 moves the balls 39 radially inwardly in bores 41, causing fluid to be forced by the balls 39 through an outlet passage 51. At the same time, return fluid flows through pump inlet passage 53 and fills the bores 41 as the balls 39 move radially outwardly in contact with the race 37. An appropriate control arrangement, generally designated 55 to vary the displacement of the pump 13 is provided. The control arrangement 55 includes a control shaft 57, a control pin 59, and a cam ring insert 61. The specific purpose of the control arrangement 55 is to pivot the cam ring assembly 35 about the cam pivot pin 45. Such pivotal movement is accomplished by rotating control shaft 57 about its axis, which turns control pin 59, and accordingly moves cam ring insert 61 and cam ring 35. Pivotal movement of cam ring 35 allows the pump 13 to vary from full displacement in one direction to zero displacement to full displacement in the other direction. Referring now to FIG. 4, the manifold portion 15 will be described in structural detail. The manifold portion 15 includes a manifold housing 63 which defines an inlet port 65 and an outlet port 67. The manifold housing 63 is adapted to be fixedly and sealingly attached to the pump 13, and more specifically, to the pintle assembly 49 by means of a plurality of bolts 69, part of which is shown both in FIG. 3 and in FIG. 4. By aligning the pump 13 with the manifold portion 15, it may be seen that the outlet passage 51 is in fluid communication with the manifold inlet port 65, while the manifold outlet port 67 is in fluid communication with the pump inlet passage 53. The manifold housing 63 defines an ax-ially-oriented passage 71, and a passage 73 interconnecting the inlet port 65 and the axial passage 71. The manifold housing 63 further defines a large central chamber 75 which is in open, relatively unrestricted fluid communication with the outlet port 67. The manifold housing 63 further defines left and right generally cylindrical recesses 77 and 79. The recesses 77 and 79 are preferably arranged to be oppositely and symmetrically disposed. The manifold housing 63 also defines left and right annular grooves 81 and 83, the function of which will be described subsequently. Finally, the manifold housing 63 defines left and right end faces 85 and 87, the function of which will also be described subsequently. Referring now to FIG. 5, in conjunction with FIG. 4, the left axle assembly 17 will be described in structural detail, it being understood that the right axle assembly 19 is a mirror image of the left axle assembly 17. Thus, only the left axle assembly 17 will be described. The left axle assembly 17 comprises a plurality of sections including an axle support casing 91, a wear plate 93, a gerotor displacement mechanism 95, and a port plate 97. These elements 9l, 93, 95, and 97 are secured together, and held in fixed sealing engagement with the left end face 85 of the manifold housing 63 by some suitable means, such as a plurality of bolts 99 (shown only in FIGS. 1 and 2). Thus, the end face 85 and recess 77 serve as a receiving (or mounting portion) for the axle assembly 17. The gerotor displacement mechanism 95 is well known to those skilled in the art, and will be described only briefly herein. In the subject embodiment, the gerotor mechanism 95 is a Gerole mechanism comprising an internally toothed assembly 101, and an externally toothed rotor member 103, eccentrically disposed within the internally toothed assembly 101. The assembly 101 includes a stationary ring member 105 defining a plurality of semi-cylindrical openings, with a cylindrical roller member 107 disposed in each of the openings. Typically, the rotor 103 has one less tooth than the number of rollers 107, thus permitting the rotor 103 to orbit and rotate relative to the internally toothed assembly 101. This orbital and rotational movement of the rotor 103 defines a plurality of expanding and contracting volume chambers 109. Referring now primarily to FIG. 5, the left axle shaft 21 is positioned within the axle support casing 91, and rotatably supported therein by suitable bearing sets 111 and 113. Toward its right end in FIG. 5, the axle shaft 21 defines a generally cylindrical portion 115 within which is a set of internal, straight splines 117. In engagement with the splines 117 is a set of external, crowned splines 119 formed on one end of a main drive shaft 121. Disposed at the opposite end of the shaft 121 is another set of external, crowned splines 123, which are in engagement wlth a set of internal, straight splines 125, formed on the inside of the rotor member 103. Therefore, in the subject embodiment, because the internally toothed assembly 101 includes seven internal teeth 107, and the rotor 103 includes six external teeth, seven orbits of the rotor 103 results in one complete rotation thereof. and one complete rotation of the drive shaft 121 and axle shaft 21. Also in engagement with the internal splines 125 is a set of external splines 127 formed about one end of a valve drive shaft 129 which has, at its opposite end, another set of external splines 131. The splines 131 are in engagement with a set of