Robot long-life light-weight CQ double-cycloid hollow speed reducer

Abstract

The invention belongs to the technical field of robot speed reducers, and particularly relates to improvement of Japanese RV speed reducers, in particular to a robot long-service-life light-weight CQ double-cycloid hollow speed reducer which comprises an inner cycloid gear ring, a planet carrier, a double-eccentric hollow shaft, cycloidal gears, bearings and other parts, and is characterized in that eccentric sections on the double-eccentric hollow shaft are connected with the cycloidal gears through the RN bearings; the cycloid gear teeth are meshed with the inner cycloid gear to drive the planet carrier to realize transmission output, so that a single-stage cycloid speed reducing mechanism is formed; and a concave-convex double-cycloid transmission structure is adopted, so that the bearing capacity is improved. The RV speed reducer has the technical effects that (1) the service life is long: the precision service life of the whole machine reaches 13000h, which is more than twice of the 6000h of the existing RV speed reducer; (2) light weight: a planetary stage in an existing RV speed reducer is removed, and light weight is realized; and (3) the adaptability is high, a concave-convex double-cycloid transmission structure is adopted, the reduction ratio is increased, the bearing capacity is improved, and the device is more suitable for a humanoid robot cycloid joint module.

Description

Technical Field

[0001] The present invention relates to the technical field of robot reducers, and in particular to an improvement on the Japanese RV reducer with a service life of 6000 hours, and a robot long-life lightweight CQ double cycloid hollow reducer with a service life of 13000 hours.

[0002] The present invention removes the planetary stage in the Japanese RV reducer and achieves a high degree of lightweight. It can not only replace the existing RV reducer, but also replace nearly half of the harmonic reducers in humanoid robots. Background Art

[0003] In 1983, a Japanese company patented a cycloidal-planetary two-stage reducer, the RV reducer. With its high torsional stiffness and exceptional impact resistance, the RV reducer quickly replaced harmonic reducers and became widely used in industrial robotics, precision machine tools, aerospace, and other fields. The four major international industrial robot manufacturers—Yaskawa, ABB, KUKA, and FANUC—all use Japanese RV reducers in their global industrial robots. Together, they command 70% of the global industrial robot reducer market. Japan aims to reach an annual production capacity of 2 million RV reducers by 2026.

[0004] The reason why the Japanese robot reducer's forward design adopts a cycloid-planetary two-stage structure is because: there is no stress concentration point at the cycloid arc tooth root, so the instantaneous impact torque can be as high as 5 times the rated torque without breaking the teeth; in addition, the reducer must have different output speeds, and planetary transmission is the easiest to change the reduction ratio.

[0005] However, the problem with the cycloid-planetary two-stage structure is as stated on page 15 of the Japanese RV reducer technical manual: "The service life of 6000 hours is due to the needle roller bearing (i.e., the needle roller bearing has a low rated dynamic load)."

[0006] Another problem with RV reducers is that they have many parts and are small in size, so they can only be lubricated with grease. Not only does the reducer have poor heat dissipation, but the grease injection process is also inefficient, and it is easy for debris to be brought in to contaminate the grease. Special grease is extremely expensive.

[0007] US invention patents published between 2023 and 2024 confirm that a Japanese company still uses a planetary-cycloid two-stage reduction structure, and the rated precision life is still 6000 hours. Examples are as follows:

[0008] (1) U.S. Patent No. 15, June 2023, entitled “Eccentric Oscillating Gear Device”

[0009] In the figure: 18a and 18b are needle roller bearings without inner ring and outer ring.

[0010] (2) U.S. Patent "Reducer" published on March 28, 2024,

[0011] In the figure: 218a and 218b are needle roller bearings without inner ring and outer ring.

[0012] (3) U.S. Patent No. 1851555 published on December 24, 2024, entitled “Eccentric Oscillating Gear Device”

[0013] In the figure: 18a and 18b are needle roller bearings without inner ring and outer ring.

[0014] (4) The US patent "Reducer" published on July 9, 2024, did not mention how to improve the accuracy and life of the RV reducer:

[0015] According to the speed reducer relating to one aspect of the presentdisclosure, the outer pins are provided between the casing and the external gear. This can contribute to improve the rigidity and heat dissipation while the reduction in size and weight is still successful. As a result, the speed reducer can effectively avoid failures and operate more reliably.

