The auxiliary gearbox main shaft is a key component in the gearbox (especially the multi-speed gearbox of heavy vehicles or engineering machinery). It is usually located in the auxiliary gearbox (auxiliary gearbox) and cooperates with the main gearbox to achieve a wider transmission ratio range and torque output. Its importance is mainly reflected in the hub role of power transmission, the core carrier of transmission ratio expansion, and reliability assurance. The specific analysis is as follows:
I. The core function and importance of the auxiliary gearbox main shaft
1. As the core hub of auxiliary gearbox power transmission
Connecting the main gearbox with the output end: one end of the auxiliary gearbox main shaft is meshed with the output shaft (or intermediate shaft) of the main gearbox through gears, and the other end is connected to the output gear, synchronizer and other components of the auxiliary gearbox. It is the "bridge" for the transmission of power from the main gearbox to the auxiliary gearbox.
Example: In the gearbox of a heavy truck, after the main gearbox completes the initial speed change, the power is transmitted to the high and low gear sets of the auxiliary gearbox through the auxiliary gearbox main shaft, realizing a wider range of speed ratio switching (such as from low-speed and high-torque climbing gear to high-speed economic gear).
Bear high torque load: The auxiliary box main shaft needs to bear the high torque output by the engine (especially when the heavy-loaded vehicle starts or climbs a slope). Its material (such as high-strength alloy steel) and processing accuracy (such as surface quenching and grinding) directly affect the transmission reliability.
2. Realize the transmission ratio expansion and improve the performance of the gearbox
Cooperate with the auxiliary box gear set to expand the speed ratio range: Multiple gears (such as high and low gears) are usually installed on the auxiliary box main shaft, and the meshing state is switched through the synchronizer or shift mechanism to achieve the "upshift" or "downshift" of the auxiliary box.
Core function: The main box provides the basic gear, and the auxiliary box further expands the speed ratio range through the main shaft gear set (such as the main box speed ratio range of 4:1, the auxiliary box speed ratio range of 2:1, and the overall speed ratio can reach 8:1), so that the vehicle can start at low speed and high torque, and can also travel at high speed and low fuel consumption.
Adapt to complex working conditions:
Construction machinery: The auxiliary box spindle can help excavators, cranes and other equipment quickly switch between "heavy load and low speed" (such as excavation operations) and "light load and high speed" (such as transfer driving).
Heavy trucks: Through the high and low gear switching of the auxiliary box spindle, the vehicle can operate efficiently in mountain roads (requiring low gear and high torque) and plain high speed (requiring high gear and low speed) scenarios.
3. Ensure transmission accuracy and smooth shifting
Support the precise meshing of the synchronizer and gear: The coaxiality, surface roughness and other precision indicators of the auxiliary box spindle directly affect the meshing efficiency of the synchronizer and gear. If the spindle processing error is large, it may cause gear shifting stagnation, gear hitting or abnormal noise.
Reducing power interruption time: During the gear shifting process, the auxiliary box spindle quickly synchronizes the speed of the gear to be meshed through the synchronizer, shortening the power interruption time and improving the smoothness of the gear shifting (especially in multi-speed gearboxes, the shifting efficiency of the auxiliary box has a significant impact on the overall driving experience).
4. Impact on the reliability and life of the gearbox
Key to anti-fatigue and wear resistance: The auxiliary gearbox main shaft works under alternating loads for a long time. If the material strength is insufficient or the heat treatment process is poor, fatigue fracture or wear may occur (such as wear of the journal leading to increased gear meshing clearance), which in turn leads to gearbox failure (such as shifting and abnormal noise).
Carrier for lubrication and heat dissipation: The main shaft is usually designed with oil channels or oil holes, which cooperate with the gearbox lubrication system to provide lubricating oil for gear meshing points, bearings and other parts to reduce friction and heat generation and extend the life of components.
2. Structure and design points of the auxiliary gearbox main shaft
1. Typical structural composition
Shaft body: The main body is a stepped shaft with different shaft sections of different diameters, which is used to install gears, synchronizers, bearings and other components.
Gear installation position: Splines or keyways are processed on the shaft to fix gears (such as sliding gears or fixed gears). Some main shafts and gears are integrated designs (such as gear shafts).
Synchronizer installation position: Cooperate with the synchronizer gear sleeve to achieve gear switching, and the surface needs to be wear-resistant (such as high-frequency quenching treatment).
Bearing support position: The main shaft is supported by tapered roller bearings or cylindrical roller bearings to bear radial and axial loads.
2. Key design parameters
Material selection: Commonly used low-carbon alloy steels such as 20CrMnTi and 20CrNiMo can reach a surface hardness of 58-62HRC after carburizing and quenching treatment, and the core maintains toughness, taking into account both wear resistance and impact resistance.
Strength calculation: Torque verification, bending strength verification and fatigue life calculation are required to ensure that no deformation or fracture occurs under maximum load.
Processing accuracy: The journal size tolerance, coaxiality, surface roughness, etc. must be controlled at the micron level (such as IT6-IT7 level accuracy) to ensure gear meshing accuracy and bearing operation stability.
III. Impact and maintenance points of auxiliary box main shaft failure
1. Common failures and consequences
Journal wear: causes loose bearing fit, abnormal noise, vibration, and even poor gear meshing (such as eccentric wear and tooth breakage).
Spline wear: If the clearance between the gear or synchronizer and the main shaft spline is too large, it may cause gear shifting difficulties and gear skipping (especially under heavy load conditions).
Fatigue fracture: Long-term high-load operation may cause the main shaft to break, resulting in gearbox failure, sudden loss of power of the vehicle or equipment, and safety hazards.
2. Maintenance and care recommendations
Regularly check the quality of lubricating oil: Gear oil deterioration or excessive impurities will aggravate the wear of the main shaft and gears. Lubricating oil needs to be replaced periodically (such as every 50,000 kilometers or one year) and the inside of the gearbox needs to be cleaned.
Pay attention to abnormal gear shifting: If there is a gear shift jam, abnormal noise or power interruption, it may be a main shaft or synchronizer failure, which needs to be repaired in time.
Avoid overload: Heavy vehicles should avoid long-term overload driving to prevent the auxiliary box main shaft from being subjected to torque beyond the design range and shortening its life.