Manual or automatic? This is one of the classic questions that many ask themselves when buying a vehicle. The evolution of automatic boxes has been spectacular in recent decades and today we can find them of different types. Next, we show you everything you need to know about the automatic transmission of a car.
Motorists are divided between those who prefer the manual gearbox and those who prefer the automatic gearbox, although it is true that, in recent years, the second is imposing more and more on the first.
About automatic transmissions have always existed all kinds of not very favorable comments, as they increase consumption, do not offer the same benefits, are less reliable or that people who like to drive prefer a manual transmission. And maybe some of that was true, but in past times.
However, today we do not want to review the history of the automatic transmission, but rather, focus on the more technical part of the matter: how an automatic transmission works, what advantages and disadvantages they offer and what types of automatic transmissions there are in the market.
How automatic transmission works
The first thing is to explain how an automatic transmission works and what its characteristics are. Most automatic boxes work with a series of positions that are determined by the initials P, R, N, D, to which others can be added that vary the operation of the electronics.
P (Parking): is the parking position and is used to lock the gearbox, either with the engine started or stopped, without engaging any gear. In this way, it prevents the car from moving, even if it is on a slope without the parking brake activated.
R (Reverse): Equivalent to gear R on manual gearboxes and is used for reversing.
N (Neutral): is the neutral position. When this is engaged, no gear is engaged, but unlike P, the gearbox is not locked here, so the car will move if you don’t use the brakes.
D (Drive): forward position, with which it automatically engages the gears, both ascending and descending. Here, the driver only has to think about accelerating, braking and steering the car.
Others: in recent times, many automatic gearboxes include functions or driving programs that modify their behavior, offering greater acceleration or retention, smoother or more abrupt changes, etc., depending on the driver’s demands. For example, Sport or ECO mode.
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Currently, we can find several types of automatic changes on the market. Mainly two: the changes by torque converter and those of the continuous variator type.
Then there are two other changes that are rather robotized manual transmissions. We refer to the robotic and dual-clutch gearboxes. In general, we usually call all these changes automatic, since they lack the clutch pedal.
change with torque convert
The change with torque converter works through a system made up of several elements, among which the torque converter stands out, which is responsible for connect transmission to engine.
The torque converter is made up of three elements inside an airtight container: a disc shaped pump attached to the engine, some cross-shaped grooves to direct the oil, attached to a turbine which, in turn, is linked to the gearbox, and a reactor coupled to the gearbox that redirects the oil to the pump.
When the car is stopped, the pump and the turbine rotate independently, and as the car moves forward, the flow of oil becomes more and more intense, until the pump and the turbine rotate together. This is what is known as the torque transmission phase.
Stepless Variable Type Shift
This is the change known as CVT and that is present in many hybrid cars, such as Toyota, or Subaru models. This type of automatic change is characterized by a very peculiar operation, with infinite ratios that produce what is known as scooter effect.
When you step on the accelerator fully, the engine revs a lot, but the speed gain does not correspond to the rate of rotation. This problem has been alleviated in recent years through electronics, introducing a manager that simulates the relations of a conventional change.
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A CVT is made up of two tapered pulleys with different diameters, connected by a strap. One of the pulleys is connected to the output of the crankshaft and the other sends movement to the transmissions.
Depending on the operation of the car and the driver’s demand, the electronic change management will also vary the diameter of the pulleys. When one increases its diameter, the other decreases it, thus avoiding belt tension changes and changing transmission ratios.
This is basically a manual gearbox with a electronic clutch managed by a switchboard. Through the electronics, the control unit receives numerous parameters, such as throttle position, speed or revolutions. With this information, the control unit determines if the clutch should be engaged or not.
To replace the clutch and gear lever, it uses electronic or hydraulic lifters and, using an electronic calculator, determines the best time to change gear.
This system also allows the driver to choose between automatic operation or manual mode, in which he decides when to change gear.
double clutch transmission
In this case, we are facing another robotic manual checkout, although with nuances. The manual and robotic gearboxes have one clutch and two gearboxes and the double-clutch ones have, as their name indicates, two clutches and two pairs of gear shaftstwo primary and two secondary.
One of the pairs of gears is in charge of the even gears and the other pair of oddIn the same way, there is a clutch for the even ratios and another for the odd ones. This makes changes much faster.
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When the electronics detect that you are about to shift from second to third gear, for example, before the even gear clutch disengages, the odd gear pair is already engaged, without engaging the clutch (but yes prepared).
By the time the even-numbered clutch is released, the odd-numbered one is already engaged and shifting occurs quickly.
Advantages and disadvantages of automatic transmission
Today, automatic boxes have a series of advantages, such as offering a better performance of the car and a reduction in consumption.
To this must be added a greater comfortabove all, in situations of intense traffic in large cities, a safer drivingsince the driver only has to be aware of the traffic and to accelerate or brake, and the mechanical safety that it provides to the engine the smoothness in the gears.
Although not everything is positive and the automatic transmission also has some drawbacks. The most important is your price: automatic cars are usually more expensive than their equivalents with manual gearbox.
Also, the maintenance it is also usually more exhaustive and expensive, since they have a greater number of components