JESSICA部落格

1. Introduction to helical planetary gearboxes
A helical planetary gearbox is a mechanical transmission device composed of a planetary gear mechanism and helical gears. The core lies in the layout of the planetary gears. The central sun gear is surrounded by multiple planetary gears, and the outer side of the planetary gears wraps around the annular gear ring, and all gear axes remain parallel. The characteristic of the helical gear is that the tooth shape is inclined at an angle to the axis, and the common angle range is between 15 degrees and 30 degrees. This design makes the gear meshing process more coherent and effectively reduces the operating noise and vibration amplitude.

2. Working principle of helical planetary gearboxes
The working principle of the helical planetary gearbox is mainly based on the combination of planetary gear mechanisms and helical gears. The core lies in the layout of the planetary gears. The central sun gear is surrounded by multiple planetary gears, and the outer side of the planetary gears wraps around the annular gear ring, and all gear axes remain parallel. The characteristic of the helical gear is that the tooth shape is inclined at an angle to the axis, and the common angle range is between 15 degrees and 30 degrees. This design makes the gear meshing process more coherent and effectively reduces the operating noise.

3. Design features of helical planetary gearbox
1. Structural features: The helical planetary gearbox is composed of a planetary gear mechanism and helical gears. The core lies in the layout of the planetary gears. The central sun gear is surrounded by multiple planetary gears, and the outer side of the planetary gears is wrapped with an annular gear ring, and all gear axes remain parallel.
‌2. Transmission principle: When the motor drives the sun gear to rotate, the planetary gear generates a reaction force during the self-rotation process, pushing the planetary carrier to start rotating. The unique meshing method of the helical gears makes each contact point have an axial component force, which is transmitted to the output shaft through the planetary carrier.
‌3. Performance advantages: The inclination angle of the helical gear brings two significant advantages. First, the length of the meshing contact line is more than 1.5 times that of the spur gear, the pressure per unit area is reduced, and the gear life is extended. Secondly, the progressive contact of the helical teeth reduces the vibration amplitude of the transmission process to 30% of that of the spur gear, which is particularly suitable for occasions requiring high precision and low noise.
‌4. Material selection: The sun gear generally uses 20CrMnTi carburized steel with a surface hardness of HRC60. The planetary gears use the same material but are shot peened to improve the fatigue resistance of the tooth surface. The gear ring material is mostly 42CrMo quenched and tempered steel, and the housing is made of HT250 cast iron to ensure structural rigidity.

4. Main faults of helical planetary gearboxes
1. Gear damage: Common forms of gear damage include tooth breakage, tooth surface fatigue and bonding. Tooth breakage may be caused by bending stress exceeding the material strength limit, tooth surface fatigue is the surface crack propagation caused by alternating loads, and bonding is the destruction of the lubricating oil film between the tooth surfaces under high speed and heavy load, resulting in direct metal contact and adhesion.
2. Bearing damage: Bearings play the role of supporting the rotating shaft in the reducer. During long-term operation, problems such as wear, fatigue peeling and overheating will occur. Wear will cause the bearing clearance to increase, affecting the rotation accuracy; fatigue peeling will increase the bearing vibration and noise; overheating will accelerate the aging and damage of the bearing.
‌3. Shaft breakage‌: Shaft breakage is mainly caused by the failure to eliminate stress concentration factors during the manufacturing of the shaft, which exceeds the fatigue limit of the material under the action of overload or alternating stress.
‌4. Oil high temperature‌: The abnormal high temperature phenomenon of the gearbox may be due to insufficient supply of lubricating oil or poor lubrication, resulting in insufficient lubrication and cooling of gears and bearings.
‌5. Tooth profile error‌: Tooth profile error includes manufacturing error, installation error and error after use, such as plastic deformation of the tooth surface, uneven surface wear and surface fatigue, etc.
6‌. Shaft misalignment‌: Shaft misalignment refers to the problem that the shafts at both ends of the coupling are parallel but not aligned due to problems in the design, manufacturing, installation or use process, resulting in distributed tooth profile errors of the gears.
‌7. Box resonance‌: Box resonance is a resonance phenomenon caused by external excitation, which will generate a lot of impact vibration energy and is a serious fault.
‌8. Shaft bending‌: Shaft bending includes mild bending and severe bending, which will cause gears to have tooth profile errors and affect transmission accuracy.
‌9. Shaft imbalance‌: Shaft imbalance is caused by eccentricity of the shaft, which leads to increased vibration and noise, and in severe cases will affect the normal operation of the gear‌.
‌10. Seal failure‌: After long-term use, seals will experience aging, wear, deformation and other problems, leading to lubricating oil leakage and affecting the normal operation of the gearbox‌.

Source:https://plaza.rakuten.co.jp/stepperonline/diary/202503310000/