Cooley On Cars
Your emails: Why don't electric cars have geared transmissions?Brian Cooley explains why EVs lack geared transmissions and how these automobiles deliver power and torque.
Hey folks, Brian Cooley from OnCars, taking another one of your emails about high-tech cars and modern driving. This one comes in from Carson C. who says, I've noticed that a lot of electric cars like the Nissan Leaf or a Chevy Bolt that's on the way, don't have geared transmissions. Why is that, he says, and would it be an advantage for them to have one in those cars? Okay, well, Carson, the reason the electric cars don't have transmissions, is because electric cars have electric motors. Electric motors deliver power and torque very differently than a combustion engine and frankly they don't need so much of a crutch, which is really all a transmission is. An electric motor has so much torque almost from one RPM it does need to rev up. To get a lot of torque, which is what really moves the car. As a result, it doesn't need a little stump-puller, low first gear to get going. The second thing is, the electric motor has a very wide range of RPMs and functions. Much wider than your average combustion engine. As a result, it doesn't necessarily need second, third, fourth. To allow it to have to hit a sweet spot. It has a great big fat sweet spot, and therefore needs fewer gears to focus on a certain range of RPMs. Let me give an example here. Here's a chart of an electric car versus the combustion engine car. As you can see from the very beginning, the electric car has. Gobs of torque from almost zero RPM where the combustion car has to rev up to get to its torque peak. Now, both begin to peter out in terms of their peak torque as you get in to the mid-thousands of RPMs. At this point the combustion engine is done revving and about to hit red line and blow apart, and then it's got to go down, catch a gear, and rev back up again. That's where the electric motor car can typically just Keeps revving for thousands more RPM. So there's two big reasons the electric car doesn't need a whole smattering of gears. A wide, fat band of torque up here, and a whole lot of RPM range, even beyond that. Two Major ways that it can dispense with most gears. Most electric cars will have a just a very simple, planetary reduction to match RPM to road wheel, but that's not the same as a big old six, seven, eight, nine, ten gear box.