Research On Valve Train NVH In A Engine At Idle Speed

The valve train dominates the vibration and noise of engine, the research andoptimizes NVH performance of it is of great significance. The valve train of onedeveloping engine of Chery Automobile has obvious impact noise at hot idle speed.This paper is based on this valve train which is a finger follower type, and does aresearch work to find the reasons for vibration and noise at idle speed.The kinematic formulas of the finger follower type valve train were deduced. Theyinclude the valve lift, the contact point between rocker arm and valve, the pressure angleof roller, the load force of cam and etc. The ramp height of valve lift has been checkedfrom the point of deformation of valve train which is caused by the load of spring andacceleration force and incline of valve. The study results find two problems: The contacttrack between the rocker arm and valve is offset to the valve center. This offset wouldlead to a big side load to the valve and thus lead to noise; the ramp height of exhaustvalve was too low and would lead to big impactive seating force.As oil temperature increases the noise becomes worse, a dynamic model has beenestablished through AVL Timing Drive and the simulation of vibration of valve underdifferent oil temperature, pressure and aeration has been done. The results showed thatoil aeration has the biggest influence on vibration of the valve; the next biggestinfluence is the oil pressure. It illustrated that oil aeration increase with temperatureincreasing leads to greater noise at hot idle speed.To test and verify the results of the kinematic study and dynamic simulation, amotor test rig of a valve train has been build. The dynamic performances of valve, thevibration of cylinder head and near-field voice pressure of port have been test whenonly one intake and exhaust valve operated at different oil temperature, pressure andaeration. The test results find there was a severe closing impacting of the exhaust valve.It coincides with the results of the kinematic study which found the ramp height ofexhaust valve was too low. The test has also been done when16valves operated atsame test condition. There was an abnormal vibration at the open side of the intakevalve under high oil temperature condition. This vibration coincides with the angleacceleration increasing of intake camshaft. After finding the reasons of the noise, the ramp height of exhaust valve and oilgallery to intake cam phaser have been optimized. Three ramp heights of exhaust valvehave been tested and the height of0.18mm shows the best NVH performance.Increasing the diameter of the oil gallery, which supply oil to intake cam phaser andassembling a check valve to it, also improves the NVH performance of intake valves.The noise problem of the valve train at hot idle speed has been solved completely beforelaunching to market.This paper solved NVH problem of valve train at idle speed by combining thedynamic simulation with a test. The optimizations of same valve train type can get avaluable reference from the methods and results of this paper.