Hydraulic power generation pump control

Abstract

To provide a hydraulic power unit and a method of operating the hydraulic power unit.SOLUTION: A hydraulic power unit includes a reservoir containing hydraulic fluid, a main output, a pressure sensor, at least one active valve hydraulic pump, and at least one passive valve hydraulic pump. A main flow of the hydraulic fluid is discharged through the main output. The pressure sensor includes a pressure signal that is indicative of a pressure of the main flow. Each active valve hydraulic pump is configured to drive a first flow portion of the main flow from the reservoir to the main output when the pressure signal is below a first pressure setpoint. Each passive valve hydraulic pump is configured to drive a second flow portion of the main flow from the reservoir to the main output when the pressure signal is below a second pressure setpoint.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] [CROSS REFERENCE TO RELATED APPLICATIONS] This application claims the benefit of priority from U.S. Provisional Patent Application No. 63 / 517,180, filed Aug. 2, 2023, entitled "Hydraulic Power Generation Pump Control," the contents of which are incorporated herein by reference.

[0002] FIELD OF THE DISCLOSURE Embodiments of the present disclosure relate generally to the generation of fluid power, and more specifically, to the generation of fluid power using two different types of hydraulic pumps. [Background technology]

[0003] Dynamic testing systems, such as those developed by MTS Systems Corporation, include test stations that perform various tests by applying loads and displacements to a test object using hydraulic actuators. Test stations may include, for example, a vehicle test station that applies simulated driving situations to a moving vehicle, or a building test station that applies simulated seismic activity to a building.

[0004] The hydraulic actuators of the test station are driven by the working fluid flow generated by a fluid power unit. A conventional fluid power unit includes multiple passive valve hydraulic pumps with variable displacement volumes. Such passive valve hydraulic pumps include, for example, hydraulic piston pumps having multiple piston pumps (e.g., piston and cylinder assemblies) with adjustable working volumes for varying the delivered working fluid flow. The working fluid flow into and out of the working volumes is controlled using passive (e.g., pressure actuated) valves. One common type of passive valve hydraulic pump used in fluid power units is a variable displacement axial piston pump that utilizes a swash plate to vary the working volume of the piston pump.

[0005] While passive valve hydraulic pumps having variable displacement can be effective in efficiently providing large volumes of working fluid flow, they generally cannot respond quickly to changes in fluid flow demand. Summary of the Invention

[0006] SUMMARY OF THE DISCLOSURE Embodiments of the present disclosure relate to generating fluid power for dynamic testing systems, including fluid power units and methods of operating fluid power units, fluid power systems, and methods of operating fluid power systems.

[0007] One embodiment of a fluid power unit (HPU) includes a reservoir containing a working fluid, a main output, a pressure sensor, at least one active valve hydraulic pump, and at least one passive valve hydraulic pump. A housing houses the reservoir, the at least one active hydraulic pump, and the at least one passive hydraulic pump. A main stream of the working fluid is discharged through the main output. The pressure sensor includes a pressure signal indicative of a pressure of the main stream. Each active valve hydraulic pump is configured to drive a first flow portion of the main stream from the reservoir to the main output when the pressure signal is below a first pressure set point. Each passive valve hydraulic pump is configured to drive a second flow portion of the main stream from the reservoir to the main output when the pressure signal is below a second pressure set point.

[0008] In some embodiments of the present HPU, the first pressure set point is lower than the second pressure set point, or the first pressure set point is higher than the second pressure set point.

[0009] In some embodiments of the present HPU, the first pressure set point is approximately 1% to 5% lower than the second pressure set point.

[0010] In some embodiments of the present HPU, the first pressure set point is approximately 1% to 5% higher than the second pressure set point.

[0011] In some embodiments of the present HPU, the first pressure set point is equal to the second pressure set point.

[0012] In some embodiments, the fluid power unit comprises at least one controller configured to set the first pressure set point and the second pressure set point.

[0013] In some embodiments of the present HPU, the at least one passive valve hydraulic pump includes a plurality of passive valve hydraulic pumps.

[0014] In some embodiments of the present HPU, the at least one active valve hydraulic pump includes a plurality of active valve hydraulic pumps.

[0015] In some embodiments of the present HPU, the at least one active valve hydraulic pump includes a plurality of active valve hydraulic pumps.

[0016] In some embodiments of the HPU, each active-valve hydraulic pump includes a low pressure port connected to a fluid reservoir, a high pressure port connected to the main output, a plurality of piston pumps, a motor configured to drive a cyclic change to a working volume of each piston pump, a plurality of active valves, each corresponding to one of the piston pumps and configured to set the piston pump to an operating state in which the cyclic change to the working volume drives a first flow portion of the working fluid from the working volume through the high pressure port, and a stopped state in which a fluid path is formed between the working volume and the reservoir or the low pressure port, and a pump controller configured to control each of the active valves to individually set the piston pump to an operating state or a stopped state.

[0017] In some embodiments of the HPU, each passive valve hydraulic pump includes a low pressure port connected to a fluid reservoir, a high pressure port connected to the main output, a plurality of piston pumps, each configured to draw working fluid into an adjustable working volume through the low pressure port and drive a second flow portion of the working fluid from the adjustable working volume through the high pressure port, and a motor configured to drive a cyclic change to the adjustable working volume of each piston pump.

[0018] In one example of a method of operating a fluid power unit, a first flow portion of the mainstream is driven using one or more of the at least one active valve hydraulic pump when a pressure signal indicates that the pressure of the mainstream falls below a first pressure set point. The at least one active valve hydraulic pump is stopped when the pressure signal indicates that the pressure of the mainstream is above the first pressure set point. A second flow portion of the mainstream is driven using one or more of the at least one passive valve hydraulic pump when the pressure signal indicates that the pressure of the mainstream is below a second pressure set point. The at least one passive valve hydraulic pump is stopped when the pressure signal indicates that the pressure of the mainstream is above the second pressure set point.

[0019] In some embodiments of the method, the first pressure set point is lower than the second pressure set point, or the first pressure set point is higher than the second pressure set point.

[0020] In some embodiments of the method, the first pressure set point is about 1% to 5% lower than the second pressure set point.

[0021] In some embodiments of the method, the first pressure set point is about 1% to 5% higher than the second pressure set point.

[0022] In some embodiments of the method, the first pressure set point is equal to the second pressure set point.

[0023] In some embodiments of the method, the at least one passive valve hydraulic pump comprises a plurality of passive valve hydraulic pumps.

[0024] In some embodiments of the method, the at least one active valve hydraulic pump comprises a plurality of active valve hydraulic pumps.

[0025] In some embodiments of the method, the at least one active valve hydraulic pump comprises a plurality of active valve hydraulic pumps.

