Patent Publication Number: US-8522988-B2

Title: Jib stowing device for jib crane vehicle

Description:
TECHNICAL FIELD 
     The present invention relates to a jib stowing device for a jib crane vehicle. 
     BACKGROUND ART 
     On a jib crane vehicle, a jib is extended forward from a distal portion of a top boom of a telescopic boom when the jib is used, and the jib is stowed on one side of a base boom of the telescopic boom when the jib is not used. 
     In a jib crane vehicle of this type, the operations to extend and stow the jib are performed as described below. 
     First, in a jib stowage position, a boss (with a pin hole) on a distal portion of the top boom and a boss (with a pin hole) on a proximal portion of the jib are uncoupled, and the jib is supported in a position extending along one side of the base boom by first stowing means located on the distal side on the base boom and second stowing means located on the proximal side on the base boom. To bring the jib from the stowage position to the extended position, the telescopic boom is fully contracted and the second stowing means on the proximal side on the base boom is uncoupled. Then, bosses on a first side portion of the top boom distal portion and bosses on a first side portion of the jib proximal portion are aligned with each other and these bosses are coupled to each other by a common pivot pin. Next, the first stowing means on the distal side on the base boom is uncoupled and the jib is rotated to the front of the top boom distal portion about the pivot pin. Then, bosses (with a pin hole) on a second side portion of the top boom distal portion and bosses (with a pin hole) on a second side portion of the jib proximal portion are aligned with each other and the bosses are coupled to each other by a coupling pin. 
     When the jib is brought from the stowage position to the extended position, the telescopic boom is fully contracted and the coupling pin on the non-pivot side between the top boom distal portion and the jib proximal portion is pulled out. Then, the jib is rotated into a space on one side of the telescopic boom about the pivot pin coupling the bosses on the first side portion of the top boom distal portion and the bosses on the first side portion of the jib proximal portion until the jib lies along a lateral side of the base boom, and a lateral side of the jib is coupled to the lateral side of the base boom by the first stowing means located on the distal side on the base boom. Then, the pivot pin that couples the top boom distal portion and the jib proximal portion is pulled out, and a distal portion of the jib is coupled to a proximal portion of the base boom by the second stowing means located on the proximal side on the base boom. 
     When the jib is extended to the front of the top boom distal portion from the stowage position, it is very dangerous to uncouple the first stowing means by mistake when the bosses on the top boom distal portion and the bosses on the jib proximal portion are not coupled with each other by the pivot pin, because there is a possibility of the jib falling off. Especially, when the first stowing means is configured to be manually operated from below the jib, the possibility of the jib falling off could lead to a physical injury. 
     Therefore, the applicant of the present invention has proposed a jib stowing device in which the first stowing means cannot be uncoupled unless the boss on the top boom distal portion and the boss on the jib proximal portion are coupled by the pivot pin (JP-A-2003-226486 as Patent Document 1). The jib stowing device of Patent Document 1, which is shown in  FIG. 12  to  FIG. 15 , is constituted as described below. 
     The jib stowing device of the related art (Patent Document 1) includes bosses ( 14   a  and  14   b ) with a pin hole provided on a first side portion of a distal portion  13  of a top boom  12  of a telescopic boom  1  and bosses ( 24   a  and  24   b ) with a pin hole provided on a first side portion of a proximal portion  23  (jib support) of a jib  2  which are removably couplable to each other by means of a pivot pin  30  (upper pivot pin  31  and a lower pivot pin  32 ), and first stowing means A provided between a distal position on a lateral side of a base boom  11  of the telescopic boom  1  and a proximal position of a lateral side of the jib  2  as shown in  FIG. 12  to  FIG. 13 . Second stowing means (not shown) for coupling a distal portion of the jib to the base boom is provided between a distal lateral side of the jib  2  and a proximal lateral side of the base boom  11 . 
     The bosses ( 14   a  and  14   b ) on the top boom distal portion  13  and the bosses ( 24   a  and  24   b ) on the jib proximal portion  23  are provided at two locations vertically separated from each other as shown in  FIG. 13 . That is, the bosses on the top boom distal portion  13  includes an upper boss  14   a  and a lower boss  14   b  (one each), and the bosses on the jib proximal portion  23  includes upper bosses  24   a  and lower bosses  24   b  (two each). 
     The pivot pin  30  includes a threaded rod  33 , and an upper pivot pin  31  and a lower pivot pin  32 , each of which is formed of a female-threaded cylinder, threaded over upper and lower portions, respectively, of the threaded rod  33  as shown in  FIG. 13 . Threads running in the opposite directions are formed on the upper and lower halves of the threaded rod  33 , and the upper pivot pin  31  and the lower pivot pin  32  are threaded on the oppositely threaded portions. Therefore, by rotating a lower end of the threaded rod  33  to the right or left with a rotary tool, the upper and lower pivot pins  31  and  32  can be moved toward (in a pin retracting direction) or away from (in a pin inserting direction) each other. 
     The pivot pin  30  is located between the upper and lower bosses  24   a  and  24   b  on the jib proximal portion  23 . In the jib stowage state, the upper pivot pin  31  and the lower pivot pin  32  are retracted out of the upper boss  14   a  and the lower boss  14   b , respectively, on the top boom distal portion  13  (the coupling between the top boom distal portion  13  and the jib proximal portion  23  is released) when the upper and lower pivot pins  31  and  32  are operated in a direction toward each other, and the upper pivot pin  31  and the lower pivot pin  32  are inserted into the upper boss  14   a  and the lower boss  14   b , respectively, on the top boom distal portion  13  (the top boom distal portion  13  and the jib proximal portion  23  are coupled to each other) when the upper and lower pivot pins  31  and  32  are operated in a direction away from each other. 
     As shown in  FIG. 13 , the first stowing means A has upper bosses (with a pin hole)  17   a  and lower bosses (with a pin hole)  17   b  provided at two vertically separated locations on a lateral side of the base boom  11  ( FIG. 12 ), an upper boss (with a pin hole)  27   a  and a lower boss (with a pin hole)  27   b  provided at two vertically separated locations on a lateral side of the jib  2 , upper and lower coupling pins  41  and  42  for coupling and uncoupling the upper and lower bosses ( 17   a  and  27   a , and  17   b  and  27   b ), and a hydraulic cylinder  45  for moving the upper and lower coupling pins  41  and  42  toward and away from each other. The hydraulic cylinder  45  is disposed with its tube  46  located above its rod  47 . The upper coupling pin  41  is connected to the upper end of the tube  46 , and the lower coupling pin  42  is connected to the lower end of the rod  47 . The hydraulic cylinder  45  and the upper and lower coupling pins  41  and  42  are attached to the base boom  11 . 
     When the jib  2  is laid along the base boom  11  as shown in  FIG. 12 , the upper bosses  17   a  on the base boom  11  and the upper boss  27   a  on the jib  2 , and the lower bosses  17   b  on the base boom  11  and the lower boss  27   b  on the jib  2  are aligned with each other as shown in  FIG. 13 . When the hydraulic cylinder  45  is extended with the upper and lower bosses aligned with each other, the upper coupling pin  41  is inserted into the upper bosses  17   a  and  27   a  and the lower coupling pin  42  is inserted into the lower bosses  17   b  and  27   b  (the first stowing means A is brought into a coupled state). On the other hand, when the hydraulic cylinder  45  is contracted from the state where the upper and lower coupling pins  41  and  42  couple the upper and lower bosses, respectively, the upper and lower coupling pins  41  and  42  are retracted out of the upper and lower bosses  27   a  and  27   b  on the jib and the first stowing means A is brought into an uncoupled state. 
