EP4689415A1

EP4689415A1 - Cooling configuration for an electric motor driving an electrohydraulic actuator

Info

Publication number: EP4689415A1
Application number: EP24705338.2A
Authority: EP
Inventors: Andrea Vacca; Hassan ASSAF; Satish Kumar Raju KALIDINDI; Federico Zappaterra
Original assignee: Parker Hannifin Corp
Current assignee: Parker Hannifin Corp
Priority date: 2023-03-30
Filing date: 2024-01-18
Publication date: 2026-02-11
Also published as: WO2024205692A1

Abstract

An example hydraulic system includes: a hydraulic cylinder actuator comprising a cylinder and a piston, wherein the piston divides an internal space of the cylinder into a first chamber and a second chamber, and wherein the hydraulic cylinder actuator is unbalanced; a pump; an electric motor configured to drive the pump to provide fluid flow to the first chamber or the second chamber of the hydraulic cylinder actuator to drive the piston; and a reservoir that is fluidly coupled to the electric motor, wherein the reservoir is configured to provide boost fluid flow or receive excess fluid flow via the electric motor such that the boost fluid flow or the excess fluid flow cools the electric motor.

Description

Cooling Configuration for an Electric Motor Driving an Electrohydraulic Actuator

CROSS REFERENCE TO RELATED APPLICATION

[0001] The present application claims priority to U.S. Provisional Patent Application No. 63/493,001, filed on March 30, 2023, the entire contents of which are herein incorporated by reference as if fully set forth in this description.

BACKGROUND

[0002] A work machine, such as hydraulic excavators, wheel loaders, loading shovels, backhoe shovels, mining equipment, industrial machinery and the like, can have one or more actuated components such as lifting and/or tilting arms, booms, buckets, steering and turning functions, traveling means, etc. Commonly, in such machines, a prime mover drives a hydraulic pump for providing fluid to the actuators. Open-center or closed center valves can control the flow of fluid to the actuators. Such valves are characterized by large power losses due to throttling flow therethrough. Further, such conventional systems may involve providing a constant amount of flow from a pump regardless of how many of the actuators is being used. Thus, such systems are characterized by poor efficiencies.

[0003] It may thus be desirable to have a hydraulic system that enhances efficiency of a work machine. With the recent trend toward electrification due to the emission regulations, some hydraulic systems have been configured to include decentralized or distributed electrohydraulic actuators (EHAs) that reduce throttling losses and enables energy recovery from overrunning loads. [0004] An example EHA may include an electrohydraulic power unit having an electric motor driving a pump to provide fluid flow to an actuator such as a linear hydraulic actuator cylinder or hydraulic motor. During operation of the electrohydraulic power unit, the electric motor and pump generate heat. Efficiently cooling such power unit may improve their power density (e.g., amount of power produced per volume of the power unit).

[0005] In one example, the electric motor can be are air-cooled. In this example, a fan can be used to provide air flow to reduce the temperature of the electric motor via forced convection. However, solutions involving air cooling are typically not compact and might not provide sufficient cooling capacity.

[0006] In another example, the power unit can be cooled via a liquid cooling configuration. In one instance, cooling liquid that is different from the working fluid of the hydraulic circuit can be used to cool the power unit. However, to implement such cooling method, external piping is used, which complicates the system and renders it less reliable.

[0007] In another configuration, the working fluid could be used for cooling the power unit. Particularly, the return working fluid of the hydraulic circuit, the pressurized outlet pump flow, or the leakage of the pump can be used to cool the power unit. However, there are disadvantages associated with each of these methods.

[0008] Using leakage fluid from the pump, which is characterized by low flow rates, is typically not sufficient to cool the electrical motor. Particularly, the leakage flow might not be circulated inside the electrical motor casing, and the leakage fluid may have a high temperature as compared to the pump inlet and outlet flow, thereby reducing the capacity of leakage flow to absorb heat. [0009] If pressurized outlet pump flow is used for cooling, the pump’s volumetric efficiency may be reduced, which is undesirable and may necessitate using a pump with a higher displacement to achieve the system requirements due to losing some of the flow to cool the electrohydraulic power unit. Configurations involving the use of the return fluid (e.g., pump inlet fluid) might not provide sufficient cooling capacity, particularly when the return fluid flow rate is not sufficient. Further, routing such return fluid to cool the electrohydraulic power unit may increase the complexity of the hydraulic circuit, which may be undesirable.

[0010] As such, there remains a need for a cooling configuration of an electrohydraulic power unit that is compact and efficient. It is with respect to these and other considerations that the disclosure made herein is presented.

SUMMARY

[0011] The present disclosure describes implementations that relate to a cooling configuration for an electric motor driving an electrohydraulic actuator.

[0012] In a first example implementation, the present disclosure describes a hydraulic system. The hydraulic system includes: a hydraulic cylinder actuator comprising a cylinder and a piston, wherein the piston divides an internal space of the cylinder into a first chamber and a second chamber, and wherein the hydraulic cylinder actuator is unbalanced such that a first fluid flow rate of fluid provided to the first chamber or the second chamber to drive the piston in a given direction is different from a second fluid flow rate of fluid discharged from the other chamber as the piston moves; a pump configured to be a bi-directional fluid flow source; an electric motor configured to drive the pump in opposite rotational directions to provide fluid flow to the first chamber or the second chamber of the hydraulic cylinder actuator to drive the piston; and a reservoir that is fluidly coupled to the electric motor, wherein the reservoir is configured to provide boost fluid flow or receive excess fluid flow comprising a difference between the first fluid flow rate and the second fluid flow rate via the electric motor, such that the boost fluid flow or the excess fluid flow cools the electric motor.

[0013] In a second example implementation, the present disclosure describes a method of operating the hydraulic system of the first example implementation.

[0014] The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, implementations, and features described above, further aspects, implementations, and features will become apparent by reference to the figures and the following detailed description. BRIEF DESCRIPTION OF THE FIGURES

[0015] The novel features believed characteristic of the illustrative examples are set forth in the appended claims. The illustrative examples, however, as well as a preferred mode of use, further objectives and descriptions thereof, will best be understood by reference to the following detailed description of an illustrative example of the present disclosure when read in conjunction with the accompanying Figures.

[0016] Figure 1 illustrates is a block diagram of a hydraulic system using a reservoir as a source of boost and cooling fluid flow, in accordance with an example implementation.

[0017] Figure 2 illustrates a schematic of a hydraulic system, in accordance with an example implementation.

[0018] Figure 3 illustrates the hydraulic system of Figure 2 operating in a first mode of operation involving extending a piston while being subjected to a resistive load, in accordance with an example implementation.

[0019] Figure 4 illustrates the hydraulic system of Figure 2 operating in a second mode of operation involving extending a piston while being subjected to an assistive load, in accordance with an example implementation.

[0020] Figure 5 illustrates the hydraulic system of Figure 2 operating in a third mode of operation involving retracting a piston while being subjected to a resistive load, in accordance with an example implementation.

[0021] Figure 6 illustrates the hydraulic system of Figure 2 operating in a fourth mode of operation involving retracting a piston while being subjected to an assistive load, in accordance with an example implementation. [0022] Figure 7 illustrates a schematic representation of an integrated electrohydraulic actuator, in accordance with an example implementation.

[0023] Figure 8 is a flowchart of a method of operating a hydraulic system, in accordance with an example implementation.

DETAILED DESCRIPTION

[0024] An example hydraulic machine such as an excavator can use multiple hydraulic actuators to accomplish a variety of tasks. Many electric hybrid and battery powered machines use multiple hydraulic cylinders and electric motors to accomplish a variety of tasks. Enhancing efficiency of the machine is desirable, enabling a reduction in hybrid internal combustion engine and/or battery size while reducing the cost of thermal management of the battery.

