Abstract:
An apparatus for ventilating the cabin of a locomotive wherein the ducts serve both a ventilating and a structural function. Horizontal duct provides support for floor in place of one or more of the regularly spaced joists. Horizontal duct may include stringers recessed into sound absorbing insulation within the duct. Vertical duct is formed in part from a portion of a wall of the control compartment of the locomotive cabin, thereby eliminating the need for separate wall sections. The space saved by using such structures for dual purposes may be used to increase the cross-sectional area of the ventilating apparatus, thereby allowing the speed of fan to be reduced to provide the desired ventilation at a reduced level of sound.

Description:
This application claims the benefit of the Nov. 30, 1999, filing date of U.S. provisional patent application Serial No. 60/168,071. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates generally to the field of heating, ventilating and air conditioning (HVAC), and more specifically to the HVAC system for the operator&#39;s cabin of a locomotive, and particularly to a method and apparatus for reducing the noise generated by the HVAC system of a locomotive. 
     It is known to provide an HVAC system for controlling the environmental conditions inside the operator&#39;s cabin of a railroad locomotive. A typical system, as provided by the assignee of the present invention, includes a fan and heat exchanger assembly installed below the floor of the cabin, horizontal ducts running beneath the floor between the floor joists, a vertical duct running through the control compartment forming one wall of the cabin, and a plurality of outlets connected to both the horizontal ducts and the vertical duct. Because the space for ductwork is very limited in a locomotive, the velocity of air moving through the ductwork must be maintained at a generally high level in order to satisfy the heat load specifications established for such systems. As a result, there is a considerable amount of sound energy generated by the HVAC system in a locomotive cabin. In one application, the HVAC system of a locomotive operating at maximum fan speed generates a sound level of approximately 75 dbA in the locomotive cabin. 
     BRIEF SUMMARY OF THE INVENTION 
     There is a desire on the part of some owners and operators of locomotives to reduce the background level of sound energy in the locomotive cabin. Because the HVAC system contributes significantly to the overall sound level, there is a particular need to provide a ventilation system for a locomotive that will provide the desired level of conditioning while generating a reduced sound level compared to prior art systems. There is also a particular need to produce such results with an apparatus that occupies a minimum amount of space. 
     Accordingly, an apparatus for ventilating a locomotive cabin is described herein having ductwork that is used for the dual function of conveying ventilating air and for some other structural purpose. By combining the function of the ductwork, one or more structural members may be eliminated, thereby providing space for increasing the size of the ducts. As the duct size is increased, the speed of the ventilating fan may be reduced without reducing the total volume of air flow, thereby reducing the level of sound generated by the apparatus. 
     Specifically, a low noise HVAC apparatus for a locomotive cabin is described herein as having: a fan for supplying air; a horizontal duct comprising a top portion operative to support a floor of the locomotive cabin and opposed side portions attached to the top portion and to respective opposed joists disposed under the floor, the horizontal duct in fluid communication with the fan for conveying the air; and an outlet in fluid communication with the horizontal duct for distributing the air into the locomotive cabin. By using the duct as a structural support member for the floor, one or more joists may be eliminated, thereby providing increased area under the floor for conveying ventilating air. 
     The apparatus is further described as including a stringer attached at opposed ends to the respective opposed joists and in contact with the horizontal duct top portion opposed the floor. The stringer provides additional support for the floor. Furthermore, the apparatus may include insulation disposed against the horizontal duct top portion opposed the floor; a cavity formed in the insulation; and the stringer at least partially disposed within the cavity. The insulation absorbs sound, thereby reducing the sound energy emitted from the apparatus. The apparatus is further described as having a vertical duct in fluid communication between the horizontal duct and the outlet, the vertical duct comprising a portion of a wall of a control compartment of the locomotive. The portion of a wall may be insulated to absorb sound and to prevent condensation from forming within the control compartment. 
     Similarly, a method for ventilating a locomotive cabin is described herein, the method comprising the steps of: providing a fan; replacing a joist in a floor of a locomotive cabin with a floor duct, the floor duct being operative to support the floor between adjoining opposed joists; and connecting the fan in fluid communication with the floor duct to provide air into a locomotive cabin. A further method for ventilating a locomotive cabin is described as including the steps of: providing a fan; forming a duct comprising a portion of a wall of a control compartment of a locomotive; and connecting the duct in fluid communication with the fan to provide air to the cabin of the locomotive. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The features and advantages of the present invention will become apparent from the following detailed description of the invention when read with the accompanying drawings in which: 
     FIG. 1 is a partial perspective view of a locomotive cabin illustrating a ventilation apparatus. 
