JPH0437281B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field to which the Invention Pertains] This invention relates to a hydraulic control circuit, and in particular to a method for smoothly controlling the flow rate of a switching valve associated with a driven pump when a plurality of switching valves constituting a tandem circuit are simultaneously operated. The present invention relates to a tandem hydraulic control circuit.

[Prior art and its problems]

Conventionally, when a tandem hydraulic control circuit is configured by connecting a plurality of switching valves in series, when a fixed capacity pump is used as the driving pump serving as the hydraulic pressure source, metering (flow rate adjustment) of the switching valve is performed as follows: Generally, a structure is adopted in which the center bypass passages of each switching valve are closed by a spool, thereby reducing the flow rate flowing into these center bypass passages and increasing the flow rate to the cylinder port communicating with the controlled object.

Therefore, in the conventional 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, so it passes through the center bypass passage of the upstream switching valve to the downstream switching valve. The flow rate can also be approximately the full flow rate of the pump. Therefore, in this type of hydraulic control 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 cylinders connected to the upstream switching valve and the downstream switching valve as controlled objects can be respectively operated. In particular, when operating the spool of the downstream switching valve over a full stroke and operating the cylinder connected to the upstream switching valve at a small speed, the speed of the cylinder connected to the downstream switching valve is hardly reduced. It is possible to operate both cylinders.

However, in recent years, from the standpoint of energy conservation, pump flow control has been implemented in such a way that 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 in accordance with the displacement of the stroke of the switching valve spool. A hydraulic control circuit has been proposed. In this case, if the pump flow rate is to be controlled by pilot pressure, the pump flow rate control method is a negative control method in which the pump flow rate is increased by decreasing the pilot pressure, and a negative control method in which the pump flow rate is increased by increasing the pilot pressure. It is broadly divided into positive control methods that increase the flow rate. However, in any of these pump flow rate control methods, 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 is designed to control the minimum pump discharge flow rate. Therefore, the opening area is also very small. Therefore, when a tandem circuit is configured with multiple switching valves having such spool notches, 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). Then, at the start of metering of the spool of the upstream switching valve, the entire pump discharge amount passes through a spool notch with a very small opening area provided in the center bypass passage, so the pump discharge pressure increases 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 port of the switching valve, worsening the metering of the spool of the upstream switching valve. Moreover, at the same time, the amount of oil flowing downstream of the hydraulic circuit is almost eliminated, and the speed of the cylinder connected to the downstream switching valve is also rapidly reduced. Therefore, in such a state, when the spool of the upstream switching valve is returned to the neutral position, the cylinder connected to the cylinder port begins to move rapidly,
There are problems such as not being able to smoothly control the hydraulic pressure of the controlled object.

[Purpose of the invention]

An object of the present invention is to provide a tandem hydraulic control circuit in which a plurality of switching valves are connected in tandem to control pump flow rate, and when the upstream switching valve and the downstream switching valve are operated simultaneously, the hydraulic circuit without suddenly reducing the amount of oil supplied to the downstream side.
To provide a tandem hydraulic control circuit capable of preventing a sudden rise in upstream pressure and deterioration of spool metering of an upstream switching valve, and maintaining a pump discharge flow rate at the minimum when the spool is in neutral.

[Key points of the invention]

A tandem hydraulic control circuit according to the present invention includes a center bypass type multiple switching valve connected in tandem;
In a tandem hydraulic control circuit consisting of a common pump and a common pump that sets a pilot pressure so that the pump maintains a minimum flow rate when the multiple switching valve is in a neutral state, switching is performed in conjunction with an upstream switching valve of the multiple switching valve. The metering notch of the spool of the upstream switching valve is configured to have a large opening area, comprising a selector valve that is operated, and configured to supply a predetermined pilot pressure to the flow rate control section of the pump via the selector valve. However, the pilot pressure is set so that the pump discharge flow rate becomes maximum near the start of metering.

In this case, when the multiple switching valve is in the neutral state, a part of the amount of oil that returns to the tank via the center bypass passage is taken out as pilot pressure and supplied to the flow rate control section of the pump via the selector valve. The pump can be effectively operated as a negative flow rate control system.

