Exhaust heat recovery device

Abstract

An exhaust heat recovery device includes an evaporator disposed to evaporate a working fluid by exchanging heat between a heating fluid and the working fluid, a condenser disposed to cool and condense the working fluid by exchanging heat between a fluid to be heated and the working fluid evaporated by the evaporator, an evaporation side connection portion for guiding the working fluid evaporated by the evaporator to the condenser, and a condensation side connection portion for guiding the working fluid condensed by the condenser to the evaporator. Furthermore, at least one of the evaporation side connection portion and the condensation side connection portion has a curved portion.

Description

CROSS REFERENCE TO RELATED APPLICATION

This application is based on Japanese Patent Applications No. 2007-170078 filed on Jun. 28, 2007, and No. 2008-034082 filed on Feb. 15, 2008, the contents of which are incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates to an exhaust heat recovery device used for a vehicle.

BACKGROUND OF THE INVENTION

In recent years, techniques have been known which are adapted to recover heat of an exhaust gas from an exhaust gas system of an engine of a vehicle using the principle of a heat pipe, so as to use the recovered exhaust heat for promotion of warming or the like. Such an exhaust heat recovery device includes an evaporator of the heat pipe disposed in an exhaust pipe of the engine and a condenser of the heat pipe disposed in a coolant passage of the engine. Furthermore, the exhaust heat recovery device is configured to heat coolant of the engine by the exhaust heat of the exhaust gas (see, for example, JP-A-62-268722).

A heat-pipe heat exchanger is proposed as a heat exchanger using the principle of the heat pipe (see, for example, JP-A-4-45393). The heat exchanger includes a sealed circulation route for forming a closed loop path, a working fluid sealed into the circulation route and which can be evaporated and condensed, and an evaporator disposed in the circulation route for evaporating the working fluid by heat transmitted from an external heating fluid. The heat exchanger also includes a condenser disposed at a higher position than the evaporator in the circulation route and adapted for exchanging heat between the working fluid evaporated at the evaporator and a fluid to be heated.

FIG. 4 shows an example of the exhaust heat recovery device. The exhaust heat recovery device shown in FIG. 4 is configured to include an evaporator J1 and a condenser J2 which are horizontally arranged adjacent to each other. Each of the evaporator J1 and the condenser J2 includes a plurality of heat pipes J3. The exhaust heat recovery device also includes an evaporation side connection portion J71 for guiding the working fluid evaporated at the evaporator J1 to the condenser J2, and a condensation side connection portion J72 for guiding the working fluid condensed at the condenser J2 to the evaporator J1. In this case, the evaporator J1 is disposed in an exhaust gas passage through which exhaust gas serving as a heating fluid flows, and the condenser J2 is disposed in a fluid passage through which a fluid to be heated flows.

In a case where the coolant of the engine is used as the fluid to be heated, the exhaust heat recovery device causes a difference in temperature between the evaporator J1 which becomes high temperature due to the exhaust gas flowing therethrough, and the condenser J2 which becomes a relatively low temperature due to the engine coolant flowing therethrough. The difference in temperature between the evaporator J1 and the condenser J2 may disadvantageously cause thermal stress due to a difference in thermal expansion between the evaporation side connection portion J71 and the condensation side connection portion J72.

For this reason, a structure including a bellows disposed in each connection portion is proposed so as to absorb the thermal stress. The structure, however, may be complicated, resulting in high manufacturing cost. Further, the bellows has to be thinned so as to be movable. This may cause holes in the bellows due to corrosion from an external side, that is, from the side in contact with atmosphere.

SUMMARY OF THE INVENTION

The invention has been made in view of the foregoing problems, and it is an object of the invention to provide an exhaust heat recovery device that can release thermal stress with a simple structure, while preventing occurrence of holes due to external corrosion.

According to an aspect of the present invention, an exhaust heat recovery device having a working fluid sealed therein includes: an evaporator disposed in a first passage through which a heating fluid flows, and being adapted to evaporate the working fluid by exchanging heat between the heating fluid and the working fluid; a condenser disposed in a second passage through which a fluid to be heated flows, and being adapted to cool and condense the working fluid by exchanging heat between the fluid to be heated and the working fluid evaporated by the evaporator; an evaporation side connection portion for guiding the working fluid evaporated by the evaporator to the condenser; and a condensation side connection portion for guiding the working fluid condensed by the condenser to the evaporator. Furthermore, at least one of the evaporation side connection portion and the condensation side connection portion has a curved portion.

