GB2310015A

GB2310015A - Vehicle brake assemblies

Info

Publication number: GB2310015A
Application number: GB9702441A
Authority: GB
Inventors: Andrew John Ward; Ian Douglas Poole
Original assignee: Lucas Industries Ltd
Current assignee: ZF International UK Ltd
Priority date: 1996-02-07
Filing date: 1997-02-06
Publication date: 1997-08-13
Anticipated expiration: 2017-02-06
Also published as: GB2310015B; GB9702441D0

Abstract

A vehicle brake includes brake lining wear monitoring means for monitoring the wear condition of the brake assembly. The brake comprises adjusting means 13 adapted to be driven by actuating means 6 for the purpose of maintaining the friction member 4, 5 in close proximity to the brake rotor 1, and wear sensors 70, 71, 72 responsive to actuation movement of the brake in the brake-applying direction. A lost-motion connection 78, 79 is incorporated in the wear sensor means to compensate for deflections of the brake components.

Description

VEHICLE BRAKE ASSEMBLIES This invention relates to vehicle brake assemblies of the kind in which an actuator is adapted to apply at least one friction member into engagement with at least one face of a rotor.

In one known brake of the kind set forth a floating caliper straddles a brake carrier, and the actuator is adapted to apply the one friction member to the rotor, the reaction of that friction member on the rotor causing the caliper to move bodily in the opposite direction with respect to the brake carrier in order to urge a second friction pad assembly into engagement with the opposite face of the rotor.

Some brakes of the known kind referred to above are used in commercial vehicles and comprise components which are massive in construction in order to generate and absorb the substantial forces which are produced when the brake assemblies are applied in order to achieve desired stopping distances. Often deflection, typically bending, of the components takes place during the application of the brake, which, if measured by a wear sensor, would provide a false signal, indicating that friction linings had reached the end of their wear life whereas, in fact, the linings may have been only partly worn. In addition a problem may arise due to movement of the wear sensor due to take up of the normal running clearance within the brake. For example, as the brake is actuated, the actuator first moves the friction member into engagement with the rotor at which point force is applied to the rotor to generate braking. This take up or brake stroke will also cause oscillatory wear within the sensor. In the case of a potentiometer the track will be eroded where a large number of applications have been made. It is therefore desirable to eliminate such movement within the sensor generated by normal actuation of the brake.

Once this normal running clearance has been taken up any additional movement in stroke would be attributed to wear in friction linings and/or brake rotor. This additional movement would then be detected by the sensor as the sensor clearance is equal to the displacement generated by the normal stroke of the brake.

According to our invention in a vehicle brake of the kind set forth including brake lining wear monitoring means for monitoring the wear condition of the brake assembly comprising adjusting means adapted to be driven by the actuating means for the purpose of maintaining the friction member in close proximity to the brake rotor, and wear sensing means responsive to actuation movement of the brake in the brake-applying direction, a lost-motion connection is incorporated in the wear sensing means to compensate for deflections of the brake components.

This ensures that substantially a true indication of lining wear is obtained since the lost-motion connection is set to ensure that the wear sensing means only becomes operative after deflection of components and running clearances of the brake have taken place.

The wear sensing means is housed within the body of the brake itself without increasing in the overall package size of the brake.

The wear sensing means may include a linear potentiometer, a rotary potentiometer, an inductive sensor or similar device.

The wear sensing means may be operated by a transmission mechanism which incorporated the necessary degree of lost-motion to compensate for deflection of the brake components and the running clearances.

In one construction the lost-motion connection comprises a clearance between an enlarged head or abutment on an operating rod for the wear sensing means and an abutment face which defines a datum and with respect to which the head co-operates when the deflections have been taken up, whereafter further relative movement between the face and the sensing means operates a wear sensor to provide an indication of the wear condition of the lining.

One embodiment of our invention illustrated in the accompanying drawings in which: Figure 1 illustrates a disc brake assembly in part section including brake wear sensors; Figure 2 longitudinal section through a brake wear sensor; and Figure 3 is another view of a sensor driven from the brake adjuster.

In the disc brake illustrated in Figure 1-3 of the accompanying drawings the brake comprises a brake disc 1 and a brake carrier 2. A floating caliper 3 straddles the carrier member 2 and co-operates with two brake pad assemblies 4 and 5, each comprising a rigid backing plate guided to slide between circumferentially spaced drag take surfaces on the carrier, and a pad of friction material for engagement with an adjacent face of the disc 1. A brake actuating device 6 mounted in the caliper is adapted to urge the friction pad assembly 4 into engagement with the disc 1 and the reaction of disc pad assembly on the disc causes the caliper 3 to move bodily in the opposite direction with respect to the carrier 2, in turn to urge the friction pad assembly 5 into engagement with the opposite face of the disc 1.

