JPH0732603Y2 - Hydraulic circuit of hydraulic excavator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to a hydraulic circuit for operating and controlling a boom cylinder and an arm cylinder of a hydraulic excavator, and more particularly to a plurality of centers in which the hydraulic circuit constitutes a tandem circuit. The present invention relates to a hydraulic circuit that has a bypass type directional control valve (hereinafter, may be simply referred to as a directional control valve) and can smoothly control the flow rate of the directional control valve even if the pump discharge flow rate fluctuates.

[Conventional technology]

Generally, in a two-pump hydraulic circuit, one (first) unit hydraulic circuit is provided with an arm directional switching valve, and the other (second) unit hydraulic circuit is provided with a boom directional switching valve and an arm merging directional switching valve. Is provided, and the excess oil in the second unit hydraulic circuit is joined to the directional switching valve for arms via the merging directional switching valve for arms.

Further, in general, metering (flow rate adjustment) by a directional control valve reduces the flow rate flowing through the center bypass channel by closing the center bypass channel of the directional control valve with a spool, and a boom cylinder or arm cylinder (hereinafter actuator). (It may be referred to as “(may be referred to as)”) is performed by increasing the flow rate to the cylinder port communicating with the cylinder port.

By the way, in such a configuration, in the conventional hydraulic circuit, since the pump is configured in a fixed displacement type (hereinafter referred to as a fixed displacement hydraulic circuit), pump drive power for a flow rate other than that used for the actuator is wasted. Was there. Therefore, in order to avoid the wasted energy in recent years,
A hydraulic circuit (hereinafter, referred to as a variable displacement hydraulic circuit) in which a pump is configured in a variable displacement type and a flow rate of the hydraulic circuit is controlled in accordance with a flow rate used by an actuator has been promoted. In addition, in such a variable displacement hydraulic circuit,
Since the minimum discharge flow rate corresponding to the required flow rate of the pump is designed to be controlled by the spool notch of the center bypass passage portion of the directional control valve, its opening area is set to be very small.

[Problems to be solved by the device]

However, such a conventional variable displacement hydraulic circuit has the following drawbacks.

That is, the spool of the downstream side directional control valve in the tandem hydraulic circuit (the merging directional control valve in the second unit hydraulic circuit) is being operated during the entire stroke (in this case, the pump discharge flow rate of the second unit hydraulic circuit is maximum). (Set) When the spool of the upstream directional control valve (boom directional control valve) is operated, the total discharge flow rate of the pump is very small when the metering of the upstream directional control valve is started. Since it passes through the spool notch having the opening area, the pump discharge pressure rapidly rises. As a result, excessive pressure is generated in the upstream supply passage of the unit hydraulic circuit,
Excessive flow flows into the cylinder port of the directional control valve. That is, the metering characteristic of the upstream directional control valve is deteriorated. Therefore, at the same time, the flow rate flowing to the downstream side of the unit hydraulic circuit sharply decreases, and the metering characteristic of the downstream side directional control valve deteriorates. On the other hand, if the spool of the upstream side directional control valve is returned to the neutral state in such a state, a higher pressure than necessary is generated in the upstream side supply passage at this time, so the cylinder port of the downstream side directional control valve is Excessive flow rate flows in. That is, the metering characteristic of the downstream side directional control valve is deteriorated. As described above, the conventional variable displacement hydraulic circuit of this type has a drawback in that the flow rate control of the directional control valve cannot be smoothly performed.

Incidentally, in the fixed displacement hydraulic circuit, the above-mentioned difficulties do not occur. That is, in the fixed displacement hydraulic circuit, the maximum pump flow rate (fixed displacement flow rate) passes through the center bypass passage even when the directional control valve is in the neutral position, so that the center bypass passage is set to a sufficiently large opening area. And even during the operation as described above,
Unnecessary high pressure is not generated in the hydraulic circuit.

In addition, also in the variable displacement hydraulic circuit, if the opening area of the center bypass passage of the directional control valve is set to be small on the downstream side and large on the upstream side (for the boom),
The above-mentioned difficulties are solved. However, in this case, when the upstream side directional control valve is operated independently, particularly when the pump discharge flow rate is relatively small during this single operation, the flow rate flowing into the cylinder port of the directional control valve corresponds to the displacement amount of the spool. Is not set. That is, a drawback that the metering characteristic of the upstream side directional control valve is deteriorated occurs.

