JP3209885B2 - Hydraulic circuit of hydraulic excavator with loader front - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plurality of directional control valves for controlling the supply of pressure oil to a plurality of actuators each including a drive unit for a working machine divided into a first switch valve group and a second switch valve group. The present invention relates to a hydraulic circuit of a hydraulic excavator with a loader front, which is configured by the above.

[0002]

2. Description of the Related Art In a hydraulic shovel, a boom, an arm, and a bucket are rotatably connected to a revolving body in order, and the bucket is driven to bend by a cylinder connected between the boom, the arm, and the bucket. Construction work such as scraping out soil and sand. The excavated earth and sand is conveyed by a hydraulic shovel onto a waiting truck bed, discharged, and falls. By the way, in order to facilitate discharge of the earth and sand transported upward from the bucket, a bucket capable of being opened and closed between the rear part and the rear end of the basket body is rotatably attached to the tip of the working machine. A hydraulic excavator with a loader front is known which opens the space between the rear part and the rear end of the basket when the earth and sand is discharged from the bucket so that the earth and sand can drop by its own weight along the bottom of the basket of the bucket. ing.

FIG. 2 is a side view showing the appearance of such a hydraulic shovel with a loader front. As shown in the figure, the hydraulic excavator with a loader front is capable of running
A revolving unit 41 that can be pivoted in the horizontal direction is disposed on the revolving unit. The loader front includes a boom 42 rotatably mounted on the revolving unit 41 in the up-down direction, and an arm 43 rotatably mounted on one end of the boom 42.
And a bucket 44 rotatably attached to one end of the arm 43. Revolving superstructure 41, boom 42,
The direction of the bucket 44 attached to the front end of the loader front is controlled by appropriately extending and retracting the boom cylinder 45, the arm cylinder 46, and the bucket cylinder 47, which extend and extend between the arm 43 and the bucket 44, respectively. In addition, it is possible to arbitrarily select and drive a three-dimensional movement direction, and to perform construction and civil works such as excavation of earth and sand by bending and stretching operation of the work machine.

FIG. 3 is a hydraulic circuit diagram of the hydraulic excavator with a loader front. As shown in the figure, two variable displacement hydraulic pumps 1 and 2 connected to a prime mover (not shown) are provided as pressure oil supply sources, and are respectively provided to a first switching valve group and a second switching valve group. Supply pressure oil to the directional switching valve to which it belongs. The first switching valve group includes a right traveling direction switching valve 5, a first boom direction switching valve 7, a second bucket rotating direction switching valve 34, a second arm direction switching valve 8, and a bucket opening / closing direction switching valve 6. The second switching valve group includes a turning direction switching valve 9, a first arm direction switching valve 10, a second boom direction switching valve 11, a bucket rotating direction switching valve 12, and a left traveling direction switching valve 13. Belongs.

The circuit connection of the directional control valves belonging to the first directional control valve group includes a first boom directional control valve 7, which is connected in parallel with a right traveling directional control valve 5 connected to the most upstream side.
The second bucket rotating direction switching valve 34 and the second arm direction switching valve 8 are connected in tandem, and the bucket opening / closing direction switching valve 6 is connected to the outflow port at one switching position of the second bucket rotating direction switching valve 34. They are connected in series. In addition,
Since the turning operation of the revolving body 41 and the opening / closing operation of the bucket 44 are often performed simultaneously, the bucket opening / closing direction switching valve 6 does not belong to the second switching valve group to which the turning direction switching valve 9 belongs, and the first switching is performed. It is designed to belong to a valve group.

The direction switching valves 9 to 13 belonging to the second switching valve group
Is connected in parallel to all of the direction switching valves 9 to 13. However, the first arm direction switching valve 10, the bucket rotating direction switching valve 12, and the left traveling direction switching valve 13
A throttle valve is interposed in the parallel connection inflow side pipeline. The outflow port at one switching position of the second bucket rotation direction switching valve 34 is connected to the inflow port of the bucket opening / closing direction switching valve 6 connected in series as described above, and the outflow port at the other switching position. The port is a directional switching valve for bucket rotation 1 that supplies pressure oil to the head side of the bucket cylinder 47.
2 outflow ports.

