JPS60250132A - Oil pressure control circuit for construction vehicle - Google Patents

Abstract

PURPOSE:To obtain high-pressure traveling of a construction vehicle by a method in which the cut-off valve of discharge pressures of a variable oil-pressure pump is controlled by the drive signals of a traveling motor, and a low-pressure relief valve is provided to the relief valve of a higher set pressure than the cut- off pressure and other circuits. CONSTITUTION:In a variable oil-pressure pump P1, a traveling control valve 18 is connected to the uppermost stream and also in parallel through a switch valve 62 to a boom and bucket control valves 19 and 20. A variable oil-pressure pump P2 is connected through a switch valve 65 to the other traveling control valve 24 and also in parallel to slewing and arm control valves 25 and 26. When the valve 62 is switched, the pressure oil of the pump P1 is led to the upstream of the valve 24, and when the valve 65 is switched, pressure oil is not supplied to the control valve 24. The control mechanism C1 for the pumps P1 and P2 is controlled by the pilot pressure of each control valve. High-speed traveling of construction vehicles can thus be attained.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a hydraulic control circuit for a construction vehicle having a work equipment system and a traveling system.

(Conventional control circuit) Figure 3 shows a conventional control circuit for a power shovel.
One circuit system connected to the pump P1 includes a switching valve 1 connected to a travel motor, a switching valve 2 connected to a boom cylinder 2, a switching valve 3 connected to a packet cylinder, and a switching valve 4 for arm merging. In addition to being connected via a center bypass passage 5, the two switching valves 1 to 3 are also communicated via a parallel passage 6.

The other circuit system connected to the pump P2 also includes a switching valve 7 connected to the travel motor. Boom merging switching valve 8,
A switching valve 9 connected to the swing motor and a switching valve 10 connected to the arm cylinder are connected via a center/hey pass passage 11 and a parallel passage 12.

Then, set the maximum pressure of each actuator to the relief valve 1.
3.14 is used to uniformly control it.

(Problems to be Solved by the Invention) In the conventional control circuit as described above, both the pumps P
,, If the volumetric efficiency of P2 is different, or if the load on an actuator other than the travel motor is different, the speed of each travel motor will not be constant, which has the disadvantage of impairing the straight-line performance of the vehicle. Ta.

Further, the maximum pressure of each actuator in this control circuit is uniformly controlled by the set pressure of the relief valves 13 and 14. Therefore, in order to amplify the driving force of the vehicle, other actuators must also be made to have high voltage specifications.

In other words, there was a problem in that even actuators that were not used at such high pressures had to be set at high pressures.

Therefore, this invention guarantees the straightness of the vehicle, and when the actuator of the work equipment is operated,
The circuit pressure is set to a lower pressure than when the vehicle is running, and when the vehicle is traveling without operating the actuator of the work equipment system, the circuit pressure is set to a high voltage to amplify the traveling driving force. .

(Means for Solving the Problems) In order to achieve the above object, the present invention connects a variable displacement pump, a travel motor, and other work equipment system actuators to each of a pair of circuit systems. and a construction vehicle in which a switching valve for controlling the traveling motor of at least one circuit system is located most upstream with respect to other switching valves, and is connected to at least one of the other switching valves via a parallel passage. In the hydraulic control circuit, a check valve is provided in the supply passage of the switching valve that controls the travel motor of the other circuit system, and the parallel passage of the one circuit system is normally maintained in a communicating state. , a control valve is provided that is switched by a drive signal from one of the travel motors to block the parallel passage and connect the pump passage of the one circuit system to the downstream side of the check valve; A control mechanism is provided in each of the variable displacement pumps to control the discharge amount of the variable displacement pump, and a control mechanism connected to one of the circuit systems is provided with a control mechanism that controls the discharge pressure of the variable displacement pump when the discharge pressure of the variable displacement pump becomes equal to or higher than the set pressure. ,
A cant-off valve is connected that performs the cut-off control function and stops the cut-off control function in response to the drive signal of the travel motor, and one of the circuits has a pressure slightly higher than the set pressure of the cut-off valve. A relief valve that maintains the set pressure is provided, and a relief valve that is set to a relatively low pressure similar to the cut-off valve is connected to the other circuit system.

(Embodiment of the present invention) The first embodiment shown in FIG. In addition, switching valves 18 to 20 are connected to each of these actuators. Further, the other circuit system to which the variable displacement pump P2 is connected is connected to a travel motor 21, a swing motor 22, and an arm cylinder 23, and switching valves 24 to 26 are connected to each of these actuators.

