Planetary auxiliary box synchronizer structure and design method

Abstract

The invention discloses a planet auxiliary box synchronizer structure and a design method, the planet auxiliary box synchronizer structure comprises a low-gear conical ring, a supporting plate and splines, the splines comprise an inner spline and an outer spline, and an action gap is formed between the inner spline and the outer spline and used for providing a radial movement space of the low-gear conical ring. The design method comprises the following steps that S1, the total radial movement amount delta 3 of the tooth holder is obtained through calculation; s2, an action gap value delta 4 is selected in the range that delta 3 < = delta 4 < = 2 delta 3 to design a spline, a sample machine is trial-manufactured, and a noise test and a gear shifting fatigue test are carried out; s3, if the test is qualified, determining an action gap value delta 4; and if the test is not qualified, adjusting the action gap value delta 4, and repeating the step S2 until the test is qualified. Compared with the prior art, the large-gap spline is adopted to connect the low-gear conical ring and the supporting plate, the action gap is utilized to adapt to floating of the synchronizer, collision between the tooth holder and the low-gear conical ring is avoided, and the NVH performance of the planet auxiliary box synchronizer is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of planetary gearboxes, and in particular to a structure and a design method of a planetary auxiliary gearbox synchronizer. Background Art

[0002] See also Figure 1 , Chinese patent CN202111255082.0 discloses a synchronizer and a planetary auxiliary box. In its specification, an existing planetary auxiliary box is recorded, and the scheme is: the low-speed cone ring is fixedly connected to the housing through a support plate. The support plate is fixed to the housing by bolts, and the connection between the low-speed cone ring and the support plate is usually welded.

[0003] The applicant discovered that the synchronizer had abnormal noise when it was used. After repeated theoretical and experimental analysis, the applicant found that the reason for the abnormal noise was that the connection between the low-speed cone ring and the support plate did not take into account the influence of the floating of the planetary carrier and the ring gear. When the synchronizer is in high gear, the sun gear and the planetary gear are relatively stationary. Due to the existence of the tooth side clearance, dynamic balance cannot be achieved. At this time, the gear seat and the synchronizer ring float together with the planetary carrier and the ring gear, while the low-speed cone ring in contact with the synchronizer ring is restricted from floating with the synchronizer ring. There is a large speed difference between the two, which will cause continuous collision and friction, resulting in abnormal noise. Long-term use will also cause wear on the cone surface, and poor reliability and NVH (Noise, Vibration, Harshness) performance. Summary of the invention

[0004] The purpose of the present invention is to overcome the above technical deficiencies, propose a planetary auxiliary case synchronizer structure and design method, and solve the technical problem of abnormal noise caused by the fixed connection between the low-speed cone ring and the support plate in the prior art.

[0005] In order to achieve the above technical objectives, the present invention adopts the following technical solutions: In the first aspect, the present invention provides a planetary sub-box synchronizer structure, including: a low-gear cone ring, a support plate and a spline, the spline including an inner spline and an outer spline, the inner spline is fixedly connected to the low-gear cone ring, the outer spline is fixedly connected to the support plate, the inner spline is matingly plugged with the outer spline, and an effective gap is formed between the inner spline and the outer spline to provide radial movement space for the low-gear cone ring.

[0006] In some embodiments, the splines are involute splines.

[0007] In some embodiments, the surface hardness of the contact surfaces of the inner spline and the outer spline is greater than HRC50.

[0008] In a second aspect, the present invention further provides a design method for designing the working clearance of a planetary auxiliary case synchronizer structure, comprising the following steps: S1, calculate the total radial movement of the gear seat Δ3; S2. Select an effective clearance value Δ4 within the range of Δ3≤Δ4≤2Δ3 to design the spline, trial-produce a prototype and conduct a noise test and a gear shift fatigue test; S3. If the test is qualified, determine the effective gap value Δ4; if the test is unqualified, adjust the effective gap value Δ4, and repeat step S2 until the test is qualified.

[0009] In some embodiments, in step S1 , when calculating Δ3 , both the tooth side clearance and the bearing clearance take the maximum value of the tolerance zone.

