Second order steady modes in the relay control systems with time delay

The second order relay control systems with delay (SORCSD) are considered. It is shown that the average frequency of any oscillatory solution of SORCSD after a finite time interval becomes a constant. We give sufficient conditions for the existence of periodic oscillations in SORCSD for any frequency, and sufficient conditions for the orbital asymptotic stability of periodic oscillations with the minimal (zero) average frequency.