Patent Publication Number: US-8540319-B2

Title: Bit replacing device for excavating machine

Description:
TECHNICAL FIELD 
     The present invention relates to a device for replacing an excavating bit in which a roller bit (disk cutter) abraded by crushing rocks and pebbles during excavation can be replaced from a workspace provided in a cutter head of an excavating machine such as a shield machine. 
     BACKGROUND ART 
     As a technique for a bit replacing device which replaces the abraded roller bit for another roller bit from the workspace formed in the cutter head during excavation, for example, Patent Literature 1 and Patent Literature 2 have been proposed. The bit replacing devices each include a rotor having an opening and disposed on the front surface of a cutter spoke. A roller bit is disposed in the opening of the rotor. When replacing the roller bit, the rotor is turned by 90° or 180° to cause the opening of the rotor to face an opening for replacement provided on the side surface side or rear surface side of the opening of the rotor. Thus, the roller bit is removed out from the opening of the rotor into the workspace via the opening for replacement. 
     CITATION LIST 
     Patent Literatures 
     Patent Literature 1: Japanese Patent No. 3139749 
     Patent Literature 2: Japanese Patent No. 4163965 
     SUMMARY OF INVENTION 
     Technical Problem 
     In the conventional literatures, however, the rotor is disposed on the front surface of the cutter head (cutter spoke), and a sliding gap between the rotor and its supporting member is exposed so as to face the front surface of the cutter head. Thus, during excavation, muddy water pressure may be directly applied to the sliding gap or fragments of pebbles and the like may enter the gap. Accordingly, a sealing material provided at the sliding gap may be easily broken to impede the rotation of the rotor. 
     The present invention has been devised to solve the above problem. An object of the present invention is to provide a bit replacing device for an excavating machine which can improve sealing properties at the sliding gap of a rotor including a roller bit and replace the roller bit by smoothly rotating the rotor during excavation. 
     Solution to Problem 
     In order to solve the problem, the invention of a first aspect is a bit replacing unit for an excavating machine, in which the excavating machine includes, in the front part thereof, a cutter head rotatably supported about an excavating machine axial center, a roller bit for crushing rocks and pebbles, the roller bit being disposed on the front surface of the cutter head, and a workspace in which the abraded roller bit can be replaced, the workspace being formed inside the cutter head, wherein a housing is disposed in the front part of the cutter head, a bit containing path is formed in the housing along an in-and-out axis along which the roller bit is extended and retracted, a bit containing portion which opens at the front surface of the cutter head and a valve containing portion which is formed behind the bit containing portion are provided on the bit containing path, an opening for replacement is formed in the direction of an insertion-and-removal axis at a predetermined angle with relative to the in-and-out axis in the housing, the opening for replacement communicating with the valve containing portion and the workspace, a rotary valve is provided in the valve containing portion, the rotary valve being rotatable about a rotary axis substantially perpendicular to the in-and-out axis and the insertion-and-removal axis, an attachment/detachment path communicating with the bit containing portion is formed in the rotary valve, a bit case containing the roller bit is removably inserted into the attachment/detachment path, the rotary valve is turned at a predetermined angle to cause the attachment/detachment path to communicate with the opening for replacement, so that the bit case is movable between the attachment/detachment path and the workspace, a bit extending/retracting mechanism for extending and retracting the bit case between the attachment/detachment path and the bit containing portion is provided on the rotary valve, a first sealing material is provided for sealing at a gap between the bit case and the valve containing portion, and a second sealing material is provided for sealing at a gap between the periphery of the opening of the attachment/detachment path and the inner surface of the valve containing portion on the outer peripheral surface of the rotary valve. 
     The invention of a second aspect is the bit replacing unit for an excavating machine according to the first aspect wherein a reactive force support block is provided on the rear surface side of the bit case in the attachment/detachment path of the rotary valve, the reactive force support block transferring the excavating reactive force of the roller bit to the housing, and a cotter for transferring the excavating reactive force is removably fitted between the bit case and the reactive force support block in the valve containing portion. 
