Abstract:
A by-pass valve for a heat exchanger circuit includes a chamber, a fixed surface secured against movement relative to the chamber, a by-pass port including a valve seat located in the chamber, an actuator located in the chamber and that moves relative to the valve seat in response to a temperature of the actuator, a valve member, a spring contacting the surface and the valve seat and producing a force urging the valve member to engage the valve seat and to close the by-pass port, the spring having no structural connection to the actuator, and a return spring secured to the actuator and contacting the valve member for urging the actuator to retract and the valve member to open the by-pass port.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates generally to a heat exchanger circuit, and, in particular, to a bypass valve having a pressure bypass function that is insensitive to temperature changes of fluid in the circuit. 
   2. Description of the Prior Art 
   At low temperatures and while the engine of a motor vehicle is warming-up, transmission fluid is highly viscous, resulting in nearly no flow through an oil the cooler. High viscosity and low flow rate can compromise transmission durability because cooler return oil is usually routed to the transmission lubrication circuit. 
   A variety of thermal bypass valves have been designed to allow oil to bypass the cooler and return to the transmission to maintain desired flow rates to the lubrication circuit. Many of these valves use a thermal motor/actuator to actuate the valve to provide this function. When the transmission is hot, the thermal bypass valve closes. If the cooler is hot, the cooler and lubrication systems will function as intended. If, however, ambient temperature is very cold, oil in the cooler remains cold, and oil flow will is low. 
   A variety of thermal bypass valves have been developed to allow a pressure bypass function, wherein the valve opens to bypass the cooler when the oil temperature is high and the pressure drop across the cooler exceeds a designed threshold. However, an inherent problem exists in many of these thermal bypass valves with pressure bypass functions. Most will provide the desired function with features that involve a spring load balanced against a piston, washer or valve having a piston shape and piston function with a pressure differential across it. Many of these valves have a spring load that is grounded to the thermal motor/actuator, which continues to move as the oil temperature increases. This grounded relation causes the spring load to be a function of temperature and the pressure relief temperature is also a function of temperature. 
   Unfortunately, when the oil is very hot and the ambient air conditions are such that the cooler is still frozen and not flowing oil, these shortcomings cause the pressure difference to be so high that the pressure bypass function will not be available, and the transmission is at risk due to a lack of lubricating oil. 
   SUMMARY OF THE INVENTION 
   A by-pass valve for a heat exchanger circuit includes a chamber, a fixed surface secured against movement relative to the chamber, a by-pass port including a valve seat located in the chamber, an actuator located in the chamber and that moves relative to the valve seat in response to a temperature of the actuator, a valve member, a spring contacting the surface and the valve seat and producing a force urging the valve member to engage the valve seat and to close the by-pass port, the spring having no structural connection to the actuator, and a return spring secured to the actuator and contacting the valve member for urging the actuator to retract and the valve member to open the by-pass port. 
   The by-pass valve corrects the problem of variability in pressure induced bypass by grounding the over-pressurization spring directly to the valve housing, rather than to the thermal motor/actuator, as in existing designs. In conventional by-pass valves, the spring is grounded against the thermal motor/actuator, which continues to move as oil temperature increases, resulting in a higher pressure drop to invoke bypass at higher oil temperatures. 
   In the preferred by-pass valve, the spring force is not defined by the position of the thermal motor/actuator after the valve closes. Instead, the spring is compressed in a space between the valve cap and the valve member. The axial length of this space does not change after the valve closes and temperature continues to increase. Therefore, regardless of the operating temperature of the oil, the pressure drop across the cooler bypass is the same. The preferred by-pass valve produces a consistent cooler pressure drop threshold after the valve closes. 
   The scope of applicability of the preferred embodiment will become apparent from the following detailed description, claims and drawings. It should be understood, that the description and specific examples, although indicating preferred embodiments of the invention, are given by way of illustration only. Various changes and modifications to the described embodiments and examples will become apparent to those skilled in the art. 

