DIFFERENTIAL HYDRAULIC BUFFER
Hydraulic systems and methods for reducing the propagation of flow and/or pressure pulsations within a hydraulic system are described. In one embodiment, a hydraulic system may include a hydraulic device and a differential buffer fluidly connected to the hydraulic device. The differential buffer may include a piston that is exposed to pressure pulsations that propagate along separate flow paths and that are at least partially out of phase with one another. Corresponding displacement of the piston due to the out of phase pulsations may at least partially mitigate propagation of the pulsations within the hydraulic system downstream from the differential buffer.
1 . A hydraulic system comprising:
a hydraulic device with a first device port and a second device port;
a differential buffer with a first buffer port and a second buffer port;
a first flow path that fluidly connects the first device port to the first buffer port; and
a second flow path that fluidly connects the second device port with the second buffer port.
2 . The system of claim 1 wherein the differential buffer includes a first buffer chamber and a second buffer chamber that are fluidly separated by a buffer piston slidably received in the differential buffer, wherein the first buffer chamber is fluidly connected to the first device port and the second buffer chamber is fluidly connected to the second device port
3 . The system of claim 2 , further comprising a first spring configured to resist motion of the buffer piston in a first direction and a second spring configured to resist motion of the buffer piston in a second direction opposite the first direction.
4 . The system of claim 3 , wherein the first and second springs are coil springs.
5 . The system of claim 3 , wherein the first and second springs include a Belleville washer.
6 . The system of any one of claims 2 - 5 , wherein the buffer piston is configured to move in a first direction when a pressure in the first buffer chamber is greater than a pressure in the second buffer chamber and in a second direction, opposite the first direction, when the pressure in the second buffer chamber is greater than the pressure in the first buffer chamber.
7 . The system of claim 6 , wherein when the buffer piston moves in the first direction a first volume of the first buffer chamber expands and a second volume of the second buffer chamber contracts, and wherein when the buffer piston moves in the second direction opposite the first direction, the second volume of the second buffer chamber expands and the first volume of the first buffer chamber contracts.
8 . The system of any one of the preceding claims, wherein the hydraulic device is configured to operate as a hydraulic pump in at least one mode of operation.
9 . The system of any one of the preceding claims, wherein the hydraulic device is selected from the group consisting of a hydraulic pump and a hydraulic motor.
10 . The system of any of the preceding claims, wherein the first flow path has a first net compliance and the second flow path has a second net compliance, and wherein the first net compliance is within 20% of the second net compliance within a predetermined frequency range.
11 . The system of any one of claims 1 - 9 , wherein the first fluid flow path has a first net impedance and the second fluid flow path has a second net impedance, and wherein the first net impedance is within 20% of the second net impedance within a predetermined frequency range.
12 . The system of any one of the preceding claims, wherein the differential buffer includes a third port and a fourth port, and wherein the third and fourth ports are in fluid communication with a hydraulic load.
13 . The system of claim 12 , wherein the hydraulic load is an active suspension actuator.
14 . An active suspension actuator system, comprising:
a hydraulic device including a first device port and a second device port;
a differential buffer with a first buffer chamber and a second buffer chamber that are fluidly separated by a buffer piston slidably received in the differential buffer, wherein the first buffer chamber is fluidly connected to the first port of the hydraulic device and the second buffer chamber is fluidly connected to the second port of the hydraulic device; and
a hydraulic actuator with a first actuator chamber and a second actuator chamber that are fluidly separated by an actuator piston slidably received in the hydraulic actuator, wherein the first actuator chamber is fluidly connected to the first buffer chamber and the second actuator chamber is fluidly connected to the second buffer chamber.
15 . The system of claim 14 , further comprising a first spring configured to resist motion of the buffer piston in a first direction and a second spring configured to resist motion of the buffer piston in a second direction opposite the first direction.
16 . The system of claim 15 , wherein the first and second springs are coil springs.
17 . The system of claim 15 , wherein the first and second springs include a Belleville washer.
18 . The system of any one of claims 14 - 17 , wherein the buffer piston is configured to move in a first direction when a pressure in the first buffer chamber is greater than a pressure in the second buffer chamber and in a second direction, opposite the first direction, when the pressure in the second buffer chamber is greater than the pressure in the first buffer chamber.
