Abstract
When proportional solenoids driven by pulse width modulation (PWM) are employed in electromagnetic proportional control valves of tractor implements for agricultural applications, the suction force characteristics of the proportional solenoid vary with the oil temperature and supply voltage in the same duty cycle. This means that the valve produces a variety of different outputs for any particular operation signal depending on the temperature and voltage. This variation in the output makes operation of tractor implements problematic. To suppress these characteristic changes, we modified the PWM drive duty and compensated the electric current so that the average supply electric current to the solenoid was proportional to the operation signal. We describe a method of compensated electric current control and a selection method for weight coefficients suitable for tractor implements, in which the operation signals are changed frequently making it suitable for agricultural applications.
