Ever-tightening emissions requirements, teamed with consumers' lust for today's high horsepower numbers, have led to some creative valve timing and lift schemes. Infiniti's G37 will be pack some interesting tech underhood when it debuts at the upcoming New York International Auto Show. There are actually two new developments working in conjunction to give independent control over valve timing and lift. Nissan has dubbed the control technologies Variable Valve Event and Lift and Continuous Valve Timing control, or VVEL and C-VTC, respectively. VVEL uses a clever arrangement of links to actuate the valves, and moves the fulcrum for the links via a seperate shaft actuated by a DC motor. By moving the fulcrum, the valve lift is varied.

More after the jump, along with press release

[Source: Nissan via Gizmag]




Nissan's new valve actuation arrangement allows efficiency gains to be realized. Out go the throttles and their pumping losses, unnecessary now that the valve action can control engine speed. Without a throttle plate, engine responsiveness increases; not that the VQ with throttles is slow to respond to jabs at the go-pedal. CO2 emissions also see a 10 percent reduction with VVEL. The largest gains are realized in the low and middle RPM range, but the top end doesn't suffer, either. The ability to increase valve lift allows higher torque output at high RPM.

Of course, this technology has some of the same gotchas as gasoline direct injection – cylinder pressures and temperatures must be attended to during tuning and development to keep emissions in bounds. One neat trick for cold starts and quick warmups is that the VVEL and C-VTC systems will optimize the valve events to quickly put heat into the exhaust gas, lighting off the catalytic converter faster. Tuning voodoo has also led to using reduced valve lift in that low to mid RPM range to increase the velocity of the intake charge, improving fuel dispersion and atomization for more complete combustion.

The VVEL and C-VTC systems are part of Nissan's Green Program 2010, which aims to reduce gasoline engine CO2 emissions to the level of diesel engines and have the technology on sale globally by 2010. How's that for having your cake and eating it, too? The G37 will run cleaner and be able to twist the tires right off the rims even better. We wonder if the engine emissions reductions will offset all that tire smoke?


PRESS RELEASE:

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.

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.
l 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 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.