Gear mechanism with backlash elimination structure

Abstract

This invention relates to the field of gear backlash elimination technology, and more particularly to a gear mechanism with a backlash elimination structure. The gear mechanism has at least one planetary gear train, which includes an internal gear, a sun gear, and at least three planetary gears. At least one of the at least three planetary gears is a backlash-eliminating planetary gear. The backlash-eliminating planetary gear includes a first sub-planet gear and a second sub-planet gear, and a backlash elimination structure. The backlash elimination structure includes an elastic element, at least one first contact surface, and at least one second contact surface. When backlash occurs in the gear mechanism, the elastic element, under axial and radial preload, pushes the first contact surface and the second contact surface to generate relative axial and radial movement, thereby eliminating the backlash in the gear mechanism. The advantage of this invention is that the entire compensation process requires no external control or manual adjustment; real-time dynamic compensation of backlash is achieved by relying on the self-restoring characteristics of the elastic element.

Description

Technical Field

[0001] This invention relates to the field of gear backlash elimination technology, and in particular to a gear mechanism with a backlash elimination structure. Background Technology

[0002] In the field of vehicle steering technology, the kingpin reducer in the angular module steering mechanism typically employs a planetary gear train structure, which boasts high transmission efficiency and a compact design. However, the inherent gear meshing backlash problem of planetary gear trains cannot be ignored. This backlash mainly stems from gear machining accuracy, assembly tolerances, and long-term operational wear, and is particularly pronounced under traditional assembly methods, leading to unexpected relative displacements or slight vibrations between gears under different loads.

[0003] The backlash of the planetary gear train is a critical component of the transmission chain clearance in the steering system. Within the chassis architecture, precise angle control of the kingpin steering mechanism (including the reducer) is a core prerequisite for achieving steer-by-wire, integrated chassis control, and advanced autonomous driving functions. The core challenge lies in the mismatch between the transmission backlash of the kingpin steering mechanism (including the backlash at the reducer and rack and pinion), its nonlinear friction characteristics, load disturbances, and the timing delay of multi-control unit coordination on the electronic side, and the domain controller's requirements for high-precision, high-responsiveness, and high-consistency control of the steering angle.

[0004] Insufficient steering angle control precision will directly lead to: the risk of ADAS / AD (Advanced Driver Assistance Systems) malfunction (such as trajectory deviation during lane keeping and decreased accuracy of automatic parking); poor coordination of chassis integrated control (such as steering torque fluctuations when ESP (Electronic Stability Program) intervenes, and mismatch between CDC (Continuous Damping Control System) and steering posture, resulting in unstable vehicle posture); and deterioration of driving quality (manifested as steering lag, insufficient self-centering, blurred center of gravity, and even "hands-off" at low speeds and "floaty" at high speeds).

[0005] Among them, the transmission mechanism of the kingpin steering gear is the foundation of steering angle control. The core influencing factors include: 1. Transmission clearance: The clearance of each link changes with wear and temperature, resulting in "no-travel" between the input and output steering angles, causing response delay or "step jump"; 2. Friction nonlinearity: The switching between static and dynamic friction and the change in grease viscosity at low temperatures will cause "dead zone" and "stick-slip phenomenon" in the control, which manifests as no response to small angle commands and over-response when commands change abruptly. Summary of the Invention

[0006] Therefore, the present invention aims to provide a gear mechanism with a backlash-eliminating structure. This mechanism utilizes a disc spring to generate axial and radial preload, thereby effectively eliminating backlash in the gear mechanism.

