Differential hydraulic damper

Abstract

To provide hydraulic systems and methods for reducing the propagation of flow and / or pressure pulsations within a hydraulic system.SOLUTION: In one embodiment, a hydraulic system 240 may include a hydraulic device 141 and a differential damper 145 fluidly connected to the hydraulic device. The differential damper may include a piston 146 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 damper.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority under 35 U.S.C. §119(e) to U.S. Provisional Patent Application No. 62 / 935,047, filed November 13, 2019, the entire disclosure of which is incorporated herein by reference.

[0002] Field Disclosed embodiments may relate to methods and systems for mitigating flow and / or pressure pulsations in hydraulic systems. Some embodiments may be directed to hydraulic systems that include a differential hydraulic damper. [Background technology]

[0003] background Hydraulic systems that utilize fluids to store, convert, and / or transmit power are utilized across a variety of industries and applications, from large industrial plants to automobiles. These hydraulic systems may generally include various components, such as hydraulic pumps, valves, various reservoirs or accumulators, tanks, fluid chambers, filters, membranes, other hydraulic components, and fluid paths extending between these components. The flow of hydraulic fluid through and / or between these various components and connections can result in fluid pressure and / or flow pulsations that can generate component vibrations and / or acoustic noise. This pulsation may be undesirable because it generates annoying levels of noise, accelerates equipment wear, and / or reduces system performance in relevant frequency ranges. Summary of the Invention [Means for solving the problem]

[0004] overview In one embodiment, the hydraulic system includes a hydraulic device having a first device port and a second device port, a differential shock absorber having a first shock absorber port and a second shock absorber port, a first flow path fluidly connecting the first device port to the first shock absorber port, and a second flow path fluidly connecting the second device port to the second shock absorber port.

[0005] In one embodiment, the active suspension actuator system includes a hydraulic device including a first device port and a second device port. The active suspension actuator system also includes a differential shock absorber having a first shock absorber chamber and a second shock absorber chamber fluidly separated by a shock absorber piston slidably housed within the differential shock absorber. The first shock absorber chamber is fluidly connected to a first port of the hydraulic device, and the second shock absorber chamber is fluidly connected to a second port of the hydraulic device. The active suspension actuator system also includes a hydraulic actuator having a first actuator chamber and a second actuator chamber fluidly separated by an actuator piston slidably housed within the hydraulic actuator. The first actuator chamber is fluidly connected to the first shock absorber chamber, and the second actuator chamber is fluidly connected to the second shock absorber chamber.

[0006] In one embodiment, a method of operating a hydraulic system includes applying flow pulsations to a first flow path fluidly connected to a first shock absorber chamber and to a second flow path fluidly connected to a second shock absorber chamber, the flow pulsations in the first shock absorber chamber being at least partially out of phase with respect to the flow pulsations in the second shock absorber chamber; and displacing a shock absorber piston disposed between the first shock absorber volume and the second shock absorber volume at least partially due to the phase difference between the flow pulsations in the first shock absorber chamber and the flow pulsations in the second shock absorber chamber.

[0007] In one embodiment, the hydraulic system includes a hydraulic device having a first device port and a second device port, a differential shock absorber having a first shock absorber port and a second shock absorber port, a first flow path fluidly connecting the first device port to the first shock absorber port, and a second flow path fluidly connecting the second device port to the second shock absorber port.

[0008] It should be understood that the foregoing concepts, and additional concepts described below, may be arranged in any suitable combination, as the disclosure is not limited in this respect. Furthermore, other advantages and novel features of the present disclosure will become apparent from the following detailed description of various non-limiting embodiments when considered in conjunction with the accompanying drawings.

[0009] In the event that the present specification and a document incorporated by reference include conflicting and / or inconsistent disclosure, the present specification shall control. If two or more documents incorporated by reference include conflicting and / or inconsistent disclosure with respect to each other, the document having the later effective date shall control.

[0010] BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings are not intended to be drawn to scale. In the drawings, identical or nearly identical components illustrated in various figures may be represented by like numerals. For purposes of clarity, not every component may be numbered in every figure. [Brief explanation of the drawings]

[0011] [Figure 1] 1 illustrates an embodiment of a hydraulic circuit with a reversible hydraulic device and a hydraulic load. [Figure 2] 2 illustrates one embodiment of expected hydraulic behavior at each of the two ports of the reversible hydraulic device of FIG. 1 for exemplary operating conditions. [Figure 3] 2 illustrates one embodiment of expected fluid delivery and fluid intake at two ports of the reversible hydraulic device of FIG. 1 for exemplary operating conditions. [Figure 4]1 illustrates an embodiment of a hydraulic circuit with a reversible hydraulic device, a hydraulic load, and two accumulators. [Figure 5] 1 illustrates an embodiment of a hydraulic circuit with a reversible hydraulic device, a hydraulic load, and a differential shock absorber. [Figure 6] 1 illustrates an embodiment of a hydraulic circuit including a reversible hydraulic system, a hydrostatic active suspension actuator, an accumulator, and a differential shock absorber in a flow-through configuration. [Figure 7A] 1 illustrates a cross-sectional view of one embodiment of disc springs stacked in a side-by-side arrangement. [Figure 7B] 1 illustrates a cross-sectional view of one embodiment of disc springs stacked in a series arrangement. [Figure 7C] 1 illustrates a cross-sectional view of one embodiment of stacked disc springs using a combination of parallel stacked disc springs and series stacked disc springs. [Figure 8] 1 illustrates one embodiment of a through-flow differential shock absorber and hydraulic system in which the springs include a parallel arrangement of disc springs located on either side of the shock absorber piston. [Figure 9] 1 illustrates a perspective cross-sectional view of an embodiment of a differential shock absorber with springs in the form of opposing disc spring stacks positioned on either side of the shock absorber piston; [Figure 10] FIG. 10 illustrates a front cross-sectional view of the differential shock absorber of FIG. 9. [Figure 11A] 11 illustrates an embodiment of a differential shock absorber similar to that shown in FIGS. 9 and 10 with the pistons in a first, neutral operating position. [Figure 11B] 11B illustrates the differential shock absorber of FIG. 11A with the piston in a second operating position. [Figure 11C] 11B illustrates the differential shock absorber of FIG. 11A with the piston in a third operating position. [Figure 12A] FIG. 1 is a perspective view of one embodiment of a disc spring stack that may be included in a differential shock absorber. [Figure 12B] FIG. 12B is a cross-sectional perspective view of the disc spring stack of FIG. 12A. [Figure 12C] FIG. 12C is an enlarged cross-sectional perspective view of the disc spring stack of FIG. 12B. DETAILED DESCRIPTION OF THE INVENTION

[0012] The inventors have recognized that hydraulic pumps, particularly positive displacement pumps such as gerotor pumps, crescent pumps, gear pumps, and piston pumps, can induce flow and / or pressure pulsations, sometimes referred to as ripples, at both the intake and discharge ports. These pulsations can be transmitted and observed at various points throughout the hydraulic circuit. These pressure pulsations can result in increased noise and / or instability in the hydraulic system. Flexible reservoirs (e.g., accumulators) can be used to partially mitigate the transmission of flow and / or pressure pulsations to various portions of the hydraulic system. However, the inventors have recognized that the use of larger reservoirs can result in the need to move more fluid by the pump or other hydraulic devices to establish the desired pressure differential across the pump. Additionally, certain types of reservoirs may have reduced compliance (i.e., the reservoir may become stiffer) when compressed. Therefore, the inventors recognize that as a reservoir is compressed, it may become less effective at mitigating flow and / or pressure pulsations; for example, in the case of a gas-filled reservoir, this relationship may be non-linear.