     In addition, the jib stowing device of the related art is provided with pivot pin insertion state detecting means  5  for detecting whether or not the upper and lower pivot pins  31  and  32  are inserted in the upper and lower bosses  14   a  and  14   b , respectively, on the top boom distal portion  13 , coupling pin retraction restricting means  8  for restricting the upper and lower coupling pins  41  and  42  of the first stowing means A from being retracted out of the upper and lower bosses  27   a  and  27   b  on the jib  2 , and associating means (control cable)  91  for associating the pivot pin insertion state detecting means  5  and the coupling pin retraction restricting means  8  as shown in  FIG. 13  and  FIG. 14 . 
     The control cable  91  as the associating means has an outer casing  92  and an inner cable  93  movably received in the outer casing  92 . 
     As the pivot pin insertion state detecting means  5 , a protrusion  51  secured to the upper pivot pin  31  is employed. The protrusion  51  can move vertically in accordance with vertical movement of the upper pivot pin  31  to detect the insertion state of the upper and lower pivot pins  31  and  32 . In the related art, because the upper and lower pivot pins  31  and  32  are simultaneously moved toward or away from each other by the threaded rod  33 , the insertion state of both the pivot pins  31  and  32  can be detected by detecting vertical movement of one of the pivot pins (upper pivot pin  31 ). 
     A first end  93   a  of the inner cable  93  of the control cable  91  is coupled to the protrusion  51  as the pivot pin insertion state detecting means  5 , and the inner cable  93  is pushed or pulled relative to the outer casing  92  when the protrusion  51  moves vertically. 
     The coupling pin retraction restricting means  8  has a restricting member  81  which can retractably enter a gap S between the lower end of the tube  46  of the hydraulic cylinder  45  and the upper end of the lower coupling pin  42  as shown in  FIG. 13  and  FIG. 14 . The restricting member  81  has a vertical length which is slightly smaller than the width of the gap S between the lower end of the cylinder tube  46  and the upper end of the lower coupling pin  42  at the time when the hydraulic cylinder  45  has been extended. Also, the restricting member  81  is swingably pivoted by a shaft  82  on a mounting base  26  attached to the jib  2  at the first stowing means A. The restricting member  81  is urged in a restricting direction (direction toward the cylinder rod  47 ) as indicated by solid lines in  FIG. 14  by a spring  85  ( FIG. 14 ). In addition, a second end  93   b  of the inner cable  93  of the control cable  91  is coupled to the restricting member  81 , and the restricting member  81  is displaced to a non-restricting position (reference numeral  81 ) indicated by dotted lines in  FIG. 14  against the urging force of the spring  85  when the inner cable  93  is pulled as a result of vertical movement of the protrusion  51 . 
     The jib stowing device of the related art shown in  FIG. 12  to  FIG. 14  functions as shown in  FIGS. 15(A)  and (B). 
     First, when the upper and lower pivot pins  31  and  32  are not inserted in the upper and lower bosses  14   a  and  14   b  on the top boom distal portion  13  (the pivot pin  30  is in a contracted state), the restricting member  81  is positioned in the gap S between the lower end of the cylinder tube  46  and the upper end of the lower coupling pin  42  by the urging force of the spring  85  as shown in  FIG. 15(A)  because the protrusion  51  is located at its lowered position and the pulling effect of the control cable  91  (inner cable  93 ) does not act on the restricting member  81 . In the state shown in  FIG. 15(A) , because the restricting member  81  is positioned in the gap S, the restricting member  81  in the gap S prevents the hydraulic cylinder  45  from contracting even if the hydraulic cylinder  45  is operated to the contraction side. As a result, the upper and lower coupling pins  41  and  42  are not retracted out of the upper and lower bosses  17   a  and  17   b  on the jib  2  (the coupled state of the first stowing means A is maintained). 
     On the other hand, when the upper and lower pivot pins  31  and  32  are inserted in the upper and lower bosses  14   a  and  14   b  on the top boom distal portion  13  (the pivot pin  30  is in an extended state) as shown in  FIG. 15(B) , the pulling effect of the control cable  91  (inner cable  93 ) acts on the restricting member  81  because the protrusion  51  is located in its raised position, and the restricting member  81  is positioned outside the gap S between the lower end of the cylinder tube  46  and the upper end of the lower coupling pin  42  against the urging force of the spring  85  (the state indicated by reference numeral  81 ′ in  FIG. 14 ). In the state shown in  FIG. 15(B) , the hydraulic cylinder  45  can be contracted, and the upper and lower coupling pins  41  and  42  can be retracted out of the upper and lower bosses  27   a  and  27   b  on the jib  2  by contracting the hydraulic cylinder  45 . 
     In the jib stowing device according to the related art constituted as described above ( FIG. 12  to  FIG. 15 ), when the jib  2  is extended forward from the stowed state along the base boom  11  (the state shown in FIG.  15 (A)), the upper and lower coupling pins  41  and  42  of the first stowing means A are retracted out of the upper and lower bosses  27   a  and  27   b  on the jib  2  after the upper and lower pivot pins  31  and  32  have been inserted into the upper and lower bosses  14   a  and  14   b  on the top boom distal portion  13  as shown in  FIG. 15(B) . At this time, even if the upper and lower coupling pins  41  and  42  of the first stowing means A are retracted (the hydraulic cylinder  45  is contracted) by mistake with the upper and lower pivot pins  31  and  32  in the retracted state, the upper and lower coupling pins  41  and  42  cannot be retracted (pulled out) because the restricting member  81  is in the restricting position. 
     Therefore, the jib stowing device of the related art has a function of preventing the pivot pins ( 31  and  32 ) and the coupling pins ( 41  and  42 ) from being retracted (pulled out) simultaneously during a jib extending operation to secure safety during a jib extend operation.
     Patent Document 1: JP Patent Application Publication No. 2003-226486   

     DISCLOSURE OF THE INVENTION 
     Problem to be Solved by the Invention 
     The jib stowing device of the related art discussed above ( FIG. 12  to  FIG. 15 ) can secure safety against an erroneous operation when the jib is extended from a stowed state, but each of the above means (the pivot pin insertion state detecting means  5 , the coupling pin retraction restricting means  8 , the associating means  91  and so on) are not effective at all for safety when the jib is stowed from an extended state. 
     In other words, when the jib is stowed from an extended state, the jib  2  is rotated to a position where it extends along a lateral side of the base boom  11  with the upper and lower pivot pins  31  and  32  inserted in the upper and lower bosses  14   a  and  14   b  on the top boom distal portion  13 . Then, the upper and lower coupling pins  41  and  42  of the first stowing means A are inserted into the upper and lower bosses  27   a  and  27   b  on the jib  2 , and the upper and lower pivot pins  31  and  32  are retracted out of the upper and lower bosses  14   a  and  14   b  on the top boom distal portion  13 . At this time, the upper and lower pivot pins  31  and  32  could be pulled out by mistake even if the upper and lower coupling pins  41  and  42  of the first stowing means A are not inserted. In this case, the jib  2  may fall off the telescopic boom  1 . 
     It is, therefore, an object of the present invention to provide a jib stowing device for a jib crane vehicle which can eliminate the risk of the jib falling off due to an erroneous operation both during an operation to extend the jib to the front of a top boom distal portion from a stowage position on one side of the base boom and during an operation to stow the jib from the forward extended position to one side of the base boom. 
