Transmission shift control method for reduced torque transients

A transmission assembly of a power extraction system, the transmission assembly comprising:

• an input shaft coupled to a low-pressure spool of a gas turbine engine whereby rotations of the low-pressure spool between first minimum and maximum speeds drive input shaft rotations at an input rotational speed;
• an output shaft coupled to downstream components whereby output shaft rotations at an output rotational speed drive rotations of the downstream components between second minimum and maximum speeds;
• clutches by which the input shaft rotations at the input rotational speed drive output shaft rotations at the output rotational speed;
• and
• a controller configured to control openings and closings of the clutches according to an upshifting algorithm whereby a torque applied by the downstream components is used to reduce the output rotational speed to an output speed of a gear into which the transmission assembly is shifting by:
• closing a first one of the clutches in a first gear during a first ramping-up of the input rotational speed, opening the first one of the clutches at a first predefined output rotational speed, using the torque applied by the downstream components to reduce the output rotational speed to the output speed of a second gear, closing a second one of the clutches in the second gear when the output rotational speed reaches the output speed of the second gear and during a second ramping-up of the input rotational speed, opening the second one of the clutches at a second predefined output rotational speed and using the torque applied by the downstream components to reduce the output rotational speed to the output speed of a third gear.

A method of operating a power extraction system, comprising:

• a low-pressure spool of a gas turbine engine, the low-pressure spool being rotatable at an input rotational speed between first minimum and maximum speeds;
• downstream components rotatable at an output rotational speed between second minimum and maximum speeds;
• and
• a transmission assembly comprising clutches by which rotations of the low-pressure spool at the input rotational speed are transmittable at the output rotational speed to the downstream components,
• the method comprising controlling openings and closings of the clutches according to an upshifting algorithm whereby a torque applied by the downstream components is used to reduce the output rotational speed to an output speed of a gear into which the transmission assembly is shifting,
• wherein the controlling comprises closing a first one of the clutches in a first gear during a first ramping-up of the input rotational speed, opening the first one of the clutches at a first predefined output rotational speed, using the torque applied by the downstream components to reduce the output rotational speed to the output speed of a second gear, closing a second one of the clutches in the second gear when the output rotational speed reaches the output speed of the second gear and during a second ramping-up of the input rotational speed, opening the second one of the clutches at a second predefined output rotational speed and using the torque applied by the downstream components to reduce the output rotational speed to the output speed of a third gear.