[0025] An example system approach that enhances efficiency comprises an on-demand, closed- circuit system with a dedicated hydrostatic pump and electric motor for each actuator of the machine. This approach can enhance efficiency by eliminating valve metering characterizing conventional systems, pressure overproduction, and standby losses, while enabling hydraulic to electric energy recovery.

[0026] The combination of the hydrostatic pump and electric motor can be referred to as an electrohydraulic power unit. As described in more detail below, when such electrohydraulic power unit is used to operate an unbalanced actuator (e.g., a hydraulic cylinder actuator with chambers having different volumes), a reservoir can be used as a source of fluid to provide boost fluid to the unbalanced actuator. Such reservoir thus makes up for differential fluid flow rates between fluid provided to the actuator and fluid discharged from the actuator. The reservoir may also absorb excess flow when the fluid flow rate discharged from the actuator is larger than the flow rate of fluid provided to the actuator.

[0027] During operation, the electrohydraulic power unit generates heat that can be damaging to the electrohydraulic power unit and other components of the system. It may thus be desirable to cool the electrohydraulic power unit efficiently. [0028] Disclosed herein are systems and method associated with using a reservoir to provide excess or boost fluid to the actuator and to receive excess fluid from the actuator. Further, the fluid provided from the reservoir or returning to the reservoir flows through the electrohydraulic power unit (e.g., through the electric motor of the electrohydraulic power unit) to cool it.

[0029] This configuration may enhance cooling efficiency and increase the power density of the electrohydraulic power unit. Particularly, the reservoir is capable of providing enough fluid flow rate to cool the electric motor compared to configurations involving leakage flow or return flow of the pump. Further, by not using pump outlet flow to cool the electric motor, the volumetric efficiency of the pump is enhanced. In other words, there is no need to oversize the pump to account for cooling fluid being drawn from the pump outlet.

[0030] Figure 1 is a block diagram of a hydraulic system 100 using a reservoir 102 as a source of boost and cooling fluid flow, in accordance with an example implementation. The hydraulic system 100 includes a hydraulic cylinder actuator 104 having a cylinder 106 and a piston 108 slidably accommodated in the cylinder 106 and configured to move in a linear direction therein.

[0031] The piston 108 includes a piston head 110 and a rod 112 extending from the piston head 110 along a central longitudinal axis direction of the cylinder 106. The rod 112 is coupled to a load 114 (that represents, for example, an implement of a machine, e.g., boom, arm, or bucket, and any forces applied thereto). The piston head 110 divides the internal space of the cylinder 106 into a first chamber 116 and a second chamber 118.

[0032] The first chamber 116 can be referred to as head-side chamber as the fluid therein interacts with the piston head 110, and the second chamber 118 can be referred to as rod-side chamber as the rod 112 is disposed partially therein. Fluid can flow to and from the first chamber 116 through a workport 117, and can flow to and from the second chamber 118 through a workport 119. [0033] The piston head 110 can have a diameter DH, whereas the rod 112 can have a diameter DR. As such, fluid in the first chamber 116 interacts with a cross-sectional surface area of piston head £j2

110 that can be referred to as piston head area and is equal to A_H = n —. On the other hand, fluid in the second chamber 118 interacts with an annular surface area of the piston 108 that can be referred to as piston annular area A_Annuiar = n

[0034] The area AAnnuiar is smaller than the piston head area AH. Thus, as the piston 108 extends (e.g., moves to the right in Figure 1) or retracts (e.g., moves to the left in Figure 1) within the cylinder 106, the amount of fluid flow QA going into or being discharged from the first chamber 116 is greater than the amount of fluid flow Qa being discharged from or going into the second chamber 118.

[0035] Particularly, if the piston 108 is moving at a particular velocity V, then Q_A = A_HV is greater than Q_a = A_AnnularV. The difference in flow can be determined as Q_A — Q_a = A_RV, where AT? is the cross-sectional area of the rod 112 and is equal to 7i-^. With this configuration, the hydraulic cylinder actuator 104 can be referred to as an unbalanced actuator as fluid flow rate to/from the first chamber 116 is not equal to fluid flow rate to/from the second chamber 118.

[0036] The hydraulic system 100 has an electrohydraulic power unit 120 having an electric motor 122 and a pump 124. The electrohydraulic power unit 120 is configured to control the rate and direction of hydraulic fluid flow to and from the hydraulic cylinder actuator 104. Such control is achieved by controlling the speed and direction of the electric motor 122 and the pump 124, which is configured as a bi-directional fluid flow source.

[0037] The pump 124 has a first pump port 126 connected by a first fluid line 128 to the first chamber 116 of the hydraulic cylinder actuator 104, and has a second pump port 130 connected by a second fluid line 132 to the second chamber 118 of the hydraulic cylinder actuator 104. The term “fluid line” is used throughout herein to indicate one or more fluid passages, conduits or the like that provide the indicated connectivity.

[0038] The first pump port 126 and the second pump port 130 are configured to be both inlet and outlet ports based on direction of rotation of an output shaft 134 of the electric motor 122, which drives pump 124. As the electric motor 122 rotates the output shaft 134 in a first rotational direction, the pump 124 withdraws fluid from the first pump port 126 (inlet port in this case) and displaces fluid to the second pump port 130 (outlet port in this case). Conversely, as the electric motor 122 rotates the output shaft 134 in a second rotational direction, the pump 124 withdraws fluid from the second pump port 130 (inlet port in this case) and displaces fluid to the first pump port 126 (outlet port in this case).

[0039] Further, as described in more detail below, the electrohydraulic power unit 120 is configured to work in a pumping mode and a motoring mode. In the pumping mode, the electric motor 122 drives the pump 124 to provide fluid to drive the piston 108 against a resistive load.

[0040] In the motoring mode, the hydraulic cylinder actuator 104 is subjected to an assistive load (e g., the direction of force acting on the piston 108 is the same as the direction of motion of the piston 108). As such, in the motoring mode, fluid discharged from the hydraulic cylinder actuator 104 and returning to the electrohydraulic power unit 120 drives the pump 124, which in turn drives the electric motor 122. In this case, the electric motor 122 operates as an electric generator where fluid energy received at the electrohydraulic power unit 120 is converted to electric power by the electric motor 122. The electric power generated in this mode can be stored in a battery, for example. As such, the electric motor 122 can generally be referred to as an electric machine configured to operate as an electric motor and an electric generator. [0041] As depicted in Figure 1, the pump 124 and the hydraulic cylinder actuator 104 are configured in a closed-circuit, i.e., a closed-loop hydraulic circuit. The term “closed-circuit” is used herein to indicate that fluid is being recirculated in a loop between the pump 124 and the hydraulic cylinder actuator 104. Particularly, in the hydraulic system 100, the pump 124 provides fluid through the first pump port 126 to the workport 117 or through the second pump port 130 to the workport 119, and fluid being discharged from the other workport returns to the corresponding port of the pump 124. As such, fluid is being recirculated between the pump 124 and the hydraulic cylinder actuator 104.

[0042] In an example, the pump 124 can be a fixed displacement pump and the amount of fluid flow provided by the pump 124 is controlled by the speed of the electric motor 122 (i.e., by rotational speed of the output shaft 134 of the electric motor 122 coupled to the pump 124). For example, the pump 124 can be configured to have a particular pump displacement PD that determines the amount of fluid generated or provided by the pump 124 in, for example, cubic inches per revolution (in³/rev). The electric motor 122 can be running at a commanded speed having units of revolutions per minute (RPM). As such, multiplying the speed of the electric motor 122 by PD determines the fluid flow rate 0 in cubic inches per minute (in³/min) provided by the pump 124 to the hydraulic cylinder actuator 104.

