March 30, 2007 Over the last century of automobile development, we have seen an enormous range of valve actuation technologies, ranging from pushrod, through single then double overhead camshafts, then a range of more recent technologies to enable variable cam timing. Nissan has now announced a new method of valve actuation that delivers a balance of responsiveness and power, fuel efficiency and low emissions. The system combines Nissan’s new Variable Valve Event and Lift (VVEL) and continuous valve timing control (C-VTC) technologies to deliver significantly enhanced performance. A rocker arm and two types of links close the intake-valves by transferring the rotational movement of a drive shaft with an eccentric cam to the output cam. The movement of the output cam can be varied by rotating the control shaft within the DC motor and changing the fulcrums of the links. This makes a continuous adjustment of the valve lift possible. The advanced technologies will be made available initially through the Infiniti G37 coupe, scheduled to be unveiled at the upcoming New York International Auto Show next week. Nissan plans to install the VVEL system, which contributes up to a 10% reduction in carbon-dioxide emissions, on its products worldwide starting from FY07 under the Nissan Green Program 2010.
While conventional engines control air intake using a throttle valve, VVEL-equipped engines do this directly at the intake valves, continuously controlling their valve events and lifts. C-VTC and VVEL together control the valve phases and its valve events and lifts, allowing free-control of the valve timing and lift. This results in more efficient airflow through the cylinder and significantly improves responsiveness, optimising the balance between power and environmental performance. The new engine offers the following advantages depending on driving range:
Higher fuel efficiency - at low-to-mid load ranges, the system controls air intake at the intake-valve, immediately before it enters the combustion chamber, in contrast with conventional engine air intake via a throttle valve, leading to increased efficiency by easing airflow through the cylinder. In the low- and medium-rpm ranges, intake-valve lift is kept low to reduce camshaft friction and improve fuel efficiency.
Better response - Controlling air intake at the intake-valves improves acceleration response by allowing more dense air into the cylinders from the start of acceleration.
More power - in the low-rpm range, the intake-valves open for a shorter period, preventing blowback of the air-fuel mixture and improving torque. In the high range, greater intake-valve lift allows increased air intake to deliver greater torque outputs.
Cleaner emissions - intake-valve timing is optimised on startup, when the engine is still cool, to quickly raise the temperature of exhaust gases and more quickly activate the catalytic converter. Hydrocarbon emissions are reduced in the low-to-medium range by keeping intake-valve lift low, speeding intake flow and dispersing the fuel into a fine mist, resulting in more efficient full combustion.
The VVEL improves fuel efficiency most effectively in the low-to-medium operating range, thus it is best matched to the multiple-cylinderÅ@and higher displacement engines, that typically operate within that range.
Under the Nissan Green Program 2010, Nissan has announced plans to develop gasoline-powered engines with CO2 emissions reduced to levels comparable with diesel engines, to be available globally by 2010. For multiple-cylinder, high-displacement engines, Nissan will combine VVEL technology with the direct-injection system.
