U.S. patent application number 09/161502 was filed with the patent office on 2002-02-21 for heater unit.
Invention is credited to ABE, FUMIO.
Application Number | 20020021989 09/161502 |
Document ID | / |
Family ID | 17819998 |
Filed Date | 2002-02-21 |
United States Patent
Application |
20020021989 |
Kind Code |
A1 |
ABE, FUMIO |
February 21, 2002 |
HEATER UNIT
Abstract
A heater unit includes a metallic casing, and a honeycomb heater
held in the casing via a metallic holding member, comprising a
metallic honeycomb structure having a large number of parallel
passages extending in the direction of the flow of an exhaust gas
passing through the heater unit and at least one electrode for
electrical heating of the honeycomb structure, attached to the
honeycomb structure. In the heater unit, the holding member has
such a structure as (1) is fitted to part of the outer surface of
the honeycomb heater to allow the honeycomb heater to have a stable
shape and (2) substantially blocks the flow path of exhaust gas
between the honeycomb heater and the casing. This heater unit can
withstand severe operating conditions such as experienced in
automobiles; moreover, in this heater unit, the by-pass flow of
exhaust gas is made substantially zero and the whole exhaust gas
can pass through the honeycomb heater.
Inventors: |
ABE, FUMIO; (HANDA-CITY,
JP) |
Correspondence
Address: |
PARKHURST & WENDEL
1421 PRINCE STREET
SUITE 210
ALEXANDRIA
VA
223142805
|
Family ID: |
17819998 |
Appl. No.: |
09/161502 |
Filed: |
September 28, 1998 |
Current U.S.
Class: |
422/174 ;
422/177; 422/179; 422/180 |
Current CPC
Class: |
Y02A 50/20 20180101;
Y02A 50/2322 20180101; Y02T 10/26 20130101; Y02T 10/12 20130101;
F01N 3/2013 20130101; F01N 3/2875 20130101 |
Class at
Publication: |
422/174 ;
422/177; 422/179; 422/180 |
International
Class: |
F01N 003/28; F01N
003/10; B01D 053/88 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 28, 1997 |
JP |
9-295389 |
Claims
What is claimed is:
1. A heater unit comprising: a metallic casing, and a honeycomb
heater held in the casing via a metallic holding member, comprising
a metallic honeycomb structure having a large number of parallel
passages extending in the direction of the flow of an exhaust gas
passing through the heater unit and at least one electrode for
electrical heating of the honeycomb structure, attached to the
honeycomb structure, in which heater unit the holding member has
such a structure as (1) is fitted to part of the outer surface of
the honeycomb heater to allow the honeycomb heater to have a stable
shape and (2) substantially blocks the flow path of exhaust gas
between the honeycomb heater and the casing.
2. A heater unit according to claim 1, wherein the holding member
is fitted to the side and/or the periphery of face, of the
honeycomb heater.
3. A heater unit according to claim 1, wherein the holding member
and the honeycomb heater are insulated from each other via an
insulating member.
4. A heater unit according to claim 3, wherein the holding member
is buried in a groove formed at the side and/or the periphery of
face, of the honeycomb heater and fixed.
5. A heater unit according to claim 1, wherein the holding member
consists of at least one ring.
6. A heater unit according to claim 1, wherein the holding member
consists of a plurality of divided parts.
7. A heater unit according to claim 1, wherein the holding member
substantially blocks the flow path of exhaust gas at the peripheral
portion of the honeycomb heater which is not heated, or at the
portion of the honeycomb heater which is inferior in
heat-generating property to the central portion of the honeycomb
heater.
Description
BACKGROUND OF THE INVENTION
[0001] (1) Field of the Invention
[0002] The present invention relates to a heater unit suitably
usable for purposes such as purification of exhaust gas emitted
from automobile engine, and the like.
[0003] (2) Description of Related Art
[0004] Porous ceramic honeycomb structures are known for use as a
catalyst, a catalyst carrier or the like for purification of the
nitrogen oxides (NOx), carbon monoxide (CO) and hydrocarbons (HC)
contained in the exhaust gases emitted from internal combustion
engines of automobiles, etc. In recent years, metallic honeycomb
structures came to draw attention for the same purpose. Meanwhile,
as the regulation of exhaust gas became stricter, it is desired to
develop a heater or the like for reduction in exhaust gas during
the cold start of engine.
