Estimation of Torques Transmitted by Twin-Clutch of Dry Dual-Clutch Transmission During Vehicle's Launching Process

The key to the launching control of a dual-clutch transmission (DCT) lies in the coordination control of the engine and dual clutches, along with the accurate closed-loop control of the torque transmitted by each clutch and the output torque of the engine. The implementation feasibility and precision of the clutch torque closed-loop control are completely dependent on the effective real-time estimation of the clutch torque, which cannot be directly measured. Therefore, the high-order sliding-mode observer and unknown input observer are used to estimate the transmitted torque of the twin clutches on the basis of the self-designed control strategy and estimation of the vehicle drag torque. First, for the launching clutch slipping phase, an improved engine constant speed control is proposed based on the dynamic equations of a dry DCT with dual intermediate shafts, and the minimum value principle is applied to achieve the optimum launching control of the clutches. Meanwhile, the separating conditions of the separated clutch and the torque distribution are determined to ensure approximate friction work and avoid power cycle, and the target curve of the clutch-transmitted torque is obtained according to different conditions. Then, the vehicle drag torque is estimated using the recursive least-square method with a double forgetting factor, the angular acceleration of the engine and output shaft is refactored utilizing a high-order sliding-mode observer algorithm, and the transmitted torque of the twin clutches are estimated using the unknown input observer. Then, the DCT launching process is simulated under different driving conditions on the MATLAB/Simulink software platform. Finally, the bench test is conducted to verify the effectiveness of the self-designed clutch torque estimation method. The simulation and hardware-in-the-loop (HIL) test results show that the proposed methods of high-order sliding-mode observer and unknown input observer can effectively estimate the clutch-transmitted torque and lay a solid foundation for the subsequent development of the launching control strategy for a real vehicle with a DCT.

I. Introduction

The coordination control between engine and two clutches is critical to the launching control of a dual-clutch transmission (DCT). In view of the particularity of DCT structure, two launching modes can be selected based on the launching conditions and driving intention, namely, launching with a single clutch (similar to an automated mechanical transmission (AMT)) and launching with the simultaneous involvement of the twin clutches.