Abstract:
A tubular vehicle axle includes a primary air brake actuator within the axle. A tubular wall of the axle defines a pressure vessel of the primary actuator. The primary actuator has an output axis coincident with a rotary axis of the axle. An auxiliary air actuator can be directly operable on the primary actuator.

Description:
REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims priority to Great Britain Patent Application GB 0608740.7 filed on May 3, 2006. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     This invention relates generally to vehicle braking systems, and in particular with actuators for wheel brakes of commercial vehicles.  
         [0003]     Passenger and light commercial vehicles generally use hydraulic fluid as an actuation medium in a closed system. Heavy commercial vehicles rely upon air under pressure as the actuating medium; such systems are open in that air is exhausted to atmosphere from a vicinity of wheel brakes.  
         [0004]     One difficulty with air systems is that the necessary air actuator has a relatively large diameter and axial length in order to achieve the necessary actuation force, while keeping piston travel and lever ratio within acceptable limits. Such an actuator is typically mounted on a backplate of a drum brake, or directly onto a caliper of a disc brake, and protrudes into a wheel arch space. However, the space available is severely constrained by the vehicle chassis, the suspension, the axle, the hub and the wheel design.  
         [0005]     What is required is an improved actuator which has a reduced space requirement, but remains compatible with existing actuation systems and wheel brake components.  
       SUMMARY OF THE INVENTION  
       [0006]     According to a first aspect of the invention, there is provided a primary air brake actuator of a vehicle. A housing of the primary air brake actuator includes an axle of the vehicle. A tubular wall of the axle defines a pressure vessel of the primary air brake actuator. According to a second aspect of the invention, a tubular axle of a vehicle defines a primary air brake actuator within the tubular axle, and a tubular wall of the tubular axle defines a pressure vessel of the primary air brake actuator.  
         [0007]     A moving component of the primary air brake actuator may be a diaphragm anchored relative to an inner surface of an axle wall. The moving component may be a piston slidable directly on the inner surface of the axle wall. The primary air brake actuator may alternatively be a self-contained unit including a drum-like housing and adapted for insertion and retention within the axle housing.  
         [0008]     In one embodiment, the primary air brake actuator has an output rod co-axial with an axis of rotation of the axle and a corresponding lever protruding through a casing to operate a brake of the axle. In one embodiment, the lever is generally radial of the axis of rotation and is pivoted immediately adjacent a radially outer end. The lever passes through a narrow slot in a wall of the axle, and the slot extends parallel to the axis.  
         [0009]     In one embodiment, the axle further defines an auxiliary air brake actuator in series with the primary air brake actuator, and in one example axially inboard of the primary air brake actuator. The auxiliary air brake actuator is the springboard kind in which air under pressure holds the auxiliary air brake actuator in an off condition. The moving component of the auxiliary air brake actuator may be a diaphragm or piston of the type mentioned above. The primary and auxiliary air brake actuators can be co-axial and on a rotary axis of the axle.  
         [0010]     In one embodiment, a helical spring is provided inboard of the auxiliary air brake actuator and is operable to urge the moving component axially outward. The helical spring is anchored directly on an interior of the axle housing, in one example.  
         [0011]     According to a further aspect of the present invention, there is provided a tubular vehicle axle having a primary air brake actuator in the tubular vehicle axle. The primary air brake actuator has an output axis coincident with a rotary axis of an axle.  
         [0012]     According to a still further aspect of the present invention, there is provided a tubular vehicle axle having a primary air brake actuator in the tubular vehicle axle and an auxiliary air actuator in the tubular vehicle axle and directly operable on the primary air brake actuator. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]     Other features of the invention will be apparent from the following description of an embodiment with reference to the accompanying drawings in which:  
         [0014]      FIG. 1  is a schematic representation of a prior art brake arrangement;  
         [0015]      FIG. 2  is a schematic representation of a brake arrangement according to the present invention; and  
         [0016]      FIG. 3  is a more detailed schematic representation of the kind of arrangement illustrated in  FIG. 2 . 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0017]     With reference to the drawings,  FIG. 1  illustrates a conventional arrangement in which a vehicle axle  11  has a centerline axis  12 . Rotatable about the centerline axis  12  is a hub  13  having a flange  14  for vehicle wheel studs  15  and a brake rotor  16 . A brake caliper  17  extends on either side of the brake rotor  16  and has an actuator  18  whereby opposite brake pads (not shown) can be urged against opposite annular faces of the brake rotor  16 . The actuator  18  generally includes a cylindrical container within which a piston or diaphragm can be urged axially by the admission of air under pressure to one side. Typically, the actuator  18  acts via a lever onto a pad centerline, and a suitable wear adjuster and return spring is incorporated. The brake caliper  17  may be fixed, but is more typically floating. Brake torque is reacted by suitable mountings of the vehicle axle  11 .  
