WO2021225645A1

WO2021225645A1 - Hydraulic dissipation of electric power

Info

Publication number: WO2021225645A1
Application number: PCT/US2021/014840
Authority: WO
Inventors: Blake A. CARL
Original assignee: Parker-Hannifin Corporation
Priority date: 2020-05-05
Filing date: 2021-01-25
Publication date: 2021-11-11

Abstract

An example electrohydraulic system includes: a hydraulic actuator configured to generate regenerative hydraulic power; a first pump coupled to a first electric motor, wherein the first pump is configured to receive the regenerative hydraulic power from the hydraulic actuator, thereby driving the first electric motor, causing the first electric motor to generate regenerative electric power; a second electric motor configured to drive a second pump, wherein the second electric motor is configured to receive at least a portion of the regenerative electric power generated by the first electric motor, thereby driving the second pump, causing the second pump to discharge fluid flow therefrom; and a valve fluidly coupled to the second pump, wherein the valve is configured to throttle the fluid flow discharged from the second pump, thereby dissipating power as heat.

Description

Hydraulic Dissipation of Electric Power

CROSS-REFERENCE TO RELATED APPLICATION [0001] This application claims priority to U.S. Provisional Application No. 63/020,319, filed May 5, 2020, which is incorporated herein by reference in their entirety.

BACKGROUND

[0002] It is common for a work machine, such as hydraulic excavators, wheel loaders, loading shovels, backhoe shovels, mining equipment, industrial machinery and the like, to 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 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] To enhance efficiency, an electrohydraulic system can be used where an electric motor drives a pump, which then provides fluid to the actuators of the work machine. Such system can enhance efficiency by controlling speed of the actuator by the speed of the electric motor and the system provides fluid on demand, rather than continually.

[0004] Further, under some operating conditions, an actuator can be subjected to overrunning loads and regenerative electric power can be generated by the electric motor. The electric power can be used to charge a battery, for example. It may be desirable to have an electrohydraulic system that can manage the regenerative electric power and maintain the health of the battery. It is with respect to these and other considerations that the disclosure made herein is presented.

SUMMARY

[0005] The present disclosure describes implementations that relate to a hydraulic dissipation of electric power.

[0006] In a first example implementation, the present disclosure describes an electrohydraulic system. The electrohydraulic system includes: (i) a hydraulic actuator configured to operate in a regenerative mode in which the hydraulic actuator generates regenerative hydraulic power as the hydraulic actuator is subjected to a negative load; (ii) a first pump coupled to a first electric motor, wherein the first pump is configured to receive the regenerative hydraulic power from the hydraulic actuator, thereby driving the first electric motor, causing the first electric motor to generate regenerative electric power; (iii) a second electric motor configured to drive a second pump, wherein the second electric motor is configured to receive at least a portion of the regenerative electric power generated by the first electric motor, thereby driving the second pump, causing the second pump to discharge fluid flow therefrom; and (iv) a valve fluidly coupled to the second pump, wherein the valve is configured to throttle the fluid flow discharged from the second pump, thereby dissipating power as heat.

[0007] In a second example implementation, the present disclosure describes a machine. The machine includes: (i) a first hydraulic actuator configured to operate in a regenerative mode in which the first hydraulic actuator generates regenerative hydraulic power as the first hydraulic actuator is subjected to a negative load; (ii) a first pump coupled to a first electric motor, wherein the first pump is configured to receive the regenerative hydraulic power from the first hydraulic actuator, thereby driving the first electric motor, causing the first electric motor to generate regenerative electric power; (iii) a second hydraulic actuator; and (iv) a second electric motor configured to drive a second pump to operate the second hydraulic actuator when the second hydraulic actuator is actuated, wherein the second electric motor is configured to receive at least a portion of the regenerative electric power generated by the first electric motor, thereby driving the second pump, causing the second pump to discharge fluid flow therefrom.

[0008] In a third example implementation, the present disclosure describes a method. The method includes: (i) receiving, at a controller of an electrohydraulic system, sensor information indicative of a state of a battery of the electrohydraulic system, wherein the electrohydraulic system comprises: (a) a hydraulic actuator configured to operate in a regenerative mode in which the hydraulic actuator generates regenerative hydraulic power as the hydraulic actuator is subjected to a negative load, (b) a first pump coupled to a first electric motor, wherein the first pump is configured to receive the regenerative hydraulic power from the hydraulic actuator, thereby driving the first electric motor, causing the first electric motor to generate regenerative electric power, (c) a second electric motor configured to drive a second pump, and (d) a valve fluidly coupled to the second pump; (ii) determining, by the controller based on the sensor information, that the regenerative electric power generated by the first electric motor exceeds a capacity of the battery to accommodate the regenerative electric power; and (iii) providing at least a portion of the regenerative electric power generated by the first electric motor to the second electric motor, thereby driving the second pump, causing the second pump to discharge fluid flow therefrom, wherein the valve is configured to throttle the fluid flow discharged from the second pump, thereby dissipating power as heat.

[0009] 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

[0010] 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.

[0011] Figure 1 illustrates a machine, in accordance with an example implementation.

[0012] Figure 2 illustrates a block diagram of an electrohydraulic control system, in accordance with an example implementation.

[0013] Figure 3 illustrates a block diagram of an electrohydraulic control system configured to dissipate excess regenerative power via an active component, in accordance with an example implementation.

[0014] Figure 4 illustrates a block diagram of an electrohydraulic control system configured to dissipate excess regenerative power from a first electric motor via a second electric motor, in accordance with an example implementation.

[0015] Figure 5 illustrates a partial hydraulic system of a machine, in accordance with an example implementation.

[0016] Figure 6 illustrates another partial hydraulic system of a machine, in accordance with an example implementation.

[0017] Figure 7 is a flowchart of a method for operating a hydraulic system, in accordance with an example implementation. DETAILED DESCRIPTION

[0018] An example hydraulic machine, such as an excavator, can use multiple hydraulic actuators to accomplish a variety of tasks. To enhance efficiency of a hydraulic machine, an electrohydraulic actuator system can be used to control the hydraulic actuators. An electrohydraulic actuator system can include an electric motor that is connected to a pump for providing fluid to an actuator such as a hydraulic cylinder for controlling motion of the actuator. In one example, the speed and direction of the electric motor controls the flow of fluid to the actuator. In another example, the electric motor speed can be maintained constant, while varying flow capacity of the pump, e.g., by changing swash plate angle of a variable displacement piston pump.

[0019] The hydraulic machine can include an electric power source, such as a battery, that provides electric power to the electric motor. The electric motor then drives the pump, which provides hydraulic fluid to the hydraulic actuator to drive it.

[0020] Hydraulic actuators can be subjected to negative or overrunning loads, e.g., gravity- assisted loads. For instance, when lowering a boom of an excavator while not digging (i.e., boom moving in the air), gravity assists the motion of the boom. In these examples, fluid returning to the pump can drive the pump, i.e., the pump operates as a hydraulic motor, and the pump then drives the electric motor. As such, regenerative electric power can be generated by the electric motor. The term “regenerative electric power” is used here to indicate that an electric motor operates as a generator to convert the kinetic energy transmitted thereto by the pump operating as a hydraulic motor into electric energy that can be stored.

[0021] Particularly, the electric motor can operate as an electric generator and produce electric power, rather than consume electric power. The regenerative electric power can then be provided to the battery. In some examples, the battery might not be able to handle or accommodate the entirety of the electric power generated. It may thus be desirable to manage the regenerative electric power in a manner that does not affect the health of the battery. Disclosed herein are machines, systems, and methods for managing the regenerative electric power while maintaining the health of the battery.

[0022] Figure 1 illustrates a machine 100, in accordance with an example implementation. The machine 100 can include a boom 102, an arm 104, bucket 106, and cab 108 mounted to a rotating platform 110. The rotating platform 110 can sit atop an undercarriage with wheels or tracks such as track 112. The arm 104 can also be referred to as a dipper or stick.

[0023] Movement of the boom 102, the arm 104, the bucket 106, and the rotating platform 110 can be achieved through the use of hydraulic fluid, with hydraulic cylinders and hydraulic motors. Particularly, the boom 102 can be moved with a boom hydraulic cylinder actuator 114, the arm 104 can be moved with an arm hydraulic cylinder actuator 116, and the bucket 106 can be moved with a bucket hydraulic cylinder actuator 118.

