Pin gear of high-precision RV speed reducer

Abstract

The invention discloses a pin gear of a high-precision RV speed reducer, and relates to the field of speed reducer pin gear design. Based on the contact characteristics between pin gear housings, the tightness of meshing and gaps between involute tooth profiles is analyzed, the shape design of the pin gear is optimized, and the pin gear of a vertically symmetrical segmented structure is designed, namely, the upper half part is in a circular arc drum shape, and the lower half part is in a circular arc drum shape; the contact stress distribution of the pin gear and the pin gear housing is effectively improved, automatic centering and error compensation are achieved, lubrication is optimized, the involute tooth profile of the lower half portion is achieved, transmission and movement stability are effectively and accurately achieved, load sharing is optimized, and edge contact is avoided. Based on the meshing area and load stress distribution of the pin teeth and the involute gear, the design of the number of the pin teeth is optimized, the contact pressure of a single pin tooth is reduced, and therefore abrasion is reduced; the 18CrNiMo7-6 steel is selected to manufacture the pin gear, the heat treatment process is optimized, and the effects of reducing the material consumption, reducing the weight, enhancing the flowing of internal lubricating oil, reducing the temperature rise and reducing the heat treatment deformation risk can be achieved.

Description

Technical Field

[0001] The present invention relates to the field of mechanical transmission technology, and in particular to the high-precision design of a pin tooth component in an RV reducer. The invention aims to improve the transmission accuracy and stability of the RV reducer by optimizing the structure, number and material of the pin teeth. Background Art

[0002] RV reducers, as high-precision, high-reliability mechanical transmission devices, are widely used in industrial robots, precision machine tools, and automated equipment. Pin teeth, a key component in RV reducers, have a direct impact on the performance of the entire reducer due to their precision and stability. However, traditional pin tooth designs often present challenges such as difficult machining and limited precision. This leads to transmission errors and vibrations in RV reducers over long periods of use, compromising the accuracy and stability of the equipment. Therefore, the present invention designs a high-precision pin tooth for RV reducers. Summary of the Invention

[0003] The purpose of the present invention is to solve the problems in the prior art and to propose a high-precision pin gear for an RV reducer.

[0004] A high-precision RV reducer pinion tooth, the pinion tooth adopts an upper and lower symmetrical segmented structure, including an upper half and a lower half, the upper half is a drum shape with a slightly larger diameter in the middle and slightly smaller at both ends, and the lower half is an involute tooth profile, wherein the involute tooth profile portion in the lower half is responsible for the main torque transmission, and its meshing characteristics include high overlap and load dispersion, while the drum shape in the upper half adopts local conjugate correction, optimizes the contact area through Hertz contact theory, and mainly bears radial force, realizes functional zoning, and extends the overall life.

[0005] In the design of the above-mentioned high-precision RV reducer pin teeth, the surface roughness of the pin teeth is reduced from Ra≤3.2μm to Ra≤0.4μm.

[0006] In the design of the above-mentioned high-precision RV reducer pin teeth, the main calculation formulas for the upper and lower symmetrical segmented structure of the pin teeth include:

[0007] Involute equation:

[0008]

[0009] where r bg : Gear base circle radius, θ: Development angle (radians);

[0010] Arc radius:

[0011]

[0012] The parametric equation form of the arc drum shape is:

[0013]

[0014] R: Radius of the drum arc, r p : Needle tooth radius, △: drum shape, φ: angle parameter φ, δ: center offset.

[0015] In the design of the pin teeth of the above-mentioned high-precision RV reducer, the number of pin teeth in the pin gear housing is optimized based on increasing the total meshing area, making the load distribution more uniform, reducing the contact pressure of a single pin tooth, thereby reducing wear, and the meshing area is increased by:

[0016]

[0017] Where: η is the area increase ratio, A is the meshing area after the number of pin teeth, and the formula for unit area pressure P is: Where: F is the meshing force and A is the meshing area.

[0018] In the design of the above-mentioned high-precision RV reducer needle teeth, the needle teeth are made of 18CrNiMo7-6 alloy steel, and the needle teeth are subjected to appropriate heat treatment to improve the material structure and mechanical properties, increase the hardness and toughness of the needle teeth, and improve the load-bearing capacity and wear resistance of the needle teeth.

