In vertical shaft transmissions, the axial force deviation in bevel gear actuators directly affects the stability and reliability of the transmission. Therefore, the structural design must employ multi-dimensional technical means to effectively balance the axial force. Firstly, the tooth profile design of the bevel gear is crucial for controlling the axial force. Curved bevel gears (such as spiral bevel gears) have helical tooth lines, causing the axial force direction to dynamically adjust with the tooth surface contact position during transmission. By rationally designing the helix angle (typically 35°-40°), the axial forces generated in forward and reverse rotation can be made to be opposite in direction, creating a natural cancellation effect. For example, when the driving bevel gear rotates clockwise, its axial force points towards the larger end; when it rotates counterclockwise, the axial force points towards the smaller end. This bidirectional symmetry significantly reduces the risk of unidirectional axial force deviation.
The bearing arrangement is also critical for axial force balance. Tapered roller bearings, capable of withstanding combined radial and axial loads, are widely used in bevel gear actuators. To further optimize axial force distribution, "back-to-back" or "face-to-face" bearing configurations can be adopted: Back-to-back arrangement increases the distance between the support reaction points of the two bearings, improving shaft stiffness and effectively resisting bending deformation caused by axial forces; face-to-face arrangement shortens the support reaction distance, enhancing the shaft's torsional stiffness and adapting to high torque conditions. Furthermore, precise adjustment of bearing preload is crucial. By adding or removing shims or tightening bearing adjusting nuts, bearing clearance can be eliminated and appropriate preload applied, preventing axial displacement of the gear shaft under axial force and ensuring proper meshing of the bevel gear pair.
A bidirectional fixing design for the gear shaft is another important means of preventing axial force deviation. During transmission, regardless of the rotation direction, the axial force of the bevel gear always points from the smaller end to the larger end; therefore, the shaft system must have bidirectional axial fixing capability. A common solution is to install the shaft system in a sleeve, which is then embedded in the outer shell hole. By increasing or decreasing the thickness of the shims between the sleeve end face and the outer shell, the axial position of the shaft system can be adjusted, achieving bidirectional fine-tuning. Meanwhile, the axial positioning of the gears on the shaft should employ a combination of shaft shoulders, elastic retaining rings, or round nuts to ensure that the gears do not move under axial force and maintain the stability of the meshing position.
Optimizing the support structure can further improve the axial force balance. For high-speed bevel gears, a simple support is recommended, where both ends of the gear are fixed by bearings. This structure can disperse axial force and reduce local stress concentration. For low-speed or high-torque applications, a cantilever support (one end of the gear fixed, the other free) may be more suitable, but insufficient rigidity needs to be compensated by increasing the shaft diameter or adding auxiliary support surfaces. Furthermore, shaft deflection control is a key indicator; the design must ensure that the shaft deflection is less than 0.025mm to avoid poor tooth surface contact due to shaft deformation, which could lead to axial force deviation.
Material selection and heat treatment processes have an indirect impact on axial force balance. High-strength alloy steel (such as 20CrMnTi) possesses excellent mechanical properties and wear resistance, which can reduce elastic deformation during gear transmission, thereby reducing axial force fluctuations. In terms of heat treatment, carburizing and quenching or surface hardening can significantly improve tooth surface hardness and contact fatigue strength, preventing uneven axial force distribution caused by tooth surface wear. Simultaneously, precision machining processes (such as CNC gear grinding) can ensure tooth surface roughness and tooth profile accuracy, reduce transmission errors, and further stabilize axial force.
Precision control during installation and commissioning is the last line of defense against axial force deviation. During assembly, it is crucial to ensure that the cone apexes of the bevel gears coincide, and the meshing imprint should be located in the middle of the tooth surface or slightly offset towards the smaller end. This ensures that the meshing position is appropriately offset towards the larger end after load bearing, compensating for shaft and bearing deformation. Furthermore, it is necessary to optimize the meshing clearance and tooth flank clearance by adjusting the shims under the differential bearings or the left and right lock nuts of the differential, preventing impact loads caused by excessive clearance, which could lead to sudden changes in axial force.
In vertical shaft transmission, bevel gear actuators require multi-dimensional technical means, including tooth profile design, bearing arrangement, shaft system fixation, support structure optimization, material selection, precision machining, and installation and commissioning, to achieve dynamic balance and stable transmission of axial force. These design strategies not only improve transmission efficiency and reliability, but also extend equipment lifespan, meeting the high precision and stability requirements of modern industry for vertical shaft drives.
