Abstract: Hybrid electric vehicles can achieve good fuel economy through modes switching. However, the speed difference between the high-efficiency working range of the engine and the drive motor will reduce the coupling drive efficiency, and the transient impact of the engine startup will also destroy the longitudinal ride comfort of the vehicle. To solve the above problems, an innovative design of a speed-increasing clutch that allows the efficient working area of the engine and drive motor to overlap is developed, and the application research of engine startup smoothness control is carried out. At first, the three-dimensional solid structure of the speed-increasing clutch is designed, and the functional characteristics are introduced. Next, the gear transmission mechanism model,actuator drive motor model and braking system model of the speed-increasing clutch are established. Then, a dual closed loop controller of the actuator were designed based on the sliding mode control and the single neuron force control. After that, the genetic algorithm was used to optimize the force curve to determine the optimal joint speed and final bonding force. Finally, the principle prototype of the speed-increasing clutch was developed and the rapid prototype test was carried out to verify the proposed engine smooth start control method. The research results show that the designed speed-increasing clutch can not only improve the coupling efficiency of the engine and the drive motor, but also can effectively reduce the impact, frictional power and torque overshoot based on the engine startup control, and greatly improves the longitudinal ride comfort of the vehicle when the engine is started

Key words: hybrid electric vehicle, speed-increasing clutch, innovation design, engine startup, longitudinal ride comfort