.ObsoleteModelica3.Mechanics.Rotational.GearEfficiency

Information

THIS COMPONENT IS OBSOLETE and should no longer be used. It is only kept for backward compatibility purposes. Use model Modelica.Mechanics.Rotational.LossyGear instead which implements gear efficiency in a much more reliable way.

This component consists of two rigidly connected flanges flange_a and flange_b without inertia where an efficiency coefficient eta reduces the driven torque as function of the driving torque depending on the direction of the energy flow, i.e., energy is always lost. This can be seen as a simple model of the Coulomb friction acting between the teeth of a gearbox.

Note, that most gearbox manufacturers provide tables of the efficiency of a gearbox as function of the angular velocity (efficiency becomes zero, if the angular velocity is zero). However, such a table is practically useless for simulation purposes, because in gearboxes always two types of friction is present: (1) Friction in the bearings and (2) friction between the teeth of the gear. (1) leads to a velocity dependent, additive loss-torque, whereas (2) leads to a torque-dependent reduction of the driving torque. The gearbox manufacturers measure both effects together and determine the gear efficiency from it, although for simulation purposes the two effects need to be separated. Assume for example that only constant bearing friction, i.e., bearingTorque=const., is present, i.e.,

   (1)  loadTorque = motorTorque - sign(w)*bearingTorque

Gearbox manufacturers use the loss-formula

   (2)  loadTorque = eta*motorTorque

Comparing (1) and (2) gives a formula for the efficiency eta:

   eta = (1 - sign(w)*bearingTorque/motorTorque)

When the motorTorque becomes smaller as the bearingTorque, (2) is useless, because the efficiency is zero. To summarize, be careful to determine the gear efficiency of this element from tables of the gear manufacturers.