LAYERED HEAT EXCHANGERS

Abstract: The invention relates to a layered heat exchanger, for example, for use as a layered heat exchanger for motor vehicle coolers. To provide a turn portion in the heat exchanger for changing the direction of flow of a fluid which flows zigzag through a fluid circuit, a metal plate for fabricating the exchanger is provided at the upper end or the lower end of a partition ridge with a fluid flow direction changing passage forming caved portion having a bottom wall of circular-arc cross section. Front and rear upper tank portions of a flat tube portion or front and rear lower tank portions thereof are held in communication with each other through a fluid flow direction changing passage having an approximately circular cross section and formed by the caved portions which are opposed to each other. The turn portion is diminished in the concentration of stress thereon due to the fluid internal pressure and given an increased resistance to pressure to effectively prevent tank side walls from breaking, consequently making it possible to decrease the thickness of the metal plates for fabricating the heat exchanger, to achieve a cost reduction by the decreased thickness of plates and to assure an improved heat exchange efficiency.

Description: DESCRIPTION LAYERED HEAT EXCHANGERS CROSS REFERENCE TO RELATED APPLICATION This application is an application filed under 35 U.S.C. §lll(a) claiming the benefit pursuant to 35 U.S.C. §119(e)(l) of the filing data of Provisional Application No. 60/306,851 filed July 23, 2001 pursuant to 35 U.S.C. §lll(b). TECHNICAL FIELD The present invention relates to layered heat exchangers, for example, for use as layered evaporators for motor vehicle coolers. BACKGROUND OF THE INVENTION FIGS. 17 and 18 show part of an aluminum plate for use in fabricating an aluminum layered heat exchanger for use as a conventional evaporator for motor vehicle coolers. With reference to these drawings, the aluminum plate 40 conventionally has formed in one surface thereof front and rear fluid channel forming recessed portions 42a, 42b divided by a vertically elongated partition ridge 41, front and rear upper tank forming recessed portions 43a, 43b continuous with the upper ends of these portions 42a, 42b and having a larger depth than these portions, and front and rear lower tank forming recessed portions (not shown) continuous with the lower ends of these portions 42a, 42b and having a larger depth than these portions. The front and rear upper tank forming recessed portions 43a, 43b have respective fluid passage apertures 44a, 44b formed in their bottom wall. The front and rear lower tank forming recessed portions (not shown) have respective fluid passage apertures formed in their bottom wall . Two adjacent aluminum plates 40, 40 are fitted together in superposed layers with their recessed surfaces opposed to each other to join the opposed partition ridges 41, 41 of the aluminum plates 40, 40 to each other and to join opposed peripheral edges 45, 45 thereof to each other, whereby a flat tube portion is formed which has front and rear flat channels, and front and rear upper tank portions, and front and rear lower tank portions continuous with the channel portions. Many such flat tube portions are arranged in parallel to cause the front upper tank portions of the adjacent parallel tube portions to communicate with each other, the rear upper tank portions thereof to communicate with each other, the front lower tank portions thereof to communicate with each other, and the rear lower tank portions thereof to communicate with each other. To improve the heat exchanger in heat exchange efficiency, the refrigerant circuit is so designed as to cause the refrigerant to flow zigzag through the entire core of the exchanger. For this purpose, the assembly of many flat tube portions is divided into flat tube blocks. The refrigerant circuit has turn portions provided in one of the blocks for changing the direction of flow of the refrigerant from one side of each flat tube portion thereof to the other side, for example, from the front upper tank portion to the rear upper tank portion. The turn portion comprises a communication portion 50 for holding the front and rear upper tank forming recessed portions 43a, 43b of the aluminum plate 40 in communication with each other. A refrigerant flow direction changing passage is formed by the communication portions 50, 50 which are opposed to each other when the adjacent aluminum plates 40, 40 are fitted and joined to each other with their recessed surfaces opposed to each other . With the conventional layered heat exchanger, however, the communication portion 50 for holding in communication the front and rear upper tank forming recessed portions 43a, 43b of the aluminum plate 40 has a bottom plate 51 which is flush with the bottom walls 46, 46 of these, recessed portions 43a, 43a, and these portions 43a, 43b and the communication portion 50 have the same depth. This increases the capacity of the entire tank portion at the turn portion for changing the direction of flow of the refrigerant in the flat tube portion, with the result that the stress due to the internal pressure of the refrigerant concentrates on the tank side walls, especially on the upper and lower walls 52, 52 as indicated by arrows in FIG. 16. Thus the heat exchanger has the problem that the tank side walls are lower than the other portions in limit strength against the internal pressure of the refrigerant. Especially in recent years, it has been urgently requested to provide a structure capable of effectively preventing the tank side walls from being broken by the stress concentration due to the internal pressure of the refrigerant acting on the turn portion, in view of the cost reduction achieved by a reduction in the thickness of the plates for fabricating the heat exchanger while ensuring the efficiency of the heat exchanger. An object of the present invention is to meet the above request by overcoming the problem of the prior art and to provide a heat exchanger wherein the tank side walls at the turn portion for changing the direction of flow of the fluid can be given an increased limit strength against the internal pressure of the refrigerant to diminish the concentration of stress on the turn portion due to the fluid internal pressure, give the turn portion sufficient resistance to pressure and effectively prevent the tank side walls from breaking, consequently making it possible to decrease the thickness of the plates for fabricating the heat exchanger, to assure the exchanger of a high efficiency and to achieve a cost reduction by the decreased thickness of metal