Electro-hydraulic braking dynamics for pressure demand control of brake-by-wire system
Brake-by-wire system for self-driving vehicles requires hydraulic pressure response of the master cylinder to be quick in the braking process, making its long-term precision paramount. This is particularly challenging for braking in response to the command of virtual driver instead of the real driver, for which the hydraulic pressure is nonlinear with the electric motor’s torque. While much of the research on brake-by-wire has focused on improving energy regeneration and vehicle stability, comparatively little is known about the braking pressure control of self-driving vehicles. Therefore, we develop a novel architecture of the electro-hydraulic brake-by-wire adopting ball screw for the self-driving, in which there is a quadratic-polynomial relationship between the position of the electric motor and the brake pressure of the master cylinder. The brake-by-wire dynamics model is built by the speed of the electric motor and the brake pressure of the master cylinder, and a sliding mode control law is designed based on the pressure demand of the master cylinder. Here we discuss a series of studies on electro-hydraulic braking dynamics that, collectively, design a pressure demand control approach of how the sliding mode controller operates the master cylinder pressure by the electric motor torque. Testing and analyzing the designed approach embedded into the braking control unit is applied to a vehicle test bench brake-by-wire to fully realize the accurate pressure tracking of the electro-hydraulic brake-by-wire system.