Patent Publication Number: US-2023160173-A1

Title: Drive device and construction machine

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based on and claims the benefit of priority from Japanese Patent Application Serial Nos. 2021-189635 (filed on Nov. 22, 2021) and 2022-083048 (filed on May 20, 2022), the contents of which are incorporated herein. 
     TECHNICAL FIELD 
     The present disclosure relates to a drive device and a construction machine. 
     BACKGROUND 
     Construction machines such as an excavator includes a self-propelled undercarriage and a slewable upper structure provided on top of the undercarriage. See, for example, Patent Literature 1: Japanese Patent Application Publication No. 2020-204172. The slewable upper structure includes a cab for an operator. One end of an operating unit is rotatably (swingably) coupled to the slewable upper structure. The operating unit includes, for example, a boom, an arm rotatably coupled to the boom, and a bucket rotatably coupled to the arm. One end of the boom is rotatably coupled to the slewable upper structure. One end of the arm is rotatably coupled to the other end of the boom (the end facing away from the slewable upper structure). The bucket is rotatably coupled to the other end of the arm (the end facing away from the boom). 
     In many cases, a hydraulic actuator having a linear motion mechanism is provided as a drive device in the coupling portion between the slewable upper structure and the boom, the coupling portion between the boom and the arm, and the coupling portion between the arm and the bucket. Driving the hydraulic actuators can cause the slewable upper structure to rotate relative to the undercarriage and cause the boom, arm, and bucket to swing. 
     Each coupling portion of a construction machine tends to be heavily loaded depending on its service environment. Therefore, for coupling portions of a construction machine, there has been a demand to equalize the rotational driving forces transmitted to the opposite ends in the rotation axis direction. In particular, when rotary actuators and speed reducers are mounted on both sides of the coupling portion in the rotation axis direction, a difference in load sharing could occur due to the phase difference, resulting in the undesired unevenness of the rotational forces. Therefore, there has been an issue to alleviate this drawback. 
     SUMMARY 
     The present disclosure provides a drive device and a construction machine capable of alleviating the difference in the load sharing and ensuring sufficient operation stability and excellent controllability. 
     (1) A drive device according to one aspect of the present disclosure comprises: two fluid motors serving as drive sources for generating rotational forces; and a channel member having a supply channel for supplying a pressure fluid to the two fluid motors. Each of the two fluid motors includes: a casing having a supply port and a discharge port for the pressure fluid; a drive shaft rotatably supported to the casing; and a motive power generating unit provided in the casing and configured to rotate the drive shaft with the pressure fluid, the pressure fluid being supplied to the motive power generating unit through the supply port and discharged from the motive power generating unit through the discharge port. The two fluid motors are arranged such that the respective drive shafts are disposed parallel to each other and oriented toward opposite sides along rotation axes of the drive shafts. The supply channel supplies the pressure fluid to the supply ports of the two fluid motors. The channel member includes two separated supply channels into which the supply channel on a common supply source side is separated. 
     With this configuration, the drive shafts of the two fluid motors are oriented outward, such that the two fluid motors are opposed to each other in a direction along the rotation axes. This enables the rotational driving force to be shared between both sides. In addition, the pressure fluid can be separated by the separated supply channels and supplied to the associated fluid motors. Therefore, the rotational driving forces are balanced between the two fluid motors, such that differences in load sharing can be inhibited from occurring, and the loads can be equalized between both sides. 
     (2) The drive device may further comprise two reduction units each including an input portion and an output shaft, the input portion being coupled to associated one of the two fluid motors, the output shaft being configured to decelerate rotation of the input portion and output the decelerated rotation. The two reduction units may be arranged such that respective rotation axes are coaxial, and the two reduction units may be spaced apart from each other. 
     (3) The drive shafts of the two fluid motors may be coaxial. The supply ports of the two fluid motors may be opposed to each other along the rotation axes of the drive shafts. 
     (4) The channel member may serve as a part of the casings of the two fluid motors. 
     (5) A construction machine according to an aspect of the present disclosure comprises: a first member having two fluid motors serving as drive sources for generating rotational forces; a second member coupled to the first member so as to be rotatable about a rotation axis; two reduction units; and a channel member. Each of the two fluid motors includes: a casing having a supply port and a discharge port for the pressure fluid; a drive shaft rotatably supported to the casing; and a motive power generating unit provided in the casing and configured to rotate the drive shaft with the pressure fluid, the pressure fluid being supplied to the motive power generating unit through the supply port and discharged from the motive power generating unit through the discharge port. The two reduction units each have a main axis coaxial with the rotation axis, the two reduction units are spaced apart from each other in a direction along the rotation axis, and the two reduction units are configured to transmit the rotational forces from the two fluid motors to the second member. The channel member is disposed between the two reduction units in the direction along the rotation axis, the channel member is disposed between the two fluid motors in the direction along the rotation axis, and the channel member has a supply channel for supplying the pressure fluid to the two fluid motors. The supply channel supplies the pressure fluid to the supply ports of the two fluid motors. The channel member includes two separated supply channels into which the supply channel on a common supply source side is separated. The supply ports of the two fluid motors are opposed to each other along rotation axes of the drive shafts. 
     With this configuration, the drive shafts of the two fluid motors are oriented outward, such that the two fluid motors are opposed to each other in a direction along the rotation axes. This enables the rotational driving force to be shared between both sides. Thus, the outputs of the reduction units can be shared between both sides, irrespective of the phase difference occurring in mounting the fluid motors and the reduction units on both sides in the axial direction. In addition, the pressure fluid can be separated by the separated supply channels and supplied to the associated fluid motors. Therefore, the rotational driving forces are balanced between the two fluid motors, such that differences in load sharing can be inhibited from occurring, and the loads can be equalized between both sides. Thus, the outputs of the reduction units are balanced between both sides, such that differences in load sharing can be inhibited from occurring, and the loads can be equalized between both sides. Accordingly, the stability and efficiency in operation of the operating unit can be increased. 
     (6) The construction machine may further comprise: a self-propelled undercarriage; a slewable upper structure provided on top of the undercarriage via a slewing mechanism and configured to slew relative to the undercarriage; and an operating unit provided on and coupled to the slewable upper structure so as to be rotatable by a rotating unit about a first rotation axis extending in a horizontal direction. The operating unit may include a plurality of members coupled to each other so as to be rotatable by the rotating unit about a rotation axis parallel to the first rotation axis, and the first member and the second member may be selected from the plurality of members coupled to each other by the rotating unit. 