[0013] In view of the above, the present inventors have recognized advantages associated with using a phase difference in flow and / or pressure pulsations present at locations along different flow paths connected to separate ports of a hydraulic device to reduce the magnitude of the flow and / or pressure pulsations propagating to other portions of a hydraulic system. Specifically, the phase difference and relative magnitude of the flow and / or pressure pulsations between two flow paths may result in a pressure differential at a given location that differs from the nominal pressure differential between the flow paths imposed by the hydraulic device. Thus, the portion of the pressure differential associated with the out-of-phase flow and / or pressure pulsations along the different flow paths may be used to at least partially mitigate the flow and / or pressure pulsations propagating to another portion of the hydraulic system. For example, in some embodiments, this pressure differential between two flow paths associated with the flow and / or pressure pulsations may be used to cause a corresponding volume change in a buffer chamber associated with each flow path to at least partially mitigate, and in some cases substantially eliminate, the flow and / or pressure pulsations. For example, a volume change in a first shock absorber chamber may result in a corresponding opposite volume change in a second shock absorber chamber, which may at least partially regulate at least partially out-of-phase flow and / or pressure pulsations experienced by the separate shock absorber chambers. In some embodiments, this volume change may be achieved using a shock absorber piston slidably disposed between and separating the two shock absorber chambers, which may be displaced by the out-of-phase flow and / or pressure pulsations experienced by the two shock absorber chambers. Specific embodiments are described in further detail below.

[0014] In one embodiment, the hydraulic system may include a hydraulic device (e.g., a hydraulic motor or pump) with a first device port and a second device port. For example, the hydraulic device may be a hydraulic pump that operates as a hydraulic pump in at least one operating mode, or a hydraulic motor that operates as a hydraulic pump in at least one operating mode. An embodiment may include a differential shock absorber with a first shock absorber port and a second shock absorber port. A first flow path may fluidly connect the first device port to the first shock absorber port, and a second flow path may fluidly connect the second device port to the second shock absorber port. The differential shock absorber may function to reduce flow and / or pressure pulsations generated by the hydraulic device that are transmitted from the differential shock absorber to one or more hydraulic loads fluidly connected to the differential shock absorber.

[0015] In some embodiments, the differential shock absorber may include a housing with an internal volume including a first shock absorber chamber and a second shock absorber chamber. A shock absorber piston disposed within the differential shock absorber housing between the first shock absorber chamber and the second shock absorber chamber may be configured to slide back and forth under the influence of a pressure differential applied across the shock absorber piston between the two shock absorber chambers. A first spring may resist movement of the shock absorber piston in a first direction, and a second spring may resist movement of the shock absorber piston in a second direction opposite the first direction. Thus, the piston may move under an applied pressure differential associated with flow and / or pressure pulsations generated by a hydraulic system, which may correspondingly change the volumes of the first and second shock absorber chambers to at least partially counteract at least partially out-of-phase flow and / or pressure pulsations transmitted to the first and second chambers.

[0016] While the differential shock absorbers and systems disclosed herein may be used with any suitable hydraulic load, in some embodiments, the hydraulic load fluidly connected to the hydraulic device, as described herein, may be an active suspension actuator. In one such embodiment, the active suspension actuator system may include a hydraulic device, such as a hydraulic pump or a hydraulic motor. The hydraulic device may include a first device port and a second device port. Embodiments may also include a differential shock absorber with a first shock absorber chamber and a second shock absorber chamber fluidly separated by a shock absorber piston disposed between the first and second shock absorber chambers. The shock absorber piston may be configured to slide within a housing of the differential shock absorber between the first and second shock absorber chambers. For example, the shock absorber piston may be slidably retained within a cylindrical volume at least partially defining the first and second shock absorber chambers. The first shock absorber chamber may be fluidly connected to a first device port of the hydraulic device, and the second shock absorber chamber may be fluidly connected to a second device port of the hydraulic device. The active suspension system may also include a hydraulic actuator having a first actuator chamber and a second actuator chamber. In some embodiments, the first actuator chamber and the second actuator chamber may correspond to the actuator's extension and compression chambers, respectively. In either case, the first actuator chamber and the second actuator chamber may be fluidly separated by an actuator piston. In some embodiments, the actuator piston may be slidably housed within a cylindrical volume disposed within an interior volume of the actuator body that at least partially defines the first actuator chamber and the second actuator chamber. Regardless of the specific configuration, the first actuator chamber may be fluidly connected to a first shock absorber chamber, and the second actuator chamber may be fluidly connected to a second shock absorber chamber. As described in more detail below, such a configuration may help reduce the amount of flow and / or pressure pulsations that may be transmitted from the hydraulic system through the differential shock absorber to the actuator.

[0017] Certain parameters associated with the operation of a hydraulic system, including the ability of a differential damper to dampen flow and / or pressure pulsations within the hydraulic system, may be related, at least in part, to the operating frequency range of the hydraulic system and the frequency range of the resulting excited flow and / or pressure pulsations. Thus, in some embodiments, various operating parameters and performance characteristics described herein may correspond to operating parameters and / or performance characteristics within the operating frequency ranges and flow and / or pressure pulsation frequency ranges described below.

[0018] Depending on the embodiment, the hydraulic device may exhibit any suitable operating frequency range. For example, the maximum response frequency of the hydraulic device may be 1 Hz or greater, 5 Hz or greater, 10 Hz or greater, 20 Hz or greater, and / or any other suitable frequency range. Correspondingly, the hydraulic device may have a maximum response frequency that is 100 Hz or less, 50 Hz or less, 40 Hz or less, 30 Hz or less, 20 Hz or less, and / or any other suitable frequency range. Combinations of the above-mentioned frequency ranges are contemplated, including hydraulic devices capable of responding with a maximum frequency response that is 1 Hz or greater to 50 Hz or less. Furthermore, the hydraulic device may have an operating frequency range that extends from 0 Hz or greater to any of the above-mentioned maximum response frequencies. However, the disclosure is not so limited, and embodiments in which the hydraulic device has a different lower limit on the operating frequency range greater than 0 Hz are also contemplated. Additionally, although specific frequency ranges for the maximum response frequency of the hydraulic device are described above, it should be understood that the disclosure is not limited in this manner, and any suitable operating frequency range for the hydraulic device, including ranges both wider and narrower than the above-mentioned ranges, may be used depending on the particular application. Additionally, while maximum response frequencies are discussed above, the operating speed of a particular hydraulic device may be greater than the frequency associated with the device's maximum response time in certain embodiments. For example, a hydraulic device such as a gerotor, or other similar device, may exhibit rotational speeds with periodic excitations having frequencies greater than the maximum response frequencies discussed above in some embodiments.

[0019] In some embodiments, the hydraulic device may generate flow and / or pressure pulsations within different pulsation frequency ranges. For example, the flow and / or pressure pulsations generated by the hydraulic device may have frequencies that are 10 Hz or greater, 20 Hz or greater, 30 Hz or greater, 40 Hz or greater, 50 Hz or greater, 100 Hz or greater, 500 Hz or greater, 1000 Hz or greater, 2000 Hz or greater, 3000 Hz or greater, and / or any other suitable frequency range. Correspondingly, the frequency range associated with the flow and / or pressure pulsations may be 10,000 Hz or less, 5000 Hz or less, 4000 Hz or less, 3000 Hz or less, 2000 Hz or less, 1000 Hz or less, 500 Hz or less, 100 Hz or less, 50 Hz or less, and / or any other suitable frequency range. Combinations of the foregoing frequency ranges are contemplated, including, for example, frequency ranges of flow and / or pressure pulsations that are 10 Hz or greater to 10,000 Hz or less and 30 Hz or greater to 300 Hz or less. Of course, it should be understood that greater and lesser flow rate and / or pressure pulsation frequency ranges than those set forth above are contemplated, depending on the specific hydraulic system configuration, as the present disclosure is not so limited.

