Height-adjustable automobile seat headrest

Abstract

The utility model relates to the technical field of automobile accessories, and discloses a height-adjustable automobile seat headrest. The automobile seat headrest comprises a seat main body, a headrest main body, a lifting rod, a self-locking driving mechanism and a rotating handle, and the lifting rod is arranged on the headrest main body and located in a seat backrest of the seat main body; the self-locking driving mechanism is arranged on the lifting rod and located in the seat backrest, one end of the rotating handle is inserted into the seat backrest and connected with the self-locking driving mechanism, the other end of the rotating handle is located outside the seat backrest, and during work, the rotating handle applies driving force to the self-locking driving mechanism to drive the lifting rod to do lifting motion. The headrest main body is driven to do lifting motion; and in a non-working state, the self-locking driving mechanism is self-locked. A user can sit on the seat main body to adjust the height of the headrest main body, the self-locking driving mechanism not only has the function of driving the lifting rod to do lifting motion, but also has the self-locking function, the stability and safety of the headrest main body are improved, and the structural design is compact and simple.

Description

Technical Field

[0001] The utility model relates to the technical field of automobile accessories, in particular to a height-adjustable automobile seat headrest. Background Art

[0002] The car headrest is a component installed on the upper part of the seat to support the head and relieve the pressure on the head and neck. When the vehicle is driving, the pressure of acceleration or deceleration is concentrated on the fragile neck and head of the human body, and the headrest plays a buffering role to protect the human head.

[0003] Most of the existing car seat headrests are integrated fixed structures. The fixed position cannot be flexibly and conveniently adjusted, cannot meet the needs of different groups of people, have poor applicability, and greatly reduce comfort. Some adjustable seat headrests also require users to adjust them first, and then sit on the seat to feel whether they are adjusted in place, but cannot support users to sit directly on the seat and make real-time adjustments. In addition, an additional locking structure is required to prevent the headrest body from being displaced due to external forces, which increases the complexity of the structure. Utility Model Content

[0004] The main purpose of the utility model is to provide a height-adjustable automobile seat headrest, aiming to solve the technical problems that the existing automobile seat headrest cannot support the user to directly sit on the seat and make real-time adjustments, and has a complex structure.

[0005] To achieve the above object, the utility model provides a height-adjustable automobile seat headrest, the automobile seat headrest comprising a seat body and a headrest body, characterized in that the automobile seat headrest also includes:

[0006] a lifting rod, one end of which is disposed on one end of the headrest body, and the lifting rod is located in a seat back of the seat body;

[0007] A self-locking drive mechanism, one end of which is disposed on the other end of the lifting rod and is located inside the seat back, and is used to drive the lifting rod to move up and down;

[0008] A rotating handle, one end of which is inserted into the seat back and connected to the other end of the self-locking drive mechanism, and the other end of which is located outside the seat back, wherein:

[0009] In the working state, the rotating handle applies a driving force to the self-locking driving mechanism to drive the lifting rod to move up and down, thereby driving the headrest body to move up and down;

[0010] In a non-working state, the self-locking drive mechanism is self-locking.

[0011] Furthermore, in one embodiment, the self-locking drive mechanism includes a first worm and a first worm wheel, one end of the first worm is arranged on the rotating handle, and the other end of the first worm is meshingly connected with the first worm wheel, and the first worm wheel is movably mounted on the lifting rod. In the working state, the rotating handle applies a driving force to the first worm, so that the first worm rotates and drives the first worm wheel to rotate, and the first worm wheel rotates and drives the lifting rod to perform a lifting motion, thereby driving the headrest body to perform a lifting motion. In the non-working state, the first worm is self-locking.

[0012] Furthermore, in one embodiment, a first thread segment is provided on the outer peripheral side of one end of the lifting rod connected to the self-locking drive mechanism, and a second thread segment matching the first thread segment is provided on the inner side wall of the center hole of the first worm wheel, and the lifting rod passes through the center hole of the first worm wheel, and the first thread segment is meshed and connected with the second thread segment.

