Patent Description:
In many engine actuator applications, an actuator is sent into or positioned in a fail-safe position in an event of an electrical failure. This fail-safe position may be an extended or retracted position. In helicopters, however, the notion of automatically positioning an actuator in a fail-safe position instead of a last-commanded position in the event of an electrical failure might not be desirable because of a need to maintain certain flight control parameters. Indeed, in at least some cases, while it is actually desirable to hold the actuator in the last commanded position instead of the fail-safe position in the event of an electrical failure, the nature of control systems of typical hydraulically powered actuators of helicopters makes doing so difficult. Accordingly, improved fail-safe position actuator are desirable. <CIT> describes a fail fixed actuator. <CIT> describes an actuator.

According to some aspects of the present invention, fail-fixed hydraulic actuator systems for aircraft are provided. The fail-fixed hydraulic actuator systems include a hydraulic actuator having a housing with a piston arranged within the housing, the piston having a piston head separating the housing into a retract cavity and an extend cavity, a sleeve arranged within the housing and movable therein, the sleeve having a sleeve aperture that is aligned with the piston head during normal operation, and a driving mechanism configured to drive movement of the sleeve to maintain alignment between the sleeve aperture and the piston head. A low pressure cavity is defined between an interior surface of the housing and the sleeve, and, when the piston head is offset from the sleeve aperture, the low pressure cavity is hydraulically connected to one of the retract cavity or the extend cavity to cause a pressure differential with the other of the extend cavity and the retract cavity and cause movement of the piston head to align with the sleeve aperture.

In accordance with additional or alternative embodiments, the fail-fixed hydraulic actuator systems may further include a controller configured to control operation of the drive mechanism.

In accordance with additional or alternative embodiments, the fail-fixed hydraulic actuator systems may further include that the controller is integrated into the drive mechanism.

In accordance with additional or alternative embodiments, the fail-fixed hydraulic actuator systems may further include a position sensor configured to detect a position of at least one of the piston and the piston head within the housing, wherein the position sensor is configured in communication with the controller.

In accordance with additional or alternative embodiments, the fail-fixed hydraulic actuator systems may further include a position sensor configured to detect a position of at least one of the piston and the piston head within the housing.

In accordance with additional or alternative embodiments, the fail-fixed hydraulic actuator systems may further include that the driving mechanism is an electric motor.

In accordance with additional or alternative embodiments, the fail-fixed hydraulic actuator systems may further include at least one seal configured to sealing engage the sleeve with the housing and define the low pressure cavity.

In accordance with additional or alternative embodiments, the fail-fixed hydraulic actuator systems may further include a first high pressure source hydraulically coupled to the retract cavity, a second high pressure source hydraulically coupled to the extend cavity, and a low pressure source hydraulically coupled to the low pressure cavity, wherein a pressure of the first and second high pressure sources is greater than a pressure of the low pressure source.

In accordance with additional or alternative embodiments, the fail-fixed hydraulic actuator systems may further include an aircraft system, wherein the piston is configured to actuate a component of the aircraft system.

According to some embodiments, methods of operating the fail-fixed hydraulic actuator systems of the previous embodiments are provided. The methods include operating the actuator to perform an actuating operation, moving the sleeve within the housing of the actuator to maintain alignment between the piston head within the actuator and the sleeve aperture of the sleeve, hydraulically connecting the low pressure cavity defined by the sleeve to one of the retract cavity or the extend cavity of the actuator when the piston head is offset from the sleeve aperture, and moving the piston head into alignment with the sleeve aperture in response to the connection between the low pressure cavity and the one of the retract cavity or the extend cavity.

In accordance with additional or alternative embodiments, the methods may further include monitoring a position of at least one of the piston head or the piston within a housing of the actuator.

In accordance with additional or alternative embodiments, the methods may further include that moving of the sleeve is controlled by a drive mechanism operably coupled thereto.

In accordance with additional or alternative embodiments, the methods may further include detecting a position of piston head within the actuator and controlling the position of the sleeve aperture to maintain alignment of the sleeve aperture and the piston head in response to the detected position.

In accordance with additional or alternative embodiments, the methods may further include that movement of the piston head to align with the sleeve aperture is in response to a power failure of the actuator.

In accordance with additional or alternative embodiments, the methods may further include that the low pressure cavity has a lower pressure than a pressure of the retract cavity or the extend cavity.

