Negative stiffness hydraulic system

Patent metadata

Field	Value
Publication number	US-9593739-B2
Application number	US-201414561185-A
Country	US
Kind code	B2
Filing date	Dec 4, 2014
Priority date	Dec 6, 2013
Publication date	Mar 14, 2017
Grant date	Mar 14, 2017

Abstract

A variable stiffness structure configured to support a variable load, the variable stiffness structure including a positive stiffness element coupled to the variable load, a negative stiffness element, a hydraulic system coupled to the positive and negative stiffness elements and configured to adjust a relative position of the positive and negative stiffness elements in response to a change in the variable load, while the variable stiffness structure supports the variable load.

First claim

What is claimed is:

1. A variable stiffness structure configured to support a variable load, the variable stiffness structure comprising:
a positive stiffness element coupled to the variable load;
a negative stiffness element; and
a hydraulic system coupled to the positive and negative stiffness elements and configured to adjust a relative position of the positive and negative stiffness elements in response to a change in the variable load, while the variable stiffness structure supports the variable load.

2. The variable stiffness structure according to claim 1 ,
wherein the positive stiffness element is configured to couple the variable load to an external body, and
wherein the negative stiffness element is configured to isolate vibrations of the variable load from the external body.

3. The variable stiffness structure according to claim 2 ,
wherein the change in the variable load produces a displacement in the relative position of the variable load and the external body exceeding an operational range of displacement within which the negative stiffness element provides a negative stiffness constant to an aggregate stiffness constant of the variable stiffness structure, and
wherein, in response to the change in the variable load, the hydraulic system is configured to return the variable stiffness structure to the operational range of displacement by applying fluidic pressure to adjust the relative position of the positive and negative stiffness elements.

4. The variable stiffness structure according to claim 1 , wherein the variable stiffness structure is configured to maintain a substantially constant stiffness as the relative position of the positive and negative stiffness elements is adjusted in response to a change in the variable load.

5. The variable stiffness structure according to claim 1 , wherein the positive stiffness element is configured to provide a positive stiffness constant to an aggregate stiffness constant of the variable stiffness structure.

6. The variable stiffness structure according to claim 1 , wherein the hydraulic system comprises an actuator and is configured to disengage the negative stiffness element prior to adjusting the relative position of the positive and negative stiffness elements, and to re-engage the negative stiffness element after the adjusting the relative position of the positive and negative stiffness elements.

7. The variable stiffness structure according to claim 1 , wherein the hydraulic system comprises:
a hydraulic chamber coupled to the negative stiffness element;
an accumulator; and
a valve system configured to move fluid between the hydraulic chamber and the accumulator,
wherein the hydraulic chamber is configured to exert fluidic pressure on the negative stiffness element to adjust the position of the negative stiffness element relative to the positive stiffness element, in response to the change in the variable load.

8. The variable stiffness structure according to claim 7 , wherein the valve system is configured to increase or decrease the fluidic pressure inside the hydraulic chamber according to the change in the variable load.

9. The variable stiffness structure according to claim 7 , wherein the valve system comprises two or more pressure relief valves arranged in opposite directions and configured to permit flow of fluid between the hydraulic chamber and the accumulator, when a fluid pressure in either the hydraulic chamber or the accumulator exceeds a relief pressure.

10. The variable stiffness structure according to claim 9 , wherein the two or more pressure relief valves comprise passive valves.

11. The variable stiffness structure according to claim 7 , wherein the valve system comprises one or more of a passive valve and an active valve.

12. The variable stiffness structure according to claim 1 , wherein the hydraulic system comprises:
a first hydraulic chamber coupled between the negative stiffness element and the variable load;
a second hydraulic chamber coupled between the negative stiffness element and a body; and
a valve system configured to move fluid between the first hydraulic chamber and the second hydraulic chamber to adjust the position of the negative stiffness element relative to the positive stiffness element, in response to the change in the variable load.

13. The variable stiffness structure according to claim 1 , wherein the positive stiffness element comprises a first rubber disc and a second rubber disc, and is coupled to the variable load through an inner post.

14. The variable stiffness structure according to claim 13 , wherein the negative stiffness element comprises a pair of buckled discs having a first end coupled to a body and a second end configured to slide along a length of the inner post.

15. The variable stiffness structure according to claim 14 , wherein the hydraulic system comprises:
a first hydraulic chamber between the first rubber disc and the negative stiffness element;
a second hydraulic chamber between the first rubber disc and the negative stiffness element; and
a valve system configured to move fluid between the first hydraulic chamber and the second hydraulic chamber to adjust the position of the negative stiffness element relative to the inner post, in response to the change in the variable load.

16. The variable stiffness structure according to claim 15 , wherein a stiffness of the negative stiffness element remains substantially constant as the valve system adjusts the position of the negative stiffness element relative to the inner post.

17. The variable stiffness structure according to claim 1 , wherein the hydraulic system comprises:
a first hydraulic chamber coupled between the negative stiffness element and the variable load;
a second hydraulic chamber coupled between the negative stiffness element and a body;
a first accumulator; and
a valve system configured to move fluid between the first accumulator and the first and second hydraulic chambers,
wherein the each of the first and second hydraulic chambers is configured to exert fluidic pressure on the negative stiffness element to adjust the position of the negative stiffness element relative to the positive stiffness element, in response to the change in the variable load.

18. The variable stiffness structure according to claim 17 , wherein the valve system is configured to increase or decrease fluidic pressures inside the first and second hydraulic chambers according to the change in the variable load.

19. The variable stiffness structure according to claim 17 , wherein the valve system is configured to balance fluidic pressures between the first and second hydraulic chambers according to the change in the variable load.

20. The variable stiffness structure according to claim 17 , further comprising a sensor coupled to one of the first and second hydraulic chambers,
wherein the sensor is configured to sense a fluid pressure inside one of the first and second hydraulic chambers, and
wherein the valve system is further configured to control the stiffness of the negative stiffness element according to the sensed fluid pressure.

21. The variable stiffness structure according to claim 17 , wherein the hydraulic system further comprises a first actuator configured to push fluid from one of the first and second hydraulic chambers into another one of the first and second hydraulic chambers.

22. The variable stiffness structure according to claim 17 , wherein the hydraulic system further

Assignees

• Hrl Lab Llc

Inventors

• Churchill Christopher B
• Herrera Guillermo A
• Mcknight Geoffrey P
• Mikulsky Jacob J

Classifications

• F16F2228/063

  Negative stiffness · CPC title

• F16F2228/066

  Variable stiffness · CPC title

• F16F15/022 Primary

  using dampers and springs in combination · CPC title

• F16F13/28

  specially adapted for units of the bushing type (F16F13/30 takes precedence) · CPC title