GB2336188A

GB2336188A - A disc brake

Info

Publication number: GB2336188A
Application number: GB9807381A
Authority: GB
Inventors: Enrique Scalabroni
Original assignee: Akebono Research and Development Centre Ltd
Current assignee: Akebono Research and Development Centre Ltd
Priority date: 1998-04-06
Filing date: 1998-04-06
Publication date: 1999-10-13
Anticipated expiration: 2018-04-06
Also published as: GB9807381D0; GB2336188B; JPH11344058A

Abstract

A disc brake comprises a fixed caliper 16 supported, in use, on a stationary part of a vehicle, and a piston 1, 6 driven by a lever 21 to directly advance brake shoe 9 and pad 10 into engagement with one side of brake disc 11 and to advance, via bell-crank levers 7 and shafts 8, brake shoe 12 and pad 10 into engagement with the other side of the brake disc. Upon brake wear, piston part 6 will be retained in an advanced position by a pawl and ratchet mechanism (13, 14 Fig.2) and return movement of lever 21 will cause piston part 1 to rotate relative to piston part 6. Pawl and ratchet mechanism 4, 30 prevents relative rotation between the parts 1, 6 on application of the brake.

Description

1 DISC BRAKES 2336188 This invention relates to disc brakes for use in

railway vehicles, commercial road vehicles, industrial machines, etc.

Disc brakes for vehicles have been in use for a number of years. Such disc brakes (e.g. W092/09201) operate by urging a shoe into engagement with one side of a disc attached to a wheel of the vehicle. The force resulting from engagement of the shoe into one side of the disc urges a caliper slidably retained on a pin in a direction which results in a second brake shoe, retained on the caliper, engaging with the other side of the disc. The pin in such an arrangement is attached to the vehicle. Such an is arrangement has a number of problems associated with it. Firstly, such an arrangement requires a large number of heavy components which are not connected with an even balance to the vehicle. This means that the load applied to the pin during a braking operation is considerable and not balanced. This is a particular problem in larger vehicles.

A further problem is that vibration on the system during vehicle travel can, due to the forces on the pin, deform the pin, leading to problems associated with the correct positioning and movement of the caliper slidably supported thereby.

The present invention is directed toward overcoming the above and other problems.

According to the present invention there is provided a disc brake comprising:

caliper supported on a stationary part; piston driven, by an actuation device, the piston arranged so that, when driven by the actuation device, the piston urges a first shoe into engagement with a first face of the disc; a second shoe slidably supported on the caliper; and 2 a lever mechanism for urging, upon receipt of an actuating force from the actuating member, the second shoe into engagement with a second face of the brake disc.

The lever mechanism may comprise one or more bell cranks pivotally attached to the caliper. If such bell cranks are provided they may also be in pivotal engagement with the piston. Two bell cranks may be provided, with each bell crank being arranged to engage with a shaft, each shaft being attached to a second shoe support member. At least one sprung member may be provided to bias either one or both of the brake shoes into a position in which they are not in engagement with the disc.

The piston may be provided with an adjustment mechanism in order to allow a user to adjust the relative position of the piston and an actuating member attached to the actuating means. Alternatively, one or more adjustment mechanisms may be provided to allow the user to adjust the relative positions of one or both shoes with respect to the caliper.

It will be appreciated that the present invention provides an arrangement that generates instantaneously generally equal but opposite forces on both sides of the brake disc, overcoming many of the problems associated with prior art devices.

According to the present invention there is also provided a brake system including a disc, an actuating device, and a brake caliper as defined above.

One example of the present invention will now be described with reference to the accompanying drawings, in which:

Figure 1 is a cross-sectional plan view of an example of the present invention; Figure 2 is an enlarged view of a portion of the example of figure 1; and Figure 3 is a cross-sectional view of a second example of the invention.

3 Referring to figure 1, a brake caliper is supported on a stationary part of a vehicle body (not shown). A first shoe 9 and pad 10 is slidably supported on a guide rail 19 in the caliper in such a manner that it is able to slide in a direction parallel to the axial direction of a disc 11 which is connected to a vehicle wheel. The shoe 9 distributes force over the whole pad 10.

An actuation device 20 (Fig. 3) is connected to a piston 6 via a force multiple lever 21 and bearings 2. The piston 6 is, in turn, connected to the shoe 9. Pivotally attached to the caliper and in engagement with the piston 6 are two bell cranks 7 which, in turn, are each connected to a shaft 8. The bell cranks 7 are supported at their middle sections on the caliper on low friction needle bearings 23.

