GB1591710A

GB1591710A - Vehicle brakes

Info

Publication number: GB1591710A
Application number: GB5325476A
Authority: GB
Original assignee: Girling Ltd
Current assignee: Girling Ltd
Priority date: 1976-12-21
Filing date: 1976-12-21
Publication date: 1981-06-24
Also published as: BR7708467A; PL202672A1; PL112982B1; DE2757050A1

Description

(54) IMPROVEMENTS IN VEHICLE BRAKES (71) We, GIRLING LIMITED, a British Company of Kings Road, Tyseley, Birmingham 11, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to improvements in vehicle brakes of the kind comprising cooperating friction members having relatively rotatable friction surfaces which are urged into engagement when the brake is applied by means of brake applying means actuated by a pull-rod which projects from a housing in which the friction members are located.

It is known to provide vehicle brakes of the kind set forth with slack adjusters which are operable automatically to maintain the braking clearances between the friction surfaces in an "off" position of brake within predetermined limits, in order to compensate for wear of friction linings. Usually such adjusters are installed within the housing but, in certain types of vehicle brake, insufficient space is available within the housing to accommodate such adjusters, or the brakes themselves cannot be adapted to include such adjusters. These problems arise particularly with vehicle brakes in which at least one friction disc provided with a friction lining and slidably keyed to a shaft assembly is adapted to be urged into engagement by the applying means with a radial face on the housing, which is relatively stationary.

According to our invention in a vehicle brake of the kind set forth the pull-rod comprises two aligned, non-rotatable transmission members which are relatively movable by means of an automatic slack adjuster, the members being interconnected at spaced-apart adjacent ends by an adjusting component of the automatic slack adjuster, the adjusting component being movable to reduce the spacing between the transmission members to adjust the effective length of the pull-rod, thereby maintaining the braking clearances between the friction surfaces within predetermined limits to compensate for wear of the friction linings.

In one construction the adjacent ends of the transmission members are provided with screw-threads of opposite hand which are screwed into opposite ends of the adjusting component which comprises a sleeve which is rotatable to move the transmission members longitudinally in opposite directions and the sleeve is connected to a part movable with the pull-rod through a clutch mechanism of the slack adjuster arranged to rotate the sleeve to reduce the effective length of the pull-rod when movement of the pull-rod in a brake-applying direction exceeds a predetermined distance which, when no adjustment is required, is sufficient to take up the braking clearances and apply the brake.

One embodiment of our invention is illustrated in the accompanying drawings in which: Figure 1 is a longitudinal section through a brake-applying mechanism for a vehicle brake of the self-energising disc type showing a part of the brake; Figure 2 is a section through the mechanism on an enlarged scale; and Figure 3 is an end elevation of one end of the mechanism.

In the brake-applying mechanism illustrated in the drawings a rotatable brakeapplying shaft 1 is keyed to a sleeve 2 rigid with three axially spaced radial arms 3, 4 and 5. The outermost arms 4 and 5 are of substantial length and are superimposed, and the arm 3 is located between, and is spaced from, both the outermost arms 4 and 5.

A pull-rod 6 for actuating a brake 7 comprises a pair of axially aligned transmission members 8 and 9 of which the outer end of the transmission member 8 carries a bifurcated fitting 10 which is pivotally connected to the free end of the arm 3 by means of a pivot pin 11 and the outer end of the transmission member 9 is coupled by means of a pivot pin 12 to, and forms a pivotal connection between adjacent inner ends of a pair of toggle links 13 and 14, which form part of the brake-applying means, of which the outer ends are movable relatively towards each other to apply the brake 7. The pivot pins 11 and 12 hold the transmission members 8 and 9 against rotation. The inner adjacent ends of the members 8 and 9 are provided with screw-threads of opposite hand which are screwed into opposite ends of an adjusting component in the form of a sleeve 15 in an axially spaced relationship so that rotation of the sleeve 15 causes the members 8 and 9 to move in opposite directions with respect to each other. The sleeve 15 is connected to a part movable with the pull-rod 6, which comprises an open-ended body 16 through which the sleeve extends. The body 16 is provided with trunnions 17 and the trunnions 17 are received in superimposed openings in the free ends of the arms 4 and 5.

The body 16 defines a housing for a clutch mechanism 18 which, together with the sleeve 15, defines an automatic slack adjuster. The clutch mechanism 18 comprises an annular plate 19 which is keyed to the inside of the body 16 and is urged into engagement with a shoulder 20 at the end of the body 16 adjacent to the toggle links 13 and 14 by means of a compression spring 21, and a drive ring 22 having a screw-threaded engagement with an external fast-thread 23 on the sleeve 15 and having an inclined drive face 24 which is normally biassed into engagement with a complementary face 25 on the plate 19 by means of a Belleville or like spring washer 16.

