Patent Publication Number: US-8123237-B2

Title: Mobile power generator apparatus

Description:
FIELD OF THE INVENTION 
     The present invention relates to mobile power generator apparatus in which the power generator is mounted in a frame and left and right wheels are attached to the frame for carrying the power generator. 
     BACKGROUND OF THE INVENTION 
     Among the conventionally-known mobile power generator apparatus are ones in which the power generator is mounted in a frame, and in which left and right wheels are attached to lower end portions of left and right side walls of the frame for carrying the power generator and a pulling handle is attached to an upper end portion of the frame. Such portable power generator apparatus can be moved via the moving wheels by a user or human operator gripping a grip portion of the pulling handle to lift the handle. One example of the mobile power generator apparatus of the aforementioned type is disclosed in Japanese Patent Application Laid-Open Publication No. 2006-271122. 
     In the mobile power generator apparatus disclosed in the 2006-271122 publication, an axle extends through the interior of the frame, the left and right wheels are mounted on left and right end portions, respectively, of the axle. If the axle is provided to extend through a relatively high interior region of the frame, it would be difficult to secure, inside the frame, a space for accommodating therein the power generator due to the presence of the axle. Thus, in the disclosed mobile power generator apparatus, the axle is provided to extend through a relatively low interior region of the frame, so as to secure a sufficient space for accommodating therein the power generator without being hindered by the axle. However; in the case where the axle extends through a relatively low interior region of the frame, it is necessary that the left and right wheels have a relatively small outer diameter, in order to reduce the overall height of the portable power generator apparatus. 
     Generally, where the mobile power generator apparatus is used on an uneven surface, it can move more smoothly if the left and right wheels have a greater outer diameter. With the left and right wheels having a great outer diameter, however, the centers of the left and right wheels would be located at a high position, and thus, the axle has to be provided to extend through a relatively high interior region of the frame. In such a case, however, it is difficult to secure, inside the frame, a space for accommodating therein the power generator due to the presence of the axle. Further, if the left and right wheels have a great outer diameter, left and right side walls of the frame are covered with the left and right wheels, which would make it difficult to form, in left and right side walls of the frame, openings to be used for maintenance of the power generator. 
     SUMMARY OF THE INVENTION 
     In view of the foregoing prior art problems, it is an object of the present invention to provide an improved mobile power generator apparatus which can have left and right wheels of a great outer diameter, can have a sufficient space inside the frame for accommodating therein the power generator and can have, in left and right side walls of the frame, openings to be used for maintenance of the power generator. 
     In order to accomplish the above-mentioned object, the present invention provides an improved mobile power generator apparatus, which comprises: left and right wheels mounted to a frame having a power generator mounted therein at least three guide rollers provided, for each of the wheels, for rotatably supporting a rim of the wheel at least three positions of the rim; and mounting sections for respectively mounting the at least three guide rollers, provided for each of the wheels, on a side wall of the frame. Thus, each of the left and right wheels is rotatably supported by the at least three guide rollers on one of the side walls (i.e., left or right side wall) of the frame. 
     Each of the left and right wheels can be provided on the left or right side wall of the frame via the at least three guide rollers provided on the left or right side wall. Thus, each of the left and right wheels can be formed in a large outer diameter without the height of the frame being increased. Further, with the rim of each of the left and right wheels rotatably supported via the at least three guide rollers, the present invention can dispense with a conventional axle used to support the wheels. Thus, even where each of the wheels is formed in a large outer diameter, it is not necessary that the axle extend through a relatively high interior region of the frame. As a result, the present invention can secure a space inside the frame for accommodating therein the power generator etc. even with the wheels formed in a large outer diameter. 
     In an embodiment, the apparatus has a free space area formed at and around the center of the rim. Thus, even with the wheels formed in a large outer diameter, there can be secured a so-called maintenance opening in the side walls. 
     Preferably, one of the at least three guide rollers, provided for each of the rollers, is a movable roller supported via the mounting means in such a manner that the movable guide roller is movable in a radial direction of the rim, and the movable guide roller is normally urged by a resilient member in resilient abutment against the rim. Thus, it is possible to absorb or accommodate a manufacturing error of the rim, which allows the rim to constantly rotate smoothly. 
     The following will describe embodiments of the present invention, but it should be appreciated that the present invention is not limited to the described embodiments and various modifications of the invention are possible without departing from the basic principles. The scope of the present invention is therefore to be determined solely by the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Certain preferred embodiments of the present invention will hereinafter be described in detail, by way of example only, with reference to the accompanying drawings, in which: 
         FIG. 1  is a perspective view showing a mobile power generator apparatus according to an embodiment of the present invention; 
         FIG. 2  is a front view of the mobile power generator apparatus of the present invention 
         FIG. 3  is an exploded perspective view of the mobile power generator apparatus of the present invention with its carriage unit detached therefrom for clarity; 
         FIG. 4  is a side view of the mobile power generator apparatus of the present invention with its right side cover detached therefrom; 
         FIG. 5  is a perspective view showing the carriage unit employed in the mobile power generator apparatus of the present invention; 
         FIG. 6  is an enlarged view of an encircled section  6  of  FIG. 4 ; 
         FIG. 7  is a sectional view taken along line  7 - 7  of  FIG. 6 ; 
         FIG. 8  is an enlarged view of an encircled section  8  of  FIG. 4 ; 
         FIG. 9  is a sectional view taken along line  9 - 9  of  FIG. 8 ; 
         FIG. 10  is an exploded perspective view showing a pulling unit employed in the mobile power generator apparatus of the present invention; 
         FIG. 11  is a perspective view of the pulling unit in its expanded position; 
         FIG. 12  is an enlarged view of an encircled section  12  of  FIG. 4 ; 
         FIG. 13  is a side view showing the pulling unit in the expanded position; 
         FIG. 14  is a sectional view taken along line  14 - 14  of  FIG. 13 ; 
         FIG. 15  is an enlarged view of an encircled section  15  of  FIG. 13 ; 
         FIG. 16  is a view explanatory of an example manner in which maintenance (repair and inspection) of the mobile power generator apparatus is performed; 
         FIGS. 17A and 17B  are views explanatory of an example manner in which the pulling unit is shifted to the expanded position; 
         FIGS. 18A and 18B  are views showing the pulling unit having been expanded partway; 
         FIG. 19  is a view showing the pulling unit having been expanded to the pulling position; 
         FIGS. 20A and 20B  are views explanatory of the pulling unit held in the pulling position; 
         FIG. 21  is a view explanatory of an example manner in which the mobile power generator apparatus is pulled by a human operator via the pulling unit; 
         FIGS. 22A and 22B  are views explanatory of an example manner in which the pulling unit is collapsed from the expanded position; 
         FIG. 23  is a view showing the pulling unit having been collapsed partway; 
         FIGS. 24A and 24B  are views showing the pulling unit having been collapsed to a collapsed position; and 
         FIGS. 25A and 25B  are views explanatory of an example manner in which a power cord is moved away from the left and right wheels by means of the pulling unit. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference is now made to  FIG. 1  showing in perspective a mobile power generator apparatus  10  according to an embodiment of the present invention, as well as to  FIG. 2  showing in front elevation the mobile power generator apparatus  10 . The mobile power generator apparatus  10  includes a frame  11  forming a framework of the power generator, an engine/power generator unit  12  (see also  FIG. 4 ), a left side cover  13  provided on the left side of the frame  11 , a right side cover  14  provided on the right side of the frame  11 , a carriage unit  15  attached to the frame  11 , and a pulling unit  16  provided on a front section  11   a  of the frame  11 . 
