阅读说明：本技术 工程机械的回转接头 (Swivel joint for construction machine ) 是由 冈田修自 竹田一之 新居晴夫 望月大辅 于 2020-03-02 设计创作，主要内容包括：提供一种工程机械的回转接头,能够检测上部回转体的回转角度,且具有很高的维护性。回转接头(4)包括：主体(41)、轴杆(43)、下盖(45)和传感器单元(5)。传感器单元(5)具有固定在轴杆(43)的上端侧的旋转角度传感器(51)、以及在远端具有能够被旋转角度传感器(51)检测到的被检测部(55)且基端侧连结于下盖(45)的棒状的杆(53)。轴杆(43)形成有供杆(53)插入的杆插入孔(431)、以及供排放油通过的轴杆侧泄油油路(433)。(Provided is a rotary joint for construction machinery, which can detect the rotation angle of an upper rotary body and has high maintainability. The swivel joint (4) comprises: a main body (41), a shaft (43), a lower cover (45), and a sensor unit (5). The sensor unit (5) has a rotation angle sensor (51) fixed to the upper end side of the shaft (43), and a rod-shaped lever (53) having a detection section (55) at the distal end thereof, the detection section being capable of being detected by the rotation angle sensor (51), and the proximal end side of the lever being connected to the lower cover (45). The stem (43) is formed with a stem insertion hole (431) into which the stem (53) is inserted, and a stem-side oil drain passage (433) through which drain oil passes.)

1. A swing joint of a work machine, the work machine comprising: a lower traveling body including a lower pipe, an upper slewing body including an upper pipe, and a slewing portion interconnecting the lower traveling body and the upper slewing body so that the upper slewing body can slew about a slewing center axis extending in an up-down direction, the slewing joint being provided in the slewing portion of the construction machine, the slewing joint of the construction machine comprising:

a main body fixed to the lower traveling body, having a cylindrical shape with the center axis of rotation as the center, and having an upper opening and a lower opening formed therein, respectively;

a lower cover attached to the main body so as to seal the lower opening of the main body, and having an attachment hole formed in a position overlapping the rotation center axis and penetrating the lower cover in a vertical direction;

a shaft rod fixed to the upper slewing body, having a cylindrical shape centered on the slewing center axis, and fitted into the cylindrical interior of the main body so as to pass through the upper opening of the main body so as to be relatively rotatable with respect to the main body centered on the slewing center axis; and the number of the first and second groups,

a sensor unit capable of detecting a rotation angle of the upper slewing body with respect to the lower traveling body,

the shaft rod has a lower surface portion facing the lower cover, and the shaft rod is formed with: a sensor mounting space formed at a position overlapping the rotation center axis, a rod insertion hole formed along the rotation center axis so as to communicate the sensor mounting space with the lower surface portion and to face the mounting hole, and a rod-side drain oil passage located radially outward of the rod with respect to the rod insertion hole, provided separately from the rod insertion hole, communicating with the upper pipe, and allowing drain oil to flow in the vertical direction,

a cap-side drain oil passage is formed in the lower cap, is isolated from the rod insertion hole and the mounting hole in a state where the lower cap is mounted to the main body, and communicates the rod-side drain oil passage of the rod and the lower pipe with each other,

the sensor unit has:

a rotation angle sensor mounted in the sensor mounting space of the shaft so as to be rotatable integrally with the shaft about the center axis of gyration; and the number of the first and second groups,

and a rod-shaped rod extending in a vertical direction and relatively rotatable with respect to the shaft around the rotation center axis together with the main body, wherein the rod includes a distal rod portion including a detected portion detectable by the rotation angle sensor, and a proximal rod portion detachably attached to the attachment hole of the lower cover, and in a state where the lower cover is attached to the main body, the distal rod portion is insertable into the rod insertion hole through the attachment hole of the lower cover up to a position where the detected portion is detectable by the rotation angle sensor, and the distal rod portion is detachable below the attachment hole through the rod insertion hole.

2. The swivel joint of a working machine according to claim 1, further comprising:

and a sub-cap that holds the rod base end portion and is detachably attached to the lower cap so as to seal the attachment hole of the lower cap.

