Abstract:
A brake assembly having a single brake capable of applying a braking torque to both axle half shafts in a drive axle is provided. The brake assembly includes a piston that selectively actuates both a differential locking clutch and a braking clutch each of which may comprise a friction plate assembly. The piston urges the differential locking clutch against a friction surface formed on a differential hub that is mounted on a differential carrier and is axially movable relative to the carrier. The braking clutch is then urged by movement of the differential hub against another braking surface formed on a stationary brake housing. The plates of the braking clutch are coupled to the differential carrier allowing a braking torque to be transmitted through the carrier to both axle half shafts using a single braking device.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to vehicle wheel differentials and, in particular, to a brake assembly for use with the differential. 
     2. Disclosure of the Related Art 
     A conventional drive axle assembly for driving one or more wheels on opposite sides of a vehicle includes a drive axle comprised of two axle half shafts. The axle assembly further includes a differential that drives the axle half shafts and enables the shafts to rotate at different speeds. The axle assembly further includes two separate braking devices used to brake the wheel or wheels driven by the respective axle half shafts. 
     The use of multiple braking devices to brake the driven wheels has several disadvantages. For example, the use of multiple braking devices requires additional parts and materials and increases assembly time-all of which increase the cost of the drive axle assembly. The use of multiple braking devices also increases the size and weight of the drive axle assembly. 
     U.S. Pat. No. 3,994,375 illustrates the use of a single brake assembly for use in braking the wheels on both sides of the drive axle. The disclosed brake assembly, however, still requires the use of multiple actuators and significantly increases the size of the axle and differential housings thereby creating potential interference with other vehicle components. 
     There is thus a need for a brake assembly that will minimize or eliminate one or more of the above-mentioned deficiencies. 
     SUMMARY OF THE INVENTION 
     The present invention provides a brake assembly for a drive axle. 
     A brake assembly for a drive axle in accordance with the present invention includes a brake housing. The brake housing may be coupled to a differential carrier that is disposed about a first axis and the brake housing may include a first portion extending radially and a second portion extending axially from the first portion. The brake assembly also includes a differential hub that is coupled to the differential carrier and is axially movable relative to the differential carrier and the brake housing. The brake assembly further includes first and second friction plate assemblies. The first friction plate assembly is disposed on a first side of the differential hub between the differential hub and the brake housing and is axially movable relative to the differential carrier and the brake housing. The second friction plate assembly is disposed on a second side of the differential hub and is also axially movable relative to the differential carrier. Finally, the brake assembly includes a piston that selectively urges the second friction plate assembly, the differential hub, and the first friction plate assembly in a first axial direction against the brake housing. The inventive brake assembly both provides locking capacity to the differential, thereby preventing or limiting the two axle half shafts of the drive axle from rotation at different speeds, and provides braking capacity to the axle half shafts for stopping the vehicle. 
     A brake assembly in accordance with the present invention represents a significant improvement as compared to conventional drive axle brake assemblies. In particular, the use of a single brake assembly to brake the driven wheels reduces the number of parts and materials required as compared to conventional drive axle assemblies and decreases assembly time thereby reducing the cost of the drive axle assembly. The use of a single brake assembly also decreases the size and weight of the drive axle assembly relative to conventional drive axle assemblies. 
     These and other features and objects of this invention will become apparent to one skilled in the art from the following detailed description and the accompanying drawings illustrating features of this invention by way of example. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a top view of a drive axle assembly. 
     FIG. 2 is a partial cross-sectional view of the drive axle assembly of FIG. 1 illustrating a brake assembly in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the drawings wherein like reference numerals are used to identify identical components in the various views, FIG. 1 illustrates a drive axle assembly  10  disposed about an axis  12 . Assembly  10  is provided to drive one or more wheels disposed at either axial end of assembly  10 . The illustrated assembly  10  is configured for use with an off-highway vehicle. It should be understood, however, that the present invention may find use in wide variety of conventional vehicles. Assembly  10  includes axle half shafts  14 ,  16  and a differential  18 . Referring to FIG. 2, assembly  10  may also include a brake assembly  20  in accordance with the present invention. 
     Referring again to FIG. 1, shafts  14 ,  16  are provided to transfer torque to one or more vehicle wheels disposed at either axial end of assembly  10 . Shafts  14 ,  16  are conventional in the art and may be disposed within an axle housing  22 . 
