A method for enhancing the output force of a stroke-controlled electro-mechanical converter of 2D servo-proportional valves based on the principle of “magnetic dam”

Force-controlled electro-mechanical converter (FCEMC) commonly drives two-dimensional servo-proportional valve (2D-SPV) but requires external mechanical springs, complicating the structure and reducing reliability due to potential spring fatigue. In contrast, the stroke-controlled electro-mechanical converter (SCEMC) does not require mechanical springs and can directly output displacement, greatly simplifying the valve structure. The existing SCEMC suffers from significant leakage flux due to the magnetic circuit topology, resulting in a smaller output force. This paper proposes a method for enhancing the output force of SCEMCs, which involves blocking tooth slot leakage flux by filling the tooth slots with permanent magnets (PMs) to form a magnetic dam structure. An analytical model based on the field-circuit combined method is established to verify the enhancement effect of the magnetic dam on the output force and to quickly and quantitatively calculate the output force. This model can not only consider the complicated flux distribution of PMs and working air gaps but also cope with the nonlinear permeability of the soft magnetic material. Combined with the structure, formulas for the sub-models of air gap reluctance, PMs, and soft magnetic components' reluctance in the magnetic circuit of the stroke-controlled solenoid with magnetic dam (SCS-MD) are presented. Two prototypes of SCS, one with and one without the magnetic dam structure, are designed and machined. The cogging force, force-displacement characteristics, and step response are measured. The experimental results show good agreement with the analytical results, verifying the correctness of the analytical modeling. At 800 AT, the magnetic dam increases the peak output force of SCS from 50.5 N to 265.7 N, and improves the step response time from 59.5 ms to 38.2 ms. Consequently, the performance of SCS-MD is compared with commercial products, which demonstrates its application potential in servo-proportional valves.