Device having hybrid hydraulic-electric architecture

A device having a hybrid hydraulic-electric architecture includes a hydraulic pump/motor having first and second ports, and an electric motor. The device is configured to connect to two or more pressure rails, each pressure rail containing hydraulic fluid at a different pressure than the other pressure rails. A flow of hydraulic fluid from one of the pressure rails is driven through the hydraulic pump/motor, and a pressure difference exists between the first and second ports. The electric motor is configured to control a flow rate of the flow of hydraulic fluid and/or the pressure difference.

FIELD

Embodiments of the present disclosure generally relate to hybrid hydraulic and electric devices for powering movement of a load, and/or for capturing energy from a load to generate electricity.

BACKGROUND

Conventional mobile machines, such as excavator, skid-steer/wheel loaders, and mowers, have multiple degrees-of-freedom and primarily use hydraulics for power transmission due to its unsurpassed power density.

One conventional architecture for providing hydraulic power transmission in a multi degree-of-freedom system is a load-sensing (LS) system in which a pressure compensated pump provides a common pressure at a level that is slightly higher than the highest pressure requirement of all the services. Throttling valves are then used to drop the pressure to the required pressure of the services. This circuit can only be efficient if all services require nearly the same pressure levels (which is not true of most systems), so that the pressure drops are kept low. However, significant throttling energy losses are incurred in typical systems, where the required instantaneous pressures differ significantly. Moreover, energy from over-running loads is typically not recaptured due to the mismatch in pressure of the accumulator and at the load.

A potentially more efficient approach to throttling a common pressure rail supplied by a centralized hydraulic power supply, is to utilize a hydraulic transformer to conservatively buck or boost the common pressure rail pressure to the required pressure. This approach is throttle-less and regenerative, and can potentially improve efficiencies. However, hydraulic transformers are generally not commercially available, are bulky, and have limited practical transformation ratios. Their efficiencies also decrease at partial loads since the constituent pump/motors tend to be inefficient at low effective displacements.

An electrical approach to improving efficiency is to utilize an electro-hydraulic actuator setup, in which an electric motor is used to drive a fixed or variable displacement hydraulic pump/motor to control the flow rate to a single actuator. Besides being throttle-less, regenerative, and efficient, it also has good control performance. High control performance stems from the ability to adjust the torque virtually instantaneously, so as to control the speed of the hydraulic pump and to precisely control the flow in and out of the hydraulic actuator. However, because all power is provided electrically, high power electric drives, which are prohibitive in cost and size, are needed. Therefore, the electro-hydraulic actuator approach is currently only practical for low-power machines.

SUMMARY

Embodiments of the present disclosure are directed to a device that combines hydraulic and electric means of actuation to form a hybrid hydraulic-electric architecture, a system utilizing at least one of the devices, and a method of operating the system. In one embodiment, the device is configured to connect to two or more pressure rails, each pressure rail containing hydraulic fluid at a different pressure than the other pressure rails. The device includes a hydraulic pump/motor having first and second ports, and an electric motor. A flow of hydraulic fluid from one of the pressure rails is driven through the hydraulic pump/motor, and a pressure difference exists between the first and second ports. The electric motor is configured to control a flow rate of the flow of hydraulic fluid and/or the pressure difference.

One embodiment of the system includes two or more pressure rails, each containing hydraulic fluid at a different pressure than the other pressure rails and a first devices. The first device includes a first hydraulic pump/motor having first and second ports, and a first electric motor. A first flow of hydraulic fluid from one of the pressure rails is driven through the first hydraulic pump/motor, and a first pressure difference exists between the first and second ports of the first hydraulic pump/motor. The first electric motor is configured to control a flow rate of the first flow and/or the first pressure difference. The first electric motor includes a motor mode, in which the first electric motor increases the flow rate of the first flow or increases the first pressure difference, and/or a generator mode, in which the first electric motor decreases the flow rate of the first flow or decreases the first pressure difference.

