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CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a U.S. National stage application of International Application No. PCT/JP2015/068061, filed on Jun. 23, 2015. This U.S. National stage application claims priority under 35 U.S.C. §119(a) to Japanese Patent Application No. 2014-131345, filed in Japan on Jun. 26, 2014, and Japanese Patent Application No. 2015-052028, filed in Japan on Mar. 16, 2015, the entire contents of which are hereby incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    Field of the Invention 
         [0003]    The present invention relates to a quick coupler. 
         [0004]    Background Information 
         [0005]    Various types of attachments such as a bucket, a cutter, a breaker, a fork and the like are attached to a work vehicle such as a hydraulic excavator. A quick coupler is known as a component for easily attaching these types of attachments to the work vehicle. The quick coupler is attached to the work vehicle. 
         [0006]    For example, the quick coupler described in Japanese Laid-Open Patent Publication No. H7-166571 includes a fixed hook and a moveable hook and these hooks lock with two pins provided on the attachment whereby the attachment is connected to the quick coupler. 
         [0007]    When the attachment is attached to the quick coupler with the abovementioned hooks, a lock member is preferably provided to retain the pins in the hooks. For example, the quick coupler described in Japanese Laid-Open Patent Publication No. H7-166571 is made to retain the pins in the hooks by inserting a lock pin in a boss provided on the moveable hook. 
         [0008]    However, the lock pin is installed by an operator in the quick coupler described in Japanese Laid-Open Patent Publication No. H7-166571. Because this type of work is complicated, a retaining function is preferably carried out automatically with the lock member when attaching the attachment. 
         [0009]    A first arm and a second arm are pivotally attached via a support pin in the quick coupler described in Japanese Laid-open Patent Publication No. 2008-174920. Moreover, a hydraulic cylinder is attached across the first arm and the second arm. Due to the extension of the hydraulic cylinder, a gap between the first arm and the second arm widens whereby an attachment pin is connected to the first arm and the second arm. Moreover, the hydraulic cylinder rotates so as to become horizontal due to the extension of the hydraulic cylinder. Retaining is maintained by a lock member due to the rotation of the hydraulic cylinder and the rotation of the lock member. 
       SUMMARY 
       [0010]    A retaining function can be automatically actuated due to the lock member when attaching the attachment in the above quick coupler described in Japanese Laid-open Patent Publication No. 2008-174920. However, in order to operate the lock member, the large action of rotating the hydraulic cylinder is required. As a result, there is a problem that the size of the quick coupler is increased. 
         [0011]    An object of the present invention is to provide a quick coupler that is small in size and that can enable the automatic actuation of a retaining function with the lock member when attaching the attachment. 
         [0012]    A quick coupler according to a first aspect of the present invention is provided with a coupler body, a lock member, a second hook, a hydraulic cylinder, and a connecting pin. The coupler body includes a first hook. The lock member is able to move between a locking position and an unlocking position. The lock member protrudes into an opening of the first hook in the locking position. The lock member retracts from the locking position in the unlocking position. The second hook is provided in a manner that allows sliding with respect to the coupler body. The hydraulic cylinder includes a first end part connected to the coupler body and a second end portion connected to the second hook. The hydraulic cylinder extends to cause the second hook to slide away from the first hook. The hydraulic cylinder contracts to cause the second hook to slide towards the first hook. The connecting pin connects the first end portion of the hydraulic cylinder and the coupler body. The coupler body includes a support hole. The support hole moveably supports the connecting pin in the extension and contraction direction of the hydraulic cylinder. The first end portion of the hydraulic cylinder moves away from the second end portion within the movability range of the connecting pin and thereby moves the lock member from the unlocking position to the locking position. 
         [0013]    The second end portion of the hydraulic cylinder moves way from the first end portion due to the extension of the hydraulic cylinder in the quick coupler according to the present aspect. As a result, the second hook slides away from the first hook. Consequently, the first hook and the second hook both lock with the pins of the attachment and the attachment is attached to the quick coupler. 
         [0014]    Moreover, the support hole in the coupler body moveably supports the connecting pin in the extension and contraction direction of the hydraulic cylinder. As a result, when the hydraulic cylinder extends, the first end portion of the hydraulic cylinder also moves away from the second end portion within the movability range of the connecting pin. The lock member moves from the unlocking position to the locking position along with the motion of the first end portion. 
         [0015]    As described above, the retaining function can be automatically actuated due to the lock member when attaching the attachment in the quick coupler according to the present aspect. Moreover, by allowing the first end portion of the hydraulic cylinder to move within the movability range of the connecting pin, the retaining function by the lock member can be actuated. Therefore, the retaining function with the lock member can be actuated due to a small motion of the first end portion. As a result, the size of the quick coupler can be reduced. 
         [0016]    Preferably, the support hole is an elongated hole that extends in the extension and contraction direction of the hydraulic cylinder. In this case, the first end portion moves in the extension and contraction direction of the hydraulic cylinder along the elongated hole whereby the retaining function with the lock member can be actuated. As a result, the structure of the quick coupler can be simplified. 
         [0017]    The quick coupler preferably is a member for attaching an attachment via a first pin and a second pin and the coupler body further includes a pin retaining portion. The pin retaining portion is disposed facing the opening of the second hook. The width of a gap between the tip of the second hook and the pin retaining portion is less than the diameter of the second pin when the second hook is locked with the second pin. 
         [0018]    In this case, even if the first hook is damaged, the pin is prevented from going through the gap between the tip of the second hook and the pin retaining portion. As a result, detachment of the attachment can be prevented. 
         [0019]    The quick coupler is preferably further provided with an urging member. The urging member urges the second end portion so that the second end portion moves away from the first end portion. In this case, even if the extension force of the hydraulic cylinder is lost due to a breakdown of the hydraulic system, the second hook is maintained in the locked state with the pin due to the urging member. Moreover, because the state of the first end portion being spaced away from the second end portion is maintained by the urging member, the lock member is held in the locking position. As a result, detachment of the attachment can be prevented. 
         [0020]    The urging member preferably is disposed inside the hydraulic cylinder. In this case, when the quick coupler is operated, the urging member is prevented from coming into contact with another member such as a hydraulic pipe around the hydraulic cylinder. 
         [0021]    The quick coupler is preferably further provided with an elastic member inserted into the support hole. In this case, resistance is brought about due to the elastic force of the elastic member when the first end portion moves. As a result, the timing of the actuation or the release of the retaining function with the lock member can be adjusted. 
         [0022]    The lock member preferably includes a proximal end portion, a distal end portion, and a recessed portion. The proximal end portion is supported in a rotatable manner on the coupler body. The distal end portion protrudes into the opening of the first hook in the locking position. The recessed portion is positioned between the proximal end portion and the distal end portion. The first end portion of the hydraulic cylinder includes a convex portion that protrudes towards the lock member. The lock member is positioned in the unlocking position when the convex portion is positioned in the recessed portion. 
         [0023]    In this case, the lock member can be positioned in the unlocking position by disposing the first end portion in the position so that the convex portion is positioned in the recessed portion. 
         [0024]    The lock member preferably includes an inclined surface connected to the recessed portion. The inclined surface is disposed in the direction from the second end portion to the first end portion with respect to the recessed portion. The convex portion moves from the recessed portion to the inclined surface and presses against the inclined surface whereby the lock member moves to the locking position. 
         [0025]    In this case, the convex portion moves from the recessed portion to the inclined surface and presses against the inclined surface when the hydraulic cylinder extends and the first end portion moves in the direction away from the second end portion. As a result, the lock member can be moved from the unlocking position to the locking position. 
         [0026]    The coupler body preferably includes a wall portion. The wall portion is disposed facing the first end portion in the extension and contraction direction of the hydraulic cylinder. In this case, the hydraulic cylinder remains inside the coupler body due to the wall portion even if the connecting pin is damaged. As a result, the pins of the attachment can be prevented from coming off from the first hook and the second hook. As a result, detachment of the attachment can be prevented. 
