ROTATION SIGNAL DETECTING DEVICE FOR ENGINE AND DISTRIBUTOR

PURPOSE:To improve rotation signal detecting performance by a method wherein a signal rotor is mounted on a rotary shaft driven by a reduction mechanism being a different system from a cam shaft reduction mechanism and reducing a crank shaft to a 1/2 angular speed. CONSTITUTION:Rotation of a crank shaft 3 is re duced to a 1/2 angular speed by 1/2 reduction mechanisms 12 and 13 being a different system from a cam shaft reduction mechanism, transmitting rotation of a crank shaft 3 to the cam shaft of an engine 6, to transmit rotation to a rotary shaft 2 of a signal rotor 16. Thus, unlike a case in which a shaft, e.g. a cam shaft, having a high weight is reduced for rotation, a small light rotary shaft 2 simply equipped with the rotor 16 can be reduced for rotation. As a result, even when, in addition to a case in which the 1/2 reduction mechanism is formed with a gear, the reduction is formed by a timing belt, elongation with a time as in a timing belt used for a cam shaft reduction mechanism is prevented from occurring. Since there is no margin for the rotor rotary shaft 2 to be influenced by the opening and closing motion of the cam valve of a cylinder by means of a cam shaft, a stable and smooth rotation motion freed from vibration can be effected.