plates. DISCLOSURE OF THE INVENTION The present invention provides a layered heat exchanger comprising generally rectangular metal plates each having formed in one surface thereof front and rear fluid channel forming recessed portions divided by a vertically elongated partition ridge, front and rear upper tank forming recessed portions continuous with the upper ends of these channel forming portions and having a larger depth than these channel forming portions, and front and rear lower tank forming recessed portions continuous with the lower ends of these channel forming portions and having a larger depth than these portions, the front and rear upper tank forming recessed portions having respective fluid passage apertures formed in their bottom wall, the front and rear lower tank forming recessed portions having respective fluid passage apertures formed in their bottom wall, each pair of adjacent metal plates being fitted together in superposed layers with their recessed surfaces opposed to each other to join the opposed partition ridges of the metal plates to each other, to join opposed peripheral edges thereof to each other and to thereby form a flat tube portion having front and rear flat channels, and front and rear upper tank portions and front and rear lower tank portions which are continuous with the channels, a multiplicity of flat tube portions being arranged in parallel to cause the front upper tank portions of the adjacent parallel flat tube portions to communicate with each other, the rear upper tank portions thereof to communicate with each other, the front lower tank portions thereof to communicate with each other, and the rear lower tank portions thereof to communicate with each other. The layered heat exchanger is characterized in that the metal plate is provided at one of the upper end and the lower end of the partition ridge with a fluid flow direction changing passage forming caved portion having a bottom wall of circular-arc cross section, the front and rear upper tank portions of the flat tube portion or the front and rear lower tank portions thereof being held in communication with each other through a fluid flow direction changing passage having an approximately circular cross section and formed by the caved portions which are opposed to each other. In the layered heat exchanger of the invention described, the bottom wall having a circular-arc cross section of the caved portion preferably has a depth smaller than the depth of the tank forming recessed portions. In the layered heat exchanger of the invention described, the passage formed by the opposed caved portions preferably has a circular cross section. Preferably, the caved portion comprises circular-arc portions corresponding respectively to angles of at least 60 deg to less than 90 deg each, above and below a center line of the caved portion and circular arc in cross section so as to have the same radius of curvature. In the layered heat exchanger of the invention described, the passage is preferably elliptical in cross section. In the layered heat exchanger of the invention, the bottom wall, circular-arc in cross section, of the caved portion preferably has a depth 1/5 to 4/5 of the depth of the tank forming recessed portions. Alternatively, the bottom wall, circular-arc in cross section, of the caved portion preferably has a depth 1/4 to 3/4 of the depth of the tank forming recessed portions. In the layered heat exchanger of the invention, a front side and a rear side of the heat exchanger provided respectively by the front and rear flat channels are preferably the same in the number of passes. Alternatively, in the layered heat exchanger of the invention, a front side and a rear side of the heat exchanger provided respectively by the front and rear flat channels are preferably different in the number of passes. Further in the layered heat exchanger of the invention, an air outlet side and an air inlet side of the heat exchanger provided respectively by the front and rear flat channels are preferably different in the number of passes, and the air outlet side is greater than the air inlet side in the number of passes. In the case of the layered evaporator of the present invention, the fluid flow direction changing passage is made narrower by the opposed bottom walls of a circular- arc cross section and is consequently formed by side wall portions which have a diminished area and are reinforced by the bottom walls of circular-arc cross section. At the fluid flow direction changing passage, i.e., the turn portion, the tank side walls can be given an increased limit strength against the internal pressure of the refrigerant to diminish the concentration of stress on the turn portion due to the fluid internal pressure, give the turn portion sufficiently high resistance to pressure and effectively prevent the tank side walls from breaking. This entails the advantage of making it possible to decrease the thickness of the plates providing the heat exchanger, to assure a high heat exchange efficiency and to achieve a cost reduction by the decreased thickness of the metal plates. The bottom wall, circular-arc in cross section, of the caved portion for forming the fluid flow direction changing passage is given a smaller depth than the tank forming recessed portions to ensure the above advantage more reliably. When the fluid flow direction changing passage in the layered heat exchanger of the invention is circular or elliptical in cross section, the passage portion is enhanced in pressure resistance. Especially if circular in cross section, the passage portion has the advantage of outstanding pressure resistance, an enlarged cross section and diminished resistance to the flow of fluid therethrough. If the bottom wall, circular-arc in cross section, of the passage forming caved portion of the layered heat exchanger of the invention has less than 1/5 the depth of the tank forming recessed portions, the communication passage fails to have a sufficient cross sectional area, offers increased resistance to the flow therethrough and is therefore undesirable. Further if the bottom wall has a depth in excess of 4/5 of the depth of the tank forming recessed portions, the caved portion is difficult to make by drawing, permitting the plate to develop cracks, so that the excessive depth is not desirable. More preferably, the depth of the bottom wall is 1/4 to 3/4 of the depth of the tank forming recessed portions . With the layered heat exchanger of the present invention, the air outlet side and the air inlet side thereof provided respectively by the front and rear flat channels may be the same or different in the number of passes. In the case where these sides are different in the number of passes, the air outlet side is preferably greater than the air inlet side in the number of passes for the following reason. When the layered heat exchanger of the present invention is intended, for example, for use as a layered evaporator for motor vehicle coolers, an increase in the number of passes in the entire evaporator usually results in uniform distribution of the refrigerant but entails an increased pressure loss. The refrigerant is introduced into the evaporator via the flat channels on the air outlet side, and the refrigerant flowing through these channels is low in dryness ( in the state wherein a large amount of liquid is present relative to gas) and is therefore less likely to involve an increased pressure loss. Accordingly, it is desirable that the air outlet side be greater than the air inlet side in the number of passes. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic front view showing a first embodiment of layered heat exchanger of the invention. FIG. 2 is a schematic perspective view for illustrating the refrigerant circuit of the heat exchanger of FIG. 1. FIG. 3 is a perspective view partly broken away and showing a pair of aluminum plates of the heat exchanger. FIG. 4 is a perspective view partly broken away and showing a pair of aluminum plates each having a caved portion for forming a refrigerant flow direction changing passage. FIG. 5 is a perspective view partly broken away and showing an aluminum plate having partition walls. FIG. 6 is an enlarged fragmentary view in vertical section partly broken away and showing the heat exchanger of FIG. 1. FIG. 7 is an enlarged fragmentary view in horizontal section of lower tank portions of the heat exchanger. FIG. 8 includes enlarged views in section taken along the line X-X in FIG. 7; FIG. 8a showing a first example of cross sectional shape of aluminum plate caved portion for forming a refrigerant flow direction changing passage, FIG. 8b is a second example of cross sectional shape of caved portion, FIG. 8c is a third example of cross sectional shape of caved portion, and FIG. 8d is a fourth example of cross sectional shape of caved portion. FIG. 9 is an enlarged fragmentary view in horizontal section of the heat exchanger of FIG. 1. FIG. 10 is an enlarged right side elevation of the heat exchanger. FIG. 11 is an enlarged right side elevation of the same showing refrigerant inlet and outlet pipes in section. FIG. 12 is a schematic perspective view for illustrating the refrigerant circuit of second embodiment of layered heat exchanger of the invention. FIG. 13 is a schematic perspective view for illustrating the refrigerant circuit of third embodiment of layered heat exchanger of the invention. FIG. 14 is a schematic perspective view for illustrating the refrigerant circuit of fourth embodiment of layered heat exchanger of the invention. FIG. 15 is an enlarged fragmentary front view of a modified aluminum plate of the heat exchanger. FIG. 16 is an enlarged view in section taken along the line Y-Y in FIG. 15. FIG. 17 is an enlarged fragmentary front view showing an aluminum plate of a conventional layered heat exchanger. FIG. 18 is an enlarged view in section taken along the line Z-Z in FIG. 17. FIG. 19 is an enlarged fragmentary view in section of an aluminum plate having the passage forming caved portion with the cross sectional shape of the first example shown in FIG. 8a. BEST MODE OF CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings . The terms "front," "rear," "left," "right," "upper" and "lower" as used herein are based on FIG. 1; "left" refers to the left-hand side of FIG. 1, "right" to the right-hand side thereof, "front" to the rear side of the plane of the drawing, "rear" to the front side of the plane thereof, "upper" to the upper side of the drawing, and "lower" to the lower side thereof. The drawings show layered heat exchangers of the invention for use as layered evaporators for motor vehicle coolers. FIGS. 1 to 11 show a first embodiment of layered evaporator of the present invention. First with reference to FIG. 1, the layered evaporator 1 of the invention is made from aluminum ( including aluminum alloys ) , comprises a multiplicity of flat tube portions A arranged side by side, and has a refrigerant circuit which is designed to cause a refrigerant to flow zigzag through the entire interior of the evaporator 1. With reference to FIG. 2 showing the first embodiment, the entire assembly of many flat tube portions A is divided into left and right two flat tube blocks Bl, B2. Each of the blocks Bl, B2 has a plurality of flat tube portions A. The refrigerant circuit is four in the number of passes, causing the refrigerant to flow upward and downward through the two blocks Bl, B2 along front and rear flat channels 11a, lib. In this case, the front side and the rear side of the evaporator provided respectively by the front and rear groups of flat channels 11a, lib are equal in the number of passes. The left block B2 of the refrigerant circuit has a turn portion 18 for changing the direction of flow of the refrigerant from the front lower tank portion 12a at one side of each flat tube portion A to the rear lower tank portion 12b at the other side thereof. This feature will be described later. Each of the flat tube blocks Bl, B2 comprises, for example, 2 to 20, preferably 2 to 15, more preferably 3 to 10, flat tube portions A. Next with reference to FIG. 3, generally rectangular aluminum plates 2 providing the layered evaporator 1 each have formed in one surface thereof front and rear refrigerant channel forming recessed portions 4a, 4b divided by a vertically elongated partition ridge 6, front and rear upper tank forming recessed portions 3a, 3b continuous with the upper ends of these portions 4a, 4b, having a larger depth than these portions and circular when seen from the front, and front and rear lower tank forming recessed portions 5a, 5b continuous with the lower ends of these portions 4a, 4b, having a larger depth than these portions and circular when seen from the front. The front and rear upper tank forming recessed portions 3a, 3b have respective refrigerant passage apertures 13a, 13b formed in their bottom wall and circular when seen form the front. The front and rear lower tank forming recessed portions 5a, 5b have respective refrigerant passage apertures 15a, 15b formed in their bottom wall and circular when seen form the front. The ridges 6 have approximately the same height as the depth of the refrigerant channel forming recessed portions 4a, 4b. One of the apertures 13a, 13b of the front and rear upper recessed portions 3a, 3b is provided with