对于搭载大功率液力自动变速器和全程调速柴油机的重型越野车辆而言，换档执行元件油压实时估计能反映车辆行驶工况的变化，有助于改善液力自动变速器换档品质。建立3自由度行星自动变速器动力学统一模型，并以1-2动力升档为例，进行升档过程瞬态动力学分析，与传统建模相比，统一模型有效提高了换档分析计算效率，并提供在档状态下变速器转动惯量计算方法。结合发动机-变矩器的动力特性匹配，实现对换档执行元件油压的实时估计，油压估计能够体现车辆工况变化，从而提高换档过程执行元件油压的调节速度，据此制定升档过程控制策略并进行实车变工况试验研究。试验结果表明，估计油压能实时准确反映换档系统动态特性，基于油压估计的换档过程控制能有效提高自动变速器换档品质，改善整车性能。

On-line estimation of oil pressure for shifting actuators can be useful for the development of close-loop control of automatic transmission fitted to heavy off-road vehicle for good shift quantity under complex working condition. The unified dynamic model for a 3 degree-of-freedom planetary automatic transmission is given, and the power-on 1st-2nd up shift is considered as an example. The unified model is more efficient than conventional model for the dynamic analysis, meanwhile, it provides a computational method for the inertia of transmission in-gear. The real-time estimation of oil pressure for shifting actuators during sliding viz. torque phase and inertia phase is addressed. The changes of vehicle operating conditions is reflected in the pressure estimation, and the regulate of pressure for shifting actuators is improved. Then the up shift controlling scheme is developed and validated via a heavy off-road vehicle test bench. Experimental results show that the model-based oil pressure estimation is able to reflect the system dynamic characteristics in the changing condition, and the according control strategy can improve the shift quality and the vehicular performance effectively.