JPH0893706A - Hydraulic driving circuit - Google Patents

Abstract

PURPOSE: To reliably prevent a drop in a load in an actuator load at crawling speed starting by arranging a circuit switching device to cut off a signal bypass line in a hydraulic driving circuit. CONSTITUTION: A circuit switching device 60 is constituted to control so as to open and close an opening-closing cutoff valve 62 arranged on a signal bypass line 50 through pressure oil of a pilot pump 68 actuated by sector valves 64 and 66 added to respective directional control valves 20 and 22. Since the circuit switching device 60 is arranged to cut off the signal bypass line 50 by switching the opening closing cutoff valve 62 when an actuator is started at crawling speed and is constituted so as to check a conterflow of operating fluid to load detecting lines 28 and 30 from actuator lines 24a, 24b, 26a and 26b, a drop in an actuator load generated so far at crawling speed starting, can be reliably prevented. Therefore, operability and safety of a hydraulic driving circuit can be improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydraulic drive circuit for an actuator for a construction machine or the like, and more particularly to a hydraulic drive circuit for preventing the actuator load from dropping when the actuator is started.

[0002]

2. Description of the Related Art Generally, since a hydraulic drive circuit of this type operates a plurality of actuators having different loads at the same time,
Preferably, it is configured as a load sensing control type hydraulic drive circuit having excellent so-called combined operability.

That is, a load sensing control type hydraulic drive circuit (hereinafter simply referred to as a conventional hydraulic drive circuit)
In FIG. 7, the branch discharge lines 16 and 18 of the discharge line 14 of the variable displacement pump 12 provided with the negative flow rate control type discharge flow rate control means 10 for decreasing or increasing the discharge flow rate with the increase or decrease of the applied pressure. A plurality (two in the illustrated embodiment) of closed center type switching valves 20 and 22 are connected in parallel. The switching valves 20 and 22 are connected to the actuators 24 and 26 via actuator lines 24a, 24b, 26a and 26b, respectively.
The individual and / or maximum load pressures of the actuators 24, 26 when operating the actuators 0, 22 individually or simultaneously to drive the actuators 24, 26 are respectively detected by the load detection lines 28, 30, the high voltage selection means 32 and the maximum load signal line. It is configured to detect via 34. The maximum load pressure of the maximum load signal line 34 is applied to the flow control valve 38 with pressure compensation provided on the bypass line 36 of the variable displacement pump discharge line 14, and the bypass line 3
6 is provided with pressure generating means 40 on the downstream side of the flow control valve with pressure compensation 38 to release it to the tank 42, and the pressure in the upstream line 44 of the pressure generating means 40 is supplied to the variable displacement pump 12 via the pump control signal line 46. Discharge flow control means 1
0, and the highest pressure signal line 34 has a diaphragm 48.
Is configured to be connected to the tank 42 via a signal bypass line 50 including The load detection line 2
8 and 30 are connected to the tank 42 when the switching valves 20 and 22 are in the neutral state.

Therefore, in such a hydraulic drive circuit, when the actuators having different loads are operated in combination, the amount of oil supplied to the low load side actuator is limited so that the pump discharge pressure is automatically adjusted to the drive pressure of the high load side actuator. Therefore, good composite operability can be achieved without causing any trouble such as cavitation.

[0005]

However, the conventional hydraulic drive circuit described above still has the following drawbacks.

