Patent Publication Number: US-2022227608-A1

Title: Expansion device and crane

Description:
TECHNICAL FIELD 
     The present invention relates to an expansion device that expands and contracts an expandable boom of a mobile crane, and a crane on which the expansion device is mounted. 
     BACKGROUND ART 
     As an expansion device of an expandable boom of a mobile crane, an expansion device in which a boom element constituting an expandable boom expands and contracts stage by stage by a single expandable cylinder (hydraulic cylinder) built in the expandable boom has been put into practical use (hereinafter, referred to as a “single-cylinder expansion device”). Since the single-cylinder expansion device has a single expandable cylinder, a weight of the entire expansion device can be reduced, and lifting performance of the mobile crane can be improved (see, for example, Patent Literature 1). 
     A characteristic configuration of the single-cylinder expansion device includes boom connecting means, connecting pin driving means, and cylinder-boom connecting means to be described below. 
     The boom connecting means is provided on an inner boom element of a pair of adjacent boom elements. The boom connecting means has a connecting pin (hereinafter, referred to as a “B pin”) for connecting (fixing) the inner boom element and an outer boom element. The boom connecting means connects the inner boom element and the outer boom element adjacent to each other (hereinafter, referred to as “adjacent boom elements”) by inserting the B pin into a fixing hole provided at an appropriate position of the outer boom element. On the other hand, the boom connecting means releases the connection between the adjacent boom elements by removing the B pin from the fixing hole. The boom connecting means maintains an expanded state of the expandable boom expanded by the single-cylinder expansion device. Such a boom connecting means is indispensable means for the single-cylinder expansion device. 
     The connecting pin driving means (hereinafter, referred to as “B-pin driving means”) is disposed in a movable part of the expandable cylinder. The B-pin driving means moves the B pin provided on the inner boom element in target adjacent boom elements (adjacent boom elements including a boom element to be expanded and contracted). The B-pin driving means shifts states of the adjacent boom elements from the connected state to the released state (also referred to as a disconnected state) or from the released state to the connected state. Similarly to the boom connecting means, the B-pin driving means is indispensable means for the single-cylinder expansion device. The B-pin driving means includes a B-pin cylinder for moving the B pin. The B-pin cylinder is disposed in a narrow space of the movable part of the expandable cylinder. Since such a B-pin cylinder requires a relatively large output, the B-pin cylinder is constituted by a hydraulic cylinder. 
     The cylinder-boom connecting means is disposed in the movable part of the expandable cylinder. The cylinder-boom connecting means includes a connecting pin (hereinafter, referred to as a “C pin”) for connecting the movable part of the expandable cylinder and a target boom element (boom element to be expanded and contracted). The cylinder-boom connecting means selectively connects the movable part of the expandable cylinder and the boom element by inserting the C pin into the connecting hole of the boom element to be expanded and contracted. The cylinder-boom connecting means releases the connection between the movable part of the expandable cylinder and the boom element by removing the C pin from the connecting hole of the boom element to be expanded and contracted. The cylinder-boom connecting means is indispensable means for the single-cylinder expansion device that expands and contracts all the boom elements by the single expandable cylinder. The cylinder-boom connecting means includes C-pin driving means such as a C-pin cylinder for moving the C pin. The C-pin cylinder is disposed in a narrow space of the movable part of the expandable cylinder. Since such a C-pin cylinder requires a relatively large output, the C-pin cylinder is constituted by a hydraulic cylinder. 
       FIG. 10  is an example of a hydraulic circuit of a hydraulic supply unit  3  of the related art for supplying a working fluid to a B-pin cylinder  1  and a C-pin cylinder used in a single-cylinder expansion device. The B-pin cylinder  1  drives a B pin  4 . Such a B-pin cylinder  1  is a single-acting hydraulic cylinder. The B-pin cylinder  1  has a compression coil spring  5  that is returned into the cylinder. A working fluid is supplied to the B-pin cylinder  1  via one hydraulic pipeline  6 . The C-pin cylinder  2  drives a C pin  7 . Such a C-pin cylinder  2  is a single-acting cylinder. The C-pin cylinder  2  is returned to a contraction side by an extension coil spring  8  that biases a C-pin driving lever  21 . A working fluid is supplied to the C-pin cylinder  2  via one hydraulic pipeline  9 . 
     A working fluid is supplied to a movable part  11  of an expandable cylinder from a fixed part side  10  of the expandable cylinder via a hydraulic hose  13 . One end of the expandable cylinder is supported on the fixed part side  10  of the expandable cylinder. The hydraulic hose  13  is one long hose delivered from a hose reel  12 . In an expansion and contraction step of the single-cylinder expansion device, the B-pin cylinder  1  and the C-pin cylinder  2  are driven in a predetermined order. Thus, a first electromagnetic switching valve  14  is disposed on the fixed part side  10  of the expandable cylinder. A second electromagnetic switching valve  15  and a third electromagnetic switching valve  16  are arranged in the movable part  11  of the expandable cylinder. A controller  18  disposed on a slewing frame (the fixed part side  10  of the expandable cylinder) sends a control signal to the second electromagnetic switching valve  15  and the third electromagnetic switching valve  16  via a cable reel  17  and a control signal line  19 . 
     CITATION LIST 
     Patent Literature 
     
         
         Patent Literature 1: JP 2002-332194 A 
       
    
     SUMMARY OF THE INVENTION 
     Problems to be Solved by the Invention 
     However, in the case of the expansion device for the expandable boom as described above, when a viscosity of the working fluid increases at a low temperature, since a pressure loss in the hydraulic hose  13  increases, operations of the B-pin cylinder  1  and the C-pin cylinder  2  are delayed. Thus, there is a possibility that the operations of the B-pin driving means and the cylinder-boom connecting means are delayed and thus, the single-cylinder expansion device is not normally operated. In order to avoid the operation delay at the low temperature, it is necessary to increase a size of the hydraulic hose  13  to suppress the pressure loss in the hydraulic hose  13 . However, when the size of the hydraulic hose  13  is increased, the hose reel  12  becomes large. When the hose reel  12  becomes large, there is a possibility that it is difficult to secure a space for mounting the hose reel  12  on a crane vehicle. 
     On the other hand, there is also a method for incorporating the expandable cylinder in an oil feed pipe and supplying the working fluid from the fixed part side  10  of the expandable cylinder to the movable part  11  of the expandable cylinder via the oil feed pipe. However, the expandable cylinder with the built-in oil feed pipe has a complicated internal structure and is difficult to be manufactured. The expandable cylinder with the built-in oil feed pipe cannot solve the problem of securing operability at the low temperature. A technique of acquiring the working fluid pressurized based on an operation of the expandable cylinder from the expandable cylinder and accumulating the working fluid in a hydraulic accumulator has been known. However, in the case of such a technique, when the pressurized working fluid is accumulated in the hydraulic accumulator, the hydraulic accumulator is affected by an operation cycle of the expandable cylinder. An object of the present invention is to provide an expansion device that is not affected by an operation cycle of an expandable cylinder. 
     Solutions to Problems 
     An aspect of an expansion device according to the present invention is an expansion device that expands and contracts an expandable boom having a first boom element and a second boom element which expandably overlap each other. The device includes a first hydraulic source that discharges a first working fluid, an expandable cylinder that has a fixed part and a movable part movable with respect to the fixed part, is operated based on supply of the first working fluid, and moves the first boom element with respect to the second boom element in a stretching direction, a second hydraulic source that is provided in the movable part, discharges a second working fluid, and is a hydraulic source different from the first hydraulic source, a first connecting mechanism that is provided in the movable part, is operated based on supply of the second working fluid, and switches between a connected state and a disconnected state between the first boom element and the movable part, and a second connecting mechanism that is provided in the movable part, is operated based on the supply of the second working fluid, and switches between a connected state and a disconnected state between the first boom element and the second boom element. 
     Another aspect of a crane according to the present invention includes an expandable boom having a first boom element and a second boom element which expandably overlap each other, and the above-described expansion device. 
     Effects of the Invention 
     According to the present invention, it is possible to provide an expansion device that is not affected by an operation cycle of an expandable cylinder. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a hydraulic circuit diagram of a hydraulic supply unit in an expansion device according to an embodiment of the present invention. 
         FIG. 2  is a cross-sectional view of a 6-stage expandable boom on which the expansion device is mounted. 
         FIG. 3  is a cross-sectional view taken along a line A-A of  FIG. 2 . 
         FIG. 4  is a diagram taken along an arrow B-B of  FIG. 3 . 
         FIG. 5  is a control block diagram of the expansion device and a hydraulic circuit. 
         FIG. 6  is a display screen by expansion and contraction information display means. 
         FIG. 7  is a diagram taken along an arrow D-D of  FIG. 2 . 
         FIG. 8  is a diagram taken along an arrow C-C of FIG.  3 . 
         FIG. 9  is a diagram illustrating a crane vehicle on which the expansion device is mounted. 
         FIG. 10  is an example of a hydraulic circuit of the related art of a hydraulic supply unit. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. 
