U.S. patent application number 13/057894 was filed with the patent office on 2011-06-09 for exhaust heat recovery system.
This patent application is currently assigned to TOYOTA JIDOSHA KABUSHIKI KAISHA. Invention is credited to Hideyuki Komisu, Toshio Murata, Masao Toi.
Application Number | 20110131962 13/057894 |
Document ID | / |
Family ID | 41510864 |
Filed Date | 2011-06-09 |
United States Patent
Application |
20110131962 |
Kind Code |
A1 |
Toi; Masao ; et al. |
June 9, 2011 |
EXHAUST HEAT RECOVERY SYSTEM
Abstract
An exhaust heat recovery system (18) includes first and second
loop heat pipes (20 and 30). The first loop heat pipe (20) recovers
exhaust heat downstream of a catalyst (5) in an exhaust passage (4)
of an internal combustion engine (1) to exchange heat with the
catalyst (5). The second loop heat pipe (30) recovers heat of the
catalyst (5) to exchange heat with coolant that is once delivered
from the internal combustion engine (1).
Inventors: |
Toi; Masao; (Aichi-ken,
JP) ; Komisu; Hideyuki; (Aichi-ken, JP) ;
Murata; Toshio; (Aichi-ken, JP) |
Assignee: |
TOYOTA JIDOSHA KABUSHIKI
KAISHA
Toyota-shi, Aichi-ken
JP
|
Family ID: |
41510864 |
Appl. No.: |
13/057894 |
Filed: |
August 7, 2009 |
PCT Filed: |
August 7, 2009 |
PCT NO: |
PCT/IB09/06842 |
371 Date: |
February 7, 2011 |
Current U.S.
Class: |
60/320 ; 60/660;
60/670 |
Current CPC
Class: |
F01P 3/12 20130101; F28D
7/106 20130101; F01N 5/02 20130101; F01N 13/1855 20130101; F01N
13/009 20140601; F28D 1/053 20130101; F28D 15/0266 20130101; Y02T
10/16 20130101; F01P 2003/2278 20130101; F28D 15/06 20130101; F01N
13/1827 20130101; F28D 1/0408 20130101; Y02T 10/12 20130101 |
Class at
Publication: |
60/320 ; 60/670;
60/660 |
International
Class: |
F01N 5/02 20060101
F01N005/02; F01K 23/06 20060101 F01K023/06; F01K 13/02 20060101
F01K013/02 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 8, 2008 |
JP |
2008-205285 |
Jun 23, 2009 |
JP |
2009-148818 |
Claims
1. An exhaust heat recovery system comprising: a first loop heat
pipe that recovers exhaust heat downstream of a first catalyst in
an exhaust passage of an internal combustion engine and that
exchanges heat with the first catalyst; and a second loop heat pipe
that recovers heat of the first catalyst and that exchanges heat
with coolant that is delivered from the internal combustion
engine.
2. The exhaust heat recovery system according to claim 1, wherein
the first loop heat pipe includes a first heat receiving unit that
vaporizes working fluid, which is hermetically sealed and filled
inside the first heat receiving unit, by exhaust heat downstream of
the first catalyst in the exhaust passage, a first heat radiating
unit that is attached in an upstream region in the first catalyst
and that causes heat exchange between working fluid, transferred
from the first heat receiving unit, and the first catalyst to
condense the working fluid, a first transfer pipe that is used to
transfer working fluid from the first heat receiving unit to the
first heat radiating unit, and a first return pipe that is used to
return working fluid from the first heat radiating unit to the
first heat receiving unit, and wherein the second loop heat pipe
includes a second heat receiving unit that is attached in a
downstream region in the first catalyst and that vaporizes working
fluid, which is hermetically sealed and filled inside the second
heat receiving unit, by heat of the first catalyst, a second heat
radiating unit that causes heat exchange between working fluid,
transferred from the second heat receiving unit, and coolant,
delivered from the internal combustion engine, to condense the
working fluid, a second transfer pipe that is used to transfer
working fluid from the second heat receiving unit to the second
heat radiating unit, and a second return pipe that is used to
return working fluid from the second heat radiating unit to the
second heat receiving unit.
3. The exhaust heat recovery system according to claim 2, wherein a
first valve device is provided for the first return pipe or the
first transfer pipe, and a second valve device is provided for the
second return pipe or the second transfer pipe.
4. The exhaust heat recovery system according to claim 3, further
comprising a communication passage connected to the first heat
radiating unit and the second heat receiving unit, and wherein a
third valve device is provided in the communication passage.
5. The exhaust heat recovery system according to claim 4, further
comprising: a controller that controls the opening degrees of the
first, second and third valve devices by actuators, wherein when it
is determined that it is necessary to activate the first catalyst,
the controller opens the first valve device and closes the second
and third valve devices, and when it is determined that it is
necessary to heat the coolant in a state where the first catalyst
is activated, the controller closes the first valve device and
opens the second and third valve devices.
6. The exhaust heat recovery system according to claim 5, wherein
when it is determined that the temperature of the first catalyst
has not reached a first catalyst upper limit temperature in a state
where the first catalyst is activated and when it is determined
that the temperature of the coolant has not reached a coolant upper
limit temperature in a state where the coolant has been warmed up,
the controller closes the first valve device and opens the second
and third valve devices, and when it is determined that the
temperature of the first catalyst has reached the first catalyst
upper limit temperature and it is determined that the temperature
of the coolant has reached the coolant upper limit temperature, the
controller closes the first and second valve devices and opens the
third valve device.
7. The exhaust heat recovery system according to claim 2, wherein a
first valve device is provided for the first return pipe or the
first transfer pipe, a bypass pipe that bypasses the second heat
radiating unit is connected to the second transfer pipe and the
second return pipe, and a switching valve is provided at a portion
at which the bypass pipe is connected to the second transfer pipe
and is used to switch between a heat exchange route from the second
transfer pipe toward the second heat radiating unit and a bypass
route from the second transfer pipe toward the bypass pipe.
8. The exhaust heat recovery system according to claim 7, further
comprising: a controller that controls the opening degree of the
first valve device by an actuator, wherein the switching valve is a
three-way valve, the controller controls the switching valve by an
actuator for switching, when it is determined that it is necessary
to activate the first catalyst, the controller opens the first
valve device and secures the bypass route by the switching valve,
when it is determined that it is necessary to heat the coolant in a
state where the first catalyst is activated, the controller closes
the first valve device and secures the heat exchange route by the
switching valve, and when it is determined that the temperature of
the coolant has reached a coolant upper limit temperature, the
controller closes the first valve device and secures the bypass
route by the switching valve.
9. The exhaust heat recovery system according to claim 7, further
comprising a communication passage connected to the first heat
radiating unit and the second heat receiving unit, and wherein a
third valve device is provided in the communication passage.
10. The exhaust heat recovery system according to claim 9, further
comprising: a controller that controls the opening degrees of the
first and third valve devices by actuators, wherein the switching
valve is a three-way valve, the controller controls the switching
valve by an actuator for switching, when it is determined that it
is necessary to activate the first catalyst, the controller opens
the first valve device, closes the third valve device and secures
the bypass route by the switching valve, when it is determined that
it is necessary to heat the coolant in a state where the first
catalyst is activated, the controller closes the first valve
device, opens the third valve device and secures the heat exchange
route by the switching valve, and when it is determined that the
temperature of the coolant has reached a coolant upper limit
temperature, the controller closes the first valve device, opens
the third valve device and secures the bypass route by the
switching valve.
11. The exhaust heat recovery system according to claim 3, wherein
the first valve device automatically controls its opening degree in
accordance with a predetermined actuating condition, and the first
valve device opens when a condition that it is necessary to
activate the first catalyst is satisfied, while the first valve
device closes when a condition that it is necessary to heat the
coolant is satisfied in a state where the first catalyst is
activated.
12. The exhaust heat recovery system according to claim 3, wherein
the second valve device automatically controls its opening degree
in accordance with a predetermined actuating condition, and the
second valve device closes when a condition that it is necessary to
activate the first catalyst is satisfied, while the second valve
device opens when a condition that the first catalyst is activated
is satisfied.
13. The exhaust heat recovery system according to claim 3, wherein
the second valve device automatically controls its opening degree
in accordance with a predetermined actuating condition, and the
second valve device closes when a condition that it is necessary to
activate the first catalyst is satisfied or when it is determined
that the temperature of the coolant has reached a coolant upper
limit temperature, while the second valve device opens when a
condition that it is necessary to heat the coolant is satisfied in
a state where the first catalyst is activated.
14. The exhaust heat recovery system according to claim 4, wherein
the third valve device automatically controls its opening degree in
accordance with a predetermined actuating condition, and the third
valve device closes when a condition that it is necessary to
activate the first catalyst is satisfied, while the third valve
device opens when a condition that it is necessary to heat the
coolant is satisfied in a state where the first catalyst is
activated or when a condition that the temperature of the coolant
has reached a coolant upper limit temperature is satisfied.
15. The exhaust heat recovery system according to claim 4, wherein
the first heat radiating unit includes a first hollow sleeve that
is provided so as to surround an upstream region in the first
catalyst and that has a first inner annular space, wherein the
first transfer pipe and the first return pipe are connected to the
first inner annular space and are in fluid communication with the
first inner annular space, and a radially outward-directed fin that
is provided on an inner peripheral wall of the first hollow sleeve,
wherein the second heat receiving unit includes a second hollow
sleeve that is provided so as to surround a downstream region in
the first catalyst and that has a second inner annular space,
wherein the second transfer pipe and the second return pipe are
connected to the second inner annular space and are in fluid
communication with the second inner annular space, and a radially
outward-directed fin that is provided on an inner peripheral wall
of the second hollow sleeve, and wherein the first and second
hollow sleeves are connected next to each other in an axial
direction thereof at a connecting portion at which the
communication passage is provided.
16. The exhaust heat recovery system according to claim 2, wherein
a vibration transmission damping portion is provided at a location
adjacent to the internal combustion engine in the exhaust passage,
and the second heat radiating unit is attached in a region from the
vibration transmission damping portion to the first catalyst.
17. The exhaust heat recovery system according to claim 2, further
comprising: a second catalyst provided downstream of the first
catalyst in the exhaust passage, wherein the first heat receiving
unit is provided downstream of the second catalyst.
18. The exhaust heat recovery system according to claim 7, wherein
the first valve device automatically controls its opening degree in
accordance with a predetermined actuating condition, and the first
valve device opens when a condition that it is necessary to
activate the first catalyst is satisfied, while the first valve
device closes when a condition that it is necessary to heat the
coolant is satisfied in a state where the first catalyst is
activated.
19. The exhaust heat recovery system according to claim 9, wherein
the third valve device automatically controls its opening degree in
accordance with a predetermined actuating condition, and the third
valve device closes when a condition that it is necessary to
activate the first catalyst is satisfied, while the third valve
device opens when a condition that it is necessary to heat the
coolant is satisfied in a state where the first catalyst is
activated or when a condition that the temperature of the coolant
has reached a coolant upper limit temperature is satisfied.
20. The exhaust heat recovery system according to claim 9, wherein
the first heat radiating unit includes a first hollow sleeve that
is provided so as to surround an upstream region in the first
catalyst and that has a first inner annular space, wherein the
first transfer pipe and the first return pipe are connected to the
first inner annular space and are in fluid communication with the
first inner annular space, and a radially outward-directed fin that
is provided on an inner peripheral wall of the first hollow sleeve,
wherein the second heat receiving unit includes a second hollow
sleeve that is provided so as to surround a downstream region in
the first catalyst and that has a second inner annular space,
wherein the second transfer pipe and the second return pipe are
connected to the second inner annular space and are in fluid
communication with the second inner annular space, and a radially
outward-directed fin that is provided on an inner peripheral wall
of the second hollow sleeve, and wherein the first and second
hollow sleeves are connected next to each other in an axial
direction thereof at a connecting portion at which the
communication passage is provided.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The invention relates to an exhaust heat recovery system
that is able to accelerate an increase in temperature of a portion
to be heated in a vehicle, such as an automobile, using exhaust
heat of an internal combustion engine.
[0003] 2. Description of the Related Art
[0004] It is known that heat of exhaust gas from an internal
combustion engine mounted on a vehicle, such as an automobile, is
recovered by a heat pipe and is used, for example, to facilitate
activation of a catalyst and to accelerate the internal combustion
engine to warm up. (see Japanese Utility Model Application
Publication No. 63-22321 (JP-U-63-22321) and Japanese Patent
Application Publication No. 2008-14304 (JP-A-2008-14304)).