In this way, at least one of the evaporation side connection portion and the condensation side connection portion has a part (or the whole) thereof curved. When a difference in temperature between the evaporator and the condenser is generated, an elastic deformation of the curved portion can absorb thermal stress caused by a difference in thermal expansion. At this time, bellows do not need to be provided in the evaporation side and condensation side connection portions, thereby releasing the thermal stress with a simple structure while preventing the occurrence of holes due to external corrosion.

In the exhaust heat recovery device, the working fluid evaporated by the evaporator flows into the condenser through the evaporation side connection portion. The condensed liquid fluid flows into the evaporator through the condensation side connection portion. Thus, there occurs a difference in water level (water head) of the working fluid (liquid) between the evaporator and the condenser, depending on a balance between evaporation of the working fluid at the evaporator and condensation of the working fluid at the condenser. The difference in water head allows the working fluid to be refluxed from the condenser to the evaporator, thereby causing the circulation of the working fluid.

For example, only the condensation side connection portion among the evaporation side connection portion and the condensation side connection portion may have the curved portion.

Alternatively, the curved portion may be formed into a spiral shape such that a center axis of the spiral shape is in parallel to a vertical direction.

The expression as used herein “the center axis of the spiral shape of the curved portion is in parallel to the vertical direction” means not only that the center axis of the spiral shape of the curved portion is precisely in parallel to the vertical direction, but also that the center axis is slightly inclined with respect to the vertical direction.

Alternatively, the curved portion may be formed into an S-like shape, a U-like shape, or an arc shape.

For example, the condensation side connection portion may have the curved portion. In this case, the condensation side connection portion includes a first end connected to the evaporator and a second end connected to the condenser, and the condensation side connection portion is arranged such that a liquid level in the condensation side connection portion is not higher than that in the condenser. Furthermore, the second end of the condensation side connection portion may be positioned higher than the first end of the condensation side connection portion.

BRIEF DESCRIPTION OF THE DRAWINGS

Additional objects and advantages of the present invention will be more readily apparent from the following detailed description of preferred embodiments when taken together with the accompanying drawings. In which:

FIG. 1 is a schematic sectional view showing an exhaust heat recovery device according to a first embodiment of the invention;

FIG. 2A is a sectional view showing an exhaust heat recovery device according to a second embodiment of the invention, and FIG. 2B is a diagram viewed along an arrow IIB in FIG. 2A;

FIGS. 3A to 3D are diagrams showing condensation side connection portions according to the other embodiments of the invention, when being viewed from the vertically lower side; and

FIG. 4 is a schematic sectional view showing an exhaust heat recovery device in a related art.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

First Embodiment

A first embodiment of the invention will be described with reference to FIG. 1. An exhaust heat recovery device of this embodiment is adapted to recover exhaust heat of an exhaust gas from an exhaust system of an engine (e.g., internal combustion engine) of a vehicle, and to use the exhaust heat for promotion of warning or the like.

FIG. 1 is a schematic sectional view showing an example of the exhaust heat recovery device of the first embodiment. As shown in FIG. 1, the exhaust heat recovery device of this embodiment includes an evaporator 1 and a condenser 2. The evaporator 1 and the condenser 2 are connected to each other to form a loop-type heat pipe 3.

The heat pipe 3 is provided with an sealing portion (not shown), from which the heat pipe 3 is evacuated to vacuum (decompressed). After being filled with a working medium, the sealing portion is sealed. The working fluid in use is water, for example. The working fluid for use may include alcohol, fluorocarbon, flon, and the like, in addition to water.

The evaporator 1 is provided in a first casing 100 disposed in an exhaust pipe of the engine. The evaporator 1 is adapted to evaporate the working fluid by exchanging heat between the exhaust gas and the working fluid as will be described later. The exhaust gas is an example of a heating fluid for heating the working fluid in the exhaust heat recovery device.

