Heat exchanger and seal therefor

Abstract: A junction (16) includes a gasket (18) between a tank (12) and header (14) of a heat exchanger (10). The gasket has a substantially flat bottom surface (40), a convex upper section (42), and a lip (46) at its inner periphery (44) which extends upwardly. A concave recess (52) is interposed between the convex section (42) and lip (46). The lip (46) is positioned to fill a crevice (56) formed between the tank (12) and header (14) when the heat exchanger (10) is assembled.

Description: The present invention relates to a heat exchanger and to a seal therefor. Heat exchangers are used in the vast majority of motor vehicles powered by an internal combustion engine. The heat exchangers are used for engine cooling and passenger compartment heaters. Most heat exchangers include a header and a tank at each end core surface. It has become common practice to manufacture the tank from a plastics material and the header from a heat-conductive metal material such as aluminium. The plastics tank is mechanically joined to the header. It is vital that the junction between the tank and header be leak-free and durable even with the sometimes corrosive fluid which flows through the heat exchanger. It is also common practice to use elastomeric gaskets in the junction between the tank and header to prevent leakage between the header and tank. The junction between the tank and header poses a major problem to the durability of the heat exchanger. Usually the junction is designed to have a channel formed in the header to receive edge portions of the tank. An elastomeric gasket is compressed therebetween. In many of these junction designs, a narrow crevice between the tank wall and inner wall of the channel allows fluid to seep therein, but has either limited or no fluid flow therethrough. The narrowness of the crevice prevents the normal washing action of the coolant flow through the crevice. Under certain conditions, particles within the coolant become lodged in the crevice and inside channel section which can initiate crevice corrosion. Eventually, the progression of the crevice corrosion results in a leak in the heat exchanger. Several attempts have been made to eliminate crevice corrosion. Some of these efforts use extensive redesign of the tank foot to provide flow channels to wash the particles from the inside channel section. Headers have also been manufactured with a zinc alloy or an alloy of aluminium, magnesium and zinc on the inner surfaces exposed to the coolant. These tank foot redesigns and use of the mentioned alloys are expensive and do not eliminate the basic conditions which instigate crevice corrosion. Both the crevice and the contact of the coolant with the header within the channel remain in these redesigns. Gaskets have undergone many different designs. Many of these gaskets are used with a tank foot having a compression rib formed therein. Some gasket designs have been developed with beads to provide sealing forces in the channel. Other gaskets have been designed to extend into the tank interior. While these gaskets fill the channel and the crevice formed between the tank foot and header channel, they create their own crevices with the header to form other areas of potential corrosion. In US Patent No. 4,305,459 a gasket 8 is shown which has an inner peripheral lip 9 which extends beyond the crevice formed between the tank foot and the header channel. Similarly, US Patent No. 4,544,029 discloses a gasket with an inner peripheral lip extending beyond the crevice. In both of these known arrangements, because the lip of the gasket does not terminate within the crevice, the aforementioned disadvantages accrue in use. The present invention seeks to provide an improved heat exchanger and seal therefor. According to an aspect of the present invention, there is provided a heat exchanger as specified in claim 1. According to another aspect of the present invention, there is provided an elastomeric seal for a heat exchanger as specified in claim 8. The present invention can provide a seal with a truncated lip which can fill the crevice between a tank foot and an inner channel wall and which may have a distal end under compression between the foot and channel wall so that coolant can be prevented from passing between the seal and the header or tank foot. The present invention can also provide a seal having the convenience of assembly of an O-ring with increased joint rigidity. In a preferred embodiment, there is provided a heat exchanger which has a tank sealingly secured to a header. The tank has a foot having an outwardly directed shoulder from a substantially vertical wall. The foot has a lower surface, an outer surface and an inner heel surface. The header is configured to receive the tank foot within a channel. The channel has an outer wall with a bendable end for gripping the foot. The channel has a lower wall spaced from and opposing the lower surface of the flange. The channel has an inner wall also opposing a heel of the foot. The top of the inner wall is connected to an end plate section of the header. The preferred embodiment also includes an annular gasket of elastomeric material seated within the channel. The gasket in its relaxed state has a substantially flat lower surface with rounded corners leading into the side portions and an upper convex section. A lip extends upwardly from a radially inner side portion of the annular gasket and is interposed between the channel inner wall and the tank foot. When the gasket is in its relaxed state, the lip is separated from the upper convex section by a recess interposed therebetween. Preferably, the recess has a concave contour. The lip may have a distal end vertically aligned with the upper point of the convex section. The gasket lower portion of this embodiment is preferably shaped in cross-section to conform with the walls of the channel to substantially fill the lower portion of the channel. The gasket when installed in the junction has its lip displaced under compression to extend and fill the crevice between the foot and channel inner wall. The distal end of the lip is in proximity to the heel of the foot and remains under compression between the foot and inner wall of the channel. The distal end preferably remains outboard of the substantially vertical tank wall's inner surface and below the header end plate section. An embodiment of the present invention is described below, by way of illustration only, with reference to the accompanying drawings, in which: Figure 1 is a partially segmented perspective view of a tank and header illustrating one embodiment of the invention; Figure 2 is an enlarged segmented view of a junction shown in Figure 1; Figure 3 is a plan view of an annular gasket shown in Figure 1; and Figure 4 is an enlarged cross-sectional view taken along line 4-4 of Figure 3. Referring to Figure 1, a heat exchanger 10 has a tank 12 joined to a header 14 at junction 16 which includes seal or gasket 18. As shown more clearly in Figure 2, the header 14 includes an end plate section 21 having a peripheral channel 20 of a size adapted to receive a foot 22 of the tank 12. The channel 20 includes an inner or second channel wall 24, lower or base wall 26, and outer or first channel wall 28. The walls are joined by rounded corners 27. The distal end 30 of wall 28 is deformable to grip the foot 22. The tank 12 has a substantially vertical inner wall surface 23. The foot 22 extends outwardly from wall surface 23 and has a second side wall or heel section 31 which opposes inner wall 24 of channel 20. The foot 22 also includes a base wall or lower surface 34, outer surface or first side wall 36 and upper grip surface 38. The foot 22 is of a size suitable to be received in the channel 20 along with the gasket 18. The foot 22 is positioned into channel 20 to compress the gasket 18. The distal end 30 of wall 28 is then deformed about grip surface 38 to affix the tank 12 in place and to compress gasket 18. The gasket 18 is shown in it relaxed state in Figures 3 and 4. As shown in Figure 3, the gasket 18 has a generally annular configuration of a rectangular form with rounded corners 39, substantially matching the shape of most tanks and headers. Other shapes of header would be provided to fit differently shaped tanks and headers. As shown in Figure 4, the gasket 18 has a substantially flat lower surface or seal base wall 40, side wall portions 41 and 43, and a convex upper section 42. The lower half of side wall portions 41 and 43 and the lower surface 40 are shaped to conform substantially to the cross-sectional shape of the lower portion of channel 20. The inner periphery 44 of the annular gasket 18 includes an upwardly extending lip portion 46. The lip 46 extends such that its distal end 48 is approximately aligned with an uppermost extent 50 of the convex upper section 42. The lip 46 is separated from the convex upper section 42 by a recess 52 interposed therebetween. The recess 52 has a generally curved concave contour. When the gasket 18 is installed in the channel 20, the side wall portions 41 and 43 with lower surface 40 substantially fill the lower half of channel 20. When fitted, the foot 22 compresses the gasket 18 to flatten the convex upper surface 42, while the lip 46 is positioned and compressed in the crevice 56 formed between the heel section 31 and the inner wall 24 of channel 20. The gasket material is deformed substantially to fill the space 54 within the channel below the foot 22. The gasket 18, foot 22, and channel 20 are designed to allow sufficient volume for gasket deformation during assembly so that the channel space 54 is filled. The gasket 18 is compressed by approximately 30% when the foot 22 is secured within channel 20. The lip 46 is urged into the crevice 56 during its compression. The distal end 48 of lip 46 is in proximity to the heel 31 and is retained in compression between the heel 31 and the inner wall 24 of channel 20. The distal end 48 remains positioned below end plate 25 and outboard of wall surface 23. The position of end 48 of lip 46 ensures that the lip 46 is retained in compression to reduce the possibility of formation of a crevice between the lip 46 and either the foot 22 or channel wall 24. In this manner, sources of crevice corrosion can be eliminated by eliminating crevices which may be filled with corrosive coolant. Furthermore, the junction has increased rigidity compared to a junction using a comparable O-ring gasket because of the greater force required to obtain optimum compression of the gasket. Furthermore, since greater force is necessary to compress the gasket, there is also an increased residual reactionary force within the junction to provide more reliable sealing capability across the width of the channel. The compression of gasket 18 results in the seal compression forces pushing against substantially all areas of wall contact. The improved seal compression can reduce the chances of leakage due to irregularities within the gasket or foreign particles and debris settling on the tank and header mating surfaces. Manufacture of the design can be facilitated with compression of approximately 30% being substantially consistently achieved.