[0024] The rotating platform 110 can be rotated by a swing drive. The swing drive can include a slew ring or a swing gear to which the rotating platform 110 is mounted. The swing drive can also include a swing hydraulic motor actuator 120 (see, e.g., Figure 6) disposed under the rotating platform 110 and coupled to a gear box. The gear box can be configured to have a pinion that is engaged with teeth of the swing gear. As such, actuating the swing hydraulic motor actuator 120 with pressurized fluid causes the swing hydraulic motor actuator 120 to rotate the pinion of the gear box, thereby rotating the rotating platform 110.

[0025] The cab 108 can include control tools for the operator of the machine 100. For instance, the machine 100 can include a drive-by-wire system have a right joystick 122 and a left joystick 124 that can be used by the operator to provide electric signals to a controller of the machine 100. The controller then provides electric command signals to various electrically-actuated components of the machine 100 to drive the various actuators mentioned above and operate the machine 100. As an example, the left joystick 124 can operate the arm hydraulic cylinder actuator 116 and the swing hydraulic motor actuator 120, whereas the right joystick 122 can operate the boom hydraulic cylinder actuator 114 and the bucket hydraulic cylinder actuator 118.

[0026] To enhance efficiency of the hydraulic system driving the actuators of the machine 100, an electrohydraulic system can be used, rather than conventional pump and throttle valve systems. Particularly, the machine 100 can include one or more electric motors that drive respective pumps to drive the various hydraulic actuators of the machine 100. For instance, an electric motor can drive a pump, which then provides fluid to an actuator of the machine 100 (e.g., any of the boom hydraulic cylinder actuator 114, the arm hydraulic cylinder actuator 116, the bucket hydraulic cylinder actuator 118, or the swing hydraulic motor actuator 120) to drive it.

[0027] Figure 2 illustrates a block diagram of an electrohydraulic control system 200, in accordance with an example implementation. The electrohydraulic control system 200 can include an electric power source such as a battery 202 configured to provide electric power to, and receive regenerative electric power from, an electric motor 204. The electric motor 204 can have an output shaft that is coupled to an input shaft of a pump 206. The pump 206 is configured to provide hydraulic fluid to an actuator 208. The actuator 208 can represent any of the boom hydraulic cylinder actuator 114, the arm hydraulic cylinder actuator 116, the bucket hydraulic cylinder actuator 118, or the swing hydraulic motor actuator 120, for example.

[0028] In one mode of operation, the battery 202 provides electric power to the electric motor 204, and the electric motor 204 converts the electric power into a mechanical power, and the output shaft of the electric motor 204 rotates. As the output shaft of the electric motor 204 rotates, the input shaft of the pump 206 coupled thereto rotates, causing the pump 206 to provide hydraulic power (i.e., provide fluid flow at a particular pressure level) to the actuator 208 to drive it.

[0029] In another mode of operation, the electrohydraulic control system 200 can operate in a regenerative mode. For example, the actuator 208 can represent the boom hydraulic cylinder actuator 114, and during gravity-assisted lowering of the boom 102, the actuator 208 provides hydraulic power back to the pump 206 rather than consume hydraulic power therefrom. The pump 206 in turn can drive the output shaft of the electric motor 204. In this case, the electric motor 204 operates as an electric generator that produces, rather than consumes, electric power.

[0030] The battery 202 can be configured as a rechargeable battery, and the regenerative electric power generated by the electric motor 204 can be used to charge the battery 202. Particularly, the kinetic energy of the actuator 208 is converted to electric power by the electric motor 204, and the electric power is then converted into chemical energy stored in the battery 202, where the energy can be used later to drive the machine 100. This way, the electrohydraulic control system 200 can recover energy from the actuator 208 rather than waste such energy, and efficiency of the machine 100 can be enhanced.

[0031] In some examples, however, the battery 202 might not be able to receive and store all the regenerative electric power generated by the electric motor 204. For example, the battery 202 may be fully charged, and might thus not be able to absorb and store more energy.

[0032] In another example, the charge rate of the battery 202 might not be sufficient to absorb the regenerative electric power produced by the electric motor 204. Charge and discharge rates of a battery can be designated by a “C-rate.” A C-rate is a measure of the rate at which a battery is discharged relative to its maximum capacity. A 1C rate, for example, indicates that the discharge electric current can discharge the entire battery in 1 hour. As an example for illustration, the battery 202 can be capable of at a 2C continuous discharge rate, but only a 0.8C to 1C charge rate. This indicates that the rate of charging is limited to no more than 40-50% of discharging on a continual basis. An excessive charging rate can result in a higher cell temperature in the cells of the battery 202. Such high cell temperature can be exacerbated when temperature of the external environment of the battery 202 is high.

[0033] Further, if the battery 202 is a lithium based battery, excessive charging rate can cause the lithium ions to be plated as metal onto the cathode. As a result the battery 202 may lose capacity and deteriorate over time.

[0034] Therefore, in some examples, the battery 202 might not be able, or it may not be desirable, to absorb or covert all the electric power generated by the electric motor 204. In other words, the regenerative electric power may exceed a capacity of the battery 202 to accommodate the regenerative electric power. Exceeding the capacity of the battery 202 to accommodate the regenerative electric power is used herein to encompass any condition rendering the battery 202 in a state in which it is not preferable to provide the regenerative electric power to the battery 202, e.g., limited storage capacity of the battery 202 due to a charge state thereof, temperature of the battery 202, environmental temperature, etc. It may thus be desirable to configure the control system with a way to handle excess power that is not stored or absorbed by the battery 202.

[0035] Figure 3 illustrates a block diagram of an electrohydraulic control system 300 configured to dissipate excess regenerative power via an active component, in accordance with an example implementation. Components of the electrohydraulic control system 300 that are the same as the components in the electrohydraulic control system 200 are designated with the same reference numbers.

[0036] The electrohydraulic control system 300 can include an active valve 302 as shown in Figure 3. The active valve 302 is interposed between the actuator 208 and the pump 206. Particularly, the active valve 302 is fluidly coupled to the actuator 208 and the pump 206 and is configured to throttle or control fluid flow rate from the actuator 208 to the pump 206 when the electrohydraulic control system 300 operates in a regenerative mode.

[0037] The term “active” is used herein to indicate that the active valve 302 is actuatable by a signal (e.g., electric, hydraulic, pneumatic). For example, the active valve 302 can be an electronically-controlled proportional valve having a solenoid actuator. A solenoid coil of the solenoid actuator can be energized upon receiving an electric signal, thereby causing a movable element (e.g., a poppet, piston, or spool) within the active valve 302 to move and throttle fluid flow therethrough. The movable element can move or be displaced by a particular axial distance that is proportional to the magnitude of the electric signal provided to the solenoid coil.

[0038] When the electrohydraulic control system 300 operates in a normal (non-regenerative) mode of operation where power is provided from the pump 206 to the actuator 208, the active valve 302 can be fully opened to minimize power loss therethrough. However, when the electrohydraulic control system 300 operates in a regenerative mode of operation where power is provided from the actuator 208 to the pump 206, the active valve 302 can be actuated to throttle fluid flow therethrough.

[0039] A controller (not shown) of the electrohydraulic control system 300 can be configured to detect that the battery 202 might not be able to store all the regenerative electric power generated by the electric motor 204 if all the regenerative hydraulic power generated by the actuator 208 is provided to the pump 206. For instance, the controller may receive sensor information indicative of a charge state of the battery 202, e.g., whether the battery 202 if fully charged or within a threshold capacity such as 5% from being fully charged. The controller can also receive sensor information indicative of a temperature of the battery and/or temperature of an external environment of the battery 202.

[0040] Based on sensor information from one or more sensors, the controller can responsively actuate the active valve 302 (e.g., provide an electric signal command to the solenoid coil of the active valve 302) to throttle fluid flow therethrough. When the active valve 302 is opened all the way, most of the hydraulic power returning from the actuator 208 can be provided to the pump 206. When the controller determines that the battery 202 might not be able to store all the regenerative electric power, the controller can provide a command to the active valve 302 to restrict fluid flow therethrough.

[0041] Restricting fluid flow through the active valve 302 causes a pressure drop across the active valve 302. The pressure drop is the pressure differential between pressure level of fluid received at the active valve 302 from the actuator 208 and pressure level of fluid discharged from active valve 302 to the pump 206. The pressure drop multiplied by the fluid flow rate through the active valve 302 represents the hydraulic power dissipated or lost through the active valve 302 in the form of heat.

