How automatic transmissions are controlled

Compared to manual transmissions, modern automatic transmissions enhance driving comfort and can also save on fuel, which is because they independently determine the point at which the engine runs most efficiently. In series-produced vehicles, there are now up to nine gears to choose from.

Modern transmissions are equipped with a great deal of digital intelligence so that they are always capable of identifying the engine’s ideal operating point. Bosch supplies the control units, sensors, and solenoid valves for all major types of transmissions. The control unit is a miniature computer that enables the complex operation of different types of automatic transmissions. The processing capacity of a modern transmission control unit is 160 times more powerful than that of the computer used for the first lunar flight.Bosch Transmission control unit

Bosch controls for automatic transmissions

Automatic transmission

The tried-and-tested transmission shifts automatically using programs stored in the control unit. In many cars, the driver also has the option of shifting to another gear with switches on the steering wheel, which prevents shifting errors. The traditional automatic often has six gears, though some ultra-efficient versions now feature up to nine gears.

Automated manual transmission (Also known as robotized transmission or AMT)

This type of transmission theoretically combines the best of an automatic and a manual transmission. It offers the comfort and convenience of an automatic with the individual control of a manual transmission. The clutch remains open when idle and only uses energy when being closed. This transmission therefore also saves fuel, reducing CO2 emissions in the process.

Dual-clutch transmission

This particular model actually comprises two separate transmissions. One is used for the even gear set and the other for the odd. Two clutches shift back and forth between both transmissions within a split second, allowing for especially swift gear changes. The complex coordination in a dual-clutch transmission is only made possible by a sophisticated transmission control system with powerful processing.

Continuously variable transmission (CVT)

The CVT is an automatic transmission without any fixed shifting point, which completely eliminates shifting response delays. As a result, the driver can accelerate without any interruption as the driving force is available at all times. The vehicle does not have to shift back and forth between fixed shifting points – a feature that provides extra driving comfort, especially when going up an incline. CVT is widespread in Asia and North America.


The Bosch eClutch introduces the comfort of an automatic to a manual transmission in a cheaper way than with an AMT. Thanks to this technology, drivers can go into first gear simply by stepping on the gas pedal. The eClutch automates the clutch only, not the transmission. The clutch pedal transmits an electric signal to an actuator, which decouples the clutch. This affordable alternative to a fully automatic transmission is especially useful for drivers of compact cars that frequently find themselves in stop-and-go traffic within urban settings. The eClutch also represents an option for drivers in emerging markets.Bosch eClutch

The future of transmission technology at Bosch


Thanks to the eClutch, manual transmissions can also benefit from the fuel-saving coasting function, which is otherwise only possible with modern automatic transmissions. Coasting expands on the start-stop function and enables additional fuel savings of up to ten percent. When this function is used, the engine not only switches off at traffic lights, but also while the vehicle is moving.

Electronic horizon

Bosch Electronic horizonBosch is driving forward connecting transmissions with the latest available navigation information. Navigation systems know the lay of the land and can transmit this data to the automatic transmission, which, in turn, can shift into neutral and use the residual momentum if city limits are coming up after a long bend, for example. This intelligent automatic transmission with electronic horizon can potentially provide additional double-digit fuel savings.

Source: Bosch

Romain’s opinion:

Bosch software and hardware development teams are releasing products for nearly every aspect of a car (engine, transmission, vehicle dynamics…). How big are these teams? How are they collaborating between different applications? Do they use the same tools?

1 thought on “How automatic transmissions are controlled”

  1. Dear Sir,

    We are company who specialize in converting diesel engines to CNG in Turkey.

    Now we have a issue in hand that we need to solve whatever it takes.

    We are working on a 2015 Mercedes Axor 1840 with engine om457 (Full auto transmission)

    We succesfuly converted the engine without any problems but we have a problem with the Mercedes MR control unit.

    Our CNG ecu supports J1939 and is 250 bits and we would like to replace Mercedes MR unit with our CNG ecu , would you be able to create us a gateway for this operation ? or is there any other way you can help us with this issue ?

    We are anxioulsy waiting for your reply cause this is an urgent matter for us…,

    Thanks in advance


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