DIFFERENTIAL GEAR

Abstract: A differential gear for distribution of torque between a forward driven wheel shaft and a rear driven wheel shaft on a vehicle in which the rear wheel shaft can be raised has an input shaft (3) which via differential pinions (6) is in engagement with a rear differential wheel (7) connected to an output shaft (4). The input shaft (3) and the rear differential wheel (7) are mutually supported via a bearing (15) which transmits axial forces between them. This bearing is fitted with preloading to eliminate axial play.

Description: Differential gear Technical area The invention relates to a differential gear according to the preamble to patent claim 1. State of the art Vehicles with tandem-driven rear axle bogies generally incorporate a differential gear for distributing the drive torque delivered by the engine to the forward and rear wheel shafts. It has been usual for both wheel shafts to be continuously powered. The increasingly common use of air-sprung wheel shafts affords the possibility even in a tandem bogie of raising one of the wheel shafts, normally the rear one, which thereby comes off load but continues to rotate. This also eliminates the force via the differential which provides guidance of the input shaft, consequently impairing not only gear engagement in the transfer gearbox but also the differential locking function, and causing undesirable wear. These problems arise from the occurrence of axial play in the differential gear, with the result that the now off-load input shaft is no longer guided as well as previously. These problems do not occur when the rear wheel shaft is lowered and the input shaft is subjected to normal torque load. Object of the invention The object of the invention is to provide a differential gear which eliminates the problem of uncentred drive and inferior functioning of the differential lock in a tandem bogie when the rear wheel shaft is raised and off load. A further object is to provide as a simple a solution as possible involving the least possible amount of modification of a previously used design. Description of the invention The problem is solved according to the invention by providing the differential gear with the features indicated in the characterising part of patent claim 1. Fitting in accordance with the invention a preloaded taper bearing eliminates axial play of the input shaft when the differential is off load. This leads to the input shaft being held in a well-fixed position even when the output shaft is not subject to any torque load. Further features and advantages of the invention are indicated in the ensuing description and patent claims. Description of the drawings The invention is explained below in more detail with reference to an embodiment depicted in the attached drawings, in which: Fig.1 shows a longitudinal section through a differential gear according to the invention, and Fig.2 shows on a larger scale a detail of Fig.1. Description of a preferred embodiment A differential gear 1 according to the invention has a housing 2 in which a driven input shaft 3 is supported. An output shaft 4 is intended to transmit torque to the rear wheel shaft in a tandem bogie on a vehicle and an output shaft 5 is intended to transmit torque to the forward wheel shaft in the tandem bogie. The two output shafts 4 and 5 each drive their respective wheel shaft via their conventional rear axle differential, which is not described further in this respect. The differential gear 1 depicted is used in order to allow the wheel shafts to rotate at mutually different speeds. The input shaft 3, which is driven by the vehicle's engine and is coaxial with the output shaft 4, bears in common rotation with it a number of differential pinions 6 for driving not only a rear differential wheel 7 connected for common rotation with the output shaft 4 but also a forward differential wheel 8 mounted for rotation about the input shaft 3. A differential lock 9 can be used to couple the forward differential wheel 8 for common rotation with the input shaft 3. This enables the input shaft 3 to drive, via the forward differential wheel 8, a pinion 10 which is mounted for common rotation with the output shaft 5 so that torque is transmitted to the forward wheel shaft. The differential gear is similar in form to a bevel gear in which the toothing on the differential pinions 6 and the toothing on the cooperating rear and forward differential wheels 7,8 is conical in shape. It is this shape which gives rise to the axial forces which occur in the gear and cause the problem mentioned in the introduction of axial imbalance of forces when only one differential wheel is on load. The differential lock 9 incorporates a pinion 11 which is movable axially on but rotates together with the input shaft 3 and which by being moved towards the forward differential wheel 8 can be brought into torque-transmitting engagement with the latter. Moving the pinion 11 in the opposite direction disengages the forward differential wheel 8. The input shaft 3 is supported in the housing 2 via a forward bearing 12. Correspondingly, the output shaft 4 via the rear differential wheel 7 is supported in the housing 2 via a rear bearing 13. During torque transmission between the input shaft 3 and the output shaft 4, these two bearings 12 and 13 serve as a path for transmitting to the walls of the housing 2 the mutually parting axial forces which the differential pinions 6 impart to the respective forward and rear differential wheels 8 and 7. As depicted in more detail in Fig.2, the end 14 of the input shaft 3 adjacent to the rear differential wheel 7 is supported in the latter via an axial-force-transmitting inner bearing 15 which is fitted in an axial recess 16 in the rear differential wheel 7. The results of designing the differential gear 1 in such a way that the bearings 12, 13 and 15 are preloaded include the rear differential wheel 7 being subjected to an axial load directed away from the input shaft 3. This means that the input shaft 3 and the rear differential wheel 7 are at all times held well fixed in position even when there is no need to transmit any torque owing to the rear wheel shaft being raised and the differential lock 9 being brought into engagement and transmitting the incoming torque from the input shaft 3 to the output shaft 5 and the wheel connected to the latter on the forward wheel shaft. As may be seen in the drawings, it is advantageous for the bearings 12, 13 and 15 to be of the taper roller bearing type which withstands large radial and axial loads. The desired preloading may with advantage be achieved by means of suitably dimensioned spacing discs. In the version here depicted, the bearing 15 in the axial direction has its outer ring abutting against a shoulder in the rear differential wheel 7 and its inner ring against a shoulder on the input shaft 3. An opposite arrangement is also possible.

