U.S. patent application number 11/920017 was filed with the patent office on 2008-10-30 for sheathed element glow plug having a combustion chamber pressure sensor.
Invention is credited to Michael Bauer, Peter Boehland, Markus Jungemann, Sebastian Kanne, Godehard Nentwig, Tobias Reiser.
Application Number | 20080264373 11/920017 |
Document ID | / |
Family ID | 36337419 |
Filed Date | 2008-10-30 |
United States Patent
Application |
20080264373 |
Kind Code |
A1 |
Boehland; Peter ; et
al. |
October 30, 2008 |
Sheathed Element Glow Plug Having a Combustion Chamber Pressure
Sensor
Abstract
A sheathed element glow plug includes an integrated combustion
chamber pressure sensor for a self-igniting internal combustion
engine for measuring combustion chamber pressures, in particular
for combustion chamber signal-based engine control. The sheathed
element glow plug has a heating element and a glow plug housing, as
well as a glow plug axis. The glow plug housing has a receptacle
area for receiving the heating element, a housing body, and at
least one flexibility area situated between the housing body and
the receptacle area. At least one force measuring element is
installed in the glow plug housing.
Inventors: |
Boehland; Peter; (Marbach,
DE) ; Kanne; Sebastian; (Schwaikheim, DE) ;
Reiser; Tobias; (Ehningen, DE) ; Nentwig;
Godehard; (Palo Alto, CA) ; Bauer; Michael;
(Gerlingen, DE) ; Jungemann; Markus; (Stuttgart,
DE) |
Correspondence
Address: |
KENYON & KENYON LLP
ONE BROADWAY
NEW YORK
NY
10004
US
|
Family ID: |
36337419 |
Appl. No.: |
11/920017 |
Filed: |
March 9, 2006 |
PCT Filed: |
March 9, 2006 |
PCT NO: |
PCT/EP06/61576 |
371 Date: |
June 5, 2008 |
Current U.S.
Class: |
123/145A |
Current CPC
Class: |
G01L 23/22 20130101;
F23Q 2007/002 20130101; F02P 19/028 20130101; F23Q 7/001
20130101 |
Class at
Publication: |
123/145.A |
International
Class: |
F23Q 7/00 20060101
F23Q007/00 |
Foreign Application Data
Date |
Code |
Application Number |
May 9, 2005 |
DE |
10 2005 021 229.8 |
Claims
1-11. (canceled)
12. A sheathed element glow plug for a self-igniting internal
combustion engine, comprising: a heating device; a glow plug
housing; and a glow plug axis; wherein the glow plug housing
includes a receptacle area configured to receive the heating
device, a housing body and at least one flexibility area arranged
between the housing body and the receptacle area, at least one
force measuring device arranged in the glow plug housing.
13. The sheathed element glow plug according to claim 12, further
comprising at least one force transmission device configured to
transmit a combustion chamber pressure to the at least one force
measuring device.
14. The sheathed element glow plug according to claim 12, wherein
the at least one flexibility area includes at least one area in
which the glow plug housing has a lower rigidity parallel to the
glow plug axis than in an area of the housing body.
15. The sheathed element glow plug according to claim 12, wherein
the at least one flexibility area includes at least one of: (a) an
undulation; (b) a bellows having at least one fold turned to one of
(i) an inside and (ii) an outside of the glow plug housing; (c) an
area having a small wall thickness of the glow plug housing; (d) an
elastic device; and (e) an device having a low modulus of
elasticity.
16. The sheathed element glow plug according to claim 12, wherein
the at least one force measuring device is accommodated in the
housing body.
17. The sheathed element glow plug according to claim 12, wherein
the at least one force transmission device includes at least one
of: (a) a pressure rod; (b) a substantially cylindrical pressure
rod; (c) a pressure sleeve; and (d) a substantially cylindrical
sleeve-shaped pressure sleeve.
18. The sheathed element glow plug according to claim 13, wherein
one end of the at least one force transmission device is supported
by the at least one force measuring device and the other end is
supported by at least one of: (a) the heating device; (b) the at
least one flexibility area; and (c) an area of the glow plug
housing arranged between the at least one flexibility area and the
at least one heating device.
