WO2007125416A2

WO2007125416A2 - Heat exchanger

Info

Publication number: WO2007125416A2
Application number: PCT/IB2007/001943
Authority: WO
Inventors: Takato Ishihata; Yoshihiro Kamiya
Original assignee: Toyota Jidosha Kabushiki Kaisha
Priority date: 2006-04-28
Filing date: 2007-04-26
Publication date: 2007-11-08
Also published as: WO2007125416A3; JP2007298228A

Abstract

An exhaust gas secondary flow path (20c) is formed between cooling passages (20d, 20e) such that heat exchange can take place between exhaust gas and a cooling medium from both the inside and the outside. The space of this exhaust gas secondary flow path (20c) has wide areas and narrow areas which repeatedly alternate in the circumferential direction. The cross-sectional shape of the exhaust gas secondary flow path (20c) at a wide area is asymmetrical with respect to an axis (Za).

Description

HEAT EXCHANGER

FIELD OF THE INVENTION

[0001] The invention relates to a heat exchanger. More specifically, the invention relates to a heat exchanger that performs heat exchange between coolant and hot gas by a cooling passage formed around a hot gas (exhaust) flow passage and a secondary flow path for hot gas formed inside this cooling passage.

BACKGROUND OF THE INVENTION

[0002] An exhaust cooling system is known which is provided around an exhaust pipe in an attempt to recover heat from exhaust gas of an internal combustion engine of a vehicle, for example, and reduce exhaust noise by cooling the exhaust gas, and the like. In Japanese Patent Application Publication No. JP-A-2004-293395 (pgs. 4-5, FIG. 1; hereinafter referred to as "Patent Document 1"), exhaust gas is led into a plurality of pipes arranged in a cooling passage in order to efficiently perform heat exchange between coolant and the exhaust gas. In Japanese Utility Model Application Publication No. JP-U-63-198411 (pgs. 5-7, FIG. 1; hereinafter referred to as "Patent Document 2"), heat exchange is performed by covering a second exhaust passage with a water jacket from the outside instead of using pipes.

[0003] However, because the structure in Patent Document 1 has multiple pipes arranged within a cooling passage, the manufacturing process is complicated, which increases manufacturing costs. On the other hand, although the structure described in Patent Document 2 does not use pipes, heat exchange is performed between exhaust gas in a second exhaust passage and coolant simply by running coolant around the outer periphery of the second exhaust passage. In order to prevent a decrease in heat exchange efficiency with this structure, straight fins extending in the axial direction are formed on the second exhaust passage side and helical fins which agitate the coolant are formed on the water jacket side, at a partition portion (referred to as an outer passage member in Patent Document 2) between the water jacket and the second exhaust passage. Even with this kind of heat cooling system described in Patent Document 2, the structure of the partition portion is complicated which increases the manufacturing cost of this portion. In addition, heat exchange is performed only from the area outside of the exhaust gas in the second exhaust passage so the heat exchange efficiency may be lower than that of the technology described in Patent Document 1.

DISCLOSURE OF THE INVENTION

[0004] This invention thus aims to provide a heat exchanger that performs heat exchange between coolant and gas by a cooling passage formed around a gas flow passage and a secondary flow path for gas formed inside this cooling passage, which can achieve high heat exchange efficiency with a relatively simple structure. [0005] One aspect of the invention relates to a heat exchanger. This heat exchanger includes i) a cooling passage through which a cooling medium for cooling a gas that flows through a gas flow passage flows, and which is formed around the gas flow passage, and ii) two cylindrical dividing members which are arranged inside the cooling passage and surround the gas flow passage. A space between the two cylindrical dividing members serves as a secondary flow path with respect to the gas flow passage. The heat exchanger performs heat exchange between the cooling medium and the gas flowing through the secondary flow path by diverting gas from the gas flow passage to the secondary flow path. The space between the two cylindrical dividing members has wide areas and narrow areas that repeatedly alternate in the circumferential direction, and a cross-sectional shape of the secondary flow path between two adjacent narrow areas is asymmetrical with respect to a vertical axis in the radial direction of the cylindrical dividing members.

[0006] In the secondary flow path for the gas, two cylindrical dividing members are arranged instead of multiple pipes, and the space in between those two cylindrical dividing members serves as the secondary flow path for the gas so the secondary flow path can easily be formed in the cooling passage. The shapes of the cylindrical dividing members are formed so that the space has wide areas and narrow areas that repeatedly alternate in the circumferential direction, so the cylindrical dividing members themselves can also be manufactured easily.

