Hydraulic vehicle brake with blocking means and method for operating same

A method for operating a hydraulically actuable vehicle brake system as an emergency brake upon failure of the hydraulic actuation, the system comprising a plurality of wheel brakes, each wheel brake comprising a brake piston which acts upon a friction member and which, by means of hydraulic pressure which can be supplied into a hydraulic chamber cooperating with the brake piston, can be moved into an actuating position in which it presses the friction member against a rotor of the vehicle brake, and having a spindle/nut arrangement driven by an electric motor, which arrangement is arranged coaxially to a center axis of the brake piston, for the mechanical blocking of the brake piston in the actuating position, the nut of said arrangement is secured against rotation and, by rotation of the spindle, can either be moved into contact with the brake piston or moved away from the brake piston translatorily depending on the sense of rotation, characterized by the steps of:

• rotationally driving the spindle by means of an electric motor in a first sense of rotation in such a manner that the nut of the spindle/nut arrangement comes into contact with the brake piston;
• further rotationally driving the spindle in the first sense of rotation and comparing the achieved vehicle deceleration with a specified minimum deceleration;
• and
• rotationally driving the spindle in a controlled manner in the first sense of rotation or opposite thereto depending on the result of the previously performed comparison in such a manner that the achieved vehicle deceleration does not fall below the specified minimum deceleration;
• characterized in that a controlling means which cooperates with the vehicle brakes permits the execution of the method only if the vehicle wheels which are associated to two diagonally opposite vehicle brakes are rotating.

A method for operating a hydraulic vehicle brake as a hand brake comprising a brake piston which acts upon a friction member and which, by means of hydraulic pressure which can be supplied into a hydraulic chamber cooperating with the brake piston, can be moved into an actuating position in which it presses the friction member against a rotor of the vehicle brake, and having a spindle/nut arrangement driven by an electric motor, which arrangement is arranged coaxially to a center axis of the brake piston, for the mechanical blocking of the brake piston in the actuating position, the nut of said arrangement is secured against rotation and, by rotation of the spindle, can either be moved into contact with the brake piston or moved away from the brake piston translatorily depending on the sense of rotation, said method comprising the following steps:

• rotationally driving the spindle by means of an electric motor in a first sense of rotation in such a manner that the nut of the spindle/nut arrangement is moved towards the brake piston, characterized by the steps of:
• measuring the speed n and the current consumption I of the electric motor as a function of time;
• sensing a sudden speed drop and a corresponding increase in the current consumption and storing the previously applicable value of speed and/or current consumption as (a) reference value(s) no or Io, respectively, in a memory;
• further rotationally driving the spindle in the first sense of rotation until a specified maximum current consumption Imax is reached which corresponds to a predetermined clamping force and subsequently switching off the electric motor;
• rotationally driving the spindle in a second sense of rotation opposite to the first sense of rotation and comparing the momentary speed n and/or the momentary current consumption I with the reference value no or Io respectively;
• sensing a point of time (t4) in which n=no and/or I=Io applies;
• and
• further rotationally driving the spindle in the second sense of rotation for setting a specified distance between the nut and the brake piston.