Patent ID: 12196228

DETAILED DESCRIPTION

Disclosed herein are systems and electrohydraulic power units that can operate efficiently without using complex electro-hydraulic components, systems, or configurations. An example power unit includes an electric motor driving a pump to provide fluid flow to an external hydraulic circuit. A fluid signal is generated by the hydraulic circuit, where the fluid signal is indicative of a fluid flow demand (e.g., the fluid flow rate required to operate the hydraulic circuit) in a desired state. A pressure sensor is configured to provide sensor information indicating pressure level of the fluid signal to a controller of the electric motor. The controller then changes the speed of the electric motor to decrease or increase the speed based on the sensor information.

In an example, a fixed displacement pump is used. A fixed-displacement pump is a positive displacement type where the amount of displacement (or amount of fluid pumped per revolution of the pump's input shaft) cannot be varied while operating at a given speed. In this case, changing the speed of the electric motor is used to change the fluid flow rate output of the pump.

In another example, a variable displacement pump is used. With a variable displacement pump, the displacement, or amount of fluid pumped per revolution of the pump's input shaft, can be varied while the pump is running. For example, the pump can have a swash plate, the angle of which determines the displacement of the pump, and thus varying the swash plate angle varies the displacement of the pump. In an example, the angle of the swash plate can be used to change the amount of fluid flow output by the pump. In another example, the electric motor can be used to change the speed of the input shaft to control the amount of fluid flow rate, while the angle of the swash plate can be changed to vary the torque load on the electric motor.

As such, the disclosed systems and power units can provide a power output that meets is the demand of the hydraulic circuit, without producing excess power that is wasted. This way the efficiency of the system can be enhanced.

FIG.1illustrates a block diagram of a system100, in accordance with an example implementation. The system100has an electrohydraulic power unit including an electric motor102driving a pump104(i.e., the output shaft of the electric motor102is coupled to the input shaft of the pump104).

The pump104draws fluid from a fluid reservoir106, which is configured as a hydraulic fluid tank storing or containing hydraulic fluid at a low pressure level, e.g., 0-70 pounds per square inch (psi). The pump104then provides fluid flow to a hydraulic circuit108. The hydraulic circuit108can include several hydraulic components such as valves and actuators (e.g., hydraulic cylinder or motors). As such, the fluid flow provided by the pump104drives the actuators of the hydraulic circuit108.

The hydraulic circuit108is configured to generate a fluid signal in a hydraulic line110coupled to the hydraulic circuit108. The fluid signal is configured such that the pressure level of the fluid signal provides an indication of whether fluid flow is demanded by the hydraulic circuit108. If fluid flow is demanded by the hydraulic circuit108, the pressure level of the fluid signal can further provide an indication of the amount of fluid flow rate demanded by the hydraulic circuit108to operate the hydraulic circuit108in a desired or commanded state.

The system100includes a pressure sensor112disposed in the hydraulic line110, and is configured to provide sensor information indicative of the pressure level of the fluid signal in the hydraulic line110. The system100also includes a controller114that receives the sensor information from the pressure sensor112.

The fluid signal in the hydraulic line110can then be provided to the fluid reservoir106. In an example, the system100includes a valve116or other component that is fluidly-coupled to the hydraulic line110and receives the fluid signal from the hydraulic circuit108. As described below, the valve116is configured to create counter-pressure or back-pressure effect to allow pressure level to increase in the hydraulic line110. The valve116can further be configured to limit the pressure level of the fluid signal, and preclude back-flow from the fluid reservoir106to the hydraulic line110.

The controller114can have a microprocessor that can include one or more processors. A processor can include a general purpose processor (e.g., an INTEL® single core microprocessor or an INTEL® multicore microprocessor), or a special purpose processor (e.g., a digital signal processor, a graphics processor, or an application specific integrated circuit (ASIC) processor). A processor can be configured to execute computer-readable program instructions (CRPI) to perform the operations described throughout herein. A processor can be configured to execute hard-coded functionality in addition to or as an alternative to software-coded functionality (e.g., via CRPI).

The controller114is configured to control the speed of the electric motor102via an inverter118. The inverter118can include, for example, an arrangement of semiconductor switching elements (transistors) that can support conversion of direct current (DC) electric power provided from a power source120(e.g., a battery or electric generator) to three-phase electric power capable of driving the electric motor102. The power source120can also be electrically-coupled to the controller114to provide power thereto and receive commands therefrom.

In particular, the controller114can control the speed of the electric motor102in response to or based on the pressure level indicated by the sensor information received from the pressure sensor112. This way, the controller114can vary the speed of the electric motor102such that the pump104produces a particular fluid flow rate demanded by the hydraulic circuit108.

If the hydraulic circuit108does not demand fluid flow or demands a small amount of fluid flow, the electric motor102is commanded to rotate at a low standby speed so as to avoid producing excessive fluid flow that is then wasted as heat. If the hydraulic circuit108demands more flow, the pressure level of the fluid signal in the hydraulic line110changes, and the controller114responsively increases the speed of the electric motor102to generate the required fluid flow from the pump104.

Components of the system100may be configured to work in an interconnected fashion with each other and/or with other components coupled to respective systems. One or more of the described operations or components of the system100may be divided up into additional operational or physical components, or combined into fewer operational or physical components. In some further examples, additional operational and/or physical components may be added to the system100. For example, the controller114and the inverter118can be combined into a single package. The electrohydraulic power unit can include the electric motor102, the pump104, and the fluid reservoir106in a single package with fluid and electric connections connected to other parts of the system100. The electrohydraulic power unit can also include the controller114and the inverter118.

The implementation of the system100can take various forms based on the configuration of the hydraulic circuit108. For example, the hydraulic circuit108can include a closed-center valve, a load-sensing valve, or an open center valve. As another example, the pump104can be a fixed displacement pump or a variable displacement pump.FIGS.2,5, and6provide example implementations of the system100in various configurations.

FIG.2illustrates a system200with a hydraulic circuit202having a valve assembly204configured to provide a load-sense fluid signal, in accordance with an example implementation. The system200is an example implementation of the system100when the hydraulic circuit108includes a load-sensing valve. Components that are similar between the system100and the system200are designated with the same reference numbers.

As depicted, the electric motor102drives the pump104, which is configured as a fixed displacement pump inFIG.2, and the pump104provides fluid flow to the hydraulic circuit202. The hydraulic circuit202is an external circuit relative to the power unit and is not part of the power unit. Rather, the power unit, which includes the electric motor102and the pump104provides hydraulic power to operate the hydraulic circuit202.

The valve assembly204includes an inlet section206, a first worksection208, a second worksection210, a third worksection212, a fourth worksection214, and an outlet section216. The inlet section206, the worksections208-214, and the outlet section216can be coupled together by fasteners (e.g., bolts screws, clamps, tie rods, etc.) to provide an assembly of valve sections. The outlet section216can receive fluid from any of the inlet section206and/or the worksections208-214.