[0007] To achieve the above objectives, the invention provides a gear mechanism with a backlash-free structure. The gear mechanism has at least one planetary gear train, which includes an internal gear, a sun gear, and at least three planetary gears. At least one of the three planetary gears is a backlash-free planetary gear. The backlash-free planetary gear includes a first sub-planetary gear and a second sub-planetary gear coaxially arranged, and a backlash-free structure disposed between the first and second sub-planetary gears. The backlash-free structure includes: an elastic element disposed between the first and second sub-planetary gears, used to provide axial and radial preload to the first and second sub-planetary gears; at least one first contact surface disposed on the end face of the first sub-planetary gear facing the second sub-planetary gear; and at least one second contact surface disposed on the end face of the second sub-planetary gear facing the first sub-planetary gear, and adapted to the first contact surface. When backlash occurs in the gear mechanism, the elastic element, under the action of axial and radial preload, pushes the first and second contact surfaces to generate relative axial and radial movement, thereby eliminating the backlash in the gear mechanism.

[0008] Furthermore, the elastic element is one or a combination of a disc spring, a wave spring, and a diaphragm spring.

[0009] Furthermore, at least one first protrusion is provided on the end face of the first sub-planet gear facing the second sub-planet gear, and the side of the first protrusion forms a first contact surface; on the end face of the second sub-planet gear facing the first sub-planet gear, a second protrusion is provided that is opposite in position to the first protrusion and is adapted in shape, and the side of the second protrusion opposite to the first protrusion forms a second contact surface.

[0010] Furthermore, the first contact surface and the second contact surface are mutually mating spiral surfaces.

[0011] Furthermore, the first contact surface and the second contact surface are mutually cooperating inclined surfaces.

[0012] Furthermore, there are multiple first protrusions and multiple second protrusions; multiple first protrusions are evenly arranged on the end face of the first sub-planet gear along the circumference of the first sub-planet gear, and together with the end face, they form a positioning space; multiple second protrusions are evenly arranged on the end face of the second sub-planet gear facing the first sub-planet gear along the circumference of the second sub-planet gear; one end of the elastic element is accommodated in the positioning space, and a radial gap is provided between the circumferential side of the end and the first protrusion; the other end of the elastic element abuts against the end face of the second sub-planet gear facing the first sub-planet gear.

[0013] Furthermore, the first contact surface and the second contact surface are respectively the tooth side mating surfaces of the mating external spline and the internal spline; wherein, the internal spline is disposed on the end face of the first sub-planet gear facing the second sub-planet gear, and the external spline is disposed on the end face of the second sub-planet gear facing the first sub-planet gear.

[0014] Furthermore, the inner spline and the end face of the first sub-planet gear together form a receiving space, the large-diameter end of the elastic element is disposed in the receiving space, and the small-diameter end of the elastic element abuts against the end face of the outer spline.

[0015] Compared with existing technologies, inventions and creations can achieve the following beneficial effects:

[0016] Two sub-planetary gears slide relative to each other along a helical or inclined plane, converting axial displacement into circumferential relative rotation, automatically filling the meshing gap; after the gap is completely eliminated, the contact surfaces are tightly fitted again, and the elastic element returns to a stable preload state. The entire compensation process requires no external control or manual adjustment, relying on the self-recovering characteristics of the elastic element to achieve real-time dynamic compensation of the backlash.

[0017] The preload ensures that the contact surfaces are always tightly fitted, avoiding meshing impacts and vibrations caused by gaps during transmission, and reducing wear on the tooth surface and contact surface; the buffering effect of the elastic element can absorb part of the peak transmission load and protect the planetary gears and shaft components.

[0018] The backlash and nonlinear friction in the gear transmission are significantly suppressed, the mechanical characteristics of the system are closer to linear, the dependence on complex compensation algorithms is reduced, the computational load of the electronic control unit is reduced, and the timing of multi-unit coordination is optimized.

[0019] In addition to the aforementioned core technological advantages, this gear mechanism with a backlash-free structure, when applied to a kingpin steering mechanism, can also achieve the following significant technical effects:

[0020] Improved friction and control characteristics suppress "stick-slip" and control "dead zones," enhancing smoothness of small-angle steering response and preventing over-response during sudden changes in steering commands. Ensured ADAS / AD performance, significantly reducing lane-keeping trajectory deviation and automatic parking positioning errors, improving functional reliability. Enhanced chassis coordination, providing more stable steering torque output, improving coordination with ESP, CDC, and other systems, preventing vehicle instability. Optimized driving feel, effectively improving steering lag, insufficient self-centering, and vague center of gravity, suppressing low-speed "thrust" and high-speed "floatiness." Attached Figure Description

[0021] The accompanying drawings, which form part of the invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0022] Figure 1 This is a schematic diagram of a gear mechanism with a backlash-free structure according to a first embodiment of the present invention;

[0023] Figure 2This is a schematic diagram of a gear mechanism with a backlash-free structure according to a second embodiment of the present invention.