[0013] Furthermore, in one embodiment, the self-locking drive mechanism includes a second worm, a second worm wheel, a gear and a transmission shaft, one end of the second worm is arranged on the rotating handle, the other end of the second worm is meshingly connected with the second worm wheel, the gear is meshingly connected with the lifting rod, the gear and the second worm wheel are coaxially arranged on the transmission shaft, and in a working state, the rotating handle applies a driving force to the first worm, the first worm rotates and drives the first worm wheel to rotate, the first worm wheel rotates and drives the gear to rotate at the same time, the gear rotates and drives the lifting rod to perform a lifting motion, thereby driving the headrest body to perform a lifting motion, and in a non-working state, the second worm is self-locking.

[0014] Furthermore, in one embodiment, a plurality of tooth grooves are provided on one side of the outer peripheral side of one end of the lifting rod connected to the self-locking drive mechanism, and the plurality of tooth grooves are distributed along the longitudinal direction of the lifting rod to form a rack, and a plurality of teeth matching the tooth grooves are provided on the outer peripheral side of the gear, and the tooth grooves are meshingly connected with the teeth.

[0015] Furthermore, in one embodiment, the headrest body includes a headrest body and a connecting piece, one end of the connecting piece is arranged on the headrest body, and the other end is inserted into the seat back and connected to the lifting rod.

[0016] Furthermore, in one embodiment, the car seat headrest also includes a first limit block and a second limit block, the first limit block and the second limit block are both arranged on the lifting rod, and the first limit block and the second limit block are respectively located at two ends of the first threaded segment.

[0017] Furthermore, in one embodiment, the car seat headrest also includes a third limit block and a second limit block, the first limit block and the second limit block are both arranged on the lifting rod, and the first limit block and the second limit block are respectively located at two ends of the rack.

[0018] Further, in one embodiment, the rotating handle includes a connecting rod, a rotating disk and a protrusion, one end of the connecting rod is arranged on the self-locking drive mechanism, and the other end is arranged on the rotating disk, and the protrusion is arranged on a side of the rotating disk away from the connecting rod.

[0019] Furthermore, in one embodiment, the first worm is a single-line worm, and a helix angle of the first worm is smaller than a friction angle of contact between the first worm wheel and the first worm.

[0020] In the technical solution provided by the utility model, a self-locking drive mechanism and a lifting rod are arranged in the seat body, and one end of the lifting rod is connected to the headrest body located outside the seat body, and the other end of the lifting rod is connected to one end of the self-locking drive mechanism, and one end of the self-locking drive mechanism is connected to a rotating handle protruding from the seat body, so that the user can sit on the seat body, reach out to hold and rotate the rotating handle, and the rotating handle rotates and applies a driving force to the self-locking drive mechanism, and the self-locking drive mechanism drives the lifting rod to perform a lifting movement, thereby driving the headrest body to perform a lifting movement, so that the user can adjust the height of the headrest body while sitting on the seat body, and the self-locking drive mechanism not only has the function of driving the lifting rod to perform a lifting movement, but also has a self-locking function, thereby improving the stability and safety of the headrest body, and there is no need to add an additional locking structure, so that the structural design of the car seat headrest is compact and simple. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] One or more embodiments are exemplarily described by corresponding drawings, which do not constitute limitations on the embodiments. Elements with the same reference numerals in the drawings represent similar elements, and the figures in the drawings do not constitute proportional limitations unless otherwise stated.

[0022] Figure 1 It is a cross-sectional view of the first embodiment of the utility model;

[0023] Figure 2 This is a schematic diagram of the folded state of the protrusion of the utility model;

[0024] Figure 3 A three-dimensional diagram of the connection between the self-locking drive mechanism and the connecting member of the first embodiment of the utility model;

[0025] Figure 4 It is a cross-sectional view of the second embodiment of the utility model;

[0026] Figure 5 This is a three-dimensional diagram of the connection between the self-locking drive mechanism and the connecting piece of the second embodiment of the utility model.