As shown inFIG.2, the pump104receives fluid from the fluid reservoir106to provide fluid flow to the valve assembly204. Particularly, an outlet port217of the pump104is fluidly-coupled to an inlet port218disposed in the inlet section206of the valve assembly204such that output fluid flow from the pump104is received at the inlet port218.

The valve assembly204is also configured to be fluidly-coupled to a fluid reservoir such as the fluid reservoir106or a different fluid reservoir. For example, the inlet section206or the outlet section216can have a tank port (not shown) that is fluidly-coupled to the fluid reservoir106. This way, fluid is allowed to return to the fluid reservoir106from the valve sections of the valve assembly204through the tank port. The tank port and the fluid connection from the valve assembly204to the fluid reservoir106is not shown to reduce visual clutter in the drawing.

Each worksection of the worksections208-214is configured to control fluid flow to and from a hydraulic actuator such as a hydraulic cylinder or hydraulic motor. For example, the first worksection208includes a first workport220and a second workport222that are fluidly-coupled to corresponding ports of a hydraulic cylinder actuator224. The hydraulic cylinder actuator has a cylinder219divided into a first chamber221and a second chamber223via piston225that is movable within the cylinder. Particularly, as depicted, the piston225has a piston head that divides the cylinder into the first chamber221and the second chamber223, and a piston rod that extends from the piston head along a longitudinal axis of the cylinder.

The piston rod can be coupled to an implement or other movable component to exert forces on objects and be subjected to forces. For example, if the hydraulic circuit202controls a hydraulic mobile machinery such as a backhoe or excavator, the piston rod can be coupled to an implement such as a bucket or arm to move the implement and dig in the ground or move material from one location to another. Thus, the hydraulic actuators apply forces and are subjected to forces that induce pressures in the chambers (e.g., the chambers221,223) of the hydraulic actuator during operation of the machinery.

The other worksections210-214are similarly configured to control fluid flow to and from respective actuators. As depicted, the worksection210has workports that control fluid flow to and from a hydraulic cylinder actuator226, the worksection212has workports that control fluid flow to and from a hydraulic cylinder actuator228, and the worksection214has workports that control fluid flow to and from a hydraulic cylinder actuator230. The hydraulic cylinder actuators226-230are configured similar to the hydraulic cylinder actuator224. In other examples, the hydraulic circuit202can include other types of actuators such as hydraulic motors.

Each of the worksections208-214can include a respective spool movable in a spool bore within the respective worksection. The spool can be actuated in either direction via various types of mechanisms. As an example for illustration, the spools can be actuated manually where an operator can move a joystick or handle connected to the spool and can thus move the spool manually. In another example, the spool can be actuated via hydraulic pilot fluid signal where an operator moves a joystick, and responsively, a hydraulic fluid signal is provided to one side of the spool to move the spool in a given direction.

When the spool moves in a given direction, fluid is provided to the respective hydraulic cylinder actuator to move a piston thereof in a first direction. When the spool moves in an opposite direction, fluid is provided to the respective hydraulic cylinder actuator to move the piston in a second direction, opposite the first direction. The larger the stroke of the spool, the larger the amount of fluid flow to the hydraulic cylinder actuator. In other words, the larger the stroke of the spool, the larger the fluid flow demand by the hydraulic cylinder actuator.

As mentioned above, the valve assembly204is configured to be a load-sensing valve. When the piston of a hydraulic cylinder actuator applies a force or is subjected to force, fluid pressure level in at least one of the chambers (e.g., the chambers221,223) of the hydraulic cylinder actuator increases. The pressure in the chambers can be referred to as load-induced pressure. Such pressure level in the chamber is indicative of the force or load that the piston applies or is subjected to.

Each worksection includes a respective load-sense passage, and when a spool of a worksection is actuated to provide fluid to a respective hydraulic cylinder actuator, the load-sense passage is fluidly-coupled to the hydraulic cylinder actuator via the respective workport of the worksection. Thus, the load-sense passage provides or transmits a pressure feedback signal from the workport, wherein the pressure feedback signal indicates the load on the hydraulic cylinder actuator.

As such, the pressure feedback signal may be referred to as a load-sense fluid pressure signal. When a load-sense fluid pressure signal is generated or the load-sense fluid pressure signal has a non-zero pressure level, then the respective hydraulic cylinder actuator has been actuated and thus fluid flow is demanded. Conversely, when the hydraulic cylinder actuator is not commanded to move, the spool of the associated worksection is not actuated and no load-sense fluid pressure signal is generated. In other words, the load-sense fluid pressure signal has a pressure level of zero psi. Thus, if the load-sense fluid pressure signal has a pressure level of zero psi (e.g., no signal is generated) no fluid flow is demanded by the corresponding hydraulic cylinder actuator. As such, the load-sense fluid pressure signal generated by a worksection provides an indication of whether fluid flow is demanded by the hydraulic cylinder actuator controlled by the worksection.

Each worksection of the worksections208-214is configured to produce a respective load-sense fluid pressure signal. The valve assembly204can further includes a network of check valves and/or shuttle valves that compares the pressure levels of the different load-sense fluid pressure signals, and then outputs the load-sense fluid pressure signal having the highest pressure level. This load-sense fluid pressure signal is a “universal” or “global” load-sense fluid pressure signal indicative of the highest load that the hydraulic cylinder actuators controlled by the valve assembly204are subjected to.

The load-sense fluid pressure signal is then provided to a hydraulic line231, which is fluidly-coupled to the valve assembly204. Although the hydraulic line231is shown inFIG.2to be connected to the inlet section206, in other example implementation, the hydraulic line231can be fluidly-coupled to other sections such as the outlet section216or other blocks/manifolds coupled to the valve assembly204.

The system100further includes an unloading valve232. Although the unloading valve232is shown external to the valve assembly204, in other example implementations, the unloading valve232can be disposed within or integrated within the valve assembly204. For instance, the unloading valve232can be integrated within the inlet section206. Thus, the hydraulic circuit202can be considered to include the valve assembly204, the hydraulic cylinder actuators224-230, and the unloading valve232.

The unloading valve232has an inlet port234that is fluidly-coupled to the outlet port217of the pump104. The unloading valve232also has a pilot port236that is fluidly-coupled to the hydraulic line231, and thus receives the load-sense fluid pressure signal indicative of the highest load among the loads of the hydraulic cylinder actuators224-230.

The unloading valve232further includes an outlet port238that is fluidly-coupled to the valve116via the hydraulic line110. The pressure sensor112is disposed in the hydraulic line110that fluidly couples the outlet port238to the valve116. This way, the pressure sensor112is configured to provide sensor information indicative of pressure level of fluid discharged from the outlet port238.