A parallel passage 28 is connected to the pump passage 27 of the pump P1, and the switching valves 18 to 20 are connected in parallel to the second parallel passage. Further, in this embodiment, a switching valve 28 for arm merging is connected to the parallel passage 28 at the most downstream side of each of the switching valves 18 to 20.

A parallel passage 31 is also connected to the pump passage 30 of the pump P2, and the switching valves 24 to 26 are connected in parallel to this parallel passage 31. A valve 32 is connected.

Each of the switching valves as described above switches in proportion to the amount of operation of the pilot operating mechanisms 33 to 35 and 36 to 38 provided in each circuit system. Pilot pressure is from shuttle valve 38 to
43 and 70. The highest pressure is selected by 44 to 4 and 71, and the highest pressure is the control mechanism C1 of pumps P1 and P2.
and C2. In addition, in one circuit system, the shuttle valve 39 is directly connected to the control mechanism C, so that when the travel motor 15 is driven, the pilot pressure at that time is always guided to the control mechanism C. ing.

The specific configuration of the one control mechanism C1 is as shown in FIG. 2.

That is, the branch passage 49 is connected to the pump passage 27 of one circuit system, and the rod side chamber 50a of the control cylinder 50 that controls the tilt angle of the variable displacement pump P is connected to the pump passage 27 of one circuit system.
It communicates with the pump passage 27 (which may be a branch passage 49).

Also, from the upstream side of the branch passage 48, the horsepower control valve 51,
A control valve 52 and a cut-off valve 53 are provided.

The horsepower control valve 51 causes a spring 54 to act on one end of the spool portion 51a, and also causes a spring 54 to act on one end of the spool portion 51a.
The pilot chamber 51b on the opposite side from the pilot chamber 4 is connected to the branch passage 49. The first baud) 51 of this control valve 51
c is connected to the branch passage 49, the second boat 51d is connected to the first port 52a of the control valve 52, and the third boat 51e is connected to the first port 52a of the cut-off valve 53 via the bypass passage 55. 53a, and further connect to the 4th baud)
51f is connected to tank T.

The control valve 51 thus configured maintains the right position in the drawing by the action of the spring 54 until the discharge pressure of the variable displacement pump P1 overcomes the spring force of the spring 54. In this left position, the 1.2 boats 51c, 51d
communicates with each other, and supplies JT oil from the branch passage 48 to the first port 52a of the control valve 52. In addition, this horsepower control valve 5
1 holds the intermediate position, the 1st to 4th ports 5
When all communication between 1C to 51f is cut off and the right position is maintained, the third boat 51e and the fourth port 51f
The passageway 55 is made to communicate with the tank T.

The sleeve portion 5'1g of the horsepower control valve 51 thus constructed
is connected to the control cylinder 50 no piston rond 50c via an interlocking mechanism 60.

As described above, the control valve 52 connects its first port 52a to the second port 51d of the control valve 51, and connects its second port 52b to the first port 51d of the cut-off valve 53.
port) 53a. Further, the third boat 52c of this control valve 52 is communicated with the tank T.

Furthermore, a spring 56 is applied to one end of the spool portion 52d of the control valve 52, and a pilot chamber 52e is provided on the opposite side of the spring 56.
It is connected to the shuttle valve 70. Also, in this control valve 52, its sleeve portion 52f is connected to the interlocking mechanism 60.

When no pilot pressure acts on the pilot chamber 52e, in other words, when no pilot operating mechanism is operated, the control valve 52 maintains the right position in the drawing by the action of the spring 56. , 1.2 ports 52a and 52b are communicated with each other. When the spool portion 52d moves against the spring 5B and maintains the intermediate position shown in the figure, it blocks communication between the first to third ports 52a to 52c, and when the spool portion 52d maintains the right side position in the figure, the second , 3 ports) 52b and 52c, and the first port) 53a of the cut-off valve 53 is connected to the tank T.

The cut-off valve 53 connects its second boat 53b to the bottom side chamber 50 of the control cylinder 50. b, and a spring 57 is applied to one end of the cut-off valve 53. A pilot chamber 53d is provided on the opposite side of the spring 57, and the pilot chamber 53d is connected to a release valve 53d for canceling the cut-off function.
It is connected to 8.

This release valve 58 has a pilot chamber 58 provided at one end thereof.
is connected to the shuttle valve 39, and this pilot chamber 5
When no pilot pressure is applied to the cut-off valve 8a, the spring 58 holds the cut-off valve 8a in the lower position shown in the figure, and the pilot chamber 53d of the cut-off valve 53 communicates with the branch passage 48.

