Abstract
This paper presents a control-oriented LPV (Linear Parameter-Varying) model for commercial vehicle air brake systems, where a pneumatic valve actuator is used to control the brake chamber pressure. To improve the brake system response time and reduce the vehicle stopping distance, the traditional treadle valves used in the air brake system are replaced by electro-pneumatic valves. Also, to develop the model-based brake control strategy, a nonlinear mathematical model is developed based on Newton’s second law, fluid dynamics of the orifice, force balance of spool, and solenoid dynamic characteristics. The brake chamber dynamics is also considered during the charging and discharging processes. The developed nonlinear model is calibrated based on both valve actuator geometry and test bench experimental results. It is proposed to model the nonlinear system in the LPV form so that gain-scheduling controllers can be developed. To obtain the LPV model, system identification is conducted using the calibrated nonlinear model to obtain a set of linearized models under different brake chamber pressure levels, and the resulting identified linear models are assembled to form the LPV model with brake chamber pressure as the varying parameters. A linear infinite-horizon continuous-time LQR (Linear Quadratic Regulator) controller was designed for the braking system based on the developed LPV model with the fixed parameter to demonstrate the effectiveness of the developed LPV model.
Highlights
The vehicle brake system is a crucial component of commercial vehicles and it is closely related to driving safety, especially under downhill braking and other emergency conditions to avoid an accident.Over 90% of vehicle rear-end accidents and 60% of frontal collisions could be avoided effectively if the brake response time could be reduced by one second based on the National Transportation Safety Board (NTSB) special investigation report [1]
Since the developed system model is highly nonlinear with respect to control inputs and supply pressure and it is well-known that design a nonlinear controller with guaranteed performance is a challenge, a Linear Parameter-Varying (LPV) model for the system is developed so that a gain-scheduling controller can be designed for the air brake system in future
By tuning both Q and R matrices in Equation (38), the optimal control performance can be achieved based on the developed LPV model
Summary
The vehicle brake system is a crucial component of commercial vehicles and it is closely related to driving safety, especially under downhill braking and other emergency conditions to avoid an accident. The developed model was used to predict the brake chamber transient performance and estimate brake chamber actuator displacement, and it is used to detect brake system leaks This model is a useful tool for a control system to reduce response time and stopping distance [6]. A nonlinear pneumatic brake system model with electro-pneumatic proportional valves was developed To make it feasible to design LPV gain-scheduling controllers for improving brake chamber pressure regulation performance, the developed nonlinear system model is linearized using the PRBS q-Markov Cover [25] at multiple brake chamber pressure levels, and linked into a single LPV model [26]. Note that the development of the LPV model enables Model Predictive Control (MPC) and gain-scheduling control strategies for improving air braking system performance
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