MXPA05004532A

MXPA05004532A - A vibration isolator assembly having altered stress characteristics and method of altering stress characteristics of same.

Info

Publication number: MXPA05004532A
Application number: MXPA05004532A
Authority: MX
Inventors: Paladichuck Robert
Original assignee: Cooper Standard Automotive Inc
Priority date: 2003-06-10
Filing date: 2004-06-10
Publication date: 2005-11-23
Also published as: EP1631753A2; JP2007500332A; KR20060036902A; WO2005001305A2; BRPI0406220A; CA2520739A1; EP1631753A4; WO2005001305A3

Abstract

A vibration isolator assembly, such as an isolator bushing or cradle mount, includes a housing and an isolator connected to the housing. A shaft assembly includes first and second mating components, the first component being connected to the elastomer and having a cavity of a first dimension for receiving the second component having a different, second dimension therein. The differing dimensions alter the stress characteristics of the vibration isolator assembly. In the preferred arrangement, the shaft assembly includes a first component comprising first and second portions, a thin layer of elastomer interposed between the first and second components and a second component which is inserted between the portions to relieve tensile stress in the isolator and, if desired, to impart a compressive stress in the isolator. The thin layer of elastomer permits the first components to be made more economically. The first component of the shaft assembly is made at a lower dimensional tolerance and subsequently produced to a higher dimensional tolerance by molding the thin layer of elastomer to a precision tolerance.

Description

INSULATING VIBRATION ASSEMBLY THAT HAS ALTERED TENSION CHARACTERISTICS AND METHOD TO ALTER CHARACTERISTICS BACKGROUND OF THE INVENTION

[0001] This invention relates to an insulating assembly of vibration which generically refers to a device that absorbs vibrations and dampens relative movement between two structures, such as an insulating assembly, bushing assembly, cradle assembly structure, etc.

[0002] A typical vibration isolator includes an outer housing and an internal mounting shaft joined by an insulator such as a molded elastomer (eg rubber). The elastomer provides insulation between the housing of the mounting shaft. Typically, the elastomer is molded with the housing arrow in a high temperature molding operation. This provides a desirable connection between the elastomer and the housing as well as between the elastomer and the mounting shaft. After the molding operation, the elastomer undergoes shrinkage as the piece cools. Depending on the design, an undesirable effect of this shrinkage is imparting tensile strength to the elastomer. In these cases, the fatigue resistance of the vibration insulator assembly is generally improved by relieving tension. A common way to relieve stress is to pass the external housing through a funnel or aperture of reduced diameter, to permanently reduce the diameter of the assembly. This structure is illustrated and described in the prior art representation of Figures 11-13 of the US patent. No. 6,094,818, and is also known to people with skill in the specialty.

[0003] Also, due to the general fatigue deficient performance of an elastomer under tension load, further improvements to the fatigue life can be achieved by going beyond the simple relief of imparted tensile strengths and imparting compressive strength to the elastomer Unfortunately, conventional methods for reducing the outer diameter of the insulator are limited in their effectiveness when there is desire to impart compression stresses to the elastomer. This is due, for example, to negative effects on the bond between the insulating and receiving materials, ie the adhesive layer between the insulation and the housing and the insulator and the mounting arrow. There are also limits on the extent of deformation to which the housing material can be subjected.

[0004] It will also be appreciated that a substantial amount of time and money is required to design, redesign, adapt a set of tools and machinery to manufacture a product and adapt, revise or reorganize a new set of tools and machinery to manufacture a new product. . The development cycle requires significant engineering and design time to ensure that the final product meets the final product specifications. If the specifications are altered during the development process, there is a need to remove, modify and reinstall the assembly in a short window of time. With respect to producing vibration and assembly insulators manufactured for drive trains, ie engines / transmissions in various consumer and commercial vehicles, as well as a tool for engineering purposes that allows use and adjustment of a train assembly system motor for improved insulation and performance, there is a need to address the aspects of fit and durability. If these aspects arise later in a program cycle, it is necessary to implement changes without a major re-design or a long revision time, even when the basic characteristics of the insulation are modified.

