What is an Automatic Gearbox? How Does it Differ From a Manual?
On the surface, we might feel as though we all know what the difference between a manual and automatic transmission is. We know which cars are automatics because they have a prominent central gear shifter that moves between P, R, D, N, and so on. A manual, on the other hand, has a gear shift that moves between different gear ratios, first, second, third, reverse, and so on.
There may be a great deal of surface information that we know about the differences between automatics and manuals, but do you know in more detail what an automatic gearbox is and how it works? Do you know how those workings are different from those of a manual? Did you know that the automatic gearbox is actually a much older invention than you may have first thought? These questions and more we will try to answer in today’s blog.
What is an Automatic Transmission?
The term automatic transmission is sometimes abbreviated by mechanics to simply “AT” and refers to any multi-speed automotive transmission that works without drive input when shifting between different gear ratios. Currently, automatic transmissions exist in a number of different forms, the most common of which is known simply as the torque converter. For many years, this has been the industry standard.
Besides torque converter transmissions with their planetary gearset and hydraulic controls, there is an ever-increasing variety of automatic options out there, such as:
- Continuously Variable Transmission or CVT – Common in hybrid cars and entry-level sedans, especially Japanese brands such as Toyota.
- Automated Manual Transmissions or AMT
- Dual-Clutch Transmissions or DCT – A high-end alternative to both torque converters and CVT units, found most often in top-level trims and sportier car models
How Does it Work?
For this explanation, we’ll focus on the torque converter model since that remains the most common form of automatic transmission out there. Other systems work on the same principles but with some changed components within. An automatic transmission is made up of three key parts, namely:
- Torque Converter – Arguably the most critical piece of the puzzle, and the key technological breakthrough that made the entire idea possible in the first place. A torque converter is what replaces the mechanical clutch in a manual, enabling the engine and driveline to connect and disconnect as needed.
- Planetary Gears – These are the gears that shift in order to allow your car to safely and comfortably access higher speeds. They are constructed differently to the typical gearset of a manual car, instead using planetary gears controlled by hydraulics.
- Clutches and Brake Bands – These components are like binding and connecting forces that keep the transmission working, allowing the gear to spin, gear ratios to be shifted, and more. They are the “actuators” of the entire transmission system.
When you’re driving an automatic car, you typically start with the gear shifter in “P” which of course stands for park. This secures it in place and ensures that it won’t roll off anywhere. When you want to move the car, you move it either into “R” for reverse, or “D” for drive. When you’re in “D” the system is active and we can start to see gear shifting.
Let’s say you’ve reversed out of your parking space, and now you’ve put the car in “D” and are ready to go. You place your foot on the accelerator, setting the engine’s crankshaft into motion, and thus you’re on your way. Pressing on the accelerator causes the crankshaft to rotate more rapidly, which in turn creates added pressure within the torque converter. The car’s on-board computer and electronics can sense both the car’s speed and its engine speed, which prompts the clutches, bands and hydraulics to begin shifting gear ratios to match it.
It used to be that the automatic transmission could only rely on hydraulics to sense those changes in speed, and those systems were indeed a lot more clunky overall and less efficient in getting the car to the right gear ratio. Thanks to the electronics and computing revolution that has since occurred, we can now make automatic transmissions that are so seamless and smooth, that they are actually as if not more efficient than manual cars.
When Was the Automatic Transmission Invented?
When asked about the history of automatic transmissions, most people might only think back to the 1950s or 1960s, but in fact the automatic gearbox is about as old as the automotive industry itself. The first proper automatic transmission is thought to have been the 1904 Sturtevant “horseless carriage gearbox” which was developed in Boston, Massachusetts. As revolutionary as it was, the system was notoriously unreliable and prone to the most sudden and terrible failure.
It was the invention of planetary gear sets for manual transmissions that would prove decisive in the evolution of automatics. By 1923, a standardised design had been generated and patented by Henry R. Hoffman, and the automatic transmission was born. While some contend that it was Canadian Alfred Munro whose patent was the first true automatic transmission, they are wrong because Munro used a compressed air design, not a hydraulic fluid design, which was nowhere near as powerful, and found no commercial application.
One reason people think that automatics only go back to the 1960s is because that’s when they really started to expand. Improvements to transmission fluid, and the introduction of electronics meant that from 1965, gear ratios on automatic models (previously very limited) could now be expanded.
What Are the Differences Between Automatic and Manual Cars?
Besides the aesthetic differences, there are a number of other things to note when comparing the two types of vehicle.
- Fuel efficiency – While some modern automatics like DCT systems have greatly narrowed the gap between manual and automatic, the general picture remains that manual cars are more fuel efficient
- Cost – The price of automatic cars remains higher than those of manual cars. The increased complexity of the transmission adds to production costs, and makes the car heavier, too.
- Complexity – A manual car is infinitely more straightforward than an automatic, to a mechanic, at least. Maintenance and repairs on automatics are thus much more difficult to get right.
- Care – Your automatic car tends to need more attention paid to the transmission fluid, as well as to the appearance of overheating or strange noises. The expense and complexity of the system mean that all problems must be addressed as early as possible.
While there are indeed some downsides to owning an automatic, none seem to detract enough from the bigger reasons that push people to buy them, namely their comfort and convenience. When you’re in traffic, the “creep” mode that moves you forward very slowly is a welcome break from tapping on the accelerator for microseconds at a time. It’s also nice not to have to keep switching between first and second, first and second, as you do when driving a manual in traffic.
Automatic transmissions have made driving easier for millions of people, and now that they’re getting more efficient, and even sportier, people are opting for them more and more instead of manual cars. Even now, the UK has become a nation that adopts new automatic cars more than new manual cars.