Abstract:
A light bar incorporates an extruded base and top panel where the top panel is supported above the base by two ruggedly constructed electronics enclosures. The base top panel and electronics enclosures form a structure to which various light units, lenses and covers are attached to form the finished light bar. The top panel is one of the last components to be installed, leaving the internal components of the light bar accessible during assembly. Each electronics enclosure may surround a power supply that includes a heat-generating component, such as a power transistor. Each enclosure is provided with an opening through which the heat-generating component protrudes to form a heat transfer interface with a heat sink plate mounted to the outside of the enclosure. A further heat transfer interface is formed between the heat sink plate and the top panel in the assembled light bar.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to warning light systems intended primarily for installation on land and marine vehicles and particularly to a light bar assembly having an integrated modular design and a method of assembly therefor. 
     2. Description of the Related Art 
     Warning light assemblies in the form of light bars mounted on emergency vehicles are well known in the art. The modern trend is toward compact, low profile, self contained light bar assemblies. Compact and low profile light bar assemblies improve the aerodynamic efficiency and significantly reduce wind noise typically generated by a light bar. 
     U.S. Pat. No. 4,620,268 to Ferenc represents a significant advance in the design of such light bar assemblies. The Ferenc light bar is built around an I-beam structural member and includes lens elements that engage the front and rear edges of upper and lower horizontal structural elements of the I-beam so as to span the horizontal length of the light bar. Each end of the light bar assembly is provided with a molded plastic end cap which abuts the ends of the I-beam and lenses to define an enclosure. 
     While this design represents an important advance over the prior art and has enjoyed significant commercial success, the patented monolithic I-beam support member complicates the manufacture and service of the light bar assembly. The strengthening web connecting the upper and lower structural members of the I-beam support member holds the upper and lower portions at a fixed distance. Any light bar design requiring an alternative height must use a different I-beam support member. Additionally, since the top and bottom structural members of the I-beam are permanently attached to each other, any work on the interior of the light bar must be performed through openings at the ends and along the sides of the I-beam. Further, the space inside the I-beam support member is necessarily bifurcated by the support web. This bifurcated space is inherently less useful than a unitary space. 
     There is a modern trend toward self contained light bars where the light bar includes the power supplies and signal processing equipment necessary for operation of a light bar. Such self-contained assemblies are desirable because they require fewer interconnections with a host vehicle, simplifying installation and maintenance. 
     SUMMARY OF THE INVENTION 
     These and other deficiencies of the prior art are overcome by the present invention. A preferred embodiment of a light bar in accordance with the present invention comprises an elongated base and top panel supported above the elongated base by a plurality of ruggedly constructed electronics enclosures. The electronics enclosures serve multiple functions. First, each enclosure surrounds and supports the electronic components of the power supply. Second, each enclosure provides a robust mechanical connection between the base and top plate. Third, each enclosure includes means for transmitting heat generated within the power supply to an externally mounted heat sink plate. A thermal transfer interface is formed between the heat sink plate and the top plate. 
     An object of the present invention is to provide a light bar with improved ease of manufacture and maintenance. 
     Another object of the invention is to provide a new and improved light bar that can be assembled from interchangeable components into a variety of configurations. 
    
    
     These and other objects, features and advantages of the invention will become readily apparent to those skilled in the art upon reading the description of the preferred embodiments, in conjunction with the accompanying drawings. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an exploded perspective view of a light bar in accordance with the present invention; 
     FIG. 2 is an exploded perspective view illustrating the assembly order and configuration of some components of an alternative embodiment of a light bar in accordance with the present invention; 
     FIG. 3 is an exploded perspective view of a power supply for use in conjunction with the light bar of FIG. 1; 
     FIG. 4 is a sectional view through a base top panel, lenses and power supply assembled in accordance with the present invention; 
     FIG. 5 is an enlarged, exploded sectional view through a portion of the power supply of FIG. 3; 
     FIG. 6 illustrates the components of FIG. 5 in an assembled configuration; 
     FIG. 7 is an enlarged, exploded sectional view through a portion of the power supply of FIG. 3; and 
     FIG. 8 illustrates the components of FIG. 7 in an assembled configuration. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring more particularly to FIGS. 1 through 8, wherein like numbers refer to similar parts, a light bar  10  in accordance with the present invention is illustrated in FIGS. 1 and 4. Throughout the figures, it will be understood by those of skill in the art that some features and components of the light bar assembly are omitted for clarity. 
     FIG. 1 is an exploded view illustrating many of the components of a first embodiment of a light bar  10  in accordance with the present invention. The light bar  10  is characterized by the interdependence of its modular components. The primary structural components of the light bar  10  are a longitudinally extending base  20  and a complementary longitudinally extending top panel  30 . The base  20  and top panel  30  are preferably extruded from high strength materials such as aluminum, although other methods of manufacture and materials may also be appropriate. Extrusion is an efficient means of producing components that have a uniform transverse cross-section. 