The condenser 2 is provided in a second casing 200 outside the exhaust pipe. The second casing 200 is separate from the first casing 100, and is disposed in a coolant passage of the engine. The condenser 2 is adapted to cool and condense the working fluid by exchanging heat between the working fluid evaporated by the evaporator 1 and engine coolant. The second casing 200 is provided with a coolant inlet (not shown) connected to a coolant outlet side of the engine, and a coolant outlet (not shown) connected to a coolant inlet side of the engine. The coolant is an example of a fluid to be heated in the invention.

The evaporator 1 and the condenser 2 are horizontally arranged adjacent to each other. Since the exhaust pipe is normally provided across the vehicle in the front-back direction, the arrangement direction of the evaporator 1 and the condenser 2 is identical to the direction of width of the vehicle.

Now, the structure of the evaporator 1 will be described below. The evaporator 1 includes a plurality of evaporation side tubes 41a and corrugated fins 42a connected to the outer surfaces of the evaporation side tubes 41a. The evaporation side tube 41a is formed in a flat shape such that a flow direction of the exhaust gas is identical to the direction of the major axis of the flat tube in cross section. In FIG. 1, the flow direction of the exhaust gas is orthogonal to the paper surface. The tubes 41a are arranged in parallel to each other such that the longitudinal direction of the tube is identical to the vertical direction (top-bottom direction) of the evaporator.

In the evaporator 1, evaporation side headers 5a for communication with all evaporation side tubes 41a are provided at both ends in the longitudinal direction of the evaporation side tube 41a, to extend in the direction of lamination of the tubes 41a. Among the two evaporation side headers 5a, the evaporation side header 5a located on the upper end side of the exhaust heat recovery device is hereinafter referred to as a first evaporation side header 51a, and the header 5a located on the lower end side is referred to as a second evaporation side header 52a.

Next, the structure of the condenser 2 will be described below. The condenser 2 includes a plurality of condensation side tubes 41b and corrugated fins 42b connected to the outer surfaces of the condensation side tubes 41b. The evaporation side tube 41b is formed in a flat shape such that a flow direction of the exhaust gas in the first casing 100 is identical to the direction of the major axis of the tube in cross section. The tubes 41b are arranged in parallel to each other such that the longitudinal direction of the tube 41b is identical to the vertical direction (top-bottom direction) of the condenser 2.

In the condenser 2, condensation side headers 5b for communication with all condensation side tubes 41b are provided at both ends in the longitudinal direction of the condensation side tube 41b to extend in the direction of lamination of the tubes 41b. Among the two condensation side headers 5b, the condensation side header 5b located on the vertically upper end side of the exhaust heat recovery device is hereinafter referred to as a first condensation side header 51b, and the header 5b located on the vertically lower end side is referred to as a second condensation side header 52b. The second condensation side header 52b is positioned above the second evaporation side header 52a when the exhaust heat recovery device is mounted on the vehicle in a horizontal state. In the example shown in FIG. 1, the first condensation side header 51b is located substantially at the same height position as that of the first evaporation side header 51a, and the second condensation side header 52b is located at a position higher than the second evaporation side header 52a.

A valve mechanism 6 (valve unit) is disposed in the second condensation side header 52b. The valve mechanism 6 serves as a diaphragm-type opening and closing unit adapted to form a flow path connecting the condensation side tubes 41b with the second evaporation side header 52a. The valve mechanism 6 is configured to open and close the flow path according to an internal pressure of the evaporation side tube 41a (i.e., pressure of the working fluid). Specifically, when the internal pressure increases from a normal valve opening state of the mechanism 6 to exceed a first predetermined pressure at a predetermined temperature of the working fluid, the valve mechanism 6 is closed. Conversely, when the internal pressure decreases to fall below a second predetermined pressure that is lower than the first predetermined pressure, the valve mechanism 6 is opened again.

The evaporation side header 5a is connected in communication with the condensation side header 5b via a cylindrical connection portion 7. The evaporation side and condensation side tubes 41a and 41b, the evaporation side and condensation side headers 5a and 5b, and the connection portion 7 form a closed loop. That is, the evaporation side and condensation side tubes 41a and 41b, the evaporation side and condensation side headers 5a and 5b, and the connection portion 7 are connected in an annular shape to form the heat pipe 3. This allows the working fluid to circulate through the evaporator 1 and the condenser 2.