     The frame  11  includes a bottom wall  21 , an upper wall  22 , a front wall  23 , a rear wall  24  (see  FIG. 4 ), a left side wall  24  and a right side wall  26 , which together constitute a rectangular parallelepiped shape. Left and right leg portions  28  are vertically movably attached to a lower end portion  24   a  (see  FIG. 4 ) of the rear wall  24 . 
     The upper wall  22  has a fixed grip portion  31  provided on a substantial middle in a width or left-right direction (i.e., substantial widthwise middle) region of the power generator apparatus  10 , and left and right cassette accommodating portions  32  and  33  are provided to the left and right of the fixed grip portion  31 . 
     The fixed grip portion  31  has front and rear ends  31   a  and  31   b  fixed to the upper wall  22 . The mobile power generator apparatus  10  can be carried by a user or human operator gripping the fixed grip portion  31  with a hand to thereby lift the grip portion  31 . 
     The left and right cassette accommodating portions  32  and  33  are each provided for accommodating therein a cassette gas canister  35  containing a gas fuel to be supplied to an engine  18  (see  FIG. 4 ) of the engine/power generator unit  12 . More specifically, the right cassette accommodating portion  33  is provided in a right half area of the upper wall  22  and has an openable/closable right cassette cover  36  attached thereto. The cassette gas canister  35  can be loaded into the right cassette accommodating portion  33  with the right cassette cover  36  opened, and it is accommodated in the right cassette accommodating portion  33  with the right cassette cover  36  kept in the closed position. The left cassette accommodating portion  32  is constructed and disposed in left-right symmetrical relation to the right cassette accommodating portion  33 , and thus, a detailed description of the left cassette accommodating portion  32  is omitted here. 
       FIG. 3  is an exploded perspective view of the mobile power generator apparatus  10  with is carriage unit detached therefrom for clarity, and  FIG. 4  is a side view of the mobile power generator apparatus  10  with the right side cover  14  detached therefrom. 
     The right side wall  26  of the frame  11  has an outer periphery extending along the bottom wall  21 , upper wall  22 , front wall  23  and rear wall  24 , and a water-resistant wall  41  of a substantially ring shape is provided inwardly of and with a predetermined gap from the outer periphery of the right side wall  26 . Front resonator  42  is provided on a front end portion  41   a  of the water-resistant wall  41 , while a rear resonator  43  is provided on a rear end portion  41   b  of the water-resistant wall  41 . 
     Right maintenance opening  45  is defined by upper and lower portions  41   c  and  41   d  of the water-resistant wall  41  and front and right resonators  42  and  43 . The right maintenance opening  45  is in communication with an accommodating space  46  inside the frame  11  where the engine/power generator unit  12  is accommodated. 
     Two screw holes  48  are formed in diagonally opposite portions of the water-resistant wall  41 , and the right side cover  14  is detachably attached at its circular outer peripheral portion  14   a  to the right side wall  26  by means of bolts  49  screwed into the screw holes  48 . 
     The outer peripheral portion  14   a  of the right side cover  14  is slightly greater in size than an outer peripheral portion of the right side cover  14 . The right maintenance opening  45  is covered with the right side cover  14  attached to the right side wall  26  by means of the two bolts  49 . Thus, by loosing the bolts  49  and detaching the right side cover  14  from the right side wall  26  to thereby open the maintenance opening  45 , repair and inspection (maintenance) of the engine/power generator unit  12  can be performed through the maintenance opening  45 . 
     The left side wall  25  is constructed and disposed in left-right symmetric relation to the aforementioned right side wall  26  and thus will not be described in detail. Similarly to the right side wall  26 , the left side wall  25  has an outer periphery extending along the bottom wall  21 , upper wall  22 , front wall  23  and rear wall  24 , and a peripheral wall (not shown) is provided inwardly of and with a predetermined gap from the outer periphery of the left side wall  25 . 
     Left maintenance opening (not shown) is defined by the peripheral wall and in communication with the accommodating space  46 . The left maintenance opening is covered with the left side cover  13 . The left side cover  13  is constructed and disposed in left-right symmetric relation to the right side cover  14  and detachably attached to the left side wall  25  by means of two bolts (not shown). Thus, by loosing the two bolts and detaching the left side cover  13  from the left side wall  25  to thereby open the left maintenance opening, maintenance of the engine/power generator unit  12  can be performed through the left maintenance opening. 
     The engine/power generator unit  12  comprises the engine  18  drivable with a gas fuel supplied from the cassette gas canister  35 , and a power generator  19  mounted coaxially with the drive shaft (crankshaft) as the engine  18 . Electric power is generated by the rotor (not shown) of the power generator  19  being rotated by the engine  18 . 
     As the engine  18  is driven, external air is directed into the right maintenance opening  45  through the gap between the right side cover  14  and the water-resistant wall  41 , during which time intake sound of the external air can be silenced in a resonating chamber defined by the front and rear resonators  42  and  43 . 
     The carriage unit  15  includes a right guide section  55  attached to the right side wall  26 , a right wheel  56  rotatably supported via the right guide section  55 , a left guide section (not shown) attached to the left side wall  25 , a left wheel  58  ( FIG. 2 ) rotatably supported via the left guide section, and a caster section  61  provided on a lower end portion  23   a  of the front wall  23 . 
     Because the left guide section is constructed and disposed in left-right symmetric relation to the right guide section  55 , the following description mainly describes in detail the right guide section  55  with a detailed description of the left guide section omitted. Further, because the left wheel  58  is constructed and disposed in left-right symmetric relation to the right wheel  56 , the following description mainly describes in detail the right wheel  56  with a detailed description of the left wheel  58  omitted. 
       FIG. 5  is a perspective view showing the carriage unit  15  employed in the present invention. The right wheel  56  of the carriage unit  15  includes a ring-shaped rim  64 , and a tire disposed on and around the outer periphery of the rim  64 . The rim  64  is made, for example, of resin or metal and has a ring-shaped ridge  67  (see also  FIG. 7 ) formed on an inner peripheral wall  64   a  and projecting radially inward. The rim  64  is supported via the right guide section  55  for rotation about a center axis  57 . 
     The right guide section  55  includes first and second fixed guide rollers  71  and  62 , a movable guide roller  73 , a first fixedly mounting section  75  for rotatably mounting the first fixed guide roller  71  to the right side wall  26  (see  FIG. 4 ), a second fixedly mounting section  76  for rotatably mounting the second fixed guide roller  72  to the right side wall  26 , and a movably mounting section  77  for rotatably mounting the movable guide roller  73  to the right side wall  26 . 