     The invention of a third aspect is the bit replacing unit for an excavating machine according to the first or second aspect, wherein the bit containing path penetrates through the cutter head, the attachment/detachment path penetrates through the rotary valve, the reactive force support block is removably inserted into the attachment/detachment path, and the reactive force support block is removably inserted into the workspace from the rear opening of the attachment/detachment path of the rotary valve via the opening for replacement. 
     The invention of a fourth aspect is the bit replacing unit for an excavating machine according to the third aspect, wherein a first soil removal path containing the roller bit penetrates through the bit case in the direction of the in-and-out axis, a second soil removal path communicating with the first soil removal path penetrates through the reactive force support block in the direction of the in-and-out axis, and soil excavated by the roller bit can be discharged from the first soil removal path to the rear surface side of the cutter head via the second soil removal path. 
     Advantageous Effects of Invention 
     According to the configuration of the first aspect, the valve containing portion containing the rotary valve is formed behind the bit containing portion which opens at the front surface of the cutter head, and the bit case including the roller bit is moved from the attachment/detachment path of the rotary valve so as to protrude into the bit containing portion. Thus, a sliding gap between the rotary valve and the valve containing portion is covered by the bit case and is not exposed to the front surface of the cutter head. Further, the first sealing material stops water at a gap between the bit containing portion and the bit case, and muddy water pressure is supported by the first sealing material during excavation. Thus, fragments of pebbles and the like do not enter the gap between the rotary valve and the valve containing portion together with muddy water and muddy water pressure is not directly applied to the second sealing material during excavation. Hence, the sliding gap between the rotary valve and the valve containing portion can be favorably sealed, so that the rotary valve can be smoothly rotated when replacing the abraded roller bit. 
     According to the configuration of the second aspect, the excavating reactive force transferred from the bit case via the cotter can be supported by the housing via the reactive force support block on the rear surface side of the attachment/detachment path. Thus, a large excavating reactive force can be effectively supported. 
     According to the configuration of the third aspect, the reactive force support block is first removed from the attachment/detachment path, and then the bit case is removed from the attachment/detachment path, so that the roller bit can be easily replaced. Further, options for the rotation direction of the rotary valve can be increased. 
     According to the configuration of the fourth aspect, soil excavated by the roller bit can be smoothly discharged from the first soil removal path to the rear surface side of the cutter head via the second soil removal path, so that rocks and pebbles can be favorably crushed. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a cross-sectional view of a main cutter spoke illustrating a first embodiment of a bit replacing unit according to the present invention. 
         FIG. 2  is a central cross-sectional view of the bit replacing unit. 
         FIG. 3  is a cross-sectional view taken along the arrows A-A of  FIG. 1 . 
         FIG. 4  is an enlarged view of the major part of  FIG. 3 . 
         FIG. 5  is a partially cutaway perspective view of the main cutter spoke illustrating the bit replacing unit. 
         FIG. 6  is a front view illustrating the bit replacing unit. 
         FIG. 7  is a cross-sectional view taken along the arrows B-B of  FIG. 1 . 
         FIG. 8  is an exploded longitudinal sectional view illustrating a state in which a bit case and a reactive force support block are removed from a rotary valve. 
         FIG. 9  is an exploded perspective view illustrating the bit case and the reactive force supporting block. 
         FIG. 10  is a perspective view illustrating sealing materials. 
         FIG. 11  is a front view illustrating a cutter head of a shield machine having bit replacing units. 
         FIG. 12  is a central longitudinal sectional view illustrating the shield machine having the bit replacing units. 
         FIG. 13  is a central cross-sectional view of the bit replacing unit illustrating the retraction position of the bit case in the replacement of a roller bit. 
         FIG. 14  is a central longitudinal sectional view of the bit replacing unit illustrating the retraction position of the bit case in the replacement of the roller bit. 
         FIG. 15  is a central cross-sectional view of the bit replacing unit illustrating the replacement position of the rotary valve in the replacement of the roller bit. 
         FIG. 16  is a central cross-sectional view of the bit replacing unit illustrating a state in which the bit case and the reactive force support block are removed out in the replacement of the roller bit. 
