Hydraulic Strut Assembly for Semi-Levered Landing Gear

Abstract

A hydraulic strut assembly, for use in a semi-levered landing gear in an aircraft, comprising an actuator and a manifold associated with the actuator. The actuator comprises a housing, a first piston, a second piston, and a third piston. The first piston is positioned between outer and inner cylindrical structures of the housing. The outer and inner cylindrical structures and first piston form an outer chamber that receives a first fluid. The inner cylindrical structure, the first piston, and the second piston, which is nested within the first piston, form an inner chamber, which holds a second fluid comprising a gas. A volume of the inner chamber changes when at least one of the first and second pistons moves. The third piston is positioned between the outer cylindrical structure and the first piston. The first, second, and third pistons move in a direction parallel to an axis through the housing.

What is claimed is: 
     
         1 . A hydraulic strut assembly comprising:
 a housing comprising an outer cylindrical structure and an inner cylindrical structure;   a first piston positioned between the outer cylindrical structure and the inner cylindrical structure, wherein an outer chamber configured to receive a first fluid is formed between the outer cylindrical structure, the inner cylindrical structure, and the first piston;   a second piston nested within the first piston, wherein the inner cylindrical structure, the first piston, and the second piston form an inner chamber in which a volume of the inner chamber changes when at least one of the first piston and the second piston move and in which the inner chamber is configured to hold a second fluid comprising a gas; and   a third piston positioned between the outer cylindrical structure and the first piston, wherein the first piston, the second piston and the third piston are configured to move in a direction parallel to an axis through the housing.   
     
     
         2 . The hydraulic strut assembly of  claim 1 , wherein at least one of the first piston and the second piston are configured to move such that the gas in the inner chamber compresses as the volume of the inner chamber is reduced. 
     
     
         3 . The hydraulic strut assembly of  claim 1  further comprising:
 an elongate member associated with the second piston, wherein the elongate member is configured to connect a first sub-chamber of the inner chamber to a second sub-chamber of the inner chamber in which the second sub-chamber of the inner chamber is formed by a cavity within the second piston and wherein the elongate member is configured to draw any hydraulic liquid that is part of the second fluid from the second sub-chamber into the first sub-chamber when at least one of the second piston and the first piston extends. 
 
     
     
         4 . The hydraulic strut assembly of  claim 1 , wherein the third piston is configured to divide the outer chamber into a first sub-chamber and a second sub-chamber and wherein movement of the third piston changes a volume of the first sub-chamber and a volume of the second sub-chamber. 
     
     
         5 . The hydraulic strut assembly of  claim 4  further comprising:
 a manifold, wherein the first fluid is configured to flow into the second sub-chamber of the outer chamber from the manifold and wherein the first fluid is configured to return to the manifold from the first sub-chamber of the outer chamber. 
 
     
     
         6 . The hydraulic strut assembly of  claim 5 , wherein the manifold comprises:
 a plurality of channels configured to allow the first fluid to flow through the manifold; and   a plurality of valves configured to control flow of the first fluid from the manifold into the second sub-chamber of the outer chamber and from the first sub-chamber of the outer chamber into the manifold.   
     
     
         7 . The hydraulic strut assembly of  claim 6 , wherein the plurality of valves comprises:
 a multi-mode pressure-reducing valve;   a first solenoid shut-off valve;   a second solenoid shut-off valve; and   a multi-mode pressure-relief valve.   
     
     
         8 . The hydraulic strut assembly of  claim 1  further comprising:
 a spring system associated with at least one of the first piston and the second piston, wherein the spring system is configured to compress in response to a load applied to the spring system. 
 
     
     
         9 . The hydraulic strut assembly of  claim 1 , wherein the inner chamber is divided into a first sub-chamber and a second sub-chamber and further comprising:
 a seal system associated with at least one of the first piston and the second piston, wherein the seal system is configured to divide the first sub-chamber of the inner chamber into a first portion and a second portion and wherein the seal system provides a seal between the first portion and the second portion of the first sub-chamber when the second piston retracts.   
     