[0020] As described above, a hydraulic device, such as a pump or hydraulic motor, may generate flow and / or pressure pulsations along two separate flow paths fluidly connected to separate ports of the hydraulic device. These pulsations propagating along the separate flow paths may be at least partially out of phase with each other. If the pressure pulsations at a particular location along the flow paths, such as within two opposing buffer chambers, are completely out of phase with each other, e.g., 180° apart, a maximum amount of flow and / or pressure pulsation mitigation may be achieved, as described in more detail below. Alternatively, if the pulsations at a particular location along the flow paths, such as within two opposing buffer chambers, are partially out of phase with each other, i.e., less than 180° apart, a lesser amount of flow and / or pressure pulsation mitigation may be achievable. Additionally, to further enhance the amount of pulsation mitigation provided by the differential buffer, it may be desirable for the magnitudes of the flow and / or pressure pulsations transmitted from the two separate flow paths to the opposing buffer chambers to be approximately equal to each other. As described in more detail below, the phase and magnitude of pulsations present along separate flow paths of a hydraulic system to an associated differential shock absorber may depend on the mass, damping, and / or flow rate of fluid in the flow paths and / or the stiffness of those fluid flow paths extending between and including the hydraulic device generating the pressure pulsations and the separate chambers of the differential shock absorber connected to the fluid flow paths. Accordingly, there may be appropriate transfer functions, which may be the result of a particular hydraulic system design, that relate the magnitude and / or phase of pulsations emitted from ports of the hydraulic device to the magnitude and phase of pulsations generated at ports of the differential shock absorbers in the system. These transfer functions may be experimentally measured, as described in more detail below, to determine various operating parameters of the hydraulic system.

[0021] In view of the above, the flow and / or pressure pulsations transmitted to the opposing first and second chambers of the differential shock absorber may be matched relative to one another, at least within a desired frequency range, such that the opposing chambers of the differential shock absorber are approximately 180° out of phase with one another or are effectively 180° out of phase with one another. In some embodiments, the flow and / or pressure pulsations imparted to the opposing chambers of the differential shock absorber, at least within a desired frequency range of the pulsations, may be within a range of 40°, 30°, 20°, 10°, 5°, 1°, and / or any other suitable offset from 180° out of phase with one another (e.g., 140° or more to 220° or less out of phase with one another). However, pressure pulsations that are offset from 180° out of phase with one another by amounts greater than those described above are also contemplated, as the disclosure is not so limited.

[0022] In some embodiments, the magnitudes of flow and / or pressure pulsations within a desired or target frequency range transmitted from the hydraulic system to opposing shock absorber chambers of a differential shock absorber may be substantially or effectively equal to one another. For example, the difference in magnitude of flow and / or pressure pulsations imparted to opposing shock absorber chambers within a desired or target frequency range of pulsations may be no more than 20%, 15%, 10%, 5%, 1%, and / or any other suitable percentage of the larger amplitude pulsation in the shock absorber chamber at a given frequency. Of course, differences in magnitude of pulsations imparted to different chambers that are greater than the aforementioned ranges are also contemplated, as the disclosure is not so limited.

[0023] To help achieve a desired relationship between the magnitude and / or phase of pulsations imparted to opposing chambers of the differential shock absorber within a desired or target frequency range of the pulsations, it may be desirable to provide flow paths connecting ports of the hydraulic device to corresponding shock absorber chambers of the differential shock absorber with approximately equal compliances corresponding to expected volume changes for a given pressure change. It should be noted that because the flow paths contain a substantially incompressible fluid, such as hydraulic fluid, a majority of the compliance along these flow paths may be provided by the differential shock absorber itself. In any case, the difference in compliance between a first flow path fluidically connecting a first device port of the hydraulic device to a first shock absorber chamber of the differential shock absorber and a second flow path fluidically connecting a second device port of the hydraulic device to a second shock absorber chamber of the differential shock absorber may be no more than 20%, 15%, 10%, 5%, 4%, 3%, 2%, 1%, and / or any other suitable percentage of the greater compliance, as the disclosure is not so limited. However, differences in compliance between the two fluid flow paths greater than the aforementioned compliance differences are also contemplated, as the disclosure is not so limited.

[0024] Alternatively or additionally, it may be desirable to provide approximately equal fluid impedances for separate flow paths connecting separate ports of the hydraulic device to corresponding buffer chambers of the differential buffer to help provide a desired relationship between the magnitude and / or phase of pulsations imparted to opposing chambers of the differential buffer within a desired frequency range of the pulsations. The fluid impedance along each flow path may include contributions from flow resistance and the mass of fluid extending between the hydraulic device and the differential buffer. However, in some embodiments, the fluid impedance may be dominated by friction losses along the flow path. In any case, the difference between the fluid impedance along a first flow path fluidly connecting a first device port of the hydraulic device to a first buffer chamber of the differential buffer and the fluid impedance along a second flow path fluidly connecting a second device port of the hydraulic device to a second buffer chamber of the differential buffer may be no more than 20%, 15%, 10%, 5%, 4%, 3%, 2%, 1%, and / or any other suitable percentage of the greater fluid impedance, as the disclosure is not so limited. However, differences in fluid impedance between the two fluid flow paths greater than the differences in fluid impedance discussed above are also contemplated, as the disclosure is not so limited.

[0025] In some embodiments, the magnitude of the flow and / or pressure pulsations transmitted from the differential shock absorber to the hydraulic load may be reduced relative to the magnitude of the flow and / or pressure pulsations generated by and transmitted from the hydraulic device to the differential shock absorber. The magnitude reduction may be any suitable percentage, depending on the desired application. For example, the reduction in the magnitude of the transmitted pulsations may be 1%, 5%, 20%, 50%, or any other suitable percentage or more of the original magnitude of the pressure and / or flow fluctuations prior to reduction by the differential shock absorber. Correspondingly, the magnitude reduction may be 80%, 50%, 20%, 5%, 1%, and / or any other suitable percentage or less of the original magnitude of the pressure and / or flow fluctuations. Combinations of the foregoing are also contemplated, including reductions of 50% or more to 80% or less of the magnitude of the flow and / or pressure pulsations transmitted from the differential shock absorber to the fluidly connected hydraulic load. Of course, different combinations of the foregoing ranges, as well as reductions both greater and less than those stated above, are also contemplated, as the disclosure is not so limited.

[0026] Depending on the particular embodiment, the above-described frequency and phase offset of the flow and / or pressure pulsations in the system may be measured in any suitable manner. However, in some embodiments, the frequency and phase of the pulsations may be measured using pressure sensors associated with separate shock absorber chambers located in a differential shock absorber. For example, separate pressure sensors and / or differential pressure sensors may be used to measure pressure pulsations in different shock absorber chambers or other portions of the hydraulic system. However, it should be understood that other methods of measuring the frequency and / or phase of the flow and / or pressure pulsations using the system may also be used, as the disclosure is not limited in this manner.

[0027] The aforementioned compliances and fluid impedances along the various flow paths may also be determined in any suitable manner. For example, in one embodiment, a computational fluid dynamics (CFD) analysis may be performed to determine the compliances and fluid impedances associated with different flow paths in a hydraulic system. In another embodiment, these parameters may be measured experimentally.

[0028] The transfer function of the flow path between the pressure ripple source and the differential shock absorber can be measured experimentally. For example, this measurement can be achieved by placing pressure sensors capable of measuring pressure in an appropriate frequency range, e.g., 10-3,000 Hz or 10-10,000 Hz, at positions at both ends of the flow path. In some embodiments, during experimentation, the hydraulic device can be replaced with an external volumetric flow source that can be used to induce a volumetric flow displacement at the same location as the pump (e.g., location 141). An excitation sweep with the external flow source at frequencies across the desired range can measure the impedance of the flow path. In some embodiments, the magnitude and phase of the transfer function of the flow path connecting the first port of the hydraulic device and the first chamber of the differential shock absorber can be 20%, 15%, 10%, 5%, 4%, 3%, 2%, 1%, and / or any other suitable percent smaller than the magnitude and phase of the transfer function of the flow path connecting the second port of the hydraulic device and the second chamber of the differential shock absorber.

