A new technique for temporary adhesion improvement via dry-air jetting and its application in reducing the braking distance of railway vehicles

This study proposes a technique to temporarily improve the friction force by jetting dry air with less than 30% humidity on the contact surface. The tangential contact force was first measured under the condition that a very small amount of water was on the contact surface and the velocity was 30 km/h to confirm that the proposed technique is effective even in rainy weather. The findings revealed that the adhesive force increased by reducing the amount of water on the contact surface. These experimental results indicate that the dry-air jetting technique effectively increases the friction coefficient, even under rainy conditions, because dry-air jetting can remove water droplets on the surface. Subsequently, an experiment was conducted on the tangential contact force using a twin-disc sliding-frictional rolling machine to verify our proposed technique under different dry conditions. The tangential contact force coefficient increased simultaneously with dry-air jetting and remained stable during dry-air jetting under dry and high-humidity environmental conditions. Furthermore, the findings clarified that the tangential contact force improvement effect of dry-air jetting depends on the combination of the contact patch and its surface properties. Finally, based on these experimental results, we compared the same rail vehicles with and without considering the braking distance as an example of a dry-air jetting system application, using a vehicle dynamics analysis constructed using the SIMPACK commercial software. Consequently, the validity of the proposed technique was confirmed for actual rail vehicles.