[0024] Figure 3 This is a schematic diagram of the structure of a backlash-free planetary gear according to a first embodiment of the present invention;

[0025] Figure 4 This is a schematic diagram of the structure of the first sub-planetary gear according to the first embodiment of the invention.

[0026] Figure 5 This is a schematic diagram of the backlash-free planetary gear according to the second embodiment of the invention.

[0027] Figure 6 This is a schematic diagram of the structure of the first sub-planetary gear according to the second embodiment provided by the invention;

[0028] Figure 7 This is a schematic diagram of the structure of the second sub-planetary gear according to the second embodiment of the present invention.

[0029] The reference numerals in the accompanying drawings include: 10, internal gear; 20, sun gear; 30, backlash-free planetary gear; 31, first sub-planet gear; 32, second sub-planet gear; 33, elastic element; 34, first protrusion; 35, second protrusion; 36, first contact surface. Detailed Implementation

[0030] To make the purpose, technical solution, and advantages of the invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are for illustrative purposes only and do not constitute a limitation on the invention.

[0031] It should be noted that, where there is no conflict, the embodiments and features in the embodiments of the invention can be combined with each other.

[0032] In the description of an invention, it should be understood that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating orientation or positional relationships based on the orientation or positional relationships shown in the accompanying drawings, are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature specified with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of an invention, unless otherwise stated, "a plurality of" means two or more.

[0033] In the description of the invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in the invention based on the specific circumstances.

[0034] The invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0035] like Figures 1 to 7 As shown in the figure, an embodiment of the present invention provides a gear mechanism with a backlash-free structure. The gear mechanism has at least one planetary gear system, which includes an internal gear 10, a sun gear 20, and at least three planetary gears. Among the at least three planetary gears, at least one planetary gear is a backlash-free planetary gear 30. In this embodiment, the number of planetary gears is four, one of which is a backlash-free planetary gear 30. Furthermore, the internal gear 10, the sun gear 20, and all planetary gears are spur gears.

[0036] like Figure 3 and Figure 4 As shown, the backlash-free planetary gear 30 includes a first sub-planet gear 31 and a second sub-planet gear 32 arranged coaxially, and a backlash-free structure disposed between the first sub-planet gear 31 and the second sub-planet gear 32.

[0037] Specifically, bearings (such as needle roller bearings or sliding bearings) are installed in the inner holes of the first sub-planetary gear 31 and the second sub-planetary gear 32, respectively. An axial spacer is provided between the two bearings to limit their movement. The connecting shaft passes through the bearing of the first sub-planetary gear 31, the spacer, and the bearing of the second sub-planetary gear 32 in sequence, realizing the coaxial installation and relative rotational support of the two sub-planetary gears.

[0038] The backlash elimination structure includes: an elastic element 33, at least one first contact surface 36, and at least one second contact surface. At least one first contact surface 36 is disposed on the end face of the first sub-planetary gear 31 facing the second sub-planetary gear 32. At least one second contact surface is disposed on the end face of the second sub-planetary gear 32 facing the first sub-planetary gear 31 and is adapted to the first contact surface 36.

[0039] An elastic element 33 is disposed between the first sub-planetary gear 31 and the second sub-planetary gear 32 to provide axial and radial preload to the first sub-planetary gear 31 and the second sub-planetary gear 32. When backlash occurs in the gear mechanism, the elastic element 33, under the action of the axial and radial preload, pushes the first contact surface 36 and the second contact surface to generate relative axial and radial movement, thereby eliminating the backlash in the gear mechanism.