[0029] As described further below, in some embodiments, one or more springs may be operably coupled to a shock absorber piston slidably disposed between a first shock absorber chamber and a second shock absorber chamber of a differential shock absorber. In some embodiments, the one or more springs may include one or more springs disposed on either side of the shock absorber piston such that the springs bias the shock absorber piston toward a neutral position. Specific structures are further described below in conjunction with the figures. However, it should be understood that the present disclosure is not limited to any particular type of spring, and any suitable type of spring capable of applying a desired force to bias a shock absorber piston of a differential shock absorber toward a desired neutral position may be used. Accordingly, suitable springs may include, but are not limited to, coil springs, Belleville springs, and / or any other suitable type of spring capable of applying an appropriate force.

[0030] As used herein, the terms flow and / or pressure pulsation, flow and / or pressure ripple, flow pulsation, pressure pulsation, pulsation, and other similar terms may be used interchangeably to refer to the same or equivalent physical phenomena that may occur in some hydraulic systems. Specifically, flow and / or pressure pulsation may refer to the occurrence of flow and / or pressure pulsations, whether constant or variable, that deviate from a nominal flow rate and / or pressure associated with commanded operation of a hydraulic device along a given flow path fluidly connected to the hydraulic device. In some cases, these pulsations may vary periodically, such that the actual flow rate and pressure vary periodically around the nominal commanded flow rate and / or pressure. For example, as further described below with reference to the figures, during operation of a particular type of pump, the flow and pressure along different flow paths connected to separate ports of the pump may vary throughout a given cycle of the pump's pumping mechanism.

[0031] As used herein, the terms “hydraulic device,” “hydraulic pump,” and “hydraulic motor” may be used interchangeably. Thus, various embodiments described herein may include a hydraulic device corresponding to any suitable hydraulic device capable of being driven to provide desired fluid flow and / or pressure differentials to various points within a hydraulic system. The hydraulic device may include a hydraulic pump and a hydraulic motor that may be configured to operate as a pump to drive fluid flow in at least one operating mode. Additionally, in some embodiments, the hydraulic device may include a pump or a hydraulic motor that is configured to operate as a hydraulic motor in at least one operating mode in which fluid flow is used to drive the hydraulic device. Depending on the particular application, it may be desirable for a hydraulic device, such as a hydraulic pump and / or a hydraulic motor, to be reversible, allowing fluid to flow through the hydraulic device in both a first direction and an opposite second direction. However, embodiments in which flow through the hydraulic device is unidirectional are also contemplated. Additionally, in some embodiments, the hydraulic device may operate at a variable nominal speed or a constant nominal speed, as the disclosure is not so limited. Suitable types of hydraulic devices may include, but are not limited to, positive displacement pumps such as gerotors, crescent pumps, gear pumps, piston pumps, and swash plate pumps.

[0032] The present disclosure is not limited to any particular type of hydraulic system, and the hydraulic systems and differential shock absorbers disclosed herein may be used with any suitable type of hydraulic load. However, in some embodiments, hydraulic loads that may be included in the hydraulic systems disclosed herein may include, but are not limited to, active suspension actuators, hydraulic actuators, and / or any other suitable type of hydraulic load.

[0033] As used herein, a flow path may refer to a conduit or other enclosed passageway through which a fluid may flow between two or more points in a hydraulic circuit, such as, for example, between two ports of separate hydraulic components in a hydraulic system. Suitable types of flow paths may include, but are not limited to, hydraulic tubing, channels formed in solid elements, passages extending between two opposing surfaces of separate components (e.g., between concentric tubes or housings), and / or any other suitable structure capable of functioning as a flow path to allow fluid flow between two or more points in a hydraulic system.

[0034] As used herein, "fluidly connect," "fluidly connected," "fluid communication," and other similar terms may refer to a fluid connection between different points in a hydraulic circuit. For example, a fluid path may fluidly connect two portions of a hydraulic circuit such that fluid may be exchanged between these two portions of the hydraulic circuit during at least some operating conditions. Although the disclosure is not limited in this manner, it should be understood that a fluid connection between two points in a hydraulic circuit may be either a direct fluid connection without an intervening component, e.g., a flow control device such as a valve, between the two points, or an indirect connection in which a fluid path may extend between one or more intervening components between the two points.

[0035] Specific, non-limiting embodiments will now be described in further detail with reference to the figures. It should be understood that the present disclosure is not limited to only the specific embodiments described herein, and that the various systems, components, features, and methods described in connection with these embodiments can be used individually and / or in any desired combination.

[0036] FIG. 1 illustrates a hydraulic circuit 100 that includes a reversible hydraulic device 101, such as a pump or hydraulic motor. The hydraulic device 101 illustrated in FIG. 1 (as well as FIGS. 4, 5, and 6) is shown to be reversible and capable of operating as a hydraulic pump and a hydraulic motor. It should be noted that in some embodiments, a non-reversible hydraulic pump or motor may be used. The hydraulic device 101 of the hydraulic circuit 100 includes a first port 102 and a second port 103. Because the hydraulic device 101 is reversible, either port may operate as an inlet or outlet port, depending on the specific operating conditions. For example, in the case of a gerotor, crescent pump, or gear pump, the second port 102 may be an outlet port when the pump rotates in a first direction and an inlet port when the pump rotates in a second direction opposite the first direction. As shown in FIG. 1, the hydraulic device 101 may also operate as a hydraulic motor under certain operating conditions of a hydraulic load 104.

[0037] FIG. 2 presents a graph of pressure pulsations that may propagate along flow paths 105 and 106 illustrated in hydraulic circuit 100 of FIG. 1. In FIG. 2, dashed line 110 represents the system pressure, i.e., the system precharge pressure, when the hydraulic device is not operating. When the hydraulic device is operating at a constant speed, the nominal command pressure at the outlet port may be nominally constant and higher than the precharge pressure, which is higher than the intake pressure (which is nominally constant and may be lower than the precharge pressure). However, although the pressure at the inlet and outlet ports may be nominally constant, as illustrated by traces 111 and 112 in FIG. 2, pressure fluctuations, i.e., pulsations, may exist at the inlet and outlet ports, respectively, even when the pump is operating at a constant nominal speed. These pressure fluctuations may vary periodically around the nominal command pressure at each port. Additionally, the pressure fluctuations may occur over a range of frequencies, as illustrated by the traces containing multiple fluctuations of different frequencies superimposed on the nominal command pressure at each port. Additionally, depending on the type of hydraulic device used to create the pressure differential, and as can be seen in Figure 2, pressure traces 111 and 112 may be mirror images of each other, corresponding to pressure pulsations at the two ports being at least partially out of phase with each other (e.g., in Figure 2, the pressure pulsations are shown to be 180 degrees out of phase at the two ports).

[0038] Figure 3 illustrates a positive flow rate 121 at the outlet port and a negative flow rate 122 at the inlet port for a hydraulic device similar to that shown in Figure 1 when operated, for example, at a constant nominal speed. In a manner similar to the pressures at the corresponding ports shown in Figure 2, the flow rate traces include flow rate pulsations corresponding to oscillations superimposed on the nominal commanded flow rate over different frequency ranges, causing the flow rates associated with the separate flow paths and ports to vary periodically around the nominal commanded flow rate at each port. As before, traces 121 and 122 are mirror images of each other, as the pulsations are at least partially out of phase with each other (e.g., 180 degrees out of phase).

[0039] It should be noted that the traces included in Figures 2 and 3 are not data, but rather represent expected flow rates and pressures at ports of a hydraulic device, such as a hydraulic pump, operating under a constant commanded nominal flow rate and pressure differential. However, if the hydraulic device is not operated under constant operating conditions, e.g., speed or flow rate, the nominal flow rate and nominal pressure may also vary. In such cases, flow and pressure pulsations corresponding to the cyclical variations shown in the figures may be superimposed on the changing nominal flow rate and / or pressure at any given operating point of the system. Thus, disclosed embodiments for mitigating flow and / or pressure pulsations are not limited to operating only under constant nominal operating conditions.

