JPS5969505A - Cavitation preventing circuit - Google Patents

Abstract

PURPOSE:To prevent cavitation occurrence and to decrease the dischaging pressure at a time of feathering of a variable (volumetric) pump by delaying the operation of the pump discharge control valve and maintaining the flow rate of the pump when a throttle-switching valve used to control a hydraulic motor is at the neutral position. CONSTITUTION:A pump line 2 of a variable delivery pump 1 is connected with a hydraulic motor 4 via a throttle-swtiching valve 3, while a pressure compensating valve 13 is connected between the pump line 2 and a tank line 75. The pump line 2 is connected to a discharge control valve 22. The pressure oil is switched over to a tank 23 or to a discharge rate control part 21 of the variable delivery pump 1 by means of the valve 22. The valve 22 connects its spring chamber 26 to the line 2 via a throttle 27 and also to a pilot passage 8 of the throttle- switching valve 3 via a pilot line 29. In addition, a hydraulic remote control valve 100 is installed. The secondary ports X and Y of said control valve 100 are connected to a chamber 82 of a discharge control valve 22 via pilot chambers 101 and 102 of the throttle-switching valve 3, a shuttle valve 95, and a throttle valve 85.

Description

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

Recently, the applicant has designed an energy-saving hydraulic circuit by interposing 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 well is connected between the double pump line and the tank to control the differential pressure before and after the throttle in the throttle switching valve to a constant level, and - The pump line is connected to a pilot chamber of a discharge rate control valve which is switchably connected to the pump line and the tank, and the pump line is connected to a spring chamber of the discharge rate control valve via a throttle, and the spring chamber is connected to the spring chamber. By connecting the bypass type pressure compensation valve to the pilot passage of the double restrictor switching valve via the 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 throttle switching valve is in the neutral state, the spring chamber of the discharge rate control valve is communicated with the tank via the pilot passage, and by operating the double discharge rate control valve, the discharge rate of the double variable pump is reduced to an extremely small amount. He proposed a system in which power loss was eliminated when the vehicle was in neutral by controlling the power to the vehicle (Japanese Patent Application No. 56-2 [44] No. 3).

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 attempting to stop the actuator by returning the throttle valve (particularly one connected to ABR) to neutral, the actuator (for example, a hydraulic motor) moves by itself due to inertia. Because the swash plate of the pump is suddenly returned to neutral (feathering position), the pressure in the tank line decreases rapidly and is already at a low pressure, causing the oil to flow from the tank line against the free movement of the actuator. There is a problem that replenishment becomes difficult and cavitation occurs.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems, and to maintain the energy saving effect while maintaining the neutral position of the discharge amount control section of the variable pump when the throttle switching valve is returned to the neutral position. The purpose is to prevent cavitation from occurring by delaying the return to the position.

In order to achieve the above object, the structure and operation of the present invention is such that a throttle switching valve having a pilot passage that is closed at the switching position, opened at the neutral position, and communicates with the tank is interposed in the pump line of the variable pump. 1. 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 a constant level, and the discharge rate control section of the variable displacement pump is controlled as described above. While connecting the pump line to the pilot chamber of the discharge amount control valve which is switchably connected to the pump line and the tank,
The pump line is connected to the spring chamber of the discharge amount control valve via a throttle, and the spring chamber is connected to the pilot passage of the throttle switching valve via a pilot line to neutralize the throttle switching valve. At times, by communicating the spring chamber of the discharge rate control valve with the tank via the pilot passage, the discharge rate of the variable pump is controlled to an extremely small amount by operation of the discharge rate control valve, and throttle switching is performed. In order to eliminate power loss when the valve is in the neutral state, a chamber is formed outside the spring chamber of the discharge rate control valve, and a spool of the discharge rate control valve is formed on the partition wall between this chamber and the spring chamber. A part of the can be slid freely ((through it and protruded into the above chamber, and
The secondary port of the hydraulic remote control valve is throttled to communicate with the pilot chamber (C) of the switching valve, and the secondary port of the hydraulic remote control valve is connected to the pilot chamber (C) of the switching valve. port,
By communicating with the chamber of the discharge control valve through a line having a throttle valve, when the throttle switching valve is in the neutral state,
providing resistance to the discharge of the fluid in the chamber by a double throttle valve and delaying the movement of the spool of the discharge amount control valve;
The response of the variable pump's discharge rate 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. 4. Hereinafter, this invention will be described in more detail with reference to the illustrated embodiment (C).