[0040] Specifically, the elastic element 33 is one or a combination of a butterfly spring, a wave spring, and a diaphragm spring. In this embodiment, the elastic element 33 is a single butterfly spring. In another embodiment, the elastic element 33 may also be two or more butterfly springs, wave springs, or diaphragm springs.

[0041] Example 1:

[0042] A plurality of first protrusions 34 are provided on the end face of the first sub-planetary gear 31 facing the second sub-planetary gear 32. The plurality of first protrusions 34 are evenly arranged on the end face of the first sub-planetary gear 31 along its circumference and together with the end face form a positioning space. The large-diameter end of the elastic element 33 is accommodated in the positioning space and abuts against the inner wall of the positioning space, while the small-diameter end of the elastic element 33 abuts against the end face of the second sub-planetary gear 32 facing the first sub-planetary gear 31.

[0043] The side of the first protrusion 34 forms a first contact surface 36. On the end face of the second sub-planet gear 32 facing the first sub-planet gear 31, there are a plurality of second protrusions 35 that correspond one-to-one with the positions of the first protrusions 34 and are adapted in shape. The side faces of the second protrusions 35 opposite to the first protrusions 34 form a second contact surface.

[0044] In this embodiment, the number of the first protrusion 34 and the second protrusion 35 is preferably four. The first contact surface 36 and the second contact surface are mutually mating helical surfaces.

[0045] In another embodiment, the first contact surface 36 and the second contact surface are mutually cooperating inclined surfaces.

[0046] It should be noted that the multiple second protrusions 35 and their respective end faces also together form a positioning space. This structure supports bidirectional assembly of the elastic element 33 to adapt to different preload application directions: when the elastic element 33 is opposite to the above-mentioned installation direction, the large-diameter end of the elastic element 33 is accommodated in the positioning space formed by the second protrusions 35.

[0047] Backlash elimination working principle:

[0048] After assembly, the elastic element 33 is in a compressed state, storing elastic potential energy and continuously applying axial and radial preload to the two sub-planetary gears, so that the first contact surface 36 and the second contact surface are always in close contact, reducing back gaps from the source.

[0049] The axial and radial preload applied by the elastic element 33 is transmitted to the two sub-planet gears through the contact surfaces of the end fits. For example, the first sub-planet gear 31 generates a preload force with a clockwise circumferential rotation tendency, while the second sub-planet gear 32 obtains a reverse preload force. The reverse preload force acts tangentially along the sub-planet gears, causing the two to generate a reverse relative rotation tendency or a preload state.

[0050] When the planetary gear meshes with the sun gear 20 and the internal gear 10, there is an inherent meshing clearance, and the preload force can drive the first sub-planetary gear 31 and the second sub-planetary gear 32 to rotate relative to each other.

[0051] The relative rotation causes one side of the meshing tooth of the first sub-planet gear 31 to form a reverse pressing state with the other side of the corresponding meshing tooth of the second sub-planet gear 32, thereby pushing the meshing teeth of the two sub-planet gears to open up each other and reducing the meshing clearance between the sun gear 20 and the internal gear 10.

[0052] The separate first sub-planetary gear 31 and second sub-planetary gear 32 effectively "widen" the meshing tooth profile of the planetary gear in the side view direction, thereby significantly reducing meshing backlash.

[0053] When the gear mechanism experiences backlash due to wear from long-term operation, load changes, or temperature fluctuations, the elastic element 33 releases potential energy, and the preload applied by it pushes the first contact surface 36 and the second contact surface to undergo axial and radial relative displacement.

[0054] The two sub-planetary gears slide relative to each other along the helical surface or inclined surface, converting axial displacement into circumferential relative rotation, automatically filling the meshing gap; after the gap is completely eliminated, the contact surfaces fit tightly again, and the elastic element 33 returns to a stable pre-tightened state.

[0055] The entire compensation process requires no external control or manual adjustment, relying on the self-recovering characteristics of the elastic element 33 to achieve real-time dynamic compensation of the back gap.