[0040] In some embodiments, flow pulsations resulting from flow entering an intake port and exiting an outlet port of a hydraulic device can be at least partially mitigated by incorporating a reservoir partially filled with a compressible medium (e.g., gas). FIG. 4 illustrates an embodiment of a hydraulic system 130 including a reversible hydraulic device 131 (e.g., a pump or hydraulic motor), a hydraulic load 104, a first flow path 132, and a second flow path 133. The hydraulic circuit of the illustrated system also includes reservoirs 134 and 135 fluidly connected to the first and second flow paths, respectively, at locations disposed between the hydraulic device and the hydraulic load. Reservoir 134 includes piston 134a and gas-filled volume 134b. Reservoir 135 includes piston 135a and gas-filled volume 135b. In certain embodiments, reservoirs 134 and 135 may serve to mitigate pulsating flow of hydraulic fluid at ports 131 a and 131 b by at least partially regulating flow pulsations by directing fluid into or out of the reservoirs to reduce the magnitude of pulsations transmitted to the hydraulic load along the associated flow path. The inventors have recognized that the larger the gas volumes 134 b and 135 b in the reservoirs, the more effective they will be at reducing pump-induced pulsations. However, the inventors have also recognized that the larger the reservoirs, the more fluid will need to be pumped by hydraulic device 131 to establish a desired pressure differential between ports 131 a and 131 b.

[0041] In addition to the above, and without wishing to be bound by theory, the inventors further recognize that the effectiveness of a gas-filled reservoir in damping pulsations may be proportional to the compliance of the reservoir. Thus, as pressure in flow path 132 or flow path 133 increases by operating the pump, the gas volume in the associated reservoir may be compressed. As the gas volume of a reservoir is compressed, its compliance decreases (i.e., the reservoir becomes stiffer), and the reservoir may become less effective at damping hydraulic pulsations. Additionally, the relationship between compliance and pressure of a gas-filled reservoir is nonlinear. Thus, while one or more reservoirs may be fluidly connected to any flow path in the various embodiments described herein, the inventors recognize the need for a structure that can further dampen flow and / or pressure pulsations present in a hydraulic system.

[0042] FIG. 5 illustrates a hydraulic system including a hydraulic device 141, a hydraulic load 104, a first fluid path 142, and a second fluid path 143. The hydraulic device 141 includes a first device port 141a and a second device port 141b. The hydraulic system 140 also includes a differential shock absorber 145. The differential shock absorber 145 includes a shock absorber piston 146 that is slidably received within the interior volume of the differential shock absorber 145. For example, as shown in the embodiment of FIG. 5, the piston 146 may be slidably received within a cylindrical portion of the interior volume such that the shock absorber piston 146 fluidly separates the interior volume into a first shock absorber chamber 145a and a second shock absorber chamber 145b. The shock absorber piston 146 is disposed between the first shock absorber chamber 145a and the second shock absorber chamber 145b such that movement of the shock absorber piston 146 increases the volume of one shock absorber chamber and decreases the volume of the other shock absorber chamber. In the embodiment of FIG. 5, opposing piston faces 146a and 146b are exposed to the pressure of hydraulic fluid in first and second shock absorber chambers 145a and 145b, respectively.

[0043] The hydraulic device 141 is fluidly connected to the hydraulic load 104 by a first flow path 142 and a second flow path 143, respectively. Specifically, a first port of the hydraulic device 141a may be fluidly connected to a first port of the hydraulic load 104a by the first flow path 142. Correspondingly, a second port of the hydraulic device 141b may be fluidly connected to a second port of the hydraulic load 104b by the second flow path 143. The first shock absorber chamber 145a and the second shock absorber chamber 145b are fluidly connected to the flow paths 142 and 143, respectively, by two branch flow paths. For example, the shock absorber chambers 145a and 145b may also include ports 147a and 147b. Thus, the port 147a of the first shock absorber chamber may be fluidly connected to the first flow path 142 at a position along the first flow path 142 between the hydraulic device 141 and the hydraulic load 104. Correspondingly, port 147b of second buffer chamber 145b may be fluidly connected to second flow path 143 at a location along second flow path 143 between hydraulic device 141 and hydraulic load 104.

[0044] In some embodiments, it may be desirable to bias the snubber piston 146 of the differential snubber 145 toward a neutral position when the hydraulic device 141 of the hydraulic system 140 is not operating, e.g., not creating a pressure differential between its two ports. Thus, in some embodiments, the differential snubber 145 may include one or more springs operatively coupled to the snubber piston 146 to bias the snubber piston toward a desired neutral position within the interior volume of the differential snubber 145. For example, in the embodiment illustrated in FIG. 5, the differential snubber 145 may include a first spring 148a and a second spring 148b disposed on either side of the snubber piston and contacting opposing piston surfaces 146a and 146b, respectively. In some embodiments, a first end of each spring may be positioned against a surface of the snubber piston 146, and the opposite end of the spring may be positioned against a support surface, such as the inner surface of the housing of the differential snubber 145, as shown, with the springs extending between the piston and opposing inner surfaces of the housing. However, the present disclosure should not be limited to any particular type of support structure for maintaining the springs in a desired position and / or orientation relative to the shock absorber piston. In either case, the pair of springs may be configured to maintain the position of the piston 146 relative to the differential shock absorber housing by applying equal and opposite, or effectively equal and opposite, forces to the piston 146 when the differential pressure across the piston 146 is zero or effectively zero. In some embodiments, the spring constants of the two springs may be selected to be equal or effectively equal. For example, the effective spring constant of one or more springs on either side of the piston may be within 20%, 10%, 5%, 1%, and / or any other suitable percentage of the spring constant of the larger spring. Because the present disclosure is not limited to the use of any particular number or type of springs, in some embodiments, either or both of the springs shown in the figures may be replaced by multiple springs that, in combination, are equivalent to the single spring shown.

[0045] The above embodiments have described a branched connection between the flow paths and the differential shock absorber and a typical hydraulic load. However, the present disclosure is not limited to this configuration. For example, hydraulic systems including a differential shock absorber connected to the system's hydraulic system and / or one or more hydraulic loads in a manner different from that shown in FIG. 5 are also contemplated. FIG. 6 illustrates one such embodiment.

[0046] As with the previous embodiment, FIG. 6 illustrates a hydraulic system 240 including a hydraulic device 141 with device ports 141a and 141b. The hydraulic system 240 also includes a differential shock absorber 145 similar to that described above. Again, the differential shock absorber 145 may include a shock absorber piston 146 slidably received within the shock absorber's internal volume, fluidly separating the internal volume into a first shock absorber chamber 145a and a second shock absorber chamber 145b with associated first and second springs 145a and 145b. However, rather than using a branched connection, the differential shock absorber 145 is constructed in a flow-through configuration. Specifically, as shown, the first shock absorber chamber 145a may include two flow ports corresponding to the first and second ports 147a and 147b, respectively, as shown. The second shock absorber chamber 145b may also include two communication ports corresponding to a third port 147c and a fourth port 147d. The first device port 141a of the hydraulic device 141 may be fluidly connected to the first port 147a of the first shock absorber chamber 145a via a first flow path 142a extending between the hydraulic device 141 and the first shock absorber chamber 145a. Similarly, the second port 147b of the first shock absorber chamber may be fluidly connected to the first port 154a of a hydraulic load, such as the illustrated active suspension actuator 150, by a third flow path 142b extending between the first shock absorber chamber and the hydraulic load. Similarly, the second device port 141b of the hydraulic device may be fluidly connected to a port 147c of the second shock absorber chamber, i.e., the third port 147c, by a second flow passage 143a extending between the hydraulic device 141 and the second shock absorber chamber 145b. The other port of the second shock absorber chamber, i.e., the fourth port 147d, may be fluidly connected to the second port 154b of the hydraulic load by a fourth fluid flow passage 143b extending between the second shock absorber chamber 145b and the hydraulic load.

