JP2001050209A - Hydraulic circuit for construction vehicles - Google Patents

Abstract

(57) [Problem] To provide a circuit for a construction vehicle capable of guaranteeing straight traveling of a vehicle when right and left traveling switching valves 1 and 3 are controlled with less than a full stroke. SOLUTION: There is provided a communication passage 25 connecting a first supply passage A and a second supply passage B, and a communication switching valve 26 provided in the communication passage 25, and the communication switching valve 26 is in a normal position. To cut off the communication between the first supply passage A and the second supply passage B, and the left and right traveling switching valves 1 and 3 and one circuit system a
When any one of the work switching valves is switched, the switch is switched to the open position, and the first supply passage A and the second supply passage B are communicated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a circuit for a construction vehicle which assures straight traveling of a construction vehicle, for example, when traveling while moving a shovel up and down.

[0002]

2. Description of the Related Art Japanese Patent Application Laid-Open No. 5-969 discloses this type of circuit.
The one described in Japanese Patent Application Publication No. 64 is conventionally known.
This conventional circuit has one circuit system a and the other circuit system b, as shown in FIG. A first pump P1 and a second pump P2 are connected to one circuit system a. The first pump P1 and the second pump P2 discharge the same flow rate at the same rotation speed.

The first pump P1 has a first supply passage A
Are connected. The right supply motor 1 and the arm switching valve 2 are connected to the first supply passage A.
Further, the switching valve for right traveling 1 and the switching valve for arm 2 are also connected to a tandem through a neutral flow path 6.
The right traveling switching valve 1 controls a right traveling motor (not shown).
Is for controlling an arm cylinder (not shown).

The second pump P2 has a second supply passage B
Are connected. The second supply passage is connected to the left traveling switching valve 3, the boom switching valve 4, and the bucket switching valve 5. The left traveling switching valve 3 and the boom switching valve 4 are connected in tandem via a neutral flow path 7, but the boom switching valve 4 and the bucket switching valve 5 are connected to the first parallel valve. They are connected in parallel via a passage 9. The left traveling switching valve 3 controls a left traveling motor (not shown), and the boom switching valve 4 controls a boom cylinder (not shown). The bucket switching valve 5 controls a bucket cylinder (not shown). The neutral flow path 6 and the neutral flow path 7 join downstream of the arm switching valve 2 and the bucket switching valve 5, and communicate with the tank T via the tank passage 8.

The switching valves 1 to 5 connected as described above include:
When it is in the illustrated neutral position, it opens the neutral channels 6,7. Therefore, the discharge fluid of the first pump P1 is:
It is returned to the tank via the right running switching valve 1 and the arm switching valve 2. The discharge fluid of the second pump P2 is returned to the tank T via the left traveling switching valve 3, the boom switching valve 4, and the bucket switching valve 5.

When the right travel switching valve 1 and the left travel switching valve 3 are fully stroked in any direction from the above state, all of the fluid discharged from the first pump P1 is supplied to the right travel motor. All of the fluid discharged from the second pump P2 is supplied to the left traveling motor. Therefore, although the vehicle travels straight, the first and second pumps are provided in the arm switching valve 2, the boom switching valve 4, and the bucket switching valve 5 located downstream of the left and right traveling switching valves 1, 3. The discharge fluid of P1 and P2 is not supplied.

On the other hand, a third pump P3 is connected to the other circuit system b. The third pump P3 is connected to a switching valve for turning 10, a switching valve for blade 11, a spare switching valve 12, and a merging switching valve 13. The switching valve for turning 10 controls a turning motor (not shown), and the switching valve for blade 11 controls a blade (not shown). Also, a spare switching valve 1
Numeral 2 controls another actuator, and the merging switching valve 13 causes the third pump P3 to communicate with the tank passage 8 or the third parallel passage 19.

The turning switching valve 10 and the blade switching valve 11 are connected in parallel via a second parallel passage 15, but the blade switching valve 11 and the spare switching valve 1 are connected in parallel.
2 is connected in tandem via a neutral flow path 14. Further, the merging switching valve 13 is tandemly connected to the preliminary switching valve 12 via a neutral flow path 14. The switching valves 10 to 13 connected as described above open the neutral flow path 14 when the switching valves 10 to 13
The discharged fluid of No. 3 is returned to the tank T.