     The first and second fixed guide rollers  71  and  72  and the variable guide rollers  73  are at least three guide rollers employed in the mobile power generator apparatus  10 . Because the first and second fixed guide rollers  71  and  72  are identical in construction, the following description will mainly describe in detail the first fixed guide roller  71  with a detailed description of the second fixed guide roller  72  omitted. Further, because the first and second fixedly mounting sections  75  and  76  are identical in construction, the following description will mainly describe the first fixedly mounting section  75  with a detailed description of the second fixedly mounting section  76  omitted; whenever necessary, elements of the second fixedly mounting section  76  will be mentioned using the same reference characters as counterparts of the first fixedly mounting section  75 . 
       FIG. 6  is an enlarged view of an encircled section  6  of  FIG. 4 , and  FIG. 7  is a sectional view taken along the  7 - 7  line of  FIG. 6 . The first fixed guide roller  71  has a central through-hole  81  for mounting on the first fixedly mounting section  75 , and an annular engagement groove or recess  82  formed in the outer periphery  71   a  for engagement with the ring-shaped ridge  67  of the rim  64 . 
     The first fixedly mounting section  75  includes a fixed-roller supporting bolt  84  for rotatably supporting the guide roller  71 , a pair of fixed-plate supporting bolts  85  provided on both sides of the fixed-roller supporting bolt  84  with predetermined intervals from the supporting bolt  84 , collars  86  fitted over the corresponding fixed-plate supporting bolts  85 , a fixed plate  87  supported by the fixed-plate supporting bolts  85 , and nuts  88  for fixing the fixed plate  87  to the fixed-roller supporting bolt  84  and pair of fixed-plate supporting bolts  85 . 
     The fixed-roller supporting bolt  84  has its head  84   a  embedded in the right side wall  26  so that its shank projects from the right side wall  26  toward the fixed plate  87 . The pair of fixed-plate supporting bolts  85 , provided on both sides of the fixed-roller supporting bolt  84  and at predetermined intervals from the bolt  84 , have their heads  85   a  embedded in the right side wall  26  so that their shanks project from the right side wall  26  toward the fixed plate  87 . 
     The fixed plate  87  is a flat plate of a substantially triangular shape. The fixed plate  87  has a central through-hole  87   a  formed centrally therein for insertion therethrough of the fixed-roller supporting bolt  84 , and through-holes  87   b  (see also  FIG. 5 ) formed in its opposite end portions for insertion therethrough of the fixed-plate supporting bolts  85 . 
     In the first fixedly mounting section  75 , the mounting hole  81  of the first fixed guide roller  71  is fitted over the fixed-roller supporting bolt  84 , and the collars  86  are fit over the corresponding fixed-plate supporting bolts  85 . Further, the central through-hole  87   a  of the fixed plate  87  is fitted over the fixed-roller supporting bolt  84 , and the through-holes  87   b  of the fixed plate  87  is fitted over the fixed-plate supporting bolts  85 . 
     The fixed-roller supporting bolt  84  has a threaded portion  84   b  projecting out of the central through-hole  87   a  and screwed into one of the nuts  88 , and the fixed-plate supporting bolts  85  have their respective threaded portions  85   b  projecting out of the through-holes  87   b  and screwed into the other nuts  88 . 
     Thus, the first fixed guide roller  71  is rotatably supported by the fixed-roller supporting bolt  84  and prevented by the fixed plate  87  from accidentally getting out of engagement with the fixed-roller supporting bolt  84 . In such a state, the ridge  67  of the rim  64  fits in the engagement recess  82  of the first fixed guide roller  71 , and a bottom surface  82   a  of the engagement recess  82  is kept in abutment against an inner peripheral surface  67   a  of the ridge  67 . 
     Referring back to  FIG. 5 , the second fixed guide roller  72  is identical in construction to the first fixed guide roller  71 , and the second fixedly mounting section  76  is identical in construction to the first fixedly mounting section  75 . The ridge  67  of the rim  64  fits in an engagement recess  91  of the second fixed guide roller  72 , and the bottom surface of the engagement recess  91  is kept in abutment against an inner peripheral surface  67   a  of the ridge  67 . The engagement recess  91  of the second fixed guide roller  72  is identical in shape to the engagement recess  82  of the first fixed guide roller  71 . 
       FIG. 8  is an enlarged view of an encircled section  8  of  FIG. 4 , and  FIG. 9  is a sectional view taken along the  9 -line of  FIG. 8 . The movable guide roller  73  has a mounting hole  93  formed centrally through the thickness thereof for mounting the guide roller  73  to the movably mounting section  77 , and it has an annular engagement recess  94  formed along the outer periphery  73  thereof for fitting engagement with the ridge  67  of the rim  64 . Note that the movable guide roller  73  is identical in shape to the first and second fixed guide rollers  71  and  72 . 
     The movably mounting section  77  includes a movable-roller supporting bolt  95  for rotatably supporting the movable guide roller  73 , a pair of movable-plate supporting bolts  96  provided on both sides of the movable-roller supporting bolt  95  with predetermined intervals from the supporting bolt  95 , collars  97  fitted over the corresponding movable-plate supporting bolts  96 , inner and outer movable plates  98  and  99  supported by the movable-plate supporting bolts  96 , and nuts  101  for fixing the inner and outer movable plates  98  and  99  to the movable-roller supporting bolt  95  and pair of movable-plate supporting bolts  96 . The movably mounting section  77  also includes a supporting shaft portion  103  for pivotably supporting respective one end portions  98   a  and  99   a  of the inner and outer movable plates  98  and  99 , a sliding shaft portion  104  for pivotably supporting respective other end portions  98   b  and  99   b  of the inner and outer movable plates  98  and  99 , and a biasing section  105  for normally urging the movable-roller supporting bolt  95  toward the rim  64 . 
     The movable-roller supporting bolt  95  has its head  95   a  embedded in the inner movable plate  98  so that its shank projects from the inner movable plate  98  toward the outer movable plate  99 . The pair of movable-plate supporting bolts  96 , provided on both sides of the movable-roller supporting bolt  95  and at predetermined intervals from the bolt  95 , have their heads  96   a  embedded in the inner movable plate  98  so that their shanks project from the inner movable plate  98  toward the outer movable plate  99 . 
     The inner movable plate  98  is a flat plate of a curved shape. The head  95   a  of the movable-roller supporting bolt  95  is embedded in a central portion of the inner movable plate  98 , and the heads  96   a  of the movable-plate supporting bolts  96  are embedded in portions, located at both sides of the bolt  95 , of the inner movable plate  98 . Further, a through-hole  98   c  is formed in one end portion  98   a  of the inner movable plate  98 , while a slide hole  98   d  is formed in another end portion  98   b  of the plate  98 . 
     The through-hole  98   c  is a hole through which a supporting shaft bolt  107  of the supporting shaft portion  103  is inserted. The slide hole  98   d  is an elongated hole through which a bolt  112  of the sliding shaft portion  104  is inserted for sliding movement along the edge the slide hole  98   d.    
