Abstract: In order to improve the power performance of heavy trucks,a new hydraulic assistance drive system ( HADS) is developed for the traditional heavy trucks,which can make the trucks on the roads of low adhesion coefficients reconfigure the traditional rear-wheel drive into the all-wheel drive.Then,a feedforward + feedback controller for a pump displacement controller in the developed system is designed to improve the transmission efficiency of the trucks.By the feedforward controller,the reference pump displacement is determined according to gears,and by the feedback controller,the final value of pump displacement is dynamically corrected according to the velocity tracking error between front wheels and rear wheels.Co-simulation results on the Matlab /Simulink and AMESim platforms show that,after employing HADS on the typical roads of low adhesion coefficients,the maximum climbing grade and traction of the trucks can be improved respectively by 14.4% 17.2% and 13.4% 15.6%.The real vehicle test results show that HADS works efficiently and smoothly,and the simulation model is accurate.

Key words: hydraulic assistance drive system, feedforward, feedback, heavy truck, transmission efficiency, simulation modeling