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 continuous-ly changing its output speed from zero to maximum, and in the hydraulic governor system with electro-hydraulic ser-vo displacement control mechanism,the intrinsic dead zone characteristic of the solenoid valve of variable displace-ment pump has great effect on the delay in vehicle starting. Aiming at the great inertia of heavy truck and the low ef-ficiency of hydraulic governor system in heavy load and low speed conditions, a new control strategy for vehicle start-ing 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.%介绍了液压机械式无级变速器( HMCVT)的工作原理，通过分析开环控制台架试验数据可知，它具备从零速到最高输出转速全程无级变速的能力；而在采用电液伺服排量控制机构的液压调速系统中，变量泵比例电磁阀固有的死区特性对车辆的起步延迟具有严重影响。针对载货汽车的大惯量特性和重载低速工况下液压调速系统的低效率问题，提出了与制动踏板位置相关的起步过程控制策略和相应的电磁阀死区处理方法，并设计开发了增量式PID闭环控制系统。实车试验结果表明：车辆起步平稳、无延时，说明控制策略设计合理，可满足带HMCVT的载货汽车起步控制的要求。
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