A solution so obvious, it must be wrong.
August 17, 2011 8:48 PM Subscribe
Why don't electric cars use smaller motors with multiple-speed transmissions?
posted by davejay to Travel & Transportation (15 answers total) 1 user marked this as a favorite
Everything I've read while researching an electric car purchase says that, since electric motors produce the most torque at rest, and produce such copious amounts of it, that (with one exception) electric cars don't use multiple-speed transmissions -- because they're too fragile, and because you can get away without it. For instance, Tesla tried like the dickens to work out a two-speed transmission, but eventually shipped the cars with a single-speed (the higher gear.) Similarly, to avoid halfshafts breaking along with transmissions, it is apparently typical to limit current to the motor initially, so that it puts out less power. Unfortunately, running single speed transmissions means that the motors have to run at high (and significantly less efficient) speeds as the car's speed increases.
Given that combination -- motors too powerful at low speeds, and not efficient enough at high speeds -- it seems like a no-brainer to run a much smaller electric motor and a multiple-speed transmission. The full low-speed torque output (without current limiting) would presumably be sufficient to get the car moving, but low enough not to break the gearbox, and the inability to produce as much power at higher speeds would be solved with the now not-imploding multiple-speed gearbox. Plus, smaller motor and lower speeds equals better battery life and less heat.
It seems so obvious, in fact, that I don't understand why manufacturers aren't taking this approach...but they're the geniuses, I'm not, so there must be a good reason. Please advise.