Gears: O que é a velocidade da linha de pitch e por que ela é importante?

Gears: What is pitch line speed and why is it important?

gear pitch line speed

When sizing the gearbox, it is important to determine the required input speed in rpm and ensure that it does not exceed the maximum speed capability. But also the linear speed of gear teeth, known as pitch line speed, plays a significant role in gearbox performance.

Pitch line speed is measured at the gear pitch line, which is half the length of the gear teeth. For circular gears, the pitch circle is more correctly called the pitch circle, which is an imaginary circle that rolls without slipping when aligned with the pitch circle of the corresponding gear.

Technically speaking, a linear rack has a “pitch line” and a circular gear has a “pitch circle”.

The pitch speed is a function of the pitch diameter of the gear and its rotational speed:

pace line speed

Where:

PLV = pitch line speed (m/s)

d p ​​= pitch diameter (m)

ω = rotation speed (rpm)

Pitch line speed is important to gear design and selection for several reasons. First, the American Gear Manufacturers Association standard 9005-D94, Industrial Gear Lubrication, specifies that the pitch line speed of a gear is one of the main criteria for selecting gear lubrication. The pitch line speed determines the contact time between the gear teeth, which has a significant impact on the required oil viscosity. High pitch line speeds are generally accompanied by light loads and short contact times, making low viscosity oils suitable. However, low pitch line speeds are associated with high loads and long contact times, making high viscosity, or even EP, oils necessary.

In addition to lubrication considerations, pitch line speed also affects load capacity and gear tooth life. The ability of gears to transmit the torque required for the desired operational life depends on the ability of the gear teeth to resist bending stresses. The bending stress of the tooth is determined by the Lewis formula:

Lewis formula

Where:

σ = tooth bending stress (MPa)

C t = tangential force on the tooth (N)

P = diametric pitch (mm -1 )

F = visible width (mm)

Y = Lewis shape factor

But when the gear teeth make initial contact, they experience greater stress, depending on the speed of the gear.

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