[0019] In the design of the above-mentioned high-precision RV reducer needle teeth, the needle teeth adopt precision machining technology and CNC grinding to ensure that the machining accuracy and surface roughness of the needle teeth meet the design requirements; during the machining and assembly process of the needle teeth, high-precision measurement technology is adopted, and a three-coordinate measuring instrument is used to accurately measure the size and shape of the needle teeth to ensure the accuracy and assembly quality of the needle teeth.

[0020] Compared with the existing technology, the advantages of the present invention are:

[0021] 1. Improve transmission accuracy: By optimizing the structure, material and manufacturing process of the needle teeth, the RV reducer needle teeth of the present invention have higher processing accuracy and assembly accuracy, which can significantly improve the transmission accuracy and stability of the RV reducer.

[0022] 2. Enhanced load-bearing capacity: The needle teeth are made of high-strength and high-hardness materials and subjected to appropriate heat treatment, which significantly improves the load-bearing capacity and wear resistance of the needle teeth and extends the service life of the RV reducer.

[0023] 3. Reduce vibration and noise: The optimized needle tooth structure and manufacturing process can reduce errors and vibrations during the transmission process, reduce the noise level of the RV reducer, and improve the operation quality of the equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1Schematic diagram of the RV reducer structure in the present invention;

[0025] Figure 2 Schematic diagram of the surface metallographic structure of 18CrNiMo7-6 steel obtained by heat treatment of the present invention;

[0026] Figure 3 This is a wear morphology diagram of 18CrNiMo7-6 steel obtained by heat treatment according to the present invention;

[0027] Figure 4 This is a front view of the needle teeth with upper and lower symmetrical segmented structures according to the present invention;

[0028] Figure 5 A three-dimensional diagram of the needle teeth of the present invention with a symmetrical upper and lower segmented structure;

[0029] Figure 6 This is a diagram of the meshing of the pin teeth and the gear of the present invention.

[0030] In the figure: 1 involute center gear, 2 involute planetary gears, 3 crankshaft, 4 cycloid gear, 5 pinion gear, 6 output disc, 7 pinion gear housing. DETAILED DESCRIPTION

[0031] Reference Figure 1-6 The present invention provides a high-precision RV reducer pinion gear, wherein reference is made to Figure 1 The figure shows the structural design of the RV reducer, which includes an involute center gear 1, an involute planetary gear 2, a crank shaft 3, a cycloid gear 4, a pinion gear 5, an output disc 6 and a pinion gear housing 7. The pinion gear 5 adopts a pinion gear with a symmetrical upper and lower segmented structure. The segmented design can optimize the pressure angle or shape of the involute segment separately to further reduce transmission fluctuations. It includes an upper half and a lower half. The upper half is a drum shape with a slightly larger diameter in the middle and slightly smaller diameters at both ends. The lower half is an involute tooth shape. The involute tooth shape part in the lower half is responsible for the main torque transmission. Its meshing characteristics include high overlap. It can disperse the load, and the arc drum design in the upper part changes the contact between the needle teeth and the needle tooth housing 7 from line contact to local point contact or an optimized elliptical contact area, which can significantly reduce the Hertzian contact stress, avoid edge stress concentration, and reduce the risk of wear and pitting corrosion; the arc surface of the drum structure can adapt to the slight installation deviation or deformation of the needle tooth housing, and realize load uniformity through self-adjustment of the contact area, thereby improving the system rigidity and reducing the stringent requirements for processing accuracy; the arc contact area is more likely to form an elastic fluid dynamic lubrication (EHL) oil film, reducing friction loss, and is particularly suitable for high-speed or heavy-load conditions.

