JP3005869B2 - Circuit for preventing sudden change in low-pressure actuator speed during combined operation - Google Patents

Description

Description: BACKGROUND OF THE INVENTION The present invention relates to a circuit for preventing a sudden change in the speed of a low-pressure actuator during combined operation, and in particular, to a bucket (fork grab) cylinder for a discharge circuit of a single variable displacement pump. , A plurality of actuators such as a swing motor and an arm cylinder are connected in parallel, the plurality of actuators can be driven simultaneously or specially, and the low-pressure actuator is stopped when the high-pressure actuator is stopped during the combined operation of the plurality of actuators The present invention relates to a circuit for preventing a sudden change in speed.

(Prior art) A plurality of actuators, such as a bucket (fork grab) cylinder, a swing motor, and an arm cylinder, are connected in parallel to the discharge circuit of a conventional single variable displacement pump to enable simultaneous or special operation. For example, there is one disclosed in Japanese Patent Application Laid-Open No. 1-176803.

In this type, multiple actuators such as a bucket (fork grab) cylinder, a swivel motor, and an arm cylinder are connected in parallel to the discharge circuit of a single variable displacement pump, and each actuator can be operated simultaneously or separately. It was made.

Such conventional examples include: (a) gripping of an object by a bucket (fork grab); (b) driving of a swing motor in the state (a); (c) pilot operation valve for a bucket (fork grab) cylinder. There are three operation states of operation stop (neutral), and the hydraulic pressure, flow rate, and the like required by each actuator in each operation state are set as follows. (A) Grasping state of target object by bucket (fork grab) Drive pressure PF and set flow rate of bucket (fork grab) cylinder in a state of grasping target object such as waste material at the time of house demolition by fork grab as QF, for example, the drive pressure of the bucket cylinder (relief pressure) PF = 220Kg / cm ² pump discharge pressure Pp = 220 + 20 = 240Kg / cm 2 in the formula "20 Kg / cm ^2" flow rate control of the variable溶量pump 1 Valve setting differential pressure flow rate (when switching valve fully open) QF = 100 / min is required.

(B) Driving of Swing Motor in State (a) Next, in the state of (a), that is, when the swivel base is driven to be swiveled by the swivel motor while grasping the object by the bucket (fork grab), the swivel is performed. The motor driving pressure Ps and design quantity Qs are as follows: Ps = 60 kg / cm ² (after starting) Qs = 50 / min (when the switching valve is fully open), and the total set flow rate Qt in this state is Qt = 100 + 50 = 150 / min The set flow rate of 150 / min is set by the opening degree (spool stroke) of the directional control valve.

By the way, since the hydraulic pressure source for supplying pressure oil to each actuator is constituted by a variable displacement pump having a normal characteristic curve, its driving pressure Pp (for example, Pp = 240K)
g / cm ² ) (not shown, but in this case, Qp = 60 / min), which itself is a second characteristic curve diagram of the variable displacement pump according to the embodiment of the present invention. This corresponds to the discharge amount Qp = 60 / min at Pp = 240 Kg / cm ² in the figure.

The discharge amount (supply flow rate) Qp is equal to the set flow rate.
Since the flow rate is smaller than Qt and the set flow rate 150 / min> discharge rate 60 / min, the anti-saturation mechanism of the pressure compensation flow control valve (control cylinders 31A to 3
7A) will work.

That is, the set flow rate QF of the bucket (fork grab) cylinder is, for example, assuming that the set flow rate decrease rate during the anti-saturation operation is 60/150, QF = 100 / min → Q′F = 100 × (60/150 ) = 40 / min.

 Also, the set flow rate Qs of the swing motor becomes Qs = 50 / min → Q's = 50 x (60/150) = 20 / min, and the composite value Qt of these set flow rates is reduced to Qt = 40 + 20 = 60 / min. Make it small.

Further, the supply flow rate Qp in this state is Qp = 60 / min, which is balanced with the total value Qt = 60 / min of the set flow rates, and it can be understood that the so-called anti-saturation effect is functioning.

In addition, by a bucket (fork grab), for example,
When grasping an object such as waste material of a house to be destroyed, once the object is once grasped by a bucket (fork grab), usually, a bucket (fork grab) cylinder for operating the fork grab is further extended. There is no need to move the operation lever slightly so that the directional control valve is slightly opened in order to prevent the object such as waste material from falling off from the fork grab. It is only necessary to continue to supply pressure oil to the (grab) cylinder, stop oil supply to the bucket (fork grab) cylinder, and supply oil only to other low-pressure actuators. (Fork grab) As the driver's psychological state in the state of being gripped by the (fork glove), try not to drop the sandwiched object and tilt the operation lever to the maximum It is usual to operate sea urchin.