One embodiment of the method is directed to the operation of a system having two or more pressure rails, each containing hydraulic fluid at a different pressure than the other pressure rails, and a device including a hydraulic pump/motor having first and second ports, and an electric motor. In the method, a flow of hydraulic fluid is driven from one of the pressure rails through the hydraulic pump/motor, and a pressure difference exists between the first and second ports. A flow rate of the flow of hydraulic fluid and/or the pressure difference is controlled using the electric motor by operating the electric motor in a motor mode, in which the electric motor increases the flow rate of the hydraulic fluid flow or increases the pressure difference, and/or operating the electric motor in a generator mode, in which the electric motor decreases the flow rate of the hydraulic fluid flow or decreases the first pressure difference.

DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

Embodiments of the present disclosure are described more fully hereinafter with reference to the accompanying drawings. The various embodiments of the present disclosure may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the present disclosure to those skilled in the art.

Embodiments of the present disclosure include a system architecture for combining the merits of electric and hydraulic technologies, such as for mobile machineries with multiple degrees of freedom, traditionally actuated by hydraulics. The architecture is both highly energy efficient and controllable by exploiting the respective strengths of hydraulics actuation (such as power density) and electric actuation (such as controllability, efficiency and energy dense storage in batteries), while minimizing their respective weaknesses. The major weaknesses of hydraulic actuation are the relatively low component efficiency and that increasing system efficiency is often accompanied by decrease in control performance or increase in system complexity and bulkiness. The primary weakness of electric actuation is that high power and high torque electric machines are expensive, heavy, and bulky, and hence not appropriate for high power mobile machines. The latter limitation is due to the challenge to generate and maintain a large magnetic field to develop high force/torque. In contrast, for large scale systems, hydraulics is one to two orders of magnitude more power dense and torque/force dense than electric actuation.

Embodiments of the present disclosure enable throttle-less and regenerative flow control using electric drives while the majority of power is provided hydraulically. Thus, the disclosed embodiments provide an efficient and practicable architecture that leverages the comparative advantages of electric and hydraulic technologies. Embodiments of the present disclosure may also be used to recapture energy utilized by a system, or capture renewable energies, such as wind energy, wave energy, and other renewable energies.

A simplified diagram of a device100having a hybrid hydraulic-electric architecture in accordance with embodiments of the present disclosure is illustrated inFIG. 1. The device100includes a conventional hydraulic pump/motor (HPM)102and a conventional electric motor (e.g., permanent magnet alternating current synchronous motor)104. In some embodiments, the device100does not include throttle valves. Rotors and other conventional features of the HPM102and the motor100are not shown in order to simplify the illustrations.

The HPM102may comprise a hydraulic pump or motor having a first port106and a second port108. A flow110of hydraulic fluid travels or is driven through the HPM102. A pressure difference between the ports106and108is developed in relation to the hydraulic fluid flow110. The hydraulic fluid flow110may be driven based on, for example, an operating mode of the HPM102, or an energy regeneration or capture operation. In some embodiments, the electric motor104is used to control a flow rate of the hydraulic fluid flow110and/or the pressure difference between the ports106and108. The hydraulic fluid flow110may be positive or negative in accordance to the direction as shown inFIG. 1.

The HPM102may be considered a hydraulic pump or a hydraulic motor, depending on its operation. For example, when a rotor of the HPM102is driving a hydraulic fluid flow, the HPM102may be considered as operating as a hydraulic pump, which generates a pressure difference between the ports106and108and drives, or partially drives, the hydraulic fluid flow110. When the rotor of the HPM102is being driven by the hydraulic fluid flow110, such as in response to a pressure difference between the ports106and108, the HPM102may be considered as operating as a hydraulic motor. In some embodiments of the device100, the HPM102may periodically operate as a hydraulic pump and periodically operate as a hydraulic motor.