Among the two connection portions 7, the connection portion disposed on the upper side is hereinafter referred to as an evaporation side connection portion 71. The evaporation side connection portion 71 is adapted to connect the first evaporation side header 51a to the first condensation side header 51b and to guide the working fluid evaporated by the evaporator 1 to the condenser 2. Among the two connection portions 7, the connection portion disposed on the lower side is hereinafter referred to as a condensation side connection portion 72. The condensation side connection portion 72 is adapted to connect the second evaporation side header 52a to the second condensation side header 52b and to guide the working fluid cooled and condensed by the condenser 2 to the evaporator 1.

The condensation side connection portion 72 includes a lower member 701 having one end connected to the second evaporation side header 52a and extending substantially in the horizontal direction from its one end toward the condenser 2, and an upper member 702 having one end connected to the second condensation side header 52b and extending substantially in the horizontal direction from its one end toward the evaporator 1. The condensation side connection portion 72 also includes a spiral portion 703 formed in a spiral shape, while extending from the other end of the lower member 701, that is, the end of the lower member 701 away from the evaporator 1, to the other end of the upper member 702, that is, the end of the upper member 702 away from the condenser 2. The center axis of the spiral of the spiral portion 703 is approximately in parallel to the vertical direction (top-bottom direction). That is, in the spiral portion 703, working fluid is positioned on the lower side as it goes toward the downstream side of a flow of the working fluid. The spiral portion 703 is an example of a curved portion of the present invention.

As described above, the spiral portion 703 is provided in the condensation side connection portion 72. Thus, when a difference in temperature between the evaporator 1 and the condenser 2 is generated, the elastic deformation of the spiral portion 703 can absorb thermal stress caused by a difference in thermal expansivity. At this time, bellows do not need to be provided in the evaporation side and condensation side connection portions 71 and 72, and thereby it is possible to release the thermal stress with a simple structure while preventing the occurrence of holes due to external corrosion.

Because the volume of working fluid evaporated at the evaporator 1 is about 1000 times as large as that of working fluid condensed by the condenser 2, a sectional area of a passage of the evaporation side connection portion 71 is made larger than that of the condensation side connection portion 72. Thus, in this embodiment, the spiral portion 703 is provided only in the condensation side connection portion 72 having the smaller passage sectional area among the two connection portions 71 and 72. Accordingly, it can improve workability as compared to the case in which the spiral portion 703 is provided in the evaporation side connection portion 71 having the larger passage sectional area.

The center axis of the spiral of the spiral portion 703 is in parallel to the vertical direction, and the working fluid in the spiral portion 703 is allowed to be positioned downward as toward the downstream side of the working fluid flow. This can eliminate the necessity of temporarily positioning the working fluid in a high position within the spiral portion 703, thus preventing degradation of circularity of the working fluid. Since the liquid level of the working fluid in the spiral portion 703 is not higher than the liquid level of the working fluid in the condenser 2, the working fluid can be refluxed sufficiently from the condenser 2 to the evaporator 1, thereby ensuring the heat exchange performance.

In the exhaust heat recovery device in which the condenser 2 is located in a relatively higher position than that of the evaporator 1, a difference in water head of the working fluid can be sufficiently ensured between the evaporator 1 and the condenser 2. This eliminates the necessity of setting the center axis of the spiral of the spiral portion 703 provided in the condensation side connection portion 72, in parallel to the vertical direction. However, since the exhaust heat recovery device is mounted on the vehicle, the heat recovery device is desired to have a compact structure with the excellent mounting performance, that is, the structure including the evaporator 1 and the condenser 2 horizontally disposed adjacent to each other like this embodiment. Thus, in the exhaust heat recovery device with the compact structure, the center axis of the spiral of the spiral portion 703 provided in the condensation side connection portion 72 is set in parallel to the vertical direction. This can reflux the working fluid in a sufficient amount from the condenser 2 to the evaporator 1, while improving the mounting performance on the vehicle.

Second Embodiment

Now, a second embodiment of the invention will be described below based on FIGS. 2A and 2B. The elements having the same functions as those of the first embodiment will be designated by the same reference numerals, and a description thereof will be described below.

FIG. 2A is a sectional view showing an exhaust heat recovery device according to the second embodiment, and FIG. 2B is a diagram viewed along an arrow IIB in FIG. 2A. In FIGS. 2A and 2B, representation of the detailed structure of the condenser 2 will be omitted.

