Patent Application
20250010837
The present application relates to an output stage of an electric brake actuator, such as for example for use in an aircraft braking system.
The current state of the art in aerospace wheel electric brake systems is to use a motor to drive a ball screw through a gear train to apply brake pressure. There are certain disadvantages of ball screw configurations. For example, there are limited suppliers of ball screws which results in associated cost and delivery issues, and limited gain may be available with ball screw configurations due to minimum lead versus load which necessitates additional gear stages being implemented into the ball screw design.
In view of such issues, an alternative electric brake system configuration employs a brake actuator having an output shaft that is driven against the brake stack. In such brake actuators, at a neutral position prior to a braking operation, an air gap is maintained between an end of the output shaft and the brake stack. The air gap initially is set to a suitable dimension for operability for efficient braking. However, as brake stack plates wear from repeated braking operations, the air gap can change, and particularly enlarge beyond the suitable operable dimension. Accordingly, the air gap needs to be adjusted periodically to ensure the air gap remains at the operable dimension for efficient braking. In conventional configurations, the air gap is set and adjusted electronically with the settings stored in memory, which has the possible risk of losing settings during certain failure modes. Conventional solutions for maintaining the air gap in an electric brake system, particularly for an aircraft brake system, have been deficient.
Embodiments of the present application are used as the output stage of an electric brake actuator, and are particularly suitable for use, for example, as the output stage of an electric brake actuator for an aircraft brake system. The described actuator output stage provides the output force to energize the brake plates of the brake stack, and further includes an auto-gap adjustment mechanism to maintain an air gap in an operable dimension of the output shaft relative to the brake stack as the brake plates wear. The actuator output stage uses a ball ramp assembly that has multiple ramp angles at various degrees of rotation to tailor the output stroke and force to the desired application. The actuator output stage also includes an automatic brake air gap adjusting configuration to maintain the air gap at the operable dimension of the output shaft relative to the brake stack.
A ramp assembly with auto-gap adjustment mechanism includes an output ball ramp that is connected to an output shaft through a threaded interface. The output ball ramp has ramped ball tracks containing one or more bearing balls, with one ball per ramp track. An input ball ramp has a matching set of ramped ball tracks that interface with the bearing balls. As such, rotation of the input ball ramp relative to the output ball ramp will cause axial movement of the output ball ramp relative to the input ball ramp. The output shaft, which is threaded to the output ball ramp, will move axially in concert with the output ball ramp. The input ball ramp is driven or rotated by reduction gearing, and the input ball ramp may rotate in either direction depending on the mode of operation being a braking operation versus an auto-adjustment operation. The output ball ramp is fitted with ratchet teeth that interface with a ratchet pawl that is energized by an external or integral spring mechanism. The output ramp can only rotate in one direction due to the interaction of the ratchet and pawl to perform the auto-adjustment operation.
The opposing input and output ball ramps form a conjugate ramp track having portions of variable gain. The output ball ramp includes an output ball ramp track that guides a bearing ball, and the input ball ramp includes a matching input ball ramp track that when facing the output ball ramp form the conjugate ramp track. There may be multiple conjugate ramp tracks that are comparably configured, each receiving a respective bearing ball. The bearing balls are maintained in their respective circumferential positions with a ball cage to ensure each ramp-to-ball relationship is the same. The input and output ball ramp tracks combine to form a conjugate ramp track that has a plurality of different ramp angles for different gains depending on the stage of operation. In a neutral position, the bearing balls sit at the bottom of the conjugate ramp track.
During a braking operation, the input ball ramp is rotated in a first direction (e.g., clockwise) relative to the output ball ramp, and the bearing balls initially roll up the conjugate ramp track over a transition area. The gain of a given portion of the conjugate ramp track is defined by force output divided by torque input, and therefore the gain is relatively low between neutral position and transition area. This portion of the conjugate ramp track is intended to take up the air gap between the output shaft and the first stationary brake plate in the brake stack, and thus the output shaft rapidly closes the air gap with little rotation of the input ball ramp. The output ball ramp is held fixed from rotation by the ratchet and pawl. Continued first direction rotation of the input ball ramp relative to the output ball ramp past the transition area positions the bearing balls on a high gain portion of the conjugate ramp track, which allows for very high output force on the output ball ramp relative to input torque on the input ball ramp. This high force is applied across the brake stack assembly causing braking torque to be generated to slow the rotation of the wheel. The end of the conjugate ramp track is a functionally very steep ramp which has very low gain and effectively acts as an end of stroke stop for the braking operation.
