Information
-
Patent Grant
-
6759796
-
Patent Number
6,759,796
-
Date Filed
Wednesday, September 26, 200122 years ago
-
Date Issued
Tuesday, July 6, 200420 years ago
-
Inventors
-
Original Assignees
-
Examiners
- Patel; Vip
- Zimmerman; Glenn
Agents
-
CPC
-
US Classifications
Field of Search
US
- 313 143
- 313 144
- 126 169 E
-
International Classifications
-
Abstract
A spark plug is described having a partially cylindrical insulator element and a housing surrounding the insulator element on the side of a base part. The insulator element and the housing are connected with one another by at least one material bond and/or one friction-lock connection aligned in the radial direction. A compact spark plug can be produced using this type of connection. In particular, the diameter of the spark plug is smaller than the diameter of known spark plugs having the same characteristics.
Description
FIELD OF THE INVENTION
The present invention relates to a spark plug which includes a partially cylindrical insulator element and a housing which surrounds the insulator element. The present invention also relates to a corresponding method of production. The insulator element typically includes a ceramic material. In contrast, the housing is made of metal.
BACKGROUND INFORMATION
Various methods are known for connecting the insulator element and the housing. Basically, these can be divided into hot assembly and cold assembly. In hot assembly, the insulator is inserted into the housing. The insulator is then pretensioned in the axial direction by reshaping an inwardly curved flange on the housing. The final pretension in the axial direction is achieved through a shrink fit process. During the shrink fit process, a shrinkage recess which surrounds the housing circumferentially is inductively heated to approximately 1050° C. by a current pulse. As the shrinkage recess cools, the material in the region of the shrinkage recess shrinks. The housing is thus essentially secured on a projection of the insulator element by axial forces. At the same time, the housing is axially friction-locked between two shoulders of the insulator.
In cold assembly, a talcum powder packet is inserted between the flange, which is not yet curved, and the insulator element. Subsequently, the talcum powder packet is compressed by the reshaping process of the flange. In cold assembly as well, the insulator element must have a projection on which the inwardly curved flange is secured.
The known spark plugs do have connections which have high mechanical strength and are gas-tight, but they require a comparatively costly reshaping process.
SUMMARY OF THE INVENTION
An object of the present invention is the provision of a spark plug having a simple construction and a corresponding method of production, with the spark plug particularly being more compact than spark plugs, produced with typical methods of production, having similar or identical operating characteristics, e.g., with regard to thermal conductivity and with regard to electrical characteristics.
The present invention is based on the consideration that reshaping is only possible if the housing has a significantly larger diameter than the insulator element at the reshaping position. In addition, a peripheral projection of the insulator element in the region of the reshaping position must secure the housing.
In the spark plug according to the present invention, the insulator element and the housing are connected to one another by at least one material bond and/or one friction-lock connection aligned in the radial direction. The material bond is, e.g., a metallic soldered or welded connection and the radial friction-lock is a shrink fit connection.
This connection forms at least a significant portion of the cohesion of the housing and the insulator element. If the material bond and/or the friction-lock connection aligned in the radial direction absorb a part, e.g., approximately half, of the forces which act between housing and insulator element, reshaping can be reduced or even avoided completely, because the cohesion of insulator element and housing is achieved in another way. In addition, the peripheral projection on the insulator element can be designed smaller or even be dispensed with completely. If the other properties are unchanged, the spark plugs according to the present invention are more compact than comparable typical spark plugs, because the diameter of the housing selected can be smaller. Spark plugs according to the present invention have smaller internal thread diameters and smaller screw-in devices than known spark plugs having the same thermal value. For example, the outer diameter of the internal thread can be reduced from M14 to M12. Spark plugs produced until now with M8 threads can now be produced with M6 threads.
In a refinement of the spark plug according to the present invention, the diameter of the insulator core remains approximately the same or increases as the distance to the free end of the base part of the insulator (referred to in short in the following as base part) increases in the entire region surrounded by the housing. For example, the insulator core tapers in a stepped shape toward the free end of the base part. In other words, the insulator core does not have a projection in the region of the housing used to secure the housing and is therefore more compact than comparable known insulator elements.
In a subsequent refinement, the inner diameter of the housing in the region of the connection remains approximately the same or increases as the distance to the free end of the base part increases. In other words, the housing no longer has an edge which is curved inward. This allows the use of a housing with a smaller diameter, because reshaping of the edge is no longer necessary.
