R&D For Vehicle Control Unit Of Electric Vehicle Based On MC9S12XE

With the dual advantages of environmental protection and energy saving, pure electric car is an important direction for automotive development. Powertrain control technology is one of the three electric vehicles’key technologies, and its core is vehicle control unit. Supported by Shandong province scientific and technological program "Study on pure electric vehicle powertrain matching technology ", combined with the project needs, this paper focuses on the pure electric vehicle powertrain and vehicle control unit.As the maincenter of electric vehicle powertrain control system, vehicle control unit was developed based on a dual-core MC9S12XE according to the technology needs. The hardware including the minimum system, signal acquisition and processing, power drive unit, bus driver and other modules was designed to meet performance indexes, following the principle of versatility and low-cost. The software designed with hierarchical modular architecture was carried out and flow chart was shown. The vehicle control unit’s functions ware defined, including CAN network management, vehicle driving control, energy regeneration control, high-voltage safety management, energy management and diagnosis service. And then the control strategy was developed and test validated.According to the pedal, gear and vehicle state, control modes and its switching conditions were made, including start, normal drive, failure, and regenerative braking mode. The drive control strategy formulated with pedal and motor speed was studied to meet the driving needs. Without changing the conventional braking system and affecting operation safety and driving feel, sliding mode for maximum energy recovery energy and braking mode with TS fuzzy regeneration were developed according to vehicle speed, pedal, battery and motor status. Following the basic principles of communication protocols development, CAN communication protocol was adopted based on SAE J1939between the vehicle controller and other powertrain components, achieving network status monitoring, node management and information sharing. The vehicle controller integrated with GPS and GPRS data transfer functions and remote monitoring of vehicle performance was realized; the KWP2000fault diagnosis with K-line was developed for vehicle diagnosis and control parameters calibration. The high-voltage safety management module for insulation monitoring and collision signal extraction was studied, and the response of high-voltage contactors disconnect was tested to ensure vehicle operation and personal safety. Not only the motor-driven strategy was considered, the management of air conditioning, cooling water pump and other accessories was studied to extend vehicle driving range.Following the test standards, the refitted car was used to verify the control strategy of the vehicle control unit, and the test results of acceleration performance, maximum speed and driving range meet the vehicle performance requirements. Also, strategy for energy regeneration and vehicle control mode switching ware tested. The vehicle speed, range, energy consumption and other parameters of two representative sections ware analyzed and the result showed that the control modes switched smoothly, vehicles energy consumption reduced by12.7%to22.1%, and control strategies meet the development requirements.