         [0018]     In the inventive arrangement according to  FIG. 2 , the actuator  18  is housed within a tubular axle  21 , which in this embodiment acts directly acts as a cylinder for a piston  22 . A lever  23  passes through a slot  24  in the tubular axle  21  to actuate brake pads. Suitable return spring and dust bats are provided. A much smaller housing  25  is provided on a body of the brake caliper  17 , thus making valuable space available in a wheel arch area inboard of the brake caliper  17 . Because the space within the tubular axle  21  is not used for any other purpose, there are no consequent space constraints for other components. Furthermore, an entire axial length of the tubular axle  21  is available for use, which means that travel restrictions of conventional actuators need not apply.  
         [0019]     A detailed schematic arrangement is illustrated in  FIG. 3 , in which an undriven tubular axle  31  has a reduced diameter end portion on which a rotatable hub  32  is mounted via suitable roller bearings. A brake rotor  33  is bolted to and rotatable with the rotatable hub  32 , and the brake rotor  33  extends inboard of the rotatable hub  32 . Located over the brake rotor  33  is a floating brake caliper  34  having opposite brake pads  35 . The floating brake caliper  34  is anchored on the tubular axle  31  in any suitable manner to resist braking torque.  
         [0020]     An actuation assembly  36  includes a housing  37  and one end  38  of a lever  39  pivoted in the housing  37 . The lever  39  acts directly on an inboard brake pad via an adjuster mechanism  41  and indirectly on an outboard brake pad via a usual caliper yoke  42  (such an arrangement is conventional).  
         [0021]     Within the tubular axle  31  is provided a primary piston  43  having a strut  44  acting as the other end  45  of the lever  39 . Inboard of the primary piston  43 , a partition wall  46  defines a closed chamber  47  having an inlet/outlet port  48  in the wall of the tubular axle  31 .  
         [0022]     An auxiliary piston  49  defines a closed chamber  50  on the other side of the partition wall  46 . An inlet/outlet port  51  is in the wall of the tubular axle  31 . The auxiliary piston  49  has a strut  52  which extends in a sealed manner through the partition wall  46 , as illustrated in  FIG. 3 . A heavy coil spring  53  urges the auxiliary piston  49  in an outboard direction and reacts against an internal abutment of the tubular axle  31 , which is not shown. Suitable boots  54  and  55  seal the interior of the tubular axle  31  against moisture and dirt.  
         [0023]     In use, admission of air under pressure via the inlet/outlet port  48  causes the primary piston  43  to move to the right as viewed in  FIG. 3 , thus causing the lever  39  to pivot clockwise and apply the brake pads to the brake rotor  33  via the adjuster  41 . When the inlet/outlet port  48  is connected to exhaust, the primary piston  43  returns. An additional release spring may be provided if necessary.  
         [0024]     The auxiliary piston  49  provides a park brake/emergency brake. In normal operation, air under pressure is admitted via the inlet/outlet port  51  so that the auxiliary piston  49  is urged to the right as viewed in  FIG. 3 , compressing still further the heavy coil spring  53 . If air is exhausted from the closed chamber  50 , the auxiliary piston  49  moves to the left under the action of the heavy coil spring  53 , and the strut  52  directly acts on the primary piston  43  to apply the brake pads to the brake rotor  33 .  
         [0025]     One end of an axle is illustrated. Corresponding mirror image components will be provided for the wheel brake at the other end of the axle.  
         [0026]     Instead of a piston acting directly on the interior of the axle casing, a tubular sleeve may be provided. The actuator may have diaphragms in place of the pistons. Furthermore, the actuator may includes one or more self contained units inserted into the axle upon assembly of the actuator.  
         [0027]     The foregoing description is only exemplary of the principles of the invention. Many modifications and variations are possible in light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced otherwise than using the example embodiments which have been specifically described. For that reason the following claims should be studied to determine the true scope and content of this invention.