Abstract:
A heat sink system with reduced airborne debris clogging, for cooling power electronics, the heat sink system including a heat sink having a plurality of fins, a housing configured to direct air flow around the side, top, and/or bottom of the heat sink and then through the fins of the heat sink at a back of the heat sink, and an inlet airway passage formed between a wall of the housing and said side, top, and/or bottom of the finned heat sink to allow air to pass within the housing, wherein said side, top, and/or bottom of the heat sink comprises at least one of said plurality of fins disposed directly in contact with the inlet airway passage.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a Continuation of U.S. application Ser. No. 11/291,247 filed Dec. 1, 2005, now U.S. Pat. No. 7,472,742 which is incorporated herein by reference in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to transportation vehicles that use high power electronics which require cooling systems and, more particularly, to a heat sink assembly for reducing airway blockage. 
     Locomotives and related transportation vehicles are equipped with power electronics whose cooling systems use finned heat sinks to aid in heat dissipation. These heat sinks are cooled by forced air. Previous heat sink designs have been used which employ typical fin arrangements with uniform spacing. The number of fins and spacing and the shape and size of the fins determine the cooling capability of the heat sink. An exemplary heat sink that is currently used in locomotives is one developed by Aavid Thermalloy. 
     In some situations, airflow is directed to flow through the heat sink. Such designs may be susceptible to plugging with airborne debris such as diesel fumes, dust, dirt, etc. When plugged, the heat sink&#39;s effectiveness is dramatically reduced, resulting in poor cooling of the power electronics and increased failure rates due to the excessive temperatures the electronics may experience. 
     BRIEF DESCRIPTION OF THE INVENTION 
     Embodiments of the present invention relate to a system and an assembly for cooling power electronics where reduced airborne debris clogging in the heat sink is preferred. The heat sink system includes a heat sink having a plurality of fins. The heat sink system further includes a housing configured to direct air flow around the side, top, and/or bottom of the heat sink and then through the fins of the heat sink at a back of the heat sink. The heat sink system also includes an inlet airway passage formed between a wall of the housing and said side, top, and/or bottom of the finned heat sink to allow air to pass within the housing, wherein said side, top, and/or bottom of the heat sink comprises at least one of said plurality of fins disposed directly in contact with the inlet airway passage. 
     In another embodiment, in a cooling system that has a heat sink system that has air passing therethrough an inlet airway passage to reach a plurality of fins on a heat sink, the heat sink system includes a transition seal between the heat sink and the inlet airway passage. The heat sink system also includes a slot proximate the inlet airway passage to receive an outer fin of the heat sink. The outer fin is of a thickness to contact the inner edges of the slot. At least one fin of the plurality of fins is in thermal connection with the inlet airway passage. 
     In another embodiment, the heat sink assembly includes a base element defining two dimensions of the heat sink assembly. The heat sink assembly further includes a plurality of fins attached to and extending from the base element. The heat sink assembly also includes an inlet airway passage through which air travels to reach the plurality of fins, and a transition seal between the heat sink and the inlet airflow passage. The heat sink assembly also includes a slot proximate the inlet airflow passage to receive an outer fin of the heat sink wherein the outer fin is of a thickness to contact the inner edges of the ribbed slot, wherein at least one fin of the plurality of fins is in thermal connection with the inlet airflow passage. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more particular description of the invention briefly described above will be rendered by reference to specific embodiments thereof that are illustrated in the appended drawings. Understanding that these drawings depict only typical embodiments of the invention and are not therefore to be considered to be limiting of its scope, the invention will be described and explained with additional specificity and detail through the use of the accompanying drawings in which: 
         FIG. 1  depicts an exemplary illustration of a prior art housing with a prior art finned heat sink; 
         FIG. 2  depicts an exemplary embodiment of a finned heat sink cross section illustrating a center-by-pass area; 
         FIG. 3  depicts an exemplary embodiment of housing guide vanes within a housing holding a finned heat sink; 
         FIG. 4  depicts a top view of an exemplary embodiment of a finned heat sink within a housing where the housing&#39;s solid divider wall is removed; 
         FIG. 5  depicts a top view of an exemplary embodiment of a finned heat sink within a housing where the heat sink expands into an inlet passage area; 
         FIG. 6  depicts a detailed view of a transition seal between a heat fin and the housing; 
         FIG. 7  depicts a heat sink within a housing where the housing has no divider walls; 
         FIG. 8  depicts exemplary leading edge designs for a heat sink fin; 
         FIG. 9  depicts exemplary embodiments of various fin arrangements; 
         FIG. 10  depicts an exemplary prior art embodiment of how fins are divided to provide support to the fins; 
         FIGS. 11(   a ) and  11 ( b ) depict illustrations of exemplary embodiment of fins of varying length; and 
         FIG. 12  depicts a top view illustration of an exemplary embodiment of fins that are contoured. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     With reference to the figures, exemplary embodiments of the invention will now be described. However, it should be noted that, though the present invention describes various inventions or improvements that may be used in a heat sink system, these improvements may be used individually in a single application or various combinations, including all versions at once, may be used together. Towards this end, the exemplary embodiments discussed herein should not be viewed as individual inventions since they can be used collectively as well. 
