Electromagnetic Compatibility Design Of On-Board SCR Controller

In 2005 and 2008, China had already issued the relative regulations GB17691 and HJ437 for vehicle gas emission. Selective Catalytic Reduction (SCR) technology is the mainstream of controlling engine emmisions. SCR controller is the key of the whole after-treatment emission control system. It can attain the engine's working condition and spurt urea in a certain time and amount by the controlling strategy so that it could reduce the emission of pollution, at the same time, it could also supervise the condition of the after-treatment system components on real time and give alarming when malfunctioned. What's more, SCR controller should meet the EMC requirements by the "Automotive Electric Product Basic Technology".Based on the after-treatment system and the SCR controller and the requirements from automotive electronic product standard together with the basic electrical electronic knowledge and EMC theory, the paper has proposed a measurement to improve the SCR controller's EMC ability and verified it by experiment.Main tasks of the author are as follows:1. Power design of the PCB board. Based Controller features and test requirements, power module and power protection circuit for surge voltage were designed.2. Anti-interference circuit board design. Based on the influence factors and suppression measures of EMC, the controller circuit board was designed.3. EMC design of CAN bus. Design the CAN bus interface circuit, enhance its immunity and ESD performance.4. Reliability designs of the controller's mechanical and environmental performance. Combined the requirements for the high and low temperature, low humidity, mechanical shock, random vibration from the standard of electronic controller unit, the tolerance capability of the components were analyzed and optimized.Tests about EMC environmental load, electrical load, and mechanical load were made by Shanghai Research Institute of Industrial Automation Instrumentation with this design. The results show that the design can meet the basic requirements for automotive electronics.