     The outer movable plate  99  is a flat plate of a curved shape similarly to the inner movable plate  98 . The outer movable plate  99  has a central through-hole  99   c  formed centrally therein, and through-holes  99   d  formed in its intermediate portions, located on both sides of the central through-hole  99   c , for insertion therethrough of the movable-plate supporting bolts  96 . Further, a through-hole  99   e  is formed in one end portion  99   a  of the outer movable plate  99 , while a slide hole  99   f  is formed in another end portion  99   b  of the plate  99 . 
     The through-hole  99   e  is a hole through which the supporting shaft bolt  107  of the supporting shaft portion  103  is inserted. The slide hole  99   f  is an elongated hole through which the bolt  112  of the sliding shaft portion  104  is inserted for sliding movement along the edge of the slide hole  99   f.    
     The supporting shaft portion  103  includes a supporting shaft nut  106 , a supporting shaft bolt  107  screwed in the nut  106 , and first and second supporting shaft collars  108  and  109  fitted over the shaft bolt  107 . The first supporting shaft collar  108  is inserted through the through-hole  98   c  of the inner movable plate  98  and through-hole  99   e  of the outer movable plate  99 . 
     The first supporting shaft collar  108  is sandwiched between the inner and outer movable plates  98  and  99 , and the second supporting shaft collar  109  is sandwiched between the inner movable plate  98  and the right side wall  26 . 
     The sliding shaft portion  104  includes a sliding shaft nut  111  embedded in the right side wall  26 , a sliding shaft bolt  112  screwed in the nut  111 , and first and second sliding shaft collars  113  and  114  fitted over the sliding shaft bolt  112 . The sliding shaft bolt  112  is slidably inserted through the slide hole  98   d  of the inner movable plate  98 , and through the slide hole  99   f  of the outer movable plate  99  for sliding movement along the edge of the slide hole  99   f.    
     The first sliding shaft collar  113  is sandwiched between the inner and outer movable plates  98  and  99 , and the second sliding shaft collar  114  is sandwiched between the inner movable plate  98  and the right side wall  26 . 
     The biasing section  105  includes an upper stopper portion  115  provided on the inner movable plate  98 , a lower stopper portion  116  provided on the right side wall  26 , and a compression spring (resilient member)  117  interposed between the upper and lower stopper portions  115  and  116 . 
     In the movably mounting section  77 , the mounting hole  93  of the movable guide roller  73  is fitted over the movable-roller supporting bolt  95 , and the collars  97  are fitted over the two movable-plate supporting bolts  96 . 
     Further, the central through-hole  99   c  of the outer movable plate  99  is fitted over the movable-roller supporting bolt  95 , and the through-holes  99   d  of the outer movable plate  99  are fitted over the two movable-plate supporting bolts  96 . 
     The movable-roller supporting bolts  95  has a threaded portion  95   b  projecting out of the central through-hole  99   c  and screwed in one of the nuts  101 , and the movable-plate supporting bolts  96  have their threaded portions  96   b  projecting out of the corresponding through-holes  99   d  and screwed into the other nuts  101 . 
     Thus, the movable guide roller  73  is rotatably supported by the movable-roller supporting bolt  95  and prevented by the movable plates  98  from accidentally getting out of engagement with the movable-roller supporting bolt  95 . 
     Further, the supporting shaft bolt  107  is inserted through the through-holes  98   c  and  99   e  of the inner and outer movable plates  98  and  99 , and the first and second supporting shaft collars  108  and  109  are fitted over the supporting shaft bolt  107 . Threaded portion  107   a  of the supporting shaft bolt  107  projecting out of the second supporting shaft collar  109  is screwed in the supporting shaft nut  106 . 
     Further, the sliding shaft bolt  112  is inserted through the slide holes  98   d  and  99   f  of the inner and outer movable plates  98  and  99 , and the first and second sliding shaft collars  113  and  114  are fitted over the sliding shaft bolt  112 . Threaded portion  112   a  of the sliding shaft bolt  112  projecting out of the second sliding shaft collar  114  is screwed into the sliding shaft nut  111 . 
     Thus, the inner and outer movable plates  98  and  99  are pivotable about the supporting shaft bolt  107  toward and away the rim  64  as indicated by arrows of  FIG. 8 . In the aforementioned manner, the movable guide roller  73  is supported in such a manner that it is movable in the radial direction of the rim  64 . 
     The compression spring  117  is interposed between the upper and lower stopper portions  115  and  116  so that the movable guide roller  73  is normally pressed against the rim  64  by the biasing force of the compression spring  117 . Thus, the engagement recess  94  of the movable guide roller  73  is normally resiliently fitted over the ridge  67  of the rim  64 , and the outer periphery  73   a  of the movable guide roller  73  is normally resiliently abutted against the inner peripheral wall  64   a  of the rim  64 . In the aforementioned manner, it is possible to absorb or accommodate a manufacturing error of the rim  64 , and thus, the rim  64  can be rotated smoothly. 
     As described above, the right wheel  56  is rotatably supported, on the right side wall of the frame  11 , by the right wheel  56  (i.e., rim  64 ) being supported by the first and second fixed guide rollers  71  and  72  and the movable guide roller  73 . Therefore, the right wheel  56  can be formed in a large outer diameter D without the height H 1  of the frame  11  being increased. In the above-described embodiment, the outer diameter D of the right wheel  56  is set substantially equal to the height H 1  of the frame  11 . 
     Further, with the rim  64  rotatably supported via the first and second fixed guide rollers  71  and  71  and movable guide roller  73 , the instant embodiment can dispense with a conventional axle used to support the wheel; thus, even where the wheel  56  is formed in a large outer diameter, it is not necessary that the axle extend through a relatively high interior region of the frame  11 . Thus, the instant embodiment can secure the space  46  ( FIG. 4 ) for accommodating therein the engine/power generator unit  12  etc. even with the wheel  56  formed in a large outer diameter. 
     Further, by dispensing with the conventional axle used to support the wheel, the apparatus  10  has a sufficient free space area  121  secured at and around the center of the rim  64  (hereinafter also referred to as “central area  121 ”). Further, because the central area  121  faces the opening  45  (see also  FIG. 4 ) of the side wall  26 , maintenance operation can be performed using the central area  121  of the rim  64  and opening  45  of the side wall  26 . 
     Furthermore, as set forth above, the left guide section of the carriage unit  15  is constructed and disposed in left-right symmetric relation to the right guide section  55 , and the left wheel  58  is constructed and disposed in left-right symmetric relation to the right wheel  56 . Thus, similarly to the right wheel  56 , the left wheel  58  is rotatably disposed on the left side wall  25  of the frame  11 . 
     Referring back to  FIGS. 1 and 2 , the caster section  61  is provided on the lower end portion  23   a  of the front wall  23 . The caster section  61  includes a pivot shaft  124  rotatably mounted on the front wall  23 , a bracket  125  fixed to the pivot shaft  124 , a steering wheel  126  rotatably supported on the bracket  125 , and a caster stopper  185  fixed to the bracket  125 . 
     In the caster section  61 , the steering wheel  126  has a centerline  128  offset from a downward extension line of the pivot shaft  124  by a distance L 1  as shown in  FIG. 1  and  FIG. 11  as well. 