[0042] With this configuration, the regenerative hydraulic power from the actuator 208 can be divided into a first portion provided to the pump 206 and a second portion dissipated through the active valve 302. This way, the controller can control the amount of regenerative electric power that is provided to the battery 202. The more restrictive the active valve 302 is, the less the regenerative electric power provided to the battery 202. As such, the controller can modulate the amount of regenerative electric power provided to the battery 202 based on the state of the battery 202 (e.g., the charge rate the battery 202 can handle or accommodate without jeopardizing its health) by varying the signal provided to the active valve 302.

[0043] In some applications, the added cost of the active valve 302 might not be desirable, especially that the active valve 302 might not be needed when the electrohydraulic control system 300 operates in a normal (non-regenerative) mode of operation. As such, in such applications, it may be desirable to use other existing components of the machine 100 to dissipate regenerative power rather than add costly components. It may also be desirable to use a passive component, e.g., a passive valve, which may generally be cheaper than an active valve, to dissipate regenerative power.

[0044] Figure 4 illustrates a block diagram of an electrohydraulic system 400 configured to dissipate excess regenerative power from the electric motor 204 via a second electric motor 402, in accordance with an example implementation. Components of the electrohydraulic system 400 that are the same as the components in the electrohydraulic control systems 200, 300 are designated with the same reference numbers.

[0045] The machine 100 can include the electric motor 204 and the pump 206 configured to control the actuator 208 (e.g., the boom hydraulic cylinder actuator 114) and can include other electric motors and pumps controlling other actuators (e.g., the arm hydraulic cylinder actuator 116, the bucket hydraulic cylinder actuator 118, or the swing hydraulic motor actuator 120). For example, the electrohydraulic system 400 a second electric motor 402 coupled to, and configured to drive, a pump 404. If the actuator 208 represents the boom hydraulic cylinder actuator 114, for example, then the pump 404 can be configured to drive any of the remaining actuators (the arm hydraulic cylinder actuator 116, the bucket hydraulic cylinder actuator 118, or the swing hydraulic motor actuator 120). [0046] The electrohydraulic system 400 can further include a passive valve (e.g., a pressure relief valve) fluidly coupled to the pump 404. The term “passive” is used herein to indicate that no actuation signal from a controller of the electrohydraulic system 400 is used to operate the passive valve.

[0047] When the controller of the electrohydraulic system 400 determines that the battery 202 might not be able to store all the regenerative electric power generated by the electric motor 204, the controller can provide or direct at least a portion of the regenerative electric power (e.g., excess electric power that the battery 202 might not be capable of handling) to the second electric motor 402. The second electric motor 402 in turn drives the pump 404, which discharges fluid flow therefrom.

[0048] Fluid flow path to the actuator associated with the second electric motor 402 and the pump 404 (e.g., arm hydraulic cylinder actuator 116) may be blocked as the actuator might not be actuated by the operator of the machine 100. As such, fluid flow from the pump 404 can be diverted to the passive valve 406. The passive valve 406 can then restrict or throttle fluid flow therethrough to dissipate the fluid power provided thereto.

[0049] For example, as mentioned above, the passive valve 406 can be a pressure relief valve (PRV). A PRV is a valve configured to control pressure level in a hydraulic system. Particularly, A PRV can be configured to open at a predetermined set pressure to protect components of a hydraulic system from excessive pressure levels that might damage the components. When the set pressure is exceeded, the PRV becomes the “path of least resistance” as the valve is forced open and a portion of the fluid is diverted to a fluid reservoir, e.g., a tank having fluid at low pressure level, e.g., 0-70 pounds per square inch

(psi). [0050] For instance, a PRV can have a movable element (e.g., a poppet) biased toward a seat in a valve body by a spring. The PRV can block fluid flow therethrough as long as the movable element is seated. Pressure level of fluid is allowed to increase or build up until it reaches a pressure level that overcomes the biasing force of the spring and the movable element is unseated. Fluid is then throttled through the PRV as it flows to a fluid reservoir fluidly coupled thereto.

[0051] A PRV is used herein as an example for illustration only. Other types of passive valves or passive components can be used, e.g., a fixed orifice, a variable orifice, ball valve, a passive flow regulator, etc.

[0052] Thus, in the implementation of Figure 4, pressure level of fluid being discharged from the pump 404 as a result of excess regenerative electric power being provided to the second electric motor 402 can build up in a hydraulic line between the pump 404 and the passive valve 406. Once the pressure level exceeds the pressure setting of the passive valve 406, the passive valve 406 can open, thereby allowing fluid flow to a fluid reservoir.

[0053] As fluid flows through the passive valve 406, fluid flow is throttled or restricted, causing a pressure drop to occur thereacross and causing fluid power to be dissipated in the form of heat. The power dissipated at the passive valve 406 can amount to the pressure drop across the passive valve 406 multiplied by the fluid flow rate therethrough. This way, the excess electric power provided to the second electric motor 402 can be dissipated as heat, while protecting the battery 202.

[0054] With this configuration, existing components of the machine 100 can be used to dissipate the excess electric power, rather than adding components. Further, the passive valve 406 can be cheaper than the active valve 302. Figures 5 and 6 provide example implementations of the electrohydraulic system 400. [0055] Figure 5 illustrates a partial hydraulic system 500 of the machine 100, in accordance with an example implementation. In particular, Figure 5 illustrates an electrohydraulic system for two actuators of the machine 100. It should be understood that other actuators of the machine 100 can be controlled in a similar manner. The machine 100 is depicted as a tracked excavator. However, it should also be understood that other types of machines can utilize the disclosed systems. For example, the hydraulic system 500 can be associated with a two-actuator machine such as a skid steer.

[0056] The hydraulic system 500 includes an electro-hydrostatic actuator system (EHA) 502A. The EHA 502A can be used to drive any type of actuator such as a hydraulic cylinder actuator 504A as depicted in Figure 2. The hydraulic cylinder actuator 504A can represent the boom hydraulic cylinder actuator 114 of the machine 100, for example.

[0057] The hydraulic cylinder actuator 504A includes a cylinder 506A and a piston 508A slidably accommodated in the cylinder 506 A and configured to move in a linear direction therein. The piston 508 A includes a piston head 510A and a rod 512A extending from the piston head 510A along a central longitudinal axis direction of the cylinder 506 A. The rod 512A is coupled to a load 514A (that represents, for example, the boom 102, the arm 104, or the bucket 106 and any forces applied thereto). The piston head 510A divides the internal space of the cylinder 506A into a first chamber 516A and a second chamber 518 A.

[0058] The first chamber 516A can be referred to as head side chamber as the fluid therein interacts with the piston head 510A, and the second chamber 518A can be referred to as rod side chamber as the rod 512A is disposed partially therein. Fluid can flow to and from the first chamber 516A through a workport 515 A, and can flow to and from the second chamber 518 A through a workport 517 A. [0059] The piston head 510A can have a diameter DH, whereas the rod 512A can have a diameter DR. As such, fluid in the first chamber 516A interacts with a cross-sectional surface area of piston head 510A that can be referred to as piston head area and is equal to A_H = p—. On the other hand, fluid in the second chamber 518A interacts with an annular surface

4 area of the piston 508Athat can be referred to as piston annular area A_Annular = p ^{H R}.

[0060] The area AAnnular is smaller than the piston head area AH. Thus, as the piston 508A extends (e.g., moves to the left in Figure 5) or retracts (e.g., moves to the right in Figure 5) within the cylinder 506A, the amount of fluid flow QH going into or being discharged from the first chamber 516A is greater than the amount of fluid flow QAmuiar being discharged from or going into the second chamber 518A. Particularly, if the piston 508 A is moving at a particular velocity V, then Q_H = A_HV is greater HhmQ_Annuiar = A_AnnuiarV. The difference in flow can be determined as Q_H — Q _Annu_lar = A_RV, where AR is the cross-sectional area of the rod 512A and is equal to p— . With this configuration, the hydraulic cylinder actuator

504A can be referred to as an unbalanced actuator as fluid flow to/from one chamber thereof is not equal to fluid flow to/from the other chamber.

[0061] The EHA 502A is configured to control the rate and direction of hydraulic fluid flow to the hydraulic cylinder actuator 504A. Such control is achieved by controlling the speed and direction of an electric motor 520A used to drive a pump 522A configured as a bi directional fluid flow source. The pump 522A has a first pump port 524A connected to a fluid flow line 526A and a second pump port 528A connected to a fluid flow line 530A. The term “fluid flow line” is used throughout herein to indicate one or more fluid passages, conduits or the like that provide the indicated connectivity.

