Experimental research on modulation characteristics of wheel cylinder pressure in electro-hydraulic braking system

The electro-hydraulic brake (EHB) system consists of mechanical, electromagnetic and hydraulic parts. The pressure characteristic of its wheel cylinder is essential to the brake force modulation. But this characteristic is hard to be expressed with theoretical models because of the heavy nonlinearity and coupling of the system's main parts. In the research, the experiments are carried out to study this characteristic. The essential affecting factors considered in the experiment design contain the initial pressure and the duty cycle of PWM signal. The stable variation MAP is got from the experimental results. The analysis shows that there are the inflection points in the stable variation value and initial pressure curves. The inflection point is defined as the piston travel end pressure. In this system, the pressure is 2.8 MPa. The analysis also shows that the relationship between the pressure variation and duty cycle is linear. But the line does not go across the origin point. The cross point is at 3% of the duty cycle during pressurizing, while it is at -5% of the duty cycle during depressurizing. In the research on pressure characteristics, the nonlinear characteristics of the system are expressed by MAP, and some parts with linear relation in the system are found.