CROSS REFERENCE TO RELATED APPLICATION 
     This application is related to the following pending applications being concurrently filed herewith and assigned to the assignee of the present invention: 
     
       
         
               
               
             
           
               
                   
               
               
                   
                 Our 
               
               
                 Title 
                 Docket No.: 
               
               
                   
               
             
             
               
                 Modular Rooftop Air Conditioner for a Bus 
                 210_546 
               
               
                 Modular Bus Air Conditioning System 
                 210_545 
               
               
                 Supply Air Blower Design in Bus Air Conditioning Units 
                 210_549 
               
               
                 Bus Rooftop Condenser Fan 
                 210_550 
               
               
                 Method and Apparatus for Refreshing Air in a Bustop Air 
                 210_548 
               
               
                 Conditioner 
               
               
                 Coil Housing Design for a Bus Air Conditioning Unit 
                 210_547 
               
               
                 Integrated Air Conditioning Module for a Bus 
                 210_558 
               
               
                 Fresh Air Intake Filter and Multi Function Grill 
                 210_554 
               
               
                 Integrated Air Conditioning Module for a Bus 
                 210_557 
               
               
                 Modular Air Conditioner for a Bus 
                 210_561 
               
               
                 Modular Air Conditioner for a Bus Rooftop 
                 210_562 
               
               
                 Evaporator Section for a Modular Bus Air Conditioner 
                 210_564 
               
               
                 Wide Evaporator Section for a Modular Bus Air 
                 210_565 
               
               
                 Conditioner 
               
               
                 Condensate Pump for Rooftop Air Conditioning Unit 
                 210_568 
               
               
                 Condensate Removal System Rooftop Air Conditioning 
                 210_551 
               
               
                 Modular Rooftop Unit Supply Air Ducting Arrangement 
                 210_577 
               
               
                 Configuration for Modular Bus Rooftop Air Conditioning 
                 210_595 
               
               
                 System 
               
               
                 Unibody Modular Bus Air Conditioner 
                 210_596 
               
               
                   
               
             
          
         
       
     