[0047] In the illustrated embodiment of active suspension actuator 150, the actuator includes a piston 152 slidably disposed within an interior volume of the actuator's housing between a boost volume 151 a and a compression volume 151 b. A piston rod 153 is attached to and extends from at least a first side of the piston 152. The piston may extend externally of the actuator housing. In the illustrated embodiment, the boost volume 151 a is in fluid communication with a first port 154 a of the actuator, and the compression volume 151 b is in fluid communication with a second port 154 b of the actuator. Of course, while a particular active suspension actuator is illustrated in the figures, it should be understood that any suitable hydraulic load may be included in the illustrated system, as the disclosure is not so limited.

[0048] In the illustrated embodiment including an active suspension actuator 150 with a piston 152, operation of the hydraulic system may cause the piston to extend into the interior volume of the actuator by varying amounts. Accordingly, the hydraulic system 240 may also include an accumulator 155, or other suitable reservoir, that may be configured and dimensioned to contain hydraulic fluid displaced by the advancement or withdrawal of the piston rod 153 into or from the actuator housing. In the embodiment of FIG. 6, during the extension stroke, the extension volume 151a decreases and the compression volume 151b increases. During the compression stroke, the extension volume increases and the compression volume decreases.

[0049] During operation of the hydraulic system 240 of Figure 6, a hydraulic device 141, such as a pump, may be used to draw fluid from the compression volume 151b and force fluid into the rebound volume 151a, causing the active suspension actuator 150 to compress. In the embodiment of Figure 6, a quantity of fluid may be pumped from the first port 141a of the hydraulic device 141 into the first flow path 142a, into the first port 147a of the first shock absorber chamber 145a, through the first shock absorber chamber to the second port 147b of the first shock absorber chamber, through the third flow path 142b, through the first port 154a of the active suspension actuator, and into the rebound volume 151a. This causes the piston 152 to move in a compression direction, causing a quantity of fluid to flow out of the compression volume 151b and through the second port 154b of the actuator 150 or other suitable hydraulic load. A portion of the fluid volume exiting the compression volume flows through the fourth flow path 143b to a port in the second shock absorber chamber 145b (i.e., fourth port 147d), through the second shock absorber chamber 145b to another port in the second shock absorber chamber (i.e., third port 147c), and through the second flow path 143a to the second device port 141b of the hydraulic device. The remaining portion of the flow out of port 154b may enter the accumulator 155. It should be noted that in the configuration of FIG. 6, for a given displacement of the piston 152, the amount of fluid passing through the hydraulic device 141 is equal to the volume swept by the cross-sectional area of ​​the piston 152 minus the cross-sectional area of ​​the piston rod 153. The difference between this volume and the volume swept by the piston cross-sectional area either flows into or out of the accumulator 155, depending on the direction of movement of the piston 152. As a result, the amount of fluid that needs to be pumped by hydraulic device 141 to establish a desired pressure differential can be significantly less than the embodiment of FIG. 4, which requires a larger amount of fluid to be pumped from one reservoir to another to establish the same pressure differential.

[0050] The above description describes the compression cycle of motion of the active suspension actuator 150. However, the active suspension actuator 150 may also undergo an extension cycle, which displaces the piston rod 153 further out of the actuator housing. Thus, operating the hydraulic system 141 in the reverse direction may cause fluid to flow in the opposite direction through the various components described above. Additionally, similar fluid flows through different flow paths and differential dampers 145 may occur when the system is controlled to operate different hydraulic loads than the active suspension actuator 150 illustrated in FIG. 6.

[0051] As previously mentioned, operation of the hydraulic system 141 may result in flow pulsations that propagate along the flow paths 142a and 143a extending between the hydraulic system 141 and the differential shock absorber 145. Thus, flow pulsations may be generated at the system ports 141a and 141b of the hydraulic system 141 and propagate to the differential shock absorber 145 and into the first and second shock absorber chambers 145a and 145b. As previously mentioned, the flow pulsations may be at least partially out of phase within the first and second shock absorber chambers 145a and 145b. Due to pressure differences associated with these out-of-phase flow pulsations across the shock absorber piston 146, the flow pulsations reaching the first and second shock absorber chambers 145a and 145b may induce the shock absorber piston 146 to move. The resulting movement of the shock absorber piston 146 may be unidirectional and may have a magnitude associated with out-of-phase pulsations such that the magnitude of pulsations propagating downstream from the differential shock absorber 145 toward one or more associated hydraulic loads may be reduced, and in some cases substantially or effectively eliminated, relative to the magnitude of pulsations upstream of the differential shock absorber 145 (e.g., between the differential shock absorber 145 and the hydraulic device 141). For example, the magnitude of pulsations transmitted along the flow paths 142b and 143b extending between the first and second shock absorber chambers 145a and 145b and the associated hydraulic loads may be less than the magnitude of pulsations transmitted between the first and second shock absorber chambers 145a and 145b and the hydraulic device 141. This may correspondingly reduce the magnitude of pulsations imparted to the hydraulic loads.

[0052] The inventors have recognized that the degree of mitigation of flow pulsations using a differential shock absorber may depend, at least in part, on how close the pressure pulses are to being 180° out of phase in opposing chambers of the differential shock absorber. The further the pulsations are from being 180° out of phase in the separate shock absorber chambers, the less effective the disclosed pulse mitigation strategy using a differential shock absorber may be because there is less destructive interference between the pulses. Thus, in some embodiments, it may be desirable to match the compliance and / or impedance of the fluid flow paths 142a and 143a extending between and including the hydraulic device 141 and the corresponding first and second shock absorber chambers 145a and 145b so that the compliance and / or impedance of the fluid flow paths 142a and 143a are substantially equal to each other, or at least within some desired tolerance of each other. With the flow paths balanced in this manner, the pulsations reaching opposing chambers are approximately 180 degrees out of phase with each other and can therefore be more effectively countered by the motion induced in the piston by these pulsations.

[0053] While operation of the differential shock absorber to at least partially mitigate flow and / or pressure pulsations propagating from the hydraulic system to associated hydraulic loads was described in connection with FIG. 6 , a similar method of operation is applicable to the embodiment of FIG. 5 . Specifically, the shock absorber piston 146, located between the first shock absorber chamber 145 a and the second shock absorber chamber 145 b of the differential shock absorber 145, may still be exposed to pulsations generated at the first port 141 a and the second port 141 b of the hydraulic system 141. Thus, the shock absorber piston 146 may again move under periodic pressure differentials resulting from out-of-phase pulsations imposed on the separate shock absorber chambers 145 a and 145 b. This may also result in movement of the shock absorber piston 146, which may at least partially mitigate pulsations from propagating downstream from the connections of the differential shock absorber 145 to associated flow paths, even though the embodiment of FIG. 5 illustrates branch connections rather than through-flow connections. It should therefore be understood that the differential shock absorbers of the present disclosure may be subjected to pulsations present in separate flow paths using direct flow-through fluid connections, indirect fluid connections, and / or another suitable type of connection that allows fluid communication between the shock absorber chambers and the associated flow paths within a desired frequency range associated with the pulsations.

[0054] Referring to FIG. 6 , the damper piston 146 may have a mass m, which refers to the inertial mass of both the piston and the fluid that moves as the piston moves. Like other mass-spring systems, the differential damper 145 may have natural resonant modes. This means that the differential damper 145 does not require the same amount of excitation energy to move the damper piston at the frequency of the natural resonant mode compared to other frequencies. The resonant modes of the differential damper 145 may be generated by the mass m of the damper piston 146 oscillating on the springs 148 a and 148 b. The mass m may be selected taking into account the desired stiffness of the differential damper 145. While it may be desirable to minimize the mass m to reduce its effect on noise or volume ripple suppression in general, the mass m and compliance of the springs may also be selected to generate resonant modes (caused by the mass m of the damper piston 146 oscillating on the springs 148 a and 148 b) that may further enhance the effectiveness of the differential damper 145.

