Multistage control method of flow control valve using DC motor

A multistage control method of a flow rate control valve which is opened or closed when a motor rotates so that a flow rate is adjusted, the multistage control method comprising:

• determining an operating range of angular speeds of the motor;
• dividing the operating range by stages into angular speed limit areas that are bounded by a plurality of permanently assigned limit values (SP0, SP1, SP2, SP3, SP4, . . . ) so that angular speed values of the motor are determined depending on motor drive voltages that are scheduled depending on the stages,
• generating angular speed instructions that correspond to respective stages;
• ascertaining a current angular speed of the motor;
• and
• controlling the motor to rotate at a predetermined angular speed value in response to an angular speed instruction (Sn) if the current angular speed is within the angular speed limit area bounded by adjacent limit values (SPn−1) and (SPn),
• wherein, when the current angular speed value is above the limit value (SPn), the angular speed instruction is changed to (SPn+1) so as to rotate the motor at another predetermined angular speed value until the motor reaches the limit value (SPn+1), and
• wherein the speed limit area bounded by SPn−1 and SPn is larger than the speed limit area bounded by SPn and SPn+1 for integers n that are set within a range in which neither a substantial overshoot nor a substantial undershoot of the angular speed of the motor occurs.