     BACKGROUND OF THE INVENTION 
     This invention relates generally to air conditioning systems and, more particularly, to an air conditioning system for the rooftop of a bus. 
     The most common approach for air conditioning a bus is to locate the air conditioning components on the rooftop thereof. Inasmuch as power is available from the engine that drives the bus, it has become common practice to locate the air conditioning compressor near the drive engine such that the drive engine is drivingly connected to the compressor, with the compressor then being fluidly interconnected to the air conditioning system on a rooftop of a bus. This, of course, requires rather extensive piping between the engine compartment and the air conditioning unit, thereby increasing installation and maintenance costs. 
     Another problem with such existing systems is that the speed that the compressor is driven is dependent on the speed in which the drive engine is running. Thus, when the drive engine is idling in a parking lot, for example, the compressor is running at a relatively slow speed which may not be sufficient to provide the desired degree of air conditioning. It is therefore generally necessary to oversize the compressor in order to obtain the performance needed under these conditions. 
     Others problems associated with such a motor driven compressor system is that the open drive compressor needs a shaft seal and a mechanical clutch, both of which are subject to maintenance problems. Further, since DC power is available on a bus, DC motors have been used for the air conditioning system. In general, DC motors are not as reliable as AC motors since they have brushes that wear out, and brushless motors are relatively expensive. 
     In addition to the problems discussed hereinabove, it is recognized, that because the wide variety of bus types and application requirements, it has been necessary to provide many different types and variations of air conditioning systems in order to meet these different requirements and vehicle interfaces. As a result, the manufacturing and installation costs, and sustaining engineering resources that are necessary in order to properly maintain and service these units, are relatively high. 
     It is therefore an object of the present invention to provide an improved bustop air conditioning system. 
     Another object of the present invention is the provision for a bus air conditioning system which is effective at all operating speeds of the bus, while at the same time does not require an oversized compressor. 
     Yet another object of the present invention is the provision for reducing the manufacturing, installation, and maintenance costs of a bus air conditioning system. 
     Yet another object of the present invention is the provision for a bus rooftop air conditioning system which is economical to manufacture and effective in use. 
     These objects and other features and advantages become more readily apparent upon reference to the following descriptions when taken in conjunction with the appended drawings. 
     SUMMARY OF THE INVENTION 
     Briefly, in accordance with one aspect of the invention, an air conditioning module is assembled with its condenser coil, evaporator coil and respective blowers located within the module and so situated that a standard module can accommodate various installation interfaces with different types and locations of return air and supply air ducts on a bus. 
     By yet another aspect of the invention, each of the identical modules includes all the necessary components with electrical power being provided to the electrical components by an inverter/controller that is powered by a motor driven generator. 
     By yet another aspect of the invention, a flexible duct is provided with its one end interconnected to the air conditioning module, and its other end connected to the supply air duct of the bus. Such a duct can accommodate openings of varying width and at different lateral spacings from the centerline of the bus. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a module as installed on the rooftop of a bus in accordance with a preferred embodiment of the invention. 
     FIG. 2 is a perspective view of a module with the top cover removed. 
     FIG. 3 is a schematic illustration of the electrical and refrigerant circuits within the module in accordance with the preferred embodiment of the invention. 
     FIG. 4 is a front elevational view of the condenser section of the module. 
     FIG. 5 is a front elevational view of the evaporator section of the module. 
     FIGS. 6-8 are front elevational views of the evaporator section as applied to different types of bus rooftops. 
     FIGS. 9-11 are front elevational views of the flexible duct arrangement of the present invention as applied to different types of bus rooftops. 
     FIG. 12 is a perspective view of a flexible duct with end plates in accordance with a preferred embodiment of the invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The inventive module is shown generally at  10  as applied to the rooftop  11  of a bus in accordance with the present invention. Electrical power is provided to the module  10  by way of line  12 , which in turn receives its power from a generator  13  driven by the bus engine  14  as shown. 
     The module  10  interfaces with openings in the bus top so that fans within the module  10  cause the return air from the passenger compartment to flow upward into the module  10  where it is conditioned, and the conditioned air to then flow downwardly into supply air ducts that carry the conditioned air to the passenger compartment. The various structures and the manner in which they interface with the bus rooftop  11  will more fully described hereinafter. 
