Hydraulic power generation pump control

Abstract

To provide a hydraulic power unit which 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.SOLUTION: 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] 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]

[0002] 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.

[0003] 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.

[0004] For example, there is a continuing need for improvements in dynamic testing systems, including improved production of working fluid flow to meet rapidly changing flow demands, and improved control of hydraulic pumps to increase energy efficiency, reduce energy spikes, and reduce wear and tear on pump components, among other things. Summary of the Invention

[0005] SUMMARY OF THE DISCLOSURE Embodiments of the present disclosure relate to a method of controlling a fluid power unit of a dynamic test system, and a dynamic test system configured to perform the method.

[0006] In some embodiments, a fluid power unit of the dynamic testing system comprises at least one controller and a plurality of hydraulic pumps configured to generate a variable main flow of the working fluid for driving hydraulic actuators of at least one test station during execution of at least one test. In one embodiment of the method, at least one test flow profile is obtained, each of the at least one test flow profile identifying a working fluid flow demand estimate over time corresponding to one execution of the at least one test. A variable main flow of the working fluid is generated using a plurality of unique subsets of the hydraulic pumps during execution of the at least one test, each unique subset being selected based on the at least one test flow profile.

[0007] In some embodiments, the method includes identifying, for each of a plurality of time periods based on the at least one test flow profile, a corresponding one of the unique subset of hydraulic pumps required to generate a main flow that exceeds a sum of the working fluid flow demand estimates corresponding to the time period, and generating the variable main flow includes generating the variable main flow during each of the plurality of time periods using the identified corresponding unique subset of hydraulic pumps.

[0008] In some embodiments, each of the hydraulic pumps is configured to produce working fluid up to a maximum flow, and a sum of the maximum flows of the determined subset of hydraulic pumps exceeds a sum of the estimated working fluid flow demands for a corresponding time period.

[0009] In some embodiments, during each of the plurality of time periods, a corresponding sum of the working fluid flow demand estimates lies between a lower boundary flow threshold and an upper boundary flow threshold of the plurality of flow thresholds, each flow threshold corresponding to one of the unique subsets of hydraulic pumps, and wherein identifying the corresponding one of the unique subsets of hydraulic pumps for each time period includes identifying the corresponding one of the unique subsets based on the upper flow threshold.

[0010] In some embodiments, each of the hydraulic pumps includes an operating state in which the hydraulic pump substantially contributes to the variable mainstream and a stopped state in which the hydraulic pump does not substantially contribute to the variable mainstream, and for at least one of the time periods, generating the variable mainstream includes transitioning one or more of the corresponding unique subset of hydraulic pumps from the stopped state to the operating state.

[0011] In some embodiments, transitioning one or more of the hydraulic pumps of the corresponding unique subset from a stopped state to an operating state occurs a predetermined time period prior to the start of at least one of the time periods.

[0012] In some embodiments, the predetermined period of time is greater than about 3 seconds.

[0013] In some embodiments, each hydraulic pump comprises a motor having an operating state in which it is powered to drive the hydraulic pump and a stopped state in which the motor is not powered, and transitioning one or more of the hydraulic pumps of the determined subset from the stopped state to the operating state includes transitioning the motor of the one or more hydraulic pumps from the stopped state to the operating state.

[0014] In some embodiments, the stop condition of each hydraulic pump includes an idle condition of the hydraulic pump with the motor running.

[0015] In some embodiments, for one or more of the time periods, motors of hydraulic pumps that are not in the determined subset for that time period are set to a stopped state.

[0016] In some embodiments, the fluid power unit comprises a reservoir that contains the working fluid.

[0017] A main output at which a variable main flow of the working fluid is discharged, and a plurality of hydraulic pumps including at least one active valve hydraulic pump having a variable displacement volume and at least one passive valve hydraulic pump having a variable displacement volume.

[0018] In some embodiments, each subset includes one of the at least one active valve hydraulic pump.

[0019] In some embodiments, each active-valve hydraulic pump comprises: a low pressure port connected to a fluid reservoir; a high pressure port connected to a 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 active state in which the cyclic change to the working volume drives at least a portion of the variable 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 a pump controller configured to control each of the active valves to individually set the piston pump to an active state or a stopped state.

[0020] In some embodiments, each passive valve hydraulic pump comprises 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 hydraulic fluid into an adjustable working volume through the low pressure port and drive at least 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 piston pump.

[0021] In some embodiments, obtaining the at least one test flow profile includes measuring at least one flow rate of the working fluid during a previous run of at least one test.

[0022] In some embodiments, measuring the at least one flow rate includes measuring at least one flow rate of the working fluid over time using one or more flow meters, including one or more flow meters each located at a flow input to one of the at least one test stations, one or more flow meters each located at a flow output from one of the at least one test stations, and / or a flow meter located at a main output of the fluid power unit.

[0023] One example of a dynamic testing system includes at least one test station, a fluid power unit, and at least one controller. Each test station is configured to apply a force and / or a displacement to a test object using a hydraulic actuator during execution of a test. The fluid power unit includes a plurality of hydraulic pumps configured to generate a variable main flow of a working fluid that drives the hydraulic actuator of the at least one test station during execution of the at least one test. The at least one controller is configured to: obtain at least one test flow profile, each of the at least one test flow profile corresponding to a execution of one of the at least one test; identify a working fluid flow demand estimate over time, the working fluid flow demand estimate corresponding to a execution of the at least one test; and generate the variable main flow of the working fluid using a plurality of unique subsets of the plurality of hydraulic pumps during execution of the at least one test. Each unique subset is selected based on the at least one test flow profile.

[0024] In some embodiments, the at least one controller is configured to: identify, for each of a plurality of time periods based on the at least one test flow profile, a corresponding one of the unique subset of hydraulic pumps required to generate a main flow that exceeds a sum of the working fluid flow demand estimates corresponding to the time period; and generate a variable main flow during each of the plurality of time periods using the identified corresponding unique subset of hydraulic pumps.

[0025] In some embodiments, each of the hydraulic pumps is configured to produce working fluid up to a maximum flow, and the sum of the maximum flows of the determined subset of hydraulic pumps exceeds the sum of the estimated working fluid flow demands for the period.

[0026] In some embodiments, during each of the plurality of time periods, a corresponding sum of the working fluid flow demand estimates lies between a lower boundary flow threshold and an upper boundary flow threshold of the plurality of flow thresholds, each flow threshold corresponding to one of the unique subsets of hydraulic pumps, and for each time period, a corresponding one of the unique subsets of hydraulic pumps is identified based on the upper flow threshold.