       FIG. 1  illustrates a typical heat sink that is currently used to cool power electronics in a locomotive. The heat sink  10  is contained in a housing  12  that directs the airflow  13  through the heat sink  10 . The heat sink  10  is held in position by its placement between two solid divider walls  27  separating the heat sink from an inlet airflow passages  19 . The heat sink  10  has fins  14  through which airflow is directed. As the airflow  13  travels through the housing though inlet airflow passages, or passageways,  19  and experiences the bends  15  in the housing  12 , heavier debris particles will be forced to the outside of the bend radius, and will impinge upon the center  17  of the heat sink face  18  where the two inlet paths converge. This phenomenon has been further verified through debris ingestion testing of heat sinks  10 . Once debris clogging is initiated in the center of the heat sink  17 , the plugging then proceeds to grow across the face  18  of the heat sink. 
       FIG. 2  depicts an exemplary embodiment of a finned heat sink cross section illustrating a center-by-pass area. By creating a center by-pass  20  in the heat sink  10 , an open channel  20  through the center of the heat sink fins  14  is created which allows for debris to pass through the heat sink  10  without depositing on the inlet face  18  of the heat sink  10 . To offset the removal of heat sink fins  14 , the overall size of the heat sink  10  is modified in overall width, fin height, length, and number of fins to achieve equivalent thermal performance when compared to the original heat sink. This is achieved with constant spacing of the fins  14  and a bigger spacing in the bypass area  20  or by having a gradually increased spacing of the fins  14  towards the center  17  of the heat sink  10 . Those skilled in the art will readily recognize that depending on where the airflow is directed and where the highest concentration of debris is expected to be deposited, the by-pass area  20  need not be in the center  17  of the face  18 , but located where the highest concentration of debris is expected. 
       FIG. 3  depicts an exemplary embodiment of housing guide vanes fixed within a housing that holds a finned heat sink. Including turning vanes  25  in the housing  12  may further enhance the effectiveness of the by-pass configuration discussed above. These vanes  25  may be used to more precisely control the amount and specific portion of the airflow  13  that gets diverted through the by-pass  17 . The turning vanes  25  direct heavier particles to the bigger opening so as to delay and/or avoid the initiation of plugging. Though only two vanes  25  are illustrated, a plurality of vanes  25  may be utilized. 
     As disclosed above, the present heat sink  10  is mounted within two solid divider walls  27  which act to locate the heat sink  10  so as to channel the airflow  13 . Additional concepts of packaging the heat sink  10  may be employed to increase the volume of the heat sink  10  without increasing its overall size and/or weight. Increasing the volume allows for fins  14  to be removed/moved, which in turn allows for increased fin gap, without the apparent respective loss in heat transfer area. 
       FIGS. 4 &amp; 5  illustrate the present design with two alternative approaches. Specifically,  FIG. 4  depicts a top view of an exemplary embodiment of a finned heat sink within a housing  12  where the housing&#39;s solid divider wall is removed. In this exemplary embodiment, the divider walls  27  are removed. In an exemplary embodiment the outside heat sink fins may be made thicker than the interior fins so as to provide additional structural support and/or to improve heat transfer rates of the cooling system. 