The actuating device 6 comprises a rotary member 7 which is mounted in an opening in the caliper 2 between respective pairs of needle bearings 8 and 9 carried by a casing 10 and a cover 11 for the outer end of the casing. Two adjustable tappets 13 are housed in the casing 10 of the actuating device 6. Each of these tappets comprises a first internally threaded member 14, and a second externally threaded member 15. The tappets are disposed on opposite sides of a plane of symmetry E, parallel to and spaced from the same. The two second threaded members 15 are interconnected by a thin metal plate 16 so that they cannot be rotated, the metal plate at the same time serving as a heat shield between the members 15 and the friction pad assembly 4.

The rotary member 7 comprises two eccentrics 16 which are arranged in a terminal zone of the rotary member, acting through a roller body 17 onto a respective one of the first threaded members 14. The rotary member 7 is formed with a pair of journal pins 18 between the two eccentrics and the journal pins are supported in a depression 19 at the inner side of the cover 11 through an outer ring of the needle bearings 8.

Both first threaded members 14 are connected to the rotary member 7 by a gear connection which comprises an angle drive and a coupling arrangement 20 also the angle drive is formed by meshing bevel teeth. A pinion 24 engages directly with external teeth 25 on the adjacent first threaded member 14 and only then does an intermediate gear 26 follow.

The intermediate gear meshes with the external teeth of both first threaded members 14.

The pinion 24 is formed with an inner hexagon 50 which cooperates with a complementary hexagonal formation 51 on a return adjuster shaft 52.

A first sleeve 27 surrounds the shaft 52 and discs 28 between the coupling arrangement 20 and a second sleeve 29 provide a drive connection therebetween.

On actuation of the brake, rotation of the rotary member 7 is converted by the angle drive formed by the two bevel teeth 22 and 23 into rotation of the first leaf 27 supported on the shaft 52 of the coupling arrangement 20. Once a rotational clearance has been overcome between the disc 28 and the second sleeve 29, a torque will act on the second sleeve 29, through a wrap spring 30, onto the pinion 24, and finally onto the first threaded member 14 through the intermediate gear 26 and the external teeth 25.

The threaded member 14 will not rotate, however, if a brake relief clearance, has been overcome by the above mentioned rotational clearance so the two brake pad assemblies 4 and 5 have engaged the brake disc 1 which consequently transmits reactive force, in correspondence with the actuating force, to the two eccentrics 16 through a tappet formed by the two threaded members 14 and 15. The friction occurring in the readjustment thread pair 13 on that occasion is greater than the torque which the coupling 21 can transmit.

If the rotational clearance between the discs 28 and the second sleeve 29 is overcome upon actuation of the brake, and the brake pad assemblies 4,5 do not reach the brake disc to give rise to a corresponding reactive force, rotation of the first sleeve 27 will be transmitted through the stack of discs 28 to the second sleeve 29 and on through the wrap spring 30 to the pinion 24 and finally to the first threaded member 14 which consequently will be turned in the sense that the tappet is presents together with second threaded member 15 extends in length.

On release of the brake, the rotational movement of the rotary member 8, which is now in the opposite sense, is transmitted to the first leaf 27 but not further onto the pinion 24 because, in this direction of rotation, the wrap spring 30 opens and thus prevents the pinion 24 from accompanying the rotational movement.

Wear sensing means in the form of wear sensors 70, 71, 72 may be incorporated in the brake assembly at suitable locations.

The sensor 70 is adapted to respond to wear of the outboard friction pad assembly 5 by monitoring movement of the caliper 3 relative to the carrier member 2. The sensor 71 is adapted to respond to total wear of both pad assemblies 4 and 5 by monitoring axial movement of the threaded member 15, as it moves forward to compensate for wear of the linings. The sensor 72 is adapted to respond to movement of the inboard friction pad assembly 4 by monitoring movement of that pad assembly 4 itself with respect to the caliper 3.

The sensor 72 is an alternative to the sensor 71, since the movement of the inboard pad 4 with respect to the brake housing also includes the displacement of the outboard pad. Therefore this sensor, as well as sensor 71, measures the total brake wear. Therefore if the outboard pad wear 70 is subtracted from the total lining wear 71, 72 then the inboard pad wear can be calculated.

