CN113715896A

CN113715896A - Forklift steering control system with efficient vibration isolation

Info

Publication number: CN113715896A
Application number: CN202111116550.6A
Authority: CN
Inventors: 钱正旺; 毕胜; 王平; 张冬林
Original assignee: Anhui Heli Co Ltd
Current assignee: Anhui Heli Co Ltd
Priority date: 2021-09-23
Filing date: 2021-09-23
Publication date: 2021-11-30

Abstract

The invention discloses a forklift steering control system with efficient vibration isolation, wherein a steering column comprises a column body and a rotary seat fixedly sleeved at the lower end of the column body, the side wall of the column body is connected with a front and back adjusting bracket, and an upper adjusting bracket for adjusting the position of the steering column is arranged on a front plate on a vehicle body; two sides of the rotary seat are provided with symmetrical rotary holes, a buffer bush is inserted in each rotary hole, the rotary seat is connected with a lower rotary frame through a rotary bolt, the rotary bolt penetrates through the lower rotary frame in a threaded mode and is inserted into the buffer bush, and the lower rotary frame is fixedly connected to the front end of the front plate under the automobile body. The buffering bush is designed at the rotating seat rotating hole of the steering column, so that the vibration transmitted from the lower front plate of the vehicle body to the rotating seat of the steering column by a forklift power system is isolated; the vibration of the forklift power system transmitted to the front and rear adjusting supports of the steering column from the upper front plate of the vehicle body is isolated by designing the vibration damping pad between the upper adjusting frame and the upper front plate of the vehicle body.

Description

Forklift steering control system with efficient vibration isolation

Technical Field

The application relates to the technical field of forklift steering systems, in particular to a forklift steering control system with efficient vibration isolation.

Background

Along with industrial progress and technical development, a forklift user puts higher requirements on the human-computer interaction performance such as the whole machine control comfort, the use convenience and the like on the premise that a forklift product meets the functional requirements. For the control working condition of frequent reversing of the forklift in a small range, the flexibility and the comfort of the steering control system directly feed back the human-computer interaction level of the whole forklift. Traditional fork truck turns to operating system and whole car automobile body rigid connection, and whole machine driving system vibration is transmitted to user's hand by front axle, front bezel, steering mechanism to the steering wheel, and it is relatively poor to control the travelling comfort. The vibration transmitted to the hand of the steering wheel can be reduced to a certain degree by adopting a universal joint flexible connection mode for a forklift steering mechanism, but the vibration of the rotary root of the steering mechanism cannot be eliminated, and the universal joint mechanism has the defects of low transmission efficiency, high cost and the like.

Disclosure of Invention

In view of the above-mentioned shortcomings of the prior art, the present patent application aims to provide a highly efficient vibration isolation forklift steering system, which solves the above-mentioned problems of the prior art.

In order to achieve the purpose, the invention provides the following technical scheme:

a forklift steering control system with efficient vibration isolation comprises a steering column, wherein the upper end of the steering column is provided with a steering wheel, the lower end of the steering column is connected with a steering gear, and the middle part of the lower end of the steering wheel is connected with a transmission shaft of which the lower end penetrates through the steering column and is connected with the steering gear;

the steering column comprises a column body and a rotary seat fixedly sleeved at the lower end of the column body, the side wall of the column body is connected with a front and rear adjusting support, the front and rear adjusting support is installed at the front end of a front plate on the vehicle body, and an upper adjusting frame for adjusting the position of the steering column is installed on the front plate on the vehicle body;

two sides of the rotary seat are provided with symmetrical rotary holes, a buffer bush is inserted in each rotary hole, the rotary seat is connected with a lower rotary frame through a rotary bolt, the rotary bolt penetrates through the lower rotary frame in a threaded mode and is inserted into the buffer bush, and the lower rotary frame is fixedly connected to the front end of the front plate under the automobile body.

Further, the gyration seat includes the flange seat, and the upper end of flange seat is connected with integrated into one piece's gyration boss, sets up the through-hole that supplies the tubular column body to run through on the gyration boss, and two gyration holes are seted up in the both sides of flange seat, set up the mounting hole that is matrix distribution on the flange seat, and the flange seat passes on the up end of mounting hole screw in steering gear through the screw.