[0005] Under the situation, a honeycomb heater comprising a
metallic honeycomb structure and electrodes attached thereto for
electrical heating of the structure was developed. Ordinarily, a
honeycomb heater is provided in the exhaust gas flow path of
automobile or the like, in the form of a heater unit comprising a
metallic casing and said honeycomb heater held in the casing via an
appropriate holding member.
[0006] As such a heater unit, the present applicant proposed, in
Japanese Patent Application Kokai (Laid-Open) No. 259543/1995, a
heater unit comprising a metallic casing and an electrically
heatable honeycomb heater held in the metallic casing via a
metallic holding member, wherein at least either of the boundary
between the honeycomb heater and the holding member and the
boundary between the holding member and the casing has been
subjected to an insulation treatment and the holding member can
absorb the displacement of the honeycomb heater taking place in a
direction vertical to the flow direction of exhaust gas and can fix
the honeycomb heater against the flow of exhaust gas.
[0007] The present applicant also proposed, in Japanese Patent
Application Kokai (Laid-Open) No. 4521/1996, an improvement in the
heater unit disclosed in Japanese Patent Application Kokai
(Laid-Open) No. 259543/1995, that is, a flow-controlling means for
keeping the by-pass flow of exhaust gas at 20% or less.
[0008] The heater unit comprising a casing and a honeycomb heater
held in the casing, used in an automobile or the like must firstly
have a structure for holding the honeycomb heater so that the
honeycomb heater is not damaged even under severe operating
conditions such as vibration, thermal impact and the like. Further
in the heater unit, it is desired that the amount of the unpurified
exhaust gas passing through the gap between the casing and the
honeycomb heater, i.e. the by-pass flow is minimized.
[0009] With respect to the reduction in the by-pass flow, it is
described, in the above-mentioned Japanese Patent Application Kokai
(Laid-Open) No. 259543/1995, to provide a ceramic mat on the outer
periphery (side) of a honeycomb heater for prevention of the
by-pass flow of exhaust gas. However, this ceramic mat has a fear
that it is worn owing to the vibration of the metallic holding
member under actual use conditions, inviting gradual increase in
by-pass flow.
[0010] Also, in the above-mentioned Japanese Patent Application
Kokai (Laid-Open) No. 4521/1996, it is disclosed to suppress the
by-pass flow of exhaust gas to 20% or less, specifically by
constructing the casing so that the distance between the casing and
the outer surface of the honeycomb heater became 3 mm or less at
the gas inlet and/or the side of the honeycomb heater. However,
making small the distance between the casing and the honeycomb
heater has a limitation because of a fear of short-circuiting
between the casing and the honeycomb heater.
SUMMARY OF THE INVENTION
[0011] In view of the above situation, the present invention aims
at providing a heater unit comprising a casing and a honeycomb
heater held in the casing, wherein the honeycomb heater is not
damaged even under severe use conditions and has sufficient
durability and wherein the by-pass flow of exhaust gas is prevented
and the whole exhaust gas can pass through the honeycomb
heater.
[0012] According to the present invention, there is provided a
heater unit comprising:
[0013] a metallic casing, and
[0014] a honeycomb heater held in the casing via a metallic holding
member, comprising a metallic honeycomb structure having a large
number of parallel passages extending in the direction of the flow
of an exhaust gas passing through the heater unit and at least one
electrode for electrical heating of the honeycomb structure,
attached to the honeycomb structure,
[0015] in which heater unit the holding member has such a structure
as (1) is fitted to part of the outer surface of the honeycomb
heater to allow the honeycomb heater to have a stable shape and (2)
substantially blocks the flow path of exhaust gas between the
honeycomb heater and the casing.
[0016] In the heater unit of the present invention, it is preferred
that the holding member is fitted to the outer periphery (side)
and/or the periphery of face, of the honeycomb heater. It is also
preferred that the holding member and the honeycomb heater are
insulated from each other via an insulating member. It is also
preferred that the holding member is buried in a groove formed at
the outer periphery (side) and/or the periphery of face, of the
honeycomb heater, and fixed. It is also preferred that the holding
member consists of at least one ring. The holding member may
consists of a plurality of divided parts. It is also preferred that
the holding member substantially blocks the flow path of exhaust
path at the peripheral portion of the honeycomb heater which is not
heated, or at the portion of the honeycomb heater which is inferior
in heat-generating property to the central portion of the honeycomb
heater.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 is drawings showing an embodiment of the heater unit
of the present invention.
[0018] FIG. 2(a) and FIG. 2(b) are drawings showing an example of
the holding member used in the present invention. FIG. 2(a) is a
plan view and FIG. 2(b) is a side view.
