Brakes – Wheel – Transversely movable
Patent
1994-11-21
1998-06-02
Ballato, Josie
Brakes
Wheel
Transversely movable
188196BA, F16D 6556
Patent
active
057587507
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to the field of drum brakes, particularly those intended to equip motor vehicles, and it relates more precisely to the automatic adjustment devices intended to compensate for the wear of the friction pads on the shoes of such drum brakes, these devices bringing about the extension of a strut, which is located between the shoes, depending on the wear of the friction pads, in order to define a minimal separation distance between the shoes depending on the wear of the friction pads carried by these shoes, that is to say to provide a relatively constant travel for the means for actuating the drum brake.
BACKGROUND OF THE INVENTION
Such struts with an automatic adjustment device are well known in the prior art, such as, for example, from documents EP-A-0,077,726 (U.S. Pat. No. 4,503,949), EP-A-0,219,384 (U.S. Pat. No. 4,729,457) or EP-A-0,262,014.
SUMMARY OF THE INVENTION
In these documents, the strut comprises a screw-nut assembly controlled by a pawl urging toothing secured to one of the elements of the screw-nut system, the pawl being carried by an elastic strip secured to the strut, the elastic strip being separated from the strut, when the brake is in the position of rest, by means of a lever which, by tilting, allows the elastic strip and the strut to be brought closer together when the shoes are urged apart by the actuating means, the lever including a first arm bearing on the nut of the screw-nut system and pierced with an opening through which the screw of the screw-nut system passes, and a second arm forming an angle greater than 90.degree. with respect to the first arm and located between the strut and the elastic strip.
The design of the known devices imposes, particularly on the nut of the screw-nut system, parasitic loads which increase the friction of the nut on the screw and which may thus prevent extension of the strut until the external loads which are exerted on it are sufficient to overcome this friction and bring about the desired extension. This results in erratic operation of the known automatic adjustment devices.
In addition, the detrimental effect of these parasitic loads is very much amplified through the manufacturing tolerances of the various elements of which these devices are composed, so that the extension obtained is very variable from one strut to the other, all other things moreover being equal.
As a result, known struts only very imperfectly fulfil their role of fixing a minimal distance between the shoes, and very often define a distance which is less than the desired minimal distance, following the absence of extension of the strut. This then results in an excessive travel of the actuating means when these are mechanical, or an excessive consumption of fluid when the actuating means are hydraulic.
The object of the present invention is consequently to provide an automatic adjustment strut for a drum brake which does not exhibit these drawbacks, that is to say which is exempt of parasitic loads at the screw-nut system level so as to provide optimal operation of the automatic adjustment device and a distance between the shoes which corresponds effectively to the desired minimal distance.
To this end, according to the invention, the first arm of the lever controlling the tilting of the elastic strip bears on two substantially diametrically opposed zones of the nut of the screw-nut system. In that way, the loads exerted by the lever on the nut have a substantially axial resultant, and therefore do not generate parasitic loads on it.
The invention will be better understood and other objects, features and advantages will emerge clearly from the description while viewing the drawings:
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a plan view of a drum brake of the prior art, and capable of receiving an automatic adjustment strut produced in accordance with the present invention;
FIG. 2 is an enlarged view, in partial section on the line II--II of FIG. 1, of an automatic adjustment strut of the prior art;
FIG. 3 is an even more enlarged view of
REFERENCES:
patent: 4503949 (1985-03-01), Carre et al.
patent: 4646881 (1987-03-01), Denree et al.
patent: 4729457 (1988-03-01), Cousin et al.
Le Moigne Daniel
Tempestini Serge
Ballato Josie
Bosch Systems de Freinage
McCormick Jr. Leo H.
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