(C) Operation of the bucket (fork grab) cylinder pilot operation valve is stopped (neutral) When the operation of the bucket (fork glove) cylinder operation valve is stopped, the hydraulic pressure of the pilot circuit 11c becomes 0, and the spool of the direction switching valve 11 is turned off. Is in a neutral state, and the flow rate QF to the bucket cylinder 21 is QF = 0 / min, while the swing motor continues to require the flow rate Qs Qs = 20 / min for driving, and their total set flow rate Qt is Qt = 0 + 20 = 20 / min.

As for the total set flow rate Qt = 20 / min, the supply flow rate in this state is less than 180 / min corresponding to Ps = 60 kg / cm ² and Pp = 60 + 20 = 80 kg / cm ² from FIG. In this case, since the flow rate exceeds the set flow rate of 160 / min, the anti-saturation function is deactivated.

Therefore, when the swing motor is operated simultaneously with the bucket (fork grab) cylinder, when the bucket (fork grab) cylinder stops, the swing motor 26 is provided with an anti-saturation mechanism (control cylinder).
31A to 37A) is actuated and, unlike the corrected pressure oil supply flow rate Q's = 20 / min, the turning corresponding to the adjustment of the opening (spool stroke) of the directional control valve 11 in this state is performed. The flow rate increases to Qs = 50 / min.

(Problems to be Solved by the Invention) However, in this case, a swing motor is driven or an arm cylinder is expanded and contracted while grasping an object by a high-pressure actuator such as a bucket (fork grab) cylinder 21. When driving other low-pressure actuators simultaneously, the bucket (fork grab) is stopped, that is, its pilot operation valve 11A
When the operation is stopped or the bucket (fork grab) cylinder is operated to the reduction side, as described above, the entire amount of the pressure oil from the variable displacement pump 1 is transferred to, for example, a low-pressure actuator such as the swing motor 26, At the required flow rate Q's = 20 / min of the swing motor 26, in fact, the entire supply Qs = 50 / min is supplied via the directional control valve 16, so that the swing motor 26 There was a problem that the speed of 26 suddenly changed, which could lead to an accident of a worker working around the low-pressure actuator.

Further, in the hydraulic control circuit of the working machine described in Japanese Patent Application Laid-Open No. 1-250531, the opening area of the control valve for a hydraulic cylinder having a low load pressure is solely operated only when two links having different load pressures are simultaneously operated. Although it has been disclosed that the two links that are operated simultaneously can be rotated at substantially the same speed without lowering the link rotation speed at the time of the single operation because the rotation speed is made smaller than that at the time of the independent operation, this is not the case. In addition, there is a problem in performing the switching operation of the high-pressure actuator at an arbitrary time since the convencator valve is not provided in each of the direction switching valves of the plurality of actuators.

SUMMARY OF THE INVENTION The present invention has been made in view of the problems of the conventional example as described above, and one or several pumps are provided in a discharge circuit of a single variable displacement pump through a plurality of control cylinder-equipped convencator valves and direction switching valves. High pressure actuators such as bucket cylinders and one or more swing motors, low pressure actuators such as arm cylinders are connected in parallel,
A third pilot circuit is branched from a pilot circuit of a pilot control valve of one or several direction switching valves of the high-pressure actuator, and each of the third pilot circuits is provided with a solenoid switching valve appropriately operated by a switch. In addition, a second relief valve having a low relief pressure is provided via a second switching valve to which a pilot pressure of a second pilot circuit selected by a shuttle valve of each pilot operated valve of one or several of the low pressure actuators is applied. Or application of a pilot pressure of the second pilot circuit selected by a proportional solenoid valve switchable by a control switch operated at an appropriate amount to the third pilot circuit and a shuttle valve of a pilot operation valve of a low-pressure actuator to the third pilot circuit. High pressure actuator by providing a second switching valve By switching the pilot pressure of the directional control valve to a low pressure and reducing the opening degree of the directional control valve, the movement of the fork glove based on the deformation of the object gripped by the bucket (fork glove) is corrected. In order to maintain the gripping pressure, the set flow rate of the bucket (fork grab) cylinder can be reduced to a flow rate required to replenish the pressure oil of the bucket (fork grab) cylinder as a high pressure actuator, Accordingly, an object of the present invention is to provide a circuit for preventing a sudden change in the speed of a low-pressure actuator during a combined operation, which can solve the above-mentioned problem without operating the anti-saturation mechanism in this case.