[0007] Furthermore, the secondary flow path for gas is formed in the cooling passage so heat exchange is performed between the gas in the secondary flow path and the cooling medium from both the inside and the outside, hi this heat exchange, the wide areas and the narrow areas of the space repeatedly alternate in the circumferential direction so there is sufficient flow path area for the gas at the portions between narrow areas. Also, the cross-sectional shape of the secondary flow path between these narrow areas is asymmetrical with respect to a vertical axis in the radial direction of the cylindrical dividing members. Therefore, the center regions between narrow areas in the secondary flow path will not be very far from the two cylindrical dividing members. As a result, the heat of all of the gas flowing through the secondary flow path is more easily absorbed by the cooling medium on the inside or outside of the cylindrical dividing members. Moreover, heat exchange is performed more effectively because this asymmetry disturbs the flow of gas flowing between the two cylindrical dividing members, as well as the flow of cooling medium flowing on the inside or outside of the two cylindrical dividing members, to some degree so that the gas in the center region of the gas flow changes places with the gas at the portion contacting the cylindrical dividing members, and similarly, the cooling medium in the center region of the cooling medium flow changes places with the cooling medium at the portion contacting the cylindrical dividing members. Accordingly, there is no need to provide fins or the like on the cylindrical dividing members.

[0008] The heat exchanger according to this aspect of the invention is thus able to achieve high heat exchange efficiency with a relatively simple structure. Also, in the heat exchanger according to this aspect of the invention, each of the two cylindrical dividing members may have a high convex portion and a low convex portion arranged alternately in the circumferential direction with respect to the secondary flow path, with the high convex portion of one cylindrical dividing member opposing the low convex portion of the other cylindrical dividing member.

[0009] According to this structure, the wide and narrow areas can be repeatedly alternated in the circumferential direction in the space between the two cylindrical dividing members. Furthermore, the cross-sectional shape of the secondary flow path between two adjacent narrow areas can easily be made asymmetrical with respect to a vertical axis in the radial direction of the cylindrical dividing members. Therefore, the heat exchanger according to this structure is able to be easily manufactured so manufacturing costs are effectively reduced.

[0010] The heat exchanger according to the foregoing aspect of the invention may also be such that the space has the wide areas and the narrow areas which repeatedly alternate in the circumferential direction due to the two cylindrical dividing members being formed in a wavy shape in the circumferential direction, and a phase difference of waveforms between the two cylindrical dividing members with respect to the secondary flow path is a phase difference other than 0° and 180° when one cycle of the waveform is 360°.

[0011] Forming the wavy shapes in the circumferential direction in the two cylindrical dividing members and providing the phase difference in this way enables wide and narrow areas to be repeatedly alternated in the circumferential direction in the space between the two cylindrical dividing members, as well as enables the cross-sectional shape of the secondary flow path between two adjacent narrow areas to be asymmetrical with respect to a vertical axis in the radial direction of the cylindrical dividing members. Therefore, the heat exchanger according to this structure is able to be easily manufactured so manufacturing costs are effectively reduced.

[0012] The heat exchanger according to the foregoing aspect of the invention may also be such that the phase difference of the waveforms between the two cylindrical dividing members is one of a phase difference that is between 30°and 150°, inclusive, and a phase difference that is between 210°and 330°, inclusive. [0013] In particular, a phase difference between either 30° and 150° or 210° and 330° will enable both high heat exchange efficiency and a sufficient flow path sectional area for the exhaust gas to be obtained. In the heat exchanger according to the foregoing aspect of the invention, the cooling passage on the inside of the cylindrical dividing member that is on the inside may be kept watertight by the cylindrical dividing member on the inside being joined around the entire periphery at two locations in the axial direction to a cylindrical inner peripheral member that forms an inner peripheral surface of the cooling passage, and the cooling passage on the outside of the cylindrical dividing member that is on the outside may be kept watertight by the cylindrical dividing member on the outside being joined around the entire periphery at two locations in the axial direction to a cylindrical outer peripheral member that forms an outer peripheral surface of the cooling passage.

[0014] The cylindrical dividing members enable the secondary flow path to be kept watertight by this simple structure even if that secondary flow path is in the cooling passage. As a result, the heat exchanger of this invention is able to be manufactured easily, which effectively enables manufacturing costs to be reduced.

[0015] In the heat exchanger according to the foregoing aspect of the invention, the two cylindrical dividing members may be integrated by forming a joining portion where the two cylindrical dividing members are joined together at portions of opposing surfaces.

[0016] Directly joining the cylindrical dividing members together with this kind of joined portion increases the rigidity and thus improves the durability of the heat exchanger with a simple structure. Also, a through-hole may be formed in the joining portion, with the entire periphery of the through-hole being surrounded by a joining region, and this through-hole may enable cooling medium to flow between the cooling passage on the inside of the cylindrical dividing member on the inside and the cooling passage on the outside of the cylindrical dividing member on the outside.

