Proximal position stop arrangement of an electromechanical actuator

Description

FIELD

[0001] The present invention relates to electromechanical actuators ("EMAs"), and more particularly, to a stopping assembly for EMAs.BACKGROUND

[0002] EMAs are braking assemblies that forcefully move a translating member (such as a "ball nut") against a brake disk stack to generate an actuation force. This actuation force drives the ball nut into forceful engagement with the brake disk stack to generate a braking force. FR 2848171 describes an electromechanical bridle operating method.SUMMARY

[0003] An electromechanical actuator (EMA) is disclosed and defined in claim 1. The EMA comprises an EMA housing, a ball nut extending axially within the EMA housing, a ball screw extending axially within the ball nut, and / or an actuator drive unit (ADU) housing extending axially within the ball screw, the ADU housing having a proximal stop that extends radially outward of the ADU housing. The ball nut is configured to translate axially in a proximal direction in response to a rotation by the ball screw, and the ball nut is configured to be halted in the axially proximal translation in response to contact with the proximal stop. The proximal stop is coupled to the ADU housing. The proximal stop comprises a continuous annular structure. The ball nut contacts with the proximal stop as the ball nut translates axially to halt the axially proximal translation of the ball nut. The proximal stop includes a compliant surface. The ball nut is configured to advance axially in a distal direction away from the proximal stop and / or to retract axially in the proximal direction towards the proximal stop. A position of the ball nut may be determined based upon a gear ratio.BRIEF DESCRIPTION OF THE DRAWINGS

[0004] 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 drawing figures, wherein like numerals denote like elements. Figure. 1A illustrates a cross-sectional schematic view of a conventional EMA; Figure. 1B illustrates top perspective view of a conventional ball nut; Figure 1C illustrates a top perspective view of a conventional ball screw; Figure. 2A illustrates, in accordance with various embodiments, a cross-sectional schematic view of an EMA; and Figure 2B illustrates, in accordance with various embodiments, a partial cross-sectional schematic view of an EMA. DETAILED DESCRIPTION

[0005] The detailed description of exemplary embodiments herein makes reference to the accompanying drawings, which show exemplary embodiments by way of illustration and their best mode. While these exemplary embodiments are described in sufficient detail to enable those skilled in the art to practice the inventions, it should be understood that other embodiments may be realized and that logical, chemical and mechanical changes may be made without departing from the scope of the present invention as defined by the appended claims. Thus, the detailed description herein is presented for purposes of illustration only and not of limitation. For example, the steps recited in any of the method or process descriptions may be executed in any order and are not necessarily limited to the order presented. Furthermore, any reference to singular includes plural embodiments, and any reference to more than one component or step may include a singular embodiment or step. Also, any reference to attached, fixed, connected or the like may include permanent, removable, temporary, partial, full and / or any other possible attachment option. Additionally, any reference to without contact (or similar phrases) may also include reduced contact or minimal contact.

[0006] As used herein, an "inner surface" may comprise any surface that is situated radially inward of any other surface with respect to the axis, as defined herein, labeled A-A'. Thus, an inner surface may be situated radially inward of an "outer surface" with respect to the axis A-A'.

[0007] In addition, the EMA may extend along the axis defined by the line marked A-A'. The portion near A may be referred to as proximal and the portion near A' may be referred to as distal. In that regard, A is proximal to A' and A' is distal to A. Translation in an axial direction towards A is considered movement in a proximal direction and translation in an axial direction towards A' is considered movement in a distal direction.

[0008] With reference to Figure 1A, a cross-sectional schematic view of a conventional EMA 100 is shown. The EMA 100 may comprise an EMA housing 102, an actuator drive unit ("ADD") housing 111, a ball nut 104, a ball screw 106, and a disc or "puck" 108. The EMA housing 100 may comprise a generally annular structure configured to house the ball nut 104 and extending along the axis A-A'. The ball nut 104 may comprise a generally annular housing that extends axially along the axis A-A' within the EMA housing 102. The ball screw 106 may comprise a generally annular housing that extends axially along the axis A'A' within the ball nut 104. The ADU housing 111 may comprise a generally annular housing that extends axially along the axis A-A' at least partially radially inward of the ball screw 106. A variety of drive components may be housed within the ADU housing 111, such as, for example, an electromechanical drive motor, drive shaft, gearing system, and the like. The ADU housing 111 may comprise a stationary (non-rotating, non-translating) component. The puck 108 may comprise a generally disc shaped element, and the puck 108 may be coupled to a distal portion of the ball nut 104.

