Patent Publication Number: US-10787345-B2

Title: Crane

Description:
CROSS REFERENCE TO PRIOR APPLICATION 
     This application is a National Stage Patent Application of PCT International Patent Application No. PCT/JP2017/014541 (filed on Apr. 7, 2017) under 35 U.S.C. § 371, which claims priority to Japanese Patent Application No. 2016-077669 (filed on Apr. 7, 2016), which are all hereby incorporated by reference in their entirety. 
     TECHNICAL FIELD 
     The present invention relates to a crane, particularly to a mobile crane with a detachable derricking hydraulic cylinder. 
     BACKGROUND ART 
     There has conventionally been known a mobile crane provided with a swivel base turnable by a hydraulic motor or the like on the frame of a vehicle and with a crane apparatus made up of a telescoping boom, a main winch, a sub-winch, a cabin, and the like on the swivel base. For some cranes, during travelling on a public road, the telescoping boom and like components need to be detached from the swivel base according to a weight limitation or the like. In a hydraulic circuit of a crane with a detachable telescoping boom, the associated hydraulic actuator is also configured to be detachable in addition to the telescoping boom, and thus hydraulic piping connected to the actuator and hydraulic piping connected to a hydraulic pump provided in the vehicle are connected to each other through a joint. In this way, for the crane, a given hydraulic actuator can easily be detached from the hydraulic circuit together with the telescoping boom. 
     In the hydraulic circuit of the crane with such a configuration, when hydraulic fluid is supplied from a supply-side oil passage while a joint of a return-side oil passage is disconnected, the hydraulic fluid supplied to the hydraulic actuator cannot return from the hydraulic actuator to a hydraulic tank. Consequently, the hydraulic pressure increases with supply of hydraulic fluid in the hydraulic circuit; thus, precaution is made to avoid breakage and oil leakage in the hydraulic actuator by providing a relief valve for releasing hydraulic pressure at a predetermined pressure (relief pressure). However, when the allowable hydraulic pressure of the hydraulic actuator is lower than such a predetermined pressure, even if the relief valve releases hydraulic fluid at the predetermined pressure, the hydraulic actuator is subjected to a hydraulic pressure higher than the allowable hydraulic pressure. For this reason, a known hydraulic circuit is provided with a multi-stage relief valve to change the relief pressure between a low pressure and a high pressure depending on the discharge pressure of the hydraulic pump. An example is described in PTL 1. 
     The hydraulic circuit described in PTL 1 is configured to determine that the return-side joint is connected when the discharge pressure of the hydraulic pump is below a predetermined value while the operating oil is circulated, and to switch the relief pressure of the multi stage relief valve from the low pressure to the high pressure. Thus, a hydraulic pressure higher than the relief pressure of the low pressure is not applied to the hydraulic circuit until the return-side joint is determined to be connected. However, in the technique described in PTL 1, the hydraulic pressure of the hydraulic circuit goes higher than the predetermined pressure of the relief valve when the discharge of the hydraulic pump exceeds the allowable relief flow rate of the relief valve. Moreover, when the hydraulic actuator is a hydraulic cylinder, because of the structure, the hydraulic pressure in a rod side oil chamber is amplified due to the hydraulic pressure in a head side oil chamber. In other words, in the hydraulic circuit described in PTL 1, when control is made for maximizing the operating speed of the hydraulic actuator, the flow rate of the hydraulic fluid exceeds the allowable relief flow rate of the relief valve, so that the pressure of the head side oil chamber of the hydraulic cylinder may rise and the amplified hydraulic pressure may be applied to the rod side oil chamber. 
     CITATION LIST 
     Patent Literature 
     
         
         PTL 1 
         Japanese Patent Application Laid-Open No. 2014-163464 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     An object of the present invention is to provide a crane capable of suppressing the supply of hydraulic fluid while in poor connection with a hydraulic circuit to protect the hydraulic cylinder. 
     Solution to Problem 
     A crane according to the present invention includes a detachable hydraulic cylinder including a head side oil chamber and a rod side oil chamber both to be connected to a control valve through a joint, in which a head side hydraulic detecting section and a rod side hydraulic detecting section are each provided to the hydraulic cylinder, and when a rod side hydraulic pressure becomes greater than or equal to a head side hydraulic pressure by the time when a predetermined time elapses after supply of electric power to the head side hydraulic detecting section and the rod side hydraulic detecting section is started and the control valve is switched to a state of supplying hydraulic fluid to the head side oil chamber, it is determined that the rod side oil chamber and the control valve are not connected to each other through the joint. 
     In the crane according to the present invention, when power supply to the head side hydraulic detecting section and the rod side hydraulic detecting section is started and the control valve is switched to a state of supplying hydraulic fluid to the head side oil chamber, regardless of the amount of operation of the operation tool for hydraulic cylinder, preferably, the behavior of the control valve is limited such that the amount of hydraulic fluid supplied to the head side oil chamber is less than or equal to a predetermined value by the time when the predetermined time elapses. 
