JPH0960032A - Self-leveling device of shovel loader - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the amount of natural forward inclination of a bucket when the bucket is exerted with a load in a horizontal position and to secure smooth and simultaneous operability of a lift arm with the bucket in the self- leveling device of a shovel loader. SOLUTION: When a lift arm is raised, oil returned from a lift cylinder is fed to a flow dividing valve 22 from the open center passage 12 of a control valve 7 via a first leveling spool 21. Part of pressure oil divided here is fed to the end of a dump cylinder 6, while oil returned from the rod side of the dump cylinder is returned to a tank 11 via a second leveling spool 25 to level a bucket. When the lift arm and the bucket are operated simultaneously, the oil returned from the dump cylinder 6 is returned to the tank 11 by opening a check valve 27 in a bypass circuit 26 connecting a passage 19 with a return passage 20.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydraulic self-leveling device for holding a bucket in a horizontal position during operation of a lift arm in a shovel loader.

[0002]

2. Description of the Related Art As a conventional hydraulic self-leveling device, for example, U.S. Pat. No. 4,561,342 and drawings are known, and FIG. 6 shows a circuit diagram of the self-leveling device. There is. This includes the lift spool 38 for controlling the lift cylinder 34 and the dump cylinder 3.
In a hydraulic circuit having a cargo handling control valve 37 including a 6-control dump spool 39 in the form of a series circuit, the return oil from the lift cylinder 34 is supplied to the self-leveling valve 42 before returning to the control valve 37. The self-leveling valve 42 is configured to divide the flow into the dump cylinder 36 via the flow dividing valve, and the self-leveling valve 42 includes a flow dividing valve 43 having two fixed and variable orifices for dividing the return oil and two check valves 44, 45 and an unload spool 46.

Then, when the lift spool 38 is switched to the raised position in order to raise the lift arm 33, the pressure oil supplied from the hydraulic pump 40 is lifted by the lift spool 38.
Through the end of the lift cylinder 34 to raise the lift arm 33. At this time, the oil pushed out from the rod side of the lift cylinder 34 flows into the A port of the self-leveling valve 42, and the flow dividing valve 43 Oil is diverted to the B port and the D port by the fixed orifice and the variable orifice, and the oil flowing out from the D port flows into the end side of the dump cylinder 36. Then, the pressure on the rod side of the dump cylinder 36 rises, and the unload spool 4
When the pressure at the right end of 6 in the figure becomes high and overcomes the spring force, the oil pushed out from the rod side of the dump cylinder 36 enters the C port, passes through the unload spool 46, and B
It flows out of the port and returns to the tank 41.

As described above, in the conventional self-leveling device, a part of the return oil flowing out from the rod side of the lift cylinder 34 is made to flow into the dump cylinder 36 via the self-leveling valve 42 before returning to the control valve 37. Thus, the bucket 35 is tilted forward in accordance with the rise of the lift arm 33 to perform self-leveling. Note that the self-leveling is not performed when the lift arm 33 descends.

By the way, in a horizontal state in which a load (such as earth and sand or gravel) is loaded on the bucket 35, a load acts in a direction in which the bucket 35 is tilted forward, and pressure is exerted on the rod side of the dump cylinder 36. This pressure acts on the rod side port of the dump spool 39 in the control valve 37 in the case of levelingless without the self-leveling function. Therefore, although there is a risk that the bucket 35 naturally tilts forward due to oil leakage from the rod side port, the influence degree is small because there is only one oil leakage portion. However, in the case of the above-described conventional self-leveling device, since the lift cylinder 34, the dump cylinder 36, and the self-leveling 42 are connected to each other, the rod-side pressure of the dump cylinder 36 becomes the following part. Acts to cause oil leakage.