[0005] Thus, there is a need to improve the durability and adjustability of a vibration insulator assembly. Means for relieving tensile stress as well as varying the pre-compression level of the elastomer portion, they are desired. There is also a need to vary the travel limits of the elastomer portion. Finally, there is a need to overcome these problems without major revision or reprocessing of the prototype or production tools. SUMMARY OF THE INVENTION

[0006] The present invention describes an insulating vibration assembly having an arrow housing and an interconnected assembly by an insulator. The arrow assembly includes first and second coupling components, the first component of which is connected to the elastomer. The first arrow component forms a cavity of a first dimension to receive the second component having a second dimension slightly larger than the first dimension to alter tension characteristics of the vibration insulator assembly.

[0007] In a preferred embodiment of the invention, the insulator is an elastomer and the housing can already be metal or non-metal.

[0008] The second mention of the second component of the arrow assembly is pre-selected to relieve tensile stress in molding or impart compressive strength to the insulator.

[0009] In one embodiment, the first component of the arrow assembly is a split member and the second component is received on the divided plane.

[0010] The first and second components of the arrow assembly have a keyed contour relationship to selectively alter the deflection coefficient development characteristics against applied load.

[0011] In one embodiment, the first component of the arrow assembly is constituted by first and second mirror portions and the second component is received between the portions.

[0012] A thin layer of elastomer is sandwiched between the first and second components of the arrow assembly.

[0013] The first and second arrow mounting components have a control relationship "I" to selectively alter the accumulation characteristics of the deflection coefficient against applied load.

[0014] A primary benefit of the invention resides in the ability to relieve molded tensile stress and if it is desired to impart compressive strength without affecting the housing or the bonded layer between the housing and the elastomeric material.

[0015] Another benefit of the invention resides in the ability to manipulate the magnitude of the deflection coefficient against applied load, coefficient ratios, accumulation of coefficients and fatigue characteristics of components of the vibration insulator assembly.

[0016] Still another benefit resides in reducing costs of adjusting the set of required tools and reducing the development times or times associated with different designs, so that more options may become available within the constraints of a fixed development budget or predetermined.

[0017] Still another benefit resides in the ability to manufacture the first components more economically with a lower form tolerance by employing the elastomer layer that is produced to precision tolerance through mold design, to take into account variation and allow easy assembly of the arrow assembly.

[0018] Still another benefit is the ability to make changes to a design and adjust specifications without impacting a product launch program.

[0018] Still other benefits and advantages of the invention will be apparent to those skilled in the reading and compression art of the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] A more complete application of the present invention and many of its advantages can be obtained by reference to the following detailed description in conjunction with the accompanying drawings.

[0021] Figure 1 is a cross-sectional view illustrating a conventional vibration insulator assembly or suspension bushing.

[0022] Figure 2 is an elevation view of one embodiment of the present invention.

[0023] Figure 3 is a cross-sectional view taken generally on lines 3-3 of Figure 2.

[0024] Figure 4 is a perspective view of a second component of the arrow assembly separated from the rest of the vibration isolator assembly.

[0025] Figure 5 illustrates a separation of a first component of the arrow assembly on a split plane to receive the second component.

[0026] Figure 6 illustrates partial insertion of the second component into the remainder of the vibration insulator assembly.

[0027] Figure 7 is a perspective view of the final structure.

[0028] Figure 8 is an elevation view of another embodiment of the present invention, ie a cradle mounting structure.

[0029] Figure 9 is a cross-sectional view taken generally on lines 9-9 of Figure 8.

[0030] Figure 10 is an exploded perspective view of individual components of the assembly.

[0031] Figure 11 illustrates a further step of assembling the vibration insulator assembly or cradle assembly.

[0032] Figure 12 shows enlarging the cavity of a first component of the arrow assembly.

[0033] Figure 13 illustrates partial insertion of the second component of the arrow assembly.

[0034] Figure 14 illustrates the complete assembly of the second embodiment.

[0035] Figure 15 is a perspective view of the assembly or complete assembly of individual components of a third embodiment.

[0036] Figure 16 is a perspective view of another embodiment of the housing, insulator and first component of an arrow assembly.

[0037] Figure 17 is a perspective view of a second component of the arrow assembly of the third embodiment.

[0038] Figure 18 is a perspective view of a fourth embodiment of the housing, insulator and first component of the arrow assembly.

[0039] Figure 19 is a perspective view of the first component of the arrow assembly.

[0040] Figure 20 is a perspective view of the second component of the arrow assembly. DETAILED DESCRIPTION OF THE INVENTION

[0041] As a brief description, a conventional vibration insulator assembly A, is illustrated in Figure 1. The assembly includes a housing A and an arrow B which are interconnected by an insulator such as elastomer C As noted above, the elastomer typically is attached by mold to the arrow and the housing and provides vibration damping between the arrow attached to a first structure or component that moves relative to the housing and is attached to a second structure or component. .