[0007] The pressure oil discharged from the hydraulic pumps 1 and 2 also flows through the oil passages T1 and T2 connected in series, respectively. When the second arm directional switching valves 8 are in the neutral positions, they flow downstream via the series-connected oil passage T1, and the second switching valve group includes a turning directional switching valve 9, a first arm directional switching valve. 10, when the bucket rotating direction switching valve 12 and the left traveling direction switching valve 13 are at the neutral positions, respectively, they flow downstream through the serially connected oil passage T2.

A fixed throttle valve 15 and a pressure regulating valve 17 and a fixed throttle valve 16 and a pressure regulating valve 18 are connected in parallel at the most downstream of the serially connected oil passages T1 and T2, respectively. The maximum values of the hydraulic pressures p1, p2 on the upstream side of the fixed throttle valves 15, 16 are regulated respectively. Also,
The hydraulic pressure p1, upstream of the fixed throttle valve 15 and the fixed throttle valve 16,
p2 is guided to discharge flow control devices 3 and 4 for controlling the discharge flow rates of the hydraulic pumps 1 and 2, respectively. The discharge flow control devices 3 and 4 respectively control the hydraulic pumps 1 and 2 based on the introduced hydraulic pressures p1 and p2. The discharge flow rate of the hydraulic pumps 1 and 2 is controlled by adjusting the tilt angle.

When the bucket rotation operation lever 21 for rotating the bucket 44 upward (tilt operation) and downward (dump operation) is operated, one of the corresponding pilot valves 19 and 20 is switched according to the operation direction. The pressure oil on the outflow side flows into one of the control chambers 12a and 12b of the bucket rotating direction switching valve 12, and the spool 44 of the bucket rotating direction switching valve 12 is switched, whereby the bucket 44 is tilted or dumped. I do.
The pilot pressure oil on the outflow side of the tilt operation side pilot valve 19 is guided to one control chamber 34 b of the second bucket rotating direction switching valve 34 via the switching valve 48.

Therefore, when the switching valve 48 is at the switching position shown in the drawing, when the bucket rotating operation lever 21 is operated in the tilting direction, the pilot pressure oil flowing out of the pilot valve 19 is guided to the control chamber 34b. By
The spool position of the second bucket rotation direction switching valve 34 is switched to the right position in the drawing, and the pressure oil discharged from the hydraulic pump 1 is supplied to the bucket cylinder 47 via the second bucket rotation direction switching valve 34 and the backflow prevention valve 35. It is led to the head side inflow port.

When the bucket opening / closing operation lever 36 is operated, the pilot valves 37 and 3 are operated depending on the operation direction.
8, the pressure oil on the outflow side flows into one of the control chambers 6a, 6b of the bucket opening / closing direction switching valve 6. The high-pressure-side pilot pressure oil selected by the high-pressure selection valve 39 connected between the pilot lines on the outflow side of the pilot valves 37 and 38 is supplied to the other control chamber 34 a of the second bucket rotating direction switching valve 34. It is led to the control room of the switching valve 48. As a result, the spool position of the switching valve 48 is switched to the lower position in the drawing, so that the supply of the pilot pressure oil from the outflow side of the pilot valve 19 to one control chamber 34b of the second bucket rotating direction switching valve 34 is shut off. Is done.

Therefore, the second bucket rotating direction switching valve 3
4, the spool position is switched to the left position in the drawing by the pilot pressure oil guided to the other control chamber 34a, regardless of whether the bucket rotation operation lever 21 is operated or not, and the pressure oil discharged from the hydraulic pump 1 is the second position. The bucket opening / closing direction switching valve 6 is guided through the bucket rotation direction switching valve 34. Therefore, the spool position of the bucket opening / closing direction switching valve 6 is switched by the pilot pressure oil flowing into one of the control chambers 6a and 6b, whereby the bucket 44 is opened and closed between the rear portion and the basket body.