In accordance with additional or alternative embodiments, the methods may further include supplying the retract cavity with a high pressure from a first high pressure source, supplying the extend cavity with a high pressure from a second high pressure source, and supplying the low pressure cavity with a low pressure from a low pressure source. The low pressure is less than the pressure of either of the first and second high pressure sources.

It should be understood, however, the following description and drawings are intended to be illustrative and explanatory in nature and non-limiting.

The subject matter, which is regarded as the invention, is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which:.

As will be described below, a system and method are provided to allow for tight control of a fail-fixed position in a hydraulically controlled actuator. Hydraulic actuation systems are useful for high load and slew rate capabilities, but such actuators may tend to revert to an extend or retract stop point at a time of failure, even if the piston of the actuator is not at an end position. That is, in a failure condition, conventional actuators may be biased to one end-stop (e.g., fully retracted or fully extended). However, it may be desirable to have an actuator that remains in a last commanded position despite a failure. That is, it may be beneficial to have an actuator that remains in a current position rather than fully extending or fully retracting at a time of failure. Such failures may be the result of power loss, control loop failure, or the like.

Referring to <FIG>, schematic illustrations of a fail-fixed position actuator system <NUM> in accordance with an embodiment of the present invention are shown. The fail-fixed position actuator system <NUM> is suitable for an aircraft and may be used onboard aircraft to perform an actuating operation through actuation or movement of a piston <NUM> within a housing <NUM>. The piston <NUM> includes a piston head <NUM> that is configured to have hydraulic pressure applied thereto such that the piston head <NUM> translates or otherwise moves within the housing <NUM>. The housing <NUM> defines a retract cavity <NUM> and an extend cavity <NUM> which are defined on opposite sides of the piston head <NUM>.

To cause movement of the piston <NUM> relative to the housing <NUM>, the retract cavity <NUM> and the extend cavity are each hydraulically (and/or fluidly) coupled to respective pressure sources which can be controlled to increase or decrease a pressure within the cavities <NUM>, <NUM>. For example, the retract cavity <NUM> may be coupled (hydraulically and/or fluidly) to a first high pressure source <NUM> by a first high pressure line <NUM>. Similarly, the extend cavity <NUM> may be coupled (hydraulically and/or fluidly) to a second high pressure source <NUM> by a second high pressure line <NUM>.

In a normal state of operation, high pressure fills both the retract cavity <NUM> and the extend cavity <NUM>. It is noted that pressure in either cavity may not necessarily be equal, and that the pressures will be what is needed to maintain the actuator in force balance. The pressure levels of the two cavities <NUM>, <NUM> may be adjusted or controlled to control operation and actuation of the piston <NUM>. In accordance with embodiments of the present invention, an electric motor <NUM> is configured to translate a windowed sleeve <NUM> axially to a desired actuator position. The electric motor <NUM> may be coupled to or attached to the housing <NUM> or may be arranged in proximity to the housing <NUM>. The electric motor <NUM> may be operably coupled to the sleeve <NUM> to control movement of the sleeve <NUM> within the housing <NUM>. That is, the sleeve <NUM> is arranged within the housing <NUM> and is positioned such that the piston head <NUM> may slidingly and sealingly engage with the sleeve <NUM>. During normal operation, the sleeve <NUM> may be moved with the piston <NUM> such that the piston head <NUM> remains in sealing engagement with the sleeve <NUM> (shown in <FIG>). For example, as the pressure in the extend cavity <NUM> is decreased and the pressure in the retract cavity <NUM> is increased, the piston <NUM> will perform an extension actuation (e.g., to the right on the page). As the piston head <NUM> moves with the piston <NUM> during the extension, the motor <NUM> will drive movement of the sleeve <NUM> such that the sleeve <NUM> moves with the piston head <NUM>. The piston head <NUM> includes one or more seals <NUM>.

As noted, the sleeve <NUM> is a windowed sleeve, including a sleeve aperture <NUM>. In the normal position (<FIG>), the piston head <NUM> is aligned with the sleeve aperture <NUM> and is sealingly engaged with the sleeve <NUM> by the seals <NUM>. When in this position, a low pressure cavity <NUM> is defined between the piston head <NUM> and the sleeve <NUM> on a first side and a portion of the housing <NUM> on a second side. The low pressure cavity <NUM> is hydraulically and/or fluidly connected to a low pressure source <NUM> by a low pressure line <NUM>. As such, during normal operation, the low pressure cavity <NUM> is filled with low pressure fluid, and the two cavities <NUM>, <NUM> are filled with high pressure fluid.