[0017] Accordingly, of the cooling passages that are divided into the inside cooling passage and the outside cooling passage by the two cylindrical dividing members, cooling medium can be supplied to both the inside and the outside cooling passages by providing a coolant inlet for only the outside or the inside cooling passage. As a result, the heat exchanger of this invention is able to achieve high heat exchange efficiency with a simple structure. [0018] In the heat exchanger according to the foregoing aspect of the invention, the gas flow passage may be an exhaust pipe and the gas may be exhaust gas, and heat exchange may be performed between the exhaust gas and the cooling medium by introducing the cooling medium into the cooling passage.

[0019] Accordingly, the invention can be used to perform heat exchange with exhaust gas and can achieve high heat exchange efficiency with a relatively simple structure.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The foregoing and further objects, features and advantages of the invention will become apparent from the following description of preferred embodiments with reference to the accompanying drawings, wherein like numerals are used to represent like elements and wherein:

FIG. 1 is a longitudinal sectional view of an exhaust cooling system according to a first example embodiment of the invention;

FIG. 2 is a longitudinal sectional view showing a state in which exhaust gas is being supplied to a heat exchanger of the exhaust cooling system;

FIGS. 3A and 3B are perspective views of the heat exchanger shown arranged around an exhaust pipe; FIG. 4 is an exploded perspective view of the exhaust cooling system;

FIGS. 5 A to 5D are views of the structure of an inner cylindrical dividing member of the heat exchanger;

FIGS. 6Ato 6D are views of the structure of an outer cylindrical dividing member of the heat exchanger; FIGS. 7Aand 7B are views of the structure of a secondary flow path member;

FIGS. 8Ato 8C are cross-sectional views of the exhaust cooling system;

FIG. 9 is a view showing the relationship between wave shapes of a heat exchange portion; FIG. 10 is a view showing the relationship between wave shapes of a heat exchange portion according to a second example embodiment of the invention;

FIG. 11 is a view showing the relationship between other examples of wave shapes of the heat exchange portion;

FIGS. 12A and 12B are views showing the relationships between yet another example of wave shapes of the heat exchange portion; and

FIGS. 13A and 13B are views showing the relationships between still another example of wave shapes of the heat exchange portion.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] FIG. 1 is a longitudinal sectional view of an exhaust cooling system 2 of an internal combustion engine for a vehicle according to a first example embodiment of the invention. Exhaust gas discharged form the internal combustion engine flows through an exhaust pipe 4 (which corresponds to a hot gas flow passage) from left to right in the drawing, as shown by the arrows. Two branch ports 4a are open opposing one another on the upstream side of the exhaust pipe 4 in the portion shown in the drawing.

A switching valve 4b which can be driven open and closed by an actuator 4c mounted to an external portion is provided near the branch ports 4a on the downstream side thereof.

[0022] A heat exchanger 6 is arranged downstream of the portion where the switching valve 4b is provided so as to surround the outer periphery of the exhaust pipe 4. A guide cover 8 that guides the exhaust gas flowing from the branch ports 4a to outside the exhaust pipe 4 is arranged upstream of this heat exchanger 6. A downstream merger pipe 10 that combines the exhaust gas has gone through the heat exchange process in the heat exchanger 6 with the exhaust gas from the outlet of the exhaust pipe 4 and leads that combined exhaust gas downstream is arranged downstream of the heat exchanger 6.

[0023] FIG. 1 shows the switching valve 4b in an open state so almost all of the exhaust gas passes through the exhaust pipe 4 and is discharged to the downstream merger pipe 10. As a result, almost no exhaust gas is supplied to the heat exchanger 6. When the switching valve 4b is closed, the exhaust gas is unable to flow straight through the exhaust pipe 4 so it instead flows out of the exhaust pipe 4 from the branch ports 4a and is led to the heat exchanger 6 by the guide cover 8, as shown in FIG. 2. Then the exhaust gas that has undergone heat exchange in the heat exchanger 6 flows out to the downstream merger pipe 10. [0024] FIGS. 3 A and 3B are perspective views of the heat exchanger 6 shown arranged around (i.e., encompassing) the exhaust pipe 4. FIG. 3B shows the structure in FIG. 3A rotated 180 degrees on its vertical axis. An inflow pipe 12 and a discharge pipe 14 through which coolant is supplied to and discharged from cooling passages inside the heat exchanger 6 are provided on an outer peripheral portion of the exhaust pipe 4. [0025] The heat exchanger 6 shown in FIGS. 3A and 3B has a secondary flow path member 20 for exhaust gas arranged between a small diameter cylindrical inner pipe 16 and a large diameter cylindrical outer pipe 18, as shown in the exploded perspective view of FIG. 4. The structure shown in FIGS. 1 to 3 A and 3B has the exhaust pipe 4 arranged in the center space of this heat exchanger 6. Metal mesh 22 is arranged between the exhaust pipe 4 and the inner pipe 16 so that they are not in direct contact with each other to absorb heat distortion. The metal mesh 22 also prevents heat exchange between the exhaust gas flowing through the exhaust pipe 4 and the inner pipe 16 side when heat exchange is unnecessary.

