Traditional tractor transmissions face challenges in achieving compactness, lightweight design, and multi-gear configurations. This study introduces a novel transmission architecture utilizing face gears combined with a planetary gear system to address these limitations. The design leverages the unique advantages of planetary gear trains, including torque distribution stability and structural compactness, while integrating face gears for enhanced power transmission efficiency.
1. Power Matching and Design Specifications
The transmission is designed for heavy-duty tractors requiring 16+8 gear ratios. Key parameters are summarized in Table 1:
| Parameter | Value |
|---|---|
| Speed Range (km/h) | 2-40 |
| Engine Power (kW) | 95 |
| Engine Torque (Nm) | 450 |
| Final Drive Ratio | 14.2 |
2. Transmission Architecture
The planetary gear system combines face gears and cylindrical gears in a compound arrangement. Key components include:
- Four face gears (Z4, Z5, Z6, Z7)
- Planetary carrier with multiple planet gears
- Multi-plate clutches (C1-C4) and brakes (B1-B5)
The kinematic relationship for planetary gears is expressed as:
$$k_p = \frac{Z_{\text{ring}}}{Z_{\text{sun}}}$$
$$\omega_{\text{carrier}} = \frac{\omega_{\text{sun}} + k_p\omega_{\text{ring}}}{1 + k_p}$$
3. Gear Ratio Analysis
Eight primary transmission modes are achieved through different clutch/brake combinations. The gear ratio formulas are derived using planetary gear dynamics:
| Mode | Gear Ratio Expression |
|---|---|
| 1 | $$\frac{Z_6}{Z_5}$$ |
| 2 | $$\frac{Z_7}{Z_5}$$ |
| 3 | $$\frac{Z_6}{Z_4}$$ |
| 4 | $$\frac{Z_7}{Z_4}$$ |
4. Parameter Optimization
MATLAB-based optimization yielded optimal tooth numbers:
$$Z_4=54,\ Z_5=30,\ Z_6=74,\ Z_7=27$$
Resulting gear ratios are distributed as shown in Table 3:
| Primary Ratios | Secondary Ratios |
|---|---|
| 0.27, 0.50, 0.73 | 1.0 (Direct), 2.0 (Reduction), -1.5 (Reverse) |
| 0.90, 1.36, 1.37, 1.99, 2.47 |
5. Dynamic Performance
The planetary gear system demonstrates superior load distribution:
$$T_{\text{sun}}:T_{\text{ring}}:T_{\text{carrier}} = 1:k_p:(1+k_p)$$
Where torque relationships ensure balanced power transmission across all planet gears.
6. Structural Advantages
- 40% reduction in axial length compared to conventional designs
- 15% weight reduction through planetary gear optimization
- 200% increase in torque density per unit volume
This innovative planetary gear-based transmission architecture successfully addresses the conflicting requirements of multi-gear configurations and compact packaging. The integration of face gears with planetary gear trains enables smooth power transmission while maintaining structural rigidity, demonstrating significant potential for heavy-duty vehicle applications.