Optimizing mode transitions between dual power electro-hydrostatic control systems

The present disclosure relates to a blended or hybrid power system with increased operating efficiency. The blended power system combines the advantages of electrical power with the advantages of hydraulic power when delivering power to a hydraulic actuator. The hydraulic power provides higher power density and the electrical power provides high efficiency and control accuracy in the blended power system. In a blended power system, a control system may be configured to select different modes of operation based on the loads encountered in the combined hydraulic and electrohydrostatic system. The blended power system also allows for smooth and uninterrupted transitions between the different modes of operation within the blended power system. Thus, jerkiness in the blended power system may be minimized or eliminated.

TECHNICAL FIELD

The disclosure relates to hydraulic actuators, and more particularly to the control of dual power electro-hydrostatic actuators.

BACKGROUND

Electro-hydrostatic actuators (EHAs) replace hydraulic systems with self-contained actuators operated solely by electrical power. An EHA system may include an extendable hydraulic linear actuator having a cylinder and a piston, a hydraulic pump, and an electric motor. The hydraulic system may be for extending and retracting a hydraulic linear actuator in a work machine, such as but not limited to hydraulic excavators, loading shovels, backhoe shovels, mining equipment, industrial machinery and the like, having one or more actuated components such as lifting and/or tilting arms, booms, buckets, steering and turning functions, etc.

EHAs have been utilized for low power, stationary applications. When it comes to higher power applications, such as off-highway (i.e., off-road) vehicles, the current state-of-the-art technology has not provided a cost effective and energy efficient solution.

SUMMARY

Aspects of the present disclosure relate to increasing operating efficiency in a blended or hybrid power system. The blended power system combines the advantages of electrical power with the advantages of hydraulic power when delivering power to a hydraulic actuator. The hydraulic power provides higher power density and the electrical power provides high efficiency and control accuracy in the blended power system. In a blended power system, a control system may be configured to select different modes of operation based on the loads encountered in the combined hydraulic I and electro-hydrostatic system. The blended power system also allows for smooth and uninterrupted transitions between the different modes of operation within the blended power system. Thus, jerkiness in the blended power system may be minimized or eliminated.

One aspect of the disclosure relates to a hydraulic system that may include a bi-directional hydraulic pump that has a first pump port and a second pump port. The hydraulic system may include an electric motor/generator mechanically coupled to the bi-directional hydraulic pump and a hydraulic pressure source. The hydraulic system may also include a first actuator port; a second actuator port; and a valve arrangement configured for operating the hydraulic system in a plurality of modes. The hydraulic system may further include a control system for coordinating operation of the valve arrangement.

In certain examples, one of the plurality of modes may include a first combined hydraulic and electro-hydrostatic mode in which: a) the first pump port is fluidly connected to the first actuator port; b) the second pump port is fluidly connected to the hydraulic pressure source; and c) the second actuator port is fluidly connected to tank.

In certain examples, one of the plurality of modes may include a second combined hydraulic and electro-hydrostatic mode in which: a) the first pump port is fluidly connected to the hydraulic pressure source; b) the second pump port is fluidly connected to the second actuator port; and c) the first actuator port is fluidly connected to tank.

In certain examples, one of the plurality of modes may include a load-holding mode in which: a) the hydraulic pressure source is connected to the first and second pump ports; b) the first and second actuator ports are disconnected from the first and second pump ports; and c) hydraulic fluid flow through the first and second actuator ports is locked.

In certain examples, one of the plurality of modes may include an electro-hydrostatic mode in which the hydraulic pressure source is disconnected from the first and second pump ports, and a closed hydraulic circuit is defined between the hydraulic pump and the first and second actuator ports.

The control system may have a transition control protocol used for transitioning the hydraulic system between two different modes. A first of the two different modes may include one of the first combined hydraulic and electro-hydrostatic mode, the second combined hydraulic and electro-hydrostatic mode or the load-holding mode. A second of the two different modes may include one of the first combined hydraulic and electro-hydrostatic mode, the second combined hydraulic and electro-hydrostatic mode or the load-holding mode.

In certain examples, the transition control protocol includes operating the hydraulic system temporarily in the electro-hydrostatic mode as an intermediate step that takes place as the hydraulic system is transitioned between the first and second different modes.