In FIG. 1, J is, for example, 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 1. The pump line 3 was installed in the pump line 2. The connected throttle switching valve 4 is 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 further communicates with the tank 5 in the neutral position, while in the switching position it is located behind one throttle (not shown) of the throttle switching valve 3. 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
A bypass line 12 is connected to the tank IIK via a tank line 75 from the pump line 2 on the upstream side of the throttle switching valve 3 described in -1-. branching, and interposing a bypass type pressure compensation valve 13 in the bypass line 12,
The spring chamber 14 of the pressure compensation valve 13 is connected to the pilot line 1
5 to the load pressure detection port 7a 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 valve 13 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 line 75 connected to the tank port RK of the throttle switching valve 3.

Further, the pump line 2 and the tank 23 are connected via a chamber 21aU on the opposite spring side of the swash plate control cylinder 21 as a discharge amount control section of the variable pump 1, and a 3-port throttle switching valve 22 as an example of a discharge amount control valve. This makes it possible to switch connections between the two. In the pilot chamber 24 of the discharge amount control valve 22,
The pump line 2 is connected via a pilot line 25, and the spring chamber 26 of the discharge amount control valve 22 is connected to the pump line 2 via a tail line 28 with a throttle 27 interposed in the middle. Pilot passage 80 primary port sa of throttle switching valve 3 via line 29
is connected to. The spring pressure of the spring 30 in the spring chamber 26 of the discharge amount control valve 22 is set smaller than the spring pressure of the spring 16 in the spring chamber 14 of the bypass type pressure compensation valve 13.

Furthermore, as the specific structure is shown in FIG. 2, a chamber 82 is formed outside the spring chamber 26 of the discharge amount control valve 23 with a partition wall 81 in between. On the other hand, the spool 83 of the discharge amount control valve 22 is integrally formed with a piston portion 83a that penetrates the spring chamber 26 and further slidably penetrates the partition wall 81 and projects into the chamber 82. A central port 95a of a shuttle valve 95 is connected to the chamber 82 via a line 86 having a check valve equipped throttle valve 85 as an example of a throttle valve.
Connecting. ” Ports 95b at both ends of the double shuttle valve 95
, 95C, respectively, secondary port of hydraulic remote control valve 100)
, connect to Y. When the lever 100a of the hydraulic remote control valve 100 is in the neutral position, the secondary port
, Y are connected to the tank port TVc that communicates with the tank 104, and when the lever 100a is switched, the pump port P connected to the pressure source 105 is connected to the secondary port X and the secondary port Y. . ” Dual secondary port
The pilot chamber 101 of the throttle switching ff3 is installed between the and the one @ of the shuttle valve 95, -f neat 95b, and the throttle is connected between the secondary port Y and the port 95C at the other end of the shuttle valve 95. The pilot chamber 102 of the switching valve 3 is connected.

In FIG. 2, 88 is a spacer and 89 is a drain port. In the specific structure shown in FIG. 2, the same components as those in FIG. 1 are given the same reference numerals and their explanations will be omitted.

Further, a tank 35 is connected to the spring chamber 26 of the discharge amount control valve 22 via a pilot line 34 having a pilot relief valve 33 interposed therebetween.

In the cavitation prevention circuit having the above configuration, the lever 100a of the hydraulic remote control valve 100 is now switched to the right in FIG. The pressure of the pressure source 105 is guided to +02 and the throttle switching valve 3 is switched to the switching position 5I.
VC position, secondary port Y, shuttle valve 95
and the pressure source 105 through the throttle valve 85 with check valve.
It is assumed that the pressure of .

