Abstract:
A disc brake includes a brake disc, a sliding caliper, a single piston, and a brake pad carrier comprising a leading part and a trailing part. The brake pad carrier includes mounting features for securing the brake pad carrier to an associated structure of a vehicle. The mounting features define a mounting side and a non-mounting side of the brake. A mounting side brake pad comprises mounting side friction material and a non-mounting side brake pad comprising non-mounting side friction material. The center of pressure of the non-mounting side friction material is circumferentially aligned with the piston and the center of pressure of the mounting side friction material is offset in relation to the piston towards the leading part of the brake pad carrier.

Description:
RELATED APPLICATION 
       [0001]    This application claims priority to GB Patent Application 1009030.6, filed Jun. 1, 2011. 
       FIELD OF THE INVENTION 
       [0002]    This invention relates to a disc brake, in particular an air actuated disc brake, for a commercial vehicle. 
       BACKGROUND 
       [0003]    Disc brakes are commonly used on both commercial (heavy) and private (light) vehicles. Some are hydraulically operated, while others are air operated. Some disc brakes are operated by pistons acting on one side of the brake. Due to vehicle space limitations it is common to mount such pistons on the inboard side of the wheel in question, as there is generally more space inboard than outboard of a vehicle&#39;s brake disc. 
         [0004]    Certain disc brake pads wear in a tapered manner. Thus a leading edge of an outboard brake pad and an inboard brake pad will wear more than the trailing edge of those brake pads. 
         [0005]    It is known to counter the problem of tangential taper wear by offsetting the inboard pad in the direction of its leading edge and offsetting the outboard pad in the direction of the trailing edge. Such offset pads can be seen in U.S. Pat. No. 3,422,935 (Van House). Moving the pads in this way counters the rotational forces and balances the pads against the brake disc more evenly. A similar arrangement can be seen in U.S. Pat. No. 4,533,025 (Carré). U.S. Pat. No. 3,422,935 does not differentiate between wear on the inboard and outboard pads, referring only to tapered lining wear of both pads. U.S. Pat. No. 3,422,935 maintains that offsetting both pads in this way will lead to equal and opposite force couples around the point where the braking force is applied. U.S. Pat. No. 4,533,025 also refers to the correction of tapering wear of each brake pad. 
         [0006]    Offsetting of the inboard pad in the leading direction moves the center of pressure of that pad in the leading direction and hence the center of pressure of the reaction force of the disc in the leading direction. Offsetting the outboard pad in the trailing direction offsets the center of pressure of the outboard brake pad in the trailing direction, hence offsetting the reaction force of the disc against the outboard pad in the trailing direction. The pads therefore create a couple on the disc. The offset center of pressure of the inboard and outboard brake pads also creates unequal forces in the caliper bridge. 
         [0007]    U.S. Pat. No. 5,022,500 shows an arrangement wherein the mounting side brake pad has no offset in relation to the piston but the non-mounting side brake pad is offset towards the trailing edge. 
         [0008]    JP932870 FIG. 1 shows a mounting side brake pad offset towards the leading edge with respect to the piston and a non-mounting side brake pad offset towards the leading edge with respect to the piston. In FIG. 3 of JP932870 the mounting side brake pad is offset towards a leading edge whereas the non-mounting side brake pad is offset towards a trailing edge with respect to the piston. 
         [0009]    FIG. 1 of U.S. Pat. No. 5,386,890 shows mounting side brake pad offset towards the trailing edge with respect to the single piston. 
         [0010]    All of the above documents relate to hydraulic brakes on light vehicles such as cars. An advantage of such brakes is their size and weight in comparison to those used on commercial vehicles such as lorries and trucks. Manipulating these smaller, lighter brakes, for example when changing brake pads, is much easier than performing the same operation with their commercial counterparts. The calipers of light vehicles can be partially unscrewed and manually raised away from the disc in order to allow the replacement of brake pads. It does not matter, therefore, if the bridge arm of the caliper or carrier normally impedes access to the brake pads. In contrast, the brake pads of commercial vehicles should be accessible without the need for removal or manipulation of the much heavier carriers used (since these carriers are so heavy that they cannot safely be manually handled by a single person), and hence they incorporate spaced caliper bridge arms between which the pads can be removed and replaced without having to disturb the caliper fixings. 
