Emulation system for a motor vehicle drivetrain

In a motor vehicle engine testing arrangement including a motor vehicle engine and an electric dynamometer coupled to the output shaft of such engine and adapted to regulate the engine speed in accordance with a speed control signal applied thereto, a method of operating the dynamometer so as to emulate the combined effect of a motor vehicle and conventional motor vehicle drivetrain elements including a fluidic torque converter and a shiftable ratio automatic transmission, such method comprising the steps of:

• defining first and second differential equations relating the ability of the drivetrain input torque to accelerate the engine inertia, and the ability of the drivetrain output torque to overcome the road load and accelerate the vehicle inertia;
• modeling the combined operation of a fluidic torque converter and a shiftable ratio automatic transmission, and coupling the first and second differential equations therewith such that the drivetrain input torque is determined as a function of measured engine output torque and the load that would be imposed on the engine by the torque converter and the drivetrain output torque is determined as a function of the transmission output torque and the road load of the vehicle;
• periodically integrating the first and second differential equations forward in time assuming substantially constant engine output torque during the integration period to thereby predict the engine speed that would occur were the engine driving a motor vehicle through the defined drivetrain elements in opposition to the road load;
• and
• generating a speed control signal for the dynamometer in accordance with the predicted engine speed to thereby load the engine as though it were actually installed in an motor vehicle with the modeled drivetrain elements.