an annular wall 14 formed by burring and projecting outward from the recess portion 3a or 3b. One of the apertures 15a, 15b of the front and rear lower recessed portions 5a, 5b is provided with an annular wall 16a, 16b formed by burring and projecting outward from the recess portion 5a or 5b. Two adjacent aluminum plates 2, 2 are fitted together in superposed layers with their recessed surfaces opposed to each other, and the opposed partition ridges 6, 6 of the plates 2, 2, as well as opposed peripheral edges 7, 7 thereof, are joined to each other, whereby a flat tube portion A is formed which has front and rear flat channels 11a, lib, front and rear upper tank portions 10a, 10b and front and rear lower tank portions 12a, 12b. Inner fins 9, 9 are inserted in the respective flat channels 11a, lib formed by the refrigerant channel forming recessed portions 4a, 4b of the adjacent aluminum plates 2, 2 (see FIGS. 3, 4 and 9). Many such flat tube portions A are arranged side by side, and the opposed aluminum plates 2, 2 of each pair of adjacent left and right flat tube portions A, A are fitted to each other. At this time, at the front or rear upper tank portion 10a or 10b, and at the front or rear lower tank portion 12a or 12b, the annular wall 14 around the refrigerant aperture 13a or 13b in the upper tank forming recessed portion 3a or 3b of one of the aluminum plates 2 is fitted into the other aperture 13b or 13a, and the annular wall 16a or 16b around the refrigerant aperture 15a or 15b in the lower tank forming recessed portion 5a or 5b is fitted into the other aperture 15b or 15a. This causes the front upper tank portions 10a, 10a of the adjacent tube portions A, A to communicate with each other, the rear upper tank portions 10b, 10b thereof to communicate with each other, the front lower tank portions 12a, 12a thereof to communicate with each other, and the rear lower tank portions 12b, 12b thereof to communicate with each other. Further as shown in FIG. 1, corrugated fins 24 are interposed between the front and rear channels of each pair of adjacent flat tube portions A, A. Side plates 22, 22 are arranged on the left and right outer sides of the evaporator 1, and corrugated fins 24 are also provided between each side plate 22 and the front and rear channels 11a, lib of the tube portion A. Further with reference to FIGS. 1, 10 and 11, a refrigerant inlet pipe 30 is connected to the front lower tank portion 12a at the right end of the right flat tube block Bl of the layered evaporator 1. A refrigerant outlet pipe 31 is connected to the rear lower tank portion 12b at the right end of the block Bl . These refrigerant inlet pipe 30 and outlet pipe 31 are arranged to extend along the right side plate 22. A joint member 33 having a refrigerant inlet 34 and a refrigerant outlet 35 are attached to the upper ends of the pipes 30, 31. As shown in FIG. 2, the entire assembly of flat tube portions A of this embodiment is divided into left and right two flat tube blocks Bl, B2 and has a refrigerant circuit which is designed to permit a refrigerant to flow zigzag through the entre interior of the evaporator 1 to achieve an improved heat exchange efficiency. Especially with the layered evaporator of the present invention, the flat tube portion A of the left flat tube block B2 of the refrigerant circuit has a turn portion for changing the direction of flow of the refrigerant from the front lower tank portion 12a at one side of the flat tube portion A to the rear lower tank portion 12b at the other side thereof. At the boundary between the left and right tube blocks Bl, B2, the front upper tank portion 10a at the left end of the right block Bl and the front upper tank portion 10a at the right end of the left block B2 are in communication with each other, and the rear upper tank portion 10b at the left end of the right block Bl and the rear upper tank portion 10b at the right end of the left block B2 are similarly in communication with each other. On the other hand, the junction of the front lower tank portion 12a at the left end of the right block Bl and the front lower tank portion 12a at the right end of the left block B2 is blocked, and the junction of the rear lower tank portion 12b at the left end of the right block Bl and the rear lower tank portion 12b at the right end of the left block B2 is similarly blocked. Thus, at the boundary between the left and right tube blocks Bl, B2, the aluminum plate 2 shown in FIG. 5 is used for the end aluminum plates 2, 2 providing the flat tube portion A at the left end of the right tube block Bl and the flat tube portion A at the right end of the left tube block B2. The front and rear lower tank forming recessed portions 5a, 5b of these aluminum plates 2, 2 are not apertured in their bottom wall for the passage of the refrigerant but are provided with partition walls 8, 8. Since the aluminum plate 2 shown in FIG. 5 is otherwise the same as the usual aluminum plate 2 shown in FIG. 3, like parts are designated by like reference numerals or symbols in the drawings concerned. FIG. 4 further shows aluminum plates 2 which are used in the left flat tube block B2 of the refrigerant circuit shown in FIG. 2 for the turn portion for changing the direction of flow of the refrigerant from the front lower tank portion 12a at one side of the flat tube portion A to the rear lower tank portion 12b at the other side thereof. As shown in FIG. 4, and also as shown in FIGS. 7 and 8a in detail, the aluminum plate 2 has at the lower end of its partition ridge 6 a caved portion 17 having a bottom wall 17a of circular-arc cross section and having a depth smaller than the depth of the front and rear lower tank forming recessed portions 5a, 5b. When the flat tube portion A is formed by fitting adjacent aluminum plates 2, 2 to each other in superposed layers with their recessed surfaces opposed to each other, joining the opposed ridges 6, 6 to each other and joining the opposed peripheral edges 7, 7 to each other, a passage 18 having an approximately circular cross section for changing the direction of flow of the refrigerant is formed by the caved portions 17, 17 which are opposed to each other. The front and rear lower tank portions 12a, 12b are caused to communicate with each other through the direction changing passage 18. Since the aluminum plates 2 shown in FIG. 4 are otherwise the same as the usual aluminum plates 2 shown in FIG. 3, like parts are designated by like reference numerals or symbols in the drawings concerned. For example, the intermediate aluminum plates 2 included in the foregoing embodiment are prepared from an aluminum blazing sheet, and the side plates 22, 22 are prepared