As described above, when the tilting operation is performed in a state in which the back portion of the bucket 44 does not open and close with the basket, the pilot valve 19 is moved from the state shown in FIG. By switching, the pilot pressure oil flowing out of the pilot valve 19 is guided to the control chamber 12b, so that the spool position of the bucket rotation direction switching valve 12 is switched to the right position in the drawing, and the hydraulic pressure flowing out of the bucket rotation direction switching valve 12 is switched. The discharge oil of the pump 2 flows into the head-side inflow port of the bucket cylinder 47, and the pilot pressure oil flowing out of the pilot valve 19 is supplied via the switching valve 48 to one control chamber 34b of the second bucket rotating direction switching valve 34. And the spool position of the second bucket rotation direction switching valve 34 is switched to the right position in the drawing. Even pressure oil discharged from the pump 1 flows into the leading conduit to the head-side inlet port of the bucket cylinder 47 via the second bucket pivot directional switching valve 34 joins the oil discharged from the hydraulic pump 1. Thus, the pressure receiving area on the head side of the bucket cylinder 47 is set to be about twice as large as the pressure receiving area on the rod side, and the tilting operation of the bucket 44 is quickly performed with a strong force at the time of excavation of earth and sand. In other words, the lifting operation of the bucket 44 that generally requires a powerful and quick operation can be efficiently performed.

On the other hand, when the rear portion of the bucket 44 is opening and closing with the basket, the switching valve 48 is switched to the lower position in the figure, and the second bucket rotating direction switching valve 34 is switched.
The oil passage connected to one control chamber 34b is an oil tank 29
And the spool position of the second bucket rotating direction switching valve 34 is switched to the left position in the figure by the pilot pressure oil flowing out of one of the pilot valves 37 and 38, and the pressure oil discharged from the hydraulic pump 1 is It is guided to the bucket opening / closing direction switching valve 6 via the second bucket rotation direction switching valve 34 and is not guided to the bucket cylinder 47 side.

Therefore, even if the tilting operation is performed by operating the bucket rotating operation lever 21 during the opening / closing operation of the bucket 44, it is generally considered that there is little need to perform a quick and powerful operation. In this case, the flow rate of the pressure oil required by the bucket cylinder 47 when the bucket 44 rotates is sufficient only by the discharge oil from the hydraulic pump 2 supplied from the bucket rotation direction switching valve 12.

[0016]

In the above-mentioned prior art,
Depending on the operation state of the bucket opening / closing operation lever 36, the outflow direction of the pressure oil discharged from the hydraulic pump 1 toward the bucket cylinder 47 or the bucket opening / closing direction is switched by the second bucket rotation direction switching valve 34. Since it can be switched to the valve 6 side, when performing a powerful and quick operation such as excavation of earth and sand, the hydraulic oil discharged from the hydraulic pump 1 and the hydraulic oil discharged from the hydraulic pump 2 are combined. By guiding the bucket 44 to the head-side inflow port of the bucket cylinder 47, the bucket 44 can be quickly rotated with a strong force.
Side, only the pressure oil discharged from the hydraulic pump 2 can be introduced, so that the flow rate of the pressure oil supplied to the head side of the bucket cylinder 47 at the time of the slow tilt operation of the bucket 44 without applying a large load is appropriately adjusted. The opening / closing operation between the bucket 44 and the cage body at the back of the bucket 44 can be controlled while keeping the value at an appropriate value.

In general hydraulic excavators, a directional control valve for controlling the flow rate of hydraulic oil supplied to an actuator is mass-produced as a main hydraulic control device of the hydraulic excavator. It is incorporated as a valve connecting body combining seven direction switching valves in which the direction switching valves 5 to 13 and 34 except for the use direction switching valve 6 are connected. Therefore, in order to realize a hydraulic circuit to which the above-described conventional technology is applied, a bucket opening / closing direction switching valve specially ordered for a mass-produced product in which the direction switching valves 5 to 13 and 34 excluding the bucket opening / closing direction switching valve 6 are provided. 6 or all the directional control valves 5 to 13 and 34 including the directional control valve 6 for opening and closing the bucket.
Must be newly produced in small quantities.

The former means requires a space for installing the bucket opening / closing directional switching valve 6 and for laying a pipeline between the directional switching valves, which increases the size of the machine room and the mounting structure. Becomes complicated, and the labor and cost required for the production are significantly increased. The latter means not only adds to the cost of custom-designed products and molds, but also increases the manufacturing cost for small-scale production. The present invention solves such a problem in the prior art, and when tilting a bucket, hydraulic oil from a plurality of hydraulic pumps can be combined into a bucket cylinder and driven with a large flow of hydraulic oil. An object of the present invention is to provide a hydraulic circuit of a hydraulic shovel with a loader front, which can simplify a configuration of a hydraulic circuit and reduce a space occupied by a hydraulic drive unit by eliminating a direction switching valve for merging.