[0026] In some embodiments of the method, each active-valve hydraulic pump includes a low pressure port connected to a fluid reservoir, a high pressure port connected to the primary output, a plurality of first piston pumps, a motor configured to drive a cyclic change to a working volume of each of the first piston pumps, and a plurality of active valves, each configured to set one of the first piston pumps to an operating state in which the cyclic change to the working volume drives a portion of the first flow portion of the working fluid through the high pressure port and a stopped state in which a fluid path is formed between the working volume and the reservoir or the low pressure port, and a motor configured to control each of the active valves. and a pump controller configured to individually set the first piston pumps to an on or off state, each passive valve hydraulic pump comprising a low pressure port connected to a fluid reservoir, a high pressure port connected to the main output, a plurality of second piston pumps, each configured to draw hydraulic fluid into an adjustable working volume through the low pressure port and drive a portion of a second flow portion of the hydraulic fluid from the adjustable working volume through the high pressure port, and a motor configured to drive a cyclical change to the adjustable working volume of each of the second piston pumps.

[0027] One embodiment of a fluid power system includes at least one first fluid power unit, at least one second fluid power unit, and a flow aggregator, each of the first fluid power units including a first reservoir containing a working fluid, a first main output at which a first mainstream of the working fluid is discharged, a first pressure sensor having a first pressure signal indicative of a first pressure of the first mainstream, and at least one active valve hydraulic pump configured to drive a flow portion of the first mainstream from the first reservoir to the first main output when the first pressure signal indicates that the first pressure is below a first pressure set point. Each second fluid power unit comprises a second reservoir containing the working fluid, a second main output at which a second mainstream of the working fluid is discharged, a second pressure sensor having a second pressure signal indicative of a second pressure of the second mainstream, and at least one passive-valve hydraulic pump each configured to drive a flow portion of the second mainstream from the second reservoir to the second main output when the second pressure signal indicates that the second pressure is below a second pressure set point. A flow aggregator is configured to combine the first and second mainstreams into a combined mainstream.

[0028] In some embodiments of the system, the first pressure set point is lower than the second pressure set point, or the first pressure set point is higher than the second pressure set point.

[0029] In some embodiments of the system, the first pressure set point is about 1% to 5% lower than the second pressure set point.

[0030] In some embodiments of the system, the first pressure set point is about 1% to 5% higher than the second pressure set point.

[0031] In some embodiments of the system, the first pressure set point is equal to the second pressure set point.

[0032] In some embodiments, the system comprises at least one controller configured to set the first pressure set point and the second pressure set point.

[0033] In some embodiments of the system, the at least one passive valve hydraulic pump includes a plurality of passive valve hydraulic pumps.

[0034] In some embodiments of the system, the at least one active valve hydraulic pump includes a plurality of active valve hydraulic pumps.

[0035] In some embodiments of the system, the at least one active valve hydraulic pump includes a plurality of active valve hydraulic pumps.

[0036] In some embodiments of the system, each active valve hydraulic pump includes a low pressure port connected to a fluid reservoir, a high pressure port connected to the main output, a plurality of first piston pumps, a motor configured to drive a cyclic change to a working volume of each of the first piston pumps, and a plurality of active valves, each configured to set one of the first piston pumps to an operating state in which the cyclic change to the working volume drives a portion of the first main flow from the working volume through the high pressure port, and a stopped state in which a fluid path is formed between the working volume and the reservoir or the low pressure port, and each of the active valves. and a pump controller configured to control the hydraulic pumps to individually set the first piston pumps to an active or inactive state, each passive valve hydraulic pump comprising a low pressure port connected to a fluid reservoir, a high pressure port connected to the main output, a plurality of second piston pumps, each configured to draw hydraulic fluid into an adjustable working volume through the low pressure port and drive a portion of a second main flow from the adjustable working volume through the high pressure port, and a motor configured to drive a cyclical change to the adjustable working volume of each of the second piston pumps.

[0037] In some embodiments, one or more of the sensors described above are each replaced by a flow sensor having a flow signal indicative of the flow rate of the corresponding fluid stream rather than the pressure, and the pump is controlled based on the flow signal from the flow sensor.

[0038] This Summary herein is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter. The claimed subject matter is not limited to implementations that solve any or all of the shortcomings discussed in the Background. [Brief description of the drawings]

[0039] [Figure 1] 1 is a simplified diagram of an example dynamic testing system according to an embodiment of the present disclosure.

[0040] [Diagram 2] 1 is a simplified diagram of an example fluid power unit according to an embodiment of the present disclosure.

[0041] [Diagram 3] 1 is a simplified diagram of an example fluid power system according to an embodiment of the present disclosure.

[0042] [Figure 4] 1 is a simplified diagram of an example of a passive valve hydraulic pump, according to an embodiment of the present disclosure.

[0043] [Diagram 5] FIG. 1 is a simplified side cross-sectional view of an example variable displacement axial pump, in accordance with an embodiment of the present disclosure.

[0044] [Figure 6] 1 is a simplified diagram of an example of an active valve hydraulic pump, according to an embodiment of the present disclosure.

[0045] [Figure 7A] 7A-7C are simplified schematic diagrams illustrating different operating modes of one of the piston pumps of the active valve hydraulic pump of FIG. 6 in accordance with an embodiment of the present disclosure. [Figure 7B] 7A-7C are simplified schematic diagrams illustrating different operating modes of one of the piston pumps of the active valve hydraulic pump of FIG. 6 in accordance with an embodiment of the present disclosure. [Figure 7C] 7A-7C are simplified schematic diagrams illustrating different operating modes of one of the piston pumps of the active valve hydraulic pump of FIG. 6 in accordance with an embodiment of the present disclosure.

[0046] [Figure 8] 2 is a simplified diagram of a controller according to an embodiment of the present disclosure.

[0047] [Figure 9] 1 is a chart illustrating an exemplary operation of a fluid power unit in accordance with an embodiment of the present disclosure.

[0048] [Figure 10] 1 is a chart illustrating an exemplary operation of a fluid power unit in accordance with an embodiment of the present disclosure.

[0049] [Figure 11] 4 is a flow chart illustrating an example method of operating a fluid power unit in accordance with an embodiment of the present disclosure.

[0050] [Figure 12] 1 is a flow chart illustrating an example method of operating a fluid power system according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0051] The embodiments of the present disclosure are described more fully hereinafter with reference to the accompanying drawings. Elements identified using the same or similar reference numerals refer to the same or similar elements. However, various embodiments of the present disclosure may be embodied in many different forms and should not be considered limited to the embodiments described herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the present disclosure to those skilled in the art.

[0052] 1 is a simplified diagram of an example dynamic testing system 100 according to an embodiment of the present disclosure. The testing system 100 can include one or more testing stations 102, each of which can be configured to perform a test or situation simulation by applying forces and / or displacements to a test object 103 (e.g., a vehicle, a building, etc.) using a hydraulic actuator 104.