[0019] FIG. 3 is a plan view showing an example of the holding
member with slits, used in the present invention.
[0020] FIG. 4 is a perspective view showing other example of the
holding member with slits, used in the present invention.
[0021] FIG. 5 is a plan view showing the honeycomb heater of the
present invention having a groove for holding member, formed at the
outer periphery (side).
[0022] FIG. 6 is drawings showing other embodiment of the heater
unit of the present invention.
[0023] FIG. 7 is a plan view showing the honeycomb heater of the
present invention having a groove for holding member, formed at the
periphery of face.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0024] The heater unit of the present invention comprising a casing
and a honeycomb heater held in the casing via a holding member is
constructed so that (1) it has sufficient durability even under
severe use conditions of automobile or the like and (2) there is
substantially no by-pass flow between the casing and the honeycomb
heater and the whole bypass can pass through the honeycomb heater.
The present invention is described below in detail with reference
to the accompanying drawings.
[0025] The heater unit of the present invention comprises a
honeycomb heater comprising a metallic honeycomb structure having a
large number of parallel passages and at least one electrode for
electrical heating of the honeycomb structure, attached to the
honeycomb structure. The material of the honeycomb structure can be
any metallic material which can generate heat when electrified. It
is preferably a material having a Fe-Cr-Al type composition
superior in heat resistance and oxidation resistance, in view of
the conditions (e.g. high temperatures of automobile exhaust gas)
to which the honeycomb structure is exposed.
[0026] With respect to the cell shape of the honeycomb structure,
i.e. the passage sectional shape of the honeycomb structure in a
direction vertical to the lengthwise direction of the passages,
there is no particular restriction. However, it is preferably a
shape such as polygon (e.g. hexagon or higher polygon), corrugated
shape or the like (which is more flexible to stretching or
shrinkage than triangle or tetragon), in view of the thermal impact
resistance required for the honeycomb structure. There is no
particular restriction, either, with respect to the cell number of
the honeycomb structure. However, the cell number is preferably 100
to 1,500 cells/in..sup.2 in view of the thermal conductivity and
exhaust gas purifiability of the honeycomb structure. With a cell
number exceeding 1,500 cells/in..sup.2, there is a high possibility
that a problem arises with respect to the pressure loss of exhaust
gas.
[0027] As the honeycomb structure, there can be used a wound type
obtained by attaching a corrugated sheet to a rolled foil and
winding the resulting material, or an extrudate type obtained by
powder metallurgy and extrusion, with the latter type being
preferred from the standpoint of the structural durability. Typical
examples of the honeycomb structure are shown in Japanese Patent
Application Kokai (Laid-Open) No. 295184/1991 and WO
10471/1989.
[0028] To the honeycomb structure is attached at least one
electrode for electrical heating of the honeycomb structure. In
order to apply a desired electric power to the honeycomb structure
to generate a desired heat therein, it is generally necessary to
adjust the resistance of the honeycomb structure. Hence, it is
preferable to form a resistance-adjusting means, for example, slits
[described in Japanese Patent Application Kokai (Laid-Open) No.
295184/1991] in the case of the extrudate type honeycomb heater.
When such a honeycomb structure (a honeycomb heater) is used as a
catalytic converter, a catalyst is generally loaded thereon.
[0029] In the following, description is made mainly on the
honeycomb heater having slits formed therein. The slits refer to
all kinds of slits formed in a honeycomb heater for resistance
adjustment, and may be linear or curved. With respect to the
honeycomb heater in which slits are to be formed, there is no
particular restriction as to the production method; and slits can
be formed in any of, for example, a wound type and an extrudate
type both mentioned above.
[0030] The honeycomb heater is accommodated in a metallic casing so
that the lengthwise direction of the passages of the honeycomb
heater becomes parallel with the direction of the flow of the
exhaust gas passing in the casing. That is, the lengthwise
direction of the passages of the honeycomb heater becomes parallel
with the lengthwise (thickness) direction of the casing;
consequently, the most part of the exhaust gas passes through the
passages of the honeycomb heater. The casing is a cylinder into
which the honeycomb heater can be inserted, and an example thereof
is a metallic cylinder. The sectional shape of the casing in a
direction vertical to the lengthwise direction is not restricted to
a circle and can be appropriately determined so as to match the
shape of the honeycomb heater.