     Embodiment 
     An expansion device according to the embodiment of the present invention will be described with reference to  FIG. 1 . 
       FIG. 1  is a diagram illustrating an example of a hydraulic circuit of a hydraulic supply unit  20  included in the expansion device. In the description of the hydraulic supply unit  20  illustrated in  FIG. 1 , the same components as those of the hydraulic supply unit  3  of the related art illustrated in  FIG. 10  will be described by using the same reference signs. 
     &lt;Hydraulic Supply Unit&gt; 
     As illustrated in  FIG. 1 , the hydraulic supply unit  20  includes cylinder-boom connecting means  64  and boom connecting means  70 . The hydraulic supply unit  20  has a hydraulic unit  24 , a first electromagnetic switching valve  14 , a second electromagnetic switching valve  15 , a third electromagnetic switching valve  16 , and the like. 
     &lt;Cylinder-Boom Connecting Means&gt; 
     The cylinder-boom connecting means  64  has a C-pin cylinder  2 . The C-pin cylinder  2  is disposed in a movable part  11  of an expandable cylinder  43  (see  FIG. 2 ). The C-pin cylinder  2  inserts and removes a C pin  7  into and from a connecting hole of a target boom by moving the C pin  7 . The cylinder-boom connecting means  64  corresponds to an example of a first connecting mechanism. The first connecting mechanism is operated based on the supply of a working fluid (also referred to as a second working fluid) discharged from the hydraulic supply unit  20 , and switches between a connected state and a disconnected state between a boom element (for example, a second boom  52  illustrated in  FIG. 2 ) to be moved and the expandable cylinder  43 . 
     Specifically, the C-pin cylinder  2  selectively connects the movable part  11  of the expandable cylinder  43  and the boom by inserting the C pin  7  into the connecting hole of the boom. The C-pin cylinder  2  releases the connection between the movable part  11  and the boom by removing the C pin  7  from the connecting hole of the boom. 
     The C pin  7  is biased toward the connection side by an extension coil spring  8 . The C-pin cylinder  2  and the C pin  7  are connected by a C-pin driving lever  21 . The C-pin cylinder  2  is a single-acting hydraulic cylinder. A hydraulic pressure is supplied to the C-pin cylinder  2  from the hydraulic unit  24  (specifically, a hydraulic accumulator  31 ) to be described later via a hydraulic pipeline  9 , and thus, the C-pin cylinder is expanded. 
     As a result, the C-pin cylinder  2  moves the C pin  7  to the release side. When the supply of the hydraulic pressure to the hydraulic pipeline  9  is blocked, the C-pin cylinder  2  is contracted by a biasing force of the extension coil spring  8 . As a result, the C pin  7  moves to the connection side by the biasing force of the extension coil spring  8 . 
     &lt;Boom Connecting Means&gt; 
     The boom connecting means  70  has a B-pin cylinder  1 . The B-pin cylinder  1  is disposed in the movable part  11  of the expandable cylinder  43 . The B-pin cylinder  1  connects  12 ) a pair of adjacent booms by moving a B pin  4  of a target boom. The boom connecting means  70  corresponds to an example of a second connecting mechanism. The second connecting mechanism is operated based on the supply of a working fluid (also referred to as a second working fluid) discharged from the hydraulic supply unit  20 , and switches between a connected state and a disconnected state between a first boom element (for example, the second boom  52  illustrated in  FIG. 2 ) and a second boom element (for example, a base boom  51 ). 
     The B-pin cylinder  1  is biased toward the contraction side by a compression coil spring  5  built in the B-pin cylinder  1 . The B-pin cylinder  1  is a single-acting hydraulic cylinder. The B pin  4  is biased toward the fixation side by a compression coil spring  22 . 
     The B-pin cylinder  1  and the B pin  4  are connected by a B-pin driving lever  74 . When the movable part  11  of the expandable cylinder  43  moves alone, the connection between the B-pin driving lever  74  and the B pin  4  can be released. A hydraulic pressure is supplied to the B-pin cylinder  1  from the hydraulic unit  24  (specifically, the hydraulic accumulator  31 ) to be described later via one hydraulic pipeline  6 , and thus, the B-pin cylinder is expanded. 
     The expanded B-pin cylinder  1  moves the B pin  4  to the release side. When the supply of the hydraulic pressure to the hydraulic pipeline  6  is blocked, the B-pin cylinder  1  is contracted by a biasing force of the compression coil spring  5 . As a result, the B pin  4  is driven toward the fixation side by a biasing force of the compression coil spring  22 . 
     &lt;Hydraulic Unit&gt; 
     As illustrated in  FIG. 1 , the hydraulic unit  24  is mounted on the movable part  11  of the expandable cylinder  43 . The hydraulic unit  24  has an electric motor  25 , a hydraulic pump  26 , a tank  27 , a hydraulic accumulator  31 , a hydraulic sensor  34 , and the like. 
     The hydraulic unit  24  has a discharge pipeline  30  and a return pipeline  32 . In such a hydraulic unit  24 , as an example, the elements constituting the hydraulic unit  24  are arranged in a housing (not illustrated) and are unitized. 
     The elements constituting the hydraulic unit  24  enter a state in which the working fluid can flow or are electrically connected to each other. The hydraulic unit  24  corresponds to an example of a second hydraulic source. The working fluid discharged from the hydraulic unit  24  corresponds to an example of the second working fluid. 
     The electric motor  25  drives the hydraulic pump  26  under the control of a control unit (specifically, a controller  35 ). When the hydraulic pump is driven by the electric motor  25 , the hydraulic pump  26  sucks up the working fluid stored in the tank  27  from a suction port. The hydraulic pump  26  discharges the sucked working fluid from the discharge port. The working fluid discharged from the discharge port of the hydraulic pump  26  flows into the discharge pipeline  30  via a check valve  28  and a high-pressure filter  29 . A pipe connecting the hydraulic pump  26  and the tank  27  corresponds to an example of a first pipe. 
     A relief valve  33  is provided between the discharge pipeline  30  and the return pipeline  32 . The relief valve  33  decides a maximum pressure of the discharge pipeline  30 . That is, when a pressure in the discharge pipeline  30  becomes larger than a predetermined threshold value, the relief valve  33  causes the discharge pipeline  30  and the return pipeline  32  to be fluidly communicatively connected with each other, and causes the working fluid in the discharge pipeline  30  to flow to the return pipeline  32 . 
     The hydraulic accumulator  31  is connected to the discharge pipeline  30 . The hydraulic accumulator  31  absorbs the working fluid in the discharge pipeline  30  and accumulates the pressure. A pipe connecting the hydraulic accumulator  31  and the hydraulic pump  26  corresponds to an example of a second pipe. The second pipe may include the valve (for example, the check valve  28 ) and the filter (For example, the high-pressure filter  29 ). 
     The hydraulic sensor  34  is connected to the discharge pipeline  30 . The hydraulic sensor  34  measures the pressure of the discharge pipeline  30 . 
     As illustrated in  FIG. 1 , the first electromagnetic switching valve  14 , the second electromagnetic switching valve  15 , and the third electromagnetic switching valve  16  are arranged in the movable part  11  of the expandable cylinder  43 . The first electromagnetic switching valve  14 , the second electromagnetic switching valve  15 , and the third electromagnetic switching valve  16  are connected in series. 
     The first electromagnetic switching valve  14 , the second electromagnetic switching valve  15 , and the third electromagnetic switching valve  16  constitute a switching valve unit. The switching valve unit switches between a state in which the working fluid is supplied from the hydraulic unit  24  to the B-pin cylinder  1  or the C-pin cylinder  2  and a state in which the working fluid in the B-pin cylinder  1  or the working fluid in the C-pin cylinder  2  is returned to the tank  27  according to the states of the first electromagnetic switching valve  14 , the second electromagnetic switching valve  15 , and the third electromagnetic switching valve  16 . The switching valve unit corresponds to an example of a switching valve. 
     A state in which the working fluid is supplied from the hydraulic unit  24  to the B-pin cylinder  1  is referred to as a first supply state of the hydraulic supply unit  20  (hereinafter, may be simply referred to as a first supply state). A state in which the working fluid is supplied from the hydraulic unit  24  to the C-pin cylinder  2  is referred to as a second supply state of the hydraulic supply unit  20  (hereinafter, may be simply referred to as a second supply state). A state in which the working fluid in the B-pin cylinder  1  is returned to the tank  27  is referred to as a first discharge state of the hydraulic supply unit  20  (hereinafter, may be simply referred to as a first discharge state). A state in which the working fluid in the C-pin cylinder  2  is returned to the tank  27  is referred to as a second discharge state of the hydraulic supply unit  20  (hereinafter, may be simply referred to as a second discharge state). 
     The first electromagnetic switching valve  14  is a 3-port 2-position switching valve. The discharge pipeline  30 , the return pipeline  32 , and the first connection pipeline connecting the first electromagnetic switching valve  14  and the second electromagnetic switching valve  15  are connected to the first electromagnetic switching valve  14 . 
