# Multi-Physics Analysis of a Magnetorheological Valve Train with Experimental Validation
## 1 Introduction  
Magnetorheological (MR) fluid is a smart material that can be used to develop control systems for engineering applications. This fluid reacts to a magnetic field and provides a corresponding flow resistance. This reaction is extremely quick, can realize the required control operation, and is reversible. Therefore, researchers have been using MR fluid to convert passive actuators, such as dampers, brakes, clutches, mounts, and valves, into semicative control devices. First, active MR dampers can be used in civil construction works to decrease the vibration caused by earthquakes, and they can be used to isolate automobiles from road shocks [1, 2]. In both applications, the frequency and magnitude of vibrations change actively. Passive dampers cannot vary the damping effect as required. Therefore, active and semicative dampers are becoming increasingly popular. In conventional active dampers, the damping force is regulated by adjusting the damper orifice area, but the speed of this change is extremely low. To mitigate this problem, MR fluid technology is the most suitable and least energy-consuming alternative. The second application is the MR brake. The flow resistance force of MR fluid can be used as a braking force. Based on this concept, disc-type, drum-type, single-pole, multipole, single-layer, and multilayer brakes have been developed [3, 4, 5]. Moreover, MR technology is being used in clutches, seat suspension, and engine mounts. [PERSON] [6] developed a rotaryMR damper for heavy-duty vehicle seat suspension, and [PERSON] [7] designed an MR mount to isolate the vibrations caused by engines. Finally, another MR-fluid-based device is the MR valve, which is used in hydraulic and engine intake control systems. It is an excellent substitute for mechanical valves owing to advantages such as its low weight, ease of control, and lack of moving parts [8]. To improve MR valve actuation, several MR valve structures have been developed, for example, the multistage structure, modular structure, and modular structure with meandering flow [9]. In this context of MR valve application, the valve actuation requirements of internal combustion (IC) engines must be discussed. In an IC engine, the fuel valve must open and close in accordance with the engine's operation cycle timing. Conventionally, cams and mechanical linkages with fixed timings are used to realize this control objective. However, to enhance performance, reduce emissions, and keep the engine running in its \"sweet spot\", this actuation should be dynamic, that is, the valve opening timing and valve lift magnitude must vary with the engine's speed and load [10]. Therefore, engine developers have introduced variable valve timing (VVT) and variable valve lift (VVL) systems that contain various actuators. Several mechanical, hydraulic, and electronic actuators have been established to achieve VVT and VVL, and they all have their unique advantages and disadvantages [11; 12; 13]. [PERSON] [14] developed the first-generation MR valve for IC engines; this was a highly innovative concept in the domain of MR fluid applications. However, the design of that device is extremely complex; oil leakage from the buffer zone is a major problem, and the device's volume is too high. Therefore, in the next-generation MR valve, the buffer zone was replaced with a buffer spring, and a key component called the magnetic plate block was optimized [15; 16]. MR valve train devices remain at the conceptual study level. Therefore, detailed and realistic analyses are needed to estimate their actual performance. Magnetic simulations, thermal field simulations, and coupled-effects simulations are necessary to understand the realistic conditions under which these devices could be used. [PERSON] [17] studied the temperature rise in an MR brake by using the physics coupling technique. In [17], the author performed a multiphysics analysis (coupled magnetic and thermal analysis) to optimize the magnetic plate block.