Patent Publication Number: US-11031684-B2

Title: Earth-moving machine

Description:
TECHNICAL FIELD 
     The present invention relates to an earth-moving machine. 
     BACKGROUND ART 
     An earth-moving machine including an antenna for GNSS (Global Navigation Satellite System) has been conventionally known. In an earth-moving machine disclosed in Japanese Patent Laying-Open No. 2015-21320 (PTD 1), antennas are disposed on an upper surface of a device chamber on the rear side of a cab and on an upper surface of a hydraulic oil tank. 
     CITATION LIST 
     Patent Document 
     PTD 1: Japanese Patent Laying-Open No. 2015-21320 
     SUMMARY OF INVENTION 
     Technical Problem 
     When an earth-moving machine includes a plurality of antennas for receiving satellite positioning signals, it is required to arrange the antennas at the largest possible distance from one another in a lateral direction in order to improve the accuracy of positioning. 
     In the case of a small-sized earth-moving machine, an area of a vehicular body frame is small. In the case of a short tail swing hydraulic excavator, a vehicular body frame on the rear side of a vehicular body is formed in an arc shape centered at a swing center when viewed from above, and thus, an area of the vehicular body frame on the rear side of the vehicular body is particularly small. Therefore, it is difficult to arrange a plurality of antennas at positions separate from one another. 
     An object of the present invention is to provide an earth-moving machine in which a plurality of antennas for receiving satellite positioning signals can be appropriately arranged. 
     Solution to Problem 
     An earth-moving machine according to the present invention includes: a vehicular body; a cab placed on the vehicular body; and a plurality of antennas for receiving satellite positioning signals, the plurality of antennas including a first antenna and a second antenna. The first antenna is attached to the cab. The second antenna is attached to the vehicular body without the cab being interposed. 
     Advantageous Effects of Invention 
     According to the present invention, the plurality of antennas for receiving satellite positioning signals can be appropriately arranged. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a side view schematically showing a construction of a hydraulic excavator based on an embodiment. 
         FIG. 2  is a plan view of the hydraulic excavator shown in  FIG. 1 . 
         FIG. 3  is a rear view of the hydraulic excavator shown in  FIG. 1 . 
         FIG. 4  is a perspective view of the hydraulic excavator shown in  FIG. 1  when viewed from the right rear. 
         FIG. 5  is a perspective view of a state in which an engine hood and a soil cover are open. 
         FIG. 6  is an enlarged perspective view showing a support structure of a sub-antenna. 
         FIG. 7  is an enlarged perspective view showing a support structure of a main antenna. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     An embodiment will be described hereinafter with reference to the drawings. In the following description, the same components are designated by the same reference characters. Names and functions thereof are also the same. Therefore, the detailed description of them will not be repeated. 
     Although a short tail swing hydraulic excavator  1  will be described as one example of an earth-moving machine in the embodiment, the idea of the embodiment is also applicable to other types of earth-moving machines. 
       FIG. 1  is a side view schematically showing a construction of hydraulic excavator  1  based on an embodiment.  FIG. 2  is a plan view of hydraulic excavator  1  shown in  FIG. 1 .  FIG. 3  is a rear view of hydraulic excavator  1  shown in  FIG. 1 .  FIG. 4  is a perspective view of hydraulic excavator  1  shown in  FIG. 1  when viewed from the right rear. As shown in  FIGS. 1 to 4 , hydraulic excavator  1  in the present embodiment mainly has a travel unit  2 , a revolving unit  3 , and a work implement  4 . A vehicular body of hydraulic excavator  1  is constituted of travel unit  2  and revolving unit  3 . 
     Travel unit  2  has a pair of left and right crawler belts  2 A. Hydraulic excavator  1  is constructed to be self-propelled as the pair of left and right crawler belts  2 A is rotationally driven. Revolving unit  3  is revolvably attached to travel unit  2 . Revolving unit  3  mainly has a cab  5 , an exterior panel  6 , and a counterweight  7 . 
     Cab  5  is arranged on a front left side of revolving unit  3  (a front side of the vehicle). Cab  5  is placed on the vehicular body of hydraulic excavator  1 . An operator&#39;s compartment is formed inside cab  5 . The operator&#39;s compartment is a space for an operator to operate hydraulic excavator  1 . An operator&#39;s seat for an operator to have a seat is arranged in the operator&#39;s compartment. 
