When the stick is digging (retracting inward), the function of returning the oil pushed out from the side of the piston rod of the stick hydraulic cylinder to the bottom of the hydraulic cylinder (the side without the piston rod) is called the quick action function. When the stick is shoveling soil, the oil is discharged from the piston rod side of the hydraulic cylinder under the gravity of the stick (including the bucket). Therefore, if the oil path returning to the oil tank is not throttled and restricted, Then the stick hydraulic cylinder will extend too fast, and the amount of oil supplied to the bottom of the hydraulic cylinder from the hydraulic pump will not be enough to make up, and the hydraulic cylinder will generate cavitation. However, if the oil return path is throttling, the working speed of the stick will be reduced, and the pressure of the hydraulic pump will be increased, which will increase the energy loss. In order to prevent this situation, when the pressure at the bottom of the hydraulic cylinder is low, increase the throttle of the oil return path to limit the amount of oil return, and at the same time return a part of the oil return to the bottom of the oil to connect it to the hydraulic pump. The incoming oil merges to prevent cavitation and increase the working speed of the hydraulic cylinder.
When the pressure at the bottom of the hydraulic cylinder is high, reduce the throttling degree of the oil return path to make more oil return to the oil tank to prevent the working pressure of the hydraulic pump from rising excessively.
Especially in the combined action of stick extension and boom lifting or bucket excavation, the oil return of the stick hydraulic cylinder is subject to adjustable throttling and the flow is restricted, and most of the oil returns to the bottom of the hydraulic cylinder, so Even if it is supplied by a hydraulic pump, the bucket
The movement speed of the lever is not much slower than when the two hydraulic pumps are used for independent operation. The quick action function of the stick is realized by the structure of the main reversing valve.
1. With the quick action function of the stick (stick shovel), when the spool valve of the stick is operated in the Crowd direction, the spool valve moves to the right, the central parallel passage is cut off, and the parallel circuit (Parallel passage) is blocked. The oil will push open the one-way valve C1 and enter the bottom of the stick hydraulic cylinder through the high-pressure oil supply channel.
2. When the pressure on one side of the piston rod is high (Pa>pA), the stick digging will push open the check valve C2 and enter the bottom of the stick hydraulic cylinder through the high-pressure oil supply channel. At this time, the quick-action switching spool valve B is in the state shown in Figures 16-57, and the oil passages 3 and 4 are cut off, so the oil returning from the piston rod side of the hydraulic cylinder cannot reach the oil return path to the oil tank.
3. When the pressure at the bottom of the hydraulic cylinder is high (PA>Pa, stick digging), the oil returning from the piston rod side is cut off by the check valve C, and the channels 1 and 2 are closed. On the other hand, the pressure oil at the bottom of the hydraulic cylinder acts on the quick-action switching piston A. When the pressure of the pressure oil exceeds the set pressure of the spring C, the piston A is pushed and the slide valve moves to the right to make the oil passages 3 and 4 Connect. In this way, the oil return on the piston rod side of the hydraulic cylinder passes through the oil passages 3 and 4 from the low pressure passage to the oil return passage leading to the oil tank.