         FIG. 17  is a central cross-sectional view of the bit replacing unit illustrating a state in which the bit case is removed out in the replacement of the roller bit according to a modified example of the first embodiment. 
         FIG. 18  is a front view of a main cutter spoke illustrating the arrangement of bit replacing units according to a second embodiment of the present invention. 
         FIG. 19  is a longitudinal sectional view of the main cutter spoke. 
         FIG. 20  is a cross-sectional view taken along the arrows C-C of  FIG. 18 . 
         FIG. 21A  is a central longitudinal sectional view of the bit replacing unit illustrating the excavation position of a roller bit. 
         FIG. 21B  is a central longitudinal sectional view of the bit replacing unit illustrating the retraction position of a bit case. 
         FIG. 21C  is a central longitudinal sectional view of the bit replacing unit illustrating a state in which the bit case is removed out. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Embodiments of the present invention will be described. 
     First Embodiment 
     The following will describe an embodiment of a bit replacing unit which is a bit replacing device for a shield machine (excavating machine) according to the present invention. 
     First Embodiment 
     A first embodiment will be described with reference to  FIGS. 1 to 16 . 
     [Shield Machine] 
     As shown in  FIG. 12 , a pressure bulkhead  12  keeping a face colluvium pressure is provided in the front part of a cylindrically-shaped shield body (excavating machine body)  11 , and a rotary ring body  14  is supported by the pressure bulkhead  12  via a rotary bearing  13  so as to rotate about shield axial center O (excavating machine axial center). A circular cutter head  16  is supported at the front ends of a plurality of support legs  15  projecting forward from the rotary ring body  14 . An atmospheric pressure chamber  19  kept at atmospheric pressure is provided behind the pressure bulkhead  12 . A cutter drive device  17  for rotationally driving the cutter head  16  is provided in the atmospheric pressure chamber  19 . The cutter drive device  17  includes a ring gear  17   a  provided on the backside of the rotary ring body  14 , a plurality of drive pinions  17   b  engaged with the ring gear  17   a , and a plurality of rotation drive devices (hydraulic or electric motors)  17   c  for rotationally driving the drive pinions  17   b . A screw conveyor for soil removal  18  is provided on the pressure bulkhead  12  to discharge soil excavated by the cutter head  16  from the front part of the pressure bulkhead  12  toward the atmospheric pressure chamber  19  while keeping the face colluvium pressure. 
     As shown in  FIG. 11 , the cutter head  16  includes a plurality of main spoke members  21  extended along a radial direction from a center member  20  disposed on the shield axial center O, a plurality of sectorial intermediate face plates  22  disposed between the main spoke members  21 , and an intermediate ring member  23  and an outer peripheral ring member  24  which are placed in a circumferential direction centered about the shield axial center O to connect the main spoke members  21  and the intermediate face plates  22 . Soil inlets  25  for introducing excavated soil are formed between the members  21  to  24 . 
     A plurality of bit replacing units  30  according to the present invention are arranged on the main spoke member  21 . A roller bit  31  for crushing rocks and pebbles is provided on each bit replacing unit  30  so as to be rotatable about an axis in a radial direction of the shield body  11 . The roller bits  31  on all the bit replacing units  30  are positioned such that the turning radii from the shield axial center O are different from each other. Thus, the roller bits  31  can excavate and crush different turning regions. A center roller bit is provided on the center member  20 , and a plurality of fixed bits  26  are provided on two sides of each main spoke member  21 . 
     As shown in  FIG. 12 , a manhole  27  is provided behind the center member  20  so as to face the atmospheric pressure chamber  19 . The manhole  27  passes through the pressure bulkhead  12  and communicates with a workspace  28  in the main spoke member  21  from the atmospheric pressure chamber  19 , so that an operator can enter and exit the workspace  28  through the manhole  27 . 
     First Embodiment of Bit Replacing Unit 
     A first embodiment of the bit replacing unit will be described with reference to  FIGS. 1 to 10  and  13  to  16 . 
