Types Of Automatic Transmissions: What’s The Best?
With different types of automatic transmissions available today, they are slowly, but steadily, gaining popularity in India. We can thank two things for the change: traffic and technology.
The traffic is getting worse and we’re all looking at ways to relive our left set of limbs. The technology has gotten better now and we can expect automatic transmissions to be fairly responsive.
Fuel efficiency was another area where the automatics fell far behind their manual counterparts. Today, they either beat or match their manual siblings in the km/l area.
Contents
There are basically five types of automatic transmissions
- Torque Converter
- Continuously Variable Transmission
- Dual-Clutch Transmission
- Automated Manual Transmission
- Koenigsegg’s Light Speed Transmission
Torque Converter
Also referred to as slushboxes or conventional automatics, these are the oldest of the lot and responsible for ruining automatics for India.
They sap power from the engine in two ways: 1. they’re heavy and 2. they transmit power through the fluids. Getting fluids in motion is a demanding task and this is what earned it the nickname ‘slushbox’.
The whirlpool causes the turbine to rotate transmitting the power to a conventional set of gears via a friction clutch.
They do stand out in heavy-duty circumstances as the toroidal motion of the transmission fluid can get the car moving even on an incline with a full load. They’re also called ‘torque converters’ because of their ability to push out more torque at the wheels to get them rolling.
They have been around for the better part of the last century. The main part of the torque converter includes fluid coupling, which doesn’t contain gears rubbing against each other thereby minimizing wear for the automatic transmission. Just replace the transmission fluid timely and you should be able to keep the car around for more than 5,00,000km.
Fuel Efficiency: 5/10 Drivability: 7/10 Reliability: 9/10 Examples: Honda Brio, Toyota Corolla Altis, Hyundai Grand i10
Geek out on this Torque Converter Video
Continuously Variable Transmission
CVTs are relatively new and haven’t had enough time to prove their reliability. In a CVT, there are no gears but there’s a belt connecting two pulleys.
The variation in engine speed and wheel speed is managed using the pair of pulleys that can change their diameter. This allows the car to have infinite ratios that keep changing quite frequently. Hence the name, ‘continuously variable transmission’.
Internal combustion engines aren’t very efficient. They offer their best efficiency (and longevity), best acceleration (power) and best hauling ability (torque), at three different RPMs. This is where the CVT shines by getting the engine RPM to where it needs to be based on the requirement and then keeping it there to give the driver what he wants.
This is also where the CVTs stutter because of the infamous ‘rubber band’ effect. Say you’re cruising at 80km/h with engine speed at 2000RPM and decide to floor it. The engine will first reach its performance RPM zone while the ratios are dropped to maintain the speed and keep the belt from breaking.
Then the transmission will gradually alter the ratios to give you the acceleration you desired two seconds ago. Seeing the engine speed increase without any serious change in the actual speed has kept it out of the view of performance-hungry buyers.
CVTs are very fuel efficient and also very light. The transmission fluid needs to be changed roughly 50,000km compared to slushy’s 1,00,000km. Other than that they don’t need any serious maintenance for up to 2,00,000km. Hyundai launched the latest i20 with CVT automatic gearbox
Fuel Efficiency: 7/10 Drivability: 7/10 Reliability: 7/10 Examples: Nissan Micra, Maruti Suzuki Baleno, Honda City
Informative video about CVT Transmission
That’s the basics of how a CVT gearbox works. CVT gearbox can be segmented further into 2 types:
Belt-type CVT
Belt types CVT is also called “push-type”. In this, the belt is clamped in the pulleys with pressure reaching as much as four tons. The belt is then pushed through its circuit by the pulleys. The compression loads on the belt’s individual plates will vary according to the engine size. But it’s quite high, starting at 550 kg for a small four-cylinder engine.
The limiting factor for this system is that it can’t handle heavy torque. The clamping force is so high that the belt might break if used with a big powerful engine.
Chain-type CVT
This works on the same principle as above but instead of a belt, it has a chain (usually made by German manufacturer, Luk). The chain is held together by multiple pins and it also acts as a contact surface for the pulleys.
The chain is pulled through the circuit by the engine pulley and hence, it’s also called “pull type” CVT. For high power engines, chain type CVT is quite successful in handling the torque. Audi A4 uses this type of CVT system.
Dual-Clutch Transmission
This is for those who care about nothing but speed and 0-100km/h times. A dual-clutch gearbox will give you acceleration figures no Schumacher can match with a manual.
There are two clutches, one for odd numbered gears and another for even numbered. Every time you change a gear, there’s a loss of power during the upshifts. The twin-clutch setup eliminates that loss by keeping the next gear ready to be engaged.
So, when you’re in first, the transmission is ready to slot the car in second with the clutch already engaged. When you’re in second, the odd clutch for third gear is engaged and ready to deploy. Just disengage the even clutch and you’re good to go onto the higher gear.
Technically speaking, dual-clutch automatics fall under the automated manual transmission (AMT) category. The main difference is that the dual-clutch automatics have two clutches instead of one.
These are very advanced and require a heavy investment for research and are, therefore, very pricey. Volkswagen group cars prefer using dual-clutch transmissions for a thrilling drive and impossibly quick acceleration. Of course, their punchy engines also co-operate.
However, they don’t handle too much torque very well. That’s the reason why high-performance cars like Audi RS7 and Lamborghini can’t use twin-clutch gearbox even though they are more responsive.
