With reference to reduction gears, state the advantages and disadvantages of EACH of the following:
(a) helical teeth compared with spur teeth;(5)
(b) double helix compared to single helix.(5)
Advantages of Helical Gears over Spur Gears in Reduction Gearboxes
Helical gears offer several advantages over spur gears in reduction gearboxes for marine propulsion systems:
- Smoother operation: The gradual engagement of helical gear teeth reduces shock loads and vibration, resulting in quieter operation.
- Higher load capacity: Due to the increased contact area between gear teeth, helical gears can transmit higher loads compared to spur gears.
- Improved efficiency: The smoother meshing of helical gears reduces power losses due to friction.
- Reduced noise: The gradual engagement of teeth results in lower noise levels compared to spur gears.
Disadvantages of Helical Gears Compared to Spur Gears
- Axial thrust: Helical gears generate axial thrust due to the angled tooth profile, requiring additional thrust bearings.
- Increased complexity: Helical gears are more complex to manufacture compared to spur gears.
- Higher cost: The manufacturing process for helical gears is generally more expensive.
Despite these disadvantages, the overall benefits of helical gears often outweigh the drawbacks, making them the preferred choice for most marine propulsion reduction gearboxes.
Advantages and Disadvantages of Double Helical Gears Compared to Single Helical Gears
Advantages of Double Helical Gears
- Reduced Vibration and Noise: The overlapping tooth contact results in smoother operation and lower noise levels.
- Higher Load Capacity: The increased contact area between gears allows for higher load transmission.
- Balanced Axial Thrust: Double helical gears inherently balance axial thrust, eliminating the need for additional thrust bearings.
- Improved Efficiency: The smoother operation and higher load capacity contribute to improved efficiency.
Disadvantages of Double Helical Gears
- Increased Complexity: The manufacturing process is more complex compared to single helical gears.
- Higher Cost: Due to the increased complexity, double helical gears are generally more expensive.
- Lubrication Challenges: The complex tooth geometry can make lubrication more challenging.
While single helical gears offer simplicity and lower cost, double helical gears generally provide superior performance in terms of smoothness, load capacity, and efficiency, making them the preferred choice for many high-performance applications.