AU2019101146A4 - Built-in landing leg - Google Patents

Abstract

A built-in landing leg with a compact structure, comprising: an outer pipe (11), a composite gear (5), a second gear (6), a first gear (3), an input gear (2), and a gear shaft (1). The composite gear (5) and the second gear (6) are provided in the outer pipe (11) and are meshed with each other; the second gear (6) is further connected to a double-head screw assembly (10); the first gear (3) is provided outside the outer pipe (11) and is in linkage with the composite gear (5); the input gear (2) is provided on the gear shaft (1) and is provided outside the outer pipe (11); when the gear shaft (1) moves along a direction extending into or away from the outer pipe (11), the gear shaft (1) is meshed with the composite gear (5) or the input gear (2) is meshed with the first gear (3). Figure 1

Description

2019101146 30 Sep 2019

BUILT-IN LANDING LEG [0001] The application claims the priority to Chinese patent application No. 201720696215.0 titled BUILT-IN LANDING LEG, filed with the China National Intellectual Property Administration on June 15, 2017, which is incorporated herein by reference in its entirety.

FIELD [0002] The present disclosure relates to the technical field of landing legs, and in particular to a built-in landing leg.

BACKGROUND [0003] A landing device, that is, a landing leg, is usually equipped under left and right side beams of a chassis of a semi-trailer for assistedly supporting the semi-trailer during loading and unloading goods or a parking inspection, and the height of the semi-trailer can be adjusted according to the actual height of traction seats of various tractors. The landing leg should generally be retracted during the semi-trailer driving, thereby reliably avoiding the active landing leg from contacting the ground and preventing to induce a safety accident.

SUMMARY [0004] A built-in landing leg with a compact structure is provided according to the present disclosure.

[0005] The technical solutions of the built-in landing leg according to the present disclosure include:

[0006] A built-in landing leg, which includes: an outer tube, a combined gear, a second gear, a first gear, an input gear and a gear shaft; the combined gear and the second gear are provided in the outer tube, and engaged with each other, the second gear is further connected to a double-head screw assembly; the first gear is externally provided on the outer tube and linked

-1 2019101146 30 Sep 2019 with the combined gear; and the input gear is provided on the gear shaft and externally provided on the outer tube, and the gear shaft is engaged with the combined gear or the input gear is engaged with the first gear during a movement of the gear shaft in a direction inserting into or away from the outer tube.

[0007] An end of the gear shaft is provided with gear teeth that are selectively engaged or disengaged with the combined gear.

[0008] A diameter of the gear teeth at the end of the gear shaft is larger than a diameter of a remaining portion.

[0009] The built-in landing leg further includes an oil groove under the gear shaft, the gear shaft is configured to insert into the oil groove to engage with the combined gear, and a gap between the gear shaft and the oil groove is provided with lubricated oil.

[0010] The double-head screw assembly is further connected to a square nut, and a side of the square nut adjacent to the second gear is embodied as a square shape having an empty groove.

[0011] A support pad is provided between the second gear and the square nut, and the oil groove is provided on the support pad.

[0012] An inner side of the outer tube is further provided with an inner tube, and the square nut is fixed on the inner tube.

[0013] The built-in landing leg further includes a gearbox fixed on the outer tube, the gearbox includes a gearbox inner cover and a gearbox outer cover, the input gear and the first gear are both located in the gearbox, and a shaft sleeve for allowing the gear shaft to pass through is fixed on the gearbox outer cover.

[0014] The first gear and the combined gear are linked by an output shaft.

[0015] The gearbox inner cover is provided with openings for allowing the output shaft and the gear shaft to pass through, and a flange extending in a direction close to the gearbox outer cover is provided on the openings.

[0016] An inner liner is provided in one of the openings, the inner liner is tightly cooperated with the flange, a gear sleeve is sleeved on the gear shaft, the gear sleeve is provided in the

-22019101146 30 Sep 2019 inner liner and is in sliding cooperation with the inner liner, and an outer diameter of the gear sleeve is larger than an outer diameter of the gear teeth on the gear shaft.