     As shown in  FIG. 1 , the main spoke member  21  is a hollow member with a front surface plate  21 F, a rear surface plate  21 B, and left and right side surface plates  21 L and  21 R. The main spoke member  12  has a substantially trapezoidal cross-section in which the rear parts of the left and right sides surface plates  21 L and  21 R are inclined inward. The bit replacing unit  30  is disposed at a predetermined distance from the center of the main spoke member  21  on one side in the width direction thereof, and the workspace  28  is formed on the other side in the width direction of the main spoke member  21 , when the main spoke member  21  is viewed from the front. 
     As shown in  FIGS. 2 to 4 , the bit replacing unit  30  includes a housing  32  connecting a mounting opening  21   a  formed on the front surface plate  21 F and a duct for soil removal  21 D penetrating through the rear surface plate  21 B. A bit containing passage  33 , which communicates with the duct for soil removal  21 D, penetrates through the housing  32  along an in-and-out axis OP parallel to the shield axial center O and perpendicular to the front surface of the cutter head  16 . On the bit containing passage  33 , there are formed a bit containing portion  34  which opens at the front surface of the main spoke member  21 , a cylindrical valve containing portion  35  formed around the radial axis (an axis of rotation which will be described later) OR behind the bit containing portion  34 , and a plug containing portion  36  formed behind the valve containing portion  35  with a reactive force support plug  32 E fitted and fixed to the plug containing portion  36 . The housing  32  includes an opening for replacement  37  which communicates with the valve containing portion  35  and the workspace  28 , the opening for replacement  37  being formed along a tangent axis (an insertion-and-removal axis which will be described later) OE intersecting with the in-and-out axis OP and the radial axis OR extended along the radial direction of the cutter head  16 . A door for replacement  37   a  is attached to the opening for replacement  37  via a hinge so as to be openable and closable. 
     In the present embodiment, the in-and-out axis OP is parallel to the shield axial center O. The cutter head on which the roller bit  31  is provided has a front surface plate. The outer peripheral side of the front surface plate may be inclined or curved rearward. Further, the roller bit is provided so as to extend and retract substantially perpendicular (for example, 85° to 95°) to the front surface plate of the cutter head. Alternatively, the roller bit is provided so as to extend and retract while being tilted at a predetermined angle of, for example, about 45° to 85° relative to the front surface of the cutter head. In such cases, even when the in-and-out axis OP of the roller bit is positioned substantially perpendicular to the front surface plate of the cutter head, the in-and-out axis OP of the roller bit is not parallel to the shield axial center O but tilted at a predetermined angle relative to the shield axial center O. 
     Moreover, the opening for replacement  37  is formed in the direction of the tangent axis OE perpendicularly intersecting with the in-and-out axis OP and the radial axis OR. The opening for replacement  37  may be inclined at a predetermined angle relative to the tangent axis OE, for example, in a range of 15° forward to 60° rearward, as long as the roller bit  31  and a reactive force support block  44  can be extended and retracted, which will be described later, and the roller bit  31  and the reactive force support block  44  can be contained in the space of the main cutter spoke  21 . 
     A cylindrical rotary valve  39  is placed in the valve containing portion  35  so as to freely rotate about the radial axis OR. The rotary valve  39  includes a cylindrical outer peripheral plate  39   a  and an expanding cylinder  39   b  which penetrates through the outer peripheral plate  39   a  in the diameter direction thereof to form an attachment/detachment path  38 . The attachment/detachment path  38  has an elliptical cross-section whose longer diameter is formed along the tangent axis OE, and has a front surface opening communicated with the bit containing portion  34 . Further, the attachment/detachment path  38  has a larger diameter than that of a soil removal path  49  of the reactive force support plug  32 E. The rotary valve  39  is rotated to turn the attachment/detachment path  38  by 90° from a use position, so that the attachment/detachment path  38  can be communicated with the opening for replacement  37  while taking up a replacement position along the tangent axis OE. 
