GB1571387A

GB1571387A - Internal shoe-drum brakes for vehicles

Info

Publication number: GB1571387A
Application number: GB1361776A
Authority: GB
Original assignee: Girling Ltd
Current assignee: Girling Ltd
Priority date: 1976-04-03
Filing date: 1976-04-03
Publication date: 1980-07-16
Also published as: DE2714711A1; ES457341A1; FR2346602B1; FR2346602A1

Description

(54) IMPROVEMENTS IN INTERNAL SHOE-DRUM BRAKES FOR VEHICLES (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 internal shoedrum brakes for vehicles of the kind in which arcuate shoes carrying friction linings for engagement with a rotatable drum are adapted to be separated at both pairs of adjacent ends for normal service braking by means of double-ended hydraulic piston and cylinder actuator assemblies each comprising opposed pistons working in bores in a relatively stationary housing so that the brake operates as a brake of the two leading-shoe type for both directions of drum rotation and the drag on each shoe is taken by an abutment on the actuator assembly at the leading end of that shoe.

In known shoe-drum brakes of the kind set forth the bores in which the pistons work are aligned axially and due to the space available being limited, difficulty is experienced in accommodating the actuators in the brake in such a position that brake applying forces can be applied to the shoes in directions to avoid substantially uneven wear of the friction linings, and that both shoes can be of identical size and configuration.

According to our invention in an internal shoe-drum brake of the kind set forth for vehicles the axes of the bores in the housing of at least one of the actuator assemblies are relatively inclined inwardly in a plane normal to the axis of the brake and with respect to a chord of the brake passing through the point of intersection of the axes of the bores.

Relatively inclining the axes of the bores conserves space and enables shoes of identical size and configuration to be utilised.

Also it provides substantially radially arrarged engagements between the pistons and the shoe ends which, in turn, reduces side loading on the bores consequently reducing bore wear. The substantially radially arranged engagements also enable the shoes to adjust or centralise their positions automatically with respect to the pistons under the influence of return springs which reduces substantially any tendency for the linings to wear unevenly.

Preferably the pistons working in the inclined bores incorporate or are combined or otherwise associated with automaticallyoperated slack adjusters for determining an advanced retracted position for the shoes to compensate for wear of the friction linings and the reduction in the side loading applied to the bores facilitates operation of the slack adjusters.

Conveniently the angle of inclination between the bores is substantially 20 but this may vary slightly depending on the diameter of the drum.

One embodiment of our invention is illustrated in the accompanying drawings in which: Figure I is a plan of an internal shoe-drum brake; Figure 2 is a plan on an enlarged scale of a double-ended actuator assemble incorporated in the brake of Figure 1 including a section at the inner ends of the relatively inclined bores; and Figure 3 is a longitudinal section through the housing of the actuators on the line 3-3 of Figure 1 including a section through a slack adjuster embodied in one of the pistons.

In the shoe-drum brake illustrated a pair of arcuate shoes 1, 2 carrying friction linings 3 for engagement with a rotatable drum (not shown) are mounted on a stationary backplate or dirt shield 4.

For normal service braking the shoes 1, 2 are separated at both pairs of adjacent ends by double-ended hydraulic piston and cylinder actuator assemblies 5, 6 so that the brake operates as a brake of the two leading shoe type for both directions of drum rotation.

For parking or emergency braking the actuator assembly 5 incorporates manual7 operable means (not shown) by operation o: which only those ends of the shoes 1, 2 are separated so that the brake then operates as a brake of the one-leading one-trailing shoe type for both directions of drum rotation.

The actuator assembly 6 comprises a housing 7 mounted on the back-plate or dirt shield 4 against relative movement. The housing 7 is provided with opposed stepped bores 8. 9 which are interconnected at tie ir inner ends through a passage 10 so that bott bores can be pressurised at the same time from a common supply. The axes of the bores 8 and 9 are relatively inclined inwardly in a plane normal to a chord 11 of the brake passing through the point of intersection of the axes of the bores 8 and 9.

A piston assembly 12, 13 is located in each bore 8, 9. The piston assemblies 12 and 13 are identical in construction and each comprises an hydraulic piston 14 working in the outer portion of the respective bore 8, 9 which is of greater diameter and a thrust member 15 through which the piston 14 acts on a respective shoe end. Each piston 14 has a blind bore 16 opening towards the inner end of the respective bore 8, 9 and in which an automatic slack adjuster 17 of known construction is located. Each slack adjuster 17 acts between the inner end of the respective blind bore 15 and a drag-teking abutment face 18 at the inner end of the respective bore 8, 9.

Chordal return springs 19 and 20 are connected between the shoe to urge them into engagement with the four pistons.

