Abstract:
A shovel includes: a speed reducer configured by stacking a plurality of gear speed reducers each having a sun gear, a planetary gear, an internal gear, and a carrier member supporting the planetary gear provided in a case, in a direction of an axis of rotation of an upper turning body; and a movement restriction section which is provided between the sun gear of one gear speed reducer among the gear speed reducers stacked in a plurality and another gear speed reducer stacked so as to face the sun gear and restricts movement of the sun gear of the one gear speed reducer toward the other gear speed reducer, wherein the movement restriction section is provided at the case.

Description:
RELATED APPLICATIONS 
     Priority is claimed to Japanese Patent Application No. 2014-064651, filed Mar. 26, 2014, the entire content of which is incorporated herein by reference. 
     BACKGROUND 
     1. Technical Field 
     A certain embodiment of the invention relates to a shovel having a turning speed reducer. 
     2. Description of Related Art 
     A shovel is provided with a turning drive device which drives an upper turning body so as to turn it. The turning drive device often reduces the power from a power source (a hydraulic motor, an electric motor, or the like) in a turning speed reducer (hereinafter referred to simply as a speed reducer) and turns the upper turning body by increased output torque. 
     As the speed reducer, in terms of being compact, in terms of a change in reduction ratio being easy, or the like, a planetary gear speed reducer in which a sun gear is used as an input element and a planetary carrier of a planetary gear is used as an output element is frequently used. Further, in order to obtain a predetermined reduction ratio, a multistage speed reducer in which a plurality of planetary gear speed reducers are stacked is also frequently used (refer to the related art). 
     SUMMARY 
     According to an aspect of the present invention, there is provided a shovel including: a speed reducer configured by stacking a plurality of gear speed reducers each having a sun gear, a planetary gear, an internal gear, and a carrier member supporting the planetary gear provided in a case, in a direction of an axis of rotation of an upper turning body; and a movement restriction section which is provided between the sun gear of one gear speed reducer among the gear speed reducers stacked in a plurality and another gear speed reducer stacked so as to face the sun gear and restricts movement of the sun gear of the one gear speed reducer toward the other gear speed reducer, wherein the movement restriction section is provided at the case. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side view of a shovel according to an embodiment of the present invention. 
         FIG. 2  is a block diagram showing the configuration of a drive system in an embodiment of the present invention. 
         FIG. 3  is a block diagram showing the configuration of a turning drive device in an embodiment of the present invention. 
         FIG. 4  is a top view of the turning drive device. 
         FIG. 5  is a cross-sectional view along a line V-V in FIG.  4 . 
         FIG. 6  is a cross-sectional view showing the vicinity of a movement restriction mechanism in the turning drive device in an enlarged manner. 
     
    
    
     DETAILED DESCRIPTION 
     A planetary carrier is supported on a case by a bearing member (a bearing or the like), whereby the movement of the planetary carrier in a thrust direction (an axial direction) is restricted. However, a shovel is used in a harsh environment, and thus there is a concern that a great external force may be applied to a lower traveling body and an upper turning body during work. 
     In a case where the external force is applied, a low-speed side sun gear provided in a low-speed planetary gear speed reducer disposed on the lower side is sometimes biased so as to move toward a high-speed planetary gear speed reducer disposed at an upper portion. The movement and biasing force is applied to the bearing member through a high-speed side planetary carrier. Accordingly, there is a problem in that there is a concern that the bearing member may be damaged due to the movement and biasing force. 
     It is desirable to provide a shovel in which a bearing member supporting a carrier member is prevented from being damaged. 
     According to a certain aspect of the present invention, the movement of a carrier member in a thrust direction is restricted, and thus a bearing member can be prevented from being damaged. 
     Next, a non-limiting exemplary embodiment of the present invention will be described with reference to the accompanying drawings. 
