Development Of Control Strategy For Fast Idling Condition Of Vehicle Diesel Engine Based On Target Torque

Increasingly strict emission regulations increase the proportion of cold start cycle test.However,when the diesel engine is idling and warming up,the cooling water temperature rises slowly,and the cumulative fuel injection and cumulative air pollutant emissions are more.Therefore,how to warm up quickly while reducing fuel consumption has become a research hotspot.Therefore,the concept of fast idling is put forward in this paper,that is,the fast warm-up process that the engine speed increases from the starting speed(230r / min)to a set speed and then decreases to the idle speed(800r / min)is called fast idling process.In order to make the results representative,the cooling water temperature was chosen as normal temperature(300K),the refrigerator(253k),and the maximum speed of fast idle was chosen as1200 r / min,1350 r / min,1500 r / min.In order to develop the fuel injection control strategy,the idle warm-up and fast idle warm-up experiments were carried out.Based on the 2.8tc prototype,this research independently developed the control strategy of high-pressure common rail diesel engine under fast idle condition,and further improved the ECU control system function.The main research contents and results are as follows:1)GT power and GT cool models are built according to the prototype.The GT power model is validated according to the output effective torque of different speed and pedal opening of the prototype.After the GT power model meets the requirements,the GT power and GT cool models are coupled.Verification of the coupled GT model based on the change of cooling water outlet temperature during idle warm-up of the prototype.2)In this paper,the concept of target indicated torque is put forward,and the target indicated torque is regarded as the "link" of each cycle fuel injection quantity.According to the characteristics and influencing factors of diesel engine working process,the composition of target torque under different working conditions isanalyzed.The target indicated torque is equal to the sum of the drag torque and the inertia resistance torque in the rising stage of the fast idle,and the compensation torque needs to be added when the engine is cold.The target indicated torque in the fast idle descent phase is equal to the drag torque minus the inertia drag torque.The composition of the target indicated torque of the starting condition is the same as that of the fast idle rising stage.The target indicated torque under idle condition is equal to the sum of driving torque and PI controller regulation.The target indication torque control strategy of starting,idling and fast idling is built in Simulink.The state flow simulation tool is used to realize the switch between torque control strategies with different target indication when the engine is warm up.The conversion coefficient between target indicated torque and fuel injection quantity is deduced,and its value is inversely proportional to indicated thermal efficiency.The control strategy of conversion coefficient is built in Simulink.Finally,integrating the control strategies such as target indication torque,different target indication switching,torque fuel conversion coefficient and so on,the injection control strategies of idling after starting and fast idling are built in Simulink.The GT integrated model is coupled with the fuel injection control strategy of idling warm-up in Simulink,and a joint simulation platform of idling warm-up is established.In the same way,a joint simulation platform for fast idle warm-up can be established.3)Using the joint simulation platform,the warm-up process is studied.The comparison of the experimental results between the start-up condition and the fast idling condition indicates that the fast idling period is short(no more than 4S),and the influence on the cooling water temperature of the whole warm-up process can be ignored;At the same time of the fast idle rising stage and the starting condition,the fuel injection quantity in the fast idle rising stage is a little larger,which will be conducive to the smooth starting of the engine when the engine is cold.The comparison of idle and fast idle warm-up test results shows that: when the engine is cold,the fast idle condition with the highest speed of 1350 r / min saves the most fuel,about 4.5% fuel and 32.5% time.At the same time,the average indicated thermal efficiency of warm-up process is 1.5% higher than that of idle warm-up condition,which will help to reduce the total emission of HC and other pollutants.Warm-upunder the fast idle condition at normal temperature does not save fuel,but saves time,When the maximum speed of fast idle is 1350 r / min,the fuel consumption increases at least,about 2.7%.The results of warm-up experiments show that the smaller the acceleration is,the more time-saving and fuel-efficient the warm-up is;the greater the acceleration is,the better the fuel economy is.The larger the acceleration is in the fast idling decreasing stage,the longer the idling condition takes up when the engine is warmed up,otherwise,the longer the fast idling condition takes up,so it is inferred that: when the engine is cold,use the fast idling condition to warm up,and use the idling condition to warm up at normal temperature.In conclusion,it can be seen from the experimental results that when the engine is cold,the engine shall be warmed up under the fast idle condition with the highest speed of 1350 r / min;when the engine is warm up under normal temperature,the engine shall be warmed up under the idle condition.