JPH0255568B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION A hydraulic circuit for a construction machine according to the present invention includes at least one variable displacement pump, an actuator driven by hydraulic pressure discharged from the pump, and an operating valve for controlling these actuators, The present invention relates to a hydraulic control device for construction machinery that controls a variable discharge rate pump so that the pump discharge rate automatically becomes the minimum flow rate when all of the operation valves are in neutral positions.

Conventional construction machinery, such as hydraulically driven swinging excavation machines, uses hydraulic pressure to drive, swing, and power the work equipment, and a variable discharge pump is used as the hydraulic power source.
During operation, the swash plate tilt angle is controlled so that when the load is light, the variable discharge rate pump reaches the maximum flow rate, and when the load is heavy, the flow rate of the variable discharge rate pump is decreased. For this reason, even when each operating valve is in the neutral position, the maximum discharge amount flows through the circuit, resulting in a drawback of large horsepower loss.

This invention was made for the purpose of improving this drawback, and when all the operating valves are in the neutral position,
We provide a hydraulic control device for construction machinery that controls the tilting angle of the swash plate so that the discharge volume of a variable discharge volume pump is minimized, thereby reducing horsepower loss and improving energy efficiency by improving fuel efficiency. It is something that we try to do. In addition, by attaching a check valve externally to the existing operating valve and connecting the operating valve and the pilot switching valve via the check valve,
This method can be easily applied to existing construction machinery.

The present invention will be explained in detail below with reference to an illustrated embodiment. Figure 1 shows the hydraulic circuit of a construction machine such as a hydraulically driven revolving excavator.It is equipped with two variable displacement pumps 1 and 2, and the hydraulic pressure discharged from each pump 1 and 2 is independent on the left and right sides. The liquid flows into the operating valve groups 3 and 4 of the operating system, respectively. As shown in FIG. The operating valves are not shown), and these operating valves 5
The spools 5b, 6b, and 7b are operated by operating the levers 5a, 6a, and 7a, and the left steering operation valve 5 allows oil to flow to the left traveling motor 9 via the counterbalance valve 8, and also to the arm. The operation valve 6 allows oil to flow to the arm cylinder 10 that drives the arm a of the working machine A, and the boom operation valve 7.
are adapted to control the oil flowing to the boom cylinder 11 that drives the boom b of the working machine A, respectively. Further, each operating valve 5 to 7 has _a pump port 51 _{to 71} that communicates with each other when the spool 5b to 7b is in the neutral position (the position shown in FIG. 2).
and tank ports 5 ₄ and _{5 5} or 7 ₄ and 7 ₅ communicate with each other, and the pilot port 5 ₂ is adjacent to the ports 5 ₄ and 5 ₅ or 7 ₄ and 7 ₅ .
and ₅₆ to ₇₂ and ₇₆ , and the pump ports ₅₁ to ₇₁ have spools 5b to 7.
The pilot ports 5 ₂ and 5 6 to 7 ₂ and 7 ₆ are connected to the tank 13 through the neutral drain circuit ₁₂ of the spool 5 b to the neutral tank port 5 ₄ and 5 5 to 7 4 and _{7 5} of the spool ₅ b to 7 _b . more blocked.

Furthermore, the ports _{53 and 57} and the ports 73 and 77, which communicate with the pump ports 51 to 71 via the check valves _{5c to 7c} , are shut off.

That is, pilot ports ₅₂ and ₅₆ to _{72 and 76} are located between ports ₅₃ and _{57 to 73 and 77 and tank} ports ₅₄ and ₅₅ to ₇₄ and ₇₅ ; Pilot ports ₅₂ and ₅₆ or ₇₂ and ₇₆ are connected to passages _25b5 or _25c5 to _25b7 or Connected to _25c7 . Therefore, if even one of the spools 5b to 7b is operated, the passage 25b ₅ or 2
5c ₅ or 25b ₇ or 25c ₇ is connected to the tank port 5 ₄ through the check valve 25d ₅ or 25e ₆ or 25d ₇ or 25e ₇ in the check valve block 25.
or notch _5c or 5d or 7 of spool 5b or 7b that communicates 5 5 to _{7 4} or 7 5
Tank port 5 ₄ or 5 ₃ via c or 7d
to ₇₄ or ₇₅ , _so that pressure does not build up in the pilot port ₅₂ or ₅₆ to 72 or ₇₆ and the passage _25b5 or _25c5 to _25b7 or _25c7 in the check valve body 25a. It's summery. Further, the check valve group 25 is connected to each operating valve group 3, 4 of the existing hydraulic circuit.
It is fixed with a fixing device 26 every 7 to 7, and allows flow only from the passage 25b ₅ or 25c ₅ to 25b ₇ or 25c ₇ side to the direction across the pilot port 5 ₂ or 5 ₆ to _{7 2} , and The passages 25b ₅ or 25c ₅ to 25b ₇ or 25c ₇ are communicated with the pilot port 15 ₁ of the pilot changeover valve 15 by a conduit 14. The pilot switching valve 15 is connected to each variable discharge amount pump 1 and 2.
The valve body 15a has a spool 15b biased in one direction (to the left in the figure) by a compression spring 16, and the spool 15b has a spool 15b in the periphery. Pilot port 1
5 ₁ and tank port 15 ₂ , pump port 15 ₃ and output port 15 ₄ on both sides of tank port 15 ₂
A tank port 15 ₂ is connected to the tank 13 and a pump port 15 ₃ is connected to a fixed charge pump 18 via a line 17 .
A passage 15d is formed in the spool 15b of the pilot switching valve 15 and opens at the end on the pressure chamber 15c side that communicates with the pump port ₁₅₃ , and this passage 15d communicates with the pressure chamber 15c through a through hole 15e. At the same time, the compression spring 16 of the passage 15d
The side communicates with the spring chamber 15g via an orifice 15f. The spring chamber 15g communicates with the pilot port 151 when the spool 15b is pressed against the end plate 15h by the compression spring 16, and the pressure chamber 15c communicates with the output port ₁₅₄ by the small diameter portion _15i of the spool 15b. .