(Means for Solving the Problems) In order to solve the above-mentioned problems, the present invention provides a convensator with a plurality of control cylinders (31A to 37A) in a discharge circuit (3) of a single variable displacement pump (1). High-pressure actuator (21) such as one or several bucket cylinders via valves (31 to 37) and directional control valves (11 to 17)
To 23) and one or several low-pressure actuators (24 to 27) such as a swing motor and an arm cylinder are connected in parallel, and the direction switching valve (1 to several) of the high-pressure actuators (21 to 23) is connected. 11 to 13) a pilot operated valve (pilot circuit of from 11A 13A) (from to no 11c 13c), the third pilot circuit (50 ₁ to 50 ₃₎
The branches respectively, (from 50 ₁ to 50 ₃₎ the third pilot circuit each providing a switch (57 ₁ to 57 ₃₎ solenoid switching valve (51 ₁ to 51 ₃₎ which is timely operated by the, also from 1 Several of the low pressure actuators (24
To 27) pilot operated valves (14A to 1
Shuttle valve 7A) (to 55 ₄ to via a second pilot circuit being selected (second switching valve (52 ₄ to 52 ₇ to 55B ₄ not applied pilot pressure 55B ₇₎₎ by 55 _7), low the second relief valve relief pressure (53 ₄ to 53 ₇₎ is provided, and the third pilot circuit (50 ₁ to 50 ₃₎ second switching valve provided in the (52 ₁ to 52 _3), said low pressure actuator (24 to 27) pilot operated valves (14A to 17A)
Pilot circuit shuttle valve (55 ₄ to 55 ₇₎ the pilot pressure selected by the (to no 14c 17c, to no 14d 17d) are applied by the selected pilot pressure to the second switching valve (52 ₄ to 52 ₇ ) This is a circuit for preventing sudden change of the low-pressure actuator speed at the time of the combined operation, which is configured to be able to automatically switch the item ₇ ).

The discharge circuit (3) of the single variable displacement pump (1)
A high-pressure actuator (21 to 23) such as one or a plurality of bucket cylinders is connected to one or more bucket cylinders or the like via a plurality of control valves (31A to 37A) with a convener valve (31 to 37) and a direction switching valve (11 to 17). Or multiple low-pressure actuators (24 to
27) and the directional control valves (11 to 13) of the one or more high-pressure actuators (21 to 23) from the pilot circuits (11c to 13c) of the pilot operated valves (11A to 13A). Third pilot circuit (50
₁ to 50 ₃ ), and the third pilot circuit (50 ₁
To 50 ₃ ), the proportional solenoid valve (61) switchable by a control switch (67 ₁ to 67 ₃ )
₁ to 61 ₃ ), and low-pressure actuator (24 to 27)
Pilot operated valve (14A to 17A) shuttle valve (55
₄ to 55 ₇ ), the second pilot circuit (55
It second switching valve (52 _{4 to} the applied pilot pressure to B ₄ no 57B ₇₎ 52 ₇₎ in which the provided.

(Operation) Since the present invention has the above-described configuration, the plurality of actuators 21 to 27 connected in parallel can be simultaneously or individually driven by the discharge circuit 3 of the single variable displacement pump 1. During operation such as grasping of an object by the high-pressure actuators 21 to 23, the low-pressure actuators 24 to
If 27 to simultaneously driven, a third pilot circuit 50 ₁ to 50 ₃ of the pilot pressure branching from the high-pressure actuator 21 to 23 of the directional control valve 11 to not the pilot operated valve 11A of 13 to 13A of the pilot circuit 11C to 13C, the the third is provided to the pilot circuit 50 ₁ to 50 _3, to no change-over switch 57 ₁ 57 ₃ or to control switch 67 ₁ 6
7 ₃ to the solenoid switching valve 51 ₁ is switched operated by 51 ₃
Or, a proportional solenoid valve 61 ₁ to 61 ₃ and a second relief valve 53 ₄
To comprise a 53 with _7, or the second to changeover valve 53 ₁ which is not provided
By switching 53 ₃ of the either the same third pilot circuit 50 ₁ to 50 ₃ of Hairotto pressure, switched to timely low relief pressure, the set flow rate of the high-pressure actuator 21 to 23, the second relief valve 53 ₄ to reduce the relief pressure corresponding amount of 53 _7, by decreasing the degree of opening of the directional control valve 11 to 13, buckets (fork grab)
Bucket (fork grab) based on deformation of the object gripped by the high-pressure actuators 21 to 23, etc.
Setting of the high-pressure actuators 21 to 23 such as bucket (fork grab) cylinders up to the flow rate necessary to replenish the pressure oil for holding the gripping pressure etc. to correct the movement of the high-pressure actuators 21 to 23 by reducing the flow rate, the low pressure actuator 24 to 27 were driven at a normal speed without abrupt speed change, also, the third pilot circuit 50 ₁ to the solenoid switching valve provided in the 50 ₃ 51
Switch ₁ to 51 ₃ or proportional solenoid valve 61 ₁ to 61 ₃ with switch 57
The ₁ to 57 ₃ or control switch 67 ₁ to 67 _3, the third pilot circuit 50 ₁ to 50 ₃ of the solenoid switching valve 51 ₁ to 51 _3, and the second relief valve 53 ₄ to 53 ₇
The provided, or switches the second switching valve 52 ₄ to 52 ₇ without the same second relief valve 53 ₄ to 53 ₇ to return to the old position,
Thereby, the plurality of actuators 21 to 27 are returned to the normal operation state.

