| With the fuel consumption and emission regulations getting gradually stricter,the variable valve timing system is becoming one of the most effective technical to improve the engine performance,fuel economy and emissions.This paper is based on the Chery’s 2.0L VVT engine which the camshaft phaser is redesigned when it’s localization.According to the principle of the camshaft phaser,a formula to calculate the cam phase adjusting speed is established by the force balance equation and liquid flow balance equation.It simulate the cam phase adjusting speed in different rotation moments of inertia of camshaft phaser,oil supply pressure and the driving torque of the camshaft by GT-SUITE software.The study results find that the oil supply pressure and camshaft driving torque are the main factors that affect the phase adjusting speed.The rotation moments of inertia of phaser is the main factor that affect the system’s stability performance.There are two camshaft phaser have different main parameters are designed and made prototype samples according to the simulation results.To test and verify the results of the variable camshaft phaser’s response time,phase adjusting speed and system’s stability characteristic parameters,a motor test rig of the camshaft phaser is built.It has a linear proportional relationship of the phase adjusting speed and oil supply pressure.When the rotation moment of the inertia is greater,the system’s stability performance is better.The oil supply temperature and the bias spring rate have the greater influence on the hydraulic driving torque of camshaft phaser.The excitation source from the crankshaft is not significantly effect the driving torque of camshaft phaser.The dynamic parameters of valvetrain test on the separate dynamotor testing rig.From the test results find that the rotation moment of inertia of the camshaft phase is the main factor influencing on the valve motion characteristics.Large rotation moment of inertia will cause larger valve acceleration and jerk,but it can make the camshaft system running more smoothly.The timing belt dynamic parameters can be tested on the fired engine.The test results find that the rotation moment of inertia of the camshaft phaser,oil supply temperature and phase opening angle are the main factors influencing on the timing belt dynamic characteristics.Large rotation moment of inertia causes the larger phase angular vibration and tensioner arm vibration under the low engine speeding,at the same time it affect the reliability of the whole timing driving system.According to the dynamic characteristic results of camshaft phaser,and the matching results of camshaft phaser and valvetrain and timing belt system,the different parameters of phaser are optimized and selected.The optimized phaser completed the engine performance test and durability test,the cost of phaser decreased about 50% after localization. |