[0026] The secondary flow path member 20 is formed of two cylindrical dividing members 24 and 26, one inside the other. FIGS. 5A to 5D show the structure of the inner cylindrical dividing member 24. FIG. 5A is a plan view, FIG. 5B is a front view, FIG. 5C is a perspective view, and FIG. 5D is a right side view. The inner cylindrical dividing member 24 includes a center portion 24a formed in a wavy shape in the circumferential direction, and two end portions 24b formed in a tapered shape at both ends of the center portion 24a. The center portion 24a and the two end portions 24b are integrally formed together as a single unit. Not all of the center portion 24a is wavy shaped. That is, the center portion 24a has heat exchange portions 24c which are wavy shaped, and joining portions 24d which are cylindrical planar portions in three locations in the circumferential direction in between the heat exchanger portions 24c. An opening 24e is formed near each end of the joining portion 24d that is the widest of the three joining portions 24d. These openings 24e provide communication between the inside and the outside of the inner cylindrical dividing member 24. The end portions 24b of the inner cylindrical dividing member^" 24 are each formed of a taper portion 24f that gradually becomes smaller in diameter toward the tip end, and a ring shaped joining portion 24g at the tip most end.

[0027] FIGS. 6 A to 6D show the structure of the outer cylindrical dividing member 26. FIG. 6 A is a plan view, FIG. 6B is a front view, FIG. 6C is a perspective view, and FIG. 6D is a right side view. The outer cylindrical dividing member 26 includes a center portion 26a formed in a wavy shape in the circumferential direction, and two end portions 26b formed in a tapered shape at both ends of the center portion 26a. The center portion 26a and the two end portions 26b are integrally formed together as a single unit. Not all of the center portion 26a is wavy shaped. That is, the center portion 26a has heat exchange portions 26c that are wavy shaped and joining portions 26d which are cylindrical planar portions in three locations in the circumferential direction in between the heat exchanger portions 26c. An opening 26e is formed near each end of the joining portion 26d that is the widest of those three joining portions 26d. These openings 26e provide communication between the inside and the outside of the inner cylindrical dividing member 26. The end portions 26b of the inner cylindrical dividing member 26 are each formed of a taper portion 26f that gradually becomes larger in diameter toward the tip end, and a ring shaped joining portion 26g at the tip most end.

[0028] The outer peripheral surface of the joining portion 24d of the inner cylindrical dividing member 24 described above has the largest diameter of any portion of the inner cylindrical dividing member 24. The inner peripheral surface of the joining portion 26d of the outer cylindrical dividing member 26 described above has the smallest diameter of any portion of the outer cylindrical dividing member 26. The outer peripheral surface of the joining portion 24d of the inner cylindrical dividing member 24 and the inner peripheral member of the joining portion 26d of the outer cylindrical dividing member 26 are formed with substantially the same diameter so that when the inner cylindrical dividing member 24 is arranged inside the outer cylindrical dividing member 26, the joining portions 24d and 26d can contact one another.

[0029] Accordingly, with the inner cylindrical dividing member 24 arranged inside the outer cylindrical dividing member 26 and the openings 24e and 26e aligned, the joining portions 24d and 26d, including the entire periphery around the openings 24e and 26e, are joined by welding or the like to form the single secondary flow path member 20, as shown in FIGS. 7A and 7B. FIG. 7A is a perspective view and FIG. 7B is a left side view. Two coolant communicating flow passages 20a and 20b are formed by matching up the openings 24e and 26e. [0030] In the examples shown in FIGS. 5A to 5D and 6A to 6D, the openings

24e and 26e are first formed in the cylindrical dividing members 24 and 26. The invention is not limited to this, however. That is, the joining portions 24d and 26d of the inner cylindrical dividing member 24 and the outer cylindrical dividing member 26 may first be joined together and then the two coolant communicating flow passages 20a and 20b formed by opening (forming) through-holes in that joining region.