As shown in FIGS. 2A and 2B, in the second embodiment, a condensation side connection portion 72 includes a lower member 701 having one end connected to the second evaporation side header 52a and extending substantially in the horizontal direction toward the condenser 2, and an upper member 702 having one end connected to the lower end of the second condensation side header (not shown) of the condenser 2 and extending substantially in the vertical direction toward the lower side. The condensation side connection portion 72 also includes a connection portion 704 for connecting the other end of the lower member 701, that is, the end away from the evaporator 1, to the other end of the upper member 702, that is, the end away from the condenser 2.

In FIG. 2B, arrows EF indicate the flow direction of the exhaust gas. As shown in FIG. 2B, a connection portion 704 is formed in an S shape when being viewed from the lower side in the vertical direction. That is, the connection portion 704 has two curved portions 8 each of which is formed in an arc shape. The two curved portions 8 are parts of the connection portion 704, and are continuously connected to form the S-shaped connection portion 704. In short, the connection portion 704 is provided with two arc curved portions 8. In this embodiment, the two curved portions 8 have substantially the same curvature radius as each other.

As shown in FIG. 2A, the connection portion 704 is formed in a linear shape extending at a slant so as to be positioned downward in the vertical direction toward the evaporator 1, when being viewed from the flow direction EF of the exhaust gas. In the example of FIG. 2A, the flow direction EF of the exhaust gas corresponds to the face-back direction of the paper. Because the connection portion 704 extends in total downwardly as toward the downstream side of the working fluid while having the S shape, the working fluid is allowed to be positioned downward in the vertical direction as toward the downstream side of the working fluid flow in the connection portion 704.

As described above, the condensation side connection portion 72 has the arc curved portion 8 formed in a part thereof. When there occurs a difference in temperature between the evaporator 1 and the condenser 2, the elastic deformation of the curved portion 8 can absorb thermal stress caused by a difference in thermal expansivity. At this time, bellows do not need to be provided in the evaporation side and condensation side connection portions 71 and 72, so that it can release the thermal stress with a simple structure while preventing the occurrence of holes due to external corrosion.

The volume of working fluid evaporated at the evaporator 1 is about 1000 times as large as that of working fluid condensed by the condenser 2, so that a sectional area of a passage of the evaporation side connection portion 71 is generally larger than that of the condensation side connection portion 72. Thus, in this embodiment, the curved portion 8 is provided only in the condensation side connection portion 72 having the smaller passage sectional area among the two connection portions 71 and 72. This can improve workability as compared to the case in which the curved portion 8 is provided in the evaporation side connection portion 71 having the larger passage sectional area.

The working fluid in the connection portion 704 with the two curved portions 8 is allowed to be positioned downward as toward the downstream side of the working fluid flow. This can eliminates the necessity of temporarily positioning the working flow in a high position of the connection portion 704, thus preventing degradation of circularity of the working fluid. Since the liquid level of the working fluid in the connection portion 704 is not higher than the liquid level of the working fluid in the condenser 2, the working fluid can be refluxed sufficiently from the condenser 2 to the evaporator 1, thereby ensuring heat exchange characteristics.

Other Embodiments

Although the present invention has been fully described in connection with the preferred embodiments thereof with reference to the accompanying drawings, it is to be noted that various changes and modifications will become apparent to those skilled in the art.

For example, in the above-described first embodiment, the valve mechanism 6 is provided in the second condensation side header 52b, as shown in FIG. 1. However, the valve mechanism 6 may not be provided.

Although in each of the above-described embodiments, one end of the lower member 701 of the condensation side connection portion 72 is connected to the second evaporation side header 52a, the invention is not limited thereto. The one end of the lower member 701 may be connected directly to the evaporation side tube 41a which is closest to the condenser 2 among the evaporation side tubes 41a.

Although in each of the above-described embodiments, coolant is used as a fluid to be heated, the fluids to be heated may include engine oil, oil in a torque converter for a vehicle automatic transmission, water for a heater and the like.

Although in the first embodiment, the spiral portion 703 is provided only in the condensation side connection portion 72 among the two connection portions 71 and 72, the invention is not limited thereto. The spiral portion 703 may be provided only in the evaporation side connection portion 71, or in both of the two connection portions 71 and 72.