[0032] In this application, the main goal is to optimize the shape of the needle teeth 5: the needle teeth 5 are symmetrically divided into sections along the axial direction (the upper half is an arc drum shape, and the lower half is an involute tooth shape). The upper half has a slightly larger diameter in the middle and slightly smaller diameters at both ends, forming a slightly outwardly bulging drum shape 5, while the lower half is designed as an involute tooth shape. The following are the calculations for the design of the needle teeth 5:

[0033] (1) Involute gear meshing with the involute portion of the pinion 5

[0034] In this embodiment, the pitch circle diameter is set to: d g =mZ g =1.5×39mm=58.5mm

[0035] The base circle diameter is set to: d bg =d g cosα=58.5×cos20°mm≈54.97mm

[0036] The diameter of the tooth tip circle is set to: d′ ag =d ag -2δ=m(Z g +2)-2×0.06m=[1.5×(39+2)-2×0.06×1.5]mm=61.32mm(considering the trimming amount)

[0037] The root diameter is set to: d fg =d g -2.5mm=(58.5-2.5×1.5)m=54.75mm

[0038] Then the gear involute equation is: Involute equation (parameterized)

[0039] θ: expansion angle (radians), must satisfy

[0040] Polar coordinate form:

[0041]

[0042] Valid values of θ:

[0043] Starting point: base circle (θ=0)

[0044] End point: at the tooth top circle:

[0045]

[0046] Maximum expansion angle:

[0047] A safety margin of 0.094 rad is left to avoid tooth tip edge contact, so θ∈[0,0.4]rad

[0048]

[0049] (2) Involute tooth profile design of the lower half of the pin tooth 5

[0050] Pitch circle diameter: d c =mZ c =1.5×40mm=60mm

[0051] Base circle diameter: d bc =d c cosα=60×cos20°mm≈56.38mm

[0052] Tip circle diameter:

[0053] Root circle radius:

[0054]

[0055] Radius of needle tooth 5: r p =1.5m=1.5×1.5mm=2.25mm

[0056] θ range of the involute segment of needle tooth 5

[0057] Meshing limit calculation: maximum expansion angle θ max

[0058] The radius of the center track of needle tooth 5:

[0059] Maximum meshing radius r1 = R + r P =(30.45+2.25)mm=32.7mm

[0060] So the maximum expansion angle is:

[0061] Leave a safety margin of 0.047rad, so take: θ max =0.6rad

[0062] Tooth root transition curve processing:

[0063] when

[0064] Transition curve type: Hob corner transition (ISO standard): ρ a =0.38m=0.38×1.5mm=0.57mm

[0065] Parametric equations:

[0066]

[0067] Minimum expansion angle θ min :

[0068] Initial contact point between the gear and the pinion 5: When the top circle of the gear and the involute of the pinion 5 first come into contact, the meshing begins. At this time, the meshing point satisfies: r2=r′ ag -r P =(30.66-2.25)mm=28.41mm

[0069]

[0070] so

[0071] Taking into account:

[0072] Assembly error: ±0.005rad

[0073] Elastic deformation: The needle teeth 5 deflect slightly under load (about 0.002rad)

[0074] Lubricating film thickness: Angle compensation corresponding to the minimum oil film thickness (approximately 0.001rad)

[0075] So the comprehensive safety margin is:

[0076] θ min =(0.262+0.005+0.002+0.001)rad=0.27rad

[0077]

[0078] (3) Meshing characteristics analysis

[0079] Contact angle α=20°, α c , α g is the tooth tip pressure angle

[0080]

[0081] End face overlap:

[0082]

[0083] High transmission stability.

[0084] (4) The upper part of the needle tooth 5 is designed in an arc drum shape

[0085] The arc drum shape of the upper part has a certain curvature. The curvature of the needle tooth 5 is the curvature radius or curvature shape of the surface of the needle tooth 5. The needle tooth 5 is designed to be drum-shaped in order to reduce contact stress and improve meshing performance. The curvature of the needle tooth 5 is mainly based on the following geometric relationships and design principles:

[0086] Take the drum shape amount △=0.06m=0.06×1.5mm=0.09mm

[0087] Arc radius:

[0088] Center offset: δ = r p -R+△=(2.25-28.17+0.09)mm=-25.83mm

[0089] Arc drum coordinate equation

[0090] Local coordinate system definition:

[0091] Origin: The intersection of the needle tooth 5 axis and the drum symmetry plane

[0092] Y axis: radially outward along the needle teeth 5 (drum-shaped protrusion direction)

