GB2243352A - Vehicle transaxle housing for hydrostatic transmission - Google Patents

Abstract

The transaxle housing, e.g. for a small-sized vehicle such as a grass-mowing lawn tractor, encloses an internally located hydrostatic transmission in association with speed reducing gearing and mechanical differential for reasons of compactness and simplicity of manufacture. The axle housing comprises two members connected together alone a parting plane to define a number of internal chambers, at least one chamber (30) enclosing the hydrostatic transmission and another chamber 31 enclosing speed reducing gearing and differential (34). One housing element is provided with a vertical input shaft which is operatively connected through bevel gearing (53) to a hydraulic pump (20), the pump fluidly coupled to a hydraulic motor (21), the rotary axis of the hydraulic motor 21 being coincident with the parting plane of the housing and parallel to the rotating axes of the half shafts (40, 41) of the transaxle. The bevel gearing is located within either the chamber enclosing the hydrostatic transmission or within one of the remaining chambers enclosing the reduction gearing and differential. <IMAGE>

Description

VARIABLE SPEED TRANSAXLE BACKGROUND OF THE INVENTION The field of the invention relates to hydrostatic machines in association with transaxle driving apparatus for use in light grass-mowing vehicles, such as ride-on tractors and walk-behind mowers, where in particular it becomes advantageous to manufacture the hydrostatic unit and transaxle as one unitary item.

The present invention is directed towards providing improvements to hydrostatic variable speed transaxles of the type as shown in our co-pending application, Serial No. 222,513, filed July 1, 1988, entitled "Variable Speed Transaxle" (Ser;al Mo.US 49eS 583).

The prior application has disclosed therein embodiments for a hydrostatic unit disposed within a transaxle housing including vertical input drive means operatively connecting with rotary cylinder barrel of the hydraulic pump. The hydraulic pump is fluidly coupled to a hydraulic motor, and the hydraulic motor is connected via gearing that includes bevel gearing, to the differential and axle drive shafts of the transaxle.

The large distance from the hydraulic motor to the differential has to be bridged by a number of gear trains, and by contrast, the present invention offers a method of reducing the size of the housings through the use of bevel gearing between the vertical input drive shaft and the hydraulic pump of the hydrostatic unit.

Furthermore, there is an advantage in achieving overall compaction of the transaxle by obtaining a close relative position of the input drive shaft to the differential.

Furthermore, in order to reduce noise and vibration, in addition to also obtaining the most power efficient operating range of the hydrostatic unit, it is preferrable to limit the maximum rotational speed of the pump and motor to a level below that of the engine.

This can be achieved by gear reduction as disclosed in U.S.

Patent No. 4,691,512, or through the use of two unequal sizes of pulley in a Vee belt drive train. The Vee belt being used to transmit power from the vehicle's engine to the transaxle, speed reduction being obtained by the use of a small pulley on the engine shaft, by the Vee belt, a larger pulley on the transaxle input shaft. The degree of speed reduction being determined -by the ratio of the pulley diameters.

In the field of hydrostatic units, speed reduction by Vee belt rather than by gearing has become widely used by the industry for reasons of economy.

A typical grass-mower lawn tractor has for instance, a requirement for a maximum forward speed of about 6 miles per hour, and is most frequently fitted with an internal combustion engine operating at a rotational speed of about 3,400 revimin at full throttle. For reasons of efficient grass cutting, it is necessary to operate the cutting blades at about the same rotational speed as the engine.

To obtain a maximum vehicle speed of 6 mph, speed reduction is required between the engine and the drive wheels, the maximum rotational speed of the drive wheels being typically of the order of 110 rev/min. A proportion of this speed reduction being obtained by the Vee belt drive-line as already described, so that less final gear reduction is required inside the transaxle.

During the test and development of such a Vee belt drive system in a lawn tractor fitted with a prototype hydrostatic transaxle, it has been found that on occasion insufficient engine torque can be transmitted through the Vee belt to the hydrostatic transaxle, and furthermore, that the Vee belts wear out prematurely. Also the required tension in the Vee belt is such that during prolonged use, the belt becomes loose with the result that the transmittable power to the transaxle is further reduced.

