JPH01261502A - Hydraulic device - Google Patents

Abstract

PURPOSE:To smooth the operability in the title device by providing a bypass passage which is branched from the feed passage of an upstream switching valve and passed through the feed passage of a downstream switching valve via a flow rate control valve. CONSTITUTION:There is provided a bypass passage 21 which is partially branched from the feed passage 15 of an upstream switching valve 12 and passes through the feed passage 17 of a downstream switching valve 13 via a flow rate control valve 16. Thus, the necessary oil quantity is fed into the upstream switching valve 12 and the excessive oil quantity is fed into the downstream switching valve 13 so that, when the upstream switching valve 12 is operated together with the downstream switching valve 13, it is possible to prevent the abrupt decrease in the oil quantity fed on the downstream side and the abrupt increase in the pressure on the upstream side and also the deterioration in the metering performance of the spool in the upstream switching valve 12. Accordingly it is possible to smooth the operability without reducing the effect of energy-saving.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a hydraulic system, and in particular, to control the flow rate of a switching valve associated with a driven pump when a plurality of switching valves constituting a tandem circuit are operated simultaneously. This relates to a hydraulic system that operates smoothly.

[Prior art] In recent years, from the viewpoint of energy saving, pump flow control has been developed in which the pump flow rate is maintained at the minimum discharge flow rate when the switching valve is in the neutral state, and the pump flow rate is increased according to the displacement of the stroke of the switching valve spool. A hydraulic control circuit that performs this has been proposed.

[Problems to be Solved by the Invention] In these pump flow rate control systems, the metering of the switching valve depends on the pump flow rate control, and the spool notch in the center bypass passage of the switching valve controls the pump minimum discharge flow rate. The opening area is also very small. Therefore, when a tandem circuit is configured with multiple switching valves having such spool notches, if the spool of the upstream switching valve is operated while the spool of the downstream switching valve is being operated at full stroke (maximum pump discharge amount), At the start of metering of the spool of the upstream switching valve, the entire pump discharge amount passes through the spool notch, which is provided in the center bypass passage and has a very small opening area, so that the pump discharge pressure rises rapidly. As a result, more pressure than necessary is generated in the upstream supply passage of the hydraulic circuit, and an excessive amount of oil flows into the cylinder boat of the upstream switching valve, deteriorating metering performance.

At the same time, the amount of oil flowing into the downstream switching valve also becomes almost nonexistent, and the speed of the cylinder connected to the downstream switching valve also decreases rapidly. Therefore, in such a state, if the spool of the upstream switching valve is returned to the neutral position, the cylinder connected to the downstream switching valve will begin to move rapidly, causing problems such as the inability to smoothly control the hydraulic pressure of the controlled object. There is.

Therefore, an object of the present invention is to prevent the downstream side of the hydraulic circuit from operating when the upstream side switching valve and the downstream side switching valve are operated simultaneously in a hydraulic circuit configured to control pump flow rate by connecting a plurality of switching valves in tandem. To provide a hydraulic circuit capable of preventing a sudden rise in upstream pressure and deterioration of metering performance of a spool of an upstream switching valve without rapidly reducing the amount of oil supplied to the upstream side.

[Means for Solving the Problem] In order to achieve the above object, the hydraulic circuit according to the present invention has the following features:
A pump whose discharge flow rate can be increased or decreased by a predetermined pilot signal, a multiple switching valve connected in tandem, and a supply passage of the upstream switching valve of the multiple switching valve via a flow rate control valve to the downstream switching valve. A bypass passage communicating with the supply passage is provided so that when more oil than necessary flows into the cylinder boat of the upstream switching valve, the excess oil can be supplied to the downstream switching valve.

[Function] According to the above-described means, when the upstream switching valve and the downstream switching valve are operated at the same time, the upstream switching valve is activated while the spool of the downstream switching valve is being operated at the full stroke (maximum pump discharge amount). When the spool is operated, the pump discharge pressure increases as in the past, and more oil than necessary tends to flow into the upstream switching valve. Therefore, by providing a bypass passage that branches from the supply passage of the upstream switching valve and leading to the supply passage of the downstream switching valve via the flow control valve, the upstream switching valve can be switched in accordance with the operation of the flow control valve. Excess oil, which would otherwise flow into the cylinder boat of the valve in an amount greater than necessary, is supplied to the downstream switching valve, thereby preventing an excess amount of oil from being supplied to the upstream switching valve.

[Example] Next, an example of a hydraulic circuit according to the present invention will be described with reference to the accompanying drawings.

As a first embodiment, a hydraulic circuit will be described below with reference to FIG. 1 in the case of negative flow control in which the pump flow rate is increased as the pilot pressure decreases in a pump flow rate control system in which the pump flow rate is controlled by a pilot signal. In this example, only the hydraulic circuits of the switching valves when two center bypass type switching valves connected in tandem are used are shown, and the hydraulic circuits of various control objects connected to each cylinder boat are shown below. It is omitted.

