JPH09195947A - Hydraulic driving device for construction machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To maintain well controllability of an actuator in returning from the automatic idling state to the normal state regardless of the set engine speed. SOLUTION: When an operation lever 9 is operated from the automatic idling state, the operation is detected by a pilot switch 12, and the target engine speed is set to the set engine speed N1 . The target displacement D larger than that based on the target torque curve T2 of the idling speed N2 is calculated on the basis of the target torque curve T1 of the set engine speed N1 , and the capacity of a hydraulic pump 4 is returned to the normal capacity. In returning, the target displacement D of the hydraulic pump 4 is gradually increased by taking time according to the deviation between the set engine speed N1 and the idling speed N2 by using the correcting target torque curve T21 in which the target torque curve T2 is increased to the target torque curve T1 at the constant rate as the target torque curve of the hydraulic pump 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a construction machine such as a hydraulic excavator, and more particularly to a hydraulic drive system for a construction machine having a so-called automatic idle function.

[0002]

2. Description of the Related Art Conventionally, as a known technique relating to this type of hydraulic drive device, there is, for example, the one described in Japanese Patent Application Laid-Open No. 1-170730. That is, according to this known technique, when the operator returns all the operation levers to the neutral position, the low speed rotation speed (second rotation speed) lower than an arbitrary engine setting rotation speed (= first rotation speed) set by the throttle lever is set. Is issued, and the engine is operated at the low speed (auto idling state). Then, when at least one of the operating levers is operated from this auto idling state to return to the normal state, the absorption horsepower of the hydraulic pump is set significantly lower than that in the light work mode until the engine speed reaches the first speed. That is, as shown in FIG. 6, until the engine speed reaches the first speed, regardless of the horsepower diagram based on the first speed,
The horsepower is reduced using a horsepower diagram (a horsepower diagram) that is lower than this by a fixed value. As a result, the rise time of the engine speed is shortened and the discharge amount of the hydraulic pump is rapidly increased, so that the speed of the hydraulic actuator can be set to a value corresponding to the operation amount of the operation lever in a short time.

[0003]

However, the above-mentioned known technology has the following problems. That is, since the horsepower diagram based on the first speed is not used until the first speed is reached, the horsepower reduction diagram is used. Therefore, when the first speed is originally set relatively high, the engine speed As soon as the number reaches the first speed and the horsepower reduction control is released, the tilt angle (pump flow rate) rapidly increases. In this case, as a result, the operating speed of the actuator may be accelerated midway, and there is room for further improvement in operability in this respect.

An object of the present invention is to provide a hydraulic drive system for a construction machine, which can maintain good operability of an actuator when returning from an auto idling state to a normal state regardless of the set speed of the engine. That is.

[0005]

In order to achieve the above object, according to the present invention, an engine, a variable displacement hydraulic pump driven by the engine, and pressure oil discharged from the hydraulic pump are used. At least one actuator that drives, at least one flow control valve that controls the flow of pressure oil supplied from the hydraulic pump to the at least one actuator, and at least one that controls the stroke amount of the flow control valve.
Control valve operating means, rotation speed instruction means for setting and operating the rotation speed of the engine, rotation speed operation amount detection means for detecting an operation amount of the rotation speed instruction means, and engine speed idling A switching means for switching between a restricted state in which the rotational speed is limited and a normal state in which the restriction is not performed, and an operation amount detected by the rotational speed operation amount detection means when the switching means is switched to the normal state. Accordingly, the first target rotation speed of the engine is calculated, and the second target rotation speed corresponding to the idling rotation speed smaller than the first target rotation speed when the switching unit is switched to the limited state is calculated. A rotation speed setting means for calculating a target rotation speed and an engine control for controlling the rotation speed of the engine according to the first and second target rotation speeds calculated by the rotation speed setting means. Means for limiting the target input torque of the hydraulic pump to a value equal to or less than the first output torque of the engine corresponding to the first target rotation speed when the switching means and the switching means are switched to the normal state. While calculating the first target displacement of the hydraulic pump,
When the switching means is switched to the limited state, the target input torque of the hydraulic pump is less than or equal to the second output torque of the engine that corresponds to the second target rotation speed and is smaller than the first output torque. Displacement volume setting means for calculating a second target displacement volume of the hydraulic pump, which is limited to, and a displacement of the hydraulic pump according to the first and second target displacement volumes set by the displacement volume setting means. In a hydraulic drive system for a construction machine having a pump control means for controlling the displacement, the displacement setting means, when the switching means is switched from a limited state to a normal state, the first target rotation speed and the The target displacement of the hydraulic pump is changed from the second target displacement to the first target displacement over a period of time corresponding to the deviation from the second target rotation speed. A hydraulic drive device for a construction machine is provided, wherein the pump control means controls the displacement volume of the hydraulic pump according to the incremental target displacement volume. It