[0042] A first embodiment of the present invention is illustrated in Figures 2-7. The vibration insulator assembly 20 includes a housing 22. Typically, the housing is a metal structure, although as will be appreciated in accordance with the present invention, alternate materials including non-metallic materials such as nylon can be employed to form the housing. As illustrated in Figures 2 and 3, when used as a mounting bushing, the housing typically assumes a generally cylindrical, ie circular, cross-sectional conformation. Subject to an inner surface 24 of the housing is an insulator 30. The insulator is often an elastomer or rubber construction due to the ability to insulate and reduce through-transmitted noise and vibration, due to the elastic nature of the material. Rubber in general is a non-compressible material that moves during loading and exhibits the desirable or desirable property that the more the rubber is compressed, the higher the rigidity. This accumulation ratio controls the noise, vibration and hardness associated for example with the environment of the vehicle. The elastomer is preferably bonded by mold to the inner surface 24 although it will be appreciated that other bonding arrangements such as adhesive bonding may be employed without departing from the scope and intent of the present invention. Likewise, an inner diameter portion 24 of the insulator is fastened to an arrow assembly 40, which preferably consists of first and second components 42, 44. The insulator is fastened to a first or outer surface 46 of the first component and again it is illustrated united by mold to it. As will be more apparent below, the first component 42 in this embodiment is defined with first and second portions 42a, 42b that are spaced apart and have exterior surfaces 46a, 46b attached to the insulator respectively. Front, inner surfaces 48a, 48b of the first component are separated on a split plane and slidably engage the second component 44 of the arrow assembly. As is probably best illustrated in Figure 2, and Figures 4-7, the first and second components 42, 44 of the arrow assembly have engagable keyed configurations that provide sliding insertion of the second component into a cavity defined on the plane divided by the first and second portions 42a, 42b of the first component, and equally resists relative movement between the first and second components in other directions. This vented, coupling shell configuration provides an interlocking feature that allows separate components (here three separate pieces) to melt and merge as a single component. For example, as illustrated in Figure 2, the first and second portions 42a, 42b of the first component have dovetail keyways 60 formed on opposite axial sides of the central axis 62. The keyways are dimensioned to receive projections or tail keys dovetail members 64 extending outwardly from the second component 44 of the arrow assembly. In this way, with continued reference to Figure 2, and further reference to Figures 4 and 5, it is seen that the first component 42 includes first and second mirror image portions 42a, 42b having a central rounded portion 66 that is fused in portions. outer radial generally planar 78. The first and second portions 42a, 42b are separable or are divided on the plane 70 that passes through the longitudinal axis 62. The second component is similarly contoured, has a central rounded portion 76 that is fused into portions outer radial generally planar 78 disposed on diametrically opposite sides of the rounded portion. As will be appreciated, although this contour has been successfully satisfied, still other variations or contours can be employed without departing from the scope and intent of the present invention.

[0043] As shown in Figure 4, the mirror-image portions 42a, 42b of the first component of the arrow assembly are integrally joined to the insulator. The portions are separable on the facing, coupling surfaces on the divided plane 70. In this manner, as illustrated in Figure 4, the front dovetail keyways 60 define an outer radial cavity portion and the rounded portions 66a 66b define a central cavity portion 80. When the portions 42a, 42b are placed in abutting relationship as illustrated in Figure 4, the cavities 80 defined by the keyways present a first dimension of the first component of the arrow assembly that it is smaller than a second dimension that is provided by the preselected coupling contour of the second component. In this way, and as will be appreciated from a comparison of Figures 4 and 5, the first and second portions 42a, 42b of the first component of the arrow assembly are separated on the divided plan 70 to enlarge the opening cavity 80 and allow reception selective slide of the first component 44 of the arrow assembly ah !. This sliding reception is shown in Figure 6, where the second component is partially received in the first component of the arrow assembly. Finally, the complete insertion of the second component in the first component is achieved and represented in Figure 7.

