GB2029521A - Drive units for tandem-axle motor vehicles - Google Patents

Abstract

A drive unit for a tandem-axle motor vehicle includes first and second differential gear units 18, 17 disposed within a three-part housing 15, coaxially disposed input and output members 20 and 25, and opposed laterally extending axle shafts 8, 16. The first differential gear unit 18 has a differential casing 21 driven by the input member 20, an output gear 23 driving a hollow hypoid pinion 2, and another output gear 22 driving the output member 25 by way of a torque-trasmitting through shaft 9 which is coaxial with the input and output members and extends through the hollow interior of the hypoid pinion. The second differential gear unit 17 is offset to the lefthand side of the through shaft 9, and has a differential casing 3 driven by a hypoid gear 1 meshing with the hypoid pinion 2, and output gears 27, 5 driving the respective axle shafts 8, 16. The right- hand axle shaft 8 crosses over the through shaft 9 with very small spacing, at a location clear of the second differential gear unit and its adjacent support bearing 7, so permitting a very small hypoid offset. <IMAGE>

Description

SPECIFICATION Drive unit for tandem-axle motor vehicles This invention relates to drive units for tandem-axle motor vehicles.

By the present invention there is provided a drive unit for a tandem-axle motor vehicle, comprising a first differential gear unit having a differential casing that is rotatably supported within a housing of the drive unit and is connected to be driven by a rotary input member of the drive unit, first and second output gears of the first differential gear unit connected to drive, respectively, a torquetransmitting shaft that is connected to drive a rotary output member of the drive unit coaxial with the shaft and with the input member, and a hollow hypoid pinion that coaxially surrounds a portion of the shaft, a second differential gear unit having a differential casing that is rotatably supported within the housing of the drive unit by first and second bearings and is connected to be driven by a hypoid gear that surrounds the said casing and is in meshing engagement with the hypoid pinion, and first and second output gears of the second differential gear unit connected to drive, respectively, first and second axle shafts that extend in opposite directions from a central region of the second differential gear unit, in a configuration such that the axle shaft extends closely adjacent the torquetransmitting shaft at right angles thereto, and the second axle shaft and the torque-transmitting shaft cross at a location on the side of the said second bearing remote from the central region of the second differential gear unit.

Such an arrangement allows the drive to be taken out to the rear without the need for a costly transfer gear drive to take the drive over the inter-axle differential (the first differential gear unit).

Also, because the torque-transmitting through shaft and the respective axle shaft cross each other at a location which is clear of the second differential gear unit and the adjacent one of its support bearings, the shafts can cross each other with minimal clearance, so permitting a very small hypoid offset, for efficient and cool running.

Further, a rear support bearing for the hypoid pinion can be positioned in the vicinity of one of the support bearings for the inter-wheel differential (the second differential gear unit), such that these two bearings can be mounted in a common carrier member extending from the housing of the drive unit.

A universally jointed shaft may be connected to the output member of the drive unit to transmit drive by way of a further interwheel differential to opposed wheels of a trailing driving axle of the tandem set.

For ease of assembly, and to permit easy access for removal and exchange of parts, the housing of the drive unit may be of three-part construction, including a removable front cover accommodating the inter-axle differential and adjacent support bearings, and a removable rear cover supporting a rearmost support bearing for the through shaft, with a split bearing cap forming a mounting for the outboard bearing of the inter-wheel differential for the leading driving axle of the tandem set.

A drive in the normally accepted sense of a rear driving axle is conveniently obtained by having the inter-wheel differential for the leading driving axle offset to the left-hand side of the through shaft, with the through shaft passing closely beneath the right-hand axle shaft of this differential unit. Alternatively, however, the differential unit could be offset to the right-hand side, with the through shaft passing closely above the left-hand axle shaft.

In the accompanying drawings: Figure 1 is a fragmentary horizontal section, with some parts in elevation, showing one embodiment of a drive unit for a tandem-axle motor vehicle in accordance with the present invention; and Figure 2 is a longitudinal vertical section, with some parts in elevation, of the embodiment of the drive unit for a tandem-axle motor vehicle which is shown in Fig. 1.

The embodiment of a drive unit for a tandem-axle motor vehicle in accordance with the present invention which is shown in the drawings basically comprises a housing of threepart construction containing an inter-axle differential unit driving an inter-wheel differential unit by means of a set of right angle drive hypoid pinion and hypoid gear, and includes coaxially disposed input and output members, and laterally extending opposed axle shafts driven by the inter-wheel differential unit.