   
     DESCRIPTION OF THE DRAWINGS 
     These and other advantages will become readily apparent to those skilled in the art from the following detailed description of a preferred embodiment when considered in the light of the accompanying drawings in which: 
       FIG. 1  is a perspective, schematic view of a heat exchanger employing a by-pass valve; 
       FIG. 2  is a sectional view taken at plane  2 - 2  of  FIG. 1  showing the by-pass valve in its open state;  FIG. 3  is a sectional view similar to  FIG. 2  but showing the by-pass valve in its closed state; and 
       FIG. 4  is a side view, partly in cross section, of the valve cartridge or subassembly used in the by-pass valve of  FIGS. 2 and 3 . 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring to  FIG. 1 , a heat exchange circuit  10  includes a heat exchanger  12  of any type, and a by-pass valve  14 . In  FIG. 1 , a two-pass heat exchanger has a first manifold  16 , which could be an inlet or an outlet manifold, a return manifold  18 , and a second manifold  20 . Spaced-apart heat exchange conduits  22 ,  24  are connected between the manifolds such that, if first manifold  16  is an inlet manifold, fluid flows from inlet manifold  16  through conduits  22  into return manifold  18 , where it reverses direction and flows back through conduits  24  to second manifold  20 , which is then an outlet manifold. The flow direction can be reversed such that second manifold  20  is the inlet manifold and first manifold  16  is the outlet manifold. Heat exchanger  12  can be a single pass heat exchanger with manifolds  16 ,  20  located at respective ends of the heat exchanger, in which case, return manifold  18  would not be required. 
   If first manifold  16  is the inlet manifold, it is formed with an inlet opening  26 , which communicates with an inlet conduit  28 . If second manifold  20  is the outlet manifold, it is formed with an outlet opening  30 , which communicates with an outlet conduit  32 . 
   If the flow direction is reversed, conduit  32  becomes the inlet conduit and conduit  28  becomes the outlet conduit. Conduits  28 ,  32  are connected to inlet and outlet ports in by-pass valve  14 , and supply conduits  34 ,  36  are also connected to ports in by-pass valve  14 , as will be described further below. 
   Conduits  34 ,  36  have end fittings  38 ,  40  for attaching flow lines to conduits  34 ,  36 . Where heat exchanger  12  is a transmission oil cooler, end fittings  38 ,  40  can be hose barbs for attaching rubber hoses between the transmission and heat exchange circuit  10 . However, any type of end fittings  38 ,  40  can be used to suit the type of oil lines running to and from heat exchange circuit  10 . 
   By-pass valve  14  is referred to as a four port by-pass valve, because four conduits  28 ,  32 ,  34  and  36  are connected to by-pass valve  14 . Referring next to  FIG. 2 and 3 , the four port by-pass valve  14  includes a housing  46  formed with a chamber  48 . Housing  46  has main ports or openings  50 ,  52  and a valve port  54 , which communicates with two lower branch ports  56 ,  58 . Conduits  28 ,  36  are connected, respectively to the branch ports  56 , 58 . 
   Valve port  54  has a peripheral valve seat  60  facing chamber  48 . A movable valve member  62  is adapted to engage valve seat  60 , thereby closing valve port  54 , and to disengage valve seat  60 , thereby opening valve port  54 . 
   A temperature responsive thermal motor/actuator  64 , located inside chamber  48 , is encircled by a helical compression spring  74 . A thermal motor/actuator  64 , includes a piston located in a cylinder, which contains a thermal sensitive material, such as wax, which expands and contracts in response to its temperature, thereby causing the thermal motor/actuator to extend axially upon being heated to a predetermined temperature and to retract upon being cooled below the predetermined temperature. Where by-pass valve  14  is used in conjunction with an automotive transmission oil cooler, this predetermined temperature is such that the oil returning to the transmission from heat exchange circuit  10  is typically 70° C. to 100° C. 
   Referring next to  FIGS. 2 ,  3  and  4 , thermal motor/actuator  64  is located along a central axis of chamber  48 . The cylinder of thermal motor/actuator  64  forms a central shaft  66  directed along the central axis of valve port  54  and surrounded by the coils of spring  74 . The lower end of central shaft  66  is formed with a closed end portion  68 , which partially closes valve port  54 . Valve member  62  extends radially outward from the outer surface of central shaft  66  to engage valve seat  60  and close valve port  54 , as indicated in  FIG. 3 . 
   The upper end of spring  74  contacts the lower surface  72  of closure  80 , which is secured to housing  46 . The lower end of spring  74  contacts valve member  62 . Spring  74  is installed with a compression pre-load. Valve member  62  is in the form of an annular disc, which slides axially on central shaft  66  toward valve seat  60  due to the force continually applied by spring  74 . The upper end  75  of a return spring  70  is secured to the closed end portion  68  by being inserted into a groove (not shown) formed in the closed end portion  68 . The upper end  75  of return spring  70  moves with the central shaft  66 , and the lower end of spring  70  is seated on a planar surface. Return spring  70  acts as a stop for preventing valve member  62  from sliding off central shaft  66 . 
