Patent Description:
A torque limiter is a device that provides a limit to the torque that can be transmitted by a connection, for example between an input and an output shaft. This limiting of the transmissible torque through the connection is able to protect components either comprised by or connected to the connection from mechanical overload and thereby reduce the chance of damage incurred by the overload.

In certain applications, a torque limiter may be used to limit torque in both directions of torque, that is, in both a clockwise and an anticlockwise direction. Of those applications, the transmissible torque limit may be different in each rotational direction.

An asymmetric torque limiter is a torque limiter with a different transmissible torque limit in each torque direction. For example, the torque that can be transmitted through the asymmetric torque limiter may be higher in a clockwise direction than in an anticlockwise direction.

Documents: <CIT> and <CIT> disclose asymmetric torque limiters.

Asymmetric torque limiters may be used in a variety of applications. One such application is in the actuation of flight control surfaces (such as flaps, slats, spoilers, ailerons, and/or spoilerons) on an aircraft, for example on a wing of the aircraft. The flight control surfaces, and their actuators in turn, experience differing loads during extension (or deployment) and retraction due to the airflow interacting with the flight control surface. Greater torque is required to extend or deploy the flight control surface than to retract the flight control surface. There is therefore a requirement for a higher transmissible torque limit in the direction which deploys the flight control surface than the transmissible torque limit in the direction which retracts the flight control surface.

In previous systems active torque limit control, for example by electronically limiting the torque in each direction, has been used. However, there is a desire for a passive, mechanical, asymmetric torque limiter, to avoid dependence on electronic controls, for example to mitigate risk arising in the event of electronic failure.

There is also a desire to provide a compact and light asymmetric torque limiter.

There is a desire for a passive asymmetric torque limiter having a different torque limit in each of a clockwise and anti-clockwise direction.

While described in the context of aircraft flight control surfaces, it is noted that the presently described asymmetric torque limiter will be useful in a variety of applications.

According to one aspect of the present invention, there is provided an asymmetric torque limiter having an axis of rotation including a first annular friction disk, a second annular friction disk, a skewed roller disk, a first resilient member and a second resilient member. The second annular friction disk is concentrically arranged with the first annular friction disk. The skewed roller disk is in contact with the second annular friction disk. The skewed roller disk includes a plurality of skewed rollers mounted in an annular retainer. The plurality of skewed rollers are each rotatable about a respective roller axis, each roller axis being skewed with respect to a radial direction passing through the skewed roller from the axis of rotation. The first resilient member is attached to the first annular friction disk and is configured to bias the first annular friction disk toward an input shaft. The second resilient member is configured to bias the skewed roller disk toward the second annular friction disk.

In some examples in accordance with the above, the asymmetric torque limiter may include an annular spacer mounted between the second resilient member and the skewed roller disk. The annular spacer is in contact with the skewed roller disk.

In some examples in accordance with any of the above, the second annular friction disk is arranged radially outwardly of first annular friction disk.

In some examples in accordance with any of the above, the second annular friction disk is arranged radially inwardly of the first annular friction disk.

In some examples in accordance with any of the above, the first resilient member includes a Belleville spring.

In some examples in accordance with any of the above, the second resilient member includes a Belleville spring.

In some examples in accordance with any of the above, each of the first and the second annular friction disks are carbon friction disks.

In some examples in accordance with any of the above, each roller axis is skewed at an angle of <NUM> degrees with respect to the radial direction passing through the skewed roller from the axis of rotation (A).

There is also provided an assembly including an input shaft, an output shaft coaxial with the input shaft and an asymmetric torque limiter in accordance with any of the above mounted axially between the input shaft and the output shaft.

In some examples in accordance with the above, the output shaft includes an outer circumferential ring located radially outwardly of the skewed roller disk.

In some examples in accordance with any of the above, the assembly includes a static body and a thrust bearing mounted axially between a portion of the static body and a portion of the input shaft.

There is also provided an aircraft wing including a flight control surface and the assembly of any of the above. The output shaft is configured to actuate the flight control surface.

