• Jan 19, 2012
Automatic transmissions are found in almost every car t... Automatic transmissions are found in almost every car these days (Chrysler).
What is it?

Automatic transmissions in today's vehicles are very different from the "slushboxes" of years past. In fact, in many new cars and trucks, automatic transmissions actually return higher fuel economy than manuals. While the first automatic transmissions only had two forward gears, and even as late as the 1990's it was common to see three-speed automatics, these transmissions have been entirely supplanted by modern designs. The automatics in today's cars use computers to control when they shift, and they almost always have at least five forward gears, though six- and even eight-speed automatics are becoming the norm.

How does it work?

Inside a conventional automatic transmission, there are what's called "planetary gears," and clutches and bands, a pump and valves, and a whole lot of transmission fluid. If that sounds complicated, it is – the whole operation is actually too complex to fully explain here, but we will describe the basics.

Conventional automatic transmissions use a hydraulic fluid, the transmission fluid, to connect the engine of the car to the driveshaft as well as operate the transmission. It's this fluid that serves to transfer the mechanical energy of the engine's rotating crankshaft through the transmission. This in turn spins the driveshaft, which turns the differential, which turns the axle, which rotates the wheels of the car.

The automatic transmission is capable of changing the gears for you, which is why automatics don't have clutch pedals and you just shift the car into "D" and go. This is accomplished thanks to the torque converter, which is what actually makes the fluid coupling to the engine. It also helps increase power when accelerating, by using the difference in the rotational speed of the fluid in the torque converter versus the speed of the engine's crankshaft to multiply the torque of the engine. At higher speeds, the torque converter will "lock," that is, rotate at the same speed as the engine. This is desirable for efficiency's sake, as one of the biggest ways in which automatic transmissions are inherently less efficient than manual transmissions is because of the torque converter.

Why would I want it?

Besides not having to coordinate the clutch pedal and stick shift, which many people don't want to have to mess with, automatics often return better fuel economy today, which is a real turnabout from years past. To better understand why, we spoke with Torsten Karnahl, the general manager for product strategy at Volkswagen. He told us that there are really two ways that automatic transmissions have so dramatically improved.

The first is rather simple: With more gears in modern automatics, the transmissions are better able to match the engine's torque and power curve with what's needed while driving. Or to put it more simply, extra gears allow an engine to operate more efficiently under the same driving demand. The second way in which automatics have improved is through computer control, which not only affects when the transmissions shift, but how quickly the torque converter locks for greater efficiency. "Computer-controlled modern gearboxes let the machine do the work to decide," Karnahl told us.

He said that when comparing manual transmissions to automatics, drivers of manuals often run the engines at higher revolutions per minute, or rpms, than is ideal. This consumes more fuel, and it's one reason why cars sold in Europe are required to have a shift indicator, he said, which recommends that you shift as fast as possible into the highest gear.

Once again, computers do the job better than humans. Depressing, but true.

"There's a rule of thumb," Karnahl said, "the fewer rpms you use to move the car, the better it is for fuel economy."

Allowing a modern, six-speed automatic transmission to determine that is almost always going to produce better fuel economy than doing it yourself.

Is there any downside?

Automatic transmissions can be less durable and more costly to repair than manual transmissions. Automatics are generally considered less sporty to drive, although some modern automatics have shift-it-yourself capabilities, which can even include steering-wheel-mounted paddle shifters.

What vehicles offer it?

Almost every vehicle on the market that's not a high-powered sports car has an automatic available, and automatics are standard on most cars sold in the U.S. Manufacturers tell us that even on models they offer with manuals, about 95 percent of buyers choose automatic transmissions. That said, some automakers have been adding a "manual" version to some new cars where previously they didn't because of the image it presents. The new Buick Regal, for example, comes in a version that includes a manual shifter.

Bottom line

Being able to operate your car while you drink a coffee is great, especially when you're saving enough on gas to pay for the cup of joe.


