Electrical Propulsion System Design of Chevrolet Bolt Battery Electric Vehicle

The propulsion system design of General Motors' Chevrolet Bolt battery electric vehicle (BEV) incorporates the use of a permanent magnet synchronous motor. Magnets are buried inside the rotor in double layer “V” arrangement and the rotor design optimizes the magnet placement between the adjacent poles asymmetrically to lower torque ripple and radial force. Rotor design also optimizes the placement of a pair of small slots stamped near the rotor outer surface at different locations in adjacent poles to provide further reduction in torque ripple and radial force. As a result of all these design features, the Chevrolet Bolt BEV electric motor is able to meet the GM stringent noise and vibration requirements without implementing rotor skew, which is known to lower the motor performance and add complexity to the rotor manufacturing. Similar to Chevrolet Spark BEV, a bar-wound stator construction known to provide high slot fill, shorter end-turn length, and other benefits is implemented in Chevrolet Bolt BEV. To lower the winding ac effect at higher speeds, the Chevrolet Bolt BEV motor implements six conductors per slot design while four conductors per slot design was used in the Chevrolet Spark motor design. As a result, individual conductor size is smaller in new design resulting in reduced winding ac effects and improved joule loss at high-speed operations. Chevrolet Bolt BEV stator design also adopts a special feature, introduced in Gen2 (2nd generation) Chevrolet Volt; the size and placement of stator slot openings under each pole are optimized to lower torque ripple and radial force. This feature acts as a supplement to the torque ripple and radial force reduction features introduced in the rotor design as described above.