[0027] In some embodiments, each of the hydraulic pumps includes an operating state in which the hydraulic pump substantially contributes to the variable mainstream and a stopped state in which the hydraulic pump does not substantially contribute to the variable mainstream, and for at least one of the time periods, one or more of the hydraulic pumps of the corresponding unique subset are transitioned from the stopped state to the operating state to generate the variable mainstream.

[0028] In some embodiments, for at least one of the time periods, one or more of the hydraulic pumps of the corresponding unique subset are transitioned from a stopped state to an operating state a predetermined time period prior to the start of at least one of the time periods to generate the variable main flow.

[0029] In some embodiments, the predetermined period of time is greater than about 3 seconds.

[0030] In some embodiments, each hydraulic pump comprises a motor having an operating state in which it is powered to drive the hydraulic pump and a stopped state in which the motor is not powered, and one or more of the hydraulic pumps of the determined subset are transitioned from the stopped state to the operating state by transitioning the motor of one or more hydraulic pumps of the determined subset from the stopped state to the operating state.

[0031] In some embodiments, the stop condition of each hydraulic pump includes an idle condition of the hydraulic pump with the motor running.

[0032] In some embodiments, for one or more of the time periods, motors of hydraulic pumps that are not in the determined subset for that time period are set to a stopped state.

[0033] In some embodiments, the fluid power unit comprises a reservoir containing a hydraulic fluid, a main output from which a variable main flow of the hydraulic fluid is discharged, and a plurality of hydraulic pumps including at least one active valve hydraulic pump having a variable displacement volume and at least one passive valve hydraulic pump having a variable displacement volume.

[0034] In some embodiments, each subset includes one of the at least one active valve hydraulic pump.

[0035] In some embodiments, each active-valve hydraulic pump comprises: a low pressure port connected to a fluid reservoir; a high pressure port connected to a 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 active state in which the cyclic change to the working volume drives at least a portion of the variable 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 a pump controller configured to control each of the active valves to individually set the piston pump to an active state or a stopped state.

[0036] In some embodiments, each passive valve hydraulic pump comprises 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 hydraulic fluid into an adjustable working volume through the low pressure port and drive at least 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 piston pump.

[0037] In some embodiments, the system includes one or more flow meters each located at a flow input to one of the at least one test stations, one or more flow meters each located at a flow output from one of the at least one test stations, and / or a flow meter located at a main output of the fluid power unit, each flow meter configured to measure a flow rate of the working fluid.

[0038] In another method of controlling a fluid power unit of a dynamic testing system using at least one controller, the fluid power unit includes a reservoir containing a hydraulic fluid, a main output at which a main flow of the hydraulic fluid is discharged, a pressure sensor having a pressure signal indicative of a main pressure of the main flow, and a plurality of variable displacement hydraulic pumps each configured to drive a portion of the main flow. Each variable displacement hydraulic pump includes a plurality of piston pumps, a motor having an on state and an off state that drives a cyclic change in the working volume of each piston pump, and a pressure set point. The pressure set points are selectable between a range of inoperative pressure set points below an expected operating range of the main pressure where the variable displacement hydraulic pump does not contribute to the main flow, and an operable pressure set point within the expected operating range of the main pressure where the variable displacement hydraulic pump is driven to contribute to the main flow. In one embodiment of the method, one of the variable displacement hydraulic pumps is controlled by operating the variable displacement hydraulic pump for a first predetermined period while the pressure set point is set to a first inoperative pressure set point within a range of the inoperative pressure set points and operating the variable displacement hydraulic pump while the pressure set point is set to an operational pressure set point.

[0039] In some embodiments, operating the variable displacement hydraulic pump for a first predetermined period occurs prior to operating the variable displacement hydraulic pump while the pressure set point is set to the operational pressure set point.

[0040] In some embodiments, operating the variable displacement hydraulic pump for a first predetermined period of time includes transitioning the motor from a stopped state to a running state.

[0041] In some embodiments, after operating the variable displacement hydraulic pump for a first predetermined period of time and before operating the variable displacement hydraulic pump while the pressure set point is set to the operational pressure set point, the variable displacement hydraulic pump is operated for a second predetermined period of time while the pressure set point is set to a second inoperative pressure set point within the range of the inoperative pressure set point, the second pressure set point being higher than the first pressure set point.

[0042] In some embodiments, the first period and the second period are substantially equal, the first period is longer than the second period, or the first period is shorter than the second period.

[0043] In some embodiments, operating the variable displacement hydraulic pump for a first predetermined period occurs after operating the variable displacement hydraulic pump while the pressure set point is set to an operational pressure set point.

[0044] In some embodiments, operating the variable displacement hydraulic pump for a first predetermined period of time includes transitioning the motor from an on state to a off state.

[0045] In some embodiments, after operating the variable displacement hydraulic pump while the pressure set point is set to the operational pressure set point and before operating the variable displacement hydraulic pump for the first predetermined period of time, the variable displacement hydraulic pump is operated for a second predetermined period of time while the pressure set point is set to a second inoperative pressure set point within the range of the inoperative pressure set point, the second pressure set point being higher than the first pressure set point.

[0046] In some embodiments, the first period and the second period are substantially equal, the first period is longer than the second period, or the first period is shorter than the second period.

[0047] In some embodiments, operating the variable displacement hydraulic pump for a first predetermined period includes setting, using the controller, a pressure set point to a first inoperative pressure set point, and operating the variable displacement hydraulic pump while the pressure set point is set to one of the operable pressure set points includes setting, using the controller, the pressure set point to the operable pressure set point.

[0048] 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]

[0049] [Figure 1] 1 is a simplified diagram of an example dynamic testing system according to an embodiment of the present disclosure.

[0050] [Diagram 2] 1 is a simplified diagram of an example fluid power unit according to an embodiment of the present disclosure.

[0051] [Diagram 3] 1 is a simplified diagram of an example fluid power system according to an embodiment of the present disclosure.

[0052] [Figure 4] 1 is a simplified diagram of an example of a passive valve hydraulic pump, according to an embodiment of the present disclosure.

[0053] [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.

[0054] [Figure 6] 1 is a simplified diagram of an example of an active valve hydraulic pump, according to an embodiment of the present disclosure.

[0055] [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.

[0056] [Figure 8] 2 is a simplified diagram of a controller according to an embodiment of the present disclosure.

[0057] [Figure 9] 1 is a schematic diagram of an example test station according to an embodiment of the present disclosure.

[0058] [Figure 10] 1 is a chart illustrating a test flow profile according to an embodiment of the present disclosure.