         [0027]    The first end portion of the hydraulic cylinder preferably moves toward the second end portion within the movability range of the connecting pin whereby the lock member is moved from the locking position to the unlocking position. In this case, the retaining function with the lock member can be automatically released when removing the attachment. Moreover, by allowing the first end portion of the hydraulic cylinder to move within the movability range of the connecting pin, the retaining function by the lock member can be released. Therefore, the retaining function with the lock member can be released due to a small motion of the first end portion. As a result, the size of the quick coupler can be reduced. 
         [0028]    The second hook preferably includes a protruding portion. The coupler body includes a groove in which the protruding portion is disposed. The protruding portion moves along the groove whereby the second hook slides with respect to the coupler body. Preferably, a stopper member for retaining the second hook is attached to the groove. In this case, the retaining of the second hook can be strengthened. 
         [0029]    Next, a first aspect of the hydraulic cylinder will be discussed. 
         [0030]    Conventionally, a spring is provided inside the hydraulic cylinder, and the position of a piston is held in a predetermined position with the force of the spring when no hydraulic fluid is supplied, and the spring is compressed and the piston contracts when hydraulic fluid is supplied (see, for example, Japanese Laid-Open Patent Publication No. H05-256307). 
         [0031]    The spring is disposed on the outer periphery of a piston rod via a spring seat in the hydraulic cylinder described in Japanese Laid-Open Patent Publication No. H05-256307. Spring seats are disposed on both ends of the spring and are provided to prevent the spring from becoming excessively compressed. 
         [0032]    However, because the spring seats are disposed for bearing the spring in the hydraulic cylinder described in Japanese Laid-Open Patent Publication No. H05-256307, the spring can only be contracted to the position where the two spring seats come into contact and a loss occurs in the contraction margin. 
         [0033]    As a result, there is a need for the size of the hydraulic cylinder itself to be increased to make the stroke larger. 
         [0034]    The hydraulic cylinder according to the present aspect may be provided with the following features for the purpose of providing a hydraulic cylinder that takes into account the above conventional problem. 
         [0035]    The hydraulic cylinder is provided with a cylinder tube, a piston rod, a piston, and a spring member. The piston rod is inserted into the cylinder tube such that the longitudinal direction of the piston rod extends in the extension and contraction direction. The piston is fixed to the piston rod and slides inside the cylinder tube. The spring member is disposed in the extension and contraction direction of the piston rod and urges the piston rod in the extension direction. An opening is held on an end surface on the contraction direction side of the piston rod and an internal space is formed from the opening in the extension direction. The spring member is inserted in the internal space. 
         [0036]    According to the hydraulic cylinder as in the present aspect, a hydraulic cylinder that can achieve a large stroke in a compact manner can be provided. 
         [0037]    A cylindrical guide member is preferably further provided. The spring member has a coil shape. The guide member is disposed inside the spring member so that the longitudinal direction of the guide member follows the extension and contraction direction. One end of the guide member is held on the bottom surface of the cylinder tube facing the end surface of the piston rod. 
         [0038]    At least one end side of the guide member preferably has a cylindrical shape. The cylinder tube includes a protruding portion that projects from the bottom surface in the extension direction. The one end of the guide member is held on the bottom surface due to the protruding portion being fitted to the cylindrical inner side. 
         [0039]    The spring member preferably has a coil shape. The length of the spring member is less than the natural length in the state in which the hydraulic cylinder is extended the most. 
         [0040]    The hydraulic cylinder is further preferably provided with a ring-like member. The ring-like member is disposed between the outer circumferential surface of the guide member and the inner circumferential surface of the internal space and slides on the outer circumferential surface and the inner circumferential surface. The spring member is divided into a first spring member and a second spring member with the ring-like member sandwiched therebetween. 
         [0041]    The guide member preferably includes a protrusion that protrudes toward the outside in the radial direction. The end on the extension direction side of the first spring member abuts the inner surface on the extension direction side of the internal space. The end on the contraction direction side of the second spring member abuts the protrusion. 
         [0042]    The guide member preferably is formed integrally with the bottom surface. 
         [0043]    The spring member preferably has a coil shape. The cylinder tube includes a protruding portion that projects in the extension direction from the bottom surface facing the end surface of the piston rod. The protruding portion fits into the inside of the end of the spring member. 
         [0044]    According to the present invention, a quick coupler can be provided that is small in size and that can enable the automatic actuation of a retaining function with the lock member when attaching the attachment. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0045]      FIG. 1  is a side surface view of a portion of a hydraulic excavator including a quick coupler according to a first embodiment attached thereto. 
           [0046]      FIG. 2  is a perspective view of the quick coupler according to the first embodiment. 
           [0047]      FIG. 3  is an exploded view of the quick coupler according to the first embodiment. 
           [0048]      FIG. 4  is a side surface sectional view of a schematic configuration of the inside of the quick coupler according to the first embodiment. 
           [0049]      FIG. 5  is a side surface sectional view of a schematic configuration of the inside of the quick coupler according to the first embodiment. 
           [0050]      FIG. 6  is a side surface sectional view of a schematic configuration of the inside of the quick coupler according to the first embodiment. 
           [0051]      FIG. 7  is a side surface sectional view of a schematic configuration of the inside of the quick coupler according to the first embodiment. 
           [0052]      FIG. 8  is a side surface sectional view of a schematic configuration of the inside of the quick coupler according to the first embodiment. 
           [0053]      FIG. 9  is a side surface view of a support hole and an elastic member. 
           [0054]      FIG. 10  is a side surface view of the support hole and the elastic member. 
           [0055]      FIG. 11  is a side surface sectional view of a schematic configuration of the inside of the quick coupler according to a second embodiment. 
           [0056]      FIG. 12  is an external view of a hydraulic cylinder. 
           [0057]      FIG. 13  is a view of the internal configuration while the hydraulic cylinder is contracted. 
           [0058]      FIG. 14  is a view of the internal configuration while the hydraulic cylinder is extended. 
           [0059]      FIG. 15  is a view of the internal configuration while the hydraulic cylinder is contracted according to a modified example. 
           [0060]      FIG. 16  is a view of the internal configuration while the hydraulic cylinder in  FIG. 15  is extended. 
           [0061]      FIG. 17  is a perspective view of the external appearance of a hydraulic cylinder according to a modified example. 
           [0062]      FIG. 18  is a view of the internal configuration while the hydraulic cylinder in  FIG. 17  is contracted. 
           [0063]      FIG. 19  is a view of the internal configuration while the hydraulic cylinder in  FIG. 17  is extended. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0064]    A quick coupler according to the embodiments will be discussed with reference to the drawings. 
         [0065]      FIG. 1  is a side surface view of a portion of a hydraulic excavator  100  including a quick coupler according to a first embodiment attached thereto. The work vehicle  100  is a hydraulic excavator for example. However, the work vehicle  100  is not limited to a hydraulic excavator and may be another type of work vehicle. 
         [0066]    As illustrated in  FIG. 1 , the work vehicle  100  includes an arm  101 , a link member  102 , and an attachment  103 . While the attachment  103  is depicted as a bucket as an example in  FIG. 1 , the attachment  103  is not limited to a bucket and may be another type of attachment such as a cutter, a breaker, or a fork and the like. 
         [0067]    A quick coupler  1  is connected to the arm  101  via an arm pin  104 . The quick coupler  1  is connected to the link member  102  via a link pin  105 . The quick coupler  1  is connected to the attachment  103  via a first pin  106  and a second pin  107 . 
         [0068]      FIG. 2  is a perspective view of the quick coupler  1 .  FIG. 3  is an exploded view of the quick coupler  1 . As illustrated in  FIGS. 2 and 3 , the quick coupler  1  includes a coupler body  2  and a second hook  3 . The coupler body  2  includes an arm pin support hole  11  and a link pin support hole  12 . The arm pin  104  is inserted into the arm pin support hole  11 . The link pin  105  is inserted into the link pin support hole  12 . 
         [0069]    The coupler body  2  includes a first hook  4 . The first hook  4  locks the first pin  106 . The second hook  3  is separate from the coupler body  2 . The second hook  3  locks the second pin  107 . 