[0027] Among them, 100, car seat headrest; 10, seat body; 101, seat back; 102, seat body; 20, headrest body; 201, headrest body; 202, connecting piece; 30, lifting rod; 301, first threaded section; 302, tooth groove; 303, rack; 40, self-locking drive mechanism; 401, first worm; 402, first worm wheel; 403, second worm; 404, second worm wheel; 405, gear; 406, teeth; 407, transmission shaft; 50, rotating handle; 501, connecting rod; 502, rotating disk; 503, protrusion; 60, first limit block; 70, second limit block; 80, third limit block; 90, fourth limit block. DETAILED DESCRIPTION

[0028] In order to facilitate the understanding of the utility model, the utility model is described in more detail below in conjunction with the accompanying drawings and specific embodiments. It should be noted that when an element is described as "fixed to" another element, it can be directly on another element, or there can be one or more centered elements therebetween. When an element is described as "connected" to another element, it can be directly connected to another element, or there can be one or more centered elements therebetween. The terms "vertical", "horizontal", "left", "right", "inside", "outside" and similar expressions used in this specification are only for illustrative purposes. In the description of the utility model, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating relative importance or implicitly indicating the number of technical features indicated. Therefore, unless otherwise specified, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features; the meaning of "multiple" is two or more. The term "include" and any variation thereof means non-exclusive inclusion, and one or more other features, integers, steps, operations, units, components and / or combinations thereof may be present or added.

[0029] In addition, unless otherwise expressly specified and limited, the terms "installed", "connected" and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, an indirect connection through an intermediate medium, or a connection between two components. All technical and scientific terms used in this specification have the same meaning as those generally understood by technicians in the technical field of the present utility model. The terms used in the specification of the present utility model are only for the purpose of describing specific embodiments and are not used to limit the present utility model. The term "and / or" used in this specification includes any and all combinations of one or more related listed items.

[0030] In addition, the technical features involved in different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0031] Please refer to Figure 1-Figure 5 , an embodiment of the utility model discloses a height-adjustable automobile seat headrest 100 .

[0032] In one embodiment, if Figure 1-Figure 5 As shown, the car seat headrest 100 includes a seat body 10, a headrest body 20, a lifting rod 30, a self-locking drive mechanism 40 and a rotating handle 50, wherein the seat body 10 includes a seat body 102 and a seat back 101, the seat back 101 is arranged on the seat body 102 at a preset angle, the seat body 102 is used for users to sit, and the headrest body 20 is adjustably installed on the top of the seat back 101.

[0033] The headrest body 20 includes a headrest body 201 and a connecting member 202. One end of the connecting member 202 is fixed to the headrest body 201, and the other end is inserted into the seat back 101 and connected to the lifting rod 30. The headrest body 201 is located outside the seat back 101. Exemplarily, the connecting member 202 is a "U"-shaped structure, and the open end of the "U" is connected to the headrest body 201, so that the headrest body 201 has two balanced force points, which prevents the headrest body 201 from tilting when the headrest body 201 is lifted and driven, and the closed end of the "U" is connected to the lifting rod 30, so that the lifting rod 30 can better drive the headrest body 201 to move up and down.

[0034] The lifting rod 30 is rod-shaped, preferably cylindrical, but can also be a rectangular or other shaped rod. The lifting rod 30 drives the headrest body 20 to move up and down under the action of the driving force, and the cylindrical design has a simple structure, saving space and cost. The lifting rod 30 is installed in the seat back 101, and one end of the lifting rod 30 is fixedly connected to the connecting piece 202 of the headrest body 20.

[0035] The self-locking drive mechanism 40 is used to drive the lifting rod 30 to move upward and downward, and can be self-locking to prevent the headrest body 20 from being reversely driven by an external force to move the self-locking drive mechanism 40, thereby improving the stability and safety of the headrest body 20. The self-locking drive mechanism 40 is installed in the seat back 101, and one end of the self-locking drive mechanism 40 is arranged on the other end of the lifting rod 30.

[0036] The rotating handle 50 is used to provide a force support for the user. One end of the rotating handle 50 is inserted into the seat back 101, and the end of the rotating handle 50 is connected to the other end of the self-locking drive mechanism 40. The other end of the rotating handle 50 is located outside the seat back 101. In the working state, the user holds and rotates the part of the rotating handle 50 protruding outside the seat back 101, and the rotating handle 50 rotates and applies a driving force to the self-locking drive mechanism 40, driving the self-locking drive mechanism 40 to rotate. When the self-locking drive mechanism 40 rotates, the lifting rod 30 is driven to move up or down, so that the lifting rod 30 drives the headrest body 20 to move up or down, so that the height of the headrest body 20 is adjusted. In addition, when the self-locking drive mechanism 40 is not in the working state, the self-locking drive mechanism 40 has a self-locking function to prevent the headrest body 20 from being reversely driven by the self-locking drive mechanism 40 due to the action of external force, thereby improving the stability and safety of the headrest body 20.