19 . The system of claim 18 , wherein when the buffer piston moves in the first direction a first volume of the first buffer chamber expands and a second volume of the second buffer chamber contracts, and wherein when the buffer piston moves in the second direction opposite the first direction, the second volume of the second buffer chamber expands and the first volume of the first buffer chamber contracts.
20 . The system of any one of claims 14 - 19 , wherein the hydraulic device is configured to operate as a hydraulic pump in at least one mode of operation.
21 . The system of any one of claims 14 - 20 , wherein the hydraulic device is selected from the group consisting of a hydraulic pump and a hydraulic motor.
22 . The system of any one of claims 14 - 21 , wherein a first flow path extending between and including the first device port and the first buffer chamber has a first net compliance and a second flow path extending between and including the second device port and the second buffer chamber has a second net compliance, and wherein the first net compliance is within 20% of the second net compliance within a predetermined frequency range.
23 . The system of any one of claims 14 - 22 , wherein a first flow path extending between and including the first device port and the first buffer chamber has a first net impedance and a second flow path extending between and including the second device port and the second buffer chamber has a second net impedance, and wherein the first net impedance is within 20% of the second net impedance within a predetermined frequency range.
24 . The system of any one of claims 14 - 23 , wherein the differential buffer includes a third port fluidly coupled to the first buffer chamber and a fourth port fluidly coupled to the second buffer chamber, and wherein the third port of the differential buffer is fluidly connected to the first actuator chamber and the fourth port is fluidly connected to the second actuator chamber.
25 . A method for operating a hydraulic system, the method comprising:
applying flow pulsations to a first flow path fluidly connected to a first buffer chamber and a second flow path fluidly connected to a second buffer chamber, wherein the flow pulsations in the first buffer chamber are at least partially out of phase with the flow pulsations in the second buffer chamber; and
displacing a buffer piston disposed between the first buffer volume and the second buffer volume due at least in part to a phase difference between the flow pulsations in the first and second buffer chambers.
26 . The method of claim 25 , wherein displacing the buffer piston varies a volume of the first buffer chamber and a volume of the second buffer chamber to reduce a magnitude of the flow pulsations transmitted to a hydraulic load.
27 . The method of claim 26 , wherein the hydraulic load is an active suspension actuator.
28 . The method of any one of claims 25 - 27 , further comprising biasing the buffer piston towards a neutral configuration.
29 . The method of any one of claims 25 - 28 , further comprising moving the buffer piston in a first direction when a pressure in the first buffer chamber is greater than a pressure in the second buffer chamber and in a second direction, opposite the first direction, when the pressure in the second buffer chamber is greater than the pressure in the first buffer chamber.
30 . The method of any one of claim 29 , wherein when the buffer piston moves in the first direction a first volume of the first buffer chamber expands and a second volume of the second buffer chamber contracts, and wherein when the buffer piston moves in the second direction opposite the first direction, the second volume of the second buffer chamber expands and the first volume of the first buffer chamber contracts.
31 . The method of any one of claims 25 - 30 , further comprising generating the flow pulsations with a hydraulic device.
32 . The method of claim 31 , wherein the hydraulic device is configured to operate as a hydraulic pump in at least one mode of operation.
33 . The method of any one of claims 31 and 32 , wherein the hydraulic device is selected from the group consisting of a hydraulic pump and a hydraulic motor.
34 . The method of any one of claims 25 - 33 , wherein the phase difference of the hydraulic flow pulsations on each side of the buffer piston are between or equal to 140 degrees and 220 degrees out of phase.
35 . A hydraulic system comprising:
a hydraulic device with a first device port and a second device port;
a differential buffer with a first buffer port and a second buffer port;
a first flow path that fluidly connects the first device port to the first buffer port; and
a second flow path that fluidly connects the second device port with the second buffer port.
36 . The system of claim 35 , wherein the differential buffer includes a first buffer chamber and a second buffer chamber that are fluidly separated by a buffer piston slidably received in the differential buffer, wherein the first buffer chamber is fluidly connected to the first device port and the second buffer chamber is fluidly connected to the second device port
37 . The system of claim 36 , further comprising a first spring configured to resist motion of the buffer piston in a first direction and a second spring configured to resist motion of the buffer piston in a second direction opposite the first direction.
38 . The system of claim 37 , wherein the buffer piston is configured to have a resonance mode within a frequency range of flow pulsations generated by the hydraulic device.