Redundant pivot bearing with mechanical detection

A pivot assembly for a control lever. The pivot assembly include a primary pivot bearing arranged about a longitudinal axis (A) and a redundant pivot bearing arranged about the longitudinal axis (A). The redundant pivot bearing is configured to become operative as a bearing in the event that the primary pivot bearing malfunctions, and to produce haptic feedback in the control lever throughout operation of the redundant pivot bearing.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to European Patent Application No. 21290058.3 filed Sep. 17, 2021, the entire contents of which is incorporated herein by reference.

TECHNICAL FIELD

This disclosure relates to a pivot assembly of a control lever for a vehicle, in particular (although not exclusively) for an aircraft.

BACKGROUND

In a vehicle, a control stick or lever, or another type of mechanical input control device, may be provided to control the range of movement of the vehicle. The control stick may control a number of control parameters. For example, a control stick in an aircraft can be arranged to control the pitch and roll of the aircraft by allowing rotation of the control stick about a number of axes. A thrust lever in an aircraft can be used to control the thrust provided by the aircraft engines. A pedal assembly can be used to control the yaw and the wheel brakes of an aircraft, for example.

In order to facilitate rotation of the control stick about one of its axes, the shaft of the control stick may be mounted to a pivot bearing. Typical pivot bearings include rolling-element bearings, e.g., comprising balls or rollers. Rolling-element bearings, while providing a low-friction pivot, are susceptible to shock loads, breakage of the rolling-element, breakage of the bearing races, or wear due to dust or dirt entering the bearing. This can lead to a jamming of the bearing which may prevent movement of the control stick (or lever or pedal). In the example of an aircraft, jamming of the bearing of a control stick or lever may prevent control over the rotation of the aircraft about the axes or control of the thrust of the engines. This can lead to serious safety issues such as the aircraft crashing.

To obviate these disadvantages, conventional control stick pivots often incorporate a second bearing assembled concentrically with the primary rolling-element bearing to provide redundancy; the second, redundant bearing becomes operable as a sliding bearing in the event that the primary rolling-element bearing fails. Thus, in the case of a control stick for an aircraft, the pilot is able to continue using the control stick should the rolling-element bearing fail.

FIG.1of the accompanying drawings shows a prior art pivot assembly100as disclosed in WO 2017/182836 A1 (the content of which is incorporated herein by reference in its entirety). The pivot assembly100comprises a shaft110having a longitudinal axis R-R about which said shaft110can rotate, and control stick pivot200provided about an end of said shaft110within a housing120.

The control stick pivot200comprises a primary pivot bearing210and a redundant pivot bearing220, both concentric about shaft110and configured to rotate about axis R-R. Primary pivot bearing210is a rolling-element bearing comprising an outer bearing race212with an outer surface213fixed to the housing120and an inner bearing race214provided about the redundant pivot bearing220. Redundant pivot bearing220comprises a bushing225provided between the primary pivot bearing210and the shaft110.

As shaft110rotates about axis R-R, redundant pivot bearing220and inner bearing race214rotate with the shaft110. Should the primary pivot bearing210malfunction, such that primary pivot bearing210seizes or fails to operate efficiently, sliding contact between the redundant pivot bearing220and inner element214or between the redundant pivot bearing220and the shaft110commences. Thus, the redundant pivot bearing220becomes operative as a pivot.

The torque required to turn shaft110is inherently greater when the control stick pivot200is operating with sliding contact rather than rolling contact. Thus the user may detect a failure of the primary pivot bearing210as the control stick will feel stiffer to manoeuvre. The choice of material for the redundant pivot bearing220may be selected to require a desired level of friction torque in the shaft110before it becomes operative which is not significantly different to impart control issues but which might still be observable to an alert pilot. WO 2017/182836 A1 also discloses that visual indicators, such as a frangible link or an alignment guide, or sensors, such as optical, electrical or magnetic sensors, may also be used to alert the user or a maintenance engineer that the primary pivot bearing210has malfunctioned.

However, there are improvements that can be made in the detection of failure of the primary pivot bearing.