A further disadvantage of obtaining a large speed reduction with the Vee belt drive, is that the cooling fan attached to the input shaft of the transaxle is rotating at less than engine speed.

This can be a severe disadvantage during extremely hot spells in the summer as the oil viscosity of the power transmitting hydraulic fluid in the hydrostatic unit drops with temperature rise, causing a corresponding fall in speed performance of the tractor.

What is needed is a variable speed transaxle of more compact form then hitherto, such that its envelope dimensions are either similar of preferably smaller then transaxles of the mechanical-shift type, where the overall number of internal component parts are reduced and material savings are made due to the smaller housings required.

What is further needed is an improved transaxle assembly with a hydrostatic unit for use with a vertically aligned input shaft operating at approximately the same rotational speed as the engine for reasons of both efficient torque transmission and fan cooling, with speed reducing bevel gearing disposed between the input shaft and the hydrostatic pump for improved operation.

SUM2RY OF THE INVENTION In the present invention the hydraulic pump and the motor of the hydrostatic unit are mounted within an axle assembly, such that the rotating axis of the hydraulic motor is parallel to the rotating axis of the axle half shafts attached to the drive wheels of the vehicle.

A bevel pinion gear attached and driven by the vertically aligned input shaft of the transaxle is used in combination with a further bevel gear which drives the rotary cylinder barrel of the hydraulic pump. These bevel gears turn the drive axis through ninety degrees from the vertical to the horizontal plane.

Location of such bevel gearing at the input end of the hydrostatic unit, in a position between the input drive shaft and the cylinder barrel of the hydraulic pump, has the further advantage in that it encounters lower torque loadings than when positioned between the hydraulic motor and drive shafts of the transaxle. Therefore this invention teaches that bevel gear means should be placed at the least torque loaded location in the transaxle, namely between the input shaft and the cylinder unit of the hydraulic pump, rather than in the more highly stress loaded area between the hydrostatic motor and differential.

The invention therefore, as here disclosed applies most beneficially to both common types of hydrostatic units employing either axial pistons or radial pistons disposed with a rotary cylinder barrel.

These and other aims of the invention will become more apparent in the detailed description and examples which follows.

BRIEF DESCRIPTION OF THE DRAWINGS The above mentioned and other features and objects of the invention, and the manner of attaining them, may be performed in various ways and will now be described by way of examples with reference to the accompanying drawings, in which: Figure 1 is a side view of a typical grass cutting lawn or garden tractor vehicle.

Figure 2 is an underneath view of the vehicle in Fig.1.

Figure 3 is a plan view of the variable speed transaxle with the upper housing element removed to show a hydrostatic unit of the axial piston type.

Figure 4 is a part section view along I-I of Fig. 3 disclosing the drive installation comprising input shaft and bevel gearing.

Figure 5 is a plan view of a alternative variable speed transaxle with the upper housing element removed to show a hydrostatic unit of the axial piston type and where the bevel gears are disposed within a separate chamber from the chamber containing the hydrostatic unit.

Figure 6 is a plan view downwards of a further embodiment of the transaxle according to the invention, where the upper housing element is removed to show the internal components.

Figure 7 is a part sectioned side view on line II-II of Figure 6 of the transaxle as viewed from the left wheel side of the lawn tractor.

Figure 8 is a part sectioned side view of an alternative embodiment of Figure 6 allowing the location of the bevel gearing in a separate compartment within the transaxle.

DETAILED DESCRIPTION OF THE FIRST EMBODIMENT Almost all manufacturers of light duty lawn tractor grass mowers have an increasing tendency to install vertical crank-shaft internal combustion engines to such vehicles, thereby enabling them to fit simple belt drives from the engine to the mower deck and transaxle.

The engine can be mounted on the chassis of the vehicle either over the front or rear wheels, whereas the transaxle is in direct driving connection with the driving wheels.

This installation allows a simple Vee belt operating in the horizontal plane to transfer engine power from the engine pulley to a drive pulley keyed to the input shaft of the transaxle.