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. The pressure in the spring chamber 26 is the same as the pressure in the pump line 2, and the pressure in the discharge rate control valve 2 is the same as that in the pump line 2.
Since the pilot chamber 24 of No. 2 is also in communication with the pump line 2 through the pilot line 25, it has the same pressure as the pump line 2. Further, the pressure in the chamber 82 is equal to the pressure source 1
It will be the same as 05. Note that the pressure source 105 is set to approximately the same pressure as the pump line 2. Therefore, the discharge amount control valve 22 is located at the symbol position vI due to the spring force of the spring 30, and the discharge amount control valve 22 is positioned at the symbol position vI due to the spring force of the spring 30.
u Communicates with the tank 23 via the discharge amount control valve 22, and swash plate control/linda 2 + &t,'i:'[The plate is tilted to the maximum inclination side to discharge the maximum flow 11''-\.

On the other hand, at the switching position SI of the throttle switching valve 3, the feedback passage 7 communicates with the rear part of the throttle of the throttle switching valve 3. Load pressure is introduced, and the bypass type pressure compensation valve 13 controls the differential pressure before and after the throttle to be constant, and discharges excess fluid to the tank 11.

In this way, at the switching position 81 (the same applies to 82) of the throttle switching valve 3, 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, so the response is Fast 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, the hydraulic motor 4 is overloaded for some reason,
Assume that the hydraulic motor 4 has stopped.

Then, the pressure in the pump line 2 increases by 1, and the pilot relief valve 33 to which this pressure is guided operates.
The IJ-f state is reached, and the discharge amount control valve 2 is adjusted to the set pressure.
The pressure in the second spring chamber 26 is controlled.

For this reason, the discharge amount control valve 22 is operated in its pilot chamber 24.
It is located at symbol position ■1 or symbol position ■2 so that the differential pressure between the The discharge flow rate of the pump 1 is controlled.At this time, the pressure in the discharge gutter body of the variable pump 1 is high and corresponds to the pressure set in the pilot relief valve 33, but the discharge flow rate is controlled by the small pressure in the pilot line 28. Since the differential pressure before and after the throttle 270 is only 7Th of the value corresponding to the spring pressure of the spring 30 of the discharge amount control valve 27, it is extremely small, reducing power loss and achieving an energy saving effect. - Note that when the hydraulic motor 4 is stopped or in the IJ-) state, no fluid flows through the throttle switching valve 3, so the pilot chamber 38 of the bypass type pressure compensation valve 13 and the spring chamber 1
6 is the same pressure, and the bypass type pressure compensation valve 1
3 is stopped in a closed state by the spring force of the spring 16.

Next, while the hydraulic motor 4 is rotating, the lever 100a of the hydraulic remote control valve 100 is placed in the neutral position, and the secondary port is
Connect both ports X and Y to the tank port P, and connect the pilot chambers 101 and 102 of the throttle switching valve 3 to the tank 104.
It is assumed that the throttle switching valve 3 is placed in a neutral position of 5oVc.

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 communicates with the tank 5vc via the pilot line 29 and the pilot passage 8, and the discharge amount control valve 220
A line 86 in which the chamber 26 has a throttle valve 85 with a check valve
, secondary port of shuttle valve 95 and hydraulic remote control valve 100) X, Y.

In order to communicate with the tank 104 through the tank port (tank port) T, the spool 83 of the discharge amount control valve 22 moves to the right in FIG.
The discharge flow rate of the variable pump 1 is attempted to be decreased. However, even if the spool 83 tries to move to the right in FIG. Since it is discharged into the tank 104 only through the throttle valve part 85a, 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 variable pump 1
The discharge flow rate will be maintained. 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 force 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 104, the spool 83 of the discharge amount control valve 22 is located on the right side in FIG. , the discharge amount control valve 22 (1 located at symbol position 2 in Fig. 1, and the pilot chamber 24 of the discharge amount control valve 22
It is located at symbol position Vl or ■2 so that the differential pressure between the The discharge flow rate of the variable pump 1 is controlled by being located between them. The discharge flow rate of the variable pump 1 is determined by the differential pressure before and after the small throttle 27 of the pilot line 28.
Since the amount is enough to give a spring pressure of 0, it is extremely small, and the discharge pressure of the variable pump 1 is extremely low, corresponding to the spring pressure of the spring 30, so the power loss is minimal. There is. 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 where both the discharge pressure and the discharge flow rate are small.

