Exhaust heat exchanger

A profile of the casing 20 is formed into a circular pipe shape, and the two gas coolers 10a, 10b are integrated into one body so that the longitudinal directions of the respective gas coolers can be substantially parallel with each other. Due to the above structure, it is possible to make the coolant flow smoothly in the casing 20 and stagnation of the coolant seldom occurs. Accordingly, as boiling of the coolant can be suppressed, it is possible to prevent the heat transfer coefficient from being remarkably deteriorated. Further, it is possible to suppress the generation of cracks, in the tubes 11, which are caused by heat stress.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an exhaust heat exchanger for exchanging heat between an exhaust gas, which has been discharged from a heat engine (especially, the exhaust gas which has been discharged from an internal combustion engine), and a coolant used to cool the heat engine. The present invention is effectively applied to a gas cooler for cooling the exhaust gas used for an EGR (exhaust gas recirculation) device.

2. Description of the Related Art

As a gas cooler used for EGR device, a multitube type heat exchanger (for example, a multitube type heat exchanger disclosed in Japanese Unexamined Patent Publication No. 2001-108390) is well known. This multitube type heat exchanger includes: a casing formed into a shell having an inlet and outlet for the coolant; a tube seat, which is accommodated in the casing, for supporting a large number of exhaust gas pipes; and bonnets arranged on both sides of the casing, in which an inlet and outlet of the exhaust gas are formed.

In this connection, as stringent regulations have been recently adopted against exhaust gas emissions, to reduce a quantity of NOx contained in the exhaust gas, it is desired to enhance the cooling performance of an EGR gas cooler.

In the case where the multitube type heat exchanger described in the above prior art is used for the gas cooler, in order to enhance the cooling performance, it is possible to adopt a structure where the length of the exhaust pipe is extended so as to increase a heat exchanging area of the heat exchanger.

However, when the length of the exhaust pipe is extended, there is caused a problems in which a vibration proof property, with respect to the vibration generated in a vehicle, is deteriorated.

In order to solve the above problems, when the number of exhaust gas pipes is increased so as to enhance the cooling performance, a size of the gas cooler in the direction perpendicular to the longitudinal direction is extended, that is, a size of the cross section of the gas cooler is extended.

However, as shown inFIG. 6, a space in the engine compartment in which the gas cooler is mounted is not sufficiently large in the vertical direction. In detail, various components such as an intake manifold and others are arranged in an upper portion of the EGR gas cooler. Therefore, it is impossible to provide a sufficiently large space for the gas cooler in the vertical direction. Accordingly, it is difficult for a multitube type heat exchanger, the number of exhaust pipes of which is increased, to be mounted on a vehicle.

In order to solve the above problems, the present inventors made investigations and produced the multitube type heat exchanger shown inFIG. 5, by way of a trial, in which the casing is formed into a flat rectangle. However, the following new problems may be encountered in this multitube type heat exchanger.

In the multitube type heat exchanger, which was produced by way of trial, the cross section of the casing is rectangular. Therefore, a current of the coolant flowing in the casing is remarkably deteriorated. Accordingly, there is a tendency for the occurrence of stagnation of the coolant in which the coolant hardly flows. When stagnation is caused in the current of the coolant, the coolant boils, and the heat transfer coefficient is remarkably lowered. Further, as the temperature of the exhaust gas passage is increased, cracks tend to occur, due to heat, in the tubes composing the exhaust gas passage.

SUMMARY OF THE INVENTION

The present invention has been accomplished in view of the above points. It is a first object of the present invention to provide a new exhaust heat exchanger different from the exhaust heat exchanger of the prior art. It is a second object of the present invention to enhance the cooling capacity of an exhaust heat exchanger without deteriorating the durability and the heat exchange efficiency (the heat transfer coefficient).

In order to accomplish the above objects, the present invention provides an exhaust heat exchanger for exchanging heat between an exhaust gas generated by combustion and a coolant, comprising: at least two casings (20) composing a coolant passage (16) in which the coolant flows, formed into a circular pipe shape; and

heat exchanging cores respectively arranged in the two casings (20), having an exhaust gas passage (11a) in which the exhaust gas flows, wherein

both casings (20) are integrated with each other into one body so that the longitudinal directions of the casings can be substantially parallel with each other.