[0055] In one example, if the hydraulic device 141 outputs a pressure ripple at 100 Hz, in a system with a shock absorber piston 146 of very small mass m, the stiffness of the hydraulic circuit may be primarily spring-based (i.e., spring-dominant). At frequencies above the natural resonance frequency, the mass m prevents the shock absorber piston 146 from moving in response to the pressure ripple, so the stiffness of the hydraulic circuit may appear higher than the spring stiffness (i.e., mass-dominant here). However, if the mass m of the shock absorber piston 146 is selected so that the natural resonance occurs when the pressure ripple is output at 100 Hz, the stiffness of the hydraulic circuit may be much softer than just the spring stiffness.

[0056] While the embodiments shown in FIGS. 5 and 6 include one or more coil springs, the disclosure is not so limited. For example, the coil springs of the illustrated embodiments could be replaced with one or more disc springs. As shown in FIGS. 7A-7C, multiple disc springs could be stacked in parallel 171, series 172, or a combination of parallel and series 173, depending on the desired spring characteristics. Thus, it should be understood that the disclosure is not limited to any type of spring and / or spring arrangement. FIG. 8 illustrates one such exemplary embodiment in which hydraulic system 340 includes hydraulic device 141 and differential shock absorber 345 includes shock absorber piston 346. As with the previous embodiment, differential shock absorber 345 includes one or more springs 348a and 348b positioned against opposing surfaces of the shock absorber piston. However, in the illustrated embodiment, the springs correspond to four disc springs positioned in a parallel configuration on either side of the shock absorber piston. Of course, different numbers and arrangements of disc springs relative to the shock absorber piston may also be used as the present disclosure is not so limited.

[0057] FIG. 9 illustrates a perspective cross-sectional view of a compact differential shock absorber 445 including a piston 446 that is subjected to a force generated by springs 448a and 448b in the form of Belleville spring stacks disposed on either side of the shock absorber piston 446. FIG. 10 illustrates a front cross-sectional view of the differential shock absorber 445 with an outer housing 560 that covers a portion of the differential shock absorber 445. The differential shock absorber 445 includes an inner housing 561 that includes one or more openings 562 formed in separate first and second portions of the inner housing 561. These openings 562 can be in fluid communication with either the first shock absorber chamber 545a or the second shock absorber chamber 545b, respectively. Thus, separate first and second fluid volumes 563 and 564 can be formed between the outer and inner housings. The first fluid volume 563 and the second fluid volume 564 may be separated from one another by one or more seals, such as the illustrated O-ring, disposed between the inner housing 561 and the outer housing 560. The differential buffer 445 may also include a base portion 565 that is fluidly sealed to the outer housing 560 or to other suitable portions of the differential buffer 445. In the illustrated embodiment, ports for the differential buffer 445 may be formed in the base portion 565 of the differential buffer 445 and / or in the outer housing 560. For example, as shown in FIG. 10 , a first port 547a in fluid communication with the first buffer chamber 545a is formed in the base portion 565, such as the illustrated central support shaft, and a separate port 547b in fluid communication with the first buffer chamber 545a is formed in the outer housing 560. Thus, fluid may flow between the first and second ports through the first shock absorber chamber 545a and a corresponding first volume 563 disposed between the outer housing 560 and the inner housing 561. Correspondingly, a third port 547c may also be formed in the base portion 565 to be in fluid communication with the second shock absorber chamber, and a fourth port 547d may be formed in the outer housing 560 such that fluid may flow between the third and fourth ports through the second shock absorber chamber and a corresponding second volume disposed between the outer housing and the inner housing.

[0058] While the above embodiments primarily illustrate differential shock absorbers in which fluid flows directly through the shock absorber chambers, embodiments in which fluid does not flow directly through the shock absorber chambers of the differential shock absorber to the hydraulic load are also contemplated. For example, a T-junction similar to that shown in FIG. 5 may be used, in which fluid may enter and exit the differential shock absorber from a main flow path. Additionally, an embodiment similar to that shown in FIG. 10 may be used, in which two or more ports are formed in the outer housing 560 and are in fluid communication with the same fluid volume disposed between the inner housing 561 and the outer housing 560. In such an embodiment, fluid may flow between two ports formed in the outer housing 560 through a fluid connection volume. However, that volume of fluid may be in fluid communication with the associated shock absorber chamber through one or more openings formed in the inner housing 561. Thus, while the pistons may still be subject to flow pulsations emitted by an associated hydraulic device, the flow path extending between the hydraulic device and the hydraulic load may not pass directly through the shock absorber chambers of the differential shock absorber. Therefore, it should be understood that the present disclosure is not limited to any particular configuration and is intended to include any number of different arrangements of ports, housings, and fluid connections associated with a differential buffer.

[0059] 11A-11C illustrate three cross-sectional front views of another embodiment of a differential shock absorber 645 similar to the differential shock absorber shown in FIGS. 9-10. Again, the differential shock absorber includes a shock absorber piston 646 disposed between a first shock absorber chamber 645a and a second shock absorber chamber 645b. The shock absorber piston 646 is illustrated in different positions in the different views. FIG. 11A illustrates the differential shock absorber 645 with the shock absorber piston 646 in a neutral position where the pressure on the two faces of the shock absorber piston 646 is equal or effectively equal; a first spring 648a and a second spring 648b operably coupled to either side of the piston may also be in a neutral state. Figure 11B shows that increased pressure in the first shock absorber chamber relative to the second shock absorber chamber causes the shock absorber piston 646 to move downward, expanding the first shock absorber chamber 645a and first spring 648a while compressing the second shock absorber chamber 645b and associated second spring 648b. Figure 11C illustrates the reverse pressure differential across the shock absorber piston 646, where increased pressure exists in the second shock absorber chamber 645b relative to the first shock absorber chamber 645a, causing the shock absorber piston 646 to move upward in the opposite direction, compressing the first shock absorber chamber 645a and first spring 648a while expanding the second shock absorber chamber 645b and second spring 648b. Again, this relative movement of the damper piston 646 due to the pressure differential across the piston allows the differential damper to help dampen flow and / or pressure pulsations generated by a fluidly connected hydraulic system.

[0060] FIG. 12 illustrates aspects of a disc spring stack that may be used in various embodiments of the differential shock absorber disclosed herein. In the illustrated embodiment, the disc spring 700 may include one or more through-holes 702 extending from a first planar surface of the disc spring to an opposite second planar surface. In embodiments in which a central axis extends through the disc spring stack, these one or more through-holes may be separate from the central hole formed in the disc spring stack. Without wishing to be bound by theory, the presence of these one or more through-holes formed in the disc spring may help to avoid fluid trapping between two opposing disc springs that are compressed toward each other. This may help promote free flow of fluid through a differential shock absorber including such a spring arrangement. In some embodiments, the disc spring may also include one or more linkage mechanisms 704, such as the illustrated tongue-and-groove arrangement, between adjacent portions of the contacting disc springs. These interlocking mechanisms may help prevent both lateral and rotational movement of the disc springs relative to one another, which may improve the stability of the overall disc spring stack during operation.

[0061] While the present teachings have been described in conjunction with various embodiments and examples, it is not intended that the present teachings be limited to such embodiments or examples. Rather, the present teachings encompass various alternatives, modifications, and equivalents, as will be appreciated by those skilled in the art. Accordingly, the foregoing description and drawings are by way of example only.