     
         10 . The hydraulic strut assembly of  claim 9 , wherein the second fluid comprises the gas and a hydraulic liquid and wherein a volume of the first portion of the first sub-chamber increases and a volume of the second portion of the second sub-chamber decreases in response to the second piston extending such that the hydraulic liquid is forced past the seal system to provide resistance to movement of the second piston. 
     
     
         11 . The hydraulic strut assembly of  claim 10 , wherein the hydraulic liquid is configured to lubricate the seal system. 
     
     
         12 . The hydraulic strut assembly of  claim 1 , wherein the first fluid comprises a hydraulic liquid and the second fluid comprises the gas and the hydraulic liquid in which the gas is compressible. 
     
     
         13 . The hydraulic strut assembly of  claim 1 , wherein the housing, the first piston, the second piston, and the third piston form an actuator in the hydraulic strut assembly and wherein the actuator is configured to have a position selected from one of a compressed position, a retracted position, and a fully extended position. 
     
     
         14 . The hydraulic strut assembly of  claim 13 , further comprising:
 a manifold, wherein the actuator and the manifold are part of a landing gear assembly in an aircraft.   
     
     
         15 . An actuator for use in a hydraulic strut assembly, the actuator comprising:
 a housing comprising an outer cylindrical structure and an inner cylindrical structure;   a first piston positioned between the outer cylindrical structure and the inner cylindrical structure, wherein an outer chamber configured to receive a first fluid is formed between the outer cylindrical structure, the inner cylindrical structure, and the first piston in which the first fluid comprises a hydraulic liquid;   a second piston nested within the first piston, wherein the inner cylindrical structure, the first piston, and the second piston form an inner chamber in which a volume of the inner chamber changes when at least one of the first piston and the second piston move and in which the inner chamber is configured to hold a second fluid comprising the hydraulic liquid and a gas; and   a third piston positioned between the outer cylindrical structure and the first piston, wherein the first piston, the second piston and the third piston are configured to move in a direction parallel to an axis through the housing.   
     
     
         16 . The actuator of  claim 15 , wherein the at least one of the first piston and the second piston are configured to move such that the gas in the inner chamber compresses as the volume of the inner chamber is reduced. 
     
     
         17 . The actuator of  claim 15  further comprising:
 an elongate member associated with the second piston, wherein the elongate member is configured to connect a first sub-chamber of the inner chamber to a second sub-chamber of the inner chamber in which the second sub-chamber of the inner chamber is formed by a cavity within the second piston. 
 
     
     
         18 . The actuator of  claim 15 , wherein the third piston is configured to divide the outer chamber into a first sub-chamber and a second sub-chamber and wherein movement of the third piston changes a volume of the first sub-chamber and a volume of the second sub-chamber. 
     
     
         19 . A method for operating an aircraft to perform an alternate landing, the method comprising:
 operating the aircraft to perform the alternate landing, wherein an actuator in a landing gear assembly for the aircraft comprises:
 a housing comprising an outer cylindrical structure and an inner cylindrical structure; 
 a first piston positioned between the outer cylindrical structure and the inner cylindrical structure, wherein an outer chamber configured to receive a first fluid is formed between the outer cylindrical structure, the inner cylindrical structure, and the first piston; 
 a second piston nested within the first piston, wherein the inner cylindrical structure, the first piston, and the second piston form an inner chamber in which a volume of the inner chamber changes when at least one of the first piston and the second piston move and in which the inner chamber is configured to hold a second fluid comprising a gas; and 
 a third piston positioned between the outer cylindrical structure and the first piston, wherein the first piston, the second piston and the third piston are configured to move in a direction parallel to an axis through the housing; and 
   retracting the second piston and the first piston in response to a load being applied to the second piston when the landing gear assembly contacts a ground on which the aircraft is landing, wherein the gas in the inner chamber compresses when the second piston retracts.   
     
     
         20 . The method of  claim 19 , wherein the step of retracting the second piston and the first piston in response to the load being applied to the second piston when the landing gear assembly contacts the ground on which the aircraft is landing further comprises:
 retracting the second piston and the first piston in response to the load being applied to the second piston when the landing gear assembly contacts the ground on which the aircraft is landing such that the actuator changes from a fully extended position to a compressed position, wherein the first piston and the second piston compress the gas that is in the inner chamber.