[0037] Further, the rotating handle 50 includes a connecting rod 501, a rotating disk 502 and a protrusion 503, one end of the connecting rod 501 is arranged on the self-locking drive mechanism 40, the other end of the connecting rod 501 is arranged on the rotating disk 502, and the protrusion 503 can be folded and arranged on a side of the rotating disk 502 away from the connecting rod 501. Figure 2 As shown, Figure 2 It is a schematic diagram of folding the protrusion 503. The protrusion 503 and the rotating disk 502 can be connected by a hinge connection to realize the folding function of the protrusion 503. When not in use, the protrusion 503 can be folded up to save space. The folding function of the protrusion 503 can also be realized by an axle pin connection.

[0038] In one embodiment, if Figure 1 and Figure 3 As shown, the self-locking drive mechanism 40 is a worm gear mechanism, and the self-locking drive mechanism 40 includes a first worm 401 and a first worm wheel 402. One end of the first worm 401 is fixedly mounted on the rotating handle 50, and the other end of the first worm 401 is provided with a thread, and the first worm wheel 402 is provided with teeth adapted to the thread. The thread and the teeth are meshingly connected, so that the first worm 401 and the first worm wheel 402 realize meshing transmission, and the first worm wheel 402 is movably mounted on the lifting rod 30.

[0039] Specifically, a first thread segment is provided on the outer peripheral side of one end of the lifting rod 30 connected to the self-locking drive mechanism 40, and a second thread segment 301 is provided on the inner side wall of the center hole of the first worm gear 402. The lifting rod 30 passes through the center hole of the first worm gear 402, and the first thread segment 301 is meshed and connected with the second thread segment.

[0040] In the working state, the user sits directly on the seat body 102, reaches out to hold and turn the rotating handle 50, and applies a driving force to the first worm 401 by turning the rotating handle 50. The first worm 401 rotates and drives the first worm wheel 402 to rotate. The first worm wheel 402 rotates and drives the lifting rod 30 to move up or down, thereby driving the headrest body 20 to move up or down. In the non-working state, the first worm 401 is self-locking.

[0041] Among them, the first worm 401 is a single-line worm, and the helix angle (lead angle) of the first worm 401 is smaller than the friction angle of the first worm wheel 402 and the first worm 401. The first worm 401 can be self-locking, that is, when the first worm 401 stops rotating, the first worm wheel 402 gives the first worm 401 a reverse sliding force, which cannot make the first worm 401 rotate in the reverse direction. Therefore, the self-locking drive mechanism 40 has a self-locking function while driving, reducing additional locking structures, making the structural design of the car seat headrest 100 more compact and simple.

[0042] Exemplarily, when the friction coefficient of the first worm gear 402 is 0.08, the helix lead angle (lead angle γ) is <4 degrees 38 minutes 39 seconds, and the first worm 401 is self-locking; or when the friction coefficient of the first worm gear 402 is 0.06, the helix lead angle (lead angle γ) is <3 degrees 29 minutes 11 seconds, and the first worm 401 is self-locking.

[0043] Further, such as Figure 1 and Figure 3 As shown, the car seat headrest 100 also includes a first limit block 60 and a second limit block 70. The first limit block 60 is arranged on the lifting rod 30 and is located at the first end of the first threaded segment 301. The second limit block 70 is arranged on the lifting rod 30 and is located at the second end of the first threaded segment 301. Specifically, the first limit block 60 and the second limit block 70 can be annular blocks, which are sleeved on the lifting rod 30. The annular block is easy to install. The first limit block 60 and the second limit block 70 are used to limit the moving stroke of the first worm gear 402 within the first threaded segment 301 to ensure the meshing transmission of the first worm gear 402 and the lifting rod 30, thereby ensuring effective height adjustment of the headrest body 20.

