JPH0329399Y2 - - Google Patents

Description

[Detailed description of the invention] [Field of industrial application] This invention relates to hydraulic control circuits, and in particular to switching valves associated with pumps when multiple switching valves including tandem circuits are operated simultaneously in the hydraulic control circuit of a hydraulic excavator. The present invention relates to a hydraulic control circuit that smoothly controls the flow rate of water.

[Prior Art] Conventionally, hydraulic excavators use two independent circuits each consisting of a multiple switching valve connected to a plurality of switching valves and a hydraulic power source pump, and each circuit is connected to a single actuator as necessary. A merging circuit is often added to combine and supply the discharge amounts of the pumps.

In the case where a fixed capacity pump is used as the pump, the flow rate adjustment (hereinafter referred to as metering) by moving the spool of the switching valve is performed by temporarily closing the center bypass passage of each switching valve with the spool to reduce the flow rate passing through the center bypass passage. A structure that increases the flow rate to the actuator connection port that communicates with the actuator connection port is generally employed. In this type of hydraulic control circuit, the center bypass passage at the start of metering has an opening area that allows most of the pump's total flow to pass through, and the center bypass passage of the upstream switching valve for the pump has an opening area that allows most of the pump's total flow to pass through. The entire flow rate of the pump can be passed through the center bypass passage of the downstream switching valve.

When the upstream and downstream switching valves are connected to form a tandem circuit, when the spool of the downstream switching valve is operated by a full stroke and the spool of the upstream switching valve is operated by a half stroke, the upstream switching valve and The actuators connected to the downstream switching valves as control objects can be respectively operated. In particular, when operating the spool of the downstream switching valve over a full stroke and operating the actuator connected to the upstream switching valve at a small speed, the speed of the actuator connected to the downstream switching valve is hardly reduced. It is possible to operate both actuators.

Furthermore, from the viewpoint of energy conservation, variable displacement pumps have recently been used, and when the switching valve is in neutral, the pump flow rate is maintained at the minimum discharge flow rate, and the flow rate is increased according to the displacement of the stroke of the switching valve spool. Hydraulic control circuits that control pump flow rates have been proposed. Control methods for controlling the pump flow rate include a negative control method in which the pump flow rate is increased by decreasing the pilot pressure, and a positive control method in which the pump flow rate is increased by increasing the pilot pressure.

[Problems to be solved by the invention] However, in any of these pump flow rate control methods, the metering of the switching valve depends on the pump flow rate control, and furthermore, the spool notch in the center bypass passage of the switching valve is It is designed to control the pump's minimum discharge flow rate, and its opening area is also extremely small. Therefore, if a tandem circuit is configured with multiple switching valves having such spool notches and the spool of the upstream switching valve is operated while the downstream spool is operating at full stroke (maximum pump discharge amount), the upstream switching At the beginning of metering of the valve spool, the pump discharge pressure rises rapidly because the entire pump discharge amount passes through the spool notch provided in the center bypass passage and having a very small and limited opening area. As a result, more pressure than necessary will be generated in the upstream supply passage of the hydraulic circuit, and an excessive flow will flow into the actuator connection port of the switching valve, impairing the metering of the spool of the upstream switching valve. Also,
At the same time, the amount of oil flowing to the downstream side of the hydraulic circuit also almost disappears, causing a rapid decrease in the speed of the cylinder connected to the downstream switching valve. Therefore, in such a state, if the spool of the upstream switching valve is returned to the neutral position, the actuator connected to the actuator connection port will begin to move rapidly, causing problems such as difficulty in smoothly controlling the hydraulic pressure of the controlled object. be.

[Means for Solving the Problems] This invention solves the above-mentioned problems, and the details thereof will be explained below using FIG. 1 corresponding to an embodiment.

Regulator 3 in response to a drop in pilot pressure.
Pump 1 that can increase the discharge amount by
A plurality of switching valves 12 to 15 are connected to the switching valves 12 to 15 to control the direction and speed of the actuator, and a plurality of switching valves 12 to 15 are connected to the tank 34 through a throttle 16 and a relief valve 17 that are cut off by the deviation of the spool from the neutral position. A pilot conduit 7 connected from the center bypass passage 18 to the regulator 3 of the pump 1 is provided to constitute a one-side circuit.

