BMW has been grabbing the headlines in recent weeks after revealing details of its i3 and i8 models (i3, pictured): and now it has shed some light on the technology that is driving their success.
As the heart of the vehicles will be a new eDrive motor, which is a hybrid synchronous motor meant to exploit both the reluctance effect and the permanent magnet motors. BMW believes it is the ultimate answer for achieving the best possible blend of power density and efficiency while also minimising the use of rare earth metals.
BMW's focus when producing the motor was on using a limited amount of installation space inside the vehicle: it believes that motors with higher output and torque, as well as low weight, are generally the most efficient. In addition, with high voltage batteries generally expensive, it wanted to attain the highest vehicle range from the available battery power by focusing on improving efficiency.
As such, it placed a firm focus on permanent magnet motors that can deliver permanent magnet torque and reluctance torque.
The motor inside the i3 is largely a synchronous permanent magnet motor but it includes specific dimensions and an arrangement to produce the best possible self-magnetising effect that would only otherwise appear in reluctance motors. With this additional excitation, the electromechanical field can be stable even at high revs.
The results are impressive too: the 50kg electric motor in the BMW i3 can generate 125kW of specific power with maximum revs of 11,400rpm: that compares to 80kW from the 58kg motor in the Nissan LEAF.
According to BMW, the method is flexible and could potentially be used with a host of different electric drive motors. This should allow motors to be produced at a low cost and drive down the prices of its vehicles while offering an extensive battery cruising range.