(Embodiment) Hereinafter, an embodiment of a circuit for preventing a sudden change in the low-pressure actuator speed during combined operation (of a plurality of actuators by a single variable displacement pump) according to the present invention will be described with reference to the drawings.

(First Embodiment) FIGS. 1 and 2 are a circuit diagram of a first embodiment of a circuit for preventing a sudden change in the speed of a low-pressure actuator during combined operation according to the present invention, and a diagram illustrating a characteristic curve of a variable displacement pump thereof. 1 and 2, 1 is a variable displacement pump, 1A is a tilting unit for adjusting the discharge amount of the variable displacement pump, 2 is a pilot pump, 3 is a discharge circuit of the variable displacement pump 1, 4 is a discharge circuit, and 5 is a discharge circuit. Is the main relief valve, 6 is the unload valve, 7
Is a pump command pilot circuit, 10 is a direction switching valve block, 11 to 17 are direction switching valves for switching the supply and discharge direction of pressure oil to and from each actuator (21 to 27), and 11A is a direction switching valve for fork glove cylinder 21. A pilot operation valve for switching the direction switching valve 11 for switching the supply / discharge direction, 11E to 17E are drive circuits for the direction switching valves 11 to 17 and subsequent, and 16A is a pilot operation for switching the direction switching valve 16 of the swing motor 26. It is a valve.

Although not specifically shown, the same pilot operated valves (11A to 15A and 11A to 15A) are also provided for the directional control valves 12 to 15 and 17 of the other actuators (22 to 25 and 27).
17A) are provided.

In FIG. 1, fork grab bucket cylinder
Two high-pressure actuators outside of 21 (total of three), and three low-pressure actuators outside of swing motor 26 (total of four)
Assuming an example in which the pilot operation valve is 11A, the pilot operation valve as another member corresponding to the pilot operation valve 11A is (11A to 13A), and the pilot operation valve as another member corresponding to the pilot operation valve 16A is (14A To 17A) are indicated by a combination of parentheses ().

21A and 21B are port relief valves provided in a drive circuit 11E for supplying and discharging pressure oil to and from the bucket (fork grab) cylinder 21, and 31 to 37 are the discharge circuit 3 and the respective directional control valves 11 to 17
In between, each provided convensator valve, 42 to 46,
48 is a shuttle valve, 50 is a third pilot circuit branched from the pilot circuit 11b of the pilot operation valve 11A, 51 and 52
Numeral denotes a solenoid switching valve and a second switching valve provided in the third pilot circuit 50, and both of the switching valves 51 and 52 are directional switching valves 11
It may be provided on the side.

Reference numeral 53 denotes a second relief valve provided in the second pilot circuit 50 at a position rearward of the two switching valves 51 and 52 (at a position separated from the pilot operation valve 11A), and the relief pressure of the second relief valve 53 changes direction. It is set lower than the pilot pressure required for the valve 11 to fully open. 55 is a shuttle valve, and T is a tank.

(Operation of First Embodiment) First, the operation of the single variable displacement pump 1 is started, and the pressure oil is supplied, for example, by operating the pilot operation valve 11A of the directional control valve 11 of the bucket (fork grab) cylinder 21 by lever operation. The direction switching valve 11 is moved via the pilot circuit 11c, and the pressure oil is transferred to the bucket (fork grab) cylinder 21.
Then, the bucket cylinder 21 is extended and the bucket (fork grab) grips an object, for example, various members such as pillars of abandoned houses, concrete walls, and the like.

At this time, the same pilot pressure is applied to the third pilot circuit 50 branched from the pilot circuit 11c. However, when the switch 57 provided in the cabin (not shown) is turned off, the solenoid switching valve 51 rises (FIG. 1). ) If the third
The pilot circuit 50 is closed.