     FIG. 2 is a partial cross-sectional view of the locomotive cabin of FIG. 1 illustrating the horizontal duct and adjoining joists providing support for the floor of the cabin. 
     FIG. 3 is a second cross-sectional view of the locomotive cabin of FIG. 1 illustrating the stringers used to provide additional support for the floor of the cabin. 
     FIG. 4 is a partial top cross-sectional view of the locomotive cabin of FIG. 1 illustrating a vertical duct forming a portion of the wall of a control compartment of the locomotive. 
    
    
     Similar components illustrated in more than one figure are numbered consistently in each of the figures. 
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 illustrates a portion of the cabin  10  of a locomotive with a portion of the floor  12  removed to illustrate portion of a ventilation apparatus  14 . The ventilation apparatus  14  includes a horizontal duct  16  disposed between joists  18  used to support the floor  12 . The ventilation apparatus  14  also includes a fan assembly  20  operable to supply air to the horizontal duct  16 . Fan assembly  20  may be used to provide heated, cooled, or unconditioned air to the cabin  10  through outlet  22 . One wall of the cabin  10  is formed by a control compartment  24  enclosing various controls used by an operator for controlling the operation of the locomotive. Control compartment  24  defines a sealed volume which is supplied with cooling air by a ventilation system that is separate from apparatus  14 . Horizontal duct  16  is also in fluid communication with a vertical duct (not shown) formed at the rear of control compartment  24 , which in turn is in fluid communication with outlet  26  for providing a second flow of ventilation to the locomotive cabin  10 . 
     Joists  16  are regularly spaced under floor  12  to provide adequate support. In one embodiment, joists  16  are spaced XXX inches on center. However, at the location of horizontal duct  16 , one such joist is missing from the regularly spaced pattern, and the support for floor  12  in that area is provided by duct  16 . Prior art ventilation systems for locomotives utilized ducts that were placed between the regularly spaced floor joists, with the duct providing no structural support function. Such designs were limited in cross-sectional area by the spacing between adjacent joists. By eliminating one or more joists and using horizontal duct  16  as a support member for floor  12 , the inventors have found that an increased cross-sectional floor area may be provided for ventilation air being supplied by ventilation apparatus  12 . The increase in cross-sectional area allows the air moving through the duct  16  to flow at a lower velocity, thereby generating less pressure loss than in prior art designs. This improved efficiency can be used to increase the ventilation flow rate, or alternatively, for applications where cabin noise levels are of concern, for decreasing the speed of the fan  20 . 
     FIG. 2 is a partial cross-sectional view of the horizontal duct  16  and adjoining joists  16 A, 16 B supporting floor  12 . Horizontal duct  16  has a top portion in contact with and operative to support floor  12 . Horizontal duct  16  also has opposed side portions  30 A, 30 B, preferably formed to be integral with top portion  28  and in support thereof. In one embodiment, top and side portions  28 , 30 A, 30 B are formed of 0.125 inch thick sheet metal. Side portions  30 A, 30 B are attached to respective joists  16 A, 16 B, such as by welding, for additional support of top portion  28  and floor  12 . 
     A bottom portion  32  of duct  16  is sealingly and removeably attached to the opposed side portions  30 A, 30 B. In one embodiment, fasteners  34  are used to compress a gasket  36  between the two portions to form an airtight seal defining ventilation cross-sectional area  38 . To reduce the sound energy conveyed through area  38 , insulating material  40  may be disposed within the duct  16  with a top portion  42  disposed proximate the horizontal duct top portion  28  and opposed side portions  44  disposed proximate the horizontal duct opposed side portions  30 A, 30 B. The insulation  40  may be fiberglass or other material known in the art. A perforated plate  46  may be disposed against the inside surface of the insulation  40  for allowing sound energy to pass through holes  48  to be dissipated within the insulation  40 , while providing a relatively smooth air flow surface along cross-sectional area  38 . 
