The present invention relates to a reinforced locking washer by which a screw/nut system can be maintained with a high level of tightening locked against rotation.

The known locking washers comprise two washer crowns applied coaxially against each other, and they are adapted to mesh between a bearing element and a nut, while a threaded member connects the bearing element and the nut while traversing the washer. They each have an engagement face and an opposite ribbed bearing face, The engagement faces of the washer crowns are caused to cooperate with each other, and each of them has asymmetrical radial teeth. The asymmetrical radial teeth have, on the one hand, a crest and a tooth bottom spaced angularly from the crest at an angle being, substantially, smaller than about 80 ^° , and, on the other hand, two opposed sides. One of the sides is substantially inclined relative to the median plane defined by the washer crown, and it extends angularly between the crest and the tooth bottom. It is intended to form a sliding side. The angle with the greatest slope of the sides substantially inclined relative to the median plane should be substantially superior to the helix angle of the screw/nut system. The other side is substantially perpendicular to the inclined side of the following tooth, and it constitutes a stop side, Thus, the engagement faces of the washer crowns are intended for being applied against each other, such that, on the one hand, the inclined sliding sides come into contact with each other, respectively, and, on the other hand, the stop sides come into abutment with each other, respectively.

Also, when the nut is screwed onto the threaded member, the locking washer is held in a vise-grip between the bearing element and the nut, and the engagement faces are then brought along axially towards each other under pressure. In turn, when the nut tends to loosen, it brings along the washer crown against which it bears in rotation, and consequently the sliding sides of that washer crown are brought along slidingly against the sliding sides of the other washer crown, while forming a ramp, In this manner, the washer crowns are separated axiaHy from each other according to a modulus which is higher than that of the translation movement of the nut relative to the screw. Consequently, the axial tension which is exercised in the screw/nut system increases significantly. Due to that, the friction forces generated in the screw/nut system increase considerably and bring about the locking of the nut against rotation. More specifically, since the sliding side is inclined relative to the axis of the screw/nut system at an angle greater than that of the helix angle of the system, at the moment when the nut brings the washer crown into rotation when it loosens, the latter is brought atong axially against it, and locks it by wedge effect. This type of washer which is described in particular in EP 0131558 is, however, associated with certain drawbacks.

Actually, when the tensions exerted by the screw/nut system are very high, the deformation of the washer crowns, and more specifically the teeth, attenuates the locking effect, Moreover, when the screw/bolt system is dismounted frequently, and the washer is reused, the teeth of the washer crowns are also deformed. Besides, particular means are necessary for the manufacture of this type of washers and for the forging of washer crowns. Also, a problem that arises and which the present invention is aimed at solving is to provide a locking washer which is more resistant and which can be manufactured at a better cost.

To this end, the present invention proposes a locking washer intended for being compressed axially between a bearing element and a screwable element, wherein said locking washer comprises two washer crowns having each an engagement face, said engagement face having a plurality of teeth, each of said teeth having, on the one hand, a crest extending in a radial direction of the washer crown while defining an axial plane comprising the axis of symmetry of the washer crown, and two tooth bottoms separated by said crest, and, on the other hand, a sliding side extending between said crest and one of said tooth bottoms, and a bearing side extending between the crest and the other one of the tooth bottoms, wherein the engagement faces of said washer crowns are suitable for being applied against each other, whereas the sliding sides come into contact with each other, respectively, said washer crowns being suitable for meshing with the screwable element and the bearing element, respectively, when the screwable element loosens, so that the washer crowns are caused to rotate relative to each other, wherein the respective sliding sides are brought along slidingly against each other while forming a ramp to separate the washer crowns axialiy from each other to bring about the locking against rotation of the screwable element. According to the invention, the bearing side and the sliding side of each of the teeth are symmetrical to each other relative to the axial plane defined by the crest and the axis of symmetry of the washer crown.

