CN215761131U

CN215761131U - Transmission and door opener

Info

Publication number: CN215761131U
Application number: CN202121114592.1U
Authority: CN
Inventors: 郑犁; 刘槟
Original assignee: Smart Electronic Industrial Dong Guan Co ltd
Current assignee: Smart Electronic Industrial Dong Guan Co ltd
Priority date: 2021-05-21
Filing date: 2021-05-21
Publication date: 2022-02-08
Anticipated expiration: 2031-05-21

Abstract

The utility model discloses a transmission device and a door opener, wherein the transmission device comprises a driving assembly, an installation assembly and an execution assembly, a coupler and a limit switch are positioned in a limit cavity, a nut is provided with a first connecting section and a second connecting section which are integrally connected, the first connecting section is in threaded connection with a screw rod, a position avoiding cavity is arranged in the second connecting section, an opening of the position avoiding cavity faces the coupler, the coupler enters and exits the position avoiding cavity while the nut enters and exits the limit cavity, and the second connecting section touches or is far away from the limit switch; the door opener comprises the transmission device. The shaft coupling can not interfere the removal of nut, and when the shaft coupling got into and keeps away a chamber, can touch limit switch simultaneously, the connection of each part is comparatively compact, need not to lengthen the part, has reduced the volume of door opener, has improved the convenience that the door opener used.

Description

Transmission and door opener

Technical Field

The utility model relates to the technical field of door openers, in particular to a transmission device and a door opener.

Background

The door opener can receive external signal and automatically open of the door body, close, the door opener generally is through the cooperation motion of screw rod and nut, make the nut drive the action of push tube, with the switching door body, among the correlation technique, the screw rod passes through the shaft coupling and is connected with the motor, nut touching limit switch, it is spacing to realize opening of catch bar and stop, the shaft coupling is located the stroke route of nut, block the removal of nut, consequently, need to increase the length and the length of screw rod that hold the limit switch part, lead to the holistic volume of door opener great, the degree of convenience in use is poor.

Disclosure of Invention

The present invention is directed to solving at least one of the problems of the prior art. Therefore, the utility model provides a transmission device which has a limiting function and a compact structural connection and can reduce the volume of a door opener.

The utility model also provides a door opener with the transmission device.

A transmission according to an embodiment of the first aspect of the utility model includes:

the driving assembly comprises a driving element and a coupler, and the coupler is connected to the output end of the driving element;

the mounting assembly comprises a mounting shell and a mounting bracket, the driving element and the mounting bracket are accommodated in the mounting shell, the driving element is connected with the mounting bracket, a limiting cavity is formed in the mounting bracket, and the coupler is positioned in the limiting cavity;

the limit switch is positioned in the limit cavity and is arranged on the side wall of the mounting bracket;

the actuating assembly comprises a screw rod and a nut, one end of the screw rod is connected with the driving element through the coupler, the nut is sleeved on the screw rod, the nut is provided with a first connecting section and a second connecting section which are integrally connected, the first connecting section is in threaded connection with the screw rod, a position avoiding cavity is arranged inside the second connecting section, and an opening of the position avoiding cavity faces the coupler;

the driving element is used for driving the nut to reciprocate along the screw rod, the second connecting section which enters the limiting cavity and moves to a set position can trigger the limiting switch, and at least part of the coupling extends into the avoiding cavity.

The transmission device provided by the embodiment of the utility model has at least the following beneficial effects:

the transmission device provided by the embodiment of the utility model can limit the nut through the limit switch, the nut is provided with the position avoiding cavity for the coupler to pass in and out, the coupler cannot interfere with the movement of the nut, and the coupler and the limit switch are both positioned in the limit cavity, so that the second connecting section enters the limit cavity and moves to a set position, the coupler enters the position avoiding cavity, the second connecting section can trigger the limit switch, the connection of all the parts is compact, the parts do not need to be lengthened, the size of the door opener is reduced, and the convenience in use of the door opener is improved.

According to some embodiments of the utility model, the mounting assembly further comprises a first end cap, a part of the mounting housing and a part of the mounting bracket are inserted into the first end cap, one end of the mounting bracket close to the mounting housing is provided with a mounting step, the mounting step protrudes relative to the outer surface of the mounting bracket, and the mounting step is clamped between the end surface of the mounting housing and the inner end surface of the first end cap.