     In the crane according to the present invention, when power supply to the head side hydraulic detecting section and the rod side hydraulic detecting section is started and the control valve is switched to a state of supplying hydraulic fluid to the head side oil chamber, regardless of the amount of operation of the operation tool for hydraulic cylinder, preferably, the behavior of the control valve is limited such that the pressure of hydraulic fluid supplied to the head side oil chamber is less than or equal to a predetermined value by the time when the predetermined time elapses. 
     The crane according to the present invention further includes an informing section, in which, when it is determined that the rod side oil chamber and the control valve are not connected to each other, preferably, the informing section informs of a poor connection between the rod side oil chamber and the control valve. 
     In the crane according to the present invention, when it is determined that the rod side oil chamber and the control valve are not connected to each other, preferably, the control valve is switched to a state of not supplying hydraulic fluid to the head side oil chamber. 
     Advantageous Effects of Invention 
     In the crane of the present invention, the connection state of a return side joint providing a connection between the rod side oil chamber and the control valve is determined according to the states of the hydraulic pressures of the rod side oil chamber and head side oil chamber of the hydraulic cylinder. Thus, the actuation of the hydraulic cylinder in poor connection with the hydraulic circuit is suppressed, thereby protecting the hydraulic cylinder. 
     In the crane of the present invention, the increase rates of the hydraulic pressures of the rod side oil chamber and head side oil chamber in the hydraulic cylinder are suppressed, thereby preventing the application of an excessive hydraulic pressure to the hydraulic cylinder due to the operation by the operator. Thus, the actuation of the hydraulic cylinder in poor connection with the hydraulic circuit is suppressed, thereby protecting the hydraulic cylinder, 
     In the crane of the present invention, the operator is made recognize a poor connection of the hydraulic cylinder with the hydraulic circuit. Thus, the actuation of the hydraulic cylinder in poor connection with the hydraulic circuit is suppressed, thereby protecting the hydraulic cylinder. 
     In the crane of the present invention, regardless of whether the operator recognizes a poor connection of the hydraulic cylinder with the hydraulic circuit, supply of hydraulic fluid to the hydraulic cylinder is forcibly stopped. Thus, the supply of hydraulic fluid in poor connection with the hydraulic circuit is suppressed, thereby protecting the hydraulic cylinder. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a side view showing the entire configuration of a crane according to one embodiment of the present invention; 
         FIG. 2  is a partially enlarged view showing a derricking cylinder part of a crane according to one embodiment of the present invention; 
         FIG. 3  is a diagram showing an operator&#39;s seat of the crane according to one embodiment of the present invention; 
         FIG. 4  is a diagram showing a hydraulic circuit for a derricking cylinder of the crane according to one embodiment of the present invention; 
         FIG. 5  is a diagram showing a configuration of a control apparatus of the crane according to one embodiment of the present invention; 
         FIG. 6  is a graph showing the relationship between the pressure of the head side oil chamber of the derricking cylinder and the pressure of the rod side oil chamber in the crane according to one embodiment of the present invention; and 
         FIG. 7  is a flow chart showing a control mode of derricking cylinder&#39;s poor connection determination control and derricking cylinder protection control in the crane according to one embodiment of the present invention. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Crane  1  according to one embodiment of a crane will now be described with reference to  FIGS. 1 to 4 . 
     As shown in  FIG. 1 , crane  1  is a mobile crane relocatable to an unspecified location. Crane  1  includes vehicle  2  and crane apparatus  6 . 
     Vehicle  2  carries crane apparatus  6 . Vehicle  2  has operator&#39;s cab  2 A and a plurality of wheels  3  and is mounted with engine  4  which serves as a power source (see  FIG. 4 ). Vehicle  2  is configured to transmit the driving force of engine  4  to the plurality of wheels  3  according to the operation from operator&#39;s cab  2 A to travel. Vehicle  2  is provided with outrigger  5 . Outrigger  5  is made up of an overhang beam which can be extended by hydraulic pressure in the width direction of vehicle  2  toward both sides and hydraulic jack cylinders which can be extended in a direction perpendicular to the ground. In vehicle  2 , outrigger  5  can be extended in the width direction of vehicle  2  and the workable range of crane  1  can be extended by grounding the jack cylinders. 
     Crane apparatus  6  lifts an object to be carried, with a wire rope. Crane apparatus  6  includes swivel base  7 , telescoping boom  8 , main hook block  13 , sub-hook block  14 , derricking cylinder  15 , main winch  17 , sub-winch  18 , main wire rope  19 , sub-wire rope  20 , cabin  21 , and safety apparatus  23 . 