[0031] In the present invention, in fixing the honeycomb heater in
the casing, first a metallic holding member is fitted to the outer
surface of the honeycomb heater. When the honeycomb heater has
slits (for resistance adjustment) formed therein, the slits often
show expansion or shrinkage, making the external shape of the
honeycomb heater unstable, in many cases. Therefore, the fitting of
the holding member can stabilize the shape of the honeycomb heater,
and moreover suppresses the movement (e.g. expansion or shrinkage)
of slits and allows the honeycomb heater to have higher
durability.
[0032] FIG. 1 is a drawing showing an embodiment of the heater unit
of the present invention, wherein a honeycomb heater 1 is fitted to
a casing 3 via a holding member 5. The inner periphery of the
ring-shaped holding member 5 is buried in a groove 7 formed at the
outer periphery (side) of the honeycomb heater 1, and fixed to the
honeycomb heater 1 so that the gap between the holding member 5 and
the honeycomb heater 1 becomes minimum. The outer periphery of the
holding member 5 is fitted to the inner surface of the casing 3 so
that the gap between the holding member 5 and the casing 3 becomes
minimum. The fixing between the holding member 5 and the casing 3
is ordinarily conducted by welding, and total welding or partial
welding (spot welding) is used appropriately. Incidentally, the
honeycomb heater 1 has slits (for resistance adjustment) formed
therein.
[0033] The material for the holding member 5 is a metal. Since the
material for the honeycomb heater 1 is generally a metal having a
thermal expansion coefficient as large as 10.times.10.sup.-6 to
20.times.10.sup.-6/.degree. C., a metal having about the same
thermal expansion coefficient is used as the material for the
holding member 5. By matching the thermal expansion coefficients of
the two materials, it is possible to reduce the stress caused by
the difference in thermal expansion coefficient between the holding
member 5 and the honeycomb heater 1.
[0034] For example, when the honeycomb heater 1 is made of ferrite,
the holding member 5 is preferably made of a heat-resistant steel
such as ferrite, austenite or the like. Since the outer periphery
of the honeycomb heater 1 has a lower temperature than the central
portion of the honeycomb heater 1, use of austenite having a high
thermal expansion property can reduce the thermal stress generated
between the honeycomb heater 1 and the holding member 5. The
holding member 5 preferably has a heat resistance equivalent to
that of the honeycomb heater 1. However, since the holding member 5
is fitted to part of the outer surface of the honeycomb heater 1,
the heat resistance of the holding member 5 need not be as high as
that of the honeycomb heater 1 and can generally be 600.degree. C.
or higher.
[0035] An insulating area must be formed at the boundary between
the metallic holding member 5 and the honeycomb heater 1 to avoid
their mutual contact via the insulating area. Formation of such an
insulating area can be conducted by, as shown in FIG. 1, forming,
by coating, an insulating film (e.g. a ceramic film) 9 on the outer
surface of a holding member 5 and then filling an insulator 11
between the holding member 5 and a honeycomb heater 1.
[0036] Formation of the insulating film 9 on the holding member 5
is conducted by thermal spraying, electrostatic coating, dipping or
the like. As the insulator 11, there are used a heat-resistant
inorganic adhesive, a heat-resistant mortar, a glassy cloth, etc.
As the isolator 11, a heat-resistant inorganic adhesive is most
preferred because it can fix the honeycomb heater 1 strongly. It is
not always necessary to use both the insulating film 9 and the
insulator 11, and only either of them may be used as long as
insulation and durability are ensured between the holding member 5
and the honeycomb heater 1.
[0037] In FIG. 1, the holding member 5 is shown like a single ring.
In actual production, the holding member 5 ordinarily consists of
two or more parts and they are provided in the groove 7 at the
outer periphery of the honeycomb heater 1, in a connected state.
FIG. 2(a) (plan view) and FIG. 2(b) (side view) show a holding
member 5 consisting of two half rings, and each half ring has a
ceramic insulating film 9 on the inner periphery of the holding
member 5 which is fitted to the honeycomb heater via the insulating
film 9. These plural parts need not be bonded at the boundaries by
welding or the like as long as they can fasten the honeycomb heater
1 strongly in a casing.
[0038] In the holding member may be formed slits so that the
holding member can have flexibility and the stress applied to the
honeycomb heater can be reduced. FIG. 3 is an example of the
holding member having slits formed therein for stress reduction. In
this example, slits 13 are radially formed in a holding member 15
consisting of a half ring. FIG. 4 is also an example of the holding
member having slits formed therein for stress reduction. In FIG. 4,
formation of a plurality of slits 17 in a holding member 21 results
in formation of legs 19 of rectangular shape in the holding member
21, and only an area 19' of the front end of each leg 19 is fitted
to a casing; thereby, the holding member 21 can have good
flexibility. When slits are formed in a holding member, a by-pass
flow arises through the slits; however, the by-pass flow can be
made negligibly small by controlling the width of each slit at
about 1 mm.