3. Swivel joint for a working machine according to claim 2,

the sub-cap and the rod base end portion are detachably coupled to each other by a screw structure.

4. Swivel joint for a working machine according to any of claims 1 to 3,

the sensor unit further has a restricting member provided at the rod distal end portion, having an outer diameter larger than an outer diameter of the rod, for restricting a relative position of the detected portion with respect to the rotation angle sensor in a direction orthogonal to an axial direction of the rotation center shaft,

the inner diameter of the mounting hole is set larger than the outer diameter of the restricting member.

5. Swivel joint for a working machine according to claim 4,

the restricting member is formed of a non-magnetic resin material.

6. Swivel joint for a working machine according to any of claims 1 to 5,

a recessed portion opposed to the rotation angle sensor is formed at the distal end portion of the rod,

the detected portion includes a magnet disposed in the recess and engaged with the distal end portion of the rod.

7. The swivel joint of a working machine according to any one of claims 1 to 6, further comprising:

a seal member, located between the shaft and the lower cover, for preventing oil from flowing from the cover-side oil drain oil passage into the rod insertion hole and the mounting hole.

Technical Field

The present invention relates to a rotary joint provided at a rotation center of a construction machine such as a hydraulic excavator.

Background

In the field of construction machines, a related art has been proposed in which a rotary joint provided in a rotary portion connecting a lower traveling structure and an upper revolving structure is connected.

For example, patent document 1 discloses a swivel joint in which an upper pipe and a lower pipe are connected to a center portion of a swivel support.

Specifically, the swivel joint includes a cylindrical main body fixed to the bottom frame of the lower traveling structure, and a cylindrical shaft (stem) fixed to the upper frame of the upper revolving structure and rotatably fitted to the main body. In addition, the central part of the upper end surface of the shaft lever is provided with an oil drainage hole which penetrates along the axial direction.

As another technique, patent document 2 discloses a swivel joint including a rotation angle sensor for detecting a swivel angle of an upper swivel body and a lever.

Specifically, a rod for detecting a rotation angle of the upper slewing body is inserted into a pilot oil passage extending in the axial direction. The upper end of the rod faces the rotation angle sensor attached to the inner body with a gap therebetween.

Documents of the prior art

Patent document

Patent document 1: japanese laid-open patent publication No. 2016-3519

Patent document 2: japanese patent laid-open publication No. 2017-82494.

According to the above patent documents 1 and 2, it is conceivable to provide a sensor unit (a rotation angle sensor and a lever) and detect a rotation angle of the upper rotation body by using an oil passage and an oil drain hole formed at a rotation center of the shaft.

However, in the structure in which the rod is inserted into the oil passage or the oil drain hole formed in the rotation center of the shaft, there is a possibility that the working oil leaks from the oil passage or the oil drain hole as the rod is inserted and removed, which causes a problem in terms of maintenance.

Disclosure of Invention

The invention aims to provide a rotary joint of a construction machine, which is provided with a sensor unit for detecting the rotary angle of an upper rotary body and can inhibit oil leakage when a rod is inserted and pulled out.

