Selespeed, Multitronic, Dualogic, DFN, Tiptronic, F1, SensoDrive, SMG, DSG ... and so on and so forth! Behind these names, abbreviations, imaginative and compelling, that make a lot of hi-tech, hiding a new generation of transmissions. At one time (not very far) the automatic transmissions were often a waste of fuel, poor ability to run your vehicle, and mortification of the performance. Now, thanks to the evolution of technology is still in demand and appreciated, so as to be used by these homes as effective weapons for winning new customers, and, highly topical subject, to reduce fuel consumption and emissions inquinanti.Orientiamoci, therefore, in this fascinating world to see what's hidden ... besides the lack of clutch! CHANGE AUTOMATICOE 'automatic transmission "proper", the most widespread, since the first automotive applications written in the fifties, when it made its appearance in the U.S. market on various Ford models General Motors and Chrysler. Although during the history of the automobile were invented many types of automatic transmissions, when we talk about we refer to classical automatic gearbox with hydraulic torque converter and planetary gears. What lies behind these abstruse technical terms? They are the heart and vital organs of an automatic transmission. Let's see in detail. The torque converter is a hydraulic device which, in practice, the place of the classic clutch manual transmissions used in the traditional: his task is to create a pair, more or less strong, between the engine and the gearbox itself. The word "plumber" comes from the fact that to perform its function, the torque converter using a fluid, usually a low viscosity oil. The drive comes as a big and strong donut metal inside which can be identified by the two elements also form a ring: on the one hand, connected directly to motor shaft, we find the pump, on the other, connected to the shaft input of the gearbox, there is a hydraulic motor or turbine. The two sides are very close together but not in contact, and are immersed in the fluid. Both the pump and the turbine blades are provided with channels which are willing to haul but at a certain angle (a bit 'like a star with the tips curved) in which the fluid is forced to flow along a certain route. The pump is driven to rotate by the motor, the fluid collects in the center and pushes it to the centrifugal force, to the outside giving it a whirling motion. The fluid is then collected from the turbine, but now comes from the periphery and is driven by its channel to the center where it is expelled from there through a third element called the stator, which has the task of leading as efficiently as possible, and then is then recaptured by the pump to restart the cycle. To recap: in the pump fluid follows the path of the center-periphery, periphery-center in the turbine. Now, one might rightly ask, all this great swirl of fluid as able, to move a car? To understand this, we must return to the channels in the pump and turbine and think about the shape. In fact, the fluid pushed into the channels of the turbine undergoes a deviation, and the laws of physics, if you want to change the direction of a body (liquid, solid or gas does not matter) on the move is necessary to apply a force, and Newton teaches us that every force there is an equal and opposite. So as channels of the turbine deflect the fluid (previously energized by the pump driven by the motor), the diverted fluid exerts a force on the turbine blades ... and finally puts it into rotation, along with the gearbox and the drive wheels. The exchange of power between pump and turbine, through the fluid is such that a low torque and high speed input of the device are the high torque and low speed output, hence the name of the drive. The torque converter, while creating a separation between engine and transmission, is able, as seen, to make them united by a working fluid, being able to perform two tasks: first, middle and upper regimes and the growth of forces in the fluid, allows the transfer of torque between engine and transmission, and second, a tapering regimen, the device is always less efficient and generating more and more forces available, allowing a gradual shift that allows the engine to fail to stop while the vehicle is stationary. The latter task, for a vehicle with manual transmission, it is obviously done by the friction with the intervention of the driver. The shift, which occurs even at higher engine speeds albeit to a lesser extent, however, represents an energy loss (part of the engine work is dispersed in the form of heating fluid) which results in increased consumption of fuel in the vehicle and ' acoustically unpleasant effect of "slipping clutch"; to limit these phenomena, the modern converters incorporate a clutch system that combines mechanical pump and turbine speed costante.Ultima function that affects the torque converter is "parking". With the engine off, unlike a manual transmission in which gear you get, leaving a wheel lock, an automatic transmission in the manner described is not any kind of rigid connection between engine and transmission (the fluid is at rest and can not exercise any power) leaving, in fact, the wheels of the car free. For this reason, in vehicles with automatic transmission is a special parking facility (identified on the switch by the letter "P") that blocked mechanically by a pin, the transmission. As with a manual transmission, clutch transfers the motion to change, here the torque converter transfers the motion to all the gears epicicloidali.Per "planetary gear" means a system of gears composed of three elements: the satellites, the sun and the crown. The terms are due to them "astronomical" in the middle we have the sun or pinion gear that is surrounded by two or more gears (satellites), mounted on a carrier body said planetary satellites, the whole is placed inside a circular ring, the crown, with teeth in internamente.Il name of this device stems from the fact that the movement of the planet gears is similar to what was supposed to have the planets of the Solar System in the Ptolemaic system, which assumed the existence of such motions epicycles. The planetary gear is an ingenious device: the sun is only in contact with the satellites which engage only with the crown, while there is no meshing between the sun and crown. Each component can be either the input of the motion (related to motor through the torque converter) and the output (connected to the wheels via the differential), or be kept steady, the choice of a role for each of them determines ultimately, the transmission ratio adopted during operation by an automatic transmission. This choice is made by a brake system acting, as appropriate, on the crown, the planet or the sun, and sometimes through the use of friction (usually multi) making it joined together two of these three elements: Indeed, blocking the entrance to the outer ring applied to the output pinion planetary reduction ratio is obtained (an output rate lower than that of entry, a virtual march "short"), while blocking the pinion, with the 'entry and exit to the planetarium to the crown, it has a multiplication ratio (a gear "long", also known as overdrive), and