JPS5973601A - Cavitation preventive conduit - Google Patents

Abstract

PURPOSE:To prevent a cavitation from occurring by delaying a delivery output control section of a variable pump to return to its neutral position at the time when a throttle switch valve is returned to the neutral position. CONSTITUTION:Even when a spool 83 pushes a delay piston 84 in order to move to the right, since the operating fluid in a chamber 82 is drained to a spring chamber 26 only through a throttle 85, the movement of the delay piston 84 is slow, and because of that, the movement of the spool 83 is delayed, the response of a swash plate control cylinder 21 of the variable pump is also delayed, and proportionate to the delay the delivery rate of the variable pump is maintained. Therefore, there exists operating fluid which is drained from a by-pass type pressure compensation valve 13 to a tank line 75, maintaining the pressure in the tank line 75 for a while. Therefore, even when a hydraulic motor 4 coasts due to an inertial force with the throttle switch valve 3 in its neutral position So, a cavitation is prevented from being generated as the pressure in the tank line 75 is maintained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an energy-saving cavitation anti-failure circuit using a variable displacement pump (hereinafter referred to as variable pump).

Recently, as an energy-saving hydraulic circuit, the applicant has installed in the pump line of a variable pump a throttle switching valve with a pilot passage that is closed in the switching position and open in the neutral position leading to the tank, and A bypass type pressure compensation valve is connected between the pump line and the tank to control the differential pressure before and after the throttle in the throttle switching valve to a constant level,
The pump line is connected to a pilot chamber of a discharge rate control valve which switches and connects the discharge rate control section of the variable pump to the pump line and the tank, and the discharge rate is connected to the spring chamber of the discharge rate control valve via a throttle. Connect the pump line and
By connecting the spring chamber to the pilot passage of the throttle switching valve through a pilot line, the bypass type pressure compensation valve can also serve as a surge absorption valve, making it possible to omit the surge absorption valve. When the switching valve is in the neutral state, the spring chamber of the discharge control valve is communicated with the tank via the pilot passage, and the discharge amount control valve is operated.
A method was proposed in which the discharge flow rate of the variable pump was controlled to an extremely small amount to eliminate power loss during neutral operation (Japanese Patent Application No. 1983-214413).

However, the inventor of the present invention has discovered that the energy-saving hydraulic circuit described above has the following problems.

In other words, when trying to stop the actuator by returning the aperture switching method (especially the ABR connection) to neutral,
An actuator (for example, a hydraulic motor) moves by itself due to inertia. At this time, as mentioned above, because the swash plate of the variable pump is suddenly returned to the neutral (feathering position), the pressure in the tank line drops rapidly and has already reached the normal pressure, causing the actuator to act automatically. There is a problem in that it becomes difficult to replenish oil from the tank line when driving, and cavitation occurs.

Therefore, an object of the present invention is to solve the above-mentioned problem, and to maintain the energy saving effect, when the throttle switching method is returned to the neutral position, the discharge amount control section of the variable pump is moved to the neutral position. The purpose of this is to prevent the occurrence of cavitation by delaying the return of the fuel.

In order to achieve the above object, the structure and operation of the present invention include interposing a throttle switching valve in the pump line of the variable pump, which has a pilot passage that is closed at the switching position, opened at the neutral position, and communicates with the tank; A bypass type pressure compensating valve is connected between the pump line and the tank line to control the differential pressure before and after the throttle in the throttle switching valve to be constant, and the discharge M control section of the town displacement pump is connected to the pump. The pump line is connected to a pilot chamber of a discharge control valve which is switched between the line and the tank, while the pump line is connected to a spring chamber of the discharge control valve via a throttle, and the spring chamber is connected to a pilot chamber of the discharge control valve. The discharge amount control valve is connected to the pilot passage of the throttle switching valve via a line and communicates the spring chamber of the discharge amount control valve with the tank via the pilot passage when the throttle switching valve is in neutral. Controlling the discharge flow rate of the variable pump to a small amount by operating the valve to eliminate power loss when the throttle switch No. 1 is in the neutral state, further forming a chamber outside the spring chamber of the discharge amount control valve, A delay piston is slidably fitted into the partition wall between this chamber and the spring chamber to project into the spring chamber and the chamber, and the spring chamber and the chamber are connected through a passage having a throttle. At the same time, the delay piston is biased toward the spring chamber by a spring, and the delay piston delays the operation of the spool of the discharge m control valve life toward the spring chamber. The response of the pump's discharge amount control unit is delayed, the pump flow rate is maintained for a while, and the tank line pressure is maintained to prevent cavitation from occurring even when the actuator operates with inertial force. It has characteristics in points.