     Furthermore, in the present embodiment, the radial axis OR as the rotation center of the rotary valve  39  perpendicularly intersects with the in-and-out axis OP and the tangent axis OE. However, the radial axis OR may intersect with the shield axial center O and the tangent axis OE at about 90° (for example, 85° to 95°) to rotate the rotary valve  39 . 
     (Bit Case and Reactive Force Support Block) 
     As shown in  FIG. 8 , a bit case  41  containing the roller bit  31  and the reactive force support block  44  are removably inserted into the attachment/detachment path  38 . The reactive force support block  44  causes the housing  32  to support excavating reactive force applied from the roller bit  31  via the bit case  41 , from the reactive force support plug  32 E. 
     As shown in  FIGS. 7 and 9 , the bit case  41  is cylindrically-shaped to have an elliptical cross-section, a soil removal path  42  having an elliptical cross-section penetrates through the bit case  41  along the in-and-out axis OP, and the roller bit  31  is rotatably supported by the front part of the soil removal path  42  via an axial portion  31   a  parallel to the radial axis OR. A pair of cam rollers  43  shown in  FIG. 4  is detachably provided so as to protrude at the symmetric positions of the radial axis OR on the rear part of the bit case  41 . 
     The reactive support block  44  includes a block body  45  with a large diameter which is fitted into the attachment/detachment path  38 , and a guide cylinder  46  with a small diameter which protrudes from a reactive force receiving surface  45   a  on the front surface of the block body  45  and is slidably fitted into the soil removal path  42  of the bit case  41 . The block body  45  and the guide cylinder  46  are cylindrically-shaped to have an elliptical cross-section, and a soil removal path  47  having an elliptical cross-section along the in-and-out axis OP penetrates through the block body  45  and the guide cylinder  46 . Further, an arc-like reactive force transmission surface  45   b  is formed along the outer peripheral surface of the rotary valve  39  on the rear end surface of the block body  45 . 
     Thus, as shown in  FIG. 13 , the attachment/detachment path  38  in the use position parallel to the shield axial center O is aligned with the bit containing portion  34 , the bit case  41 , the reactive force support block  44 , and the reactive force support plug  32 E of the housing  32 . The soil removal path  42 , the soil removal path  47 , the soil removal path  49 , and the duct for soil removal  21 D linearly communicate with each other. In the replacement position of  FIG. 15  in which the rotary valve  39  is turned by 90° about the radial axis OR in the arrow direction of  FIG. 13 , the bit case  41  and the reactive force support block  44  are inserted or removed for replacement between the attachment/detachment path  38  communicated with the opening for replacement  37  and the workspace  28 . 
     Reference numeral  48  in  FIG. 7  denotes a pair of left and right cotters interposed between the bit case  41  protruding into the bit containing portion  34  and the reactive force receiving surface  45   a  of the block body  45 . The cotters  48  are interposed between the rear surface of the bit case  41  and the reactive force receiving surface  45   a  of the block body  45  in an excavation position where the bit case  41  is moved so as to protrude into the bit containing portion  34  to fix the bit case  41 . The cotters  48  are removably fitted into cotter inserting holes  40  which are formed in the direction of the short diameter of the attachment/detachment path  38 . The cotter inserting holes  40  penetrate through the expanding cylinder  39   b  in the direction of the radial axis OR. The cotters  48  transfer the excavating reactive force of the roller bit  31  from the bit case  41  to the reactive force support block  44 . Further, the excavating reactive force is transferred from the reactive force transmission surface  45   b  of the reactive force support block  44  to the reactive force support plug  32 E of the housing  32 . 
     (Valve Rotating Mechanism and Bit Extending/Retracting Mechanism) 
     As shown in  FIGS. 1 ,  5 , and  7 , the bit replacing unit  30  includes: a valve rotating mechanism  51  provided in the housing  32  to turn the rotary valve  39  between the use position and the replacement position; and a bit extending/retracting mechanism  55  provided on the rotary valve  39  to extend and retract the bit case  41  between an excavation position and a retraction position in the attachment/detachment path  38 . 
