Simulation and Optimization of Wet Double Clutch Transmission (DCT)

Abstract

This work focused on the longitudinal 7-speed wet DCT that is used by some high performance sport cars due to its capability to handle high rpm and torque output engine. This capability is coming from the use of wet friction clutch which able to dissipate more heat generated by high torque engine in slipping clutch during engagement process. One of inefficiency comes from the use of clutch fluid which tends to stick the clutch pairs, causing the drag torque when the fluid sheared by the clutch pair that rotates with different speed after the gear preselects action. The other drawback is occurred in the manual shift mode when the next gear that automatically preselected by the TCU before the gear shift is unmatched to the next gear as wished by the driver. The research was done to overcome the explained wet DCT drawback by improving the gear preselect action strategy so-called the seamless gear preselect strategy. This new strategy is achieved by improving the software of control algorithm rather than the DCT hardware for cost efficiency through software in the loop (SiL) method. This new strategy was achieved by simultaneously activate the gear preselect action during the fast filling phase of the ongoing clutch hydraulic system. The new gear preselect strategy make the reduction of unnecessary drag torque that normally occurs in wet DCT after gear preselect action in steady condition. The state of the art focusing on the subject of DCT construction, empiric system modeling, objectification and optimization method that were presented using a simulation environment to prepare the virtual gear shift optimization. After the model is fully confirmed, the optimization of wet DCT gear shift using genetic algorithm method was explained to meet the optimization objectives including the shift qualities, the uninterrupted torque during gear shifting and the limited heat generated as losses energy. The new gear preselect strategy is superior particularly for manual gear shift mode. The proposed strategy was carefully prepared in regards to the capability of the particular wet DCT construction particularly the hydraulic valve and gear shift actuator structure, while this optimization was done on the software basis alone without any further modification on the hardware. The optimization result confirmed the new gear preselect strategy is possible to be adapted in the particular seven speed wet DCT.