Although in the first embodiment, the condensation connection portion 72 is constructed of the lower member 701, the upper member 702, and the spiral portion 703 formed in a spiral shape from the end of the lower member 701 to the end of the upper member 702, the invention is not limited thereto. For example, the entire of the condensation side connection portion 72 may be formed in the spiral shape, that is, the condensation side connection portion 72 may be formed in the spiral shape from the second evaporation side header 52a to the second condensation side header 52b.

Although in the first embodiment, the center axis of the spiral shape of the spiral portion 703 is approximately in parallel to the vertical direction, the spiral portion 703 may not be in parallel to the vertical direction. For example, the center axis of the spiral portion 703 may be tilted relative to the vertical direction.

Although in the second embodiment, the upper member 702 of the condensation side connection portion 72 is formed to extend toward the lower side substantially in a vertical direction, the invention is not limited thereto. For example, as shown in FIG. 3A, the condensation side connection portion 72 may be formed to extend substantially in the horizontal direction toward the side of the evaporator 1.

Although in the second embodiment, the two curved portions 8 have the same curvature radius, the invention is not limited thereto. As shown in FIG. 3B, the two curved portions 8 may have different curvature radiuses.

Although in the second embodiment, the connection portion 704 is formed in the S shape when being viewed from the lower side in the vertical direction, the invention is not limited thereto. For example, as shown in FIG. 3C, the connection portion 704 may be formed in an approximately U-like shape when being viewed from the lower side in the vertical direction. In this case, the connection portion 704 has one arc curved portion 8. As shown in FIG. 3D, the connection portion 704 may have three arc curved portions 8. Furthermore, the connection portion 704 may have curved portions more than three.

Although in the second embodiment, the curved portion 8 is provided only in the condensation side connection portion 72 among the two connection portions 71 and 72, the invention is not limited thereto. The curved portion 8 may be provided only in the evaporation side connection portion 71, or in both of the two connection portions 71 and 72.

Although in the second embodiment, the connection portion 704 is formed in the linear shape extending at a slant so as to be positioned downward in the vertical direction as toward the evaporator 1, when being viewed from the direction of an exhaust gas flow, the invention is not limited thereto. The connection portion 704 may not be positioned downward in the vertical direction as toward the evaporator 1, or may not be formed linearly when being viewed from the direction of the exhaust gas flow.

Such changes and modifications are to be understood as being within the scope of the present invention as defined by the appended claims.

Claims

1. An exhaust heat recovery device having a working fluid sealed therein and capable of being evaporated and condensed by exchanging heat, the exhaust heat recovery device comprising: an evaporator disposed in a first passage through which a heating fluid flows, the evaporator being adapted to evaporate the working fluid by exchanging heat between the heating fluid and the working fluid;a condenser disposed in a second passage through which a fluid to be heated flows, the condenser being adapted to cool and condense the working fluid by exchanging heat between the fluid to be heated and the working fluid evaporated by the evaporator;an evaporation side connection portion for guiding the working fluid evaporated by the evaporator to the condenser; anda condensation side connection portion for guiding the working fluid condensed by the condenser to the evaporator,wherein at least one of the evaporation side connection portion and the condensation side connection portion has a curved portion.

2. The exhaust heat recovery device according to claim 1, wherein only the condensation side connection portion among the evaporation side connection portion and the condensation side connection portion has the curved portion.

3. The exhaust heat recovery device according to claim 1, wherein the curved portion is formed into a spiral shape such that a center axis of the spiral shape is approximately in parallel to a vertical direction.

4. The exhaust heat recovery device according to claim 1, wherein the curved portion is formed into an S-like shape.

5. The exhaust heat recovery device according to claim 1, wherein the curved portion is formed into a U-like shape.

6. The exhaust heat recovery device according to claim 1, wherein the curved portion has an arc shape.

7. The exhaust heat recovery device according to claim 1, wherein the condensation side connection portion has the curved portion,wherein the condensation side connection portion includes a first end connected to the evaporator and a second end connected to the condenser, andwherein the condensation side connection portion is arranged such that a liquid level in the condensation side connection portion is not higher than that in the condenser.

8. The exhaust heat recovery device according to claim 7, wherein the second end of the condensation side connection portion is positioned higher than the first end of the condensation side connection portion.