Thus, it is a characteristic feature of the invention to provide washer crowns whose teeth are symmetrical relative to the axial plane they define, which includes the axis of symmetry of the washer crown, In this manner the strains exerted axiai!y on the washer by the bearing element and the screwable element connected to each other by a threaded member that traverses the washer induces forces that are uniformly distributed onto the respective teeth of the two washer crowns. In this way the teeth do not deform, or they deform very slightly, when the strains are applied, and they revert to their initial shape when the screw/nut system is dismounted and when the crowns are used again to form a washer. Besides, when the tensions in the screw/nut system are very high, the washer according to the invention consisting of two washer crowns does not deform or it deforms very slightly.

During mounting of the screw/nut system, the two washer crowns are paired, bearing face against bearing face and teeth in teeth, respectively, so as to bring about that the teeth of one of the washer crowns engage at the tooth bottoms of the other washer crown and vice versa. The threaded member engages through the washer, and the nut is screwed onto the threaded member so as to hold, in a vise-grip, the two washer crowns mating between the bearing element and the nut, The two washer crowns are now held matingly until tightening of the nut with a view to preventing the movement of one of the washer crowns relative to the other. During the tightening, the bearing sides of the teeth of the two washer crowns come to bear against each other, respectively. Then, following the tightening, the nut is no longer capable of inadvertently loosening. Actually, when it tends to do so, it meshes against the washer crown on which it bears and tends to rotate it along. Consequently, it tends to be brought into rotation relative to the other washer crown, and its sliding sides are brought along in angular movements against the sliding sides of the other washer crown. In consequence, the sliding sides form a ramp, and the washer crowns will tend to become separated from each other to an extent which is greater than the extent to which the nut and the bearing element are separated as a consequence of the loosening. Also, due to wedge effect, the loosening of the nut is stopped. Besides, it will appear how the forging of the washer crowns enabling the formation of the teeth becomes much easier and less expensive when the teeth are symmetrical.

According to a first alternative embodiment of the invention, the section of the teeth, through a cylinder intersecting coaxially the washer crown, defines a sinusoidal profile of the teeth. The teeth thus form a regular wave line on the engagement face of the washer crowns. The forces that are then exerted onto the interface between the sliding sides and the bearing faces, respectively, are homogeneous and continuous. Besides, the total of forces exerted on any tooth is contained within the axial plane that it defines and is substantially parallel to the axis of symmetry of the washer crown. Also, the teeth are not in any risk of becoming deformed by the strains. Additionally, the washer crowns do not deform either.

According to a further embodiment, the crests and the tooth bottoms respectively define crest lines and tooth bottom lines, whereas the bearing and sliding sides are plane. Thus, the teeth have a corner which is then caused to be arranged in a corresponding tooth bottom, which is itself formed by two sides that join along a tooth bottom line or an inward corner. In this manner, one obtains a unique equilibrium position of maximal approximation between the two washer crowns.

Advantageously, the teeth of the plurality of teeth of each of the washer crowns have an identical profile, whereby the corresponding engagement faces can be in contact with each other throughout the entire expanse of their surface, in this way, the washer crowns will, under strain, form a self- contained washer suitable for tolerating strong strains.

Besides and according to a particularly advantageous embodiment of the invention, the sliding sides enter info contact with each other, respectively, along a contact face, and the engagement face of at least one of the washer crowns has a recess for reducing the contact face of the sliding sides. In this way, the nut and the washer crown on which it bears mesh much easier when the nut tends to loosen. Owing to this, due to the recess, the contact faces are reduced and consequently so are the friction forces between the sliding sides. Advantageously, the engagement face has a circular groove forming said recess which makes it possible to obtain identical friction forces, irrespective of the angular position of the washer crowns relative to each other.

According to a further embodiment of the invention, the washer has a conical shape and its locking is eiastica!ly deformable in order to enable deformation thereof to a flat configuration while forming a spring effect between the bearing element and the screwabie element, in this way the friction forces between the nut and the washer on which it bears remain constant, irrespective of the relative separation of the nut and the bearing element, eg due to the axial dilatation of the threaded member.