     Specifically, an end of the discharge pipeline  30  is connected to a first port of the first electromagnetic switching valve  14 . An end of the return pipeline  32  is connected to a second port of the first electromagnetic switching valve  14 . An end of the first connection pipeline is connected to a third port of the first electromagnetic switching valve  14 . 
     The first electromagnetic switching valve  14  communicatively connects the second port and the third port in a first state (unenergized state). In the first state of the first electromagnetic switching valve  14 , the working fluid flowing into the first electromagnetic switching valve  14  from the second electromagnetic switching valve  15  is returned to the tank  27 . 
     The first electromagnetic switching valve  14  communicatively connects the first port and the third port in a second state (energized state). In the second state of the first electromagnetic switching valve  14 , the working fluid flowing from the hydraulic unit  24  into the first electromagnetic switching valve  14  is supplied to the second electromagnetic switching valve  15 . 
     The second electromagnetic switching valve  15  is a two-port two-position switching valve. The second electromagnetic switching valve  15  is provided between the first electromagnetic switching valve  14  and the third electromagnetic switching valve  16 . Specifically, the end of the first connection pipeline is connected to a first port of the second electromagnetic switching valve  15 . 
     An end of a second connection pipeline connecting the second electromagnetic switching valve  15  and the third electromagnetic switching valve  16  is connected to a second port of the second electromagnetic switching valve  15 . 
     The second electromagnetic switching valve  15  communicatively connects the first port and the second port in a first state (unenergized state). In the first state of the second electromagnetic switching valve  15 , the working fluid flows between the first connection pipeline and the second connection pipeline. 
     The second electromagnetic switching valve  15  blocks the first port and the second port in a second state (energized state). In the second state of the second electromagnetic switching valve  15 , the flow of the working fluid is blocked between the first connection pipeline and the second connection pipeline. 
     The third electromagnetic switching valve  16  is a 3-port 2-position switching valve. The third electromagnetic switching valve  16  is provided between the B-pin cylinder  1  and the C-pin cylinder  2  and the second electromagnetic switching valve  15 . 
     Specifically, the end of the second connection pipeline is connected to a first port of the third electromagnetic switching valve  16 . 
     An end of a third connection pipeline connecting the third electromagnetic switching valve  16  and the B-pin cylinder  1  is connected to a second port of the third electromagnetic switching valve  16 . An end of a fourth connection pipeline connecting the third electromagnetic switching valve  16  and the C-pin cylinder  2  is connected to a third port of the third electromagnetic switching valve  16 . 
     The third electromagnetic switching valve  16  communicatively connects the first port and the third port in a first state (unenergized state). In the first state of the third electromagnetic switching valve  16 , the working fluid flowing from the second electromagnetic switching valve  15  into the third electromagnetic switching valve  14  is supplied to the C-pin cylinder  2 . 
     The third electromagnetic switching valve  16  communicatively connects the first port and the second port in a second state (energized state). That is, in the second state of the third electromagnetic switching valve  16 , the working fluid flowing from the second electromagnetic switching valve  15  into the third electromagnetic switching valve  14  is supplied to the B-pin cylinder  1 . 
     Hereinafter, a relationship between the states of the first electromagnetic switching valve  14 , the second electromagnetic switching valve  15 , and the third electromagnetic switching valve  16 , the first supply state, the second supply state, the first discharge state, and the second discharge state will be described. 
     In the first supply state, the first electromagnetic switching valve  14  is in the second state (energized state), the second electromagnetic switching valve  15  is in the first state (unenergized state), and the third electromagnetic switching valve  16  is in the second state (energized state). 
     In the second supply state, the first electromagnetic switching valve  14  is in the second state (energized state), the second electromagnetic switching valve  15  is in the first state (unenergized state), and the third electromagnetic switching valve  16  is in the first state (unenergized state). 
     In the first discharge state, the first electromagnetic switching valve  14  is in the first state (unenergized state), the second electromagnetic switching valve  15  is in the first state (unenergized state), and the third electromagnetic switching valve  16  is in the second state (energized state). 
     In the second discharge state, the first electromagnetic switching valve  14  is in the first state (unenergized state), the second electromagnetic switching valve  15  is in the first state (unenergized state), and the third electromagnetic switching valve  16  is in the first state (unenergized state). 
     The controller  35  is disposed at a slewing platform of a crane vehicle (a fixed part side of the expandable cylinder  43 ). The electric motor  25  is connected to the controller  35  via a cable reel  37  and a power line  38  wound around the cable reel  37 . The power line  38  corresponds to an example of a cable. The power line  38  is delivered from the cable reel  37  as a cylinder tube  44  (movable part, see  FIG. 2 ) of the expandable cylinder  43  moves. 
     The hydraulic sensor  34 , the first electromagnetic switching valve  14 , the second electromagnetic switching valve  15 , and the third electromagnetic switching valve  16  are connected to the controller  35  via the cable reel  37  and control signal lines  39 ,  40 ,  41 , and  42 . 
     A function of the hydraulic unit  24  of the hydraulic supply unit  20  (see  FIG. 1 ) is as follows. The hydraulic pump  26  is rotated by the electric motor  25 . The hydraulic pump  26  sucks the working fluid from the tank  27 . The hydraulic pump  26  discharges the working fluid to the discharge pipeline  30  via the check valve  28  and the high-pressure filter  29 . The working fluid in the discharge pipeline  30  is absorbed and accumulated in the hydraulic accumulator  31 . 
     When the pressure of the discharge pipeline  30  becomes higher than a set pressure (also referred to as a first predetermined pressure), the relief valve  33  releases the working fluid in the discharge pipeline  30  to the return pipeline  32  by opening an internal passage. That is, the relief valve  33  enters an opened valve state when the pressure of the discharge pipeline  30  is higher than the first predetermined pressure. The relief valve  33  enters a closed valve state when the pressure of the discharge pipeline  30  is equal to or lower than the first predetermined pressure. 
     The hydraulic sensor  34  constantly measures the pressure of the discharge pipeline  30 . The hydraulic sensor  34  transmits a detection signal to the controller  35 . The discharge pipeline  30  corresponds to an example of a pipeline to which an accumulator is connected. 
     When the pressure of the discharge pipeline  30  rises to an upper limit set pressure of the relief valve  33 , the controller  35  stops the power transmission to the electric motor  25 . The electric motor  25  stops rotating. As a result, the pressure rise in the discharge pipeline  30  and the hydraulic accumulator  31  is stopped. 
     The working fluids in the discharge pipeline  30  and the hydraulic accumulator  31  are confined by the first electromagnetic switching valve  14  and the check valve  28 , and thus, the pressures are maintained. 
     When the working fluid accumulated in the hydraulic accumulator  31  is consumed by the operations of the B-pin cylinder  1  and the C-pin cylinder  2 , the pressure of the discharge pipeline  30  drops. When the pressure of the discharge pipeline  30  becomes lower than a lower limit set pressure (also referred to as a second predetermined pressure), the controller  35  supplies power to the electric motor  25 . The hydraulic pump  26  is rotated by the electric motor  25 . As a result, the working fluid discharged from the hydraulic pump  26  flows into the discharge pipeline  30 , and the pressure in the discharge pipeline  30  increases. 
     As stated above, the hydraulic pump  26  is intermittently rotated by the hydraulic sensor  34  and the controller  35  that monitor the pressure of the discharge pipeline  30 . Accordingly, the pressures of the working fluids in the discharge pipeline  30  and the hydraulic accumulator  31  are constantly maintained at a pressure equal to or higher than the lower limit set pressure (second predetermined pressure) and equal to or lower than the upper limit set pressure (first predetermined pressure). 
     As described above, the hydraulic unit  24  can constantly supply the hydraulic pressure for driving the B-pin cylinder  1  and the C-pin cylinder  2 . As the lower limit set pressure and the upper limit set pressure, pressures necessary and sufficient for driving the B-pin cylinder  1  and the C-pin cylinder  2  are selected. 
     The hydraulic supply unit  20  according to the present invention has the hydraulic unit  24  in the movable part  11  of the expandable cylinder  43 . Since the hydraulic unit  24  supplies the hydraulic pressure to the B-pin cylinder  1  and the C-pin cylinder  2 , there is no long hydraulic pipeline such as a hose reel or an oil feed pipe in the expandable cylinder. Thus, the operability of the B-pin cylinder  1  and the C-pin cylinder  2  at a low temperature is improved. 
     Since a large and heavy hose reel is not required, the mountability of the crane vehicle is improved. There is no need for the expandable cylinder that is complicated and difficult to be manufactured, such as the expandable cylinder with the built-in oil feed pipe. 
     The pressure accumulation in the hydraulic accumulator  31  in the hydraulic unit  24  is independent of an expansion and contraction step of the single-cylinder expansion device. Thus, the control (operation step) of the single-cylinder expansion device is independent of the control of the pressure accumulation of the hydraulic accumulator  31 . That is, a degree of freedom of the control of the single-cylinder expansion device is high. 
