GB2504211A

GB2504211A - Washer with relieved face

Info

Publication number: GB2504211A
Application number: GB201311216A
Authority: GB
Inventors: Ioaniss Eleftheriou
Original assignee: Ford Global Technologies LLC
Current assignee: Ford Global Technologies LLC
Priority date: 2012-07-20
Filing date: 2013-06-25
Publication date: 2014-01-22
Anticipated expiration: 2033-06-25
Also published as: CN203717600U; GB201212889D0; DE102013107641A1; RU2013133859A; GB201311216D0; RU2639633C2; GB2504211B

Abstract

A washer 210 has a first face 211 for abutment by a threaded fastener and a second relieved face 212 for abutment against an object to be secured in position by the threaded fastener. The relieved face 212 is configured to ensure that initial contact between the washer 210 and the object occurs at an outer peripheral edge 212e of the relieved face 212 thereby maximising the radius of contact between the washer 210 and the object and reducing the risk of the washer 210 slipping when the threaded fastener is tightened. The relieved face 212 may be concave or more particularly a frusto-conical concave face, or may be a concave spherical surface.

Description

An Improved Washer for a Threaded Fastener This invention relates to threaded fasteners and in particular to an improved washer for use with a threaded fastener.

It is well known to provide a washer between a threaded fastener and an object secured by the threaded fastener.

Such washers are normally in the form of a flat disc having a pair of flat faces arranged parallel to one another and a central bore through which in use part of the threaded fastening means extends. In the case where the fastening means is in the form of a threaded bolt, a shank of the bolt will extend through the central bore and a head of the bolt will abut against one of the two faces of the washer and the other face of the washer will abut against the object being secured.

It is a problem with such a prior art washer that, if the bolt is tightened using an electric nut runner, rotation of the washer during tightening can occur. The effect of such washer rotation or slippage is to reduce the clamp load and, with a reduced clamp load, the clamped joint can fail.

Such a failure can be serious if the threaded fastener is being used to secure a critical component of a device such as for example an accessory drive pulley of an engine of a motor vehicle.

It is an object of the invention to provide an improved washer that overcomes or minimises the occurrence of the aforementioned problem.

According to a first aspect of the invention there is provided a washer for use between a threaded fastener and an object to be secured by the threaded fastener wherein the washer has a first face for abutment by the threaded fastener and a relieved face for abutment against the object, the relieved face being configured to ensure that in±tial contact between the washer and the object occurs at an outer peripheral edge of the relieved face.

The relieved face may be a concave face.

The relieved face may be defined by a concave frusto-conical surface.

The relieved face may be defined by a concave spherical surface.

The first face may be a substantially flat faoe.

The first face may be a convex frusto-conical face.

The first face may be a convex frusto-conical face, the relieved face may be a concave frusto-conical surface and a surface of the first face may be arranged substantially parallel to the surface of the relieved face.

The initial contact may be line contact.

The washer may be substantially rigid.

According to a second aspect of the invention there is provided a threaded fastener assembly comprising a threaded fastener and a washer constructed in accordance with said first aspect of the invention in which the washer is trapped between the threaded fastener and an object secured by the threaded fastener wherein, at least during initial tightening of the threaded fastener, the threaded fastener abuts against part of the first face of the washer and an outer peripheral edge of the relieved face of the washer abuts against the object being secured.

The threaded fastener may be a bolt having a head and the washer is trapped between the head of the bolt and the object.

Alternatively, the threaded fastener may be a nut and the washer is trapped between the nut and the object.

