A Study of Friction Characteristics of Continuously Variable Valve Event & Lift (VEL) System 2006-01-0222
A continuously variable valve event and lift (VEL) system, actuated by oscillating cams, can provide optimum lift and event angles matching the engine operating conditions, thereby improving fuel economy, exhaust emission performance and power output. The VEL system allows small lift and event angles even in the engine operating region where the required intake air volume is small and the influence of valvetrain friction is substantial, such as during idling. Therefore, the system can reduce friction to lower levels than conventional valvetrains, which works to improve fuel economy.
On the other hand, a distinct feature of oscillating cams is that their sliding velocity is zero at the time of peak lift, which differs from the behavior of conventional rotating cams. For that reason, it is assumed that the friction and lubrication characteristics of oscillating cams may differ from those of conventional cams. This paper describes the friction and lubrication characteristics of the variable valvetrain with oscillating cams, which were made clear on the basis of elastohydrodynamic lubrication (EHL) analyses taking into account mixed lubrication, durability tests and other experiments.