Furthermore, the lower rotating frame comprises a U-shaped frame, two inner walls of the vertical section of the U-shaped frame are connected with limiting bosses located on the same horizontal plane, and the limiting bosses and the side wall of the U-shaped frame are provided with threaded holes with the same axle center.

Furthermore, the rotary bolt comprises a first thread section in threaded connection with the threaded hole and a rotating shaft inserted in the buffer bush.

Furthermore, the buffer bush comprises an inner bush, a buffer layer sleeved on the outer ring of the inner bush, and an outer bush sleeved on the outer ring of the buffer layer.

Further, go up the alignment jig and include the base of fixing on the front bezel on the automobile body through locking bolt, connect and be left branch fagging and the right branch fagging that the symmetry was laid at the base front end, the front and back regulation support is located between left branch fagging and the right branch fagging, set up the arc notch that link up on the front and back regulation support, the both sides that the front and back regulation support is located the arc notch are equipped with rotating sleeve pipe and locking sleeve pipe, it is equipped with the adjusting bolt who passes the arc notch to run through between rotating sleeve pipe and the locking sleeve pipe, adjusting bolt is rotated to the positive and negative direction and makes rotating sleeve pipe and locking sleeve pipe press from both sides tightly or loosen front and back regulation support.

Furthermore, a positioning hole is formed in the left supporting plate, and a special-shaped hole is formed in the right supporting plate;

the rotating sleeve comprises an end shaft which is rotatably inserted in the positioning hole, a supporting sleeve connected to one end of the end shaft and a first positioning boss connected to one end of the supporting sleeve far away from the end shaft;

the locking sleeve comprises a positioning pin shaft inserted in the special-shaped hole, a threaded sleeve connected to one end of the positioning pin shaft and a second positioning boss connected to one end, far away from the positioning pin shaft, of the threaded sleeve, the section of the positioning pin shaft is a polygonal shaft, and the special-shaped hole is a polygonal hole matched and inserted with the positioning pin shaft;

the adjusting bolt is sequentially provided with a conical boss with a conical surface, a limiting table, a screw rod and a second thread section from left to right, the screw rod is in threaded connection with the rotating sleeve, and the second thread section is in threaded connection with the locking sleeve in a thread groove at one end close to the front and rear adjusting supports.

Furthermore, a thread groove is formed in one end, away from the limiting table, of the conical boss, a handle mounting bolt is connected to the thread groove in an inner thread mode, one end of the handle mounting bolt extends outwards, and one section, located outside the thread groove, of the handle mounting bolt is connected with a handle convenient to hold.

Further, a plurality of installation notches that supply locking bolt to pass are seted up to the tip of base, are connected with the shock pad of pegging graft in the mounting groove mouth between the front bezel on base and the automobile body, and it has spacing bush to peg graft with one heart in the shock pad, and locking bolt overlaps in proper order after passing front bezel and spacing bush on the automobile body and establishes flat pad, bullet pad and nut and fasten and decide.

Furthermore, the sum of the thicknesses of the first positioning boss and the second positioning boss is not more than the thickness of the arc-shaped notch, and the diameters of the first positioning boss and the second positioning boss are both smaller than the width of the narrow part of the arc-shaped notch.

Compared with the prior art, the invention has the beneficial effects that:

1. the buffering bush is designed at the rotating seat rotating hole of the steering column, so that the vibration transmitted from the lower front plate of the vehicle body to the rotating seat of the steering column by a forklift power system is isolated; the vibration of the forklift power system transmitted to the front and rear adjusting supports of the steering column from the upper front plate of the vehicle body is isolated by designing the vibration damping pad between the upper adjusting frame and the upper front plate of the vehicle body. The vibration of the whole steering column and the steering wheel is reduced fundamentally. The driving comfort of the driver is greatly improved.

2. The steering column assembly adopts a straight-through structure, and is directly connected with a steering wheel through the upper end of a transmission shaft, and the lower end of the transmission shaft is directly connected with a steering gear; the lower end rotates around the rigid lower rotating frame, the upper end is fixed or the front-back adjusting support is released through the adjusting bolt, the forklift steering and the front-back adjusting of the steering wheel are realized, the mechanism is efficient and reliable, and the cost is low.

