Research On Application Of Variable Displacement Technology To A GDI Engine

Along with the development of automobile number and increasingly severe energycrisis in China, both problems require the automotive manufacturer to reduce fuel economyand improve emissions. When vehicle engine is working at high load, we know that theengine fuel economy is better. As the increasingly mass urban traffic, our cars work atpartial load in long time. So it is very difficult to output its maximum power. At the sametime, when the car is cruising in low speed, fuel economy is not ideal too. We can changeengine’s displacement through variable displacement technology, raising the load rate ofsingle cylinder, so that it will be more fuel-efficient. But when the engine’s displacementinstantaneous switch, torque will fluctuate, affecting drivers’ driving comfort. According toabove problems, this paper has studied the following two aspects.First aspect is to establish the steady-state model of GDI engine through the GT-powersoftware. In the range of1200-4000r/min, this paper makes a preliminary analysis on thecalculation of range, and compared the two types of variable displacement influence on fueleconomy and optimized cylinder deactivation area. Conclusions are as follows:1. Cylinder heat transfer loss, exhaust gas heat loss and pumping loss are reducedthrough the waste gas return variable displacement engine in the same condition. At thesame time, as stopping cylinder number increase, the fuel consumption is decrease. As theload decrease, the improvement degree of fuel economy increase.2. For the variable displacement engine by stopping valve, the effect of deactivationcylinder position on the improvement of fuel economy is not obvious in the same outputtorque. In order to guarantee the stability of the engine after stopping cylinder, we choosethe middle2and3cylinders to make sure the ignition order maintain uniform and eliminatethe differences between cylinders. For stopping one cylinder, we choose3cylinders.3. In order to ensure the torque of the variable displacement engine by stopping valve,the best inlet timing of different working cylinder is studied when the throttle is fullyopening. In cylinder deactivation area, compared with the waste gas return flow mode, theeffect of stopping valve type of variable displacement method is obvious well in low speed,and the improvement effect is weak in high speed.Another important aspect is to establish transient-state model of GDI engine through the GT-power software and Matlab/Simulink software. At40%load and2000r/min speed,the effect of different control strategies on engine torque fluctuations is studied whendisplacement is switching. Conclusions are as follows:1. When the displacement is decreasing, studies show that improve throttle increasingrate, adjust the increasing time and characteristic of throttle, increase the mixtureconcentration and adjust it’s time, properly adjust the three-cylinders working time, canreduce the torque fluctuation of engine; When the displacement is increasing, studies showthat accelerated throttle reducing rate, adjust the throttle reducing time and characteristic ofthrottle, properly increase excess air coefficient and adjust it’s time, extend thethree-cylinders working time, can reduce the torque fluctuation of engine too.2. Some control modules are established in this article through Simulink, such asfurther establish cylinder deactivation area, set up decision module of torque stability,further optimize the decision module of cylinder numbers, According to instantaneousworking condition, engine automatically adjust stopping cylinder number through thecontrol modules, and the effect of the preliminary study is able to meet the expectedrequirements.