The invention provides a swivel joint of an engineering machine, which comprises: the hydraulic control device includes a lower traveling body including a lower pipe, an upper revolving body including an upper pipe, and a revolving portion interconnecting the lower traveling body and the upper revolving body so that the upper revolving body can revolve around a revolving center axis extending in an up-down direction, and the revolving joint is provided in the revolving portion of the construction machine. This swivel joint includes: a main body fixed to the lower traveling body, having a cylindrical shape with the center axis of rotation as the center, and having an upper opening and a lower opening formed therein, respectively; a lower cover attached to the main body so as to seal the lower opening of the main body, and having an attachment hole formed in a position overlapping the rotation center axis so as to penetrate the lower cover in a vertical direction; a shaft rod fixed to the upper slewing body, having a cylindrical shape centered on the slewing center axis, and fitted into the cylindrical interior of the main body so as to pass through the upper opening of the main body so as to be relatively rotatable with respect to the main body centered on the slewing center axis; and a sensor unit capable of detecting a rotation angle of the upper revolving structure with respect to the lower traveling structure. The shaft has a lower surface facing the lower cover, and the shaft has: the oil drain device includes a sensor mounting space formed at a position overlapping the rotation center axis, a rod insertion hole formed along the rotation center axis so as to communicate the sensor mounting space with the lower surface portion and to face the mounting hole, and a rod-side oil drain passage located radially outward of the rod insertion hole from the rod insertion hole, provided separately from the rod insertion hole, and communicating with the upper pipe to allow a drain oil to flow vertically. A cover-side oil drain passage is formed in the lower cover, and is isolated from the rod insertion hole and the mounting hole in a state where the lower cover is mounted to the main body, and communicates the rod-side oil drain passage of the rod with the lower pipe. The sensor unit has: a rotation angle sensor mounted in the sensor mounting space of the shaft so as to be rotatable integrally with the shaft about the center axis of gyration; and a rod extending in the vertical direction. The lever includes a distal lever portion including a detected portion detectable by the rotation angle sensor, and a proximal lever portion detachably attached to the attachment hole of the lower cover, the distal lever portion being insertable into the lever insertion hole through the attachment hole of the lower cover until a position where the detected portion is detectable by the rotation angle sensor in a state where the lower cover is attached to the main body, the distal lever portion being detachable from below the attachment hole through the lever insertion hole, the lever being relatively rotatable with respect to the shaft around the rotation center axis together with the main body.

Drawings

Fig. 1 is a side view showing a hydraulic excavator according to an embodiment of the present invention.

Fig. 2 is a side view showing an appearance of a swivel joint according to an embodiment of the present invention.

Fig. 3 is a bottom view of the swivel joint of fig. 2 as viewed along arrow III.

Fig. 4 is a plan view of the swivel joint of fig. 2 as viewed along arrow IV.

Fig. 5 is a cross-sectional view of the swivel joint of fig. 2 cut at the V-V position.

Fig. 6 is a cross-sectional view of the swivel joint of fig. 2 cut at the VI-VI position.

Fig. 7 is a sectional view showing a state where a lever is removed from the swivel joint of fig. 6.

Fig. 8 is a cross-sectional view of the swivel joint of fig. 4 cut at a position VIII-VIII.

Fig. 9 is a cross-sectional view of the swivel joint of fig. 4 cut at position IX-IX.

Fig. 10 is a cross-sectional view showing a swivel joint according to a modified embodiment of the present invention.

Detailed Description

A swivel joint of a construction machine according to an embodiment of the present invention is described with reference to fig. 1 to 9. Hereinafter, the hydraulic excavator 1 (see fig. 1) is given as an example of a construction machine, and the swing joint 4 is given as an example of a swing joint (see fig. 2).

As shown in fig. 1, the hydraulic excavator 1 includes a lower traveling structure 2, an upper revolving structure 3 rotatably mounted on the lower traveling structure 2, and a revolving portion 1S including a slewing bearing 25. The lower traveling body 2 includes a hydraulic traveling motor 21, a pair of left and right crawler belts 22 driven to rotate by the traveling motor 21, a lower frame 23, and a lower pipe 52 connected to the traveling motor 21. The revolving portion 1S couples the lower traveling structure 2 and the upper revolving structure 3 to each other, and the upper revolving structure 3 can revolve around a revolving axis AX (revolving central axis) extending in the vertical direction.

The upper slewing body 3 includes an upper frame 31, a machine chamber 37A, a machine chamber cover 37, and an upper pipe 50. Upper frame 31 is supported by lower traveling body 2 via slewing bearing 25, and constitutes a base of upper slewing body 3. The upper frame 31 is configured to be rotatable about an axis of rotation AX.

The machine chamber 37A houses an engine, hydraulic equipment (for example, the control valve 36, a hydraulic pump), and the like, which are not shown. The machine chamber cover 37 is provided to cover the machine chamber 37A.

The turning portion 1S has a turning joint 4 provided at the center of the turning support 25. The rotary joint 4 is a longitudinally long substantially cylindrical member provided upright at the center of the lower frame 23, and the center thereof coincides with the rotation axis AX. The swivel joint 4 relays and connects an upper pipe 50 connected to the control valve 36 of the upper swivel 3 and a lower pipe 52 connected to the travel motor 21 of the lower traveling structure 2.