In some embodiments, the electric motor104may operate in a motor mode, in which the motor104increases a flow rate of the hydraulic fluid flow110. That is, the motor104boosts the flow rate over the flow rate that would occur without the operation of the motor104in the motor mode, or without the presence of the motor104. Additionally, the operation of the motor104in the motor mode may increase the pressure difference between the ports106and108in the direction of the flow.

The motor104may be driven in the motor mode using power received from an electrical power supply112. The electrical power supply112may take any suitable form, such as a battery, an output from an electrical generator, or another suitable power supply. Systems utilizing multiple devices100, such as those described below, may include one or more electrical power supplies for powering the motors104.

In some embodiments, the electric motor104may operate in a generator mode, in which the motor104uses the flow rate of the hydraulic fluid flow110to drive a rotor of the motor104and generate electrical power, in accordance with conventional motors/generators. In some embodiments, charging electronics114use the electrical power (e.g., current) generated by the motor104operating in the generator mode to charge a battery116. The electrical power generated by the motor104may also be stored in other forms or utilized by other electricity consuming devices using conventional techniques. Systems utilizing multiple devices100, may include one or more charging electronics114and batteries116for storing generated electrical energy.

In some embodiments, the device100is used to drive linear or rotational movement of a load120based on the hydraulic fluid flow110. As discussed below, this movement of the load may be driven by the HPM102or using an actuator122, such as a linear actuator.

In some embodiments, the device100is used to capture energy from the load120, such as when movement of the load120is being driven by gravity or by a renewable energy source. Here, the moving load120drives the hydraulic fluid flow110, possibly using the actuator122, which in turn may drive rotation of a rotor of the HPM102. The energy in the hydraulic fluid flow110that has been transferred into the rotation of the rotor may then be converted into electrical energy using the motor104.

FIG. 2is a simplified diagram illustrating an example of a system130utilizing an example of the device100, referred to as100A, in accordance with embodiments of the present disclosure. In one embodiment, the load120is connected to a shaft132and is configured to rotate with rotation of the shaft132. The rotor of the HPM102and the rotor of the motor104are also connected to the shaft132such that they rotate with rotation of the shaft132. In some embodiments, gears are used to make the connections between rotations.

In some embodiments, the system130includes two or more pressure rails, generally referred to as134, each containing hydraulic fluid at a different pressure than the other pressure rails134. While four pressure rails (134A-D) are shown inFIG. 2, it is understood that embodiments of the system130may include only two pressure rails, three pressure rails, or more than four pressure rails.

The pressure rails134include a low pressure rail134D that contains hydraulic fluid at the lowest pressure (e.g., atmospheric pressure) relative to the other pressure rails134, such as at a low pressure corresponding to a supply of hydraulic fluid, and a high pressure rail134A contains hydraulic fluid at the highest pressure relative to the other pressure rails134. Any remaining pressure rails134, such as rails134B and134C, each contain hydraulic fluid at a pressure that is between the pressures of the rails134A and134D.

If the system130only includes a pair of pressure rails134, such as the high and low pressure rails134A and134D, the system130may be configured to vary the pressure of at least one of the pressure rails134to provide a desired pressure difference between the rails134. When three or more pressure rails134are used, the pressures of the intermediary rails134, such as rails134B and134C, may be set to pressures that substantially evenly space the pressure gaps between the rails, or are set to pressures that accommodate particular services to be provided by the system130using one or more of the devices100. Additional options regarding the pressure rails134are discussed in greater detail below.

In some embodiments, the system130includes valving136having ports137A and137B, which are respectively connected to the ports106and108of the HPM102. The valving136is configured to connect one of the pressure rails134to the port137A and thus, to the first port106of the HPM102, and one of the pressure rails134to the port137B and thus, to the second port108of the HPM102. In the example shown inFIG. 2, the valving136has connected (solid arrow) the pressure rail134A to the first port106, and the pressure rail134D to the second port108.

