Method of operating a brake

Abstract

A method of operating a mechanically operated brake having an electric motor for operating an adjuster mechanism that may include the steps of: a) providing a brake rotor and friction material for selective engagement with the brake rotor, b) providing a target running clearance between the brake rotor and the friction material, c) applying the brake by forcing the friction material into engagement with the brake rotor, d) determining that the friction material is set in a compressed condition, e) releasing the brake, f) operating the electric motor to operate the adjuster mechanism to adjust the instantaneous running clearance towards the target running clearance, g) then applying the brake.

Claims

1. A method of operating a mechanically operated brake having an electric motor for operating an adjuster mechanism comprising the steps of: a) providing a brake rotor and friction material for selective engagement with the brake rotor; b) providing a target running clearance between the brake rotor and the friction material with an electronic controller; c) applying the brake by forcing the friction material into engagement with the brake rotor; d) determining with the electronic controller that the friction material is set in a compressed condition; e) releasing the brake; f) operating the electric motor with the electronic controller to operate the adjuster mechanism to adjust an instantaneous running clearance towards the target running clearance; and g) then applying the brake.

2. The method of claim 1 wherein step d) is based on one or more of: i) a previous temperature of a brake component at a time of applying the brake in step c), ii) an elapsed time since applying the brake in step c), iii) a force of engagement between the brake rotor and the friction material during application of the brake in step c), iv) a thickness of the friction material, and v) a type of friction material.

3. The method of claim 1 in which step d) includes determining an amount of set of the friction material.

4. The method of claim 3 in which an amount of adjustment in step f) is based on the amount of set of the friction material determined by step d).

5. The method of claim 1 wherein step d) occurs before step e).

6. The method of claim 1 wherein step e) occurs before step d).

7. The method of claim 6 wherein step d) is based on at least a time since releasing the brake at step e).

8. The method of claim 1 wherein step f) occurs after step e).

9. The method of claim 8 wherein step f) occurs within five seconds after step e).

10. The method of claim 8 wherein step f) occurs within one second after step e).

11. The method of claim 1 including the step of: h) after step g) the brake is released and applied a plurality of times to condition the friction material such that it is not set in the compressed condition.

12. The method of claim 11 wherein during step h) the electric motor is selectively operated to operate the adjuster mechanism to adjust the instantaneous running clearance towards the target running clearance as conditioning of the friction material occurs.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will now be described, by way of example only, with reference to the accompanying drawings in which:

(2) FIG. 1 shows a brake system according to the present invention.

DETAILED DESCRIPTION

(3) As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention that may be embodied in various and alternative forms. The figures are not necessarily to scale; some features may be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention.

(4) With reference to FIG. 1 there is shown a vehicle 10 having a brake 12. The brake 12 includes a caliper 14 which is slidably mounted via pins 16 (only one shown) on a brake carrier 15. Brake carrier 15 is mounted on the vehicle 10, typically on a suspension component of the vehicle 10. Accordingly the caliper 14 can move in the direction of arrow A and in the direction of arrow B.

(5) The vehicle 10 includes a brake rotor, in this case a brake disc 18 which is rotatably mounted about axis C. The brake disc 18 is rotatably fast with a wheel (not shown) which also rotates about axis C.

(6) On opposite axial sides of the brake disc there are brake pads 20 and 22. Brake pad 20 includes a brake pad back plate 20A and friction material 20B. Brake pad 22 includes a brake pad back plate 22A and friction material 22B.

(7) Adjacent brake pad 22 is an adjuster mechanism 24. The adjuster mechanism includes a thrust assembly 24A and an adjuster system operable to change the length of the thrust assembly. The thrust assemblies shown in EP0995923 and EP1000263 are suitable for use in the present invention. An actuation shaft (or operating shaft) 26 is mounted in the caliper 14 and is rotatable about axis D. A roller 28 is supported on the actuation shaft 26 and engages a right hand end (when viewing FIG. 1) of the thrust assembly 24A.

(8) Operating lever 30 is attached to the actuation shaft 26. An actuator 32 is mounted on the caliper 14, and includes an actuator rod 34, which engages an end 30A of the actuating lever 30.

(9) The actuator 32 is a mechanically operated actuator, in this case an air operated actuator e.g. a pneumatically operated actuator.

(10) As shown in FIG. 1 the brakes are in a released condition, operating lever 30 having being rotated clockwise about axis D such that a gap G1 exists between brake pad 20 and brake disc 18 and a gap G2 exists between brake pad 22 and brake disc 18. Accordingly, the running clearance is G1+G2.

