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The duration measurement for a camshaft is affected by the amount of lift that is chosen as the start and finish point of the measurement. A lift value of 0.050 in (1.3 mm) is often used as a standard measurement procedure, since this is considered most representative of the lift range that defines the RPM range in which the engine produces ...
Cam switching can also provide variable valve lift and variable duration, however the adjustment is discrete rather than continuous. The first production use of this system was Honda's VTEC system. VTEC changes hydraulic pressure to actuate a pin that locks the high lift, high duration rocker arm to an adjacent low lift, low duration rocker arm(s).
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 ...
One of the first practical VVT systems used a variator to change the phase [note 1] of the camshaft and valves. This simple system cannot change the duration of the valve opening, or their lift. [note 2] Later VVT systems, such as the helical camshaft or the movable fulcrum systems, could change these factors too. Despite this limitation, the ...
The Porsche patent used an oscillating cam to increase the valve lift and duration. The desmodromic cam driven via a push/pull rod from an eccentric shaft or swashplate. It is unknown if any working prototype was ever made. Fiat was the first auto manufacturer to patent a functional automotive variable valve timing system which included ...
A helical camshaft is a type of mechanical variable valve actuation (VVA) system. More specifically, it is a camshaft that allows the valve opening duration to be varied over a wide, continuous, step-less range, with all of the added duration being at full valve lift.
However, the duration of the intake event can be controlled (the "cut-off") using the reversing gear and this reduces steam usage under cruising conditions. Caprotti valve gear is more closely related to that of an internal combustion engine, uses poppet valves, and was developed to allow independent timing of the intake and exhaust events. It ...
A dual AVCS system phases both the intake and exhaust camshafts on the EZ36 found in the 2008+ Tribeca, 2009+ Outback 3.6R, 2009+ Legacy 3.6R, and on the 2008+ STi EJ257 (W25 heads). Dual AVCS is present on the new FA20 engines in the 2015+ WRX, Forester and BRZ and the FB20 engines in the 2012+ Impreza / Crosstrek, though they actuate with a ...