Throttle valve device of internal combustion engine

A throttle valve device for use in an internal combustion engine having an air induction passage, comprising:

• a valve shaft extending across said air induction passage;
• a valve plate fixed to said valve shaft to rotate therewith in said air induction passage;
• an electric actuator connected to one end of said valve shaft to rotate said valve shaft with the aid of electric power;
• and
• a biasing cam structure incorporated with said valve shaft to bias said valve plate toward a predetermined intermediate open position, said biasing cam structure including a cam plate which is secured to the other end of said valve shaft to rotate therewith and has a generally V-shaped cam edge;
• a loading lever which has a base end pivotally connected to a fixed portion;
• a roller which is rotatably connected to a leading end of said loading lever and runs on and along said V-shaped cam edge;
• and a biasing member which biases said loading lever in a direction to press said roller against said V-shaped cam edge,
• wherein said V-shaped cam edge includes comprises first and second inclined parts which are joined at their lower ends to form a curved bottom part of said V-shaped cam edge;
• and
• wherein a radius of said roller is greater than a radius of curvature of said curved bottom part.