There is also provided an aircraft including the aircraft wing of the above.

There is also provided a method of passively limiting torque asymmetrically using the asymmetric torque limiter of any of the above. The method includes: providing an input shaft with a first input torque in one of a clockwise and anticlockwise direction and transmitting the first input torque from the input shaft to an output shaft when the first input torque is less than a first torque threshold and preventing transmission of torque higher than the first torque threshold when the first input torque is greater than the first torque threshold; and providing the input shaft with a second input torque in the other of the clockwise and anticlockwise direction and transmitting the second input torque from the input shaft to the output shaft when the second input torque is less than a second torque threshold and preventing transmission of torque higher than the second torque threshold when the second input torque is greater than the second torque threshold. The second torque threshold is larger than the first torque threshold.

There is also provided a method of controlling a flight control surface on an aircraft wing including the method above, wherein providing the input shaft with the second input torque deploys the flight control surface and providing the input shaft with the first input torque retracts the flight control surface.

The features of the above aspects and examples may be used in any combination.

Various embodiments of this invention will now be described by way of example only, with reference to the accompanying drawings in which:.

With reference to <FIG>, there is described an aircraft <NUM> in which the asymmetric torque limiter is used. The aircraft <NUM> includes wings <NUM> and a tail assembly <NUM> including a vertical stabiliser <NUM> and horizontal stabilisers <NUM>.

The illustrated wings <NUM> and the tail assembly <NUM> include flight control surfaces <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> which include ailerons <NUM>, flaps <NUM>, slats <NUM>, spoilers <NUM>, elevators <NUM> and a rudder <NUM>.

Together, these flight control surfaces <NUM>-<NUM> are extended (or deployed), retracted and adjusted as appropriate to control the yaw <NUM>, the roll <NUM>, the pitch <NUM>, and the lift <NUM> of the aircraft <NUM> when in flight by the interaction of the flight control surfaces <NUM>-<NUM> with the airflow.

The flight control surfaces <NUM>-<NUM> are controlled by the action of respective actuators, which include of a motor and a gearbox. These actuators provide rotary motion as their output, which is connected to the respective flight control surface <NUM>-<NUM>. These actuators may be suitable for use on thin wing configurations.

There is a requirement to limit the amount of torque transmitted from the actuator to the flight control surfaces <NUM>-<NUM> in order to avoid mechanical overload from an input shaft working against the airflow interacting with the flight control surface <NUM>-<NUM>. For this reason, a torque limiter is provided on the input of each flight control surface <NUM>-<NUM>. The torque limit required is different for the extension (or deployment) of the flight control surface <NUM>-<NUM> and the retraction of the flight control surface <NUM>-<NUM>. The torque required to extend (or deploy) the flight control surface <NUM>-<NUM> is greater than the torque required to retract the flight control surface <NUM>-<NUM>, and thus an asymmetric torque limiter is required.

The asymmetric torque limiter allows torque to be transmitted therethrough when the input torque is below a threshold torque.

The threshold torque in the extension direction is greater than the threshold torque in the retraction direction. In this way, the asymmetric torque limiter allows the transmission of a greater torque in the extension direction than in the retraction direction. The extension direction corresponds to one of a clockwise and anti-clockwise direction and the retraction direction corresponds to the other of the clockwise and anticlockwise direction of input torque, depending on the configuration of the actuator.

An asymmetric torque limiter <NUM> is described below with reference to <FIG>.

The illustrated asymmetric torque limiter <NUM> is provided between an input shaft <NUM> and an output shaft <NUM>. The input shaft <NUM> and output shaft <NUM> are arranged coaxially on an axis of rotation A. The output shaft <NUM> is located in a distal direction with respect to the input shaft <NUM>.

