EMX has developed a special cooling system for induction machines which advances the art of forced-cooled rotors. This is particularly relevant to EV and HEV applications, where the size of electric machine has to be kept to a minimum, but it could be applied to other industries as well.

Our cooling system employs special conducting tubes which form part of the rotor bars where most of the rotor losses are created. The heat is removed directly at source, keeping rotor temperatures down and minimising thermal expansion of the rotor. This allows a smaller running airgap, which improves the electrical performance of the machine.

The tubes have special features to induce spiral motion of the cooling medium which significantly increases the heat transfer compared with plain tubes. These features also increase the cross-sectional area of the rotor bar compared with the plain tube case, helping to reduce the bar resistance and minimising the electrical consequences of embedded cooling ducts.

Unlike most forced-cooled rotors, the cooling medium in our technology flows within the rotor. The airgap remains dry, avoiding stator winding insulation complications, airgap viscous drag losses and the need for cans which increase airgap size and induce additional losses.