The motor <NUM> may be operated to control the position of the sleeve <NUM> and particularly the sleeve aperture <NUM> within the housing <NUM>. If the piston head <NUM> is moved away from the sleeve aperture <NUM>, the low pressure cavity <NUM> will be exposed to and fluidly connected to either the retract cavity <NUM> or the extend cavity <NUM>. When the low pressure cavity <NUM> is in fluid communication with one of the cavities <NUM>, <NUM>, the pressure within that cavity <NUM>, <NUM> will be decreased and the pressure on the other side of the piston head <NUM> will be relatively higher. This pressure differential across the piston head <NUM> will cause the piston head <NUM> to move toward the lower pressure side and thus the piston head <NUM> may be aligned again with the sleeve aperture <NUM>. That is, when the piston head <NUM> is moved to cover the sleeve aperture <NUM>, the forces on opposing sides of the piston head <NUM> may be equalized and ensure that the piston <NUM> is held in a desired position.

Stated another way, when the piston <NUM> is not at a desired position, the position may be corrected through the positioning of the sleeve <NUM> within the housing <NUM>. For example, the sleeve <NUM> may be moved (by operation of the motor <NUM>) to position the sleeve aperture <NUM> at a location that is desired for the piston head <NUM> to be located. Then, when the piston head <NUM> is moved, such as due to an external load application to the piston <NUM>, the sleeve aperture <NUM> will be exposed to one of the actuator cavities (i.e., the retract cavity <NUM> or the extend cavity <NUM>) to low pressure. This exposure to low pressure will cause a pressure differential and the piston head <NUM> will be caused to move until the sleeve aperture <NUM> is covered by the piston head <NUM> and the associated seals <NUM>.

The motor <NUM> may be operably coupled to the sleeve <NUM> and configured to control movement of the sleeve <NUM> within the housing <NUM> through a control connection <NUM>. The control connection <NUM> may be a drive shaft, induction coil, magnetic system or the like that is configured to cause movement of the sleeve <NUM> within the housing <NUM>. In some non-limiting examples, a linear motor and worm gear may be configured to drive the position of the sleeve <NUM>. The motor <NUM> may be an electric motor that is supplied with electrical power from other sources onboard an aircraft, as will be appreciated by those of skill in the art. The motor <NUM> is configured to control the position of the sleeve <NUM> within the housing <NUM> and specifically the location of the sleeve aperture <NUM>. The sleeve aperture <NUM> defines the position that the piston head <NUM> should be located in a force balance between the retract cavity <NUM> and the extend cavity <NUM>. As such, if the piston head <NUM> is not located at the appropriate position, the exposure of the low pressure cavity <NUM> to one of the retract cavity <NUM> or the extend cavity <NUM> will cause movement of the piston head <NUM> such that the sleeve aperture <NUM> is covered by the piston head <NUM>. As such, load is balanced passively in the event of a failure of the fail-fixed position actuator system <NUM> (e.g., loss of electrical power). Accordingly, the actuation of the fail-fixed position actuator system <NUM> may be maintained in a last-issued command position based on the location of the sleeve <NUM>, the sleeve aperture <NUM>, and the piston head <NUM>.

In accordance with embodiments of the present invention, a fail-fixed hydraulic actuator is presented containing a windowed sleeve (sleeve aperture) that is translated by a motor (e.g., linear electric motor). Both extend and retract cavities are connected to high pressure via respective orifices to high pressure sources. When moved, the sleeve exposes one of the cavities of the hydraulic actuator to low pressure through the sleeve aperture. This exposure to low pressure causes the actuator to slew until the sleeve aperture is covered (or partially covered) and the actuator is in force balance with an external load (e.g., applied to the piston).

Although <FIG> illustrates the low pressure cavity <NUM> fluidly connected to the extend cavity <NUM> through the sleeve aperture <NUM>, such configuration is not to be limiting but rather is for illustrative and explanatory purposes. In some instances, the piston head <NUM> may end on the opposite side of the sleeve aperture <NUM> such that the retract cavity <NUM> fluidly couples to the low pressure cavity <NUM>. Accordingly, the fail-fixed position actuator system <NUM> can provide a fail-fixed position of the piston <NUM> relative to the housing <NUM>, regardless of the position of the piston head <NUM> at the time of the failure (e.g., loss of electrical power). The location of the sleeve aperture <NUM> defines the final fail position of the piston head <NUM> and thus the piston <NUM>.