     The valve rotating mechanism  51  includes: an arc-like internal gear rack  52  attached to the inner surface of the outer peripheral plate  39   a  of the rotary valve  39  within a predetermined range; a pinion  53  rotatably supported by the housing  32  via a supporting member and engaged with the internal gear rack  52 ; and a valve rotating handle  54  for rotating the pinion  53  via a driving mechanism with a wrapping connector  54   a  composed of a chain and a sprocket. 
     The bit extending/retracting mechanism  55  includes: the pair of cam rollers  43  protruding in the symmetric position of the bit case  41 ; guide holes  56  formed in an extending/retracting direction on the expanding cylinder  39   b  of the rotary valve  39  to guide the bases of the cam rollers  43 ; a pair of cam axes  57  for extension/retraction which is supported on the outer surface of the expanding cylinder  39   b  so as to freely rotate about an axis parallel to the in-and-out axis OP and has cam grooves  57   a  formed on the outer peripheral surfaces thereof, the cam grooves  57   a  being engaged with the leading ends of the cam rollers  43 ; and bit extending/retracting handles  58  for rotating the extending/retracting cam axes  57  via worm gears  58   a , driving shafts  58   b , and driving mechanisms with wrapping connectors  58   c.    
     The bit extending/retracting mechanism  55  may be composed of a linear drive device such as a feed screw mechanism, a hydraulic cylinder, or an electric jack. 
     (Seal Structure) 
     As shown in  FIGS. 4 and 10 , in the bit replacing unit  30 , a plurality of sealing materials stop water to prevent water leakage into the workspace  28 . 
     Specifically, a first sealing material  61  is provided on the outer periphery of the front end of the bit case  41 . The first sealing material  61  stops water at a gap between the inner surface of the bit containing portion  34  of the housing  32  and the outer peripheral surface of the bit case  41  in an excavation position. 
     Second sealing materials  62 A and  62 B and third sealing materials  63 A and  63 B are provided on the rotary valve  39 . The second sealing materials  62 A and  62 B are provided on the inner circumferential surface of the valve containing portion  35  so as to surround the opening surface and the rear opening surface of the valve containing portion  35  to seal a sliding gap between the inner circumferential surface of the valve containing portion  35  and the outer peripheral plate  39   a  of the rotary valve  39 . The third sealing materials  63 A and  63 B are provided over the peripheries around two end surfaces of the outer peripheral plate  39   a  of the rotary valve  39  to seal the sliding gap between the outer peripheral plate  39   a  of the rotary valve  39  and the inner circumferential surface of the valve containing portion  35 . Further, as shown in  FIG. 9 , a fourth sealing material  64  is attached over the outer peripheral surface of the block body  45  in the reactive force support block  44  to seal a gap between the reactive force support block  44  and the attachment/detachment path  38 . A fifth sealing material  65  is attached over the outer periphery of the front end of the guide cylinder  46  to seal a gap between the guide cylinder  46  in the reactive force support block  44  and the soil removal path  42 . 
     Thus, when the bit case  41  is located at an excavation position, muddy water and pebbles with a small diameter, which are about to flow into the gap between the rotary valve  39  and the valve containing portion  35 , are prevented by the first sealing material  61  from flowing into the bit containing portion  34 . Moreover, the second sealing materials  62 A and  62 B and the third sealing materials  63 A and  63 B prevent water leakage into the workspace  28 . 
     In the retraction position of the bit case  41 , the first sealing material  61  seals a gap between the inner surface of the attachment/detachment path  38  and the bit case  41 . The second sealing materials  62 A and  62 B and the third sealing materials  63 A and  63 B prevent water leakage from the gap between the rotary valve  39  and the valve containing portion  35  into the workspace  28 . Even when the rotary valve  39  is turned by 90° from the use position to the replacement position, the second sealing materials  62 A and  62 B, the third sealing materials  63 A and  63 B, the fourth sealing material  64 , and the fifth sealing material  65  prevent water leakage into the workspace  28 . 
     (Replacement of Roller Bit) 
     The procedure for replacing the roller bit  31  in the above configuration will be described. 
