Engineering firm Munro & Associates has dissected electric motors from the Tesla Cybertruck and Chevrolet Equinox, uncovering stark contrasts in their cooling strategies. General Motors opts for a simple, physics-based method, while Tesla employs precise, pump-driven cooling. These differences highlight trade-offs between simplicity and efficiency in electric vehicle powertrains.
Recently, Munro & Associates conducted a teardown of two electric traction motors: one from the Tesla Cybertruck and the other from the Chevrolet Equinox. The analysis, presented by engineer Paul Turnbull, illustrates how Tesla and General Motors pursue divergent paths to manage heat in their EV drive units.
GM's cooling system emphasizes simplicity. It leverages the motor's rotation as a gear mechanism to fling oil upward into cast channels, allowing gravity to distribute it as a 'rainfall' over the windings, magnets, and cast metal components. This approach requires no complex plumbing or pumps, minimizing moving parts and avoiding additional battery drain for cooling hardware. Turnbull notes its similarity to a technique Toyota employed over a decade ago in the Prius C. However, the method's effectiveness depends on motor speed—it provides ample cooling at highway velocities up to around 10,000 RPM but less so in stop-and-go traffic. On steep inclines or demanding tracks, the oil flow may shift, potentially compromising targeted cooling.
In contrast, Tesla uses a high-pressure pump to direct oil through channels onto critical areas like the electrical windings and magnets. This precision enables the use of cost-effective neodymium magnets rather than pricier rare earth alternatives. By focusing cooling internally, the motor casing remains warmer, which boosts its electrical resistance and mitigates eddy currents—unwanted electrical loops that generate heat and reduce efficiency as the motor's magnetic fields change during rotation. The downside includes energy consumption by the pump and added complexity from extra machining, parts, and plumbing.
Ultimately, GM trusts physics for a low-cost, reliable solution, while Tesla's engineering prioritizes performance gains. Both methods prove effective, underscoring the varied strategies in EV design that balance efficiency against simplicity.