     With reference to FIG. 4, it can be seen that the base and top panel are generally planar and include a plurality of uniform longitudinally extending features. Strengthening ribs  25  project perpendicular to the base  20  along its length. Corresponding strengthening ribs  35  project perpendicular to the top panel  30  along its length. The strengthening ribs  25 ,  35  provide stiffness to the base  20  and top panel  30 , respectively, while also serving as location and assembly aids as will be discussed below. The longitudinal edges of the base  20  and top plate  30  define elongated slots. The light bar  10  is configured to be mounted on an emergency vehicle with the length of the light bar perpendicular to the path of vehicle travel, presenting a horizontally extended pattern of warning lights fore and aft of the emergency vehicle. Therefore, one longitudinally extending edge of the base  20  and top plate  30  will face in the direction of vehicle travel and are designated the base forward slot  22 , and top plate forward slot  32 , respectively. The rearward facing longitudinal slots are designated the base rear slot  24  and the top panel rear slot  34 . 
     The base  20  also includes a plurality of extruded fastener receptacles  23 . Since the fastener receptacles  23  are another extruded feature of the base  20 , any longitudinal section of the base  20  includes screw receptacles  23  disposed at intervals across the opposed transverse ends. The aluminum material defining the screw receptacles  23  readily accepts self-tapping hardware to form a secure threaded engagement. The extruded top plate  30  includes similar complementary extruded screw receptacles  33 . 
     The illustrated preferred embodiment of the base  20  also includes spaced apart, inward facing top and bottom mounting tracks  21 ,  26 , respectively. The bottom mounting tracks  26  define a location for fixing mounting hardware, such as mounting brackets extending from the host vehicle (not illustrated), to the base  20 . The longitudinally extending bottom mounting tracks  26  allow the light bar  10  to be secured to a host vehicle anywhere along the length of the base  20 . 
     With reference to FIGS. 1,  2  and  4 , the top mounting tracks  21  provide a longitudinally extending mounting location for components of the light bar  10  that will be enclosed between the base  20  and the top plate  30 . The base  20  and top plate  30  may be configured with additional longitudinally extending channels and features  27 ,  37  for engagement of outward facing lighting components installed behind the longitudinally extending lenses  70  as will be further discussed below. 
     FIGS. 1 and 2 are exploded views of selected pre-assembly components of alternative illustrated embodiments of a light bar  10  in accordance with the present invention. FIG. 1 illustrates the base  20 , power supply  40  and top plate  30  of FIG. 4 in an exploded view. In accordance with one aspect of the invention, the electronic components of the light bar  10  are supported above the base  20  on structures engaged with the top mounting tracks  21 . Accordingly, input/output assembly  90  and power supply enclosure  40  are equipped with protruding feet  92 ,  42 , respectively, configured to be received by top mounting tracks  21 . Once received in the top mounting tracks  21 , the I/O assembly  90  is slidably moveable relative to the base  20 . Fastening hardware  93  secures the I/O assembly  90  relative to the base  20  and may also provide a ground path to the metal base  20 . In some embodiments, the ground path may be extended to the top plate  30  by means of a spring loaded grounding pin  92  (FIG.  2 ). 
     In accordance with a particularly significant aspect of the present invention, each power supply enclosure  40  is equipped with mounting brackets  43  arranged along the longitudinal median of the light bar  10 . In the illustrated embodiments, each mounting bracket  43  receives a screw  38  which extends through the top plate  30  to rigidly secure the top plate to the respective power supply enclosure  40 . The screws  38  are preferably a self-tapping screw with a thread configured for engagement with plastic of the type from which the power supply enclosures are molded. Further, the screws  38  preferably have a head that forms a water resistant seal with the top plate  30 . Each power supply enclosure  40  is preferably molded as a single-piece from durable high-strength plastic. A preferred plastic is DuPont Zytel®. Thus, the power supply enclosure  40  serves as a primary structural link between the base  20  and the top plate  30 . 
     FIG. 3 is an exploded perspective view of the primary pre-assembly components of a power supply in accordance with the present invention. The electronic components of the power supply are mounted to a printed circuit (PC) board  44  and include at least one power transistor  47 . The power transistor  47  generates heat as is known in the art and is provided with a through hole  56  for securing the power transistor to a heat sink. The power supply housing  40  includes a plate recess  50  in the top exterior surface. The plate recess  50  is configured to receive a heat sink plate  45 . 
