Background to the Invention

For aircraft with retractable landing gear, each landing gear assembly typically includes a number of pin joint assemblies that allow separate elements of the landing gear assembly to pivot about the pin joint. Pin joints will typically be included in the side-stay assemblies to allow the upper and lower elements of the side-stay to pivot both with respect to one another and with respect to the main sliding tube of the landing gear and the aircraft frame itself. As the landing gear assembly can experience both lateral and longitudinal loadings during take-off and landing events it is normal for some deflection to occur in the lugs of the side-stays through which the pin joint passes. At present, the forces induced as a result of these lug deflections are reacted by the headed pin and nut of the pin joint assembly that passes through the lugs and allows the relative rotation of the two side-stay elements. Consequently, the headed pin and nut must be designed so as to be capable of carrying these deflection loads, with the necessary safety margin additionally provided. To achieve this increased load carrying capability increases the weight of the pin joint assembly, typically by approximately 2.5kg per pin joint. Therefore, on a dual stay landing gear assembly with six pin joints approximately 15kg is added to the mass of each landing gear assembly simply to provide the requisite additional load carrying capability of the pin joint assemblies. In addition to the increased manufacturing cost arising from the larger pin joint assemblies, this added weight is undesirable in terms of the overall weight of the aircraft as it has a direct bearing on the fuel efficiency and fuel capacity of the aircraft. It would therefore be desirable to reduce the weight of a pin joint assembly without comprising its load carrying capability.

Summary of the Invention According to an aspect of the present invention there is provided a pin joint assembly for an aircraft landing gear comprising an elongate joint pin, at least one first lug through which the joint pin passes and at least one second lug through which the joint pin passes, wherein the joint pin includes first and second retaining elements located at opposite ends t pin and arranged to maintain the location of the joint pin relative to the first and second lugs, and wherein the pin join assembly further comprises a respective resilient member located between each of the retaining elements and a respective one of the first and second lugs, each resilient element being elastically deformable.

One or more of the first and second retaining elements may comprise a retaining nut arranged to be in threaded engagement with the joint pin.

Alternatively, at least one of the first and second retaining elements may comprise an end cap secured to the joint pin. In this case, either one or both of the first and second retaining elements may be secured to the joint pin by means of a retaining nut threaded to a portion of the joint pin passing through the or each respective retaining element.

Alternatively, either or both of the first and second retaining elements may be secured to the joint pin by means of a retaining nut threaded to a bolt passing through the or each respective retaining element and the joint pin.

The or each resilient member of the pin joint assembly may comprise any one of a wave spring washer, a belleville washer, a coil spring, and an O-ring.

Brief Description of the Drawings

Some embodiments of the present invention will now be described in more detail, with reference to the accompanying figures, of which:

Figure 1 schematically illustrates a cross-section of a pin joint assembly according to the prior art;

Figure 2 schematically illustrates in cross-section a pin joint assembly according to an embodiment of the present invention; and

Figure 3 schematically illustrates a pin joint assembly according to a second embodiment of the present invention. 'escription of Embodiments of the Present Invention

A pin joint assembly according to the prior art is schematically illustrated in cross-section in Figure 1. The pin joint assembly includes a pair of first lugs 2, 2a and a second lug 4 interposed between the first lugs, and a joint pin 6 passing through the first and second lugs and about which the lugs can rotate. The joint pin 6 has an integral head 8 located at one end of the pin preventing the pin from passing all the way through the first and second lugs, and has a threaded portion 10 provided at the opposite end to which a retaining nut 12 is secured, thus completing the pin joint assembly. Any deflections in the first and second lugs 2, 2a, 4 caused by radial loading of the pin joint cause the lugs to contact either the pin head 8 or retaining nut 12 and consequently load the stiff joint pin (bolt) 6 potentially to the point where the load is so high that the pin will fail. To prevent such failure the nut 12, and also pin head 8, must be oversized so as to be able to accommodate the additional lug defection loadings over and above the normal operational loadings of the pin joint. This adds weight and cost to the pin joint assembly.

