JPS6238499B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a hydraulic circuit for a hydraulic excavator that increases the speed of a specific actuator of a hydraulic excavator and improves single operability and combined operability.

FIG. 1 is a front view of the hydraulic excavator, and FIG. 2 is a plan view thereof. In the figure, 91 and 92 are crawlers, 93 is a revolving body rotatably supported by a traveling body having crawlers 91 and 92, 97 is a boom rotatably supported by the revolving body 93, and 98 is rotatable by the boom 97. The arm attached to 99 is arm 9
bucket rotatably supported on 8, 80,90
40 is a swing hydraulic motor for rotating the rotating structure 93; 50 is a boom hydraulic cylinder for rotating the boom 97; 60 is for rotating the arm 98. Arm hydraulic cylinder for, 70 is bucket 9
9 is a bucket hydraulic cylinder for rotating, and 4 is a prime mover mounted on the revolving body 93.

Conventionally, the hydraulic excavator shown in FIG. 1 includes a swing hydraulic motor 40, a boom hydraulic cylinder 50, an arm hydraulic cylinder 60, and a bucket hydraulic cylinder 7.
The six actuators, 0 and left and right hydraulic motors 80 and 90, are operated by pressure oil from two or three pumps driven by the prime mover 100, and usually two to three actuators are operated simultaneously, so each pump In many cases, multiple actuators are connected in parallel circuits. Therefore,
The greater the number of pumps, the better the operability.
Recently, various hydraulic circuits for three-pump type hydraulic excavators have been proposed.

One of the typical ones is disclosed in Japanese Patent Application Laid-open No. 132106/1983, which will be explained with reference to FIG.

The prime mover 100 drives main pumps 1 and 2 and a speed increasing pump 3, and the pumps 1 and 2 are connected to switching valve groups 8 and 13, respectively.
Directional switching valve 5 for right travel, directional switching valve 6 for bucket, and directional switching valve 7 for boom in switching valve group 8
is connected in parallel to pump 1, switching valve group 1
The left travel directional control valve 9, the boom directional control valve 10, the arm directional control valve 11, and the swing directional control valve 12 of No. 3 are connected in parallel to the pump 2, and by switching each direction control valve, Then, each actuator is activated. The pump 3 is connected to a pilot switching valve 18, and the pilot switching valve 18 is connected to a second spool 182 which is operated by the differential pressure across a constriction section 20 provided in a conduit 19 communicating with the rod side chamber of the arm hydraulic cylinder _60. and swing motor 15
The first spool 181 is operated by the pressure difference between the pressure introduced from the shuttle valve 21 and the pressure inside the pipe line 22, which is provided in parallel with the first spool ₁₈₁ . When the arm hydraulic cylinder 60 is not in use, the pressure oil from the pump 3 passes through the neutral positions of the first spool 18 ₁ and the second spool 18 ₂ and drains into the tank 23, and when pressure oil is supplied to the arm hydraulic cylinder 60, A pressure difference is generated before and after the throttle part 20, and the second spool valve 18
₂ is switched to the a or b position, and the pressure oil from the pump 3 is merged into the discharge side of the pump 2 via the pipe line 24, thereby causing the arm hydraulic cylinder 60
The amount of hydraulic pressure supplied to the pump becomes the total discharge amount of the pumps 2 and 3, and the operation of the arm 98 (see FIG. 1) is accelerated. Next, when pressure oil is supplied to the swing motor 40 in order to swing the swing body 93 (see Figure 1), the first spool ₁₈₁ switches to the a position, but the second spool ₁₈₂ is in the neutral position, so the pump 3 The pressure oil is directly drained into the tank 23. Furthermore, when the arm 98 and the rotating body 93 are operated simultaneously, the first and second spools 18 ₁ , 18 ₂
Since both are switched to the a or b position, the pressure oil of the pump 3 flows into the swing switching valve 12 through the pipe 25 to drive the swing motor 40, and the pressure oil of the pump 2 flows into the arm hydraulic cylinder 60. Therefore, rotation and arm operation are performed by separate pumps 3 and 2, respectively. Further, when the pressure in the conduit 22 becomes equal to or higher than the set pressure during arm operation, the first spool ₁₈₁ is switched to the b position and the pressure oil in the pump 3 is unloaded.