[0017] An outer end portion of the gear teeth on the gear shaft is recessed toward an inner side of the gear shaft to form a stepped surface, an inner end surface of the gear sleeve abuts against the stepped surface, the input gear is sleeved on the gear shaft and an inner side surface of the input gear abuts against the outer end surface of the gear sleeve, and the input gear is fixed to the gear shaft in a welded manner.

[0018] The inner side surface of the input gear is provided with an avoiding recess for avoiding the inner liner and the flange at an outer circumference of the inner liner.

[0019] A distance between convex teeth of the input gear and convex teeth of the first gear is dl, an axial dimension of the gear teeth on the gear shaft is d2, and in a case that the gear teeth of the gear shaft are engaged with the combined gear, a distance between the inner end of the gear sleeve and the outer end of the inner liner is d3, where d3>d2>dl.

[0020] The combined gear and the first gear are each embodied with a flat through hole for extending into the output shaft, and the output shaft is a cylinder-like cylinder a shape of a cylindrical shaft being cut in an axial direction by an upper plane and a lower plane.

[0021] The outer tube has a square structure, and a symmetrical outer circumference of one side of the combined gear includes a curved surface, the curved surface includes a first circular arc segment, an intermediate circular arc connecting segment and a second circular arc segment which are sequentially connected, a diameter of a circle where the intermediate circular arc connecting segment is located is smaller than circles where the first circular arc segment and the second circular arc segment are located.

[0022] An inner wall of the outer tube is provided with a recess recessed toward the outer side of the outer tube for avoiding an outer circumference of the combined gear.

[0023] The beneficial effects according to the above technical solutions are as follows.

[0024] Firstly, the combined gear and the second gear of the built-in landing leg are provided in the outer tube and the combined gear and the gear are engaged with each other, the first gear is externally provided on the outer tube and linked with the combined gear, the input gear is

- 3 2019101146 30 Sep 2019 externally provided on the outer tube, and the combined gear are engaged with the gear teeth on the gear shaft or the input gear is engaged with the first gear, it can be seen that some gears are designed to be mounted inside the landing leg, which fully utilizes the inner space of the landing leg, reduces the height of the external gearbox of the landing leg and reduces the size of the gearbox, so that the structure of the landing leg is compact, the weight is reduced, and the space occupied by the landing leg on the semi-trailer is reduced;

[0025] Secondly, the gear teeth on the gear shaft are engaged with the combined gear or the first gear is engaged with the input gear to achieve the transmission of the power in the high and low gear positions.

BRIEF DESCRIPTION OF THE DRAWINGS [0026] For clearer illustration of the technical solutions according to embodiments of the present disclosure or conventional techniques, hereinafter are briefly described the drawings to be applied in embodiments of the present disclosure or conventional techniques. Apparently, the drawings in the following descriptions are only some embodiments of the present disclosure, and other drawings may be obtained by those skilled in the art based on the provided drawings without creative efforts.

[0027] Figure 1 is a schematic view showing the engagement of a gear shaft and a combined gear and the disengagement of an input gear and a gear one according to a built-in landing leg of the present disclosure;

[0028] Figure 2 is a schematic view showing the engagement of an input gear and a gear one and the disengagement of a gear shaft and a combined gear according to a built-in landing leg of the present disclosure;

[0029] Figures 3, 3(a), 3(b), and 3(c) are schematic views showing the cooperation of a gear shaft, a tooth sleeve and an input gear according to a built-in landing leg of the present disclosure;

[0030] Figure 4 is a structural view of a combined gear according to a built-in landing leg of the present disclosure;

-42019101146 30 Sep 2019 [0031] Figure 5 is a structural view of a gear two according to a built-in landing leg of the present disclosure;

[0032] Figure 6 is a structural view of a double-head screw assembly according to a built-in landing leg of the present disclosure;

[0033] Figures 7(a) and 7(b) are structural views of an outer tube according to a built-in landing leg of the present disclosure;

[0034] Figures 8, 8(a), 8(b), 8(c) and 8(d) are structural views of a gearbox inner cover according to a built-in landing leg of the present disclosure;

[0035] Figures 9(a), 9(b) and 9(c) are structural views of a square nut according to a built-in landing leg of the present disclosure;

[0036] Figure 10 is a schematic view of a square nut and an inner tube according to a built-in landing leg of the present disclosure;

[0037] Figure 11 is a partially enlarged view of a built-in landing leg according to the present disclosure; and [0038] Figure 11 (a) is a schematic view of a support pad, an oil groove and an oil barrier according to a built-in landing leg of the present disclosure.

