The engine mount is a mechanical device used in holding an engine with the frame or chassis. It consists of an elastomer rubber placed in between the metal casing and center core. The functions are to support the engine mass and to absorb and isolate the vibration occurring in the engine, thus reducing it from transferring to the rest of the vehicle’s structure (Yu et al., 2001; Ooi and Ripin, 2011). To date, rubber has been widely used as a material in the engine mounting system (Wang and Kari, 2019) due to the low damping properties and elastic stiffness in absorbing the vibration. In order to fit the desired applications, few types of engine mounts have been designed and developed until today, such as the elastomeric mount, hydraulic mount, semi-active mount, and active mount (Yang et al., 2019). The elastomeric engine mount or conventional engine mount utilized the conventional rubber compound, having uniform and rigid mechanical properties in which the vibration control and attenuation are generally effective at narrow frequency ranges (Jung et al., 2010; Xu et al., 2010; Ubaidillah et al., 2015) and are unable to operate satisfactorily in a wide range of conditions. While the hydraulic engine mount, consisting of the usage of liquid medium (Shangguan, 2009), greatly increased damping at low frequency, the degraded isolation performance is at high frequency (Yu et al., 2001) and is limited in durability (Jeong et al., 2013). Nowadays, moving out of the boundary of passive type device utilization, active versions of engine mounting systems have drawn the awareness of vibration absorption designers and researchers. An active engine mount, which consists of an active force generator and controller, possesses superior performance not only in the vibration reduction ability but also for its fast response (Swanson, 1993; Yu et al., 2001; Lerner and Cunefare, 2008). However, it is also reported that such devices have several limitations such as higher system cost and heavier weight (Sun et al., 2018; Soliman and Kaldas, 2019), having system complexity and decreasing its stability (Th et al., 1985; Kela and Vähäoja, 2009). It is for these reasons that the semi-active engine mount such as MRE engine mounts have attracted the attention of current researchers due to its simplicity in design yet being effective (Liao et al., 2011; Hoang et al., 2013; Sun et al., 2015, 2018).

The MRE engine mount is a device in which the elastomeric rubber part was replaced with an MRE sample that consists of micron-size magnetizable particles suspended in its matrix material. In the presence of a magnetic field, this type of material exhibits tunable stiffness, which has an effect on its storage and loss modulus (Nam et al., 2020). The end purpose of the device’s performance development is to fabricate an MRE engine mount with a good MR effect, low damping ratio, and a good tensile and fatigue strength (Burgaz and Goksuzoglu, 2020). The good MR effect is denoted by the proportionate change in storage modulus (G′) toward the applied strength of the magnetic field, while a good tensile strength is denoted by a high tensile strength of the matrix material used such as the natural rubber (NR). Recently, numbers of semi-active MRE engine mounts have been proposed and tested for their performance using various types of device design and configuration (Albanese and Cunefare, 2003; Hoang et al., 2011; Kavlicoglu et al., 2011; Xin et al., 2017). Different configurations of the proposed device vary in fulfilling the requirement of the device fundamental aspect and are generally divided into three criteria, which are the matrix material selection, shape, and size of the compound used together with the employed coil configuration. Detailed research studies have been carried out as well, using a series of numerical models due to the viscoelastic characteristic of the material which exhibits nonlinear properties with the displacement amplitudes and frequencies under magnetic field stimuli (Nguyen et al., 2018; Yu et al., 2019). Understanding and modeling the mechanical behaviors of MREs under different magnetic field strengths are necessary to design an appropriate MRE-based semi-active control device (Nguyen et al., 2019).

In terms of device configuration involving the matrix material, silicone rubber has been widely utilized as a medium in MRE fabrication due to its easy sample preparation since it can be easily processed during compounding and retains various enhancement capabilities such as high field-induced relative stiffness (Shenoy et al., 2020). Deng et al. (2006) has reported an increase of 147% in terms of relative frequency for the devices utilizing silicone rubber, while Liao et al. (2011) revealed a device capability in the resonant frequency increment from 11 to 18 Hz. Meanwhile, Sun et al. (2014) also reported on a natural frequency shift from 37 to 67 Hz, and Dargahi et al. (2019) revealed an astonishing 1672% increase of storage modulus for vibration control devices. In general, all of these reported performance materials are capable to be applied for the potentially relevant engineering applications. However, there were evidences that proved this type of soft matrix was not suitable to be used in the load-bearing device due to its low strength and fatigue life (Fuchs et al., 2007; Qiao et al., 2012; Zhu et al., 2012). Natural rubber, on the other hand, offers high elasticity, tensile and tear strength, excellent wearability, abrasive resistance, easy availability, and low cost (Schaefer, 2002; Jung et al., 2015; Belluci et al., 2016; Fan et al., 2018) and is also capable to sustain a wide range of deformation and flexibility in industrial applications (Alam et al., 2020).