[0019]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides at least one variable displacement hydraulic system for a number of actuators including a boom cylinder, an arm cylinder, a bucket cylinder, a bucket opening / closing cylinder and two traveling motors. The pressure oil supplied from the pump is controlled to be supplied to each of the first switching valve group and the second switching valve group.
A plurality of divided directional control valves, a fixed throttle valve belonging to the first directional control valve group and connected downstream of the directional control valve located at the most downstream side thereof, and Hydraulic pressure of a hydraulic shovel with a loader front provided with discharge flow rate control means for detecting a hydraulic pressure of pressure oil supplied to one switching valve group upstream of the fixed throttle valve and controlling a discharge flow rate of the variable displacement hydraulic pump. An open / close switching valve connected to an oil pipeline immediately upstream of the fixed throttle valve, and the open / close switching in conjunction with an operation for tilt operation of a bucket rotating operation lever for tilting and dumping the bucket. Close the valve and operate for dumping
To keep the open / close switching valve open without interlocking
Has a belt interlocking means, bucket directional changeover valve for supplying control pressure oil from the hydraulic pump to said bucket cylinder not located on the most upstream side belonging to the second switching valve groups, also the opening and closing switch An oil pipeline immediately upstream of the valve and an inflow port of the bucket direction switching valve are connected by a branch pipeline via a check valve.

[0020]

A plurality of directional switching valves belonging to the first switching valve group and a plurality of directional switching valves belonging to the second switching valve group are supplied with pressure oil from a variable displacement hydraulic pump. When the driver operates the bucket pivoting operation lever for causing the bucket tilting operation (upward rotation operation), with the bucket rotated for direction switching valve is switched, in conjunction with this chill
The interlocking means closes the open / close switching valve. Due to the closing operation of the on / off switching valve, the pressure oil supplied from the variable displacement hydraulic pump to the first switching valve group passes through a branch line branched from an oil line immediately upstream of the on / off switching valve via a check valve. Flow into the inflow port of the bucket directional switching valve. Accordingly, the pressure oil flowing through the branch pipe line and the pressure oil supplied to the second switching valve group merge into the inflow port of the bucket direction switching valve, and a large amount of pressure oil flows to the bottom side of the bucket cylinder. Flows into the bucket and the bucket performs a quick and powerful tilt operation.

[0021]

An embodiment of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a hydraulic circuit diagram of a hydraulic shovel with a loader front according to an embodiment of the present invention. The same reference numerals are given to portions which are the same as or can be regarded as the same as those in the conventional example, and redundant description will be omitted. In the figure, 7a, 7
b, 8a, 8b, 10a, 10b and 11a, 11b
Are control chambers for driving the spools of the first boom direction switching valve 7, the second arm direction switching valve 8, the first arm direction switching valve 10, and the second boom direction switching valve 11, respectively, in opposite directions. , 14 are pilot hydraulic pumps, 2
Reference numerals 2 and 23 denote boom operation levers and arm operation levers, and reference numerals 24 and 25 denote pilot valves that are switched by operating the boom operation lever 22 and the arm operation lever 23, respectively.

Reference numeral 28 denotes a bucket rotating operation lever 2.
The operation is switched by the pilot pressure oil flowing out of the pilot valve 19, which is switched when the tilt operation is performed by the operation 1, and is switched to the lower position in the figure when the arm operating lever 23 is operated in the direction to extend the arm cylinder 46. An open / close switching valve that controls the flow of the pilot pressure oil flowing out of the pilot valve 27 to one control chamber 8b of the second arm direction switching valve 8 to be cut off;
Reference numeral 30 denotes a fixed throttle valve 15 for the pressure oil flowing through the series-connected oil passage T1 by the pilot pressure oil flowing out of the pilot valve 19.
This is an open / close switching valve that switches the intermittent flow out of the tank.