Therefore, an object of the present invention is to supply excess oil of a unit variable displacement hydraulic circuit that connects two center bypass type directional switching valves in tandem to another unit variable displacement hydraulic circuit via a downstream side directional switching valve of this hydraulic circuit. In the hydraulic circuit of the hydraulic excavator that merges, the metering characteristics of the two-way directional control valve of the tandem variable displacement unit hydraulic circuit can be maintained well both when the two-way directional control valve is operated simultaneously and when the upstream directional control valve is operated independently. To provide a hydraulic circuit for a hydraulic excavator.

[Means for Solving the Problems]

In order to achieve the above object, the hydraulic circuit of the hydraulic excavator according to the present invention has a first unit hydraulic circuit to which the discharge oil of the first variable displacement pump is supplied and a discharge oil of the second variable displacement pump. A second unit hydraulic circuit to be supplied, wherein the first unit hydraulic circuit is provided with a center bypass type directional control valve for an arm which is connected to a pump discharge oil supply passage and operates an arm cylinder; and a downstream side thereof. A first pilot pressure generating means connected to a center bypass to control the discharge amount of the first variable displacement pump; and the second unit hydraulic circuit connected to a pump discharge oil supply path to form a boom. A boom center bypass type directional control valve that operates a cylinder, and an arm center bypass valve that is connected to the downstream center bypass and joins the bleed flow rate to the arm center bypass type directional control valve. Type merging control valve means, a center bypass type flow rate switching valve connected to the downstream side center bypass and connected to the boom center bypass type directional control valve to throttle the center bypass, and connected to the downstream side center bypass And a second pilot pressure generating means for controlling the discharge amount of the second variable displacement pump.

In this case, the arm center bypass merge control valve means is
It is composed of a center bypass type merging direction switching valve, and the cylinder port pipeline of this arm center bypass type merging direction switching valve and the cylinder center pipeline of the arm center bypass type directional switching valve are connected via a merging pipeline. Or a center bypass type merging switching valve, and a merging pipe with a check valve interposed between the upstream center bypass of the arm center bypass type merging switching valve and the supply path to the arm center bypass type directional switching valve. It can be configured to connect via a path. Alternatively, the arm center bypass type merge control valve means and the center bypass type flow rate switching valve may be configured by a common center bypass type switching valve.

Further, the center bypass type directional control valve for the boom may be configured so that the center bypass passage portion is not closed in the stroke end state of the boom cylinder extending operation.

[Action]

In the tandem unit hydraulic circuit of the hydraulic circuit according to the present invention, when the boom direction switching valve on the upstream side is operated, the center bypass type flow switching valve is operated in conjunction with this operation signal. As a result, even if the opening area of the center bypass passage of the boom directional control valve is set large, the flow rate of the boom cylinder port inflow when the boom directional control valve is operated independently is set according to the displacement of the spool. To be done. That is, the metering characteristic of the boom directional control valve is not deteriorated even during the single operation.

Further, in this way, in the tandem unit hydraulic circuit of the present invention, the opening area of the center bypass passage portion of the boom directional control valve can be set large, so that the upstream side merging control valve for the arm is operated at the upstream side. Even if the boom directional control valve is operated, sudden pressure fluctuations will not occur in the hydraulic circuit. Therefore, the metering characteristics are not deteriorated.

〔Example〕

An embodiment of the hydraulic circuit of the hydraulic excavator according to the present invention will be described in detail below with reference to the accompanying drawings.

The hydraulic circuit of the present invention includes a first unit hydraulic circuit 12 to which the discharge oil of the first variable displacement pump 10 is supplied and a second unit hydraulic circuit to which the discharge oil of the second variable displacement pump 14 is supplied. It consists of 16 and.

The first unit hydraulic circuit 10 includes an arm center bypass type directional control valve 20 connected to the pump discharge oil supply passage 18, and a first pilot pressure generating means 24 connected to a downstream side center bypass 22 thereof. The arm directional control valve 20 has an arm cylinder 30 which is driven and operated via a supply passage 26 and a cylinder port passage 28. First pilot pressure generating means
Reference numeral 24 denotes a pump control pressure generated in the upstream side center bypass 22 of the first variable displacement pump 10 via a pilot line 32 and a negative regulator 34.
To control the discharge flow rate to the minimum flow rate corresponding to the flow rate used by the arm cylinder 30.

