Abstract:
A drive unit assembly including an input element, a first output element, a second output element and a drive unit housing containing a differential unit, the differential unit drivingly coupling the input element, the first output element and the second output element, the input element having input coupling features positioned externally of the drive unit housing, the first output element having output coupling features positioned externally of the drive unit housing, wherein the drive unit housing includes at least one mounting feature for securing the drive unit housing externally relative to an axle assembly and the second output element is suitable for driving an axle assembly.

Description:
TECHNICAL FIELD 
     The present invention relates to drive unit assemblies, in particular drive unit assemblies for driving axles, in particular rear axles of vehicles, in particular heavy vehicles such as lorries and trucks. 
     BACKGROUND 
     Heavy vehicles, such as trucks and lorries, are known which have two rear axles, namely a forward-rear axle assembly and a rear-rear axle assembly. The rear-rear axle assembly is behind the forward-rear axle assembly. Each axle is a driven axle and includes a differential unit for driving the right and left wheels associated with that axle. Engine power is transmitted through a gear box or the like along a prop shaft to a front drive flange of the forward-rear axle assembly. Housed within the forward-rear axle assembly housing is an inter-axle differential unit which transfers power to both the forward-rear differential unit (also housed within the forward-rear axle assembly housing) and the rear-rear differential unit. Power is transmitted to the forward-rear differential unit via gears and the like within the forward-rear axle housing. Power is transmitted to the rear-rear differential unit via a shaft which is mainly housed within the forward-rear axle housing but projects rearwardly out of the forward-rear axle housing. A prop shaft or the like connects the shaft to a drive flange of the rear-rear axle housing. 
     As will be appreciated the forward-rear axle housing includes two differential units namely the inter-axle differential unit and the forward-rear differential unit. However, the rear-rear axle housing only includes a single differential unit, namely the rear-rear axle differential unit. Such an arrangement results in a forward-rear axle housing that necessarily must be larger (to accommodate the greater number of components) than the rear-rear axle housing which can be smaller. Consequently the forward-rear axle housing is different from the rear-rear axle housing. This in turn requires two sets of manufacturing components, and two different assembly lines for assembling the two different axle housings. 
     SUMMARY 
     According to a first aspect of the present invention there is provided a drive unit assembly including an input element, a first output element, a second output element and a drive unit housing containing a differential unit, the differential unit drivingly coupling the input element, the first output element and the second output element, the input element having input coupling features positioned externally of the drive unit housing, the first output element having output coupling features positioned externally of the drive unit housing, wherein the drive unit housing includes at least one mounting feature for securing the drive unit housing externally relative to an axle assembly having a differential carrier and an axle housing and wherein the second output element is suitable for driving an axle assembly. 
     According to a second aspect of the present invention there is provided an axle arrangement including a drive unit assembly having an input element, a first output element, a second output element and a drive unit housing containing a differential unit, the differential unit drivingly coupling the input element, the first output element and the second output element, the input element having input coupling features positioned externally of the drive unit housing, the first output element having output coupling features positioned externally of the drive unit housing, wherein the drive unit housing includes at least one mounting feature. 
     The axle arrangement may further include an axle assembly having an axle input element defined by a differential carrier, a right wheel output element, a left wheel output element and an axle housing containing a single axle differential unit, the single axle differential unit drivingly coupling the axle input element, the right wheel output element and the left wheel output element. 
     The drive unit housing may be secured to the axle assembly externally relative to the axle housing via the at least one mounting feature such that the second output element selectively drives the axle input element. 
     An axis of the input element may be coincident with an axis of the first output element. An axis of the input element may be parallel to an axis of the second output element. An axis of the first output element may be parallel to an axis of the second output element. An axis of the second output element may be coincident with an axis of the axle input element. 
