# Multi-Physics Analysis of a Magnetorheological Valve Train with Experimental Validation
## 2 New Lightweight MR Valve Train  
The proposed MR-fluid-based variable valve comprises the following: a rocker arm; an upper piston; a lower piston; a magnetic plate block; three springs, namely a buffer spring, an upper spring, and a return spring, as depicted in Figure 1a. The upper piston is placed in the upper cylinder and connected to the rocker arm through the upper spring. The lower piston is positioned in the lower cylinder and connected to the valve and the return spring. These upper and lower cylinders are filled with MR fluid, and a magnetic plate block separates them. Figure 1b illustrates the arrangement of these cylinders and pistons. The magnetic plate block comprises an electromagnetic coil area, which generates the required magnetic field; a rectangular channel, which transfers the field, and several thin and parallel plates, which facilitate the flow of MR fluid from the upper cylinder to the lower cylinder through the gaps between the aforementioned thin parallel plates. When the cam rotates with default engine timing, the rocker arm follows the cam, and it transfers equal lift forces to the upper and buffer springs. Then, the upper piston pushes the MR fluid into the cylinder. Thereafter, the MR fluid transfers this pushing force to the lower piston by flowing through the magnetic plate block. The magnetized thin plates in the magnetic plate block resist the MR fluid flow that eventually acts against the lift force distribution from the rocker side to the valve side. The magnitude of this force is proportional to the current in the coil. Therefore, the valve opening timing and lift can no longer follow the default cam timing; they change with the coil current. The working mechanism of the proposed valve train can be explained by dividing the mechanism into three modes: the fully lifted, fully closed, and partially open modes. First, Figure 2a shows the MR valve in the fully lifted mode. The cam force is transferred to the rocker arm, then to the body's upper piston, and finally to the magnetic plate block. At this juncture, the magnetic pole coil does not generate any current, that is, the MR fluid layers do not offer any resistance. Therefore, the valve opens smoothly and completely. During this process, the upper and lower springs, as well as the side-by-side spring, are compressed simultaneously, and the rocker arm moves downward to the horizontal position. Figure 1: New magnetorheological (MR) valve train: (**a**) block diagram and (**b**) sectional view of the cylinders and plate block. The second mode is the fully closed mode. The positions of the components in this mode are illustrated in Figure 2b. The supply current to the coil is at its maximum, and this increases the resistance force in the MR fluid layers to its maximum level. This resistance force stops the distribution of the lift force, and all the lift force from the rocker is transferred to the buffer spring, meaning that the valve lift is zero. Finally, in the partially open mode, the valve lift can be controlled by varying the magnitude of the supply current. The supply current generates a magnetic field, which changes the resistance of the MR fluid in the plate block. At this point, the degree to which the valve is open is proportional to the magnitude of the resistance force in the MR fluid. Figure 2c illustrates the partially lifted mode. In this manner, VVL can be realized. Moreover, by varying the time at which the current is applied, the valve opening time can be varied. However, this device cannot be used to vary the timing of the valve closing. The MR fluid used in this device is MRF-140 CG (Lord Corporation, Cary, NC, USA), which is a well-known high-grade MR fluid. Its operating temperature is \(-40\) to \(130\)\({}^{\circ}\)C, its liquid viscosity at \(40\)\({}^{\circ}\)C is \(0.280\) Pa\(\cdot\)s, density is \(3.74\) g/cm\({}^{3}\), and its flashpoint is higher than \(150\)\({}^{\circ}\)C [19].