Window stays are widely used in residential and commercial settings, to secure window sashes to window frames while allowing the sashes to open. Known window stays use friction joints between elements of the window stay to hold the weight of the sash and contribute to sealing of the window sash against the window frame when closed. Typical integrated friction window stay functions include: supporting the weight of the window sash, holding the window sash in a desired opening position, providing an adequate weather seal to prevent water and air infiltration (otherwise known as seal compression, stay pull-in or weather tightness), and providing sufficient ventilation when desired.

Window stays may be 4-bar stays, of the general configuration shown in Figures 1 to 3. The stay includes a frame plate 1 for attachment to a window frame and a sash plate 2 for attachment to a window sash. Two arms 3, 4 join the frame plate and sash plate and provide the rotating movement that allows the window to be opened and closed. A 4-bar stay is the most common form of integrated friction window stay but 5-bar and 6-bar stays also exist.

Typical stays include friction joints at pivot points 5, 6, 7, 8. The joint design produces the required integrated joint friction by clenching (also known as "clinching") a stay plate (i.e. frame plate or sash plate) and stay arm together and creating friction force between them. Most friction stays use rivets as the joint fastener and washers to control wear and friction within the joint. The friction force in the joint is critical to the stay performance. It enables the window stay to support the weight of the window sash at a desired open position whilst meeting operating force requirements (e.g. the acceptable force required to open or close the window). It also assists the stay geometry in generating the sealing of the window sash to the window frame when closed.

An existing joint design is shown in Figure 4, which is a cross section through a friction joint. The arm 10 is attached to the plate 11 with a rivet 12 with washers 13, 14 clenched between them.

The arm 10 is counterbored on both sides to provide a cavity in which to recess the washers 13, 14. The counterboring of the arm 10 is an additional manufacturing step after the arm 10 is made. Usually it is a machining process that is expensive, time consuming and must be accurate in diameter, depth and radii. The counterbored recesses 15, 16 are dimensioned to stop the washer from extruding upon clenching. This washer extrusion is a general characteristic of compressed washers and must be prevented to maintain the integrity of the joint. Washers 13, 14 are normally straight sided and of even thickness and when two are used they are usually of the same diameter and thickness.

Existing joint designs also require a portion of the washer 13 (either pushed into place or the washer is shaped) to be positioned between the rivet shaft 17 and the arm 10 to create a bearing surface. Washer 13 may be forced around a curved surface as shown, but before assembly will generally be the same as washer 14. The washer 13 (typically nylon or similar material) separates the two metal faces of rivet and arm (typically aluminium). Over time the washer wears and this creates space within the joint. Recent trends in house design show a movement towards larger windows. Changes to building codes have resulted in increased use of double glazed windows to improve thermal efficiency of buildings. These two factors have given rise to the installation of heavier and larger windows. This increase in size and weight puts greater load on the integrated friction window stays currently used to support and hold open windows.

This creates new challenges in satisfying customer requirements for handle force to open or close a window, the need to comply with national and international standards for operating force and maintaining the sash in position in wind of specified strength. With an increase in window sash weight and size, the friction and load carrying capacity required to maintain the stay functions are increased.

Reference to any prior art in this specification does not constitute an admission that such prior art forms part of the common general knowledge. It is an object of the invention to provide an improved friction pivot joint and/or an improved window stay, or at least to provide the public with a useful choice.

SUMMARY OF THE INVENTION In one aspect the invention provides a window stay having a riveted friction pivot joint, the window stay including: a first element having an inner side, an outer side, a first aperture and a recess surrounding the aperture on the inner side; a second element having an inner side, an outer side and a second aperture; a rivet having a head, a shaft and a tail, wherein: the rivet head is engaged with the outer side of the second element; an underside of the rivet head is concave; the rivet shaft passes through the first and second apertures; and the rivet tail is clenched to engage with the outer side of the first element; a first washer positioned between the inner side of the first element and the inner side of the second element, the first washer residing at least partly within the recess; and a second washer positioned between the rivet head and the outer side of the second element, the second washer residing at least partly within the concave region of the underside of the rivet head; wherein the rivet, first washer and second washer provide a friction pivot joint between the first element and the second element.

