Abstract:
A fluid heater apparatus supplies heat to wash fluid via a flow path in a thermally conductive body. A heat source is disposed in the thermally conductive body for imparting heat to the body. Fluid flowing through the thermally conductive body in a flow path enveloping the heat source to absorb heat from the body. A seal member and a metal plate are fixed to one surface of the thermal body. A high thermally conductive pad is disposed between a printed circuit board carrying a control with heat generating switch elements. The pad conducts heat generated by control switching elements to the plate to reduce the temperature differential between the plate and the thermally conductive body to balance the temperature of the heater apparatus.

Description:
BACKGROUND  
         [0001]    This invention relates, in general, to fluid heater apparatus and, more particularly, to fluid heater apparatus which provide a heated wash fluid to a cleanable surface, and, still more specifically, to a heated wash fluid apparatus for a vehicle windshield wash system.  
           [0002]    It is necessary in many diverse applications to quickly elevate the temperature of a fluid to a higher use temperature. For example, it is desirable to be able to provide instant hot water, for use in homes, offices and campers, as well as for industrial processes.  
           [0003]    In cleaning applications, it is known that hot fluid removes dirt and other debris from a surface much better and much faster than colder fluids. One heated fluid application is a vehicle wash fluid system, such as a windshield wash system as well as vehicle wash systems applied to camera lenses, exterior lamps and lamp lenses, mirrors, etc. Vehicles are typically provided with at least one and usually multiple windshield washers which are used to clear the field of vision in a windshield or rear backlight.  
           [0004]    Typically, a nozzle or spray device is provided adjacent to or as part of the windshield wiper to disperse a pattern of wash fluid onto the windshield prior to and during the wiping operation to improve the efficiency of the wiping operation so as to provide a clear field of vision for the driver or vehicle passengers. The wash fluid is typically stored in a reservoir in the engine compartment and is pumped through the spray device upon manual activation of a control actuator by the vehicle driver.  
           [0005]    Since it is known that warm or heated fluid provides better cleaning efficiency than cold fluid, it is known to provide a heated wash fluid to a vehicle window spray device. Various wash fluid heating devices have been developed, but all typically utilize a heat exchanger design wherein a heat source is disposed in a body through which the wash fluid flows. The wash fluid picks up heat in the heat exchange body which elevates its temperature prior to dispersion through the spray nozzle onto a vehicle window.  
           [0006]    However, such prior wash fluid heating devices are inefficient in terms of heat transfer capability as well as being able to only provide a small quantity or a short duration of heated wash fluid onto a vehicle window. Further, direct contact of the fluid with the heat source causes higher temperature hot spots in the fluid and lower temperature fluid portions which do not contact the heat source.  
           [0007]    The control circuit used to operate such windshield wash fluid heating devices must provide high amperage such as 50 amps at 12 volts. The switching devices in the control circuit, which typically utilize MOSFETs, generate considerable heat themselves, but still must be thermally insulated from the heated fluid.  
           [0008]    However, the temperature of the primary heating source and the heated fluid is much greater than the heat generated by the MOSFETs so that heat escaping from the thermal mass of the body of the heating device heats the upper portion of the heating device if the temperature gradient between the heating device and the surrounding ambient temperature across the upper plate or surface of the heating device is too high.  
           [0009]    Thus, it would be desirable to provide a fluid heater apparatus which provides a heated fluid in an efficient manner, which has improved operating efficiency, which provides heat balancing for the thermal mass, which balances the heating device temperature, and which reduces power consumption.  
         SUMMARY  
         [0010]    The present invention is a heater apparatus for elevating the temperature of a fluid.  
           [0011]    In one aspect, the heater apparatus includes a thermally conductive mass, heating means thermally coupled to the thermally conductive mass for imparting heat to the thermally conductive mass, and a fluid flow path formed in the thermally conductive mass between an inlet and an outlet. The fluid flow path contacts the heating means to absorb heat from the thermally conductive mass as fluid flows through the fluid flow path between the inlet and the outlet.  