[0044] As noted in the above background discussion, the insulator is typically an elastomer molded between the housing and the arrow, here between the housing and the first component 42 of the arrow assembly. When cured, the elastomer ends with residual tensile strength. As noted, the previous technique has addressed this in a different way. Here, using a two-part arrow assembly alters the voltage characteristics of the vibration insulator assembly. At a predetermined dimension of the second component 44, the residual tensile strength in the elastomer is removed upon complete insertion of the second component in the first component. If the second component becomes even larger, then a predetermined compressive tension is formed in the insulator / elastomer. All this is achieved without affecting or adversely impacting the connection between the housing and the elastomer and also between the elastomer and the arrow assembly.

[0045] By varying the thickness of the second component, variable compressive stresses can be introduced into the elastomer. This has two basic effects. The first effect is associated with coefficient of deflection against applied load. The compression ratio characteristics of the main elastomer elements will increase in magnitude, approximately in proportion to the degree of pre-compression, while the shear coefficient characteristics of the elastomer elements themselves will remain relatively unaffected. This results in a change in the compressive-to-shear ratio of the final assembly.

[0046] The second effect deals with the life of fatigue. In general, an elastomer or rubber can tolerate increased levels of compressive strength under a much better cyclic load that tolerates lower amounts of tensile strength. In this way, by introducing compression stress by this method, the fatigue life of the assembly can be improved. The force separation of the molded split arrow assembly relieves the tensile strength resulting from shrinkage of the part, and imparts or introduces a desired compression strength to the molded rubber, if desired.

[0047] It is also known in these insulating assembly or bushing assembly structures to incorporate one or more openings in the elastomer. Thus, as illustrated in Figures 2-7, the elastomer is radially continuous between the housing and the arrow assembly in a diametral dimension (e.g. in the vertical direction as illustrated) and is discontinuous in another diametral direction ( for example in the horizontal direction as illustrated) through the inclusion of openings 90, 92. Here, the openings 90, 92 are generally symmetrical in the vertical and horizontal directions, but do not necessarily need to be symmetrical or similar. Likewise, the bordering rubber or border 94, 96 (Figure 2) defines cushion rubber that extends inward from the housing in the horizontal direction. By selectively altering the width dimension of the second component of the arrow assembly, ie by extending the planar portions 78 radially outwardly, the space between the arrow assembly and the border rubber is selectively altered. As the width of the arrow assembly increases, the amount of travel that the arrow assembly advances before contacting the border rubber in the housing will decrease. This transfers the load and tension more quickly from the central and main rubber elements to the external damping elements or borders and effectively alters the characteristics of accumulation of deflection coefficient against applied load. This has the effect of providing additional adjustment options and improved fatigue durability.

[0048] The present invention is also useful in other vibration isolating assemblies such as the cradle assembly shown in Figures 8-14. Since much of the structure and function are substantially identical, reference numbers with a premium suffix refer to similar components (for example the housing is referred to by the reference number 22 '), and the numbers identify the components. The primary distinction refers to the frame 100 of the vehicle wherein the housing 22 'of the cradle mounting structure 20' is also molded to the first component portions 42a, 42b of the arrow assembly. The sub-assembly, ie the housing 22", is initially inserted in the frame 100, ie the aperture 102. Instead of encountering high insertion forces as is typical with conventional structures, smaller frictional forces during insertion may be provided. of the housing in the frame according to the present invention Subsequently, the first portions of components of the arrow assembly are separated (Figure 12) to house the second component 44 'The second component is slidably received there (Figure 13), this way altering the tension characteristics of the insulator / elastomer, and also improving the abutting confining force between the housing 22 'and the frame 100.

[0049] The housing 22' is preferably metal, but it should be noted that others Composite or hard metals can be used, and the outer dimension of the housing can be related to any shape such as rectangular, square, a, circular, triangular, or any other shape or surface depending on the size and requirements necessary for the final use. Similarly, the arrow assembly is illustrated located at or near the center point of the housing, although that can be varied. Similarly, although it is preferred to extrude the arrow mounting components from aluminum, occasionally other materials, for example extruded castings, powdered metal, forgings, cold-worked steel or still other construction materials, may be used without departing from the scope of the invention. intention of the invention. The number and / or shape of the openings can also be varied and the elastomer insulation that is attached to the housing components can be attached with any other type of joint.