[0005] JP-U-63-22321 describes a configuration that one end of the
heat pipe is connected to an exhaust passage of the internal
combustion engine at a portion downstream of a catalytic device to
serve as a heating portion (corresponding to a heat receiving
unit), the other end of the heat pipe is connected to the exhaust
passage at a portion upstream of the catalytic device to serve as a
cooling portion (corresponding to a heat radiating unit) and then
exhaust gas upstream of the catalytic device is heated to increase
its temperature to indirectly increase the temperature of the
catalytic device.
[0006] The heat pipe is hermetically sealed and filled with working
fluid, such as pure water, in the inner space and heats one end
thereof to vaporize the working fluid to feed the working fluid to
the other end. Then the heat pipe causes the vaporized working
fluid to radiate heat to condense at the other end, and is returned
back to the one end.
[0007] JP-A-2008-14304 describes an exhaust heat recovery system.
The exhaust heat recovery system includes a vaporizing portion
(corresponding to a heat receiving unit) and a condensing portion
(corresponding to a heat radiating unit). The vaporizing portion
recovers exhaust heat in the exhaust passage of the internal
combustion engine to vaporize working fluid. The condensing portion
condenses the vaporized working fluid. The vaporizing portion and
the condensing portion are integrally connected in a state where
they are arranged next to each other to form a closed loop. Part of
a coolant passage of the internal combustion engine is arranged
adjacent to the condensing portion to exchange heat between the
coolant and the gaseous working fluid.
[0008] In this example, a loop heat pipe, in which the vaporizing
portion and the condensing portion are integrated next to each
other is used, and the vaporizing portion is arranged so as to
cross the exhaust passage.
[0009] Other than the above, Japanese Utility Model Application
Publication No. 2-76508 (JP-U-2-76508) is, for example, known in
which a heat receiving unit and condensing portion (corresponding
to a heat radiating unit) of a loop heat pipe are arranged away
from each other. JP-U-2-76508 describes a configuration that the
heat receiving unit of the loop heat pipe is provided in the
exhaust passage of the internal combustion engine at a portion
downstream of a catalyst, and the condensing portion of the loop
heat pipe is provided near a heater core of a hot-air heater
installed midway of a coolant passage that once delivers the
coolant of the internal combustion engine and then returns the
coolant back.
[0010] The above exhaust heat recovery system includes only any one
of the heat pipe for increasing the temperature of the catalyst
provided in the exhaust passage of the internal combustion engine
or the heat pipe for increasing the temperature of the coolant of
the internal combustion engine, and there is no exhaust heat
recovery system that includes both.
SUMMARY OF THE INVENTION
[0011] The invention is able to, where necessary, execute a process
of accelerating an increase in temperature of a catalyst provided
in an exhaust passage of an internal combustion engine and a
process of accelerating an increase in temperature of coolant of
the internal combustion engine.
[0012] A first aspect of the invention relates to an exhaust heat
recovery system. The exhaust heat recovery system includes: a first
loop heat pipe that recovers exhaust heat downstream of a first
catalyst in an exhaust passage of an internal combustion engine and
that exchanges heat with the first catalyst; and a second loop heat
pipe that recovers heat of the first catalyst and that exchanges
heat with coolant that is once delivered from the internal
combustion engine.
[0013] With the above configuration, it is possible to recover
exhaust heat by the first loop heat pipe to heat the catalyst from
the outside to thereby accelerate an increase in temperature of the
catalyst, and it is possible to recover heat of the catalyst by the
second loop heat pipe to cool the catalyst while accelerating an
increase in temperature of the coolant of the internal combustion
engine.
[0014] In this way, it is possible to efficiently increase the
temperature of the catalyst attached to the internal combustion
engine and to efficiently increase the temperature of the coolant
of the internal combustion engine.
[0015] The first loop heat pipe may include a first heat receiving
unit that vaporizes working fluid, which is hermetically sealed and
filled inside the first heat receiving unit, by exhaust heat
downstream of the first catalyst in the exhaust passage, a first
heat radiating unit that is attached in an upstream region in the
first catalyst and that causes heat exchange between working fluid,
transferred from the first heat receiving unit, and the first
catalyst to condense the working fluid, a first transfer pipe that
is used to transfer working fluid from the first heat receiving
unit to the first heat radiating unit, and a first return pipe that
is used to return working fluid from the first heat radiating unit
to the first heat receiving unit, and wherein the second loop heat
pipe may include a second heat receiving unit that is attached in a
downstream region in the first catalyst and that vaporizes working
fluid, which is hermetically sealed and filled inside the second
heat receiving unit, by heat of the first catalyst, a second heat
radiating unit that causes heat exchange between working fluid,
transferred from the second heat receiving unit, and coolant, once
delivered from the internal combustion engine, to condense the
working fluid, a second transfer pipe that is used to transfer
working fluid from the second heat receiving unit to the second
heat radiating unit, and a second return pipe that is used to
return working fluid from the second heat radiating unit to the
second heat receiving unit.
[0016] Here, the configuration of each of the first and second loop
heat pipes is specified, and it becomes easy to implement the
exhaust heat recovery system through this specification.
[0017] A first valve device may be provided for the first return
pipe or the first transfer pipe, and a second valve device is
provided for the second return pipe or the second transfer
pipe.
[0018] With the above configuration, it is possible to circulate
heat or stop heat circulation by the first loop heat pipe by
opening or closing the first valve device. In addition, it is
possible to circulate heat or stop heat circulation by the second
loop heat pipe by opening or closing the second valve device.
Therefore, for example, when it is necessary to warm up the
catalyst, it is possible to preferentially warm up the catalyst
with exhaust heat using the first loop heat pipe only. In addition,
for example, when the catalyst has been warmed up and then it is
necessary to warm up the internal combustion engine, only the
second loop heat pipe is used to make it possible to recover heat
of the catalyst to cool the catalyst while accelerating an increase
in temperature of the coolant of the internal combustion
engine.
[0019] Note that in a state where the first and second valve
devices are provided for the first and second return pipes, as the
first and second valve devices are closed, working fluid condensed
in the first and second heat radiating units cannot be returned to
the first and second heat receiving units. Thus, heat circulation
is stopped by the first and second loop heat pipes. In addition, in
a state where the first and second valve devices are provided for
the first and second transfer pipes, as the first and second valve
devices are dosed, working fluid vaporized in the first and second
heat receiving units cannot be transferred to the first and second
heat radiating units. Thus, heat circulation is stopped by the
first and second loop heat pipes.
[0020] A communication passage may be connected to the first heat
radiating unit and the second heat receiving unit, and a third
valve device may be provided in the communication passage.
[0021] With the above configuration, as the third valve device is
closed, the first heat radiating unit and the second heat receiving
unit function as separate heat exchange portions, while, as the
third valve device is opened, the first heat radiating unit and the
second heat radiating unit function as a single large-volume heat
exchange portion.
[0022] For example, when it is necessary to warm up the catalyst,
as heat is circulated using the first loop heat pipe only and the
third valve device is closed, it is possible to heat the upstream
region in the catalyst with exhaust heat. In addition, for example,
when the catalyst has been warmed up and then it is necessary to
warm up the internal combustion engine, as heat is circulated using
the second loop heat pipe and the third valve device is opened,
heat of the entire region in the catalyst may be recovered to cool
the catalyst while accelerating an increase in temperature of the
coolant of the internal combustion engine.
[0023] The exhaust heat recovery system may further include a
controller that controls the opening degrees of the first, second
and third valve devices by actuators, wherein, when it is
determined that it is necessary to activate the first catalyst, the
controller may open the first valve device and close the second and
third valve devices, and, when it is determined that it is
necessary to heat the coolant in a state where the first catalyst
is activated, the controller may close the first valve device and
open the second and third valve devices.
[0024] With the above configuration, the opening and closing of the
first to third valve devices may be controlled by the controller at
appropriate timings. By opening or closing the first to third valve
devices on the basis of the coolant temperature of the internal
combustion engine and the temperature of the catalyst, it is
possible to optimally use the first loop heat pipe and the second
loop heat pipe.
[0025] For example, when the temperature of the catalyst is
increased to an activation temperature, heat is circulated using
the first loop heat pipe only to make it possible to preferentially
warm up the catalyst with exhaust heat. In addition, when the
catalyst has been warmed up and then it is necessary to warm up the
internal combustion engine, heat is circulated using the second
loop heat pipe only to make it possible to cool the catalyst while
accelerating an increase in temperature of the coolant of the
internal combustion engine with heat of the catalyst.
[0026] When it is determined that the temperature of the first
catalyst has not reached an upper limit temperature in a state
where the first catalyst is activated and it is determined that the
temperature of the coolant has not reached an upper limit
temperature in a state where the coolant has been warmed up, the
controller may close the first valve device and open the second and
third valve devices, and, when it is determined that the
temperature of the first catalyst has reached the upper limit
temperature and it is determined that the temperature of the
coolant has reached the upper limit temperature, the controller may
close the first and second valve devices and open the third valve
device.
[0027] In this case, furthermore, under the condition that the
temperature of the catalyst or the coolant temperature of the
internal combustion engine tends to excessively increase, heat
circulation using the first and second loop heat pipes is stopped.
By so doing, it is possible to prevent a decrease in function due
to excessive heating of the catalyst and overheating of the
internal combustion engine.
[0028] A first valve device may be provided for the first return
pipe or the first transfer pipe, a bypass pipe that bypasses the
second heat radiating unit may be connected to the second transfer
pipe and the second return pipe, and a switching valve may be
provided at a portion at which the bypass pipe is connected to the
second transfer pipe and may be used to switch between a heat
exchange route from the second transfer pipe toward the second heat
radiating unit and a bypass route from the second transfer pipe
toward the bypass pipe.
[0029] With the above configuration, it is possible to circulate
heat or stop heat circulation in the first loop heat pipe by
opening or closing the first valve device. In addition, as the heat
exchange route is secured by the switching valve, it is possible to
circulate heat using the second loop heat pipe, while, as the
bypass route is secured by the switching valve, it is possible to
stop heat circulation using the second loop heat pipe. Therefore,
for example, when it is necessary to warm up the catalyst, it is
possible to preferentially warm up the catalyst with exhaust heat
using the first loop heat pipe only. In addition, for example, when
the catalyst has been warmed up and then it is necessary to warm up
the coolant of the internal combustion engine, only the second loop
heat pipe is used to make it possible to recover heat of the
catalyst to cool the catalyst while accelerating an increase in
temperature of the coolant of the internal combustion engine.
[0030] The exhaust heat recovery system may include a controller
that controls the opening degree of the first valve device by an
actuator, wherein the switching valve may be a three-way valve, the
controller may control the switching valve by an actuator for
switching, when it is determined that it is necessary to activate
the first catalyst, the controller may open the first valve device
and secure the bypass route by the switching valve, when it is
determined that it is necessary to heat the coolant in a state
where the first catalyst is activated, the controller may close the
first valve device and secure the heat exchange route by the
switching valve, and, when it is determined that the temperature of
the coolant has reached an upper limit temperature, the controller
may close the first valve device and secure the bypass route by the
switching valve.
[0031] With the above configuration, the opening and closing of the
first valve device and the switching of the switching valve may be
controlled by the controller at appropriate timings. By controlling
the first valve device and the switching valve on the basis of the
coolant temperature of the internal combustion engine and the
temperature of the catalyst, it is possible to optimally use the
first loop heat pipe and the second loop heat pipe.
[0032] A communication passage may be connected to the first heat
radiating unit and the second heat receiving unit, and a third
valve device may be provided in the communication passage.
[0033] With the above configuration, as the third valve device is
closed, the first heat radiating unit and the second heat receiving
unit function as separate heat exchange portions, while, as the
third valve device is opened, the first heat radiating unit and the
second heat radiating unit function as a single large-volume heat
exchange portion.
[0034] For example, when it is necessary to warm up the catalyst,
as heat is circulated using the first loop heat pipe only and the
third valve device is closed, it is possible to heat the upstream
region in the catalyst with exhaust heat. In addition, for example,
when the catalyst has been warmed up and then it is necessary to
warm up the internal combustion engine, as heat is circulated using
the second loop heat pipe only and the third valve device is
opened, heat may be recovered from the entire region in the
catalyst to heat the coolant of the internal combustion engine. As
the heat is recovered from the catalyst, the catalyst is
cooled.
[0035] The exhaust heat recovery system may include a controller
that controls the opening degrees of the first and third valve
devices by actuators, wherein the switching valve may be a
three-way valve, the controller may control the switching valve by
an actuator for switching, when it is determined that it is
necessary to activate the first catalyst, the controller may open
the first valve device; close the third valve device and secure the
bypass route by the switching valve, when it is determined that it
is necessary to heat the coolant in a state where the first
catalyst is activated, the controller may close the first valve
device, open the third valve device and secure the heat exchange
route by the switching valve, and when it is determined that the
temperature of the coolant has reached an upper limit temperature,
the controller may close the first valve device, open the third
valve device and secure the bypass route by the switching
valve.