Simultaneously with the supply of the pressure oil to the bucket (fork grab) cylinder 21, the pilot pressure from the pilot pump 2 causes the pilot circuit 16c or 16d to operate through the lever operation of the pilot operation valve 16A of the direction switching valve 16 of the swing motor 26. Is applied to the spool of the directional control valve 16 via the directional control valve 16, the spool moves by a required amount, and the pressure oil of the variable displacement pump 1 is sent from the discharge circuit 3 to the swing motor 26 via the convencator valve 36, the directional control valve 16, and the like. After being oiled, the turning motor 26 is driven to rotate in a required direction.

At this time, the same pilot pressure is also applied to the third pilot circuit 50 branched from the pilot circuit 11c. However, when a switch 57 provided in a cabin (not shown) is turned off, the solenoid switching valve 51 rises (FIG. 1). ), The third pilot circuit 50 is closed.

Simultaneously with the supply of the pressure oil to the bucket (fork grab) cylinder 21, the pilot pressure from the pilot pump 2 causes the pilot circuit 16c or 16d to operate through the lever operation of the pilot operation valve 16A of the direction switching valve 16 of the swing motor 26. Is applied to the spool of the directional control valve 16 via the directional control valve 16, the spool moves by a required amount, and the pressurized oil of the pump 1 is supplied from the discharge circuit 3 through the convencator valve 36, the directional control valve 16, etc.
The turning motor 26 is rotationally driven in a required direction.

At this time, the spool of the second switching valve 52 is pushed to the right (FIG. 1) against the spring by the pilot pressure selected by the shuttle valve 55 via the second pilot circuit 55B, and the third pilot Switch the circuit 50 to the second relief valve with low relief pressure
Connect to 53.

The pilot pressure of the pilot circuit 11c of the pilot operation valve 11A for the direction switching valve 11 is
A solenoid switching valve 51 provided in a third pilot circuit 50 branched from 1c is connected to a switch provided in a cabin (not shown).
When the second switching valve 52 is switched to the right (FIG. 1), the second relief valve 53 is turned on.
Is released at the low relief pressure, and becomes lower than the pressure set by the pilot operation valve 11A.

As a result, the opening degree of the direction switching valve 11 decreases, the flow rate of the pressure oil to the drive circuit 11E decreases, and the flow rate supplied to the low-pressure actuator such as the swing motor 26 via the direction switching valve 16 is substantially set. Secured as value.

Also in this state, pressure oil is supplied from the variable displacement pump 1 to the bucket (fork grab) cylinder 21 to ensure that the bucket (fork grab) grips the target object such as waste material of the house.

By the way, the relief pressure of the second relief valve 53 is set lower than the pressure required for fully opening the directional control valve 11 and slightly higher than the pressure required for the directional control valve 11 to start opening from the neutral position. Is done.

A switch 57 installed in a cabin (not shown)
Is turned off, the solenoid valve 51 rises from the position shown in FIG. 1 to shut off the third pilot circuit 50, and the pilot circuit 11c for the bucket (fork grab) cylinder 21 rises to the operation pressure of the pilot operation valve 11A. The spool stroke of the directional control valve 11 is increased, and the set flow rate is increased.

Further, the pilot pressure of the second switching valve 52 is
In addition to the pilot pressure of the pilot operation valve 16A, although not shown, another shuttle valve having the same structure as the shuttle valve 55 (three high-pressure actuators and four low-pressure actuators in the assumed example, 4th fourth to seventh shuttle valve 55 ₄ to 55 ₇ corresponding to the actuator 24 through the seventh actuator 27, the second pilot circuit 55B ₄ to 55B _7, the second switch valve 52 ₄ to 52 _7, second
The combined use of any one of the relief valve 53 _{from 4} 53 _7), using any of the pilot pressure or the like for the arm cylinder pilot-operated valve (pilot pressure, the arm cylinder pilot operated valve not shown) (not shown) Alternatively, the pilot pressure of any of the pilot operation valves 14A to 17A of the plurality of low-pressure actuators 24 to 27 may be targeted.

When the turntable is turned by the turning motor 26 (low-pressure actuator) while maintaining the gripping state of the object by the bucket (fork grab) cylinder 21 (high-pressure actuator), the pilot control valve of the direction switching valve 16 is turned on.
The pilot pressure of one of the pilot circuits 16c and 16d of 16A is selected by the shuttle valve 55, and the second pilot circuit 55
B, the second switching valve 52 of the third pilot circuit 50 is switched, and the pilot pressure of the direction switching valve 11 is reduced by the second relief valve 53.
And the spool stroke of the directional control valve 16 is switched to a position corresponding to the low relief pressure of the second relief valve 53, thereby reducing the flow rate of the pressure oil to the bucket (fork grab) cylinder 21. Even if the operation lever of the pilot operation valve 11A is tilted to the maximum, the actual opening (spool stroke) of the directional control valve 11 is reduced, and the set flow rate is reduced.