     In the present embodiment, positional relation among components will be described with work implement  4  being defined as the reference. 
     A boom  4 A of work implement  4  rotationally moves around a boom pin with respect to revolving unit  3 . A trajectory of movement of a specific portion of boom  4 A which pivots with respect to revolving unit  3 , such as a tip end portion of boom  4 A, is in an arc shape, and a plane including the arc is specified. When hydraulic excavator  1  is planarly viewed, the plane is shown as a straight line. A direction in which this straight line extends is a fore/aft direction of the vehicular main body of the work vehicle or a fore/aft direction of revolving unit  3 , and it is also simply referred to as the fore/aft direction below. A lateral direction (a direction of vehicle width) of the vehicular main body or a lateral direction of revolving unit  3  is a direction orthogonal to the fore/aft direction in a plan view and also simply referred to as the lateral direction below. The lateral direction refers to a direction of extension of the boom pin. An upward/downward direction of the vehicular main body or an upward/downward direction of revolving unit  3  is a direction orthogonal to the plane defined by the fore/aft direction and the lateral direction and also simply referred to as the upward/downward direction below. 
     A side in the fore/aft direction where work implement  4  projects from the vehicular main body is defined as the fore direction, and a direction opposite to the fore direction is defined as the aft direction. A right side and a left side in the lateral direction when one faces the fore direction are defined as a right direction and a left direction, respectively. A side in the upward/downward direction where the ground is located is defined as a lower side and a side where the sky is located is defined as an upper side. 
     The fore/aft direction refers to a fore/aft direction of an operator who sits at the operator&#39;s seat in cab  5 . The lateral direction refers to a lateral direction of the operator who sits at the operator&#39;s seat. The upward/downward direction refers to an upward/downward direction of the operator who sits at the operator&#39;s seat. A direction in which the operator sitting at the operator&#39;s seat faces is defined as the fore direction and a direction behind the operator sitting at the operator&#39;s seat is defined as the aft direction. A right side and a left side at the time when the operator sitting at the operator&#39;s seat faces front are defined as the right direction and the left direction, respectively. A foot side of the operator who sits at the operator&#39;s seat is defined as a lower side, and a head side is defined as an upper side. 
     Exterior panel  6  has an engine hood  6 A, a soil cover  6 B and a sheet metal cover  6 C. Engine hood  6 A, soil cover  6 B and sheet metal cover  6 C form a part of an upper surface of revolving unit  3 . Engine hood  6 A forms the upper surface of revolving unit  3  in the rear of cab  5 . Soil cover  6 B and sheet metal cover  6 C form a part of the upper surface of revolving unit  3  on the right of cab  5 . Sheet metal cover  6 C forms a rear right corner portion of the upper surface of revolving unit  3  other than engine hood  6 A. Soil cover  6 B is arranged on the left side and front side of sheet metal cover  6 C. 
     Engine hood  6 A and soil cover  6 B are formed of a lightweight resin material. An upper surface of hydraulic excavator  1  in the rear of cab  5  is formed of a resin material. Sheet metal cover  6 C is formed of a metal material such as a steel material. 
     A front edge of engine hood  6 A extends in the lateral direction. Engine hood  6 A is configured to be relatively rotatable with respect to revolving unit  3  with the front edge serving as a pivot point. Engine hood  6 A is configured to be openable and closable with respect to the vehicular body of hydraulic excavator  1 . When engine hood  6 A rotates and moves upward, an engine compartment  14  is opened. When engine hood  6 A moves downward, engine compartment  14  is covered with engine hood  6 A and becomes unexposed to the outside. Engine hood  6 A is configured to be capable of opening and closing engine compartment  14 . 
     A rear edge of soil cover  6 B extends in the lateral direction. Soil cover  6 B is configured to be relatively rotatable with respect to revolving unit  3  with the rear edge serving as a pivot point. Soil cover  6 B can rotate in parallel with boom  4 A of work implement  4 . Soil cover  6 B covers, from above, an accommodation space that accommodates a fuel tank, a hydraulic oil tank and the like. Soil cover  6 B is configured to be capable of opening and closing the accommodation space.  FIG. 5  is a perspective view of a state in which engine hood  6 A and soil cover  6 B are open. When engine hood  6 A is opened, engine compartment  14  is exposed.  FIG. 5  does not show the components such as, for example, an engine  12  and the fuel tank that are accommodated in the accommodation space covered with soil cover  6 B and in engine compartment  14 . 