Further, each of the multiple switching valves is configured to be switched by pilot pressure using a pilot pressure pump and a pilot valve, and the selector valve is connected between the pilot pressure flow paths of the upstream switching valves of the multiple switching valves. The switching operation is performed by pilot pressure derived through a shuttle valve, and when the upstream switching valve is in a neutral state, the pilot pressure is derived from between the flow paths of each of the multiple switching valves via the shuttle valve. The pilot pressure derived from the pilot pressure pump is supplied to the flow rate control section of the main pump via the selector valve, and when the upstream switching valve is operated, the pilot pressure derived from the pilot pressure pump is controlled via the selector valve to control the flow rate of the main pump. By supplying the flow rate to the control unit, the main pump can be effectively operated as a positive flow rate control system.

[Embodiments of the invention]

Next, embodiments of the tandem hydraulic control circuit according to the present invention will be described in detail below with reference to the accompanying drawings. In this example, only the center bypass and pilot pressure hydraulic circuits of the switching valves when two center bypass switching valves connected in tandem are used, and various control objects connected to the cylinder ports are shown. The hydraulic circuit is omitted.

FIG. 1 shows an embodiment of the hydraulic control circuit of the present invention in which the pump flow rate control method is negative flow control. That is, in FIG. 1, reference numeral 10 indicates a variable displacement pump, 12 indicates an upstream switching valve, 14 indicates a downstream switching valve, and 16 indicates a selector valve. In FIG. 1, the upstream switching valve 12 and the downstream switching valve 14 are in a neutral state, and the total amount of oil discharged from the variable displacement pump 10 is transmitted through the center bypass passage of each switching valve 12, 14, and through the orifice 18 and the relief. The valve 20 is arranged to be returned to the tank 22 via a parallel connected flow path. On the other hand, in this case, a flow path 24 (indicated by a broken line) is led out from the upstream side of the flow path where the orifice 18 and the relief valve 20 are connected in parallel, and this flow path is variable via the selector valve 16. It is communicatively connected to the flow rate control section 26 of the displacement pump 10. The selector valve 16 is connected to a flow path 28 which is switched and connected to the flow path 24 connected to the flow rate control section 26 of the variable displacement pump 10 and communicated with the tank 22.

Generally, when a fixed capacity pump is used, the relationship between the flow rate with respect to the spool stroke in the switching valve and the opening area of the center bypass is as shown in FIGS. 2 and 3. Further, when a flow rate control pump is used instead of a fixed capacity pump, the relationship between the flow rate and the opening area of the center bypass with respect to the spool stroke in the switching valve is as shown in FIGS. 4 and 5. Therefore, when comparing the two, when using a flow rate control pump, the response characteristics of the flow rate to the displacement of the spool stroke deteriorates, and the opening area of the center bypass also requires fine adjustment, so fixed displacement pumps are not practical. It will be understood that this is advantageous.

However, in this embodiment, when the spool of the upstream switching valve 12 is in a neutral state, the variable displacement pump 10 has a minimum discharge amount, and has a full discharge characteristic near the start of metering of the spool of the upstream switching valve 12. It is configured to switch the pilot pressure for controlling the pump flow rate. Therefore, in this embodiment, as shown in FIG. 6, it is preferable that the metering notch 32 of the spool 30 of the upstream switching valve 12 be a large notch for fixed capacity. Further, the selector valve 16 has its spool coupled to, for example, a spool of the upstream switching valve 12 so as to be interlocked with the spool. In this case, in the illustrated example, the selector valve 1
6 and the spool of the upstream switching valve 12 are mechanically connected, and when the switching valves 12 and 14 are in a neutral state, the total discharge oil amount of the variable displacement pump 10 is equal to the amount of oil discharged from each switching valve 12 and 14. is returned to the tank 22 via the center bypass, and at this time the flow path 24
The pilot pressure generated in the variable displacement pump 10 is configured to be applied to the flow rate control section 26 of the variable displacement pump 10 via the selector valve 16. Therefore, in the circuit of this embodiment, since the variable displacement pump 10 performs negative flow rate control, the discharge flow rate of the variable displacement pump 10 is reduced to the minimum level in accordance with the magnitude of the pilot pressure.