     According to the present disclosure, the outputs of the reduction units can be shared between both sides, and differences in load sharing can be inhibited from occurring, irrespective of the phase difference occurring in mounting the fluid motors and the reduction units on both sides in the axial direction. Therefore, it is possible to provide a drive device and a construction machine with increased stability and efficiency in operation. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    schematically illustrates a configuration of an excavator according to a first embodiment of the present disclosure, viewed from the side. 
         FIG.  2    schematically illustrates details of a drive device in a coupling portion between an arm and a bucket according to the first embodiment of the disclosure. 
         FIG.  3    schematically illustrates a configuration of a hydraulic motor according to the first embodiment of the disclosure. 
         FIG.  4    schematically illustrates a configuration of a reduction unit according to the first embodiment of the disclosure. 
         FIG.  5    schematically illustrates a drive device in a coupling portion between an arm and a bucket according to a second embodiment of the disclosure. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     The following describes a drive device and a construction machine relating to a first embodiment of the disclosure with reference to the accompanying drawings. 
     First Embodiment 
     &lt;Excavator&gt; 
       FIG.  1    schematically illustrates an excavator  100 , which is an embodiment of a construction machine according to one aspect of the disclosure, viewed from the side. In the following description, an operator for operating the excavator  100  is supposed to sit in the driver&#39;s cab of the excavator  100  in the state shown in  FIG.  1   . The direction toward which the operator is facing is herein referred to simply as the front. The opposite side to the front in the horizontal direction is referred to as the rear. The upper and lower directions for the excavator  100  placed on a road surface are simply referred to as the vertical direction. Further, the direction orthogonal to the front-rear direction and the vertical direction is referred to as the vehicle width direction.  FIG.  1    shows the excavator  100  as viewed from the vehicle width direction. 
     As shown in  FIG.  1   , the excavator  100  includes a self-propelled undercarriage  101 , a slewable upper structure  103  that is provided on top of the undercarriage  101  via a slewing mechanism  102  and slews or rotates relative to the undercarriage  101 , and an operating unit  104  provided on the slewable upper structure  103 . The undercarriage  101  and the slewing mechanism  102  are driven, for example, by an unshown electric motor with a speed reducer. The undercarriage  101  includes, for example, two continuous tracks  105  arranged side by side in the vehicle width direction. This configuration is not limitative, and it is also possible to use wheels or the like instead of the continuous tracks  105 . The slewable upper structure  103  is provided with a pressure oil source (e.g., a hydraulic pump) for supplying a pressure fluid used as a working fluid. The slewable upper structure  103  and the operating unit  104  are driven by the hydraulic oil (pressure oil) discharged from the pressure oil source. 
     The operating unit  104  includes a boom  108  and an arm  109  both extending in the front-rear direction, and a bucket  110 . The boom  108 , the arm  109 , and the bucket  110  are coupled to each other via a drive device  1  so as to be rotatable about a first rotation axis C 1 . The first rotation axis C 1  extends in the horizontal direction. Specifically, one end of the boom  108  in the longitudinal direction is coupled to the slewable upper structure  103  via the drive device  1  so as to be rotatable about the first rotation axis (one example of the rotation axis recited in the claims).  FIG.  1   , however, does not show the one end of the boom  108  and the drive device  1  provided on that end. The operating unit  104  does not necessarily include the bucket  110  but may include any other attachment selected and connected for use in construction works. 
     The other end  108   a  of the boom  108  in the longitudinal direction is coupled to one end  109   a  of the arm  109  in the longitudinal direction via the drive device  1  such that the arm  109  is rotatable about the first rotation axis C 1 . The other end  109   b  of the arm  109  is coupled to the bucket  110  via the drive device  1  such that the bucket  110  is rotatable about the first rotation axis C 1 . All of the drive devices  1  provided in the coupling portions have the same configuration. Therefore, in the following description, only the drive device  1  that couples the bucket  110  to the other end  109   b  of the arm  109  will be described, and description of the other drive devices  1  will be hereunder omitted. 
       FIG.  2    schematically illustrates the details of the coupling portion between the arm  109  and the bucket  110 . In  FIG.  2   , the arm  109  and the bucket  110  are drawn with dashed-two dotted lines for ease of understanding. As shown in  FIG.  2   , the drive device  1  is provided on the other end  109   b  of the arm  109 . The drive device  1  includes hydraulic motors  8 A,  8 B serving as the drive source, and the rotational driving force of the hydraulic motors (fluid motors)  8 A,  8 B is transmitted to the bucket  110 . The arm  109  is an example of the first member recited in the claims. The bucket  110  is an example of the second member recited in the claims. 
     &lt;Drive Device&gt; 
     The drive device  1  is disposed on the first rotation axis C 1  of the bucket  110  relative to the arm  109 . The drive device  1  is interposed between attachment brackets  110   a  of the bucket  110  arranged on the first rotation axis C 1 . With the attachment brackets  110   a  fixed to the drive device  1 , the bucket  110  is rotatable about the first rotation axis C 1  relative to the arm  109 . The first rotation axis C 1  is oriented horizontally so as to be orthogonal to the longitudinal direction of the arm  109 . 
     The drive device  1  includes two hydraulic motors  8 A,  8 B and two reduction units. The two hydraulic motors  8 A,  8 B are contained in a housing  4  fixed to the other end  109   b  of the arm  109 . The two reduction units, namely, a first reduction unit  3 A and a second reduction unit  3 B, are disposed on opposite sides of the hydraulic motors  8 A,  8 B. The first and second reduction units  3 A,  3 B are connected to the hydraulic motors  8 A,  8 B, respectively. The two hydraulic motors  8 A,  8 B are driven with the hydraulic oil supplied from the pressure oil source (e.g., a hydraulic pump) provided, for example, in the slewable upper structure  103 . The hydraulic motors  8 A,  8 B have drive shafts  76   a,    76   b,  respectively, that rotate about a second rotation axis C 2 . The second rotation axis C 2  extends horizontally so as to be orthogonal to the longitudinal direction of the arm  109 . 
