During the process of turntable start-up, the root cause of overflow loss of hydraulic system is the contradiction between supply and demand of flow. Especially in the initial stage of the turntable start, the rotary hydraulic motor has very low speed and little absorption flow. Most of the hydraulic system overflows through overflow valve, so the hydraulic system is in the state of high pressure and large flow overflow, and the overflow loss is the largest. The fundamental reason for the loss of flow during braking is that the inertia energy of the turntable has not been recovered. According to the characteristics of hydraulic excavator rotary hydraulic system, an energy recovery device is adopted to recover the brake energy of the turntable and release it when the turntable is started in reverse direction, so as to realize the recovery and reuse of the brake energy of the turntable.
When the change-over valve is in the left position, the hydraulic oil output by the hydraulic pump enters the rotary hydraulic motor after passing the change-over valve, which enables the turntable to start, and the excess hydraulic oil enters the accumulator for storage through the hydraulic control check valve. With the speed of rotary table, the flow absorbed by the rotary hydraulic motor is increasing. When the flow is equal to the output flow of the pump, the system pressure drops and the first stage of start-up is over. After that, the accumulator releases the stored oil, supplies the rotary hydraulic motor with the flow of the hydraulic pump, so that the turntable accelerates here, which is the end of the first stage of start-up. After that, the accumulator releases the stored oil, supplies the rotary hydraulic motor with the flow of the hydraulic pump, so that the turntable accelerates again. This is the second stage of start-up. The oil in the accumulator is basically discharged, so as to prepare for the energy recovery during the brake of the turntable.
When braking, the control oil of the pilot valve causes the change-over valve to return to the middle position, and the inlet and return oil circuit of the swing hydraulic motor is cut off. The rotary table continues to rotate under inertia, and the rotary hydraulic motor is in pump condition, and the oil discharged from the rotary hydraulic motor enters the accumulator through a one-way valve. The pressure of the original return oil chamber of the rotary motor increases to form the braking torque, thus realizing the brake and energy recovery of the turntable.
After one brake, the accumulator fills in oil because of the recovery of brake energy of the turntable. The subsequent rotation is called general rotation condition. The starting process of general rotating condition consists of two phases:
1. the accumulator supplies oil and the hydraulic pump is unloaded. At this stage, the oil in the accumulator is released into the rotary hydraulic motor to start the turntable. In the initial stage of start-up, the energy recovered during braking is regenerated.
2. continue the oil supply stage of the pump. After the accumulator is drained, the pressure drops. When the pressure drops to less than or equal to the set pressure of the unloading valve, the unloading valve closes and the oil discharged by the pump is supplied to the rotary hydraulic motor. After the start-up, when braking, the rotary hydraulic motor fills the accumulator with oil for filling brake and energy recovery.