         [0011]    Because commercial vehicle brakes have to withstand far higher forces, they tend to be heavier. Typically a commercial vehicle brake might include one or more, or all, of the following features:
       a) a fixed carrier which reacts the tangential (braking) forces from both the mounting side pad and the non-mounting side pad,   b) a sliding caliper which is designed to apply forces to the mounting side brake pad and non-mounting side brake pad so that the brake disk is clamped and therefore braked,   c) the floating caliper acting so as to not transfer the tangential braking loads to the vehicle (this function being carried out by the fixed carrier),   d) mounting side and non-mounting side brake pads which are removable through spaced arms of the carrier,   e) mounting side and non-mounting side brake pads which are removable through spaced arms of the caliper.       
 
         [0017]    Tapering pad wear can also occur on heavy vehicle brakes, for example commercial vehicle brakes such as those used on lorries and trucks. 
         [0018]    US2007/0256900 shows a mounting side brake pad aligned with the piston and a non-mounting side brake pad offset towards a trailing edge. U.S. Pat. No. 7,461,725 is similar in this respect. 
         [0019]    What is required is a way to reduce tangential tapering wear of the mounting side pad (e.g. the inboard side pad when the brake operating piston is mounted on the inboard side of the brake disc) of a commercial disc brake that minimizes the creation of imbalanced forces in the brake caliper or in the brake disc, in particular in the spaced bridge arms. This is particularly important since the clamp forces involved when using commercial vehicle disc brakes are far higher than the clamp forces involved on disc brakes of lighter vehicles such as cars and motorcycles. 
       SUMMARY 
       [0020]    An air operated disc brake comprises a brake disc, a sliding caliper, a single piston, and a brake pad carrier comprising a leading part and a trailing part determined by the usual direction of rotation of the brake disc. The brake pad carrier includes mounting features for securing the brake pad carrier to an associated structure of a vehicle. The mounting features defines a mounting side and a non-mounting side of the brake. A mounting side brake pad comprises mounting side friction material and a non-mounting side brake pad comprises non-mounting side friction material. The non-mounting side friction material is circumferentially aligned with the piston and the mounting side friction material is offset in relation to the piston towards the carrier leading part. 
         [0021]    Advantageously, this arrangement of the non-mounting side and mounting side pads in relation to the piston counters rotation of the mounting side pad due to the points at which forces are applied, and thus also counters tangential wear at its leading edge. The location of the non-mounting side pad prevents an imbalance of force from occurring. 
         [0022]    There is also provided a method of manufacturing a first and second brake pad carrier comprising the steps of: 
         [0023]    creating a carrier mold; 
         [0024]    casting first and second carrier castings from said mold; 
         [0025]    machining said first carrier casting such that a first brake pad aperture is offset in relation to a second brake pad aperture to form a first carrier; 
         [0026]    machining said second carrier casting such that a third brake pad aperture is offset in relation to a fourth brake pad aperture to form a second carrier; and 
         [0027]    wherein the position of the first and second brake pad apertures on the first carrier is a mirror image of the position of the third and fourth brake pad apertures on the second carrier. 
         [0028]    Advantageously, this method reduces manufacturing costs by using the same molds for left and right side carriers, despite the required difference between them. 
         [0029]    The carrier may be configured as a fixed carrier operable to transfer brake torque forces from a mounting side brake pad and a non-mounting side brake pad to other vehicle structures. The caliper may be a sliding caliper. 
         [0030]    These and other features of the present invention can be best understood from the following specification and drawings, of which the following is a brief description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0031]      FIG. 1  is a perspective view of a disc brake assembly according to the present invention; 
           [0032]      FIG. 2  is a plan view of a carrier of the disc brake assembly  FIG. 1 ; 
           [0033]      FIG. 3  is a plan view of the carrier of  FIG. 2  with brake pads and a piston; and 
           [0034]      FIG. 4  is a side view of the embodiment of  FIG. 3  with a brake disc, taken in the direction of arrow O, showing a mounting side pad. 
