Spark Plug Center Electrode Thermal Expansion Control

The center electrode is designed with a composite structure where the core member and cover layer have different material properties. The core member has high thermal conductivity to dissipate heat, while the cover layer has low thermal expansion coefficient to maintain dimensional stability. This local differentiation of material properties allows the electrode to handle thermal loads without excessive axial expansion.

The center electrode employs a composite structure combining a core member made of highly thermal conductive material with a cover layer made of material having low linear expansion coefficient. This composite design leverages the complementary properties of both materials: the core efficiently conducts heat away from the discharge tip, while the cover minimizes thermal expansion in the axial direction, thereby maintaining a stable spark discharge gap.

The cover layer is selectively applied only to specific portions of the center electrode where dimensional stability is most critical, rather than covering the entire electrode. This allows the exposed portions of the core member to maintain high heat dissipation efficiency while the covered portions provide thermal expansion control.

The design changes the material parameters (thermal conductivity and thermal expansion coefficient) at different locations along the center electrode. The cover layer material has low thermal expansion coefficient to suppress axial expansion, while the core member material has high thermal conductivity for heat dissipation. The selective coverage optimizes both parameters in their respective zones.