[0053] The hydraulic actuators 104 are driven by flows of working fluid 106 generated by one or more fluid power units (HPUs) 110. The flows 106 can be coupled to provide the desired flows required by the test station 102.

[0054] System 100 may also include one or more hydraulic power systems (HPS) 114. Each HPS 114 includes a combination of two or more HPUs 110, such as HPU 110A and HPU 110B. The working fluid streams 106 output by each of the HPUs 110 are controlled to produce a desired combined working fluid stream, as discussed below.

[0055] The system 100 may include an accumulator 116 that stores the pressurized working fluid received from the HPU 110 and / or the HPS 114. The accumulator 116 may deliver a working fluid stream 118 that may be provided to the test station 102.

[0056] In some embodiments, the system 100 may include a distributor 120 that receives the working fluid flow from the HPU 110, the HPS 114, and / or the accumulator 116 and distributes the working fluid flow to the test station 102 as indicated by arrows 122. Other configurations may be used to form the system 100.

[0057] The system 100 may be a closed system, for example, where the low pressure working fluid flow 124 used by the test station 102 is returned to the HPU 110 through a hydraulic distribution system 120 or the like.

[0058] The system controller 126 may operate to control various aspects of the system 100, including the function of the HPU 110, the HPS 114, the valving (e.g., the accumulator and / or distributor valving), and / or other aspects of the system 100 to supply the required working fluid flow 122 to the test station 102.

[0059] 2 is a simplified diagram of an example of an HPU 110, according to an embodiment of the present disclosure. In some embodiments, each HPU 110 is configured to generate a main working fluid stream 106 that may have a flow rate of 50 gallons / minute or more, such as up to about 200 gallons / minute or more.

[0060] Each HPU 110 may include an HPU controller 128 that controls operation of the HPU 110 to generate the desired working fluid flow 106. In some embodiments, the HPU 110 includes two or more pumps 130, each configured to drive a flow of working fluid 132 that forms at least a portion of the main flow 106, which is discharged through a main output 133. Each of the pumps 130 may take the form of a variable displacement hydraulic pump, such as, for example, an axial piston pump, a radial piston pump, a bent-axis piston pump, a rotary vane pump, and / or any other type of variable displacement hydraulic pump suitable for use in the system 100.

[0061] Each pump 130 includes an electric motor 134 for driving the pump 130, such as through a suitable gear arrangement. The motors 134 may be, for example, 45 kilowatt or 60 horsepower motors. A cooling system (not shown) may be employed in the HPU 110 to cool the motors 134 and other components of the HPU 110.

[0062] In one embodiment, one or more pumps 130 of the HPUs 110 of the system 100 include one or more first pumps 130A of a first type and one or more second pumps 130B of a second type different from the first type. For example, the HPU 110 can include one to five pumps 130A and one to five pumps 130B, such as one or two pumps 130A and two to five pumps 130B. As discussed below, the pumps 130A and 130B can each have the ability to complement the other to provide improved performance over a conventional HPU 110 utilizing a single type of pump.

[0063] In one embodiment, each of pumps 130A is an active valve hydraulic pump having a variable displacement volume, and each of pumps 130B is a passive valve hydraulic pump having a variable displacement volume. Examples of pumps 130A and 130B are described in more detail below.

[0064] In some embodiments, system 100 may include one or more HPUs 110 having only pump 130A and / or one or more HPUs 110 having only pump 130B. System 100 may also utilize one or more HPSs 114 that include a combination of at least one HPU 110 having pump 130A and at least one HPU 110 having only pump 130B, as discussed below.

[0065] In some embodiments, the HPU 110 may include a reservoir 136 of working fluid in which each of the pumps 130 may be submerged, as shown in Figure 2. The low pressure working fluid 124 may be returned to the reservoir 136 through a return port 138. Alternatively, the pumps 130 may be located outside of the working fluid in the reservoir 136, for example, using a supercharger to draw working fluid from the reservoir 136.

[0066] A housing 139 may enclose the reservoir 136 and the pump 130, as shown in FIG.

[0067] In some embodiments, each HPU 110 includes a pressure sensor 140 (FIG. 2) configured to sense the pressure of the working fluid stream 106 at the main output 133 and generate a pressure signal 142 indicative of the sensed pressure. The pressure signal 142 can be used to control the pump 130 of the HPU 110.

[0068] In some embodiments, each HPU includes redundant pressure sensors 140, such as sensors 140A and 140B that generate pressure signals 142A and 142B, respectively, indicative of the pressure of the mainstream 106. The redundant pressure signals 142A and 142B may be used to ensure continued operation of the HPU 110 in the event that one of the pressure sensors 140 fails. Additionally, the pressure signals 142 generated by the redundant pressure sensors 140 may be used to detect anomalies, as discussed below.

[0069] 3 is a simplified diagram of an example of an HPS 114, according to an embodiment of the present disclosure. As mentioned above, each HPS 114 includes two or more of the HPUs 110, each formed according to an embodiment described herein. Thus, while the example HPS 114 of FIG. 3 shows two HPUs 110A and 110B combined, it will be understood that the HPS 114 may include three or more HPUs 110.

[0070] The HPU 110 can be controlled by at least one controller, such as the system controller 126, the HPU controller 128, and / or the HPS controller 146, to generate main flows 106 (e.g., flows 106A and 106B) that are combined by a flow aggregator 148 to generate a desired combined main flow 150 that is used to satisfy at least a portion of the working fluid flow demands of the test station 102 (FIG. 1).

[0071] In some embodiments, the HPS 114 comprises an HPU 110A having one or more pumps 130A of a first type and an HPU 110B having only pumps 130B of a second type, allowing the HPS 114 to utilize the advantages of each type of pump in generating the combined main flow 150.

[0072] The HPS 114 may utilize one or more of the pressure sensors 140 to measure the pressure of the combined main flow 150 discharged through the aggregator 148, as shown in Figure 3. In one example, the pressure sensors 140 may take the form of one or more pressure sensors 140 in each HPU 110 measuring the pressure at a corresponding main output 133. Alternatively, the HPS 114 may include one or more pressure sensors 140 downstream of a main output, such as at the output of the aggregator 148, as shown in Figure 3.

[0073] In some embodiments, each of the pumps 130B is in the form of a passive valve variable displacement hydraulic pump (e.g., a variable displacement analog pump) having an adjustable working volume, such as those used in conventional HPUs of dynamic test systems. These may include conventional variable displacement radial pumps, variable displacement vane pumps, variable displacement axial pumps, or another suitable conventional variable displacement pump.

