Power shift transmissions

A transmission comprising a torque convertor having an input shaft and an output shaft,

• a power shift gear box having rotatable input and output shafts and multi-ratio drive means to produce different speeds of rotation of the output shaft relative to the input shaft, said drive means including gears which are in constant mesh and clutches, which are engageable and disengageable under load, to connect the gears in a desired drive path,
• a variable torque capacity clutch located between the torque convertor output shaft and the multi-ratio drive means,
• means under the manual control of an operator for controlling the instantaneous torque transmittal capacity of said clutch, and
• control means for operating the clutches of the multi-ratio drive means to change the ratio of the gear box in dependence upon an electrical signal derived from rotation of a first element associated with the torque convertor input shaft and of a second element associated with an intermediate shaft upstream of the multi-ratio drive means and downstream of said variable torque capacity clutch.