The unloading valve232includes a movable element such as a poppet, spool, or piston therein, and also includes a spring240applying a biasing force on the movable element toward a seat. When seated, the movable element blocks fluid flow from the inlet port234to the outlet port238.

The load-sense fluid pressure signal received at the pilot port236applies a first fluid force on the movable element toward the seat. As such, the first fluid force of the load-sense fluid pressure signal and the biasing force of the spring240cooperate to drive the movable element toward a seated position. Thus, the combined force or resultant force comprising the first fluid force of the load-sense fluid pressure signal and the biasing force of the spring240can be referred to as a closing force.

On the other hand, fluid received from the pump104at the inlet port234applies a second fluid force on the movable element that opposes the closing force, i.e., the second fluid force tends to act on the movable element to be unseated. Thus, the second fluid force can be referred to as an opening force.

As long as the opening force of fluid from the pump104does not exceed the closing force, the unloading valve232remains closed and no fluid flow is allowed from the inlet port234to the outlet port238. In other words, pressure level in the hydraulic line110is substantially zero (e.g., between zero and a low pressure valve such as 5-10 psi).

The closing force can remain larger than the opening force when most of the fluid flow from the pump104is provided to, and consumed by, the valve assembly204. For example, if several spools of several worksections of the worksections208-214are actuated at the same time (or one spool is actuated to a maximum stroke to move an actuator at maximum speed), most of the fluid output by the pump104is consumed by the valve assembly204and provided to the hydraulic cylinder actuator(s).

In some cases, the flow demanded by the hydraulic cylinder actuators224-230may exceed the flow capacity of the pump104at a given speed of the electric motor102. Thus, all the flow produced by the pump104is provided to the valve assembly204, and the pressure level of fluid at the inlet port234of the unloading valve232is not sufficient to overcome the closing force applied by the load-sense fluid pressure signal and the spring240. This way, the pressure level in the hydraulic line110remains low (e.g., zero).

In this case, the pressure sensor112indicates to the controller114that the flow demand exceeds the capacity of the pump104at the current motor speed. Responsively, the controller114can command the electric motor102to increase the speed and increase the flow output of the pump104. For example, if the pressure level in the hydraulic line110is zero, the controller114can command the electric motor102to operate at maximum speed.

If the pressure level of the fluid received from the pump104at the inlet port234increases such that the opening force exceeds the closing force, the movable element of the unloading valve232is lifted off its seat and fluid flows from the inlet port234to the outlet port238. The unloading valve232is configured as a proportional valve such that the amount of fluid flow passing therethrough is proportional to the difference in pressure level between the fluid at the inlet port234and fluid at the pilot port236.

Particularly, the larger the pressure differential between the fluid at the inlet port234and the load-sense fluid pressure signal at the pilot port236, the larger the movement of the movable element of the unloading valve232, and thus the larger the opening through the unloading valve232, thereby causing a larger amount of fluid flow to the outlet port238. Conversely, the smaller the pressure differential between the fluid at the inlet port234and the load-sense fluid pressure signal at the pilot port236, the smaller the amount of fluid flow through the unloading valve232. As such, the pressure level of the fluid signal output from the outlet port238to the hydraulic line110is based on a difference between the second fluid force and a combination of the first fluid force and the biasing force.

The valve116is configured to restrict the fluid flow to the fluid reservoir106. Thus, the larger the fluid flow rate through the hydraulic line110, the larger the pressure level induced in the hydraulic line110(i.e., the back pressure) due to the presence of the valve116. With this configuration, when the pump104provides a larger amount of fluid flow than demanded by the valve assembly204and the hydraulic cylinder actuators224-230, the fluid flow rate through the hydraulic line110and the pressure level therein increase. Such increase in pressure level is provided by the pressure sensor112to the controller114, which responsively reduces the speed of the electric motor102to reduce the fluid flow output of the pump104.

With this configuration, the controller114modifies, changes, or adjusts the speed of the electric motor102such that the speed of the electric motor102has an inverse relation with the pressure level in the hydraulic line110indicated by the pressure sensor112. If flow demand by the hydraulic circuit202(e.g., by the hydraulic cylinder actuators224-230) increases, the pressure level of fluid output by the pump104, and thus the pressure level of fluid provided to the hydraulic line110decreases and can reach zero when the flow demand exceeds the pump capacity at a given motor speed. Responsively, the controller114increases the speed of the electric motor102to cause the pump104to increase flow output to an amount that meets the flow demand.

Conversely, if flow demand by the hydraulic circuit202(e.g., by the hydraulic cylinder actuators224-230) decreases, the pressure level of fluid output by the pump104, and thus the pressure level of fluid provided to the hydraulic line110increases as the pump104provides more flow than being consumed by the valve assembly204. Responsively, the controller114decreases the speed of the electric motor102to cause the pump104to decrease flow output to an amount that meets the flow demand. This way, the system200operates efficiently as the pump104provides sufficient flow to operate the hydraulic circuit202, as opposed to providing a particular fixed amount of fluid flow output regardless of the flow demand.

In an example, the inverse relation between the speed of the electric motor102and the pressure level in the hydraulic line110can be an inverse proportional relationship. For instance, if the pressure level in the hydraulic line110is 280 psi, the controller114operates the electric motor102at a standby speed, e.g., 600 revolutions per minute (RPM). If the pressure level in the hydraulic line110decreases to 0 psi (over-demand scenario where all flow from the pump104is consumed by the hydraulic cylinder actuators224-230), the controller114operates the electric motor102at a maximum speed, e.g., 2000 RPM. An inverse proportional relationship, indicates that the controller114varies the speed linearly with the pressure level such that as the pressure level increases, the speed decreases and vice versa. However, in other examples, the inverse relationship is not linear. Rather, an inverse non-linear relationship or schedule can be tuned as desired.

Without the valve116, the hydraulic line110is directly coupled to the fluid reservoir106, and thus pressure level in the hydraulic line110remains at a pressure level substantially equal to the pressure level of fluid in the fluid reservoir106regardless of flow demand. The presence of the valve116allows pressure level in the hydraulic line110to vary, thereby indicating the amount of flow demand by the hydraulic circuit202.

The valve116can take several forms. As mentioned above, the valve116is configured to create a counter or back pressure and allow pressure level in the hydraulic line110to increase. Further, the valve116can be configured to limit the maximum pressure level in the hydraulic line110. The valve116can also be configured to preclude back-flow from the fluid reservoir106to the hydraulic line110. As such, the valve116can be a relief valve or any valve or combination of components that mimics the operation of a relief valve.

