Patent Abstract:
A motor vehicle power transfer unit for distributing torque from a transmission assembly between a front wheel drive line and rear wheel drive line. The power transfer unit includes a housing that encloses a parallel gear set and a non-parallel gear set, which are coupled between an input portion and an output portion of the power transfer unit. The parallel gear set includes a driving gear, and idler gear and a driven gear and the idler gear is rotatably supported on a non-rotating support member that extends through the idler gear. Constructed in this manner, reduced lateral compactness of the power transfer unit is achieved.

Full Description:
BACKGROUND 
     1. Field of the Invention 
     The present invention relates to the power train of a motor vehicle. More specifically, the present invention relates to a power transfer unit for distributing power to the rear wheels of the vehicle. 
     2. Description of the Prior Art 
     Most automobiles in the United States have typically utilized a rear wheel drive power delivery scheme. In adapting these rear wheel drive schemes into four wheel drive applications, a transfer case was, and often still is, positioned at the output of the transmission assembly. When engaged, the transfer case diverts a portion of the power coming from the transmission assembly from the rear wheels to the front wheels. 
     Currently in the United States, a significant portion of new automobiles are front wheel drive based vehicles. In a front wheel drive vehicle, typically both the engine and the transmission assembly are transversely oriented in the vehicle. By positioning the power plant and transmission assembly transversely, more direct coupling of the transmission assembly to the vehicle&#39;s transaxle and front wheels can be achieved. 
     With front wheel drive vehicles themselves becoming a mature market, a recent trend in the automobile industry has been to adapt front wheel drive schemes into all-wheel-drive or four-wheel-drive applications. This is accomplished by providing a power transfer unit that diverts a portion of the power from the front wheels to a rear wheel drive shaft and, subsequently, the rear wheels. 
     As a way of maximizing manufacturing resources, it is desirable to develop automotive products that can be utilized and incorporated across a variety of platforms. When incorporated into a vehicle, the power transfer unit is attached to the output face of the vehicle transmission. It is therefore in close proximity to the engine, the transmission, the steering rack and the exhaust manifold. Additionally, new PZEV catalytic converters are required to be located closer to the exhaust manifold so that they can achieve a quicker “light-off” of the catalyst. These PZEV catalytic converters also tend to be larger and generate higher temperatures than previous non-PZEV catalytic converters. The proximity to the engine, transmission and the other under hood components accordingly limits the size of the power transfer unit. Further, the high temperature of “manicat” catalytic converters and the previously mentioned PZEV catalytic converters means that polymer based products, such as lubricants and seals, need to be placed at as great a distance as possible from the PZEV catalytic converter. 
     One manner in which the overall size of the power transfer unit can be reduced is to similarly reduce the size of the gears, bearings and shafts of the power transfer unit itself. However, reducing the size of these components limits their overall torque carrying capacity. 
     An end result of all of the above is a desire for lateral compactness in the design of the power transfer unit. By compacting this lateral size of the power transfer unit, the power transfer unit can be configured as multiplatform assembly, in that the system itself can be designed for the worst case scenario, in other words the minimum lateral width available for a power transfer unit. 
     In order to achieve the greatest lateral compactness possible, the gears and bearings located inside the power transfer unit need to be located in the most space efficient manner possible. This can result in conflicts in the sizing and shaping of various components of the unit. 
     For example, in a three axis power transfer unit, a conflict can exist between the sizing of a hypoid ring gear and clearance between that ring gear and the support shaft of an idler gear. As used herein, the term “three axis power transfer unit” is one in which a driving gear, an idler gear and a driven gear, all located on parallel axes, are utilized in the power transfer unit. Because of the size of the ring gear typically required in power transfer units and because of the size of the bearings required to support the shaft upon which the idler gear is mounted, the ring gear and the idler gear bearing support are too large and located too longitudinally close together to enable these components to be mounted in a common plane. This results in these components being staggered laterally, forcing the power transfer unit to be wider than it might otherwise be. Even then, the size of the ring gear encroaches on the idler gear support shaft thereby limiting the size of that shaft. Clearly, merely reducing the cross-sectional diameter of the idler gear support shaft would result in reduced strength in the shaft and thereby limiting the size and capacity of the shaft, as well as the supporting bearing. 
     As seen from the above, there exists a need for increasing the lateral compactness of a power transfer unit so as to minimize its occupation of space in the engine bay and beneath the body of the vehicle and additionally to provide for a power transfer unit which exhibits multiplatform characteristics. 
     It is also and object of this invention to provide novel constructions for supporting an idler gear in situations where the ring gear positioning would be in conflict with the idler gear support, without increasing the lateral compactness of the power transfer unit. 