Hereinafter, this invention will be explained in detail with reference to the illustrated embodiments.

In Fig. 1, l is a variable pump consisting of a swash plate type variable displacement piston pump whose swash plate is always biased in the direction of maximum inclination to discharge the maximum flow rate, and 2 is connected to the discharge port of variable pump l. The pump line 3 was installed in the pump line 2. ABR connection type throttle switching valve having pump port P, load port) A, B and tank port R;
Reference numeral 4 denotes a hydraulic motor whose operating direction and speed are controlled by the throttle switching valve 3.

The throttle switching valve 3 has the functions of a throttle valve and a directional switching valve, and communicates with the tank 5 in the neutral position, while being located behind the throttle (not shown) of the throttle switching valve 3 in the switching position. In addition to the feedback passage 7 that communicates with the (downstream side) to detect the load pressure, the feedback passage 7 that communicates with the tank 5 that is open at the neutral position
The pilot passage 8 is provided with one pilot passage 8 which is in communication with the other and which is closed in the switching position.

Further, from the pump line 2 on the upstream side of the throttle switching -jf3, a bypass line 12 that communicates with the tank 11 via the tank line 75 is branched, and a bypass type pressure compensation valve 13 is interposed in the bypass line 12. With,
The spring chamber 14 of the pressure compensation valve 13 is connected to the pilot line 1
5 to the load pressure detection port %-172 on the primary side of the feedback passage 7 of the throttle switching valve 3. Therefore, when the throttle switching valve 3 is switched, the bypass type pressure compensation 'jf13 controls the differential pressure before and after the throttle of the throttle switching valve 3 to a constant value corresponding to the spring pressure of the spring 16 of the spring chamber 14. The excess fluid is then discharged into the tank 11. Further, the bypass line 12 downstream of the bypass type pressure compensation valve 13 is connected to a tank and a line 75 connected to the tank port R of the throttle switching valve 3.

Further, the chamber 21a on the opposite spring side of the swash plate control cylinder 21 as a discharge amount control section of the variable pump l is connected to the pump line 2 and the tank 23 via a 3-port restrictor rThjT22 as an example of a discharge amount control valve. This makes it possible to switch connections between the two. Pilot chamber 24 of the discharge amount control valve 22
The pump line 2 is connected to the pump line 2 via a pilot line 25, while the spring chamber 26 of the discharge amount control valve 22 is connected to the pump line 2 via a pilot line 28 with a throttle 27 interposed in the middle. , pilot line 2
The primary bow of the pilot passage 8 of the throttle switching valve 3 is connected through the line 9. Said 111:1.1011-
The spring pressure of the spring 30 in the spring chamber 26 of the control valve 22 is set to be smaller than the spring pressure in the spring chamber 14 of the no-pass type pressure compensation-1i'13.

Further, as shown in the second figure, a chamber 82 is formed outside the spring chamber 26 of the discharge amount control valve 23 via a partition wall 81. - The delay piston 84 is slidably fitted into the partition wall 81 and projects into the spring chamber 26 and the chamber 82. The delay piston 84,
A spring 90 compressed in the chamber 82 urges the spring chamber 26 to bring the outer flange 84a provided on the delay piston 84 into contact with the inner wall surface of the chamber 82. A passage 8 having a throttle 85 at the axis of the delay piston 84
6 is provided to communicate the spring chamber 26 and the chamber 82.

In FIG. 2, 86a is a radial notch, 88 is a spacer, and 89 is a drain port. In the specific structure ζ shown in FIG. 2, first, the same constituent parts as those in the figure are given the same reference numerals and the description thereof will be omitted.

In addition, the spring chamber 26 of the valve 1all valve 22 includes:
A tank 35 is connected via a pilot line 34 with a pilot relief valve 33 interposed therebetween.

In the cavitation prevention IL circuit configured as described above, it is assumed that the throttle switching valve 3 is now positioned at the switching position S□ and the hydraulic motor 4 is rotated in one direction (9).

