Brakes – Wheel – Axially movable brake element or housing therefor
Reexamination Certificate
2000-01-21
2002-05-28
Schwartz, Christopher P. (Department: 3613)
Brakes
Wheel
Axially movable brake element or housing therefor
C188S072800, C188S10600P, C303S003000, C303S015000, C303S192000
Reexamination Certificate
active
06394235
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a hydraulic vehicle brake and to a method for operating same.
From EP 0 729 871 A1 a hydraulic vehicle, brake is known, wherein a friction pad can be pressed against a brake disk by means of a brake piston using hydraulic fluid, in order to brake its rotation. For this purpose, hydraulic fluid is fed under pressure in a conventional, manner into a hydraulic chamber, the boundary wall of which is formed by the brake piston. The pressure in the hydraulic chamber, then leads to a displacement of the brake piston and thus of the friction pad towards the brake disk. In order to enable this known vehicle brake to be used not only as a service brake, but also as a hand brake—also referred to as parking brake—, it comprises a spindle
ut arrangement for mechanically blocking the brake piston in a condition in which the friction pad is in engagement with the brake disk.
SUMMARY OF THE INVENTION
The invention is based on the object to provide a hydraulic vehicle brake which can be used both as a service brake and a parking brake, and the construction of which is more compact than that of the vehicle brake known from EP 0 729 871 A1. In addition, the hydraulic vehicle brake to be provided must be adaptable to various vehicle models in an economical manner.
According to the invention, this object is solved by a hydraulic vehicle brake which comprises the features of the present invention.
The electric motor which rotationally drives the spindle according to the invention is arranged in such a manner that its output shaft which extends at a distance and parallel to the longitudinal center axis of the brake piston exits the electric motor at the side facing away from the brake piston. This arrangement is space saving, in particular with respect to the length of the construction. The reduction gear connected between the electric motor and the spindle with its reduction in the order of 200:1 enables the employment of a small space saving electric motor.
The electric motor and the reduction gear which is coupled with same are designed as a standardized subassembly which can be handled independently and can be combined with various vehicle brakes of one type. Thereby, the production quantities of such a motor/gear unit increase, which has a favorable effect on the unit cost. Moreover, the motor/gear unit designed as an independent assembly enables an attachment at the brake housing in a simple manner in any desired angular position so that spatial restrictions at the installation site of the brake can easily be complied with by a correspondingly different positioning of the subassembly.
The reduction gear is advantageously designed as a planetary gear, a harmonic drive gear, an eccentric disk gear, or a swash plate gear, because these gear types are compact and, at a small weight, have a good efficiency. The reduction gear can be designed to be single-stage, but also multistage, in particular, two-stage. A two-stage gear is particularly advantageous with respect to saving installation space, one stage of which is formed by one of the previously mentioned gear types with a reduction in the range of 50:1, upstream or downstream of which a second stage with a reduction in the range of 4:1 is connected, so that an overall reduction in the range of 200:1 is achieved. In a multistage reduction gear, in particular in a two-stage reduction gear, preferably the stage with the lower reduction is designed as a simple spur gear or, more advantageously, as a belt gear, in particular, as a toothed-belt gear. The use of a belt gear or a toothed-belt gear results in a particularly good noise decoupling between the driving electric motor and the remaining parts of the vehicle brake, and thus to a comfortable, low-noise operation.
In all embodiments of the vehicle brake according to the invention the spindle
ut arrangement is advantageously designed to be self-locking, generally by a suitable selection of the pitch of a thread which connects the nut with the spindle. A self-locking spindle
ut arrangement allows to dispense with a locking device after the vehicle brake has been locked by rotating the spindle.
The spindle
ut arrangement is preferably arranged in the hydraulic chamber. This leads to a still more compact construction and, moreover, ensures the lubrication of the in spindle
ut arrangement. According to a further development of this embodiment, the brake piston is designed as a hollow piston which is open at one side so that the spindle
ut arrangement is at least partially accommodated in the brake piston in a space-saving manner.
In preferred embodiments of the vehicle brake according to the invention, the translational movement of the nut, which is caused by the rotation of the spindle, is sensed by means of a sensor. In this manner, a predetermined small distance between the brake piston and the nut, and thus an optimum function of the hand brake or the emergency brake, respectively, can be ensured. In practical use with the hand brake or the emergency brake, respectively, not actuated, a distance between the nut and the brake piston of approx. 0.5 mm is desired. A distance between the nut and the brake piston, which remains constant at all times, makes it possible, on the one hand, to achieve the desired maximum clamping force of the hand brake within a short period of time, i.e. within the range of approx. 1 second, and, on the other hand, allows the brake piston to return after an actuation in accordance with the so-called “rollback” principle, and to not contact the nut prematurely, which might result in a residual sliding moment between the friction member and the rotor to be braked. Those with skill in the art understand the “rollback” principle as the resetting of the brake piston following a braking operation, which is caused by the resetting force of the elastomeric seal sealing the brake piston, which seal has been elastically deformed during the braking operation. The mentioned sensor for sensing the translational movement of the nut can, for example, be a sensor which directly senses the travel of the nut. For this purpose resistive sensors, inductive sensors, or capacitive sensors as well, are suitable. In order to improve the brake control, in addition to the sensor sensing the nut's travel, a force sensor sensing the clamping force can be provided which, for example, can be arranged in the or at the friction member, or in the brake piston as well.
The sensor sensing the translational movement of the nut can alternatively be a sensor which measures the revolutions of the output shaft of the electric motor driving the spindle. Instead of measuring the revolutions of the output shaft of the electric motor itself, it is also possible to measure the revolutions of a gearwheel in the downstream reduction gear. For measuring the revolutions, a Hall sensor is particularly suited, which provides a square wave output signal. If such a Hall sensor is aligned, for example, with the teeth of a gearwheel which is coupled with the output shaft of the electric motor, one revolution of the output shaft will correspond to a certain number of square wave pulses, i.e. to the number of teeth of the gearwheel. With the high resolution of the rotational movement of the output shaft of the electric motor, which is achieved in this manner, the translational movement of the nut, which is caused by the rotation of the spindle, can be sensed with a very high accuracy since there is a fixed correlation given by the existing reduction between the revolutions of the electric motor, on the one hand, and the translational movement of the nut, on the other hand. Moreover, a Hall sensor is very well suited for an integration into the already mentioned unit consisting of the electric motor and the reduction gear so that long electrical connections which are therefore potentially more susceptible to failure between the Hall sensor and the electric motor are avoided. A control unit controlling the functional sequences of the vehicle brake according to the in
Erben Ralf
Poertzgen Gregor
Wörsdorfer Karl Friedrich
Zenzen Guido
Lucas Industries plc
MacMillan Sobanski & Todd LLC
Schwartz Christopher P.
Williams Thomas J.
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