Reference numeral 31 denotes a check valve provided in the middle of the branch line T3 from the outflow port of the direction change valve 8 for the second arm of the series connection oil path T1. A check valve 33 is provided in the middle of the branch line T6 of the parallel connection line via a throttle. Reference numeral 33 denotes a middle portion of the branch line from the series connection oil line T2 side of the bucket rotating direction switching valve 12 to the inflow port. It is a check valve provided in the. As shown in the figure, the branch pipe line T6 joins the series connection oil path T2 from the series connection oil path T2 to the inflow port of the bucket turning direction switching valve 12 downstream of the check valve 33 in the branch pipe line.
The branch line T3 from 1 is connected to the check valve 32 of the branch line T6.
Merge downstream of.

The pilot pipes on the outflow side of the pilot valves 20 and 19 of the bucket rotating operation lever 21 are connected to the control chambers 12a and 12b of the bucket rotating direction switching valve 12, respectively.
The pilot valves 24, 25 of the operating lever 22 for the boom
The pilot lines on the outflow side of the arm are respectively connected to the control chambers 7a, 7b of the first boom directional control valve 7 and the control chambers 11a, 11b of the second boom directional control valve 11, respectively. The pilot pipes on the outflow side of the pilot valves 26 and 27 are connected to the control chambers 10a and 10b of the first arm direction switching valve 10, respectively. The pilot line on the outflow side of the pilot valve 26, which is switched to the lower position in the figure when the arm operation lever 23 is operated to extend the arm cylinder 46, is controlled by one of the second arm direction switching valves 8. The pilot line on the outflow side of the pilot valve 27 is connected to the chamber 8a via the open / close switching valve 28 to the other control chamber 8b of the second arm direction switching valve 8 respectively.

The hydraulic pressure p1 on the upstream side of the fixed throttle valves 15, 16
, P2 are transmitted to the discharge flow controllers 3, 4, respectively. The discharge flow controllers 3, 4 transmit the transmitted hydraulic pressures p1, p.
2 and the well-known configuration and operation of the hydraulic pumps 1 and 2
The discharge flow rates of the hydraulic pumps 1 and 2 are respectively controlled by adjusting the tilt angle of. In addition, it is constituted of a left and right traveling operation lever, a bucket opening / closing operation lever, a turning operation lever, a pilot valve switched by operation of these operation levers, and a pipeline connecting the control chambers of the corresponding direction switching valves. The hydraulic circuit is similar to that of the pilot hydraulic circuit including the boom operation lever 22 and the pilot valves 24 and 25, and is not shown.

Next, the operation of this embodiment will be described. The left and right running operation, the turning operation, and the raising / lowering operation of the boom 42 are not different from those of the conventional example, and thus the description thereof is omitted. The operation will be described. First, when the pushing operation of the arm 43 is performed,
The pilot valve 27 is operated by operating the arm operation lever 23.
Is switched to the lower position in the figure, and the pilot pressure oil from the pilot hydraulic pump 14 flows out into the pilot line on the outflow side. This pilot pressure is guided to the control chamber 10 b of the first arm direction switching valve 10 and flows into the inflow port of the on-off switching valve 28. When the bucket 44 is not tilted, the control pressure of the open / close switching valve 28 is equal to the tank pressure. Therefore, the switching position of the open / close switching valve 28 is in the open position shown in FIG. The pilot pressure oil is guided to the other control chamber 8b of the second arm direction switching valve 8 via the open / close switching valve 28, and switches the spool position of the second arm direction switching valve 8 to the right switching position in FIG. Let it.

