Crashworthy landing gear shock

• US 5,944,283 A
• Filed: 12/05/1997
• Issued: 08/31/1999
• Est. Priority Date: 12/05/1997
• Status: Expired due to Term

• Current Assignee: Carter Aviation Technologies, LLC
• Original Assignee: Cartercopters LLC
• Inventors: Carter, Jay W. Jr.
• Primary Examiner(s): Jordan, Charles T.
• Assistant Examiner(s): Dinh, Tien
• Application Number:
  US08/985,892
• Time in Patent Office: 634 Days
• Field of Search: 244/104 FP, 244/104 R, 244/100 R, 267/64.13, 267/64.15, 188/289, 188/182.14, 188/322.19, 188/319.1, 188/319.2, 188/313, 188/314
• US Class Current: 244/104.0FP
• CPC Class Codes: B64C 25/00 Alighting gear air-cushion alighting gear B60V3/08
• CPC Class Codes: B64C 25/60 Oleo legs
• CPC Class Codes: F16F 9/06 using both gas and liquid F16F9/486 take precedence; self-pumping fluid springs B60G17/044

Abstract

A shock absorber, optionally operable as a retractable landing gear actuator, includes a sealed cylinder divided by a cylinder head to define an upper chamber and a lower chamber, the lower chamber further divided by a piston having a piston rod passing in sealed manner through the lower cylinder end. The cylinder head includes one or more orifices, the effective opening of each orifice controlled by a valve, the valve having a stem attached to and passing through the upper cylinder end to the atmosphere, such that the pressure between the piston and the cylinder head is limited to a certain value above atmospheric pressure, regardless of the velocity or position of the piston. The valve is forced toward the closed position by a spring against a stop such that it is always at least partially open. During hard or crash landings, high fluid pressure on the piston or in the upper chamber forces the valve further open.

Claims

1. A shock absorber for fitting to the landing gear of an aircraft, the shock absorber comprising:

a cylinder having a first end and a second end and containing a hydraulic fluid;

a piston located in the cylinder, the piston having a rod extending outward from the second end of the cylinder;

an orifice in the cylinder, through which the hydraulic fluid flows as the piston moves toward the first end due to a shock applied; and

a valve mounted to the cylinder, having a first end adjacent the orifice and a second end exposed to atmospheric pressure, the valve being movable relative to the orifice from a less restrictive position to fluid flow through the orifice to a more restrictive position and being urged toward the more restrictive position by a spring, wherein if a shock applied to the shock absorber is of sufficient magnitude, a pressure differential between atmospheric pressure and pressure between the valve and the piston causes the valve to move toward the less restrictive position to allow a greater flow rate through the orifice.

2. The shock absorber according to claim 1, further comprising a cylinder head fixedly mounted in the cylinder between the first end and the piston, the orifice being located in the cylinder head.

3. The shock absorber according to claim 1, further comprising a cylinder head fixedly mounted in the cylinder between the first end and the piston, the orifice being located in the cylinder head;

and wherein the second end of the valve extends sealingly through the first end of the cylinder.

4. The shock absorber according to claim 1, wherein in the more restrictive position, the valve allows a limited flow through the orifice.

5. The shock absorber according to claim 1, wherein the second end of the valve extends sealingly through the cylinder and has a cross-sectional area where it is sealed to the cylinder which is substantially equal to a cross sectional area of the orifice.

6. The shock absorber according to claim 1, further comprising:

an adjustment mechanism mounted to the valve for adjusting a minimum gap between the first end of the valve and the orifice.

7. A shock absorber according to claim 1, further comprising:

an adjustment mechanism mounted between the valve and the cylinder for adjusting a compression force of the spring to adjust the force at which the valve is urged toward the orifice.

8. A shock absorber according to claim 1, wherein in the more restrictive position, the first end of the valve contacts the orifice;

and wherein the shock absorber further comprises;

a flowby passage which allows a limited amount of fluid flow through the orifice while the first end of the valve is in contact with the orifice.

9. A shock absorber according to claim 1, wherein the first end of the valve comprises:

a valve head slidably carried by the valve and movable between an upper position and a lower position relative to the valve.

10. A shock absorber according to claim 1, wherein:

the second end of the valve is a valve stem; and

the first end of the valve is a valve head movable between an upper and a lower position relative to the valve stem, and wherein the shock absorber further comprises;

a valve head spring for urging the valve head to the upper position;

a valve head piston mounted to the valve head for movement therewith and configured to move the valve head to the lower position, further restricting the orifice, at a preset pressure drop across the orifice.