     FIG. 3 is a partial cross-sectional view of the horizontal duct  16  and adjoining joists  16 A, 16 B at a different section than that of FIG.  2 . This view illustrates a stringer  50  attached at opposed ends to the respective opposed joists  16 A, 16 B, such as by weld joints  52 . Stringer  50  supports floor  12  by supporting the top portion  28  of horizontal duct  16 . Stringer  50  is at least partially disposed within a cavity  54  formed in the insulation  40 . A plurality of stringers  50  may be used along a length of horizontal duct  16  as needed to provide additional support for floor  12 . The presence of stringer  50  does not reduce the cross-sectional flow area  38  of the ventilation apparatus because the stringer  50  is recessed into cavity  54 . Stringer  54  may be formed of a metal, plastic or reinforced composite material, for example, and it may have a channel, I-beam, or T-beam cross-sectional shape, for example. The use of one or more stringers  50  permits the top portion  28  and side portions  30 A, 30 B of duct  16  to be fabricated of a lighter material while still maintaining the required support for floor  12 . The location where stringer  50  passes through the side portion  30 A, 30 B should be maintained as airtight, such as by welding of the side portions  30 A, 30 B to the stringer  50 . 
     Referring again to FIG. 1, in one embodiment of this invention the ventilating air is conveyed from fan assembly  20  to the cabin  10  by a vertical duct passing through control compartment  24  in fluid communication with outlet  26 . FIG. 4 is a partial cross-sectional view of a portion of control compartment  24  showing the vertical duct  55 . Vertical duct  55  is formed in part by a portion of a wall  56  of control compartment  24  of the locomotive. In the embodiment illustrated in FIG. 4, the portion of the wall  56  of the control compartment forms three sides of the generally rectangular cross-section of duct  55 . The fourth side of the duct  55  is formed by a cover plate  58  attached to control compartment  24  by fasteners  60  to define a cross-sectional flow area  62 . Space within the control compartment  24  of a locomotive is very limited. The use of a portion of the wall  56  of the control compartment  24  as a portion of the wall of duct  55  eliminates the need for a separate structure for these two functions, thereby providing the opportunity for an increased cross-sectional flow area  62  when compared to prior art devices. Insulation  64  is disposed against the portion of the wall  56  of the control compartment  24  to reduce the noise conveyed through the duct  55 , but more importantly, in order to prevent the formation of condensation in the interior of the control compartment  24  when the air conveyed by duct  55  is cooled. A similar structure may be used to form a horizontal duct  62  along the top of control compartment  24 . As seen in FIG. 1, the common wall between horizontal duct  62  and the control compartment  24  forms only one side of the generally rectangular cross-section of duct  62 . It may be appreciated that in other embodiments the common wall may form any subset of the overall perimeter of a duct. 
     Ducts  16 , 55 , 62  are connected together in fluid communication with fan  20  to provide ventilating air to cabin  10  through outlets  22 , 26 . It may be appreciated that this invention includes a method for ventilating a locomotive cabin and a method of reducing the noise in a locomotive cabin that includes the steps of providing the structures illustrated in FIGS. 1-4. By providing an increased cross-sectional flow area  38 , 62  when compared to prior art devices, the ventilating apparatus  14  of the present invention will generate a reduced level of sound energy in cabin  10 . The level of sound energy is further reduced by the use of insulation  40 , 64 , and by the avoidance of obstructions in the air flow path, such as by the use of recessed stringers  50 . This invention may be implemented in the design of a new locomotive, or it may be implemented by back-fitting such improvements into an existing locomotive design. By replacing one or more of the regularly spaced floor joists, additional area for ventilating ducts may be provided. By using a ventilating duct to support the floor in the area of a replaced joist, the stability of the floor is maintained. Because the floor of a locomotive is subject to significant low frequency bending stress and displacement, it is desirable to avoid long runs of horizontal duct  16  without providing a bend or other means for accommodating displacements. In one embodiment, horizontal duct  16  is limited to a maximum straight length of approximately seven feet. Furthermore, sharp bends should be avoided in the ductwork to avoid the generation of sound energy as air passes through the bend. By combining the steps and structure described above, the overall level of sound energy produced by the HVAC system operating at maximum fan speed was reduced in one application from approximately 75 dbA to approximately 65 dbA. 
     While the preferred embodiments of the present invention have been shown and described herein, it will be obvious that such embodiments are provided by way of example only. Numerous variations, changes and substitutions will occur to those of skill in the art without departing from the invention herein. Accordingly, it is intended that the invention be limited only by the spirit and scope of the appended claims.