Automatic transmission- types and which is the best type of automatic transmission

Audible

Automatic transmissions have gone through many changes since being introduced by Oldsmobile for 1940. There are four types of Automatic transmission.



1. Torque converter(Conventional automatic)
2.Continuously variable transmission(CVT)
3.Automated manual  
4.Dual-clutch automated manual(DSG)

Torque converter(Conventional automatic)

The current generation of conventional automatics use a torque converter to transfer power from the engine to the transmission. The transmission itself typically contains several sets of gears, and the different “speeds” are chosen by engaging electronically controlled, hydraulically operated clutch packs. Most earlier automatics worked much the same way but didn’t have as many speeds and lacked electronic controls.

Conventional automatics tend to be very smooth in operation—both upon starting from a stop and in gear changes—but lose some efficiency (and thus fuel economy) due to the slight “slip” of the fluid-filled torque converter and driving the hydraulic pump that operates the clutch packs.

Continuously variable transmission(CVT)

Rather than sets of gears, CVTs use a belt that runs between two variable-diameter pulleys to give a wide range of ratios and a smooth transition between them. In automotive applications, some CVTs use a fluid-filled torque converter (as with a conventional automatic) to transfer power from the engine to the transmission, others a clutch similar to that used for a manual transmission, but with automatic activation (there is no clutch pedal).

The advantage of a CVT is that the engine can be kept at its most efficient speed while the transmission adjusts to changes in load or road speed. Under brisk acceleration, for example, the engine revs up to where it produces the most power and is held there as the transmission constantly adjusts to the increasing speed of the car. Under cruise conditions, the transmission can adjust for small changes in road speed while the engine is kept at a consistent rpm for best fuel economy. A limiting factor is that because CVTs rely on friction between the belt and the pulleys, they haven’t yet been designed to handle a lot of power.

Automated manual  

There are two types of automated manual transmissions in use, with the more modern one (which is now far more common) being called a “Dual Clutch Automated Manual”; it’s described below. Both are essentially manual transmissions where the clutch and shift actions are carried out by computer-controlled, electronically activated mechanisms, so they work without driver interaction, just like a conventional automatic transmission. However, they can also be shifted manually (though still without the driver using a clutch) via a conventional gear lever or steering-column-mounted “paddles.”

Automated manuals are more efficient than conventional automatics because there’s no “slip” of a torque converter and no losses from driving an internal hydraulic pump. The earliest versions – which were found primarily in European performance cars – were based on a conventional manual transmission with a single clutch, but the only car still using this kind is the very non-performance-oriented Smart ForTwo.

Dual-clutch automated manual(DSG)

It gets its name from the fact that there are two gear shafts – one for the odd-numbered gears (1, 3, 5, 7), another for the even-numbered gears (2, 4, 6) – each having its own clutch. When the car moves off from a stop, 1st gear is already selected, and the “odd” clutch is engaged to start the car moving. While this is going on, the computer puts the other gear shaft into 2nd gear. When it comes time to shift to second, the “odd” clutch disengages and the “even” clutch engages, and presto; you’re in second gear. It does the same with the higher gears, which are “preselected” before the clutch for that shaft is engaged. This results in much quicker – and usually much smoother – gear changes than with a “single clutch” automated manual.

Automated manuals are often used in performance cars today because they’re more efficient than a conventional automatic transmission, and can handle much more power than a CVT.

Branded examples of dual-clutch automated manual transmissions include Ford’s “PowerShift” available in the Fiesta and Focus, and Porsche’s “PDK” available in several of the maker’s vehicles

Conclusion

Although the four types of automatic transmissions —conventional, CVT, automated manual, and dual clutch automated manual — all operate without a clutch pedal and can be set to shift for themselves, they each exhibit slightly different driving characteristics. You’re probably already familiar with how a conventional automatic “feels,” so we’ll compare the others to that.