     Swivel base  7  makes crane apparatus  6  rotatable. Swivel base  7  is provided on the frame of vehicle  2  through an annular bearing. The annular bearing is disposed such that its rotation axis can be perpendicular to the installation surface of vehicle  2 . Swivel base  7  is configured to be rotatable about a rotation axis that passes the center of the annular bearing. Moreover, swivel base  7  is configured to be rotated through a hydraulic rotation motor which is not shown in the drawing. 
     Telescoping boom  8  serving as a boom supports a wire rope so that an object to be carried can be lifted. Telescoping boom  8  is made up of a plurality of boom members: base boom member  8 A, second boom member  8 B, third boom member  8 C, fourth boom member  8 D, fifth boom member  8 E, and top boom member  8 F. The boom members are hollow cylinders with polygonal cross-sections similar to each other. The boom members have such sizes that they can be inserted in one another in descending order of cross sectional area, in other words, top boom member  8 F with the smallest cross sectional area has such a size that it can be inserted in fifth boom member  8 E with a cross sectional area following that of top boom member  8 F. Fifth boom member  8 E has such a size that it can be inserted in fourth boom member  8 D with a cross sectional area following that of fifth boom member  8 E. In this manner, in telescoping boom  8 , second boom member  8 B, third boom member  8 C, fourth boom member  8 D, fifth boom member  8 E, and top boom member  8 F are nested in base boom member  8 A, which has the largest cross sectional area, in descending order of cross sectional area. 
     Moreover, in telescoping boom  8 , second boom member  8 B, third boom member  8 C, fourth boom member  8 D, fifth boom member  8 E, and top boom member  8 F are configured to be movable in the axial direction of telescoping boom  8  with respect to base boom member  8 A. In other words, telescoping boom  8  is configured to be telescopic by moving each boom member with a telescoping cylinder or the like not shown in the drawing. In telescoping boom  8 , the base end of base boom member  8 A is provided on swivel base  7  so that it is swingable. Thus, telescoping boom  8  is configured to be horizontally rotatable on the frame of vehicle  2 . Further, telescoping boom  8  is configured to be swingable about the base end of base boom member  8 A with respect to swivel base  7 . 
     The distal end of top boom member  8 F of telescoping boom  8  is provided with main guide sheave  9 , sub-guide sheave  10 , main sheave  11 , and sub-sheave  12 . Main guide sheave  9  around which main wire rope  19  is wound and sub-guide sheave  10  around which sub-wire rope  20  is wound are rotatably provided to the back surface of the distal end of top boom member  8 F (the side surface of standing telescoping boom  8  in the swinging direction). Sub-sheave  12  around which sub-wire rope  20  is wound and a plurality of main sheaves  11  around which main wire rope  19  is wound are rotatably provided, in this order from the distal end side, to the ventral surface of the distal end of top boom member  8 F (the side surface of standing telescoping boom  8  in the direction opposite to the swinging direction). Moreover, jib support unit  8 G is provided at the distal end of top boom member  8 F. 
     An object to be carried is suspended on main hook block  13 . A plurality of hook sheaves  13 A around which main wire rope  19  is wound, and main hook  13 B which suspends an object to be carried are provided to main hook block  13 . An object to be carried is suspended on sub-hook block  14 . Sub-hook block  14  is provided with sub-hook  14 A on which an object to be carried is suspended. 
     Derricking cylinder  15  (gray portion) makes telescoping boom  8  stand and lie down and holds the attitude of telescoping boom  8 . Derricking cylinder  15  is composed of a hydraulic cylinder which is made up of cylinder unit  15 A and rod unit  15 B. In derricking cylinder  15 , an end of cylinder unit  15 A is swingably coupled to swivel base  7  through cylinder-side swinging shaft  15 C, and an end of rod unit  15 B is swingably coupled to base boom member  8 A of telescoping boom  8  through rod-side swinging shaft  15 D. In derricking cylinder  15 , head side oil chamber  15 E (see  FIG. 4 ) is connected to derricking direct-acting selector valve  28  (see  FIG. 4 ) of derricking hydraulic circuit  24  (see  FIG. 4 ) through derricking one side oil passage  29  (see  FIG. 4 ), and rod side oil chamber  15 F (see  FIG. 4 ) is connected to derricking direct-acting selector valve  28  through derricking other side oil passage  30  (see  FIG. 4 ). Moreover, derricking cylinder  15  includes head side hydraulic sensor  32  which is a head side hydraulic detecting section for detecting the value of hydraulic pressure Ph which is the head side hydraulic pressure of head side oil chamber  15 E, and rod side hydraulic sensor  33  which is a rod side hydraulic detecting section for detecting the value of hydraulic pressure Pr which is the rod side hydraulic pressure of rod side oil chamber  15 E Head side hydraulic sensor  32  and rod side hydraulic sensor  33  are connected to control apparatus  34  which will be described below (see  FIGS. 4 and 5 ). 