     Means for Solving the Problem 
     As means for solving the above problem, the present invention has the following configuration. The present invention is directed to a jib stowing device for a jib crane vehicle. 
     The jib crane vehicle according to the present invention is provided with a jib removably attachable to a distal portion of a top boom of a telescopic boom mounted on a vehicle. The telescopic boom is attached to a rotating platform mounted on the vehicle for arcuate movement. 
     A jib stowing device for a jib crane vehicle according to the present invention comprises a common pivot pin retractably insertable into a boss (with a pin hole) provided on a first side portion of the distal portion of the top boom and a boss (with a pin hole) provided on a first side portion of a proximal portion of the jib when the bosses are aligned with each other so that the jib can be rotated about the pivot pin in a space on one side of the telescopic boom with the telescopic boom in a fully contracted state between an extended position in which the jib is extended to the front of the distal portion of the top boom and a stowage position in which the jib is located along one side of a base boom of the telescopic boom, and stowing means provided between the base boom and the jib for stowing the jib on a lateral side of the base boom. 
     In the following description, the term “insertion” of a pivot pin or coupling pin is intended to refer to coupling between a boss on the boom and a boss on the jib with the pin, and the term “retraction” of the pivot pin or coupling pin is intended to refer to “uncoupling” of the boss on the boom from the boss on the jib. 
     While the stowing means disposed between the base boom and the jib preferably include first stowing means located on the distal side on the base boom and second stowing means located on the proximal side on the base boom as in the related art discussed above so that the jib can be supported at two points, only one stowing means may be provided generally at the center of the base boom (in the vicinity of the center of gravity of the jib). 
     The stowing means has a boss (with a pin hole) provided on the lateral side of the base boom, a boss (with a pin hole) provided on a lateral side of the jib, and a coupling pin removably insertable into the bosses. 
     On the jib, there are provided pivot pin insertion state detecting means for mechanically detecting whether or not the pivot pin is in an inserted position, pivot pin retraction restricting means for mechanically restricting movement of the pivot pin to a retracted side, coupling pin insertion state detecting means for mechanically detecting whether or not the coupling pin is in an inserted position, coupling pin retraction restricting means for mechanically restricting movement of the coupling pin to a retracted side, first associating means for mechanically associating the pivot pin insertion state detecting means and the coupling pin retraction restricting means, and second associating means for mechanically associating the coupling pin insertion state detecting means and the pivot pin retraction restricting means. 
     In the jib stowing device according to the present invention, movement of the coupling pin to the retracted side is restricted by the coupling pin retraction restricting means via the first associating means when the pivot pin insertion state detecting means has detected a retracted state of the pivot pin, and the restriction of movement of the coupling pin to the retracted side by the coupling pin retraction restricting means via the first associating means is released when the pivot pin insertion state detecting means has detected an inserted state of the pivot pin, while movement of the pivot pin to the retracted side is restricted by the pivot pin retraction restricting means via the second associating means when the coupling pin insertion state detecting means has detected a retracted state of the coupling pin, and the restriction of movement of the pivot pin to the retracted side by the pivot pin retraction restricting means via the second associating means is released when the coupling pin insertion state detecting means has detected an inserted state of the coupling pin. 
     The jib stowing device according to the present invention has the following effects. 
     First, when the jib is extended from the stowed state on one side of the base boom, the coupling pin of the stowing means is retracted after the pivot pin has been inserted into the boss on a first side portion of the top boom distal portion and the boss on a first side portion of the jib proximal portion. At this time, the pivot pin insertion state detecting means, the coupling pin retraction restricting means and the first associating means prevent the coupling pin of the stowing means from being retracted if the pivot pin is in a retracted state. Thus, even if the coupling pin of the stowing means is retracted by mistake with the pivot pin in a retracted state (uncoupled state), the coupling pin cannot be retracted (a coupled state provided by the coupling pin is maintained). Therefore, both the pivot pin and the coupling pin cannot be (simultaneously) retracted during a jib extending operation even if there is an erroneous operation (misconception). 
     When the jib is stowed to one side of the base boom from the extended state in front of the top boom distal portion, the pivot pin is retracted after the jib has been rotated about the pivot pin to one side of the base boom and the coupling pin has been inserted into the stowing means. At this time, the coupling pin insertion state detecting means, the pivot pin retraction restricting means and the second associating means prevent the pivot pin from being retracted if the coupling pin is in a retracted state. Thus, even if the pivot pin is retracted by mistake with the coupling pin in a retracted state (uncoupled state), the pivot pin cannot be retracted, (a coupled state provided by the pivot pin is maintained). Therefore, both the pivot pin and the coupling pin cannot be (simultaneously) retracted during a jib stowing operation even if there is an erroneous operation (misconception). 
     Also, the pivot pin insertion state detecting means, the coupling pin insertion state detecting means, the pivot pin retraction restricting means, the coupling pin retraction restricting means, the first associating means, and the second associating means used in the jib stowing device according to the present invention are collectively provided on the jib. Therefore, each of the means does not interfere with the extension and contraction of the boom even when a crane operation (extension and contraction of the boom) is performed only with the telescopic boom in the jib stowage state (state in which the jib is separate from the top boom). In addition, because each of the above means is mechanically installed, there is no need to provide a connector for power source connection (requiring connecting and disconnecting operations) between the telescopic boom and the jib or provide a control controller in contrast to means which operates on electricity or hydraulic pressure. 
     In the jib stowing device according to the present invention, wherein the coupling pin of the stowing means is provided on the base boom. The coupling pin insertion state detecting means on the jib is removably engageable with the coupling pin. Thus, the coupling pin insertion state detecting means is engaged with the coupling pin when the jib is stowed on one side of the base boom so that the coupling pin insertion state detecting means can detect an insertion state of the coupling pin. 
     When the coupling pin of the stowing means is inserted and extracted by a hydraulic cylinder, for example, as in a related art shown in  FIG. 12  to  FIG. 15 , the hydraulic cylinder and the coupling pin must be provided on the base boom because the hydraulic cylinder for moving the coupling pin needs to be connected to a hydraulic source. When the coupling pin is provided on the base boom and the coupling pin insertion state detecting means is provided on the jib, the coupling pin and the coupling pin insertion state detecting means need to be removably engageable with each other because the jib is displaced between a stowage position and a separate position relative to the base boom. 
     Therefore, in the jib stowing device according to the present invention, coupling pin insertion state detecting means which is removably engageable with the coupling pin is used so that the insertion state of the coupling pin can be detected when the coupling pin is provided on the base boom. 
     Effect of the Invention 
     The jib stowing device according to the present invention has the following effects. 
     According the present invention, both when the jib is extended from the stowed state and when the jib is stowed from the extended state, even if either the pivot pin  30  or the coupling pin undergoes a retracting operation by mistake, the operated pin is not retracted (pulled out) if the other of the pivot pin or the coupling pin is in the retracted state (uncoupled state). Thus, a trouble of both the pivot pin and the coupling pin being pulled out by an erroneous operation can be prevented from occurring both during a jib stowing operation and during a jib extending operation. Therefore, the effect is obtained that safety can be secured both when the jib is stowed and when the jib is extended (the possibility of the jib falling off is eliminated). 
