Identification of the performance mechanical secondary safety brake under hydraulic failure conditions: experimental assessment under fluid leakage

The object of the study is the hydraulic braking system of heavy vehicles under conditions of progressive brake fluid leakage, with particular emphasis on its effect on braking performance and failure behavior. The problem addressed is the loss of braking performance due to hydraulic brake failure caused by fluid leakage, which reduces hydraulic pressure and may lead to total brake failure. This study presents the design and experimental analysis of an independent mechanical wheel-clamp-based secondary safety brake for heavy vehicle braking systems. Experimental evaluation was conducted using a rotational test rig under varying load conditions. The results show that brake failure is strongly dependent on load. Under low load (5 Hz), total failure occurs at approximately 70 mL leakage and 5 bars, whereas under high load (50 Hz), failure occurs at only 25 mL and 9.3 bar, indicating increased sensitivity to leakage. This behavior is explained by the loss of hydraulic fluid and the compressibility of trapped air in the braking circuit, which prevents pressure from reaching its maximum level and reduces effective force transmission. Under total hydraulic failure, the secondary safety brake is capable of stopping wheel rotation across all tested conditions; however, the stopping time is longer, reaching up to 6.5 s compared to 1.4–2.9 s for the primary brake. These results demonstrate that the proposed system provides a fully independent fail-safe braking mechanism capable of maintaining braking functionality when the primary system fails, thereby addressing the problem of brake performance loss under hydraulic failure conditions. The system can be applied in heavy vehicle braking systems as a risk mitigation solution under failure scenarios, particularly in high-load operating conditions, with potential for further development, experimental refinement, and real vehicle implementation, including integration with activation strategies