Patent Publication Number: US-2020288598-A1

Title: Electronics cooling using bimetal

Description:
TECHNICAL FIELD 
     The disclosed embodiments relate generally to cooling systems and in particular, but not exclusively, to a cooling system using bimetal elements. 
     BACKGROUND 
     Modern cooling systems have become quite complex. Typically they involve multiple temperature sensors that are coupled by wire to a central computer or controller. The central computer is also coupled to a cooling or heating source or to motors, solenoids, or other activation mechanisms that can directly flow from a cooling or heating source to the area that requires heating or cooling, as determined by the central computer based on input received from its multiple temperature sensors. 
     Although they work well, these modern cooling systems have various disadvantages. The large number of components, and the labor involved in their installation and tuning, makes the systems more expensive. The large number of components also decreases system reliability, because with more components in the system there is a higher probability of a component failure. 
     SUMMARY 
     Embodiments are disclosed of an apparatus including a first enclosure having an interior that is at a first temperature and a second enclosure having an interior that is at a second temperature. An opening allows fluid to flow between the interior of the first enclosure and the interior of the second and enclosure. A bimetal valve is positioned in the opening to regulate fluid flow between the first enclosure and the second enclosure depending on the first temperature or on the difference between the first temperature and the second temperature. 
     Embodiments are disclosed of a system that includes a vehicle. An electronics compartment is positioned within the vehicle, and an interior of the electronics compartment is at a first temperature. A cooling duct is positioned within the vehicle, and the interior of the cooling duct is at a second temperature. An opening allows fluid to flow from the cooling duct into the electronics. A bimetal valve positioned in the opening regulates fluid flow between the cooling duct and the electronics compartment depending on the first temperature or on the difference between the first temperature and the second temperature. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Non-limiting and non-exhaustive embodiments of the present invention are described with reference to the following figures, wherein like reference numerals refer to like parts throughout the various views unless otherwise specified. 
         FIGS. 1A-1B  are schematic drawings of an embodiment of a cooling system. 
         FIGS. 2A-2D  are schematic drawings of an embodiment of a bimetal valve in the cooling system of  FIGS. 1A-1B . 
         FIGS. 3A-3B  are schematic drawings of another embodiment of a bimetal valve in the cooling system of  FIGS. 1A-1B . 
         FIGS. 4A-4B  are schematic drawings of another embodiment of a bimetal valve in the cooling system of  FIGS. 1A-1B . 
         FIG. 5  is a plan view schematic of a vehicle illustrating an embodiment of a vehicle application of the cooling system of  FIGS. 1A-1B . 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments are disclosed of a cooling system that includes a bimetal valve to regulate the flow of cooling fluid into an enclosure with heat-generating components such as electronics. The bimetal valve automatically directs cooling air into the enclosure when needed, thus eliminating the need for complex and expensive computers, sensors and their associated wiring and software. 
