The hydraulic actuator of boom, stick, bucket, bucket, bucket opening and walking device is supplied by four main working pumps. Each main working pump controls the hydraulic actuator through a group of multi-channel valves. Two groups of the four multi-channel valves are sequential single action control, the other two groups are parallel and sequential single action group control, and then flow control is carried out for hydraulic actuator through the combination of valve outer flow, and four sets of hydraulic actuators can be realized The main working pump supplies oil to the actuator separately.
In order to make full use of engine power and shorten the working cycle time, multiple mechanisms are often required to perform composite action simultaneously during the working process. Therefore, during the boom lifting or lowering, it will act simultaneously with other hydraulic actuators. When the combined operation is performed, the flow of main working pump shall meet the supply of all the flow required for the operation.
The combined action of boom mainly includes full bucket lifting and turning, excavation is finished and full bucket lifting rotation is completed. In the process of lifting the boom, in order to keep the bucket translation, the stick and bucket hydraulic cylinder are required to work together, and the rotary hydraulic motor makes the turntable turn to the unloading position. And when unloading, turn to unloading position, brake the turntable, open bucket hydraulic cylinder to open bucket for unloading. In order to adjust the unloading position, there is a need for the cooperation between bucket hydraulic cylinder and stick hydraulic cylinder, and boom action is required if necessary.
During boom lowering, when the same main control valve control circuit is used during the boom lowering, the hydraulic pump supplies oil to two boom hydraulic cylinders with rod cavity. Due to the action of boom self weight, the oil supply pressure of hydraulic pump is not high, but the flow rate of hydraulic pump to the upper chamber of hydraulic cylinder is large, and the power of pump required for lowering is about 18.7kw. At the same time, the boom without rod cavity oil flows through the throttle port of multi-channel valve and back end When the pressure valve flows back to the oil tank, the power loss of the return oil of the two hydraulic cylinders is about 336.8kw. This part of the power loss is almost all converted into heat, and the hydraulic system is cooled by the hydraulic motor driven fan, which is equivalent to the secondary power loss of the system.
At the same time, when the boom is lowered, the hydraulic pump supplies oil to the upper cavity of the boom hydraulic cylinder with a large flow. When the boom and other actuators act together, the flow provided by the hydraulic pump to other actuators will inevitably decrease, which will inevitably lead to the increase of the working cycle time and the decrease of working efficiency.
Therefore, when the boom is lowered, the flow regeneration circuit is used to reduce the dead weight of the boom to improve the efficiency of the system.
The boom of the big excavation of the front shovel is different from that of the backhoe small excavation boom. The boom drop of the small excavation is divided into the no-load lowering stage and the on load excavation stage. The boom falling of the large excavation is only no-load drop, and generally does not participate in the excavation. Therefore, the boom drop of the large excavation is more suitable for the flow regeneration circuit than the small excavation.