19. The sheathed element glow plug according to claim 13, wherein
one end of the at least one force transmission device is supported
by the at least one force measuring device and the other end is
supported by an area of the glow plug housing arranged between the
at least one flexibility area and the at least one heating device,
the sheathed element glow plug further comprising at least one
supporting device configured to support the at least one force
transmission device on the glow plug housing.
20. The sheathed element glow plug according to claim 12, further
comprising at least one external thread configured to connect the
sheathed element glow plug to a cylinder head of the internal
combustion engine, the at least one external thread being a
component of the housing body.
21. The sheathed element glow plug according to claim 12, wherein
the at least one force measuring device is one of (a) annular- and
(b) disk-shaped.
22. The sheathed element glow plug according to claim 13, wherein
the at least one force measuring device is arranged in the glow
plug housing such that a tensile pre-stress is applied to at least
part of the glow plug housing, and a compression pre-stress is
applied to the at least one force transmission device.
23. The sheathed element glow plug according to claim 22, wherein
the at least one force measuring device is one of (a) screwed in
and (b) caulked to the glow plug housing.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a sheathed element glow
plug having an integrated combustion chamber pressure sensor.
Sheathed element glow plugs of this type are used in particular in
self-igniting internal combustion engines for measuring a
combustion chamber pressure.
BACKGROUND INFORMATION
[0002] As a result of increasingly strict exhaust gas legislation,
in particular for diesel engines, the demands for reduced emissions
of harmful substances by self-igniting internal combustion engines
are becoming stricter. Today's engine management systems are
expected to ensure low emissions of harmful substances and low fuel
consumption, in addition to having a long service life at the same
time. Combustion may be optimized in the combustion chamber of a
diesel engine in particular by using regulated injection of fuel.
Regulated injection may be controlled in particular by electronic
engine control units, which are already routinely used in today's
motor vehicles. Successful operation of a combustion signal-based
control system (CSC) depends, however, on the availability of
pressure sensors that are industrially manufacturable and meet high
demands regarding price, reliability, accuracy, and compactness. At
this time, measuring devices having so-called "stand-alone sensors"
are widely used. However, for using such devices, a separate bore
hole must be provided in the cylinder head wall, which is not
always feasible for reasons of space and it also means additional
assembly effort, including additional operations. In particular, in
today's four-valve internal combustion engines, making additional
bore holes is hardly implementable in practice due to the extremely
tight space constraints. Furthermore, in general, systems of this
type are relatively expensive and the service life of systems of
this type is significantly shorter than that of a typical vehicle,
mostly due to the high operating temperatures.
[0003] Therefore, there have been conventional approaches to
integrate combustion chamber pressure sensors into existing
components of the cylinder head. For example, there are approaches
to integrate combustion chamber pressure sensors in sheathed
element glow plugs. For example, German Published Patent
Application No. 196 80 912 describes a device and a method for
detecting the cylinder pressure in a diesel engine. The device has
a pressure sensor, a heating section of a glow plug, which is
installed in the interior of a cylinder of the diesel engine and
can be acted upon by the cylinder pressure, and a fastening element
for fastening the heating section in a body of the glow plug. The
pressure sensor is situated between the heating section and the
fastening element of the glow plug. The cylinder pressure is
transmitted to the pressure sensor via the heating section.
[0004] The device described in German Published Patent Application
No. 196 80 912 has, however, numerous practical disadvantages. In
particular, in the device, the housing of the sheathed element glow
plug is essentially fixedly connected to the cylinder head, while
the heating section introduces the force and, in doing so, performs
a relative movement, however comparatively small it may be, with
respect to the housing. This in turn may result in friction and
thus in a corruption of the combustion chamber pressure signal; in
particular there is the additional risk of soot deposition on the
guide between the stationary part (i.e., the part fixedly connected
to the cylinder head) and the moving part of the sheathed element
glow plug. Another disadvantage of the device described in German
Published Patent Application No. 196 80 912 is that the housing and
the force-transmitting components expand differently. These
different expansions, which are caused by the temperature
differences during the use of the internal combustion engine and
different thermal expansion properties of the components involved,
cause strong fluctuations in the pre-tension of the sensor used,
which in turn may result in service life problems. Furthermore, the
device described in German Published Patent Application No. 196 80
912 has the disadvantage that the pressure sensor is directly
connected to the heating section and is thus exposed to high
thermal stresses and temperature fluctuations. In addition,
assembly of the above-described device is relatively complex.