The tractor vehicle illustrated in Figs. 1 and 2 comprises a vertically installed internal combustion engine 1 with the crank shaft 2 pointing down to the ground. The engine 1 is shown mounted at the front end of the tractor chassis 3, and the transaxle 5 containing an internally disposed hydrostatic unit is mounted towards the rear of the tractor chassis 3 and engaged to the rear drive wheels 5. A Vee belt 10 operating in the horizontal plane connects the engine pulley 11 with the input drive pulley 12 of the transaxle 5, with a simple jockey pulley 17 acting as tensioning means for the Vee belt as shown in Fig.

2. On occasion, a clutch pedal connected via linkages to the jockey pulley 17 is required to release the tension of the Vee belt before the engine is started.

In Fig. 1, a grass mower deck 15 is shown located beneath the vehicle chassis 3 in a position between the rear two drive wheels 6 and the front two steering wheels 7 of the tractor. The mower deck 15 is attached to the tractor chassis 3 by way of height-adjusting supports 8 and is driven from the engine 1 by means of a short Vee belt 16.

The hydrostatic unit 19 illustrated in Figs. 3 & 4 comprises a hydraulic pump 20 fluidly coupled to a hydraulic motor 21. The transaxle 5 comprises two housing elements 22, 23, each of which includes a number of pockets such as those pockets 24, 25 shown in Fig. 4. When the two housing elements 22, 23 are attached together, pockets combine to form internal chambers, one chamber 30 contains the hydraulic pump 20 and hydraulic motor 21 of the hydrostatic unit 19, and chamber 31 contains the speed reducing gearing 33 and mechanical differential 34.

Chambers 30, 31 need to be sealed against the loss of lubricant, and this is achieved by applying sealing means such as liquid gasket between the abutting surfaces of the two housing elements 22, 23. Shaft seal 36 is also provided to segregate hydraulic chamber 30 from chamber 31. However, for some low-cost applications, shaft seal 36 may be omitted allowing all chambers to be flooded in a common oil bath.

The two housing elements 22, 23 are attached together by a plurality of screws 38 which are inserted through holes 39. When screws 38 are tightened down, housing elements 22, 23 form a stiff housing structure which is attached to the chassis 3 of the vehicle.

In these embodiments, housing elements 22, 23 are shown separable at a parting plane along the longitudinal axes of the half shafts 40, 41 of the transaxle 5.

The housing elements 22, 23 are preferrably formed to include an integral fluid expansion chamber (not shown) linked to chamber 30 to allow contraction and expansion of the working hydraulic fluid within chamber 30 due to temperature fluctuation.

The transaxle 5 is provided with a vertical input drive shaft 43 and supported on bearings 44 in housing element 22. A fluid seal 45 is provided to prevent the escape of fluid from hydraulic chamber 30. Input drive shaft 43 protrudes through the upper housing element 22 and is keyed 5 to the pulley 12 on which vee belt 10 operates in transmitting power from the prime mover 1 to the transaxle 5. A cooling fan 47 is attached to pulley 12 and acts a simple cooling means for the hydrostatic unit 19.

At the other end of the input drive shaft 43, a bevel pinion 50 is engaged at 51 for rotation with shaft 43. Gear 50 is arranged to mesh with a further bevel gear 53 which is attached at 54 to shaft 55. The rotary cylinder barrel 57 of hydraulic pump 20 is supported and driven by way of splines 58 on shaft 55, where bearings 60, 61 disposed at each end of shaft 55 act to support shaft 55 in housing elements 22, 23.

The use of such bevel gearing 50, 53 allows the axis of rotation to be turned through ninety degrees so that the rotating axes of the hydrostatic unit 19 are along the same plane as the half shafts 40, 41 of the transaxle 5. Furthermore, the rotational speed of the input shaft mounted cooling fan 47 will produce a generous air flow over the housing elements 22, 23 of the transaxle 5.

Hydraulic pump 20 and motor 21 of the hydrostatic unit 19 are mounted perpendicular to one another and are of generally similar construction with minor points of difference as described below.

The cylinder barrel 57 of hydraulic pump 20 is formed with a number of axial cylinders 64 into which are disposed pistons 65.

A spring 66 behind each piston 65 acts to hold pistons 65 against a thrust ring 68 which is located to cradle 69.