     Also, the pivot pin insertion state detecting means, the coupling pin insertion state detecting means, the pivot pin retraction restricting means, the coupling pin retraction restricting means, the first associating means, and the second associating means are collectively provided on the jib. Therefore, the effect is obtained that each of the means does not interfere with the extension and contraction of the boom even when a crane operation (extension and contraction of the boom) is performed only with the telescopic boom in the jib stowage state (state in which the jib is separate from the top boom). 
     In addition, because each of the above means is mechanically installed, there is no need to provide a connector for power source connection (requiring connecting and disconnecting operations) between the telescopic boom and the jib or to provide a control controller. Therefore, the effect is obtained that the safety during stowage and extension of the jib can be secured with a simple configuration in contrast to means which operates on electricity or hydraulic pressure. 
     In the invention, the coupling pin insertion state detecting means is removably engageable with the coupling pin so that the insertion state of the coupling pin can be detected by the coupling pin insertion state detecting means in a jib stowage state even when the coupling pin of the stowing means is provided on the base boom and the insertion state of the coupling pin is detected by coupling pin insertion state detecting means on the jib. 
     Therefore, the present invention has the effect that the insertion state of the coupling pin can be detected on the jib side even when the coupling pin of the stowing means is provided on the base boom. In other words, the effect is obtained that the pivot pin can be restricted from being retracted even when the coupling pin is provided on the base boom in the jib stowing device according to claim  1  in which the pivot pin is restricted from being retracted depending on the insertion state of the coupling pin of the stowing means. 
    
    
     EMBODIMENT 
     Description is hereinafter made of a jib stowing device for a jib crane vehicle according to an embodiment of the present invention with reference to  FIG. 1  to  FIG. 11 . 
     The jib crane vehicle used in this embodiment has a telescopic boom  1  mounted for arcuate movement on a rotating platform equipped on a vehicle, and a jib  2  removably attachable to a distal portion  13  of a top boom  12  of the telescopic boom  1 . 
     The telescopic boom  1  includes a base boom  11 , a top boom  12  and a plurality of intermediate booms, and the booms are telescopically connected to each other. In this embodiment, the jib  2  includes a base jib  21 , a top jib  22  retractably fitted in the base jib  21 , and a jib support  23  attached to a proximal portion of the base jib  21 . In this jib  2 , the jib support  23  serves as a jib proximal portion. 
     As shown in  FIG. 2  to  FIG. 4 , the distal portion  13  of the top boom  12  and the jib proximal portion (which is hereinafter referred to as “jib support”)  23  are coupled to each other by inserting a pivot pin  30  (upper pivot pin  31  and lower pivot pin  32 ) into upper and lower bosses (with a pin hole)  14   a  and  14   b  provided on a first side portion of the top boom distal portion  13  and upper and lower bosses (with a pin hole)  24   a  and  24   b  provided on a first side portion of the jib support  23 . The top boom distal portion  13  has one upper boss  14   a  and one lower boss  14   b , and the jib support  23  has two upper bosses  24   a  with a small vertical distance therebetween and two lower bosses  24   b  with a small distance therebetween. 
     By rotating the jib  2  about the pivot pin  30  in a space on one side of the telescopic boom  1  with the pivot pin  30  (the upper pivot pin  31  and the lower pivot pin  32 ) inserted in the bosses ( 14   a  and  24   a , and  14   b  and  24   b ), the jib  2  can be moved between a stowage position where the jib is disposed along one side of the base boom  11  ( FIG. 2 ) and an extended position where the jib extends in front of the top boom distal portion  13  (not shown). 
     Stowing means for stowing the jib  2  on a lateral side of the base boom  11  is provided between the base boom  11  and the jib  2 , and, in this embodiment, first stowing means A (the detailed configuration of which is described later) located on the distal side on the base boom  11  and second stowing means B located on the proximal side on the base boom  11  are provided as the stowing means as shown in  FIG. 1  and  FIG. 2 . In the jib stowage state shown in  FIG. 1 , the jib  2  is supported on the lateral side of the base boom  11  by the first stowing means A and the second stowing means B with the pivot pin  30  (the upper pivot pin  31  and the lower pivot pin  32 ) extracted out of the upper and lower bosses ( 14   a  and  24   a , and  14   b  and  24   b ). 
     While the stowing means disposed between the base boom  11  and the jib  2  preferably include first stowing means A located on the distal side on the base boom  11  and second stowing means B located on the proximal side on the base boom  11  as in this embodiment so that the jib  2  can be supported at two points, only one stowing means may be provided generally at the center of the base boom  11  (in the vicinity of the center of gravity of the jib  2 ) in another embodiment. In such a case (a case where only one stowing means is provided), the stowing means is the same in configuration as the first stowing means A discussed above. 
     As shown in  FIG. 4  and  FIG. 5 , the pivot pin  30  has a threaded rod  33  having upper and lower portions with which the upper pivot pin  31  and the lower pivot pin  32 , each of which is in the form of a female-threaded cylinder, are threaded, respectively. As shown in  FIG. 5 , the threaded rod  33  has a right-hand thread  33   a  formed on the upper half thereof and a left-hand thread  33   b  formed on the lower half thereof, and is provided with a rotary tool coupling portion  34  for coupling a rotary tool for rotating the threaded rod at its lower end. The upper pivot pin  31  is threaded with the right-hand thread  33   a  formed on the upper half of the threaded rod  33 , and the lower pivot pin  32  is threaded with the left-hand thread  33   b  formed on the lower half of the threaded rod  33 . 
     The pivot pin  30  is disposed to extend between the upper and lower bosses  24   a  and  24   b  on the jib support  23  as shown in  FIG. 5 . The upper pivot pin  31  and the lower pivot pin  32  of the pivot pin  30  have vertical grooves  31   a  and  32   a , respectively, formed in an outer surface thereof and anti-rotation pins (bolts)  38  and  38  are inserted in the vertical grooves  31   a  and  32   a  from the side of the upper and lower bosses  24   a  and  24   b  so that the upper pivot pin  31  and the lower pivot pin  32  cannot rotate together with the threaded rod  33 . 
     The upper pivot pin  31  and the lower pivot pin  32  of the pivot pin  30  can be simultaneously retracted out of or inserted into the upper and lower bosses  14   a  and  14   b  on the top boom distal portion  13  by manually rotating the threaded rod  33  to the right or left. In other words, the upper pivot pin  31  and the lower pivot pin  32  are simultaneously moved toward each other (to the pin retracting side) when the rotary tool coupling portion  34  at the lower end of the threaded rod  33  is rotated to the right (as viewed from below) with a rotary tool, and the upper pivot pin  31  and the lower pivot pin  32  are simultaneously moved away from each other (to the pin inserting side) when the rotary tool is rotated to the left (as viewed from below). 
     The state shown in  FIG. 5  is a state where the upper pivot pin  31  and the lower pivot pin  32  have been inserted into the upper and lower bosses  14   a  and  14   b , respectively, on the top boom distal portion  13 . In this state, a gap T with a considerable length is formed between the lower end of the upper pivot pin  31  and the upper end of the lower pivot pin  32  on the outside of the threaded rod  33 , and a restricting member  71 , which is described later, can enter the gap T. 
     As shown in  FIG. 4  and  FIG. 9 , the first stowing means A has upper bosses (with a pin hole)  17   a  and lower bosses (with a pin hole)  17   b  provided at two vertically separated locations on a lateral side of the base boom  11 , an upper boss (with a pin hole)  27   a  and a lower boss (with a pin hole)  27   b  provided at two vertically separated locations on a lateral side of the base jib  21 , and a coupling pin  40  for coupling and uncoupling the upper and lower bosses ( 17   a  and  27   a , and  17   b  and  27   b ). 
