Patent Document

FIELD OF THE INVENTION 
   This invention relates generally to engine driven, electrical generators, and in particular, to a method and an apparatus for reducing the fan noise associated with operating an engine driven, electrical generator. 
   BACKGROUND AND SUMMARY OF THE INVENTION 
   Engine driven, electrical generators are used in a wide variety of applications. Typically, such electrical generators utilize a single driving engine directly coupled to a generator or alternator through a common shaft. Upon actuation of the engine, the crankshaft thereof rotates the common shaft so as to drive the alternator which, in turn, generates electricity. It can be appreciated that since the engine and the alternator are housed in a single enclosure, a significant amount of heat is generated within the enclosure during operation of the electrical generator. Typically, the electrical generator includes a radiator operatively connected to the engine such that engine coolant from the engine circulates through the radiator during operation of the engine. A fan, coupled to the crankshaft of the engine, rotates during operation of the electrical generator and draws air across the plurality of radiator tubes of the radiator so as to effectuate the heat exchange between the engine coolant flowing through the plurality of radiator tubes of the radiator and the air within the enclosure. In such a manner, it is intended that the air passing over the radiator tubes of the radiator having a cooling effect thereon so as to maintain the temperature of the engine coolant, and hence the temperature of the engine, below a safe operating limit. 
   As is known, operation of an engine driven, electrical generator can produce unwanted noise. The noise generated by the electrical generator during operation is often a result of the rotation of the fan used to cool the engine coolant flowing through the radiator tubes of the radiator of the electrical generator. Consequently, various attempts have been made to limit the time period and the speed at which the fan rotates during operation of the electrical generator to those situations wherein the engine coolant flowing through the radiator must be cooled. By way of example, a sensor may be provided to monitor the temperature of the engine coolant. The fan is operatively connected to the crankshaft of the engine when the temperature of the engine coolant exceeds a predetermined threshold. Alternatively, in automotive applications, the fan may be connected to the crankshaft by a thermally responsive clutch. The clutch interconnects the fan to the crankshaft of the engine when the air drawn through the radiator by the fan exceeds a predetermined temperature threshold. 
   While these prior methods of minimizing rotation of the fan of an engine driven, electrical generator have been somewhat successful, each of these methods has significant limitations. By way of example, the use of a sensor and the associated electronics for selectively connecting the fan to the crankshaft of the engine can be cost prohibitive. Alternatively, by drawing air inward through the radiator as provided in various automotive applications, it has been found that the thermally responsive clutch interconnects the fan to the crankshaft at the engine for a longer period of time than is necessary to cool the engine coolant flowing through the radiator to a safe operating level. Hence, it can be appreciated that these prior art fan systems will generate more noise than necessary and/or desired by an end user. 
   Therefore, it is a primary object and feature of the present invention to provide a method and apparatus for reducing the fan noise associated with the operation of an engine driven, electrical generator. 
   It is a further object and feature of the present invention to provide a method and apparatus for reducing the fan noise associated with operation of an engine driven, electrical generator that is simple and inexpensive to implement. 
   It is a still further object and feature of the present invention to provide a method and apparatus for reducing the fan noise associated with the operation of an engine driven, electrical generator that sufficiently cools the engine coolant flowing through the radiator of the electrical generator with the fan. 
   In accordance with the present invention, a method of cooling a generator set having a radiator operatively connected to an engine is provided. The method includes the steps of positioning the fan on a first inward side of the radiator and monitoring the temperature adjacent the first side of the radiator. The fan is rotated in response to the temperature of air on the first side of the radiator exceeding a threshold. 
   The method also includes the conditional step of urging air with the fan from the first side to the second side of the radiator in order to cool the radiator. A portion of the air urged from the first side to the second side of the radiator is recirculated back to the first side of the radiator. The fan is slowed and ultimately stopped in response to the temperature of the air on the first side of the radiator dropping below a predetermined value. Thereafter, the method contemplates returning to the step of rotating the fan after the fan has been stopped. 
   The fan may be selectively connected to a drive shaft of the engine with a thermally responsive clutch. The clutch is movable between an engaged condition where the rotation of the drive shaft is translated to the fan and a disengaged condition wherein the fan is disconnected from the drive shaft. The clutch moves between the engaged condition and the disengaged condition in response to the temperature monitored. 
   In accordance with a further aspect of the present invention, a method is provided for cooling a generator set having a radiator operatively connected to an engine. The method includes the step of urging air to flow from a first side to second side of the radiator such that a portion of the air returns to the first side of the radiator. The temperature of the air on the first side of the radiator is monitored and the flow of air to the first side to the second side of the radiator is slowed or stopped in response to the temperature of the air on the first side of the radiator dropping below a threshold. 
