US3838207A

US3838207A - Electrical insulating member such as a distributor cap

Info

Publication number: US3838207A
Application number: US00396193A
Authority: US
Inventors: W Anselment; W Holl
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1972-09-12
Filing date: 1973-09-11
Publication date: 1974-09-24
Anticipated expiration: 1991-09-24
Also published as: DE2244583B2; FR2199210B1; FR2199210A1; IT993206B; BR7307029D0; JPS4992431A; DE2244583C3; GB1444766A; ES418671A1; DE2244583A1; SE393840B

Abstract

A hollow insulating member has a wall which consists of two layers, one of which at least partly surrounds the other. One of these layers is composed of an electrically insulating substance whereas the other of these layers is composed of a thermally insulating foam material. Air is entrapped in the foam material, and may also be entrapped in an air gap between the two layers.

Description

United States Patent Anselment et al.

1 Sept. 24, 1974 ELECTRICAL INSULATING MEMBER SUCH AS A DISTRIBUTOR CAP Inventors: Wolfgang Anselment; Walter Holl,

both of Stuttgart, Germany Assignee: Robert Bosch GmbH, Stuttgart,

Germany Filed: Sept. 11, 1973 Appl. No.: 396,193

Foreign Application Priority Data Sept. 12, 1972 Germany 2244583 US. Cl 174/138 F, 174/209, 200/19 WG Int. CL. HOlr 39/60, l-lOlh 19/06, HOlb 17/60 Field of Search 174/77 S, 110 F, 138 F, 174/139, 209; 123/143 C, 146.5 R, 146.5 A, 169 P, 169 PA, 169 PH; 200/19 DC, 19 DR, 19 WG, 168 G; 220/9 F; 339/26, 116 R References Cited UNITED STATES PATENTS 2/1957 Ebel et a1. 174/110 F UX 3,009,986 11/1961 Stephens 174/138 F X 3,037,652 6/1962 Wa1lace....-

220/9 F X 3,243,504 3/1966 Johnson 174/138 F 3,625,785 12/1971 Loberod et a1 220/9 F X FOREIGN PATENTS OR APPLICATIONS 1,932,127 1/1971 Germany 123/1465 R 2,011,242 9/1971 Germany 123/1465 A Primary Examiner-Laramie E. Askin Attorney, Agent, or Firm-Michael S. Striker A hollow insulating member has a wall which consists of two layers, one of which at least partly surrounds the other. One of these layers is composed of an electrically insulating substance whereas the other of these layers is composed of a thermally insulating foam material. Air is entrapped in the foam material, and may also be entrapped in an air gap between the two layers.

ABSTRACT 15 Claims, 2 Drawing Figures ELECTRICAL INSULATING MEMBER SUCH AS A DISTRIBUTOR CAP BACKGROUND OF THE INVENTION The invention relates generally to insulators or insulating members. More particularly, the invention relates to hollow insulators which are adapted to receive a current-conducting lead and the wall or walls of which have electrically insulating properties. Of special interest are distributor caps which are adapted to receive a current-conducting lead connected to the ignition system of a combustion engine.

The electrically insulating walls of the known articles of the type under discussion are composed of a solid or dense substance, and the base material for the latter is advantageously a polyester resin. This particular base material is used because of its good electrical insulating properties. However, if a known article of this type is used, for example, in the motor of a motor vehicle, to seal or enclose a space therein and a large amount of heat is generated, then, if the article is cooled from exteriorly thereof, e.g., due to atmospheric changes, due to water being sprayed thereon or the like, condensation of water takes place on the inner surfaces of the walls of the article. If this condensed water comes into contact with dirt particles or with the nitric oxide produced by electrical sparks, creepage or leakage paths may form, i.e., paths along which electrical current will flow preferentially. Such leakage paths decrease the electrical insulating properties of the article and even- SUMMARY OF THE INVENTION It is, accordingly, a general object of the invention to provide a novel insulator.

More particularly, it is an object of the invention to.

provide a hollow insulating member of the type under discussion which satisfactorily avoids the abovementioned shortcomings associated with the known constructions.

Still more specifically, it is an object of the invention to provide a hollow insulating member of the type under discussion, wherein the condensation of water is at least minimized.

In accordance with these and other objects, the invention provides, as a novel article of manufacture, a hollow insulating member, particularly a distributor cap adapted to receive at least one current-conducting lead connected to the ignition system of a combustion engine, which comprises a wall having a first layer composed of an electrically insulating substance, and a second layer composed of a thermally insulating material. One of the layers surrounds at least a portion of the other of the layers and the wall has at least one body of air entrapped therein.

