Abstract:
A passive louver system providing supplemental and localized cooling for an engine compartment is implemented using magnetic catches for opening and closing of the louvers.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Technical Field  
         [0002]     The present invention relates generally to louvers used to control engine compartment ventilation for cooling of the compartment on a motor vehicle.  
         [0003]     2. Description of the Problem  
         [0004]     Elevated engine compartment air temperatures on motor vehicles have been a design issue essentially since the introduction of internal combustion engines to motor vehicles. The problem has not abated, but become worse, in recent years. This stems in part from the increasing use of exhaust gas recirculation and catalytic converters to reduce exhaust emissions. It also results from the addition of vehicle accessories such as air conditioning. Higher underhood air temperature drives component material selection, cooling system capacity and other design considerations, all of which can add to expense and vehicle complexity. Currently, the problem is solved by the addition of cooling system capacity and heavy reliance on active monitoring. Adding cooling capacity requires more space under the hood. Louver systems have also long been used to control air flow through the engine compartment to aid cooling. Increased fan speed has been used to increase air flow through the engine compartment and under the cab. Heat shields have been used to protect temperature sensitive areas.  
         [0005]     It would be advantageous to simplify engine compartment cooling by limiting the need for human or control system intervention while, at the same time, taking advantage of monitoring of operation of a passive cooling system.  
       SUMMARY OF THE INVENTION  
       [0006]     The invention provides a plurality of fins or louvers that are located strategically through a vehicle body, including the hood, adjacent the vehicle&#39;s engine compartment. As the temperatures under the hood locally approach critical temperatures that could damage adjacent systems and sub-systems, the fins open promoting air circulation through the engine compartment adjacent the critical area thereby releasing heated air into the atmosphere. Control of the fins&#39; position is local and relatively passive.  
         [0007]     Fin position is controlled through control of magnetic attraction between the fin and the hood or body. Fin and hood are each equipped with magnets with their poles oriented to draw the fin toward the hood. Magnetic closure occurs when a catch made of material with good magnetic susceptibility, but a low Curie point, is cool enough to transmit magnetic flux between the permanent magnets. The magnetic catch is located between permanent magnets affixed to the hood and the fin. As local engine compartment temperature rises and the magnetic catch loses magnetic susceptibility a spring urges the fin to an open position. The spring is preferably internal to the fin or an integral part of the fin. The fin may rotate on a pivot though this is not the preferred arrangement. The fin is inherently limited in travel, or subject to an external travel limiting structure, allowing the magnetic attraction to close the fin once the catch regains magnetic susceptibility. The fin spring may be a bimetallic structure which urges the fin open with increasing force as local temperature climbs and can be designed to retract the fin to a closed position at low temperatures.  
         [0008]     Advantageously, little or no active control intervention is required to implement this system. In one embodiment the system appears completely passive to the vehicle&#39;s control systems. This does not prevent monitoring of the louvers/fins by the control system, which may be done to trigger active cooling system response to louver movement or to signal faults. Active cooling system components that can be integrated into the system are; fan speeds, logic for activating the fan to exhaust the air and engine controller activity that would provide indications of an upcoming engine event that would generate increased heat. Where louver movement appears abnormal in view of measured engine temperature, an indication may be provided an operator.  
         [0009]     Additional effects, features and advantages will be apparent in the written description that follows. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]     The novel features believed characteristic of the invention are set forth in the appended claims. The invention itself however, as well as a preferred mode of use, further objects and advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying drawings, wherein:  
         [0011]      FIG. 1  is a perspective view of a truck tractor incorporating the present invention.  
         [0012]      FIG. 2  is a high level schematic of the control system for the truck tractor of  FIG. 1 .  
         [0013]      FIG. 3  is a perspective view of the truck tractor hood illustrating a symmetric positioning of vents and louvers.  
         [0014]      FIG. 4  is a cross sectional view of a possible arrangement of louvers to support air intake as well as exhaust.  
         [0015]     FIGS.  5 A-B illustrate the louver of the present invention.  
         [0016]      FIG. 6  is a schematic illustration of an engine compartment illustrating possible distribution for louvers of the invention.  
         [0017]      FIG. 7  is a flow chart illustrating a possible control method using louver position as a control input. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0018]     Referring to the drawings and in particular referring to  FIG. 1 a  truck tractor  101  is illustrated, conventionally built as a body  105  on a chassis  102 . A cab is accessed through a door  103  and a windshield  110  allows easy viewing forward from the cab. Truck tractor rolls on wheels  104  and includes an engine (not shown) enclosed under portions of the body including a hood  109 . An array  111  of louvers  117  is shown along one side of body  105  adjacent the engine compartment.  
         [0019]      FIG. 2  is a simplified schematic of a control system  200  installed on truck tractor  101 . While in its basic form the invention does not require intervention of control system  200 , the control system  200  may be used to monitor operation of the louvers. Control system  200  is built around a public SAE J1939 compliant data bus  218  to which are connected a body computer (ESC)  224 , an engine controller  220 , a gauge cluster controller  214  which controls cab displays including warning indications, a transmission controller  216  and an antilock brake system (ABS) controller  222 . ESC  224  is also independently connected to supply and receive discrete outputs  252  and discrete inputs  250 . ESC  224  may also be connected to a switch pack  243  over an SAE J1708 bus. For purposes of the present invention it is assumed that sensors  245  indicating whether a particular louver is open or closed are connected to ESC  224  as discrete inputs  250 . Louver position sensor  245  inputs can also be connected to the ESC  224  as part of a switch pack  243  with status communicated over the J1708 bus  249 . Any one of the engine controller  220 , the transmission controller  216  or the ABS controller  222  can be adapted to provide a vehicle speed signal. The engine controller  220  operates to control an engine  230 , and monitors one or more temperature sensors which relate to engine operating temperature (e.g. coolant temperature). Temperature sensor  234  provides a reading relating to ambient temperature (e.g. an air intake temperature sensor) already provided on the vehicle to the engine controller  220 .  