     In derricking cylinder  15 , the direction of movement of rod unit  15 B is changed by selective supply of hydraulic fluid to head side oil chamber  15 E and rod side oil chamber  15 F through derricking direct-acting selector valve  28 . Thus, in derricking cylinder  15 , hydraulic fluid is supplied to head side oil chamber  15 E in such a manner that rod unit  15 B is pushed out from cylinder unit  15 A so that base boom member  8 A stands, and hydraulic fluid is supplied to rod side oil chamber  15 F in such a manner that rod unit  15 B is pushed back to cylinder unit  15 A so that base boom member  8 A lies down. 
     As shown in  FIG. 2 , one side joint  16 A, which divides derricking one side oil passage  29  into a cylinder side part and a switching valve side part, is provided in the middle of derricking one side oil passage  29  for connection between head side oil chamber  15 E of derricking cylinder  15  (gray portion) and derricking direct-acting selector valve  28 . Similarly, other side joint  16 B, which divides derricking other side oil passage  30  into a cylinder side part and a switching valve side part, is provided in the middle of derricking other side oil passage  30  for connection between rod side oil chamber  15 F of derricking cylinder  15  and derricking direct-acting selector valve  28 . One side joint  16 A and other side joint  16 B are configured to close the ends of separated oil passages. Such a configuration prevents hydraulic fluid from flowing out from separated derricking one side oil passage  29  and derricking other side oil passage  30 . Further, in the middle of a communication line for connection between head side hydraulic sensor  32  and control apparatus  34 , and between rod side hydraulic sensor  33  and control apparatus  34 , connector  16 C (see  FIGS. 4 and 5 ), which divides the communication line into a sensor side part and a control apparatus  34  side part, is provided. 
     Derricking cylinder  15  is separated from swivel base  7  and telescoping boom  8  upon detachment of cylinder-side swinging shaft  15 C and rod-side swinging shaft  15 D. Derricking cylinder  15  is separated from derricking hydraulic circuit  24  (see  FIG. 4 ) upon separation of one side joint  164  and other side joint  16 B. Further, as for derricking cylinder  15 , separation of connector  16 C allows head side hydraulic sensor  32  and rod side hydraulic sensor  33  to be separated from control apparatus  34  (see  FIGS. 4 and 5 ). Thus, derricking cylinder  15  is configured to be separable from swivel base  7 , telescoping boom  8 , derricking hydraulic circuit  24 , and control apparatus  34 . 
     As shown in  FIG. 1 , main winch  17  draws in (winds up) and draws out (winds down) main wire rope  19 . Main winch  17  is configured such that main drum  17 B around which main wire rope  19  is wound can be rotated through main hydraulic motor  17 A. Main winch  17  is provided to swivel base  7  so that the rotation shaft of main drum  17 B can he orthogonal to the telescoping direction of telescoping boom  8 . As for main hydraulic motor  17 A, the rotation direction is changed between one direction and the other direction by selective supply of hydraulic fluid to a draw-in side plunger (hereinafter simply referred to as “draw-in side part”) and a draw-out side plunger (hereinafter simply referred to as “draw-out side part”). Thus, in main winch  17 , hydraulic fluid is supplied such that main hydraulic motor  17 A can rotate in one direction and main wire rope  19  wound around main drum  17 B can thus be drawn out, and hydraulic fluid is supplied such that main hydraulic motor  17 A can rotate in the other direction and main wire rope  19  can thus be drawn in while being wound around main drum  17 B. 
     Sub-winch  18  draws (winds up) and draws out (winds down) sub-wire rope  20 . Sub-winch  18  is configured such that sub-drum  18 B around which sub-wire rope  20  is wound is rotated through sub hydraulic motor  18 A. Sub-winch  18  is provided to swivel base  7  so that the rotation shaft of sub-drum  1813  can be orthogonal to the telescoping direction of telescoping boom  8 . As for sub hydraulic motor  18 A of sub-winch  18 , the rotation direction is changed between one direction and the other direction by selective supply of hydraulic fluid to the draw-in side part and the draw-out side part. Thus, in sub-winch  18 , hydraulic fluid is supplied such that sub hydraulic motor  18 A can rotate in one direction and sub-wire rope  20  wound around sub-drum  18 B can thus be drawn out, and hydraulic fluid is supplied such that sub hydraulic motor  18 A can rotate in the other direction and sub-wire rope  20  can thus be drawn in while being wound around sub-drum  18 B. 
     Main wire rope  19  is passed from main winch  17  to a plurality of main sheaves  11  and a plurality of hook sheaves  13 A through main guide sheave  9  and wound around them. An end of main wire rope  19  is fixed to top boom member  8 F. Further, sub-wire rope  20  from sub-winch  18  is connected to sub-hook block  14  through sub-guide sheave  10  and sub-sheave  12 . 
     Cabin  21  covers operator&#39;s seat  22  (see  FIG. 3 ). Cabin  21  is provided on a side of swivel base  7  adjacent to telescoping boom  8 . Operator&#39;s seat  22  is provided in cabin  21 . 