[0010] In some embodiments, in step S3, if the test result is that the abnormal noise is eliminated but the spline is worn, the effective clearance value Δ4 is ​​reduced; if the test result is that the spline is not worn but the abnormal noise exists, the effective clearance value Δ4 is ​​increased.

[0011] In some embodiments, in step S1, Δ3=Δ1+Δ2, wherein Δ1 is the radial movement of the first ball bearing, and Δ2 is the radial movement of the gear seat relative to the planet carrier.

[0012] In some embodiments, , , Where C3 is the radial clearance value of the second ball bearing, L1 is the distance between the planetary gear and the second ball bearing, L2 is the distance between the first ball bearing and the second ball bearing, and Δ0 is the radial play of the planetary gear shaft.

[0013] In some embodiments, Δ0=C1+X1, where C1 is the radial clearance value of the planetary roller, and X1 is the tooth side clearance value of the sun gear-planet gear.

[0014] In some embodiments, , , Where C2 is the radial clearance value of the first ball bearing, L3 is the distance between the planetary gear and the first ball bearing, L4 is the distance between the first ball bearing and the gear seat, and X2 is the tooth side clearance value of the planetary gear-ring gear.

[0015] Compared with the prior art, the planetary sub-box synchronizer structure provided by the present invention adopts a large-gap spline to connect the low-gear cone ring and the support plate, and uses the action gap in the spline to adapt to the synchronous floating of the low-gear cone ring and the gear seat, avoiding the collision between the low-gear cone ring and the gear seat, improving the NVH performance of the planetary sub-box synchronizer, and reducing the cone surface wear of the low-gear cone ring. The design method of the planetary sub-box synchronizer structure provided by the present invention provides a selection range and calculation scheme for the action gap. Those skilled in the art can adjust the action gap value within this range to obtain the action gap value that can eliminate abnormal noise and avoid spline wear, which delimits the scope and direction of the debugging work, and avoids the blindness and randomness of the debugging work. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a structural schematic diagram of a planetary auxiliary box in the prior art; Figure 2 is a schematic structural diagram of a planetary auxiliary box synchronizer in an embodiment of the present invention; Figure 3 is a flow chart of a design method in an embodiment of the present invention; Figure 4 It is a power route diagram of the planetary auxiliary box in the embodiment of the present invention; Figure 5 yes Figure 2 Schematic diagram of the structure of the middle planet carrier with planetary gears; Figure 6 It is a schematic diagram of tooth side clearance; Figure 7 It is a schematic diagram of bearing clearance; Figure 8 This is the floating schematic diagram of the planet carrier and ring gear; Fig. 9 Schematic diagram of sun gear-planet gear support in an embodiment of the present invention; Fig.10 It is a schematic diagram of the radial movement of the planet carrier; Fig.11 It is a schematic diagram of the radial movement of the ring gear-support seat. DETAILED DESCRIPTION

[0017] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0018] See also Figure 1 As shown, Figure 1It is a planetary auxiliary box structure in the prior art, which mainly includes a shaft 1', a sun gear 2', a planetary gear 3', a ring gear 4', a planetary carrier 5', a gear sleeve 6', a low-speed synchronizer ring 7', a support column 8', a high-speed synchronizer ring 9', a high-speed cone ring 10', a spring 11', a gear seat 12', a low-speed cone ring 13', a support seat 14', a ball bearing 15' and a support plate 16'. The power is input from the sun gear 2' and output to the planetary carrier 5'. The auxiliary box has two gears: low gear and high gear, which are switched by a synchronizer. In high gear, the ring gear 4' is engaged with the planetary carrier 5', and the auxiliary box speed ratio is 1. In low gear, the ring gear 4' is connected to the housing and is fixed. The power is output through the sun gear 2', the planetary gear 3', and the planetary carrier 5'. Since the speed of the planetary carrier is the revolution speed, a large reduction ratio can be obtained.

