Torque: Fill & Download for Free

Electric engines provide 100% torque when they are stalled, not turning. They do NOT provide 100% torque as they deliver power at higher rpm. Here’s a real world comparison:The electric motor torque curve is nearly flat at lower rpm, which means the delivered power is going up in proportion to the RPM. But above some point the back EMF starts to reduce the torque. Notice that the Camaro uses its transmission to keep in the power band.

There are a couple of reasons. The hardest part of pulling a train is getting it moving from a stop. The weight of the train is measured in hundreds, sometimes thousands of tons. A gasoline engine won’t do it, it makes its maximum torque at around 3 or 4000 RPM. With a manual transmission, the clutch would be turned into a cloud of stinking smoke before any thing else happened, such as moving the train.A diesel makes more torque than a gas engine, but the same problem is there, getting it to move from a dead stop. I’m not aware of anyone making an automatic transmission that could pull a train and remain in one piece. But guess what? An electric motor makes its maximum torque at stall. What that means is, the instant electricity is supplied to the motor, its maximum torque is reached as it starts from a stop. The slower it runs, the more torque it has, as it revs up, torque drops off, but the load is already moving.The Diesel engine in the locomotive doesn’t drive the train, it runs a really big generator that feeds electricity to the electric traction motors, usually, but not always, one per axle, that actually make the whole train go.I don’t know the power of the motors, or if they run on AC or DC, but we don’t need to know to in order to explain how the system works. The torque curve of an electric motor is backwards from an internal combustion engine, but it’s exactly what’s needed to pull such a huge load.

So here’s the thing: Transmissions are a hack. They’re an ugly, clumsy kludge to work around the greatest defect of internal combustion engines: poor torque management.Internal combustion engines have a narrow range of useful torque, and it’s at higher RPMs. At zero RPM, an internal combustion engine produces……zero torque.This really sucks, for a number of reasons I hope are self evident. The biggest is that an internal combustion engine must be uncoupled from its load to start moving, and gradually coupled to the load to get it going.On top of that, the narrow range of torque means that with internal combustion, torque management is the name of the game. That’s what the transmission is: a big, heavy, complex torque-management machine. All because internal combustion engines have such stupid, complex, fiddly torque-mollycoddling needs.That’s not to say electric motors never have transmissions. They can and do. But the needs are very different; electric motors produce maximum torque at zero RPM. So the needs of the transmission are quite different.A manual transmission on an electric vehicle would be a very exotic thing indeed. I can’t imagine any benefit to such a baroque thing.