Theory and Simulation of Fluid Couplings
Report 2002.TT.5658, Transport Engineering and Logistics.
In the area of drive technology it often occurs that the form of power supplied
by an energy source (motor) does not comply with the form of power
required by the energy consumer (load). To overcome this problem, hydrodynamic
couplings can be used to convert the energy supply into a usable form.
The main components of a hydrodynamic coupling, also called fluid coupling,
are two bladed wheels, that is an outer wheel (pump wheel) and inner wheel
(turbine wheel), and a shell. The pump wheel is connected to the motor.
The torque transmitted by the drive motor is converted into kinetic energy
of the operating fluid. In the turbine wheel, which is connected to the driven
machine, this kinetic energy is converted back into mechanical energy. The
transmitted coupling torque always equals the input torque.
To realize a higher relief of the drive motor during start up, a smoother start
of the driven machine and a better efficiency of the drive system, the fluid
coupling can be equipped with a delay-fill chamber and annular chamber. By
using these auxiliary chambers, the amount of operating fluid that takes part
in the torque transfer can be changed during operation.
Determination of the nominal operating point of a drive system (the nominal
operating speed and nominal operating torque) is relatively simple. Also, the
insight of the qualitative start up characteristics of the drive system can be
estimated without much difficulty. However, it is quite complicated to
determine the quantitative characteristics of the start up process and the
dynamic behaviour of the whole drive system. To make a proper estimation of the
start up performance of the drive system, it is almost insurmountable to do
this without any aid of computer software.
Software, called T-Cycle, is available to determine the behaviour of a simple
drive system for several operating characteristics. However, this software is
not suitable for detailed calculations on the operating characteristics of a
drive train. Therefore, a new software tool, called TurboSIM, has been
developed and programmed. TurboSIM is capable of simulating the operating
characteristics of a drive system, consisting of a motor, a hydrodynamic
coupling, a reduction gear and a machine. These elements are connected to each
other with shafts and flexible couplings. By using a dynamic model (with mass,
damping and stiffness properties for all drive system components) the new
software can be used to optimise the design of a drive system, already in the
design stage, by means of parameter variation.
Verification of TurboSIM shows that qualitative operation of the new software
is satisfying. The validation of the software is done by means of a
comparison of simulation results with measured data of a test stand. This
evaluation shows that there is a significant difference between the results of
the simulation software and the results of the test stand. It is very likely
that this deviation is the consequence of a simplification of the model of the
fluid distribution at the coupling's start up.
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