Duty ratio control method for solenoid control valve means

A method of controlling a duty ratio with which solenoid control valve means arranged in a fluid passage is to be driven, to thereby control the flow rate of fluid flowing in said fluid passage to a desired value, the method comprising the steps of:

• (1) dividing into a plurality of flow rate value regions a range of flow rate values between a first extreme flow rate value and a second extreme flow rate value which can be assumed by said fluid, respectively, when the duty ratio for said solenoid control valve means produced in each lot assumes a predetermined miminum value and a predetermined maximum value;
• (2) setting beforehand a first predetermined value of duty ratio corresponding to each of said divided flow rate regions of the step (1), and a second predetermined value of duty ratio corresponding to said each of said divided flow rate regions and larger than said first predetermined value of duty ratio, said first and second predetermined values of duty ratio being dependent upon the magnitude of variations of duty ratio-to-flow rate characteristic of said solenoid control valve means in each lot;
• (3) detecting an actual value of the flow rate of said fluid;
• (4) setting the duty ratio for said solenoid control valve means to said second predetermined value corresponding to one of said divided flow rate regions to which said desired flow rate value pertains, when the actual value of the flow rate of said fluid detected in the step (3) is on the side of said first extreme flow rate value with respect to said desired flow rate value;
• (5) driving said solenoid control valve means with the duty ratio set in the step (4);
• (6) setting the duty ratio for said solenoid control valve means to said first predetermined value corresponding to one of said divided flow rate regions to which said desired flow rate value pertains, when the actual value of the flow rate of said fluid detected in the step (3) is on the side of said second extreme flow rate value with respect to said desired flow rate value;
• and
• (7) driving said solenoid control valve means with the duty ratio set in the step (6).