The Impact Of The Fully Variable Valve System On The Intake Performance Of The Vehicle Engine

Gas exchange plays an important role in the work cycle of the engine, how the gas exchange finished matters the engine’s dynamic property and economic performance. So the main target of the design for the engine intake system is to improve the volumetric efficiency and reduce the pumping loss at part load. Fully variable valve system can realize the continuous variability of the maximum valve lift, valve open duration and late close angle by the different drainage angle, for the diesel, it can realize the Variable effective compression ratio and miller cycle, for the gasoline engine, it can replace the throttle to reduce the pumping loss.A new fully variable hydraulic valve system is introduced in this paper, based on the work theory, a SD2100engine is refitted into a test engine for the fully variable hydraulic valve and a test bench is set up; an engine compute model is established based on AVL-Boost. By the means of the test and simulation compute, this paper study the impact of the fully variable valve system on the intake performance of the vehicle engine, namely to realize the Miller cycle and reduce the pumping loss of the gasoline engine. The main content of this paper include the flowing.Firstly, refit the SD2100engine based on the work theory of the fully variable hydraulic valve system, set up motored engine test bench for the fully variable hydraulic valve system, refit the injector to set up the pressure sensor. Do the motored test to measure the cylinder pressure under the different valve curve. By comparing the different pressure results, it shows that with the latter of the drainage angle, the pressure of the cylinder is higher, that is due to the latter the drainage angel is, the larger the valve lift and late closing angel are, and the more the air get into the cylinder is, causing the enlargement of pressure at the top dead center in the cylinder. The test shows that fully variable hydraulic valve system can work well, and can realize the effective control of the valve curve. For the diesel, it can realize variable effective compression ratio, miller cycle and low-temperature combustion, to improve the emissions performance, economical performance and ride comfort.Secondly, use the parameters of the original engine to build the engine intake one-dimensional flow calculation model, Simplify the fully variable hydraulic valve system, build the valve movement curve calculation model, and then get the numerical solution of the first order differential equations, that is the test engine’s valve movement curve. Use this valve curve and the Boost model to calculate the intake pressure and pumping loss. Control the speed and the volumetric efficiency, to compare the intake pressure and cylinder pressure of the throttle control and fully variable valve system, and then use the P-V map based on the cylinder pressure to calculate the pumping loss. The results of the simulation calculation shows that in the same speed and same air inflow, the pressure of the fully variable valve system is much higher than the throttle control, pumping loss is reduced, especially under the part load when the throttle open is little. It shows that fully variable hydraulic valve can replace the throttle to control engine load, it can enhance intake pressure and reduce pumping loss, especially under the part load, can improve the economic performance of the engine.