[0009] The merging switching valve 13 has a pilot chamber 1
6, and a signal generating pump P4 is connected to the pilot chamber 16 via a pilot line 18. A spring force of a spring 17 is applied to a side of the merging switching valve 13 opposite to the pilot chamber 16. The junction switching valve 13 thus configured normally keeps the illustrated normal position by the action of the spring force of the spring 17,
The other circuit system b communicates with the neutral passage 14 and the tank passage 8. The switching is performed in accordance with an increase in the pressure in the pilot chamber 16, and the neutral flow path 14 and the third parallel path 19 are switched.
And communicate.

The third parallel passage 19 communicates with the first parallel passage 9. This first parallel passage 9
Is connected to the inflow side of the arm switching valve 2 in addition to connecting the boom switching valve 4 and the bucket switching valve 5 in parallel as described above. Therefore, the neutral flow path 1
If the fourth and fourth parallel passages 19 are in communication with each other, the third
The discharge fluid of the pump P3 is supplied to the boom switching valve 4, the bucket switching valve 5, and the arm switching valve 2.

In the first parallel passage 9, check valves 20 and 21 are provided in opposite directions, and a third parallel passage 19 is connected between the check valves 20 and 21. And one check valve 20
As a result, the boom switching valve 4
And only the flow to the bucket switching valve 5 is allowed, and the other check valve 21 allows only the circulation from the third parallel passage 19 to the arm switching valve 2.

The pilot line 18 includes first to third
The branch passages 22 to 24 are connected. The first branch passage 22 is connected to the right traveling switching valve 1. The first branch passage 22 communicates with the tank T when the right traveling switching valve 1 is in the illustrated neutral position, but communicates with the tank T when the right traveling switching valve 1 is switched to a position other than neutral. Is shut off. The second branch passage 23 is connected to the left traveling switching valve 3. The second branch passage 23 communicates with the tank T when the left traveling switching valve 3 is at the neutral position shown in the figure. When the left traveling switching valve 3 is switched to a position other than the neutral position, the second branch passage 23 communicates with the tank T. Communication is interrupted.

The third branch passage 24 is connected to the boom switching valve 4 and also to the bucket switching valve 5 and the arm switching valve 2 in tandem.
The third branch passage 24 communicates with the tank T when the switching valves 4, 5, and 2 are in the illustrated neutral position. Communication is interrupted.

Next, the operation of this conventional example will be described. When all the switching valves 1 to 5 and 10 to 13 are at the neutral positions in the drawing, the discharge fluid from each of the pumps P1 to P4 is returned to the tank T. That is, the discharge fluid of the first pump P1 is returned to the tank T via the neutral flow path 6 and the tank passage 8,
The fluid discharged from the second pump P2 is returned to the tank T via the neutral flow path 7 and the tank passage 8. The discharge fluid of the third pump P3 is returned to the tank T via the neutral flow path 9 and the tank passage 8, and the discharge fluid of the signal generation pump P4 is discharged from the pilot line 18 to the first to third branch passages 22 to 22.
It is returned to the tank T through the tank 24 and the tank passage 8.

From the above state, the left and right traveling switching valves 1, 3
When a full stroke is applied to one side, the left and right traveling switching valves 1 and 3 communicate with the left and right traveling motors, and the neutral flow paths 6 and 7
Is completely shut off. Therefore, the first and second pumps P1,
The discharge fluid of P2 is supplied only to the traveling motor and does not flow to the switching valves 2, 4, and 5 connected in tandem downstream of the traveling switching valves 1 and 3. When the left and right traveling switching valves 1 and 3 are switched in this way, the first and second branch passages 22 and 23 connected to the traveling switching valves 1 and 3 are also closed.

When any of the arm switching valve 2, the boom switching valve 4, and the bucket switching valve 5 is switched from the above state, the third branch passage 24 is also closed. Therefore, all of the first to third branch passages 22 to 24 are closed, so that the communication between the pilot line 18 and the tank passage 8 is cut off. If the communication between the pilot line 18 and the tank passage 8 is thus interrupted,
The pressure in the pilot chamber 16 of the junction switching valve 13 increases, and the junction switching valve 13 switches to the left position in the drawing.