     SUMMARY 
     In satisfying the above need, as well as overcoming the enumerated drawbacks and other limitations of the related art, the present invention provides a power transfer unit in which the conflict between the ring gear and the idler gear support are resolved so as to enable a more laterally compact unit. 
     The output of the transmission assembly is coupled to an input member and to a first gear wheel, the driving gear, in a parallel gear set. The driving gear transfers rotation through an idler gear to a driven gear. That driven gear is mounted on a shaft whose rotational axis is generally parallel to the rotational axis about which the driving gear rotates. On the end of this transfer shaft is mounted a first bevel gear or gear ring of the non-parallel gear set. The first bevel gear engages a second bevel gear, such as a hypoid pinion gear, mounted to or formed with a shaft; this shaft being oriented generally perpendicularly to the rotational axis of the ring gear. The opposing end of the shaft is the output of the power transfer unit. 
     The idler gear is rotatably supported on a non-rotating support members that extends through the idler gear. In one embodiment, the non-rotating support member is a boss extending from one side of the housing toward an opposing side of the housing. In another embodiment, the non-rotating support member is a stationary shaft. 
     By providing the support for the idler gear through a non-rotating support member, bearing supports for that support member are eliminated. By eliminating these bearing supports, additional area within the power transfer unit is freed up so as to accommodate the ring gear of the non-parallel gear set in a more laterally compact construction. In other words, the ring gear of the non-parallel gear set need not be laterally staggered or spaced so as to avoid conflict with the bearing support for the idler gear. 
     Further objects, features and advantages of this invention will become readily apparent to persons skilled in the art after review of the following description, with reference to the drawings and the claims that are appended to and form a part of this specification. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is perspective view, with portions cut away, of a power transfer unit embodying the principles of the present invention; 
         FIG. 2  is a layout view of a power transfer unit according to a first embodiment of this invention; and 
         FIG. 3  is a layout view of a power transfer unit according to a second embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Referring now to the drawings,  FIG. 1  illustrates a power transfer unit  10  incorporating the principles of the present invention. The power transfer unit  10  includes a housing  12  in which the primary components of the unit  10  are integrally packaged. These components principally include a non-parallel gear set  14  and a parallel gear set  16 . 
     As used herein, the term “parallel gear set” is intended to refer to mechanisms with gear wheels that transfer power from a first shaft to a second shaft; the first and second shafts defining axes that are generally parallel to one another. 
     The term “non-parallel gear set”, as used herein, is intended to refer to any mechanism, (including, without limitation, mechanisms with gear wheels, mechanisms without gear wheels, gear trains, chain gears and belt systems) for transferring power from a first shaft to a second shaft; wherein the first and second shafts define axes that are generally not parallel to one another. 
     As mentioned above, the primary components of the power transfer unit  10  are all integrally packaged together and provided within a common housing  12 . Input and outputs  18 ,  20  of the unit  1  Omay or may not protrude from the housing  12  depending on the specific design criteria and the application in which the power transfer unit  10  is being employed. 
     Rotation from an output of a transmission assembly (not shown) is coupled to the input  18  (hereafter “driving shaft  18 ”) of the power transfer unit  10 , and in particular, of the parallel gear set  16 . To facilitate engagement of the driving shaft  18  with the output of the transmission assembly, the end of the driving shaft  18  may be internally or externally splined as seen at  19 . 
     The first gear wheel, driving gear  22 , of the parallel gear set  16  is mounted to the driving shaft  18  by conventional means, such as unitarily forming the driving gear  22  with the driving shaft  18  (as illustrated) or welding the driving gear  22  to the driving shaft  18 , so as to rotate with rotation of the driving shaft  18 . This rotation thus occurs about an axis  24  defined by the driving shaft  18 . To facilitate rotation of the driving shaft  18  and the driving gear  22 , the driving shaft  18  is supported on bearings  26 , one such kind being tapered bearings, supported by the housing  12 . 
     Rotation from the driving gear  22  is transferred to an intermediate gear wheel, hereafter idler gear  28 , by means of external teeth  30  on the driving gear  22  which intermesh with external teeth  32  on the idler gear  28 . Preferably, the driving gear  22  and the idler gear  28  are helical gears so as to increase the torque transferring efficiency of the power transfer unit  10 . Alternatively, however, the teeth  30 ,  32  could be formed straight. As the specific design criteria will dictate, the idler gear  28  may be larger, smaller or the same diameter as the driving gear  22 . 