         [0070]    The direction in which the link pin support hole  12  is positioned with respect to the arm pin support hole  11  is referred to as forward and the opposite direction is referred to rearward in the quick coupler  1  according to the present embodiment. The direction where the first hook  4  and the second hook  3  are positioned with regard to the arm pin support hole  11  and the link pin support hole  12  is referred to as downward and the opposite direction is referred to as upward. The direction of the axis line of the arm pin support hole  11  and the axis line of the link pin support hole  12  is referred to as the width direction or laterally. However, the terms indicating the directions are specified when viewing the quick coupler  1  as described above and are not limited to the attachment direction of the quick coupler  1 . 
         [0071]    The coupler body  2  includes a first side surface portion  13 , a second side surface portion  14 , and a wall portion  15 . The first side surface portion  13  and the second side surface portion  14  have a planar shape that extends in the front-back direction and the up-down direction. The first side surface portion  13  and the second side surface portion  14  are disposed with a gap therebetween in the width direction. The wall portion  15  extends in the width direction and is disposed across the first side surface portion  13  and the second side surface portion  14 . 
         [0072]    The coupler body  2  includes a first upper surface portion  16  and a second upper surface portion  17 . The first upper surface portion  16  and the second upper surface portion  17  have a planar shape that extends in the front-back direction and the up-down direction. The first upper surface portion  16  protrudes upward from the first side surface portion  13 . The second upper surface portion  17  protrudes upward from the second side surface portion  14 . The arm pin support hole  11  and the link pin support hole  12  are provided so as to penetrate the first upper surface portion  16  and the second upper surface portion  17  in the width direction. 
         [0073]      FIG. 4  is a side surface sectional view of a schematic configuration of the inside of the quick coupler  1 . As illustrated in  FIG. 4 , the first hook  4  and the second hook  3  are provided respectively with openings for locking the first pin  106  and the second pin  107 , and are members including a curved recessed portion. The first hook  4  and the second hook  3  open in directions opposite from each other. Specifically the first hook  4  opens toward the rear. The second hook  3  opens toward the front. The second hook  3  is disposed in front of the first hook  4 . The coupler body  2  includes a pin retaining portion  29 . The pin retaining portion  29  is disposed facing the opening of the second hook  3 . 
         [0074]    The second hook  3  is supported by the coupler body  2  in a manner that allows sliding in the front-back direction. Specifically, a groove  18  that extends in the front-back direction is provided on the inside side surface of the first side surface portion  13 . Although not illustrated in the drawings, a groove that extends in the front-back direction is provided similarly on the inside side surface of the second side surface portion  14 . As illustrated in  FIG. 3 , the side surfaces of second hook  3  are each provided with protruding parts  19   a  and  19   b  that extend in the front-back direction. The protruding portion  19   a  of the second hook  3  is disposed inside the groove  18  on the first side surface portion  13 . The protruding portion  19   b  of the second hook  3  is disposed inside the groove of the second side surface portion  14 . The protruding parts  19  move along the groove  18  whereby the second hook  3  slides with respect to the coupler body  2 . A component  3   a  connected to the opening of the recessed portion of the second hook  3  is parallel to the direction of the groove  18  extending in the front-back direction as seen from the side surface as illustrated in  FIG. 4 . 
         [0075]    As illustrated in  FIG. 3 , the quick coupler  1  is provided with a hydraulic cylinder  5 , a first urging member  6 , a second urging member  7 , and a lock member  8 . The hydraulic cylinder  5  is connected to a hydraulic system of the work vehicle  100  via a hydraulic pipe  21 . The hydraulic cylinder  5  extends and contracts due to hydraulic pressure from the hydraulic pipe  21 . 
         [0076]    The hydraulic cylinder  5  includes a first end portion  22  and a second end portion  23 . The first end portion  22  is connected to the coupler body  2 . The second end portion  23  is connected to the second hook  3 . Specifically, the hydraulic cylinder  5  includes a cylinder tube  24  and a piston rod  25 . The first end portion  22  is included in the cylinder tube  24 . The second end portion  23  is included in the piston rod  25 . 
         [0077]    The coupler body  2  includes a support hole  26 . The support hole  26  is provided so as to penetrate the first side surface portion  13  and the second side surface portion  14 . The first end portion  22  is supported by the coupler body  2  via a first connecting pin  27 . The first end portion  22  includes a through-hole  221  that extends in the width direction. The first connecting pin  27  is inserted into the first end portion  22  and the support hole  26 . The first connecting pin  27  connects the first end portion  22  of the hydraulic cylinder  5  to the coupler body  2 . The support hole  26  is an elongated hole that extends the extension and contraction direction of the hydraulic cylinder, that is, in the front-back direction. As a result, the support hole  26  moveably supports the first connecting pin  27  in the extension and contraction direction of the hydraulic cylinder  5 . 
         [0078]    The second end portion  23  is connected to the second hook  3  via a second connecting pin  28 . Specifically, the second end portion  23  includes a through-hole  231  that extends in the width direction. Moreover, the front portion of the second hook  3  includes a through-hole  301  that extends in the width direction. The second connecting pin  28  is inserted into the through-hole  231  of the second end portion  23  and the through-hole  301  of the second hook  3 . 
         [0079]      FIG. 5  is a side surface sectional view illustrating a state in which the hydraulic cylinder  5  is extended from the state illustrated in  FIG. 4 .  FIG. 6  is a side surface sectional view illustrating a state in which the hydraulic cylinder  5  is further extended from the state illustrated in  FIG. 5 . As illustrated in  FIGS. 5 and 6 , the second end portion  23  moves away from the first end portion  22  due to the extension of the hydraulic cylinder  5 . As a result, the hydraulic cylinder  5  causes the second hook  3  to slide so that the second hook  3  moves away from the first hook  4 . 
         [0080]      FIG. 7  is a side surface sectional view illustrating a state in which the hydraulic cylinder  5  is contracted from the state illustrated in  FIG. 6 .  FIG. 8  is a side surface sectional view illustrating a state in which the hydraulic cylinder  5  is contracted further from the state illustrated in  FIG. 7 . As illustrated in  FIGS. 7 and 8 , the second end portion  23  moves toward the first end portion  22  due to the contraction of the hydraulic cylinder  5 . As a result, the hydraulic cylinder  5  causes the second hook  3  to slide so as to move closer to the first hook  4 . 
         [0081]    The first urging member  6  illustrated in  FIG. 3  urges the second end portion  23  so that the second end portion  23  moves away from the first end portion  22 . As illustrated in  FIG. 4 , the first urging member  6  includes a spring  31 , a spring cover  32 , and a shaft  33 . The spring  31  is a coil spring and is disposed inside the spring cover  32 . As illustrated in  FIG. 5 , an end portion  34  of the spring cover  32  is supported by the coupler body  2  via a connecting pin  35 . The spring  31  inside the spring cover  32  is in a compressed state and presses the shaft  33 . An end portion  36  of the shaft  33  protrudes from the spring cover  32 . The second hook  3  includes a connecting portion  37 . The connecting portion  37  is provided on the upper surface of the second hook  3 . The end portion  36  of the shaft  33  is connected to the connecting portion  37  via a connecting pin  40 . The second urging member  7  has the same configuration as the first urging member  6  and a detailed explanation will be omitted. 
         [0082]    The abovementioned wall portion  15  is disposed above the first urging member  6  and the second urging member  7 . Moreover, a portion of the wall portion  15  is disposed behind the hydraulic cylinder  5  and is disposed facing the first end portion  22  in the extension and contraction direction of the hydraulic cylinder  5 . 
         [0083]    As illustrated in  FIGS. 2 and 3 , the wall portion  15  includes an opening  151 . The opening  151  is positioned above the first end portion  22 . The hydraulic pipe  21  passes through the opening  151  and is guided into the coupler body  2 . 
         [0084]    The lock member  8  is disposed above the first hook  4 . The lock member  8  is connected to the coupler body  2  via a lock connecting pin  48 . As illustrated in  FIG. 3 , the coupler body  2  includes a through-hole  51 . The lock member  8  includes a through-hole  52 . The lock connecting pin  48  is inserted into the through-hole  51  of the coupler body  2  and the through-hole  52  of the lock member  8 . 
