| Mining truck is an ideal conveyance in large mines for its high efficiency and good economy, and tends to be larger. Now, the payload of main trucks abroad has been up to 360 tons, but internal manufacturers have not produced mining trucks over 200 tons. Owing to large weight and high speed of trucks and more curve and slope in mines, the system of steering, brake and hoisting must be reliable. Hydraulic power steering, hydraulic hoisting and full hydraulic brake have been applied in mining trucks. So the safety of trucks and production has been affected by hydraulic system seriously.In this paper, hydraulic systems of mining trucks have been analyzed. Considering hydraulic component, the manufacture of valve body and saving energy, a hydraulic system has been designed for first internal 220 tons mining truck. It features that: 1) Steering system is full hydraulic power steering system with flow amplifier, which is supplied by accumulators charged by a pressure compassionated piston pump. There is no unloading valve which often fails. Emergency steering can be done when steering pump fails. The pump is easy to be stocked for its little displacement, sucks oil well and has good coldstart performance. 2) Hoisting system is controlled by cartridge valves and supplied by gear pump and steering pump of piggy-back design. There is no tandem pump of piggy-back design and special valves hard to be stocked. With hoisting pump, all hoisting movements can be completed when steering pump break down. And the system is energy-saving and reliable. 3) Brake system is dual service brakes with relay valves controlled by a MICO pedal/pilot actuated tandem valve. The problem of larger difference of pressure and flow between rear brakes and front brakes has been solved. It features second service brake, automatic apply, loading brake and so on.Due to large inertia of dump body and the mutation of valid piston area of hoisting cylinder, hydraulic impact comes into being in hoisting easily. To solve this problem, hoisting system designed has been modeled in Amesim. And the movements of hoisting, powering down and floating have been simulated. The results show that, when dump body fully loaded is being hoisted, pressure impact due to mutation of valid piston area is lower than that due to starting or stopping movements. Impact pressure is less than 16Mpa and impact time is short. The impact pressure is less than 5Mpa when empty dump body has been hoisted, powered down and floated. With dynamic performance, the system designed is up to request. The system in this paper can be applied in design of other dump trucks and the method for modeling and simulating hoisting system can be applied in similar system. |
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