The hydraulic system may include a first hydraulic flow path for fluidly connecting the hydraulic pressure source to the first pump port. A first valve may be positioned along the first hydraulic flow path for opening the first hydraulic flow path such that fluid communication is provided between the first pump port and the hydraulic pressure source and for closing the first hydraulic flow path such that fluid communication is blocked between the hydraulic pressure source and the first pump port.

The hydraulic system may also include a second hydraulic flow path for fluidly connecting the hydraulic pressure source to the second pump port. A second valve may be positioned along the second hydraulic flow path for opening the second hydraulic flow path such that fluid communication is provided between the second pump port and the hydraulic pressure source and for closing the second hydraulic flow path such that fluid communication is blocked between the hydraulic pressure source and the second pump port.

The hydraulic system may also include a third hydraulic flow path for fluidly connecting the first pump port to the first actuator port. A third valve may be positioned along the third hydraulic flow path. The third valve may have a first valve position in which the third hydraulic flow path is open between the first actuator port and the first pump port, a second valve position in which the third hydraulic flow path is blocked and flow through a portion of the third hydraulic flow path located between the third valve and the first actuator port is hydraulically locked, and a third valve position in which fluid communication between the first pump port and the first actuator port through the third hydraulic flow path is interrupted and the first actuator port is fluidly connected to tank.

The hydraulic system may further include a fourth hydraulic flow path for fluidly connecting the second pump port to the second actuator port. A fourth valve may be positioned along the fourth hydraulic flow path. The fourth valve may have a first valve position in which the fourth hydraulic flow path is open between the second actuator port and the second pump port, a second valve position in which the fourth hydraulic flow path is blocked and flow through a portion of the fourth hydraulic flow path located between the fourth valve and the second actuator port is hydraulically locked, and a third valve position in which fluid communication between the second pump port and the second actuator port through the fourth hydraulic flow path is interrupted and the second actuator port is fluidly connected to tank.

In certain examples, the hydraulic system may include a pump charge circuit for providing pump charge flow to the third and fourth hydraulic flow paths.

DETAILED DESCRIPTION

FIG.1is a schematic representation of an example hydraulic actuation system100in accordance with the principles of the present disclosure. The hydraulic actuation system100may include a bi-directional hydraulic pump102that has a first pump port104and a second pump port106. The hydraulic actuation system100may also include an electric motor/generator108. In one example, the electric motor/generator108is a servo electric motor/generator. The electric motor/generator108includes a motor drive110that may be coupled to an electrical power source (not shown). The electric motor/generator108may be mechanically coupled to the bi-directional hydraulic pump102by a drive shaft112.

The hydraulic actuation system100may also include a hydraulic pressure source114. In certain examples, the hydraulic pressure source114includes a common pressure rail. The common pressure rail can be pressurized by a hydraulic pump or the like and can include a hydraulic accumulator for storing and/or supplying hydraulic pressure as needed.

The hydraulic actuation system100may include a first hydraulic flow path116for fluidly connecting the hydraulic pressure source114to the first pump port104, and a second hydraulic flow path118for fluidly connecting the hydraulic pressure source114to the second pump port106.

The hydraulic actuation system100may further include a first actuator port120and a second actuator port122. A third hydraulic flow path124may be provided in the hydraulic actuation system100for fluidly connecting the first pump port104to the first actuator port120. A fourth hydraulic flow path126may be provided in the hydraulic actuation system100for fluidly connecting the second pump port106to the second actuator port122. The hydraulic actuation system100may include a pump charge circuit128for providing pump charge flow to the third and fourth hydraulic flow paths124,126.

A valve arrangement130may be configured in the hydraulic actuation system100for operating the hydraulic actuation system100in a plurality of modes. In certain examples, the valve arrangement130may include a first valve132, a second valve134, a third valve136, and a fourth valve138. In certain examples, the first and second valves132,134may include a two position spool valve. In certain examples, the third and fourth valves136,138may include a three position spool valve. It will be appreciated that the first, second, third, and fourth valves132,134,136,138can each be moved between different positions by a corresponding actuator such as a solenoid or a voice coil actuator, and/or can have movement which is spring and/or pilot assisted. The first and second valves132,134may be separate valves that are independently movable relative to one another. The third and fourth valves136,138may be separate valves that are independently movable relative to one another.