     The upper and lower bosses  17   a  and  17   b  on the base boom  11  are provided transversely on a mounting base  16  disposed on a lateral side of the base boom  11 . The upper and lower bosses  27   a  and  27   b  on the base jib  21  are provided transversely on a mounting base  26  disposed on a lateral side of the base jib  21 . The base boom  11  has two upper bosses  17   a  with a small vertical distance therebetween and two lower bosses with a small vertical distance therebetween, and the base jib  21  has one upper boss  27   a  and one lower boss  27   b.    
     The coupling pin  40  has the same structure as the pivot pin  30 . That is, the coupling pin  40  has a threaded rod  43  with which an upper coupling pin  41  and a lower coupling pin  42 , each of which is in the form of a female-threaded cylinder, are threaded at upper and lower portions thereof, respectively. As shown in  FIG. 9 , the threaded rod  43  has a right-hand thread  43   a  formed on the upper half thereof and a left-hand thread  43   b  formed on the lower half thereof, and is provided with a rotary tool coupling portion  44  for coupling a rotary tool for rotating the threaded rod at its lower end. The upper coupling pin  41  is threaded with the right-hand thread  43   a  formed on the upper half of the threaded rod  43 , and the lower coupling pin  42  is threaded with the left-hand thread  43   b  formed on the lower half of the threaded rod  43 . 
     As shown in  FIG. 9 , the coupling pin  40  is disposed to extend between the upper and lower bosses  17   a  and  17   b  on the mounting base  16  on the base boom  11 . The upper coupling pin  41  and the lower coupling pin  42  of the coupling pin  40  have vertical grooves  41   a  and  42   a , respectively, formed in an outer surface thereof and anti-rotation pins (bolts)  48  and  48  are inserted in the vertical grooves  41   a  and  42   a  from the side of the upper and lower bosses  17   a  and  17   b  so that the upper coupling pin  41  and the lower coupling pin  42  cannot rotate together with the threaded rod  43 . 
     The upper coupling pin  41  and the lower coupling pin  42  of the coupling pin  40  can be simultaneously retracted out of or inserted into the upper and lower bosses  27   a  and  27   b  on the base jib  21  by manually rotating the threaded rod  43  to the right or left. In other words, the upper coupling pin  41  and lower coupling pin are simultaneously moved toward each other (to the pin retracting side) when the rotary tool coupling portion  44  at the lower end of the threaded rod  43  is rotated to the right (as viewed from below) with a rotary tool, and the upper coupling pin  41  and the lower coupling pin  42  are simultaneously moved away from each other (to the pin inserting side) when the rotary tool is rotated to the left (as viewed from below). 
     In the jib crane vehicle according to this embodiment, the operations to extend and stow the jib are performed as described below. 
     First, in a jib stowage position, the boss  14   a  (the lower boss  14   b  is below it) on the top boom distal portion  13  and the boss  24   a  (the lower boss  24   b  is below it) on the jib support  23  are uncoupled from each other (the upper pivot pin  31  and the lower pivot pin  32  are adjacent to each other as shown in  FIG. 8 ) and the jib  2  is supported in a position extending along one side of the base boom  11  by the first stowing means A located on the distal side on the base boom  11  and the second stowing means B located on the proximal side on the base boom  11  as shown in  FIG. 1 . At this time, the upper coupling pin  41  and the lower coupling pin  42  of the coupling pin  40  of the first stowing means A are separate from each other and couples the upper and lower bosses ( 17   a  and  27   a , and  17   b  and  27   b ) as shown in  FIG. 9 . In the jib stowage state, the telescopic boom  1  can be extended and contracted with the jib  2  stowed on a lateral side of the base boom  11 . 
     To bring the jib  2  from the stowage position ( FIG. 1 ) to an extended position, the second stowing means B on the proximal side on the base boom is uncoupled (so that the jib  2  can be swung about the coupling pin  40  of the first stowing means A) with the telescopic boom  1  fully contracted, and the boss  14   a  ( 14   b ) on a first side portion of the top boom distal portion  13  and the boss  24   a  ( 24   b ) on a first side portion of the jib support  23  are aligned with each other as shown in  FIG. 2  (the state shown in  FIG. 8 ). Then, the rotary tool coupling portion  34  of the threaded rod  33  of the pivot pin  30  is rotated to the left (to separate the upper pivot pin  31  and the lower pivot pin  32  from each other) to couple the upper bosses  14   a  and  24   a  to each other by the upper pivot pin  31  and to couple the lower bosses  14   b  and  24   b  to each other by the lower pivot pin  32 . Thereafter, when the threaded rod  43  of the coupling pin  40  of the first stowing means A is rotated to the right to retract the upper coupling pin  41  and the lower coupling pin  42  out of the upper and lower bosses  27   a  and  27   b , respectively, on the base jib  21 , the entire jib  2  can be rotated about the pivot pin  30  (the upper pivot pin  31  and the lower pivot pin  32 ) in a space on one side of the telescopic boom  1 . Then, the jib  2  can be set in an extend position by rotating the jib  2  to the front of the top boom distal portion  13 , aligning the bosses on the non-pivot side of the jib support  23  with the bosses on the non-pivot side of the top boom distal portion  13 , and inserting another coupling pin into the bosses. 
     When the jib  2  is moved from the stowage position to the extended position, or when the jib  2  is moved from the extended position to the stowage position, it is necessary to insert and retract the pivot pin  30  and the coupling pin  40  alternatively. In an ordinary jib stowing device, there is a possibility of both the pivot pin  30  and the coupling pin  40  being retracted simultaneously by an erroneous operation as described in the section of “Background Art.” In this case, there is a danger of the jib falling off. 
     Therefore, the jib stowing device according to this embodiment is provided with a safety mechanism to prevent both the pivot pin  30  and the coupling pin  40  from being retracted simultaneously during operations to extend and stow the jib  2 . 
     That is, the safety mechanism includes, in the jib stowing device having the above configuration, pivot pin insertion state detecting means  5  provided on the jib  2  for mechanically detecting whether or not the pivot pin  30 , which serves as a pivot for jib rotation, is in an inserted position, pivot pin retraction restricting means  7  for mechanically restricting movement of the pivot pin  30  to a retract side, coupling pin insertion state detecting means  6  for mechanically detecting whether or not the coupling pin  40  of the first stowing means A is in an inserted position, coupling pin retraction restricting means  8  for mechanically restricting movement of the coupling pin  40  to a retracting side, first associating means  91  for mechanically associating the pivot pin insertion state detecting means  5  and the coupling pin retraction restricting means  8 , and second associating means  94  for mechanically associating the coupling pin insertion state detecting means  6  and the pivot pin retraction restricting means  7 . It should be noted that the term “mechanically” in these means ( 5 ,  6 ,  7 ,  8 ,  91  and  94 ) refers to achieve their functions without the use of any power such as electricity or hydraulic pressure. In this embodiment, these means ( 5 ,  6 ,  7 ,  8 ,  91  and  94 ) are constituted as described below. 