[0043] The flow rate Q in turn determines the linear speed of the piston 108. For instance, if the electric motor 122 is driving the pump 124 is a first rotational direction to provide fluid to the first chamber 116, the piston 108 can extend at a speed V) = — . On the other hand, if the electric AH motor 122 is driving the pump 124 is a second rotational direction to provide fluid to the second chamber 118, the piston 108 can retract at a speed f₂ ⁼ — ~ —

^Annular [0044] As mentioned above, the hydraulic cylinder actuator 104 is unbalanced such that the amount of fluid flow rate provided to or discharged from the first chamber 116 is greater than the amount of fluid flow rate provided to or discharged from the second chamber 118. As such, the amount of fluid flow rate provided from or received at the first pump port 126 (to or from the first chamber 116) is greater than the amount of fluid flow rate provided from or received at the second pump port 130 (to or from the second chamber 118). Such discrepancy between the fluid flow rate provided by the pump 124 and fluid flow rate received thereat can cause cavitation and the pump 124 might not operate properly.

[0045] The hydraulic system 100 includes a reservoir 102 configured to boost the fluid flow rate, or receive any excess flow, to make up for such discrepancy in fluid flow rate. The reservoir 102 may be configured to provide fluid flow at a particular pressure range e.g., between 0 and 15 bar. As a particular example, the reservoir 102 can provide fluid at a pressure level of 4-5 bar.

[0046] The reservoir 102 can, for example, include an accumulator configured to provide fluid in the particular pressure range. In another example, the reservoir 102 is a tank or container storing fluid at atmospheric pressure or at a pressure level higher than atmospheric pressure.

[0047] The reservoir 102 is configured to provided boost fluid flow to and receive excess fluid from the hydraulic cylinder actuator 104. Notably, however, boost fluid provided to, and excess fluid returning from, the hydraulic cylinder actuator 104 first flows through or within a casing or housing 138 of the electric motor 122 to cool the electric motor 122.

[0048] Particularly, the electric motor 122 can be disposed within the housing 138, which is configured as an enclosure in which the stator and rotor of the electric motor 122 are disposed. In some example implementations, the pump 124 can also be integrated within the housing 138, such that the electrohydraulic power unit 120 comprises an assembly of the electric motor 122 and the pump 124 within the same housing.

[0049] When the hydraulic system 100 operates in a mode where boost fluid flow is provided to the hydraulic cylinder actuator 104, the boost flow is provided from the reservoir 102 via reservoir fluid line 140 to the electrohydraulic power unit 120, and particularly to the housing 138 which has a first motor port 142 to receive fluid from the reservoir 102.

[0050] Fluid may circulate or flow within or through the housing 138 to cool the electric motor 122. For example, the housing 138 may have channels formed therein through which fluid from the reservoir 102 flows to absorb heat generated by the electric motor 122. In another example, the fluid can be provided in a chamber within the housing 138 in which components of the electric motor 122 (e.g., the stator and rotor of the electric motor 122) are disposed. As fluid from the reservoir 102 flows through the chamber, it absorbs heat from the electric motor 122.

[0051] After flow from the reservoir 102 flows through the housing 138, the fluid is discharged through a second motor port 144 of the housing 138 to flow through a boost flow line 146 to valve(s) 148. The valve(s) 148 are configured to direct fluid flow between the boost flow line 146 and the hydraulic cylinder actuator 104, for example. With this configuration, the reservoir 102 is fluidly coupled to the valve(s) 148 and the hydraulic cylinder actuator 104 via the housing 138 of the electric motor 122, such that fluid provided by or returning to the reservoir 102 cools the electric motor 122.

[0052] The valve(s) 148 can include one or more valves including a shuttle valve, relief valves, check valves, etc. In an example, the valve(s) 148 can be configured as separate components connected together via fluid lines (e.g., hoses, pipes, etc ). In another example, the valve(s) 148 can be integrated in a valve assembly or manifold. The system described next with respect to Figure 2 is an example implementation of the hydraulic system 100. However, it should be understood that the implementation of Figure 2 is an example implementation for illustration only. Different types of reservoirs and valves could be used.

[0053] Figure 2 illustrates a schematic of a hydraulic system 200, in accordance with an example implementation. The hydraulic system 200 is an example implementation of the hydraulic system 100. Components that are common between the hydraulic system 100 and the hydraulic system 200 are designated with the same reference numbers.

[0054] The hydraulic system 200 includes an accumulator 202 that performs the operations of the reservoir 102. Particularly, as described in more detail below, the accumulator 202 is configured to provide boost fluid flow to the boost flow line 146 and receive excess fluid flow therefrom. However, as mentioned above, the accumulator 202 is fluidly coupled to the boost flow line 146 via the electric motor 122 such that fluid to and from the boost flow line 146 flows from and to the accumulator 202 via the housing 138 of the electric motor 122, thereby cooling the electric motor 122 by absorbing heat generated therefrom.

[0055] The accumulator 202 is configured as a pressure storage reservoir in which an incompressible hydraulic fluid is held under pressure that is applied by an external source of mechanical energy. The external source can be an engine, a spring, a raised weight, or a compressed gas. For example, the accumulator 202 can have a cylindrical chamber, which has a piston in it. This piston can be spring-loaded or can be pressurized by a gas disposed on one side of the piston.

[0056] As fluid is provided into the accumulator 202 (which operates as a sealed container having a fixed volume), fluid volume inside the accumulator 202 increases, and its pressure increases due to the spring or gas pressure acting on the other side of the piston. This way, the accumulator 202 can provide pressurized fluid via the reservoir fluid line 140 and the electric motor 122 to the boost flow line 146.

[0057] Other types of accumulators can be used. For instance, the accumulator 202 can be a bladder-type accumulator. Such accumulator can include a bladder fdled with nitrogen and fitted in a welded or forged steel pressure vessel. The bladder is made of an elastic material (elastomer), e.g., rubber. The gas pre-charge pressure can be adapted via the gas inlet/outlet valve on top of the bladder accumulator. When pressure level of hydraulic fluid within the accumulator decreases, the compressed gas in the bladder expands and pushes the stored fluid into the hydraulic circuit. Conversely, when fluid is provided to the accumulator, it compresses the bladder, thereby increasing pressure level of fluid within the accumulator.

[0058] The hydraulic system 200 includes a plurality of valves that represent the valve(s) 148 of the hydraulic system 100. For example, the hydraulic system 200 includes a pressure relief valve 204, a pressure relief valve 206, a reverse shuttle valve 208, a fdter 210, and a check valve 212. These components can be integrated into a valve assembly or manifold or can be separate components.

[0059] In some cases, the hydraulic cylinder actuator 104 can be subjected to a large force via the load 114, and such force causes over-pressurization in either of the chambers 116, 118. In other examples, pump 124 can also be subjected to over-pressurization at the pump ports 126, 130. To protect the pump 124 and/or the hydraulic cylinder actuator 104 from the possibility of overpressurization, the hydraulic system 200 includes the pressure relief valves 204, 206.

[0060] The pressure relief valve 204 is configured to protect the first chamber 116 and the first pump port 126. Particularly, the pressure relief valve 204 is connected between the first fluid line 128 and the second fluid line 132, and is configured to open and provide a fluid flow path from the first fluid line 128 to the second fluid line 132 when pressure level of fluid in the first fluid line 128 (e.g., in the first chamber 116 or at the first pump port 126) exceeds a threshold pressure value, such as 300 bar or 4350 pounds per square inch (psi).