SUMMARY

An aspect of the present disclosure provides a pivot assembly for a control lever, the pivot assembly comprising a primary pivot bearing arranged about a longitudinal axis, and a redundant pivot bearing arranged about the longitudinal axis, the redundant pivot bearing configured to become operative as a bearing in the event that the primary pivot bearing malfunctions, and to produce haptic feedback (e.g., in the control lever) throughout operation of the redundant pivot bearing. The haptic feedback may be produced by a variation in the torque required to pivot the redundant pivot bearing or control lever when the redundant pivot bearing is operative as a bearing. Using haptic feedback throughout operation of the redundant pivot bearing provides improvements, in that the operator knows for sure that there has been a change in operation whenever they move the lever. Small, frequent variations could be used to provide the haptic feedback as a vibration effect that could be felt by a user. Alternatively, a smaller number (e.g., one or two) large variations could be used. This concept can be modified within the scope of this aspect to provide various types of haptic feedback that could be felt by a user throughout operation of the redundant pivot bearing.

For example, the redundant pivot bearing may comprise a detent mechanism to produce the haptic feedback, for example by varying the torque required to pivot the redundant pivot bearing.

The redundant pivot bearing may comprise a detent ring and a carrier ring arranged about the longitudinal axis. The detent ring and carrier ring may be configured such that, when the redundant pivot bearing is operative as a bearing, one of the detent ring and carrier ring rotates about the longitudinal axis relative to the other, and the detent ring and carrier ring cooperate to provide the detent mechanism to produce the haptic feedback.

The detent ring may comprise a detent profile and the carrier ring may comprise one or more protruding elements and one or more springs. The detent ring and carrier ring may be arranged such that the one or more protruding elements are directly opposite and in contact with the detent profile, the one or more springs are preloaded to bias the at least one protruding element against the detent profile, and the detent profile and one or more protruding elements are shaped to produce the haptic feedback under the bias of the spring when there is relative rotational motion between the detent ring and carrier ring about the longitudinal axis.

The carrier ring may comprise one or more bores in the second surface, each spring arranged within each bore. Each protruding element may comprise a ball bearing received within an opening of each bore at the second surface, wherein the spring is preloaded to bias the ball bearing against the detent profile.

The detent profile may be on a radially inner surface of the detent ring directly opposite a radially outer surface of the carrier ring. The carrier ring may comprise a radially inner surface, a circumferential recess in the radially inner surface, and one or more bores extending between the circumferential recess and the radially outer surface. The one or more protruding elements may be received within each bore and protrude into the circumferential recess and out from the radially outer surface. The one or more springs may comprise a spring ring arranged within the circumferential recess in contact with the one or more protruding elements, the spring ring preloaded to bias the one or more protruding elements against the detent profile. Each protruding element may comprise a ball bearing.

The detent profile may comprise at least one groove configured to receive the one or more protruding elements such that the haptic feedback is produced as the at least one protruding element enters and/or exits the at least one groove when there is relative rotational motion between the detent ring and carrier ring about the longitudinal axis.

The primary pivot bearing may be fixed to or integral with the detent ring such that, in the event that the primary pivot bearing malfunctions, the primary pivot bearing transfers torque to the detent ring so that the primary pivot bearing and detent ring rotate together about the longitudinal axis relative to the carrier ring.

The primary pivot bearing may be fixed to or integral with the carrier ring such that, in the event that the primary pivot bearing malfunctions, the primary pivot bearing transfers torque to the carrier ring so that the primary pivot bearing and carrier ring rotate together about the longitudinal axis relative to the detent ring.

The redundant pivot bearing may comprise at least one spring that is preloaded to produce an axial force on the primary pivot bearing.

The pivot assembly may comprise a sensor, such as a strain gauge, to detect the haptic feedback from the redundant pivot bearing.

The primary pivot bearing may be a rolling-element bearing. The redundant pivot bearing may be a friction bearing or a rolling-element bearing.

The pivot assembly may further comprise a shaft and a housing, wherein the pivot assembly is mounted about the shaft within the housing. The detent ring may be replaced by a detent profile on the shaft.

Another aspect of the present disclosure provides a control lever assembly comprising a control lever and the pivot assembly of any of the above embodiments, arranged such that the redundant pivot bearing produces haptic feedback in the control lever throughout operation of the redundant pivot bearing.

Another aspect of the present disclosure provides a method for detecting malfunction of a control lever assembly, the method comprising pivoting a control lever on a shaft using a pivot assembly, the pivot assembly comprising a primary pivot bearing arranged about a longitudinal axis of the shaft and a redundant pivot bearing arranged about the longitudinal axis, the redundant pivot bearing becoming operative as a bearing in the event that the primary pivot bearing malfunctions, and throughout operation of the redundant pivot bearing, the redundant pivot bearing producing haptic feedback in the control lever. As discussed above in respect of the first aspect, the haptic feedback may be produced by a variation in the torque required to pivot the redundant pivot bearing or control lever when the redundant pivot bearing is operative as a bearing.

