Brakes – Wheel – Transversely movable
Reexamination Certificate
1999-09-24
2001-04-10
Schwartz, Christopher P. (Department: 3613)
Brakes
Wheel
Transversely movable
C188S079510
Reexamination Certificate
active
06213258
ABSTRACT:
The present invention relates to drum brakes of the type equipped with a mechanism for automatically compensating for clearance, able to compensate for the wear of the friction linings.
BACKGROUND OF THE INVENTION
More specifically, the invention relates to a drum brake comprising at least: a drum; two shoes in the shape of arcs of a circle, arranged facing an internal face of the drum and carrying respective friction linings; an actuator inserted between the shoes and operated selectively to make the shoes move, in a centrifugal movement towards the internal face of the drum; a spring connecting the shoes to move them closer together, in a centripetal movement counter to the centrifugal movement as soon as the actuator is no longer being operated; a rocking lever carrying an adjustment blade and which moves in a back and forth angular movement consisting of two pivoting movements in opposite directions, correlated with the centrifugal and centripetal movements of the shoes; an adjustable-length strut inserted between the shoes to limit their centripetal movement, and comprising two threaded elements forming a screw-nut connection, the length of this strut being adjusted by unscrewing the screw-nut connection as the friction linings wear; and a toothed wheel secured to one of the elements of the screw-nut connection and selectively rotated by the adjustment blade during a first of the pivoting movements of the rocking lever, the adjustment blade extending, lengthwise, transversely with respect to the toothed wheel, developing widthwise in a mean plane parallel to the first pivoting movement, and interfacing with the toothed wheel, during the first pivoting movement, rather more tangentially than radially.
This type of drum brake is well known to those skilled in the art and is, for example, illustrated in U.S. Pat. No. 4,502,574 the teaching of which is incorporated into this description.
Despite their attraction as a result of the simplicity of their structure, such brakes sometimes tend to lock when subjected to an excessive actuating force, particularly if they have been used in extreme conditions which have led to a significant rise in temperature.
SUMMARY OF THE INVENTION
In this context, the specific objective of the present invention is to propose a drum brake of this type, but which is less sensitive to such extreme service conditions.
To this end, of the invention [sic] employs a rocking lever equipped with an inhibitor blade capable of intercepting the toothed wheel as soon as a risk of excessive adjustment occurs, and of causing the adjustment blade to disengage from the toothed wheel, thus preventing any subsequent rotation of the toothed wheel at least until the risk of excessive adjustment has disappeared.
More specifically, the drum brake of the invention, which in other respects is in accordance with the description given in the above preamble, is essentially characterized in that the lever bears an inhibitor blade extending lengthwise parallel to the adjustment blade, developing widthwise in a plane essentially perpendicular to the mean plan of the adjustment blade, flexible transversely with respect to its plane, adopting within its plane a position of rest from which it can move elastically by limited-amplitude deflections in the direction of its width, and selectively intercepting the toothed wheel, and in that the adjustment blade follows the deflections of the inhibitor blade, the toothed wheel thus escaping the influence of the adjustment blade when it is driving the inhibitor blade after having been intercepted by this inhibitor blade.
According to an advantageous embodiment of the invention, the inhibitor blade consists of a bimetallic element and moves closer to the toothed wheel by a movement that is transverse with respect to its plane, when there is a rise in temperature.
The lever may, for example, have a branch arranged at right angles to the adjustment blade and attached to it by a common base, this branch being, on the one hand, mounted so that it can pivot, via an end distant from the base, on a pin secured to one of the shoes and, on the other hand, mounted so that it can pivot, via an end adjacent to the base, on one end of the strut, and the spring bearing upon a point of the branch that is part way between the ends of this branch.
Finally, the lever preferably has a fold adjacent to the base that is common to the adjustment blade and to the branch, that is parallel to the plane of the inhibitor blade, and with which the inhibitor blade is integral.
Other features and advantages of the invention will emerge clearly from the description thereof given hereafter by way of non-limiting indication with reference to the appended drawings.
REFERENCES:
patent: Re. 36312 (1999-09-01), Muzzy
patent: 5388671 (1995-02-01), Rupprecht
patent: 5752586 (1998-05-01), Evans
patent: 5913390 (1999-06-01), Hostetler
Comstock Warren
McCormick Jr. Leo H
Robert & Bosch GmbH
Schwartz Christopher P.
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