Claims

1. 1. A hydraulic system comprising: a hydraulic device having a first device port and a second device port; a differential shock absorber having a first shock absorber port and a second shock absorber port; a first flow path fluidly connecting the first device port to the first shock absorber port; a second flow path fluidly connecting the second device port to the second shock absorber port; Hydraulic system, including:

2. 2. The system of claim 1, wherein the differential shock absorber includes a first shock absorber chamber and a second shock absorber chamber fluidly separated by a shock absorber piston slidably housed within the differential shock absorber, the first shock absorber chamber fluidly connected to the first device port and the second shock absorber chamber fluidly connected to the second device port.

3. 3. The system of claim 2, further comprising a first spring configured to resist movement of the shock absorber piston in a first direction and a second spring configured to resist movement of the shock absorber piston in a second direction opposite the first direction.

4. The system of claim 3 , wherein the first spring and the second spring comprise coil springs.

5. The system of claim 3 , wherein the first spring and the second spring comprise disc springs.

6. 6. The system of claim 2, wherein the shock absorber piston is configured to move in a first direction when a pressure in the first shock absorber chamber is greater than a pressure in the second shock absorber chamber, and to move in a second direction opposite to the first direction when the pressure in the second shock absorber chamber is greater than the pressure in the first shock absorber chamber.

7. 7. The system of claim 6, wherein when the shock absorber piston moves in the first direction, a first volume of the first shock absorber chamber increases and a second volume of the second shock absorber chamber decreases, and when the shock absorber piston moves in the second direction opposite the first direction, the second volume of the second shock absorber chamber increases and the first volume of the first shock absorber chamber decreases.

8. The system of any one of claims 1 to 7, 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 claims 1 to 8, wherein the hydraulic device is selected from the group consisting of a hydraulic pump and a hydraulic motor.

10. 10. The system of claim 1, wherein the first flow path has a first net compliance and the second flow path has a second net compliance, the first net compliance being within 20% of the second net compliance within a predetermined frequency range.

11. 10. The system of claim 1, wherein the first fluid flow path has a first net impedance and the second fluid flow path has a second net impedance, the first net impedance being within 20% of the second net impedance within a predetermined frequency range.

12. 12. The system of claim 1, wherein the differential damper includes a third port and a fourth port, the third port and the fourth port being in fluid communication with a hydraulic load.

13. The system of claim 12 , wherein the hydraulic load is an active suspension actuator.

14. 1. An active suspension actuator system, comprising: a hydraulic system including a first system port and a second system port; a differential shock absorber including a first shock absorber chamber and a second shock absorber chamber fluidly separated by a shock absorber piston slidably received within the differential shock absorber, the first shock absorber chamber being fluidly connected to the first port of the hydraulic device and the second shock absorber chamber being fluidly connected to the second port of the hydraulic device; a hydraulic actuator comprising a first actuator chamber and a second actuator chamber fluidly separated by an actuator piston slidably housed within the hydraulic actuator, the first actuator chamber being fluidly connected to the first shock absorber chamber and the second actuator chamber being fluidly connected to the second shock absorber chamber; an active suspension actuator system comprising:

15. 15. The system of claim 14, further comprising a first spring configured to resist movement of the shock absorber piston in a first direction and a second spring configured to resist movement of the shock absorber piston in a second direction opposite the first direction.

16. The system of claim 15 , wherein the first spring and the second spring comprise coil springs.

17. The system of claim 15 , wherein the first spring and the second spring comprise disc springs.

18. 18. The system of claim 14, wherein the shock absorber piston is configured to move in a first direction when a pressure in the first shock absorber chamber is greater than a pressure in the second shock absorber chamber, and to move in a second direction opposite to the first direction when the pressure in the second shock absorber chamber is greater than the pressure in the first shock absorber chamber.

19. 19. The system of claim 18, wherein when the shock absorber piston moves in the first direction, a first volume of the first shock absorber chamber increases and a second volume of the second shock absorber chamber decreases, and when the shock absorber piston moves in the second direction opposite the first direction, the second volume of the second shock absorber chamber increases and the first volume of the first shock absorber chamber decreases.

20. A system according to any one of claims 14 to 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 to 20, wherein the hydraulic device is selected from the group consisting of a hydraulic pump and a hydraulic motor.

22. 22. The system of claim 14, wherein a first flow path extending between and including the first equipment port and the first shock absorber chamber has a first net compliance, and a second flow path extending between and including the second equipment port and the second shock absorber chamber has a second net compliance, the first net compliance being within 20% of the second net compliance within a predetermined frequency range.

23. 23. The system of claim 14, wherein a first flow path extending between the first equipment port and the first shock absorber chamber and including the first equipment port and the first shock absorber chamber has a first net impedance, and a second flow path extending between the second equipment port and the second shock absorber chamber and including the second equipment port and the second shock absorber chamber has a second net impedance, and the first net impedance is within 20% of the second net impedance within a predetermined frequency range.

24. 24. The system of claim 14, wherein the differential shock absorber includes a third port fluidly coupled to the first shock absorber chamber and a fourth port fluidly coupled to the second shock absorber chamber, the third port of the differential shock absorber being fluidly connected to the first actuator chamber and the fourth port being fluidly connected to the second actuator chamber.

25. 1. A method of operating a hydraulic system, comprising: applying flow pulsations to a first flow path fluidly connected to a first shock absorber chamber and to a second flow path fluidly connected to a second shock absorber chamber, the flow pulsations in the first shock absorber chamber being at least partially out of phase with the flow pulsations in the second shock absorber chamber; displacing a shock absorber piston disposed between the first shock absorber volume and the second shock absorber volume at least partially due to a phase difference between the flow pulsation in the first shock absorber chamber and the flow pulsation in the second shock absorber chamber; A method comprising:

26. 26. The method of claim 25, wherein displacing the shock absorber piston changes the volume of the first shock absorber chamber and the volume of the second shock absorber chamber to reduce the magnitude of the flow pulsations transmitted to a hydraulic load.

27. 27. The method of claim 26, wherein the hydraulic load is an active suspension actuator.

28. The method of any one of claims 25 to 27, further comprising biasing the snubber piston towards a neutral configuration.

29. 29. The method of any one of claims 25 to 28, further comprising moving the shock absorber piston in a first direction when a pressure in the first shock absorber chamber is greater than a pressure in the second shock absorber chamber, and in a second direction opposite to the first direction when the pressure in the second shock absorber chamber is greater than the pressure in the first shock absorber chamber.

30. 30. The method of claim 29, wherein when the shock absorber piston moves in the first direction, a first volume of the first shock absorber chamber increases and a second volume of the second shock absorber chamber decreases, and when the shock absorber piston moves in the second direction opposite the first direction, the second volume of the second shock absorber chamber increases and the first volume of the first shock absorber chamber decreases.

31. The method of any one of claims 25 to 30, further comprising generating the flow pulsations using a hydraulic device.

32. 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. 33. The method of claim 31 or 32, wherein the hydraulic device is selected from the group consisting of a hydraulic pump and a hydraulic motor.

34. 34. A method according to any one of claims 25 to 33, wherein the phase difference of the hydraulic flow pulsations on either side of the shock absorber piston is between 140 degrees and 220 degrees out of phase.

35. 1. A hydraulic system comprising: a hydraulic device having a first device port and a second device port; a differential shock absorber having a first shock absorber port and a second shock absorber port; a first flow path fluidly connecting the first device port to the first shock absorber port; a second flow path fluidly connecting the second device port to the second shock absorber port; Hydraulic system, including:

36. 36. The system of claim 35, wherein the differential shock absorber includes a first shock absorber chamber and a second shock absorber chamber fluidly separated by a shock absorber piston slidably housed within the differential shock absorber, the first shock absorber chamber fluidly connected to the first device port and the second shock absorber chamber fluidly connected to the second device port.

37. 37. The system of claim 36, further comprising a first spring configured to resist movement of the snubber piston in a first direction and a second spring configured to resist movement of the snubber piston in a second direction opposite the first direction.

38. 38. The system of claim 37, wherein the damper piston is configured to have a resonant mode within a frequency range of flow pulsations produced by the hydraulic device.

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