Patent Description:
Actuators used in aircraft braking typically cover a lead distance at zero force before reaching a brake surface. Once reaching the brake surface, the actuator applies force against the brake surface to effectuate braking. Typical electromechanical linear actuators may comprise a motor, reduction gear, and a ball screw assembly with a thrust bearing. The reduction gear ratio and ball screw lead constant may be fixed. Thus, a compromise may be made between the speed of the actuator and the force applied by the actuator under load. Gear shifting solutions may add components, controllers, and actuators that increase system complexity. A more complex system may have more failure points and increased weight than a less complex system. <CIT> relates to a ball screw and method for displacing a threaded spindle in a ball screw. <CIT> relates to a device for operating a vehicle brake.

According to independent claim <NUM>, an electromechanical actuator (EMA) is provided. Advantageous embodiments are described in the dependent claims.

In particular according to claim <NUM>, a brake system comprising an electromechanical actuator (EMA) is provided.

The subject matter of the present invention is particularly pointed out and distinctly claimed in the concluding portion of the specification. A more complete understanding of the present invention, however, may best be obtained by referring to the detailed description and claims when considered in connection with the figures, wherein like numerals denote like elements.

The detailed description of exemplary embodiments herein makes reference to the accompanying drawings, which show exemplary embodiments by way of illustration. While these exemplary embodiments are described in sufficient detail to enable those skilled in the art to practice the exemplary embodiments of the invention, it should be understood that other embodiments may be realized and that logical changes and adaptations in design and construction may be made in accordance with this invention as defined by the appended claims. Thus, the detailed description herein is presented for purposes of illustration only and not limitation.

Also, any reference to attached, fixed, connected or the like may include permanent, removable, temporary, partial, full and/or any other possible attachment option. Surface shading lines may be used throughout the figures to denote different parts but not necessarily to denote the same or different materials.

With reference to <FIG>, an electromechanical actuator <NUM> (EMA) is shown in a retracted position and in proximity to mechanical load member <NUM> (e.g., a brake stack), in accordance with various embodiments. EMA <NUM> may have a housing <NUM> with cylindrical geometry surrounding internal components. Within housing <NUM>, EMA <NUM> may include a rotor <NUM> configured to rotate about axis of rotation A. Rotor <NUM> may have magnets <NUM> mechanically coupled to rotor <NUM> and magnetically coupled to stator <NUM>. Stator <NUM> may be electromagnetically coupled to magnets <NUM> by coils to convert electrical energy into rotational kinetic energy in rotor <NUM>. Rotor <NUM> may be mechanically coupled to dual ball screw <NUM>, which is also configured to rotate about axis A. Dual ball screw <NUM> may have a screw <NUM> (i.e., a threaded member) disposed about its outer diameter <NUM> and a nut <NUM> (i.e., a threaded member) disposed about its inner diameter <NUM>. As used herein, a screw or nut may also be referred to as a threaded member.

In various embodiments, an inner ball screw <NUM> may be disposed radially inward from inner diameter <NUM> of dual ball screw <NUM>. Inner ball screw <NUM> may have a thread <NUM> disposed about its outer diameter <NUM> and may be configured to rotate about axis A. Thread <NUM> may mechanically engage nut <NUM> through balls <NUM> and thereby enable relative axial movement between inner ball screw <NUM> and dual ball screw <NUM>. A first ball re-circulation feature may be added to the outer threads of screw <NUM> and a second ball re-circulation feature may be added to the outer threads of inner ball screw <NUM> to provide for contained circulation of the balls in their respective screw track (or tracks) while the screws rotate. Spring <NUM> may provide a force to translate inner ball screw <NUM> axially towards mechanical load member <NUM> during use of EMA <NUM>, as described in further detail below.

In various embodiments, an outer ball nut <NUM> may comprise an annular geometry and be disposed radially outward from dual ball screw <NUM> and inner ball screw <NUM>. Outer ball nut <NUM> may have nut <NUM> disposed about an inner diameter <NUM> of outer ball nut <NUM>. Nut <NUM> of outer ball nut <NUM> may mechanically engage screw <NUM> of dual ball screw <NUM> through balls <NUM> and thereby enable relative axial movement between dual ball screw <NUM> and outer ball nut <NUM>. Outer ball nut <NUM> may be fixedly coupled to housing <NUM>. Dual ball screw <NUM>, inner ball screw <NUM>, and outer ball nut <NUM> may thus each comprise threaded members configured to interface with one another as described herein. Stopping feature <NUM> may engage inner ball screw <NUM> and prevent inner ball screw <NUM> from extending beyond an intended extended position under residual spring torque.