FIG.3illustrates a partial view of the system200with the valve116configured as a relief valve300, in accordance with an example implementation. The relief valve300is a pressure relief valve (PRV) configured to control or limit the pressure in the hydraulic line110. When the pressure level of fluid from the pump104is sufficient to overcome the load-sense fluid pressure signal and the biasing force of the spring140, the unloading valve232opens and fluid flows to the hydraulic line110.

Pressure of fluid in the hydraulic line110can increase or build up until it reaches a pressure setting of the relief valve300. When the pressure setting is exceeded, the relief valve300opens, and fluid is allowed to flow to the fluid reservoir106. Once the pressure level is reduced to a level less than the pressure setting (e.g., when flow demand of the hydraulic circuit202increases), the relief valve300closes again. Thus, the relief valve300allows pressure level to vary in the hydraulic line110, thereby enabling the pressure sensor112to measure the pressure level in the hydraulic line110and provide an indication of the flow demand by the hydraulic circuit202as described above to the controller114.

Further, the relief valve300can also limit the pressure level in the hydraulic line110such that it does not exceed a threshold value (e.g., 300 psi). This way, pressure level in the hydraulic line110is allowed to vary between zero and a maximum pressure level value, and the controller114can vary the speed of the electric motor102inversely with the pressure level in the range between a maximum motor speed and a standby speed.

Also, the relief valve300prevents back-flow from the fluid reservoir106into the hydraulic line110. For example, if pressure level in the hydraulic line110is zero when the unloading valve232is closed, and pressure level of fluid in the fluid reservoir106is slightly higher than zero, fluid can back flow to the hydraulic line110. The relief valve300blocks such back-flow from the fluid reservoir106such that the pressure level in the hydraulic line110provides an accurate indication of the flow demanded by the hydraulic circuit202.

Other configurations can be used to accomplish the same operations of the relief valve300described above.FIG.4illustrates a partial view of the system200with the valve116configured as a combination of a spring-loaded check valve400in parallel with an orifice402, in accordance with an example implementation. Both the spring-loaded check valve400and the orifice402fluidly couple the hydraulic line110to the fluid reservoir106.

The spring-loaded check valve400can have a movable element such as a ball or poppet biased by a spring toward a seated position. As long as pressure level of fluid in the hydraulic line110is not sufficient to overcome the spring, the movable elements remains seated, blocking fluid flow to the fluid reservoir106.

The orifice402can be configured to have a small size such that the orifice402is “saturated,” with a small amount of fluid flow, i.e., allows pressure level of fluid in the hydraulic line110to increase or build up as the orifice402restricts fluid flow to the fluid reservoir106. Pressure level of fluid in the hydraulic line110is allowed to increase until it reaches a pressure setting determined by the spring of the spring-loaded check valve400. Once the pressure setting is reached, the spring-loaded check valve400opens to allow fluid flow to the fluid reservoir106. With this configuration, the combination of the spring-loaded check valve400and the orifice402can operate similar to the relief valve300.

As mentioned above, in the system200, the pump104is configured as a fixed displacement pump. Thus, the pump104provides a fixed amount of fluid flow at a particular speed of the electric motor102. To vary the output flow rate of the pump104, the controller114changes the speed of the electric motor102. In other example implementations, a variable displacement pump can be used. In this example, in addition or alternative to changing the speed of the electric motor10to change fluid flow rate, the controller114can change the displacement of the pump to change the fluid flow rate output by the pump. In another example, the controller114can change the displacement of the pump so as to change the torque load on the electric motor102in addition to the varying the speed of the electric motor102. This way, the controller114can control the pressure level and flow rate of fluid output by the pump104.

FIG.5illustrates a system500with a variable displacement pump502, in accordance with an example implementation. The system500is an example implementation of the system100. Also, the system500is the same as the system200except that rather than using a fixed displacement pump, the electric motor102drives a variable displacement pump.

The variable displacement pump502can have a block or cylinder housing a plurality of pistons therein. A spring pushes each piston against a swash plate504that is stationary. When the swash plate504is not tilted and the cylinder rotates, the variable displacement pump502does not discharge fluid. However, when the swash plate504is tilted such that it forms an angle relative to the block having the pistons, as the block rotates the pistons suck in fluid during half a revolution and push fluid out during the other half. Varying the tilt angle of the swash plate504varies the flow rate of fluid discharged from the variable displacement pump502. For example, the greater the angle, the further the pistons move, and the higher the fluid flow rate.

For a given motor speed of the electric motor102, varying the angle of the swash plate504varies the power output of the power unit. The power output can be determined as a multiplication of the flow rate by the pressure level of fluid output by the variable displacement pump502or a multiplication of the speed of the electric motor102by a torque applied by the electric motor102on the variable displacement pump502. Thus, for a given motor speed, varying the angle of the swash plate504can control the torque of the electric motor102.

The variable displacement pump502can have a control actuator mechanism that controls the angle of the swash plate504. For example, a cylinder-piston arrangement can be used, where a piston is coupled to the swash plate504. A solenoid valve can control fluid flow to the cylinder to move the piston and the swash plate504coupled thereto. The controller114is in communication with and is configured to command such solenoid valve. As such, the controller114can vary the angle of the swash plate504to control the torque load on the electric motor102.

This way, by controlling both the speed and the torque of the electric motor102, the controller114can adjust the output power of the electric motor102. As such, the controller114can vary the power consumption from the power source120. For instance, if the power source120is a battery, the controller114can increase the life of the battery and the inverter118by reducing power consumption when temperature level of either the battery or the inverter118exceeds a threshold value.

The systems200,500are example implementations of the system100. Other examples are possible. For example, rather than having a load-sensing closed-center valve assembly such as the valve assembly204, the methods and systems described herein can be used with an open-center valve.

FIG.6illustrates a system600with a hydraulic circuit602having a valve assembly604with an open-center configuration, in accordance with an example implementation. The system600is an example implementation of the system100when the hydraulic circuit108includes an open-center valve configuration. Components that are similar between the systems100,200and the system600are designated with the same reference numbers.

The valve assembly604includes an inlet section606, a first worksection608, a second worksection610, a third worksection612, a fourth worksection614, and an outlet section616. The worksections608-614are positioned adjacent to one another between the inlet section606and the outlet section616. The valve assembly604may have a greater or fewer number of valve sections based on an application and a number of actuators controlled by the valve assembly604.

The inlet section606has an inlet port618that is configured to be fluidly-coupled to the outlet port217of the pump104via inlet line619. The outlet section616has a reservoir port620that is configured to be fluidly-coupled to the fluid reservoir106via reservoir line621.

Each worksection of the worksections608-614includes a housing that defines therein a longitudinal bore configured to receive a spool that is axially movable in the longitudinal bore. The housing includes an open-center passage intercepting the longitudinal bore. The inlet section606and the outlet section616also have respective open-center passages. The respective open-center passages of the inlet section606, the worksections608-614, and the outlet section616together form an open-center passage622that traverses the valve assembly604.

