A research on the starting characteristics and its control strategy for a heavy truck with HMCVT

The working principle of hydro-mechanical continuously variable transmission (HMCVT) is presented. Analyses on the data of open-loop-control bench test reveal that HMCVT has the capability of continuously changing its output speed from zero to maximum, and in the hydraulic governor system with electro-hydraulic servo displacement control mechanism, the intrinsic dead zone characteristic of the solenoid valve of variable displacement pump has great effect on the delay in vehicle starting. Aiming at the great inertia of heavy truck and the low efficiency of hydraulic governor system in heavy load and low speed conditions, a new control strategy for vehicle starting process related to the position of brake pedal and corresponding scheme of eliminating dead zone effect are put forward with an incremental PID closed-loop control system developed. The results of real vehicle test show that with the strategy proposed, the vehicle starts smoothly without delay, indicating the rationality of control strategy, being able to meet the requirements of start control of heavy truck with HMCVT.