If the gearbox did not exist, the wheels would suddenly receive all the torque provided, and this would make the transmission impractical. A manual transmission uses gear pairs, that is, gear ratios. They regulate, that is, transform the amount of torque transmitted to the wheels. The clutch is a disc located between the gearbox and the engine: it prevents the engine from stalling and allows the car to start moving and also makes shifting easier. Instead, how is an automatic transmission made?
The various automatic transmission systems can be divided into four main types:
- automatic transmission with a torque converter;
- robotic gearbox;
- dual-clutch transmission.
Automatic transmission with torque converter
In an automatic transmission with a torque converter, instead of using gears, torque is transmitted through a hydraulic converter located between the engine and the gearbox.
This is a very complex mechanism that, through a series of valves, causes a differential pressure of a certain oil, and so the gear changes. The torque converter replaces the clutch. In the past, this system was completely mechanical, very expensive and heavy. Today many parts have been replaced by electronic systems, resulting in reduced complexity, cost and weight.
Robotic automatic transmission
This is a semi-automatic transmission: the gear ratios are always mechanical, and the gear selection and engagement operations are electronic. The driver selects the gear by pressing the lever or buttons; in this way, an electrical impulse is generated, which is sent to the box control unit; he, based on the predefined programs, decides which coefficients to use.
This gearbox is used in racing cars because it is very quick to engage; for the same reason, it is also adopted in some road models, albeit tuned for sweeter changes.
Automatic transmission with continuous variation
The automatic continuously variable transmission is also called CVT (ContinuousVariableTransmission). Instead of using cogwheels, it has a pair of pulleys (or rollers, or cones) around which a belt is wound; depending on the engine speed, the pulleys move, changing the belt diameter. This variable movement determines the gear ratio.
Since this movement is continuous, there are endless relationships. The CVT system allows the engine to run continuously, always close to maximum torque, that is, in a situation of maximum efficiency. For this reason, there is better fuel economy.
Automatic transmission with dual clutch
Depending on the manufacturer, the automatic dual-clutch transmission is also called DSG (Direct Shift Gearbox) or DCT (Dual-clutch Transmission). This is the evolution of a robotic gearbox.
There are two clutches, one for even gear ratios and one for odd gear ratios, connected to two transmission shafts. They rotate at the same time, so the relationship is always ready, and they engage two at a time, but only the chosen is passed on to the pair. The clutch is fully automatic and electronically controlled. Thus, the rate of change is very high.
Automatic or mechanical switching, which is better?
The determination of whether an automatic or a manual transmission is better depends, as always, on one’s own needs. The manual transmission is cheaper and, in the hands of the experts, allows you to use all the power available exactly when you need it.
Great sportiness and complete freedom for the driver. The disadvantage is the use in the city and in traffic jams, where there is a great inconvenience of continuously pressing the pedal and the lever for several meters.
The traditional automatic transmission with torque converter provides excellent driving comfort. The disadvantage is the significantly higher cost and weight, although in recent years electronics has allowed some reduction.
The CVT offers maximum fuel economy and better driving comfort considering weight, dimensions and not excessive costs. The main disadvantage is that it does not allow for sporty driving, if not due to complex electronic configurations that add significant costs. It’s also noisy.
A robotic transmission and its dual-clutch evolution are slightly more expensive than a manual transmission. They provide the comfort of both classic automatic and speed modes, suitable for sporty driving, with shift times that no one can handle, and also allow the driver to select the gear and when to engage it (within certain limits).
If you have an old car with a faulty gearbox and you are looking to upgrade, you should consider selling your car and save towards your new car. A cash for cars service would be very ideal to sell your car quickly.