Cradle 69 is supported in two trunnion shafts at each side, (only one trunnion shaft 70 being shown in Fig. 3.) that allow cradle 69 to tilt within limits, usually about fifteen degrees either side from center. Shaft 70 is connected to an external linkage outside the transaxle 5 to a control lever through which the vehicle operator controls the speed and direction of the vehicle.

Movement of the control lever causes shaft 70 to turn, with the result that the inclination of cradle 69 (and thrust ring 68) is adjusted relative to the axis of the pistons 65.

Each cylinder 64 is provided with a port 72 through which fluid can pass into and out of the cylinder 64, and each port 72 is arranged to fluidly connect in sequence with arcuate ports 74, 75 formed on one end face 76 of the valve member 77.

Valve member 77 is a one-piece casting which is rigidly secured to either or preferably both housing elements 22, 23 of the transaxle 5. Within valve member 77 are two internal passages 79, 80 that link arcuate ports 74, 75 of the hydraulic pump 20 to arcuate ports 81, 82 for the hydraulic motor 21 that are formed on end face 83 of the valve member 77.

The construction of the hydraulic motor 21 differs from the hydraulic pump 20 in one main respect in that the thrust ring 85 is not adjustable and is in fact mounted at a fixed angle to the wall 86 provided by the housing elements 22, 23.

The cylinder barrel 90 of hydraulic motor 21 is engaged at 91 to shaft 92 which is supported by bearings 93 and 9 at each end.

Cylinder barrel 90 has a number of cylinders 96 each containing a piston 97 which is loaded against the thrust ring 85 by means of spring 98 . Each cylinder 96 is provided with a port 99 through which fluid can pass into and out of the cylinder 96, and each port 99 is arranged to fluidly connect in sequence with arcuate ports 81, 82 formed on end face 83 of the valve member 77.

Each arcuate port 81, 82 being linked through respective internal fluid passages 79, 80 in valve member 77 to related arcuate ports 74, 75 serving hydraulic pump 20, and where each internal fluid passage 79, 80 is arranged to connect with both a check valve and preferably a fluid dump valve that are included within the body of valve member 77 that act to release or draw fluid between oil chamber 30 and passages 79, 80 in a manner known to those skilled in the art.

Shaft 92 is extended at one end to pass into chamber 31 where it is engaged at 100 to gear 101 with bearing 102 providing further support, shaft 92 being further extended so as to protrude out from the transaxle 5 housing to connect with a brake assembly 105. Brake assembly 105 being of conventional type employing a disc 106 which is engaged to shaft 92 and when held by calipers (not shown), prevents shaft 92 from rotating.

Gear 101 meshes with larger gear 108 which is engaged by splines 109 to shaft 110 supported by bearings 111, 112. Shaft 110 is engaged by splines 114 to final drive pinion gear 115 which is in mesh with ring gear 116 of the differential 34.

The differential 34 has a centrai shaft 120 on which bevel gears 121, 122 are mounted and which mesh with bevel gears 123, 124 that are nonrotatably connected to respective ones of half shafts 40, 41 as described in more detail in U.S. Patent No. 4,480,501.

Bevel gears 121, 122, 123, 124 of the differential 34 acts to transmit the drive from the ring gear 116 to the half shafts 40, 41 and the rear drive wheels 6 of the vehicle as known to those skilled in the art. The inclusion of a differential 34 is important as it allows normal differentation between left and right drive wheels 6 of the vehicle and helps prevent lawn damage especially when tight turns are undertaken.

Preferably, half shafts 40, 41 are supported by bearings 125 in the housing elements 21, 22, although for low-duty applications, half shafts 40, 41 can be supported directly on the material of the housing elements.

The hydrostatic transaxle of FIG. 5 differs from the transaxle described above in that the input bevel gear set are now disposed outside fluid chamber 30 of the hydrostatic unit 19. The advantage being that during operation, no metal contamination from the bevel gears is introduced to fluid chamber 30 containing the hydrostatic unit 19, and as a result, the useful life of the hydrostatic unit 19 may be increased.

Therefore chamber 130 is provided within housing elements 21, 22 into which the bevel pinion 50 and gear 53 are located. Seal 133 on shaft 55 and located in housing wall 134 prevents fluid from within chamber 30 from escaping into chamber 130.