Therefore, in this state, when the pressure in the branch passage 49, that is, the discharge pressure of the variable displacement pump P1 becomes equal to or higher than the set pressure determined by the spring 57, the cutoff valve 53 is switched to the right position in the drawing. In this right position, the second port 53b communicates with the third port 53c, so the bottom chamber 50b of the control cylinder 50 communicates with the tank T. Further, when the pilot pressure, which is a running signal, acts on the pilot chamber 58a of the release valve 58, the release valve 58 is switched to the upper position in the drawing, and the pilot chamber 58a of the cut-off valve 53 is switched to the upper position in the drawing.
d into tank T. In this way, the pilot room 53
d is opened to the tank T, the cut-off valve 53 releases the spring 57 regardless of the discharge pressure of the variable displacement pump P1.
As a result, the left side position shown in the figure is maintained and the cut-off control function is stopped.

When none of the pilot operating mechanisms is being operated, the control valve 52 is pushed to the left by the action of the spring 56 and held at the right position in the drawing, so the control cylinder 5
The bottom side chamber 50b of No. 0 is opened to the tank T. For this purpose, the control cylinder 50 moves the piston rod 50c to the right in the drawing by the pressure inside the rod side chamber 50a,
The discharge amount of the variable displacement pump P1 is decreased to minimize the discharge amount. When the variable displacement pump P1 maintains the minimum discharge amount in this way, the horsepower control valve 51
However, due to the action of the spring 54, the left side position in the drawing is maintained.

If one of the pilot operating mechanisms is operated from the above state, the pilot pressure at that time acts on the pilot chamber 52e of the control valve 52, switching the spool portion 52d to the left position in the drawing.

Therefore, the discharge pressure of the variable displacement pump P1 is the 1.2nd boats 51c, 51d of the horsepower control valve 51, the 1.2nd boats 52a, 52b of the control valve 52, and the 1.2nd boats 53a of the cutoff valve 53. It flows into the bottom side chamber 50b of the control cylinder 50 via 53b.

As described above, when the discharge oil of the variable displacement pump P flows into the bottom side chamber 50b, both chambers 50a of the control cylinder 50,
The piston rod 50c moves leftward in the drawing due to the difference in pressure receiving area of the piston rod 50b, thereby increasing the discharge amount of the variable displacement pump P1.

When the piston rod 50c moves to the left in the drawing, the interlocking mechanism 60 connected thereto rotates clockwise in the drawing about the fulcrum 61, so that the sleeve of the control valve 5-2 connected to the interlocking mechanism 80 rotates clockwise in the drawing. The portion 52f moves,
When the rightward force due to the pilot pressure in the pilot chamber 52e and the leftward force due to the spring 56 are balanced, the sleeve portion 52f catches up with the spool portion 52d and stops, maintaining the illustrated intermediate position. That is, the discharge amount of the variable displacement pump P1 is controlled according to the pilot pressure at that time.

The discharge pressure of the variable displacement pump P1 acts on the pilot chamber 51b of the horsepower control valve 51, but when the acting force of the pilot chamber 51b overcomes the spring force of the spring 54, the spool portion 51a moves to the left. Then, the horsepower control valve 51 is switched to the right position in the drawing, and the bypass passage 55 is communicated with the tank T.

Therefore, since the bottom side chamber 50b of the control cylinder 50 is opened to the tank T, the piston rod 50c moves rightward due to the pressure action of the rod side chamber 50a, reducing the discharge amount of the variable displacement pump P.

Then, when the control cylinder 50 moves as described above,
When the sleeve portion 51g moves via the interlocking mechanism 80, the leftward force due to the pressure in the pilot chamber 51e (discharge pressure of the variable displacement pump 2) and the rightward force due to the spring 54 are balanced. , sleeve part 51g
Since the variable displacement pump P1 catches up with the spool portion 51a and stops, the discharge amount of the variable displacement pump P1 is controlled according to the discharge pressure at that time. In other words, the product of the discharge amount and the discharge pressure is controlled to be always constant.

Furthermore, in the above state, when the vehicle is stopped without driving the travel motor 15, in other words, when no pilot pressure is acting on the pilot chamber 58a of the release valve 58, the variable displacement pump P1 is activated. The discharge pressure acts on the pilot chamber 53d of the cutoff valve 53. and,
When this discharge pressure exceeds the set pressure determined by the spring 57 of the cut-off valve 53, the cut-off valve 53 switches to the right position in the drawing, opens the bottom side chamber 50b of the control cylinder 50 to the tank T, and the control cylinder 50 Move the piston rod 50c to the right in the drawing to minimize the discharge amount of the variable displacement pump P. That is, when the pump discharge pressure becomes equal to or higher than the above set pressure, the cutoff valve 53 performs the cutoff control function.