[0093] x-axis: the horizontal direction perpendicular to the y-axis

[0094] Cross-sectional profile equation:

[0095] The center of the arc is at:

[0096] (0, δ) = (0, -25.83): (x-δ) 2 +y 2 =R 2

[0097] Parametric equation form (angle parameter φ starts from the negative semi-axis):

[0098]

[0099] Right now:

[0100]

[0101] Starting angle (drum bottom):

[0102]

[0103] End angle (top of drum):

[0104]

[0105] Table 1

[0106]

[0107] Drum height:

[0108] y max -y min =(2.34-2.2497)mm=0.0903

[0109] The unilateral drum volume is strictly established.

[0110] The basis for taking drum volume △ = 0.06m

[0111] Elastic deformation compensation

[0112] Estimation of the bending deformation of the needle tooth 5 (cantilever beam model):

[0113]

[0114] Single tooth load F n : Load distribution assumes that 40% of the teeth 5 participate in the load

[0115] Z′=Z c × 40% = 40 × 0.4 = 16

[0116]

[0117] Cantilever length l: The total length of the needle tooth 5 is L = 20 mm. The effective meshing area is usually the middle 50% to 60% (avoiding edge contact). Assuming that the meshing is concentrated within the range of ±4 mm in the middle of the needle tooth 5, the cantilever length is:

[0118] l = 50% × (total length of needle teeth L - width of meshing area) = 0.5 × (20-4) mm = 8 mm

[0119] Since the material of the needle tooth 5 is 18CrNiMo7-6, its elastic modulus is:

[0120] E1=205GPa

[0121] Section moment of inertia:

[0122]

[0123] so:

[0124]

[0125] Taking the impact coefficient as 1.5, we have:

[0126] δ bend,max =1.5δ bend =1.5×0.0442mm=0.0663mm

[0127] Comprehensive compensation requirements:

[0128] 1. Elastic deformation compensation:

[0129] δ bend,max =0.0663mm,

[0130] 2. Thermal deformation (△T = 40℃): Linear expansion coefficient of material 18CrNiMo7-6:

[0131] α=11.5×10 -6 / ℃

[0132] δ thermal =α·△T·l=11.5×10 -6 ×40×8mm=0.00368mm

[0133] 3. Assembly error (ISO 5): ±0.015mm, so the total drum volume

[0134] △ required =δ bend,max +δ thermal +0.015=(0.0663+0.00368+0.015)m

[0135] =0.08498mm

[0136] So take △ required =0.09mm=0.06m

[0137] (5) Strength verification

[0138] ①Contact stress

[0139] Single tooth load F n : Load distribution assumes that 40% of the teeth 5 participate in the load

[0140] Z′=Z c × 40% = 40 × 0.4 = 16

[0141]

[0142] Comprehensive curvature radius: Actual meshing situation: Involute part contact (lower half):

[0143]

[0144] Drum contact (upper part):

[0145]

[0146] Conservative calculation takes the maximum value:

[0147]

[0148] Elastic modulus: Needle tooth 5 (18CrNiMo7-6):

[0149] E1=205GPa,ν1=0.3

[0150] Gear (20CrMnTi): E2 = 207 GPa, ν2 = 0.3

[0151]

[0152] Contact line length b1:

[0153] b1≈0.5×total length of needle teeth-2△=(0.5×20-2×0.09)mm=9.82mm

[0154] Round b1 = 10 mm

[0155] Contact stress:

[0156]

[0157] 18CrNiMo7-6 H ]=1.8GPa

[0158] σ H <[σ H ],Reasonable

[0159] ②Bending strength

[0160]

[0161] Tangential force F distributed to a single tooth t

[0162] Determine the input torque T input

[0163]

[0164] Output torque T output

[0165] T output =T input ×i×η=25.47×50×0.9N·m=1146.15N·m Consider the load distribution unevenness coefficient K A (generally 1.2~1.5), take K A =1.3

[0166] So the tangential force distributed to a single tooth is:

[0167]

[0168] Gear tooth width b2: ψ m : Tooth width coefficient, usually 6 to 12, take ψ m =10

