A construction vehicle includes vehicle frames, an operator cab, a hydraulic oil tank, and engine, and an engine cover. The operator cab is mounted on the vehicle frames. The hydraulic oil tank is disposed to the rear of the operator cab and stores hydraulic oil. The engine is disposed to the rear of the hydraulic oil tank. The engine cover is a member that covers the engine. A rear face of the hydraulic oil tank and a front face of the engine cover are the same size in a widthwise direction. A rear end of an upper face of the hydraulic oil tank is positioned at the same height as a front end of the upper face of the engine cover. The upper face and side faces of the hydraulic oil tank are exposed to outside.

CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to D.E. Patent Application No. 10 2007 023 568.4-16, filed on May 21, 2007. 
       BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates to an operator seat that is disposed in a construction machine, such as a wheel loader, and a cab and a construction machine that include this seat. 
         [0003]    Conventionally, a construction machine such as a wheel loader is provided with a cab. The cab includes a compartment that is formed by walls that includes a stepping into/off door and windows and encloses an operator seat, and is provided with a working machine operation device, a traveling control device, and so on. 
         [0004]    For example, Japanese Patent Laid-Open Publication TOKUKAI No. 2000-168499 discloses an operator seat device for a construction machine that includes a seat portion, a backrest portion, an arm rest portion, and so on and is mounted on a seat support that is secured on a floor of a cab. 
         [0005]    However, the aforementioned known cab for a construction machine has the following problem. 
         [0006]    In recent years, in order to protect operators in cabs in rollover accidents of construction machines, ROPS (Rollover Protective Structure) of a cab is used. Nevertheless, in case that unpredictable shock hits a ceiling surface or the like of a cab, the structure of the aforementioned operator seat device for a construction machine disclosed in Patent Document 1 may have possibility not to provide more sufficient space above operator's head. The reason is that the seat portion and so on are mounted on the seat support that stands on the floor. 
         [0007]    The object of the present invention is to provide an operator seat for a construction machine capable of providing more sufficient space above the head of an operator in a cab, and a cab and a construction machine that include this seat. 
       SUMMARY OF THE INVENTION 
       [0008]    An operator seat for a construction machine according to a first aspect of the present invention that isdisposed in a cab of the construction machine and includes a seat portion, and a hanging portion. The seat portion includes a seat section, and a backrest section. An operator sits on the seat section. The backrest section is mounted to the seat section, preferably to the rear thereof, in a direction that intersects the seat section. The hanging portion is mounted to connects a part of the seat portion to a ceiling surface of the cab, and supports to suspend the seat portion from above. 
         [0009]    In this configuration, a hanging-from-above system that hangs the operator seat from the ceiling surface of the cab is used for the operator seat that is disposed in the cab of the construction machine. 
         [0010]    The hanging-from-above system for an operator seat referred herein includes a system that hangs an operator seat from a ceiling surface, differing from a conventional support system that mounts an operator seat on a support section that stands on a floor of a cab. The hanging portion that is mounted to the ceiling surface can support a part of the backrest section of the operator seat, or can support the seat section. Types of the construction machines that are provided with the operator seat according to the present invention are a wheel loader, a bulldozer, a hydraulic excavator, a motor grader, and so on. 
         [0011]    In this configuration, it is possible to provide space between the bottom of the operator seat and the floor of the cab. Accordingly, even in case that the ceiling surface is damaged due to a load applied onto the ceiling surface, the operator seat can move to the height corresponding to the floor, therefore, it is possible to provide more sufficient space above operator's head as compared with conventional operator seats. 
         [0012]    An operator seat for a construction machine according to a second aspect of the invention, in the operator seat according to the first aspect of the invention, further includes a rotation mechanism that allows the seat portion to rotate in a substantially horizontal direction. 
         [0013]    In this configuration, the operator seat further includes a mechanism that allows the seat portion to rotate in a substantially horizontal direction. The seat portion is included in the operator seat of the aforementioned hanging-from-above system. 
         [0014]    In this case, the rotation mechanism can rotate the seat portion together with the hanging portion about a rotation shaft that is disposed on the ceiling surface, or can rotate the seat portion independently of the hanging portion. 
         [0015]    Accordingly, rotation of the operator seat allows the operator to easily step into/off the cab. In addition, even in a case where the operator is required to turns operator's face to the rear when operating the construction machine, the operator can rotate the operator seat and thus can easily look behind. 
         [0016]    An operator seat for a construction machine according to a third aspect of the invention, in the operator seat according to the second aspect of the invention, further includes a rotation locking mechanism that selectively restricts the rotation of the seat portion and selectively releases the restriction. 
