GB2172675A - Overrun operated trailer brake with reversing capabilities - Google Patents

Abstract

An overrun operated trailer brake which reduces braking torque during reversing, comprises two brake shoes having between their first ends an expander and between their second ends a mechanism which permits the distance between the second ends to reduce during reversing. The mechanism includes a lever pivoted to the leading shoe (in forward braking), a strut extending between that lever and the other shoe, an abutment on the back plate engaged by the leading shoe and lever only during forward braking, and a stop on the leading shoe engaged by the lever during reversing when the clearance C has been taken up. <IMAGE>

Description

SPECIFICATION Improvements in trailer brakes This invention relates to brakes which are operated by an inertia overrun system. To prevent a lock up condition during reversing a mechanism is fitted within the brakes. To improve the parking brake performance said mechanism is also arranged to increase the ratio of input force to brake torque in the reverse direction. As a further performance gain, particularly of the parking, brake automatic adjustment for lining wear may also be fitted.

A diagrammatic illustration of one form of the brake is shown in Fig. 1. This operates as a leading and trailing type in the forward mode and as a duo servo (where one shoe drives the other) in the reverse direction. Fig.

4 shows alternative design In reverse the distance 0 (between the shoe expander points during forward operation) is increased, the amount depending on the degree of clearance C and the lever ratio A:B. It is arranged that the distance 0 is increased to an extent that it is equal to or greater than the travel which is available from the overrun mechanism.

The automatic adjuster may take either of two forms-see Figs. 2. and 3. The former is a simple bell crank lever pivoted to an extension of lever which operates directly the leading shoe. One arm of the bell crank reacts on to a stop fixed to the backplate and the other arm (the pawl) actuates the ratchet wheel rotation of which controls the adjustment. (see also U.K. Patent 1,586,063.

Fig. 3. operates on the same principle but here the bell crank is made (effectively) in two parts spring loaded together so that one arm drives the other. Arm a.will be moved in respect of arm b. if the trailing shoe moves closer to the drum due to lining wear of that shoe. This movement arises because arm a.

contacts the other side of the backplate stop.

Arm b. contacts stop c. during this readjustment.

A spring is attached to arm b. to assist in the adjustment during retraction and also to ensure effective contact between pawl and ratchet wheel.

The shape of the backplate stop contact arm in Fig. 2. may be arranged so that only a limited angular movement of the bell crank can be imparted during one stroke of the actuating mechanism.

1. A brake of the type described which operates in a leading and trailing shoe mode in the forward direction of drum rotation and as a duo servo type in the reverse direction, the brake comprising a sliding actuating assembly mounted on a torque carrying backplate, and located between one one end of each of the brake shoes; an abutment member rigidly mounted on said backplate being located diametrically opposite the actuator and between the other ends of said shoes; mechanism which will cause the distance between the shoe ends remote from the actuator to be reduced to a predetermined extent when the brake is operating in the reverse direction; characterised in that the actuator housing is arranged to bear torque in the reverse braking direction only and the abutment member will carry the torque only in the forward braking direction.

2. A brake as described in claim 1 in which the mechanism controlling the distance between the shoe ends remote from the actuating end takes the form of a lever or a pair of levers pivotally mounted on to the shoe web at the heel of the normal shoe, one arm of said lever reacting on to the abutment and another arm of said lever being connected to the other shoe via a strut, said lever being arranged to have a limited angular in respect of the shoe web.

3. A brake as claimed in claims 1 and 2 in which the adjustment for lining wear is a load bearing part of the actuator mechanism.

4. A brake according to any one of the preceeding claims including an adjuster operable to adjust the brake for lining wear when the shoe travel during forward braking exceeds a preset distance the adjuster being so arranged that it does not respond during the reversing mode or if the drum is stationary.

5. A brake according to claim 4 wherein the adjuster includes a pawl pivoted to a point on the actuator assembly which moves in the same direction and in a direct ratio to that of the leading shoe.

6. A brake as claimed in claim 6 where one arm of the pawl receives the adjustment signal from a point attached to the backplate.

7. A brake according to claims 4,5, and 6 where the pawl has a spring attached between itself and the trailing brake shoe.

