Design and Development of a Switching Roller Finger Follower for Discrete Variable Valve Lift in Gasoline Engine Applications

Global environmental and economic concerns regarding increasing fuel consumption and greenhouse gas emission are driving changes to legislative regulations and consumer demand. As regulations become more stringent, advanced engine technologies must be developed and implemented to realize desired benefits. Discrete variable valve lift technology is a targeted means to achieve improved fuel economy in gasoline engines. By limiting intake air flow with an engine valve, as opposed to standard throttling, road-load pumping losses are reduced resulting in improved fuel economy. This paper focuses on the design and development of a switching roller finger follower system which enables two mode discrete variable valve lift on end pivot roller finger follower valvetrains. The system configuration presented includes a four-cylinder passenger car engine with an electro-hydraulic oil control valve, dual feed hydraulic lash adjuster, and switching roller finger follower. Mode switching (i.e., from low to high lift or vice versa) is accomplished within one camshaft revolution resulting in transparency to the driver. The switching roller finger follower was designed to prevent significant changes to the overhead. Load carrying surfaces at the camshaft interface were optimized including a roller bearing for low lift operation, and a diamond like carbon coated slider pad for high lift operation. Optimization focused on minimizing mass and moment of inertia while increasing stiffness to achieve desired dynamic performance in low and high lift modes. Validation test results reveal that the system meets dynamic and durability requirements.