Abstract:
A sound suppression system for suppressing the noise of an engine within an enclosure of an outdoor unit for a transport refrigeration system. A resonator is provided to suppress noise caused by the inflow of air to the air intake manifold of the engine, and a sound panel is provided in the bottom wall of the enclosure to suppress noise emanating from the engine. The resonator and the sound panel are co-located in the same plane and are preferably integrally formed of a molded plastic material.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates generally to mobile refrigeration units and, more particularly, to a sound attenuation method and apparatus for a refrigeration unit powered by an internal combustion engine. 
     One well known method of transporting perishable goods is by way of a truck or trailer having a container which is refrigerated by way of an attached refrigeration unit. The refrigeration unit has an internal evaporator coil portion and an external portion that contains a condenser coil, a compressor, and an engine for driving the compressor. Since the engine is relatively loud when operating, it is important to suppress the sound from emanating to the surrounding area as much as is practicable. This is particularly true such as when, for example, the truck/trailer is parked for the night, since the truck/trailer may be in a residential or otherwise populated area. 
     In such a refrigeration system, there are commonly two methods for limiting the sound emanating therefrom. First, the compartment containing the internal combustion engine is closed as much as possible from the outside, and sound attenuating material is placed at various locations within the containing structure. Secondly, in order to attenuate the sound of air passing to the intake manifold of the engine by way of the air cleaner, a resonator is provided. A resonator is typically a cylindrical shaped “dead air space” or tin can that is fluidly connected to the intake manifold, and is placed somewhere in the containing structure. Whereas the particular location is not important, there is a desire to conserve and effectively use the available space within the containing structure. 
     It is therefore an object of the present invention to provide an improved sound attenuation system for a mobile transport refrigeration system. 
     Another object of the present invention is to provide a suitable structure for attenuating both the sound of an internal combustion engine and the sound of air entering the inlet manifold thereof. 
     Another object of the present invention is the provision for effectively using the available space and for reducing the number of components included in the sound attention component. 
     Briefly, the objects of the present invention are attained by the use of a single structure that combines the elements of a resonator and a sound attenuating wall in one extremity of the containing structure. In this way, the available space is very effectively used and the number of components is reduced. 
     In the preferred embodiment of the invention, a single plastic component is formed of both a tubular resonator portion located in a plane, and a planer portion is integrally attached to the resonator so as to form an extension thereof in the same plane. 
     In accordance with a further aspect of this invention, the single component is comprised of a resonator portion and a planer portion. The two plastic halves are vacuum molded together to form the final single component that is placed in one wall of the containing structure for the outdoor unit. 
     The above, and other objects, features and advantages of the present invention will become more apparent from the following description when read in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a partial perceptive view of an outdoor refrigeration unit with the present invention incorporated therein. 
     FIG. 2 is a partial perceptive view of the resonator/sound attenuating panel portion thereof. 
     FIG. 3 is another perceptive view of the resonator/sound attenuator panel in its unassembled form. 
     FIG. 4 is a top view of the resonator/sound attenuator panel in accordance with the present invention. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENT 
     Referring now to FIG. 1 the invention is shown generally at  10  as incorporated into a lower section  11  of a frame  12  which is adapted for mounting on the outside of a transportable refrigerated container such as a truck or trailer or the like. 
     An upper section  13  of the frame  12  contains a condenser coil which, together with the components within the lower section  11  comprise the high pressure side of a refrigeration system for maintaining a predetermined temperature within the transportable container. The low pressure side of the refrigeration system includes an evaporator coil and cool air distribution system which is located on the inner side of the container (not shown). 
     Mounted in frame lower section  11  is an internal combustion engine  16 , such as a diesel engine, and a refrigeration compressor  17  which is drivingly attached to the engine  16 . During periods in which a temperature sensor in the container indicates that the container is at a higher temperature then desired, the engine  16  is operating at a relatively fixed speed to drive the compressor  17  in order that the refrigerant will be cycled through the refrigeration system to cool the container. Generally, the system is adapted for two speed operation, i.e., either at a relatively high speed or a relatively low speed, depending on the demands (i.e., the difference between the desired temperature and the actual sensed temperature in the container). 
     The engine  16  includes an air intake manifold  18  for channeling air into the cylinders of the engine  16  for combustion purposes. Attached to the air intake manifold  18  is a Y fixture  19  having a non-bifurcated end  21  fluidly attached to an air cleaner  22  which in turn, is adapted to receive ambient air into its other end. At the other end of the Y fixture  19  is a pair of legs  23  and  24 . The leg  23  fluidly connects the air cleaner  22  to the air intake manifold  18 , and leg  24  fluidly connects the air cleaner  22  to an input end  27  of a resonator  28 . The resonator  28  operates in a conventional manner to attenuate the noise that would otherwise by caused by the flow of intake air into the intake manifold  18 . 
     Referring now to FIGS. 2-4, there is shown a lower panel  29  which is mounted in a lower opening  30  of the frame  12  so as to close that lower opening  30  for purposes of isolating the motor noise within the frame  12 . 
     The lower panel  29  comprises a single element that is integrally formed of the resonator portion  28  and a surrounding planar portion  31 . The lower panel is made of a high strength, low weight plastic material, and is preferably formed by way of vacuum molding process. That is, a pair of halves, with each half being essentially the mirror image of the other and being of a thickness which is one half the thickness of the lower panel  29  as shown, are separately formed. The two halves are then put together in a clam shell fashion and vacuum molded together such that the two halves are fused into a single integral structure. Such a structure provides the tubular resonator portion  28  which is surrounded by, and integrally formed with the planar portion  31  which functions to close the bottom opening  30  and attenuate the nosie that would otherwise emanate therethrough. 
     The lower panel  29  is fastened to the frame  12  at its two sides  32  and  33  by a fastener or the like. At side  32 , there are a plurality of indents  34  through which fasteners are passed and secured to frame  12 . At the other side  33 , there are a plurality of flanges  36  extending obliquely upwardly and having integrally attached thereto a generally horizontal extension  37  having a slot  38  formed therein. A fastener is passed through slot  38  that engages with supporting structure on frame  12 . 
     At the end  39  opposite the input end  27  there is provided a an upwardly extending barrier structure  41  which functions to seal off an end area that would otherwise be open to the emanation of noise from the area above the panel  29  to an end cavity. 
     The lower panel  29  thus serves the purpose of attenuating sound in two ways. It serves to position the resonator  28  which attenuates the sound of the incoming air to the inlet manifold  18 , and it also serves as a bottom cover to prevent the engine noise from traveling downwardly through the bottom end of the frame  12 . 
     It will be seen in FIGS. 1-4 that the resonator  28  includes two sides on each of the inputs ends  27 . Side  42  has a pair of shorter tubes with a closed end  43 , whereas side  45  has a pair of longer tubes with a closed end  45 . Each of these sides  42  and  44  is designed to accommodate the attenuation of sound that results from a predetermined engine speed. That is, generally, the shorter side  42  is sized such that when the engine is operating at the relatively slow speed, this side is effective in attenuating the sound of the incoming air into the manifold  18 . The longer side  44  is similarly tuned to be effective in attenuating the sound of the incoming air when the engine is operating at the relatively higher speed. During the period when one side is responsive to the particular speed of the engine the other side is essentially nonfunctional in that it does little to attenuate the sound, but is not necessary because of the sound characteristics of that particular speed. 
     Having described a preferred embodiment of the invention with reference to the accompanying drawings, it is understood that the invention is not limited to that precise embodiment, and various changes and modifications may be effected therein by one skilled in the art without departing from the scope or spirit of the invention as defined in the appended claims.