Preferably the recess tends to restrict extrusion of the first washer.

Preferably the concave region of the underside of the rivet head tends to restrict extrusion of the second washer.

Preferably the second aperture defines one or more bearing surfaces that bear against the rivet shaft across at least substantially the full thickness of the second element, without the use of a washer between the bearing surface or surfaces and the rivet shaft.

Preferably the one or more bearing surfaces bear against the rivet shaft across the full thickness of the second element.

Preferably the second aperture is a plain aperture defining a single cylindrical bearing surface. Preferably the second aperture is a plain aperture without counterbores, countersinks or the like.

Preferably the window stay includes a coating on the second element, and the coating covers the one or more bearing surfaces. Preferably the coating is a powder coating. Preferably the rivet is a semi-tubular rivet.

Preferably the rivet remains fixed with respect to the first element when the second element rotates relative to the first element. Preferably the first aperture is non-circular, such that the clinched rivet tail engages with the first aperture to prevent rotation of the rivet relative to the first element. Preferably the first aperture is polygonal. Preferably the first washer has a rounded cross-section. Preferably the first washer has a substantially oval cross-section.

Preferably the second washer has a rounded cross-section. Preferably the second washer has a substantially oval cross-section.

Preferably the first element is a frame plate or a sash plate.

Preferably the second element is an arm. Preferably the first washer is thicker than the second washer, in a dimension parallel to the rivet shaft.

In a second aspect the invention provides a window stay having a riveted friction pivot joint, the window stay including: a first element having an inner side, an outer side, and a first aperture; a second element having an inner side, an outer side and a second aperture; a rivet having a head, a shaft and a tail, wherein the rivet shaft passes through the first and second apertures and the rivet head and tail engage with the outer sides of the second and first elements respectively; a first washer positioned between the inner side of the first element and the inner side of the second element; and a second washer positioned between the rivet head and the outer side of the second element; wherein the second aperture defines one or more bearing surfaces that bear against the rivet shaft across at least substantially the full thickness of the second element, without the use of a washer between the bearing surface or surfaces and the rivet shaft; and wherein the rivet, first washer and second washer provide a friction pivot joint between the first element and the second element. Preferably the one or more bearing surfaces bear against the rivet shaft across the full thickness of the second element. Preferably the second aperture is a plain aperture defining a single cylindrical bearing surface. Preferably the second aperture is a plain aperture without counterbores, countersinks or the like.

Preferably the window stay includes a coating on the second element, and the coating covers the one or more bearing surfaces. Preferably the coating is a powder coating.

Preferably the first element has a recess surrounding the first aperture on the inner side and the first washer resides at least partly within the recess.

Preferably an underside of the rivet head is concave and the second washer resides at least partly within the concave region of the underside of the rivet head.

Preferably the recess tends to restrict extrusion of the first washer.

Preferably the concave region of the underside of the rivet head tends to restrict extrusion of the second washer.

Preferably the rivet is a semi-tubular rivet.

Preferably the rivet remains fixed with respect to the first element when the second element rotates relative to the first element.

Preferably the first aperture is non-circular, such that the clinched rivet tail engages with the first aperture to prevent rotation of the rivet relative to the first element. Preferably the first aperture is polygonal. Preferably the first washer has a rounded cross-section. Preferably the first washer has a substantially oval cross-section. Preferably the second washer has a rounded cross-section. Preferably the second washer has a substantially oval cross-section.

Preferably the first washer is thicker than the second washer, in a dimension parallel to the rivet shaft.