[0036] With the above configuration, the operations of the first
valve device, switching valve and third valve device may be
controlled by the controller at appropriate timings. By controlling
the first valve device, the switching valve and the third valve
device on the basis of the coolant temperature of the internal
combustion engine and the temperature of the catalyst, it is
possible to optimally use the first loop heat pipe and the second
loop heat pipe.
[0037] For example, when the temperature of the catalyst is
increased to an, activation temperature, heat is circulated using
the first loop heat pipe only to make it possible to preferentially
warm up the catalyst with exhaust heat. In addition, when the
catalyst has been warmed up and then it is necessary to warm up the
coolant of the internal combustion engine, heat is circulated using
the second loop heat pipe only to make it possible to cool the
catalyst while accelerating an increase in temperature of the
coolant of the internal combustion engine with heat of the
catalyst.
[0038] In this case, furthermore, under the condition that the
temperature of the catalyst or the coolant temperature of the
internal combustion engine tends to excessively increase, heat
circulation using the first and second loop heat pipes is stopped.
By so doing, it is possible to prevent a decrease in function due
to excessive heating of the catalyst and overheating of the
internal combustion engine.
[0039] The first valve device to the third valve device each may be
of a self-actuated type that automatically controls its opening
degree in accordance with a predetermined actuating condition.
[0040] Then, the self-actuated first valve device may open when a
condition that it is necessary to activate the first catalyst is
satisfied, while the self-actuated first valve device may close
when a condition that it is necessary to heat the coolant is
satisfied in a state where the first catalyst is activated.
[0041] In addition, the self-actuated second valve device may close
when a condition that it is necessary to activate the first
catalyst is satisfied, while the self-actuated second valve device
may open when a condition that the first catalyst is activated is
satisfied. Alternatively, the second valve device may close when a
condition that it is necessary to activate the first catalyst is
satisfied or when it is determined that the temperature of the
coolant has reached an upper limit temperature, while the second
valve device may open when a condition that it is necessary to heat
the coolant is satisfied in a state where the first catalyst is
activated.
[0042] Furthermore, the self-actuated third valve device may close
when a condition that it is necessary to activate the first
catalyst is satisfied, while the self-actuated third valve device
may open when a condition that it is necessary to heat the coolant
is satisfied in a state where the first catalyst is activated or
when a condition that the temperature of the coolant has reached an
upper limit temperature is satisfied.
[0043] In this way, when the first valve device to the third valve
device each are of a self-actuated type, a control system (for
example, control programs, wires, and the like) for the first valve
device to the third valve device is unnecessary, so it is
advantageous in reducing facility costs.
[0044] The first heat radiating unit may include a first hollow
sleeve that is provided so as to surround an upstream region in the
first catalyst and that has an inner annular space, wherein the
first transfer pipe and the first return pipe may be connected to
the inner annular space and may be in fluid communication with the
inner annular space, and a radially outward-directed fin that is
provided on an inner peripheral wall of the first hollow sleeve,
wherein the second heat receiving unit may include a second hollow
sleeve that is provided so as to surround a downstream region in
the first catalyst and that has an inner annular space, wherein the
second transfer pipe and the second return pipe are connected to
the inner annular space and are in fluid communication with the
inner annular space, and a radially outward-directed fin that is
provided on an inner peripheral wall of the second hollow sleeve,
and wherein both the first and second hollow sleeves may be
connected next to each other in an axial direction thereof at a
connecting portion at which the communication passage is
provided.
[0045] Here, the outer shape of each of the first heat radiating
unit and the second heat receiving unit is an annular shape so as
to surround the catalyst, and it is possible to efficiently
transfer heat to the catalyst and efficiently recover heat of the
catalyst through this specification.
[0046] A vibration transmission damping portion may be provided at
a location adjacent to the internal combustion engine in the
exhaust passage, and the second heat radiating unit may be attached
in a region from the vibration transmission damping portion to the
first catalyst.
[0047] Here, in short, vibrations transferred from the internal
combustion engine to the exhaust passage are damped by the
vibration transmission damping portion. Thus, the heat receiving
units of the first and second loop heat pipes are provided in a
region downstream of the vibration transmission damping portion in
the exhaust passage.
[0048] This means that, as the region downstream of the vibration
transmission damping portion in the exhaust passage vibrates, the
heat receiving units of the first and second loop heat pipes and
the heat radiating units all substantially synchronously move, so
bending stress due to the vibrations tends to be applied to the
proximal portions of the transfer pipes and return pipes that are
connected to and are in fluid communication with the heat receiving
units and heat radiating units.
[0049] Thus, it is possible to achieve long service life, for
example, such that the first and second loop heat pipes undergo
temporal fatigue breaking. Here, when the bending stress is
applied, it is necessary to take measures that the thickness or
outer diameter of each of the transfer pipes and the return pipes
is increased to enhance rigidity or the transfer pipes and the
return pipes are formed of a flexible pipe. However, when the above
vibration transmission damping portion is provided, such measures
need not be taken.
[0050] The exhaust heat recovery system according to the aspect of
the invention is able to, where necessary, carry out a process of
accelerating an increase in temperature of the catalyst provided in
the exhaust passage of the internal combustion engine and a process
of accelerating an increase in temperature of the coolant of the
internal combustion engine.
BRIEF DESCRIPTION OF THE DRAWINGS
[0051] The foregoing and further objects, features and advantages
of the invention will become apparent from the following
description of example embodiments with reference to the
accompanying drawings, wherein like numerals are used to represent
like elements and wherein:
[0052] FIG. 1 is a schematic configuration diagram that shows an
exhaust heat recovery system according to a first embodiment of the
invention;
[0053] FIG. 2 is a cross-sectional view that shows a spherical
joint shown in FIG. 1;
[0054] FIG. 3 is a cross-sectional view that shows the specific
configuration of the exhaust heat recovery system of FIG. 1;
[0055] FIG. 4 is a flowchart used to illustrate the operation of
the exhaust heat recovery system of FIG. 1;
[0056] FIG. 5 is a schematic configuration diagram that shows an
exhaust heat recovery system according to another embodiment of the
invention;
[0057] FIG. 6A and FIG. 6B are cross-sectional views that show the
specific configuration of a second valve device shown in FIG.
5;
[0058] FIG. 7 is a schematic configuration diagram that shows an
exhaust heat recovery system according to a second embodiment of
the invention;
[0059] FIG. 8A, FIG. 8B and FIG. 8C are cross-sectional views that
show the specific configuration of a second valve device shown in
FIG. 7;
[0060] FIG. 9 is a flowchart used to illustrate the operation of
the exhaust heat recovery system of FIG. 7;
[0061] FIG. 10 is a schematic configuration diagram that shows an
exhaust heat recovery system according to a third embodiment of the
invention; and
[0062] FIG. 11 is a flowchart used to illustrate the operation of
the exhaust heat recovery system of FIG. 10.
DETAILED DESCRIPTION OF EMBODIMENTS
First Embodiment
[0063] FIG. 1 to FIG. 4 show the first embodiment of the invention.
The first embodiment describes an example of an exhaust heat
recovery system applied to an internal combustion engine mounted on
a vehicle.
[0064] The schematic configuration of the exhaust heat recovery
system will be described with reference to FIG. 1. In the drawing,
a water-cooled internal combustion engine 1 supplies an air-fuel
mixture to a combustion chamber of the internal combustion engine 1
to burn, and then discharges exhaust gas in the combustion chamber
from an exhaust system to the atmosphere. The air-fuel mixture is
obtained by mixing air, supplied from an intake system, with fuel,
supplied from a fuel supply system, at an appropriate air-fuel
ratio.
[0065] The exhaust system at least includes an exhaust manifold 2
and an exhaust pipe 4. The exhaust manifold 2 is installed to the
internal combustion engine 1. The exhaust pipe 4 is connected to
the exhaust manifold 2 via a spherical joint 3. The exhaust
manifold 2 and the exhaust pipe 4 form an exhaust passage.
[0066] As shown in FIG. 2, the spherical joint 3 includes a flat
flange 3a, a semi-spherical flange 3b, a gasket 3c, bolts 3d and
nuts 3e, and coil springs 3f. The flat flange 3a is directed
radially outward and is provided at a downstream open end of the
exhaust manifold 2. The semi-spherical flange 3b is provided at an
upstream open end of the exhaust pipe 4. The gasket 3c is held
between the flat flange 3a and the semi-spherical flange 3b. The
bolts 3d and the nuts 3e are used to fasten the flat flange 3a to
the semi-spherical flange 3b. The coil springs 3f are interposed in
a compressed state between the bolts 3d and the flat flange 3a.
[0067] One side of the gasket 3c, which contacts the flat flange
3a, is formed in a planar shape, and the other side of the gasket
3c, which contacts the inner surface of the semi-spherical flange
3b, is formed in a semi-spherical shape that follows the shape of
the inner surface of the semi-spherical flange 3b. The gasket 3c
seals a contact surface with the flat flange 3a and a contact
surface with the semi-spherical flange 3b by the elastic restoring
forces of the coil springs 3f. When an external force is applied to
cause the exhaust manifold 2 and the exhaust pipe 4 to pivot about
a pivot center 3g, the gasket 3c and the semi-spherical flange 3b
slide on each other to allow the pivot naturally. That is, the
spherical joint 3 blocks transmission of vibrations and movement of
the internal combustion engine 1 to the exhaust pipe 4, or damps
the vibrations and movement and then transmits the vibrations and
movement. Thus, the spherical joint 3 may be regarded as a
vibration transmission damping portion.
[0068] Two catalysts 5 and 6 are serially provided for the exhaust
pipe 4. Exhaust gas is purified by these two catalysts 5 and 6.
[0069] Between these catalysts 5 and 6, the catalyst 5 provided
upstream in a direction in which exhaust gas flows in the exhaust
pipe 4 is a so-called start catalyst (S/C) and is termed an
upstream catalyst, while the catalyst 6 provided downstream in the
direction in which exhaust gas flows in the exhaust pipe 4 is a
so-called main catalyst (M/C) or underfloor catalyst (U/F) and is
termed a downstream catalyst.
[0070] These catalysts 5 and 6 each may be, for example, a
three-way catalyst. The three-way catalyst exhibits purification
action in which carbon monoxide (CO), hydrocarbons (HC) and
nitrogen oxides (NOx) are collectively changed into harmless
components by a chemical reaction.
[0071] Refrigerant (hereinafter, simply referred to as coolant)
called long life coolant (LLC) is filled inside the internal
combustion engine 1. The refrigerant is once delivered from a
coolant delivery passage 8 and supplied to a radiator 7, and is
then returned from the radiator 7 back to the internal combustion
engine 1 via a coolant return passage 9. The radiator 7 cools
coolant, circulated by a water pump 10, through heat exchange with
outside air.
[0072] Then, the flow rate of the coolant that flows through the
radiator 7 and the flow rate of the coolant that flows through a
bypass passage 12 are adjusted by a thermostat 11. For example,
when the engine is being warmed up, the flow rate of the coolant in
the bypass passage 12 is increased to facilitate the engine to warm
up, and to prevent overcooling of the coolant by the radiator
7.
[0073] A heater core 14 is provided midway of a heater passage 13.
The heater passage 13 is branched from the coolant delivery passage
8 and is connected to an upstream side of the water pump 10 in the
coolant return passage 9. The heater core 14 is a heat source for
heating a vehicle cabin using the coolant. Air heated by the heater
core 14 is introduced into the vehicle cabin 17 by a blower fan 15.
Note that a hot-air heater 16 is formed of the heater core 14 and
the blower fan 15. The temperature of the coolant that flows in a
region downstream of the heater core 14 in the heater passage 13
becomes low because of heat radiation from the heater core 14.
[0074] The thus configured exhaust system of the internal
combustion engine 1 is equipped with an exhaust heat recovery
system 18.
[0075] The exhaust heat recovery system 18, for example, recovers
heat of exhaust gas exhausted from the internal combustion engine 1
to make it possible to accelerate an increase in temperature of the
upstream catalyst 5 or recovers heat of the upstream catalyst 5 to
accelerate an increase in temperature of the coolant returned from
the heater core 14 to the internal combustion engine 1. The exhaust
heat recovery system 18 mainly includes two loop heat pipes 20 and
30 and a controller 40.
[0076] The first loop heat pipe 20 mainly includes a first heat
receiving unit 21, a first heat radiating unit 22, a first transfer
pipe 23, a first return pipe 24, and a first valve device 25. The
second loop heat pipe 30 mainly includes a second heat receiving
unit 31, a second heat radiating unit 32, a second transfer pipe
33, a second return pipe 34, and a second valve device 35.