     As shown in  FIG. 3 , operator&#39;s seat  22  is provided rotation telescoping operation tool  22 A for performing rotation operation for swivel base  7  and telescoping operation for telescoping boom  8 , derricking operation tool  229  for performing draw-in and draw-out operation for main winch  17  and derricking operation for telescoping boom  8 , alarm apparatus  22 C serving as an informing section, safety apparatus  23  for inputting the work content or the like of crane  1 , and power switch  35  for crane  1 , for example. 
     Safety apparatus  23  is used to set the type of work showing the mode of use of telescoping boom  8 , and the number of turns. Safety apparatus  23  is made up of a display monitor such as a touch panel. The safety apparatus  23  allows various settings to be made from the display screen of the display monitor and serves as an informing section informing the operator of a warning or an alarm. 
     In crane  1  with such a configuration, crane apparatus  6  can be moved to an arbitrary position by running vehicle  2 . Moreover, in crane  1 , the lifting height and operating radius of crane apparatus  6  can be increased by making telescoping boom  8  stand at an arbitrary derricking angle with derricking cylinder  15  and making telescoping boom  8  telescope to an arbitrary boom length or connecting a jib. Further, for crane  1 , selection can be made between use of main winch  17  or use of sub-winch  18  according to the weight and the desired lifting rate of the object to be carried. Meanwhile, for crane  1 , the allowable lifting load can be changed by changing the number of turns of main wire rope  19  according to the weight of the object to be carried. 
     Derricking hydraulic circuit  24  related to derricking cylinder  15  in crane  1  will be now described with reference to  FIG. 4 . 
     As shown in  FIG. 4 , derricking hydraulic circuit  24  actuates derricking cylinder  15 . Derricking hydraulic circuit  24  includes derricking cylinder  15 , one side joint  16 A, other side joint  16 B, derricking operation tool  22 B, which is an operation tool for hydraulic cylinder, hydraulic pump  25 , derricking direct-acting selector valve  28 , derricking counter balance valve  31 , head side hydraulic sensor  32 , rod side hydraulic sensor  33 , and control apparatus  34 . 
     In derricking cylinder  15 , head side oil chamber  15 E (dark gray portion) connected to one port of derricking direct-acting selector valve  28  through derricking one side oil passage  29 . Further, in derricking cylinder  15 , rod side oil chamber  15 F (light gray portion) is connected to the other port of derricking direct-acting selector valve  28  through derricking other side oil passage  30 . In this case, derricking cylinder  15  is configured to be detachable from derricking direct-acting selector valve  28  through one side joint  16 A. Similarly, derricking cylinder  15  is detachable from derricking direct-acting selector valve  28  through other side joint  16 B. One side joint  16 A and other side joint  16 B are configured to block the passage of hydraulic fluid when derricking cylinder  15  is separated from derricking direct-acting selector valve  28 . Such a configuration prevents hydraulic fluid from flowing out from derricking one side oil passage  29  and derricking other side oil passage  30  from which derricking cylinder  15  is separated. 
     Derricking operation tool  22 B controls the behavior of derricking cylinder  15 . Derricking operation tool  22 B is configured to transmit a pump signal from the electromagnet of derricking direct-acting selector valve  28  to control apparatus  34 . When located in neutral position S through operation, derricking operation tool  22 B transmits a signal that instructs not to excite the electromagnet of derricking direct-acting selector valve  28 . When located in standing position U through operation, derricking operation tool  22 B transmits a signal that instructs to excite the electromagnet that opens one port of derricking direct-acting selector valve  28 , to control apparatus  34 . When located in lying position D through operation, derricking operation tool  22 B transmits a signal that instructs to excite the electromagnet that opens the other port of derricking direct-acting selector valve  28 , to control apparatus  34 . 
     Hydraulic pump  25  discharges hydraulic fluid. Hydraulic pump  25  is driven by engine  4 . Hydraulic fluid discharged from hydraulic pump  25  is supplied to derricking direct-acting selector valve  28 . Discharged oil passage  26  of hydraulic pump  25  is provided with relief valve  27 . 
     Derricking direct-acting selector valve  28  serving as a control valve switches the direction of hydraulic fluid supplied to derricking cylinder  15 . The supply port of derricking direct-acting selector valve  28  is connected to hydraulic pump  25  through discharged oil passage  26 . One port of derricking direct-acting selector valve  28  is connected to head side oil chamber  15 E of derricking cylinder  15  through derricking one side oil passage  29 . The other port of derricking direct-acting selector valve  28  is connected to rod side oil chamber  15 F of derricking cylinder  15  through derricking other side oil passage  30 . Further, derricking direct-acting selector valve  28  is connected to control apparatus  34 . 
