In European countries, people rarely delve into the technical intricacies of transmission design — there, the key criterion when choosing a gearbox is its fuel efficiency. Ukrainian car enthusiasts, however, when choosing an automatic transmission, primarily pay attention to durability and reliability. This issue is especially relevant when buying a used car.
In this article, we will explain in simple terms the design differences between automatic transmissions and list the strengths and weaknesses of each.
Torque converter (classic) automatic transmission
This transmission is quite complex in design, and it appeared later than the CVT or robotic gearbox. However, it was the first to achieve widespread use in cars. The development of the other two types was held back by the lack of reliable ways to control the transmission of force — in other words, imperfect electronics.
The first production samples of such transmissions began to be produced in the early 40s of the last century. American engineers installed Hydramatic gearboxes on Oldsmobile cars. Those first units had only three gears, but given the huge engine displacement and cheap fuel in the US, that was enough. It is worth noting that one of them was reverse, so the gearbox was effectively two-speed.
However, the low efficiency, mediocre acceleration dynamics, and other drawbacks forced engineers to refine the design, and over time the number of gears increased. The torque converter remained to perform the clutch function, ensuring smooth transmission of torque from the engine to the gearbox. This scheme is still used today, having undergone a long modernization and gained electronic control.
The main drawback of classic automatic transmissions — low efficiency and, as a result, higher fuel consumption — has also been minimized. In modern cars, the torque converter is used only for smooth starts, and then electronics rigidly lock it, eliminating unnecessary energy losses.
Electronic systems also help with gear shifting. A modern gearbox selects the moment of gear change more accurately, analyzing the vehicle's load, driving style, and even the road incline (an incline sensor is present in many automatic transmissions).
The development of computer technology has allowed drivers to choose the gearbox's operating algorithm: economical, sport, manual, winter, etc. Modern hydraulic automatic transmissions have more gears, and the units themselves have become smaller in size and weight. Classic gearboxes are still in demand in large and powerful cars. They are also found in small cars, mostly budget ones, which are equipped with almost "ancient" 4-speed units. Examples include the new Lada Granta and Nissan Almera.
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Top 5 popular cars with classic automatic transmission: Honda Civic, Nissan Note, Toyota Camry, KIA Sportage, Mitsubishi Pajero Wagon
CVT
Oddly enough, the idea of transmitting force from one cone to another via a belt has been known since the Middle Ages. Millers used it. At that time, the belt was moved manually, and the loads were small, so for a long time it was not possible to adapt this scheme for cars.
The principle of operation can be illustrated with a bicycle, where instead of several sprockets there are two cones, and instead of a chain, a belt. If the electronics quickly and accurately moves the belt from a cone of larger diameter to a cone of smaller diameter on one end, then the transmitted force changes accordingly on the other end, which rotates the wheel. This is similar to what a cyclist does when shifting the chain from one sprocket to another.
Initially, the CVT performed excellently on low-power equipment, such as scooters. But powerful engines quickly killed the belt. Over time, it was replaced by a steel segmented belt, and cones are no longer used either. However, the principle of force transmission remains the same. For starting off, a torque converter is most often used (there are also CVTs with wet clutches, etc.). Therefore, energy losses, albeit smaller than in the classic, are also present in the CVT.
Modern CVTs are quite reliable and, as claimed in advertising materials, are designed for the entire service life of the car. However, failures of the control unit sometimes occur, and this part can cost several tens of thousands of hryvnias. True, such a malfunction is typical for cars with old CVTs.
The advantages of the CVT include the absence of steps, and therefore no interruption in power delivery to the drive wheels during movement. Many drivers consider it a drawback that the engine runs at the same revs during acceleration, emitting a monotonous hum. But modern electronics can smooth this out too, artificially changing the character of the engine sound.
The CVT is noticeably more economical than the classic automatic transmission, and the absence of gears provides decent dynamics. It loses to the "classic" only at the start, in the first meters of the journey, but then quickly catches up, being in the operating rev range.
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Top 5 popular cars with CVT: Honda Jazz, Toyota Yaris, Subaru Impreza, Mitsubishi ASX, Nissan Teana
Robotic automatic transmission
The robot was conceived as an inexpensive replacement for the classic automatic. In essence, it is a regular manual, where the clutch release and gear shifting are handled by electronics.
Hence the main problem of such gearboxes — increased clutch wear. Not everyone knows that at traffic lights, the selector of such a gearbox should be moved to neutral — this way the clutch will last longer.
Another nuance is the inconsistency of the robot's actions with the driver's wishes. For example, when entering a highway, the driver wants to add gas in second gear, in which he is driving, but instead of smooth acceleration, he gets a jerk forward (as if the car braked), and only after a while — a sharp jump in speed. The reason is that the robot's algorithm repeats the "manual": to shift, you need not only to press the gas but also to release it. The second way to cope with jerks is to switch to manual mode. Therefore, such a gearbox requires getting used to and certain skills.
In addition to the low price, such an "automatic" attracts with decent efficiency. Robots are common in small cars of classes A, B, less often C.
Overall, robots are quite reliable, except for clutch problems. Failures in the control electronics are also possible.
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Top 5 popular cars with robotic automatic transmission: Peugeot 107, Fiat 500, Peugeot 208, Lancia Ypsilon, Citroen C4,
Preselective automatic transmission (with dual clutch)
Unlike a simple robot, this transmission combines two robotic gearboxes in one housing. Therefore, it has two clutches and two secondary shafts, each with its own set of gears. There are also two primary shafts, with one passing inside the hollow second.
This design allows two gears to be engaged simultaneously, with one of the clutches always "released." It turns out that during acceleration, to shift to the next gear, it is enough to disengage one clutch and engage the other. This happens synchronously and takes only 0.1 seconds.
Such an automatic transmission provides not only fast acceleration and full use of the engine's potential but also saves fuel, since it constantly shifts and has at least six gears. Moreover, the interruption of power flow during shifts is practically imperceptible.
This transmission has many advantages, and essentially only one drawback — price. Both the gearbox itself and its repair are expensive. There were many complaints about the first generations. Today, such units have become much more reliable, although much depends on the manufacturer.
Porsche, Mercedes, Audi, Volkswagen — all of them use this type of automatic transmission. And in the future, according to experts' forecasts, the CVT and the dual-clutch robot will become the main ones. Other types will likely become exotic and remain only on certain models.
Since the design of preselective gearboxes is not yet fully refined and unsuccessful versions are found, it is too early to talk about the average service life. But the latest generations of such transmissions easily pass more than 200 thousand km, and this is far from the limit.
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Top 5 popular cars with preselective automatic transmission: Volkswagen Polo, Audi A3, Mercedes-Benz B-Class, Ford Mondeo, Volkswagen Passat
Summary
Summing up, the following recommendations can be given to a buyer of a new car:
- CVT — for small class cars (A, B, C);
- dual-clutch robot — for cars from C-class and above;
- classic hydromechanics — for SUVs that regularly drive off-road.
The service life of any automatic transmission depends on its design, manufacturer, and operating conditions. After all, an expensive automatic gearbox can be quickly ruined if you neglect common sense and the manufacturer's recommendations.
If we are talking about a used car, an automatic — regardless of type — requires careful inspection and consultation with a specialist. Read about how to properly handle a particular automatic and how to extend its service life in our next article.