That is, in the present invention thus constructed, when the operator does not work for a relatively long period of time, the switching means is switched to a restriction state for restricting the engine to the idling speed. So, for example,
When the command switch for switching the engine speed to the idling speed is turned on without operating the control valve operating means, all the control valve operating means for controlling the stroke amount of the flow control valve are in the non-operated state. It is detected by the operation state detection means, and the rotation speed setting means calculates a relatively small second target rotation speed corresponding to the idling rotation speed. Then, the engine control means controls the engine speed in accordance with the second target engine speed, whereby the engine speed follows this and drops to the idling speed. At this time, at the same time, the displacement volume setting means calculates a second target displacement volume that corresponds to the second target rotation speed and limits the hydraulic pump target input torque to the comparatively small second output torque of the engine or less. The pump control means controls the displacement of the hydraulic pump according to the second target displacement, and the displacement of the hydraulic pump follows this and becomes small.

From this state, when the operator restarts the work, the switching means is switched from the restricted state to the normal state. That is, for example, when at least one control valve operating means is operated to stroke the corresponding flow rate control valve to supply pressure oil to the actuator, the operating state of the control valve operating means is detected by the operating state detecting means, and the rotation speed setting means. Then, a first target speed that is higher than the second target speed is calculated. In this case, the same applies when the operator turns off the auto idle switch. Then, the engine control means controls the engine speed in accordance with the first target engine speed, and the engine speed follows this and returns from the idling engine speed to the normal engine speed. On the other hand, at this time, the displacement volume setting means calculates the first target displacement volume that limits the target input torque of the hydraulic pump to the first output torque of the engine which is larger than the second output torque, and the pump control means. Then, the displacement of the hydraulic pump is controlled according to the first target displacement, and the displacement of the hydraulic pump follows this and returns from the small displacement to the normal displacement. At the time of such a return, the displacement setting means makes a transition from the state in which the second target displacement is calculated to the state in which the first target displacement is calculated. Here, in general, the response of the actual engine speed in the control by the engine control means is relatively slow, and it takes a longer time to follow the response of the actual pump displacement in the control by the pump control means. , The switching means is switched from the limited state to the normal state, and at the same time, the second target displacement calculation state is not changed to the first target displacement calculated state, but the switching means is switched from the limited state to the normal state. After a lapse of a sufficient time until the engine speed reaches the first speed from the time when the engine speed is changed, the first target displacement is calculated. However, in this case, although the engine speed can be increased quickly by reducing the absorption torque of the hydraulic pump,
As soon as the engine speed reaches the first speed and the predetermined time ends, the pump displacement rapidly increases from the second target displacement to the first target displacement.
As a result, the operating speed of the actuator may be accelerated from the middle. On the other hand, in the present invention, the displacement volume setting means is set to the second position after a predetermined time elapses after the switching means is switched from the limited state to the normal state as in the conventional case.
The transition from the target displacement calculation state of No. 1 to the first target displacement calculation state is not performed at once, but the hydraulic pressure is changed over a time period corresponding to the deviation between the first target rotation speed and the second target rotation speed. The target displacement of the pump is increased from the second target displacement to the first target displacement.
As a method for increasing the displacement in this way, for example, the target displacement of the hydraulic pump may be increased at a constant rate.
As a result, regardless of the magnitude of the first target rotation speed set by the rotation speed instruction means, the pump displacement volume smoothly increases with the increase of the engine rotation speed, so that the operating speed of the actuator is reduced as in the conventional case. The possibility of continuous sudden acceleration is eliminated, and maneuverability can be improved in this respect.

Preferably, in the hydraulic drive system for the construction machine, the displacement setting means sets the target displacement of the hydraulic pump from the second target displacement to the first target displacement at a constant rate. Provided is a hydraulic drive system for a construction machine, which is characterized by increasing the number of units.