[0044] In another embodiment, Figure 4 and Figure 5As shown, the self-locking drive mechanism 40 includes a second worm 403, a second worm wheel 404, a gear 405 and a transmission shaft 407. One end of the second worm 403 is fixedly mounted on the rotating handle 50, and the other end of the second worm 403 is provided with a thread. The second worm wheel 404 is provided with teeth matching the thread. The thread and the teeth are meshingly connected, so that the second worm 403 and the second worm wheel 404 achieve meshing transmission.

[0045] A plurality of tooth grooves 302 are provided on one side of the outer peripheral side of one end of the lifting rod 30 connected to the self-locking drive mechanism 40. The plurality of tooth grooves 302 are distributed along the longitudinal direction of the lifting rod 30 to form a rack 303. A plurality of teeth 406 matching the tooth grooves 302 are provided on the outer peripheral side of the gear 405. The tooth grooves 302 are meshingly connected with the teeth 406, so that the lifting rod 30 and the gear 405 realize meshing transmission, and the gear 405 and the second worm gear 404 are coaxially arranged on the transmission shaft 407, that is, the transmission shaft 407 passes through the center hole of the gear 405 and the center hole of the second worm gear 404 in sequence, so that the second worm gear 404 and the gear 405 are synchronously driven.

[0046] In the working state, the user directly sits on the seat body 102, reaches out to hold and rotate the rotating handle 50, so as to adjust the height of the headrest body 20. Specifically, after the rotating handle 50 is rotated, a driving force is applied to the second worm 403, and the second worm 403 rotates and drives the second worm wheel 404 to rotate. Because the second worm wheel 404 and the gear 405 are coaxially arranged, the rotation of the second worm wheel 404 simultaneously drives the gear 405 to rotate, and the gear 405 rotates and drives the lifting rod 30 to rise or fall, thereby driving the headrest body 20 to rise or fall, so that the user can sit on the seat and adjust the height of the headrest body 20 by rotating the rotating handle. In the non-working state, the second worm 403 is self-locking. Therefore, the automobile seat headrest 100 of the utility model can simultaneously realize that the user sits on the seat and adjusts the height of the headrest body 20 by rotating the rotating handle and self-locks, thereby improving the stability and safety of the headrest body 20.

[0047] Among them, the second worm 403 is a single-line worm, and the helix angle (lead angle) of the second worm 403 is smaller than the friction angle of the second worm wheel 404 and the second worm 403. The second worm 403 can be self-locking, that is, when the second worm 403 stops rotating, the second worm wheel 404 gives the second worm 403 a reverse sliding force, which cannot make the second worm 403 rotate in the reverse direction. Therefore, the self-locking drive mechanism 40 has a self-locking function while driving, reducing additional locking structures, making the structural design of the car seat headrest 100 more compact and simple.

[0048] Exemplarily, when the friction coefficient of the second worm gear 404 is 0.08 and the helix lead angle (lead angle γ) is less than 4 degrees 38 minutes 39 seconds, the second worm 403 is self-locking; or when the friction coefficient of the second worm gear 404 is 0.06 and the helix lead angle (lead angle γ) is less than 3 degrees 29 minutes 11 seconds, the second worm 403 is self-locking.

[0049] Further, such as Figure 4 and Figure 5 As shown, the car seat headrest 100 also includes a third limit block 80 and a fourth limit block 90. ​​The third limit block 80 is arranged on the lifting rod 30 and is located at the first end of the rack 303. The third limit block 80 is arranged on the lifting rod 30 and is located at the second end of the rack 303. Specifically, the third limit block 80 and the fourth limit block 90 can be annular blocks, which are sleeved on the lifting rod 30. The annular block is easy to install. The third limit block 80 and the fourth limit block 90 are used to limit the moving stroke of the gear 405 within the rack 303 to ensure the meshing transmission of the gear 405 and the lifting rod 30, thereby ensuring effective height adjustment of the headrest body 20.

[0050] The utility model solves the problem that the existing car seat headrest 100 cannot support the user to make real-time adjustments directly while sitting on the seat and has a complex structure. The self-locking drive mechanism 40 not only has the function of driving the lifting rod 30 to perform lifting and lowering movements, but also has a self-locking function, thereby improving the stability and safety of the headrest body 20. No additional locking structure is needed, so that the structural design of the car seat headrest 100 is compact and simple.