For example, the redundant pivot bearing may comprise a detent mechanism to produce the haptic feedback, for example by varying the torque required to pivot the redundant pivot bearing.

The redundant pivot bearing may comprise a detent ring and a carrier ring arranged about the longitudinal axis, the method may comprise operating the redundant pivot bearing by rotating one of the detent ring and carrier ring about the longitudinal axis relative to the other to provide the detent mechanism and thereby produce the haptic feedback.

The detent ring may comprise a detent profile and the carrier ring may comprise one or more protruding elements and one or more springs. The detent ring and carrier ring may be arranged such that the one or more protruding elements are directly opposite and in contact with the detent profile, the one or more springs are preloaded to bias the at least one protruding element against the detent profile, and the detent profile and one or more protruding elements are shaped to produce the haptic feedback under the bias of the spring when there is relative rotational motion between the detent ring and carrier ring about the longitudinal axis.

The carrier ring may comprise one or more bores in the second surface, each spring arranged within each bore. Each protruding element may comprise a ball bearing received within an opening of each bore at the second surface, wherein the spring is preloaded to bias the ball bearing against the detent profile.

The detent profile may be on a radially inner surface of the detent ring directly opposite a radially outer surface of the carrier ring. The carrier ring may comprise a radially inner surface, a circumferential recess in the radially inner surface, and one or more bores extending between the circumferential recess and the radially outer surface. The one or more protruding elements may be received within each bore and protrude into the circumferential recess and out from the radially outer surface. The one or more springs may comprise a spring ring arranged within the circumferential recess in contact with the one or more protruding elements, the spring ring preloaded to bias the one or more protruding elements against the detent profile. Each protruding element may comprise a ball bearing.

The detent profile may comprise at least one groove configured to receive the one or more protruding elements such that the haptic feedback is produced as the at least one protruding element enters and/or exits the at least one groove when there is relative rotational motion between the detent ring and carrier ring about the longitudinal axis.

The primary pivot bearing may be fixed to or integral with the detent ring such that, in the event that the primary pivot bearing malfunctions, the primary pivot bearing transfers torque to the detent ring so that the primary pivot bearing and detent ring rotate together about the longitudinal axis relative to the carrier ring.

The primary pivot bearing may be fixed to or integral with the carrier ring such that, in the event that the primary pivot bearing malfunctions, the primary pivot bearing transfers torque to the carrier ring so that the primary pivot bearing and carrier ring rotate together about the longitudinal axis relative to the detent ring.

The redundant pivot bearing may comprise at least one spring that is preloaded to produce an axial force on the primary pivot bearing.

The method may comprise detecting the haptic feedback from the redundant pivot bearing with a sensor, such as a strain gauge.

The primary pivot bearing may be a rolling-element bearing. The redundant pivot bearing may be a friction bearing or a rolling-element bearing.

The detent ring may be replaced by a detent profile on the shaft.

In any of the aspects described above, by “throughout operation” it is meant that the haptic feedback is provided whenever the redundant pivot bearing is operative. For example, the haptic feedback remains substantially the same and does not diminish over time (e.g., the variation in torque remains substantially the same).

DETAILED DESCRIPTION

FIG.2shows a control lever assembly10for an aircraft. The control lever assembly10comprises a control lever12, such as a control stick or pedal, and a pivot assembly14which, when assembled, is mounted about a shaft16within a housing18. The shaft16has a longitudinal axis A. The pivot assembly14allows the lever12to pivot about the longitudinal axis A of the shaft16. The lever12can be pivoted about the shaft16by a user, such as a pilot of an aircraft. For example, the control lever12may be a thrust lever that enables a pilot to control the thrust of the aircraft. Although particularly beneficial in this context, other applications are of course possible and the technical effects disclosed herein are not limited to this particular context. For example, the pivot assembly14is not limited to use with a control lever12and may be used in other pivoting systems. The control lever12may be any kind of mechanical input control device, including, for example, a pedal.