Drawings

FIG. 1 is a schematic structural diagram of a forklift steering system with efficient vibration isolation according to the invention;

FIG. 2 is a schematic view of a steering column according to the present invention;

FIG. 3 is a schematic view of a rotary base according to the present invention;

FIG. 4 is a schematic view of a cushion collar of the present invention;

FIG. 5 is a schematic structural view of a lower turret according to the present invention;

FIG. 6 is a schematic view of a swivel bolt according to the present invention;

FIG. 7 is a schematic view of an upper adjustment frame according to the present invention;

FIG. 8 is a schematic view of an upper adjustment bracket mounting structure according to the present invention;

FIG. 9 is a schematic view of a fore-aft adjustment bracket according to the present invention;

FIG. 10 is a schematic view of the locking structure of the fore-aft adjustment bracket of the present invention;

FIG. 11 is a schematic view of an adjusting bolt according to the present invention;

FIG. 12 is a schematic view of a rotating sleeve according to the present invention;

fig. 13 is a schematic view of the locking sleeve structure of the present invention.

The reference numbers illustrate: the steering column comprises an upper vehicle body front plate 1, a lower vehicle body front plate 2, a steering column 3, a rotary seat 31, a rotary boss 311, a rotary hole 312, a flange seat 313, a mounting hole 314, a column body 32, a front and rear adjusting bracket 33, an arc-shaped notch 331, a buffer bush 34, an inner bushing 341, a buffer layer 342, an outer bush 343, a lower rotary frame 4, a limit boss 41, a threaded hole 42, an upper adjusting frame 5, a base 51, a mounting notch 511, a left support plate 52, a positioning hole 521, a right support plate 53, a special-shaped hole 531, a steering wheel 6, a steering gear 7, a rotary bolt 8, a first threaded section 81, a rotating shaft 82, a shock pad 9, a limit bush 10, a locking bolt 11, a flat pad 12, an elastic pad 13, a nut 14, an adjusting bolt 15, a cone boss 151, a limit table 152, a screw 153, a second threaded section 154, a rotary sleeve 16, a support sleeve 161, a first positioning boss 162, an end shaft 163, a locking sleeve 17, a threaded sleeve 171, a, A second positioning boss 172, a positioning pin 173, a threaded groove 174, a handle mounting bolt 18, and a handle 19.

Detailed Description

The following description of the embodiments of the present application is provided by way of specific examples, and other advantages and effects of the present application will be readily apparent to those skilled in the art from the disclosure herein. The present application is capable of other and different embodiments and its several details are capable of modifications and variations in various respects, all without departing from the spirit of the present application. It should be noted that the embodiments and features of the embodiments in the present application may be combined with each other without conflict.

Referring to fig. 1-13, the present invention provides a technical solution:

the utility model provides a fork truck of high-efficient vibration isolation turns to control system, as shown in figure 1, including steering column 3, lower rotating frame 4, go up alignment jig 5, lower rotating frame 4 is fixed at the front end of front bezel 2 under the automobile body, goes up alignment jig 5 and fixes the front end at front bezel 1 on the automobile body, and steering column 3's upper end is equipped with steering wheel 6, the lower extreme is connected with steering gear 7, and steering wheel 6's lower extreme middle part is connected with the transmission shaft that the lower extreme passed steering column 3 and is connected with steering gear 7.

As shown in fig. 2, the steering column 3 includes a swivel base 31, a column body 32, a front-rear adjusting bracket 33, and a cushion bush 34, and as shown in fig. 9, the front-rear adjusting bracket 33 is provided with an arc-shaped notch 331.

As shown in fig. 1 and 3, the rotary seat 31 includes a flange seat 313 and a rotary boss 311 integrally connected to the flange seat 313, a through hole for the tubular column body 32 to pass through is formed in the rotary boss 311, two rotary holes 312 are symmetrically formed in two sides of the flange seat 313, mounting holes 314 distributed in a matrix are formed in the flange seat 313, and the flange seat 313 is screwed into the upper end surface of the steering gear 7 through screws passing through the mounting holes 314.

As shown in fig. 4, the buffer bush 34 includes an inner bush 341, a buffer layer 342 sleeved on an outer ring of the inner bush 341, and an outer bush 343 sleeved on an outer ring of the buffer layer 342, the three are sequentially formed into a "concentric roll" structure, there are two buffer bushes 34, and the two buffer bushes 34 are respectively inserted into the rotary holes 312 on the left and right sides of the flange seat 313 in fig. 3. The buffer layer 342 is made of rubber and plays a role in buffering and vibration isolation, the inner bushing 341 and the outer bushing 343 are made of metal, when the steering column 3 is adjusted forwards and backwards, the rotary seat 31 rotates around the rotary bolt 8, and the inner bushing 341 and the outer bushing 343 play a role in wear prevention and protection.