Also, at this time, the pilot line 2 having the aperture 27
8 and into the spring chamber 26 of the discharge amount control valve 22 is extracted into the tank 5 through the pilot line 29 without passing through the throttle valve 85 with check valve. Therefore, the discharge pressure during unloading of the variable pump 1, so-called feathering, is a low pressure corresponding to approximately the spring pressure of the spring 30, and power loss is small. Also, at this time, the pilot line 29 is filled with flowing fluid, so next time when the throttle switching valve 3 is switched to operate the discharge amount control valve 22, the pressure in the spring chamber 26 and the chamber 82 will be reduced. The valve can be raised quickly and the response can be made quick, and since hydraulic oil is supplied to the chamber 82 through the check part 85b of the throttle valve 85 with a check valve, the response can be made quick. When the spring chamber 14 of the bypass type pressure compensation valve 13 (d communicates with the tank 5 via the pilot line 15 and the feedback passage 7, the spring pressure of the spring 16 of the spring chamber 14 is lower than the discharge amount control valve 22). Since the spring pressure is larger than the spring pressure of the spring 30, the bypass type pressure compensation valve 13 remains closed. Parts having the same functions as those shown in FIG.

In FIG. 3, 50 is a pilot valve for constant horsepower control, and a signal from the swash plate indicating the discharge amount of the variable pump 1 and a pressure signal 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 M or M2 so that the horsepower obtained by multiplying the discharge pressure and the discharge flow rate of the variable pump 1 is constant. If the discharge flow rate is excessive relative to the pressure, the valve is located at symbol position M2 and the fluid is supplied to the discharge rate control unit 21 via the line 52 regardless of the operating state of the discharge rate control valve 22. to reduce the discharge amount of the variable pump 1, and if the discharge amount is too small with respect to the discharge pressure, the pilot valve 22 is moved to the symbol position M, but this is the position.

13a is the primary port 56 and the normally open decompression port 57
A preferential expansion pressure compensation valve having a normally closed bypass port 58 and also functioning as a bypass type pressure compensation valve,
The opening degree between the primary port 56 and the pressure reduction port 57 is controlled to preferentially compensate the pressure of the priority line 59 on the pressure reduction port 57 side, while draining excess fluid from the bypass port 58.

61 is the throttle switching valve 3a connected to the priority line 59
, 3b is selected and the priority expansion pressure compensation valve 56 is activated.
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 fluid that is lost through the bypass type pressure compensation valve 13 is supplied to the tank line 75.

In addition, the pilot passages 8.8, 8.8 of the above-mentioned calibration switching valves 3, 3.3a, 3a are connected in series to the pilot line 29, so that all the throttle switching valves 3, 3, 3a, 3a are in the neutral state. The spring chamber of the discharge rate control filTI well 22 is communicated with the tank 5 ((), and the variable pump 1 is operated in an unloaded state only when the variable pump 1 is in the position.

Also, 65.65 is a hydraulic motor for driving a hydraulic excavator,
66 is a swing hydraulic motor, 67 is an arm oil field cylinder, 68 is a boom hydraulic 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.

Although the throttle switching valves 3, 3.3a, and 3a are used in each of the above embodiments, the throttle valve and the switching valve may be provided separately.

Further, the oil field remote control valve may be of a type having only one secondary port.