DETAILED DESCRIPTION [0039] The technical solutions according to embodiments of the present disclosure are described clearly and completely hereinafter in conjunction with the drawings in the embodiments of the present disclosure. Apparently, the described embodiments are only a part of the embodiments of the present disclosure, rather than all embodiments. Based on the embodiments in the present disclosure, all of other embodiments, made by the person skilled in the art without any creative efforts, fall into the scope of the present disclosure.

[0040] As shown in Figure 1 to Figure 11(a), a built-in landing leg according to the present disclosure includes: an outer tube 11, an inner tube 9, a gearbox, a gear shaft 1, an input gear 2, a first gear 3, an oil barrier 19, an output shaft 4, a combined gear 5, a second gear 6, a support

- 5 2019101146 30 Sep 2019 pad 7, a square nut 8, and a double-head screw assembly 10.

[0041] The details of each of the above members will be described below.

(1) Relationships between gear shaft 1 and input gear 2 and between gear shaft 1 and combined gear 5 [0042] As shown in Figures 1 and 2, the gear shaft 1 may insert into the outer tube 11 for being engaged with the combined gear 5. Specifically, an end of the gear shaft 1 may be provided with machined gear splines, that is, gear teeth, and the gear teeth may insert into the outer tube 11 and be engaged with the combined gear 5. The gear shaft 1 may also be moved away from the outer tube 11 until the gear teeth are disengaged with the combined gear 5 and the input gear 2 are engaged with the first gear 3.

[0043] As shown in Figures 7(a) and 7(b), the combined gear 5 is located inside the outer tube 11. When the outer tube 11 is of a square structure, the outer circumference, corresponding to a surface that is close to the combined gear 5, of the outer tube 11 includes a curved surface, the curved surface includes a first circular arc segment 111, an intermediate circular arc connecting segment 112 and a second circular arc segment 113 which are sequentially connected, diameters of arcs 112a, 112b at two ends of the intermediate circular arc connecting segment 112 are both smaller than diameters of circles where the first circular arc segment 111 and the second circular arc segment 113 are located.

[0044] Of course, it can be understood that an inner wall of the outer tube 11 is provided with a recess recessed toward an outer side of the outer tube 11 for avoiding an outer circumference of the combined gear 5. That is, at a position where the outer tube 11 is mounted with the combined gear, the tube wall of the outer tube 11 is deformed outward by an extrusion or other molding process to increase the inner cavity gear of the outer tube 11 and adapt to the mount of the combined gear 5, so that the landing leg can be applied with a larger-sized combined gear, which improves the range of using the landing leg.

[0045] A surface, close to the combined gear 5, of the outer tube 11 is used for the output shaft 4 to insert into, and the first gear 3 is located in the gearbox outside the outer tube 11 and provided on the output shaft 4 to link the combined gear 5 and the first gear 3. Specifically,

- 6 2019101146 30 Sep 2019 mounting holes of the combined gear 5 and the first gear 3 are both flat square through holes, and the output shaft 4 has a shape corresponding to the flat square through holes, which facilitates the assembly and cooperation of the combined gear 5, the first gear 3 and the right output shaft 4. The right output shaft 4 may specifically have a shape of a cylindrical shaft being cut in an axial direction by an upper plane and a lower plane, and flat structural areas on the output shaft 4 can radially limit the combined gear 5 and the first gear 3, and then a split pin 16 and a spacer 17 are then used for axial limitation to reduce cost and reduce the number of parts. The difficulty of the entire assembly process is low and the assembly efficiency is improved.

[0046] The input gear 2 is mounted on the gear shaft 1 and located in the gearbox outside the outer tube 11.