     As seen in  FIG. 2  in the first embodiment the idler gear  28  is rotatably supported on a stationary member extending through the idler gear  28 . As illustrated in the embodiment of  FIG. 2 , the stationary member  34  is a stationary shaft “shaft  34 ”). The shaft  34  includes first and second ends  36 ,  38  that are respectively received within first and second seats  40 ,  42  defined in the housing  12 . To prevent rotation of the shaft  34  relative to the housing  12 , one or both of the first and second ends  36 ,  38  may be fixed by welding, keying, press-fitting or otherwise fixedly engaging the ends  36 ,  38  with the housing  12  at the seats  40 ,  42 . 
     To enable enhanced lateral compactness of the power transfer unit  10 , and as further described below, the shaft  34  is provided with a part  44  defining a first diameter  46  and, a second part  48  defining a second diameter  50 , the second diameter  48  being less than the first diameter  46 . The idler gear  28  is rotatably supported on the first part  44  by radial bearings  52 . Axially, the idler gear  28  is supported by axial support members  54 . Since the axial loads applied to the idler gear  28  tend to be modest, the axial members  54  may be needle thrust bearings or simple thrust washers. The radial loads handled by the radial bearings  52  can be large and, accordingly, the radial bearings  52  must be relatively wide. In this instance, a pair of radial needle bearings are used. Through the use of needle bearings as the radial bearings  52 , their narrow radial dimension allows for the larger first diameter  46  of the first part  44 . Utilization of radially thicker tapered roller bearings would require the diameter of the first part  44  to be decreased resulting in a decrease in the strength of the stationary shaft  34 . However, if a lower strength shaft was acceptable for a given design, tapered roller bearings could be utilized or, if reduced diameter tapered roller bearings were designed, they could be used. 
     In order to provide lubrication to the radial needle bearings  52 , the stationary shaft  34  is provided with one or more lubrication ports  56 ,  58 . The lubrication port  56  is located such that it delivers lubrication to annular space between the pair of radial needle bearings  52 . Accordingly, the lubrication port  56  includes a discharge opening on the exterior surface of the first part  44  of the stationary shaft  34 . To provide lubricant to the lubrication port  56 , another lubrication port  58  extends to the exterior surface of the shaft  34  at a location to entrain lubricant from the sump  60  of the power transfer unit  10 . As seen in the figure, the inlet opening of the lubrication port  58  is located in the region transitioning from the first part  44  to the second part  48 . To further facilitate the transfer of lubricant, the first part  44  of the stationary shaft  34  is provided with a hollow interior generally designated at  62 . Accordingly, both lubrication ports  56 ,  58  extend from the exterior surface of the shaft  34  to the hollow interior  62 . As will be readily appreciated, other locations for the ports may be employed. 
     In order to locate and retain the idler gear  28  on the first part  44  of the stationary shaft  34 , a shoulder  64  is formed on the stationary shaft  34  in the region transitioning from the first part  44  to the second part  48  and axial members  54  engage the shoulder  64 . Axial movement of the idler gear  28  in the opposing direction is limited by appropriate portions of the housing  12 . Initial retention of the idler gear  28  on the stationary shaft  34  may be achieved by a snap ring  66  received within an appropriately located groove in the first part  44  of the stationary shaft  34 . 
     From the idler gear  28 , rotation is transferred to a third gear, driven gear  68 , of the parallel gear set  16 . The driven gear  68  is supported by a driven shaft  70  which is in turn rotatably supported on bearings  72  within the housing  12 . The driven gear  68  may be fixed to the driven shaft  70  in a conventional manner, including unitarily forming the driven gear  68  with the driven shaft  70  (as illustrated) or welding the driven gear  68  thereto. To facilitate the transfer of rotation from the idler gear  28  to the driven gear  68 , external teeth  74  on the driven gear  68  engage the teeth  32  of the idler gear  28 . 
     Provided in the above described manner, the driven shaft  70  defines the third axis  76  of the parallel gear set; the second axis  78  being defined by the stationary shaft  34  and about which the idler gear  28  rotates. The power transfer unit  10  is therefore known as a three axis unit. 
     In order to transfer rotation from the parallel gear set  16  to the non-parallel gear set  14 , a first bevel gear, ring gear  80 , of the non-parallel gear set  14  is mounted to the driven shaft  70 . Often, the location and diameter of the ring gear  80  is such that the ring gear  80  would typically encroach upon the support shaft of an idler gear. For this reason, ring gears have conventionally been laterally spaced on the driven shaft so as to be staggered from the idler gear support. This in turn forces the power transfer unit to be wider than if the encroachment did not occur. With the present invention, the encroachment is accommodated so as to allow for reduced lateral compactness in the power transfer unit. Specifically, the location of the ring gear  80  on the driven shaft  70  is such that the ring gear  80  extends to an area adjacent to that part of the stationary shaft  34  having a smaller diameter  50 , the second part  48 . Since the stationary shaft  34  does not require support bearings, additional area is freed up to accommodate and accept the ring gear  80  without requiring staggering or axial spacing thereof along the driven shaft  70 . This results in the lateral compactness of the power transfer unit  10  being reduced. 