     A hydraulic circuit (also referred to as a first hydraulic circuit, see  FIG. 1 ) of the hydraulic supply unit  20  is a circuit independent of a hydraulic circuit (also referred to as a second hydraulic circuit) of the entire crane vehicle. The second hydraulic circuit may be regarded as a hydraulic circuit including an expandable cylinder hydraulic supply unit  105  (see  FIG. 5 ). The first hydraulic circuit and the second hydraulic circuit are provided as independent hydraulic circuits. That is, the first hydraulic circuit and the second hydraulic circuit are not connected by a pipe or the like. 
     Thus, there is a low possibility that contaminants intrude into the hydraulic circuit of the hydraulic supply unit  20  from the outside. Since the hydraulic circuit of the hydraulic supply unit  20  is independent of the hydraulic circuit of the entire crane vehicle, a dedicated oil type can be used as the working fluid of the hydraulic supply unit  20 . In other words, a type of an oil to be used in the hydraulic supply unit  20  may be an oil different from a type of an oil used in the hydraulic circuit of the entire crane vehicle. 
     Since the entire hydraulic supply unit  20  is collectively mounted on the movable part  11  of the expandable cylinder  43 , it is possible to modularize the entire hydraulic supply unit  20 . 
     The B-pin cylinder  1  and the C-pin cylinder  2  are operated intermittently during an expansion and contraction operation of the single-cylinder expansion device. Since a size of the B-pin cylinder  1  and a size of the C-pin cylinder  2  are small, a small amount of oil supplied by the hydraulic supply unit  20  is sufficient. Accordingly, the electric motor  25 , the hydraulic pump  26 , the hydraulic accumulator  31 , and the like constituting the hydraulic unit  24  can be downsized. 
     In preparation for a failure, a plurality of electric motors  25  and a plurality of hydraulic pumps  26  may be provided in the hydraulic unit  24 . In preparation for disconnection of a power supply line, a plurality of power supply lines connecting the controller  35  and the hydraulic supply unit  20  may be provided. A battery that supplies electricity to the electric motor  25  may be provided in the movable part  11  of the expandable cylinder  43 . The number of batteries may be singular or plural. 
     In the present embodiment, an example in which the controller  35  that controls the entire single-cylinder expansion device controls the electric motor  25  of the hydraulic unit  24  has been described. That is, in the present embodiment, a control unit that controls the single-cylinder expansion device and the control unit that controls the electric motor  25  of the hydraulic unit  24  are common control units. 
     As an example, a controller dedicated to the electric motor  25  may be disposed inside the hydraulic unit  24 . In other words, the control unit that controls the electric motor  25  may be provided separately from the control unit that controls the single-cylinder expansion device. The control unit of the electric motor  25  may be unitized together with the hydraulic unit  24 . 
     An overall configuration of the expansion device according to the present embodiment will be described with reference to  FIG. 2 .  FIG. 2  is a cross-sectional view illustrating an overall configuration of the expansion device according to the present embodiment. In  FIG. 2 , a base end of the expansion device mounted on a 6-stage expandable boom  50  in a fully contracted state is illustrated in a cross section along a longitudinal direction of the expandable cylinder  43 . The expansion device according to the present embodiment does not need to include all the elements illustrated in  FIG. 2 . 
     As illustrated in  FIG. 2 , the expandable boom  50  has intermediate booms  52  to  55  (the second boom  52 , a third boom  53 , a fourth boom  54 , and a fifth boom  55  in order from the outside) and a top boom  56  that are expandably combined in the base boom  51 . The top boom  56  is disposed on the innermost side in an internal space of the base boom  51 . Such an expandable boom  50  has a housing space therein. 
     The base boom  51  corresponds to an example of the second boom element. When the base boom  51  corresponds to an example of the second boom element, the intermediate boom (in the present embodiment, the second boom  52 ) disposed adjacent to the inner side of the base boom  51  corresponds to an example of the first boom element. 
     When the second boom  52  corresponds to an example of the second boom element, the third boom  53  corresponds to an example of the first boom element. When the third boom  53  corresponds to an example of the second boom element, the fourth boom  54  corresponds to an example of the first boom element. When the fourth boom  54  corresponds to an example of the second boom element, the fifth boom  55  corresponds to an example of the first boom element. When the fifth boom  55  corresponds to an example of the second boom element, the top boom  56  corresponds to an example of the first boom element. 
     The expandable cylinder  43  is provided in the housing space of the expandable boom  50 . The expandable cylinder  43  has a cylinder tube  44  and a cylinder rod  46 . The cylinder tube  44  corresponds to an example of the movable part (also referred to as a movable side member) of the expandable cylinder. The cylinder rod  46  corresponds to an example of a fixed part (also referred to as a fixation side member) of the expandable cylinder. The cylinder tube  44  may correspond to an example of the fixation side member of the expandable cylinder. In this case, the cylinder rod  46  may correspond to an example of the movable side member of the expandable cylinder. 
     The expandable cylinder  43  expands and contracts under the control of the controller  35 . Specifically, when the working fluid is supplied from a tank T (see  FIG. 5 ) to the inside of the cylinder tube  44 , the cylinder tube  44  moves in a direction (hereinafter, referred to as an expansion direction) in which the entire expandable cylinder  43  expands with respect to the cylinder rod  46  under the control of the controller  35 . In other words, when the working fluid is supplied, the expandable cylinder  43  expands under the control of the controller  35 . 
     On the other hand, when the working fluid inside the cylinder tube  44  is discharged, the cylinder tube  44  moves in a direction in which the entire expandable cylinder  43  contracts (hereinafter, referred to as a contraction direction) with respect to the cylinder rod  46  under the control of the controller  35 . In other words, when the working fluid is discharged, the expandable cylinder  43  contracts under the control of the controller  35 . 
     The hydraulic unit  24  described above is mounted on the cylinder tube  44 . Specifically, the hydraulic unit  24  is fixed to an outer peripheral surface of the cylinder tube  44 . Such a hydraulic unit  24  includes the electric motor  25 , the hydraulic pump  26 , and the like described above. 
     The cable reel  37  is rotatably provided at a base boom base end  51   a . A cable  60  is wound around the cable reel  37 . The cable  60  has the power line  38 , the control signal lines  39 ,  40 ,  41 , and  42  (see  FIG. 1 ), and the like. The cable  60  can be pulled out from the cable reel  37 . 
     The cable  60  is connected to a support  61  of a cylinder tube rod side end  45 . A length detector  62  (see  FIG. 2 ) is provided at the base boom base end  51   a . A cord  63  pulled out from the length detector  62  is connected to the support  61  of the cylinder tube rod side end  45 . 
     Next, the cylinder-boom connecting means  64  in the expansion device will be described with reference to  FIG. 3 .  FIG. 3  is a cross-sectional view taken along a line A-A of  FIG. 2 .  FIG. 3  illustrates a case where the cylinder-boom connecting means  64  is positioned in a connecting hole  56   b  provided in a top boom base end  56   a . Similarly to the top boom base end  56   a , as illustrated in  FIG. 3 , connecting holes are also provided in a second boom base end  52   a , a third boom base end  53   a , a fourth boom base end  54   a , and a fifth boom base end  55   a , respectively. 
     As illustrated in  FIG. 3 , the cylinder-boom connecting means  64  has the C-pin cylinder  2 , the C pin  7 , the C-pin driving lever  21 , and the like. 
     The C-pin cylinder  2  is provided at the cylinder tube rod side end  45 . The C pin  7  is connected to the C-pin cylinder  2  via the C-pin driving lever  21 . The C pin  7  is slidably assembled to a C-pin housing hole  66  of a trunnion member  65  constituting the cylinder tube rod side end  45 . 
     The C pin  7  can be inserted into and removed from connecting holes  52   b  to  56   b  (in  FIG. 3 , the connecting hole  56   b  provided in the top boom base end  56   a ) provided in the boom base ends  52   a  to  56   a.    
     A pair of the C pin  7  and the C-pin driving lever  21  are provided on the left and right of the expandable cylinder  43 . The C-pin driving lever  21  is supported by a pin  67  on an integrally formed support (not illustrated) above the trunnion member  65 . The C-pin driving lever  21  is swingable. 
     One end of the C-pin driving lever  21  is connected to the C pin  7 . The C pin  7  is biased toward the connection side by the extension coil spring  8  via the C-pin driving lever  21 . 
     The boom connecting means  70  in the expansion device will be described with reference to  FIGS. 3 and 4 .  FIG. 3  is a cross-sectional view taken along a line A-A of  FIG. 2 .  FIG. 4  is a diagram taken along an arrow B-B of  FIG. 3 .  FIGS. 3 and 4  illustrate the boom connecting means  70  at a fixing portion between the top boom  56  and the fifth boom  55 . 
     As illustrated in  FIGS. 3 and 4 , the boom connecting means  70  has B-pin driving means  73 , B pins  56   d , the compression coil spring  22 , and the like. 