Further preferably, in the hydraulic drive system for the construction machine, the displacement volume setting means is configured such that when the switching means is switched to a normal state, the first displacement
First target input torque calculating means for calculating a first target input torque of the hydraulic pump corresponding to the target rotation speed of
When the first target displacement calculation means for calculating the first target displacement corresponding to the first target input torque and the switching means are switched to the restricted state, the first engine displacement of the engine is reduced. The target input torque reduction amount calculation means calculates the reduction amount of the target input torque of the hydraulic pump based on the deviation between the target rotation speed and the second target rotation speed, and the first target input torque calculation means. A second target having a value obtained by subtracting the target input torque reduction amount calculated by the first target input torque reduction amount calculation means from the first target input torque as a second target input torque of the hydraulic pump. The input torque calculation means, the second target displacement calculation means for calculating the second target displacement corresponding to the second target input torque, and the switching means are in a restricted state. And a target input torque reduction amount correction means for gradually reducing the target input torque reduction amount calculated by the first target input torque reduction amount calculation means by a predetermined amount stepwise when switched to the normal state. The pump control means keeps the target input torque reduced while the target input torque reduction amount calculated by the target input torque reduction amount calculation means and corrected by the target input torque reduction amount correction means is a positive value. The displacement volume of the hydraulic pump is controlled according to the second target displacement volume corresponding to the second target input torque calculated by the second target input torque calculation means using the torque reduction amount. A hydraulic drive system for a construction machine is provided.

Further, preferably, in the hydraulic drive system for the construction machine, the switching means detects an operation state of at least one of the control valve operating means, and an engine speed idling rotation. And a command switch for changing the number of rotations of the engine when the command switch is ON and the operation state detecting means detects a non-operation state of all the control valve operating means. Is limited to the idling speed, when the command switch is OFF, and when the command switch is ON and the operation state detection means detects at least one operation state of the control valve operation means, There is provided a hydraulic drive system for a construction machine, wherein the restriction on the engine speed is lifted.

[0011]

An embodiment of the present invention will be described below with reference to the drawings. FIG. 2 shows a hydraulic circuit diagram of the hydraulic drive system for the construction machine according to the present embodiment. In FIG.
The hydraulic drive device is mounted on a construction machine such as a hydraulic excavator, and includes an engine 2, a variable displacement hydraulic pump 4 driven by the engine 2, an auxiliary pump 17 for generating pilot pressure, and a hydraulic pressure. A so-called known electronic regulator 24 that adjusts the displacement (tilt angle) of the pump 4 and a hydraulic actuator that is driven by the pressure oil sent from the hydraulic pump 4 (a hydraulic motor is shown as an example, but a hydraulic cylinder Etc.) 6, a load (for example, a boom, an arm, an upper swing body of a construction machine) 7 operated by driving the hydraulic actuator 6, and a direction and a flow rate of pressure oil discharged from the hydraulic pump 4. The pilot type flow control valve 8, the operating lever 9 for controlling the switching direction of the flow control valve 8, and the rotational speed of the engine 2 are operated. Rotational speed operating means, for example, the throttle lever 13, and switching means for switching between a restricted state (= auto idle state) for limiting the engine rotational speed to the idling rotational speed and a normal state without this restriction, for example, low speed rotation Several operation command switch 11 and pilot switch 12, a maximum of pilot pressure for operating flow control valve 8 is selected, and shuttle valve 10 for guiding to pilot switch 12 and discharge pressure of hydraulic pump 4 are detected and handled. The detection signal P ₀ for
And a discharge pressure sensor 25 for outputting to.

The revolution speed of the engine 2 is controlled by driving the governor lever 20 provided inside by a stepping motor inside the governor driving device 22 outside the engine 2 via the cable 14 and displacing it at a predetermined angle. At this time, an engine speed command signal S _c (described later) from the controller 29 is input to the governor drive device 22. The pilot switch 12 has a function of detecting whether the operating lever 9 is in an operated state or a non-operated state, based on the maximum pilot pressure for operating the flow control valve 8.
Further, the low-speed rotation speed operation command switch 11 is provided with the operation lever 9
Performs a function of selecting whether to switch the engine 2 to the idling state or not when the engine is in the neutral position in the non-operating state.