[0077] Working fluid is filled inside the entire loop heat pipes 20
and 30 in a vacuumed state. The working fluid is, for example, pure
water, or the like. The boiling point of water is 100.degree. C. at
1 atmospheric pressure; however, the pressures in the loop heat
pipes 20 and 30 are reduced (for example, 0.01 atmospheric
pressure), so the boiling point is, for example, 5 to 10.degree. C.
Note that the working fluid may be, for example, an alcohol, a
fluorocarbon, a chlorofluoro carbon, or the like, other than pure
water. In addition, the main components of the loop heat pipes 20
and 30 are, for example, made of a stainless material having high
corrosion resistance.
[0078] The controller 40, similar to a generally known electronic
control unit (ECU), includes a central processing unit (CPU), a
program memory (ROM), a data memory (RAM), a backup memory
(nonvolatile RAM), and the like, that are connected to one another
by a bidirectional bus. The controller 40 at least controls the
operation of the exhaust heat recovery system 18.
[0079] Next, the components of the first loop heat pipe 20 will be
described in detail with reference to FIG. 3.
[0080] The first heat receiving unit 21 is provided downstream of
the downstream catalyst 6 in the exhaust pipe 4. The first heat
receiving unit 21 is configured to recover heat as heat of
vaporization in such a manner that liquid working fluid that is
hermetically sealed and filled inside the first heat receiving unit
21 vaporizes with exhaust heat.
[0081] Specifically, the heat receiving unit 21 is provided in a
direction perpendicular to a direction in which exhaust gas flows
through the exhaust pipe 4. The heat receiving unit 21 is formed so
that an upper tank 21a and a lower tank 21b are in fluid
communication via a plurality of tubes 21c, and fins 21d connected
to outer wall surfaces of the tubes 21c are arranged within gaps
between the adjacent tubes 21c.
[0082] The gaps between the adjacent tubes 21c are flow passages of
exhaust gas that flows through the exhaust pipe 4. The fins 21d
arranged within these gaps are of a corrugated type so as to
increase the area of heat exchange with exhaust gas that passes
through the gaps. The corrugated-type fins 21d are, for example,
the ones such that a thin belt-like plate material is formed into a
corrugated shape by roller working in short, heat of exhaust gas is
absorbed by the fins 21d to heat and vaporize working fluid that
flows through the tubes 21c. Thus, the tubes 21c and the fins 21d
serve as a heat exchanger.
[0083] The first heat radiating unit 22 is attached in an upstream
region in the upstream catalyst 5. The upstream catalyst 5 is
heated by vaporized working fluid transferred from the first heat
receiving unit 21 to condense the working fluid.
[0084] Specifically, the first heat radiating unit 22 includes a
hollow sleeve 22a and fins 22b. The hollow sleeve 22a surrounds the
upstream region in the upstream catalyst 5. The fins 22b are
directed radially outward and connected to an inner peripheral wall
of the hollow sleeve 22a.
[0085] The fins 22b are of a corrugated type so as to increase the
area of heat exchange with vaporized working fluid passing though
the inner space of the hollow sleeve 22a. The corrugated-type fins
22b are, for example, the ones such that a thin belt-like plate
material is formed into a corrugated shape in the circumferential
direction by roller working.
[0086] The first transfer pipe 23 transfers working fluid,
vaporized at the first heat receiving unit 21, to the first heat
radiating unit 22. The first transfer pipe 23 is arranged near and
along the exhaust passage (the exhaust pipe 4, the upstream
catalyst 5 and the downstream catalyst 6) via an appropriate
clearance.
[0087] Specifically, the first transfer pipe 23 is located away
from the exhaust passage (the exhaust pipe 4, the upstream catalyst
5 and the downstream catalyst 6) at a distance that is necessary to
maintain a temperature at which vaporized working fluid,
transferred through the first transfer pipe 23, does not condense.
The distance is desirably obtained through an experiment, or the
like, and empirically set on the basis of the overall length of the
first transfer pipe 23, material, thickness, facing area, and the
like.
[0088] In order to implement such arrangement of the first transfer
pipe 23, a plurality of portions (two portions in this embodiment)
of the first transfer pipe 23 are supported on an outer wall of the
downstream catalyst 6 and the exhaust pipe 4 via brackets 26a and
26b. The brackets 26a and 26b are desirably made of a material (for
example, stainless steel, or the like) having a high thermal
conductivity.
[0089] The first return pipe 24 returns working fluid, condensed at
the first heat radiating unit 22, to the first heat receiving unit
21. The first return pipe 24, different from the above described
first transfer pipe 23, is arranged away from the exhaust passage
(the exhaust pipe 4, the upstream catalyst 5 and the downstream
catalyst 6) and the first transfer pipe 23 as much as possible so
that liquid working fluid flowing through the first return pipe 24
is not vaporized again. In addition, the first return pipe 24 has
an appropriate down grade so as to make it easy to return condensed
liquid working fluid to the heat receiving unit 21.
[0090] Specifically, the first return pipe 24 is located away from
the exhaust passage (the exhaust pipe 4, the upstream catalyst 5
and the downstream catalyst 6) at a distance that is necessary to
maintain a state where liquid working fluid flowing through the
first return pipe 24 is not vaporized again by radiation heat from
the exhaust passage. The distance is desirably obtained through an
experiment, or the like, and empirically set on the basis of the
overall length of the first return pipe 24, material, thickness,
facing area, and the like. In addition, the down grade may be, for
example, about 6 degrees; however, it may be selected.
[0091] The first valve device 25 is provided midway of the first
return pipe 24. The first valve device 25 is able to switch between
an open state that allows working fluid to flow from the first heat
radiating unit 22 to the first heat receiving unit 21 and a closed
state that prohibits working fluid from flowing from the first heat
radiating unit 22 to the first heat receiving unit 21. The first
valve device 25 is, for example, an electromagnetic valve.
[0092] Note that it is possible to adjust the amount of working
fluid returned from the first heat radiating unit 22 to the first
heat receiving unit 21 in such a manner that the controller 40
steplessly controls the opening degree of the first valve device
25.
[0093] Next, the components of the second loop heat pipe 30 will be
described in detail with reference to FIG. 3.
[0094] The second heat receiving unit 31 is attached in a
downstream region in the upstream catalyst 5. The second heat
receiving unit 31 is configured to recover heat as heat of
vaporization in such a manner that liquid working fluid that is
hermetically sealed and filled inside the second heat receiving
unit 31 vaporizes with heat received from the upstream catalyst
5.
[0095] Specifically, the second heat receiving unit 31 includes a
hollow sleeve 31a and fins 31b. The hollow sleeve 31a surrounds the
downstream region in the upstream catalyst 5. The fins 31b are
directed radially outward and connected to an inner peripheral wall
of the hollow sleeve 31a. The fins 31b are of a corrugated type so
as to increase the area of heat exchange with vaporized working
fluid passing though the inner space of the hollow sleeve 31a. The
corrugated-type fins 31b are, for example, the ones such that a
thin belt-like plate material is formed into a corrugated shape in
the circumferential direction by roller working.
[0096] The second heat radiating unit 32 is attached near the
spherical joint 3 between the upstream catalyst 5 and the spherical
joint 3. The coolant that is returned from the heater core 14 to
the internal combustion engine 1 is heated by vaporized working
fluid, transferred from the second heat receiving unit 31, to
condense the working fluid.
[0097] Specifically, the second heat radiating unit 32 is formed so
that a downstream end of the second transfer pipe 33 and an
upstream end of the second return pipe 34 each are connected to a
case 32a of which the inside is hermetically sealed. A region
downstream of the heater core 14 in the heater passage 13 is
inserted in the inner space of the case 32a. Fins 13a are provided
on the outer periphery of the region inserted in the case 32a in
the heater passage 13 to increase the area of heat exchange. As for
operation, in short, as working fluid vaporized at the second heat
receiving unit 31 is transferred to the second heat radiating unit
32 via the second transfer pipe 33, heat of the working fluid is
absorbed by the fins 13a, and the absorbed heat heats the coolant
that flows through the heater passage 13.
[0098] The second transfer pipe 33 transfers working fluid,
vaporized at the second heat receiving unit 31, to the second heat
radiating unit 32. The second return pipe 34 returns working fluid,
condensed at the second heat radiating unit 32, to the second heat
receiving unit 31.
[0099] The second valve device 35 is provided midway of the second
return pipe 34. The second valve device 35 is able to switch
between an open state that allows working fluid to flow from the
second heat radiating unit 32 to the second heat receiving unit 31
and a closed state that prohibits working fluid from flowing from
the second heat radiating unit 32 to the second heat receiving unit
31. The second valve device 35 is, for example, an electromagnetic
valve.
[0100] Note that it is possible to adjust the amount of working
fluid returned from the second heat radiating unit 32 to the second
heat receiving unit 31 in such a manner that the controller 40
steplessly controls the opening degree of the second valve device
35.
[0101] In the first embodiment, as shown in FIG. 3, the first heat
radiating unit 22 of the first loop heat pipe 20 and the second
heat receiving unit 31 of the second loop heat pipe 30 are
integrated and arranged side by side in the direction in which
exhaust gas flows.
[0102] Specifically, the hollow sleeve 22a of the first heat
radiating unit 22 and the hollow sleeve 31a of the second heat
receiving unit 31 are connected next to each other in the axial
direction. A communication passage 36 is provided at the connected
portion, and a third valve device 37 is provided in the
communication passage 36.
[0103] The third valve device 37 is able to switch between an open
state that allows working fluid to flow from the first heat
radiating unit 22 to the second heat receiving unit 31 and a closed
state that prohibits working fluid from flowing from the first heat
radiating unit 22 to the second heat receiving unit 31. The third
valve device 37 includes a valve case 37a, a valve element 37b and
an actuator 37c serving as a driving source.
[0104] Note that the operation of the actuator 37c is controlled by
the controller 40. For example, the controller 40 adjusts the
amount of working fluid that flows from the first heat radiating
unit 22 to the second heat receiving unit 31 by steplessly
controlling the opening degree of the third valve device 37.
[0105] Next, the operation of the exhaust heat recovery system 18
related to the operation of the internal combustion engine 1 will
be simply described.
[0106] In short, when the internal combustion engine 1 is
cold-started, the temperatures of the upstream catalyst 5, the
downstream catalyst 6 and the coolant of the internal combustion
engine 1 all are low. However, exhaust gas of, for example, 300 to
400.degree. C. is exhausted from the internal combustion engine 1
to the exhaust pipe 4 via the exhaust manifold 2, and the
temperatures of the two catalysts 5 and 6 are increased from the
inside by exhaust gas, while the coolant is returned to the
internal combustion engine 1 via the bypass passage 12 without
passing through the radiator 7 to thereby warm up the engine.
[0107] Then, when the engine is cold-started, the second loop heat
pipe 30 is halted to stop heating the coolant that is returned from
the heater core 14 to the internal combustion engine 1, and the
function of the first loop heat pipe 20 is enabled. Thus, the
upstream catalyst 5 is preferentially heated from the outside by
exhaust heat that has passed through the downstream catalyst 6. By
so doing, the upstream catalyst 5 is heated from both inner side
and outer side, so an increase in temperature of the upstream
catalyst 5 is accelerated to early activate the upstream catalyst
5. Note that the temperature of the downstream catalyst 6 is
increased by exhaust gas of which the temperature is increased as
it is purified by the upstream catalyst 5.
[0108] Then, as the temperature of the upstream catalyst 5 is
increased to an activation temperature, the first loop heat pipe 20
is halted to stop heating the upstream catalyst 5 by exhaust heat,
and the function of the second loop heat pipe 30 is enabled. Thus,
heat of the upstream catalyst 5 is recovered to heat the coolant
that is returned from the heater core 14 to the internal combustion
engine 1. This cools the upstream catalyst 5, while facilitating
the internal combustion engine 1 to warm up.
[0109] In the first embodiment, control as to whether heat is
circulated by the first loop heat pipe 20 of the exhaust heat
recovery system 18 is mainly executed by the controller 40 and the
first valve device 25, and control as to whether heat is circulated
by the second loop heat pipe 30 of the exhaust heat recovery system
18 is mainly executed by the controller 40 and the second valve
device 35.
[0110] Next, the operation of the exhaust heat recovery system 18
will be described in detail with reference to the flowchart shown
in FIG. 4.
[0111] The flowchart shown in FIG. 4 is predominantly formed of the
operation of the controller 40. As the routine enters the
flowchart, it is determined in step S1 whether the temperature Tsc
of the upstream catalyst 5 is lower than a first threshold T1. Note
that the temperature Tsc of the upstream catalyst 5 may be, for
example, recognized on the basis of an output from a sensor (not
shown) that detects the catalyst bed temperature of the upstream
catalyst 5. In addition, the first threshold T1 is, for example,
appropriately set on the basis of the temperature (for example, 300
to 400.degree. C.) at which the upstream catalyst 5 is
activated.
