Abstract:
A braking system for a final drive for a wheel assembly of an independently powered wheeled vehicle. The system includes a service brake having a displaceable element actuatable to retard rotation of the individual wheel assembly. A park brake is positioned closely adjacent to the service brake and is actuatable independently of the service brake to displace the displaceable element to retard rotation of the wheel. Both the service brake and park brake are accessible without disturbing an electric motor with which they are associated.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to brake assemblies, and more specifically to brake assemblies incorporated in final drives of axles used in heavy duty vehicles. 
       BACKGROUND OF THE INVENTION 
       [0002]    When a vehicle&#39;s weight goes beyond a threshold of about 20 metric tons it is frequently more cost effective to use a vehicle power train that incorporates a large internal combustion engine such as a diesel engine connected to a generator. Through appropriate control systems, the generator powers electric motors for final drives in individual axles. This type of power train enables a great deal of flexibility in the application of torque, speed, and/or braking to individual wheels for the vehicle. Such a feature is particularly advantageous for off-road vehicles that have to negotiate difficult and un-even terrain. 
         [0003]    Such vehicles have service brake assemblies adjacent the wheel powered by the final drive. In addition, such vehicles require park brakes to hold the vehicle stationary when it is not in an operational mode. Typically, park brakes have been incorporated somewhere on the electric motor shaft that is connected to the wheel hub through a speed reduction transmission. These park brake assemblies have the disadvantage of crowding the overall installed envelope for the electric motors and making it difficult to direct high current cables from the motor to a central current supply and control system for the vehicle. 
         [0004]    In addition, it becomes difficult to service such park brakes because it usually is necessary to remove the wheel assembly and then remove the motor to gain access to the park brake. Braking systems have a finite service life so that periodic maintenance and replacement is necessary over the vehicle life. By providing the park brake adjacent the motor, servicing costs and complexity are greatly increased. 
         [0005]    What is therefore needed in the art is a brake assembly avoiding the problems of the previous systems. 
       SUMMARY OF THE INVENTION 
       [0006]    The invention, in one form, includes a braking system for a final drive for a wheel assembly. The system includes a service brake having a displaceable element actuatable to retard rotation of the wheel assembly. A park brake is closely adjacent the service brake and is actuatable independently of the service brake to displace the displacable element to retard rotation of the wheel. 
         [0007]    In another form the invention includes a vehicle having a chassis in which a prime mover powers an electric generator and a plurality of axle assemblies having electric motors as a portion of a final drive for individual wheels. A service brake system has a displaceable element actuatable to retard rotation of the wheel assemblies. A park brake is positioned closely adjacent the service brake and is actuatable independently of the service brake to displace the displaceable element to retard rotation of the wheel. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  shows a schematic drawing of a vehicle embodying a brake system in accordance with the present invention; 
           [0009]      FIG. 2  is a longitudinal section view of a brake assembly and associated final drive elements for one embodiment of the present invention; 
           [0010]      FIG. 3  is a longitudinal section view of a brake assembly and associated final drive elements which embodies an alternative form of the present invention; and 
           [0011]      FIG. 4  is a longitudinal section view of a brake assembly and associated final drive elements for still another embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0012]      FIG. 1  shows a large capacity, off-road vehicle  10  in schematic form. Vehicle  10  has a chassis or frame  12  supporting axle assemblies  14  and  16 . Each axle assembly supports a rotatable wheel  18 . Typically, the axles would have mechanisms for steering one or both sets of axles. However, these details are not shown to simplify the understanding of the invention. The vehicle  10  has a prime mover  20 , usually in the form of a diesel engine which mechanically drives a generator  22 . Current from generator  22  is connected by appropriate control systems and cables (also not shown) to electric motors in final drives  23  positioned in the axle assemblies adjacent the wheels  18 . 
         [0013]    The final drives  23  each have a braking system in accordance with the present invention that is described in detail in  FIGS. 2 and 3 . The braking system utilizes pressurized fluid from a pump  24  driven by engine  20  through a mechanical connection  25 . Pump  24  distributes the pressurized fluid, usually in liquid form, via lines  26  to the brake assemblies located at each wheel  18 . 
         [0014]      FIG. 2  shows a first embodiment of the brake assembly, generally indicated by reference character  28 . Brake assembly  28  comprises an annular adapter plate  30  secured to the end of an axle tube  32  of the axle assemblies  14  and  16  by screws threaded into bores  31 . The axle tube  32  houses the electric motor  34 , shown schematically by dashed lines within the final drive  23 . The adapter plate  30  has a central opening, generally indicated by  36 , that provides a journaling function for a shaft (not shown) connecting the output of the motor  34  to a final drive gear box  38 . An annular wheel spindle  40  is secured to the adapter plate  30  by appropriate screws (not shown) and forms a base for a pair of bearing assemblies  42  and  44 . Bearing assemblies  42  and  44  provide rotational and axial mounting of a wheel bearing housing  46  that is annular in shape. Wheel bearing housing  46  has a flange  48  that provides a mounting for a rim  50  for the wheel assemblies  18 . 