[0169] b2=ψ m m = 10 × 1.5 mm = 15 mm

[0170] Tooth form factor: Gear: Y Fg =2.32

[0171] Needle tooth 5: Y Fc =2.07

[0172] Stress correction factor: Gear: Y Sg =1.85

[0173] Needle tooth 5: Y Sc =1.7

[0174] Coincidence coefficient:

[0175]

[0176] Allowable bending stress: gear (20CrMnTi):

[0177] σ FP1 =400MPa (after carburizing and quenching)

[0178] Needle tooth 5 (18CrNiMo7-6):

[0179] σ FP2 =450MPa (after carburizing and quenching)

[0180] Gear calibration:

[0181]

[0182] Safety factor:

[0183] (Satisfy S F ≥2.0)

[0184] Needle tooth 5 calibration:

[0185]

[0186] Safety factor:

[0187] (Satisfy S F ≥2.0)

[0188] ③Fatigue limit

[0189] Size factor Y x : Take 0.95

[0190] Surface quality coefficient Y Z :Take 1.0 (grinding)

[0191] Lifespan Y N : Take 1.0 (infinite lifespan)

[0192] σ′ FP =σ FP ·Y x ·Y Z ·Y N

[0193] gear

[0194] σ′ FPg =σ FPg1 ·Y x ·Y Z ·Y N =400×0.95×1×1MPa=380MPa Needle tooth 5:

[0195] σ′ FPc =σ FPg2 ·Y x ·Y Z ·Y N =450×0.95×1×1MPa=427.5MPa

[0196] Check: Gear:

[0197] σ Fg =172.91MPa<σ′ FPg =380MPa

[0198] Needle tooth 5:

[0199] σ Fc =141.77MPa<σ′ FPc =427.5MPa

[0200] The shape of the upper and lower segmented structure needle teeth 5 is as follows Figure 4 、 Figure 5 This optimizes the shape design of the needle tooth 5, making it mesh more closely with the gear, reducing meshing clearance and improving transmission accuracy.

[0201] The tightness of the meshing and clearance between the pinion 5 and the gear, the total number of pinion 5 in the RV reducer Z c and the number of gear teeth Z g Best Relationships:

[0202] Z c =Z g +1

[0203] Deduced through the gear meshing principle and kinematic analysis. The meshing of the gear and the pinion 5 needs to meet the following conditions: Continuous meshing: Each tooth of the gear must be able to mesh smoothly with the pinion 5 to ensure the continuity of the transmission; Uniform load distribution: Multiple teeth are involved in the meshing at the same time to share the load and reduce the wear of a single tooth; Single tooth difference meshing: In order to ensure the smoothness and accuracy of the transmission, the number of teeth of the pinion 5 should always be 1 more than the gear. Kinematic analysis: The relative motion between the gear and the pinion 5: The gear rotates around its own axis and revolves around the center of the pinion 5 at the same time. Due to the number of teeth Z of the gear g and needle teeth 5 number Z c Different, the angle of rotation of the gear for each revolution is:

[0204]

[0205] Conditions for single tooth difference meshing: In order to achieve single tooth difference meshing, the angle of rotation of the gear should be equal to the angle of one tooth for each revolution of the gear, that is:

[0206]

[0207] Combining the two formulas, we get:

[0208]

[0209] After simplification, we get: Z c =Z g +1.

[0210] The parameters of the RV reducer in this invention are as follows: output torque T = 500 N m, transmission ratio i = 50, pitch circle diameter of needle teeth 5 D = 60 mm, diameter of needle teeth 5 d = 5 mm, minimum gap △ between needle teeth 5 = 0.2 mm, transmission accuracy requirement: hysteresis less than 1 arcmin, radius of needle teeth 5: r p =2.25mm, gear tooth profile radius: r=2.6mm, number of pin teeth 5 Z c =40, number of gear teeth: Z g =39, the number of pin teeth 5 engaged at the same time: 16; the theoretical clearance between the pin teeth 5 and the gear: δ = rr p =0.1mm; processing error △r p =0.02mm, assembly error △r c =0.03mm. The actual clearance will be affected by machining error, assembly error and wear, so the actual clearance is: δ 实际 =δ+△r p +△r c =0.1mm+0.02mm+0.03mm=0.15mm. The meshing tightness can be measured by the ratio of the actual gap to the radius of the needle teeth 5, that is, The smaller the value, the tighter the meshing.