finally, with the global firm, the entrance to the pinion and the exit on the crown, you get a reduction but with a reversed rotation, ie retromarcia.Nella simplest configuration, with a planetary gear ratios you can have two forward and one back, but we know that modern automatic transmissions have a number of speeds ranging from 4 to 7, plus the back. This is possible by connecting gears in series, with each planetary pinion fixed to the next, creating a cohesive group, capable of a lot of gear ratios and with the input and output axes aligned. Now let's see how logic automatically switches from one speed to another. Who drove a car with automatic transmission will certainly have noticed some typical behaviors: When Speeding gradually, gear changes occur at a lower speed than if you accelerate hard, if you manually insert a low ratio, the climb will take place only if the car does not proceed at a speed too high for that relationship, quickly pressing the gas pedal, transmission switches to the lower ratio (the famous kick-down). All these situations are handled by a complex hydraulic system consists of several components, said actuator. The "brain" consists of a metal box in which they are taken of the channels, which appear to form an intricate labyrinth through the same system of pipes, would require much more space and a large number of connections. A special pump, connected the engine sucks the oil (the same as the torque converter) and pushes him in this circuit. The release is controlled by a valve called the regulator, whose opening is directly proportional to the speed of transmission. To function properly, however, requires an automatic transmission to ascertain the conditions under which the engine works: this is obtained simply by measuring the position or the accelerator or, more accurately, considering the depression that is formed in the intake manifold (The higher, the higher the load applied to the motor). The phase of changing the ratio is entrusted to a game that takes place in special pressure valves pistons on the one hand are placed in communication with the oil regulator, the other with the air intake system: the piston moves in one direction or another depending on the pressure (and hence the force) acting on its faces, allowing oil to flow only in some channels of the actuator. The oil under pressure, driven along predetermined channels, go to the brakes and clutches present in epicyclic gears by determining the transmission ratio. Wanting to be pragmatic, to understand its functioning, we must imagine that the air acts on the piston to move to higher gear, while the oil acts to maintain the relationship grafted or climb to the lower ratio. The balance (or imbalance) between these two forces, which act in opposition, determined to maintain the relationship or the transition to march higher or lower. We try to simulate a change of gear in case of a gradual acceleration. With increasing vehicle speed, increases with the amount of oil passing through the regulator (which corresponds to a physical law, a lesser burden on the oil itself), while the air in the manifold vacuum will be low (because 'accelerator is slightly down) and then, on the side of the piston acts on which the oil will be, during the acceleration phase, under a progressively lower than that on the side where the air acts, and the valve will move quickly in the direction that allows the transition into higher gear. If, however, accelerate hard, the depression that is created in the collector, following the opening value of the butterfly, it will be so high as to create a small force on the piston valve actuator. You will then be kept in gear until the oil on the other side of the piston reaches a pressure to generate an even smaller force, and this only occurs if the regulator (and thus the engine) is open to maximum, or high speed. In this condition, the gear shift occurs automatically at high speeds. During the kick-down is exactly the opposite: it generates a strong and sudden depression in the collector, which destroys the force acting on the air side of the piston, so the oil pressure "wins" and moves in the opposite direction allowing climb to the lower ratio. The use of a single valve would only choose between two gears, so that the automatic transmissions are more valves each of which works only in a certain range of pressure. Moreover, in modern automatic transmissions valves are electro-mechanical units that control and ruled by many other mathematical parameters: engine speed, if the brake pedal and accelerator are pressed and how much, the yaw rate (which indicates if and how you take a curve), any signals from ABS, if you are traveling uphill or downhill ... in order to ensure report the most appropriate in all driving conditions and adapting to the driving style of the pilot. With such a sophisticated electronic management, modern automatic transmissions no longer have those annoying behaviors of transmissions of the past, such as the inclusion of the longest running upon releasing the team (for the game of pressure ...), the scaled curve which can unbalance the car, and offered reduced engine braking. The automatic classic is presented to the driver, despite the complexity of the mechanics that is, very simply: a lever that can be moved back and forth (not "H" as the manual transmissions) in certain locations. Common to all these changes are the parking position (P), reverse (R), the neutral (N) and the normal running position ("D", ie Drive) where the changes occur automatically, there are also two others, three positions that allow you to select and maintain fixed ratios are useful in some circumstances. City buses, where the machines are a constant for almost thirty years, are generally a small panel in place of the selector lever, while a number of years, the cars most important sports facilities and the possibility of using the automatic transmission as if it were manual, leaving the driver to decide which value to insert (with the supervision of the omnipresent e): to do this simply move the selector lever to the side and taps to small forward and back to go up or down gear. The first automaker to introduce this feature is nothing less than the Porsche with the sporty '911 Carrera "in 1990 equipped with the ZF automatic' Tiptronic '. Rebuffed by most drivers, a bit 'wrong and a bit' to reason, automatic torque converter is experiencing a growing popularity, not only on the representation of large sedans, but also on the 'medium', up to the super, as the aforementioned Porsche or Jaguar, even the Ferrari, which has adopted a program to (only) 4 reports "456 M GTA." Among the reasons for this appeal, there is no doubt the happy pair with modern diesel-rich couple (just mentioned, because of their exuberance, and other popular machines such as those continuously variable CVT), the fine electronic management that has blurred its weaknesses, the smoothness of operation, the ability to "have fun" by manually selecting the speed without sacrificing comfort. The only hints are still grieving its cost, higher than a manual transmission, and can greatly affect the price of a car, and its high construction complexity.