         [0085]    The lock member  8  includes a proximal end portion  38  and a distal end portion  39 . The proximal end portion  38  is supported in a rotatable manner on the coupler body  2 . The distal end portion  39  has a hook-like shape that is curved downward. That is, the distal end portion  39  includes a hook-like shape that is curved toward the first hook  4 . 
         [0086]    The lock member  8  is provided to allow movement between a locking position and an unlocking position.  FIG. 4  illustrates a state of the lock member  8  positioned in the unlocking position.  FIG. 6  illustrates a state of the lock member  8  positioned in the locking position. 
         [0087]    As illustrated in  FIG. 6 , the distal end portion  39  of the lock member  8  protrudes into the opening of the first hook  4  in the locking position. As a result, the first pin  106  is retained in the first hook  4 . As illustrated in  FIG. 4 , the distal end portion  39  of the lock member  8  enters a state of retracting from the locking position in the unlocking position. Specifically, the distal end portion  39  of the lock member  8  enters a state of retracting from the inside of the opening of the first hook  4  in the unlocking position. 
         [0088]    The first end portion  22  of the hydraulic cylinder  5  moves to a holding position by moving away from the second end portion  23 .  FIG. 6  illustrates a state of the first end portion  22  positioned in the holding position. The first end portion  22  holds the lock member  8  in the locking position in the holding position. Conversely, the first end portion  22  moves to a release position by moving toward the second end portion  23 .  FIG. 4  illustrates a state of the first end portion  22  positioned in the release position. The first end portion  22  releases the hold of the lock member  8  in the release position. 
         [0089]    Specifically, the first end portion  22  of the hydraulic cylinder  5  includes a convex portion  222  that protrudes toward the lock member  8 . The convex portion  222  protrudes downward. The lock member  8  includes a recessed portion  41  and a receiving portion  42 . The recessed portion  41  and the receiving portion  42  are positioned between the proximal end portion  38  and the distal end portion  39 . The recessed portion  41  has a shape that is recessed downward from the upper surface of the lock member  8 . The receiving portion  42  is positioned behind the recessed portion  41 . 
         [0090]    As illustrated in  FIG. 6 , the convex portion  222  comes into contact with the receiving portion  42  while the first end portion  22  is in the holding position, and the convex portion  222  presses the lock member  8  toward the first hook  4 . As a result, the lock member  8  is held in the locking position. As illustrated in  FIG. 4 , the convex portion  222  is positioned inside the recessed portion  41  while the first end portion  22  is positioned in the release position. As a result, the lock member  8  is held in the unlocking position. 
         [0091]    More specifically, the lock member  8  includes an inclined surface  43  and a step portion  44  connected to the recessed portion  41 . The inclined surface  43  and the step portion  44  are positioned between the proximal end portion  38  and the distal end portion  39 . The inclined surface  43  is disposed in the direction extending from the second end portion  23  to the first end portion  22  with respect to the recessed portion  41 . That is, the inclined surface  43  is disposed behind the recessed portion  41 . The step portion  44  is disposed in the direction extending from the first end portion  22  to the second end portion  23  with respect to the recessed portion  41 . That is, the step portion  44  is disposed in front of the recessed portion  41 . 
         [0092]    As illustrated in  FIGS. 4 to 6 , the convex portion  222  moves from the recessed portion  41  to the inclined surface  43  and presses against the inclined surface  43  whereby the lock member  8  moves to the locking position. Moreover, as illustrated in  FIGS. 7 and 8 , the convex portion  222  moves from the recessed portion  41  to the step portion  44  and presses against the step portion  44  whereby the lock member  8  rotates and moves to the unlocking position. 
         [0093]    An elastic member  45  illustrated in  FIG. 3  is inserted into the abovementioned support hole  26 . The elastic member  45  is made of rubber for example. However, the elastic member  45  is not limited to rubber and may be another material so long as the material produces an elastic force. The elastic member  45  has a long thin shape that follows the support hole  26 .  FIG. 9  is a side surface view of the support hole  26  and the elastic member  45 . As illustrated in  FIG. 9 , the elastic member  45  is disposed forward of the first connecting pin  27  inside the support hole  26 . That is, the elastic member  45  is disposed so as to be compressed by the first connecting pin  27  as illustrated in  FIG. 10  when the hydraulic cylinder  5  contracts. That is, the elastic member  45  is disposed so that the first connecting pin  27  receives resistance due to an elastic force when the first end portion  22  moves from the holding position to the release position. As illustrated in  FIGS. 2 and 3 , the support hole  26  is closed on the side by a cover member  46 . 
         [0094]    Next, operations for attaching the attachment  103  to the quick coupler  1  will be discussed. First, as illustrated in  FIG. 4 , the first pin  106  is locked with the first hook  4  (see arrow A 1 ). Further, the quick coupler  1  or the attachment  103  rotates around the first pin  106  whereby the second pin  107  is disposed between the second hook  3  and the pin retaining portion  29  (see arrow A 2 ). The hydraulic cylinder  5  is then extended. 
         [0095]    As illustrated in  FIG. 5 , the first end portion  22  moves rearward along the support hole  26  so as to move away from the second end portion  23  when the hydraulic cylinder  5  extends. As a result, the convex portion  222  moves from the recessed portion  41  of the lock member  8  to the inclined surface  43  and the lock member  8  is rotated due to the convex portion  222  pressing against the inclined surface  43  (see arrow A 3 ). 
         [0096]    As illustrated in  FIG. 6 , the first end portion  22  then moves further rearward and when the first end portion  22  reaches the release position, the convex portion  222  presses against the receiving portion  42  of the lock member  8 . As a result, the lock member  8  reaches the locking position and the first pin  106  is retained in the first hook  4  due to the lock member  8 . Moreover, the convex portion  222  presses against the receiving portion  42  whereby the lock member  8  is held in the locking position. 
         [0097]    Moreover, the second end portion  23  moves forward so as to move away from the first end portion  22  due to the extension of the hydraulic cylinder  5 . As a result, the second hook  3  slides forward so as to approach the pin retaining portion  29  and locks the second pin  107  (see arrows A 4 ). The second hook  3  is held while the second hook  3  is locked with the second pin  107 . Because the second hook  3  applies pressure to the second pin  107  due to the hydraulic cylinder  5 , the first connecting pin  27  is firmly held at the rear end of the support hole  26 . As a result, the lock member  8  is firmly held in the locking position. 
         [0098]    As described above, the attachment  103  is attached to the quick coupler  1 . As illustrated in  FIG. 6 , the second hook  3  is nearest to the pin retaining portion  29  while the attachment  103  is attached to the quick coupler  1 . In this state, a width W 1  of the gap between the tip of the second hook  3  and the pin retaining portion  29  is less than a width W 2  of the opening of the second hook  3 . Moreover, the width W 1  of the gap between the tip of the second hook  3  and the pin retaining portion  29  is less than the diameter of the second pin  107 . 
         [0099]    Next, operations for detaching the attachment  103  from the quick coupler  1  will be discussed. As illustrated in  FIG. 7 , the second end portion  23  moves rearward so as to approach the first end portion  22  due to the contraction of the hydraulic cylinder  5 . As a result, the second hook  3  slides rearward so as to move away from the pin retaining portion  29  (see arrow A 5 ). As a result, the gap between the pin retaining portion  29  and the second hook  3  becomes wider than the diameter of the second pin  107 . 
         [0100]    The second hook  3  moves as far as the stoke end toward the rear due to the contraction of the hydraulic cylinder  5 . As illustrated in  FIG. 8 , the first end portion  22  moves forward along the support hole  26  so as to approach the second end portion  23  due to the further contraction of the hydraulic cylinder  5 . As a result, the convex portion  222  passes from the receiving portion  42  of the lock member  8  to the inclined surface  43  and moves to the recessed portion  41 . The convex portion  222  then rotates the lock member  8  by further moving rearward and locking with the step portion  44  (see arrow A 6 ). As a result, the lock member  8  moves to the unlocking position and the retaining function of the first pin  106  due to the lock member  8  is released. 
