GB2580048A - Elastic washer and screw-nut connection therefore - Google Patents

Abstract

An elastic washer comprises a hollow, truncated metallic cone (100) having an inclined sidewall (11), a top opening at the top of the cone, and a bottom opening at the bottom of the cone. The top opening is parallel to the bottom opening, larger than the bottom opening and concentric therewith. The inclined sidewall (11) bends radially inward into a raised edge (12) obliquely oriented towards the inclined sidewall (11). An associated screw-nut connection is also provided, between a first plate provided with a threaded bore and a second plate provided with a countersink (s) of a shape similar to the truncated cone shape of the elastic washer.

Description

Description

Elastic washer and screw-nut connection therefore The invention relates to an elastic washer for screw-nut connections that work in vibrational environment, and to a screw connection therefore.

There are known several solutions for keeping a screw-nut connection tight under vibrations and shocks, namely: employing an anti-rotational device (castellated nut or tab washer); increasing the friction torque in the screw-nut connection by inserting an elastic washer (for example, spring washer or star washer); increasing the friction torque by adding blocking glue on thread.

DE 73 38 638 U discloses a screwing unit having a hollow screw and an annular flange, in which a sealing ring between the screw head and the annular flange is designed as a normal flat gasket, but the opposite gasket has an initially conical region projecting from the thorax. However, the production of such a seal is relatively expensive, since several operations to form the thoro-shaped geometry with a conical region are required.

EP 2210031 B1 describes an annular coupling with a hollow screw, an annular connector, a flat ring seal and a sealing washer. The sealing washer is of conical design and has a cylindrical bore, so that it can be pushed onto and pulled off again from the hollow screw; when assembled, the sealing washer is deformed back into a flat shape. By means of said deformation back, the sealing washer can no longer be pulled off from the hollow screw, therefore the components of said annular coupling are captively connected to each other.

However, problems arise in case of a shock, when the admissible contact pressure of soft materials is exceeded; thus, the material under the screw head is plastically deformed, leading to torque lose in the screw-nut connection.

The invention has for its object to improve the residual torque of a screw-nut connection.

According to the invention, this object is achieved by the 10 subject-matter of the independent claims, namely an elastic washer and a screw-nut connection therefore.

This object is achieved by an elastic washer for screw-nut connection, comprising a hollow, truncated metallic ccne having an inclined sidewall that bends radially inward into a raised edge obliquely oriented towards the inclined sidewall. After inserting a screw through the elastic washer and tightening it, said raised edge is deformed into a flat edge upon which the screw head comes to rest.

The main advantages of using an elastic washer according to the invention consist into better shock absorbing on all three axes (xyz), and an improved connection between soft material parts, with high tolerance torque.

Further special features and advantages of the present invention can be taken from the following description of advantageous embodiments by way of the accompanying drawings: Fig. 1 illustrates a cross section of a screw connection employing an elastic washer according to invention; Fig. 2 shows a cross section of a countersink engaging the elastic washer, with specific dimensional parameters defining the countersink; Fig. 3 shows the elastic washer with specific dimensional parameters; Figs. 4 show step by step how the elastic washer deforms as the screw is tight, namely: Fig. 4a presents an unloaded state of the elastic washer; Fig. 4b presents the elastic washer partially loaded, when the screw advances on thread, but it is not entirely tight; Fig. 4c presents the elastic washer fully loaded; Figs. 5 illustrate an embodiment of a screw-nut connection using an elastic washer, for a compact braking unit also known as MK Cl: Fig. 5a shows said unloaded elastic washer; Fig. 5b shows said washer fully loaded.

Fig. 1 shows a screw connection 1 according to the invention, whereby a first part P1 (in this case, a plate), provided with a threaded bore b, is coupled to a second part P2 (in this case, another plate) provided with a countersink s, by means of an elastic washer 100 and a screw 200.

Fig. 2 shows the dimensional parameters that define the countersink s, namely an inner diameter D, a height H and a top opening angle y. In order to accommodate said elastic washer 100, second part P2 has to be first drilled as to ensure a hollow, straight portion of inner diameter D and height H; then, a truncated cone portion of top opening angle y has to be machined.