[0059] [Figure 11] 1 is a flow chart illustrating a method of controlling a fluid power unit to generate a variable main flow for driving a hydraulic actuator of at least one test station during the performance of at least one test in accordance with an embodiment of the present disclosure.

[0060] [Figure 12] 10A-10C include charts illustrating an example pair of overlapping test flow profiles and operation of a fluid power unit in accordance with an embodiment of the present disclosure.

[0061] [Figure 13] 4 is a flow chart illustrating a method of controlling a hydraulic pump of a fluid power unit in accordance with an embodiment of the present disclosure.

[0062] [Figure 14] 4 is a chart illustrating an example of adjusting a pressure set point of a hydraulic pump over time to transition the pump between a stopped state and an on state in accordance with an embodiment of the present disclosure. [Figure 15]4 is a chart illustrating an example of adjusting a pressure set point of a hydraulic pump over time to transition the pump between a stopped state and an on state in accordance with an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0063] 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.

[0064] 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.

[0065] 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.

[0066] 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.

[0067] 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.

[0068] 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.

[0069] 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.

[0070] 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.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] 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.

[0075] 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.

[0076] 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.

[0077] 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.

[0078] A housing 139 may enclose the reservoir 136 and the pump 130, as shown in FIG.

[0079] 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.

[0080] 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.

[0081] 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.

[0082] 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).

[0083] 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.

[0084] 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.

[0085] 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.

[0086] 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.

[0087] 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.

[0088] 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.

[0089] 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.

[0090] 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.

[0091] 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.

[0092] 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.

[0093] 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.

[0094] 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.

[0095] 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).

[0096] 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.

[0097] 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.

[0098] 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.

[0099] 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.

[0100] 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).

[0101] 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.

[0102] 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.

[0103] 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.

[0104] 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.

[0105] 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 be equipped with one or more remote pressure control valves (e.g., proportional 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.

[0106] 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.

[0107] The first pressure set point may be greater than the second pressure set point. In one example, the first pressure set point is about 1%-5% greater than the second pressure set point, for example 2%-3% greater. If the pressure at the main output 133 is less than the first pressure set point but greater 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 pump 130A is unable to meet the demand for increased flow or is already operating at its maximum limit, 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 increases 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.

[0108] 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 primary output 133 fluctuates around the first and second pressure set points. If the flow demand increases suddenly, causing a drop in pressure at the primary output 133, flows 132A and 132B increase to meet the demand, with flow 132A generally increasing more rapidly than flow 132B. Similarly, if the flow demand decreases, the pressure at the primary output 133 increases, and pumps 130A and 132B decrease their flows 132A and 132B until the pressure stabilizes around the first and second pressure set points.

[0109] 9 is a schematic diagram of an example of a test station 102, according to an embodiment of the present disclosure. As described above, the test station 102 includes a number of hydraulic actuators 104, such as hydraulic actuators 104A-104D, configured to apply forces and / or drive motion to a test object 103. Each of the hydraulic actuators 104A-104D is driven by a corresponding flow portion 122A-122D of a working fluid flow 122 generated by one or more of the fluid power units 110 (FIG. 1).

[0110] Each test station 102 may include a test station controller 220, which may take the form of an example controller 200 shown in FIG. 8. The test station controller 220 is generally configured to perform tests on the test object 103 based on, for example, executing a test program (e.g., stored in memory 204) using one or more processors 202. In response to the execution of the test program, the test station controller 220 controls the hydraulic actuators 104 using actuating fluid flow 122 provided by one or more of the fluid power unit 110 and a valve mechanism (not shown) to apply force and / or motion to the test object 103 in a conventional manner using the actuators 104.

[0111] As a test is performed, the actuating fluid flow 122 varies in response to varying operation of the actuator 104. As a result, the pattern of flow 122 is repeated each time a test is performed.

[0112] Embodiments of the present disclosure include a method for controlling a fluid power unit based on a pattern or test flow profile of flow 122 provided to a test station 102 during a test operation.

[0113] In some embodiments, each test flow profile is obtained through measurement of the volumetric flow rate (hereinafter "flow rate") of the working fluid stream 122 into a given test station 102 over time while a test is being performed. Each measured test flow profile thus corresponds to a flow rate pattern of the stream 122 during the test. The test flow profile can then be used later, during the test execution, to control the activation and deactivation of hydraulic pumps 130 of one or more fluid power units 110 involved in providing the working fluid stream 122 during the test execution.

[0114] For example, rather than operating all of the hydraulic pumps 130 throughout the entire test run, only various subsets of the hydraulic pumps 130 may be operated as needed to provide the required fluid flow 122. Thus, if it is not necessary to operate all of the hydraulic pumps 130 for the required working fluid flow 122 during a test, only the subset of hydraulic pumps 130 required to provide the required fluid flow 122 may be operated and the other hydraulic pumps 130 may be shut off. This not only results in significant energy savings, but also avoids unnecessary wear and tear on the hydraulic pumps 130 and other components of the system 100.

[0115] 1 and 9, the system 100 may include one or more flow meters 224 for measuring the flow rate of the flow 122 through each test station 102. For example, as shown in FIG. 1, the system 100 may include a flow meter 224A located at a flow input of each test station 102 to measure the flow rate of the working fluid stream 122, and / or a flow meter 224B located at a flow output of each test station 102 to measure a flow rate of the working fluid stream 228 discharged from each test station 102 that is substantially equal to the corresponding input fluid stream 122.

[0116] Flow meter 224C may be used to measure the flow rate of working fluid stream 106 discharged from fluid power unit 110 and / or flow meter 224D may be used to measure the flow rate of working fluid stream returned to fluid power unit 110. The flow rates measured by flow meter 224C and / or flow meter 224D may indicate the flow rate of working fluid stream 122 to one or more of the test stations 102 during the performance of one or more tests.

[0117] 9, a flow meter 224E can be used to measure the flow rate of the working fluid streams (e.g., streams 122A-122D) to each actuator 104. Here, the flow rate of the input working fluid stream 122 or the output working fluid stream 228 can be determined by summing the flow rates measured by the flow meter 224E.

[0118] 10 is a chart illustrating a test flow profile 230 according to an embodiment of the present disclosure. The test flow profile 230 represents the changing flow rate 232 (gray line) of the influent 122 (and effluent 224) over time during a given test run, as measured using one or more of the flow meters 224 described above during previous runs of the test.

