Abstract:
A final drive for a road vehicle comprises a pinion gear ( 10 ) on a pinion axle ( 4 ) journaled in a housing ( 11 ), the pinion gear being in gear engagement with a crown gear ( 12 ) journaled for rotation transversely to the pinion axle ( 4 ). The final drive is combined with an all wheel drive (AWD) coupling, comprising a disc package ( 2 ) axially controlled by a hydraulic piston ( 5 ) for optionally transmitting torque from an ingoing axle ( 3 ) to the pinion axle ( 4 ) as well as a disc drum ( 2 A) or similar means for rotatably connecting the disc package ( 2 ) to the pinion axle. The ingoing axle ( 3 ) of the AWD coupling is radially journaled only by the pinion axle ( 4 ) in the final drive.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a final drive for a road vehicle, comprising a pinion gear on a pinion axle journaled in a housing, the pinion being in gear engagement with a crown gear journaled for rotation transversely to the pinion axle, in combination with an all wheel drive (AWD) coupling, comprising a disc package axially controlled by a hydraulic piston for optionally transmitting torque from an ingoing axle to the pinion axle as well as a disc drum or similar means for rotatably connecting the disc package to the pinion axle. 
       BACKGROUND OF THE INVENTION 
       [0002]    A final drive of the above-mentioned kind is customary on rear-wheel driven road vehicles—cars. The trend nowadays, however, is towards all wheel drive (AWD) cars. In such a car, a front wheel drive can be supplemented with an intermediate axle, an AWD coupling, and a final drive for driving also the rear wheels. 
         [0003]    When a car is to be provided with an AWD coupling, it is presently customary that the AWD coupling and the final drive (including the differential) are supplied from different sources. The design is often such that an AWD coupling/final drive-unit is formed in that the housing of the AWD coupling is physically attached to the housing of the final drive, the disc drum or similar means being connected to the pinion axle. 
         [0004]    The supplier of the final drive thus provides the proper journaling therefore. 
         [0005]    As is well known in the art, the journaling of the pinion axle in the final drive is rather intricate, because a certain pre-stress has to be provided, especially if the pinion gear/crown gear set is a hypoid gear set. The pinion axle is thus normally journaled by two conical roller bearings or angular contact bearings, which are prestressed by a nut arrangement to be manually tightened to the correct prestress value. 
         [0006]    The rotatable parts of the AWD coupling are likewise to be separately journaled in the coupling housing (although one of the bearings may be provided between the ingoing axle of the coupling and the pinion axle). 
         [0007]    Generally speaking, the provision of the final drive and the AWD coupling as in principle two separate, “self-contained” (but connected) units means high cost, weight, space requirement, and losses. 
         [0008]    The main object of the invention is to remove this and other disadvantages with the present design. 
       THE INVENTION 
       [0009]    An improved solution for the journaling of the rotating parts of the AWD coupling when combined with the final drive is according to the invention attained in that the ingoing axle of the AWD coupling is radially journaled only by the pinion axle in the final drive. 
         [0010]    In a practical embodiment a radial bearing arrangement, preferably consisting of two radial bearings, is arranged between a stub axle at the end of the pinion axle and a bearing sleeve at the end of the ingoing axle. Conversely, a stub axle may be provided at the end of the ingoing axle and a bearing sleeve at the end of the pinion axle. 
         [0011]    The length of the bearing arrangement is such that the required journaling stability is obtained. 
         [0012]    By the omission of the otherwise required, separate radial bearing for the ingoing axle, the bearing losses are greatly reduced. The rotational speed differential between the ingoing axle and the pinion axle is namely normally low. Also, the mounting together of the two units may be facilitated. 
         [0013]    The radial bearings may be needle bearings. 
         [0014]    In order to accommodate the normally small axial forces in the ingoing axle, locking rings can be arranged at either side of the disc package on a hub on the ingoing axle. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    The invention will be described in more detail below under reference to the accompanying drawings, in which 
           [0016]      FIG. 1  is a sketch of a typical prior art arrangement of a vehicle final drive and an added AWD coupling and 
           [0017]      FIG. 2  is a similar sketch of an integrated final drive and AWD coupling according to the invention. 
           [0018]      FIG. 3  is a similar sketch of an integrated final drive and AWD coupling according to another embodiment. 
       
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       [0019]    A typical prior art combination of a final drive and an AWD coupling in a road vehicle—a car—is shown in  FIG. 1 . 
         [0020]    The description below—also of the inventive arrangement shown in  FIG. 2 —is focused on parts that are of importance for the proper understanding of the invention, as both the final drive and the AWD coupling are per se known and understood by persons skilled in the art. 
