Abstract:
A system ( 10 ) and method for removing heat from an engine compartment in a motor vehicle where heat generated by operation of a heat engine ( 12 ) that propels the vehicle tends to collect. Engine heat is collected in a thermofluid in a reservoir forming an evaporator ( 14 ) where the thermofluid absorbs heat sufficient to evaporate it. The vapor naturally migrates to a condenser ( 22 ) that is cooled sufficiently to condense the vapor back to liquid phase. The liquid falls by gravity back to the condenser.

Description:
FIELD OF THE INVENTION 
   This invention relates to motor vehicles that are powered by heat engines and more particularly to a system for removing heat from any location in a vehicle that is prone to undesirably high temperatures, especially heat generated by a heat engine in an engine compartment. 
   BACKGROUND OF THE INVENTION 
   The nature of the thermodynamic cycle on which a heat engine operates requires that heat of combustion be rejected to a waste heat medium. In an air-cooled engine, the medium is air that surrounds the engine. In a liquid-cooled engine, the medium is liquid that circulates through coolant passages in the engine where it is heated before passing to a radiator where the heat is transferred to air that flows through the radiator, although some amount of heat is also rejected directly to air surrounding the engine by radiation and convection. 
   A motor vehicle typically houses the engine in some sort of a compartment. Most cars and trucks have a front engine compartment that is bounded frontally by a front end structure that includes the radiator and rearwardly by the occupant compartment, or cab. The sides of the engine compartment are bounded by fender structures, and the top by a hood that can be opened to provide access to the engine compartment. 
   Underhood temperature is a matter of concern to vehicle designers because excessively high temperatures can have adverse effects on the performance and durability of various devices and systems. Space within an engine compartment is often at a premium, and the more crowded an engine compartment becomes, more components are exposed to engine compartment heat, and the movement of air through the engine compartment that can aid to some extent in limiting underhood temperatures becomes more difficult. 
   Engine operating temperature is affected by various factors. Higher operating temperatures may be necessary in order to enable compliance with relevant emission control regulations. That can add to engine compartment heating. 
   The cooling system of a liquid cooled engine is typically sized to allow the engine to operate at a desired engine operating temperature, but even when a cooling system is sized to accommodate higher engine operating temperatures, more engine heat is transferred by convention, conduction, and/or radiation to devices in the engine compartment, to the structure bounding the engine compartment, and to air in the engine compartment, and that heat isn&#39;t removed by the liquid cooling system. Moreover, placement of a radiator in certain vehicles causes at least some of the engine heat that is rejected at the radiator to pass through the engine compartment. 
   SUMMARY OF THE INVENTION 
   The present invention relates to a system for removing significant engine heat from an engine compartment in a motor vehicle, especially heat generated by operation of a heat engine in an engine compartment. By using the thermosyphon principle, the inventive system enables heat to be removed by natural circulation of thermofluid thereby rendering the system passive in the sense that it does not draw power from either the engine or the electrical system. The amount of heat that can be removed can be large enough to provide a significant limitation on excessive underhood temperatures. 
   The invention can be adapted for various types of vehicles, including those having front engine compartments as described above, and also “cab-over” vehicles. Moreover, components of the inventive system can be constructed to fit in ways that are not overly intrusive. For example, an evaporator can be constructed with a small vertical dimension (thickness) and a more expansive length and width for overlying the expanse of an engine both fore-and-aft and side-to-side. 
   According to one generic aspect, the invention relates to a motor vehicle comprising a chassis supporting a heat engine that propels the vehicle, and a thermosyphon system that comprises a collector that collects heat generated by running the engine and transfers collected heat to a thermofluid that due to heating is forced to circulate to a dissipator where heat is rejected and then back to the collector to collect more heat. 
   According to another generic aspect, the invention relates to a method of removing heat from a space in a motor vehicle where heat generated by operation of a heat engine that propels the vehicle tends to collect. Engine heat is collected via a collector that transfers collected heat to a thermofluid to force the thermofluid to circulate to a dissipator where heat is rejected and from the dissipator back to the collector. 
   The foregoing, along with further features and advantages of the invention, will be seen in the following disclosure of a presently preferred embodiment of the invention depicting the best mode contemplated at this time for carrying out the invention. This specification includes drawings, now briefly described as follows. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic diagram illustrating principles of a thermosyphon in application to a motor vehicle engine compartment in accordance with the present invention. 
       FIG. 2  is a left side elevation view of an internal combustion engine inside an engine compartment at a front of a motor vehicle, including a portion of a thermosyphon system. 
       FIG. 3  is a left side elevation view similar to a portion of  FIG. 2  but showing a further embodiment of the invention. 
       FIG. 4  is a left side elevation view of an internal combustion engine inside an engine compartment of a cab-over type motor vehicle, including a portion of a thermosyphon system. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1  shows a schematic representation of a thermosyphon system  10  associated a heat engine  12  in a motor vehicle, such as a truck. Engine  12  is mounted on a chassis frame and forms the powerplant that propels the vehicle. 