SUMMARY
[0005] Therefore, according to example embodiments of the present
invention, a sheathed element glow plug for a self-igniting
internal combustion engine has an integrated combustion chamber
pressure sensor and which avoids the disadvantages of the devices
as described above. In particular, the sheathed element glow plug
permits the fluctuations in the sensor pre-tension, caused by
temperature, and the mechanical friction of individual components
of the sheathed element glow plug during operation, which, as
described above, may result in problems in certain conventional
devices to be minimized. The sheathed element glow plug for a
self-igniting internal combustion engine has a heating element, a
glow plug housing, and a glow plug axis. Example embodiments of the
present invention provide a fixed and, e.g., fully gas-tight
connection established between the glow plug housing and the
heating element. The functionality of the combustion chamber
pressure sensor is achieved through the flexibility of the glow
plug housing in the area between its combustion chamber-side end
and its end screwed into the cylinder head.
[0006] The sheathed element glow plug has a receptacle area for
receiving the heating element as well as a housing body and at
least one flexibility area situated between the housing body and
the receptacle area. The flexibility area may be configured such
that it has at least one area in which the glow plug housing has a
lower rigidity parallel to the glow plug axis than in the area of
the housing body. At least one force measuring element, e.g., a
force measuring element which may generate an electrical signal as
a function of a force exerted on the at least one force measuring
element, is provided in the glow plug housing. Basically a
conventional force measuring elements, based on any principle, for
example, piezoelectric force measuring elements of almost any
design or also capacitive force measuring elements or force
measuring with the aid of strain gages, may be used. The at least
one force measuring element may be installed in the housing
body.
[0007] The pressure prevailing in the combustion chamber must be
transmitted to the at least one force measuring element as a force.
This force may be transmitted, for example, directly from the
heating element to the at least one force measuring element or
indirectly, for example, via the glow plug housing or sections of
the glow plug housing. Alternatively or additionally, for the
purpose of pressure transmission the sheathed element glow plug may
also have at least one separate force transmission element for
transmitting the combustion chamber pressure to the at least one
force measuring element, e.g., for transmitting a force from the
heating element to the at least one force measuring element. For
example, this at least one separate force transmission element may
be a pressure rod, e.g., an essentially cylindrical pressure rod,
and/or a pressure sleeve, e.g., an essentially cylindrical
sleeve-shaped pressure sleeve. By "essentially" it is to be
understood here that a slight deviation from a cylindrical shape or
cylindrical sleeve shape is also possible, for example, a slightly
conical shape, which is adapted, for example, to the design of the
sheathed element glow plug or of an interior of the sheathed
element glow plug. The heating element projects into the combustion
chamber of the internal combustion engine and applies a pressure
corresponding to the combustion chamber pressure to a pressure
surface, for example, an end face. This pressure is converted by
the heating element into a force, which is transferred from the
heating element to the sheathed element glow plug. The at least one
force transmission element transmits this force directly or
indirectly (i.e., with or without additional intermediary elements)
from the heating element to the at least one force measuring
element, where this force is converted into an electrical signal,
which may be read by an appropriate electronic circuit and made
available, for example, to an engine controller. In this manner,
up-to-the-minute information about the combustion chamber pressure
may be generated.
[0008] The at least one flexibility area may be configured in
different manners. Its function is to be able to displace the
entire front part of the sheathed element glow plug, i.e., the part
facing the combustion chamber of the internal combustion engine
which includes the receptacle area and the heating element, along
the glow plug axis when a pressure is applied to the heating
element due to the combustion chamber pressure, and thus to apply a
corresponding force and thus a pre-tension to the at least one
force transmission element. In contrast, the housing body expands
very little or not at all and remains substantially rigid during
this elastic deflection. The pressure force, which is introduced
into the sheathed element glow plug via the at least one force
transmission element, may thus be detected by the at least one
force measuring element. This pressure force differs from the total
force introduced into the sheathed element glow plug via the
combustion chamber pressure only by a substantially constant
factor, which is a function of the rigidity of the glow plug
housing in the receptacle area and in the flexibility area of the
glow plug housing. The rigidity of the at least one force
transmission element also affects this essentially constant
factor.