Next, in the circuit of this embodiment having the above-described configuration, the operation when operating the spool of the upstream switching valve 12 will be explained with reference to the characteristics shown in FIG.

Now, if the spool 30 of the upstream switching valve 12 is operated in the right direction (see Fig. 6), the selector valve 16 interlocked with this spool 30 will switch near the start of metering, and the switching valve 12,
The pilot pressure supplied from the center bypass passage 14 is cut off, and the pilot pressure acting on the variable displacement pump 10 side is led to the tank 22 via the flow path 28. Therefore, the variable displacement pump 10 achieves negative control in which the amount of oil discharged from the pump increases as the pilot pressure decreases.
At this time, the amount of oil discharged from the pump reaches its maximum flow rate. Thereafter, when the spool 30 moves further, a flow rate characteristic similar to that of the fixed displacement pump described above is obtained depending on the spool stroke (see Figs. 2 and 3).
(see figure). In addition, the spool 3 of the upstream switching valve 12
In the fine operation range of 0, since the opening area of the center bypass is large, the lead flow rate to the downstream switching valve 14 can be maintained large, and the cylinders connected downstream can also be effectively operated. Furthermore, when the spool of the downstream switching valve 14 reaches its maximum stroke, the amount of oil discharged from the variable displacement pump 10 reaches its maximum and flows to the spool of the downstream switching valve 14 via the center bypass of the upstream switching valve 12. However, even if the spool of the upstream switching valve 12 is slightly operated at this time, the flow rate supply to the downstream side will not be abruptly cut off, so simultaneous operation of these switching valves 12 and 14 can be smoothly achieved. be able to.

In addition, in the above embodiment, the upstream switching valve 12
The selector valve 16 provided in conjunction with the upstream switching valve 12 may be configured to switch in synchronization with the operation of the spool of the upstream switching valve 12. For example, the spool of the selector valve 16 may be operated using a solenoid valve, pilot pressure, etc. In this case, the selector valve 16 may be of a two-position switching type.

FIG. 7 shows another embodiment of the hydraulic circuit of the present invention, which is a modification of the embodiment shown in FIG. 1, in which the pump flow rate control method is negative flow control. That is, the circuit configuration of this embodiment is basically the same as the embodiment shown in FIG.
This figure shows the deformation of the pilot pressure flow path 24 when it is configured with a one-port valve. In this case, the embodiment is completely the same as the first embodiment except that the orifice 34 is provided in the pilot pressure flow path 24, and the same components are given the same reference numerals and detailed explanation thereof will be omitted. The operation of the circuit of this embodiment is also exactly the same as that of the embodiment described above.

FIG. 8 shows yet another embodiment of the hydraulic circuit of the present invention. This embodiment shows a case where the pump flow rate control method is positive flow rate control. Therefore, in the circuit of this embodiment, the upstream switching valve 12, the downstream switching valve 14, and the selector valve 16 are all configured to be switched by pilot pressure. Therefore, in FIG. 8, a pilot pressure pump 36 is installed in the pilot pressure flow path.
and pilot valves 38, 40, and are configured to perform switching operations of the respective switching valves 12, 14. Further, the selector valve 16 is configured to perform a switching operation between the flow paths of the pilot pressure derived from the pilot valve 38 using the pilot pressure derived via the shuttle valve 42. In this case, the pressure of the pilot pressure pump 36 is directly led to the selector valve 16, and when the upstream switching valve 12 is switched under the action of the pilot valve 38, the selector valve 16 is switched and the pump is switched. The pressure is directly controlled by the flow rate controller 2 of the variable displacement pump 10.
6, the amount of oil discharged from the pump can be increased. In addition, in FIG. 8, reference numeral 22
indicates a tank, and 44 indicates a relief valve. Regarding the operation of the circuit of this embodiment, the variable displacement pump 10
The only difference is that the flow rate control is positive flow rate control, and the control operation by the selector valve 16 is basically the same as the embodiment circuit shown in FIG.