As mentioned above, according to JP-A-53-132106,
When the arm is driven alone, the arm movement is accelerated by the total flow rate of the two pumps 2 and 3, and when the arm and swing are operated simultaneously, the arm and the swing body can be driven by separate pumps, so the arm movement is slow when swinging. Problems such as sagging and poor movement of the revolving body when the arm is operated are eliminated, and although it has a total of three pumps, it can be driven with the same engine horsepower as a two-pump system.

However, the hydraulic circuit disclosed in JP-A-53-132106 has the following drawbacks.

(1) Pressure oil from the third speed-increasing pump is used to increase the speed of the arm and improve the combined maneuverability of the swing and arm, and for this purpose, the first spool 18 ₁ ,
A pilot switching valve 18 with _{a second} spool 182 is required, and an arm hydraulic cylinder 6
It is necessary to provide a throttle and a shuttle valve in the pressure oil supply circuit of the hydraulic pressure oil supply circuit 0 and the swing motor 40, and to provide pilot piping from this valve to the pilot switching valve 18, which increases the cost of the hydraulic circuit and makes the circuit complicated.

(2) The first spool ₁₈
When the arm is operated, the spool ₁₈₁ is switched after a certain amount of flow flows into the pressure oil supply circuit of the arm hydraulic cylinder 60, and pressure oil from the third pump suddenly flows into the arm hydraulic cylinder 60. As the flow rate increases, the fine controllability of the arm becomes extremely poor.

(3) When performing a combined operation of clouding and turning the arm, the weight of the arm 98 acts on the side that pushes the rod of the arm hydraulic cylinder 60, so the pressure in the bottom side chamber is low and most of the pressure oil in the pump 2 is flows from the parallel circuit to the bottom side chamber of the arm hydraulic cylinder 60, and since the swing hydraulic motor 40 is driven by the pressure oil of the pump 3, it is possible to match the operating speeds of both actuators during combined operation. However, when performing a combined operation of dumping and swinging the arm, for example when loading earth and sand onto a dump truck, the pressure in the rod side chamber of the arm hydraulic cylinder 60 is high, and the driving pressure of the swing hydraulic motor 40 is also high. Pump 2 because it's expensive
Pressure oil is supplied to the arm hydraulic cylinder 60 from the parallel circuit.
and the swing hydraulic motor 40 according to the load pressure of each actuator. Therefore, the swing hydraulic motor 40 is sped up by the total flow rate of the full flow rate of the pump 3 and the partial flow rate of the pump 2,
is driven by the remaining flow rate of pump 2. For this reason, the rising speed of the bucket during arm dumping cannot keep up with the turning speed, resulting in poor workability.
In particular, when loading earth and sand onto a dump truck, if the turning is completed before the bucket truck rises higher than the dump truck, there is a risk that the bucket truck, arm, etc. will collide with the loading platform of the dump truck.

The present invention was made to solve the problems of the prior art as described above, and it increases the speed of a specific actuator, improves the operability when operating alone, and improves the relationship between the specific actuator and other actuators. The purpose of this system is to provide a hydraulic circuit for a hydraulic excavator with improved combined operability, in which the pressure oil supply circuit of at least one speed-increasing pump is connected to a directional switch located at the most downstream of one switching valve group. It is connected to the center bypass circuit between the valve and the directional control valve located second from the most downstream position, and connects to the two pressure oil ports P ₁ and P ₂ of the directional control valve located most downstream and the pressure oil supply to the main pump. The circuits connecting the circuits and the center bypass circuit were connected through each circuit provided with a check valve for blocking flow to the center bypass side.