First, oil leakage from the rod side port of the dump spool 39 (same as levelingless). Secondly, oil leaks from the end side port of the dump spool 39 through the C port of the self-leveling valve 42 and the D port.
Thirdly, in the case where oil leaks from the rod side port of the lift spool 38 through the C port of the self-leveling valve 42 through the B port, or when the lift cylinder 34 naturally descends, to the rod side of the lift cylinder 34. Flow of. As described above, in the case of the conventional self-leveling device, the total amount of oil leakage increases due to the large number of oil leak points, and the bucket 35 placed in a horizontal state has a considerably large natural forward lean as compared with the levelingless type. It can happen.

Therefore, as a solution to the above problems, the present applicant returns the pressure oil extruded from the rod side of the lift cylinder to the control valve, diverts it by the self-leveling valve, and then sends it to the dump cylinder. Excavator loader self-leveling device designed to perform bucket self-leveling (Japanese Patent Application No. 7-
128171) is proposed. Hereinafter, this is referred to as a prior invention.

FIG. 7 shows the invention of the prior application, the outline of which will be described below. A lift spool 54 for controlling the lift cylinder 51 and a dump spool 55 for controlling the dump cylinder 52 are provided downstream of the open center passage 56 of the control valve 53 in the form of a serial circuit. A self-leveling valve 59 for leveling a bucket (not shown) by operating 52 in the forward tilt direction is installed.

When the lift spool 54 is switched to the rising side and pressure oil from the hydraulic pump 57 is sent to the end side of the lift cylinder 51 to lift a lift arm (not shown), the return oil on the rod side of the lift cylinder 51 The oil that has flown into the self-leveling valve 59 through the open center passage 56 of the control valve 53, is divided into the tank side passage 61 and the cylinder side passage 62 by the flow dividing valve 60, and the oil divided into the cylinder side passage 62 is leveled spool 6
Sent to 3. At this time, the leveling spool 63 is provided with a throttle 65 provided in the end side passage 64 of the lift cylinder 51.
Since the non-leveling position a is switched to the leveling position b by the pilot pressure introduced from before and after, the oil flowing from the flow dividing valve 60 is sent to the end side of the dump cylinder 52, and the return oil on the rod side flows through the return passage 70. After that, it is returned to the tank. Thus, bucket leveling is performed.

[0010]

However, according to the above-mentioned prior invention, the pressure on the rod side of the dump cylinder 52, which is the load side in the horizontal state when the bucket is loaded with the load, is determined by the rod side port of the dump spool 55. And, since it only acts at two places, the rod side port of the leveling spool 63, the oil leakage part is reduced compared to the conventional one, but the effect is still not sufficient compared to the levelingless, and the lift The operability may be impaired when the arms and the bucket are simultaneously operated, particularly when the lift arm is raised and the bucket is tilted backward.

That is, FIG. 8 is a circuit diagram showing the simultaneous operation of raising the lift arm and tilting the bucket backward, and the arrows indicate the flow of pressure oil. In this case, the lift cylinder 51
Since the leveling spool 63 is shifted to the leveling position b by the pilot pressure introduced from before and after the throttle 65 of the end side passage 64, the pressure oil that should flow into the rod side of the dump cylinder 52 via the dump spool 55. A circuit that flows from the throttle 68 of 63 to the tank 58 via the return passage 67 is configured. At this time, since the bucket load acts on the rod side and the pressure is high, the pressure oil does not flow to the rod side but tends to flow to the tank side. Therefore, when the diaphragm 68 is set to be considerably strong, simultaneous operation is possible, but at that time, the operating speed of the dump cylinder 52, that is, the backward tilting speed of the bucket is slowed down, and the lifting speed of the lift cylinder 51 is also increased. Will result in a decline.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a self leveling device for a shovel loader when a bucket is placed in a horizontal state under load. The effect of reducing the amount of natural forward tilt of the bucket can be further enhanced, and the operability during simultaneous operation of the lift arm and the bucket is not impaired.