     In addition, in the description in all the accompanying drawings, the same or corresponding members or components are denoted by the same or corresponding reference numerals and overlapping description is omitted. Further, the drawings are not intended to show the relative ratio between members or components unless otherwise specified. Therefore, specific dimensions can be determined by those skilled in the art in the light of the following non-limiting embodiment. 
     Further, an embodiment described below is not intended to limit the invention and is illustrative, and all the features which are described in the embodiment or the combinations thereof are not necessarily essential for the invention. 
       FIG. 1  shows a shovel  100  according to an embodiment of the present invention. 
     In the shovel  100 , an upper turning body  3  is mounted on an upper portion of a lower traveling body  1  through a rotation mechanism  2 . The upper turning body  3  is provided with an engine compartment  3   a , a boom  4 , an arm  5 , a bucket  6 , and a cabin  10 , and the like. 
     The arm  5  is attached to the tip of the boom  4 , and the bucket  6  is attached to the tip of the arm  5 . The boom  4 , the arm  5 , and the bucket  6  are respectively hydraulically driven by a boom cylinder  7 , an arm cylinder  8 , and a bucket cylinder  9 . 
     In the cabin  10 , an operating device  26  (refer to  FIG. 2 ) which is operated by a driver, and the like are disposed. Further, in the engine compartment  3   a , a power source such as an engine is mounted. 
     In addition, as the shovel according to this embodiment, a so-called hybrid shovel having a power storage device which stores electric power which is supplied to a turning drive device is given as an example. However, the present invention can also be applied to, for example, an electrically-driven shovel to which charging power is supplied from an external power supply, and a hydraulic shovel in which the rotation mechanism  2  is driven by a hydraulic motor, as long as they are shovels adopting a mechanical brake (described later). 
       FIG. 2  is a block diagram showing the configuration of a drive system of the shovel. In addition, in  FIG. 2 , a mechanical power system is shown by a double line, a high-pressure hydraulic line is shown by a thick solid line, a pilot line is shown by a dashed line, and an electric drive and control system is shown by a thin solid line. 
     The drive system of the shovel has an engine  11 , a motor generator  12 , a main pump  14 , a pilot pump  15 , a control valve  17 , the operating device  26 , a controller  30 , a turning drive device  40 , a power storage system, and the like. 
     The engine  11  and the motor generator  12  are respectively connected to two input shafts of a transmission  13 . The main pump  14  and the pilot pump  15  are connected to an output shaft of the transmission  13 . Both the main pump  14  and the pilot pump  15  are hydraulic pumps. 
     The control valve  17  is connected to the main pump  14  through a high-pressure hydraulic line  16 . Further, the operating device  26  is connected to the pilot pump  15  through a pilot line  25 . 
     The control valve  17  performs the control of a hydraulic system in the hybrid shovel. Accordingly, hydraulic motors  1 A and  1 B for the lower traveling body, the boom cylinder  7 , the arm cylinder  8 , the bucket cylinder  9 , and the like are connected to the control valve  17  through the high-pressure hydraulic lines. 
     The motor generator  12  is connected to a power storage system  120  through an inverter  18 . The power storage system  120  has a capacitor (a power storage device) as an electric condenser. Further, the power storage system  120  is connected to the turning drive device  40 . 
     The turning drive device  40  has an electric motor for turning  21 , a resolver  22 , a mechanical brake  23 , a turning speed reducer  24 , and the like. The power storage system  120  is connected to the electric motor for turning  21  through an inverter  20 . Further, an output shaft  21   b  of the electric motor for turning  21  is connected to the resolver  22  and the turning speed reducer  24 . 
     The electric motor for turning  21  functions as an electric motor for turning which drives the upper turning body  3  so as to turn it. Further, the mechanical brake  23  functions as a brake device which mechanically applies braking to the upper turning body  3 . 
     The operating device  26  has a lever  26 A, a lever  26 B, and a pedal  26 C. The lever  26 A, the lever  26 B, and the pedal  26 C are respectively connected to the control valve  17  and a pressure sensor  29  through hydraulic lines  27  and  28 . Further, the pressure sensor  29  is connected to the controller  30  which performs the drive control of an electric system. 