[0112] In short, in step S1, it is checked whether the upstream
catalyst 5 is activated, that is, whether it is necessary to warm
up the upstream catalyst 5.
[0113] Here, when affirmative determination is made in step S1,
that is, the temperature Tsc of the upstream catalyst 5 has not
reached the activation temperature of the upstream catalyst 5, it
is necessary to warm up the upstream catalyst 5 and then the
process proceeds to step S2.
[0114] In step S2, the first valve device 25 is opened to enable
the function of the first loop heat pipe 20, that is, heat is
circulated, and the second valve device 35 is closed to disable the
function of the second loop heat pipe 30, that is, heat circulation
is stopped. Then, the third valve device 37 is closed to shut off
fluid communication between the first heat radiating unit 22 and
the second heat receiving unit 31.
[0115] First, as the first valve device 25 is opened, working fluid
is allowed to circulate between the first heat receiving unit 21
and the first heat radiating unit 22. Thus, the function of the
first loop heat pipe 20 is enabled. By so doing, exhaust gas
exhausted from the internal combustion engine 1 to the exhaust pipe
4 reaches the first heat receiving unit 21 of the first loop heat
pipe 20 via the two catalysts 5 and 6, working fluid in the first
heat receiving unit 21 is vaporized by heat of the exhaust gas, and
then the vaporized working fluid is transferred to the first heat
radiating unit 22 via the first transfer pipe 23. At this time, the
third valve device 37 is closed to shut off fluid communication
between the first heat radiating unit 22 and the second heat
receiving unit 31. Thus, the upstream region in the upstream
catalyst 5 is heated by the vaporized working fluid in the first
heat radiating unit 22. As the working fluid is condensed through
this heating, the condensed working fluid is returned to the first
heat receiving unit 21 via the first return pipe 24. Note that, as
the temperature of the upstream catalyst 5 increases, the
temperature of the downstream catalyst 6 located downstream of the
upstream catalyst 5 is also increased by the action of purifying
exhaust gas.
[0116] On the other hand, as the second valve device 35 is closed,
working fluid liquefied at the second heat radiating unit 32 cannot
be returned back to the second heat receiving unit 31. Thus,
working fluid cannot be vaporized at the second heat receiving unit
31. Therefore, vaporized working fluid cannot be transferred from
the second heat receiving unit 31 to the second heat radiating unit
32, so the function of the second loop heat pipe 30 is disabled.
Thus, heat of the upstream catalyst 5 is not recovered, and an
increase in temperature of the upstream catalyst 5 is not
prevented.
[0117] In such a state, heat of exhaust gas that passes through the
first heat receiving unit 21 is recovered, so the volume of the
exhaust gas reduces to reduce exhaust noise.
[0118] Incidentally, when negative determination is made in step
S1, that is, when the temperature Tsc of the upstream catalyst 5 is
higher than or equal to the activation temperature of the upstream
catalyst 5, it is not necessary to warm up the upstream catalyst 5;
rather, it is necessary to cool the upstream catalyst 5 for
preventing an excessive increase in temperature, and then the
process proceeds to step S3.
[0119] In step S3, it is determined whether the temperature Tw of
the coolant delivered from the internal combustion engine 1 is
lower than a second threshold T2. Note that the coolant temperature
Tw may be, for example, recognized on the basis of an output from a
coolant temperature sensor (not shown) that detects the temperature
of the upstream side of the coolant delivery passage 8 extending
from the internal combustion engine 1. In addition, the second
threshold T2 may be set at a temperature, for example, 40.degree.
C., that is lower than a lower limit temperature of a coolant
temperature range (for example, 60 to 80.degree. C.) during normal
operation after the engine is warmed up, that is, a temperature at
which it is necessary to warm up the engine.
[0120] In short, in step S3, it is checked whether it is necessary
to warm up the internal combustion engine 1.
[0121] Here, when affirmative determination is made in step S3,
that is, when the coolant temperature Tw is lower than the
temperature during normal operation, it is necessary to warm up the
internal combustion engine 1, and the process proceeds to step.
S4.
[0122] In step S4, the first valve device 25 is closed to disable
the function of the first loop heat pipe 20, that is, to stop heat
circulation, and the second valve device 35 is opened to enable the
function of the second loop heat pipe 30, that is, to circulate
heat. Then, the third valve device 37 is opened to provide fluid
communication between the first heat radiating unit 22 and the
second heat receiving unit 31.
[0123] As the first valve device 25 is closed, working fluid
liquefied at the first heat radiating unit 22 cannot be returned
back to the first heat receiving unit 21. Thus, working fluid
cannot be vaporized at the first heat receiving unit 21. By so
doing, vaporized working fluid cannot be transferred, that is, heat
cannot be transferred, from the first heat receiving unit 21 to the
first heat radiating unit 22, so the function of the first loop
heat pipe 20 is disabled.
[0124] On the other hand, as the second valve device 35 is opened,
working fluid is allowed to circulate between the second heat
receiving unit 31 and the second heat radiating unit 32. Thus, the
function of the second loop heat pipe 30 is enabled. At this time,
the third valve device 37 is opened, so the first heat radiating
unit 22 is in fluid communication with the second heat receiving
unit 31. Therefore, the first heat radiating unit 22 and the second
heat receiving unit 31 are united to function as a single heat
receiving heat exchanging unit. Thus, the heat receiving capacity
of the second heat receiving unit 31 increases.
[0125] In such a state, heat of the upstream catalyst 5 is
recovered to heat the coolant that is returned from the heater core
14 to the internal combustion engine 1. Thus, the upstream catalyst
5 is cooled.
[0126] On the other hand, when negative determination is made in
step S3, that is, when the coolant temperature falls within the
temperature range during normal operation, the process proceeds to
step S5.
[0127] In step S5, it is determined whether the temperature Tsc of
the upstream catalyst 5 is higher than or equal to a third
threshold T3 that is higher than the first threshold T1. Note that
the third threshold T3 is appropriately set, for example, on the
basis of the heat-resistant temperature (for example, 800 to
900.degree. C.) of the upstream catalyst 5.
[0128] In short, in step S5, it is checked whether the temperature
of the upstream catalyst 5 is excessively increased.
[0129] When negative determination is made in step S5, that is,
when the temperature Tsc of the upstream catalyst 5 is not
excessively increased, the process proceeds to step S4. That is,
during a period since the temperature of the upstream catalyst 5
has reached the activation temperature until the temperature of the
upstream catalyst 5 is excessively increased, only the function of
the second loop heat pipe 30 is enabled to draw heat away from the
upstream catalyst 5.
[0130] Incidentally, when affirmative determination is made in step
S5, that is, when the temperature Tsc of the upstream catalyst 5 is
excessively increased, the process proceeds to step S6, and then it
is further determined whether the coolant temperature Tw is higher
than or equal to a fourth threshold T4 higher than the second
threshold T2.
[0131] Note that the fourth threshold T4 is appropriately set
within a range that is higher than an upper limit temperature of a
coolant temperature range (for example, 60 to 80.degree. C.) during
normal operation and lower than an overheating temperature (for
example, 110.degree. C.). In this way, the reason why the fourth
threshold T4 is not set at the overheating temperature but at a
value lower than the overheating temperature is to provide a
temporal margin before overheating.
[0132] In short, in step S6, it is checked whether the coolant of
the internal combustion engine 1 tends to overheat.
[0133] When affirmative determination is made in step S6, the
temperature Tsc of the upstream catalyst 5 is excessively
increased, and the coolant temperature Tw is excessively increased.
Thus, the process proceeds to step S7 in order to stop warming up
the upstream catalyst 5 and stop warming up the coolant.
[0134] In step S7, the first valve device 25 is closed to disable
the function of the first loop heat pipe 20, that is, to stop heat
circulation, and the second valve device 35 is closed to disable
the function of the second loop heat pipe 30, that is, to stop heat
circulation, and then the third valve device 37 is opened to
provide fluid communication between the first heat radiating unit
22 and the second heat receiving unit 31.
[0135] First, as the first valve device 25 is closed, working fluid
liquefied at the first heat radiating unit 22 cannot be returned
back to the first heat receiving unit 21. Thus, working fluid is
not vaporized at the first heat receiving unit 21. By so doing,
vaporized working fluid cannot be transferred from the first heat
receiving unit 21 to the first heat radiating unit 22, so the
function of the first loop heat pipe 20 is disabled.
[0136] In addition, as the second valve device 35 is closed,
working fluid liquefied at the second heat radiating unit 32 cannot
be returned back to the second heat receiving unit 31. Thus,
working fluid is not vaporized at the second heat receiving unit
31. Therefore, vaporized working fluid cannot be transferred from
the second heat receiving unit 31 to the second heat radiating unit
32, so the function of the second loop heat pipe 30 is
disabled.
[0137] In addition, the third valve device 37 is opened, so the
first heat radiating unit 22 is in fluid communication with the
second heat receiving unit 31. As a result, part of working fluid
in the first heat radiating unit 22 flows into the second heat
receiving unit 31, and the working fluid is vaporized at both the
first heat radiating unit 22 and the second heat receiving unit 31.
Thus, the working fluid is transferred to the second heat radiating
unit 32 and stored. Therefore, the second valve device 35 is
desirably closed after the third valve device 37 is opened.
[0138] As the above state is achieved, heating of the upstream
catalyst 5 and heating of the coolant returned from the heater core
14 to the internal combustion engine 1 are stopped.
[0139] On the other hand, when negative determination is made in
step S6, the temperature Tsc of the upstream catalyst 5 is
excessively increased; however, the coolant temperature Tw is not
excessively increased. Thus, it is not necessary to warm up the
coolant, and the process proceeds to step S8.
[0140] In step S8, the first valve device 25 is closed to disable
the function of the first loop heat pipe 20, that is, to stop heat
circulation, and the second valve device 35 is opened to enable the
function of the second loop heat pipe 30, that is, to circulate
heat. Then, the third valve device 37 is opened to provide fluid
communication between the first heat radiating unit 22 and the
second heat receiving unit 31.
[0141] First, as the first valve device 25 is closed, working fluid
liquefied at the first heat radiating unit 22 cannot be returned
back to the first heat receiving unit 21. Thus, working fluid is
not vaporized at the first heat receiving unit 21. By so doing,
vaporized working fluid cannot be transferred, that is, heat cannot
be transferred, from the first heat receiving unit 21 to the first
heat radiating unit 22, so heat circulation using the first loop
heat pipe 20 is stopped.
[0142] On the other hand, as the second valve device 35 is opened,
working fluid is allowed to circulate between the second heat
receiving unit 31 and the second heat radiating unit 32. Thus, the
function of the second loop heat pipe 30 is enabled. At this time,
the third valve device 37 is opened, so the first heat radiating
unit 22 is in fluid communication with the second heat receiving
unit 31. Therefore, the first heat radiating unit 22 and the second
heat receiving unit 31 are united to function as a single heat
receiving heat exchanging unit. Thus, the heat receiving capacity
of the second heat receiving unit 31 increases.
[0143] In such a state, exhaust heat downstream of the downstream
catalyst 6 is not transferred to the upstream catalyst 5, whereas
heat of the upstream catalyst 5 is transferred to the second heat
radiating unit 32. Thus, the upstream catalyst 5 is cooled. At this
time, the coolant returned to the internal combustion engine 1 is
continuously heated using heat of the upstream catalyst 5.
[0144] As described above, in the first embodiment according to the
invention, the first loop heat pipe 20 is used to recover heat of
exhaust gas exhausted from the internal combustion engine 1, thus
making it possible to accelerate an increase in temperature of the
upstream catalyst 5 by heating the upstream catalyst 5 from the
outside. In addition, the second loop heat pipe 30 is used to
recover heat of the upstream catalyst 5, thus making it possible to
cool the upstream catalyst 5 while accelerating an increase in
temperature of the coolant of the internal combustion engine 1. In
this way, it is possible to efficiently warm up the catalysts 5 and
6 attached to the internal combustion engine 1 and to efficiently
warm up the coolant of the internal combustion engine 1.
[0145] In addition, under a condition that the temperature of the
upstream catalyst 5 or the coolant temperature of the internal
combustion engine 1 tends to be higher than a predetermined upper
limit, both the first and second loop heat pipes 20 and 30 are
halted. By so doing, it is possible to prevent a decrease in
function due to excessive heating of the upstream catalyst 5 and
overheating of the internal combustion engine 1.
