Diesel Engine Valve Train And Timing Drive Dynamics Characteristics Of Study

Valve train is one part of the engine, which is very important. A good valve train should have characteristics with full intake, completed exhaust process, small pump gas losses, precise valve timing, working smoothly, small vibration and noise and so on, therefore, the design of valve train's parts affect power and reliability of the engine at large. With the engine developing to the direction of low-emission, low fuel consumption, high speed, the increasingly high demand has required to the valve train of modern vehicles.In this paper, the valve train and timing driven system of a four-cylinder diesel engine equipped with turbocharger and mid-cooler were studied. With the application of software AVL EXCITE TD, the kinematics and dynamics models of the valve train were established. Through simulation, the valve timing and cam shape line were optimized. At the same time, aiming the phenomenon that the idler gear tooth of timing driven system were broken in actual operation, the timing-driven system was simulated to find the reasons of the broken idler gear tooth and put forward initial optimization method by using the software AVL EXCITE TD.The results of investigation showed that:(1) The kinematics lift, velocity and acceleration curves of intake and exhaust valve were smooth and continuous, the smallest spring margin and lubrication characteristics met what the kinematics required, the kinematics characteristics was good; the contacting stress of intake and exhaust cam with tappet was between the kinetics of the material, and the phenomenon of flying off did not exists; the valve spring worked naturally, there was no phenomenon that springs were merged; but there was great impact in the acceleration when the intake valve opened and closed and the exhaust valve closed, and this resulted in the impact and rebound when it was seated. That needs to be optimized. (2) Through optimizing the valve timing and cam profile, the impact and anti-jumping problems of original engine was improved. By comparing with the original engine's performance, we learned that when the velocity of engine is at 3400r/min, the torque and power were increased by 2%, fuel consumption decrease by 2.5%, but the exhaust gas temperature was just increase lightly; when the engine speed is at 3600r/min, it increased by 6℃, and the increasing range was 1.8%. therefore, optimizing increased engine's power and economy to a certain extent.(3) The contact force of the driver side, backlash of the idler gear and the torque fluctuation were larger. At the same time, through the gear strength calculation and found that idler gear bending fatigue factor of safety was less than the minimum, which could easily lead to fatigue damage th the gear.