The open-center passage622receives fluid provided to the inlet port618via branch623that can be formed in the inlet section606as depicted inFIG.6. As described below, the valve assembly604permits continual flow through the open-center passage622when all the spools of all worksections are in neutral non-operative positions. Upon shifting one or more spools to actuate the associated hydraulic cylinder actuators, the spools variably restricts or shuts off the open-center flow.

Also, the housing includes a return passage intercepting the longitudinal bore. The respective return passages of the worksections608-614together form a return passage624that traverses the valve assembly604. The return passage624is fluidly-coupled to the reservoir port620via the outlet section616, and is thus fluidly-coupled to the fluid reservoir106.

Further, the housing includes a supply passage intercepting the longitudinal bore. The respective supply passages of the worksections608-614together form a supply passage626that traverses the valve assembly604. The supply passage626is fluidly-coupled to the inlet port618, and is thus fluidly-coupled to the pump104.

Each worksection is configured to control fluid flow to and from a respective hydraulic actuator of the hydraulic cylinder actuators224-230. For example, the first worksection608is fluidly-coupled to the first chamber221of the hydraulic cylinder actuator224via a first workport passage628, and is fluidly-coupled to the second chamber223of the hydraulic cylinder actuator224via a second workport passage630. Each workport passage includes an internal passage inside the housing of the first worksection608that is fluidly-coupled to a workport, and includes a fluid line that connects the workport to the respective chamber of the hydraulic cylinder actuator224.

The worksections610-614are similarly configured to control fluid flow to and from the hydraulic cylinder actuators226-230, respectively. Particularly, as depicted, the worksection610has workports passages that control fluid flow to and from the hydraulic cylinder actuator226, the worksection612has workport passages that control fluid flow to and from the hydraulic cylinder actuator228, and the worksection614has workports that control fluid flow to and from the hydraulic cylinder actuator230.

The spool in each worksection varies in diameter along its length to form lands of variable diameters capable of selectively interconnecting the various passages intercepting the longitudinal bore to control flow of fluid to and from the actuator. When the spool is in a neutral (e.g., unactuated, centered, or unbiased), the open-center passage622is open or unobstructed. As such, the open-center passage622is the path of least resistance, and fluid received at the inlet port618flows through the branch623, and then through the open-center passage622.

Fluid then exits the open-center passage622and the valve assembly604via open-center outlet port632. The open-center outlet port632can be referred to as a “power beyond” port that might be connected to other functions of a machine or vehicle to provide flow thereto. Further, as depicted inFIG.6, the hydraulic line110is fluidly-coupled to the open-center outlet port632.

Thus, when none of the spools of the worksections608-614is actuated, all the output flow of the pump104flows through the open-center passage622, exits the valve assembly604via the open-center outlet port632, and flows through the hydraulic line110. The valve116(either the relief valve300or the combination of the spring-loaded check valve400and the orifice402) allows pressure level to increase in the hydraulic line110to the maximum value allowed by the valve116. The pressure sensor112thus provides sensor information to the controller114indicating such high pressure level, and the controller114responsively commands the electric motor102to operate at a standby speed (low speed) to reduce the amount of flow and power loss.

Upon shifting the spool to actuate its associated actuator (e.g., when the spool of the first worksection608is shifted to actuate the hydraulic cylinder actuator224), the shifted spool restricts fluid flow through the open-center passage622. As fluid is restricted from flowing through the open-center passage622, fluid at the inlet port618flows through the supply passage626.

Further, when the spool is shifted, fluid flowing through the supply passage626flows to one of the workport passages of the worksection (e.g., either the first workport passage628or the second workport passage630) based on the direction of the shift of the spool. This way, fluid is provided to the respective hydraulic cylinder actuator to move its piston. Fluid returning from the hydraulic cylinder actuator is also directed by the spool to the return passage624, and then flows to the fluid reservoir106via the reservoir port620and the reservoir line621.

As the shifted spool restricts fluid flow through the open-center passage622, pressure level in the open-center passage622downstream from the spool decreases. Particularly, the spool forms a variable orifice between one or more of its lands with the internal surfaces of the housing of the respective worksection. The size of the variable orifice depends on the extent of movement or the stroke of the spool.

As fluid flows through such variable orifice, pressure level decreases, i.e., a pressure drop occurs from the pressure level of fluid received at the inlet port618to pressure level of fluid in the open-center passage622downstream from the spool. The larger the amount of fluid flow demanded by the hydraulic cylinder actuator (i.e., the larger the commanded speed for its piston), the larger the shift of the spool. The larger the shift of the spool, the larger the amount of fluid flow diverted to the supply passage626to feed the hydraulic cylinder actuator, and the more restrictive the variable orifice becomes. The more restrictive the variable orifice, the larger the pressure drop thereacross, and thus pressure level downstream of the spool in the open-center passage622and the hydraulic line110coupled thereto decreases further.

As the pressure level in the hydraulic line110decreases and the pressure sensor112provides sensor information indicative of the pressure level to the controller114, the controller114responsively commands the electric motor102to increase its speed to increase the output flow rate of the pump104to meet the demand. If the spool is shifted all the way (i.e., maximum stroke) indicating maximum flow demand by the hydraulic cylinder actuator(s), the open-center passage622can be blocked, and no fluid flow is provided to the open-center passage622or the hydraulic line110. In this case, pressure level in the hydraulic line110can be zero, and the controller114commands the electric motor102to operate at maximum speed.

Conversely, if flow demand by the hydraulic cylinder actuator decreases and the spool is shifted back toward the neutral position, the variable orifice becomes less restrictive, and the pressure level in the open-center passage622and the hydraulic line110increases.

Responsively, the controller114commands the electric motor102to decrease it speed to reduce the output flow rate of the pump104and meet the flow demand, without providing excessive flow.

Although the description above involves one spool being shifted, more spools can be actuated at the same time. The operations described above remain the same. In other words, the higher the flow demand by one or more hydraulic cylinder actuators, the smaller the pressure level in the open-center passage622and the hydraulic line110, and the controller114increases the speed of the electric motor102, and vice versa.

With this configuration, the controller114modifies, changes, or adjusts the speed of the electric motor102such that the speed of the electric motor102has an inverse relation with the pressure level in the hydraulic line110indicated by the pressure sensor112. If flow demand by the hydraulic circuit602(e.g., by the hydraulic cylinder actuators224-230) increases, the pressure level of fluid provided to the hydraulic line110decreases and can reach zero when the flow demand exceeds the pump capacity at a given motor speed (i.e., when one or more spools are shifted such that maximum flow is provided to the hydraulic cylinder actuators). Responsively, the controller114increases the speed of the electric motor102to cause the pump104to increase flow output to an amount that meets the flow demand.

