Brakes – Wheel – Axially movable brake element or housing therefor
Reexamination Certificate
1999-06-14
2001-07-10
Swann, J. J. (Department: 3613)
Brakes
Wheel
Axially movable brake element or housing therefor
C188S156000, C188S161000, C188S162000
Reexamination Certificate
active
06257377
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to an electromechanically actuatable brake.
From British Patent GB 2 190 441, one such electromechanically actuatable brake is known with a two-part actuating device, namely a first part for overcoming the air clearance and a second part for pressing a brake lining against a brake body. Both parts of the actuating device have a separate spindle drive, drivable by its own electric actuating motor. The two parts of the actuating device can be driven simultaneously or successively to execute a brake actuation, by putting the two motors into operation. Both parts of the actuating device are joined together by a blocking bracing means embodied as a pair of levers. The pair of levers is pivotably supported about a stationary shaft. The first part of the actuating device engages the pair of levers with slight spacing from the shaft, while the second part of the actuating device engages the pair of levers with major spacing from the shaft. Because of this arrangement, the first part of the actuating device, which acts directly on the brake lining, is capable of rapidly overcoming the air clearance; via the pair of levers and the first part of the actuating device, the second part of the actuating device can generate a high contact-pressure force on the brake lining. Both motors of the actuating device can be equipped with a brake. Thus, unintended adjustment of the brake during braking operations can be avoided with a constant braking force while the motors are turned off.
The known brake is intended particularly for use in railroad vehicles. There the requisite installation space for the two parts of the actuating device and the relatively large-volume for the pair of levers is available in the known brake device. But because of its weight and volume, the brake would be unsuited to disposition in the bowl of a wheel rim of a road vehicle. Moreover, because of the two motors, the brake is expensive and requires increased expense for control. Thus, the bracing means is blocked only when, in successive drive of the two parts of the actuating device, the part serving to press the brake lining is not driven, or in other words only whenever only the air clearance is overcome. If both parts of the actuating device are driven simultaneously, conversely, the bracing means is not blocked. The bracing means can be released by swiveling the pair of levers about the fixed shaft. Pivoting the pair of levers is done by driving the motor of the part of the actuating device used to press the brake lining. If one or both motors of the actuating device fail, problems can arise in releasing the actuating brake.
From GB 2 190 441, a brake is also known for pressing a brake lining against a rotating brake body (brake disk, brake disk or the like), which has an actuating device with a threaded roller drive, which is drivable by an electric motor. Both tightening and releasing the known brake are accomplished with the electric motor. To prevent residual braking moments caused by hysteresis of the actuating unit from acting on the brake body in the event of a malfunction, such as failure of an electronic control system of the brake during braking, a preferably spiral restoring spring is provided in one embodiment of the known brake; this spring engages the actuating unit and drives the actuating unit, together with the electric motor, to rotate in the release direction so that the brake lining is lifted from the brake body.
This brake has the disadvantage that when brake pressure is built up, the force of the restoring spring must additionally be overcome, and the electric motor must therefore be dimensioned correspondingly larger and supplied with a higher current. In addition, there is a dynamic loss, and a loss of efficiency.
Another disadvantage is that to keep a built-up brake force constant, the electric motor must be supplied with such a high current that it keeps the brake lining pressed against the brake body with a constant contact pressure, counter to the force of the restoring spring, which entails thermal problems. Another factor is that the known brake cannot be used as a parking brake, because it releases when it has no current. Another disadvantage is that the brake cannot be released if the threaded roller drive is jammed.
Another disadvantage is that an air clearance, that is, a spacing between the brake lining and the brake body when the brake is released, increases with increasing wear of the brake linings. As a result, on the one hand a positioning travel of the brake lining until the brake lining contacts the brake body becomes greater and accordingly it takes longer until the brake grabs. The dynamic loss is additionally increased. Furthermore, the force necessary to overcome the force of the restoring spring increases, because the restoring spring is deformed more markedly. The energy that has to be brought to bear by the electric motor of the actuating device to deform the restoring spring is equivalent to the product of the deformation travel and deformation force; thus as the air clearance increases, this energy increases at least quadratically, which quite severely worsens the efficiency of the brake when the brake linings become worn.
ADVANTAGES OF THE INVENTION
The electromechanically actuatable brake of the invention as defined by the characteristics of claim
1
has a bracing means that is releasable by rotation and is blocked against rotation by an anti-jam device. For instance, the bracing means can be embodied on the order of a bayonet mount, which can be released by turning the mount by a small angle and displacing the mount axially away from the brake body. Another option is a bracing means that has a screw thread, which can be moved away from the brake body by turning the bracing means and is blocked against rotation by the anti-jam device. Thus, a screw thread that extends over less than one full revolution can be adequate.
The actuating device is braced against the bracing means when the brake is actuated, or in other words for pressing the brake lining against the brake body. In braking and when the brake is released, the bracing means acts as a fixed abutment for the actuating device but otherwise has no function. The brake is actuated and released with the actuating device. Thus the bracing means affects neither the actuating device itself nor its efficiency.
If in a malfunction, for instance a failure of the current supply to the electric motor or a failure of its electronic control system, or if a spindle drive of the actuating device jams or becomes hard to move, the brake cannot be released with the actuating device, then the blocking of the bracing means is released, making the bracing means freely rotatable. The rotation of the bracing means can be done by a reaction force, with which the brake lining, pressed against the brake body, acts on the actuating device, if the bracing means is embodied as a self-locking device. The rotation of the bracing means can also be done by means of a prestressed spring element, which rotates the bracing means in the release direction when the anti-jam device is released. With the release, the bracing means moves away from the brake body, or if the bracing means is embodied like a bayonet mount, the bracing means is displaceable freely away from the brake body, so that the actuating device together with the brake lining is also released from the brake body; in other words, the bracing means acting as an abutment for the actuating device is removed or at least its distance from the brake body is increased. The invention has the advantage that its bracing means neither affects the function of the actuating device nor worsens its efficiency.
By the provision of a prestressed spring element, which rotates the bracing means when the anti-jam device is released and thus releases the bracing means, the brake linings are lifted from the brake body. A residual braking moment is prevented from acting in the event of a malfunction, and the complete release of the brake is assured. This i
Divine David
Greigg Edwin E.
Greigg Ronald E.
Robert & Bosch GmbH
Swann J. J.
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