[0061] Similarly, the pressure relief valve 206 is connected between the second fluid line 132 and the first fluid line 128. The pressure relief valve 206 is configured to open and provide a fluid flow path from the second fluid line 132 to the first fluid line 128 when pressure level of fluid in the second fluid line 132 (e.g., in the second chamber 118 or at the second pump port 130) exceeds a threshold pressure value, such as 300 bar or 4350 psi.

[0062] As mentioned above, the hydraulic cylinder actuator 104 is unbalanced such that the amount of fluid flow rate provided to or discharged from the first chamber 116 is greater than the amount of fluid flow rate provided to or discharged from the second chamber 118. However, the fluid flow rate at the first pump port 126 cannot be different from the fluid flow rate at the second pump port 130, and thus the hydraulic system 200 is configured to provide boost flow or absorb excess flow to make up for the difference in fluid flow rate.

[0063] Particularly, the hydraulic system 200 can include a reverse shuttle valve 208 configured to fluidly couple the chambers 116, 118 of the cylinder 106 to the boost flow line 146. The reverse shuttle valve 208 is configured to be responsive to pressure difference across the pump 124 (i.e., pressure difference between the first fluid line 128 and the second fluid line 132).

[0064] In an example, the reverse shuttle valve 208 can be configured as a pilot-operated, three- position shuttle valve having a shuttle element therein (e.g., a poppet or spool) the position of which is determined by differential pressure across the pump 124. The reverse shuttle valve 208 can have a first pilot port 214 fluidly coupled to the first fluid line 128 and a second pilot port 216 fluidly coupled to the second fluid line 132. [0065] The reverse shuttle valve 208 also has a boost port 218 fluidly coupled to the boost flow line 146. The reverse shuttle valve 208 is operated by differential pressure between the fluid lines 128, 132 to either: (i) connect the second fluid line 132 to the boost flow line 146 when pressure in the first fluid line 128 exceeds the pressure level in the second fluid line 132, or (ii) connect the first fluid line 128 to the boost flow line 146 when pressure in the second fluid line 132 exceeds the pressure level in the first fluid line 128.

[0066] For example, if the pump 124 is driven by the electric motor 122 to supply fluid to the first fluid line 128 for extension of the piston 108, the pressure differential across the pump 124 shifts the shuttle element of the reverse shuttle valve 208 to connect the boost port 218 to the second pilot port 216, thereby fluidly coupling the second fluid line 132 to the boost flow line 146 while blocking flow from the first fluid line 128 to the boost flow line 146. As such, the reverse shuttle valve 208 provides a fluid flow path from the boost flow line 146 to the second pump port 130 to make up for the difference between flow rate of fluid provided to the first chamber 116 and flow rate of fluid returning through the second fluid line 132 from the second chamber 118.

[0067] Conversely, when the pump 124 is driven in the opposite direction to retract the piston 108, the pressure differential across the pump 124 shifts the shuttle element of the reverse shuttle valve 208 to connect the first pilot port 214 to the boost port 218, thereby fluidly coupling the first fluid line 128 to the boost flow line 146 while blocking flow from the second fluid line 132 to the boost flow line 146. This way, the reverse shuttle valve 208 provides a fluid flow path for the excess flow of fluid returning through the first fluid line 128 from the first chamber 116 to the boost flow line 146. Different modes of operation of the hydraulic system 200 and the reverse shuttle valve 208 are described below with respect to Figures 3-6. [0068] The term “reverse” is ascribed to the reverse shuttle valve 208 as it differs from a traditional shuttle valve. A traditional shuttle valve may have a first inlet, a second inlet, and an outlet. A valve element moves freely within such traditional shuttle valve such that when pressure from fluid is exerted through a particular inlet, it pushes the valve element toward the opposite inlet. This movement may block the opposite inlet, while allowing the fluid to flow from the particular inlet to the outlet. This way, two different fluid sources can provide pressurized fluid to an outlet without back flow from one source to the other. The reverse shuttle valve 208 does not have a designated outlet port, but rather either provides fluid flow from the boost port 218 to the second pilot port 216 or provide fluid flow from the first pilot port 214 to the boost port 218.

[0069] In the example configuration described above, the reverse shuttle valve 208 is a pilot- operated valve where the shuttle element moves in response to differential pressure between the fluid lines 128, 132. In other examples, the reverse shuttle valve 208 can be electrically-actuated such that an electronic controller of the hydraulic system 200 can provide electric signals that move the shuttle element based on sensed pressure levels in the fluid lines 128, 132.

[0070] The filter 210 is configured to filter fluid in the boost flow line 146 to remove any contaminants in the fluid. The check valve 212 is configured to prevent back flow from the second fluid line 132 to the boost flow line 146.

[0071] The hydraulic system 200 is configured to operate in at least four modes of operation. A first mode of operation involves extending the piston 108 (e.g., moving the piston 108 to the right in Figure 2) while the piston 108 is subjected to a resistive load. The term “resistive” indicates that the load 114 applies a force on the piston 108 in a direction that is opposite to the direction of motion of the piston 108. A second mode of operation involves extending the piston 108 while the piston 108 is subjected to an assistive load. The term “assistive” indicates that the load 114 applies a force on the piston 108 that is in the same direction as the direction of motion of the piston 108. This could occur, for example, if the motion of the piston 108 is gravity assisted.

[0072] In the first and second modes of operation, the accumulator 202 is configured to provide boost flow through the electric motor 122 to the boost flow line 146. In other words, the accumulator 202 operates in a discharge mode, where fluid is being discharged from the accumulator 202.

[0073] A third mode of operation involves retracting the piston 108 (e.g., moving the piston 108 to the left in Figure 2) while the piston 108 is subjected to a resistive load. A fourth mode of operation involves retracting the piston 108 while the piston 108 is subjected to an assistive load. In the third and fourth modes of operation, the accumulator 202 is configured to receive excess flow from the boost flow line 146 through the electric motor 122. In other words, the accumulator 202 operates in a charge mode, where excess fluid is used to charge the accumulator 202.

[0074] Figures 3-6 show the four modes of operation of the hydraulic system 200. In Figures 3- 6, dashed lines represent low pressure fluid lines, and dotted-dashed lines represent high pressure fluid lines.

[0075] Figure 3 illustrates the hydraulic system 200 operating in the first mode of operation involving extending the piston 108 while being subjected to a resistive load, in accordance with an example implementation. To extend the piston 108 (i.e., move the piston 108 to the right in Figure 3), a controller of the hydraulic system 200 can send a command signal to a power electronics module to operate the electric motor 122 and drive the pump 124 in a first rotational direction. A fluid flow rate Q_A is thus provided from the first pump port 126 through the first fluid line 128 to the first chamber 116 to extend the piston 108. As the piston 108 extends, fluid is discharged from the second chamber 118 at a fluid flow rate Q_a to the second fluid line 132. [0076] At the same time, the accumulator 202 can provide make-up or boost flow Q_acc through the reservoir fluid line 140 through the electric motor 122 to the boost flow line 146. This way, the accumulator flow Q_acc cools (e.g., absorbs heat generated by) the electric motor 122 before flowing to the boost flow line 146.

[0077] As depicted in Figure 3, the high pressure fluid in the first fluid line 128 causes the reverse shuttle valve 208 to shift to a state where it fluidly couples the boost flow line 146 to the second fluid line 132. Particularly, the reverse shuttle valve 208 operates in a state where the second pilot port 216 is fluidly coupled to the boost port 218, and thus the boost flow provided by the accumulator 202 joins fluid discharged from the second chamber 118 in the second fluid line 132. The make-up or boost flow rate Q_acc provided by the accumulator 202 is determined as Q_acc — A_RV, where AR is the cross-sectional area of the rod 112 and J⁷ is the speed of the piston 108 as mentioned above. The combined flow rate Q_A = Q_a + Q_acc from the second chamber 118 and the accumulator 202 then flows to the second pump port 130.