[0016] The present disclosure can effectively achieve improved rigidity and heat dissipation while accomplishing smaller size and lighter weight and also prevent failures and realize more reliable operation.

[0017] According to a speed reducer related to one aspect of the present disclosure, an outer pin is provided between the housing and the external gear. This helps to improve rigidity and heat dissipation while still successfully reducing size and weight. Therefore, the speed reducer can effectively avoid failure and operate more reliably.

[0018] "While achieving a smaller size and lighter weight, this invention can also effectively improve rigidity and heat dissipation, prevent malfunctions, and achieve more reliable operation."

[0019] The domestic research on double cycloid transmission is briefly described as follows:

[0020] (1) In 1989, Li Kezhi and Shen Peiji’s article “Development of Cycloid Equidistant Gears” pointed out: “The double cycloid system uses mutually fully enveloping cycloid equidistant lines as a conjugate curve. Compared with the cycloid pinwheel reducer, it has a simple structure: the double cycloid nodes K and K1 are concave-convex meshing, and the equivalent curvature radius is small, so the load capacity is large, and the load capacity can be increased by about 40-50%; a high-pressure oil film is formed near the meshing nodes, so that excellent lubrication performance can be obtained, and the transmission efficiency can be increased by 5 percentage points or more.

[0021] (2) In 2006, Li Yuanqing’s article “Cycloidal Speed ​​Reducer without Pinwheel” pointed out: “If the internal gear cycloid and the external gear cycloid are made of the same material, their strength is equivalent; if the internal gear cycloid replaces the pinwheel, the strength and rigidity will be greatly improved. Therefore, under the condition of the same output power, the reducer model can be reduced by one level; in addition, the single-stage reduction ratio is much higher than the 87 of the cycloid, reaching more than 200.”

[0022] (3) The patent "Closed Cycloid Precision Reducer" by Chen Bingkui et al. of Chongqing University (Patent No.: ZL2014101197746) states: "The closed cycloid envelope reducer includes an internal gear, a cycloid gear, a planetary carrier, a crankshaft and a bearing. The beneficial effects of the present invention are: improved bearing capacity, improved transmission accuracy and reduced processing and assembly error requirements; smaller backlash than RV reducers, compact structure, longer service life, simple process and low cost." Summary of the Invention

[0023] The present invention applies the theory of double cycloid transmission to solve the problems of service life and lightweight of existing RV reducers. It provides a long-life lightweight robot CQ double cycloid hollow reducer, which not only has a service life of 13,000 hours, but also removes the planetary stage to achieve lightweight. At the same time, it adopts a concave-convex double cycloid transmission structure to increase the reduction ratio and improve the load-bearing capacity. It is more suitable for the cycloid joint module of humanoid robots and can replace the existing RV reducer and nearly half of the harmonic reducers.

[0024] The technical solutions of the present invention are as follows:

[0025] A long-life lightweight CQ double cycloid hollow reducer for robots, comprising a hypocycloid ring gear and a planetary carrier, a main bearing, a cycloid wheel, a double eccentric input shaft and other parts arranged inside the hypocycloid ring gear;

[0026] The inner holes on both sides of the hypocycloid gear ring are respectively provided with the first main bearing and the second main bearing. There is a raised annular belt between the two inner holes, and the annular belt is processed with evenly distributed hypocycloid teeth, which mesh with the cycloid wheel teeth.

[0027] The planet carrier includes an input disc, an output disc and a pin;

[0028] The journals of the input and output discs are respectively matched with the inner holes of the first and second main bearings, and the main bearings are radial thrust ball bearings or tapered roller bearings or other bearings;

[0029] The cycloid wheel comprises a first cycloid wheel and a second cycloid wheel, and pin holes are evenly distributed around the center line of the cycloid wheel. The number of pin holes is an even number. This is because after the two cycloid wheels are integrally processed, one of the cycloid wheels can be turned over and assembled. A spacer is provided between the two cycloid wheels.

[0030] The input end of the double-eccentric hollow shaft is supported by a left tapered bearing in the center hole of the input disc, and the output end is supported by a right tapered bearing in the center hole of the output disc. The outer axial sides of the two tapered bearings are respectively limited by left and right retaining rings. The tapered bearing is the abbreviation of tapered roller bearing, and the retaining ring is the abbreviation of elastic retaining ring for hole.