     The controller  30  is a control device as a main control unit which performs the drive control of the hybrid shovel. The controller  30  is configured with an arithmetic processing unit which includes a central processing unit (CPU) and an internal memory. The controller  30  executes predetermined drive control by executing a program for drive control stored in the internal memory by the CPU. 
     Specifically, the controller  30  converts a signal which is supplied from the pressure sensor  29  into a speed command and performs the drive control of the electric motor for turning  21  based on the signal. At this time, the signal which is supplied from the pressure sensor  29  is a signal indicating an operation amount by which a driver operates the operating device  26  in order to turn the rotation mechanism  2 . 
     Further, the controller  30  performs the operation control of the motor generator  12 . Here, the operation control of the motor generator  12  refers to control performing switching between an electric (assist) operation and a power-generating operation. 
     In addition, the controller  30  performs the charge and discharge control of a capacitor provided in the power storage system  120 . Specifically, the controller  30  performs the switching control between a step-up operation and a step-down operation of a step-up/down converter of the power storage system  120  based on a charge state of the capacitor, an operating state of the motor generator  12 , and an operating state of the electric motor for turning  21 . 
     In this embodiment, the operating state of the motor generator  12  includes two operating states, an electric (assist) operation state and a power-generating operation state. Further, the operation state of the electric motor for turning  21  includes two operating states, a power running operation and a regenerative operation. In addition, the controller  30  also performs the control of an amount (a charging current or charging power) which is charged to the capacitor, as will be described later. 
     The shovel having the above-described drive system drives the electric motor for turning  21  by electric power which is supplied through the inverter  20 , when driving the upper turning body  3  so as to turn it. The rotary force of the output shaft  21   b  of the electric motor for turning  21  is transmitted to an output shaft  40 A of the turning drive device  40  through the turning speed reducer  24 . 
       FIG. 3  is a block diagram of the turning drive device  40  which is mounted on the shovel according to an embodiment of the present invention. The turning drive device  40  has the electric motor for turning  21 , the resolver  22 , the mechanical brake  23 , the turning speed reducer  24 , the output shaft  40 A, and the like. 
     The electric motor for turning  21  is an electric motor. The turning speed reducer  24  is connected to the output shaft side of the electric motor for turning  21 . The turning speed reducer  24  has a first turning speed reducer  24 - 1  and a second turning speed reducer  24 - 2 . Each of the first turning speed reducer  24 - 1  and the second turning speed reducer  24 - 2  is configured with a planetary gear speed reducer. 
     The first turning speed reducer  24 - 1  of a first stage is assembled to the electric motor for turning  21 . Further, the mechanical brake  23  is provided at a planetary carrier  46  serving as an output shaft of the first turning speed reducer  24 - 1 . Further, the second turning speed reducer  24 - 2  of a second stage is assembled to the first turning speed reducer  24 - 1  with the mechanical brake  23  interposed therebetween. Then, an output shaft of the second turning speed reducer  24 - 2  of the second stage serves as the output shaft  40 A of the turning drive device  40 . 
     In addition, although not shown in the drawings, the output shaft  40 A of the turning drive device  40  is connected to the rotation mechanism  2 , and the rotation mechanism  2  is driven by the rotary force of the output shaft  40 A. 
     Next, a specific configuration of the turning drive device  40  will be described with reference to  FIGS. 5 and 6 . 
     In addition,  FIG. 5  is a cross-sectional view of the turning drive device  40 , and  FIG. 6  is a cross-sectional view of the vicinity of the mechanical brake  23  of the turning drive device  40  in an enlarged manner. 
     As shown in  FIG. 4 , the first turning speed reducer  24 - 1  is configured with a planetary gear speed reducer having a sun gear  42 , a planetary gear  44 , the planetary carrier  46 , an internal gear  48 , and the like. The first turning speed reducer  24 - 1  is accommodated in a first gear case  50  and a second gear case  52 . 