The piston 6 has a hollow central portion in which bearings 24 on an end of each of the bell cranks 7 sit in engagement therewith. The two shaf ts 8 are arranged so that they slide in a direction parallel to the axis of the disc 11. The two shafts 8 are in engagement with a second shoe 12 which supports a second pad 10. Springs 17 are provided to bias the shafts 8 and second shoe 12 so that, unless actuated, the second pad 10 is out of engagement with the face of the disc 11.

An adjustment mechanism is provided to allow for calibration of the disc brake to compensate for pad wear. This adjustment mechanism adjusts the position of the first shoe 9 and bearings 24 relative to lever 21. The operation of the adjustment mechanism is described below.

When force is applied to the piston 22 from the actuating device 20, the first shoe 9 moves into engagement with one face of the disc 11. At the same time, bell cranks 7 pivot, causing the two shafts 8 to slide by an amount corresponding to the movement of the first shoe 9 and causing the second shoe 12 to engage with a second face of the disc 11.

4 The adjustment mechanism referred to above operates during actuation to ensure that pad wear is compensated for. The piston 22 is divided into a number of components which assist in the operation of the adjustment mechanism.

A rotatable piston head 1 is engaged with a second piston portion 6 by means of a screw thread 25. Formed on a portion of the piston 6 is a series of teeth 14 (shown in figure 2) into which a sliding retaining member 13 is urged by a biasing spring 26. This allows for forward movement of the piston 6, with the teeth 14 sliding the retaining member 13 against force of the spring during forward movement of the piston 6, but being restrained by the retaining member 13 during movement of the piston 6 rearward. This means that the piston 6 and corresponding shoe 9 are always in a position such that the pad 10 is in close proximily to the surface of the disc 11. It also ensures that the position of the shaft 8 (and hence shoe 12) is adjusted accordingly. Because of the screw thread engagement between the piston 6 and piston head 1, the piston head 1 would be rotated by application of an actuating force but for the presence of a ratchet mechanism 4. The ratchet mechanism 4 is biased into engagement with a series of teeth 30 on the outer circumference of the piston head 1 by a spring 27. When the actuating force is removed and the lever 21 drawn back the ratchet mechanism 4 slides over the teeth 30 in the piston head 1, allowing rotation and hence relative axial movement between piston head 1 and piston 6 (because of the screw thread 25) to compensate for the forward movement of the piston 6.

Figure 3 shows a second example of the present invention in which components corresponding to those in the first example are numbered identically. Much of the operation of the second example is similar, although a different actuating lever 21 and corresponding connection is provided in order to multiply by a more significant factor the force applied by an actuating device in use.

From the above it will be appreciated that, unlike the prior art, the arrangement of the present invention can be supported by a stationary part (e.g. a vehicle body), reducing the effects of vehicle vibration and the problems associated with supporting a slidable unbalanced heavy mass.

6

Claims

A disc brake comprising:

a caliper supported on a stationary part; a piston driven, by an actuation device, the piston arranged so that, when driven by the actuation device, the piston urges a first shoe into engagement with a first face of the disc; second shoe slidably supported on the caliper; and lever mechanism for urging, upon receipt of an actuating force from the actuating member, the second shoe into engagement with a second face of the brake disc.
2. A disc brake according to claim 1, wherein the lever is mechanism comprises one or more bell cranks pivotally attached to the brake caliper.
3. A disc brake according to claim 2, wherein the bell cranks are in pivotal engagement with the piston.
4. A disc brake according to claim 2 or claim 3, wherein two bell cranks are provided, each bell crank being arranged to engage with a shaft, each shaft being in engagement with the second shoe.
5. A disc brake according to claim 4, wherein the bell cranks are supported at a middle portion by the brake caliper.
6. A disc brake according to any preceding claim, at least one sprung member is provided to bias either one or both of the brake shoes into a position in which they are not in engagement with the disc.
7. A disc brake according to any preceding claim, wherein the piston is provided with an adjustment mechanism in order to allow a user to adjust the relative position of 7 the piston and an actuating member attached to the actuating means.
8. A disc brake according to any of claims 1 to 6, wherein one or more automatic adjustment mechanisms are provided to adjust the relative positions of one or both shoes with respect to the brake caliper during use of the brake.
9. A brake system including a disc, an actuating device, and a brake caliper according to any preceding claim.