         [0020]      FIG. 3  is a perspective view of a truck tractor hood  109  illustrating a symmetric distribution of vents  330  including positionable louvers according to the invention. As shown in  FIG. 4 , fins  407  and fins  409  of inlet and outlet louver systems  401 ,  402  may be constructed to admit air or to allow exhaust of air from an engine compartment  410 .  
         [0021]     FIGS.  5 A-B illustrate construction of a preferred embodiment of a fin  502  for a louver system in which the fin flexes into and out of closed and open positions as indicated by double arrow A. Alternatively, fin  502  could be mounted on a pivot. Fin  502  is mounted in a hood or body section  500  as an aerodynamic shell around an engine compartment  410 . Fin  502  is affixed to hood  500  along one edge, illustrated as a section  512  which bends under hood  500 . The opposite edge  505  of fin  502  is beveled to make sealing contact with a inwardly turned border  504  of hood  500  adjacent vent hole  516 . Set in or affixed to inwardly turned border  504  is a permanent magnet  506 . Set in beveled edge  505  of fin  502  opposite magnet  506  is a second magnet  508  oriented so that magnets  506  and  508  present opposite poles to one another for attraction. Intermediate to magnets  506  and  508  is a magnetic catch  510 , which a made of a material exhibiting high magnetic susceptibility at normal atmospheric temperatures but which has a relatively low Curie point selected so that the magnetic catch  510  loses susceptibility at the desired temperature. The material of the catch  510  is selected or blended to exhibit a Curie point which corresponds to a level at which local cooling of engine compartment  410  is required. With loss of susceptibility magnetic flux is not transmitted through catch  506  with an accompanying loss of attractive force between the two permanent magnets  506 ,  508 .  
         [0022]     Fin  502  is flexible and incorporates springs  514  which urge the fin to curl open in the outward direction of arrow A. Springs  514  may be bimetallic so that the force urging the fin  502  open increases with increasing temperature. When temperature catch  510  regains its high susceptibility, the fin  502  is pulled closed by magnetic attraction. Where springs  514  are bimetallic, they may be designed to contribute to this operation.  FIG. 5B  illustrates fin  502  from a top view illustrating the lateral distribution of springs  514  along the fin and placement of magnets  508  along on edge thereof. Fin  502  may also be made of a material have shape memory which becomes pliable at elevated temperatures to ease opening of the fin but countering action of the springs when the material cools and return to its “remembered” shape.  
         [0023]      FIG. 6  is a schematic illustration of how vents  606  and  608  might be positioned for cooling of particular accessories installed with an engine  600 . Accessory  602  may be a supercharger compressor. Vent  606  is located behind the compressor  602  allowing air flowing over the compressor an outlet. Whether vent  606  is open or closed by a fin is sensed by a contact sensor  610 . Similarly vent  608  is located behind and to one side of an air conditioner compressor  604  with a second contact sensor  610  situated to data at opening of the vent. The signals from the sensors  610  are coupled to ESC  224 . ESC  224  is also connected to determine the operating status of some accessories, such as an air conditioning compressor.  
         [0024]     Referring to  FIG. 7 , a flow chart  700  illustrates a possible algorithm executed by ESC  224  utilizing fin position information. The program is driven by the contact sensors  610 , which indicate whether particular vents are open (step  702 ). Detection of whether one or more sensors is open is made at step  704 . If none are open, execution of the program moves to step  706  where the engine temperature signal is read. Elevated temperatures may be taken as an indication that one or more vents should be open. Engine temperature exceeding a level where one or more vents is expected to be open is determined at step  708 . A possible problem (i.e. failure of a contact sensor to open at an elevated temperature threshold is indicated at step  710  along the YES branch from step  708 . After step  710  or along the NO branch from step  708  processing returns to step  702  to poll the contact sensors again.  
         [0025]     If one or more vents is determined to be open at step  704 , the YES branch is followed to step  712  for a look up operation to determine which vent locations have opened. This information is used to determine if operating conditions are such that it would be expected that the vent be open. This may be done from simply looking at engine temperature, or additional factors may be considered.  
         [0026]     Steps  714  through  720  are optional. In order, they provide for reading vehicle speed (step  714 ), reading fuel flow (step  716 , possibly as an indication of engine loading or power output as an indicator of soon to increase temperature), reading ambient temperature ( 718 ) and determining if particular accessories are running (step  720 ). Finally engine temperature is read (step  721 ). The operating variables available may then be used as arguments for a look up table to generate an expected operating temperature in the vicinity of the vent which is open (step  722 ). For example, there may be different expectations relating to local temperature adjacent an air conditioning compressor depending on any or all of the variables considered, and thus it may be possible to predict temperature in that area. If the vent is opened in area when it is not expected to be it may be an indication that a particular component is running hotter than expected. Such comparisons of expected state with actual state are made at step  724 . If the expected state is met processing returns to step  702  along the YES branch. If not, step  726  is executed along the NO branch to alert the operator before program execution loops back to step  702 .  
         [0027]     The invention provides a louver system for engine compartment cooling requiring little or no control intervention to implement. Where louver movement appears abnormal in view of engine temperature sensors an indication may be provided an operator.  
         [0028]     While the invention is shown in only one of its forms, it is not thus limited but is susceptible to various changes and modifications without departing from the spirit and scope of the invention.