In the present invention, the casing (20) is formed into a circular pipe shape. Therefore, it is possible for the coolant flowing in the casing (20) to flow smoothly. Therefore, stagnation seldom occurs in the current of the coolant. Accordingly, it is possible to prevent the coolant from boiling, and it is also possible to prevent the heat transfer coefficient from remarkably deteriorating. Further, it is possible to prevent the occurrence of cracks, which are generated by thermal stress, in the components composing the exhaust gas passage (11a).

As at least two casings (20) are integrated into one body, so that the respective longitudinal directions can be substantially parallel with each other, it is possible to increase a total heat exchanging area between the exhaust gas and the coolant without increasing the size in the longitudinal direction of the exhaust heat exchanger. In this way, it is possible to provide a new exhaust heat exchanger different from the conventional one.

As described above, according to the exhaust heat exchanger of the present invention, it is possible to enhance the cooling capacity without lowering the durability and the heat exchanging efficiency (the heat transfer coefficient).

In the present invention, it is preferable that a cross section of the exhaust gas passage (11a) is circular.

In the present invention, it is also preferable that bonnets (21,22) for closing the longitudinal direction of the casing (20) and-communicating the exhaust gas passage (11a) with the exhaust gas pipe (30) are provided at both end portions of the two casings (20) in the longitudinal direction, and the two casings (20) are integrated into one body by the bonnets (21,22).

Further, in the present invention, it is preferable that the two casings (20) are integrated into one body by a detachable joining means (23).

The present invention may be more fully understood from the description of preferred embodiments of the invention, as set forth below, together with the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In this embodiment, an exhaust heat exchanger of the present invention is applied to an exhaust gas cooling device used for a Diesel engine.FIG. 1is a schematic illustration showing a model of an EGR gas cooling device (exhaust gas recirculating device) in which an exhaust gas cooling device of an embodiment of the present invention is used. This exhaust gas cooling device will be referred to as a gas cooler10, hereinafter.

The exhaust gas recirculating pipe30is a pipe used for recirculating one portion of the exhaust gas, which has been discharged from the engine31, to the intake side of the engine31.

The EGR valve32, which is of a well-known type, is arranged in the middle of the flow of exhaust gas of the exhaust gas recirculating pipe30and adjusts the quantity of exhaust gas according to a state of operation of the engine31. The gas cooler10is arranged between the exhaust side of the engine31and the EGR valve32and exchanges heat between the exhaust gas and the engine coolant so as to cool the exhaust gas.

Next, the structure of the gas cooler10will be described below.

FIGS. 2A to 2Dare four side views of the gas cooler10andFIG. 3is a sectional view taken on line III—III inFIG. 2A. As shown inFIGS. 2B to 2D, this gas cooler10is composed in such a manner that two gas coolers, the shapes of which are the same, are arranged in the horizontal direction so that the longitudinal directions of the two gas coolers are substantially parallel with each other, and the two thus-arranged gas coolers are integrated into one body. The gas cooler located on the upper side of theFIG. 2Dis referred to as a first gas cooler10a, and the gas cooler located on the lower side of theFIG. 2Dis referred to as a second gas cooler10b.

The structure-of the first and the second gas cooler10a,10bwill be described while the first gas cooler10ais taken as an example for the explanation.

As shown inFIG. 3, the tube11is a circular pipe, that is, the tube11is a pipe, the cross section of which is circular, composing the exhaust gas passage11ain which the exhaust gas circulates. The casing20accommodates the heat exchanging core composed of a plurality of tubes11which are arranged on a concentric circle at regular intervals. The casing20is formed into a circular pipe shape in which the coolant passage16is provided so that the coolant can be circulated around the heat exchanging core.

In this connection, the tube11and the casing20are made of metal, the anticorrosion property of which is excellent. In this embodiment, the tube11and the casing20are made of stainless steel.

As shown inFIG. 2D, in the opening portion on one end side of the casing20in the longitudinal direction, that is, on the right of the casing20, there is provided a tank portion, which is arranged so that it can close this opening portion, for distributing and supplying the exhaust gas to the tubes11. The first bonnet21for connecting the exhaust gas recirculating pipe30is soldered or welded to the opening portion. On the other hand, in the opening portion of the other end side of the casing20in the longitudinal direction, that is, on the left of the casing20, there is provided a tank portion for collecting and recovering the exhaust gas, which has completed a heat exchange, from the tubes11. The second bonnet22for connecting the exhaust gas recirculating pipe30is soldered or welded to the opening portion.