As shown in fig. 1 and 5, the lower rotating frame 4 includes a U-shaped frame, the U-shaped frame is fixedly connected to the front plate 2 under the vehicle body, two inner walls of a vertical section of the U-shaped frame are connected with a limiting boss 41 located on the same horizontal plane, and a threaded hole 42 coaxial with the limiting boss 41 and the side wall of the U-shaped frame is formed.

As shown in fig. 1 and 6, the rotary bolt 8 includes a first threaded section 81 threadedly coupled to the threaded hole 42 and a rotating shaft 82 inserted into the buffer bushing 34. Between the rotary seat 31 on the steering column 3 and the lower rotary frame 4, two sides are respectively fixedly connected through the rotary bolt 8, the rotary bolt 8 respectively penetrates through the threaded hole 42 from two sides and then is locked and fixed through the first threaded section 81, and the rotating shaft 82 is respectively inserted into the buffer bushes 34 on two sides.

As shown in fig. 7, the upper adjustment frame 5 includes a base 51, a left support plate 52 and a right support plate 53, the base 51 is provided with a plurality of mounting notches 511, positioning holes 521 are formed thereon, the right support plate 53 is provided with a shaped hole 531, and the centers of the positioning holes 521 and the shaped hole 531 are coaxial.

As shown in fig. 8, a shock pad 9 inserted in the mounting notch 511 is connected between the base 51 and the upper front plate 1 of the vehicle body, a limit bushing 10 is concentrically inserted in the shock pad 9, and a lock bolt 11 passes through the upper front plate 1 of the vehicle body and the limit bushing 10 and then is sequentially sleeved with a flat pad 12, an elastic pad 13 and a nut 14 and is fastened. No metal direct contact between the front plate 1 and the upper trim 5 on the vehicle body is ensured.

As shown in fig. 10, the front-rear adjusting bracket 33 is located between the left support plate 52 and the right support plate 53, the rotating sleeve 16 and the locking sleeve 17 are respectively arranged between the left support plate 52 and the right support plate 53 and between the front-rear adjusting bracket 33, the adjusting bolt 15 penetrating through the arc-shaped notch 331 is arranged between the rotating sleeve 16 and the locking sleeve 17 in a penetrating manner, and the adjusting bolt 15 is rotated in the forward and reverse directions to clamp or loosen the front-rear adjusting bracket 33 by the rotating sleeve 16 and the locking sleeve 17.

As shown in fig. 10, 11, 12 and 13, the adjusting bolt 15 is sequentially provided with a conical boss 151 with a conical surface, a limiting table 152, a screw 153 and a second thread section 154 from left to right, a thread groove is formed in one end of the conical boss 151 away from the limiting table 152, a handle mounting bolt 18 with one end extending outwards is connected to the thread groove in a threaded manner, and a section of the handle mounting bolt 18 located outside the thread groove is connected with a handle 19 convenient to hold by hand; the rotating sleeve 16 comprises an end shaft 163 rotatably inserted into the positioning hole 521, a supporting sleeve 161 connected to one end of the end shaft 163, and a first positioning boss 162 connected to one end of the supporting sleeve 161 far away from the end shaft 163; the locking sleeve 17 comprises a positioning pin 173 inserted in the special-shaped hole 531, a threaded sleeve 171 connected to one end of the positioning pin 173, and a second positioning boss 172 connected to one end of the threaded sleeve 171 far away from the positioning pin 173, the cross section of the positioning pin 173 is a polygonal shaft, and the special-shaped hole 531 is a polygonal hole matched with and inserted in the positioning pin 173; the screw 153 is threadedly engaged with the rotary sleeve 16, and the second thread section 154 is threadedly engaged in the thread groove 174 of the locking sleeve 17 at an end thereof adjacent to the forward-rearward adjustment bracket 33. The sum of the thicknesses of the first positioning boss 162 and the second positioning boss 172 is not greater than the thickness of the arc-shaped notch 331, and the diameters of the first positioning boss 162 and the second positioning boss 172 are both smaller than the width of the narrow portion of the arc-shaped notch 331.