During an auto-adjustment operation, the input ball ramp is rotated in a second direction opposite from the first direction (e.g., counterclockwise) relative to the output ball ramp, and the bearing balls roll onto an auto-adjust portion of the conjugate ramp track. The auto-adjust portion of the conjugate ramp track includes a low gain ramp that provides a displacement of the output ball ramp relative to the input ball ramp equal to the operable dimension of the air gap. Additional second direction rotation of the input ball ramp relative to the output ball ramp causes the bearing ball to come up against an adjustment stop ramp that constitutes an end of stroke stop for the auto-adjustment operation. At such point, the conjugate ramp track gain goes to nearly zero, and this action sets the air gap to the operable dimension. Additional second direction rotation of the input ball ramp drives the output ball ramp to rotate in the ratchet free direction when there is an additional air gap present beyond the operable dimension. In this manner the air gap is adjusted to the operable dimension, and the system is returned to the neutral position pending a braking command.
To the accomplishment of the foregoing and related ends, the invention, then, comprises the features hereinafter fully described and particularly pointed out in the claims. The following description and the annexed drawings set forth in detail certain illustrative embodiments of the invention. These embodiments are indicative, however, of but a few of the various ways in which the principles of the invention may be employed. Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the drawings.
Embodiments of the present application will now be described with reference to the drawings, wherein like reference numerals are used to refer to like elements throughout. It will be understood that the figures are not necessarily to scale.
The output shaft 26, which as referenced above is threaded to the output ball ramp 50 via the threaded interface 52, will move axially in concert with the output ball ramp 50. Accordingly, when the input ball ramp 56 rotates, such rotation is imparted through the output ball ramp 50 to axially drive the output shaft 26 against the brake stack 17 shown in
Referring to
As referenced above, when the input ball ramp 56 rotates during a braking operation, such rotation is imparted through the output ball ramp 50 to axially drive the output shaft 26 against the brake stack 17. More specifically, the shaft end 82 is driven against the first one of the stationary brake plates 18, thereby eliminating the air gap 30 (and 32). The air gap dimension is to be minimized and adapted for a particular application, and the air gap, for example, may have an operable dimension of approximately 0.040-0.070 inches in certain aircraft applications, although any suitable air gap operable dimension may be employed depending on the particular vehicle or application. As the brake stack components wear, however, a dimension of the air gap 30 (and 32) at the non-braking neutral position changes, and particularly enlarges and can become greater than the operable dimension. Periodically, therefore, the neutral position of the output shaft 26 needs to be adjusted to reset the air gap dimension to be within the operable dimension. An aspect of the invention, therefore, is an auto-adjustment mechanism that automatically implements an air gap adjustment when the air gap becomes larger than the operable dimension.
Referring to the torque tube side viewpoint of
Referring to the strut side viewpoint of
Referring principally to the isolated view of
The input ball ramp 56 and output ball ramp 50 cooperate to form a variable gain conjugate ramp track 130, which have portions of variable gain due to the relationship of opposing input and output ball ramps at different portions of the conjugate ramp track 130. The output ball ramp includes an output ball ramp track that guides the bearing ball, and the input ball ramp includes a matching input ball ramp track that when facing the output ball ramp track forms the conjugate ramp track 130. As referenced above, there may be more than one conjugate ramp track, there being one bearing ball located in each respective conjugate ramp track. Three conjugate ramps tracks are present in the depicted example, although any suitable number may be employed. The bearing balls are maintained in their respective circumferential position with a ball cage to ensure each ramp-to-ball relationship is the same. The input and output ball ramp tracks thereby combine to form the conjugate ramp track that has a plurality of different ramps angles. In a neutral position, the bearing balls sit at the bottom of the conjugate ramp track. The conjugate ramp track also has an auto-gap adjust portion of the ball ramp track, which is a low gain ramp that provides a displacement of the output ball ramp relative to the input ball ramp to position the output shaft at an operable air gap dimension relative to the brake stack.