     Since engine hood  6 A and soil cover  6 B that are relatively movable with respect to revolving unit  3  are formed of a lightweight resin material, a service person who tries to open and close engine hood  6 A and soil cover  6 B can manually open and close engine hood  6 A and soil cover  6 B without the need for a special device. Since engine hood  6 A and soil cover  6 B are resin mold products and can be easily molded into a desired shape, the design of an outer appearance of hydraulic excavator  1  is improved. 
     Sheet metal cover  6 C covers, from above and the right, an accommodation space that accommodates a main valve and the like. Sheet metal cover  6 C is fixed to revolving unit  3 . After sheet metal cover  6 C is fixed to revolving unit  3  during assembly of hydraulic excavator  1 , sheet metal cover  6 C is relatively immovable with respect to revolving unit  3 . 
     Soil cover  6 B and sheet metal cover  6 C are arranged in front of engine hood  6 A. Soil cover  6 B and sheet metal cover  6 C are arranged on the front side of the front edge of engine hood  6 A. Since engine hood  6 A covers engine  12  from above, soil cover  6 B and sheet metal cover  6 C are arranged in front of engine  12 . 
     Engine hood  6 A and counterweight  7  are arranged on a rear side of revolving unit  3  (a rear side of the vehicle). Engine hood  6 A is arranged to cover engine compartment  14  from above and the rear. An engine unit (such as engine  12  and an exhaust gas treatment unit) is accommodated in engine compartment  14 . Engine hood  6 A is arranged above engine  12 . Engine hood  6 A is provided with an opening  6 A 1  formed by cutting a part of engine hood  6 A. An exhaust pipe  8  for discharging the exhaust gas of engine  12  into the air projects above engine hood  6 A through opening  6 A 1 . 
     Counterweight  7  is arranged in the rear of the engine compartment for keeping balance of the main body of hydraulic excavator  1  during excavation or the like. Hydraulic excavator  1  is formed as a short tail swing hydraulic excavator having a reduced swing radius of a rear surface. Therefore, a rear surface of counterweight  7  viewed planarly is formed in an arc shape centered at the swing center of revolving unit  3  when viewed from above. 
     Soil cover  6 B and sheet metal cover  6 C are arranged on the right of revolving unit  3 . Soil cover  6 B and sheet metal cover  6 C are provided on the right of work implement  4 . 
     Work implement  4  serves for such work as excavation of soil. Work implement  4  is attached on the front side of revolving unit  3 . Work implement  4  has, for example, boom  4 A, an arm  4 B, a bucket  4 C, and hydraulic cylinders  4 D,  4 E, and  4 F. Work implement  4  can be driven as boom  4 A, arm  4 B, and bucket  4 C are driven by respective hydraulic cylinders  4 F,  4 E, and  4 D. 
     A base end portion of boom  4 A is coupled to revolving unit  3  with the boom pin being interposed. Boom  4 A is attached to revolving unit  3  so as to be rotatable around the boom pin in both directions with respect to revolving unit  3 . Boom  4 A can be operated in the upward/downward direction. A base end portion of arm  4 B is coupled to a tip end portion of boom  4 A with an arm pin being interposed. Arm  4 B is attached to boom  4 A so as to be rotatable around the arm pin in both directions with respect to boom  4 A. Bucket  4 C is coupled to a tip end portion of arm  4 B with a bucket pin being interposed. Bucket  4 C is attached to arm  4 B so as to be rotatable around the bucket pin in both directions with respect to arm  4 B. 
     Work implement  4  is provided on the right of cab  5 . Arrangement of cab  5  and work implement  4  is not limited to the example shown in  FIGS. 1 and 2 , and for example, work implement  4  may be provided on the left of cab  5  arranged on a front right side of revolving unit  3 . 
     Cab  5  includes a roof portion arranged to cover the operator&#39;s seat and a plurality of pillars supporting the roof portion. Each pillar has a lower end coupled to a floor portion of cab  5  and an upper end coupled to the roof portion of cab  5 . The plurality of pillars have a front pillar  40  and a rear pillar. Front pillar  40  is arranged in a corner portion of cab  5  in front of the operator&#39;s seat. The rear pillar is arranged in a corner portion of cab  5  in the rear of the operator&#39;s seat. 