In a subsequent refinement, the diameter of the insulator element at the end further from the base part in the region adjoining the region surrounded by the housing is approximately equal to the largest diameter of the insulator core in the surrounded region. The insulator element is preferably cylindrical both inside a section of the housing and outside the housing, i.e., it has a uniform diameter. The fewer the projections and constrictions that are located on the insulator element, the more crack resistant it is.
In a subsequent refinement, the housing has at least one tubular section in which the diameter of the insulator core is only slightly smaller than the inner diameter of the housing lying at the same distance to the free end of the base part. The connection lies along the circumference of the insulator element in the gap between insulator element and housing. In this refinement, the connection has a double function, because it is used both for connecting insulator element and housing and for sealing the combustion chamber in which the spark plug is to be inserted.
The tubular section lies close to the base part and/or further from the base part. If the section is close to the base part, it is subjected to greater mechanical load and higher temperatures. On the other hand, the insulator element is thin near the base part, so that the circumference is smaller than further away from the base part. If the connection also seals the combustion chamber gas-tight, the combustion chamber is enlarged only insignificantly if the connection is near the free end of the base part. If the connection is at a greater distance from the free end of the base part, for example at the end of the housing further from the base part, the mechanical loads and the temperature effect are less. The connection will not be loaded as strongly during operation of the spark plug. If the connection is in multiple zones, the disadvantages of one position can be avoided by the advantages of the other position.
In embodiments, the connection is a soldered connection, e.g., a hard soldered connection, an active soldered connection, a welded connection, and/or an adhesive connection. For the welded connection, the known welding methods are used, e.g., friction welding or gas fusion welding. Reactive adhesives, whose components react during curing, are, for example, used as the adhesive for the adhesive connection. However, hard-setting adhesive materials whose components do not react during curing are, for example, also used.
In an alternative refinement, the housing contains at least one tubular section in which the diameter of the insulator element is slightly larger than the inner diameter of the housing, when the insulator element is not in place, lying at the same distance to the free end of the base part. Therefore, this is a compression connection, for example a longitudinal compression connection or a transverse compression connection. During the production of the transverse compression connection, for example, the housing is heated. Subsequently, the insulator core is inserted into the expanded housing. As the housing cools, it shrinks and tightly surrounds the insulator element.
In a refinement of the spark plug according to the present invention, insulator element and housing are connected with one another using an interlayer which was produced before housing and insulator were connected. The interlayer is produced from a material which is capable of being connected well on one side with the ceramic and on the other side with the metal of the housing. The interlayer can, for example, be formed by a thin sheet steel sleeve. However, interlayers made of other materials, e.g., plastic or glass melt, are also used. The interlayer is applied or attached to the insulator element. Thus, interlayers can be deposited directly on the insulator element. The interlayer is attached to the housing using a material bond and/or a friction-lock connection.
If, in an embodiment, the interlayer also extends into regions which lie outside the connection region, the interlayer can be attached better to the insulator, because the connection surface between the insulator and the interlayer is larger.
In a refinement, there is a gap between the housing and the interlayer in the region of the section lying closer to the base part. In the region of a section lying further away from the base part than this section, the interlayer is connected with the housing. In the section lying further away, the interlayer can also be connected with the insulator. However, in an alternative, there is a gap between interlayer and insulator in the section lying further away. In this refinement, a small peripheral ring of the interlayer is exposed in the gap between the insulator and housing. The ring-shaped section forms a kind of membrane which absorbs mechanical loads.
In refinements of the spark plug, the insulator element includes ceramic. The surface of the ceramic is treated in the region of the connection in such a way that the load capacity of the connection is enhanced. Roughening of the surface and/or applying a metallic topcoat are suitable methods.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1A
is a first illustration of a compact spark plug with a damping resistor made of a solidified glass melt.
FIG. 1B
is a second illustration of the compact spark plug shown in FIG.
1
A.
FIG. 2A
is a first illustration of a compact spark plug without a damping resistor.
FIG. 2B
is a second illustration of the compact spark plug shown in FIG.
2
A.
FIG. 3A
is a first illustration of a compact spark plug with a nondestructively replaceable damping resistor.
FIG. 3B
is a second illustration of the compact spark plug shown in FIG.