     When the mobile power generator apparatus  10  is to be moved via the left and right wheels  58  and  56 , the orientation (i.e., operating direction) of the steering wheel  126  can be changed in accordance with a direction where the mobile power generator apparatus  10  is to be moved (i.e., moving direction of the mobile power generator apparatus  10 ). 
     Further, in the caster section  61 , the steering wheel  126  is vertically pivotably supported on a support shaft  129  and normally urged downward by a spring member (not shown). Thus, as the mobile power generator apparatus  10  is moved via the left and right wheels  58  and  56  on an uneven ground surface, the steering wheel  126  can be pivotally moved up and down in response to the unevenness of the ground surface. 
     Because the orientation (i.e., operating direction) of the steering wheel  126  can be changed in accordance with the moving direction of the mobile power generator apparatus  10  and pivotally moved up and down in response to the unevenness of the ground surface, the mobile power generator apparatus  10  can achieve an enhanced mobility and operability. 
     Further, the steering wheel  126  can be held in a stationary state by a longitudinal middle portion  138   c  of a lower connecting rod  138  being brought to engagement with the caster stopper  185 . Details of the longitudinal middle portion  138   c  of the lower connecting rod  138  will be discussed later with reference to  FIGS. 10 and 11 . 
     Further, in the instant embodiment of the mobile power generator apparatus  10 , the left and right leg portions  28  are vertically movably attached to the lower end portion  24   a  (see  FIG. 4 ) of the rear wall  24 . Each of the left and right leg portions  28  can be locked at a stationary position for retaining the mobile power generator apparatus  10  in the stationary state and a moving position for retaining the mobile power generator apparatus  10  in a movable state. The stationary position is a lowered position of the leg portion  28 , while the moving position is a raised position of the leg portion  28 . 
       FIG. 10  is an exploded perspective view showing the pulling unit  16  employed in the instant embodiment of the mobile power generator apparatus  10 , and  FIG. 11  is a perspective view of the pulling unit  16  in an expanded position. The pulling unit  16  is provided on the front section  11   a  of the frame  11  and operable by the human operator to pull the mobile power generator apparatus  10 . 
     The pulling unit  16  includes a right pivoting link unit  132  provided on a right side portion  131  of the front section  11   a , a right link cover  133  covering the right pivoting link unit  132 , a left pivoting link unit  136  provided on a left side portion  35  of the front section  11   a , a left link cover  137  covering the left pivoting link unit  136 , the above-mentioned lower connecting rod  138  interconnecting the right pivoting link unit  132  and the left pivoting link unit  136 , and a pulling handle  141  connected at opposite ends to the right and left pivoting link units  132  and  136 . 
     Because the left and right pivoting link units  136  and  132  are constructed and disposed in left-right symmetric relation to each other, the following description mainly describes in detail the right pivoting link unit  132  with a detailed description of the left pivoting link unit  136  omitted. Further, because the left and right link covers  137  and  133  are constructed and disposed in left-right symmetric relation to each other, the following description mainly describes in detail the right link cover  133  with a detailed description of the left link cover  137  omitted. 
     The right pivoting link unit  132  includes a right upper pivoting link  145  vertically pivotably supported on the right side portion  131  of the front section  11   a , and a right lower pivoting link  146  vertically pivotably supported on the right side portion  131  of the front section  11   a . The right upper pivoting link  145  and right lower pivoting link  146  are disposed parallel to each other. 
     The right upper pivoting link  145  is formed in a curved shape to extend along the front wall  23  of the frame  11 , and it has an upper end portion  145   a  pivotably connected, by means of a bolt  147 , to a first upper mounting portion (upper end portion)  131   a  of the right side portion  131 . 
     The right lower pivoting link  146  is formed in a curved shape to extend along the right upper pivoting link  145  and has a right tire stopper  158  provided near its upper end portion  146   a  and projecting toward the right wheel  56 . The right lower pivoting link  146  is pivotably connected at the upper end portion  146   a  to a second upper mounting portion (upper end portion)  131   b  of the right side portion  131  by means of a bolt  147 . The second upper mounting portion  131   b  is located slightly forwardly and downwardly of the first upper mounting portion  131   a.    
     As shown in  FIG. 4 , the right tire stopper  158  is a member that abuts against the outer periphery of the right wheel  56  when the pulling handle  141  is in a collapsed position. By the right tire stopper  158  abutting against the outer periphery of the right wheel  56 , the rotation of the wheel  56  can be prevented. Namely, the rotation of the wheel  56  can be prevented as desired by the simple construction calling for only the tire stopper  158 . 
     The right lower pivoting link  146  is located immediately below and parallel to the right upper pivoting link  145 . The right lower pivoting link  146  and right upper pivoting link  145  are supported together for integral vertical pivoting movement about their respective upper end portions  146   a  and  145   a.    
     The right lower pivoting link  146  and right upper pivoting link  145  are covered with the right link cover  133 . The right link cover  133  has an upper end portion  133   a  that is pivotably connected, by means of the bolt  147 , to the first upper mounting portion  131   a  along with the upper end portion  145   a  of the right upper pivoting link  145 , and the right link cover  133  is fixed at its lower end portion  133   b  to a lower end portion (lower boss)  145   b  of the right upper pivoting link  145 . 
     The right link cover  133  has a substantially U cross-sectional shape and has the right upper and right lower pivoting links  145  and  146  accommodated in its interior space  149  (see also  FIG. 14 ). The right link cover  133  has a handle holder  153  formed on a substantial longitudinal middle portion of an inner wall thereof. The handle holder  153  has a substantially U cross-sectional shape so as to sandwichingly hold a right handle section  161  of the pulling handle  141 . 
       FIG. 12  is an enlarged view of an encircled section  12  of  FIG. 4 . The right link cover  133  has a holding recess  152  formed in the lower end portion  133   d  of an outer wall  133   d . The holding recess  152  has a curved shape such that it can engage a lower end portion (or lower boss)  146   b  of the right lower pivoting link  146 . The holding recess  152  and lower end portion (or lower boss)  146   b  of the right lower pivoting link  146  together constitute a right holding section  151 . Details of the right holding section  151  will be discussed later with reference to  FIGS. 13-15 . 
     Referring back to  FIGS. 10 and 11 , the lower end portion  145   b  of the right upper pivoting link  145  and lower end portion  155   b  of a left upper pivoting link  155  are interconnected via the above-mentioned lower connecting rod  138 . 
     More specifically, the lower connecting rod  138  has a right end portion  138   a  connected to the lower end portion  145   b  of the right upper pivoting link  145 , and a left end portion  138   b  connected to a lower end portion  155   b  of the left upper pivoting link  155 . 
     The longitudinal middle portion  138   c  of the lower connecting rod  138  is bent to project forward, so that the middle portion  138   c  is located at a position where it can engage with the caster stopper  185 . The right handle section  161  of the pulling handle  141  is connected to the lower end portion  145   b  of the right upper pivoting link  145  and lower end portion  146   b  of the right lower pivoting link  146 . 
