Patent Description:
One or more stay assemblies may be provided to support the orientation of the main strut when the landing gear assembly is in the deployed condition. A stay assembly generally includes a stay and a lock link arranged to maintain the stay in a condition which corresponds to the landing gear assembly being in the deployed condition. The lock link is 'broken' and folded to enable the stay to be folded, permitting the main strut to be moved by a retraction actuator towards the stowed condition.

It is common for landing gear assemblies to be arranged to move towards the deployed condition in the event of a failure of the retraction actuator. Initially the assembly will move by way of gravity and in doing so the landing gear assembly forces the stay to move towards the condition which corresponds to the landing gear assembly being in the deployed condition. One or more 'down-lock' springs may be provided to assist in moving landing gear assembly to the deployed condition and locking it in that state by biasing the lock link to lock. Landing gear assemblies for larger aircraft may be provided with a pair of down-lock springs on each stay assembly.

In order to meet down-lock requirements, particularly on larger aircraft, such as those requiring four or six wheeled bogie beams on the main landing gear assembly (MLG), large down-lock springs are required. In some cases this is due to the characteristics of a 'four point' attachment dual stay MLG, where the dual stays provide attachment points on the forward and aft sides of the landing gear to transfer drag and side loads into the airframe. Springs with a large wire diameter can however be undesirably heavy and can be difficult to manufacture.

<CIT> discloses a landing gear lock assembly includes a first lock link, and a second lock link, a first end of the second lock link being rotatably coupled to the second end of the first lock link so that the first and second lock links unfold relative to each other in a first rotation direction. <CIT> discloses a landing gear assembly, with locking means using a spring.

The present inventor has devised a new type of aircraft landing gear assembly which can enable the use of lighter springs.

There is provided an aircraft landing gear according to claim <NUM>.

Thus, an aircraft landing gear assembly according to the invention includes a linkage assembly which builds lost motion into the down-lock spring mounting mechanism. As the structural members move from the first angular condition to the second angular condition, the control link moves over centre such that, in contrast to known landing gear assemblies, the down-lock spring does not continue to extend as the gear is retracted, thereby enabling a smaller and/or lighter down-lock spring to be provided.

The linkage assembly can be arranged such that, as the structural members move from the first angular condition to the second angular condition, the spring extension is increased or magnified in comparison to a direct connection arrangement for a first portion of the movement and/or is reduced in comparison to a direct connection arrangement for a second portion of the movement.

The second portion of the movement can start within the first half of the total movement of the landing gear from the fully deployed to the fully stowed condition.

The magnification can be by at least a factor of <NUM> and preferably at least a factor of <NUM>, <NUM> or <NUM>, which can particularly assist the spring in locking the gear in the deployed condition as it nears the deployed condition. The magnification factor can refer to a maximum value.

The degree of magnification can vary throughout the first portion of the movement. The variation can be in accordance with the angle of the structural member (to which the arm member is pivotally coupled) relative its orientation when in the first angular condition, in which the landing gear is in the deployed condition.

At least some magnification can occur throughout the first portion of the movement. The first portion of the movement can comprise less than <NUM> degrees of movement of the structural member (to which the arm member is pivotally coupled) relative its orientation when in the first angular condition. In one embodiment the first portion can comprise <NUM> to <NUM> degrees.

The reduction can be by at least a factor of <NUM> and preferably at least a factor of <NUM> or <NUM>. This can reduce maximum spring extension during retraction of the gear, enabling the use of lighter and/or smaller down-lock springs. The reduction factor can refer to a maximum value.

The reduction factor can result in the spring being shorter at some point during retraction than when the gear is in the deployed condition, preferably when the gear is in the stowed condition.

The degree of reduction can vary throughout the second portion of the movement. The variation can be in accordance with the angle of the structural member (to which the arm member is pivotally coupled) relative its orientation when in the first angular condition, in which the landing gear is in the deployed condition.

At least some reduction can occur throughout the second portion of the movement. The second portion of the movement can start at <NUM> or more degrees of movement of the structural member (to which the arm member is pivotally coupled) relative its orientation when in the first angular condition and can extend to <NUM> degrees or more.