According to some embodiments of the utility model, the mounting assembly further comprises a second end cover and a wire buckle, part of the mounting housing is inserted into the second end cover, the side wall of the second end cover is provided with a wire passing hole, and the wire buckle is clamped in the wire passing hole.

According to some embodiments of the utility model, an end of the second end cap, which is away from the mounting housing, is integrally connected with a connecting column, and the connecting column is provided with a connecting hole.

A door opener according to an embodiment of a second aspect of the present invention includes:

the above-mentioned transmission device;

the positioning pipe is sleeved outside the pushing pipe, part of the first connecting section is inserted into and fixed in the pushing pipe, and one end of the positioning pipe is connected with the mounting shell.

The door opener provided by the embodiment of the utility model at least has the following beneficial effects:

according to the door opener disclosed by the embodiment of the utility model, the transmission device is arranged, so that the nut can be limited by the coupler, and the nut can be moved by the coupler, the compactness among all the structures is high, the size of the door opener is reduced, and the door opener is convenient to use.

According to some embodiments of the utility model, the mounting assembly further comprises a first end cap and a mounting ring integrally connected, the mounting housing and the positioning tube are respectively located on two opposite sides of the first end cap, a part of the mounting housing is inserted into the first end cap, and a part of the positioning tube is inserted into the mounting ring.

According to some embodiments of the utility model, the anti-swing device further comprises an anti-swing assembly, the anti-swing assembly comprises an anti-swing ring, one end of the screw rod, which is far away from the coupler, is provided with a mounting boss, the anti-swing ring is sleeved outside the mounting boss, the anti-swing ring is accommodated in the push pipe, the inner side of the anti-swing ring is in contact with the outer surface of the screw rod, and the outer side of the anti-swing ring is in contact with the inner wall of the push pipe.

According to some embodiments of the utility model, the anti-swing assembly further comprises a fixing ring, the fixing ring is sleeved and fixed on the screw rod, the fixing ring is located on one side of the anti-swing ring, which is far away from the coupler, and the anti-swing ring is clamped between the end face of the fixing ring and the end face of the mounting boss.

According to some embodiments of the present invention, the push tube further includes a sealing assembly and a third end cap, the sealing assembly is sleeved outside the push tube, one end of the positioning tube, which is far away from the installation housing, is inserted into the third end cap, a limiting step is disposed on an inner wall of the third end cap, and the sealing assembly is accommodated inside the third end cap and located between the limiting step and an end surface of the positioning tube.

According to some embodiments of the utility model, the sealing assembly comprises a dust ring and two retaining rings, which are arranged to overlap in the moving direction of the thrust tube, and the two retaining rings are respectively located on both sides of the dust ring.

Additional aspects and advantages of the utility model will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the utility model.

Drawings

The utility model is further described with reference to the following figures and examples, in which:

FIG. 1 is a cross-sectional view of one embodiment of the transmission of the present invention;

FIG. 2 is a cross-sectional view of the transmission of FIG. 1 in another state;

FIG. 3 is a cross-sectional view of one embodiment of the door opener of the present invention;

fig. 4 is an enlarged view of a portion a in fig. 3.

Reference numerals: drive assembly 100, drive element 110, coupling 120; the mounting assembly 200, the mounting shell 210, the mounting bracket 220, the limiting cavity 221, the mounting step 222, the first end cover 230, the second end cover 240, the wire buckle 241, the connecting column 250, the connecting hole 251, the pin shaft hole 252 and the mounting ring 260; the device comprises an execution assembly 300, a screw rod 310, a mounting boss 311, a nut 320, a first connecting section 321, a second connecting section 322 and an avoiding cavity 323; a limit switch 400; pushing the tube 500; a positioning tube 600; an anti-swing assembly 700, an anti-swing ring 710, a fixed ring 720; seal assembly 800, wiper 810, retainer ring 820; a third end cap 900, a limit step 910; fourth end cap 1000, mounting hole 1010, through hole 1020.

Detailed Description

Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like or similar reference numerals refer to the same or similar elements or elements having the same or similar function throughout. The embodiments described below with reference to the accompanying drawings are illustrative only for the purpose of explaining the present invention, and are not to be construed as limiting the present invention.

