A Calibration And Data Acquisition System Of EPS Control Unit Based On CCP Protocol

In today’s vehicles industry, EPS (Electric Power Steering system) has become the standard for passenger cars. The development priorities of latest technology have been focused in the research and development of ECU (Electronic Control Unit) in EPS. ECU calibration and data collection required in the development was mainly based on a standard PC and ECU data exchange protocol, CCP (CAN Calibration Protocol).After extensive analysis of the development status of the calibration system, a calibration and data acquisition system based on CCP Protocol of EPS which was constituted by upper-computer software and slave ECU underlying software was designed. The control parameters of EPS could be calibrated. Both analog and digital signals in EPS could be collected. And a model of CAN signal transmission was set up which was used to analyze the signal of EPS for ensuring calibration and data acquisition of the upper computer in the full vehicle CAN network.The basic framework of the calibration system was as following. The interface of the upper computer was developed by Labview which was a kind of graphical programming software. And the CAN data communication was based on the open-source USB-CAN tool. The lower layer system was the EPS control units which was developed by the MC9S12XS128. The underlying CAN calibration protocol was used to read and write the specific data in control units which was stored in the FLASH, could also be used to on-line debug and acquire the real-time data in RAM. The EPS can be suit for different steering system by calibrating the related data to achieve the required steering effect. And the data acquisition module can collect the dynamic behavior of key data in real-time which can support the next calibration, match different vehicles easily and quickly and also produce the ECU standardly.By the experiment rig test, testing simulation of multiple nodes CAN network and the real vehicle test, the paper verified the calibration system for EPS calibrating functions, the collection of data and the transmission result of data signal in the multiple nodes CAN network. In the experiment rig test, the upper-computer was used to modify the slope of the broken-line characteristic curve, and the change of data was acquired before and after the calibration to verify the calibration results. The several nodes CAN transmission model was used to simulate and analyze the differential voltage of each moment for verification that the signal of EPS in CAN multi-nodes could transmit correctly. Finally, the calibration and DAQ modules were tested in the real vehicle. The slope of the characteristic curve of EPS on the stopping vehicle and the gain of steering return in low speed was calibrated which was collected the data of steering angle and torque to verify that the calibration system could work with several CAN nodes in the vehicle. The various periods of data collection frequency of DAQ module wouldn’t overload the CAN bus, and the period of data transmission was controlled precisely.