Claims: PATENT CLAIMS 1. Differential gear for distribution of torque between a forward driven wheel shaft and a rear driven wheel shaft on a vehicle in which the rear wheel shaft can be raised, which differential gear is provided with an input shaft (3) and a mutually coaxial output shaft (4) for the rear wheel shaft, which input shaft (3) bears conical differential pinions (6) for driving not only a rear differential wheel (7) which is connected for common rotation with the output shaft (4), but also a forward differential wheel (8) which is mounted for rotation about the input shaft (3), can by means of a differential lock (9) be coupled for common rotation with the input shaft (3) and drives a pinion (10) for the forward wheel shaft, while axially parting forces caused by the differential pinions (6) and travelling along the input and output shafts are transmitted to a differential housing (2) via a forward bearing (12) and a rear bearing (13) respectively, and the end (14) of the input shaft (3) situated adjacent to the rear differential wheel (7) is supported in the latter via an inner bearing (15), characterised in that the inner bearing (15) serves for axial force transmission between the input shaft and the rear differential wheel. 2. Differential gear according to claim 1, characterised in that said inner bearing (15) for the end (14) of the input shaft, like the forward bearing (12) and the rear bearing (13), is fitted with preloading to eliminate axial bearing play so that when the input shaft (3) is in a raised position for the rear wheel shaft, together with the rear differential wheel (7), it maintains play-free coupling with upline drive elements. 3. Differential gear according to claim 1 or 2, characterised in that the input shaft (3) has a rearward-facing shoulder for the bearing (15) which is arranged within the rear differential wheel (7) and which itself abuts against a forward-facing shoulder in the rear differential wheel. 4. Differential gear according to any one of claims 1-3, characterised in that at least the inner bearing (15) is a taper roller bearing. 5. Differential gear according to claim 4, characterised in that the forward bearing (12) and the rear bearing (13) are also of taper roller bearing type.

Inventors: JOHANSSON ALF, JOHANSSON, ALF
Applicants: JOHANSSON ALF, SCANIA CV ABP, JOHANSSON, ALF, SCANIA CV AKTIEBOLAG (PUBL)
Application year: 1998
Main classification: B60K17
IPC codes: B60K17, F16H48, F16H57