     Front pillar  40  has a right pillar  41  and a left pillar  42 . Right pillar  41  is arranged at the front right corner of cab  5 . Left pillar  42  is arranged at the front left corner of cab  5 . Work implement  4  is arranged on the right of cab  5 . Right pillar  41  is arranged on a side close to work implement  4 . Left pillar  42  is arranged on a side distant from work implement  4 . 
     A space surrounded by right pillar  41 , left pillar  42 , and a pair of rear pillars provides an indoor space in cab  5 . The operator&#39;s seat is accommodated in the indoor space in cab  5 . A door for an operator to enter and exit from cab  5  is provided in a left side surface of cab  5 . 
     A front window  47  is arranged between right pillar  41  and left pillar  42 . Front window  47  is arranged in front of the operator&#39;s seat. Front window  47  is formed of a transparent material. An operator seated at the operator&#39;s seat can visually recognize the outside in front of cab  5  through front window  47 . For example, the operator seated at the operator&#39;s seat can directly look at bucket  4 C excavating soil and existing topography to be executed through front window  47 . 
     Cab  5  has an upper surface  5 A forming an outer surface above cab  5 , and a rear surface  5 B forming an outer surface in the rear of cab  5 . Upper surface  5 A forms the roof portion of cab  5 . A part of rear surface  5 B is formed by a rear window  48 . Rear window  48  is arranged in the rear of the operator&#39;s seat. Rear window  48  is formed of a transparent material. An operator can visually recognize the outside in the rear of cab  5  through rear window  48 . 
     A pair of antennas  9  are attached to revolving unit  3 . The pair of antennas  9  are provided on the upper surface of revolving unit  3 . Antennas  9  are antennas for GNSS. Antennas  9  are antennas for receiving satellite positioning signals. 
     The pair of antennas  9  have a main antenna  9 A and a sub-antenna  9 B. Main antenna  9 A and sub-antenna  9 B are spaced apart from each other in the lateral direction and arranged on the rear side of revolving unit  3 . Of the pair of antennas  9 , main antenna  9 A is arranged on the left of revolving unit  3  and sub-antenna  9 B is arranged on the right of revolving unit  3 . Main antenna  9 A and sub-antenna  9 B are arranged at positions where main antenna  9 A and sub-antenna  9 B do not protrude from revolving unit  3  when viewed planarly. Main antenna  9 A and sub-antenna  9 B are arranged within the swing radius of revolving unit  3 . 
     Main antenna  9 A is attached to cab  5 . Main antenna  9 A is attached to cab  5  with a bracket  10  being interposed. Main antenna  9 A is attached to a rear portion of cab  5 . Main antenna  9 A is attached to an upper portion of cab  5 . 
     Main antenna  9 A is arranged outside cab  5 . Main antenna  9 A is not covered with an exterior cover of cab  5 . Main antenna  9 A is arranged in the rear of rear surface  5 B of cab  5 . Main antenna  9 A is arranged in front of counterweight  7 . Main antenna  9 A is arranged above engine hood  6 A. Main antenna  9 A is arranged at a position overlapping with engine hood  6 A in a plan view. 
     Main antenna  9 A is not supported by engine hood  6 A and soil cover  6 B formed of a resin material. Main antenna  9 A is not attached to engine hood  6 A and soil cover  6 B that are openable and closable with respect to the vehicular body of hydraulic excavator  1 . 
     Main antenna  9 A is arranged at a height position equal to or lower than that of upper surface  5 A of cab  5 . Main antenna  9 A is arranged below upper surface  5 A of cab  5 . Main antenna  9 A is arranged above an upper end of the operator&#39;s seat in cab  5 . 
     When viewed from the rear, main antenna  9 A is arranged at a position overlapping with a part of rear window  48 . When viewed in the fore/aft direction, main antenna  9 A overlaps with a part of a region near an upper edge portion of rear window  48 . The upper edge of rear window  48  is arranged at a height position identical to a height position of a part of main antenna  9 A. 
     Main antenna  9 A is exposed upward. Main antenna  9 A is arranged at a position where rear surface  5 B of cab  5  does not obstruct a skyward angular range of view of main antenna  9 A. In order to receive a radio wave from a GNSS satellite, main antenna  9 A is arranged such that the minimum elevation angle of 15° can be ensured. 