As shown, the sleeve <NUM> is configured to move within the housing <NUM>. The sleeve <NUM> may sealingly engage with an interior surface of the housing <NUM> using one or more seals <NUM>. The seals <NUM> are provided to ensure that there is no fluid or pressure bleed between the low pressure cavity <NUM> and the high pressure cavities (e.g., retract cavity <NUM>, extend cavity <NUM>) except when the sleeve aperture <NUM> is exposed to one of the cavities <NUM>, <NUM>.

The motor <NUM> that drives the position of the sleeve <NUM> within the housing <NUM> may include a controller <NUM> (or may be in communication with a controller external thereto). The controller <NUM> may be configured to control the movement and position of the sleeve <NUM> within the housing <NUM>. In some embodiments, and as shown, the piston <NUM> may include a position sensor <NUM> that provides information regarding the current position of the piston <NUM> or piston head <NUM> within the housing <NUM>. The position sensor <NUM> may be in communication with the controller <NUM> such that the controller <NUM> receives the position information of the piston <NUM> and controls the position of the sleeve <NUM> relative thereto. Although shown with the position sensor <NUM> as part of the piston head <NUM>, such location is not to be limiting. Various types of position sensors may be employed without departing from the scope of the present invention. Optical position sensors, proximity sensors, direct coupling to the piston head and/or piston shaft, control data from an actuator controller, or the like may all be used individually and/or in combination to monitor the position of the piston within the housing.

<FIG> illustrates an example of an aircraft <NUM> having aircraft engines surrounded by (or otherwise carried in) nacelles <NUM>. The aircraft <NUM> includes wings <NUM> that extend from an aircraft fuselage <NUM>. Each wing <NUM> may include one or more slats <NUM> on a forward edge or leading edge and one or more flaps <NUM> on an aft, rear, or trailing edge thereof. The wings <NUM> may also include ailerons <NUM> on the trailing edges, as will be appreciated by those of skill in the art. The aircraft <NUM>, as shown, includes a tail structure <NUM> which can include various flaps, ailerons, slats, and the like, as will be appreciated by those of skill in the art. The flaps, slats, ailerons, and the like are generally referred to herein as "aerostructures" as they are movable under aircraft power systems and are configured to control flight and motion of the aircraft <NUM>. An aerostructure actuator system <NUM> may be connected to one or more of the aerostructures. For example, each wing <NUM> and the tail structure <NUM> may include one or more aerostructure actuator systems <NUM>. The aerostructure actuator systems <NUM> may be operably connected to the various aerostructures and configured control the operation/position of the aerostructures to control flight of the aircraft <NUM>. In some embodiments, the aerostructure actuator systems <NUM> can include one or more actuator systems such as shown and described above with respect to <FIG>. Further, the engines of the aircraft <NUM> may include various actuators and control mechanisms that can incorporate one or more actuator systems such as shown and described above with respect to <FIG>. As such, the described actuator systems of the present disclosure may be incorporated into aircraft engine systems and/or aircraft flight systems. It will be appreciated that such actuator systems as described herein may be used for other purposes onboard aircraft, such as for actuating doors, landing gear, or the like.

Turning now to <FIG>, a flow process <NUM> for operating the actuator system in accordance with an embodiment of the present invention. The flow process <NUM> is designed for operating an actuator system such as that shown and described above. The flow process <NUM> may be performed using a controller or the like that is configured to monitor a position of the piston within the housing and also control the position of the sleeve within the housing, through control and operation of a motor or other driving mechanism.

The flow process <NUM> operation is functional with a hydraulic actuator having the piston actuator arranged within the housing with the sleeve positioned relative to the piston head within the housing. The sleeve includes the sleeve aperture and is drivingly moveable within the housing of the hydraulic actuator by a motor operably connected to the sleeve. The positioning of the sleeve aperture within the housing is controlled to ensure that the piston head is placed where needed in the event of a failure of the actuator system. That is, the positioning of the aperture ensures a fixed end or stop position of the piston head in the event of failure of the system (as compared to ending at a full extension or full retraction).

At block <NUM>, the piston is caused to move within the housing to actuate the hydraulic actuator. The control of the motion of the piston may be achieved through control of hydraulic and/or fluid pressure on opposing sides of the piston head. For example, the piston may be arranged within the housing and an electrohydraulic servo valve may be operably coupled thereto to control fluid and/or hydraulic pressure on opposing sides of the piston head to control actuation of the actuator. In some operations, the piston will slide within the sleeve, as shown and described above, and is applicable for a case where an external load causes the piston (and piston head) to move. Further, in some operations of the actuator, a new actuator position is desired and the flow process will start with positioning the sleeve to a new position, thus exposing the piston head to the force imbalance, as described herein.