[0078] As such, the amount of flow rate received at the second pump port 130 is substantially equal to the amount of flow rate provided by the pump 124 through the first pump port 126 and the first fluid line 128 to the first chamber 116. Notably, the fluid returning through the second fluid line 132 to the second pump port 130 from the chamber 118 has a low pressure level, and therefore, the boost flow Q_acc provided by the accumulator 202 can be provided at a low pressure level that matches the low pressure level of flow returning to the second pump port 130. For example, the boost flow can have a pressure level in the range of 0-15 bar compared to high pressure levels such as 300 bar that might be provided by the pump 124 to the first chamber 116 to extend the piston 108 against a resistive load. [0079] In this mode, the electrohydraulic power unit 120 (i.e., the electric motor 122 and the pump 124) provide hydraulic power PEHU to the hydraulic cylinder actuator 104 to move the piston 108 at a speed x against a resistive load F.

[0080] Figure 4 illustrates the hydraulic system 200 operating in the second mode of operation involving extending the piston 108 while being subjected to an assistive load, in accordance with an example implementation. In this mode of operation, the piston 108 can extend at a speed x with an assistive load F acting in the same direction.

[0081] As the piston 108 extends with assistance from the load, fluid in the first fluid line 128 is low pressure fluid, whereas fluid discharged from the second chamber 118 to the second fluid line 132 can be a high pressure fluid. The pump 124 receives fluid flow discharged from the second chamber 118 at the second pump port 130 at a flow rate of Q_a, and thus provides fluid to the first fluid line 128 at the same flow rate Q_a. In this case, the high pressure fluid received at the second pump port 130 drives the pump 124, which in turn drives the electric motor 122 in a regenerative mode, thereby generating power PEHU rather than consuming power.

[0082] Also, as depicted in Figure 4, the high pressure fluid in the second fluid line 132 causes the reverse shuttle valve 208 to shift to a state where it fluidly couples the boost flow line 146 to the first fluid line 128. Particularly, the reverse shuttle valve 208 operates in a state where the first pilot port 214 is fluidly coupled to the boost port 218, and thus the boost flow Q_acc provided by the accumulator 202 flows through the electric motor 122, then through the boost flow line 146 to the boost port 218, then to the first pilot port 214 to join fluid flow Q_a provided by the pump 124 in the first fluid line 128. This way, the accumulator flow Q_acc cools (e.g., absorbs heat generated by) the electric motor 122 before flowing to the boost flow line 146. The combined fluid flow

QA ⁼ Qa + Qacc is provided to the first chamber 116 of the hydraulic cylinder actuator 104. [0083] Notably, the fluid provided by the pump 124 to the first fluid line 128 has a low pressure level. Therefore, the boost flow Q_acc provided by the accumulator 202 can be provided at a low pressure level (e g., between 0 and 15 bar) that matches the low pressure level of flow provided via the first pump port 126.

[0084] Figure 5 illustrates the hydraulic system 200 operating in the third mode of operation involving retracting the piston 108 while being subjected to a resistive load, in accordance with an example implementation. To retract the piston 108 (i.e., move the piston 108 to the left in Figure 5), the controller of the hydraulic system 200 can send a command signal to a power electronics module to operate the electric motor 122 and drive the pump 124 in a second rotational direction, opposite the first rotational direction associated with extension of the piston 108. A fluid flow rate Q_a of high pressure fluid is thus provided from the second pump port 130 through the second fluid line 132 to the second chamber 118 to retract the piston 108. As the piston 108 retracts, fluid is discharged from the first chamber 116 at a fluid flow rate Q_A to the first fluid line 128.

[0085] As the pump 124 provides fluid flow rate Q_a at the second pump port 130, it receives the same amount of fluid flow rate at the first pump port 126. The difference in flow (excess flow) between Q_A and Q_a branches to the first pilot port 214 of the reverse shuttle valve 208 and is provided to the accumulator 202 as flow rate Q_acc to charge the accumulator 202.

[0086] Particularly, as depicted in Figure 5, the high pressure fluid in the second fluid line 132 causes the reverse shuttle valve 208 to shift to a state where it fluidly couples the boost flow line 146 to the first fluid line 128. Specifically, the reverse shuttle valve 208 operates in a state where the first pilot port 214 is fluidly coupled to the boost port 218, and thus the differential excess flow Qacc = QA ~ Qa flows from the first fluid line 128 to the first pilot port 214, then to the boost port

218, to the boost flow line 146, then through the electric motor 122 to the reservoir fluid line 140, then to the accumulator 202 to charge it. This way, the excess flow Q_acc cools the electric motor 122 before charging the accumulator 202.

[0087] In this mode, the electrohydraulic power unit 120 (i.e., the electric motor 122 and the pump 124) provide hydraulic power PEHU to the hydraulic cylinder actuator 104 to retract the piston 108 at a speed x against a resistive load F.

[0088] Figure 6 illustrates the hydraulic system 200 operating in the fourth mode of operation involving retracting the piston 108 while being subjected to an assistive load, in accordance with an example implementation. In this mode of operation, the piston 108 can retract at a speed x with an assistive load F acting in the same direction.

[0089] As the piston 108 retracts with assistance from the load, the pump 124 provides low pressure fluid through the second pump port 130 to the second fluid line 132, whereas fluid discharged from the first chamber 116 to the first fluid line 128 can be a high pressure fluid. The pump 124 receives flow discharged from the first chamber 116 at the first pump port 126 at a flow rate Q_A, and thus provides fluid to the first fluid line 128 at the same flow rate Q_A. In this case, the high pressure fluid received via the first fluid line 128 drives the pump 124, which in turn drives the electric motor 122 in a regenerative mode, thereby generating power PEHU rather than consuming power.

[0090] While the pump 124 provides fluid flow rate Q_A to the second fluid line 132, the second chamber 118 receives fluid flow rate Q_a. The differential or excess flow Q_A — Q_ais provided as accumulator flow Q_acc to charge the accumulator 202.

[0091] Particularly, as depicted in Figure 6, the high pressure fluid in the first fluid line 128 causes the reverse shuttle valve 208 to shift to a state where it fluidly couples the boost flow line 146 to the second fluid line 132. Specifically, the reverse shuttle valve 208 operates in a state where the second pilot port 216 is fluidly coupled to the boost port 218, and thus the excess flow Q_acc — QA ~ Qa flows from the second fluid line 132 to the second pilot port 216, to the boost port 218, then to the boost flow line 146, then through the electric motor 122 to the reservoir fluid line 140, then to the accumulator 202 to charge it. As such, the accumulator flow Q_acc cools the electric motor 122 before charging the accumulator 202.

[0092] In one example, components of the hydraulic systems 100, 200 (e.g., the accumulator 202, the valve(s) 148, the electrohydraulic power unit 120, and the hydraulic cylinder actuator 104) can be separate components connected to each other via fluid lines. However, in another example, such components can be integrated into a self-contained electrohydraulic actuator (EHA) unit, where the hydraulic cylinder actuator 104, accumulator 202, the valve(s) 148, and the electrohydraulic power unit 120 are integrated into a single unit or assembly to increase the power- to-volume ratio. This configuration may eliminate the need for couplings and hoses.

[0093] Further, in such integrated configuration, the cooling method described above where fluid provided to or from the accumulator 202 cools the electric motor 122 is advantageous as the working fluid is used to cool the electric motor 122 and no external cooling is required. This is particularly advantageous given the tight spaces in such an integrated configuration.

[0094] Figure 7 illustrates a schematic representation of an EHA 300, in accordance with an example implementation. As shown in Figure 7, the EHA 300 integrates the accumulator 202, the electrohydraulic power unit 120, the valve(s) 148, and the hydraulic cylinder actuator 104 into a single unit or assembly.