[0056] The core of this backlash elimination structure lies in the fact that, under the preload of the elastic element 33, the first sub-planetary gear 31 and the second sub-planetary gear 32 can generate a precise and controllable axial relative displacement and the resulting circumferential rotational offset. The offset is typically ≤10% of the pitch of a single sub-gear. This offset can be precisely controlled by adjusting the preload compression of the elastic element 33. The larger the expected clearance, the larger the set preload and the corresponding offset, achieving targeted clearance compensation. This design allows for the retention of a moderate initial clearance during assembly for operation, and then the preload forces the meshing teeth of the two sub-planetary gears to press against the sides of the sun gear 20 and the internal gear 10 tooth surfaces, actively eliminating meshing backlash.

[0057] Unlike traditional rigid adjustment structures, elastic preload can dynamically compensate for wear-induced gaps in real time, eliminating "idle travel" and "step jump" in the transmission chain, reducing response delay from the source, and achieving high-precision and high-consistency angle control.

[0058] The helical or inclined surface contact form can effectively disperse meshing impact and reduce operating noise and vibration; the guiding effect of the contact surface allows the sub-planetary gears to gradually fit together during meshing, avoiding rigid collisions and improving the smoothness of power transmission, which is especially suitable for high-speed or high-frequency start-stop conditions.

[0059] The elastic element 33 is preferably a disc spring, a wave spring, a diaphragm spring, or a combination thereof: disc springs have high stiffness and strong load-bearing capacity, making them suitable for heavy-duty scenarios; wave springs have small size and large deformation, making them suitable for light-duty transmissions with limited installation space; diaphragm springs have uniform preload and good stability, making them suitable for high-precision and low-noise transmission requirements.

[0060] It should be noted that the elastic element 33 can also be other springs that can generate axial force.

[0061] The contact surface is available in two forms: helical and bevel. The helical surface is suitable for heavy-duty scenarios with high torque and low wear; the bevel is easier to process and has a lower cost, making it suitable for light-duty or cost-sensitive scenarios.

[0062] The backlash elimination structure is highly integrated into the end face of the planetary gear. The installation of the protrusion and the elastic element 33 does not require additional couplings, locating pins or adjusting bolts, which simplifies the overall size of the gear mechanism and saves installation space.

[0063] The protrusions are positioned and shaped to fit each other, giving them self-positioning assembly characteristics. No complex alignment tooling is required during installation, improving assembly efficiency. Subsequent maintenance only requires checking the wear of the contact surfaces and replacing or repairing the planetary gears, without having to disassemble the entire transmission system.

[0064] The preload ensures that the contact surfaces are always tightly fitted, avoiding meshing impacts and vibrations caused by gaps during transmission, and reducing wear on the tooth surface and contact surface; the buffering effect of the elastic element 33 can absorb part of the peak transmission load and protect the planetary gears and shaft components.

[0065] The backlash and nonlinear friction in the gear transmission are significantly suppressed, the mechanical characteristics of the system are closer to linear, the dependence on complex compensation algorithms is reduced, the computational load of the electronic control unit is reduced, and the timing of multi-unit coordination is optimized.

[0066] Example 2:

[0067] like Figures 5 to 7 As shown, the first contact surface 36 and the second contact surface are the tooth flank mating surfaces of the mating external spline and internal spline, respectively. The spline is a helical spline, with its tooth lines extending helically along the axial direction. The internal spline is located on the end face of the first sub-planet gear 31 facing the second sub-planet gear 32, and its tooth flank forms the first contact surface 36. The external spline is located on the end face of the second sub-planet gear 32 facing the first sub-planet gear 31, and its tooth flank forms the second contact surface.

[0068] The internal spline and the end face of the first sub-planet gear 31 together form a receiving space. The large-diameter end of the elastic element 33 is disposed in this receiving space, and the small-diameter end of the elastic element 33 is close to the end face of the second sub-planet gear 32 and abuts against the axial spacer, thereby positioning the elastic element 33. After assembly, the elastic element 33 is in a compressed state, storing elastic potential energy.