[0013]

In order to solve the above problems, the present invention takes the following means. That is, claim 1
Is a self-leveling excavator loader including a machine base, a lift arm attached to the machine base and vertically operated by a lift cylinder, and a bucket attached to the lift arm and tilted forward and backward by a dump cylinder. A cargo control valve including a lift spool for controlling the lift cylinder and a dump spool for controlling the dump cylinder in the form of a series circuit, and an inflow device provided downstream of an open center passage of the control valve. A first leveling spool capable of switching between a non-leveling position for returning the pressure oil to the tank and a leveling position for sending the pressure oil to the dump cylinder side, and the pressure oil sent from the first leveling spool to the tank side and the dump cylinder side. A diversion valve for diversion, the dump spool, and the dump cylinder. Second leveling spool that is switchable between a non-leveling position that allows the flow of pressure oil between the rod sides of the damper and a leveling position that returns the pressure oil on the rod side of the dump cylinder to the tank, and the open center passage. A pressure control valve that allows pressure oil in the passage to flow out to a return passage to the tank when the pressure in the passage exceeds a set pressure, and the first and second leveling spools include the lift valve. It is characterized in that it is configured to be switched to the leveling position when the spool is independently operated on the lift arm rising side.

According to the invention of claim 1 configured as described above, when the lift spool is switched to raise the lift arm and pressure oil from the hydraulic pump is sent to the end side of the lift cylinder, the rod side of the lift cylinder is moved. The return oil returns to the lift spool and flows into the first leveling spool through the open center passage. At this time, since the first and second leveling spools are respectively switched to the leveling positions, the inflow pressure oil is sent from the first leveling spool to the flow dividing valve, and divided into the tank side and the cylinder side, and The oil diverted to the cylinder side is sent to the end side of the dump cylinder. At this time, the return oil pushed out from the rod side of the dump cylinder flows out to the tank through the second leveling spool. Thus,
The bucket is leveled as the lift arm rises.

By the way, in a horizontal state where a load is loaded on the bucket, a load acts in a direction in which the bucket is inclined forward, and pressure is exerted on the rod side of the dump cylinder. According to the invention of claim 1, the pressure only acts on the rod side port of the second dump spool of the self-leveling valve.
That is, the oil leakage point related to the horizontal holding of the bucket is
Limited to the rod side port of the second dump spool,
Therefore, the leak amount is very small.

Further, according to the first aspect of the invention, when the lift arm and the bucket are simultaneously operated, the pressure oil sent through the dump spool is directly supplied to the dump cylinder or the second.
The return oil from the dump cylinder is returned to the open center passage of the control valve, and then flows out to the tank via the pressure control valve of the self-leveling valve. As a result, simultaneous operation of the lift arm and the bucket can be smoothly performed.

[0017]

The present invention is preferably implemented in the following modes. (A) In the self-leveling device for a shovel loader according to claim 1, a self-leveling valve is obtained by combining and integrating a first leveling spool, a flow dividing valve, a second leveling spool, and a pressure control valve. Configure. When such a configuration is adopted, the self-control valve can be made compact, which is advantageous in handling the piping.

[0018]

Embodiments of the present invention will be specifically described below with reference to FIGS. FIG. 2 is a schematic side view of the shovel loader. As shown, the shovel loader is mounted on the machine base 1
A lift arm 3 attached to a pillar 2 at the rear of the machine base 1, and a bucket 5 attached to the tip of the lift arm 3. The lift arm 3 is lifted and lowered by a lift cylinder 4, and the bucket 5 is a dump cylinder. The tilting operation is performed by 6 in the forward and backward directions.

FIG. 1 is a hydraulic circuit diagram of a hydraulic self-leveling device for holding the bucket 5 in a horizontal posture when the lift arm 3 is raised. The self-leveling device will be described below with reference to FIG. As shown in the drawing, the control valve 7 for cargo handling has a circuit configuration of lift operation priority (position on the upstream side), and a lift spool 8 for controlling the lift cylinder 4 and a dump spool 9 for controlling the dump cylinder 6 are connected in series. It is included in the form of a (series) circuit and is provided with an open center passage 12 for sending the pressure oil sent from the hydraulic pump 10 downstream when both spools 8 and 9 are in the neutral position.

