Patent ID: 7685979

Claim:
A variable valve timing mechanism comprising: a drive shaft arranged to open and close at least one of an intake/exhaust valve via a rocker arm in response to rotation of the drive shaft; a control shaft operatively coupled to the rocker arm to change a position of the rocker arm to continuously change valve lift characteristics of the intake/exhaust valve in response to rotation of the control shaft by driving a control shaft actuator, the control shaft actuator including a drive source, a ball-screw mechanism linked to the drive source, and a linking mechanism linking the ball-screw mechanism to the control shaft; a stopper arranged relative to the control shaft to regulate an operating range of rotation of the control shaft between an upper limit and a lower limit; a first spring member arranged to urge the control shaft with a first urging force towards the upper limit in a first rotational direction; and a second spring member arranged to urge the control shaft with a second urging force towards the lower limit in a second rotational direction, with the first and second spring members being disposed on the ball-screw mechanism, the first and second spring members and the control shaft being further arranged such that the first and second urging forces of the first and second spring members return the control shaft to a balance position between the upper limit position and the lower limit position when the internal combustion engine stops with the control shaft disposed on either side of the balance position, and the first spring member and the second spring member having spring characteristics such that the valve lift characteristics of the intake/exhaust valve have a smaller lift amount and a smaller operating angle when the control shaft is held in the balance position than when held at a center rotation angle position of the operating range of the control shaft.