Brakes – Wheel – Axially movable brake element or housing therefor
Patent
1990-08-08
1991-10-29
Halvosa, George E. A.
Brakes
Wheel
Axially movable brake element or housing therefor
188 726, 188 727, 188106F, 188196D, 192 7023, 192 7025, 192 93R, 192111A, F16D 6556
Patent
active
050607650
DESCRIPTION:
BRIEF SUMMARY
The invention relates to an actuating device with automatic readjustment for a vehicle brake, especially a disc brake, comprising
a casing which includes a bottom and a shell formed with a cylindrical bore which is open toward the brake,
a piston which is displaceable hydraulically within the cylindrical bore to actuate the brake,
a shaft for mechanical parking brake application which is rotatably supported in the bottom of the casing, coaxially with the piston, and sealed,
two ramp arrangements, one being secured to the casing and the other one rotatable by means of the shaft, thus being adjustable axially away from the bottom of the casing,
a pair of strut members screwed together so as to form an adjustable strut between the axially adjustable ramp arrangement and the piston, and
a return spring which is positioned under axial bias between a thrust bearing secured to the casing and a thrust bearing at one of the two strut members and tends to keep the adjustable ramp arrangement in an inoperative position.
In a known actuator of this kind (DE-A-24 08 706, especially FIG. 6) the bottom of the casing is a structural member made separately from the casing and then screwed to the same. The ramp arrangement which is secured to the casing is formed directly at the axially inner side of said member. The thrust bearing which is secured to the casing is formed at an intermediate annular wall which is formed in one piece with the casing and separates the cylindrical bore from a rear space housing the adjustable ramp arrangement, a thrust bearing at one of the two strut members, and an axial load bearing disposed between said strut member and the adjustable ramp arrangement.
The first strut member is rotatable and has an irreversible external thread by which it is screwed into the sleeve-like second strut member. The second strut member is guided for axial displacement within the cup-shaped piston but is non-rotatable and biased by an additional spring with respect to the piston in the actuating direction of the piston. The first strut member is connected to the adjustable ramp arrangement by a directional locking mechanism. Furthermore, the first strut member is embodied by an auxiliary hydraulic piston guided sealingly in the annular intermediate wall of the casing and arranged such that readjustment is prevented when the hydraulic pressure in the cylindrical bore has reached a value at which elastic deformations of parts of the brake are to be expected.
This known actuating device requires considerable finishing and mounting expenditure and practically cannot be installed in casings whose cylinder bore has a diameter of no more than 40 mm or less. The diameter of the cylindrical bore at the front wheels of motor vehicles admittedly usually is much greater, for example 60 mm. However, as the front wheels normally are steerable, there is generally not enough space to mount a disc brake with optional hydraulic and mechanical actuation. For this reason front wheel brakes so far usually were not provided with an hydraulic actuating device and in addition with a mechanical actuator so as to be useful as parking brakes. In view of the usual load distribution, on the other hand, with the front wheels normally being loaded by more than 50% of the weight of the vehicle, it is desirable in general to select a relatively small diameter for the cylinder bore of hydraulic actuators at rear wheel brakes. For example, in the case of passenger cars, at the rear wheel brakes the bore and piston diameter may be 38 mm and it may be 62 mm at the front wheel brakes so as to avoid overbraking of the rear wheels. That is why it is difficult with rear wheel brakes to find room for a combined hydraulic and mechanical actuating device which is sufficiently strong in dimension and automatically readjustable so as to be just as well suited for completely safe parking braking as it is for operational braking.
In the case of another known hydraulic and mechanical actuating device with automatic readjustment (DE-A-21 43 575) the piston likewi
REFERENCES:
patent: 3701400 (1972-10-01), Burnett et al.
patent: 3765513 (1973-10-01), Brooks
patent: 3991859 (1976-11-01), Coulter et al.
patent: 4596315 (1986-06-01), Takeuchi et al.
Halvosa George E. A.
Lucas Industries Public Limited Company
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