     The B pin  56   d  is a fixing pin for fixing the top boom  56  and the fifth boom  55 . A pair of B pins  56   d  are provided on the left and right. Similarly, in the second boom base end  52   a , the third boom base end  53   a , the fourth boom base end  54   a , and the fifth boom base end  55   a , a pair of B pins  52   d  of the second boom  52 , a pair of B pins  53   d  of the third boom  53 , a pair of B pins  54   d  of the fourth boom  54 , and a pair of B pins  55   d  of the fifth boom  55  are provided on the left and right, respectively (see  FIG. 2 ). 
     The fifth boom  55  has fixing holes  55   f  through which the B pins  56   d  are inserted on a side surface. A plurality of fixing holes  55   f  is provided along a length direction according to an expansion length of the top boom  56 . The arrangement of the fixing holes is substantially similar in the other booms (the base boom  51 , the second boom  52 , the third boom  53 , and the fourth boom  54 ). 
     In the description of the overall configuration of the expansion device, the B pins corresponding to the booms will be described as the B pins  52   d  to  56   d , but are the same as the B pin  4  described with reference to  FIG. 1 . That is, in  FIG. 1 , only the B pin for one stage of the boom is illustrated for the purpose of describing the outline of the hydraulic supply unit  20 . 
     The B pin  56   d  is slidably assembled to a B-pin housing member  56   e  of the top boom base end  56   a . The B pins  56   d  can be inserted into and removed from the fixing holes  55   f  provided on the side surface of the fifth boom  55 . The B pin  56   d  is biased toward the fixation side by the compression coil spring  22  disposed on an outer peripheral portion of the B pin  56   d.    
     The B pin  56   d  has a connecting member  72  at the inner end. The connecting member  72  has a box shape partially opened. The connecting member  72  can be connected to the B-pin driving lever  74  via a roller  75  of the B-pin driving means  73 . 
     The B-pin driving means  73  has the B-pin cylinder  1 , the B-pin driving lever  74 , and the roller  75 . The B-pin driving lever  74  is swingably supported by the support  76  provided at the cylinder tube rod side end  45  (the movable part  11  of the expandable cylinder  43 ). A pair of B-pin driving levers  74  are provided on the left and right. 
     The roller  75  is rotatably supported at one end of the B-pin driving lever  74 . A rod side end and a cylinder side end of the B-pin cylinder are supported by the other ends of the B-pin driving levers  74 , respectively.  FIG. 4  illustrates a state in which the roller  75  is fitted in the connecting member  72  and the B pin  56   d  of the top boom  56  and the B-pin driving means  73  are connected. 
     The B-pin driving means  73  has an integral structure with the cylinder tube rod side end  45  illustrated in  FIG. 2  as a whole. Thus, the B-pin driving means  73  can drive the selected B pin in a state in which the roller  75  is positioned in the connecting member  72  corresponding to the B pin selected from the B pins  52   d  to  56   d  provided at the base ends  52   a  to  56   a  of the booms according to the expansion and contraction of the expandable cylinder  43 . 
     The connecting member  72  provided at an inner end of each of the B pins  52   d  to  56   d  has a box shape in which a part is opened. Thus, during the expansion and contraction operation of the expandable cylinder  43 , the B-pin driving lever  74  passes through an opened portion of the connecting member  72  of the B pin that is not a driving target. 
     Next, a control block and the hydraulic circuit of the expansion device according to the present embodiment will be described with reference to  FIG. 5 . As illustrated in  FIG. 5 , the expansion device includes expansion and contraction operation means  80 , expansion and contraction state detecting means  90 , the controller  35 , the hydraulic supply unit  20 , and the expandable cylinder hydraulic supply unit  105 . 
     The expansion and contraction operation means  80  has an expansion and contraction operation lever  81 , final boom state input means  82 , and an expansion and contraction information display means  83 . 
     The expansion and contraction operation lever  81  converts a lever operation direction and an operation amount of an expansion and contraction operation into an electric signal and outputs the electric signal to the controller  35 . 
     The final boom state input means  82  is used to input a target expanded state (final boom state) after the expansion and contraction operation when the expandable boom  50  is expanded and contracted. The final boom state input means  82  is operated integrally with the expansion and contraction information display means  83  to be described later. An operation signal of the final boom state input means  82  is output to the controller  35 . 
     The expansion and contraction information display means  83  graphically displays information regarding an operation of the expansion device based on a display control signal from the controller  35 . 
       FIG. 6  illustrates an example of a display screen  84  by the expansion and contraction information display means  83 . Contents of the display screen  84  can be switched. A boom condition when the expandable boom  50  is expanded and contracted is displayed on the display screen  84 . 
     The boom condition indicates a boom state after the expansion of the expandable boom  50 , and an expansion length  85  of the expandable boom  50  and an expansion ratio  86  of each stage boom are associated with each other. 
     A plurality of boom conditions is displayed on the display screen  84 . On the display screen  84 , an operator can select a desired boom condition by operating a forward-backward key of the final boom state input means  82  to move a box-shaped cursor  88  up and down. 
     For example, the operator can input the boom condition to the controller  35  by moving the box-shaped cursor  88  to a row of a target boom condition and then operating a set key of the final boom state input means  82 . In  FIG. 6 , the selected boom condition is indicated by a circle  87 . 
     The expansion and contraction state detecting means  90  has the following specific detecting means. That is, the expansion and contraction state detecting means  90  has boom base end position detecting means  91 , cylinder length detecting means  92 , C-pin state detecting means  93 , and B-pin state detecting means  94 . 
     The boom base end position detecting means  91  detects the base end of the boom at which the cylinder-boom connecting means  64  is positioned, and outputs a detection signal to the controller  35 . 
     The cylinder length detecting means  92  detects a cylinder length of the expandable cylinder  43  and outputs a detection signal to the controller  35 . 
     The controller  35  acquires a specification expansion and contraction length set so as to correspond to a position of the fixing hole of the boom connecting means  70  based on a detection value of the cylinder length detecting means  92 . The controller  35  sets the acquired specification expansion and contraction length as an expansion and contraction length in a boom expansion and contraction step. The specification expansion and contraction length may be stored in a storage unit (not illustrated) or the like. 
     The C-pin state detecting means  93  detects a state of the C pin  7  driven by the cylinder-boom connecting means  64 , and outputs a detection signal to the controller  35 . 
     The B-pin state detecting means  94  detects the states of the B pins  52   d  to  56   d  driven by the B-pin driving means  73 , and outputs detection signals to the controller  35 . 
       FIG. 7  illustrates a specific example of the boom base end position detecting means  91 .  FIG. 7  is a diagram taken along an arrow D-D of  FIG. 2 . In  FIG. 7 , the boom base end position detecting means  91  includes proximity switches  95  to  99 . 
     The proximity switches  95  to  99  are attached to the cylinder tube rod side end  45  (trunnion member  65 ) of the expandable cylinder  43  via supports  100  and  101 . 
     A detection piece  56   g  is provided at a position corresponding to the proximity switch  95  at the top boom base end  56   a .  FIG. 7  illustrates a state in which the detection piece  56   g  of the top boom base end  56   a  is detected by the proximity switch  95 . 
     Similarly, detection pieces  52   g  to  55   g  are provided at positions corresponding to the proximity switches  96  to  99  on the base ends  52   a  to  55   a  of the other booms, respectively. 
     The controller  35  can specify the connecting hole of the boom to which the C pin  7  of the cylinder-boom connecting means  64  is connected according to which of the proximity switches  95  to  99  detects the detection pieces  52   g  to  56   g.    
     The cylinder length detecting means  92  includes, for example, the length detector  62  attached to the base boom base end  51   a  on the fixed part side of the expandable cylinder  43  (see  FIG. 2 ). The cord  63  pulled out from the length detector  62  is connected to the support  61  of the cylinder tube rod side end  45  of the expandable cylinder  43 . 
     The cord  63  is taken in and out from the length detector  62  along with the expansion and contraction of the expandable cylinder  43 . The cylinder length detecting means  92  can detect the cylinder length of the expandable cylinder  43  based on a pulled-out amount of the cord  63 . 
       FIG. 8  illustrates a specific example of the C-pin state detecting means  93 .  FIG. 8  is a diagram taken along an arrow C-C of  FIG. 3 . In  FIG. 8 , the C-pin state detecting means  93  includes proximity switches  102  and  103 . 
     The proximity switches  102  and  103  are provided at a cylinder part of the C-pin cylinder  2 . A U-shaped detection piece  104  is provided at a rod part of the C-pin cylinder  2 . In a state in which the C pin  7  of the cylinder-boom connecting means  64  is removed from the connecting hole  56   b  of the top boom  56  (also referred to as a cylinder-boom disconnected state, see  FIG. 3 ), one proximity switch  102  detects the detection piece  104 . 
     When the maintaining of the expanded state of the C-pin cylinder  2  is released and a distal end of the C pin  7  is inserted into the connecting hole  56   b  by the biasing force of the extension coil spring  8  (see  FIG. 3 ), the other proximity switch  103  detects the detection piece  104 . 
       FIG. 4  illustrates a specific example of the B-pin state detecting means  94 . In  FIG. 4 , the B-pin state detecting means  94  includes proximity switches  114  and  115 . 