As used herein, independent valve movement may be defined as valves that have the capability of being moved independently with respect to each other. For example, a first valve may remain stationary while a second valve may be moved and vice versa. Independent valve movement may also include examples where movement of the valves, for example sequenced movement, may be coordinated by a controller.

The first valve132may be positioned along the first hydraulic flow path116for opening the first hydraulic flow path116such that fluid communication is provided between the first pump port104and the hydraulic pressure source114. The first valve132may also be configured for closing the first hydraulic flow path116such that fluid communication is blocked between the hydraulic pressure source114and the first pump port104.

The second valve134may be positioned along the second hydraulic flow path118for opening the second hydraulic flow path118such that fluid communication is provided between the second pump port106and the hydraulic pressure source114. The second valve134may also be configured for closing the second hydraulic flow path118such that fluid communication is blocked between the hydraulic pressure source114and the second pump port106.

The third valve136may be positioned along the third hydraulic flow path124. In the example depicted inFIG.1, the third valve136is in a first valve position in which the third hydraulic flow path124is open between the first actuator port120and the first pump port104.

In other examples, the third valve136may be positioned in a second valve position in which the third hydraulic flow path124is blocked and flow through a portion of the third hydraulic flow path124located between the third valve136and the first actuator port120is hydraulically locked.

In still other examples, the third valve136may be configured in a third valve position in which fluid communication between the first pump port104and the first actuator port120through the third hydraulic flow path124is interrupted and the first actuator port120is fluidly connected to tank140(seeFIG.5).

The fourth valve138may be positioned along the fourth hydraulic flow path126. The fourth valve138may have a first valve position in which the fourth hydraulic flow path126is open between the second actuator port122and the second pump port106, a second valve position in which the fourth hydraulic flow path126is blocked and flow through a portion of the fourth hydraulic flow path126located between the fourth valve138and the second actuator port122is hydraulically locked, and a third valve position in which fluid communication between the second pump port106and the second actuator port122through the fourth hydraulic flow path126is interrupted and the second actuator port122is fluidly connected to tank140.FIG.1depicts the fourth valve138in the third valve position.

The hydraulic actuation system100may include a control system142for coordinating operation of the valve arrangement130. The control system142may have a transition control protocol used for transitioning the hydraulic actuation system100between two different modes. In low power applications, the control system142may select a single EHA mode operation and when a higher load application is encountered, the control system142may select the dual EHA mode operation.

The control system142may include a controller or controllers that each have one or more processors. The processors can interface with software, firmware, and/or hardware. Additionally, the processors can include digital analog processing capabilities and can interface with memory (e.g., random access memory, read-only memory, or other data storage). In certain examples, the processors can include a programmable logic controller, one or more microprocessors, or like structures.

FIG.2schematically illustrates four-quadrant operations Q1-Q4of a dual power electro-hydrostatic actuator144in accordance with the principles of the present disclosure. The actuator144may be depicted as a hydraulic cylinder. Transitioning between the various quadrants of operation can be controlled by the control system142. The operating mode may be selected based on the power/force conditions in the hydraulic actuation system100. The four-quadrant operations refer to actuator extension or retraction under passive or overrunning loads, which is described in further detail below.

The valve arrangement130may be configured for operating the hydraulic actuation system100in a plurality of operating modes. The plurality of operating modes may include a first combined hydraulic and electro-hydrostatic mode20(seeFIG.3andFIG.4) in which: a) the first pump port104is fluidly connected or coupled to (i.e., in fluid communication with) the first actuator port120; b) the second pump port106is fluidly connected or coupled to the hydraulic pressure source114; and c) the second actuator port122is fluidly connected or coupled to tank140.

The plurality of operating modes may also include a second combined hydraulic and electro-hydrostatic mode40(seeFIG.5andFIG.6) in which: a) the first pump port104is fluidly connected or coupled to the hydraulic pressure source114; b) the second pump port106is fluidly connected or coupled to the second actuator port122; and c) the first actuator port120is fluidly connected or coupled to tank140.

The plurality of operating modes may further include a load-holding mode60(seeFIG.8) in which: a) the hydraulic pressure source114is connected to the first and second pump ports104,106; b) the first and second actuator ports120,122are disconnected from the first and second pump ports104,106; and c) hydraulic fluid flow through the first and second actuator ports120,122is locked.