     Sub-antenna  9 B is attached to the vehicular body of hydraulic excavator  1  without cab  5  being interposed. Sub-antenna  9 B is provided above sheet metal cover  6 C. Sub-antenna  9 B overlaps with sheet metal cover  6 C in a plan view. Sub-antenna  9 B is supported by a mast  13 . Mast  13  extends in the upward/downward direction. Mast  13  projects upward from sheet metal cover  6 C. Mast  13  penetrates through sheet metal cover  6 C. Sub-antenna  9 B is fixed to an upper end of mast  13 . Sub-antenna  9 B is exposed upward, and thus, a skyward angular range of view of sub-antenna  9 B is ensured. 
     Sub-antenna  9 B is not supported by engine hood  6 A and soil cover  6 B formed of a resin material. Sub-antenna  9 B is not attached to engine hood  6 A and soil cover  6 B that are openable and closable with respect to the vehicular body of hydraulic excavator  1 . 
     Sub-antenna  9 B is arranged in front of the front edge of engine hood  6 A. Since engine hood  6 A covers engine  12  from above, sub-antenna  9 B is arranged in front of engine  12 . A hydraulic pump is directly coupled to engine  12 . Engine hood  6 A covers, from above, a machine compartment that accommodates the hydraulic pump, and can open and close the machine compartment. Sub-antenna  9 B is arranged in front of the machine compartment that accommodates the hydraulic pump. 
     Sub-antenna  9 B is arranged in front of counterweight  7 . Sub-antenna  9 B is arranged in front of rear surface  5 B of cab  5 . Sub-antenna  9 B is arranged in front of main antenna  9 A. In the fore/aft direction, rear surface  5 B of cab  5  is interposed between main antenna  9 A and sub-antenna  9 B. In the fore/aft direction, the front edge of engine hood  6 A is interposed between main antenna  9 A and sub-antenna  9 B. In the fore/aft direction, a rear edge of sheet metal cover  6 C is interposed between main antenna  9 A and sub-antenna  9 B. 
     Sub-antenna  9 B is arranged at a height position lower than that of upper surface  5 A of cab  5 . Sub-antenna  9 B is arranged at a height position lower than that of main antenna  9 A. 
     In the arrangement shown in  FIGS. 1 to 4  in which crawler belts  2 A of travel unit  2  extend in the fore/aft direction, main antenna  9 A overlaps with left crawler belt  2 A in a plan view. In the arrangement shown in  FIGS. 1 to 4 , sub-antenna  9 B overlaps with right crawler belt  2 A in a plan view. 
     A mirror  11 A is attached to cab  5  with a stay  11 B being interposed. Stay  11 B is fixed to rear surface  5 B of cab  5  and extends rearward from rear surface  5 B of cab  5 . Mirror  11 A is attached to a tip end portion of stay  11 B. Mirror  11 A is arranged in the rear of cab  5 . Mirror  11 A is arranged in the rear of the rear surface of cab  5 . Mirror  11 A is arranged below upper surface  5 A that forms the roof portion of cab  5 . 
       FIG. 6  is an enlarged perspective view showing a support structure of sub-antenna  9 B. As shown in  FIG. 6 , revolving unit  3  has a revolving frame  50 . Cab  5  as well as work implement  4 , engine  12  and the like that are not shown in  FIG. 6  are mounted on revolving frame  50  and arranged on an upper surface of revolving frame  50 .  FIG. 6  shows only a part of the components mounted on revolving frame  50 . Exterior panel  6  including engine hood  6 A, soil cover  6 B and sheet metal cover  6 C is not shown in  FIG. 6 . 
     Revolving unit  3  has a partition plate  51 . Partition plate  51  has a flat plate-like outline shape extending in the lateral direction and in the upward/downward direction. Partition plate  51  constitutes a front side wall of engine compartment  14 . Partition plate  51  serves as a partition between cab  5  and engine compartment  14 . Engine compartment  14  is defined by being covered by engine hood  6 A, partition plate  51  and counterweight  7  from above and the side. 
     A post member  52  is provided at a right edge portion of partition plate  51 . Post member  52  extends in the upward/downward direction. Post member  52  has a lower end portion fixed to the upper surface of revolving frame  50 . Post member  52  supports partition plate  51 . Post member  52  is a member that constitutes a support structure for supporting partition plate  51 . 
