JPH093976A - Hydraulic circuit of hydraulic excavator with loader front - Google Patents

Abstract

(57) [Summary] (Modified) [Purpose] To provide a hydraulic circuit of a hydraulic excavator that can combine hydraulic oil from a plurality of hydraulic pumps into a bucket cylinder and drive with a large flow of hydraulic oil. [Structure] Right travel direction switching valve 5 to which pressure oil is supplied from variable displacement hydraulic pump 1, bucket opening / closing direction switching valve 6, first boom direction switching valve 7, first arm direction switching valve 8 Fixed throttle valve 1 provided downstream of the first switching valve group consisting of
5, an open / close switching valve 30 is provided, and the open / close switching valve 30 is controlled to open / close by the outflow pressure oil of the pilot valve 19 that outputs pilot pressure when the bucket rotation operation lever 21 is operated in the tilting direction. By supplying the pressure oil from the hydraulic pump 1 to the confluence with the branch pipe line T6 via the branch pipe line T3 branched from the series connection oil pipe T1 immediately upstream of the switching valve 30, it is required when the bucket tilts. It is possible to supply a large amount of pressure oil to the head side of the bucket cylinder 47.

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 switching valves for controlling the supply of pressure oil to a plurality of actuators including a drive means for a working machine which is divided into a first switching valve group and a second switching valve group. The present invention relates to a hydraulic circuit of a hydraulic excavator with a loader front, which includes

[0002]

2. Description of the Related Art In a hydraulic excavator, a boom, an arm, and a bucket are sequentially rotatably connected to a revolving structure, and are flexibly driven by a cylinder connected between them so that the bucket abuts against the ground or the bucket. Construction work such as scraping out earth and sand is carried out. The earth and sand scraped out are conveyed by the hydraulic excavator to the loading platform of the truck waiting, discharged, and fall. By the way, in order to facilitate the discharge of the earth and sand transported upward from the bucket, a bucket that can be opened and closed between the back part and the rear end of the basket is rotatably attached to the tip part of the working machine. , When excavating the sand from the bucket, a hydraulic excavator with a loader front is known that opens the space between the rear part of the bucket and the rear end of the basket so that the sediment can drop by its own weight along the bottom of the basket of the bucket. ing.

FIG. 2 is a side view showing the external appearance of such a hydraulic excavator with a loader front. As shown in the figure, the hydraulic excavator with a loader front has a traveling body 40 that can travel.
A revolving structure 41 which is rotatable in the horizontal direction is provided on the upper part of the upper part, and a loader front which is a working machine is attached to the front part of the revolving structure 41. The loader front has a boom 42 rotatably attached to the revolving structure 41 in a vertical direction, and an arm 43 rotatably attached to one end of the boom 42.
And a bucket 44 rotatably attached to one end of the arm 43. Revolving structure 41, boom 42,
Direction of the bucket 44 attached to the tip of the loader front by appropriately extending and retracting the boom cylinder 45, the arm cylinder 46, and the bucket cylinder 47, which are attached to extend and retract between the arm 43 and the bucket 44, respectively. Further, the three-dimensional movement direction can be arbitrarily selected and driven, and construction work such as excavation of earth and sand can be performed by bending and extending the working machine.

FIG. 3 is a hydraulic circuit diagram of the hydraulic excavator with the 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 the first and second switching valve groups are provided respectively. Supply pressure oil to the directional control valve. The first switching valve group includes a right traveling direction switching valve 5, a first boom direction switching valve 7, a second bucket rotation direction switching valve 34, a second arm direction switching valve 8 and a bucket opening / closing direction switching valve 6. Belongs to the second switching valve group, the turning direction switching valve 9, the first arm direction switching valve 10, the second boom direction switching valve 11, the bucket rotation direction switching valve 12, and the left traveling direction switching valve 13. Belongs to.

The circuit connection of the direction switching valves belonging to the first switching valve group is such that the right traveling direction switching valve 5 connected on the most upstream side is connected to the first boom direction switching valve 7 connected in parallel to each other.
The second bucket rotation 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 provided in the outflow port at one switching position of the second bucket rotation direction switching valve 34. It is connected in series. In addition,
Since the swing operation of the swing body 41 and the opening / closing operation of the bucket 44 are often performed at the same time, the bucket opening / closing direction switching valve 6 does not belong to the second switching valve group to which the swing direction switching valve 9 belongs, and the first switching It is designed to belong to the valve group.