Meanwhile, the second criterion of the device structure is characterized by the geometrical shape and size of the prepared matrix compound. Many research studies generally focus on small and thin samples, which geometrically include square, rectangular, and circular or round pieces. Moreover, most of the study basically focused on the use of thick MRE samples in the range of 3–10 mm due to their easy laboratory sample preparation for performing the test. As such, Ginder et al. (2001) explored a tuneable device performance using an MRE material having the size of 60 mm in diameter with 2 mm thickness. In another study, Jeong et al. (2013) proposed a differential mount using a rectangular MRE sample with an initial size of 30 × 12 mm² with 5 mm thickness. Xin et al. (2017) proposed a powertrain mount utilizing a circular cylindrical MRE with 68 and 56 mm of the outer and inner diameter, respectively, and 10 mm thickness. Zhang and Ren (2019) designed an automobile vibration-reducing device using MRE samples having thickness of 3 and 6 mm. However, limited study was observed in the study based on the actual size of the rubber composite or MRE used in the engine mount device. Therefore, it is interesting to observe the behavior and the performance of the industrial scale MRE-based engine mount with an industrial scale size of the MRE sample fabricated using the industry’s compression molding machine.

The last criterion of the device structure is characterized by the device design including coil configuration for an optimum magnetic field distribution throughout the device, especially at the MRE effective area. Furthermore, coil configuration is identified by its location, placed either internally or externally, and also by the number of the coil used, either single or multicoil. Albanese and Cunefare (2003) discussed a semi-active absorber device which consisted of MR silicone of 0.5 cm in length in between the steel loops of 3.6 cm in length, wound with a magnet wire as the coil. They found that the size of the device was seven times bigger than the MR composite and was capable of shifting the initial natural frequency of 45 up to 183 Hz. Due to its small size, the device was suitable to be used in constraint space. Kavlicoglu et al. (2011) reported an MRE mount consisting of four MRE layers, each with 12.7 mm thickness and two electromagnetic coils sandwiched in between the mounting plates and secured by epoxy glue. The generated magnetic field from the coils directly penetrated the MRE layers toward the outer mounting plates and thus gained the maximum stiffness change under magnetic fields up to 0.4 T, resulting in 90% change of the compression stiffness. Meanwhile, Hoang et al. (2011) designed a vibration absorption device consisting of an MRE material placed in between an inner and outer cylinder, excited by the three external magnetic coils, with each coil capable of generating a magnetic field up to 0.3 T. Xin et al. (2017) proposed a powertrain mount device, composed of a semi-active vibration absorption unit, which utilized an O-ring type MRE with an outer diameter of 68 mm, inner diameter of 56 mm, and thickness of 10 mm. The device utilized a single internal magnetic coil covered with high magnetic permeability structures made from pure iron to ensure a closed property of the magnetic circuit and increase the magnetic flux intensity through the MRE. Such a design prevented unnecessary field leakage, thus capable of generating a high magnetic field intensity up to 0.68 T with a supplied current of 2 A. In general, the main and critical criteria in the reliable device design and coil configuration lie in the sufficient distribution of the magnetic field in which the circulation of the magnetic flux reaches throughout the MRE area (Li et al., 2020). Moreover, the design with a closed loop property of the magnetic circulation also plays an important role in avoiding unnecessary field leakage.

From these studies, the results demonstrated the possibility and potential of the proposed semi-active MRE engine mounts in absorbing and isolating the vibration. However, most of the studies focused on the device utilizing the lab-scale soft matrix compound for high performance results and ease of fabrication processes. Therefore, this study contributes to the MRE property characterization of the material carried out by the static test, representing the elastomer as “high elastic” rather than the viscoelastic nature which is carried out by dynamic tests (Shenoy et al., 2020), in evaluating an industrial scale device of an engine mount utilizing an appropriate load bearer matrix carrier, which is also fabricated industrially to be tested under magnetic field stimuli. The selection of materials together with the carbonyl iron particle (CIP) content is considered in order to obtain an optimum device design with high magnetic field strength throughout the effective area. The device’s conceptual design and the magnetic distribution analysis are being validated by Finite Element Method Magnetics (FEMM), and such an approach of validating the magnetic distributions using a simulation method is being carried out by most of the eminent researchers in this field (Xin et al., 2017; Samal et al., 2020; Shenoy et al., 2020; Huang et al., 2021). Future works will focus in the dynamic method together with the control system evaluation.

