JP3240286B2 - Hydraulic system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydraulic system applied to a construction machine or the like, and more particularly to a hydraulic system which is excellent in complex operability and controls the supply of pressurized oil to a plurality of actuators according to the characteristics or working conditions of the actuators. The present invention relates to a hydraulic system that can be optimally performed according to the conditions.

[0002]

2. Description of the Related Art Conventionally, in a hydraulic system configured to supply and discharge pressure oil discharged from a variable displacement pump to an actuator via a switching valve, a switching means is used as a means for adjusting a discharge flow rate of the variable displacement pump. There is known a system in which a valve is configured as an open center type or a closed center type.

However, as a hydraulic system used in construction machines such as hydraulic excavators, for example, when supplying pressure oil from a variable displacement pump to a control valve having a plurality of switching valves, a center bypass passage of the control valve is provided. There is known a hydraulic system comprising a pressure generating means at an outlet and a means for adjusting the discharge flow rate of the variable displacement pump in accordance with the pressure on the upstream side of the pressure generating means (Japanese Utility Model Application Laid-Open No. 51-332).
No. 01).

In the prior art of this type, in the process of moving the switching valve from the neutral position to the full operating position by the switching spool, the entire amount of oil discharged from the variable displacement pump in accordance with the operation amount of the switching spool is transferred to the center bypass passage. To the tank circuit, or to the cylinder port through the opening of the cylinder port and part of it to the center bypass passage, or to supply the entire amount to the cylinder port, and then discharge the center bypass passage during this process. The discharge flow rate of the variable displacement pump is adjusted by adjusting the characteristic of the pressure generating means so as to be inversely proportional to the flow rate.

Further, as another conventional hydraulic system, a plurality of closed center type switching valves connected in parallel to a pressure oil supply passage of a variable displacement pump include:
In accordance with the movement of the switching spool of the switching valve, the pressure oil is supplied from the pressure oil supply passage to the cylinder port through the cutout portion of the switching valve that opens to the pressure oil supply passage, and the pressure oil is supplied from the pressure oil supply passage to the cylinder port. To detect the pressure between
The detection pressure is connected to the discharge flow rate adjusting means of the variable displacement pump so that the differential pressure between the detected pressure and the pressure in the pressure oil supply passage becomes constant, and the discharge flow rate of the variable displacement pump is adjusted. (Japanese Patent Laid-Open Publication No. 6-58305).

[0006]

However, in the above-mentioned conventional hydraulic system, there are still various problems to be improved.

That is, the control method of the discharge flow rate of the conventional variable displacement pump as the former is a negative flow rate control method. However, in a hydraulic system based on this control method, the switching spool is located at an intermediate position, In a state where the pressure oil supply passage from the displacement pump is connected to the tank circuit via the cylinder port and the center bypass passage, the switching valve for operating the load is operated in accordance with the magnitude of the load connected to the cylinder port. Since the operation amounts are different from each other, the switching valve has such a characteristic that the operator can intuitively judge the magnitude of the load. As a result, while there is an advantage in operational safety, there is a problem that fine operation becomes difficult.

In such a conventional hydraulic system, when applied to a versatile machine such as a hydraulic excavator, a switching valve for driving an additional actuator is required in addition to a standard actuator. Becomes In addition, even when the additional actuator and the existing standard actuator are simultaneously operated, if a good combined operability is required, the switching valve for the additional actuator and the switching valve for the existing actuator can be used together. Appropriate flow distribution means is required. However, in the conventional open center type switching valve technology, an appropriate means has not yet been proposed or implemented.

Further, in the conventional hydraulic system, when it is desired to set the supply flow rate of the pressure oil from the variable displacement pump to the added actuator at an intermediate value of the maximum capacity of the variable displacement pump, Although a certain amount of pressure oil must be discharged from the center bypass passage, the flow rate in this case varies depending on the magnitude of the load of the added actuator, and the speed of the additional actuator differs depending on the load. Operation becomes difficult.

On the other hand, the control method of the discharge flow rate of the conventional variable displacement pump as described above is a load sensing type flow rate control method. In a hydraulic system based on this control method, a load of a load connected to a switching valve is controlled. Regardless of the size, there is an advantage that the operation amount of the switching valve that operates the load is substantially constant. Further, in this control method, even when applied to a versatile machine such as a hydraulic excavator, the flow distribution with an additional actuator uses the highest pressure among the detected pressures at the respective switching valves, There is an advantage that it can be performed.

However, in this hydraulic system, the supply of the pressure oil to the actuator connected to the switching valve is always pressure compensated, so that there is a problem that there is a feeling of popping out at the start. Further, even if the load on the actuator is very large, the load always operates at the same operation position of the switching valve. Therefore, while this characteristic is an advantage in this control method, the operator of the switching valve cannot judge the magnitude of the load sensibly, which may cause a problem in operational safety. In other words, even when the load handled by the corresponding actuator suddenly changes in the process of operating the switching spool of the switching valve at the neutral position, there is no bypass oil amount passing through the bypass passage unlike the negative flow rate control method, The discharge rate of the variable displacement pump is not reduced, which results in a sudden increase in the pressure of the hydraulic system, which poses a safety problem.