The invention will now be described by way of example with reference to the accompanying drawing of which:-Fig.l is a side view of a first embodiment fastener assembly according to a second aspect of the invention including a washer according to a first aspeot of the invention; Fig.2 is a view in the direction of arrow Z on Fig.1; Fig.3a is a oross section through the washer shown in Figs.l and 2; Fig.3b is a view on an enlarged scale of the area b' shown on Fig.3a; Fig.4 is a side view of a second embodiment of a fastener assembly shown securing a pulley to a shaft; Fig.5 is a diagrammatio oross section of a first embodiment of the washer shown in Figs.l to 4 showing the shape of the washer in an exaggerated form; Fig.6 is a diagrammatic cross section through a second embodiment of the washer shown in Figs.l to 4 showing the shape of the washer in an exaggerated form; and Fig.7 is a diagrammatic cross section through a third embodiment of the washer shown in Figs.1 to 4 showing the shape of the washer in an exaggerated form.

With particular reference to Figs.l to 3 there is shown a fastener assembly 1 comprising a threaded fastener in the form of a bolt 2 and a washer 10.

The bolt 2 has a threaded shank 3 and a head 4. The head 4 is hexagonal in shape and has a flange end 5 for abutment in use against the washer 10.

The washer 10 has a first face 11 against which the flange end 5 abuts in use and a second relieved face 12 having an outer peripheral edge 12e for abutment against an object to be secured in place by the bolt 2 so that the washer 10 is trapped between the head 4 of the bolt 2 and the object.

The washer 10 has an outer circumferential face 14 defining a major diameter D' of the washer 10 and a bore 15 defining a minor diameter d' of the washer 10. In use the threaded shank 3 extends through the bore 15 of the washer so as to secure the object such as a pulley in place. A chamfer 13 joins the flat face 11 to the outer circumferential face 14 of the washer 10.

In Fig.3b an cpticnal feature is shown in which the outer peripheral edge 12e is formed by a step l4s in the outer circumferential face 14 of the washer 10. In such a case the outer peripheral edge 12e is not coincident with the outer circumference of the washer 10 but is located slightly inset from the outer periphery of the washer 10.

The washer 10 is thick relative to its diameter so that it is not easily deformed by the clamping load applied by the bolt 2 and during tightening of the bolt 2 the washer 10 can be said to be substantially rigid. That is to say, there is minimal deflection of the washer 10 when the bolt 2 is tightened.

The relieved face 12 is formed so that only the outer peripheral edge 12e of the relieved face 12 is in contact with the object being clamped when the washer 10 is initially clamped between the flanged end 5 of the head 4 of bolt 2 and the object by tightening of the bolt 2. This washer configuration ensures that the maximum possible radius is provided for the position of contact between the washer 10 and the object being clamped. The initial area of contact between the washer 10 and the object is very small and is effectively line contact thereby greatly increasing the load per unit area.

The combination of these two features have been found by the inventor to be very effective in preventing spinning of the washer 10 if the bolt 2 is tightened using a direct current nut runner.

In one embodiment of the invention, a washer 10 having a major diameter of 40 mm a thickness of 6.5mm and a relieved face 12 with a concave frusto-conical surface arranged at between 0.2 and 0.8 degrees to a plane arranged parallel to the first surface 11 provided between 15 and 20% increase in slip torque. That is to say, more torque was required to cause the washer 10 to slip.

With reference to Fig.4 there is shown an alternative fastening assembly to that previously described but which includes a washer 110 having the same or similar features to those described with reference to any of Figs.l to 3b.

The only significant difference between this embodiment and the embodiment shown in Figs.1 and 2 is that the threaded fastener is in this case formed by a nut 104 and stud 102 having a threaded end portion 103 rather than the bolt 2 shown in Figs. 1 and 2.

In Fig.4 the washer 110, whioh is essentially the same as the washer previously desoribed, is interposed or trapped between the nut 104 and a pulley 102 that is secured or clamped to a shaft 130 by the stud 102 and the nut 104. The pulley 120 has a splined bore for engagement with a splined nose 132 of the shaft 130.

The washer 110 has as before a relieved face (not visible on Fig.4) in contact with pulley 120 and a further face 111 that is abutted by the nut 104.