Direction switching valves 9 to 13 belonging to the second switching valve group
In the circuit connection, all the directional control valves 9 to 13 are connected in parallel. However, the first arm direction switching valve 10, the bucket rotation direction switching valve 12, and the left traveling direction switching valve 13
A throttle valve is provided in the parallel connection inflow side pipe line. 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 bucket rotation direction switching valve 1 that supplies pressure oil to the head side of the bucket cylinder 47.
It is connected to two outflow ports.

The pressure oil discharged from the hydraulic pumps 1 and 2 also flows into the oil passages T1 and T2 connected in series, respectively. The right traveling direction switching valve 5, the first boom direction switching valve 7 and When the second arm directional control valve 8 is in the neutral position, the second arm directional control valve 8 flows downstream via the series-connected oil passage T1, and the second directional control valve group includes a swiveling directional control valve 9 and a first arm directional control valve. 10. When the bucket rotation direction switching valve 12 and the left traveling direction switching valve 13 are respectively in the neutral position, they flow downstream via the series-connected oil passage T2.

A fixed throttle valve 15, 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 series-connected oil passages T1, T2, respectively. The maximum values of the hydraulic pressures p1 and p2 on the upstream side of the fixed throttle valves 15 and 16 are regulated, respectively. Also,
Oil pressure p1 on the upstream side of the fixed throttle valve 15 and the fixed throttle valve 16,
p2 is guided to the discharge flow rate control devices 3 and 4 which control the discharge flow rates of the hydraulic pumps 1 and 2, respectively, and the discharge flow rate control devices 3 and 4 of the hydraulic pumps 1 and 2 are respectively based on the introduced hydraulic pressures p1 and p2. The discharge flow rates of the hydraulic pumps 1 and 2 are 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, either of the corresponding pilot valves 19 and 20 is switched depending on the operation direction. Pressure oil on the outflow side flows into either of the control chambers 12a and 12b of the bucket rotation direction switching valve 12, and the spool position of the bucket rotation direction switching valve 12 is switched, so that the bucket 44 tilts or dumps. To do.
Further, 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 rotation direction switching valve 34 via the switching valve 48.

Therefore, when the switching valve 48 is in 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 from the pilot valve 19 is guided to the control chamber 34b. Due to
The spool position of the second bucket rotation direction switching valve 34 is switched to the right side position in the drawing, and the pressure oil discharged from the hydraulic pump 1 is transferred to the bucket cylinder 47 via the second bucket rotation direction switching valve 34 and the backflow prevention valve 35. Guided to the head side inlet port.

When the bucket opening / closing operation lever 36 is operated, the pilot valves 37, 3 are changed depending on the operation direction.
Any one of 8 switches and the pressure oil on the outflow side flows into either of the control chambers 6a and 6b of the bucket opening / closing direction switching valve 6. Further, the high-pressure side pilot pressure oil selected by the high-pressure selection valve 39 connected between the outflow-side pilot pipes of the pilot valves 37 and 38 is supplied to the other control chamber 34a of the second bucket rotation direction switching valve 34. At the same time, it is guided to the control chamber 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 pilot pressure oil from the outflow side of the pilot valve 19 to the one control chamber 34b of the second bucket rotation direction switching valve 34 is shut off. To be done.

Therefore, the second bucket rotating direction switching valve 3
Regardless of whether or not the bucket rotating operation lever 21 is operated, the spool position is switched to the left side position in the drawing by the pilot pressure oil guided to the other control chamber 34a, and the pressure oil discharged from the hydraulic pump 1 is the second pressure oil. It is guided to the bucket opening / closing direction switching valve 6 via the bucket rotation direction switching valve 34. Therefore, the pilot pressure oil that flows into either of the control chambers 6a and 6b switches the spool position of the bucket opening / closing direction switching valve 6 to open / close between the rear portion of the bucket 44 and the basket.