       FIGS. 1A-1B  illustrate an embodiment of cooling system  100  including a bimetal valve  108 ;  FIG. 1A  illustrates the bimetal valve when closed,  FIG. 1B  when open. System  100  includes a first enclosure  102  and a second enclosure  104 . An opening  106  permits a fluid (e.g. air) such as air in one embodiment, to flow between the first and second enclosures. As used in this application the meaning of the term “fluid” is the meaning used in physics: a fluid can be any material or substance capable of flowing, which can include liquids, gases, and plasmas. In an embodiment where the fluid is a gas, the fluid can be a gas mixture such as air, but in other embodiments the fluid can be a pure gas, such as nitrogen. In an embodiment where the fluid is a liquid, the fluid can be water, automotive anti-freeze (mostly ethylene glycol), or some other liquid with the desired thermal characteristics. A bimetal valve  108  is positioned in opening  106  block or unblock the opening, thus regulating the flow of fluid between first enclosure  102  and second enclosure  104 . 
     First enclosure  102  is bounded by a housing or other combination of impermeable surfaces  101  and has an interior within which the fluid, air in one embodiment, is at temperature T 1 . The interior of first enclosure  102  can have therein at least one heat-generating component. In an embodiment in which first enclosure  102  is an electronics compartment in a vehicle, the heat-generating components can include one or more of the illustrated components: a stereo receiver, a stereo amplifier, a controller, a computer, and vehicle control electronics. Some heat-generating components can be partially in the interior of first enclosure  102  and partially outside. A display, for instance, can have its screen outside the enclosure where a user can see it while having other parts of the display within the enclosure. Opening  106 , when not blocked by bimetal valve  108 , permits fluid to flow in or out of first enclosure  102 , while one or more outlets  112  allow fluid to flow out of first enclosure  102 . 
     Second enclosure  104  is bounded by a housing or other combination of solid surfaces  105  and has an interior within which the fluid, air in one embodiment, is at temperature T 2 . Fluid in second enclosure  104  can be at a higher or lower pressure than the fluid in first enclosure  102  and/or can be made to flow through the enclosure, for instance by a fan or pump (not shown) coupled to the second enclosure. In a vehicle embodiment, second enclosure  104  can be a cooling duct coupled to the vehicle&#39;s air conditioning system, or can be a duct that collects atmospheric air from outside the vehicle (see, e.g.,  FIG. 5 ). 
     Second enclosure  104  is fluidly coupled to first enclosure  102  by opening  106 . Opening  106  allows fluid to flow between the first and second enclosures. In one embodiment fluid can flow from the first to the second enclosure, but in other embodiments the fluid can flow the other way, from the second enclosure to the first. In still other embodiments, fluid can flow both ways. In the illustrated embodiment second enclosure  104  is adjacent to first enclosure  102 , such that opening  106  is formed by alignment of an opening in housing  101  with a similar opening in housing  105 . But other embodiments can have different configurations of opening  106 . In one embodiment, for instance, opening  106  can be a duct or other fluid conduit between first enclosure  102  and second enclosure  104 . 
     A bimetal valve  108 , together with a seal  110  around all or part of its perimeter, cover opening  106 ; when closed the bimetal valve  108  prevents fluid from flowing between the first and second enclosures, but when open the bimetal valve permits fluid to flow between the first and second enclosures. Bimetal valve  108  includes a bimetal element that is designed to open or close automatically based on the temperature difference between the interiors of the first and second enclosures—i.e., based on T 1 −T 2 . Generally, the design of bimetal valve  108  can take into account one or more of the following factors:
         The temperature range ΔT in which the door will be used.   The maximum temperature the door will experience.   Movement, force, or both movement and force, required of the door.   Space limitations.   Service conditions.
 