         [0017]    In this configuration, the rotation locking mechanism brings the seat portion of the operator seat in a rotatable state or in a rotation-restricted state. 
         [0018]    In this case, an example of the locking mechanism is provided by an insertion opening and an insertion rod that can be inserted into the insertion opening to restrict rotation of the rotatable seat portion. The insertion opening is formed on the seat portion side. 
         [0019]    In this configuration, the seat portion can rotate when the operator steps into/off the cab, on the other hand, rotation of the seat portion is restricted after the operator sits on the seat portion, therefore, it is possible to improve operability when operator operates the construction machine. In addition, in a case where the operator turns operator's face to the rear to look behind when operating the construction machine, for example, the operator releases the restriction of the locking mechanism to allow the seat portion to rotate, and thus can easily look behind as compared with conventional operator seats. 
         [0020]    Accordingly, the operator can switch the locking mechanism between restriction of rotation of the seat portion and release of the restriction if necessary. Therefore, it is possible to extensively improve operability, and ease of stepping into/off the cab for the operator as compared with conventional operator seats. 
         [0021]    An operator seat for a construction machine according to a fourth aspect of the invention, in the operator seat according to any of the first to third aspects of the invention, further includes a slide mechanism that allows the seat section of the seat portion to slide frontward and rearward relative to the hanging portion. 
         [0022]    In this configuration, in the operator seat that employs the aforementioned hanging-from-above system, the seat section that is included in the seat portion slides frontward and rearward relative to the hanging portion. 
         [0023]    In this case, since the seat section slides rearward relative to the hanging portion, it is possible to provide space required for the operator to step into/off the cab as much as possible when the operator steps into/off the cab. In addition, in a case where the angle of the backrest section is adjusted in accordance with slide movement of the seat section, it is possible to improve the comfort for the operator. 
         [0024]    An operator seat for a construction machine according to a fifth aspect of the invention, in the operator seat according to any of the first to fourth aspects of the invention, further includes an angle adjustment mechanism that adjusts the angle of the backrest section of the seat portion with respect to the seat section. 
         [0025]    In this configuration, the angle of the backrest section that is included in the seat portion can be adjusted by the angle adjustment mechanism. 
         [0026]    In this case, since the backrest section can tilt to the rearmost position when the operator steps into/off the cab, it is possible to improve ease of stepping into/off the cab. Additionally, the angle of the backrest section can be adjusted to meet operator's need. 
         [0027]    An operator seat for a construction machine according to a sixth aspect of the invention, in the operator seat according to any of the first to fifth aspects of the invention, the hanging portion includes a protection structure that extends from a ceiling part of the cab to a connection part between the hanging portion and the seat portion and protects to protect an operator's head. 
         [0028]    In this configuration, the hanging portion that is secured and hung from the ceiling surface of the cab includes a protection structure that has strength to protect operator's head. 
         [0029]    Accordingly, since the protection structure is provided by stiffness of the hanging portion of the operator seat is added separately from protection for the operator that is provided by stiffness of the cab such as ROPS of the cab, it is possible to more surely provide sufficient space above operator's head. 
         [0030]    A cab for a construction machine according to a seventh aspect of the invention includes the operator seat for a construction machine according to in any of the first to sixth aspects of the invention, and a door that is disposed in the side or the rear of the operator seat. 
         [0031]    In this configuration, the aforementioned operator seat is provided in the cab that includes the door that is disposed in the side or the like of the operator seat. 
         [0032]    Accordingly, even in case that the ceiling surface is damaged due to a load applied onto the ceiling surface, the operator seat can move to the height corresponding to the floor, therefore, it is possible to provide a cab that can provide more sufficient space above operator's head similarly to the above effect as compared with conventional cabs. 
         [0033]    A cab for a construction machine according to an eighth aspect of the invention, in the cab according to the seventh aspect of the invention, further includes an operation portion that is disposed in the front or the side of the seat portion and can tilt upward and downward. 
         [0034]    In this configuration, in the operator seat that employs the aforementioned hanging-from-above system, the operation portion that is tiltable upward and downward is used as an operation device for the operation of the construction machine. 
         [0035]    Herein, the term “tiltable upward and downward” referred includes meaning of “swingable frontward and rearward about a pivot axis that is disposed in the front of or in the rear of the seat portion so as to move to a predetermined position to get out of the way”, for example. In addition, the operation portion can include a joystick, a lever handle, and a typical steering wheel. Additionally, the above terms “in the front of” and “in the rear of” are used in a sense that the front-to-rear direction is defined by the “front” that is a direction that the operator who steps into/off the cab of the construction machine faces when sitting on the operator seat to operate the construction machine. 
