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Thread: Nissan/Infiniti Variable Valve Timing

  1. #1
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    Nissan/Infiniti Variable Valve Timing

    Variable Valve Timing


    Variable valve timing helps the engine deliver remarkable power at high speeds and still run smoothly and efficiently at low engine speeds.

    One of the keys to superior engine performance and efficiency is the way the engine “breathes.” During the intake stroke of the combustion cycle, the intake valves open and air is drawn into the cylinder and mixed with fuel as the piston compresses the mixture in the cylinder.

    When this air/fuel mixture is ignited by a spark plug, it combusts, producing power. What’s left over after combustion becomes exhaust emissions.

    Engines operate most efficiently when the air/fuel mixture varies to match driving conditions. The ideal air/fuel mixture in a given driving condition generates optimum engine power and produces the fewest exhaust emissions. A computer determines this ideal air/fuel mixture by measuring the amount of air coming in and then directing injectors to spray a precise amount of fuel at just the right moment.

    At any given time, the quantity of air required in the engine's cylinders depends on engine speed. The farther you depress the accelerator (causing engine speed to rise), the more air the engine has to induct to achieve the optimum air/fuel mixture inside each cylinder. Conversely, the engine requires less air at low engine speeds — such as when idling.

    The more precise the control of air intake, the more powerful and efficient the engine is.

    Infiniti vehicles use one of three different variable valve timing control systems:

    Several pre-owned vehicles use Nissan Valve Timing Control System (NVTCS).
    Most current vehicles have Continuously Variable Valve Timing Control System (CVTCS).
    Selected models feature Variable Valve Event & Lift (VVEL).



    Nissan Valve Timing Control System (NVTCS) (Pre-Owned)
    NVTCS varies valve timing depending on whether engine speed is low or high. Valve timing changes at fixed intervals.

    NVTCS is similar to the highly publicized VTEC (Variable Valve Timing and Lift Electronic Control System) on Acura and Honda vehicles, but NVTCS is simpler, quieter, and requires no maintenance.

    VTEC uses a series of traditional rocker arms and differently profiled camshaft lobes to externally actuate the valves at different rpm, hence variable valve timing. The system is more complex and requires periodic inspection and adjustment of clearances between the rocker arms and camshafts, which can increase operating expense.


    Honda VTEC's complex system requires

    periodic inspection and adjustment.


    Compared to VTEC, NVTCS is simpler, quieter, and

    requires no maintenance.






    Continuously Variable Valve Timing Control System (CVTCS)

    On select vehicles, CVTCS controls both intake and

    exhaust valve timing.

    With the more advanced CVTCS, a computer continuously monitors and adjusts valve timing to provide optimum performance and efficiency in all operating conditions, not just two.

    On most vehicles, CVTCS controls intake valve timing only. However, on selected high-performance vehicles, it also applies to exhaust valve timing.

    Intake valve timing control feeds more air in at the perfect moment of combustion depending on driving status.
    Exhaust valve timing control magnetically controls cam phase continuously with the fixed operating angle of the exhaust valve. The ECM receives signals such as crankshaft position, camshaft position, engine speed, and engine oil temperature. Then, the ECM sends ON/OFF pulse duty signals to the exhaust valve timing control magnet retarder depending on driving status. This makes it possible to control the shut/open timing of the exhaust valve to increase the engine torque and output in a range of high engine speed.
    If the CVTCS malfunctions, the Engine Control Module (ECM) enters a fail-safe mode.



    Variable Valve Event and Lift (VVEL)

    VVEL varies the size of the intake valve opening.

    VVEL works with CVTCS to monitor and adjust intake valve timing so it matches all operating conditions. However, it also varies valve lift, which refers to the size of the intake valve opening that can be changed to match driving conditions.

    Pressing down on the accelerator pedal signals the engine management system to calculate power output demand. The system measures engine speed, load, temperature, and airflow. It then activates an electric motor that changes valve lift by means of a driveshaft with an eccentric cam and two types of links.

    VVEL varies valve lift to a far greater degree that any other system. In fact, it varies valve lift so much that it could replace the traditional engine throttle. However, an electronic drive-by-wire throttle is retained for use under certain driving conditions. The intake valves completely control engine breathing (air intake). This results in more efficient airflow through the cylinder and significantly improves responsiveness, optimizing the balance between power and environmental performance.

    Currently, BMW is the only other manufacturer that offers continuous variable valve lift technology, which BMW calls Valvetronic. But Valvetronic is less responsive, is less compact, requires more moving parts, and has a lower rev limit than VVEL.

  2. #2
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    so in other words, VVEL > VTEC

  3. #3
    Join Date
    Nov 2007
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    Well VVEL FTL because we neee to use special oil for it.

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