On the other hand, the output port ₁₅₄ of the output pilot switching valve 15 is connected to the pressure chamber 20d of the pump neutral control (PNC) device 20 through a conduit 26. Pump neutral control device 20 is cylinder main body 20
Each swash plate 1 of the variable discharge amount pumps 1 and 2 is installed in a.
It has a piston 20b that mechanically interlocks with the pumps a and 2a, and one end side of the piston 20b is connected to a servo cylinder 21 that controls the discharge amount of each variable discharge amount pump 1 and 2. Also piston 20
The other end of b is connected to the pressure chamber 20 via the operating rod 20c.
The pressure chamber 20d is connected to the piston 20e housed in the pressure chamber 20d, and is configured so that the pressure introduced into the pressure chamber 20d presses the piston 20b in the direction of decreasing the discharge amount via the operating rod 20c.

In the figure, reference numeral 22 denotes fixed capacity pumps, and the hydraulic pressure discharged from these pumps 22 is supplied to a swing motor (not shown) via a swing operation valve 23, thereby swinging the upper revolving body of the swing excavator.

However, now that the construction machine is in operation, operation valve group 3,
When one or more operating valves 5 to 7 of 4 are operated, the spool 5 of each operating valve 5 to 7
The pilot port 5 2 or 5 6 or 7 ₂ or 7 ₆ and the tank port 5 ₄ or 5 ₅ are connected by the notches 5 c or 5 d or 7 _c or 7 _d from b to 7 b.
7 ₄ or 7 ₅ are communicated with each other, the oil supplied from the fixed charge pump 18 to the pump port 15 ₃ of the pilot switching valve 15 flows into the passage 15 d through the through hole 15 e, and then through the orifice 15.
f through the spring chamber 15g, the pipe line 14 and the check valve group 25 to the pilot port ₅₂ or ₅₆
It is drained from 7 ₂ or 7 ₆ to tank port 5 ₄ or 5 ₅ or 7 ₄ or 7 ₅ . Also, from the passage 15d, through the orifice 15f, the spring chamber 15
When flowing to g, the resistance of orifice 15f causes passage 1 to
5d and the spring chamber 15g, and this pressure difference pushes the spool 15b to the right (see FIG. 5) against the compression spring 16, thereby causing the small diameter portion 15i of the spool 15b to push the pump. Since the port 15 ₃ and the tank port 15 ₂ are blocked and the output port 15 ₄ is communicated with the tank port 15 ₂ , the pressure of the output port 15 ₄ becomes the pressure of the tank port 15 ₂ and the pressure chamber of the pump neutral control device 20 20d
Since the pressure of the pump also decreases, the action of pushing the piston 20b to the right against the springs 21a and 21b disappears, and the pump tilting angle is maintained at a position that generates a discharge amount according to the pump load as before. Therefore, the existing functions will not be impaired. (In other words, when the load on each variable discharge amount pump increases, the performance follows curve A in Figure 4, which reduces the discharge amount.) Also, when operating the operating valves 5 to 7, the pilot ports ₅₂ and ₅₆ to The high pressure of the pump ports ₅₁ to ₇₁ acts on ₇₂ or ₇₆ , and this high pressure tries to flow back from the pipe line 14 to the pilot switching valve 15 side, but the check valve externally attached to the operating valves 5 to 7 Since the group 25 blocks the flow toward the pipe line 14, the normal operation of the pilot switching valve 15 can be prevented from being disturbed.

Similarly, when the operation valves 5 to 7 are operated simultaneously, if the spools 5b to 7b of the upstream operation valves 5 to 7 are in the fine operation range, the downstream spools 5b to 7b move the pump ports _{51 to 71} to the tank. Flow to ports ₅₄ to ₇₄ is blocked and high pressure is created on the upstream side.