Chamber 130 may be formed to connect with chamber 31 containing speed reducing gearings 33 and differential 34.

The complete transaxle package as shown is extremely compact compared to those known to date as the relative position of the input drive shaft to the differential and connecting half shafts of the transaxle is in close proximity.

As a result, notable and worthwhile savings in the weight of material forming the housing envelope is achieved.

As both transaxles operate in same manner, only a description of operation of the first emboidment will be given.

By appropriate positioning of control shaft 70 by the vehicle operator turning it, say clockwise, cradle 69 is tilted with respect to the axis of the pistons 55. As a result, the speed ratio of the hydrostatic unit 19 is adjusted. For instance, for forward motion of the vehicle, rotation of the input shaft 43 drives through bevel pinion 50 and gear 53 the drive shaft 55 of the hydraulic pump 20. Rotation of the pump cylinder barrel 57 and consequent axial reciprocation movement of the pistons 65, causes pressurized fluid to flow out from the cylinder bore 64, through port 72 into arcuate port 74 and along passage 79. The action of the incoming fluid through arcuate port 81 and into port 99 in the cylinder barrel 90 of hydraulic motor 21 causes pistons 97 to stroke as thrust ring 85 is set at fixed inclination with respect to piston 97 axis.

The pressure force acting behind the piston 7 onto the inclined thrust ring 85, produces a side force on the cylinder wall 96 of cylinder barrel 90 which causes the cylinder barrel 90 to rotate.

As cylinder barrel 90 is engaged by splines 91 to shaft 92, mechanical power is transfered from the shaft 92 mounted pinion gear 101 to meshing gear 108.

As gear 108 and final drive pinion 115 are both splined to a common shaft 110, power is transfered through gear 115 to ring gear 116 of the differential 34. Internal bevel gears 121, 122, 123, 124 of the differential 34 operate in transmitting the power directly to the half shafts 40, 41 and thereby the rear drive wheels 6 of the vehicle.

To reverse direction of the vehicle, the operator turns control shaft 70 anti-clockwise so that cradle 59 is tilted the other way. In this case, rotation of the pump cylinder barrel 57 and consequent axial reciprocation movement of the pistons 65, causes fluid to flow out from the cylinder bore 64, through port 72 into arcuate port 75 and along passage 80. The action of the incoming fluid through arcuate port 82 and into port 99 in the cylinder barrel 90 of hydraulic motor 21 causes pistons 97 to stoke against thrust ring 85. However, because in this case, arcuate port 82 is pressurized, the pressure force acting behind piston 97 on thrust ring 85 causes the cylinder barrel 90 to rotate in opposite direction to the above described example when the other arcuate port 81 was pressurized.

Speed reducing gearing 33 transmits power from the cylinder barrel 90 rotating in reverse direction, to the half shafts 40, 41 with the result that the vehicle moves backwards.

Finally, when the operator turns control shaft 70 to it central position, cradle 69 is then aligned perpendicular to the piston 65 axis, with the result that there is reciprocation of the pistons 65 and the vehicle is set at rest. The operator may then engage the calipers onto disc 106 of brake assembly 105 and the vehicle is parked.

DETAILED DESCRIPTION OF THE SECOND EMBODIMENT In the second embodiment of the invention illustrated in Figs. 6, 7, and 8 discloses the use of a radial piston hydrostatic unit within the transaxle assembly.

The transaxle 139 includes a hydrostatic unit 140 which comprises a hydraulic radial piston pump 141 fluidly coupled to a radial piston hydraulic motor 142.

Upper and lower housing elements 144, 145 enclose the hydrostatic unit 140 in a chamber 147 which also contains the hydraulic fluid for the hydrostatic unit 140, the housing elements 144, 145 being attached together by a plurality of bolts 148 which are inserted through holes 149.

As shown in Fig. 7, one end of the input shaft 150 protrudes through housing element 148 for engagement with a drive pulley 12 and fan 13 in a similar manner as described and shown in Fig. 4 for the first embodiment. At the other end of input shaft 150 is a bevel gear pinion 151, fixedly mounted. Gear 151 driving a larger diameter bevel gear 152 that engages with the hydraulic pump 141.