[0062] The first pump port 524A and the second pump port 528A are configured to be both inlet and outlet ports based on direction of rotation of the electric motor 520A and the pump 522A. As such, the electric motor 520A and the pump 522A can rotate in a first rotational direction to withdraw fluid from the first pump port 524A and pump fluid to the second pump port 528A, or conversely rotate in a second rotational direction to withdraw fluid from the second pump port 528A and pump fluid to the first pump port 524A.

[0063] As depicted in Figure 5, the pump 522A and the hydraulic cylinder actuator 504A are configured in a closed-loop hydraulic circuit. Particularly, fluid is being recirculated in a loop between the pump 522A and the hydraulic cylinder actuator 504A rather than in an open-loop circuit where a pump draws fluid from a reservoir and fluid then return to the reservoir. In the EHA 502A, the pump 522A provides fluid through the first pump port 524A to the workport 515 A or through the second pump port 528Ato the workport 517A, and fluid being discharged from the other workport returns to the corresponding port of the pump 522A. As such, fluid is being recirculated between the pump 522A and the hydraulic cylinder actuator 504 A.

[0064] In an example, the pump 522A can be a fixed displacement pump and the amount of fluid flow provided by the pump 522A is controlled by the speed of the electric motor 520A (i.e., by rotational speed of an output shaft of the electric motor 520A coupled to an input shaft of the pump 522A). For example, the pump 522A can be configured to have a particular pump displacement PD that determines the amount of fluid generated or provided by the pump 522A in, for example, cubic inches per revolution (irrVrev). The electric motor 520A can be running at a commanded speed having units of revolutions per minute (RPM). As such, multiplying the speed of the electric motor 520A by PD determines the fluid flow rate Q in cubic inches per minute (in³/min) provided by the pump 522A to the hydraulic cylinder actuator 504A.

[0065] The flow rate Q in turn determines the linear speed of the piston 508A. For instance, if the electric motor 520A is rotating the pump 522A in a first rotational direction to provide fluid to the first chamber 516A, the piston 508A can extend at a speed V₁ = — . On the other

^AH hand, if the electric motor 520A is rotating the pump 522A is a second rotational direction to provide fluid to the second chamber 518A, the piston 508A can retract at a speed V₂ = Q

^A Annular

[0066] The implementation in Figure 5 with a closed-loop circuit, a variable speed motor, and a fixed displacement pump is an example implementation for illustration. In another example configuration, an open-loop circuit can be used, and the electric motor can be a fixed speed motor driving a variable displacement pump. For instance, the pump can be a variable displacement piston pump with a swash plate, the angle of which can be varied to vary the amount of fluid flow discharged by the pump. Fluid can be drawn by the pump from a fluid reservoir and provided to the hydraulic cylinder actuator 504A, and fluid returning from the hydraulic cylinder actuator 504A flows to the fluid reservoir.

[0067] The EHA 502 A can further include a first load-holding valve 532 A disposed in the fluid flow line 526A between the first pump port 524A and the workport 515A. The EHA 502A can also include a second load-holding valve 534A disposed in the fluid flow line 530A between the second pump port 528A and the workport 517A. The load-holding valves 532A, 534A are configured to prevent the piston 508A from moving (e.g., prevent the load 514A from dropping) in an uncontrolled manner. For example, the load-holding valves 532A, 534A can be configured to allow free flow from the pump 522A to and from the chambers 516A, 518A when actuated, while blocking fluid flow to and from the chambers 516A, 518A when unactuated. The term “block” is used throughout herein to indicate substantially preventing fluid flow except for minimal or leakage flow of drops per minute, for example.

[0068] As an example, the load-holding valves 532A, 534A can have solenoid actuators comprising solenoid coils 535A, 537A respectively, that when energized cause a moving element (e.g., a poppet) within the respective load-holding valves 532A, 534A to move and allow fluid flow between the respective chamber 516A, 518A and the pump 522A. For instance, to extend the piston 508A, the pump 522A can provide fluid flow from the first pump port 524A through the load-holding valve 532A (which is actuated) to the first chamber 516A through the workport 515A. The load-holding valve 534A is also actuated to allow fluid being discharged from the second chamber 518A to flow therethrough to the second pump port 528A.

[0069] Conversely to retract the piston 508A, the pump 522A can provide fluid flow from the second pump port 528A through the load-holding valve 534A (which is actuated) to the second chamber 518A through the workport 517A. The load-holding valve 532 A is also actuated to allow fluid being discharged from the first chamber 516A to flow therethrough to the first pump port 524A.

[0070] In an example, the load-holding valves 532A, 534A can be on/ofif valves that fully open upon actuation. In another example, it may be desirable to control pressure level of fluid in the chamber (either of the chambers 516A, 518A) from which fluid is being discharged. In this example, the load-holding valves 532A, 534A can be configured as proportional valves that can be modulated to have a particular size opening therethrough that achieves a particular back pressure in the respective chamber from which fluid is being discharged.

[0071] In some cases, the hydraulic cylinder actuator 504A can be subjected to a large force caused by the load 514A (e.g., the bucket 106 hits a hard rock during a digging cycle) that causes over-pressurization in either of the chambers 516A, 518A as the load-holding valves 532A, 534A block fluid flow from the chambers 516A, 518A. To protect the cylinder 506A from the possibility of over-pressurization, the EHA 502A can include a workport pressure relief valve assembly disposed between the load-holding valves 532A, 534A and the hydraulic cylinder actuator 504A.

[0072] The workport pressure relief valve assembly can include a pressure relief valve 538A configured to protect the first chamber 516A and connected between the fluid flow line 526A and a common fluid flow line 540A. The workport pressure relief valve assembly can also include a pressure relief valve 542A configured to protect the second chamber 518A and connected between the fluid flow line 530A and the common fluid flow line 540A. The pressure relief valves 538A, 542A are configured to open and provide a fluid flow path to the common fluid flow line 540A, which is fluid coupled to boost flow line 544 described below, when pressure level of fluid in the respective chamber 516A, 518A exceeds a threshold pressure value, such as 300 bar or 4350 psi.

[0073] The workport pressure relief valve assembly can further include anti-cavitation check valves 541A, 543A disposed in parallel with the pressure relief valves 538A, 542A, respectively. The anti-cavitation check valves 541A, 543A are configured to prevent or reduce the likelihood of cavitation in either of the chambers 516A, 518A. Particularly, the anti-cavitation check valves 541A, 543A provide fluid flow paths from the common fluid flow line 540A to the chambers 516A, 518A when pressure level of fluid in the chambers 516A, 518A drops below pressure level of fluid in the common fluid flow line 540 A.

[0074] Further, the pump 522A can also be subjected to over-pressurization at the pump ports 524A, 528A. For example, the pump ports 524A, 528A can be subjected to over pressurization if both load-holding valves 532A, 534A are momentarily unactuated together while the pump 522A is running or if pressure levels in either of the chambers 516A, 518A increases substantially due to an overload situation while the corresponding load-holding valve is actuated). To protect the pump 522A from the possibility of over-pressurization, the EHA 502A may also include a pump pressure relief valve assembly disposed between the pump 522A and the load-holding valves 532A, 534A.

[0075] The pump pressure relief valve assembly can include a pressure relief valve 546A configured to protect the first pump port 524A and connected between the fluid flow line 526A and the common fluid flow line 540A. The pump pressure relief valve assembly can also include a pressure relief valve 548A configured to protect the second pump port 528A and connected between the fluid flow line 530A and the common fluid flow line 540A. The pressure relief valves 546A, 548A are configured to open and provide a fluid flow path to the common fluid flow line 540A when pressure level of fluid in the fluid flow lines 526A, 530A exceeds a threshold pressure value such as 250 bar or 3625 psi. As such, in an example, pressure settings of the pressure relief valves 546A, 548A can be lower than respective pressure settings of the pressure relief valves 538A, 542A.

[0076] The pump pressure relief valve assembly can further include anti-cavitation check valves 550A, 552A disposed in parallel with the pressure relief valves 546A, 548A, respectively. The anti-cavitation check valves 550A, 552A are configured to prevent or reduce the likelihood of cavitation at either of the pump ports 524A, 528A. Particularly, the anti-cavitation check valves 550A, 552A provide fluid flow paths from the common fluid flow line 540A to the pump ports 524A, 528A via the fluid flow lines 526A, 530A when pressure level at the pump ports 524A, 528A is below pressure level of fluid in the common fluid flow line 540 A.

