Studies On EGR Closed-loop Control Strategy With CAN Communication

With the increase in the amount of vehicles, more and more attention is paid to vehicleexhaust emissions,which threat human health and damage to the environment,All countrieshave enacted emissions regulations to limit car emissions. Vehicle during operation has beenin the constant acceleration and deceleration work conditions, with the superchargertechnology on heavy-duty diesel engines to meet Euro Ⅲ Emission Regulation, intake lagsbehind the shortcomings inherent in the turbocharger makes equipped with EGR system ofdiesel engine during transient operation conditions,the emission levels are different withsteady-state conditions. Therefore, the studies on the performance of EGR system intransient operating conditions have far-reaching significance.A lot of research work has been done on EGR system performance in transientconditions. In transient conditions, due to the inherent lag characteristics of theturbocharger,in step transient conditions, EGR response is not fast enough,EGR duringtransient conditions exist the EGR rate higher than the steady EGR rate, the overshoot of theEGR, but also further lead to the deterioration of combustion, making the sharp increase ofsoot emissions.In this study, we use the EGR valve of the DC motor, Freescale control unit, theUSB-to-CAN and LabVIEW structures the EGR closed-loop control system. The EGRsystem combines CA4DC bench reasonable arrangement to develop the best strategy ofEGR system in transient conditions, through the analysis to prototype CA4DC performancein the transient conditions, we found that:（1）The CA4DC diesel equipped with EGR system in the step change operations haspoor transient response. With the electronically controlled EGR system, we study theimprovement of the peak impact meathod at step conditions. The test results show that thetest conditions consuming1s transition from B10to B25, the original engine EGR rate,consuming approximately3.7s before the transition to steady state. With the peak impactmethod of EGR control strategy, when the peak duration is1s, EGR rate from the transitionto the steady state time down to2.5s,Therefore, we can see the peak impact method caneffectively improve the transient response of the EGR step conditions.（2）During EGR transient conditions, the test proved the original engine in the time-consuming5s,8s,10s transition from B10to B90operating conditions, the EGR rateis overshoot than the steady conditions, and with the transient rate of increase in ultra-Thetune is increasingly evident. And the5s transient operating compared to steady-stateconditions, the EGR rate increase of62.5%. Overshoot of the EGR rate, making the EGRexhaust gas back to the flow increases, which leads to burning deterioration, apparent sootdeterioration, and smoke peak at the transient rate of5s is9.4%, compared to steady-statethe smoke peak increase of135%, serious deterioration of the smoke.(3) We discuss the5s,8s,10s transient conditions, smoke and NOx trends with theEGR valve opening degree at0,10%,20%.....100%, for the flexible control strategyprovide the basis. Determine the work strategy of EGR valve at5s,8s,10s of transientoperating conditions, the control strategy in accordance with the second interval makes thesmoke and NOx were able to achieve the ideal state. The results showed that the EGRsystem with flexible control strategy, mitigation transient operating conditions of EGR rate,the overshoot in the transient conditions can make the EGR rate closer to the steady-stateconditions corresponding to the EGR rate; deterioration of soot greatly improved. Theoriginal engine in transient conditions, the maximum peak is nearly9.4%, the flexiblecontrol strategy at EGR transient conditions will be control the peak of the smoke in lessthan5.3%. Therefore, the EGR system with flexible control strategy can ease the EGR rateovershoo, which is also can effectively control the deterioration of the smoke at EGRtransient conditions.