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As the electric vehicle (EV) market matures, supply chain resilience, cost optimization, and performance continue to shape powertrain innovation. In this teardown, Munro & Associates examines Nissan’s groundbreaking magnet-free EV motor used in the Ariya — officially known as an Externally Excited Synchronous Motor (EESM). This motor stands out for its clever engineering, strategic reuse of components, and total avoidance of rare-earth magnets — solving one of the most persistent supply chain headaches in modern EV manufacturing.
Why Go Magnet-Free?
Rare-earth magnets, while highly efficient, pose critical vulnerabilities. They’re expensive, environmentally challenging to mine, and geopolitically sensitive — most are sourced from a few countries. Nissan’s magnet-free EESM sidesteps these issues entirely, using copper-wound coils instead of permanent magnets. This lean design move doesn’t just lower supply risk — it redefines what’s possible in EV motor architecture.
The Wound Field Rotor: How It Works
At the heart of the Ariya’s EESM is a copper-wound rotor. Unlike a permanent magnet motor, which always maintains a fixed magnetic field, the EESM dynamically creates its magnetic field using electricity. The rotor becomes an electromagnet only when energized, allowing precise field control.
The copper windings are arranged into an eight-pole structure. At high speeds — where back electromotive force (EMF) in permanent magnet motors becomes a performance bottleneck — the EESM shines. Field weakening, traditionally a challenge in permanent magnet systems, is handled here simply by reducing current to the rotor. This makes the EESM more efficient during highway driving, precisely where electric range matters most to consumers.
Retaining Copper Windings at 12,000 RPM
Spinning at over 12,000 RPM, retaining the rotor’s copper windings requires sophisticated engineering. Nissan adopted a design pioneered by its alliance partner Renault: plastic wedges, dual steel end-rings, and a bolt-through assembly that ensures even clamp load and secure retention. A Torx head is used to stabilize the bolt during torque application — preventing fastener failure at high rotational speeds.
Munro typically favors fastener-free designs. However, when bolts are required, they must be engineered with precision. In this case, Nissan rises to the challenge. The result is a design that ensures both reliability and manufacturability.
Brush System Durability and Serviceability
Energizing the rotor requires carbon brushes and slip rings. The Ariya’s EESM uses four brushes — two for positive and two for negative — to equalize current load and reduce wear. These brushes are designed for longevity, conservatively rated for at least 150,000 miles, with expectations they could last up to 250,000.
Crucially, brush replacement is user-serviceable. A simple access panel on the motor housing allows brush holder removal without dismantling the entire transmission — a rare nod to long-term maintainability in modern EV design.
Optimizing the Stator with Legacy Tooling
The stator, responsible for delivering the bulk of the motor’s power, features stranded copper windings. Rather than adopt a more complex hairpin configuration, Nissan leveraged existing tooling. This decision minimizes launch costs, avoids unnecessary reengineering, and enhances manufacturing yield — a textbook example of lean product development.
Inverter Design: Dual Current Control
Powering the EESM requires more than a standard inverter. Nissan’s solution includes both a traditional three-phase inverter for the stator and a field control circuit dedicated to managing rotor excitation. This Pulse Width Modulated (PWM) board delivers a controlled DC current to the slip rings, allowing the rotor’s magnetic strength to be adjusted in real-time.
This capability unlocks an additional dimension of motor control — unavailable in fixed-field permanent magnet motors — and further boosts efficiency under varying load conditions.
Efficiency: City vs. Highway Driving
Efficiency is speed-dependent. Permanent magnet motors excel at low-speed, stop-and-go scenarios because they don’t need to energize a rotor. However, at highway speeds, the EESM wins. The motor avoids efficiency losses from field weakening and leverages its adjustable rotor field to reduce drag and back EMF.
Nissan made a deliberate bet that matters: highway range is what drivers care about most. When you’re on a road trip, calculating your next charge stop, a few extra miles make all the difference.
Practical Maturity: Design Details that Matter
The Ariya’s motor showcases Nissan’s decades of EV experience in small but crucial details:
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Oil Cooling: The motor is oil-cooled but uses a simple and proven approach. Rather than over-design the stator’s cooling channels, Nissan balances cost with actual thermal load — an optimized compromise for this vehicle’s use case.
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Reuse of Proven Components: The drivetrain includes a conventional park pawl, a mechanical component found in automatic transmissions. Many EVs eliminate it for cost, relying solely on brake-hold systems. Nissan retains it for an added layer of safety and customer familiarity.
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Bearing Protection: High-frequency voltages in the rotor can cause arcing through the bearings, leading to premature failure. Nissan includes a grounding brush that discharges stray voltages — preventing race pitting and extending bearing life.
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Water Fording Capability: A clever snorkel design elevates the motor’s breather intake, allowing the Ariya to safely ford up to 30 inches of water without risking oil contamination — an important feature for markets with varying weather and terrain.
These decisions reflect a philosophy that prizes reliability, serviceability, and end-user peace of mind — hallmarks of a mature OEM.
Resolver and Thermal Management
As a synchronous motor, precise rotor position is critical. A resolver sensor delivers this data to the control electronics, enabling efficient torque production. Additionally, an integrated oil-to-water heat exchanger ensures that motor heat is efficiently routed to the vehicle’s broader thermal management system — further enhancing range and performance.
Strategic Advantage: Supply Chain and Cost
By avoiding rare-earth magnets, Nissan has created a power-dense, competitive motor without reliance on vulnerable materials. This provides a strategic hedge against geopolitical disruptions, fluctuating prices, and environmental concerns — while keeping motor costs stable and predictable.
This kind of resilience is increasingly important as EV production scales globally.
Final Thoughts: A Blueprint for the Future?
The Nissan Ariya’s magnet-free EV motor is more than a technical curiosity — it’s a potential blueprint. Other automakers may follow this path, especially as supply chain risks intensify. With competitive horsepower (239 hp), compact packaging, and class-leading efficiency at highway speeds, the Ariya’s EESM proves that performance and pragmatism aren’t mutually exclusive.
Nissan, aided by its alliance with Renault, is ahead of the curve. They’ve delivered an EV motor that’s not just innovative — but industrialized, cost-conscious, and user-centric.
Explore More from Munro
For more teardown reviews, expert analysis, and EV cost breakdowns, visit Munro & Associates or subscribe to Munro Live. From motor reports to deep-dive vehicle studies, we reveal the engineering decisions shaping the future of mobility.