As shown in fig. 2, the swivel joint 4 includes a main body 41, a shaft 43 rotatably fitted to the main body 41, a cover 45 (lower cover), and a cover 47 (sub cover). The cover 45 and the cover 47 constitute a cover unit 44.

As shown in fig. 2 and 4, the body 41 is fixed to the lower frame 23 of the lower traveling body 2, and is a cylindrical member centered on the rotation axis AX, which is also referred to as a lower turning portion or the like. The body 41 is open at the upper and lower sides thereof, and has an upper opening and a lower opening.

As shown in fig. 2, 4, and 5, the shaft 43 is fixed to the upper frame 31 of the upper revolving structure 3, and is a columnar member centered on the revolving axis AX, which is also referred to as an upper revolving portion or the like. The shaft 43 is inserted through the upper opening of the body 41 so as to be rotatable about the rotation axis AX with respect to the body 41, and is fitted into the cylindrical interior of the body 41. The shaft 43 has a lower surface portion facing the cover 45.

As shown in fig. 6, the stem 43 further has a thrust plate 432 disposed at the lower end of the stem 43. The thrust plate 432 is a member for preventing the shaft 43 from being pulled out from the main body 41 in the rotation axis direction.

As shown in fig. 3 and 8, the cover 45 is fixed to the lower side of the body 41 by bolts. The cover 45 is attached to the main body 41 so as to seal the lower opening of the main body 41. As shown in fig. 6, a mounting hole 45H for mounting a cap 47 (described later) is formed in the cap 45 at a position overlapping the center axis (rotation axis AX) of the shaft 43, and the mounting hole 45H penetrates the cap 45 in the vertical direction. That is, the cover 45 forms the shape of a donut. The cover 45 is an example of a first cover according to the present invention.

As shown in fig. 3 and 6, a cover 47 is attached to the cover 45 via an attachment hole 45H. Specifically, a female screw is formed in the mounting hole 45H of the cover 45, a male screw is formed in a coupling portion 47S (see fig. 7) of the cover 47, and the cover 47 is coupled to the mounting hole 45H of the cover 45.

Further, as described above, since the cover 45 is fixed to the main body 41, the cover 45 is maintained in the attached state to the main body 41 even if the cover 47 is detached from the cover 45 (see fig. 7).

As shown in fig. 6, the revolving joint 4 further includes a sensor unit 5 capable of detecting a revolving angle of the upper revolving structure 3 with respect to the lower traveling structure 2. The sensor unit 5 has a rotation angle sensor 51 and a lever 53.

The rotation angle sensor 51 is fixed to the upper end side of the shaft 43, and rotates together with the shaft 43 following the rotation of the upper revolving unit 3. That is, the rotation angle sensor 51 is attached to the sensor attachment space 430 of the spindle 43 so as to be rotatable integrally with the spindle 43 about the rotation axis AX.

The lever 53 is a rod-shaped member provided at a distal end with a magnet 55 that can be detected by the rotation angle sensor 51. The rod 53 has a distal rod end portion 53A and a proximal rod end portion 53B, and extends in the vertical direction (axial direction of the rotation axis AX).

A countersink (not shown) (concave portion) into which the magnet 55 (detected portion) can be fitted is formed on the distal end surface of the distal end portion 53A of the rod 53 so as to face the rotation angle sensor 51. The spot facing is formed to a size (here, 0.5mm (millimeter) or less) that does not affect the magnetic field density of the magnet 55.

The magnet 55 is disposed in the spot facing formed on the distal end surface of the rod 53, and is directly attached to the rod distal end portion 53A via an adhesive. As a result, the rod distal end portion 53A contains the magnet 55 that can be detected by the rotation angle sensor 51. The rod base end portion 53B of the rod 53 is directly and detachably coupled to the cover 47 by a screw structure. As a result, when the rod base end portion 53B is coupled to the cover 47, the cover 47 holds the rod base end portion 53B. In addition, the lever 53 is relatively rotatable about the rotation axis AX with respect to the shaft 43 together with the body 41.