   After the flow of air is stopped, the method contemplates returning to the step of urging air to flow from the first side to the second side of the radiator in response to the temperature of the air on the first side of the radiator exceeding a predetermined value. The step of urging air to flow from a first side to a second side of the radiator includes the additional steps of positioning a rotatable fan on the first side of the radiator and interconnecting the fan to a crankshaft of the engine. In order to stop the flow of air from the first side to the second side of the radiator, the fan is disconnected from the crankshaft. 
   It is contemplated to operatively connect the rotatable fan to a crankshaft of the engine with a thermally responsive clutch. The clutch is movable between a first engaged condition wherein the fan rotates with the crankshaft and a second disengaged condition wherein the crankshaft rotates independent of the fan. 
   In accordance with a still further aspect of the present invention, a device for cooling engine coolant flowing through a radiator of an engine driven, electrical generator set is provided. The engine has a rotatable crankshaft. The device includes the rotatable fan position between the engine and the radiator. A thermally responsive clutch selectively connects the fan to the crankshaft in response to the temperature of the air adjacent thereto. The clutch is movable between a disengaged condition wherein the crankshaft rotates independent of the fan and an engaged condition wherein the fan is driven by the crankshaft. The fan is orientated to draw air from over the engine and urge the air through the radiator with the clutch in the engaged position. 
   The clutch is positioned adjacent the first side of the radiator between the radiator and the engine. The crankshaft rotates in a first direction such that the fan also rotates in the first direction with the clutch in the engaged position. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The drawings furnished herewith illustrate a preferred construction of the present invention in which the above advantages and features are clearly disclosed as well as others which will be readily understood from the following description of the illustrated embodiment. 
     In the drawings: 
       FIG. 1  is a schematic view of a prior art method and apparatus for reducing the fan noise associated with the operation of an engine; and 
       FIG. 2  is a schematic view of a method and apparatus for reducing the fan noise associated with the operation of an engine driven, electrical generator in accordance with the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring to  FIG. 1 , a prior art noise reduction system for use with an engine driven cooling system is generally designated by the reference numeral  10 . Noise reduction system  10  includes fan  12  having a plurality of fan blades  14  extending radially from central hub  16 . Central hub  16  is positioned on first side  19  of a conventional radiator  18  and is operatively connected to fan shaft  20  by thermally responsive fan clutch  22 . As is conventional, fan shaft  20  is connected to the crankshaft of an engine which, in turn, drives an alternator that generators electricity. As described, fan  12  is configured such that counterclockwise rotation of fan  12  by fan shaft  20  draws air, generally indicated by lines  26 , axially through the plurality of radiator tubes of radiator  18 , from second side  25  of radiator  18  to first side  19  of radiator  18 . 
   Fan clutch  22  and fan  12  are disposed axially between the engine (not shown) and first side  19  of radiator  18 . Fan clutch  22  may take the form of a viscous fan drive that includes a bimetallic temperature sensing element  24  that senses ambient temperature and causes fan clutch  22  to operate in a disengaged condition when the ambient temperature is below a predetermined temperature and to operate in an engaged position when the ambient temperature is above the predetermined temperature. By way of example, temperature sensing element  24  senses the temperature of the air immediately forward thereof. With fan clutch  22  in a disengaged condition, fan shaft  20  rotates independently of fan  12 . With fan clutch  22  in an engaged condition, fan  12  rotates in unison with fan shaft  20 . 
   In operation, upon actuation of the engine, the crankshaft rotates fan shaft  20 . Once the temperature of the ambient air adjacent temperature sensing element  24  exceeds the predetermined temperature, fan clutch  22  moves from the disengaged condition to the engaged condition. As a result, fan  12  rotates in unison with fan shaft  20  thereby drawing air  26  through radiator  18 . Thereafter, the air, generally indicated by lines  28 , is urged axially by fan  12  over the engine of the electrical generator. It can be appreciated that ambient air  26  which engages temperature sensing element  24  is preheated as the ambient air  26  passes over the radiator tubes of radiator  18 . As a result, fan clutch  22  is maintained in its engaged position for an extended period of time. Once the temperature of the ambient air sensed by temperature sensing element  24  drops below the predetermined temperature, fan clutch  22  returns to the disengaged condition wherein fan shaft  20  rotates independently of fan  12 . 
   Referring to  FIG. 2 , a noise reduction system for an engine-driven electrical generator set in accordance with the present invention is generally designated by the reference numeral  30 . Noise reduction system  30  includes fan  32  having a plurality of blades  34  extending radially from central hub  36 . Central hub  36  is positioned on first side  47  of a conventional radiator  44  and is operatively connected to fan shaft  38  by thermally responsive fan clutch  40 . Fan shaft  28  is also operatively connected to the crankshaft of an engine (not shown) used to drive the stand-by electrical generator. As described, crankshaft fan shaft  38  rotates in counterclockwise direction in response to operation of the engine. 