[0077] As mentioned above, the hydraulic cylinder actuator 504Ais unbalanced such that the amount of fluid flow rate provided to or discharged from the first chamber 516A is greater than the amount of fluid flow rate provided to or discharged from the second chamber 518A. As such, the amount of fluid flow rate provided from or received at the first pump port 524A to or from the first chamber 516A is greater than the amount of fluid flow rate provided from or received at the second pump port 528 A to or from the second chamber 518A. Such discrepancy between the fluid flow rate provided by the pump 522A and fluid flow rate received thereat can cause cavitation and the pump 522A might not operate properly. The EHA 502 A provides for a configuration to make up for such discrepancy in fluid flow rate.

[0078] Particularly, The EHA 502A includes a boost circuit 554 configured to boost the fluid flow rate, or consume any excess flow, to make up for the discrepancy in fluid flow rates. The boost circuit 554 can, for example, include a charge pump that is configured to draw fluid from a fluid reservoir 555 and provide the flow to the boost flow line 544. The fluid reservoir 555 can be configured as a fluid storage containing fluid at a low pressure level, e.g., 75-100 psi. In another example, the boost circuit 554 can comprise an accumulator configured to store pressurized fluid, and the fluid reservoir 555 might not be used. The boost circuit 554 can also be configured to receive excess fluid flowing through the boost flow line 544 and provide a path for such excess fluid to the fluid reservoir 555.

[0079] The EHA 502A can further include a reverse shuttle valve 556A configured to fluidly couple the chambers 516A, 518A of the cylinder 506A to the common fluid flow line 540 A, which is connected to the boost flow line 544. The reverse shuttle valve 556A is configured to be responsive to pressure difference across the pump 522A (i.e., pressure difference between the fluid flow line 526A and the fluid flow line 530A).

[0080] In an example, the reverse shuttle valve 556A 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 522A. The reverse shuttle valve 556A can have a first pilot port 558A fluidly coupled to the fluid flow line 526A and a second pilot port 560A fluidly coupled to the fluid flow line 530A. [0081] The reverse shuttle valve 556A also has a third or boost port 562A fluidly coupled to the boost flow line 544 via the common fluid flow line 540 A. The reverse shuttle valve 556A is operated by differential pressure between the fluid flow lines 526A and 530A to: (i) connect the fluid flow line 530A to the common fluid flow line 540A when pressure in the fluid flow line 526A exceeds the pressure level in the fluid flow line 530A to supply boost fluid through the common fluid flow line 540A to the fluid flow line 530A, and (ii) connect the fluid flow line 526A to the common fluid flow line 540A when pressure in the fluid flow line 530A exceeds the pressure level in the fluid flow line 526A such that excess fluid from the first chamber 516A can be received by the common fluid flow line 540A and provided to the boost flow line 544.

[0082] Specifically, if the pump 522A is driven by the electric motor 520A to supply fluid to the fluid flow line 526A for extension of the piston 508A, the pressure differential across the pump 522A shifts the shuttle element of the reverse shuttle valve 556A to connect the boost port 562Ato the second pilot port 560 A, thereby fluidly coupling the fluid flow line 530Ato the common fluid flow line 540A (and the boost flow line 544) while blocking flow from the fluid flow line 526A to the common fluid flow line 540 A. As such, the reverse shuttle valve 556A provides a fluid flow path from the boost flow line 544 to the pump port 528A to make up for the difference between flow rate of fluid provided to the first chamber 516A and flow rate of fluid returning through the fluid flow line 530Afrom the second chamber 518A.

[0083] Conversely, when the pump 522A is driven in the opposite direction to retract the piston 508A, the pressure differential across the pump 522A shifts the shuttle element of the reverse shuttle valve 556Ato connect the first pilot port 558Ato the boost port 562A, thereby fluidly coupling the fluid flow line 526A to the common fluid flow line 540A while blocking flow from the fluid flow line 530A to the common fluid flow line 540A. This way, the reverse shuttle valve 556A provides a fluid flow path for the excess flow of fluid returning through the fluid flow line 526A from the first chamber 516A to the boost flow line 544.

[0084] The term “reverse” is ascribed to the reverse shuttle valve 556A 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 556A does not have a designated outlet port, but rather either provides fluid flow from the boost port 562A to the second pilot port 560A or provide fluid flow from the first pilot port 558 A to the boost port 562 A.

[0085] In the example configuration described above, the reverse shuttle valve 556A is a pilot-operated valve where the shuttle element moves in response to differential pressure between the fluid flow lines 526A, 530A. In other examples, the reverse shuttle valve 556A can be electrically-actuated such that an electric controller (e.g., controller 564 described below) of the EHA 502A can provide electric signals that move the shuttle element based on sensed pressure levels in the fluid flow lines 526 A, 530A.

[0086] As depicted in Figure 5, the EHA 502A can include a controller 564. The controller 564 can include one or more processors or microprocessors and may include data storage (e.g., memory, transitory computer-readable medium, non-transitory computer-readable medium, etc.). The data storage may have stored thereon instructions that, when executed by the one or more processors of the controller 564, cause the controller 564 to perform operations described herein. [0087] The controller 564 can receive input information comprising sensor information via signals from various sensors or input devices, and in response provide electrical signals to various components of the EHA 502A. For example, the controller 564 can receive a command or an input (e.g., from the joysticks 122, 124 of the machine 100) to move the piston 508A in a given direction at a particular desired speed (e.g., to extend or retract the piston 508 A).

[0088] The controller 564 can also receive sensor information indicative of one or more of position or speed of the piston 508A, pressure levels in various hydraulic lines, chambers, or ports of the EHA 502A, magnitude of the load 514A, etc. Responsively, the controller 564 can provide command signals to the electric motor 520A via a power electronics module such as an inverter 566A and to the solenoid coil 535A or the solenoid coil 537A to move the piston 508A in the commanded direction and at a desired commanded speed in a controlled manner. Command signals lines from the controller 564 to the solenoid coils 535A, 537A are not shown in Figure 5 to reduce visual clutter in the drawing. However, it should be understood that the controller 564 is electrically-coupled (e.g., via wires or wireless) to various solenoid coils, input devices, sensors, etc. of the EHA 502A and the machine 100.

[0089] The hydraulic system further includes a battery 568, which represents the battery 202 described above, for example. The inverter 566 A can comprise, for example, an arrangement of semiconductor switching elements (transistors) that can support conversion of direct current (DC) electric power provided from the battery 568 of the machine 100 to three-phase electric power capable of driving the electric motor 520A. The battery 568 can also be electrically-coupled to the controller 564 to provide power thereto and receive commands therefrom. The battery 568 can also include sensors configured to provide sensor information indicative of a charge state of the battery 568, health of the battery 568, and/or whether the battery 568 can receive and store regenerative electric power as described above with respect to the battery 202.

[0090] To extend the piston 508A (i.e., move the piston 508A to the left in Figure 5), the controller 564 can send a command signal to the inverter 566A to operate the electric motor 520A and rotate the pump 522A in a first rotational direction. The controller 564 can also send command signals to energize the solenoid coils 535A, 537A to open respective fluid paths to and from the chambers 516A, 518A. Fluid is thus provided from the pump port 524A through the fluid flow line 526A and through the load-holding valve 532A to the first chamber 516A to extend the piston 508A.

[0091] Pressurized fluid provided by the pump 522A through the fluid flow line 526A shifts the shuttle element of the reverse shuttle valve 556A to connect the boost flow line 544 to the fluid flow line 530A to provide make-up or boost flow that joins fluid discharged from the second chamber 518 A before flowing together to the pump port 528 A. The make-up of boost flow Qe_oost^ determined as Q_Boost

where AR is the cross-sectional area of the rod 512A and V is the speed of the piston 508A as mentioned above.