[0009] The flexibility area may have an undulation or a bellows
having at least one fold turned to the inside of the glow plug
housing or to the outside. Alternatively or additionally, the at
least one flexibility area may also have at least one area having a
small wall thickness of the glow plug housing, in particular a wall
thickness that is less than in the adjacent areas of the glow plug
housing or than in the entire rest of the glow plug housing. This
arrangement also results in a reduced rigidity of the glow plug
housing parallel to the glow plug axis in the flexibility area.
Alternatively or additionally, an elastic element, for example, a
spring element, e.g., a helical spring or a similar spring element
or also an elastic element made of metallic material or a plastic,
for example, an elastomer, may also be used, which ensures
flexibility in the at least one flexibility area parallel to the
glow plug axis. In general, an element, e.g., a material, having a
low modulus of elasticity may also be used. A low modulus of
elasticity is to be understood here in particular as a modulus of
elasticity which is smaller than the moduli of elasticity of the
surrounding wall areas or of the entire glow plug housing.
[0010] The heating element may be fixedly and pressure-tightly
connected to the glow plug housing in the receptacle area, e.g.,
via press-fitting. The glow plug housing is connected to the
cylinder head, e.g., via a threaded connection. For this purpose,
the sheathed element glow plug may also have at least one external
thread for connecting the sheathed element glow plug to the
cylinder head of the internal combustion engine.
[0011] This at least one external thread may be a component of the
housing body of the sheathed element glow plug. Between the
receptacle area for receiving the heating element and the
connection to the cylinder head, there is at least one flexibility
area, for example, in the form of a metallic bellows, in which the
glow plug housing has minimum rigidity parallel to the glow plug
axis.
[0012] The at least one force transmission element is supported,
e.g., as far to the front toward the combustion chamber as possible
by the glow plug housing or even directly by the heating element.
On its opposite end, the at least one force transmission element is
supported, directly or indirectly, by the at least one force
measuring element, so that a force is transmissible, as described
above, from the at least one heating element to the at least one
force measuring element. When installed, the glow plug housing may
be tensile stressed and the at least one force transmission element
may be compression stressed. This stressing (pre-tension) may take
place, for example, with the aid of a thread or a caulking of the
at least one force measuring element in the glow plug housing,
e.g., in the housing body. An advantage of the flexibility area is
that different thermal expansions of the glow plug housing and of
the at least one force transmission element are compensated by the
flexibility of the housing in the area of the at least one
flexibility area and thus cause only a relatively small fluctuation
of the pre-tension force exerted on the at least one force
measuring element. This results in better signal quality and avoids
signal correction in the different operating states of the internal
combustion engine which usually also result in corresponding
temperature fluctuations. Fluctuations in the outside temperatures
are also at least partially compensated. In rest operation of the
internal combustion engine, e.g., no axial forces act on the
heating element, the connection between heating element and glow
plug housing being unstressed in. rest operation.
[0013] As described above, one end of the at least one force
transmission element may be supported directly or indirectly (for
example, via an intermediary element) by the at least one force
measuring element. The other end of the transmission element may be
supported directly by the heating element, for example, or,
alternatively or additionally, by the at least one flexibility
area. For example, the at least one force transmission element may
be supported by an undulation of the flexibility area directed
toward the inside of the glow plug housing. Alternatively or
additionally, the at least one force measuring element may also be
supported by an area of the glow plug housing which is situated
between the at least one flexibility area and the at least one
heating element. For example, for this purpose, at least one
additional supporting element may be used, which is used for
supporting the at least one force transmission element on the glow
plug housing in the area between the flexibility area and the
heating element. For example, a circular disk may be used, whose
periphery is connected, for example, screwed or caulked, to the
wall of the glow plug housing. These options for supporting the at
least one force transmission element cause the force transmission
element to be supported, as described above, as far to the front
toward the combustion chamber as possible, causing minimum tensions
to occur in the rigid area of the glow plug housing which faces
away from the combustion chamber. The at least one flexibility area
may be directly adjacent to the heating element in the glow plug
housing or, alternatively or additionally, a gap between the
heating element and the flexibility area is additionally filled
with a filling material. The effect of this refinement is that no
excessive flexibility occurs prior to the introduction of force
from the heating element to the at least one force transmission
element. For this purpose, the filling material may be, for
example, a highly rigid and, e.g., poorly heat-conducting material.
