Design Of Decoding System For Diesel Engine Based On KWP 2000 Protocol

Automobile is a complicated mechanical system.Engine is one of the most important components of automobile,and it is the power resources of automobile.Some basic technology performances of automobile maybe decided by correlative performances of engine.So getting parameters and fault information means a lot to improve the reliability and security of automobile in the condition of ensuring the intergrity of the engine.It can also decrease the expense for the blindness repair.In recent years,with the continuous development of automobile electronics industry,the electronic control unit(ECU)has been widely used in the vehicle's electronic control system.So in this case,a scheme for reading and analyzing the data of disel engine ECU is proposed,in the meantime the engine operating parameters and fault will be real-time displayed by the diagnostic software.The main content of this paper includes the theoretical research,software development and system testing.Firstly,studying the physical layer,link layer and application layer of the K-line and CAN bus which are mainstream communication protocols in the diesel bus combined with the diagnostic protocol KWP 2000.Then the data information contained in each instruction will be analyzed,and the algorithm is illustrated by examples.This step provides basic data foundation for the design of decoding software.Secondly,the hardware design scheme of decoding terminal for fault diagnostic protocols of ISO 14230 and SAE J1939 of diesel vehicle is presented which include power supply unit,protocol communication unit,serial port conversion unit and wireless communication unit.The protocol communication unit mainly includes K line communication circuit and CAN bus circuit which are responsible for the level conversion with the controller.The wireless communication unit SIM808 sends the received message to the designated cellphone for early warning.The power supply unit provides power to modules which contains 12 V to 5V circuit and 5V to 3.3V circuit.Thirdly,considering the framework of the overwall system,the warning mode program is designed which can realise the function that sending messages to the user's cellphone by the way of AT command which of effective bytes from instructions that sended from the ECU when the vehicles break down.Next,to expand the data processing algorithms which performing operations in the backstage that under the interface which has been completed,different types of engine ECU's diagnostic protocols are loaded into the diagnostic backstage,and the data can be real-time displayed through serial port.Finally,the system is divided into several parts for function test.The ECU which made by the company of BOSCH is used to the simulated test for the decoding terminal as well as the functional test of the wireless communication module,namely SIM808.Then,to verify the algorithm through the software whose name is ECU Simulator by the means of inputting the same value.If there is no obvious difference between the interface of the software and the diagnostic equipment,that is to say,the algorithm is of no mistake.At last,the experiment on the actual diesel engined car is carried out to ensure the feasibility of the system by the way of testing the vehicle which has a known failure The experiment shows that the function of reading parameters is normal,and the diagnostic software can display the detailed fault information and driving data,meanwhile,the designated mobile phone can receive the vehicle warning information.So the system is basically completed the goal of the scheduled design.