[ my celica ]
[ factory specs ]
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[ vvtl-i details ]
toyota's intelligent variable valve lift system uses a cam change-over mechanism to increase the lift of the intake and exhaust valves when engine revolutions exceed 6000rpm.
the hydraulically activated variable-lift mechanism is electronically controlled by the engine ecu and shares some of its hydraulic control hardware with the vvti system.
it has the same system inputs as the vvti system - crankshaft angle and revolutions, air flow, throttle position, inlet camshaft angle and engine coolant temperature.
the variable-lift system will not operate until coolant temperature reaches 60ºC (140ºF).
the mechanism includes camshafts with two sets of cam profiles, for low-to-medium engine speed and high engine speed (high lift).
the full system includes eight rocker arms (one for each pair of valves), two rocker shafts (located inboard of the camshafts) and a spool-type oil control valve on the aft end of the inlet camshaft.
the rocker arms are the heart of system.
they have an integrated needle roller cam follower, a rocker arm pad and hydraulic rocker arm pin.
in normal operation, the low-to-medium speed cam acts on the needle-roller cam follower and the rocker arm operates its pair of valves.
meantime, the rocker arm pad rides against the high-lift cam lobes, but moves freely within the rocker arm.
in this state, the rocker pad does not contribute to rocker arm movement and therefore makes no contribution to valve activation.
when the engine is operating in the low-to-medium speed ranges, the oil control valve is open to the drain side.
however, when engine revolutions exceed 6000rpm, the oil control valve closes the drain side and hydraulic pressure flows through the rocker shafts to the hydraulic rocker arm pin.
the hydraulic pressure pushes the rocker arm pin out to lock the bottom of the rocker arm pad.
with the rocker pad locked in its full extended position, the high-lift (high-speed) cam lobes now operate the rocker arm and hence its pair of valves.
when engine revolutions drop below 6000rpm, the oil control valve opens on the drain side, to relieve pressure on the cam changeover mechanism and allow the system to return to normal lift conditions.
celica's 2zz-ge engine has shim-type valve clearance adjusters and narrow valve stems to optimise gas flow.
data & photo taken from the 2000 toyota celica press kit.