Conversely, if flow demand by the hydraulic circuit602(e.g., by the hydraulic cylinder actuators224-230) decreases by shifting the spools back toward the neutral position, the pressure level of fluid provided to the hydraulic line110increases. Responsively, the controller114decreases the speed of the electric motor102to cause the pump104to decrease flow output to an amount that meets the flow demand, without providing excessive flow. This way, the system600operates efficiently as the pump104provides sufficient flow to operate the hydraulic circuit602, as opposed to a particular fixed amount of fluid flow rate output regardless of the flow demand.

In an example, the inverse relation between the speed of the electric motor102and the pressure level in the hydraulic line110can be an inverse proportional relationship. For instance, if the pressure level in the hydraulic line110is 280 psi, the controller114operates the electric motor102at a standby speed, e.g., 600 RPM. If the pressure level in the hydraulic line110decreases to 0 psi (over-demand scenario where all flow from the pump104is consumed by the hydraulic cylinder actuators224-230), the controller114operates the electric motor102at a maximum speed, e.g., 2000 RPM.

An inverse proportional relationship, indicates that the controller114varies the speed linearly. In other examples, the inverse relationship is not linear. Rather, an inverse non-linear relationship or schedule can be tuned as desired.

In describing the system600, the pump104is shown as a fixed displacement pump. However, it should be understood that the variable displacement pump502can be used instead. In this case, the controller114can control both the speed of the electric motor102, and can also control the torque output of the electric motor102by controlling the angle of the swash plate504as described above with respect toFIG.5.

Controlling the electric motor102can involve a closed-loop feedback system for precise control of speed and/or torque of the electric motor102. The closed-loop feedback system can be implemented in the controller114or the inverter118.

FIG.7illustrates a block diagram of a motor control system700of the electric motor102, in accordance with an example implementation. In an example, the motor control system700is implemented by or comprises the inverter118. In another example, the motor control system700is implemented by the controller114. In another example, a portion (e.g., speed loop) of the motor control system700is implemented by the controller114and another portion (e.g., the current loop) is implemented by the inverter118.

In the example implementation shown inFIG.7, the motor control system700is a closed-loop feedback control system having two control loops or control modules. The first control module is a speed control module702and the second control module is a current control module704.

The motor control system700receives the sensor information indicative of the pressure level in the hydraulic line110from the pressure sensor112. The motor control system700can have a look-up table705or something similar with an inverse relation between the pressure level and the commanded speed of the electric motor102as described above. The look-up table705converts the signal from the pressure sensor112to a speed command for the electric motor102(i.e., rotational speed of an output shaft coupled to a rotor of the electric motor102). The speed command is provided as a speed command signal706to the speed control module702.

The speed control module702then determines a reference current command708based on an error or difference between the speed command signal706and a speed sensor information signal714from a sensor coupled to the electric motor102. For example, the electric motor102includes a speed sensor (e.g., a tachometer) that provides the speed sensor information signal714to the speed control module702, which implements closed-loop speed control to control the speed of the electric motor102.

The speed control module702provides the reference current command708to the current control module704. The current control module704then provides a current command710to drive the electric motor102. The electric motor102includes a current sensor that provides current sensor information signal712to the current control module704, which implements closed-loop current control to control the current provided to the electric motor102.

As an example for illustration, the speed control module702and the current control module704can include a proportional-integral (PI) controller. A PI controller is used herein as an example for illustration; however, it should be understood that other types of closed-loop feedback control systems can be used, such as a proportional-integral-derivative (PID) controller.

FIG.8illustrates a block diagram of a PI controller800, in accordance with an example implementation. The PI controller800represents either a PI speed controller of the speed control module702or a PI current controller of the current control module704.

An error signal802representing the difference between a commanded value (e.g., commanded speed or current) and a feedback value (actual speed or actual current provided by a respective sensor) is determined. As such, the error signal802represents a difference between the speed command signal706and speed sensor information signal714or the difference between the reference current command708and the current sensor information signal712.

The error signal802is multiplied by a proportional gain KPat block804. The error signal802is also integrated (e.g., accumulated overtime) at block806. The result of the integration at the block806is then multiplied by an integral gain KIat block808. The output of the block808is then summed with the output of the block804at summation block810to generate a reference command812(e.g., the reference current command708or the current command710).

FIG.9is a flowchart of a method900for operating a system, in accordance with an example implementation. For example, the method900can be implemented with the systems200,500,600by the controller114.

The method900may include one or more operations, or actions as illustrated by one or more of blocks902-904. Although the blocks are illustrated in a sequential order, these blocks may also be performed in parallel, and/or in a different order than those described herein. Also, the various blocks may be combined into fewer blocks, divided into additional blocks, and/or removed based upon the desired implementation. It should be understood that for this and other processes and methods disclosed herein, flowcharts show functionality and operation of one possible implementation of present examples. Alternative implementations are included within the scope of the examples of the present disclosure in which functions may be executed out of order from that shown or discussed, including substantially concurrent or in reverse order, depending on the functionality involved, as would be understood by those reasonably skilled in the art.

In addition, for the method900and other processes and operations disclosed herein, the flowchart shows operation of one possible implementation of present examples. In this regard, each block may represent a module, a segment, or a portion of program code, which includes one or more instructions executable by a processor (e.g., a processor or microprocessor of the controller114) for implementing specific logical operations or steps in the process. The program code may be stored on any type of computer readable medium or memory, for example, such as a storage device including a disk or hard drive. The computer readable medium may include a non-transitory computer readable medium or memory, for example, such as computer-readable media that stores data for short periods of time like register memory, processor cache and Random Access Memory (RAM). The computer readable medium may also include non-transitory media or memory, such as secondary or persistent long term storage, like read only memory (ROM), optical or magnetic disks, compact-disc read only memory (CD-ROM), for example. The computer readable media may also be any other volatile or non-volatile storage systems. The computer readable medium may be considered a computer readable storage medium, a tangible storage device, or other article of manufacture, for example. In addition, for the method900and other processes and operations disclosed herein, one or more blocks inFIG.9may represent circuitry or digital logic that is arranged to perform the specific logical operations in the process.

At block902, the method900includes receiving, at the controller114of an electrohydraulic power unit, sensor information from the pressure sensor112mounted to the hydraulic line110that fluidly couples the electrohydraulic power unit to the hydraulic circuit (e.g., the hydraulic circuit108,202,602) external to the electrohydraulic power unit, wherein the electrohydraulic power unit comprises the electric motor102and a pump (e.g., the pump104or the variable displacement pump502) coupled to, and driven by, the electric motor102, wherein the pump provides fluid flow to the hydraulic circuit, and wherein the hydraulic circuit provides a fluid signal to the hydraulic line110, wherein the fluid signal is indicative of a fluid flow demand of the hydraulic circuit.

