In order to select the right speed and torque for the right load some times even the manual transmission could not do the task perfect and it is always near perfect. Which results in the power produced could not be utilized for its optimum and it means always some loss of efficiency in terms of power and fuel consumption. Though the loss seems to be negligible one, but for the fleet operators with larger fleet operation there will be considerable savings in the long run.
In the Automatic Transmission,
1. No clutch pedal is in place and
2. No Gear shift lever available.
The automatic transmission's primary job is to allow the engine to operate in its narrow range of speeds while proving wides range of output speeds. The key difference between a manual and an automatic transmission is that the manual transmission locks and unlocks different sets of gears to the output shaft to achieve the various gear ratios, while in an automatic transmission; the same set of gears produces all of the different gear ratios. This is being achieved by the planetary gear set in the automatic transmission.
The auto transmission unit consists of;
1. Planetary gear set
2. Set of bands to lock parts of a gear set
3. Set of three wet-plate clutches to lock other parts of the gear set
4. An incredibly odd hydraulic system that controls the clutches and bands
5. A Gear pump to move transmission fluid around.
An automatic transmission contains two complete planetary gear sets folded together into one component.
Any planetary gear set has three main components:
1. The sun gear (S)
2. The planet gears and the planet gears' carrier (C)
3. The ring gear (R)
Each of these three components either acting as input or out put or stationary. Choosing which piece plays which role determines the gear ratio for the gear set. Let's take a look at a single planetary gear set.
Assumption: No of teeth on Ring Gear : 72 and No of teeth on Sun Gear: 30
Gear Ratio: 1
Input: Sun gear (S)
Out put: Planet Gear and Planet Carrier (C)
Stationary: Ring Gear (R)
Gear Ratio: 1+ R/S ie. 1+ 72/30 ie 1+2.4= 3.4. Hence the ratio is 3.4:1
The Gear ratio shown above is reduction because the output speed is lower than the input speed.
Gear Ratio:2
Input: Planet carrier (C)
Output: Ring gear (R)
Stationary: Sun gear (S)
Gear Ratio: 1/ (1+ S/R), ie 1/ (1+ 30/72)= 0.71. Hence the Gear Ratio is 0.71:1
The Gear Ratio shown above is Overdrive, because the output speed is faster than the input speed.
Gear Ratio:3
Input: Sun gear
Output: Ring Gear
Stationary: Planet Carrier (C)
Gear ratio: -R/S ie= – 72/30 = -2.4. Hence the Gear Ratio is -2.4:1
The Gear Ratio shown above is again reduction but in negative. ie: the reverse.
We get several other gear ratios from this planetary gear sets, and these are the ones that are relevant to our Automatic Transmission. This one sets of Gears can produce these different gear ratios without having to engage or disengage any other gears. With two of these gear sets in a row we can get the four forward gears and one reverse gear.
NEXT SESSION: …………………..Technical Definitions.
It is true that implementing Auto transmission in commercial vehicles will increase fuel efficiency. As per my practical knowledge due to Auto Transmission speed driving will increase. Simultaneously accident ratio also increase. For commercial vehicles it was not preferable. Because our drivers attitude was not suitable for this technology. It was only suitable for the self driven cars, taxi’s which are running in urban traffic. For example power steering system introduced in commercial vehicles since near about 20 years back in India, but still we are facing problems with drivers to absorb.
Thanks for the feedback Mr. T. Srinivas Rao ,
I believe fuel saving is really important for a country like India where the fuel prices are steeply on the rise frequently. Failing to do so can affect even the smallest fleet owners adversely. So automatic transmission can only do good economically for the vehicle owners.
Like Volvo buses are coming with such transmission. It is also useful for trucks in some application like marble quarry where gear need to engage in many permutation and combination frequently, there it is useful. Also it is useful for application like mining, ODC where drivers are trained.
I agree completely with you say on driving issue. Having said this, I believe that this has to be countered via improving traffic awareness among drivers. Alternatively providing better traffic systems, increase width of the road and so on will help a bit.
I agree. Commercial Vehicles deserve new technology. This cannot be kept on hold on name of safety. Similar arguments have cropped up while power steering was introduced; now it is liked. As Arun concluded in reply, we need to improve driving training systems; rules are there implementation needs improvement. Also the highways need to be better & improved for safe driving. Even Mumbai – Pune express highway is not safe in few stretches, with oncoming vehicles’ head lights directly hitting into driver’s eyes, leading to accidents. So we need improvements on all fronts for better utilisation of improvements.
Can you come out with an article on two spees rear axles & i-shift.
I agree on implementing Auto Transmission for commercial vehicles. Probably introduce thru’ phased manner, initially with LCV and then to HCV. It may impact the fuel consumption and has the added advantage of human factor on safety.
Great post! This is really interesting. I guess this only suggest that automatic transmission makes driving easier. This is because you don’t need to shift gear and you only have two pedals to focus on.