CN112879650A

CN112879650A - Electronic expansion valve

Info

Publication number: CN112879650A
Application number: CN201911202844.3A
Authority: CN
Inventors: 不公告发明人
Original assignee: Zhejiang Sanhua Intelligent Controls Co Ltd
Current assignee: Zhejiang Sanhua Intelligent Controls Co Ltd
Priority date: 2019-11-29
Filing date: 2019-11-29
Publication date: 2021-06-01

Abstract

The invention discloses an electronic expansion valve, which comprises a valve seat, a screw rod, a rotor and a planetary reduction mechanism, wherein a gear ring part of the planetary reduction mechanism is fixed on the valve seat; the output end of the planet carrier of the N-1 stage planetary wheel assembly is meshed with each planet wheel of the N stage planetary wheel assembly, and the output end of the planet carrier of the last stage planetary wheel assembly is connected with the upper end of the screw rod; the speed reducing mechanism of the electronic expansion valve adopts a planetary speed reducing mechanism, a sun gear and planet gears at all levels are coaxially arranged, the radial space occupation is small, the transverse volume of the speed reducing mechanism is greatly reduced, the axial structure of the planetary speed reducing mechanism is compact, the axial size is small, the mechanism has the advantages of high transmission efficiency and large transmission power range, and the electronic expansion valve can meet the requirements of high precision and miniaturization when the flow control range is enlarged.

Description

Electronic expansion valve

Technical Field

The invention relates to the technical field of refrigeration, in particular to an electronic expansion valve.

Background

The electronic expansion valve is used for an air-conditioning refrigeration system, and is used for throttling and decompressing high-pressure liquid refrigerant and conveying the throttled and decompressed refrigerant to the evaporator.

The speed reducing electronic expansion valve for frequency converting air conditioner is one widely used electronic expansion valve and consists of two parts: one part is a valve body part for flow regulation; the other part is a coil part for driving. As shown in fig. 1, wherein the coil part includes: the permanent magnet type stepping motor 1 ', the gear reducer 2 ' and the screw pair structure 5 ' which converts the rotation motion of the motor into the vertical motion of the screw rod 3', and the valve body part comprises a valve seat 10 ', a valve needle 8, a corrugated pipe 7 and other core components. The electromagnetic coil is electrified, the output shaft of the stepping motor 1 'rotates, the stepping motor 1' is matched with the gear reducer 2 'to drive the output shaft of the gear reducer 2' to rotate, the output shaft of the gear reducer 2 'is matched with the screw rod to drive the screw rod 3' to rotate, and then the screw rod 3 'is matched with the thread pair structure 5' to enable the screw rod to move up and down. When the screw rod moves downwards, the steel ball 11 ' is propped against the lining 6 ', and the lining 6 ' is propped against the valve needle 8, so that the valve needle 8 and the screw rod can synchronously move downwards until the valve needle 8 is positioned at a closing position. When reverse pulse is applied, the screw rod 3' moves upwards, and the valve needle 8 continuously moves upwards under the action of the return elasticity of the corrugated pipe 7 and the system pressure, so that the opening degree of the valve port part 9 is changed, the flow area is changed, and the purpose of controlling the flow and adjusting the superheat degree is achieved. Fig. 2 shows a specific structure of a three-stage reduction gear reducer in the background art. The first-stage speed reducing mechanism comprises a gear 1a and a gear 1b, the second-stage speed reducing mechanism comprises a gear 2a and a gear 2b, and the third-stage speed reducing mechanism comprises a gear 3a and a gear 3 b. The motor shaft 12 'is arranged coaxially with the gear 1a, the gear 1a is driven to rotate by the motor shaft 12', and the gear 1b is driven to rotate by the gear 1 a. The gear 1b drives the gear 2a of the second-stage speed reducing mechanism to rotate, and the gear 2a drives the gear 2b to rotate. The gear 2b drives the gear 3a of the third-stage speed reducing mechanism to rotate, and the gear 3a drives the gear 3b to rotate, and finally drives the output shaft 13' to rotate.

Disclosure of Invention

The invention provides an electronic expansion valve, which comprises a valve seat, a screw rod, a rotor and a planetary reduction mechanism, wherein the planetary reduction mechanism comprises a sun gear, a gear ring component and at least one stage of planetary wheel component; the output end of a planet carrier of the N-1 stage planetary wheel assembly is meshed with each planet wheel of the N stage planetary wheel assembly, and the output end of the planet carrier of the last stage planetary wheel assembly is connected with the upper end part of the screw rod; wherein N is an integer of 1 or more.