       FIG. 6  depicts a detailed view of a transition seal between a heat fin and the housing. The walls  27  are removed except a sloped portion  31  at the end of the housing  12  is provided so as to have a transition seal between the heat sink  10  and the assembly  12 , including the inlet airflow passage  19 , and the weldment  33 . Also, a ribbed slot  35  is placed in the housing  12  to facilitate the easy location and application of a sealing member  37 , such as a gasket, preferably with pressure sensitive adhesive on one side, though any sealing material may be used. 
     The heat sink  10  is constructed with an outer solid fin  14  that has a matching radius to the sloped portion  31  and the appropriate thickness so as to fit into the ribbed slot  35  and compresses the gasket  37  running the length of the fin  14 . By such means, the heat sink  10  replaces the original divider  27 . 
     Even though a transition seal and slope portion are disclosed to provide a seal between a heat sink and a base, those skilled in the art will readily recognize that other embodiments are possible to achieve the same connection wherein the heat sink fins  14  are in thermal connection with a base. For example, the fins  14 , with their rectangular shape, may have an end that extends to the weldment. Likewise, the fins  14  that may be located in the inlet airflow passageway  19  may also be in thermal connection with the airflow passageway  19 . 
     In addition to keeping the pressure drop constant to allow sharing of air through many parallel heat sinks, a controlled restriction element  40  is provided. As illustrated in  FIG. 7 , the restriction element  40  is attached to the housing assembly  12 . Those skilled in the art will readily recognize that where the housing is not used, the element can be part of the heat sink. This element  40  is used to control and/or regulate a pressure drop through the heat sink  10  due to increased spacing of fins  14 . In addition with respect to the housing  12 , an access port  41  (not visible but having its location(s) identified by arrows  41  in  FIG. 7 ) is provided to facilitate inspection of heat sink clogging and/or cleaning of the heat sink  10 . 
     In an exemplary embodiment a plurality of heat sinks, up to as many as thirty-six (36), may be used on a locomotive. The pressure drop across all heat sinks is uniform. Thus, if a new heat sink replaces a current heat sink on the locomotive, the pressure drop across this new heat sink must be uniform to the existing pressure drops across the other heat sinks. Towards this end, the restriction element  40  is sized to insure a uniform pressure drop across the replacement heat sink. By doing this, one heat sink may have a different sized restriction element  40  than another. This allows for insuring that all future heat sinks are backwards compatible with existing heat sinks in a system, such as a locomotive. 
       FIG. 5  depicts a top view of an exemplary embodiment of a finned heat sink within a housing assembly where the heat sink extends into an inlet passage area of the housing. In this embodiment, the divider walls  27  are removed and the heat sink  10  is larger whereas the inlet air passage  19  is converted to usable heat sink volume. 
       FIG. 8  depicts exemplary leading edge designs for a heat sink fin. An improved leading edge design can assist in reducing a rate of plugging of the heat sink  10 . In the conventional heat sink fin design, illustrated in  FIG. 8(   a ), the leading edge has a flat surface. In an improved design the leading edge is shaped with a pointed, beveled edge, illustrated in  FIG. 8(   b ), or a rounded off edge, illustrated in  FIG. 8(   c ). These improved leading edge designs may be applied to both the leading edge and/or trailing edge of the fins  14 . In the case of fin designs that are not solid or continuous, such as the segmented or augmented fins disclosed below, these improved leading edge designs may also be extended to the leading and/or trailing edges of each of the fin segments. 
     Yet another concept is to improve the surface finish to reduce the propensity of particles sticking to the surface of the fins. To achieve a non-stick fin, the fin may be processed to have a very fine surface finish, or coatings may be applied to produce a non-stick surface. Teflon, fluoropolymers, PFA, PTFE, and FEP are just some of the common coatings available in industry that may be applied. 
