Aircraft undercarriage suspension

Abstract

An aircraft undercarriage suspension includes a liquid filled telescopic suspension strut and a gas spring. Liquid displaced by the strut into the gas spring is selectively directed through alternative flow restrictors, one of which is matched for optimum damping during aircraft landing and the other of which is matched for optimum damping during taxing. A ride control valve operates on the nose wheel undercarriage to control aircraft pitching, the ride control hydraulic system being separated from the damping oil by a floating piston.

We claim: 
     
       1. An aircraft undercarriage for supporting an aircraft structure comprising: a ground contacting element;   a variable length liquid-filled strut operatively connected to the aircraft structure and the ground contacting element to support a proportion of the weight of the aircraft structure;   resilient means for controlling the length of said strut in dependence on the load supported thereby;   a first liquid-filled chamber in said strut from which liquid is displaced by upward movement of the ground contacting element relative to the aircraft structure;   a second liquid-filled chamber closed by a movable wall acting on said resilient means in a direction to increase the load thereon under the pressure of liquid displaced from said first chamber;   a valve block;   first and second flowpaths defined by the valve block connecting said first chamber and said second chamber;   first flow restricting means in said first flow path and second flow restricting means in said second flow path to damp movement of the ground contacting element relative to the aircraft structure;   a selector valve in the valve block operable to direct the displaced liquid selectively through each of said flow paths;   .[.and means responsive to.]. .Iadd.and switch means operated by compression of said strut on .Iaddend.aircraft landing to control said selector valve such that said first flow path is operative while the aircraft is landing and the second flow path is brought into operation when the aircraft is taxiing.  .[.   
     
     
       2.  The aircraft undercarriage of claim 1 wherein said means responsive to aircraft landing comprise a switch operated by movement of the ground contacting element relative to the aircraft structure..]. 
     
     
       3. The aircraft undercarriage of claim .[.2.]. .Iadd.1, .Iaddend.wherein a time delay circuit is connected between the switch and the selector valve. 
     
     
       4. The aircraft undercarriage of claim 1 further comprising a relief valve connected in parallel with said second flow restricting means. 
     
     
       5. The aircraft undercarriage of claim 4 wherein said relief valve is double acting. 
     
     
       6. The aircraft undercarriage of claim 1 further comprising a third flow path in said valve block for said displaced liquid, further resilient means, and a further movable wall acting on said further resilient means in a direction to increase the load thereon under the pressure of liquid displaced by said strut. 
     
     
       7. .[.The aircraft undercarriage of claim 1 further comprising.]. .Iadd.An aircraft undercarriage for supporting an aircraft structure comprising: a ground contacting element;   a variable length liquid-filled strut operatively connected to the aircraft structure and the ground contacting element to support a proportion of the weight of the aircraft structure;   resilient means for controlling the length of said strut in dependence on the load supported thereby;   a first liquid-filled chamber in said strut from which liquid is displaced by upward movement of the ground contacting element relative to the aircraft structure;   a second liquid-filled chamber closed by a movable wall acting on said resilient means in a direction to increase the load thereon under the pressure of liquid displaced from said first chamber;   a valve block;   first and second flowpaths defined by the valve block connecting said first chamber and said second chamber;   first flow restricting means in said first flowpath and second flow restricting means in said second flowpath to damp movement of the ground contacting element relative to the aircraft structure;   a selector valve in the valve block operable to direct the displaced liquid selectively through each of said flowpaths;   means responsive to aircraft landing to control said selector valve such that said first flowpath is operative while the aircraft is landing and the second flowpath is brought into operation when the aircraft is taxiing;   and .Iaddend.ride control valve means for connecting said strut selectively to a source of liquid pressure or a drain and a ride control mechanism, connected to said ride control valve means and controlled by sensing means sensitive to displacement of the ground contacting element relative to the aircraft structure.   
     
     
       8. The aircraft undercarriage of claim 7 wherein said means responsive to aircraft landing operate to inhibit operation of said ride control valve means during aircraft landing. 
     
     
       9. The aircraft undercarriage of claim 8 wherein said selector valve isolates the ride control valve from the liquid pressure source when said selector valve is moved to direct said displaced liquid through said first flow path. 
     
     
       10. The aircraft undercarriage of claim 7 further comprising another movable wall in said strut to isolate said displaced liquid from the liquid supplied from the pressure source. 
     
     
       11. The aircraft undercarriage of claim 7 wherein said ride control mechanism comprises a mass suspended so that vertical movement of the mass relative to the aircraft structure operates said ride control valve means, and a spring in parallel with a dashpot connecting the mass to the ground contacting element. 
     
     
       12. The aircraft undercarriage of claim 11 wherein a spring-box link connects the spring and dashpot to the ground contacting element, said spring-box link comprising a preloaded spring which is strained during excessive movement of the ground contacting element relative to the aircraft structure. 
     
     
       13. The aircraft undercarriage of claim 7 wherein said ride control valve means comprises an electro-hydraulic servo valve. 
     
     
       14. An aircraft undercarriage for supporting an aircraft structure comprising: a ground contacting element;   a variable length liquid filled strut operatively connected to the aircraft structure and the ground contacting element to support a proportion of the weight of the aircraft structure;   resilient means for controlling the length of said strut in dependence on the load supported thereby;   a first movable wall acting on said resilient means in a direction to increase the load thereon under the pressure of the liquid displaced by said strut;   a liquid pressure source and a liquid drain;   ride control valve means to selectively connect said strut to said source and said drain;   sensing means sensitive to displacement of the ground contacting element relative to the aircraft structure;   a ride control mechanism operatively connected to said ride control valve means and to said sensing means;   and a second movable wall in said strut to isolate said displaced liquid from the liquid supplied from the pressure source.   
     
     
       15. The aircraft undercarriage of claim 14 wherein means responsive to aircraft landing operate to inhibit operation of said ride control valve means during aircraft landing. 
     
     
       16. The aircraft undercarriage of claim 15 wherein said means responsive to aircraft landing comprise a switch operated by movement of the ground contacting element relative to the aircraft structure. 
     
     
       17. The aircraft undercarriage of claim 16 wherein said switch controls a selector valve operative to isolate said ride control valve from said liquid source. 
     
     
       18. The aircraft undercarriage of claim 17 wherein a time delay circuit is connected between said switch and the selector valve. 
     
     
       19. The aircraft undercarriage of claim 14 wherein said ride control mechanism comprises a mass suspended so that vertical movement of the mass relative to the aircraft structure operates said ride control valve means, and a spring in parallel with a dashpot connecting the mass to the ground contacting element. 
     
     
       20. The aircraft undercarriage of claim 19 wherein a spring-box link connects the spring and dashpot to the ground contacting element, said spring-box link comprising a preloaded spring which is strained during excessive movement of the ground contacting element relative to the aircraft structure. 
     
     
       21. The aircraft undercarriage of claim 14 wherein said ride control valve means comprises an electro-hydraulic servo valve.