Brakes – With condition indicator – Electrical
Reexamination Certificate
1997-10-02
2001-01-23
Oberleitner, Robert J. (Department: 3613)
Brakes
With condition indicator
Electrical
C188S00111E, C188S072100
Reexamination Certificate
active
06176352
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to an electric brake system for a motor vehicle such as a passenger car which, inter alia, is equipped with a wheel brake for each wheel of the vehicle. Each wheel brake includes a brake actuator having, inter alia, a braking-force device which applies a braking force to a brake lining during a braking operation whereby a braking force is generated at the wheel. The brake actuator includes an element which supports the applied braking force. the invention further related to a brake actuator for an electric brake system.
BACKGROUND OF THE INVENTION
In recent times, brake systems of the brake-by-wire type were developed for motor vehicles, especially for passenger cars. In a brake system of this kind, the brake command of the driver is made apparent by applying a foot force to a brake pedal and the effect of the foot force on the pedal is detected by a sensor and converted into an electric signal. The signal is then transmitted to brake actuators of which one is assigned to each wheel of the motor vehicle and each brake actuator exercises, inter alia, a braking force on the brake lining with the aid of a braking-force device. The braking-force device is driven by an electric motor. The brake linings are pressed against the brake discs of the wheel brakes under the influence of the braking force whereby a braking force is generated at the wheel of the motor vehicle.
The braking force which is applied by the braking-force device must be controlled in dependence upon the brake command of the driver of the motor vehicle. A simpler possibility to do this comprises supplying a specific motor current to the electric motors of the brake actuators in dependence upon the brake command of the driver in consequence of which a specific braking force is applied by the braking-force device of the brake actuators.
This possibility is however problematic in that the brake actuators always exhibit an internal friction which leads to a hysteresis in the brake actuators. For this reason, it is not possible to clearly assign a braking force to a pregiven motor current; instead, for a pregiven motor current, the braking force always occurs at an undetermined point within a braking-force interval. Accordingly, only via a measurement of the braking force in the brake actuators can it be clearly and precisely determined which braking force is generated for a pregiven motor current by a braking-force device of a brake actuator. The measured value can be used for the purpose of adapting the actual braking force to the desired braking force corresponding to the brake command of the driver of the motor vehicle. For the above reasons, it is desirable that the braking force be measurable in the brake actuators as easily as possible.
SUMMARY OF THE INVENTION
It is an object of the invention to provide an electric brake system wherein the braking force applied by the braking-force device can be easily measured in at least one of the brake actuators. It is still another object of the invention to provide a brake actuator suitable for a brake system of this kind.
The electric brake system of the invention is for a motor vehicle including a passenger car having a wheel brake for each wheel thereof, each wheel brake including a brake lining to which a braking force is imparted during a braking operation. The electric brake system includes: brake actuators corresponding to respective ones of the wheel brakes; each one of the brake actuators including a braking-force device for applying a braking force to the brake lining during a braking operation whereby a braking force is generated at the wheel; the one brake actuator also including an element for supporting the braking force; at least one of the braking-force device and the element being elastically deformable during the braking operation; and, at least one of the brake actuators including at least one sensor for measuring the elastic deformation occurring at one of the braking-force device and the element and for providing a signal representing the elastic deformation from which the braking force can be determined.
The advantages achieved by the invention are seen in that the braking force, which is generated by the braking-force device, is determined from the elastic deformation of a component of the brake actuator. This component is anyhow always present in the brake actuator. In this way, the sensor can be configured of a few components and be integrated into the brake actuator and be well protected against external mechanical loads.
According to another feature of the invention, at least a portion of the sensor is within the braking-force device, that is, within the element which supports the braking force. The advantage of this embodiment is seen in that the sensor, or at least a portion of the sensor, is surrounded on all sides by the braking-force device or by the element which supports the brake lining. In this way, protection against external mechanical loads is especially good.
According to still another feature of the invention, the stiffness of the braking-force device or the element which supports the brake lining, is reduced in the measuring range of the sensor. This can take place, for example, via a reduction in the cross section of the material or by inserting a resilient element or by inserting a material having a lower modulus of elasticity than the remaining material of the braking-force device or of the element which carries the brake lining. The advantage of this feature of the invention is that even a slight change of the braking force generates an additional elastic deformation of the braking-force device or of the element which supports the brake lining which can be measured by the sensor. Accordingly, the measurement is especially precise which makes possible a correspondingly good control of the electric brake system on the basis of the measured actual braking forces.
According to still another feature of the invention, the sensor is built into the brake actuator in such a manner that a clear measurement signal is generated thereby in the force-free state of the braking-force device. This clearly distinguishes from the measurement signals generated when the braking-force device applies a braking force. The advantage of this feature of the invention is that the force-free state of the braking-force device is reliably recognized. Accordingly, the situation described below cannot occur.
An elastic deformation and therefore a braking force (because of measurement inaccuracies) is detected by the sensor even though no braking force is applied by the braking-force device. In this case, the braking-force device is driven back further by the motor of the brake actuator until an elastic deformation identical to 0 is indicated by the sensor and therefore a force-free condition of the braking-force device. This can, in some instances, lead to damage to the brake actuator.
With this further feature of the invention, the case is reliably avoided that no elastic deformation and therefore the force-free condition of the braking-force device is indicated by the sensor (again, because of measuring inaccuracies) even though the braking-force device still applies force to the brake linings. Because of the defective indication of the sensor, the braking-force device is not driven back further by the electric motor so that the brake lining rubs continuously on the brake disc of the brake. In summary, it can be said that a destruction of the brake actuator or excessive wear of the brake linings is reliably avoided by this further feature of the invention.
A reliable indication of the force-free state of the braking-force device can be provided by the sensor. This is done in that the sensor is assembled from at least two parts. A measurement signal is only generated by the sensor when one part of the sensor is located in the operating region of the other part of the sensor and the sensor is built into the brake actuator in such a manner that the one part of the sensor in the force-free state of the braking-force
Dieckmann Thomas
Hauck Stefan
Henken Immanuel
Maron Christof
Continental Aktiengesellschaft
Oberleitner Robert J.
Ottesen Walter
Sy Mariano
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