     A flat plate-like support portion  53  is fixed to an upper end portion of post member  52 , Support portion  53  is also fixed to partition plate  51  directly or with another member being interposed. Support portion  53  has an upper surface to which a lower end portion of mast  13  is fixed. Mast  13  has a fixed plate portion  13 A at the lower end portion. Fixed plate portion  13 A is fixed to support portion  53  using a plurality of bolts. Since mast  13  is planarly fixed to an upper surface of support portion  53 , mast  13  is more firmly fixed to support portion  53 . 
     A main body portion of mast  13  extending in the upward/downward direction and fixed plate portion  13 A are coupled by a rib portion  13 B. Since rib portion  13 B is formed, the strength of mast  13  is improved. 
     Sub-antenna  9 B is fixed to a tip end portion (upper end portion) of mast  13 . Sub-antenna  9 B is fixed to partition plate  51  with mast  13  being interposed. Sub-antenna  9 B is fixed to revolving frame  50  with mast  13  and partition plate  51  being interposed. Sub-antenna  9 B is fixed to revolving unit  3  without cab  5  being interposed. 
     Since mast  13  is fixed to revolving unit  3  with high strength and the strength of mast  13  itself is also high, the accuracy of positioning of sub-antenna  9 B supported by mast  13  with respect to revolving unit  3  is improved. 
       FIG. 7  is an enlarged perspective view showing a support structure of main antenna  9 A. As shown in  FIG. 7 , bracket  10  has a fixed portion  10 A. Fixed portion  10 A has a substantially flat plate-like shape and is fixed to upper surface  5 A of cab  5  using a plurality of bolts. 
     Bracket  10  has a fixed portion  10 B. Fixed portion  10 B has a substantially flat plate-like shape. Fixed portion  10 B is continuous to a rear edge of fixed portion  10 A. Fixed portion  10 B has a shape of being bent with respect to fixed portion  10 A. Fixed portion  10 B is bent with respect to fixed portion  10 A. Fixed portion  10 B is bent downward from fixed portion  10 A. Since fixed portion  10 A is fixed to upper surface  5 A of cab  5 , fixed portion  10 B and a mounting portion  10 C described below are bent downward from upper surface  5 A of cab  5 . 
     Fixed portion  10 B is arranged to face rear surface  5 B of cab  5 . Fixed portion  10 B is fixed to rear surface  5 B of cab  5  using a bolt. Since fixed portion  10 A is fixed to upper surface  5 A of cab  5  and fixed portion  10 B is fixed to rear surface  5 B of cab  5 , bracket  10  is more firmly fixed to cab  5 . 
     A part of fixed portion  10 B is cut out to form a through hole. Stay  11 B for attaching mirror  11 A is arranged to pass through this through hole and is fixed to rear surface  5 B of cab  5 . A suspending device fixed to rear surface  5 B of cab  5  and extending rearward from rear surface  5 B is arranged to penetrate through the through hole formed in fixed portion  10 B. 
     Bracket  10  has mounting portion  10 C. Mounting portion  10 C is continuous to a lower edge of fixed portion  10 B. Mounting portion  10 C is arranged at a height position lower than that of upper surface  5 A of cab  5 . Mounting portion  10 C has a shape of being bent with respect to fixed portion  10 B. Mounting portion  10 C is bent with respect to fixed portion  10 B. Mounting portion  10 C is bent rearward from fixed portion  10 B. Since bracket  10  is formed to have a shape obtained by bending a plate member a plurality of times, the strength of bracket  10  is improved. 
     Fixed portion  10 B and mounting portion  10 C are coupled by a rib portion  10 D. Since rib portion  10 D is formed, the strength of bracket  10  is improved. 
     Main antenna  9 A is placed on an upper surface of mounting portion  10 C. Main antenna  9 A is fixed to mounting portion  10 C. Main antenna  9 A has a fixed portion  9 A 1  fixed to mounting portion  10 C. Fixed portion  9 A 1  of main antenna  9 A is arranged at a height position lower than that of upper surface  5 A of cab  5 . Main antenna  9 A is attached to cab  5  with bracket  10  being interposed. Fixed portion  9 A 1  of main antenna  9 A is fixed to cab  5  with mounting portion  10 C of bracket  10  being interposed. Main antenna  9 A is fixed to revolving unit  3  with bracket  10  and cab  5  being interposed. 
     Since bracket  10  is fixed to cab  5  with high strength and the strength of bracket  10  itself is also high, the accuracy of positioning of main antenna  9 A supported by bracket  10  with respect to revolving unit  3  is improved. 