[0074] 4 is a simplified diagram of an example of a pump 130B according to an embodiment of the present disclosure. Pump 130B can include multiple piston pumps 160, each with a piston 162 housed in a cylinder 164. Each piston 162 is driven in a cyclic or reciprocating manner within its cylinder 164 by a cyclic drive 166 using a motor 134. Motor 134 drives the relative motion between cyclic drive 166 and piston pump 160, similar to a conventional variable displacement hydraulic pump.

[0075] A valve mechanism 168 connects the working volume 170 of each piston pump 160 to a high pressure port 172 connected to the main output 133 and a low pressure port 174 connected to the reservoir 136. The working volume 170 of each piston pump 160 is the maximum volume of hydraulic fluid that can be drawn into or expelled from the cylinder 164 through its port 176 during a stroke cycle of the piston 162.

[0076] Pump 130B includes a conventional working volume regulator 178 that operates in a conventional manner to regulate the working volume 170 of each of piston pumps 160. This allows pump 130B to transition from a zero or near-zero displacement mode (e.g., an idle mode), in which pump 130B drives little, if any, working fluid flow 132B through high pressure port 172, to a maximum displacement mode, in which pump 130B drives maximum working fluid flow 132B through high pressure port 172, while motor 134 drives relative motion between piston pump 160 and cyclic drive 166.

[0077] The valve mechanism 168 may be a conventional valve mechanism comprising a passive valve, such as, for example, a poppet check valve, that allows hydraulic fluid to flow in and out of the working volume 170 of each piston pump 160 in response to movement of the piston 162. For example, when the cyclic drive 166 moves the piston 160 toward its port 176, as indicated by arrow 180, hydraulic fluid flow is driven through the port 176. The valve mechanism 168 allows flow to be delivered to the high pressure port 172 while preventing flow from being delivered to the low pressure port 174, as shown in FIG. 4. When the cyclic drive 166 moves the piston 162 away from its port 176, as indicated by arrow 182, hydraulic fluid flow is drawn from the reservoir 136 through the low pressure port 174 and port 176 into the cylinder 164. Thus, in this manner, the cyclical movement of the piston 162 can drive the flow 132B of working fluid received from the reservoir 136 through the high pressure port 172 to the main output 133 to form the main flow 106, as shown in FIG.

[0078] The cyclic drive 166 and the working volume adjuster 178 may take any suitable form. Where pump 130B is in the form of a conventional variable displacement radial pump, cyclic drive 166 may take the form of a cam and working volume adjuster 178 may, for example, adjust the eccentricity of the axis of rotation of piston pump 160 relative to the cam or the axis of rotation of the cam relative to piston pump 160 to adjust the working volume. Where pump 130B is in the form of a conventional variable displacement vane pump, cyclic drive 166 may take the form of a cam ring which engages vanes of piston 162 as piston pump 160 rotates relative to the cam ring. Here, working volume adjuster 178 may take the form of, for example, the eccentricity of the axis of rotation of piston pump 160 relative to the cam ring.

[0079] Alternatively, pump 130B may take the form of a conventional variable displacement axial pump, an example of which is provided in a simplified side cross-sectional view in FIG. 5. Here, motor 134 may rotate shaft 184, to which piston pumps 160 are attached, relative to swashplate 186, which acts as cyclic drive 166. Swashplate 186 drives cyclic movement of pistons 162 to either draw hydraulic fluid into or drive hydraulic fluid out of working volumes 170 of piston pumps 160 in response to movement of piston pumps 160 relative to swashplate 186. An angle 188 of swashplate 186 relative to axis 189 of shaft 184 determines the working volumes 170 of the respective piston pumps 160. Working volume adjuster 178 may adjust angle 188 from, for example, 90 degrees, at which pump 130B is in its idle mode, to an angle 188 that maximizes the working volumes 170 of the piston pumps.

[0080] 6 is a simplified diagram of an active valve hydraulic pump 130A according to an embodiment of the present disclosure. In some embodiments, pump 130A is in the form of a conventional active valve variable displacement hydraulic pump, commonly referred to as a synthetically commutated hydraulic pump or digital displacement hydraulic pump. Some aspects of pump 130A are similar to pump 130B and are similarly numbered. Thus, the cyclic drive 166 and piston pump 160 of pump 130A may be similar to pump 130B. Additionally, pump 130A may take the form of a variable displacement radial pump, a variable displacement vane pump, or a variable displacement axial pump as disclosed in U.S. Pat. No. 5,190,446.

[0081] Pump 130A can have a fixed working volume 190. As a result, pump 130A does not have the working volume regulator 178 of pump 130B. Instead, the variable displacement of the flow of working fluid 132A produced by pump 130A is controlled by controlling an active valve mechanism 192 by a pump controller 193.

[0082] 7A-7C are simplified diagrams illustrating different operating modes of one of the piston pumps 160 of pump 130A enabled by an active valve mechanism 192. The active valve mechanism 192 may include a solenoid-actuated poppet valve 194 for each piston pump 160 having a first state in which a poppet valve 196 is aligned with a port 176 of the piston pump 160 to block the flow of hydraulic fluid from the working volume 190 to the low pressure port 174, as shown in FIG. 7A. The valve 194 also includes a second state in which a flow passage 198 is open between the port 176 and the low pressure port 174 of the piston pump 160, as shown in FIG. 7C. The second state of the valve 194 is typically its default (de-energized) state. The active valve mechanism 192 may also include a passive valve 199 (e.g., a poppet check valve) that allows the flow of hydraulic fluid from the port 176 of the piston pump 160 to the high pressure port 172 when a pressure threshold is reached, as shown in FIG. 7B.

[0083] When the valve 194 is in the first state and the cyclical driver 166 moves the piston 162 away from the port 176, working fluid is drawn from the reservoir 136 through the low pressure port 174 into the working volume 190 of the piston pump 160, as shown in FIG. 7A. When the valve 194 is in the first state and the cyclical driver 166 moves the piston 162 toward the port 176, working fluid is driven from the working volume 190 through the port 176. Because the poppet valve 196 is positioned to block fluid flow from moving to the low pressure port 174, the movement of the piston 162 pressurizes the working fluid and opens the passive valve 199, allowing the working fluid flow to move to the high pressure port 172, as shown in FIG. 7B. As a result, when the active valve 194 is in the first state, the piston pump 160 of the pump 130A operates similarly to the piston pump 160 of the pump 130B (FIG. 4).

[0084] When the valve 194 is in the second state, as shown in FIG. 7C , a fluid path 198 is open between the low pressure port 174 and the port 176 of the piston pump 160. Movement of the piston 162 toward the port 176, driven by the cyclic driver 166, causes hydraulic fluid to be expelled from the working volume 190. Because the expelled hydraulic fluid is not pressurized enough to overcome the threshold pressure of the passive valve 199, the hydraulic fluid moves through the fluid path 198 to the low pressure port 174. Similarly, hydraulic fluid may be drawn into the working volume 190 from the low pressure port 176 through the fluid path 198 as the piston 162 moves away from the port 176 by the cyclic driver 166. Thus, when the active valve 194 is in the second state, the pump 130A can be in an idle state in which the pump 130A does not drive the flow of working fluid 132A to the main output 133 while the motor 134 drives relative motion between the piston pump 160 and the cyclic drive 166.