At this time, the spring chamber 26 of the discharge amount control valve 22 communicates with the pump line 2 via the throttle 27 and the pilot line 28, and the pilot passage 8 of the throttle switching valve 3 is closed. Spring chamber 26 and chamber 8
The pressure of the pump line 2 is the same as that of the pump line 2, and the pilot chamber 24 of the discharge amount control valve 22 also communicates with the pump line 2 via the pilot line 25, so the pressure of the pump line 2 is the same as that of the pump line 2. Therefore, the discharge amount control valve 22 is positioned at the symbol position V□ by the spring force of the spring 30, and the chamber 21a on the opposite side of the swash plate control cylinder 21 is moved to the symbol position V□.
communicates with the tank 23 via the discharge amount control valve 22, and the swash plate control cylinder 21 inclines the swash plate to the maximum inclination side to discharge the maximum flow rate.

- At the switching position S□ of the throttle switching valve 3, the feedback passage 7 communicates with the rear part of the throttle of the throttle switching valve 3, so the spring chamber of the bypass type pressure compensation valve 13 is connected to the spring chamber through the pilot line 15. The bypass type pressure compensation valve 13 (10) controls the differential pressure before and after the throttle to be constant, and discharges the excess fluid to the tank 11.

In this way, at the switching position S□ of the throttle switching valve 3 (the same applies to S2), the pressure of the throttle of the throttle switching valve 3 is compensated by the valve control method using the bypass type pressure compensation valve 13. Fast response and bypass type pressure compensation valve 1
3, excess fluid can be discharged to the tank 11, so the bypass type pressure compensating valve 13 can act as a surge absorbing valve to absorb surge pressure.

Next, suppose that the hydraulic motor 4 is overloaded for some reason and the hydraulic motor 4 is stopped.

Then, the pressure in the pump line 2 increases and the pilot relief valve 33 to which the pressure is guided operates and enters the relief state, controlling the pressure in the spring chamber 26 and chamber 82 of the discharge amount control valve 22 to the set pressure. do. For this reason,
The discharge amount control valve 22 has a pilot chamber 24 and a spring chamber 2.
The variable pump 1 is located at the symbol position V11 or at the symbol position v2 so that the differential pressure between the variable pump 1 and the spring 30 becomes the spring pressure of the spring 30. Control the discharge flow rate. At this time, the pressure of the fluid discharged from the variable pump 1 is high and corresponds to the set pressure of the pilot relief valve 33, but the discharge flow - mold is caused by the differential pressure before and after the small throttle 27 of the pilot line 28. Since the amount is just enough to correspond to the spring pressure of the spring 30 of the discharge amount control valve 27, it is an extremely small amount and can reduce power loss.
Energy saving effect can be achieved.

Note that in the relief state where the hydraulic motor 4 is stopped, no fluid flows through the throttle switching valve 3, so the pilot chamber 38 and spring chamber 16 of the bypass type pressure compensation valve 13
The pressures are the same, and the bypass type pressure compensation valve 13
is stopped in a closed state by the spring force of the spring 16.

Next, while the hydraulic motor 4 is rotating, the throttle switching valve 3 is suddenly moved to the neutral position S. Suppose that it is located at .

Then, the pilot passage 8 of the throttle switching valve 3 is opened and communicated with the tank 5, and the spring chamber 2 of the discharge amount control valve 22 is opened.
6 and the chamber 82 communicate with the tank 5 via the pilot line (12) and the pilot passage 8, the spool 83 of the discharge amount control valve 22 moves to the right in FIG. The valve 22 is located at the symbol position v2 in FIG. 1 and attempts to reduce the discharge flow rate of the variable pump l. However, even if the spool 83 tries to move to the right in FIG. 2 and pushes the delay piston 84 to the right in FIG. Since the air is discharged into the chamber 26, the operation of the delay piston 84 is slow.
Therefore, the movement of the spool 83 is delayed, the response of the swash plate control cylinder 21 of the variable pump 1 is delayed, and the discharge flow rate of the variable pump 1 is maintained accordingly.

Therefore, there is hydraulic oil discharged from the bypass type pressure compensation valve 13 to the tank line 75, and the pressure in the tank line 75 is maintained for a while. Therefore, even if the hydraulic motor 4 moves by itself due to inertia at the neutral position So of the throttle switching valve 3, the pressure in the tank line 75 is maintained, so cavitation is prevented from occurring. .

