Abstract:
Several embodiments of prime mover driven electrical generators wherein the power output is increased without increasing the driving speed by driving both of the generator elements in opposite directions.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     This invention relates to an electrical generating apparatus and more particularly to an improved generator that produces a large power output at a lower driven speed.  
         [0002]     The use of electrical generators powered by a prime mover such as an internal combustion engine are well known. Although various constructions have been proposed, the generator normally is comprised of an armature having a number of ferromagnetic pole teeth around which electrical coils are wound. These coils or more particularly the pole teeth face a plurality of circumferentially spaced permanent magnets and one of the elements, generally the one carrying the magnets is rotated so as to induce a current flow through the coils.  
         [0003]     Such an internal combustion engine driven generator is shown in Japanese Published Application JP Hei 8-80095. As is well known the amount of electrical power generated by such a generator is generally proportional to the speed at which it is driven. Therefore when large electrical power outputs are required, the speed of the driving engine is increased.  
         [0004]     However when the engine speed is increased, the engine noise may become objectionable. This can be avoided if a step up transmission of some type is interposed between the engine and the generator to increase the rotational speed in relation to the engine speed, but the inertial force of the generator is proportional to the square of the speed at which it is driven, putting increased loading on the bearings and causing vibrations both of which will adversely affect the unit life and increase the need for servicing.  
         [0005]     Therefore it is a principal object of the invention to provide a driven generator that can produce greater electrical power without requiring high rotational speeds achieved by either higher engine driving speeds or the use of step up transmissions.  
       SUMMARY OF THE INVENTION  
       [0006]     This invention is adapted to be embodied in an engine driven generator comprised of a first element comprising at least one permanent magnet and a second element having at least one pole tooth around which an electrical coil is wound. A prime mover arrangement is provided for driving both of the elements for rotation in opposite directions. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]      FIG. 1  is a side elevational view of an electrical generating apparatus constructed in accordance with a first embodiment of the engine with a portion of the electrical generator broken away to more clearly show the construction.  
         [0008]      FIG. 2  is an enlarged view of the broken away portion in  FIG. 1 .  
         [0009]      FIG. 3  is a view in part similar to  FIG. 2  and shows another embodiment of the electrical generator.  
         [0010]      FIG. 4  is a side elevational view, in part similar to  FIG. 1  and shows a third embodiment of the invention.  
         [0011]      FIG. 5  is an end elevational view taken in the direction of the arrow  5  in  FIG. 4 . 
     
    
     DETAILED DESCRIPTION  
       [0012]     Referring now in detail to the drawings and initially to  FIG. 1 , an electrical generating apparatus constructed in accordance with a first embodiment is indicated generally by the reference numeral  11 . The apparatus  11  includes a base  12  upon which an electrical generator, indicated generally by the reference numeral  13 , is mounted in a manner to be described. The generator  13  is positioned, in this embodiment, between a pair of prime movers in the form of internal combustion engines  14  and  15  which are also supported on the base  12  in a suitable manner.  
         [0013]     Preferably the engines  14  and  15  are of the same type, which may be suitable for producing the desired electrical power from the generator  13  for its intended purposes. Each engine has a respective crankshaft  14   a  and  15   a  journalled in the respective engine crankcase  14   b  and  15   b  and driven in a known manner by one or more pistons (not shown) reciprocating in respective cylinder blocks  14   c  and  15   c.    
         [0014]     As noted, preferably the engines  14  and  15  are of the same construction and the crankshafts  14   a  and  15   a  rotate in the same directions. However since the engines  14  and  15  face in opposite directions so the protruding ends of the crankshafts face toward the generator  13 , their rotation will be in opposite directions as indicated by the arrows A and B respectively. The reason for this will become apparent shortly.  
         [0015]     Turning now additionally to  FIG. 2 , the construction of the generator  13  will be described in detail. The generator  13  is comprised of first and second elements  16  and  17  that are supported for rotation about a common axis  18  by respective bearings  19  and  21 . These bearings  19  and  21  are supported in respective upstanding posts  22  and  23  mounted on the base  12  between the engines  14  and  15  and on opposite sides of the generator  13   
         [0016]     The first generator element  16  is comprised of a cup shaped shell  24 . A stub shaft  25  is suitably fixed to an end wall  26  of the shell and is journalled for rotation about the axis  18  in the bearing  19 . At least one and preferably more circumferentially spaced permanent magnets  27  of opposite plurality are suitably affixed to the interior of the cup shaped shell  24  in facing relation to the axis  18 .  
         [0017]     The second element  17  is comprised of an armature comprised of a laminated ferromagnetic core having a cylindrical inner portion  28  from which at least one and preferably a plurality of pole teeth  29  extend radially outwardly in confronting relation to the permanent magnets  27 . Electrical coils  31  are wound around the pole teeth  29  in any manner known in the art.  
         [0018]     The cylindrical inner portion  28  of the armature element  17  is fixed suitably, as by fasteners  32  to a second stub shaft  33  that is in turn journalled for rotation about the axis  18  by the bearing  21 .  
         [0019]     A pair of slip rings  34  are fixed to the stub shaft  33  between the bearing  21  and the cylindrical armature portion  28 . Ends  35  of the coil windings  31  are led out through a hollow portion of the shaft  33  and connected to these slip rings in a suitable pattern. In the illustrated example two wire ends  35  and two slip rings  34  are shown, but it will be apparent to those skilled in the art that other winding arrangements are possible. Brushes  36  in a number equal to the number of slip rings  34  (two here) cooperate with slip rings  34  to deliver the generated electrical current to a load such as a storage battery  37  through a conductor  38 . The brushes  36  and end of the conductor are carried by the post  23  in a known manner.  