The input shaft <NUM> is supported by a stationary casing <NUM> (or a body) by means of thrust bearings <NUM>. The thrust bearings <NUM> are located axially between a portion of the casing <NUM> and a portion <NUM> of the input shaft <NUM>. The portion <NUM> of the input shaft <NUM> is a radially extending flange <NUM> at a distal end of the input shaft <NUM>. The thrust bearings <NUM> may have any appropriate construction, such as roller bearings supported by distal and proximal races attached to the portion <NUM> of the input shaft <NUM> and the portion of the casing <NUM> respectively. Alternative thrust bearings may be used, such as a three-part ball thrust bearing. The thrust bearing <NUM> allows the input shaft <NUM> to rotate with minimal friction with respect to the casing <NUM> and supports a predominantly axial load between the input shaft <NUM> and the casing <NUM>.

The asymmetric torque limiter <NUM> includes a first annular friction disk <NUM> located between the input shaft <NUM> and the output shaft <NUM>. The first annular friction disk <NUM> is arranged coaxially about the axis of rotation A. The first annular friction disk <NUM> in some embodiments is a carbon friction disk; however, other materials may be used for the first annular friction disk <NUM>. The first annular friction disk <NUM> acts as a symmetrical torque limiter in that it provides a torque threshold (the first individual torque threshold described below) that is the same in each of a clockwise direction and an anti-clockwise direction.

In one embodiment, the first annular friction disk <NUM> is mounted to a first resilient member <NUM>, and biased by the first resilient member <NUM> toward the input shaft <NUM> to be in contact therewith. The first resilient member is mounted to the output shaft <NUM>. The first resilient member <NUM> may be a spring, for example a Belleville spring <NUM> (which is a plurality of stacked Belleville washers, or stacked coned-disc springs). The illustrated first resilient member <NUM> is coaxial to the axis of rotation A.

The first annular friction disk <NUM> and the first resilient member <NUM> have characteristics that allow a torque to be transmitted from the input shaft <NUM>, through the first annular friction disk <NUM> and first resilient member <NUM> to the output shaft <NUM>, when the torque is below a first individual torque threshold. The first individual torque threshold is the same in both the clockwise and anticlockwise directions. Above the first individual torque threshold, the surface of the input shaft <NUM> in contact with the first annular friction disk <NUM> will slip such that any excess torque above the first individual torque threshold will not be transmitted. Those characteristics that set the first individual torque threshold include: an inner radius R<NUM> of the annular friction disk <NUM>; an outer radius R<NUM> of the annular friction disk <NUM>, a spring load, and a friction coefficient between the material of the first annular friction disk <NUM> and that of the input shaft <NUM>.

The friction coefficient may be from <NUM> to <NUM>, or more particularly about <NUM>. The spring load may be <NUM>-<NUM> N, or more particularly about <NUM> N. The inner radius R<NUM> may be from <NUM> to <NUM>, or more particularly about <NUM>. The outer radius R<NUM> may be from <NUM> to <NUM>, or more particularly about <NUM>. The first individual torque threshold may be from <NUM> to <NUM>, or more particularly about <NUM>.

For alternative applications where different torque thresholds are required, these characteristics can be different to those listed above.

Taken in isolation (for example if the second annular friction disk and skewed roller disk described below were removed), the first annular friction disk <NUM> would allow torque in both clockwise and anticlockwise directions to be transmitted therethrough from the input shaft <NUM> to the output shaft <NUM> when the torque input to the input shaft <NUM> is below the first individual torque threshold and prevent any further torque being transmitted when the torque input to the input shaft <NUM> is above the first individual torque threshold. When the torque input to the input shaft <NUM> is above the first individual torque threshold, the input shaft <NUM> will slip with respect to the first annular friction disk <NUM> and thereby rotate without transmitting all of the input torque.

The asymmetric torque limiter <NUM> also includes a second annular friction disk <NUM> located between the input shaft <NUM> and the output shaft <NUM>. The second annular friction disk <NUM> is arranged coaxially about the axis of rotation A. The illustrated second annular friction disk <NUM> is located radially outwards of the first annular friction disk <NUM>. The second annular friction disk <NUM> in some embodiments is a carbon friction disk; however, other materials may be used for the second annular friction disk <NUM>.