A self-leveling valve 18 is provided downstream of the open center passage 12 of the control valve 7.
Is connected, and the pressure oil flowing out from the A port of the control valve 7 flows into the B port of the self-leveling valve 18. Next, the self-leveling valve 18 will be described. The self-leveling valve 18 includes a first leveling spool 21 that controls the flow direction of the pressure oil that flows into the passage 19 from the B port, a diversion passage 24 that is provided on the downstream side thereof and that communicates the pressure oil to the tank 11, and a dumper. The diversion valve 22 that diverts to a diversion passage 23 that communicates with the end side of the cylinder 6 and a second leveling spool 25 that controls the pressure oil flow direction on the rod side of the dump cylinder 6 are provided.

The first leveling spool 21 is a 6-port 2-position pilot control type switching valve, which is always held by a spring at a non-leveling position a shown in the figure and is switched to a leveling position b by pilot pressure. Then, at the non-leveling position a, the pressure oil flowing from the passage 19 is sent to the return passage 20, and at the leveling position b,
The pressure oil is sent to the flow dividing valve 22. The return passage 20
After being discharged from the C port, the pressurized oil is flown into the D port of the control valve 7, passes through the return passage 17, and is discharged into the tank 11.

The passage 19 is connected to the return passage 20 by a bypass passage 26, and the bypass passage 26 is provided with a spring-equipped check valve which allows outflow of pressure oil when the pressure in the passage 19 exceeds a set value. A valve 27 is provided. The check valve 27 is one of the pressure control valves according to claim 1.
An example is shown, and the set pressure is set higher than the pressure required to tilt the dump cylinder 6 forward. On the other hand, the second leveling spool 25 for controlling the pressure oil flow direction on the rod side of the dump cylinder 6 is a 3-port 3-position pilot control type switching valve, and is always a spring for the leveling position shown. It is held at a and is switched to the non-leveling position b or c by the pilot pressure.

Thus, the end side and rod side conduits 15 and 16 connecting the dump cylinder 6 and the dump spool 9 are connected.
Respectively pass through the self-leveling valve 18, of which the rod side conduit 16 is connected to the second leveling spool 25. The second leveling spool 25 communicates with the return passage 28 that communicates the rod-side conduit 16 with the tank 11 when in the leveling position a, but blocks the communication in the non-leveling position b or c. It is controlled by the pilot pressure on the upstream side and the downstream side.

Furthermore, the end side and rod side conduits 1 connecting the lift spool 8 and the lift cylinder 4 to each other.
Of the parts 3 and 14, the end-side passage 13 is connected via a first leveling spool 21 in a self-leveling valve 18 in the middle thereof, and is blocked when the leveling spool 21 is in a non-leveling position a. There is. Further, the end side pipe line 12 is connected by a bypass passage 29, and the check valve 3 with a spring which allows the flow from the cylinder side to the lift spool side is connected to the bypass passage 29.
0 is provided.

The self-leveling device for the shovel loader according to this embodiment is constructed as described above, and its function and effect will be described below. FIG. 1 shows a neutral state in which the lift spool 8 and the dump spool 9 of the control valve 7 are in the neutral position, and the first leveling spool 21 of the self-leveling valve 18 is held in the non-leveling position a and the second leveling The spool 25 is held at the leveling position a. In this state, the pressure oil sent from the hydraulic pump 10 flows into the self-leveling valve 18 through the open center passage 12 of the control valve 7, then returns from the passage 19 to the control valve 7 via the return passage 20, and returns to the return passage 17 It flows out to the tank 11 through.