     Further, a left handle section  162  of the pulling handle  141  is connected to the lower end portion  155   b  of the left upper pivoting link  155  and lower end portion  156   b  of the left lower pivoting link  156 . 
     The pulling handle  141  includes the above-mentioned right handle section  161  located inwardly of the right link cover  133 , i.e. closer to the longitudinal centerline of the mobile power generator apparatus  10  than the right link cover  133  (see also  FIG. 2 ), the above-mentioned left handle section  162  located inwardly of the left link cover  137 , i.e. closer to the longitudinal centerline of the mobile power generator apparatus  10  than the left link cover  137  (see also  FIG. 2 ), a connecting section  163  interconnecting respective distal ends  161   a  and  162   a  of the right and left handle sections  161  and  162 , and a movable grip portion  164  provided concentrically with the connecting section  163 . 
     The right handle section  161  is located closer to the longitudinal centerline of the mobile power generator apparatus  10  than the right link cover  133  with a predetermined interval from the right upper pivoting link  145  and right lower pivoting link  146 . 
     The right handle section  161  has first and second lower mounting portions  167  and  168  formed on its proximal end portion  161   b . The right handle section  161  is pivotably connected at the first lower mounting portion  167  to the lower end portion  145   b  of the right upper pivoting link  145  by means of a bolt  171 , and also pivotably connected at the second lower mounting portion  168  to the lower end portion  146   b  of the right lower pivoting link  146  by means of a bolt  171 . 
     The left handle section  162  is constructed and disposed in left-right symmetric relation to the right handle section  161 , and thus, the following description mainly describes in detail the right handle section  161  with a detailed description of the left handle section  162  omitted; whenever necessary, elements of the left handle section  162  will be mentioned using the same reference characters as counterparts of the right handle section  161 . 
     Namely, in the pulling handle  141 , the right handle section  161  is connected at its proximal end portion  161   b  to the respective lower end portions  145   b  and  146   b  of the right upper pivoting link  145  and right lower pivoting link  146  in such a manner that the right handle section  161  is movable in interlocking relation to the pivoting links  145  and  146 , and the left handle section  162  is connected at its proximal end portion  162   b  to the respective lower end portions  155   b  and  156   b  of the left upper pivoting link  155  and left lower pivoting link  156  in such a manner that the left handle section  162  is movable in interlocking relation to the pivoting links  155  and  156 . Further, the movable grip portion  164  is provided on the connecting section  163  interconnecting the respective distal ends  161   a  and  162   a  of the right and left handle sections  161  and  162 . 
     The pulling unit  16  is also constructed so that the pulling handle  141  is expandable in a direction where the movable grip portion  164  moves away from the right and left pivoting link units  132  and  136  in interlocked relation to upward pivotal movement of the link units  132  and  136 . 
     The pulling unit  16  is constructed so that the pulling handle  141  is collapsible in a direction where the movable grip portion  164  moves toward the right and left pivoting link units  132  and  136  in interlocked relation to downward pivotal movement of the link units  132  and  136 . 
     Namely, the pulling unit  16  is collapsible or bendable at its substantial longitudinal middle portion. Further, the right and left pivoting link units  132  and  136  each have a length substantially equal to a length of the pulling handle  141 . Thus, the pulling unit  16  can have an increased overall length when it is in the expanded position and a reduced overall length when it is in the collapsed (or retracted) position. 
     Further, in the pulling handle  141 , the right handle section  161  is connected at the first and second lower mounting portions  167  and  168  to the lower end portions  145   b  and  146   b , respectively, of the right upper pivoting link  145  and right lower pivoting link  146 , and the left handle section  162  is connected at the first and second lower mounting portions  167  and  168  to the lower end portions  155   b  and  156   b , respectively, of the left upper pivoting link  155  and left lower pivoting link  156 . 
     Namely, the right handle section  161  is connected at the proximal end portion  161   b  to the lower end portions  145   b  and  146   b  of the right upper pivoting link  145  and right lower pivoting link  146 , while the left handle section  162  is connected at the proximal end portion  162   b  to the lower end portions  155   b  and  156   b  of the left upper pivoting link  155  and left lower pivoting link  156 . 
     Thus, the pulling handle  141  is prevented from moving independently of the lower end portions  145   b  and  146   b  and lower end portions  155   b  and  156   b . Consequently, when the pulling handle  141  is moved or shifted to the collapsed or expanded position, the movement of the pulling handle  141  can be controlled by the right and left pivoting link units  132  and  136  in such a manner that the movable grip portion  164  moves in a predetermined trajectory  181  ( FIG. 18A ). 
       FIG. 13  is a side view showing the pulling unit  16  of the mobile power generator apparatus  10  in the expanded position,  FIG. 14  is a sectional view taken along the  14 - 14  line of  FIG. 13 , and  FIG. 15  is an enlarged view of an encircled section  15  of  FIG. 13 . 
     As the pulling handle  141  is expanded so that the movable grip portion  164  is shifted from a retracted position P 1  ( FIG. 4 ) to a pulling position P 2 , not only the right lower pivoting link  146  interferes with the right upper pivoting link  145 , but also the left lower pivoting link  156  interferes with the left upper pivoting link  155 . 
     More specifically, the lower end portion (lower boss)  146   b  of the right lower pivoting link  146  interferes with a region  145   c  of the right upper pivoting link  145  near the lower end portion  145   b . The lower end portion (lower boss)  146   b  is oriented toward the near-lower-end region  145   c . Thus, the lower end portion  146   b  can be reliably abutted against the near-lower-end region  145   c  of the right upper pivoting link  145 . 
     Similarly, the lower end portion (lower boss)  156   b  of the left lower pivoting link  156  interferes with a region  155   c  of the left upper pivoting link  155  near the lower end portion  155   b . The lower end portion (lower boss)  156   b  is oriented toward the near-lower-end region  145   c . Thus, the lower end portion  156   b  can be reliably abutted against the near-lower-end region  155   c  of the left upper pivoting link  155 . 
     With such arrangements, the pulling handle  141  can be prevented from being expanded beyond the pulling position P 2 . Thus, the instant embodiment can dispense with a separate stopper that was required in the prior art to prevent the pulling handle  141  from being expanded beyond the pulling position, and consequently, the instant embodiment of the mobile power generator apparatus  10  can be simplified in construction. 
     The pulling unit  16  further includes right and left retaining sections  151  and  191 . The right retaining section  151  has a retaining recess  152 , and it includes the lower end portion (lower boss)  146   b  of the right lower pivoting link  146 . The left retaining section  191  is constructed and disposed in left-right symmetric relation to the right retaining section  151 , and thus, the following description mainly describes in detail the right retaining section  151  with a detailed description of the left retaining section  191  omitted; whenever necessary, elements of the left retaining section  191  will be mentioned using the same reference characters as counterparts of the right retaining section  151 . 
     As the pulling handle  141  is expanded so that the movable grip portion  164  is shifted to the pulling position P 2  where the human operator can pull the movable grip portion  164 , the lower end portion (lower boss)  146   b  of the right lower pivoting link  146  is fitted into the retaining recess  152  while the lower end portion (lower boss)  156   b  of the left lower pivoting link  156  is fitted into the left retaining recess  152 . In this way, the pulling handle  141  can be prevented from being accidentally collapsed by the weights of the pulling handle  141 , right and left pivoting link units  132  and  136 , etc. 
