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Efficiency of K R F S Helical gear units

Author : Date : 2015/7/16 23:16:36

The efficiency of the gear units is mainly determined by the gearing and bearing friction. Please note that the starting efficiency of a gear unit is always less than its efficiency at operating speed. This is particularly pronounced in helical-worm gear units.

R, F, K gear units

The efficiency of helical, parallel shaft and helical-bevel gear units varies according to the number of gear stages, between 94% (3-stage) and 98% (1-stage).

S gear units

The gearing of helical-worm gear units produces a high proportion of sliding friction. As a result, these gear units may have higher gearing losses than R, F or K gear units, and thus be less efficient.

This depends on the following factors:

• Gear ratio of the worm gear stage

• Input speed

• Gear unit temperature

S series helical-worm gear units are designed with a helical gear set in the first stage which makes them significantly more efficient than one and two stage worm gear units. The efficiency may reach η < 0.5 if the worm gear stage has a very high gear ratio.

Self-locking of S series worm helical gear units

Back driving torques on helical-worm gear units produce a reverse efficiency of η' = 2 - 1/η, which is significantly less

favorable than the forwards efficiency η.

Running-in phase

The tooth flanks of new helical-worm gear units are not completely smooth. The friction angle is greater and thus efficiency is lower than during later operation. This effect becomes more pronounced the greater the gear ratio. Subtract the following values from the listed efficiency during the running-in phase:

Worm	i range	η reduction
1 start	approx. 50 – 280	approx. 12 %
2 start	approx. 20 – 75	approx. 6 %
3 start	approx. 20 – 90	approx. 3 %
4 start	-	-
5 start	approx. 6 – 25	approx. 3 %
6 start	approx. 7 – 25	approx. 2 %

The running-in phase normally lasts 24 hours. The helical-worm gear units achieve the rated efficiency levels specified in the list when

• the gear unit has been run-in completely,

• the gear unit has reached nominal operating temperature,

• the recommended lubricant is used and

• the gear unit is working within the rated load range.

Churning losses

In certain gear unit mounting positions (refer to "Mounting Positions and Important Order Information") the first reduction stage is completely immersed in the lubricant. With larger gear unit sizes and high circumferential velocities of the input stage, this gives rise to churning losses constituting a factor which cannot be ignored. Please contact us if you wish to use gear units of this type.

If possible, use the basic mounting position M1 for R, K and S gear units in order to keep the churning losses low.

Efficiency of K R F S Helical gear units

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