〔Effect of the invention〕

As is clear from the embodiments described above, the tandem hydraulic control circuit according to the present invention is provided with a selector valve that is operated in conjunction with the upstream switching valve of the multiple switching valves connected to the tandem. By configuring the system to obtain a pilot pressure signal for controlling the flow rate of the variable displacement pump in accordance with valve switching, an energy saving effect is achieved by reducing the amount of pump discharged oil when the multiple switching valve is in a neutral state, Furthermore, all the control objects connected to the multiple switching valves can be smoothly operated when the variable displacement pump is at maximum discharge.

Therefore, according to the hydraulic control circuit of the present invention, an economical hydraulic circuit can be provided at low cost, and the effect of contributing to improving the performance and reliability of this type of hydraulic circuit is extremely large.

Although the preferred embodiments of the present invention have been described above, it goes without saying that various design changes can be made without departing from the spirit of the present invention.

[Brief explanation of drawings]

Fig. 1 is a main part system diagram showing an embodiment of the tandem hydraulic control circuit according to the present invention, Fig. 2 is a flow rate characteristic curve diagram of a switching valve using a fixed capacity pump, and Fig. 3 is a diagram showing the characteristics shown in Fig. 2. Relationship diagram between the spool stroke of the switching valve and the opening area of the center bypass,
Figure 4 is a flow rate characteristic curve diagram of the switching valve using a flow rate control pump, Figure 5 is a relationship diagram between the spool stroke of the switching valve and the opening area of the center bypass based on the characteristics shown in Figure 4, and Figure 6 is a diagram of the flow rate characteristic curve of the switching valve based on the characteristics shown in Figure 4. A correspondence diagram showing the correlation between the flow rate characteristics of the switching valve and the spool in the circuit of the invention, FIG. 7 is a main part system diagram showing a modification of the circuit of the invention shown in FIG. 1, and FIG. 8 is a diagram showing a further variation of the circuit of the invention. FIG. 10... Variable displacement pump, 12... Upstream switching valve,
14...Downstream switching valve, 16...Selector valve, 18...
Orifice, 20... relief valve, 22... tank,
24...Pilot pressure flow path, 26...Flow rate control section,
28... Flow path, 30... Spool, 32... Metering notch, 34... Orifice, 36... Pilot pressure pump, 38, 40... Pilot valve, 42
...Shuttle valve, 44...Relief valve.

Claims (1)

[Claims] 1. Consists of center bypass type multiple switching valves connected in tandem, and a common pump that sets pilot pressure so that the pump maintains a minimum flow rate when the multiple switching valves are in a neutral state. The tandem hydraulic control circuit includes a selector valve that is switched in conjunction with the upstream switching valve of the multiple switching valve, and is configured to supply a predetermined pilot pressure to the flow rate control section of the pump via the selector valve. The tandem hydraulic control is further characterized in that the opening area of the metering notch of the spool of the upstream switching valve is set large, and the pilot pressure is set so that the pump discharge flow rate is maximized near the start of metering. circuit. 2. In the tandem hydraulic control circuit according to claim 1, when the multiple switching valve is in a neutral state, a part of the amount of oil that returns to the tank via the center bypass passage is taken out as pilot pressure, and the oil is supplied to the pump via the selector valve. A tandem hydraulic control circuit configured to supply a flow rate controller to a flow rate control section of the pump, and to control the pump in a negative flow rate. 3. In the tandem hydraulic control circuit according to claim 1, each of the multiple switching valves is configured to be switched by pilot pressure using a pilot pressure pump and a pilot valve,
The selector valve is configured to be switched by pilot pressure derived from between the pilot pressure flow paths of the upstream switching valves of the multiple switching valves via a shuttle valve, and when the upstream switching valve is in the neutral state, The pilot pressure derived from the pilot pressure flow path of each multiple switching valve via the shuttle valve is supplied to the flow control section of the main pump via the selector valve, and when the upstream switching valve is operated. A tandem hydraulic control circuit configured to supply pilot pressure derived from the pilot pressure pump to a flow rate control section of the main pump via a selector valve, and to control the main pump in a positive flow rate.