[0031] The heat exchanger 6 can be formed by first arranging the inner pipe 16 in the center portion of this secondary flow path member 20, as shown in FIG. 4, and joining the inner pipe 16 to the secondary flow path member 20 at the locations of the ring shaped joining portions 24g of the inner cylindrical dividing member 24 along the entire periphery. This secondary flow path member 20 is then arranged inside the outer pipe 18 and joined to it along the entire periphery at the locations of the ring shaped joining portions 26g of the outer cylindrical dividing member 26. The coolant inflow pipe 12 is then inserted up to a predetermined location into an inlet 18a formed in the outer pipe 18 and connected thereto, and the discharge pipe 14 is inserted up to a predetermined location into an outlet 18b and connected thereto. Incidentally, a small diameter through-hole 14a is formed in the discharge pipe 14. This small diameter through-hole 14a opens to an outer cooling passage 2Oe, as shown in FIGS. 1 and 2, and thus serves as a vent to allow air to escape from the outer cooling passage 2Oe. [0032] The exhaust pipe 4 is arranged in the center of the inner pipe 16 of the heat exchanger 6 via the metal mesh 22. The heat exchanger 6 is then sandwiched from the front and the back between the guide cover 8 and the downstream merger pipe 10. The guide cover 8 is joined to the exhaust pipe 4. As a result, the heat exchanger 6 is integrated with the exhaust pipe 4. [0033] The structure shown in FIGS. 1 and 2 is obtained by arranging the switching valve 4b in the exhaust pipe 4 and mounting the actuator 4c to an outer peripheral portion of the guide cover 8 so that the switching valve 4b can be driven open and closed.

[0034] FIG. 8A is a sectional view taken along line I-I in FIG. 1, FIG. 8B is a sectional view taken along line II-II in FIG. 1, and FIG. 8C is a sectional view taken along line III-III in FIG. 1. An exhaust gas secondary flow path 20c is formed in the area between the inner cylindrical dividing member 24 and the outer cylindrical dividing member 26 which are separated from each other except for at the joining portions 24d and 26d, as shown in the drawing. When exhaust gas is introduced to the guide cover 8 side from the branch ports 4a, exhaust gas is introduced into the exhaust gas secondary flow path 20c from between the end portion 24b of the inner cylindrical dividing member 24 and the end portion 26b of the outer cylindrical dividing member 26.

[0035] An inner cooling passage 20d is formed between the inner cylindrical dividing member 24 and the inner pipe 16 which are separated from one another at the center portion in the axial direction. This inner cooling passage 2Od is made watertight with the exception of the outlet 18b and the coolant communicating flow passages 20a and 20b by being joined and sealed at the portions of the ring shaped joining portions 24g at both ends in the axial direction.

[0036] An outer cooling passage 20e is formed between the outer cylindrical 43

12

dividing member 26 and the outer pipe 18 which are separated from each other at the center portion in the axial direction. This outer cooling passage 2Oe is made watertight with the exception of the inlet 18a and the coolant communicating flow passages 20a and 20b by being joined and sealed at the portions of the ring shaped joining portions 26g at both ends in the axial direction.

[0037] The tip end of the coolant inflow pipe 12 opens inside of the outer pipe 18, i.e., opens to the outer cooling passage 2Oe, as shown in FIG. 8A. Meanwhile, the tip end of the discharge pipe 14 extends all the way to the coolant communicating flow passage 20a of the secondary flow path member 20 and opens to the inner cooling passage 2Od so as to entirely block off that coolant communicating flow passage 20a from the outer cooling passage 2Oe.

[0038] From this kind of structure, coolant that was introduced from the inflow pipe 12 to the outer cooling passage 2Oe first flows in to fill up the outer cooling passage 2Oe and then flows into the inner cooling passage 2Od from the coolant communicating flow passage 20b. Then after filling up the inner cooling passage 2Od, the coolant flows out of the discharge pipe 14 of the coolant communicating flow passage 20a. In this way, heat exchange is performed between the exhaust gas that is introduced into the exhaust gas secondary flow path 20c and the coolant that flows through the outer cooling passage 2Oe and the inner cooling passage 2Od. [0039] Here, FIG. 9 shows the relationship between the two heat exchange portions 24c and 26c which both are wavy shaped in the circumferential direction. Making the heat exchange portions 24c and 26c wavy shaped in this way results in the exhaust gas secondary flow path 20c that is formed in the space between these heat exchange portions 24c and 26c having wide and narrow areas that repeatedly alternate in the circumferential direction.

[0040] When the peaks on each of the heat exchange portions 24c and 26c which point out away from the exhaust gas secondary flow path 20c are designated concave portions and the peaks on each of the heat exchange portions 24c and 26c which point in toward the exhaust gas secondary flow path 20c are designated convex portions, all of the concave portions Mb on the heat exchange portion 24c of the inner cylindrical dividing member 24 are approximately the same distance away from the center axis. Moreover, all of the concave portions Nb on the heat exchange portion 26c of the inner cylindrical dividing member 26 are approximately the same distance away from the center axis.