[0051] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them. Under the concept of the present invention, the technical features in the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other changes in different aspects of the present invention as described above, which are not provided in detail for the sake of simplicity. Although the present invention has been described in detail with reference to the aforementioned embodiments, a person of ordinary skill in the art should understand that the technical solutions described in the aforementioned embodiments can still be modified, or some of the technical features can be replaced by equivalents. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A height-adjustable automobile seat headrest, the automobile seat headrest comprising a seat body and a headrest body, characterized in that: The automobile seat headrest also includes: a lifting rod, one end of which is disposed on one end of the headrest body, and the lifting rod is located in a seat back of the seat body; A self-locking drive mechanism, one end of which is disposed on the other end of the lifting rod and is located inside the seat back, and is used to drive the lifting rod to move up and down; A rotating handle, one end of which is inserted into the seat back and connected to the other end of the self-locking drive mechanism, and the other end of which is located outside the seat back, wherein: The self-locking drive mechanism includes a first worm and a first worm wheel, one end of the first worm is arranged on the rotating handle, the other end of the first worm is meshed and connected with the first worm wheel, and the first worm wheel is movably sleeved on the lifting rod. In the working state, the rotating handle applies a driving force to the first worm, so that the first worm rotates and drives the first worm wheel to rotate, and the first worm wheel rotates and drives the lifting rod to perform a lifting motion, thereby driving the headrest body to perform a lifting motion. In the non-working state, the first worm is self-locking; or, The self-locking drive mechanism includes a second worm, a second worm wheel, a gear and a transmission shaft, one end of the second worm is arranged on the rotating handle, the other end of the second worm is meshed and connected with the second worm wheel, the gear is meshed and connected with the lifting rod, the gear and the second worm wheel are coaxially arranged on the transmission shaft, in a working state, the rotating handle applies a driving force to the second worm, the second worm rotates and drives the second worm wheel to rotate, the second worm wheel rotates and drives the gear to rotate, the gear rotates and drives the lifting rod to perform a lifting motion, thereby driving the headrest body to perform a lifting motion, and in a non-working state, the second worm is self-locking.

2. The automobile seat headrest according to claim 1, characterized in that: A first thread segment is provided on the outer peripheral side of one end of the lifting rod connected to the self-locking drive mechanism, and a second thread segment matched with the first thread segment is provided on the inner side wall of the center hole of the first worm wheel. The lifting rod passes through the center hole of the first worm wheel, and the first thread segment is meshed and connected with the second thread segment.

3. The automobile seat headrest according to claim 1, characterized in that: A plurality of tooth grooves are provided on one side of the outer circumference of one end of the lifting rod connected to the self-locking drive mechanism. The plurality of tooth grooves are distributed along the longitudinal direction of the lifting rod to form a rack. A plurality of teeth matching the tooth grooves are provided on the outer circumference of the gear. The tooth grooves are meshed with the teeth.

4. The automobile seat headrest according to claim 1, characterized in that: The headrest body comprises a headrest body and a connecting piece, one end of the connecting piece is arranged on the headrest body, and the other end is inserted into the seat back and connected with the lifting rod.

5. The automobile seat headrest according to claim 2, characterized in that: The car seat headrest also includes a first limit block and a second limit block, wherein the first limit block and the second limit block are both arranged on the lifting rod, and the first limit block and the second limit block are respectively located at two ends of the first threaded section.

6. The automobile seat headrest according to claim 3, characterized in that: The car seat headrest also includes a third limit block and a fourth limit block, both of which are arranged on the lifting rod, and the third limit block and the fourth limit block are respectively located at two ends of the rack.

7. The automobile seat headrest according to claim 1, characterized in that: The rotating handle comprises a connecting rod, a rotating disk and a protrusion, one end of the connecting rod is arranged on the self-locking drive mechanism, and the other end is arranged on the rotating disk, and the protrusion is arranged on a side of the rotating disk away from the connecting rod.

8. The automobile seat headrest according to claim 1, characterized in that: The first worm is a single-line worm, and a helix angle of the first worm is smaller than a friction angle between the first worm wheel and the first worm.

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