Each sensor 70, 71, 72 is of similar construction and is illustrated in Figure 2 of the accompanying drawings.

As illustrated in Figure 2 each sensor comprises a rotary or linear sensing device, in the form of a potentiometer 75, which is operated by a longitudinal extending rod 76 slideably guided into a bearing 77 with sufficient friction to ensure that the sensor does not move under vibrations. The rod 76 is provided at the end remote from the potentiometer 75 with an enlarged head 78 and which is normally spaced from an abutment face 79 surrounding an opening in a relatively moveable part 80 and through which the rod 76 projects.

In operation, during initial application of the brake in which the components deflect, the clearance, or lost-motion, within the sensor arrangement prevents the potentiometer 75 from being operated. The lost-motion, as shown with reference to the sensor 70 comprises the spacing between the head 78 and the abutment face 79, which corresponds to deflection of the brake components during application of the brake.

This ensures that the sensor is only operated to provide an indication of the wear of the friction lining, or of the linings, and is not affected by deflection of the components of the brake.

When the sensor comprises the sensing arrangement as shown at 70, the sensor 75 is fixed to the caliper 3, and the head 78 is adapted to engage with an abutment face 79 carried by a slide pin 80, or other similar movable member such as the tappet or pad assemblies, which acts to move the sensor rod 76 in a longitudinal direction.

When the sensor comprises the sensor 71, the potentiometer 75 is carried by the caliper 3, and the abutment face 79 is moveable with the threaded member 15.

When the sensor comprises the sensor 72, the potentiometer 75 is carried by the caliper 3, and the abutment face is provided in a backing plate 81 which carries a friction pad 82 to define the friction pad assembly 4.

Figure 3 illustrates a sensing arrangement where the sensor is already only driven by movement generated by actual wear in the brake linings, as it is operatively connected to the adjuster, and therefore there is no need to eliminate sensor movement that would be generated by take up of the normal running clearance of the brake. The sensor is provided that is housed within and secured to the outer portion of the brake housing. In operation this sensor detects movement within a mechanism which is housed within and secured to an inner portion of the brake housing. As the brake applied, the tappets apply a force to the brake rotor, the reaction of which is supported by the brake housing. It is possible, upon heavy brake application to generate a discernible bending moment within the brake housing which is substantially within the safe working range of the brake but which causes a small relative displacement in parts of the brake and/or brake housing. Specifically we are interested in eliminating the effects of any such relative displacement that would normally affect the sensor output. This is achieved by providing a clearance within the sensing arrangement preferably within the sensor itself which is equivalent to the maximum relative displacement that could be seen across the brake. Such a clearance 90, is provided between the sensing element 91 and an abutment 92 operatively secured to the sensor rod. Thus as the brakes are applied to the level that could cause an increase in distance between the outer and inner parts of the brake housing, the sensor rod would be displaced up to a distance as defined by clearance 90 but would not engage with the sensing element 91.

Claims

1. A vehicle brake of the kind set forth including brake lining wear monitoring means for monitoring the wear condition of the brake assembly comprising adjusting means adapted to be driven by the actuating means for the purpose of maintaining the friction member in close proximity to the brake rotor, and wear sensing means responsive to actuation movement of the brake in the brake-applying direction in which a lost-motion connection is incorporated in the wear sensing means to compensate for deflections of the brake components.

2. A vehicle brake according to claim 1, in which the wear sensing means is housed within a body of the brake itself without increasing in the overall package size of the brake.

3. A vehicle brake according to claim 1 or claim 2, in which the wear sensing means includes a linear potentiometer.

4. A vehicle brake according to claim 1 or claim 2, in which the wear sensing means includes a rotary potentiometer.

5. A vehicle brake according to claim 3, in which the wear sensing means comprises an inductive sensor.

6. A brake according to any preceding claim, in which the wear sensing means is operated by a transmission mechanism which incorporates a degree of lost-motion necessary to compensate for deflection of the brake components and the running clearances.

7. A vehicle brake according to any preceding claim, in which the lost-motion connection comprises a clearance between an enlarged head or abutment on an operating rod for the wear sensing means and an abutment face which defines a datum and with respect to which the head co-operates when the deflections have been taken up, whereafter further relative movement between the face and the sensing means operates a wear sensor to provide an indication of the wear condition of the lining.

8. A vehicle brake substantially as described herein with reference to and as illustrated in the accompanying drawings.