     The second rotation axis C 2 , which is the main axis of the first and second reduction units  3 A,  3 B, is coaxial with the first rotation axis C 1 . In other words, the rotation axis of the first and second reduction units  3 A,  3 B is the second rotation axis C 2  coaxial with the first rotation axis C 1  which is the rotation axis of the bucket  110 . In this embodiment, the second rotation axis C 2  and the first rotation axis C 1  form a common axis. In the following description, the direction parallel to the first rotation axis C 1  may be referred to as an axial direction, the circumferential direction around the first rotation axis C 1  may be referred to as a circumferential direction, and the direction orthogonal to the axial direction and the circumferential direction may be referred to as a radial direction. 
     The drive device  1  includes the first reduction unit (reduction unit)  3 A, the first hydraulic motor (hydraulic motor)  8 A, the second hydraulic motor (hydraulic motor)  8 B, and the second reduction unit (reduction unit)  3 B arranged from the right side to the left side in  FIG.  2    along the first rotation axis C 1  or the second rotation axis C 2 . The first reduction unit  3 A, the first hydraulic motor  8 A, the second hydraulic motor  8 B, and the second reduction unit  3 B are all coaxially arranged. The rotating shafts of the first reduction unit  3 A, the first hydraulic motor  8 A, the second hydraulic motor  8 B, and the second reduction unit  3 B are separate members divided in the axial direction. A channel member  9  is disposed between the first hydraulic motor  8 A and the second hydraulic motor  8 B in the direction along the second rotation axis C 2 . The first hydraulic motor  8 A and the second hydraulic motor  8 B are arranged symmetrically with respect to the channel member  9 , and the first reduction unit  3 A and the second reduction unit  3 B are arranged symmetrically with respect to the channel member  9 . In the following description, the first hydraulic motor  8 A and the second hydraulic motor  8 B may be referred to simply as the hydraulic motor  8 A and the hydraulic motor  8 B, respectively. Likewise, the first reduction unit  3 A and the second reduction unit  3 B may be referred to simply as the reduction unit  3 A and the reduction unit  3 B, respectively. 
     As shown in  FIG.  3   , the channel member  9  has a supply channel  9   c  and a discharge channel  9   d  formed therein. The supply channel  9   c  is used to supply the hydraulic oil from the pressure oil source (e.g., a hydraulic pump) to the hydraulic motor  8 A and the hydraulic motor  8 B, and the discharge channel  9   d  is used to return the hydraulic oil discharged from the hydraulic motor  8 A and the hydraulic motor  8 B to the pressure oil source. The channel member  9  also serves as a casing  81  that forms the back sides of the hydraulic motor  8 A and the hydraulic motor  8 B, as will be described later. In other words, the hydraulic motor  8 A and the hydraulic motor  8 B are connected to each other on their back sides via the channel member  9 . The hydraulic motor  8 A and the hydraulic motor  8 B are disposed such that their respective back sides are opposed to each other in the direction along the first rotation axis C 1  or the second rotation axis C 2 . 
     The hydraulic motor  8 A is connected to the reduction unit  3 A, such that the rotational driving force of the hydraulic motor  8 A is transmitted via the reduction unit  3 A to the attachment bracket  110   a  on the right side shown in  FIG.  2    with a reduced speed. Likewise, the hydraulic motor  8 B is connected to the reduction unit  3 B, such that the rotational driving force of the hydraulic motor  8 B is transmitted via the reduction unit  3 B to the attachment bracket  110   a  on the left side shown in  FIG.  2    with a reduced speed. The hydraulic motor  8 A and the hydraulic motor  8 B are arranged on the second rotation axis C 2  so that the drive shaft  76   a  and the drive shaft  76   b  project toward opposite sides. The drive shaft  76   a  of the hydraulic motor  8 A projects to the right in  FIG.  2    and transmits the rotational driving force to the reduction unit  3 A. The drive shaft  76   b  of the hydraulic motor  8 B projects to the left in  FIG.  2    and transmits the rotational driving force to the reduction unit  3 B. 
     &lt;Hydraulic Motors&gt; 
     The hydraulic motors of the embodiment will now be described with reference to the drawings. In the following description, components having the same or like functions are denoted by the same reference signs. Description of such components may not be herein repeated. 
     The following describes the definition of the +Z direction, the −Z direction, and the R direction. The +Z direction is an example of the first rotation axis direction, and as shown in  FIG.  2   , the drive shaft  76   a  of the hydraulic motor  8 A projects in this direction. Thus, the +Z direction is the direction along the first rotation axis C 1  of the drive shaft  76   a.  The −Z direction is the direction opposite to the +Z direction and is an example of the first rotation axis direction. The drive shaft  76   b  of the hydraulic motor  8 B projects in the −Z direction. The R direction is an example of a radial direction orthogonal to the first rotation axis C 1 . The R direction is the direction intersecting (e.g., substantially orthogonal to) the +Z direction and the −Z direction. For example, the R direction is the longitudinal direction of the arm  109 . 
     The following describes the definition of one example of installation of the hydraulic motors  8 A,  8 B. In one example of installation of the hydraulic motors  8 A,  8 B, the +Z direction is oriented toward the right (the state shown in  FIGS.  2  and  3   ). The installation of the hydraulic motors  8 A,  8 B is not limited to this case. 
       FIG.  3    shows an example of configuration of the hydraulic motors  8 A,  8 B of the embodiment. The configurations of the two hydraulic motors  8 A,  8 B are the same. Further, the two hydraulic motors  8 A,  8 B are arranged in line symmetry with each other in the direction along the first rotation axis C 1  and the second rotation axis C 2  with respect to the center of the other end  109   b  of the arm  109 . Therefore, in the following description, basically only the first hydraulic motor  8 A will be described, and redundant description of the second hydraulic motor  8 B will be hereunder omitted. For the second hydraulic motor  8 B, the +Z direction and the −Z direction referred to in the description of the first hydraulic motor  8 A should be interchanged. 
     As shown in  FIG.  3   , the hydraulic motor  8 A includes a casing  81 , a drive shaft  76   a  for outputting a rotational power, a motive power generating unit  83  for providing the rotational power to the drive shaft  76   a,  bearings  84 ,  85  that rotatably support the drive shaft  76   a  and the motive power generating unit  83 , and an oil seal  86  that seals the casing  81 . 
     A description is given of the casing  81 . The casing  81  is made of a metal, for example. The casing  81  forms the most part of the contour of the hydraulic motor  8 A. The casing  81  is formed by combining a first casing member (housing)  87  having a substantially bottomed cylindrical shape and a second casing member (cover)  9  having a substantially plate-like shape. The second casing member  9  is formed of the channel member described above. The second casing member (channel member)  9  is used as a common cover for closing the respective second openings  89  of the first casing member  87  of the hydraulic motor  8 A and the first casing member  87  of the hydraulic motor  8 B. The first casing member  87  of the hydraulic motor  8 A and the first casing member  87  of the hydraulic motor  8 B may have the same shape. 
