VALIDATION OF THE HARSHNESS PROBLEM OF AUTOMOTIVE ACTIVE SUSPENSIONS

The advantages of an automotive fully active suspension system have be en promised for many years. Among them, simultaneously achieving good body and wheel mode damping is of the most fundamental. However, imple mentations of such concepts with hydraulic actuators have generally ex hibit worse-than-passive harshness performance when such vehicles are driven through small irregularities on the road. Additional forces are transmitted through the hydraulic active suspension to the vehicle bo dy at high frequencies. Conventional wisdom blames the non-ideal actua tor in practice for the problem since most analytical papers assume it an ideal force-producing element. However, the mechanism of generatin g such excessive force as well as the methodology of solving it has no t been systematically demonstrated in the literature. In this paper, a high fidelity mathematical quarter vehicle model is first developed a nd identified with vehicle test data. This model captures realistic dy namic behaviors of the hydraulic active suspension. The mechanism of c reating such harshness problem is then explained with this model. To v alidate such mechanism, a frequency domain methodology that yields an equal-to-passive high frequency performance while maintaining a good a ctive body behavior was developed based on this model and demonstrated with a test vehicle. The model predicts the test results almost exact ly.