[0146] Note that the second valve device 35 described in the first
embodiment may be provided in the second transfer pipe 33 instead
as shown, for example, in FIG. 5. The operation in this case may be
basically similar to that of the first embodiment. In addition,
although not shown in the drawing, the first valve device 25
described in the first embodiment may be provided in the first
transfer pipe 23 instead. The operation in this case may be
basically similar to that of the first embodiment.
[0147] Furthermore, the second valve device 35 provided in the
second transfer pipe 33 may be of a self-actuated type that
automatically controls the opening degree in accordance with a
predetermined actuating condition. The self-actuated second valve
device 35, for example, includes a cylinder case 35a, a valve
element 35b and a diaphragm spring 35c as shown in FIG. 6A and FIG.
6B.
[0148] An introducing port 35e for working fluid is provided in a
peripheral wall of a cylinder chamber 35d of the cylinder case 35a,
and a drain port 35f for working fluid is provided in one end wall
of the cylinder chamber 35d. The second transfer pipe 33 is split
at a midpoint, and an end portion of the split second transfer pipe
33 adjacent to the second heat receiving unit 31 is coupled to the
introducing port 35e so as to be in fluid communication with the
introducing port 35e, while an end portion of the split second
transfer pipe 33 adjacent to the second heat radiating unit 32 is
coupled to the drain port 35f so as to be in fluid communication
with the drain port 35f.
[0149] The valve element 35b is slidably accommodated in the
cylinder chamber 35d so as to open or close the drain port 35f. A
guide wall 35g is provided on an inner peripheral wall of the
cylinder chamber 35d to guide sliding action of the valve element
35b.
[0150] A valve stem end of the valve element 35b is attached to the
other end inner wall surface 35h of the cylinder chamber 35d via
the diaphragm spring 35c. The diaphragm spring 35c is elastically
deformed into an extended shape or elastically restored into a
curved shape in accordance with a variation in internal pressure of
the cylinder chamber 35d, which correlates with the temperature Tsc
of the upstream catalyst 5. The diaphragm spring 35c slides the
valve element 35b in accordance with the elastic deformation or the
elastic restoration to open or close the drain port 35f.
[0151] The operation of the self-actuated second valve device 35
will be described. First, when the condition that it is necessary
to activate the upstream catalyst is satisfied, that is, when the
internal pressure of the cylinder chamber 35d is lower than a
prescribed value, the diaphragm spring 35c is formed in a curved
natural shape, and then the valve element 35b closes the drain port
35f, as shown in FIG. 6A. By so doing, working fluid vaporized at
the second heat receiving unit 31 cannot be transferred to the
second heat radiating unit 32, so heat circulation using the second
loop heat pipe 30 is stopped. Note that the prescribed value is,
for example, set at a pressure value that correlates with the
activation temperature (first threshold T1) of the upstream
catalyst 5.
[0152] On the other hand, when the condition that the upstream
catalyst 5 is activated is satisfied, that is, when the internal
pressure of the cylinder chamber 35d is higher than or equal to the
prescribed value, the diaphragm spring 35c is elastically deformed
into an extended shape, and then the valve element 35b opens the
drain-port 35f, as shown in FIG. 6B. By so doing, working fluid
vaporized in the second heat receiving unit 31 can be transferred
to the second heat radiating unit 32, so heat is circulated using
the second loop heat pipe 30.
Second Embodiment
[0153] FIG. 7 to FIG. 9 show a second embodiment of the invention.
In the second embodiment, the basic configuration of the exhaust
heat recovery system 18 is similar to that of the first embodiment;
however, the actuator-driven second valve device 35 described in
the first embodiment is replaced with a self-actuated second valve
device 50, and the second valve device 50 is provided in the second
transfer pipe 33.
[0154] In the second embodiment, control as to whether heat is
circulated by the first loop heat pipe 20 of the exhaust heat
recovery system 18 is mainly executed by the controller 40 and the
first valve device 25, and control as to whether heat is circulated
by the second loop heat pipe 30 of the exhaust heat recovery system
18 is mainly executed by the self-actuated second valve device 35
only.
[0155] As shown in FIG. 8A to FIG. 8C, the self-actuated second
valve device 50 includes a single cylinder case 51, two valve
elements 52 and 53 and diaphragm springs 54 and 55. The cylinder
case 51 has a horizontally long shape, and three cylinder chambers
56, 57 and 58 are formed inside the cylinder case 51.
[0156] The second transfer pipe 33 is split at a midpoint, and an
end portion of the split second transfer pipe 33 adjacent to the
second heat receiving unit 31 is coupled to the first cylinder
chamber 56 so as to be in fluid communication with the first
cylinder chamber 56, while an end portion of the split second
transfer pipe 33 adjacent to the second heat radiating unit 32 is
coupled to the third cylinder chamber 58 so as to be in fluid
communication with the third cylinder chamber 58. Then, a partition
wall that comparts into the first cylinder chamber 56 and the
second cylinder chamber 57 has a first communication passage 51a
for fluid communication between both the cylinder chambers 56 and
57. In addition, a partition wall that comparts into the second
cylinder chamber 57 and the third cylinder chamber 58 has a second
communication passage 51b for fluid communication between both the
cylinder chambers 57 and 58.
[0157] A first valve element 52 is slidably accommodated in the
first cylinder chamber 56 so as to open or close the first
communication passage 51a. A guide wall 51c is provided in the
first cylinder chamber 56 to guide sliding action of the first
valve element 52. A valve stem end of the first valve element 52 is
attached to an end wall surface 51d of the first cylinder chamber
56 via the first diaphragm spring 54. The first diaphragm spring 54
is elastically deformed into an extended shape or elastically
restored into a curved shaped in accordance with a variation in
internal pressure of the first cylinder chamber 56, which
correlates with the temperature Tsc of the upstream catalyst 5. The
first diaphragm spring 54 slides the first valve element 52 in
accordance with the elastic deformation or the elastic restoration
to open or close the first communication passage 51a.
[0158] The second valve element 53 is slidably accommodated in the
third cylinder chamber 58 so as to open or close the second
communication passage 51b. A valve stem end of the second valve
element 53 is attached to an end wall surface 51e of the third
cylinder chamber 58 via the second diaphragm spring 55. The second
diaphragm spring 55 is elastically restored into a curved shape or
elastically deformed into an extended shape in accordance with a
variation in internal pressure of the second cylinder chamber 57,
which correlates with the temperature of the coolant delivered from
the internal combustion engine 1. The second diaphragm spring 55
slides the second valve element 53 to open or close the second
communication passage 51b.
[0159] Next, the operation of the self-actuated second valve device
50 will be described.
[0160] First, when the condition that it is necessary to activate
(warm up) the upstream catalyst 5 is satisfied, that is, when the
internal pressure of the first cylinder chamber 56 is lower than a
first actuation value, the first diaphragm spring 54 is formed into
a curved shape by elastic restoring force, and then the first valve
element 52 is slid to a position at which the first communication
passage 51a is closed, as shown in FIG. 8A. In this state, the
second cylinder chamber 57 and the first cylinder chamber 56 are
not in fluid communication with each other, so heat circulation
using the second loop heat pipe 30 is stopped irrespective of
whether the second valve element 53 is open or closed. Note that
the first actuation value is, for example, set at a pressure value
that correlates with the activation temperature (first threshold
T1) of the upstream catalyst 5.
[0161] However, when the condition that the upstream catalyst 5 is
activated is satisfied, that is, when the internal pressure of the
first cylinder chamber 56 is higher than or equal to the first
actuation value, the first diaphragm spring 54 is elastically
deformed into an extended shape against the elastic restoring
force, and then the first valve element 52 is slid to a position at
which the first communication passage 51a is opened, as shown in
FIG. 8B and FIG. 8C. In this state, the second cylinder chamber 57
and the first cylinder chamber 56 are in fluid communication with
each other, so heat is circulated by the second loop heat pipe 30
when the second valve element 53 is open, while heat circulation
using the second loop heat pipe 30 is stopped when the second valve
element 53 is closed.
[0162] In addition, when the condition that it is necessary to heat
(warm up) the coolant delivered from the internal combustion engine
1 and the temperature of the coolant has not reached an upper limit
temperature is satisfied, that is, when the internal pressure of
the second cylinder chamber 57 is higher than or equal to a second
actuation value and lower than a third actuation value, the second
diaphragm spring 55 is formed into a curved shape by the elastic
restoring force, and then the second valve element 53 is slid to a
position at which the second communication passage 51b is opened,
as shown in FIG. 8A and FIG. 8B. In this state, the second and
third cylinder chambers 57 and 58 and the second heat radiating
unit 32 are in fluid communication with each other. At this time,
heat is circulated by the second loop heat pipe 30 when the first
valve element 52 is open, while heat circulation using the second
loop heat pipe 30 is stopped when the first valve element 52 is
closed. Note that the second actuation value is set at a pressure
value that correlates with a necessary temperature (second
threshold T2) to which the temperature Tw of the coolant delivered
from the internal combustion engine 1 needs to be increased. The
third actuation value is set at a pressure value that correlates
with an upper limit temperature (fourth threshold T4) to which the
temperature Tw of the coolant delivered from the internal
combustion engine 1 is increased.
[0163] However, when the condition that the temperature of the
coolant delivered from the internal combustion engine 1 has reached
the upper limit temperature is satisfied, that is, when the
internal pressure of the second cylinder chamber 57 is higher than
or equal to the third actuation value, the second diaphragm spring
55 is elastically deformed into an extended shape against the
elastic restoring force, and then the second valve element 53 is
slid to a position at which the second communication passage 51b is
closed, as shown in FIG. 8C. In this state, the second and third
cylinder chambers 57 and 58 and the second heat radiating unit 32
are not in fluid communication with each other, so heat circulation
using the second loop heat pipe 30 is stopped irrespective of
whether the first valve element 52 is open or closed.
[0164] Next, the operation of the controller 40 will be described
in detail with reference to FIG. 9. The flowchart shown in FIG. 9
is predominantly formed of the operation of the first loop heat
pipe 20 controlled by the controller 40.
[0165] As the routine enters the flowchart, it is determined in
step S11 whether the temperature Tsc of the upstream catalyst 5 is
lower than the first threshold T1. Note that the temperature Tsc of
the upstream catalyst 5 may be, for example, recognized on the
basis of an output from a sensor (not shown) that detects the
catalyst bed temperature of the upstream catalyst 5. In addition,
the first threshold T1 is, for example, appropriately set on the
basis of the temperature (for example, 300 to 400.degree. C.) at
which the upstream catalyst 5 is activated.
[0166] Here, when the temperature Tsc of the upstream catalyst 5 is
lower than the first threshold T1, affirmative determination is
made in step S11, and then the process proceeds to step S12.
[0167] In step S12, the first valve device 25 is opened to
circulate heat using the first loop heat pipe 20, and the third
valve device 37 is closed to shut off fluid communication between
the first heat radiating unit 22 and the second heat receiving unit
31. At this time, as for the self-actuated second valve device 50,
as shown in FIG. 5A, the first diaphragm spring 54 is formed into a
curved shape to cause the first valve element 52 to close the first
communication passage 51a, while the second diaphragm spring 55 is
formed into a curved shape to cause the second valve element 53 to
open the second communication passage 51b. Thus, heat circulation
using the second loop heat pipe 30 is stopped. As a result, exhaust
heat that passes through the downstream catalyst 6 may be recovered
by the first loop heat pipe 20 to heat the upstream catalyst 5
without recovering heat of the upstream catalyst 5 by the second
loop heat pipe 30. Thus, it is possible to accelerate an increase
in temperature of the upstream catalyst 5.
[0168] On the other hand, when the temperature Tsc of the upstream
catalyst 5 is higher than or equal to the first threshold T1,
negative determination is made in step S11, and then, in step S13,
it is checked whether it is necessary to warm up the internal
combustion engine 1. Here, it is determined whether the temperature
Tw of the coolant delivered from the internal combustion engine 1
is lower than the second threshold T2.
[0169] Here, when affirmative determination is made in step S13,
that is, when the coolant temperature Tw is lower than the
temperature during normal operation, it is necessary to warm up the
internal combustion engine 1, and the process proceeds to step
S14.
[0170] In step S14, the first valve device 25 is closed to stop
heat circulation using the first loop heat pipe 20, and the third
valve device 37 is opened to provide fluid communication between
the first heat radiating unit 22 and the second heat receiving unit
31. At this time, as for the self-actuated second valve device 50,
as shown in FIG. 8B, the second diaphragm spring 55 is formed into
a curved shape to cause the second valve element 53 to open the
second communication passage 51b, and, in addition, because the
temperature Tsc of the upstream catalyst 5 is higher than or equal
to the first threshold T1, the first diaphragm spring 54 is formed
into an extended shape to cause the first valve element 52 to open
the first communication passage 51a. Thus, heat is circulated by
the second loop heat pipe 30. As a result, heating of the upstream
catalyst 5 using the first loop heat pipe 20 is stopped, and heat
of the upstream catalyst 5 is recovered by the second loop heat
pipe 30 to heat the coolant in the heater passage 13. Thus, it is
possible to cool the upstream catalyst 5 while accelerating an
increase in temperature of the coolant.
