Patent ID: 8256397

Claim:
An engine assembly comprising: an engine structure defining a combustion chamber and a first intake port in communication with the combustion chamber; a piston located within the combustion chamber and reciprocally displaceable from a top dead center position to a bottom dead center position during an intake stroke and displaceable from the bottom dead center position to the top dead center position during a compression stroke immediately subsequent the intake stroke; an intake manifold in communication with the first intake port; a vacuum actuated mechanism including a vacuum chamber in communication with the intake manifold; a first intake valve supported by the engine structure and selectively opening and closing the first intake port; and a valve actuation assembly engaged with the first intake valve and operable in first and second modes, the valve actuation assembly operated in the first mode when an operating pressure in the vacuum chamber is below a predetermined limit and operated in the second mode when the operating pressure in the vacuum chamber is above the predetermined limit, the first mode providing a first opening duration of the first intake valve during one of the intake stroke and the compression stroke and the second mode providing a second opening duration of the first intake valve during the one of the intake stroke and the compression stroke that is different than the first opening duration to produce a greater vacuum in the intake manifold than the first opening duration.