In various embodiments, EMA <NUM> may apply load by translating puck <NUM> axially towards mechanical load member <NUM> and applying force against mechanical load member <NUM> through puck <NUM>. With reference to <FIG> and <FIG>, graph <NUM> plots the force F applied by EMA <NUM> against position s of puck <NUM> of EMA <NUM>. EMA <NUM> is depicted in a retracted state at position s0 in <FIG>. The force applied by EMA <NUM> as puck <NUM> is actuated axially towards mechanical load member <NUM> at position s0 is force F0. Force F0 denotes the force exerted by EMA <NUM> to actuate puck <NUM> through air.

With reference to <FIG> and <FIG>, EMA <NUM> is depicted partially deployed at position s1 of graph <NUM> with puck <NUM> contacting mechanical load member <NUM>, in accordance with various embodiments. Rotation of rotor <NUM> may turn and advance dual ball screw <NUM> along with inner ball screw <NUM> in an axial direction at a relatively high rate of travel determined by lead constant b1 of outer ball nut <NUM>. A lead constant may describe a ball screw in terms of the axial distance traveled per angular rotation of rotor <NUM>. The rate of travel of dual ball screw <NUM> and inner ball screw <NUM> relative to outer ball nut <NUM> may be determined by lead constant b1 as puck <NUM> of EMA <NUM> moves from position s0 to position s1.

In various embodiments, EMA <NUM> exerts force F0 while moving from position s0 to position s1. As puck <NUM> contacts and presses against mechanical load member <NUM>, friction builds between mechanical load member <NUM> and puck <NUM>. Inner ball screw <NUM> may rotate in response to the rotation of rotor <NUM> and dual ball screw <NUM> as EMA <NUM> moves from position s0 to position s1 and maintain its axial position relative to dual ball screw <NUM> from position s0 to position s1. Inner ball screw <NUM> may stop rotating in response to friction between puck <NUM> and mechanical load member <NUM> when sufficient friction has built. A reaction force between mechanical load member <NUM> and ball screw builds as puck <NUM> of EMA <NUM> moves from position s1 to position s2.

With reference to <FIG> and <FIG>, EMA <NUM> is shown in a deployed position s2 on graph <NUM>, in accordance with various embodiments. EMA <NUM> may apply greater force (increasing from force F0 to force F1) through puck <NUM> against mechanical load member <NUM> as EMA <NUM> moves from position s1 to position s2. The lead constant b1 for outer ball nut <NUM> may be selected to be slightly greater than the lead constant b2 of inner ball screw <NUM>. For example, lead constant b2 may be within <NUM>%, within <NUM>%, or within <NUM>% of lead constant b1. Inner ball screw <NUM> may be back-driven towards rotor <NUM> as EMA <NUM> moves from position s1 to position s2. In that regard, inner ball screw <NUM> may act as a thrust bearing that returns a torque opposite the drive torque provided by the EMA, thereby reducing the net torque required to turn rotor <NUM>.

In various embodiments, the slope angle (i.e. lead constant) of the threads in outer ball nut <NUM> may further differ from the slope angle (i.e. lead constant) of the threads of inner ball screw <NUM> so that the effective lead constant b3 is equal to the difference between b1 and b2 (i.e., b3 = b1 - b2) in response to ceasing the rotation of inner ball screw <NUM>. In that regard, the mechanical advantage of EMA <NUM> may increase to apply greater force in response to inner ball screw <NUM> ceasing rotation and dual ball screw <NUM> actuating axially toward mechanical load member <NUM>. The dual ball screw configuration of EMA <NUM> provides a faster translation speed and lesser force as puck <NUM> of EMA <NUM> moves from s0 to s1 (across region R1) relative to a greater force and slower translation speed as puck <NUM> of EMA <NUM> moves from s1 to s2 (across region R2). EMA <NUM> may also provide the foregoing advantages without the use of a traditional gearbox. Stated another way, the linking of two ball screws with relatively large but slightly different lead constants creates a ball screw system with a new, much smaller virtual lead constant that is equal to the difference between the two individual lead constants.