Closest in terms of perception to a conventional automatic is the dual clutch automated manual. One difference can often be felt when you’re barely moving. If you’re stopped on a slight upward incline, a conventional automatic will “hold” you there without having your foot on the brake; likewise, your car will creep forward on level ground if you are stopped and take your foot off the brake. Automated manuals often won’t hold you on an upward incline, and may not creep forward on flat ground quite as smoothly as a conventional automatic does. This is most noticed in stop-and-go traffic.

Many automated manuals also feel different if you floor the throttle, either from a stop or when cruising down the road. From a stop, they sometimes lurch a bit where a conventional automatic is smoother. If you’re cruising down the road and floor the throttle to pass, an automated manual can often be felt “stepping down” one gear at a time rather than dropping from, say, sixth gear straight down to second. As a result, the time that passes between flooring the throttle and the car actually accelerating is sometimes a bit longer.

These all sound like negative traits, so why do some manufacturers use automated manuals? Efficiency. Automated manuals are often credited with about a 10-percent increase in fuel economy. And they’re usually better from a performance standpoint, as there’s less power loss through an automated manual, and under hard acceleration, they are often quicker to upshift into the next gear.

A CVT exhibits even more of a difference, notably under acceleration. The objective of a CVT is to have the transmission make most of the adjustments necessary to maintain different road speeds while letting the engine turn at a fairly constant speed—which results in about 10 percent better fuel economy. Under even moderate throttle applications from a stop, however, a CVT maximizes engine power by letting the engine quickly rev up to where it makes more power and then holds it there while the transmission adjusts to the car’s increasing road speed. This means the engine is held at a steady, high-revving speed where it usually makes a lot of noise and sometimes is rather ragged, and this is what is most obvious — and annoying — to many drivers.

It used to be that nearly every car that offered both a manual and an automatic transmission scored significantly better EPA fuel-economy numbers with the manual. Not anymore. Although there are a few examples where the manual is still thriftier, many of today’s cars score better with an automatic. Part of this is due to the greater number of “speeds” now used even in conventional automatics — which allow the engine to run more efficiently at any given road speed — and to the use of automated manuals and CVTs.

Currently, most manufacturers still rely on conventional automatic transmissions, but the use of CVTs and particularly dual clutch automated manuals is growing. In their best applications, CVTs and dual clutch automated manuals behave much the same as conventional automatics in everyday driving, and the goal is to make them nearly indistinguishable — except for a noticeable boost in fuel economy.

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Engine transmission- An overview of types of transmission, advantages & disadvantages.

Audible

Transmission refers simply to the gearbox that uses gears and gear trains to provide speed and torque conversions from a rotating power source to another device. There are two types of transmission mainly Manual transmission and Automatic transmission.

Manual transmission:-

A manual transmission, also known as a stick shift or manual gearbox, is a type of vehicle transmission that requires the driver to manually shift gears.

Advantages of manual transmission:

•Driving with manual transmission gives you more control of the vehicle because you shift the gears. It will be easier to slow down or stop when you drive a manual vehicle.

•Manual transmission requires less maintenance and is cheaper to repair.

•Manual vehicles are more fuel-efficient than their automatic counterparts.

•Manual vehicles are less likely to be stolen because they are not as popular as automatic vehicles.

Disadvantages of manual transmission:

•Driving a manual transmission vehicle can present more safety challenges because it requires the driver to take one hand off of the wheel.

•The driver of a manual transmission vehicle has to constantly work three different foot pedals: the clutch, the brake, and the accelerator.

•It is much more difficult to learn how to drive a manual transmission vehicle.

•It is difficult to sell a manual transmission vehicle.

Automatic Transmission:-          

An automatic transmission, also called auto, self-shifting transmission, , is a type of transmission that can automatically change gear ratios as the vehicle moves, freeing the driver from having to pressing the clutch and shift gears manually. Like other transmission systems on vehicles, it allows an internal combustion engine, best suited to run at a relatively high rotational speed, to provide a range of speed and torque outputs necessary for vehicular travel.