[0069] The axial and radial preload applied by the elastic element 33 is transmitted to the tooth side contact surface of the spline, making the tooth sides of the inner and outer splines fit tightly together, while giving the two sub-planet gears a reverse circumferential preload tendency.

[0070] When the planetary gear meshes with the sun gear 20 and the internal gear 10, there is inherent clearance, and the preload of the elastic element 33 will drive the first sub-planetary gear 31 and the second sub-planetary gear 32 to rotate relative to each other.

[0071] The inner spline tooth side of the first sub-planet gear 31 forms a reverse pressure with the outer spline tooth side of the second sub-planet gear 32; this pressure causes the meshing teeth of the two sub-planet gears to "spread out" respectively, and each of them is close to the sides of the meshing teeth of the sun gear 20 and the internal gear 10, which is equivalent to "widening" the effective meshing tooth profile of the planet gears and reducing the meshing clearance from the source.

[0072] When the gear mechanism experiences wear and backlash due to long-term operation and load fluctuations, the elastic element 33 releases potential energy, causing axial relative displacement of the contact surfaces of the inner and outer splines. Due to the guiding constraint of the spline tooth sides, this axial displacement is converted into a small circumferential rotation of the two sub-planet gears, automatically filling the newly generated meshing backlash. At the same time, the multi-tooth meshing of the spline provides excellent circumferential and radial dual positioning accuracy, suppressing runout and vibration.

[0073] After the gap is completely eliminated, the spline teeth fit together tightly again, and the elastic element 33 returns to a stable pre-tight state. The whole process does not require external control, realizing real-time dynamic compensation of back clearance.

[0074] The above structure has the following advantages:

[0075] The spline teeth have multiple tooth surfaces for contact, resulting in a larger contact area. This allows the load to be evenly distributed across each spline tooth, effectively avoiding localized stress concentration and significantly improving the structure's fatigue resistance and heavy-load adaptability, making it suitable for high-torque transmission scenarios.

[0076] The meshing of the internal and external splines can simultaneously achieve precise circumferential and radial positioning of the two sub-planetary gears. Combined with the coaxial constraint of the bushing, radial movement and circumferential slippage during operation are eliminated, ensuring the consistency of the transmission ratio. The tight fit of the spline teeth can also suppress vibration and noise during transmission, improving the smoothness of operation.

[0077] Splines are standardized mechanical structures with mature processing technology and easy precision assurance. Compared with customized helical surfaces and inclined surfaces, they have lower production and testing costs. At the same time, the elastic element 33 supports bidirectional assembly and can be adapted to different preload application directions. Combined with the coaxial positioning design of the bushing, no complex tooling is required during assembly, improving assembly efficiency.

[0078] The rigid constraint of the spline tooth side, combined with the flexible preload of the elastic element 33, avoids the risk of jamming in the rigid adjustment structure and is more stable than the compensation of the helical surface and inclined surface. Even under high-frequency start-stop and load change conditions, the spline tooth side can always maintain surface contact to ensure the reliability of backlash compensation. It is suitable for high-precision scenarios such as servo drives and precision reducers.

[0079] In summary, the gear mechanism with a backlash-free structure of the present invention brings significant benefits to the kingpin steering mechanism:

[0080] Improve friction and control characteristics, suppress "stick-slip phenomenon" and control "dead zone", enhance the smoothness of small-angle steering response, and avoid over-response when commands change abruptly.

[0081] It ensures ADAS / AD performance, significantly reduces lane keeping trajectory deviation and automatic parking positioning errors, and improves functional reliability.

[0082] Enhanced chassis coordination provides more stable steering torque output, improves coordination with ESP, CDC and other systems, and avoids vehicle instability.

[0083] It optimizes driving feel, effectively improves problems such as steering lag, insufficient self-centering, and unclear center of gravity, and suppresses the "thrust" phenomenon at low speeds and the "drift" phenomenon at high speeds.