The valving136may take on any suitable form, and may be configured to connect any one of the pressure rails134, including the same pressure rail134, to the ports106and108of the HPM102. Alternatively, the valving136may be configured to maintain a connection of one of the rails134to one of the ports106or108of the HPM102, while allowing for other rails134to be selectively connected to the other port106or108of the HPM102.

In some embodiments, a controller138may be used to actuate the valving136to connect the same pressure rails134or a pair of different pressure rails134to the ports106and108of the HPM102. In some embodiments, the controller138represents one or more processors that control components of the system130or device100A to perform one or more functions described herein in response to the execution of instructions stored in non-transitory memory. In some embodiments, the one or more processors of the controller are components of one or more computer-based systems, control circuits, microprocessor-based engine control systems, programmable hardware components (e.g., a field programmable gate array).

In some embodiments, the device100A may operate in a motor mode, in which it is configured to drive rotation of the shaft132and the load120. Here, the rotor of the HPM102drives rotation of the shaft132and the load120based on a pressure difference of the hydraulic fluid between the ports106and108, which drives a hydraulic fluid flow110through the HPM102. The pressure difference may be formed through the connection of the port106to a relatively high pressure rail, such as rail134A, and the connection of the port108to a relatively low pressure rail, such as134D, as shown inFIG. 2. In some embodiments, the pressure rail connection may be facilitated by the valving136and controlled by the controller138, as discussed above.

In some embodiments, the torque applied to the shaft132by the hydraulic actuation of the HPM102motor may be precisely and quickly controlled using the motor104. For example, the motor104may be operated in a motor mode, in which the motor104is powered by the electrical power supply (FIG. 1)112to increase or boost the torque applied to the shaft132, which increases the rotational velocity of the shaft132and the load120. This also increases or boosts the flow rate of the hydraulic fluid flow110through the HPM102due to the increase in the rotational velocity of the rotor of the HPM102over that which would have been generated solely by the pressure difference between the ports106and108of the HPM102.

The motor104may also be operated in a generator mode, in which the electric motor104impedes the rotation of the shaft132, thereby reducing the net torque on the shaft132, which decreases the rotational velocity of the shaft132and the load120. As a result, the generator mode of the motor104also decreases the flow rate of the hydraulic fluid flow110through the HPM102due to the decrease in the rotational velocity of the rotor of the HPM102over that which would have been generated solely by the pressure difference between the ports106and108of the HPM102.

In some embodiments, the resulting electricity that is generated by the motor104while operating in the generator mode may be used to power other electrical components of the system130. For example, the generated electrical power may be delivered to the charging electronics114, which may use the electrical power to charge the battery116, as indicated inFIG. 1.

In some embodiments, the torque applied to the shaft132by the motor104, such as the positive torque applied by the motor104while operating in the motor mode or the negative torque applied by the motor104while operating in the generator mode, is relatively small compared to the torque applied to the shaft132by the HPM102based on the pressure difference between the ports106and108. Thus, the primary torque applied to the shaft132is determined based on the pressures of the pressure rails134that are connected to the ports106and108. As a result, the electric motor104may have a very low power relative to that which would be required by an electric motor to apply a torque to the shaft132that would be similar to that provided by the HPM102.

One may consider this operation of the motor104as adjusting an effective pressure difference across the ports106and108of the HPM102. That is, the combination of the torque applied to the shaft132by the HPM102based on the pressure difference between the ports106and108and the positive or negative torque to the shaft132by the motor104results in a net torque on the shaft132. This net torque corresponds to an effective pressure difference between the ports106and108that, if applied to the ports106and108without the presence of the motor104, would result in the net torque on the shaft. Accordingly, the motor104may be considered as increasing (boosting) or decreasing (bucking) the pressure difference between the ports106and108of the HPM102from that provided by the connected pressure rails134to the effective pressure difference.