In the description of the present invention, it should be understood that the orientation or positional relationship referred to in the description of the orientation, such as the upper, lower, front, rear, left, right, etc., is based on the orientation or positional relationship shown in the drawings, and is only for convenience of description and simplification of description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus, should not be construed as limiting the present invention.

In the description of the present invention, the meaning of a plurality is one or more, the meaning of a plurality is two or more, and the above, below, exceeding, etc. are understood as excluding the present numbers, and the above, below, within, etc. are understood as including the present numbers. If the first and second are described for the purpose of distinguishing technical features, they are not to be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated or implicitly indicating the precedence of the technical features indicated.

In the description of the present invention, unless otherwise explicitly limited, terms such as arrangement, installation, connection and the like should be understood in a broad sense, and those skilled in the art can reasonably determine the specific meanings of the above terms in the present invention in combination with the specific contents of the technical solutions.

In the description of the present invention, reference to the description of the terms "one embodiment," "some embodiments," "an illustrative embodiment," "an example," "a specific example," or "some examples," etc., means that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the terms used above do not necessarily refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

Referring to fig. 1 and 2, in an embodiment of the present invention, a transmission device is provided to limit a nut. The transmission device comprises a driving component 100, a mounting component 200 and an executing component 300, wherein the driving component 100 comprises a driving element 110 and a coupler 120, and the coupler 120 is connected to the output end of the driving element 110; the mounting assembly 200 is used for providing a mounting and connecting basis for the actuating assembly 300 and the mounting assembly 200, the mounting assembly 200 comprises a mounting shell 210 and a mounting bracket 220, the driving element 110 and the mounting bracket 220 are both accommodated in the mounting shell 210, the driving element 110 is connected with the mounting bracket 220, so that the driving element 110 is fixed in the mounting shell 210, a limit cavity 221 is formed in the mounting bracket 220, the coupler 120 and the limit switch 400 are positioned in the limit cavity 221, and the limit switch 400 is mounted on the side wall of the mounting bracket 220; the actuating assembly 300 includes a screw 310 and a nut 320, one end of the screw 310 is connected to the driving element 110 through the coupler 120, the nut 320 is sleeved outside the screw 310, the nut 320 has a first connecting section 321 and a second connecting section 322 which are integrally connected, the first connecting section 321 is screwed with the screw 310, the second connecting section 322 has an avoiding cavity 323 inside, and an opening of the avoiding cavity 323 is disposed toward the coupler 120.

The driving element 110 can be selected as a driving component such as a motor, a motor and the like, or a driving module formed by combining the motor, the motor and a gear box, when the driving element 110 works, the driving element drives the screw 310 connected with the driving element to rotate, so that the nut 320 screwed with the screw 310 reciprocates along the length direction of the screw 310, when the nut 320 moves towards the direction close to the limit switch 400, along with the movement of the nut 320, the nut 320 gradually enters the limit cavity 221, the coupler 120 gradually enters the avoiding cavity 323, and when the nut 320 moves to a set position, the second connecting section 322 touches the limit switch 400, the driving element 110 stops working, and fixed-point stop of the nut 320 is realized.

Therefore, the transmission device provided in the embodiment of the present invention can limit the nut 320 through the limit switch 400, and the nut 320 has the avoiding cavity 323 for the coupler 120 to go in and out, so that the coupler 120 does not interfere with the movement of the nut 320, and the coupler 120 and the limit switch 400 are both located in the limiting cavity 221, so that the second connecting section 322 enters the limiting cavity 221 and moves to the set position, the coupler 120 enters the avoiding cavity 323, and the second connecting section 322 touches the limit switch 400, so that the connection of the components is relatively compact, the components do not need to be lengthened, the volume of the door opener is reduced, and the convenience in use of the door opener is improved.