     The pre-assembly and assembled configurations of the power supply are best discussed with reference to FIGS. 5-8. FIG. 5 shows an exploded view of some preassembly power supply components. The illustrated components are the PC board  44 , power supply housing  40 , heat sink plate  45 , co-therm seal  41 , mounting stud  46  and nut  48 . These components are assembled in a sandwich configuration as illustrated in FIG.  6 . An opening  51  is provided in the upper surface of the power supply housing  40 , permitting the power transistor  47  to protrude through the power supply housing  40  and form a heat transfer interface with the co-therm seal  41  and ultimately with the heat sink plate  45 . So, while the PC board  44  is mounted within and protected by the power supply enclosure  40 , the power transistor  47  is disposed flush with the outside surface of the power supply housing  40  in the heat sink recess  50 . As can be seen from FIG. 6, this allows the co-therm seal  41  to be captured between the heat sink plate  45  and the outside surface of the power supply housing  40  while also being engaged by the power transistor  47 . A standoff  52  molded inside the power supply housing  40  permits tension to be accumulated between the heat sink plate  45  and the PC board  44  by the nut  48  and mounting stud  46  while reducing the risk that the power transistor  47  will be damaged. The standoff  52  also maintains a pre-determined distance between the PC board  44  and the power supply housing  40 . 
     FIGS. 7 and 8 are exploded and assembly sectional views, respectively, through the PC board  44 , power supply housing  40  and heat sink plate  45 . The power supply housing  40  is provided with an opening  57  through which a mounting stud  46  passes to provide a connection between the heat sink plate  45  on the outside of the housing and the PC board  44  on the inside of the housing. Each through hole  57  in the power supply housing  40  is configured with a standoff  54  on the inside of the housing to maintain the predetermined separation between the PC board  44  and the power supply housing  40 . A lip seal  53  projects toward the heat sink plate  45  from the outside surface of the power supply housing surrounding the through hole  57 . This lip seal  53  is approximately 0.015″ high and configured to deform or crush in response to tension exerted on the mounting stud  46  by a nut  48 . FIG. 8 illustrates the components in an assembled configuration. The tightly compressed co-therm seal  41  and lip seal  53  provide water-resistant barriers between the interior and exterior of the power supply housing  40 . 
     It will be understood by those of skill in the art that electronic components including power transistor  47  must be interconnected as a power supply circuit and supported structurally to resist vibrations and shocks present in an automotive or marine emergency vehicle environment. Therefore a power supply and associated housing are necessary components of a light bar. The inventive light bar, as illustrated in FIG. 4, efficiently integrates the power supply housing  40  into the light bar assembly  10  as a structural member extending between the base  20  and the top plate  30 . Thus, the power supply housing  40  not only supports and protects the power supply, but also serves as a structural support and mounting location for the top panel  30 . 
     Each power supply housing  40  has a lateral dimension A and a height B. The height B of the power supply housing  40  determines the space defined between the top plate  30  and the base  20 . The lateral dimension A of the power supply housing  40  is matched to the lateral spacing between top mounting tracks  21  and strengthening ribs  25  and  35 . Alternative light bar configurations may require larger or smaller height dimensions B to accommodate alternative light emitting apparatus. Conveniently, such alternative light bar configurations will also likely require alternative power supply configurations. In the inventive light bar  10 , alternative power supplies may be configured to provide the appropriate height dimension B as well as provide power for the alternative light bar configurations. 
     With reference to FIG. 4, the light bar  10  includes lenses  70  with longitudinally extended protrusions  71  configured to mate with a pair of slots defined along the front and rear edges of the base  20  and top plate  30 . The protrusions  71  of each lens mate to a respective pair of, for example, base forward slot  22  and top plate forward slot  32  or base rear slot  24  and top plate rear slot  34  and are inserted into the slots until the lens  70  is aligned with the ends of the base  20  and top plate  30 . Together, the base  20 , top plate  30  and lenses  70  define a substantially sealed interior space. Each lens may be a monolithic extrusion or alternatively, may be comprised of different colored lens portions (not illustrated) mounted end to end with a compressive seal between them. 
     Lighting components  80  are arranged along the length of the front and rear edges of the light bar  10 . Each lighting component  80  comprises a number of standard parts such as a reflector  84 , a lamp holder  83  and lens  82  that are selected from interchangeable parts, permitting customization of the light bar to specifications. The light unit housing  85  is configured to engage the longitudinally extending channels  27  of the base  20 . The top plate  30  can be left off the light bar  10  during assembly, which simplifies making the electrical interconnections between the light units  80 , the I/O assembly  90  and power supplies. 
     End caps  60  are configured to engage the ends of the top plate  30  and base  20  as well as the lateral ends of the longitudinally extending lenses  70 . Each junction of an end cap with the top plate, base and lenses is preferably provided with a flexible seal to prevent water penetration. Fasteners pass through the end cap  60  to engage the fastener receptacles  23 ,  33  in the base  20  and top plate  30 , respectively. The end cap light unit  64  is mounted within the end cap  60  by fasteners that pass through the exteriorly mounted lens  62 . It will be understood by those of skill in the art that the end cap light units  64  can be wired into the light bar and later secured within the end cap  60 . 