In various embodiments, rotor <NUM> and dual ball screw <NUM> may translate axially toward mechanical load member <NUM> and compress spring <NUM> in response to EMA <NUM> moving from position s0 as shown in <FIG> to position s2 as shown in <FIG>. The spring constant of spring <NUM> may be selected to provide sufficient expansive force to translate inner ball screw <NUM> axially relative to rotor <NUM> as EMA <NUM> retracts back from position s2 as shown in <FIG> to position s0 as shown in <FIG>. In that regard, spring <NUM> provides a small pre-load relative to the force exerted by EMA <NUM> to assure that inner ball screw <NUM> is in a fully extended position as s0 as shown in <FIG>.

With reference to <FIG>, an EMA <NUM> similar to EMA <NUM> of <FIG> is shown, in accordance with various embodiments. EMA <NUM> may have a housing <NUM> with cylindrical geometry surrounding internal components. Within housing <NUM>, EMA <NUM> may include a rotor <NUM> configured to rotate about axis of rotation B. Rotor <NUM> may have magnets <NUM> mechanically coupled to rotor <NUM> and electromagnetically coupled to stator <NUM>. Stator <NUM> may be electromagnetically coupled to magnets <NUM> by coils to convert electrical energy into rotational kinetic energy in rotor <NUM>. Rotor <NUM> may be mechanically coupled to dual ball screw <NUM> and inner ball screw <NUM>, which is also configured to rotate about axis B. A puck <NUM> may be coupled to inner ball screw <NUM>. Stationary ball nut <NUM> may be disposed radially outward from dual ball screw <NUM>. EMA <NUM> may comprise an anti-rotation post <NUM>. The anti-rotation post <NUM> may prevent rotation of inner ball screw <NUM>, thereby providing a mechanical advantage similar to that of EMA <NUM> of <FIG> at position s2 of <FIG>.

The dual speed nature of EMAs described herein may enable relatively quiet operation compared to a traditional gear box. Similarly, the dual speed EMA may operate with fewer moving parts and less volume than an EMA including a standard gear box. Additionally, the nested threaded members may have fairly large lead constants and/or lead angles while maintaining a low effective lead angle as force is applied, for example, to a brake stack.

Benefits and other advantages have been described herein with regard to specific embodiments. However, the benefits, advantages, and any elements that may cause any benefit or advantage to occur or become more pronounced are not to be construed as critical, required, or essential features or elements of the disclosure.

In the detailed description herein, references to "various embodiments", "one embodiment", "an embodiment", "an example embodiment", etc., indicate that the embodiment described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. After reading the description, it will be apparent to one skilled in the relevant art(s) how to implement the invention in alternative embodiments.

Claim 1:
An electromechanical actuator, EMA, (<NUM>, <NUM>), comprising:
a rotor (<NUM>) comprising a magnet configured to rotate about an axis;
a stator electromagnetically coupled to the magnet, the rotor configured to move axially relative to the stator;
a ball nut (<NUM>, <NUM>) having an annular geometry centered about the axis;
a dual ball screw (<NUM>, <NUM>) disposed radially inward from the ball nut and configured to rotate about the axis, the dual ball screw (<NUM>, <NUM>) mechanically coupled to the ball nut; and
an inner ball screw (<NUM>, <NUM>) disposed radially inward from the ball nut and configured to rotate about the axis, the inner ball screw (<NUM>, <NUM>) mechanically coupled to the dual ball screw;
a puck (<NUM>, <NUM>) coupled to the inner ball screw, wherein the inner ball screw is configured to stop rotating in response to the puck contacting a mechanical load member (<NUM>, <NUM>); and
characterized by comprising a spring (<NUM>) coupled to the inner ball screw (<NUM>, <NUM>) and configured to position the inner ball screw (<NUM>, <NUM>) axially relative to the rotor (<NUM>) and configured to provide a force to translate the inner ball screw (<NUM>, <NUM>) axially towards the mechanical load member during use of the EMA.