GB2183309A - Improvements in self-energising disc brakes - Google Patents

Abstract

An automatic adjuster means is incorporated in the hydraulic actuator (6) of a disc brake of the spreading type. The adjuster means, which progressively increases the spacing between adjacent ends of two opposed pistons (11, 12) working in the bore (10) of a cylinder (9) to compensate for wear of the friction linings, comprises a member (21) projecting axially from the piston (12) and a conical spring disc (23) which has a spragging engagement with the member (21) and a limited axial movement with respect to the piston (11). A resilient friction ring (30, Figs. 2 and 3) may be employed instead of the spring disc, and the member (21) may be provided with a rib (32, Fig. 3) for retaining the ring on the member and thus holding the pistons in an initial position for assembly of the actuator in the brake. <IMAGE>

Description

SPECIFICATION Improvements in self-energising disc brakes This invention relates to self-energising disc brakes of the kind in which rotatable friction discs provided with linings of friction material are adapted to be brought into engagement with spaced opposed braking surfaces in a housing by pressure plates located between the frictions discs and centred by stationary pilot lugs, balls or rollers are located in co-operating oppositely inclined angularly spaced recesses in the adjacent faces of the pressure plates, and the application of the brake is initiated by moving the pressure plates angularly in opposite directions, the pressure plates then moving apart by a tendency for the balls or rollers to ride up ramps defined by the edges of the recesses so that the pressure plates move into engagement with the friction discs which are urged, in turn, into engagement with the braking surfaces, the pressure plates being carried round with the friction discs until one is arrested by the engagement of a lug on the plate with a drag-taking stop abutment in the housing, and the continued angular movement of the other pressure plate provides a servo action.

Self-energising brakes of the kind set forth may be dry or they may be of the liquid cooled type, and such brakes are commonly used in tractors and like vehicles and are hereinafter called brakes of the kind set forth.

It is known to actuate brakes of the kind set forth hydraulically for normal service braking. In one known construction the pressure plates are moved angularly in opposite directions by means of an hydraulic piston and cylinder assembly of which the main axis is tangential to the axis of the plates.

In brakes of the kind set forth it is desirable to incorporate means for automatically adjusting the relative positions of the pressure plates to compensate for wear of the friction linings. This can be achieved by incorporating an automatic adjuster in a mechanical transmission for applying the brake manually, for example by means of a pull-rod which acts on the pressure plates through a pair of toggle links. In such a construction the adjuster is usually positioned outside the housing.

In another construction disclosed in GB 2 036 899, an automatic adjuster located within the housing acts between the two pressure plates to adjust their relative retracted positions.

According to our invention in a disc brake of the kind set forth incorporating an hydraulic piston and cylinder assembly for moving the plates angularly in opposite directions to apply the brake hydraulically, the main axis of the assembly is tangential to the axis of the plates, and an automatic adjuster acts between the two relatively movable components of the assembly to determine their relative positions and, in turn, the relative positions of the pressure plates, the automatic adjuster comprising an axially extending member fast with one of the components, and a ring cooperating with the member and also coupled to the other of the two components for relative movement through a limited distance corresponding to the braking clearances, relative movement between the components through a distance greater than the said limited distance causing the ring to slide on the member, whereafter, on release of the brake, the ring cooperates with the said other component to determine an adjusted release position for the components.

When the piston and cylinder assembly comprises first and second opposed pistons working in a common bore in a cylinder, the member projects from one piston into a bore in the other piston, and the ring is retained in a counterbored recess in the said other piston, the braking clearances being defined by movement of the ring in the recess through a distance defined by the spacing between first and second stop.

Our adjuster is simple in construction and easy to install and replace.

Some embodiments of our invention are illustrated in the accompanying drawings in which: Figure 1 is a longitudinal section through an hydraulic actuator including portions of the pressure plates and friction discs of a brake of the kind set forth.

Figure 2 is a longitudinal section through another hydraulic actuator; and Figure 3 is a longitudinal section through yet another hydraulic actuator.

A brake of the spreading type of which a portion is illustrated in the drawings comrises a pair of rotatable frictions discs 1, 2 provided on opposite sides with linings of friction materiai which are adapted to be brought into engagement with spaced opposed braking surfaces in a housing by pressure plates 3,4 which are located between the discs, are centred by three angularly spaced stationary pilots, and are urged towards each other by tension return springs coupled at opposite ends to the plates. Balls or rollers are located in co-operating oppositely inclined recesses in the opposite faces of the pressure plates which are adjacent in the brake.