[0092] As such, the amount of flow rate provided to the pump port 528A is substantially equal to the amount of flow rate provided by the pump 522A through the pump port 524A and the fluid flow line 526A to the first chamber 516A. Notably, the fluid returning through the fluid flow line 530A to the pump port 528A from the chamber 518A has a low pressure level, and therefore, the boost flow can be provided at a low pressure level that matches the low pressure level of flow returning to the pump port 528A. For example, the boost flow can have a pressure level in the range of 10-35 bar or 145-500 psi, compared to high pressure levels such as 4500 psi that might be provided by the pump 522A to the first chamber 516A to extend the piston 508A against the load 514A, assuming the load 514A is resistive. [0093] To retract the piston 508A (i.e., move the piston 508A to the right in Figure 5), the controller 564 can send a command signal to the inverter 566A to operate the electric motor 520A and rotate the pump 522A in a second rotational direction, opposite the first rotational direction. The controller 564 also sends command signals to energize the solenoid coils 535A, 537A to open respective fluid paths to and from the chambers 516A, 518A. Fluid is thus provided from the pump port 528A through the fluid flow line 530A and through the load-holding valve 534A to the second chamber 518A to retract the piston 508A.

[0094] Pressurized fluid provided by the pump 522A through the fluid flow line 530A shifts the shuttle element of the reverse shuttle valve 556A to connect the fluid flow line 526A to the boost flow line 544, thereby providing excess flow returning from the first chamber 516A to the boost flow line 544. The excess flow can be determined as Qsx_cess = A_RV. As such, the amount of flow rate of fluid returning to the pump port 524 A from the first chamber 516 A is substantially equal to the amount of flow provided by the pump 522A through the pump port 528 A and the fluid flow line 530A to the second chamber 518A, while excess flow from the first chamber 516 A is provided to the boost flow line 544.

[0095] In some example operations, the EHA 502A can operate in a regenerative mode as the piston 508A retracts. For example, the hydraulic cylinder actuator 504A can represent the boom hydraulic cylinder actuator 114, and during gravity-assisted lowering of the boom 102, the load 514A is a negative load. As such, the hydraulic cylinder actuator 504A provides hydraulic power (pressurized fluid at a given flow rate) back to the pump 522A rather than consume hydraulic power therefrom. The pump 522A in turn can drive the output shaft of the electric motor 520A. In this case, the electric motor 520A operates as an electric generator that produces rather than consumes electric power.

[0096] The battery 568 can be configured as a rechargeable battery and the regenerative electric power generated by the electric motor 520A can be provided through the inverter 566A to the battery 568 to charge it. In some examples, however, as mentioned above with respect to the battery 202, the battery 568 might not be able to receive and store the regenerative electric power generated by the electric motor 520A.

[0097] The hydraulic system 500 is configured to dissipate at least a portion of the regenerative electric power rather than provide all the power back to the battery 568. In particular, the hydraulic system 500 is configured to use existing components of the machine 100 and passive elements to dissipate any excess regenerative electric power.

[0098] As shown in Figure 5, the hydraulic system 500 of the machine 100 can include another EHA 502B that controls a hydraulic cylinder actuator 504B. The hydraulic cylinder actuator 504B can, for example, represent the arm hydraulic cylinder actuator 116 or the bucket hydraulic cylinder actuator 118. Although the EHA 502B is shown as controlling a hydraulic cylinder actuator, the operations described herein can be implemented with an EHA that controls a hydraulic motor actuator such as the swing hydraulic motor actuator 120.

[0099] The EHA 502B comprises the same components of the EHA 502A described above. Therefore, the components or elements of the EHA 502B are designated with the same reference numbers used for the EHA 502A with a “B” suffix to correspond to the EHA 502B. Components of the EHA 502B operate in a similar manner to components of the EHA 502A as described above.

[00100] Rather than adding active valves to dissipate excess regenerative power, the hydraulic system 500 can utilize the EHA 502B to dissipate it. As shown in Figure 5, the inverter 566A is electrically-coupled to the inverter 566B. As such, at least a portion of the regenerative electric power provided by the electric motor 520A to the inverter 566A can be provided to the inverter 566B. The inverter 566B can then provide the received portion of electric power to the electric motor 520B to drive it. The electric motor 520B in turn drives the pump 522B.

[00101] For instance, the pump 522B can rotate in a first rotational direction to provide fluid to the fluid flow line 530B. In an example, the hydraulic cylinder actuator 504B might not be actuated by the operator of the machine 100, and therefore the controller 564 does not actuate the load-holding valves 532B, 534B. As such, the load-holding valve 534B blocks fluid flow from the pump 522B. As a result, pressure level of fluid in the fluid flow line 530B can increase or build up until it reaches a pressure setting of the pressure relief valve 548B.

[00102] Once the pressure level reaches or exceeds the pressure setting of the pressure relief valve 548B, the pressure relief valve 548B opens to provide a flow path from the fluid flow line 530B to the common fluid line 540B, to the boost flow line 544, then through the boost circuit 554 to the fluid reservoir 555. Therefore, the excess regenerative electric power provided to the inverter 566B is dissipated across the pressure relief valve 548B in the form of heat. This way, existing components of the machine 100, i.e., the components associated with controlling the hydraulic cylinder actuator 504B, and particularly passive components (the pressure relief valve 548B) to dissipate the excess energy.

[00103] In another example, the hydraulic cylinder actuator 504B may be actuated by the operator of the machine 100 at the same time the hydraulic cylinder actuator 504A is providing regenerative electric power that is in excess of the capacity of the battery 568. In this example, the controller 564 can actuate the load-holding valves 532B, 534B to allow fluid flow to and from the hydraulic cylinder actuator 504B.

[00104] Rather than providing all the electric power to the inverter 566B from the battery 568 to drive the hydraulic cylinder actuator 504B, the battery 568 may provide the difference between the electric power requested for the hydraulic cylinder actuator 504B and the regenerative electric power provided from the inverter 566A to the inverter 566B. This way, the hydraulic system 500 reduces the total amount of electric power consumption, thus operating more efficiently.

[00105] In an example, the electric motors 520A, 520 B share a direct current (DC) bus. Thus, if a first electric motor of the electric motors 520A, 520B operates as an electric generator providing power to the DC bus, and the second electric motor is commanded to drive the respective hydraulic actuator, the battery 568 provides the difference between the electric power generated by the first electric motor and the electric power requested by the second electric motor. This mode of operation involving consuming regenerative power as it is produced may be more efficient than first storing the regenerative power in the battery 568 and then releasing it later.

[00106] As mentioned above, the implementation of the hydraulic system 500 is example implementation of the electrohydraulic system 400. The example implementation of the hydraulic system 500 includes two EHAs. In other example implementations, a hydraulic system may include one or more EHA controlling a subset of actuators, and another open loop circuit controlling at least one other actuator.

[00107] Figure 6 illustrates a partial hydraulic system 600 of the machine 100, in accordance with an example implementation. In particular, Figure 6 illustrates control system for two actuators of the machine 100. It should be understood that other actuators of the machine 100 can be controlled in a similar manner. It should also be understood that other types of machines can utilize the disclosed systems. For example, the hydraulic system 600 can be associated with a two-actuator machine such as a skid steer.

[00108] The hydraulic system 600 includes the EHA 502A, which comprises a closed-loop hydraulic circuit. The hydraulic system 600 can also include another hydraulic circuit 602 that is an open-loop hydraulic circuit for controlling the swing hydraulic motor actuator 120. It should be understood that, in other examples, the hydraulic circuit 602 can control a hydraulic cylinder actuator, such as the arm hydraulic cylinder actuator 116 or the bucket hydraulic cylinder actuator 118 (assuming that the hydraulic cylinder actuator 504A represents the boom hydraulic cylinder actuator 114).

[00109] Components of the hydraulic circuit 602 that are the same as components of the EHA 502A and the EHA 502B are designated with the same reference numbers with a “C” suffix. For example, the hydraulic circuit 602 comprises an inverter 566C and an electric motor 520C that operate similar to their corresponding components of the EHA 502A and the EHA502B.

[00110] As another example of similar components, the hydraulic circuit 602 includes a workport pressure relief valve assembly that protects the swing hydraulic motor actuator 120 against over-pressurization. The workport pressure relief valve assembly can include a pressure relief valve 538C, a pressure relief valve 542C, and anti-cavitation check valves 541C, 543C disposed in parallel with the pressure relief valves 538C, 542C, respectively. These components of the workport pressure relief valve assembly operate in a similar manner to their corresponding components with “A” or “B” suffix in Figure 5.