The first angular condition can be an aligned condition, in which longitudinal axes of the first and second structural members are generally aligned with one another, and the second angular condition can be a non-aligned condition in which the longitudinal axes of the first and second structural members are generally not aligned with one another. In such embodiments, the spring acts across the folding joint of a stay or lock link for example.

The arm member can be longitudinally nonlinear.

The arm member can be longitudinally C shaped.

The arm member can comprise a plurality of linear portions rigidly coupled to form the longitudinal C shape.

The arm member can be pivotally coupled to the second structural member, the arm pivot point being at a first end region of the arm and the control link being pivotally coupled to the first structural member.

The second control link pivot point can be located on the arm at a location which is closer to the arm pivot point than the point via which the arm is pivotally coupled to the spring.

The arm pivot point can be at a central region of the arm.

The arm member can be pivotally coupled to the first structural member, the control link being pivotally coupled to the second structural member and the second control link pivot point being located at a second end region of the arm opposite to the first end region which is pivotally coupled to the down-lock spring.

The arm member can be pivotally coupled to the first structural member, the control link being pivotally coupled to the second structural member and the linkage assembly further comprising a second C shaped arm pivotally coupled to the second structural member at a second arm pivot point located at a central region of the second arm, the second control link pivot point being located at a first end region of the second arm, the linkage assembly further comprising a second control link pivotally coupled to one of the first and second structural members at a first control link pivot point and pivotally coupled to a second end of the second arm at a third control link pivot point and pivotally coupled to a second end of the C shaped arm at a fourth control link pivot point such that, as the first and second structural members move relative to one another from the aligned condition towards the non-aligned condition, the first control link pivot point moves over centre, though an axis or plane bisecting the apex pivot point and the second control link pivot point and the third control link pivot point moves over centre, though an axis or plane bisecting the arm pivot point and the fourth control link pivot point. Thus, a cascading arrangement can be provided.

The aircraft landing gear assembly can further comprise:.

The down-lock spring can be helical in shape.

In accordance with a second aspect of the invention, there is provided an aircraft including one or more aircraft landing gear assemblies according to the first aspect.

Embodiments of the invention will now be described, strictly by way of example only, with reference to the accompanying drawings, of which:.

<FIG> is a diagram of an aircraft <NUM>. The aircraft <NUM> includes assemblies such as a nose landing gear <NUM>, main landing gear <NUM> and engines <NUM>. The landing gear <NUM>, <NUM> each includes a shock absorber strut for damping landing loads and supporting the weight of the aircraft <NUM> when it is on the ground. The term aircraft as used herein can include aeroplanes, helicopters and the like having mass in excess of <NUM>.

Referring now to <FIG>, an aircraft assembly, namely an aircraft landing gear assembly, is shown generally at <NUM>. <FIG> are an example of an aircraft landing gear assembly which can include a shock absorber strut according to an embodiment of the invention. It will however be appreciated that shock absorber struts according to embodiments of the invention can be used in a range of types of aircraft landing gear.

The landing gear assembly <NUM> includes a foldable stay <NUM>, a lock link <NUM> and a down-lock spring assembly <NUM> mounted to the stay <NUM> and arranged to urge the lock link <NUM> to assume a locked state. The landing gear assembly also includes a main shock absorber strut <NUM>, comprising an outer cylinder <NUM> and an inner cylinder <NUM>, as well as a wheel and brake assembly <NUM>.

The aircraft landing gear assembly is movable between a deployed condition, for take-off and landing, and a stowed condition for flight. An actuator (not shown) is provided for moving the landing gear between the deployed condition and the stowed condition. This actuator is known in the art as a retraction actuator, and more than one can be provided. A retraction actuator can have one end coupled to the airframe and another end coupled to the outer cylinder such that extension and retraction of the actuator results in movement of the outer cylinder between deployed and stowed conditions.