     The second casing member (channel member)  9  has a separation portion  9   a,  a supply channel  9   c,  and separated supply channels (supply ports)  9   e  formed therein. The supply channel  9   c  is a channel for supplying the pressure oil to supply ports  91  of the two hydraulic motors  8 A,  8 B. The supply channel  9   c  is in communication with the common pressure oil source for the two hydraulic motors  8 A,  8 B, such as a hydraulic pump. The separated supply channels  9   e  are channels for supplying the pressure oil to the supply ports  91 . The supply channel  9   c  is separated at the separation portion  9   a  into the two separated supply channels  9   e.  Each of the separated supply channels  9   e  has one end side communicating with the supply channel  9   c  at the separation portion  9   a  and the other end side that forms the supply port  91  communicating with the supply inlet  8   a  of the hydraulic motor  8 A or  8 B. 
     Likewise, the second casing member (channel member)  9  has a joining portion  9   b,  a discharge channel  9   d,  and separated discharge channels (discharge ports)  9   f  formed therein. The two separated discharge channels  9   f  communicate with discharge outlets  8   b  in the two hydraulic motors  8 A,  8 B. The two separated discharge channels  9   f  are channels for discharging the pressure oil from the discharge ports  92  in the two hydraulic motors  8 A,  8 B. The pressure oil discharged from the separated discharge channels  9   f  joins at the joining portion  9   b  and flows into the discharge channel  9   d.  The discharge channel  9   d  is in communication with a hydraulic oil tank or the like connected to the hydraulic pump serving as the common pressure oil source for the two hydraulic motors  8 A,  8 B. Each of the separated discharge channels  9   f  has one end side communicating with the discharge channel  9   d  at the joining portion  9   b  and the other end side that forms the discharge port  92  communicating with the discharge outlet  8   b  of the hydraulic motor  8 A or  8 B. 
     As shown in  FIG.  3   , the first casing member  87  has a substantially bottomed cylindrical shape. The first casing member  87  has a first end portion e 1  from which the drive shaft  76   a  projects and a second end portion e 2  located on the opposite side to the first end portion e 1 . The first end portion e 1  has a first opening  88  through which the drive shaft  76   a  extends. The second end portion e 2  has a second opening  89  for inserting the drive shaft  76   a  and the motive power generating unit  83  into the first casing member  87 . 
     The second casing member (channel member)  9  has a block-like shape. The second casing member  9  is attached to the second end portion e 2  of the first casing member  87  to close the second opening  89 . Thus, an internal space S that can accommodate a part of the drive shaft  76   a  and the motive power generating unit  83  is formed between the first casing member  87  and the second casing member  9 . 
     The first casing member  87  of the hydraulic motor  8 A is attached to the +Z side of the second casing member (channel member)  9 . The first casing member  87  of the hydraulic motor  8 B is attached to the −Z side of the second casing member  9 . Further, the second casing member  9  may have a make-up port, a make-up line, and a communication channel that communicates with these. For example, the make-up port and the make-up line can constitute a part of a hydraulic circuit. The make-up port is connected to the pressure oil source via a supply line and a control valve unit provided outside the casing  81 . The make-up port is supplied with pressure oil at a predetermined pressure. In addition, a communication channel may be provided that serves as a relief passage for the oil inside the casing  81 . 
     The supply port  91  is connected to the pressure oil source (e.g., a hydraulic pump) via a supply line and a control valve unit provided outside the channel member  9 . Thus, the supply port  91  is supplied with pressure oil from the pressure oil source. The discharge port  92  is connected to the hydraulic oil tank via a discharge line provided outside the channel member  9 . The pressure oil discharged from the motive power generating unit  83  flows into the discharge port  92 . The discharge port  92  directs the pressure oil discharged from the motive power generating unit  83  to the discharge line. 
     Next, the drive shaft  76   a  will now be described. As shown in  FIG.  3   , the drive shaft (first drive shaft)  76   a  has a cylindrical shape. The drive shaft  76   a  has a part that is housed inside the casing  81  and also has an output-side end portion  76   c.  The output-side end portion  76   c  projects through the first opening  88  to the outside of the casing  81  in the +Z direction. The drive shaft  76   a  is rotatably supported to the casing  81  by a second bearing  85 . As shown in  FIGS.  2  and  3   , the reduction unit  3 A is disposed on the +Z side of the hydraulic motor  8 A. The output-side end portion  76   c  of the drive shaft  76   a  has teeth formed in the circumferential surface thereof, and the teeth are meshed with the reduction unit  3 A. The teeth of the output-side end portion  76   c  of the drive shaft  76   a  are connected with a reduction input portion  18  of the reduction unit  3 A. On the −Z side of the drive shaft  76   a,  a support-side end portion  76   g  projects from an end surface  93   e  of a cylinder block  93  toward the second casing member  9 . The support-side end portion  76   g  is rotatably supported to a supporting recess  9   j  of the second casing member  9  by a first bearing  84  (described later). 
     &lt;Motive Power Generating Unit&gt; 
     Next, a description is given of the motive power generating unit  83 . As shown in  FIG.  3   , the motive power generating unit  83  is disposed inside the casing  81 . The motive power generating unit  83  is disposed between the drive shaft  76   a  and the second casing member  9 . The motive power generating unit  83  rotates the drive shaft  76   a  with the pressure oil supplied and discharged via the supply port  91  and the discharge port  92  of the casing  81 . Specifically, the motive power generating unit  83  includes a cylinder block  93 , a valve plate  94 , a plurality of pistons  95 , a swash plate  96 , and a plurality of shoes  97 . 
     The cylinder block  93  is disposed between the drive shaft  76   a  and the second casing member  9 . The cylinder block  93  is shaped like a cylinder thicker than the drive shaft  76   a.  A through hole is formed in the radially central portion of the cylinder block  93 , and the drive shaft  76   a  is inserted or fitted in this through hole. The outer circumferential surface of the drive shaft  76   a  and the inner circumferential surface of the through hole have splines. The spline of the through hole is coupled with the spline of the drive shaft  76   a.  Thus, the drive shaft  76   a  and the cylinder block  93  rotate integrally. The cylinder block  93  is not necessarily formed separately from the drive shaft  76   a,  but may be formed integrally with the drive shaft  76   a.    
