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The timing, duration and lift of these valve events has a significant impact on engine performance. Without variable valve timing or variable valve lift, the valve timing is the same for all engine speeds and conditions, therefore compromises are necessary to achieve the desired result in intake and exhaust efficiency . This has been described ...
The Alfa Romeo Twin Spark engine, introduced in the 1987 Alfa Romeo 75, also uses variable valve timing. [3] [4] The Alfa system varies the phase (not the duration) of the cam timing and operates on the inlet camshaft. [5] Alfa Romeo's variator is a cylindrical chamber that contains a pressure chamber and piston along with helical splines.
The blue valve body is visible in-line with the pipe. The valve actuator opens or closes the butterfly disc of the valve based on electrical signals sent to the actuator. Another valve actuator is visible in the background, with windows to indicate the valve position. A valve actuator is the mechanism for opening and closing a valve. Manually ...
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.
VVT-iE (Variable Valve Timing - intelligent by Electric motor) is a version of Dual VVT-i that uses an electrically operated actuator to adjust and maintain intake camshaft timing. [1] The exhaust camshaft timing is still controlled using a hydraulic actuator. This form of variable valve timing technology was developed initially for Lexus vehicles.
VCT is used in Ford's Triton 5.4L 3-valve V8 engine, the Australian Barra 182 and 240 Inline-6s, and Ford's 4.6L 3-valve V8 engine used in the 2006-2010 Ford Explorer and 2005-2010 Ford Mustang GT. The 2.0L Zetec inline-4 used in the 1998–2003 Ford Escort ZX2, Ford Contour, and 1999–2002 Mercury Cougar used VCT on the exhaust camshaft.
The system has the advantage that it is continuously variable rather than switching in at a set speed. Its disadvantage is the complexity of the system and corresponding price. Other systems will achieve similar results with less cost and simpler design (electronic control).
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.
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