Next, the operation state of the first embodiment will be described in more detail with reference to an example in which the operation is performed under substantially the same conditions as the conventional example.

For example, when the bucket cylinder 21 is driven, the bucket cylinder driving pressure PF = 220 kg / cm ² pump discharge pressure Pp = 220 + 20 = 240 kg / cm ² set flow QF = 100 / min swing motor drive Ps = 60 kg / cm ² set flow Qs = 50 / min, but according to this first embodiment, the bucket cylinder
The drive 21, the pilot pressure is lowered by a bucket cylinder driving pressure PF PF = 220Kg / cm ² pump discharge pressure Pp Pp = 220 + 20 = 240Kg / cm 2 second relief valve 53, the opening of the directional control valve is reduced For example, assuming that the set flow rate QF = 7 / min, the swing motor drive pressure Ps = 60 kg / cm ² (after starting) If the set flow rate Qs = 50 / min, the total set flow rate Qt is Qt = 7 + 50 = 57 / min. On the other hand, since the supply flow rate Qp of the variable displacement pump 1 in this state is Qp = 60 / min, the supply flow rate 60 / min> the total set flow rate 57 / min. In this case, the anti-saturation function (control cylinders 31A to 37A) ) Does not work from the beginning.

Therefore, there is no change in the flow rate of the pressure oil to the turning motor 26 during turning, and the motor 26 rotates at the same speed.

Generally, once the bucket (fork grab) grasps the target object, it is only necessary to maintain the grasped state thereafter, so that the flow rate to the bucket (fork grab) cylinder 21 may be small.

When the turntable is turned by the turn motor 26 while maintaining this gripping state, the pilot pressure by the lever operation of the pilot operation valve 16A of the direction switching valve 16 of the turn motor 26 becomes:
The second switching valve 52 is selected by the shuttle valve 55 via the pilot circuits 16c and 16d, and is selected via the second pilot circuit 55B.
To change the pilot pressure of the third pilot circuit 50 to the second
The relief pressure of the relief valve 53 is set to be low, and the spool stroke of the directional switching valve 11 (the opening degree of the directional switching valve 11) is reduced.

作 動 Operation example during combined operation of (fork grab) bucket and swivel table swing 旋回 When the operating lever of pilot operating valve 16A of swing motor 26 is operated, pilot pressure for moving the spool of direction switching valve 16 of swing motor 26 is increased. Then, the pilot pressure is selected by the shuttle valve 55, and the second directional control valve 52 provided in the second pilot circuit 50 is switched.

(When the solenoid valve switch is turned ON) When the lever of the pilot operation valve 11A of the bucket (fork grab) cylinder 21 on the grip side is operated, the direction switching valve 11
A pilot pressure for moving the spool is generated, the pilot pressure acts on the spool of the direction switching valve 11 of the bucket (fork grab) cylinder 21, and the solenoid valve 51 and the second switching valve 52 of the third pilot circuit 50 are operated. (In their open state) via the second relief valve 53.

Therefore, the set pressure of the second relief valve 53 is changed to the direction switching valve 11.
If the pressure is set below the pressure required for the full stroke of the pilot operating valve 11A, even if the operating lever angle is maximized,
The pilot pressure of the pilot circuit 11c does not increase to the maximum value, and therefore, the maximum value of the spool stroke of the directional control valve 11 becomes smaller than its full opening stroke.

(When the solenoid switching valve switch is OFF) When the solenoid switching valve switch is OFF, that is, when the switch 57 provided in the cabin (not shown) is turned OFF, the solenoid switching valve 51 rises (FIG. 1). ) Third
Since the pilot circuit control 50 is closed, the pilot pressure for operating the direction switching valve of the bucket (fork grab) cylinder 21 is determined only by operating the operation lever of the pilot operation valve 11A.
The bucket (fork grab) cylinder 21 is operated in an operation state similar to that of a shovel operation in a normal power shovel having the following.

As the pilot pressure for switching the second switching valve 52, the pilot pressure of the pilot operating valve 16A of the swing motor 26 of the swivel table as shown in the figure is the same as the pilot pressure of the second switching valve via the second pilot circuit 55B. In addition to the application to 52, although not shown, by using a shuttle valve similar to the shuttle valve 55, the pilot pressure of a pilot operation valve of another low-pressure actuator such as an arm cylinder or a boom cylinder may be used. In this case, the operation can be performed in substantially the same manner as described above.