As described above, when the tilting operation is performed in a state where the back portion of the bucket 44 is not opened and closed with the basket, the bucket rotation operation lever 21 is operated to move the pilot valve 19 from the illustrated state. By switching and pilot pressure oil flowing out of the pilot valve 19 being guided to the control chamber 12b, the spool position of the bucket rotation direction switching valve 12 is switched to the right side position in the drawing, and the hydraulic pressure flowing out of the bucket rotation direction switching valve 12 is changed. The oil discharged from the pump 2 flows into the head-side inflow port of the bucket cylinder 47, and the pilot pressure oil flowing out from the pilot valve 19 is transferred via the switching valve 48 to the one control chamber 34b of the second bucket rotation 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, the hydraulic pressure is changed. 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. As a result, 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 when excavating earth and sand. Therefore, the lifting operation of the bucket 44, which generally requires a powerful and quick operation, can be efficiently performed.

On the other hand, when the rear part of the bucket 44 is performing the opening / closing operation with the basket, the switching valve 48 is switched to the lower position in the figure, and the second bucket rotation direction switching valve 34 is moved.
The oil passage connected to one of the control chambers 34b is the oil tank 29.
And the spool position of the second bucket rotation direction switching valve 34 is switched to the left side position in the drawing by the pilot pressure oil that has flowed out of either the pilot valve 37 or 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 the operation of the bucket rotating operation lever 21 during the opening / closing operation of the bucket 44, it is generally considered that it is not necessary to perform the quick and powerful operation. Therefore, when the bucket 44 rotates, the flow rate of the pressure oil required by the bucket cylinder 47 is sufficient only with the oil discharged from the hydraulic pump 2 supplied from the bucket rotation direction switching valve 12.

[0016]

In the above-mentioned prior art,
Depending on the operating state of the bucket opening / closing operation lever 36, the pressure oil discharged from the hydraulic pump 1 is directed to the bucket cylinder 47 side by the second bucket rotation direction switching valve 34, or the bucket opening / closing direction switching is performed. Since it can be switched to the valve 6 side, when performing a powerful and quick operation such as excavating earth and sand, combine the pressure oil discharged from the hydraulic pump 1 with the pressure oil discharged from the hydraulic pump 2. The bucket 44 can be swung quickly with a strong force by guiding it to the head side inflow port of the bucket cylinder 47, and when the back part of the bucket 44 is opening and closing with the basket, the bucket cylinder 47
Since only the pressure oil discharged from the hydraulic pump 2 can be introduced to the side, the flow rate of the pressure oil supplied to the head side of the bucket cylinder 47 is appropriately adjusted when the bucket 44 is tilted slowly without applying a large load. It is possible to control the opening / closing operation between the bucket 44 and the basket on the back of the bucket 44 while suppressing the value to any value.

By the way, in a general hydraulic excavator, the direction switching valve for controlling the flow rate of the pressure oil supplied to the actuator is mass-produced as a main hydraulic control device of the hydraulic excavator. The directional switching valves 5 to 13, 34 excluding the directional switching valve 6 are assembled as a valve connecting body that is a combination of seven directional switching valves. Therefore, in order to realize the hydraulic circuit to which the above-mentioned conventional technique is applied, a bucket opening / closing directional switching valve specially ordered for a mass-produced product in which the directional switching valves 5 to 13, 34 excluding the bucket opening / closing directional switching valve 6 are connected in series. 6 or all direction switching valves 5 to 13, 34 including the bucket switching direction switching valve 6
It is necessary to newly produce a small quantity of custom-made products that are lined up.

The former means requires a space for attaching the directional switching valve 6 for opening and closing the bucket and for laying a pipe line between these directional switching valves, which increases the size of the machine room and the mounting structure. However, the manufacturing process becomes complicated, and the labor and cost required for manufacturing are significantly increased. The latter method not only adds new costs for custom-designed products and molds, but also increases the manufacturing unit price due to small-scale production. The present invention solves such a problem in the prior art, and when tilting the bucket, the pressure oil from a plurality of hydraulic pumps can be combined with the bucket cylinder to drive with a large flow of pressure oil. An object of the present invention is to provide a hydraulic circuit for a hydraulic excavator with a loader front, which can simplify the structure of the hydraulic circuit and reduce the space occupied by the hydraulic drive unit by eliminating the need for a direction switching valve for merging.