At block <NUM>, as the piston is moved within the housing, a motor is operated to control the position of the sleeve within the housing. The movement of the sleeve may be substantially similar to the movement of the piston head within the housing. As such, during normal operation, the sleeve may not impact the operation of the piston in the process of actuating the hydraulic actuator. The movement of the sleeve within the housing is made to ensure that the sleeve aperture is located at a desired location at all times. For example, the position of the sleeve aperture may be moved to ensure that in the event of a failure of the hydraulic aperture that the sleeve aperture is located at a position desired for the piston to stop and stay and hold the piston in the desired position due to force balancing.

At block <NUM>, the piston head is moved away from the sleeve aperture. Such offset of the piston from the sleeve aperture may occur due to a failure of some kind related to the hydraulic actuator. In the event of a failure, the pressures on opposing sides of the piston head may be unbalanced, thus causing the piston head to move toward one end of the housing, and thus offset the piston head from the sleeve aperture.

At block <NUM>, as the piston head is offset from the sleeve aperture, a pressure change is induced in the housing to cause the piston head to move and align with the sleeve aperture. For example, as shown and described above, by moving the piston head away from the sleeve aperture, the sleeve aperture is exposed and thus allows for hydraulic and/or fluid connection between a low pressure cavity of the hydraulic actuator and one of the high pressure cavities thereof. This connection causes a pressure change (decrease) in the high pressure cavity that is connected to the low pressure cavity, thus causing movement of the piston head to realign with the sleeve aperture.

Advantageously, embodiments of the present invention provide for improved actuators and fail-fixed position for such actuators. In accordance with embodiments of the present invention, upon failure of electrical power, the hydraulic actuator will remain in a last commanded position and will retain an ability to oppose variable external loads. This is achieved through a passive fail-fixed position process that is achieved through a moveable sleeve within the actuator with an aperture or window that, when exposed to a cavity of the actuator, will allow low pressure into the cavity and thus cause movement of the piston to the fail-fixed position. Accordingly, embodiments provided herein provide for a passive failure operation for an actuator to ensure the actuator stays in a last commanded position at the time of failure, whether the piston of the actuator is at an end stop or between ends of the actuator. Further, because the fail-fixed position is maintained by a force balance, after the failure, the actuator may remain in the fixed position and resist or oppose external loads even without a supply of power.

The terms "about" and "substantially" are intended to include the degree of error associated with measurement of the particular quantity based upon the equipment available at the time of filing the application.

Additionally, the term "exemplary" is used herein to mean "serving as an example, instance or illustration. " Any embodiment or design described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments or designs. The terms "at least one" and "one or more" are understood to include any integer number greater than or equal to one, i.e., one, two, three, four, etc. The term "a plurality" is understood to include any integer number greater than or equal to two, i.e., two, three, four, five, etc. The term "connection" can include an indirect "connection" and a direct "connection".

For example, two blocks shown in succession may, in fact, be executed substantially concurrently (or simultaneously), or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved. It is also noted that each block of the block diagrams and/or flowchart illustration, and combinations of blocks in the block diagrams and/or flowchart illustration, can be implemented by special purpose hardware-based systems that perform the specified functions or acts or carry out combinations of special purpose hardware and computer instructions.

Claim 1:
A fail-fixed hydraulic actuator system for an aircraft, the fail-fixed hydraulic actuator system comprising:
a hydraulic actuator having a housing (<NUM>) with a piston (<NUM>) arranged within the housing (<NUM>), the piston (<NUM>) having a piston head (<NUM>) separating the housing (<NUM>) into a retract cavity and an extend cavity;
a sleeve (<NUM>) arranged within the housing (<NUM>) and movable therein, the sleeve (<NUM>) having a sleeve aperture (<NUM>) that is aligned with the piston head (<NUM>) during normal operation; and
a driving mechanism configured to drive movement of the sleeve (<NUM>) to maintain alignment between the sleeve aperture (<NUM>) and the piston head (<NUM>),
wherein a low pressure cavity is defined between an interior surface of the housing (<NUM>) and the sleeve (<NUM>), and
wherein when the piston head (<NUM>) is offset from the sleeve aperture (<NUM>) the low pressure cavity is hydraulically connected to one of the retract cavity or the extend cavity to cause a pressure differential with the other of the extend cavity and the retract cavity and cause movement of the piston head (<NUM>) to align with the sleeve aperture (<NUM>).