         [0021]    In a coupling housing  1  a disc package  2  comprising a number of discs is arranged. These discs are alternatingly connected on one hand to a rotatably journaled ingoing axle  3  and on the other hand to a rotatably journaled outgoing axle  4  in the form of a pinion axle of the final drive (to be described). The connection to the outgoing axle  4  is performed via a disc drum  2 A. The disc drum  2 A is in splines engagement with the axle  4  and thus axially movable in relation thereto. 
         [0022]    The disc package  2  is controlled by hydraulic pressure applied on a hydraulic piston  5  in the housing  1  such that the piston  5  moves towards the pinion gear  10  when controlled to actuate the disc package  2 . The magnitude of the force from the hydraulic piston  5  will control the clamping force on and thus the torque transmitted by the disc package  2  from the ingoing axle  3  to the outgoing axle  4 . The force from the piston  5  is transmitted to the disc package  2  and back into the housing  1  by means of axial bearings  6 , preferably needle bearings. 
         [0023]    In the shown example, the ingoing axle  3  is journaled in the housing  1  by means of only a radial bearing  7 , but the pinion axle  3  extends in a supporting fashion into the opposite end, where there is a radial bearing  8 , preferably a needle bearing. In other examples there may be more than one bearing for the ingoing axle  3 . 
         [0024]    A pinion gear  10  (integral with the pinion axle  4 ) is rotatably journaled in a final drive housing  11 , which is connected to the coupling housing  1 . The final drive comprises the pinion gear  10  and a crown gear  12  to form a bevel gear set, normally a hypoid gear set. A differential housing  13  is connected to the crown gear  12  and contains a conventional differential mechanism, from which two half-axles  14  extend out to driving wheels of the vehicle. The arrangement may be journaled in the final drive housing  11  by combined axial and radial bearings  15 . 
         [0025]    Shown in  FIG. 1  is a conventional journaling for a pinion gear in a hypoid gear set of a final drive. This journaling comprises two bearings, a forward bearing  16  and a rearward bearing  17 . These two bearings  16 ,  17  shall be capable of taking up the radial and axial forces from the gear engagement in the hypoid gear set. They have to have the capability of handling forces in both axial directions, because the force direction changes for example between driving the vehicle in the forward and the reverse direction. The bearings  16 ,  17  are normally conical roller bearings or angular contact ball bearings. 
         [0026]    For the proper functioning of the final drive, it is of great importance to prevent play from occurring in the journaling of the pinion gear  10 . The normal way to accomplish this is to apply an axial prestress on the journaling by means of a nut  18 , which is threaded on the pinion axle  4  and applies an axial force on the inner ring of the forward bearing  16 . For ensuring that the nut  18  does not get loose under service, there is a plate sleeve  19  between the inner rings of the two bearings  16 ,  17 . This sleeve is first deformed elastically and then plastically during the tightening of the nut  18 . The elastic force will then remain and keep the nut  18  from loosening. 
         [0027]    The magnitude of the prestress is so chosen that the deformation due to loads and temperature expansion does not result in any play. The constant pretress over the bearings  16 ,  17  results in considerable energy losses. 
         [0028]    The construction shown in  FIG. 1  is just one example of how to arrange the journaling of an AWD coupling mounted together with the final drive. Another construction is to journal the AWD coupling quite independently of the final drive. 
         [0029]    In the inventive solution according to  FIG. 2  and  FIG. 3  the integration between the AWD coupling and the final drive is more advanced. 
         [0030]    The main construction of the different elements in the inventive solution according to  FIG. 2  and  FIG. 3  has so much in common with the known arrangement shown in  FIG. 1  that reference is mainly made to the description above. Elements in  FIG. 2  and  FIG. 3  may be provided with the same numerals as in  FIG. 1 , even if they are not identical in the two embodiments. For the sake of clarity,  FIG. 2  and  FIG. 3  are only provided with reference numerals to the extent necessary for a proper understanding. 
         [0031]    In the known embodiment according to  FIG. 1  the ingoing axle  3  is journaled in the housing  1  by means of a radial bearing  7 . It is also supported by the pinion axle  4  by means of a radial bearing  8 . 