[0211] 2. Determine the optimal number of needle teeth 5, based on increasing the total meshing area, making the load distribution more uniform, reducing the contact pressure of a single needle tooth 5, and thus reducing wear. The number of needle teeth 5 is Z c =40, check the clearance of needle teeth 5: Meet the minimum clearance requirement, then you can c =40 up and down to try to determine whether Z c =40 is the best number of needle teeth. The data are shown in Table 2 below:

[0212] Table 2

[0213] <![CDATA[Number of pin teeth 5, Z c > 37 38 39 40 41 42 43 Needle tooth 5 gap △ 0.59 0.46 0.33 0.21 0.09 -0.01 -0.12

[0214] From the table above, we can see that when the number of needle teeth 5 is Z c =37~40, pd>△ min =0.2mm, both meet the minimum clearance requirement; when the needle teeth 5 number Z c =41~43, pd<△ min =0.2mm, neither of which meets the minimum clearance requirement. Therefore, it can be concluded from the table that the optimal number of pin teeth 5 of the RV reducer of the invention is Z c = 40. The optimal number of needle teeth 5 also optimizes the increase in the total meshing area, reduces the contact pressure of a single needle tooth 5, and reduces wear.

[0215] Reduce the contact pressure of a single needle tooth 5: Assume that the total number of needle teeth 5 is Z c1 =36, number of gear teeth Z g1 =37, effective length of the needle tooth 5 L = 20mm, contact width W = 1mm; initial meshing area: number of needle teeth 5 simultaneously engaged n1 = 18, contact area of a single needle tooth 5 A = L × W = 20mm × 1mm = 20mm 2 , total meshing area A1=n1×A=18×20mm=360mm 2 , the meshing area after increasing the number of pin teeth 5: the number of pin teeth 5 increases to Z c =40, then the number of pin teeth 5 that are simultaneously engaged is n2 = 20, and the number of gear teeth Z g =39, total meshing area A2 = n2 × A = 20 mm × 20 mm = 400 mm 2 ; Increase ratio of meshing area The formula for unit area pressure P is: F is the meshing force and A is the meshing area. A1=360mm 2 ,but After increasing the number of pin teeth 5, P2 < P1, so the contact pressure of a single pin tooth 5 is reduced.

[0216] Select 18CrNiMo7-6 alloy steel, a high-strength and high-hardness material, to manufacture the pin teeth 5, improving the bearing capacity and wear resistance of the pin teeth 5. Normalizing: Place the 18CrNiMo7-6 steel in a heating furnace, raise the temperature to 900 °C, and hold for 2 h; Carburizing: Transfer the normalized 18CrNiMo7-6 steel to a carburizing furnace and carburize for 20 h at a temperature of 930 °C; Quenching: First, hold the carburized 18CrNiMo7-6 steel at a temperature of 850 °C for 1 - 1.5 h, perform air quenching in the air, then hold at a temperature of 850 °C for 2 - 2.5 h, and perform oil quenching in an oil medium; Tempering: Temper the quenched 18CrNiMo7-6 steel at a temperature of 200 °C for 2 h. Further, the specific process of first air quenching and then oil quenching in the quenching is: Hold the carburized 18CrNiMo7-6 steel at a temperature of 850 °C for 1 - 1.5 h, perform air quenching in the air, and then hold the carburized 18CrNiMo7-6 steel at a temperature of 850 °C for 2 - 2.5 h, and perform oil quenching in an oil medium. Further, in the normalizing, the 18CrNiMo7-6 steel is placed in a heating furnace, the temperature is raised to 900 °C, and held for 2 h. Further, in the carburizing, the normalized 18CrNiMo7-6 steel is transferred to a carburizing furnace and carburized for 20 h at a temperature of 930 °C. Further, in the tempering, the quenched 18CrNiMo7-6 steel is tempered at a temperature of 200 °C for 2 h. Further, in the carburizing, the strong carburizing holding time is set to 12 h, and the carbon potential is 1.1 - 1.2%; the diffusion holding time is 8 h, and the carbon potential is 0.8 - 0.9%. Application of the 18CrNiMo7-6 steel obtained by the above heat treatment method on the pin teeth 5 of the RV reducer. Conduct friction and wear test analysis, using ball-on-disk friction, with a load of 100 N, a rotational speed of 300 rpm, and a time of 30 min. The result is a wear amount of 7.1 g. Observe the wear morphology, and the wear scar depth is approximately 13 μm.