[0019] In the prior art, the planetary sub-box has a gear seat 12' connected to the gear ring 4' through a support seat 14'. For radial positioning, a ball bearing 15' is installed between the support seat 14' and the planet carrier 5'. Multiple groups of support columns 8' and springs 11' are installed in the gear seat 12', and the pre-synchronization function is realized by the swing of the support column 8'. In addition, the synchronizer ring is divided into a low-speed synchronizer ring 7' and a high-speed synchronizer ring 9'. Because the support seat 14' blocks it, the low-speed cone ring 13' can only be installed at the front end of the left end housing, and is fixed to the housing through the support plate 16'. The high-speed cone ring 10' is connected to the planet carrier 5' through a spline. The gear sleeve 6' moves axially under the push of the shift fork to achieve gear switching.

[0020] In view of the technical problem that in the above structure, the low gear cone ring 13' is fixedly connected to the housing through the support plate 16', resulting in the collision of the low gear cone ring 13' with the gear seat 12' and generating abnormal noise, the present invention provides a planetary auxiliary case synchronizer structure that can eliminate such abnormal noise.

[0021] It should be noted that the planetary sub-box synchronizer structure described in the present invention is used for but not limited to synchronizers of this structure. For the convenience of explanation, in the present invention, only the planetary sub-box synchronizer structure applied to synchronizers of this structure is used as an example for explanation. The principle of applying the planetary sub-box synchronizer structure to synchronizers of other structures is essentially the same as the principle of the present application, and will not be repeated here.

[0022] See also Figure 2 , Figure 2 Schematic diagram of the structure of a planetary auxiliary box synchronizer in an embodiment of the present invention. The planetary auxiliary box synchronizer includes a low-speed cone ring 8, a support plate 10, and a spline 18.

[0023] The spline 18 includes an inner spline and an outer spline. The inner spline is fixedly connected to the low-speed cone ring 8, and the outer spline is fixedly connected to the support plate 10. The inner spline and the outer spline are plugged in. An action gap is formed between the inner spline and the outer spline to accommodate the radial movement of the low-speed cone ring 8, so that the low-speed cone ring 8 and the gear seat 15 float synchronously, avoiding the collision between the low-speed cone ring 8 and the gear seat 15. The value of the action gap is greater than the national standard parameter of the spline, which is specially designed to solve the abnormal sound problem. The specific design method is given below.

[0024] In some embodiments, the spline 18 is an involute spline, and the value of the corresponding effective clearance is greater than the national standard parameter of the involute spline.

[0025] In some embodiments, the surface hardness of the contact surfaces of the inner spline and the outer spline is greater than HRC50. The hardness of ordinary 45 steel increased after heat treatment is HRC. HRC is the symbol of Rockwell hardness. HRC50 steel is slightly softer than the hardness of general tool steel, that is, slightly softer than the hardness of tools such as saw blades and steel files, and is a material that can be machined.

[0026] In this embodiment, the planetary auxiliary case synchronizer further includes a sun gear 1, a planetary gear 2, a planetary carrier 3, a planetary gear shaft 4, a planetary gear needle roller 5, a gear ring 6, a support seat 7, a low-speed synchronizer ring 9, a housing 11, a gear sleeve 12, a high-speed synchronizer ring 13, a high-speed cone ring 14, a gear seat 15, a first ball bearing 16, and a second ball bearing 17. Except that the low-speed cone ring 8 is connected to the support plate 10 through a spline 18, the connection relationship between the other components is the same as that of the prior art, and will not be repeated.

[0027] The planetary sub-box synchronizer structure utilizes the working clearance in the spline 18 to adapt to the synchronous floating of the low-gear cone ring 8 and the gear seat 26, avoiding the collision between the low-gear cone ring 8 and the gear seat 15, improving the NVH performance of the planetary sub-box synchronizer, and reducing the cone surface wear of the low-gear cone ring 8.

[0028] See also Figure 3 , Figure 3 It is a flow chart of the design method in an embodiment of the present invention.

[0029] The design method is used to design the action clearance of the planetary auxiliary case synchronizer structure, and includes the following steps: S1. Calculate the total radial movement Δ3 of the gear holder 15.

[0030] S2. Select an effective clearance value Δ4 within the range of Δ3≤Δ4≤2Δ3 to design the spline, produce a prototype and conduct noise test and gear shift fatigue test.

