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Nissan Variable Valve Event and Lift (VVEL)
Higher response and power, lower emissions

VVEL (bigger image) controls the intake air mass directly via the intake valves. 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 amount possible.

14 November 2007.

Nissan's Variable Valve Event and Lift (VVEL) system is one of the new technologies aimed at getting better engine throttle response, higher power and torque output with lower fuel consumption and cleaner emissions.

The new VVEL technology has been applied first to the 3.7-litre V6 engine (VQ37VHR) used in the new Infiniti G37 Coupe and Nissan Skyline Coupe (the latter was launched last month in Japan).

While a conventional engine controls the intake air mass by means of the throttle valve, the VVEL system controls the intake air mass directly via the intake valves, by variably controlling the event angle (timing) and lift (distance) of the intake valves continuously, according to the pressure applied to the accelerator.

Combining the VVEL system with continuously variable valve timing control (C-VTC) makes it possible to control valve lift, event angle and phase simultaneously to achieve highly flexible management of valve timing and lift. This improves intake air response and reduces intake air resistance (pumping loss), thereby optimally improving both power output and environmental performance.

Main advantages of the new VVEL technology:

* 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 (accelerator pedal pressed halfway or less), 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 optimized 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 finer 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-cylinder and higher displacement engines that typically operate within that range.

Nissan says that the VVEL system contributes up to a 10% reduction in carbon-dioxide emissions. It plans (Nissan Green Program 2010) 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.

It its worth mentioning that the principle of the continuously variable valve timing and lift, with the elimination of the throttle valve, was first launched in the BMW Valvetronic system in 2001 (316i Compact). Similarly, the new Toyota Valvematic technology starts this year in a 4-cylinder 2.0-litre engine. Finally, Honda announced last year in September the development of an "Advanced VTEC" (AVTEC) system for launch within three years.

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