A pump 2 whose discharge amount can be increased by a regulator 4 according to a decrease in pilot pressure through the same type of circuit on the other side as described above, and a plurality of switching valves 22 to 25 connected to the pump 2 and which control the direction and speed of the actuator. Consists of a pilot conduit 8 connected to the regulator 4 of the pump 2 from a center bypass passage 28 that passes through the switching valves 22 to 25 and is shut off by the deflection of the spool from the neutral position and connected to the tank 34 via the throttle 26 and the relief valve 27. do.

Pressure oil for one of the switching valves 15 is supplied through the center bypass passages of the upstream switching valves 12 to 14 in a tandem connection. A pipe branched to one side of the pipe connected to an actuator 31 controlled by an upstream switching valve 14 in the tandem connection is connected to one actuator connection port 23b of the switching valve 23 on the other side.

The spool of the switching valve 23 is pulled out in synchronization with the movement of the spool of one of the switching valves 14 and returned to the neutral position, but does not follow the pushing direction of the spool of the switching valve 14 and is brought into contact with the operating stick. It does not move away from the neutral position to the pushing side.

The pilot line 7 of the regulator 3 on one side is provided with a throttle 6, and the regulator 3 further includes a switching valve 2.
3 is connected to the other side actuator connection port 23a.

[Operation] When all the switching valves are in the neutral position as shown in the figure,
The pressure oil supplied from each pump passes through the center bypass passage 18 or 28 of the switching valve, and the pressure generated by the passage resistance of the throttle 16 or 26 and the upper limit controlled by the relief valve 17 or 27 is
It acts via the pilot line 7 or 8 on the pump regulator 3 or 4 to minimize the capacity of the pump 1 or 2 and reduce energy losses.

The other switching valves except the switching valve 14 have a small opening area formed by the spool notch of the center bypass passage so as to control the minimum discharge flow rate of the pump.

The center bypass passage portion of the switching valve 14 has a large opening, receives the maximum discharge amount of the pump, and does not obstruct the supply of fluid to the downstream switching valve 15.

When the spool of the switching valve 15 is inserted or removed, the discharge amount of the pump 1 is blocked by the reduced center bypass passage, and some of the diverted fluid is transferred to the actuator 32.
The pressure in the pilot pipe 7 decreases and the discharge amount of the pump 1 increases in accordance with the decrease in the flow rate supplied to the pump 1 and passing through the throttle 16 downstream of the center bypass passage. Therefore, when the spool of the switching valve 15 is moved in and out, the actuator 32 expands and contracts at a speed corresponding to the stroke of the spool.

When the spool of the switching valve 14 is pulled out by the operation stick 41, the discharge amount of the pump 1 is supplied to the head end of the actuator 31, and the switching valve 2 is synchronously
The spool 3 is pulled out, and the discharge amount of the pump 2 is combined with the discharge amount of the pump 1 and supplied to the head end of the same actuator 31. The return oil from the rod end of the actuator 31 is transferred to the switching valve 14.
It returns to tank 34 through the chisel.

Depending on the operating amount of the spool of the switching valve 23 in the output direction, the discharge amount of the pump 2 supplied to the actuator 31 increases in the same manner as described for the switching valve 15 and the pump 1 described above.

When operating the spool of the switching valve 14 in the output direction, the switching valve 23 communicates the pilot line 7 with the tank 34 at the position where the spool of the switching valve 14 starts metering under the maximum discharge state of the pump 1, and the throttle 16
The pressure generated by this and applied to the regulator 3 of the pump 1 decreases to near the tank pressure due to the pressure loss when passing through the throttle 6, so the pump 1 discharges at maximum. The spool notch in the center bypass passage of the switching valve 14 has a large opening and smoothly controls the flow rate, which is fixed at the maximum discharge rate.

When performing a combined simultaneous operation of pulling out the upstream switching valve 14 in the exit direction while switching the downstream switching valve 15, the throttle 16 is changed by switching the downstream switching valve 15.
The fluid supply to the pump 1 is cut off, and the pressure transmitted to the regulator 3 of the pump 1 through the pilot line is reduced. Since the pump 1 has already delivered the maximum discharge amount, the flow rate is smoothly controlled by the switching valves 14 and 23. controlled.