[0009] An inner surface of the ball nut 104 may be helically threaded. Likewise, an outer surface of the ball screw 106 may be helically threaded. As described above, the ball screw 106 may be housed within the ball nut 104, and the threading on the outer surface of the ball screw 106 may interface with or mate with the threading on the inner surface of the ball nut 104.

[0010] During operation, the ball screw 106 may rotate about an axis A-A'. As the ball screw 106 rotates, the threading on the ball screw 106 may cooperate with the threading in the ball nut 104 to drive the ball nut 104 in a distal direction. As the ball nut 104 translates distally, the puck 108 coupled to the ball nut 104 may also translate distally. The puck 108 may contact a brake stack (e.g., a brake stack associated with an aircraft wheel) to apply force to the brake stack, thereby slowing and / or halting the rotation of the aircraft wheel.

[0011] With reference to Figure 1B, a longitudinal perspective view of a conventional ball nut 104 (looking from A to A' toward a distal portion of the ball nut 104 along the longitudinal axis A-A') is shown. This ball nut 104 includes a concentrically situated projection 110 or "tooth," located at a distal portion of the ball nut 104.

[0012] With reference to Figure 1C, a longitudinal perspective view of a distal portion of a conventional ball screw 106 is shown. The ball screw 106 includes a concentrically situated projection 112 or tooth as well. This projection 112, like the projection 110, is situated at a distal portion of the ball screw 106.

[0013] In operation, as described above, as the ball screw 106 rotates, the ball nut 104 may translate proximally (and / or distally) along the axis A-A' until the projection 112 in the ball screw 106 rotates into contact with the projection 110 in the ball nut 104. As the projection 112 makes contact with the projection 110, the ball nut 104 may be halted in its proximal progress, even as the ball screw 106 may attempt to rotate in an effort to force the ball nut 104 proximally into a home stop or stowed position.

[0014] A variety of disadvantages are associated with the conventional system depicted at Figures 1A-1C. For example, the projection 112 may rotate with substantial angular momentum into the projection 110. As this occurs, the projection 112 and / or the projection 110 may chip or break. Failure of either projection 110 and / or 112 may result in expulsion of the entire ball nut 104 from its housing within the EMA housing 102, leaving the ball nut 104 (and / or other components) behind as litter and / or other dangerous debris. Such an event may, in addition, result in brake failure. Thus, a variety of disadvantages are associated with existing conventional systems.

[0015] Now, with reference to Figure 2A, an EMA 200 is shown. The EMA 200 may, like the EMA 100, comprise an EMA housing 202, a ball nut 204, a ball screw 206, an ADU housing 207, and a disc or puck 208. As above, the EMA housing 200 may comprise a generally annular structure configured to house the ball nut 204 and extending along the axis A-A'. The ball nut 204 may comprise a generally annular housing that extends axially along the axis A-A' within the EMA housing 202. The ball screw 206 may comprise a generally annular housing that extends axially along the axis A-A' within the ball nut 204. The ADU housing 207 may comprise a generally annular housing that extends axially along the axis A-A' at least partially radially inward of the ball screw 206.

[0016] According to the invention an electromechanical drive motor is housed in the ADU housing. A variety of further drive components may be housed within the ADU housing 207, such as, for example, drive shaft, gearing system, and the like. The puck 208 may comprise a generally disc shaped element, and the puck 208 may be coupled to a distal portion of the ball nut 204.

[0017] However, as shown in greater detail at Figure 2B, the EMA 200 described herein may comprise an ADU housing 207 comprising a projection or stop 210 extending radially outward of the ADU housing 207. The stop 210 may extend radially outward such that it is raised above an outer surface of the ADU housing 207. In addition, the stop 210 may be disposed substantially at a proximal portion of the ADU housing 207 and may comprise a "T-shaped" or doglegged structure.