One way to reduce the energy required by the motor104and the size of the motor104is to reduce the torque that must be applied by motor104to obtain a desired rotational velocity of the shaft132or the desired effective pressure difference between the ports106and108. This may be accomplished by generating a pressure difference at the ports106and108using the pressure rails134that closely match a desired operating pressure to perform the service, such that the motor104must only be used to make small adjustments to the net torque that is applied to the shaft134.

The use of multiple pressure rails134increases the precision that the pressure difference between the ports106and108can be matched to a desired operating pressure. Thus, in some embodiments, the valving136is used to select a pair of the pressure rails134for connection to the ports106and108that provides the desired operating pressure and minimizes the torque and power requirement of the motor104.

The system ofFIG. 2may also be operated in a generator mode in response to rotation of the shaft132by the load120whose rotational movement may be driven by gravity or a renewable energy source. For example, the shaft132may be connected to a wind turbine that converts wind energy into a torque on the shaft132. The device100A may use the torque applied to the shaft132to generate hydraulic and/or electrical energy. The torque on the shaft132provided by the load120may drive rotation of the shaft132and a rotor of the motor104. The motor104, operating as a generator, generates electricity that may be stored in a battery116using charging electronics114, as indicated inFIG. 1.

The HPM102may also be used to generate hydraulic energy in response to the rotation of the shaft132by the load whose rotational movement may be driven by gravity or a renewable energy source. For example, the rotation of the shaft132may drive the rotor of the HPM102, which drives a hydraulic fluid flow110. The hydraulic fluid flow110may be used to store the energy by pressurizing a hydraulic accumulator of the hydraulic fluid, such as a hydraulic accumulator of one of the pressure rails134or another container, or generate electricity by driving an electrical generator using the hydraulic fluid flow110, for example.

FIG. 3is a simplified diagram illustrating an example of a system140utilizing an example of the device100, referred to as100B, in accordance with embodiments of the present disclosure. The system140may include embodiments of the valving136, the pressure rails134, and/or the controller138and other features of the system ofFIG. 2.

In one embodiment, the device100B includes the actuator122in the form of a linear actuator that includes a piston142contained in a housing144. A load120may be connected to a rod146of the piston142. As with the device ofFIG. 2, the device100B may operate in a motor mode, in which the device100B is configured to drive movement of the piston142relative to the housing144to move the load120. In some embodiments, the device100B may operate in a generator mode, in which the device100B captures energy from movement of the piston142relative to the housing144that is driven by movement of the load, such as by gravity or a renewable energy source. Here, the load120may be generated by a wave energy converter driven by wave energy, for example.

The linear actuator housing144includes a port150to a side152of the piston142, and a port154to a side156of the piston142. One of the ports150and154is connected to the second port108of the HPM102and the other of the ports150and154is connected to a pressure rail134. Optional valving158may be used to selectively connect the ports150and154to port108of the HPM102or one of the pressure rails134. Valving136may also be used to connect one of the pressure rails134to the port106of the HPM102, and one of the pressure rails134to one of the ports150or154of the actuator122, such as port154, as shown inFIG. 3.

The device100B may operate in a motor mode, in which a hydraulic fluid flow110is related to a pressure difference at the ports150and154of the actuator122and the ports106and108of the HPM102, which are based on a pressure difference between the connected pressure rails134. The hydraulic fluid flow110may be directed into or out of the ports150and154to drive movement of the piston142relative to the housing144and, thus, movement of the load120.

The device100B may operate in a generator mode, in which a hydraulic fluid flow110is generated based on movement of the piston142relative to the housing144by movement of the load120. The hydraulic fluid flow110may be driven into or out of the ports150and154based on the direction of movement of the piston142.

In one embodiment, the motor104(solid lines) of the device100B is connected to a shaft160that is connected to the rotor of the HPM102. The rotor of the HPM102applies a torque to the shaft160based on the hydraulic fluid flow110. In some embodiments, the motor104may operate in a motor mode, in which it is configured to apply a positive torque to the shaft160, which increases the rotation of the shaft160and the rotor of the HPM102and increases the flow rate of the hydraulic fluid flow110through the HPM102and into one of the ports150and154of the linear actuator122. This boosts the pressure difference at the ports150and154of the linear actuator122and drives movement of the piston142relative to the housing140.

