Brakes – Wheel – Axially movable brake element or housing therefor
Reexamination Certificate
2000-03-20
2001-09-25
Butler, Douglas C. (Department: 3613)
Brakes
Wheel
Axially movable brake element or housing therefor
C188S072700, C188S1960BA
Reexamination Certificate
active
06293371
ABSTRACT:
This invention relates to disc brake assemblies for vehicles of the kind in which pad assemblies provided with friction linings for engagement on opposite faces of a rotor are mounted in opposed limbs of a carrier which extends over a peripheral edge of the rotor, and an actuating mechanism provided in one of the limbs is adapted to apply one of the pad assemblies to an adjacent face of the rotor, the other pad assembly being applied to the opposite face of the rotor as a result of the reaction of the actuating mechanism.
It is known to mount the carrier on sliding pins to allow relative movement between the limbs of the carrier and the rotor. In such a brake assembly, application of the actuating mechanism applies one of the pad assemblies to the rotor and the reaction force thereby produced moves the carrier to bring the other pad into contact with the rotor.
Alternatively, the carrier may be fixed relative to a hub supporting the brake assembly and the rotor may be adapted to move slightly relative to the hub. In this case, application of the actuating means moves one of the pads into contact with the rotor which displaces the rotor towards and into engagement with the other pad assembly. This arrangement is the preferred choice for use in the present invention.
In order to ensure smooth operation of the brakes, a small brake clearance should be provided between the pad assemblies and the rotor when the brakes are inoperative. As the friction linings wear this clearance will increase and it is necessary to provide compensation for this increased wear to ensure consistent braking operation.
In high performance brake assemblies, the generation of heat between the brake rotor and the stator can be excessive. The use of materials such as carbon in the rotor and pad assemblies can alleviate such problems, but to ensure good levels of braking force whilst simplifying the design of the brake it is proposed to employ an annular pad assembly which acts over the whole or part of the rotor.
The main difficulty with the use of an annular pad assembly is that of ensuring that even application of the annular pad assembly to the rotor is achieved in a simple manner using a minimum of parts.
To meet the requirements of producing a high performance brake assembly employing annular pad assemblies, the inventor proposes the use of an annular piston as the actuating mechanism which can generate substantially even braking force around a circumference of the rotor.
In accordance with the present invention, in a vehicle brake assembly of the kind set forth, the actuating mechanism comprises an annular piston working in an annular bore in the first limb defined by inner and outer concentric walls and moveable between a retracted position which determines the braking clearance and an advanced brake-applying position, a ball and a ramp assembly housed in an annular space between the walls and acting between the piston and the first limb to urge the piston towards the rotor in the brake applying position to apply the brake, and an annular adjustment ring through which the expander acts on the piston, the ring being in screw threaded engagement with one of the walls, and an adjuster adapted to rotate the ring with respect to the piston to advance the piston relatively towards the rotor to compensate for wear of the friction linings thereby to maintain the piston in a retracted position in which the braking clearance is substantially consistent.
By providing an annular piston which applies the pad assemblies to the rotor which is substantially concentrically aligned with the rotor, it is possible to ensure even application of the pad assemblies around the rotor circumference. It also overcomes potential problems which occur with the use of multiple pistons which require some method of synchronising the rate of advance of each piston to ensure even application. Parts count is also reduced, increasing reliability and reducing cost.
Preferably, annular pad assemblies are employed having a single continuous annular friction lining. Of course, the annular pad assemblies may comprise a number of pad segments spaced around a circumference of the rotor (i.e. a discontinuous friction surface).
The ball and ramp mechanism, in one advantageous arrangement, includes at least one rotating plate and one advancing plate comprising an annular ring. On rotational operation of the ball and ramp assembly the rotating plate rotates about its axis causing the advancement plate which is prevented from rotating by the first limb to advance towards the friction linings. This advancement plate may be adapted to act upon the adjustment ring, in turn to advance the piston towards the rotor. To prevent rotation of the piston, a lug on the piston may co-operate with a key way on the carrier.
It will be appreciated that operation of the ball and ramp mechanism may advance the advancement plate towards the piston before advancing the piston towards the rotor. The rotor, which is axially displaceable between the pad assemblies is then displaced by the friction lining supported by the amount of axial displacement of the advancement plate required to apply both friction linings to the rotor is dependent upon the degree of brake clearance. As the friction linings wear, the amount of displacement needed in order to engage the brakes will increase, and hence the amount of displacement of the advancement plate will be larger for large clearances than for small clearances.
In order to facilitate automatic adjustment of brake clearance, an automatic adjuster is provided which is adapted to rotate the adjustment ring relative to the piston. Since the advancement plate acts upon the piston through the adjustment ring, by rotating the advancement ring relative to the piston, the spacing between the ring and the adjustment plate can be varied. This causes the piston to advance for a given position of the advancement plate as the adjustment ring is moved along the screw thread on the piston.
In order to automatically rotate the adjustment ring, to compensate for friction material wear and maintain constant brake clearance, in a most preferred embodiment the adjuster comprises a first and second axially displaced cog connected via a spring means which allows relative rotation between the cogs against the spring force, the first cog-operating with the rotating plate of the ball and ramp assembly and the second cog co-operating with the adjustment ring.
The connection means between the first and second cog is that of a bidirectional clutch. This clutch is arranged such that in the direction of drive provided to the first cog by the rotation of the rotating plate during brakes being applied, there is sufficient torque transferred to the adjustment ring via the second cog, to rotate the adjustment ring in the direction that reduces the brake clearance whilst there is still brake clearance. After brake clearance has been removed the frictional forces in the brake increase to such a level that there is no longer sufficient torque transferred to the adjustment ring via the second cog to rotate the adjustment ring in the direction that reduces the brake clearance. Thus the clutch slips allowing relative rotation of the first and second cog without adjustment. In the direction of rotation of the rotating plate during brakes being released, there is in-sufficient torque transferred to the adjustment ring via the second cog, to rotate the adjustment ring in the direction that increases brake clearance and thus the adjustment ring does not rotate.
Preferably there is a rotational clearance between the meshing of the teeth of either or both of the cogs and its co-operating part. This clearance is equivalent to the amount of rotation of the rotating plate that gives an axial travel of the advancement plate equal to the intended brake clearance.
The operation of the automatic adjuster may be as follows. On operation of the brakes, the rotating plate rotates relative to the carrier whilst advancing the advancing plate towards the rotor. After advancement of the
Butler Douglas C.
Carlson & Gaskey & Olds
Meritor Automotive Inc.
Williams Thomas J.
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