Coil Wound Spacer

Technical Field

This invention relates generally to screw- threaded fasteners and more particularly to washers or spacers used in connection therewith.

Background Art

During the construction of motor vehicles, bolts are used to secure parts together such as bolt- ing an oil pan on the underside of an engine block and bolting a manifold to an engine.

Since engine components are exposed to heat and resulting thermal stresses, important considerations are given to parts bolted together and to the bolts used. For example, when adjacent engine components heat up, they expand and stress the bolts which extend through mating surfaces of the abutting components.

When bolts are torqued to tightly secure a manifold to an engine block, the bolt is torqued within known limits to stretch or pre-stress that bolt. If this were not done, then the repetitive heating and cool¬ ing of the manifold, block and bolts could cause the bolts to eventually be loosened to a point where there was no longer a satisfactory tight abutment between the manifold and block. Thus, pre-stressing the bolt in a cold condition to a point which allows further bolt stretch in a hot condition, and which does not over- stress the bolt to a yield or even a failure point is preferred. Under these conditions ,_ bolts of increased length are advantageous since there is more material available to assume the stress. "Bolt stretch", as it

is commonly referred to, is the capability of a bolt to axially expand ^" without exceeding its elastic limit and thus yield or be permanently deformed. Therefore, using bolts of increased length enhances bolt stretch. In the past, spacers have been employed to permit the use of bolts of increased length where shorter bolts would otherwise be more appropriate. Such spacers are generally cylindrical and elongated, similar to a stack of flat washers formed into a solid wall cylindrical member.

A problem with such spacers is that, since they are usually formed from tubing stock, they have a tendency to be stiff and to split or yield when stressed due to such stock having seams, stringers or inclusions. To avoid this problem, thicker solid wall spacers have been used but this increases cost and adds some weight to the vehicle.

Another problem occurs when such spacers are inserted through molded organic plastic parts. The plastic parts, such as synthetic sound suppression panels used around engines and oil pans, etc., also attached to the engine with bolts, cannot withstand highly torqued bolts, otherwise the synthetic parts will crack and split. The spacers are inserted to relieve the plastic part of high torque loads placed on the bolts. However, the spacers generally have smooth outer cylindrical walls which eventually become loose relative to the plastic part.

In view of the above, it would be advantageous to provide an improved spacer which overcomes the prob¬ lems associated with the prior art.

Disclosure of Invention

In one aspect of the present invention, the problems pertaining to the known prior art, as set forth above, are advantageously avoided by the present invention.

This is accomplished by providing a coil wound spacer including a spiral wall cylindrical body having inner and outer annular surfaces . Each spiral includes a first portion which abuts each adjacent spiral and a second portion which is free of such abutment. The first portion is adjacent the inner surface and the second portion is adjacent the outer surface.

The foregoing and other advantages will become apparent from the following detailed description of the invention when considered in conjunction with the accom¬ panying drawings. It is ,to be expressly understood, however, that the drawings are not intended as a defini¬ tion of the invention but are for the purpose of ill¬ ustration only.

Brief Description of the Drawings

FIGURE 1 is a graphic view illustrating a portion of a vehicle including a synthetic oil pan cover bolted to an engine:

FIGURE 2 is a partial plan view illustrating a manifold bolted to an engine;

FIGURE 3 is a partial side elevational view taken along the lines III-III of Figure 2 ;

FIGURE 4 is a side elevational view illustra¬ ting the coil wound spacer of this invention.* FIGURE 5 is an isometric view illustrating a bolt and spacer in accordance with this invention;

FIGURE 6 is a side elevational view in partial cross-section illustrating a spacer in a synthetic

material member bolted to a metallic material member-

FIGURE 7 is a graph illustrating test re¬ sults comparing bolt torque in foot pounds vs. bolt microstrain between a solid spacer and a spiral spacer; and

FIGURE 8 is a side elevational view in partial cross-section illustrating a coil spacer compressed between a bolt head and a receptacle.

Best Mode for Carrying Out the Invention A spacer, Figure 4, is generally designated 10 and is formed of spiral wound coil 12 to form a cylindri¬ cal body 20. Preferably, coil 12 is formed of either square or rectangular stock and is made as a helical torsion spring with each spiral or winding 14 of coil 12 abutting each adjacent winding. Opposite ends 16,18 are ground flat.