Embodiments of bimetal valve  108  are described below in connection with  FIGS. 2A-2B, 3A-3B, and 4A-4B .
       

     In one embodiment of operation of cooling system  100 , the temperature inside first enclosure  102  is T 1  and the temperature inside second enclosure  104  is T 2 , with T 2  less than T 1 . The fluid in second enclosure  104  can be pressurized or made to flow with a fan or pump (not shown) coupled to the second enclosure. Initially bimetal valve  108  is closed, as shown in  FIG. 1A , so that no fluid can flow between the first and second enclosures. The one or more heat generating components in the interior of first enclosure  102  heat the fluid in the interior, so that temperature T 1  slowly increases over time and the temperature difference ΔT=T 1 −T 2  between the first and second enclosures slowly increases. As temperature difference ΔT increases, bimetal valve  108  opens, as shown in  FIG. 1B , so that there is an inflow of cooler fluid from second enclosure  104  into first enclosure  102  through opening  106 . The cooler fluid flowing into first enclosure  102  flows over the heat-generating components, which transfer heat to the flowing fluid. The fluid then flows out of first enclosure  102  through outlets  112 , carrying the heat extracted from the heat-generating components out of the enclosure. 
     Because T 2  is lower than T 1 , as fluid flows from second enclosure  104  into first enclosure  102  and extracts heat from the heat-generating components inside, temperature T 1  will begin to fall and ΔT decreases. As ΔT decreases, bimetal valve  108  closes until it returns to its fully-closed position, as shown in  FIG. 1A , at which time the heating/cooling cycle begins again. Hence bimetal valve  108  regulates the flow of cooling air into first enclosure  102 , thus also regulating temperature T 1 . 
     Other embodiments of operation of system  100  are also possible. For instance, in another embodiment the pressure in second enclosure  104  can be kept lower than the pressure in first enclosure, so that when bimetal valve  108  opens air is drawn into first enclosure  102  through outlets  112  and exits though opening  106  into second enclosure  104 . In other words, such an embodiment would reverse the flow direction compared to the other embodiment described above. 
       FIGS. 2A-2D  together illustrate an embodiment of a cooling system  200  with a bimetal valve  202 .  FIGS. 2A and 2B  show system  200  with bimetal valve  202  in its closed and open positions, respectively, while  FIGS. 2C-2D  illustrate an embodiment of the construction of bimetal valve  202 . Cooling system  200  is substantially similar to cooling system  100 : as before, opening  106  between first enclosure  102  and second enclosure is covered by bimetal valve  202 , aided by seal  204 . The primary difference between cooling systems  100  and  200  is the embodiment of bimetal valve  202 . 
     Bimetal valve  202  is fixed to an edge of opening  106  and is a door  205  having substantially the same shape as opening  106 . As shown in  FIGS. 2C-2D , door  205  is formed from a pair of layers  208  and  210  laminated together. Layers  208  and  210  are made of different materials—typically but not necessarily metals or metal alloys—having different coefficients of thermal expansion, so that upon being exposed to an increase in temperature the metals expand by a different amount, thus deforming the door. In another embodiment, door  205  can be made partially of bimetal and partially of a non-bimetal material, so that deflection of the bimetal part deflects the non-bimetal part, thus opening and closing bimetal valve  202 . Bimetal laminates that can be used in bimetal valve  202  are commercially available, for instance from Engineered Material Solutions of Attleboro, Mass., USA. 
     To help bimetal valve  202  prevent fluid flow between the first and second enclosures, a seal  204  can be fixed around the perimeter of opening  106 . Alternatively, a seal  206  can be fixed around the perimeter of bimetal valve  202 . In still other embodiments a multi-part seal including seal  204  and seal  206  can be used. 
     In one embodiment, cooling system  200  operates similarly to cooling system  100 . Initially bimetal valve  202  is closed, as shown in  FIG. 2A , so that no fluid flows between the first and second enclosures. The one or more heat generating components in the interior of first enclosure  102  heat the fluid in the interior, so that temperature T 1  slowly increases and the temperature difference ΔT=T 1 −T 2  between the first and second enclosures slowly increases. As temperature difference ΔT increases, door  205  deforms as the different material layers  208  and  210  that form the door expand by different amounts in response to the temperature increase. As door  205  deforms, its free end (the end opposite where it is fixed to an edge of opening  106 ) deflects by a distance D, as shown in  FIG. 2B , unsealing opening  106  and allowing an inflow of cooler fluid from second enclosure  104  into first enclosure  102  through opening  106 . Deflection distance D will depend mostly on temperature difference ΔT and on the particular combination of materials used to build door  205 . For an embodiment with a cantilever-type door such as door  205 , deflection distance D can be calculated according to the formula: 
     
       
         
           
             
               D 
               = 
               
                 
                   
                     0 
                     . 
                     5 
                   
                    
                   3 
                    
                   
                     F 
                      
                     
                       ( 
                       
                         
                           T 
                            
                           2 
                         
                         - 
                         
                           T 
                            
                           1 
                         
                       
                       ) 
                     