8. A brake according to claims 4,5 and 6 where the pawl has a spring attached between itself and the actuator body.

9. A brake as claimed in claims 2 and 3 where a spring is fitted between the lever attached to the leading shoe and the backplate adjacent the other shoe.

10. A brake of the type described and as shown in Figs. 1 and 2 of the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (10)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Improvements in trailer brakes This invention relates to brakes which are operated by an inertia overrun system. To prevent a lock up condition during reversing a mechanism is fitted within the brakes. To improve the parking brake performance said mechanism is also arranged to increase the ratio of input force to brake torque in the reverse direction. As a further performance gain, particularly of the parking, brake automatic adjustment for lining wear may also be fitted. A diagrammatic illustration of one form of the brake is shown in Fig. 1. This operates as a leading and trailing type in the forward mode and as a duo servo (where one shoe drives the other) in the reverse direction. Fig. 4 shows alternative design In reverse the distance 0 (between the shoe expander points during forward operation) is increased, the amount depending on the degree of clearance C and the lever ratio A:B. It is arranged that the distance 0 is increased to an extent that it is equal to or greater than the travel which is available from the overrun mechanism. The automatic adjuster may take either of two forms-see Figs. 2. and 3. The former is a simple bell crank lever pivoted to an extension of lever which operates directly the leading shoe. One arm of the bell crank reacts on to a stop fixed to the backplate and the other arm (the pawl) actuates the ratchet wheel rotation of which controls the adjustment. (see also U.K. Patent 1,586,063. Fig. 3. operates on the same principle but here the bell crank is made (effectively) in two parts spring loaded together so that one arm drives the other. Arm a.will be moved in respect of arm b. if the trailing shoe moves closer to the drum due to lining wear of that shoe. This movement arises because arm a. contacts the other side of the backplate stop. Arm b. contacts stop c. during this readjustment. A spring is attached to arm b. to assist in the adjustment during retraction and also to ensure effective contact between pawl and ratchet wheel. The shape of the backplate stop contact arm in Fig. 2. may be arranged so that only a limited angular movement of the bell crank can be imparted during one stroke of the actuating mechanism. CLAIMS

1. A brake of the type described which operates in a leading and trailing shoe mode in the forward direction of drum rotation and as a duo servo type in the reverse direction, the brake comprising a sliding actuating assembly mounted on a torque carrying backplate, and located between one one end of each of the brake shoes; an abutment member rigidly mounted on said backplate being located diametrically opposite the actuator and between the other ends of said shoes; mechanism which will cause the distance between the shoe ends remote from the actuator to be reduced to a predetermined extent when the brake is operating in the reverse direction; characterised in that the actuator housing is arranged to bear torque in the reverse braking direction only and the abutment member will carry the torque only in the forward braking direction.

2. A brake as described in claim 1 in which the mechanism controlling the distance between the shoe ends remote from the actuating end takes the form of a lever or a pair of levers pivotally mounted on to the shoe web at the heel of the normal shoe, one arm of said lever reacting on to the abutment and another arm of said lever being connected to the other shoe via a strut, said lever being arranged to have a limited angular in respect of the shoe web.

3. A brake as claimed in claims 1 and 2 in which the adjustment for lining wear is a load bearing part of the actuator mechanism.

4. A brake according to any one of the preceeding claims including an adjuster operable to adjust the brake for lining wear when the shoe travel during forward braking exceeds a preset distance the adjuster being so arranged that it does not respond during the reversing mode or if the drum is stationary.

5. A brake according to claim 4 wherein the adjuster includes a pawl pivoted to a point on the actuator assembly which moves in the same direction and in a direct ratio to that of the leading shoe.

6. A brake as claimed in claim 6 where one arm of the pawl receives the adjustment signal from a point attached to the backplate.

7. A brake according to claims 4,5, and 6 where the pawl has a spring attached between itself and the trailing brake shoe.

8. A brake according to claims 4,5 and 6 where the pawl has a spring attached between itself and the actuator body.

9. A brake as claimed in claims 2 and 3 where a spring is fitted between the lever attached to the leading shoe and the backplate adjacent the other shoe.

10. A brake of the type described and as shown in Figs. 1 and 2 of the accompanying drawings.