[0217] Improve the machining accuracy: Select a high-precision CNC machine tool and use cemented carbide cutting tools for machining. Determine the optimal cutting speed, feed rate, and cutting depth through experiments. The cutting speed may be set to 120 m / min, the feed rate is 0.1 mm / rev, and the cutting depth is 1 mm.

[0218] Improve surface roughness: In order to reduce surface roughness, the cutting speed can be appropriately increased to 150m / min, while the feed rate can be reduced to 0.08mm / rev. The cutting depth remains unchanged or is slightly adjusted, and the machined surface roughness reaches Ra≤3.2μm; during the processing, high-performance cutting fluids such as synthetic cutting fluids or extreme pressure cutting fluids are used to reduce cutting temperature and friction coefficient, reduce tool wear and workpiece deformation; use a diamond grinding wheel for grinding to make the surface roughness of the needle tooth 5 reach Ra≤0.4μm.

[0219] Ensure the accuracy and assembly quality of the needle tooth 5: Use a three-dimensional coordinate measuring machine to accurately measure the size and shape of the needle tooth 5. Check the equipment to ensure that the power supply, grating or laser, and distance measurement system of the three-dimensional coordinate measuring machine are operating normally; calibrate the equipment according to the calibration method provided by the manufacturer to ensure the accuracy of the measurement results; prepare the sample and place the needle tooth 5 to be measured on the workbench to ensure that its surface is flat, free of oil and scratches, etc.; start the power supply and turn on the equipment according to the requirements of the equipment manual; select the appropriate measurement mode and three-dimensional space measurement according to the characteristics and requirements of the needle tooth 5; adjust the parameters of the grating or laser, pulse width, power, etc. according to the actual measurement conditions to obtain the best measurement effect, select a suitable point on the needle tooth 5 as a reference, establish a measurement coordinate system, and use the probe of the three-dimensional coordinate measuring machine to measure points on the surface of the needle tooth 5. For key size and shape features, it is necessary to increase the point density to improve measurement accuracy; aim the grating or laser at the needle tooth 5 to be measured, start the measurement program, and wait for the measurement to be completed. After the measurement is completed, data processing is performed based on the measured data to obtain information such as the size and shape of the needle teeth 5, as follows Figure 4 As shown in Table 3:

[0220] Table 3

[0221] Measurement items Measuring point Measurement value (mm) Allowable tolerance (mm) Remark highest point diameter Section 1 4.632 ±0.005 average value length full length 20.005 ±0.01 - surface roughness Area 1 Ra0.4 Ra0.4 - surface roughness Area 2 Ra0.4 Ra0.4 -

[0222] 6. Basis for selecting the number of holes:

[0223] Dynamic balance: The number of holes is usually 4 to 6 (even number symmetry to avoid dynamic imbalance)

[0224] Strength verification: hole edge stress concentration factor K t ≤2.0, must meet the following requirements:

[0225] (A net : Net cross-sectional area)

[0226] The basis for taking the number of holes as 6:

[0227] Symmetry: Six holes (60° intervals) form a hexagonal support structure, evenly transferring the load to the gear tooth root and avoiding the local high stress problem of four holes (90° intervals). Six holes can completely offset the 2nd to 5th order centrifugal force harmonics, and the measured vibration acceleration is 42% lower than that of four holes (ISO 10816 standard).

[0228] Critical speed: The first-order critical speed reaches 6500Hz, far away from the meshing frequency.

[0229] Indexing efficiency: 60° intervals can be completed with a standard indexing plate in one clamping, saving 25% of working hours compared to 8 holes (45°).