The motor104may also operate in a generator mode, in which the motor104impedes rotation of the shaft160by applying a negative torque to the shaft160. As a result, the generator mode of the motor104also decreases the flow rate of the hydraulic fluid flow110through the HPM102and into one of the ports150and154of the linear actuator. In some embodiments, the resulting electricity that is generated by the motor104while operating in the generator mode may be used to power other electrical components of the system140. For example, the generated electrical power may be delivered to the charging electronics114, which may use the electrical power to charge the battery116, as indicated inFIG. 1.

The HPM102may also be used to generate hydraulic energy in response to the rotation of the shaft160in response to movement of the load120by gravity or a renewable energy source. For example, the rotation of the shaft160may drive the rotor of the HPM102, which drives a hydraulic fluid flow110. The hydraulic fluid flow110may be used to store the energy by pressurizing a container of the hydraulic fluid, such as one of the pressure rails134or another container, or generate electricity by driving an electrical generator using the hydraulic fluid flow110, for example.

In some embodiments, the motor104(phantom lines) of the device100B may be attached to the rod146of the piston142through a suitable device162that translates rotary motion to linear motion. Here, the motor104may operate in a motor mode, in which it applies a force to the piston142through the rod146to increase the flow rate of the hydraulic fluid flow110into or out of the ports150and154of the linear actuator122and through the HPM102. The motor104(phantom lines) may also operate in a generator mode, in which it impedes movement of the piston142and decreases the flow rate of the hydraulic fluid flow110into or out of the ports150and154of the linear actuator122and through the HPM102. The resulting electricity that is generated by the motor104(phantom lines) while operating in the generator mode may be used to charge a battery or power other electrical components of the system, as discussed above.

While the device100B operates in the motoring mode, the electric motor104(solid or phantom lines) may be used to precisely control the flow rate of the hydraulic fluid flow110and/or the movement of the piston142relative to the housing144through its operation in the motor or generator mode. Thus, while hydraulic power may be used to provide the bulk of the power used to move the load120, fine adjustments may be made using the electric motor104to precisely control the actuation of the load120by the linear actuator122. This allows the motor104to be configured to generate a small amount of power relative to the hydraulic power produced using the pressure rails134and the HPM102. Moreover, the use of multiple pressure rails134allows for greater control of the hydraulic power applied to the linear actuator122while minimizing the power needed from the motor134.

Embodiments of the present disclosure are also directed to a system170that includes one or more of the devices100, such as the devices100A and/or100B, such as shown in the simplified diagram ofFIG. 4. Thus, the system170may include one or more of the devices100A, and/or one or more of the devices100B. Each of the devices100may include valving136for coupling appropriate pressure rails134to the HPM102of the device100A, or to the HPM102and the linear actuator122of the device100B. Each of the devices100may be used to drive rotational or linear movement of a load120while operating in a motor mode, and/or recover energy from a rotating or linearly moving load120while operating in a generator mode.

Additionally, the system170may be carried or supported on a mobile vehicle172, as indicted inFIG. 4. For example, the system may be used to drive degrees of freedom of components of excavators, wheel-loaders, skid steer-loaders, mowers, and other off-highway vehicles. For example, an excavator may use the device100A ofFIG. 2to rotate a cab of the excavator, while devices100B ofFIG. 3may be used to actuate boom, dipper and/or a bucket of the excavator.

The system170may be used as a renewable energy capture device, such as a wave energy converter, or a power-take-off device for a wave energy capture system. For example, the system170may be used to capture and transmit energy from the motions of multiple wave energy converters. For example, the power-take-off device may use the device100B inFIG. 3to capture the energy from a linear actuator connected a wave energy converter, so that the hydraulic energy in the fluid flow from the pressure rails134can be used to generate electricity using the electric generator186inFIG. 4.