Claims: A heat exchanger comprising a tank (12), a header (14) and an elastomeric seal (18) for sealing the tank to the header, the tank comprising a tank foot (22) which includes a base wall (34) and first and second side walls (36,31) extending from respective sides of the base wall; the header comprising a channel (20) which includes a first channel wall (28) adapted to grip the foot, a second channel wall (24) opposed to the second side wall (31) of the tank foot when the tank is fitted on the header, and a channel base wall (26) opposed to and spaced from the base wall (34) when the tank is fitted on the header; the seal (18) being adapted to fit within the channel of the header and including a first section (42) having a convex shape when in a relaxed state, a seal base wall (40) adapted to cooperate with the channel base wall and a lip portion (46) in use interposed between the second side wall of the tank foot and the second channel wall with a distal end (48) of the lip portion being retained in compression between the second side wall of the tank foot and the second channel wall, characterised in that the lip portion (46) extends, in a relaxed state of the seal, such that its distal end (48) is approximately aligned with an uppermost extent (50) of the convex shaped section (42). A heat exchanger according to claim 1, wherein the lip portion (46) and the first section (42) of the seal (18) are separated by a recess (52). A heat exchanger according to claim 2, wherein the recess (52) has a concave form. A heat exchanger according to claim 2 or 3, wherein the lip portion (46) and the first section (42) of the seal (18) when in a relaxed state extend by substantially equal amounts from the recess (52). A heat exchanger according to any preceding claim, wherein the seal substantially conforms to the shape of the channel between the channel base wall and at least a part of the first and second channel walls (28,24). A heat exchanger according to any preceding claim, wherein the channel base wall (26) and the seal base wall (40) are substantially flat. A heat exchanger according to any preceding claim, wherein the seal (18) has a substantially annular form. An elastomeric seal for a heat exchanger comprising a substantially flat base wall (40), a convex wall (42) substantially opposite the base wall and a lip portion (46) at an inner radial edge of the seal; the lip portion and convex wall being separated by a recess (52), characterised in that the lip portion (46) extends, in a relaxed state of the seal, such that its distal end (48) is approximately aligned with an uppermost extent (50) of the convex wall (42). A seal according to claim 8, wherein the recess (52) has a concave form.

Inventors: KROETSCH KARL PAUL, KROETSCH, KARL PAUL
Applicants: GEN MOTORS CORP, GENERAL MOTORS CORPORATION
Application year: 1993
Main classification: F28F9
IPC codes: F28F9