     Next, the function and effect of the present embodiment will be described. 
     According to hydraulic excavator  1  based on the embodiment, main antenna  9 A is attached to cab  5  and sub-antenna  9 B is attached to the vehicular body of hydraulic excavator  1  without cab  5  being interposed, as shown in  FIG. 4 . Since main antenna  9 A and sub-antenna  9 B are disposed as described above, main antenna  9 A and sub-antenna  9 B can be arranged at positions separate from each other in the lateral direction of revolving unit  3 . Therefore, the accuracy of measurement of the current position of hydraulic excavator  1  can be improved. 
     If work implement  4  is present within a reception range of main antenna  9 A, work implement  4  blocks a radio signal to be received by main antenna  9 A and disallows main antenna  9 A to receive a radio wave, or reflects a radio wave to cause a disturbance in a radio signal received by main antenna  9 A. Particularly, hydraulic excavator  1  in the embodiment is a short tail swing hydraulic excavator, and thus, work implement  4  raised to the highest position is arranged in the more rear portion of revolving unit  3  in order to reduce the swing radius. As shown in  FIG. 4 , main antenna  9 A is attached to the rear portion of cab  5 , and thus, main antenna  9 A is arranged on the rear side of revolving unit  3 . As a result, blockage of the radio signal to main antenna  9 A by work implement  4  can be suppressed. An influence that work implement  4  has on the reception environment of main antenna  9 A can be reduced, and thus, a reduction in accuracy of measurement of the current position of hydraulic excavator  1  can be suppressed. 
     In addition, in order to prevent cab  5  itself from blocking the radio signal to main antenna  9 A attached to cab  5 , it is necessary to arrange main antenna  9 A and cab  5  such that cab  5  is not present within the reception range of main antenna  9 A. Therefore, as shown in  FIG. 4 , main antenna  9 A is attached to the upper portion of cab  5 , and thus, obstruction of the skyward angular range of view of main antenna  9 A by cab  5  can be suppressed. An influence that cab  5  has on the reception environment of main antenna  9 A can be reduced, and thus, a reduction in accuracy of measurement of the current position of hydraulic excavator  1  can be suppressed. 
     In addition, since main antenna  9 A is attached to the upper portion of cab  5 , blockage of the window, e.g., rear window  48  provided in cab  5  by main antenna  9 A is suppressed. Therefore, it is possible to ensure a direct field of view of an operator in the operator&#39;s compartment in cab  5  seeing the outside of cab  5 . 
     In addition, as shown in  FIGS. 1 and 3 , main antenna  9 A has fixed portion  9 A 1  fixed to cab  5  and fixed portion  9 A 1  is arranged at a height position lower than that of upper surface  5 A of cab  5 . Therefore, main antenna  9 A can be arranged at a position that is relatively lower than that of upper surface  5 A of cab  5 . As shown in  FIGS. 1 and 3 , main antenna  9 A is arranged at a height position equal to or lower than that of upper surface  5 A of cab  5 , and thus, it is possible to reliably avoid a situation in which main antenna  9 A projects upward from upper surface  5 A of cab  5  and exceeds a transport height limit of hydraulic excavator  1 . 
     In addition, as shown in  FIGS. 4 and 7 , main antenna  9 A is attached to cab  5  with bracket  10  being interposed. Bracket  10  has fixed portion  10 A fixed to upper surface  5 A of cab  5 , and fixed portion  10 B and mounting portion  10 C extending rearward from upper surface  5 A of cab  5  and bent downward. Since main antenna  9 A is placed on mounting portion  10 C located below upper surface  5 A of cab  5 , main antenna  9 A can be more reliably arranged at a height position equal to or lower than that of upper surface  5 A of cab  5 . 
     In addition, as shown in  FIG. 2 , main antenna  9 A and sub-antenna  9 B are arranged within the swing radius of revolving unit  3 . Therefore, contact of main antenna  9 A or sub-antenna  9 B, or cables connected to these antennas, with a foreign object during swing of revolving unit  3  can be suppressed. Thus, the reliability of hydraulic excavator  1  can be improved. 