[0230] Tolerance control: Hole position accuracy of ±0.02mm is easily guaranteed (the error of 8 holes increases by 30% due to tool wear).

[0231] Finite element data comparison:

[0232] Number of holes Maximum stress (MPa) Stress nonuniformity coefficient 4 210 1.25 6 175 1.10 8 180 1.15

[0233] It was found that the maximum stress of the 6-hole solution was reduced by 16.7% and the distribution was smoother.

[0234] For 20CrMnTi carburized and quenched gears, the allowable stress [σ] is ≈ 450 MPa.

[0235] The number of holes is 6; the hole diameter is usually (0.2-0.3) × web width. If the web width is 20mm, the hole diameter is 0.3 × 20mm = 6mm; hole distribution: evenly distributed on the pitch circle diameter (PCD), PCD ≈ 0.7 × gear outer diameter; hole edge chamfer: C0.5 ~ C1

[0236] Related calculations:

[0237]

[0238] Take the concentrated stress coefficient K t =2.0

[0239]

[0240] Yield strength σ of 20CrMnTi material S =850MPa

[0241] Safety factor:

[0242]

[0243] It is understood from common technical knowledge that the present invention may be implemented by other embodiments that do not depart from its spirit or essential features. Therefore, the embodiments disclosed above are, in all respects, merely illustrative and not exclusive. All modifications within the scope of the present invention or equivalent to the scope of the present invention are intended to be encompassed by the present invention.

Claims

1. A high-precision RV reducer pinion gear, characterized in that: The invention comprises an involute center wheel (1), an involute planetary wheel (2), a crank shaft (3), a cycloid wheel (4), a pinion (5), an output disc (6) and a pinion housing (7). The pinion (5) adopts a pinion with an upper and lower symmetrical segmented structure, including an upper half and a lower half. The upper half is a drum with a slightly larger diameter in the middle and slightly smaller diameters at both ends, and the lower half is an involute tooth profile. The involute tooth profile in the lower half is responsible for the main torque transmission, and its meshing characteristics include high overlap and load dispersion, while the drum profile in the upper half adopts local conjugate correction, optimizes the contact area through Hertz contact theory, and mainly bears radial force, thereby realizing functional partitioning and extending the overall life.

2. The pin gear of a high-precision RV reducer according to claim 1, characterized in that: The surface roughness of the needle teeth (5) is reduced from Ra≤3.2μm to Ra≤0.4μm.

3. The pin gear of a high-precision RV reducer according to claim 1, characterized in that: The main calculation formulas for the upper and lower symmetrical segmented structure of the needle teeth (5) include: Involute equation: where r bg : Gear base circle radius, θ: Development angle (radians); Arc radius: The parametric equation form of the arc drum shape is: R: Radius of the drum arc, r p : Needle tooth radius, △: drum shape, φ: angle parameter φ, δ: center offset.

4. The pin gear of a high-precision RV reducer according to claim 1, characterized in that: The number of pin teeth in the pinion housing is optimized to increase the total meshing area, resulting in a more uniform load distribution and reduced contact pressure on individual pin teeth, thereby reducing wear. The meshing area is increased by: Where: η is the area increase ratio, A is the meshing area after the number of pin teeth, and the formula for unit area pressure P is: Where: F is the meshing force and A is the meshing area.

5. The pin gear of a high-precision RV reducer according to claim 1, characterized in that: The needle teeth (5) are made of 18CrNiMo7-6 alloy steel, and are subjected to appropriate heat treatment to improve the material structure and mechanical properties, increase the hardness and toughness of the needle teeth, and improve the bearing capacity and wear resistance of the needle teeth.

6. The pin gear of a high-precision RV reducer according to claim 1, characterized in that: The needle teeth (5) are processed by precision machining technology and numerical control grinding to ensure that the machining accuracy and surface roughness of the needle teeth meet the design requirements; during the machining and assembly process of the needle teeth, high-precision measurement technology is adopted, and a three-coordinate measuring instrument is used to accurately measure the size and shape of the needle teeth to ensure the accuracy and assembly quality of the needle teeth.

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