On the other hand, the spool position of the first arm direction switching valve 10 is switched to the right switching position shown in the drawing by the pilot pressure oil guided from the pilot valve 27 to the control chamber 10b by operating the arm operation lever 23. ,
The hydraulic pumps 1 and 2 discharge the hydraulic pumps 1 and 2 downstream of the second arm direction switching valve 8 in the series connection oil passage T1 of the first switching valve group and downstream of the first arm direction switching valve 10 in the series connection oil passage T2. The oil hardly flows. Therefore, the discharge flow control devices 3 and 4 detect that the transmitted hydraulic pressures p1 and p2 have decreased, and perform control (negative control) so as to increase the tilt angle of the hydraulic pumps 1 and 2. Therefore, the first arm direction switching valve 10 and the second arm
A large amount of pressure oil flows in through the arm direction switching valve 8.
For example, only a small amount of pressure oil from the hydraulic pump 2 flows into the bucket rotating direction switching valve 12 located downstream of the first arm direction switching valve 10, and the series-connected oil passage T1
Since the discharge oil of the hydraulic pump 1 hardly flows to the downstream side of the second arm directional switching valve 8, that is, to the branch pipe line T3,
Although the total flow rate of the hydraulic oil flowing into the inflow port of the bucket rotation direction switching valve 12 remains slightly small, in general, in a hydraulic shovel with a loader front, the load at the time of the dumping operation of the bucket 44 is small, and quick operation is necessary. In many cases, there is no problem in actual work.

On the other hand, when the bucket 44 is being tilted, the pilot pressure oil from the pilot hydraulic pump 14 is controlled by the pilot valve 19 of the bucket rotating operation lever 21 to control the open / close switching valve 28. The switch is guided to the port, and the switching position of the open / close switching valve 28 is switched from the open state shown in FIG. As a result, the pilot pressure oil flowing out of the pilot valve 27 is blocked from flowing out of the second arm direction switching valve 8 to the other control chamber 8b by the open / close switching valve 28, so that the spool of the second arm direction switching valve 8 is spooled. The position is kept neutral. Therefore,
Only the pressure oil from the hydraulic pump 2 that flows out of the first arm direction switching valve 10 belonging to the second switching valve group is supplied to the arm cylinder 46.

On the other hand, the pilot pressure oil which has flowed out of the pilot valve 19 of the bucket rotating operation lever 21 is controlled by an open / close switching valve 30 provided downstream of the junction of the series connection oil passage T1 and the branch line T3. The switching position of the open / close switching valve 30 is switched from the open state to the right side position where the open / closed state is cut off, and the pressure flowing out of the series connection oil passage T1 to the downstream side of the second arm direction switching valve 8 is guided. Fixed throttle valve 1 for oil
Block outflow to the 5 side. The discharge flow control device 3 detects a decrease in the hydraulic pressure p1 by closing the open / close switching valve 30.
Controls the tilt angle of the hydraulic pump 1 to be greatly increased. Therefore, when the right traveling motor is not driven, the discharge oil of the hydraulic pump 1 flows at least downstream of the second arm direction switching valve 8 of the series connection oil passage T1 through the parallel circuit of the first switching valve group. Because of the outflow, the hydraulic oil from the hydraulic pump 1 is supplied to the junction with the branch line T6 via the branch line T3, and a large amount of pressure is applied to the head side of the bucket cylinder 47 required when the bucket 44 tilts. Oil supply becomes possible. The backflow prevention valves 31 and 32 prevent the discharge oil of the hydraulic pump 1 from flowing back to the series connection oil passage T1 side and the second switching valve group to the parallel pipeline side, respectively.

When the combined operation of the pivoting operation of the bucket 44 and the opening / closing operation of the back portion and the basket is performed, almost all the oil discharged from the hydraulic pump 1 flows into the bucket opening / closing direction switching valve 6, and When the bucket 44 does not perform the tilt operation, the open / close switching valve 30 is not in the disconnected state.
The discharge oil of the hydraulic pump 1 does not flow out to the third side, and the pressure oil flowing into the inflow port of the bucket rotation direction switching valve 12 is the second oil.
Although the upper limit is substantially limited to the pressure oil from the hydraulic pump 2 supplied through the parallel pipes of the switching valve group, when opening and closing the basket of the bucket 44, the bucket 44 can be quickly rotated or strongly operated. Since there is almost no movement by force, there is no problem in operability.

As described above, in this embodiment, the opening and closing for switching the intermittent flow of pressure oil to the fixed throttle valve 15 downstream of the second arm direction switching valve 8 in the series connection oil passage T1 of the first switching valve group. A switching valve 30 is provided, and a branch line T3 is branched from the series connection oil line T1 on the upstream side of the on-off switching valve 30. The discharge oil of the hydraulic pump 1 is supplied to the second switching valve group via the branch line T3. Since the hydraulic fluid from the hydraulic pump 2 flowing into the inflow port of the bucket rotation direction switching valve 12 to which the bucket 44 belongs is merged, the bucket cylinder 47 is operated by the opening / closing switching valve 30 that closes when the bucket 44 tilts.
A large amount of pressure oil is supplied to the head side, and the bucket 44 can be quickly and powerfully tilted.

