Autonomous emergency lubrication of aircraft gearboxes

A tiltrotor aircraft having a helicopter mode and an airplane mode, the tiltrotor aircraft comprising:

• a proprotor assembly;
• a first gearbox assembly in mechanical communication with the proprotor assembly;
• a second gearbox assembly in mechanical communication with the first gearbox assembly;
• an engine in mechanical communication with the second gearbox assembly and configured to provide torque and rotational energy to the proprotor assembly via the first and second gearbox assemblies;
• a first pressurized lubrication system configured to circulate a first lubricant through the first gearbox assembly;
• a second pressurized lubrication system configured to circulate a second lubricant through the second gearbox assembly;
• and
• an emergency lubrication system including first and second passive valve assemblies positioned between the first pressurized lubrication system and the second pressurized lubrication system, the emergency lubrication system configured to autonomously supply a portion of the first lubricant to the second gearbox assembly responsive to a change in differential pressure between the first pressurized lubrication system and the second pressurized lubrication system and configured to autonomously supply a portion of the second lubricant to the first gearbox assembly responsive to a change in differential pressure between the second pressurized lubrication system and the first pressurized lubrication system;
• wherein, the first and second passive valve assemblies each include a valve element having a first side subjected to a biasing pressure from the first pressurized lubrication system and a second side subjected to a biasing pressure from the second pressurized lubrication system, each valve element moveable between a plurality of positions in response to a change in the biasing pressure from at least one of the first pressurized lubrication system or the second pressurized lubrication system;
• wherein, pressure in the second pressurized lubrication system maintains the first passive valve assembly in a closed position during normal operating conditions of the second pressurized lubrication system such that the first lubricant does not pass through the first passive valve assembly;
• and
• wherein, responsive to a loss of pressure in the second pressurized lubrication system, the first passive valve assembly shifts to an open position such that the portion of the first lubricant is autonomously supplied to the second gearbox assembly.

An aircraft comprising:

• a rotor assembly;
• a first gearbox assembly in mechanical communication with the rotor assembly;
• a second gearbox assembly in mechanical communication with the first gearbox assembly;
• an engine in mechanical communication with the second gearbox assembly and configured to provide torque and rotational energy to the rotor assembly via the first and second gearbox assemblies;
• a first pressurized lubrication system configured to circulate a first lubricant through the first gearbox assembly;
• a second pressurized lubrication system configured to circulate a second lubricant through the second gearbox assembly;
• and
• an emergency lubrication system including first and second passive valve assemblies positioned between the first pressurized lubrication system and the second pressurized lubrication system, the emergency lubrication system configured to autonomously supply a portion of the first lubricant to the second gearbox assembly responsive to a change in differential pressure between the first pressurized lubrication system and the second pressurized lubrication system and configured to autonomously supply a portion of the second lubricant to the first gearbox assembly responsive to a change in differential pressure between the second pressurized lubrication system and the first pressurized lubrication system;
• wherein, the first and second passive valve assemblies each include a valve element having a first side subjected to a biasing pressure from the first pressurized lubrication system and a second side subjected to a biasing pressure from the second pressurized lubrication system, each valve element moveable between a plurality of positions in response to a change in the biasing pressure from at least one of the first pressurized lubrication system or the second pressurized lubrication system;
• wherein, pressure in the second pressurized lubrication system maintains the first passive valve assembly in a closed position during normal operating conditions of the second pressurized lubrication system such that the first lubricant does not pass through the first passive valve assembly;
• and
• wherein, responsive to a loss of pressure in the second pressurized lubrication system, the first passive valve assembly shifts to an open position such that the portion of the first lubricant is autonomously supplied to the second gearbox assembly.