After a severe lane change, a wind gust, or another disturbance, the driver might
be unable to recover the intended motion. Even though this fact is known by any
driver, the scientific investigation and testing on this phenomenon is just at
its very beginning, as a literature review, focusing on SAE Mobilus®
database, reveals. We have used different mathematical models of car and driver
for the basic description of car motion after a disturbance. Theoretical topics
such as nonlinear dynamics, bifurcations, and global stability analysis had to
be tackled. Since accurate mathematical models of drivers are still unavailable,
a couple of driving simulators have been used to assess human driving action.
Classic unstable motions such as Hopf bifurcations were found. Such bifurcations
seem almost disregarded by automotive engineers, but they are very well-known by
mathematicians. Other classic unstable motions that have been found are
“unstable limit cycles.” The driving simulator results have been reproduced by
experimental tests on track. We have assessed that the driver’s steering action
can make the car motion unstable if a proper disturbance has acted. The delay of
the driver’s steering action is the primary cause for the generation of limit
cycles. Future automated vehicles should be conceived by focusing on the
addressed phenomenon.