In FIG. 1, oil discharged from a variable displacement pump 1o passes through an upstream switching valve 12 and a downstream switching valve 13, and returns to a tank 2o via a pressure generator 14. In addition, it partially branches from the supply passage 15 of the upstream side switching valve 12, and the flow rate control valve 1
A bypass passage 21 is provided which communicates with the supply passage 17 of the downstream switching valve 13 via the valve 13, and a check valve 18 prevents a passage from flowing backward from the supply passage 17 to the center bypass passage. Here, the flow control valve 16 is controlled by the opening area of a metering notch for supplying the supply from the supply passage provided in the spool of the upstream switching valve 12 to the cylinder boat (in the embodiment shown in FIG. 1, the spool is moved to the right). The metering performance is determined by the supply metering notch so that it is almost the same as the metering performance by pump flow control during single operation (Figure 2).
figure).

When using a flow rate control pump, the relationship between the flow rate and opening area of the spool stroke in the switching valve is as follows:
As shown in FIGS. 2 and 3.

In addition, the pump discharge flow rate becomes the minimum pump discharge flow rate when the switching valve is neutral due to the pilot signal pressure generated on the upstream side of the pressure generator at14, and the generated pressure is reduced by the center/hay pass flow rate that is closed according to the stroke of the switching valve. The structure is such that the discharge flow rate is increased in response to a decrease.

Here, when only the spool of the upstream side switching valve 12 is operated independently, since the discharge oil of the flow rate control valve 16 is blocked, the control is performed in the same way as in the conventional independent operation.

Furthermore, when the downstream switching valve 3 is operated at its maximum stroke, the amount of oil discharged from the variable displacement pump 10 is at its maximum, and the upstream switching valve 12 is operated to the right in the figure, as compared to the conventional one. Similarly, if the pump discharge pressure increases and a flow rate greater than necessary flows into the upstream switching valve 12, the cylinder port opening area determined by the supply metering notch provided in the supply passage to the cylinder port, A differential pressure is generated between the downstream side, and if the differential pressure is greater than the force of the spring 19, the flow control valve 16 opens and the flow is caused to flow into the downstream switching valve 13. Flow rate is not supplied more than necessary.

In the embodiment shown in FIG. 1, the flow rate control valve 16 is operated when the upstream switching valve 12 is operated to the right in the figure. It can also be a form.

Next, as a second embodiment shown in FIG. 4, a case will be explained in which the pump flow rate control method is positive flow control in which the pump discharge flow rate is controlled by an external signal and the pump flow rate increases as the pilot pressure increases. In figure 0,
A pilot signal pressure pump 36 and pilot valves 38 and 4o are provided, and 42 is a shuttle valve, respectively.

The same functional members already explained in the drawings of the first embodiment are given the same reference numerals. Therefore, the effects of this hydraulic circuit are the same as those of the first embodiment described above.

FIG. 5 shows yet another embodiment of the first embodiment shown in FIG. 1, in which the check valve 18 of FIG. It is also connected to the center bypass passage, so that the metering flow rate based on the center bypass flow rate when the upstream switching valve 12 is operated alone is larger than the metering flow rate when using the flow rate control valve 16 based on the cylinder port opening area. If set, the flow rate control valve 16 will operate even when operated alone and control the pump discharge flow rate, and the metering performance of the upstream switching valve 12 will be the same when operated alone and when operated simultaneously.

[Effects of the Invention] As explained above, according to the present invention, in a hydraulic circuit that has a configuration in which a plurality of switching valves are connected in tandem and performs pump flow rate control for the purpose of energy saving effect, the upstream switching valve When operating the and downstream switching valve at the same time,
This solves the problem of preventing a sudden drop in the amount of oil supplied to the downstream side, a sudden increase in the upstream pressure, and a deterioration in the metering performance of the spool of the upstream switching valve, and smoothly without reducing the energy saving effect. You can get easy operability.

[Brief explanation of the drawing]

Fig. 1 is a system diagram of the main parts of the hydraulic circuit of the first embodiment using the negative flow rate control method according to the present invention, Fig. 2 is a flow characteristic curve diagram of a switching valve using a flow rate control pump, and Fig. 3 is a diagram of the flow rate characteristic curve of a switching valve using a flow rate control pump. FIG. 4 is a diagram showing the relationship between the spool stroke of the switching valve and the opening area of the center bypass based on the characteristics shown in FIG. FIG. 5 is a system diagram of essential parts showing still another embodiment of the first embodiment shown in FIG. io... Variable capacity pump, 12... Upstream switching valve, 13... Downstream switching valve, 14... Pressure generator, 15.17... Supply passage, 16... Flow rate control valve 18...Check valve, 20...
Tank, 21... Bypass passage, 36... Pilot signal pressure pump, 38.40.
...Pilot valve, 42...Shuttle valve.

Claims (1)

[Claims] A pump whose discharge flow rate can be increased or decreased by a predetermined pilot signal, a multiple switching valve connected in tandem, and a supply passage of the upstream switching valve of the multiple switching valve via a flow rate control valve to the downstream switching valve. What is claimed is: 1. A hydraulic system comprising a bypass passage to a supply passage and supplying surplus oil from the upstream switching valve to the downstream switching valve.