In the throttle lever 13, the operation amount (stroke) is electrically detected by a detection means (not shown) provided side by side, and a stroke signal S _t corresponding to this is output. Then, this stroke signal _St is input into the controller 29. Then, the detection signal S ₂ from the low rotation speed operation command switch signal S ₁ is the signal S ₁ is turned on in and pilot switch 12 from the case or slow rotational speed operation command switch 11 off from the 11 is on (= control lever 9), an engine speed command signal S _c processed to have a predetermined engine speed is created in the controller 29, and the governor drive unit 2 is operated.
2 is output. And based on this, the governor lever 2
When 0 is driven, the target rotation speed of the engine 2 is set to the set rotation speed N corresponding to the operation amount of the throttle lever 13.
It becomes ₁ . Throttle lever 13 by such processing
FIG. 3 shows the relationship between the manipulated variable and the target engine speed.
That is, in FIG. 3, according to a predetermined operation amount (stroke) range L ₀ ≦ S _t ≦ H _i of the throttle lever 13, set rotational speed N ₁ is any value between N _l ≦ N ₁ ≦ N _h Can be set to. On the other hand, when it is detected by the pilot switch 12 that the low speed rotation speed operation command switch 11 is on and the operation lever 9 is not operated,
Based on the engine rotation speed command signal S _c from the controller 29, the target rotation speed of the engine 2 is set to the idling rotation speed N ₂ which is smaller than the set rotation speed N ₁ via the governor drive device 22 and the governor lever 20. (See FIG. 3).

The discharge pressure sensor 25 detects the discharge pressure of the hydraulic pump 4, and a pressure signal P ₀ corresponding to this is output and input into the controller 29. In the controller 29, based on a predetermined target input torque curve (described later), a drive signal S _r processed to have a predetermined target pump displacement is created from this pressure signal P ₀ and output to the regulator 24. It By driving the regulator 24 based on this, the hydraulic pump 4 becomes the target displacement volume D corresponding to the discharge pressure of the hydraulic pump 4. Pump pressure P ₀ by such processing
FIG. 4 shows the relationship between the displacement of the hydraulic pump and the target displacement D of the hydraulic pump. That is, FIG. 4 shows a target input torque (= absorption torque) curve of the hydraulic pump 4, where the horizontal axis is the pump pressure P ₀ and the vertical axis is the target pump displacement D. That is, the target torque curve of the hydraulic pump 4 is T in accordance with the rotation speed range of the engine 2 (from low rotation speed to high rotation speed).
Set a variable in the range from ₁ to T _h. For example, when the engine target speed is the set speed N ₁ shown in FIG. 3, the target torque curve T _{1 in} FIG. 4 is set, and the engine target speed is the idling speed in FIG. If that is the N _2, the torque reduction amount ΔT of a predetermined amount from the target torque curve T ₁ is a reduced (more information calculation method will be described later) the target torque curve T ₂ of the in Figure 4 is set.
Using the target input torque curve of the hydraulic pump 4 set in this way, the target pump displacement D is obtained from the pump pressure P ₀ , and the drive signal S _r for setting the target pump displacement D is obtained. It is created and output from the controller 29 to the regulator 24, and the swash plate of the hydraulic pump 4 is driven to adjust the discharge flow rate.

In the above structure, when the operation lever 9 is operated, the pilot pressure generated by the auxiliary pump 17 is guided to the both side drive parts of the flow control valve 8 according to the operation amount,
As a result, the stroke amount of the flow control valve 8 is adjusted. As a result, the pressure oil discharged from the hydraulic pump 4 is guided to and driven by the hydraulic actuator 6 to operate the load 7.

Next, the control for switching from the normal state to the auto idle state and for returning from the auto idle state to the normal state, which is the main part of this embodiment, will be described with reference to FIG. For simplification of description, a case where the low speed rotation speed operation command switch 11 is always on will be described as an example. Therefore, the procedure of inputting the signal S ₁ from the low speed rotation speed operation command switch 11 is omitted. FIG. 5 is a flowchart showing the control contents of the controller 29 regarding this switching / returning. In FIG. 5, first, in step 100, an operation flag of ACT = 1 representing the operation of the engine 2 at the set rotation speed N ₁ is set, and in step 101, the detection signal S ₂ from the pilot switch 12 and the throttle lever 13 The stroke signal S _t and the detection signal P ₀ from the discharge pressure sensor 25 are input. After that, the procedure proceeds to step 102, and it is determined which one of the operation flags ACT representing the operating state is 1 to 3.

During normal operation of the engine 2, ACT
= 1 remains, the process moves to step 103, and the operation lever 9
Is determined based on the detection signal S ₂ input from the pilot switch 12 in step 101.

If the operator is operating the operating lever 9, it is determined that the operating lever 9 is in the operating state, and the process proceeds to step 104. Based on the table shown in FIG. 3, the throttle signal S _t input in step 101 is entered. The engine rotation speed command signal S _c for setting the engine rotation speed N ₁ corresponding to is generated. Then, in step 105, the pump corresponding to the detection signal P ₀ input from the discharge pressure sensor 25 in step 101 based on the target pump torque curve T ₁ at the set engine speed N ₁ shown in FIG. The target displacement D is obtained, and the drive signal S _r for setting the target displacement D is created. After that, the procedure proceeds to Step 106 and Step 10
The engine speed command signal S _c obtained in step 4 is output to the governor drive device 22, the drive signal S _r obtained in step 105 is output to the regulator 24, and the process returns to step 101. In this way, during the normal operation (ACT = 1) at the set rotation speed N ₁ , steps 101 → 102 → 103 →
Repeat 104 → 105 → 106.