     The proximity switches  114  and  115  are provided at a cylinder part of the B-pin cylinder  1 . A U-shaped detection piece  116  is provided at a rod part of the B-pin cylinder  1 . 
     As illustrated in  FIG. 4 , one proximity switch  114  detects the detection piece  116  in a state in which a distal end of the B pin  56   d  of the top boom base end  56   a  is removed from the fixing hole  55   f  of the fifth boom  55  (also referred to as a boom disconnected state). 
     When the maintaining of the expanded state of the B-pin cylinder  1  is released, the B-pin cylinder  1  is contracted by the biasing force of the built-in compression coil spring  5  (see  FIG. 1 ). When the distal end of the B pin  56   d  is inserted into the fixing hole  55   f  by the biasing force of the compression coil spring  22 , the other proximity switch  115  detects the detection piece  116 . 
       FIG. 5  illustrates the expandable cylinder hydraulic supply unit  105  that supplies the working fluid to the expandable cylinder  43 , and the hydraulic supply unit  20  that supplies the working fluid to the C-pin cylinder  2  of the cylinder-boom connecting means  64  and the B-pin cylinder  1  of the B-pin driving means  73 . 
     The expandable cylinder hydraulic supply unit  105  supplies the working fluid to the expandable cylinder  43  based on a control signal from the controller  35 . The hydraulic supply unit  20  supplies the working fluid to one cylinder selected by the controller  35  out of the C-pin cylinder  2  and the B-pin cylinder  1  based on a control signal from the controller  35 . 
     Hereinafter, the expandable cylinder hydraulic supply unit  105  will be described. Details of the hydraulic supply unit  20  are as described above with reference to  FIG. 1 , and thus, the description is omitted. 
     The expandable cylinder hydraulic supply unit  105  has a counterbalance valve  106 , a pilot type switching valve  107 , an electromagnetic proportional valve  108 , an electromagnetic proportional valve  109 , and a flow control valve  110 . 
     A hydraulic source P is connected to a pump port of the pilot type switching valve  107  via the flow control valve  110 . The tank T is connected to a tank port of the pilot type switching valve  107 . The hydraulic source P is provided around the base boom base end  51   a . A position of the hydraulic source P is not limited to the case of the present embodiment. The hydraulic source P corresponds to an example of a first hydraulic source. A working fluid discharged from the hydraulic source P corresponds to an example of a first working fluid. 
     The electromagnetic proportional valves  108  and  109  are proportionally controlled by a control signal from the controller  35 . The pilot type switching valve  107  is switched by output pilot pressures of the electromagnetic proportional valves  108  and  109 . 
     A first outlet port of the pilot type switching valve  107  and an expansion side oil chamber of the expandable cylinder  43  are connected by a hydraulic pipeline  111  via the counterbalance valve  106 . A second outlet port of the pilot type switching valve  107  and a contraction side oil chamber of the expandable cylinder  43  are connected by a hydraulic pipeline  112 . 
     Hereinafter, the operation of the expansion device according to the present embodiment will be described with reference to  FIGS. 1 to 8 . Specifically, an expansion operation of the expansion device from the fully contracted state of the 6-stage expandable boom  50  (see  FIG. 2 ) to a state in which the top boom  56  and the fifth boom  55  of the crane vehicle  113  are expanded (see  FIG. 9 ) will be described as an example. In the following description, the top boom  56  corresponds to an example of an inner boom. The fifth boom  55  corresponds to an example of an outer boom. 
     At the start of the expansion operation, the expandable boom  50  is in the fully contracted state as illustrated in  FIG. 2 . At this time, the cylinder-boom connecting means  64  is connected to the base end  56   a  of the top boom  56 . All of the pair of adjacent booms are fixed by the boom connecting means  70 . The B-pin driving means  73  is connected to the B pin  56   d  of the top boom  56 . 
     First, the operator selects the boom condition on the display screen  84  of the expansion and contraction information display means  83  by operating the forward-backward key of the final boom state input means  82 . As an example, when the operator selects boom condition No. 5 (see  FIG. 6 ) in which the top boom (sixth stage) is expanded by 93% and the fifth boom (fifth stage) is expanded by 93% and operates the set key of the final boom state input means  82 , the selected boom condition is output to the controller  35  and is stored. Hereinafter, the boom condition selected by the operator is referred to as a selected boom condition. 
     Subsequently, the operator operates the expansion and contraction operation lever  81  to the expansion side and maintains the operation state. The controller  35  automatically controls the expansion device to expand the expandable boom  50  until the selected boom condition (in this example, boom condition No. 5 of  FIG. 6 ) is satisfied. At this time, the controller  35  repeatedly performs the following plurality of steps as one cycle until the selected boom condition is satisfied. 
     Specifically, in the above one cycle, the controller  35  sequentially performs a boom disconnection step, a boom expansion and contraction step (here, a boom expansion step), a boom connection step, a cylinder-boom disconnection step, an expandable cylinder contraction step, and a cylinder-boom connection step. When the operator returns the expansion and contraction operation lever  81  to a neutral position in the middle of the expansion and contraction operation of the expandable boom  50 , the controller  35  stops the operation of the expansion device. 
     (Boom Disconnection Step) 
     The boom disconnection step has a step of moving the B pin  4  to disconnect the pair of adjacent booms (hereinafter, referred to as a first step of the boom disconnection process) and a step of maintaining the B pin  4  at a moved position (hereinafter, referred to as a second step of the boom disconnection step). 
     First, in the first step of the boom disconnection step, the controller  35  outputs a control signal instructing the hydraulic supply unit  20  to remove the B pin  56   d  of the top boom  56  from the fifth boom  55  (to expand the B-pin cylinder  1 ) based on an operation of the operator on the expansion and contraction operation lever  81 . Specifically, the controller  35  outputs a control signal for turning on energization to the first electromagnetic switching valve  14 , turning off energization to the second electromagnetic switching valve  15 , and turning on energization to the third electromagnetic switching valve  16 . 
     In the first step of the boom disconnection step, the first electromagnetic switching valve  14  is in the second state (energized state). In the boom disconnection step, the second electromagnetic switching valve  15  is in the first state (unenergized state). In the boom disconnection step, the third electromagnetic switching valve  16  is in the second state (energized state). 
     The working fluid of the hydraulic unit  24  (the pressurized working fluid accumulated in the hydraulic accumulator  31 ) is supplied to the B-pin cylinder  1  through the first electromagnetic switching valve  14 , the second electromagnetic switching valve  15 , the third electromagnetic switching valve  16 , and the hydraulic pipeline  6 . The B-pin cylinder  1  is driven to the expansion side while compressing the built-in compression coil spring  5 , and moves the B pin  4  to the release side. 
     An operation of the boom connecting means  70  in the first step of the boom disconnection step will be described with reference to  FIG. 4 . The B-pin cylinder  1  expands, and thus, the B-pin driving lever  74  is moved to the release side. The B pin  56   d  of the top boom  56  retreats against the biasing force of the compression coil spring  22  and is removed from the fixing hole  55   f . The controller  35  recognizes that the fixing between the pair of adjacent booms is released based on a detection signal from the proximity switch  115  of the B-pin state detecting means  94 . 
     Subsequently, in the second step of the boom disconnection step, the controller  35  outputs a control signal for turning off the energization to the first electromagnetic switching valve  14 , turning on the energization to the second electromagnetic switching valve  15 , and turning on the energization to the third electromagnetic switching valve  16 . 
     In the second step of the boom disconnection step, the first electromagnetic switching valve  14  is in the first state (unenergized state). In the second step of the boom disconnection step, the second electromagnetic switching valve  15  is in the second state (energized state). In the second step of the boom disconnection step, the third electromagnetic switching valve  16  is in the second state (energized state). 
     In the second step of the boom disconnection step, the working fluid is retained in the hydraulic pipeline  6  between the second electromagnetic switching valve  15  and the B-pin cylinder  1 . In this state, the expanded state of the B-pin cylinder  1  is maintained. That is, the B pin  56   d  is maintained in a state of being removed from the fixing hole  55   f  of the fifth boom  55 . 
     As stated above, the fixed state between the top boom base end  56   a  and the fifth boom  55  is released. When the boom disconnection step is ended, the step proceeds to the next boom expansion step. 
     Since the hydraulic pipeline  6  from the hydraulic unit  24  to the B-pin cylinder  1  is very short, the hydraulic pipeline is hardly affected by a viscosity change due to a temperature decrease. As a result, very good responsiveness is obtained in the boom disconnection step. 
     (Boom Expansion Step) 
     In the boom expansion step, the controller  35  outputs a control signal instructing the expandable cylinder hydraulic supply unit  105  to expand the expandable cylinder  43 . Specifically, the controller  35  outputs a control signal to the electromagnetic proportional valve  109  such that a pilot pressure proportional to an operation amount of the expansion and contraction operation lever  81  is applied to the pilot type switching valve  107 . 