[0047] As shown in Figures 3, 3(a), 3(b), and 3(c), an end of the gear shaft 1 may be provided with gear teeth that are engaged with the combined gear 5, and a diameter of the gear teeth at the end of the gear shaft is larger than a diameter of a remaining portion, so as to form a step. A gear sleeve 14 is fixedly provided on the gear shaft 1, and the input gear 2 is axially limited by the gear sleeve 14 mounted on the gear shaft 1.

[0048] The gear shaft 1 and the gear sleeve 14 may be separately and independently machined; or after the input gear 2 and the gear sleeve 14 are independently machined and connected, the input gear 2 and the gear sleeve 14 are fixed to the gear shaft 1 to better reduce the machining difficulty and improve the cooperation precision. The gear teeth at the end of the gear shaft 1 are directly machined on the shaft body, and the gear sleeve 14 thereon limits the position of the input gear 2 and supports the axial movement of the entire gear shaft assembly.

[0049] In addition, in order to prevent the gear sleeve 14 and the input gear 2 from rotating and slipping on the gear shaft 1, the input gear 2 is fixedly mounted on the gear shaft 1 by welding; of course, to prevent the gear sleeve 14 and the input gear 2 from rotating and slipping on the gear shaft 1, the gear sleeve 14 and the input gear 2 can be fixedly mounted on the gear shaft 1 by an interference fit, or can be further fixed to the gear shaft 1 by a pin.

[0050] The gear shaft 1 is movable in a direction inserting into or away from the outer tube

-72019101146 30 Sep 2019

11. When the gear shaft 1 moves and further inserts into the outer tube 11, and, the upper gear teeth thereof are engaged with the combined gear 5, the input gear 2 and the first gear 3 are misplaced, that is, in a disengaged state; when the gear shaft 1 moves in a direction away from the outer tube 11 until the input gear 2 is engaged with the first gear 3, the gear teeth of the gear shaft 1 and the combined gear 5 are in a disengaged state. Of course, the movement of the gear shaft 1 in the direction away from the outer tube 11 can make the input gear 2 disengage with the gears one 3, but in order to save space and achieve miniaturization and weight reduction, the space of the gearbox cover is only required to meet the following: the input gear 2 is engaged with the first gear 3 when the gear teeth of the gear shaft 1 and the combined gear 5 are in the disengaged state.

(2) Gearbox [0051] The gearbox is located outside the outer tube 11, and includes a hollow cavity composed of a gearbox inner cover 12 and a gearbox outer cover 13. The first gear 3 and the input gear 2 are located in the hollow cavity, and a shaft sleeve for allowing the gear shaft to pass through is fixed on the gearbox outer cover 13.

[0052] As shown in Figures 8, 8(a) and 8(b), the gearbox inner cover 12 and the gearbox outer cover 13 are both provided with openings for allowing the output shaft 1 and the gear shaft 4 to pass through.

[0053] As shown in Figure 8(b), a flange 121 extending in a direction close to the gearbox outer cover 13 is provided on the openings of the gearbox inner cover 12, and an inner sleeve 122 and an inner liner 123 are respectively provided at the two openings of the gearbox inner cover 12. A reverse flange machining is performed on the openings of the inner sleeve 122 and the inner liner 123 mounted on the gearbox inner cover 12, which increases the contact area of the gear shaft 4 with the inner sleeve 122 and the inner liner 123, thereby increasing the support strength of the inner sleeve 122 and the inner liner 123.

[0054] The above gear sleeve 14 is located in the inner liner 123 and is in sliding cooperation with the inner sleeve. The outer diameter of the gear sleeve 14 is larger than the outer diameter of the gear teeth on the gear shaft 1, that is, when the gear shaft 1 is laterally displaced, the gear

- 8 2019101146 30 Sep 2019 teeth on the shaft 1 can be accommodated in the inner liner 123, thereby ensuring the gear shaft to be smoothly engaged or disengaged with the combined gear.

