Brakes – Wheel – Transversely movable
Patent
1993-07-30
1995-08-08
Oberleitner, Robert J.
Brakes
Wheel
Transversely movable
188196BA, F16D 6556
Patent
active
054390796
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a drum-brake device comprising:
a clevis;
first and second arcuate brake shoes having respective first and second ends facing one another;
an expander fastened to the clevis and actuatable to move apart the first ends of the two shoes;
a spacer of which the length is adjusted by a screw element and which holds the second ends of the two shoes at a distance from one another, and
regulation means for regulating the length of the spacer in dependence on the wear of the shoes, said means comprising a toothed wheel fastened to the screw element, a rocking lever which carries a click and is pivoted on the second shoe and which is capable of turning the toothed wheel in a direction such as to lengthen the spacer, and a linkage for actuating the rocking lever, said linkage in turn comprising a lever pivoted at a point on the second shoe and two rods connected by said lever, the first rod having a first end pivoted on a support point and a second end pivoted on the lever to move the latter in the event of the actuation of the expander, and the second rod having a first end pivoted on the lever and a second end pivoted on the rocking lever such as to transmit to the latter the motion of the lever.
Devices of this kind are known in the prior art for use in land motor vehicles, and a similar device is for example illustrated in DE Patent 1 269 424, in which the linkage effectively comprises two rods and one lever, unlike for example the devices of U.S. Pat. Nos. 3,958,674 and 3,216,533, in which a simple cable is used as the linkage.
Nevertheless, brake devices designed in accordance with an arrangement of this kind are known only in applications in which they constitute the main braking member and in which the clearance adjustment is effected and can occur only through the action of a rotation of the braked wheels and the corresponding drums.
The problem which the present invention is provided to solve consists in adapting the automatic clearance adjustment system used in known devices such as to make it also usable for auxiliary brake devices, particularly those consisting of a mechanically actuated drum-brake (for example a hand brake) and housed inside a disk-brake, in accordance with an arrangement known by the English language expression "drum-in-hat", and having no fixed point, that is to say adopting the design termed "duo-servo".
To achieve this adaptation numerous difficulties have to be overcome.
Firstly, except in emergencies, it is always during stops that the auxiliary brake is engaged, so that the stresses to which the shoes are subjected are very different from those occurring in a main brake, particularly because of the absence of the phenomenon of wrapping which, in the duo-servo design, is applied to both segments at the same time.
Moreover, precisely because it is normally applied only during stops, the auxiliary brake is subject to only minimum wear, so that the clearances to be adjusted for are much smaller than in a main brake.
Finally, an auxiliary brake is generally actuated by a mechanical expander, which develops only a relatively small force compared with that developed by a hydraulic actuator, thus leading to a further limitation of the movement of the brake shoes.
In order to overcome these difficulties the brake device of the invention is essentially characterized in that the support point of the first rod is a point on the first brake shoe, whereas the first and second shoes are mounted floating on the clevis, this arrangement making it possible to adjust for clearance by operating the brake either when the vehicle is braked and at rest or during forward or re- verse motion.
The device thus constituted can in particular be actuated by an expander of a mechanical type.
The pivot point of the lever, the second end of the first rod, and the first end of this same rod preferably define a first angle close to 120.degree. or greater than that value.
In a preferred embodiment of the invention, the pivot point of the lever is substantially equidistant from the s
REFERENCES:
patent: 3128849 (1964-04-01), Swift
patent: 3216533 (1965-11-01), Hagerty et al.
patent: 3294202 (1966-12-01), Helvern
patent: 3893548 (1975-07-01), Bolenbaugh
patent: 3958674 (1976-05-01), Borkowski
Bendix Europe Services Techniques
McCormick Jr. Leo H.
Oberleitner Robert J.
Palguta Larry
Poon Peter M.
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