Thereafter, while discharging the hydraulic oil in the chamber 82 outside the spring chamber 26 of the discharge amount control valve 22 toward the tank 5, the spool 83 of the discharge amount control valve 22 is moved together with the delay piston 84 to the right in FIG. The discharge amount control valve 22 is located at the symbol position v2 in FIG.
The symbol positions Vl and v2 are set so that the differential pressure between the pilot chamber 24 and the spring chamber 26 becomes the spring pressure of the spring 30, that is, the pressure of the pump line 2 becomes the spring pressure of the spring 30.
This is located in the middle of these and controls the discharge flow rate of the variable pump 1.
The discharge flow rate is determined by the small throttle 27 of the pilot line 28.
Since the differential pressure before and after is small enough to correspond to the spring pressure of the spring 30, it is extremely small, and the discharge pressure of the variable pump l is extremely low, corresponding to the spring pressure of the nosine 30. Power loss is reduced. That is, by communicating the spring chamber 26 of the discharge amount control valve 22 with the tank 5,
The variable pump 1 is caused to perform an unload operation in which both the discharge pressure and the discharge flow rate are small.

At this time, the pilot line 2 with the aperture 27
8 and into the spring chamber 26 of the discharge amount control valve 22 is discharged to the tank 5 through the pilot line 29 without passing through the throttle 85, so that the pressure in the spring chamber 26i ( Therefore, the discharge pressure during unloading of the variable pump 1, so-called feathering, becomes a low pressure corresponding to approximately the spring pressure of the spring 30, and power loss is small. ′! At this time, the pilot line 29 is filled with fluid, so next,
When the throttle switching valve 3 is switched to operate the discharge amount control valve 22, the pressures in the spring chamber 26 and the chamber 82 can be quickly increased to increase the responsiveness.

Also, at this time, the spring chamber 1 of the bypass type pressure compensation valve 13
4 is a pilot line 15 and a feedback passage 7
However, since the spring pressure of the spring 16 of the spring chamber 14 is greater than the spring pressure of the spring 30 of the discharge (15) quantity control valve 22, the bypass type pressure compensation valve 13 It remains closed.

FIG. 3 shows a modification in which the present invention is used as a hydraulic circuit for a hydraulic excavator. Parts having the same functions as those shown in FIG.

In FIG. 3, 50 is a pilot valve for constant horsepower control, and signals from the swash plate indicating the discharge pressure of the variable pump 1 and pressure signals of the pump line 2 are transmitted via a signal transmission means 51 such as a link mechanism. The discharge amount control unit 21 is controlled by being located at the symbol position M1 or M2 so that the horsepower resulting from the product of the discharge pressure of the variable pump l and the discharge fM amount becomes constant. If the discharge flow rate is too large relative to the pressure, the line 5 is located at the symbol position M2, regardless of the operating state of the discharge amount control valve 22.
2 to the discharge amount control unit 21 to reduce the discharge amount of the variable pump 1, and if the discharge amount is too small relative to the discharge pressure, the above-mentioned PA (16) pilot valve 22 is moved to the symbol position. In this case, since a check valve 54 is provided in the line 52, the discharge amount control valve 21 is controlled depending on the symbol position of the discharge amount control valve 22.

In addition, 13a is the primary port 56 and the normally open decompression port)
57 A priority type pressure compensation valve having a bypass port 58 of 57 and F[, which also functions as a bypass type pressure compensation valve, and controlling the opening degree between the primary port 56 and the pressure reduction port 57. The pressure of the priority line 59 on the side of the pressure reduction port 57 is compensated for preferentially, while surplus fluid is discharged from the bypass port 58.

Further, 61 is a throttle switching valve 3a connected to the priority line 59.
, 3b is selected and the priority type pressure compensation valve 56 is selected.
62 is the throttle switching valve 3, 3.
This is a shuttle valve that selects the maximum load pressure of and transmits it to the spring chamber of the bypass type pressure compensation valve 13. The hydraulic oil discharged from the bypass type pressure compensation valve 13 is supplied to the tank line 75.

In addition, the pilot passages 8, 8, 8, 8 of each of the calibration switching valves 3+3, 3a+32 are serially connected to the pilot line 29.
The spring chamber of the discharge amount control valve 22 is connected to the tank 5 only when all the throttle switching valves 3, 3, 3a, and 3a are in the neutral position, and the variable pump l is unloaded. That's what I do.

Also, 65.65 is a hydraulic motor for driving a hydraulic excavator,
66 is a swing hydraulic motor, 67 is an arm hydraulic cylinder, 68 is a boom cylinder, and 69 is a packet hydraulic cylinder.

Note that in FIG. 3, the circuit configuration on the left half is substantially the same as the circuit configuration on the right half, so a description thereof will be omitted.

