Abstract:
A differential axle assembly for a work machine having a differential lock capability. The differential axle has a differential gear housing, which utilizes a sealed housing on the outside thereof and a bleed flow path for pressurized liquid lubricant actuating a differential lock feature to provide adequate cooling flow for the differential gear set and differential lock mechanism under heavy duty circumstances.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to work machines axles having differential gears and limited slip capability. 
       BACKGROUND OF THE INVENTION 
       [0002]    Over the years, work machines, particularly those that operate off highway, require a differential drive mechanism for sets of wheels to accommodate vehicle turning, but, in addition, require a limited slip feature so that torque may be transferred from a slipping wheel to one that can obtain better traction. This has evolved design efforts to the point where axles can accommodate significant torque levels and, at the same time, deal with variable traction on one or the other of the drive wheels. Design efforts have taken place that minimize windage losses in axle assemblies where a portion, or all, of the differential gears are immersed in a lubricating liquid. As a result of the improvements in reducing windage losses, the ability to cool and lubricate various components in the differential gear assembly is challenged. Specifically, the ability to provide adequate lubrication for all of the gears is constrained by the need for reducing windage losses. 
         [0003]    Accordingly, a need exists for an axle assembly with a differential feature that provides adequate lubrication of the components while, at the same time, reducing windage losses of the axle set. 
       SUMMARY 
       [0004]    In one form, the invention is an power train axle assembly including an elongated housing and first and second shafts journaled in the elongated housing for providing a rotary output shaft at the outer ends thereof. A differential gear housing is rotatably positioned within the elongated housing and receives the inner ends of the first and second shafts. A ring gear is fixed to the differential gear housing for receiving a rotary power input. A differential gear set is positioned within the differential gear set housing and has opposed gears fixed to the inner ends of the first and second shaft and are journaled relative to the differential gear set housing. A plurality of planetary gears are journaled within the differential gear housing and mesh with the opposed gears for providing a differential action. A fluid pressure actuated differential lock mechanism has one portion thereof fixed to the differential gear housing and the other to one of the opposed gears. A source of selective fluid pressure is fluidly connected to the differential lock mechanism and provides high and low pressure levels to selectively lock the differential gear housing and one of the gears. The differential gear housing has a bleed flow path to provide pressurized fluid flow into the differential gear housing irrespective of the pressure level with the differential gear housing having a controlled seal so that fluid passes inward and out to lubricate the gears. 
         [0005]    In another form, the invention is a work machine including a frame, a prime mover supplying power to the work machine, and a power train including an axle assembly, which has an elongated housing and first and second shafts journaled in the housing for providing a rotary output to wheels at outer ends of the first and second shafts. A differential gear housing is rotatably positioned within the elongated housing and receives the inner ends of the first and second shafts. A ring gear is fixed to the differential gear housing for receiving a rotary power input from the prime mover. A differential gear set is positioned within the differential gear housing and has opposed gears affixed to the inner ends of the first and second shafts with the gears being journaled relative to the differential gear housing. A plurality of planetary gears are journaled within the differential gear housing and mesh with the opposed gears for providing a differential action. A fluid pressure actuated lock mechanism has one portion thereof fixed to the differential gear housing and the other to one of the opposed gears. A source of selective fluid pressure is fluidly connected to the differential lock mechanism and provides high and low pressure levels to selectively lock and unlock the differential gear housing and one of the gears. The differential gear housing has a bleed flow path to provide pressurized flow into the differential gear housing interior irrespective of the pressure level with the differential gear housing having a controlled seal so that fluid passes inward and out to lubricate the gears. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings, wherein: 
           [0007]      FIG. 1  is a longitudinal section view of a work machine and an axle assembly embodying the present invention along with schematic illustrations of interconnections to additional components of the work machine; 
           [0008]      FIG. 2  is an expanded view of a portion of the axle assembly of  FIG. 1  showing a lubricant flow path. 
       
    
    
       [0009]    Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate one embodiment of the invention and such exemplifications are not to be construed as limiting the scope of the invention in any manner. 
       DETAILED DESCRIPTION 
       [0010]    Referring now to the drawings, and more particularly to  FIG. 1 , there is shown a work machine  10 , which includes a frame and a prime mover  12  mounted in the frame, usually in the form of a compression ignition, or diesel engine,  12 , which is mechanically interconnected by a shaft  14  to an appropriate transmission  16  and through mechanical connection  18  to an axle assembly generally indicated by reference character  20 . Axle assembly  20  includes left and right elongated housings  22  and  24  respectively mounted from a central housing  26 . Elongated housings  22  and  24  provide a journal support for shafts  28  and  30  extending to wheels  32  and  34  respectively. It should be apparent to those skilled in the art that the shafts  28  and  30  may be connected to the respective wheels through reduction gear sets in order to provide the torque requirements demanded of heavy duty work machines. The central housing  26  is generally annular in form, is appropriately suspended from work machine  10 , and provides a mounting for housings  22  through flange  38  by screws  36  and through flange  40  or housing  24  also by screws  36 . The outer ends of shafts  28  and  30  are connected to the wheels  32  and  34  respectively and the inner ends  42  and  44  extend into a differential gear housing  46  positioned within central housing  26 . 