At block904, the method900includes, based on the sensor information indicating a pressure level of the fluid signal in the hydraulic line110, controlling a speed of the electric motor102to vary fluid flow rate provided by the pump to the hydraulic circuit to meet the fluid flow demand.

The method900can further include any of the operations throughout the disclosure. For example, controlling the speed of the electric motor can include: controlling the speed of the electric motor via an inverse relationship between the pressure level of the fluid signal and the speed of the electric motor102, such that the speed of the electric motor102is increased to increase the fluid flow rate discharged by the pump as the pressure level of the fluid signal decreases.

In examples, the electrohydraulic power unit further includes: the fluid reservoir106containing fluid at a low pressure level, wherein the pump is configured to draw fluid from the fluid reservoir106and discharge the fluid flow to the hydraulic circuit. The electrohydraulic power unit can also include the valve116that fluidly couples the hydraulic line110to the fluid reservoir106, wherein the valve116is configured to allow the pressure level in the hydraulic line110to increase to a threshold pressure value before opening and relieving fluid to the fluid reservoir106.

In a first example, the valve116comprises the relief valve300. In another example, the spring-loaded check valve400and the orifice402disposed in parallel with the spring-loaded check valve400.

The hydraulic circuit can take different forms as described above with respect toFIGS.2and6, as examples.

The detailed description above describes various features and operations of the disclosed systems with reference to the accompanying figures. The illustrative implementations described herein are not meant to be limiting. Certain aspects of the disclosed systems can be arranged and combined in a wide variety of different configurations, all of which are contemplated herein.

Further, unless context suggests otherwise, the features illustrated in each of the figures may be used in combination with one another. Thus, the figures should be generally viewed as component aspects of one or more overall implementations, with the understanding that not all illustrated features are necessary for each implementation.

Additionally, any enumeration of elements, blocks, or steps in this specification or the claims is for purposes of clarity. Thus, such enumeration should not be interpreted to require or imply that these elements, blocks, or steps adhere to a particular arrangement or are carried out in a particular order.

Further, devices or systems may be used or configured to perform functions presented in the figures. In some instances, components of the devices and/or systems may be configured to perform the functions such that the components are actually configured and structured (with hardware and/or software) to enable such performance. In other examples, components of the devices and/or systems may be arranged to be adapted to, capable of, or suited for performing the functions, such as when operated in a specific manner.

By the term “substantially” or “about” it is meant that the recited characteristic, parameter, or value need not be achieved exactly, but that deviations or variations, including for example, tolerances, measurement error, measurement accuracy limitations and other factors known to those with skill in the art, may occur in amounts that do not preclude the effect the characteristic was intended to provide.

The arrangements described herein are for purposes of example only. As such, those skilled in the art will appreciate that other arrangements and other elements (e.g., machines, interfaces, operations, orders, and groupings of operations, etc.) can be used instead, and some elements may be omitted altogether according to the desired results. Further, many of the elements that are described are functional entities that may be implemented as discrete or distributed components or in conjunction with other components, in any suitable combination and location.

While various aspects and implementations have been disclosed herein, other aspects and implementations will be apparent to those skilled in the art. The various aspects and implementations disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope being indicated by the following claims, along with the full scope of equivalents to which such claims are entitled. Also, the terminology used herein is for the purpose of describing particular implementations only, and is not intended to be limiting.

Embodiments of the present disclosure can thus relate to one of the enumerated example embodiments (EEEs) listed below.

EEE 1 is a system comprising: an electric motor: a pump coupled to, and driven by, the electric motor: a hydraulic circuit fluidly-coupled to the pump and configured to receive fluid flow from the pump: a hydraulic line fluidly-coupled to the hydraulic circuit, wherein the hydraulic circuit is configured to provide a fluid signal to the hydraulic line, wherein the fluid signal is indicative of a fluid flow demand of the hydraulic circuit: a pressure sensor mounted to the hydraulic line and configured to provide sensor information indicative of pressure level of fluid in the hydraulic line; and a controller configured to perform operations comprising: receiving the sensor information from the pressure sensor, and based on the pressure level indicated by the sensor information, controlling a speed of the electric motor to vary fluid flow rate provided by the pump to the hydraulic circuit to meet the fluid flow demand.

EEE 2 is the system of EEE 1, wherein controlling the speed of the electric motor comprises: increasing the speed of the electric motor to increase the fluid flow rate provided by the pump as the pressure level in the hydraulic line decreases.

EEE 3 is the system of any of EEEs 1-2, further comprising: a fluid reservoir containing fluid at a low pressure level, wherein the pump is configured to draw fluid from the fluid reservoir and discharge the fluid flow to the hydraulic circuit; and a valve fluidly-coupling the hydraulic line to the fluid reservoir, wherein the valve is configured to allow the pressure level in the hydraulic line to increase to a threshold pressure value before opening and relieving fluid to the fluid reservoir.

EEE 4 is the system of EEE 3, wherein the valve comprises a relief valve.

EEE 5 is the system of EEE 3, wherein the valve comprises: a spring-loaded check valve; and an orifice disposed in parallel with the spring-loaded check valve.

EEE 6 is the system of any of EEEs 1-5, wherein the hydraulic circuit comprises: a valve assembly comprising a plurality of worksections, each worksection configured to control fluid flow to and from a respective hydraulic actuator, wherein the valve assembly comprises a load-sense passage traversing the plurality of worksections and configured to communicate a load-sense fluid pressure signal that represents highest load-induced pressure among respective hydraulic actuators controlled by the plurality of worksections; and an unloading valve comprising: (i) an inlet port configured to receive fluid from the pump, (ii) a pilot port configured to receive the load-sense fluid pressure signal, and (iii) an outlet port fluidly-coupled to the hydraulic line to provide the fluid signal thereto.

EEE 7 is the system of EEE 6, wherein the unloading valve further comprises: a movable element, wherein the load-sense fluid pressure signal applies a first fluid force on the movable element, and wherein fluid from the inlet port applies a second fluid force on the movable element opposite the first fluid force: and a spring applying a biasing force on the movable element, wherein: when the second fluid force overcomes the first fluid force and the biasing force, the unloading valve opens to provide the fluid signal to the hydraulic line that is fluidly coupled to the outlet port, such that the pressure level of the fluid signal is based on a difference between the second fluid force and a combination of the first fluid force and the biasing force, and when a combined force of the second fluid force and the biasing force exceeds the first fluid force, the unloading valve blocks fluid flow to the hydraulic line, such that the pressure level of the fluid signal is substantially zero.