In the above-mentioned hydraulic system, since the signal for controlling the discharge flow rate from the control valve to the variable displacement pump is a high-pressure signal, the stability of the control depends on the capacity of the signal line, the environmental temperature and the like. It is susceptible and requires careful consideration.

The inventor of the present invention has made intensive studies and studies and, as a result, connected a control valve having a plurality of open center type switching valves to the variable displacement pump, and provided an actuator to each of the plurality of switching valves. Connected, the supply and discharge of the pressure oil from the variable displacement pump to these actuators by operating each of the switching valves, provided with a pressure generating means at the most downstream of the center bypass passage of the switching valve, A hydraulic system is configured to adjust the discharge flow rate of the variable displacement pump in accordance with the upstream pressure of the pressure generating means. In this case, each switching valve is provided with a pressure oil supply passage from the variable displacement pump. To connect in parallel,
The pressure oil from the pressure oil supply passage is moved from the neutral position of the switching spool of each of the switching valves to the intermediate chamber provided on the passage from the pressure oil supply passage to the cylinder port. To guide through an opening formed between the intermediate chamber, a cylinder port of each of the switching valves,
An auxiliary port is provided between a tank line that guides return oil from the cylinder port to the tank, and first flow rate adjusting means is provided between the auxiliary port and the tank line. Pressure detecting means for detecting the pressure of the chamber are provided, and the pressure of the intermediate chamber related to the first flow rate adjusting means is acted on the first flow rate adjusting means in the opening direction. The highest pressure among the pressures detected by the pressure detecting means is caused to act in the closing direction, a bypass passage is provided by branching the pressure oil supply passage from the variable displacement pump, and this bypass passage is provided by the pressure generating means. A second flow control means is provided in communication with the upstream side and is provided on the bypass passage. In the opening direction of the second flow control means, the upstream pressure is applied and the second flow control means is closed. A maximum pressure of the spring force and the pressure detected by the pressure detection means is applied, and further, a discharge flow rate of the variable displacement pump is adjusted according to an upstream pressure of the pressure generation means. Then, when the maximum oil supply amount to the actuator is equal to or less than the maximum discharge amount of the variable displacement pump, by appropriately adjusting the opening degree of the throttle of each switching valve according to each actuator, the load on the actuator is reduced. Regardless of the size,
An optimal maximum flow rate can be set, and when starting the actuator, an operation without a feeling of popping out can be obtained. In addition, the maximum speed to the actuator is:
It has been found that a constant speed can be obtained regardless of the magnitude of the load on which the actuator operates.

Accordingly, an object of the present invention is to solve the problems of the conventional open center type open center type flow control system and closed center type flow control system and to provide the advantages of each flow type control system and simplify the structure. It is an object of the present invention to provide a hydraulic system having high reliability and high operability and stability in combined operation.

[0015]

In order to achieve the above object, a hydraulic system according to the present invention comprises connecting a variable displacement pump to a control valve containing a plurality of open center type switching valves, and connecting the plurality of switching valves to each other. Are respectively connected to the actuators, and the supply and discharge of the pressure oil from the variable displacement pump to these actuators is performed by operating each of the switching valves, and a pressure generating means is provided at the most downstream of a center bypass passage of the switching valve. In the hydraulic system provided and configured to adjust the discharge flow rate of the variable displacement pump in accordance with the upstream pressure of the pressure generating means, each of the switching valves is connected to a pressure oil supply passage from the variable displacement pump. Connect in parallel,
The pressure oil from the pressure oil supply passage is moved from the neutral position of the switching spool of each of the switching valves to the intermediate chamber provided on the passage from the pressure oil supply passage to the cylinder port. It is configured to guide through an opening formed between the intermediate chamber and the cylinder port of each switching valve,
An auxiliary port is provided between a tank line that guides return oil from the cylinder port to the tank, and first flow rate adjusting means is provided between the auxiliary port and the tank line. Pressure detecting means for detecting the pressure of the chamber are provided, and the pressure of the intermediate chamber relating to the first flow rate adjusting means is caused to act on the first flow rate adjusting means in the opening direction. The maximum pressure among the pressures detected by the detection means is configured to act in the closing direction, a bypass passage is provided by branching the pressure oil supply passage from the variable displacement pump, and this bypass passage is provided by the pressure generation means. A second flow control means is provided in communication with the upstream side and is provided on the bypass passage. In the opening direction of the second flow control means, the upstream pressure is applied and the second flow control means is closed. Is configured to apply the maximum pressure of the spring force and the pressure detected by the pressure detection means, and further configured to adjust the discharge flow rate of the variable displacement pump according to the upstream pressure of the pressure generation means. It is characterized by having done.