Fig. 3 presents the elastic washer 100, namely a hollow, truncated metallic cone provided with a top opening at the top of said cone, and a bottom opening of angle T at the bottom of said cone, the top opening being parallel to said bottom opening, larger and concentric therewith. Elastic washer 100 has inclined sidewall 11 that, at said bottom opening, bends inward into a raised edge 12 obliquely oriented towards the inclined sidewall 11. Also, there are extensively represented the dimensional parameters that define said washer 100: thickness t, top opening angle 9, bottom opening angle 7, inner diameter d of raised edge 12, outer diameter G of raised edge 12, and deflection h meaning the height of raised edge 12, measured up from bottom opening.

In order to be able to accommodate said elastic washer 100, it is obvious that some of the above-enumerated dimensional parameters must be correlated, for example, outer diameter G must be smaller or at most equal to the countersink inner diameter D; inner diameter d of raised edge 12 must be large enough as to allow screw 200 to go through, but the difference between outer diameter G and inner diameter d of raised edge 12 must leave enough bearing surface for screw 200.

Figures 4 show step by step how the elastic washer deforms as the screw is tight, namely: Fig. 4a presents an unloaded state of the elastic washer; Fig. 4b presents the elastic washer partially loaded, when the screw advances on thread, but it is not entirely tight; and Fig. 4c presents the elastic washer fully loaded under the action of the screw fully tight. In this respect, raised edge 12 acts like a spring highly deformed, and produces a damping effect by compensating possible plastic deformations of parts P1, P2 or absorbing the shock energy produced by vibrations or shocks; in this case, the residual screwing torque is less affected.

Figures 5 illustrate an embodiment of a screw-nut connection using an elastic washer to ensure the connection of a compact brakingunitMEC, specifically for connecting a front bolt flange (not referenced). Fig. 5a shows said elastic washer, unloaded (initial state); Fig. 5b shows said elastic washer fully loaded (flattened, final state).

There were conducted simulations for the front bolt flange mentioned earlier, where a screw-nut connection employing an elastic washer according to invention has been used. There were chosen as parameters: countersink top opening angle, y= 90 deg; countersink top opening angle, e -95 deg; bottom opening angle T of said elastic washer 100, t = 180 deg (when flattened). The screw axial force was chosen 15000N on a M8 Gr8.8 class.

Conclusion was that the stress on the washer is under 500MPa, lower than the maximum stress for classical washers (1100MPa). From the point of view of the used materials, this solution is feasible and allows for more configurations and functionalities.

While certain embodiments of the present invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention as defined by the following claims.

List of reference signs P1 First part F2 Second part NKC Braking unit Elastic washer 11 Sidewall 12 Raised edge Screw S Countersink Countersink inner diameter Countersink height Countersink opening angle Deflection of elastic washer d Inner diameter of raised edge Thickness of elastic washer Outer diameter of raised edge Bottom opening angle Top opening angle

Claims (2)

1. Patent claims 1. Elastic washer for screw connection comprising a hollow, truncated metallic cone having an inclined sidewall, a top opening at the top of said cone, and a bottom opening at the bottom of said cone, the top opening being parallel to said bottom opening, largerthanthebottomopeningandconcentrictherewith, wherein the inclined sidewall bends radially inward into a raised edge obliquely oriented towards the inclined sidewall.
2. 2. A screw-nut connection with anti-losing torque mechanism, comprising: a) a screw with a head and an elongated threaded bolt; b) a nut having a threaded bore extending therethrough for 15 cooperating with the threaded bolt; c) an elastic washer with a hollow, truncated metallic cone having a top opening at the top of said cone, and a bottom opening at the bottom of said cone, the top opening being parallel to said bottom opening, larger than the bottom opening and concentric therewith, the elastic washer further having an inclined sidewall that at the bottom opening bends radially inward into a raised edge obliquely oriented towards the inclined sidewall, wherein when the threaded bolt is inserted in the bottom opening of the elastic washer and engages the threaded bore of said nut, the elastic washer moves axially along the threaded bolt and is fixed in rotation relative to the threaded bolt, while its raised edge progressively flattens down.