     1) When the abraded roller bit  31  is replaced at an excavation position where the bit case  41  is contained in the bit containing portion  34 , the cutter head  16  is stopped at a predetermined position, operators enter the workspace  28  in the main spoke member  21  from the manhole  27  to replace the roller bit  31 . 
     2) After the pair of cotters  48  is removed from the cotter inserting holes  40 , the bit extending/retracting handle  58  is operated to rotate the extending/retracting cam axis  57 , so that the bit case  41  is retracted from the excavation position to the retraction position of the attachment/detachment path  38  via the cam rollers  43 . 
     3) The valve rotating handle  54  is operated to turn the rotary valve  39  by 90° from the use position to the replacement position, thereby causing the rear opening of the attachment/detachment path  38  to face the opening for replacement  37 . 
     4) The door for replacement  37   a  is opened, and an operating tool such as a jack is used to draw out the reactive force support block  44  in the direction of the tangent axis OE from the attachment/detachment path  38  to the workspace  28  via the opening for replacement  37 . Next, the bit case  41  is retracted to the rear opening side, the cam rollers  43  are detached from the bit case  41  and removed from the guide holes  56 , and then the bit case  41  is drawn out from the attachment/detachment path  38  to the workspace  28  through the opening for replacement  37 . 
     5) The bit case  41  with another roller bit  31  mounted thereon is inserted into the attachment/detachment path  38  from the opening for replacement  37 , the cam rollers  43  are attached to the bit case  41  and pushed into the inner side of the attachment/detachment path  38 , and the cam rollers  43  are fitted into the guide holes  56  and engaged with the cam grooves  57   a  of the extending/retracting cam axes  57 . Further, the reactive force support block  44  is fitted from the workspace  28  into the attachment/detachment path  38  via the opening for replacement  37 . 
     6) After the door for replacement  37   a  is closed, the valve rotating handle  54  is operated to turn the rotary valve  39  by 90° from the replacement position to the use position to align the front opening of the attachment/detachment path  38  with the bit containing portion  34 . 
     7) The bit extending/retracting handle  58  is operated to rotate the extending/retracting cam axes  57 , the bit case  41  is moved from the retraction position of the attachment/detachment path  38  in the direction of the in-and-out axis OP via the cam rollers  43  so as to protrude into the bit containing portion  34 , and stops at the excavation position. Further, the cotters  48  are inserted from the cotter inserting holes  40  and fitted between the rear surface of the bit case  41  and the reactive force receiving surface  45   a  of the reactive force support block  44  to fix the bit case  41 . 
     According to the first embodiment, the bit case  41  contained in the attachment/detachment path  38  of the rotary valve  39  is moved so as to protrude into the bit containing portion  34  which opens at the front surface of the main cutter spoke  21 , and is fixed to excavate soil. Thus, the sliding gap of the rotary valve  39  in the valve containing portion  35  is closed by the bit case  41 , is not exposed to the front surface of the main cutter spoke  21 , and is not directly subjected to the muddy water pressure of an excavated portion. 
     The first sealing material  61  surrounding the bit case  41  and the second sealing material  62 A surrounding the front opening of the valve containing portion  35  favorably stop water at the sliding gaps. Thus, muddy water pressure is not directly applied to the sliding gap of the rotary valve  39  and fragments do not flow into the sliding gap. This enables the sliding gap between the rotary valve  39  and the valve containing portion  35  to be favorably sealed, thereby increasing sealing properties. Hence, the rotary valve  39  can be smoothly rotated. 
     The excavating reactive force transferred from the bit case  41  to the rear surface of the attachment/detachment path  38  via the cotters  48  can be supported by the reactive force support plug  32 E of the housing  32  via the reactive force support block  44 . Thus, a large excavating reactive force applied to the roller bit  31  can be effectively supported. 
     The reactive force support block  44  is removed from the attachment/detachment path  38  and the bit case  41  is then removed from the attachment/detachment path  38 , so that the roller bit  31  can be easily replaced. 