       
    
    
     DETAILED DESCRIPTION 
       [0035]    Heavy vehicles such as commercial trucks have a usual (forward) direction of travel. In the following description the terms “leading” and “trailing” refer to parts of the brake assuming the usual direction of rotation of a brake disc, i.e. that of a vehicle moving forward rather than in reverse. The amount of time spent travelling in the reverse direction is minimal in comparison to that spent travelling forwards (and is at much lower speeds). 
         [0036]      FIG. 1  shows part of a disc brake assembly  10  comprising a sliding caliper  2  mounted on a carrier  11  which is in turn mounted on a suspension component of a vehicle (not shown). The caliper  2  comprises an inboard side  4  and an outboard side  6 . The inboard and outboard sides  4 ,  6  are connected by a leading bridge arm  7  and a trailing bridge arm  8 . The bridge arms  7 ,  8  are positioned at either end of the caliper  2 , leaving an aperture substantially extending along a length of the brake pads. 
         [0037]    The carrier  11 , as shown in  FIGS. 2 and 3 , comprises an inboard side  12  and an outboard side  13 , the two sides being joined by a leading carrier bridge arm  38  and a trailing carrier bridge arm  39 . The inboard side  12  of the carrier  11  includes fixing holes  15  ( FIG. 1 ) used for attaching (or mounting) the carrier onto a vehicle (not shown). The fixing holes  15  define the “mounting” side of the brake. In this case the mounting side is the inboard side. The side of the brake opposite the mounting side is known as the non-mounting side, which in this case is the outboard side. The carrier bridge arms  38 ,  39  are positioned at either end of the carrier  11 , and extend beyond and below the caliper bridge arms  7 ,  8 . The arms are spaced sufficiently far apart so as to be able to remove the inboard and outboard pads  14 ,  16  from between the arms. The carrier  11  further comprises an inboard leading abutment  35  and an inboard trailing abutment  34 , as well an outboard leading abutment  37  and an outboard trailing abutment  36 . The inboard brake pad  14  fits between the inboard abutments  34 ,  35  and the outboard brake pad  16  fits between the outboard abutments  36 ,  37 . 
         [0038]    The inboard brake pad  14  comprises a back plate  20  and frictional material  22 , and has a leading edge  14   a  and a trailing edge  14   b . Similarly, the outboard brake pad  16  comprises a back plate  24  and friction material  26 , and has a leading edge  16   a  and a trailing edge  16   b . The inboard back plate  20  in this embodiment is thicker than the outboard back plate  24 . 
         [0039]      FIG. 4  shows a brake disc  40  positioned in the aperture  18  (see  FIG. 3 ) defined between the two brake pads  14 ,  16 . In operation, a braking force is applied by an air-operated piston  28  (see  FIG. 3 ), moving the inboard brake pad  14  outboard until it comes into contact with the brake disc  40 . The piston  28  continues to apply a braking force, causing reaction forces to slide the caliper  2  inboard along pins (not shown) until the outboard brake pad  16  contacts the brake disc  40 . 
         [0040]    When a vehicle is moving forwards, the brake disc  40  is turning in the direction indicated by the arrow X of  FIGS. 1 ,  2 ,  3  and  4 , defining a leading part  30  and a trailing part  32  of the carrier  11 . The centerline A of the piston  28  is aligned with the centerline C of the outboard brake pad  16 . The centerline B of the inboard pad  14  is offset with respect to the centerline A in the direction of the leading part  30  of the carrier  11 . In order to create this offset the inboard side abutments  34 ,  35  are offset 5 mm in relation to the outboard side abutments  36 ,  37  respectively. 