     According to a third aspect of the present invention there is provided a vehicle including an axle arrangement including a drive unit assembly having an input element, a first output element, a second output element and a drive unit housing containing a differential unit, the differential unit drivingly coupling the input element, the first output element and the second output element, the input element having input coupling features positioned externally of the drive unit housing, the first output element having output coupling features positioned externally of the drive unit housing, wherein the drive unit housing includes at least one mounting feature. 
     The axle arrangement may further include an axle assembly having an axle input element defined by a differential carrier, a right wheel output element, a left wheel output element and an axle housing containing a single axle differential unit, the single axle differential unit drivingly coupling the axle input element, the right wheel output element and the left wheel output element. 
     The drive unit housing may be secured to the axle assembly externally relative to the axle housing via the at least one mounting feature such that the second output element selectively drives the axle input element, the axle arrangement defining a forward-rear axle arrangement of the vehicle and the differential carrier defining a forward-rear differential carrier. 
     The vehicle may include a rear-rear axle assembly positioned behind the forward-rear axle arrangement. 
     The rear-rear axle assembly may include a rear-rear differential carrier upon which is mounted a single rear-rear differential unit. 
     The forward-rear differential carrier may be substantially the same as the rear-rear differential carrier. 
     An axis of the right wheel output element may be coincident with the axis of the left wheel output element. An axis of the right wheel output element may be arranged laterally relative to an axis of the input element, and/or an axis of the first output element, and/or an axis of the second output element and/or an axis of the axle input element. An axis of the left wheel output element may be arranged laterally relative to an axis of the input element, and/or an axis of the first output element, and/or an axis of the second output element, and/or an axis of the axle input element. 
     The differential unit of the drive unit assembly may be an interaxle differential unit. 
     The drive unit assembly may define a first lubricant reservoir. The axle assembly may define a second lubricant reservoir separate from the first lubricant reservoir. The rear-rear axle assembly may define a third lubricant reservoir separate from the second lubricant reservoir and/or separate from the first lubricant reservoir. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will now be described, by way of example only, with reference to the accompanying drawings in which: 
         FIG. 1  is an isometric view of a drive unit assembly according to the present invention mounted on an axle assembly, 
         FIG. 2  is an alternate view of the components shown in  FIG. 1 , 
         FIG. 3  is a cross-section of certain of the components of the drive unit assembly of  FIG. 1 , 
         FIG. 4  is a view similar to  FIG. 1  with the drive unit housing not shown, 
         FIG. 5  is an alternate view of  FIG. 4 , and 
         FIG. 6  is a schematic plan view of a vehicle including a drive unit assembly according to the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention that may be embodied in various and alternative forms. The figures are not necessarily to scale; some features may be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention. 
     With reference to  FIG. 6  there is shown a vehicle  10  having a front F and a rear R. The vehicle includes a front axle  11 , a forward-rear axle assembly  12  and a rear-rear axle assembly  13 . In this case, the front axle  11  is a non-driven axle and includes wheels  14 L and  14 R which are steerable. The forward-rear axle assembly includes a pair of right wheels  15 R and a pair of left wheels  15 L. The rear-rear axle assembly includes a pair of right wheels  16 R and a pair of left wheels  16 L. Each axle is mounted via suspension on a chassis  17 . The forward-rear axle assembly  12  and rear-rear axle assembly  13  are driven axles. An engine  18  drives a gear box  19  which in turn drives a prop shaft  20 . The prop shaft  20  is connected to a drive unit assembly  30  which selectively can drive both the forward-rear axle assembly and rear-rear axle assembly as will be described below. 
     With reference to  FIGS. 1 to 5 , there is shown in greater detail, the forward-rear axle assembly  12 . As can be seen from  FIG. 1 , an axle arrangement  31  consists of the drive unit assembly  30  and the forward-rear axle assembly  12 . 
     The drive unit assembly  30  includes a housing  32  which includes a front portion  33  shaped to receive components as will be further described below, and a rear portion  34  which is generally elongate and cylindrical. The housing  32  also includes a front cover  35  which generally closes an opening of the front portion  33 . 