     Soil excavated by the roller bit  31  can be smoothly discharged from the soil removal path  42  to the duct for soil removal  21 D via the soil removal path  47  and the soil removal path  49 , so that rocks and pebbles can be favorably crushed. 
     Modified Example of First Embodiment 
       FIG. 17  shows that the rotary valve  39  is turned by 90° in an opposite direction to the turning direction of the rotary valve  39  in the first example. Only the bit case  41  can be first removed. The cam rollers  43  obstruct the replacement of the bit case  41 . However, this problem can be solved by detaching the cam rollers  43  after the extending/retracting cam axes  57  of the bit extending/retracting mechanism  55  are detached. In this modified example, the reactive force support block  44  can be fixed to the rotary valve  39  or the reactive support block  44  and the rotary valve  39  can be integrated. 
     According to the modified example of the first embodiment, in addition to the effects of the first embodiment, the roller bit  31  can be further easily replaced only by removing the bit case  41 . 
     Second Embodiment 
     A second embodiment of the bit replacing unit will be described with reference to  FIGS. 18 to 20 . The same members as those in the first embodiment are indicated by the same reference numerals, and an explanation thereof is omitted. 
     Bit replacing units  70  are disposed on left and right sides of a main cutter spoke  21 , and a rotary valve  75  contained in a housing  71  is rotated about a tangent axis (rotary axis) OE to replace a roller bit  31  from above or below. 
     As shown in  FIG. 18 , for shifting the excavation position and keeping a workspace  28  inside the main cutter spoke  21 , the bit replacing units  70  are disposed at interval L in the direction of a radial axis (insertion-and-removal axis) OR and at interval W in the direction of the tangent axis OE, and when the main cutter spoke  21  is viewed from the front, the roller bits  31  on the left and right are displaced in the radial direction in a zigzag pattern. 
     As shown in  FIGS. 20 and 21 , a bit containing portion  34  and a valve containing portion  35  are formed, in this order from the front surface of the housing  71 , on a bit containing path  33  penetrating through the housing  71 . A reactive force support portion  72  is formed integrally with the housing  71  on the rear surface side of the valve containing portion  35 . A soil removal path  73  is formed on the axial center portion of the reactive force support portion  72 . A reactive force receiving portion  76  is integrally formed on the rear surface side of an attachment/detachment path  38  of the rotary valve  75  to prevent a reactive force support block  44  from being removed. A communicating soil removal path  77  is formed on the axial center portion of the reactive force receiving portion  76 . Thus, an excavating reactive force applied to the roller bit  31  can be entirely supported by the rotary valve  75  via the bit case  41 , the reactive force support block  44 , and the reactive force receiving portion  76 . Moreover, the excavating reactive force can be supported by the housing  71  from the rotary valve  75  via the reactive force support portion  72 . 
     An opening for replacement  76  having an opening/closing door  76   a  is formed on one side in the direction of the radial axis OR (on the outer peripheral surface) [or on the other side (on the surface on the shield axial center O side)] of the housing  71 . 
     As shown in  FIG. 19 , the bit replacing unit  70  includes a valve rotating mechanism  51  for rotating the rotary valve  75  about the tangent axis OE and a bit extending/retracting mechanism  54  for extending and retracting the roller bit  31  between an excavation position and a retraction position, the valve rotating mechanism  51  and the bit extending/retracting mechanism  54  having the same structures as those in the first embodiment. 
     In the above configuration, as shown in  FIGS. 21A to 21C , the bit extending/retracting mechanism  54  retracts the rotary valve  75  from the bit containing portion  34  in the excavation position into the attachment/detachment path  38  in the retraction position. The valve rotating mechanism  51  rotates the rotary valve  75  by 90° about the tangent axis OE, thereby causing the front surface of the attachment/detachment path  38  to face the opening for replacement  76 . Thus, as in the modified example of the first embodiment, the bit case  41  can be removed out from the opening for replacement  76  into the workspace  28 . 
     According to the second embodiment, the same effects as the first embodiment and the modified example can be produced. Further, multiple bit replacing units  70  can be disposed on the main cutter spoke  21 , which is preferable to a large excavating machine.