Suspension control apparatus utilizing a PWM type proportional solenoid valve

A method for controlling a dithering current in a suspension control apparatus comprising:

• a proportional solenoid valve having a solenoid and a movable member adapted to be displaced according to an intensity of a current applied to said solenoid;
• PWM signal generating means for generating a PWM signal having a variable duty ratio;
• and switching means provided between a power source and said solenoid to be switched on and off according to said PWM signal,
• said method comprising:
• changing the PWM signal to be switched between a decrease duty ratio and an increase duty ratio, so that the PWM signal having said decrease duty ratio and the PWM signal having said increase duty ratio are applied during a decrease switching time and an increase switching time, respectively, to thereby obtain a dithering current to be superimposed on a predetermined target current, said dithering current and said target current constituting said current applied to the solenoid;
• and
• also changing the PWM signal in such a manner that in a first current intensity range where said decrease duty ratio is 0%, said decrease switching time is prolonged and said increase switching time is determined so that the total of said prolonged decrease switching time and said increase switching time is substantially constant, said increase duty ratio being determined so that an amplitude of said dithering current obtained by application of the PWM signal having the decrease duty ratio and an amplitude of said dithering current obtained by application of the PWM signal having the increase duty ratio are substantially the same.