[0019]

In order to solve the above problems, the present invention provides at least one variable displacement hydraulic pressure for a plurality of actuators including a boom cylinder, an arm cylinder, a bucket cylinder, a bucket opening / closing cylinder and two traveling motors. A plurality of directional switching valves for respectively controlling the supply of the pressure oil supplied from the pump, and the first switching valve in which the plurality of directional switching valves are divided into a first switching valve group and a second switching valve group. Of the fixed throttle valve connected to the downstream side of the direction switching valve that belongs to the group and is located on the most downstream side, and the fixed throttle valve of the pressure oil supplied from the variable displacement hydraulic pump to the first switching valve group. In a hydraulic circuit of a hydraulic excavator with a loader front equipped with a discharge flow rate control means for detecting a hydraulic pressure on the upstream side and controlling a discharge flow rate of the variable displacement hydraulic pump, An opening / closing switching valve connected to an oil pipe immediately upstream of the constant throttle valve; and interlocking means for closing the opening / closing switching valve in conjunction with operation of a bucket rotation operation lever for tilting the bucket. The bucket direction switching valve that controls the supply of the pressure oil from the hydraulic pump to the bucket cylinder belongs to the second switching valve group, is not located on the most upstream side, and is located immediately upstream of the on-off switching valve. A branch pipeline branched from the oil pipeline is connected to an inflow port of the bucket directional control valve via a check valve.

[0020]

Operation: The plurality of directional switching valves belonging to the first switching valve group are supplied with pressure oil from the variable displacement hydraulic pump, and the plurality of directional switching valves belonging to the second switching valve group are supplied with pressure oil from the hydraulic pump. . When the driver operates the bucket rotation operation lever for tilting the bucket (upward rotation operation), the bucket rotation direction switching valve switches and
In conjunction with this, the interlocking means causes the on-off switching valve to close.
By the closing operation of the open / close switching valve, the pressure oil supplied from the variable displacement hydraulic pump to the first switching valve group passes through the branch pipe branched from the oil pipe immediately upstream of the open / close switching valve through the check valve. Flow into the inflow port of the bucket directional control valve. Therefore, the pressure oil from the variable displacement hydraulic pump that flows in through the branch pipe and the pressure oil from the hydraulic pump that is supplied to the second switching valve group merge into the inflow port of the bucket direction switching valve, A large amount of pressure oil flows into the bottom side of the bucket cylinder, and the bucket tilts quickly and powerfully.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a hydraulic circuit diagram of a hydraulic excavator with a loader front according to an embodiment of the present invention. Parts that are the same as or can be regarded as the same as those in the conventional example are denoted by the same reference numerals, and duplicate description thereof 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 in mutually opposite directions. , 14 are pilot hydraulic pumps, 2
Reference numerals 2 and 23 are boom operation levers and arm operation levers, respectively, and 24, 25 and 26, 27 are pilot valves which are switched by operating the boom operation lever 22 and the arm operation lever 23, respectively.

Further, 28 is an operation lever 2 for rotating the bucket.
It is switched by the pilot pressure oil flowing out from the pilot valve 19 which is switched when the tilting operation is performed by the operation 1 and is switched to the lower position in the drawing when the arm operating lever 23 is operated in the direction to extend the arm cylinder 46. An on-off switching valve that controls so that the outflow of the pilot pressure oil that has flowed out from the pilot valve 27 to the one control chamber 8b of the second arm direction switching valve 8 is blocked.
Reference numeral 30 denotes a fixed throttle valve 15 for the pressure oil flowing through the serially connected oil passage T1 by the pilot pressure oil flowing out from the pilot valve 19.
It is an open / close switching valve that can switch on and off of the outflow to.

Further, 31 is a backflow prevention valve provided in the middle of the branch pipe line T3 from the outflow port of the second arm direction switching valve 8 of the series connection oil path T1, and 32 is the bucket rotation direction switching valve 12. A check valve is provided in the middle of the branch line T6 of the parallel connection line via a throttle, and 33 is the middle of the branch line from the series connection oil line T2 side of the bucket rotation direction switching valve 12 to the inflow port. Is a check valve provided in the. As shown in the figure, the branch pipe T6 joins the series-connecting oil passage T2 downstream of the check valve 33 of the branch pipe reaching the inflow port of the bucket rotation direction switching valve 12 to join the series-connecting oil passage T6.
The branch line T3 from 1 is the check valve 32 of the branch line T6.
Merge downstream of.