An embodiment of the present invention will be described below with reference to FIGS. 4 and 5. Figure 4 shows a switching valve group 13 in which an arm directional switching valve 11, a boom directional switching valve 10, a swing directional switching valve 12, and a left running directional switching valve 9 are arranged in one valve block V from the downstream side. This shows the internal structure. The pressure oil supply circuit 26 of the main pump 2 is connected to the switching valve group 13, and within the switching valve group 13, left and right parallel circuits 124, 11
4. Branches to center bypass circuit 134. The left parallel circuit 124 connects each direction switching valve 11, 10, 12,
9 each pressure oil port and each parallel circuit 120, 121,
122, 123, right parallel circuit 11
4 is each pressure oil port of each directional control valve 11, 10, 12, 9 and each parallel circuit 110, 111, 112, 1
13. Further, the center bypass circuit 134 communicates with the tank 23 via each directional switching valve and center bypass circuits 133, 132, 131, and 130 between the directional switching valves when all the directional switching valves are in neutral. Each direction switching valve 11,1
0, 12, and 9 are normal three-position directional control valves having left and right switching positions and a neutral position, and directional control valve 1
Reference numerals 1 and 10 have a built-in load check valve. A center bypass circuit 130 between the arm directional control valve 11 and the boom directional control valve 10 is connected to the parallel circuit 110 and the parallel circuit 120 via a check valve 200 and a check valve 300. Each check valve 200 and 300 is connected to the directional control valve 11 in a parallel circuit 110 and a parallel circuit 120.
The flow from the center bypass circuit 130 to the center bypass circuit 130 is blocked. A diaphragm 400 is provided in the parallel circuit 120. Further, the pressure oil supply circuit 27 of the speed increasing pump 3 connects to the center bypass circuit 130 at a confluence point 140.
are connected at. Directional switching valve for arm 1
1 is a normal switching valve as mentioned above, and the parallel circuit 1
Pressure oil port P ₁ connected to 20 and parallel circuit 110
pressure oil port P ₂ connected to the left/right switching position, pressure oil ports P ₁ and P ₂ connected to the load check valve 21
0 and 220, and the bottom side oil chamber 60a (see FIG. 5) and the rod side chamber 60b of the arm hydraulic cylinder 60 (see FIG. 5).
It has actuator side ports A and B that communicate with the actuator (see FIG. 5). Reference numerals 210 and 220 are load check valves built into the arm directional control valve 11. The turning directional control valve 12 is a three-position directional control valve, and has a pressure oil port P ₃ connected to the parallel circuit 121;
The pressure oil port P ₄ is connected to the parallel circuit 111, and communicates with the pressure oil ports P ₃ and P ₄ at the left/right switching position, as well as the swing motor 40 (see Fig. 5) and the pipes u and v (see Fig. 5). It has actuator side ports C and D that communicate through the actuator. The reference numeral 600 indicates a relief valve of the switching valve group 13.

FIG. 5 shows an overall diagram of the hydraulic circuit of the hydraulic excavator of the present invention.
This is a strict circuit representation of the internal structure of 3. In the figures, the same reference numerals as in FIGS. 3 and 4 indicate the same or equivalent items. Symbols s and t indicate conduits connecting the bottom side chamber and the rod side chamber of the arm hydraulic cylinder 60 and ports A and B of the directional control valve 11. Further, reference numerals 11a and 11b indicate left and right switching positions of the arm directional switching valve 11. The switching valve group 8 has a bucket directional switching valve 7, a boom directional switching valve 6, and a traveling directional switching valve 5 arranged in a valve block (not shown) from the downstream side, as shown in FIG. The directional switching valves 7, 6, 5 are normal 3-position switching valves,
The directional control valves 7 and 6 are of a type having built-in load check valves. The reference numeral 500 indicates a relief valve provided in the switching valve group 8.

Next, the operation of this invention configured as described above will be explained.

1 Arm independent operation (a) When performing arm cloud (see Fig. 1) independent operation When the arm directional control valve 11 is operated to the 11a side in Fig. 5, that is, in Fig. 4, the arm directional control valve 11 When the spool is moved in the direction, the pressure oil of the pump 3 reaches the confluence 140 of the center bypass 131 of the switching valve group 13 from the pressure oil supply circuit 27. The pressure oil of the pump 2 passes through the pressure oil supply circuit 26, enters the valve block of the switching valve group 13, and is divided. One of the divided pressure oils is connected to the center bypass circuit 134, 133, 132,
131 and reaches the confluence 140. Confluence point 14
At 0, the pressure oils of pumps 2 and 3 merge, and the check valve 300 is opened. The other branched pressure oil passes through the parallel circuit 120 and the throttle 400, opens the check valve 300, joins the inflowing pressure oil, and enters the pressure oil port _P1 . The pressure oil entering port P ₁ opens the load check valve 210, passes through the actuator side port A and the pipe s, flows into the bottom side chamber 60a of the arm hydraulic cylinder 60, and clouds the arm 98. Hydraulic cylinder for arm 6
The pressure oil in the rod side chamber 60b is connected to the pipe t, the actuator side port B, and the load check valve 220.
After that, return to tank 23. Since the flow rate of the pressure oil of the pump 2 passing through the throttle 400 is small, the pressure loss there is small. Since the arm hydraulic cylinder 60 performs crowding of the arm 98 with the total flow rate of the pumps 2 and 3, the operation speed of the arm is increased.

