Source: https://www.electronicdesign.com/au...a7bcd2a64a645e711e&oly_enc_id=8010I2616490C1C
Today's electric drives are usually designed without transmission; at the most, they may include a reduction gear to lower rpm speed. In addition, the absence of a gearbox makes the drive units simpler and thus more robust and cheaper. They are also more compact than a unit with a transmission.
Ricardo's engineers took exactly the opposite approach when developing their scalable electric drive unit (EDU). The unit is intended to provide state-of-the-art power and torque density as well as system efficiency, and all of that with high noise, vibration, and harshness (NVH) performance.
Why did Ricardo's engineers choose such an adversarial approach? “A multi-speed transmission is clearly more costly than a single speed unit, but it's use can give benefits in terms of weight reduction and more compact sizing of the electric motor, improved whole system cost, energy efficiency, and a hence the potential for a reduced battery size or extended range”, explained a company spokesperson. He was convinced that “the use of multi-speed EDUs is likely to be an increasing trend in the market in the coming five years.”
. . .
I understand the reasoning but am not a fan of this approach because it has too many parts. On the positive side, lower traction battery voltages can be used because keeping the motor rpm low minimizes reverse EMI. BUT lower voltages come at the expense of higher currents. Worse, I hate shift points.
Bob Wilson
Today's electric drives are usually designed without transmission; at the most, they may include a reduction gear to lower rpm speed. In addition, the absence of a gearbox makes the drive units simpler and thus more robust and cheaper. They are also more compact than a unit with a transmission.
Ricardo's engineers took exactly the opposite approach when developing their scalable electric drive unit (EDU). The unit is intended to provide state-of-the-art power and torque density as well as system efficiency, and all of that with high noise, vibration, and harshness (NVH) performance.
Why did Ricardo's engineers choose such an adversarial approach? “A multi-speed transmission is clearly more costly than a single speed unit, but it's use can give benefits in terms of weight reduction and more compact sizing of the electric motor, improved whole system cost, energy efficiency, and a hence the potential for a reduced battery size or extended range”, explained a company spokesperson. He was convinced that “the use of multi-speed EDUs is likely to be an increasing trend in the market in the coming five years.”
. . .
I understand the reasoning but am not a fan of this approach because it has too many parts. On the positive side, lower traction battery voltages can be used because keeping the motor rpm low minimizes reverse EMI. BUT lower voltages come at the expense of higher currents. Worse, I hate shift points.
Bob Wilson