The first and second layers may be fast with one another. Due to the provision of a thermally insulating layer, the degree of water condensation on the inner surface or surfaces of the novel article when the latter is heated and a cold substance is applied to the outer surface or surfaces of the same, is substantially less than in the known constructions.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a perspective view, partly in section, of a distributor cap according to one embodiment of the invention; and

FIG. 2 is a view similar to FIG. 1, but showing another embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS For purposes of this specification, the invention will be described with reference to a distributor cap, i.e., to the cap of a distributor which is used in the electrical ignition system of a motor vehicle. It is to be understood, however, that this is in no way intended to limit the invention to such an application only. A

Referring now to FIG. 1, the cap of a non-illustrated distributor is indicated generally at I. The wall of the cap 1 comprises an electrically insulating layer 2, that is, the layer 2 is of an electrically insulating substance. The layer 2 issubstantially cup-shaped and is composed of a dense substance. Advantageously, although not necessarily, the material of the layer 2 is a polyester resin. The layer 2 may have a thickness of substantially 2 to 4 millimeters, a currently preferred thickness being about 3 millimeters.

The cap 1 has a tubular wall portion and another wall portion which extends transversely to the axis of the tubular wall portion so that the cap I has the form of a hollow body. The transverse wall portion is provided with

tubular projections

3, 4, 5, 6 and 7 each of which is adapted to receive a non-illustrated currentconducting lead. The middle projection 3 is adapted to receive a lead connected to the ignition coil provided in the ignition system of a combustion engine and to which the ignition voltage derived from the secondary winding of the ignition coil is supplied. On the other hand, each of the

projections

4, 5, 6 and 7 is adapted to receive a lead which distributes the ignition voltage to the spark plugs provided in the respective cylinders of the combustion engine. For the sake of clarity, the component parts of the combustion engine have not been illustrated here. The

projections

3, 4, 5, 6 and 7 may be formed integrally with the cap 1 if desired, and this is the case in the embodiment shown in FIG. 1.

In order to prevent, or at least substantially reduce, the condensation of water on the inner surface or surfaces of the cap 1, the wall of the cap 1 is further provided with a heat or thermally insulating sleeve or jacket 8. In the exemplary embodiment of FIG. 1, the sleeve 8 is shown as being in the form of a layer 9 composed of a foam material. The layer 9, which may be fast with or connected with the layers 2, is illustrated here as being provided exteriorly of the layer 2 although it might also be provided interiorly thereof. It may be seen that the layer 9 surrounds at least a portion of the layer 2. The layer 9 may be provided on the layer 2 in simple fashion by selecting for the layer 9 a hard foam which, during production of the cap 1, may be formed as a coating on the exterior of the electrically insulating layer 2 by spraying or injection molding. It is preferable to use a closed-cell hard foam (a foam material wherein the cells do not communicate with one another) or, at least, a hard foam having a substantially non-porous outer surface. The reason is to prevent penetration of dirt and moisture into the cells of the foam material, since this could destroy the effectiveness of the layer 9 as a thermal insulator. It has been found that a polyurethane foam is particularly, although not exclusively, suitable for this purpose.

It is self-understood that, instead of providing the cap 1 with a hardened layer 9 of a foam material which is fixedly secured thereto, the layer 9 of the thermally insulating sleeve 8 may also be composed of an elastic material. An elastic foam material such as, for example, foam rubber, is especially suitable in such an instance, although other elastic materials may also be used. When the sleeve 8 comprises an elastic material, the sleeve 8 may be fastened to or connected with the cap 1 by providing the former with a shape which corresponds to that of the cap 1 but choosing the inner dimensions of the sleeve 8 to be smaller than the outer dimensions of the layer 2. By then prestressing the sleeve 8, placing the same over the layer 2 and the

pro jections

3, 4, 5, 6 and 7 and then releasing the tension, the sleeve 8 is held in an expanded state by the layer 2 and thereby caused to elastically bear against the same. This type of construction of the sleeve 8 has the advantage that it may be subsequently provided on distributors which have already been mounted, whenever desired.

The use of foam (i.e., cellular) material for the layer 9 is highly advantageous, because the body of air entrapped in the totality of cells of the layer 9 acts as a very efficient insulator. Evidently, the employment of the layer 9 makes it possible to make the layer 2 of lesser thickness, since the layer 2 now exclusively has an electrically insulating function, and thus to save material and reduce manufacturing expenses. Moreover, the cap 1 can now also be lighter in weight, a consideration which may be of importance in some circumstances.

The embodiment of FIG. 2 is largely similar to that of FIG. l, and like reference numerals have been used to designate like elements.