The stay <NUM> serves to support the orientation of the outer cylinder <NUM> when the landing gear is in the deployed condition. The stay <NUM> generally includes a two bar linkage that can be unfolded to assume a generally straight or aligned, over centre condition in which the stay <NUM> is locked to inhibit movement of the outer cylinder, as shown in <FIG> and <FIG>. When the stay is broken, it no longer prevents pivotal movement of the outer cylinder <NUM> and the outer cylinder <NUM> can be moved by the retraction actuator towards the stowed condition, as shown in <FIG>. During flight the stay <NUM> is arranged in the folded condition, while during take-off and landing the stay <NUM> is arranged in the generally straight or aligned condition. Some main landing gear assemblies include a pair of stays coupled to a common shock absorber strut.

The stay <NUM> has an elongate upper stay arm 18a having a lower end defining a pair of lugs pivotally coupled via a pivot pin <NUM> to a pair of lugs defined at an upper end of an elongate lower stay arm 18b. The stay arms 18a and 18b can therefore pivotally move relative to one another about the pivot pin <NUM>. The upper end of the upper stay arm 18a defines a pair of lugs that are pivotally coupled to a lug of a connector <NUM> which in turn is pivotally coupled to the airframe <NUM>. The lower end of the lower stay arm 18b defines a pair of lugs pivotally coupled to a lug of a connector <NUM> which in turn is pivotally coupled to the outer cylinder <NUM>.

The lock link <NUM> has an elongate upper link arm 20a having a lower end pivotally coupled to an upper end of an elongate lower link arm 20b via a pivot pin <NUM>. The link arms 20a, 20b can therefore pivotally move relative to one another about the pivot pin <NUM>. An upper end of the upper link arm 20a defines a pair of lugs that are pivotally coupled to a lug of a connector <NUM> which in turn is pivotally coupled to the outer cylinder <NUM>. A lower end of the lower link arm 20b defines a lug that is pivotally coupled to lugs of the stay arms 18a, 18b via the pivot pin <NUM>. Lugs of the upper stay arm 18a are in this example disposed between the lugs of the lower stay arm 18b and the lugs of the lower link arm 20b.

When the lock link <NUM> is in the locked condition, as illustrated in <FIG> and <FIG>, the upper and lower link arms 20a, 20b are generally longitudinally aligned or coaxial, and can be 'over-centre', such that the lock link <NUM> is arranged to oppose a force attempting to fold the stay <NUM>, so as to move the landing gear assembly from the deployed condition towards the stowed condition. The lock link <NUM> must be broken to enable the stay <NUM> to be folded, thereby permitting the outer cylinder <NUM> to be moved by the retraction actuator towards the stowed condition.

One or more down-lock springs <NUM> are generally provided to assist in moving the landing gear assembly to the deployed condition and locking it in that state. Down-lock springs typically attach between two members either side of a joint such that one spring end is stretched in an arc relative to the other end, i.e. as a simple crank mechanism. The two members typically comprise a combination of lock links, stay members or landing gear shock absorber outer cylinder/main fitting. In the illustrated example the down-lock spring <NUM> is arranged to bias the lock link <NUM> towards the locked condition by way of spring tension. A distal end of the spring 22a is coupled to the lower stay arm 18b via a lower engagement formation 22b which in turn is coupled to an anchor point defined by the lower connector 22c.

Referring to <FIG>, a lock stay actuator <NUM> is coupled between the upper stay arm 18a and lower link arm 20b and arranged to pivotally move the link arms 20a, b so as to 'lock' and 'unlock' the lock link <NUM>, as illustrated in <FIG>. The actuator <NUM> can break the lock link <NUM> against the down-lock spring bias, allowing the landing gear assembly to be folded and stowed as described previously.

The down-lock spring <NUM> is at its shortest when the landing gear assembly is in the deployed condition, as shown in <FIG>, and at its longest when the landing gear assembly approaches the stowed condition, as shown in <FIG>. As the landing gear assembly is retracted towards the stowed condition, the spring of each spring assembly extends, resulting in increased spring load and torsional stress. The down-lock springs are required to provide a high load when the gear is locked down, and when it is close to being locked down, but load capability is not as important when the gear is retracted. The kinematics of known spring attachment points, in the simple crank form, result in continued displacement of the spring, such as stretching in the case of a tension spring, beyond the point when maximum load is required.