[0041] However, the distances of the convex portions MaI and Ma2 of the heat exchange portion 24c of the inner cylindrical member 24 from the center axis are different. That is, the convex portion MaI is higher and thus farther away from the center axis than the convex portion Ma2 which is lower, and these high and low convex portions MaI and Ma2 are formed alternately. Similarly, the distances between the convex portions NaI and Na2 of the heat exchange portion 26c of the outer cylindrical dividing member 26 and the center axis also differ, with the convex portion NaI being higher and thus closer to the center axis than the convex portion Na2 which is lower, and these high and low convex portions NaI and Na2 are formed alternately. [0042] Between these cylindrical dividing members 24 and 26, the high convex portion MaI on the inner cylindrical dividing member 24 side and the low convex portion Na2 on the outer cylindrical dividing member 26 side are formed opposing one another at the same phase position around the center axis. Further, the low convex portion Ma2 on the inner cylindrical dividing member 24 side and the high convex portion NaI on the outer cylindrical dividing member 26 side are formed opposing one another at the same phase position around the center axis. According to this relationship, the wide areas and narrow areas of the exhaust gas secondary flow path 20c repeatedly alternate in the circumferential direction.

[0043] Also from this kind of wave shape relationship, when the radial direction of the cylindrical dividing members 24 and 26 is made a vertical axis Za, the cross-sectional shape of the exhaust gas secondary flow path 20c between two adjacent narrow areas Xa and Ya is asymmetrical with respect to this axis Za. The narrow area Xa is formed by the high convex portion MaI and the low convex portion Na2, while the narrow area Ya is formed by the low convex portion Ma2 and the high convex portion NaI.

[0044] By forming the exhaust cooling system 2 of an internal combustion engine for a vehicle as described above, the switching valve 4b can be closed by driving the actuator 4c with an electronic control apparatus provided in the vehicle when it is necessary to reduce exhaust noise by cooling the exhaust or recover heat from the exhaust gas or the like, according to the operating state of the internal combustion engine. Accordingly, by switching from the state shown in FIG. 1 to the state shown in FIG. 2, instead of flowing straight through the exhaust pipe 4, the exhaust gas of the internal combustion engine flows out from the branch ports 4a to the guide cover 8 side and then flows into the exhaust gas secondary flow path 20c from upstream of the heat exchanger 6. At this time, coolant that is supplied either directly or indirectly from a coolant pump that is driven by the internal combustion engine flows through the inflow pipe 12, the outer cooling passage 2Oe, the coolant communicating flow passage 20b, the inner cooling passage 2Od, the coolant communicating flow passage 20a, and the discharge pipe 14 in that order, as described above. Through this process heat exchange takes place between the exhaust gas and the coolant via the heat exchange portions 24c and 26c of the cylindrical dividing members 24 and 26.

[0045] The first example embodiment of the invention described above yields the following effects. (A). By arranging the two cylindrical dividing members 24 and 26, instead of multiple pipes, in the secondary flow path member 20 used in the heat exchanger 6 of this example embodiment, the space therebetween forms the exhaust gas secondary flow path 20c through which hot gas (exhaust gas from the internal combustion engine in this case) flows. In particular, the inner cooling passage 2Od is able to be kept watertight by joining the inner cylindrical dividing member 24 along the entire periphery at the end portions 24b of both ends to the inner pipe 16 which serves as the cylindrical inner peripheral member. Similarly, the outer cooling passage 2Oe is able to be kept watertight by joining the outer cylindrical dividing member 26 along the entire periphery at the end portions 26b of both ends to the outer pipe 18 which serves as the cylindrical outer peripheral member. Therefore, the exhaust gas secondary flow path 20c can be easily formed between the cooling passages 2Od and 2Oe with a simple structure. Moreover, in terms of shape, the cylindrical dividing members 24 and 26 are formed such that the space that forms the exhaust gas secondary flow path 20c alternates between being wide and narrow (i.e., is a series of repeatedly alternating wide areas and narrow areas) in the circumferential direction so the cylindrical dividing members 24 and 26 themselves can also be easily manufactured.

[0046] Furthermore, the exhaust gas secondary flow path 20c is formed between the cooling passages 2Od and 2Oe so that heat exchange can take place between the exhaust gas and the coolant from both the inside and the outside (i.e., from two sides). By forming the space that forms the exhaust gas secondary flow path 20c with repeatedly alternating wide and narrow areas, a flow path of sufficient area for the exhaust gas can be ensured by the wide areas that are between narrow areas.

[0047] In addition, the cross-sectional shape of the exhaust gas secondary flow path 20c at the wide area is asymmetrical with respect to the axis Za, as described above, which keeps the center region of each wide area in the exhaust gas secondary flow path 20c from being very far away from the two cylindrical dividing members 24 and 26. This facilitates the absorption of heat by the coolant on the inside or outside of the cylindrical dividing members 24 and 26. Furthermore, heat exchange is performed more effectively because this asymmetry disturbs the flow of exhaust gas flowing between the two cylindrical dividing members 24 and 26, as well as disturbs the flow of coolant flowing on the inside or outside of the two cylindrical dividing members 24 and 26, to some degree so that the exhaust gas in the center region of the flow changes places with the exhaust gas at the portion contacting the cylindrical dividing members 24 and 26, and similarly, the coolant in the center region of the flow changes places with the coolant at the portion contacting the cylindrical dividing members 24 and 26. Accordingly, there is no need to provide fins or the like on the cylindrical dividing members 24 and 26.