(b) When performing arm dumping (see Figure 1) alone When the arm directional control valve 11 is operated to the 11b side in Figure 5, that is, in Figure 4, the arm directional control valve 11's spool is , the pressure oil of the pump 3 is transferred from the pressure oil supply circuit 27 to the center bypass circuit 131 of the switching valve group 13.
reaches a confluence 140. The pressure oil of the pump 2 enters the valve block of the switching valve group from the pressure oil supply circuit 26 and is divided. One side of the divided pressure oil is the center bypass circuit 134, 133, 132, 1
31 and reaches the confluence 140. Confluence point 140
At this point, the pressure oil of pumps 2 and 3 join together, and check valve 200 is opened. The other branched pressure oil passes through the parallel circuit 110 and is connected to the check valve 20.
0 opens and joins the inflowing pressure oil to the pressure oil port P ₂
to go into. The pressure oil entering the pressure oil port _P2 opens the load check valve 220, passes through the actuator side port B and the pipe t, flows into the rod side chamber 60b of the arm hydraulic cylinder 60, and dumps the arm 98. The pressure oil in the bottom side chamber 60a of the arm hydraulic cylinder 60 passes through the pipe s, the actuator side port A, and the load check valve 210 to the tank 2.
Return to 3. Pressure oil does not pass through any restrictions, so there is little loss in the circuit. Since the arm hydraulic cylinder 60 dumps the arm 98 with the total flow rate of pumps 2 and 3, the operation of the arm is accelerated.

2 Combined operation of arm and swing (a) When clouding and swinging the arm at the same time In Figure 4, move the spool of the arm directional control valve in the direction, and move the spool of the swing directional control valve 12 in the direction or direction. When the pump 3 moves to , the pressure oil of the pump 3 reaches the confluence 140 of the center bypass circuit 131 of the switching valve group 13 via the discharge side pipe 80 and opens the check valve 300 . Pressure oil from the pump 2 enters the switching valve group 13 from the discharge side pipe line 40. Since the flow of the pressure oil in the center bypass circuit 132 is blocked by the turning directional control valve 12, a portion of the pressure oil in the pump 2 is transferred to the parallel circuit 122 or the parallel circuit 112, the pressure oil port P ₃ , the actuator side port C or the pressure oil. The oil is supplied to the swing hydraulic motor 40 via the oil port P ₄ , the actuator side port D, and the pipe u or v. The other pressure oil of the pump 2 passes through a parallel circuit 120, a throttle 400,
The check valve 300 is opened and the inflowing pressure oil from the pump 3 is merged with the pressure oil port P ₁ , the load check valve 210, the actuator side port A, and the pipe s.
It is supplied to the bottom side chamber 60a of the arm hydraulic cylinder 60 through the. Therefore, the rotating body 93
pivots to the left or right, and the arm 98 clouds. Normally, when the arm 98 is clouded, the weight of the arm 98 acts on the side that pushes the rod of the arm hydraulic cylinder 60, so the load pressure in the bottom side chamber 60a of the arm hydraulic cylinder 60 is low, but the throttle 400 is connected to the parallel circuit 120. Because of this provision, the pressure oil of the pump 2 can ensure sufficient pressure in the parallel circuit 122 to rotate the swing hydraulic motor 40, and the swing hydraulic motor 40 is rotated at a predetermined speed. Further, the speed of the arm 98 is increased in order to perform clouding with a part of the flow rate of the pump 2 and a full flow rate of the pump 3.

