Vehicle hydraulic brake system operating with power assistance

A vehicle hydraulic brake system which comprises a twin circuit emergency brake pressure source which can be put into operation by a pedal, wheel brakes which can be supplied from the emergency brake pressure source, emergency brake main conduits laid as a twin circuit and extending from the emergency brake pressure source to the wheel brakes and with a power-assisted brake device which can be controlled electrically by means of the pedal, said brake device has at least one fluid pump which can be supplied from a reservoir, a power reservoir which can be charged by said at least one pump, and at least one controllable first valve arrangement (29, 30) per brake circuit, for the selection of a brake pressure source, between the emergency brake pressure source and wheel brakes and said brake device has at least one electrically controllable second valve arrangement (37, 38, 39, 40, 37a, 37b, 37c), for brake pressure setting, a required brake pressure value generator (35) which can be controlled by means of the pedal, and a control unit (36) connected to the required brake pressure value generator (35), said control unit (36) controls the at least one second valve arrangement (37, 38, 39, 40, 37a, 37b, 37c in order to generate brake pressures from the energy of the power source and to change these brake pressures, wherein the at least one first valve arrangement (29, 30) for selecting the brake pressure sources (6, 23) is arranged to open the associated emergency brake main conduits (12, 13) to a return conduit (59) which leads to the reservoir (7), wherein the at least one second valve arrangement (37, 38, 39, 40, 37a, 37b, 37c) is connected to the emergency brake main conduits (12, 13) and at least one of the wheel brakes (8, 9, 10, 11) to set brake pressures while relaying a pressure medium from the power source (23) and is arranged in such a way that said at least one second valve arrangement connects the emergency brake main conduits (12, 13) to the wheel brakes (8, 9, 10, 11) when no electrical current is applied to the at least one electromagnet (71, 73, 83) and separates the wheel brakes (8, 9, 10, 11) from the power source (23) and, in power-assisted brake operation, connects the wheel brakes (8, 9, 10, 11) to the power source (23) for the purpose of a brake pressure increase and to the emergency brake main conduits (12, 13), which can be opened to the reservoir (7), for the purpose of brake pressure reduction.