[00111] The hydraulic circuit 602 is configured to control the rate and direction of hydraulic fluid flow to the swing hydraulic motor actuator 120. Such control is achieved by controlling the speed and direction of the electric motor 520C used to drive a pump 604. The pump 604 can be configured to operate as a unidirectional fluid flow source, for example. Particularly, the pump 604 has an inlet port 606 fluidly coupled to a fluid flow line 608 and an outlet port 610 fluidly coupled to a fluid flow line 612. [00112] The inlet port 606 and the fluid flow line 608 are also fluidly coupled to the fluid reservoir 555. The fluid reservoir 555 is drawn in two locations in Figure 6 to reduce visual clutter but it should be understood that the hydraulic system 600 can include one fluid reservoir to which return fluid can be provided via fluid passages. The pump 604 can be configured to draw fluid from the fluid reservoir 555 through the inlet port 606 then discharge the fluid through the outlet port 610 to the fluid flow line 612.

[00113] In the example implementation of Figure 6, the pump 604 can be a fixed displacement pump and the amount of fluid flow provided by the pump 604 is controlled by the speed of the electric motor 520C. In other example implementations, the pump 604 may be configured as a variable displacement pump, while the electric motor 520C can be a fixed or variable speed motor. For instance, the pump 604 can be a variable displacement piston pump with a swash plate, the angle of which can be varied to vary the amount of flow discharged by the pump 604.

[00114] As mentioned above, the pump 604 can be unidirectional, while the swing hydraulic motor actuator 120 is bi-directional to be able to rotate the cab 108 of the machine 100 in both rotational directions. As such, the hydraulic circuit 602 can further include a directional control valve 614 configured to direct fluid from the pump 604 to either the workport 515C or the workport 517C of the swing hydraulic motor actuator 120.

[00115] Particularly, the directional control valve 614 has a valve inlet port 616 fluidly coupled to the outlet port 610 of the pump 604 via the fluid flow line 612. The directional control valve 614 also has a return port 618 fluidly coupled to the fluid reservoir 555 via the fluid flow line 608.

[00116] The directional control valve 614 further includes (i) a valve workport 620 that is fluidly coupled to the workport 517C of the swing hydraulic motor actuator 120 via fluid flow line 622, and (ii) another valve workport 624 that is fluidly coupled to the workport 515C of the swing hydraulic motor actuator 120 via fluid flow line 626.

[00117] The directional control valve 614 is configured to fluidly couple one of the valve workports 620, 624 to the outlet port 610 of the pump 604 while fluidly coupling the other valve workport to the fluid reservoir 555 based on a state of actuation of the directional control valve 614. Particularly, the directional control valve 614 can have solenoid coil 628 and solenoid coil 630. The solenoid coils 628, 630 can be energized by the controller 564 (the signal lines to the solenoid coils are not drawn to reduce visual clutter in the drawing).

[00118] When neither of the solenoid coils 628, 630 is actuated, the directional control valve 614 operates in a neutral state that blocks fluid flow therethrough and the swing hydraulic motor actuator 120 does not move. When the solenoid coil 628 is energized, the directional control valve 614 operates in a first state in which fluid received from the outlet port 610 of the pump 604 at the valve inlet port 616 flows to the valve workport 624, then to the workport 515C of the swing hydraulic motor actuator 120, causing the swing hydraulic motor actuator 120 to rotate in a first direction. Fluid discharged from the workport 517C is received at the valve workport 620 and flows to the return port 618 then to the fluid reservoir 555.

[00119] When the solenoid coil 630 is energized, the directional control valve 614 operates in a second state in which fluid received from the outlet port 610 of the pump 604 at the valve inlet port 616 flows to the valve workport 620, then to the workport 517C of the swing hydraulic motor actuator 120, causing the swing hydraulic motor actuator 120 to rotate in a second direction. Fluid discharged from the workport 515C is received at the valve workport 624 and flows to the return port 618 then to the fluid reservoir 555. [00120] The directional control valve 614 can be an on/off valve or can be a proportional valve where the magnitude of the electric command signal to the solenoid coils 628, 630 can be proportional to the fluid flow rate through the directional control valve 614. This way, the directional control valve 614 can meter fluid flow to further control the rotational speed of the swing hydraulic motor actuator 120 and/or pressure levels at the workports 515C, 517C.

[00121] The hydraulic circuit 602 further includes a pressure relief valve 632 disposed in parallel with the directional control valve 614 and fluidly couples the fluid flow line 612 to the fluid flow line 608. The pressure relief valve 632 can protect the pump 604 against over pressurization. For example, if the pump 604 is actuated and provides fluid to the fluid flow line 612, while the directional control valve 614 is in a neutral (unactuated) state, pressure level can rapidly build up in the fluid flow line 612. Once, the pressure level in the fluid flow line 612 exceeds the pressure setting of the pressure relief valve 632, the pressure relief valve 632 opens and vents fluid from the fluid flow line 612 to the fluid flow line 608, which is fluidly coupled to the fluid reservoir 555. This way, pressure level in the fluid flow line 612 might not exceeds the pressure setting of the pressure relief valve 632.

[00122] The hydraulic system 600 can utilize the hydraulic circuit 602 to dissipate any excess regenerative power generated by the EHA 502A. As shown in Figure 6, the inverter 566A is electrically-coupled to the inverter 566C. As such, at least a portion of the regenerative electric power provided by the electric motor 520A to the inverter 566A can be provided to the inverter 566C. The inverter 566C can then provide the received portion of electric power to the electric motor 520C to drive it. The electric motor 520C in turn drives the pump 604, which provides fluid to the fluid flow line 612.

[00123] In an example, the swing hydraulic motor actuator 120 might not be actuated by the operator of the machine 100, and therefore the controller 564 does not actuate the directional control valve 614, which thus remains in a neutral state blocking fluid flow from the pump 604 at the valve inlet port 616. As a result, pressure level of fluid in the fluid flow line 612 can increase or build up until it reaches the pressure setting of the pressure relief valve 632.

[00124] Once the pressure level reaches or exceeds the pressure setting of the pressure relief valve 632, the pressure relief valve 632 opens to provide a flow path from the fluid flow line 612 to the fluid flow line 608, then to the fluid reservoir 555. Therefore, the excess regenerative electric power provided to the inverter 566C is dissipated across the pressure relief valve 632 in the form of heat. This way, existing components of the machine 100, i.e., the components associated with controlling swing hydraulic motor actuator 120, and particularly passive components (the pressure relief valve 632) to dissipate the excess energy.

[00125] In another example, the swing hydraulic motor actuator 120 may be actuated by the operator of the machine 100 at the same time the hydraulic cylinder actuator 504A is providing regenerative electric power that is in excess of the capacity of the battery 568. In this example, the controller 564 can actuate the directional control valve 614 to allow fluid flow to and from the swing hydraulic motor actuator 120.

[00126] Rather than providing all the electric power to the inverter 566C from the battery 568 to drive the swing hydraulic motor actuator 120, the battery 568 may provide the difference between the electric power requested for the swing hydraulic motor actuator 120 and the regenerative electric power provided from the inverter 566A to the inverter 566C. This way, the hydraulic system 600 can reduce the total amount of electric power consumption, thus operating more efficiently.

[00127] In an example, the regenerative power provided by the electric motor 520A can be used to drive the electric motor 520C, which in turn drives the pump 604. The pump 604 discharges fluid flow therefrom. The directional control valve 614 is actuated and a first portion of the fluid flow discharged from the pump 604 is used to drive the swing hydraulic motor actuator 120, while a second portion of fluid flow discharged from the pump 604 is throttled by either the directional control valve 614 or the pressure relief valve 632. In this example, a portion of the regenerative power is dissipated as heat, while another portion is used to drive the swing hydraulic motor actuator 120.

[00128] Figure 7 is a flowchart of a method 700 for operating an electrohydraulic system, in accordance with an example implementation. For example, the method 700 can be implemented with the electrohydraulic system 400 and its example implementations in the hydraulic system 500 or the hydraulic system 600.

[00129] The method 700 may include one or more operations, or actions as illustrated by one or more of blocks 702-706. 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.

[00130] At block 702, the method 700 includes receiving, at a controller (e.g., the controller 564) of the electrohydraulic system (e.g., the electrohydraulic system 400), sensor information indicative of a state of a battery (e.g., the battery 202 or the battery 568) of the electrohydraulic system, wherein the electrohydraulic system comprises: (i) a hydraulic actuator (e.g., the hydraulic cylinder actuator 504A) configured to operate in a regenerative mode in which the hydraulic actuator generates regenerative hydraulic power as the hydraulic actuator is subjected to a negative load, (ii) a first pump (e.g., the pump 206 or the pump 522A) coupled to a first electric motor (e.g., the electric motor 204 or the electric motor 520A), wherein the first pump is configured to receive the regenerative hydraulic power from the hydraulic actuator, thereby driving the first electric motor, causing the first electric motor to generate regenerative electric power, (iii) a second electric motor (e.g., the second electric motor 402, the electric motor 520B, or the electric motor 520C) configured to drive a second pump (e.g., the pump 404, the pump 522B, or the pump 604), and (iv) a valve (e.g., the passive valve 406, the pressure relief valve 548B, or the pressure relief valve 632) fluidly coupled to the second pump.