Reduction gear train comprising gears 155, 156, 157 is included to connect the hydraulic motor 142 to a mechanical differential component 160, and where differential component 160'engages with half shafts 161, 162 to form the vehicle's driving axle.

Housing elements 144, 145 being separable at a parting plane generally containing the longitudinal axes of the half shafts 161, 162 of the transaxle 139, and formed to inciude an integral oil expansion chamber linked to main chamber 147.

A groove 154 is provided on lower housing element 145 to seat an O' ring type seal 165 to prevent hydraulic fluid from escaping from the main chamber 147 of the hydrostatic unit 140. However, sealing compound may also be used as an alternative to the O' ring.

Hydraulic pump 141 and motor 142 of hydrostatic unit 140 are shown mounted coaxially back-to-back with their rotating axis parallel with the rotating axis of the axle half shafts 161, 162, and their construction being generally similar with minor points of difference as described below.

Both hydraulic pump 141 and motor 142 as shown in Fig. 6 comprise each a rotary cylinder barrel 167, 168, mounted to rotate on each respective end of a cylindrical member 169. To enable rotation of both pump 141 and motor 142, the cylindrical member 169 is circular in shape and preferrably has two fluid galleries 170, 171 located within its outer walls. Cylindrical member 169 provides an axis for the rotation of cylinder barrels 157,168, and is provided with two sets of arcuate shaped ports, one set being 173,.1740that are arranged to connect with gallery 170, the other set being 175, 176 that are arranged to connect with gallery 171. As a result, the galleries 170, 171 provide a communication for fluid to pass between the pump 141 and motor 142.

The cylindrical member 169 is rigidly secured to the lower housing element 145 by means of two U'bolt type clamps 179, 180.

The ends of both bolts 179, 180 are threaded 181 and pass through holes 182 in lower housing element 145 so that a washer 183 and nut 184 can be spun on the threaded ends and tightened thereby resulting in cylindrical member 169 being held firmly down into channel 185 formed in the lower housing element 145.

Check valves are arranged to connect with each respective gallery 170, 171 in a manner as described in U.S. Patent 4,686,829.

Cylinder barrel 167 for the hydraulic pump 141 comprise a plurality of cylinders 186 which are a fixed axial distance relative to the arcuate ports 173, 175 formed in cylindrical member 169. Each cylinder 186 includes a duct 187 which matches with pintle ports 173, 175 during rotation of cylinder barrel 1 67.

Each cylinder 186 receives a piston 188 which is attached to a slipper shoe 189, these components rotating according to the cylinder unit 167 within a surrounding annular track ring 190, where the annular track ring 190 is arranged to be adjustable into eccentric relationship with respect to cylindrical member 169. Each piston 188 being attached to its respective slipper 189 by known means such as a rivet, and where the slippers 189 act against the track ring 190.

Cylinder barrel 168 of hydraulic motor 142 comprises a plurality of cylinders 191 which are in fixed axial distance relative to their respective set of arcuate ports 174, 176 formed in cylindrical member 169.

Each cylinder 191 includes a duct 192 which is fluidly connected to arcuate ports 174, 176 during rotation of cylinder barrel 168.

Furthermore, each cylinder receives a piston 194 which is attached to a slipper shoe 195, and the cylinder barrel 168 rotates within a surrounding annular track ring 197.

The slippers act against their respective track rings through the action of centrifugal force and may further be radially urged against the track ring by means of a discontinuous expander band as described in U.S. Patent 4,635,535.

Annular track ring 197 of hydraulic motor 142 remains permanently set in eccentric relation to cylindrical member 169, and is purposely provided with two holes 198, 199 into which rocking spindle 200 and tube 201 respectively pass through to provide support.

The role of the hydraulic pump 141 is to convert mechanical energy in the form of speed and torque provided by the prime mover 1 into fluid energy in the form of pressure and flow. The role of the hydraulic motor 142 is to reverse this process by converting the fluid energy back to mechanical energy.

In order that the speed of the vehicle can be changed without changing the rotational speed of the prime mover 1, it is necessary to alter both the rate and direction of fluid energy supplied by the hydraulic pump 1 41.

