Method for controlling an electronically slip-controllable power-brake system with redundant generation of brake pressure

A method for controlling an electronically slip-controllable power-brake system with redundant generation of brake pressure, the power-brake system being equipped with a braking-request detection device for specifying a braking request, with a brake pressure generator for supplying wheel brakes in at least one connected brake circuit with pressure medium under a brake pressure corresponding to the braking request, the brake pressure generator being equipped with a controllably drivable first pressure-medium delivery device, which includes a displacement device which can be driven within a cylinder to build up brake pressure in a pressure build-up direction up to an outer reversal point and to decrease pressure in the brake pressure decrease direction, which is contrary to the brake pressure build-up direction, up to an inner reversal point, and which, with the cylinder, delimits a working chamber having a variable volume, the power-brake system further being equipped with a brake pressure modulator for individually setting brake pressure in each of the wheel brakes of the brake circuit, the brake pressure modulator being connected to the brake circuit in parallel with the brake pressure generator, and having a controllably drivable second pressure-medium delivery device, with a reservoir for pressure medium, an electrically activatable plunger discharge valve configured to control a first pressure-medium connection between the first pressure-medium delivery device and the reservoir of the power-brake system, an electrically activatable pressure control valve configured to control the brake pressure in the brake circuit, and with at least one electronic control unit configured to electrically activate the first and second pressure-medium delivery devices and the directional valves as required, the method comprising the following steps:

• ascertain a volume of pressure medium which has been delivered by the second pressure-medium delivery device to build up a brake pressure in the brake circuit;
• comparing the ascertained pressure-medium volume to a limit value, which indicates a maximum value for a pressure-medium volume to be displaced;
• decreasing the brake pressure, including a pressure decrease phase in which a pressure-medium connection is created, via which pressure medium is released from the brake circuit into the reservoir of the power-brake system;
• and
• controlling the volume of the pressure medium which is released into the reservoir by adapting an electrical activation of the pressure control valve, when the ascertained pressure-medium volume is equal to or greater than the limit value;
• wherein the method is carried out when the brake pressure in the brake circuit is higher than a maximum pressure that can be applied in the brake circuit by the first pressure-medium delivery device;
• wherein a further third pressure decrease phase is carried out, in which, through electrical activation of the pressure control valve, a controllable pressure-medium connection between the working chamber of the first pressure-medium delivery device and the brake circuit is created, and the activation of the pressure control valve during the third pressure decrease phase is performed such that the pressure in the working chamber is lowered to the maximum pressure that can be applied to the brake circuit by the first pressure-medium delivery device.