At this time, when the operator stops the operation and the operation lever 9 is in the neutral position, it is determined in step 103 that the operation lever 9 is in the non-operation state. Set the operation flag of. Then, in step 108, the engine speed command signal S _c is generated so as to limit the engine speed to the idling speed N ₂ which is smaller than the set speed N ₁ (see FIG. 3). Further, the deviation ΔN (= the set rotational speed N ₁ and the idling rotational speed N ₂ used in ACT = 1)
N ₁ −N ₂ ) and a predetermined hydraulic pump torque operation gain β, the pump torque reduction amount ΔT (= β
・ Calculate ΔN). Further, the reduction amount ΔT from the target pump torque curve T ₁ at the set rotation speed N ₁ used when ACT = 1.
To reduce the target pump torque curve T as shown in FIG.
Ask for ₂ .

Then, in step 109, the pump target displacement volume D corresponding to the detection signal P ₀ input from the discharge pressure sensor 25 in step 101 is obtained based on this target pump torque curve T ₂ , and this target displacement volume D is obtained. Drive signal S _r is set such that Then, step 10
6, the engine speed command signal S _c obtained in step 108 is output to the governor drive device 22, and the step 1
The drive signal S _r obtained in 09 is output to the regulator 24, and the process returns to step 101. If the idling speed N _{2 is} still in the standby operation, ACT = 2. Therefore, in step 102, the state is determined and the process proceeds to step 110. It is checked whether the operating lever 9 is in the operating state or not.
In step 01, the determination is made based on the detection signal S ₂ input from the pilot switch 12. Here, if the operation lever 9 is in the non-operation state, the process proceeds to step 108 and the above-described step 108
The subsequent control is repeated again. That is, during the standby operation (ACT = 2) at the idling speed N ₂ , the procedure 1 is performed.
The sequence of 01 → 102 → 110 → 108 → 109 → 106 is repeated.

At this time, when the operator restarts the operation and the operation lever 9 is changed from the neutral position to the operation state, it is determined in step 110 that the operation lever 9 is in the operation state, and the step 111 is performed.
ACT indicating that the standby operation at the idling speed N ₂ is returning to the normal operation at the set speed N ₁
The operation flag of = 3 is set. Then move to step 112,
Based on the table shown in FIG. 3, the engine speed command signal S _c for setting the engine speed N ₁ corresponding to the throttle signal S _t input in step 101 is created.
After that, the routine proceeds to Step 113, and the pump torque reduction amount ΔT (= β · Δ calculated in Step 108 in the state of ACT = 2 described above).
The predetermined pump torque increase amount X (fixed value) stored in the controller 29 which is determined in advance is subtracted from N), and the value is again set as the pump torque reduction amount ΔT.
Then, in step 114, it is determined whether or not this ΔT is positive, and if it is positive, the process proceeds to step 115 to reduce the pump torque from the target pump torque curve T ₁ at the set rotation speed N ₁ used in ACT = 1. A return target pump torque curve T ₂₁ is calculated by subtracting the amount ΔT. The return target pump torque curve T ₂₁ is slightly higher than the target pump torque curve T ₂ (close to the target pump torque curve T ₁ side). After that, in step 116, the pump target displacement D corresponding to the detection signal P ₀ input from the discharge pressure sensor 25 in step 101 is obtained based on this return target pump torque curve T ₂ , and this target displacement D
Drive signal S _r is set such that Then, the flow proceeds to step 106, and outputs an engine speed command signal S _c determined in Step 112 to the governor drive unit 22,
The drive signal S _r obtained in step 116 is output to the regulator 24, and the process returns to step 101.