[00131] At block 704, the method 700 includes determining, by the controller based on the sensor information, that the regenerative electric power generated by the first electric motor exceeds a capacity of the battery to accommodate the regenerative electric power.

[00132] At block 706, the method 700 includes providing at least a portion of the regenerative electric power generated by the first electric motor to the second electric motor, thereby driving the second pump, causing the second pump to discharge fluid flow therefrom, wherein the valve is configured to throttle the fluid flow discharged from the second pump, thereby dissipating power as heat.

[00133] 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.

[00134] 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.

[00135] 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.

[00136] 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.

[00137] 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

[00138] 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. [00139] 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.

Claims

CLAIMS What is claimed is:

1. An electrohydraulic system comprising: a hydraulic actuator configured to operate in a regenerative mode in which the hydraulic actuator generates regenerative hydraulic power as the hydraulic actuator is subjected to a negative load; a first pump coupled to a first electric motor, wherein the first pump is configured to receive the regenerative hydraulic power from the hydraulic actuator, thereby driving the first electric motor, causing the first electric motor to generate regenerative electric power; a second electric motor configured to drive a second pump, wherein the second electric motor is configured to receive at least a portion of the regenerative electric power generated by the first electric motor, thereby driving the second pump, causing the second pump to discharge fluid flow therefrom; and a valve fluidly coupled to the second pump, wherein the valve is configured to throttle the fluid flow discharged from the second pump, thereby dissipating power as heat.

2. The electrohydraulic system of claim 1, wherein the portion of the regenerative electric power generated by the first electric motor is a first portion, wherein the electrohydraulic system further comprises: a battery configured to receive a second portion of the regenerative electric power generated by the first electric motor.

3. The electrohydraulic system of claim 2, further comprising: a controller configured to perform operations comprising: receiving sensor information indicative of a state of the battery; determining, based on the sensor information, that the regenerative electric power generated by the first electric motor exceeds a capacity of the battery to accommodate the regenerative electric power; and responsively, providing the first portion of the regenerative electric power generated by the first electric motor to the second electric motor.

4. The electrohydraulic system of claim 3, wherein the controller is further configured to perform operations comprising: determining that the battery is within a threshold capacity from being fully charged; and responsively, providing all the regenerative electric power generated by the first electric motor to the second electric motor.

5. The electrohydraulic system of claim 1, wherein the valve is a passive valve configured to throttle the fluid flow discharged from the second pump without an actuation signal.

6. The electrohydraulic system of claim 5, wherein the passive valve is a pressure relief valve configured to open and throttle the fluid flow discharged from the second pump as pressure level of fluid exceeds a pressure setting of the pressure relief valve.

7. The electrohydraulic system of claim 1, further comprising: a first inverter electrically-coupled to the first electric motor and configured to receive the regenerative electric power generated by the first electric motor; and a second inverter electrically-coupled to the first inverter and the second electric motor, wherein the first inverter is configured to provide the portion of the regenerative electric power generated by the first electric motor to the second inverter, causing the second inverter to drive the second electric motor.

8. A machine comprising: a first hydraulic actuator configured to operate in a regenerative mode in which the first hydraulic actuator generates regenerative hydraulic power as the first hydraulic actuator is subjected to a negative load; a first pump coupled to a first electric motor, wherein the first pump is configured to receive the regenerative hydraulic power from the first hydraulic actuator, thereby driving the first electric motor, causing the first electric motor to generate regenerative electric power; a second hydraulic actuator; and a second electric motor configured to drive a second pump to operate the second hydraulic actuator when the second hydraulic actuator is actuated, wherein the second electric motor is configured to receive at least a portion of the regenerative electric power generated by the first electric motor, thereby driving the second pump, causing the second pump to discharge fluid flow therefrom.

9. The machine of claim 8, further comprising: a first valve configured to allow fluid flow from the second pump to the second hydraulic actuator when the second hydraulic actuator is actuated and block fluid flow from the second pump to the second hydraulic actuator when the second hydraulic actuator is unactuated; and a second valve fluidly coupled to the second pump, wherein as the second electric motor receives the portion of the regenerative electric power generated by the first electric motor, the first valve is configured to block fluid flow to the second hydraulic actuator, thereby causing the fluid flow discharged from the second pump to be diverted to the second valve, wherein the second valve is configured to throttle the fluid flow discharged from the second pump, thereby dissipating power as heat.

10. The machine of claim 9, wherein the first valve comprises a load-holding valve or a directional control valve.

11. The machine of claim 9, wherein the second valve is a pressure relief valve configured to open and throttle the fluid flow discharged from the second pump as pressure level of fluid exceeds a pressure setting of the pressure relief valve.

12. The machine of claim 8, further comprising: a valve fluidly coupled to the second pump, wherein a first portion of fluid flow discharged from the second pump is used to drive the second hydraulic actuator and a second portion of fluid flow discharged from the second pump is throttled by the valve, thereby dissipating power as heat.

13. The machine of claim 8, wherein the portion of the regenerative electric power generated by the first electric motor is a first portion, wherein the machine further comprises: a battery configured to receive a second portion of the regenerative electric power generated by the first electric motor.

14. The machine of claim 13, further comprising: a controller configured to perform operations comprising: receiving sensor information indicative of a state of the battery; determining, based on the sensor information, that the regenerative electric power generated by the first electric motor exceeds a capacity of the battery to accommodate the regenerative electric power; and responsively, providing the first portion of the regenerative electric power generated by the first electric motor to the second electric motor.

15. The machine of claim 14, wherein the controller is further configured to perform operations comprising: determining that the battery is within a threshold capacity from being fully charged; and responsively, providing all the regenerative electric power generated by the first electric motor to the second electric motor.

16. The machine of claim 8, further comprising: a first inverter electrically-coupled to the first electric motor and configured to receive the regenerative electric power generated by the first electric motor; and a second inverter electrically-coupled to the first inverter and the second electric motor, wherein the first inverter is configured to provide the portion of the regenerative electric power generated by the first electric motor to the second inverter, causing the second inverter to drive the second electric motor.

17. A method comprising: receiving, at a controller of an electrohydraulic system, sensor information indicative of a state of a battery of the electrohydraulic system, wherein the electrohydraulic system comprises: (i) a hydraulic actuator configured to operate in a regenerative mode in which the hydraulic actuator generates regenerative hydraulic power as the hydraulic actuator is subjected to a negative load, (ii) a first pump coupled to a first electric motor, wherein the first pump is configured to receive the regenerative hydraulic power from the hydraulic actuator, thereby driving the first electric motor, causing the first electric motor to generate regenerative electric power, (iii) a second electric motor configured to drive a second pump, and (iv) a valve fluidly coupled to the second pump; determining, by the controller based on the sensor information, that the regenerative electric power generated by the first electric motor exceeds a capacity of the battery to accommodate the regenerative electric power; and providing at least a portion of the regenerative electric power generated by the first electric motor to the second electric motor, thereby driving the second pump, causing the second pump to discharge fluid flow therefrom, wherein the valve is configured to throttle the fluid flow discharged from the second pump, thereby dissipating power as heat.

18. The method of claim 17, wherein the portion of the regenerative electric power generated by the first electric motor is a first portion, wherein the method further comprises: providing a second portion of the regenerative electric power generated by the first electric motor to the battery.

19. The method of claim 18, further comprising: determining that the battery is within a threshold capacity from being fully charged; and responsively, providing all the regenerative electric power generated by the first electric motor to the second electric motor.

20. The method of claim 17, wherein the electrohydraulic system further comprises: (i) a first inverter electrically-coupled to the first electric motor and configured to receive the regenerative electric power generated by the first electric motor, and (ii) a second inverter electrically-coupled to the first inverter and the second electric motor, and wherein providing the portion of the regenerative electric power generated by the first electric motor to the second electric motor comprises: causing the first inverter to provide the portion of the regenerative electric power generated by the first electric motor to the second inverter, causing the second inverter to drive the second electric motor.