The failure modes study for the electric vacuum brake booster system

The traditional brake booster utilizes the pressure difference between atmosphere and vacuum to provide auxiliary force for brake. For the conventional vehicle, the vacuum is generated by the internal combustion engine. In order to use the same brake booster on the electric vehicle, the vacuum has to be created by an electric vacuum pump. The control of the electric vacuum pump can be achieved by an electromechanical pressure sensor which detects the change of the vacuum chamber and activates the pump. However, there is some concern that this system is not safe because the driver can not be noticed when the pump or the sensor failed. Therefore, the new system architecture of the electric vacuum brake booster system was proposed in this paper. The electronic pressure sensor replaces the electromechanical pressure sensor in the original system; as a result, the pressure of the vacuum chamber can be fed back to the electronic control unit, which achieves more precise pressure control. The electronic control unit also monitors the power source and the current of the electric vacuum pump, which can give information about whether the auxiliary brake force is available. Besides, four fail-safe strategies are developed for ensuring that all the failures can be found and handled. The electronic control unit was implemented with a microprocessor, and the functions were validated in the bench test as well as in a prototype vehicle. The results indicate that the driver can be informed the conditions of the electric vacuum brake booster system so that the driver has no unexpected and dangerous situations.