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  • 5 Comments
      • 2 Years Ago
      I own Both autos and manuals and i would Much prefer My Manuel any day. And i say bull to autos being more efficient. All the toque converter dose is steal the horse power the car creates. and don't get me started on locking torque converters, My crown Vic has one and that is the most annoying thing in the world. its like waging war to get the damn thing to disengage, and when they go bad your screwed, i have witnessed 5 automatics go bad in 5 different cars But have never once had any issue outta manual....Ill take reliability over so called better gas mileage any day. P.S. If it dose not have a Clutch peddle Its not a manual, i can shift through the gears on my 32 year old Monte Carlo and its an automatic.
      • 2 Years Ago
      It makes me sound anachronistic when I say this, but a manual transmission really is the only way to truly enjoy (and become engaged in) the act of driving a car. I've never driven an automatic that made gear-choices that I agreed with, thus forcing me to constantly override it by moving the lever into the proper gear. People are always telling me that modern automatics (such as those found in performance cars from BMW, Porsche and Ferrari) shift gears WAY faster than a human can. To which I say "who cares?". Of course a computer & associated mechanical system can shift faster than I can - that's not the point. I'm sure a computer could steer and brake better than me too. If that's the point, why not just automate the entire car, and I'll take a nap in the back seat.
      • 2 Years Ago
      "Besides not having to coordinate the clutch pedal and stick shift, which many people don't want to have to mess with" and this is what wrong with America right there. I'm only 23 but I learned how to drive on a Manual car. Just about everyone I know has never even experienced a manual so have never had the pleasure or experience with them. Its sad the the only reason Auto's are so abundant in the US, unlike other countries, is that we are too lazy to use them.
      • 2 Years Ago
      I have come to the unfortunate conclusion that the author of this... "info blog?" has no idea what he is talking about. He says it takes to long to explain an automatic transmission (AT) and then proceeds with two paragraphs that do nothing but misinform anyone who reads it. I'm going to attempt to clear this up. There are a few different types of ATs. Most, tho, have planetary gears (consists of sun gear in the middle with planetary gears that rotate around the sun gear with an outer ring gear holding it together. Get it? Sun, planets, revolving? See? wasn't as hard as the author made it seem) which use transmission fluid to lock or unlock certain gears to output a different axle rotational speed than the input. Actually, you know what? Go to howstuffworks.com . If you are reading this, you have internet. If you have internet, then you have Google. If you have Google, then you shouldn't make a huge mistake and post such a stupid article online without doing research on sites like howstuffworks.com . No, I don't work for them. I just dislike "dumb". Let me sum up what you need to get out of this article. 1.If you find opening a "push and twist" lid on a pill bottle difficult, buy a car with an AT. 2.If you watch Jersey Shore... AT 3.If you have $1000-$1500 dollars extra that you don't want... AT 4.If you think you will only drive a MT in 1st gear all the time because you can't function at a higher level than a computer that compares throttle position, engine speed, and wheel speed ... AT 5.If you don't think you could let your coffee sit in the cup holder for 15 frickin seconds until you are in top gear and cruising before you sip it... AT 6.If you believe that "Almost every vehicle on the market that's not a high-powered sports car has an automatic available, and automatics are standard on most cars sold in the U.S." despite the fact that most high-end, high-powered sports cars have automated manuals *they don't have clutch pedals* and most not-high-end not-high-powered cars have a base model with a MT and you have to shell out money for an AT... AT 7. When someone ask, "Do you have an AT or a MT?" you say "Both" because it has flappy paddles... You shouldn't have a license. 8. If you enjoy NOT having a torque converter converting all your torque to friction; if you know you can leave your car unlocked because you know either the thief won't know how to drive a MT or you know that if he does, he would have been able to steal your car with it locked anyways; if you understand how traffic signal patterns work; if you can open a child safety pill bottle and you are fully capable of holding coffee in your left hand while driving... MT is for you.
        • 2 Years Ago
        Amen Manuel for life