Electric cars

Do electric cars have transmissions? A guide to what powers your EV

When you are driving an electric vehicle for the first time, your car may not even have a gearshift or shifter that allows you to change gears. Step on the accelerator (not the “accelerator pedal”) and you won’t feel any transmission shifting. So, do electric vehicles even have transmissions?

The answer depends on who you ask. Scan reputable automotive websites and you will find different answers, from “no transmission” To “a kind of transmission” and “single speed transmission. “Here we are going to clarify the facts and get to the bottom of what powers your electric vehicle.

What is a transmission for?

This helps define what a transmission does first. A transmission is a machine that transmits power, so in the strictest sense of mechanical engineering, every car has a transmission.

A vehicle transmission transmits rotational power from the power source, whether it is an electric motor or an internal combustion engine (ICE), through a set of gears to a differential, the unit that turns the wheels. But in common parlance, many people think of the transmission as the part of an engine that shifts gears from low speed to high speed or from forward to reverse, as in the “manual transmission” and the “automatic transmission”. This is where things get confused.

A conventional transmission

In a gasoline-powered car, an internal combustion engine must run at different speeds so that it does not stall (because it spins too slowly) or overheats (because it spins too fast). This range is roughly between 500 and 7,000 revolutions per minute (RPM). To compensate for this limitation, the transmission adjusts the ratio between engine rotation and wheel rotation by shifting between lower and higher gears.

An automatic gearbox in a gasoline vehicle.

Florin Patrunjel / Getty Images

Lower gear rotation is slower than the engine, allowing the engine to run at revs high enough not to stall. The lower gear spins slowly because it is the largest gear in size, which transfers more force but less speed to the wheels, as the gear has to move the vehicle forward from neutral.

The higher gear, on the other hand, is the smallest and works in “overdrive” which means that it spins faster than the engine, allowing the car to go at high speed without the engine overheating. In a manual transmission vehicle, engaging the clutch disengages one gear so you can shift to another. An automatic transmission does the same thing, but without driver intervention.

What is power?

The power of an engine is defined by speed and torque. Speed ​​is defined as the speed at which the motor spins, while torque is the amount of rotational force that the motor turns off. When a motor with constant power runs quickly, it loses torque. When it turns slower, the torque increases.

How does an EV motor work?

One of the distinguishing features of electric vehicles is silent, instantaneous and smooth acceleration. This is because propulsion in an electric vehicle works differently. As the names suggest, the main difference between electric vehicles and gasoline-powered cars is the source of the fuel. When you step on the accelerator of an electric vehicle, electricity is sent from the battery to the electric motor, causing it to spin quickly.

An electric vehicle gearbox.

kool99 / Getty Images

Most electric vehicles have a single AC motor (alternating current) connected to a gearbox. What is in the gearbox is what some call a transmission since it is indeed a set of gears that transmits the rotation of the engine to the rotation of the wheels. But it is more accurately called a one-speed reducer because the multiple gears in the gearbox are always connected to each other and therefore all rotate at the same time.

The speed reduction unit reduces engine RPMs to the more reasonable wheel RPMs in a ratio of about 10 to 1. There is therefore no clutch, no disengagement of gears and no gear change between gears of different sizes according to the needs of the vehicle, that is to say no transmission.

Is there a reverse gear?

Since the motor of an electric vehicle generally uses alternating current, reverse gear is not necessary. The motor simply turns in the opposite direction.

An AC motor can run from zero to 10,000 rpm or more. (The engine of a 2021 Tesla Model S Plaid can run up to 23,308 rpm, one of the reasons it can accelerate up to 200 miles per hour.) This gives EVs a lot of torque at a wide speed range, with an “ideal spot” between sufficient torque and speed. sufficient in the 30-40 mph range. Energy passes directly and almost instantly from the engine through the gearbox to the wheels rather than through a transmission, and the transition from one gear to another does not have to go from one gear to the next. other, which allows smooth and quiet acceleration.

The absence of a transmission reduces the friction (and therefore the wear) that accompanies the engagement and disengagement of several gears. Smooth transition also maintains a vehicle’s forward momentum better than shifting gears, which is one reason EVs are much more energy efficient.

Overall, an electric vehicle converts on average 77% of electricity stored in its battery to keep the car moving, while a gasoline car converts 12% to 30% of the stored energy into the gasoline in its tank. Much of the rest is wasted as heat. The transmission power of an EV’s engine to its wheels is 89% to 98% efficient, depending on the vehicle, while in an ICE car, the same process from engine to wheels is only 14% efficient at 26 %.

Can electric vehicles have multiple speeds?

Any vehicle, ICE or EV, needs more torque than speed to propel the car from neutral, and more speed than torque once the vehicle already has forward momentum. So, wouldn’t electric vehicles benefit from multiple speeds? Yes, but at the cost of a more complex system requiring more parts, more weight, more labor and a larger supply chain, in other words, more costs to the consumer, to both upstream and in maintenance.

Some new electric vehicles, including the Audi e-tron GT and the Porsche Taycan, have multiple speeds, which allows them to deliver more torque to the wheels to increase acceleration. The planned Jeep Magneto will even have a multi-speed manual transmission. Race cars like all-electric ones Formula E have transmissions also.

When electric trucks, especially 18-wheelers, hit the market, it is possible that they will have multiple gears and transmissions, but given the wide range of revs possible with an electric motor, they may have as little as two: one for torque, the other for cruising speed, with a change from one to the other at around 30 mph. (The next Tesla Semi will only have one speed reduction to one speed.) The same goes for small vehicles where the ability to tow or carry heavy loads is important.

Continuously variable transmission

Some ICEs and hybrid vehicles have continuously variable transmissions (CVTs), a form of automatic transmission that accelerates seamlessly from gear to gear, using pulleys rather than gears. CVT systems have was recently introduced for electric vehicles, which can increase torque at low speeds to accommodate heavier vehicles and loads. This eliminates the need for electric vehicle engineers to find an “ideal” compromise between torque and speed.

Greater efficiency promises, CVT systems can allow electric vehicles to increase their range, a major concern for potential buyers of electric vehicles.

Several motors rather than several gears

All-electric twin-engine Tesla Model S sedan.

Sjoerd van der Wal / Getty Images

Some EVs solve this problem by having multiple motors with different gear ratios to provide more or less torque, depending on the vehicle’s needs, with the electronics more efficiently transferring electrons to different motors rather than a transmission shifting less efficiently. . The high performance Lucid Air is available in double or tri-motor versions, for example, as many Tesla vehicles do.

And unlike the gears of an ICE vehicle, the multiple motors of an EV can be used simultaneously, giving the vehicle both speed and torque, increased traction, or greater agility. Rivian electric pickup trucks even have independent motors attached to each wheel, allowing the truck to run. “the tank turns. ”

Buckle your belt

The future of electric vehicles is open, with new ways to provide propulsion at all times. Elon Musk even promises that the next iteration of the Tesla Roadster will have a “SpaceX cold gas thruster system. “Buckle up and stay tuned.

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