Hydraulic vehicle braking systems can be implemented as external vehicle braking systems and in addition to a master brake cylinder actuated by muscle power, to which the wheel brakes are hydraulically connected and which provides the pressure and volume for operating wheel brakes. An electrically controlled pressure and volume supply device actuates the wheel brakes in a “brake-by-wire” operating mode. In the event of failure of the electrically controlled pressure and volume supply device, operation of the wheel brakes is carried out solely by the muscle power of the driver of the vehicle.
It is to be expected that in the future vehicle braking systems will also come into use that are suitable for automatically driving vehicles. Said braking systems could be in principle be externally actuated systems or “brake-by-wire” systems. This means that a braking demand is made by means of electronic or electrical control signals and can be implemented by the system without the aid of the driver. In this case, for safety reasons sufficiently high availability of the braking system or the externally actuated braking function is desired.
In DE 10 2012 205 861 A1, a “brake-by-wire” braking system is described, which in addition to a brake pedal-operated master brake cylinder comprises a first and a second pressure supply device. The second pressure supply device is arranged to increase the pressure in each of the brake circuits for supplying the wheel brakes compared to the pressure supplied by the master brake cylinder. The driver of the vehicle can thus comfortably achieve an adequate service brake deceleration despite a failure of the first pressure supply device.
The master brake cylinder, the first pressure supply device, the isolating valves, the supply valves and the simulator with the simulator release valve are disposed in the first module with the first electronic control and regulating unit, and the second pressure supply device and the inlet and outlet valves are disposed in the second module with the second electronic control and regulating unit. Just one pressure medium reservoir is provided, which is disposed on the first module.
The suction sides of the pumps of the second pressure supply device of the second module are likewise hydraulically connected to said pressure medium reservoir. In the event of a small leak in the hydraulic connection between the second module and the pressure medium reservoir disposed on the first module, the leak could not be detected rapidly enough by the container warning device of the pressure medium reservoir, so that the pump of the second pressure supply device sucks air in via the small leak and thus contaminates the two brake circuits with air.
Furthermore, the pressure ports of the second pressure supply device are connected to the input-side connections of the inlet valves of the wheel brakes, so that the inlet valves are disposed between the respective pressure port of the second pressure supply device and the wheel brake. Because of the throttling effect of the inlet valves, obstruction of the flow of pressure medium that is output by the second pressure supply to the wheel brake can occur.
The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.