This refinement causes the most direct force transmission possible
from the heating element to the at least one force transmission
element, which further improves the force transmission function of
the combustion chamber pressure onto the at least one force
measuring element.
[0014] The power may be supplied to the heating element for example
via one of the steel terminal studs located centrally near the glow
plug axis. The use of flexible glow wire power supply leads is,
however, also possible.
[0015] The sheathed element glow plug having an integrated
combustion chamber pressure sensor has numerous advantages compared
to conventional devices. One important advantage is the
independence of the combustion chamber pressure signal from the
operating temperature of the internal combustion engine because
temperature fluctuations and related differing material expansions
are compensated in an optimum manner. Another advantage is that an
almost constant force transmission function is ensured. This means,
e.g., that the combustion chamber pressure is transmitted to the at
least one force measuring element in an identical or similar manner
in almost all ranges of the combustion chamber pressure and thus in
almost all operating ranges of the internal combustion engine. The
force transmission factor by which the electrical signal of the at
least one force measuring element is to be multiplied to deduce the
actual combustion chamber pressure from this signal is thus largely
independent of the operating state of the internal combustion
engine. Additional corrections which involve complex calculations
and must include, for example, appropriate correction functions,
etc., may thus be avoided. The electrical signal of the at least
one force measuring element may thus be used directly or after only
minor electronic processing for a corresponding engine control, for
example, for engine control based on the combustion chamber
pressure signal.
[0016] Example embodiments of the present invention are described
in greater detail with reference to the Figures.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 shows a sheathed element glow plug according to an
example embodiment of the present invention having an integrated
combustion chamber pressure sensor;
[0018] FIG. 2 shows a simulated curve of a sensor signal of a force
measuring element, compared to the combustion chamber pressure, at
different crankshaft positions;
[0019] FIG. 3 shows a combustion chamber pressure sensor according
to an example embodiment of the present invention, and
[0020] FIG. 4 shows a combustion chamber pressure sensor according
to an example embodiment of the present invention.
DETAILED DESCRIPTION
[0021] FIG. 1 shows a sheathed element glow plug 110 according to
an example embodiment of the present invention having an integrated
combustion chamber pressure sensor. Sheathed element glow plug 110
has a heating element 112 and a glow plug housing 114. Glow plug
housing 114 is subdivided into three areas: a receptacle area 116
facing the combustion chamber for receiving heating element 114, a
flexibility area 118, and a housing body 120 situated on the side
of sheathed element glow plug 110 facing away from the combustion
chamber.
[0022] Heating element 112 is designed as a ceramic heating element
112 in this exemplary embodiment. However, other designs of heating
elements 112 are also possible. In this exemplary embodiment,
electrical power is applied to heating element 112 via a steel
terminal stud 122. In this exemplary embodiment, according to FIG.
1, steel terminal stud 122 is designed as a solid central stud,
which extends axially along a glow plug axis 124 through glow plug
housing 114. Sheathed element glow plug 110 has a threaded
connection 126 on its end facing away from the combustion chamber.
Steel terminal stud 122 axially projects out from glow plug housing
114 through this threaded connection 126 and is connected to an
appropriate electrical power supply. Furthermore, glow plug housing
114 has an external thread 128 in housing body 120. Using this
external thread 128, sheathed element glow plug 110 may be screwed
into a cylinder head such that heating element 112 projects into
the combustion chamber of the internal combustion engine. In
flexibility area 118, glow plug housing 114 is provided with a fold
130 in which glow plug housing 114 has an inward contraction. Fold
130 thus acts as a metallic bellows having a single fold and
provides glow plug housing 114 with a lower rigidity parallel to
glow plug axis 124 in flexibility area 118 than in housing body
120.