     The cylinder block  93  has a recess  93   a  formed therein so as to encircle the drive shaft  76   a.  The recess  93   a  is formed in the cylinder block  93  so as to extend from the second casing member  9  side to the spline of the through hole. The recess  93   a  receives a spring  93   b  (described later). The cylinder block  93  has a plurality of cylinder bores  98 . The plurality of cylinder bores  98  are located radially outside the recess  93   a  in the second rotation axis C 2  and are arranged in the circumferential direction. The plurality of cylinder bores  98  extend in the +Z direction. The plurality of cylinder bores  98  are arranged at regular angular intervals in the circumferential direction of the cylinder block  93  around the central axis of the cylinder block  93 . 
     The cylinder block  93  has an end surface  93   e  on the −Z side. The end surface  93   e  faces the second casing member  9 . The end surface  93   e  is in contact with the valve plate  94  disposed between the end surface  93   e  and the second casing member  9 . 
     The spring  93   b  disposed in the recess  93   a  of the cylinder block  93  is, for example, a coil spring. The spring  93   b  is compressed between a retainer disposed in the recess  93   a  and a curved surface member  82 . Therefore, the spring  93   b  generates a biasing force in a direction of extension by its elastic force. The biasing force of the spring  93   b  in the −Z direction is transmitted to the drive shaft  76   a  via the retainer and others. The biasing force of the spring  93   b  in the +Z direction is transmitted to the cylinder block  93 . The curved surface member  82  is fitted on the outer circumferential surface of the portion of the drive shaft  76   a  located on the +Z side relative to the recess  93   a.    
     The curved surface member  82  has a substantially spherical outer circumference on the +Z side. The outer circumference of the curved surface member  82  is smaller toward the +Z direction. The biasing force of the spring  93   b  is transmitted through the cylinder block  93  to the end surface of the curved surface member  82  on the −Z side. The biasing force of the spring  93   b  received by the curved surface member  82  is used as a stress for pressing shoe retaining members  82   a  (described later), which are in contact with the outer circumferential curved surface of the curved surface member  82 , outward in the radial direction of the drive shaft  76   a.    
     The valve plate  94  is disposed between the end surface  93   e  of the cylinder block  93  and the second casing member  9 . The valve plate  94  is fixed to the second casing member  9 . The valve plate  94  has a ring-like shape. The valve plate  94  includes the supply inlet  8   a,  which communicates with the supply port  91  of the channel member  9 , and the discharge outlet  8   b,  which communicates with the discharge port  92  of the channel member  9 . 
     The supply inlet  8   a  has an arc-like shape extending along the circumferential direction of the cylinder block  93 . The supply inlet  8   a  communicates with several cylinder bores  98  included in the plurality of cylinder bores  98 . The supply inlet  8   a  supplies the pressure oil supplied through the supply port  91  of the casing  81  to the cylinder bores  98 . The discharge outlet  8   b  has an arc-like shape extending along the circumferential direction of the cylinder block  93 . The discharge outlet  8   b  communicates with several remaining cylinder bores  98  included in the plurality of cylinder bores  98 . The discharge outlet  8   b  directs the pressure oil discharged from the cylinder bores  98  to the discharge port  92  of the casing  81 . 
     Each of the pistons  95  is inserted in associated one of the cylinder bores  98  of the cylinder block  93 . The piston  95  can slide relative to the cylinder bore  98 . When the pressure oil is supplied to the cylinder bore  98 , the piston  95  moves toward the +Z direction. When the piston  95  moves toward the −Z direction, the pressure oil is discharged from the cylinder bore  98 . 
     Each of the shoes  97  is provided at the end of associated one of the pistons  95  in the +Z direction. The end portion of the piston  95  on the +Z side has a spherical head  95   a.  The shoe  97  is pivotably coupled to the piston  95  via the spherical head  95   a.  The shoe  97  slidably contacts the swash plate  96 . The plurality of shoes  97  are retained integrally by the shoe retaining member  82   a.  The shoe retaining member  82   a  rotates around the drive shaft  76   a  while being inclined by the curved surface member  82  along the swash plate  96 . Further, the rotation of the shoe retaining member  82   a  causes the shoes  97  to rotate around the drive shaft  76   a  while being pushed toward the swash plate  96 . 
     The swash plate  96  is provided on the +Z side of the pistons  95  and the shoes  97 . The swash plate  96  is fixed to the inner surface  87   a  of the first casing member  87 . The swash plate  96  is inclined at an angle to the drive shaft  76   a.    
     The inclination of the swash plate  96  serves to regulate the movement of the pistons  95  along the axial direction. The swash plate  96  has an annular shape as viewed from the cylinder block  93  side located in the −Z direction. The radially central portion of the swash plate  96  has a through hole extending in the axial direction. The drive shaft  76   a  is inserted in (extends through) the through hole. The swash plate  96  has a flat sliding surface  96   a  on the cylinder block  93  side. Each of the shoes  97  is movably pressed against the sliding surface  96   a.    
     Next, a description is given of the two bearings in the casing  81  including the channel member  9 . The first bearing  84  is disposed between the circumferential surface of the supporting recess  9   j  of the second casing member  9  and the circumferential surface of the support-side end portion  76   g  of the drive shaft  76   a  projecting from the end surface  93   e  of the cylinder block  93  toward the second casing member  9 . The first bearing  84  rotatably supports the cylinder block  93  to the second casing member  9 . For example, the first bearing  84  is a ball bearing or a needle bearing. The first bearing  84  is not limited to these types. 
     The second bearing  85  is disposed between the inner surface  87   a  of the first casing member  87  and the circumferential surface of the output-side end portion  76   c  of the drive shaft  76   a.  The second bearing  85  rotatably supports the drive shaft  76   a  to the first casing member  87 . For example, the second bearing  85  is a ball bearing or a tapered roller bearing. The second bearing  85  is not limited to these types. 
     Next, a description is given of the oil seal  86 . The oil seal  86  is disposed on the +Z side of the second bearing  85 . For example, the oil seal  86  is disposed between the second bearing  85  and the end portion  87   e  of the first casing member  87  on the +Z side. The oil seal  86  is disposed between the inner surface  88   a  of the first opening  88  of the first casing member  87  and the circumferential surface of the output-side end portion  76   c  of the drive shaft  76   a.  The oil seal  86  seals between the inner surface  88   a  of the first opening  88  of the first casing member  87  and the circumferential surface of the output-side end portion  76   c  of the drive shaft  76   a.  With this arrangement, the oil seal  86  prevents leakage of the oil from the first opening  88 . 