In actual operation, the steering gear 7 is fixed by screw connection through the mounting hole 314; the steering wheel 6 is directly connected with the steering gear 7 through a transmission shaft, so that the steering operation of the forklift is realized. The steering column 3 is rotated around the rotation shaft 82 to adjust the steering wheel 6 of the forklift forward and backward.

When a certain front-back position of the steering wheel 6 needs to be fixed, the adjusting bolt 15 is rotated through the handle 19, and the locking sleeve 17 is driven to be close to the front-back adjusting bracket 33 due to the threaded connection effect of the second threaded section 154 and the threaded groove 174. Meanwhile, under the action of the limit table 152 and the end shaft 163 in a matched manner, the rotating sleeve 16 is pushed to the front-rear adjusting bracket 33, the front-rear adjusting bracket 33 is clamped by the rotating sleeve 16 and the locking sleeve 17, and the front position and the rear position of the steering wheel 6 are fixed. The polygonal cross section of the positioning pin 173 is matched with the special-shaped hole 531, and the locking sleeve is prevented from rotating along with the second threaded section 154 under the positioning action of the positioning pin 173 with the polygonal cross section.

By designing the buffer bush 34 at the rotary hole 312, the vibration of the forklift power system transmitted from the lower front plate 2 of the forklift body to the rotary seat 31 is isolated; the vibration of the forklift power system transmitted from the upper front plate 1 of the vehicle body to the front and rear adjusting supports 33 on the steering column 3 is isolated by designing the damping pad between the upper adjusting frame 5 and the upper front plate 1 of the vehicle body. Fundamentally has reduced the vibration of whole steering column 3 and steering wheel 6, has promoted driver's control travelling comfort by a wide margin. The steering column 3 adopts a straight-through structure, the lower end of the steering column rotates around the rigid lower rotating frame 4, and the upper end of the steering column is locked or released through the front-back adjusting support 13, so that the front-back adjustment of the steering wheel 6 of the forklift is realized, and the mechanism is efficient and reliable and has low cost.

The steering control system provided by the invention has the advantages of small vibration, higher reliability and higher cost performance.

The above-described embodiments are merely illustrative of the principles and utilities of the present patent application and are not intended to limit the present patent application. Modifications and variations can be made to the above-described embodiments by those skilled in the art without departing from the spirit and scope of this patent application. Accordingly, it is intended that all equivalent modifications or changes which can be made by those skilled in the art without departing from the spirit and technical concepts disclosed in the present application shall be covered by the claims of the present application.

Claims

1. A forklift steering control system with efficient vibration isolation comprises a steering column (3), wherein the upper end of the steering column (3) is provided with a steering wheel (6), the lower end of the steering column (3) is connected with a steering gear (7), and the middle part of the lower end of the steering wheel (6) is connected with a transmission shaft of which the lower end penetrates through the steering column (3) and is connected with the steering gear (7);

the method is characterized in that: the steering column (3) comprises a column body (32) and a rotary seat (31) fixedly sleeved at the lower end of the column body (32), the side wall of the column body (32) is connected with a front-back adjusting support (33), the front-back adjusting support (33) is installed at the front end of an upper front plate (1) of the vehicle body, and an upper adjusting frame (5) for adjusting the position of the steering column (3) is installed on the upper front plate (1) of the vehicle body;

two sides of the rotary seat (31) are provided with symmetrical rotary holes (312), a buffer bush (34) is inserted in each rotary hole (312), the rotary seat (31) is connected with a lower rotary frame (4) through a rotary bolt (8), the rotary bolt (8) penetrates through the lower rotary frame (4) in a threaded mode and is inserted into the buffer bush (34), and the lower rotary frame (4) is fixedly connected to the front end of the front plate (2) below the automobile body.

2. The high efficiency vibration isolating forklift steering system according to claim 1, wherein: the rotary seat (31) comprises a flange seat (313), the upper end of the flange seat (313) is connected with an integrally formed rotary boss (311), a through hole for the tubular column body (32) to penetrate through is formed in the rotary boss (311), two rotary holes (312) are formed in two sides of the flange seat (313), mounting holes (314) distributed in a matrix mode are formed in the flange seat (313), and the flange seat (313) penetrates through the mounting holes (314) through screws to be screwed into the upper end face of the steering gear (7).

