Speed control of hydrodynamic dynamometers for internal combustion engine test benches

Hydrodynamic dynamometers are primarily used in stationary testing of large internal combustion engines. They are inexpensive, have a small moment of inertia and cover the entire range of internal combustion engines, so their use for dynamical testing would be interesting, but actually they are not used for this purpose due to the strongly nonlinear behavior. Against this background, this paper proposes a cascaded speed control approach based on an inversion of the output nonlinearities. Available degrees of freedom are used to take into account boundaries on fluid temperatures. Measurements on a dynamic truck engine test bench show that the proposed approach is able to offer a significantly better performance with respect to the standard control, allowing an extension of the application of hydrodynamic dynamometers from purely stationary tests to dynamic testing used e.g. in emission legislation.