     &lt;Reduction Unit&gt; 
       FIG.  4    schematically shows the configuration of the first reduction unit  3 A. As shown in  FIG.  2   , the configurations of the two reduction units  3 A,  3 B are the same. Further, the two reduction units  3 A,  3 B are arranged in symmetry with each other in the direction of the first rotation axis C 1  with respect to the other end  109   b  of the arm  109 . Therefore, in the following description, basically only the first reduction unit  3 A will be described, and redundant description of the second reduction unit  3 B will be hereunder omitted. As shown in  FIG.  4   , the first reduction unit  3 A includes a case  11  having a cylindrical shape, a carrier  14  disposed radially inside the case  11 , and an input portion (reduction input portion)  18  that rotates the carrier  14  at a rotation speed reduced at a predetermined ratio with respect to the rotation speed of the first drive shaft  76   a.    
     &lt;Case&gt; 
     An outer flange portion  11   a  projecting outward in the radial direction is integrally formed with the outer circumferential surface of the case  11 . The outer flange portion  11   a  has a rectangular section along the axial direction. The housing  4  is disposed on the end surface  11   b  of the outer flange portion  11   a  on the hydraulic motor  8 A side (the left side in  FIG.  4   ). The housing  4  is fastened and fixed to the outer flange portion  11   a  by bolts  5 . Internal teeth  24  are provided on an inner circumferential surface of the case  11 . The internal teeth  24  are pin-shaped (cylindrical) teeth provided on the inner circumferential surface of the case  11 . Two or more internal teeth  24  are arranged at equal intervals in the circumferential direction. 
     &lt;Carrier&gt; 
     The carrier  14  is rotatably supported by the case  11  via a pair of main bearings (bearings)  26  disposed at a distance from each other in the axial direction. The main bearings  26  are, for example, angular contact ball bearings. The carrier  14  is positioned coaxially with the case  11  and the first rotation axis C 1 . 
     The carrier  14  includes a base plate portion  32  situated on the hydraulic motor  8 A side in the axial direction, and an end plate portion  30  disposed on a side of the base plate portion  32  away from the hydraulic motor  8 A, and three pillar portions  33  with a columnar shape that are integrally molded with the base plate portion  32  and protrude out from the base plate portion  32  toward the end plate portion  30 . The pillar portions  33  are arranged at equal intervals in the circumferential direction. The end plate portion  30  is disposed at the distal end  33   a  of the pillar portions  33 . The attachment bracket  110   a  of the bucket  110  is arranged on one surface  30   a  of the end plate portion  30  facing away from the base plate portion  32 . The end plate portion  30  and the attachment bracket  110   a  are fastened and fixed to the pillar portions  33  by bolts  34 . In this state, a space having a predetermined width in the axial direction is formed between the base plate portion  32  and the end plate portion  30 . 
     A pin  36  for positioning the end plate portion  30  with respect to the base plate portion  32  is provided slightly inside the bolt  34  of the pillar portion  33  in the radial direction. The pin  36  is disposed such that it spans the pillar portion  33  and the end plate portion  30 . The pillar portion  33  and the base plate portion  32  may be formed separate from each other. In this case, the pillar portion  33  is fastened to the base plate portion  32 . The configuration of the pillar portions  33  is not limited to such a columnar shape. The pillar portions  33  may be formed in any shape or configuration provided that they form a space having a certain width in the axial direction between the base plate portion  32  and the end plate portion  30 . 
     The end plate portion  30  and the base plate portion  32  have a plurality (for example, three in this embodiment) of through holes  30   c  and  32   b,  respectively, into which crankshafts  46  (described later) of the reduction input portion  18  are inserted The through holes  30   c  and through holes  32   b  are arranged at equal intervals in the circumferential direction. 
     &lt;Reduction Input Portion&gt; 
     The reduction input portion  18  includes two or more (for example, three in this embodiment) transmission gears  44  that mesh with the teeth of the output-side end portion  76   c  of the first drive shaft  76   a,  two or more (for example, three in this embodiment) crankshafts  46  each having one end fixed to one of the transmission gears  44 , a first external gear (external teeth member)  48   a  and a second external gear (external teeth member)  48   b  that rotate oscillatorily with the rotation of the crankshafts  46 . 
     Since the transmission gears  44  are fixed to one end of the crankshafts  46 , the rotation of the first drive shaft  76   a  is transmitted to the crankshafts  46  via the transmission gears  44 . The crankshafts  46  extend along the axial direction. In other words, each of the crankshafts  46  rotates about a crank rotation axis C 4  (an example of the other rotation axis in the claims) parallel to the second rotation axis C 2 . The crankshaft  46  is rotatably supported by the end plate portion  30  via a first crank bearing  51 . The crankshaft  46  is also rotatably supported by the base plate portion  32  via a second crank bearing  52 . The first crank bearing  51  and the second crank bearing  52  are, for example, tapered roller bearings. 
     At the center of the crankshaft  46  in the axial direction, there are provided a first eccentric portion  46   a  and a second eccentric portion  46   b  disposed eccentrically from the axis of the crankshaft  46 . The first and second eccentric portions  46   a,    46   b  are disposed adjacent to each other in the axial direction between the first crank bearing  51  and the second crank bearing  52 . The first eccentric portion  46   a  is disposed adjacent to the first crank bearing  51 . The second eccentric portion  46   b  is disposed adjacent to the second crank bearing  52 . Further, the first eccentric portion  46   a  and the second eccentric portion  46   b  are out of phase with each other. The crankshaft  46  thus configured is inserted into the through holes  30   c  and  32   b  in the end plate portion  30  and the base plate portion  32 , respectively. Thus, the crankshafts  46  are arranged at equal intervals in the circumferential direction like the through holes  30   c  and  32   b.    
     A first roller bearing  55   a  is attached to the first eccentric portion  46   a  of the crankshaft  46 . A second roller bearing  55   b  is attached to the second eccentric portion  46   b.  The first roller bearing  55   a  is, for example, a cylindrical roller bearing. In this case, the first roller bearing  55   a  includes a plurality of rollers and a cage for holding the plurality of rollers. The second roller bearing  55   b  has the same configuration as the first roller bearing  55   a.  The first external gear  48   a  and the second external gear  48   b  are oscillatorily rotated in conjunction with the rotation of the crankshafts  46  via the roller bearings  55   a  and  55   b.    