           [0012]    In another aspect, the present invention is a wash apparatus including a fluid reservoir contain a wash fluid, a pump coupled to the fluid reservoir for pumping fluid from the reservoir, a spray nozzle fluidically coupled to the pump for discharging fluid pumped from the reservoir onto a cleanable surface, and the heater apparatus disposed in fluid flow communication between the pump, the reservoir and the nozzle.  
           [0013]    The inventive apparatus also includes a controller for supplying power to heater elements of the heater apparatus. The controller includes high amperage switching devices, such as MOSFETs mounted on a printed circuit board affixed to an upper plate joined to the thermal mass of the heater apparatus.  
           [0014]    According the present invention, a highly thermal conductive pad is located between the upper plate of the housing and a heater core. The pad conducts heat generated by the switching devices on the printed circuit board to the upper housing plate to lower the temperature gradient or differential across the housing so as to balance the temperature of the heating device thereby requiring less electrical power to maintain the heating apparatus at a preselected temperature.  
           [0015]    The fluid heater apparatus of the present invention affords a highly efficient heater apparatus which quickly raises and maintains fluid temperature to an operating temperature. The heater apparatus is constructed to provide balanced temperature across the heater for heat loss and reduced power consumption. The high amperage switching devices, such as MOSFETs, utilize the upper plate as a heat sink to inhibit heat loss and additionally reduce power consumption. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0016]    The various features, advantages and other uses of the present invention will become more apparent by referring to the following detail description and drawing in which:  
         [0017]    [0017]FIG. 1 is a block system diagram of a fluid heater apparatus according to the present invention used in an exemplary vehicle window wash fluid delivery system;  
         [0018]    [0018]FIG. 2 is a perspective view of a heater module according to one aspect of the present invention;  
         [0019]    [0019]FIG. 3 is an exploded perspective view of the heater module shown in FIG. 2;  
         [0020]    [0020]FIG. 4 is a perspective view, taken from the right side of FIG. 3, of the heater module of the present invention;  
         [0021]    [0021]FIG. 5 is a top perspective view of the heater module thermal mass;  
         [0022]    [0022]FIG. 6 is a bottom elevational view of the heater module thermal mass shown in FIG. 5;  
         [0023]    [0023]FIG. 7 is a plan view of the interior of the heater module shown in FIG. 4;  
         [0024]    [0024]FIG. 8 is a longitudinal, cross-sectional view of the heater module shown in FIGS.  2 - 7 ; and  
         [0025]    [0025]FIG. 9 is an enlarged, side cross-sectional view of a portion of the heater module shown in FIG. 8. 
     
    
     DETAILED DESCRIPTION  
       [0026]    Referring now to FIG. 1, there is depicted an environment in which a heater apparatus or module  10  constructed in accordance with the teachings of the present invention can be advantageously utilized. Although the following use of the heater module  10  of the present invention is described in conjunction with a vehicle window wash system, it will be understood that the present heater module may be employed in other applications requiring heated fluid, such as any cleaning system used to clean any vehicle window, i.e., the windshield, rear backlight, or side windows, as well as cleaning systems for vehicle mirrors, camera, lenses, or sensor covers, etc.  
         [0027]    As is conventional, a vehicle window  12 , such as a windshield, rear backlight or window, etc., has one or more fluid delivery devices, such as spray nozzles  14  located in a position to dispense or spray a pattern  16  of wash fluid onto the exterior surface of the window  12 . The dispersion of the wash fluid  16  is usually in conjunction with activation of a windshield wiper  18  over the window  12 .  
         [0028]    The wash fluid  16  is supplied from a fluid source, such as a reservoir or container  20 . The fluid in the reservoir  20  is pumped to the nozzle(s)  14  by means of a pump  22  usually located in close proximity or attached to the reservoir  20 .  
         [0029]    As is conventional, an on/off switch  24 , which may be mounted on a vehicle steering column stalk switch, is suppled with power from the vehicle battery  26  and enables the vehicle driver to control the on or off operation of the wash pump  22 .  