In each of the above embodiments, the throttle switching valve 3.3.31.3a is used, but the throttle valve and the switching valve may be provided separately.

FIG. 4 shows a modification of the discharge amount control valve 22 shown in FIG. 2, and the first difference from FIG. 2 is that a throttle 85 is formed on the outer periphery of the delay piston 84. The second point is that a check valve 100 that allows a free flow from the spring chamber 26 to the chamber 82 is built into the delay piston 84, and by opening this check valve lOO, the return response of the delay piston 8.4 is increased. Specifically, it incorporates a check valve 100 as shown in FIG.

As is clear from the above description, the present invention provides the pump line of a variable pump with a throttle switching valve having a pilot passage that is closed in the switching position, opens in the neutral position, and communicates with the tank, and also connects the pump line with the throttle valve. A bypass type pressure compensating valve is connected between the tank line and the differential pressure before and after the throttle in the throttle switching valve is controlled to be constant, and a discharge amount control section of the variable pump is switchably connected between the pump line and the tank. The pump line is connected to the pilot chamber of the discharge rate control valve, and the pump line is connected to the spring chamber of the discharge rate control valve via a throttle, and the spring chamber is connected to the throttle switching valve via the pilot line. When the throttle switching valve is in neutral, the spring chamber of the discharge amount control valve is communicated with the tank via the pilot passage; A delay piston is slidably fitted into a partition wall between this chamber and the spring chamber to project into the spring chamber and the chamber, and the spring chamber and the chamber are throttled. The delay piston is biased toward the spring chamber by a spring, and the delay piston delays the movement of the spool of the discharge amount control valve toward the spring chamber. By delaying the response of the discharge needle control section of the variable pump, temporarily holding the pump flow meter, and maintaining the pressure in the tank line, cavitation can be prevented even if the actuator operates with inertial force. Moreover, the discharge flow rate and discharge pressure during unloading of the variable pump are small, and in particular, since the fluid discharged from the spring chamber does not pass through the throttle valve, pressure is built up in the spring chamber. The discharge pressure during feathering of the variable pump can be reduced, reducing power loss.

[Brief explanation of drawings]

(20) Fig. 1 is a circuit diagram of an embodiment of the present invention, Fig. 2 is a sectional view of a discharge amount control valve, Figs. 3 and 4 are circuit diagrams of modified examples, and Fig. 5 is a circuit diagram of a modified example. FIG. 1... variable pump, 2... pump line,
3... Throttle switching valve, 4... Hydraulic motor, 8.
... Pilot passage, 13 ... Bypass type pressure compensation valve, 22 ... Discharge-amount control valve, 27.85
...Aperture, 29...Pilot line, 3
0.90...Spring, 81...Partition wall, 82...
- Chamber, 83... Spool, 84... Delay piston, 85... Throttle valve with check valve, 86...
line. Patent applicant Daikin Industries, Ltd. Representative Patent attorney Aoyama Aoyama and 2 others (21)
-6

Claims (1)

[Claims] (1) Variable displacement pump (Suno pump line (2)
ic, a throttle switching valve having a pilot passage (8) that is closed in the switching position and open in the neutral position and communicating with the tank is interposed, and a bypass type pressure compensating valve is provided between the pump line (2) and the tank line. (13) is connected to control the differential pressure before and after the throttle in the throttle switching valve to be constant, and the discharge amount control unit (21) of the variable displacement pump (1) is connected to the Bon Ply pump (C2). and tank (2
The pump line C2) is connected to the pilot chamber (24) of the discharge rate control valve (22), which is switch-connected to the discharge rate control valve (22).
27], and the spring chamber (26) is connected to the pilot passage (8) of the throttle switching valve via a pilot line (29). When the above discharge amount control valve (22
) is communicated with the tank via the pilot passage (8), and the discharge amount control valve (22
) A chamber (82) is formed outside the spring chamber (26), and a partition wall (8υ) is formed between this chamber (82) and the spring chamber (26).
A delay piston (84) is slidably fitted to protrude into the spring chamber (26) and the chamber (B2), and
The spring chamber (26) and the chamber (82) are communicated via a passage 06 having a throttle (85), while the delay piston (8) is connected to the spring chamber (26) by a spring (90).
6, and the delay piston (84) delays the operation of the discharge amount control valve (22nd spool (8th) toward the spring chamber (26,). cavitation prevention circuit.