At this time, the idling speed N ₂
Is in the state of ACT = 3 during the recovery from the set rotational speed N ₁ to the set rotational speed N ₁ , the state is determined in step 102, the process directly proceeds to step 111, and after step 112, the pump torque reduction amount ΔT is further changed to the pump torque. The increase target X is subtracted, and in step 115, the pump target torque reduction amount ΔT is reduced to obtain a return target pump torque curve T ₂₁ that has moved upward.
In step 116, the target displacement D is calculated based on this, and the corresponding drive signal S _r is created and output in step 106. That is, the procedure 101 → 102 →
111 → 112 → 113 → 114 → 115 → 116 → 1
By repeating 06, the return target pump torque curve T
Target displacement volume D while shifting ₂₁ in small increments
Is gradually increased over time. This repetition is continued until ΔT ≦ 0, that is, until the return target pump torque curve T ₂₁ matches the target pump torque curve T ₁ . Here, since the pump torque increase amount X is a fixed value, this means that if the deviation between the set rotational speed N ₁ and the idling rotational speed N ₂ is large, it takes a relatively long time to perform the torque curve. Is increased and the target displacement D is increased, and the set rotational speed N
If the deviation between ₁ and the idling speed N ₂ is small, the torque curve shifts upward and the target displacement D increases in a relatively short time. In other words, the target displacement volume D increases over time depending on the deviation between the set speed N ₁ and the idling speed N ₂ .

When steps 101 to 106 are repeated a predetermined number of times and the return target pump torque curve T ₂₁ matches (or exceeds) the target pump torque curve T ₁ , if ΔT ≦ 0, then step 114 is executed. If the determination is not satisfied, the process proceeds to step 117, ΔT = 0 is set, and
A that represents the operation at the set speed N ₁ by assuming that the return is complete
Set an operation flag of CT = 1. Then, step 115 →
After returning to step 101 through step 116 → step 106,
From step 102, the steps after step 103 described above are performed.

The operation and effect of this embodiment for performing the above control will be described with reference to FIG. From the top,
Operation amount of operation lever 9, detection signal S ₂ from pilot switch 12, target speed of engine 2, actual speed of engine 2, target input torque of hydraulic pump 4, target displacement D of hydraulic pump 4, hydraulic pressure The behavior of the actual displacement of the pump 4 is shown. For the sake of simplification of description, the low-speed revolution operation command switch 1
The case where 1 is always on will be described as an example. According to this embodiment, when the operator sets the operation lever 9 to the neutral position, the non-operation state of the operation lever 9 is detected by the pilot switch 12, and the detection signal S ₂ is turned off. Then, sets the target rotational speed to the idling rotational speed N ₂ by the controller 29, the idling speed N ₂
The engine drive unit 2 outputs the rotation speed command signal S _c
2 to thereby follow the rotation speed of the engine 2 after a predetermined response delay and reduce it to the idling rotation speed N ₂ . At this time, at the same time, the controller 29 calculates a relatively small target displacement D based on the target torque curve T ₂ of the hydraulic pump 4 corresponding to this idling speed N ₂ , and according to the corresponding drive signal C _r. The regulator 24 controls the displacement of the hydraulic pump 4, and the capacity of the hydraulic pump 4 follows this and becomes a small capacity.

From this state, the operator operates the operating lever 9 to restart the work, and the corresponding flow control valve 8
Supplying hydraulic fluid to stroke the actuator 6, the operation state is detected by the pilot switch 12 via the shuttle valve 10, receives the corresponding detection signal S ₂ is turned on, the target rotation the controller 29 The number of revolutions is set to the number of revolutions N ₁ set by the throttle lever 13, and the number of revolutions command signal S _c that achieves this set number of revolutions N ₁ is output to the engine drive unit 22. Following the response delay, it follows and increases to the set speed N ₁ . On the other hand, at this time, the controller 29
In, the target torque curve T ₁ corresponding to the setting rotational speed N ₁
Based on the above, the target displacement D larger than the target displacement based on the above-mentioned target torque curve T ₂ is calculated, and the regulator 24 controls the displacement of the hydraulic pump 4 according to the corresponding drive signal C _r , The capacity of 4 follows this and returns to a large capacity (normal capacity).
Here, at the time of such a return, the response of the actual engine speed is usually relatively slow (A in the solid line in the figure indicates
(Refer to the CT = 3 part), because it takes a longer time to follow the response of the pump displacement, conventionally, the engine speed is set from the moment the auto idle state is switched to return to the normal state. after sufficient time Δt has passed expected required until the rotational speed N _1, had to shift to a state for computing a target displacement volume D corresponding to the set rotational speed N ₁ and the target torque curve T ₁ (Fig. (See the broken lines in and). However, in this case, although the engine speed can be increased relatively quickly by reducing the input torque (= absorption torque) of the hydraulic pump 4, the actual engine speed almost reaches the set speed N ₁ and the predetermined time elapses. As soon as Δt ends, the pump displacement increases rapidly ((*) in the broken line in the figure)
Therefore, as a result, the operating speed of the actuator 6 may be accelerated from the middle. On the other hand, in the present embodiment, at the time of this return, as the target torque curve of the hydraulic pump 4, the modified target torque curve T ₂₁ that increases at a constant rate from the target torque curve T ₂ to the target torque curve T ₁ is used. , The target displacement D of the hydraulic pump 4 is gradually increased over a period of time according to the deviation between the set rotational speed N ₁ and the idling rotational speed N ₂ (see the solid line in the figure where ACT = 3). ). Therefore, regardless of the magnitude of the set speed N _1, the pump displacement volume increases smoothly and gradually with the increase of the engine speed (see the part of the solid line in the figure where ACT = 3).
It is possible to improve the operability by eliminating the possibility that the operating speed of the actuator is suddenly accelerated discontinuously as in the conventional case.