The plurality of operating modes may include an electro-hydrostatic mode80(seeFIG.9) in which the hydraulic pressure source114is disconnected from the first and second pump ports104,106, and a closed hydraulic circuit is defined between the bi-directional hydraulic pump102and the first and second actuator ports120,122. Each one of the plurality of operating modes will be described in further detail with reference toFIGS.3-6.

The control system142may be configured to sense a load transition condition. The load transition condition may be a condition in which a load applied to the actuator144fluidly coupled to the first and second actuator ports120,122is transitioning from a passive state to an over-running state and vice versa. The four-quadrant operations Q1-Q4of a dual power electro-hydrostatic actuator144depicted inFIG.2illustrate the transition between a passive state and an over-running state. Each quadrant is described herein.

FIG.3schematically illustrates the first quadrant QI in which the hydraulic actuation system I00is operating in the first combined hydraulic and electro-hydrostatic mode20and the actuator load is in an over-running condition. When the hydraulic actuation system I00is in this mode, fluid from the actuator144may be directed through the third hydraulic flow path124to the bi-directional hydraulic pump I02thereby driving the bi-directional hydraulic pump I02as a hydraulic motor. The actuator144is indicated with different sign conventions. The arrow labeled F represents the direction that load is being applied to the rod of the actuator144. The arrow labeled V represents the direction of movement of the piston rod of the actuator144relative to the actuator body of the actuator144. An upward direction of the velocity arrow V represents a positive direction while a downward direction of the velocity arrow V represents a negative direction.

Still referring toFIG.3, the arrow F is directed in an upward direction to indicate that the load corresponds to a positive force value. Likewise, the velocity arrow V is directed in an upward direction. That is, the first quadrant QI ofFIG.2represents an operational condition in which the velocity V of the piston rod and the load force F acting on the piston rod are both in a positive direction. This represent an overrunning condition in which the actuator144is extending and a rod side146of the actuator144is the load holding side of the actuator144.

When the hydraulic actuation system I00is operating in the first quadrant QI, energy from a load is directed from the actuator144back to the bi-directional hydraulic pump I02where energy is captured for re-use. In this condition, the force of the load applied to the piston rod drives hydraulic fluid flow from the rod side146of the actuator144back through the third valve136to the bi-directional hydraulic pump102to drive movement of the bi-directional hydraulic pump102. As such, the third valve136is in the first valve position in which the third hydraulic flow path124is open between the first actuator port120and the first pump port104. That is, energy corresponding to the hydraulic fluid flow Q from the actuator144can be captured by an accumulator at the hydraulic pressure source114and/or can be used to drive the electric motor/generator108through the drive shaft112thereby causing electricity to be generated which can be stored at a battery corresponding to an electrical power source (not shown).

Turning toFIG.4, a second quadrant Q2operation of the four different quadrants of operation depicted inFIG.2is illustrated. The second quadrant Q2is a passive operating condition in which the actuator144is retracting and the rod side146of the actuator144is the load-holding side of the actuator144. The arrow F is directed in an upward direction and the velocity arrow V is directed in a downward direction.

That is, the second quadrant Q2ofFIG.4represents an operational condition in which the load force F acting on the piston rod of the actuator144is positive and the velocity V of the piston rod is negative. In this condition, hydraulic energy is directed from the bi-directional hydraulic pump102to the actuator144to drive movement of the load. When accommodating second quadrant operation, hydraulic power directed through the bi-directional hydraulic pump102from the hydraulic pressure source114can be directed to the rod side146of the actuator144and used to drive downward movement of the piston rod against the load force F applied to the piston rod. In the operating condition ofFIG.4, the first hydraulic flow path116is closed, the second hydraulic flow path118is open, the third valve136is in the first valve position in which the third hydraulic flow path124is open between the first actuator port120and the first pump port104and the fourth valve138is in the third valve position in which fluid communication between the second pump port106and the second actuator port122through the fourth hydraulic flow path126is interrupted and the second actuator port122is fluidly connected to tank140.

