Abstract:
Bypass valves and heat exchangers employing same are shown where the bypass valves cause the flow through the heat exchangers to be short-circuited under certain temperature conditions. The heat exchangers are formed of stacked plate pairs or tubes having enlarged communicating distal end portions forming inlet and outlet manifolds. The bypass valves can be plugged in where desired between the enlarged distal end portions to produce bypass flow between the inlet and outlet manifolds. The bypass valves include a housing which can be brazed in place during brazing of the heat exchanger. The housing has inlet and outlet openings in communication with the respective inlet and outlet manifolds for bypass flow therebetween. A removable temperature responsive actuator is located in the housing for blocking and unblocking the bypass flow through the valve.

Description:
[0001]     This application is a continuation of U.S. application Ser. No. 09/918,082 filed Jul. 30, 2001, the entire disclosure of which is incorporated herein by reference, which itself claims priority to Canadian Application No. 2,354,217 filed on Jul. 26, 2001. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     This invention relates to heat exchangers, and in particular, to bypass valves for bypassing or short-circuiting flow from the heat exchanger inlet to the heat exchanger outlet under conditions where the heat transfer function of the heat exchanger is not required or is only intermittently required.  
         [0003]     In certain applications, such as in the automotive industry, heat exchangers are used to cool or heat certain fluids, such as engine oil or transmission fluid or oil. In the case of transmission fluid, for instance, a heat exchanger is usually used to cool the transmission fluid. The heat exchanger is usually located remote from the transmission and receives hot transmission fluid from the transmission through supply tubing, cools it, and delivers it back to the transmission again through return tubing. However, when the transmission is cold, such as at start-up conditions, the transmission oil is very viscous and does not flow easily through the heat exchanger, if at all. In such cases, the transmission can be starved of fluid and this may cause damage to the transmission or at least erratic performance. Damage can also be caused to the transmission if the quantity of fluid returned is adequate, but is over-cooled by the heat exchanger due to low ambient temperatures. In this case, water may accumulate in the transmission fluid as a result of condensation (which normally would be vaporized at higher temperatures) and this may cause corrosion damage or transmission fluid degradation.  
         [0004]     In order to overcome the cold flow starvation problem, it has been proposed to insert a bypass valve between the supply and return tubing to and from the heat exchanger. This bypass valve may be temperature responsive so that it opens causing bypass flow when the transmission fluid is cold, and it closes to prevent bypass flow when the transmission fluid heats up to operating temperature An example of such a bypass valve is shown in U.S. Pat. No. 6,253,837 issued to Thomas F. Seiler et al. While this approach works satisfactorily, the heat exchanger and bypass valve assembly becomes quite large and includes fluid inlet and outlet tubing that may not otherwise be required.  
         [0005]     In the present invention, the bypass valve can be incorporated as an integral part of the heat exchanger as a plug-in item that can be located anywhere desired between the inlet and outlet flow manifolds of the heat exchanger.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]     Preferred embodiments of the invention will now be described by way of example, with reference to the accompanying drawings, in which:  
         [0007]      FIG. 1  is an elevational view of a heat exchanger having a preferred embodiment of a bypass valve according to the present invention mounted therein;  
         [0008]      FIG. 2  is an enlarged view of the portion of  FIG. 1  indicated by circle  2 ;  
         [0009]      FIG. 3  is a perspective view, partly broken away of the bypass valve of  FIG. 2  shown in the closed position;  
         [0010]      FIG. 4  is a perspective view similar to  FIG. 3  but showing the bypass valve in the open position;  
         [0011]      FIG. 5  is an elevational view similar to  FIG. 2 , but showing another preferred embodiment of a bypass valve according to the present invention, the valve being shown partially in cross-section;  
         [0012]      FIG. 6  is an elevational view similar to  FIG. 2 , yet showing another preferred embodiment of a bypass valve according to the present invention, the valve being shown in cross-section and in the closed position;  
         [0013]      FIG. 7  is an elevational view similar to  FIG. 6 , but showing the bypass valve of  FIG. 6  in the open position;  
         [0014]      FIG. 8  is a schematic view of a heat exchanger having multiple passes and more than one bypass valve; and  
         [0015]      FIG. 9  is an elevational view of a portion of another preferred embodiment of a heat exchanger and bypass valve according to the present invention.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0016]     Referring firstly to  FIGS. 1 and 2 , a heat exchanger is generally indicated by reference in  10 , and a preferred embodiment of a bypass valve according to the present invention is generally indicated by reference numeral  12 . Heat exchanger  10  is formed of a plurality of parallel, spaced-apart, tubular members  14  preferably with enlarged distal end portions  16  that have adjacent wall portions  17  defining flow openings (not shown) in communication. Tubular members  14  are preferably formed of mating plate pairs with transversely protruding cupped end portions to form these enlarged end portions  16  that also together form flow manifolds  19  and  21 . However, tubular members  14  could be formed of tubes with separate joined enlarged end portions  16 , if desired. Alternatively, tubular members of uniform width or thickness could be used, in which case tubular spacers could be used between the tube ends in place of enlarged distal end portions  16 . If it is not necessary to space tubular members  14  apart transversely, then such spacers would not be required. Yet another possibility would be to use transversely orientated tubular manifolds  19  and  21  attached in communication with the ends of tubular members  14 . For the purpose of this disclosure, the term “distal end portions” is intended to include all of the above-mentioned tube member communicating wall structures. Corrugated cooling fins  18  are located between the tubular members  14  where the tubular members  14  are spaced apart transversely.  
