Without getting too much in to the technical details of how each transmission works, I am going to focus on the performance aspect and which one I prefer.
If you are looking to know how different transmissions work, just use a search engine and you will find plenty of explanations.
As an overall package of performance, reliability and maintenance, the conventional automatic transmission, know as the torque converters, or slush boxes, are my preferred choice. Torque converters have been around since the time automatic cars first came equipped with auto boxes. For this reason many people believe that this is old and out-dated technology. They couldn't be more wrong.
Screen memory would leave permanent imprints on the tv screen even when the unit was switched off. Let's say you watched HBO a lot. So the logo of HBO that always shows in the corner would get permanently imprinted on the screen and would show faintly even when the tv was powered off. Of course this took a long time to happen. The old plasma screens were also heavier and guzzle more electricity.
But over the years most of these 'defects', if you can call them that, were greatly improved upon. They no longer had the screen memory problem that in earlier models could leave a permanent pixel mark on the screen. They became much more power friendly. And lighter. And yet, they have all been replaced by the 3 times more expensive LED televisions, even though they have picture quality issues of their own. Yes, they are lighter and thinner and save some power. But you are still paying 3 times the cost of a plasma.
I'm getting diverted. The point here is that the torque converter technology old, but it is a work horse. There is a reason why it has been around for all these many years and it has improved greatly over the years. In fact it is the only 'proven' automatic transmission out there. We are still waiting to see how the others like dual-clutch and the CVT hold out in the long term. Even though people have successfully managed to put a few hundred miles on their cars with these transmissions as well, there are other issues. We will talk about them.
Okay, I said I wouldn't get into the technicalities, but if you must know, a torque converter works by transferring power from the engine to the wheel through a fluid. The simple explanation is that the two ends, that is, the engine and the wheels are not directly connected. There is a turbine attached to the engine that churns the transmission fluid in the gear box. On the other side if the gear box is another turbine connected to the wheels. This turbine rotates with the churning transmission fluid and since there is no direct contact with the transmission end, there is some loss of power in the fluid.
The newer cars have sophisticated computers and more sophisticated torque converters that handle power transmission better, removing the loss of efficient to about 10%.
At high speeds there is virtually no loss of power in the transmission because almost all torque converters are now equipped with something called the 'converter lock up' mechanism.
When the car is moving at uniform high speeds, the two turbines that usually rotate the other through a fluid actually make contact and lock into each other, making the transmission behave like regular clutch.
More good things about the torque converter automatic transmissions.
They are robust, perhaps the most reliable and the hardest working of all transmissions. Like I said, they are proven work horses.
The shifting between the gears is smooth. You can blame the transmission fluid for this. Since there is no direct contact between the transmission and the engine, the fluid absorbs some of the jerks making the gear changes muted and soft. While the dual-clutch transmissions have lighting fast gear changes making them super smooth at high speeds, they can lurch when moving in slow moving traffic or when trying to park in tight places.
They are easier and cheaper to maintain. When and if you even need a transmission repair, you are going to thank your wisdom in having an automatic car with a torque converter as opposed to other kinds. The cost of repairing a dual-clutch transmission can be an bafflingly large sum, where you might find it more feasible to purchase a new vehicle all together. To make things more sinister, those kind of transmissions have more chances of failing as well.
So torque converters check almost all boxes for an automatic transmission. And yet, we have others.
Let's tackle the Cvt transmission next.
By varying the size of the wheels, the transmission is made to rotate the wheels faster or slower. It's just like gears on a bicycle except that there is just one gear or cone over which the belt / chain runs. This single cone becomes bigger and smaller.
You must have heard of the famous 'rubber band effect'. It can be very less in modern vehicles with advanced CVT's, but it is very much there. The car doesn't feel like it's changing gears. The engine drone is constant. And if you like the feel of how a car typically catches speed, you will find CVT's to be dull. I thought this was an exaggeration when I read other people complain about this nature of a CVT transmission, but I know better now.