In the operating condition ofFIG.4, the electric motor/generator108and the hydraulic pressure source114cooperate to cause the bi-directional hydraulic pump102to direct hydraulic fluid to the first actuator port120. Power for driving movement of the actuator144can be provided by the hydraulic pressure source114coupled to the second pump port106of the bi-directional hydraulic pump102by an electrical power source which drives the electric motor/generator108coupled to the bi-directional hydraulic pump102; or by blended power provided by both hydraulic power source coupled to the second pump port106and the electrical power source which drives the electric motor/generator108coupled to the bi-directional hydraulic pump102by the drive shaft112.

Depending upon the magnitude of power required to drive movement of the piston rod (i.e., the differential pressure required between the rod side146of the actuator144and the pressure provided by the hydraulic pressure source114), the electric motor/generator108can either be operated as a generator which extracts energy from the bi-directional hydraulic pump102through the drive shaft112and stores the extracted energy at a battery for later use, or can be operated as a motor in which energy is transferred to the bi-directional hydraulic pump102through the drive shaft112to provide a boost of hydraulic pressure/flow to the actuator144.

It will be appreciated that when the electric motor/generator108is operated as a motor, blended power (e.g., power derived from the electrical power source and the hydraulic power source) is used to drive the actuator144. It will be appreciated that when the electric motor/generator108is operated as a generator, the hydraulic pressure source114drives movement of the actuator144and the motor/generator captures excess power provided by the hydraulic pressure source114that is not needed to drive the actuator144.

Turning toFIG.5, a third quadrant Q3is schematically illustrated in which the hydraulic actuation system100is operating in the second combined hydraulic and electro-hydrostatic mode40and the actuator load is in an over-running condition. In the second combined hydraulic and electro-hydrostatic mode40, the second hydraulic flow path118is closed, the first hydraulic flow path116is open, the third valve136is in the third valve position in which fluid communication between the first pump port104and the first actuator port120through the third hydraulic flow path124is interrupted and the first actuator port120is fluidly connected to tank140, and the fourth valve138is in the first valve position in which the fourth hydraulic flow path126is open between the second actuator port122and the second pump port106. In this over-running condition, energy can be transferred from the actuator144back to the bi-directional hydraulic pump102. Such power can be recaptured by means such as an accumulator at the hydraulic pressure source114and/or by operating the electric motor/generator108as a generator such that the hydraulic energy transferred from the actuator144can be converted to electrical energy which can be stored at a battery, capacitor or other structure.

FIG.6illustrates the hydraulic actuation system100operating according to a fourth quadrant Q4operation in which the direction of movement of the piston rod of the actuator144is opposite as compared to the load forced direction (e.g., the actuator144is extending with the piston moving upward against a downward load force F). The fourth quadrant Q4is a passive operating condition in which the actuator144is retracting and the rod side146of the actuator144is the load-holding side of the actuator144. The arrow F is directed in a downward direction and the velocity arrow V is directed in an upward direction. That is, the fourth quadrant Q4ofFIG.6represents an operational condition in which the load force F acting on the piston rod of the actuator144is negative and the velocity V of the piston rod is positive. The piston rod is driven in an upward direction and the load force applied to the piston rod by the load is in a downward direction. It will be appreciated that power for driving movement of the actuator144can be provided by the hydraulic pressure source114, by the electric motor/generator108, or through blended power provided by both the hydraulic pressure source114and the electric motor/generator108. For example, power for driving the actuator144can be provided by pressurized hydraulic fluid from the hydraulic pressure source114which is directed through the bi-directional hydraulic pump102. The power directed through the bi-directional hydraulic pump102can be boosted as needed by operating the electric motor/generator108as a motor via power from an electrical power source, or can be reduced as needed by operating the electric motor/generator108as a generator which taps power from the bi-directional hydraulic pump102and directs the tapped power back to the electrical power source.

The control system142can be configured to coordinate operation of the first valve132, the second valve134, the third valve136, the fourth valve138, the bi-directional hydraulic pump102, and the electric motor/generator108.

The control system142may have a transition control protocol for transitioning the hydraulic actuation system I00between two different modes where a first of the two different modes includes one of the first combined hydraulic and electro-hydrostatic mode, the second combined hydraulic and electro-hydrostatic mode or the load-holding mode. A second of the two different modes includes one of the first combined hydraulic and electro-hydrostatic mode the second combined hydraulic and electro-hydrostatic mode or the load-holding mode.

