GB2057075A

GB2057075A - Drum brake

Info

Publication number: GB2057075A
Application number: GB8021773A
Authority: GB
Original assignee: Deutsche Perrot Bremse GmbH
Current assignee: Deutsche Perrot Bremse GmbH
Priority date: 1979-08-13
Filing date: 1980-07-02
Publication date: 1981-03-25
Also published as: FR2463324A1; GB2057075B; IT8012605A0; IT1133464B; DE2932733A1

Abstract

A drum brake has fixed abutment 21 against which adjacent end surfaces 7, 8 of the brake shoes 5, 6 bear, formed so that end surface 7 of the normally leading shoe 5 bears against a bearing surface 3 inclined at an acute angle (preferably 5 DEG +/- 1 DEG ) to the centre line A of the brake assembly, and the end surface 8 of the normally trailing show 6 bears against a bearing surface 4 parallel to the centre line A. In braking for rotation contrary to normal direction, surface 4 provides a greater servo effect on the non-leading shoe 6. <IMAGE>

Description

SPECIFICATION Drum brake The invention relates to a Simplex drum brake, that is a drum brake having two floatinglymounted internal brake shoes which bear radially movably by adjacent end surfaces against an abutment fixedly fitted on a stationary carrier plate and which are rendered operative by mechanical or hydraulic means at their opposite ends.

Simplex brakes are known in which the two brake shoes bear slidingly on the abutment, the slide surfaces of which are parallel to the centre line of the brake. On actuation of the brake the parallel surfaces cause a servo-action 6f the brake shoes, which is not always desired.

For this reason brakes have already been proposed in which the two bearing surfaces make equal angles with the centre line and as a result the servo-action is reduced or even eliminated, according to the angle selected.

Initially Simplex brakes having such symmetrical surface formation on the abutment have the same braking effect for both directions of brake drum rotation. In use on vehicles which travel mainly in one "preferred" direction with a corresponding ratio of braking occurrences, the difference of braking force, in the ratio of about 3:1, between the leading brake shoe and the trailing brake shoe has the effect that the brake drum is deformed out of circular truth and asymmetrically in relation to the brake shoes. Thus the linings of the brake shoes become unevenly worn. The deformation of the brake drum lies in the elastic range and recovers after termination of the braking action, and the deformation varies according to the direction of rotation.This means that, when braking the drum as it is rotating in the opposite direction to the preferred direction, the normally trailing shoe does not achieve its ideal contact pattern and thus cannot build up the corresponding braking force. Specifically when braking for parking on a slope, especially if the brake shoes are actuated by a spring reservoir giving a fixed application force, the maintenance of the braking moment once fixed is important.

The invention seeks to provide a Simplex brake which even when there is a greatly "preferred" direction of brake drum rotation and consequent irregular wearing of the brake linings, adequate braking forces can be generated even in the reverse direction of rotation, while the actuation forces adapted to the characteristic behaviour in the preferred direction of rotation are retained.

According to the invention, in a Simplex brake the bearing surface on the abutment for the brake shoe which leads in the preferred direction of rotation makes with the centre line an acute angle a and the bearing face for the trailing brake shoe extends parallel to the centre line.

By suitable inclination of the bearing face, the servo-action of the brake shoe which leads in the preferred direction of rotation is predetermined to the desired extent, while the release behaviour is especially taken into account. At the same time the reduction of brake force, which normally occurs when braking for reverse rotation and which is due to uneven wear of the brake linings, is compensated for by an intensification of braking force by the parallel bearing surface.

This has the consequence that the actuating elements, such as slave cylinders or spring reservoirs, which hitherto had to be made large to achieve the desired effect, can be made correspondingly smaller and thus less costly.

The acute angle a made with the centre line by the inclined bearing surface preferably is 50+1 0 Due to the fact that the braking forces occurring in the preferred direction of rotation are increased, when braking in the reverse direction adequate braking forces can be achieved on the then leading brake shoe, while retaining the actuation forces adapted to the behaviour in the preferred direction of rotation.

Further details, advantages and features of the invention appear from the following description and the drawing which shows a Simplex drum brake partially in section.

In the drawing, an abutment 2 having bearing surfaces 3 and 4 is fixedly arranged on a stationary carrier plate 1. Two floatingly-mounted brake shoes 5 and 6 bear slidingly by their lower end surfaces 7 and 8 against the bearing surfaces 3 and 4. They can be pressed against the internal surface of a brake drum 14 by actuation of a hydraulic slave cylinder 9 the pistons 10 and 11 of which apply a load on the upper end faces 12 and 13 of the brake shoes 5 and 6. Springs 1 5 and 16 are provided to retract the brake shoes 5 and 6 after termination of a braking action. An automatic readjuster 1 7 can effect the compensation between the brake shoes for wear of the brake linings.

The bearing surface 3 of the brake shoe 5 which leads in the preferred direction of rotation is inclined at an angle of about 5 to the centre line A of the brake assembly and the surface 4 is parallel to the centre line. The servo-effect of the brake shoe 5 which leads in the preferred direction of rotation is consequently somewhat less than that of the brake shoe 6 when the latter becomes the leading brake shoe on braking for reverse rotation.

When braking for rotation contrary to the preferred direction B of rotation, for example braking for parking on a hill, the brake shoe 5 becomes the trailing shoe and conversely the brake shoe 6 becomes the leading shoe. The parallel bearing face 4 effects a greater servoeffect on the now leading brake shoe 6, whereby the reduction of braking force occurring by reason of the irregular wear is compensated.