         [0011]    Differential gear housing  46  has first and second annular housings  48  and  50  interconnected at about the center line thereof. As described below, annular housings  48  and  50  have a substantially sealed outer periphery so as to retain any liquid introduced to the interior thereof within the differential gear housing  46 . Housings  48  and  50  are journaled for rotation within the elongated housing  20  by bearing assemblies  52  and  54  respectively, ultimately fixed to the central housing  26 . The differential gearing housing half  48  has affixed to it a ring gear  56  by screws  58 . Ring gear  56  intermeshes with an UNSEEN input PINION gear receiving input from mechanical interconnection  18 . A pair of opposed end gears  62  and  64  are splined to and fixed to the inner ends of shafts  42  and  44  and are positioned within the differential gear housing  46 . 
         [0012]    As shown herein, end gear  62  and  64  are bevel gears and intermesh with bevel planetary gears  66  and  68  journaled within a differential gear housing  46 . As such, the input from prime mover  12  through ring gear  56  to differential gear housing  46  is transmitted to shafts  28  and  30  through planetary gears  66  and  68 . As a result, the differential load on the wheels is accommodated through the differential action of the planetary gear set  66  and  68  in a manner that is well-known and understood. 
         [0000]    Because work machine  10  is heavy duty and frequently used off road where there is a difference in traction between wheels  32  and  34 , a differential lock mechanism  70  is provided that selectively interconnects one of the shafts (in this case, shaft  28 ) to the differential gear housing  46  so as to transfer load between the shafts  28  and  30 . Differential lock mechanism  70  comprises an interdigitated series of annular plates  72  and  74  received within chamber  76  in housing  48  (see  FIG. 2 ). The annular plates  72  and  74  each have tabs  78  and  80  respectively received within slots  82  and  84  in the housing  48  and end gear  62  respectively. Plates  72  and  74  are acted on by an annular piston assembly  86  also received within chamber  76  and abutting an axial end face of one of the annular interdigitated plates  72 . To the left of piston assembly  86 , as shown in  FIG. 2 , there is a chamber  88  fluidly connected via primary passage  90  and  92  extending through housing  48  to passages  94  in housing  50  and ultimately to a connector  96  fixed to central housing  20 . The interconnection between the passages  92  and  94  and fitting  96  permits transmission of pressure when there is relative rotation between the differential gear housing  46  and central housing  20 . 
         [0013]    Pressure fitting  96  connects with an appropriate line  98  to a controller  100  directing pressurized flow from a pressurized flow source  102  through passages  98 , fitting  96 , passages  94  and  92  to chamber  88 . As illustrated herein, the fluid pressurized by system  102  is lubricant used to both reduce friction between the adjacent relatively rotating bearing parts and to provide a cooling function for the multi plate differential lock. The control system  100  uses appropriate control logic to apply the differential lock mechanism  70  as-needed to transfer torque from one axle to the other in conditions in which one of the two wheels has reduced traction. 
         [0014]    The differential axle assembly  20  is of a type that has efficient utilization of lubricant flow in order to reduce windage losses caused by gears rotating through liquid lubricant. In a standard differential housing arrangement, the housing for the opposed gears and planetary gears is significantly porous so that the differential gear set, when rotating, splashes through the liquid level within a chamber to lubricate the planetary and opposed gears. However, with efficient utilization of lubricant, there is insufficient liquid level to provide splash lubrication of the differential gear set including the differential lock assembly so as to meet the required heavy duty functions under extreme conditions. 
         [0015]    In accordance with the present invention, the differential gear housing  46  is provided with means for providing adequate lubricant and cooling functions from the liquid, while at the same time enabling efficient overall lubricant utilization. This function is shown particularly in  FIG. 2  in which the primary flow path  90  to chamber  88  has a bleed flow path  104  extending from inlet passage  90  to the opposite side of annular piston  86  and into the interdigitated set of discs  72  and  74 . The control system  100  directs a pressure supply from pressure source  102  of approximately 300 psi during engagement of the differential lock mechanism  70  but, in addition, provides a flow of a pressure level of between approximately 15-20 psi during disengagement of the differential lock mechanism  70  so as to provide a continuous flow of lubricant through passage  104  through the interdigitated discs  72  and  74 . Furthermore, unlike previous differential gear housings, this differential gear housing  46  has the outer periphery substantially sealed so that the liquid lubricant flowing in through bleed passage  104  is maintained at a level within differential gear housing  46  that provides lubrication of the differential gear set, namely, the end gears  62 ,  64 , and planetary gears  66  and  68 . The liquid lubricant flows from the differential gear housing  46  past gear splines and bearings adjacent the centerline into the interior of housings  22 ,  24  and  26 . When the differential lock mechanism  70  is actuated, the higher pressure flows into the disc set  72  and  74  to provide cooling thereof on account of the additional frictional forces. 
         [0016]    The above arrangement allows for a significant improvement in the efficiency and effectiveness of the axle assembly  20  in that windage losses within the central housing  26  are minimized but, at the same time, adequate liquid coolant level is maintained within differential gear housing  46  to lubricate and cool the gear set and bearings, even under the most extreme conditions encountered in an off road heavy duty work machine. 
         [0017]    While this invention has been described with respect to at least one embodiment, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.