[0119] The test flow profile 230 may take any suitable form. For example, the test flow profile 230 may reflect the measured flow rate 232 over time. Alternatively, the test flow profile 230 may generally follow a contour of a maximum value that excludes frequent changes in the measured flow rate 232, as shown by the black line 234 in FIG. 10. The test flow profile 230 may also be represented by delta values ​​at various times that indicate the change in the flow rate 232 or the change in the contour line 234 at times t1, t2, t3, etc. Other forms of the test flow profile 230 may also be used.

[0120] 11 is a flow chart illustrating a method of controlling the fluid power unit 110 using at least one controller to generate a variable main flow 106 for driving the hydraulic actuators 104 of at least one test station 102 during the performance of at least one test, according to an embodiment of the present disclosure. The controller may take the form of the system controller 126, the fluid power unit controller 128, the test station controller 220, and / or another controller in the system 100. This controller will hereinafter be referred to as the fluid power unit controller 128.

[0121] At least one test flow profile 230 is obtained at 240. As discussed above, each test flow profile 230 identifies an estimated working fluid flow demand for the flow 122 to the test station 102 over time corresponding to the execution of a test performed by the test station 102.

[0122] In one example, each test station controller 220 may notify the fluid power unit controller 128 that a given test is to begin or that a test will begin at a later time. The fluid power unit controller 128 retrieves the test flow profile corresponding to the notification, such as from its memory 204. The notification from each test station 102 may include an identification of the test station 102 or the test to be performed, which may be mapped to one of the test flow profiles 230. This information may be used by the fluid power unit controller 128 to retrieve the corresponding test flow profile 230. These notifications may take any suitable form, such as an electrical signal, a data communication, or other type of notification.

[0123] In the method 242, the fluid power unit 110 is controlled to generate a variable main flow 106 of the working fluid using a plurality of unique subsets of the hydraulic pumps 130 during the execution of at least one test. Each of the unique subsets is selected based on at least one test flow profile 230. Thus, the test flow profile 230 of the one or more tests is used to determine different subsets of the plurality of hydraulic pumps 130 of the one or more fluid power units 110 to be activated and / or deactivated over time to provide a main flow 106 that satisfies the flow demand 122 of one or more tests being performed by one or more of the test stations 102.

[0124] In some embodiments, the flow thresholds (FIG. 10) are used to determine a unique subset of hydraulic pumps 130 to be used in step 242 to satisfy the estimated flow demand 122 of the test station 102 presented in the flow profile 230. Since each pump 130 is configured to provide the main flow 106 up to a maximum flow portion 132, a single pump 130 may be operated to provide the flow portion 132 that sums up to a first flow threshold 244A, two of the pumps 130 may be operated to provide the flow portion 132 that sums up to a second flow threshold 244B, three of the pumps 130 may be operated to provide the flow portion 132 that sums up to a third flow threshold 244C, and so on for additional flow thresholds 244, such as flow thresholds 244D and 244E shown in FIG. 10. Pumps 130 that are not required to satisfy the estimated flow demands presented in the test flow profile 230 of the test or tests being performed may be set to a stopped state by the controller 128 in step 242.

[0125] The operating state of each pump 130 generally corresponds to a state in which the pump 130 is prepared during step 242 to substantially contribute to the variable mainstream 106 or to generate a flow portion 132 that substantially contributes (e.g., greater than 3%) to the mainstream 106. In one embodiment, a pump 130 is placed in an operating state when the motor 134 of the pump 130 is in an operating state powered to drive operation of the pump 130.

[0126] In one embodiment, the pump 130 is in a stopped state when the motor 134 of the pump 130 is in an unpowered stopped state.

[0127] Alternatively, the stopped state of the pump 130 may correspond to an idle state in which the motor 134 is operating but none of the flow portion 132 generated by the pump 130 contributes substantially (e.g., more than 3%) to the mainstream 106. For example, an active-valve hydraulic pump 130A (FIG. 6) may be set to a stopped state by controlling the active valve mechanism 192 to direct the working fluid flow to the low pressure port 174 while the corresponding motor 134 is operating, and a passive-valve hydraulic pump 130B (FIG. 4) may be set to a stopped state using the working volume regulator 178 to set the flow portion 132 to a minimum value that does not substantially contribute to the mainstream 106 while the corresponding motor 134 is operating.

[0128] The flow rate thresholds 244 may be determined based on the type of hydraulic pump 130 (e.g., 130A or 130B) and its flow rate limitations. In some embodiments, the flow rate thresholds 244 include a buffer such that the flow rate thresholds 244 span a range of flow rates and are generally below the flow production limits of the corresponding hydraulic pumps 130. For example, if the pumps 130 each have a flow production limit of 100 gallons / minute, the flow rate thresholds 244 may be spaced apart by, for example, 90 gallons / minute.

[0129] The flow rate threshold 244 may be applied to the flow rate profile 230 to determine a unique subset of hydraulic pumps 130 that will be activated during various periods of the test to drive the main flow 106 during step 242 to satisfy the flow(s) 122 requested during the execution of the test. If the test flow rate profile 230 indicates that the currently requested flow rate of the flow 122 is between the upper boundary flow rate threshold 244 and the lower boundary flow rate threshold 244, the upper boundary flow rate threshold 244 may be used to determine the unique subset of hydraulic pumps 130 that will be used to provide the currently requested flow 122. The buffer causes the sum of the maximum flow portions 132 of the pumps 130 of the unique subset to exceed the flow rate indicated by the upper boundary flow rate buffer 244.

[0130] For example, during a time period t0-t2 when the flow rate of the flow 122 for a given test estimated by the flow profile 230 (FIG. 10) falls below a first flow rate threshold (upper flow rate threshold) 244A, a first one of the hydraulic pumps 130 (e.g., one of the pumps 130A) constituting the unique subset of pumps 130 may be activated in step 242 to provide a flow portion 132 that meets the required flow 122 of the test during that time period. During the time period t0-t2, other pumps 130 of the fluid power unit 110 that are not in the unique subset for that time period may be stopped as they are not needed to provide the required flow 122. Thus, for example, if the fluid power unit 110 includes six hydraulic pumps 130 as shown in FIG. 2, during the time period t0-t2, for example, the subset consisting of the first pump 130 may be activated and the remaining five pumps 130 that are not in the subset may be stopped.