Axially adjacent (with respect to the rotational axis A) to the second annular friction disk <NUM> is a skewed roller disk <NUM>, distal of the second annular friction disk <NUM>. The skewed roller disk <NUM> includes an annular retainer <NUM> and a plurality of skewed rollers <NUM>. As can be appreciated from <FIG>, the skewed rollers <NUM> are mounted in the annular retainer <NUM> in a manner such that each skewed roller <NUM> may freely rotate about a respective roller axis <NUM>. As shown, each respective roller axis <NUM> is arranged at an angle α with respect to a radial direction <NUM> of the skewed roller disk <NUM> extending through the centre of the respective skewed roller <NUM>. The angle α may be called a skew angle or a tilt angle. The angle α is an acute angle. In some embodiments the angle α is between <NUM> and <NUM> degrees, or, more particularly, between <NUM> and <NUM> degrees, or about <NUM> degrees.

With reference again to <FIG>, axially adjacent (with respect to the rotational axis A) to the skewed rollers <NUM> is a spacer <NUM>. The spacer <NUM> is distal of and in contact with the skewed rollers <NUM>. The spacer <NUM> is coaxially arranged about the rotational axis A.

A second resilient member <NUM> is arranged axially adjacent the spacer <NUM>. The second resilient member <NUM> is mounted to the output shaft <NUM> and biases the spacer <NUM> and the skewed roller disk <NUM> toward the second annular friction disk <NUM>. Due to the action of the second resilient member <NUM> both the spacer <NUM> and the second annular friction disk <NUM> are maintained in contact with the skewed rollers <NUM>. The second resilient member <NUM> may be a spring, for example a Belleville spring <NUM> (which is a plurality of stacked Belleville washers, or stacked coned-disc springs). The illustrated second resilient member <NUM> is coaxial with the rotational axis A and is arranged concentrically with the first resilient member <NUM>.

The illustrated output shaft <NUM> includes an outer circumferential ring <NUM> located radially outwardly of the skewed roller disk <NUM>. The outer circumferential ring <NUM> maintains the skewed roller disk <NUM>, the spacer <NUM> and the second resilient member <NUM> in its coaxial position about the rotation axis A.

Taken in isolation (that is, if the first annular friction disk <NUM> were removed), the second annular friction disk <NUM>, the skewed roller disk <NUM>, the spacer <NUM> and the second resilient member <NUM> allow the transmission of torque in a single direction below a second individual torque threshold.

Considering <FIG>, when the input shaft <NUM> rotates in a clockwise direction <NUM> with respect to the skewed roller disk <NUM> (which is equivalent to the skewed roller disk <NUM> rotating in an anticlockwise direction <NUM> in the frame of reference of the input shaft <NUM>), the skewed rollers <NUM> are not able to freely rotate about their roller axes <NUM>. If the input torque is below a second individual torque threshold, the second annular friction disk <NUM> will frictionally engage the skewed rollers <NUM> to drive rotation of the skewed roller disk <NUM>. The skewed roller disk <NUM> will in turn frictionally engage and drive rotation of the spacer <NUM> and thus ultimately drive rotation of the output shaft <NUM>. If the input torque is above the second individual torque threshold, the second annular friction disk <NUM> will slip in the clockwise direction with respect to the skewed roller disk <NUM>, and/or the skewed roller disk <NUM> will slip in the clockwise direction with respect to the spacer <NUM>. In this case, the input shaft <NUM> will thereby rotate freely without transmitting all of the input torque. In this torque direction the skewed roller disk <NUM> is said to be in a sliding condition.

When the input shaft <NUM> rotates in an anti-clockwise rotation <NUM> with respect to the skewed roller disk <NUM>, the skewed rollers <NUM> are able to rotate about their roller axes <NUM> and thereby allow the input shaft <NUM> to rotate with minimal friction and thereby without driving the skewed roller disk <NUM> or the spacer <NUM> and thus the output shaft <NUM>. In this situation the skewed roller disk <NUM> is said to be in a rolling condition.