[0031] S3, if the test is qualified, determine the effective gap value Δ4. If the test is unqualified, adjust the effective gap value Δ4, and repeat step S2 until the test is qualified.

[0032] In some embodiments, in step S1 , when calculating Δ3, each tooth side clearance and bearing clearance in the planetary auxiliary case synchronizer structure takes the maximum value of the tolerance band.

[0033] See also Figure 2 , Figure 4 and Figure 5 This scheme fully considers the floating influence of the planet carrier 3 and the ring gear 6 in high gear, and also considers the radial clearance influence of the planetary wheel needle roller 5, the first ball bearing 16, and the second ball bearing 17. When the gear sleeve 12 is engaged in high gear (the gear sleeve 12 moves to the right for high gear and moves to the left for low gear), the ring gear 6 is connected to the planet carrier 3 through the support seat 7, the gear seat 15, the gear sleeve 12, the high gear cone ring 14 and the planet carrier 3 to rotate together. At this time, the sun gear 1 and the planetary gear 2 are equivalent to spline connection, and the two do not rotate relative to each other. The front end of the planetary carrier 3 is supported by the planetary wheel 2-sun wheel 1, and the rear end is supported by the second ball bearing 17. The ring gear 6 and the support seat 7 are placed on the planetary carrier 3, and the front end is supported by the planetary wheel 2-ring gear 6, and the rear end is supported by the first ball bearing 16. The planetary wheels 2 generally use 3-5, which are connected to the planetary carrier 3 through the planetary wheel shaft 4 and the planetary wheel needle roller 5. Due to the existence of tooth side clearance and bearing play, and under the influence of gravity and the dynamic unbalance of the planet carrier 3, the entire system will produce swing around the first ball bearing 16 and radial and axial movement during operation.

[0034] See also Figure 6 , Figure 6 This is a schematic diagram of the tooth side clearance. When the gears are meshing, in order to form a lubricating oil film between the meshing tooth profiles and avoid the gear teeth from getting stuck due to heat expansion caused by friction, a gap must be left between the tooth profiles. This gap is called the tooth side clearance. When the working tooth surfaces of the two gears are in contact with each other, their non-working tooth surfaces are separated from each other. The shortest distance j between the non-working tooth surfaces is n is the normal tooth side clearance. The distance j between the working tooth surface and the non-working tooth surface along the pitch arc t It is the circumferential tooth side clearance. Because of the existence of tooth side clearance, there is relative play when the gears are meshing.

[0035] See also Figure 7 , Figure 7 This is a schematic diagram of bearing clearance. In order to accommodate manufacturing errors and prevent the bearing from getting stuck during operation, the bearing needs to have a certain amount of clearance, which is divided into radial clearance, C r and axial clearance C n Because of the existence of clearance, the inner and outer rings of the bearing can swing and move relative to each other.

[0036] See also Figure 8 , Figure 8This is the floating principle diagram of the planetary carrier and the ring gear. Because there are inevitable gaps between bearings and gears, the planetary carrier floats in actual operation. The floating includes radial and axial translation and swinging around the bearings. Because the axial clearance of the synchronizer is relatively large, the collision noise is mainly caused by radial movement and swinging. Since the vertical component of the swing can also be added to the radial movement, the radial movement is the largest and is used as the main assessment indicator. The traditional shaft system uses bearings for support at both the left and right ends. The bearing clearance is relatively small, the shaft floating amount is small, and the synchronizer installed on the shaft will not produce abnormal noise. In order to ensure that multiple planetary gears are in uniform contact with the sun gear, the planetary system needs to allow the planetary carrier to have a large floating amount. Therefore, the left end uses a large tooth side clearance gear support and the right end uses a large clearance ball bearing support. This results in a relatively large floating amount, which is the fundamental reason for the synchronizer collision noise.

[0037] In this embodiment, the total radial movement Δ3 of the gear holder 15 is calculated as follows. It should be noted that the low-speed synchronizer ring 9 moves synchronously with the gear holder 15, that is, the total radial movement is also Δ3. At the same time, for the convenience of calculation, the planet carrier 3 (including the planetary gear shaft 4) and the gear holder 15 float from top to bottom in the vertical direction.