The essential difference here is that the layer 10, which replaces the layer 9 of FIG. 1, is spaced from the layer 2 and defines with the same an airgap 11. The layer 10 may be of rigid synthetic plastic material, for example of solid (non-foamed) polyester, of polyester or polypropylene foam, or rigid polyurethane foam having a non-cellular integral skin. Openings 12 are provided, through which the

tubular portions

3, 4, 5, 6 and 7 extend to the exterior of layer 10.

In this embodiment, the body of air entrapped in the gap 11 provides excellent thermal insulating properties, which are further improved if the layer 10 is of foam material and thus contains additional air which is entrapped in its cells.

In this embodiment, also, the layer 10 can be applied subsequently to an already mounted distributor. For this purpose, the

layers

2 and 10 are releasably connected, the layer 10 being provided with the illustrated radially inwardly extending projections 14, which are located between respective circumferentially spaced axial slots 13 and which each snap behind a bevel 15 provided on the layer 2 at the open side of the cap 1.

In the region of the open side of the cap 1, the layer 10 has a portion of enlarged inner diameter. The shoulder 16 formed at the juncture between the smaller and the larger inner diameter engages a bead 17 formed on the layer 2. In addition to or in lieu of this arrangement, the juxtaposed surfaces of the

layers

2 and 10 may be provided with projections 18 (only one shown) which serve to maintain these layers at the desired spacing, to thus create and maintain the gap 11.

As has been previously pointed out, the novel article has been illustrated in the form of a distributor cap, but is not limited to this application. It could as well be an ignition coil housing or a part thereof, for example, a closure cap for such a housing, or be used in still a different form and for a still different application.

It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of applications differing from the types described above.

While the invention has been illustrated and described as embodied in a distributor cap, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims What is claimed as new and desired to be protected by Letters Patent is set forth in the appended:

l. A hollow insulating member having an open end and a closed end, particularly a distributor cap adapted to receive at least one current-conducting lead connected to the ignition system of a combustion engine, comprising a wall having a first layer composed of an electrically insulating substance, a second layer composed of a thermally insulating material, one of said layers being an outer layer and surrounding at least a portion of the other of said layers which is an inner layer, said wall having at least one body of air entrapped therein; a bead located on an outer surface of the inner layer of said wall, a shoulder located on an inner surface of the outer layer of said wall engaging said bead, so as to at least in part connect said inner layer to said outer layer, and a plurality of tubular projections extending from said closed end and each adapted to receive a current-conducting lead.

2. An article as defined in claim 1, whereinrsaid layers are fast with one another.

3. An article as defined in claim 1, wherein said one layer is said second layer.

4. An article as defined in claim 3, said second layer having an outer surface; and wherein said outer surface is substantially non-porous.

S. An article as defined in claim 3, wherein said material is an elastic material.

6. An article as defined in claim 5, wherein said elastic material is a foam material having cells wherein said body of air is entrapped.

7. An article as defined in claim 5, wherein said first layer has first outer dimensions, and said second layer has second inner dimensions smaller than the corresponding ones of said first outer dimensions so that said first layer maintains said second layer in an expanded state and causes the latter to bear elastically against said first layer.

8. An article as defined in claim 1, wherein said material is a foam material having cells wherein said body of air is entrapped.

9. An article as defined in claim 8, wherein said foam material is a hard foam.

10. An article as defined in claim 9, wherein said hard foam is a closed-cell foam.

11. An article as defined in claim 9, wherein said hard foam is polyurethane foam.

12. An article as defined in claim 1, wherein said first and second layers are spaced apart over at least part of said portion and define with one another a gap in which air is entrapped.

13. An article as defined in claim 12; and further comprising spacing means intermediate said first and second layers for spacing the same from each other to thereby provide said gap.

14. An article as defined in claim 1, wherein said second layer is of a rigid synthetic resin.

15. An article as defined in claim 1, wherein said first and second layers are releasably connected with one another.

Claims

1. A hollow insulating member having an open end and a closed end, particularly a distributor cap adapted to receive at least one current-conducting lead connected to the ignition system of a combustion engine, comprising a wall having a first layer composed of an electrically insulating substance, a second layer composed of a thermally insulating material, one of said layers being an outer layer and surrounding at least a portion of the other of said layers which is an inner layer, said wall having at least one body of air entrapped therein; a bead located on an outer surface of the inner layer of said wall, a shoulder located on an inner surface of the outer layer of said wall engaging said bead, so as to at least in part connect said inner layer to said outer layer, and a plurality of tubular projections extending from said closed end and each adapted to receive a currentconducting lead.

2. An article as defined in claim 1, wherein said layers are fast with one another.

5. An article as defined in claim 3, wherein said material is an elastic material.

9. An article as defined in claim 8, wherein said foam material is a hard foam.