The device includes a solenoid valve having a supply conduit communicating with the delivery of the pump, a drain conduit, an electromagnet energizable to control an armature controlling a shutter, and reducing means for reducing disturbance in the delivery pressure of the pump when the electromagnet is energized. The reducing means include a chamber having a predetermined volume and located between the supply conduit and the drain conduit; and a fixed shield having an opening in which slides a small-diameter portion of the stem of the armature. The electromagnet is controlled by an electronic unit via a modulator for modulating the duty cycle of the control pulses, and via a circuit for selecting the frequency of the control pulses on the basis of an estimate of hydraulic disturbances depending on at least one operating parameter.