FINAL DRIVE UNIT FOR A VEHICLE

Abstract: A final drive unit for driving a pair of axles (13) of a vehicle wherein the pinion shaft (28) extends through the final drive unit housing (11) past the portion (20) of a differential gear carrier so that the forward end of the pinion shaft (28) may be coupled to an input shaft and the rear end (37) may be connected to an output shaft for coupling to a further drive unit coupled to a further pair of axles.

Description: FINALDRIVEUNITFORAVEHICLE This invention relates to a final drive unit for a vehicle which incorporates a differential gear system to permit independent rotation of the respective axles connected to the wheels on opposite sides of the vehicle. There is an increasing use of tandem rear axle assemblies on light to medium weight vehicles, and particular "off the road" vehicles. At the present time the majority of such vehicles only provide drive power to one of the axles. In order to improve the traction of such vehicles, it is desirable for both axles of the tandem assembly to be driven, however, to incorporate a convent¬ ional tandem drive in a light weight vehicle would unduly increase the cost of such vehicles. It is known to incorp¬ orate tandem drive axles in heavy truck vehicles wherein there is provided a transfer gearbox between the main vehicle gearbox and the final drive unit so that there are two drive output shafts from the transfer box, one connected to the final drive unit of each of the tandem axles . Although this construction is effective and reliable in service, it is particularly expensive to manu¬ facture and results in a significant increase in weight. Such an increase in expense and weight is tolerable in heavy duty trucks but is not acceptable in the current light to medium weight vehicles particularly the "off road" pleasure vehicles . It is, therefore, the object of the present invention to provide a final drive unit for a vehicle which will permit the use of tandem drive axles on the vehicle without the necessity of providing a transfer box and the resultant associated equipment, and consequential increase in cost and weight of the overall vehicle. With this object in view, there is provided according to the present invention a final drive unit for a vehicle comprising a housing, a crown wheel and differ¬ ential gear carrier mounted for rotation in the housing, a set of differential gear mounted in said carrier and adapted for drive coupling to respective axle shafts arranged coaxial with the crown wheel, a pinion shaft rotatably supported in the housing and having respective end portions projecting from opposite sides of the housing, each end portion being adapted for coupling to an input or output shaft respectively, said pinion shaft having a pinion attached thereto and in mesh with the crown wheel, the axis of the pinion shaft being in a plane normal to the crown wheel axis and offset therefrom a distance so that the crown wheel and differential carrier can rotate without interference with the pinion shaft. Preferably the pinon shaft is made in two parts, one of which is adapted for connection to an input shaft and which carries the pinion to mesh with the crown wheel, and the other part is adapted for connection to the output shaft, and is drive coupled to the first mentioned pinion shaft portion. The provision of a pinion shaft which is offset sufficiently from the center line of the crown wheel to permit the pinion shaft to pass through the housing without interference with the rotation of the pinion shaft or differential carrier, eliminates the need for a transfer box as has been the case in the prior art heavy duty trucks. The output end of the pinion shaft may be coupled to a second final drive unit located rearwardly of the first final drive unit, so as to provide a tandem axle assembly with both axles driven. In previously known final drive units, it has not been possible for the pinion shaft to extend completely through the final drive unit housing as it would foul the differential carrier which rotates within the housing jointly with the crown wheel. As previously mentioned, this problem has been overcome in the prior art by providing a transfer box forward of the final drive, from which there are two output shafts, one connectable to each of the final drive units of the two tandem axles. Thus, the present invention provides a convenient, cheap and relatively light weight final drive OMPI unit which will permit both axles of a tandem axle assembly to be driven. This construction is particularly advan¬ tageous in light "off the road" vehicles such as the now popular recreational vehicles. Where the pinion shaft is made in two parts, one being adapted for connection to the power input to the differential unit and the other adapted for connection to the output from the differential unit, the two parts may be selectively drive connectable so that at the operator's discretion, one or both of the final drive units may be operated. The selective connection of the two portions together may