With additional reference toFIG.3, the lever12comprises a lever ring20and the pivot assembly14is arranged radially between the lever ring20and the shaft16. The pivot assembly14comprises at least one primary pivot bearing22and at least one redundant pivot bearing24. The pivot assembly14shown inFIGS.2and3has a primary pivot bearing22and a redundant pivot bearing24on each side of the lever12in opposing orientations. However, the pivot assembly14may comprise just one primary pivot bearing22and one redundant pivot bearing24, or more than two of each bearing22,24, depending on, for example, the arrangement of the lever12on the shaft16and the situation at hand.

In normal operation (i.e., without a malfunction of the primary pivot bearing22), the primary pivot bearing22is operative to allow the lever12to pivot about the shaft16, and the redundant pivot bearing24is inoperative. If the primary pivot bearing22malfunctions, for example due to breakage or wear, then the redundant pivot bearing24becomes operative to allow continued operation of the lever12through the pivotal motion about the shaft16. Control levers in the cockpit of an aircraft may be safety critical, and so providing a redundant pivot bearing helps to avoid any failure in the operation of the aircraft.

The primary pivot bearing22is a rolling-element bearing comprising an outer race26and an inner race28. The redundant pivot bearing24may comprise a sliding or friction bearing through contact with the shaft16, as shown in the figures. A sliding bearing is chosen typically due to its low complexity, but any suitable type of bearing may be used as the redundant bearing24. For example, the redundant bearing24may comprise a rolling-element or other suitable type of bearing.

The redundant pivot bearing24comprises two elements30,32that are arranged to provide relative movement between them. One of the elements30,32is fixed to (or integral with) the primary pivot bearing22and the other element30,32is fixed to (or integral with) the shaft16. If the primary pivot bearing22malfunctions such that relative rotation between the outer race26and inner race28is prevented, the primary pivot bearing22transfers the torque from the lever12to the element30,32that is fixed to the primary pivot bearing22, and this element30,32then rotates about the shaft16with the lever12while the other element30,32remains static.

When the primary pivot bearing22malfunctions, it is important that the malfunction is discovered as soon as possible in order to preserve the function of the lever12and (particularly for a friction bearing) avoid wearing on the redundant pivot bearing24. If the redundant pivot bearing24were to also fail, the control lever12could become unusable, which could cause safety issues.

To allow the detection of the malfunction of the primary pivot bearing22and the operation of the redundant pivot bearing24, the redundant pivot bearing24is configured to mechanically produce haptic feedback, which may be transmitted to the control lever12to be felt by someone operating the lever12, and/or detected by a sensor such as a strain gauge. The feeling of the haptic feedback can be interpreted by the operator as an indication that the primary pivot bearing has failed and the redundant pivot bearing is in operation.

The haptic feedback may be produced throughout the operation of the redundant pivot bearing24. The haptic feedback may be produced as a defined pattern of vibrations, and/or as a defined variation in the control lever driving force profile while the redundant pivot bearing24is operative that may or may not repeat, for example depending on how far the control lever12and redundant pivot bearing24are pivoted. In some embodiments, operation of the redundant pivot bearing24provides a varying driving force profile for the control lever12comprising a single force maximum across a complete stroke of the lever12. In other embodiments, the varying driving force profile comprises a series of force maxima across a complete stroke of the lever12, as demonstrated inFIG.4and discussed below.

In comparison to prior art systems in which a redundant pivot bearing may merely feel stiffer than a primary pivot bearing (for example if the primary pivot bearing is a rolling element bearing and the redundant pivot bearing is a sliding bearing), the present disclosure makes the operation of the redundant pivot bearing24more noticeable and the primary pivot bearing failure detection more robust in order to enable the time of exposure to the failure of the primary pivot bearing22to be minimised. In other words, the prior art systems may employ a constant load to drive the lever even when the redundant pivot bearing is operational, which may not be discernible to normal operation for (e.g.) an inexperienced operator. Using haptic feedback throughout operation of the redundant bearing is an improvement over such situations, in that the operator knows for sure that there has been a change in operation whenever they move the lever.

In embodiments, the redundant pivot bearing is provided with a detent function that causes a variation in the torque required to rotate the redundant pivot bearing24while the redundant pivot bearing is operative, and therefore a variation in the force that needs to be applied to the control lever12to drive the control lever12when the redundant pivot bearing24is operative. This variation creates the haptic feedback that may be felt by someone operating the lever12, and/or detected by a sensor such as a strain gauge.