The industrial fabricated engine mount possesses a cylindrical shape with an external casing diameter of 68 mm and a center core diameter of 12 mm with the height of 40 mm. The external casing and the center core are separated by the MRE compound. The center core is attached to the vehicle’s engine by means of a bolted shaft, while the external casing is attached to the vehicle’s frame via the structure casing, thus holding the engine at its position and supporting the engine’s weight. As the engine is in operation and subjected to vibration, the MRE compound will isolate and attenuate the vibration from transferring to the rest of the vehicle’s structure. Subjected under the industrial product specification is the engine mount having the maximum amplitude of 7 mm and maximum load capacity of 2 kN. Figure 1A represents the cross-sectional area of the entire proposed structure of the MRE engine mount. The conceptual design structure consists of an outermost cylindrical housing, covered with two cover plates, in which each plate is located at the top and bottom of the structure, a bobbin core, an electromagnetic coil winding around the bobbin, and finally the cylindrical MRE engine mount was press-fitted at the very center of the design to ensure its rigidity. Figure 1B shows a schematic representation of the entire structure.

Because of the current being supplied to the electromagnetic coil, the magnetic fluxes were generated and circulated throughout the structure, and the flows were then directed toward the MRE area, as shown by the red arrows in Figure 1B, representing the magnetic passage. As the ranges of the magnetic field excitation are being imposed on the engine mount, the stiffness of the MRE could be tuned by adapting the supplied current, and simultaneously, the vibration of the engine mounting system could be attenuated correspondingly. Further analysis of the magnetic distribution in the results and discussion section represented by Figure 9A indicates that the magnetic flux distribution formed a closed loop path, and thus, the magnetic leakage was optimally prevented. The structural parameters of the design are listed in Table 1.

The diameter of the entire structure d ₁ represents the overall diameter measurements for the cylindrical housing, while h ₁ represents the height or the width of the structure consisting of the top and bottom cover plates together with the height of the electromagnetic coil. As such, the entire structure is having a general size of 150 mm × 60 mm. The design concept has been modified by using an external magnetic coil instead of an internal magnetic coil, in which the original work of the vibration absorber utilizing the internal coil for the powertrain mount system was carried out by Xin et al. (2017). By using an external magnetic coil, the simulation result of the magnetic flux distribution in Figure 9A had shown that the full coverage of the magnetic flux could be provided throughout the area, which was from the top side of the MRE effective area toward the bottom side. The dimensions of the coil are represented by l ₁ and h ₂ , which are the width and the length of the coil area, respectively. In this study, a 24 SWG-coated copper wire with the diameter of 0.6 mm has been selected to generate the magnetic field in the MRE engine mount. A total number of 3,500 turns were wound around the coil, together with 56 layers, with each layer having 63 turns of the copper wire.

The fabrication of the entire structure consisted of three major stages, which were the MRE compound preparation, electromagnetic coil designing and fabrication, and finally the fabrication of the MRE engine mount. In addition, the experimental setup and procedures were then explained in the following section, which include several tests comprising the MRE compound test and the engine mount test in terms of the static compression in evaluating the device performance.

In this work, an industrial scale engine mount equipped with an appropriate load bearer matrix carrier was fabricated industrially and tested for the compression load performance under the influence of magnetic field stimuli. The entire structure was designed accordingly and analyzed using FEMM for an optimum magnetic flux density throughout the effective area of the MRE, where an average value of 0.31 T of the magnetic flux density was obtained. Based on the structured analysis of each part, the fabrication process was carried out. Starting with compound preparation and the test of mechanical properties, the results showed that the MRE compound held a good tensile strength and hardness of 12.65 MPa and 48, respectively. The static compression tests at off- and on-state conditions were then carried out to test the effect of the engine mount at various ranges of the supplied current. At the off-state test, the MRE engine mount recorded the highest force with 12% increment at 3 mm of extension compared to the normal engine mount utilizing a conventional rubber. While at the on-state test, the MRE engine mount showed an increase in the compression force as the current was being increased gradually up to 2.4 A. At 3 mm of extension, the force with 2.4 A was increased by 106% with the supplied current. A linear relationship of stiffness with the increasing supplied currents has demonstrated that the MRE engine mount was influenced by the presence of the magnetic field. Thus, the proposed design of the MRE engine mount can be effectively utilized in generating controllably required stiffness by tuning the applied current (magnetic density) accordingly. The necessity of the dynamic test subjected under different amplitudes and frequencies together with the control system of the proposed device is very well taken into consideration that will be undertaken as the second phase of this work.