The second unit hydraulic circuit 16 includes a boom center bypass type directional control valve 38 connected to the pump discharge oil supply passage 36, and an arm center bypass type merging directional control valve 42 connected to the downstream center bypass 40. A center bypass type flow rate switching valve 44 connected to the downstream side center bypass 40, and a second pilot pressure generating means 46 connected to the downstream side center bypass 40. The boom direction switching valve 38 is
The boom cylinder 52 is operated and driven via the supply passage 48 and the cylinder port pipe passage 50. Merging directional valve for arm
42 is driven in conjunction with the arm directional switching valve 20 via the operation valve 66 and the pilot line 68, and the bleed flow rate from the boom directional switching valve 38 is supplied to the arm via the supply path 54 and the merging conduit 56. Cylinder port line of directional valve 20
Join 28. The flow rate switching valve 44 interlocks with the boom extension operation of the boom direction switching valve 38 via the operation valve 58 and the pilot line 60, and throttles the center bypass 40. The second pilot pressure generating means 46 has an upstream center bypass 40.
The pump control pressure generated in the
Is applied to the variable displacement pump 14 to control the discharge flow rate to the minimum flow rate corresponding to the flow rates used by the boom cylinder 52 and the arm merging direction switching valve 42. The opening area of the center bypass passage of the boom directional control valve 38 is set to a sufficient size.

Therefore, in such a hydraulic circuit, when the arm directional control valve 20 of the first hydraulic circuit 12 is extended, the arm merging directional control valve 42 of the second hydraulic circuit 16 is also operated in conjunction with the arm cylinder. Reference numeral 30 denotes a discharge flow rate of the first variable displacement pump 10 and a boom direction switching valve of the second variable displacement pump 14.
Since the bleed flow rates from 38 are merged and supplied, the arm cylinder 30 can be driven at high speed.

Next, the operation of the hydraulic circuit of the present invention having such a configuration will be described. Since the first unit hydraulic circuit 12 does not require any particular explanation, only the second unit hydraulic circuit 16 will be described.

First, in the hydraulic circuit of the present invention, the boom cylinder
When the boom direction switching valve 38 is operated via the operation valve 58 to extend 52, the flow rate switching valve 44 is simultaneously operated via the pilot line 60 by this operation signal. At this time, the flow rate supplied to the boom cylinder 52 via the supply passage 48 and the cylinder port pipe passage 50 is equal to the boom direction switching valve.
In 38, since the opening area of the center bypass passage portion is large, it is difficult to control the flow rate according to the spool displacement amount of the boom direction switching valve 38. By narrowing 40, the corresponding flow control is achieved. That is, the metering characteristic of the boom directional control valve 38 during the single operation is favorably maintained.

On the other hand, when the arm merging direction control valve 42 is operated, that is, when the oil of the second hydraulic circuit 16 is joined to the arm directional switching valve 20 of the first hydraulic circuit 12, the boom directional switching valve on the upstream side.
When operating 38, in the conventional hydraulic circuit of this kind,
As described above, at the start of metering of the boom directional control valve 38, the pump discharge pressure rises sharply, and an excessive flow rate flows into the cylinder port line 28 to deteriorate the metering characteristics. In the circuit, the opening area of the center bypass passage of the boom directional control valve 38 is set to be sufficiently large, so that the abrupt pressure fluctuation as described above does not occur in the hydraulic circuit, and the metering characteristic is prevented. Is well retained. In other words, in the hydraulic circuit of the present invention, since the center bypass passage of the upstream boom directional control valve 38 is set to have a large opening area, the spool of the boom directional control valve 38 has a large opening area. Since the bleed flow rate to the arm merging direction switching valve 42 is kept large in the fine operation range, the control of the merging flow rate by the arm merging direction switching valve 42 is smoothly performed. That is, the metering characteristic is maintained well. Further, at the time of the maximum stroke of the spool of the arm merging direction control valve 42, the discharge flow rate of the second variable displacement pump 14 becomes maximum at this time, and this maximum discharge flow rate passes through the center bypass passage portion of the boom directional control valve 38. Although it is flowing to the spool of the arm merging direction switching valve 42, even if the spool of the boom direction switching valve 38 is finely operated at this time, the flow rate to the arm merging direction switching valve 42 side is suddenly cut off. Therefore, the flow rate control of the two-way switching valves 38 and 42 is smoothly performed. That is, the metering characteristics are kept good even during simultaneous operation.

As described above, in the hydraulic circuit of the present invention, even when the directional control valve for the boom on the upstream side is operated independently, or when the directional control valves for the upper and the downstream booms and the arms for merging are simultaneously operated, these Both of the metering characteristics of the two-way switching valve can be maintained well.