(Second Embodiment) Next, a second embodiment of the present invention will be described by using a solenoid switching valve 51 provided in a third pilot circuit 50 in the first embodiment.
A description will be given with reference to FIG. 3 schematically showing a circuit diagram of a circuit provided with a proportional solenoid valve 61 and a control switch 67 for switching the proportional solenoid valve 61 instead of the switch 57 for switching the solenoid switching valve 51. The illustration of the parts common to the first embodiment schematically shown in FIGS. 1 and 2 is omitted, and the parts common to the first embodiment are denoted by the reference numerals and names in FIGS. It will be briefly described.

In FIG. 3, reference numeral 50 denotes a third pilot circuit similar to the third pilot circuit in FIG.
Is a control switch, a proportional solenoid valve in FIG.
The dashed line extending to the right of 61 indicates the pilot operation valve 11A side (FIG. 1) in the first embodiment, and the dashed line extending to the left (FIG. 3) from the proportional solenoid valve 61 is the second line in the first embodiment.
The second switching valve 52 of the second embodiment is connected to the tank (T) via a switching valve 52 (the second relief valve 53 of low relief pressure in the first embodiment is not provided).

Therefore, the proportional solenoid valve 61 (61 ₁ to 61 ₃₎ is operated so as to be proportional to the electrical signal (voltage) which is based on timely adjusting the control switch 67, a third pilot circuit
Change (adjust) the relief pressure of 50.

In the second embodiment, the installation of the second relief valve 53 provided in the second switching valve 52 of the first embodiment (FIG. 1) is unnecessary.

The remaining structure and operation are almost the same as in the first embodiment.

(Effects of the Invention) The present invention has the above-described configuration and operates, so that the following effects can be obtained.

(1) In the discharge circuit of a single variable displacement pump, through a plurality of convener valves, control cylinders and directional control valves,
A high-pressure actuator such as a bucket cylinder and a low-pressure actuator such as a swing motor and an arm cylinder are connected in parallel with the same number of actuators as the direction switching valve, and a pilot circuit of a pilot operation valve of the direction switching valve of the high-pressure actuator. From a third pilot circuit, and a switch (or a control switch) is connected to the third pilot circuit via a solenoid switching valve (or a proportional solenoid valve) and a second control valve, which are operated as appropriate.
Since the second relief valve having a low relief pressure is provided (however, if the proportional solenoid valve is provided, the second relief valve is not necessary), the pilot pressure of the pilot operation valve of the direction switching valve of the high pressure actuator is increased. The second relief valve is appropriately switched to a pressure lower than the pressure required to fully open the directional control valve of the actuator, and the set flow rate of the high-pressure actuator is adjusted. There is no risk of suddenly changing the low-pressure actuator suddenly.

(2) There is no risk of suddenly changing the low-pressure actuator suddenly when the high-pressure actuator stops the gripping operation of the target object, which may cause inadvertent danger to the operator working around the low-pressure actuator. There is no.

(3) The shuttle circuit selects a pilot circuit pressure of a pilot operation valve of a swing motor as a low-pressure actuator, applies the same to a spool of a second switching valve of a third pilot circuit, and automatically controls the second switching valve. Since the switching operation is enabled, even if the high-pressure actuator is suddenly stopped from the combined operation state of the high-low actuator, there is no possibility that the speed of the low-pressure actuator such as the swing motor is rapidly increased.

(4) In a device for driving a plurality of actuators simultaneously or separately by a single variable displacement pump, a third pilot circuit is branched from a pilot circuit of a pilot control valve of a direction switching valve of the high-pressure actuator, and A comparatively simple structure change, in which a second switching valve and a solenoid switching valve that can be switched by a control switch 57 that is appropriate for the pilot circuit and a directional switching valve for each actuator are provided alongside, a relatively simple structural change, allows the same type of existing switching valve to be used. The present invention can be easily applied to a composite hydraulic operation circuit.

[Brief description of the drawings]

