Electric brake system and method for operating the same

#The invention relates to an electric brake system for a motor vehicle which, inter alia, includes the following components: at least one energy consumer; at least one computer unit; at least one voltage source, which can be connected to the energy consumers; and, an ignition switching device, which connects the voltage source to the energy consumer when a switch-on signal is applied. The invention also relates to a method for operating such an electric brake system for a motor vehicle.

#Electric brake systems of the above-mentioned kind are already known and are referred to also as brake-by-wire brake systems. The electric brake system includes several electric energy consumers such as at least one computer unit and a brake actuator for each wheel of the motor vehicle. By applying a switch-on signal, the energy consumers are connected to a voltage source so that the electric brake system is operational and is ready for braking operations. If a braking command is issued by a driver of the motor vehicle by applying foot force on a brake pedal, then the effect of the foot force on the pedal is detected by a sensor and is converted into an electric signal. The signal is then transmitted to the brake actuators and each brake actuator exercises, inter alia, a brake force on the wheel of the motor vehicle assigned thereto with the aid of an electric motor.

#Electric brake systems of this kind can be considered as reliable especially because they are configured in two loops as are the conventional brake systems and therefore a channel is provided for each electric signal in each brake loop. If one of the signals is absent or one of the channels fails and if a brake loop thereby becomes inoperative, then the other brake loop remains operational and the electric brake system is operational to a limited extent. It is, however, noted that the switch-on signal is a one-channel signal. Accordingly, if the switch-on signal is absent (for example, because of a connector becoming separated or because of a break in a cable, which transmits the switch-on signal), then a complete failure of the entire electric brake system can occur (that is, both electric brake loops) and the motor vehicle can no longer be braked. The failure of the electric brake system is especially critical when the motor vehicle is otherwise operational and in movement. In summary, the failure of the switch-on signal can lead to a situation wherein the safe operation of the vehicle is affected and this is unacceptable.

#The invention will now be described with reference to the drawings wherein:

#FIG. 1 is a schematic representation of the electric brake system according to the invention;

#FIG. 2 is a block circuit diagram showing the voltage supply of the electric brake system;

#FIG. 1 is a schematic of a two-loop electric brake system for a motor vehicle. Only those components are shown which are necessary for explaining the invention. The reference numerals identifying the components of the first brake loop are each provided with the letter "a" and the reference numerals which identify the components of the second brake loop are each provided with the letter "b". A foot force, which corresponds to the braking command of the driver of the motor vehicle, is applied to brake pedal 2 which causes this brake pedal to be moved. The distance through which the brake pedal 2 is moved is converted into an electric signal by sensor 4 and this signal corresponds to the brake command of the driver. The electric signal is conducted via the signal line 22 to the computer units 8a of the first brake loop as well as to the computer units 14b of the second brake loop. There, control signals are generated from the electric brake signal and are conducted to the brake actuators 10a of the forward wheels 12a and to the brake actuators 16b of the rear wheels 18b. The brake actuators 10a and 16b are activated in correspondence to the control signals which causes a braking force to be generated at the forward wheels 14a and at the rearward wheels 18b. The computer units 8a and 14b can exchange data with the central computer unit 6 via the serial data bus 20.

#FIG. 2 is a circuit block diagram showing the voltage supply of the electric brake system shown in FIG. 1. In FIG. 2 also, the reference numerals identifying the components of the first brake loop are provided with a letter "a" and the reference numerals identifying the components of the second brake loop are provided with the letter "b".

#For each brake loop, the electric brake system includes a voltage source (24a or 24b), which supplies voltage via a supply path (34a or 34b) to the following: the brake actuators (10a or 16b), the computer units (30a or 30b) and the central computer unit 6. The computer unit 30a includes the computer units 8a and the computer unit 30b includes the computer units 14b. An ignition-switch device 28a is connected between the voltage source 24a and the above-mentioned energy consumers and an ignition-switch device 28b is connected between the voltage source 24b and the above-mentioned energy consumers.