The check valve group 25 can prevent this high pressure from flowing back from the pipe line 14 to the pilot switching valve 15.

Next, when all the spools 5b to 7b of the operation valve groups 3 and 4 are returned to the neutral position due to a temporary stoppage of work on the construction machine, etc., the pilot ports ₅₂ and 56 to ₇₂ of each operation valve 5 to 7 are opened _. and 7 ₆ and tank ports 5 ₄ and 5 ₅ or 7 ₄ and 7 ₅ are shut off. This eliminates the flow in the pipe line 14, so the pressure chamber 1 of the pilot switching valve 15
5c and the spring chamber 15g have the same pressure, and the spool 15
b is pressed leftward by the compression spring 16, and the charge pressure of the pump port ₁₅₃ is supplied to the pressure chamber 20d of the pump neutral control device 20 through the output port ₁₅₄ , so that the piston 20e in the pressure chamber 20d moves to the right. In order to press the piston 20b via the operating rod 20c to the position where the discharge amount of the variable discharge amount pumps 1 and 2 is the minimum value, the discharge amount of each variable discharge amount pump 1 and 2 is the minimum value. is set to

As described above, when at least one of the operating valves 5 to 7 of the operating valve groups 3 and 4 is operated, each variable discharge amount pump 1 and 2 is maintained at the maximum flow rate or the flow rate set by the servo cylinder 21. However, the swash plate tilt angle is now controlled so that the flow rate is automatically the minimum when all of the operation valves 5 to 7 are in the neutral position, and the pressure loss at the neutral position is also reduced compared to the conventional point RO (Fig. 4). (see), it can be reduced to point C.

In the above embodiment, the hydraulic circuit was explained in the case where two variable discharge amount pumps 1 and 2 were provided.
Of course, it can be employed in a hydraulic circuit having one or more hydraulic circuits.

As described in detail above, this invention automatically controls the discharge volume of the variable discharge volume pump to be minimized when all of the operation valves that control the travel of working machines and construction machinery are returned to their neutral positions. As a result, horsepower loss can be significantly reduced compared to conventional valves that maintain maximum discharge even when all operating valves are in neutral.
This will lead to energy savings through improvements in fuel efficiency, etc. In addition, by attaching a check valve externally to the existing operating valve and connecting the operating valve and the pilot switching valve with a conduit through this check valve, the high pressure at the pump port is transferred from the pilot port when the operating valve is operated. There is no risk of backflow to the pilot switching valve side and impairing the normal operation of the pilot switching valve, and it also saves energy on existing construction machinery without having to manufacture a new operating valve and replace the existing operating valve. It is economical because it allows for

[Brief explanation of drawings]

The drawings show one embodiment of the present invention, and FIG. 1 is an overall circuit diagram, FIG. 2 is an enlarged view of the main parts, FIG. 3 is a sectional view taken along the line of FIG. 2, and FIG. 4 is a pump. A diagram showing the relationship between pressure and tilt angle, FIG. 5 is an enlarged sectional view of the PC pilot switching valve, and FIG. 6 is an enlarged sectional view of the pump neutral control device. 1 and 2 are variable discharge pumps, 5 to 7 are operating valves, 5 ₂ and 5 ₆ to 7 ₂ and 7 ₆ are pilot ports, 5 ₄ and 5 ₅ to 7 ₄ and 7 ₅ are operating valves on the downstream side. When not in use, it becomes a tank port, 14 is a pipe, 15 is a pilot switching valve, ₁₅₄ is an output port, 20 is a pump neutral control valve, and 25 is a check valve.

Claims (1)

[Scope of Claims] 1 It has a plurality of individually operable spools, and when these spools are operated, hydraulic pressure is supplied to the work equipment actuator from a pump port connected to a variable discharge amount pump, and all of the spools are an operating valve that connects the pump port to the drain circuit when the pump is in a neutral position; A pilot port that is shut off from the tank port when the valve is in the neutral position, and a pump port that is externally attached to the operating valve and that flows into the pilot port of the operating valve to prevent high pressure from flowing toward the pipeline, It has a check valve that allows flow from the pipeline side to the pilot port side, a pilot port connected to the check valve via a pipeline, and a pump port connected to a fixed charge pump, and these pilot ports and the pump The ports are communicated through a restriction provided on the spool, and when the operation valve is operated, the spool is operated by the differential pressure generated when pressure oil flows from the pump port to the pilot port through the restriction. , a pilot switching valve that communicates the output port with the tank port, and the output port of the pilot switching valve and the pressure chamber are connected by a pipe, and the pressure oil introduced from the output port into the pressure chamber controls the variable displacement pump. A hydraulic control device for construction machinery, comprising a pump neutral control device that sets a discharge amount to a minimum flow rate and cancels the setting while removing pressure at an output port of the pilot switching valve.