Hydraulic actuator with a frequency dependent relative pressure ratio
Disclosed herein are hydraulic actuators and methods for the operation of actuators having variable relative pressure ratios. Further disclosed are methods for designing and/or operating a hydraulic actuator such that the actuator exhibits a variable relative pressure ratio. In certain embodiments, the relative pressure ratio of the hydraulic actuator may be dependent on one or more characteristics (such as, for example, frequency or rate of change) of an oscillating input to the hydraulic actuator.
1. A hydraulic actuator comprising:
a hydraulic cylinder that includes an extension chamber and a compression chamber;
a hydraulic pump, with a first port and a second port, capable of generating a pressure differential between the compression chamber and the extension chamber;
a hydraulic circuit including an extension-side and a compression-side, wherein the extension-side of the circuit includes the extension chamber and a first fluid flow path fluidically connecting the first port to the extension chamber, and wherein the compression-side of the circuit includes the compression chamber and a second fluid flow path fluidically connecting the second port to the compression chamber;
wherein the hydraulic actuator exhibits a first relative compliance factor when exposed to a first oscillating input, and a second relative compliance factor when exposed to a second oscillating input, wherein:
the frequency of the first oscillating input is less than the frequency of the second oscillating input, and
the first relative compliance factor is greater than the second relative compliance factor.
2. The hydraulic actuator of claim 1 , wherein the extension-side of the circuit has a first compliance that is at least partially determined by a first compliance element and the compression-side of the circuit has a second compliance that is at least partially determined by second compliance element.
3. The hydraulic actuator of claim 2 , wherein the first compliance element is one of a gas charged accumulator in fluid communication with the first fluid flow path via an intervening restriction element, an accumulator with a spring loaded piston in fluid communication with the first fluid flow path via an intervening restriction element, and a hydraulic hose with a flexible wall segment that forms at least a portion of the first fluid flow path; and wherein the second compliance element is one of a gas charged accumulator in fluid communication with the second fluid flow path, an accumulator with a spring loaded piston in fluid communication with the second fluid flow, and a hydraulic hose with a flexible wall segment that forms at least a portion of the first fluid flow path.
4. A hydraulic actuator comprising:
a hydraulic cylinder that includes an extension chamber and a compression chamber;
a hydraulic pump, with a first port and a second port, capable of generating a pressure differential between the compression chamber the extension chamber;
a first compliance element;
a second compliance element;
a first fluid flow path fluidically connecting the first port to the first compliance element;
a second fluid flow path fluidically connecting the first port to the extension chamber;
a third fluid flow path fluidically connecting the second port to the second compliance element;
a fourth fluid flow path fluidically connecting the second port to the compression chamber;
wherein the hydraulic actuator exhibits a first relative compliance factor when exposed to a first oscillating input, and a second relative compliance factor when exposed to a second oscillating input, wherein:
the frequency of the first oscillating input is less than the frequency of the second oscillating input, and
the first relative compliance factor is greater than the second relative compliance factor.
5. The hydraulic actuator of claim 4 , wherein the first compliance element is one of a gas charged accumulator and an accumulator with a spring-loaded piston, wherein the second compliance element is one of a gas charged accumulator, and an accumulator with a spring loaded piston; and wherein the first flow path includes an intervening restriction element.
6. The hydraulic actuator of claim 5 , wherein at least a portion of the first flow path and a portion of the second flow path are the same flow path and at least a portion of the third flow path and the fourth flow path are the same flow path.
7. The hydraulic actuator of claim 5 , wherein the frequency of the first oscillating input is between 0-3 Hz and the frequency of the second oscillating input is between 8-20 Hz.
8. The hydraulic actuator of claim 5 , wherein the intervening restriction element is at least one of poppet valve, shim stack, electrically controlled valve, pneumatically controlled valve and an orifice.