         [0030]    According to the invention, the wash fluid pumped from the reservoir  20  to the spray nozzles  14  is heated from ambient temperature to a predetermined higher temperature, such as 160° F.-170° F., by example only, by the heater module  10 . A suitable control circuit or controller  28  is provided for controlling the operation of the heater elements in the heater module  10 . The controller  28  is also supplied with electric power from the vehicle battery  26 . The controller  28  is activated by a “on” signal from the vehicle ignition  30  so as to heat the fluid contained within the flow paths in the heater module  10 , as described hereafter, whenever the vehicle ignition is in an “on” state.  
         [0031]    An optional on/off switch  25  may be connected between the battery  26  and the controller  28  to provide on and off operation for the entire heater system by disconnecting power to the controller  28 . This enables the heater system to be activated or remain in an inactive state at the selection of the vehicle driver. As described hereafter, the on/off switch  25  may also be replaced by a separate input signal to the controller  28  from an external signal source, such as a vehicle body controller, to provide for selective deactivation of the heater module  10  under certain circumstances, such as a thermal event, low battery power, etc.  
         [0032]    Referring now to FIGS.  2 - 9 , there is depicted one aspect of the heater module  10  according to the present invention.  
         [0033]    The heater module  10  includes a heat exchange mass or body  40  formed of a suitable high thermally conductive material. Although the mass  40  is described as being formed of diecast, molded or machined aluminum, other materials, either homogenous or non-homogenous, may also be employed. For example, the mass  40  can be formed of alumina particles, ceramic materials, etc.  
         [0034]    The mass  40 , as described in greater detail hereafter, includes a fluid flow path between an inlet  42  and an outlet  44 . The inlet and outlet  42  and  44 , respectively, receive a fitting  46  and an outer sleeve  48  which are joined together for receiving a fluid sealed connection to a fluid flow conduit, element or tube, not shown. The inlet  42  will be connected to receive the pump output from the window wash fluid reservoir  20 ; while the outlet  44  will be connected to the spray nozzle(s)  14 .  
         [0035]    As vehicles typically have several spray nozzles  14 , usually one for each of the two windshield wipers, and at least one nozzle  14  for the rear backlight or rear window wiper, it will be understood that the following description of a single heater module  10  for heating all of the fluid discharge from the fluid reservoir  20  will encompass multiple parallel paths, each containing a separate heater module, for heating fluid from the reservoir  20  for each different nozzle  14 .  
         [0036]    The heat exchange mass  40  is disposed within an insulated enclosure formed by a first cover  50  and a mating second cover  52 . The first and second covers  50  and  52  have complementary shapes with a major wall surface  54  and  56 , respectively, and a surrounding peripheral lip  60  and  62 , respectively.  
         [0037]    A necked-down end portion  64  and  66  is formed in each of the first and covers  50  and  52 , and forms an extension from one end of the respective major walls  54  and  56  as well as from the peripheral edge lips  60  and  62 . The necked-down portions  64  and  66 , when joined together, form an end cavity for receiving a connector assembly  70  which connects electrical conductors to the heating element(s) mounted in the joined first and second covers  50  and  52 .  
         [0038]    The first and second covers  50  and  52  and the heat exchange mass  40  are fixedly joined together, after the connector assembly  70  has been disposed in the extensions  64  and  66  of the first and second covers  50  and  52  by suitable means, such as by heat stake rivets or projections  76  projecting outwardly from opposite major surfaces of the heat exchange mass  40 . The projections  76  engage apertures in the major surfaces  60  and  62  of the first and second housing parts  50  and  52  and are heat welded together to join the first and second housing parts  50  and  52  together in a fixed connection.  
         [0039]    A pair of seal elements  71  and  72 , each having a peripheral shape substantially the same as the peripheral shape of the heat exchange mass  40  are disposed on opposite surfaces of the heat exchange mass  40  as shown in FIG. 3. The seal members  71  and  72  are formed of a high thermal resistant, insulating material. The seal members  71  and  72  seal the open ends of the flow paths through the heat exchange mass  40  as described hereafter.  