Therefore, first, before explaining the above-mentioned difficulties, the circuit operation (actuator drive) associated with the switching valve operation in this type of hydraulic drive circuit will be briefly described. That is, first, assuming that the switching valve 20 is operated to the left in FIG. 7 to perform the opening operation, the branch discharge line 16 is routed to the actuator line 24b and the load detection line 28 via the switching valve passage 20a. Connected. As a result, the load detection line 28 is further connected via the high pressure selection means 32 and the load signal line 34 so as to act on the flow control valve 38 with pressure compensation, so that the variable displacement pump 12 turns on the control valve 38. The discharge flow rate is set to a predetermined value via the pump control signal line 46 and the discharge flow rate control means 10 by the pressure of the upstream line 44 which is set to the predetermined pressure via the pump control signal line 46. That is, the actuator 24 is driven to a predetermined state. At this time, the signal pressure oil in the load signal line 34 is squeezed to a very small amount.
Bleed off into the tank 42 via No. 8. Next, in this state, when the switching valve 20 is closed and returned to the neutral position, the branch discharge line 16 becomes the actuator line 24.
Since the connection to b and the load detection line 28 is cut off, the actuator 24 stops. At this time, since the signal pressure oil in the load signal line 34 is constantly bleeding off into the tank 42 as described above, the pressure thereof decreases. Therefore, the flow control valve with pressure compensation 38 is opened via the discharge bypass line pressure 36a, and the variable displacement pump 12 maintains its discharge flow rate set to the minimum by the upstream pressure 44 where the pressure rises.

To explain the above-mentioned drawbacks, in the conventional hydraulic drive circuit, when the actuator is driven (started) at an extremely low speed (fine speed), in other words,
When the switching valve is operated with an extremely small opening (small opening range), the following problems have occurred. That is, referring to FIG. 8, in the minute opening range operation (symbol diagram B) of the switching valve 20, the branch discharge line 16 has the same path as in the normal opening range operation (symbol diagram A). 20
It is connected to the actuator line 24b and the load detection line 28 via a (therefore, both lines 24
However, in this case, the former passage opening 20b 'is extremely smaller than the latter passage opening 20b. For this reason,
The pressure oil in the actuator 24 carrying the load 24c is
Backflow from the actuator line 24b toward the load detection line 28 (because the signal bypass line 50 is connected to the inside of the tank 42), and as a result, the branch discharge line 16
From this, the amount of pressure oil supplied to the actuator line 24b is insufficient (because the passage opening 20b 'is extremely small), which causes the load 24c to drop (especially when it is large).

That is, the above-mentioned conventional hydraulic drive circuit has a drawback that the actuator load 24c drops when the actuator is started at a very low speed (the switching valve is operated to open in the minute opening range). It is clear that this difficulty impairs operation and safety.

SUMMARY OF THE INVENTION An object of the present invention is to provide a hydraulic drive circuit capable of reliably preventing the load from dropping when the actuator load is started at a very low speed, even when the load is large.

[0010]

In order to achieve the above object, the hydraulic drive circuit according to the present invention is a negative flow rate control type discharge flow rate control means for decreasing or increasing the discharge flow rate with increase or decrease of applied pressure. A plurality of closed center type switching valves are connected in parallel to the discharge line of a variable displacement pump equipped with, and actuators are connected to these switching valves, and these switching valves are operated to drive the actuators individually or simultaneously. When detecting the individual and / or maximum load pressure of the actuator, the maximum load pressure is applied to a flow control valve with pressure compensation provided on the bypass line of the variable displacement pump discharge line, and the bypass discharge line is also applied. Is provided with pressure generating means downstream of the flow control valve with pressure compensation to release it to the tank. In the hydraulic drive circuit configured to apply the upstream pressure of the generating means to the discharge flow rate control means of the variable displacement pump, and to connect the highest pressure signal line to the tank through a signal bypass line having a throttle, In the hydraulic drive circuit, when the switching valve is operated, the connection opening before the actuator line and the actuator load pressure detection line in this switching valve is connected and / or the connection opening between the pump discharge line and the actuator line is in a very small opening range. A circuit switching device for cutting off the signal bypass line while it is inside is provided.

In this case, the circuit switching device includes a pilot operated valve in which an open / close shutoff valve provided on the signal bypass line is connected to a selector valve attached to and interlocking with each switching valve and / or a pilot pressure chamber of each switching valve. It is possible to open and close the signal bypass line itself via a pilot pump pressure oil that operates in accordance with the above, or to open and close the signal bypass line itself via a selector valve provided in each switching valve so as to pass through the signal bypass line. it can.

