# Principle of helical gear drive

The helical gear transmission is composed of two pairs of helical gears, which is a gear transmission between staggered shafts, also known as the staggered shaft helical gear transmission. The meshing condition of the helical gear is that the modulus of normal surface and the pressure angle of normal surface are equal. In the process of transmission, there is relative sliding along the direction of tooth direction and tooth width, so the transmission efficiency is low and the wear is fast, which is commonly used in the auxiliary transmission of instruments and small load.

The helical gear mechanism is used to drive the movement of two staggered shafts. From the point of view of a single helical gear, it is exactly the same as the helical cylindrical gear, but the difference between it and the helical gear drive is that in the helical gear drive, the axes of the two wheels are parallel, while in the helical gear drive, the axes of the two wheels are wrong.

Helical gear transmission is a kind of gear transmission composed of two pairs of helical gears, which is also called cross axis helical gear transmission.

In the principle of helical gear transmission in the above figure, the common section of two indexing cylinders is made through the tangent point of two indexing circles. The included angle of the projection of the axis of two wheels on the plane is called the axial intersection angle [∑] when the helix angles of two wheels are in the same direction, Σ] |||1|+ |||2|; when the helix angles of two wheels are in the opposite direction, Σ] |||. For the matched helical gear drive, the normal module must be equal; if the helical angle is not equal, their end module is not equal. As with the cylindrical gear transmission between parallel shafts, the transmission ratio of this kind of transmission is equal to the inverse ratio of the number of teeth of two wheels. Because the sliding speed between teeth is often large, the transmission efficiency is low, and the wear is fast; the two tooth surfaces are point contact, and the contact stress is large, so the bearing capacity is poor, and the service life is short. Therefore, the helical gear drive is only used to transmit movement or small power.

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