     In addition, as shown in  FIG. 2 , the upper surface of hydraulic excavator  1  in the rear of cab  5  is formed by engine hood  6 A and engine hood  6 A is made of a resin material. With such a configuration that main antenna  9 A is attached to cab  5  in arranging main antenna  9 A in the rear of cab  5 , it is not necessary to change the shape of engine hood  6 A made of a resin material. Therefore, engine hood  6 A can be used in common both in hydraulic excavator  1  in the embodiment including antenna  9  and a hydraulic excavator not including an antenna. Preparation of a new mold to mold engine hood  6 A in the embodiment is not required, and thus, the manufacturing cost of hydraulic excavator  1  can be reduced. 
     In addition, as shown in  FIG. 2 , sub-antenna  9 B is arranged in front of engine  12 , and thus, it is not necessary to change the shape of engine hood  6 A covering engine  12  from above. Since engine hood  6 A can be used in common both in hydraulic excavator  1  in the embodiment including antenna  9  and a hydraulic excavator not including an antenna, the manufacturing cost of hydraulic excavator  1  can be reduced. 
     In addition, sheet metal cover  6 C is formed of a metal material represented by a steel material, and thus, processing is easy. As shown in  FIGS. 2 and 4 , mast  13  for supporting sub-antenna  9 B can be arranged to penetrate through the cut-out part of sheet metal cover  6 C. Therefore, with such a configuration that sub-antenna  9 B is arranged above sheet metal cover  6 C, sub-antenna  9 B can be easily attached to revolving unit  3 . 
     In addition, as shown in  FIGS. 4 and 5 , engine hood  6 A is openable and closable with respect to revolving unit  3 . When antenna  9  is fixed to a structure that relatively moves with respect to revolving unit  3 , antenna  9  moves along with the movement of the structure, and thus, calibration is frequently required, which is troublesome. Main antenna  9 A in the embodiment is attached to cab  5 , sub-antenna  9 B in the embodiment is arranged in front of engine compartment  14 , and main antenna  9 A and sub-antenna  9 B are not attached to engine hood  6 A. Therefore, even when engine hood  6 A is moved to open and close engine compartment  14 , main antenna  9 A and sub-antenna  9 B do not move, and thus, recalibration is not required. Thus, an increase in frequency of calibration of antenna  9  can be avoided and a service person&#39;s burden associated with maintenance work can be reduced. 
     In the above-described embodiment, description has been given of the example in which bracket  10  has fixed portion  10 A fixed to upper surface  5 A of cab  5  and fixed portion  10 B fixed to rear surface  5 B of cab  5 . Bracket  10  may be configured to be fixed only to rear surface  5 B of cab  5  and extend rearward from rear surface  5 B of cab  5 . Main antenna  9 A is not limited to the configuration in which main antenna  9 A is fixed to cab  5  with bracket  10  being interposed, and main antenna  9 A may be directly fixed to cab  5 . 
     In the above-described embodiment, description has been given of the example in which main antenna  9 A as a whole is arranged at a height position equal to or lower than that of upper surface  5 A of cab  5 . When a structure that is not removed even during transport of hydraulic excavator  1  is mounted on upper surface  5 A of cab  5 , the transport height limit of hydraulic excavator  1  is defined by an upper end portion of the structure. In this case, main antenna  9 A does not exceed the transport height limit as long as main antenna  9 A is arranged at a height position equal to or lower than that of the upper end portion of the structure. Therefore, a part of main antenna  9 A may be arranged at a position higher than that of upper surface  5 A of cab  5 . 
     It should be understood that the embodiment disclosed herein is illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims. 
     REFERENCE SIGNS LIST 
       1  hydraulic excavator;  2  travel unit;  2 A crawler belt;  3  revolving unit;  4  work implement;  4 A boom;  4 B arm;  4 C bucket;  4 D,  4 E,  4 F hydraulic cylinder;  5  cab;  5 A upper surface;  5 B rear surface;  6  exterior panel;  6 A engine hood;  6 A 1  opening;  6 B soil cover;  6 C sheet metal cover;  7  counterweight;  8  exhaust pipe;  9  antenna;  9 A main antenna;  9 A 1  fixed portion;  9 B sub-antenna;  10  bracket;  10 A,  10 B fixed portion;  10 C mounting portion;  10 D,  13 B rib portion;  11 A mirror;  11 B stay;  12  engine;  13  mast;  13 A fixed plate portion;  14  engine compartment;  40  front pillar;  41  right pillar;  42  left pillar;  47  front window;  48  rear window;  50  revolving frame;  51  partition plate;  52  post member;  53  support portion.