Investigation of and Compensation for Time-Delays in Driveline Control Systems

Abstract: Time-delays occur in all real-time control systems. The driveline control system considered in this thesis is such a system. It is of interest to know if it is possible to move the cruise control from the engine management system to another control unit that communicates with the engine using CAN (Communication Area Network). Since the amount of data sent over CAN is increasing, it is of concern how large time-delays a controller can handle and if there is any simple method to compensate for time-delays while maintaining good performance. Measurements of time-delays between the control units of the engine and the gearbox have been done in a Scania heavy truck. The results show that the time-delays are very small and that a few percent of the sent messages are overwritten due to the time-delays varying in length and the clocks drifting in relation to each other. Four different methods for compensation of time-delays have been studied and compared to a prototype cruise controller from Scania. Three of the alternative controllers are PID controllers and the fourth is a Smith predictor. All of them are more robust to time-delays than the prototype, but all except one also have the disadvantage of not eliminating the impact of a load disturbance in a reasonably short time, which the prototype does. Since the time-delays on the concerned CAN bus are very small and the prototype controller is robust to time-delays of significantly larger magnitude, the conclusion is that it is probably safe to move the cruise control to another control unit that communicates with the engine using CAN, without compensating for time-delays. If compensation for time-delays were to be required in the future, there is no obvious choice out of the compensation methods evaluated in this work. They all have drawbacks but they might be applicable after some modifications to improve their performance.