As will be appreciated, if the direction of the skew of the skewed rollers <NUM> is reversed, then the directions in which free rotation and torque limited transmission is allowed are also reversed.

The second individual torque threshold is determined by certain characteristics of the second annular friction disk <NUM>, the skewed roller disk <NUM> and the second resilient member <NUM>. Those characteristics include: an inner radius R<NUM> of the second annular friction disk <NUM>; an outer radius R<NUM> of the second annular friction disk <NUM>, a spring load, a friction coefficient between the material of the second annular friction disk <NUM> and that of the skewed rollers <NUM>, and the skew angle α of the skewed rollers <NUM>.

The friction coefficient may be from <NUM> to <NUM>, or more particularly about <NUM>. The spring load may be <NUM>-<NUM> N, or more particularly about <NUM> N. The inner radius R<NUM> may be from <NUM> to <NUM>, or more particularly about <NUM>. The outer radius R<NUM> may be from <NUM> to <NUM>, or more particularly about <NUM>. The second individual torque threshold may be from <NUM> to <NUM>, or more particularly about <NUM>.

When the first annular friction disk <NUM> is used in combination with the second annular friction disk <NUM> and the skewed roller disk <NUM> in the asymmetric torque limiter described herein, two load paths are provided between the input shaft <NUM> and the output shaft <NUM>. The first load path is through the first annular friction disk <NUM> and the first resilient member <NUM> and the second load path is through the second annular friction disk <NUM>, the skewed roller disk <NUM>, the spacer <NUM> and the second resilient member <NUM>.

In a first direction of torque applied by the input shaft <NUM> (the clockwise direction <NUM> as described above, wherein the skewed roller disk <NUM> is in the sliding condition) a first combined torque threshold (or a first torque threshold) below which all of the torque is transmitted to the output shaft <NUM> is the sum of the first individual torque threshold and the second individual torque threshold. In a second direction of torque applied to the input shaft <NUM> opposite the first direction (the anticlockwise direction <NUM> as described above, wherein the skewed roller disk <NUM> is in the rolling condition) a second combined torque threshold (or a second torque threshold) below which torque is transmitted to the output shaft <NUM> is equal to the first individual torque threshold. Accordingly, the first combined torque threshold is higher than the second combined torque threshold. This means that higher torque can be transmitted in the first (or clockwise) direction <NUM> than in the second (or anticlockwise) direction <NUM>.

For example, when the first individual torque threshold is <NUM> and the second individual torque threshold is <NUM>, as in the examples above, the first combined torque threshold is <NUM> and the second combined torque threshold is <NUM>.

When used in an aircraft, the first direction <NUM> (with its higher torque threshold) is used for extension of the aircraft flight control surface <NUM>-<NUM> and the second direction <NUM> (with its lower torque threshold) is used for retraction of the aircraft flight control surface <NUM>-<NUM>.

It will be appreciated that when the skewed roller disk <NUM> is in the rolling condition, which is when the second (or anticlockwise) direction of torque is applied to the input shaft <NUM>, the rolling of the skewed rollers <NUM> may provide a small amount of friction such that the second combined torque threshold (or second torque threshold) is slightly higher than the first individual torque threshold, for example by up to about <NUM>%. In this manner, when the second direction of torque is applied to the input shaft <NUM> the first annular friction disk <NUM> still accounts for <NUM>% or more of the second combined torque threshold (or the global retraction torque threshold).

In this way, the asymmetric torque limiter provides a passive means to limit the torque transmissible in each direction of the torque input from the input shaft <NUM> at different torque limits.

An alternative embodiment of an asymmetric torque limiter <NUM>' is illustrated in <FIG>. Like reference numerals have been used for similar elements, and unless described otherwise below, the elements of <FIG> share the same characteristics as those of <FIG>.

