So trying to figure out why electrical engine only needs a single gear while a combustion engines needs multiple gears. Cant wrap my head around it for some reason
EDIT: Thanks for all the explanation, but now another question popped up in my head. Would there ever be a point of having a manual electric car? I’ve heard rumors of Toyota registering a patent for a system which would mimic a manual transmission, but through all this conversation I assume there’s really no point?
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Electrics motors typically have a relatively linear torque curve, starting at maximum torque (at 0 rpm), and tapering down to zero at their maximum RPM. This greatly reduces the need for selectable gearing, so long as you have sufficient starting torque and adequate high-RPM torque to reach maximum vehicle speed.
In fact, there may not be a need for gears at all, though I think it’s more common to use a single reduction gear to make better use of available power. e.g. ballpark 8:1 or 9:1 on a modern Tesla, which is in the ballpark of a typical transmission’s first gear * rear end ratio (e.g. 2.88:1 * 3.08:1). The motor can also turn ~23000 rpm, about 3-4x faster than a typical ICE unit.
So, how do CVTs (continuous variable transmission) work/relate?
To add to other answers: reciprocal mass is a problem in a gas engine that simply doesn’t exist in electric motors.
In a gas engine, to spin faster, pistons and valves must move up and down thousands of times a second. every time the piston and valves reach the end of their travel, all of that mass has to come to a stop, and then accelerate in the opposite direction, taking dozens of Gs of force. At a certain point, this force becomes so high that the rods holding them will break, and pistons will fly out of the engine.
Take your arm and move it up and down slowly, notice how much effort it takes. Now do it as fast as you possibly can, notice it takes a significant amount more to move. Your engine is doing this thousands of times a minute and the rods inside it (your bones in this case) can only take so much force before they just simply break. If you were capable of faster movement, you would be able to break your bones if you moved your arm too fast back and forth. Your engine has this happen to it too when forced to spin too fast.
None of this is a problem in an electric motor. When a motor runs, it is a circle spinning faster and faster, like a wheel. There is no mass that has to come to a stop and change direction every cycle.
I’ve read all answers and all good, I can understand that an electric engine can produce a very high torque when starting.
But still. Wouldn’t it be more efficient to have a gearbox on cars? That’s actually what happens on electric bikes. It’s good to put a low gear for starting up, else you feel the motor is struggling, and torque is not enough to give you a good acceleration. Why it’s not the case for electric cars?
Think of a bike, if the gearing is too low, you’ll over-work your legs to move a tiny amount. If it’s too high, it’ll be super hard move at all. Instead, you start moving at the low gear, and as you pick up speed, you gradually work your way up. The key is that the whole time your legs are pedaling at just enough resistance that maximizes your power. That’s exactly what your engine is like, there’s a narrow window where it “digs in” the same way your legs dig into bike pedals.
Electric motors aren’t like this, their torque curve is flat. It’s on or off, no in between.
HOWEVER
there are some race cars that have electric motors with transmissions, I’ve seen a two gear, but I’m sure there have been experiments with more. Basically one gear is normal driving, and there’s an overdrive gear that raises the top speed without overheating the motor through gears.
Petrol engines have a narrow rev range where peak torque is produced. Electric engines have a flat torque curve (equal torque at all rev ranges).
For your edit question: there is no real reason to add a manual. It is solely for the end user to feel satisfied.
You need the most wheel turning power (torque) when the car starts moving.
The problem with gas engines is they make the most torque at a specific spinning speed (rpm) thats pretty fast. And they can’t work at all when they’re not spinning (0 rpm). Gas engines are actually started by a small electric motor so you don’t have to start it by hand. they need gears to keep the engine at a good spinning speed even as the wheels change spinning speed. You also need something to allow the engine to keep spinning when the car is stopped (a clutch in manual transmissions, a torque converter in automatics).
Electric motors, on the other hand, have the most turning power (torque) when not moving and it slowly fades as it spins faster. This is exactly what cars need so you can hook the motor directly up to the wheels (or often with a simple non-changing gear ratio to make the motor as happy as possible).
EDIT: I don’t know about Toyotas patent, but from a purely functional standpoint a manual transmission would be useless AFAIK. I suspect it’s more of a fun gimmick for those of us that enjoy the feel of a manual transmission. But I could be wrong.
Limitations of combustion engine design due to maximum engine speed and lowest engine speed is why they have multiple gears.
Maximum engine speed is just we cant go to very high rotational speeds due to the way that combustion engines operate. So to be able to keep speeding up the vehicle, you need to have different gears so that you keep the engine speed at a safe operating level.
Limitations of low engine speeds is due to the engine needing a minimum of approx 1000 rpm plus gearing to provide enough torque to move the car. IE. Low gears on a car.
Electric motors have maximum torque at 0 rpm, so you don’t need additional gearing to provide torque to move the car from stationary. IE. The reason for gearing at low RPM on a combustion engine.
For high rpm, the design of electric motors have the moving parts all rotating in the same direction instead of the up and down motion of a piston in a combustion engine. This allows an electric motor to safely rotate at higher speeds than a combustion engine, hence not requiring mutiple gears to stay within a safe operating engine speed.
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