     As the pivot pin insertion state detecting means  5 , a protrusion  51  secured to the upper pivot pin  31  is employed as shown in  FIG. 3  to  FIG. 6  and  FIG. 11 . The protrusion  51  can move vertically in accordance with vertical movement of the upper pivot pin  31  to detect the insertion state of the upper and lower pivot pins  31  and  32 . Because the upper and lower pivot pins  31  and  32  are simultaneously moved toward or away from each other by the threaded rod  33 , the insertion state of both the pins  31  and  32  can be detected by detecting vertical movement of one of the pivot pins (the upper pivot pin  31 ). 
     The pivot pin retraction restricting means  7  has a restricting member  71  pivoted at a position in the vicinity of the pivot pin  30  for swinging movement toward and away from the threaded rod  33  of the pivot pin  30  as shown in  FIG. 3  to  FIG. 6  and  FIG. 11  (especially in  FIG. 5  and  FIG. 6 ). As shown in  FIG. 5 , the restricting member  71  has a height which is slightly smaller than the width of the gap T between the lower end of the upper pivot pin  31  and the upper end of the lower pivot pin  32  at the time when the upper and lower pivot pin  31  and  32  are inserted in the upper and lower bosses  14   a  and  14   b , respectively, on the top boom distal portion  13 . The restricting member  71  is pivoted by a shaft  72  on a mounting base  29  provided on the jib support  23  as shown in  FIG. 6 . 
     The restricting member  71  is provided with two arms  73  and  74  extending outward in opposite directions, and one of the arms, the arm  74 , is urged in a direction in which the restricting member  71  approaches the threaded rod  33  of the pivot pin  30  by a spring  75 . A first end  96   a  of an inner cable  96  of the second associating means (control cable)  94 , which is described later, is coupled to the other arm  73  of the restricting member  71 . 
     When the restricting member  71  is in a free state, the restricting member  71  is swung by the urging force of the spring  75  to a position where it abuts against (or is adjacent to) an outer surface of the threaded rod  33  as indicated by dotted lines (reference numeral  71 ′) in  FIG. 6 . Therefore, when the restricting member  71  is brought into the free state with the upper and lower pivot pins  31  and  32  inserted in the bosses  14   a  and  14   b , respectively, on the top boom distal portion  13  as shown in  FIG. 5 , the restricting member  71  enters the gap T between the lower end of the upper pivot pin  31  and the upper end of the lower pivot pin  32  by the urging force of the spring  75 . The restricting member  71  can enter the gap T between the lower end of the upper pivot pin  31  in an inserted state and the upper end of the lower pivot pin  32  in an inserted state with clearances above and below it. However, when the threaded rod  33  is operated to the pivot pin retracting side (rotated to the left) with the restricting member  71  positioned in the gap T, the lower end of the upper pivot pin  31  and the upper end of the lower pivot pin  32  abut against the upper and lower faces, respectively, of the restricting member  71  before the upper and lower pivot pins  31  and  32  are retract out of the upper and lower bosses  14   a  and  14   b  on the top boom distal portion  13  as shown in  FIG. 7  and the threaded rod  33  cannot be further rotated to the pivot pin retracting side after the abutment. While the lower end of the upper pivot pin  31  and the upper end of the lower pivot pin  32  simultaneously abut against the upper and lower faces of the restricting member  71  in the state shown in  FIG. 7 , only either one of the upper pivot pin  31  or the lower pivot pin  32  may be configured to abut against the restricting member  71 . 
     As the coupling pin insertion state detecting means  6 , an L-shaped lever  61  which swings in accordance with vertical movement of the upper coupling pin  41  is employed as shown in  FIG. 4  and  FIG. 9  to  FIG. 11 . The L-shaped lever  61  is pivoted at the corner of the L-shaped body by a shaft  62  at a position in the vicinity of the upper coupling pin  41  in the jib stowage state on the mounting base  26  on the base jib  21 . A protrusion  63  protrudes from a first lever end of the L-shaped lever  61  toward the upper coupling pin  41 . A push plate  64  against which the protrusion  63  is abuttable is attached to an outer surface of the upper coupling pin  41 . 
     The L-shaped lever  61  on the base jib  21  and the protrusion  63  on the upper coupling pin  41  are configured such that the L-shaped lever  61  is separated from the push plate  64  when the jib  2  is separated from the base boom  11  and the protrusion  63  of the L-shaped lever  61  is engaged with the push plate  64  on the upper coupling pin  41  when the jib  2  is located in the stowage position on one side of the base boom  11 . 
     The coupling pin insertion state detecting means  6  swings a second lever end of the L-shaped lever  61  in the jib length direction via the protrusion  63  when the push plate  64  moves vertically in accordance with vertical movement of the upper coupling pin  41 , and can detect the insertion state of the upper and lower coupling pins  41  and  42  based on the amount by which the second lever end is swung. Because the upper and lower coupling pins  41  and  42  of the coupling pin  40  are also simultaneously moved toward or away from each other by the threaded rod  43 , the insertion state of both the coupling pins  41  and  42  can be detected by detecting a vertical movement of one of the coupling pins (the upper coupling pin  41 ). 
     The coupling pin retraction restricting means  8  has a restricting member  81  pivoted at a position in the vicinity of the coupling pin  40  of the first stowing means A for swinging movement toward and away from the threaded rod  43  of the coupling pin  40  as shown in  FIG. 3  to  FIG. 4  and  FIG. 9  to  FIG. 11  (especially  FIG. 9  and  FIG. 10 ). As shown in  FIG. 9 , the restricting member  81  has a height which is slightly smaller than the width of the gap S between the lower end of the upper coupling pin  41  and the upper end of the lower coupling pin  42  at the time when the upper and lower coupling pins  41  and  42  are inserted in the upper and lower bosses  27   a  and  27   b , respectively, on the base jib  21 . The restricting member  81  is pivoted by a shaft  82  on the mounting base  26  provided on the base jib as shown in  FIG. 10 . The restricting member  81  is provided with an arm  84  extending outward, and the arm  84  is urged in a direction in which the restricting member  81  approaches the threaded rod  43  of the coupling pin  40  by a spring  85 . When the restricting member  81  is in a free state, the restricting member  81  is swung by the spring  85  to a position where it abuts against (or is adjacent to) an outer surface of the threaded rod  43  as indicated by dotted lines (reference numeral  81 ′) in  FIG. 10 . Therefore, when the restricting member  81  is brought into the free state with the upper and lower coupling pins  41  and  42  inserted in the bosses  27   a  and  27   b , respectively, on the base jib  21  as shown in  FIG. 9 , the restricting member  81  enters the gap S between the lower end of the upper coupling pin  41  and the upper end of the lower coupling pin  42  by the urging force of the spring  85 . 
     As each of the first associating means  91  and the second associating means  94 , a control cable is employed. Each of the control cables  91  and  94  has an outer casing  92  and an inner cable  93  movably received in the outer casing  92 . 
