10
Project planning
MOVIMOT® advanced
Operating Instructions – MOVIMOT
®
advanced
229
10.3.4 Project planning notes – R, F, K, S, W gear units
Efficiency of gear units
General information
The efficiency of the gear units is mainly determined by the gearing and bearing fric-
tion as well as by churning losses. Keep in mind that the starting efficiency of a gear
unit is always less than its efficiency at operating speed. This factor is particularly true
for helical-worm and SPIROPLAN
®
right-angle gear units.
INFORMATION
For information on churning losses and thermal rating, refer to chapter "Churning
losses and thermal rating"(→2231).
R, F, K gear units
Depending on the number of gear stages, the gearing efficiency of helical, parallel-
shaft and helical-bevel gear units is up to 96% (3-stage), 97% (2-stage) and 98% (1-
stage).
S and W gear units
The gearing in helical-worm and SPIROPLAN
®
gear units produces a high proportion
of sliding friction. This is the reason why these gear units have higher tooth friction
losses and lower efficiency than R, F or K gear units.
Other factors influencing the efficiency:
• Gear ratio of the helical-worm or SPIROPLAN
®
stage
• Input speed
• Ambient temperature
Helical-worm gear units from SEW‑EURODRIVE are helical gear/worm combinations
that are significantly more efficient than plain worm gear units; see chapter Technical
data S. SF. SA. SAF 37 and subsequent chapters.
The efficiency may reach η<0.5 if the helical-worm gear stage has a very high gear
ratio.
Self-locking
Retrodriving torque in helical-worm or SPIROPLAN
®
gear units produces an efficiency
of η’=2-1/η, which is significantly less favorable than the forward efficiency. The hel-
ical-worm or SPIROPLAN
®
gear unit is self- static locking if the forward efficiency η
is≤0.5. SPIROPLAN
®
gear units W..10 – W..30 are dynamically self-locking to some
extent (with highest ratios). Contact SEW‑EURODRIVE if you want to make technical
use of the braking effect of self-locking characteristics.
INFORMATION
Note that the self-locking effect of helical-worm and SPIROPLAN
®
gear units is not
permitted as the sole safety function for hoists.
25891936/EN – 05/2020
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