Study On Power Driveline Integrated Control Technology Of Vehicle Equipped With Hydro-mechanical Continuously Variable Transmission

By taking a heavy vehicle equipped with a hydro-mechanical continuously variabletransmission (HMT) as the object, the following contents are studied, including theefficiency model of the HMT, the optimal control strategy of the speed ratio aiming atensuring the maximum vehicle’s acceleration and an engine-HMT integrated controlstrategy based on road resistance estimation, which are of great importance for improvingthe acceleration performance as well as the capability to drving on complex roadconditions of a heavy vehicle.Firstly, the efficiency model of the HMT overcasting the entire working range isbuilt up. During the researching on the efficiency of HMT hydraulic system, by takinginto account of the influence of the working roles exchange between the variabledisplacement pump and the fixed displacement motor during the different HMT workingranges. Then by solving the problem of the negative values in the calculation formulawhen the displacement ratio is relatively small, we establishes the general efficiencymodel in which the range of working pressure is from0to40Mpa, the displacement ratio0~1and the input speed0~2500r/min. Based on the analysis of power transmission, anall-work-range HMT efficiency model is build up, which lays a foundation ofdetermining the optimal HMT speed ratio control law aiming at ensuring the maximumvehicle acceleration in any working condition.By taking the maximum vehicle acceleration as the control target and consideringthe influence of HMT efficiency and the coefficient of the revolving mass changes tolinear mass, the objective function and the constraint condition of the optimal-powertarget speed ratio are determined, then the optimization algorithm are designed andrealized and the optimal speed ratio is obtained to obtain the maximum vehicleacceleration at any condition of the throttle opening, the HMT working pressure p andthe vehicle speed u are of random values. As for the discontinuous problems of theoptimized objective speed ratio, the paper adopts multi-parameter nonlinear fitting tosolve the rotation rate fluctuation which may occur during the practical control processresulted from the problems mentioned above. Finally, the simulation result obtained from the study on vehicle acceleration performance at level road shows that, the HMT speedratio control law acquired by the paper is of obvious advantage compared to that of thetraditional power operation line on improving vehicle acceleration performance.An engine-HMT integrated control strategy based on road resistance estimation isput forward. Taking advantage of that the working pressure of HMT can be easilymeasured and used to reflect the road load, a real time road resistance estimation model isestablished for all working range regarding to a certain HMT. The validity of roadresistance estimation model is proved with the simulation. Then a power compensationmodule based on road resistance estimation is designed and realized, which can respondquickly when the road resistance changes by regulating the throttle opening initiatively tostabilize the engine rotating speed and the vehicle velocity. The simulation analysiscertifies the effectiveness of the integrated control strategy, which playes a significantrole in enhancing the adaptation to complex road conditions of heavy vehicles.