Brakes – Operators – Electric
Reexamination Certificate
1998-09-28
2001-01-30
Schwartz, Chris (Department: 3613)
Brakes
Operators
Electric
C188S072100
Reexamination Certificate
active
06179097
ABSTRACT:
PRIOR ART
The invention relates to a braking device claims defined by the preamble to the main claim.
One such braking device is known from European Patent Disclosure EP 0 520 525 B1. The known braking device has an electric motor, which via a gear drive both actuates and again releases a friction brake. This has the disadvantage that if the electric motor or its power supply fails, the friction brake is not released or at least not completely; that is, at least a considerable residual braking force continues to act on a vehicle wheel. This results in a yawing moment, that is, a torque exerted on the vehicle about its vertical axis, which impairs the stability of the vehicle while driving.
A further factor is that the magnitude of the yawing moment depends not only on the residual braking force but also on the coefficient of friction between the vehicle wheel and the roadway and consequently varies with the condition of the roadway. When the coefficient of friction is low or there is an abrupt change in the coefficient of friction, the vehicle wheel tends to lock. If the affected vehicle wheel is a front wheel, the steerability of the vehicle is restricted. Furthermore, on cornering, a braked vehicle wheel can cause the vehicle to spin, while a blocked vehicle wheel is highly likely to cause vehicle spinning during cornering.
ADVANTAGES OF THE INVENTION
The braking device according to the invention having the haracteristics of the main claim has a second electric motor for releasing the friction brake. Especially when the two electric: motors are connected to mutually independent power supplies, this has the advantage that the friction brake can be released completely even in the event of a defect, which is intended to mean a failure of one of the two electric motors or of its power supply; in other words, a residual braking force is no longer operative, and a vehicle wheel that can be braked with the braking device of the invention can rotate freely. The steerability and driving stability of the vehicle also fully assured even in the event of a defect.
Another advantage of the invention is that in the event of a defect, at least a partial braking force can be brought to bear with the remaining electric motor; the braking device never fails completely.
The dependent claims have advantageous features and further refinements of the invention defined by the main claim as their subject.
The two electric motors can be designed in terms of their power and torque in such a way that only the first of them generates a maximum braking force, which suffices for instance to block a vehicle wheel. The second electric motor can be designed with less power, since it is needed only to release the friction brake. It is also possible for both the electric motors to be designed such that the maximum braking force can be generated with each of them (claim
3
). The has the advantage that the braking device remains fully operational, even if one electric motor fails.
The two electric motors may also be designed such that each brings to bear only about half the maximum braking force (claim
4
). To generate the maximum braking force, accordingly both electric motors have to be turned on. This makes it possible to reduce the necessary installation space and weight of the braking device according to the invention. Another advantage is that the friction brake in the event of a defect is still actuatable even if not with maximum braking force.
According to claim
5
, the braking device of the invention has a return path sensor for ascertaining the return path of brake linings upon release of the friction brake and thus for ascertaining the gap between the brake lining and the brake disk or brake drum. The return path can thus be adjusted to a constant value, that is, a defined air clearance between the brake lining and the brake disk or brake drum, regardless of the wear of the brake linings. This has a dynamic advantage because the actuation path always remains constantly short, and because of a constantly short response time upon actuation of the friction brake until it first grips, even in the event of increasing wear of its brake linings. Furthermore, all the wheel brakes of a vehicle grip at the same time and thus, from the onset of a braking event, with uniform braking force distribution in the vehicle, even if the brake linings are worn to different extents. The vehicle is not pulled out of its lane by any one wheel brake coming into action earlier than the others. Another advantage of this embodiment of the invention is that the defined air clearance adjustment is accomplished without expensive mechanisms.
A locking gear according to claim
8
, that is, a gear that allows no motion from the impingement of force or moment on its drive side but can be driven and moved only from one drive side has the advantage that the electric motors need not be supplied with electric current in order to keep the braking force constant. This also has the advantage that the braking device can be used as a non-self-releasing parking brake. A self-locking gear also offers the aforementioned advantages of a locking gear, at least to a limited extent. The term self-locking gear is meant as a gear which allows a motion from the imposition of force or moment, if the imposed force or moment exceeds a threshold value. Examples of self-locking gears are gear drives or planetary gears. Such gears increase a torque, required to turn the electric motors when they are not being supplied with electric current, toward their power takeoff by the factor of the gear reinforcement. Internal friction of the self-locking gear is a further factor; overcoming it on the power takeoff side, because of the gear reinforcement, requires greater torque than on the drive side.
REFERENCES:
patent: 4546298 (1985-10-01), Wickham et al.
patent: 4804073 (1989-02-01), Taig et al.
patent: 4858490 (1989-08-01), Grant
patent: 5090518 (1992-02-01), Schenk et al.
patent: 5348123 (1994-09-01), Takahashi et al.
patent: 5829557 (1998-11-01), Halasy-Wimmer et al.
patent: 5931268 (1999-08-01), Kingston et al.
Greigg Edwin E.
Greigg Ronald E.
Robert & Bosch GmbH
Schwartz Chris
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