Fuel Efficiency: 8/10 Drivability: 10/10 Reliability: 6/10 Example: Ford Figo, Volkswagen Polo GT TSI and Ameo
Know how DSG Gearbox works in this video
Common DSG gearbox Problems:
DSG gearbox is fantastic to use but their complex nature can make it problematic in some cases. Various automatic transmissions have their unique problems. These are some issues that several owners have experienced with DSG transmissions:
1) Mechatronic Failure: Mechatronic unit is unique to the twin-clutch gearbox and this sometimes fails. When it does, the car goes into limp mode and often stuck in single gear as a preventative measure. The issue can be fixed simply by changing clutch pack or resetting adaptation through diagnostics tool. But sometimes, the damage can be severe and requires complete replacement of the mechatronic unit.
2) Juddering on idle: The car can start vibrating and juddering at idle due to a worn out flywheel. Flywheel basically softens the gearchanges and makes the ride smooth. One the flywheel wears out the gearshifts can become clunky. It’s better to replace the flywheel if this issue is found as it can potentially damage the internals of the DSG gearbox by increasing stress.
3) Worn Bearings: The internals of DSG gearbox is quite robust so if you notice metallic noise from the transmission, it’s probably the worn out bearings.
Automated Manual Transmission
The AMTs were born out of the sheer need to make automatic cars affordable and fuel efficient. The Maruti Suzuki Celerio was the first one in India to come with an AMT and the market accepted them with open arms.
This led to the launch of a whole batch of AMT cars. Tata Zest, Nano, Renault Duster, Maruti Alto K10, Swift Dzire now offer AMT. But believe it or not AMT gearbox was also seen in BMW M performance cars in the past. Read: Nissan Terrano is recently launched with AMT gearbox
AMT transmission is quite simple and affordable. They’re also not very expensive to repair should something go down south. Fuel efficiency is their top priority and they do deliver.
AMTs are the newest to enter India and it’s unclear what our traffic and climate can do to them. The driving experience of an AMT car comes with a mixed bag of reactions. They’re slow to respond and you can forget about covering those gaps in traffic the way you do with a manual. There’s no clutch lever accessible for you to ‘dump n jump’. The gear selection tuning gives priority to the fuel-efficiency, so you’ll always find yourself in a higher gear.
Cruising in automatic mode is comfortable though. To get the best out of an AMT, switch to the Tiptronic mode and choose the ratios yourself. If the revs are too high or too low, the car will take care of it. This makes it much more livable and you’ll appreciate the convenience if you can’t drive stick. Kwid AMT is doing very well in terms of sales
Fuel Efficiency: 9/10 Drivability: 6/10 Reliability: 8/10 Examples: Tata Nano, Renault Duster, Maruti Suzuki Alto K10, Swift Dzire
Check out Maruti Suzuki’s AMT Gearbox
Koenigsegg Light Speed Transmission
The transmission requirements of a hypercar are different than regular cars. The gearbox should be able to handle a lot of torque, should be lightweight and should also shift gears fast.
These challenges pushed Koenigsegg to develop a proprietary transmission system called the “Light Speed Transmission”. While its earlier generation hypercar made use of DCT transmission, the latest 2019 Jesko pushed so much power that it needed something more durable for 1600 Nm of torque.
Just wrap your head around it: V8 powered supercars from Ferrari, Lamborghini, or Mclaren makes under 800 Nm of torque.
Koenigsegg Light Speed Transmission is lighter that DCT gearbox, has integrated starter motor, clutches, and flywheel. And it weighs just 90 kg. It also has an advantage of transitioning between any gear straight away. This makes it lightning fast, that’s how it gets its name.
Christian von Koenigsegg said: “In many ways, it’s very simple. We have eight actuators and eight pressure sensors. One for each hydraulic clutch. There are seven clutches, but there’s an eighth for the electronic differential. We carry that over from the Agera RS. And then there’s one actuator for reverse, and six for the forward gears, on three shafts. So, two clutches per shaft. That makes it possible to mix and match three gears in pairs.”
What’s The Best Automatic Transmission?
There are numerous automatic cars in India. So, what type of transmission is best for you? The conventional automatics can play with a good amount of torque. The technology is dated and they’re not the best option you can pick today.
They do offer decent drivability, although, fuel efficiency is not their strong point. Dual-clutch transmissions are for the Mr. Lap Time. Fuel efficiency is also respectable but they have had problems dealing with the Indian climatic conditions. It is a complex system with several moving components with mechatronics, so when they fail, it’s expensive to repair them.
AMT gearbox brings the joy of driving an automatic with simple mechanicals. Green Goblins can rejoice with improved fuel efficiency that’s at par with their manual counterparts. Be prepared to make way for others as the drivability won’t be as good and you’ll often find yourself in the wrong gear at the wrong time.
Koenigsegg Light Speed Tranmission is yet to be tested properly in the real world condition and at large scale. On paper this simple solution looks amazing but this system it yet to trickle down to regular cars.
Overall, the best variety of automatic appears to be CVT, which doesn’t excel in any area but also doesn’t fail miserably in any either. It offers a good mix of efficiency, drivability, and reliability. Just don’t expect to lead the pack when the lights turn green as they’re not designed to handle a lot of power. Now you know what to say when someone asks: what are the different types of automatic transmissions and which one is the best?
What's better? CVT or DSG Gearbox?
CVT excel in terms of smoothness and reliability. DSG gearbox offer fast gearshift and sportier drive.
Also See: Different Types of Manual Gearboxes
Also See: Collision Prevention: What companies are doing?
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