internal splines 133 formed about the inner periphery of a valve member 135. The valve member 135 is rotatably disposed within the cylindrical recess 77 defined by the manifold housing 63, and by means of the valve drive shaft 129, the valve member 135 rotates at the speed of rotation of the rotor 103, as is generally well known in the art. Disposed in sealing engagement with the right end face of the valve member 135 is a balancing ring assembly 137, which is shown and described in greater detail in U.S. Pat. No. 3,572,983, assigned to the assignee of the present invention, and incorporated herein by reference. The valve member 135 and balancing ring assembly 137 cooperate to devide the cylindrical recess 77 into an annular outer chamber 139 and an annular inner chamber 141. The outer chamber 139 surrounds the valve member 135 and is in constant fluid communication with the manifold inlet port 65, through the passage 71. At the same time, the inner chamber 141 is in constant fluid communication with the manifold outlet port 67 through the central chamber 75. The valve member 135 defines a plurality of alternating valve passages 143 and r# ±°.¯ passages 143 being in communication with the outer chamber 139, while the valve passages 145 are in communication with the inner chamber 141. The port plate 97 defines a plurality of fluid passages 147, each of which is disposed to be in continuous fluid communication with an adjacent one of the volume chambers 109. Based upon the knowledge of those skilled in the art, and the incorporation of 3,572,983, the structural details relating to the valve passages 143 and 145 and the fluid passages 147 will not be described further herein. Operation When the vehicle operator rotates the control shaft 57, to move the pump 13 from its zero displacement condition, pressurized fluid begins to flow from the outlet passage 51 of the pump, through the inlet port 65 and passage 73 into the axial passage 71. When the vehicle is moving in a straight path, and the resistance to turning of each of the axle shafts 21 and 23 is substantially equal, pressurized fluid entering the axial passage 71 will flow in substantially equal proportions to the outer chambers 139 of the left and right axle assemblies 17 and 19. Pressurized fluid in the outer chambers 139 flows through valve passages 143 and port plate passages 147 into the expanding volume chambers 109, thus causing each of the rotors 103 to orbit and rotate at the same speed. As was described previously, the orbital and rotational movement of the rotors 103 is translated by the drive shafts 121 into pure rotational movement of the axle shafts 21 and 23. At the same time, low pressure fluid is exhausted from the contracting volume chambers 109 flows through the adjacent port plate passages 147, and by means of the valve passages 145 flows through the annular inner chambers 141 into the central chamber 75. As described previously, low pressure return fluid in the chamber 75 flows to the outlet port 67, and then into the pump inlet passage 53. When the vehicle is in a turn condition, the transaxle assembly 11 of the present invention has built-in differentiation capability. For example, if the vehicle is making a right turn, the axle shaft 23 will be rotating at a slower speed than the axle shaft 21. Because the tires, and thus the motors, turn at different speeds and are "tied" to the ground, the motors act as a flow divider. As a result, the flow of pressurized fluid from the pump 13 into the axial passage 71 will not be divided evenly, as was the case during straight movement, but instead, relatively less fluid will flow to the right axle assembly 19, and relatively more fluid will flow to the left axle assembly 17. In general, the flow of pressurized fluid to the axle assemblies 17 and 19 will be proportional to the speed thereof, and inversely proportional to the torque being transmitted. Thus, the transaxle assembly of the present invention includes a single, rigid axle housing which is suitable for mounting of the vehicle frame and various vehicle accessories and implements. At the same time, the invention provides a transaxle assembly having inherent, built-in differential capability and gear reduction capability. In certain vehicles applications, it may be desirable to separate the pump 13 from the manifold portion 15 and axle assembles 17 and 19. In such situations, it should be apparent to those skilled in the art that the pump 13 may be located remotely with appropriate porting and hoses to connect passage 51 to port 65 and passage 53 to port 67. It should be noted that with the pump being located remotely, the transaxle assembly of the invention still retains the features and advantages des#i#e'# above The present invention has been described in detail sufficient to enable one skilled in the art to practice the invention It is believed that upon a reading and understanding of the specification, various alterations and modifications will become apparent to those skilled in the art, and it is intended that the invention include all such alterations and modifications, insofar as tbey come within the scope of the appended claims.