The transition control protocol may include operating the hydraulic actuation system I00temporarily in the electro-hydrostatic mode as an intermediate step that takes place as the hydraulic actuation system I00is transitioned from one of the first and second combined hydraulic and electro-hydrostatic modes to the other of the first and second combined hydraulic and electro-hydrostatic modes.

The hydraulic actuation system I00may further include pressure sensors148(seeFIG.1) for sensing pressures corresponding to the first and second actuator ports120,122. The control system142uses the sensed pressures to determine when a load transition condition is occurring. When a load transition condition occurs, the high pressure side and the low pressure side of the actuator144equalize and then switch. The control system142will recognize the pressures sensed as a result of the pressure sensors148equalizing and then switching. That is, before the load transition occurs, the hydraulic actuation system I00can be operated with a first pressure P1at one side of the actuator144being greater than a second pressure P2at the opposite side of the actuator144. As the load transition condition begins to occur, the values of the first pressure P1and the second pressure P2converge. After the load transition has occurred, the hydraulic actuation system I00can be operated with the second pressure P2being greater than the first pressure P1.

FIG.7schematically depicts the dual power electro-hydrostatic actuator (dEHA) with three operating modes. The first operating mode is the dual power mode (dual-EHA) in which the hydraulic power and the electric power are combined before they are delivered to the actuator144. The second operating mode is the EHA mode in which all power delivered to the actuator144is originally from an electrical power source. The third operating mode is a load holding mode in which the actuator144is stationary with a load. A switching sequence can occur between the three operating modes as indicated by the arrows generally referenced as arrows I, II, III. That is, a switching sequence can occur as follows: I) dual-EHA to/from EHA, II) dual-EHA to/from Load-Holding, and III) EHA to/from Load-Holding.

FIG.8schematically illustrates the load-holding mode shown inFIG.7. The hydraulic actuation system100can provide a load-holding mode to handle stationary load encountered by the actuator144. When the hydraulic actuation system100is operating in the load-holding mode, the first and second hydraulic flow paths116,118are open and the third and fourth valves136,138are in the second valve position. In the second valve position, the third hydraulic flow path124is blocked and flow through a portion of the third hydraulic flow path124located between the third valve136and the first actuator port120is hydraulically locked and the fourth hydraulic flow path126is blocked and flow through a portion of the fourth hydraulic flow path126located between the fourth valve138and the second actuator port122is hydraulically locked. Thus, the load is held by both the third and fourth valves136,138.

Turning toFIG.9, a schematic of the electro-hydrostatic (EHA) mode shown inFIG.7is depicted. The hydraulic actuation system100is operable in the EHA mode in which the first and second hydraulic flow paths116,118are closed and the third and fourth valves136,138are in the first valve position. The first valve position occurs when the third hydraulic flow path124is open between the first actuator port120and the first pump port104and the fourth hydraulic flow path126is open between the second actuator port122and the second pump port106.

The control system142can be configured to ensure uninterrupted operations in all four-quadrant operations. That is, the mode transition logic of the control system142allows one mode to transit to another mode smoothly.

FIG.10schematically illustrates a switching sequence between the second dual-EHA quadrant Q2and the third dual-EHA quadrant Q3in accordance with the principles of the present disclosure. When a load transition occurs between the second and third dual-EHA quadrants Q2, Q3, initially the hydraulic actuation system100is in the second dual-EHA quadrant Q2mode for a large passive load. As the passive load decreases, the hydraulic actuation system100shifts into a second EHA quadrant Q2mode, then into a third EHA quadrant Q3mode as the load switches to overrun, and finally into the third dual-EHA quadrant Q3mode as the overrun load becomes large. The second and third EHA quadrant Q2, Q3modes are temporary modes in the hydraulic actuation system100that act as intermediate steps between transitions of the second dual-EHA quadrant Q2to/from the third dual-EHA quadrant Q3. The second and third EHA quadrant Q2, Q3modes allow the second dual-EHA quadrant Q2to transit to/from the third dual-EHA quadrant Q3and vice-versa smoothly and without interruption. Thus, the hydraulic actuation system100may operate without unwanted jerkiness. The transition from the third dual-EHA quadrant Q3to the second dual-EHA quadrant Q2is in the reverse sequence.