     In derricking direct-acting selector valve  28 , when the electromagnet is not excited (derricking operation tool  22 B is located in neutral position S through operation), derricking one side oil passage  29  and derricking other side oil passage  30  are closed. This keeps the position of rod unit  15 B of derricking cylinder  15 . In derricking direct-acting selector valve  28 , when the electromagnet is excited such that one port can be opened (when derricking operation tool  22 B is located in standing position U through operation), hydraulic fluid from hydraulic pump  25  is supplied to head side oil chamber  15 E of derricking cylinder  15  through derricking one side oil passage  29 . Thus, in derricking cylinder  15 , rod unit  15 B is pushed out from cylinder unit  15 A so that telescoping boom  8  can stand. In derricking direct-acting selector valve  28 , when the electromagnet is excited such that the other port can be opened (when derricking operation tool  22 B is located in lying position D through operation), hydraulic fluid from hydraulic pump  25  is supplied to rod side oil chamber  15 F of derricking cylinder  15  through derricking other side oil passage  30 . Thus, in derricking cylinder  15 , rod unit  15 B is pushed back to cylinder unit  15 A so that telescoping boom  8  can lie down. Although derricking direct-acting selector valve  28  is a control valve for controlling the flow rate of hydraulic fluid in this embodiment, this is not necessarily the case and it may be a pressure control valve for controlling the supply pressure. 
     Derricking counter balance valve  31  prevents rod unit  15 B of derricking cylinder  15  from being pushed back by the load on telescoping boom  8 . Derricking counter balance valve  31  is provided to derricking one side oil passage  29 . Further, derricking counter balance valve  31  is configured such that the hydraulic pressure in derricking other side oil passage  30  is applied as pilot pressure. Derricking counter balance valve  31  always permits hydraulic fluid to flow into head side oil chamber  15 E of derricking cylinder  15 . On the other hand, derricking counter balance valve  31  permits the flow of hydraulic fluid to be discharged from head side oil chamber  15 E of derricking cylinder  15  only when rod side oil chamber  15 F of derricking cylinder  15  is supplied with hydraulic fluid. 
     Head side hydraulic sensor  32  and rod side hydraulic sensor  33  detect values of hydraulic pressure. Head side hydraulic sensor  32  is provided in head side oil chamber  15 E of derricking cylinder  15 , and is configured to detect hydraulic pressure Ph in head side oil chamber  15 E. Rod side hydraulic sensor  33  is provided in rod side oil chamber  15 F of derricking cylinder  15 , and is configured to detect hydraulic pressure Pr in rod side oil chamber  15 F. Head side hydraulic sensor  32  and rod side hydraulic sensor  33  are connected to control apparatus  34  through connector  16 C. In other words, head side hydraulic sensor  32  and rod side hydraulic sensor  33  are configured to be detachable from control apparatus  34  through connector  16 C. Further, head side hydraulic sensor  32  and rod side hydraulic sensor  33  are supplied with electric power from control apparatus  34 . 
     Crane  1  including derricking hydraulic circuit  24  with such a configuration controls derricking direct-acting selector valve  28  according to a signal from derricking operation tool  22 B, thereby changing the flow of hydraulic fluid supplied to derricking cylinder  15 . Thus, for crane  1 , telescoping boom  8  can be freely made stand and lie down with derricking cylinder  15  by the operation of derricking operation tool  22 B. 
     Next, with reference to  FIGS. 5 to 7 , the configuration of control apparatus  34  of crane  1  with the above-described configuration, determination of a poor connection of derricking cylinder  15  through control apparatus  34 , and protection control of derricking cylinder  15  will be described. 
     As shown in  FIG. 5 , control apparatus  34  controls the operation of derricking cylinder  15 . Substantively, control apparatus  34  may have a configuration in which a CPU, a ROM, a RAM, and an HDD, for example, are connected through a bus, or may include a one-chip LSI, or the like. Control apparatus  34  stores various programs or data for controlling the operation of derricking cylinder  15 . 
     Control apparatus  34  is connected to derricking operation tool  22 B and can obtain a signal indicating an operational position from derricking operation tool  22 B. 
     Control apparatus  34  is connected to alarm apparatus  22 C and can issue an alarm through alarm apparatus  22 C. 
     Control apparatus  34  is connected to safety apparatus  23  and can obtain information such as the type of work input from safety apparatus  23  and allows safety apparatus  23  to display various information, an alarm, and the like on the screen. 
     Control apparatus  34  is connected to derricking direct-acting selector valve  28  and can selectively excite the electromagnet of derricking direct-acting selector valve  28  based on the derricking signal obtained from derricking operation tool  22 B, thereby switching the position of the spool of derricking direct-acting selector valve  28 . 
     Control apparatus  34  is connected to head side hydraulic sensor  32  and rod side hydraulic sensor  33  and can obtain hydraulic pressure Ph value of head side oil chamber  15 E of derricking cylinder  15  from head side hydraulic sensor  32 , and hydraulic pressure Pr value of rod side oil chamber  15 F of derricking cylinder  15  from rod side hydraulic sensor  33 . Further, control apparatus  34  is connected to head side hydraulic sensor  32  and rod side hydraulic sensor  33  through connector  16 C. 
