Patent ID: 8794720

Claim:
Method for the secured release of an electromechanically actuable parking brake which has a brake piston, which acts on a friction element and is displaceable into an actuation position in a brake caliper in which it presses the friction element against a brake disc, and wherein a spindle/nut arrangement, which is driven by an electric motor, is coaxial with respect to a central axis of the brake piston and is configured to mechanically lock the brake piston in the actuation position, wherein the nut of the spindle/nut arrangement is secured against rotation and moved by a rotation of the spindle in a translatory fashion along the central axis either in abutment against the brake piston or away from the brake piston depending on a rotational direction, said method comprising the step of: driving the spindle by the electric motor in a brake application direction until a predefined, maximum power drain (I max ), corresponding to a predefined brake application force (F), is reached, said driving step comprising the sub-steps of: (a) detecting a first travel distance (x 0 ) of the brake piston which corresponds to the brake application force (F), by a stiffness characteristic curve, stored in a memory, of the brake caliper in a locked state, (b) determining a second travel distance (x 1 ) by addition of a third travel distance value (x 11 ), which corresponds to a desired clearance value, to the first travel distance (x 0 ), such that x 1 =x 0 +x 11 , (c) driving the electric motor in a release direction until the second travel distance (x 1 ) has been covered by the brake piston, (d) comparing a vehicle speed (v) with a predefined first speed value (v 1 ) greater than zero, and when the vehicle speed (v) exceeds the predefined first speed value (v 1 ), the electric motor is driven once more in the release direction until a fourth predefined travel distance (x 12 ) has been covered, during which it is insured, in a secured fashion, that no contact takes place between the friction element and the brake disc of the vehicle brake, and (e) comparing the vehicle speed (v) with a predefined second speed value (v 2 ) greater than zero and less than the predefined first speed value (v 1 ), and when the vehicle speed (v) falls below the predefined second speed value (v 2 ) after exceeding the predefined first speed value (v 1 ), the electric motor is driven in the brake application direction until the fourth predefined travel distance (x 12 ) has been covered.