         [0036]    Accordingly, since the operation portion, which may interfere with the operator when the operator steps into/off the cab, tilts upward and downward so as to move to a predetermined position to get out of the way, it is possible to ensure that the operator easily steps into/off the cab. In addition, in a case of combination with the aforementioned rotation mechanism of the seat portion, it is possible to extensively improve ease of stepping into/off the cab as compared with conventional cabs. 
         [0037]    A cab for a construction machine according to a ninth aspect of the invention, in the cab according to the eighth aspect of the invention, the operation portion includes an arm section that includes an operation part that is configured and arranged to be operated by the operator, and a support section that supports the arm section. In addition, both the arm and support sections are mounted to be tiltable upward and downward. 
         [0038]    In this configuration, both the arm and support sections that are included in the operation portion are tiltable upward and downward. 
         [0039]    In this case, the operation part that is disposed on the arm section can include a plate member with a various types of operation levers and buttons that are disposed thereon, a joystick, a lever handle, and so on. 
         [0040]    Accordingly, the operation portion can tilt to two tilt-up positions. As a result, the degree of tilt can be adjusted depending on the situation. For example, the operation portion is swingable upward to the furthest position in two tilt-up positions to get out of the way, when the operator steps into/off the cab. Therefore, it is possible to sufficiently provide ease of stepping into/off the cab for the operator. 
         [0041]    A construction machine according to a tenth aspect of the invention includes the cab according to any of the seventh to ninth aspects of the invention. 
         [0042]    Types of the construction machines provided with a cab are as a wheel loader, a bulldozer, a hydraulic excavator, and a motor grader. 
         [0043]    Accordingly, as stated above, even in case that the ceiling surface is damaged due to a load applied onto the ceiling surface, the operator seat can move to the height corresponding to the floor, therefore, it is possible to provide a construction machine that can provide more sufficient space above operator's head similarly to the above effect as compared with conventional construction machines. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0044]      FIG. 1  is a perspective view showing overall configuration of a wheel loader that is provided with a cab that includes an operator seat according to one embodiment of the present invention. 
           [0045]      FIG. 2  is a perspective view showing the configuration of the cab of the wheel loader shown in  FIG. 1 . 
           [0046]      FIG. 3  is a perspective view showing the configuration of the operator seat and so on provided in the cab shown in  FIG. 2 . 
           [0047]      FIG. 4  is a perspective view showing the configuration of a steering device that is disposed in front of the operator seat shown in  FIG. 3 . 
           [0048]      FIG. 5  is a perspective view showing a state where the steering device in  FIG. 4  is moved to a standing position. 
           [0049]      FIG. 6  is a perspective view showing the configuration of a rotation mechanism that is located on a ceiling surface of the cab shown in  FIG. 2  to rotate the operator seat. 
           [0050]      FIG. 7  is a perspective view showing a monitor that is mounted to the steering device shown in  FIG. 4 . 
           [0051]      FIG. 8  is a perspective view showing the configuration of an operator seat according to another embodiment of the present invention. 
           [0052]      FIG. 9  is a perspective view showing the configuration of a cab that includes an operator seat according to still another embodiment. 
           [0053]      FIG. 10  is a perspective view showing the positional relationship between a steering device and the operator seat that are provided in the cab shown in  FIG. 9 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0054]    With reference to  FIGS. 1 to 7 , the following description will describe an operator seat portion (seat portion, operator seat)  22  that is disposed in a cab  20  of a wheel loader (construction machine)  10  according to one embodiment of the present invention. 
         [0055]    As used herein to describe the present invention, the following terms “front”, “rear”, “right”, and “left” refer to the directions as follows. The term “front” should be defined as a direction that an operator faces in a state where the operator sits on the operator seat (the advance side of the wheel loader  10 ). The term “rear” should be defined as the reverse side of the wheel loader  10 . The term “right” should be defined as the right side of the operator in a state where the operator faces toward the advance side, and the term “left” should be defined as a direction opposite to the right side of the operator. 
       Overall Configuration of Wheel Loader  10   
       [0056]    As shown in  FIG. 1 , a cab structure according to this embodiment is applied to a cab  20  that is mounted on the wheel loader  10 . 
         [0057]    The wheel loader  10  includes a body unit  11 , a lift arm  12 , a bucket  13 , four tires  14 , and the cab  20 . The lift arm  12  is mounted to the front part of the body unit. The bucket  13  is mounted to the fore end of the lift arm  12 . The tires  14  support the body unit  11 , and rotate so that the body unit runs. The cab  20  is mounted on an upper part of the body unit  11 . 
         [0058]    The body unit  11  includes an engine room and an actuator portion. The engine room accommodates an engine (not shown). The actuator portion actuates the lift arm  12  and the bucket  13 . 