The present inventor has devised a new type of aircraft landing gear assembly which can use smaller and/or lighter down-lock springs in comparison to known landing gear assemblies.

Referring to <FIG>, part of an aircraft landing gear assembly, not falling within the scope of the claims, is shown generally at <NUM>.

The landing gear assembly is similar to the landing gear assembly described with reference to <FIG> and, for brevity, the following description will focus on the differences.

A first structural member <NUM>, which could for example be a lower stay arm, is provided with a protruding lug member 52a at the end carrying the apex pivot pin P1. The lug member 52a is pivotally coupled to a control link <NUM> via pivot pin P2. The lug member 52a is angularly offset with respect to an axis through the apex pivot pin P1 and distal mounting pivot pin P3 of the first structural member <NUM>, such that the pivot pin P2 is offset, in this embodiment, by an angle of roughly <NUM> degrees. In other examples the whole linkage can be 'clocked round' for example, to bring the lug member onto the axis.

A second structural member <NUM>, which could for example be an upper stay arm, is pivotally coupled to the first structural member <NUM> via the apex pivot pin P1. A generally C-shaped arm member <NUM> is pivotally mounted to the second structural member <NUM> via pivot pin P4 at a location which is generally in line with the pivot pin P2 when the first and second structural members <NUM>, <NUM> are axially aligned, as shown in <FIG>. In this example the C shaped member <NUM> is formed from four straight sections rigidly fixed to one another to define the C shape, but can take any suitable form, such as a T shape or bell crank. The distance between the axes of pivot pin P4 and pivot pin P2 can be roughly equal to the distance between the axes of pivot pin P2 and pivot pin P1.

The control link <NUM> is pivotally coupled to arm member <NUM> via pivot pin P5. The free end of arm member <NUM> is pivotally coupled to one end of a down-lock spring <NUM> via pivot pin P6. The down-lock spring <NUM> is a coil spring arranged in tension. Pivot pin P5 is situated on the arm member <NUM> closer to pivot pin P4 than pivot pin P6. The other end of the down-lock spring <NUM> is coupled to a suitable structure, which could be the first structural member <NUM>, via pivot pin P7.

Referring additionally to <FIG>, as the first structural member <NUM> pivots relative to the second structural member <NUM> about the apex pivot pin P1, as the landing gear assembly begins to move from the fully deployed condition towards the stowed condition, the first control link pivot pin P2 moves in an arc towards an axis or plane bisecting the apex pin P1 and the second control link pivot pin P5, thereby increasing the distance D1 between the apex pin P1 and the second control link pivot pin P5 which in turn causes the arm member <NUM> to pivot about pin P4 in a first direction away from the apex pin P1. This in turn increases the distance D2 between the down-lock spring mounting pins P6, P7, thereby stretching the down-lock spring <NUM>. This extended state assists the down-lock spring in biasing the structural members <NUM>, <NUM> to assume the aligned condition shown in <FIG>.

Referring additionally to <FIG>, as the first structural member <NUM> continues to pivot relative to the second structural member <NUM> about the apex pivot pin P1, as the landing gear assembly continues to move towards the stowed condition, the first control link pivot pin P2 continues to moves in an arc through and beyond the axis or plane bisecting the apex pin P1 and the second control link pivot pin P5, thereby decreasing the distance D1 between the apex pin P1 and the second control link pivot pin P5 which in turn causes the arm member <NUM> to pivot about pin P4 in a second direction towards the apex pin P1. This in turn decreases or maintains the distance D2 between the down-lock spring mounting pins P6, P7, as the gear continues to move to the stowed condition.

Thus, in contrast to known landing gear assemblies, the down-lock spring <NUM> does not continue to extend as the gear moves from the extended to stowed condition, thereby enabling a smaller and/or lighter down-lock spring to be provided. Moreover, the linkage enables spring extension to be initially increased relative to the extension that would occur with a conventional, direct connection, and for later extension to be reduced relative to a direct connection. The successive extension increase and decrease phases can occur early in the total movement window of the landing gear, for example within the first half of the total movement from fully deployed to fully retracted. The extension decrease phase can continue through to fully retracted.