Car manufacturers are fighting this resistance by introducing fixed steps in to the CVT transmission. In stead of the limitless gear ratios, they are being programmed to replicate the behaviour of conventional automatics. So the question arises, if we want the CVTs to behave like other automatics, why are they being made in the first place. There are a couple of reasons for doing that.
Secondly, it's not a bad transmission altogether. You see, in theory, it is supposed to be more fuel friendly and therefore more eco-friendly. And it also has it's driving advantages.
A CVT transmission is able to hold you in the power band RPM of the engine. This is very useful in situations like climbing hills. It is also no doubt smooth and you feel no gear shifts, because there are no gears to change. These transmission are light, easy to build and no so expensive to repair. Most of the time, the only replacement required is the belt or the transmission chain, and while it is not a cheap component, it is not all that expensive and is quickly and easily replaced.
So if the car manufacturers can somehow do away with the listless behaviour of the CVT, its pretty good to use. I have not driven a car with a stepped up CVT like a 7 step CVT transmission, so I can't comment on how well those drive.
If you are looking to know how different transmissions work, just use a search engine and you will find plenty of explanations.
Torque Converter Automatic Transmission / Slush Box / Conventional Automatic Transmission
As an overall package of performance, reliability and maintenance, the conventional automatic transmission, know as the torque converters, or slush boxes, are my preferred choice. Torque converters have been around since the time automatic cars first came equipped with auto boxes. For this reason many people believe that this is old and out-dated technology. They couldn't be more wrong.
Torque Converter Autos Are Not Outdated
Not all old technology is out-dated and 'not-so-good' as the newer replacements. And older technology is liable to improve over the years with research and development. Televisions are a great example. The original plasma tv's had great picture quality, the best in fact. Nothing comes close to the picture contrast and the black points of those screens, even today. But they were plagued with a few defects like screen memory.Screen memory would leave permanent imprints on the tv screen even when the unit was switched off. Let's say you watched HBO a lot. So the logo of HBO that always shows in the corner would get permanently imprinted on the screen and would show faintly even when the tv was powered off. Of course this took a long time to happen. The old plasma screens were also heavier and guzzle more electricity.
But over the years most of these 'defects', if you can call them that, were greatly improved upon. They no longer had the screen memory problem that in earlier models could leave a permanent pixel mark on the screen. They became much more power friendly. And lighter. And yet, they have all been replaced by the 3 times more expensive LED televisions, even though they have picture quality issues of their own. Yes, they are lighter and thinner and save some power. But you are still paying 3 times the cost of a plasma.
I'm getting diverted. The point here is that the torque converter technology old, but it is a work horse. There is a reason why it has been around for all these many years and it has improved greatly over the years. In fact it is the only 'proven' automatic transmission out there. We are still waiting to see how the others like dual-clutch and the CVT hold out in the long term. Even though people have successfully managed to put a few hundred miles on their cars with these transmissions as well, there are other issues. We will talk about them.
Historical Drawbacks and improvement in torque converter technology
One of the main complaints against torque converters was poor fuel mileage as compared to manual transmissions. This has been corrected to a large extent with the help of new technology like converter lock-up, that makes the converter behave like a regular clutch and does away with the loss of power through the transmission fluid.Okay, I said I wouldn't get into the technicalities, but if you must know, a torque converter works by transferring power from the engine to the wheel through a fluid. The simple explanation is that the two ends, that is, the engine and the wheels are not directly connected. There is a turbine attached to the engine that churns the transmission fluid in the gear box. On the other side if the gear box is another turbine connected to the wheels. This turbine rotates with the churning transmission fluid and since there is no direct contact with the transmission end, there is some loss of power in the fluid.
The newer cars have sophisticated computers and more sophisticated torque converters that handle power transmission better, removing the loss of efficient to about 10%.
Converter Lockup
At high speeds there is virtually no loss of power in the transmission because almost all torque converters are now equipped with something called the 'converter lock up' mechanism.