         [0017]     In the heat exchangers shown in  FIGS. 1 and 2 , the tubular members  14  are formed into two upper and lower groups separated by central back-to-back dimpled plates  20  having offset end portions  22 ,  24 . As seen best in  FIG. 2 , the space between offset end portions  22 ,  24  provides a location where bypass valve  12  can be plugged into heat exchanger  10 . Bypass valve  12  includes a hollow plug portion  26  located in this space, and which will be described in further detail below.  
         [0018]     As mentioned above, the enlarged distal end portions  16  have transverse openings therethrough (not shown), so that the distal end portions  16  located above bypass valve  12  are all in communication and form either an inlet or an outlet manifold  19  depending on the direction in which fluid is to flow through heat exchanger  10 . Similarly, the enlarged distal end portions  16  located below bypass valve  12  are all in communication and form a respective outlet or inlet manifold  21 . As seen best in  FIG. 1 , an inlet or outlet fitting  28  communicates with the enlarged distal end portions below it and an inlet or outlet fitting  30  communicates with the enlarged distal end portions above it. So, for example, fluid entering inlet fitting  28  travels from right to left as shown in  FIG. 1  through all of the tubular members  14  located above dimpled plates  20 , to a similar left hand manifold formed by enlarged distal end portions  32 , and then downwardly through a crossover fitting  34  into a left hand manifold in the lower section of heat exchanger  10  formed by enlarged distal end portions  32 , and then back to the right end and out through outlet fitting  30 . Heat exchanger  10  is thus called a two-pass heat exchanger and can have any number of tubular members  14  above or below the dimpled plates  20 . In fact, there could just be one tubular member  14  above or below dimpled plates  20 , as illustrated in the embodiment shown in  FIG. 9  and as described further below.  
         [0019]     Heat exchanger  10  also has upper and lower dimpled plates  36 . Suitable mounting brackets  40  are attached to dimpled plates  36 ,  38  as are the inlet and outlet fittings  28 ,  30 .  
         [0020]     Referring next to  FIGS. 3 and 4 , bypass valve  12  includes a housing  42  having a hollow plug portion  26  with spaced-apart, opposed, flat, parallel plug side walls  43  defining transversely located inlet and outlet openings  44 ,  46  formed therein for the flow of fluid through plug portion  26  when valve  12  is in the open position as shown in  FIG. 4 . Plug walls  43  are sealingly mounted between selected adjacent tubular member wall portions  17  of the enlarged distal end portions  16  of tubular members  14 . The distal end portions  16  have flat mating surfaces. The offset end portions  22  mate flush against their adjacent distal end portion flat surfaces and the flat housing side walls  43  mate flush against the flat offset end portions  22 . However, housing side or plug walls  43  would mate flush against the flat portions of distal end portions  16 , if dimpled plates  22  were not used in heat exchanger  10 . This mounting allows bypass fluid flow directly between selected distal end portions  16 , or respectively between the flow manifolds  19  and  21  and the inlet and outlet openings  44  and  46 , or between the inlet and outlet fittings  28 ,  30  when bypass valve  12  is open. Bypass valve side or plug walls  43  are spaced apart a predetermined distance so as to determine the spacing between adjacent heat exchanger tubular members, especially if dimpled plates  20  are not used.  