     Next, with primary reference to  FIG. 16 , a description will be given about an example manner in which maintenance (repair and inspection) of the mobile power generator apparatus  10  is performed. First, the two bolts  49  are removed from the screw holes  48 , and the right side cover  14  is detached from the right side wall section  26  to open the central area  121  of the rim  64  and opening  45 . 
     Air cleaner  193  of the engine  18 , engine oil cap  194 , carburetor  195 , mixer (not shown) are provided at positions facing the maintenance opening  45 . Thus, with the maintenance opening  45  opened in the aforementioned manner, it is possible to replace an element of the air cleaner  193 , remove the engine oil cap  194  to thereby replace engine oil, and replace the carburetor  195  and mixer. The mixer is a device that mixes the gas fuel, supplied from the cassette canister  35 , with air introduced via the air cleaner and feeds a resultant fuel/air mix into the cylinder of the engine  18 . 
     Thus, maintenance (repair and inspection) of the mobile power generator apparatus  10  can be performed through the central area  121  and maintenance opening  45 . 
     Next, with reference to  FIGS. 17 to 21 , a description will be given about an example of how to pull the mobile power generator apparatus  10  using the pulling unit  16  after shifting the pulling unit  16  from the collapsed position P 1  to the pulling position P 2 . In  FIGS. 17 to 21 , only the construction of the right side of the pulling unit  16  is shown with the construction of the left side of the pulling unit  16  omitted, to simplify illustration and facilitate understanding of the pulling unit  16 . 
       FIGS. 17A and 17B  are views explanatory of how the pulling unit  16  is shifted to the expanded position;  FIG. 17B  is an enlarged view of an encircled section  17   b  of  FIG. 17A . In  FIG. 17A , the pulling unit  16  is shown as being in the collapsed position P 1 . The lower end portion (lower boss)  146   b  of the right lower pivoting link  146  is located below the retaining recess  152 . Under this condition, the human operator starts expanding the pulling unit  16  by gripping the movable grip portion  164  with a hand  198  and pulling the pulling unit  16  toward the pulling position P 2  (see  FIG. 19 ) as indicated by arrow A. During that time, the right upper and right lower pivoting links  145  and  146  pivot upward about the bolts  147  as indicated by arrow B. At the same time, the lower end portion (lower boss)  146   b  of the right lower pivoting link  146  angularly moves about the lower end portion (lower boss)  145   b  of the right upper pivoting link  145  as indicated by arrow C of  FIG. 17B . 
       FIGS. 18A and 18B  are views showing the pulling unit  16  having been expanded partway;  FIG. 18B  is an enlarged view of an encircled section  18   b  of  FIG. 18A . As the human operator continues to pull the movable grip portion  164  toward the pulling position P 2  as indicated by arrow A, the movable grip portion  164  continues to move in the predetermined trajectory  181 . During that time, the right upper and right lower pivoting links  145  and  146  continue to pivot upward about the bolts  147  as indicated by arrow B, and the lower end portion (lower boss)  146   b  of the right lower pivoting link  146  angularly moves toward the retaining recess  152 . 
       FIG. 19  is a view showing the pulling unit  16  having been expanded to the pulling position P 2 . By the human operator further pulling the movable grip portion  164  toward the pulling position P 2  as indicated by arrow A, the movable grip portion  164  further moves in the predetermined trajectory  181  to reach the pulling position P 2 . 
       FIGS. 20A and 20B  are views showing the pulling unit  16  having been expanded to the pulling position P 2 . More specifically,  FIG. 20A  is a sectional view taken along the  20   a - 20   a  line of  FIG. 19 , and  FIG. 20B  is an enlarged view of an encircled portion  20   b  of  FIG. 19 . 
     The lower end portion (lower boss)  146   b  of the right lower pivoting link  146  interferes with the near-lower-end region  145   c  of the right upper pivoting link  145 . Thus, the pulling handle  141  can be prevented from being expanded beyond the pulling position P 2 . 
     At the same time the lower end portion (lower boss)  146   b  of the right lower pivoting link  146  interferes with the near-lower-end region  145   c , the lower end portion (lower boss)  146   b  of the right lower pivoting link  146  fits into the retaining recess  152  of the right retaining section  151 . 
     In this way, the pulling handle  141  can be prevented from being accidentally collapsed by the weights of the pulling handle  141 , pivoting link units  132 , etc. Thus, the movable grip portion  164  can be retained in the pulling position P 2  even while the human operator&#39;s hand is off the grip portion  164 . As a consequence, the instant embodiment can enhance the usability of the mobile power generator apparatus  10 . 
     Referring back to  FIG. 19 , the pulling unit  16  is bendable at its substantial longitudinal middle portion. Further, the right and left pivoting link units  132  and  136  each have a length substantially equal to the length of the pulling handle  141 . Thus, the pulling unit  16  can have an increased overall length by being expanded to the expanded position. 
     Further, as the pulling handle  141  is expanded, the right upper and right lower pivoting links  145  and  146  pivot upward about the bolts  147 , so that the lower end portions (lower bosses)  145   b  and  146   b  of the right lower pivoting links  145  and  146  move upward. Thus, the pulling handle  141  connected with the lower end portions (lower bosses)  145   b  and  146   b  is lifted, so that the movable grip portion  164  of the pulling handle  141  can be located at a high position H 2 . 
     Further, because the right upper and right lower pivoting links  145  and  146  pivot upward about the bolts  147  as the pulling handle  141  is expanded, the lower end portions (lower bosses)  145   b  and  146   b  of the right lower pivoting links  145  and  146  move forward, and thus, the pulling handle  141  connected with the lower end portions (lower bosses)  145   b  and  146   b  also moves forward. By the pulling handle  141  moving forward like this, the movable grip portion  164  of the pulling handle  141  can be located at a great distance L 2  from the frame  11 . 
       FIG. 21  is a view showing an example manner in which the mobile power generator apparatus  10  is pulled by the human operator via the pulling unit  16 . As illustrated in the figure, the human operator  197  walks forward gripping the movable grip portion  164  with the hand  198 . In this way, the right and left wheels  56  and  58  rotate, and thus, the mobile power generator apparatus  10  can be pulled forward. During that time, the left and right leg portions  28  are kept locked in the moving position, and the movable grip portion  164  is held at the high position H 2 . Namely, the movable grip portion  164  of the pulling handle  141  shifted to the expanded position can be held at a suitable height corresponding to the height of the human operator&#39;s hand. 
     Further, in the state shown in  FIG. 11 , the movable grip portion  164  is located forwardly of and at the great distance L 2  from the frame  11 , and thus, the body of the mobile power generator apparatus  10  is located at a sufficient distance from the human operator, which can prevent the human operator  197  from contacting the body of the mobile power generator apparatus  10 . 