In the above embodiment, only one operating lever 9, one flow control valve 8, one actuator 6 and one load 7 are provided, but the number is not limited to this, and a plurality of each is provided. May be. At this time, a plurality of shuttle valves 10 are provided accordingly.
By configuring so that the maximum one of the operating pressures of the operating levers 9 is guided to the pilot switch 12, the same effect as this embodiment can be obtained. In the above embodiment, the operation lever 9 reduces the pilot pressure from the auxiliary pump 17 and guides it to the drive portion of the flow rate control valve 8, but the invention is not limited to this, and a so-called known electric lever may be used. In this case, the operation state / non-operation state may be detected by inputting an electric signal from a potentiometer attached to an electric lever to the controller 29 and making a judgment. In this case, a similar effect is obtained. Further, in the above-described embodiment, the regulator 24 is a so-called electronic regulator, but a known hydraulic regulator may be used. In this case, a similar effect is obtained. In the above embodiment, the pump torque increase amount X is determined by the controller 29.
Although it is stored inside, it may be manually input from the outside when the operation is started. Furthermore, the pump torque increase amount is not limited to a fixed value. Thus, for example, while a last minute complete return starting immediately and return or smaller than the other portions of the value of X, or gradually decreases the value of X approaches the set rotational speed N _1, the set rotational speed N ₁ As the deviation between the idling speed N ₂ and the idling speed N ₂ increases, a modification such as increasing or decreasing the value of X can be considered. The point is that it depends on the deviation between the set speed N ₁ and the idling speed N ₂ . It suffices to increase the target displacement volume D of the hydraulic pump 4 over time, and the same effect can be obtained in these cases.

Further, in the above-mentioned embodiment, only so-called horsepower control is performed as the control of the target displacement of the hydraulic pump 4, but the present invention is not limited to this, and for example, negative control or positive control may be performed. In this case, of the target displacements by the horsepower control and the target displacements by these other controls, the smallest one may be selected as the final target displacement. Similar effects are obtained in these cases as well.

[0028]

According to the present invention, the displacement setting means sets the target displacement of the hydraulic pump to the second displacement by taking a time corresponding to the deviation between the first target rotation speed and the second target rotation speed. Since the target displacement volume of the first target displacement volume is increased to the first target displacement volume, the first displacement amount set by the rotation speed instruction means is set.
Regardless of the target speed of the engine, the displacement of the pump increases smoothly as the engine speed increases. Therefore, unlike the conventional case, there is no possibility that the operating speed of the actuator is suddenly accelerated discontinuously, and operability can be improved in this respect.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an operation amount of an operation lever, a detection signal from a pilot switch, a target engine speed, an actual engine speed, a target input torque of a hydraulic pump, and a target displacement of a hydraulic pump according to an embodiment of the present invention. It is a figure showing the behavior of the volume and the actual displacement of the hydraulic pump.

FIG. 2 is a hydraulic circuit diagram of the hydraulic drive system for a construction machine according to the embodiment of the present invention, showing the behavior of FIG.

FIG. 3 is a diagram showing a relationship between an operation amount of a throttle lever and an engine target speed in the hydraulic drive system shown in FIG.

FIG. 4 is a diagram showing a relationship between pump pressure and hydraulic pump target displacement in the hydraulic drive system shown in FIG.

FIG. 5 is a flowchart showing the control contents of the controller regarding switching from the normal state to the auto idle state and returning from the auto idle state to the normal state.

FIG. 6 is a horsepower diagram in the related art.