The speed reducing mechanism of the electronic expansion valve adopts a planetary speed reducing mechanism, the sun gear and the planet gears at all levels are coaxially arranged, the radial space occupation is small, the transverse volume of the speed reducing mechanism is relatively reduced, the axial structure of the planetary speed reducing mechanism is compact, and the axial size is relatively small.

Drawings

FIG. 1 is a schematic diagram of an electronic expansion valve according to the prior art;

FIG. 2 is a schematic diagram of a three-stage reduction gear reducer of the prior art;

FIG. 3 is a schematic structural diagram of an electronic expansion valve according to an embodiment of the present invention;

FIG. 4 is a schematic diagram of a portion of the electronic expansion valve shown in FIG. 3;

FIG. 5 is a schematic structural view of a valve seat, ring gear member, screw and spool member forming assembly of the present invention;

FIG. 6 is a schematic cross-sectional view of a position of engagement of a sun gear with a first stage planetary gear assembly in an electronic expansion valve in accordance with an embodiment of the present invention;

FIG. 7 is a schematic view of the outer configuration of a ring gear member mounted on a valve seat in one embodiment of the present invention;

FIG. 8 is a schematic split view of a first stage planetary wheel assembly in accordance with an embodiment of the present invention;

FIG. 9 is a schematic split view of a third stage planetary wheel assembly in accordance with an embodiment of the present invention.

Wherein, in fig. 1 to 2:

the device comprises a stepping motor 1 ', a gear reducer 2 ', a screw rod 3', a thread pair structure 5 ', a lining 6 ', a corrugated pipe 7, a valve needle 8, a valve opening part 9, a valve seat 10 ' and a steel ball 11 ';

gears

1a, 1b, 2a, 2b, 3a, 3 b; a motor shaft 12'; an output shaft 13'.

Wherein, in fig. 3 to 9:

the valve seat 10, the valve needle 11, the external adapter 11a, the external adapter 12a, the spring 12, the screw rod 20, the nut 21, the nut mounting seat 22, the planetary reduction mechanism 30, the sun gear 301, the first-stage planet carrier 302, the planet gear 303, the gasket 3024, the boss 3021, the output shaft 3022, the mounting shaft 3023, the second-stage planet carrier 304, the gear ring component 32, the sleeve 321, the through-hole 321a, the gear ring 322, the housing 40, the rotor guide frame 42, the rotor 50, the spring 60, the mandrel 70, and the coil fixing frame 80;

a shim 221, a planet wheel 222, a third stage planet carrier 305, a mounting shaft 2231, a boss 2232.

Detailed Description

In the case of the speed reducing mechanism described in the background art, in order to increase the flow rate control range, the output torque must be increased, and in order to improve the control accuracy, a large speed reduction ratio must be set without changing other conditions (e.g., without changing the input torque).

There are two ways to increase the reduction ratio: one is to increase the reduction ratio of each stage of gears, i.e. to increase the number of teeth of the large gear, but the above structure will inevitably result in the increase of the outer diameter of the large gear, and thus the volume of the gear reducer is increased. The other is to increase the number of gear reduction steps, but the above structure will inevitably result in an increase in the number of gears, and therefore also in an increase in the volume of the gear reducer. Finally, the requirements of high precision and miniaturization cannot be met. In addition, the increase in the number of stages also results in a reduction in the transmission efficiency and stability of the overall system.

Therefore, how to consider both the transmission reduction ratio and the expansion valve volume and provide an electronic expansion valve with a high reduction ratio and a small volume is an urgent technical problem to be solved in the field.

Therefore, the present invention provides an electronic expansion valve with a deceleration mechanism with a new structure, and in order to make those skilled in the art better understand the technical solution of the present invention, the present invention will be further described in detail with reference to the accompanying drawings and specific embodiments.

Referring to fig. 3 to 9, the present invention provides an electronic expansion valve, which includes a valve body portion and a coil, wherein the valve body portion is mainly used for flow rate adjustment, and the coil portion provides a driving force.

The valve body portion of the electronic expansion valve of the present invention includes a valve seat portion, a transmission mechanism, a speed reducing mechanism, a housing 40, and a rotor 50.