[0095] The electric motor 122 can have a stator 302 and a rotor 304 disposed within the stator 302.

The rotor 304 is coupled to the output shaft 134, which drives the pump 124. The electric motor 122 can have a housing or housing 305 that houses at least some of the components of the electric motor 122.

[0096] The electric motor 122 drive the pump 124, which then provides fluid to and receives return fluid from the hydraulic cylinder actuator 104. The pump 124 also provides fluid to and receives fluid from a manifold or valve block that integrates the valve(s) 148 (e.g., the reverse shuttle valve 208, the pressure relief valves 204, 206, the filter 210, and the check valve 212). The manifold or valve block is in fluid communication with the hydraulic cylinder actuator 104 to provide fluid thereto and received fluid therefrom.

[0097] The accumulator 202 is depicted as a piston-type accumulator having a piston 306 that separates a gas chamber 308 from a fluid chamber 310. When the accumulator 202 is in a discharge mode as the piston 108 extends, the gas in the gas chamber 308 pushes the piston 306 to cause fluid flow Q_acc to be discharged from the fluid chamber 310 through the first motor port 142 of the electric motor 122. Such fluid from the accumulator 202 flows within the housing 305 or through channels formed therein to cool the electric motor 122.

[0098] Fluid is then provided through the second motor port 144 and through fluid passages (that represent the boost flow line 146) to the manifold or valve block that integrates the valve(s) 148. The manifold or valve block then provides fluid to the hydraulic cylinder actuator 104 to extend the piston 108.

[0099] When the piston 108 retracts, fluid is discharged from the hydraulic cylinder actuator 104 and is provided to the pump 124 and to the valve block, then flows through the second motor port 144, through the electric motor 122, through the first motor port 142 to the fluid chamber 310 of the accumulator 202, thereby charging the accumulator 202 and compressing the gas in the gas chamber 308. Although a piston-type accumulator is depicted, other types of accumulators such as a bladder type accumulator could be used.

[00100] Figure 8 is a flowchart of a method 400 of operating a hydraulic system, in accordance with an example implementation. The method 400 can be used to operate the hydraulic system 100, 200, for example.

[00101] The method 400 may include one or more operations, or actions as illustrated by one or more of blocks 402-404. 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.

[00102] At block 402, the method 400 includes operating the electric motor 122 to drive the pump 124 to provide fluid flow via the first fluid line 128 to extend the piston 108 within the cylinder 106 of the hydraulic cylinder actuator 104 against a resistive load, wherein the piston 108 divides an internal space of the cylinder 106 into the first chamber 116 and the second chamber 118, and wherein the hydraulic cylinder actuator 104 is unbalanced such that a first fluid flow rate of fluid provided to the first chamber 116 via the first fluid line 128 to extend the piston is larger than a second fluid flow rate of fluid discharged from the second chamber 118 as the piston 108 extends, wherein fluid discharged from the second chamber 118 returns to the pump 124 via the second fluid line 132.

[00103] At block 404, the method 400 includes providing boost fluid flow from the reservoir 102 (e.g., the accumulator 202) through the electric motor 122 to the second fluid line 132 such that the boost fluid flow joins fluid returning to the pump 124 via the second fluid line 132 and makes up for a difference between the first fluid flow rate and the second fluid flow rate, and wherein the boost fluid flow cools the electric motor 122 as the boost fluid flow is provided from the reservoir 102 through the electric motor 122 to the second fluid line 132.

[00104] The method 400 can further include other steps as described throughout herein. For example, while the blocks 402, 404 are associated with operating the hydraulic system 100, 200 in the first mode of operation described above with respect to Figure 3, the method can also include steps of operating the hydraulic systems 100, 200 in the second, third, and fourth modes of operation associated with Figures 4-6, respectively.

[00105] 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.

[00106] 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. [00107] 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.

[00108] 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.

[00109] 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 skill in the art, may occur in amounts that do not preclude the effect the characteristic was intended to provide.

[00110] 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.

[00111] 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.

[00112] Embodiments of the present disclosure can thus relate to one of the enumerated example embodiment (EEEs) listed below.

[00113] EEE 1 a hydraulic system comprising: a hydraulic cylinder actuator comprising a cylinder and a piston, wherein the piston divides an internal space of the cylinder into a first chamber and a second chamber, and wherein the hydraulic cylinder actuator is unbalanced such that a first fluid flow rate of fluid provided to the first chamber or the second chamber to drive the piston in a given direction is different from a second fluid flow rate of fluid discharged from the other chamber as the piston moves; a pump configured to be a bi-directional fluid flow source; an electric motor configured to drive the pump in opposite rotational directions to provide fluid flow to the first chamber or the second chamber of the hydraulic cylinder actuator to drive the piston; and a reservoir that is fluidly coupled to the electric motor, wherein the reservoir is configured to provide boost fluid flow or receive excess fluid flow comprising a difference between the first fluid flow rate and the second fluid flow rate via the electric motor, such that the boost fluid flow or the excess fluid flow cools the electric motor.

[00114] EEE 2 is the hydraulic system of EEE 1, further comprising: a boost flow line configured to provide the boost fluid flow to, and receive the excess fluid flow from, the hydraulic cylinder actuator, wherein the reservoir is fluidly coupled to the boost flow line via the electric motor.

[00115] EEE 3 is the hydraulic system of EEE 2, wherein the electric motor comprises a first motor port fluidly coupled to the reservoir and a second motor port fluidly coupled to the boost flow line, such that the boost fluid flow provided by the reservoir flows through the electric motor to the boost flow line, and the excess fluid flow is provided from the boost flow line through the electric motor to the reservoir.

[00116] EEE 4 is the hydraulic system of EEE 3, wherein the electric motor comprises a housing having the first motor port and the second motor port, wherein boost fluid flow provided by the reservoir and the excess fluid flow received by the reservoir are provided within or through the housing to cool the electric motor.

[00117] EEE 5 is the hydraulic system of any of EEEs 1-4, wherein the reservoir comprises an accumulator.

[00118] EEE 6 is the hydraulic system of any of EEEs 1-5, wherein the pump comprises (i) a first pump port fluidly coupled to the first chamber via a first fluid line, and (ii) a second pump port fluidly coupled to the second chamber via a second fluid line, and wherein the hydraulic system further comprising: a reverse shuttle valve comprising (i) a first pilot port fluidly coupled to the first fluid line, (ii) a second pilot port fluidly coupled to the second fluid line, and (iii) a boost port fluidly coupled to the reservoir via the electric motor, wherein the reverse shuttle valve is responsive to pressure difference between the first fluid line and the second fluid line.

[00119] EEE 7 is the hydraulic system of EEE 6, wherein when pressure level in the first fluid line is higher than pressure level in the second fluid line as the piston extends within the cylinder, a shuttle element of the reverse shuttle valve shifts therein to fluidly couple the boost port to the second pilot port to provide the boost fluid flow from the reservoir via the electric motor to the second fluid line. [00120] EEE 8 is the hydraulic system of any of EEEs 6-7, wherein when pressure level in the second fluid line is higher than pressure level in the first fluid line as the piston extends within the cylinder, a shuttle element of the reverse shuttle valve shifts therein to fluidly couple the boost port to the first pilot port to provide the boost fluid flow from the reservoir via the electric motor to the first fluid line.

[00121] EEE 9 is the hydraulic system of any of EEEs 6-8, wherein when pressure level in the second fluid line is higher than pressure level in the first fluid line as the piston retracts within the cylinder, a shuttle element of the reverse shuttle valve shifts therein to fluidly couple the first pilot port to the boost port to provide the excess fluid flow from the first fluid line to the reservoir via the electric motor.

