Gears are widely used for power transmission in automobiles. These components transmit rotating motion and torque (the force that makes an object rotate around a point or an axis) from one to another shaft of a machine. Among the different types of gears, the helical gear is extensively used. Their high load-carrying capacity makes them ideal for high-speed applications, such as automotive transmissions.
However, it also has certain downsides. Knowing them is crucial to achieving optimal torque output. Let’s dive into the design of helical gear, its pros and cons, and how they differ from spur gears.
What Is Helical Gear?
Helical gears feature teeth that are set at an angle. The teeth are bent into a helix shape, so the contact line between each tooth is inclined. The helix angle of helical gear varies from 5° to 45°. A careful selection of this angle ensures the gear teeth mesh smoothly. It also enables even load evenly and prevents misalignment during operation.
A helical gear allows you to connect non-parallel shafts. They allow power transmission between shafts that are at an angle to each other. Since the angled teeth engage gradually, helical gears facilitate quiet operation.
The gradual tooth engagement also leads to a bigger contact area. So, compared with spur gears, helical gears can handle heavy loads with reduced noise and vibration.
Advantages and Disadvantages of Helical Gear
Helical gears have high strength and can carry high torque and load seamlessly. But their design also has a few drawbacks. Explore them in detail below.
Advantages of a Helical Gear
High Load-carrying Capacity
The helix angle of helical gear positively affects its load-carrying capacity. It increases the contact ratio of the gear, so the load is dispensed along a longer line of contact. This allows for an increased load-bearing capability, including tooth bending and tooth contact stress.
Moreover, as the helix angle increases, it causes a reduction in tooth bending and contact stress. This superior load-carrying strength is also a difference between spur and helical gear.
A spur gear has a straight and not angled teeth design. It results in a smaller contact point between meshing teeth. Only one tooth can take most of the load at a particular time. This reduces the load-carrying capacity.
Smooth Operation with Reduced Noise and Vibration
The engagement and disengagement of helical gear teeth is gradual. They mesh together gradually, facilitating a quieter power transmission compared to spur gears.
A benefit of smoother engagement and disengagement of teeth and increased contact ratio is minimized vibrations. When vibrations are minimal, the machine runs quietly. This is why a major application of helical gear is in medical equipment and precision mechanical systems where low noise levels are needed.
Power Transmission Efficiency Between Non-Parallel Shafts
The diagonal teeth design of a helical gear allows it to mesh slowly with a properly aligned gear. As the teeth of two gears meet, it leads to a longer time in contact. This results in efficient power transmission, which is in the range of 94%-98%. Thus, industrial applications requiring higher speeds and loads benefit the most from helical gear uses.
Another point to note is that power transmission between non-parallel shafts is more difficult than parallel shafts. A helical gear allows efficient power transfer between non-parallel shafts or shafts at an angle. It’s why they are used extensively in power plants, steel and rolling mills, conveyors, elevators, compressors, blowers, and cutters.
High Durability and Life
Helical gears are durable because of a high number of angled teeth and increased contact area. The even distribution of load reduces wear and prolongs their life span. It also reduces localized stress and makes helical gear more suitable for high-load applications that demand durability, like automotive transmissions, conveyors, mixers, and propulsion systems.
Read: Enhancing Efficiency And Safety In The Food Industry
Disadvantages of Helical Gear
Additional Axial Thrust That Negatively Affects Bearings
The sliding contact of the meshing teeth while turning in the helical gear generates axial forces (forces along the gear’s length) and heat. It creates thrust loads or forces that push gears sideways during operation. They are pushed perpendicular to the tooth’s surface. So, compared with spur gear, helical gear‘s greater axial thrust leads to a reduction in efficiency.
The higher the helix angle of helical gear, the greater the axial force. However, double helical gears counteract the additional axial forces as the opposing helices cancel it out. You can also use thrust bearings to combat this problem.
Potential for Power Loss
The additional axial load caused by the sliding frictional forces of the teeth makes the helical gear susceptible to increased heat. It subsequently causes power loss and lowers the efficiency of the machine at low speeds.
Studies deem natural convection and heat exchange rates as the principal factors for this loss. Besides, tooth breakage at the root and pitting because of heat on the surface of helical gears can also lead to power loss and reduce the performance of the gear system.
Calculate Power Loss in Helical Gear
P_loss = ÎĽ * F_n * v_s
Where:
- ÎĽ is the coefficient of friction,
- F_n is the normal force acting on the gear tooth,
- v_s is the sliding velocity at the point of contact.
High Manufacturing Cost
A helical gear has a complex design because of the slanted teeth, so it demands specialized machining equipment. This type of gear also needs bearings that can handle axial forces, which adds to the complex geometry.
The entire manufacturing process requires extreme accuracy, from casting to forging and extrusion. The advanced level of precision affects the cost.
Moreover, helical gears are made from high-quality materials like alloy steels, which have a fair strength-to-weight ratio. Steel can also be heat-treated for enhanced properties. It increases the material cost.
Spur Gear Vs. Helical Gear – Key Differences
Both helical and spur gears are used for parallel shafts. However, the design of the teeth is what makes them different. In this table, we have summed up the key variations so you can decide better about the suitability of a spur or helical gear for your machine.
| Point of difference | Spur gear | Helical gear |
|---|---|---|
| Direction of teeth | Parallel to the gear's axis | Inclined at 5° to 45° to the gear's axis |
| Load imposed on the bearings | Radial load | Radial load and axial thrust load |
| Type of bearings needed | Radial bearings | Bearings designed for radial and axial load |
| Impact effect | Mating teeth engage in impact or sudden loading | Mating teeth engage gradually |
| Noise and vibration produced | High | Low |
| Change in pitch diameter | Calculated by teeth divided by pitch | Increases with the helix angle |
| Bidirectional capability | No | Yes |
| Variation in speed ratios | Not possible | Possible |
| Suitability for applications | Low-speed applications | High-speed applications |
Conclusion
Helical bearings are long-lasting and capable of carrying high torque. They are a part of varied machine tools, automotive transmissions, and engines in aircraft. However, if you require low speed and power efficiency, considering spur gears will be ideal.
If you want to optimize your gear sets and are looking to invest in high-quality helical or spur gears, feel free to contact us. As a top authorized distributor of Helical gears, we stock a variety of gears from reputable brands. Our engineers and experts will also help you determine the most relevant gear for your needs.