         [0020]     The generator elements  16  and  17  are driven from the engine shafts  14   a  and  15   a  respectively at the same speed and in opposite directions by respective belt transmissions, indicated generally by the reference numerals  39  and  41 . Each of these transmissions is comprised, in this embodiment, by a driving pulley pair  39   a  and  41   a  coupled to the respective engine crankshaft  14   a  and  15   a.  These pulley pairs drive respective belt pairs  39   b  and  41   b,  that in turn drive driven pulley pairs  39   c  and  41   c  fixed for rotation with the stub shafts  25  and  33  respectively.  
         [0021]     Since the generator magnet carrying element  16  and the coil carrying element  17  are driven at the same speed but in opposite directions the same electrical power output may be obtained as if one element was driven with the other one fixed at twice the speed. Hence it is possible to increase the electrical power without the high driving speeds previously required. This permits lower noise levels, reduces inertia and vibrations thus providing longer life and service intervals. In addition, if one of the engines  14  or  15  must be shut down for any reason, electrical power output may be obtained unlike the prior art arrangements.  
         [0022]     In addition, by placing the slip rings  34  between the generator  13  and the post  23  the length of the wire ends  35  can be kept quite short simplifying the construction and reducing cost.  
         [0023]     The foregoing description is based on the first embodiment of  FIGS. 1 and 2 . In addition to the possible modifications already discussed, the permanent magnets  27  may be replaced by electro magnets a voltage externally through slip rings. The common axis  18  may be vertical or tilted. In addition, the bearings  19  and  21  may be replaced with bushings. The generating apparatus also may be provided with three slip rings  34  to output a three-phase alternating current, or provided with five slip rings  34  to provide two different outputs such as a single-phase alternating current as in the case of the illustrated embodiment and a three-phase alternating current.  
         [0024]     In addition the specifications of the first and second engines  14  and  15  may be freely selected in terms of number of cylinders, total displacement, engine layout, such as in-line type and V-type, and the like, or may be different from each other. In addition and as will be described shortly a single engine may be provided with a separate output shaft other than the crankshaft  5  or may be provided with two oppositely rotating output shafts.  
         [0025]     Furthermore, the belt transmissions means may be replaced by toothed belts, chain type or a set of gears such as planetary gears.  
         [0026]      FIG. 3  is of the same area as shown in  FIG. 2 , but shows another embodiment. This embodiment differs from that previously described by reference to  FIGS. 1 and 2  only in the location of the slip rings  34  and how the wire ends  35  are connected thereto. Since this is the only difference, like components are identified by like reference numerals and will be described again only insofar as is necessary to permit those skilled in the art to utilize this embodiment.  
         [0027]     In this embodiment the slip rings  34  are positioned between the post  23  and the transmission  41 . This permits the bearing  21  to be positioned closer to the stub shaft  33  to reduce cantilever loading. Thus the stub shaft  33  is provided with an elongated opening  51  to permit attachment of the wire ends  35  to the slip rings  34 .  
         [0028]     As previously mentioned, it is not necessary to drive the elements  16  and  17  of the generator  13  in opposite directions by two separate prime movers. That is in many cases an engine has itself two shafts that are driven at the same speed, but in opposite directions. These two shafts may be employed for driving the generator elements and  FIGS. 4 and 5  show such an embodiment. Because this is the only difference from the embodiments previously described, where elements have the same or substantially the same construction they have been identified by like reference numbers and will be described again only to make the construction and operation of this embodiment clear to those skilled in the art.  
         [0029]     As seen in this embodiment the generator  13  has the same elements as already described and is mounted on the base  12  between the posts  22  and  23  with the slip rings  34  and brushes  36  at one end of the generator  13  between these posts  22  and  23 .  
         [0030]     A single engine  15  is placed on the other side of the post  23  from the generator  13  and as in the previously illustrated embodiments is driven by the belt transmission  41  from the engine crankshaft  15   a.  In this case the engine  15  has its cylinder block  15   c  inclined slightly from the vertical for a reason that will become apparent shortly.  
         [0031]     In this case the engine  15  has a further shaft  61 , which may comprise a balancer shaft that rotates at the same speed as the crankshaft  15   a  but in the opposite direction. This is done by a pair of intermeshing gears  62  and  63  positioned, for example, externally of the body of the engine  15 , as shown in solid lines or internally as shown in broken lines.  
         [0032]     In accordance with this embodiment the balancer shaft  61  is extended beyond the engine body to pass one side of the post  23 , because of the offset of the engine body from the vertical and be journalled in the post  22  by a bearing  64  and drive the magnet carrying element  16  of the generator  13  through the transmission  39  at the same speed as the armature element  17 , but in the opposite direction. Thus with this embodiment only one engine is required.  
         [0033]     Thus from the foregoing description it should be readily apparent that the described embodiments provide a generator arrangement wherein large electrical power outputs are possible without requiring high driving speeds with the attendant disadvantages. Of course those skilled in the art will readily understand that the described embodiments are only exemplary of forms that the invention may take and that various changes and modifications may be made without departing from the spirit and scope of the invention, as defined by the appended claims.