         [0059]    The lift arm  12  is an arm member that lifts the bucket  13  mounted to the fore end of the lift arm  12 , and is actuated by a lift cylinder that is installed together. 
         [0060]    The bucket  13  is mounted to the fore end of the lift arm  12 . A bucket cylinder controls dumping and tilting of the bucket  13 . 
         [0061]    The cab  20  has Rollover Protective Structure (hereinafter, referred to as ROPS), and includes a door  25  that is disposed on the right side surface of the cab  20 . The cab  20  forms an operator compartment for the operator that is composed of combination of a plurality of steel pipes and plates. The cab  20  is disposed slightly frontward of the middle part of the body unit  11 . The structure of the cab  20  and its mount structure will be described bellow. 
       Structure of Cab  20   
       [0062]    As shown in  FIG. 2 , the operator seat portion  22  and a steering device (operation portion)  24  are disposed in the interior compartment of the cab  20  according to this embodiment. The interior compartment is formed by the door  25 , a front windshield FG, and so on that are mounted to a frame portion. The frame portion is formed by a plurality of pole members  21   a - 21   f,  and so on. 
         [0063]    In the pole members  21   a - 21   f,  the front-right, front-left, rear-right and rear-left corner pole members  21   a,    21   b,    21   c  and  21   d  are arranged in the proximity of four corners of the cab  20 , and the right-middle and left-middle pole members  21   e  and  21   f  are arranged on the left and right side surfaces of the cab  20 , respectively. 
         [0064]    As shown in  FIG. 3 , the operator seat portion  22  includes a seat section  22   a  and a backrest (backrest section)  22   b.  The operator (driver) who operates the wheel loader  10  sits on the seat section  22   a.  The backrest  22   b  supports operator's back. The operator seat portion  22  is located in the proximity of a middle part of the cab  20 . The operator seat portion  22  moves frontward and rearward along slide rails (not shown) that are included in a slide mechanism  41 . The slide mechanism  41  is disposed on a bottom-side support section  23   d  of a hanging-from-above mechanism (hanging portion, rotation mechanism, operator seat)  23 . In addition, the angle of the backrest  22   b  of the operator seat portion  22  can be also adjusted by an angle adjustment mechanism  42 . Specifically, the angle adjustment mechanism  42  adjusts the angle of the backrest  22   b  by frontward and rearward movement of the bottom end of the angle adjustment mechanism  42  in accordance with frontward and rearward slide movement of the seat section  22   a.  In this configuration, the operator slides the seat section  22   a  frontward and rearward, or adjusts the backrest section  22   b  to a desired angle to meet operator's need when stepping into/off the cab or operating the wheel loader, therefore, it is possible to improve the comfort for the operator in the cab  20 . The hanging-from-above mechanism  23  that supports the operator seat portion  22  from above will be described bellow. 
         [0065]    As shown in  FIG. 2 , for example, the steering device  24  is disposed between the operator seat portion  22  and the front windshield FG. The operator operates operation levers (operation part)  31 , a switch panel (operation part)  32  and so on (see  FIG. 4 , described later) to changes the traveling direction of the wheel loader  10  or to control the bucket  13 , and so on. The structure of the steering device  24  will be also described later. 
         [0066]    The door  25  is attached to the right side of the cab  20 , and pivots about hinges as a pivot axis that are secured to the right-middle pole member  21   e  so that the door  25  is opened/closed outside the cab  20 . 
       Structure of Hanging-From-Above Mechanism  23  of Operator Seat Portion  22   
       [0067]    As shown in  FIG. 3 , for example, the operator seat portion  22  according to this embodiment is supported by the hanging-from-above mechanism  23 . The hinging-from-above mechanism  23  supports the operator seat portion  22  from above so that the operator seat portion  22  is hung. The hanging-from-above mechanism  23  is connected to a ceiling surface  20   a  of the cab  20 . 
         [0068]    The hanging-from-above mechanism  23  connects the operator seat portion  22  to the ceiling surface  20   a  of the cab  20 , and serves as a rotation mechanism that changes the orientation of the operator seat portion  22 . The hanging-from-above mechanism  23  includes a rotation shaft  23   a,  a ceiling-side support section  23   b,  a backside support section  23   c,  and a bottom-side support section  23   d.    
         [0069]    As shown in  FIG. 3 , the rotation shaft  23   a  is disposed substantially perpendicular to the ceiling surface  20   a,  and serves as a rotation axis for changing the orientation of the operator seat portion  22  when the operator steps into/off the cab. The rotation shaft  23   a  is inserted into an opening that is formed in the ceiling-side support section  23   b.    
