Performance Analysis And Improvement On The Valve-train Of A Small High-speed And Gasoline Engine

It is an effective measure to improve the engine power performance and economic performance to improve the valve train.At present,with the domestic small high-speed gasoline engine less than 250ml using for motorcycle,universally the combustion at idle condition is poor stability,low speed torque is small;the economic speed range is relatively narrow,the overall fuel consumption level is higher;the maximum power is on the small side at high speed condition,it is poor emissions at the full range of operating conditions.In this paper,through improving the gas distribution mechanism of a motorcycle gasoline engine in an enterprise,with gas phase improvement of the inlet and exhaust cam profile was redesigned and calculated,finally realizes the dynamic performance and economic performance of the original machine were improved.The main work of this paper is as follows:(1)Using AVL_EXCITE TD software to build the original valve train model,respectively,kinematics and dynamics of valve-train of the original engine to carry on the analysis,found that the original engine has poor matching between the intake buffer and valve clearance,causing the intake valve to fluctuate,but also affecting the dynamic performance.Also found in the kinematic analysis,the original engine,there are large gaps between the intake exhaust valve and piston,thus increasing the intake and exhaust valve lift space will increase the maximum lift of the intake valve to the exhaust valve 8mm,the maximum lift increases to 7.6mm,reduce the pumping loss.The dynamic results show that the original air inlet has the phenomenon of "flying off',and the stress of the arc contact surface between the cam and the rocker arm is too large.(2)To the original engine bench test result analysis,put forward the improvement scheme of original machine with valve phase,and in order to design the cam profile corresponding to the engine performance simulation calculation of each phase corresponding with GT-Power,and analyzed the merit,determine the timing phase eventually improved.The simulation results than the original engine volumetric efficiency generally increased by about 3%,the highest increase of 5.33%;the power increase is more obvious in the low speed,maximum power than the original machine increases 1.98%;in terms of fuel economy,increase the range of fuel economy.(3)According to the improved gas distribution phase,and the maximum valve lift,re design of the cam profile,in dynamic analysis,adjustment of valve clearance is different,to determine the valve clearance is appropriate,in order to solve the problems of the original machine side valve mechanism.The improved valve-train of the kinematics and dynamics analysis,effectively solve some problems in the original valve-train,and the original machine rocker arm is improved,the original ordinary to roller rocker arm,to improve the force between the cam and the rocker arm is too big.