     The sun gear  42  is fixed to the output shaft  21   b  of the electric motor for turning  21 . In this embodiment, three planetary gears  44  are engaged with the sun gear  42 . 
     Each of the planetary gears  44  is rotatably supported on a pin  44   a  provided to be erect at the planetary carrier  46 . A flange-shaped portion  44   b  which prevents the planetary gear  44  from being separated from the pin  44   a  is provided at an upper end portion of the pin  44   a . For this reason, the planetary gear  44  is configured so as not to be separated from the planetary carrier  46 . 
     Further, each of the planetary gears  44  is engaged with the internal gear  48  formed in the inner surface of the first gear case  50 . The first gear case  50  with the internal gear  48  formed therein is fixed to an end plate  21   a  of the electric motor for turning  21 . Accordingly, the internal gear  48  (the first gear case  50 ) cannot rotate by itself. 
     On the other hand, a lower portion of the planetary carrier  46  serves as the output shaft of the first turning speed reducer  24 - 1 . The planetary carrier  46  serving as the output shaft is rotatably supported on the second gear case  52  fixed to the first gear case  50 , through a bearing  56 . 
     The bearing  56  has an inner ring  56   a , an outer ring  56   b , balls  56   c , and the like (refer to  FIG. 6 ). The inner ring  56   a  is disposed integrally with the planetary carrier  46 , and the outer ring  56   b  is disposed at the second gear case  52 . Further, the balls  56   c  are disposed between the inner ring  56   a  and the outer ring  56   b . In this way, the planetary carrier  46  can rotate with respect to the second gear case  52 . 
     Further, a bearing collar  58  which fixes the bearing  56  to the planetary carrier  46  is provided at a lower portion of the bearing  56 . In addition, the first turning speed reducer  24 - 1  having the above-described configuration is lubricated by lubricating oil LB 1 . 
     In the first turning speed reducer  24 - 1  having the configuration as described above, if the output shaft  21   b  of the electric motor for turning  21  rotates and thus the sun gear  42  rotates, the planetary gear  44  rotates (rotates on its own axis). The planetary gear  44  is engaged with the internal gear  48  formed in the inner surface of the first gear case  50 . Accordingly, the first gear case  50  with the internal gear  48  formed therein tries to rotate by the rotary force of the planetary gear  44 . 
     However, the first gear case  50  cannot rotate because it is fixed to the end plate  21   a  of the electric motor for turning  21 , as described above. In contrast, the planetary carrier  46  has a configuration in which it can rotate with respect to the second gear case  52 . 
     As a result, the rotary force of the planetary gear  44  acts as a force to rotate the planetary carrier  46 , and thus the planetary carrier  46  rotates. Due to this, the rotation of the output shaft  21   b  of the electric motor for turning  21  is reduced in speed at the first turning speed reducer  24 - 1  and is output from the planetary carrier  46 . 
     Next, the second turning speed reducer  24 - 2  will be described. A sun gear  82  of the second turning speed reducer  24 - 2  is connected to the planetary carrier  46  serving as the output shaft of the first turning speed reducer  24 - 1 . The sun gear  82  is engaged with a plurality of planetary gears  84 . In addition, the planetary gears  84  are engaged with an internal gear  88  formed in the inner wall of a third gear case  54 . Accordingly, the planetary gear  84  revolves while rotating between the sun gear  82  and the internal gear  88 . 
     In this embodiment, the second turning speed reducer  24 - 2  has three planetary gears  84 . Each of the planetary gears  84  is rotatably supported on a planetary carrier  86  through a pin  84   a  and revolves while rotating, thereby rotating the planetary carrier  86 . 
     Each of the planetary gears  84  is rotatably supported on the pin  84   a  provided to be erect at the planetary carrier  86 . A flange-shaped portion  84   b  which prevents the planetary gear  84  from being separated from the pin  84   a  is provided at an upper end portion of the pin  84   a . For this reason, the planetary gear  84  is configured so as not to be separated from the planetary carrier  86 . 