During winding of coil 12, greater stress occurs at the outer surface 22 of body 20 and, as a re¬ sult, the thickness of coil 12 is reduced at outer sur- face 22. Thus, a spiral groove 24 is formed in outer surface 22 and extends from first end 16 to opposite second end 18 functioning as a means for limiting abut¬ ment between each adjacent spiral 14.

The thickness reduction at outer surface 22 causes a partial abutment between adjacent spirals 14. That is, a first portion 26 of each spiral 14 abuts each adjacent spiral at inside surface 28 and a second portion 30 of each spiral 14, formed by groove 24, is free of abutment with each adjacent spiral 14 (see Fig. 8) .

A spacer formed as described above includes a basic torsion spring function, that is, storage and release of energy due to torsional deflection. How¬ ever, spacer 10, due to partial abutment between

spirals 14 provides a solid height designated "h" sim¬ ilar to that of a solid wall spacer, but exhibits spring-like deflective qualities through twisting or torsional loadings. Also, a spacer thus formed includes a continuous spiral abutment surface 32 (Fig. 8) ex¬ tending from first end 16 to second end 18 which func¬ tions as a means providing a continuous frictional surface between opposite ends 16,18.

Spacer 10 (Figs. 2 and 3) may be used in com- bination with bolt 34 for retaining a member such as a manifold 36 bolted to a receptacle such as an engine 38 of vehicle 39. In this instance, spacer 10 is compressed between bolt head 40 and receptacle 38. If desired, a washer 55 may be used in connection with bolt head 40 to enhance load distribution. Thus, spiral abutment surface 32 provides a continuous frictional surface interconnecting bolt head 40 and receptacle 38 via a flange 48.

Figs. 1 and 6 illustrate bolt 34 in combination with a synthetic material member such as an organic plastic cover 50 for an oil pan 52 bolted to engine 38. Spacer 10 extends through cover 50 and is compressed between bolt head 40 and oil pan 52 which may be metal or organic plastic as is well known. As best shown in Fig. 6, the synthetic material 54 of cover 50 extends into groove 24 and thus aids in mechanical retention of spacer 10 within cover 50.

Figure 5 illustrates bolt 34 including a clock¬ wise spiral or right-hand thread 42 and spacer 10 in- eluding a left-hand or counterclockwise spiral or coil 12 indicated by an arrow designated 45. Thus, it can be seen that tightening bolt 34 in a clockwise direction indicated by an arrow designated 44 will tend to tor¬ sionally wind coil 12 in a similar direction indicated

by an arrow designated 46. It is shown in Fig. 7 that coil spacer 10, due to its ability to torsionally wind, is less stiff than previously known solid spacers. For example, the following table is based on test results illustrated in Fig. 7, comparing torque (in foot pounds) applied to a 3/8" bolt and spacer versus bolt micro- strain in pounds per square inch.

EXAMPLE

Torque Bolt Microstrain (psi) (foot pounds) Coil Solid

5 250 650

10 470 800

15 600 1160

20 820 1720

25 1020 2120

30 1240 2450

Based on the foregoing, it is believed that some of the clockwise torque applied to the bolt 34 is assumed by the clockwise torsional winding tendency of spacer 10 due to thread 42 and coil 12 being in opposite spiral directions as illustrated in Fig. 5. As a result of the ability of spacer 10 to torsionally wind, the spacer is less stiff than conventional spacers and less strain is experienced by bolt 34. Once torqued to a de¬ sired amount, it is believed that the stored energy in torqued coil 12 induces tensile stress on bolt 34.

Industrial Applicability

Bolt 34 is threaded into a receptacle 38 and spacer 10 is compressed between bolt head 40 and recep- tacle 38, Fig. 8. A first portion 26 of each spiral 14 abuts each adjacent spiral 14 adjacent inner surface 28 and a second portion 30 is free of such abutment adjacent outer surface 22 due to groove 24. Spiral abutment 32 extends from bolt head 40 at first spacer end 16 to

receptacle 38 at second spacer end 18 to provide a con¬ tinuous frictional surface when spacer 10 is compressed between bolt head Q and another member such as recep¬ tacle 38 or the like. The torsional flexibility of spacer 10 reduces spacer stiffness and bolt strain while continuous spiral surface 32 provides solid spacer height "h".

The foregoing has described a spacer formed from wound coil to form a spiral wall cylindrical body having abutting surfaces between adjacent coils.

Other aspects, objects and advantages of this invention can be obtained from a study of the drawings, the disclosure and the appended claims.