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In this paper, we propose a hardware and a software design method considering functional safety for an electro-mechanical brake (EMB) control system which is used as a brake actuator in a brake-by-wire (BBW) system. A BBW system is usually composed of electro-mechanical calipers, a pedal simulator, and a control system. This simple by-wire structure eliminates the majority of bulky hydraulic brake devices such as boosters and master cylinders. The other benefit of a BBW system is its direct and independent response; this leads to enhanced controllability, thus resulting in not only improved basic braking performance but also considerably easier cooperative regenerative braking in hybrid, fuel-cell, and electric cars. The importance of a functional safety based approach to EMB electronic control unit (ECU) design has been emphasized because of its safety critical functions, which are executed with the aid of many electric actuators, sensors, and application software.

In this paper, for the fault-tolerant control of electro-mechanical brakes (EMBs), we continuously estimate several system variables and utilize these estimates to detect faulty sensor outputs. The clamping force is estimated by using the motor position and hysteresis phenomenon during clamping and releasing. Current sensor faults can be easily derived from the characteristics of a three-phase balanced circuit, and the motor position is estimated by applying different methods in low-speed and high-speed regions where a model-based approach is adopted. Using the proposed fault-tolerant logic, we can detect which sensor has a fault during driving or braking. Then, we use a bumpless transfer technique so that the control performance does not deteriorate when the estimated values are substituted for the measured values.