FIG. 3 shows a state in which the lift arm 3 is raised, and the flow of pressure oil is shown by arrows. Lift spool 8
Is switched to the raised position a, the pressure oil from the hydraulic pump 10 is sent from the lift spool 8 to the end side conduit 13. At this time, the first leveling spool 21 is in the non-leveling position a and closes the end side pipe line 13. However, as the pressure on the upstream side rises, it is switched to the leveling position b by the pilot pressure and the end side pipe Connect to road 13. Therefore, the pressure oil is sent to the end side of the lift cylinder 4 to raise the lift arm 3. In this case, the first leveling spool 21 is held at the leveling position b due to the pressure difference between the upstream side and the downstream side of the throttle provided in the spool internal passage.

On the other hand, the return oil pushed out from the rod side of the lift cylinder 3 flows into the self-leveling valve 18 through the rod side pipe line 14, the lift spool 8 and the open center passage 12. Then, it flows into the flow dividing valve 22 through the first leveling pool 21 that has been switched to the leveling position b, and is divided into the flow dividing passage 24 on the tank side and the flow dividing passage 23 on the cylinder side. The pressure oil is sent to the end side of the dump cylinder 6 via the end side pipe line 15 and tilts the bucket 5 forward.

The pressure oil in the flow dividing passage 24 flows out to the tank 11 through the passage 28, the first leveling spool 21, the return passage 20 and the return passage 17 of the control valve 7, and also on the rod side of the dump cylinder 6. The return oil extruded from the second oil is held at the leveling position a.
From the leveling spool 25 through the passage 28 and merges with the pressure oil in the diversion passage 24 on the tank side and returns to the tank 11. Thus, according to this embodiment, the lift spool 8
Is independently operated to the ascending side, the bucket 5 can be leveled according to the ascent of the lift arm 3.

On the other hand, when the lift spool 8 is switched to the lowered position b in order to lower the lift arm 3, the pressure oil from the hydraulic pump 10 is sent to the rod side of the lift cylinder 4 via the rod side conduit 14. Then, the return oil pushed out from the end side to the end side pipeline 13 pushes open the check valve 30 in the bypass passage 29 and returns to the flow lift spool 8. After that, it flows out to the tank 11 via the self-leveling valve 18 as in the case of rising. Therefore, the self-leveling of the bucket 5 is not performed when the lift arm 3 descends.

Next, the forward / backward tilting operation of the bucket 5 alone will be described. FIG. 4 shows the state in which the bucket 5 leans forward, and the flow of pressure oil is shown by arrows. When the dump spool 9 is switched to the forward tilt position a, the pressure oil from the hydraulic pump 10 is sent to the end side of the dump cylinder 6 via the end side pipe line 15, and the bucket 5 is tilted forward. At this time, the second leveling spool 25 connected to the rod side conduit 16
Is switched to the non-leveling position c by the pilot pressure on the upstream side.
After returning to the dump spool 9 through 6 and then into the self-leveling valve 18 through the open center passage 12, it returns to the tank 11 through the passage 19, the return passage 20 and the return passage 17 of the control valve 7. in this case,
The second leveling spool 25 is held at the non-leveling position c by the pressure difference between the upstream side and the downstream side of the throttle provided in the internal passage of the spool.

When the dump spool 9 is switched to the backward tilt position b, the pressure oil from the hydraulic pump 10 is sent to the rod side conduit 16, and the pilot pressure of the second leveling spool 25 causes the second leveling spool 25 to move to the non-leveling position b. Is switched to. Therefore, the pressure oil is sent to the rod side of the dump cylinder 6, and the bucket 5 is tilted backward. The return oil pushed out from the end side returns to the dump spool 9 via the end side pipe line 15 and then returns to the tank 11 through the return route similar to the above.

