The invention relates to a braking system for a vehicle including an electronic service braking system (EBS) having at least one brake cylinder and a control valve assigned to the brake cylinder (referred to herein as a pressure control module or DRM). The pressure control module comprises at least a control chamber as well as a working chamber. The working chamber is connected by way of a supply line to the air supply reservoir, and the control chamber is connected by way of an inlet solenoid valve with the air supply.
For reducing pressure, the control chamber is connected with the atmosphere by way of an outlet solenoid valve and, as required, by way of a sound absorber.
By actuating the inlet or outlet solenoid valve, a pressure defined by the electronic brake control system is controlled into the control chamber during braking. In this case, the pressure in the control chamber controls the pressure in the working chamber through the use of a relay valve mechanism.
Furthermore, the control chamber of the pressure control module is connected by way of a backup line and a backup valve with a conventional backup system, in which a pressure is applied during braking by means of a pneumatic foot brake valve. This pressure is used for nevertheless permitting braking of the vehicle when the electric pressure control fails. For this purpose, the inlet and outlet solenoid valves are closed in their non-energized condition, and the backup solenoid valve is open in its non-energized condition.
Such pressure control modules control the pressure in the brake cylinder when braking takes place during which the wheels do not tend to lock up as well as during an ABS intervention.
In the case of an ABS intervention, the pressure at the brake cylinder of the wheel tending to lock is reduced considerably. When, subsequently, the wheel starts to run again, the pressure must be raised again as fast as possible in order to again build up the maximally possible braking force at the corresponding wheel as fast as possible and, thus, minimize the braking distance of the vehicle.
In the case of electronic service braking systems used so far, air for increasing the pressure was guided into the control chamber exclusively from the supply connection by way of the inlet solenoid valve.
Particularly in the case of rapid and large pressure increases during ABS braking, this had the disadvantage that, because of the limited passage cross-section of the inlet solenoid valve, the gradient of the pressure increase was not sufficiently large.
It is therefore an object of the invention to provide a braking system which permits increasing the pressure in the control chamber during ABS braking more rapidly than in the systems known to date. According to the invention, this is achieved in that the backup valve is opened together with the inlet valve when an ABS signal demands a large and rapid pressure increase. As a result of the brief opening of the backup solenoid valve at the beginning of the pressure increase, air from the backup connection of the pressure control module can also be guided into the control chamber and, thus, a faster pressure increase can be achieved.
This achievement is possible because the brake pedal is always operated during an ABS intervention and, therefore, at the moment of the demanded pressure increase, the pressure is always higher in the backup system than in the control chamber of the pressure control module.
Since ventilation takes place by way of the cross-sections of the inlet valve, as well as the backup solenoid valve, the opening of the backup solenoid valve according to the invention achieves a significantly larger pressure gradient. This leads to a significantly faster response by the wheel brakes after an ABS-caused pressure reduction.
In a particularly preferred embodiment, the backup valve and the inlet valve are constructed as solenoid valves, particularly and preferably as proportional valves.
In addition to the braking system, the invention also provides a method of rapidly ventilating electronically controlled vehicle braking systems during ABS braking.