Brakes – Wheel – Axially movable brake element or housing therefor
Reexamination Certificate
1999-12-27
2001-11-06
Oberleitner, Robert J. (Department: 3613)
Brakes
Wheel
Axially movable brake element or housing therefor
C188S072700, C188S156000, C188S1960BA
Reexamination Certificate
active
06311807
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention is related to a brake calliper for a disc brake, comprising a yoke carrying a pair of opposite brake pads and an actuating mechanism connected to said yoke, said actuating mechanism engaging a displaceable support member for displacing the brake pads towards and from each other, wherein the actuating mechanism is driveable over a first range of rotations as well as over a second range of rotations, one of which ranges being for displacing the pads towards and from each other for exerting a braking effect on an associated brake disc, and the other range of which being for wear compensation of the pads.
Such a brake calliper is known from GB-A-1 303 133.
2. Description of Related Art
In service, the brake pads gradually wear down which means that the screw mechanism will have to be rotated over more revolutions before the desired braking effect is obtained. From a point of view of proper brake behaviour, it is however desirable to maintain a desired air gap between the brake pads on the one hand, and the brake disc on the other hand. As an example, a desired air gap of about 0.2 mm is usually preferred.
Due to wear however, the air gap may become much larger, e.g. in the order of about 20 mm, and therefore a larger stroke will be required to engage the brake disc. Such magnitude of the air gap is less desirable, as it impairs the proper functioning of the brake.
Said prior art actuator comprises a ramp-raceway mechanism, which allows a predefined maximum axial travel of the brake pads. Once this maximal travel is reached, a screw-threaded compensator can be activated for diminishing the play.
SUMMARY OF THE INVENTION
Said ramp-raceway mechanism as well as the compensator is activated by a rotational movement in one and the same direction. The control possibilities of said actuator are therefore limited: the compensator can only be activated after a predefined amount of play has been reached. The object of the invention is to provide an actuator of this kind, which can be controlled in a more flexible way. This object is achieved in that the first range of rotations has a starting rotation in one rotating direction, and the second range of rotations has a starting rotation in the opposite direction.
According to an important aspect of the invention, the actuators are controlled independently from each other.
By means of a control device which may control the compensating and normal braking actions, it is possible to start a compensating action for compensating brake pad wear, independently from the normal braking actions.
Generally, the wear compensation will only be activated once the deviation from the ideal air gap has become too large. However, said compensation will not occur in an automatic, unavailable way, but can be controlled as desired, i.e. after a small or large wear increment in the air gap. In summary, the actuating mechanism is rotatable over a first range of rotations for obtaining a braking effect, and over a second range of rotating for obtaining a compensation effect.
The electric actuating mechanism only to a limited extent will be driven over the second range of revolutions, e.g. in the order of 10,000 cycles. In contrast, the first range of revolutions, which determines the braking action, will be used in the order of 1.000.000 cycles, in the presence of relatively high loads. By selecting two different ranges for these different circumstances of actuation, the actuating mechanism can be adapted better to the requirements of reliability and cost-effectiveness.
According to a preferred embodiment, the actuating mechanism comprises two actuators, one actuator being for displacing the pads towards and from each other for exerting a braking effect, and the other actuator being for wear compensation of the pads.
These actuators can be selected on the basis of the loadings and cycles to be expected. Preferably, they are driven by a single drive part.
In order to be able to withstand the high number of braking cycles, the single drive part is a rotatable drive part which engages the displaceable support member by means of a first actuator comprising a ramp raceway mechanism, which ramp raceway mechanism provides a linear movement of the displaceable support member over a first range of rotations, and a compensation movement of the displaceable support member over the second range of rotations.
A ramp raceway mechanism represents a sturdy and reliable means, fit for performing relatively small displacements in a high cycle duty environment. Relatively large displacements will not have to be dealt with by this mechanism, having regard to the compensation movement of the displaceable support member which compensates for the wear of the brake pads.
The ramp raceway mechanism may have a locking position, from which position a linear movement of the displaceable support member away from the rotatable part is obtained in response to a rotation in a first direction, and from which position a locking of the displaceable support member with respect to the rotatable part is obtained in response to a rotation in the opposite direction.
Furthermore, the displaceable support member may engage a second actuator comprising a nut, which nut engages the rotatable part by means of the ramp raceway mechanism, and a screw which is connected to one of the brake pads and engaging the nut by means of screw threads which provide for a brake pad wear compensation displacement of the screw upon rotation of the nut from its locking position with respect to the rotatable part of the motor in response to said rotation in opposite direction.
In this embodiment, the wear compensation displacement is obtained by means of the relative rotations between the nut/screw mechanism. Such mechanism is particularly fit for providing large displacements. On the other hand, it is not necessary for this mechanism to withstand high cycle duties, as it will be activated much less than the brake mechanism and will not be used for effecting a braking action.
The nut engages the housing, connected to the yoke, by means of a one-way locking mechanism which locks the nut against rotations over the first range, and which allows rotations over the second range; for instance, the nut engages the housing by means of a ratchet pawl mechanism.
According to a preferred embodiment of the ramp raceway mechanism, the rotatable part and the displaceable support member have facing radial surfaces, each comprising three ramps, a roller being clamped between each opposing pair of said ramps.
Each ramp at its lowest region has a stop for locking the associated roller against further rotations. It is also possible to connect both parts in a different way, e.g. by means of pegs or ridges.
In order to obtain reliable information concerning the air gap between air pads and brake disc, it is desirable to establish the point of contact between said components. To that end, preferably one of the brake pads is connected to a load cell.
Alternatively, the measurement can be carried out optically.
Once the load cell establishes a loss of contact between brake pads and brake disc, the count of revolutions of the actuator is started. The differences from said starting point up to the point of the rest position then provides the desired information concerning the air gap.
Preferably, the actuating mechanism comprises an electric motor.
The invention is furthermore related to a method for operating the brake calliper, comprising the steps of
monitoring the rotary movement of the actuating mechanism in the range of rotations for displacing the brake pads towards respectively from each other for exerting a braking effect on an associated brake disc respectively releasing said braking effect,
comparing an actual value related to the maximal number of rotations in said range of rotations with a threshold value,
controlling the actuating mechanism so as to make it to rotate outside said range of rotation, in order to compensate for wear, once the actual value has become larger tha
Kramer Devon
Oberleitner Robert J.
Oliff & Berridg,e PLC
SKF Engineering and Research Centre B.V.
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