This is achieved by means of providing a hole 202 in track ring 190 through which tube 201 is inserted. Thereby tube 201 supports track ring 190 and further acts as the pivot point for the track ring 190. Tube 201 which extends through holes 202, 199 in each track ring 190, 197, respectively, is extended at ends 204, 205 and supported between the housing elements 144, 145. Seals 206, 207 act to prevent fluid in chamber 147 from escaping.

Tube 201 is fixed in position relative to cylindrical member 169, and track ring 190 can move in a short arc centered on tube 201.

Track ring 190 is provided with a hole 208 generally diametrically opposite to tube 201, and into which a projecting pin 209 is inserted which engages with an adjusting arm 210 attached to rocking spindle 200 operated externally, for example by a manual control lever. Spindle 200 is supported directly in the housing elements 144, 145 or by means of bearings if required. Seals 212 acts to prevent hydraulic fluid from seeping out of chamber 147 Projecting pin 209 and adjusting arm 210 allow movement of spindle 200 and translates the rotary movement of the externally operated control lever attached to spindle 200, into lateral swinging movement of the track ring 190.

Movement of the lever and spindle 200 causes track ring 190 to swing through a small angle about tube 201 into an eccentric relationship with the rotating cylinder barrel 167 supported by the cylindrical member 169. This causes pistons 188 to reciprocate radially outwards within their respective cylinders 186, and fluid is drawn from the low-pressure gallery 170 and arcuate port 173 and through duct 187 of the cylinder 186. As the piston 188 returns radially inwards into its cylinder 186, the fluid is expelled through the same duct 187 but into the opposite arcuate port 175 connecting to gallery 171 which leads to the hydraulic motor 142.

Fluid from gallery 171 enters hydraulic motor 142 via arcuate port 176 and is directed into cylinder barrel 168 through duct 192 to cylinder 191.

The pressurized fluid acting behind piston 194 pushes the piston 194 out of its respective cylinder 191 and by nature of angle that piston 194 have to accommodate due to the eccentrically positioned track ring 197, a side force is created on the cylinder wall which causes a turning moment on cylinder barrel 168 which is then obliged to rotate.

A slot 214 is provided in track ring 190 to allow spindle 200 to pass through. This is necessary in order to allow the track ring 190 to pivot on tube 201 so that spindle 200 does not impede the movement of track ring 190.

Movement of control lever by the vehicle operator causes spindle 200 to rotate, and by means of arm 210 and pin 209, track ring 1 90 pivots through a small angle on tube 201. A degree of eccentricity of the track ring 190 is produced and thus, the effective fluid output capacity of the hydrostatic pump 141 is altered, with the result that the vehicle's speed is changed.

A Vee belt 10 transmits mechanical power from the vertically aligned crank shaft engine 1 of the vehicle, to a pulley 12 and fan 13, keyed 216 to input drive shaft 150. Shaft 150 extending through the upper housing element 144 of the transaxle 139 and into the oil chamber 147 of the hydrostatic unit 140.

Seal 217 in upper housing element 144 seals chamber 147 on input shaft 150, and two needle bearings 218 are included to rotatively support shaft 150.

Shaft 150 transmits mechanical power to the rotary cylinder barrel 167 of the hydraulic pump 141 by means of a bevel pinion 151 and gear 152, the bevel pinion 151 being splined at 220 to input shaft 150 and bevel gear 152 being mechanically coupled at 222 to the cylinder barrel 167. Bevel gear 152 is supported on the cylindrical member 169 by means of a bearing bush 224.

By this structure, rotation is imparted to hydraulic pump 141 at a lower level than the rotational speed of input shaft 150. This also results in efficient cooling for the transaxle 139 by way of the fan 13 rotating at a higher speed than the hydraulic pump 141, and thereby providing a larger volume of air passing over the transaxle housing elements 144, 145.

Hydraulic motor 142 is connected to a first shaft 230 by means of a misalignment coupling 231 such as the well known "oldham" type.