As shown inFIGS.2and3, the elements30,32of the redundant pivot bearing24are embodied as a detent ring30and a carrier ring32. A detent profile40provided on the detent ring30cooperates with spring-loaded protruding elements36carried by the carrier ring32to provide a detent mechanism33. In the illustrated embodiment, the detent mechanism33comprises a series of ball detent mechanisms33, each comprising a spring-loaded ball bearing36carried by the carrier ring32, such that the ball bearing36is held in position between the carrier ring32and the detent profile40. The detent ring30and carrier ring32are arranged next to each other such that a surface42of the detent ring30is directly opposite a surface44of the carrier ring32. The detent profile40is provided in this embodiment on the surface42of the detent ring30. Bores38are provided in the surface44of the carrier ring32, with a compression spring34and ball bearing36provided within each bore38. The springs34force the ball bearings36against the opposed surface42of the detent ring30to enable the ball bearings36to cooperate with the detent profile40to provide the detent function. The detent profile40comprises a series of grooves or cavities46that can receive the ball bearings36.

The inner race28of the primary pivot bearing22is fixed to the detent ring30of the redundant pivot bearing24, or may be integral with the detent ring30. The inner and outer races26,28, detent ring30and carrier ring32will typically be mounted coaxially on the shaft16. The lever12can be mounted about the pivot assembly14, as shown, with the radially outer surface of the outer race26of the primary pivot bearing22fixed to the radially inner surface of the lever ring20.

In normal operation, when the primary pivot bearing22is functioning correctly, the lever12, lever ring20and outer bearing race26can pivot about the shaft axis16, and the inner bearing race28, redundant pivot bearing24and shaft16are fixed. The springs34bias the ball bearings36towards the detent ring30and into the grooves or cavities46in the detent profile40to provide the detent function. The detent mechanism33thereby acts to help prevent (undesired) relative rotational motion between the detent ring30and carrier ring32when the primary pivot bearing22is operational. If the primary pivot bearing22malfunctions, for example such that relative rotation between the outer and inner races26,28is no longer permitted or heavily restricted, the pivoting is instead provided by the redundant pivot bearing24rotating about the shaft16.

When the primary pivot bearing22malfunctions in this manner, the redundant pivot bearing24is operational and the detent ring30rotates relative to the carrier ring32. The ball bearings36in the carrier ring32then cooperate with the detent profile40to provide the detent function which produces haptic feedback in the lever12that may be felt by an operator of the lever12in order to notify the operator that the primary pivot bearing22has failed and the redundant pivot bearing24has become operational.

When the primary pivot bearing22first fails such that relative rotation between the outer and inner races26,28is no longer permitted or heavily restricted, continued application of force to turn the lever12increases the torque applied to the redundant pivot bearing24through the primary pivot bearing22, compared to when the primary pivot bearing22is operative. This enables enough torque to be applied to the redundant pivot bearing24to provide relative movement between the ball bearings36and the detent profile40, so that the detent ring30is able to pivot about the shaft16with the lever12and primary pivot bearing22relative to the carrier ring32. The torque needed to overcome the friction of the redundant pivot bearing24between the detent ring30and shaft16may be about the same as the torque needed to overcome the detent force between the detent ring30and carrier ring32to maximise the variation in the required lever driving force and the haptic feedback through the lever12when the redundant pivot bearing24becomes operative.

As the detent ring30rotates relative to the carrier ring32, the grooves or cavities46in the detent profile40of the detent ring30move past the ball bearings36to successively align and misalign the grooves or cavities46with the ball bearings36. The force exerted by the springs34on the ball bearings36(and towards the detent ring30) causes the ball bearings36to enter the grooves46when aligned. As the ball bearings36enter and exit the successive grooves46within the detent profile40when the detent ring30rotates, the torque required to rotate the detent ring30changes according to the relative positions of the ball bearings36and grooves46.

The graph inFIG.4shows how the force required to drive the control lever12to rotate the redundant pivot bearing24varies between a maximum force39and a minimum force41depending on the angular position of the lever12(i.e., as controlled by an operator), due to the relative positions of the ball bearings36and grooves46. In this embodiment, when the redundant pivot bearing24first becomes operative, the detent ring30and carrier ring32are positioned so that the ball bearings36are received within corresponding grooves46. The maxima43of the curve correspond to the ball bearings36exiting the grooves46, and the minima47of the curve correspond to the ball bearings36entering the grooves46. The flat sections45of the curve correspond to the ball bearings36being located between the grooves46. The shape of the lever driving force profile shown inFIG.4depends on the number, shape and spacing of the grooves46and ball bearings36, and the spring force of the springs34.