[0131] At time t2, when the estimated demand flow of the flow 122 for the test indicated by the test flow profile 230 increases above a first flow threshold (lower flow threshold) 244A and below a second flow threshold (upper flow threshold) 244B, a second one of the hydraulic pumps 130 (e.g., one of the pumps 130B) may be operated to provide an additional flow portion 132 that, when combined with the flow portion 132 provided by the first pump 130, satisfies the estimated demand flow of the flow 122 indicated by the test flow profile 230. Thus, a subset of two of the pumps 130 of the fluid power unit may be operated in step 242 to provide the required flow 122, while the other pump 130 may be stopped. Similarly, at time t3, the required flow rate exceeds the second flow rate threshold (lower flow rate threshold) 244B and falls below the third flow rate threshold (upper flow rate threshold) 244C, requiring the third pump 130 to be operated to meet the estimated flow demand, thus constituting a subset of three pumps 130 that are operated in step 242 to drive the flow 122, while the other pumps 130 may remain stopped.

[0132] Similarly, if the flow profile 230 indicates that the demanded flow 122 transitions from above the lower flow threshold to below the lower flow threshold, the lower flow threshold becomes the upper flow threshold and is used to determine the subset of pumps 130 required to drive the demanded flow 122. For example, from time t7 to t8, the flow profile 230 indicates that the demanded flow 122 is between the upper flow threshold 244E and the lower flow threshold 244D, but at time t8, the estimated demand flow drops below flow threshold 244D while remaining above flow threshold 244C. Thus, during the period t8 to t9, the flow threshold 244D acts as the upper flow threshold and determines the subset of four pumps 130 used to satisfy the demanded flow 122 in step 242. As a result, the pumps 130 corresponding to the flow threshold 244E that were activated during the period t7 to t8 may be shut down at or around time t8.

[0133] In some embodiments, the controller 128 transitions the pumps 130 from a stopped state to an active state a predetermined time period before the start of the period during which the pumps 130 are included in the active subset used to contribute to the variable mainstream 106 and help meet the requested flow 122. In some embodiments, the predetermined time period allows the corresponding motors 134 to transition from a stopped state to an active state and begin to drive the pumps 130 such that the pumps 130 can substantially contribute to the mainstream 106. Examples of the predetermined time period include about 2 seconds to 6 seconds, such as greater than about 3 seconds. Other predetermined time periods may be used based on the characteristics of the pumps 130 and their motors 134. Thus, referring again to FIG. 10, the controller 128 may activate the pumps 130 corresponding to the flow threshold 244B a predetermined time period before time t2 such that the pumps 130 are ready to contribute to the mainstream 106 and help meet the requested flow 122 at or around time t2.

[0134] In some embodiments, the fluid power unit 110 may provide a main flow 106 that is used to supply the required flow 122 to perform multiple, sometimes overlapping, tests with the test station 102. In such cases, the fluid power unit controller 128 aggregates the test flow profiles 230 of the tests in the overlapping time periods to determine a unique subset of hydraulic pumps 130 to be actuated to generate the variable main flow 106 that meets the required flow rate 122 during those time periods.

[0135] An example of this is shown in Figure 12, which includes a chart illustrating an example pair of test flow profiles 230A and 230B corresponding to a first test and a second test, respectively, and the operation of the fluid power unit 110 while the tests are being performed, according to embodiments of the present disclosure. In some embodiments, the test station 102 performing the first test notifies the fluid power unit controller 128 of the start of the first test, and the controller 128 obtains the test flow profile 230A corresponding to the first test (step 240). The test station 102 performing the second test notifies the fluid power unit controller 128 of the start of the second test, and the controller 128 obtains the test flow profile 230B corresponding to the second test (step 240).

[0136] Because the test flow profile 230A indicates that the test requires that the flow 122 fall below the first flow threshold 244A at time t1, the controller 128 activates the first pump 130 corresponding to the first flow threshold 244A, such as a predetermined period of time prior to time t1, and uses the first pump 130 to generate the main flow 106 and generate a flow portion 132 that satisfies the estimated demand flow indicated by the test flow profile 230A. Similarly, the controller activates the second pump 130 corresponding to the second flow threshold 244B to generate a flow portion 132 at time t2 that contributes to the flow portion 132 of the first pump 130 and generates the main flow 106 that satisfies the increased flow indicated at time t2.

[0137] The second test begins at time t3. Thus, the main flow 106 must satisfy both the flow 122 required for the test station 102 performing the first test and the flow 122 required for the test station 102 performing the second test. As a result, the controller 128 aggregates the test flow profiles 230A and 230B to form an aggregate test flow profile 230C that controls the operation of the fluid power unit 110. At time t3, the sum of the estimated demand flow rates indicated by the aggregate test flow profile 230C remains below the second flow threshold 244B, so no changes are required to the activated pumps 130. However, at time t4, the increase in the estimated demand flow rate indicated by the test flow profile 230A causes the aggregate estimated demand flow rate of profile 230C to exceed the second flow threshold 244B. As a result, a third pump 130 is activated by the controller 128 to ensure that the main flow 106 corresponds to the total required flow to perform the first test and the second test over the time period t4 to t5. Similarly, the controller 128 activates additional pumps 130 at times t5 and t6.

[0138] At time t7, the estimated demand flow indicated by the test flow profile 230C transitions from above the third flow threshold 244C to below the third flow threshold 244C, causing one of the subset of pumps 130 used to drive the main flow 106 during time period t6-t7 to be shut down, leaving the subset of three pumps 130 to drive the main flow 106 and provide the flow 122 requested by the test station 102 during times t7 and t7-t8. Similar adjustments are made at time t9 when the second test is completed, and at time t 10 It is held in.

[0139] This process can be used to provide a mainstream 106 that meets the required flow 122 of multiple test stations 102, each performing a test where a test flow profile 230 has been established through measurements of the flow 122 when the test was previously performed.

[0140] In some embodiments, when the fluid power unit 110 includes both active valve hydraulic pumps 130A and passive valve hydraulic pumps 130B, one of the active valve hydraulic pumps 130A is selected to satisfy the first flow threshold 244A due to its ability to rapidly change its flow portion 132 to match rapid changes in the required flow(s) 122. Each of the higher flow thresholds 244 may be matched to one of the other active valve hydraulic pumps 130A or one of the passive valve hydraulic pumps 130B, which generally function to provide the flow portion 132 that meets the majority of the required flow(s) 122.

[0141] Each hydraulic pump 130 of the unit 110 may be matched to one of the flow thresholds 244 that trigger their activation and deactivation by the fluid power unit controller 128 based on one or more factors related to the other hydraulic pumps 130 of the unit 110. These factors may include, for example, the age of the hydraulic pump 130, the total operational runtime (e.g., time used) of the hydraulic pump 130, the time since the pump 130 was last operated, and / or other factors. Thus, embodiments of the present disclosure include using the fluid power unit controller 128 to assign pumps 130 of the fluid power unit 110 to flow thresholds 244 based on weighting one or more of these factors.