The valve seat portion has members including the valve seat 10 and an internally threaded member, the detailed structure of which will be described later in detail. The outer surface of the valve seat 10 is provided with a first port and a second port, the valve port is arranged in the valve seat 10, the first port and the second port are communicated through the valve port, the first port and the second port are generally used for installing an external connecting pipe, as shown in fig. 3, the first port is provided with an external connecting pipe 11a, and the second port is provided with an external connecting pipe 12 a. The first port can be a refrigerant inlet or a refrigerant outlet, and correspondingly, when the first port is the refrigerant inlet, the second port is the refrigerant outlet; when the first port is a refrigerant outlet, the second port is a refrigerant inlet.

The external refrigerant flows from the external connection pipe of the first port (or the second port) to the interior of the valve seat 10, passes through the valve port, and flows out from the external connection pipe of the second port (or the first port).

The screw rod 20 is one of the main components of the transmission mechanism, and the screw rod 20 is provided with an external thread part which is matched with the internal thread of the internal thread component.

The speed reducing mechanism provided by the invention is a planetary speed reducing mechanism 30, and the planetary speed reducing mechanism comprises a sun gear, a gear ring component 32 and at least one stage of planetary wheel component, namely, the number of the planetary wheel components in the invention can be determined according to the practical electronic expansion valve, and can be one, or two or more. The planet wheel subassembly includes planet carrier and two at least planet wheels, and planet carrier mainly plays supporting role and transmission power's effect to the planet wheel, and the primary structure of planet carrier can be by multiple form, does not do specific limit here. For example, the planetary carrier may include a mounting platform, an upper end surface of the mounting platform is provided with mounting shafts 3023 corresponding to the planetary gears one to one, please refer to fig. 8, the planetary gears are mounted on the corresponding mounting shafts 3023, in order to prevent the planetary gears from sliding out of the mounting shafts, a gasket 3024 may be further provided at a free end portion of the mounting shafts, and the gasket 3024 may serve to block the planetary gears. In addition, in order to facilitate the installation of the gasket, a bump may be further disposed on the upper end surface of the installation platform, and the gasket 3024 is partially supported on the bump and fixedly connected to the bump 3021, which may be welded and fixed, or may be fixedly connected in other manners.

As shown in the figure, a boss 3021 can be machined on the upper end face of the bump, a through hole is formed in the corresponding position of the gasket, and the boss 3021 is clamped into the through hole, so that the bump and the gasket can be conveniently welded. In addition, the gasket can be also provided with a hole for the mounting shaft to pass through, so that the gasket is convenient to mount quickly.

Of course, the spacer has a through hole for the sun gear to pass through to ensure that the sun gear engages with the planet gears of the first stage.

The ring gear part 32 is fixed on the valve seat 10, the ring gear part 32 has inner meshing sections which are correspondingly meshed with each stage of planet gears, of course, all the inner meshing sections of the ring gear part 32 can be of a continuous integral structure, and also can be of a segmented form, namely, the ring gear part 32 is provided with a plurality of discontinuous inner meshing sections along the axial direction, and the inner meshing sections are in one-to-one correspondence with each stage of planet gears. In this embodiment, the axially inner engaging section is a continuous unitary structure.

The sun gear 301 is mounted on the rotating shaft of the rotor 50, and the rotating shafts of the sun gear 301 and the rotor 50 may be separated, that is, the sun gear 301 is mounted on the rotating shaft of the rotor 50, but of course, the rotating shafts of the sun gear 301 and the rotor 50 may be integrated, that is, the sun gear is directly formed on the rotating shaft of the rotor.

Sun gear 301 is in mesh with the planet gears of the first stage planetary gear assembly. The output end of the planet carrier of the N-1 stage planetary wheel assembly is meshed with each planet wheel of the N stage planetary wheel assembly, and the output end of the planet carrier of the last stage planetary wheel assembly is connected with the upper end part of the screw rod 20, so that the last stage planet carrier drives the screw rod 20 to synchronously rotate; wherein N is an integer of 1 or more.

Of course, when there is only one stage of planetary gear assembly, the output end of the planet carrier of the planetary gear assembly is directly connected to the upper end of the screw rod 20.