In this case, the first flow rate adjusting means provided between the auxiliary port and the tank line has an auxiliary port.
Force that urges the passage between the tank line and the tank line to the open position
It may be configured so as to act.

[0017] The first flow rate adjusting means provided between the auxiliary port and the tank line has a timer connected to the auxiliary port.
Spring force to urge the passage between
It can be configured to use.

Further, a check valve may be provided in the passage of the pressure oil between the intermediate chamber and the cylinder port.

On the other hand, at the most downstream of the center bypass passage of each of the switching valves, the center bypass passage is opened and closed and the opening is adjusted by an external operation at a position upstream of the connection with the bypass passage from the second flow rate adjusting means. It is possible to adopt a configuration in which a possible opening / closing means is provided.

Further, the pressure on the upstream side of the second flow rate adjusting means is caused to act on the second flow rate adjusting means provided on a bypass passage formed by branching the pressure oil supply path. A secondary pressure of a pressure reducing valve having a maximum pressure in each intermediate chamber of each switching valve detected as a primary pressure of the pressure oil supply passage as a control pressure in a closing direction thereof; The secondary pressure may be applied in the closing direction of the first flow rate adjusting means provided in each switching valve.

Further, the set load of the spring force of the first flow control means can be set to a load different from the set load of the spring force of the second flow control means.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an embodiment of a hydraulic system according to the present invention will be described in detail with reference to the accompanying drawings.

Embodiment 1 FIG. 1 is a hydraulic circuit diagram of a hydraulic control device showing an embodiment of a hydraulic system according to the present invention. That is, in FIG. 1, reference numeral 10 denotes a variable displacement pump. The variable displacement pump 10 includes a variable control mechanism 12, and a pressure generating means provided on a hydraulic oil discharge passage side of a hydraulic control valve having a plurality of switching valves. Is transmitted to the variable control mechanism 12 as a signal pressure, and the discharge flow rate of the variable displacement pump 10 is adjusted. In this case, the characteristics of the pressure generating means and the variable control mechanism 12 use the characteristics of the conventional negative flow control method.

However, the variable displacement pump 10 includes:
A plurality of switching valves 16, 17 are connected via a pressure oil supply passage 14, and actuators 18, 19 are connected to these switching valves 16, 17. A bypass passage 20 is branched from the pressure oil supply passage 14, and the bypass passage 20 is sequentially connected to the tank T via a (second) flow rate adjusting unit 22 and a pressure generating unit 24. The flow rate adjusting means 22 applies the pressure of the bypass passage 20 in the opening direction and the spring force of the spring 23 and the pressure of the communication passage (66) described later in the closing direction. Be composed.

The first and second switching valves 16 and 17 are connected to (first) flow rate adjusting means 26 and 27, respectively, and the flow rate adjusting means 26 and 27 are connected to an actuator when each switching valve is operated. The return oil from 18 and 19 is configured to be discharged through the internal passages 28 and 29 of the flow rate adjusting means 26 and 27. The flow rate adjusting means 26 and 27 are provided with check valves 30 and 31, respectively.

From the pressure oil supply passage 14, a center bypass passage 36 is branched.
Passes through each of the switching valves 17 and 16 sequentially, and the outlet passage 37 thereof
Through the bypass passage 2 on the upstream side of the pressure generating means 24.
0.

However, of the hydraulic control valves having the plurality of switching valves 16 and 17 having the above-described configuration, one of the switching valves 1
6 is as shown in FIG. For convenience of explanation, the same components as those of the hydraulic control device shown in FIG. 1 will be described with the same reference numerals.

In FIG. 2, reference numeral 40 denotes a valve body.
Common pressure oil supply passage 14 receiving the supply of pressure oil from 0
A switching spool 42, an intermediate chamber 44 for receiving the supply of pressure oil from the pressure oil supply passage 14 by movement of the switching spool 42, cylinder ports 46a and 46b for communicating with the actuator 18, and the intermediate chamber 44. 48, 48 to the cylinder port 46a or 46b, the check valve 64, and the auxiliary port 50, 50 and the tank line 52 for discharging the pressure oil of the cylinder port 46a, 46b to the tank T by the movement of the switching spool 42. , Respectively.

The switching spool 42 is provided with a notch 47 for connecting the pressure oil supply passage 14 to the intermediate chamber 44 as the switching spool 42 moves. The switching spool 42 is provided with the switching spool 42.
Notches 49, 49 'and 51, 51' are provided for connecting the cylinder port 46a or 46b to the passage 48 and the auxiliary port 50 as the cylinder moves.

The auxiliary ports 50, 50 are provided between the cylinder ports 46a, 46b and the tank line 52, and are provided between the auxiliary ports 50, 50 and the tank line 52 from the cylinder ports 46a, 46b to the tank line 52. Opening degree A of passage (internal passage 28 in FIG. 1) to line 52
Is provided for adjusting the flow rate.