[0055] Further, an outer end portion of the gear teeth on the gear shaft 1 is recessed toward an inner side of the gear shaft 1 to form a stepped surface on the end portion of the gear teeth of the gear shaft 1, an inner end surface of the gear sleeve 14 abuts against the stepped surface, the input gear 2 is mounted on the gear shaft 1 and an inner side surface of the input gear 2 abuts against the outer end surface of the gear sleeve 14, and, the input gear 2 is fixed to the gear shaft 1 in a welded manner. With such a structure, the axial dimension of the gear sleeve 14 can be precisely set, so that the spacing between the gear teeth on the gear shaft 1 and the input gear has a high precision, which achieves the design requirements. During assembly, the axial dimension of the gear sleeve 14 can be adjusted according to the size of each gear on the transmission mechanism of the landing leg, which ensures that after the entire transmission mechanism is assembled, when the input gear 2 is engaged with the first gear 3, the gear teeth on the gear shaft 1 is disengaged with the combined gear 5, and when the gear teeth on the gear shaft 1 is engaged with the combined gear 5, the input gear 2 and the gear 3 have sufficient spacing to prevent interference. In addition, the gear sleeve 14 can also accurately position the input gear 2 during assembly; besides, during use, the gear sleeve 14 is in sliding cooperation with the inner liner 123 for guiding and supporting the lateral movement of the gear shaft 1, and preventing the gear shaft 1 from swinging away from its central axis when the gear shaft 1 is subjected to a large external force. Moreover, the engagement of the gear sleeve 14 and the inner liner 123 can effectively transmit the large load carried by the gear shaft 1 to the outer tube of the landing leg and the gearbox cover to avoid stress concentration.

[0056] The inner side surface of the input gear 2 is provided with an avoiding recess for avoiding the inner liner 123 and the flange at an outer circumference of the inner liner 123. In the present application, according to the above configuration, the avoiding recess is provided on the input gear 2, and the convex teeth of the input gear 2 are moved inward, so that the convex teeth of the input gear 2 and the convex teeth of the gears 3 have a spacing satisfying the use condition and avoid interference, and the distance between the gearbox outer cover and the outermost end surface of the output gear 2 is sufficiently close, thereby the size of the gearbox

-92019101146 30 Sep 2019 cover in the axial direction of the gear shaft 1 is reduced, that is, the volume of the entire landing leg is reduced.

[0057] In the present application, according to the above technology solution, a distance between convex teeth of the input gear 2 and convex teeth of the first gear 3 is dl, an axial dimension of the gear teeth on the gear shaft 1 is d2, and in a case that the gear teeth of the gear shaft 1 are engaged with the combined gear 5, a distance between the inner end of the gear sleeve 14 and the outer end of the inner liner 123 is d3, where d3>dl>d2. The state in which the gear teeth of the gear shaft 1 is engaged with the combined gear 5 is a low gear position (that is, a low speed transmission state), and the state in which the input gear 2 is engaged with the first gear 3 is a high gear position (that is, a high speed transmission state). When the gear shaft 1 moves to the high gear position from the low gear position, the actual moving distance of the gear shaft 1 is dl, the input gear 2 is completely engaged with the first gear 3, and a part of the gear sleeve 14 is still placed in the inner liner 123, so that the inner liner 123 can play a supporting role for the gear sleeve 14 and form two support positions for supporting the gear shaft 1 by cooperating with the shaft sleeve on the gearbox outer cover 13. At the high gear position, the gear shaft 1 plays a good supporting role. Since dl>d2, and it can be satisfied that the gear teeth 1 is disengaged with the combined gear 5 after the gear shaft 1 is moved by the distance dl, at the low gear position, most parts of the gear sleeve 14 are placed in the inner liner 123, that is, the portion where the gear sleeve 14 and the inner liner 123 are cooperated with each other has a larger axial dimension, under the cooperation of the shaft sleeve on the gearbox outer cover 13, the gear shaft 1 has a higher supporting effect, so that when the gear shaft 1 receives a large torque at the low gear position, the gear shaft 1 does not yaw.

[0058] As shown in Figure 1, the output shaft 4 is in contact with the inner wall of the inner sleeve 122, and a spacer 17 is provided between the first gear 3 and the inner sleeve 122.

[0059] As shown in Figure 1, when the combined gear 5 is engaged with the gear shaft 1 and the input gear 2 is disengaged with the first gear 3, the gear teeth of the gear shaft 1 insert into the outer tube 11 to engage with the combined gear 5, and the gear sleeve 14 and the input gear 2 are in contact with the inner wall of the inner liner 123.

