US Patent 7690339 Control device and method for variable valve mechanism

A variable valve timing and lift mechanism includes an actuator that adjusts the period in which an intake valve is held open by moving a drive element. When a control unit switches the duration, the control unit controls the actuator so that the duration is changed at a first speed when the duration is equal to a first value, and at a second speed when the duration is equal to a second value that is smaller than the first value. The absolute value of the second speed is smaller than the absolute value of the first speed. In effect, the actuator is controlled so that when the duration is in a short-duration range, the duration changes more slowly than when the duration is in a long-duration range.