[0031] The planet carrier, main bearing and double eccentric hollow shaft share a center line a, and are characterized by:

[0032] (A) The eccentric section on the double-eccentric hollow shaft is connected to the cycloid wheel through an RN bearing. The cycloid wheel teeth mesh with the inner cycloid teeth to drive the planetary carrier to achieve transmission output, forming a single-stage cycloid reduction mechanism, making the reducer lightweight; the concave-convex double cycloid transmission structure increases the reduction ratio and improves the load-bearing capacity, making it more suitable for the cycloid joint module of a humanoid robot;

[0033] (B) The pin passes through corresponding pin holes on the two cycloid wheels, and its two shaft ends are transitionally matched with corresponding holes on the input disc and the output disc respectively; further characterized in that: a first retaining ring is provided at one shaft end of the output disc, and a threaded hole is provided at one shaft end of the input disc, screws are sequentially covered with butterfly springs and washers, and screwed into the threaded holes and tightened, and the pin is connected to the input and output discs to form an integral rigid planetary carrier, and the thickness of the washers and the compression force of the butterfly springs are used to maintain a reasonable preload between the two main bearings, ensuring that the main bearings have high load characteristics;

[0034] The output disc is provided with multiple screw holes for connecting to the robot working machine;

[0035] (C) A clearance adjustment plate is provided between the outer side of the right tapered bearing and the right retaining ring. By varying the thickness of the adjustment plate, the left and right tapered bearings on the double eccentric input shaft can obtain a reasonable axial preload force, thereby improving the bearing load capacity;

[0036] (D) The first RN type bearing on the eccentric section b of the double eccentric input shaft cooperates with the center hole of the first cycloid wheel, and the second RN type bearing on the eccentric section c cooperates with the center hole of the second cycloid wheel. The RN type bearing is a cylindrical roller bearing without an outer ring.

[0037] (E) The input end of the double eccentric hollow shaft is connected to a driven gear, which is engaged with a driving gear on a servo motor or a stepper motor. The motor is connected to a circular end cover, which is connected to the end face of the hypocycloid gear ring to press the first main bearing.

[0038] The eccentric section b and the reverse eccentric section c are asymmetrical, that is, the phase difference is ≠180°, and the backlash is eliminated or reduced by using the gear anti-backlash principle, so that the backlash of the reducer is ≤1′.

[0039] The double eccentric hollow shaft input end is provided with an eccentric balancing gasket and a second retaining ring, and the second retaining ring is used to lock the position of the eccentric balancing gasket. The function of the eccentric balancing gasket is to eliminate the static imbalance of the input shaft, so that the double eccentric input shaft reaches static balance and avoids vibration when the input shaft rotates at high speed.

[0040] The dynamic load rating of the RN bearing on the double-eccentric hollow shaft of this invention is significantly greater than that of the needle roller bearing on the eccentric shaft of the existing RV reducer. Furthermore, bearing life is also related to the reducer's needle tooth center circle radius, eccentricity, short amplitude coefficient, and bearing force. Calculation results show that the precision service life of the RN bearing is 13,000 hours, as shown in the following table:

[0041] Swing arm bearing (kN) <![CDATA[L h =(10 6 / 60 nH )(Cr / R) 3.333 ]]> CQ-40 RN305E:Cr=38.5 13012(h) CQ-80 RN209E: Cr = 58.5 14353(h)

[0042] The pin is a hollow cylindrical sleeve. The good elasticity of the hollow cylindrical sleeve increases elastic deformation, so that multiple sleeves are evenly loaded, the load-balancing performance is improved, and the bearing capacity of the pin is increased.

[0043] The meshing components within the hypocycloid gear ring are lubricated with oil. Therefore, the housing is equipped with a refill hole, an oil drain hole, and a vent cap. The vent cap is used to maintain pressure balance between the inside and outside of the reducer and prevent oil leakage. Because these refill holes, oil drain holes, and vent caps can be installed in various ways, they are not individually labeled in the accompanying drawings.