During operation, the coil is electrified to drive the rotor 50 to rotate, the sun gear 301 rotates along with the rotating shaft of the rotor 50 synchronously, each planetary gear of the first stage meshed with the sun gear 301 rotates to drive the first-stage planetary carrier 302 to rotate, the output end of the first-stage planetary carrier 302 is further meshed with the planetary gear of the next stage, so that the power of the sun gear is finally transmitted to the last-stage planetary gear assembly through each planetary gear assembly, and is transmitted to the screw rod 20 through the last-stage planetary gear carrier, and the rotation of the screw rod 20 is realized. By changing the direction of the current flowing through the coil, the rotation of the sun gear in different directions can be realized, and the up-and-down reciprocating motion of the screw rod 20 can be further realized.

The speed reducing mechanism is shown in fig. 4 to have three-stage planetary wheel assemblies, and the planetary speed reducing mechanism 30 includes a sun gear 301, a first-stage planetary gear carrier 302, a first-stage planetary gear 303, a second-stage planetary gear carrier 304 and a third-stage planetary gear carrier 305, wherein the structures of the planetary wheel assemblies in the first two stages may be the same, and the structure of the planetary wheel assembly in the last stage is slightly different, and the main difference is that the structure of the output shaft, the output shaft of the planetary wheel assembly in the first two stages is a gear structure, and the output shaft of the planetary wheel assembly in the last.

The planetary reduction mechanism 30 further includes a ring gear member 32 fixedly disposed on the valve seat 10, the sun gear 301, the first-stage carrier 302, the second-stage carrier 304, the ring gear member 32, and the lead screw 2022 are preferably coaxially disposed, the sun gear 301 and the rotor 50 are fixedly connected, the rotor 50 is rotated by the driving mechanism, the sun gear 301 drives the planetary gears 303 to rotate along its own axis, the ring gear member 32 is provided with engaging teeth, the planetary gears 303 are engaged with the engaging teeth so that the plurality of planetary gears 303 revolve along the axis of the ring gear member 32 to drive the first carrier 302 to rotate around its own axis, and since the output shaft 3022 is formed on the first carrier 302, the output shaft 3022 can rotate along the axis of the output shaft 3022, and the output shaft 3022 serves as a sun gear of the next-stage planetary gear (second-stage planetary gear assembly). The output shaft of the last stage is connected with a screw rod 20, and the screw rod 20 and the internal thread part are connected through threads to realize the movement of the valve needle 11 between the opening position and the closing position.

As shown in fig. 9, the output shaft of the third stage planet carrier 305 of the third stage planetary gear assembly is connected to the screw 20, but the third stage planet carrier 305 may be integrated with the screw 20 or may be a separate structure. The third-stage planet carrier 305 is provided with a mounting shaft 2231, a planet wheel 222, a gasket 221 and a boss 2232, and the mounting and the effect of each component are the same as those of the first-stage planet wheel assembly, which is not described herein.

Compared with the speed reducing mechanism adopting a fixed-axis gear train in the background technology, the speed reducing mechanism of the electronic expansion valve adopts a planetary speed reducing mechanism, the sun gear and each level of planetary gear are coaxially arranged, the radial space occupation is small, the transverse volume of the speed reducing mechanism is greatly reduced, the axial structure of the planetary speed reducing mechanism is compact, the axial size is small, and the mechanism has the advantages of high transmission efficiency and large transmission power range, so that the electronic expansion valve can meet the requirements of high precision and miniaturization when the flow control range is enlarged.

Further, the electronic expansion valve may further include a housing 40, the housing 40 is mounted on the valve seat 10 and encloses a mounting cavity with the valve seat 10, and the lead screw 20, the rotor 50 and the planetary reduction mechanism are all disposed inside the mounting cavity. The electronic expansion valve further includes a mandrel 70, an upper end portion of the mandrel 70 is mounted to the housing 40, a central axis of the sun gear, a central axis of the output shaft of each stage of the planetary carrier, and a central axis of the mandrel 70 are collinear, and the mandrel 70 is inserted into the sun gear and the output shaft of each stage of the planetary carrier.

That is to say, the sun gear and the planetary carriers at all levels rotate around the mandrel 70, the mandrel 70 can ensure that the sun gear and the planetary carriers at all levels rotate coaxially, the eccentric phenomenon is avoided, the coaxial rotation of all the parts is further ensured, the coaxiality of the valve needle 11 and the valve port is facilitated, and the work reliability of the electronic expansion valve is improved.

