A transmission control unit or TCU is a device that controls modern electronic
automatic transmissions. A TCU generally uses sensors from the vehicle
as well as data provided by the Engine Control Unit to calculate how and when
to change gears in the vehicle for optimum performance, fuel economy and shift
quality.
Electronic automatic transmissions have been shifting from
purely hydromechanical controls to electronic controls since the late 1980’s.
Since then, development has been iterative and today designs exist from several
stages of electronic automatic transmission control development. Transmission
solenoids are a key component to these control units.
The evolution
of the modern automatic transmission and the integration of electronic controls
have allowed great progress in recent years. The modern automatic transmission
is now able to achieve better fuel economy, reduced engine emissions, greater
shift system reliability, improved shift feel, improved shift speed and improved
vehicle handling. The immense range of programmability offered by a TCU allows
the modern automatic transmission to be used with appropriate transmission characteristics
for each application.
On some applications, the TCU and
the ECU are combined into one unit, a Powertrain Control Module or PCM.
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