                   
                    
                   
                     L 
                     2 
                   
                 
                 t 
               
             
             , 
           
         
       
     
     where F is the flexivity of the door (e.g., (in/in)/(° F.)); T 2 −T 1  is the temperature change in ° F., L is the length of the door, and t is the door&#39;s thickness. Depending on the materials used, in one embodiment the useful deflection temperature change for door  205  can be from −70° C. to 540° C., although the exact range can also depend on the dimensions of the materials used. Once door  205  opens, the cooler fluid flowing into first enclosure flows over the heat-generating components, which transfer heat to the flowing fluid. The flowing fluid then exits first enclosure  102  through outlets  112 , carrying the heat extracted from the heat-generating components out of the enclosure. 
     Because T 2  is lower than T 1 , as fluid flows from second enclosure  104  into first enclosure  102  and extracts heat from the heat-generating components inside, temperature T 1  will begin to fall and ΔT decreases. As ΔT decreases, door  205  again deforms, but in the opposite direction, until it returns to its fully-closed state (i.e., D=0) as shown in  FIG. 1A , at which time the heating/cooling cycle begins again. Hence bimetal valve  108  regulates the flow of cooling air into first enclosure  202 , thus also regulating temperature T 1 . 
       FIGS. 3A-3B  together illustrate an embodiment of a cooling system  300 .  FIG. 3A  shows system  300  with its bimetal valve  302  in the closed position,  FIG. 3B  in the open position. Cooling system  300  is substantially similar to cooling system  200 : as before, opening  106  between first enclosure  102  and second enclosure is covered by bimetal valve  302 , aided by seal  308 . The primary difference between systems  300  and  200  is the embodiment of bimetal valve  302 . 
     In system  300 , bimetal valve  302  includes a rigid door  303  coupled to a bimetal coil  306 . Rigid door  303  has substantially the same shape as opening  106  and can formed from metals or non-metals. The rigid door is coupled by a hinge  304  to an edge of opening  106 . To help bimetal valve  302  prevent fluid flow between the first and second enclosures, a seal  308  can be fixed around the perimeter of opening  106  or fixed around the perimeter of rigid door  303 . Bimetal coil  306  is coupled to one of the walls of first enclosure  102  and also coupled to rigid door  303 . Bimetal coil is a coil formed from multiple layers of materials—typically but not necessarily metals or metal alloys—with different coefficients of thermal expansion, such that when heated the bimetal coil converts the different expansions of the two metals into a rotational motion. Bimetal coils are commercially available, for instance from Engineered Material Solutions of Attleboro, Mass., USA. 
     In one embodiment, cooling system  300  operates similarly to cooling systems  100  and  200 , although because bimetal coil  306  is entirely within first enclosure  102  its operation depends more heavily on temperature T 1  instead of on the temperature difference ΔT=T 1 −T 2 . Initially bimetal valve  302  is closed, as shown in  FIG. 3A , so that no fluid flows between the first and second enclosures. The one or more heat generating components in the interior of first enclosure  102  heat the fluid in the interior, so that temperature T 1  slowly increases over time, as does temperature difference ΔT between the first and second enclosures. As T 1  increases, bimetal coil  306  slowly deforms and, as it does, it rotates door  303  about hinge  304 . As door  303  rotates about hinge  304 , its free end (i.e., the end opposite hinge  304 ) deflects by an angle A, as shown in  FIG. 3B , unsealing opening  106  and allowing an inflow of cooler fluid from second enclosure  104  into first enclosure  102  through opening  106 . Deflection angle A will depend mostly on the change in temperature T 1  to which bimetal coil  306  is exposed and on the particular combination of materials used to build bimetal coil  306 . For an embodiment with a bimetal coil  306 , deflection angle A can be calculated according to the formula: 
     
       
         
           
             