Claims: CLAIMS 1. A hydrostatic transaxle assembly (11) for use with a hydrostatic pump (13) on a vehicle having a vehicle frame (F), a source of motive power, and a pair of driven wheels (W), the pump having a fluid outlet (51) and a fluid inlet (53), said transaxle assembly comprising: (a) manifold housing means (63) defining an inlet port (65) adapted to be in fluid communication with the pump fluid outlet and an outlet port (67) adapted to be in fluid communication with the pump fluid inlet, said manifold housing means defining a pair of oppositely disposed, generally symmetrical axle assembly receiving portions (85,87) defining an axis of rotation, said mani fold housing means further defining inlet passage means (71) in fluid communication with said inlet port and return passage means (75) in fluid communication with said outlet port; ; (b) a pair of axle assemblies (17,19) received in said axle assembly receiving portions of said manifold housing means; (c) each of said axle assemblies comprising station ary axle housing means (91) fixedly mounted rela tive to said manifold housing means, an axle shaft (21,23) disposed within said axle housing means and mounted for rotation relative thereto, a fluid pressure actuated rotary displacement mechanism (95), means (121) for transmitting the rotary output of said displacement mechanism to said axle shaft, said displacement mechanism defining expanding and contracting fluid chambers (109), and valve means (135) operable to provide fluid communication between said inlet passage means and said expanding fluid chamber and between said contracting fluid chamber and said return passage means; and (d) said displacement mechanism comprising an inter nally toothed member (105) and an externally toothed member (103) eccentrically disposed in said internally toothed member for relative orbi tal and rotational movement therein, said inter nally toothed member comprising a portion of said stationary axle housing means. 2. A transaxle assembly as claimed in claim 1 wherein said displacement mechanism comprises a gerotor gear set, said internally toothed membercomprises a gerotor ring (105) having a plurality Ntl of internal teeth (107) and said externally toothed member comprises a gerotor star (103) having a plurality N of external teeth. 3 A transaxle assembly as claimed In claim I whnre in each of said stationary axle housing means include mounting means (25) adapted to rigidly mount said axle housing means to the vehicle frame. 4. A hydrostatic transaxle assembly (11) for use with a hydrostatic pump (13) to drive a pair of vehicle wheels (W) on a vehicle having a source of motive power, the pump having a fluid outlet (51) and a fluid inlet (53), said transaxle assembly comprising: (a) manifold housing means (63) defining an inlet port (65) adapted to be in fluid communication with the pump fluid outlet and an outlet port (67) adapted to be in fluid communication with the pump fluid inlet, said manifold housing means defining a pair of oppositely disposed, generally symmetrical axle assembly receiving portions (85,87) defining an axis of rotation, said mani fold housing means further defining inlet passage means (71) in fluid communication with said inlet port and return passage means (75) in fluid com munication with said outlet port; ; (b) a pair of axle assemblies If7,19) received in said axle assembly receiving portions of said manifold housing means; (c) each of said axle assemblies comprising station ary axle housing means (91) fixedly mounted rela tive to said manifold housing means, an axle shaft (21,23) disposed within said axle housing means and mounted for rotation relative thereto, a fluid pressure actuated rotary displacement mechanism (95), said displacement mechanism defining expanding and contracting fluid chambers (109), and valve means (135) operable to provide fluid communication between said inlet passage means and said expanding fluid chamber and between said contracting fluid chamber and said return passage means; and (d) said displacement mechanism (95) comprising an internally toothed member (105) mounted to be prevented from rotating relative to said station ary axle housing means, and an externally toothed member (103) eccentrically disposed in said internally toothed member for relative orbital and rotational movement therein, drive shaft means (121) cooperating with said externally toothed member to define first universal connec tion means (123,125) and with said axle shaft to define second universal connection means (117,119) to translate said orbital and rota tional movement of said externally toothed member into rotational movement of said axle shaft. 