When the junction switching valve 13 is switched to the left position in the drawing as described above, the fluid discharged from the third pump P3 is discharged to the third pump P3.
Passing through the parallel passage 19 and the first parallel passage 9;
It is supplied to the actuator via one of the switching valves 2, 4, and 5 which has been switched. In other words, when the left and right traveling switching valves 1 and 3 are made full-stroke to drive these traveling motors, the first and second pumps P
Since all of the discharge fluids P1, P2 are supplied to the switching valves 1, 3 for traveling, they are not supplied to the switching valves 2, 4, 5 on the downstream side. The discharge fluid of the third pump P3 is supplied from the other circuit system b side. Note that, as described above, the first and second pumps P
If all of the discharge fluids P1 and P2 are supplied to the respective traveling motors, the straight traveling performance of the vehicle is maintained.

On the other hand, if the left and right traveling switching valves 1 and 3 are stroked by the same amount less than the full stroke,
The flow rate according to the opening is supplied to the left and right traveling motors. That is, a flow rate according to the opening degree of the left and right travel switching valves 1 and 3 is supplied to the left and right travel motors, and a flow rate other than the supply flow rate is returned to the tank T. When the discharge flow rates of the first and second pumps P1 and P2 are divided into the traveling motor side and the tank side, the speed is lower than when the left and right traveling switching valves 1 and 3 are fully stroked. The vehicle travels straight.

[0019]

In the above conventional example, when the left and right traveling switching valves 1 and 3 are made to have a full stroke, the switching connected in tandem downstream of the left and right traveling switching valves 1 and 3 is performed. Valves 2, 4, 5 and first pump P1 and second
Since the communication with the pump P2 is shut off, the straight traveling performance of the vehicle is maintained even if another actuator is operated. However, when the left and right traveling switching valves 1 and 3 are controlled with less than a full stroke, these traveling switching valves 1 and 3 are controlled.
The neutral passages 6 and 7 of the 3 are not completely blocked but are connected. Therefore, when, for example, the arm switching valve 2 connected to the downstream side of the switching valve 1 is switched from this state, the load of the arm cylinder acts on the first pump P1. When the load on the arm cylinder is greater than the load on the right-hand drive motor,
Most of the fluid discharged from the first pump P1 is supplied.

Therefore, at this time, if the flow rate supplied to the left traveling motor is constant, the flow rate supplied to the right traveling motor becomes larger than the flow rate supplied to the left traveling motor, and the vehicle is driven to the left. There was a problem of bending in the direction. In other words, in this conventional example, when the vehicle is traveling straight by switching the left and right traveling switching valves 1 and 3 with less than full stroke, if another actuator is operated, the straight traveling performance of the vehicle is impaired. Was sometimes An object of the present invention is to provide a circuit for a construction vehicle that can guarantee straight traveling of a vehicle when the left and right traveling switching valves 1 and 3 are controlled with less than a full stroke.

[0021]

According to the present invention, there is provided a switching valve for right traveling and a switching valve for left traveling provided in one circuit system,
A first pump connected to the right traveling switching valve via a first supply passage, a second pump connected to the left traveling switching valve via a second supply passage, and a downstream side of the right traveling switching valve. A work switching valve connected to the tandem, a work change valve connected to the tandem downstream of the left traveling change valve, a work change valve provided in the other circuit system, and connected to the third pump; A junction switching valve provided at the most downstream side of the switching valve, and switching means for switching the junction switching valve.

The switching means switches the merging switching valve when one of the left and right traveling switching valves and the working switching valve of one of the circuit systems is switched, while the merging switching valve is in the normal position. For a construction vehicle having a configuration in which the neutral flow path of the other circuit system is communicated to the tank at one time, and when switched, the neutral flow path of the other circuit system is communicated in parallel with the work switching valve in one circuit system. Assume a hydraulic circuit.

