Gear preselector characteristics and control strategy of dual clutch transmission

Gear preselector is a key component for gear shifting of dual clutch transmission (DCT) and a premise for clutch interaction. To realize quick and comfortable shifting, the control of gear preselector must be immediate and steady. As the odd and even gear of DCT belong to different clutches, this paper firstly analyzed the principle and power transmission line of gear preselector and then formulated gear preselection strategy that could take full use of its structural advantage. Through pressure control of target gear under special operating condition, the speed regulation of gear shaft in to-be-connected gear ring was realized, and thus the speed difference between master and slave part of synchronizer was reduced as much as possible, and smaller degree of sliding friction and shorter synchronization time during synchronizing process could be achieved. Subsequently, from the perspective of kinematics and dynamics and based on the mechanical structure of gear preselector, the neutral gear self-lock resistance, frictional force, synchronizing force of joint sleeve, resistance force of joint ring gear, and shifting fork self-lock force were investigated. Through calculating the resistance forces related with fork position during different stages, the relation between synchronizing force and synchronization time could be revealed, and the resistance model of preselection process could be established. After that, by selecting degree of shock and slipping friction work as 2 evaluation indices for gear preselector, the relationships between degree of shock and shifting force during synchronizing process and during joint sleeve-joint gear ring engagement process were analyzed, as well as the relationship between slipping friction work and shifting force during synchronizing process. On the basis of guaranteeing the smoothness of preselection process and under the premise that the synchronizing ring would not be worn, allowable values of degree of shock and extreme sliding power were set. Based on these 2 extreme values and combined with gear shifting resistance, shifting forces during various stages of preselection process were determined. Then, the preselection process was divided into different stages according to preselection theory and characteristics. The time length of each stage of preselection process was determined using empirical data based on the relation between synchronizing force and synchronization time. The target position of shifting fork at any time during engaging and disengaging gear process was set using structural parameters of shifting fork and synchronizer. On this basis, the closed-loop fuzzy control strategy for fork position was proposed. That was, the target position of shifting fork was firstly determined according to preselection process time-series, and then target position and actual position of shifting fork were compared to obtain the position difference and position difference change rate, which would be used as inputs of fuzzy controller. Shift force adjustment was generated through fuzzy rule, which was then combined with shifting resistance force at actual position. The combination force was be used as output of target shifting force, which was applied on shifting fork and to realize preselection process. In this process, the fuzzy controller adopted a triangle uniform distribution function as membership function, Mamdani algorithm was adopted as inferential principle, and centroid method was employed against blurring. Finally, gear preselection test was conducted on a smooth road surface based on a certain test vehicle with 6DCT, wherein the process of engaging a gear when vehicle decreased from second gear to first gear was selected as gear engagement condition, while the process of disengaging a gear after vehicle increased from first gear into second gear was selected as out-of-gear condition. In this test, the comparative analyses were conducted between target displacement and actual displacement of shifting fork, between shifting force and resistance force, between gear ring rotation speed and joint sleeve rotation speed, and between actual degree of shock and allowed value of degree of shock. The analyses results showed that the resistance model of gear preselector could well simulate the resistance characteristics during preselection process of DCT, the proposed preselection control strategy (including coordination control strategy for reducing master-slave rotation speed difference and tracking control strategy for shifting fork target position) could realize accurate tracking of target position of shifting fork with the maximum tracking error no more than 4.67%, and the preselection process was quick and smooth, which could meet the requirement of gear preselector quality. This study provides reference for the research of DCT preselection characteristics and control. © 2018, Editorial Department of the Transactions of the Chinese Society of Agricultural Engineering. All right reserved.