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Introduction

Linear electromagnetic actuators with solenoid type, are widely used in industrial applications. They are part of various electromagnetic devices based on different controlling mechanisms; they are used in electromagnetic valve actuation systems, fuel injection, exhaust gas recirculation systems, washing machines, etc.

In order to develop an electromagnetic actuator with optimal actuation force, high reliability and low energy consumption, a new generation of actuators design has been developed with the addition of a ferrofluid in the working gap. Such type of fluid with an increased magnetic permeability could significantly reduce the magnetic reluctance of the actuator.

Ferrofluids, also known as magnetic fluids, are a special category of smart Nano-materials. The fluid exhibits both fluidity and superparamagnetism, with strong magnetic dipoles which can be effectively controlled by magnetic fields [1]. Nowadays, ferrofluid liquids are exploited in numerous industrial and laboratory applications. They are usually formed of a colloidal solution with very fine ferromagnetic particles diluted in sufficiently viscous carrier liquids. Higher viscosity of these liquids ensures their relatively good spatial and temporal homogeneity. Some of their physical parameters (permeability and viscosity) strongly depend on external magnetic field.

Electromagnetic systems with ferrofluid nanoscale materials are characterized by a better work performance and a reduced energy consumption. One of their prospective technical applications is represented by classical electromagnetic actuators where the working-space is filled with ferrofluidic liquid, which can offer more interesting magnetic force enhancements. The total magnetic resistance of the actuators is lower, and the required magnetic flux density may be achieved with lower field current.

Problem description

The studied electromagnetic actuator consists of a stationary ferromagnetic core surrounding a copper DC coil, a movable ferromagnetic plunger and a working gap filled with ferrofluid (as shown in Figure 2).  The coil consists of 500 turns copper wire with a diameter 1mm. The material of core and plunger is Carbon Steel 12040 with B-H characteristic.

The working principle of the actuator is based on exciting the ferromagnetic circuit with a coil carrying DC current, which will produce a magnetic field (B) that pulls the plunger through magnetic force (Fm). If this force is higher than the sum of various resistances (friction, hydrodynamic resistance, external force), the plunger then moves.

Table 1 - Component` Dimensions

Material properties

Table 2 - Material properties

	Density (Kg/)	Magnetic permeability	Electrical conductivity (S/m)
Copper (Cu)	8900	0.99	6 E+07

Figure 3 - BH curve of Carbon steel 12040

Meshing

The meshed model is shown in Figure 4. Fine mesh control was applied to whole model for accurate results.

To evaluate the effect of the Ferrofluid on the behavior of actuator for different plunge positions, a succession of simulations was executed for a range of the Ferrofluid permeability between 1 and 50. The obtained results are shown below.

Magnetic field results

Case 1: Linear ferromagnetic Carbon steel

For the case of linear ferromagnetic Carbon Steel material, the flux density and magnetic field distribution for different values of Ferrofluid permeability and plunger positions are shown by the cross-sectional view plots in the figure 5,6 and 7.

 

Figure 5 - a) Magnetic flux density and b) Magnetic field distribution for µ=1, d=2.5 mm.

Figure 6 - a) Magnetic flux density and b) Magnetic field distribution for µ=5, d=2.5 mm.       
 

Table 3 - Comparative table of Flux density results between EMS and Ref [3].

Case 2: Non-Linear ferromagnetic Carbon steel

For the case of Non-linear ferromagnetic Carbon Steel material, the simulations revealed the magnetic flux results below:

 

 

Magnetic force results

Case 1: Linear ferromagnetic Carbon steel

For the case of linear problem, the generated electromagnetic force is evaluated according to relative magnetic permeability of ferrofluid at different working gaps.

The variation of force versus the plunger position, for a ferrofluid permeability of 50, is shown by the Figure 10. The variation of plunger position acts inversely on the generated magnetic force. This last achieves considerable values for lower ferrofluid gaps.

For a fixed plunger position set to d=2.5 mm from the core base, the obtained force results are presented by the figure 11. It is noticed that with higher magnetic permeabilities of the ferrofluid, the generated force achieved higher values. The maximum value of electromagnetic force is Fmax73 N with µ = 50.A comparison between EMS and Reference [3] results show a good coincidence between them.

Figure 10 - EMS and Reference [3] results for different plunger positions for µ=50.   

   
 Figure 11 - EMS and Reference [3] results for different ferrofluid permeabilities at plunger position of d=2.5 mm.

Case 2: Non-Linear ferromagnetic Carbon steel

For the case of Non-linear ferromagnetic carbon steel, a succession of simulations was executed for different plunger positions and Ferrofluid permeability values, to compute the generated force under the effect of the Ferrofluid gap.

The variation of force versus the plunger position, for a ferrofluid permeability of 5, is shown by the Figure 12. The variation of plunger position acts inversely on the generated magnetic force. This last achieves negligible values at large ferromagnetic gaps.

For a fixed plunger position set to d=2.5 mm from the core base, the obtained force results are presented by the figure 13. In small gaps electromagnetic force is increasing significantly at range of relative magnetic permeability from 1 to 5. With higher relative magnetic permeability, electromagnetic force is decreasing. The maximum value of electromagnetic force is Fmax29 N with µ = 5.A comparison between EMS and Reference [3] results show a good coincidence between them.

 

Figure 12 - EMS and Reference [3] results for different plunger positions for µ=5


Figure 13 - EMS and Reference [3] results for different ferrofluid permeabilities at plunger position of d=2.5 mm.

Conclusion

The use of Ferrofluid materials with increased magnetic permeability could significantly decreases the magnetic reluctance of the systems. Ferrofluid is characterized with high magnetization saturation with no remanence. Ferrofluid in the working gap of electromagnetic actuators increases electromagnetic force and thus, with such setting, greater force could be obtained with more compact actuator.

Ferrofluid perfectly adapts to any geometry and could moves through very small channels. It is used to eliminate or substantially reduce the noise caused by the actuator plunger striking the core. Furthermore, magnetic flux leakage is usually a significant problem associated with solenoid actuators. This leakage can be reduced through the use of the ferrofluid in magnetic circuit of the actuator.

References

[1] http://112.216.150.106:8080/paros/download/pdf/E1MGAB_2017_v22n1_109.pdf
[2] https://www.computerhope.com/jargon/f/ferrofluid.htm
[3] Terzova, A. I., V. M. Mateev, and I. Y. Marinova. "Modelling of electromagnetic actuator with ferrofluid." CEMBEF 2013(2013): 75-78.