Here are the main advantages of an automatic transmission:

•Vehicles with automatic transmission are a lot easier to use because the transmission will do the gear shifting for you.

•Automatic vehicles allow you to keep both your hands on the steering wheel for added safety in driving.

•Driving an automatic vehicle facilitates greater comfort for the driver because his feet have to work just two pedals – the accelerator and the brake.

An automatic transmission presents disadvantages, too, including the following:

•Automatic vehicles are more expensive than manual transmission vehicles. They are also more expensive to maintain and repair.

•An automatic vehicle depends on the torque convertor to switch gears, making it less fuel-efficient.

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How does manual transmission in cars work?

A manual transmission transfers power from the engine to the differential using a clutch and pairs of gears that are manually selected using the gear selector and locked to the output shaft. Most cars today with manual transmissions have four, five or six different forward gear ratios.

 The five-speed manual transmission is fairly standard on cars today. Internally, it looks something like this:

 

There are three forks controlled by three rods that are engaged by the shift lever. Looking at the shift rods from the top, they look like this in reverse, first and second gear:

 

The clutch is positioned between the engine’s flywheel and the transmission. Normally when the clutch is engaged, it locks the transmissions input shaft to the flywheel. When the clutch pedal is depressed, the clutch is disengaged by a thrust bearing, and no power is transferred. With the clutch disengaged it is possible to select gears. To start the vehicle moving, the clutch is slowly released, and slipped slightly. It is important not to ride the clutch once you are moving  because this can lead to clutch slippage or premature thrust bearing problems. Gears are normally selected using a shift lever, often mounted on the floor, but sometimes mounted on the dash or steering column. The gears are usually laid out in an H pattern with neutral being a space between gears.

 

Early manual transmissions (and those found in some trucks, heavy machinery, and racecars) use an unsynchronized design. In an unsynchronized transmission the gears are selected by sliding them on shafts until they have engaged the dog clutch. In order for the gears to engage properly they need to be spinning at the same speed as the output shaft, otherwise the gears (actually the dog clutches) will grind. To do this you can either double clutch by essentially using the clutch to shift into neutral, and then again to shift into the desired gear, or you can rev match by matching the engine’s RPM with the RPM the engine will be at for the road speed in the desired gear. Unsynchronized transmissions are generally tougher than synchronized ones, as the synchros are usually made out of soft brass that wear much more quickly than the steel gears. Because of this added strength, unsynchronized transmissions can usually be shifted quickly without using the clutch, especially when designed with fewer teeth on the dog clutches, as in some race cars.

 Most transmissions found in modern cars are synchronized. The synchronizer is attached to the dog clutch, and consists of a cone clutch and a baulk ring. When you try to shift gears and the parts aren’t at the same speed, the cone clutch contacts first, bringing the gears and output shaft to the same speed using friction. The baulk rings prevents the dog clutch from engaging until everything is synchronized. The synchros are usually made out of a soft metal such as brass, which makes it important to use the clutch when shifting, because imperfect rev matching will be masked by the synchros. Continuous abuse will lead to synchronizer failure, and grinding. Rev matching while using the clutch can reduce wear on the synchros as they will need to work less hard to match the speeds of the gears and output shaft.

 

 

In a sequential gear box (usually found in race cars) there is no neutral between gears, and the gears are selected in sequential order instead of in an H pattern, often without using the clutch. In a semi-automatic manual gearbox the actual rev matching, gear shifting and clutch control is handled by a computer. In these transmissions the clutch is usually only used to get the vehicle moving. When the driver presses a button or pulls a lever the computer takes the car out of the current gear, blips the throttle or waits for the engine RPM to drop to the appropriate level, and then changes into the requested gear.

 

Manual transmissions are generally more fuel efficient than automatic transmissions because there is no fluid coupling or fluid pump like in a traditional automatic transmission, and no belt to slip like in a continuously variable transmission. A standard transmission also allows the driver more control over which gear they are in, potentially allowing for a lower engine RPM.

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