Method and apparatus for testing motor vehicles under simulated road conditions

A dynamometer for simulating an inertia and road load for a motor vehicle having an engine comprising:

• a power supplying and/or absorbing unit, PAU, coupled to the engine for applying a torque to or receiving a torque from the engine;
• force sensing means coupled to the engine for providing a force achieved signal Fa which is a function of the torque supplied to or received from the PAU minus a force attributable to parasitic losses associated with the dynamometer, and a force attributable to an out-of-loop inertia of the dynamometer;
• speed sensing means coupled to the engine for providing a speed achieved signal Va which is a function of engine speed;
• means for generating a vehicle inertia signal Iv which is a function of a force attributable to the inertia to be simulated for the vehicle;
• means for generating a road load signal RL which is a function of a road load force for the vehicle;
• means for generating a dynamometer parasitic loss signal PL which is a function of the force attributable to the parasitic losses of the dynamometer;
• means for generating an out of loop inertia signal Id representative of the out-of-loop inertia of the dynamometer;
• means for providing a velocity error signal Ve in accordance with:
• ##EQU5## where dt=an interval of integration;
• means for providing a feed-forward signal Fs representative of at least a portion of an inertial force to be simulated by the PAU in accordance with:
• Fs=(Iv-Id) Ac
• where:
• ##EQU6## and means responsive to Ve and Fs for controlling the PAU.

In a method for simulating the inertia and road load forces for motor vehicles on a chassis dynamometer installation, the dynamometer installation including at least one driven roll for engaging driven wheels of the vehicle, at least one power supplying and/or absorbing unit, PAU, connected to the driven roll, force sensing means for providing a measured force signal Fm representative of a force applied to or received from the vehicle wheels by the driven roll, minus a forces attributable to parasitic losses associated with the dynamometer and an out-of-loop inertia of the dynamometer;

• velocity sensing means for providing a velocity signal Va representative of the speed of the roll;
• means for providing a roll acceleration signal As;
• inertia signal generating means for providing a signal Iv representative of a simulated inertia for the vehicle under test, road load signal generating means for providing a road load signal RL representative of the road load forces of the vehicle under test, parasitic loss signal generating means for providing a parasitic loss signal representative of the forces attributable to the parasitic losses of the dynamometer and vehicle, the method comprising:
• a) actuating the power supplying and/or absorbing unit coupled to the roll;
• b) generating a velocity error signal in accordance with:
• ##EQU7## where:
• Fm=the measured force signal;
• PL=the dynamometer parasitic loss signal;
• RL=the road load signal;
• dt=interval of integration;
• Iv=the vehicle inertia signal;
• and
• Va=the measured velocity signal;
• c) generating a feed-forward signal representative of at least a portion of the simulated inertia force required from the PAU;
• and
• d) controlling the PAU in accordance with the velocity error signal and the feed-forward signal.