Brakes – Wheel – Axially movable brake element or housing therefor
Reexamination Certificate
1999-11-02
2001-07-24
Butler, Douglas C. (Department: 3613)
Brakes
Wheel
Axially movable brake element or housing therefor
C188S071900, C188S072100, C188S1960BA, C188S156000
Reexamination Certificate
active
06264011
ABSTRACT:
FIELD OF THE INVENTION
The invention concerns a device for actuating a vehicle brake, said device comprising a threaded spindle which is secured against rotation in a stationary housing while being axially displaceable toward and away from a brake disc of the vehicle brake, the device further comprising a nut which surrounds the threaded spindle and effects a displacement thereof, said nut having a longitudinal axis and being mounted for rotation about this longitudinal axis in the stationary housing while being connected to a rotor of a drive motor.
BACKGROUND OF THE INVENTION
Devices of the predated type serve to convert a rotary motion into a translational motion. They are suitable for use in fields where only a limited stroke of the threaded spindle is required e.g., in an actuator of an electromechanical brake or in an electrically operated parking brake of a vehicle.
In such a device known from the published application DE 197 05 106 A1, two ball screw drives are combined with each other, namely, an inner screw drive made up of the spindle, the nut and inner rolling elements, and an outer screw drive made up of the nut, an additional nut surrounding this nut and outer rolling elements. By the cooperation of the two screw drives a desired, small total pitch is obtained as the difference between the individual pitches of the two screw drives. This enables the use of standard threads to achieve a very small resultant pitch of the brake device. Such a combination of ball screw drives, however, has the drawback of an expensive structural configuration and increased design space requirement.
OBJECTS OF THE INVENTION
It is therefore an object of the invention to provide an economically manufacturable actuating device which at the same time has a small space requirement and is highly efficient.
This and other objects and advantages of the invention will become obvious from the following detailed description.
SUMMARY OF THE INVENTION
The invention achieves the above objects by the fact that a motion-transmitting ramp unit equipped with rolling elements is arranged between the nut and the drive motor. The concept of the invention is based on the reasoning that low-friction rolling motion should be used only where it is really needed. As shown in
FIG. 3
of the drawings, the stroke S of the threaded spindle can be divided into the following stages:
S
1
=overcoming the clearance between the brake linings and the brake disc,
S
2
=pressure build-up with a low force (5 to 10 % of the maximum load),
S
3
=pressure build-up with a high force.
FIG. 3
shows the force F. measured in kilonewtons, acting between the threaded spindle and the brake disc, as a function of the stroke S measured in millimeters. This allows the confusion that a cheap sliding spindle, that is to say a spindle that does not require rolling elements, can be used for the stages S
1
and S
2
which make up approximately 50 % of the total stroke. It is only during the stage S
3
that the ramp unit comes into action inasmuch as the rolling elements then roll on the ramps.
The invention thus provides a combined sliding and rolling spindle assembly which is comprised of two simple elements, viz., a sliding spindle which may have, for example, a trapezoid thread, and a ramp unit equipped with rolling elements. The combination of these two elements enables the realization of an economic spindle assembly having a high degree of efficiency and a small space requirement.
The ramp unit comprises a set of rolling elements surrounding the threaded spindle and arranged axially between two flange bodies each of which comprises ramps and depressions. One of these flange bodies is configured as a nut flange fixed on the nut and the other flange body is configured as a drive flange formed on a drive sleeve which is connected to the rotor of the motor.
The nut flange can be urged axially toward the rolling element set and the drive flange within the stationary housing by a compression spring which may be configured as a disc spring having one end supported on a step of the housing and another end supported on a bearing ring of a thrust rolling bearing for the nut flange.
Besides this, a bearing ring of a thrust rolling bearing for the drive flange can be supported within the stationary housing on an end rim thereof.
The rotating and sliding motion of the nut in the stationary housing can be achieved by mounting the nut through a linear ball bearing.
Examples of embodiment of the invention are represented in the drawings and will be described more closely in the following.
REFERENCES:
patent: 3081644 (1963-03-01), Hudgens et al.
patent: 3404755 (1968-10-01), Keatley et al.
patent: 4278152 (1981-07-01), Tosi
patent: 5107967 (1992-04-01), Fujita et al.
patent: 1530617 (1969-12-01), None
patent: 3106011 (1982-01-01), None
patent: 4418701 (1995-11-01), None
patent: 196 21 533 (1997-12-01), None
patent: 197 05 106 (1998-08-01), None
patent: 19853721 (1999-06-01), None
Bierman, Muserlian and Lucas
Butler Douglas C.
Ina Walzlager Schaeffler OHG
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