Pilot lines on the outflow side of the pilot valves 20, 19 of the bucket rotation operation lever 21 are respectively in control chambers 12a, 12b of the bucket rotation direction switching valve 12.
In addition, the pilot valves 24 and 25 of the boom operation lever 22
Of the first operation direction switching valve 7 for the first boom and the respective control rooms 11a, 11b of the second direction switching valve 11 for the second boom. The pilot lines on the outflow side of the pilot valves 26 and 27 are connected to the control chambers 10a and 10b of the first arm directional control valve 10, respectively. Further, the pilot line on the outflow side of the pilot valve 26, which is switched to the lower position in the drawing when the arm operation lever 23 is operated to extend the arm cylinder 46, controls one side of the second arm direction switching valve 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 and to the other control chamber 8b of the second arm direction switching valve 8 respectively.

Oil pressure p1 upstream of the fixed throttle valves 15 and 16
, P2 are transmitted to the discharge flow rate control devices 3 and 4, respectively, and the discharge flow rate control devices 3 and 4 are transmitted to the hydraulic pressures p1 and p, respectively.
The hydraulic pumps 1 and 2 are constructed according to the known configuration and operation based on 2.
The discharge flow rates of the hydraulic pumps 1 and 2 are controlled by adjusting the tilt angle of the hydraulic pump. The left and right traveling operation levers, bucket opening / closing operation levers, turning operation levers, and pilot valves that can be switched by operating these operation levers, and pipelines that connect the control chambers of the corresponding direction switching valves The hydraulic circuit for this is the same as the pilot hydraulic circuit including the boom operation lever 22 and the pilot valves 24, 25, and is not shown.

Next, the operation of this embodiment will be described. The left and right traveling motions, the turning motions, and the raising and lowering motions of the boom 42 are the same as those of the conventional example, and therefore the description thereof will be 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 drawing, and the pilot pressure oil from the pilot hydraulic pump 14 flows out to the pilot line on the outflow side. This pilot pressure is guided to the control chamber 10b of the first arm direction switching valve 10 and flows into the inflow port of the opening / closing switching valve 28. When the bucket 44 is not tilted, the control pressure of the on-off switching valve 28 is equal to the tank pressure, so the switching position of the on-off switching valve 28 is at 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 the spool position of the second arm direction switching valve 8 is switched to the right switching position in the figure. Let

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 figure by the pilot pressure oil guided from the pilot valve 27 to the control chamber 10b by operating the arm operating lever 23. ,
Discharge of the hydraulic pumps 1, 2 to the downstream side of the second arm directional switching valve 8 of the series connection oil passage T1 of the first switching valve group and the downstream side of the first arm directional switching valve 10 of the series connection oil passage T2. Almost no oil 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) to increase the tilt angles of the hydraulic pumps 1 and 2. Therefore, the head side inflow port of the arm cylinder 46 is connected to the first arm direction switching valve 10 and the second arm direction switching valve 10.
A large amount of pressure oil flows in through the arm direction switching valve 8.
For example, a small amount of pressure oil from the hydraulic pump 2 flows into the bucket rotation direction switching valve 12 located on the downstream side of the first arm direction switching valve 10, and the serial connection oil passage T1.
Since the discharge oil of the hydraulic pump 1 hardly flows to the downstream side of the second arm directional control valve 8 and therefore to the branch pipe line T3,
Although the total flow rate of the pressure oil flowing into the inflow port of the bucket rotation direction switching valve 12 is small, generally, in a hydraulic excavator with a loader front, the load at the time of the dumping operation of the bucket 44 is small, and quick operation is also required. Since there are many cases where this is not done, no problem will occur in the actual work.