     The first and second external gears  48   a,    48   b  are disposed in a space between the base plate portion  32  and the end plate portion  30  of the carrier  14 . The first external gear  48   a  and the second external gear  48   b  have external teeth  49   a  and  49   b,  respectively, that mesh with the internal teeth  24  of the casing  11 . In the first external gear  48   a  and the second external gear  48   b,  there are formed first through holes  48   c  into which the pillar portions  33  are inserted, and second through holes  48   d  into which the eccentric portions  46   a  and  46   b  of the crankshafts  46  are inserted. 
     The first eccentric portion  46   a  of the crankshaft  46  and the first roller bearing  55   a  are inserted into the second through hole  48   d  of the first external gear  48   a.  The second eccentric portion  46   b  of the crankshaft  46  and the second roller bearing  55   b  are inserted into the second through hole  48   d  of the second external gear  48   b.  The first eccentric portion  46   a  and the second eccentric portion  46   b  are oscillatorily rotated by the rotation of the crankshaft  46 , and thus the first external gear  48   a  and the second external gear  48   b  are oscillatorily rotated while they mesh with the internal teeth  24  of the case  11 . 
     &lt;Operation of Drive Device&gt; 
     Next, a description is given of operation of the drive device  1 . 
     &lt;Operation of Hydraulic Motors&gt; 
     In this case, the pressure oil is supplied from the hydraulic pump or the like serving as the pressure oil source to the drive device  1  provided on the arm  109 . As shown in  FIG.  3   , the pressure oil supplied flows through the supply channel  9   c  and separates at the separation portion  9   a  into the two separated supply channels  9   e,  and then the pressure oil is supplied to the supply inlets  8   a  of the hydraulic motor  8 A and the hydraulic motor  8 B via the respective supply ports  91 . Since the pressure oil is separated at the separation portion  9   a  into the two separated supply channels  9   e,  the hydraulic motor  8 A and the hydraulic motor  8 B can be driven simultaneously. At the same time, the hydraulic oil discharged from the discharge outlets  8   b  of the hydraulic motor  8 A and the hydraulic motor  8 B into the respective separated discharge channels  9   f  joins at the joining portion  9   b.  The hydraulic oil that has joined together flows through the discharge channel  9   d  and returns to the hydraulic oil tank or the like connected to the hydraulic pump serving as the common pressure oil source. 
     A description is given of operation of the motive power generating unit  83 . The following describes operation of the first hydraulic motor  8 A among the two hydraulic motors  8 A,  8 B. The cylinder bore  98  for the piston  95  at the position immediately after the dead center on the −Z side is in communication with the supply inlet  8   a  of the valve plate  94 . Thus, the cylinder bore  98  receives the pressure oil from the supply inlet  8   a  of the valve plate  94 . The piston  95  in the cylinder bore  98  that has received the pressure oil is moved toward the +Z direction by the pressure oil. This causes the shoe  97  provided on the distal end portion of the piston  95  to be pressed against the swash plate  96 . When the shoe  97  is pressed against the swash plate  96 , a part of the reaction force generated at that time acts on the cylinder block  93  for rotating the cylinder block  93 . Thus, the cylinder block  93  and the drive shaft  76   a  rotate. 
     On the other hand, the cylinder bore  98  for the piston  95  that has moved to the position immediately after the dead center on the +Z side communicates with the discharge outlet  8   b  of the valve plate  94 . Thus, the cylinder bore  98  is allowed to discharge the pressure oil to the discharge outlet  8   b  of the valve plate  94 . At this time, the piston  95  is pushed toward the −Z direction by the swash plate  96  as the cylinder block  93  rotates. Thus, the piston  95  moves toward the −Z direction while discharging the pressure oil from the cylinder bore  98 . The piston  95  then returns to the dead center on the −Z side. 
     &lt;Operation of Reduction Unit&gt; 
     In the drive device  1 , the rotation of the drive shaft  76   a  in the hydraulic motor  8 A is transmitted to the reduction input portion  18  of the reduction unit  3 A connected with the teeth of the output-side end portion  76   c  of the drive shaft  76   a.  Likewise, the rotation of the drive shaft  76   b  in the hydraulic motor  8 B is transmitted to the reduction input portion  18  of the reduction unit  3 B connected with the teeth of the output-side end portion  76   c  of the drive shaft  76   b.  The operation of the first reduction unit  3 A among the two reduction units  3 A,  3 B will be now described. 
     As shown in  FIGS.  3  and  4   , in the first reduction unit  3 A, each of the transmission gears  44  that mesh with the first drive shaft  76   a  is rotated by the rotation of the first drive shaft  76   a.  Thus, the crankshaft  46  is rotated integrally with the transmission gear  44  about the crank rotation axis C 4 . When the crankshaft  46  is rotated, the oscillation of the first eccentric portion  46   a  causes the first external gear  48   a  to rotate while meshing with the internal teeth  24 . In addition, the oscillation of the second eccentric portion  46   b  causes the second external gear  48   b  to rotate while meshing with the internal teeth  24 . That is, the crankshaft  46  rotates about the crank rotation axis C 4  and revolves around the first rotation axis C 1 . 
     In the present embodiment, each of the pillar portions  33  penetrating the first through hole  48   c  of the external gears  48   a,    48   b  is fixed in a predetermined position together with the base plate portion  32 . Therefore, the carrier  14  is rotated about the first rotation axis C 1  relative to the case  11  at a rotation speed lower than that of the first drive shaft  76   a.  The other end  109   b  of the arm  109  in the longitudinal direction is fixed to the case  11  via the housing  4 . The attachment bracket  110   a  of the bucket  110  is fixed to the end plate portion  30  of the carrier  14 . Thus, driving the hydraulic motors  8 A,  8 B provided on the arm  109  causes the bucket  110  to rotate about the first rotation axis C 1  relative to the arm  109 . 
     As described above, in the drive device  1  of the embodiment, the crankshafts  46  of the reduction units  3 A,  3 B serve as input shafts to which the rotation of the drive shafts  76   a,    67   b  of the hydraulic motors  8 A,  8 B is input. The drive shafts  76   a,    76   b  are substantially coupled to the input shafts of the reduction units  3 A,  3 B. The carrier  14  serves as the output shaft that decelerates the rotation of the drive shaft  76   a,    76   b  and outputs the decelerated rotation to the bucket  110 . 