[0044] Effects of the Invention

[0045] (1) Long life: The precision of the whole machine can maintain a service life of 11941h to 15919h, creating great economic value;

[0046] (2) Lightweight: The planetary stage in the existing RV reducer is deleted to achieve lightweight;

[0047] (3) Strong adaptability: The concave-convex double cycloid transmission structure increases the reduction ratio and improves the load-bearing capacity, making it more suitable for the cycloid joint module of humanoid robots;

[0048] (4) Low cost: shortens machining time, thereby reducing manufacturing costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 This is a schematic structural diagram of an embodiment of the present invention;

[0050] In the figure: circular housing 1, first main bearing 2, second main bearing 3, input disc 4, output disc 5, pin 6, first cycloid wheel 7, second cycloid wheel 8, spacer 9, double eccentric input shaft 10, left tapered bearing 11,

[0051] Right tapered bearing 12, first RN bearing 13, second RN bearing 14, eccentric balancing washer 15, butterfly spring 16, left retaining ring 17, screw 18, washer 19, gap adjustment plate 20, right retaining ring 21, pin hole 22, first retaining ring 23, oil seal 24, driving gear 25, driven gear 26, round end cover 27, second retaining ring 28.

[0052] Figures 2 to 4 This is a schematic diagram of the RV reducer invention patent structure disclosed by a Japanese company in the United States. DETAILED DESCRIPTION

[0053] In order to make the technical problems, technical solutions and beneficial effects to be solved by this application more clear, this application is further described in detail below with reference to the accompanying drawings and embodiments.

[0054] The terms "front, back, left, right, inside, outside" in this application are merely indications of the orientation or positional relationship based on the drawings and should not be understood as limitations on this application; the terms "first, second" and so on are merely marks of the components shown in the drawings and should not be understood as indicating or implying relative importance.

[0055] A robot long-life lightweight CQ double cycloid hollow reducer includes a hypocycloid ring gear 1 and a planetary carrier, a main bearing, a cycloid wheel, a double eccentric input shaft 10 and other parts arranged in the hypocycloid ring gear 1;

[0056] The inner holes on both sides of the hypocycloid gear ring 1 are respectively provided with the first main bearing 2 and the second main bearing 3. There is a raised annular belt between the two inner holes, on which are processed evenly distributed hypocycloid teeth, which mesh with the cycloid gear teeth.

[0057] The planet carrier includes an input disc 4, an output disc 5 and a pin 6;

[0058] The journals of the input disc 4 and the output disc 5 are respectively matched with the inner holes of the first main bearing 2 and the second main bearing 3, and the main bearings are radial thrust ball bearings or tapered roller bearings;

[0059] The cycloid wheel comprises a first cycloid wheel 7 and a second cycloid wheel 8. Pin holes 22 are evenly distributed around the center line of the cycloid wheel. The number of pin holes is an even number. This is because after the two cycloid wheels are integrally processed, one of the cycloid wheels can be turned over and assembled on the other side. A spacer 9 is provided between the two cycloid wheels.

[0060] The input end of the double eccentric input shaft 10 is supported by a left tapered bearing 11 in the center hole of the input disc 4, and the output end is supported by a right tapered bearing 12 in the center hole of the output disc 5. The outer axial sides of the two tapered bearings are respectively limited by a left retaining ring 17 and a right retaining ring 21. The tapered bearing is the abbreviation of a tapered roller bearing, and the retaining ring is the abbreviation of an elastic retaining ring for the hole.

[0061] The planet carrier, main bearing and double eccentric input shaft share a common center line a, and are characterized by:

[0062] (A) The eccentric section on the double eccentric input shaft 10 is connected to the cycloid gear via an RN bearing. The cycloid gear teeth engage the inner cycloid teeth to drive the planetary carrier to achieve transmission output, forming a single-stage cycloid reduction mechanism. The concave-convex double cycloid transmission structure is adopted to improve the load-bearing capacity.

[0063] (B) The pin 6 passes through corresponding pin holes 22 on the two cycloid wheels, and its two shaft ends are transitionally matched with corresponding holes on the input disc 4 and the output disc 5 respectively; further features: a first retaining ring 23 is provided at one shaft end of the output disc, and a threaded hole is provided at one shaft end of the input disc. Screws 18 are sequentially mounted on the butterfly spring 16 and the washer 19 and screwed into the threaded holes and tightened. The pin is connected to the input and output discs to form an integral rigid planetary carrier. The thickness of the washer 19 and the compression force of the butterfly spring 16 ensure that the two main bearings 2 and 3 are under a reasonable preload force, ensuring that the main bearings have high load characteristics;

[0064] The output disc 5 is provided with a plurality of screw holes for connecting the robot working machine;

[0065] (C) An adjustment sheet 20 is provided between the outer side of the right tapered bearing 12 and the right retaining ring 21. By varying the thickness of the adjustment sheet, the left and right tapered bearings on the double-eccentric input shaft 10 can be placed under a reasonable axial preload, thereby increasing the bearing load capacity.

