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Old 23rd December 2015, 14:52   #1
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Post A novice's view: How transmissions work

Friends, this post is based on what I have read and understood about transmissions. As I am not an expert, pardon me for the errors, if any. It would help to correct such errors

Now to the post - this post is to shed light on the various transmission types and associated terminology. Trust this will help understand the basics - with most text sources in a single place for the following topics:-
1. Primer on Gears and gear ratio
2. General type of transmissions
2.1. Manual (with clutch)
2.2. Automatic (without clutch)
2.2.1. Explain D, N, P, 2, L, OD
2.2.2. Explain torque convertor
3. Well-known brand specific transmission technology

1. Primer on Gears and gear ratio:
Gears are generally used for the following reasons:
1. To reverse the rotation direction
2. To increase/decrease the rotation speed
3. To change axis of rotation motion
4. To keep the rotation of two axes synchronized
Source: How Stuff Works

Cars use gear to achieve points 1, 2 and 3 above. Gear ratios are calculated by dividing the number of teeth on the output gear by the number of teeth on the input gear.
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For example, consider a 6-tooth input gear meshed together with a 9-tooth output gear. So the gear ratio here is output/input, 9/6 = 1.5/1 = 1.5:1. In other words, the input gear has to spin 1.5 times to drive the output gear once.

In a car, the crankshaft (input) in the engine spins at high RPMs (revolution per minute or rpm). This rotation is passed on to the wheels by means of a driveshaft (output). The engine spins around say 1000rpm during idling. At high speed, it can be anything up to say 8000rpm. At this speed, it's not advisable to simply connect the wheels to the crankshaft end, because the speed is just too high/fluctuating/variable. Moreover, the engine would need to be stalled every time the vehicle came to a stop. Instead, the speed (i.e. rpm) of the crankshaft needs to be decreased to a usable/manageable speed. This is known as gearing down i.e. use of meshed gears to reduce the rpm of something that is spinning

Okay, now how do we relate gear ratio to the vehicle speed/acceleration?
Let me try and explain. We will use the scientific formula: Power ~ RPM x Torque
Power: Rate of doing work. This is calculated from RPM and Torque
Torque: It is the turning force around a given point. This is a measured engine quantity
Good reads:
1. Power and Torque
2. RPM/Torque comparison for two very different engines - with same power

Consider the following hypothetical gear ratios (for an easy explanation):
A novice's view: How transmissions work-gearratioexample.jpg
NOTE: Kindly click the image above, for a better view

Hope the table above explains why we tend to downshift while accelerating (e.g. for overtaking other vehicles) - due the need for more torque. The gear system helps transform the engine's output so that it can supply high torque at low speeds. This also enables engine operation (within it's limits) at cruising/highway speeds.

Have a look at this cool video -

Last edited by KomS_CarLog : 9th June 2016 at 08:45.
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Old 9th June 2016, 08:01   #2
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Default re: A novice's view: How transmissions work

Initially, I thought of explaining the entire topic but then decided against that. After all, I don't want to re-invent the wheel. There are many cool websites and videos that do most of the explaining. Hence, I have simply made an attempt to capture such information sources.

2. General type of transmissions
I just love this video

2.1. Manual (with clutch)
Start by reading this very simple description here. Do read until the end of the article. And then move onto wikipedia. You would need a lot of time to digest the material here, as it contains many other links.
Youtube also contains some good collection of videos on this subject. Check this out - Manual drive-train.

2.2. Automatic (without clutch)
Start here and then move onto this. This also explains the general D, N, P, 2, L and OD automatic modes.
Check out these Youtube videos too - Automatic Transmission

Automatic transmission would be incomplete without talking about the Torque convertor. Start here. Graduate to this article. Do have a look at
Read about Dual Clutch transmission (DCT) here and Tiptronic here

Just for fun (and knowledge of-course), do check these vintage videos - How Cars Work and Stuff Like. This playlist contains some good old American videos.

3. Well-known brand specific transmission technology - Indulge yourself with various brand names in the transmission world e.g. DSG, Tiptronic, etc. - here
Read through the Audi Technology portal - transmission

I hope this collection of articles and videos do help. I will add more sources as and when I come across them. Cheers!