[0018] The proximal portion of the stop 210 incorporates a compliant or shock absorbing material, such as foam or rubber. This material may dissipate energy, as described below, as the ball nut 204 comes into contact with the stop 210. The stop 210 may be coupled to the ADU housing 207 in any suitable manner. For instance, the stop 210 may be screwed into the ADU housing 207, heat bonded to the ADU housing 207, forged integral to the ADU housing 207, riveted to the ADU housing 207, bolted into the ADU housing 207, adhesively bonded to the ADU housing 207, and the like.

[0019] In operation, as the ball nut 204 translates axially in a proximal direction, the ball nut 204 comes into contact with the stop 210. As the ball nut 204 comes into contact with the stop 210, the proximal translation of the ball nut 204 is halted. The stop 210 may however, unlike other conventional systems, resist or eliminate EMA 200 failure. For example, the stop 210, comprising a continuous annular structure, may not rely upon one or more simple projections (e.g., projections 110 and 112) to arrest the angular momentum of the ball nut 104. Rather, the large (continuous) surface area of the stop 210 may permit the dissipation of angular and axial momentum over a much larger, surface area.

[0020] Dissipation of angular and axial momentum over this larger surface area reduces the overall stress experienced by any particular portion of the ball nut 204 and / or ball screw 206 (e.g., the projections 110 and 112 in the conventional system), particularly as the ball nut 204 and / or the ADU housing 207 and / or stop 210 may be manufactured, for durability and strength, from steel or a steel alloy, such as, for example, a hardened steel. The system of the present invention therefore embodies a much more reliable, failure-resistant, ball nut 204 stopping system. The cost and weight of the system of the present invention may also be reduced over that associated with more conventional systems, as projections 110 and 112 may be eliminated in favor of the stop 210.

[0021] In various embodiments, from the stop 210, a computer-based system comprising a processor and a tangible, non-transitory, memory coupled to the processor may track or count the number of motor rotations or revolutions as the ball nut 204 advances distally from the stop 210. This information, in combination with a gear ratio and / or a distance of a portion of the ball nut 204 (e.g., the distal edge of the ball nut 204) from the stop 210 may permit the computer-based system to calculate the position of the ball nut 204 and / or the ball nut 204 actuating mechanism. The location of the ball nut 204 and / or actuator may be fed back into the computer-based system to control the advancement and / or retraction of the ball nut 204 during operation.

[0022] Benefits, other advantages, and solutions to problems have been described herein with regard to specific embodiments. However, the benefits, advantages, solutions to problems, and any elements that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as critical, required, or essential features or elements of the inventions. The scope of the inventions is accordingly to be limited by nothing other than the appended claims, in which reference to an element in the singular is not intended to mean "one and only one" unless explicitly so stated, but rather "one or more."

Claims

1. An electromechanical actuator, EMA, (200) for use as a braking assembly comprising: an EMA housing (202); a ball nut (204) extending axially within the EMA housing (202); an actuator drive unit, ADU, housing (207) disposed radially inward to the bull nut and extending axially within the ball screw (206), the ADU housing (207) having a proximal stop (210) that is coupled to and protrudes from an outer surface of a proximal portion of the ADU housing (207); and a ball screw (206) extending axially within the ball nut (204); and wherein the ball nut (204) is configured to advance axially in a distal direction away from the proximal stop (210) and to retract axially in a proximal direction in response to a rotation by the ball screw (206), and wherein the ball nut (204) is configured to be halted in the axially proximal translation in response to contact with the proximal stop (210); characterised in that the EMA further comprises: an electromechanical drive motor housed in the ADU housing (207), and in that the proximal stop comprises a continuous annular structure and includes a compliant surface comprising at least one of a foam or rubber.

2. The EMA of any preceding claim, wherein the ball nut (204) makes contact with the proximal stop (210) as the ball nut (204) translates axially to halt the axially proximal translation of the ball nut (204).

3. The EMA of any preceding claim, wherein the ball nut (204) is configured to retract axially in the proximal direction towards the proximal stop (210).

4. The EMA of any preceding claim, wherein a position of the ball nut (204) is determined based upon a gear ratio.