Electric throttle device

An electric throttle device configured to be provided in an intake passage of a naturally aspirated gasoline engine, comprising:

• a throttle body including a bore wall portion defining the intake passage;
• a throttle valve fixed to a valve shaft rotatably supported by the throttle body;
• an opening spring configured to apply a torque to the throttle valve in an opening direction depending on an opening degree θ of the throttle valve from a fully closed position;
• and
• an electric motor configured to rotate the throttle valve between the fully closed position and a fully open position via a reduction gear mechanism,
• wherein the opening spring satisfies G>T(θ)−S(θ) in a closing direction of the throttle valve and |−G|>|T(θ)−S(θ)|in the opening direction,
• wherein T(θ) is a vacuum-induced torque acting on the throttle valve at the opening degree θ in the closing direction, the vacuum-induced torque being produced by a negative pressure generated when the naturally aspirated gasoline engine is assumed to operate at a maximum intake air flow,
• wherein −S(θ) is an elastic torque acting on the throttle valve at the opening degree θ in the opening direction, the elastic torque being generated by the opening spring, and
• wherein G and −G are a closing-side holding limit torque in the closing direction and an opening-side holding limit torque in the opening direction, respectively, the closing-side holding limit torque and opening-side holding limit torque being minimum torques capable of rotating the throttle valve, when stationary, regardless of the opening degree of the throttle valve in a state where there is no air flow in the intake passage, the opening spring is not provided, and the electric motor is not energized.