Study On Power Train Matching Control And Simulation For Mild Hybrid Electric Vehicle

Continuously variable transmission (CVT) with reflux power has a wide speed ratio range. Based on this characteristic, a small motor was used in a mild Hybrid electric vehicle (HEV) worked as the second power source. This kind of HEV can realize idle stop/start control and recover energy during braking. It also can drived alone by electrical motor during low speed and reverse condition. This vehicle can improve the fuel economy and environment protection performance. The motor power is small, so it requests less power from battery. This makes the cost of the vehicle is lower than other hybrid electric vehicle in the marketing.The research subject of this article is hybrid electric vehicle installing continuously variable transmission with reflux power. After the parameter matching design for the power train, the overall vehicle simulation model was set up. The details of control methods in each operation condition were confirmed. The control results in each operation condition were got by computer simulation.First of all, the operation mode of mild HEV was analyzed. Then the layout of the power train was designed. Based on analyzing the characteristics of CVT and in considering of the performance target of the original vehicle, configuration parameters of the transmission were designed. The engine mathematic model was set up according to the rig test data of engine JL472Q1 in vehicle SC7101. The best fuel economy working line of the engine was confirmed base on the rig test data. This line was the target of transmission speed ratio controlment. The type choosing and parameter matching of motor and battery was carried out due to the requirement of each operation condition. The efficiency data model of the motor and battery was established. The most efficiency working line of motor was confirmed.Next step, the vehicle control strategy was brought forward based on the control focus of hybrid electric vehicle. Control methods of each part were determined base on the vehicle control strategy. The vehicle simulation model of mild HEV was developed using Matlab/Simulink The detail of each component model and control idea was described in each simulation model. This simulation model is the base for setting up detail control methods and carrying out simulating analysis of the vehicle.After that, the identifying regulations of starting process were set up. Base on the dynamic analysis of the CVT system in starting process, the starting process control methods were put forward with the control method of keeping engine speed partly constant and combining the driver's intention. In the way of controlling throttle opening and the clutch engagement oil pressure in starting process, the starting action was carried out smoothly and quickly. This control method of each start mode was designed separately, including normal start, idle stop/start and creeping start condition. The control strategy was verified by simulation.After getting the identifying regulation of each operation condition in driving process, the control methods were verified separately in each operation condition: such as low speed cruising, normal driving, braking, reversing and low SOC charging condition. The braking force distribution for mild HEV was confirmed. Also, the movement control strategy of the brake clutch in large power required condition was put forward. The operation state changing control of the CVT was designed base on the dynamic analysis.Finally, the detail dynamics and fuel economy performance of mild HEV were got via overall performance simulation. The overall control strategy was also be verified by simulated in three typical drive cycles. The advantage of mild HEV was measured quantitative through comparing the vehicle performance with common vehicle.