         [0041]    As shown in  FIG. 3 , the force F 1  from the piston acts on the inboard back plate  20  to apply the brakes. Note the force F 1  is applied over a relatively small area (the piston area) to the back plate  20 . This creates a friction force at F 3  as the inboard brake pad bears against the disc brake  40 . The friction force F 3  is reacted by force F 2  created by abutment  34 . It can be seen from  FIGS. 3 and 4  that moving the centerline B of the inboard brake pad  14  towards the leading edge relative to the centerline A of the piston  28  will go some way to countering rotation of the inboard brake pad  14  in a counter-clockwise direction (when viewing  FIG. 3 ) and will thus reduce tangential taper wear at the leading edge. 
         [0042]    It can be seen in  FIG. 2  that in order to accommodate the offset inboard brake pad  14 , the abutments  34 ,  35  on the inboard side of the carrier  11  have been moved a distance Y towards the leading part  30  of the carrier  11  in relation to the abutments  36 ,  37  on the outboard side of the carrier  11 . In the present embodiment the distance Y is 5 mm. In other embodiments, this distance may be varied between 3 mm and 15 mm, alternatively between 3 mm and 10 mm. The optimum offset distance depends largely on the size of the disc brake pad. 
         [0043]    As the inboard brake pad  14  engages the brake disk  4 , the caliper  11  moves inboard drawing with it the caliper outboard side  6  which in turn causes the outboard brake pad  16  to move inwardly and ultimately to engage and brake the outboard side of the brake disk  40 . Significantly, the caliper outboard side  6  engages the outboard brake pad  16  over substantially the entire area of the outboard back plate  24 . Because the outboard brake pad  16  is being pushed onto the brake disk  40  over substantially the entire area of the outboard back plate  24 , then the tendency of the outboard brake pad  16  to taper wear as a result of tipping is significantly reduced. Significantly, because the outboard brake pad back plate  24  reacts against the abutment  36  and because the outboard back plate  24  is thinner than the inboard back plate  20 , then the distance between the reactional force created by abutment  36  and the outboard side of the brake disk  40  is less than the distance between F 2  and F 3  on the inboard side. As such, because the outboard brake pad back plate  16  is thinner than the inboard brake pad back plate  20  then the tendency of the outboard brake pad  16  to tip as a result of reactional forces is less than on the inboard side. Thus, the difference in thickness between the inboard brake pad back plate  20  and outboard brake pad back plate  24  contributes to reducing taper wear on the outboard brake pad  16 . 
         [0044]    Due to the positioning of the caliper bridge arms  7 ,  8  and the carrier bridge arms  38 ,  39 , the brake pads  14 ,  16  can easily be removed from the carrier  11  with no need for dismantling of the carrier. A strap  9 , shown in  FIG. 1 , is provided to prevent dislodging of the brake pads  14 ,  16  when in use. 
         [0045]      FIGS. 1 to 4  show a disc brake arrangement for the right-hand side of a vehicle. 
         [0046]    Where a vehicle is fitted with both right and left hand brakes, the right hand brake can be as shown in  FIGS. 1 to 4 . However, the left hand brake would require a mirror image version of the pad abutments of the carrier  11 . However, it is not necessary for there to be a mirror image version of the caliper  2  fitted to the left hand side of the vehicle. 
         [0047]    Advantageously, carriers suitable for fitting to the right and left hand side of the vehicle can be economically produced as follows: 
         [0048]    A mold is first produced, and then two identical carrier castings are cast from the mold. The first carrier casting is machined to provide a right hand carrier and the second carrier casting is machined to provide a left hand carrier. 
         [0049]    The right hand carrier will have the pad abutments machined appropriately to provide a right hand carrier whereas the left hand carrier casting will have the pad abutments machined differently, thereby providing a left hand carrier. The position of the pad abutments on the right hand carrier will be at a mirror image position when considering the left hand carrier. Note in particular it is not necessary for the right and left hand carriers to be mirror images of each other, all that is required is that the position of the pad abutments on the right hand carrier are a mirror image of the position of the pad abutments on the left hand carrier. 
         [0050]    Thus, the right and left hand carriers may be identical other than the mirror image positioning of the pad abutments. As such, it is possible to use identical calipers on both the right and left hand side of the vehicle (it is not necessary to use mirror image (or opposite handed) versions of the caliper on the right and left hand sides). 
         [0051]    Although an embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.