The cover 47 is coupled to the cover 45, and the cover 45 is fixed to the body 41. And particularly the cover 47 is detachably mounted on the cover 45 to seal the mounting hole 45H of the cover 45. The main body 41 is fixed to the lower traveling body 2. Therefore, the lever 53 connected to the cover 47 and the magnet 55 provided at the distal end of the lever 53 do not rotate following the rotation of the upper rotation body 3 unlike the rotation angle sensor 51. Further, the rod base end portion 53B will be described, wherein the rod base end portion 53B is detachably attached to the attachment hole 45H of the cover 45, so that the rod distal end portion 53A can be inserted through the attachment hole 45H of the cover 45 and into the rod hole 431 until the position where the magnet 55 can be detected by the rotation angle sensor 51 in a state where the cover 45 is attached to the main body 41, and the rod distal end portion 53A can be detached below the attachment hole 45H through the rod hole 431.

In order to accurately detect the rotation angle of the upper slewing body, the rotation angle sensor 51 and the magnet 55 are preferably arranged concentrically. Therefore, in the present embodiment, the distal end side of the lever 53 is provided with a collar 57 (restricting member). The collar 57 is a member for suppressing the misalignment of the rod 53, and is made of a non-magnetic resin material. That is, the collar 57 is disposed at the rod distal end portion 53A, and has an outer diameter larger than that of the rod 53. The collar 57 regulates the relative position of the magnet 55 with respect to the rotation angle sensor 51 in the direction orthogonal to the axial direction of the rotation axis AX.

As shown in fig. 7, the inner diameter of the mounting hole 45H for mounting the cover 47 is configured to be larger than the outer diameter of the collar 57. This is so that the rod 53 including the collar 57 can be inserted into or pulled out from the rod hole 431.

As shown in fig. 5, the shaft 43 has formed therein: the sensor mounting space 430, a rod hole 431 (rod insertion space) extending in the axial direction at the center axis of the stem 43, a drain hole 433 (stem-side drain oil passage) extending in the axial direction at a position of the stem 43 offset from the center axis, and 4 vertical holes 435 extending in the axial direction at a position of the stem 43 offset from the center axis. The sensor mounting space 430 is formed at a position where the upper end of the shaft 43 coincides with the rotation axis AX. The rod hole 431 communicates between the sensor mounting space 430 and the lower surface portion of the shaft 43, and is formed along the rotation axis AX so as to face the mounting hole 45H. The drain hole 433 is provided apart from the rod hole 431 on the radially outer side of the stem 43 with respect to the rod hole 431, communicates with the upper pipe 50, and allows the drain oil to flow in the vertical direction.

As shown in fig. 7, the rod hole 431 is a dedicated hole for inserting and extracting the rod 53, and is a hole through which oil does not pass. As shown in fig. 6, when the cover 47 is attached to the cover 45, the rod 53 coupled to the cover 47 is inserted into the rod hole 431 from the attachment hole 45H. The magnet 55 at the distal end of the rod 53 approaches the rotation angle sensor 51.

As shown in fig. 8, the drain hole 433 is a hole through which the drain oil passes, and communicates with a drain oil passage 451 (a hatched area in fig. 9) formed in the cover 45 (a cover-side drain oil passage). The drain oil passage 451 is an oil passage isolated from the rod hole 431 and the attachment hole 45H in a state where the cover 45 is attached to the main body 41, and communicates the drain hole 433 of the stem 43 and the lower pipe 52 with each other.

As shown in fig. 9, the oil drain passage 451 is constituted by a doughnut-shaped oil chamber 451A provided on the outer periphery of the stem 43, and an L-shaped oil passage 451B connecting the oil chamber 451A and the side surface of the cover 45. As shown in fig. 8, the drain hole 433 communicates with the oil chamber 451A of the drain oil passage 451.

As shown in fig. 9, a sealing member 6 for preventing leakage of the discharged oil is provided at a contact portion of the shaft 43 and the cover 45. The seal member 6 is an annular elastic member, is located between the stem 43 and the cover 45, and prevents oil from flowing from the drain oil passage 451 into the rod hole 431 and the attachment hole 45H. This is because the drain oil path 451 is formed in the cover 45, and therefore there is a possibility that drain oil may leak out at a contact portion between the stem 43 and the cover 45, thereby causing leakage.

