Variable Valve Event and Lift system (VVEL)
Inspired (Probably) by diesel engines which runs without throttle bodies, Nissan comes up with brilliant VVEL system.
Diesel engines have no throttle body. Behind the intake valve you’ll find air at slightly less than atmospheric pressure; (in case of Naturally Aspirated ones, due to air friction inside the intake manifold); ready to enter the combustion chamber in each intake stroke.
Whilst in Nissan’s VVEL engines you’ll find a throttle body fully open such as that of the VQ37HRs. However, these throttles are only present for safety in case of any familiar in VVEL system, and it closes completely when the engine is switched off. Yet, in conventional one, the throttle’s body flap varies upon the position of the gas pedal pressed by the driver, to account more or less air into the intake manifold.
During idling or partial loads in conventional engines, throttle body flaps opening is very narrow, which scores increasing piston load as it sucks air into the combustion chamber (think of it as if the piston ;during the intake stroke; traveling to BDC and sucking air from a negative pressure space) so this accounts as an additional work to the compression stroke cycle. The following figure for illustration.
By adopting VVEL simply, sufficient air will be filling the intake manifold and ready just behind the valve to fill the chamber whenever the intake valve opens. That’s one of the significant reasons why VQ37HRs gains noticeable power and torque with just aftermarket high flow-nonrestrictive cold intakes and a tune.
All the throttling control is done at the intake valve through the VVEL. This system can keep the intake valve shut completely (in case of engine braking) even if the engine is running and the crank shaft is rotating.
At different engine loads and speed, VVEL controls the incoming charge at the intake valves by managing each of the valves' up and down characteristics, specifically lift and duration.
As a performance outcome, instantaneous response will be incredibly noticeable. Air ready to enter the chamber, is accumulated behind the valve rather than behind the throttle body… Shortening the distance of air travel to reach the combustion chamber accounts for high torque and 30% swift response whenever pressing the pedal. In this case, the latter is not controlling the throttle body, but now it’s a position sensor serving the VVEL system.
Further, Nissan considered intake valve timing during start-up conditions, when the catalytic converters are still cold and not working as effectively. Intake timing is optimized here to build exhaust heat quicker, essentially making the catalytic converter work sooner. Additionally, hydrocarbons are kept low through less intake valve lift at lower engine speeds. The lower valve lift helps promote additional airspeed, which creates a fine mist of fuel for more complete combustion.
The above diagram illustrates the flow of air at the instant the valve opens, by comparing VVEL control and conventional throttle controlled engines.
It’s clear that in VVEL the throttle is fully open and air-flow-rate is exceeding that that of the conventional system even though the valve lift is much lower.
This is a brief explanation of VVEL system, Nissan adopted starting with the high revving engines in 2007+ 350z and 370z models, also in the current Patrol 5.6L V8 engines. Nissan is a leading Japanese car manufacturers, but currently passing through sales crises that I'm hoping they will overcome soon. No one can deny the legendary cars they had vastly produced in market, that gained attention of both enthusiast and non.. such as skyline/GTRs/ Godzillas, the Datsun/ Z series, and the Patrol.
I'm a a big fan of Nissan's Z cars especially the latest 370z. all in all it's a drivers car. many youtubers shed lights that this car is out-dating, but Nissan engineers aren't stupid, they are building something just for drivers, who want to drive the car themselves and hindering technology to take control of it. Although Nissan's manual transmission suffers from catastrophic clutch slave cylinder broke and heavy clutch, but the transmission itself and the engine are very reliable and a marvelous piece of technology.
One wish is to see an inline turbo air cooled 6 cylinder engine in the upcoming Z35.