The flow rate adjusting means 26 has a spool 54 and a spring 32. The spool 54 is provided with spool holes 57, 58, 5 and 5 formed in the valve body 40.
9 are slidably and liquid-tightly held at one end, and one end is surrounded and held by a cover 56. One end of the internal passage 60 provided in the spool 54 is connected to the back chamber 6 formed in the cover 56 via the check valve 30 and the passage 61.
2, and the other end is open to the front chamber 63. In this case, the check valve 30 is moved from the back chamber 62 to the front chamber 6.
3 to prevent the flow of pressurized oil.

On the other hand, the front chamber 63 is connected to the intermediate chamber 44 via a passage 67, accommodates the spring 32 in the front chamber 63, and resiliently connects the other end of the spool 54. keeping.

Thus, the flow rate adjusting means 26
As the spool 54 moves downward against the elasticity of the spring 32, the shoulder A 54a of the spool 54 is engaged with the spool hole 58, and the opening A thereof is regulated by the notch 54b and gradually decreases. It is configured to be.

Further, the intermediate chamber 4 communicating with the front chamber 63
In contrast to the fourth embodiment, a check valve 64 is provided in a direction in which the flow of the pressure oil to the front chamber 60 is blocked.

The back chamber 62 provided for the spool 54 constituting the flow rate adjusting means 26 is provided with the other switching valve 17.
Is connected through a communication passage 66 to a back room (for example, 62 ') corresponding to the changeover spool, and the communication passage 66 is connected to the tank T via a throttle 68 as appropriate. The check valves 30 and 31 are also connected to the communication passage 66 so as to communicate with each other. Further, the pressure in the communication passage 66 acts on the flow rate adjusting means 22 via the passage 38 so as to control the flow adjusting means 22 in the closing direction (see FIG. 1).

A part of the switching spool 42 is provided with a center bypass passage 36 for supplying the pressure oil branched to the pressure oil supply passage 14 for receiving the supply of the pressure oil from the variable displacement pump 10. Consists of

As shown in FIG. 1, the bypass passage 20 branched from the pressure oil supply passage 14 is connected to the tank T via a flow rate adjusting means 22 and a pressure generating means 24, and is connected to the tank T at the same time. The generating means 24 is connected and arranged so as to be located at the outlet passage 37 of the center bypass passage 36, that is, at the most downstream.

In this manner, the upstream pressure of the pressure generating means 24 is transmitted to the variable control mechanism 12 via the pressure signal line 70, and the variable displacement pump 10 is controlled in accordance with the upstream pressure of the pressure generating means 24. (See FIG. 1).

Next, the operation of the hydraulic system according to the present embodiment having the above configuration will be described.

(1) When each switching valve is in the neutral position When each switching valve 16 and 17 is in the neutral position (see FIG. 3), the pressure oil in the pressure oil supply passage 14 of the variable displacement pump 10 is supplied to the center bypass. In the flow regulating means 22 which reaches the upstream side of the pressure generating means 24 through the passages 36 and 37 and is connected to the bypass passage 20, the pressure of the communication passage 66 which is a pressure for controlling the flow in the closing direction is compared with the pressure of the communicating passage 66. It is connected to the tank T via a throttle 68 having a small opening. In this case, the pressure in the communication passage 66 is controlled by each switching valve 1.
Since there is no supply of pressure oil from 6, 17 and the pressure is maintained at a low level, the flow rate adjusting means 22 releases the upstream pressure against the spring force of the spring 23. Therefore,
The outlet passage 37 of the center bypass passage 36 and the pressure oil that has passed through the flow regulating unit 22 flow out to the pressure generating unit 24.

In this case, regardless of the flow path of the pressure oil to the pressure generating means 24, the pressure generating means 24
The relationship between the amount q of oil passing therethrough and its upstream pressure p is
As shown in FIG. 4, since it is univocally determined, the discharge flow rate Q of the variable displacement pump 10 is kept to a minimum by the negative flow control method as shown in FIG.

(2) Operate one of the switching valves to the intermediate position
And next time, one of the switching valve 16, for example, when operated to the intermediate position M shown in FIG. 3, while in this state center bypass passage 36 is throttled by the opening of the passage 36M downstream (outlet passageway 3
7).

In this case, the flow rate adjusting means for the switching valve 16
In the step 26, the spring force of the spring 32
The pressure in the intermediate chamber 44 acts via the signal line 32 ',
In the closing direction, the pressure of the intermediate chamber 44 passes through the check valve 30.
After that, it operates via the signal line 34 '. Signal line
Is connected to the communication passage 66, and the communication passage 66
It is connected to the tank T via the throttle 68. Toko
The opening of the throttle 68 is set relatively small.
Therefore, the pressure of the signal line 34 ′ is almost equal to the pressure of the intermediate chamber 44.
Since they are equal, the flow control means 26 is maintained in the open position.
It is.