The shaft 43 has a small diameter portion including the rotation axis AX at a lower end thereof, and a large diameter portion disposed above the small diameter portion. The lower surface of the shaft 43 corresponds to the lower surface of the small diameter portion. The rod hole 431 communicates with the lower surface of the small diameter portion. On the other hand, the cap 45 is inserted into the small diameter portion 43 of the stem 43 in the cylinder, and the upper surface portion of the cap 45 abuts against the lower surface portion of the large diameter portion of the stem (fig. 6). The cover 47 is fitted into the lower part of the cylindrical interior of the cover 45 from below. The seal member 6 is located between the inner peripheral surface of the cap 45 and the outer peripheral surface of the small diameter portion of the stem 43, and prevents the drain oil from flowing into the stem hole 431 side from the drain oil passage 451.

The 4 vertical holes 435 function as oil passages for supplying and discharging hydraulic oil between the control valve 36 and the travel motor 21. One of the 4 longitudinal holes 435 is shown in fig. 9. The vertical hole 435 has the same structure as that of the conventional art (for example, patent document 1).

As described above, according to the above embodiment, since the rod 53 is inserted into the rod hole 431 which does not pass oil, oil leakage is not likely to occur even if the rod 53 is pulled out during maintenance operation. Further, since the drain hole 433 is formed separately from the rod hole 431 and communicates with the drain oil passage 451 of the cover 45 fixed to the main body 41, even if the cover 47 is detached from the cover 45, the cover 45 is still attached to the main body 41, and thus the drain hole 433 is kept in a closed state. Thus, there is no possibility that oil leaks out of the oil drain hole 433. Therefore, the rotary joint 4 according to the present embodiment can easily replace the rod 53, and the sensor unit 5 including the rod 53 has high maintainability.

In addition, according to the above embodiment, since neither the rotation angle sensor 51 nor the magnet 55 is in contact with the operating oil, these members do not need to have oil resistance.

Further, according to the above embodiment, the angle detection function can be added without greatly changing the layout design of the hydraulic excavator 1, and the attachment/detachment performance is not inferior to that of a normal swing joint.

Further, according to the above embodiment, when the cover 47 is removed from the cover 45, the lever 53 connected to the cover 47 can be removed. Therefore, the magnet 55 can be replaced without detaching the main body 41 or the shaft 43 of the swing joint 4 from the excavator main body.

In addition, according to the above embodiment, since the collar 57 is provided on the distal end side of the rod 53, it is sufficient to prevent the rod 53 from being misaligned, and the magnet 55 does not come out of the sensing range of the rotation angle sensor 51. Further, since the collar 57 is made of a resin material that is a non-magnetic material, the inner peripheral surface of the rod hole 431 of the stem 43 is not worn.

Further, according to the above embodiment, since the magnet 55 is directly attached to the spot facing (recess) formed at the distal end of the rod 53 via the adhesive, it is not necessary to provide another non-magnetic member between the magnet 55 and the rod 53 as a magnetic body, and the number of parts can be reduced.

The rotary joint of a construction machine according to the present invention is not limited to the above-described embodiments, and various modifications and improvements can be made within the scope of the claims.

In the above embodiment, as shown in fig. 7, the cover 45 is fixed to the body 41, and the cover 47 including the lever 53 is detachable from the cover 45, but the present invention is not limited thereto. For example, the swivel joint may include a cover fixed to the main body 41 and a lever directly connected to the cover. That is, the swivel joint may include a cover and a rod that can be connected thereto.

Specifically, as shown in fig. 10, in the swivel joint according to the modified embodiment of the present invention, a cover 49 having a drain oil path 491 formed therein is fixed to the main body 41. The rod base end portion of the rod 530 can be screwed to the cover 49 by a screw structure. The diameter of the proximal end of the rod 530 connected to the cap 49 is larger than the diameter of the collar 570.

According to the modified embodiment, since the number of parts constituting the rotary joint 4 is reduced, the mounting tolerance can be reduced, and misalignment of the rod 530 with respect to the rotary joint 4 (specifically, the rod hole 431 of the shaft 43) can be suppressed.

As described above, the present invention is applied to a swing joint of a hydraulic excavator including a sensor unit for detecting a swing angle of an upper swing body.