3
B.
DETAILED DESCRIPTION
FIG. 1A
shows a compact spark plug
10
in a partial section view. Spark plug
10
includes a cylindrical insulator
12
which tapers at its end toward an insulator base
14
. Insulator
12
is penetrated along its longitudinal axis
16
by a through hole
18
, whose diameter in the region of a central electrode
20
is somewhat smaller than along the rest of insulator
12
. The half of insulator
12
containing insulator base
14
is almost completely surrounded by a housing
22
. Viewed from insulator base
14
outward, housing
22
includes, in this sequence, a ground electrode
24
, a threaded sleeve
26
having, for example, M14 external thread
28
, a peripheral groove
30
for a sealing ring which provides a seal in the conical seal seat, a central part
32
, and a double hex insertion nut
34
. Housing
22
is screwed into an engine block of the vehicle and is connected with the ground electrode. Insulator
12
, which is made of ceramic, insulates housing
22
and central electrode
20
as well as further elements for current conduction located in through hole
18
.
In through hole
18
there are, in sequence from central electrode
20
to a terminal stud
36
screwed onto insulator
12
for connection of an ignition cable, an electrically conducting contact
38
, a glass melt
40
, which forms a damping resistor, an electrically conducting contact
42
, and an electrode
44
. Electrode
44
tapers toward insulator base
14
and forms a section
46
having a somewhat smaller diameter than the main part of electrode
44
.
Housing
22
is connected to insulator
12
by a welded connection
48
. Welded connection
48
extends longitudinally up into threaded sleeve
26
from the end of housing
22
further from the base part. Welded connection
48
extends completely around the circumference lying transverse to the longitudinal direction. A gap between insertion nut
34
and insulator
12
is completely closed by welded connection
48
. A gap formed between the end of threaded sleeve
26
further from the base part and insulator
12
is also completely closed by welded connection
48
.
FIG. 1B
shows a connection
48
b
, in which a housing
22
b
, constructed like housing
22
, of a spark plug
10
b
having an insulator
12
b
is only welded in a region
50
which extends along the half of a threaded sleeve
26
b
further from the base part. Region
50
extends, for example, 10=10 mm in the longitudinal direction, i.e. in the direction of a longitudinal axis
16
b
of insulator
12
b
. Welded connection
48
b
extends along the lateral surface of insulator
12
b
in region
50
.
In the region of a insertion nut
34
b
constructed like insertion nut
34
, a peripheral gap
52
remains between insulator
12
b
and insertion nut
34
b
. Otherwise, spark plug
10
b
is constructed like spark plug
10
.
Due to welded connection
48
or
48
b
, spark plug
10
can be made very compact. The largest diameter D of insulator
12
is, for example, 10.4 mm. Diameter D remains constant in the main part of insulator
12
and therefore essentially determines the overall space for the installation of spark plug
10
. Insertion nut
34
is implemented as a double hex nut, e.g., for a width
14
across flats. This is only possible because insulator
12
has no projections in the region of insertion nut
34
.
In other exemplary embodiments, an interlayer is used, in place of welded connection
48
or
48
b
, which is welded or soldered onto insulator
12
or
12
b
and onto housing
22
or
22
b
. The welded or soldered connections, respectively, between the interlayer and insulator
12
and between the interlayer and housing
22
are in the region of central part
32
and threaded sleeve
26
and in the region of insertion nut
34
. Alternatively, there are connections between the interlayer and insulator
12
b
both in the region of threaded sleeve
26
b
and in the region of insertion nut
34
b
. In the alternative, a connection exists between the interlayer and housing
22
b
only in the region of threaded sleeve
26
b
. A gap remains between the interlayer and insertion nut
34
b
in the region of insertion nut
34
b.
FIG. 2A
shows, in a partial section view, a compact spark plug
10
c
which has no damping resistor. Functional elements shown in
FIG. 2A
which are constructed essentially like those described with reference to
FIG. 1A
have the same reference numbers in
FIG. 2A
but are suffixed with the lowercase letter c. This particularly applies to reference numbers
12
c
to
36
c
. Central electrode
20
c
has a diameter in its main part which is smaller than the diameter of central electrode
20
. This allows the diameter of through hole
18
c
and outer diameter Dc of insulator
12
c
to be reduced. Central electrode
20
c
is coated with a hard solder paste and then inserted through hole
18
c
into insulator
12
c
. A contact pin
100
, made of, for example, a brass alloy, is inserted into through hole
18
c
. When terminal stud
36
c
is screwed in, contact pin
100
is compressed and buckles at multiple buckling positions.