[0085] Thus, the flow 132A of working fluid delivered by pump 130A to main port 133 can be controlled based on the number of piston pumps 160 that are "activated" by setting active valve 194 to a first state, and the timing of activation of the piston pumps 160, as would be understood by one of ordinary skill in the art.

[0086] The controllers of the system, such as system controller 126, HPU controller 128, HPS controller 146, and pump controller 193, may take any suitable form for controlling the various functions described herein, such as that of an example controller 200 shown in the simplified diagram of FIGURE 8. The controller 200 may include one or more processors 202 and a memory 204. The one or more processors 202 are configured to perform the various functions described herein in response to execution of instructions stored in the memory 204.

[0087] The one or more processors 202 may be components of one or more computer-based systems and may include one or more control circuits, a microprocessor-based engine control system, and / or one or more programmable hardware components, such as a field programmable gate array (FPGA). The memory 204 represents local and / or remote memory or computer-readable media. Such memory 204 comprises any suitable patent-eligible computer-readable medium and does not include transitory waves or signals. Examples of memory 204 include conventional data storage devices, such as hard disks, CD-ROMs, optical storage devices, magnetic storage devices, and / or other suitable data storage devices. The controller 200 may include circuitry 206 used by the one or more processors 202 to receive input signals 208 (e.g., sensor signals 100), issue control signals 210 (e.g., signals to control a pump, signals to actuate an active valve mechanism, etc.), and / or communicate data 212, for example, in response to the one or more processors 202 executing instructions stored in the memory 204.

[0088] Some embodiments of the present disclosure relate to the operation of the HPU 110 having a combination of pumps 130A and 130B, where each type of pump 130 may be utilized based on its particular attributes to provide improved responsiveness to changes in the demand for working fluid flow by the test station 102 while efficiently delivering the required flow of working fluid. In general, an active valve hydraulic pump 130A has the ability to adjust the output flow 132A of working fluid much more quickly than a passive valve hydraulic pump 130B. For example, the pump 130A can adjust the output flow 132A of working fluid by adjusting the number of piston pumps 160 operating by controlling the state of the active valve 194 and adjusting the timing of the operation. However, the pump 130B must use the actuating volume regulator 178 to adjust the output flow 132B of working fluid. This takes a significantly longer time to effect a given change in the output flow 132B relative to the time required to effect a similar change in the output flow 132A by the pump 130A. For example, pump 130A may have a response time (eg, 50 milliseconds) that is approximately 10 times faster than the response time of pump 130B (eg, 2 to 4 seconds).

[0089] Passive valve hydraulic pumps 130B generally incur higher heat losses and have lower volumetric energy efficiency than pumps 130A when operating at idle, however pumps 130B have higher volumetric efficiency when operating under pressure at approximately 70% or more of their outlet flow capacity.

[0090] In some embodiments of the present disclosure, the passive valve hydraulic pump 130B is used to provide flow 132B that generally meets the majority of the (e.g., steady-state) hydraulic flow 106 required at the main output 133, and the active valve hydraulic pump 130A is used to quickly provide the necessary flow of working fluid 132A to meet increases or decreases in the required flow 106. Thus, by using pumps 130A and 130B in combination, the HPU 110 can efficiently meet the majority of the flow demands, such as in steady-state conditions, using pump 130B, and can provide a much faster response to changes in flow demands than conventional HPUs using pump 130A.

[0091] When a test performed by one or more of the test stations 102 calls for an increase in the flow 106 of working fluid, the pressure at the main output 133 will drop. Similarly, a decrease in the flow 106 called for by the test stations 102 will result in an increase in the pressure at the main output 133. These pressure changes are detected by the HPU controller 128 using, for example, a pressure signal 142 from a sensor 140. Thus, the output flows 132A and 132B from the pumps 130A and 130B can be controlled based on the pressure sensed at the main output 133.

[0092] In some embodiments, one or more of the active valve hydraulic pumps 130A operate to generate a corresponding flow 132A when the pressure indicated by the pressure signal 142 drops below a first pressure set point, and one or more of the passive valve hydraulic pumps 130B operate to generate a corresponding flow 132B when the pressure indicated by the pressure signal 142 drops below a second pressure set point. Additionally, the pumps 130 are controlled to reduce the generated flow 132 of working fluid when the pressure at the main output rises above the first pressure set point, such as by shutting down one or more of the piston pumps 160 of the active valve hydraulic pump 130A and adjusting the working volume 170 of the piston pump 160 of the passive valve hydraulic pump 130B using the working volume regulator 178.

[0093] The HPU controller 128, or another controller, can store the desired first pressure set point in its memory 204 and issue a control signal 210 to the pump controller 193 of the pump 130A to cause the pump 130A to operate as described above. The second pressure set point can be controlled manually (e.g., a pressure control valve) or through a signal issued by the HPU controller 128 or another controller of the system 100. In one example, each pump 130B can include one or more remote pressure control valves, each of which controls the second pressure set point in response to a control signal 210 issued by the HPU controller 128 or another controller of the system 100.

[0094] In one embodiment, the first pressure set point is lower than the second pressure set point. In one example, the first pressure set point is about 1%-5% lower than the second pressure set point, for example 2%-3% lower. As a result, while the pressure at the main output 133 is lower than the second pressure set point but higher than the first pressure set point, one or more of the passive valve hydraulic pumps 130B attempt to substantially meet the requested flow 212 by adjusting the working volume 170 of the piston pumps 160 using the working volume regulators 178. If the pumps 130B are slow to react to the demand to increase the flow or are already operating at their maximum capacity, the pressure at the main output 133 drops below the first pressure set point, thus triggering the activation of one or more of the piston pumps 160 of the active valve hydraulic pumps 130A and the generation of the flow 132A. This results in a rapid increase in the main flow 106 (line 212) to meet the requested flow 210. When the pressure at the main output 133 rises above the first pressure set point, the output flow 132A from the one or more pumps 130A decreases as pump 130B can take over and produce most of the flow 106 (line 212) through the main output 133.

[0095] This process is illustrated in the chart of Figure 9. Line 210 indicates the demand for working fluid flow 106 through main output 133, such as by test station 102, grey line 212 indicates the main flow of working fluid 106 discharged through main output 133 and produced by flows 132A and 132B of pumps 130A and 130B, line 214 indicates working fluid flow 132B produced by pump 130B, and dashed line 216 indicates working fluid flow 132A produced by pump 130A.