The application of the brake is initiated by moving the pressure plates 3,4 angularly in opposite directions which causes the pressure plates to move axially relatively away from each other due to the tendency for the balls or rollers to ride up ramps defined by the end faces of the recesses. This urges the friction discs 1, 2 into engagement with the faces in the housing. The pressure plates 3,4 are then carried round with the discs 1,2 until one is arrested by the engagement of a lug on a respective plate with a drag-taking abutment whereafter continued angular movement of the other plate provides a servo action.

The brake is applied mechanically for parking or in an emergency by a pull-rod (not shown) which extends through a radial opening in the housing and is coupled to a bell-crank lever 5 which acts between lugs on the two pressure plates 3, 4.

For normal service braking the brake is applied hydraulically by an hydraulic actuator 6 which acts between lugs 7,8 on the respective pressure plates.

The hydraulic actuator 6 comprises a cylinder 9 which is carried from the housing of the brake and has a longitudinally extending open-ended bore 10 in which work a pair of opposed pistons 11, 12 each provided with a seal 13 adjacent to its Inner end. The axis of the cylinder 9 is tangential to the pressure plates 3,4 and lies in a plane which is angled with respect to a transverse plane parallel to the plane of each plate.

An automatic slack adjuster 20 is incorporated in the actuator 6. As illustrated the adjuster 10 comprises a member 21 in the form of a rod which projects axially from the inner end of the piston 12 and is slidably guided in a complementary blind bore 22 in the inner end of the piston 11. A sprag ring 23 retained in a counterbored recess 24 at the inner end of the bore 22 by means of a circlip 25 has a sprag gripping engagement with the external surface of rod 21.

The sprag ring 23 has a limited axial movement in the recess 24 between its base 26, which defines a first stop and the circlip 25, which defines a second stop, through a distance equivalent to the brake clearances, and the sprag ring 23 has a spragging engagement with the rod 21 to permit relative movement between the pistons 11 and 12 only in a direction away from each other.

When the brake is to be applied hydraulically, hydraulic fluid admitted to the cylinder bore 10 between adjacent ends of the pistons 11 and 12 urges the pistons 11 and 12 away from each other, in turn to move the pressure plates 3 and 4 angularly in opposite directions to initiate application of the brake as described above.

Normally, when no adjustment is required, the relative movement between the pistons 11 and 12 will be insufficient to cause the ring 23 to sprag over the rod 21 and the retracted position of the pistons 11 and 12 is defined bythe engagement of the ring 23 with the base 26. However, should adjustment be required, additional relative movement between the pistons 11 and 12 will cause movementofthesprag ring 23 with the rod 21 to be arrested by the circlip 25, whereafter further relative movement between the pistons 11 and 12 causes the member 21 to be withdrawn through the sprag ring 23.

When the brake is released, the pistons 11 and 12 retract but are held in an adjusted, spaced apart, position by the further engagement of the ring 23 with the face 26.

In the construction described above the sprag ring 23 comprises a conical sprag disc, and the member 21 is held in the piston 12 against relative movement by means of a snap ring 27.

In a modification both pistons 11 and 12 may be of identical construction.

In the actuator 6 illustrated in Figure 2 of the accompanying drawings the sprag ring 23 is replaced by a resilient friction snap ring or circlip 30 through which the rod 21 is slidable and the wall of the counterbored recess 24 includes a frusto-conical portion 31 of which the end of smaller diameter terminates at the base 26 of the recess. The external diameter of the ring 30 is greater than the end of the frusto-conical portion 31 which is of smaller diameter but is smaller than the end of greater diameter. In a retracted position the spacing between the pistons 11, and 12 is defined by an engagement between the ring 30 and the frustoconical portion 31, at a point which defines the first stop and by means of which the ring 30 is clamped againstthe rod 21 by the wedging action of the portion 31.This prevents movement of the rod 21 through the ring 30 in a direction towards the piston 11.

As in the actuator of Figure 1, when fluid is admitted to the cylinder bore 10 and pistons 11 and 12 move away from each other, the rod 21, which is retained firmly in the piston 12, moves with the piston 12 carrying the ring 30 with it and relatively away from the portion 31.

Normally, when no adjustment is required, the relative movement between the pistons 11 and 12 will only be sufficient to cause the ring 30 to engage with the circlip 25 when the brake is applied fully.