(b) When dumping and swinging the arm at the same time In FIG. The pressure oil is transferred from the discharge side pipe 80 to the center bypass circuit 13 of the switching valve group 13.
1 and the check valve 200 is opened. A part of the pressure oil of the pump 2 is delivered to the swing hydraulic motor 40 via the parallel circuit 122 or the parallel circuit 112, the pressure oil port P ₃ , the actuator side port C or the pressure oil port P ₄ , the actuator side port D, and the pipe u or v. supplied to The other pressure oil of pump 2 passes through parallel circuit 110 and is connected to check valve 2.
00 is opened to join the inflowing pressure oil of the pump 3, and the pressure oil port _P2 , the load check valve 220,
It is supplied to the rod side chamber 60b of the arm hydraulic cylinder 60 via the actuator side port B and the pipe t. Therefore, the rotating body 93 turns to the left or right, and the arm 98 dumps. Arm 9
8, the pressure in the rod side chamber of the arm hydraulic cylinder 60 is sufficient to drive the swing motor 40, so the flow rate of the pressure oil from the pump 2 is distributed according to the loads on both actuators. Therefore, the arm 98 is sped up with the sum of the total flow rate of the pump 3 and the partial flow rate of the pump 2, and the swing hydraulic motor 40 is driven with the remaining flow rate of the pump 2. In this case, the operating speeds of both actuators can be matched, and since the bucket lift speed is fast during arm dumping, danger during the work of loading earth and sand onto the dump truck is eliminated.

In addition, if the pressure in the rod side chamber of the arm hydraulic cylinder 60 is insufficient to drive the swing when the arm 98 is dumped, the throttle pressure is set to be smaller than that of the throttle 400 in the parallel circuit 110 shown in FIG. It is also possible to include a diaphragm (not shown).

According to the present invention described above in FIGS. 4 and 5,
A separate directional switching valve such as a pilot switching valve and pilot piping for merging the pressure oils of the speed increasing pumps 3 are not required, and the hydraulic circuit is simple and costs are reduced. Further, since only the arm direction switching valve is switched when increasing the speed of the arm, the arm command operability is good. Furthermore, during arm single operation and combined swing operation, the pressure oil of the main pump is made to pass through the restriction only when the load pressure on the arm is small and the combined operation of arm cloud and swing is performed, so that the circuit is closed during other operations. There is little pressure loss, and it is possible to reduce the temperature rise in the circuit and the fuel consumption of the prime mover. Further, when a combined operation of arm dumping and turning is performed, the speed of the arm is increased relative to the turning speed, so that the working speeds can be matched and work efficiency is improved.

Next, another embodiment of the present invention will be described with reference to FIGS. 6 to 8. 6 to 8, the same reference numerals as in FIGS. 4 and 5 indicate the same or equivalent parts. FIG. 6 shows a sectional view of the switching valve group 13 in which the load check valves 210 and 220 of the arm directional switching valve 11 of FIG. 4 are integrated with the check valves 300 and 200.
FIG. 7 is a perspective view showing the integrated check valve 300 and load check valve 230 in an exploded state.
A spring 300c is inserted into the cylindrical portion 300b fixed to the seat portion 300a of the check valve 300, and the cylindrical portion 3
00b is the hole 230a of the load check valve 230
slidably inserted into. Load check valve 23
The 0 seat portion 230b is provided so as to oppose the oil chamber 300e that communicates with the throttle 400 bored in the cylinder 300d. Groove 230 as a pressure oil passage
b is provided on the outer periphery of the cylindrical body of the load check valve. One end of the spring 300c contacts the cylindrical portion 300b, and the other end contacts the load check valve 230. The integral structure of the check valve 200 and the load check valve 240 is similar to that shown in FIG. 7, except that the restrictor 400 in FIG. 7 is replaced with a passage 500 having a wide flow path shape.

In FIG. 4, when the arm directional control valve 11 is operated, the combined flow of pressure oil from the pumps 2 and 3 passes through a narrow hole machined inside the spool of the arm directional control valve 11 to the load check valve 210 or 220. The pressure drop is extremely large as it passes through the On the other hand, in FIG. 6, only the pressure oil from the parallel circuit 120 or 110 out of the pressure oil from the pump 2 passes through the load check valve 230 or 240. The pressure oil of the pumps 2 and 3 that passes through the arm directional control valve 11 through the arm directional control valve 200 does not need to pass through the load check valve 230 or 240, resulting in less pressure loss in the circuit. Further, since it is not necessary to provide a load check valve on the spool of the arm directional control valve 11, there is no need to drill holes inside the spool. 2
Since it is only necessary to add it to 00, the number of parts is small and the processing cost is low. Furthermore, load check valve 23
0,240 is a groove 23 provided with pressure oil on the outer periphery of the cylinder.
0b, the flow path area can be larger than in the case of Fig. 4, and the parallel circuit 12
Load check valve 230, 2 from 0 or 110
It is possible to reduce the pressure loss of the pressure oil passing through 40.