       FIG. 9  depicts exemplary embodiments of various fin arrangements. As illustrated four different concepts for the fin arrangement are disclosed. The options depicted in  FIG. 9(   a ), an augmented fin, and  9 ( b ), a straight fin, are prior art concepts. An augmented fin has parts of the fin that extend into the area where airflow passes, which in turn may cause turbulence. The area of turbulence can result in debris buildup, or plugging. The configuration depicted in  FIG. 9(   c ) is a segmented fin design which provides similar turbulence as an augmented design without providing edges sticking into the air stream. By not having parts of the fin extending into the airflow the probability of plugging reduces.  FIG. 9(   d ) depicts a wavy fin design that likewise attempts to increase turbulence and heat transfer while removing leading edges that promote accretion of debris. 
     In addition to providing enhanced clog resistance, edge treatment of the fins and various fin configurations may be performed or combined with other key parameters such as varied fin geometry (i.e. thickness, height, etc.) and fin spacing, to tune and/or reduce the airflow induced noise generation of the heat sink. For example, as further illustrated in  FIG. 10 , a straddle mount fin support system is typically used to attach each fin  14  to a base plate  29  on the heat sink  10 . Since the fin thickness is usually small, the support is done by bending portions of the fins  14  in opposite direction and then supporting it on the heat sink base  29 . This technique, however, increases the overall cost of the heat sink  10 . By using the techniques discussed herein wherein thicker fins  14  are used and more space is provided between fins  14 , the new heat sink fins  14  may be made thicker, such as illustrated in  FIG. 2 , so as to have a better heat transfer rate and to be able to support without the complicated/costly support mechanism required to bend portions of the fins in opposite directions. 
     In conventional heat sinks, the fins  14  are used for cooling and the cover and the wall dividers  27  of the housing  12  are used for airflow control. In the present invention the fins are used both for heat dissipation and airflow control. Referring back to  FIG. 5 , the fins are located in the airflow passage  19 .  FIGS. 11(   a ),  11 ( b ), and  12  are exemplary embodiments of fin arrangements of varying lengths. These illustrations only show one side of fins in a heat sink, such as a side of the heat sink taken along line A-A of  FIG. 5  wherein the fin arrangement is different than those shown in  FIG. 5 . Specifically, the areas designated as “inlet” in each figure are fins on the heat sink that are located within one side of the airflow passage. As illustrated where the fins are in the airflow passage  19 , the fins in this area can be of varied length to direct the path of the airflow  13 . Those skilled in the art will readily recognize that these figures are exemplary only wherein using the invention disclosed herein in other varied length fins may also be utilized to achieve a similar result. 
     As illustrated in  FIG. 11(   a ), the fins in the airflow passage are longer at the outer edge of the heat sink and then reduce in length the closer the fins are to the heat sink fins that are used as an outlet for air flow. The outlet fins are also varied in length where the fins  14  closer to the inlet fins are shorter than the fins further away from the inlet fins. In another exemplary embodiment, though not shown, the outlet fins are of a constant length wherein the cascading lengths of the inlet fins will turn airflow towards the outlet fins. In another exemplary embodiment, shown in  FIG. 11(   b ), the inlet fins are removed and the air passage directs airflow to the varying length fins. 
     In another exemplary embodiment, as illustrated in  FIG. 12 , the fins are of a longer length and curved, thus incorporating the turning vanes discussed above in the fins as opposed to being part of the housing. Not every fin needs to have a vane. For example, as illustrated every other fin has a vane as part of the fin. The vanes are of varied lengths and are used to improve turning efficiency and flow distribution of airflow. Though vanes are illustrated on the inlet fins, in another exemplary embodiment the inlet fins may not include the vanes. 
     When fins of varying length are used, as discussed above, housing for the heat sink may no longer be required. The housing is no longer required since the heat sink directs and controls the airflow. Towards this end, one less element is required within the cooling system, which results in a cost savings. 
     While the invention has been described in what is presently considered to be a preferred embodiment, many variations and modifications will become apparent to those skilled in the art. Accordingly, it is intended that the invention not be limited to the specific illustrative embodiment but be interpreted within the full spirit and scope of the appended claims.