[0084] The specific embodiments described above do not constitute a limitation on the scope of protection of this invention. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A gear mechanism with a backlash-free structure, the gear mechanism having at least one planetary gear train, the planetary gear train comprising an internal gear, a sun gear, and at least three planetary gears, characterized in that, Of the at least three planetary gears, at least one planetary gear is a backlash-free planetary gear; the backlash-free planetary gear includes a first sub-planetary gear and a second sub-planetary gear arranged coaxially, and a backlash-free structure disposed between the first sub-planetary gear and the second sub-planetary gear; The gap-eliminating structure includes: An elastic element is disposed between the first sub-planetary gear and the second sub-planetary gear, for providing axial and radial preload to the first sub-planetary gear and the second sub-planetary gear; At least one first contact surface is disposed on the end face of the first sub-planetary gear facing the second sub-planetary gear; At least one second contact surface is disposed on the end face of the second sub-planet gear facing the first sub-planet gear, and the second contact surface is adapted to the first contact surface; At least one first protrusion is provided on the end face of the first sub-planet gear facing the second sub-planet gear, and the side of the first protrusion forms the first contact surface; On the end face of the second sub-planet gear facing the first sub-planet gear, there is a second protrusion that is opposite in position and adapted in shape to the first protrusion. The side of the second protrusion opposite to the first protrusion forms the second contact surface. The number of the first protrusion and the number of the second protrusion are both multiple; the multiple first protrusions are evenly arranged on the end face of the first sub-planet gear along the circumference of the first sub-planet gear, and together with the end face, they form a positioning space; the multiple second protrusions are evenly arranged on the end face of the second sub-planet gear facing the first sub-planet gear along the circumference of the second sub-planet gear. One end of the elastic element is housed within the positioning space, and the other end of the elastic element abuts against the end face of the second sub-planetary gear facing the first sub-planetary gear. When backlash occurs in the gear mechanism, the axial and radial preload applied by the elastic element pushes the first contact surface and the second contact surface to undergo relative axial and radial displacement, thereby eliminating the backlash in the gear mechanism.

2. The gear mechanism with a backlash-free structure according to claim 1, characterized in that, The elastic element is one or a combination of a disc spring, a wave spring, and a diaphragm spring.

3. The gear mechanism with a backlash-free structure according to claim 1, characterized in that, The first contact surface and the second contact surface are mutually mating spiral surfaces.

4. The gear mechanism with a backlash-free structure according to claim 1, characterized in that, The first contact surface and the second contact surface are mutually cooperating inclined surfaces.

5. A gear mechanism with a backlash-free structure, the gear mechanism having at least one planetary gear train, the planetary gear train comprising an internal gear, a sun gear, and at least three planetary gears, characterized in that, Of the at least three planetary gears, at least one planetary gear is a backlash-free planetary gear; the backlash-free planetary gear includes a first sub-planetary gear and a second sub-planetary gear arranged coaxially, and a backlash-free structure disposed between the first sub-planetary gear and the second sub-planetary gear; The gap-eliminating structure includes: An elastic element is disposed between the first sub-planetary gear and the second sub-planetary gear, for providing axial and radial preload to the first sub-planetary gear and the second sub-planetary gear; At least one first contact surface is disposed on the end face of the first sub-planetary gear facing the second sub-planetary gear; At least one second contact surface is disposed on the end face of the second sub-planet gear facing the first sub-planet gear, and the second contact surface is adapted to the first contact surface; The first contact surface and the second contact surface are respectively the tooth side mating surfaces of the mating external spline and the internal spline; The internal spline is disposed on the end face of the first sub-planet gear facing the second sub-planet gear, and the external spline is disposed on the end face of the second sub-planet gear facing the first sub-planet gear; The internal spline and the end face of the first sub-planet gear together form a receiving space, and the large-diameter end of the elastic element is embedded in the receiving space; When backlash occurs in the gear mechanism, the axial and radial preload applied by the elastic element pushes the first contact surface and the second contact surface to undergo relative axial and radial displacement, thereby eliminating the backlash in the gear mechanism.

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