be achieved by providing coaxial external splines on the adjacent ends of the respective portions of the pinion shaft, with an internally splined sleeve axially movable on the spline shaft. In one position the two spline portions of the shaft are each in engagement with the sleeve to establish a drive between the two shaft portions. In a second position the sleeve disengages from the spline on one of the shaft portions to release the drive connection between the two shaft portions. Preferably when the pinion shaft is made in two portions, then one of the portions is provided with a co¬ axial spigot, which is received in a recess in the other portion housing a plurality of needle roller bearings. Thus the two shaft portions are held in precise axial align¬ ment, but when not drive coupled together may rotate relative to one another. Also, in order to assist the provision of clearance for the pinion shaft to pass completely through the housing of the final drive unit, the set of differ¬ ential gears carried by the differential carrier may be offset, in the axial direction of the crown wheel, from the plane of the pinion axis a greater distance than is customary in final drive units . Thus the outside diameter dimension of the carrier in the plane of the axis of the pinion shaft is reduced from that normally experienced in known final drive units . OMPI WIPO It will be ' appreciated that if the differential gear set is located within the carrier immediately adjacent the crown wheel, then it is convenient to reduce the diameter of a carrier at that point without risking undue weakening of the carrier. The invention will be more readily understood from the following description of one practical arrangement of the differential final drive unit as illustrated in the accompanying drawings. In the drawings Figure 1 is a sectional view along the crown wheel axis of the final drive unit. Figure 2 is a section view along the axis of the pinion shaft. Referring now to the drawings the final drive unit comprises a differential gear carrier 10, mounted in the final drive unit housing 11 for rotation in bearings 12 coaxial with the respective axle shafts 13. The crown wheel 15 is mounted coaxially on the differential gear carrier 10, preferably in a detachable manner, so that the crown wheel may be replaced in the event of wear or damage in use. Rotatably supported within the differential gear carrier are a pair of bevel gears 16 drivably connected to the respective axle shafts 13 by meshing spline section 17. Also supported in the differential gear carrier are a pair of differential pinions 18 which each mesh with the bevel gears 16 on the axle shafts 13. The differential pinions 18 are supported for rotation on the shaft 19 carried by the differential gear carrier and located at right angles to the axis of the crown wheel 15, and hence also of the bevel gears 16 connected to the axles. This arrangement of bevel gears on the axle shafts and meshing pinions mounted on a shaft within the differential carrier is of a conventional construction to permit differential movement between the respective axles. The final drive unit housing carries coaxial bearings 25 in opposite sides of the housing with the axis of the bearings in a plane at right angles to the differ¬ ential gear carrier and crown wheel. The axis of the bearings 25 are offset from the axis of the crown wheel by an amount as hereinafter discussed. Each one of the bearings 25 in the housing rotatably supports forward and rear portions 26 and 27 res¬ pectively of the pinion shaft 28. The forward and rear portions are coaxially arranged, with the forward portion 26 carrying the spigot 29 which is received in a neede roller bearing assembly 30 provided in the bore 31 in the end of the rear portion 27 of the pinion shaft. The forward portion 26 of the pinion shaft carries the bevel pinion 35, having a tooth formation to mesh with the crown wheel 15 and taking into account the degree of offset between the pinion shaft 28 and crown wheel 15 axes. However the bevel gear assembly 16 and 18 is located towards the crown wheel from the pinion shaft, so that the assembly is substantially clear of the area above the pinion shaft. This permits the effect diameter of the portion 20 of the differential carrier to be reduced and allow the pinion shaft 28 to pass below the differ¬ ential carrier. The end 36 of the forward portion 26 of the pinion shaft, projects outwardly from the final drive housing 11, and is splined and threaded to receive a similar spline portion of a conventional universal joint, which forms the coupling between the transmission or tail shaft of the vehicle and the pinion shaft 28. Similarly, the end 37 of the rear portion 27 of the pinion shaft, out- wardly of the final drive housing, is splined and threaded to receive portion of a further universal joint which in turn will be coupled to a short jack shaft to provide the drive coupling to another final drive unit of an adjacent axle assembly. Preferably the pinion gear 35 is keyed