1. A Simplex drum brake characterised in that the bearing surface of the abutment for the brake shoe which leads in the preferred direction of rotation makes an acute angle a with the centre line of the brake assembly and the bearing surface

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Drum brake The invention relates to a Simplex drum brake, that is a drum brake having two floatinglymounted internal brake shoes which bear radially movably by adjacent end surfaces against an abutment fixedly fitted on a stationary carrier plate and which are rendered operative by mechanical or hydraulic means at their opposite ends. Simplex brakes are known in which the two brake shoes bear slidingly on the abutment, the slide surfaces of which are parallel to the centre line of the brake. On actuation of the brake the parallel surfaces cause a servo-action 6f the brake shoes, which is not always desired. For this reason brakes have already been proposed in which the two bearing surfaces make equal angles with the centre line and as a result the servo-action is reduced or even eliminated, according to the angle selected. Initially Simplex brakes having such symmetrical surface formation on the abutment have the same braking effect for both directions of brake drum rotation. In use on vehicles which travel mainly in one "preferred" direction with a corresponding ratio of braking occurrences, the difference of braking force, in the ratio of about 3:1, between the leading brake shoe and the trailing brake shoe has the effect that the brake drum is deformed out of circular truth and asymmetrically in relation to the brake shoes. Thus the linings of the brake shoes become unevenly worn. The deformation of the brake drum lies in the elastic range and recovers after termination of the braking action, and the deformation varies according to the direction of rotation.This means that, when braking the drum as it is rotating in the opposite direction to the preferred direction, the normally trailing shoe does not achieve its ideal contact pattern and thus cannot build up the corresponding braking force. Specifically when braking for parking on a slope, especially if the brake shoes are actuated by a spring reservoir giving a fixed application force, the maintenance of the braking moment once fixed is important. The invention seeks to provide a Simplex brake which even when there is a greatly "preferred" direction of brake drum rotation and consequent irregular wearing of the brake linings, adequate braking forces can be generated even in the reverse direction of rotation, while the actuation forces adapted to the characteristic behaviour in the preferred direction of rotation are retained. According to the invention, in a Simplex brake the bearing surface on the abutment for the brake shoe which leads in the preferred direction of rotation makes with the centre line an acute angle a and the bearing face for the trailing brake shoe extends parallel to the centre line. By suitable inclination of the bearing face, the servo-action of the brake shoe which leads in the preferred direction of rotation is predetermined to the desired extent, while the release behaviour is especially taken into account. At the same time the reduction of brake force, which normally occurs when braking for reverse rotation and which is due to uneven wear of the brake linings, is compensated for by an intensification of braking force by the parallel bearing surface. This has the consequence that the actuating elements, such as slave cylinders or spring reservoirs, which hitherto had to be made large to achieve the desired effect, can be made correspondingly smaller and thus less costly. The acute angle a made with the centre line by the inclined bearing surface preferably is 50+1 0 Due to the fact that the braking forces occurring in the preferred direction of rotation are increased, when braking in the reverse direction adequate braking forces can be achieved on the then leading brake shoe, while retaining the actuation forces adapted to the behaviour in the preferred direction of rotation. Further details, advantages and features of the invention appear from the following description and the drawing which shows a Simplex drum brake partially in section. In the drawing, an abutment 2 having bearing surfaces 3 and 4 is fixedly arranged on a stationary carrier plate 1. Two floatingly-mounted brake shoes 5 and 6 bear slidingly by their lower end surfaces 7 and 8 against the bearing surfaces 3 and 4. They can be pressed against the internal surface of a brake drum 14 by actuation of a hydraulic slave cylinder 9 the pistons 10 and 11 of which apply a load on the upper end faces 12 and 13 of the brake shoes 5 and 6. Springs 1 5 and 16 are provided to retract the brake shoes 5 and 6 after termination of a braking action. An automatic readjuster 1 7 can effect the compensation between the brake shoes for wear of the brake linings. The bearing surface 3 of the brake shoe 5 which leads in the preferred direction of rotation is inclined at an angle of about 5 to the centre line A of the brake assembly and the surface 4 is parallel to the centre line. The servo-effect of the brake shoe 5 which leads in the preferred direction of rotation is consequently somewhat less than that of the brake shoe 6 when the latter becomes the leading brake shoe on braking for reverse rotation. When braking for rotation contrary to the preferred direction B of rotation, for example braking for parking on a hill, the brake shoe 5 becomes the trailing shoe and conversely the brake shoe 6 becomes the leading shoe. The parallel bearing face 4 effects a greater servoeffect on the now leading brake shoe 6, whereby the reduction of braking force occurring by reason of the irregular wear is compensated. CLAIMS

1. A Simplex drum brake characterised in that the bearing surface of the abutment for the brake shoe which leads in the preferred direction of rotation makes an acute angle a with the centre line of the brake assembly and the bearing surface for the trailing brake shoe extends parallel to the centre line.

2. A Simplex drum brake according to claim 1, characterised in that the bearing face of the abutment piece for the brake shoe which leads in the preferred rotation direction makes an angle of 50+10 with the centre line of the brake assembly.

3. A Simplex drum brake substantially as hereinbefore described with reference to and as shown in the accompanying drawing.