     The planetary carrier  86  configures an output shaft of the second turning speed reducer  24 - 2 . In this embodiment, the second turning speed reducer  24 - 2  is a final stage speed reducer. Accordingly, the planetary carrier  86  serving as the output shaft of the second turning speed reducer  24 - 2  serves as the output shaft  40 A of the turning speed reducer  24 . The second turning speed reducer  24 - 2  is lubricated by lubricating oil LB 2 . 
     Due to the above-described configuration, the turning drive device  40  reduces the rotation speed of the output shaft  21   b  of the electric motor for turning  21  and increases the torque of the output shaft  40 A. 
     In addition, in this embodiment, the turning speed reducer  24  has been described as being a speed reducer configuration having a two-stage configuration which is composed of the first turning speed reducer  24 - 1  and the second turning speed reducer  24 - 2 . However, the number of stages of the speed reducers of the turning speed reducer  24  is not limited thereto and can be appropriately set based on the output of the electric motor for turning  21 , torque which is required for the rotation mechanism  2 , or the like. 
     Next, the mechanical brake  23  will be described. 
     The mechanical brake  23  is a displacer brake having a brake disc  60  and a brake plate  62 . The mechanical brake  23  is provided between the second gear case  52  which is a fixed portion and the planetary carrier  46  which is an output shaft. 
     The brake disc  60  has a disc shape, as shown in  FIG. 6 , and an insertion hole  65  into which the planetary carrier  46  is inserted is formed at the center. Further, spline teeth are formed in the inner periphery of the insertion hole  65 . 
     A spline is formed in an outer peripheral portion (a portion on which the brake disc  60  is mounted) of the planetary carrier  46 . The spline is formed in the outer periphery of the planetary carrier  46  so as to extend in an up-down direction (a direction shown by arrows Z 1  and Z 2  in the drawings). 
     In addition, in the following description, the electric motor for turning  21  side with respect to the planetary carrier  46  is sometimes referred to as an upper side (a side of a direction of the arrow Z 1 ) and the side opposite to the electric motor for turning  21  side with respect to the planetary carrier  46  is sometimes referred to as a lower side (a side of a direction of the arrow Z 2 ). 
     Spline teeth formed in the brake disc  60  are configured so as to be engaged with the spline formed in the planetary carried  46 . Accordingly, in a state where the brake disc  60  is mounted on the planetary carrier  46 , a structure in which the brake disc  60  and the planetary carrier  46  are spline-connected is made. 
     In a state where the brake disc  60  and the planetary carrier  46  are spline-connected in this manner, the brake disc  60  is in a state of extending toward the outside in a direction of a radius of rotation from the planetary carrier  46 . Further, the brake disc  60  cannot rotate with respect to the planetary carrier  46  but is in a state of being movable in an axial direction (the direction shown by the arrows Z 1  and Z 2  in  FIGS. 5 and 6 ) of the planetary carrier  46 . 
     The brake plates  62  are disposed on both upper and lower sides of the brake disc  60 . The brake plate  62  has a disc shape with a hole formed at the center. Further, spline teeth are formed in the outer periphery of the brake plate  62 . 
     A spline is formed in an annular inner wall portion (a portion on which the brake plate  62  is mounted) of the second gear case  52 . The spline is formed in the inner wall of the second gear case  52  so as to extend in the above-described axial direction (the direction shown by the arrows Z 1  and Z 2 ). 
     The spline teeth formed in the brake plate  62  are configured so as to be engaged with the spline formed in the second gear case  52 . Accordingly, in a state where the brake plate  62  is mounted on the second gear case  52 , a structure in which the brake plate  62  and the second gear case  52  are spline-connected is made. 