In detail, the drive unit has a housing 1 5 which includes a front cover 14 and a rear cover 26 closing front and rear apertures respectively of the housing, the front cover being accurately located to a face in a differential carrier portion of the housing. A securing bolt for the front cover is indicated at 28.

An inter-axle differential 1 8 (first differential gear unit) is housed within the front cover 14, and includes a differential casing 21 the front end of which is rotatably supported by a front bearing 1 9 (fifth bearing) and secured by bolts to an input flange 20 constituting a rotary input member of the drive unit. The usual differential pinion gears rotatably mounted on cross pins carried by the differential casing mesh with front and rear side gears 22 and 23 constituting first and second output gears respectively of the inter-axle differential.

A differential unit of the planetary gear type could alternatively be utilised.

The output gear 22 of the differential unit 1 8 is connected to drive a torque-transmitting through shaft 9 which extends the full length of the housing 1 5 and in the region of its rear end is rotatably supported by a rear bearing 24 (sixth bearing) mounted on the rear cover 26 and is connected to an output flange 25 constituting a rotary output member of the drive unit.

The input and output flanges 20 and 25, and the through shaft 9, are coaxially disposed, having a common axis of rotation extending longitudinally of the drive unit. In other words, a "straight-through" drive is provided to the output flange 25. Thereby, the drive can be taken out to the rear without the need for a costly transfer drive to take the drive over the inter-axle differential unit.

The output gear 23 of the differential unit 18 is connected by means of a sleeve portion to drive a hollow (annular) right angle drive hypoid pinion 2 coaxially surrounding part of the through shaft. The hypoid pinion has a front support bearing 1 3 (fourth bearing) in the form of a double-row tapered roller bearing interposed between the sleeve portion and the interior of the front cover 14, and a rear support bearing 1 2 (third bearing) in the form of a roller bearing mounted in an aperture in a carrier member 11 that is integral with the drive unit housing 1 5 and projects into the interior of the housing, as is best seen in Fig.

2.

The hypoid pinion 2 is in meshing engagement with a ring gear constituted by an annular hypoid gear 1, the axis of rotation of the hypoid gear being at a different level from the axis of the hypoid pinion. The hypoid gear is secured by bolts 29 to a rotary differential casing 3 of an inter-wheel differential 1 7 (second differential gear unit) that is offset to the left-hand side of the through shaft 9. The differential casing 3 is rotatably supported by a spaced pair of support bearings 6 and 7 (first bearing and second bearing, respectively), for rotation about an axis which, in the application shown, extends above and at right angles to the axis of rotation of the through shaft 9.The outboard support bearing 6 (thus, the support bearing on the left-hand side of the differential casing 3) is located to the drive unit housing in a conventional manner by a split bearing cap 10, and the righthand support bearing 7, which is disposed between the central region of the differential unit 1 7 and the through shaft 9, is located into a recess in the carrier member 11. Thus the support bearings 7 and 12, which are disposed relatively close to each other, are mounted in recesses in a unitary piece which is integral with the drive unit housing 1 5.

The rotary differential casing 3 of the interwheel differential 1 7 carries cross pins on which are rotatably mounted differential pinion gears 4 meshing with differential gears (side gears) 5 and 27 constituting first and second output gears respectively of the interwheel differential. The first output gear 5 is connected to drive a left-axle shaft 1 6 that extends transversely of the drive unit through an axle tube to drive a left-hand wheel (not shown) of the leading driving axle of a tandem set. The second output gear 27 is connected to drive a right-hand axle shaft 8 that extends transversely of the drive unit in the opposite direction above the through shaft 9 and through an axle tube to drive a right-hand wheel (not shown) of the leading driving axle.

Because the shafts 8 and 9 cross each other at a location which is completely clear of the second differential gear unit and the adjacent one of its support bearings (and also clear of the hypoid gear), the shafts can cross each other with minimal clearance, for example with a clearance of as little as 1 mm. In the context of a tandem-axle truck, this allows the hypoid offset to be as little as 10-15% of the diameter of the ring gear, such that there is less sliding and a lower siiding velocity at the gear tooth engagement surfaces, and hence cooler running and greater efficiency, than would be the case with a larger hypoid offset.

The manner of operation of the drive unit will be largely self-evident from the foregoing description. Drive from the vehicle engine applied at the input flange 20 will result in the torque being divided proportionally between the two side gears 22 and 23 of the inter-axle differential 18. Thereby, the part of the torque transmitted via the hypoid set 2, 1 will be divided proportionally by the gears 5 and 27 of the inter-wheel differential 1 7 for driving the left- and right-hand axle shafts 1 6 and 1 8 of the leading driving axle, and the torque transmitted via the through shaft 9 to the output flange 25 can be taken out via a universally jointed shaft to a further interwheel differential for driving opposed axle shafts of a trailing driving axle of the tandem set.