[0142] To reduce wear on the pumps 130 and extend their life, it may be desirable to reduce usage of the hydraulic pumps 130 of the units 110 that are the oldest and / or have the longest operating runtime. Thus, in one embodiment, pumps 130 with older ages or longer total operating runtimes are weighted toward higher flow thresholds 244 and pumps 130 with younger ages or shorter total operating runtimes are weighted toward lower flow thresholds 244. This tends to cause pumps 130 with older ages or longer operating runtimes to be assigned to higher flow thresholds 244 and have a lower operating frequency compared to pumps 130 assigned to lower flow thresholds 244. The age and / or operating runtime of the pumps 130 may be monitored and maintained in memory 204 of the fluid power unit controller 128 and / or system controller 126 using conventional techniques.

[0143] The last activation time may be used to reduce the frequency of activation of the most recently activated pumps 130. This may help to distribute the usage of the hydraulic pumps 130 more evenly. For example, the most recently activated pumps 130 may be weighted toward a higher flow threshold 244 than pumps 130 that were not recently activated. This tends to assign the most recently activated pumps 130 to a higher flow threshold 244 that will have a lower activation frequency, and the pumps 130 that were not recently activated to a lower flow threshold 244 that will be more likely to be activated. The time since the last activation of each pump 130 may be monitored and maintained in memory 204 by the fluid power unit controller 128 and / or the system controller 126 using conventional techniques.

[0144] An additional embodiment of the present disclosure relates to a method of turning on and / or stopping the hydraulic pump 130. Conventional fluid power units 110 typically operate a variable displacement hydraulic pump having a working volume regulator 176 (e.g., swash plate 186) in an on or off state. That is, the motor 134 of the pump 130 is turned on to drive the pump 130 to maximum pressure at start-up, and the pump 130 immediately attempts to drive the flow portions 132 to form the main flow 106 based on their pressure set points. The sudden turning on and off of the motor 134 creates undesirable rapid power changes that generate electrical spikes and strain the pump components (e.g., bearings). In addition, when the newly operated pump 130 reaches an operating pressure at which it begins to generate flow portions 132 that contribute to the mainstream 106 output by the fluid power unit 110, undesirable pressure oscillations may be formed in the main output flow 106 about the pressure set point of the pump 130, causing vibrations of the working volume regulator 178, such as vibrations in the angular orientation of the swash plate 186, thereby generating oscillating flow portions 132 that contribute to unstable pressure in the mainstream 106.

[0145] Some embodiments of the present disclosure relate to a method for controlling the transition of a variable displacement hydraulic pump 130 of a fluid power unit 110 between an active state and an inactive state to avoid electrical spikes and pressure oscillations in the mainstream 106. The unit 110 may be configured according to one or more embodiments described herein. For example, the fluid power unit 110 includes a reservoir 136, a main output 133 at which the mainstream 106 is discharged, a pressure sensor 140 having a pressure signal 142 indicative of a main pressure of the mainstream 106, and a number of variable displacement hydraulic pumps 130, such as active valve hydraulic pumps 130A and / or passive valve hydraulic pumps 130B.

[0146] Each pump 130 includes a plurality of piston pumps 160 and a motor 134 having an active state and an inactive (e.g., unpowered) state that drives a cyclic change to the working volume of each piston pump 160. As discussed above, each pump 130 has a pressure set point such that when the main pressure drops below the pressure set point, the pump 130 operates to generate a flow portion 132 that contributes to the main flow 106, and when the main pressure exceeds the pressure set point, the pump 130 does not operate to generate a flow portion 132 that contributes to the main flow 106. The main pressure may be, for example, in the range of 2500 pounds per square inch to 3500 pounds per square inch.

[0147] The pump 130 may have an adjustable pressure set point that can be set to different values ​​via a control signal from the fluid power unit controller 128 using, for example, a proportional valve, as discussed above. In some embodiments, the controller 128 adjusts the pressure set point of the pump 130 when the pump 130 transitions from a stopped state to a running state or from a running state to a stopped state to reduce power spikes, strain on the components of the pump 130, and pressure oscillations in the main flow 106.

[0148] In some embodiments, the pressure set point of each pump 130 is adjustable between a value that is within a range of inoperative pressure set points and a value that is an operational pressure set point. The inoperative pressure set point represents a pressure value below the expected operating range of the main pressure at which the pump 130 does not produce a flow portion 132 that contributes substantially to the mainstream 106. For example, the inoperative pressure set point can range from a minimum pressure set point (e.g., 200 psi) to about 93% of the expected operating range of the main pressure, e.g., 30%-90% of the expected operating range of the main pressure.

[0149] The operational pressure set point corresponds to a value within the expected operating range of the main pressure such that pump 130 can generate flow portion 132 that contributes to mainstream 106 when the main pressure drops below the operational pressure set point. Thus, the operational pressure set point generally corresponds to a conventional pressure set point for pump 130, such as, for example, 95%-99% of the expected operating range of the main pressure.

[0150] Figure 13 is a flow chart illustrating a method of controlling one of the pumps 130 of a fluid power unit according to an embodiment of the disclosure. Figures 14 and 15 are charts illustrating example adjustments to the pressure set point of the pump 130 over time according to the method of Figure 13 to transition the pump between an on state and an off state according to an embodiment of the method.

[0151] In method 250, pump 130 is operated for a predetermined period 252 (times t1-t2) while the pressure set point of pump 130 is set to a first inoperative pressure set point (PS1) within inoperative pressure set point range 254, as shown in Figure 14. Thus, in some embodiments of step 250, fluid power unit controller 128 sets the pressure set point of pump 130 to a value within inoperative pressure set point range 254, such as, for example, 50% of the expected operating range of the main pressure.

[0152] The predetermined period 252 is set to a value that allows the pump 130 to gradually transition from a stopped state to an operating state at time t2 without driving the flow portion 132 that contributes substantially (e.g., more than 3%) to the mainstream 106, which may include transitioning the motor 134 from a stopped state to an operating state. Thus, during the predetermined period 252, the pump 130 does not disturb the mainstream 106 or contribute to pressure oscillations in the mainstream 106. Additionally, because the pump 130 does not attempt to drive the flow portion 132 at the pressure of the mainstream, large transient power spikes as well as strain on the components of the pump 130 are avoided.