   System  10  comprises a reservoir  14  and a heat collector  16 . The latter is disposed to collect heat from engine  12  via conduction and/or convention, and/or radiation. Removal of heat by conduction occurs when collector  16  is placed in physical contact with engine  12 . Removal of heat by convection occurs when air that has been heated passes across a surface of collector  16 . Removal of heat by radiation occurs when collector  16  is radiantly heated by engine  12 . Collector  16  transfers collected heat to thermofluid  18  in reservoir  14 . 
   By making collector  16  a “black body” as that term is understood in physics, it becomes an ideal absorber of radiant heat. Hence, a surface of collector  16  is exposed to the radiant heat source, and it is through that surface that collector  16  is heated. Heat is removed from collector  16  by transfer to thermofluid  18  in reservoir  14 . Because  FIG. 1  is schematic, it should not be construed to imply that collector  16  is disposed entirely inside reservoir  14 . A collector can be a separate element assembled to a reservoir, or it can be a portion of a wall of the reservoir. 
   System  10  comprises a closed circuit through which thermofluid  18  naturally circulates when the system is removing heat from engine  12 . A conduit  20  conveys thermofluid from reservoir  14  to a dissipater, or condenser,  22 . A conduit  24  conveys thermofluid from dissipater  22  to reservoir  14 . 
   Reservoir  14  forms an evaporator where thermofluid in liquid phase is evaporated to gas phase by engine heat collected by collector  16  and transferred to the thermofluid. The rate of evaporation depends on factors such as the temperature to which liquid is heated, with heating of liquid to its boiling point typically creating the greatest rate of evaporation. 
   Because the vapor tends to rise, it migrates through conduit  20  to the higher elevation of dissipater  22 . The latter is constructed and arranged to transfer thermofluid heat to any suitable medium, such as air  26 , at a location remote from the engine compartment within which engine  12  is located. Consequently, as the thermofluid vapor gives up heat to air  26 , it begins to condense within dissipater  22 . Liquid fluid collects at the bottom of dissipater  22  where the entrance to conduit  24  is located. The condensate then falls by gravity through conduit  24  to return to reservoir  14  where it can be re-heated. 
   Thus, a continuous natural circulation of thermofluid through system  10  can continually remove heat from the engine compartment. 
     FIG. 2  shows placement of a suitably shaped reservoir  14  on the underside of a hood  30  covering an engine compartment at the front of a motor vehicle forward of an occupant compartment or cab. The reservoir is relatively small vertically and has a broad horizontal expanse to overlie engine  12  in spaced relation to the top of the engine when hood  30  is closed as shown. This means that the reservoir&#39;s average vertical dimension is smaller than its average horizontal dimensions. Conduits  20  and  24  are arranged to flex with the hood as the latter swings open to expose engine  12  inside the engine compartment. The engine compartment is forwardly bounded by a front end  32  that includes a cooling module  34  containing a radiator. Dissipater  22  is not specifically shown, but is placed at any suitable location.  FIG. 2  does not specifically identify the collector by its reference numeral, but this is an example of where the collector can be incorporated as the bottom wall of the reservoir constructed of a material that is a good absorber of radiant energy. 
     FIG. 3  shows placement of a suitably shaped reservoir  14  atop engine  12  below the hood, which is not specifically shown. This reservoir is also relatively small vertically and has a broad horizontal expanse to overlie the engine with some clearance to both the top of the engine and also to the overlying hood. Conduits  20  and  24  do not have to flex with opening and closing of the hood. Dissipater  22  is not specifically shown, but is placed at a suitable location. Here too the reservoir wall can form the collector. 
     FIG. 4  shows placement of a suitably shaped reservoir  14  on the underside of the floor of the cab  36  of a “cab-over” type vehicle where the reservoir is in overlying relation to engine  12 . A cooling module  34  is disposed in front of engine  12 . This reservoir is also relatively small vertically and has a broad horizontal expanse to overlie engine  12  in spaced relation to the top of the engine. Conduits  20  and  24  do not have to flex in as much as the entire cab swings upwardly and forwardly to expose the engine. Dissipater  22  is also not specifically shown, but is placed at a suitable location. An aerodynamic pod is mounted atop the cab roof, and the dissipator can associated and/or integrated with the pod to render it effective for heat transfer to air without being visibly prominent. 
   It is believed that certain components that convey fluids involved in combustion processes occurring in a heat engine can benefit by association with a thermosyphon system. For example, an EGR (exhaust gas recirculation) valve conveys hot exhaust gases from the exhaust system to the intake system and often requires an associated an EGR cooler to cool the exhaust gases before they enter the valve. Associating the thermosyphon system with an EGR valve could eliminate the need for a separate EGR cooler. Similarly charge air from the compressor of a turbocharger typically passes through a charge air cooler, and use of the thermosyphon system to cool charge air could perform that function. 
   Because a motor vehicle may operate in geographical areas that experience a substantial range of temperatures, a thermofluid should be selected for suitability over the relevant temperature range. 
   While a presently preferred embodiment of the invention has been illustrated and described, it should be appreciated that principles of the invention apply to all embodiments falling within the scope of the following claims.