         [0101]    Next, the quick coupler  1  or the attachment  103  rotates around the first pin  106  whereby the second pin  107  is detached from between the second hook  3  and the pin retaining portion  29  (see arrow A 7 ). The first hook  4  then is detached from the first pin  106  (see arrow A 8 ). As described above, the attachment  103  is detached from the quick coupler  1 . 
         [0102]    Moving the lock member  8  to the locking position (arrow A 3  in  FIG. 5 ) and sliding the second hook  3  (arrow A 4  in  FIG. 6 ) may be performed in any order when attaching the attachment  103  to the quick coupler  1 . Similarly, moving the lock member  8  to the unlocking position (arrow A 6  in  FIG. 8 ) or sliding the second hook  3  (arrow A 5  in  FIG. 7 ) may be performed in any order when removing the attachment  103  from the quick coupler  1 . 
         [0103]    As described above, the retaining function can be automatically carried out due to the lock member  8  when attaching the attachment  103  to the quick coupler  1  according to the present embodiment. Moreover, the retaining function can be actuated by the lock member  8  by moving the first end portion  22  of the hydraulic cylinder  5  along the support hole  26 . As a result, the size of the quick coupler can be reduced. 
         [0104]    The width W 1  of the gap between the tip of the second hook  3  and the pin retaining portion  29  is less than the width W 2  of the opening of the second hook  3  while the second hook  3  is nearest the pin retaining portion  29 . Consequently, even if the first hook  4  is damaged, the second pin  107  is prevented from going through the gap between the tip of the second hook  3  and the pin retaining portion  29 . As a result, detachment of the attachment  103  can be prevented. 
         [0105]    The second end portion  23  is urged so that the second end portion  23  moves away from the first end portion  22  due to the first urging member  6  and the second urging member  7 . As a result, even if the extension force of the hydraulic cylinder  5  is lost due to a breakdown of the hydraulic system and the like, the second hook  3  is held in place by the first urging member  6  and the second urging member  7  while the second hook  3  is locked with the second pin  107 . Moreover, the lock member  8  is held in the locking position even if the extension force of the hydraulic cylinder  5  is lost because the state of the first end portion  22  being spaced away from the second end portion  23  is maintained due to the first urging member  6  and the second urging member  7 . As a result, detachment of the attachment  103  can be prevented. 
         [0106]    The elastic member  45  is inserted into the support hole  26 . That is, the first connecting pin  27  receives resistance due to the elastic force when the first end portion  22  moves from the holding position to the release position. As a result, the movement toward the release position of the first end portion  22  can be delayed. Consequently, the second pin  107  is first removed from the second hook  3  and then the lock member  8  can be released. The elastic member  45  may be disposed so that the lock member  8  is released first and then the second pin  107  is removed from the second hook  3 . 
         [0107]    The wall portion  15  of the coupler body  2  is disposed facing the first end portion  22  in the extension direction of the hydraulic cylinder  5 . As a result, the hydraulic cylinder  5  remains inside the coupler body  2  due to the wall portion  15  even if the first connecting pin  27  is damaged. As a result, the first pin  106  and the second pin  107  can be prevented from being respectively slipping out of the first hook  4  and the second hook  3 . As a result, detachment of the attachment  103  can be prevented. 
         [0108]    Next, a quick coupler  10  according to a second embodiment will be explained.  FIG. 11  is a side surface sectional view of a schematic configuration of the inside of the quick coupler  10  according to the second embodiment. The first urging member  6  and the second urging member  7  from the first embodiment are omitted in the quick coupler  10  according to the second embodiment, and a hydraulic cylinder  61  housing an urging member is provided in place of the first urging member  6  and the second urging member  7 . The structure of the hydraulic cylinder  61  is described below. 
         [0109]    A stopper spring member  94  for retaining the second hook  3  is provided in the groove  18  of the coupler body  2  in the quick coupler according to the second embodiment. However, the stopper spring member  94  may be omitted. The same reference numerals are attached to the components common to the first embodiment in  FIG. 11  and detailed explanations of these components are omitted. 
         [0110]    Next, the hydraulic cylinder  61  will be discussed in detail. 
         [0111]      FIG. 12  is an external view of the hydraulic cylinder  61  according to the embodiment.  FIG. 13  and  FIG. 14  are sectional views of the internal configuration of the hydraulic cylinder  61  of the present embodiment.  FIG. 13  illustrates a contracted state of the hydraulic cylinder  61  and  FIG. 14  illustrates an extended state of the hydraulic cylinder  61 . 
         [0112]    The hydraulic cylinder  61  of the present embodiment is provided with a cylinder tube  62 , a piston rod  63 , a piston  64 , a guide member  65 , a first urging member  66 , a second urging member  67 , and a hold ring  68 . 
         [0113]    The piston  64  of the hydraulic cylinder  61  of the present embodiment slides inside the cylinder tube  62  due to the supply of hydraulic fluid, and the piston rod  63  connected to the piston  64  extends and contracts. The extension direction of the piston rod  63  is indicated by arrow A and the direction in which the piston rod  63  is drawn into the cylinder tube  62  (also referred to as contraction direction) is indicated by arrow B. A second end portion  76  of the piston rod  63  forms a connecting portion with a member to be moved by the hydraulic cylinder  61  as illustrated in  FIG. 12 . The second end portion  76  includes the through-hole  76   b . The second connecting pin  28  illustrated in  FIG. 11  is inserted into the through-hole  76   b . Consequently, the second end portion  76  is connected to the second hook  3  illustrated in  FIG. 11 . 
         [0114]    As illustrated in  FIG. 14 , the piston rod  63  is urged in the extension direction A by the first urging member  66  and the second urging member  67 . 
         [0115]    The cylinder tube  62  is a member in which the external appearance thereof is substantially a cylinder as illustrated in  FIG. 12 . The cylinder tube  62  includes a cylindrical portion  71 , a first end portion  72 , a lid portion  73 , and a support portion  92 . 
         [0116]    As illustrated in  FIGS. 13 and 14 , the cylindrical portion  71  has a substantially cylindrical shape with a space formed thereinside. The longitudinal direction (center axis) of the cylindrical portion  71  matches the extension and contraction direction of the piston rod  63 . 
         [0117]    The first end portion  72  is a cylindrically shaped member and is provided so as to cover the end on the contraction direction B side of the cylindrical portion  71 . The first end portion  72  is joined to the cylindrical portion  71 . A protruding portion  87  which protrudes in the extension direction A is formed on a bottom surface  72   a  which is the inner surface of the first end portion  72 . The protruding portion  87  mates with the below mentioned guide member  65 . 
         [0118]    The lid portion  73  is provided so as to close the end in the extension direction A of the cylindrical portion  71 . The lid portion  73  is a cylindrically shaped member including an insertion hole  88  into which the piston rod  63  is inserted. A sealing member is provided on the edge of the insertion hole  88  of the lid portion  73  and the sealing member seals the gap between the lid portion  73  and the piston rod  63  so that hydraulic fluid does not leak. 
         [0119]    An insertion portion  89  which is inserted into the cylinder tube  62  is provided on the end on the contraction direction B side of the lid portion  73 . The outer circumferential surface of the insertion portion  89  is formed in a threaded shape. 
         [0120]    A threaded shape is formed on the inside of an end portion  86  on the extension direction A side of the cylindrical portion  71 . The end portion  86  and the insertion portion  89  are engaged by screwing the lid portion  73  to the cylindrical portion  71 . 
         [0121]    A recessed portion  90  is formed on the outer circumference of the insertion portion  89  and an O-ring and the like is inserted into the recessed portion  90  to seal the gap between the cylindrical portion  71  and the lid portion  73 . 