     In FIG. 2, the module  10  is shown with its cover removed to include a frame  16  with an evaporator section  17  attached to one end thereof and a condenser section  18  attached to the other end thereof. Adjacent the condenser section  18  is a power section  19  which includes a compressor  21  and an inverter/controller  22 . The manner in which they provided motive power to the refrigerant circuit and electrical power to the electrical components of the module  10  will be more fully described hereinafter. 
     The evaporator section  17  comprises a pair of identical units in abutting end-to-end relationship with each unit including an evaporator blower  23  with is evaporator blower motor  24 , and an evaporator coil  26 . Briefly, the evaporator blower  23  draws in return air from the passenger compartment of the bus, and fresh air from outside and passes a mixture of the two through the evaporator coil  26  to be conditioned, after which it flows back to the passenger compartment by way of the supply air ducts. This will be more fully described hereinafter. 
     Within the condenser section  18 , there is provided a condenser fan  27  driven by an electric motor, and a pair of condenser coils  28  and  29 . Briefly, the condenser fan draws air upwardly to create a vacuum below, which in turn causes fresh air to be drawn through the condenser coils  28  and  29  to condense the refrigerant flowing through the coils  28  and  29 . The resulting warm air is then discharged upwardly to the atmosphere by the fan  27 . 
     Referring now to FIG. 3, the module  10  is shown with its electrical connection by way of line  12  to the generator  13  and driving motor  14 . The inverter/controller  22  receives AC power from the generator, or alternator, and, in turn provides discretely controlled AC power to the evaporator blower motor  24 , the drive motor  31  of the condenser fan  27  and the drive motor  32  of the compressor  21 . A plurality of control sensors, shown generally at  33  provide feedback to the inverter/controller  22  as necessary for it to control the AC power being delivered to the various drive motors. 
     As will be seen, the refrigeration circuit is a closed circuit through which the refrigerant flows from the compressor  21  to the condenser  29 , an expansion valve  34 , the evaporator  26  and finally back to the compressor  21 . This is accomplished in a conventional manner. 
     It will be seen that the module  10  is self-contained with all of the necessary components, with the only input thereto being the electrical power by way of the electrical line  12 . Other modules, indicated as numbers  2 - 6  are identically configured and are powered and controlled in the same manner. 
     Returning now to the condenser section  18  as shown in FIG. 4, the flow of air as caused by the condenser fan  27  is shown by the arrows. Fresh air is drawn in through the fresh air intake openings  36  and  37 , passes through the respective condenser coils  28  and  29  and then flow upwardly through the condenser fan  27  and the condenser outlet air opening  38  as shown. 
     Within the evaporator section  17  as shown in FIG. 5, the relatively warm return air flows upwardly from a return air duct communicating with the passenger compartment and enters a return air compartment  39  of the evaporator section  17  as shown by the arrows. The evaporator blower  23  causes the return air to flow upwardly to its inlet at the top, and at the same time, fresh air may be brought in by way of a fresh air flap in a manner to be described hereinafter. A mixture of the two airflow streams is thus admitted at the intake of the evaporator blower  23  and caused to flow downwardly and outwardly as indicated by the arrows to the evaporator coils  26 . After passing through the evaporator coil  26  it is then caused by a curved cowling  41  to flow downwardly to a supply air duct leading to the passenger compartment. Thus, while the module is operating, there is a constant circuitous flow of return air out of the passenger compartment and of conditioned air back into the passenger compartment. The amount of return air that is discharged to the outside, and also the amount of fresh air that is brought into the circuit from the outside is controlled by the selective movement of the fresh air flaps as will be described hereinafter. 
     There are shown in FIGS. 6-8, installations of the module  10  with various types of buses and associated return air and supply air ducts. In FIG. 6, for example, a wide bus installation is shown wherein the existing duct work within the bus includes supply air ducts  43  and  44  near the lateral sides of the bus, and return air ducts  46  and  47  that are closer to the center line of the bus, but are substantially spaced apart. Here it will be seen that the return air ducts  46  and  47  communicate directly with the return air compartment  39  of the module  10 , but at a position at near the outer end thereof. Cowlings  35  fluidly interconnect the flow from the evaporator coils  26  with the supply air ducts  43  and  44 . 
     In FIG. 7, which shows a narrow bus installation, again the supply air ducts  48  and  49  are near the transverse sides of the bus. But the return air ducts  51  and  52  are abutting each other at the center line of the bus. Again, the return air ducts  51  and  52  fluidly communicate with the return air compartment  39 , but at the other end thereof. Smaller cowlings  40  fluidly interconnect the conditioned air discharge to the supply air ducts  48  and  49 . 
     Finally, in FIG. 8 there is shown a curved top bus wherein the supply air ducts  53  and  54  are again near the transverse sides of the bus, but the return air ducts  56  and  57  are in intermediate positions, relatively close to the center line but substantially spaced apart. Again, the return air ducts  56  and  57  fluidly communicate with the return air compartment  39 , but at a position intermediate the two ends thereof. Cowlings  45  interconnect the conditioned air flow from the evaporator coils  26  to the respective supply air ducts  53  and  54 . 