[0066] (D) The first RN type bearing 13 on the eccentric section b of the double eccentric input shaft 10 cooperates with the center hole of the first cycloid wheel 7, and the second RN type bearing 14 on the eccentric section c cooperates with the center hole of the second cycloid wheel 8. The RN type bearing is a cylindrical roller bearing without an outer ring.

[0067] (E) The input end of the double eccentric hollow shaft 10 is connected to a driven gear 26, which is engaged with a driving gear 25 on a servo motor or a stepper motor. The motor is connected to a circular end cover 27, which is connected to the end face of the hypocycloid gear ring 1 to press the first main bearing 2.

[0068] The eccentric section b and the reverse eccentric section c are asymmetrical, that is, the phase difference is ≠180°, and the backlash is eliminated or reduced by using the gear anti-backlash principle, so that the backlash of the reducer is ≤1′.

[0069] An eccentric balancing gasket 15 and a second retaining ring 25 are provided at the input end of the double eccentric hollow shaft 10. The second retaining ring 25 is used to lock the position of the eccentric balancing gasket 15. The eccentric balancing gasket 15 eliminates the static imbalance between the eccentric section b and the eccentric section c of the double eccentric input shaft 10, thereby avoiding vibration when the input shaft rotates at high speed.

[0070] The RN bearings used in the dual-eccentric input shaft 10 of the CQ reducer of this invention have a significantly greater dynamic load rating than the needle roller bearings used in the eccentric shafts of existing RV reducers. Furthermore, bearing life is also related to the needle tooth center radius, eccentricity, short-amplitude coefficient, and bearing force. Calculation results for the RN bearing life are shown in the following table:

[0071] Theoretical calculated life of RN type bearing of CQ reducer of the present invention (h)

[0072] Reducer model CQ6 CQ20 CQ40 CQ80 CQ110 CQ160 CQ320 CQ450 RN bearing life 13036 15866 13012 14353 13255 13582 11941 15919

[0073] The pin is a hollow cylindrical sleeve 6. The elastic deformation of the hollow cylindrical sleeve 6 is utilized to improve the load-balancing performance of the multiple sleeves and increase the bearing capacity of the pin.

[0074] The meshing components within the hypocycloid gear ring 1 are lubricated with oil, rather than the specialized grease used in existing RV reducers. Therefore, the housing is equipped with a refill port, an oil drain port, and a vent cap. The vent cap ensures pressure balance between the inside and outside of the reducer to prevent oil leakage. Because these ports, drain ports, and vent caps can be installed in various ways, they are not individually labeled in the accompanying drawings.

[0075] The article "Tesla Humanoid Robot...Domestic Components Expected to Continue Gains" published on October 21, 2022, points out:

[0076] (1) RV reducers: They have high rigidity and strong impact resistance, and are mainly used in heavy-load areas such as arms, shoulders, and legs. The market size of RV reducers for humanoid robots is estimated to reach RMB 12.2 billion by 2030.

[0077] (2) Harmonic reducers: These are generally used for light loads such as forearms, wrists, or hands. The market size of harmonic reducers for humanoid robots is estimated to reach RMB 9.3 billion by 2030.

[0078] in conclusion

[0079] "Ten Strategic Industries: The main technical indicators of key robot components have reached the international leading level, the robot cycloid reducer has a backlash of ≤1 arc min and a service life of ≥6000 hours"

[0080] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by any technician familiar with this technical field within the technical scope disclosed by the present invention should be covered by the protection scope of the present invention.

