Method for operating a vehicle brake system, and a vehicle brake system

A vehicle brake system comprising:

• a vehicle brake having a brake piston, an electrohydraulic service brake device, an electromotive parking brake device having a spindle drive driven by an electric motor, a counting mechanism, and at least one data processing unit, wherein the electrohydraulic service brake device and/or the electromotive parking brake device act on the brake piston, wherein the vehicle brake system is configured to:
• A) detect, by the counting mechanism, a number of signal oscillations per unit time of a machine signal of the electric motor actuated for applying the parking brake device,
• B) determine, by the data processing unit, a piston position and/or piston speed of the brake piston displaced by the electric motor at least on the basis of the number of signal oscillations detected in step A,
• C) determine, by the data processing unit, a chamber volume of a piston chamber of the brake piston that is displaced by the brake piston at least on the basis of the piston position and/or the piston speed determined in step B,
• D) determine an additional volumetric quantity of a brake fluid to be delivered at least on the basis of the displaced chamber volume determined in step C, a total volume of the piston chamber for the brake fluid and a target clamping force (Fz-Soll), and
• E) control a control valve fluidically coupled with the piston chamber and a brake fluid reservoir to admit brake fluid to the piston chamber based on the additional volumetric quantity determined in step D, thereby applying the parking brake device and achieving a clamping force corresponding to the target clamping force Fz-Soll).

A method for operating a vehicle brake system which comprises a vehicle brake having a brake piston, an electrohydraulic service brake device, and an electromotive parking brake device having a spindle drive driven by an electric motor, wherein the electrohydraulic service brake device and/or the electromotive parking brake device act on the brake piston, wherein the service brake device further has at least one control valve which is fluidically coupled with a piston chamber associated with the brake piston, for brake fluid and with a brake fluid reservoir, wherein the method determines an additional brake fluid volume to be delivered by the electrohydraulic service brake device in order to ensure a target clamping force (Fz-Soll) for a brake pad of the parking brake device on application of the parking brake device, as well as applying or releasing the parking brake device, and comprises:

• A) detecting, by a counting mechanism, a number of signal oscillations per unit time of a machine signal of the electric motor actuated for applying the parking brake device,
• B) determining, by a data processing unit, a piston position and/or piston speed of the brake piston displaced by the electric motor at least on the basis of the number of signal oscillations detected in step A,
• C) determining, by the data processing unit, a chamber volume of a piston chamber of the brake piston that is displaced by the brake piston at least on the basis of the piston position and/or the piston speed determined in step B,
• D) determining an additional volumetric quantity of brake fluid to be delivered at least on the basis of the displaced chamber volume determined in step C, a total volume of the piston chamber for the brake fluid and the target clamping force (Fz-Soll), and
• E) admitting the brake fluid to the piston chamber by controlling and/or regulating the control valve at least on the basis of the additional volumetric quantity of brake fluid to be delivered by means of the electrohydraulic service brake device determined in step D.