FIG. 8 shows an overall diagram of the hydraulic circuit of the hydraulic excavator, which strictly represents the internal structure of the switching valve group 13 in FIG. 6 as a circuit, and has the same effect as the embodiment shown in FIG. In addition to reducing the pressure loss in the circuit as described in Fig. 6,
Moreover, the number of parts of the arm directional switching valve can be reduced and the processing cost can be reduced.

FIG. 9 is a hydraulic circuit diagram of a hydraulic excavator showing only the main parts of still another embodiment of the present invention. The same reference numerals as in FIG. 8 indicate the same or equivalent parts. In the figure, the relief valve 450 is the eighth
This serves as the throttle 400 and the load check valve 230 provided in the parallel circuit 120 shown in the figure. That is, when the cloud and swing operations of the arm are performed simultaneously, the setting pressure of the relief valve 450 is set to a pressure sufficient to drive the swing motor, thereby matching the arm and swing speeds, and , the relief valve 450 is the arm directional control valve 11
Prevents backflow of pressure oil from the pressure oil ports P ₁ and P ₂ side to the main pump side.

FIG. 10 shows another embodiment of the present invention, in which the same reference numerals as in FIGS. 5 and 8 indicate the same or equivalent components. FIG. 10 shows a parallel circuit 150, 151, 15 in which each directional control valve 11, 10, 12, 9 is connected to a common parallel circuit at each left and right switching position.
2, 153 shows a hydraulic circuit in which the present invention is applied to a switching valve group 13 of the type that is supplied with pressure oil from the pump 2. In the figure, 200' and 300' are the pressure oil ports P ₁ and P ₂ of the arm directional control valve 11 and the parallel circuit 15.
A check valve provided between the circuits 150a, 150b connecting the center bypass circuit 131 and the center bypass circuit 131;
250 is a load check valve provided in the parallel circuit 140, and 400' is a throttle provided in the circuit 140b. In the case of FIG. 10 having the above-mentioned configuration, when the arm directional control valve 11 is operated independently (when the arm cloud and arm dump are operated independently), a common Through the parallel circuit 140, the arm directional control valve 11
Pressure oil from pump 2 flows into. In addition, when the arm directional control valve 11 and the swing directional control valve are operated in combination, a common parallel circuit 15 is used at each left and right switching position of the arm directional control valve 11 and the swing directional control valve 12.
0 and the pump 2 to the arm directional control valve 11 and the swing directional control valve 12 through the parallel circuit 152.
of pressure oil flows in. The embodiment shown in FIG. 10 has exactly the same functions and effects as the embodiment shown in FIG. 8 except for the above-mentioned points.

In the embodiments shown in FIGS. 4 to 10 above, the directional control valve located at the most downstream of the control valve group is used as the directional control valve for the arm, the arm hydraulic cylinder is accelerated, and the arm can be operated independently and the arm and swing can be combined. Although we have described the case where the operability is improved, this invention uses the directional control valve located at the most downstream of the control valve group as a boom directional control valve, increases the speed of the boom hydraulic cylinder, and enables independent operation of the boom and simultaneous operation of the boom. It is also possible to improve the combined maneuverability of turning, and even if the combination of the directional control valve located at the most downstream position and the actuator that is subjected to combined operation is changed, the present invention produces the same effect.

Further, in the above embodiment, a case has been described in which two main pumps and one speed increase pump are provided, but the number of main pumps and speed increase pumps is not limited to the number of speed increase pumps.

As explained above, the present invention has the following effects.

(1) When increasing the speed of a specific actuator by combining the pressure oil from the speed increase pump, a directional switching valve or pilot piping for the directional valve must be installed in the middle of the pressure oil supply circuit of the speed increase pump. This is not necessary, making the circuit simple and inexpensive.

(2) Not only can the speed of a specific actuator be increased, but also the fine operability of that actuator can be improved.