         [0122]    As illustrated in  FIGS. 13 and 14 , a first flowpath  74  and a second flowpath  75  (omitted in  FIG. 12 ) are formed in the cylinder tube  62  for supplying and discharging hydraulic fluid to and from the inside of the cylinder tube  62 . The first flowpath  74  is formed at a position of the cylindrical portion  71  on the contraction direction B side of the lid portion  73 , and forms an opening on an inner circumferential surface  71   a  of the cylindrical portion  71 . The first flowpath  74  forms a rod-side port of the hydraulic cylinder  61 . The second flowpath  75  is formed on the first end portion  72  and forms an opening on the bottom surface  72   a . The second flowpath  75  forms a bottom-side port of the hydraulic cylinder  61 . The first flowpath  74  is connected to a first hydraulic pipe  95  illustrated in  FIG. 11 . The second flowpath  75  is connected to a second hydraulic pipe  96 . The first hydraulic pipe  95  and the second hydraulic pipe  96  are connected to the abovementioned hydraulic pipe  21 . 
         [0123]    The support portion  92  is positioned between the first end portion  72  and the lid portion  73  in the longitudinal direction of the cylinder tube  62 . Specifically, the support portion  92  is positioned between the first end portion  72  and the cylindrical portion  71  in the longitudinal direction of the cylinder tube  62 . The support portion  92  includes a convex portion  922  that corresponds to the convex portion  222  of the first embodiment. Moreover, a first connecting pin  93  which corresponds to the first connecting pin  27  of the first embodiment is provided on the support portion  92 . The cylinder tube  62  is supported by the coupler body  2  via the first connecting pin  93 . 
         [0124]    The piston rod  63  is inserted into the insertion hole  88  of the lid portion  73  in a manner that allows movement in the longitudinal direction (extension and contraction direction), and the longitudinal direction of the piston rod  63  matches the extension and contraction direction. 
         [0125]    The piston rod  63  includes a cylindrically shaped cylindrical portion  77  including openings at both ends, and the second end portion  76  disposed so as to close the opening on the extension direction A side of the cylindrical portion  77 . As a result, an internal space  78  which extends in the extension direction A from an end surface  77   b  on the contraction direction B side of the cylindrical portion  77 , is formed in the piston rod  63 . 
         [0126]    That is, the internal space  78  is formed by being enclosed by an inner circumferential surface  77   a  of the cylindrical portion  77  and an inside surface  76   a  on the contraction direction B of the second end portion  76 . The internal space  78  includes an opening  78   a  (see  FIG. 14 ) on the contraction direction B side. 
         [0127]    A connecting portion for connecting the members driven by the abovementioned hydraulic cylinder  61  is formed on the second end portion  76  which is the end on the extension direction A side. 
         [0128]    The piston  64  is a toric member and is fixed to the outer circumference of the piston rod  63 . The piston  64  is disposed in the proximity of the end surface  77   b  on the contraction direction B side of the piston rod  63 . The piston  64  slides over the inner circumferential surface  71   a  of the cylindrical portion  71  of the cylinder tube  62 . 
         [0129]    The space inside the cylinder tube  62  is divided by the piston  64  into a first space  69  on the extension direction A side of the piston  64  and a second space  70  on the contraction direction B of the piston  64 . The first flowpath  74  is connected to the first space  69  and the second flowpath  75  is connected to the second space  70 . 
         [0130]    The piston rod  63  is inserted into the piston  64  and the end surface  77   b  on the contraction direction B of the piston rod  63  abuts the bottom surface  72   a  in the contracted state illustrated in  FIG. 13 . 
         [0131]    The guide member  65  is a cylindrical member for guiding the below mentioned first urging member  66  and the second urging member  67 , and is disposed inside the cylinder tube  62  so that the longitudinal direction of the guide member  65  extends in the extension and contraction direction. The guide member  65  is disposed on the inside in the radial direction of the cylindrical portion  77  of the piston rod  63  in the hydraulic cylinder  61  ( FIG. 13 ) in the contracted state. 
         [0132]    The guide member  65  includes an opening  82  in an end  81  in the contraction direction B and the protruding portion  87  is mated with the opening  82 . The end  81  of the guide member  65  is held in the middle of the bottom surface  72   a  due to the protruding portion  87  mating with the end  81  in this way. 
         [0133]    A protrusion  83  is formed around the circumference protruding toward the outside in the radial direction in the proximity of the bottom surface  72   a  of the guide member  65 . An end  85   b  on the contraction direction B side of the below mentioned second urging member  67  abuts with the protrusion  83 . 
         [0134]    The guide member  65  is formed so that the length in the extension and contraction direction of the guide member  65  overlaps the piston rod  63  in the state in which the piston rod  63  is extended the most as illustrated in  FIG. 14 . 
         [0135]    The first urging member  66  and the second urging member  67  have coil shapes and are disposed in a row in the extension and contraction direction. The first urging member  66  and the second urging member  67  are coil springs. However, the first urging member  66  and the second urging member  67  may be members other than coil springs. 
         [0136]    The first urging member  66  and the second urging member  67  are disposed so that the center axes thereof follow the extension and contraction direction. The first urging member  66  and the second urging member  67  are inserted into the internal space  78  of the piston rod  63  and are disposed between the outer circumferential surface  65   a  of the guide member  65  and the inner circumferential surface  77   a  of the piston rod  63 . The first urging member  66  is disposed on the extension direction A side of the second urging member  67 . 
         [0137]    A protruding portion  91  which protrudes in the contraction direction B is formed on the inside surface  76   a  on the contraction direction B side of the second end portion  76 . An end  84   a  on the extension direction A side of the first urging member  66  is formed on the ring-like gap formed between the protruding portion  91  and the cylindrical portion  77 . 
         [0138]    The end  85   b  on the contraction direction B side of the second urging member  67  abuts with the protrusion  83 . 
         [0139]    The hold ring  68  is a member for holding the guide member  65  in the approximate middle of the internal space  78 , and is disposed between the outer circumferential surface  65   a  of the guide member  65  and the inner circumferential surface  77   a  of the piston rod  63 . The hold ring  68  is disposed between an end  84   b  on the contraction direction B side of the first urging member  66  and an end  85   a  on the extension direction A side of the second urging member  67 , and the ends  84   b  and  85   a  abut with the hold ring  68 . 
         [0140]    The hold ring  68  slides over the outer circumferential surface  65   a  of the guide member  65  and the inner circumferential surface  77   a  of the piston rod  63  during extension and contraction. The hold ring  68  is disposed in approximately the middle in the extension and contraction direction of the guide member  65  in  FIG. 13 . As illustrated in  FIG. 14 , the hold ring  68  is positioned between the outer circumferential surface  65   a  of the guide member  65  and the inner circumferential surface  77   a  of the piston rod  63  while the piston rod  63  is extended the most. 
         [0141]    By providing the hold ring  68  in this way, the guide member  65  is held in approximately the middle of the piston rod  63  by the hold ring  68 . The guide member  65  is held by the hold ring  68  and the end  81  of the guide member  65  is held in the middle of the bottom surface  72   a  by the protruding portion  87 . In this way, the guide member  65  is held in two locations and is disposed with precision in the middle of the piston rod  63 . 
         [0142]    As described above, the first urging member  66 , the hold ring  68 , and the second urging member  67  are disposed in order from the extension direction A side, and the first urging member  66  and the second urging member  67  elastically urge the piston rod  63  in the extension direction A. 
         [0143]    The first urging member  66 , the second urging member  67 , and the hold ring  68  are not joined to other members and are fit loosely with the guide member  65 . Moreover, the guide member  65  is engaged only with the protruding portion  87  of the cylinder tube  62  and is not joined to the first end portion  72 . 
         [0144]    As a result, the hydraulic cylinder  61  can be assembled easily by performing: a step for disposing the second urging member  67 , the hold ring  68 , and the first urging member  66  in order on the guide member  65 ; a step for fitting, to the protruding portion  87 , the guide member  65  including the second urging member  67 , the hold ring  68 , and the first urging member  66  disposed thereon; and a step for attaching by screwing the lid portion  73  onto the cylindrical portion  77  while inserting the piston rod  63 . 