Specifically, the sun gear and the carrier are provided with coaxial mounting holes, and the spindle 70 is provided inside each mounting hole. Of course, the spindle 70 should be mounted so as not to interfere with the normal rotational operation of the components, thereby avoiding power loss.

In order to further ensure that the screw rod 20 is coaxial with the speed reducing mechanism, the upper end face of the screw rod 20 is provided with an axially extending central hole, and the tail end of the mandrel 70 penetrates through an output shaft of the last-stage planet carrier and is arranged in the central hole of the screw rod 20; therefore, the screw rod 20 also rotates around the mandrel 70, and the coaxial rotation of the screw rod 20, the sun gear and each planet carrier can be further ensured.

In the above embodiments, the electronic expansion valve may further include a rotor guide frame 42, the rotor guide frame 42 is mounted inside the mounting cavity of the housing 40, the rotor guide frame 42 is fixedly connected to the inner wall of the housing 40, the upper end of the mandrel 70 is fixed to the rotor guide frame 42, specifically, a mounting hole is provided in the center of the rotor guide frame 42, the upper end of the mandrel 70 is mounted and fixed in the mounting hole, and the mandrel 70 and the rotor guide frame 42 are coaxially disposed. Thus, the rotor guide 42 is embedded in the housing 40 to guide the spindle 70.

In the above embodiments, the spring 60 may be further disposed between the upper end surface of the sun gear 301 and the rotor guide frame 42, and the spring 60 may be sleeved on the mandrel 70 to support the rotor 50, each planet carrier, and the planet gear.

Specifically, the ring gear member 32 may include a sleeve 321 and a ring gear 322, each inner engaging section being provided to the ring gear 322, the lower end of the sleeve 321 being supported on the valve seat 10, the ring gear 322 being mounted to the upper end opening of the sleeve 321, and at least a part of the shaft section of the ring gear 322 being located inside the rotor 50.

The ring gear member 32 is divided into two parts, which can reduce the processing difficulty of the ring gear member on the one hand and is beneficial to reducing the weight of the ring gear member 32 on the other hand.

In the above embodiment, the ring gear is partly inside the sleeve 321 and partly outside the sleeve 321, and the peripheral wall of the sleeve 321 where the ring gear is mounted is provided with the through-hole 321a in the circumferential direction. The number of the through holes 321a may be one or two or more, and the through holes provided in the peripheral wall of the sleeve 321 may increase the torque of the ring gear 322.

The sleeve 321 and the gear ring 322 can be integrally formed through an injection molding process, so that the coaxiality of the sleeve 321 and the gear ring can be guaranteed. Of course, the sleeve 321 and the gear ring 322 may be fixedly connected by interference or other methods.

In the above embodiments, the lower end of the screw rod 20 may be provided with a valve needle member, the upper opening of the valve seat 10 is provided with an internal thread member, the internal thread member is provided with a through hole, the hole section of the through hole portion is provided with an internal thread portion engaged with the external thread of the screw rod 20, and the lower end of the valve needle member passes through the through hole of the internal thread member and extends to the outside of the through hole to engage with the valve port inside the valve seat 10 to control the flow.

The valve needle component in the above embodiment may include a spring 12 and the valve needle 11, the spring 12 is vertically compressed between the upper end of the valve needle 11 and the inner wall of the through hole, and the spring 12 provides the upward restoring force of the valve needle 11. The outlet section of the through-hole can be connected in a suitable manner to the valve needle 11 for guidance. The lower end of the screw 20 is connected to the upper end of the needle 11.

In each of the above embodiments, the female screw member includes a nut mounting seat 22, a through hole is formed in the nut mounting seat 22, a nut 21 is mounted in the through hole, and the screw rod 20 is in threaded engagement with the nut 21. Specifically, the end of the lead screw 20 may be a ball contact.

In order to reduce the influence of fluid medium in the nut mounting seat 22 on the movement of the screw rod 20 as much as possible, a balance channel can be processed on the nut and is used for communicating a cavity where the valve core component is located with a cavity where the planetary speed reducing mechanism is located.

In the above embodiments, the screw rod 20 and the planet carrier of the last stage of planetary wheel assembly are integrally formed by injection molding.