An improved pin joint assembly according to an embodiment of the prior art is schematically illustrated in cross-section in Figure 2. As with the prior art pin assembly shown in Figure 1, first and second lugs 102, 102a & 104 are provided though which a joint pin 106 extends. The joint pin 106 includes a retaining element in the form of an integral pin head 108 and also includes a threaded portion onto which a retaining nut 112 is secured. Located between the inner face of the pin head 108 and the outer surface of the first lug 102a is a resilient member 114, which in the particular embodiment illustrated in Figure 2 is represented as a wave spring washer. A second resilient member 114a is located between the second first lug 102 and the retaining nut 112.

In use, if the pin joint assembly illustrated in Figure 2 is loaded so as to induce a deflection of the first and/or second lugs, then this deflection causes one or more of the resilient elements 114, 114a to elastically deform. Although the compression of the resilient member will still exert a force on either the retaining nut 112 or retaining element 108 of the pin joint assembly, this force is significantly lower than in the prior art pin joint assemblies for the same lug deflection. The reason that load experienced by the retaining element 108 and/or retaining nut 112 of the pin joint assembly of the present invention in Figure 2 is lower than for a corresponding pin joint assembly according to the prior art is that the introduction of the resilient element 114 changes the load path in the pin joint assembly to an indeterminate load path. Where indeterminate load paths are concerned, the stiffer an element the more load it takes. Consequently, the introduction of the resilient elements 114 greatly reduces the stiffness of the pin joint assembly at the location of the resilient elements, thus reducing the loads transmitted from the lugs as they experience deflection to the retaining nut or pin head 108. As a consequence of the reduced load transmitted from the lugs to the pin head 108 or retaining nut 112, these elements can be significantly reduced in size and weight in comparison with a joint pin assembly of the same load carrying capability of the prior art.

A further embodiment of a pin joint assembly according to the present invention is schematically illustrated in the cross-section of Figure 3. As with the previously illustrated pin joint assemblies, first and second lugs 202, 202a & 204 are provided through which a joint pin 206 extends. Retaining caps 208 are provided at either end of the pin joint 206 as separate elements through which a portion of the joint pin 206 extends. The portions of the joint pin that extend through the retaining elements 208 are threaded and respective retaining nuts 212, 212a are fastened to the threaded portions, thereby securing the retaining elements 208 in place and maintaining the physical arrangement of the pin joint assembly. In a further alternative embodiment, rather than threaded portions of the joint pin 206 extending through the retaining elements 208, a bolt 216 having threaded portions at either end passes through both the retaining elements 208 and a corresponding bore in the joint pin 206 with the retaining nuts 212, 212a being secured to the threaded portions of the bolt 216. First and second resilient members 214, 214a are provided in between the inner faces of the retaining elements 208 and the outer face of the adjacent first or second lugs, as arranged and described with reference to Figure 2.

Any combination of integral or separate end caps and retaining nuts may be provided in further embodiments of the present invention. For example, in place of the separate end caps 208 illustrated in Figure 3, large retaining nuts 212 may be used instead, in an analogous fashion to the retaining nut 112 illustrated in Figure 2. Similarly, where end caps are provided then the means of securing these to the joint pin 206 may vary within the other embodiments of the present invention, i.e. other means of securing the end caps 208 t pin 206 may be utilised or the end caps may be formed as an integral part of the pin joint. For example, separate end caps may be provided as illustrated in Figure 3, but with two or more lightweight bolts and corresponding retaining nuts rather than the single bolt and paired retaining nuts shown in Figure 3. Equally, the resilient members 114, 114a may be of any suitable design and elastically deformable material. For example, rather than the wave spring washer illustrated in Figures 2 and 3, one or more belleville washers may be provided, as may one or more coil springs or elastomeric O-rings.

By reducing the stiffness of the pin joint assembly of embodiments of the present invention by the introduction of the resilient elements to absorb local deflections, the resulting pin joint assembly can be significantly smaller and lighter than the corresponding prior art pin joint assemblies. For example, for a typical dual stay aircraft landing gear with six joints approximately 15kg of weight reduction can be achieved using pin joint assemblies according to the present invention.