[0039] In fitting the holding member to the honeycomb heater, it is
also possible to force a honeycomb heater into a one-piece ring as
holding member to allow the honeycomb heater to have a stable
shape. In this case, however, there is a fear that the insulation
and fitting between the ring and the honeycomb heater are
insufficient.
[0040] As shown in FIG. 5, in a honeycomb heater 1 wherein slits 23
for resistance adjustment are formed in a honeycomb structure
between electrodes 31a and 31b, an electric path is formed between
the slits 23 and heat is generated. However, when, as in the case
of the embodiment of FIG. 1, a ring-shaped groove 7 is formed at
the outer periphery (side) of the honeycomb heater 1 and a holding
member 5 is buried in and fixed to the groove 7, it is preferred to
set the diameter d1 of the groove 7 so that substantially all the
honeycomb heater portion inside the groove 7 becomes a
heat-generating portion.
[0041] When the holding member 5 is buried in the groove 7 having
such a diameter, the holding member 5 substantially blocks the flow
path of exhaust gas at the peripheral portion of the honeycomb
heater 1 which is not heated, or at the portion of the honeycomb
heater 1 which is inferior in heat-generating property to the
central portion of the honeycomb heater 1; as a result, the whole
exhaust gas passing through the honeycomb heater 1 can be heated
and favorable emission control is achieved.
[0042] In the present invention, the holding member has such a
structure as (1) allows a honeycomb heater to have a stable shape
and holds the honeycomb heater in a casing and (2) substantially
blocks the flow path of exhaust gas between the honeycomb heater
and the casing. Therefore, the shape and dimension of the outer
periphery of the holding member is made nearly conformable to the
shape and dimension of the inner surface of the casing to which the
holding member is fitted. The holding member is fitted to the
casing by means of welding or the like. The holding member
preferably has a skirt-like shape as shown in FIG. 1, whereby the
holding member can have a spring property as compared with a flat
plate, making it possible to absorb the displacement of honeycomb
heater 1 caused by its expansion and shrinkage in the radial
direction and also suppress the displacement in the axial
direction.
[0043] In the present invention, the position of fitting the
holding member is not restricted to the outer periphery (side) of
the honeycomb heater as in the above embodiment. For example, as
shown in FIG. 6, it is possible to form a ring-shaped groove 29 in
a honeycomb heater 25 at an area of the end of the honeycomb heater
25 in its lengthwise (thickness) direction (the end is hereinafter
referred to simply as face), close to the outer periphery (side) of
the honeycomb heater 25, i.e. at the periphery of face and fix a
ring-shaped holding member 27 matching the groove 29, in the groove
29.
[0044] In this case, it is preferred to set the diameter d2 of the
groove 29 so that substantially all the honeycomb portion inside
the groove 29 becomes a heat-generating portion, as shown in FIG.
7. When the holding member 27 is buried in the groove 29 having
such a diameter, the holding member 27 substantially blocks the
flow path of exhaust gas at the peripheral portion of the honeycomb
heater 25 which is not heated, or at the portion of the honeycomb
heater 25 which is inferior in heat-generating property to the
central portion of the honeycomb heater 25; as a result, the whole
exhaust gas passing through the honeycomb heater 25 can be heated
and favorable emission control is achieved.
[0045] In holding such a honeycomb heater 25 in a casing 3, the
holding member 27 may be fitted to the honeycomb heater 25 at the
exhaust gas-incoming side or the exhaust gas-leaving side. The
holding member 27 may be fitted to one face or both faces of the
honeycomb heater 25.
[0046] In the above have been described embodiments of the present
invention in detail. Needless to say, the present invention is in
no way restricted to these embodiments. It should be understood
that various changes, modifications, improvements, etc. can be made
based on the knowledge of those skilled in the art, as long as they
do not depart from the scope of the present invention.
[0047] As stated above, in the heater unit of the present invention
comprising a honeycomb heater and a casing therefor, the honeycomb
heater has high shape stability and high durability because a
holding member is fitted to the honeycomb heater. Further, since
the holding member has such a structure as substantially blocks the
flow path of exhaust gas between the honeycomb heater and the
casing, there is substantially no by-pass flow of exhaust gas, in
the present heater unit. Therefore, when mounted on an automobile,
the present heater unit has high durability and shows an excellent
exhaust gas purifiability during the cold start of engine.
* * * * *