   Thermal motor/actuator  64  includes a piston  76 , which is attached or press fitted into an axial recess  78  (see  FIG. 4 ) formed in the removable closure  80 , which is secured to housing  46 . Closure  80 , which includes an  0 -ring seal  82 , is secured to housing  46  by a suitable pin or set screw or other type of fastener, such as a “C”-clip or snap ring  81 . 
   When thermal motor  64  reaches a predetermined temperature, piston  76  extends axially from its cylinder in the central shaft  66 . Because the position of piston  76  is fixed, central shaft  66 , which is part of thermal motor  64 , moves axially downward through valve port  54 , compressing return spring  70 . The force of spring  74  causes valve member  62  to engage valve seat  60  and to close valve port  54 . When the temperature inside chamber  48  drops below the reference temperature, piston  76  retracts into the central shaft  66 . The return spring  70  urges central shaft  66  and valve element  62  upward, thereby lifting valve element  62  off valve seat  60 , opening valve port  54 , and compressing spring  74 . When valve port  54  is opened as indicated in  FIG. 3 , return spring  70  extends through valve port  54  and into chamber  48 , but it does not materially affect the flow through valve port  54 . 
   As  FIG. 4  shows, closure  80 , thermal motor  64 , coil spring  74 , valve member  62  and return spring  70  form a cartridge or subassembly  84  for by-pass valve  14 . When subassembly  84  is removed from by-pass valve  14 , the various conduits can be attached, such as by brazing, to housing  46  without damaging thermal motor  64  or springs  70 ,  74 . Cartridge  84  is then installed in housing  46  with closure  80  located opposite to valve port  54  and heat exchange circuit  10  is then ready for use. 
   The operation of by-pass valve  14  is now described with reference to  FIGS. 1-4 . Heat exchange circuit  10  can be operated with either conduit  34  or conduit  36  being the inlet conduit, the other one being the outlet conduit. When conduit  34  is the inlet conduit, i.e., when it receives hot transmission oil from the transmission, this condition is sometimes referred to as the normal flow condition. In this case, conduit  36  is the outlet conduit and returns the transmission oil to the transmission after it has been cooled in heat exchanger  12 . 
   When conduit  36  is the inlet conduit receiving the hot transmission fluid or oil from the transmission and conduit  34  is the outlet or return conduit delivering cooled oil back to the transmission, this condition is sometimes referred to as the reverse flow condition. 
   Dealing first with the normal flow condition, if the temperature of transmission oil in heat exchange circuit  10  is above the reference temperature, by-pass valve  14  appears as in  FIG. 3 . Hot engine oil enters through inlet conduit  34  and passes in series through main port  52 , chamber  48  and main port  50  to heat exchanger inlet conduit  32 . The hot fluid passes through heat exchanger  12  and returns through outlet conduit  28 , passes through branch ports  56 ,  58 , exits through outlet conduit  36 , and returns to the transmission. In this case, there is no by-pass flow, because valve port  54  is closed. 
   If the temperature of fluid returning to the transmission through conduits  28 ,  36  drops below the reference temperature, which is 70° C to 100° C, piston  76  of thermal motor/actuator  64  retracts causing valve member  62  to lift off valve seat  60  opening valve port  54 . This creates by-pass flow from conduit  34 , through chamber  48  and valve port  54 , which flow joins flow in conduit  36  and returns to the transmission. If the temperature of the flow or oil is very cold, such as at engine start-up conditions, the oil may be so viscous that virtually no flow goes through heat exchanger  12 , and the flow is totally by-passed from inlet conduit  34  to outlet conduit  36 . As the temperature of the oil increases, flow through conduit  32  and heat exchanger  12  increases due to expansion of the thermal actuator/motor, until the oil temperature reaches the desired operating temperature. Then full flow occurs through heat exchanger  12 , valve member  62  closes valve port  54 , thereby discontinuing by-pass flow. When valve member  62  is disengaged from seat  60 , valve port  54  becomes an outlet port. The other main ports  52  and  50  become respective inlet and outlet ports in this regular flow condition. 
   In the regular flow condition, branch port  56  becomes an inlet port, and branch port  58  becomes an outlet port communicating with inlet port  56 . Valve port  54  becomes an outlet port for by-pass valve  14 , and the other main ports  52  and  50  become, respectively, inlet and outlet ports for by-pass valve  14 . 