As before, the relieved face ensures that initial contact between the washer 110 and the pulley 120 occurs at an outer periphery of the relieved face and, in this case, adjacent an outer peripheral face 114 of the washer 110.

The initial area of contact between the washer 110 and the pulley 120 is very small and is effectively line contact thereby greatly increasing the load per unit area.

Figs.5 to 7 show three possible configurations for the washer 10, 110 shown in Figs.1 to 4. Tn each case the configuration of the washer is shown exaggerated for illustration purposes.

In Fig.5 the washer 210 has a substantially flat planer face 211 arranged normal to a central axis of the washer 210, a relieved face 212, a bore 215 and an outer circumferential face 214. In this case the relieved face is defined by a concave frustc-conical surface 212. The frusto-conical surface 212 is arranged at an angle B to a plane arranged parallel to the flat surface 211. The angle e is very small and typically falls in the range of 0.1 to 2.0 degrees so that an included angle of between 179.9 and 176 degrees is produced. In one example an included angle of 178 degrees was used with good effect.

The purpose of the concave frusto-conical surface 212 is to ensure that initial contact between the washer 210 and an object being clamped occurs at an outer peripheral edge 212e of the concave face 212. In this case the outer peripheral edge 212e is located at the juncture of the concave face 212 with the outer circumferential face 214 of the washer 210 thereby maximising the effective contact radius between the washer 210 and the object to be clamped.

As before the washer 210 is thick relative to its diameter so that it is substantially rigid when clamped by a threaded fastener such as a bolt or nut. This ensures that the large effective contact radius is maintained during initial tightening of the threaded fastener and only during the final stages of tightening will any significant deflection of the washer 210 occur by which time slipping of the washer 210 cannot occur due to the applied load.

As before, the initial area of contact between the washer 210 and the object being secured is very small and contact is effectively line contact thereby greatly increasing the load per unit area.

In Fig.6 the washer 310 has a first convex frusto-conical planar face 311, a concave relieved face 312, a bore 315 and an outer circumferential face 314.

In this case the relieved face is defined by a concave frusto-conical surface 312 in which the conical surface 312 is arranged at an angle e to a plane arranged parallel to a plane 311' arranged normal to a central axis of the washer 310. The angle e is very small and typically falls in the range of 0.1 to 2.0 degrees so that an included angle c1 of between 179.9 and 17 degrees is produced. In one example an included angle of 178 degrees was used with good effect.

The purpose of the conoave frusto-conical surface 312 is to ensure that initial contact between the washer 310 and an object being clamped occurs at an cuter peripheral edge 312e cf the concave face 312. In this case the outer peripheral edge 312e is located at the juncture of the concave face 312 with the outer circumferential face 314 of the washer 310 thereby maximising the effective contact radius between the washer 310 and the object to be clamped.

As before the washer 310 is thick relative to its diameter so that it is substantially rigid when clamped by a threaded fastener such as a bolt or nut. This ensures that the large effective contact radius is maintained during initial tightening of the threaded fastener and only during the final stages of tightening will any significant deflection of the washer 310 occur by which time slipping of the washer 310 cannot occur due to the applied load.

The first convex frusto-conical planar face 311 is arranged at the same angle e to the plane 311' arranged normal to a central axis of the washer 310. As before the angle e is very small and typically falls in the range of 0.1 to 2.0 degrees so that an external angle 5 of between 180.2 and 184 degrees is produced. Tn one example an external angle of 182 degrees was used with good effect.

Therefore a surface defining the first convex frusto-conical planar face 311 is arranged substantially parallel to the concave frusto-conical planar face 312. That is to say, the washer 310 is of substantially uniform thickness.

Such a washer can be produced by initially manufacturing a completely flat washer to the required dimensions and then hot pressing or stamping the washer in a die to produce the two frusto-conical faces 311,312. With such a production method it is preferable if the edge step structure shown in Fig.3b is used to produce a defined outer edge for the concave frusto-conical surface 312.