     Because the movable grip portion  164  of the pulling handle  141  shifted to the expanded position can be held at a suitable height corresponding to the height of the human operator&#39;s hand and the human operator  197  can be prevented from contacting the body of the mobile power generator apparatus  10 , the instant embodiment can achieve an enhanced mobility and operability of the mobile power generator apparatus  10 . 
     As the mobile power generator apparatus  10  is pulled by the human operator, the steering wheel  126  can be changed in orientation in accordance with a moving direction of the power generator apparatus  10  and moved up and down in accordance with unevenness of the ground surface. As a consequence, the mobility of the mobile power generator apparatus  10  can be even further enhanced. 
     Next, with reference to  FIGS. 22 to 24 , a description will be given about an example manner in which the pulling unit  16  of the mobile power generator apparatus  10  is shifted from the pulling position P 2  to the collapsed position P 1 . In  FIGS. 22 to 24 , only the construction of the right side of the pulling unit  16  is shown with the construction of the left side of the pulling unit  16  omitted, to simplify illustration and facilitate understanding of the pulling unit  16 . 
       FIGS. 22A and 22B  are views showing an example manner in which the pulling unit  16  is collapsed from the expanded position;  FIG. 22B  is an encircled portion  22   b  of  FIG. 22A . As the movable grip portion  164  is pushed with a force as indicated by arrow F 1 , the pulling handle  141  pivots as indicated by arrow D about the lower end portion (lower boss)  145   b  of the right upper pivoting link  145 , and simultaneously the lower end portion (lower boss)  146   b  of the right lower pivoting link  146  pivots as indicated by arrow E about the lower end portion (lower boss)  145   b  of the right upper pivoting link  145 . By pivoting as indicated by arrow E, the lower end portion (lower boss)  146   b  of the right lower pivoting link  146  gets out of engagement with, and thus is released from retention by, the retaining recess  152  of the right link cover  133 . 
     Then, the right upper pivoting link  145  and the right lower pivoting link  146  start pivoting downward as indicated by arrow F about the bolts  147  due to the weights of the pulling handle  141 , pivoting link unit  132 , etc. Thus, the movable grip portion  164  starts collapsing toward the collapsed position P 1  in the predetermined trajectory  181  as indicated by arrow G. 
       FIGS. 23A and 23B  are views showing the pulling unit  16  having been collapsed partway. In this state, the right upper pivoting link  145  and the right lower pivoting link  146  further pivots downward as indicated by arrow F due to the weights of the pulling handle  141 , pivoting link unit  132 , etc. Thus, the movable grip portion  164  moves toward the collapsed position P 1  in the predetermined trajectory  181  as indicated by arrow G. 
       FIGS. 24A and 24B  are views showing the pulling unit  16  having being collapsed to the collapsed position P 1 . As shown in  FIG. 24A , the movable grip portion  164  moves in the predetermined trajectory  181  (see  FIG. 23 ) as indicated by arrow G to reach a position immediately short of the collapsed position P 1 . Then, the human operator pushes the movable grip portion  164  toward the frame  11  as indicated by arrow F 2 . 
     Thus, as shown in  FIG. 24B , the right handle section  161  is engaged by the handle holder  153  of the right link cover  133 , while the left handle section  162  is engaged by the handle holder  154  of the left link cover  137 . In this way, the pulling handle  141  can be retained in the collapsed position P 1  (see  FIG. 24A ). 
     As described above in relation to  FIGS. 17-24 , the mobile power generator apparatus  10  is constructed in such a manner that the movable grip portion  164  moves in the predetermined trajectory  181  (see  FIGS. 19 and 22 ) as the pulling handle  141  is shifted from the collapsed position P 1  to the expanded position P 2 . Thus, the human operator  197  can readily collapse/expand the pulling handle  141  by just shifting the hand  198 , gripping the movable grip portion  164 , along the predetermined trajectory  181 . As a result, the operation to be performed by the human operator  197  when collapsing/expanding the pulling handle  141  can be facilitated, which can significantly enhance the usability of the power generator apparatus  10 . 
     Further, the movement trajectory  181  of the movable grip portion  164  can be set to have a substantially constant gradient (more specifically a substantially S-shaped gradient) from the collapsed position P 1  to the expanded position P 2 , as seen in  FIG. 19 . Thus, the pulling handle  141  can be readily expanded from the collapsed position P 1  to the expanded position P 2  by the human operator  197  merely pulling the movable grip portion  164  obliquely upward. Thus, the operation for expanding the pulling handle  141  can be even further facilitated, which can even further enhance the usability of the power generator apparatus  10 . 
     Then, the pulling handle  141  is retained in the collapsed position P 1  where it is engaged by the handle holders  153  and  154 , and the longitudinal middle portion  138   c  of the lower connecting rod  138  engages the caster stopper  185 . In this way, the steering wheel  126  of the caster section  61  can be prevented from undesirably pivoting about the pivot shaft  124  and moving up and down. 
     Further, because not only the pulling handle  141  is engaged by the handle holders  153  and  154  but also the right tire stopper  158  abuts against the outer periphery of the right tire  65 , undesired rotation of the right wheel  56  can be prevented by the right tire stopper  158 . Similarly, the left tire stopper (not shown) abuts against the outer periphery of the left tire  65 . Thus, undesired rotation of the left wheel  58  can be prevented by the left tire stopper. 
     Also, the left and right leg portions  28  are lowered to the stationary position, so that the mobile power generator apparatus  10  can be stably held in a stationary position. 
       FIGS. 25A and 25B  are views explanatory of an example manner in which a power cord is moved away from the left and right wheels by means of the pulling unit  16 . Output terminal  202  is provided on an operation panel  201  of the mobile power generator apparatus  10 . Electric power generated by the power generator apparatus  10  can be output by a plug of the power cord  203  being inserted in the output terminal  202 . According to the embodiment, the mobile power generator apparatus  10  may be moved with the plug  204  of the cord  202  kept inserted in the output terminal  202 . 
     As the pulling handle  141  of the pulling unit  16  is expanded from the collapsed position, the lower connecting rod  138  ascends to lift the power cord  203 . Thus, the power cord  203  can be moved away from the left and right wheels by means of the pulling unit  16 , so that it can be prevented from getting tangled with the left and right wheels. 
     Whereas the preferred embodiment has been described above in relation to the case where the rim  64  of each of the wheels  56  and  58  is supported at its three portions via the three guide rollers, i.e. first and second fixed guide rollers  71  and  72  and movable guide roller  73 , the present invention is not so limited; for example, the rim  64  may be supported at its four or more portions via four or more guide rollers. 
     Whereas the preferred embodiment has been described above in relation to the case where the first and second fixed guide rollers  71  and  72  and movable guide roller  73  are supported via the first and second fixedly mounting sections  75  and  76  and variably mounting section  77 , these mounting sections may be constructed in any other desired manner than the aforementioned. 
     Furthermore, whereas the preferred embodiment has been described as employing the compression spring  117  as the resilient member of the variably mounting section  77 , the present invention is not so limited, and the resilient member may be a tension spring or the like. 
     The present invention is well-suited for application to mobile power generator apparatus where the power generator is mounted in a frame and wheels are attached to the frame for moving the power generator.