         [0070]    The ceiling-side support section  23   b  rotates together with the operator seat portion  22  in a substantially horizontal direction about a part corresponding to the opening that is provided with the rotation shaft  23   a  inserted thereto. As shown in  FIG. 6 , for example, the rotation range of the ceiling-side support section  23   b  is restricted by a recessed portion  20   b  that is formed on the ceiling surface  20   a  of the cab  20  and has a stepped shape. That is, the side surfaces of the ceiling-side support section  23   b  come in contact with the stepped-shape parts of the recessed portion  20   b  as a recessed part of the ceiling surface  20   a.  This contact restricts the ceiling-side support section  23   b  into a predetermined rotation angle in the rightward and leftward rotation directions. Accordingly, the operator seat portion  22  is rotated in a desired rotational direction, when the operator steps into/off the cab  20 . Therefore, it is possible to improve ease of stepping into/off the cab. In addition, in operation of the wheel loader, when the operator turns operator's face to the rear to look behind in a state where the operator sits on the operator seat portion  22 , rotation of the operator seat portion  22  allows the operator to easily look behind. The restriction of the rotation range within the predetermined range can prevent the operator seat portion from rotating too much than required. The ceiling-side support section  23   b  is connected to the backside support section  23   c  at an L-shaped part. A protection structure that protects an area in the proximity of operator's head is formed by integrally forming the ceiling-side support section  23   b  and the backside support section  23   c,  or by employing a structure that firmly connects both sections. As a result, even in case that a large load is applied onto an upper part of the cab  20  and the upper part of the cab  20  is deformed, the area in the proximity of operator's head can be protected by the protection structure composed of the ceiling-side support section  23   b  and the backside support section  23   c.    
         [0071]    The backside of the backrest  22   b  of the operator seat portion  22  is attached to the backside support section  23   c.  The top and the bottom of the backside support section  23   c  are connected to the ceiling-side support section  23   b  and the bottom-side support section  23   d,  respectively. 
         [0072]    The bottom-side support section  23   d  is a substantially L-shaped support member that is connected to the bottom of the backside support section  23   c,  and supports the bottom surface of the seat section  22   a  of the operator seat portion  22 . 
         [0073]    In this embodiment, since thus-constructed hanging-from-above mechanism  23  supports the operator seat portion  22 , it is not necessary to provide a member that is disposed on the floor of the cab  20  to support the operator seat portion  22 . For this reason, as shown in  FIG. 3 , space S is provided under the bottom-side support section  23   d.    
         [0074]    Accordingly, even in case that the cab  20  is deformed due to a large load that is applied on to the ceiling surface of the cab  20 , the operator seat portion  22  can be moved into the space S that is provided between the operator seat portion  22  and the floor of the cab  20 . As a result, even in case that an upper part of the cab  20  is deformed, for example, it is possible to efficiently prevent that shock is applied to an area in the proximity of operator's head as compared with conventional operator seats. In addition, in a normal condition, since the space S is normally provided under the operator seat portion  22 , it is possible to improve ease of cleaning up the interior of the cab  20 . 
       Structure of Steering Device  24   
       [0075]    In this embodiment, the steering device  24  includes left and right arm sections (arm sections)  24   a  and  24   b,  and a support section  24   c.    
         [0076]    As shown in  FIG. 4 , the operation levers  31  and the switch panel  32  are disposed on the top surfaces of the left and right arm sections  24   a  and  24   b  in a horizontal position, respectively. The left and right arm sections  24   a  and  24   b  are connected to the support section  24   c  that stands on the floor of the cab  20  through a pivot shaft  24   d.  The left and right arm sections  24   a  and  24   b  integrally pivot upward and downward relative to the support section  24   c  about the pivot shaft  24   d.  As shown in  FIGS. 3 and 4 , the left and right arm sections  24   a  and  24   b  extends in a substantially horizontal direction. In this horizontal position, the fore ends of the left and right arm sections  24   a  and  24   b  extend in the front-to-rear direction to reach a part in the proximity of the backrest  22   b  of the operator seat portion  22  so that the operator who sits on the operator seat portion  22  is surrounded by the left and right arm sections  24   a  and  24   b,  for example. On the other hand, in a standing position, as shown in  FIG. 5 , the left and right arm sections  24   a  and  24   b  pivot to a position along the front windshield FG so that the operator can freely approach space between the operator seat portion  22  and the steering device  24 , and space in the side of the operator seat portion  22 . 
