Sarah Forst posted on January 10, 2009 12:00
Can you explain the whole valve lift concept in the VQ37VHR? I heard something like it doesn't use a camshaft?
Peter Quincy
Baltimore, MD
In a conventional engine, the throttle valve opens and closes to control air intake. In a VVEL engine, the throttle valve is open and the intake air amount is controlled at the intake valves, by the VVEL system continuously controlling the valve lifts and duration. Combined with CVTC, VVEL enables continuous valve movement control. A rocker arm with a moving fulcrum and two types of links transfer the rotational movement of a drive shaft with an eccentric cam to the output cam. The ECU controls a DC stepper motor that can rotate the eccentric cam in order to change the fulcrums of the links. This adjusts the movement of the output cam, creating a continuously variable valve lift and duration.
There are a couple of advantages to this design. Since the throttle valve is always open, a supply of dense air is always available at the intake valve by the combustion chamber entrance and can be delivered more quickly, resulting in better response. Also, the variable intake lift can be kept low at low load and low speed driving conditions. This reduces pumping loss and decreases valve train friction, producing better fuel efficiency. By controlling the optimal valve lift and duration for every condition, such as opening the intake valves for a shorter period at low rpm (preventing reversion) and for a greater period at high rpm, the engine can deliver greater more torque throughout the entire powerband. Finally, VVEL stabilizes combustion even at cooler engine temperatures, helping the catalytic converter to warm up more quickly and producing cleaner emissions, including a 10% reduction in carbon-dioxide emissions.
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