[0060] As shown in Figure 2, when the gear teeth of the gear shaft 1 are disengaged with the

- io 2019101146 30 Sep 2019 combined gear 5 and the input gear 2 is engaged with the first gear 3, the gear sleeve 14 is still in part contact with the inner wall of the inner liner 123. The input gear and the gear sleeve are supported by the inner liner 123 on the gearbox inner cover 12 without a need to machine a long hole groove on the support pad 7 for support.

(3) Relationships between the gear teeth of the gear shaft 1, the input gear 2, the first gear 3, the combined gear 5, and the second gear 6 [0061] The combined gear 5 is a combined gear with a tapered column shape, is always engaged with the second gear 6, and may be selectively engaged or disengaged with the gear teeth of the gear shaft 1.

[0062] The second gear 6 can be a bevel gear that is connected to a double-head screw assembly 10.

[0063] As shown in Figure 1, when the gear teeth is engaged with the combined gear 5, since the combined gear 5 is larger than the gear teeth of the gear shaft 1, it is a low gear position, and the power transmission path is: gear shaft 1—gear teeth—combined gear 5—gear two 6 — double-head screw assembly 10—landing leg is raised and lowered.

[0064] As shown in Figure 2, when the input gear 2 is engaged with the first gear 3, it is a high gear position, and the power transmission path is the gear shaft 1—the input gear 2—the first gear 3—the combined gear 5—the second gear 6—the double-head screw assembly 10— the landing leg is raised and lowered.

[0065] An oil groove 18 is provided on a side of the outer tube 11 close to the gear teeth, and an oil barrier 19 is provided above the oil groove 18. The oil groove 18 can be a cylindrical groove structure having an opening, and is mounted on the support pad 7 to store a certain amount of lubricating grease. The grease in the working process of the gear shaft 1 and the combined gear 5 will be stored in the oil groove 18, thereby ensuring that the gear shaft 1 and the combined gear 5 are continuously lubricated during operation.

(4) Gear two 6 and double-head screw assembly 10 [0066] The double-head screw assembly 10 is connected to the second gear 6 and is further connected to a square nut 8 in a threaded manner. A support pad 7 is further provided between

-11 2019101146 30 Sep 2019 the double-head screw assembly 10 and the square nut 8. As shown in Figure 1, the support pad 7 is located between the second gear 6 and the square nut 8.

[0067] The top of the square nut 8 is provided with an empty groove, which has a structure of an oil sump, and the oil sump has a large space, which can reduce the daily maintenance frequency and improve the feasibility of the later maintenance.

[0068] The square nut 8 is placed on the inner tube 9. As shown in Figure 1, the square nut 8 has a square structure, and is mounted on the inner tube 9 in an invert manner. The square nut 8 is designed with a structure of a limited pin hole, and the square nut 8 is further limited by a cylindrical pin 15, and the assembly process is simple. The double-head screw assembly 10 and the square nut 8 can be freely replaced during use, and the parts can be easily interchanged.

[0069] The above embodiments are only used to illustrate the technical solutions of the present disclosure, and are not limited thereto. Although the present disclosure has been described in detail in conjunction with the above embodiments, those skilled in the art should understand that: the technical solutions described in the above embodiments may be modified, or some of the technical features may be equivalently replaced; and these modifications and replacement do not depart from the spirit and scope of the technical solutions according to the embodiments of the present disclosure.

