GB1560939A

GB1560939A - Vehicle wheel internal shoe drum brakes

Info

Publication number: GB1560939A
Application number: GB4041775A
Authority: GB
Original assignee: Girling Ltd
Current assignee: Girling Ltd
Priority date: 1975-10-02
Filing date: 1975-10-02
Publication date: 1980-02-13
Also published as: IT1081488B; FR2326619B1; DE2644266A1; JPS5243072A; FR2326619A1; JPS5645006B2; DE2644266C2

Description

(54) IMPROVEMENTS IN OR RELATING TO VEHICLE WHEEL INTERNAL SHOE DRUM BRAKES (71) We, GIRLING LIMITED, a British Company, of Kings Road, Tyseley, Birmingham 11, do hereby declare the invention, for which 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 vehicle wheel internal shoe drum brakes.

The invention is particularly concerned with brakes of the leading/trailing shoe type having a pair of arcuate brake shoes, an actuator acting between one pair of adjacent shoe ends and a fixed abutment engaged by the other pair of adjacent shoe ends.

In one form of known brake the abutment has opposed abutment surfaces which are parallel with each other and with a diameter of the brake joining the centres of the actuator and the abutment. In operation, the leading shoe, under the action of input forces and drum torques, tends to move outwards and towards the abutment, and the trailing shoe, under similar forces, tends to move outwards and away from the abutment.

In practice this gives rise to a shoe lining wear pattern in which wear is greatest at the radial line along which the shoe tends to move. This line is known as the centre of maximum pressure (CMP).

For maximum utilisation of the lining material it is desirable for the CMP to be normal to the diameter passing through the centres of the actuator and the abutment, so that the maximum volume of lining material is worn off the shoe before the metal backing of the shoe is bared to contact the drum, assuming that the lining is also substantially equally disposed about that normal. The known form of brake having parallel abutment surfaces has the disadvantage that this desirable feature does not occur.

It is known that for a leading shoe the desired wear pattern can be obtained by angling the abutment surface so that it is more radial, the angle of the surface being referred to as a positive angle.

Another form of known leading/trailing shoe brake has an abutment which has positively angled face for the leading shoe, and is symmetrical about a line passing through the centres of the actuator and the abutment, i.e. the abutment is positively angled on both abutting faces.

The use of the abutment with two positively angled faces corrects the lining wear pattern of the leading shoe, but has the disadvantage that a slightly worse lining wear pattern on the trailing shoe is obtained, i.e. the CMP moves further away from the lining centre. This is, however, acceptable in some cases since the lining wear on the trailing shoe is much less than the wear on the leading shoe due to the servo effect of the drum torque. However the CMP position can be adversely affected by manufacturing tolerances, with the possible result that only part of the arc of the trailing shoe lining is in contact with the drum, which causes alteration in brake effectiveness and sometimes leads to customer complaints.

The present invention aims at reducing or removing the above-mentioned disadvantages and provides a vehicle wheel internal shoe drum brake, comprising two opposed arcuate brake shoes, an actuator acting on one pair of adjacent shoe ends, and a fixed abutment having opposed abutment surfaces engaged by the other pair of adjacent shoe ends, wherein the abutment surface which is engaged by the shoe constituting the trailing shoe during forward rotation of the drum is inclined with respect to a plane passing through the drum axis and the abutment axis and extending perpendicularly to a back plate, the inclination being in a sense to resist the travel of the trailing shoe with the drum during forward rotation.

Preferably, the abutment surface which is engaged by the leading shoe constituting the backing shoe during forward rotation of the drum is inclined in the same sense as the abut ment surface engaging the trailing shoe. The abutment surfaces are preferably parallel with each other.

In a presently preferred embodiment of the invention described in more detail below the abutment is a unitary member and is symmetrical to permit its connection to the brake back plate in one of two alternative positions, the selected position depending on the direction of forward rotation of the drum.

Two forms of vehicle wheel internal shoe drum brake in accordance with the invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a plan view of the brake, Figures 2 and 3 are respectively sections taken along lines A-A, C-C of Figure 1, and Figure 4 is a view similar to Figure 1 of an alternative form of brake.

Referring to Figures 1 to 3, the brake comprises two arcuate brake shoes 1, 2 for engagement with a drum (not shown) whose direction of forward rotation is anti-clockwise as shown by the arrow in Figure 1. An hydraulic actuator 3 is located between one pair of adjacent shoe ends and is operable to separate the shoe ends, and an abutment 4 is located between the other pair of adjacent shoe ends.

The shoes 1, 2 can also be separated by a mechanical hand brake mechanism 7 which is most clearly illustrated in Figure 3 and requires no detailed description here.

The abutment 4 is a unitary member fixed to the brake back plate 5 and having parallel opposed abutment surfaces 4A, 4B engaged respectively by the leading shoe 1 and the trailing shoe 2. The abutment surfaces are inclined to a plane 6 of the brake joining the centres or axes of the actuator 3 and abutment 4 and passing through the drum axis and extending perpendicularly to the back plate 5. The surfaces are so inclined that they resist movement of the respective shoes with the drum during rotation of the drum in the forward direction, the abutment surface 4B resisting radially inward movement of the leading end of the trailing shoe 2. The abutment surface 4A preferably extends substantially radially of the brake back plate 5.