When a switching sequence occurs between the second dual-EHA quadrant Q2to the second EHA quadrant Q2, the second valve134closes while at the same time the fourth valve138switches position and the supply pressure is lowered. Preferably, the second valve134closes and the fourth valve138switches position at the same time. Otherwise, if the second valve134closes first, the pump supply flow Q will be cut of off before the fourth valve138can re-connect the pump port106to the actuator144. Conversely, if the fourth valve138switches position first, the high supply pressure could create a pressure resistance to the flow coming from the cylinder rod.

When switching from the third EHA quadrant Q3to the third dual-EHA quadrant Q3, the supply pressure is increased to a value based on calculated load determined from pressure readings across the actuator144and electric-motor capacity. The first valve132is opened while at the same time the third valve136switches position. It is desired to have the first valve132open and the third valve136switch positions at the same time. Otherwise, if the first valve132opens first, the high supply pressure could create a pressure resistance to the flow coming from the cylinder rod.

Conversely, if the third valve136switches position first, the pump supply flow will be cut off before the third valve136re-connects the flow to the supply pressure.

Transitioning between the second EHA quadrant Q2and the third EHA quadrant Q3does not require any valve configuration change and is controlled through operation of the motor/generator108.

FIG.11schematically illustrates a switching sequence between the first dual-EHA quadrant QI and the fourth dual-EHA quadrant Q4in accordance with the principles of the present disclosure. When a load transition occurs between the first and fourth dual-EHA quadrants QI, Q4, initially the hydraulic actuation system100is in the first dual-EHA quadrant QI mode for a large overrun load. As the overrun load decreases, the hydraulic actuation system I00shifts into a first EHA quadrant QI mode, then into a fourth EHA quadrant Q4mode as the load switches to passive, and finally into the fourth dual-EHA quadrant Q4mode as the passive load becomes large. The first and fourth EHA quadrant Q1, Q4modes are temporary modes in the hydraulic actuation system I00that act as intermediate steps between transitions of the first dual-EHA quadrant QI to/from the fourth dual-EHA quadrant Q4. The first and fourth EHA quadrant QI, Q4modes allow the first dual-EHA quadrant QI to transit to/from the fourth dual-EHA quadrant Q4and vice-versa smoothly and without interruption. Thus, the hydraulic actuation system I00may operate without unwanted jerkiness.

Valve positions for the first dual-EHA quadrant QI (overrun load) and the second dual-EHA quadrant Q2(passive load) are the same, allowing mode transition without valve synchronization for large loads. This also applies for the third dual-EHA quadrant Q3and the fourth dual-EHA quadrant Q4.

Any of the dual-EHA or EHA operating modes may be transitioned to load-holding mode in accordance with the principles of the present disclosure.

Referring again toFIG.7, the dual-EHA mode can be switched to/from the load-holding mode. Although the transition is shown between the fourth dual-EHA quadrant Q4and the load-holding mode, a similar strategy may also be used when transitioning from the first, second, and third dual-EHA quadrants QI, Q2, Q3to the load-holding mode.

When a switching sequence occurs from the fourth dual-EHA quadrant Q4to the load-holding mode, the control system142may synchronically close the third and fourth valves136,138and de-actuate the electric motor/generator108in the system. Next, supply pressure from the hydraulic pressure source114may be lowered while at the same time opening the second valve134to relieve high pressures across the bi-directional hydraulic pump102. Thus, the load can be held by the third and fourth valves136,138. The same valve configuration would apply for the third dual-EHA quadrant Q3but with the velocity arrow V changing direction.

In certain examples, the hydraulic actuation system100may be operated temporarily in the electro-hydrostatic mode (EHA mode) as an intermediate step that takes place as the hydraulic actuation system100is switched between the dual-EHA mode to/from the load-holding mode to allow for a smooth and uninterrupted transition.

When the hydraulic actuation system100is switched from the load-holding mode to the dual-EHA mode, the second valve134closes to prevent flow re-circulating back to supply pressure provided by the hydraulic pressure source114. The supply pressure may be increased to a value based on load force from pressure readings across the actuator144and electric-motor capacity. The supply pressure may be increased to avoid load-falling or stalling of the electric motor/generator108at high torque when the third and fourth valves136,138open. The electric motor/generator108may be actuated to increase inlet pressure and match cylinder load. The opening of the third and fourth valves136,138may be synchronized to move the cylinder.