[Explanation of symbols]

 2 engine 4 variable displacement hydraulic pump 6 hydraulic actuator 8 flow control valve 9 operating lever 11 low speed revolution operation command switch 12 pilot switch 13 throttle lever 17 auxiliary pump 20 governor lever 22 governor drive device 24 regulator 25 discharge pressure sensor 29 controller

Claims (4)

[Claims] 1. An engine, a variable displacement hydraulic pump driven by the engine, at least one actuator driven by pressure oil discharged from the hydraulic pump, and from the hydraulic pump to the at least one actuator. At least one flow control valve for controlling the flow of the supplied pressure oil, at least one control valve operating means for controlling the stroke amount of the flow control valve, and for setting and operating the rotational speed of the engine. A rotation speed instruction means, a rotation speed operation amount detection means for detecting an operation amount of the rotation speed instruction means, a limit state in which the rotation speed of the engine is limited to an idling rotation speed, and a normal state in which this restriction is not performed are switched. Switching means to perform,
While the switching means is switched to the normal state, the first target rotation speed of the engine is calculated according to the operation amount detected by the rotation speed operation amount detecting means, and the switching means is set to the limited state. Rotation speed setting means for calculating a second target rotation speed corresponding to an idling rotation speed of a value smaller than the first target rotation speed when switched, and the first rotation speed setting means for calculating the second target rotation speed. 1st and 2nd
When the engine control unit that controls the engine speed according to the target engine speed and the switching unit are switched to the normal state, the target input torque of the hydraulic pump is set to the first target engine speed. A first target displacement of the hydraulic pump is calculated so as to limit it to a corresponding first output torque of the engine or less, and when the switching means is switched to the restricted state, the target input of the hydraulic pump is calculated. A displacement for calculating a second target displacement of the hydraulic pump that limits the torque to a second output torque of the engine that is smaller than the first output torque and that corresponds to the second target rotation speed. Volume setting means and displacement of the hydraulic pump according to the first and second target displacements set by the displacement setting means. In the hydraulic drive system for a construction machine, which has a pump control means for controlling the above, when the displacement means is switched from the limited state to the normal state, the displacement volume setting means has the first target rotation speed and the second target rotation speed. The target displacement of the hydraulic pump is gradually increased from the second target displacement to the first target displacement, and the pump control means A hydraulic drive system for a construction machine, characterized in that the displacement of the hydraulic pump is controlled in accordance with the target displacement that is increasing. 2. The hydraulic drive system for a construction machine according to claim 1, wherein the displacement setting means changes the target displacement of the hydraulic pump from the second target displacement to the first target displacement. A hydraulic drive system for construction machinery, which is characterized by increasing the volume at a fixed rate. 3. The hydraulic drive system for a construction machine according to claim 1, wherein the displacement volume setting means corresponds to the first target rotation speed when the switching means is switched to a normal state. First target input torque calculating means for calculating a first target input torque of the hydraulic pump, and first target displacement calculating means for calculating the first target displacement corresponding to the first target input torque. When,
A target input for calculating the reduction amount of the target input torque of the hydraulic pump based on the deviation between the first target rotation speed and the second target rotation speed of the engine when the switching means is switched to the restricted state. The torque reduction amount calculation means and the first target input torque calculation means calculated by the first target input torque calculation means.
Second target input torque calculation in which a value obtained by subtracting the target input torque reduction amount calculated by the first target input torque reduction amount calculation means from the target input torque of is the second target input torque of the hydraulic pump. Means, a second target displacement calculation means for calculating the second target displacement corresponding to the second target input torque, and the switching means when the limit state is switched to the normal state, A target input torque reduction amount correction means for gradually reducing the target input torque reduction amount calculated by the first target input torque reduction amount calculation means by a predetermined amount step by step. While the target input torque reduction amount calculated by the input torque reduction amount calculation means and corrected by the target input torque reduction amount correction means is a positive value, the target input torque reduction is performed. The corresponding second second target input torque calculated by the target input torque calculation means using the 2
A hydraulic drive system for a construction machine, wherein the displacement of the hydraulic pump is controlled according to the target displacement of the hydraulic pump. 4. The hydraulic drive system for a construction machine according to claim 1, wherein the switching means detects an operating state detecting means for detecting that at least one of the control valve operating means is operated, and an engine speed. A command switch for changing the idling speed is provided, and when the command switch is ON and the operation state detecting means detects non-operation states of all the control valve operating means, The number of revolutions is limited to the idling number of revolutions, when the command switch is OFF, and when the command switch is ON and the operation state detection means detects at least one operation state of the control valve operation means. Occasionally, the hydraulic drive system for a construction machine is characterized in that the restriction on the engine speed is lifted.