Method for testing the leak tightness of a hydraulic vehicle braking system

1. A method for a hydraulic vehicle braking system that includes a brake pressure generator for generating a hydraulic brake pressure in the vehicle braking system, the method comprising:

detecting a leakage of the vehicle braking system; and

after the detecting of the leakage, determining whether a fill level in a brake fluid reservoir of the vehicle braking system is at least as high as a predefined threshold level; and

conditional upon that a result of the determining is that the fill level is at least as high as the predefined threshold level, performing a test of a sufficiency of a tightness of the hydraulic braking system to prevent a leak of brake fluid out of the hydraulic vehicle braking system;

wherein the method includes at least one of the following two features (a)-(b):

(a) the determining of whether the fill level in the brake fluid reservoir is at least the predefined threshold level is performed by:

initially displacing brake fluid out of the brake pressure generator into the brake fluid reservoir;

subsequent to the displacement, drawing in from the brake fluid reservoir using the brake pressure generator; and

subsequent to the drawing in, testing a brake pressure build-up using the brake pressure generator; and

(b) the brake pressure generator is a power brake pressure generator that includes a motor and a hydraulic pump configured to be operated by the motor to generate the hydraulic brake pressure independently of a shifting of a manually operated brake pedal.

2. The method as recited in claim 1 , wherein the determining is performed by:

the initial displacement of the brake fluid out of the brake pressure generator into the brake fluid reservoir;

subsequent to the displacement, the drawing in from the brake fluid reservoir using the brake pressure generator; and

subsequent to the drawing in, the testing of the brake pressure build-up using the brake pressure generator.

3. The method as recited in claim 1 , wherein the brake pressure generator is the power brake pressure generator that includes the motor and the hydraulic pump configured to be operated by the motor to generate the hydraulic brake pressure independently of the shifting of the manually operated brake pedal.

4. A method for a hydraulic vehicle braking system that includes a power brake pressure generator, the power brake pressure generator including a piston-cylinder unit, the method comprising:

detecting a leakage of the vehicle braking system; and

after the detecting of the leakage:

hydraulically separating the piston-cylinder unit from another portion of the vehicle braking system by closing a valve;

applying a displacement force to a piston of the piston-cylinder unit in a cylinder of the piston-cylinder unit for a pressure build-up; and

carrying out a test of a sufficiency of a tightness of the hydraulic braking system to prevent a leak of brake fluid out of the hydraulic vehicle braking system;

wherein the method further comprises at least one of:

measuring a pressure change generated by the application of the displacement force, wherein the carrying out of the test is performed conditional upon that the measurement indicates a pressure increase at at least a predefined rate; and

measuring a movement of the piston, wherein the carrying out of the test is performed conditional upon that the measurement indicates that the piston has not shifted in the cylinder or has not shifted in the cylinder by a predetermined amount.

5. A method for a hydraulic vehicle braking system that includes a brake pressure generator for generating a hydraulic brake pressure in the vehicle braking system, the method comprising:

detecting a leakage of the vehicle braking system; and

after the detecting of the leakage:

measuring a speed of a brake pressure build-up in the vehicle braking system using the brake pressure generator; and

based on the measurement, carrying out a test of a sufficiency of a tightness of the hydraulic braking system to prevent a leak of brake fluid out of the hydraulic vehicle braking system, the test being performed conditional upon that a result of the measurement is that the speed is at least as fast as a predefined threshold speed.