Develop Of ECU And Research On The Anti-jamming Of Electric Power-Assisted Steering

EPAS (Electric Power-Assisted Steering) adopts motor to provide assist torque, which is controlled by ECU (Electric Controller Unit) according to the velocity of the vehicle and the torque of the steering wheel. With the development of automobile industry and the popular using of automobile in daily life, people are not content with using a Car as a tool instead of walk, but to purse an driving experience with intelligent, safe and comfortable. At the moment, after electric technique being applied to engine, transmission and brake system successful, EPAS is going to be perfect. Almost all the famous automobile companies abroad have developed their own EPAS and have the ability to volume-produce EPAS. Only in the recent years, the research on EPAS is carried out in china, for many reasons. But it springs up like mushrooms. EHPS (Electric Hydraulic Power Steering) is going to be replaced by EPAS, which is one of future development direction of power steering.This paper focuses on the hardware design and parameters calibration of EPAS, with which the experiments carried out in the bench of EPAS and road test, the author study on the control strategy systematically, and propose a reasonable and innovational method on target current estimate, CAN calibration protocol and numeric filter for EPAS.The ECU of EPAS is adopted an 8-bit microcontroller produced by Freescale semiconductor. MC68HC908gz60 is suitable for automotive application, and it's a highly-performance, low-cost device which comes packed with valuable features - 16 channel, 10-bit analog to digital converter; 8 channel, 16-bit pulse-width modulator and a MSCAN08 (controller area network 2.0 ). Because of the low-cost and highly integrated performance, it will reduce the quantity of device on the board, and make the product cost-effective. And then, the power source circuit, power drive circuit, predrive circuit and signal modulate circuit are most adopting the device with very good EMC (electric magnetic compatible) performance suitable for automobile and industry area, which is most useful for the process of product application.The assist characteristic of EPAS is the rule that assist torque is changing with the motion of automobile (such as steering handwheel torque, vehicle velocity). Assist characteristic in theory should meet the requirement of steering maneuverability and road feel synchronous. Straight-line type, broken-line type and curve-line type assist characteristic are discussed systematically. Based on the request of the driver for the ideal relationship between steering handwheel torque with vehicle velocity, by changing straight-line type assist characteristic coefficient can make steering handwheel torque at different lateral acceleration agree with the request of the driver at a certain velocity, then the formula of assist characteristic coefficient at different velocity is determined by fit. Using the parameters of Md, Mdmax defined by assist characteristic and the coefficient at different velocity, the value map of decision-making target current is derive from the interpolation analysis in Matlab, which lays the foundation of study on control strategy.Using the embedded CCP protocol for ECU calibration in the interface to peripheral will make the process of calibrating for PID parameter simpler. And then, CCP module will transmit the variety sampling parameter to upper PC at 250kbps velocity by CAN bus, which is more faster and highly performance than the sampling process solved by serial communication interface.Proposing a novel fast filtering algorithm based on weighted median for the signal of sensor. Because amounts of electromagnetic noise of engine and impact signal of road surface exist in the original signal simultaneous, so this paper applies a suitable numeric filter technology to preserve impact signal on an 8-bit microcontroller with short filter periods. With the analysis of the sampling data from CCP module in Matlab, we can prove that the novel filter algorithm is effective than the common numeric algorithm on maintaining the impact signal of road, reducing the size of filter window and costing few operation instructions.Analyzing the experiment result based on the bench for EPAS and pilot test is carried out. Through the experiment carried on the bench of EPAS to evaluate the assist performance and simulate the impact of road surface, the result show that the assist current follow the steering handwheel torque stably and the impact signal of road is preserved efficiently.