     Control apparatus  34  is connected to battery  36  via power switch  35  of crane  1  and can be supplied with electric power from battery  36  by turning on power switch  35  while electric power is supplied to head side hydraulic sensor  32  and rod side hydraulic sensor  33 . 
     With reference to  FIGS. 5 to 7 , determination control of a poor connection of derricking cylinder  15  of crane  1  with the above-described configuration, and protection control of derricking cylinder  15  will now be described. In this embodiment, in crane  1 , derricking cylinder  15  is assembled to swivel base  7  and telescoping boom  8 . 
     As shown in  FIG. 5 , control apparatus  34  of crane  1  is supplied with electric power from battery  36  by turning on power switch  35 . When power is supplied from battery  36 , control apparatus  34  starts to supply electric power to head side hydraulic sensor  32  and rod side hydraulic sensor  33 . In other words, control apparatus  34  obtains hydraulic pressure Ph of head side oil chamber  15 E at a predetermined interval from head side hydraulic sensor  32  and obtains hydraulic pressure Pr of rod side oil chamber  15 F at a predetermined interval from rod side hydraulic sensor  33 . Receiving a derricking signal (a control signal for derricking direct-acting selector valve  28 ) from derricking operation tool  22 B for the first time after the initiation of supply of electric power to head side hydraulic sensor  32  and rod side hydraulic sensor  33 , control apparatus  34  controls derricking direct-acting selector valve  28  so that the amount of hydraulic fluid supplied to derricking cylinder  15  can be less than or equal to predetermined value F regardless of the amount of operation of derricking operation tool  22 B. 
     As shown in  FIG. 6 , when hydraulic pressure Pr of rod side oil chamber  15 F obtained by the time when predetermined time T elapses is greater than or equal to hydraulic pressure Ph of head side oil chamber  15 E (e.g., hydraulic pressure Pr 1  or hydraulic pressure Pr 2  in  FIG. 6 ), control apparatus  34  determines that rod side oil chamber  15 F (light gray portion) of derricking cylinder  15  and derricking direct-acting selector valve  28  are not properly connected to each other through other side joint  16 B. Control apparatus  34  displays a warning on safety apparatus  23 , which is a joint informing section, and issues an alarm from alarm apparatus  22 C. Further, control apparatus  34  controls derricking direct-acting selector valve  28  so that the supply of hydraulic fluid to derricking cylinder  15  is stopped. 
     Next, with reference to  FIG. 7 , determination control of a poor connection of derricking cylinder  15  and protection control of derricking cylinder  15  through control apparatus  34  of crane  1  will be described. In this embodiment, it is assumed that control apparatus  34  of crane  1  starts to be supplied with electric power from battery  36  by operation of power switch  35  after assembling derricking cylinder  15 . 
     As shown in  FIG. 7 , in Step S 110 , control apparatus  34  determines whether or not the control signal of derricking direct-acting selector valve  28  has been received from derricking operation tool  22 B. 
     Consequently, if the control signal of derricking direct-acting selector valve  28  has been received from derricking operation tool  22 B, control apparatus  34  advances the process to Step S 120 . 
     In contrast, if the control signal of derricking direct-acting selector valve  28  has not been received from derricking operation tool  22 B, control apparatus  34  advances the process to Step S 110 . 
     In Step S 120 , control apparatus  34  determines whether or not the control signal of derricking direct-acting selector valve  28  has been received from derricking operation tool  22 B for the first time after receiving electric power from battery  36 . 
     Consequently, if the control signal of derricking direct-acting selector valve  28  has been received from derricking operation tool  22 B for the first time after receiving electric power from battery  36 , control apparatus  34  advances the process to Step S 130 . 
     In contrast, if the control signal of derricking direct-acting selector valve  28  has already been received from derricking operation tool  22 B after receiving electric power from battery  36 , control apparatus  34  advances the process to Step S 170 . 
     In Step S 130 , control apparatus  34  controls derricking direct-acting selector valve  28  so that the amount of hydraulic fluid supplied to derricking cylinder  15  is less than equal to predetermined value F, and advances the process to Step S 140 . 
     In Step S 140 , control apparatus  34  obtains hydraulic pressure Ph of head side oil chamber  15 E and hydraulic pressure Pr of rod side oil chamber  15 F and advances the process to Step S 150 . 
     In Step S 150 , control apparatus  34  determines whether or not obtained hydraulic pressure Ph of head side oil chamber  15 E is greater than hydraulic pressure Pr of rod side oil chamber  15 F. 
     Consequently, if obtained hydraulic pressure Ph of head side oil chamber  15 E is determined to be greater than hydraulic pressure Pr of rod side oil chamber  15 F, control apparatus  34  advances the process to Step S 160 . 
