Delivering 30 kW at 48 V Without Rare-Earth Magnets in 125°C Heat
The task is to develop automotive motor designs that deliver 30 kW of mechanical power from a 48 V supply, without rare-earth magnets, while operating at 125°C ambient temperature. That output requires more than 625 A once losses are included, and winding heat rises with the square of the current. With winding insulation rated to 180°C, designers have only 55°C of temperature rise available to handle that heat. Replacing rare-earth magnets typically requires extra electrical current or a larger motor, so each design needs a credible way to remove heat and must suit automotive manufacturing.
Borrowing the giant Thomson effect from thermoelectric experiments, we insert heat-pumping alloy segments into motor windings so the current that drives the motor also cools hotspots that oil cannot reach well.
How it works
A 30 kW motor running at 48 volts needs very high current, which heats its copper windings. At a surrounding temperature of 125 °C, there is little room for that extra heat before the insulation reaches its limit. We replace 2 mm of each rectangular copper hairpin conductor with iron-rhodium alloy where the conductor exits its slot, a hotspot that oil cools poorly. In laboratory experiments, researchers show that this alloy can absorb more heat than its electrical resistance produces near a temperature-triggered change in its magnetic state: the giant Thomson effect. The alloy conducts heat much less readily than copper, so a sharp temperature difference forms across the short insert. With the alloy composition tuned to winding temperatures, current flowing through that temperature difference provides local cooling. A nine-phase switched reluctance motor supplies one-way current pulses, preserving the cooling instead of reversing it on every alternating-current cycle. The design targets about 150 W of supplemental hotspot cooling across 54 inserts. Oil still removes most of the motor’s waste heat; the inserts add cooling directly inside the conductors where oil is least effective.
Borrowing from hypersonic-engine cooling, where fuel absorbs heat through a reaction that improves combustion, we put a heat-absorbing material inside motor insulation so it becomes a better electrical barrier and can be made thinner.
How it works
A motor’s copper windings need insulation from the surrounding steel, but that insulation also slows the escape of heat. For a compact, magnet-free 48V motor, we replace the usual slot liner with heat-resistant polyimide plastic containing zeolite, a mineral with tiny water-holding pores. The idea follows hypersonic-engine cooling: fuel absorbs heat as its molecules split into smaller, easier-burning molecules. Here, heat releases water from the zeolite’s pores. That release absorbs heat and removes moisture-related paths for electrical leakage. We design around the dry material’s stronger electrical insulation at operating temperature, with a proposed liner thickness of 0.20 mm instead of 0.35 mm. The thinner liner leaves more room for copper and reduces resistance to heat flow toward the oil coolant. An electrical measurement checks that the liner has reached its dry operating state before the controller allows full power.
We borrow self-oscillating heat pipes from electronics cooling and build their sealed passages into the motor’s iron to remove the heat that limits continuous power in a 30 kW, 48 V motor without rare-earth magnets.
How it works
Producing 30 kW at 48 volts requires high currents, which generate intense heat in the motor’s copper windings. In a 125 °C environment, there is little room for further temperature rise. We stamp winding passages into the thin steel sheets that form the stator, the motor’s stationary magnetic core, and bond the sheets together to seal them. Inside, water forms alternating pockets of liquid and vapor. Heat-driven pressure changes push these pockets back and forth, carrying heat from near the windings to the outer water-cooling jacket without a separate pump inside the heat pipe. Electronics researchers already use this mechanism to cool concentrated heat sources. Making the iron itself the pipe wall removes the extra pipe-to-iron contact found in inserted-tube designs and preserves winding space for copper.