         [0015]    An annular brake housing  52  is secured to the adapter plate  30  by appropriate screws (not shown) and extends towards flange  48 . Brake housing  52  has an annular chamber  54  providing a housing for a series of brake discs and separator plates, generally indicated by reference character  56 . The brake discs and separator plates  56  are alternatively keyed to the wheel bearing housing  46  and to the brake housing  52  by appropriate splines (not shown to enable a clearer understanding of the present invention). An annular reaction surface  58  is positioned at one end of chamber  54  and an annular service brake displaceable element  60  is positioned at the opposite end of chamber  54 . Element  60  has a flange  62  abutable against the discs and separator plates  56  and an annular piston element  64  received in a bore  66  in housing  52 . Springs (not shown) urge flange  62  away from reaction surface  58  so that, in the absence of fluid pressure, the state of the brake assembly  28  is disengaged with the action of the springs. 
         [0016]    The chamber within bore  66  has a first connection, shown by dashed line  68 , to the fluid supply system  26  to pressurize the end face  70  of element  60  and urge it towards the reaction surface  58  to engage the brake discs and separator plates  56 . A pair of annular brake seals  72  are positioned between end face  70  and a central retaining ring assembly  74 . The seals  72  provide sealing of fluid pressure within chamber  66  and the end face  70 . Pressurization of line  68  urges the element  60  against the brake discs and separator plates  56  to retard movement of the gear box  38  and rim  50  for the wheel assembly  18 . 
         [0017]    A park brake piston assembly  76  is also retained within brake housing  52 . Park brake piston  76  comprises an internal axially extending element  78  that, in the illustrated position, abuts the flange  62  of element  60 . Park brake piston  76  has a flange  80  that is acted on by springs (not shown) in the leftmost portion of bore  66  to urge park brake piston  76  against displaceable element  60 . It should be noted that the outer diameter of axially extending element  78  forms a portion of the chamber within bore  66  for the fluid pressure actuation of the brake assemblies. A pair of seals  82  to the left of retaining ring  74  in  FIG. 2  provides a seal for pressurized fluid that is introduced between the seals via passageway shown by dashed line  84 . Passageway  84  in turn is connected to the fluid line  26  for the overall braking system. 
         [0018]    In operation, the motor  34  drives the wheel rim  50  through the gear box  38 . When it is desired to retard the movement of wheel rim  50 , fluid pressure is provided via line  68  to the bore  66  to the right of retaining ring  74 . This urges the displaceable element  60  towards the reaction plate  58  to cause the brake disc and separator plates  56 , each of which have been keyed respectively to the wheel bearing housing  46  and the brake housing  52  to retard movement of the wheel rim  50 . The spring elements (not shown) urge the flange  62  away from the reaction surface  58  to disengage the brake discs and separator plates  56 . 
         [0019]    The park brake function is provided by the element  76  which has springs (not shown) to urge the axially extending portion  78  against moveable element  60  to, in turn, urge it towards the reaction surface  58  and thus retard movement of the wheel rim  50 . In order for the park brake to be released, fluid pressure is applied through passage  84  to urge the element  76  away from the moveable element  60 , allowing its associated spring elements to urge it out of engagement and thus release the brake assembly. With the arrangement set forth, a common fluid supply may be used to lines  26  to the wheel assemblies to control the service brake and park brake function. It should be apparent to those skilled in the art that appropriate valves are located at some point in the system to enable fluid pressure to independently. Furthermore, the pressure actuating the park brake element  76  may be controlled to be higher than that for the service brake moveable element  60 . 
         [0020]    By providing the park brake function closely adjacent the service brake function, additional space is freed up in the axle tube for the motor  34  and the electrical connections to the motor. Furthermore the arrangement set forth permits the brake functions and specifically the park brake to be serviced without disturbing the electric motor  34  and its associated components. This is done simply by removing the wheel and the elements to disengage the brake housing from the adapter plate to enable servicing of the various wearable elements in the component. 
         [0021]      FIG. 3  shows an alternative to the brake assembly of  FIG. 2 . In  FIG. 3  an adapter plate  86  is connected to the axle tube flange  88 . The electric motor  34  is secured to the axle tube flange  88  and has a shaft  90  for connection with a drive train to a reduction gear box (not shown). Adapter plate  86  provides a mounting for an annular wheel spindle  92  which is also secured to adapter plate  86  by appropriate screws (not shown). Wheel spindle  92  provides a mounting for bearing assemblies  94  that in turn journal an annular wheel bearing housing  96 . An annular brake housing  98  attaches to adapter plate  86  by appropriate screws (not shown). Wheel bearing housing  96  connects to an annular element  100  that contains a reduction gear drive to ultimately drive a wheel assembly  18 . 
