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1.9 Torque<br />
Tiso = limit torque<br />
Transmittable torque of the gearbox, with continuous operation, calculated in accordance to ISO DP6336 for<br />
gears and safety factor of 1. This torque corresponds to a life duration equal to 50.106 cycles of the most stressed<br />
element (theoretically considered unlimited by the ISO DP6336; horizontal curve in the Wöhler fatigue diagram).<br />
This torque does not represent a duration, but it is useful for a quick selection of the maximum size of the<br />
gearbox.<br />
Tcont = continuous torque<br />
Transmittable torque of the gearbox, with continuous operation, that guarantees a duration of ‘h’ hours, with a<br />
gearbox output rotation velocity of ‘n2’ RPM. Tcont is expressed as a function of the product n2 h.<br />
Teq = equivalent torque<br />
Teq represents the value of a constant torque which determines the same duration in hours of the torque<br />
induced by the work cycle. Known as T21 … T2n the torque transmitted by the gearbox at the output velocity n2i<br />
for a time duration in hours of hi, the equivalent torque is:<br />
where<br />
Timp = impulsive torque<br />
value of the static torque or an istantaneous peak load that the gearbox can withstand.<br />
1.10 Effi ciency<br />
ηm = mechanical effi ciency:<br />
ratio between the output power and input power; normally it is considered to be equal to 0,97 – 0,98 per<br />
reduction stage that makes up the gearbox; it depends upon various factors, of which velocity, torque, ratio,<br />
working position and lubrication.<br />
2. Gearbox selection method<br />
2.1 Selection<br />
Once established the selection criteria, which can be defi ned using an ISO or AGMA safety factor, based upon the<br />
class according to the F.E.M. standard or by expressing a minimum life duration, the equivalent output torque Teq is<br />
determined as well as the required duration and the reduction ratio. Using these criteria the gearbox is selected.<br />
- safety factor ISO/AGMA:<br />
the gearbox must garantee the requested theoretical lifetime;<br />
- F.E.M. class:<br />
the gearbox must garanteee that the requested theoretical lifetime correspond to that indicated by the F.E.M.<br />
class as a function of the max and Teq;<br />
- life duration:<br />
the gearbox must have a life duration greater than that required as a function of Teq.<br />
For example, table... on page F.2 / F.9 shows the continuous torques as a function of gearbox size and the reduction<br />
ratio. Please note that when an electric motor is used, the start up torque can be 2.5 times greater than its nominal<br />
value.<br />
H Y D R A U L I K<br />
Page B. 8<br />
www.jahns-<strong>hydraulik</strong>.de