Brake adjusters

Details Brake adjusters Brake adjusters

1999-02-22

2002-02-12

Oberleitner, Robert J. (Department: 3613)

Brakes

Wheel

Transversely movable

C188S079540, C188S1960BA, C188S079510

Reexamination Certificate

active

06345702

ABSTRACT:

This invention relates to brake adjusters and in particular to brake adjusters for use with drum brakes.
Such adjusters are used to maintain drum brake shoe travel substantially constant as the drum brake shoes wear.
Typically such adjusters comprise a strut which extends between the shoes of the drum brake, or between one shoe and a handbrake operating lever associated with the other shoe, the strut being arranged to increase in effective length as the shoes wear in order to advance the shoes towards the associated drum thus maintaining shoe travel substantially constant.
One problem with such adjusters is the provision of a simple, cheap and effective design which is also capable of incorporation of a temperature sensitive feature which ensures that the adjuster will not operate at brake temperatures above a predetermined level to prevent the common phenomenon of over adjustment due to brake drum expansion at higher temperatures.
It is an object of the present invention to provide a brake adjuster for a drum brake which mitigates the above problems.
Thus according to the present invention there is provided a brake adjuster for a drum brake arranged to be located either between a pair of brake shoes or between a brake shoe and a handbrake lever associated with the other shoe, the adjuster comprising a variable length strut having two end portions and an intermediate portion therebetween in screw threaded engagement with one of the end portions to vary the effective length of the strut, the other end portion being connected with the intermediate portion via a pawl and ratchet device comprising ratchet teeth on one portion and a pawl on the other portion, the pawl and ratchet device being arranged so that as the end portions of the strut move apart during a brake application (or alternatively on a brake disengagement) the pawl rides up a ratchet tooth and if the movement apart exceeds a predetermined amount engages behind said tooth, so that when the end portions move towards each other in the next brake disengagement (or alternatively on the next brake application) the intermediate portion is rotated relative to said one of the end portions to increase the effective length of the strut and hence reduce the travel apart of the end portions on the next brake application.
Preferably the pawl is bi-metallic and disengages the ratchet teeth if the temperature of the adjuster rises above a predetermined level to prevent adjustment of the effective length of the strut.
Typically the bi-metallic pawl disengages the ratchet teeth when the bi-metallic pawl reaches approximately 80° C. which represents a drum temperature of approximately 180° C.
Preferably the said one end portion is in screw threaded engagement with a first axial end of the intermediate portion and the said other end portion is in sliding engagement with the other axial end of the intermediate portion.
Preferably the other end portion extends into a bore in the intermediate portion which houses a spring which biases the end portions apart and maintains the end portions in contact with the associated shoes or lever. The end portions may be forked for easy engagement with the shoes or lever.
The ratchet teeth may extend circumferentially around the intermediate member with the pitch and angle of the teeth determining the shoe travel before adjustment takes place.
Typically the teeth will have a pitch of 1.25 mm which gives a travel of 1.00 mm before adjustment takes place.


REFERENCES:
patent: 4250980 (1981-02-01), Kluger
patent: 4385681 (1983-05-01), Conrad et al.
patent: 4706783 (1987-11-01), Rath et al.
patent: 4706784 (1987-11-01), Shellhause
patent: 4729457 (1988-03-01), Cousin et al.
patent: 575825 (1993-12-01), None
patent: 0538909 (1993-04-01), None
patent: 1033607 (1966-06-01), None
patent: 1513740 (1978-06-01), None
patent: 2246825 (1992-12-01), None
patent: 53-76262 (1978-07-01), None

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