9. The hydraulic actuator of claim 5 , wherein the hydraulic cylinder further includes:
a housing at least partially enclosing an internal volume containing a quantity of hydraulic fluid;
a piston slidably received in the housing, thereby dividing the internal volume into a compression chamber and an extension chamber;
a piston rod attached to the piston.
10. The hydraulic actuator of claim 4 , wherein the intervening restriction element is configured to vary an impedance of the first flow path based at least in part on a frequency of an input.
11. The hydraulic actuator of claim 4 , wherein the intervening restriction element is an active valve and wherein the hydraulic actuator further includes a controller configured to actuate the active valve based at least in part on a frequency of an input.
12. A hydraulic actuator comprising:
a hydraulic cylinder that includes an extension chamber and a compression chamber;
a hydraulic pump, with a first port and a second port, arranged to generate a pressure differential between the compression chamber the extension chamber;
a first gas charged accumulator;
a second gas charged accumulator;
a first fluid flow path fluidically connecting the first port to the first gas charged accumulator;
a second fluid flow path fluidically connecting the first port to the extension chamber;
a third fluid flow path fluidically connecting the second port to the second gas charged accumulator;
a fourth fluid low path fluidically connecting the second port to the compression chamber;
wherein the hydraulic actuator exhibits a first relative pressure factor in response to a first oscillating input, and a second relative pressure factor in response to a second oscillating input, and wherein:
the frequency of the first oscillating input is below the frequency of the second oscillating input; and
the first relative pressure factor is less than the second relative pressure factor.
13. The hydraulic actuator of claim 12 , wherein at least a portion of the first flow path and a portion of the second flow path are the same flow path and at least a portion of the third flow path and the fourth flow path are the same flow path.
14. The hydraulic actuator of claim 12 , wherein the frequency of the first oscillating input is between 0-3 Hz and the frequency of the second oscillating input is between 5-10 Hz.
15. The hydraulic actuator of claim 12 , further comprising a restriction element arranged along the second flow path.
16. The hydraulic actuator of claim 15 , wherein the restriction element is configured to vary an impedance or inertance of the second flow path, or a portion thereof, based at least in part on a frequency of an input.
17. The hydraulic actuator of claim 16 , wherein the restriction element is a shim stack.
18. The hydraulic actuator of claim 15 , wherein the restriction element is an actively controlled valve and wherein the hydraulic actuator further includes a controller configured to actuate the valve based at least in part on a frequency of an input.
19. The hydraulic actuator of claim 12 , wherein the hydraulic cylinder further includes:
a housing at least partially enclosing an internal volume containing a quantity of hydraulic fluid;
a piston slidably received in the housing, thereby dividing the internal volume into a compression chamber and an extension chamber;
a piston rod attached to the piston.
20. A method of operating a hydraulic actuator having a hydraulic cylinder with a piston slidably received in the hydraulic cylinder and dividing the hydraulic cylinder into an extension chamber and a compression chamber, the method comprising:
applying a first oscillating input to the actuator, wherein the first oscillating input generates a first pressure wave in the extension chamber and a second pressure wave in the compression chamber, wherein a ratio of an amplitude of the first pressure wave to an amplitude of the second pressure wave is a first relative pressure factor; and
applying a second oscillating input to the actuator, wherein the second oscillating input generates a third pressure wave in the extension chamber and a fourth pressure wave in the compression chamber, wherein a ratio of an amplitude of the third pressure wave to an amplitude of the fourth pressure wave is a second relative pressure factor;
wherein a frequency of the second oscillating input is greater than a frequency of the first oscillating input; and wherein the second relative pressure factor is greater than the first relative pressure factor.
21. The method of claim 20 , wherein the actuator includes a pump arranged to generate a pressure differential between the extension chamber and compression chamber, and wherein the first oscillating input is a first oscillating torque applied to the pump.
22. The method of claim 21 , wherein the second oscillating input is a second oscillating torque applied to the pump.
23. The method of claim 22 , wherein the frequency of the first oscillating input and the frequency of the second oscillating input are in the range of 2 to 12 Hz.