(3) Pressure oil does not pass through the throttle except during specific operations, which reduces pressure loss in the hydraulic circuit, reduces circuit temperature rise, and reduces fuel consumption of the prime mover.

(4) It is possible to increase the speed of a specific actuator and match the working speed with other actuators, improving combined operability.

[Brief explanation of the drawing]

Fig. 1 is a front view of a hydraulic excavator, Fig. 2 is a plan view thereof, Fig. 3 is a diagram showing a hydraulic circuit of a conventional hydraulic excavator, and Fig. 4 is a hydraulic circuit used in a hydraulic excavator according to the present invention. FIG. 5 is a cross-sectional view of the valve body of the switching valve group, FIG. 5 is a diagram showing the hydraulic circuit of the hydraulic excavator of this invention including the switching valve group of FIG. 4, and FIG. 6 is a diagram showing another embodiment of the invention. , FIG. 7 is a sectional view of the valve body of the switching valve group, FIG. 7 is a perspective view showing an exploded state of the integrated check valve and load check valve according to the present invention, and FIG.
FIG. 9 is a diagram showing still another embodiment of the invention, and FIG. 10 is a diagram showing still another embodiment of the invention. It is a diagram. 1, 2... Main pump, 3... Speed increase pump, 5... Directional switching valve for left travel, 6... Directional switching valve for bucket,
7... Directional switching valve for boom, 8... Switching valve group,
9... Directional switching valve for right travel, 10... Directional switching valve for boom, 11... Directional switching valve for arm, 12... Directional switching valve for swinging, 13... Switching valve group, 26... Pressure oil supply circuit for main pump, 27 ...Pressure oil supply circuit for the speed increasing pump 3, 40...Swivel motor, 50...Boom hydraulic cylinder, 60...Arm hydraulic cylinder, 7
0...Bucket hydraulic cylinder, 93...Swivel body, 9
7...Boom, 98...Arm, 99...Bucket, 1
30, 131, 132, 133, 134...center bypass circuit, 110, 111, 112, 11
3,114,120,121,122,123,
124, 150, 151, 152, 153, 15
4...Parallel circuit, 200, 200', 300, 30
0'...Check valve, 210, 220, 230, 2
40,250...Load check valve, 400,40
0'... Throttle, 450... Relief valve, P ₁ , P ₂ , P ₃ ,
P ₄ ...Pressure oil port, A, B, C, D...actuator side port.

Claims (1)

[Scope of Claims] 1. A switching valve group having a plurality of main pumps driven by a prime mover, a plurality of directional switching valves connected to each main pump, and at least one speed-increasing pump, A directional control valve is connected to each actuator of the hydraulic excavator, each actuator is driven by pressure oil from each main pump, and pressure oil from the speed increasing pump is merged with pressure oil from at least one main pump. In the hydraulic circuit of a hydraulic excavator that drives one or more actuators, the pressure oil supply circuit of at least one speed increasing pump is connected to the directional switching valve located at the most downstream position of one switching valve group and the most downstream directional switching valve. The two pressure oil ports P ₁ , P ₂ of the directional control valve located at the most downstream are connected to the center bypass circuit between the directional control valve located at the second position.
A hydraulic excavator characterized in that a circuit connecting a pressure oil supply circuit of a main pump and a pressure oil supply circuit, respectively, and the center bypass circuit are connected through each circuit provided with a check valve for blocking flow to the center bypass side. Hydraulic circuit. 2. A restriction is provided in at least one of the circuits connecting the two pressure oil ports P ₁ and P ₂ of the directional control valve located at the most downstream position and the pressure oil supply circuit of the main pump. Claim 1
Hydraulic circuit of the hydraulic excavator described in section. 3. A load check valve is provided in the parallel circuit communicating with the two pressure oil ports P ₁ and P ₂ of the directional control valve located at the most downstream position to prevent the flow from the pressure oil port side to the main pump side. A hydraulic circuit for a hydraulic excavator according to claims 1 and 2. 4. A hydraulic circuit for a hydraulic excavator according to claims 2 and 3, characterized in that the throttle is a relief valve. 5. A hydraulic circuit for a hydraulic excavator according to claims 1 to 4, wherein the directional switching valve located at the most downstream position is an arm directional switching valve.