Design and Experiment on High Precision Diaphragm Metering Pump for SCR System

Aiming at the problem of low measuring accuracy of the reciprocating pump due to unstable movement and untimely closure of the distribution one-way valve, a high precision diaphragm metering pump (DMP) with pump control metering, which is used for light commercial vehicle, was designed and developed. The DMP realized the integration of urea solution transportation and metering, simplified the structure of SCR system and reduced the cost. The structure and working principle of the DMP were introduced. The DMP was driven by a stepping motor. By setting the speed n of the stepper motor, the flow rate q can be adjusted accurately. Dynamic simulation of the DMP was carried out by using AMESim, and the response characteristics of the inlet one-way valve core were analyzed. The structure of the inlet one-way valve was optimized. Under the premise of meeting the minimum opening of the valve port, the maximum opening xmax of the valve core was limited by mechanical limit, which reduced the closing time of the valve core and the influence of urea solution reflux on the flow rate. Finally, the test system was built to test the performance of the DMP. When the rated injection pressure was 2 MPa, the single displacement of the DMP was measured to be 0.09 mL. The measuring accuracy of 4~6 DMP without structural optimization were reduced as the speed increase. The measuring accuracy were within ±5%. However, the measuring accuracy of 1~3 DMP were within the range of ±3% after structural optimization. At 150~420 r/min, the flow rate of urea solution can be adjusted in the range of 13.5~40 mL/min, and the maximum flow rate was 2.26 L/h, which can meet the requirement for urea solution of the light commercial vehicle SCR system under different working conditions. © 2018, Chinese Society of Agricultural Machinery. All right reserved.