[0048] The heat exchanger 6 which uses the secondary flow path member 20 in this way is capable of highly efficient heat exchange by means of a relatively simple structure. The amount of heat actually recovered from exhaust gas by the coolant of an internal combustion engine was measured with both the example embodiment described above and a comparative example in which the cross-sectional shape of the exhaust gas secondary flow path 20c of the wide areas is symmetrical with respect to the axis Za and the heights of the wave shapes are the same. The results showed that the flowrate of the coolant and pressure loss of the exhaust gas and the like were the same for both. However, when the amount of heat recovered with the comparative example is designated 1, the amount of heat recovered with the example embodiment is 1.1. That is, the results showed an increase of 10% in the amount of heat recovered with the example embodiment.

[0049] (B). The cylindrical dividing members 24 and 26 are not separated from one another around the entire periphery but rather are integrated by being joined together at the joining portions 24d and 26d. Directly joining the cylindrical dividing members 24 and 26 in this way increases the rigidity of the secondary flow path member 20 as well as the rigidity of the heat exchanger 6 that incorporates this secondary flow path member 20. As a result, the durability of the heat exchanger 6 is increased even with the simple structure.

[0050] (C). The coolant communicating flow passages 20a and 20b which are the through-holes are formed in the joining region of one of the joining portions 24d and 26d while being entirely surrounded around the entire periphery by this joining region. These coolant communicating flow passages 20a and 20b enable the coolant to flow between the cooling passages 2Od and 2Oe. As a result, even if separate inlets are not provided for the inner cooling passage 2Od and the outer cooling passage 2Oe, coolant can still be supplied to both of the cooling passages 2Od and 2Oe by introducing coolant to the outer cooling passage 2Oe with the lead pipe 12 and discharging coolant from the inner cooling passage 2Od with the discharge pipe 14. Accordingly, high heat exchange efficiency is made possible by a simple structure.

[0051] Hereinafter, a second example embodiment of the invention will be described. This second example embodiment differs from the first example embodiment with respect to a heat exchange portion 124c of the inner cylindrical dividing member and a heat exchange portion 126c of the outer cylindrical dividing member, as shown in the partial sectional view of FIG. 10. In all other respects, the structure of the second example embodiment is the same as the structure of the first example embodiment.

[0052] The heat exchange portions 124c and 126c have convex portions Mc and Nc, respectively, which are wave shaped and thus form wide and narrow areas of an exhaust gas secondary flow path 120c that repeatedly alternate in the circumferential direction. The convex portions Mc are all one height and the convex portions Nc are all one height. Accordingly, waves of the same shape repeat with the concave portions Md and Nd. However, the wave shapes between the heat exchange portions 124c and 126c are not at the same phase positions (i.e., the phase positions of the convex portions Mc and Nc and the concave portions Md and Nd do not match). Instead, they are offset by an amount equal to 1/4 of a wavelength (i.e., by 90° is one cycle of a waveform is 360°). [0053] Accordingly, when the radial direction of the cylindrical dividing member is made a vertical axis Zb, the cross-sectional shape of the exhaust gas secondary flow path 120c between two adjacent narrow areas, in this case, between the narrow area Xb formed by the convex portion Mc and the convex portion Nc and the adjacent narrow area Yb also formed by the convex portion Mc and the convex portion Nc, is asymmetrical with respect to this axis Zb.

[0054] The second example embodiment of the invention described above yields the following effects. In this example embodiment, the wave shapes of the heat exchange portions 124c and 126c have the same amplitudes so the same effects as those obtained with the first example embodiment can be obtained with an even simpler structure.

[0055] Incidentally, the phase difference of the waveforms between the heat exchange portions 124c and 126c needs to be a phase difference other than 0° and 180°. In particular, a phase difference between either 30° and 150° or 210° and 330° will enable both high heat exchange efficiency and a sufficient flow path sectional area for the exhaust gas to be obtained.

[0056] In both of the example embodiments described above, the heat exchange portions 24c, 26c, 124c, and 126c have cross-sections that are shaped like or similar to a sin curve, as shown in FIGS. 9 and 10. Alternatively, however, the space between the cylindrical dividing members may be made up of wide areas and narrow areas that repeatedly alternate in the circumferential direction according to wave shapes other than these concave and convex shapes. In addition, with the radial direction of the cylindrical dividing members made a vertical axis, the cross-sectional shape of the secondary flow path between two adjacent narrow areas may be asymmetrical with respect to that axis.

