Abstract
The electro-hydraulic composite braking system of a pure electric vehicle can select different braking modes according to braking conditions. However, the differences in dynamic response characteristics between the motor braking system (MBS) and hydraulic braking system (HBS) cause total braking torque to fluctuate significantly during mode switching, resulting in jerking of the vehicle and affecting ride comfort. In this paper, torque coordination control during mode switching is studied for a four-wheel-drive pure electric vehicle with a dual motor. After the dynamic analysis of braking, a braking force distribution control strategy is developed based on the I-curve, and the boundary conditions of mode switching are determined. A novel combined pressure control algorithm, which contains a PID (proportional-integral-derivative) and fuzzy controller, is used to control the brake pressure of each wheel cylinder, to realize precise control of the hydraulic brake torque. Then, a novel torque coordination control strategy is proposed based on brake pedal stroke and its change rate, to modify the target hydraulic braking torque and reflect the driver’s braking intention. Meanwhile, motor braking torque is used to compensate for the insufficient braking torque caused by HBS, so as to realize a smooth transition between the braking modes. Simulation results show that the proposed coordination control strategy can effectively reduce torque fluctuation and vehicle jerk during mode switching.
Highlights
The electro-hydraulic composite braking system of an electric vehicle (EV) consists of the motor braking system (MBS) and the hydraulic braking system (HBS), which realize the pure electric, pure hydraulic, and hybrid braking modes
If the Thebraking motortorque control parameters id and iin by the motor controller according required by driver changes, orderoutput to maintain the coordinated compensation ability to the q are of the to the hydraulic braking torque during mode switching, the target braking torque modified target motor braking torque Tm_req, so that the MBS outputs the actual motor braking torque allocated by the braking force distribution controller to the should be smaller than the maximum
The configuration of a four-wheel-drive pure electric vehicle with a dual motor is considered in this paper, and a braking torque dynamic coordinated control strategy, based on the braking intention this paper, and a braking torque dynamic coordinated control strategy, based on the braking of the driver, is proposed
Summary
The electro-hydraulic composite braking system of an electric vehicle (EV) consists of the motor braking system (MBS) and the hydraulic braking system (HBS), which realize the pure electric, pure hydraulic, and hybrid braking modes. For the problem of braking torque coordination control during mode switching, Okano et al [8] adopted a filtering algorithm to assign the MBS response to high frequency braking torque and the HBS response to low frequency braking torque, making full use of the dynamic characteristics of both systems. The aforementioned research has improved braking torque coordination control during mode switching, leading to better control of the electro-hydraulic composite braking system and reduced vehicle jerking, they did not reflect the driver’s braking intention during mode switching; that is, the motor and hydraulic braking torque cannot be adjusted reasonably according to whether the driver pays more attention to brake safety or ride comfort. The rapid response of the motor braking torque is used to compensate for the insufficient braking torque caused by the slow response of the HBS, so as to realize the smooth transition of the braking mode, which enhances braking safety and ride comfort during mode switching
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