CST – Computer Simulation Technology

Magnetostatic Simulation of a Magnetic Injection Valve

CST EM STUDIO® (CST EMS) can be used for the simulation of actuators such as a magnetic injection valve as shown in figure 1. This device was entirely constructed using the powerful user interface in CST EMS. The coil was created by defining a cross-section and sweep path to form a solenoidal shape. Alternatively, more complex devices may be imported using the comprehensive CAD Import facilities in the CST design environment. Of interest is the flux density distribution in the device as well as derived quantities such as the force on the valve armature as a function of coil current and armature-housing gap. The non-linear magnetostatic solver is applied to the simulation of the valve, utilizing either a hexahedral or tetrahedral mesh. In this particular case, the hexahedral mesh is an excellent choice since it not only provides equally accurate results but also allows the consistent control of the mesh at critical parts of the geometry, such as the air gaps, during the parameterization process....

Figure 1: Geometry of the magnetic injection valve with excitation coil

Figure 2 shows a more detailed breakdown of the geometry of the magnetic injection valve along with the magnetic materials taken for the simulation. The model was created using polygons which have been rotationally swept over 360 degrees and the coil (shown only in figure 1) was constructed using the coil tool in CST EMS. Appropriate symmetry conditions have been applied to reduce the simulation volume by a quarter. A parameter sweep is set up to sweep the current Ampere Turns in the coils in order to obtain the armature force versus gap characteristic as a function of coil Ampere-Turns.

For the correct modeling of this device, the non-linear magnetic characteristics of the materials should be taken into account. The flux density-field strength (B-H) curves for each material were taken from actual material measurements.

Figure 2: Cut-away construction and magnetic materials of the injection valve

Figure 3 shows the absolute flux density in the valve for the case where the air gap is 0.3 mm. Other quantities automatically available include the H-Field and the permeability distribution. Further secondary quantities such as system energy and force are also delivered by the solver. Post-processing templates can also be defined to obtain other user-defined secondary quantities.

Figure 3: Vector and contour plot of the Absolute magnetic flux density on a central cut-plane through the valve with a gap of 0.3 mm

The force on the armature is an important characteristic for this valve, namely, its variation with armature gap size and applied coil current. The force is automatically calculated as a post-processing step, the results of which can be captured by the post-processing templates and displayed as a family of curves as shown in figure 4. In the figure, the armature gap is shown by two red points. The number of mesh lines in the gap is defined in terms of the gap parameter to ensure that the mesh is adequately refined in the gap regardless of the gap width. This ensures a consistent result throughout the parameterization process.

Figure 4: Armature force as function of parameterised armature gap and coil Ampere-Turns. The mesh density in the gap is refined as a function of the gap width

This article has demonstrated the modeling and parameterization of a magnetic valve using CST EMS and its parameterization facilities. This model was entirely created using the user interface of CST EMS. More complex geometries can be imported and parameterized using the modification and parameterized facilities. The force can be derived effortlessly for a range of parameters to allow the engineer to investigate the effect of the model geometry and excitation on the behavior of the device.

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