When the car is moving at uniform high speeds, the two turbines that usually rotate the other through a fluid actually make contact and lock into each other, making the transmission behave like regular clutch.
More good things about the torque converter automatic transmissions.
They are robust, perhaps the most reliable and the hardest working of all transmissions. Like I said, they are proven work horses.
The shifting between the gears is smooth. You can blame the transmission fluid for this. Since there is no direct contact between the transmission and the engine, the fluid absorbs some of the jerks making the gear changes muted and soft. While the dual-clutch transmissions have lighting fast gear changes making them super smooth at high speeds, they can lurch when moving in slow moving traffic or when trying to park in tight places.
They are easier and cheaper to maintain. When and if you even need a transmission repair, you are going to thank your wisdom in having an automatic car with a torque converter as opposed to other kinds. The cost of repairing a dual-clutch transmission can be an bafflingly large sum, where you might find it more feasible to purchase a new vehicle all together. To make things more sinister, those kind of transmissions have more chances of failing as well.
So torque converters check almost all boxes for an automatic transmission. And yet, we have others.
Let's tackle the Cvt transmission next.
CVT Transmissions
CVT transmissions do not have gears. They run with the help of a belt. The engine end and the transmission end are two wheels or cones that are attached with a belt. Again, this is a simplistic explanation. Do a search for more detailed explanations.By varying the size of the wheels, the transmission is made to rotate the wheels faster or slower. It's just like gears on a bicycle except that there is just one gear or cone over which the belt / chain runs. This single cone becomes bigger and smaller.
The rubber band effect - Main fallout of the CVTs
You must have heard of the famous 'rubber band effect'. It can be very less in modern vehicles with advanced CVT's, but it is very much there. The car doesn't feel like it's changing gears. The engine drone is constant. And if you like the feel of how a car typically catches speed, you will find CVT's to be dull. I thought this was an exaggeration when I read other people complain about this nature of a CVT transmission, but I know better now.
Car manufacturers are fighting this resistance by introducing fixed steps in to the CVT transmission. In stead of the limitless gear ratios, they are being programmed to replicate the behaviour of conventional automatics. So the question arises, if we want the CVTs to behave like other automatics, why are they being made in the first place. There are a couple of reasons for doing that.
Why CVTs?
Some major car manufacturers like Honda, are heavily invested into the CVT technology. They were supposed to be the perfect answer to all woes of a regular AT. But it didn't quiet happen like that. Anyway, they now have to stick with it and make the best of it.Secondly, it's not a bad transmission altogether. You see, in theory, it is supposed to be more fuel friendly and therefore more eco-friendly. And it also has it's driving advantages.
A CVT transmission is able to hold you in the power band RPM of the engine. This is very useful in situations like climbing hills. It is also no doubt smooth and you feel no gear shifts, because there are no gears to change. These transmission are light, easy to build and no so expensive to repair. Most of the time, the only replacement required is the belt or the transmission chain, and while it is not a cheap component, it is not all that expensive and is quickly and easily replaced.
So if the car manufacturers can somehow do away with the listless behaviour of the CVT, its pretty good to use. I have not driven a car with a stepped up CVT like a 7 step CVT transmission, so I can't comment on how well those drive.
Dual Clutch Automatic Transmission
Clutch Mechanisms In An Automatic Car
There is something that many people do not realise about automatic transmission cars. They all have a clutch mechanism. Even though you do not have the clutch pedal inside the car, there has to some clutch system that allows for the gears to change and for the car to be stop without stalling when you press the brake. There needs to be some way to dis-engage the engine from the transmission.
In a torque converter, the transmission fluid acts as a clutch. Since there is no direct contact between the transmission and the engine, the engine can be kept running while bringing the transmission to a complete stop. The transmission fluid keeps turning with the engine and absorbs the torque. When the car is put in gear or when the brake is released, this fluid starts turning the transmission again.
