基于STB对DCT 4阶降挡的性能优化研究

Research on the Performance Optimization of DCT Four-Stage Downshift Based on STB

DCT的换挡是由拨叉的预挂挡控制和离合器的换挡控制两部分组成。在动力降挡过程中,预挂挡的挂挡时间较长,且对应的离合器转矩必须降为零才能开始执行挂挡过程,在某些工况下会因为等待预挂挡造成整个换挡过程的延时,进而影响整车的加速响应,这种现象在同轴动力降挡过程中表现尤其明显。为了优化某DCT车型的4阶降挡性能,提出基于STB来优化换挡时间和提升动力响应。STB是应用于DCT的一种半动力中断的换挡方式,本文对STB的整个换挡过程与正常换挡过程做了具体的对比说明,详述其优缺点。为了弥补STB换挡会有短暂动力中断的缺陷,设计了一整套控制策略。一方面开发了针对性的Kick Down逻辑,并采用与之对应的换挡规律,因此控制多阶降挡出现的时机,让4阶降挡仅在Kick Down时触发;另一方面采用开环算法将换挡过程中的发动机转速控制转化为时间控制,当预挂挡挂上并充油完毕时,发动机转速正好达到同步。经过实车上进行对比验证,STB换挡大幅缩短了4阶降挡的换挡时间,整车动力响应得到了明显优化。

The shift of DCT is composed of two parts,the pre-engagement control of the fork and the shift control of the clutch.In the process of power downshift,the engagement time of the fork is very long,and the corresponding clutch torque must be reduced to zero before the pre-engagement control can be executed.Under some working conditions,the delay of the whole gear shift process will be caused by waiting for the pre-engagement shift,affecting the acceleration response of the whole vehicle,which is especially obvious in the coaxial power downshift process.In order to optimize the four-stage downshift performance of a DCT model,the STB based shift is proposed to optimize the shift time and improve the power response of vehicles.STB is a semi power interruption shift method applied to DCT.The advantages and disadvantages of STB is elaborated in this paper by making a detailed comparison of the whole shift process with the normal shifting.In order to compensate for the temporary power interruption caused by STB shifting,a complete control strategy is designed.On the one hand,a targeted kick down logic is developed,and the corresponding shift scheduling is adopted to control the timing of multi-stage downshift,so that the fourth-stage downshift is only triggered when kick down occurs.On the other hand,an open-loop algorithm is used to convert the engine speed control into time control during the shifting process,so as to achieve the effect that the engine speed is just synchronized when the pre-engagement shift is done.After comparison and verification on actual vehicles,the STB shifting greatly shortens the shift time of the four-stage downshift,and the power response of the whole vehicle is significantly optimized.