and shrunk onto the appropriate location of the forward portion of the pinion shaft. The adjacent spigoted ends of the for¬ ward and rearward portion of the pinion shaft are splined, with the splined sleeve 41 mounted thereon for relative axial movement. Under the control of a suitable actuating mechanism (not shown), the sleeve is axially moved on the pinion shaft to couple the forward and rearward pinion portions together to rotate an unison, or to selectively disconnect the rearward pinion shaft portion from the forward pinion shaft portion, when it is not required to drive both of the axles of the tandem axle assembly. In a conventional rear axle final drive of the hypoid type the pinion shaft cannot pass completely through the housing from front to rear, as proposed by the present invention, for the following reasons. 1. The axis of the pinion is usually offset only 25 to 37mm below the axles shaft and crown wheel axis. The pinion shaft must be at least 25mm diameter to have sufficient strength. This would provide only approximately 12 to 25mm between the pinion shaft and the axis of the crown wheel to accommodate the differential gear carrier which must rotate about the crown wheel axis. This is insufficient having regard to the space and strength requirements of the differential gear carrier. 2. The bevel gear assembly, carried by the differential gear carrier, usually extends through the axial plane of the pinion shaft that is normal to the crown wheel axis. The dimensional limitation that exists with the con¬ ventional amount of offset of the pinion shaft, as .referred to above, would not accommodate the bevel gear assembly in this position if the pinion shaft extend fully through the housing. In the rear axle final drive as presently proposed the axis of the pinion shaft is offset in the order of at least 50mm from the axis of the crown wheel so that a pinion shaft of 25mm diameter would provide a dis¬ tance between the pinion shaft and the crown wheel axis of the order of at least 38mm. Also the bevel gear assembly carried by the differential carrier is displaced towards the crown wheel, so that it is substantially wholly outside of the area immediately above the pinion shaft. The portion of the ^ R OM differential carrier above the pinion shaft may thus be reduced in size and the distance of about 38mm provided is adequate. Thus with the increase of the offset of the pinion shaft, and the displacement of the bevel gear assembly, the pinion shaft may extend through the housing and the conventional size of crown wheel and housing may be retained.

Claims: THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS: 1. A final drive unit for a vehicle comprising a housing, a crown wheel and differential gear carrier mounted for rotation in the housing, a set of differential gears mounted in said carrier and adapted for drive coupling to respective axle shafts arranged coaxial with the crown wheel, a pinion shaft rotatably supported in the housing and having respective end portions projecting from opposite sides of the housing, each end portion being adapted for coupling to an input or output shaft respectively, said pinion shaft having a pinion attached thereto and in mesh with the crown wheel, the axis of the pinion shaft being in a plane normal to the crown wheel axis and offset there¬ from a distance so that the crown wheel and differential carrier can rotate without interference with the pinion sha t. 2. A final drive unit a claimed in claim 1 wherein the pinion shaft is in two coaxial parts , one part being adapted for connection to an input shaft and which carries the pinion to mesh with the crown wheel, the other part being adapted for connection to the output shaft and drive coupled to said one part of the pinion shaft. 3. A final drive unit as claimed in claim 2 wherein the two parts of the pinion shaft are drive coupled by selectively releasable means so that the drive to said other part of the shaft may be disconnected. 4. A final drive unit as claimed in any one of claims 1 to 3 wherein the set of differential gears are off¬ set from the axial plane of the pinion shaft normal to the crown wheel axis towards the crown wheel so said set of differential gears are substantially outside of the area between the pinion shaft and the crown wheel axis . 5. A final drive unit as claimed in any one of claims 1 to 4 wherein the pinion shaft passes below the axis of the crown wheel when the final drive unit is in a pos¬ ition corresponding to the operational position when fitte to a vehicle. 6. A vehicle having a tandem rear axle assembly, each axle of said assembly having a final drive unit, one of axles having a final drive unit as claimed in any one of claims 1 to 5 fitted thereto with the output shaft thereof drive coupled to the final drive unit of the other axle.

Inventors: PARSONS FRANCIS EDWARD, PARSONS, FRANCIS, EDWARD
Applicants: PARSONS FRANCIS EDWARD, PARSONS, FRANCIS, EDWARD
Application year: 1984
Main classification: F16H1
IPC codes: B60K17, F16H1, F16H48