A novel pressure control strategy of an electro-hydraulic brake system via fusion of control signals

Abstract

With the development of electro-hydraulic brake system in the automotive application, pressure control is at the top of a brake system engineer’s agenda. This work focuses on the development of a pressure-loop controller for a motor-type electro-hydraulic brake system, which is composed of an electro-mechanical actuator and a hydraulic link. The pressure control issue of motor-type electro-hydraulic brake system is influenced intensely by the nonlinearities (i.e. friction) and uncertainties (e.g. temperature variation, brake pad wear, and so on) of the system and by the very demanding performance specifications (i.e. supporting cooperative work with hydraulic control unit of anti-lock brake system). The pressure control of motor-type electro-hydraulic brake system is investigated, and a novel pressure–based control strategy via fusion of control signals is proposed to improve the pressure tracking performance. The control strategy comprises online model–based friction compensation, online dither–based friction compensation, and feedback control. Four original contributions make this work distinctive from the existing relevant literature. Selecting the Coulomb+viscous friction model can maximize to reduce difficulty of parameter identification and Stribeck effects detection based on maintaining the pressure tracking accuracy. Thanks to the model-based friction compensation torque, the signal magnitude of dither-based friction compensation torque can be decreased so that the vehicle comfort can be improved. The compensation parameters of both the model-based and dither-based friction compensation can be online modified according to the operating point of system. The robustness of the fusion controller is enhanced by employing the sliding mode control algorithm with conditional integrator. The performance of the proposed control strategy is evaluated by hardware-in-the-loop-simulation and vehicle experiment in typical braking situations. The experimental results with fusion control show improved pressure tracking performance in comparison with that without fusion control.

Master cylinder pressure reduction logic for cooperative work between electro-hydraulic brake system and anti-lock braking system based on speed servo system

“…9 A preliminary attempt to the cooperative work between EHB and ABS has been carried out in the authors’ previous work. 8 The experiment is conducted again by using the pressure-loop controller on dry asphalt road. The test vehicle and the road condition will be introduced later on.…”

“…System response by using the pressure-loop 8 under ABS-triggered situation on dry asphalt road: (a) Master cylinder pressure, (b) motor speed, (c) motor torque and (d) vehicle speed.…”

“…A double closed-loop controller, involving the master cylinder pressure outer loop and motor rotation speed inner loop, is utilized in the feedback control of EHB to improve the dynamic response performance. Different from the previous study, 8 the unknown external disturbance caused by ABS is quickly coped with in the inner-loop. These unknown disturbances usually attenuate the effectiveness of some feedback controllers such as pressure-based feedback, position-based feedback and so on.…”

“…A pressure fusion control strategy was designed for EHB and the vehicle experiment was conducted under the ABS-triggered situation. 8 The results displayed that the maximum master cylinder pressure value has exceeded 200 bar, which may degrade the performance of EHB&ABS and reduce the service life of corresponding components. Pressure reduction logic (PRL) function was proposed in order to prevent the master cylinder pressure from pressure peaks and oscillation.…”

“…The model-based friction compensation technique has been used in the previous study: Coulomb + viscous model, 11 Tustin model, 12 Gaussian model, 13 Karnopp model, 14 LuGre model 15 and so on. To solve the uncertainties caused by static friction and external disturbances, most of the studies used the pressure-based feedback control based on proportional-integral (PI) control, 16 adaptive mechanism, 13 sliding mode control (SMC), 17 adaptive sliding mode control (ASMC), 11 sliding model control with conditional integrator (SMC + CI) 8 and so on. Some studies applied not only the pressure-based feedback control but also the position-based feedback control: position-pressure switching control, 18 adaptive cascade control, 19 double closed-loop cascade control 20 and so on.…”