In this connection, as shown inFIG. 4, the distributor30afor distributing the exhaust gas supplied from the exhaust gas recirculating pipe30to the first and the second gas cooler10a,10bis connected with the first bonnet21, and the collector30bfor collecting the exhaust gas flowing out from the first and the second gas cooler10a,10bis connected with the second bonnet22.

In this connection, in the distributor30a, there is provided a distributing guide30cfor smoothly distributing the exhaust gas. In the collector30b, there is provided a collecting guide30dfor smoothly collecting the exhaust gas.

As shown inFIGS. 2A to 2D, in both bonnets21,22, there are provided insertion holes into which the bolts23, which are a joining means for integrating the first and the second gas cooler10a,10b, are inserted. Further, in both bonnets21,22, there are integrally provided flange portions21a,22ain which the joining faces of the first and the second gas cooler10a,10b, are formed.

The core plate24holds the tubes11and partitions the coolant passage16and the tank portion. This core plate24and the first and the second bonnet21,22are made of metal, the anticorrosion property of which is excellent. In this embodiment, the core plate24and the first and the second bonnet21,22are made of stainless steel.

On one side of the casing20into which the exhaust gas flows, there is provided an inlet25from which the coolant is introduced into the coolant passage16. On the other side of the casing20from which the exhaust gas flows out, there is provided an outlet26from which the coolant, which has exchanged heat, is discharged.

In this connection, the bypass port27is located at a position on the side of the casing20opposite to the inlet25. Therefore, one portion of the coolant flowing into the casing20is made to go round the heat exchanging core and is introduced to the side of the gas cooler10from which the coolant flows out. By this bypass port27, the coolant on the opposite side to the inlet25, which tends to stagnate, is made to positively flow, so that the occurrence of stagnation can be prevented.

Next, the operational effect of this embodiment will be explained below.

In this embodiment, as the profile of the casing20is formed into a circular pipe shape, the coolant can smoothly flow in the casing20, and stagnation of the coolant seldom occurs. Accordingly, it is possible to suppress boiling of the coolant. Therefore, it is possible to prevent the heat transfer coefficient from being remarkably lowered. Further, it is possible to suppress the generation of cracks, in the tubes11, which are caused by thermal stress.

In this connection, when the cross section of the casing is rectangular, stress concentration tends to occur at four corners of the cross section in the process of press forming. Accordingly, there is a high possibility that the mechanical strength of the casing is lowered and durability (reliability) of the vibration proof property is greatly deteriorated.

On the other hand, as the profile of the casing20is formed into a circular pipe shape in this embodiment, it is possible to prevent the occurrence of stress concentration in the process of forming the casing20.

As at least two gas coolers10a,10bare integrated with each other into one body so that the longitudinal directions of the two gas coolers10a,10bcan be parallel with each other, the size of the gas cooler in the longitudinal direction is not extended and the total heat exchanging area between the exhaust gas and the coolant can be increased.

As described above, in the gas cooler10of this embodiment, it is possible to enhance the cooling capacity without lowering the durability and the heat exchanging efficiency (heat transfer coefficient).

In the above embodiment, the exhaust heat exchanger of the present invention is applied to the gas cooler10, however, the exhaust heat exchanger of the present invention may be applied to a heat exchanger, which is arranged in a muffler, for recovering heat energy from the exhaust gas.

In the embodiment described above, the two gas coolers10a,10bare integrated into one body by the bolts23, however, the present invention is not limited to the above specific embodiment. For example, the two gas coolers10a,10bmay be integrated into one body by means of soldering or welding.

In the embodiment described above, the two gas coolers10a,10bare integrated into one body, however, the present invention is not limited to the above specific embodiment. For example, not less than three gas coolers may be integrated into one body so that the longitudinal directions of the respective gas coolers can be substantially parallel with each other.

In the embodiment described above, the two gas coolers10a,10bare integrated into one body by the bonnets21,22, however, the present invention is not limited to the above specific embodiment.

In the embodiment described above, the distributor30aand the collector30bare connected with the bonnets21,22, however, the present invention is not limited to the above specific embodiment. For example, the first bonnet21And the distributor30amay be integrated into one body, and the second bonnet22and the collector30bmay be integrated into one body.

While the invention has been described by reference to specific embodiments chosen for purpose of illustration, it should be apparent that numerous modifications could be made thereto by those skilled in the art without departing from the basic concept and scope of the invention.