Besides, the washer crowns are advantageously made from spring steel. This type of steel, or others, can be forged easily at an advantageous cost to make the symmetrical teeth. Actually the wear on the forging tool is smaller in case of symmetrical teeth and has a relatively high draw.

Other characteristic features and advantages of the invention will become apparent by reading of the following description of particular embodiments of the invention, given as non limiting examples with reference to the accompanying drawing, wherein:

- Figure 1 is an elevation view, seen from in front, of a screw/nut system, including a locking washer according to the invention;

» Figures 2 and 3 are perspective views of the two separate elements of the locking washer shown in figure 1 , according to a first alternative embodiment; and

- Figures 4 and 5 show a second alternative embodiment of the two separate elements of the locking washer shown in figure 1. Figure 1 illustrates a screw/nut system comprising a threaded member 10 joined with an bearing element 12, from which it extends protrudingly. Besides, it comprises a locking washer 14 according to the invention in accordance with a first alternative embodiment. It is held in a vise-grip between the bearing element 12 and a nut 18 by means of the threaded member 10 which traverses it. The nut 16 has been screwed in the clock- wise direction and there it is tightened. The locking washer 14 is intended for preventing loosening thereof as will be explained in further detail below. Before that, the construction of the locking washer 14 will be explained.

It consists of two washer crowns; the first upper one 18 in contact with the nut 18, and the second tower one in contact with the bearing element 12. The first washer crown 18 has a first engagement face 22, while the second washer crown 20 has a second engagement face 24, said engagement faces 22, 24 comprising first teeth 28 and second teeth 28, respectively. The first 28 and second 28 teeth cooperate with each other as will be explained in further detail in the following.

Before such detailed explanation, reference is made to figures 2 and 3 showing, in a perspective view, the upper washer crown 18 and the lower washer crown, respectively, having axes of symmetry A, in three-quarter view relative to their engagement face 22, 24. The two washer crowns 18, 20 are identical and they are made by forging of a steel, eg of the so-called "spring steel" type, or of any other type of steel. Also, for the sake of clarity of the figures, the details in respect of the dimensions of the washer crown 18 will be set forth with reference to figure 2 and more specifically, in respect of, the structure of the second engagement face 24 of the second washer crown 20, with reference to figure 3. Thus, the inner radius of the washer crown Ri is substantially equal to two thirds of the outer radius Re, whereas the thickness Ep is within the range of one fifth and one sixth of the outer radius Re. For instance, the outer radius Re is comprised within the range of 8 mm and 18 mm. The second washer crown 20 shown in figure 3 is identical to the first one 18. Herein its engagement face 24 has 22 second teeth 28 of undulated shape. Each of the second teeth 28 has a second crest 30 which extends in a radial direction DRc which is perpendicular to the axis of symmetry A which it intersects. Besides each second tooth 28 has, on each side, a second sliding side 32 and a second bearing side 34 which join two second tooth bottoms 36, respectively. One characteristic feature of the invention resides in the symmetry of the teeth 28. Their two opposite sides, the sliding one 32 and the bearing one 34, are effectively symmetrical to one another relative to the axial plane of each of the second teeth defined by the radial direction DRc of the second crest 30 and the axis of symmetry of the washer crown A.

In the same way, the teeth 26 of the first washer crown 18 illustrated in figure 2 are of undulated shape and they are symmetrical. They have a first crest 38 that extends radially, while intersecting the axis of symmetry A. Besides each first tooth 26 has, on each side, a first sliding side 40 and a first bearing side 42 that respectively join a first tooth bottom 44. The first sides 40, 42 are symmetrical to each other relative to an axial plane defined by the radial direction of the first crest 38 and the axis of symmetry A that it intersects