When the brake is to be applied the shaft 1 is rotated in a counter-clockwise direction to withdraw the pull-rod 6 and move the outer ends of the toggle links relatively towards each other. Initial movement of the pull-rod 6 takes up lost-motion in the screw-threads which defines the braking clearances and the body 16 moves with the pull-rod 6 but through a different distance due to differences in the length of the arms 4 and 5, and 3. If the braking clearances are within predetermined limits that initial movement will also be sufficient to apply the brake. However, should an additional movement be required, the axial force through the pull-rod 6 is transmitted to the body through clutch mechanism. Since the plate 19 is keyed to the body 16 and the drive ring 22 is held against rotation by the engagement of the clutch faces 24 and 25, the sleeve 15 is caused to rotate in a direction which, due to the threaded connection with the members 8 and 9 being of opposite hand, causes the members 8 and 9 to move axially towards each other to shorten the effective length of the pull-rod 6 to compensate for wear of the friction linings. When the brake-applying force applied through the pull-rod 6 attains a predetermined value, the plate 19 and the ring 22 both move axially, compressing the spring 21 to preclude further adjustment.

Upon release of the brake-applying force the plate 19 moves axially to its original position with the drive ring 22 rotating to establish a new datum position with respect to which adjustment will take place on a subsequent brake application since the frictional force of the engagement of the fast threads is greater than the engagement of the clutch faces 24 and 25.

Preferably the vehicle brake is of the self-energising type in which the brakeapplying means comprises an expander mechanism in which the outer ends of the toggle links 13 and 14 are pivotally connected to radially projecting lugs 27 and 28 of a pair of pressure plates which are centred on pilots in a stationary housing 29 from which the pull-rod 6 projects in a radial direction. Balls are located in complementary oppositely-inclined recesses in adjacent faces of the pressure plates, and the pressure plates are located between a pair of axially spaced friction discs which carry friction linings and are slidably keyed to a rotatable shaft. Operation of the shaft 1 to withdraw the pull-rod 6 from the housing 29 moves the pressure plates angularly in opposite directions and, due to the balls tending to move out of the recesses, causes the pressure plate to move axially away from each other to clamp the friction discs into engagement with opposed radial sufaces at opposite ends of the housing.

The pressure plates are carried round with the disc until one is arrested by the engagement of a lug on the plate with a stop abutment in the housing 29 and the continued angular movement of the other plate provides a servo-action.

The brake may be of the dry or of the "oil-immersed type".

WHAT WE CLAIM IS: 1. A vehicle brake of the kind set forth, in which the pull-rod comprises two aligned, non-rotatable transmission members which are relatively movable by means of an automatic slack adjuster, the members being interconnected at spaced-apart adjacent ends by an adjusting component of the automatic slack adjuster, the adjusting component being movable to reduce the spacing between the transmission members to adjust the effective length of the pull-rod, thereby maintaining the braking clearances between