The opening direction of the flow control means 22
3, the pressure upstream of the throttle 14M 'in FIG.
Acting via the bypass passage 20 and the signal line 25,
In the closing direction, the spring force of the spring 23 and the pressure of the intermediate chamber 44
(That is, the pressure downstream of the throttle 14M ') passes through the check valve 30
After that, the signal line 34 ', the communication path 66 and the path 38
Acting through. Therefore, the flow rate adjusting means 22
The pressure difference before and after 14M 'and the spring force of the spring 23 are balanced.
The opening is adjusted to the appropriate opening, and the flow rate corresponding to the opening is variable
Flow from the displacement pump 10 to the upstream side of the pressure generating means 24
You. The differential pressure across the throttle 14M 'depends on the amount of operation of the switching valve 16.
Therefore, the variable displacement pump 10
Of the discharge amount of the pressure
The amount of oil flowing upstream of the stage 24 depends on the amount of operation of the switching valve 16.
Will change accordingly. Further, on the upstream side of the pressure generating means 24,
Indicates that the oil passing through the throttle 36M 'in FIG.
Flow through The degree of opening of the throttle 36M 'depends on the operation of the switching valve 16.
Since it changes according to the production amount, as a result, the outlet passage 37
The flow rate flowing upstream of the pressure generating means 24 through the
It changes according to the operation amount of the switching valve 16.

As described above, the pressure generating means 24
In the upstream side of the valve, both flow according to the operation amount of the switching valve 16.
The change amount of oil is supplied to the switching valve 16 and the flow control means 22.
Flows from Therefore, upstream of the pressure generating means 24
Passes through the flow rate passing through the switching valve 16 and the flow rate adjusting means 22.
The pressure corresponding to the total flow with the flow
The pressure generated in the variable capacity via the pressure signal line 70
Guided by the variable control mechanism 12 of the pump 10
The discharge amount of the pump 10 is adjusted. Further operation of the switching valve 16
As the amount increases, the opening of the throttle 36M 'in FIG. 3 decreases.
Therefore, the flow rate passing through the outlet passage 37 decreases. On the other hand
In the third throttle 14M ', the operation amount of the switching valve 16 is increased.
As the opening increases, the opening increases, so that it is located before and after the aperture 14M '.
Differential pressure decreases. Therefore, in the flow rate adjusting means 22
When the operation amount of the switching valve 16 increases, the flow rate adjusting means 2
2 is in the closing direction and the flow rate is adjusted via the bypass passage 20
The flow rate through the means 22 decreases. That is, the switching valve 1
When the manipulated variable of 6 increases, the pressure
The flow rate that flows in is controlled by the flow rate through the outlet passage 37 and the flow rate.
Since both flow rates through means 22 decrease, the pressure
The pressure generated upstream of the generating means 24 decreases,
As a result, the discharge amount of the variable displacement pump 10 increases.

Thus, the pressure of the pressure oil supply passage 14
Is the operation amount of the switching valve 16, that is,
As it gradually rises as the stroke increases, for example
When starting a large load or depending on the load
The point at which the load starts with respect to the operation amount of the switching valve 16 is
Always get smooth start-up characteristics, even when they are different
A complete load sensor that can be used in the past
Caused by complete pressure compensation in the
You can reduce the feeling of popping out.

(3) Connect one switching valve to the stroke end.
When one of the switching valves 16 is further operated to , for example, the stroke end position E shown in FIG. 3, the center bypass passage 36 is completely closed.
Is supplied only to the passage 14E. This passage 14
Since the opening of E is set by the aperture 14E ',
The amount of oil supplied to the actuator 18 via the throttle 14E 'is such that the sum of the force due to the pressure in the communication passage 66 and the spring force of the spring 23 of the flow rate adjusting means 22 is equal to the force due to the pressure of the signal line 25. Thus, the aperture 14E '
Flow rate adjusting means 22 so that the pressure drop at
As a result of adjusting the opening degree, the discharge flow rate of the variable displacement pump 10 that is uniquely determined is supplied.

As described above, in the hydraulic system according to the present embodiment, the maximum oil supply amount to the actuator 18 is
If this is less than or equal to the maximum discharge rate of the variable displacement pump 10, each switching valve 1
By appropriately adjusting the degree of opening of the throttles 14E 'of 6 and 17, an optimum maximum flow rate can be set regardless of the magnitude of the load on the actuator.

In FIG. 1, when only one switching valve 16 is operated, the flow adjusting means 26 for the switching valve 16 has a spring 32 in the opening direction of the flow adjusting means 26.
And the pressure in the intermediate chamber 44 acts via the signal line 32 ', and in the closing direction, the pressure in the intermediate chamber 44 acts via the signal line 34' after passing through the check valve 30. ing. The signal line 34 'is connected to a communication passage 66, and the communication passage 66 is connected to the tank T via a throttle 68. The opening of the throttle 68 is set to be relatively small. Therefore, the pressure in the signal line 34 'is substantially equal to the pressure in the intermediate chamber 44, and therefore the switching valve 16
In only the operation, the flow rate adjusting means 26 is held at the open position.