As is clear from the following description, the present invention provides a throttle switching valve in the pump line of a variable pump, which is closed in the switching position, opens in the neutral position, and has a pilot passage leading to 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 a constant level, and a discharge amount control section of the variable pump is connected between the pump line and the tank. The pump line is connected to the pilot chamber of the discharge rate control valve which is connected to the discharge rate control valve, while the pump line is connected to the spring chamber of the discharge rate control valve via the throttle, and the spring chamber is connected to the pilot chamber through the pilot line. - connected to the pilot passage of the throttle switching valve, so that when the throttle switching valve is in neutral, the spring chamber of the discharge rate control valve is communicated with the tank via the pilot passage; A chamber is formed outside the chamber, a part of the spool of the discharge amount control valve is slidably penetrated through a partition wall between the chamber and the spring chamber, and projects into the chamber, furthermore, The secondary port of the hydraulic remote control valve is connected to the pilot chamber of the throttle switching valve, and the secondary port of the hydraulic remote control valve is connected to the pilot chamber of the throttle switching valve. Since the next port is communicated with the chamber of the discharge amount control valve through a line having a throttle valve, when the throttle switching valve is in the neutral state, the throttle valve provides resistance to the discharge of the fluid in the chamber. By delaying the movement of the spool of the above-mentioned discharge rate control valve, the response of the discharge rate control section of the variable pump is delayed, and the pump flow rate is maintained for a while, the pressure of the tank line is maintained, and the actuator operates with inertial force. Moreover, the discharge flow rate and discharge pressure during unloading of the variable pump are small, and especially since the fluid discharged from the spring chamber does not pass through the throttle valve, the spring chamber Therefore, the discharge pressure during feathering of the variable pump can be reduced, and power loss can be reduced.

[Brief explanation of the drawing]

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, and FIG. 3 is a circuit diagram of a modified example. 1 Variable pump, 2 Pump line, 3 Throttle switching valve, 4 Hydraulic motor, 8 Pilot passage, 13 Bypass pressure compensation valve, 22 Discharge rate control valve, 27 Throttle,
29 Pilot line, 81... Partition wall, 82 - Chamber, 83... Spool, 85... Chinic valve example throttle valve, 8
6...Line, 100...Hydraulic remote control valve. Patent applicant Daikin Industries, Ltd. Agent Patent attorney Aoyama Ao Two idiots Figure 2, 4 T''

Claims (1)

[Claims] (1) Pump line (2) of variable displacement pump (1)
) d. A throttle switching valve having a pilot passage (8) which is closed in the switching position and opened in the neutral position leading to the tank is interposed, and a bypass type pressure compensation is provided between the pump line (2) and the tank line. A valve (13) is connected to control the differential pressure before and after the throttle in the throttle switching valve to a constant value, and the discharge amount control section (21) of the variable displacement pump (1) is connected to the pump line (2) and the tank. Pilot chamber (24) of the discharge control valve (ρ) which is connected to the
At the same time, the pump line (2) is connected to the spring chamber (2B) of the discharge amount control valve (22) via the throttle (27), and +C1 is connected to the spring chamber (26). ) is connected to the pilot passage (8) of the throttle 9 switching valve through the pilot line (2)), and when the throttle switching valve is in neutral, the spring chamber (■) of the discharge amount control valve (22) is connected to the pilot The spring chamber (2) of the discharge amount control valve (ρ) is connected to the tank through the passage (8), and
A chamber (82) is formed on the outside of the chamber (82), and one of the spools (83) of the discharge amount control valve (22) is connected to the partition wall (81) between this chamber (clear) and the spring chamber (26). The section is slidably penetrated to protrude into the chamber (82), and furthermore, the secondary port (X, Y) is communicated with the tank port (T) when in neutral = pump bow when switching directions) (P ) to the secondary port (X or Y). Hydraulic remote control valve (100
) (X, Y) are communicated with the pilot chamber (101, 102) of the throttle switching valve (3), and the secondary port (X or Y) of the hydraulic remote control valve (100)
is communicated with the chamber (82''iK) of the discharge amount control valve (22) through a line (86) having a throttle valve (■),
When the throttle switching valve (3) is in neutral, the throttle valve (85) provides resistance to the discharge of the fluid in the chamber (c), thereby delaying the movement of the spool of the discharge amount control valve (22). cavitation prevention circuit.