Power take-off
199
Things to remember concerning
power take-off at the timing gears
• The limiting factor for the life of the gears is
torque.
• If a higher torque than listed is utilised, the lifetime
of the gears will be reduced.
• Remember the formula:
P = M x v
P = Output in W
M = Torque in Nm
v = Angel speed = in RAD/s
n = Driven apparatus speed in rpm
This means that if the same output (P) is utilised at
a lower engine speed, the torque will be higher and
thus resulting in shorter life for the gears.
Example:
P = 15.3 kW
M = 73 Nm
n = 2000 rpm
Now, if we want to utilise the same power at 1800 en-
gine rpm, what is the torque?
First the compressor speed must be calculated:
Crankshaft gear (Z = 30) / Compressor gear (Z = 33)
30/33 = 0.909 (compr. gear ratio)
1800 x 0.909 = 1636 rpm.
15300 = M x
M = 89.3 Nm
Example:
What is the max permissible power for the servo
pump gear at 1500 rpm (engine speed) for a 7 l en-
gine?
Max. torque M = 38 Nm
According to the Sales Guide:
Servo pump speed ratio = 1.58 : 1
1500 x 1.58 = 2370 rpm
P = 38 x
P = 9431 W = 9.4 kW
Auxiliary drives
Gear driven power take-off from
timing case
The engine specifications must be appropriate for the
power take-off equipment to be fitted.
Weight
The weight of the extra equipment to be bolted on
to the timing cases must be considered. A support
bracket from the cylinder block should be used for
heavy equipment.
Cyclic torque
Some equipment, i.e. hydraulic pumps, impose high
cyclic torque variations on the timing gears. This
means that max torque in accordance with the data
given in the Sales Guide Marine Propulsion Diesel
Engines can not be utilised.
Miscellaneous
In the case of engines fitted with keel cooling, no
seawater pump is used for systems only requiring cir-
culation pump. A power take-off can then be located
in the place of the seawater pump at the rear. A driv-
ing gearwheel must be fitted in the power take-off in
the same way as for the seawater pump.
In the case of the 74-engines, a power take-off can-
not be fitted on the front of the auxiliary drive gear
casing when the engine is fitted with a power take-off
driven from the crankshaft.
Check that the output requirement does not exceed
the maximum permissible output according to the
specifications in the sales literature.
IMPORTANT! Any power take-off equipment at-
tached directly to timing case must be approved
by Volvo Penta.
π x 2370
30
π x 1636
30
π x n
30
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