Nonlinearity in an Electromechanical Braking System

Abstract

In electromechanical brakes, central controllers require accurate information about the clamp force between brake pad and disc as a function of pad displacement. This function is usually denoted as characteristic curve of the caliper. In a typical electromechanical braking system, clamp force measurements vary with actuator displacements in a hysteretic manner. Due to ageing, temperature and other environmental variations, the hysteretic characteristic curve of calliper varies with time. Therefore, automatic caliper calibration in real time is vital for high-performance braking action and vehicle safety. Due to memory and processing power limitations, the calibration technique should be memory efficient and of low computational complexity. This chapter investigates the hysteresis as a nonlinear effect in the electromechanical brakes, and describes a technique to parametrically model this effect. This technique is a simple and memory-efficient real-time calibration method in which a Maxwell-slip model is fitted to the data samples around each hysteresis cycle. Experimental results from the data recorded in various temperatures show that this technique results in clamp force measurements with less than 0. 7% error over the range of clamp force variations. It is also shown that by using these measurements, the characteristic curve can be accurately calibrated in real time.