[0023] Heating element 112 is connected to glow plug housing 114 by
press-fitting 132 in receptacle area 116 in this exemplary
embodiment. A gas-tight connection is thus created in receptacle
area 116, which ensures that combustion chamber gases cannot
penetrate into the interior of sheathed element glow plug 110. In
receptacle area 116, heating element 112 is pressed into glow plug
housing 114. This creates a gap 134 between heating element 112 and
fold 130. It may be provided to keep this gap 134 as small as
possible, to possibly make it disappear or to fill this gap 134
with a highly rigid and/or poorly heat-conducting filling material.
In this manner, the force transfer, which is described below, is
further improved, while heat transfer from heating element 112 to
other components in the interior of sheathed element glow plug 110
is prevented.
[0024] Furthermore, a force measuring element 136, which has an
annular shape in this exemplary embodiment, in the form of an
annular piezoelectric element, is installed in housing body 120 of
glow plug housing 114. The electrical leads of this force measuring
element 136 are not illustrated in FIG. 1, and may exit glow plug
housing 114 axially, for example, parallel to steel terminal stud
122 through threaded connection 126 and be connected to an
appropriate electrical electronic analyzer circuit. In this
exemplary embodiment, force measuring element 136 is surrounded by
two spacing sleeves 138, for example, spacing sleeves of a
cylindrical sleeve shape, in particular spacing sleeves made of a
highly rigid material, for example, steel. During assembly, spacing
sleeve 138 on the combustion chamber side is first inserted into
glow plug housing 114 from the end of sheathed element glow plug
110 facing away from the combustion chamber, then force measuring
element 136, and subsequently second spacing sleeve 138, are
inserted. Subsequently glow plug housing 114 is screwed in using
threaded connection 126. A pre-tension is thus applied to force
measuring element 136.
[0025] Furthermore, a force transmission element 140 is introduced
into glow plug housing 114. In this exemplary embodiment, force
transmission element 140 has a sleeve-shaped design and also
includes, like force measuring element 136, steel terminal stud 122
on the periphery. In this exemplary embodiment, force transmission
element 140 has a slight conicity and a slightly smaller external
diameter on the combustion chamber side than on the side facing
away from the combustion chamber. On the combustion chamber side
force transmission element 140 is supported by fold 130 and on the
side facing away from the combustion chamber by spacing sleeve 138.
Therefore, in this exemplary embodiment, force transmission element
140 is indirectly supported by force measuring element 136.
[0026] On its side facing the combustion chamber, heating element
112 has a hydraulic pressure surface 142. On this pressure surface
142, the combustion chamber pressure is converted into a force F
(labeled with reference numeral 144 in FIG. 1) exerted on heating
element 112. Force transmission element 140 transmits this force
144 onto force measuring element 136, where it is converted into an
electrical signal. From this electrical signal, a conclusion can be
drawn about the combustion chamber pressure. The transmission of
force 144 from heating element 112 to force measuring element 136,
however, is not complete, but must be multiplied by a factor which
is less than 1. In the ideal case, this transmission factor attains
the exact value of 1. The fact that the transmission is incomplete
is explained by the fact that forces are absorbed by glow plug
housing 114. The advantage of the design of sheathed element glow
plug 110 illustrated in FIG. 1 is, however, that force 144 in this
case results in a negligible deformation of glow plug housing 114
outside flexibility area 118. Substantially, only receptacle area
116 is displaced by force 144 axially with respect to housing body
120, glow plug housing 114 being elastically deflected axially in
the region of flexibility area 118. This ensures that force 144 is
almost completely transmitted from heating element 112 to force
measuring element 136. Furthermore, fold 130 also absorbs thermal
stresses, so that substantially a constant pre-tension is applied
to force measuring element 136 even at different operating
temperatures.
[0027] The transmission of force 144 onto force measuring element
136 in the system according to FIG. 1 is schematically illustrated
in FIG. 2 in the form of simulation data, where the x axis, here
labeled with .phi., denotes the position of the crankshaft in
degrees, the left-hand y axis denotes combustion chamber pressure p
in arbitrary units, and the right-hand y axis denotes force F
displayed by force measuring element 136 in arbitrary units. For a
simulation, an operating point at 2000 rpm and an effective mean
pressure (PME) of one bar are assumed. Upper curve 210, which
refers to the left-hand y axis, shows the variation of the
combustion chamber pressure. Lower curve 212, which refers to the
right-hand y axis, shows the electrical signal of force measuring
element 136. As is apparent from FIG. 2, sensor signal 212 is to be
multiplied by an appropriate factor for a conclusion to be drawn
about combustion chamber pressure 210 from this sensor signal 212.