         [0077]    The support section  24   c  stands on the floor of the cab  20  to support the left and right arm sections  24   a  and  24   b.  Specifically, as shown in  FIG. 5 , the support section  24   c  is disposed between the operator seat portion  22  and the front windshield FG in the front-to-rear direction, and between an accelerator pedal  26  and a brake pedal  27  in the left-to-right direction. As shown in  FIG. 4 , the tilt angle of the support section  24   c  can be adjusted in the front-to-rear direction about a connection part between the support section  24   c  and the floor of the cab  20  as a pivot axis. In addition, as shown in  FIG. 7 , a folding monitor  28  is mounted to an upper part of the support section  24   c.    
         [0078]    The monitor  28  is unfolded at the upper part of the support section  24   c  as shown in  FIG. 7  when required, for example, when the operator operates the wheel loader, and pivots about a pivot shaft (not shown) that is disposed on the backside of the support section  24   c  and thus is folded onto the backside of the support section  24   c  when not in use. Accordingly, it is possible to minimize reduction of operator's range of front vision due to the monitor  28  installation, and to ensure the maximum operator's range of vision. 
         [0079]    In this embodiment, the steering device  24  that is tiltable upward and downward is used in combination with the operator seat portion  22  that is supported from above by the aforementioned hanging-from-above mechanism  23 . 
         [0080]    Thus, the left and right arm sections  24   a  and  24   b  pivot and swing upward from the normal horizontal position shown in  FIGS. 3 and 4  to the standing position along the front windshield FG shown in  FIG. 5 . Accordingly, this structure ensures wide space between the operator seat portion  22  and the steering device  24 . Therefore, it is possible to further improve ease of stepping into/off the cab for the operator. 
         [0081]    In a case where the tilt angle of the support section  24   c  can be changed upward and downward together with the left and right arm sections  24   a  and  24   b,  the position of the steering device  24  can be changed in two tilt-up positions. As a result, the operator can choose whether only the left and right arm sections  24   a  and  24   b  pivot to the standing position, or the support section  24   c  additionally pivots to the standing position depending on the situation when operator steps into/off the cab. 
       Features of Operator Seat Portion  22  of Wheel Loader  10   
       [0082]    (1) 
         [0083]    The operator seat portion  22  of the wheel loader  10  according to this embodiment is disposed in the cab  20  of the wheel loader  10 , as shown in  FIG. 1 . The operator seat portion  22  includes the seat section  22   a  that the operator sits on, and the backrest  22   b,  as shown in  FIG. 3 . A part of operator seat portion  22  is connected to the ceiling surface  20   a  of the cab  20 , and is supported by the hanging-from-above mechanism  23  in a hanging-from-above manner. 
         [0084]    Accordingly, the space S can be provided between the operator seat portion  22  that the operator sits on, and the floor of the cab  20 , as shown in  FIG. 3 . The space S that is formed under the operator seat portion  22  not only provides ease of cleaning up the interior of the cab  20  but also provides protection space above operator's head in case that an upper part of the cab  20  is deformed or damaged, for example. Specifically, even in case that the hanging-from-above mechanism  23  that supports the operator seat portion  22  is disconnected from the ceiling surface  20   a  due to deformation or the like of the upper part of the cab  20 , since the space S exists under the seat, the operator seat portion  22  falls onto the floor of the cab  20 . Therefore, it is possible to more surely provide the protection space above operator's head as compared with conventional cabs in case of deformation or the like of the upper part of the cab. 
         [0085]    (2) 
         [0086]    The operator seat portion  22  of the wheel loader  10  according to this embodiment is hung from the ceiling surface  20   a  of the cab  20  by the hanging-from-above mechanism  23 , as shown in  FIG. 3 . In addition, the operator seat portion  22  rotates in a substantially horizontal direction about the rotation shaft  23   a  that is included in the hanging-from-above mechanism  23 . 
         [0087]    Accordingly, in a case where the hanging-from-above mechanism  23  is used, since the operator seat portion  22  can be turned toward the stepping into/off door  25 , it is possible to sufficiently provide ease of stepping into/off the cab for the operator. In addition, in a state where the operator sits on the operator seat portion  22 , when the operator turns operator's face to the rear to look behind, rotation of the operator seat portion  22  allows the operator to easily look behind. As a result, since the operator seat portion  22  and the hanging-from-above mechanism  23  are provided, it is possible to provide the cab  20  that provides ease of stepping into/off the cab, and additionally provides excellent workability. 
         [0088]    (3) 
         [0089]    As shown in  FIGS. 4 and 5 , the operator seat portion  22  of the wheel loader  10  according to this embodiment is opposed to the steering device  24  that can pivot upward and downward and can be changed between the normal horizontal position (see  FIG. 4 ) and the standing position (see  FIG. 5 ). 