[0012]

In the present invention, when the actuator is started at a very low speed (the switching valve is operated to be opened in the minute opening range), that is, before the actuator line and the actuator load pressure detection line are connected and / or the pump discharge line is connected. While the connection opening between the actuator lines is within the minute opening range, the signal bypass line is cut off by the circuit switching device, and the signal lines including the load detection line are pressure sealed. Therefore, at the time of starting the actuator at the very low speed, it is possible to prevent the backflow of the hydraulic oil from the actuator line to the load detection line, which has occurred conventionally, and to prevent the actuator load from dropping.

[0013]

Embodiments of the hydraulic drive circuit according to the present invention will now be described in detail with reference to the accompanying drawings. For convenience of explanation, the same components as those of the conventional structure shown in FIGS. 7 and 8 are designated by the same reference numerals, and detailed description thereof will be omitted.

First, the basic construction of the hydraulic drive circuit according to the present invention is the same as the conventional one (FIG. 7).
Therefore, in order to make it easy to understand though it is redundant, the hydraulic drive circuit is basically arranged on the discharge line 14 of the variable displacement pump 12 including the negative flow rate control type discharge flow rate control means 10. , A plurality of (two) closed center type switching valves 20, 22 are connected in parallel, and actuators 24, 26 are connected to these switching valves 20, 22, respectively, and the switching valves 20, 2 are also connected.
The individual and / or maximum load pressures of the actuators 24 and 26 when operating the actuators 24 and 26 individually or simultaneously by operating the load detection lines 28 and 30, the high voltage selecting means 32 and the maximum load signal line 34, respectively. It is configured to be detected through. Then, the maximum load pressure is applied to the flow control valve with pressure compensation 38 provided on the bypass line 36 of the discharge line 14, and
The bypass line 36 is provided with pressure generating means 40 downstream of the pressure-compensated flow rate control valve 38 to release it to the tank 42, and the pressure of the upstream line 44 of the pressure generating means 40 is discharged via the pump control signal line 46. In addition to being applied to the control means 10, the highest pressure signal line 34 is configured to connect to the tank 42 via the throttle 50.

However, according to the present invention, in the above-mentioned structure, when the actuator is started at a very low speed in this circuit (that is, when the switching valve is operated, before the actuator line and the actuator load pressure detection line in the switching valve are connected. And / or a circuit switching device that shuts off the signal bypass line while the connection opening between the pump discharge line and the actuator line is within the minute opening range. Thus, it is possible to prevent the backflow of the hydraulic oil from the actuator line to the load detection line at the time of starting the actuator at the slow speed, and to prevent the actuator load from dropping.

In the present embodiment, the circuit switching device 60 basically operates an open / close shutoff valve 62 provided on the signal bypass line 50 by means of selector valves 64 and 66 attached to the respective switching valves 20 and 22. The pilot pump 68 is configured to be opened / closed via pressure oil. More specifically, the pilot pressure oil passes from the pilot pump 68 through the pilot line 70, the throttle 72, and is branched here, and one pilot line 74 is connected to the selector valve 6
4, the oil passage 78, the selector valve 66, and the oil passage 80 are opened to the tank 42, and the other pilot line 76 is connected to the opening / closing cutoff valve 62. When the switching valves 20 and 22 are both in the neutral position, the pilot lines 72 and 74,
The valve 76 is opened to the tank 42 via the neutral position of the selector valves 64 and 66. However, when either of the switching valves 20 and 22 is operated, the pilot lines 72, 74 and 76.
Is shut off from the tank 42 by switching one of the selector valves 64 and 66 to the closed position, and the line internal pressure rises.