[0153] The predetermined period 252 may be selected to ensure that the motor 134 drives the cyclic drive 166 to a desired operating speed (e.g., 1800 revolutions per minute) by time t2 to allow the pump 130 to pressurize to the inoperable pressure set point PS1. In some embodiments, the predetermined period 252 is about 1 to 6 seconds, such as, for example, about 4 to 5 or 3 seconds.

[0154] In method 256, at time t2, the pump 130 is operated while the pressure set point is set to a value within an operable pressure set point range 258, illustrated by pressure set point PS2 in FIGURE 14. In some embodiments of step 256, the fluid power unit controller 128 sets the pressure set point of the pump 130 to a value that is within the range 258 of operable pressure set points, such as, for example, 98% of the expected operating range of the main pressure, at time t2. As a result, the pump 130 transitions to a fully operational state configured to generate a flow portion 132 that substantially contributes to the mainstream 106.

[0155] In some embodiments of step 256, the pump 130 is transitioned from an off state to an on state through multiple stages (e.g., 2-5 stages) such that the pump 130 is operated at progressively increasing disable pressure set points. This is shown diagrammatically by the chart in FIG.

[0156] For example, when the pump 130 is transitioned from a stopped state to an operating state at time t1, the pressure set point of the pump 130 is initially set to a disabled pressure set point PS1 and operated for a predetermined period 252A (times t1 to t2) corresponding to a first stage. At time t2, the pressure set point of the pump 130 is adjusted to a disabled pressure set point PS2 that is greater than the disabled pressure set point PS1 and operated for a predetermined period 252B (times t2 to t3) corresponding to a second stage. For example, the disabled pressure set point PS1 may be set to 5% to 35% of the expected operating range of the primary pressure (e.g., 200 psi to 1000 psi), and the disabled pressure set point PS2 may be set between the pressure set point PS1 and the operational pressure set point PS3, such as 50% to 80% of the expected operating range of the primary pressure (e.g., 1500 psi to 2400 psi). Additional stages of operating the pump 130 at the disabled pressure set points can be added as desired. As a result, the pump 130 transitions from the stopped state to the operating state more gradually than in the example of FIG.

[0157] In some embodiments, the predetermined period 252A is substantially equal (e.g., ±5%) to, greater than, or less than the predetermined period 252B. In some embodiments, the motor reaches its full operating speed during the predetermined period 252A or during the predetermined period 252B.

[0158] The method of Figure 13 may also be performed to gradually transition pump 130 from an on state to a off state, where step 256 is performed before step 250, as shown generally by the transitions at time t3 in Figure 14 and time t4 in Figure 15. This gradual shutdown of pump 130 may occur in a single step and over a predetermined period of time 260, as shown in Figure 14, or over multiple steps and periods 260A and 260B, as shown in Figure 15.

[0159] Thus, while the pump 130 is operating in an operational state where the motor 134 is running at full speed and the pump 130 is set to an operational pressure set point (e.g., PS2 in FIG. 14 and PS3 in FIG. 15), the pressure set point of the pump 130 is reduced to one of the inoperative pressure set points. For example, the pressure set point of the pump 130 may be reduced to the inoperative pressure set point PS1 at time t3 in FIG. 14 and reduced to the inoperative pressure set point PS2 in an initial shutdown phase beginning at time t4 in FIG. 15. This prevents the pump 130 from generating a flow portion 132 that substantially contributes to the main flow 106. As shown in FIG. 15, additional shutdown phases (e.g., stages 2-5) may be used to more gradually transition the pump 130 to a fully shut down condition.

[0160] The predetermined period or periods 260 during which the pump 130 operates at the inoperative pressure set point can be set as desired. The motor 134 may be stopped (de-powered) at the beginning of a stop phase, such as at time t3, during period 260, or after time t4 in the example shown in Figure 14. If there are multiple stop phases as shown in Figure 15, the motor 134 may be stopped at the beginning of an initial stop phase (time t4), during the initial stop phase (e.g., period 260A), progressively throughout all of the stop phases (e.g., periods 260A and 260B), or during or after a final stop phase (e.g., period 260B).

[0161] When the pump 130 is a passive valve variable hydraulic pump 130B, the working volume regulator 178 may be transitioned to a minimum or idle setting only or during the initial stopping phase, throughout the entire stopping phase, or during the final stopping phase.

[0162] The gradual shut-off of the pump 130 shown in FIGS. 14 and 15 can reduce power transients, pressure oscillations in the main flow 106, and strain on the components of the pump 130.

[0163] 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 method of controlling a fluid power unit of a dynamic testing system using at least one controller, the fluid power unit comprising a plurality of hydraulic pumps configured to generate a variable main flow of a working fluid for driving hydraulic actuators of at least one test station during the performance of at least one test, the method comprising: acquiring at least one test flow profile, each of the at least one test flow profile identifying a working fluid flow demand estimate over time corresponding to one execution of the at least one test; generating the variable mainstream of working fluid using a plurality of unique subsets of the hydraulic pumps during execution of the at least one test, each unique subset being selected based on the at least one test flow profile; A method comprising:

2. The method includes, for each of a plurality of time periods, identifying a corresponding one of the unique subset of the hydraulic pumps required to generate a main flow that exceeds a sum of the working fluid flow demand estimates corresponding to the time period based on the at least one test flow profile; 2. The method of claim 1, wherein generating the variable mainstream comprises generating the variable mainstream during each of the multiple time periods using the identified corresponding unique subset of the hydraulic pumps.

3. during each of the plurality of time periods, the corresponding sum of the working fluid flow demand estimates lies between a lower boundary flow threshold and an upper boundary flow threshold of a plurality of flow thresholds; each flow threshold corresponds to one of the unique subset of the hydraulic pumps; 3. The method of claim 2, wherein for each time period, identifying the corresponding one of the unique subset of the hydraulic pumps comprises identifying the corresponding one of the unique subset based on the upper flow threshold.

4. each of the hydraulic pumps includes an operating state in which the hydraulic pump substantially contributes to the variable mainstream flow and a stopped state in which the hydraulic pump does not substantially contribute to the variable mainstream flow; For at least one of said time periods, generating said variable mainstream comprises transitioning one or more of said hydraulic pumps of said corresponding unique subset from said stopped state to said operating state, preferably wherein transitioning one or more of said hydraulic pumps of said corresponding unique subset from said stopped state to said operating state occurs a predetermined time period before the start of said at least one of said time periods; and / or each hydraulic pump comprises a motor having an operating state in which the motor is powered to drive the hydraulic pump and a stopped state in which the motor is not powered; 3. The method of claim 2, wherein transitioning one or more of the hydraulic pumps of the determined subset from the stopped state to the running state includes transitioning the motor of the one or more hydraulic pumps from the stopped state to the running state.

