JP3483313B2 - Hydraulic drive circuit - Google Patents

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, the load sensing control type hydraulic drive circuit is excellent in so-called combined operability.

That is, a load sensing control type hydraulic drive circuit (hereinafter simply referred to as a conventional hydraulic drive circuit)
5, generally, a plurality of (two in the illustrated embodiment) branch discharge lines 16 and 18 and one discharge bypass are provided in the discharge line 14 of the variable displacement pump 12 provided with the negative flow rate control type discharge flow rate control means 10. A line 20 is provided. Then, the branch discharge lines 16 and 18 are respectively provided with closed center type directional control valves 22 and 24 in parallel, and the pump discharge pressure oil is supplied to the actuators 26 and 28 via the actuator lines 26a, 26b, 28a and 28b. After being supplied to the tank 34, the return oil is returned to the tank 34 via the auxiliary valves 30 and 32, and the directional switching valves 22 and 24 are operated to operate the actuators 26 and 28 individually or simultaneously. Each signal line 3 for detecting the individual and / or maximum load pressure of the actuators 26, 28 when driven
8, 40, 44 are provided. The reference numeral 42 indicates a high voltage selecting means.

On the other hand, the discharge bypass line 20 is provided with a pressure compensating flow control valve 46 and a pressure generating means (relief valve with a throttle) 48 in this order from the upstream side so as to be connected to the tank 34 and upstream of the pressure generating means 48. The side pressure 50 is applied to the discharge flow rate control means 10 of the variable displacement pump 12 via the pump control signal line 52. The characteristics of (the upstream pressure 50 of) the pressure generating means 46 and the negative flow rate control type variable displacement pump 12 are shown in FIG.
And the pq and Qp diagrams shown in 7 and
These will be described later. And each auxiliary valve 30, 3
2, the individual load pressure 3 in the respective opening direction
8 and 40 are applied and the maximum load pressure is 4 in the closing direction.
4 is applied, the maximum load pressure 44 is applied to the flow control valve with pressure compensation 46 in the closing direction, and the maximum load signal line 44 is applied.
Is provided with a signal bypass line 56 having a diaphragm 54 and is connected to the tank 34.

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 automatically reaches the drive pressure of the high load side actuator. Therefore, good composite operability can be achieved without causing obstacles such as cavitation.

[0006]

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

Therefore, first, before describing the above-mentioned difficulties, the circuit operation (actuator drive) associated with the operation of the directional control valve in this type of hydraulic drive circuit will be briefly described. First, when the direction switching valve 22 is in the closed position at the neutral position, the branch discharge line 16 is connected to the actuator line 26b.
And both are disconnected from the individual load signal line 38. Therefore, the pump discharge pressure oil is not supplied to the branch discharge line 16 (the actuator 26 is not driven) and flows only to the discharge bypass line 20, whereby the pressure compensation flow rate control valve 46 causes the discharge bypass line pressure 20a. Is opened via. At this time, since a small amount of the signal pressure oil in the maximum load signal line 44 is constantly bleed-off into the tank 34 via the signal bypass line 56 with the throttle 54, the pressure drops. There is. Therefore, the flow rate of the discharge bypass line 20 is set to the maximum value q2 (Fig. 6). Therefore, the pressure generating means 48 is
The upstream side pressure is set to the maximum value p2, and the variable displacement pump 12 is set to the minimum value Q2 (FIG. 7) in the discharge flow rate.

Next, the directional control valve 22 is shown in FIG.
For example, when operating to the left to perform opening operation, the branch discharge line 16 passes through the directional control valve passage 22a and the actuator line 26b and the individual load signal line 38.
Connected together. Therefore, the individual load signal line 38
Further acts on the flow control valve with pressure compensation 46 via the high pressure selection means 42 and the maximum load signal line 44, and operates this in the closing direction to bring the flow rate of the bypass line to a predetermined value q (FIG. 6). Then, the pressure generating means 48 sets the upstream pressure to a predetermined value p. As a result, the variable displacement pump 12 sets the discharge flow rate to the predetermined value Q (FIG. 7). That is, the actuator 26 is driven in a predetermined state. Even in this case, the signal pressure oil in the maximum load signal line 44 is always bleed off into the tank 34 in a minute amount, as described above. Further, reference numeral p1 in the drawing indicates a bypass line flow rate, q1 indicates a minimum or minimum value of upstream pressure, and Q1 indicates a maximum value of pump discharge flow rate.

