Abstract: This paper first introduces in detail the important parts that affect the power loss of the drive axle, analyzes the influence of the geometric parameters, lubrication parameters and bearing parameters of the hypoid gears commonly used on the drive axle on the power loss of the gears, and then conducts theoretical and experimental analyses on the middle and rear drive axles of a platform in Dongfeng to discuss the influence sensitivity of various parameters on the transmission efficiency and proposes methods to improve the transmission efficiency. Finally, on the basis of theoretical calculation and bench test, the function equation of the drive axle power loss correction coefficient is fitted.
Efficiency Range: The meshing efficiency of hypoid bevel gears supported by rolling bearings and accurately installed can reach 96% – 98%.
Influence of Geometric Parameters: For hypoid gears with fixed parameters, the transmission efficiency η increases with the increase of input torque. When the offset distance of the input gear increases, the spiral angle of the gear increases, and the transmission efficiency decreases. Reducing the offset distance E and the spiral angle ψe and ψG can effectively improve the transmission efficiency of the hypoid gear.
Influence of Lubricating Oil Performance: The lower the viscosity of the lubricating oil, the smaller the power loss of the gear pair. For low-viscosity lubricating oil, a smaller friction coefficient can be selected in the formula, and vice versa.
1.2 Bearing Load Power Consumption
The calculation formula of bearing load power consumption :
1.3 Bearing Rolling Resistance and Oil Churning Power Consumption
The calculation formula of bearing rolling resistance and oil churning power consumption is:
1.4 Cylindrical Gear Power Consumption
Meshing Power Consumption: The calculation formula of cylindrical gear meshing power consumption is: The larger the kinematic viscosity of the oil, the larger the friction coefficient , and the corresponding meshing power consumption of the cylindrical gear increases, and the transmission efficiency decreases.
Gear Wind Resistance and Oil Churning Loss: The power consumption of gear wind resistance and oil churning is composed of three parts, and their respective calculation formulas :
2. Drive Axle Model Parameters and Bench Test
2.1 Model Parameters
Parameters
Driving Gear
Driven Gear
Number of Teeth
11
43
Module/mm
10.1
10.1
Midpoint Spiral Angle/(°)
43.05
33.72
Driving Tooth Surface Pressure Angle/(°)
22
22
Pinion Offset Distance/mm
35
–
2.2 Bench Test
Before the evaluation of the drive axle transmission efficiency test, use the traditional running-in procedure (100h, a total of 9230km) for pre-operation. After the running-in procedure, control the wheel end speed at 80km/h and 100km/h, and measure the drive axle transmission efficiency under a wide range of working conditions corresponding to multiple combinations of input power from 50kW to 250kW. The lubricating oil temperature is set at 80°C.
3. Transmission Efficiency Analysis
3.1 Power Consumption Contribution of Each Component
The main and driven hypoid bevel gears account for a large proportion of the system power consumption, while the influence of cylindrical gears and bearings on power consumption is small, and the influence of other components such as oil seals and oil pumps is almost negligible.
3.2 Theoretical and Bench Test Results Analysis
The transmission efficiency of the 3.9-speed ratio middle axle is higher than that of the rear axle. Compared with the rear axle, the power consumption of the middle axle also includes the power consumption brought by the inter-axle differential and cylindrical gears. Under the same input conditions, the power consumption of the middle axle is greater. The transmission efficiency trends of the three states of the drive axle in theoretical calculation and bench test are very similar. As the input power gradually increases, the transmission efficiency gradually increases, but the increase rate gradually decreases. When the input power is greater than 200kW, the theoretical calculation and bench test results are almost the same. The reason for this situation is that the main and driven hypoid gears have a great influence on the transmission efficiency, resulting in the transmission efficiency trend of the entire system developing according to the transmission efficiency of the main and driven gears, and the power consumption of other components is small, and the influence on the transmission efficiency of the entire system is relatively limited.
3.3 Efficiency Sensitivity Analysis
Serial Number
Scheme
Efficiency Change
Fatigue Safety Coefficient Change
Cost Change
1
Tooth Surface Roughness Improvement: Ra3.2→Ra0.8
200kW: +0.46, 120kW: +0.416
Tooth Contact: +0.07, Others Unchanged
Cost Increase
2
Oil Level Decrease: -10mm
200kW: +0.07, 120kW: +0.116
Unchanged
Basically Unchanged
3
Oil Level Increase: +10mm
200kW: -0.08, 120kW: -0.0811
Unchanged
Basically Unchanged
4
Lubricating Oil Viscosity: 85w→75w
200kW: +0.121, 120kW: +0.157
Unchanged
Cost Reduction
5
Bearing: Low Friction Bearing, Friction Coefficient Reduced by 30%
200kW: +0.307, 120kW: +0.424
Unchanged
Cost Increase
3.4 Power Consumption Correction Coefficient
The correction coefficient k is defined as the ratio of the bench test result of the drive axle power consumption to the theoretical calculation result. The variation law of the correction coefficient of the 3.9-speed ratio middle and rear axles and the 3.4-speed ratio rear axle with the input power, and the fourth-order function equation of the input power and the correction coefficient is fitted by the least square method. The fitting functions of the 3.9-speed ratio middle axle at 80km/h and 100km/h are shown in equations (13) and (14); the fitting functions of the 3.9-speed ratio rear axle at 80km/h and 100km/h are shown in equations (15) and (16); the fitting functions of the 3.4-speed ratio rear axle at 80km/h and 100km/h are shown in equations (17) and (18). According to the interpolation calculation principle, the power consumption correction coefficient calculation in any working condition within the speed range of 80km/h to 100km/h and the power range of 50kW to 250kW can be expressed by equation:
4. Conclusion
Combining the Gleason gear transmission efficiency calculation method, it is analyzed that the offset distance E of the driving wheel and the midpoint spiral angles ψ and ψG of the gear have a great influence on the transmission efficiency. Reducing E and ψe can effectively improve the transmission efficiency of the hypoid gear.
When other conditions are the same, the larger the kinematic viscosity v of the oil, the larger the friction coefficient fn, and the corresponding meshing power consumption of the cylindrical gear increases, and the transmission efficiency decreases.
Combining the Gleason gear transmission efficiency calculation method and the ISO14179 standard, the power consumption of the drive axle system is theoretically calculated and is consistent with the bench test results, among which the main and driven hypoid gears have the greatest influence on the power.
Combining the simulation calculation and analysis, the efficiency improvement of the axle mainly comes from improving the tooth surface roughness, using low-friction bearings, reducing the lubricating oil viscosity, and reducing the oil level, with an overall improvement of nearly 1%.
The fourth-order function equation of the input power and the power loss correction coefficient is fitted by the least square method, and the expression of the power consumption correction coefficient in a certain working condition range is obtained according to the interpolation calculation principle to predict the transmission efficiency and provide a basis for subsequent research.