     As can be seen from  FIG. 1  the drive unit assembly  30  includes an input element in the form of a drive flange  40  and a first output element in the form of a drive flange  41 . As will be appreciated the drive flanges  40  and  41  are outside of the housing  32  as defined by the front portion  33 , rear portion  34  and front cover  35 . 
     The housing  32  further includes mounting features to enable the housing  32  to be mounted on the forward rear axle assembly  12 . In this case the mounting features are defined by holes  42  (only one of which is shown) in mounting flange  43  and holes  44  in bracket  45 . Both the mounting flange  43  and the bracket  45  are secured to the housing  32 , for example by welding. 
     As best seen in  FIG. 4 , the components which are contained within housing  32  are shown. They include an interaxle differential unit  50 , a differential lock  51 , a differential lock actuator  52 , idler gear arrangement  53  and a second output element in the form of gear  54 . 
     Turning to  FIG. 3 , the drive flange  40  is secured by a nut  60  to input shaft  61 . The drive flange  40  includes a bore having spline  62  which engage with splines  63  of the input shaft  61  to ensure that the drive flange  40  is rotatably fast with the input shaft  61 . The input shaft  61  also includes splines  64  which engage with splines  65  of a differential spider  66 . Spider gears mounted on spider  66  engage with the teeth  70  on gear  71  and also with teeth  72  on gear  73 . The differential unit  50  therefore allows gear  71  and  73  to rotate at different speeds when required. 
     A bearing  74  allows gear  71  to rotate relative to the input shaft  61 . A bearing  75  allows gear  73  to rotate relative to the input shaft  61 . A bearing  76  is mounted in housing  32  to enable the gear  71  to rotate relative to the housing  32 . A bearing  77  is mounted in housing  32  to enable the input shaft  61  to rotate relative to the housing. The gear  71  has a splined bore  78  within which sits a splined end  79  of an output shaft  80 . The output shaft  80  has a further splined end  81  which is positioned in a splined bore  82  of the drive flange  41  to ensure that drive flange  41  is rotationally fast with the output shaft  80 . A nut  83  secures the drive flange  41  onto the output shaft  80 . A pair of taper roller bearings  84  is mounted in the housing  32  and enables the output shaft  80  to rotate relative to the housing. 
     The flange  40  rotates about a first axis A. The flange  41  also rotates about the first axis A. 
     A differential lock collar  86  is slideably mounted via spline  87  on the first shaft  61 . The differential lock collar is therefore rotationally fast with the input shaft  61 . The differential lock collar  86  includes a set of dog teeth  88  (see  FIG. 5 ). The gear  73  also includes a set of dog teeth  89  which face dog teeth  88 . 
     With the dog teeth  88  disengaged from dog teeth  89 , as shown in  FIG. 5 , the gear  73  can rotate relative to the input shaft  61  as described above, by virtue of the differential unit. However, the differential lock collar  86  can move in the direction of arrow B so that dog teeth  88  engage dog teeth  89 . This results in gear  73  becoming rotationally fast with the first input shaft  61  by virtue of dog teeth  88  and  89  and by virtue of splines  87 . Accordingly, the differential unit  50  can be locked. Movement of the differential lock collar  86  in the direction of arrow B is achieved by fork  90  (which includes fork tines  91  see  FIGS. 4 and 5 ) engaging in groove  92  of the lock collar  86 . Fork  90  is moved in the direction of arrow B by air pressure applied via air port  93  to diaphragm  94  which causes pin  95 , upon which fork  90  is mounted, to move in the direction of arrow B. In order to unlock the differential lock, air is vented from the region around diaphragm  94  via the air port  93  which results in spring  96  pushing pin  95  and hence fork  90  in the direction of arrow C of  FIG. 3  thereby disengaging dog teeth  89  from dog teeth  88 . 