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 opening the directional control valve 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 directional control valve 22, the branch discharge line 16 is the same as in the normal opening range operation (symbol diagram A). Actuator line 26b via inner passage 22a
And the individual load signal line 38 (hence,
Of course, both lines 26b and 38 are communicated with each other. However, in this case, however, in the case of the former, the passage opening 2
2b 'is extremely smaller than the latter passage opening 22b. Therefore, the actuator 2 carrying the load 26c
The pressure oil in 6 flows backward from the actuator line 26b toward the individual load signal line 38 (because the signal bypass line 56 is connected to the tank 34), and as a result, the pressure from the branch discharge line 16 to the actuator line 26b is increased. The oil supply amount was insufficient (because the passage opening degree 22b 'was extremely small), which caused the load 26c to drop (especially when it was large).

That is, the conventional hydraulic drive circuit has a drawback that the actuator load drops when the actuator is started at a very low speed (the directional control valve is operated to be opened in a very small 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 a load drop when an actuator load is started at a very low speed even when the load is large.

[0012]

In order to achieve the above object, a hydraulic drive circuit according to the present invention has a plurality of branch discharges in a discharge line of a variable displacement pump equipped with a negative flow control type discharge flow control means. A line and one discharge bypass line are provided, and a closed center type directional control valve is provided in parallel to each of the branch discharge lines to supply pump discharge pressure oil to each actuator and then return the return oil to each auxiliary. While returning to the tank via a valve, each of the directional valves is provided with a signal line for detecting the individual and / or maximum load pressure of the actuator when operating the actuators to drive the actuators individually or simultaneously. On the other hand, in the discharge bypass line, a flow control valve with pressure compensation and a pressure generating means are provided in order from the upstream side. Provided, the connection to the tank,
The upstream pressure of the pressure generating means is applied to the discharge flow rate control means of the variable displacement pump, the individual load pressure is applied to each of the auxiliary valves in the opening direction thereof, and the maximum load pressure is applied in the closing direction. A hydraulic drive configured to apply a maximum load pressure to the flow control valve with pressure compensation in the closing direction, and to provide a signal bypass line with a throttle in the maximum load signal line to connect to the tank. In the circuit, a shut-off switching valve that connects or shuts off the signal bypass line via the upstream pressure of the pressure generating means is provided on the signal bypass line so as to correspond to the operating state of the directional switching valve. Characterize.

In this case, the shut-off switching valve is opened before the actuator line of the directional switching valve is connected to the actuator load pressure detection line and / or the connection line between the pump discharge line and the actuator line is opened during the starting operation of the directional switching valve. The two-position operation switching valve can block the communication of the signal bypass line while the degree is within the minute opening range. Further, the shut-off switching valve may be constituted by a three-position operation switching valve that causes a response delay when the directional switching valve is stopped, when the directional switching valve is suddenly operated from the fully operated state to the neutral state.

[0014]

In the present invention, when the actuator is started at a very low speed (the directional control valve is operated to open in the minute opening range), that is, before the actuator line and the actuator load pressure signal line are connected and / or the pump discharge line. While the connection opening between the actuator line and the actuator line is within the minute opening range, the signal bypass line is shut off by the shutoff switching valve, and all signal lines including the individual and maximum load signal lines are pressure sealed. Therefore, when the actuator is started at the very low speed, the backflow of the hydraulic oil from the actuator line to the signal line, which has been conventionally generated, is prevented, and the drop of the actuator load can be prevented.

[0015]

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. 5 to 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 that of the conventional one (FIG. 5).
Therefore, in order to make it easy to understand though it is duplicated, to briefly explain again, basically, a plurality of hydraulic drive circuits are provided in the discharge line 14 of the variable displacement pump 12 provided with the negative flow rate control type discharge flow rate control means 10. (Two in the illustrated embodiment)
Branch discharge lines 16 and 18 and one discharge bypass line 20 are provided, and each branch discharge line 16 and 18 includes
The closed center type directional control valves 22 and 24 are provided in parallel to supply the pump discharge pressure oil to the respective actuators 26 and 28, and then return the return oil to the tank 34 via the respective auxiliary valves 30 and 32. To configure. Further, each of the directional control valves 22, 24 has a signal line 38 for detecting the individual and / or maximum load pressure of the actuators 26, 28 when operating the actuators 26, 28 individually or simultaneously by operating them. , 40, 44 are provided. On the other hand, the discharge bypass line 20 is provided with a flow control valve with pressure compensation 46 and a pressure generating means 48 in order from the upstream side to connect to the tank 34, and the upstream pressure 50 of the pressure generating means 48 is applied to the variable displacement pump 12. Is applied to the discharge flow rate control means 10. Then, the individual load pressures 38 and 40 are applied to the respective auxiliary valves 30 and 32 in the respective opening directions thereof, the maximum load pressure 44 is applied to the respective auxiliary valves 30 and 32 thereof, and the maximum flow pressure 44 is applied to the pressure compensation flow control valve 46. The maximum load pressure 44 is applied in the closing direction, and the maximum load signal line 44 is provided with a signal bypass line 56 having a throttle 54 so as to be connected to the tank 34.

