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Cooling concepts

Our cooling concepts are as individual as our customers

Since electric motors offer extremely high power and torque density (compared to classic industrial motors), cooling plays a key role in keeping machine temperatures low and ensuring a long lifetime.

TMW: Liquid cooling

Graphical illustration of a liquid cooling system

The motors are totally enclosed and cooled by a water jacket, located on the stator’s outer surface. The coolant is usually a mixture of water and antifreeze. The motors may be equipped with an additional inner air circuit to provide rotor cooling.

Liquid cooling is also common for permanent-magnet synchronous motors as well as for asynchronous machines.


  • Noise level kept to an absolute minimum (no fan)
  • Cooling continues even when the vehicle is not in motion
  • No ingress of dirt or water
  • Low maintenance


  • Additional installations for cooling circuit required (pipes, pumps, heat exchanger)
  • Limited power density due to low rotor cooling


TMF: Air-cooled, open design, forced ventilation

Graphical illustration of a cooling system - air-cooled, open design, forced ventilation

Airflow is provided by an external blower, usually situated inside the vehicle and guided to the traction motor via air ducts. The cooling air enters the interior of the motor, directly cools the winding head, then flows through axial cooling holes in the stator and rotor’s sheet metal package to the other side, cools the winding head again and finally leaves the machine through a grid.


  • Highest possible airflow and direct cooling to allow maximum power density
  • Cooling is independent of actual motor speed, hence, airflow can be controlled depending on actual motor temperature


  • External blower required
  • Air ducts need additional space

TME: Air-cooled, open design, self-ventilated

Graphical illustration of a cooling system - air-cooled, open design, self-ventilated

Airflow is generated by a fan directly attached to the motor’s shaft. The cooling air enters the interior of the machine through coarse metal-sheet filters, is drawn over the winding head and through the stator and rotor holes (similar to the forced ventilation concept), passes the fan and leaves the motor in radial direction.


  • Simplest and cheapest cooling concept, no additional installations required
  • Direct cooling of windings and rotor


  • Due to fan noise, maximum motor speed is limited
  • Poor cooling at standstill or low speed
  • Intrusion of water and dust
  • Metal filters require maintenance (cleaning)

You want to have the best traction drive for your vehicles?