Abstract:  Aiming at the problem that the existing pneumatic brake of mobile bridge erecting machine could not realize heavy load downhill, a new type of balance circuit which could be used in closed drive system with variable load was designed, and was applied to electro-hydraulic proportional braking system. The working principle of the closed drive system was analyzed, and the static characteristics of the overload phenomenon were analyzed. The simulation model of the braking system was established by AMESim software, and the dynamic characteristics of the system were analyzed. The results show that when the motor turns downhill, the pressure difference between the inlet and outlet of the motor decreases by 87.6%, and the speed increases by 52.4%. The motor has a large speed impact; the pressure difference and speed of the motor at the inlet and outlet decrease and rise respectively under the downhill condition; when the load is exceeded,  by increasing, the pressure of the proportional relief valve braking requirements of bridge erecting machine, the pressure difference and speed at the inlet and outlet of the motor can be stabilized and the flow can be satisfied.


Key words:  overloading;electro-hydraulic proportional control;AMESim simulation;service brake