5. A transaxle assembly as claimed in claim 4 wherein said externally toothed member (103) defines a first set of straight, internal splines (125) and said drive shaft means defines a first set of crowned external splines (123), said first sets of splines comprising said first universal connection means. 6. A transaxle assembly as claimed in claim 5 wherein said axle shaft (21) defines a second set of straight, internal splines (117) and said drive shaft means defines a second set of crowned external splines (119) said second sets of splines comprising said second universal connection means. 7. A hydrostatic transaxle assembly (11) for use with a hydrostatic (13) pump to drive a pair of vehicle wheels (W) on a vehicle having a source of motive power, the pump having a fluid outlet (51) and a fluid inlet (53), said transaxle assembly comprising: (a) manifold housing means (63) defining an inlet port (65) adapted to be in fluid communication with the pump fluid outlet and an outlet port (67) adapted to be in fluid communication with the pump fluid inlet, said manifold housing means defining a pair of oppositely disposed, generally symmetrical axle assembly receiving portions (25,S7) defining a axis of rotation; (b) a pair of axle assemblies (17,19) mounted in association with said axle assembly receiving portions of said manifold housing means; ; (c) each of said axle assemblies comprising station ary axle sousing means {91) fixedly mounted rela tive to said manifold housing means, an axle shaft (21,23) disposed within said axle housing means and mounted for rotation relative thereto, and for rotation about said axis of rotation, a fluid pressure actuated rotary displacement mech anism (95) defining expanding and contracting fluid chambers (109), means (121) for transmit ting the rotary output of said displacement mech anism to said axle shaft, and rotary valve means to35) disposed between said manifold housing means and said displacement mechanism and being operable to provide fluid communication between said inlet passage means and said expanding fluid chamber and between said contracting fluid cham ber and said return passage means; and (d) said rotary valve means comprising a rotatable disc valve member (135) cooperating with said manifold housing means to define an inlet fluid chamber (139) and a return fluid chamber (141), each of said inlet fluid chambers being in open, relatively unrestricted fluid communication with said inlet port of said manifold housing means, and each of said return fluid chambers being in open, relatively unrestricted fluid communication with said outlet port of said manifold housing means. 8. A transaxle assembly as claimed in claim 1 wherein said axle housing means defines a fluid passage (147) conimunicating with each of saId erranding and contracting fluid chambers, and said rotary disc valve member provides sequential fluid communication between said inlet fluid chamber and each of said fluid passages, and between said return fluid chamber and each of said fluid passages. 9. A transaxle assembly as claimed in claim 8 including valve drive shaft means (129) operable to translate a rotational component of movement of said displacement mechanism into rotational movement of said rotary disc valve member about said axis of rotation. 10. A transaxle assembly as claimed in claim 9 wherein said displacement mechanism comprises an internally toothed member (105) fixedly mounted relative to said stationary axle housing means7 and an externally toothed member (103) eccentrically disposed in said internally toothed member for relative orbital and rotational move ment therein, said valve drive shaft means having one end thereof in splined (125,127) engagement with said externally toothed member, and the other end thereof in splined (131,133) engagement with said rotary disc valve member.

Inventors: KORRECT, JEROLD MARK
Applicants: EATON CORPORATION
Application year: 1983
Main classification: B60K17
IPC codes: B60K17, B60B35