also from an aluminum brazing sheet. The inner fins 9 and corrugated fins 24 are prepared from an aluminum sheet. With the layered evaporator 1 described, the refrigerant introduced into the front lower tank portions 12a in the right tube block Bl via the refrigerant inlet pipe 30 rises through the front flat channels 11a of the block Bl to the front upper tank portions 10a, from which the refrigerant flows into the front upper tank portions 10a in the tube block B2 adjacent to the block Bl on the left side. The refrigerant then flows from the front tank portions 10a of the block B2 downward through the front flat channels 11a to the front lower tank portions 12a at the lower end of the block B2, further flows through the turn portion of the block B2, i.e., through the direction changing passages 18 of circular cross section of the flat tube portions A into the rear lower tank portions 12b of the same block B2. Subsequently, the refrigerant flows upward from the rear lower tank portions 12b of the block B2 to the rear upper tank portions 10b through the rear flat channels lib, and then flows from the tank portions 10b into the rear upper tank portions 10b of the adjacent tube block Bl at the right. The refrigerant further flows from the rear upper tank portions 10b in the block Bl downward through the rear flat channels lib to the rear lower tank portions 12b, from which the refrigerant flows out of the evaporator through the outlet pipe 31. As indicated at W in FIG. 2, on the other hand, air (air stream) flows through the layered evaporator 1 from the rear toward the front side, i.e., through the clearances between the adjacent flat tube portions A, A and between the flat tube portion A and each side plate 22 in which clearances the corrugated fins 24 are provided, and is thereby subjected to efficient heat exchange with the refrigerant through the wall surfaces of the aluminum plates 2 and the corrugated fins 24. In the case of the first embodiment, the air outlet side thereof provided by the front flat channels 11a is the same as the air inlet side thereof provided by the rear flat channels lib in the number of passes. With the layered evaporator 1 described, the aluminum plate 2 is provided at the lower end of its partition ridge 6 with the caved portion 17 having a bottom wall 17a of circular-arc cross section and having a depth smaller than the depth of the front and rear lower tank forming recessed portions 5a, 5b. The front and rear upper tank portions 10a, 10b of the flat tube portion A or the front and rear lower tank portions 12a, 12b thereof are caused to communicate with each other through the refrigerant flow direction changing passage 18 having an approximately circular cross section and formed by the caved portions 17, 17 which are opposed to each other. A layered evaporator 1 having the construction of the present embodiment was fabricated using aluminum plates 2 which were made 0.1 mm smaller in thickness than the aluminum plates of the layered evaporator of the conventional construction, and checked for pressure resistance in comparison with the evaporator of the conventional construction. Consequently, the layered evaporator according to the embodiment of the invention was found to be 25% greater than the conventional evaporator in pressure resistance. As will be apparent from this result, the direction changing passage 18 in the layered evaporator 1 of the present invention is made narrower by the opposed bottom walls 17a, 17a having a circular-arc cross section and smaller than the front and rear lower tank forming recessed portions 5a, 5b in depth, and is consequently formed by side wall portions which have a diminished area and are reinforced by the bottom walls 17a, 17a of circular-arc cross section. At the refrigerant flow direction changing passage 18, i.e., the turn portion, the tank side walls can be given an increased limit strength against the internal pressure of the refrigerant to diminish the concentration of stress on the turn portion due to the refrigerant internal pressure, give the turn portion sufficient resistance to pressure and effectively prevent the tank side walls from breaking. Consequently, it becomes possible to decrease the thickness of the aluminum plates 2 making the heat exchanger, to assure the exchanger of a high efficiency and to achieve a cost reduction by the decreased thickness of the aluminum plates 2. Although the passage 18 according to the first embodiment is approximately circular in cross section, the passage 18 may be elliptical or in the form of an elongated circle in cross section. FIG. 8 shows four examples of sectional shapes of the refrigerant flow direction changing passage 18 and passage forming caved portion 17 of the aluminum plate 2. First, FIG. 8a shows a first example which is according to the first embodiment described. The passage forming caved portion 17 is semicircular in cross section, and the passage 18 is accordingly generally circular in cross section. The bottom wall 17a, semicircular in cross section, of the caved porion 17 has a depth about 1/2 of the depth of the tank forming recessed portions 5a, 5b. As shown in detail in FIG. 19, the caved portion 17 for forming the refrigerant flow direction changing passage preferably comprises circular-arc portions corresponding respectively to angles θ-^ , θ 2 of at least 60 deg to less than 90 deg each, above and below the center line L of the portion 17 and circular arc in cross section so as to have the same radius of curvature. Preferably, the passage 18 of circular cross section is formed by the caved portions 17, 17 which are opposed to each other by fitting and joining an adjacent pair of aluminum plates 2, 2 to each other in superposed layers with the recessed surfaces thereof opposed to each other. The passage portion 18 thus having a circular cross section is excellent in pressure resistance, enlarged in cross section and therefore has the advantage of diminished resistance to the flow therethrough. FIG. 8b shows a second example. The aluminum plate 2 has a caved portion 17 which is semicircular in cross section like the first example. However, the caved portions 17 of two aluminum plates 2, 2 as fitted together each have small rounded (circular-arc) parts 17b, 17b at upper and lower edges thereof. FIG. 8c shows a third example. The caved portion 17 of the aluminum plate 2 has a circular-arc cross section which is shallower than in the first embodiment. Consequently, the passage 18 formed has an elliptical cross section which is vertically elongated. The caved portions 17 of two aluminum plates 2, 2 as fitted together each have small rounded (circular-arc) parts 