         [0040]    Upper and lower plates  73  and  74 , each also having a shape complimentary to the shape of the heat exchange mass  40 , are disposed in contact with the upper and lower seals  71  and  72 , respectively, and fixed thereto by suitable fastening means, such as nuts and bolts  75  which extend through apertures in each of the upper and lower plates  73  and  74 , the upper and lower seals  71  and  72  and the heat exchange mass  40 . The upper and lower plates  73  and  74  are formed of a good thermal conductive material, such as aluminum.  
         [0041]    As shown in detail in FIGS.  4 - 7 , the heat exchange mass  40  has a solid cubical shape formed of a first major surface  80 , a second opposed major surface  82 , and four sidewalls  84 ,  86 ,  88  and  90 , interconnecting the first and second surfaces  80  and  82 .  
         [0042]    A plurality of bores  92 ,  94 ,  96  and  98  are formed in the body  40  and project inwardly from the sidewall  84 . The bores  92 ,  94 ,  96  and  98  are each adapted for receiving one generally cylindrical heater element. As partially shown in FIG. 4, each bore, such as bores  96  and  98 , extend through the solid central portion of the mass  40  so as to be completely surrounded by the solid material of the mass  40 . This defines the mass  40  as a heat source after receiving heat from activation of the heater elements describe hereafter.  
         [0043]    In the aspect of the invention shown in FIGS.  4 - 7 , the heater elements are formed of “calrod”. Although different materials many be used, one example of a calrod construction is a Nichrome wire inside of a stainless steel sheath.  
         [0044]    By way of example only, at least one and preferably a plurality, i.e., two or three or more individual heater elements  100 ,  102  and  103 , with only heater elements  100 ,  102  being shown in FIG. 4, are disposed in the bores  96 ,  94  and  98 . The function of the one or more heater elements, such as heater elements  100  and  102 , will be described hereafter in conjunction with the description of the heater module  10 .  
         [0045]    As seen in FIGS. 4 and 7, one end  104 ,  106  and  107  of each heater element, elements  100 ,  102  and  103 , respectively, projects outwardly through the sidewall  84  of the body  40 . The ends  104 ,  106  and  107  of the heater elements  100 ,  102  and  103  respectively, engage individual terminals  108  extending from a printed circuit board  150  mounted by means of fasteners, adhesives, etc., to an exterior surface of the upper plate  73 . Conductive traces in the printed circuit board connect the terminals  108  with the connector terminals  70  to receive power from the vehicle electrical system.  
         [0046]    The circuit board  150  is fixedly mounted by suitable fasteners such as screws. One of the terminals  108  acts as a ground lead in that an end portion is disposed in contact with the outer stainless steel sheath of each heater element or calrod  100 ,  102  and  103 . Another of the terminals  108  is the power lead for calrod  100 . This terminal  108  provides electric power to the calrod  100  through contact with the end  104  of heater element  100  in the grid assembly  110 .  
         [0047]    The other two terminals  108  provide power connections to the other two heater elements  102  and  103 . A switch, not shown, may be interposed between the terminal  108  and the other two terminals  108  to selectively provide power to the other two terminals  108  when power is supplied to the power terminal. This switch can be a bi-metal switch, for example, which will open at a predetermined temperature, such as 50° C., as described hereafter. Alternately, a switch controlled by the circuitry on the circuit board  150  of the controller  28  will selectively connect power from the power terminal  108  to the other terminals  108 . This provides the controller  28  with the capability, when receiving suitable external input signals from the vehicle body controller, for example, to deactivate the heater module  10 , during the occurrence of low vehicle battery power, a thermal event, etc.  
         [0048]    As shown in FIGS.  4 - 7 , the thermally conductive mass  40  includes a fluid flow channel or path which extends from the inlet  42  to the outlet  44 . The fluid flow path has a labyrinthian path formed of a first fluid flow path portion  130  and a second fluid flow path or channel  132  which are connected at a generally centrally disposed bore  134 . The first fluid flow channel  130  has a generally spiral shape formed of alternating straight and arcuate sections which alternate create laminar and turbulent flow of the fluid passing through the first flow channel  130  to maximize the heat absorption of the fluid from the adjoining walls of the mass  40 . Further, the first fluid flow channel  130  has an inward directed spiral shape from the inlet  42  to the bore  134  to minimize temperature differential between adjoining portions of the spiral shaped first flow channel  130 .  