         [0090]    Accordingly, since the cab  20  is configured to have the left and right arm sections  24   a  and  24   b  of the steering device  24  that are orientated in the standing position when the operator steps into/off the cab, and are orientated in the horizontal position when the operator drives the wheel loader, for example, it is possible to provide the cab  20  that provides ease of stepping into/off the cab and excellent operability. In particular, as compared with typical steering-wheel type steering devices, it is possible to provide large space in the front of the operator seat portion  22  when the operator stepping into/off the cab. Therefore, it is possible to sufficiently provide ease of stepping into/off the cab  20 . 
         [0091]    (4) 
         [0092]    In the operator seat portion  22  of the wheel loader  10  according to this embodiment, as shown in  FIGS. 4 and 5 , the steering device  24  is disposed in front of the operation seat portion  22  and is opposed to the operator seat portion  22 . The support section  24   c  and the left and right arm sections  24   a  and  24   b  included in the steering device  24  can be pivoted. 
         [0093]    Accordingly, for example, when the operator steps into/off the cab  20 , the operator can change the position of the steering device  24  in two tilt-up positions by pivoting the left and right arm sections  24   a  and  24   b,  and the support section  24   c.  As a result, required amount of space can be provided in front of the operator seat portion  22 . Therefore, it is possible to improve ease of stepping into/off the cab. 
         [0094]    (5) 
         [0095]    The operator seat portion  22  of the wheel loader  10  according to this embodiment further includes the slide mechanism  41  that slides the seat section  22   a  frontward and rearward, as shown in  FIG. 3 . 
         [0096]    Accordingly, in a case where the hanging-from-above system is employed for the operator seat portion  22 , the operator can operate the wheel loader  10  at a comfortable seat position for the operator by sliding the seat section  22   a  frontward and rearward. In addition, it is preferable that the seat section  22   a  is slid to the rearmost position when the operator steps into/off the cab. As a result, space in front of the operator seat portion  22  can be provided as much as possible when the operator steps into/off the cab. Therefore, it is possible to sufficiently provide ease of stepping into/off the cab. 
         [0097]    (6) 
         [0098]    The operator seat portion  22  of the wheel loader  10  according to this embodiment, further includes the angle adjustment mechanism  42  that adjusts the angle of the backrest  22   b,  as shown in  FIG. 3 . 
         [0099]    Accordingly, in a case where the hanging-from-above system is employed for the operator seat portion  22 , the operator can operate the wheel loader  10  also at comfortable condition for the operator by adjusting the angle of the backrest  22   b.  In addition, it is preferable that the backrest  22   b  is tilted toward the rearmost position when the operator steps into/off the cab. As a result, space in the front of the operator seat portion  22  can be provided as much as possible. Therefore, it is possible to sufficiently provide ease of stepping into/off the cab. 
         [0100]    (7) 
         [0101]    In the operator seat portion  22  of the wheel loader  10  according to this embodiment, as shown in  FIG. 3 , the ceiling-side support section  23   b  and the backside support section  23   c  that are included in the hanging-from-above mechanism  23  are connected in an L-shaped state, and extends from the backside of to the topside of the hanging-from-above mechanism  23  to cover operator's head. 
         [0102]    Accordingly, even in case that the ceiling surface  20   a or the like of the cab  20  is damaged due to shock applied onto the ceiling surface  20   a,  for example, the ceiling-side support section  23   b  and the backside support section  23   c  can protect operator's head. In addition, in a case where the hanging-from-above mechanism  23  also serves as a protection structure for operator's head, it is preferable that the hanging-from-above mechanism  23  is designed in consideration of the material of the ceiling-side support section  23   b  and the backside support section  23   c and strength of the connection part and so on. 
         [0103]    (8) 
         [0104]    In the cab  20  of the wheel loader  10  according to this embodiment includes the aforementioned operator seat portion  22  and the hanging-from-above mechanism  23 , as shown in  FIG. 2 . 
         [0105]    Therefore, the cab  20  can have effects similar to the aforementioned effects that improve ease of cleaning up the interior of the cab, and more surely provide the protection space above operator's head in case of deformation or the like of the upper part of the cab as compared with conventional cabs. 
         [0106]    (9) 
         [0107]    The wheel loader  10  according to this embodiment includes the aforementioned cab  20 , as shown in  FIG. 1 . 
         [0108]    Therefore, the wheel loader  10  can have effects similar to the aforementioned effects that improve ease of cleaning up the interior of the cab, and more surely provide the protection space above operator's head in case of deformation or the like of the upper part of the cab as compared with conventional wheel loaders. 
       Other Embodiments 
       [0109]    The foregoing description has described one embodiment according to the present invention. However, the present invention is not limited to the foregoing embodiment. Various changes and modifications can be made without departing from the spirit of the present invention. 