Claims (17)

1. 2019101146 30 Sep 2019

   1. A built-in landing leg, comprising: an outer tube, a combined gear, a second gear, a first gear, an input gear and a gear shaft, wherein the combined gear and the second gear are provided in the outer tube, and engaged with each other, the second gear is further connected to a double-head screw assembly; the first gear is externally provided on the outer tube and linked with the combined gear; and the input gear is provided on the gear shaft and externally provided on the outer tube, and the gear shaft is engaged with the combined gear or the input gear is engaged with the first gear during a movement of the gear shaft in a direction inserting into or away from the outer tube.
2. 2. The built-in landing leg according to claim 1, wherein an end of the gear shaft is provided with gear teeth that are selectively engaged or disengaged with the combined gear.
3. 3. The built-in landing leg according to claim 2, wherein a diameter of the gear teeth at the end of the gear shaft is larger than a diameter of a remaining portion.
4. 4. The built-in landing leg according to claim 1, wherein the built-in landing leg further comprises an oil groove under the gear shaft, the gear shaft is insertable into the oil groove to engage with the combined gear, and a gap between the gear shaft and the oil groove is provided with lubricating oil.
5. 5. The built-in landing leg according to claim 4, wherein the double-head screw assembly is further connected to a square nut, and a side of the square nut adjacent to the second gear is a square shape having an empty groove.
6. 6. The built-in landing leg according to claim 5, wherein a support pad is provided

   - 13 2019101146 30 Sep 2019 between the second gear and the square nut, and the oil groove is provided on the support pad.
7. 7. The built-in landing leg according to claim 5 or 6, wherein an inner side of the outer tube is further provided with an inner tube, and the square nut is fixed on the inner tube.
8. 8. The built-in landing leg according to claim 2, wherein the built-in landing leg further comprises a gearbox fixed on the outer tube, the gearbox comprises a gearbox inner cover and a gearbox outer cover, the input gear and the first gear are both located in the gearbox, and a shaft sleeve for allowing the gear shaft to pass through is fixed on the gearbox outer cover.
9. 9. The built-in landing leg according to claim 8, wherein the first gear and the combined gear are linked by an output shaft.
10. 10. The built-in landing leg according to claim 9, wherein the gearbox inner cover is provided with openings for allowing the output shaft and the gear shaft to pass through, and a flange extending in a direction close to the gearbox outer cover is provided on the openings.
11. 11. The built-in landing leg according to claim 10, wherein an inner liner is provided in one of the openings, the inner liner is tightly cooperated with the flange, a gear sleeve is sleeved on the gear shaft, the gear sleeve is provided in the inner liner and is in sliding cooperation with the inner liner, and an outer diameter of the gear sleeve is larger than an outer diameter of the gear teeth on the gear shaft.
12. 12. The built-in landing leg according to claim 11, wherein an outer end portion of the gear teeth on the gear shaft is recessed toward an inner side of the gear shaft to form a stepped surface, an inner end surface of the gear sleeve abuts against the stepped surface, the input gear

    - 14 2019101146 30 Sep 2019 is mounted on the gear shaft and an inner side surface of the input gear abuts against the outer end surface of the gear sleeve, and the input gear is fixed to the gear shaft in a welded manner.
13. 13. The built-in landing leg according to claim 12, wherein the inner side surface of the input gear is provided with an avoiding recess for avoiding the inner liner and the flange at an outer circumference of the inner liner.
14. 14. The built-in landing leg according to claim 13, wherein a distance between convex teeth of the input gear and convex teeth of the first gear is dl, an axial dimension of the gear teeth on the gear shaft is d2, and in a case that the gear teeth of the gear shaft are engaged with the combined gear, a distance between the inner end of the gear sleeve and the outer end of the inner liner is d3, where d3>d2>dl.
15. 15. The built-in landing leg according to claim 9, wherein the combined gear and the first gear are each a flat through hole for inserting into the output shaft, and the output shaft is a cylinder-like shaft having a shape of a cylindrical shaft being cut in an axial direction by an upper plane and a lower plane.
16. 16. The built-in landing leg according to claim 1, wherein the outer tube has a square structure, and an outer circumference of corresponding to a surface that is close to the combined gear includes a curved surface, the curved surface includes a first circular arc segment, an intermediate circular arc connecting segment and a second circular arc segment which are sequentially connected, a diameter of a circle where the intermediate circular arc connecting segment is located is smaller than circles where the first circular arc segment and the second circular arc segment are located.
17. 17. The built-in landing leg according to claim 1, wherein an inner wall of the outer tube is

    - 15 2019101146 30 Sep 2019 provided with a recess recessed toward the outer side of the outer tube for avoiding an outer circumference of the combined gear.