###### Abstract  
This paper aims to present a suspension control strategy for a semi-active mount with variable damping utilizing a smart magneto-rheological fluid (MRF), which will be applied in a micro autonomous railway inspection car as a primary suspension to protect the inspection equipment from the large suspension vibration on rails. We proposed a new multi-pole structure design for a semi-active magneto-rheological mount (MR mount) that can provide both a high damping force and a wide damping force band. Firstly, the mathematical model of MR mount dynamics was derived; secondly, a skyhook control strategy was developed for the MR mount; and finally, a dynamic simulation problem using Matlab software was constructed to evaluate the performance of the MR mount. The dynamic simulation results showed that the proposed MR mount using a skyhook control strategy showed greater vibration isolation performance compared to conventional passive mounts. In particular, the absolute displacement, velocity, and acceleration of the detector device were reduced by 83.33%, 77%, and 70%, respectively. The suspension vibration transmitted to the inspection device also decreased significantly, compared to input oscillation (i.e., un-sprung mass oscillation). Specifically, the suspension vibration reduced by a half at the excitation frequency of 2-fold the natural frequency and by greater magnitudes at higher excitation frequencies. magneto-rheological fluid; semi-active mount; micro autonomous railway inspection car; suspension control strategy; mount +
Footnote †: journal: Applied  
this object [8; 9; 10; 11; 12; 13; 14]. Specifically, there are two main approaches to the design of semi-active mount: utilizing different fluid properties including a magneto-rheological (MR) fluid and an electro-rheological (ER) fluid [9; 12] and changing structural parameters including the cross-sectional area and the length of the channel [13; 14]. For example, in the latter approach, [PERSON] et al. [13] used a mechanism of through thread with a single actuator to simultaneously adjust the length and cross-sectional area of the inertia channel to change the damping force; therefore, this design can isolate vibrations within a certain frequency band. Among different types of semi-active mounts, the MR fluid mount is most concerned due to its outstanding characteristics, such as fast response, high shear stress, easy control, and good stability. In addition, the MR mount can be improved easily by adding a magnetic part and a MR fluid into a conventional rubber or hydraulic mount [15; 16; 17; 18; 19]. According to operating modes, MR mounts are classified as flow mode, squeeze mode, shear mode, and combined mode. For example, [PERSON] et al. [15] proposed an MR mount with a squeeze mode for passenger vehicle applications. An MR mount with a shear mode was also proposed by [PERSON] et al. [16]. [PERSON] et al. [17] and [PERSON] et al. [18] proposed MR mounts with a flow mode, adopting a combination of annular and radial channels to improve the damping force of the mount. However, they have some disadvantages, including a relatively complicated structure, the neck locking phenomenon, and a narrow damping force band (from a viscosity-induced damping force to a magnetic field-induced damping force). To overcome this problem, the magnetic flux should be exploited effectively by using multi-magnetic poles and space optimization for the mount, and using fluid flow channels with big gaps and short lengths to avoid the locking phenomenon. The control theories for the MR mount have been well developed, including the skyhook control theory used by [PERSON] et al. [20], the fuzzy-PID control used by [PERSON] et al. [21], and adaptive fuzzy control used by [PERSON] et al. [22].