When the stick is digging (retracting inward), the function of returning the oil pushed out from the piston rod side 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 arm is shoveling the soil, under the action of the weight of the arm (including the bucket), the oil is discharged from the piston rod side of the hydraulic cylinder, so if the oil path back to the tank is not throttled, it is restricted, Then the stick hydraulic cylinder will extend too fast, and the amount of oil supplied from the hydraulic pump to the bottom of the hydraulic cylinder is too late to make up, and the hydraulic cylinder will produce cavitation. However, if the return path is excessively throttled, the operating speed of the stick will be reduced, and the pressure of the hydraulic pump will increase, increasing energy loss. To prevent this, 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 returned, and at the same time return part of the oil back to the bottom of the oil to make it supply 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 degree of throttling in the oil return path and return more oil 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 return oil of the arm hydraulic cylinder is regulated and restricted by the throttle, and most of the oil returns to the bottom of the hydraulic cylinder, so Even if it is powered by a hydraulic pump, the bucket
The movement speed of the rod is not much slower than the speed when the two hydraulic pumps supply oil for independent operation. The fast action function of the stick is realized by the structure of the main reversing valve, as shown in Figure 16-57.
1. The stick quick action function (stick shoveling) operates the spool valve operating the stick in the direction of digging (Crowd), as shown in Figure 16-57, the spool valve moves to the right, and the central parallel path is cut off The oil in the parallel passage will push open the check valve C1 and enter the bottom of the stick hydraulic cylinder through the high-pressure oil supply passage.
2. When the pressure on the side of the piston rod is high (Pa>pA), the digging of the stick will push the check valve C2 open, and enter the bottom of the stick hydraulic cylinder through the high-pressure oil supply channel. At this time, the fast-acting switching spool valve B is in the state shown in FIGS. 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 channels 1 and 2 are closed. On the other hand, the pressure oil at the bottom of the hydraulic cylinder acts on the fast-acting switching piston A. When the pressure oil pressure exceeds the setting pressure of the spring C, the piston A is pushed and the spool moves to the right, causing the oil passages 3 and 4 Connect together. In this way, the return oil on the piston rod side of the hydraulic cylinder passes from the low-pressure passage through the oil passages 3 and 4 to the return oil passage leading to the oil tank.