Braking operation is described with respect to the conjugate ramp track illustratively starting at the neutral position 134 and oriented looking from the input ball ramp 132 towards the output ball ramp 142. The neutral position corresponds to a non-braking position. When the input ball ramp 56 is rotated in a first direction (e.g., clockwise in the depiction of the figures) relative to the output ball ramp 50, the bearing ball initially rolls up the conjugate ramp track over transition area 136. Transition area 136 may be a simple edge or may be a distinct ramp angle. The gain of a given ramp segment is defined by force output divided by torque input, and therefore the gain is relatively low between neutral position 134 and the transition area 136. This portion of the conjugate ramp track is intended to take up the air gap 30 between the brake stationary plate 18 and the output shaft 26 rapidly and with little rotation of the input ball ramp 56. As the input ball ramp rotates, the output ball ramp 50 is held fixed from rotation by the interfacing of the ratchet teeth 74 and ratchet pawl 76 identified previously. Continued first direction (e.g., clockwise) rotation of the input ball ramp 56 relative to the output ball ramp 50 past the transition area 136 positions the bearing ball on the high gain portion 138 of the conjugate ramp track, which allows for very high output force on output ball ramp 50 relative to input torque on the input ball ramp 56. As a result, the output shaft is driven against the brake stack with a high force. This high force is applied across the brake stack assembly causing braking torque to be generated to slow the rotation of the wheel. The end of the conjugate ramp track at stop ramp 140 is a functionally very steep ramp which has very low gain and effectively acts as an end of brake stroke stop.
The above description pertains to the braking operation. As referenced above, in the neutral non-braking position, there is an air gap between an end of the output shaft of the brake actuator and a first one of the stationary brake plates of the brake stack. The air gap dimension is adapted to an operable dimension for a particular vehicle type or application (again, for example an air gap of approximately 0.040-0.070 inches is an operable dimension in certain aircraft applications). As the brake components wear, however, the air gap at the non-braking neutral position changes, and particularly enlarges to a point where the air gap is larger than the operable dimension. Periodically, therefore, the neutral position of the output shaft needs to be adjusted to reset the air gap dimension to the operable dimension. Accordingly, the conjugate ramp track further is configured to provide an automatic adjustment of the air gap.
Further as to operation of the conjugate ramp track, the auto-gap adjustment feature is achieved by rotating the input ball ramp 56 in a second direction opposite from the first direction (e.g., counterclockwise). To provide for the gap adjustment, as shown in
When the input ball ramp 56 is rotated in the second direction (e.g., counterclockwise) relative to the output ball ramp 50, the bearing ball rolls onto the auto-adjustment ramp 146 portion of the conjugate ramp track. The auto-adjustment ramp 146 is a low gain ramp that provides a displacement of the output ball ramp 50 relative to the input ball ramp 56 up to an amount equal to the desired air gap 30 (and 32) shown in
If, however, the air gap has enlarged such as due to wear of the brake stack components, additional second direction (e.g., counterclockwise) rotation of the input ball ramp 56 relative to the output ball ramp 50 can occur and causes the bearing ball to come up against the adjustment stop ramp 148 constituting the end of stroke, at which point the conjugate ramp track gain goes to nearly zero. This action sets the operable air gap 30/32 as the dimensions of the components are configured in accordance with the operable air gap dimension. From this state in which there is an additional amount of air gap present beyond the operable dimension, the second direction (counterclockwise) rotation of the input ball ramp 56 drives the output ball ramp 50 to rotate in the ratchet free direction. The output shaft is prevented from rotation by the anti-rotation pins such that rotation of the output ball ramp 50 relative to the output shaft 26 causes the output shaft to be driven towards the brake stack due to the interaction of the output ball ramp/output shaft threaded interface 52 (see
Accordingly, the adjustment operation is implemented automatically initially by rotating the input ball ramp in the second direction opposite from the braking (first) direction. If the air gap has remained at an operable dimension, then the input ball ramp rotates back to return the brake actuator to the neutral position. If, however, the air gap now exceeds the operable dimension, the resultant forces advance the output shaft and ratchet mechanism to adjust the air gap back into the operable dimension, and then the input ball ramp rotates back to return the brake actuator to the neutral position. The electronic controller for the braking system may be programmed to perform the auto-adjustment operation periodically. For example, the electronic controller may be programmed to perform the auto-adjustment operation after every braking operation, and/or at aircraft (or other vehicle) startup. In this manner, an operable air gap dimension automatically is ensured for the next braking operation.
Although the invention has been shown and described with respect to a certain embodiment or embodiments, it is obvious that equivalent alterations and modifications will occur to others skilled in the art upon the reading and understanding of this specification and the annexed drawings. In particular regard to the various functions performed by the above described elements (components, assemblies, devices, compositions, etc.), the terms (including a reference to a “means”) used to describe such elements are intended to correspond, unless otherwise indicated, to any element which performs the specified function of the described element (i.e., that is functionally equivalent), even though not structurally equivalent to the disclosed structure which performs the function in the herein illustrated exemplary embodiment or embodiments of the invention. In addition, while a particular feature of the invention may have been described above with respect to only one or more of several illustrated embodiments, such feature may be combined with one or more other features of the other embodiments, as may be desired and advantageous for any given or particular application.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2022/081167 | 12/8/2022 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 63288032 | Dec 2021 | US |