As described above, in the hydraulic system of the present embodiment, when starting the actuator, an operation without a feeling of popping can be obtained, and the maximum speed to the actuator depends on the magnitude of the load on which the actuator operates. Regardless, a constant speed can be obtained. Therefore, the hydraulic system according to the present invention can dramatically improve operability as compared with the related art.

(4) When the switching valves are simultaneously operated Next, the switching valves 16 and 17 are simultaneously operated. For example, the driving pressure of the actuator 18 connected to one of the switching valves 16 is reduced by the other switching valve. It is assumed that the driving pressure is higher than the driving pressure of the actuator 19 connected to the actuator 17. In addition,
In this case, each of the switching valves 16 and 17 is operated to the left in FIG. 1, and the pressure oil from the pressure oil supply passage 14
6, 17 passages 14B, 14B and this passage 14B,
Apertures 14B ', 14B' respectively set on 14B.
Is supplied to the intermediate chambers 44 and 45. The one switching valve 16 reaches the actuator 18 via the intermediate chamber 44, the check valve 30, the passage 13B, the cylinder port 46a, and the pipe 41a.
Return oil from the pipe 41b, the cylinder port 46b,
It is configured to discharge to the tank T via the auxiliary port 50, the passage 15B, the flow rate adjusting means 26, and the tank line 52. This configuration is the same for the other switching valve 17. Reference numerals 43a and 43b denote pipes connected to the other switching valve 17, respectively.

During the operation of the switching valves 16 and 17, the pressure in the intermediate chamber 45 is lower than the pressure in the intermediate chamber 44, and these intermediate chambers 44 and 45 are connected together via the check valves 30 and 31. Since it is connected to the communication passage 66, only the pressure in the intermediate chamber 44 on the high pressure side flows into the communication passage 66 via the check valve 30. As a result, in the flow control means 26 on the high-pressure side, the opening force of the flow control means 26 is set in the opening direction of the flow control means 26 via the spring force of the spring 32 and the signal line 32 'in the same manner as in the case of the single operation of the switching valve described above. The sum of the force of the pressure in the intermediate chamber 44 and the pressure acting on the intermediate chamber 44 acts on the intermediate chamber 44 in the closing direction. Communication).

On the other hand, in the flow control means 27 on the low pressure side, the force by the pressure of the intermediate chamber 45 and the spring force of the spring 33 act in the opening direction, and the pressure of the intermediate chamber 45 in the closing direction. Operates via the signal line 33 ', the check valve 31, the communication passage 66 and the signal line 35'. However, in this case, if the spring force of the spring 33 is relatively small, the force due to the pressure of the signal line 35 'will
Intermediate chamber 4 acting via the signal line 33 'and the spring force of
5 is greater than the sum of the forces due to the pressure. Therefore, the flow rate adjusting means 27 is operated to the left in FIG. 1, whereby the opening degree of the flow rate adjusting means 27 is changed from the open position (communicated with the internal passage 29) to the position narrowed by the throttle 29M. The opening degree of the means 27 is adjusted to a position where the forces acting in the opening direction and the closing direction are balanced.
This means that the pressure in the communication passage 66, that is, the signal line 3
4 'and signal line 35' are both
, The pressure in the intermediate chamber 45 that balances this pressure is also substantially equal to the pressure in the intermediate chamber 44.

The pressure in the pressure oil supply passage 14 is common to each of the switching valves 16 and 17, and the intermediate chambers 44 and 45
Are substantially equal, the pressure differences between the passages 14B, 14B of the switching valves 16, 17 at the throttle portions 14B ', 14B' are also substantially equal. Therefore, even when the actuators 18 and 19 with different loads are simultaneously operated, the flow rate distribution of the pressure oil can be reliably performed according to the operation amounts of the switching valves 16 and 17.

When the switching valves 16 and 17 are simultaneously operated, the discharge flow rate of the variable displacement pump 10 is controlled according to the operation amount of the switching valve.
37, the control by the pressure on the upstream side of the pressure generating means 24 determined by the oil discharged from the flow rate adjusting means 22 is the same as in the case of the above-described single operation of the switching valve.

Embodiment 2 FIG. 6 shows another embodiment of the hydraulic system according to the present invention. That is, the present embodiment is a modified embodiment of the hydraulic system of Embodiment 1 shown in FIG. Therefore, the same components as those shown in FIG. 1 are denoted by the same reference numerals, and detailed description is omitted.

That is, as shown in FIG. 6, in this embodiment, a pressure reducing valve 72 is added. The pressure reducing valve 72 sets the pressure taken out from a part of the bypass passage 20 branched from the pressure supply passage 14 through the passage 73 as a primary pressure, and detects the pressure of the intermediate chamber 44 or 45 detected by the flow regulating means 26 or 27. Is acted as a control pressure via a communication passage 66, and the secondary pressure of the pressure reducing valve 72 is caused to act in the closing direction of the flow rate adjusting means 26, 27 and the flow rate adjusting means 22. Further, a spring 74 is acted on the pressure reducing valve 72 and the spring 7
4 is configured to be adjusted by an external operation signal 75. The other configuration is the same as the configuration of the hydraulic system shown in FIG.

