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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Variable frequency drives.
You can get a multitude of speed control by handling the Hz and voltage to a motor, a VFD is essentially a transmission for a motor. Without one it will spin at a set speed based of the wiring of the poles and the voltage. A VFD and specialized motor will give you a multitude of speed control / torque
Engines have transmissions that do this.
Am electrician 🙂
Torque.
Torque is the rotational force produced by an engine. An ICE engine is converting the up and down force to a rotational force. The revolutions per minute (rpm) produce torque to spin the wheels, but it’s not a linear relationship. And thus needs a complex timing system for fuel and air in and exhaust out, up to 100 times a second.
Only a limited rpm range produces practical usable torque, and it has to go through a gearing mechanism to step down a few thousand rpm engine output to usable axle rpm. The usable rpm engine range only translates to a speed range of 20-30 mph for any gear ratio. So if you want a wider speed range you need to introduce more gearing ratios.
Electric engines produce power differently and more directly. Due to this maximum torque is available from 1 rpm. (In fact electric cars need torque regulators to hold back the engines torque, or you would just wheel spin when trying to pull off.) You don’t need to spin them up to higher revs to achieve usable torque, and you can comfortably run them up to much higher revs without causing wear.
Diesel cars might rev up to 3-4000 rpm, pertrol cars to 6000 rpm. Electic car engines can rev up to 20 000+ rpm, and all of that has usable torque. So a single gear in an electric car motor can give you a massive speed range.
It’s not easy to control the rotation of an engine as it is predetermined by the manufacturer to be of certain power. So we need to use gears to get the control of the rpm(s).
But in electric motors, you can just use more current or less current to vary the rpm(s). Also, you can go reverse by just inversing the current.
My Nissan Altima is gas powered and has a trans with 1 forward gear, so I assume this isn’t correct.
Internal combustion engines (ICEs) have to spin at a minimum speed just to overcome the overhead of the engine (pistons moving back and forth and friction). Dropping below the idle speed will cause the ICE to stall. On the other end, and ICE can only go so fast before there’s a dropoff in output power. Remember that an ICE runs due to little explosions in the cylinders that push the pistons back. An explosion is really fast, but when a normal engine starts running around 5000RPM the speed of the explosions and the speed of other moving parts is no longer fast enough to keep up and there’s a drop in output power. Finally, an ICE can only work in one direction.
In order to overcome these limitations, a transmission is added between the ICE and the power output. The transmission allows the engine to continue running even when the vehicle is stopped via a neutral gear or a clutch that disengages at low speed. It has a set of gearings that allow the ratio of engine speed to wheel speed to change so that as the vehicle goes faster the engine can “reset” and go to a lower RPM, keeping it near its optimal RPM.
Electric motors and steam engines don’t require a transmission because their range is much higher (but not infinite) and they actually have maximum torque when not moving.
I would also note that not all transmissions are mechanical. Diesel train engines use an electrical transmission. The ICE turns a big electrical generator which in turn powers motors in the drive wheels. Same concept.
Gas only explodes at one speed; its usefulness in a variable speed engine is only optimal at one specific RPM, and is ineffective outside a particular range. So transmissions had to be invented. OTOH, electric engine speed varies linearly with voltage (though creating that voltage, a separate issue, eventually becomes impractical).
Combustion engine Torque is very variable. you tend to start with little and gain and then after some engine speed that torque drops off. In simple terms, Torque is what makes your car move, HP is what keeps it moving. HP is basically Torque as a specific RPM. An ICE can only spin so fast (most cars top out around 6k rpm, some get into the 8-10k) but with those moving parts going up and down and converting that up-down to rotational movement, there are limits. First gear converts the lacking torque using mechanical advantage so that the torque is multiplied but the revolutions is divided in the same way so you get the torque needed to get the car moving but only can spin the wheels up to say 15 mph. You shift to 2nd gear and you have less power but now you can rotate the wheels faster, up to 60 in a lot of cars (or at least used to mostly so they can minimize their 0-60 times as shifting is a penalty). This goes on for each gear. Eventually though you can’t go faster as you don’t have enough HP to overcome wind resistance.
Electric Motors have massive amounts of Torque that is the same from 0-XXXXX RPM. They also can spin 20k RPM+. So they have what is needed to get them started and because HP is torque * RPM / 5252. Because torque doesn’t drop and RPM just keeps going up they can keep moving. This is also why tesla’s tend to be speed limited to 150mph. (the new model s plaid motor can spin to 23k RPM).
This isn’t true of all electric cars as the Porsche has 2 gears. Transmission means weight and complexity though which electric cars would like to avoid.
Electric motors produce 100% torque from 0 RPM. Thats why we have diesel electric locomotives that can pull a tens of thousands of tons of train from standstill. The diesel engines power generators to create the electricity for the electric motors.
Diesel or gasoline engines deliver torque through a narrow RPM range so a gearbox is needed to utilize the right RPM range to maximize the corresponding torque.
Lots of jargon in the responses. Think the real eli5 is there’s a very tight range where energy can be extracted from the fuel. This is due to the fuel itself, the size of the combustion chamber that takes a certain mic of fuel and air, and the engine characteristics. This is different from an electric motor which can use a wide range of electrical power inputs.
Most of the reasons have already been touched upon by previous answers, but they all have failed to mention two things, which are essentially one: ICEs have an idle RPM and ICEs do not have start-up torque.
Internal combustion engines not only have a thin RPM range, where they are the most efficient, but looking at their [torque curve](https://images.cdn.circlesix.co/image/uploads/posts/2016/08/58863cb65bd5ff6ed7edb03f419b51c6.gif), you can see that it does not even start at 0 RPM. These engines would not be able to start on their own, they need the help of a small electric motor to turn the crankshaft first and then they also have a lower limit of the RPM, which they need to reach to maintain operation.
This means, that when you are stationary with your car, the engine is already spinning at around 1000 RPM and if you want to start moving, you will have to raise that closer to 2000 RPM, whereas the tires as still not rotating. Oversimplification: if you were to magically connect the crankshaft to the axles at this point, your wheels would suddenly start moving by the exact same RPM as the engine. You need something to reduce the RPM of the engine all the way to 0 and gradually increase it.
This something is your clutch and gearbox. The gearbox allows you to reduce your engine RPM (or increase in higher gears) and the clutch allows you two things: break the connection between the engine and the wheels, and transform some of the power of the engine to heat when you are starting. By using them, you are able to rev your engine to the required RPM to produce enough power to start your car moving, while enabling you to transmit the power from the crankshaft to the wheels.
In case of an electric motor, you can see on the [torque curve](https://qph.fs.quoracdn.net/main-qimg-f9aa7087e83644467a9f274594a304da) that there is maximum torque even on 0 RPM, which means that electric motors are able to start rotating on their own and do not require the help of complicated mechanical assemblies to match the RPM of the shaft of the motor and the wheels.
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