On the other hand, when the bucket 44 is being tilted, pilot pressure oil from the pilot hydraulic pump 14 controls the open / close switching valve 28 via the pilot valve 19 of the bucket rotating operation lever 21. Guided to the port, the switching position of the open / close switching valve 28 is switched from the open state shown in the figure to the switching position not shown in the figure. As a result, the pilot pressure oil flowing out from the pilot valve 27 is blocked from flowing out to the other control chamber 8b of the second arm directional switching valve 8 by the open / close switching valve 28, so that the spool of the second arm directional switching valve 8 is blocked. The position is kept neutral. Therefore,
Only the pressure oil from the hydraulic pump 2 flowing out from 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 flowing out from the pilot valve 19 of the bucket rotating operation lever 21 is controlled by the opening / closing switching valve 30 provided on the downstream side of the confluence of the series connecting oil passage T1 and the branch pipe passage T3. Since it is guided to the chamber, the switching position of the on-off switching valve 30 is switched from the open state to the right side position in which it is in the disconnection state, and the pressure flowing out to the downstream side of the second arm directional switching valve 8 of the series connection oil passage T1. Oil fixed throttle valve 1
Prevent outflow to the 5 side. The discharge flow rate control device 3 that detects a decrease in the hydraulic pressure p1 by closing the open / close switching valve 30.
Controls to greatly increase the tilt angle of the hydraulic pump 1. Therefore, when the right traveling motor is not driven, the discharge oil of the hydraulic pump 1 is at least downstream of the directional switching valve 8 for the second arm of the serial connection oil passage T1 via the parallel circuit of the first switching valve group. Since it flows out, pressure oil from the hydraulic pump 1 is supplied to the confluence point with the branch pipe line T6 via the branch pipe line T3, and a large amount of pressure on the head side of the bucket cylinder 47 required when the bucket 44 is tilted. Oil can be supplied. The check valves 31 and 32 prevent the discharge oil of the hydraulic pump 1 from flowing back to the side of the oil passage T1 connected in series and the side of the parallel pipes of the second switching valve group, respectively.

When the combined operation of the rotating operation of the bucket 44 and the opening / closing operation of the rear part 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 Since 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 side of the branch pipe line T3, and the pressure oil flowing into the inflow port of the bucket rotation direction switching valve 12 is the second. The upper limit of the pressure oil from the hydraulic pump 2 supplied through the parallel pipes of the switching valve group is substantially the upper limit.
Since there is almost no swiveling or moving with a strong force, there is no hindrance to the operability.

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

The pilot valve 27, which is switched by the operation of the arm operating lever 23 when the arm 43 is pushed, and the other control chamber 8b of the second arm directional switching valve 8 belonging to the first switching valve group. By providing the open / close switching valve 28 in the pilot line between them and closing the bucket 44 when the bucket 44 is tilted, the hydraulic pump 1 of the hydraulic pump 1 is operated when a combined operation of the tilting of the bucket 44 and the pushing of the arm 43 is performed. This prevents a large amount of the discharged oil from flowing into the second arm directional control valve 8 and flowing out to the branch pipe line T3 on the downstream side from being almost exhausted. As a result, the arm 4 that is often used in the case of loading the excavated earth and sand onto a truck subsequent to the earth and sand excavation work.
It is possible to prevent the operability of the tilting operation of the bucket 44 from being impaired during the combined operation with the pushing operation of No. 3.

Further, unlike the conventional example, it is not necessary to combine an additional directional switching valve as the hydraulic control device, and it is constituted only by a valve connecting body which is combined with seven directional switching valves similar to other hydraulic excavators. Therefore, it is possible to reduce the manufacturing unit price and the assembly cost, and to reduce the space occupied by the hydraulic circuit device. Further, the opening / closing operation of the basket of the bucket 44 does not need to operate the two directional switching valves as in the conventional example, and only needs to operate the single directional switching valve 6 for opening / closing the bucket.
The operability of opening and closing 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 on the upstream side of the fixed throttle valves 15 and 16 provided on the most downstream side of the serially connected oil passages T1 and T2, respectively. Although the tilt angles of 2 are controlled respectively, the differential pressure sensor detects the differential pressure between the upstream side and the downstream side of the fixed throttle valves 15 and 16, and the discharge flow rate control devices 3 and 4 use the detection signal. Tilt angle control may be performed. Further, the opening / closing switching valve 30 is opened and closed by controlling the operation amount of the bucket rotating operation lever 21 by converting it into the pilot hydraulic pressure by opening and closing the pilot valve 19, but the bucket rotating operation lever 21 is constituted by an electric lever. Then, the control may be performed according to the detected detection signal.