[00122] EEE 10 is the hydraulic system of any of EEEs 6-9, wherein when pressure level in the first fluid line is higher than pressure level in the second fluid line as the piston retracts within the cylinder, a shuttle element of the reverse shuttle valve shifts therein to fluidly couple the second pilot port to the boost port to provide the excess fluid flow from the second fluid line to the reservoir via the electric motor.

[00123] EEE 11 is the hydraulic system of any of EEEs 6-10, further comprising: a first pressure relief valve disposed between the first fluid line and the second fluid line and configured to provide a fluid flow path from the first fluid line to the second fluid line when pressure level of fluid in the first chamber exceeds a threshold pressure value; and a second pressure relief valve disposed between the second fluid line and the first fluid line and configured to provide a respective fluid flow path from the second fluid line to the first fluid line when pressure level of fluid in the second chamber exceeds the threshold pressure value. [00124] EEE 12 is a method of operating the hydraulic system of any of EEEs 1-11. For example, the method comprises: operating an electric motor to drive a pump to provide fluid flow via a first fluid line to extend a piston within a cylinder of a hydraulic cylinder actuator against a resistive load, wherein the piston divides an internal space of the cylinder into a first chamber and a second chamber, and wherein the hydraulic cylinder actuator is unbalanced such that a first fluid flow rate of fluid provided to the first chamber via the first fluid line to extend the piston is larger than a second fluid flow rate of fluid discharged from the second chamber as the piston extends, wherein fluid discharged from the second chamber returns to the pump via a second fluid line; and providing boost fluid flow from a reservoir through the electric motor to the second fluid line such that the boost fluid flow joins fluid returning to the pump via the second fluid line and makes up for a difference between the first fluid flow rate and the second fluid flow rate, and wherein the boost fluid flow cools the electric motor as the boost fluid flow is provided from the reservoir through the electric motor to the second fluid line.

[00125] EEE 13 is the method of EEE 12, wherein when the piston is subjected to an assistive load as the piston extends, fluid discharged from the second chamber returns to the pump, thereby driving the pump and the electric motor in a regenerative mode, wherein fluid is provided from the pump to the first chamber via the first fluid line, and wherein the method further comprises: providing the boost fluid flow from the reservoir through the electric motor to the first fluid line such that the boost fluid flow joins fluid provided by the pump to the first fluid line and makes up for the difference between the first fluid flow rate and the second fluid flow rate, and wherein the boost fluid flow cools the electric motor as the boost fluid flow is provided from the reservoir through the electric motor to the first fluid line. [00126] EEE 14 is the method of any of EEEs 12-13, further comprising: operating the electric motor to drive the pump to provide fluid flow via the second fluid line to the second chamber to retract the piston within the cylinder against a respective resistive load, wherein the first fluid flow rate of fluid discharged from the first chamber via the first fluid line is larger than the second fluid flow rate of fluid provided to the second chamber as the piston retracts, wherein fluid discharged from the first chamber returns to the pump via the first fluid line; and providing excess fluid flow from the first fluid line through the electric motor to the reservoir, wherein the excess fluid flow is the difference between the first fluid flow rate and the second fluid flow rate, and wherein the excess fluid flow cools the electric motor as the excess fluid flow is provided from the first fluid line through the electric motor to the reservoir.

[00127] EEE 15 is the method of EEE 14, wherein when the piston is subjected to an assistive load as the piston retracts, fluid discharged from the first chamber returns to the pump, thereby driving the pump and the electric motor in a regenerative mode, wherein fluid is provided from the pump to the second chamber via the second fluid line, and wherein the method further comprises: providing the excess fluid flow from the second fluid line through the electric motor to the reservoir, wherein the excess fluid flow cools the electric motor as the excess fluid flow is provided from the second fluid line through the electric motor to the reservoir.

[00128] EEE 16 is the method of any of EEEs 12-15, wherein the reservoir is fluidly coupled to a boost flow line via the electric motor, and wherein providing the boost fluid flow from the reservoir through the electric motor to the second fluid line comprises: providing the boost fluid flow from the reservoir through the electric motor to the boost flow line, then to the second fluid line.

[00129] EEE 17 is the method of EEE 16, wherein the electric motor comprises a first motor port fluidly coupled to the reservoir and a second motor port fluidly coupled to the boost flow line, wherein providing the boost fluid flow from the reservoir through the electric motor to the boost flow line comprises: providing the boost fluid flow from the reservoir to the first motor port, thereby allowing the boost fluid flow to flow through the electric motor; and providing the boost fluid flow through the second motor port to the boost flow line.

[00130] EEE 18 is the method of EEE 17, wherein the electric motor comprises a housing having the first motor port and the second motor port, wherein providing the boost fluid flow from the reservoir through the electric motor comprises: flowing the boost fluid flow within or through the housing to cool the electric motor.

[00131] EEE 19 the method of any of EEEs 12-18, wherein the pump comprises (i) a first pump port fluidly coupled to the first chamber via the first fluid line, and (ii) a second pump port fluidly coupled to the second chamber via the second fluid line, and wherein the first fluid line is fluidly coupled to a first pilot port of a reverse shuttle valve, the second fluid line is fluidly coupled to a second pilot port of the reverse shuttle valve, and the reservoir is fluidly coupled to a boost port of the reverse shuttle valve via the electric motor, wherein the reverse shuttle valve is responsive to pressure difference between the first fluid line and the second fluid line, wherein providing the boost fluid flow from the reservoir through the electric motor to the second fluid line comprises: causing a shuttle element of the reverse shuttle valve to shift therein to fluidly couple the boost port to the second pilot port to provide the boost fluid flow from the reservoir via the electric motor to the second fluid line.

[00132] EEE 20 is the method of any of EEEs 12-19, wherein a first pressure relief valve is disposed between the first fluid line and the second fluid line, wherein a second pressure relief valve is disposed between the second fluid line and the first fluid line, and wherein the method further comprises: opening the first pressure relief valve to provide a fluid flow path from the first fluid line to the second fluid line when pressure level of fluid in the first chamber exceeds a threshold pressure value; and opening the second pressure relief valve to provide a respective fluid flow path from the second fluid line to the first fluid line when pressure level of fluid in the second chamber exceeds the threshold pressure value.

Claims

CLAIMS What is claimed is:

1 . A hydraulic system comprising: a hydraulic cylinder actuator comprising a cylinder and a piston, wherein the piston divides an internal space of the cylinder into a first chamber and a second chamber, and wherein the hydraulic cylinder actuator is unbalanced such that a first fluid flow rate of fluid provided to the first chamber or the second chamber to drive the piston in a given direction is different from a second fluid flow rate of fluid discharged from the other chamber as the piston moves; a pump configured to be a bi-directional fluid flow source; an electric motor configured to drive the pump in opposite rotational directions to provide fluid flow to the first chamber or the second chamber of the hydraulic cylinder actuator to drive the piston; and a reservoir that is fluidly coupled to the electric motor, wherein the reservoir is configured to provide boost fluid flow or receive excess fluid flow comprising a difference between the first fluid flow rate and the second fluid flow rate via the electric motor, such that the boost fluid flow or the excess fluid flow cools the electric motor.

2. The hydraulic system of claim 1, further comprising: a boost flow line configured to provide the boost fluid flow to, and receive the excess fluid flow from, the hydraulic cylinder actuator, wherein the reservoir is fluidly coupled to the boost flow line via the electric motor.

3. The hydraulic system of claim 2, wherein the electric motor comprises a first motor port fluidly coupled to the reservoir and a second motor port fluidly coupled to the boost flow line, such that the boost fluid flow provided by the reservoir flows through the electric motor to the boost flow line, and the excess fluid flow is provided from the boost flow line through the electric motor to the reservoir.