However, should adjustment in fact be required, additional relative movement between the pistons 11,12 will cause the rod 21 to be withdrawn through the ring 30, after movement of the ring 30 with the rod 21 in that direction has been arrested by the circlip 25.

When the brake is released, the pistons 11 and 12 retract but are held in an adjusted, spaced apart, position by the further engagement of the ring 30 with the frusto-conical portion 31 to clamp the ring 30 against the rod 21 with the wedging action as described above.

The construction and operation of the actuator of Figure 2 is otherwise the same as that of Figure 1, and the corresponding reference numerals have been applied to corresponding parts.

The actuator 6 illustrated in Figure 3 of the accompanying drawings is similar to that of Figure 2 and corresponding reference numerals have been applied to corresponding parts. In Figure 3, however, the rod 21 is provided with a radial collar or rib 32 between which and the circlip 25 the snap ring 30 is trapped as a result of a force in a compression spring 33 which abuts at opposite ends between the circlip 25 and the piston 12. In this position the cooperation of the snap ring 30 with the rib 32 acts as a 'hold-together' device to hold the pistons 11 and 12 together in an initial position for assembly in the brake and in which the spacing between the pistons 11 and 12 is at a minimum.

When fluid is admitted to cylinder bore 10 and applied between the pistons 11, 12, the resultant force is sufficient to withdraw the rod 21 through the ring 30 with the ring 30 being forced over the rib 32.

Thereafter the actuator acts in a similar manner to that of the actuator in Figure 2.

Claims (14)

1. A disc brake of the kind set forth incorporating an hydraulic piston and cylinder assembly for moving the plates angularly in opposite directions to apply the brake hydraulically, in which the main axis of the assembly is tangential to the axis of the plates, and an automatic adjuster acts between the two relatively movable components of the assembly to determine their relative positions and, in turn, the relative positions of the pressure plates, the automatic adjuster comprising an axially extending member fast with one of the components, and a ring co-operating with the member and also coupled to the other of the two components for relative movement through a limited distance corresponding to the braking clearances, relative movement between the components through a distance greater than the said limited distance causing the ring to slide on the member, whereafter, on release of the brake, the ring co-operates with the said other component to determine an adjusted release position for the components.

2. A disc brake as claimed in Claim 1 in which the ring comprises a sprag ring.

3. A disc brake as claimed in Claim 2, in which the ring comprises a disc of conical outline.

4. A disc brake as claimed in Claim 1, in which the ring comprises a resilient friction ring which is urged into a wedging engagement with the member to define the adjusted release position.

5. A disc brake as claimed in any preceding claim, in which the piston and cylinder assembly comprises first and second opposed pistons working in a common bore in a cylinder, the member projects from one piston into a bore in the other piston, and the ring is retained in a counterbored recess in the said other piston, the braking clearances being defined by movement of the ring in the recess through a distance defined by the spacing between first and second stops.

6. A disc brake as claimed in Claim 5, in which the first stop comprises a face at the base of the recess, and the second stop comprises a circlip through which the member extends into the said other piston.

7. A disc brake as claimed in Claim 5, in which the recess has a wall including a portion of frustoconical outline, and the first stop comprises a part of the portion of frusto-conical outline which applies a wedge action to the ring, in turn to clamp it against the rod, the second stop comprising a circiip through which the member extends into the said other piston.

8. A disc brake as claimed in any of Claims 5 to 7, including an initial 'hold-together' device.

9. A disc brake as claimed in Claim 8, in which the hold-together device comprises a compression spring acting between the said one piston and the second stop, and a collar or rib on the member between which and the second stop the ring is trapped to hold the pistons together in an initial position in which the spacing therebetween is at a minimum, the ring being forced over the collar or rib to release the device when fluid is admitted to a space in the bore between the pistons.

10. A disc brake as claimed in any preceding claim, in which the member is held fast in the said one component by means of a snap ring.

11. A disc brake as claimed in any preceding claim, in which the main axis of the assembly is angled with respect to a transverse plane parallel to the plane of each plate.

12. A disc brake substantially as described herein with reference to and as illustrated in Figure 1 of the accompanying drawings.

13. A disc brake substantially as described herein with reference to and as illustrated in Figure 2 of the accompanying drawings.

14. A disc brake substantially as described herein with reference to and as illustrated in Figure 3 of the accompanying drawings.