11. The shock absorber according to claim 10, further comprising:

a passage for communicating pressure from below the valve head piston to above the valve head piston;

the valve head piston having a cross sectional area which is greater than a cross sectional area of the orifice; and

a one-way valve for preventing, for a limited duration, flow from above the piston to the passage.

12. A shock absorber according to claim 1, further comprising:

a below-piston fluid port for allowing the ingress and egress of fluid into and out of the cylinder between the piston and the second end of the cylinder; and

an upper fluid port between the orifice and the first end of the cylinder for allowing the ingress and egress of fluid into and out of the cylinder, so that the piston can be actuated between extended and retracted positions to raise and lower the landing gear.

13. A shock absorber according to claim 12, further comprising an air/oil separator connected to the upper fluid port such that hydraulic fluid escaping from the cylinder through the upper fluid port during landing gear retraction will be returned to the cylinder during landing gear extension.

14. A method of limiting pressure above a piston in a shock absorber during an impact, while maintaining substantial deceleration throughout the travel of the shock absorber, comprising:

providing an orifice in the cylinder which causes a dampening resistance to movement of the piston when encountering an impact;

providing a valve which moves between a restricted position and an open position relative to the orifice;

exposing a portion of the valve to atmospheric pressure such that pressure in the cylinder greater than atmospheric pressure tends to move the valve to the open position;

urging the valve toward the restricted position by a spring; and

moving the valve toward the open position when encountering an impact of sufficient magnitude to provide a pressure in the cylinder which overcomes a force exerted by the spring, thereby reducing the dampening resistance and lowering the pressure exerted by movement of the piston.

15. A shock absorber for fitting to the landing gear of an aircraft, having a cylinder sealed on an upper end and sealed on a lower end, a cylinder head fixed within the cylinder and sealingly dividing the cylinder into an upper chamber and a lower chamber, a piston sliding in sealed manner in the lower chamber and dividing the lower chamber into an above-piston chamber and a below-piston chamber, a piston rod having one end connected to the piston and extending outside of the cylinder through a sealed opening in the lower end, a quantity of hydraulic fluid in the above-piston chamber, and a quantity of pressurized gas in the upper chamber, the improvement comprising:

the cylinder head having at least one orifice, placing the above-piston volume in fluid communication with the upper chamber;

a valve having a valve head joined to a valve stem, the valve head being located adjacent to the orifice for controlling flow through the orifice, the valve stem sealingly passing through the upper end of the cylinder to atmosphere;

a spring mounted to the valve stem which urges the valve toward the orifice; and

the valve moving linearly to adjust a gap between the valve head and the orifice in response to a difference in pressure between pressure in the above-piston chamber and atmospheric pressure.

16. A shock absorber according to claim 15, wherein the valve has a closed position, and in the closed position, the orifice remains partially open.

17. A shock absorber according to claim 15, wherein

the valve stem has a cross-sectional area where it passes through the upper end of the cylinder that is generally equal to a cross sectional area of the orifice.

18. A shock absorber according to claim 15, wherein:

the volume of the above-piston chamber is substantially equal to the volume of the upper chamber when the piston rod is fully extended outside the shock absorber.

19. A shock absorber according to claim 15, further comprising:

an adjustment mechanism mounted to the valve stem for adjusting a minimum gap between the valve and the orifice.

20. A shock absorber according to claim 15, further comprising:

an adjustment mechanism mounted between the valve stem and the cylinder for adjusting a compression force of the spring to adjust the force at which the valve is urged toward the orifice.

21. A shock absorber according to claim 15, wherein the valve head is movable between an upper and a lower position relative to the valve stem, and wherein the shock absorber further comprises:

a valve head spring for urging the valve head to the upper position;

a valve head piston mounted to the valve head for movement therewith and configured to move the valve head to the lower position, further restricting the orifice, at a preset pressure drop across the orifice.

22. The shock absorber according to claim 21, further comprising:

a passage for communicating pressure from below the valve head piston to above the valve head piston;

the valve head piston having a cross sectional area which is greater than a cross sectional area of the orifice; and

a one-way valve for preventing, for a limited duration, flow from above the piston to the passage.

23. A shock absorber according to claim 15, further comprising:

a below-piston chamber fluid port for allowing the ingress and egress of fluid into and out of the below-piston chamber; and

an upper chamber fluid port for allowing the ingress and egress of fluid into and out of the upper chamber, so that the piston can be actuated between extended and retracted positions to raise and lower the landing gear.

24. A shock absorber according to claim 23, further comprising an air/oil separator connected to the upper chamber fluid port such that hydraulic fluid escaping from the upper chamber during landing gear retraction will be returned to the upper chamber during landing gear extension.