Spiral gears, also known as helical gears, offer several advantages when used in automatic transmission systems:

1. Smooth Operation: The helix shape of the gear teeth allows for a smoother operation with less vibration compared to straight gears.
2. Quiet Running: Due to the continuous engagement of the teeth, spiral gears run more quietly and produce less noise than their straight-toothed counterparts.
3. High Efficiency: The overlapping action of helical gears allows for a higher power transmission efficiency, as more teeth are in contact, which means less slippage and energy loss.
4. Increased Load Capacity: The design of spiral gears can handle higher loads without the need for larger gear sizes, which is particularly beneficial in compact designs.
5. Longer Lifespan: The even distribution of forces across the gear teeth results in less wear and a longer lifespan for the gears.
6. High Torque Transmission: Spiral gears can transmit high torque in a small space, which is ideal for applications where space is at a premium.
7. Better Alignment: They help in better alignment of the shafts, reducing the need for additional alignment components and simplifying the overall design.
8. Axial Thrust Management: The thrust generated during operation is axial, which can be more easily managed with appropriate bearing designs.
9. Suitability for High Speeds: Spiral gears are suitable for high-speed applications due to their ability to handle high loads and maintain efficiency.
10. Shock Load Resistance: They can better absorb shock loads due to the gradual engagement and disengagement of the teeth.
11. Space Efficiency: For a given power transmission capacity, spiral gears can be more compact than other gear types.
12. Low Maintenance: The precision manufacturing process and even load distribution result in gears that require less maintenance over time.
13. Reliability: Spiral gears are known for their reliability in automatic transmission systems, where consistent performance is critical.

These advantages make spiral gears a popular choice for various types of machinery and equipment that require automatic and efficient power transmission.