The hydraulic circuit of the present invention can be applied not only to the first and second unit hydraulic circuits but also to a unit hydraulic circuit having another unit hydraulic circuit, and the actuators for the arm and the boom. Of course, the present invention is not limited to the cylinder and can be applied to other actuators. Furthermore,
The configuration of the unit hydraulic circuit can be appropriately changed, for example, by changing the control of the variable displacement pump to a positive control system instead of the negative control system. Also,
The flow rate switching valve is configured to be interlocked with the boom extension operation of the boom direction switching valve, which means that in this type of hydraulic circuit, the leveling operation is performed, that is, the arm is operated in front of the boom. This is because the interlocking is required in the work of gradually extending, and in the case of another actuator, for example, the interlocking can be appropriately configured so as to correspond to the bidirectional operation of the directional control valve. is there.

FIG. 2 shows another embodiment of the hydraulic circuit of the present invention. In this embodiment, the arm center bypass type merge control valve is
Instead of the center bypass type merging direction control valve in the embodiment shown in the drawing, a center bypass type merging switching valve is configured. That is, in FIG. 2, the arm center bypass type merging control valve means includes a center bypass type merging switching valve 70 connected to a downstream side center bypass 40 of the boom direction switching valve 38, and an upstream side center bypass 40 thereof. It is composed of a connecting pipe line 74 that connects via a check valve 72 to the supply passage 26 to the arm center bypass type directional control valve 20. In the present embodiment, the arm center bypass type merging switching valve 70 is the center bypass type flow switching valve.
Although the switching valves 70 and 44 are arranged on the downstream side of 44, the same function is exerted on both the upstream and downstream sides. Also in the case of the present embodiment, the opening area of the center bypass passage of the boom directional control valve 38 is set to a sufficient size, and the metering characteristics of the boom directional control valve 38 and the merging switching for the arm are set. The merging characteristics of the valve 70 are satisfactorily achieved, as in the case of the embodiment shown in FIG.

FIG. 3 shows still another embodiment of the hydraulic circuit according to the present invention. In this embodiment, the arm center bypass type confluence switching valve 70 and the center bypass type flow rate switching valve 44 in the embodiment shown in FIG. 2 are used. Since both of the switching valves 70 and 44 have the same function of switching the center bypass, they are constituted by a common center bypass type switching valve 76.
Also in this embodiment, the same operation as in the case of the embodiment shown in FIGS. 1 and 2 is achieved. It should be noted that the present embodiment has the advantages that the configuration is simple and that it can be applied to this type of conventional hydraulic circuit mechanism easily and inexpensively.

Next, FIG. 4 shows a specific structure of the directional control valve for booms used in the hydraulic circuit of the present invention. That is, the boom center bypass type directional control valve 78 shown in FIG. 4 is provided with the center bypass passage 80 at the switching position 78a on the boom extension operation side. With such a configuration, the bleed flow rate flows from the boom switching valve 38 into the downstream side center bypass 40 even at the stroke end of the spool of the boom switching valve 38, which impairs the drive speed of the boom cylinder 52. In the range not to be applied, the drive speed of the arm cylinder 30 can be constantly increased by the bleed flow rate of the second hydraulic circuit 16. The hydraulic circuit shown in FIG. 4 is configured as the hydraulic circuit shown in FIG. 3, but it goes without saying that it can be configured as the hydraulic circuit shown in FIG. 1 or 2.

Although the present invention has been described with reference to the preferred embodiments, the present invention can be modified in many ways without departing from the spirit thereof.

[Effect of device]

As described above, in the hydraulic circuit of the hydraulic excavator according to the present invention, the surplus oil of the unit variable displacement hydraulic circuit connecting the two center bypass type directional control valves in tandem is used as the directional control valve downstream of the tandem unit hydraulic circuit. In the hydraulic circuit of the hydraulic excavator that is supplied to another unit variable displacement hydraulic circuit via the circuit, the in-circuit center bypass is throttled to a predetermined position on the downstream side in the tandem unit hydraulic circuit in conjunction with the operation signal of the upstream directional control valve. Since a center bypass type flow switching valve is provided,
Unlike the conventional hydraulic circuit of this type, the opening area of the center bypass passage portion of the upstream side directional control valve can be set to a sufficient size.

As a result, in the tandem unit hydraulic circuit of the present invention,
Even if the two-way switching valve is operated at the same time, the metering characteristic of the two-way switching valve is kept good without causing a sudden change in pressure or flow rate in the circuit. On the other hand, when the upstream directional control valve is operated independently, its metering is satisfactorily maintained by the throttling action of the flow rate control valve. As described above, according to the present invention, it is possible to prevent the deterioration of the metering characteristics when the directional control valves are simultaneously operated, which is a particularly difficult point in the conventional hydraulic circuit of this type.