     The ring gear  80  is provided with teeth  82  which engage teeth  84  of a second bevel gear  86 . The second bevel gear  86  is supported by one end of the output shaft  20 . The second bevel gear may be supported by the output shaft  20  by conventional means including unitarily forming the bevel gear  86  with the output shaft  20  (as illustrated) or welding the bevel gear  86  to the output shaft  20 . The output shaft  20  is supported within the housing  12  by bearings  88  enabling rotation of the shaft  20  about axis  90 . As seen in  FIG. 2 , this second axis  90  of the non-parallel gear set  14  is generally oriented perpendicular to the axes  24 ,  76 ,  78  of the parallel gear set  16  and extends generally longitudinally with respect to the vehicle. 
     While not readily apparent in  FIG. 2 , the axes  76  and  90 , about which the ring gear  80  and the second bevel gear  86  respectively rotate, may be such that the axes  76  and  90  intersect one another or do not intersect one another. In the later situation, which is preferred, the non-parallel gear set  16  is a hypoid bevel gear set. 
     Referring now to  FIG. 3 , a second embodiment of a power transfer unit incorporating the principles of the present invention is generally illustrated therein and designated at  100 . Since the power transfer unit  100  incorporates many of the components and features illustrated and described in connection with  FIG. 2 , common elements have been given like reference numerals. The difference between the first and second embodiments lies within the manner in which the idler gear  28  is supported in the power transfer unit. Accordingly, it is not believed that a detailed discussion regarding all of the common components of the power transfer unit from the prior embodiment is required in connection with the second embodiment. The reader&#39;s attention is therefore directed to the preceding of the detailed description in that regard. The discussion which follows will be limited to the manner in which the idler gear  28  is supported in this second embodiment. 
     Similar to the first embodiment, the idler gear  28  of the second embodiment is rotatably supported on a stationary member  92  extending through the idler gear  28 . In the second embodiment, however, the stationary member  92  is a boss (“boss  92 ”). The boss  92  is unitarily formed with the housing  12  and extends from a first side  94  of the housing toward a second side  96  of the housing  12 . The boss  92  is thus formed as an extension off of the first wall  94  and includes a cylindrical wall  98  terminating at a closed end  102 . The exterior surface of the cylindrical wall  98  defines the bearing seat for the radial needle bearings  52 . Axially, the idler gear  28  is supported by axial support members  54 , which, again, may be needle thrust bearings or simple trust washers. In order to locate and retain the idler gear on the boss  92 , a shoulder  104  is formed about the outer periphery of the end wall  102 . While the boss  92  should be sufficiently stable and rigid on its own, the boss  92  may be further stabilized and located relative the second side  96  through the providing of an interlock  106  extending between the second side  96  of the housing and the end wall  102  of the boss  92 . While the interlock  96  may take many forms, it may include, but is not limited to, means such as dowels and pins. 
     To further facilitate the lateral compactness of the power transfer unit  100 , the end wall of the boss  92  preferably terminate adjacent to the corresponding lateral end of the idler gear  28 . The second side  96  of the housing is therefore formed with a recess  108  extending toward the interior of the power transfer unit  100  so as to be immediately adjacent to the end wall  102 . The recess  108  is formed and located such that the ring gear  80  extends to a location adjacent thereto and which is laterally adjacent to at least a portion of the boss  92 . 
     In order to provide lubrication to the radial needle bearings  52 , the boss  92  is provided with at least one lubrication port  110 . The lubrication port  110  includes a discharge opening in a radially exterior surface of the cylindrical wall  98 , which is located such that it delivers lubrication to the annular space between the pair of radial needle bearings  52 . The inlet opening of the lubrication port  110  is provided so as to extend through the end wall  102  of the boss  92  into the sump  60  of the power transfer unit. In this way lubricant can be entrained from the sump  60  to the radial needle bearings  52 . 
     As a person skilled in the art will readily appreciate, the above description is meant as an illustration of an implementation of the principles of this invention. This description is not intended to limit the scope or application of this invention in that the invention is susceptible to modification, variation and change, without departing from the spirit of this invention, as defined in the following claims.

Technology Classification (CPC): 8