[0038] See also Fig. 9 , Fig. 9 It is a schematic diagram of the sun gear-planet gear support in the embodiment of the present invention. The two planetary gear shafts 4 above will eat up the radial clearance 5a of the planetary needle roller 5 and the sun gear-planet gear side clearance 5b. The planetary gear 2 presses down on the sun gear 1, and the planetary gear 2 below will be away from the sun gear 1 and will not produce any support. Let the radial clearance 5a of the planetary needle roller 5 be C1, and the sun gear-planet gear side clearance 5b be X1, then the radial movement of the planetary gear shaft 4 is Δ0=C1+X1, X1 is approximately equal to the circumferential side clearance of the gear, which can be calculated from the gear pair parameters.

[0039] See also Figure 4 and Fig.10 , Fig.10 Schematic diagram of radial movement of planet carrier 3. The distance between planet wheel 2 and second ball bearing 17 is L1, the distance between first ball bearing 16 and second ball bearing 17 is L2, and the radial clearance 17a of second ball bearing 17 is C3. Fig.10 From the upper position to the lower position), the radial movement amount Δ1 of the first ball bearing 16, , according to the triangle relationship: , , we can get:

[0040]

[0041] See also Figure 4 and Fig.11 , Fig.11 The figure is a schematic diagram of the radial movement of the ring gear-support seat. The tooth seat 15 and the ring gear-support seat are fixed together and float together with the ring gear-support seat. The distance between the planetary gear 2 and the ball bearing 16 is L3, the distance between the first ball bearing 16 and the tooth seat 15 is L4, the radial clearance 16a of the first ball bearing 16 is C2, and the tooth side clearance value of the planetary gear-ring gear is X2. The ring gear-support seat moves from the first position to the second position (i.e. Fig.11 From the upper position to the lower position), the radial movement of the gear seat 15 relative to the planet carrier 3 is Δ2, , according to the triangle relationship: , , we can get:

[0042]

[0043] Since the gear ring-support seat-gear seat is installed on the planet carrier 3 through the first ball bearing 16, the total radial movement Δ3 of the gear seat 15 is:

[0044] Under the action of gravity and the reaction force of the cone surface, the low-speed synchronizer ring 9 is always close to the gear seat 15 in the radial and axial directions, and the two rotate together, and the maximum up and down movement is equal to Δ3. In order to achieve the floating of the low-speed cone ring 8 and the low-speed synchronizer ring 9 together, the low-speed cone ring 8 needs to float relative to the support plate 10 but cannot rotate relative to it. The present application adopts a large-gap involute spline 18 connection, and the action gap Δ4 of the spline 18 should ensure Δ3≤Δ4≤2Δ3, so that the radial movement of the low-speed cone ring 8 can be accommodated, and the gap of the spline 18 can be prevented from being too large, the impact stress is large, and the reliability of the spline 18 is reduced. Because the width of the spline 18 is much smaller than the diameter of the spline 18, the spline 18 is not limited in the axial direction, and the low-speed cone ring 8 can also swing at a large angle relative to the support plate 10, which can accommodate the swing of the synchronizer ring 9 and the gear seat 15.

[0045] In step S2, both the noise test and the gear shift fatigue test adopt conventional test schemes in the art.

[0046] In some embodiments, in step S3, the method for adjusting the effective clearance value Δ4 is: if the result of the noise test is that the abnormal sound is eliminated, but the result of the gear shift fatigue test is that the spline 18 is worn, then the effective clearance value Δ4 is ​​reduced, and the prototype is trial-produced again and the noise test and gear shift fatigue test are performed. If the result of the gear shift fatigue test is that the spline 18 is not worn, but the result of the noise test is that the abnormal sound exists, then the effective clearance value Δ4 is ​​increased, and the prototype is trial-produced again and the noise test and gear shift fatigue test are performed.