It should be noted that fig. 1 is a schematic structural diagram of the transmission device when the nut 320 does not enter the limit cavity 221, and fig. 2 is a schematic structural diagram of the transmission device when the nut 320 enters the limit cavity 221, the coupler 120 enters the avoiding cavity 323, and the second connection section 322 touches the limit switch 400. In addition, the limit switch 400 is located at the side of the coupler 120, the limit switch 400 should be arranged at one end of the limit cavity 221 close to the nut 320 to shorten the length of the position avoiding cavity 323 required to be arranged on the nut 320, and the length of the position avoiding cavity 323 along the moving direction of the nut 320 should be greater than the distance between the end surface of the second connecting section 322 and the contact point of the limit switch 400, so that the position avoiding cavity 323 has enough length for the coupler 120 to be inserted; the inner diameter of the avoiding cavity 323 is larger than the outer diameter of the coupling 120, and the inner diameter of the limiting cavity 221 is larger than the inner diameter of the avoiding cavity 323, so that the coupling 120 can enter the avoiding cavity 323 to avoid the movement of the nut 320 while the nut 320 enters the limiting cavity 221.

The shaft coupling 120, the driving element 110 and the screw 310 are coaxially arranged to ensure the driving precision, the mounting housing 210 and the mounting bracket 220 can be selected to be cylindrical components, so that the transmission device has a neat and universal appearance, the driving element 110 can be fixed at the end part of the mounting bracket 220 in a thread fastening mode, the limit switch 400 is fixed at the side wall of the mounting bracket 220 in a thread fastening mode, because the limit switch 400 is mounted in the limit cavity 221, the mounting bracket 220 is used for providing the shaft hole for the output end of the driving element 110 and the screw 310 to penetrate through, and is arranged in an eccentric mode.

The mounting assembly 200 further includes a first end cap 230, a portion of the mounting housing 210 and a portion of the mounting bracket 220 are inserted into the first end cap 230, one end of the mounting bracket 220 close to the mounting housing 210 has a mounting step 222, the mounting step 222 protrudes outwards relative to the outer surface of the mounting bracket 220, and the mounting step 222 is clamped between the end surface of the mounting housing 210 and the inner end surface of the first end cap 230. First end cover 230 supplies the shaft hole that screw 310 wore to establish to set up with eccentric mode equally, and first end cover 230 can be fixed with the mode that bonds with installation shell 210, because installing support 220 is provided with installation step 222, pegs graft in first end cover 230 at installation shell 210 back, accomplishes installing support 220's fixed promptly, need not to carry out repeated fixed to installing support 220 again, and the equipment convenience is high, and the processing cost is low.

The mounting assembly 200 further includes a second end cap 240, an end of the mounting housing 210 far from the first end cap 230 is inserted into the second end cap 240, the first end cap 230 and the second end cap 240 are combined to fix two ends of the mounting housing 210, and the second end cap 240 is fixed in an adhesive manner as the mounting housing 210. In addition, a wire passing hole is formed in the side wall of the second end cap 240, and the wire passing hole is used for inserting an external cable into the installation casing 210, so that the driving element 110 and an external power supply form electric conduction, and in order to improve the firmness of cable installation and improve the sealing performance of the installation casing 210, in an embodiment of the utility model, a wire buckle 241 is further provided, the cable is inserted into the wire buckle 241, the wire buckle 241 is clamped into the wire passing hole, the installation of the cable is stable, and good sealing can be maintained between the wire buckle 241 and the cable and between the wire buckle 241 and the inner wall of the wire passing hole.

One end of the second end cap 240, which is far away from the first end cap 230, is integrally connected with a connecting column 250, the connecting column 250 is provided with a connecting hole 251, the connecting hole 251 can be used for an external element to be placed in, the side part of the connecting column 250 is provided with a pin shaft hole 252, the pin shaft hole 252 is communicated with the connecting hole 251, and a pin shaft is inserted into the connecting hole 251, so that the connection between the connecting column 250 and the external element can be realized.

Referring to fig. 3, in an embodiment of the present invention, a door opener is further provided, the door opener includes the above-mentioned transmission device, and further includes a push tube 500 and a positioning tube 600, the positioning tube 600 is sleeved outside the push tube 500, a part of the first connection section 321 is inserted into and fixed in the push tube 500, so that the push tube 500 can move along with the movement of the nut 320, the opening and closing of the door body is realized by the action of the push tube 500, one end of the positioning tube 600 is connected with the mounting housing 210, so that the positioning tube 600 is connected with the mounting assembly 200, and the positioning tube 600 and the mounting assembly 200 are combined to mount and fix the actuating assembly 300 and the push tube 500.