First shaft 230 is supported on two bearings 232, 233 in housing elements 144, 145, and where gear 155 is fixably mounted to first shaft 230 in a position between bearings 232, 233. An oil seal 235 disposed between bearing 232 and gear 155 prevents fluid loss from the hydraulic chamber 147 from seeping into the gear train compartment chamber 237.

First shaft 230 is preferrably extended axially to a brake assembly 240 having a disc 241, and a shifting mechanism (not shown) are included with transaxle 139; brake assembly 240 being of a conventional type.

It is a prefered feature of this embodiment to pass second shaft 244 through the tube 201 in order to achieve overall compactness of the transaxle 139. A small annular clearance 245 is provided inside tube 201 in order to prevent rotating second shaft 244 from touching tube 201.

Second shaft 244 is supported on bearings 246, 247, and is extended in order to drivingly engage with gears 156 and 157 disposed at each end. Gear 156 meshes with gear 155 on first shaft 230, and pinion gear 157 meshes with ring gear 250 of the differential 160.

Differential 160 further comprises centre pin 251, and bevel gear assembly 253. Bevel gear assembly 253 includes bevel gears 254 and bevel gears 255, which together with centre pin 251 are tarried within the interior of ring gear 250 in a manner which is known in the art. Proximal ends 260,251 of the half shafts 161, 162 respectively, are received through bevel gears 255 and abut against centre pin 251. Axle half axles 161, 162 are retained in place by retainer rings 262, and supported in bearings 264 in the housing elements 144, 145.

Rotation of cylinder barrel 168 of hydraulic motor 142 is transmitted by coupling 231 to first shaft 230 causing gear 155 to rotate. Gear 155 meshing with gear 156 on second shaft causes pinion gear 157 to rotate. Pinion gear 157 meshes with differential ring gear 250 and associated bevel gear assembly 253 results in the rotation of the half shafts 161, 162 of the transaxle 139.

On occasion, it may be advantageous to locate the input bevel pinion and gear within a separate compartment as illustrated in Fig. 8. In this embodiment, input drive shaft 270 supported by bearings 273 extends through upper housing element 271 of the transaxle 272 into primary compartment 274.

Bevel pinion 275 is splined 277 to input drive shaft 270, and is drivingly engaged to bevel gear 280.

Shaft 281 rotatively supported by means of needle bearings 283 and splined 285 to engage bevel gear 280. Shaft 281 passes through a partition wall 287 formed by housing elements 271, 288 where seal 299 prevents the escape of hydraulic fluid from oil chamber 300 into primary compartment 274. At the end of the shaft 281, a further spline 302 is provided to drive through a coupling 304 to the cylinder barrel 305 of hydraulic pump 306.

The advantage here being that bevel gearing 275, 280 rotate in their own bath of lubricant thereby eliminating any contamination from the gears from reaching the oil chamber 300 of the hydrostatic unit.

It is to be understood that while we have illustrated and described two embodiments of our invention, it is not to be limited to any one specific form or arrangement of parts herein described and shown except insofar as such limitations are included in the claims.

Claims (4)

"CLAIMS"

1. An axle assembly comprising: a housing including two main housing elements connected together along a parting plane and defining an internal chamber; a hydrostatic transmission encapsulated in the chamber and including a hydrostatic pump fluidly coupled to a hydrostatic motor; a primary shaft rotatably mounted in one housing element and extending into the chamber for engagment with a first bevel gear; a second bevel gear operatively connected to the hydrostatic pump, and drivingly engaged to first bevel gear; coaxial axle shaft means rotatably supported In the housing and having its axis substantially coincident with the parting plane, and differential gearing means within the chamber and drivingly connected between the hydrostatic motor and the coaxial axle shaft means.

2. An axle assembly of claim 1 wherein the first bevel gear comprises a relatively small diameter gear and the second bevel gear comprises a relatively larger diameter gear.

3. An axle assembly of claim 1 wherein the housings elements are fromed to provide a partition wall that divides the internal chamber into two compartments, one compartment for the hydrostatic transmission, the other compartment for the differential gearing means.

4. An axle assembly of claim 1 wherein the housings elements are fromed to provide two partition walls that divides the internal chamber into three compartments, one compartment for the hydrostatic transmission, the second compartment for the differential gearing means, the third compartment for the first and second bevel gears.