The automatic transmission is controlled by two friction clutches/brakes (B2, B3) which operate in a synchronised control i.e. one clutch is released while the other is engaged. To prevent engine overrun during gear change, caused by small differences in the timing of the clutches, an overrun monitoring of the engine speed provides control signals to modify the clutch controls. The overrun signal also activates a blocking control to reduce the engine speed. This can be linked to a throttle control which reduces the engine torque and keeps the engine speed within set change limits. The blocking control operates when the engine speed is above a set threshold level, but below the maximum allowed level.