   Fan clutch  40  is preferably a viscous fan drive that includes bimetallic temperature sensing element  42  that senses ambient air temperature at a location immediately adjacent temperature sensing element  42 . Temperature sensing element  42  causes fan clutch  40  to operate in a disengaged condition when the ambient air temperature sensed is below a predetermined temperature, and to operate in an engaged condition when the ambient air temperature sensed is above the predetermined temperature. In its engaged condition, fan clutch  40  operatively connects fan  32  with fan shaft  38  such that rotation of fan shaft  38  by the crankshaft of the engine of the engine driven, electrical generator set is translated to fan  32 . It can be appreciated that in its engaged condition, fan clutch  40  may be fully or partially engaged. With fan clutch  40  in the fully engaged condition, fan  32  rotates in unison with the crankshaft of the engine of the engine driven, electrical generator set. In its partially engaged condition, fan clutch  40  allows fan shaft  38  to slip with respect to the crankshaft such that fan  32  rotates at a predetermined speed less than the speed of rotation of the crankshaft. As such, it can be understood that fan clutch  40  causes fan  32  to rotate at a variable speed dependent upon the ambient air temperature sensed by temperature sensing element  42 . With fan clutch  40  in its disengaged condition, fan shaft  38  rotates independent of fan  32 . 
   As described, fan clutch  40  and fan  32  are disposed axially between the engine of the stand-by electrical generator set and first side  47  of radiator  44 . In addition, fan  32  is orientated such that with fan clutch  40  in its engaged condition, fan  32  will rotate in a counterclockwise direction drawing air over the engine of the stand-by electrical generator set. The air, generally indicated by lines  46 , is then urged axially through the radiator tubes of radiator  44  through first side  47  thereof. As best seen in  FIG. 2 , a majority of the air, generally indicated by lines  48 , passes through the radiator tubes of radiator  44  and continues to flow axially away from second side  50  of radiator  44 . However, a portion of the air, generally indicated by lines  52 , that is urged by fan  32  through radiator  44  recirculates back through radiator  44  from first side  50  to second side  47  thereof. A portion of the recirculated air, generally indicated by line  54 , is directed back towards temperature sensing element  42  of fan clutch  40 . It has been found that by recirculating a portion of the air which passes through radiator  44  of an engine driven electrical generator set, fan clutch  40  operates in its engaged condition for a shorter period of time. This, in turn, reduces the fan noise generated by fan  32  during operation of the engine driven, electrical generator set. It can be appreciated that the portion  54  of air recirculated back through radiator may be adjusted by incorporating an air duct system for directing the flow of air through the enclosure of the electrical generator or by varying the speed or pressure of the air flowing through radiator  44 . 
   In operation, the engine of the engine driven, electrical generator set is actuated such that the crankshaft rotates in a counterclockwise direction. As heretofore described, this, in turn, rotates fan shaft  38  in a counterclockwise direction. Once the temperature of the ambient air adjacent temperature sensing element  42  exceeds the predetermined temperature, fan clutch  40  moves to the engaged condition such that fan  32  rotates in unison with fan shaft  38  in a counterclockwise direction. As a result, ambient air is drawn over the engine of the stand-by electrical generator set. Thereafter, air  46  is urged through the radiator tubes of radiator  44  from through side  47  to second side  50  thereof. As heretofore described, a majority of air  48  continues to flow axially away from second side  50  of radiator  44 . However, a portion  52  of air  48  recirculates back through radiator  44  from second side  50  to first side  47 . The portion of air  54  that is recirculated back through radiator  44  flows axially towards temperature sensing element  42  of fan clutch  40 . Once the temperature of recirculated air  54  adjacent temperature sensing element  42  drops below the predetermined temperature, fan clutch  40  returns to the disengaged condition. As result, fan shaft  38  rotates independent of fan  32 . It can be appreciated that fan clutch  40  remains in its disengaged condition until such time as the ambient air temperature sensed by temperature sensing element  42  once again exceeds the predetermined temperature wherein the process heretofore described is repeated. 
   It can be appreciated that fan clutch  40  may incorporate a modulating viscous fan drive that does not immediately proceed between the disengaged condition and the engaged condition, but instead begins to engage at a predetermined ambient temperature and gradually increases it engagement with increasing ambient temperature, until fully engaged at an upper ambient temperature limit. 
   Various modes of carrying out the invention are contemplated as being within the scope of the following claims particularly pointing and distinctly claiming the subject matter that is regarded as the invention.

Technology Category: 2