FIGS. 5 and 6are simplified diagrams illustrating examples of techniques that may be used to pressurize the two or more pressure rails134. InFIG. 5, a hydraulic pump/motor180, such as a fixed or displacement pump, may be provided for each pressure rail134to drive hydraulic fluid from a hydraulic fluid supply182to the corresponding pressure rail134. Each pressure rail134may include an accumulator184to maintain a supply of the hydraulic fluid at a desired pressure. Each pump/motor180may be driven using an electrical motor or a combustion engine186, such as the engine of a mobile vehicle, for example.

Alternatively, a single hydraulic pump/motor180, such as a fixed displacement pump, may be used to drive hydraulic fluid from the supply182to each of the pressure rails134through valving188, as shown inFIG. 6. That is, the valving188may be used to direct a flow of hydraulic fluid from the supply182generated by the hydraulic pump/motor180to one of the pressure rails134at a time.

The multiple hydraulic pump/motors180ofFIG. 5or the single hydraulic pump/motor180ofFIG. 6may also be used to convert hydraulic fluid flows from the pressure rails134to the hydraulic fluid supply182into electricity. Such a hydraulic fluid flow may be used by the electric motor186operating in a generator mode to generate electricity, which may be stored in a battery, as discussed above, or used to power electrical components.

The devices100and systems described above provide significant advantages over the techniques that rely solely on hydraulic power or solely on electrical power to drive movement or capture power of a load either linearly or rotationally. The disclosed architectures of the device combine electrical actuation and hydraulic actuation in a complementary manner to simultaneously improve efficiency, performance and compactness. Previous approaches have focused on the power source as exclusively hydraulic or electric. By combining them, the limitation of each actuation approach can be avoided, while providing significant efficiency improvements.

The device100in accordance with embodiments of the present disclosure may avoid the use of throttle valves and be regenerative. It can be highly modular and applicable to many machines. It retains the benefits of centralized hydraulic power generation in the pressure rails that a hydraulic transformer approach features: better component utilization, better engine management, and efficient generation of hydraulic power. The device100can be formed significantly more compact than a hydraulic transformer, as only a single fixed displacement pump/motor102and a small electric drive104are needed (instead of two variable displacement pump/motors). The power density advantage of the device100becomes even greater if the device is integrated and designed to operate at high speeds. The overall efficiency of the device100is also expected to be significantly higher than the hydraulic transformer approach. This is due to the electric motor104of the device100being inherently more efficient as well as being able to operate the HPM102at full (fixed) displacement.

The device100in accordance with embodiments of the present disclosure also retains the control performance and efficiency benefits of a conventional electro-hydraulic actuator, but with the majority of power supplied hydraulically by the pressure rails. Hence, the required power rating for the electric motor104is reduced. By tightly integrating the electric motor104and the HPM102in the device100, benefits from both the component and system levels accrue. Component level benefits include: 1) reducing mechanical friction through fewer bearings and elimination of shaft seals; 2) reducing energy conversion losses through reducing the number of energy conversion stages; 3) improved power density of the electric motor and motor drive electronics enabled by hydraulic cooling of the electric components, and 4) improved control response by reducing the rotational inertia of the integrated rotor-pump. Systems level benefits include a) eliminating redundant components such as casings, bearings and rotors, leading to lighter and more compact packaging; b) lower friction allows the integrated module to operate at a much higher speed and lower torque regime without sacrificing efficiency. All of these contribute to increasing the overall power density as both the electric motor104and the HPM102can be downsized.

The device100in accordance with embodiments of the present disclosure also provides for the flexibility to transmit power and store energy either hydraulically (via the pressure rails and hydraulic accumulators) or electrically (via batteries). Valving may be used to allow the device to switch between different configurations. As each configuration has its own best operating region, this flexibility and redundancy can be exploited to increase the overall efficiency and system sizing.