Method for operating a hydraulic braking system, control unit and braking system

A method for operating a hydraulic braking system for a motor vehicle with an electrified drive train which has at least one electric drive machine that can be operated as a generator, wherein the braking system comprises a brake booster which has a first input member which is coupled to a brake pedal, a second input member which is coupled to a drive unit of the brake booster, and an output member which is coupled to a hydraulic pressure generation unit, the method comprising the following steps:

• a) registering a braking request by detecting a brake pedal movement that causes the first input member to be shifted in a direction of the pressure generation unit,
• b) determining, based on sensor feedback from brake pedal sensor configured to detect pedal displacement, pedal speed, or pedal acceleration, whether the braking request is to be met by pure recuperative braking, in which the drive machine is operated as a generator,
• c) shifting the second input member of the brake booster in the direction of the pressure generation unit to support the braking request, so that the second input member assumes an actuation position corresponding to the braking request, and
• d) shifting the second input member back from the actuation position in a direction away from the pressure generation unit for hydraulic pressure relief, wherein the control unit determines when to initiate and terminate the backward shift of the second input member based on whether the pedal movement has reached a substantially static condition.