5. The fluid power unit comprises: a reservoir containing a working fluid; a main output section at which the variable main flow of the working fluid is discharged; the plurality of hydraulic pumps including at least one active valve hydraulic pump having a variable displacement volume and at least one passive valve hydraulic pump having a variable displacement volume; Equipped with In one embodiment, each subset includes one of the at least one active valve hydraulic pump, and in a further embodiment, 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 at least a portion of the variable 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; 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; 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 piston pumps, each configured to draw hydraulic fluid into an adjustable working volume through the low pressure port and drive at least 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 piston pump; The method according to any one of claims 1 to 4, comprising:

6. 1. A dynamic testing system comprising: at least one test station, each configured to apply a force and / or a displacement to a test object using a hydraulic actuator during the performance of a test; a fluid power unit including a plurality of hydraulic pumps configured to generate a variable main flow of a hydraulic fluid that drives the hydraulic actuators of the at least one test station during the performance of at least one test; At least one controller, acquiring at least one test flow profile, each of the at least one test flow profile identifying a working fluid flow demand estimate over time corresponding to one execution of the at least one test; generating the variable mainstream of working fluid using a plurality of unique subsets of the plurality of hydraulic pumps during performance of the at least one test, each unique subset being selected based on the at least one test flow profile; and in one embodiment, the at least one controller is configured to: identifying, for each of a plurality of time periods, a corresponding one of the unique subset of the hydraulic pumps required to generate a main flow that exceeds a sum of the estimated working fluid flow demands corresponding to the time period based on the at least one test flow profile; generating the variable main flow during each of the plurality of time periods using the identified corresponding unique subset of the hydraulic pumps; configured to: In a further embodiment, during each of the plurality of time periods, the corresponding sum of the working fluid flow demand estimates lies between a lower boundary flow threshold and an upper boundary flow threshold of a plurality of flow thresholds; each flow threshold corresponds to one of the unique subset of the hydraulic pumps; for each time period, the corresponding one of the unique subset of hydraulic pumps is identified based on the upper flow rate threshold. At least one controller; A system comprising:

7. each of the hydraulic pumps includes an operating state in which the hydraulic pump substantially contributes to the variable mainstream flow and a stopped state in which the hydraulic pump does not substantially contribute to the variable mainstream flow; For at least one of the periods, one or more of the hydraulic pumps of the corresponding unique subset are transitioned from the stopped state to the running state to generate the variable mainstream, and in one embodiment, for at least one of the periods, one or more of the hydraulic pumps of the corresponding unique subset are transitioned from the stopped state to the running state a predetermined time period prior to the start of the at least one of the periods to generate the variable mainstream; and / or each hydraulic pump comprises a motor having an operating state in which the motor is powered to drive the hydraulic pump and a stopped state in which the motor is not powered; 7. The system of claim 6, wherein one or more of the hydraulic pumps of the determined subset are transitioned from the stopped state to the running state by transitioning the motor of the one or more hydraulic pumps of the determined subset from the stopped state to the running state.

8. The fluid power unit comprises: a reservoir containing a working fluid; a main output section at which the variable main flow of the working fluid is discharged; the plurality of hydraulic pumps including at least one active valve hydraulic pump having a variable displacement volume and at least one passive valve hydraulic pump having a variable displacement volume; Equipped with In one embodiment, each subset includes one of the at least one active valve hydraulic pump; and / or 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 at least a portion of the variable 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; 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; 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 piston pumps, each configured to draw hydraulic fluid into an adjustable working volume through the low pressure port and drive at least 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 piston pump; The system of claim 6 , comprising:

9. 1. A method for controlling a fluid power unit of a dynamic testing system using at least one controller, the fluid power unit comprising: a reservoir containing a working fluid; a main output section from which a main flow of the working fluid is discharged; a pressure sensor having a pressure signal indicative of a main pressure of the mainstream flow; a plurality of variable displacement hydraulic pumps each configured to drive a portion of the main flow; Equipped with Each variable displacement hydraulic pump is A plurality of piston pumps; a motor having an active state and an inactive state for driving the periodic change in working volume of each piston pump; A pressure set point, a range of inoperative pressure set points below the expected operating range of the main pressure, where the variable displacement hydraulic pump does not contribute to the main flow; an operable pressure set point within the expected operating range of the main pressure at which the variable displacement hydraulic pump is driven to contribute to the main pressure; a pressure set point selectable between Equipped with The method includes controlling one of the variable displacement hydraulic pumps, operating the variable displacement hydraulic pump for a first predetermined time period while the pressure set point is set to a first inoperative pressure set point within a range of the inoperative pressure set points; operating the variable displacement hydraulic pump while the pressure set point is set to the operational pressure set point; The method includes:

10. 10. The method of claim 9, wherein operating the variable displacement hydraulic pump for the first predetermined period occurs prior to operating the variable displacement hydraulic pump while the pressure set point is set to the operational pressure set point, and in one embodiment operating the variable displacement hydraulic pump for the first predetermined period includes transitioning the motor from the stopped state to the running state.

11. after operating the variable displacement hydraulic pump for a first predetermined period of time and prior to operating the variable displacement hydraulic pump while the pressure set point is set to the operational pressure set point; operating the variable displacement hydraulic pump for a second predetermined period of time while the pressure set point is set to a second inoperative pressure set point within the range of the inoperative pressure set points; The method of claim 10 , wherein the second pressure set point is higher than the first pressure set point.

12. 10. The method of claim 9, wherein operating the variable displacement hydraulic pump for the first predetermined period occurs after operating the variable displacement hydraulic pump while the pressure set point is set to the operational pressure set point.

13. 13. The method of claim 12, wherein operating the variable displacement hydraulic pump for the first predetermined period of time includes transitioning the motor from the running state to the stopped state.

14. after operating the variable displacement hydraulic pump while the pressure set point is set to the operational pressure set point and prior to operating the variable displacement hydraulic pump for a first predetermined period of time; operating the variable displacement hydraulic pump for a second predetermined period of time while the pressure set point is set to a second inoperative pressure set point within the range of the inoperative pressure set points; The method of claim 13 , wherein the second pressure set point is higher than the first pressure set point.

15. operating the variable displacement hydraulic pump for the first predetermined period includes setting, using a controller, the pressure set point to the first inoperative pressure set point; 10. The method of claim 9, wherein operating the variable displacement hydraulic pump while the pressure set point is set to one of the operational pressure set points comprises setting the pressure set point to the operational pressure set point using the controller.

Images