<FIG> shows part of an aircraft landing gear, not falling within the scope of the claims, generally at <NUM>. The landing gear assembly <NUM> is similar to the landing gear assembly described with reference to <FIG> and, for brevity, the following description will focus on the differences.

In this example, the C shaped arm <NUM> is pivotally coupled to a lug member 74a extending from a side of the first structural member <NUM> at a location close to the end of the first structural member <NUM>. The C shaped arm <NUM> is smaller than in the previous embodiment, formed from two straight sections rigidly coupled to one another and is pivoted near its centre by pivot pin P9. The control link <NUM> is pivotally coupled at a first end via pin P10 to a second lug member 78a which extends axially from the end of the second structural member <NUM> which carries the apex pin P8. The second end of the control link <NUM> is pivotally coupled to a first free end of the C shaped arm <NUM> closest to the first structural member <NUM> via pin P11. The other free end of the arm <NUM> is pivotally coupled to the down-lock spring <NUM> via pivot pin P12. As the landing gear assembly <NUM> moves from the illustrated deployed condition to the stowed condition, the pivot pin P10 at the first end of the control link <NUM> moves towards, through and beyond the central axis or plane bisecting the pin P11 at the first free end of the C shaped arm <NUM> and the apex pin P8, thereby causing the control link to move over centre.

<FIG> shows part of an aircraft landing gear assembly, not falling within the scope of the claims, generally at <NUM>. The landing gear assembly <NUM> is similar to the landing gear assembly described with reference to <FIG> and, for brevity, the following description will focus on the differences.

In this example, a pair of C shaped arms and control links are provided in a cascaded manner. More specifically, a first control link <NUM> is pivotally coupled to a lug 94a on the first structural member <NUM>, similar to lug 54a, extending at an angular offset from the longitudinal axis. The second structural member <NUM> has a lug <NUM> extending from the opposite side which carries a two component, first C shaped arm <NUM>, one end of which is pivotally coupled to the first control link <NUM> and the other end of which is pivotally coupled to a second control link <NUM>. The second control link <NUM> is in turn pivotally coupled to a second, two component C shaped arm <NUM> which is pivotally mounted on a second lug 94b, similar to lug 74a, extending from the first structural member <NUM> on the same side as the lug 96a. The other end of the second C shaped arm is pivotally coupled to the down-lock spring <NUM>.

While each of the above-mentioned examples relate to mechanisms in which the down-lock spring operates across the hinged joint of a stay or lock link for example, in other embodiments the spring can operate between a the lock link and stay, such as the spring <NUM> in <FIG>. We will now go on to describe two such embodiments which are functionally similar to the embodiments of <FIG> and <FIG> respectively and for brevity we will focus on the differences.

<FIG> show an embodiment <NUM>' which is functionally similar to the example of <FIG>, but in which the spring <NUM>' operates between the lower stay arm <NUM>' and the lower lock link <NUM>'. As the lock link is broken and the lower lock link <NUM>' pivots clockwise about the stay apex joint P1', the control link <NUM>', which has one end pivotally coupled at P2' to a lug on lower stay arm <NUM>' adjacent to the apex joint P1' and another end pivotally coupled at P5' to a mid-region of a L shaped arm <NUM>', causes the L shaped arm to pivot clockwise about pivot P4' and, as shown in <FIG>, extends the down-lock spring <NUM>' which is pivotally coupled to the free end of the L shaped arm <NUM>' at pivot P6'.

As shown in <FIG>, as the landing gear articulates towards the stowed condition, the second control link pivot pin P5' moves in an arc through and beyond an axis or plane bisecting the first control link pivot pin P2' and the spring mounting pivot pin P6', thereby decreasing the distance between the pivot pins P2' and P6'.