In the above embodiments, the electronic expansion valve may further include a coil fixing frame 80, and the coil fixing frame 80 may be fixed outside the valve seat 10 or the housing 40 by welding, so as to fix the coil.

The electronic expansion valve provided by the invention is described in detail above. The principles and embodiments of the present invention are explained herein using specific examples, which are presented only to assist in understanding the method and its core concepts. It should be noted that, for those skilled in the art, it is possible to make various improvements and modifications to the present invention without departing from the principle of the present invention, and those improvements and modifications also fall within the scope of the claims of the present invention.

Claims

1. The electronic expansion valve is characterized by comprising a valve seat (10), a screw rod and a rotor, and further comprising a planetary reduction mechanism (30), wherein the planetary reduction mechanism (30) comprises a sun wheel (301), a gear ring component (32) and at least one stage of planetary wheel component, each stage of planetary wheel component comprises a planet carrier and at least two planetary wheels, the gear ring component (32) is fixed on the valve seat (10), the gear ring component (32) is provided with an inner meshing section correspondingly meshed with each stage of planetary wheels, the sun wheel (301) is installed on a rotating shaft of the rotor, and the sun wheel (301) is meshed with each planetary wheel of the first stage of planetary wheel component; the output end of a planet carrier of the N-1 stage planetary wheel assembly is meshed with each planet wheel of the N stage planetary wheel assembly, and the output end of the planet carrier of the last stage planetary wheel assembly is connected with the upper end part of the screw rod; wherein N is an integer of 1 or more.

2. The electronic expansion valve according to claim 1, further comprising a housing (40), wherein the housing (40) is mounted on the valve seat (10) and encloses a mounting cavity with the valve seat (10), the lead screw (20), the rotor (50) and the planetary reduction mechanism are disposed inside the mounting cavity, the electronic expansion valve further comprises a spindle (70), an upper end portion of the spindle (70) is mounted on the housing (40), a central axis of the sun gear (301), a central axis of the output shaft of each stage of the planetary carrier, and a central axis of the spindle (70) are collinear, and the spindle (70) is disposed inside the sun gear (301) and the output shaft of each stage of the planetary carrier.

3. An electronic expansion valve according to claim 2, wherein the upper end face of the screw (20) has an axially extending central hole, and the end of the spindle (70) is provided in the central hole of the screw (20) through the output shaft of the last stage planet carrier.

4. The electronic expansion valve according to claim 2, further comprising a rotor guide frame (42) disposed inside the mounting cavity, wherein the rotor guide frame (42) is fixedly connected to the housing (40), an upper end portion of the mandrel (70) is fixed to the rotor guide frame (42), and the mandrel (70) and the rotor guide frame (42) are coaxially disposed.

5. An electronic expansion valve according to claim 4, wherein a spring (60) is further compressed between the upper end face of the sun gear (301) and the rotor guide frame (42).

6. An electronic expansion valve according to claim 1, wherein the screw (20) is integrally formed with the planet carrier of the last stage of the planetary wheel assembly by means of an injection moulding process.

7. An electronic expansion valve according to claim 1, wherein the ring gear member (32) comprises a sleeve (321) and a ring gear (322), each of the inner meshing sections being provided to the ring gear (322), the sleeve (321) being supported at a lower end thereof to the valve seat (10), the ring gear (322) being fitted to an upper end opening of the sleeve (321), and at least a part of a shaft section of the ring gear (322) being located inside the rotor (50).

8. The electronic expansion valve according to claim 7, wherein a peripheral wall of the sleeve (321) mounting the ring gear (322) is provided with through-process holes (321a) in a circumferential direction.

9. An electronic expansion valve according to claim 7, wherein the sleeve (321) is integrally formed with the ring gear (322) by an injection molding process.

10. The electronic expansion valve according to claim 1, wherein the lower end portion of the screw rod is provided with a valve needle member, an internal thread member is installed at an upper end opening position of the valve seat (10), the internal thread member is provided with a through hole, a hole section of the through hole portion is provided with an internal thread portion engaged with the external thread of the screw rod, and the lower end portion of the valve needle member passes through the through hole to extend to the outside of the through hole to engage with a valve port inside the valve seat (10) to control a flow rate.

11. The electronic expansion valve according to claim 10, wherein the internal thread member comprises a nut mounting seat, the nut mounting seat is provided with the through hole, a nut is mounted in the through hole, and the lead screw is in threaded engagement with the nut.