     When all the electronic components have been secured to the base  20  and the interconnections made the top plate  30  is then secured to the power supply housing fastening brackets  43  by screws  38 . The power supply housings  40  were previously restrained from moving inwardly by the power supply stop screws  55  and are now constrained from moving outwardly by their connection to the top plate  30 . In this manner the base  20  is connected to the top plate  30  by the power supply housing  40  in such a manner that the relationship between the base and top plate is substantially fixed. The longitudinally extending lenses  70  are engaged in the front slots  22 ,  32  and rear slots  24 ,  34  and moved into alignment with the top plate  30  and base  20 . The resulting configuration resembles the illustration of FIG. 4 with the exception that FIG. 4 does not show any light units  80  or  64  secured within the space enclosed by the base, top plate and lenses. 
     Next, the end caps  60  are installed. When installed, the end caps exert a compressive force against the longitudinally extended lenses  70  restraining them from sliding out of their respective slots. Light units  64  are secured to the installed end cap by fasteners through lens  62 . It will be understood by those of skill in the art that the interrelationship between the end caps  60  and the lateral ends of the top plate and base supplement the structural support provided by the power supply housings  40 . Thus, the end caps serve not only a closure function but also support a light unit and provide structural rigidity to the assembled light bar  10 . Together, the components of the light bar  10  provide a versatile, rigid, sealed enclosure. Many of the various components of the light bar  10  are interchangeable, resulting in virtually infinite custom configurations. 
     With reference to FIG. 4, it will be understood by those of skill in the art that a broad thermal interface occurs between the top plate  30  and the externally mounted heat sink plate  45 . Thus, top plate  30  acts as a large extension for the heat sink plate  45 . The heat radiating capability of the top plate is more than sufficient to dissipate heat produced by the power transistors  47  of multiple power supplies, if necessary, because the top plate  30  is generally exposed to moving outside air due to movement of the land or marine vehicle. 
     It will be understood by those of skill in the art that each electronics enclosure  40  performs at least three functions: enclosing and surrounding the power supply components; structurally connecting the top plate  20  to the base plate  30 ; and providing a heat transfer interface between the power transistor  47  and the top plate  30 . 
     With reference to the FIGS. 1-4 and the foregoing discussion, a preferred method for assembling a light bar  10  in accordance with the present invention is as follows: 
     1. select the overall length of the finished light bar; 
     2. cut a length of top plate and base that will result in the desired length light bar; 
     3. drill at least one cabling opening through the base to permit wiring the light bar  10  to the host vehicle (not illustrated); 
     4. mate an I/O assembly  90  to top mounting tracks  21  and slide the I/O assembly into the base; 
     5. secure the I/O assembly to the base in a selected location using mounting hardware; 
     6. install power supply stop screws; 
     7. mate the power supply housings  40  to the top mounting tracks  21  and slide the power supply housings onto the base until they contact the power supply stop screws; 
     8. install selected lighting components  80  in selected configurations and locations along the front and rear edges of the base  20 ; 
     9. install selected lighting components  64  adjacent the ends of the base; 
     10. make all necessary wiring interconnections between the power supply, I/O assembly and lighting components  80 ,  64 ; 
     11. prepare holes in top plate  30  for screws  38 ; 
     12. secure top plate  30  to power supply housings with screws  38 ; 
     13. select appropriate lengths of lens  70  for front and rear of light bar; 
     14. mate lenses  70  with front and rear longitudinal slots of base and top plate and slide lenses into position flush with the transverse ends of the base and top plate; 
     15. secure the end lighting fixtures  64  to the end caps  60  using hardware through lenses  62 ; 
     16. mount end caps  60  to the transverse ends of the base and top plate with screws through the end cap into the screw receptacles  23 ,  33 . 
     According to another aspect of the invention, it will be noted by those of skill in the art that all the internal components, i.e. lighting components  80 , power supply housings  40  and I/O assembly  90 , are slidable relative to the extruded base  20 . This feature of the invention facilitates efficient positioning and alignment of the components during assembly. The modular design also aids diagnosis and repair of the inventive light bar  10 . The components are held in the selected position by mounting hardware or frictional engagement, i.e. clamping, between the base  20  and top plate  30 . 
     While a preferred embodiment of the foregoing invention has been set forth for purposes of illustration, the foregoing description should not be deemed a limitation of the invention herein. Accordingly, various modifications, adaptations and alternatives may occur to one skilled in the art without departing from the spirit and the scope of the present invention.