Last edited by KomS_CarLog : 9th June 2016 at 08:44.
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Old 13th June 2016, 08:18   #3
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Default re: A novice's view: How transmissions work

Thread moved from the Assembly Line (The "Assembly Line" Forum section) to the Technical Stuff Section. Thanks for sharing!
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Old 13th June 2016, 08:37   #4
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Default re: A novice's view: How transmissions work

Excellent thread KomS_CarLog.

There are two other transmissions you missed:
1. The Automated Manual
2. The CVT

The Automated manual transmission (AMT) is essentially a manual transmission. It shares a lot of parts with the manual transmission. Instead of the clutch being operated by human effort, it is computer controlled and operated with electronic actuators.

The CVT is a belt which transmits power between 2 variable-diameter sheaves or pulleys. As the diameter varies, the desired gearing ratio can be obtained.

Here's a video explaining the working of a CVT:


The AMT is a simple and a primitive type of transmission, maximizing efficiency. It isn't smooth compared to other types of automatics. But AMT is good for lower segment cars where efficiency and price pays a big role in purchase decisions.

Nissan, Honda and Toyota are moving towards CVTs.

Last edited by landcruiser123 : 13th June 2016 at 08:39.
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Old 13th June 2016, 09:20   #5
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Default re: A novice's view: How transmissions work

Quote:
Originally Posted by landcruiser123 View Post
Excellent thread KomS_CarLog.

The AMT is a simple and a primitive type of transmission, maximizing efficiency. It isn't smooth compared to other types of automatics. But AMT is good for lower segment cars where efficiency and price pays a big role in purchase decisions.
Thanks for adding these types, landcruiser123. Tata (Zest) and Maruti Suzuki (Celerio) are providing AMT cars.
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Old 13th June 2016, 09:25   #6
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Default re: A novice's view: How transmissions work

Quote:
Originally Posted by KomS_CarLog View Post
Thanks for adding these types, landcruiser123. Tata (Zest) and Maruti Suzuki (Celerio) are providing AMT cars.
Not just these two. Maruti has a bunch of AMT cars in addition to the Celerio. Alto, Wagon R, Dzire. Tata has the Nano AMT. Mahindra has AMT in TUV300 and Nuvosport. Even Renault has the AMT in the Duster.
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Old 13th June 2016, 12:31   #7
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Default Re: A novice's view: How transmissions work

That is right, Rajeevraj. Here are a few more AMTs expected in 2016 (an old article) - Renault Lodgy, Kwid and DC Avanti 310- source
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Old 22nd June 2016, 15:18   #8
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Default Re: A novice's view: How transmissions work

Very informative thread and videos. This means that:
1. Contrary to popular belief, waiting at the traffic signal in 'D' mode with your foot on the brake pedal does not wear out an Automatic Transmission's clutch or brakepad (if your car is stand still). It's just that the transmission fluid heats up inside the Torque Converter (which is bad anyway).
2. Change from "D to R" or "R to D" only after the car has stopped completely, otherwise you risk ruining the Transmission Bands and the Clutch set.
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Old 11th August 2016, 05:22   #9
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Default Videos: Understanding the different types of Gearboxes

Now that I have your attention, put your heated barbs attacking me for questioning gearheads' competence on such a basic skill.

Shifting is at the root of all kinds of driving - be it to the grocery store, to work or at the track. It is important to be smooth to achieve the maximum effect, both comfort and speed. (Aside: even on the track, the smoothest rider is the fastest - it is pure physics. Anything that upsets the bike loses you time).

But transmission technology has come ahead a long way, particularly for old fogies like me (according to my son, I should have stuck to driving steam engines!) and some of the habits we picked up while learning are wrong or, more importantly, bad for the transmission.

Currently, we have the following types of transmission in India:

- Manual:
5 or 6 gear ratios, having a clutch. Not much assistance in terms of technology. The best if you are enjoying the driving. The worst in Bangalore, no matter what your inclination towards technology!
Key tip: Dont rest your hand on the gear shift. We all do it. But dont!
Why? I will let Jason Fenske explain it here:



- AMT
"The poor man's automatic" is how I always think of this. I understand that under the hood, this is a manual but the clutch duties are taken over by the car. Cheaper to make; not just as sophisticated. Ideal for small engined cars.

The Tata Nano, for example, has one.