The first invention presupposes the above circuit,
A communication passage connecting the first supply passage and the second supply passage; and a communication switching valve provided in the communication passage, wherein the communication switching valve is provided at a normal position with the first supply passage and the second supply passage. Is switched to the open position when one of the left and right traveling switching valves and the working switching valve of one of the circuit systems is switched, and the first supply passage and the second supply passage are communicated. It is characterized in that it was configured to be.

According to a second aspect, in the first aspect,
When the switching valve for communication is switched to the open position,
A restriction is formed in the communication flow path. Third
The present invention is characterized in that, in the first and second inventions, the communication switching valve is configured to switch in conjunction with the switching of the merge switching valve.

[0025]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the embodiment shown in FIG. 1, a first supply passage A and a second supply passage B are connected via a communication passage 25,
This communication passage 25 is provided with a communication switching valve 26, and the other configuration is the same as that of the conventional example. Therefore, the same reference numerals as in FIG. 2 denote the same components as in the related art, and a description thereof will be omitted. The communication switching valve 26 normally keeps the normal position by the spring force of the spring 27 and cuts off the communication between the first supply passage A and the second supply passage B. When the pilot pressure increases, it switches.
The first supply passage A communicates with the second supply passage B.

Further, as described above, the first supply passage A and the second
When communicating with the supply passage B, the throttle 29 is configured by the opening degree of the communication switching valve 26. The arm switching valve 2, the boom switching valve 4, and the bucket switching valve 5 in this embodiment correspond to the working switching valve of one circuit system in the present invention, and the turning switching valve 1
0, blade switching valve 11 and spare switching valve 12
Corresponds to the work switching valve of the other circuit system in the present invention.

According to the above embodiment, when the left and right traveling switching valves 1 and 3 are switched by the same amount less than the full stroke, for example, when the arm switching valve 2 is switched, the first to third branch passages 22 are switched. To 24 and the tank T are cut off. Therefore, the pilot pressure in the pilot line 18 rises, and the junction switching valve 13 is switched.
The communication switching valve 26 is also switched to the open state. When the communication switching valve 26 is opened as described above, the first supply passage A and the second supply passage B communicate with each other via the communication switching valve 26.

If the first supply passage A and the second supply passage B are in communication, the pressure in the first supply passage A is higher than the pressure in the second supply passage B due to the load of the arm cylinder. Even if this happens, the fluid in the first supply passage A on the high pressure side flows into the second supply passage B via the communication passage 25. If the flow rate flows from the first supply passage A to the second supply passage B in this manner, the flow rate supplied to the left traveling motor increases while the increase in the flow rate supplied to the right traveling motor is suppressed. Therefore, the flow rate supplied to the right traveling motor,
The difference from the flow rate supplied to the left traveling motor becomes smaller,
The straight traveling performance of the vehicle is maintained.

If the boom switching valve 4 or the bucket switching valve 5 is switched while the left and right traveling switching valves 1 and 3 are switched by the same amount less than the full stroke, the second supply passage is provided. The pressure of B becomes higher than that of the first supply passage A. Therefore, in this case, when the fluid flows from the second supply passage B side to the first supply passage A side via the communication passage 25, the flow rate supplied to the right traveling motor and the flow rate supplied to the left traveling motor are increased. The difference from the flow rate to be made is small, and the straight traveling performance of the vehicle is maintained.

As described above, according to this embodiment, when the switching valves 2, 4, 5 on the downstream side of the left and right traveling switching valves 1, 3 are operated, the load pressure is applied to only one of the flow paths. Even if it acts, the difference between the flow rates supplied to the left and right traveling motors can be kept small. If the difference between the supply flow rates is reduced in this manner, the straight traveling performance of the vehicle can be maintained. The switching valve 28 for communication is switched only when one of the switching valves 2, 4, and 5 is switched together with the left and right traveling switching valves 1 and 3, and otherwise. Since the communication between the first supply passage A and the second supply passage B is interrupted, the control state is naturally a normal control state.

On the other hand, in this embodiment, the switching valve 26 for communication is used.
When is switched to the open state, by forming the throttle 29, from the high pressure passage side to the low pressure passage side,
The fluid is restricted from flowing rapidly. The reason why the fluid is prevented from suddenly flowing from the high-pressure passage to the low-pressure passage is to prevent a shock generated when the fluid suddenly flows.