     The hydraulic source P is connected to the pilot type switching valve  107 , and the hydraulic pressure from the hydraulic source P is sent to the expansion side oil chamber of the expandable cylinder  43  via the hydraulic pipeline  111  and the counterbalance valve  106 . The expandable cylinder  43  expands. As the expandable cylinder  43  expands, the top boom  56  expands. 
     In this boom expansion step, the controller  35  calculates a distance (hereinafter, referred to as a first distance) between the B pin  56   d  of the top boom  56  connected to the B-pin driving means  73  and the fixing hole of the fifth boom  55  based on a detection signal from the cylinder length detecting means  92 . The fixing hole of the fifth boom  55  is a fixing hole into which the B pin  56   d  of the top boom  56  connected to the B-pin driving means  73  is inserted in the boom connection step to be described later. 
     In the boom expansion step, the first distance calculated by the controller  35  is a distance of the expandable boom  50  in an axial direction. When the first distance is equal to or less than a predetermined distance, the controller  35  outputs a signal (hereinafter, also simply referred to as a deceleration signal) for decelerating an expansion speed (that is, a moving speed of the cylinder tube  44 ) of the expandable cylinder  43  to the expandable cylinder hydraulic supply unit  105 . The case where the first distance is equal to or less than the predetermined distance may be regarded as a case where the B pin  56   d  reaches a deceleration start point. 
     Specifically, in the boom expansion step, the cylinder length detecting means  92  continues to send a detection signal indicating the length of the expandable cylinder  43  to the controller  35 . When the B pin  56   d  reaches the deceleration start point, the controller  35  gradually decreases an output signal value to the electromagnetic proportional valve  109 . That is, when the B pin  56   d  reaches the deceleration start point, the controller  35  outputs a control signal (also referred to as a first deceleration control signal) for gradually reducing the expansion speed of the expandable cylinder  43  to the electromagnetic proportional valve  109 . 
     Thus, the pilot pressure applied from the electromagnetic proportional valve  109  to the pilot type switching valve  107  gradually decreases in response to the first deceleration control signal. As a result, a spool of the pilot type switching valve  107  is gradually returned. 
     As the spool of the pilot type switching valve  107  is gradually returned, an opening area of the first outlet port of the pilot type switching valve  107  gradually decreases. As a result, a flow rate of the working fluid discharged from the first outlet port of the pilot type switching valve  107  decreases. Accordingly, the expansion speed of the expandable cylinder  43  decreases. 
     When it is determined that the B pin  56   d  of the top boom  56  has reached the position of the fixing hole to be inserted in the boom connection step to be described later, the controller  35  stops an expansion operation of the expandable cylinder  43 . When the boom expansion step is ended, the step proceeds to the next boom connection step. 
     (Boom Connection Step) 
     In the boom connection step, the controller  35  outputs a control signal instructing the hydraulic supply unit  20  to insert the B pin  56   d  of the top boom  56  into the fixing hole of the fifth boom  55  (to reduce the B-pin cylinder  1 ). 
     Specifically, the controller  35  outputs a control signal for turning off the energization to the first electromagnetic switching valve  14 , turning off the energization to the second electromagnetic switching valve  15 , and turning on the energization to the third electromagnetic switching valve  16 . 
     In the boom connection step, the first electromagnetic switching valve  14  is in the first state (unenergized state). In the boom connection step, the second electromagnetic switching valve  15  is in the first state (unenergized state). In the boom connection step, the third electromagnetic switching valve  16  is in the second state (energized state). 
     Accordingly, the working fluid retained between the second electromagnetic switching valve  15  and the B-pin cylinder  1  is returned to the tank  27  via the first electromagnetic switching valve  14  and the return oil pipeline  32 . The B-pin cylinder  1  is reduced by the biasing force of the built-in compression coil spring  5 , and the B pin  4  is moved to the fixation side by the biasing force of the compression coil spring  22  (see  FIG. 1 ). 
     An operation of the boom connecting means  70  in the boom connection step will be described with reference to  FIG. 4 . In the boom connection step, the B-pin driving lever  74  swings as the B-pin cylinder  1  contracts. When the B-pin driving lever  74  swings, the B pin  56   d  moves to the fixation side via the roller  75 . 
     As a result, the B pin  56   d  of the top boom  56  is inserted into the fixing hole  55   f  of the fifth boom  55 . The top boom base end  56   a  is connected to the fifth boom  55 . The controller  35  recognizes that the pair of adjacent booms are connected to each other based on a detection signal from proximity switch  115 . 
     As stated above, the top boom base end  56   a  and the fifth boom  55  are connected. When the boom connection step is ended, the step proceeds to the next cylinder-boom disconnection step. 
     In this boom connection step, since the hydraulic pipeline from the B-pin cylinder  1  to the tank  27  is also very short, an operation delay does not cause a problem. As a result, very good responsiveness is obtained also in the boom connection step. 
     (Cylinder-Boom Disconnection Step) 
     When the expansion and contraction operation lever  81  is further operated toward the expansion side, the cylinder-boom disconnection step is performed. 
     In the cylinder-boom disconnection step, the controller  35  outputs a control signal for instructing the hydraulic supply unit  20  to release the connected state between the C pin  7  and the top boom  56 . Specifically, the controller  35  outputs a control signal for turning on the energization to the first electromagnetic switching valve  14 , turning off the energization to the second electromagnetic switching valve  15 , and turning off the energization to the third electromagnetic switching valve  16 . 
     In the cylinder-boom disconnection step, the first electromagnetic switching valve  14  is in the second state (energized state). In the cylinder-boom disconnection step, the second electromagnetic switching valve  15  is in the first state (unenergized state). In the cylinder-boom disconnection step, the third electromagnetic switching valve  16  is in the first state (unenergized state). 
     Accordingly, the working fluid of the hydraulic unit  24  (the pressurized working fluid accumulated in the hydraulic accumulator  31 ) is supplied to the C-pin cylinder  2  through the first electromagnetic switching valve  14 , the second electromagnetic switching valve  15 , the third electromagnetic switching valve  16 , and the hydraulic pipeline  9 . The C-pin cylinder  2  is driven to the expansion side while expanding the extension coil spring  8 , and moves the C pin  7  to the release side. 
     The cylinder-boom disconnection step will be described with reference to  FIG. 3 . In the cylinder-boom disconnection step, the C-pin cylinder  2  expands, and thus, the C pin  7  is removed from the connecting hole  56   b  of the top boom  56  via the C-pin driving lever  21 . 
     Accordingly, the cylinder tube rod side end  45  of the expandable cylinder  43  (the movable part  11  of the expandable cylinder  43 ) and the top boom base end  56   a  are disconnected. The controller  35  recognizes that the connected state between the cylinder and the boom is released based on a detection signal from the proximity switch  102  (see  FIG. 8 ). 
     As stated above, the connected state between the top boom base end  56   a  and the movable part  11  (C pin  7 ) of the expandable cylinder  43  is released. When the cylinder-boom disconnection step is ended, the step proceeds to the next expandable cylinder contraction step. 
     In this cylinder-boom disconnection step, since the hydraulic pipeline between the hydraulic unit  24  and the C-pin cylinder  2  is also very short, an operation delay does not cause a problem. As a result, very good responsiveness is obtained also in the cylinder-boom disconnection step. 
     (Expandable Cylinder Contraction Step) 
     In the expandable cylinder contraction step, the controller  35  outputs a control signal instructing the expandable cylinder hydraulic supply unit  105  to contract the expandable cylinder  43 . Specifically, the controller  35  outputs a control signal to the electromagnetic proportional valve  108 . 
     As a result, the pilot type switching valve  107  is switched, and the hydraulic source P is connected to the second outlet port of the pilot type switching valve  107 . The working fluid from the hydraulic source P is supplied to the contraction side oil chamber of the expandable cylinder  43  through the hydraulic pipeline  112 . Accordingly, the expandable cylinder  43  starts a contraction operation alone. 
     In the expandable cylinder contraction step, the controller  35  calculates a distance (hereinafter, referred to as a second distance) between the C pin  7  and the connecting hole of the fifth boom  55  based on a detection signal from the cylinder length detecting means  92 . The connecting hole of the fifth boom  55  is a connecting hole into which the C pin  7  is inserted in the cylinder-boom connection step to be described later. 
     In the expandable cylinder contraction step, the second distance calculated by the controller  35  is a distance of the expandable boom  50  in the axial direction. When the second distance is equal to or less than a predetermined distance, the controller  35  outputs a signal (hereinafter, also simply referred to as a deceleration signal) for decelerating a contraction speed (that is, a moving speed of the cylinder tube  44 ) of the expandable cylinder  43  to the expandable cylinder hydraulic supply unit  105 . The case where the second distance is equal to or less than the predetermined distance may be regarded as a case where the C pin  7  reaches a deceleration start point. 
     Specifically, in the expandable cylinder contraction step, the cylinder length detecting means  92  continues to send a detection signal indicating the length of the expandable cylinder  43  to the controller  35 . When the C pin  7  reaches the deceleration start point, the controller  35  gradually decreases an output signal value to the electromagnetic proportional valve  108 . That is, when the C pin  7  reaches the deceleration start point, the controller  35  outputs a control signal (also referred to as a second deceleration signal) for gradually reducing the contraction speed of the expandable cylinder  43  to the electromagnetic proportional valve  108 . 