Therefore, the open / close shutoff valve 62 is switched to shut off the signal bypass line 50. That is, in the present invention, referring to FIG. 2 (note that FIG. 2 corresponds to FIG. 8 described above), the branch discharge line 16 is operated in the minute opening range operation (symbol B) of the switching valve 20. Actuator line 2 via passage 20a
4b and the load detection line 28 (thus,
When the two lines 24b and 28 are communicated with each other), even if the passage opening 20b 'is very small, the selector valve 64 is switched to the closed position at this time so that the internal pressure of the pilot line 76 increases. Is applied to the open / close shutoff valve 62 to shut off the signal bypass line 50 in advance. And thereby, it is comprised so that the backflow of the hydraulic fluid from the actuator line 24b to the load detection line 28 may be prevented. The open / close cutoff valve 62 may be configured as an open / close cutoff valve 82 with a throttle 82a as shown in FIG.

As described above, according to the present invention, by providing the circuit switching device 60 for shutting off the signal bypass line at the time of starting the actuator at a low speed, it is possible to prevent the reverse flow of the hydraulic oil from the actuator line to the load detection line. With the configuration, it is possible to reliably prevent the drop of the actuator load, which has conventionally occurred, at the time of starting at the slow speed. Therefore, the operability and safety of the hydraulic drive circuit can be improved.

4 to 6 show different embodiments of the hydraulic pressure drive circuit according to the present invention. First,
The embodiment shown in FIGS. 4 and 5 basically has the selector valves 64 and 66 in the previous embodiment (FIG. 1).
The function of the control valve is changed so that the same operation is performed by the directional control valves 84 and 86 for pilot operation attached to the respective control valves 20 and 22. That is,
In these embodiments, the pilot pressure oil from the pilot pump 68 passes through the directional control valves 84, 86 when both the directional control valves 20, 22 are in the neutral position and the directional control valves 84, 86 are in the neutral position. Although it is opened to the tank 42 through the oil passages 90 and 92, the pilot pressure oil immediately enters the pilot line 88 when any of the directional switching valves 84 and 86 is operated to operate the switching valves 20 and 22. Through the high voltage selecting means, the highest signal pressure is applied to the circuit switching device 60 provided on the signal bypass line 50 to shut off the signal bypass line 50. As a result, backflow of hydraulic oil from the actuator line to the load detection line is prevented when the actuator is started at a slow speed, and the actuator load can be prevented from dropping. In this case, the circuit switching device 60 arranged in the embodiment of FIG. 4 is the same opening / closing shutoff valve 62 as in the previous embodiment (FIG. 1),
The circuit switching device 60 shown in the embodiment is an opening / closing cutoff valve 63 different from the opening / closing cutoff valve 62, and is provided while the connection opening between the pump discharge line and the actuator line is within the minute opening range. That is, the signal bypass line 50 is cut off only when the actuator is started at a slight speed. Therefore, when the actuator is driven to a predetermined state, a small amount of the signal pressure oil in the load signal line is ensured to be bleed-off to the tank through the throttle.

Next, the embodiment shown in FIG. 6 is different from the previous embodiment (FIG. 1) in that the signal bypass line 50 is passed through the selector valves 64 and 66 without using the pilot pump 68. The signal bypass line 50 is configured to be directly opened / closed by the selector valves 64 and 66.

Since it is clear that all of these modified embodiments operate in substantially the same manner as in the previous embodiment, detailed description thereof will be omitted.

Although the preferred embodiment of the present invention has been described above, the present invention is not limited to the above embodiment, and many design changes can be made without departing from the spirit of the present invention.

[0023]

As described above, in the hydraulic drive circuit according to the present invention, a plurality of closed center type switching valves are connected in parallel to the discharge line of the variable displacement pump having the negative flow rate control type discharge flow rate control means. Actuators are connected to these switching valves, the individual and / or maximum load pressures of these actuators are detected, and this maximum load pressure is applied to the flow control valve with pressure compensation provided on the bypass line of the pump discharge line. The bypass line is provided with pressure generating means downstream of the pressure compensating flow rate control valve to release it to the tank, and the upstream side pressure of the pressure generating means is applied to the discharge flow rate controlling means. In a load-sensing controlled hydraulic drive circuit configured to connect to the tank via a signal bypass line with a throttle, this oil In the drive circuit, when the actuator is started at a very low speed (that is, when the switching valve is operated, before the actuator line and the actuator load pressure detection line in this switching valve are connected and / or the connection opening between the pump discharge line and the actuator line) Is within a small opening range), a circuit switching device for shutting off the signal bypass line is provided to prevent backflow of hydraulic oil from the actuator line to the load detection line. Can surely prevent the actuator load from dropping when the vehicle is started at the slow speed. Therefore, according to the hydraulic drive circuit of the present invention, the operability and safety of this circuit can be improved.