[0050] Similar to the aforementioned embodiments, two additional embodiments are illustrated in Figures 15-20. Since the majority of the structure and function are substantially identical, reference numbers with a double premium suffix (") refer to similar components (for example the housing is identified with the reference number 22"), and new numbers identify new ones. components in the additional mode of Figures 15-17. Likewise, reference numbers with the triple prime suffix ('") refer to similar components (for example the housing is identified by the reference number 22'") in the still further embodiment of Figures 18-20 and new numbers identify new components. The primary distinctions refer to the first component and second component of the arrow assembly.

[0051] As illustrated in Figures 15-17, the first and second components 42", 44" of the arrow assembly have engagable keyed configurations that provide slidable insertion of the second component into a cavity defined by the first component. This coupled keyed configuration provides an interlocking feature that allows the separated components to merge and function as a single component. Preferably, the first component has enlarged dovetail chavetenes 60"formed on opposite axial sides of the central longitudinal axis 62". The chavets are dimensioned to receive dovetail projections or keys 64"extending outward from the second component 44" of the arrow assembly. Thus, with continued reference to Figures 15-17, it is seen that the first component 42"has a central, rounded (though not circular) portion 66" that merges into the generally planar outer portions 68. "The second component similarly contoured, it has a central portion 76"that fuses into generally planar outer portions 78" disposed on diametrically opposite sides of the central portion.

[0052] Faced dovetail keyways 60"define an outer cavity portion and the unrounded portions 66"define a central cavity portion 80". The cavities have a first dimension of the first component of the arrow assembly that is smaller than a second dimension that is provided by the preselected coupling contour of the second component and allows selective sliding deflection of the second component 44"of the arrow assembly there. According to this, as it relates to the first embodiment and specifically when compared to the enlarged dovetail projections 64"and keyway 60", this configuration reduces the tolerance requirements for the dovetail interlock feature and simplifies assembling the arrow assembly in the cavity portion

[0053] As illustrated in Figures 18-20 and as will be more apparent below, the first component 42"'in this embodiment is defined by first and second mirror portions. 110a, 110b that are separated and having exterior surfaces 114a, 114b that are attached to the insulator 30 '"respec Inner facing surfaces 116a, 116b of the first component are separated by the insulator and slidably engage the second component 44 '"of the arrow assembly. The first and second components 42"'44"'have coupling configurations that provide sliding insertion of the second component into a cavity 80'" defined between the first and second portions 110a, 110b of the first component and the insulator 30 '"also resist relative movement between the first and second components in other directions, this coupling configuration provides an interlocking feature that allows the separate components to melt and function as a single component With reference to Figure 20, it is seen that the second component 44"'of the arrow assembly (sometimes referred to as the lay-out component) has a general outline of "I" or beam I with keyed portions 118a, 118b extending from a central portion 119. The first and second portions 110a, 110b of the first component have end portions curved 120a, 120b (Figure 19) sized to receive the contour "I" of the second component. The inner facing surfaces 116a, 116b of the first and second portions 110a, 110b of the first component 42 '"have a thin layer or skin or surface layer 122 of elastomer bonded thereto (Figure 18) .The elastomer 122 attached to the surfaces inner facing 116a, 116b of the first component, allows the first component (sometimes referred to as a capture plate or semi-arrow) to be manufactured more economically at a lower shape tolerance.The elastomer layer is produced to precision tolerances through mold design, thus compensating for any variation in the dimensions of the first component and allowing a consistent assembly of the first component and the second component As will be appreciated according to the present embodiment, alternate materials can be used to form the layer surface or elastomer layer

[0055] As shown in Figure 20, the first and second portions 110a, 110b of the first component The arrow assembly assembly is integrally joined with and separated by the insulator and defines a central cavity portion 80 '". This cavity defines the first dimension of the first component of the arrow assembly that is smaller than a second dimension that is provided by the pre-selected engagement "I" contour of the second component. In this way, the first and second portions 110a, 110b of the first component 43 '"allow sliding reception of the second component 44'" of the arrow assembly therein.

[0056] Again, it will be appreciated that the third and fourth embodiments of Figures 15-20 use first and second components that are preferably extruded designs due to ease of fabrication and assembly. The ability to use other shape designs or contours that are not extruded or brought to extrusion should be recognized to be within the scope and intent of the present invention.

[0057] In summary, manipulation of the magnitude of deflection coefficient versus applied load, coefficient relationships, coefficient accumulation, and fatigue characteristics of components is achieved using a molded insulator or common elastomer and interchangeable arrow assemblies of different designs . This is important since higher costs of required tool sets and longer development times are typically associated with the insulator / elastomer while the inserted arrow can be modified quickly and economically. The economical aspect of the vibrator insulator assembly means that more available options can also be made within the constraints of a development budget. This highlights yet another feature of the invention, where the ability to effect changes for subsequent adjustment and design specifications in the program can be achieved without impacting the product launch program.