     Gear  73  also includes an array of teeth  110 , shown schematically in  FIG. 5 . 
     Idler gear arrangement  53  is mounted on bearings (not shown) in housing  32 . The idler gear arrangement  53  rotates about axis D. The idler gear arrangement  53  has a first array of teeth  112  shown schematically on  FIG. 4  and a second array of teeth  114  shown schematically on  FIG. 4 . The array of teeth  112  are rotationally fast with the array of teeth  114 . The number of teeth in the array of teeth  112  is the same as the number of teeth in the array of teeth  114 . The array of teeth  112  engage with the array of teeth  110 . The array of teeth  114  engage with an array of teeth  116  (shown schematically in  FIG. 4 ) of gear  54 . 
     Gear  54  is secured rotationally fast via internal splines engaging external splines on input shaft  130 . A threaded nut  131  secures gear  54  axially relative to input shaft  130 . 
     The rear-rear axle assembly  13  is known in the art and includes an axle input element in the form of a drive flange  150 , a right wheel output element in the form of a wheel shaft contained within axle tube  152  and a left wheel output element in the form of an axle shaft contained within axle tube  153 . The rear-rear axle assembly  13  includes an axle housing  154  containing a single axle differential unit. The axle differential unit drivingly couples the drive flange  150  to the right and left wheel shafts contained within axle tubes  152  and  153 . The differential unit together with a ring gear and pinion are mounted on a differential carrier  156 . The differential carrier  156  is removably secured to axle housing  154  by an array of fixings, such as bolts or the like. Accordingly, the differential carrier can be removed from the axle housing  154  for servicing of the pinion, ring gear and differential etc. 
     The differential carrier  156  of the rear-rear axle assembly is substantially the same as the differential carrier  55  of the forward-rear axle assembly  12 . The only difference between differential carrier  156  and differential carrier  55  being that differential carrier  55  has gear  54  secured to input shaft  130  via nut  131  whereas differential carrier  56  has drive flange  150  secured to an input shaft the equivalent of input shaft  130  via a nut the equivalent of threaded nut  131 . 
     Significantly, a differential carrier which excludes either gear  54  or drive flange  150  can be assembled onto an axle housing. If a rear-rear axle is to be assembled, then subsequently drive flange  150  can be fitted. If a forward-rear axle is to be assembled then the drive unit assembly  30  and gear  54  can be fitted as will be further described below. 
     A prop shaft  158  is coupled at a front end to flange  41  and at a rear end to flange  150 . 
     Prop shaft  20  and  158  include a universal joint at each end and a sliding splined joint to cater for misalignment and movement between the gear box  19  and forward-rear axle assembly  12  and also misalignment and movement between the forward-rear axle assembly  12  and rear-rear axle assembly  13 . 
     Operation of the vehicle  10  is as follows: 
     The engine  18  transmits power to the gearbox  19  which in turn causes prop shaft  20  to rotate. Prop shaft  20  in turn causes flange  40  and hence input shaft  61  to rotate which, by virtue of the differential unit  50  causes gear  71  and gear  73  to rotate. Gear  73  drives the idler gear arrangement  53  which in turn drives gear  54  which turns input shaft  130 . Input shaft  130  includes a pinion (not shown) which drives a ring gear (not shown) which drives a differential unit (not shown) within the forward-rear axle assembly  12  which differential unit then drives wheels  15 R and  15 L. 
     Because the differential unit  50  causes gear  71  to rotate, gear  71  in turn causes output shaft  80  to rotate together with flange  41 . Rotation of flange  41  causes rotation of prop shaft  158  which causes rotation of flange  150  which causes rotation of the input shaft of the rear-rear axle assembly which in turn drives the ring gear (not shown) and differential unit (not shown) of the rear-rear axle assembly which in turn drives wheels  16 R and  16 L. 