[Brief description of drawings]

FIG. 1 is a hydraulic circuit diagram showing an embodiment of a hydraulic drive circuit according to the present invention.

FIG. 2 is a symbol diagram showing a connection state of each line in the switching valve when operating a small opening range of the switching valve in the hydraulic drive circuit shown in FIG.

FIG. 3 is a symbol diagram showing another embodiment of the opening / closing cutoff valve in the hydraulic drive circuit shown in FIG.

FIG. 4 is a hydraulic circuit diagram showing another embodiment of the hydraulic drive circuit according to the present invention.

5 is a symbol diagram showing another configuration example of the opening / closing cutoff valve in the hydraulic drive circuit shown in FIG.

FIG. 6 is a hydraulic circuit diagram showing still another embodiment of the hydraulic drive circuit according to the present invention.

FIG. 7 is a hydraulic circuit diagram showing a conventional hydraulic drive circuit.

8 is a symbol diagram showing a connection state of each line in the switching valve when operating the minute opening region of the switching valve in the hydraulic drive circuit shown in FIG. 7. FIG.

[Explanation of symbols]

 10 Discharge Flow Rate Control Means 12 Variable Displacement Pump 14 Discharge Lines 16, 18 Branch Discharge Lines 20, 22 Switching Valves 24, 26 Actuators 28, 30 Load Detection Lines 32 High Pressure Selection Means 34 High Pressure Load Signal Lines 38 Pressure Compensated Flow Control Valves 40 Pressure generating means 42 Tank 44 Upstream line 46 Pump control signal line 48 Throttle 50 Signal bypass line 60 Circuit switching device 62, 63 Open / close shutoff valve 64, 66 Selector valve 68 Pilot pump 70, 74, 76 Pilot line 72 Throttle 78, 80 Oil passage 82 Open / close shutoff valve 84, 86 Direction switching valve 88 Pilot line 90, 92 Oil passage

Claims (3)

[Claims] 1. A plurality of closed center type switching valves are connected in parallel to a discharge line of a variable displacement pump equipped with a negative flow rate control type discharge flow rate control means for decreasing or increasing a discharge flow rate with an increase or decrease in applied pressure. However, actuators are connected to these switching valves, and the individual and / or maximum load pressures of the actuators when operating these switching valves to drive the actuators individually or simultaneously, the maximum load pressures are detected. It is applied to a flow control valve with pressure compensation provided on the bypass line of the variable capacity pump discharge line, and the bypass discharge line is provided with pressure generating means downstream of the flow control valve with pressure compensation and released to the tank. Applying the upstream pressure of the pressure generating means to the discharge flow rate control means of the variable displacement pump In addition, in the hydraulic drive circuit configured to connect the highest pressure signal line to the tank through a signal bypass line having a throttle, in the hydraulic drive circuit, when operating the switching valve, an actuator line in the switching valve A circuit switching device for disconnecting the signal bypass line is provided before the actuator load pressure detection line is connected and / or before the connection opening between the pump discharge line and the actuator line is within the minute opening range. A hydraulic drive circuit characterized in that 2. The circuit switching device is a pilot operated valve in which an open / close shutoff valve provided on a signal bypass line is connected to a selector valve attached to and interlocking with each switching valve and / or a pilot pressure chamber of each switching valve. The hydraulic drive circuit according to claim 1, wherein the hydraulic drive circuit is configured to be opened / closed via an operating pilot pump pressure oil. 3. The hydraulic drive according to claim 1, wherein the circuit switching device is configured to open / close the signal bypass line itself via a selector valve laid on each switching valve so as to pass through the signal bypass line. circuit.