     It will thus be seen that a single module is so designed and constructed that it can accommodate any of these various installation requirements without modification of the module itself. That is, the conditioned air discharge opening  50  is sufficiently large in the transverse direction to accommodate the various supply air duct orientations, and, more importantly, the return air compartment  39  is relatively large in the transverse direction so as to accommodate each of the various types of return air duct configurations as shown. 
     As will be seen in the configurations shown in FIGS. 6-8, even though the modules themselves are identical for the various installation requirements, the cowlings  35 ,  40  and  45  must be uniquely designed to accommodate the particular installation arrangement. That is, the cowling  35  for a wide bus arrangement must be larger then the cowling  40  for a narrow bus installation. More importantly, however, is that with this arrangement, the cowlings must be substantially air tight in order to ensure that most, if not all of the conditioned air reaches the supply air ducts and does not leak out to the atmosphere. Similarly, those cowlings must be substantially water tight so as to preclude the leakage of moisture from outside into the supply air ducts. These problems are addressed by the use of a flexible duct arrangement as shown in FIGS. 9-12. 
     In FIG. 9, the module is shown as installed on a flat, wide bus roof having a supply air duct  44 . A flexible duct  61  is installed to fluidly interconnect the evaporator compartment  62  to the supply air duct  44 . Connection at each end is accomplished by use of end plates or flanges  63  and  64  which are connected, and preferably, integrally formed with the flexible duct  61  as shown in FIG.  12 . The flexible duct is made from any air tight, flexible material such as a plastic cloth or elastomeric material, and the end plates  63  and  64  are made of a metal or elastomeric material which is sufficiently rigid to accommodate a rigid attachment to the corresponding structure. That is, the end plate  63  is secured to the evaporator outlet frame  64  by fasteners  66 , and the end plate  64  is securely fastened to the rooftop by fasteners  67  as shown in FIG.  9 . 
     In the FIGS. 10 and 11 embodiments, which show use with a narrow width bus roof and a curved bus roof, respectively, the same flexible duct  61  with it end plates  63  and  64  are secured in the same manner, the difference being that the flexible duct is selectively stretched out to a different extent. This allows the same module, with the same flexible duct to be used in all three different types of installations. 
     In order to provide a finished appearance, and to protect the flexible duct  61  from the outside elements, it is necessary to provide a duct cover or cowling, which, because of the different configurations, must necessarily be uniquely designed to fit the particular arrangement. However, there are certain features that are common to each in order to provide a standard, effective attachment means. In this regard, reference is made to FIG. 12 wherein the end plate  64  is shown to include an upstanding flange  68  at its outside edge. This upstanding flange allows for interconnection of the lower end of the cover or cowling by way of a plurality of fasteners. 
     Referring again to FIG. 9, a cowling  69  has a rather long flat upper portion  71  and a rather short downwardly extending portion  72 . The upper portion  71  is secured to the module top structure  73  by a plurality of fasteners  74 , while the bottom portion  72  is secured to the upstanding flange  68  by a plurality of fasteners  76 . In a similar manner, the cowlings  77  and  78  are secured in place as shown in FIGS. 10 and 11, respectively. In this manner, the cowlings, which are generally made of a suitable material such as a flexible plastic or sheet metal, are fastened to the bracket  68  and the module top structure  73  to form a continuation of the module cover transition to the roof and also provide protection from the elements and damage to the duct disposed therebelow. The upstanding flange  68  is properly positioned by its associated end plate  64  such that the appropriate cowling  69 ,  77  or  78  will be maintained in the proper position on the roof of the bus to provide an esthetic and protective function. 
     Although the duct  61  has been shown and described as a single duct of uniform diameter, it may as well be of other shapes, sizes and configurations. For example, it may be rectangular or elliptical in cross sectional shape, or it may comprise a pair on other plurality of side by side duct like elements. 
     While this invention has been described with reference to a particular structure disclosed herein, it should be understood that it is not confined to the details set forth in this application, but is rather intended to cover any modifications and changes as may come within the scope of the following claims.
A module is provided for attachment to the roof of a bus and includes all of necessary components for conditioning the return air from the passenger compartment and delivering conditioned air thereto. Each module includes an evaporator section, a condenser section and a power section including a compressor and an inverter. The evaporator sections have a return air compartment that extends a substantial distance across the roof of the bus such that a single design can meet the needs of various return air duct installations of various types of buses. Provision is made to interconnect a evaporator discharge opening with a supply air duct for the bus by way of a flexible duct having integrally formed end plates for connection by way of fasteners. The lower end plate which is secured to the supply air duct also includes an upstanding flange for connecting a protective cover thereto.