Abstract:
A disc brake having a parking brake mechanism and in particular a parking brake mechanism which is integrally incorporated into the disc brake assembly.

Description:
PRIORITY CLAIM  
       [0001]     This application claims the benefit of Request For Grant Of A Patent No. 0523897.7 entitled DISC BRAKE ASSEMBLY WITH PARKING BRAKE MECHANISM filed Nov. 24, 2005 in the United Kingdom.  
       FIELD OF INVENTION  
       [0002]     The present invention relates to a disc brake having a parking brake mechanism and in particular to a parking brake mechanism which is integrally incorporated into the disc brake assembly.  
       BACKGROUND OF THE INVENTION  
       [0003]     Conventional disc brakes on the majority of road cars comprise a single piston caliper mounted in a cast iron housing. In the past, it has been necessary for the handbrake or parking brake to be a separate brake system mounted on the rear wheels because the leverage of the handbrake is limited and yet the parking brake is required to deliver a minimum of 20% of the performance of the footbrake, under UK law.  
         [0004]     More recently, attempts have been made to integrate a parking brake mechanism into the disc brake assembly. An example of this can be found in U.S. 2005/02117949 which describes the use of a ball-ramp assembly to translate displacement of a handbrake lever into axial displacement of the piston of the disc, brake.  FIG. 1  is taken from U.S. 2005/0217949 and shows a piston cavity  1  in which a piston  2  is slidably mounted. The piston cavity  2  is provided in a caliper body  3  (the brake pads are not illustrated). To the right of  FIG. 1  gears  4   a  and  4   b  communicate a lever displacement (from the handbake  5 ) to a first ramp plate  6   a . A second ramp plate  6   b  is aligned with the first ramp plate  6   a  with a bearing member  7  mounted therebetween. The facing surfaces of the two ramp plates  6   a ,  6   b  define between them a variable space traversed by the bearing member  7 . The second ramp plate  6   b  is slidably mounted within a ball-ramp cavity  8  and is arranged so that axial movement of the second ramp plate  6   b  causes a spindle mechanism  9  mounted within the piston  2  to move axially thereby engaging the piston of the disc brake. When the handbrake lever  5  is lifted this produces a rotational displacement of the first ramp plate  6   a  which in turn causes the bearing member  7  to move which in turn urges the second ramp plate  6   b  axially away from the first ramp plate. This axial displacement of the second ramp plate  6   b  is communicated by means of the spindle mechanism  9  to the piston  2  thereby engaging and holding the disc brake until the handbrake lever  5  is released.  
         [0005]     It will be immediately apparent that in the case of U.S. 2005/0217949, integration of the parking brake mechanism into the disc brake assembly has resulted in a complex mechanism with many parts and requiring accurate alignment not only of the piston within the piston cylinder but also the spacing of the two ramp plates and the positioning of the spindle within the piston body.  
         [0006]     In so far as top of the range road cars and racing cars are concerned, these have adopted four piston caliper disc brake assemblies, often involving an aluminium casing, for which no integrated parking brake mechanism is available.  
       SUMMARY OF THE INVENTION  
       [0007]     The present invention seeks to address the problems identified above with respect to integrating a parking brake with disc brake assemblies and in particular the present invention seeks to provide an integrated disc brake and parking brake assembly which is suited for, but not limited to, use with multiple piston disc brakes.  
         [0008]     The present invention therefore provides a disc brake assembly for a vehicle comprising a caliper body; at least one piston and cylinder arrangement provided in the caliper body; a pair of opposed friction pads; and an integral parking brake mechanism comprising at least one pair of levers mounted on the caliper body and arranged for engagement with the pair of friction pads, each lever being pivotable about a first end and having cable engaging means at an opposed second end; a cable member engaging with the second ends of the levers whereby displacement of the cable member causes at least one of said pair of levers to pivot and engage with a respective friction pad.  
         [0009]     In a preferred embodiment, the parking brake mechanism further includes biasing means biasing at least one of the pair of levers towards a disengaged position. Said biasing means may comprise a torsional spring member provided on a lever axle.  
         [0010]     Additionally, the cable member may include an eyelet provided at a free end of the cable and the second end of said one of the pair of levers includes a hook for engagement with the eyelet.  
         [0011]     Ideally, each of the levers has a curved ramp surface for engagement with a respective friction pad, the curvature of the surface being selected to maintain a substantially axially directed force on the friction pad during pivoting movement of the lever.  
         [0012]     In a preferred embodiment the disc brake assembly comprises four piston and cylinder arrangements provided in two opposed pairs and said pair of levers are positioned between said two pairs of piston and cylinder arrangements.  