         [0145]    Hydraulic fluid is supplied into the first space  69  in the contracted state illustrated in  FIG. 13 , and a force on the contraction direction B side is applied to the piston  64  by the hydraulic pressure of the hydraulic fluid. Moreover, the piston rod  63  is urged in the extension direction A by the first urging member  66  and the second urging member  67 . The piston  64  is pushed in the contraction direction B by the hydraulic pressure of the hydraulic fluid with respect to the urging force of the springs. 
         [0146]    When the hydraulic fluid is supplied to the second space  70  via the second flowpath  75  and the hydraulic fluid is discharged from the first space  69 , the piston  64  slides inside the cylinder tube  62  and moves in the extension direction A due to the hydraulic pressure from the state of the hydraulic cylinder  61  being contracted illustrated in  FIG. 13 . As a result, the piston rod  63  connected to the piston  64  moves in the extension direction A. 
         [0147]    At this time, the piston  64  moves in the extension direction A due to the hydraulic pressure and the urging force of the first urging member  66  and the second urging member  67 . 
         [0148]    The piston rod  63  and the piston  64  then moves in the extension direction A until the end surface  64   a  on the extension direction A side of the piston  64  abuts the end surface  89   a  on the contraction direction B side of the insertion portion  89  of the lid portion  73 . 
         [0149]    As a result, a stroke L attains the length between the end surface  64   a  and the end surface  89   a  in the hydraulic cylinder  61  of the present embodiment. 
         [0150]    The piston rod  63  is held in the extended state due to the hydraulic pressure brought about by the hydraulic fluid supplied to the second space  70 , and due to the urging force from the first urging member  66  and the second urging member  67  in the extended state illustrated in  FIG. 14 . 
         [0151]    The extended state illustrated in  FIG. 14  is maintained even if the hydraulic pressure is not applied to the second space  70  because the piston rod  63  is urged in the extension direction A by the first urging member  66  and the second urging member  67 . 
         [0152]    That is, the hydraulic cylinder  61  of the present embodiment is able to maintain the extended state even when hydraulic pressure is not applied to the second space  70 . 
         [0153]    The hydraulic cylinder  61  of the present embodiment is provided with the cylinder tube  62 , the piston rod  63 , piston  64 , the first urging member  66  and the second urging member  67  (examples of spring members). The piston rod  63  is inserted into the cylinder tube  62  such that the longitudinal direction of the piston rod  64  extends in the extension and contraction direction (extension direction A and contraction direction B). The piston  64  is fixed to the piston rod  63  and slides on the inner circumferential surface  71   a  of the cylinder tube  62 . The first urging member  66  and the second urging member  67  are disposed in the extension and contraction direction of the piston rod  63  and urge the piston rod  63  in the extension direction A. The piston rod  63  includes the opening  78   a  at the end surface  77   b  on the contraction direction B side and the internal space  78  extending in the extension direction A from the opening  78   a  is formed in the piston rod  63 . The first urging member  66  and the second urging member  67  are inserted into the internal space  78 . 
         [0154]    In this way, the internal space  78  is formed inside the piston rod  63  and the first urging member  66  and the second urging member  67  are inserted into the internal space  78 . Accordingly, the first urging member  66  and the second urging member  67  only contract until the end surface  77   b  of the piston rod  63  abuts the bottom surface  72   a  of the cylinder tube  62 . That is, excessive contraction of the first urging member  66  and the second urging member  67  does not occur even without the provision of a spring seat. 
         [0155]    As a result, a large stroke can be attained without increasing the size of the hydraulic cylinder. 
         [0156]    Moreover, the piston rod  63  is urged in the extension direction A and the extension state is maintained by the first urging member  66  and the second urging member  67  even if no hydraulic fluid is supplied. 
         [0157]    The hydraulic cylinder  61  of the abovementioned embodiment is further provided with the cylindrically shaped guide member  65 . The first urging member  66  and the second urging member  67  have coil shapes. The guide member  65  is disposed inside the first urging member  66  and the second urging member  67  so that the longitudinal direction of the guide member  65  follows the extension and contraction direction. The end  81  (example of one end) of the guide member  65  is held on the bottom surface  72   a  of the cylinder tube  62  facing the end surface  77   b  of the piston rod  63 . 
         [0158]    As a result, buckling of the first urging member  66  and the second urging member  67  can be prevented because the guide member  65  is able to guide the first urging member  66  and the second urging member  67  in the extension and contraction direction. As a result, the length of the piston rod  63  can be increased and the stroke can be further increased. 
         [0159]    Moreover, the position of the guide member  65  can be held in a predetermined position (for example, the middle) inside the cylinder tube  62 . 
         [0160]    At least the end  81  (example of one end) side of the guide member  65  has a cylindrical shape in the hydraulic cylinder  61  of the above embodiment. The cylinder tube  62  includes the protruding portion  87  that protrudes from the bottom surface  72   a  in the extension direction A. The end  81  (one end) of the guide member  65  is held on the bottom surface  72   a  by fitting with the protruding portion  87  in the inside of the cylindrical shape. 
         [0161]    The guide member  65  is held on the bottom surface  72   a  with the simple assembly of fitting the guide member  65  onto the protruding portion  87  in this way, and the end  81  of the guide member  65  can be held in the middle of the bottom surface  72   a  as illustrated in  FIGS. 13 and 14 . 
         [0162]    The first urging member  66  and the second urging member  67  of the hydraulic cylinder  61  of the above embodiment have coil shapes. The length of the first urging member  66  and the second urging member  67  is less than the natural length in the state in which the hydraulic cylinder  61  is extended the most. 
         [0163]    In this way, because the length of the first urging member  66  and the second urging member  67  is longer than the natural length in the state in which the piston rod  63  is extended the most from the cylinder tube  62 , the piston rod  63  is maintained in the extended state by the first urging member  66  and the second urging member  67  even when no hydraulic fluid is supplied. 
         [0164]    The hydraulic cylinder  61  of the above embodiment is further provided with the hold ring  68  (example of the ring-like member). The hold ring  68  is disposed between the outer circumferential surface  65   a  of the guide member  65  and the inner circumferential surface  77   a  of the internal space  78  and slides on the outer circumferential surface  65   a  and the inner circumferential surface  77   a . The first urging member  66  and the second urging member  67  are divided by being disposed on either side of the hold ring  68 . 
         [0165]    Due to the hold ring  68  being disposed in this way, the guide member  65  is held by the hold ring  68  as well as the bottom surface  72   a  and the guide member  65  can be held more reliably in the predetermined position. 
         [0166]    Moreover, because the guide member  65  is fitted onto the protruding portion  87 , the guide member  65  can be held in two locations by merely fitting the hold ring  68  on the guide member  65  and the guide member  65  can be held precisely with a simple assembly. 
         [0167]    The guide member  65  in the hydraulic cylinder  61  of the above embodiment includes the protrusion  83 . The protrusion  83  protrudes toward the outside in the radial direction. The end  84   a  on the extension direction A side of the first urging member  66  abuts the inside surface  76   a  on the extension direction A side of the internal space  78 , and the end  85   b  on the contraction direction B side of the second urging member  67  abuts the protrusion  83 . 
         [0168]    Due to the above configuration, the extension state is maintained by the first urging member  66  and the second urging member  67  even if no hydraulic fluid is supplied. 
         [0169]    The piston rod  63  is urged in the extension direction A and the extension state is maintained by the first urging member  66  and the second urging member  67 . 
         [0170]    While the end  85   b  of the second urging member  67  in the above embodiment abuts the protrusion  83  of the guide member  65 , the protrusion  83  may not be provided and the end  85   b  may abut the bottom surface  72   a.    
         [0171]    Moreover, while the protrusion  83  is formed in the proximity of the bottom surface  72   a  in the above embodiment, the protrusion  83  is not limited in this way and the protrusion  83  may be formed further to the extension direction A side than indicated in  FIG. 13 . 
         [0172]    While the protruding portion  91  is provided on the inside surface  76   a  of the second end portion  76  and the end  84   a  of the first urging member  66  is fitted between the protruding portion  91  and the cylindrical portion  77  in the above embodiment, the protruding portion  91  may not be provided and the end  84   a  may only abut the inside surface  76   a.    