Next, the simultaneous operation of the lift arm 3 and the bucket 5 will be described. FIG. 5 shows the lift arm raised and the bucket tilted backward, and the flow of pressure oil is indicated by arrows. When the lift spool 8 is switched to the raised position a and the dump spool 9 is switched to the rearward tilted position b, the hydraulic pump 10
The pressure oil from is sent to the end side of the lift cylinder 4 via the end side pipeline 13 and the first leveling spool 21, and the lift arm 3 rises. At this time, the switching of the first leveling spool 21 to the leveling position b is the same as when the lift arm is raised.

The return oil pushed out from the rod side of the lift cylinder 4 is transferred from the lift spool 8 to the dump spool 9
After being sent to the dump cylinder 6, it is sent to the rod side of the dump cylinder 6 through the rod side pipe line 16 and the second leveling spool 25, and the bucket 5 tilts backward. At this time, the fact that the second leveling spool 25 is switched to the non-leveling position b is the same as when the bucket is tilted backward. Then, the return oil pushed out from the end side of the dump cylinder 6 passes through the end side pipe 15 and the dump spool 9, and then flows into the passage 19 of the self-leveling valve 18.

At this time, the first leveling spool 21
Is held at the leveling position b, but since the pressure in the passage 19 rises to the set pressure, the pressure oil pushes the check valve 27 of the bypass passage 26 against the spring and opens to the return passage 20. , The return passage 17 of the control valve 7
After that, it returns to the tank 11. That is, the lifting of the lift arm 3 and the backward tilting operation of the bucket 5 can be performed without any obstacle. When the lift arm is raised and the bucket is tilted at the same time, the flow of the pressure oil with respect to the dump cylinder 6 is only opposite to that when the lift arm is raised and the bucket is tilted backward, and other aspects are exactly the same. .

When the lift arm is lowered and the bucket is tilted forward, the pressure oil from the hydraulic pump 10 is sent to the rod side of the lift cylinder 4, and the return oil pushed out from the end side returns to the lift spool 8. The pressure oil flow relating to 4 is performed in the same manner as when the lift arm 3 is independently lowered. Then, the pressure oil returned to the lift spool 8 is sent from the dump spool 9 to the end side of the dump cylinder 6 via the end side pipe line 15, and the return oil on the rod side passes to the dump spool 9 via the second leveling spool 25. After returning, it flows into the passage 19 of the self-leveling valve 18. Further, since the leveling spool 21 is held at the non-leveling position a, oil flows out to the tank 11 via the return passage 20 and the return passage 17 of the control valve 7. Thus, the lowering operation of the lift arm 3 and the forward tilting operation of the bucket 5 are simultaneously performed.

On the other hand, when the lift arm descends and the bucket tilts backward, the flow direction of the pressure oil with respect to the dump cylinder 6 is opposite to that when the lift arm descends and the bucket tilts forward, and is otherwise the same. Therefore, according to the present embodiment, the simultaneous operation of the lift arm 3 and the bucket 5 is
All of them can be implemented smoothly without any problems.

By the way, in a horizontal state in which the bucket 5 is loaded with a load of earth and sand or gravel, a load acts in a direction in which the bucket 5 is tilted forward, so that pressure is applied to the rod side of the dump cylinder 6. Therefore, oil leakage may occur from the sliding portion communicating with the rod side of the dump cylinder 6,
According to the self-leveling device of the present embodiment, the rod side of the dump cylinder 6 only communicates with the cylinder port of the second leveling spool 25. Therefore, it goes without saying in the case of the conventional self-leveling device shown in FIG. That is, oil leakage is reduced as compared with the case of the invention of the prior application shown in FIG. Therefore, the natural forward tilt amount of the bucket 5 can be significantly reduced.

The present invention is not limited to the illustrated embodiment. For example, the control system of the first and second leveling spools 21 and 25 is changed to the pilot type, and the lift spool 8 or the dump spool 9 is used. Alternatively, the switching operation may be detected by a detector such as a switch, and then electromagnetically changed based on the detection signal. Also,
The return oil from the return passage 20 of the self-leveling valve 18 may directly flow out to the tank 11 without passing through the return passage 17 of the control valve 7. Further, the check valve 27 as the pressure control valve may be a relief valve.