[0047] The technical solution of the present application adopts a large clearance spline 18 to connect the low-gear cone ring 8 and the support plate 10, replacing the traditional fixed connection method or the conventional spline connection method in accordance with the national standard. The working clearance of the spline 18 in the present application is much larger than the clearance specified in the national standard, which is used to accommodate the radial movement of the low-gear cone ring 8 and avoid the collision between the low-gear cone ring 8 and the gear seat 15, resulting in abnormal noise. At the same time, the selection range and calculation scheme of the working clearance are also given. Those skilled in the art can adjust the working clearance value within this range to obtain the value of the working clearance that can eliminate abnormal noise and avoid wear of the spline 18. The scope of the debugging work is delineated, the direction is pointed out, and the blindness and randomness of the debugging work are avoided.

[0048] In the description of the present invention, it should be understood that the terms "center", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship are based on the orientation or position relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0049] The terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "plurality" means two or more.

[0050] In the description of the present invention, it should be noted that, unless otherwise clearly 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 direct connection, or an indirect connection through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific conditions.

[0051] In the description of this specification, specific features, structures, materials or characteristics may be combined in an appropriate manner in any one or more embodiments or examples.

[0052] The specific implementation of the present invention described above does not constitute a limitation on the protection scope of the present invention. Any other corresponding changes and modifications made based on the technical concept of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A planetary auxiliary case synchronizer structure, characterized in that: include: Low gear cone ring; Support plate; The spline comprises an inner spline and an outer spline, wherein the inner spline is fixedly connected to the low-speed cone ring, and the outer spline is fixedly connected to the support plate, the inner spline and the outer spline are plugged in with each other, and an effective gap is formed between the inner spline and the outer spline to provide radial movement space for the low-speed cone ring.

2. The planetary auxiliary case synchronizer structure according to claim 1, characterized in that: The splines are involute splines.

3. The planetary auxiliary case synchronizer structure according to claim 1, characterized in that: The surface hardness of the contact surfaces of the inner spline and the outer spline is greater than HRC50.

4. A design method, characterized in that: The method for designing the working clearance of the planetary auxiliary case synchronizer structure according to any one of claims 1 to 3 comprises the following steps: S1, calculate the total radial movement of the gear seat Δ3; S2. Select an effective clearance value Δ4 within the range of Δ3≤Δ4≤2Δ3 to design the spline, trial-produce a prototype and conduct a noise test and a gear shift fatigue test; S3. If the test is qualified, determine the effective gap value Δ4; if the test is unqualified, adjust the effective gap value Δ4, and repeat step S2 until the test is qualified.

5. The design method of the planetary auxiliary case synchronizer structure according to claim 4, characterized in that: In step S1, when calculating Δ3, both the tooth side clearance and the bearing clearance take the maximum value of the tolerance zone.

6. The design method of the planetary auxiliary case synchronizer structure according to claim 4, characterized in that: In step S3, if the test result shows that the abnormal noise is eliminated but the spline is worn, the effective clearance value Δ4 is ​​reduced; if the test result shows that the spline is not worn but the abnormal noise exists, the effective clearance value Δ4 is ​​increased.

7. The design method of the planetary auxiliary case synchronizer structure according to claim 5, characterized in that: In step S1, Δ3=Δ1+Δ2, wherein Δ1 is the radial movement of the first ball bearing, and Δ2 is the radial movement of the gear seat relative to the planet carrier.

8. The design method of the planetary auxiliary case synchronizer structure according to claim 7, characterized in that: ， ， Where C3 is the radial clearance value of the second ball bearing, L1 is the distance between the planetary gear and the second ball bearing, L2 is the distance between the first ball bearing and the second ball bearing, and Δ0 is the radial play of the planetary gear shaft.

9. The design method of the planetary auxiliary case synchronizer structure according to claim 8, characterized in that: Δ0=C1+X1, where C1 is the radial clearance value of the planetary roller and X1 is the tooth side clearance value of the sun gear-planet gear.

10. The design method of the planetary auxiliary case synchronizer structure according to claim 7, characterized in that: ， ， Where C2 is the radial clearance value of the first ball bearing, L3 is the distance between the planetary gear and the first ball bearing, L4 is the distance between the first ball bearing and the gear seat, and X2 is the tooth side clearance value of the planetary gear-ring gear.

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