Here is a video of how it works:

This is probably not what is in your Duster, Celerio or Nano but it gives you an idea of what is in there! (Like a Rolls Royce gives you an idea of what to expect in a Nano!)

Unfortunately, nobody has any opinion on how to drive it! THis is largely designed for commercial vehicles & cars in low cost markets like India.
Key tip: Dont coast. Dont change from reverse to forward without coming to a complete stop. No burnouts.


- CVT
The equivalent of the erstwhile Kinetic Honda. No fixed ratios, really - ratios change as per condition. But very lossy. Smooth and great for coasting.

Good for mid engined, commuter oriented cars.

How it works:

The point is, if this is there, it is so smooth that you dont notice it. So I cant correctly recollect which car has this, even though it feels like I drove one just recently!
Key tip:Just dont touch the gear shifter if you are driving.
Why? I will let Jason Fenske explain it here:


Torque Converter/ Automatic
This technology uses what is known as a torque converter. Has more distinct gears than a CVT. Technology has made it more sophisticated.

How it works:

Ideal for large engined,high torque car which can overcome the losses easily. In such a car, it can be very good. In smaller engined cars, it can be irritating
.
Key tip:Just dont touch the gear shifter in this too, if you are driving. Be sensible.
Why? I will let Jason Fenske explain it here:


- DSG
Direkt-Schalt-Getriebe. If that mouthful broke a few teeth, "Direct Shift Gearbox" for us plebs.

Basically it has 2 clutches, one working & the other 'ready'. The car switches clutches & gears at the blink of an eye (by magic or by elves, who knows?!). The result: the smoothest, most pleasurable drive ever and huge bills if you have a VAG car!

How it works (nerdy!)

The Polo is a car with this that I enjoyed driving.
Key tip: Dont creep uphill or in traffic. Dont leave it in gear if you stopping. OF course, dont coast.
Basically it is the best of both manual & automatic. It has also inherited both their characteristics. So, if you think you shouldnt do something in a DSG, you are probably right
Why? I will let Jason Fenske explain it here:


It is important that you treat your gearbox right. Have a look at Jalopnik's original article that set me off on this.

Subscribe to Engineering Explained on YouTube - you are a gear head; you will love it!

Last edited by sridhu : 11th August 2016 at 05:50.
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Old 11th August 2016, 09:37   #10
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Default re: Videos: Understanding the different types of Gearboxes

Quote:
Originally Posted by sridhu View Post
...............
- CVT
The equivalent of the erstwhile Kinetic Honda. No fixed ratios, really - ratios change as per condition. But very lossy. Smooth and great for coasting.

Good for mid engined, commuter oriented cars.

.....
Nice write-up sir !
I've been following the 'Engineering Explained' channel ever since I saw the video of The man - Jason explaining how Dual-clutch Gearboxes work.
Love the way he explains the tech that we've pretty much taken for granted.

Now for some critique

If I may, I'd like to suggest that you change the 'mid-engined' adjective to 'moderate displacement engines in commuter-oriented cars'.
The moment us petrolheads hear mid-engined, we switch to thinking of cars where the engine is placed just ahead of the rear-axle.

Cheers !

Sundar
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Old 11th August 2016, 09:45   #11
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Engineering Explained is an amazing channel. Jason has helped me with so many topics. Guy's a geek and an enthusiast, love his style of presentation and his videos are always to the point and no BS.
P.S I am pursuing automobile engineering, 3rd year, so he is a great help.
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Old 11th August 2016, 10:18   #12
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Default re: Videos: Understanding the different types of Gearboxes

Quote:
Originally Posted by sridhu View Post
- AMT
"The poor man's automatic" is how I always think of this. I understand that under the hood, this is a manual but the clutch duties are taken over by the car. Cheaper to make; not just as sophisticated. Ideal for small engined cars.

The Tata Nano, for example, has one.

This is probably not what is in your Duster, Celerio or Nano but it gives you an idea of what is in there! (Like a Rolls Royce gives you an idea of what to expect in a Nano!)

Unfortunately, nobody has any opinion on how to drive it! THis is largely designed for commercial vehicles & cars in low cost markets like India.
Key tip: Dont coast. Dont change from reverse to forward without coming to a complete stop. No burnouts.

