Research on vibration compensation mechanism of engine ellipse timing system and belt tension distribution at meshing points

Abstract

Aiming at the problem of camshaft torsional oscillation caused by the torque of the engine camshaft spring, this paper carries out the research on the compensation of the elliptical pulley timing system for the torsional oscillation of the camshaft. In the quasi-static state, a dual overhead gasoline engine drive system model is established, and the increments of the tight and slack side belt lengths, the arc length of the pulley wrap angle and the direction angle of the pulley tangent point are studied. The relationship of the harmonic increments is determined. Based on the structure of fixed and automatic tensioners, a mathematical model of the elliptical eccentricity and the initial phase angle for compensating the harmonic oscillational torque of camshaft spring is proposed. The simulation results verify the correctness of the model. It is concluded that the elliptical eccentricity and the belt tension amplitude of the fixed tensioner are 50% smaller than the automatic tensioner, which reduces the dynamic excitation of the system. The tension distribution of the tight side and the slack side of the belt meshed with the elliptical pulley is different. The amplitude of the tension difference between the tight and side sides belts corresponding to the automatic tensioner is twice as large as that of the fixed tensioner. At the same time, the difference in tension will cause different elongation of the belt pitch between the tight and the slack sides, causing the meshing interference between the belt teeth and the elliptical pulley groove. Therefore, the tension distribution of the belt meshed with an ellipse is completely different from that of a circular pulley.

Keywords

• ellipse
• cam spring torque
• belt tension
• torque compensation
• timing system