The variation in the force required to drive the control lever12produces haptic feedback in the lever12that can be felt by the operator to indicate to the operator that the redundant pivot bearing24is operative. Only a small movement of the control lever12may be needed to produce the haptic feedback that can be felt by the operator. For example, the variation in the required driving force may produce noticeable haptic feedback through a single “cycle”, for example as a ball bearing36moves from one groove46to the next adjacent groove46. This minimises the angular distance through which the control lever12needs to be moved before the operator can tell that the primary pivot bearing22has failed and the redundant pivot bearing24is operative, which helps to minimise the safety risks associated with the failed primary pivot bearing22.

In the embodiment ofFIG.2, the detent ring30is shown to have a significantly higher number of grooves46than the number of ball bearings36carried by the carrier ring32. This embodiment has six ball detent mechanisms33(therefore six ball bearings36, six springs34and six bores38) distributed evenly about the carrier ring32. The detent profile40is arranged continuously about the surface42of the detent ring30with evenly distributed grooves46. Therefore, the ball bearings36will always be positioned within or adjacent a groove46. This configuration enables the detent function and haptic feedback to be provided at any relative orientation of the detent ring30and carrier ring32. The arrangement of the grooves46means that only a small relative rotation between the detent ring30and carrier ring32is needed to produce a variation in the force required to drive the control lever12and haptic feedback so that the failure of the primary pivot bearing22can be detected quickly.

It will be understood that other configurations of the detent profile40and ball detent mechanisms33may be used to produce a variation in the force required to drive the control lever12. The springs34, ball bearings36and/or detent profile40can be tailored to provide particular effects on the required driving force. For example, the number of ball bearings36and/or the number of grooves44within the detent profile40can be chosen to produce a variation in the required driving force at specific frequencies that would be more detectable by an operator of the lever12. The bias force of the springs34, the size of the ball bearings36and/or the depths of the grooves46in the detent profile40can be chosen to produce a variation in the required driving force at specific amplitudes that would be more detectable by an operator of the lever12, but that would not hinder the operation of the lever12. The springs34, ball bearings36and/or detent profile40may also be tailored to produce specific patterns of variations in the required driving force that may be more noticeable by an operator of the lever12.

For example, more than six ball detent mechanisms33, or less than six (but at least one) ball detent mechanisms33may be used. The ball detent mechanisms33may be evenly or unevenly distributed about the carrier ring32and the grooves or cavities46may be evenly or unevenly distributed about the detent ring30, depending on the desired variation in the required driving force. The detent profile40may be continuous, or may be arranged in a number of discrete sections.

In normal operation of the pivot assembly14, the carrier ring32and springs34may also provide the additional effect of generating an axial preload on the primary pivot bearing22which helps to avoid backlash of the lever12along the axial directions.

In other embodiments (not shown), instead of each ball bearing36having its own spring34to separately force each ball bearing36against the detent profile40, the redundant pivot bearing24may comprise a single spring arranged coaxially with the shaft16, for example having the same diameter as the carrier ring32. The ball bearings36may thus be fixed on the carrier ring32, or may be replaced by other types of protruding elements that are fixed to or integral with the carrier ring32. The single spring may force the whole carrier ring32towards the detent ring30to provide the detent function. The single spring may also generate an axial preload on the primary pivot bearing22to help avoid backlash of the lever12along the axial directions.

In the embodiment ofFIGS.2and3, the ball detent mechanisms33have an axial orientation. However, as shown inFIG.5, another embodiment of the pivot assembly14may comprise ball detent mechanisms33with a radial orientation. In the embodiment ofFIG.5, the carrier ring32is fixed to (or integral with) the inner race28of the primary pivot bearing22, and the detent ring30can be fixed to the shaft16. Therefore, in the event of malfunction of the primary pivot bearing22, the carrier ring32may rotate with the primary pivot bearing22relative to the detent ring30that is static on the shaft16. The detent ring30may be integral with the shaft16such that the detent profile40is effectively provided on the surface of the shaft16.