<FIG> show an embodiment <NUM>' which is functionally similar to the example of <FIG>, but in which the spring <NUM>' operates between the lower stay arm <NUM>' and the lower lock link <NUM>'. The control link <NUM>' is pivotally coupled at a first end via pin P10' to a lug member 78a' which extends laterally from the end of the lower lock link <NUM>' which forms part of the apex joint. As the lower lock link P8 rotates clockwise from the position shown in <FIG> to that shown in <FIG>, the control link moves over-centre.

<FIG> shows a plot of spring extension vs. lower lock link <NUM>' movement in degrees (spring velocity ratio) for the embodiment of <FIG> in comparison to an arrangement having a direct connection between the spring and lower lock link ('existing spring'). The zero degree position is the lower lock link <NUM>' relative to the lower stay <NUM>' when the landing gear is deployed and locked down, as shown in <FIG>.

The 'existing spring' curve depends upon the radius and angular position of the spring attachment to the lower link. In this case a position on the centreline has been used.

The initial magnification factor is shown in the relative gradients between the two curves (proportional to the velocity ratio of the spring ~ mechanical advantage ignoring friction). The mechanism of <FIG> has a similar or slightly greater extension rate around zero degrees (where the spring effort is most needed) but then drops off with further movement of the lock link. Depending upon how far the lower lock link swings, and the exact link lengths and angles of the new mechanism, the linkage can allow the spring to relax from its maximum extension and can contract below its initial, gear down length.

As can be seen, the mechanism of <FIG> limits this additional extension to <NUM> (units are arbitrary) whereas the direct connection spring eventually extends <NUM> (or more or less depending upon how far the lock link swings, which will depend upon the lock link and stay geometry). Since the maximum spring stress will be at maximum spring extension this would impact the sizing of the spring, requiring a lower spring stiffness to accommodate the larger stretch and hence less spring effort in earlier parts of the curve.

Thus, <FIG> illustrates a first portion of movement with a maximum magnification factor of roughly <NUM> and for later movement, assuming that the lock link swings through <NUM> degrees, a second portion of movement with an extension reduction by a factor of <NUM> or roughly a reduction of <NUM>.

Embodiments of the invention can employ a reduction in conventional spring attachment radius, or a change in link lengths of the new mechanism, so that the initial magnification factor is larger and the reduction factor less. i.e. the vertical scaling of either curve can be changed to whatever is desired. As such, the benefit may be taken either by magnifying extension and thus effort at the beginning of the retraction movement, or by reducing maximum spring extension during the retraction. The two may be traded via the characteristics of the spring.

While the embodiment of <FIG> has been illustrated in <FIG>, the mechanisms of other embodiments will have similar characteristics.

It will be appreciated that the over-centre mechanisms described herein can be applied to various types of aircraft landing gear assembly and the various link lengths can be adapted to suit slightly different stay geometries and angles between links.

Components of the aircraft landing gear assembly according to embodiments of the invention can be implemented from conventional aerospace materials, such as titanium, aluminium and/or steel for structural members, polymer or metal bearings etc..

Claim 1:
An aircraft landing gear assembly comprising:
a first structural member (<NUM>');
a second structural member (<NUM>') pivotally coupled to the first structural member at an apex pivot point (P1') so as to be movable between a first angular condition and a second angular condition distinct from the first angular condition;
wherein the first structural member (<NUM>') is a first arm of one of a stay or lock link and the second structural member (<NUM>') is a second arm of a second one of the stay or lock link;
a down-lock spring (<NUM>') having a first end region pivotally coupled to a mounting structure and being arranged under tension to bias the first and second structural members to assume the first angular condition; and
a linkage assembly, the linkage assembly comprising:
an arm member (<NUM>') pivotally coupled to one of the first and second structural members at an arm pivot point (P2'), the arm having a first end region pivotally coupled to a second end region of the down-lock spring; and characterized in that it further comprises
a control link (<NUM>') pivotally coupled to one of the first and second structural members at a first control link pivot point (P4') and pivotally coupled to the arm member at a second control link pivot point (P5') such that, as the first and second structural members move relative to one another from the first angular condition towards the second angular condition, the first control link pivot point moves over centre, through an axis or plane bisecting the apex pivot point and the second control link pivot point.