Torque observer-based control of self-energizing clutch actuator for dual clutch transmission

Abstract

Due to the environmental issues and the scarcity of energy, the needs for improving the vehicle powertrain efficiency have increased. Technical survey reveals that the anticipated fuel economy improvement ？ relative to the conventional type of automatic transmission with a torque converter ？ by the application of automated dry-type clutch actuation is substantially higher than that obtained by various other technologies in the transmission category such as increased number of gears, continuously variable transmission, and wet-type clutch usage. Hence by adopting dual clutch transmission (DCT), the fuel economy similar or higher than that of the manual transmission can be reached, as well as the convenience of automatic gear shifts and smooth shift quality for the driver. The weakness of the conventional DCT, however, is in the use of the diaphragm spring in the actuator. A diaphragm spring is installed in the dry-type clutch package to ensure satisfactory control performance of the clutch engagement force by reducing the sensitivity of the engagement force variation, and this works against the actuation efficiency by leading to greater energy consumption in the clutch actuator via having to travel through a longer displacement to reach the desired engagement force. As a resolution for this issue, the self-energizing clutch actuator (SECA) is selected as the control target for the dissertation, which replaces the diaphragm spring in conventional dry-clutch system. Here, the torque-monitoring control methodology is proposed to overcome the system’s oversensitivity. The combination of the self-energizing clutch actuator and the torque-monitoring control method can lead to both clutch actuation efficiency improvement and shift quality improvement in addition to the benefits of the conventional DCTs, and accomplishing such improvements is the utmost objective of the research dealt in this dissertation. Concerning the hardware of the system, a novel dry clutch actuator for the dual clutch transmission (DCT) using self-energizing principle is suggested. A mathematical model of the actuator and the inclusive DCT driveline is developed. The magnitude of torque amplification obtained by the self-energizing effect is studied, and it is verified via experiments by comparing the calculated and the empirical gains. Also, by analyzing the characteristics of the energy consumption in actuator motors during the vehicle launch and gear shifts, the application potential for the self-energizing clutch actuator is examined. Such work is done both through simulation and dynamometer experiments. The simulation is conducted by using the driveline and self-energizing actuator model developed by using Matlab/Simulink. The hardware-in-the-loop experiments are conducted with the driveline dynamometer that is designed and constructed exclusively for the self-energizing clutch actuator and DCT to experimentally demonstrate the suitability of the suggested actuator for DCT. Then in order to implement a torque observer-based control strategy, the torque observer specialized for the driveline with dual clutch transmission is developed. This involves the unprecedented task of accurately estimating the torque transmitted through each clutch of the dual clutch transmission. Such goal is attained by only using the measurements and data that are already available in current production vehicles. The suggested estimator requires the speed measurements of engine, input shafts, and wheels, and nominal engine torque information obtained as a function of driver input and engine speed. By synthesizing the estimations obtained by shaft model-based observer, unknown input observers, and adaptive output torque observer, the novel algorithm to estimate the torque of each clutch separately is developed. Stability of the entire combined observer system is analyzed as well. In addition, an alternative form of clutch torque observer is designed by proposing a model reference PI observer to improve the accuracy of the torque estimations. The effectiveness of the individual clutch torque estimator is demonstrated both through simulations using SimDriveline, and tests on an actual vehicle equipped with a dual clutch transmission. Finally, the strategy to control the clutch engagement for the dual clutch transmission equipped with the self-energizing clutch actuator is developed using an adaptive sliding mode control scheme based on the dual clutch torque observer. The original contribution of the proposed controller is three-fold. A sliding mode tracking controller for the actuator motor position is developed by using the information provided by the torque observer designed to estimate the torque transferred through each clutch of the DCT. Then the kissing point of each clutch is identified, also based on the torque estimation result. Also the adaptive strategy to actively alter the target position command to compensate for the model uncertainty or disturbance is proposed. The estimation performance of the designed torque observer, actuator position tracking control accuracy improvement attained by using the adaptive sliding mode controller, and most crucially, the ability for the integrated controller to cope with the system disturbance, are verified in an integrated manner via simulations and actual experiments using the driveline test bench.