Renault Rare-Earth-Free Electric Motors: EESM Technology and Strategy

Renault Group is bypassing the industry-standard reliance on rare earth magnets by mass-marketing Electrically Excited Synchronous Motors (EESM). This strategic shift aims to eliminate dependency on rare earth supply chains, which are currently dominated by China, while maintaining high efficiency and performance across its electric vehicle (EV) lineup.

The Strategic Shift to Rare-Earth-Free Motors

Renault's adoption of EESM technology is primarily a response to the geopolitical risks associated with rare earth elements. China currently produces 85% of purified light rare earths and 100% of heavy rare earths, maintaining a near-total monopoly (over 90%) of global production. By utilizing a wound rotor instead of permanent magnets, Renault removes these materials from its production process.

Comparing Electric Motor Topologies

There are three primary families of electric motors used in the automotive industry, each with distinct technical trade-offs:

  • Permanent-Magnet Synchronous Motors (PMSM): The current market dominant technology (used in 90% of EVs). These offer high efficiency and compact size but require rare earths.
  • Asynchronous Motors (ASM/Induction Motors): These are generally less efficient and are typically relegated to secondary motors on a vehicle's front axle.
  • Electrically Excited Synchronous Motors (EESM): These deliver high efficiency without the use of magnets. While slightly larger than PMSMs, they avoid rare earth dependency.

Renault's EESM Evolution and Roadmap

Renault has been mass-marketing EESM technology since 2011, evolving through several generations of hardware produced at its Cléon plant:

First and Second Generations

  • First Generation (2011-2020): Introduced in the Renault Kangoo Z.E. (2011) and Renault Zoe (2012), with outputs ranging from 57 to 100 kW. The final upgrade (5AL) appeared in the Twingo Electric with 60 kW output.
  • Second Generation (2021-Present): The 6A series motors are smaller, lighter, and more powerful. The 6AM variant (up to 160 kW) debuted in the Megane E-Tech electric in 2022 and is used in the Scenic E-Tech Electric and Alpine A290. The 6AK variant (110 kW) powers the Renault 5 E-Tech and Renault 4 E-Tech.
  • High-Performance Setup: The Alpine A390 features a combined output of approximately 345 kW (470 hp) using a 6AM motor on the front axle and a new twin-motor setup on the rear.

Third Generation (E7A) - Coming 2027

Renault is currently developing the E7A motor, with frozen specifications targeting a 2027 release:

  • Performance: 200 kW output (~270 hp) and 400 Nm of torque.
  • Efficiency: Approximately 92% efficiency.
  • Physical Impact: 30% smaller size and 30% reduction in carbon impact due to an all-in-one architecture.
  • Electrical Architecture: A shift from 400V to 800V system voltage to reduce charging times.

Technical Analysis and Industry Perspectives

While Renault promotes EESM as a strategic advantage, technical discussions highlight several engineering trade-offs inherent in wound-rotor designs.

Advantages of EESM

According to technical analysis provided in community discussions, EESMs offer several benefits over Permanent Magnet Synchronous Machines (IPMSMs):

  • Supply Chain Stability: Immunity to the price volatility of rare earth magnets.
  • Highway Efficiency: EESMs can exhibit higher cycle efficiency during highway-dominant drive cycles due to superior field-weakening characteristics at moderate torques and high speeds.
  • Thermal Stability: Output torque does not necessarily decrease as the rotor temperature increases, unlike in permanent magnet motors where flux linkage drops with heat.

Engineering Challenges

Critics and engineers note that EESMs introduce specific complexities:

  • Power Transfer: DC current must be transferred to the rotating field winding. This is typically achieved via brushes and slip rings or brushless high-frequency transformers. Brushes are subject to mechanical wear and require maintenance, while brushless solutions increase the complexity of power electronics.
  • Power Density: The need for field winding end turns and excitation systems typically results in a longer axial length and lower power density compared to PMSMs.
  • Control Complexity: High-performance current and torque regulation is more difficult to achieve in EESMs than in magnet-based motors.

Market Context

Renault is not alone in this pursuit. BMW also produces rare-earth-free motors, with some reports suggesting their current offerings are more advanced in terms of power (up to 300kW) and 800V architecture. Other manufacturers, including Nissan and various Indian automotive firms, are also integrating EESM supply chains to reduce reliance on Chinese materials.

Sources