The design, control and performance of a versatile, minimum energy dissipating regenerative road load simulator for laboratory use is described. The arrangement of the unit provides two separate controllable dynamometers for testing a wide range of conventional, electrical and hybrid propulsion systems and transmission components.
A hydrostatic pump-motor set forms one dynamometer, which will absorb or supply a maxi mum torque of 410 Nm, and up to 70 kW of tailshaft power at speeds from zero to 3000 rpm.
The second dynamometer is a Ward Leonard motor-generator set capable of absorbing or supplying up to 150 Nm to 3000 rpm, then 55 kW up to 6000 rpm. This dynamometer can also simulate the behaviour of small to medium sized IC engines.
Components of the electrical dynamometer can also be arranged as a battery simulator to supply or absorb the power for electrical components of any hybrid or electric transmission system under test. In this mode the mechanical power is absorbed or supplied by the hydrostatic regenerative dynamometer.
The two dynamometers can be used concurrently to evaluate such components as axle differentials and epicyclic gear boxes, in which case a separate prime mover is required. Negative torque capabilities in this mode will depend on the power absorbing capacity of the prime mover chosen.
When the electrical components are used to simulate a prime mover, the control system can be adapted to accept, for example, a given velocity time history and generate the required input torque to the simulator's torque control system. Parameters for any vehicle to be simulated can be entered into a torque speed generator within the control system so that actual tailshaft torque developed in either dynamometer can be used to generate the desired speed input to the speed controller. Parameters include vehicle mass, axle ratio, tyre rolling radius, aerodynamic drag, rolling resistance and road gradient.
When testing a transmission with no slip or energy storage capability, the torque system and the speed system were significantly cross-coupled as predicted. Using a non-slip manual gear box as a test transmission, the torque system was isolated from the speed system by locking the tailshaft. The torque system dynamics were then modelled and a suitable torque controlled developed. By placing the gearbox in neutral, the speed system was decoupled from the torque system, modelled, and a suitable speed controller developed. The two systems were then coupled and the overall response assessed.
A hybrid computer program was prepared to measure the steady state efficiency of a transmission and to plot contours of efficiency and power. The accuracy of the technique was validated by measuring the transmission efficiency of a solid shaft. The simulator was then used to obtain efficiency contours for positive and negative torque for the DC motor component of the electrical dynamometer and for various gears of the manual gearbox.
An automatic transmission was then installed and the control system adapted to suit. Efficiency contours of the automatic transmission with first gear selected were measured for positive and negative torques. The performance of the simulator with the automatic transmission fitted, when evaluated using the US Federal DHEW Urban Driving Schedule velocity-time history, was found to be satisfactory.