     Both ends of the outer casing  92  of the control cable  91  as the first associating means are unmovably secured, and the inner cable  93  has a first end  93   a  coupled to the protrusion  51  as the pivot pin insertion state detecting means  5  as shown in  FIG. 5  to  FIG. 6  and  FIG. 11  and a second end  93   b  coupled to the arm  84  of the restricting member  81  of the coupling pin retraction restricting means  8  as shown in  FIG. 9  to  FIG. 10  and  FIG. 11 . The first associating means (control cable)  91  can swing the restricting member  81  of the coupling pin retraction restricting means  8  between a non-restricting position (the position indicated by reference numeral  81  in  FIG. 10 ) and a restricting position (the position indicated by reference numeral  81 ′ in  FIG. 10 ) via the pivot pin insertion state detecting means  5  (the protrusion  51 ) and the inner cable  93  thereof when the upper pivot pin  31  of the pivot pin  30  moves vertically. In other words, the inner cable  93  is pulled and the restricting member  81  of the coupling pin retraction restricting means  8  is moved against the urging force of the spring  85  to the non-restricting position indicated by solid lines in  FIG. 10  when the upper pivot pin  31  is moved upward (both the upper and lower pivot pins  31  and  32  are inserted) as shown in  FIG. 5  and  FIGS. 11(B)  and (C), and the inner cable  93  is pushed (released from a tension) and the restricting member  81  of the coupling pin retraction restricting means  8  is moved to the restricting position indicated by dotted lines in  FIG. 10  (reference numeral  81 ′) by the urging force of the spring  85  when the upper pivot pin  31  is moved downward (both the upper and lower pivot pins  31  and  32  are retracted) as shown in  FIG. 8  and  FIG. 11(A) . 
     Both ends of the outer casing  95  of the control cable  94  as the second associating means are unmovably secured and the inner cable  96  has a first end  96   a  coupled to the arm  73  of the restricting member  71  of the pivot pin retraction restricting means  7  as shown in  FIG. 5  to  FIG. 6  and  FIG. 11  and a second end  96   b  coupled to one of lever ends of the L-shaped lever  61  of the coupling pin insertion state detecting means  6  as shown in  FIG. 9  to  FIG. 10  and  FIG. 11 . The second associating means (control cable)  94  can swing the restricting member  71  of the pivot pin retraction restricting means  7  between a non-restricting position (the position indicated by reference numeral  71  in  FIG. 6 ) and a restricting position (the position indicated by reference numeral  71 ′ in  FIG. 6 ) via the coupling pin insertion state detecting means  6  (the L-shaped lever  61 ) and the inner cable  96  when the upper coupling pin  41  of the coupling pin  40  is moved vertically. In other words, the restricting member  71  of the pivot pin retraction restricting means  7  is moved against the urging force of the spring  75  to the non-restricting position indicated by solid lines in  FIG. 6  because the L-shaped lever  61  is swung to the inner cable pulling side via the push plate  64  and the protrusion  63  and pulls the inner cable  96  when the upper coupling pin  41  is moved upward (both the upper and lower coupling pins  41  and  42  are inserted) as shown in  FIG. 9  and  FIGS. 11(A)  and (B), and the inner cable  96  is pushed (released from a tension) and the restricting member  71  of the pivot pin retraction restricting means  7  is moved to the restricting position indicated by dotted lines in  FIG. 6  (reference numeral  71 ′) by the urging force of the spring  75  when the upper coupling pin  41  is moved downward (the upper and lower coupling pins  41  and  42  are retracted) as shown in  FIG. 11(C) . 
     In the jib stowing device according to this embodiment, each of the above means ( 5 ,  6 ,  7 ,  8 ,  91  and  94 ) functions as described below during the operations to extend and stow the jib  2 . Each change in operation during the operations to extend and stow the jib  2  and the functions during these operations are described in conjunction with  FIGS. 11(A) , (B) and (C). 
     [Jib Extending Operation] 
     When the jib  2  is extended from the stowed state shown in  FIG. 1 , the second stowing means B is first uncoupled and then the jib  2  is swung about the coupling pin  40  of the first stowing means A to align the upper and lower bosses  24   a  and  24   b  on a first side portion of the jib proximal portion (jib support)  23  with the upper and lower bosses  14   a  and  14   b  on a first side portion of the top boom distal portion  13  as shown in  FIG. 2 . in this state, the upper and lower coupling pins  41  and  42  are in the inserted state and the restricting member  71  of the pivot pin retraction restricting means  7  is located in the non-restricting position via the coupling pin insertion state detecting means  6  and the second associating means (control cable)  94  as shown in  FIG. 11(A) . In addition, the upper and lower pivot pins  31  and  32  are located adjacent to each other (retracted) and the restricting member  81  of the coupling pin retraction restricting means  8  is located in the restricting position by the urging force of the spring  85 . Therefore, the coupling pin  40  (the upper and lower coupling pins  41  and  42 ) cannot be retracted (the threaded rod  43  cannot be operated to the coupling pin retracting side). 
     Next, in the state shown in  FIG. 11(A)  and  FIG. 8 , the threaded rod  33  of the pivot pin  30  is rotated to the left to move the upper pivot pin  31  upward and move the lower pivot pin  32  downward to insert the upper and lower pivot pins  31  and  32  into the upper and lower bosses ( 14   a  and  24   a , and  14   b  and  24   b ), respectively, aligned with each other (to establish the state shown in  FIG. 11(B) ). In this state shown in  FIG. 11(B) , the pivot pin insertion state detecting means  5  (the protrusion  51 ) and the first associating means (control cable)  91  function to place the restricting member  81  of the coupling pin retraction restricting means  8  in the non-restricting position (coupling pin retracting operation by the threaded rod  43  can be performed) because the upper pivot pin  31  has been moved upward. 
     Next, to rotate the jib  2  away from the base boom  11  from the state shown in  FIG. 2 , the threaded rod  43  of the coupling pin  40  is operated to the coupling pin retracting side to retract the upper and lower coupling pins  41  and  42  as shown in FIG.  11 (C). The coupling pin retracting operation by the threaded rod  43  can be performed only when the upper and lower pivot pins  31  and  32  of the pivot pin  30  are in the inserted state as shown in  FIG. 11(B) . That is, even if the threaded rod  43  of the coupling pin  40  is operated by mistake to the coupling pin retracting side when the pivot pin  30  is in the retracted state as shown in  FIG. 11(A) , the operation is not effective. This securely prevents a situation in which both the pivot pin  30  and the coupling pin  40  are retracted during a coupling pin retracting operation. 
     When the upper and lower coupling pins  41  and  42  of the coupling pin  40  are brought into the retracted state as shown in  FIG. 11(C) , the restriction releasing effect of the coupling pin insertion state detecting means  6  and the second associating means (control cable)  94  on the restricting member  71  of the pivot pin retraction restricting means  7  is released and the restricting member  71  is moved to the restricting position by the urging force of the spring  75  ( FIG. 6 ). 
     After the jib  2  has been rotated to the front of the top boom distal portion  13 , the jib extending operation is completed when the bosses (provided at two vertically separated locations) on a second side portion of the jib support  23  and the bosses (provided at two vertically separated locations) on a second side portion of the top boom distal portion  13  are aligned with each other and another coupling pin is inserted into the bosses aligned with each other. 
     [Jib Stowing Operation] 
     To stow the jib  2  from the extend state, the jib  2  is rotated to a position along the base boom  11  shown in  FIG. 2  with the jib proximal portion (jib support)  23  and the top boom distal portion  13  coupled to each other only by the pivot pin  30  to align the upper and lower bosses  27   a  and  27   b  on the base jib  21  with the upper and lower bosses  17   a  and  17   b  on the base boom  11 . At this time, the protrusion  63  of the L-shaped lever  61  as the coupling pin insertion state detecting means  6  on the jib side is engaged with the push plate  64  on the upper coupling pin  41 . Then, the upper and lower coupling pins  41  and  42  of the first stowing means A are inserted into the upper and lower bosses ( 17   a  and  27   a , and  17   b  and  27   b ) on the base jib  21  and the base boom  11  aligned with each other (to establish the state shown in  FIG. 11(B) ). In the state shown in  FIG. 11(B) , the restricting member  71  of the pivot pin retraction restricting means  7  and the restricting member  81  of the coupling pin retraction restricting means  8  are both in the non-restricting position, so that the threaded rods  33  and  43  can performs a pin retracting operation. 