     In contrast, if obtained hydraulic pressure Ph of head side oil chamber  15 E is determined to be not greater than hydraulic pressure Pr of rod side oil chamber  15 F, that is, if hydraulic pressure Pr of rod side oil chamber  15 F is greater than or equal to hydraulic pressure Ph of head side oil chamber  15 E, control apparatus  34  advances the process to Step S 180 . 
     In Step S 160 , control apparatus  34  determines whether or not predetermined time T has elapsed after the initiation of control of derricking direct-acting selector valve  28  so that the amount of hydraulic fluid supplied to derricking cylinder  15  is less than or equal to predetermined value F. 
     Consequently, if it is determined that predetermined time T has elapsed after the initiation of control of derricking direct-acting selector valve  28  so that the amount of hydraulic fluid supplied to derricking cylinder  15  is less than or equal to predetermined value F, control apparatus  34  advances the process to Step S 170 . 
     In contrast, if it is determined that predetermined time has not elapsed after the initiation of control of derricking direct-acting selector valve  28  so that the amount of hydraulic fluid supplied to derricking cylinder  15  is less than or equal to predetermined value F, control apparatus  34  advances the process to Step S 140 . 
     In Step S 170 , control apparatus  34  controls derricking direct-acting selector valve  28  so that hydraulic fluid supplied to derricking cylinder  15  is supplied according to the amount of operation of derricking operation tool  22 B, and advances the process to Step S 110 . 
     In Step S 180 , control apparatus  34  determines that other side joint  16 B has a poor connection, and advances the process to Step S 190 . 
     In Step S 190 , control apparatus  34  controls derricking direct-acting selector valve  28  so that supply of hydraulic fluid to derricking cylinder  15  stops, and advances the process to Step S 200 . 
     In Step S 200 , control apparatus  34  informs the operator of an alarm saying that other side joint  16 B has a poor connection through safety apparatus  23 , which is an informing section, and further informs the operator through alarm apparatus  22 C, and advances the process to Step S 110 . 
     With this configuration, in crane  1 , when electric power is supplied to head side hydraulic sensor  32  and rod side hydraulic sensor  33  through the operation of power switch  35 , it is determined that derricking cylinder  15  is assembled to swivel base  7  and derricking cylinder  15 &#39;s poor connection determination control and protection control are started. In crane  1 , the connection state of other side joint  16 B, which provides a connection between rod side oil chamber  15 F and derricking direct-acting selector valve  28 , is determined according to the states of hydraulic pressure Pr of rod side oil chamber  15 F and hydraulic pressure Ph of head side oil chamber  15 E in derricking cylinder  15 . In this case, in crane  1 , derricking direct-acting selector valve  28  is controlled such that hydraulic fluid supplied to derricking cylinder  15  is less than or equal to predetermined value F. The increase rates of hydraulic pressure Pr of rod side oil chamber  15 F and hydraulic pressure Ph of head side oil chamber  15 E in derricking cylinder  15  are suppressed, thereby preventing the application of an excessive hydraulic pressure to derricking cylinder  15  due to the operation by the operator. In crane  1 , when it is determined that other side joint  16 B providing a connection between rod side oil chamber  15 F of derricking cylinder  15  and derricking direct-acting selector valve  28  is not properly connected, derricking direct-acting selector valve  28  is controlled such that the supply of hydraulic fluid to derricking cylinder  15  is forcibly stopped. Further, in crane  1 , the operator is informed of the fact that derricking direct-acting selector valve  28  between derricking cylinder  15  and derricking hydraulic circuit  24  is not properly connected. Thus, the actuation of derricking cylinder  15  in poor connection with derricking hydraulic circuit  24  is suppressed, thereby properly protecting derricking cylinder  15 . 
     Although the above-described crane  1 , which is one embodiment of crane  1 , has a configuration including main winch  17  and sub-winch  18 , this is not necessarily the case, and it is only required that derricking cylinder  15  is configured to be detachable from vehicle  2 . Further, it is applicable to any hydraulic cylinder that is configured to be detachable from crane  1 . The above-described embodiment is mere illustration of a representative mode, and various modifications can be implemented without departing from the spirit of one embodiment. It is natural that it can be implemented in various other modes, the scope of the present invention is indicated by Claims, and equivalents and all modifications of the Claims should be included in the scope of the present invention. 
     INDUSTRIAL APPLICABILITY 
     The present invention is applicable to a crane. 
     REFERENCE SIGNS LIST 
     
         
           1  Crane 
           15  Derricking cylinder 
           15 E Head side oil chamber 
           15 F Rod side oil chamber 
           22 B Derricking operation tool 
           23  Safety apparatus 
           28  Derricking direct-acting selector valve 
           32  Head side hydraulic sensor 
           33  Rod side hydraulic sensor 
         Ph Hydraulic pressure in head side oil chamber 
         Pr Hydraulic pressure in rod side oil chamber 
           23  Safety apparatus