17b, 17b at upper and lower edges thereof. The bottom wall 17a, semicircular in cross section, of each caved porion 17 has a depth about 1/3 of the depth of the tank forming recessed portions 5a, 5b. FIG. 8d shows a fourth example, in which the caved portion 17 of the aluminum plate 2 has a circular-arc cross section deeper than in the first example. Accordingly, the passage 18 has an elliptical cross section elongated laterally. The caved portions 17 of two aluminum plates 2, 2 as fitted together each have small rounded (circular-arc) parts 17b, 17b at upper and lower edges thereof. The bottom wall 17a, semicircular in cross section, of each caved porion 17 has a depth about 3/5 of the depth of the tank forming recessed portions 5a, 5b. FIG. 12 shows a second embodiment of the present invention, i.e., a layered evaporator 1 which is divided into right and left two flat tube blocks Bl, B2. Although the refrigerant circuit is of the four pass type like the first embodiment, the refrigerant flows through the circuit in the opposite direction to the first embodiment. Stated more specifically with reference to the second embodiment, a refrigerant inlet pipe 30 is connected to the front upper tank portion 10a at the right end of the right block Bl of the evaporator 1, and a refrigerant outlet pipe 31 is connected to the rear upper tank portion 10b at the right end of the right block Bl . The front and rear upper tank portions 10a, 10b at the left end of the right block Bl, and the front and rear upper tank portions 10a, 10b at the right end of the left block B2 adjacent to the block Bl are provided with partition walls 8, 8 (see FIG. 5) and are closed therewith. On the other hand, apertures 15a, 15b (see FIG. 3) for passing the refrigerant therethrough are formed in the front and rear lower tank portions 12a, 12b at the left end of the right block Bl, and in the front and rear lower tank portions 12a, 12b at the right end of the left block B2 adjacent to the block Bl . Furthermore, the left flat tube block B2 of the refrigerant circuit has a turn portion 18 for changing the direction of flow of the refrigerant from the front upper tank portion 10a at one side of each flat tube portion A to the rear upper tank portion 10b at the other side thereof . The second embodiment has the same construction as the first embodiment except that the direction of flow of the refrigerant through the refrigerant circuit of the second embodiment is opposite to that in the first embodiment, so that like parts are designated by like reference numerals or symbols throughout the drawings concerned. FIG. 13 shows a third embodiment of the present invention, i.e., a layered evaporator 1 having a refrigerant circuit which is five in the number of passes. According to the third embodiment, an assembly of many flat tube portions A providing the evaporator 1 comprises a front half and a rear half which are different in the number of component blocks. The front half of the evaporator 1, which includes front upper tank portions 10a, front flat channels 11a and front lower tank portions 12a, is divided into three blocks Bl, B2, B3, whereas the rear half thereof including rear upper tank portions 10b, rear flat channels lib and rear lower tank portions 12b is divided into two blocks B4, B5. Thus, the front and rear sides of the evaporator provided by the front and rear flat channels 11a, lib are different in the number of passes. More specifically, the air outlet side provided by the front flat channels 11a is three in the number of passes, and the air inlet side provided by the rear flat channels lib is two in the number of passes. The evaporator 1 in its entirety is five in the number of passes. This results in the advantage of facilitating uniform distribution of the refrigerant. A refrigerant inlet pipe 30 is connected to the front lower tank portion 12a at the right end of the right front first block Bl of the evaporator 1. A refrigerant outlet pipe 31 is connected to the rear upper tank portion 10b at the right end of the right rear fifth block B5. The front lower tank portion 12a at the left end of the right front first block Bl and the front lower tank portion 12a at the right end of the central front second block B2 adjacent to the block Bl are each provided with a partition 8 (see FIG. 5) and closed therewith, whereas the front upper tank portion 10a at the left end of the right front block Bl and the front upper tank portion 10a at the right end of the central front second block B2 adjacent to the block Bl have respective apertures 15a, 15b (see FIG. 3) for passing the refrigerant therethrough. The front upper tank portion 10a at the left end of the central front second block B2 and the front upper tank portion 10a at the right end of the left front third block B3 adjacent to the block 2 are each provided with a partition 8 (see FIG. 5) and closed therewith, whereas the front lower tank portion 12a at the left end of the central front second block B2 and the front lower tank portion 12a at the right end of the left front third block B3 adjacent to the block 2 each have an aperture 15a (see FIG. 3) for passing the refrigerant therethrough. Turn portions 18 are further provided for changing the direction of flow of the refrigerant from the front upper tank portions 10a of the left front third block B3 of the refrigerant circuit toward rear upper tank portions 10b in the left rear fourth block B4. The rear upper tank portion 10b at the right end of the left rear fourth block B4 and the rear upper tank portion 10b at the left end of the right rear fifth block B5 adjacent to the block B4 are each provided with a partition wall (see FIG. 5) and closed therewith, whereas the rear lower tank portion 12b at the right end of the left rear fourth block B4 and the rear lower tank portion 12b at the left end of the right rear fifth block B5 adjacent to the block B4 each have an aperture 15b (see FIG. 3) for passing the refrigerant therethrough. In the layered evaporator 1 according to the third embodiment, the refrigerant introduced into the front lower tank portions 12a of the right front first block Bl through the inlet pipe 30 ascends the front flat channels 11a of the first block Bl to the front upper tank portions 10a, from which the refrigerant flows into the front upper tank portions 10a in the central front second block B2 adjacent to and at the left of the block Bl . The refrigerant then descends from the portions 10a of the second block B2, flows into the front lower tank portions 12a at the lower end of the second block B2 and further into the front lower tank portions 12a in the left front third block B3 at the left