Also, a running motor! 5 is driven and the vehicle is running, the pilot pressure for running acts on the pilot chamber 58a of the release valve 58, so the pilot chamber 53d of the cut-off valve 53 is opened to the tank T.

Therefore, regardless of the pressure in the branch passage 48 (the discharge pressure of the variable displacement pump P1), the force/cutoff valve 53 continues to maintain the left position in the drawing by the action of the spring 57, and stops the cutoff control function.

Note that the means for stopping the control function of the cut-off valve 53 is not limited to the above-mentioned configuration; for example, the means for stopping the control function of the cut-off valve 53 is
Pilot pressure for running may be introduced to the spring 57 side of No. 3. However, the pilot pressure from the pilot operating mechanism is usually not very high, so in this case,
It is necessary to make the pressure receiving area of the 57 springs sufficiently large.

In addition, the control mechanism 02 of the other circuit system has a configuration in which the cutoff valve 53 and release valve 58 in the control mechanism C1 of the one circuit system are omitted, and the other configuration is the same as that of the one control mechanism C1. It is.

Furthermore, although the control mechanisms c, C2 adopt the position feedback method, it is natural that a pressure feedback method may be used.

A relief valve 61 is connected to the pump passage 27 of one of the circuit systems as described above.1. The set pressure of this reserve valve 81 is set higher than the iμ constant pressure of the cutoff valve 53. In other words, the set pressure of the cut-off valve 53 is determined based on the actuator for the work equipment such as the packet cylinder 16 or the boom cylinder 17, which is set to a relatively low pressure, and the leaf valve 61 is set to a high pressure. The set pressure is determined based on the traveling motor 15 which is set to .

Therefore, when the travel motor 15 is driven, the pilot pressure at that time acts on the release valve 5B and stops the control function of the cutoff valve 53. At this time, the circuit pressure is reduced by the relief valve 81 set to a high pressure. controlled. When the travel motor 15 is not driven, the release valve 58 maintains the illustrated position and the quad-off valve 53 functions.
The circuit pressure is controlled to a relatively low pressure by the cutoff valve 53.

Further, a switching valve 62 is connected to the parallel passage 28, and a pilot chamber θ2a of this switching valve 82 is connected to the shuttle valve 38.

Therefore, when the travel motor 15 is not driven,
Although the switching valve 62 maintains the normal position X shown in the figure,
When the travel motor 15 is driven, the pilot pressure at that time switches the switching valve 82 to the switching position NY.

When the switching valve 82 is switched to the switching position Y, the parallel passage 28 is closed, so that the pump passage 27 and the switching valve 18 are closed.
Other switching valves except! While the communication with 9.20.29 is cut off, the pump passage 27 communicates with the downstream side of the check valve θ4 provided in the supply passage 83 of the other circuit system. This supply passage 83 communicates with the pump passage 30 of the other variable displacement pump P2 via a priority valve 85.

The priority valve 65 is connected to the shuttle valve θ7, which is connected to the shuttle valve 47 and the pilot line 6B of the switching valve 32 for boom merging, so when any of the switching valves 25, 26, and 32 is operated. , the priority valve 85 is switched from the normal position F to the switching position G.

Note that the symbol θ8.68 in the figure is an unload valve, which is normally operated as follows.
While holding the unload position shown, the shuttle valve 7
0.71, the control mechanism C2 is switched to the closed position without receiving the action of the pilot pressure guided to the control mechanism C2.

Further, reference numeral 72 is a relief valve that controls the circuit pressure of the other circuit system, and is connected to the pump passage 28, and
Similar to the cut-off valve 53, the pressure is maintained lower than that of the relief valve 61.

When the travel motor 15 is driven, the cutoff control function of the cutoff valve 53 is stopped as described above, and the circuit pressure is controlled by the relief valve 61 set to a high pressure, and the switching valve 62 is switched. Switch to position Y.

If the switching valve 62 is switched in this way, the variable displacement pump P
1 communicates with the travel motor 15, and the switching valve 62
It also communicates with the downstream side of the check valve 64 of the supply passage 83 via.

At this time, when the pilot operation mechanism 36 is simultaneously operated in order to drive the other travel motor 21, the other pump P2 also discharges a flow rate corresponding to the operation amount of the pilot operation mechanism 36.

In this way, when both pumps are driven at the same time and the vehicle travels straight ahead, the discharge oil from both pumps merges in the supply passage 63, so the flow rates supplied to the re-travel motors 15 and 21 become equal, and the corresponding The straightness of the vehicle is guaranteed.