[0096] Between times t0 and t1, the demand shown by line 212 is continuous and steady, and is lower than the maximum capacity of pump 130B of HPU 110. Thus, HPU 110 uses flow 132B produced by pump 130B to provide the demanded flow 212 of working fluid at main output 133. Now, the pressure at main output 133 stabilizes at or near the second pressure set point. Because the pressure is above the first pressure set point, pump 130A is substantially or completely stopped, and therefore no significant flow 132A of working fluid is produced.

[0097] At time t1, a sudden increase in the flow of working fluid is requested, as shown by line 210. Initially, the pressure at the main output 133 drops below the second pressure set point, and therefore the pumps 130B are triggered to increase their output flow 132B of working fluid, such as by varying the working volume 170 of the piston pumps 160 using the working volume regulators 178. However, because pumps 130B cannot meet the requested flow rate quickly, the pressure at the main output 133 continues to drop and falls below the first pressure set point. This triggers operation of one or more of the pumps 130A to quickly produce an output flow 132A of working fluid, which, when combined with the output flow 132B from pumps 130B, produces a combined output flow 106 (line 212) at the main output 133 that matches the requested flow 210.

[0098] Between times t2 and t3, the working fluid flow 132B output from pump 130B increases to provide a more significant contribution to the combined flow 106 (line 212), and the output flow 132A from pump 130A decreases accordingly. During this period, the pressure at the main output 133 fluctuates around the first pressure set point.

[0099] After time t3, the output flow 132B from pump 130B stabilizes and produces a majority of the desired flow 106. In the illustrated example, the desired flow is greater than the combined maximum output flows 132B of pumps 130B. Thus, unlike the period from time t0 to t1, during which pump 130B can produce the desired flow 210 and thereby shut down pump 130A, pump 130A is used to produce a portion of the desired flow 210 after time t3 in response to the pressure at the primary output 133 fluctuating about the first pressure set point.

[0100] In one embodiment, the first pressure set point is higher than the second pressure set point. In one example, the first pressure set point is about 1%-5% higher than the second pressure set point, for example 2%-3% higher. When the pressure at the main output 133 is lower than the first pressure set point but higher than the second pressure set point, one or more of the active valve hydraulic pumps 130A attempt to substantially meet the requested flow 106 by activating one or more of the piston pumps 160. If the pumps 130A are unable to meet the demand for increased flow or are already operating at their maximum capacity, the pressure at the main output 133 drops below the second pressure set point, thus triggering the activation of one or more of the passive valve hydraulic pumps 130B and the generation of flow 132B. This results in an increase in the main flow 106. As the pressure at the main output 133 rises above the second pressure set point, the output flow 132B from the one or more pumps 130B decreases as pump 130A takes over and produces the majority of the flow 106 through the main output 133.

[0101] This process is illustrated in the chart of Figure 10. Line 210 indicates the demand for working fluid flow 106 through main output 133, such as by test station 102, grey line 212 indicates the main flow of working fluid 106 discharged through main output 133 and produced by flows 132A and 132B of pumps 130A and 130B, line 214 indicates working fluid flow 132B produced by pump 130B, and dashed line 216 indicates working fluid flow 132A produced by pump 130A.

[0102] Between times t0 and t1, the demand shown by line 212 is continuous and steady, and is lower than the maximum capacity of pump 130A of HPU 110. Thus, HPU 110 uses flow 132A produced by pump 130A to provide the demanded flow 106 of working fluid at main output 133. Now, the pressure at main output 133 stabilizes at or near a first pressure set point. Because the pressure is above the second pressure set point, pump 130B is substantially or completely stopped, and therefore no significant flow 132B of working fluid is produced.

[0103] At time t1, a sudden increase in the flow of working fluid is requested, as shown by line 210. Initially, the pressure at the main output 133 drops below a first pressure set point, thus triggering pumps 130A to increase their output flow 132A of working fluid, such as by activating one or more of the piston pumps 160. However, if pump 130A is unable to meet the requested flow quickly, the pressure at the main output 133 continues to drop and falls below a second pressure set point. This triggers the activation of one or more of the pumps 130B to generate an increased output flow 132B of working fluid, such as by varying the working volume 170 of the piston pump 160 using the working volume regulator 178. When the output flow 132B is combined with the output flow 132A from pump 130A, a combined output flow 106 (line 212) is generated at the main output 133 that matches the requested flow 210.

[0104] Between times t2 and t3, the working fluid flow 132A output from pump 130A increases to provide a more significant contribution to the combined flow 106 (line 212), and the output flow 132B from pump 130B decreases accordingly. During this period, the pressure at the main output 133 fluctuates around the second pressure set point.

[0105] After time t3, the output flow 132A from pump 130A stabilizes and produces most of the demanded flow 106 (line 210). In the illustrated example, the demanded flow is less than the combination of the maximum output flows 132A of pumps 130A. Thus, after time t3, pump 130A is primarily used to produce the demanded flow 106 (line 210) in response to the pressure at the primary output 133 fluctuating about the second pressure set point.

[0106] In yet another embodiment, the first and second pressure set points are set to substantially the same pressure (e.g., ±0.8%). Thus, flows 132A and 132B from the active valve hydraulic pump 130A and the passive valve hydraulic pump 130B are generated as the pressure at the main output 133 fluctuates around the first and second pressure set points. When the demanded flow increases suddenly, causing a drop in pressure at the main output 133, the flows 132A and 132B increase to meet the demand, with the flow 132A generally increasing more rapidly than the flow 132B. Similarly, as the demanded flow decreases, the pressure at the main output 133 increases, causing the pumps 130A and 132B to reduce their flows 132A and 132B until the pressure stabilizes around the first and second pressure set points.

[0107] Additional embodiments relate to methods of operating the HPU 110, such as using the HPU controller 128. The HPU 110 may be formed according to embodiments described herein. Thus, as shown in FIG. 2, the HPU 110 may include, for example, a reservoir 136, a main output 133, a pressure sensor 140, at least one active-valve hydraulic pump 130A configured to drive a first flow portion 132A of the main stream 106 through the main output 133 when the pressure of the main stream 106, as indicated by a pressure signal 142, falls below a first pressure set point, and at least one passive-valve hydraulic pump 130B configured to drive a second flow portion 132B of the main stream 106 through the main output 133 when the pressure signal 142 indicates that the pressure falls below a second pressure set point.

[0108] 11 is a flow chart illustrating an example of a method of operating an HPU according to an embodiment of the disclosure. At 220, the method drives a portion of the main flow 106 using one or more of the at least one active valve hydraulic pump 130A when the pressure signal 142 indicates that the pressure at the main output 133 is below a first pressure set point. At 222, the at least one active valve hydraulic pump 130A is stopped when the pressure signal 142 indicates that the pressure at the main output 133 is above the first pressure set point.