In the present invention, however, the directional control valve 2 is provided on the signal bypass line 56 in the above configuration.
The pressure generating means 4 corresponds to the operation states of 2 and 24.
8 by the pressure 50 on the upstream side of shutoff switching valve control signal line 5
A disconnection switching valve 60 that connects or disconnects the signal bypass line 56 is provided via the switch 8. That is, the cutoff switching valve 6
0 is preferably formed in a two-position operation switching valve, and is normally in position I, and the signal pressure oil in the signal lines 38, 40, 44 is discharged through the throttle 54, the cut-off switching valve 60, and the signal bypass line 5.
Bleed off to tank 34 through 0, but position
II, that is, in the case of the upstream pressure 50, this pressure p is in a range II (see FIG. 2) during which the pressure p drops from the maximum pressure p2 by a slight pressure Δp, and the directional control valves 22, 24 Regarding the operation state of, when this directional control valve is started in the minute opening range (in other words,
Before the actuator line and the actuator load signal line are connected and / or while the connection opening between the pump discharge line and the actuator line is within the minute opening range, the signal bypass line 56 is disconnected. , The signal pressure oil in each signal line 38, 40, 44 is pressure-sealed. Therefore, even when the actuator is started at the slow speed, the signal load is pressure-sealed in this case, and it is clear that the actuator load does not drop. The range I in FIG. 2 is
The upstream side pressure p (5
The pressure range of 0) is shown.

As described above, according to the present invention, by providing the shut-off switching valve for shutting off the signal bypass line at the time of starting the actuator at a very low speed, the back flow of the hydraulic oil from the actuator line to the load signal line is prevented. Therefore, at the time of starting at the slow speed, it is possible to reliably prevent the drop of the actuator load that has conventionally occurred. Therefore, the operability and safety of the hydraulic drive circuit can be improved. Further, according to the present invention, there is an advantage that it can be configured extremely easily.

Next, the shut-off switching valve 62 of the embodiment shown in FIG.
Is for the two-position operation switching type cutoff switching valve 60,
The upstream side pressure p (50) is of a three-position operation switching type in which a range III is added while the upstream pressure p (50) further increases by the surge pressure Δp 'from the maximum pressure p2. According to this, when the directional control valves 22, 24 are suddenly operated from all operating states to the neutral state, the pressure sealing of the signal pressure oil in the respective signal lines 38, 40, 44 is canceled, and the directional control valves are operated. An operation response delay can be generated. The operation of the entire circuit is similar to that of the previous embodiment.

Although the preferred embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, and many design changes can be made without departing from the spirit of the present invention. For example, the diaphragm 54 on the signal bypass line 56
Can preferably be changed to a flow control valve with pressure compensation. Further, the present invention can be similarly applied to other hydraulic drive circuits, for example, circuits having no auxiliary valves 30 and 32.

[0021]

