The Retarder is one of the main components in Scania’s trucks’ braking system and is used to brake down the truck and for maintaining a steady speed on descents. This study aims to investigate if the current system which uses a proportional valve to control the air pressure in the Retarder, can be replaced with two on/off solenoid valves and a pressure chamber to control the air pressure, which would result in a cheaper and more robust system.
By varying the air pressure, the braking torque in the truck can be regulated. A model including electrical drives from a control unit, valves, pressure chamber and a regulating valve is derived. Using the model as reference, a controller is designed and implemented to control the valves, and thereby the pressure.
Based on experience from employees at Scania and former research on on/off control of an Exhaust Gas Recirculation system, a regular PID-controller is used as the base in the control. A pulsing scheme where the valves are activated separately is used to distribute the control signal to the two valves. Different ways of applying the control signal are investigated, whether the valves run digital, i.e. 0 % or 100 %, or continuously by varying the PWM signal.
A boosting action using non-linear control, and prediction are investigated in order to improve the control performance in such way that the required time response and robustness is obtained. The controller is eventually tested and verified on the real system.
Source: KTH
Author: Steinsland, Vidar