[Brief description of drawings]

FIG. 1 is a hydraulic circuit diagram showing an embodiment of a hydraulic circuit of a hydraulic excavator according to the present invention, FIG. 2 is a hydraulic circuit diagram showing another embodiment of a hydraulic circuit of a hydraulic excavator according to the present invention, and FIG. FIG. 4 is a hydraulic circuit diagram showing another embodiment of the hydraulic circuit of the hydraulic excavator according to the present invention, and FIG. 4 is an upstream (boom) center of the second unit hydraulic circuit in the hydraulic circuit of the hydraulic excavator according to the present invention. It is a hydraulic circuit diagram which shows a bypass type directional control valve. 10 ... 1st variable displacement pump 12 ... 1st unit hydraulic circuit 14 ... 2nd variable displacement pump 16 ... 2nd unit hydraulic circuit 18 ... Pump discharge oil supply path 20 ... Arm center bypass type directional control valve 22 ... Center bypass 24 ... First pilot pressure generating means 26 ... Supply path 28 ... Cylinder port conduit 30 ... Arm cylinder 32 ... Pilot line 34 ... Negative regulator 36 ... Pump discharge oil supply path 38 ... Center bypass type direction switch for boom Valve 40 ... Center bypass 42 ... Arm center bypass type merging direction switching valve 44 ... Center bypass type flow rate switching valve 46 ... Second pilot pressure generating means 48 ... Supply path 50 ... Cylinder port conduit 52 ... Boom cylinder 54 ... Supply Line 56… Merge line 58,66… Operating valve 60,62,68… Pilot line 64… Negative regulator 70… Center bypass type merge switching valve 72… Check valve 74… Merge line 76 ... Center bypass type switching valve 78 ... Boom center bypass type directional switching valve 78a ... Switching position 80 ... Center bypass passage

Claims (5)

[Scope of utility model registration request] 1. A first unit hydraulic circuit to which the discharge oil of a first variable displacement pump is supplied and a second unit hydraulic circuit to which the discharge oil of a second variable displacement pump is supplied. In the first unit hydraulic circuit, an arm center bypass type directional control valve that is connected to a pump discharge oil supply path to operate an arm cylinder, and a downstream center bypass connected to the arm center bypass type directional control valve are connected to the first variable displacement pump. A first pilot pressure generating means for controlling the amount is provided, and in the second unit hydraulic circuit, a boom center bypass type directional control valve connected to a pump discharge oil supply passage to operate a boom cylinder, and An arm center bypass type merge control valve means for connecting the bleed flow rate to the arm center bypass type directional control valve connected to the downstream side center bypass, and a connection to the downstream side center bypass. A center bypass type flow rate switching valve that throttles the center bypass in conjunction with an operation signal of the boom center bypass type directional control valve and a discharge amount of the second variable displacement pump connected to the downstream side center bypass valve. And a second pilot pressure generating means for operating the hydraulic circuit of the hydraulic excavator. 2. A center bypass type merging control valve means for an arm comprises a center bypass type merging direction switching valve, and a cylinder port line of the arm center bypass type merging direction switching valve and a center bypass type directional switching valve for the arm. The hydraulic circuit of the hydraulic excavator according to claim 1, wherein the valve and the cylinder port pipeline are connected via a confluent pipeline. 3. The arm center bypass type confluence control valve means is composed of a center bypass type confluence switching valve, and is connected to an upstream center bypass of the arm center bypass type confluence switching valve and an arm center bypass type directional control valve. The hydraulic circuit of the hydraulic excavator according to claim 1, wherein the hydraulic circuit is connected to the supply path of the hydraulic excavator via a merging pipe path having a check valve. 4. An arm center bypass type merge control valve means and a center bypass type flow rate switching valve are constituted by a common center bypass type switching valve, and the upstream side center bypass of this center bypass type switching valve and the arm center bypass are provided. The hydraulic circuit of the hydraulic excavator according to claim 1, wherein the hydraulic circuit is connected to the supply path to the mold direction switching valve via a merging pipe line with a check valve interposed. 5. A center bypass type directional control valve for booms,
The hydraulic circuit of the hydraulic excavator according to claim 1, wherein the center bypass passage is configured not to be closed in the stroke end state in the boom cylinder extending operation.