In one embodiment of such a washer 310 the washer had an overall diameter of 48mm, a thickness of 8mm and the inclination () of each two frusto-oonioal surfaoe 311, 312 to a plane arranged normal to a central axis of the washer 310 was 1 degree.

As before, the initial area of contact between the washer 310 and the object being secured is very small and contaot is effectively line contaot thereby greatly increasing the load per unit area.

In Fig.7 the washer 410 has a first substantially planar flat face 411, a relieved face 412, a bore 415 and an outer circumference 414. In this case the relieved face is formed by a concave spherical surface 412. The curvature of the part spherical surfaoe 412 is such that a ooncavity of depth 0.2 to 0.8 mm is produced compared to the situation if a flat surface were to be used. The purpose of the concave spherical surface 412 is to ensure that initial contact between the washer 10 and an object being clamped occurs at an outer peripheral edge 4l2e of the relieved face 412. In this case the outer peripheral edge 412e is at the juncture of the conical surface 412 with the outer circumferential face 414 of the washer 410 thereby maximising the effective contact radius between the washer 410 and the object.

As before the washer 410 is thick relative to its diameter so that it is substantially rigid when clamped by a threaded fastener such as a bolt or nut. This ensures that the large effective contact radius is maintained during initial tightening of the threaded fastener and only during the final stages of tightening will any significant deflection of the washer 410 occur by which time slipping of the washer 410 cannot occur due to the applied load.

-10 -As before, the initial area of oontaot between the washer 410 and the object being secured is very small and contact is effectively line contact thereby greatly increasing the load per unit area.

Although the invention has been described with reference to an embodiment in which a pulley is secured to a shaft it will be appreciated that the invention can be applied to any usage of a threaded fastener where washer slippage during tightening of the fastener is a problem.

Preferably the washer is thick so that it is substantially rigid thereby maintaining the large contact radius until the risk of slippage has been eliminated.

It will be appreciated by those skilled in the art that although the invention has been described by way of example with reference to several embodiments it is not limited to the disclosed embodiments and that alternative embodiments can be constructed without departing from the scope of the invention as defined by the appended claims.

Claims

-11 -Claims 1. A washer for use between a threaded fastener and an objeot to be scoured by the threaded fastener wherein the washer has a first faoe for abutment by the threaded fastener and a relieved face fcr abutment against the object, the relieved face being configured to ensure that initial contact between the washer and the object occurs at an outer peripheral edge of the relieved face.
2. A washer as claimed in claim 1 wherein the relieved face is a concave face.
3. A washer as claimed in claim 1 or in claim 2 wherein the relieved face is defined by a concave frusto-conical surface.
4. A washer as claimed in claim 1 or in claim 2 wherein the relieved face is defined by a concave spherical surface.
5. A washer as claimed in any of claims 1 to 4 wherein the first face is a substantially flat face.
6. A washer as claimed in any of claims 1 to 4 wherein the first face is a convex frusto-conical face.
7. A washer as claimed in claim 6 when claim 6 is dependent upon claim 3 wherein a surface of the first face is arranged substantially parallel to a surface of the relieved face.
8. A washer as claimed in any of claims 1 to 7 wherein the initial contact is line contact.
9. A threaded fastener assembly comprising a threaded fastener and a washer as claimed in any of claims 1 to 8 in -12 -which the washer is trapped between the threaded fastener and an object secured by the threaded fastener wherein, at least during initial tightening of the threaded fastener, the threaded fastener abuts against part of the first face of the washer and an cuter peripheral edge of the relieved face of the washer abuts against the object being secured.
10. An assembly as claimed in claim 9 wherein the threaded fastener is a bolt having a head and the washer is trapped between the head of the bolt and the object.
11. An assembly as claimed in claim 9 wherein the threaded fastener is a nut and the washer is trapped between the nut and the object.
12. A washer substantially as described herein with reference to the accompanying drawing.
13. A threaded fastener assembly substantially as described herein with reference to the accompanying drawing.