     Differential  18  is provided to allow shafts  14 ,  16 , and wheels, to rotate at different speeds. Differential  18  is also conventional in the art. Referring to FIG. 2, differential  18  may include a differential carrier  24 , a pinion shaft  26 , and a differential gear set  28 . 
     Carrier  24  is provided to transfer torque from a power input shaft  30  to gear set  28 . Carrier  24  may be made from conventional metals and metal alloys. Carrier  24  is disposed about axis  12  and includes first  32  and second members  34  that may be coupled together using conventional fasteners (not shown). Members  32 ,  34  are supported within the differential  18  and axle housings  22  on bearings  36 ,  38  and rotate responsive to torque provided by input shaft  26  through a pinion gear  40  mounted to one end of shaft  26  and a ring gear  42  coupled to, or integral with member  32 . Members  32 ,  34  together define a cavity  44  configured to receive gear set  28 . Members  32 ,  34  further define corresponding recesses  46 ,  48  configured to receive pinion shaft  26 . Finally, members  32 ,  34  define openings  50 ,  52  configured to receive axle half shafts  14 ,  16  and from which axle half shafts  14 ,  16  extend. Member  32 ,  34  further includes an axially extending portion  54  having one or more splines  56 . 
     Pinion shaft  26  is provided to transfer torque from carrier  24  to gears  58 ,  60  of gear set  28 . Shaft  26  is conventional in the art and may be made from conventional metals and metal alloys. Shaft  26  has a longitudinal axis  62  perpendicular to axis  12  and is received within recesses  46 ,  48  of members  32 ,  34  of carrier  24 . Gears  58 ,  60  are mounted to shaft  26  proximate either end of shaft  26 . 
     Gear set  28  is provided to transfer torque to axle half shafts  14 ,  16  and is convention in the art. Gears  58 ,  60  are disposed about pinion shaft  26  while gears  64 ,  66  are disposed about axle half shafts  14 ,  16 , respectively. Rotation of gears  58 ,  60  responsive to rotation of pinion shaft  26  and carrier  24  causes a corresponding rotation in gears  64 ,  66  and axle half shafts  14 ,  16 . 
     Brake assembly  20  is provided to brake rotation of axle half shafts  14 ,  16  and, therefore, the wheels disposed on either axial end of drive axle assembly  10 . In accordance with the present invention, assembly  20  may include a brake housing  68 , a differential hub  70 , a first friction plate assembly  72 , a second friction plate assembly  74 , and a piston  76 . Assembly may also include an adapter hub  78  and a thrust bearing  80 . 
     Brake housing  68  is provided to support and enclose several components of brake assembly  20  and also provides a friction surface used in braking axle half shafts  14 ,  16 . Housing  68  may be made from conventional metals and metal alloys known in the art. Housing  68  may include a first portion  82  and a second portion  84 . First portion  82  may extend generally radially outward from carrier  24  and may be supported thereon by bearings  36 . Second portion  84  may extend axially from first portion  82  and may include an axially extending bore  86 . Bore  86  may align with corresponding bores in axle housing  22  and differential housing  88  and may be sized to receive a fastener  90  such as a screw or bolt therethrough. Second portion  84  may also include one or more axially extending splines  92  on a radially inward side  94  for a purpose described hereinbelow. 
     Hub  70  is provided to support components of friction plate assembly  74 . Hub  70  also compresses friction plate assembly  72  upon actuation of brake assembly  20  and provides a friction surface against which friction plate assembly  72  acts. Hub  70  may be made from conventional metals and metal alloys. Hub  70  may be disposed about axis  12  and may have a generally radially extending portion  96  coupled to carrier  24  on spline(s)  56  such that hub  70  may be axially movable relative to carrier  24  and/or brake housing  20 . Hub  70  may include an axially extending portion  98  coupled to, or a integral with, portion  96 . Portion  98  may include one or more axially extending splines  100  for a purpose described hereinbelow. 
     First friction plate assembly  72  functions as a braking clutch. Assembly  72  is disposed on a first side  102  of differential hub  70 , between hub  70  and portion  82  of brake housing  68  and is axially movable relative to hub  70  and brake housing  68 . Assembly  72  may include one or more conventional friction plate members  104  and one or more corresponding conventional reaction plate members  106 . In the illustrated embodiment, assembly includes four friction plate members  104  and four reaction plate members  106 . It should be understood, however, that the number of members  104 ,  106  may vary without departing from the spirit of the present invention. Friction plate members  104  may be coupled to carrier  24  through spline(s)  56  on carrier  24  while reaction plate members  106  may be coupled to brake housing  68  through spline(s)  92  on housing  68 . 