While the vehicle does not require much driving force during normal driving, it is necessary to increase the driving force when driving on a slope or overcoming an obstacle.

In such a case, for example, if the load pressure of the travel motor 15.21 becomes equal to or higher than the set pressure of the relief valve 72, this load pressure acts on the check valve 64 as back pressure. In this state, the highest pressure of the other variable displacement pump P2 is reached by the relief valve 72.
Since the highest pressure of one variable displacement pump P1 is controlled by the relief valve 61 which is set to a high pressure, the check valve 64 is closed by the pressure on the one pump P1 side.

When the check valve 64 closes as described above, the supply passage 63
Since the communication between the pump P2 and the drive motor 1 is cut off, the
The circuit connecting 5.21 and pump P1 is independent. Since this independent circuit is controlled by the relief valve θl that maintains a higher set pressure than the normal set pressure, it is possible to increase the driving force of the vehicle.

However, this circuit pressure is limited to the above-mentioned independent circuit, and in particular, other actuators in the other circuit system connected to pump P2 are controlled by the relief valve 72, so the circuit pressure is the same as the normal one. Maintained at set pressure. In other words, since high pressure higher than the normal set pressure does not act on the other actuators mentioned above, they can withstand sufficient pressure without increasing the pressure resistance of the other actuators and the circuits connected to them, and the durability increases accordingly. will improve.

In addition, in this embodiment, when any one of the switching valves 25, 26, 32 or all of them are switched simultaneously while the travel motor is being driven, the highest pilot pressure at that time acts on the priority valve 65. The priority valve 65 is switched from the normal position F to the switching position G, and communication between the pump passage 27 and the supply passage 63 is cut off.

Therefore, for example, even if the load on the travel motor is lower than the load on the other actuators, the switching valve 25.2
This eliminates the need to supply the actuator connected to the actuator 6 or 32 with a flow rate of 100 mm, thereby slowing down its operating speed.

The pilot chamber 82a of the switching valve 62 is connected to the shuttle valve 38, and is connected to the running mode I5 of one circuit system.
The pilot chamber 62a may be connected to the shuttle valve 44 side. In other words, when the other travel motor 21 is driven, the switching valve 62 may be switched.

However, in the above case, a check valve other than the check valve 64 is provided in the pump passage 27 of one circuit system,
When the discharge amount of one pump P is zero, it is necessary to prevent the discharge oil of the other pump P2 from being unloaded from the unload valve 68.

(Effects of the Present Invention) Since the present invention is configured as described above, while the vehicle is running, its straightness is guaranteed and its running driving force can be increased.

Furthermore, while the vehicle is stopped, the maximum pressure of the circuit is set to a lower value, allowing use that matches the pressure resistance of the actuator of the work equipment system.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram, Figure 2 is a partial circuit diagram of the control mechanism of the circuit system of probe 1, and Figure 3 is a conventional circuit diagram. 15.21...1 motor running, 18~20.24~26.29.32...
・Switching valve, 27.30...Pump passage, 28.31・
...) Kurare Jshi passage, C1, C2... control mechanism, 5
3...Power/headoff valve, 61.72...1 Noleaf valve, 62...Switching valve, 64...Chain valve. Attorney attorney ± 11! Il Nobuyuki

Claims (1)

[Claims] A variable displacement pump, a travel motor, and an actuator for other work equipment are connected to each of the pair of circuit systems, and a switching valve that controls the travel motor of at least one circuit system is connected to the other switching valve. A hydraulic control circuit for a construction vehicle, which is located most upstream with respect to the valve and is connected to at least one of the other switching valves via a parallel passage,
A check valve is provided in the supply passage of the switching valve that controls the traveling motor of the other circuit system, and the parallel passage of the one circuit system is normally maintained in a communicating state and the running of either one is performed. A control valve is provided which is switched by a motor drive signal to shut off the parallel passage and connect the pump passage of one of the circuit systems to the downstream side of the check valve. is provided with a control mechanism that controls the discharge amount of the variable displacement pump, and the control mechanism connected to either circuit system has a cut-off function when the discharge pressure of the variable displacement pump exceeds the set pressure. A cant-off valve is connected that performs the control function and stops the cut-off control function in response to the drive signal of the travel motor, and one of the circuits has a pressure slightly higher than the set pressure of the cut-off valve. A hydraulic control circuit for a construction vehicle, comprising a relief valve that maintains a set pressure, and a relief valve set to a relatively low pressure that is substantially the same as the set pressure of the cut-off valve to the other circuit system.