In one embodiment, referring to fig. 2, the positioning tube 600 and the mounting housing 210 are respectively located at two opposite sides of the first end cap 230, specifically, a mounting ring 260 is integrally connected to one end of the first end cap 230 away from the mounting housing 210, an end of the positioning tube 600 is inserted into the mounting ring 260, and the mounting ring 260 and the positioning tube 600 can be fixed by adhesion. The mounting ring 260 is eccentrically positioned relative to the first end cap 230 to ensure concentricity of the screw 310 and the coupling 120.

Referring to fig. 4, the door opener further includes a swing prevention assembly 700, the swing prevention assembly 700 is located at one end of the screw 310 away from the coupler 120, the swing prevention assembly 700 includes a swing prevention ring 710, one end of the screw 310 away from the coupler 120 has a mounting boss 311, the swing prevention ring 710 is sleeved outside the mounting boss 311, the swing prevention ring 710 is accommodated inside the push pipe 500, so that the inner side of the swing prevention ring 710 contacts with the outer surface of the screw 310, and the outer side of the swing prevention ring 710 contacts with the inner wall of the push pipe 500; during the rotation of the screw 310, the anti-swing ring 710 can limit the position of the screw 310, and prevent the screw 310 from being displaced radially at the end away from the driving element 110, which may cause the screw 310 to swing and even impact the pushing tube 500.

It is conceivable that the anti-swing ring 710 is made of a self-lubricating material, such as polyoxymethylene, polytetrafluoroethylene, etc., so as to reduce friction and wear between the anti-swing ring 710 and the positioning tube 600 and between the anti-swing ring 710 and the pushing tube 500, and reduce power loss of the screw 310.

The anti-swing assembly 700 further includes a fixing ring 720, the fixing ring 720 is sleeved outside the screw 310 and fixed relative to the screw 310, the fixing ring 720 is located on one side of the anti-swing ring 710 away from the coupler 120, and the anti-swing ring 710 is clamped between an end face of the fixing ring 720 and an end face of the mounting boss 311; the fixing ring 720 is used for limiting the anti-swing ring 710, and the anti-swing ring 710 is prevented from falling off from the screw 310. The fixing ring 720 may be fixed to the screw 310 by screw fastening or bonding.

The door opener further comprises a sealing assembly 800 and a third end cap 900, wherein the sealing assembly 800 is sleeved outside the push pipe 500 and used for sealing the push pipe 500, so that external water vapor and dust are prevented from being brought into the door opener in the moving process of the push pipe 500, one end of the positioning pipe 600 far away from the installation shell 210 is inserted into the third end cap 900, a limiting step 910 is arranged on the inner wall of the third end cap 900, and the sealing assembly 800 is accommodated in the third end cap 900 and is positioned between the limiting step 910 and the end face of the positioning pipe 600; third end cover 900 is fixed with registration arm 600 accessible bonding mode, and is spacing with registration arm 600 terminal surface through spacing step 910, avoids seal assembly 800 to follow the removal of propelling movement pipe 500 and removes, influences sealed effect, and seal assembly 800 can be sealed the clearance before propelling movement pipe 500 and registration arm 600 to and the clearance between registration arm 600 and the third end cover 900, and sealed effectual.

In one embodiment, the sealing assembly 800 includes a dust ring 810 and two retaining rings 820, the dust ring 810 and the retaining rings 820 are arranged in an overlapping manner along the moving direction of the pushing pipe 500, the two retaining rings 820 are respectively located at two sides of the dust ring 810, and the retaining rings 820 can provide a supporting effect for the dust ring 810, so that the dust ring 810 is prevented from being sunk to affect the sealing effect due to the fact that the limiting step 910 or the thickness of the pipe wall of the positioning pipe 600 is too small; the check ring 820 can be made of self-lubricating materials, so that the friction between the check ring 820 and the pushing pipe 500 and between the check ring 820 and the third end cover 900 can be reduced on the basis of certain structural strength, the pushing pipe 500 can move relative to the check ring 820, and the ice and snow accumulated on the outer wall of the pushing pipe 500 can be pushed away by the check ring 820, so that ice removal is realized.