The drawings schematically show an embodiment of a circuit for preventing a sudden change in the low-pressure actuator speed during combined operation according to the present invention. FIG. 1 is an explanatory diagram of the circuit for preventing a sudden change in the low-pressure actuator speed of the first embodiment. FIG. 2 is an explanatory view of a characteristic curve of a variable displacement pump used in the sudden change prevention circuit of the first embodiment, and FIG. 3 is a diagram of the sudden change prevention circuit of the low-pressure actuator speed in the combined operation of the second embodiment of the present invention. FIG. 4 is an explanatory diagram of a switching circuit using a proportional solenoid valve (corresponding to a solenoid switching valve in the first embodiment) control switch. (Explanation of reference numerals) 1 ... Variable displacement pump 3 ... Discharge circuit 7 ... Pump command pilot circuit 11-17 ... Directional switching valve 11A ... Pilot operated valve (for bucket) 11b-13b ... Pilot circuit 11c- 13c ...... pilot circuit (12A, 13A) ...... pilot operated valve (high-pressure actuator circuit side) (14A, 15A, 17A) ...... pilot operated valve (low pressure actuator circuit side) 14c~17c ...... pilot circuit 14c ₁ ~17c ₁ … Pilot circuit 14c _{2 to} 17c ₂ … Pilot circuit 14d to 17d… Pilot circuit 16A… Pilot operated valve (for swing motor) 21 …… Bucket (fork grab) cylinder (high pressure actuator) (22, 23) …… High-pressure actuator (24, 25, 27) …… Low-pressure actuator 26 …… Turning motor (Low-pressure actuator) 31-37 …… Convensator valve 42-46 …… Shuttle valve 50 ( 50 _{1-50 3)} ...... third pilot circuit 51 (51 ₁ to 51 ₃₎ ...... solenoid switching valve 52 (52 _{4-52 7)} ... second switching valve 53 (53 _{4-53 7)} .... The 2 relief valve (low relief pressure) 55 (55 ₄ to 55 ₇₎ ...... shuttle valve 55B (55B ₄ ~55B ₇₎ ...... second pilot circuit 57 (57 ₁ to 57 ₃₎ ...... switch 61 (61 ₁ to 61 ₃ ) Electromagnetic proportional valve 67 (67 _{1 to} 67 ₃ ) Control switch

Claims (2)

(57) [Claims] (A) A discharge circuit (3) of a single variable displacement pump (1) includes: (B) a plurality of control cylinders (31A to 37A) with a convensator valve (31 to 37) and a direction switching valve (11). Or 1
7) through (C) one or several high-pressure actuators (21 to 23) such as bucket cylinders and one or several low-pressure actuators (24 to
27) are connected in parallel, and (D) the directional control valves (11 to 13) of one or several high-pressure actuators (21 to 23) are connected to the pilot circuits (11c to 11A) of the pilot operation valves (11A to 13A). 13c)
From third (to 50 ₁ 50 ₃₎ Pilot circuit branches respectively, solenoid switching valve is timely operated by a switch (57 ₁ to 57 ₃₎ to each of the third pilot circuit (50 ₁ to 50 ₃₎ ( 51 ₁ to 51 ₃ ), and (E) pilot control valves (14A to 17A) for each of one to several low-pressure actuators (24 to 27).
Via a second pilot circuit which is selected by the shuttle valve A) (55 ₄ to 55 ₇₎ (the second switching valve (52 ₄ to 52 ₇ to 55B ₄ not applied pilot pressure 55B _7)), low the second relief valve relief pressure (53 ₄ to 53 ₇₎ is provided, to (F) and the third pilot circuit (50 ₁ 5
0 ₃ ), the pilot valve (14) of the low-pressure actuator (24 to 27) is connected to the second switching valve (52 ₁ to 52 ₃ ).
A through 17A) of the pilot circuit (14c to 17c, the shuttle valve (55 ₄ to the pilot pressure selected by 55 ₇₎ of from 14d 17d) is applied, by the selected pilot pressure, the second switching valve ( 52 ₄ to 52 ₇₎ were automatically switchable configure (G) abrupt change prevention circuit of the low-pressure actuator speed during the combined operation, characterized in that. (H) The discharge circuit (3) of the single variable displacement pump (1) includes: (I) a plurality of control cylinders (31A to 37A) with a convensator valve (31 to 37) and a directional control valve (11). Or 1
7) through (J) one or more high-pressure actuators (21 to 23) such as bucket cylinders and one or more low-pressure actuators (24 to
And (K) connecting the directional control valves (11 to 13) of one or more high-pressure actuators (21 to 23) to pilot circuits (11c to 13c) of pilot operated valves (11A to 13A). )
From third pilot circuit (50 ₁ to 50 ₃₎ branches the, (L) to the third pilot circuit (50 ₁ to 50 _3), to control switch (67 ₁ to be timely appropriate amount operation 6
7 ₃₎ switchable proportional solenoid valve (61 ₁ to 61 _3), and a is selected by the pilot operated valve of the low pressure actuator (24 to 27) (14A to 17A) shuttle valves (55 ₄ to 55 ₇₎ 2nd switching valve (52 ₄ to 52 ₇ ) to which pilot pressure of 2 pilot circuit (55B ₄ to 57B ₇ ) is applied
(M) A circuit for preventing a sudden change in the speed of the low-pressure actuator during a combined operation.