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Researches on the Key Technologies of HEV Based on CVT

Author: ZhangJun
Tutor: ZhouYunShan
School: Hunan University
Course: Mechanical Engineering
Keywords: Hybrid electric vehicle(HEV) control strategy continuousvariable transmission (CVT) ratio control variable logic threshold multi-objective optimization
CLC: U469.7
Type: PhD thesis
Year: 2012
Downloads: 352
Quote: 0
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Abstract

Hybrid electric vehicle (HEV) is an important means to achieve energy saving, is also an important direction of research and development of Chinese automobile industry. Most of HEV use automatic transmission to achieve power transfer. Using automatic transmission in HEV is an urgent researching problem. Most of HEV use continuous variable transmission (CVT) as transmission program. This paper research the key technologies of HEV based on CVT. The research achievements are shown below.1) Design the HEV based on CVT, carry out the selection of the key components of the engine and motor and battery. Design the power-train mechanical connection. Design the vehicle’s CAN-bus network system and control system hardware. Based on in-depth analysis of the foreign hybrid vehicle’s structure and control strategy, and according to the characteristics of the HEV of this project, complete the vehicle’s control strategy and software process. HEV’s base functions ware realized.2) Based on MATLAB/SIMULINK platform, the forward-facing simulation model of HEV is founded. The model can accept the accelerator pedal signals as the input parameters to analyze the vehicle’s dynamic performance, and also can accept the duty cycle as the input parameters to analyze and evaluate the control strategy. The model is the foundation for the determination of the design, and also the foundation for development and optimization of control strategy.3) Proposed CVT ratio matching program in accordance with the best economy, researched motor torque algorithm in acceleration process, HEV’s dynamic performance and fuel economy are all realized at the same time. To common vehicle, the CVT speed ratio control law is between the best economy operation line and the dynamic performance operation line. Because HEV’s motor can provide back-up power, with reasonable control of motor torque, the HEV’s dynamic performance could be ensured. So the HEV’s CVT speed ratio control law can be matched with the best economy.4) HEV completed a series of system debugging and testing. The main purpose is testing dynamic performance and fuel economy performance. Testing results show that HEV achieved the intended operation mode. Compared with the engine operation mode, the dynamic performance improved significantly, and fuel consumption saved by5.6%.5) After analyzing the reasons for the fuel economy performance did not meeting the expected target, the following recommendations of the HEV’s improving program was proposed. First, active power generation timing should be selected in the engine operating point of the fuel consumption rate more than400g/kw.h. second, torque converter can be locked in advance. Third, add one-way clutch between the engine and the motor to make pure electric functions achieve high efficiency.6) Combined with the CVT speed ratio control and according to vehicle speed and throttle opening and engine target speed,a algorithm of HEV’s driving power demand was proposed.The algorithm was used in variable logic threshold control strategy.This strategy is useful in multi-objective optimization for the plug-in HEV.The vehicle’s control is according to the power requirement to switch run-mode. The mode-switching threshold is calculated by vehicle’s parameters. The variable logic threshold is calculated according to the engine output characteristics and motor output characteristics and the battery state of charge. The vehicle’s dynamic performance can be ensured by assist of motor. By equalizing drive power, ride comfort can be realized. Fuel consumption is reduced by using electric mode as much as possible during low power requirement stage. A forward-facing simulation model of the hybrid electric vehicle was founded in the MATLAB/SIMULINK platform. The model simulated on NEDC conditions. Simulation results showed that the dynamic performance is enhanced and smoothness in mode switching is realized and fuel consumption is reduced by34%. All targets were achieved satisfactory results.

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