As described above, in the hydraulic drive circuit according to the present invention, a plurality of branch discharge lines and one discharge bypass are provided in the discharge line of the variable displacement pump having the negative flow rate control type discharge flow rate control means. A line is provided, and a closed center type directional control valve is provided in parallel to each of the branch discharge lines to supply pump discharge pressure oil to each actuator, and then return oil to the tank via each auxiliary valve. Along with the return, each of the directional control valves is provided with a signal line for detecting the individual and / or maximum load pressure of the actuator when operating these actuators individually or simultaneously, while the discharge bypass is provided. The line is equipped with a flow control valve with pressure compensation and pressure generating means in order from the upstream side, and And the upstream pressure of the pressure generating means is applied to the discharge flow rate control means of the variable displacement pump, and the individual load pressure is applied to each of the auxiliary valves in their respective opening directions and the auxiliary valves are closed. Direction is applied with the maximum load pressure, the flow control valve with pressure compensation is applied with the maximum load pressure in its closing direction, and the maximum load signal line is provided with a signal bypass line having a throttle and connected to the tank. In the hydraulic drive circuit configured as
A shut-off switching valve that connects or shuts off the signal bypass line via the upstream pressure of the pressure generating means is provided on the signal bypass line so as to correspond to the operating state of the direction switching valve. It is possible to prevent the hydraulic oil from backflowing from the actuator line to the load signal line, so that 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, according to the hydraulic drive circuit of the present invention,
The operability and safety in this type of circuit can be greatly improved. Further, the hydraulic drive circuit of the present invention has an advantage that it can be constructed very easily.

[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 characteristic of the pressure generating means shown in FIG. 1 (upstream pressure).
It is a pq characteristic diagram which shows.

FIG. 3 is a symbol diagram showing another embodiment of the shutoff switching valve shown in FIG.

4 is a pq characteristic diagram showing a characteristic (upstream pressure) corresponding to the shutoff switching valve shown in FIG. 3 of the pressure generating means shown in FIG.

FIG. 5 is a hydraulic circuit diagram showing a conventional hydraulic drive circuit.

6 is a characteristic of the pressure generating means shown in FIG. 5 (upstream pressure).
It is a pq characteristic diagram which shows.

7 is a Qp characteristic diagram showing characteristics (discharge flow rate) of the negative flow rate control type variable displacement pump shown in FIG.

8 is a symbol diagram showing a connection state of each line in the direction switching valve when operating the minute opening range of the direction switching valve shown in FIG.

[Explanation of symbols]

10 Discharge flow rate control means 12 Variable displacement pump 14 Discharge line 16, 18 Branch discharge line 20 Discharge bypass line 22, 24 directional switching valve 26, 28 actuator 30, 32 Auxiliary valve 34 tanks 38, 40 Individual load signal line 42 High voltage selection means 44 Maximum load signal line 46 Flow control valve with pressure compensation 48 Pressure generating means 50 upstream pressure 52 Pump control signal line 54 Aperture 56 signal bypass line 58 Cutoff switching valve control signal line 60, 62 Shut-off switching valve

─────────────────────────────────────────────────── ─── Continuation of front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) F15B 11/00 E02F 9/22

Claims (3)

(57) [Claims] 1. A variable displacement pump having a negative flow rate control type discharge flow rate control means is provided with a plurality of branch discharge lines and one discharge bypass line, and each branch discharge line has a closed center direction. Switching valves are provided in parallel, and after pump discharge pressure oil is supplied to each actuator, the return oil is returned to the tank through each auxiliary valve, and these directional switching valves are operated by these. Signal lines for detecting individual and / or maximum load pressures of the actuators when individually or simultaneously driving the actuators, respectively, while the discharge bypass line is provided with a flow control valve with pressure compensation and a pressure in order from the upstream side. A pressure generator is provided and connected to the tank, and the upstream pressure of the pressure generator is controlled by Applying to the discharge flow rate control means of the variable displacement pump, applying the individual load pressure to each of the auxiliary valves in the respective opening direction and applying the maximum load pressure to the closing direction, the flow rate control with pressure compensation In the hydraulic drive circuit configured to apply a maximum load pressure to the valve in the closing direction, and to connect to the tank by providing a signal bypass line having a throttle in the maximum load signal line, on the signal bypass line, A hydraulic drive circuit comprising a cut-off switching valve that connects or disconnects the signal bypass line via the pressure on the upstream side of the pressure generating means so as to correspond to the operating state of the direction switching valve. 2. The shut-off switching valve, at the time of starting operation of the directional switching valve, before the actuator line and the actuator load pressure detection line of the directional switching valve are connected and / or the connection opening degree between the pump discharge line and the actuator line. 2. The hydraulic drive circuit according to claim 1, wherein the hydraulic drive circuit comprises a two-position operation switching valve that shuts off the communication of the signal bypass line while is within the minute opening range. 3. The shut-off switching valve further comprises a three-position operation switching valve that causes a response delay when the directional switching valve is stopped, when the directional switching valve is suddenly operated from the fully operated state to the neutral state. 2. The hydraulic drive circuit described in 2.