         [0049]    As shown in FIG. 6, the second fluid flow channel  132  has a substantially identical spiral shape. However, fluid flow through the second fluid flow channel  132  is in a outward spiral direction from the bore  134  to the outlet  44 . As described above, the seal members  71  and  72  sealingly close the open ends of the first and second fluid flow channels  130  and  132 .  
         [0050]    Thus, fluid flow through the first and second flow channels  130  and  132  starts from the inlet  44  then continues in a spirally inward directed manner through the first flow channel  130  to the central passage or bore  134 . Upon exiting the central passage  134  into the second flow channel  132 , fluid flow progresses in an outward spiral direction through the second flow channel  132  to the outlet  44 .  
         [0051]    In operation, the heater module  40  will be interconnected in the vehicle wash fluid flow lines between the pump  22  and the spray nozzle(s)  14  as shown in FIG. 1. The external connector is then connected to the connector housing  70  to provide electric power from the vehicle battery  26  and the controller  28  to the heater elements  100 ,  102  and  103 , in the heat exchange body  40 .  
         [0052]    Assuming that the first and second fluid flow channels  130  and  132  in the body  40  are filled with fluid, when the controller  28  activates the heater elements  100 ,  102  and  103 , the heater elements  100 ,  102  and  103  will begin radiating heat which will immediately raise the temperature of the entire surrounding portion of the heat exchange body  40 . Heat from the body  40  will, in turn, be radiated to and absorbed by the fluid disposed in the first and second flow channels  130  and  132 .  
         [0053]    The straight and arcuate portions of the first and second fluid flow channels  130  and  132  create alternating turbulent and laminar flow regions in the fluid flowing through the mass  40  which causes movement of the fluid in the first and second flow channels  130  and  132  bringing all molecules in the fluid in contact with the wall of the body  40  forming the first and second flow channels  130  and  132  to efficiently absorb the maximum amount of heat possible. This causes the temperature of the fluid to be quickly raised from ambient temperature at the inlet  42  to approximately 160° F.-170° F. at the outlet  44  in approximately sixty seconds.  
         [0054]    The fluid in the first and second fluid flow channels  130  and  132  removes or absorbs heat from the thermal mass  40  thereby increasing the fluid temperature by physical contact with the mass  40 . The heater elements  100 ,  102  and  103  maintain the heat of the thermal mass  40  at a predetermined temperature thereby preventing hot spots from occurring in the fluid. Normally, hot spots would occur when the fluid comes in direct contact the heater elements  100 ,  102  and  103 . Fluid which is not in physical contact with the heater elements  100 ,  102  and  103  passes the heater elements  100 ,  102  and  103  by and does not absorb heat. By heating the thermal mass  40 , the physical hot contact area is increased along with an increase in heat transfer efficiency. This requires less energy to heat the same volume of fluid.  
         [0055]    Although a single heater element  100  may be employed as the heat source in the body  40 , multiple heater elements, with two or three heater elements,  100 ,  102  and  103 , being described by way of example only, have been found to be most advantageous. The controller  28  can activate all of the plurality of heater elements  100 .  102  and  103  upon receiving a first command to dispense heated wash fluid onto the windshield  12 . This generates a maximum amount of heat to the body  40  to immediately and quickly raise the temperature of the body  40  high enough to transfer sufficient heat to the fluid in the fluid flow channels  130  and  132  to raise the temperature of the fluid to the desired discharge temperature of 160° F.-170° F. The multiple heater elements  100 ,  102  and  103  can remain in an activated state by the controller  28  if immediate and successive commands from the on/off switch  24  are supplied by the vehicle driver to supply additional charges of fluid onto the windshield  12 .  
