Brakes – Operators – Electric
Reexamination Certificate
1998-07-02
2001-08-28
Oberleitner, Robert J. (Department: 3613)
Brakes
Operators
Electric
C188S00111E, C303S020000
Reexamination Certificate
active
06279694
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a system for controlling or adjusting an electromechanical brake.
An electromotive brake with these features is described in U.S. Pat. No. 4,995,483. The system disclosed is used to decelerate aircraft, however, its principal structure is applicable on road vehicles as well. The brake includes a set of brake discs and an associated set of friction discs which are urged against each other by way of a clamping device. The clamping device is actuated electromotively by way of a spindle, which is driven by a roller thread drive and pressed against the outward friction disc. A force-measuring element is interposed between the first friction disc and the spindle head. A clearance is provided between the brake discs and the friction discs.
The general point is that to produce a brake force, first the clearance must be overcome. Only after the friction discs or friction elements abut on the brake discs is it possible to transmit a clamping force which causes deceleration of the wheel connected to the brake discs. To apply the friction discs on the brake discs, i.e., to overcome the clearance, only low forces are transmitted which should not exceed a defined limit value.
As soon as a limit value is exceeded, the system disclosed in the above U.S. patent interprets this fact as application of the friction discs on the brake discs.
The associated angular position of the driving electric motor is defined as the zero position.
To produce a clamping force, the motor can be readjusted by defined amounts of angle, and the interrelation between the readjustment of the motor based on the zero position and the clamping force exerted is taken into account.
When the brake is released, the spindle is initially restored until the zero position is reached. Subsequently, the spindle is reset by a further amount which corresponds to the clearance. This type of clearance adjustment is very inaccurate, and, in addition, it may only be effected during brake application. It is not possible to adjust the clearance independently of a braking operation.
The provision of a force sensor is absolutely necessary in the brake disclosed in the above-mentioned U.S. patent in order to be able to determine the neutral or zero position. The problem is that the signal of such force sensors is subjected to a drift so that it is only possible to determine the actual force exerted by using major electronic means. Therefore, the objective of development is to obviate the need for a sensor of this type and to derive the necessary data for brake application from the signals of other sensors, for example, a sensor which senses the wheel rotational speed.
However, this eliminates the possibility of performing the method of determination of the neutral position mentioned in the above U.S. patent.
Therefore, an object of the present invention is to provide a controlling or adjusting system which permits adjustment of a clearance even without the use of a force sensor.
Another object of the present invention is to provide a controlling or adjusting system to identify and readjust the clearance which operates independently of brake application and, in addition, permits readjusting the clearance even during travel of the automotive vehicle.
SUMMARY OF THE INVENTION
To be able to adjust the clearance and to actuate the brake in a defined fashion, it is necessary to detect in which angular position, i.e., neutral position, of the motor the friction elements are applied to the friction surface in order to define the neutral position.
The application of the friction element against the friction surface is determined during a so-called detection movement by means of a detection device. When the detection device produces a contact signal, the associated angular position of the driving electric motor can be defined as zero position or neutral position &phgr;
0
. Subsequently, the friction lining is controlledly reset to a position where a previously defined clearance &Dgr;&phgr; is maintained.
‘Position control’ means that the electric motor is actuated so that it rotates at an angular velocity which is predetermined by a controller. The controller calculates a nominal angular velocity value from the difference between the desired nominal motor angle value and the actual motor angle value prevailing. This way, the nominal clearance can be adjusted quickly and sensitively.
The detection device which determines whether the friction linings bear against the brake disc can be achieved in two ways.
One possibility involves actuating the electric motor with an approximately constant motor torque. To this end, the motor is driven by a constant nominal motor current value which produces an approximately constant motor torque in motors which are usually employed for actuating devices of this type.
It can be expected in this mode that the motor rotates at an increasing rate of angular velocity as long as the friction element is still in the clearance, i.e., is spaced from the friction disc. The application of the friction elements on the friction surface of the brake disc may now be determined as follows. The angular velocity and the angular acceleration of the motor shaft is observed while the clearance is overcome. The signals of a resolver are taken into account for this purpose. The signals of the resolver are also used to perform electronic commutation of the motor.
The motor torque is so adjusted that it only slightly exceeds the friction torque of the motor including the coupled mechanics. The remaining effective torque causes a low acceleration of the motor shaft and an accelerated approaching movement of the friction linings or elements in the direction of the brake disc. The result is that, after a previously unknown travel has been covered, the friction linings are applied with low force to the friction surface of the brake discs. The resulting load torque of the motor initially causes a reducing motor acceleration and, subsequently, deceleration (negative acceleration) of the motor angular velocity until standstill. Because the motor torque predetermined for this detection movement generates only a small motor acceleration torque, the application of the friction linings on the friction disc effects already an almost immediately occurring sign reversal of the motor acceleration.
The zero passage of the motor acceleration is used as a contact signal for applying the friction linings against the friction surface. The motor angle at the point of time of zero passage thus achieves the neutral or zero position of the motor.
Because the effective motor torque adopts a very small value only, the application of the friction linings on the friction surface will not produce any considerable deceleration of the wheel. Thus, the basic idea is to move the friction lining with low force against the friction surface, so that major forces which would cause deceleration of the vehicle are not transmitted upon application of the friction element on the friction surface.
A second possibility of realizing the detection device involves the provision of contact pins in the friction linings which, when applied to the brake disc, close a current circuit and thereby produce a contact signal in the detection device. The detection movement is position-controlled in this case, i.e., it is performed at a controlled angular velocity.
The contact pin arranged in the friction lining extends through the friction lining towards the brake disc and, therefore, is exposed to the same wear as the friction lining itself.
It is an advantage in both mentioned methods of determining the neutral position that there is no need for a force sensor.
The special advantage of the method of determining the neutral position, where the variation in the angular velocity of the motor is monitored, is that the signals of a rotation sensor can be used which is already provided and required for the electronic commutation of the motor.
When the detection device issues a contact signal, the friction lining in both methods is restored i
Balz Jurgen
Bill Karlheinz
Bohm Jurgen
Scheerer Peter
Semsch Martin
ITT Manufacturing Enterprises Inc.
King Bradley
Oberleitner Robert J.
Rader, Fishman & Grauer P
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