A transient driving cycle simulator test system for testing a prime mover in a laboratory environment is described, which includes an inertia wheel assembly operatively coupled to the prime mover for simulating vehicle acceleration and deceleration horsepower requirements, a dynamometer operatively coupled to the inertia wheel assembly for simulating vehicle road-load horsepower requirements, and a microcomputer control circuit for providing closed-loop control of the prime mover, the inertia wheel assembly and the dynamometer in response to a set of predetermined transient driving cycle specifications. The inertia wheel assembly features a pair of disc brakes for selectively retarding the rotation of an output shaft of the prime mover to provide forced deceleration of the vehicle being simulated.

A test bench for testing a drive train of a test vehicle from an internal combustion engine up to drive shafts for wheels includes an electronic function element or computer simulating moments of inertia, spring stiffnesses, and damping masses. The electronic function element or computer simulates the wheels and a vehicle acceleration process, with the exception of actually present vehicle components. At least two mutually independent moment-regulated electric load machines serve as a transmission element between the electronic function element or computer and the test bench having the test vehicle. The load machines are flanged directly to the drive shafts of the drive train to be tested.

A dynamic load test system simulates rotating mass torque loads encountered by specimen drive units such as complete motor vehicles, internal combustion engines, transmissions, brake systems and the like. The system includes a high pressure hydrostatic pump/motor unit which is controlled and regulated as a function of the positive or negative acceleration of the test specimen. Preferably, a portion of the total flywheel mass moment of inertia required for testing the specimen is generated by actual flywheel masses while a further portion is simulated by the hydrostatic pump/motor unit or a plurality of hydrostatic units.

Test stands for automotive vehicles at the present are required in most cases to permit dynamic tests wherein an essential criterion consists of the simulation of the actual vehicle inertia moment, in order to obtain a realistic acceleration behavior. The test stand normally has a constant inertia moment. A process and a circuit layout is proposed for the simulation of vehicle inertia moments, whereby the test stand and the test specimen represent a n-mass oscillator, the masses of which are elastically joined together. By means of electronic functional elements (24, 25, 27, 32, 33, and 34), an m number of further masses are imitated electronically so that the regulation technical structure corresponds to the differential equation system of a (n+m) mass system. An air gap moment controlled electric machine is used as the transmission element (34) between the electric functional elements (24, 25, 27, 32, 33, and 34) and the mechanical masses. By setting the time constants (T.sub.Kfz, T.sub.CKfz) and the amplification factors (K.sub.dKfz) of the functional elements (24, 25, and 27), the vehicle vibration behavior (natural frequency, attenuation) may also be imitated, in addition to the simulation of the vehicle inertia moment.

A power testing apparatus includes a brake mechanism which is operated to brake an inertial load adjusting flywheel at a desired timing. A clutch is provided for controlling transmission of an inertial load from the adjusting flywheel to a tested object. Particular advantage of providing the brake mechanism for the adjusting flywheel is that the brake mechanism is adapted to brake the adjusting flywheel when the adjusting flywheel is rotating idle where no inertial load is applied to the tested object due to the clutch being disengaged.