Further, in this embodiment, the first leveling spool 21, the flow dividing valve 22, the second leveling spool 25, and the check valve 27 are combined and integrated into one unitized self. Leveling valve 1
Since 8 is configured, the self-control valve 18
The compactness is achieved, which is advantageous in handling the piping. However, even if each of the above-mentioned valves is formed individually, there is no problem in its implementation. Furthermore, it is possible to arrange the dump spool 9 on the upstream side of the lift spool 8 so as to have a circuit configuration with a dump priority.

[0040]

As described above in detail, according to the self-leveling device of the present invention, there is a possibility that oil leaks to the rod side of the dump cylinder which is loaded in a bucket and has a high pressure in a horizontal state. Since there is only one location, it is possible to reduce the amount of natural forward tilt of the bucket as compared with the self-leveling devices of the prior art and the invention of the prior application, and prevent an unexpected slipping of the load. Further, according to the present invention, it is possible to ensure a smooth operability when the lift arm and the bucket are simultaneously operated, while ensuring the original function of the self-leveling device, that is, the bucket leveling function when the lift arm is raised.

[Brief description of drawings]

FIG. 1 is a hydraulic circuit diagram of a self-leveling device according to an embodiment of the present invention, showing a neutral state.

FIG. 2 is a schematic side view of a shovel loader.

FIG. 3 is a hydraulic circuit diagram of the self-leveling device, showing when the lift arm is raised.

FIG. 4 is a hydraulic circuit diagram of the self-leveling device when the bucket is tilted forward.

FIG. 5 is a hydraulic circuit diagram of the self-leveling device, showing a simultaneous operation of lifting a lift arm and tilting a bucket backward.

FIG. 6 is a hydraulic circuit diagram of a conventional self-leveling device.

FIG. 7 is a hydraulic circuit diagram of the self-leveling device of the invention of the prior application.

FIG. 8 is a hydraulic circuit diagram of the self-leveling device of the invention of the prior application, showing simultaneous operations (arm up / backward tilt).

[Explanation of symbols]

 1 ... Machine stand 3 ... Lift arm 4 ... Lift cylinder 5 ... Bucket 6 ... Dump cylinder 7 ... Cargo handling control valve 8 ... Lift spool 9 ... Dump spool 12 ... Open center passage 18 ... Self-leveling valve 21 ... First leveling spool 22 ... Shunt valve 25 ... Second leveling spool

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shigeto Nakajima 1782-10 Inariyama, Sarahaku City, Nagano Prefecture

Claims (1)

[Claims] 1. A self-loading excavator loader including a machine base, a lift arm mounted on the machine base and vertically moved by a lift cylinder, and a bucket attached to the lift arm and tilted forward and backward by a dump cylinder. A leveling device, comprising: a cargo control valve including a lift spool for controlling the lift cylinder and a dump spool for controlling the dump cylinder in the form of a serial circuit; and a control valve provided downstream of an open center passage of the control valve. A first leveling spool that can be switched between a non-leveling position for returning the inflowing pressure oil to the tank and a leveling position for sending it to the dump cylinder side, and the pressure oil sent from the first leveling spool between the tank side and the dump cylinder side. A shunt valve for diverting to the A second leveling spool that is switchable between a non-leveling position that allows the flow of pressure oil between the rod sides of the cylinder and a leveling position that returns the pressure oil on the rod side of the dump cylinder to the tank; and the open center passage A pressure control valve that allows pressure oil in the passage to flow out to a return passage to the tank when the pressure in the passage exceeds a set pressure, and the first and second leveling spools include the lift. A self-leveling device for a shovel loader configured to switch to a leveling position when the spool is independently operated on the lift arm rising side.