         [0022]    Brake housing  98  has a displaceable brake element  102  having an integral flange  104  adjacent a series of brake disks and separator plates  106 . The brake disks and separator plates  106  are retained between flange  104  and a reaction surface  108  on adapter plate  86 . The displaceable element  102  has a cylindrical portion  110  received within a bore  112  of brake housing  98  that connects with a smaller diameter bore  113 . A seal  114  on displaceable element  102  provides a seal for pressurized fluid. Displaceable element  102  has an axial extension  116  that abuts a park brake element  118 . Park brake element  118  has a flange  120  that abuts the end of axial extension  116  of moveable element  102 . A pair of seals  122  also provide a seal for pressurized fluid within the bores  112  and  113  in brake housing  98 . The rightmost seal  22  is retained axially to be immovable and provide a separator between chambers on opposite sides in bore  113 . The flange  104  is urged away from reaction surface  108  by spring assemblies (not shown). The park brake element  118  is urged in a direction to abut the end of axial element  116  and thus urge displaceable element  102  to engage the brake disks and separator plates  106  to retard movement of the wheel bearing housing  96  and thus the wheel  18 . Fluid connections for the displaceable element  102  and the park brake element  118  are provided by dashed lines  124  and  126 , respectively. 
         [0023]    In operation, when it is desired to operate the wheel assemblies, the fluid pressure is provided via line  126  between seals  122  and thus urge park brake element  118  away from displaceable element  102  and permit rotation of the wheel assemblies. This is so because of the action of the springs urging flange  104  away from reaction surface  108 . When it is necessary to engage the disks and separator plates, fluid pressure is applied and via line  124  to urge displaceable element  102  to the right in  FIG. 3  and against reaction surface  108 . 
         [0024]    The embodiment shown in  FIG. 3  also has the advantage of maintaining the brake assembly totally outside the axle tube and motor housing so that brake assemblies can be easily serviced without disturbing either the motor structure or the electrical connections thereto. It should be noted that this has the ability to utilize the same fluid pressure for the service brake and park brake function as in the embodiment of  FIG. 2 . 
         [0025]      FIG. 4  shows still another version of the brake assembly in which an adapter plate  128  is secured by appropriate screws to an axle tube (not shown). An annular wheel spindle  130  is secured to adapter plate  128  by appropriate fasteners and provides the mounting for annular bearing assemblies  132  which in turn support and journal wheel bearing housing  134 . Wheel bearing housing  134  has a flange  136  that provides an appropriate connection to a wheel assembly  18 . An annular brake housing  138  is fastened to adapter plate  128  and axle tube (not shown) through bores  140  by appropriate fasteners. Brake housing  138  has a plurality of disks and separator plates generally indicated by reference character  142 . Disks and separator plates are positioned between a reaction plate  143  and a flange  144  of a moveable brake element  146 . Moveable brake element  146  has an axial portion  148  extending within bore  150  in bearing housing  138 . 
         [0026]    The end of axial extension  148  abuts a flange  152  of a park brake element  154 . The axial extension  148  of displaceable element  146  defines the inner diameter of chambers between a leftmost seal  156  and a central seal  158  retained between two retaining rings  160  and a rightmost seal  162 . The leftmost seal  156  and the center seal  158  provides a seal relative to the service brake element  154 . The center seal  158  and the rightmost seal  162  provides a seal relative to the park brake element  154 . 
         [0027]    Supply pressure via a fitting  164  provides fluid pressure to urge displaceable element  146  to the left as shown in  FIG. 4  and park brake element  152  to the right as shown in  FIG. 4 . Spring assemblies  164  and  166  respectively urge the displaceable element  146  out of engagement and the park brake element  152  into engagement, respectively. In the embodiment of  FIG. 4 , an access port  168  is provided to allow inspection of the wear on the disks and separator plates  142 . 
         [0028]    The operation of the brake system shown in  FIG. 4  is similar to that for the other figures in that fluid pressure is applied to urge displaceable element  146  into engagement with the disks and separator plates  142  to retard rotation of wheel bearing housing  134 . The spring packs  164  urge displaceable element away from reaction plate  142  so that in the absence of fluid pressure the brakes are disengaged. 
         [0029]    The park brake element  154  is urged against the axial extension  148  of moveable element  146  to urge the disks and separator plates against reaction surface  142  to engage the brake in the absence of fluid pressure by the action of the spring packs  166 . Fluid pressure is applied to the left of park brake element  154  to urge it against the action of the spring packs  166  thus releasing pressure on the moveable element  146  and allowing the springs  164  to move displaceable element  146  out of engagement. 
         [0030]    This configuration also permits disassembly of the brake assembly without altering the structural connections for the electric motor. In addition through access port  168  it allows the visibility of the tab on the moveable element  146  to determine wear and inspection of the disks and separator plates  142 . Furthermore it has the advantage of three brake seals instead of the normal four thereby minimizing the number of wear elements in the system. 
         [0031]    Having described the preferred embodiment, it will become apparent that various modifications can be made without departing from the scope of the invention as defined in the accompanying claims.