Continuous Variable Valve Timing - Applications

Applications

Automakers have been testing this technology for years, as its benefits are obvious. Several automakers have begun implementing this technology in recent years, but its widespread use is still to come. Several automakers, including BMW, Nissan, and Toyota currently offer models with some form of continuous variable valve timing. Debuted in the BMW 316ti Compact in 2001, Valvetronic was the first continuous variable valve lift mechanism made into production. The goal of Valvetronic was to reduce fuel consumption, rather than to maximize power. Valvetronic regulates engine output by varying the depth of valve lift according to the position of throttle pedal. This means the conventional throttle butterfly can be disabled which reduces pumping loss. BMW achieved 10% reduction in fuel consumption with Valvetronic. BMW’s Valvetronic adds an electric motor, an eccentric shaft and an intermediate rocker arm at each intake valve. The intake camshaft acts on the intermediate rocker arms through roller bearings. When the driver calls for more power, the electric motor turns the eccentric shaft, which pushes the intermediate rocker arms and in turn pushes the valve to open deeper.

Nissan introduced its Variable Valve Event and Lift (VVEL) in 2007 as the world's second CVVL system. The first application was on the VQ37VHR V6 engine of Skyline Coupe (Infiniti G37). Nissan's system is more compact than BMW’s, involve less parts and energy loss, and is therefore more adaptable to high-performance engines. The VVEL does not use a conventional intake camshaft. Each valve is actuated by a cam which is pivoted on - but not fixed to - the camshaft. While conventional camshafts feature fixed rotating lobes, the cam in VVEL swings up and down; this is why it does not need a symmetric profile. Its movement is driven by the camshaft via a series of components. VVEL varies valve lift by the eccentric control shaft inside the rocker arm. By rotating the eccentric control shaft, the position of rocker arm is shifted, changing the swing angle of cam. The swing angle of cam determines the degree of valve lift.

Toyota introduced its Valvematic technology in 2008. Valvematic employs an intermediate shaft to achieve continuous variable valve lift. The intermediate shaft has an actuating member for each cylinder. Each actuating member is made of two finger followers on either side of a roller bearing member. The followers can rotate in relation to the roller member by means of internal gear threads and an electric motor attached to the end of the intermediate shaft. The gear threads of the roller member and finger followers are in opposing directions. This means when the shaft swivels, the roller member and finger followers will move in opposing directions, moving either apart or closer together. In this way, the axle angle between them can be varied infinitely by the electric motor. The intake valve is actuated by camshaft via the intermediate shaft. Specifically, the camshaft acts on the roller member of intermediate shaft, transferring the movement to both finger followers, then towards the roller rocker arms and ultimately to the intake valves. When the angle of the finger followers is narrow with respect to the roller member, valve lift is low. As the angle increases, so does valve lift. In this way, Valvematic can vary valve lift by adjusting the angle of the finger followers in relation to the roller bearing member.