     Thus, the pilot pressure applied from the electromagnetic proportional valve  108  to the pilot type switching valve  107  gradually decreases in response to the second deceleration control signal. As a result, a spool of the pilot type switching valve  107  is gradually returned. 
     As the spool of the pilot type switching valve  107  is gradually returned, an opening area of the second outlet port of the pilot type switching valve  107  gradually decreases. As a result, a flow rate of the working fluid discharged from the second output port of the pilot type switching valve  107  decreases. Accordingly, the contraction speed of the expandable cylinder  43  decreases. 
     When it is determined that the C pin  7  has reached the position of the connecting hole of the fifth boom  55  to be inserted in the cylinder-boom connection step to be described later, the controller  35  stops the contraction operation of the expandable cylinder  43 . When the expandable cylinder contraction step is ended, the step proceeds to the next cylinder-boom connection step. 
     In the expandable cylinder contraction step, the controller  35  determines whether or not the C pin  7  has reached a target position based on the detection signal from the cylinder length detecting means  92  and the detection signal from the boom base end position detecting means  91 . That is, when the detection piece  55   g  installed at the fifth boom base end  55   a  is detected by the proximity switch  96  (see  FIG. 7 ), the controller  35  determines that the C pin  7  has reached the target position. 
     (Cylinder-Boom Connection Step) 
     In the cylinder-boom connection step, the controller  35  outputs a control signal instructing the hydraulic supply unit  20  to connect the C pin  7  and the fifth boom  55 . Specifically, the controller  35  outputs a control signal for turning off the energization of the first electromagnetic switching valve  14 , turning off the energization of the second electromagnetic switching valve  15 , and turning off the energization of the third electromagnetic switching valve  16 . 
     In the cylinder-boom connection step, the first electromagnetic switching valve  14  is in the first state (unenergized state). In the cylinder-boom connection step, the second electromagnetic switching valve  15  is in the first state (unenergized state). In the cylinder-boom connection step, the third electromagnetic switching valve  16  is in the first state (unenergized state). 
     Accordingly, the working fluid supplied to the oil chamber of the C-pin cylinder  2  is returned to the tank  27  via the hydraulic pipeline  9 , the third electromagnetic switching valve  16 , the second electromagnetic switching valve  15 , the first electromagnetic switching valve  14 , and the return pipeline  32 . The C-pin cylinder  2  is driven to the contraction side by the biasing force of the extension coil spring  8 , and moves the C pin  7  to the connection side. 
     The C-pin cylinder  2  is contracted, and thus, the C-pin driving lever  21  is moved. Thus, the C pin  7  is inserted into the connecting hole  55   b  of the fifth boom base end  55   a . The C pin  7  is inserted into the connecting hole  55   b , and thus, the cylinder tube rod side end  45  of the expandable cylinder  43  (the movable part  11  of the expandable cylinder  43 ) and the fifth boom base end  55   a  are connected. 
     The controller  35  recognizes that the expandable cylinder  43  and the fifth boom  55  are connected based on a detection signal from the proximity switch  103  (see  FIG. 8 ). 
     In this cylinder-boom connection step, since the hydraulic pipeline from the C-pin cylinder  2  to the hydraulic unit  24  is very short, an operation delay does not cause a problem. Thereafter, the above-described steps are repeated, and thus, the fifth boom  55  is expanded. Thus, when the final boom state illustrated in  FIG. 9  is obtained, the controller of the expansion device ends the operation. 
     As described above, the expansion device according to the present embodiment includes one expandable cylinder  43  which is built in the expandable boom  50  in which the plurality of booms  51  to  56  including the base boom  51 , the intermediate booms  52  to  55 , and the top boom  56  is expandably fitted and inserted and of which one end is pivotally supported by the base end  51   a  of the base boom  51 , the boom connecting means  70  which has the B pins  52   d  to  56   d  (fixing pins) and the B-pin cylinder  1  (first hydraulic cylinder) for inserting and removing the B pins  52   d  to  56   d  and fixes two adjacent booms of the plurality of booms  51  to  56  by the B pins  52   d  to  56   d , the cylinder-boom connecting means  64  which has the C pin  7  (connecting pin) and the C-pin cylinder  2  (second hydraulic cylinder) for inserting and removing the C pin  7  and connects a specific boom to be expanded and contracted among the plurality of booms  52  to  56  and the expandable cylinder  43  by the C pin  7 , and the hydraulic supply unit  20  (hydraulic supply unit) that supplies the hydraulic pressure to the B-pin cylinder  1  and the C-pin cylinder  2 . The expansion device expands and contracts the plurality of booms  52  to  56  stage by stage by expanding and contracting the expandable cylinder  43  in a state in which the specific boom and the expandable cylinder  43  are connected and a fixed state of two adjacent booms including the specific boom is released. 
     The hydraulic supply unit  20  has the hydraulic unit  24 , the electromagnetic switching valves  14  to  16  (switching valves) that switch between delivery destinations of the working fluid from the hydraulic unit  24 , the hydraulic pipeline  6  through which the working fluid is delivered from the electromagnetic switching valves  14  to  16  to the B-pin cylinder  1 , and the hydraulic pipeline  9  through which the working fluid is delivered from the electromagnetic switching valves  14  to  16  to the C-pin cylinder  2 . 
     The hydraulic supply unit  20  is disposed in the movable part  11  of the expandable cylinder  43 . 
     Since all the hydraulic unit  24  and the electromagnetic switching valves  14  to  16  constituting the hydraulic supply unit  20  are arranged in the movable part  11  of the expandable cylinder  43 , the hydraulic pipeline connecting the hydraulic unit  24  to the B-pin cylinder  1  and the C-pin cylinder  2  is very short. Thus, very good responsiveness is obtained in the B-pin cylinder  1  and the C-pin cylinder  2  regardless of an ambient environmental temperature. Accordingly, the operability of the expansion device is secured even at a low temperature. 
     Since a large and heavy hose reel is not required, the mountability of the crane vehicle is improved. There is no need for the expandable cylinder that is complicated and difficult to be manufactured, such as the expandable cylinder with the built-in oil feed pipe. 
     REFERENCE SIGNS LIST 
     
         
           1  B-pin cylinder 
           100 ,  101  support 
           102 ,  103  proximity switch 
           104  detection piece 
           105  expandable cylinder hydraulic supply unit 
           106  counterbalance valve 
           107  pilot type switching valve 
           108 ,  109  electromagnetic proportional valve 
           110  flow control valve 
           11  movable part 
           113  crane vehicle 
           114 ,  115  proximity switch 
           116  detection piece 
           14  first electromagnetic switching valve 
           15  second electromagnetic switching valve 
           16  third electromagnetic switching valve 
           2  C-pin cylinder 
           20  hydraulic supply unit 
           22  compression coil spring 
           24  hydraulic unit 
           25  electric motor 
           26  hydraulic pump 
           27  tank 
           28  check valve 
           29  high-pressure filter 
           30  discharge pipeline 
           31  hydraulic accumulator 
           32  return pipeline 
           33  relief valve 
           34  hydraulic sensor 
           35  controller 
           37  cable reel 
           38  power line 
           39 ,  40 ,  41 ,  42  control signal line 
           4  B pin 
           43  expandable cylinder 
           44  cylinder tube 
           45  cylinder tube rod side end 
           5  compression coil spring 
           50  expandable boom 
           51  base boom 
           51   a  base boom base end 
           52  second boom (intermediate boom) 
           52   a  second boom base end 
           52   b  to  56   b  connecting hole 
           52   d  B pin 
           52   g  to  56   g  detection piece 
           53  third boom (intermediate boom) 
           53   a  third boom base end 
           53   d  B pin 
           54  fourth boom (intermediate boom) 
           54   a  fourth boom base end 
           54   d  B pin 
           55  fifth boom (intermediate boom) 
           55   a  fifth boom base end 
           55   d  B pin 
           55   f  fixing hole 
           56  top boom 
           56   a  top boom base end 
           56   b  connecting hole 
           56   d  B pin 
           6  hydraulic pipeline 
           60  cable 
           62  length detector 
           63  cord 
           64  cylinder-boom connecting means 
           65  trunnion member 
           66  C-pin housing hole 
           7  C pin 
           70  boom connecting means 
           72  connecting member 
           73  B-pin driving means 
           75  roller 
           8  extension coil spring 
           80  expansion and contraction operation means 
           81  expansion and contraction operation lever 
           82  final boom state input means 
           83  expansion and contraction information display means 
           84  display screen 
           85  expansion length 
           86  expansion ratio 
           87  circle 
           88  box-shaped cursor 
           9  hydraulic pipeline 
           90  expansion and contraction state detecting means 
           91  boom end position detecting means 
           92  cylinder length detecting means 
           93  C-pin state detecting means 
           94  B-pin state detecting means 
           95  to  99  proximity switch