     As will be appreciated, the rear-rear axle assembly  13  includes a single differential unit. The axle housing  56  of the forward-rear axle assembly  12  includes a single differential unit. The housing  32  of the drive unit assembly  30  includes a single differential unit  50 . Accordingly, the differential unit  50  is contained in a different housing to the differential unit contained within axle housing  154 . 
     Assembly of the axle arrangement  31  is as follows. 
     The differential carrier  55  is assembled together with input shaft  130 , the associated ring gear (not shown), and the associated axle differential unit (not shown). At this stage gear  54  is not assembled. The differential carrier  55  is then assembled onto the axle housing  56  and the array of bolts  57  and nuts  58  are secured in place and tightened. 
     Separately, various components are assembled into the front portion  33  and rear portion  34  of the housing  32  including assembling the input shaft  61 , the output shaft  80 , the drive flange  41 , the idler gear arrangement  53  and the gear  54 . 
     This subassembly is then mounted on the forward-rear axle assembly  12  by passing holes  42  over appropriate studs  59  and by passing bolts (not shown) through holes  44  and tightening them into holes (not shown) in the axle housing  56 . At this stage the gear  54  will be positioned around the end of input shaft  130  and it will then be necessary to screw threaded nut  131  onto the end of the input shaft  130  and tighten the nut. Once this has been done the cover  35  can be attached to the front portion  33  of the housing  32 . Once the cover is in place the flange  40  can be slid onto the input shaft  61  and nut  60  can be threaded onto the end of input shaft  61  and tightened securely. 
     Either at this stage, or later, lubricant, such as oil can be added to the axle housing  154 . Separately lubricant, such as oil can be added to housing  32 . Significantly, the lubricant in the axle housing may be different from the lubricant in the drive unit assembly. Under some circumstances it may be advantageous to have different lubricants in the axle housing and the drive unit assembly because the axle housing includes a ring gear and pinion which require a particular type of lubricant but the drive unit assembly does not include a ring gear and pinion. 
     As mentioned above, the only difference between the forward-rear and the rear-rear differential carrier subassembly is that the forward-rear differential carrier subassembly includes gear  54  and the rear-rear differential carrier subassembly includes flange  150 . Because this gear and flange can be secured in place as one of the last components to be fitted to the axle assembly, it is possible to have a single assembly line to provide both a rear-rear axle assembly  13  (which excludes a drive unit assembly  30 ) and a forward-rear axle arrangement which includes a forward-rear axle assembly  12  and a drive unit assembly  30 . In particular the axle housing for a forward-rear axle assembly can be substantially the same as or identical to the axle housing for a rear-rear axle assembly. Furthermore, the differential carrier for a forwards-rear axle assembly can be substantially similar to or identical to the differential carrier for a rear-rear axle assembly. Indeed the differential carrier for a forward-rear axle assembly may be interchangeable with the differential carrier of a rear-rear axle assembly simply by changing gear  54  with flange  150 . 
     The invention provides for a drive unit assembly that can easily convert an axle assembly into a forwards-rear axle assembly. 
     As will be appreciated, the axis of the input element is coincident with the axis of the first output element. The axis of the input element is parallel to the axis of the second output element. The axis of the first output element is parallel to the axis of the second output element. The axis of the second output element is coincident with the axis of the axle input element. The axis of the right wheel output element is coincident with the axis of the left wheel output element. The axis of the right wheel output element is arranged laterally relative to the axis of the input element, the axis of the first output element, the axis of the second output element and the axis of the axle input element. The axis of the left wheel output element is arranged laterally relative to the axis of the input element, the axis of the first output element, the axis of the second output element, and the axis of the axle input element. 
     The drive unit assembly defines a first lubricant reservoir. The axle assembly defines a second lubricant reservoir separate from the first lubricant reservoir. The rear-rear axle assembly defines a third lubricant reservoir separate from the second lubricant and separate from the first lubricant reservoir. 
     While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention. Additionally, the features of various implementing embodiments may be combined to form further embodiments of the invention.