     Second friction plate assembly  74  functions as a differential clutch or locking device. Assembly  74  is disposed on a second side  108  of differential hub  70  and is axially movable relative to carrier  24 . Assembly  74  may also include one or more conventional friction plate members  110  and one or more corresponding conventional reaction plate members  112 . In the illustrated embodiment, assembly includes two friction plate members  110  and two reaction plate members  112 . It should again be understood, however, that the number of members  110 ,  112  may vary without departing from the spirit of the present invention. Friction plate members  110  may be coupled to adapter hub  78  as described hereinbelow. Reaction plate members  112  may be coupled to portion  98  of differential hub  70  through spline(s)  100 . 
     Piston  76  is provided to selectively urge second friction plate assembly  74 , differential hub  70 , and first friction plate assembly  72  in an axial direction against first portion  82  of brake housing  68 . Piston  76  may be actuated by fluid pressure (e.g., hydraulic or pneumatic) in a known manner. Piston  76  may be disposed within axle housing  22  and may be configured to receive a dowel pin  114  extending from housing  22  by which piston  76  may be fixed against rotation. The size and shape of piston  76  may be varied relative to design considerations associated with axle housing  22 . 
     Adapter hub  78  is provided to support friction plate members  110  of friction plate assembly  74 . Hub  78  may be made from conventional metals and metal alloys. Hub  78  may be annular in construction and may be disposed about axis  12  and coupled to axle half shaft  14  through one or more splines (not shown). Hub  78  may itself include one or more splines  116  on which friction plate members  110  of assembly  74  may be supported for axial movement. Hub  78  may be adjacent to portion of  54  carrier  24 . 
     Thrust bearing  80  is provided to absorb axial thrust from piston  76  and is conventional in the art. Bearing  80  is disposed between piston  76  and assembly  74 . 
     Brake assembly  20  operates as follows. When piston  76  is actuated, piston  76  moves in a first axial direction (to the right in FIG.  1 ). Piston  76  (which may act through thrust bearing  80 ) compresses friction plate assembly  74  causing friction plate members  110  and reaction plate members  112  to move axially along splines  100 ,  116 , respectively, and against the friction surface provided by differential hub  70 . Hub  70  also moves axially along spline(s)  56  and compresses friction plate assembly  72  causing friction plate members  104  and reaction plate members  106  to move axially along spline(s)  56  and against the friction surface provided by portion  82  of brake housing  68 . Braking torque is transferred to carrier  24  through portion  54  of carrier  24  thereby preventing rotation of carrier  24  which in turn prevents rotation of both axle half shafts  14 ,  16 . 
     When a vehicle incorporating axle assembly  10  is on dry ground and stopping in a straight line, there is no relative rotation between carrier  24  and axle half shaft  14 ,  16 . As a result, assemblies  72 ,  74  are rotating in unison and the braking torque is generated by assembly  72 . 
     When a vehicle incorporating axle assembly  10  is on dry ground and stopping in a curved path, relative rotation occurs between friction plate members  110  and reaction plate members  112  of assembly  74 . This relative rotation generates a torque biasing action that provides a greater amount of braking torque to the inside wheel (relative to the turn). 
     When a vehicle incorporating axle assembly  10  stops in a straight line and there is very poor traction between the vehicle and ground (such as when one wheel is on concrete and the other wheel is on ice) and a maximum brake pressure is applied through piston  76 , friction plate assembly  72  immediately stops differential carrier  24  from rotating. Because the bias ratio of friction plate assembly  74  may be exceeded, the differential  18  and assembly  74  may begin to spin. In this event, assembly  74  will provide the braking torque with a majority of the torque provided to the wheel having superior traction (e.g., the wheel on concrete). 
     A brake assembly  20  in accordance with the present invention represents a significant improvement as compared to traditional brake assemblies for drive axles. Traditional brake assemblies have two brakes in the axle, one for each wheel. The use of multiple braking devices requires additional parts and materials and increases assembly time-all of which increase the cost of the drive axle assembly. The use of multiple braking devices also increases the size and weight of the drive axle assembly. The inventive brake assembly  20  is less expensive to manufacture because fewer materials are needed, yet maintains effective brake capacity and vehicle handling characteristics. 
     While the invention has been particularly shown and described with reference to the preferred embodiments thereof, it is well understood by those skilled in the art that various changes and modification can be made in the invention without departing from the spirit and scope of the invention.