Helical gear is type of cylindrical gear with teeth that are cut at an angle to the axis of the gear. This design allows the teeth to engage more gradually than in spur gear, which have straight teeth and engage all at once. Here’s a more detailed look into helical gear:
1. Structure and Design
- Helical Teeth: The teeth on helical gear is set at an angle (helix angle) to the gear’s axis. This angle helps in creating a gradual contact between the teeth of two meshing gear, which starts at one end of the tooth and spreads across the tooth as the gear rotate.
- Right-Handed or Left-Handed: The helix angle can be right-handed or left-handed, determining the direction in which the teeth are angled. If the gear must rotate in a specific direction, the hand of the helix can be crucial.
2. Advantages
- Smooth Operation: Because the teeth engage more gradually, helical gear operate more smoothly and quietly than spur gear.
- Higher Load Capacity: The gradual engagement of the teeth also allows helical gear to carry higher loads by distributing the forces more evenly along the length of the teeth.
- Less Vibration: The smooth operation reduces vibration, leading to less wear and tear on the gear and its housing.
3. Disadvantages
- Axial Load: One significant drawback of helical gear is that they generate axial forces. These are thrust loads along the gear’s axis which require additional bearings to manage and can lead to increased complexity in the gearbox design.
- Manufacturing Complexity: The angled teeth make these gear more complex to manufacture than spur gear, potentially increasing costs.
4. Applications
- Automobiles: Helical gear is commonly used in the transmission systems of cars and other vehicles because of their quiet operation and ability to transmit motion and power efficiently.
- Industrial Equipment: They are also used in various machines and industrial equipment, especially in high-load applications where noise reduction is critical.
5. Variations
- Double Helical Gear (Herringbone): To counteract the axial load without using extra bearings, double helical gear have a “V” shape with two opposite helix angles, effectively balancing out the axial thrust.
- Crossed Helical Gear: These are used to transmit power between non-parallel, non-intersecting shafts. They tend to have a higher rate of wear due to the less efficient contact between the teeth.
6. Operational Characteristics
- Efficiency: Helical gear is generally more efficient than spur gear, particularly at higher speeds. Their efficiency typically ranges from 98% to 99%, slightly less than spur gear due to the additional friction from the axial thrust.
- Speed and Torque Transmission: Thanks to their design, helical gear can operate at higher speeds and transmit more torque compared to similarly sized spur gears. The angled teeth provide a larger contact surface area, which translates to higher load capacity.
7. Engineering Considerations
- Helix Angle: The choice of helix angle is crucial as it affects the gear’s performance. A larger helix angle results in smoother gear operation but increases the axial load. Typical helix angles range from 15 to 30 degrees.
- Material Selection: Helical gear are usually made from materials that can withstand high stress and wear, such as hardened steel, bronze, or composites. Material selection is influenced by factors like load, speed, and environmental conditions.
- Lubrication: Adequate lubrication is vital for helical gear to minimize friction and wear. Gear lubricants are chosen based on the gear material, load, speed, and operating environment.
8. Challenges
- Axial Thrust Management: The axial forces produced by helical gear can be a challenge, as they require robust housing and bearing systems to withstand these forces. This can complicate the gearbox design and increase the cost.
- Noise Despite Reduction: While quieter than spur gear, helical gear can still produce noise at high speeds or under improper alignment. Ensuring precise alignment during installation is crucial to minimize noise and maximize lifespan.
9. Design and Installation
- Alignment: Proper alignment is critical for helical gear. Misalignment can lead to uneven load distribution and increased wear. Laser alignment tools and other precision instruments are often used during installation.
- Backlash Adjustment: Backlash, or the clearance between meshing teeth, must be carefully adjusted in helical gear to ensure smooth operation. This is especially important in high precision applications like CNC machinery or aerospace components.
Helical gear represent a significant advancement over spur gear in many applications, especially where noise and vibration control are required. They are a cornerstone in modern gear design, contributing significantly to the efficiency and durability of various mechanical systems.