     In a state where the brake plate  62  and the second gear case  52  are spline-connected in this manner, the brake plate  62  is in a state of extending toward the inside in the direction of a radius of rotation from the second gear case  52 . Further, the brake plate  62  cannot rotate with respect to the second gear case  52  but is in a state of being movable in the axial direction (the direction shown by the arrows Z 1  and Z 2 ) of the planetary carrier  46 . 
     Further, a piston  64  is disposed above the upper brake plate  62  in a state of being movable in the axial direction (the direction shown by the arrows Z 1  and Z 2 ) of the planetary carrier  46 . The piston  64  is always pressed against the upper brake plate  62  by being pressed by a spring  66 . 
     As described above, both the brake disc  60  and the brake plate  62  are movable in the axial direction of the planetary carrier  46 . For this reason, if the brake plate  62  is pressed by the piston  64 , the brake disc  60  is pressed to be sandwiched between the upper and lower brake plates  62 . The brake disc  60  is pressed to be sandwiched between the brake plates  62 , whereby a brake force to try to prevent the rotation of the brake disc  60  is generated in the mechanical brake  23 . 
     As described above, the brake disc  60  has a configuration of being unable to rotate with respect to the planetary carrier  46 . For this reason, the brake force acting on the brake disc  60  becomes a brake force (a braking force) stopping the rotation of the planetary carrier  46 . 
     A hydraulic space  68  to which hydraulic oil can be supplied is formed between the piston  64  and the second gear case  52 . Further, a brake release port  69  is connected to the hydraulic space  68 . In addition, a seal member  91  such as an O-ring is disposed between the piston  64  and the second gear case  52  and performs sealing such that the hydraulic oil in the hydraulic space  68  does not leak. 
     The brake release port  69  is connected to the operating device  26 . Then, if oil pressure is supplied from the pilot pump  15  to the hydraulic space  68  through the operating device  26 , a hydraulic line  27   a  (refer to  FIG. 2 ), and the brake release port  69 , the piston  64  is pushed up by the oil pressure. In this way, a force pressing the brake plate  62  is eliminated, and thus the mechanical brake  23  enters a state where the brake is released. 
     In addition, the mechanical brake  23  having the above-described configuration is controlled so as to enter a state where the brake is released at the time of the turning of the upper turning body  3  and the brake is activated when the upper turning body  3  has stopped. 
     Here, in the turning drive device  40  having the above-described configuration, attention is paid to the bearing  56  which supports the planetary carrier  46  in the first gear case  50  and the second gear case  52 . The planetary carrier  46  is restricted in position by the bearing  56  and the like, thereby being located at a predetermined mounting position in the first gear case  50  and the second gear case  52 . 
     However, the shovel is used in a harsh environment. Accordingly, in a case where a great external force is applied to the upper turning body  3  and each component provided therein at the time of work, the sun gear  82  configuring the second turning speed reducer  24 - 2  is sometimes biased so as to move in a thrust direction (the direction of the arrow Z 1 ) toward the first turning speed reducer  24 - 1  by the external force. 
     Since the sun gear  82  is connected to the planetary carrier  46 , if the sun gear  82  is biased so as to move in the direction of the arrow Z 1 , the planetary carrier  46  is also biased so as to move, and thus an excessive thrust load is generated in the bearing  56 , whereby there is a concern that the bearing  56  may be damaged. 
     In this embodiment, a movement restriction section  130  is provided, and thus a configuration is made in which even in a case where the sun gear  82  (the planetary carrier  46 ) moves, the bearing  56  is protected by the movement restriction section  130 . Hereinafter, the movement restriction section  130  will be described. 
     As shown in an enlarged manner in  FIG. 6 , the movement restriction section  130  is fixed to a bottom portion of the first gear case  50 . Further, the movement restriction section  130  is disposed at a position facing the sun gear  82  provided in the second turning speed reducer  24 - 2 . The disposition position is also a boundary position between the first turning speed reducer  24 - 1  and the second turning speed reducer  24 - 2 . 
     The movement restriction section  130  has a thrust plate  132 , a thrust washer  136 , a fixing bolt  138 , and the like. 