     The rotation of the drive shaft  76   a  of the hydraulic motor  8 A is transmitted to the reduction unit  3 A. Likewise, the rotation of the drive shaft  76   b  of the hydraulic motor  8 B is transmitted to the reduction unit  3 B. Therefore, the outputs of these two reduction units  3 A,  3 B are transmitted to the bucket  110 . Meshing timings of the components in the two hydraulic motors  8 A,  8 B and the two reduction units  3 A,  3 B may differ due to a slight formation error of the components and an assembly error. Therefore, at the time of an initial operation of the drive device  1 , the drive shafts  76   a,    76   b  coupled to the reduction units  3 A,  3 B respectively may receive different loads. In such a case, there is a possibility that the hydraulic motors  8 A,  8 B and the reduction units  3 A,  3 B continue to be driven with the load imbalance. 
     However, in the drive device  1  of the embodiment, the hydraulic oil can be separated in the channel member  9  disposed close to the hydraulic motors  8 A,  8 B and supplied to the hydraulic motors  8 A,  8 B, which can be driven separately in the axial direction. This allows for the absorption of the different loads on the drive shafts  76   a,    76   b.  Thereafter, the loads can be equally applied to the drive shafts  76   a,    76   b,  and the rotation of the hydraulic motors  8 A,  8 B can be transmitted to the reduction units  3 A,  3 B in this state. Further, the hydraulic motors  8 A,  8 B separately drive the reduction units  3 A,  3 B, thereby balancing the rotational driving force. Therefore, differences in load sharing can be inhibited from occurring, and the loads can be equalized between the opposite sides of the arm  109 . This allows the output to the bucket  110  to be balanced between the opposite sides of the arm  109 . Accordingly, the stability and efficiency in operation can be increased. Simultaneously, it is possible to prevent the reduction units  3 A,  3 B from continuing to be driven with the load imbalance. As a result, the product life of the drive device  1  can be extended. 
     The reduction units  3 A,  3 B each include the case  11  having a cylindrical shape, the carrier  14  disposed radially inside the case  11 , and the reduction input portion  18  that rotates the carrier  14  at a rotation speed reduced at a predetermined ratio with respect to the rotation speed of the drive shafts  76   a,    76   b  that serve as the input shaft. The reduction input portion  18  includes the two or more crankshafts  46 , and the first external gear  48   a  and second external gear  48   b  that oscillatorily rotate in conjunction with the rotation of the crankshafts  46 . With such two reduction units  3 A,  3 B, a high output can be obtained at a high reduction ratio. 
     Simultaneously, the two hydraulic motors  8 A,  8 B are disposed coaxially between the two reduction units  3 A,  3 B, and therefore, it is possible to reduce the size of the drive device  1  and allow the boom  108 , the arm  109 , and the bucket  110  to operate appropriately. Further, in the reduction units  3 A,  3 B, the internal teeth  24  and the external gears  48   a,    48   b  have a high contact ratio to each other, which improves the resistance of the drive device  1  against overloads and impact loads. Consequently, it is possible to improve the resistance against overloads and impact loads on the coupling portion between the slewable upper structure  103  and the boom  108 , the coupling portion between the boom  108  and the arm  109 , and the coupling portion between the arm  109  and the bucket  110 . 
     Second Embodiment 
     The following describes a drive device and a construction machine relating to a second embodiment of the disclosure with reference to the accompanying drawings.  FIG.  5    schematically illustrates the drive device relating to the embodiment. The second embodiment is different from the above-described first embodiment in terms of the arrangement of the hydraulic motors and the channel member. For the present embodiment, the same constituents as in the first embodiment described above are denoted by the same reference numerals and are not described here. 
     As shown in  FIG.  5   , in this embodiment, the hydraulic motors  8 A,  8 B are arranged such that the rotation axis C 2  of the hydraulic motor  8 A and the rotation axis C 2  of the hydraulic motor  8 B are spaced apart from the first rotation axis C 1  of the reduction units  3 A,  3 B. Further, the channel member  9  includes a cover  9   p  and a channel portion  9   q.  The cover  9   p  closes the second opening  89  in the casing  81  of the hydraulic motor  8 A, and the channel portion  9   q  has the supply channel  9   c  and the separation portion  9   a  formed therein. In the channel portion  9   q,  the separation portion  9   a  is formed in proximity to the first rotation axis C 1 . The separated supply channels  9   e  are each formed through the cover  9   p  and the channel portion  9   q.  The supply ports  91  are each formed in the cover  9   p.    
     The supply port  91  of the hydraulic motor  8 A and the supply port  91  of the hydraulic motor  8 B are symmetrically arranged in the circumferential and radial directions of the first rotation axis C 1 . The supply port  91  of the hydraulic motor  8 A is located on the −Z side relative to the supply port  91  of the hydraulic motor  8 B, and the supply port  91  of the hydraulic motor  8 B is located on the +Z side relative to the supply port  91  of the hydraulic motor  8 A. 
     In this embodiment, the hydraulic motor  8 A and the hydraulic motor  8 B are arranged symmetrically in the circumferential direction and the radial direction with respect to the first rotation axis C 1 . The reduction units  3 A,  3 B may each have the reduction input portion  18  formed of gears and other parts that mesh with the transmission gears  44  and the drive shaft  76   a,    76   b.    
     In this embodiment, the reduction units  3 A,  3 B and the bucket  110  have the same first rotation axis C 1 , as in the first embodiment described above. Further, the hydraulic motors  8 A,  8 B are not aligned with each other in the R direction. Therefore, for the same size of the hydraulic motors  8 A,  8 B as in the first embodiment described above, the distance between the reduction units  3 A,  3 B in the direction of the first rotation axis C 1  can be smaller. Therefore, the distance between the attachment brackets  110   a  in the direction of the first rotation axis C 1  can be smaller. This allows the drive device  1  to be downsized and space-saving in the direction of the first rotation axis C 1 . 
     This embodiment produces the same advantageous effects as the first embodiment described above. 
     In the embodiments disclosed herein, a member formed of multiple components may be integrated into a single component, or conversely, a member formed of a single component may be divided into multiple components. Irrespective of whether or not the components are integrated, they are acceptable as long as they are configured to attain the object of the invention.