Although the redundant pivot bearing24inFIG.5has a different arrangement than the redundant pivot bearing24inFIGS.2and3, the detent function is provided by a corresponding mechanism using corresponding components to produce the variation in the force required to drive the control lever12when the redundant pivot bearing24is operational. The required driving force variation provides haptic feedback to the operator of the control lever12that indicates that the redundant pivot bearing24is operative.

With reference toFIGS.6and7, another embodiment of a pivot assembly48uses a spring ring54, for example an internal snap ring, in the redundant pivot bearing74, instead of the compression springs34of the previous embodiments. The spring ring54is arranged in the redundant pivot bearing74coaxially with the detent ring50and carrier ring52.

The inner race28of the primary pivot bearing22is fixed to (or integral with) the detent ring50, and the carrier ring52may be fixed to the shaft16. The primary pivot bearing22and the detent ring50are mounted about the carrier ring52, with the radially inner surface62of the detent ring50directly opposite the radially outer surface64of the carrier ring52. The primary pivot bearing22can be coupled to a control lever12in the same way as in the embodiment ofFIG.3.

The carrier ring52comprises a circumferential recess68in its radially inner surface66for carrying the spring54. The spring54is fitted in place within the recess68such that the spring ring54is preloaded to provide a radially outward force against the carrier ring52. The carrier ring52also comprises bores58extending between the recess68and the radially outer surface64in which ball bearings56are provided such that the ball bearings56are held between the spring54and the detent ring50. As can be seen inFIG.7, the detent profile60is provided on the inner surface62of the detent ring50and comprises a circumferential series of slots or grooves70that can receive the ball bearings56. The radially outward force from the spring54drives the ball bearings56outwards and against the detent profile60. Pins72extend radially through the carrier ring52at the ends of the spring54to hold the spring54in place in the recess68.

When the primary pivot bearing22is operational, there is no relative rotation between the detent ring50and carrier ring52. If the primary pivot bearing22malfunctions, for example such that relative rotation between the outer and inner races26,28is no longer permitted or heavily restricted, the pivoting is instead provided by the redundant pivot bearing74. When the redundant pivot bearing74is operational, torque is transferred through the primary pivot bearing22to the detent ring50to rotate the detent ring50about the carrier ring52. The primary pivot bearing22rotates with the detent ring50, and the carrier ring52is fixed to the shaft16.

As the detent ring50rotates relative to the carrier ring52, the slots70in the detent ring50move past the ball bearings56to successively align and misalign the slots70with the ball bearings56. The force exerted by the spring ring54on the ball bearings56(and towards the detent ring50) drives the ball bearings56into the slots70when aligned. The entering and exiting of the ball bearings56into and out of the successive slots70within the detent profile60as the detent ring50rotates causes a variation in the torque required to rotate the redundant pivot bearing74, and therefore a variation in the force required to drive the control lever12. This variation of the required driving force provides haptic feedback to the operator that indicates that the redundant pivot bearing74is operative.

In the embodiment ofFIG.7, the detent ring50is shown to have a significantly higher number of slots70than the number of ball bearings56. This embodiment has two ball bearings arranged about 100 degrees apart around the carrier ring52, although a different angular spacing can be used. Other embodiments may use just one ball bearing56, or more than two ball bearings56.

The detent profile60comprises a continuous series of slots70around the inner circumference of the detent ring50. Therefore, both ball bearings56will always be positioned within or adjacent a slot70. This configuration enables the detent function and haptic feedback to be provided at any relative orientation of the detent ring50and carrier ring52. The arrangement of the slots70means that only a small rotation of the detent ring50is needed to produce a variation in the force required to drive the control lever12and haptic feedback so that the failure of the primary pivot bearing22can be detected quickly.

It will be understood that other configurations of the detent profile60and ball bearings56may be used to produce a variation in the force required to drive the control lever12. The spring54, ball bearings56and/or detent profile60can be tailored to provide particular effects on the required driving force. For example, the number of ball bearings56and/or the number of slots or grooves70within the detent profile60can be chosen to produce a variation in the required driving force at specific frequencies that would be more detectable by an operator of the lever12. The bias force of the spring54, the size of the ball bearings56and/or the depths of the grooves70in the detent profile60can be chosen to produce a variation in the required driving force at specific amplitudes that would be more detectable by an operator of the lever12, but that would not hinder the operation of the lever12. The spring54, ball bearings56and/or detent profile60may also be tailored to produce specific patterns of variations in the required driving force that may be more noticeable by an operator of the lever12.