[0081] Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A robot long-life lightweight CQ double cycloid hollow reducer, comprising a hypocycloid ring gear (1) and a planetary carrier, a main bearing, a cycloid wheel, a double eccentric hollow shaft (10) and other parts arranged in the hypocycloid ring gear (1); The inner holes on both sides of the hypocycloid gear ring (1) are respectively provided with a first main bearing (2) and a second main bearing (3), and a raised annular belt is provided between the two inner holes. The annular belt is provided with hypocycloid teeth, and the hypocycloid teeth mesh with the cycloid wheel teeth; The planet carrier comprises an input disc (4), an output disc (5) and a pin (6); The journals of the input disc (4) and the output disc (5) are respectively matched with the inner holes of the first main bearing (2) and the second main bearing (3), and the main bearings are radial thrust ball bearings or tapered roller bearings; The cycloid wheel comprises a first cycloid wheel (7) and a second cycloid wheel (8), the cycloid wheels are provided with pin holes (22) evenly distributed around the center line, the number of the pin holes is an even number, and a spacer (9) is provided between the two cycloid wheels; The input end of the double eccentric hollow shaft (10) is supported by a left tapered bearing (11) in the center hole of the input disc (4), and the output end is supported by a right tapered bearing (12) in the center hole of the output disc (5). The outer sides of the two tapered bearings are axially limited by a left retaining ring (17) and a right retaining ring (21). In this article: tapered bearing is the abbreviation of tapered roller bearing, retaining ring is the abbreviation of elastic retaining ring for hole; The planet carrier, main bearing and double eccentric hollow shaft (10) have a common center line a, and are characterized by: (A) The eccentric section on the double-eccentric hollow shaft (10) is connected to the cycloid wheel through the RN bearing, and the cycloid wheel teeth mesh with the inner cycloid teeth to drive the planetary carrier to achieve transmission output, forming a single-stage cycloid reduction mechanism; a concave-convex double cycloid transmission structure is adopted to improve the bearing capacity; (B) The pin (6) passes through the corresponding pin holes (22) on the two cycloid wheels, and its two shaft ends are respectively transitionally matched with the corresponding holes on the input disc (4) and the output disc (5); further features: A first retaining ring (23) is provided at one shaft end of the output disc, a threaded hole is provided at one shaft end of the input disc, a screw (18) is sequentially sleeved with a butterfly spring (16) and a washer (19), screwed into the threaded hole and tightened, and a pin is connected with the input and output discs to form an integral rigid planetary carrier; The output disc (5) is provided with a plurality of screw holes for connecting to the robot working machine; (C) A clearance adjustment sheet (20) is provided between the outer side of the right tapered bearing (12) and the right retaining ring (21), and by changing the thickness of the adjustment sheet, the left and right tapered bearings can obtain a reasonable axial preload force; (D) The first RN type bearing (13) on the eccentric section b of the double eccentric hollow shaft (10) is matched with the center hole of the first cycloid wheel (7), and the second RN type bearing (14) on the eccentric section c is matched with the center hole of the second cycloid wheel (8). The RN type is a cylindrical roller bearing without an outer ring; (E) The input end of the double eccentric hollow shaft (10) is connected to a driven gear (26), which is engaged with a driving gear (25) on a servo motor or a stepper motor. The motor is connected to a circular end cover (27), which is connected to the end face of the hypocycloid gear ring (1) to press the first main bearing (2).

2. The robot long-life lightweight CQ double cycloid hollow reducer according to claim 1 is characterized by: The eccentric section b and the reverse eccentric section c are asymmetrical, that is, the phase difference is ≠180°, and the backlash is eliminated or reduced by using the gear anti-backlash principle.

3. The robot long-life lightweight CQ double cycloid hollow reducer according to claim 1 or 2, characterized in that: An eccentric balancing gasket (15) and a second retaining ring (28) are provided at the input end of the double-eccentric hollow shaft (10), and the position of the eccentric balancing gasket (15) is locked by the second retaining ring (28).

4. The robot long-life lightweight CQ double cycloid hollow reducer according to claim 1, 2 or 3, characterized in that: The pin is a hollow cylindrical sleeve (6) to increase elastic deformation and make multiple sleeves evenly loaded.

5. The robot long-life lightweight CQ double cycloid hollow reducer according to any one of claims 1 to 4, characterized in that: The meshing parts in the hypocycloid gear ring (1) are lubricated with oil, so a refueling hole, an oil drain hole and a vent cap are provided on the casing. The vent cap is used to ensure the pressure balance between the inside and outside of the reducer to prevent oil leakage.

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