The "through" construction of drive axle on the lines described can provide single reduction ratios within the range from 1.9:1 to 5.1:1 that will cover the major requirements of a modern truck vehicle. Ratios ranging from 3.1:1 to 7.0:1 can be made available by the use of hub reduction, for high traction variants of tandem axles.

The three-part construction of the drive unit housing facilitates assembly, and offers potential flexibility for the production of several versions of drive unit utilizing a number of common parts. Thus for assembly of the differential casing 3 together with the hypoid gear 1, when the rear cover 26 and the bearing cap 10 are not in place the parts 3 and 1 can be negotiated into position through the rear aperture into the housing 1 5 in a tilted orientation to permit insertion of the right-hand support bearing 7 into the recess in the carrier member 11. When the front cover 14 is not in place, access for the hypoid pinion 2 is readily available via the front aperture of the housing 15, this aperture c.eing made large enough to permit assembly of the largest hypoid pinion envisaged.

A single drive axle version of a drive unit is possible by omission of the inter-axle differential, the through shaft and the output flange, and with modified front and rear covers, in this version the hypoid gear being driven directly by the input flange and not necessarily being of hollow (annular) construction.

Alternatively a single drive axle version may be provided by this construction by a splined connection of the through drive shaft to the hypoid pinion so as to provide a drive input at the flange opposite to the hypoid pinion (herein referred to as the output flange).

The present invention includes within its scope the subject-matter of the claims which follow, but is not necessarily limited to this subject-matter.

Claims (9)

1. A drive unit for a tandem-axle motor vehicle, comprising a first differential gear unit having a differential casing that is rotatably supported within a housing of the drive unit and is connected to be driven by a rotary input member of the drive unit, first and second output gears of the first differential gear unit connected to drive, respectively, a torque-transmitting shaft that is connected to drive a rotary output member of the drive unit coaxial with the shaft and with the input member, and a hollow hypoid pinion that coaxially surrounds a portion of the shaft, a second differential gear unit having a differential casing that is rotatably supported within the housing of the drive unit by first and second bearings and is connected to be driven by a hypoid gear that surrounds the said casing and is in meshing engagement with the hypoid pinion, and first and second output gears of the second differential gear unit connected to drive, respectively, first and second axle shafts that extend in opposite directions from a central region of the second differential gear unit, in a configuration such that the second axle shaft extends closely adjacent the torque-transmitting shaft at right angles thereto, and the second axle shaft and the torquetransmitting shaft cross at a location on the side of the said second bearing remote from the central region of the second differential gear unit.

2. A drive unit according to claim 1, in which the hypoid pinion is rotatably supported by a third bearing disposed adjacent the said second bearing.

3. A drive unit according to claim 2, in which the second and third bearings are mounted in a common carrier member extend ing from the housing of the drive unit.

4. A drive unit according to claim 2 or 3, in which the hypoid pinion is further rotatably supported by a fourth bearing mounted in the housing of the drive unit and disposed on the opposite side of the hypoid pinion to the third bearing.

5. A drive unit according to claim 4, in which the input member and the differential casing of the first differential gear unit are rotatably supported by a fifth bearing mounted in the housing of the drive unit, and the output member and the torque-transmitting shaft are rotatably supported by a sixth bearing mounted in the housing of the drive unit.

6. A drive unit according to claim 5, in which the first differential gear unit and the fourth and fifth bearings are mounted in a cover portion of the drive unit housing which is removable to permit assembly and removal of the hypoid pinion.

7. A drive unit according to claim 5 or 6, in which the first bearing is mounted in a split bearing cap supported by the drive unit housing and the sixth bearing is mounted in a rear cover portion of the drive unit which is removable to permit assembly and removal of the second differential gear unit and hypoid gear.

8. A drive unit according to any one of claims 1 to 7, in which the second differential gear unit is disposed on the left-hand side of the torque-transmitting shaft, and the torquetransmitting shaft passes closely beneath a right-hand axle shaft constituting the second axle shaft.

9. A drive unit according to any one of claims 1 to 8, in which the first and second axle shafts are connected to drive respective opposed wheels of a leading driving axle of a tandem set, and the output member is connected by way of a universally jointed shaft and a third differential gear unit to drive opposed wheels of a trailing driving axle of the tandem set.

1 0. A drive unit for a tandem-axle motor vehicle, substantially as hereinbefore particularly described and as shown in the accompanying drawings.