   When operating in the reverse flow condition, conduit  36  becomes the inlet conduit receiving hot oil from the transmission, and conduit  34  becomes the outlet conduit returning the cooled transmission oil to the transmission. In the reverse flow condition, if the transmission and heat exchange circuit  10  are at operating temperatures, the hot transmission fluid passes through branch port  58 , which becomes an inlet port. Valve member  62  is closed and there is no by-pass flow. The hot oil then continues through branch port  56 , which becomes an outlet port communicating with inlet branch port  58 . The hot oil flows through conduit  28  and the heat exchanger  12 , returns through conduit  32 , flows in series through second main port  50 , chamber  48  and third main port  52 , and flows out through conduit  34  to the transmission. 
   If the temperature of the transmission oil returning to the transmission drops below the reference temperature, thermal motor/actuator  64  causes valve member  62  to open, thereby creating by-pass flow from valve port  54  to main port  52  and conduit  34 . Again, if the oil is extremely cold, such as at engine start-up conditions, very little, if any, flow passes through heat exchanger  12 , and there is almost total by-pass through by-pass valve  14 . As the temperature of the transmission oil increases, flow enters heat exchanger  12  and returns through conduit  32  to chamber  48  and back to the transmission through conduit  34 . This causes thermal motor/actuator  64  to warm up faster than would otherwise be the case. As the transmission oil returning to the transmission through outlet conduit  34  reaches the references temperature, piston  76  of thermal motor/actuator  64  extends, closing valve member  62  and stopping the by-pass flow. During cold weather operation, it is possible that oil in the heat exchanger will still be very cold and highly viscous in spite of the transmission warming up. In this situation, it is possible that the valve will close, oil will not flow through the heat exchanger, and pressure will increase. The coil spring is designed such that in this situation, the valve member will lift off the valve seat and restore flow to the transmission. The pressure required to open the valve seat is independent of the operating temperature when operating temperature is greater than that required for the thermal motor/actuator  64  to close the valve. 
   The circuiting of the valve is such that the housing functions as a mixing chamber, in which the by-pass fluid stream and the heat exchanger outlet stream can mix in direct contact with the thermal motor/actuator, so that thermal transients are damped, and the thermal motor/actuator  64  is able to directly respond to the mixed oil temperature being returned to the transmission. Also during the transition between opening and closing, the hot by-pass stream and cooler oil cooler return stream are mixed, thereby dampening any temperature transients in the oil being returned to the transmission. 
   In the reverse flow configuration, valve port  54  becomes an inlet port for by-pass valve  14  and the other main ports  50 ,  52  become respective inlet and outlet ports for by-pass valve  14 . 
   Because by-pass valve  14  is located in chamber  48  with oil continuously flowing there, thermal motor/actuator  64  reacts quickly to temperature changes in the oil, warming and cooling quickly. Also, if the transmission oil becomes over-heated or experiences a temperature spike, thermal motor/actuator  64  is not damaged, because it is always exposed to some return flow from heat exchanger  12  in chamber  48  in the reverse flow configuration, or in branch ports  56 ,  58  in the regular flow configuration. Further, if thermal motor/actuator  64  is overheated and tends to expand too far, it will not be damaged, because central shaft  66  can extend through valve port  54  as much as is required. Any physical stops or constraints to limit the expansion of thermal motor/actuator  64  should be effective in this function only outside the range of operating temperature. 
   By-pass valve  14  has three main ports. If valve port  54  is considered to be the first main port, conduits  28 ,  36  can be considered to be a first flow conduit communicating with valve port  54  and one of the inlet and outlet openings of heat exchanger  12 , depending upon whether by-pass valve  14  is operated in the regular flow or reverse flow condition. Depending upon whether valve port  54  is connected to the inlet or the outlet of heat exchanger  12 , a second main port, namely main port  50 , is connected to the other of the inlet and outlet openings of heat exchanger  12 . A second flow conduit, namely conduit  34 , communicates with the third main port, namely main port  52  of by-pass valve  14 . In the reverse flow configuration, the first flow conduit  28 ,  36  is the heat exchanger inlet. The second conduit  34  through conduit  32  becomes the heat exchanger outlet. In the regular flow condition, the first flow conduit  28 ,  36  becomes the heat exchanger outlet, and the second flow conduit  34  through conduit  32  becomes the heat exchanger inlet. 
   In accordance with the provisions of the patent statutes, the preferred embodiment has been described. However, it should be noted that the alternate embodiments can be practiced otherwise than as specifically illustrated and described.