[0171] Then, the third valve device 37 is opened to provide fluid
communication between the first heat radiating unit 22 and the
second heat receiving unit 31 to form a single large-volume space.
Thus, it is possible to efficiently recover heat of the upstream
catalyst 5 by the working fluid present in the large-volume space
and to transfer the recovered heat to the second heat radiating
unit 32.
[0172] On the other hand, when negative determination is made in
step S13, that is, when the coolant temperature Tw falls within the
temperature range during normal operation, the process proceeds to
step S15.
[0173] In step S15, it is determined whether the temperature Tsc of
the upstream catalyst 5 is higher than or equal to a third
threshold T3 that is higher than the first threshold T1. Note that
the third threshold T3 is set as an appropriate upper limit
temperature, for example, on the basis of the heat-resistant
temperature (for example, 800 to 900.degree. C.) of the upstream
catalyst 5. In step S15, in short, it is checked whether the
temperature of the upstream catalyst 5 is excessively
increased.
[0174] When negative determination is made in step S15, that is,
when the temperature Tsc of the upstream catalyst 5 is not
excessively increased, the process returns to step S14. That is,
during a period since the temperature of the upstream catalyst 5
has reached the activation temperature until the temperature of the
upstream catalyst 5 is excessively increased, heat circulation
using the first loop heat pipe 20 is stopped, and heat is
circulated by the second loop heat pipe 30. Thus, it is possible to
cool the upstream catalyst 5.
[0175] Incidentally, when affirmative determination is made in step
S15, that is, when the temperature. The of the upstream catalyst 5
is excessively increased, the process proceeds to step S16, and
then it is further determined whether the coolant temperature Tw is
higher than or equal to a fourth threshold T4 higher than the
second threshold T2.
[0176] Note that the fourth threshold T4 is appropriately set as an
upper limit temperature within a range that is higher than an upper
limit temperature of a coolant temperature range (for example, 60
to 80.degree. C.) during normal operation and lower than an
overheating temperature (for example, 110.degree. C.). In this way,
the reason why the fourth threshold T4 is not set at the
overheating temperature but at a value lower than the overheating
temperature is to provide a temporal Margin before overheating.
[0177] In short, in step S16, it is checked whether the coolant of
the internal combustion engine 1 tends to overheat.
[0178] When affirmative determination is made in step S16, the
temperature Tsc of the upstream catalyst 5 is excessively increased
and the coolant temperature Tw is excessively increased. Thus, the
process proceeds to step S17 in order to stop warming up the
upstream catalyst 5 and stop warming up the coolant.
[0179] In step S17, the first valve device 25 is closed to stop
heat circulation using the first loop heat pipe 20, and the third
valve device 37 is opened to provide fluid communication between
the first heat radiating unit 22 and the second heat receiving unit
31. At this time, as for the self-actuated second valve device 50,
as shown in FIG. 5C, the first diaphragm spring 54 is formed into
an extended shape to cause the first valve element 52 to open the
first communication passage 51a, while the second diaphragm spring
55 is formed into an extended shape to cause the second valve
element 53 to close the second communication passage 51b. Thus,
heat circulation using the second loop heat pipe 30 is stopped. As
a result, heating of the upstream catalyst 5 using the first loop
heat pipe 20 is stopped, and heating of the coolant using the
second loop heat pipe 30 is stopped. Thus, it is possible to
prevent the upstream catalyst 5 and the coolant in the heater
passage 13 from excessively increasing.
[0180] Then, the third valve device 37 is opened to provide fluid
communication between the first heat radiating unit 22 and the
second heat receiving unit 31 to form a single large-volume space.
Thus, it is possible to efficiently recover heat of the upstream
catalyst 5 by working fluid present in the large-volume space and
to radiate the recovered heat to the atmosphere.
[0181] On the other hand, when negative determination is made in
step S16, the temperature Tsc of the upstream catalyst 5 is
excessively increased; however, the coolant temperature Tw is not
excessively increased. Thus, it is not necessary, to warm up the
coolant, and the process proceeds to step S18.
[0182] In step S18, the first valve device 25 is closed to stop
heat circulation using the first loop heat pipe 20, and the third
valve device 37 is opened to provide fluid communication between
the first heat radiating unit 22 and the second heat receiving unit
31. At this time, as for the self-actuated second valve device 50,
as shown in FIG. 8B, because the temperature Tsc of the upstream
catalyst 5 is higher than or equal to the third threshold T3, the
first valve element 52 opens the first communication passage 51a,
and, in addition, because the coolant temperature Tw is lower than
the fourth threshold T4, the second valve element 53 opens the
second communication passage 51b. Thus, heat is circulated by the
second loop heat pipe 30. As a result, heating of the upstream
catalyst 5 using the first loop heat pipe 20 is stopped, and heat
of the upstream catalyst 5 is recovered by the second loop heat
pipe 30 to heat the coolant in the heater passage 13. By so doing,
the upstream catalyst 5 is cooled.
[0183] Then, the third valve device 37 is opened to provide fluid
communication between the first heat radiating unit 22 and the
second heat receiving unit 31 to form a single large-volume space.
Thus, it is possible to efficiently recover heat of the upstream
catalyst 5 by working fluid in the large-volume space and to
radiate the recovered heat to the atmosphere. Hence, the operation
of cooling the upstream catalyst is improved.
[0184] As described above, in the second embodiment, similar
functions and advantageous effects to those of the first embodiment
may be obtained, and, in addition, it is possible to provide simple
configuration and reduction in facility costs using the
self-actuated second valve device 50 as compared with the first
embodiment.
Third Embodiment
[0185] FIG. 10 and FIG. 11 show a third embodiment of the
invention. In the third embodiment, the basic configuration of the
exhaust heat recovery system 18 is similar to that of the first
embodiment; however, the second valve device 35 described in the
first embodiment is omitted, and a bypass pipe 61, a switching
valve 62 and an atmospheric heat radiation tank 63 are additionally
provided for the second loop heat pipe 20 instead.
[0186] In the third embodiment, control as to whether heat is
circulated by the first loop heat pipe 20 of the exhaust heat
recovery system 18 is mainly executed by the controller 40 and the
first valve device 25, and control as to whether heat is
transferred to the coolant in the heater passage 13 by the second
loop heat pipe 30 of the exhaust heat recovery system 18 is mainly
executed by the controller 40 and the switching valve 62.
[0187] The bypass pipe 61 is connected to the second transfer pipe
33 and the second return pipe 34 so as to bypass the second heat
radiating unit 32.
[0188] The switching valve 62 is an actuator-driven three-way valve
that is controlled for switching by the controller 40. The
switching valve 62 is provided at a portion at which the bypass
pipe 51 is connected to the second transfer pipe 33. The switching
valve 62 is switched so as to secure a heat exchange route X or a
bypass route Y as needed. The heat exchange route X provides fluid
communication between the second transfer pipe 33 and the second
heat radiating unit 32. The bypass route Y provides fluid
communication between the second transfer pipe 33 and the bypass
pipe 51.
[0189] The atmospheric heat radiation tank 63 is provided midway of
the bypass pipe 61, and causes gaseous working fluid, introduced
from the bypass pipe 51, to condense by undergoing heat exchange
with the atmosphere. The atmospheric heat radiation tank 63 is
provided next to the second heat radiating unit 32 in the third
embodiment.
[0190] Then, when the heat exchange route X is secured by the
switching valve 62, heat is transferred from the second loop heat
pipe 30 to the coolant. On the other hand, when the bypass route Y
is secured by the switching valve 62, heat transfer from the second
loop heat pipe 30 to the coolant in the heater passage 13 is
stopped.
[0191] Next, the operation of the exhaust heat recovery system 18
according to the third embodiment will be described with reference
to the flowchart shown in FIG. 11. The flowchart shown in FIG. 11
is predominantly formed of the operation of the controller 40.
[0192] As the routine enters the flowchart, first, it is determined
in step S21 whether the temperature Tsc of the upstream catalyst 5
is lower than the first threshold T1. Note that the temperature Tsc
of the upstream catalyst 5 may be, for example, recognized on the
basis of an output from a sensor (not shown) that detects the
catalyst bed temperature of the upstream catalyst 5. In addition,
the first threshold T1 is, for example, appropriately set on the
basis of the temperature (for example, 300 to 400.degree. C.) at
which the upstream catalyst 5 is activated.
[0193] In short, in step S21, it is checked whether the upstream
catalyst 5 is activated, that is, whether it is necessary to
activate (warm up) the upstream catalyst 5.
[0194] Here, when affirmative determination is made in step S21,
that is, the temperature 11c of the upstream catalyst 5 has not
reached the activation temperature of the upstream catalyst 5, it
is necessary to activate (warm up) the upstream catalyst 5 and then
the process proceeds to step S22.
[0195] In step S22, the first valve device 25 is opened to
circulate heat using the first loop heat pipe 20, and the bypass
route Y is secured by the switching valve 60 to stop heat transfer
from the second loop heat pipe 30 to the coolant in the heater
passage 13. Then, the third valve device 37 is closed to shut off
fluid communication between the first heat radiating unit 22 and
the second heat receiving unit 31.
[0196] First, as the first valve device 25 is opened, working fluid
circulates between the first heat receiving unit 21 and the first
heat radiating unit 22 while changing its phase, so the function of
the first loop heat pipe 20 is enabled. By so doing, exhaust gas
exhausted from the internal combustion engine 1 to the exhaust pipe
4 reaches the first heat receiving unit 21 of the first loop heat
pipe 20 via the two catalysts 5 and 6, working fluid in the first
heat receiving unit 21 is vaporized by heat of the exhaust gas, and
then the vaporized working fluid is transferred to the first heat
radiating unit 22 via the first transfer pipe 23. At this time, the
third valve device 37 is closed to shut off fluid communication
between the first heat radiating unit 22 and the second heat
receiving unit 31. Thus, the upstream region in the upstream
catalyst 5 is heated by vaporized working fluid in the first heat
radiating unit 22. As the working is condensed through this
heating, the condensed working fluid is returned to the first heat
receiving unit 21 via the first return pipe 24. Note that, as the
temperature of the upstream catalyst 5 increases, the temperature
of the downstream catalyst 6 is also increased by heat of reaction
caused by the action of purifying exhaust gas.
[0197] On the other hand, as the bypass route Y is secured by the
switching valve 62, working fluid vaporized at the second heat
receiving unit 31 is not introduced into the second heat radiating
unit 32 but introduced into the atmospheric heat radiation tank 63.
Thus, heat cannot be transferred from the second heat radiating
unit 32 to the coolant in the heater passage 13. By so doing, heat
transfer from the second loop heat pipe 30 to the coolant is
stopped, so the coolant is not heated. Thus, the temperature of the
upstream catalyst 5 is preferentially increased.
[0198] In addition, in such a state, heat of exhaust gas that
passes through the first heat receiving unit 21 is recovered, so
the volume of the exhaust gas reduces to reduce exhaust noise.
[0199] Incidentally, when negative determination is made in step
S21, that is, when the temperature Tsc of the upstream catalyst 5
is higher than or equal to the activation temperature of the
upstream catalyst 5, it is not necessary to warm up the upstream
catalyst 5; rather, it is necessary to cool the upstream catalyst 5
for preventing an excessive increase in temperature, and then the
process proceeds to step S23.
[0200] In step S23, it is determined whether the temperature Tw of
the coolant delivered from the internal combustion engine 1 is
lower than a second threshold T2. Note that the coolant-temperature
Tw may be, for example, recognized on the basis of an output from a
coolant temperature sensor (not shown) that detects the temperature
of the upstream side of the coolant delivery passage 8 extending
from the internal combustion engine 1. In addition, the second
threshold T2 may be set at a temperature, for example, 40.degree.
C., that is lower than a lower limit temperature of a coolant
temperature range (for example, 60 to 80.degree. C.) during normal
operation after the engine is warmed up, that is, a temperature at
which it is necessary to warm up the engine.
[0201] In short, in step S23, it is checked whether it is necessary
to warm up (heat) the coolant of the internal combustion engine
1.
[0202] Here, when affirmative determination is made in step S23,
that is, when the coolant temperature Tw is lower than the
temperature during normal operation, it is necessary to warm up the
coolant of the internal combustion engine 1, and the process
proceeds to step S24.
