Brake wear sensor

Details Brake wear sensor Brake wear sensor

1998-12-07

2001-08-21

Oberleitner, Robert J. (Department: 3613)

Brakes

With condition indicator

Wear

C188S00111E, C188S071900

Reexamination Certificate

active

06276494

ABSTRACT:

This invention relates to vehicle brake assemblies of the kind in which a friction lining has an operative applied to a rotatable braking member, such as a drum or a disc.
It is known to sense the wear of friction lining within a brake assembly through measurement of brake adjustment to compensate the wear.
In our International relation No. WO95/09991 we disclose the use of an “in adjuster” wear sensor comprising a rotary potentiometer driven by movement of adjuster means through a reduction gearbox. The sensor is integrally mounted with the adjuster means and is both assembled to, and removable from, the brake as part of a sub assembly incorporating the adjuster means.
According to one aspect our invention comprises a vehicle brake assembly comprising a friction brake lining having an operative face adapted to be applied to a rotatable braking member and actuating means for applying the braking lining to the rotatable braking member, adjusting means adapted to be driven by the actuating means for the purpose of maintaining the brake lining in close proximity to the rotatable braking member, and wear sensing means responsive to actuation movement of the brake in a brake-applying direction, the wear sensing means comprising a sensor adapted to be operated by movement of an operating member in a linear direction, a rotatable follower member responsive to movement of the adjusting means and a transmission mechanism for translating rotary movement of the follower member into linear movement of the operating member, and characterised in that the wear sensing means is adapted to be driven by the adjuster means, and the sensor is adapted to be driven from a gear wheel on the adjuster means with the end of the sensor remote from the gear wheel being formed with electrical connector means, whereby the unit can be removed from the brake for service without dismantling the brake assembly itself.
The incorporation of the transmission mechanism enables us to utilise a sensor operable by linear movement of the operating member. This facilitates manufacture, improves reliability, and ease of re-assembly where the need for resetting of the wear sensing means with respect to the brake position is eliminated
Conveniently the sensor may comprise a linear displacement such as an inductive sensor or potentiometer.
The transmission mechanism is of adjustable length and of which components are in operative co-operation, to achieve the translation of rotary movement into linear movement.
In one construction a non-rotatable lead screw is movable in a longitudinal direction, in turn to move the operating member in a corresponding direction, and the follower member comprises a rotatable pinion which is captive against movement in a longitudinal direction, whereby rotation of the pinion in response to rotation of the gear wheel causes the lead screw to move in the longitudinal direction.
The relative sizes of the gear wheel and the pinion as well as the pitch on the lead screw can be chosen so as to produce a desired full scale input to the displacement sensor for a given range of new to fully worn brake linings.
The lead screw may carry an enlarged head to limit movement of the screw in the longitudinal direction. This prevents the screw from separating from the remainder of the transmission mechanism which otherwise might cause failure in respect of excessive pad wear or deflection of relatively movable parts of the brake assembly. This feature can also be employed to prevent the tappets within the brake housing from becoming disengaged when the brake is fully or over adjusted, as when the lead screw becomes locked the adjuster, and therefore the brake, are also prevented from being adjusted further.
Preferably components of the transmission mechanism are freely separable. This enables the wear sensor to be removed, without altering a datum position of which the sensor will automatically be re-set by re-assembly of the transmission mechanism.
For example, the lead screw may act on the sensor through an axially extending transmission member or rod with which it is in operative engagement.
Typically during servicing of the brake described above, the adjuster means and components of the actuating means, such as adjustable tappets, may be removed from a common brake housing. Upon re-assembly and replacement it is substantially impossible, or at least extremely difficult, to guarantee the positioned relationship between tappets and an output gear of the adjuster means, and therefore the input to the sensor of the wear sensing means.
According to another aspect of our invention, a vehicle brake assembly of the kind set forth incorporates reset means for resetting the relationship between a datum for the sensor and the brake during servicing of the brake assembly.
The reset means are adapted to be manipulated in a service centre or workshop, by the use of suitable tooling.
Preferably the reset means comprises means for adjusting the effective length of the lead screw to determine a desired datum position for the sensor when assembly the brake assembly with new friction linings.


REFERENCES:
patent: 5520267 (1996-05-01), Giering et al.
patent: 5848672 (1998-12-01), Brearley et al.
patent: 5848673 (1998-12-01), Strauss et al.
patent: 2 118 875 (1972-10-01), None
patent: 0 460 378 A2 (1991-12-01), None
patent: 0 567 155 A1 (1993-10-01), None
patent: WO 95/09991 (1995-04-01), None

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