Therefore, in the hydraulic system of this embodiment having such a configuration, the flow dividing ratio when the switching valves 16 and 17 are operated depends on the characteristics of the actuators 18 and 19 connected to the switching valves. Therefore, the hydraulic system can be intentionally changed, and as a result, a hydraulic system optimal for the characteristics of the mother machine to which the present invention is applied can be configured.

Embodiment 3 FIG. 7 shows still another embodiment of the hydraulic system according to the present invention. That is, the present embodiment is a further modified embodiment of the hydraulic system of Embodiment 1 shown in FIG. Therefore, the same components as those shown in FIG. 1 are denoted by the same reference numerals, and detailed description is omitted.

That is, as shown in FIG. 7, in this embodiment, an opening / closing valve 76 whose opening can be adjusted by an external operation is provided on the outlet passage 37 of the center bypass passage 36. . The other configuration is the same as the configuration of the hydraulic system shown in FIG.

The operation of the hydraulic system of the present embodiment constructed as described above is the same as that of the hydraulic system of the first embodiment shown in FIG. 1 when the on-off valve 76 is in the open position. As the opening of 76 is set smaller, the amount of discharge from the center bypass passages 36 and 37 decreases. Therefore, in this case, the discharge ratio from the flow rate adjusting means 22 increases, and accordingly, the supply of the pressure oil from each switching valve 16 or 17 to the actuator 18 or 19 is more pressure compensated. Further, the on-off valve 76
When the valve is completely closed, the supply of pressure oil to the actuator is completely pressure-compensated as in the conventional load sensing method. Becomes possible. For example, when the hydraulic system according to the present embodiment is applied to a hydraulic excavator or the like, it is possible to add a feature that a fine operation can be performed in a crane operation mode.

The case where the present invention is applied to a hydraulic excavator as a preferred embodiment has been described above. However, the present invention is not limited to the above-described embodiment, and many designs are possible without departing from the spirit of the present invention. Changes are possible.

[0063]

As described above, in the hydraulic system according to the present invention, a control valve having a plurality of open center type switching valves is connected to a variable displacement pump, and an actuator is connected to each of the plurality of switching valves. The supply and discharge of the pressure oil from the variable displacement pump to these actuators is performed by operating each of the switching valves, and pressure generating means is provided at the most downstream of a center bypass passage of the switching valve. In a hydraulic system configured to adjust the discharge flow rate of the variable displacement pump in accordance with the upstream pressure of the variable displacement pump, each switching valve is connected in parallel to a pressure oil supply passage from the variable displacement pump, The pressure oil from the pressure oil supply passage is moved to the intermediate chamber provided on the passage from the pressure oil supply passage to the cylinder port from the neutral position of the switching spool of each of the switching valves. Ri through the opening formed configured to direct between the hydraulic fluid supply passage and said intermediate chamber,
An auxiliary port is provided between a cylinder port of each switching valve and a tank line for guiding return oil from the cylinder port to the tank, and a first port is provided between the auxiliary port and the tank line.
And a pressure detecting means for detecting the pressure of the intermediate chamber in each of the switching valves, and for each of the first flow adjusting means, for each of the first flow adjusting means. The pressure of the relevant intermediate chamber is caused to act in the opening direction, and the highest pressure among the pressures detected from the respective pressure detecting means is caused to act in the closing direction,
A bypass passage is provided by branching a pressure oil supply passage from the variable displacement pump. The bypass passage is connected to an upstream side of the pressure generating means, and a second passage is provided on the bypass passage.
In the opening direction of the second flow rate adjusting means, the upstream pressure is applied, and in the closing direction, the maximum force of the spring force and the pressure detected by the pressure detecting means is applied. Open center type flow control system for adjusting the discharge flow rate of the conventional variable displacement pump by adopting a configuration in which the discharge flow rate of the variable displacement pump is adjusted in accordance with the upstream pressure of the pressure generating means. And a closed-center type flow control system to solve the problems, and to provide the advantages of each flow control system, a simple structure, high reliability, and excellent operability and stability in combined operation Obtainable.

[Brief description of the drawings]

FIG. 1 is a hydraulic circuit diagram showing one embodiment of a hydraulic system according to the present invention.

FIG. 2 is an explanatory cross-sectional view of a main part showing a schematic configuration of a hydraulic control valve included in the hydraulic system shown in FIG. 1;

FIG. 3 is an explanatory diagram showing passage configurations at a neutral position, an intermediate position, and a full stroke position shown in FIGS. 1 and 2 by hydraulic symbols.

FIG. 4 is a characteristic curve diagram showing a relationship between a passing oil amount q and an upstream pressure p in the pressure generating means shown in FIG.