[Example] An example in which the present invention is applied to a hydraulic excavator will be described below.

In FIG. 1, the pump 1 is operated by the pressure generated in the throttle valve 16 and the relief valve 17 downstream of the center bypass passage of the switching valves 12 to 15 which are connected to the pump 1 and control the right travel, bucket, boom, and arm actuators, respectively. When all the valves are in the neutral position, they are in the minimum discharge state, and when the spool of any one of the switching valves is moved in or out, the discharge amount increases as the stroke increases.

Furthermore, it is connected to pump 2, and the left travel, boom,
The pump is in the minimum discharge state when all the switching valves are in neutral due to the pressure generated in the throttle valve 26 and relief valve 27 downstream of the center bypass passage of the switching valves 22 to 25 that control the arm/swivel. When the pump is moved in and out, the discharge amount increases in accordance with the increase in stroke.

When the arm is simultaneously operated to the holding side (the extension side of the actuator 32) and the boom to the raising side (the extension side of the actuator 31), the discharge amount of both pumps 1 and 2 is supplied only to the arm actuator 32, which has a light load. The switching valves 14 and 15 are connected in tandem so that the fluid discharged from the pump 1 can be supplied to the boom actuator 31 by giving priority to the switching valve 14 over the switching valve 15 regardless of the load. . The switching valves 15 and 24 are connected to one actuator 32, and each spool is operated by one operating rod 40 via a link.
The discharge fluid of the pump 2 is then controlled by the switching valve 15.
The fluid of the pump 1 is supplied to and discharged from the arm actuator 32. In other words, two-speed control is performed by merging.

The head end of the boom actuator 31 is connected to one actuator connection port 14b and 23b of the switching valve 14 and 23, and the rod end side is connected to the other actuator connection port 1 of the switching valve 14.
4a. The other actuator connection port 23a of the switching valve 23 is connected to the regulator 3 of the pump 1.

The spool of the switching valve 23 is connected to the switching valve 14 in the exit direction.
The boom actuator 31 moves in synchronization with the spool of the pump 2 to merge the discharge volume of the pump 2 with the discharge volume of the pump 1, thereby extending the boom actuator 31, and connects the pilot pipe of the regulator 3 of the pump 1 to the tank, thereby increasing the volume of the pump 1. Increase the discharge amount.

The circuit of this embodiment operates as follows. When the operating stick 40 is pulled, the spool of the switching valve 24 is pulled out, and the discharge fluid of the pump 2 is supplied to the arm actuator 32. At the same time, the flow rate passing through the center bypass passage decreases, and the pressure in the pilot pipe 8 decreases, so that the pump 2 increases, and the extension speed of the actuator increases in accordance with the amount by which the spool is pulled out.

When the operating rod 40 is further pulled, the spool of the switching valve 15 is pulled out, and the discharge fluid of the pump 1 is supplied to the arm actuator 32 by merging with the discharge fluid of the pump 2, and the flow rate passing through the center bypass of the switching valve 15 is increased. decreases, and the pressure in the pilot line 7 decreases, causing the difference in the discharge amount of the pump 1 to increase. Therefore, in accordance with the stroke of pulling out the operating rod 40, the minimum discharge amount of pump 2 gradually increases to the maximum discharge amount, and then the discharge amount of pump 1 is superimposed, and the discharge amount of pumps 1 and 2 increases.
is smoothly supplied up to the maximum discharge amount. FIG. 2 shows the concept of the supply flow rate that changes with the stroke of the operating stick during this time. The lower part of the figure shows changes in the opening area of the center bypass passage with respect to the stroke of the operating rod, and is of the type in which the opening area rapidly decreases while the stroke is small. The upper part of the figure shows the pump discharge rate that changes depending on the opening area, the flow rate passing through the center bypass passage, and the supply flow rate to the actuator obtained as the difference between the two, and the thick line shows the confluence from pumps 1 and 2. This shows the supply flow rate obtained as a result of this change, and it changes smoothly over the entire stroke of the operating stick.