     Next, the threaded rod  33  of the pivot pin  30  is operated from the state shown in  FIG. 2  and  FIG. 11(B)  to the pivot pin retracting side to retract the upper and lower pivot pins  31  and  32  as shown in  FIG. 11(A) . The pivot pin retracting operation by the threaded rod  33  can be performed only when the upper and lower coupling pins  41  and  42  of the coupling pin  40  are in the inserted state as shown in  FIG. 11(B) . That is, even if the threaded rod  33  of the pivot pin  30  is operated to the pivot pin retracting side by mistake when the coupling pin  40  is in the retracted state as shown in  FIG. 11(C) , the operation is not effective because the restricting member  71  of the pivot pin retraction restricting means  7  is in the restricting position. This securely prevents a situation in which both the pivot pin  30  and the coupling pin  40  are retracted during a pivot pin retracting operation. 
     When the upper and lower pivot pins  31  and  32  of the pivot pin  30  are brought into the retract state as shown in  FIG. 11(A) , the restriction releasing effect of the pivot pin insertion state detecting means  5  and the first associating means (control cable)  91  on the restricting member  81  of the coupling pin retraction restricting means  8  is released and the restricting member  81  is moved to the restricting position by the urging force of the spring  85  ( FIG. 10 ). 
     Then, the jib stowing operation is completed when the distal portion of the jib is moved from the state shown in  FIG. 2  and  FIG. 11(A)  about the coupling pin  40  toward a lateral side of the base boom  11  and the distal portion of the jib is coupled to the base boom  11  by the second stowing means B as shown in  FIG. 1 . 
     As described foregoing, in the jib stowing device for a jib crane vehicle according to this embodiment, both when the jib  2  is extended from the stowed state and when the jib  2  is stowed from the extended state, even if either the pivot pin  30  or the coupling pin  40  undergoes a retracting operation by mistake, the operated pin is not retracted (pulled out) if the other of the pivot pin  30  or the coupling pin  40  is in the retracted state (uncoupled state). Thus, a trouble of both the pivot pin  30  and the coupling pin  40  being pulled out by an erroneous operation can be prevented from occurring both during a jib stowing operation and during a jib extending operation. Therefore, safety can be secured both when the jib  2  is stowed and when the jib  2  is extended (the possibility of the jib falling off is eliminated). 
     Also, the pivot pin insertion state detecting means  5 , the coupling pin insertion state detecting means  6 , the pivot pin retraction restricting means  7 , the coupling pin retraction restricting means  8 , the first associating means  91 , and the second associating means  94  are collectively provided on the jib. Therefore, each of the means ( 5 ,  6 ,  7 ,  8 ,  91  and  94 ) does not interfere with the extension and contraction of the boom even when a crane operation (extension and contraction of the boom) is performed only with the telescopic boom  1  in the jib stowage state (state in which the jib  2  is separate from the top boom  12 ). 
     In addition, because each of the above means ( 5 ,  6 ,  7 ,  8 ,  91  and  94 ) is mechanically installed, there is no need to provide a connector for power source connection (requiring connecting and disconnecting operations) between the telescopic boom  1  and the jib  2  or to provide a control controller, and the safety during stowage and extension of the jib can be secured with a simple configuration in contrast to means which operates on electricity or hydraulic pressure. 
     Further, in the illustrated embodiment, the coupling pin insertion state detecting means  6  (the L-shaped lever  61 ) is configured to be removably engageable with the upper coupling pin  41  (the protrusion  63 ). Thus, even when the coupling pin  40  is provided on the base boom  11  and the coupling pin insertion state detecting means  6  is provided on the base jib  21 , the L-shaped lever  61  is engageable with the protrusion  63  when the jib  2  is placed along one side of the base boom  11  so that the insertion state of the coupling pin (the upper coupling pin  41 ) can be detected by the coupling pin insertion state detecting means  6 . Therefore, even when the coupling pin  40  must be provided on the base boom  11  as in the case where the upper and lower coupling pins  41  and  42  are inserted and retracted with a hydraulic cylinder, the insertion state of the coupling pin  40  can be detected on the jib side. 
     While a control cable is used as the first associating means  91  and the second associating means  94  in the above embodiment, a link mechanism may be used as the first associating means  91  and the second associating means  94  instead of the control cable in another embodiment. 
     BRIEF DESCRIPTION OF DRAWINGS 
       FIG. 1  is a plan view illustrating a jib stowage state of a jib crane vehicle employing a jib stowing device according to an embodiment of the present invention. 
       FIG. 2  is a view illustrating a state changed from the state shown in  FIG. 1 . 
       FIG. 3  is an enlarged view of a part of  FIG. 2 . 
       FIG. 4  is a view taken along the line IV-IV of  FIG. 3  and viewed in the direction of appended arrows. 
       FIG. 5  is a cross-sectional view taken along the line V-V of  FIG. 4 . 
       FIG. 6  is a cross-sectional view taken along the line VI-VI of  FIG. 4 . 
       FIG. 7  is a view illustrating a state changed from the state shown in  FIG. 5  (view for explaining a retraction disabled state of upper and lower pivot pins). 
       FIG. 8  is a view illustrating a state changed from the state shown in  FIG. 5  (view explaining a retracted state of the upper and lower pivot pins). 
       FIG. 9  is a cross-sectional view taken along the line IX-IX of  FIG. 4 . 
       FIG. 10  is a cross-sectional view taken along the line X-X of  FIG. 4 . 
       FIG. 11  is a view explaining the function of the jib stowing device according to the embodiment of the present invention. 
       FIG. 12  is a partial plan view illustrating a jib stowage state of a jib crane vehicle according to a related art. 
       FIG. 13  is a cross-sectional view taken along the line XIII-XIII of  FIG. 12 . 
       FIG. 14  is a cross-sectional view taken along the line XIV-XIV of  FIG. 13 . 
       FIG. 15  is a view for explaining the function of a jib stowing device according to the related art. 
     DESCRIPTION OF REFERENCE NUMERALS 
     
         
           1 : telescopic boom 
           2 : jib 
           5 : pivot pin insertion state detecting means 
           6 : coupling pin insertion state detecting means 
           7 : pivot pin retraction restricting means 
           8 : coupling pin retraction restricting means 
           11 : base boom 
           12 : top boom 
           13 : top boom distal portion 
           14   a ,  14   b : boss on top boom distal portion 
           17   a ,  17   b : boss on base boom at first stowing means 
           21 : base jib 
           23 : jib proximal portion (jib support) 
           24   a ,  24   b : boss on jib proximal portion 
           27   a ,  27   b : boss on jib at first stowing means 
           30 : pivot pin 
           31 : upper pivot pin 
           32 : lower pivot pin 
           33 : threaded rod 
           40 : coupling pin 
           41 : upper coupling pin 
           42 : lower coupling pin 
           43 : threaded rod 
           51 : protrusion 
           61 : L-shaped lever 
           71 : restricting member of pivot pin retraction restricting means 
           81 : restricting member of coupling pin retraction restricting means 
           91 : first associating means (control cable) 
           94 : second associating means (control cable) 
         A: first stowing means 
         B: second stowing means