A Virtual Methodology to Define Air Tightness Criterion for Brake Calipers Based on Experimental Data

Air tightness in brake calipers is a critical requirement for ensuring braking system reliability and safety. However, defining a clear and practical analytical criterion for air leakage prediction remains challenging due to the complex contact behavior at the seal–piston interface. This study presents a virtual methodology to define an air tightness criterion for brake calipers based on experimental evaluation and structural analysis. The seal squeeze ratio was selected as the primary design variable to evaluate its effect on sealing performance. Test samples with different seal squeeze ratios were manufactured, and air tightness was tested under controlled pneumatic pressure to determine when leakage occurred. In parallel, a finite element (FE) structural analysis was conducted to simulate the seal installation process and quantify the resultant contact pressure distribution between the seal and the piston surface. To support reliable structural analysis, preliminary experiments were performed to determine the hyperelastic properties of the seal elastomer. Furthermore, the seal clamping force was experimentally verified. The experimental results showed that low seal squeeze ratio caused leakage, demonstrating that seal compression strongly affects sealing performance. Based on these observations, an analytical criterion was established using the contact pressure between seal and piston, with a minimum contact pressure defined to prevent air leakage. Although a direct quantitative correlation between air leakage and contact pressure was not determined, the proposed criterion provides a practical and physically meaningful basis for evaluating air tightness. This methodology allows engineers to predict sealing performance during the design stage, reducing the need for extensive testing and enabling more efficient and reliable brake caliper development.