Central electrode
20
c
is secured by contact pin
100
. Insulator
12
c
is then transported through a high vacuum furnace at a temperature of a magnitude between 600° C. and 900° C., for example 800° C. The hard solder paste melts and connects central electrode
20
c
firmly and permanently with insulator
12
c
. This connection is also gas-tight. The hard solder paste is, for example, applied in the region of a shoulder
102
, at which the inner diameter of through hole
18
c
decreases. Alternatively, central electrode
20
c
can be coated almost completely with hard solder paste, so that central electrode
20
c
and insulator
12
c
are also connected in the region of insulator base
14
c.
There is an interlayer
104
on insulator
12
c
which is less than, for example, 1mm thick. Interlayer
104
is connected to insulator
12
c
via, for example, a hard soldered connection, in the region of a step
106
d
of insulator
12
c
, which is approximately, e.g., 11=12 mm long. At the end of step
106
d
further from the base part, interlayer
104
conforms to the shape of insulator
12
c
, which widens. In a section
108
, however, interlayer
104
forms a tubular section having a larger inner diameter than outer diameter Dc of insulator
12
c
. Thus, there is a gap
110
in the region of section
108
between interlayer
104
and insulator
12
c
. In section
108
, interlayer
104
is connected on its outer side with the inner side of insertion nut
34
c
, for example by a soldered or welded connection. In the region of step
106
d
, the outer side of interlayer
104
is not connected with housing
22
c
, so that in this region a gap
111
lies between interlayer
104
and housing
22
c.
Through the shaping and nature of the attachment of interlayer
104
, forces which arise in housing
22
c
as spark plug
10
c
is screwed in cannot be transmitted directly to insulator
12
c
. Interlayer
104
absorbs these forces in the transition region between step
106
d
and section
108
.
FIG. 2B
shows a spark plug
10
d
constructed similarly to spark plug
10
c
. There are differences only in the region of an interlayer
104
d
, which is used in place of interlayer
104
. Interlayer
104
d
is connected in the region of a step
106
d
with an insulator
12
d
. In a transition region
112
, interlayer
104
d
widens conically in correspondence with the shape of insulator
12
d
. In transition region
112
, as well as in an adjacent section
114
, the inner side of interlayer
104
d
is also connected with insulator
12
d
, for example with the aid of a soldered or welded connection.
The outer side of interlayer
104
d
is exposed in the region of step
106
d
, so that a gap
110
d
is formed between interlayer
104
d
and housing
22
d
. The outer side of interlayer
104
d
is connected to housing
22
d
in the region of section
114
, for example by soldering or welding. The connection has a length of, e.g., 12=8 mm along a longitudinal axis
16
d.
Mechanical stresses which arise in the region of a groove
30
d
as spark plug
10
d
is screwed in cannot be directly transmitted to insulator
12
d
due to gap
110
d
. The force lines first run into housing
22
d
and only enter insulator core
12
d
in section
114
. The forces are, however, already less at this point than in the region of groove
30
d.
A sealing ring, not shown, is located in the region of groove
30
d
which forms a seal in the flat sealing seat between the engine block and a central part
32
d
. Otherwise, spark plug
10
d
is constructed like spark plug
10
c.
FIG. 3A
shows a partial section view of a compact spark plug
10
e
which is constructed similarly to spark plug
10
c
, see FIG.
2
A. Elements with reference numbers
12
e
to
36
e
correspond in their design and function to the elements
12
c
to
36
c
which were explained with reference to FIG.
2
A.
Central electrode
20
e
is again inserted first into through hole
18
e
. Subsequently, a replaceable damping resistor
120
is inserted, which has a shape resembling a known fuse. Only then is a contact pin
122
inserted, which buckles at multiple buckling positions as terminal stud
36
e
is screwed in. Insulator
12
e
, which was screwed on in this way, is in turn heated to approximately 800° C., with a soldering paste applied to central electrode
20
e
melting and central electrode
20
e
connecting with insulator
12
e.