In addition, the door opener further includes a fourth end cap 1000, the fourth end cap 1000 is connected to an end of the push tube 500 away from the driving element 110, and the fourth end cap 1000 is used for connecting with an external member, so that the door opener is assembled to the external member. Fourth end cover 1000's inside has mounting hole 1010, and fourth end cover 1000's lateral part has through-hole 1020, and through-hole 1020 and mounting hole 1010 communicate, and the through-hole 1020 can supply the pivot to penetrate in mounting hole 1010, realizes being connected of fourth end cover 1000 and external member.

The fourth cap 1000 is inserted into the inside of the push tube 500, and a waterproof ring is provided between the outer wall of the fourth cap 1000 and the inside of the push tube 500, for improving waterproof performance between the fourth cap 1000 and the push tube 500. It should be noted that the fourth end cap 1000 and the push tube 500, and the nut 320 and the push tube 500 can be fixed by threaded connection, and the punching point is performed in the threaded connection area, so as to prevent the threads from loosening.

In addition, the first end cap 230, the second end cap 240, the third end cap 900 and the fourth end cap 1000 can be made of PVC plastic water pipes, for example, engineering plastics such as ABS and thermoplastic polyester are adopted, and the processing cost is low.

The embodiments of the present invention have been described in detail with reference to the accompanying drawings, but the present invention is not limited to the above embodiments, and various changes can be made within the knowledge of those skilled in the art without departing from the gist of the present invention. Furthermore, the embodiments of the present invention and the features of the embodiments may be combined with each other without conflict.

Claims

1. A transmission, comprising:

2. The transmission of claim 1, wherein the mounting assembly further comprises a first end cap, a portion of the mounting housing and a portion of the mounting bracket are inserted into the first end cap, the mounting bracket has a mounting step at an end thereof adjacent to the mounting housing, the mounting step protrudes relative to an outer surface of the mounting bracket, and the mounting step is clamped between an end surface of the mounting housing and an inner end surface of the first end cap.

3. The transmission device as claimed in claim 1, wherein the mounting assembly further comprises a second end cap and a wire buckle, a part of the mounting housing is inserted into the second end cap, a wire through hole is formed in a side wall of the second end cap, and the wire buckle is clamped in the wire through hole.

4. The transmission device as claimed in claim 3, wherein the end of the second end cap remote from the mounting housing is integrally connected with a connecting column, and the connecting column is provided with a connecting hole.

5. Door opener, its characterized in that includes:

the transmission of any one of claims 1 to 4;

6. The door opener of claim 5, wherein the mounting assembly further comprises a first end cap and a mounting ring integrally connected to each other, the mounting housing and the positioning tube being disposed on opposite sides of the first end cap, a portion of the mounting housing being inserted into an interior of the first end cap, and a portion of the positioning tube being inserted into an interior of the mounting ring.

7. The door opener according to claim 5, further comprising a swing preventing assembly, wherein the swing preventing assembly comprises a swing preventing ring, a mounting boss is arranged at one end of the screw rod, which is far away from the coupler, the swing preventing ring is sleeved outside the mounting boss, the swing preventing ring is accommodated in the push pipe, the inner side of the swing preventing ring is in contact with the outer surface of the screw rod, and the outer side of the swing preventing ring is in contact with the inner wall of the push pipe.

8. The door opener of claim 7, wherein the anti-swing assembly further comprises a fixing ring, the fixing ring is sleeved on and fixed to the screw rod, the fixing ring is located on one side of the anti-swing ring away from the coupler, and the anti-swing ring is clamped between the end face of the fixing ring and the end face of the mounting boss.

9. The door opener according to claim 5, further comprising a sealing assembly and a third end cap, wherein the sealing assembly is sleeved outside the pushing pipe, one end of the positioning pipe, which is far away from the mounting housing, is inserted into the third end cap, a limiting step is arranged on an inner wall of the third end cap, and the sealing assembly is accommodated in the third end cap and is located between the limiting step and an end surface of the positioning pipe.

10. The door opener according to claim 9, wherein the sealing assembly comprises a dust seal and two retainer rings arranged to overlap in a moving direction of the push pipe, the two retainer rings being respectively located at both sides of the dust seal.