Reference is again made to figure 1 to describe in further detail the advantages of the symmetrical teeth 26, 28 of engagement faces 22, 24 of the corresponding crowns 18, 20. In that figure the second crests 30 of the second engagement face 24 are shown which extend respectively in the tooth bottoms 44 of the first engagement face 22, It will appear that the contact face between the engagement faces 22, 24 are of sinusoidal shape. Thus, the second sliding side 32 will appear which is symmetrical to the second bearing side 34 relative to the axial plane containing the axis of symmetry A and the radial direction defined by the second crest 30 and which is here perpendicular to the plane of the figure. Thus, when the locking washer 14 is held in a vise-grip between the nut 18 and the bearing element 12, the strains exercised on the two washer crowns 18, 30 translate by the symmetrical forces onto each of the teeth 28, 28. In this manner, in respect of each tooth, the sum of the isostatic forces exercised on the sliding sides 32, 40, the opposite bearing sides 34, 42, as well as on the crests 30, 18, and the tooth bottoms 38. 44, is equal to a force comprised in the axiai plane of the tooth and in parallel with the axis of symmetry A. In this way, despite the considerable tensile stress in the screw/nut system, the teeth 28, 28 of the washer crowns do not deform and they can be reused after dismounting.

Besides, by means of the sliding sides 32, 40 of the two washer crowns 18, 20 whose mean angle G is larger than the mean angle g of the threads of the threaded member 10, when the nut 16 tends to loosen in the anticlockwise direction, the first upper washer crown 18 engages with the nut and also tends to be drawn into rotation in the same direction relative to the second lower washer crown 20. Also, by means of the sliding sides 32, 40, serving thus as ramp, the nut 18 is immediately locked from rotating by a wedge effect.

Reference is now made to figures 4 and 5 illustrating the washer crowns of a locking washer according to a further alternative embodiment. Identical elements are provided with the same references followed by a prime symbol

» ^' * « ,

Figure 4 thus illustrates a third washer crown 18 ^! suitable for engagement against a fourth washer crown 20 ^! illustrated in figure 5, Relative to the difference in play of the washer crowns of the foregoing embodiment, the sliding sides 32', 40" and the respective opposite bearing sides 34', 42 of each of the teeth, are plane. Thus, crests 30', 38' form protruding corners whereas tooth bottoms 36', 44 ^! form recessed corners. By means of the plane sliding sides 32', 40\ the axial separation of the washer crowns 18', 20' is proportionate to the relative angular movement thereof.

According to a further implementation of the invention, not shown, the engagement face has a circular groove forming a recess in the sliding sides. In this manner in respect of this recess, the sliding sides are no longer in contact, and consequently the friction forces between the sliding sides will be mitigated when the nut tends to loosen.

Besides, according to a further implementation, not shown, the locking washer has a conical shape, given by the conical shapes of the washer crowns themselves. Thus, the locking washer is elastically deformable, and it may be deformed to a flat configuration while having spring effect between the bearing element and the screwabte element.

By that feature, the upper washer crown and the nut remain engaged to a certain extent even when the bearing element and the nut separate from one another.

For all embodiments above it should be understood that the washer crowns 18, 18', 20, 20' are suitable for meshing with the screwabte element 18, such as a nut 18, and the bearing element 12. The meshing can be provided with a suitable technique for the person skilled in the art. In particular the vise-grip between the bearing element and the nut provides for this meshing, as known to the person skilled in the art. Of course the meshing can be aided for example by providing small ridges or ribs on the respective faces facing the screwable element 16 and the bearing element 12. It is also thinkable to provide other means of augmenting the friction of the faces facing the screwable element 16 and the bearing element 12, for example by providing a rugged surface on faces of the washer crown that is arranged to be facing the screwab!e element 18 and the bearing element 12, for example by means of shoot blasting of the surface of these faces. The aim with this is that the respective washer crowns does not rotate against the surface they face i.e. surface of the screwable element 18 and the bearing element 12. It is of course possible in addition/ or by itself to the above, to lower the friction between the engagement faces 22, 24 for example by lubrication.