This paper studies and compares the vibration control performance of variable
damping electromagnetic damper (VD-EMD) and variable stiffness and damping
electromagnetic damper (VSD-EMD), and explores the advantages of VSD-EMD over
VD-EMD in terms of controllability and improvement of ride comfort. In VD-EMD, a
variable resistor is connected to the DC motor, the equivalent damping is
related to resistance but not to frequency, by adjusting the resistance of the
variable resistor, the damping of VD-EMD can be changed. In variable stiffness
electromagnetic damper (VS-EMD), a branch formed by connecting a variable
resistor and an inductor in series is connected to the DC motor, by adjusting
the variable resistor, the equivalent stiffness of VS-EMD can be controlled, in
addition, the equivalent stiffness also varies with the excitation frequency.
The mechanical characteristics of VD-EMD and VS-EMD have been verified. Since
shock absorber with multiple variable mechanical characteristics can achieve
better vibration reduction effects, the variable stiffness and damping functions
of VSD-EMD has been achieved by paralleling the circuits of VD-EMD and VS-EMD.
To compare the vibration control effects of VD-EMD and VSD-EMD, they are applied
to a quarter car model. A sliding mode controller is designed and two
semi-active control strategies are applied to control the vibration of vehicles
by VD-EMD and VSD-EMD respectively. Under sinusoidal excitation, the
effectiveness of the control strategies is verified and the peak acceleration of
the sprung mass of VSD-EMD has decreased. In addition, the output force of
VSD-EMD has a longer tracking time for the ideal force which means that VSD-EMD
has higher controllability. Under random road excitation, VSD-EMD has better
vibration reduction effects in the frequency range of 0.1-2.5, 7.5-10, and above
22 Hz. In addition, the root-mean-square of VSD-EMD’s sprung mass decreased by
12.9% compared to VD-EMD. Electromagnetic damper with variable damping and
stiffness functions can broaden the vibration reduction range and achieve a
better vibration reduction effect.