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. of the transmission member 8 carries a bifurcated fitting 10 which is pivotally connected to the free end of the arm 3 by means of a pivot pin 11 and the outer end of the transmission member 9 is coupled by means of a pivot pin 12 to, and forms a pivotal connection between adjacent inner ends of a pair of toggle links 13 and 14, which form part of the brake-applying means, of which the outer ends are movable relatively towards each other to apply the brake 7. The pivot pins 11 and 12 hold the transmission members 8 and 9 against rotation. The inner adjacent ends of the members 8 and 9 are provided with screw-threads of opposite hand which are screwed into opposite ends of an adjusting component in the form of a sleeve 15 in an axially spaced relationship so that rotation of the sleeve 15 causes the members 8 and 9 to move in opposite directions with respect to each other. The sleeve 15 is connected to a part movable with the pull-rod 6, which comprises an open-ended body 16 through which the sleeve extends. The body 16 is provided with trunnions 17 and the trunnions 17 are received in superimposed openings in the free ends of the arms 4 and 5. The body 16 defines a housing for a clutch mechanism 18 which, together with the sleeve 15, defines an automatic slack adjuster. The clutch mechanism 18 comprises an annular plate 19 which is keyed to the inside of the body 16 and is urged into engagement with a shoulder 20 at the end of the body 16 adjacent to the toggle links 13 and 14 by means of a compression spring 21, and a drive ring 22 having a screw-threaded engagement with an external fast-thread 23 on the sleeve 15 and having an inclined drive face 24 which is normally biassed into engagement with a complementary face 25 on the plate 19 by means of a Belleville or like spring washer 16. When the brake is to be applied the shaft 1 is rotated in a counter-clockwise direction to withdraw the pull-rod 6 and move the outer ends of the toggle links relatively towards each other. Initial movement of the pull-rod 6 takes up lost-motion in the screw-threads which defines the braking clearances and the body 16 moves with the pull-rod 6 but through a different distance due to differences in the length of the arms 4 and 5, and 3. If the braking clearances are within predetermined limits that initial movement will also be sufficient to apply the brake. However, should an additional movement be required, the axial force through the pull-rod 6 is transmitted to the body through clutch mechanism. Since the plate 19 is keyed to the body 16 and the drive ring 22 is held against rotation by the engagement of the clutch faces 24 and 25, the sleeve 15 is caused to rotate in a direction which, due to the threaded connection with the members 8 and 9 being of opposite hand, causes the members 8 and 9 to move axially towards each other to shorten the effective length of the pull-rod 6 to compensate for wear of the friction linings. When the brake-applying force applied through the pull-rod 6 attains a predetermined value, the plate 19 and the ring 22 both move axially, compressing the spring 21 to preclude further adjustment. Upon release of the brake-applying force the plate 19 moves axially to its original position with the drive ring 22 rotating to establish a new datum position with respect to which adjustment will take place on a subsequent brake application since the frictional force of the engagement of the fast threads is greater than the engagement of the clutch faces 24 and 25. Preferably the vehicle brake is of the self-energising type in which the brakeapplying means comprises an expander mechanism in which the outer ends of the toggle links 13 and 14 are pivotally connected to radially projecting lugs 27 and 28 of a pair of pressure plates which are centred on pilots in a stationary housing 29 from which the pull-rod 6 projects in a radial direction. Balls are located in complementary oppositely-inclined recesses in adjacent faces of the pressure plates, and the pressure plates are located between a pair of axially spaced friction discs which carry friction linings and are slidably keyed to a rotatable shaft. Operation of the shaft 1 to withdraw the pull-rod 6 from the housing 29 moves the pressure plates angularly in opposite directions and, due to the balls tending to move out of the recesses, causes the pressure plate to move axially away from each other to clamp the friction discs into engagement with opposed radial sufaces at opposite ends of the housing. The pressure plates are carried round with the disc until one is arrested by the engagement of a lug on the plate with a stop abutment in the housing 29 and the continued angular movement of the other plate provides a servo-action. The brake may be of the dry or of the "oil-immersed type". WHAT WE CLAIM IS:

1. A vehicle brake of the kind set forth, in which the pull-rod comprises two aligned, non-rotatable transmission members which are relatively movable by means of an automatic slack adjuster, the members being interconnected at spaced-apart adjacent ends by an adjusting component of the automatic slack adjuster, the adjusting component being movable to reduce the spacing between the transmission members to adjust the effective length of the pull-rod, thereby maintaining the braking clearances between

the friction surfaces within predetermined limits to compensate for wear of the friction linings.

2. A vehicle brake according to Claim 1, in which the adjacent ends of the transmission members are provided with screwthreads of opposite hand which are screwed into opposite ends of the adjusting component which comprises a sleeve which is rotatable to move the transmission members longitudinally in opposite directions and the sleeve is connected to a part movable with the pull-rod through a clutch mechanism of the slack adjuster arranged to rotate the sleeve to reduce the effective length of the pull-rod when movement of the pull-rod in a brake-applying direction exceeds a predetermined distance which, when no adjustment is required, is sufficient to take up the braking clearances and apply the brake.

3. A vehicle brake according to Claim 2, in which the clutch mechanism comprises a first member keyed to the part movable with the pull-rod, which comprises a housing for the clutch mechanism and a second member comprising a drive ring in screw-threaded engagement with an external face of the sleeve, a drive face on the drive ring being normally urged into engagement with a complementary face on the first member by resilient means.

4. A vehicle brake according to any preceding claim in which the friction members comprise rotatable friction discs which are adapted to be brought into engagement with opposed radial surfaces in the housing by brake-applying means comprising an expander mechanism located between the friction discs and operated by the pull-rod.

5. A vehicle brake according to Claim 4, in which the expander mechanism comprises a pair of pressure plates, balls located in co-operating oppositely inclined recesses in the adjacent faces of the pressure plates, and a pair of toggle links for moving the pressure plates angularly in relatively opposite directions to cause the pressure plates to move apart and into engagement with the friction discs which are then urged into engagement with the radial surfaces, the pressure plates then being carried round with the friction discs until one is arrested by the engagement of a lug on the plate with a stop abutment in the housing and the continued angular movement of the other pressure plate provides a servo action, the toggle links being connected between radially projecting lugs on the plates with the pull-rod connected to the junction of the links.

6. A vehicle brake of the kind set forth incorporating a brake-applying mechanism substantially as herein described with reference to and as illustrated in the accompanying drawings.