[0109] Similarly, at 224, the method drives a portion of the main flow 106 using one or more of the at least one passive valve hydraulic pumps 130B when the pressure signal 142 indicates that the pressure at the main output 133 is below the second pressure set point. At 226, the at least one passive valve hydraulic pump 130B is stopped when the pressure signal 142 indicates that the pressure at the main output 133 is above the second pressure set point.

[0110] If the second pressure set point is higher (e.g., 1%-5%) than the first pressure set point, the HPU 110 operates as described above with reference to the chart of Figure 9. For example, one or more of the passive valve hydraulic pumps 130B are used in combination with pump 130A to drive the main flow 106 during step 220, and only one or more of the passive valve hydraulic pumps 130B are used to drive the main flow 106 when the pressure at the main output 133 exceeds the first pressure set point in step 224.

[0111] If the first pressure set point is higher (e.g., 1%-5%) than the second pressure set point, the HPU 110 operates as described above with reference to the chart of Figure 10. For example, one or more of the active valve hydraulic pumps 130A are used in combination with the passive valve hydraulic pumps 130B to drive the main flow 106 during step 224, and only one or more of the active valve hydraulic pumps 130A are used to drive the main flow 106 when the pressure at the main output 133 exceeds the second pressure set point in step 224.

[0112] Embodiments of the present disclosure also relate to a method of operating the HPS 114 (FIG. 3) that is similar to a method of operating the HPU 110. FIGURE 12 is a flow chart illustrating one example of a method of operating the HPS 114 according to embodiments of the present disclosure, which may be implemented, for example, using the HPS controller 146. The HPS 114 may be formed according to embodiments described herein. Thus, the HPS 114 may, for example, comprise a first HPU 110A comprising a reservoir 136, a main output 133, and at least one active-valve hydraulic pump 130A configured to drive a flow portion 132A of a first main flow 106A through the main output 133 when a pressure indicated by a pressure signal 142 from a pressure sensor 140 falls below a first pressure set point, and a second HPU 110B comprising a main output 133 and at least one passive-valve hydraulic pump 130B configured to drive a flow portion 132B of a second main flow 106B through the main output 133 when a pressure indicated by a pressure signal 142 from a pressure sensor 140 falls below a second pressure set point. Additionally, the HPS 114 may comprise a flow aggregator 148 configured to combine the first main flow 106A and the second main flow 106B into a combined flow 150.

[0113] In method 230, the first main flow 106A is driven using one or more of the at least one active valve hydraulic pump 130A of the first HPU 110A when the pressure at the main output 133 is below a first pressure set point. In 232, the at least one active valve hydraulic pump 130A of the HPU 110A is stopped when the pressure at the main output 133 is above the first pressure set point. Similarly, in method 234, the second main flow 106B is driven using one or more of the at least one passive valve hydraulic pump 130B of the second HPU 110B when the pressure at the main output 133 is below a second pressure set point. In 236, the at least one passive valve hydraulic pump 130B of the HPU 110B is stopped when the pressure at the main output 133 is above the second pressure set point. In this manner, HPUs 110A and 110B may be used to provide the required combined flow 150.

[0114] If the second pressure set point is higher (e.g., 1% to 5%) than the first pressure set point, one or more of the passive valve hydraulic pumps 130B of the HPU 110B are used in combination with the pump 130A of the HPU 110A to generate the combined flow 150 during step 230, and only one or more of the passive valve hydraulic pumps 130B of the HPU 110B are used to generate the combined flow 150 when the pressure at the main output 133 exceeds the first pressure set point in step 236.

[0115] When the first pressure set point is higher (e.g., 1% to 5%) than the second pressure set point, one or more of the active valve hydraulic pumps 130A of the HPU 110A are used in combination with the passive valve hydraulic pump 130B of the HPU 110B to generate the combined flow 150 during step 234, and only one or more of the active valve hydraulic pumps 130A of the HPU 110A are used to generate the combined flow 150 when the pressure at the main output 133 exceeds the second pressure set point in step 230.

[0116] Additional embodiments of the present disclosure relate to the use of two or more pressure sensors 140 by the HPU 110 to measure the pressure of the mainstream 106 at the main output 133, as shown in FIG. 2, and / or the use of two or more pressure sensors 140 by the HPS to measure the pressure of the combined mainstream 150, such as the aggregator 148 or the main output 133 of one or both of the HPUs 110A and 110B, as shown in FIG. 3. In one embodiment, a controller monitoring the pressure signal 142 from the pressure sensor 140, such as the HPU controller 128 or the HPS controller 146, compares the value associated with the signal 142 to a reference range of values ​​corresponding to expected valid values, which may be stored in the controller's memory 204. If one of the signal values ​​is outside the reference range, it may be discarded, and other signal values ​​that are within the reference range may be used to facilitate the pump control functions described above. The controller may use the circuitry 206 to issue a notification of an abnormal situation regarding one of the pressure sensors to an operator or administrator of the system.

[0117] If both signal values ​​are outside of the normal range, this may indicate a serious abnormal condition (e.g., power loss, fluid leak, etc.) and the controller may issue a notification to an operator or administrator of the system indicating the abnormal condition.

[0118] In one embodiment, the controller compares the signal values ​​to one another. When the signal values ​​substantially match (e.g., ±10%), the sensors 140 of the HPU 110 or HPS 114 are presumed to be operating properly. If the signal values ​​do not substantially match, the controller may issue a notification to an operator or administrator of the system indicating an abnormal condition in the form of a problem with one of the pressure sensors 140, a loss of a sensor signal, or another abnormal condition indicated by inconsistent pressure signals 142.

[0119] The notification issued by the controller may take any suitable form and may be represented by data 212 in Figure 8. Examples of notifications include an audible and / or visual alarm and / or an electronic message (control panel message, email, text message, etc.) to an operator or administrator of the system.

[0120] Optionally, the embodiments described above may be modified by using one or more flow sensors in place of each of the one or more pressure sensors 140. Each flow sensor may generate a flow signal indicative of the flow rate of the sensed fluid stream, as well as a pressure as indicated by a pressure signal 142 from one of the pressure sensors 140, to control the pump 130. Thus, each of the one or more pressure sensors 140 shown in the drawings may represent a corresponding flow sensor, and each of the pressure signals 142 shown may represent a flow signal.

[0121] Thus, the method of FIG. 11 may be modified to utilize sensed flow rate rather than sensed pressure to control the pump. For example, step 220 of the method of FIG. 11 is adjusted such that a portion of the main flow is driven using one or more of the at least one active valve hydraulic pump when the flow rate indicated by a corresponding flow sensor falls below a first flow rate set point. At 222, the at least one active valve hydraulic pump is stopped when the flow rate rises above the first flow rate set point. At 224, a portion of the main flow is driven using one or more of the at least one passive hydraulic pump when the flow rate falls below a second flow rate set point. At 226, the at least one passive hydraulic pump is stopped when the flow rate rises above the second flow rate set point.