         [0013]     Thus, it may be seen that with the present invention a parking brake mechanism is integrated with a conventional disc brake assembly in a particularly simple and straightforward manner and in a manner which does not involve large numbers of additional components. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]     An embodiment of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:  
         [0015]      FIG. 1  is a sectional view of a known integrated single piston disc brake and parking brake mechanism;  
         [0016]      FIG. 2  is a sectional view through a four piston disc brake assembly with an integrated parking brake mechanism in accordance with the present invention;  
         [0017]      FIG. 3  is an illustration of the parking brake mechanism of  FIG. 2 ;  
         [0018]      FIG. 4  is a first perspective view illustrating the parking brake mechanism mounted in the four piston disc brake assembly of  FIG. 2 ; and  
         [0019]      FIG. 5  is a second perspective view illustrating the parking brake mechanism and disc brake assembly of  FIG. 4 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0020]     The disc brake assembly  10  of  FIG. 2 , which is adapted for use with road vehicles, generally comprises a caliper body  11  having opposed hydraulic chambers  12  within each of which are mounted pistons  13  for axial sliding movement within their respective hydraulic chamber. The disc brake assembly  10  is a four pot arrangement (two pistons either side mounted in a common caliper body) of which only two opposed pistons and their hydraulic chambers are visible in  FIG. 2 . The surface of each piston  13  which faces outwardly from its hydraulic chamber has a friction pad mounted thereon comprising a supporting backboard  14  and a friction liner  15 . In use, the disc brake assembly  10  is mounted so that the friction liners  15  are positioned either side of and engage with the disc rotor  16  of the vehicle wheel. Although not illustrated, extending through the caliper body  11  are fluid channels in communication with respective hydraulic chambers  12 . The fluid channels are in fluid communication with a common brake line so that when the vehicle footbrake (not illustrated) is depressed this is communicated as fluid pressure to each of the pistons  13  in their hydraulic chambers  12 . The pistons, in turn, urge the friction pads  14 ,  15  towards each other so that they engage with the disc rotor  16  of the vehicle wheel. The features of the disc brake assembly described above are conventional in design such as may be found on the Billet Dynalite™ caliper of Wilwood Engineering.  
         [0021]     The disc brake assembly  10  additionally includes an opposed pair of levers  17  that are mounted in open channels  18  provided between adjacent pistons  13  in each side of the caliper body  11 . Each lever  17  is attached at a first end to the caliper body  11  by means of an axle  19  whereby the lever  17  is free to pivot about the axle  19 . Each axle  19  is, in turn, mounted to the caliper body by means of a pair of cradles  20  which engage opposed ends of each axle  19 . The levers  17  are biased by suitable means towards a disengaged position where they are aligned with their channels in the caliper body  11 . A torsional spring (not illustrated) provided on each axle  19  is an example of a suitable biasing means. Each lever  17  has a ramp surface  21  which engages with the backboard  14  of a respective friction pad. The ramp surface  21  of the lever is shaped so as to remain substantially in point contact with the backboard  14  during pivoting movement of the lever about the axle  19  and so as to deliver an axial force substantially parallel to the pistons  13 .  
         [0022]     Each lever  17  also engages with a cable  22  which is, in turn, connected to the parking brake lever (not illustrated). A first one of the pair of levers  17  has a hook  23  at a second end of the lever which hook  23  freely engages with an eyelet  24  at the cable end  25  of the cable. The hook  23  faces away from the cable end  25  and projects through the eyelet  24 . The second of the pair of levers  17  has a corresponding hook  26  which also faces away from the cable end  25 . This hook  26  engages with a cable block  27  mounted on the cable  22  at a position along the length of the cable  22  which is adjustable by means of an adjuster  28  (not shown in  FIG. 3 ).  
         [0023]     In use, when the parking brake is activated, the cable  22  is pulled in a direction away from the disc brake assembly. This movement of the cable  22  causes the eyelet  24  to engage with the hook  23  of the first lever  17  and to pull the hook in the direction of the cable thereby causing the lever to pivot about its axle  19  out of its channel in the caliper body  11  to an engaging position. As a result of the pivoting action of the lever  17 , the ramp surface  21  of the lever engages with the backboard  14  of the friction pad and urges the friction pad to engage with and hold the disc rotor  16 . At the same time, the cable block  27  moves away from the disc brake assembly releasing the hook  26  of the second lever  17  which remains in position in its channel in the caliper body  11 . When the parking brake is released, the cable moves back towards the disc brake assembly which releases the tension from the first lever  17  allowing it to return to its original position within its channel in the caliper body, by means of the biasing member. This in turn releases the friction pad  14 ,  15  from engagement with the disc rotor  16 . In addition, when the parking brake is released, the cable block  27  returns to engage with the hook  26  of the second lever  17 .  
         [0024]     Thus it may be seen that the parking brake mechanism described above is integrated with a conventional disc brake assembly in a particularly simple and straightforward manner and in a manner which does not involve large numbers of additional components. Moreover, adjustment and alignment of the parking brake mechanism is easily achieved by means solely of the cable adjuster  28 , the position of which dictates the separation of the hooks  23  and  26  and hence the contact of the ramp surfaces  21  of each lever  17  with the backboards  14  of the friction pads.  
         [0025]     This parking brake mechanism may be applied to single pot disc brakes as well as multiple pot disc brakes. In the case of a single pot disc brake, ideally, each side of the disc rotor would be engaged by a pair of levers, arranged either side of the single piston, and having a common axle and a common hook provided centrally on a cross member for engagement with the cable so that a balanced force may be applied to the friction pad.  
         [0026]     The integrated disc brake assembly and parking brake mechanism of the present invention is particularly suited for use with light-weight vehicles and is adapted for retro-fitting to existing vehicles having a conventional parking brake cable.