3. The high efficiency vibration isolating forklift steering system according to claim 2, wherein: the lower rotating frame (4) comprises a U-shaped frame, two inner walls of a vertical section of the U-shaped frame are connected with limiting bosses (41) located on the same horizontal plane, and threaded holes (42) coaxial with the limiting bosses (41) and the side wall of the U-shaped frame are formed in the limiting bosses (41).

4. A highly efficient vibration isolating forklift steering system according to claim 3, wherein: the rotary bolt (8) comprises a first thread section (81) in threaded connection with the threaded hole (42) and a rotating shaft (82) inserted in the buffer bush (34).

5. An efficient vibration isolating forklift steering system according to any one of claims 1-4, wherein: the buffer bush (34) comprises an inner bush (341), a buffer layer (342) sleeved on the outer ring of the inner bush (341), and an outer bush (343) sleeved on the outer ring of the buffer layer (342).

6. The high efficiency vibration isolating forklift steering system according to claim 1, wherein: go up alignment jig (5) and include base (51) of fixing on automobile body front bezel (1) through locking bolt (11), connect left branch fagging (52) and right branch fagging (53) that are the symmetry and lay at base (51) front end, front and back regulation support (33) are located between left branch fagging (52) and right branch fagging (53), seted up through arc notch (331) on front and back regulation support (33), front and back regulation support (33) are located the both sides of arc notch (331) and are equipped with and rotate sleeve pipe (16) and locking sleeve pipe (17), it is equipped with adjusting bolt (15) that pass arc notch (331) to run through between rotating sleeve pipe (16) and locking sleeve pipe (17), adjusting bolt (15) are rotated to the positive and negative direction and are made to rotate sleeve pipe (16) and locking sleeve pipe (17) and press from both sides tightly or loosen front and back regulation support (33).

7. The high efficiency vibration isolating forklift steering system according to claim 6, wherein: the left support plate (52) is provided with a positioning hole (521), and the right support plate (53) is provided with a special-shaped hole (531);

the rotating sleeve (16) comprises an end shaft (163) rotatably inserted into the positioning hole (521), a supporting sleeve (161) connected to one end of the end shaft (163) and a first positioning boss (162) connected to one end, far away from the end shaft (163), of the supporting sleeve (161);

the locking sleeve (17) comprises a positioning pin shaft (173) inserted in the special-shaped hole (531), a threaded sleeve (171) connected to one end of the positioning pin shaft (173) and a second positioning boss (172) connected to one end, far away from the positioning pin shaft (173), of the threaded sleeve (171), the section of the positioning pin shaft (173) is a polygonal shaft, and the special-shaped hole (531) is a polygonal hole matched and inserted with the positioning pin shaft (173);

the adjusting bolt (15) is provided with a conical boss (151) with a conical surface, a limiting table (152), a screw rod (153) and a second thread section (154) from left to right in sequence, the screw rod (153) is in threaded connection with the rotating sleeve (16), and the second thread section (154) is in threaded connection with a thread groove (174) at one end of the locking sleeve (17) close to the front and rear adjusting support (33).

8. The high efficiency vibration isolating forklift steering system according to claim 7, wherein: the screw groove is formed in one end, away from the limiting table (152), of the conical boss (151), the screw groove is connected with a handle mounting bolt (18) with one end extending outwards in an internal thread mode, and one section, located outside the screw groove, of the handle mounting bolt (18) is connected with a handle (19) convenient to hold by hand.

9. The high efficiency vibration isolating forklift steering system according to claim 7, wherein: the installation notch (511) that a plurality of confession locking bolt (11) passed are seted up to the tip of base (51), are connected with shock pad (9) of pegging graft in installation notch (511) between front bezel (1) on base (51) and the automobile body, peg graft with one heart in shock pad (9) and have spacing bush (10), flat pad (12), bullet pad (13) and nut (14) and fastening are established after front bezel (1) and spacing bush (10) are gone up in proper order to locking bolt (11) pass the automobile body.

10. The high efficiency vibration isolating forklift steering system according to claim 7, wherein: the sum of the thicknesses of the first positioning boss (162) and the second positioning boss (172) is not larger than the thickness of the arc-shaped notch (331), and the diameters of the first positioning boss (162) and the second positioning boss (172) are smaller than the width of the narrow part of the arc-shaped notch (331).