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For twin-cam or DOHC engines, VCT was used on either the intake or exhaust camshaft. (Engines that have VCT on both camshafts are now designated as Ti-VCT.↓) The use of variable camshaft timing on the exhaust camshaft is for improved emissions, and vehicles with VCT on the exhaust camshaft do not require exhaust gas recirculation (EGR) as retarding the exhaust cam timing achieves the same ...
The solenoid valve regulates the amount of oil pumped by the cam action to either the valve or a bypass reservoir. When pressurized, the hydraulic line behaves like a solid body and transmits the lift schedule imparted by the intake cam directly to the intake valve. When the solenoid is disengaged, a spring takes over valve actuation duties.
The inlet camshaft position is advanced 25 degrees, thus increasing valve overlap. It remains in this advanced state until about 5000 rpm when the solenoid switches off, and the variator piston returns the valve timing to its natural state. The variable timing increases the engine's mid-range flexibility and reduces emissions.
Some time prior to 1919 Lawrence Pomeroy, Vauxhall's Chief Designer, had designed a 4.4 L engine for a proposed replacement for the existing 30-98 model to be called the H-Type. [8] In this engine the single overhead camshaft was to move longitudinally to allow different camshaft lobes to be engaged.
The disadvantage of this system is its cost. Even though it is a fairly simple device it requires very accurate helical machining and very careful assembly. The helical camshaft prototypes typically cost about $1500 in machining and materials. [citation needed] This figure would reduce greatly in production. The cost of the helical camshaft is ...
A solenoid unlocks the cam followers on one bank from their respective rockers, so the cam follower floats freely while the valve springs keep the valves closed. The system operates through controlling the flow of hydraulic engine oil pressure to locking mechanisms in the cam followers.
N-VTC varies valve timing by rotating the affected camshaft relative to the sprocket; valve lift and duration are not altered. This rotation is achieved when an electric solenoid, controlled by the car's ECU, allows pressurized engine oil to flow into and through the cam and into a slave mechanism, axially advancing camshaft timing relative to ...
The ratio is determined by the ratio of the distances from the rocker arm's pivot point to the point where it touches the valve and the point where it touches the pushrod/camshaft. A rocker ratio greater than one essentially increases the camshaft's lift. Current automotive design favors rocker arm ratios of about 1.5:1 to 1.8:1.
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