3.1.2. Type 2 DPI

As shown in Figure 8, the total number of leaf springs and pressure plates is specified as a design parameter, and the needle part is assembled by inserting the needle body, cylinder, and spring. The number of leaf springs was reduced by one and three cases were analyzed. As shown in Figure 9, the Type 2 needle configuration allows fluid to move more freely than the conventional type. When hydraulic pressure is used in the conventional type, the needle moving distance is amplified and the needle can move with a small pressure force. However, the injection responsiveness is considered to be slow. Therefore, the design purpose of Type 2 is to increase the injection responsiveness by allowing pressured fluid to flow freely without hydraulic pressure, by taking advantage of the mechanical characteristics.

Case 2-1 in Figure 8 has an available maximum injection pressure of 130 MPa, as shown in Figure 10. The injection pressures of Case 2-2 and Case 2-3 were about 100 bar lower than Case 2-1. It was found that the available maximum injection pressure can be obtained, depending on the number of leaf springs. If one leaf spring in Type 2 is absent, the force for lifting the needle under CR high pressure is insufficient. However, when two leaf springs are provided, it becomes possible to lift the

needle with a greater force, due to the increase in the elastic force. It is considered that the elastic force in the design of Type 2 is determined by the number of leaf springs.

**Figure 8.** Detailed designs of Type 2 DPIs.

**Figure 9.** Comparison of needle configuration; (**a**) Type 2, (**b**) Conventional Type DPI.

**Figure 10.** Comparison of the maximum injection pressure of Type 2 DPIs.