This factor substantially includes the material characteristics and
the design of sheathed element glow plug 110.
[0028] FIG. 3 shows a sheathed element glow plug 110 according to
an example embodiment of the present invention. Again, sheathed
element glow plug 110 has a glow plug housing 114, which is
subdivided into a receptacle area 116, a flexibility area 118, and
a housing body 120. In receptacle area 116, a heating element 112
is again pressed into glow plug housing 114 by press-fitting 132.
As also in the exemplary embodiment according to FIG. 1, sheathed
element glow plug 110 in the exemplary embodiment of FIG. 3 also
has a fold 130 in flexibility area 118. The design of this fold 130
is basically comparable to the design of fold 130 in the exemplary
embodiment of FIG. 1. A gap 134 is again formed between fold 130
and heating element 112. As in the exemplary embodiment of FIG. 1,
glow plug housing 114 again has an external thread 128 for
fastening sheathed element glow plug 110 in a cylinder head.
[0029] The difference between the exemplary embodiment of FIG. 3
and the exemplary embodiment of FIG. 1 is substantially in the
design of force measuring element 136 and the design and
positioning of force transmission element 140. In the exemplary
embodiment of FIG. 3, force transmission element 140 is designed in
the form of a cylindrical disk, whose end facing away from the
combustion chamber is inserted into housing body 120. This force
measuring element 136 is also secured and pre-tensioned by a
threaded connection 126. No spacing sleeves 138 are used in this
exemplary embodiment according to FIG. 3.
[0030] Furthermore, in the exemplary embodiment according to FIG.
3, force transmission element 140 has a rod-shaped, rather than
sleeve-shaped, design. Force transmission element 140 is inserted
into glow plug housing 114 along glow plug axis 124. On its end
facing away from the combustion chamber, force transmission element
140 is supported centrally by the combustion chamber-side end face
of force measuring element 136. On its end facing the combustion
chamber, rod-shaped force transmission element 140 is supported by
the wall of gap 134. For this purpose, an additional, circular
disk-shaped support element 310 is inserted into receptacle area
116. This support element 310 may be caulked or screwed to the wall
of glow plug housing 114 in receptacle area 116, for example. Other
types of attachment are also conceivable. Support element 310
causes a force to be transmitted from heating element 112 to force
measuring element 136 via the wall of glow plug housing 114 in
receptacle area 116, via support element 310 and finally via
rod-shaped force transmission element 140. AN advantage of an
indirect force transmission from heating element 112 to force
transmission element 140 via support element 310 is substantially
that no heat is transferred directly from heating element 112 to
force transmission element 140. Such heat transfer by force
transmission element 140 (which may be made of metal, for example)
also to force measuring element 136, might result, for example, in
temperature fluctuations in force measuring element 136, which
would negatively affect the signal quality.
[0031] In the exemplary embodiment of FIG. 3, the power lead to
heating element 112 is not illustrated. Since in this exemplary
embodiment the area along glow plug axis 124 is essentially filled
by rod-shaped force transmission element 140, there is not space
here for a steel terminal stud 122 according to the exemplary
embodiment of FIG. 1. Instead, in the exemplary embodiment of FIG.
3, a glow wire power supply lead is used, which passes by elements
310 and 136 via appropriate bore holes in the support element or
appropriate bore holes or grooves in the wall of glow plug housing
114 and exits to the outside via threaded connection 126.
[0032] FIG. 4 shows a sheathed element glow plug 110 without a
separate force transmission element 140. Force 144 is directly
transferred here from heating element 112 to force measuring
element 136. This transfer preferably takes place with the aid of a
cylindrical extension 410 of heating element 112 situated on the
side of heating element 112 facing away from the combustion
chamber. Otherwise the functionality and design of sheathed element
glow plug 110 is similar to the exemplary embodiment according to
FIG. 3.
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