- DSG
Direkt-Schalt-Getriebe. If that mouthful broke a few teeth, "Direct Shift Gearbox" for us plebs.

Basically it has 2 clutches, one working & the other 'ready'. The car switches clutches & gears at the blink of an eye (by magic or by elves, who knows?!). The result: the smoothest, most pleasurable drive ever and huge bills if you have a VAG car!


The Polo is a car with this that I enjoyed driving.
Key tip: Dont creep uphill or in traffic. Dont leave it in gear if you stopping. OF course, dont coast.
Basically it is the best of both manual & automatic. It has also inherited both their characteristics. So, if you think you shouldnt do something in a DSG, you are probably right
To me as a lay man, I can't see much difference between Dual clutch DCT (Ford) / DSG (VAG) or single clutch "poor man's" AMT (Nano), except the point about fast shifts that can be achieved because of two clutch system.


Quote:
- CVT
The equivalent of the erstwhile Kinetic Honda. No fixed ratios, really - ratios change as per condition. But very lossy. Smooth and great for coasting.

Good for mid engined, commuter oriented cars.


The point is, if this is there, it is so smooth that you dont notice it. So I cant correctly recollect which car has this, even though it feels like I drove one just recently!
Key tip:Just dont touch the gear shifter if you are driving.
Lossy?
I read that CVT offers the best fuel economy figures since it manages to utilize the most optimal engine RPM and transmission ratio in conjunction with the goal of reducing the fuel consumption.

In fact it is the hydraulic torque converter types that are lossy, and therefore some of those have hard coupling that comes into play once the Torque converter shaft slipping is below 10% or so.

In terms of technical requirements from a gearbox/transmission unit ... a CVT is ideal. It is only because manufacturers have tuned it for fuel economy that we find it boring. Otherwise, if programmed correctly it can result in being on the redline (or peak torque if you prefer) continuously even while the "gear ratios" change.
Try doing that in any other transmission (where you will be forced to start below the redline and watch the needle creep up every time you shift gear)!

Last edited by alpha1 : 11th August 2016 at 10:28.
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Old 11th August 2016, 10:32   #13
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Default re: Videos: Understanding the different types of Gearboxes

Good informative thread. Any guesses as to why a CVT is never mated to a diesel engine?

Quote:
Originally Posted by alpha1 View Post
Lossy?
I read that CVT offers the best fuel economy figures since it manages to utilize the most optimal engine RPM and transmission ratio in conjunction with the goal of reducing the fuel consumption.

In fact in terms of technical requirements from a gearbox/transmission unit ... a CVT is ideal. It is only because manufacturers have tuned it for fuel economy that we find it boring. Otherwise, if programmed correctly it can feel like being on the redline continuously even while the "gear ratios" change. Try doing that in any other transmission!
By "lossy", I think he means wasted revs when you step on the accelerator suddenly, with no corresponding increase in speed.

CVTs are ideal for hybrids - because when you step on the accelerator in a petrol-hybrid, batteries can supply power to wheels till the engine is ready.

From the Camry Hybrid Review -
http://www.team-bhp.com/forum/offici...al-review.html (Toyota Camry Hybrid : Official Review)

Quote:
The minute you turn off ECO mode, there is a noticeable change in the Camry's behaviour. The accelerator pedal suddenly feels sprightlier and more eager. A gentle dab and the petrol engine comes alive with a throaty growl. Even a slight press is enough to move the gauge into power mode, with none of that hesitation seen in ECO mode. This is a good mode to be in when you are in a hurry, or on single-lane highways which require you to overtake from the other side.

The low-end torque in ECO OFF is superb. The electric motor + petrol engine combine to give you instantaneous response. You can reach triple digit speeds in no time, this is when you really feel the 202 BHP on tap.
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Old 11th August 2016, 10:56   #14
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Default Torque Converter in CVT

Some CVT uses torque converter unit to mate engine with transmission. Then some CVT uses clutch pack to mate engine with transmision. Both types are in use now i.e., clutch cvt and tc cvt.
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Old 11th August 2016, 11:09   #15
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Default re: Videos: Understanding the different types of Gearboxes

Thanks for the excellent info and interesting compilation. What are the 4-speed automatics, 5-speed automatics etc used by Maruti, Hyundai etc? Which category is that?
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