In a further aspect the invention provides a window stay having a riveted friction pivot joint, the window stay including: a first element having an inner side, an outer side, and a first aperture; a second element having an inner side, an outer side and a second aperture; a rivet having a head, a shaft and a tail, wherein the rivet shaft passes through the first and second apertures and the rivet head and tail engage with the outer sides of the second and first elements respectively; a first washer positioned between the inner side of the first element and the inner side of the second element; and a second washer positioned between the rivet head and the outer side of the second element; wherein the first washer is thicker than the second washer, in a dimension parallel to the rivet shaft; and wherein the rivet, first washer and second washer provide a friction pivot joint between the first element and the second element.

BRIEF DESCRIPTION OF THE DRAWINGS

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

Figure 1 shows a prior art 4-bar window stay, in an open position;

Figure 2 is a further view of the stay of Figure 1 , from an opposite side of the stay; Figure 3 is a further view of the stay of Figure 1 , in a closed position;

Figure 4 is a cross-section through a prior art friction joint;

Figure 5 is a cross-section through a friction joint according to one embodiment;

Figure 6 is a more detailed view of the arm and rivet of the stay of the friction joint of Figure 5;

Figure 7 shows the rivet of the friction joint of Figure 5, before clenching;

Figure 8 is a cross-section through part of the rivet head;

Figure 9 shows the plate in the rivet joint of Figure 5;

Figure 10 shows a first washer;

Figure 10A shows a further embodiment of first washer;

Figure 11 shows a second washer;

Figure 11 A shows a further embodiment of second washer;

Figure 12 shows a 4-bar window stay incorporating friction joints of Figure 5, in an open position;

Figure 13 is a further view of the stay of Figure 12, in a closed position; and

Figure 14 is a side view of the stay of Figure 12, in a closed position.

DETAILED DESCRIPTION

Figure 5 is a cross-section through a friction joint 100 according to one embodiment. The friction joint joins an arm 101 to a plate (either sash plate or frame plate) 102. The joint allows the arm to pivot about an axis 103. The joint is substantially formed by a rivet 104 that engages with apertures in the arm 101 and plate 102, a first washer 105 and a second washer 106.

The rivet 104 has a head 107, shaft 108 and tail 109. The head 107 is positioned on a first side of the friction joint, with the tail 109 being clenched (also termed "clinched") on the other side of the friction joint. As shown in Figure 5, the rivet tail 109 may be substantially tubular, allowing the tail to be clenched outwards to engage with the plate 102. The rivet 104 may have a solid shaft and tubular tail, sometimes known as a "semi-tubular" rivet. In the embodiment shown, the tail 109 clenches directly onto the plate 102. The aperture 110 in the plate 102 may be circular, but in some embodiments may be non-circular, polygonal or have any irregular shape, which allows the tail 109 to engage with the aperture 110 to resist rotation of the rivet 104 relative to the plate 102. The tail 109 will deform against the sides of the aperture during clenching.

The rivet head 107 engages with an outer side or surface 112 of the arm 101 , but is spaced therefrom by the second washer 106. As shown in Figures 5, 7 and 8 the underside, or inner side, 113 of the rivet head 107 is formed with a generally concave shape. This creates a region between the arm 101 and the rivet head 104 that is generally narrower in an outer section than in an inner section closer to the rivet shank 108. This shape helps to resist extrusion of the second washer 106 outwards (i.e. away from the rivet shank 108).

The plate 102 is machined, pressed or stamped to form a recess or counterbore 115 on its inner surface 116. This creates a region between the arm 101 and the plate 102 that is generally narrower in an outer section than in an inner section closer to the rivet shank 108. This shape helps to resist extrusion of the first washer 105 outwards (i.e. away from the rivet shank 108). Further, the plate 102 may be shaped on its outer surface to provide a recess 117, such that the clenched rivet tail 119 sits beneath the outer surface 118 of the plate 102.