EEE 8 is the system of any of EEEs 1-5, wherein the hydraulic circuit comprises: a valve assembly comprising a plurality of worksections, each worksection configured to control fluid flow to and from a respective hydraulic actuator, wherein the valve assembly comprises: (i) a supply passage fluidly-coupled to the pump, and (ii) an open-center passage configured to receive fluid from the pump and is fluidly-coupled to the hydraulic line, wherein: when the plurality of worksections are unactuated, fluid flow from the pump is provided to the open-center passage, and then to the hydraulic line, and when one or more of the plurality of worksections are actuated, fluid flow to the open-center passage and the hydraulic line is restricted, such that fluid flow is provided to the supply passage, thereby reducing the pressure level of the fluid signal in the hydraulic line; and a valve disposed downstream from the plurality of worksections and configured to fluidly-couple the hydraulic line to the fluid reservoir, wherein the valve is configured to allow the pressure level in the hydraulic line to increase to a threshold pressure value before opening and relieving fluid to the fluid reservoir.

EEE 9 is an electrohydraulic power unit comprising: an electric motor: a pump coupled to, and driven by, the electric motor, wherein the pump is configured to provide fluid flow to a hydraulic circuit external to the electrohydraulic power unit: a pressure sensor configured to measure a pressure level of a fluid signal received from the hydraulic circuit, wherein the fluid signal is indicative of a fluid flow demand of the hydraulic circuit: and a controller configured to perform operations comprising: receiving sensor information from the pressure sensor indicating the pressure level of the fluid signal, and based on the pressure level indicated by the sensor information, controlling a speed of the electric motor to vary fluid flow rate discharged from the pump to meet the fluid flow demand of the hydraulic circuit.

EEE 10 is the electrohydraulic power unit of EEE 9, wherein controlling the speed of the electric motor comprises: controlling the speed of the electric motor via an inverse relationship between the pressure level of the fluid signal and the speed of the electric motor, such that the speed of the electric motor is increased to increase the fluid flow rate discharged by the pump as the pressure level of the fluid signal decreases.

EEE 11 is the electrohydraulic power unit of any of EEEs 9-10, further comprising: a fluid reservoir containing fluid at a low pressure level, wherein the pump is configured to draw fluid from the fluid reservoir and discharge the fluid flow to the hydraulic circuit; and a valve fluidly-coupling the fluid signal to the fluid reservoir, wherein the valve is configured to allow the pressure level of the fluid signal to increase to a threshold pressure value before opening and relieving fluid to the fluid reservoir.

EEE 12 the electrohydraulic power unit of EEE 11, wherein the valve comprises a relief valve.

EEE 13 is the electrohydraulic power unit of EEE 11, wherein the valve comprises: a spring-loaded check valve: and an orifice disposed in parallel with the spring-loaded check valve.

EEE 14 is a method comprising: receiving, at a controller of an electrohydraulic power unit, sensor information from a pressure sensor mounted to a hydraulic line that fluidly couples the electrohydraulic power unit to a hydraulic circuit external to the electrohydraulic power unit, wherein the electrohydraulic power unit comprises an electric motor and a pump coupled to, and driven by, the electric motor, wherein the pump provides fluid flow to the hydraulic circuit, and wherein the hydraulic circuit provides a fluid signal to the hydraulic line, wherein the fluid signal is indicative of a fluid flow demand of the hydraulic circuit; and based on the sensor information indicating a pressure level of the fluid signal in the hydraulic line, controlling a speed of the electric motor to vary fluid flow rate provided by the pump to the hydraulic circuit to meet the fluid flow demand.

EEE 15 is the method of EEE 14, wherein controlling the speed of the electric motor comprises: controlling the speed of the electric motor via an inverse relationship between the pressure level of the fluid signal and the speed of the electric motor, such that the speed of the electric motor is increased to increase the fluid flow rate discharged by the pump as the pressure level of the fluid signal decreases.

EEE 16 is the method of any of EEEs 14-15, wherein the electrohydraulic power unit further comprises: a fluid reservoir containing fluid at a low pressure level, wherein the pump is configured to draw fluid from the fluid reservoir and discharge the fluid flow to the hydraulic circuit; and a valve fluidly-coupling the hydraulic line to the fluid reservoir, wherein the valve is configured to allow the pressure level in the hydraulic line to increase to a threshold pressure value before opening and relieving fluid to the fluid reservoir.

EEE 17 is the method of EEE 16, wherein the valve comprises a relief valve or a combination of spring-loaded check valve and an orifice disposed in parallel with the spring-loaded check valve.

EEE 18 is the method of EEE 16, wherein the pump is a variable displacement pump having a swash plate, and wherein the method further comprises changing an angle of the swash plate of the pump.

EEE 19 is the method of any of EEEs 14-18, wherein the hydraulic circuit comprises: a valve assembly comprising a plurality of worksections, each worksection configured to control fluid flow to and from a respective hydraulic actuator, wherein the valve assembly comprises a load-sense passage traversing the plurality of worksections and configured to communicate a load-sense fluid pressure signal that represents highest load-induced pressure among respective hydraulic actuators controlled by the plurality of worksections; and an unloading valve comprising: (i) an inlet port configured to receive fluid from the pump, (ii) a pilot port configured to receive the load-sense fluid pressure signal, (iii) an outlet port fluidly-coupled to the hydraulic line to provide the fluid signal thereto, (iv) a movable element, wherein the load-sense fluid pressure signal applies a first fluid force on the movable element, and wherein fluid from the inlet port applies a second fluid force on the movable element opposite the first fluid force, and (v) a spring applying a biasing force on the movable element, wherein: when the second fluid force overcomes the first fluid force and the biasing force, the unloading valve opens to provide the fluid signal to the hydraulic line that is fluidly coupled to the outlet port, such that the pressure level of the fluid signal is based on a difference between the second fluid force and a combination of the first fluid force and the biasing force, and when a combined force of the second fluid force and the biasing force exceeds the first fluid force, the unloading valve blocks fluid flow to the hydraulic line, such that the pressure level of the fluid signal is substantially zero.

EEE 20 is the method of any of EEEs 14-18, wherein the hydraulic circuit comprises: a valve assembly comprising a plurality of worksections, each worksection configured to control fluid flow to and from a respective hydraulic actuator, wherein the valve assembly comprises: (i) a supply passage fluidly-coupled to the pump, and (ii) an open-center passage configured to receive fluid from the pump and is fluidly-coupled to the hydraulic line, wherein: when the plurality of worksections are unactuated, fluid flow from the pump is provided to the open-center passage, and then to the hydraulic line, and when one or more of the plurality of worksections are actuated, fluid flow to the open-center passage and the hydraulic line is restricted, such that fluid flow is provided to the supply passage, thereby reducing the pressure level of the fluid signal in the hydraulic line.