Blower system for vehicle air-conditioners

Claim 1

A blower system for vehicle air-conditioners, comprising: a blower; a direct current brushless motor for rotationally driving said blower; a magnetic detecting means for producing an electric pulse signal related to the position of a magnetic rotor of said motor, a frequency of said electric pulse signal varying with the rotational speed of said motor, and the cycle period and peak value of said electric pulse signal increasing with decreasing rotational speed of said motor; a setting device for producing a set signal representing a set rotational speed of the motor; control circuit means responsive to the electric pulse signal and the set signal for controlling an exciting current supplied to said motor for producing a rotational torque in the magnetic rotor; signal processing circuit means responsive to the electric pulse signal for producing a saw-tooth wave signal, said signal processing circuit means comprising means for changing the cycle period and peak value of aid saw-tooth wave signal in relation to the rotational speed of the magnetic rotor; reference signal generating means for generating a reference signal, the level of said reference signal increasing as the set rotational speed of the motor decreases; and a discrimination circuit for generating a discrimination signal based on a comparison of said saw-tooth wave signal with the reference signal and indicating whether or not said motor is in a locked state; said reference signal generating means comprising means responsive to said set signal for setting the level of the reference signal such that the time period between motor locking and output of the discrimination signal becomes shorter as the set rotational speed of the motor becomes higher.