A helical gearbox uses a set of helical gears to transfer force and motion between shafts. They are a versatile alternative to spur gears that can be used across a variety of industries and applications. They are especially good for applications that require high-speed, noise control, and vibration reduction.
The basic kinematics of a helical gear pair is similar to those of spur gears, but the teeth are cut at an angle rather than at right angles. This makes them more stable and reduces the chance of slipping, which is a significant issue for spur gears.
Helical Gears and Plane of Action
The involute teeth of a helical gear are cut at an angle to the gear’s axis, which causes them to follow a spiral path. The angle also defines the line of contact, or plane of action, between gear teeth as they mesh through a cycle. The plane of action is defined by the effective face width of the helical gears, which extends along the diagonal orange lines in the figure below.
Backlash
The angle of a helical gear is determined by the helix angle, which typically ranges between 15 and 30 degrees for helical kinds. This angle is crucial for maintaining the right balance between thrust loads and sliding friction. The helix angle is influenced by the center distance, but not tooth depth.
This can make a significant difference to the gearbox’s efficiency and performance. As a result, designers are required to take several factors into consideration when designing a helical gearbox.
Choosing the Right Mounting Options
The most common mounting option for helical gearboxes is parallel. This means that each helical gear is mounted in line with its mate, but they can also be crossed and mounted in different directions.
In the case of crossed helical gears, they must be paired with identical-handed gears. This is because the helical gears need to stagger their layers in opposite directions. This creates a need for a ball or roller bearing capable of managing the axial loading that these gears produce.
These bearings must also withstand the additional axial load created by the diagonal profile of the helical gear teeth. This can be a concern for some designs, and it can also cause the helical gears to slip more than they should if not properly chosen.
Depending on the size of the helical gears and their helix angle, this can lead to a loss of efficiency. For this reason, it’s important to ensure the correct gear ratios are chosen for each helical gear in the system.
Silent operation
The helical gears engage in small increments rather than the entire face at once, which allows for less noise. This is why helical gears are a popular choice for many automotive transmissions, and can be found in almost any mechanical application that requires a simple design with a low to medium speed.
Higher output torques
The high-efficiency and low-wear features of helical gears are ideal for heavy-duty industrial applications. In fact, they’re often the only type of gears that can handle these requirements.