         [0110]    (A) 
         [0111]    In the foregoing embodiment, the operator seat portion  22  freely pivots within the predetermined range about the rotation shaft  23   a  of the hanging-from-above mechanism  23 . However, the present invention is not limited to this configuration. 
         [0112]    For example, as shown in  FIG. 8 , a locking mechanism (rotation locking mechanism)  40  that restricts rotation of the operator seat portion  22  may be disposed on the side of the backrest  22   b  of the operator seat portion  22 , or the like. 
         [0113]    In this case, when the operator steps into/off the cab, the operator seat portion  22  can be in a rotatable state. On the other hand, after the operator sits on the operator seat portion  22 , the operator can pivot an insertion portion  40   b  of the locking mechanism  40  about a pivot shaft  40   a  so that the insertion portion  40   b  is inserted into an engagement portion  40   c  that is formed on a rear wall of the cab  20 . Thus, rotation of the operator seat portion  22  is restricted. Accordingly, operator's posture becomes stable in operation of a wheel loader, for example, therefore, it is possible to improve operability of a construction machine such as a wheel loader. 
         [0114]    (B) 
         [0115]    In the foregoing embodiment, as shown in  FIGS. 4 and 5 , the steering device  24  that is opposed to the operator seat portion  22  includes the left and right arm sections  24   a  and  24   b  that can be changed their position upward and downward. However, the present invention is not limited to this configuration. 
         [0116]    For example, as shown in  FIGS. 9 and 10 , a cab  120  that includes a steering device (operation portion)  124  with a typical steering wheel  124   a  may be used. In the cab  120 , the steering device  124  is used in combination with the operator seat portion  22  of the hanging-from-above mechanism system. In the steering device  124 , the height and the position in the front-to-rear direction of the steering wheel  124   a can be minutely adjusted depending on operators, as shown in  FIG. 10 . In this case, a typical steering device  124  can be used in combination with the operator seat portion  22 , additionally, rotation of the operator seat portion  22  ensures ease of stepping into/off the cab for the operator. 
         [0117]    In terms of ease of stepping into/off the cab for the operator, it is preferable that the steering device  24  of the swing-up system according to the foregoing embodiment is used in combination with the operator seat portion  22  of the hanging-from-above mechanism system. The reason is that space in front of the operator seat portion  22  can be sufficiently provided as compared with the configuration in which the steering device  124  that includes the typical steering wheel  124   a  shown in  FIGS. 9 and 10  is used in combination with the operator seat portion  22 . 
         [0118]    (C) 
         [0119]    In the foregoing embodiment, the hanging-from-above mechanism  23  that connects a part of the operator seat portion  22  to the ceiling surface  20   a  of the cab  20  extends from the bottom surface of the seat section  22   a  to the back surface of the backrest  22   b  of the operator seat portion  22  to support the operator seat portion  22 . However, the present invention is not limited to this configuration. 
         [0120]    For example, the hanging-from-above mechanism  23  may support only a seat section or only a backrest. 
         [0121]    (D) 
         [0122]    In the foregoing embodiment, the operator seat portion  22  rotates about the rotation shaft  23   a  that is secured to an upper part of the hanging-from-above mechanism  23  that is located on the ceiling surface  20   a  of the cab  20 . However, the present invention is not limited to this configuration. 
         [0123]    It is not always necessary to locate the rotation shaft on the ceiling surface. For example, a rotation shaft may be located in a connection part between the hanging portion and the seat portion. 
         [0124]    In this case, rotation of the seat portion when the operator steps into/off the cab allows the operator to easily step into/off the cab. 
         [0125]    (E) 
         [0126]    In the foregoing embodiment, the left and right arm sections  24   a  and  24   b  that are included in the steering device  24  integrally pivot. However, the present invention is not limited to this configuration. 
         [0127]    For example, the steering device may include the left and right arm sections that independently pivot. 
         [0128]    In this case, for example, the operator is required to pivot only one arm section that is located in the side where the operator steps into/off the cab, thus, required pivoting torque is reduced. Therefore, the position of the arm section can be more smoothly changed. 
         [0129]    (F) 
         [0130]    In the foregoing embodiment, the operator seat according to the present invention is applied to the cab of the wheel loader. However, the present invention is not limited to this configuration. 
         [0131]    For example, the cab that includes the operator seat according to the present invention may be mounted to other construction machines such as a bulldozer, a hydraulic excavator, and a motor grader other than a wheel loader. 
       INDUSTRIAL APPLICABILITY 
       [0132]    An operator seat for a construction machine according to the present invention has an effect that provides more sufficient space above operator's head as compared with conventional operator seats. Accordingly, the present invention can be widely applied to operator seats that are disposed in cabs of various types of construction machines.