         [0021]     Bypass valve housing  42  also has an actuator portion  48  located adjacent to and communicating with plug portion  26 . A temperature responsive actuator  50  is located in housing  42 . Actuator  50  has a central shaft  52  attached to a removable closure  54  located remote from plug portion  26 . Removable closure  54  has an O-ring seal  56  and is held in position by a split pin  58  passing through openings  60  in housing actuator portion  40  and a through hole  62  in closure  54 .  
         [0022]     Temperature responsive actuator  50  has a reciprocating barrel portion  64  which forms a plunger slidably located in housing plug portion  26  to block and unblock flow between inlet and outlet openings  44 ,  46 . A spring  66  is located in housing actuator portion  48  and bears against an annular shoulder  68  on barrel  64  to act as bias means to urge the actuator  50  to retract so that barrel or plunger  64  unblocks the flow of fluid through inlet and outlet openings  44 ,  46  of bypass valve  12 , when the actuator is not extended due to temperature, as described next below.  
         [0023]     Temperature responsive actuator  50  is sometimes referred to as a thermal motor and it is a piston and cylinder type device. Barrel or plunger  64  is filled with a thermal sensitive material, such as wax, that expands and contracts, causing the actuator to extend axially upon being heated to a predetermined temperature and to retract upon being cooled below this predetermined temperature. Where bypass valve  12  is used in conjunction with an automotive transmission fluid or oil cooler, this predetermined temperature is about 80° C., which is the temperature of the fluid from the transmission when bypass flow is no longer required.  
         [0024]     Referring next to  FIG. 5 , another preferred embodiment of a bypass valve according to the present invention is generally indicated by reference numeral  70 . Bypass valve  70  is similar to bypass valve  12  except that a sliding plate  72  bears against central shaft  52  and a spring  74  is located in housing actuator portion  48  to urge central shaft  52  toward the housing plug portion  26 . Spring  74  absorbs any pressure spikes or peeks that may occur in the inlet and outlet manifolds of heat exchanger  10 . A notch  76  is formed in barrel  64  to allow the fluid to act against the end of barrel  64  and provide this pressure relief even when bypass valve  70  is closed. A bleed hole through plunger or barrel  64  communicating with inlet opening  44  could also be used in place of notch  76  for this purpose. Otherwise, bypass valve  70  is substantially the same as bypass valve  12 .  
         [0025]     Referring next to  FIGS. 6 and 7 , another preferred embodiment of a bypass valve according to the present invention is generally indicated by reference numeral  80 . In bypass valve  80 , the temperature responsive actuator  50  includes a solenoid having a solenoid coil  82  and a central actuator shaft  84  attached to a plunger  86 . Plunger  86  also has a notch or bleed hole  76  to provide pressure spike relief when valve  80  is closed. Actuator shaft  84  extends upon energization of solenoid coil  82 , so that plunger  86  blocks flow between the housing inlet and outlet openings  44 ,  46 . A spring  88  located in housing plug portion  26  bears against plunger  86  to act as bias means for urging the actuator shaft  84  to retract upon the de-energization of solenoid coil  82 .  
         [0026]     A temperature sensor  90  is attached to plunger  86  and is in the form of a thermistor electrically coupled to solenoid coil  82  for actuation of the solenoid coil when the temperature of the fluid going through heat exchanger  10  reaches a predetermined temperature. Temperature sensor  90  could be located elsewhere in bypass valve  80 , or even elsewhere in heat exchanger  10 . Preferably, temperature sensor  90  is electrically connected to an electrical control circuit  92  mounted in housing actuator portion  48 . Electrical control circuit  92  is in turn is electrically connected to solenoid coil  82  for controlling the movement of plunger  86  in accordance with the temperature sensed by temperature sensor  90 . In this way, the opening of bypass valve  80  could be controlled to provide variable opening, rather than a simple on or off, but the latter is also possible.  
         [0027]     Referring next to  FIG. 8 , a heat exchanger  100  is shown schematically and it is like two heat exchangers  10  of  FIG. 1  mounted in series. Two bypass valves  102 ,  104  are used to provide thermal modulation of the fluid flowing through the heat exchanger  100 . Bypass valve  102  may have a predetermined temperature set point or activation temperature, and bypass valve  104  may have a somewhat higher temperature set point or activation temperature. Heat exchanger  100  is a four pass heat exchanger having four groups or stacks  106 ,  108 ,  110  and  112  of tubular members.  