         [0032]    In the inventive embodiment according to  FIG. 2  and  FIG. 3  the radial bearing  7  has been totally dispensed with, and the ingoing axle  3  is only journaled on the pinion axle  4 . The pinion axle  4  is provided with a bearing stub axle  4 ′ with reduced diameter, whereas the end of the ingoing axle  3  is designed as a bearing sleeve with a length at least corresponding to the length of the stub axle  4 ′. The length of the stub axle  4 ′ may e.g. be 10 mm. A prolonged radial bearing arrangement, in the shown case consisting of two radial bearings  8 , is placed between the stub axle  4 ′ and the ingoing axle  3  for providing the necessary journaling with the required stability for the ingoing axle  3 . The ingoing axle  3  is thus completely radially journaled on the pinion axle end. 
         [0033]    The radial bearings  8  may be needle bearings. The radial bearing arrangement is preferably designed in order to withstand bending forces which may occur in the interface between the ingoing axle  3  and the pinion axle  4 . 
         [0034]    There are only limited axial forces in the ingoing axle  3 . These forces may for example be handled by the axial needle bearings  6  at either side of the disc package  2 . A locking ring  2 ′ may for this purpose be arranged at either side of the disc package  2  on a hub  3 ′ on the ingoing axle  3 . 
         [0035]    As the differential rotational speed between the ingoing axle  3  and the pinion axle  4  normally is inconsiderable, the bearing losses from the journaling of the ingoing axle  3  are greatly reduced. 
         [0036]    It is within the scope of the claims to provide the journaling for the ingoing axle  3  between a stub axle on the ingoing axle and a bearing sleeve in the end of the pinion axle  4 . 
         [0037]    In  FIG. 3  a further embodiment is shown, wherein the solution of having the ingoing axle  3  only journaled on the pinion axle  4  is combined with a very advantageous solution for axially guiding the outgoing axle of the coupling on the pinion axle  4 . 
         [0038]    In the arrangements according to  FIG. 1  and  FIG. 2  there are no interactions between the axial forces in the AWD coupling and the final drive, as there are axial bearings  6  at either side of the disc package  2  and as the disc drum  2 A is in splines engagement with the pinion axle  4  without axial force transmission. The mounting together of the two units is simply performed in that the disc drum  2 A is pushed into the splines engagement with the pinion axle, whereupon the two units are bolted together. 
         [0039]    In the arrangements according to  FIG. 3  on the other hand there is axial force transmission provided from the disc drum  2 A to the pinion axle  4 , in the direction towards the pinion gear, by means of an axial stop  9 ′ or the like on the pinion gear axle. In order to point to design alternatives, the numeral  9 ′ may be said to designate an axial stop e.g. in the form of lock ring means, which would include any means integral with the axle and performing the same function as a locking ring. 
         [0040]    As in the  FIG. 1  or  FIG. 2  arrangements the clamping force from the piston  5  to the disc package  2  is transmitted by an axial bearing  6 . This axial force is, however, now transmitted via the disc drum  2 A to the pinion axle  4  and back to the housing  11  via the pinion bearings. The need for an axial bearing to the right of the disc package  2  is hereby eliminated. 
         [0041]    An obvious advantage with this is that only one axial bearing, normally a needle bearing, is needed for the disc package  2 . The result is reduced losses, costs, and weight. 
         [0042]    Further, at normal forward driving the clamping force from the disc package  2  will act on the pinion gear in opposite direction to the forces from the gear engagement in the final drive (pinion gear  10 /crown gear  12 ). The result is that the axial load on the pinion bearings  16 ,  17  will be reduced, leading to reduced losses. As the pinion bearing load added over the life span of the arrangement is reduced, smaller pinion bearings may be chosen, also leading to reduced losses, costs, and weight. 
         [0043]    As already been described, axial forces from the disc drum  2 A are transmitted to the pinion axle  4  via the axial stop  9 ′ shown in  FIG. 3 . An alternative embodiment may include replacing the radial step  9 ′by a locking ring of the pinion axle. 
         [0044]    The radial step  9 ′ forms a stop surface for the disc drum  2 A, and an optional lock ring  9 ″ may be provided on the opposite side of the pinion axle  4  (i.e. opposite relative the radial step  9 ′) for preventing the disc drum  2 A to move axially away from the radial stop  9 ′. 
         [0045]    In a yet further embodiment, the axial stop on the pinion axle  4  is achieved by arranging the pinion bearing pre-loading threaded nut  18  (see  FIG. 1 ) such that the disc drum  2 A is in axial contact with threaded nut  18 . 
         [0046]    In the description above and in the claims, reference has only been made to actuation of the disc package by hydraulic pressure. However, it is within the scope of the claims to actuate the disc package by any actuator, for example electrical or pneumatic. 
         [0047]    Other modifications are possible within the scope of the appended claims.