the discharge valves there in an application case of the abs or esp the partial volume of the brake fluid is then fed back again behind a brake pedal into the master brake cylinder 200 by means of a feedback pump driven by a motor in order to prevent the brake pedal from dropping consequently the motor cannot be actuated again either so that the transmission 120 of the non linear electrical brake booster 100 drops further in order to allow the additional force f 100 to rise the low pressure accumulator or accumulators of the abs or esp assembly must if appropriate be adapted in terms of a volume in order to ensure that the necessary partial volume of the brake fluid is taken up it is preferred that the pressure of the brake fluid in the brake circuit 300 does not drop but instead remains at least the same in particular rises apart from a possible pressure drop peak when the valve is opened in order to discharge the partial volume of the brake fluid this is achieved in that the drive 110 is correspondingly actuated as a result of which the actuator element 130 moves the piston 210 of the master brake cylinder 200 under an at least constant pressure in the.