of and adjacent to the block B2, and then ascends the front flat channels 11a of the third block B3 to the front upper tank portions 10a. The refrigerant then flows through the turn portions of the third block B3, i.e., through the refrigerant flow direction changing passages 18 of circular cross section in the flat tube portions A, into the rear upper tank portions 10b in the left rear fourth block B4. Subsequently, the refrigerant flows from these portion 10b of the fourth block 4 downward to the rear lower tank portions 12b through the rear flat channels lib, and then flows from these portions 12b into the rear lower tank portions 12b in the right rear fifth block B5 at the right of and adjacent to the block B4. The refrigerant further ascends from the rear lower tank portions 12b of the fifth block B5 to the rear upper tank portions 10b through the rear flat channels lib, and flows out of these portions 10b to the outside via the outlet pipe 31. As indicated at W in FIG. 13, on the other hand, air (air stream) flows through the layered evaporator 1 from the rear toward the front side, i.e., through the clearances between the adjacent flat tube portions A, A and between the flat tube portion A and each side plate 22 in which clearances corrugated fins 24 are provided, and is thereby subjected to efficient heat exchange with the refrigerant through the wall surfaces of the aluminum plates 2 and the corrugated fins 24. With the exception of the above features, the third embodiment has the same construction as the first embodiment described, so that like parts are designated by like reference numerals or symbols throughout the drawings concerned. Next, FIG. 14 shows a fourth embodiment of the invention, i.e., a layered evaporator 1. The evaporator comprises a multiplicity of flat tube portions A, the entire assembly of which is divided into three flat tube blocks Bl, B2, B3. The refrigerant circuit is six in the number of passes. Stated more specifically, the air outlet side of the evaporator 1 provided by the front flat channels 11a is three in the number of passes, and the air inlet side thereof provided by the rear flat channels lib is three and equal to the former in the number of passes. With the fourth embodiment, the right flat tube block Bl of the evaporator 1 and the central flat tube block B2 thereof adjacent to the block Bl are substantially the same as the blocks of the first embodiment in construction, and the left flat tube block B3 is additionally provided at the left of the central block B2. This embodiment has turn portions 18 for changing the direction of flow of the refrigerant from the front upper tank portions 10a of the left block B3 of the refrigerant circuit to the rear upper tank portions 10b of the same block B3. With the layered evaporator 1 of the fourth embodiment, the refrigerant introduced into the front lower tank portions 12a in the right front first block Bl via the inlet pipe 30 flows zigzag generally in the same manner as in the first embodiment through the entire refrigerant circuit which is six in the number of passes and provided inside the evaporator 1, and is drawn off to the outside via the outlet pipe 31. As indicated at W in FIG. 14, on the other hand, air (air stream) flows through the layered evaporator 1 from the rear toward the front side, i.e., through the clearances between the adjacent flat tube portions A, A and between the flat tube portion A and each side plate 22 in which clearances corrugated fins 24 are provided, and is thereby subjected to efficient heat exchange with the refrigerant through the wall surfaces of the aluminum plates 2 and the corrugated fins 24. With the exception of the above features, the fourth embodiment has the same construction as the first embodiment described, so that like parts are designated by like reference numerals or symbols throughout the drawings concerned. Next, FIGS. 15 and 16 show a modified aluminum plate 2 for use in the layered evaporator 1 of the present invention. The modified plate 2 is different from the plates 2 of the first embodiment in that the modified plate 2 is provided at the upper end of the partition ridge 6 with a refrigerant flow direction changing passage forming caved portion 17 having a bottom plate 17a of circular-arc cross section and having a depth smaller than the depth of front and rear upper tank forming recessed portions 3a, 3b, and that these recessed portions 3a, 3b, front and rear lower tank forming recessed portions 5a, 5b and refrigerant passing apertures 13a, 13b, 15a, 15b formed in the bottom walls of these recessed portions are each in the form of an elongated circle when seen from the front . When a flat tube portion A is formed by fitting adjacent aluminum plates 2, 2 to each other in superposed layers with their recessed surfaces opposed to each other, joining the opposed ridges 6, 6 to each other and joining the opposed peripheral edges 7, 7 to each other, a passage (not shown) having an approximately circular cross section for changing the direction of flow of the refrigerant is formed by the caved portions 17, 17 which are opposed to each other. Thus turn portions of the layered evaporator 1 are formed in the flat tube block B2 each adapted to cause the front and rear upper tank portions 10a, 10b to communicate with each other therethrough. Accordingly, such modified aluminum plates 2 are used, for example, in layered evaporators 1 according to the second to fourth embodiments described. According to the foregoing embodiments, refrigerant channels are formed by inserting inner fins 9 into the refrigerant channel forming recessed porions 4a, 4b of each aluminum plate 2 of the evaporator 1, whereas ridges of various shapes may be formed in these recessed portions 4a, 4b of the aluminum plate 2 by pressing the plate 2 itself. The flat channels 11a, lib for the flow of refrigerant can be modified variously. The overall assembly of parallel flat tube portions A providing the layered evaporator 1 may be divided into at least two blocks, or alternatively need not always be divided into blocks. With the layered heat exchanger of the present invention, all the fluid flow direction changing passages 18 for the flat channels 11a, lib are preferably circular or elliptical in cross section, whereas this feature is not limitative; some of the passages 18 for the flat channels 11a, lib of the layered heat exchanger may have a circular or elliptical cross section. Furthermore, the layered heat exchanger of the present invention is useful not only as the evaporator for use in motor vehicle coolers but similarly applicable also to oil coolers, aftercoolers, radiators or like uses.