The embodiment of <FIG> differs from that of <FIG> in that the first annular friction disk <NUM>' and first resilient member <NUM>' are radially outwardly located of the second annular friction disk <NUM>', the skewed roller disk <NUM>', the spacer <NUM>' and the second resilient member <NUM>' (i.e., they have swapped positions).

The inner radius R<NUM>' and the outer radius R<NUM>' of the first annular friction disk <NUM>' are therefore larger in the <FIG> embodiment. For example, the inner radius R<NUM>' may be between <NUM> and <NUM>, or more particularly about <NUM>, and the outer radius R<NUM>' may be between <NUM> and <NUM>, or more particularly about <NUM>. The inner radius R<NUM>' and the outer radius R<NUM>' of the second annular friction disk <NUM>' will likewise be smaller in the <FIG> embodiment. For example, the inner radius R<NUM> may be from <NUM> to <NUM>, or more particularly about <NUM> and the outer radius R<NUM> may be from <NUM> to <NUM>, or more particularly about <NUM>.

The first resilient member <NUM>' shown in <FIG> is still associated with the first annular friction disk <NUM>' in the same manner as described with reference to <FIG> and is accordingly larger than the first resilient member <NUM> shown in <FIG>.

In the embodiment of <FIG>, the skewed roller disk <NUM>', skewed rollers <NUM>', retainer <NUM>', spacer <NUM>' and second resilient member <NUM>' are still associated with the second annular friction disk <NUM>' in the same manner as described with reference to <FIG>. Each of the skewed roller disk <NUM>', skewed rollers <NUM>', retainer <NUM>', spacer <NUM>' and second resilient member <NUM>' are therefore smaller than their equivalent components from <FIG>. Each of the skewed roller disk <NUM>', skewed rollers <NUM>', retainer <NUM>', spacer <NUM>' and second resilient member <NUM>' are arranged radially inwardly of the first resilient member <NUM>'.

In the embodiment of <FIG>, the first individual torque threshold will be higher than the embodiment of <FIG> and the second individual torque threshold will be lower than the embodiment of <FIG>. As a result, there will be a smaller difference between the first and second combined torque thresholds. This is because the skewed roller disk <NUM>', which provides the asymmetric character of the torque limiter, by being positioned inside the first annular friction disk <NUM>', will provide a smaller proportion of the first combined torque threshold (that is, the torque threshold where the skewed roller disk <NUM>' is in its sliding condition).

In alternative embodiments, the second annular friction disk <NUM>, <NUM>' and the spacer <NUM>, <NUM>' could swap positions, such that the spacer <NUM>, <NUM>' is mounted to the input shaft <NUM> and the second annular friction disk <NUM>, <NUM>' is mounted to the second resilient member <NUM>, <NUM>'.

Claim 1:
An asymmetric torque limiter (<NUM>; <NUM>') having an axis of rotation (A) comprising:
a first annular friction disk (<NUM>; <NUM>');
a second annular friction disk (<NUM>; <NUM>') concentrically arranged with the first annular friction disk (<NUM>; <NUM>'),
characterized in that:
a skewed roller disk (<NUM>; <NUM>') in contact with the second annular friction disk (<NUM>; <NUM>'), wherein the skewed roller disk (<NUM>; <NUM>') includes a plurality of skewed rollers (<NUM>; <NUM>') mounted in an annular retainer (<NUM>; <NUM>'), wherein the plurality of skewed rollers (<NUM>; <NUM>') are each rotatable about a respective roller axis (<NUM>), each roller axis (<NUM>) being skewed with respect to a radial direction passing through the skewed roller (<NUM>; <NUM>') from the axis of rotation (A);
a first resilient member (<NUM>; <NUM>') attached to the first annular friction disk (<NUM>; <NUM>') and configured to bias the first annular friction disk (<NUM>; <NUM>') toward an input shaft (<NUM>); and
a second resilient member (<NUM>; <NUM>') configured to bias the skewed roller disk (<NUM>; <NUM>') toward the second annular friction disk (<NUM>; <NUM>').