[0058] The invention has been described with reference to the different modalities. Modifications and alterations will occur to others before reading and understanding this specification. For example, various other manufacturing steps may be employed or in a different sequence. Likewise, different materials may be employed or altered processes, without departing from the present invention. It is intended to include all these modifications and alterations as long as they fall within the scope of the appended claims or their equivalents.

Claims

CLAIMS | 1. An insulating assembly of vibration, characterized in that it comprises: a housing; an insulator connected to the housing to limit the transmission of vibrations; and an arrow assembly that is adapted for exposure to vibration forces, the arrow assembly includes first and second coupling components, the first component is connected to the insulator and has a cavity of a first dimension for receiving the second component having a second dimension and generally greater than the first dimension, to alter extension characteristics of the vibration insulator assembly. 2. The invention according to claim 1, characterized in that the insulator is an elastomer. 3. The invention according to claim 1, characterized in that the housing is made of metal. 4. The invention according to claim 1, characterized in that the housing is a non-metallic material. 5. The invention according to claim 4, characterized in that the housing is a nylon material. The invention according to claim 1, characterized in that the insulator is an elastomer that is molded in the housing and the first arrow mounting component. The invention according to claim 1, characterized in that the first component is contoured for slidable reception to the second component of the arrow assembly. 8. The invention according to claim 1, characterized in that the second dimension of the second component is pre-selected to relieve tensile stress molded into the insulator. T. The invention according to claim 1, characterized in that the second dimension of the second component is pre-selected to impart compression stress to the insulator. The invention according to claim 1, characterized in that the first component of the arrow assembly is a split member having first and second surfaces positioned in facing relationship. 1. The invention according to claim 10, characterized in that the second component is contoured to receive in the cavity of the first component on the first and second divided surfaces of the first component. The invention according to claim 10, characterized in that the first and second components of the arrow assembly include keyed contours to limit the relative movement of the first and second components of the arrow assembly in different directions to a direction of division between the first and second components. The invention according to claim 1, characterized in that the insulator includes at least one opening formed therein, whereby the arrow assembly is separated from the insulator by the opening at least one dimension of the second component in the direction of the At least one aperture is preselected to selectively alter the deflection coefficient accumulation characteristics against load applied in the direction. 14. The invention according to claim 1, characterized in that it also comprises a thin layer of material interposed between the first and second components of the arrow assembly. 15. The invention according to claim 14, characterized in that the thin layer of material is an elastomer that is provided in one of the first and second components of the arrow assembly. 16. The invention according to claim 15, characterized in that the thin layer of the elastomer is provided in the first component of the arrow assembly. 17. The invention according to claim 16, characterized in that the thin layer of the elastomer is provided on an inner surface of the first component. 18. Method for altering characteristics of deflection coefficient against load applied in a vibration insulator assembly having a housing, arrow and an insulator that interconnects the housing and an arrow to limit the transfer of vibration between them, the method is characterized in that it comprises the stages of: forming a cavity in the arrow; and varying a dimension in the arrow, to alter the deflection coefficient characteristics against applied load of the vibration insulator assembly. The method according to claim 18, characterized in that the step of varying includes the step of inserting a component of the arrow into the cavity. The method according to claim 18, characterized in that the step of varying includes forming an arrow assembly from a first divided component and inserting a second component of the arrow assembly between divided portions of the first component. The method according to claim 20, characterized in that the step of varying includes dimensioning the second component to relieve tensile strength in the insulator. 22. The method according to claim 20, characterized in that the step of varying includes dimensioning the second component to impart a compressive tension in the insulator. 23. The method according to claim 20, characterized in that the step of varying includes enlarging a dimension of the arrow assembly without effecting a bond formed between the insulator and the housing and between the insulator and the arrow assembly. The method according to claim 20, characterized in that it comprises the step of coating a surface of each divided component with a material to form a closed dimensional tolerance of the divided components. The method according to claim 20, characterized in that the insulator has at least one through opening, and the step of further varying includes the step of varying a dimension of the arrow in a direction of at least one opening in the insulator to alter its characteristics of deflection coefficient against applied load.