(11) In order to apply the brakes the actuator 32 is operated such that the actuator rod extends from the actuator and moves in a direction of arrow A thereby rotating the operating shaft 26 anti-clockwise about axis D. Because the roller 28 is offset from axis D, the roller 28 moves in the direction of arrow A which causes the thrust assembly 24A to move in a direction of A which forces the brake pad 22 in the direction of arrow A, thereby closing the gap G2. Continued anti-clockwise rotation of the operating shaft 26 then causes the caliper 14 to move in the direction of arrow B as the hole 17 in the caliper slides on pin 16. This causes gap G1 to close. At this moment the gaps G1 and G2 have been closed but, because the brake pads are not being forced against the brake disc 18, no braking force exists to retard to slow the vehicle. Only when the actuator 32 continues to move the actuator rod 34 in the direction of arrow A, does a clamping force of the brake pads on the discs start to be generated. The clamping (or braking) force is dependent upon, amongst other things, the force in the actuating rod 34, a higher force actuating rod 34 resulting in a higher clamping force and therefore a higher retardation of the vehicle.

(12) The adjuster mechanism 24 is electrically operated by electric motor 25. Thus the thrust assembly 24A can be extended (or lengthened) (such that end 24C moves away from end 24D) or retracted (or shortened) (such that end 24C moves towards end 24D) by operation of the electric motor 25. It will be appreciated that by extending the thrust assembly 24A the running clearance will reduce and by retracting (or shortening) the thrust assembly 24A the running clearance will increase.

(13) As will be appreciated, the adjuster mechanism 24 is a distinct component from the actuator 32. The actuator 32 performs the function of applying and releasing the brake. The adjuster mechanism 24 performs the function of adjusting (in particular the running clearance) of the brake. The adjuster mechanism is not used to apply the brake. The actuator mechanism is not used to adjust the running clearance of the brake. The actuator 32 is an air operated actuator though other types of mechanical actuator may be used. The adjuster mechanism 24 is electrically operated, i.e. in order to adjust the adjuster mechanism the electric motor 25 must be operated.

(14) The vehicle 10 includes a control system 40, the control system includes a sensor system 44, a processor 42, in one embodiment a microprocessor. There is also included a memory 46 such as data storage, such as flash memory.

(15) In summary, the control system determines situations where the friction material may be in a set compressed condition. If there is a determination that the friction material is set in a compressed condition when the brakes are released (typically from a park condition) the control system determines the instantaneous current running clearance. The control system then makes an adjustment by operating the motor 25 to operate the adjuster mechanism 24 thereby, in this example, reducing the running clearance. The running clearance may be reduced to a target running clearance, or alternatively the running clearance may be reduced towards (but not all the way to) a target running clearance. This adjustment typically takes place soon after the brakes are released, and in particular before a further application of the brakes. Thus, the adjustment may take place within five seconds of the brakes being released, or preferably within one second of the brakes being released.

(16) A target running clearance may be stored in memory 46. The target running clearance may be a single target running clearance or the target running clearance may be variable, depending upon the operating conditions or environment of the vehicle.

(17) Any known way of determining the current running clearance can be used. For example, the sensor system 44 may include position sensors and load sensors to determine when the brake is in a released condition and to determine when gaps G1 and G2 have just been closed.

(18) Circumstances wherein friction material will be set in a compressed condition is determined by many variables including:

(19) a) The temperature of the friction material and/or rotor at the time of applying the brake, in particular the park brake. The higher the temperature, then the more likely the friction material may become set in a compressed condition.

(20) b) An elapsed time since applying the brake. Thus, if the brake has been applied overnight for several hours, then the friction material is more likely to be set in a compressed condition. However, if the brake has only been applied for a few minutes, for example whilst waiting for traffic lights to change, then friction material is less likely to be set in a compressed condition.

(21) c) A time since releasing the brake. Some friction material self-conditions i.e. upon release of the brake, whilst the friction material does not immediately expand, over a period of time, the friction material will naturally expand of its own volition.

(22) d) A type of friction material. Certain friction materials have a greater tendency to be set in a compressed condition whereas other types of friction material have a lesser tendency to be set in a compressed condition.

(23) e) A force of engagement between the friction material and the brake rotor. Clearly the greater the force of engagement between the friction material and the rotor then the greater the likelihood of the friction material becoming set in the compressed condition.

(24) Thus, the control system can make a determination that the friction material is set in a compressed condition.

(25) The control system can also determine how much of a set has been taken and again this is dependent upon many factors including the factors listed above. However, additionally the thickness of the friction material will determine how much set the friction material will take and hence how much they will expand or swell during subsequent conditioning. Thus, new brake pads (where the thickness of the friction material is at a maximum) may take a larger set and hence expand during conditioning by X millimeters. However, when the friction material is half worn, the set taken and hence the expansion due to conditioning will be approximately X/2. Similarly, when the friction material is nearly worn out, then the set taken and hence the expansion due to conditioning may be negligible.

(26) The control system 40 can determine the amount of wear of the friction material by determining the total amount of adjustment of the adjuster mechanism 24, since new pads were installed in the brake.

(27) Clearly, as conditioning occurs, friction material will start to increase in thickness and the adjuster mechanism can compensate for this, in particular by increasing the instantaneous running clearance in response to increasing of the thickness of the friction material.

(28) The invention has being described in relation to disc brakes but is also applicable to other types of brake, such as brakes having brake drums.

(29) While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention. Additionally, the features of various implementing embodiments may be combined to form further embodiments of the invention.