The pilot valve 27, which is switched by operating the arm operating lever 23 when the arm 43 is pushed, is connected to the other control chamber 8b of the second arm direction switching valve 8 belonging to the first switching valve group. An open / close switching valve 28 is provided in the pilot pipeline between the valves, and is closed during the tilt operation of the bucket 44, so that when the combined operation of the tilt operation of the bucket 44 and the pushing operation of the arm 43 is performed, the hydraulic pump 1 This prevents a large amount of discharged oil from flowing into the second arm direction switching valve 8 and flowing out of the pressure oil flowing out to the downstream branch pipe line T3. This makes it possible to use the arm 4 which is frequently used in a case where the excavated earth and sand is loaded onto a truck following the excavation of the earth and sand.
It is possible to prevent the operability of the tilt operation of the bucket 44 from being impaired at the time of the combined operation with the pushing operation of No. 3.

Further, the hydraulic control device does not need to be combined with an additional directional switching valve as in the conventional example, and is constituted only by a valve connecting body combining seven directional switching valves similar to other hydraulic excavators. As a result, the manufacturing cost and assembly cost can be reduced, and the space occupied by the hydraulic circuit device can be reduced. In addition, since the opening and closing operation of the basket of the bucket 44 does not need to operate two directional switching valves as in the conventional example, it is sufficient to operate only the single bucket opening and closing directional switching valve 6.
The operability of the opening / closing operation of the basket of the bucket 44 is improved.

In this embodiment, the discharge flow control devices 3 and 4 guide the hydraulic pressures p1 and p2 upstream of the fixed throttle valves 15 and 16 provided at the most downstream of the serially connected oil passages T1 and T2, respectively. 2 is controlled respectively, but the differential pressure between the upstream side and the downstream side of the fixed throttle valves 15 and 16 is detected by the differential pressure sensor, and the detection signals are used to control the discharge flow rate control devices 3 and 4. Tilt angle control may be performed. The opening and closing of the open / close switching valve 30 is controlled by converting the operation amount of the bucket rotation operation lever 21 into pilot oil pressure by opening and closing the pilot valve 19, but the bucket rotation operation lever 21 is constituted by an electric lever. Then, the control may be performed based on the detected detection signal.

[0035]

As described above, according to the first aspect of the present invention, it is located at the most downstream side belonging to the first switching valve group in conjunction with the operation of the bucket rotating operation lever for tilting the bucket. The close / close switching valve connected to the oil line immediately upstream of the fixed throttle valve connected downstream of the directional switching valve to be closed, and the branch line branched from the oil line immediately upstream of the open / close switching valve Is connected to the inflow port of the bucket direction switching valve via a check valve, so that when the driver operates a bucket rotating operation lever for tilting the bucket, the opening / closing switching valve is interlocked with the operation. Is closed, and the pressure oil supplied from the variable displacement hydraulic pump to the first switching valve group flows into the inflow port of the bucket directional switching valve via the branch pipe line. Pressurized oil Merging is allowed to be driven with pressure oil at a high flow rate, moreover, since the direction switching valve for merging pressure oil can be eliminated, simplifying the construction of the hydraulic circuit, it is possible to reduce the space occupied by the hydraulic drive unit.

According to the second aspect of the present invention, the second arm direction switching valve for controlling the supply of the pressure oil from the variable displacement hydraulic pump to the arm cylinder belongs to the first switching valve group, and the bucket rotating operation lever is provided. In conjunction with the operation, the switching operation of the second arm direction switching valve due to the operation of the arm operation lever that pushes the arm is suppressed.
When the combined operation of the tilting operation of the bucket and the pushing operation of the arm is performed in an operation such as loading excavated earth and sand into a truck following the excavation operation of the earth and sand, the discharge oil of the hydraulic pump is directed to the second arm. It is possible to prevent the flow rate of the pressure oil flowing into the switching valve in a large amount and flowing out to the branch pipe on the downstream side from almost disappearing, so that the combined operation can be performed smoothly. According to the third aspect of the invention, the first switching valve group includes one traveling direction switching valve, a bucket opening / closing direction switching valve, a first boom direction switching valve, and a second arm direction switching valve, The second switching valve group includes a turning direction switching valve,
Since the arm direction switching valve, the second boom direction switching valve, the bucket rotating direction switching valve, and the other traveling direction switching valve are configured, a plurality of direction switching valves constituting the first and second switching valve groups are provided. Since it is possible to assemble with a valve connecting body mass-produced as a main hydraulic control device of a hydraulic excavator, it is possible to reduce the manufacturing cost and downsize the hydraulic drive unit.