When the operating rod 41 is pulled, the spools of the switching valves 14 and 23 are pulled out in synchronization, and the discharge amount of pump 1 is transferred to the switching valve 14, and that of pump 2 is combined via the switching valve 23 to the head end side of the actuator 31. The fluid supplied to the rod end side is supplied to the switching valve 14.
Pass through and return to the tank. FIG. 3 shows the concept of changes in the amount of supplied oil with respect to the stroke of the operating stick 41,
Figure 3a shows the switching valve 14 relative to the operating stick stroke.
The opening area of the center bypass passage changes gradually over the entire stroke. Switching valve 2
The spool 3 connects the regulator 3 of the pump 1 to the tank at the beginning of the stroke, so the spool shown in Figure 3b
As shown in FIG. 2, the pump 1 discharges at maximum in almost the entire region except near the neutral position, which matches the characteristics of the opening area of the center bypass passage of the switching valve 14, and smoothly changes the flow rate passing through the center bypass passage. Therefore, the actuator supply flow rate, which is obtained by subtracting the flow rate passing through the center bypass passage from the discharge amount of the pump 1, is also smoothly controlled in accordance with the movement of the operating rod. On the other hand, the characteristics of the switching valve 23 and the pump 2, which are switched in synchronization with the spool of the switching valve 14, are as follows.
3c and d which are identical to the left part of FIG. 2. Therefore, the total flow rate supplied to the actuator 31 is shown by the smooth curve in FIG. 3e, which is the sum of the supply flow rates in FIGS. 3b and 3d, and smooth control of the boom actuator 31 is possible.

When controlling the boom actuator 31 with the operation stick 41 while moving the operation stick 40 full stroke and supplying the arm actuator 32 with the combined discharge amounts of pumps 1 and 2 at high speed, the operation stick 41 controls the boom actuator 31. By switching, the discharge fluid of the pump 1, which has already reached the maximum discharge amount, can be smoothly controlled by the center bypass passage of the relief valve 14, which is suitable for metering a large flow rate. At this time, the switching valve 14
The relationship between the stroke of the spool and the amount of oil supplied to the arm actuator 32 and the boom actuator 31 is conceptually shown in FIG.

[Effects of the invention] As described above, the present invention connects the actuator connection port 23a of the four-way switching valve 23, which is provided to connect only to the extension side of the boom actuator 31, which is not used for the above purpose, to the pump 1. By simply changing the characteristics of the spool of the upper switching valve 14 by adding an inexpensive throttle 6 and pilot line 9, control of the tandem connection circuit can be made extremely smooth, and the operation can be improved. The effect of significantly reducing human fatigue was achieved through economical means.

[Brief explanation of the drawing]

FIG. 1 shows an embodiment of this invention. The hydraulic control circuit diagrams, FIGS. 2 to 4 are conceptual diagrams illustrating the discharge amount of the pump that constitutes this invention, the opening area of the center bypass passage of the switching valve, and the passage flow rate in comparison with the stroke of the operating stick. . 1, 2... pump, 3, 4... regulator,
6, 16, 26... Throttle, 17, 27... Relief valve, 12 to 15 and 22 to 25... Switching valve, 18, 28... Center bypass passage, 34...
... Tank, 40, 41... Control stick.

Claims (1)

[Scope of claim for utility model registration] A pump that increases the discharge amount in response to a decrease in pilot pressure, multiple center bypass type switching valves (hereinafter referred to as switching valves), and a center connected to a tank via a throttle and relief valve. It has two circuits consisting of a pilot pipe branched from a bypass passage and connected to a regulator that changes the capacity of the pump, and at least one point between the switching valves of one side circuit is connected in tandem, and the connection point The other side circuit has a spool that branches to one side of the duct connected to an actuator controlled by an upstream switching valve, and has a spool that moves synchronously with the spool of the switching valve on one side and does not move on the other side. In a hydraulic circuit connected to one actuator connection port of a switching valve, there is a restriction provided in a pilot pipe connected to a regulator of a pump in one side circuit, and a restriction provided in a pilot pipe connected to a regulator of a pump in one side circuit, and a restriction connected to the pilot pipe connected to a regulator of a pump in one side circuit, and a A hydraulic control circuit that includes a pilot pipe connected to the other actuator connection port of the switching valve.