In this embodiment, the communication switching valve 26 is switched by the pilot pressure.
The communication switching valve 26 may be electrically switched. For example, a solenoid may be provided in the communication switching valve 26, and the communication switching valve 26 may be switched by exciting the solenoid. When the solenoid is used as described above, a sensor for detecting the pilot pressure of the pilot line 18 may be provided, and a signal from the sensor may be converted into a current to excite the solenoid. Further, instead of detecting the pilot pressure, a sensor for directly detecting that the switching valves 1 to 5 have been switched is provided, and the right traveling switching valve 1 and the left traveling switching valve 3, and any one of the switching valves 2, When switching between 4 and 5, the solenoid may be excited.

[0033]

According to the first aspect of the invention, when the left and right traveling switching valves are switched with less than the full stroke, the load pressure acts on one pump by operating the working switching valve. Also, the flow rate supplied to one traveling motor can be guided to the other traveling motor through the communication path. Therefore, the difference between the flow rates supplied to both the traveling motors can be kept small, and the straight traveling performance of the vehicle can be maintained.

According to the second aspect, since the first supply passage and the second supply passage communicate with each other through the throttle, it is possible to prevent the fluid from rapidly flowing from the high pressure side passage to the low pressure side passage. Therefore, it is possible to prevent a shock generated when the fluid suddenly flows from the high pressure side passage to the low pressure side passage.

According to the third aspect, since the communication switching valve is switched in conjunction with the merge switching valve, the first supply passage and the second supply passage can be reliably communicated.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of an embodiment.

FIG. 2 is a circuit diagram of a conventional example.

[Explanation of symbols]

a One circuit system b The other circuit system P1 First pump P2 Second pump P3 Third pump A First supply passage B Second supply passage 1 Right traveling switching valve 2 Arm corresponding to a working switching valve of the present invention Switching valve for use 3 switching valve for left running 4 switching valve for boom corresponding to the switching valve for operation of the present invention 5 switching valve for bucket corresponding to the switching valve for the operation of 10 of the present invention 10 Corresponding to the switching valve for operation of the present invention Swivel switching valve 11 Blade switching valve corresponding to working switching valve of the present invention 12 Spare switching valve corresponding to working switching valve of the present invention 13 Merging switching valve 25 Communication passage 26 Communication switching valve 29 Throttle

 ──────────────────────────────────────────────────続 き Continued on the front page F-term (reference) BB16 CC01 CC08 DA02 DA06 DB03 DB33 DB47 DB49 EE14 EE17 EE22 GG02 JJ01

Claims (3)

[Claims] 1. A right traveling switching valve and a left traveling switching valve provided in one circuit system, a first pump connected to the right traveling switching valve via a first supply passage, and a left traveling switching valve. A second pump connected via a second supply passage, a work switching valve connected in tandem downstream of the right travel switching valve, and a work switch connected in tandem downstream of the left travel switching valve. A switching valve, a switching valve provided in the other circuit system and connected to the third pump, a junction switching valve provided at the most downstream of the switching valve for operation, and switching means for switching the junction switching valve. The switching means switches the merging switching valve when switching between the left and right traveling switching valves and one of the working switching valves in one circuit system, while the merging switching valve is in the normal position when the other is in the normal position. Connect the neutral flow path of the circuit system to the tank A first supply passage and a second supply passage in a hydraulic circuit for a construction vehicle in which a neutral flow path of the other circuit system is connected in parallel with a work switching valve in the one circuit system when being switched through And a communication switching valve provided in the communication passage, wherein the communication switching valve cuts off communication between the first supply passage and the second supply passage at a normal position, and The construction vehicle hydraulic circuit is configured to switch to the open position when any one of the traveling switching valve and the working switching valve of one of the circuit systems is switched to communicate the first supply passage and the second supply passage. . 2. The hydraulic circuit for a construction vehicle according to claim 1, wherein the communication switching valve forms a throttle in the communication flow path when the communication switching valve is switched to the open position. 3. The hydraulic circuit for a construction vehicle according to claim 1, wherein the communication switching valve is configured to switch in conjunction with switching of the merge switching valve.