[Brief description of the drawings]

FIG. 1 is a hydraulic circuit diagram of a hydraulic shovel with a loader front according to an embodiment of the present invention.

FIG. 2 is a side view showing the appearance of a conventional hydraulic excavator with a loader front.

FIG. 3 is a hydraulic circuit diagram according to a conventional example.

[Explanation of symbols]

 1, 2 hydraulic pump 3, 4 discharge flow control device 5 right running direction switching valve 6 bucket opening / closing direction switching valve 7 first boom direction switching valve 8 second arm direction switching valve 9 turning direction switching valve 10th 1-arm directional switching valve 11 2nd boom directional switching valve 12 Bucket rotation directional switching valve 13 Left running directional switching valve 14 Pilot hydraulic pump 15, 16 Fixed throttle valve 17, 18 Pressure regulating valve 19, 20, 24 ~ 27, 37, 38 Pilot valve 21 Bucket rotation operation lever 22 Boom operation lever 23 Arm operation lever 28, 30 Open / close switching valve 29 Hydraulic tank 31-33 Backflow prevention valve 34 Second bucket rotation direction switching valve 40 Running body 41 revolving unit 42 boom 43 arm 44 bucket 45 boom cylinder 46 arm cylinder 47 bucket Nda

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) E02F 9/22 F15B 11/00 F15B 11/17

Claims (3)

(57) [Claims] 1. A boom cylinder, an arm cylinder,
Bucket cylinder, bucket opening / closing cylinder and 2
A plurality of directional switches divided into a first switching valve group and a second switching valve group by controlling the supply of pressure oil supplied from at least one variable displacement hydraulic pump to a plurality of actuators including one traveling motor. A valve, a fixed throttle valve belonging to the first switching valve group and connected downstream of the direction switching valve positioned at the most downstream side thereof, and supplied from the variable displacement hydraulic pump to the first switching valve group. A hydraulic circuit of a hydraulic shovel with a loader front, comprising discharge flow rate control means for detecting the hydraulic pressure of the pressurized oil upstream of the fixed throttle valve and controlling the discharge flow rate of the variable displacement hydraulic pump. The opening / closing switching valve connected to the oil pipeline just upstream of the valve and the opening / closing switching valve are closed in conjunction with the operation for tilting the bucket rotating operation lever for tilting and dumping the bucket. For the dumping operation together to work
The open / close switching valve is kept open without interlocking with the operation of
A bucket directional switching valve for controlling the supply of pressure oil from the hydraulic pump to the bucket cylinder does not belong to the second switching valve group, and is not located on the most upstream side; A hydraulic circuit for a hydraulic shovel with a loader front, wherein an oil pipeline immediately upstream of the switching valve and an inflow port of the bucket direction switching valve are connected by a branch pipeline via a check valve. 2. A second arm direction switching valve for controlling supply of pressure oil from a variable displacement hydraulic pump to an arm cylinder belongs to a first switching valve group, and a tilt interlocking means is an arm operation lever for pushing the arm. The hydraulic circuit of a hydraulic shovel with a loader front according to claim 1, wherein a switching operation of the second arm direction switching valve by the operation of (1) is suppressed. 3. The first switching valve group includes one of a traveling directional switching valve, a bucket opening / closing directional switching valve, a first boom directional switching valve, and a second arm directional switching valve. Turning direction switching valve, first arm direction switching valve, second
2. The hydraulic circuit for a hydraulic shovel with a loader front according to claim 1, further comprising a boom direction switching valve, a bucket rotating direction switching valve, and the other traveling direction switching valve.