Technical data

Manual – Gear Units and Gearmotors
47
5
Multi-stage gearmotors (→ GM)
Project Planning for Gear Units
5.3 Multi-stage gearmotors (→ GM)
General
information
You can achieve particularly low output speeds by using multi-stage gear units or multi-
stage gearmotors. This means an additional second gear unit, usually a helical gear unit,
is installed in front of the gear unit or between gear unit and motor.
The resulting total reduction ratio may make it necessary to protect the gear units.
Limiting the
motor power
You have to reduce the maximum output motor power according to the maximum
permitted output torque on the gear unit (T
a max
). For this purpose you first have to
determine the allowable motor torque (T
N allowable
).
You can calculate the allowable motor torque as follows:
Use this allowable motor torque T
N allowable
and the load diagram of the motor to deter-
mine the associated value for the motor current.
Take suitable measures to prevent the continuous current consumption of the motor
from exceeding the previously determined value for the motor torque T
N allowable
. A suit-
able measure is, for example, to set the trip current of the protective circuit breaker to
this maximum current value. Besides, a protective circuit breaker can compensate for a
brief overload, for example during the motor’s starting phase. A suitable measure for in-
verter drives is to limit the output current of the inverter according to the determined mo-
tor current.
Checking brake
torque
If you use a multi-stage brake motor, you will have to limit the braking torque (T
B
)
according to the maximum permitted motor torque T
N allowable
. The maximum permitted
braking torque is 200 % T
N allowable
.
T
B max
≤ 200 % T
N allowable
If you have questions on the starting frequency of multi-stage brake motors, please
consult SEW-EURODRIVE.
Avoiding
blockage
Blockage on the output side of the multi-stage gear unit or multi-stage gearmotor is not
permitted. The reason is that indeterminable torques and uncontrolled overhung and
axial loads may occur. This may destroy the gear units.
GM
59717AUS
T
=
T
N allowable
η
total
a max
i
total
Consult SEW-EURODRIVE if blockages of the multi-stage gear unit or multi-stage gear-
motor cannot be avoided due to the application.