The invention provides a swivel joint of an engineering machine, which comprises: the hydraulic control device includes a lower traveling body including a lower pipe, an upper revolving body including an upper pipe, and a revolving portion interconnecting the lower traveling body and the upper revolving body so that the upper revolving body can revolve around a revolving center axis extending in an up-down direction, and the revolving joint is provided in the revolving portion of the construction machine. This swivel joint includes: a main body fixed to the lower traveling body, having a cylindrical shape with the center axis of rotation as the center, and having an upper opening and a lower opening formed therein, respectively; a lower cover attached to the main body so as to seal the lower opening of the main body, and having an attachment hole formed in a position overlapping the rotation center axis so as to penetrate the lower cover in a vertical direction; a shaft rod fixed to the upper slewing body, having a cylindrical shape centered on the slewing center axis, and fitted into the cylindrical interior of the main body so as to pass through the upper opening of the main body so as to be relatively rotatable with respect to the main body centered on the slewing center axis; and a sensor unit capable of detecting a rotation angle of the upper revolving structure with respect to the lower traveling structure. The shaft rod has a lower surface portion facing the lower cover, and the shaft rod is formed with: a sensor mounting space formed at a position overlapping the pivot center axis, a rod insertion hole formed along the pivot center axis so as to communicate the sensor mounting space with the lower surface portion and to face the mounting hole, and a rod-side oil drain passage located radially outward of the rod with respect to the rod insertion hole, provided separately from the rod insertion hole, communicating with the upper pipe, and allowing a drain oil to flow in a vertical direction. A cover-side oil drain passage is formed in the lower cover, and is isolated from the rod insertion hole and the mounting hole when the lower cover is attached to the main body, and the rod-side oil passage of the rod and the lower pipe are communicated with each other. The sensor unit has: a rotation angle sensor mounted in the sensor mounting space of the shaft so as to be rotatable integrally with the shaft about the center axis of gyration; and a rod-shaped rod extending in the vertical direction and being relatively rotatable with respect to the shaft around the rotation center axis together with the main body, wherein the rod includes a distal rod portion including a detected portion detectable by the rotation angle sensor, and a proximal rod portion detachably attached to the attachment hole of the lower cover, and in a state where the lower cover is attached to the main body, the distal rod portion is insertable into the rod insertion hole through the attachment hole of the lower cover up to a position where the detected portion is detectable by the rotation angle sensor, and the distal rod portion is detachable below the attachment hole through the rod insertion hole.

According to this configuration, since the rod is inserted into the rod insertion hole isolated from the rod-side drain oil passage, even if the rod is inserted or pulled out, leakage of oil from the rod insertion hole can be suppressed. Therefore, the rotary joint of the construction machine of the present invention can easily replace the lever having the detected portion, and has high maintainability.

In the above configuration, it is preferable that the display device further includes: and a sub-cap that holds the rod base end portion and is detachably attached to the lower cap so as to seal the attachment hole of the lower cap.

According to this configuration, since the rod-side oil passage is formed so as to be spaced apart from the rod insertion hole and communicates with the cap-side oil drain passage fixed to the lower cover of the main body, the rod-side oil drain passage remains closed even when the sub-cap is removed from the lower cover. This can suppress leakage of oil from the shaft-side oil drain passage.

In the above configuration, it is preferable that the sub-cap and the rod base end portion are detachably coupled to each other by a screw structure.

In the above configuration, it is preferable that the sensor unit further includes a restricting member that is provided at the rod distal end portion, has an outer diameter larger than an outer diameter of the rod, and restricts a relative position of the detected portion with respect to the rotation angle sensor in a direction orthogonal to an axial direction of the rotation center shaft, and an inner diameter of the mounting hole is set larger than the outer diameter of the restricting member.

In the above configuration, it is preferable that the regulating member is made of a non-magnetic resin material.

In the above configuration, it is preferable that a recess facing the rotation angle sensor is formed in the distal end portion of the rod, and the detection portion includes a magnet disposed in the recess and joined to the distal end portion of the rod.

In the above configuration, it is preferable that the display device further includes: a seal member, located between the shaft and the lower cover, for preventing oil from flowing from the cover-side oil drain oil passage into the rod insertion hole and the mounting hole.