[0203] In step S24, the first valve device 25 is closed to stop
heat circulation using the first loop heat pipe 20, and the heat
exchange route X is secured by the switching valve 62 to transfer
heat from the second loop heat pipe 30 to the coolant in the heater
passage 13. Then, the third valve device 37 is opened to provide
fluid communication between the first heat radiating unit 22 and
the second heat receiving unit 31.
[0204] As the first valve device 25 is closed, working fluid
liquefied at the first heat radiating unit 22 cannot be returned
back to the first heat receiving unit 21. Thus, working fluid is
not vaporized at the first heat receiving unit 21. By so doing,
vaporized working fluid cannot be transferred, that is, heat cannot
be transferred, from the first heat receiving unit 21 to the first
heat radiating unit 22, so the function of the first loop heat pipe
20 is disabled.
[0205] On the other hand, as the heat exchange route X is secured
by the switching valve 62, working fluid vaporized at the second
heat receiving unit 31 is introduced into the second heat radiating
unit 32. Thus, heat is exchanged between the gaseous working fluid
in the second heat radiating unit 32 and the coolant in the heater
passage 13. That is, heat is transferred from the second loop heat
pipe 30 to the coolant in the heater passage 13. Then, the third
valve device 37 is opened to unify the first heat radiating unit 22
and the second heat receiving unit 31 as a single large-volume
space. Thus, it is possible to efficiently recover heat of the
upstream catalyst 5 by working fluid present in the large-volume
space and to transfer the recovered heat to the second heat
radiating unit 32. Therefore, the performance of heating the
coolant in the heater passage 13 by the second loop heat pipe 30 is
improved, so it is advantageous in accelerating an increase in
temperature of the coolant and also advantageous in suppressing an
excessive increase in temperature of the upstream catalyst 5.
[0206] On the other hand, when negative determination is made in
step S23, that is, when the coolant temperature Tw falls within the
temperature range during normal operation, the process proceeds to
step S25.
[0207] In step S25, it is determined whether the temperature Tsc of
the upstream catalyst 5 is higher than or equal to a third
threshold T3 that is higher than the first threshold T1. Note that
the third threshold T3 is appropriately set, for example, on the
basis of the heat-resistant temperature (for example, 800 to
900.degree. C.) of the upstream catalyst 5.
[0208] In short, in step S25, it is checked whether the temperature
of the upstream catalyst 5 is excessively increased to reach an
upper limit temperature.
[0209] When negative determination is made in step S25, that is,
when the temperature Tsc of the upstream catalyst 5 has not reached
the upper limit temperature, the process returns to step S24. That
is, during a period since the temperature of the upstream catalyst
5 has reached the activation temperature until the temperature
reaches the upper limit temperature, heat of the upstream catalyst
5 is recovered by the second loop heat pipe 30 to transfer the
recovered heat to the coolant.
[0210] Incidentally, when affirmative determination is made in step
S25, that is, when the temperature Tsc of the upstream catalyst 5
has reached the upper limit temperature, the process proceeds to
step S26, and then it is further determined whether the coolant
temperature Tw is higher than or equal to a fourth threshold T4
higher than the second threshold T2.
[0211] Note that the fourth threshold T4 is appropriately set
within a range that is higher than an upper limit temperature of a
coolant temperature range (for example, 60 to 80.degree. C.) during
normal operation and lower than an overheating temperature (for
example, 110.degree. C.). In this way, the reason why the fourth
threshold T4 is not set at the overheating temperature but at a
value lower than the overheating temperature is to provide a
temporal margin before overheating.
[0212] In short, in step S26, it is checked whether the coolant of
the internal combustion engine 1 tends to overheat.
[0213] When affirmative determination is made in step S26, the
temperature Tsc of the upstream catalyst 5 has reached the upper
limit temperature, and the temperature Tw of the coolant has
reached the upper limit temperature. Thus, the process proceeds to
step S27 in order to stop warming up the upstream catalyst 5 and
stop warming up the coolant.
[0214] In step S27, the first valve device 25 is closed to stop
heat circulation using the first loop heat pipe 20, and the bypass
route Y is secured by the switching valve 62 to stop heat transfer
from the second loop heat pipe 30 to the coolant in the heater
passage 13. Then, the third valve device 37 is opened to provide
fluid communication between the first heat radiating unit 22 and
the second heat receiving unit 31.
[0215] As the first valve device 25 is closed, working fluid
liquefied at the first heat radiating unit 22 cannot be returned
back to the first heat receiving unit 21. Thus, working fluid is
not vaporized at the first heat receiving unit 21. By so doing,
vaporized working fluid cannot be transferred from the first heat
receiving unit 21 to the first heat radiating unit 22, so the
function of the first loop heat pipe 20 is disabled to stop heating
the upstream catalyst 5.
[0216] In addition, as the bypass route Y is secured by the
switching valve 62, working fluid vaporized at the second heat
receiving unit 31 is not introduced into the second heat radiating
unit 32 but introduced into the atmospheric heat radiation tank 63.
By so doing, heat cannot be transferred from the second heat
radiating unit 32 to the coolant in the heater passage 13, and heat
of the gaseous working fluid introduced into the atmospheric heat
radiation tank 63 is radiated to the atmosphere. That is, heat of
the upstream catalyst 5 is recovered by the second loop heat pipe
30 but heat transfer to the coolant in the heater passage 13 is
stopped. Thus, it is possible to decrease the temperature of the
upstream catalyst 5 without heating the coolant. Note that, in the
atmospheric heat radiation tank 63, heat of the gaseous working
fluid is radiated to the atmosphere to condense the working fluid,
and the condensed working fluid is returned to the second heat
receiving unit 31 via the second return pipe 34.
[0217] Then, the third valve device 37 is opened to provide fluid
communication between the first heat radiating unit 22 and the
second heat receiving unit 31 to form a single large-volume space.
Thus, it is advantageous in improving the action of cooling the
upstream catalyst 5 because it is possible to, for example,
efficiently recover heat of the upstream catalyst 5 by the working
fluid present in the large-volume space.
[0218] On the other hand, when negative determination is made in
step S26, the temperature Tsc of the upstream catalyst 5 has
reached the upper limit temperature, but the temperature Tw of the
coolant has not reached the upper limit temperature. Thus, the
process proceeds to step S28.
[0219] In step S28, the first valve device 25 is closed to stop
heat circulation using the first loop heat pipe 20, and the heat
exchange route X is secured by the switching valve 62 to transfer
heat from the second loop heat pipe 30 to the coolant in the heater
passage 13. Then, the third valve device 37 is opened to provide
fluid communication between the first heat radiating unit 22 and
the second heat receiving unit 31.
[0220] As the first valve device 25 is closed, working fluid
condensed at the first heat radiating unit 22 cannot be returned
back to the first heat receiving unit 21. Thus, working fluid is
not vaporized at the first heat receiving unit 21. By so doing,
vaporized working fluid cannot be transferred, that is, heat cannot
be transferred, from the first heat receiving unit 21 to the first
heat radiating unit 22, so the function of the first loop heat pipe
20 is disabled to stop heating the upstream catalyst 5.
[0221] On the other hand, as the heat exchange route X is secured
by the switching valve 62, working fluid vaporized at the second
heat receiving unit 31 is introduced into the second heat radiating
unit 32. Thus, heat is exchanged between the gaseous working fluid
in the second heat radiating unit 32 and the coolant in the heater
passage 13. That is, heat is transferred from the second loop heat
pipe 30 to the coolant. Then, the third valve device 37 is opened
to provide fluid communication between the first heat radiating
unit 22 and the second heat receiving unit 31 to form a single
large-volume space. Thus, it is possible to efficiently recover
heat of the upstream catalyst 5 by the working fluid present in the
large-volume space and to transfer the recovered heat to the second
heat radiating unit 32. By so doing, the upstream catalyst 5 is
cooled.
[0222] As described above, in the third embodiment, similar
functions and advantageous effects to those of the first embodiment
may be obtained, and, in addition, for example, when the bypass
route Y is secured to circulate heat by the second loop heat pipe
30 while heat transfer to the coolant in the heater passage 13 is
stopped, it is possible to cool the upstream catalyst 5 without
heating the coolant.
[0223] Note that the aspect of the invention is not limited to the
above embodiments; the aspect of the invention may be modified or
improved in various forms within the scope recited in the appended
claims and equivalents thereof. Alternative embodiments will be
described below.
[0224] (1) In the above embodiments, the internal combustion engine
1 is not limited to a gasoline engine, a diesel engine, or another
engine. When the internal combustion engine 1 is a diesel engine,
the catalysts 5 and 6 may b; for example, a diesel particulate
filter (DPF), a diesel particulate-NOx reduction system (DPNR), or
the like.
[0225] Note that, when the internal combustion engine 1 is a diesel
engine, the upstream catalyst 5 may be a NOx storage reduction
(NSR), and the downstream catalyst 6 may be a NOx selective
catalytic reduction (SCR).
[0226] (2) In the above embodiments, the two catalysts 5 and 6 are
provided; however, the number of catalysts is not limited. For
example, the number of catalysts may be one or three or more.
[0227] (3) In the above embodiments, each of the first heat
radiating unit 22 and the second heat receiving unit 31 that are
attached to the upstream catalyst 5 has an annular shape that
surrounds the upstream catalyst 5; however, the outer shape of each
of the first heat radiating unit 22 and the second heat receiving
unit 31 is not specifically limited. The outer shape of each of the
first heat radiating unit 22 and the second heat receiving unit 31
may be, for example, a curved shape so as to be attached to part of
a region on an outer wall surface of the upstream catalyst 5.
[0228] (4) In the above embodiments, the second heat radiating unit
32 of the second loop heat pipe 30 is provided in a region from the
spherical joint 3 to the upstream catalyst 5; however, a location
at which the second heat radiating unit 32 is provided is not
specifically limited. For example, the second heat radiating unit
32 may be provided at a location adjacent to the coolant delivery
passage 8 of the internal combustion engine 1 away from the exhaust
passage 2, 4.
[0229] (5) In the above embodiments, the second heat radiating unit
32 of the second loop heat pipe 30 is used to heat the coolant that
is returned from the heater core 14 of the hot-air heater 16 to the
internal combustion engine 1; however, the aspect of the invention
is not limited to it.
[0230] For example, a target heated by the second heat radiating
unit 32 may be the coolant introduced into the heater core 14. In
this case, under the condition that the hot-air heater 16 is
operated when the internal combustion engine 1 is warmed up, it is
possible to accelerate an increase in temperature of the coolant
introduced into the heater core 14. Thus, it is possible to early
start the heater function while the internal combustion engine 1 is
warmed up.
[0231] In addition, a target heated by the second heat radiating
unit 32 may be the coolant that flows through the bypass passage
12. The bypass passage 12 is used when it is necessary to increase
the temperature of the coolant, for example, when the internal
combustion engine 1 is warmed up. Thus, the temperature of the
coolant that flows through the bypass passage 12 may be promptly
increased by the second heat radiating unit 32, so it is possible
to quickly complete the warming up of the internal combustion
engine 1.
[0232] In any embodiments as well, when it is not necessary to
accelerate an increase in temperature of a heated target, the
second valve device 35 may be closed to stop recovery of exhaust
heat.
[0233] (6) In the above embodiments, the third valve device 37 is
configured to use the actuator 37c as a driving source, and the
opening degree of the third valve device 37 is controlled by the
controller 40. Although not shown in the drawing in detail, the
third valve device 37 may be a self-actuated valve device that uses
a diaphragm spring as a driving source to open or close its valve
element.
[0234] The valve device that uses the diaphragm spring may be, for
example, configured so that the valve is closed at normal
temperature and, when the internal pressure of the first heat
radiating unit 22 increases to a pressure corresponding to a
predetermined set temperature, the diaphragm spring is elastically
deformed by the internal pressure to displace the valve element to
open.
[0235] (7) In the above embodiments, the hollow sleeves 22a and 31a
are respectively used as the first heat radiating unit 22 and the
second heat receiving unit 31; however, the aspect of the invention
is not limited. Although not shown in the drawing, for example, it
is also applicable that the hollow sleeves 22a and 31a are not used
and a case having no inner peripheral walls of the hollow sleeves
22a and 31a is used. In this case, the fins 22b and 31b may be
provided on the radially outer side of an outer case of the
upstream catalyst 5.
[0236] (8) In the above embodiments, FIG. 1 shows an example in
which the first return pipe 24 and the second return pipe 34 are
respectively arranged above the first transfer pipe 23 and the
second transfer pipe 33; however, the aspect of the invention is
not limited to this configuration. Although not shown in the
drawing, for example, the first return pipe 24 and the second
return pipe 34 may be arranged below the exhaust pipe 4.
* * * * *