So in a dual clutch, there is very much a clutch in place, just like in a manual transmission. And as the name explains, there are not one but two clutch systems, one for changing the even number gears and the other for the odd ones.
This is what makes the gear changes really fast so much so that you do not feel them happening at all.
The reason I’m talking about clutches now is this. When you have clutch plates, there is wear and tear. So in a dual Clutch automatic transmission we have the additional component of twin clutches that are getting worn when ever you are driving.
Special conditions mean more wear and tear such as when crawling in traffic, frequent stop and go driving, pulling a trailer and even backing up slowly into the garage.
Basically any situation where you would need to use a clutch in a manual transmission, a DCT (Dual clutch transmission) will use its clutches automatically.
And when you need to replace the clutch, it is most assuredly going to cost you a bundle.
Fancy and luxury cars like the BMWs come equipped with DCT. They are a hoot to drive. But I have noticed a trend with luxury car owners. They do not keep them for more than 4 - 4 years. They sell them off just about the time when the warranty on these vehicles is about to run out and when they expected to require some heavy maintenance.
Torque converter autos differ in the regard that due to the technology, there is almost no 'clutch' wear and tear. You can sit with the brakes on in the drive mode and your transmission will not be any worse for it. It's not recommended that you do that because it's not good practise to keep an engine running on a stationery car for a long period of time. But your transmission will not be affected.
Even CVT transmissions need a clutch mechanism and most CVT's use a small torque converter for this purpose. So they also benefit from that technology. There is more reason why CVTs use a torque converter. Torque converters produce are good at making engine torque at low rpm. So they give the CVTs a better pickup boost from a standstill.
So here it is. Where DCTs are fun to drive, they undergo more wear and tear and are ferociously expensive to repair.
They are super quick in their changes but can lurch around during slower speeds.
Car makers like VW have made this a standard and affordable transmission by equipping all their automatics cars with them. But still for many, the long term reliability is suspect, specially given the history of problems they have faced.
To be fair, the initial glitches in the VW cars with the DCT have been resolved as an transmission oil issue.
Wear and tear of clutch plates in a DCT
The reason I’m talking about clutches now is this. When you have clutch plates, there is wear and tear. So in a dual Clutch automatic transmission we have the additional component of twin clutches that are getting worn when ever you are driving.
Special conditions mean more wear and tear such as when crawling in traffic, frequent stop and go driving, pulling a trailer and even backing up slowly into the garage.
Basically any situation where you would need to use a clutch in a manual transmission, a DCT (Dual clutch transmission) will use its clutches automatically.
And when you need to replace the clutch, it is most assuredly going to cost you a bundle.
Fancy and luxury cars like the BMWs come equipped with DCT. They are a hoot to drive. But I have noticed a trend with luxury car owners. They do not keep them for more than 4 - 4 years. They sell them off just about the time when the warranty on these vehicles is about to run out and when they expected to require some heavy maintenance.
Torque converter autos differ in the regard that due to the technology, there is almost no 'clutch' wear and tear. You can sit with the brakes on in the drive mode and your transmission will not be any worse for it. It's not recommended that you do that because it's not good practise to keep an engine running on a stationery car for a long period of time. But your transmission will not be affected.
Even CVT transmissions need a clutch mechanism and most CVT's use a small torque converter for this purpose. So they also benefit from that technology. There is more reason why CVTs use a torque converter. Torque converters produce are good at making engine torque at low rpm. So they give the CVTs a better pickup boost from a standstill.
Drawbacks of DCT you can't ignore
So here it is. Where DCTs are fun to drive, they undergo more wear and tear and are ferociously expensive to repair.
They are super quick in their changes but can lurch around during slower speeds.
Car makers like VW have made this a standard and affordable transmission by equipping all their automatics cars with them. But still for many, the long term reliability is suspect, specially given the history of problems they have faced.
To be fair, the initial glitches in the VW cars with the DCT have been resolved as an transmission oil issue.
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