An interlayer
124
corresponds to interlayer
104
in its design, function, and type of attachment to insulator
12
e
and housing
22
e
, see FIG.
2
A.
FIG. 3B
shows a part of a spark plug
10
f
, which is designed like spark plug
10
e
, see FIG.
3
A. An interlayer
126
f
is soldered onto insulator
12
f
of spark plug
10
f
in a section
130
. Section
130
lies within threaded sleeve
26
f
. The inner diameter of interlayer
126
f
and the diameter of insulator
12
f
increase uniformly within a transition section
132
. In the region of a section
134
lying within insertion nut
34
f
, the inner diameter of the sleeve formed by interlayer
126
f
remains constant. The diameter of insulator
12
f
also remains constant within section
134
. In section
134
, interlayer
126
f
is soldered to both insulator
12
f
and housing
22
f
. In contrast, in the region of section
130
and in the region of transition section
132
, a gap
136
lies between housing
22
f
and insulator
12
f.
Claims
- 1. A spark plug, comprising:a partially cylindrical insulator element; a housing enclosing the partially cylindrical insulator element; a connection including at least one material bond by which the partially cylindrical insulator element and the housing are connected to one another; and an interlayer produced prior to the connection and by which the partially cylindrical insulator element and the housing are connected with one another, wherein: the interlayer is one of applied and attached to the partially cylindrical insulator element; the interlayer is attached to the housing using at least one material bond; a gap is located between the housing and the interlayer in a region of a section lying closer to a base part of the partially cylindrical insulator element; and the interlayer is connected to the housing in a second section further away from the base part.
- 2. The spark plug according to claim 1, wherein:the partially cylindrical insulator element includes a base part, and a diameter further from a combustion chamber of the partially cylindrical insulator element at least one of remains approximately equal and increases with an increasing distance from a free end of the base part in an entire region surrounded by the housing.
- 3. The spark plug according to claim 1, wherein:the partially cylindrical insulator element include a base part, and an inner diameter of the housing in a region of the connection at least one of remains the same and increases with an increasing distance from a free end of the base part.
- 4. The spark plug according to claim 1, wherein:the partially cylindrical insulator element includes a base part, and a diameter of the partially cylindrical insulator element in a region on a side further from the base part adjoining a region surrounded by the housing is approximately equal to a largest diameter of the partially cylindrical insulator element in a region surrounded by the housing.
- 5. The spark plug according to claim 1, wherein:the partially cylindrical insulator element include a base part, the housing includes at least one tubular section in which a diameter of the partially cylindrical insulator element is only slightly smaller than an inner diameter of the housing at the same distance to a free end of the base part, and a connection along a circumference of the partially cylindrical insulator element close a gap between the partially cylindrical insulator element and the housing.
- 6. The spark plug according to claim 5, further comprising at least one of:first tubular section arranged near a free end of the bass part; and a second tubular section arranged further away from the base part.
- 7. The spark plug according to claim 1, wherein:the connection includes at least one of soldered connection, a welded connection, and an adhesive connection.
- 8. The spark plug according to claim 1, wherein:the housing includes at least one tubular section, and a diameter of the partially cylindrical insulator element is slightly larger than an inner diameter of the housing, when the partially cylindrical insulator element is not in place, at the same distance to a free end of a base part of the partially cylindrical insulator element.
- 9. The spark plug according to claim 8, wherein:the connection further includes a friction-lock connection aligned in a radial direction, and the friction-lock connection is produced by an installation of the partially cylindrical insulator element into the housing, the housing having a higher temperature than the partially cylindrical insulator element at a time of the installation.
- 10. The spark plug according to claim 1, wherein:the interlayer extends into regions outside the connection.
- 11. The spark plug according to claim 1, wherein:another gap is located between the partially cylindrical insulator element and the interlayer in a region of a third section of the interlayer further away from the base part.
- 12. The spark plug according to claim 1, wherein:the partially cylindrical insulator element includes a ceramic, and a surface of the ceramic is treated in a region of the connection such that a load capacity of the connection is increased.
- 13. The spark plug according to claim 1, wherein:the connection forms at least a significant portion of a cohesion of the housing and the partially cylindrical insulator element.
Priority Claims (1)
Number |
Date |
Country |
Kind |
100 47 498 |
Sep 2000 |
DE |
|
US Referenced Citations (13)