The EHA mode may also be switched to/from load holding mode in accordance with the principles of the present disclosure. When a switching sequence occurs from the EHA mode to the load-holding mode, the control system142may synchronize the closing of the third and fourth valves136,138and de-activate the electric motor/generator108. The first and second valves132,134may be opened to relieve the high pressures across the bi-directional hydraulic pump102. Thus, the load can be held by the third and fourth valves136,138.

When the hydraulic actuation system100is switched from the load-holding mode to the EHA mode, the first and second valves132,134may be closed to prevent flow from re-circulating back to the hydraulic pressure source114and the electric motor can be actuated to increase inlet pressure and match cylinder load based on pressure readings across the actuator144. The control system142may synchronize the opening of the third and fourth valves136,138while also closing the first and second valves132,134to move the actuator144.

Referring toFIG.12, the four EHA quadrant modes Q1-Q4are schematically illustrated. The valve positions for all EHA modes in all four quadrants may be the same, thus allowing mode transitions without valve synchronization between EHA modes for small loads. The second and fourth EHA quadrants Q2, Q4are passive operating conditions in which the motor/generator108functions as a motor and drives the pump102to provide energy in the system. The pump102is driven in an opposite direction in the second EHA quadrant Q2as compared to the fourth EHA quadrant Q4.

The first and third EHA quadrants QI, Q3are over-running operating conditions in which the motor/generator I08functions as a generator and is driven by the pump102. Energy is received from the weight of the load encountered such that energy can be transferred back to the generator.FIGS.13-16schematically illustrate the EHA quadrant modes Q1-Q4, respectively.

In the first EHA quadrant Q1, the arrow F is directed in an upward direction and the velocity arrow V is also directed in an upward direction. That is, the first EHA quadrant QI represents an operational condition in which the load force F acting on the piston rod of the actuator144is positive and the velocity V of the piston rod is positive.

In the second EHA quadrant Q2, the arrow F is directed in an upward direction and the velocity arrow V is in a downward direction. That is, the second EHA quadrant Q2represents an operational condition in which the load force F acting on the piston rod of the actuator144is positive and the velocity V of the piston rod is negative.

In the third EHA quadrant Q3, the arrow F is directed in a downward direction and the velocity arrow V is in a downward direction. That is, the third EHA quadrant Q3represents an operational condition in which the load force F acting on the piston rod of the actuator144is negative and the velocity V of the piston rod is also negative.

In the fourth EHA quadrant Q4, the arrow F is directed in a downward direction and the velocity arrow V is directed in an upward direction. That is, the fourth EHA quadrant Q4represents an operational condition in which the load force F acting on the piston rod of the actuator144is negative and the velocity V of the piston rod is positive.

It will be appreciated that the symmetric architecture connecting the cylinder-rod to supply pressure and cylinder-head to supply pressure allows the same valve synchronization strategies to be re-used in different operating quadrants.

It will be appreciated that for any of the example dual power electro-hydraulic motion control units in accordance with the principles of the present disclosure, such units can be operated to control movement of the corresponding actuator (e.g., hydraulic cylinder) regardless of whether the actuator is being passively driven or is experiencing an over-running condition. When the actuator is being driven passively, energy is transferred from the bi-directional hydraulic pump to the actuator. The power can be derived from a source of hydraulic power that is transferred through a hydraulic pump/motor, or by power applied to the hydraulic pump/motor by an electric motor/generator, or by blended power provided by both the source of hydraulic power and the electric motor/generator. By operating the electric motor/generator as a motor, the electric motor/generator can be used to boost power provided to the hydraulic actuator by the hydraulic power source. By operating the electric motor/generator as a generator, the electric motor can be used to reduce the power provided to the hydraulic actuator by the hydraulic power source. When the actuator is experiencing an over-running condition, energy can be transferred from the actuator back to the bi-directional hydraulic pump. Such energy can be captured and stored by operating the electric motor/generator as a generator such that hydraulic energy can be converted to electrical energy which may be stored at a battery or like structure, or can be stored as hydraulic energy within an accumulator that may correspond to the source of hydraulic power (e.g., a common pressure rail).

The various examples described above are provided by way of illustration only and should not be construed to limit the scope of the present disclosure. Those skilled in the art will readily recognize various modifications and changes that may be made without following the example examples and applications illustrated and described herein, and without departing from the true spirit and scope of the present disclosure.