               A 
               = 
               
                 
                   6 
                    
                   7 
                    
                   
                     F 
                      
                     
                       ( 
                       
                         
                           T 
                            
                           2 
                         
                         - 
                         
                           T 
                            
                           1 
                         
                       
                       ) 
                     
                   
                    
                   L 
                 
                 t 
               
             
             , 
           
         
       
     
     where F is the flexivity of the door (e.g., (in/in)/(° F.)); T 2 −T 1  is the temperature change in ° F., L is the length of the coil (i.e., the full length of the material measured along coil, or the length of the coiled material if uncoiled), and t is the thickness of the coil material. Depending on the materials used, in one embodiment the useful deflection temperature change for coil 306 can be from −70° C. to 540° C., although the exact range can also depend on the dimensions of the materials used. Once bimetal coil  306  deflects through angle A and opens door  303 , the cooler fluid flowing into first enclosure flows over the heat-generating components, which transfer heat to the flowing fluid. The flowing fluid the flows out of first enclosure  102  through outlets  112 , carrying the heat extracted from the heat-generating components out of the enclosure. 
     Because T 2  is lower than T 1 , as fluid flows from second enclosure  104  into first enclosure  102  and extracts heat from the heat-generating components inside, temperature T 1  will begin to fall and ΔT decreases. As T 1  decreases, bimetal coil  306  deforms the opposite way until it returns to its fully-closed state (i.e., D=0) as shown in  FIG. 3A , at which time the heating/cooling cycle begins again. Hence bimetal valve  302  regulates the flow of cooling air into first enclosure  102 , thus also regulating temperature T 1 . 
       FIGS. 4A-4B  together illustrate an embodiment of a cooling system  400 .  FIG. 4A  shows system  400  with its bimetal valve in the closed position,  FIG. 4B  in the open position. Cooling system  400  is substantially similar to cooling system  200 : as before, opening  106  between first enclosure  102  and second enclosure  104  is covered by a bimetal valve  402 . The primary difference between cooling systems  200  and  400  is the construction of bimetal valve  402 . In system  400 , bimetal valve  402  is a door having substantially the same shape as opening  106  and surrounded by a seal  404  that can be fixed to the edges of opening  106 . But rather than being a single unit like door  205 , bimetal valve  402  is a louvered door made up of multiple small sections or slats  403 . Each section  403  has substantially the same construction as door  205  and operates substantially as described above in connection with system  200 . 
       FIG. 5  illustrates a vehicle system  500  using an embodiment of a cooling system such as cooling systems  200 ,  300 , or  400  shown and described above. In vehicle system  500 , a vehicle  502  includes an air conditioning (AC) system  504  and an electronics compartment  506 . Electronics compartment  506  is shown as a single compartment in the vehicle&#39;s dashboard, but in other embodiments there can be multiple electronics compartments and they need not all be in the same place in vehicle  502 . Air conditioning system  504  is coupled to a duct  508  that runs between the air conditioning system  504  and electronics compartment  506 . A portion  510  of duct  508  is near electronics compartment  506 , so that in system  500  electronics compartment  506  is analogous to the first enclosure and portion  510  of duct  508  is analogous to the second enclosure of cooling system  200 ,  300 , or  400 . A bi-metal valve (not visible in this figure, but see systems  200 ,  300 , or  400 ) then regulates the flow of air between duct portion  510  and electronics compartment  506 . Duct  508  can also include one or more portions  512  that extend to the exterior of the vehicle. Similarly, electronics compartment  506  can include a duct  514  that extends to the exterior of the vehicle. Duct  512  allows exterior air to be used for cooling, and duct  514  allows warm air from electronics compartment  506  to be vented outside the vehicle. (i.e., duct  514  is analogous to outlet  112  in system  100 ). 
     The above description of embodiments is not intended to be exhaustive or to limit the invention to the described forms. Specific embodiments of, and examples for, the invention are described herein for illustrative purposes, but various modifications are possible.