[0035]

As described above, according to the first aspect of the invention, it is located on the most downstream side in the first switching valve group in association with the operation of the bucket rotation operation lever for tilting the bucket. A branch line that branches off from the oil pipe line immediately upstream of the on-off switching valve while closing the opening / closing change-over valve connected to the oil pipe line on the upstream side of the fixed throttle valve connected downstream of the direction switching valve. Is connected to the inflow port of the bucket directional switching valve via a backflow prevention valve, so when the driver operates the bucket rotation operation lever to tilt the bucket, the on-off switching valve interlocks with this. 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 through the branch pipe line. Pressure 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 invention, the directional switching valve for the second arm 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. Since the switching operation of the second arm directional switching valve by the operation of the arm operation lever for pushing the arm is suppressed in conjunction with the operation of
When a combined operation of the tilting operation of the bucket and the pushing operation of the arm is performed in the operation such as loading the excavated earth and sand into the truck following the earth and sand excavation work, the oil discharged from the hydraulic pump is directed toward the second arm. It is possible to prevent the flow rate of the pressure oil that flows in a large amount into the switching valve and flows out to the branch pipe on the downstream side from becoming almost zero, and to perform the combined operation 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 is the directional switching valve for turning, and the first
Since the arm directional switching valve, the second boom directional switching valve, the bucket rotation directional switching valve, and the other traveling directional switching valve are included, a plurality of directional switching valves forming the first and second switching valve groups are provided. Since the valve assembly can be assembled by mass production as a main hydraulic control device of a hydraulic excavator, it is possible to reduce the manufacturing unit price and downsize the hydraulic drive unit.

[Brief description of drawings]

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

FIG. 2 is a side view showing an appearance of a hydraulic excavator with a loader front according to a conventional example.

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

[Explanation of symbols]

 1, 2 hydraulic pumps 3, 4 discharge flow control device 5 right traveling 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 direction switching valve 11 second boom direction switching valve 12 bucket rotating direction switching valve 13 left traveling direction 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 Traveling body 41 Revolving Body 42 Boom 43 Arm 44 Bucket 45 Boom Cylinder 46 Arm Cylinder 47 Bucket System Nda

Claims (3)

[Claims] 1. A boom cylinder, an arm cylinder,
Bucket cylinder, bucket opening and closing cylinder and 2
A plurality of directional switching valves that respectively control the supply of pressure oil supplied from at least one variable displacement hydraulic pump to a plurality of actuators including one traveling motor; and the plurality of directional switching valves include a first switching valve group and a second switching valve group. A fixed throttle valve connected downstream of the directional switching valve located on the most downstream side and belonging to the first switching valve group divided into two switching valve groups, and the variable displacement hydraulic pump 1 Hydraulic pressure of a hydraulic excavator with a loader front equipped with discharge flow rate control means for detecting the hydraulic pressure of the pressure oil supplied to the switching valve group on the upstream side of the fixed throttle valve to control the discharge flow rate of the variable displacement hydraulic pump In the circuit, the opening / closing switching valve is closed in conjunction with the operation of the opening / closing switching valve connected to the oil pipe line immediately upstream of the fixed throttle valve and the bucket rotation operation lever for tilting the bucket. The bucket directional switching valve, which has a moving means and controls the supply of the pressure oil from the hydraulic pump to the bucket cylinder, belongs to the second switching valve group and is not located on the most upstream side, and the opening / closing switching is performed. A hydraulic circuit of a hydraulic excavator with a loader front, wherein a branch pipe branched from an oil pipe immediately upstream of the valve is connected to an inflow port of the bucket directional control valve via a check valve. 2. The directional switching valve for the second arm, which controls 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 interlocking means is the operation lever for the arm for pushing the arm. The hydraulic circuit of the hydraulic excavator with a loader front according to claim 1, wherein a switching operation of the directional control valve for the second arm by operation is suppressed. 3. The first switching valve group comprises 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, and the second switching valve group is Turning direction switching valve, first arm direction switching valve, second
The hydraulic circuit for a hydraulic excavator with a loader front according to claim 1, comprising a boom direction switching valve, a bucket rotation direction switching valve, and the other traveling direction switching valve.