         [0028]     Where both bypass valves  102  and  104  are open, such as during cold flow operation, there is full fluid bypass from inlet fitting  28  to outlet fitting  30 . Where bypass valve  102  is closed and valve  104  is open, such as during warm up or an interim temperature of fluid flowing through heat exchanger  100 , there would be fluid flow through the top two passes  106  and  108  of heat exchanger  100 , but passes  110  and  112  would be bypassed through bypass valve  104 . Where the fluid reaches its hot operating temperature, both bypass valves  102  and  104  would close giving flow through all four passes  106 ,  108 ,  110  and  112  and no bypass flow at all. Additional multiples of passes and bypass valves could be used in a single heat exchanger as well. Any of the types of bypass valves described above could be used in heat exchanger  100 .  
         [0029]     Referring next to  FIG. 9 , other preferred embodiments of a heat exchanger  113  and a bypass valve  115  are shown. In bypass valve  115 , inlet and outlet openings  44 ,  46  are formed in opposed plug walls  114 ,  116  and this shows that inlet and outlet openings  44 ,  46  can be located anywhere in plug portion  26  as long as one of these openings is blocked when valve  115  is closed. Otherwise, bypass valve  115  is substantially similar to or can incorporate the features of the bypass valves  12 ,  70  and  80  described above. In the embodiment of  FIG. 9 , plate  38  (which preferably is dimpled but may be flat) and a bottom plate  118  (which may also be dimpled or flat), together form a tubular member  120  which is one of the tubular members that make up heat exchanger  113 . Tubular member  120  is actually a bypass channel and has flow openings  122  that communicate with the flow openings in the adjacent enlarged distal end portions  16  of adjacent tubular member  14 , and as such forms part of the inlet and outlet manifolds of heat exchanger  113 . Instead of tubular member  120 , a regular tubular member  14  could be used in heat exchanger  113 , if desired. This would produce a full flood or single pass heat exchanger. Tubular members  14  may or may not have turbulizers in them or be made of dimpled plates, but the bottom tubular member  120  likely would not be turbulized or have other types of flow augmentation, such as dimples.  
         [0030]     In the assembly of heat exchangers  10 ,  100  and  113 , the various components, such as the tubular members  14  or  120  and fins  18  are stacked together along with dimpled plates  20 , if desired, and upper and lower dimpled plates  36 ,  38 . Mounting plates or brackets  40  and inlet and outlet fittings  28 ,  30  can be preassembled to upper and lower dimpled plates  36 ,  38 , or assembled along with all of the other components. The housing  42  of the preferred bypass valve  12 ,  70 ,  80  or  115  (without any other bypass valve components) is then placed in the desired location in the heat exchanger and the entire assembly is brazed together in a brazing furnace. It will be appreciated that in the preferred embodiments, aluminum or a brazing-clad aluminum is used for most of the parts of the heat exchangers, so that all of the parts can be brazed together in a brazing furnace. After this assembly is cooled, the desired actuator components of the bypass valves are inserted into housing  42  and the removable closures  54  are secured in position with split pins  58 .  
         [0031]     Having described preferred embodiments of the invention, it will be appreciated that various modifications can be made to the structures described above. For example, instead of using a thermal motor or solenoid type actuator for the bypass valves, other devices could be used as well, such as a bimetallic helix to move the barrel or plunger of the valve. The tubular members can also have other shapes or configurations as well.  
         [0032]     From the above, it will be appreciated that the bypass valves of the present invention are in the form of plugs that can be plugged in at any desired location in the heat exchanger with a simple rearrangement of the location of some components. The bypass valve housings actually act as a form of baffle plate to intermittently block flow between manifold portions of the heat exchangers. In fact, the bypass valves could be plugged in anywhere in the heat exchangers where it is desired to have bypass flow between the plate pairs or tubes. The bypass valve housings are brazed in place along with all of the other heat exchanger components. The actual valve elements in the actuators are then removably or releasably located in the bypass valve housings to complete the assembly. No external tubing or peripheral components are required to make the actuator valves active  
         [0033]     As will be apparent to those skilled in the art in the light of the foregoing disclosure, many alterations and modifications are possible in the practice of this invention without departing from the spirit or scope thereof. The foregoing description is of the preferred embodiments and is by way of example only, and it is not to limit the scope of the invention.