Double overhead cams and variable valve timing have been two recent technologies allowing modern engines to ring more power and torque out of ever-smaller amounts of fuel. Nissan has announced two new technologies that push the bounds of valve actuation efficiency even further; Variable Valve Event and Lift (VVEL) and continuous valve timing control (C-VTC). When combined, significantly enhanced performance is available via the continuous adjustment of the valve lift and CO2 emissions are cut by up to 10 percent. Nissan is planning to roll out the new VVEL system on its upcoming Infiniti G37 coupe.
Analysis: It seems that the pace of improvements to engine efficiency and improved emissions seems to be increasing which would indicate that the internal combustion engine has a long way to go yet. Nissan will include VVEL on its products worldwide starting from FY07 under the Nissan Green Program 2010.
Check out the press release after the jump for specific details on how VVEL achieves higher fuel efficiency and cleaner emissions.
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Nissan Introduces Innovative Valve Control Technology [Mar. 29, 07]
- Variable Valve Event & Lift (VVEL) delivers significant improvements in dynamic and environmental performance -
TOKYO (March 29, 2007)--Nissan Motor Co., Ltd. today introduced a new engine technology that delivers a balance of responsiveness and power, fuel efficiency and low emissions. The new system combines the technologies behind Nissan's newly developed Variable Valve Event and Lift (VVEL)*1 and continuous valve timing control (C-VTC) to deliver significantly enhanced performance. This advanced technology will be available to customers worldwide through the Nissan and Infiniti product lines.
Nissan announced plans to install the VVEL system, which contributes up to a 10%*2 reduction in carbon-dioxide emissions, on its products worldwide starting from FY07 under the Nissan Green Program 2010. The first product to feature the VVEL technology is the Infiniti G37 coupe, scheduled to be unveiled at the upcoming New York International Auto Show in April, 2007.
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, optimizing 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*3, intake-valve lift is kept low to reduce camshaft friction and improve fuel efficiency.
Controlling air intake at the intake-valves improves acceleration response by allowing more dense air into the cylinders from the start of acceleration.
In the low-rpm range, the intake-valves open for a shorter period, preventing blowback of the air-fuel mixture and improving torque.
l In the high range, greater intake-valve lift allows increased air intake to deliver greater torque outputs.
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 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-cylinder 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.
The VVEL system
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.
*1 VVEL: Variable Valve Event & Lift
*2 This percentage improvement is measured by Nissan by comparing an engine with the VVEL system to an identical engine without it.
*3 The accelerator pedal is pressed halfway or less.