Claims: CLAIMS 1. A layered heat exchanger comprising generally rectangular metal plates ( 2 ) each having formed in one surface thereof front and rear fluid channel forming recessed portions (4a), (4b) divided by a vertically elongated partition ridge ( 6 ) , front and rear upper tank forming recessed portions (3a), (3b) continuous with upper ends of these portions (4a), (4b) and having a larger depth than these portions, and front and rear lower tank forming recessed portions (5a), (5b) continuous with lower ends of these portions (4a), (4b) and having a larger depth than these portions, the front and rear upper tank forming recessed portions (3a), (3b) having respective fluid passage apertures (13a), (13b) formed in their bottom wall, the front and rear lower tank forming recessed portions (5a), (5b) having respective fluid passage apertures (15a), (15b) formed in their bottom wall, each pair of adjacent metal plates (2), (2) being fitted together in superposed layers with their recessed surfaces opposed to each other to join the opposed partition ridges (6), (6) of the metal plates (2), (2) to each other, to join opposed peripheral edges ( 7 ) , ( 7 ) thereof to each other and to thereby form a flat tube portion (A) having front and rear flat channels (11a), (lib), and front and rear upper tank portions (10a), (10b) and front and rear lower tank portions (12a), (12b) which are continuous with the channels, a multiplicity of flat tube portions (A) being arranged in parallel to cause the front upper tank portions (10a), (10a) of the adjacent parallel flat tube portions (A), (A) to communicate with each other, the rear upper tank portions (10b), (10b) thereof to communicate with each other, the front lower tank portions (12a), (12a) thereof to communicate with each other, and the rear lower tank portions (12b), (12b) thereof to communicate with each other, the layered heat exchanger being characterized in that the metal plate ( 2 ) is provided at one of an upper end and a lower end of the partition ridge ( 6 ) with a fluid flow direction changing passage forming caved portion (17) having a bottom wall (17a) of circular-arc cross section, the front and rear upper tank portions (10a), (10b) of the flat tube portion (A) or the front and rear lower tank portions (12a), (12b) thereof being held in communication with each other through a fluid flow direction changing passage (18) having an approximately circular cross section and formed by the caved portions (17), (17) which are opposed to each other. 2. A layered heat exchanger according to claim 1 wherein the bottom wall (17a) having a circular-arc cross section of the caved portion ( 17 ) has a depth smaller than the depth of the tank forming recessed portions. 3. A layered heat exchanger according to claim 1 wherein the passage (18) formed by the opposed caved portions (17), (17) has a circular cross section. 4. A layered heat exchanger according to claim 3 wherein the caved portion (17) comprises circular-arc portions corresponding respectively to angles of at least 60 deg to less than 90 deg each, above and below a center line of the caved portion and circular arc in cross section so as to have the same radius of curvature. 5. A layered heat exchanger according to claim 1 wherein the passage (18) is elliptical in cross section. 6. A layered heat exchanger comprising generally rectangular metal plates ( 2 ) each having formed in one surface thereof front and rear fluid channel forming recessed portions (4a), (4b) divided by a vertically elongated partition ridge ( 6 ) , front and rear upper tank forming recessed portions (3a), (3b) continuous with upper ends of these portions (4a), (4b) and having a larger depth than these portions, and front and rear lower tank forming recessed portions (5a), (5b) continuous with lower ends of these portions (4a), (4b) and having a larger depth than these portions, the front and rear upper tank forming recessed portions (3a), (3b) having respective fluid passage apertures (13a), (13b) formed in their bottom wall, the front and rear lower tank forming recessed portions (5a), (5b) having respective fluid passage apertures (15a), (15b) formed in their bottom wall, each pair of adjacent metal plates (2), (2) being fitted together in superposed layers with their recessed surfaces opposed to each other to join the opposed partition ridges (6), (6) of the metal plates (2), (2) to each other, to join opposed peripheral edges ( 7 ) , ( 7 ) thereof to each other and to thereby form a flat tube portion (A) having front and rear flat channels (11a), (lib), and front and rear upper tank portions (10a), (10b) and front and rear lower tank portions (12a), (12b) which are continuous with the channels, a multiplicity of flat tube portions (A) being arranged in parallel to cause the front upper tank portions (10a), (10a) of the adjacent parallel flat tube portions (A), (A) to communicate with each other, the rear upper tank portions (10b), (10b) thereof to communicate with each other, the front lower tank portions (12a), (12a) thereof to communicate with each other, and the rear lower tank portions (12b), (12b) thereof to communicate with each other, the layered heat exchanger being characterized in that the metal plate ( 2 ) is provided at one of an upper end and a lower end of the partition ridge ( 6 ) with a fluid flow direction changing passage forming caved portion (17) having a bottom wall (17a) of circular-arc cross section, the front and rear upper tank portions (10a), (10b) of the flat tube portion (A) or the front and rear lower tank portions (12a), (12b) thereof being held in communication with each other through a fluid flow direction changing passage (18) having an approximately circular cross section and formed by the caved portions (17), (17) which are opposed to each other, the bottom wall (17a) circular-arc in cross section of the caved portion (17) having a depth 1/5 to 4/5 of the depth of the tank forming recessed portions. 7. A layered heat exchanger according to claim 6 wherein the bottom wall (17a) circular-arc in cross section of the caved portion (17) has a depth 1/4 to 3/4 of the depth of the tank forming recessed portions. 8. A layered heat exchanger according to any one of claims 1 to 7 wherein a front side and a rear side of the heat exchanger provided respectively by the front and rear flat channels are the same in the number of passes. 9. A layered heat exchanger according to any one of claims 1 to 7 wherein a front side and a rear side of the heat exchanger provided respectively by the front and rear flat channels are different in the number of passes. 10. A layered heat exchanger according to claim 9 wherein an air outlet side and an air inlet side of the heat exchanger provided respectively by the front and rear flat channels are different in the number of passes, and the air outlet side is greater than the air inlet side in the number of passes.

Inventors: HIGASHIYAMA NAOHISA, HIGASHIYAMA, NAOHISA
Applicants: HIGASHIYAMA NAOHISA, SHOWA DENKO KK, HIGASHIYAMA, NAOHISA, SHOWA DENKO K.K.
Application year: 2001
Main classification: F28F9
IPC codes: F25B39, F28D1, F28F3, F28F27