[0057] For example, convex portions 225b and 227b of heat exchange portions 224c and 226c may be angular and concave portions 225a and 227a may have wave shapes that have semicircular cross-sections, as shown in FIG. 11. Alternatively, heat exchange portions 324c, 326c, 424c, and 426c may have wave shapes that have trapezoidal shaped cross-sections, as shown in FIGS. 12A and 12B. Or, heat exchange portions 524c, 526c, 624c, and 626c may have wave shapes that have triangular cross-sections, as shown in FIGS. 13A and 13B. In any case, when the radial direction of the cylindrical dividing members is made a vertical axis Z, the cross-sectional shapes of the secondary flow paths 220c, 320c, 420c, 520c, and 620c between adjacent narrow areas is asymmetrical with respect to this axis Z.

[0058] While the invention has been described with reference to what are considered to be preferred embodiments thereof, it is to be understood that the invention is not limited to the disclosed embodiments or constructions. On the contrary, the invention is intended to cover various modifications and equivalent arrangements. In addition, while the various elements of the disclosed invention are shown in various combinations and configurations, which are exemplary, other combinations and configurations, including more, less or only a single element, are also within scope of the appended claims.

Claims

CLAIMS:

1. A heat exchanger that includes i) a cooling passage through which a cooling medium for cooling a gas that flows through a gas flow passage flows, and which is formed around the gas flow passage, and ii) two cylindrical dividing members which are arranged inside the cooling passage and surround the gas flow passage, a space between the two cylindrical dividing members being a secondary flow path with respect to the gas flow passage, the heat exchanger performing heat exchange between the cooling medium and the gas flowing through the secondary flow path by diverting gas from the gas flow passage to the secondary flow path, characterized in that the space between the two cylindrical dividing members has wide areas and narrow areas that repeatedly alternate in the circumferential direction, and a cross-sectional shape of the secondary flow path between two adjacent narrow areas is asymmetrical with respect to a vertical axis in the radial direction of the cylindrical dividing members.

2. The heat exchanger according to claim 1, wherein each of the two cylindrical dividing members has a high convex portion and a low convex portion arranged alternately in the circumferential direction with respect to the secondary flow path, the high convex portion of one cylindrical dividing member opposing the low convex portion of the other cylindrical dividing member.

3. The heat exchanger according to claim 1, wherein the space has the wide areas and the narrow areas which repeatedly alternate in the circumferential direction due to the two cylindrical dividing members being formed in a wavy shape in the circumferential direction, and a phase difference of waveforms between the two cylindrical dividing members with respect to the secondary flow path is a phase difference other than 0° and 180° when one cycle of the waveform is 360°.

4. The heat exchanger according to claim 3, wherein the phase difference of the waveforms between the two cylindrical dividing members is one of a phase difference that is between 30°and 150°, inclusive, and a phase difference that is between 210°and 330°, inclusive.

5. The heat exchanger according to any one of claims 1 to 4, wherein the cooling passage on the inside of the cylindrical dividing member that is on the inside is kept watertight by the cylindrical dividing member on the inside being joined around the entire periphery at two locations in the axial direction to a cylindrical inner peripheral member that forms an inner peripheral surface of the cooling passage, and the cooling passage on the outside of the cylindrical dividing member that is on the outside is kept watertight by the cylindrical dividing member on the outside being joined around the entire periphery at two locations in the axial direction to a cylindrical outer peripheral member that forms an outer peripheral surface of the cooling passage.

6. The heat exchanger according to any one of claims 1 to 5, wherein the two cylindrical dividing members are integrated by forming a joining portion where the two cylindrical dividing members are joined together at portions of opposing surfaces.

7. The heat exchanger according to claim 6, wherein a through-hole is formed in the joining portion, the entire periphery of the through-hole being surrounded by a joining region, the through-hole enabling cooling medium to flow between the cooling passage on the inside of the cylindrical dividing member on the inside and the cooling passage on the outside of the cylindrical dividing member on the outside.

8. The heat exchanger according to any one of claims 1 to 7, wherein the gas flow passage is an exhaust pipe and the gas is exhaust gas, and heat exchange is performed between the exhaust gas and the cooling medium by introducing the cooling medium into the cooling passage.

9. A heat exchanger comprising: a gas flow passage through which gas flows; a cooling passage that surrounds the gas flow passage and through which a cooling medium that cools the gas flows; two cylindrical dividing members that are arranged in the cooling passage; and a secondary flow path i) which is surrounded by the two cylindrical dividing members, ii) through which the gas that is diverted from the gas flow passage flows, iii) which has a wide area and a narrow area that repeatedly alternate in the circumferential direction, and iv) in which a cross-sectional shape between two adjacent narrow areas is asymmetrical with respect to a vertical axis in the radial direction of the cylindrical dividing members.