Figure 4 shows a similar form of brake arranged for clockwise forward rotation of the drum, as indicated by the arrow, the shoe 1 being the trailing shoe and shoe 2 the leading shoe. The abutment 4 is of precisely the same configuration as the abutment of Figure 1, but is located relative to the back plate in an alternative position which also has the effect of resisting movement of the shoes with the drum when the drum rotates in the forward direction.

The above-described forms of brake have the advantages that the wear of the trailing shoe is more evenly distributed by inclining the abutment surface 4B at a similar angle to that of the abutment surface 4A; the unitary abutment 4 can be used for brakes having different directions of forward rotation; shoes having the same configurations but with linings differently positioned can be used for both trailing and leading shoes.

The above-described brakes can be arranged such that the centre of maximum pressure for each brake shoe is substantially at the centre of the lining arc.

WHAT WE CLAIM IS: 1. A vehicle wheel internal shoe drum brake, comprising two opposed arcuate brake shoes, an actuator acting on one pair of adjacent shoe ends, and a fixed abutment having opposed abutment surfaces engaged respectively by the other pair of adjacent shoe ends, wherein the abutment surface which is engaged by the shoe constituting the trailing shoe during forward rotation of the drum is inclined with respect to a plane passing through the drum axis and the abutment axis, and extending perpendicularly to a back plate the inclination being in a sense to resist travel of the trailing shoe with the drum during forward rotation.

2. A brake according to claim 1, wherein the abutment surface which is engaged by the shoe constituting the leading shoe during forward rotation of the drum is inclined in the same sense as the abutment surface engaging the trailing shoe.

3. A brake shoe according to claim 2, wherein the abutment surface engaging the leading shoe extends substantially radially.

4. A brake according to claim 2 or 3, wherein the abutment surfaces are parallel.

5. A brake according to any of claims 1 to 4, wherein the abutment is a unitary member.

6. A brake according to any of claims 1 to 5, wherein the abutment is symmetrical and can be fixed to a back plate of the brake in one of two alternative positions depending upon the direction of forward rotation of the drum.

7. A vehicle wheel internal shoe drum brake constructed and arranged to operate substantially as herein described with refzr- ence to Figures 1 to 3 or to Figure 4 of the accompanying drawings.

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. ment surface engaging the trailing shoe. The abutment surfaces are preferably parallel with each other. In a presently preferred embodiment of the invention described in more detail below the abutment is a unitary member and is symmetrical to permit its connection to the brake back plate in one of two alternative positions, the selected position depending on the direction of forward rotation of the drum. Two forms of vehicle wheel internal shoe drum brake in accordance with the invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a plan view of the brake, Figures 2 and 3 are respectively sections taken along lines A-A, C-C of Figure 1, and Figure 4 is a view similar to Figure 1 of an alternative form of brake. Referring to Figures 1 to 3, the brake comprises two arcuate brake shoes 1, 2 for engagement with a drum (not shown) whose direction of forward rotation is anti-clockwise as shown by the arrow in Figure 1. An hydraulic actuator 3 is located between one pair of adjacent shoe ends and is operable to separate the shoe ends, and an abutment 4 is located between the other pair of adjacent shoe ends. The shoes 1, 2 can also be separated by a mechanical hand brake mechanism 7 which is most clearly illustrated in Figure 3 and requires no detailed description here. The abutment 4 is a unitary member fixed to the brake back plate 5 and having parallel opposed abutment surfaces 4A, 4B engaged respectively by the leading shoe 1 and the trailing shoe 2. The abutment surfaces are inclined to a plane 6 of the brake joining the centres or axes of the actuator 3 and abutment 4 and passing through the drum axis and extending perpendicularly to the back plate 5. The surfaces are so inclined that they resist movement of the respective shoes with the drum during rotation of the drum in the forward direction, the abutment surface 4B resisting radially inward movement of the leading end of the trailing shoe 2. The abutment surface 4A preferably extends substantially radially of the brake back plate 5. Figure 4 shows a similar form of brake arranged for clockwise forward rotation of the drum, as indicated by the arrow, the shoe 1 being the trailing shoe and shoe 2 the leading shoe. The abutment 4 is of precisely the same configuration as the abutment of Figure 1, but is located relative to the back plate in an alternative position which also has the effect of resisting movement of the shoes with the drum when the drum rotates in the forward direction. The above-described forms of brake have the advantages that the wear of the trailing shoe is more evenly distributed by inclining the abutment surface 4B at a similar angle to that of the abutment surface 4A; the unitary abutment 4 can be used for brakes having different directions of forward rotation; shoes having the same configurations but with linings differently positioned can be used for both trailing and leading shoes. The above-described brakes can be arranged such that the centre of maximum pressure for each brake shoe is substantially at the centre of the lining arc. WHAT WE CLAIM IS:

1. A vehicle wheel internal shoe drum brake, comprising two opposed arcuate brake shoes, an actuator acting on one pair of adjacent shoe ends, and a fixed abutment having opposed abutment surfaces engaged respectively by the other pair of adjacent shoe ends, wherein the abutment surface which is engaged by the shoe constituting the trailing shoe during forward rotation of the drum is inclined with respect to a plane passing through the drum axis and the abutment axis, and extending perpendicularly to a back plate the inclination being in a sense to resist travel of the trailing shoe with the drum during forward rotation.