FIG. 5 shows an upstream pressure p in the pressure generating means shown in FIG.
FIG. 5 is a characteristic curve diagram showing a relationship between the characteristic curve shown in FIG.

FIG. 6 is a hydraulic circuit diagram showing another embodiment of the hydraulic system according to the present invention.

FIG. 7 is a hydraulic circuit diagram showing still another embodiment of the hydraulic system according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Variable displacement pump 12 Variable control mechanism 14 Pressure oil supply passage 16, 17 Switching valve 18, 19 Actuator 20 Bypass passage 22 Flow rate adjusting means (second) 23 Spring 24 Pressure generating means 25 Signal line 26, 27 Flow rate adjusting means (No. 1) 28, 29 Internal passage 30, 31 Check valve 32, 33 Spring 32 ', 33' Signal line 34 ', 35' Signal line 36 Center bypass passage 37 Exit passage 38 Passage 40 Valve body 41a, 41b Piping 42 Switching spool 43a, 43b Piping 44, 45 Intermediate chamber 46a, 46b Cylinder port 47 Notch 48 Passage 49, 51, 49 ', 51' Notch 50 Auxiliary port 52, 53 Tank line 54 Spool 54a Shoulder 54b Notch 56 Cover 57, 58, 59 Spool hole 60 Internal passage 6 Passages 62 and 62 'back chamber 63 front chamber 64, 65 a check valve 66 communicating path 67 path 68 aperture 70 pressure signal line 72 pressure reducing valve 73 the passage 74 spring 75 external operation signal 76 off valve T tank

Claims (7)

(57) [Claims] A control valve having a plurality of open center type switching valves is connected to a variable displacement pump, and an actuator is connected to each of the plurality of switching valves, and the pressure from the variable displacement pump to these actuators is connected to the variable displacement pump. The supply and discharge of oil are performed by operating each of the switching valves, and a pressure generating means is provided at the most downstream of a center bypass passage of the switching valve, and discharge of the variable displacement pump is performed in accordance with an upstream pressure of the pressure generating means. In the hydraulic system configured to adjust the flow rate, each switching valve is connected in parallel to a pressure oil supply passage from the variable displacement pump, and the pressure oil from the pressure oil supply passage is Formed between the pressure oil supply passage and the intermediate chamber by moving the switching spool of each switching valve from the neutral position to the intermediate chamber provided on the passage from the supply passage to the cylinder port An auxiliary port is provided between the cylinder port of each switching valve and a tank line for guiding return oil from the cylinder port to the tank, and an auxiliary port is provided between the auxiliary port and the tank line. First in between
And a pressure detecting means for detecting the pressure of the intermediate chamber in each of the switching valves, and for each of the first flow adjusting means, for each of the first flow adjusting means. The pressure of the intermediate chamber concerned is caused to act in the opening direction, and the highest pressure among the pressures detected by the pressure detecting means is caused to act in the closing direction, and the pressure oil supply passage from the variable displacement pump is branched. And a bypass passage is provided in communication with the upstream side of the pressure generating means.
In the opening direction of the second flow rate adjusting means, the upstream pressure is applied, and in the closing direction, the maximum force of the spring force and the pressure detected by the pressure detecting means is applied. A hydraulic system, wherein the hydraulic pump is configured to operate, and further configured to adjust a discharge flow rate of the variable displacement pump according to an upstream pressure of the pressure generating means. A first flow rate adjusting means provided between the auxiliary port and the tank line ;
The hydraulic system according to claim 1, wherein the hydraulic system is configured to apply a spring force to urge the passage between the open positions to the open position . 3. A first flow control means provided between the auxiliary port and the tank line is provided with a tank line from the auxiliary port.
The hydraulic system according to claim 1, wherein the hydraulic system is configured to apply a spring force for urging a passage between the two to the throttle position . 4. The hydraulic system according to claim 1, wherein a check valve is provided in a passage of the pressure oil between the intermediate chamber and the cylinder port. 5. The center bypass passage can be opened and closed by an external operation at the most downstream side of the center bypass passage of each switching valve and upstream of a connection with the bypass passage from the second flow rate adjusting means. The hydraulic system according to any one of claims 1 to 4, further comprising an opening / closing means. 6. An upstream pressure of the second flow rate adjusting means is acted on an opening direction of the second flow rate adjusting means provided on a bypass passage formed by branching the pressure oil supply passage. The secondary pressure of the pressure reducing valve having the highest pressure in each intermediate chamber of each switching valve detected as the primary pressure of the pressure oil supply passage as the control pressure acts in the closing direction, and 6. The system according to claim 1, wherein the secondary pressure is applied in a closing direction of the first flow control means provided in each switching valve.
The hydraulic system according to any one of the above. 7. The hydraulic system according to claim 2, wherein the set load of the spring force of the first flow rate adjusting means is set to a load different from the set load of the spring force of the second flow rate adjusting means.