The cylindrical wall of the aperture in the arm 101 forms a cylindrical bearing surface 120. This bearing surface 120 rides over the rivet shaft 108. Unlike prior joints, there is no washer provided between the arm 101 and the rivet shaft 108. A certain amount of wear resistance may be provided by the powder coat layer which is applied to the arm before assembly. As shown in Figure 6, the powder coat 121 coats the entire arm 101 , including the inside of the aperture, forming the bearing surface 120. Polymer powder coats provide wear resistance in this area that is expected to be sufficient for the life of the stay. Further, the cylindrical bearing surface 120 preferably extends the full thickness of the arm 101. As shown in Figure 4, prior stays have generally used a shaped aperture (e.g. with counterbores etc) in the arm 101 , such that only part of the arm's thickness bears against the rivet shaft 108. In contrast, Figures 5 and 6 show a plain aperture, without counterbores or other formations, such that the cylindrical bearing surface 120 is provided by the entire width of the arm. This formation is significantly cheaper to manufacture, but also provides important structure to the friction joint. The extent of this bearing surface 120 and its close proximity to the rivet shaft (i.e. without any intervening washer) provides excellent resistance to twisting of the pivot joint. In other words, this arrangement keeps the plane of the arm 101 transverse to the rivet 104 and the axis 103. Further, there is no intervening washer to wear away over the life of the stay. This means that the resistance to twisting is retained and the joint is less likely to loosen.

The arrangement shown in Figure 5 is preferred for its simplicity and ease of manufacture. However, in other embodiments a stepped rivet surface may be used, defining more than one bearing surface. In that case the two or more bearing surfaces preferably should together extend across substantially the full width of the arm 101.

Figure 9 is a cross-section through the plate 102 showing the aperture 110, inner recess 115 and outer recess 117. Figure 10 shows the first washer 105, with part of the washer cut away to show the cross-section. Figure 1 1 shows the second washer 106, with part of the washer cut away to show the cross-section. In each case the physical washer makes a full ring.

Figures 10 and 11 show how the first and second washers may have a rounded cross-section, at least on their outer edges 125. In the washers shown the inner edges 126 are also rounded. However, the washers are preferably substantially oval or elliptical (as shown in Figures 10 and 11) rather than circular in cross-section.

This shape provides the necessary separation of the rivet head, arm and plate but also assist with the prevention of washer extrusion. When compressed in the assembled joint, the washers will deform as indicated in Figure 5. However, there is less tendency to extrusion than in a square sided washer. Nevertheless, for many applications square or rectangular cross-section washers, such as those shown in Figures 10A and 11 A may be suitable.

Thicker washers provide increased friction in the joint. As the washer material is slightly resilient it tends to push outwards, against the force applied by the rivet that keeps the joint together. The thicker the washer, the more friction can be generated and the less the friction changes over time with wear. This is because wear in a thicker washer causes less loss of thickness as a percentage than in a thinner washer. Further, when clinching the rivet, the clinching force can cause some deformation of the plate in the region surrounding the aperture. This deformation can be absorbed more readily by a thicker washer, such that the deformation has no impact on the overall performance of the joint. In addition, the clinching force is absorbed to a greater degree in the washer closer to the rivet tail, so that a thicker washer is desirable in that position. For all these reasons, the Applicant's joint preferably includes two washers of different thickness, with the thicker washer preferably positioned on the rivet tail side of the joint, i.e. between the arm and the plate and the thinner washer positioned between the rivet head.

Figures 12 to 14 show a 4-bar stay incorporating 4 riveted friction pivot joints 100. However, note that other types of window stay employ similar rivet joints, and the invention is not limited to four bar stays. For example, 5 and 6 bar stays are also known. While the present invention has been illustrated by the description of the embodiments thereof, and while the embodiments have been described in detail, it is not the intention of the Applicant to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details, representative apparatus and methods, and illustrative examples shown and described. Accordingly, departures may be made from such details without departure from the spirit or scope of the Applicant's general inventive concept.