A Study On Driveline Control Strategy Of The Four-wheel Drive Hybrid Electric Vehicle Based On CVT

The shortage of resources and environmental pollution become serious increasingly with the rapid development of the automobile industrial .Because the key techniques of pure electrical automobile will be difficult made a breakthrough in the near future, especially the high performance battery with big capacity and long life. The hybrid electric vehicle will show its special advantages in a very long time. In order to improve the fuel economy of the light sport utility vehicle, a new four wheels drive hybrid electric vehicle equipped with continuously variable transmission (CVT) is proposed, the whole vehicle driveline control strategy and related techniques are also thoroughly analyzed and researched.Firstly, the preferences of the powertrain components are confirmed through the calculation, as well as the selection and design of the key components, and the arrangement of each component. And then the forward-facing simulation model of the hybrid electric vehicle is founded in the Matlab/simulink platform, the model can accept the power demanded and torque demanded as the input parameters, and also can translate the inputted duty cycle into the power or torque of the driver demanded. It can be used to optimize the control strategy of simulation model as well as the real vehicle control strategy development.Secondly, the running mode of the traditional hybrid electric vehicle are analyzed, and then based on the system configuration of the four wheels drive hybrid electric vehicle , the classification of running mode of the vehicle and its dynamics characteristic are researched. including the generate electricity mode in halt, the engine and motor cooperative drive mode, only motor drive mode and so on. At the same time, the control strategies of the clutch/engine and the motor during mode transfer are also proposed.According to the static efficiency maps of the engine /motor and the charge/ discharge character of the battery, the optimization power curve and the optimization torque region of the engine are got by taking account of the equal power curve and equal torque curve. As a result, the mode transition rules are obtained by means of the power demanded or the torque demanded, the vehicle speed, the state of the charge (SOC) of the battery. The clutch and the motor cooperation control strategy are also proposed in order to keep smooth mode switching. at the same time ,the optimization operating line of the engine/motor in each mode, the output torque of the two motor ,the speed ratio of CVT,and the output torque of engine are got based on the maximum efficiency principle of the whole vehicle. The simulation results show that the control strategy take account of the required torque and required power simultaneity can comprehensively and efficiently manage the flow of energy among the driveline and keep the stability of the SOC , including the engine fuel economy is significantly improved while at the same time attractive driving performance is achieved.An equivalent model for charge/recharge modes of the 4WD hybrid electric vehicle is proposed through the method of the equivalent fuel consumption. When the engine is operated within the ranges of the best fuel economy, the desired operation curve (DOC) is derived based on the definition of optimization target function for the effective specific fuel consumption. The optimization result is obtained by calculating in the Matlab/Simulink, and then the fuzzy logic control rules are obtained by the optimization results. The simulation results show that the instantaneous optimization fuzzy logic control strategy can improve the fuel economy greatly.Besides, the control strategy of the mode transition are profound analysis according to the structure of power coupling of the hybrid electric vehicle , By means of cooperation control of the engine, motors and clutches. The control strategy that enables the system to achieve the sufficient response and smoothness in drive mode transition is proposed.Finally, the hybrid control unit (HCU) based on CAN bus is developed by using the chip of TMSF2812.The power train test bench is also established and the validity of the CAN net, the strategy of running mode shift, the electrically controlled throttle system are tested. Finally, the remodeled hybrid electric vehicle is tested in real road, experiment results show that the hybrid system improved fuel economy approximately 8 percent and deduced 3 seconds of the 0-to 100km/h acceleration time compare with the vehicle on which it is based. And the smooth mode transition is also obtained.