         [0056]    At the completion of the fluid dispensing operation, and during other periods of non-fluid dispensing while the vehicle ignition is still “on”, the controller  28  can cyclically activate one or more of the heater elements, such as heater element  100 , to maintain the temperature of the fluid in the first and second flow channels  130  and  132  at an elevated temperature for immediate discharge onto the windshield  12  when activated by the on/off switch  24 . This minimizes electrical power requirements on the vehicle battery  26 .  
         [0057]    Although the controller  28  can provide separate switchable signals to each of the heater elements  100 ,  102  and  103 , in order to control each heater element  100 ,  102  and  103  separately under program or logic control, one simple approach includes the bi-metal element or a switch mounted between the power connections to one terminal  108  and each of the other terminals  108  connected to the additional heater elements  102  and  103 . The bi-metal element can be set to open at a predetermined temperature, such as 50° C., thereby deactivating the associated heater element. This enables the additional heater elements  102  and  103 , for example, to remain deactivated until a high heat requirement is initiated.  
         [0058]    The fasteners  75  also fix the printed circuit board  150  which forms part of the controller  28  onto the heat exchange body  40 , typically over the first plate  140 .  
         [0059]    Although the following description of the use of high amperage switching devices known as MOSFETs, are used as part of the controller  28  and to provide the necessary high current, typically 50 amps at 12 volts, to the heating elements  104 ,  106  and  107  in the thermal mass  40 , other high amperage switching devices may also be employed. Any number of MOSFETs  156  can be mounted in any configuration on the printed circuit board  150 .  
         [0060]    A plurality of bores  158  are optionally formed through the printed circuit board  150 . The bores  158  improve heat flow between the switching devices on the printed circuit board (PCB)  150  and the underlying first plate  73 .  
         [0061]    A temperature sensor  159 , such as a PTD, is mounted on the printed circuit board  150 , typically over or adjacent to the bores  158 . The temperature sensor  159  measures the temperature of the printed circuit board  150  and provides a temperature proportional signal to the controller  28  which is used by the controller  28  to control the on/off cycle of the heating elements  104 ,  106  and  107 .  
         [0062]    To further enhance transfer of the heat generated by the MOSFETs  156  to the first plate  140 , a highly conductive pad or plate  160 , hereafter referred to as a sill pad  160 , is interposed in contact between the printed circuit board  150  and the first plate  23  as shown in FIGS. 3, 8 and  9 . The sill pad  160  typically has a planar shape and dimensions to extend over at least a portion of the first plate  73 . The pad  160  isolates stray electrical currents to negative ground through the screws  75 , provides a positive contact between the MOSFETs and the thermal mass  40 , and stabilizes heat loss through the adjacent cover by maintaining the temperature of the plate  73  at a higher temperature to thereby create a lower temperature differential or gradient with respect to the thermal mass  40 .  
         [0063]    As shown in FIG. 9, a projection extends from the thermal mass  40 .  
         [0064]    The sill pad  160  preferably has a higher thermal conductivity than the thermal conductivity of the plate  73  to efficiently draw heat generated by the MOSFETs  156  to the plate  73  thereby maintaining the temperature of the plate  73  at an elevated temperature. This elevated temperature of the plate  73  is higher than the normal temperature of the plate  73  caused by heat escaping from the sides of the thermal mass  40  around the seals  71  and  72 .  
         [0065]    The projection  164  and the thermal mass  40  engage apertures in the plate  73  as shown in FIGS. 8 and 9. A portion of the sill pad  160  extends over one of the projection  164  as shown in FIG. 9 and may be disposed in contact or registry with the projection  164  to provide a direct heat exchange path from the thermal mass  40  to the sill pad  160 .  
         [0066]    In summary, there has been disclosed a fluid heater apparatus which efficiently heats fluid to a desired discharge temperature with minimum power requirements. The fluid heater apparatus is provided with a unique temperature balancing means which decreases the temperature differential between the thermal mass and exterior components of the apparatus so as to reduce power consumption required to maintain the heated fluid at a desired discharge temperature.