         [0173]    While the first urging member  66  and the second urging member  67  are provided by being divided by the hold ring  68  in the above embodiment, the first urging member  66  and the second urging member  67  may be further divided. 
         [0174]    While the guide member  65  is not joined to the first end portion  72  and the first urging member  66 , the second urging member  67 , and the hold ring  68  are not joined together for the easy assembling in the above embodiment, the above members may be joined by welding and the like. 
         [0175]    While the hold ring  68  is provided and the first urging member  66  and the second urging member  67  are provided on either side of the hold ring  68  in the above embodiment, the hold ring  68  may not be provided and the two urging members may not be divided.  FIGS. 15 and 16  are sectional views of a configuration of a hydraulic cylinder  161  not provided with the hold ring  68 .  FIG. 15  illustrates a contracted state of the hydraulic cylinder  161  and  FIG. 16  illustrates an extended state of the hydraulic cylinder  161 . The external appearance of hydraulic cylinder  161  is the same as that of the hydraulic cylinder  61  and is omitted. 
         [0176]    The guide member  65  of the hydraulic cylinder  161  illustrated in  FIGS. 15 and 16  is different from the guide member  65  of the hydraulic cylinder  61  of the above embodiment and is formed integrally with the first end portion  72  of the cylinder tube  62 . The first end portion  72  of the hydraulic cylinder  161  differs from the first end portion  72  of the hydraulic cylinder  61 . The protruding portion  87  is not formed and the cylindrically-shaped guide member  65  is formed so as to protrude in the extension direction A. The length in the extension and contraction direction of the guide member  65  is formed so as to overlap the piston rod  63  in the extended state as illustrated in  FIG. 16 . 
         [0177]    Because the hold ring  68  is not provided in the hydraulic cylinder  161  illustrated in  FIGS. 15 and 16 , there is no need to divide the urging member into two urging members and thus one urging member  166  is provided. 
         [0178]    The urging member  166  is disposed between the outer circumferential surface  65   a  of the guide member  65  and the inner circumferential surface  77   a  of the internal space  78 . An end  166   a  on the extension direction A side of the urging member  166  is disposed between the protruding portion  91  and the cylindrical portion  77 , and an end  166   b  on the contraction direction B side of the urging member  166  abuts with the bottom surface  72   a  of the cylinder tube  62  that is the inner surface of the first end portion  72 . 
         [0179]    Because the guide member  65  is formed integrally with the first end portion  72  in the hydraulic cylinder  161  illustrated in  FIGS. 15 and 16 , the guide member  65  can be held in the middle of the cylinder tube  62  even without the provision of the hold ring  68 . 
         [0180]    While the guide member  65  is formed integrally with the first end portion  72  in the hydraulic cylinder  161 , the guide member  65  may be fixed to a second end portion  76  by welding and the like. 
         [0181]    While the guide member  65  is provided in the hydraulic cylinder  161  illustrated in  FIGS. 15 and 16 , the guide member  65  may not be provided.  FIG. 17  illustrates an external appearance of a hydraulic cylinder  261  not provided with a guide member.  FIGS. 18 and 19  are sectional views illustrating a configuration of the hydraulic cylinder  261 .  FIG. 18  illustrates a contracted state of the hydraulic cylinder  261  and  FIG. 16  illustrates an extended state of the hydraulic cylinder  261 . 
         [0182]    As illustrated in  FIGS. 18 and 19 , the protruding portion  87  which protrudes in the extension direction A is formed on a bottom surface  72   a  of the cylinder tube  62  which is the inner surface of the first end portion  72 . One urging member  266  is provided in the hydraulic cylinder  261  illustrated in  FIGS. 18 and 19  in the same way as the hydraulic cylinder  161 . 
         [0183]    An end  266   a  on the extension direction A of the urging member  266  is fitted between the protruding portion  91  and the cylindrical portion  77 . Moreover, the protruding portion  87  is fitted to the inside of an end  266   b  on the contraction direction B of the urging member  266 . The position of the urging member  266  is held in the middle of the cylinder tube  62  in the extended state illustrated in  FIG. 19  due to the protruding portion  87  fitting to the inside of the end  266   b  (example of a first end) of the urging member  266  in this way. 
         [0184]    Because the guide member  65  is not provided in the hydraulic cylinder  261 , the length of the urging member  166  cannot be as long as that of the hydraulic cylinder  161 . As a result, while the cylindrical portion  71  of the cylinder tube  62  is formed shorter than the cylindrical portion  71  in the above hydraulic cylinder  161  as illustrated in the external view in  FIG. 17 , the hydraulic cylinder  261  has the advantage of having a simpler configuration than the hydraulic cylinder  161 . Moreover, because a spring seat does not need to be provided even in this case, the length of the stroke can be ensured despite the size of the hydraulic cylinder  261 . 
         [0185]    The first urging member  66  and the second urging member  67  are disposed inside the hydraulic cylinder  61  in the quick coupler  10  according to the second embodiment as discussed above. As a result, the first urging member  66  and the second urging member  67  can be prevented from coming into contact with the hydraulic pipe  21  during the operation of the quick coupler  10 . Moreover, the adhesion of foreign matter such as sand on the first urging member  66  and the second urging member  67  can be prevented. 
         [0186]    Because a space for disposing the urging member inside the coupler body  2  and a space for preventing interference between the urging member and the hydraulic pipe  21  can be omitted, an increase in the size of the quick coupler  10  can be prevented. 
         [0187]    The first connecting pin  93  is provided on the cylinder tube  62  and is disposed between the first end portion  72  and the lid portion  73  in the axial direction of the cylinder tube  62 . As a result, the overall length of the hydraulic cylinder  61  can be reduced in comparison to when the first connecting pin  93  is provided on the first end portion  72  of the cylinder tube  62 . Consequently, an increase in the size of the quick coupler  10  can be suppressed. 
         [0188]    Although embodiments of the present invention have been described so far, the present invention is not limited to the above embodiments and various modifications may be made within the scope of the invention. 
         [0189]    The shape of the support hole  26  is not limited to an elongated hole and may be changed. For example, the support hole  26  may have a circular shape or an elliptical shape larger than the first connecting pin  27 . 
         [0190]    The lock member  8  is not limited to the configuration of the above embodiments and may be changed. For example, the recessed portion  41 , the inclined surface  43 , or the step portion  44  may not be provided on the lock member  8 . The lock member  8  may move between the locking position and the unlocking position with a linear or a curved movement instead of rotating. 
         [0191]    The width of the gap between the tip of the second hook  3  and the pin retaining portion  29  may be equal to or greater than the width of the opening of the second hook  3  while the second hook  3  is nearest the pin retaining portion  29 . Alternatively, the tip of the second hook  3  and the pin retaining portion  29  may come into contact with each other. 
         [0192]    The urging member is not limited to a spring and may be configured as another member that produces an urging force such as an elastic material or a fluid such as a gas or a liquid. The number of the urging members is not limited to two and there may be two or more urging members, or one urging member. 
         [0193]    The elastic member  45  may be omitted. The wall portion  15  of the coupler body  2  may be omitted. 
         [0194]    The configuration of hydraulic cylinder  61  according to the second embodiment may be changed. 
       INDUSTRIAL APPLICABILITY 
       [0195]    According to the present invention, a quick coupler can be provided that is small in size and that can enable the automatic actuation of a retaining function with the lock member when attaching the attachment.

Summary:
A quick coupler includes a coupler body having a first hook, a lock member, a slidable second hook, a hydraulic cylinder, and a connecting pin connecting the cylinder and coupler body. The lock member is movable between locking and unlocking positions in which the lock member protrudes into and retracts from an opening of the first hook. The cylinder includes first and second end portions connected to the coupler body and the second hook, respectively. The cylinder extends and contracts to cause the second hook to slide away from and towards the first hook, respectively. The coupler body includes a support hole moveably supporting the connecting pin in an extension and contraction direction of the cylinder. The first end portion of the cylinder moves away from the second end portion within a movability range of the connecting pin to move the lock member from the unlocking to locking position.