In this paper, a novel double closed loop cascade control architecture with interconnected pressure estimation for a pressure-sensor-unequipped integrated electro-hydraulic brake (IEHB) system suitable for automobile applications is presented. Starting from a control-oriented model, an interconnected pressure estimator (IPE) is employed to estimate the pressure dealing with the nonlinear pressure-position relationship. To reduce the negative influence of system nonlinearities and uncertainties, i.e., friction, pressure-position relationship, brake pad wear, temperature variation, knock-off, a double closed-loop cascade controller (DCLC) is proposed. An outer pressure tracking loop employs sliding mode controller with conditional integrator (SMC+CI) to ensure tracking accuracy with desired position of master cylinder piston as control output; an inner position control loop is designed using the SMC to improve the response speed. By this way the bandwidth of inner position is wider than which of the outer pressure loop, which has advantages in eliminating the disturbances caused by system nonlinearities and uncertainties quickly. The overall system asymptotic stability is analytically investigated through the Lyapunov Theorem. Simulation and Experimental validation demonstrates excellent tracking performance and robustness.

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.

In the automotive field, electro-hydraulic brake systems (EHB) has been developed to take place of the vacuum booster, having the advantage of faster pressure built-up and continuously pressure regulation. Pressure control, one of the most crucial issues to be solved for EHB, is influenced by the system nonlinearities (e.g., pressure-position, friction). Recently, there are a series of studies that focus on this issue. However, the pressure control based on pressure estimation is rarely investigated in the previous literatures. In order to achieve cost-effective and highly integrated, the pressure is regulated without any add-in sensors, making it very difficult to achieve a satisfactory performance. A pressure control system based on pressure joint estimation is developed in this article according to a requirement-oriented model. The pressure joint estimation is designed considering actuator characteristics and vehicle dynamics. The wheel speed feedback is used for modification via a proportional-integral observer. A pressure control combining feedforward, torque-adaptive friction compensation with feedback controller is employed to improve the pressure-tracking performance. The constraint of feedback gain of controller is derived based on the small-gain theorem to remain the input–output stability of the overall control system. Superior to the estimation method based on actuator characteristics, the joint estimation method improves the accuracy by more than 10%. The pressure-tracking performance and robustness of system are validated by vehicle experiments under the typical common braking situations.

As one feasible solution of brake-by-wire systems, electro-hydraulic brake system has been made available into production recently. Electro-hydraulic brake system must work cooperatively with the hydraulic control unit of anti-lock braking system. Due to the mechanical configuration involving electric motor + reduction gear, the electro-hydraulic brake system could be stiffer in contrast to a conventional vacuum booster. That is to say, higher pressure peaks and pressure oscillation could occur during an active anti-lock braking system control. Actually, however, electro-hydraulic brake system and anti-lock braking system are produced by different suppliers considering brake systems already in production. Limited signals and operations of anti-lock braking system could be provided to the supplier of electro-hydraulic brake system. In this work, a master cylinder pressure reduction logic is designed based on speed servo system for active pressure modulation of electro-hydraulic brake system under the anti-lock braking system–triggered situation. The pressure reduction logic comprises of model-based friction compensation, feedforward and double closed-loop feedback control. The pressure closed-loop is designed as the outer loop, and the motor rotation speed closed-loop is drawn into the inner loop of feedback control. The effectiveness of the proposed controller is validated by vehicle experiment in typical braking situations. The results show that the controller remains stable against parameter uncertainties in extreme condition such as low temperature and mismatch of friction model. In contrast to the previous methods, the comparison results display the improved dynamic cooperative performance of electro-hydraulic brake system and anti-lock braking system and robustness.

Based on Queueing Theory, this paper conducts the analysis and optimization of a novel hydraulic brake-by-wire system configuration involving electric-mechanical brake actuators + hydraulic control unit (eActuators + HCU). The functional requirement and topological analysis of frictional brakes are stated. The queueing model is built, providing a theoretical basis to the development of the minimum hydraulic brake-by-wire system involving one eActuator + s valves. Based on the minimum hydraulic brake-by-wire system, the equivalent queueing model is proposed and the evaluation index is defined as average waiting time of wheel cylinder pressure (AWT of WCP). The queueing disciplines are designed and optimized. Integrated-electro-hydraulic brake system (IEHB), a scheme on behalf of the minimum hydraulic brake-by-wire system, is developed and modeled. In accordance to the IEHB physical system, the comparison verifications for the proposed queueing disciplines are conducted via simulations and experiments. The correlation analysis and sensitivity analysis are carried out respectively. Several typical pressure-tracking experiments have been carried out to demonstrate the IEHB control system. This work has two original contributions: 1) The topological and conjoint analysis of the novel hydraulic brake-by-wire system configuration (eActuators+valves) is conducted via Queueing Theory. 2) The performance of the minimum hydraulic brake-by-wire system is improved by using the balanced algorithm, compared with the round-robin scheduling algorithm and rotary control algorithm proposed in the previous study.