     The thrust plate  132  is an annular metal plate in which a hole into which the output shaft of the planetary carrier  46  is inserted is formed at the center. The thrust plate  132  has a predetermined strength capable of restricting the movement of the sun gear  82  when the sun gear  82  moves, as will be described later. 
     Further, the thrust plate  132  is fixed to a bottom portion of the second gear case  52  by using a plurality of fixing bolts  138  (in  FIG. 6 , only one is shown). In the fixing state, the thrust plate  132  faces the sun gear  82  of the second turning speed reducer  24 - 2 . 
     The thrust washer  136  is disposed between the sun gear  82  and the thrust plate  132 . The thrust washer  136  receives a force to the lower side of the sun gear  82 , which includes the force of gravity. Further, the thrust washer  136  performs lubrication between the sun gear  82  and the thrust plate  132 . 
     In addition, a bearing member which is disposed between the sun gear  82  and the thrust plate  132  is not limited to the thrust washer  136 , and it is also possible to use a thrust bearing or the like. 
     Next, an operation of the movement restriction section  130  having the above-described configuration will be described. 
     For example, a case where an external force is applied to the shovel and the sun gear  82  configuring the second turning speed reducer  24 - 2  moves toward the first turning speed reducer  24 - 1  due to the external force is assumed. That is, a case where the sun gear  82  moves in the thrust direction (the direction of the arrow Z 1  in the drawings) toward the first turning speed reducer  24 - 1  is assumed. 
     In this embodiment, the movement restriction section  130  is disposed at a position facing the sun gear  82 . Further, the movement restriction section  130  is fixed to the second gear case  52 . Accordingly, if the sun gear  82  moves in the direction of the arrow Z 1 , the sun gear  82  presses the thrust plate  132  through the thrust washer  136 . 
     However, the thrust plate  132  is solidly fixed to the second gear case  52 . Further, the strength of the thrust plate  132  is set to be a strength to withstand a pressing force at which the sun gear  82  presses the thrust plate  132  due to an external force. 
     Therefore, even if the sun gear  82  tries to move, the movement is restricted by the movement restriction section  130 . Further, the movement of the sun gear  82  is restricted, whereby the movement of the planetary carrier  46  to which the sun gear  82  is connected is also restricted. Accordingly, a thrust load in the thrust direction can be prevented from being generated in the bearing  56  supporting the planetary carrier  46 , and thus damage can be prevented from occurring in the bearing  56 . 
     In the embodiment described above, the second turning speed reducer  24 - 2  of a lower stage is not constrained with respect to the respective gear cases  50  and  52  and with respect to the first turning speed reducer  24 - 1  of an upper stage. In the second turning speed reducer  24 - 2  of the lower stage, in terms of the configuration thereof, there is a possibility that due to an external force or the like, the sun gear  82  may move up and down alone or the second turning speed reducer  24 - 2  (the sun gear  82 , the planetary gear  84 , the planetary carrier  86 , and the internal gear  88 ) may move up and down as a whole. 
     However, in this embodiment, as described above, the movement can be received by the movement restriction section  130 , and therefore, the occurrence of damage to the bearing  56  due to contact can be prevented. In particular, in a case where the turning speed reducer  24  has a two-stage configuration and a lower stage is a configuration such as the second turning speed reducer  24 - 2 , the present invention is particularly effective. 
     A preferred embodiment of the present invention has been described above in detail. However, the present invention is not limited to the specific embodiment described above, and various modification and changes can be made within the scope of the concept of the present invention stated in the appended claims. 
     For example, in the embodiment described above, the movement restriction section  130  is configured by fixing the thrust plate  132  to the second gear case  52  by the fixing bolt  138 . However, it is also possible to form a movement restriction section integrally with the second gear case  52 . 
     It should be understood that the invention is not limited to the above-described embodiment, and may be modified into various forms on the basis of the spirit of the invention. Additionally, the modifications are included in the scope of the invention.