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The paper mainly studied dosing pump unit and electronic control unit of exhaust after-treatment dosing system. It is based on SCR (selective catalytic reduction) technology. The ammonia combines with NO x to form harmless byproducts. New type metering pump based on stepper motor is adopted as AdBlue dosing equipment. The eccentric wheel drives plunger rod of pump. TMS320F28016 processor is the core chip in embedded control board developed. Suction speed is invariable and the fastest. Discharge speed could be dynamically changed as need. Requested dosing rate commands from the engine control unit are transmitted via CAN BUS, they can be responded within 2 milliseconds. Dosing rate of system can satisfy well requirement from 100 ml/h to 6000 ml/h. The precision of dosing rate can reach 1ml/h by setting PWM timer values. The dosing system developed can comply with State IV exhaust gas limits. This is an easy to control, very compact and inexpensive system. It is particularly suitable for retrofitting to trucks.

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