Patent ID: 6135720
Filing Date: 2000-10-24
Classification: F04C

Abstract:
An air compressor of sliding vane eccentric rotor type including a stator, which includes an inlet and an outlet and defines a substantially cylindrical bore, and a rotor eccentrically rotatably mounted in the bore, the rotor being connected to be rotated by a three-phase asynchronous electric motor of pole amplitude modulated type which is switchable between low speed six pole operation and high speed four pole operation under the control of a controller, a pressure sensor communicating with the outlet and connected to the controller which is arranged to produce a first signal when the compressor discharge pressure falls below a first threshold value and a second signal when the compressor discharge pressure rises above a second threshold value, each of the three electrical power supply lines of the motor being associated with a respective impedance, which is connected in parallel with a shunt path including a respective switching means, which is switchable under the control of the controller, whereby when the switching means is closed the impedance is shunted and is effectively switched out of the associated power supply line and when the switching means is open the shunt path is interrupted and the impedance is effectively switched into the power supply line, the controller being so arranged that when the compressor is operating at low speed and the first signal is produced the motor is switched to operate at high speed and when the compressor is operating at high speed and the second signal is produced the compressor is switched to operate at low speed, the controller also being so arranged that when the compressor is switched on or switched between high and low speeds the impedances are switched into the associated power lines for a predetermined period of time and are switched out of the associated power lines at all other times.