[0122] Although embodiments of the present disclosure have been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the present disclosure.

Claims

1. 1. A fluid power unit comprising: a reservoir containing a working fluid; a main output through which a main flow of the working fluid is discharged; and a pressure sensor having a pressure signal indicative of the pressure of the mainstream; at least one active valve hydraulic pump having a variable displacement, each configured to drive a first flow portion of the main flow from the reservoir to the main output when the pressure signal is below a first pressure set point; at least one passive valve hydraulic pump having a variable displacement, each configured to drive a second flow portion of the main flow from the reservoir to the main output when the pressure signal is below a second pressure set point; a housing containing the reservoir, the at least one active valve hydraulic pump, and the at least one passive valve hydraulic pump; A fluid power unit comprising:

2. the first pressure set point is lower than the second pressure set point, and in one embodiment the first pressure set point is about 1% to 5% lower than the second pressure set point; or the first pressure set point is higher than the second pressure set point, and in one embodiment the first pressure set point is about 1% to 5% higher than the second pressure set point; or the first pressure set point is equal to the second pressure set point; 2. The fluid power unit of claim 1.

3. The fluid power unit of claim 1 or 2, further comprising at least one controller configured to set the first pressure set point and the second pressure set point.

4. The fluid power unit of any one of claims 1 to 3, wherein the at least one passive valve hydraulic pump comprises a plurality of the passive valve hydraulic pumps.

5. The fluid power unit of any one of claims 1 to 4, wherein the at least one active valve hydraulic pump comprises a plurality of the active valve hydraulic pumps.

6. Each active valve hydraulic pump has: a low pressure port connected to the fluid reservoir; a high pressure port connected to the main output; A plurality of piston pumps; a motor configured to drive a cyclic change to the working volume of each piston pump; a plurality of active valves, each corresponding to one of the piston pumps and configured to set the piston pump between an operating state in which the cyclic change to the working volume drives the first flow portion of working fluid from the working volume through the high pressure port, and a stopped state in which a fluid path is formed between the working volume and either the reservoir or the low pressure port; a pump controller configured to control each of the active valves to individually set the piston pumps to the on state or the off state; A fluid power unit according to any preceding claim, comprising:

7. Each passive valve hydraulic pump is a low pressure port connected to the fluid reservoir; a high pressure port connected to the main output; a plurality of piston pumps, each configured to draw hydraulic fluid into an adjustable working volume through the low pressure port and drive the second flow portion of hydraulic fluid from the adjustable working volume through the high pressure port; a motor configured to drive a cyclic change to the adjustable working volume of each piston pump; The fluid power unit of claim 6 comprising:

8. 1. A method of operating a fluid power unit, the fluid power unit comprising: a reservoir containing a working fluid; a main output through which a main flow of the working fluid from the reservoir is discharged; and a pressure sensor having a pressure signal indicative of the pressure of the mainstream; at least one active valve hydraulic pump having a variable displacement; at least one passive valve hydraulic pump having a variable displacement; a housing containing the reservoir, the at least one active valve hydraulic pump, and the at least one passive valve hydraulic pump; Equipped with The method comprises: driving a first flow portion of the mainstream using one or more of the at least one active valve hydraulic pump when the pressure signal indicates that the pressure of the mainstream is below a first pressure set point; shutting off the at least one active valve hydraulic pump when the pressure signal indicates that the pressure of the mainstream exceeds the first pressure set point; driving a second flow portion of the mainstream using one or more of the at least one passive hydraulic pump when the pressure signal indicates that the pressure of the mainstream is below a second pressure set point; shutting off the at least one passive valve hydraulic pump when the pressure signal indicates that the pressure of the mainstream exceeds the second pressure set point; A method comprising:

9. the first pressure set point is lower than the second pressure set point, and in one embodiment the first pressure set point is about 1% to 5% lower than the second pressure set point; or the first pressure set point is higher than the second pressure set point, and in one embodiment the first pressure set point is about 1% to 5% higher than the second pressure set point; or the first pressure set point is equal to the second pressure set point; The method according to claim 8.

10. The method of claim 8 or 9, wherein the at least one passive valve hydraulic pump comprises a plurality of the passive valve hydraulic pumps.

11. The method of any one of claims 8 to 10, wherein the at least one active valve hydraulic pump comprises a plurality of the active valve hydraulic pumps.

12. Each active valve hydraulic pump has: a low pressure port connected to the fluid reservoir; a high pressure port connected to the main output; A plurality of first piston pumps; a motor configured to drive a cyclic change to the working volume of each of the first piston pumps; a plurality of active valves, each configured to set one of the first piston pumps to an operating state in which the cyclic change to the working volume drives a portion of the first flow portion through the high pressure port, and an off state in which a fluid path is formed between the working volume and the reservoir or the low pressure port; a pump controller configured to control each of the active valves to individually set the first piston pump to the active state or the stopped state; Equipped with Each passive valve hydraulic pump is a low pressure port connected to the fluid reservoir; a high pressure port connected to the main output; a plurality of second piston pumps, each configured to draw hydraulic fluid into an adjustable working volume through the low pressure port and drive a portion of the second flow portion of hydraulic fluid from the adjustable working volume through the high pressure port; a motor configured to drive a cyclic change to the adjustable working volume of each of the second piston pumps; The method according to any one of claims 8 to 11, comprising:

13. 1. A fluid power system comprising: at least one first fluid power unit, each comprising: a first reservoir containing a working fluid; a first main output, a first mainstream of the working fluid being discharged through the first main output; a first pressure sensor having a first pressure signal indicative of a first pressure of the first mainstream; at least one active valve hydraulic pump, each configured to drive a portion of the first mainstream flow from the first reservoir to the first main output when the first pressure signal indicates that the first pressure is below a first pressure set point; a first housing containing the first reservoir and the at least one active valve hydraulic pump; at least one first fluid power unit comprising: at least one second fluid power unit, each comprising: a second reservoir containing a working fluid; a second main output, through which a second main flow of the working fluid is discharged; and a second pressure sensor having a second pressure signal indicative of a second pressure of the second mainstream; at least one passive valve hydraulic pump, each configured to drive a portion of the second mainstream flow from the second reservoir to the second main output when the second pressure signal indicates that the second pressure is below a second pressure set point; a second housing containing the second reservoir and the at least one passive valve hydraulic pump; at least one second fluid power unit comprising: a flow aggregator configured to combine the first mainstream and the second mainstream into a combined mainstream; A fluid power system comprising:

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