4. The hydraulic system of claim 3, wherein the electric motor comprises a housing having the first motor port and the second motor port, wherein boost fluid flow provided by the reservoir and the excess fluid flow received by the reservoir are provided within or through the housing to cool the electric motor.

5. The hydraulic system of claim 1, wherein the reservoir comprises an accumulator.

6. The hydraulic system of claim 1, wherein the pump comprises (i) a first pump port fluidly coupled to the first chamber via a first fluid line, and (ii) a second pump port fluidly coupled to the second chamber via a second fluid line, and wherein the hydraulic system further comprising: a reverse shuttle valve comprising (i) a first pilot port fluidly coupled to the first fluid line, (ii) a second pilot port fluidly coupled to the second fluid line, and (iii) a boost port fluidly coupled to the reservoir via the electric motor, wherein the reverse shuttle valve is responsive to pressure difference between the first fluid line and the second fluid line.

7. The hydraulic system of claim 6, wherein when pressure level in the first fluid line is higher than pressure level in the second fluid line as the piston extends within the cylinder, a shuttle element of the reverse shuttle valve shifts therein to fluidly couple the boost port to the second pilot port to provide the boost fluid flow from the reservoir via the electric motor to the second fluid line.

8. The hydraulic system of claim 6, wherein when pressure level in the second fluid line is higher than pressure level in the first fluid line as the piston extends within the cylinder, a shuttle element of the reverse shuttle valve shifts therein to fluidly couple the boost port to the first pilot port to provide the boost fluid flow from the reservoir via the electric motor to the first fluid line.

9. The hydraulic system of claim 6, wherein when pressure level in the second fluid line is higher than pressure level in the first fluid line as the piston retracts within the cylinder, a shuttle element of the reverse shuttle valve shifts therein to fluidly couple the first pilot port to the boost port to provide the excess fluid flow from the first fluid line to the reservoir via the electric motor.

10. The hydraulic system of claim 6, wherein when pressure level in the first fluid line is higher than pressure level in the second fluid line as the piston retracts within the cylinder, a shuttle element of the reverse shuttle valve shifts therein to fluidly couple the second pilot port to the boost port to provide the excess fluid flow from the second fluid line to the reservoir via the electric motor.

11 . The hydraulic system of claim 6, further comprising: a first pressure relief valve disposed between the first fluid line and the second fluid line and configured to provide a fluid flow path from the first fluid line to the second fluid line when pressure level of fluid in the first chamber exceeds a threshold pressure value; and a second pressure relief valve disposed between the second fluid line and the first fluid line and configured to provide a respective fluid flow path from the second fluid line to the first fluid line when pressure level of fluid in the second chamber exceeds the threshold pressure value.

12. A method comprising: operating an electric motor to drive a pump to provide fluid flow via a first fluid line to extend a piston within a cylinder of a hydraulic cylinder actuator against a resistive load, wherein the piston divides an internal space of the cylinder into a first chamber and a second chamber, and wherein the hydraulic cylinder actuator is unbalanced such that a first fluid flow rate of fluid provided to the first chamber via the first fluid line to extend the piston is larger than a second fluid flow rate of fluid discharged from the second chamber as the piston extends, wherein fluid discharged from the second chamber returns to the pump via a second fluid line; and providing boost fluid flow from a reservoir through the electric motor to the second fluid line such that the boost fluid flow joins fluid returning to the pump via the second fluid line and makes up for a difference between the first fluid flow rate and the second fluid flow rate, and wherein the boost fluid flow cools the electric motor as the boost fluid flow is provided from the reservoir through the electric motor to the second fluid line.

13. The method of claim 12, wherein when the piston is subjected to an assistive load as the piston extends, fluid discharged from the second chamber returns to the pump, thereby driving the pump and the electric motor in a regenerative mode, wherein fluid is provided from the pump to the first chamber via the first fluid line, and wherein the method further comprises: providing the boost fluid flow from the reservoir through the electric motor to the first fluid line such that the boost fluid flow joins fluid provided by the pump to the first fluid line and makes up for the difference between the first fluid flow rate and the second fluid flow rate, and wherein the boost fluid flow cools the electric motor as the boost fluid flow is provided from the reservoir through the electric motor to the first fluid line.

14. The method of claim 12, further comprising: operating the electric motor to drive the pump to provide fluid flow via the second fluid line to the second chamber to retract the piston within the cylinder against a respective resistive load, wherein the first fluid flow rate of fluid discharged from the first chamber via the first fluid line is larger than the second fluid flow rate of fluid provided to the second chamber as the piston retracts, wherein fluid discharged from the first chamber returns to the pump via the first fluid line; and providing excess fluid flow from the first fluid line through the electric motor to the reservoir, wherein the excess fluid flow is the difference between the first fluid flow rate and the second fluid flow rate, and wherein the excess fluid flow cools the electric motor as the excess fluid flow is provided from the first fluid line through the electric motor to the reservoir.

15. The method of claim 14, wherein when the piston is subjected to an assistive load as the piston retracts, fluid discharged from the first chamber returns to the pump, thereby driving the pump and the electric motor in a regenerative mode, wherein fluid is provided from the pump to the second chamber via the second fluid line, and wherein the method further comprises: providing the excess fluid flow from the second fluid line through the electric motor to the reservoir, wherein the excess fluid flow cools the electric motor as the excess fluid flow is provided from the second fluid line through the electric motor to the reservoir.

16. The method of claim 12, wherein the reservoir is fluidly coupled to a boost flow line via the electric motor, and wherein providing the boost fluid flow from the reservoir through the electric motor to the second fluid line comprises: providing the boost fluid flow from the reservoir through the electric motor to the boost flow line, then to the second fluid line.

17. The method of claim 16, wherein the electric motor comprises a first motor port fluidly coupled to the reservoir and a second motor port fluidly coupled to the boost flow line, wherein providing the boost fluid flow from the reservoir through the electric motor to the boost flow line comprises: providing the boost fluid flow from the reservoir to the first motor port, thereby allowing the boost fluid flow to flow through the electric motor; and providing the boost fluid flow through the second motor port to the boost flow line.

18. The method of claim 17, wherein the electric motor comprises a housing having the first motor port and the second motor port, wherein providing the boost fluid flow from the reservoir through the electric motor comprises: flowing the boost fluid flow within or through the housing to cool the electric motor.

19. The method of claim 12, wherein the pump comprises (i) a first pump port fluidly coupled to the first chamber via the first fluid line, and (ii) a second pump port fluidly coupled to the second chamber via the second fluid line, and wherein the first fluid line is fluidly coupled to a first pilot port of a reverse shuttle valve, the second fluid line is fluidly coupled to a second pilot port of the reverse shuttle valve, and the reservoir is fluidly coupled to a boost port of the reverse shuttle valve via the electric motor, wherein the reverse shuttle valve is responsive to pressure difference between the first fluid line and the second fluid line, wherein providing the boost fluid flow from the reservoir through the electric motor to the second fluid line comprises: causing a shuttle element of the reverse shuttle valve to shift therein to fluidly couple the boost port to the second pilot port to provide the boost fluid flow from the reservoir via the electric motor to the second fluid line.

20 The method of claim 12, wherein a first pressure relief valve is disposed between the first fluid line and the second fluid line, wherein a second pressure relief valve is disposed between the second fluid line and the first fluid line, and wherein the method further comprises: opening the first pressure relief valve to provide a fluid flow path from the first fluid line to the second fluid line when pressure level of fluid in the first chamber exceeds a threshold pressure value; and opening the second pressure relief valve to provide a respective fluid flow path from the second fluid line to the first fluid line when pressure level of fluid in the second chamber exceeds the threshold pressure value.