When both actuator assemblies 5, 6 are operated simultaneously for normal service operation of the brake and all the pistons are urged outwardly, depending on the direction of drum rotation one of the pistons 14 applies a brake applying force to the trailing end of one of the shoes, and the drag on the leading end of the other shoe is transmitted to the corresponding abutment face 18 through the other piston assembly 12, 13.

Preferably the bore 8 in which works the piston assembly 12 which takes the drag on a leading shoe 1 for the normal direction of drum rotation is inclined inwardly by a greater angle with respect to the chord 11 than that by which the other bore 9 is inclined.

This ensures that the engagement between the noe 1 and the piston assembly 12 is in a substantially radial direction thereby reducing side loading on the bore 8 to a minimum and allowing the shoes to adjust or centralise their positions automatically under the influence of the return springs 19 and 20 to ensure that the linings 3 wear substantially evenly.

WHAT WE (LAIM IS:- 1. An internal shoe-drum brake of the kind set forth for vehicles in which the axes of the bores in the housing of at least one of the actuator assemblies are relatively inclined inwardly in a plane normal to the axis of the brake and with respect to a chord of the brake passing through the point of intersection of the axes of the bores.

2. An internal shoe-drum brake according to claim 1, in which the angle of inclination of each bore relative to the chord is arranged such that a substantially radial abutment is provided between each end of the actuator assembly and the shoes.

3. An internal shoe-drum brake according to claim 1 or 2, in which the bore in which works the piston assembly which takes the drag on a leading shoe for the normal direction of drum rotation is inclined inwardly with respect to the chord by a greater angle than that by which the other bore is inclined.

4. An internal shoe-drum brake according to any preceding claim in which the angle of inclination between the bores is substantially 20 .

5. An internal shoe-drum brake according to any preceding claim in which the pistons working in the inclined bores incorporate or are combined or otherwise associated with automatically-operated slack adjusters for determining an advanced retracted position for the shoes to compensate for wear of the friction linings.

6. An internal shoe-drum brake according to claim 5, in which each piston has a blind bore opening towards the inner end of the housing bore, the piston incorporating an automatically operated slack adjuster acting between the blind end of the piston bore and a drag-taking abutment face at the inner end of the housing bore.

7. An internal shoe-drum brake substantially as herein described with reference to and as illustrated in the accompanying drawings.

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. by double-ended hydraulic piston and cylinder actuator assemblies 5, 6 so that the brake operates as a brake of the two leading shoe type for both directions of drum rotation. For parking or emergency braking the actuator assembly 5 incorporates manual7 operable means (not shown) by operation o: which only those ends of the shoes 1, 2 are separated so that the brake then operates as a brake of the one-leading one-trailing shoe type for both directions of drum rotation. The actuator assembly 6 comprises a housing 7 mounted on the back-plate or dirt shield 4 against relative movement. The housing 7 is provided with opposed stepped bores 8. 9 which are interconnected at tie ir inner ends through a passage 10 so that bott bores can be pressurised at the same time from a common supply. The axes of the bores 8 and 9 are relatively inclined inwardly in a plane normal to a chord 11 of the brake passing through the point of intersection of the axes of the bores 8 and 9. A piston assembly 12, 13 is located in each bore 8, 9. The piston assemblies 12 and 13 are identical in construction and each comprises an hydraulic piston 14 working in the outer portion of the respective bore 8, 9 which is of greater diameter and a thrust member 15 through which the piston 14 acts on a respective shoe end. Each piston 14 has a blind bore 16 opening towards the inner end of the respective bore 8, 9 and in which an automatic slack adjuster 17 of known construction is located. Each slack adjuster 17 acts between the inner end of the respective blind bore 15 and a drag-teking abutment face 18 at the inner end of the respective bore 8, 9. Chordal return springs 19 and 20 are connected between the shoe to urge them into engagement with the four pistons. When both actuator assemblies 5, 6 are operated simultaneously for normal service operation of the brake and all the pistons are urged outwardly, depending on the direction of drum rotation one of the pistons 14 applies a brake applying force to the trailing end of one of the shoes, and the drag on the leading end of the other shoe is transmitted to the corresponding abutment face 18 through the other piston assembly 12, 13. Preferably the bore 8 in which works the piston assembly 12 which takes the drag on a leading shoe 1 for the normal direction of drum rotation is inclined inwardly by a greater angle with respect to the chord 11 than that by which the other bore 9 is inclined. This ensures that the engagement between the noe 1 and the piston assembly 12 is in a substantially radial direction thereby reducing side loading on the bore 8 to a minimum and allowing the shoes to adjust or centralise their positions automatically under the influence of the return springs 19 and 20 to ensure that the linings 3 wear substantially evenly. WHAT WE (LAIM IS:-

1. An internal shoe-drum brake of the kind set forth for vehicles in which the axes of the bores in the housing of at least one of the actuator assemblies are relatively inclined inwardly in a plane normal to the axis of the brake and with respect to a chord of the brake passing through the point of intersection of the axes of the bores.