JP2000161302A - Engine lug-down prevention device for hydraulic construction machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the generation of worsening of a fuel cost and the increase of black smoke in a hydraulic construction machine adopting a large sized engine as a prime mover and to decrease the lug-down of the engine to be generated when a hydraulic actuator is operated rapidly from a non-operating state. SOLUTION: A hydraulic regulator 51 controls itself in quantity so that the input torque of a hydraulic pump 2 may not exceed the rated torque T0, determined previously, when an electromagnetic proportional pressure reducing valve 54 is not illustrated. The controller 53 inputs the signal of a pressure sensor 52 which is used to detect supercharging pressure, excites the electromagnetic proportional pressure reducing valve 54, after the supercharging pressure lowers below p1 and during the period until it rises to P2, reduces the limited value of pump input torque to T1, smaller than rated torque T0, to carry out reduced torque control.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for preventing engine lug down of a hydraulic construction machine, and more particularly to a device for preventing engine lug down of a hydraulic construction machine such as a hydraulic shovel having an engine having a large lag down as a prime mover.

[0002]

2. Description of the Related Art In a hydraulic construction machine such as a hydraulic shovel, a hydraulic actuator is driven by pressure oil discharged from a hydraulic pump. The hydraulic pump is driven to rotate by a prime mover, and a diesel engine is generally used as the prime mover. In this diesel engine, the fuel injection amount is controlled by a fuel injection device called a governor, and the rotation speed is controlled. The fuel injection device includes a mechanical system and an electronic system. In each of these systems, the fuel injection amount is adjusted in accordance with the deviation between the target rotation speed and the actual rotation speed (rotation speed deviation). That is, when the engine load increases and the rotational speed deviation increases, the fuel injection amount is increased to bring the actual rotational speed closer to the target rotational speed. In this case, when the engine is in a no-load state, the engine speed is a high idle speed higher than the target speed.

[0003] In an engine equipped with such a fuel injection device, when a hydraulic actuator is suddenly operated and a load is suddenly applied to the engine, a phenomenon called lag-down occurs in which the engine rotation drops momentarily. This is because when the engine is in a no-load state, the engine speed is in the high idle state as described above, and the amount of fuel supplied to the engine in this state is small, but a sudden load is applied to the engine. When the fuel injection device attempts to supply a large amount of fuel, a response delay occurs, and the supply of the fuel cannot be made in time, and the engine speed drops momentarily.

[0004] As a technique for preventing such engine lag-down, there is an engine control device of a civil engineering construction machine disclosed in Japanese Patent Application Laid-Open No. 1-222419. In this prior art, a means for detecting an operation state of a control valve for controlling a flow rate supplied to an actuator is provided, and when the control valve is operated and a load is applied to the engine, the control valve is changed to a non-operation state. When detected, the tilt angle of the hydraulic pump is set to a discharge flow rate larger than the minimum discharge flow rate, and a drag load is applied to the engine. By applying a drag load to the engine in this manner, the engine speed is controlled to be slightly lower than the high idle speed, and does not increase to the high idle speed.
Even if a load is applied to the engine by operating the control valve thereafter, the drop in the number of revolutions is reduced, and the lag down is reduced.

[0005]

The engine, which is the prime mover, has been increasing in size with the increase in the size of construction machines. As the size of the engine increases, the lug down speed increases. This is for the following reason.

1) As the size of the engine increases, the inertia of the engine increases and the load increases. Therefore, the number of lag-down rotations increases, and the time until the rotation of the engine returns is lengthened.

2) In the case of a large engine, the input torque limit value of the horsepower control of the hydraulic pump is set to a small value in consideration of the variation in engine output characteristics, and the input torque limit value is increased during load operation by increasing the input torque limit value. There is something to do. In this case, there is an increase in the engine load due to the increased torque, and the decrease in the rotational speed when a sudden load is applied to the engine is further increased.

[0008] 3) In a large engine, high supercharging is often performed by an exhaust turbine in order to produce a high output. In such a high supercharged diesel engine, a load is suddenly applied from a no-load high idle state. In this case, there is a time delay from the low boost pressure state during high idle to the time when the exhaust turbine works effectively and the boost pressure increases, and the engine output rise is delayed, resulting in a large decrease in the engine speed. .

The remarkable decrease in the engine speed due to the above-mentioned lag down and the delay in the rise of the engine speed from that state are perceived as a large change in the engine sound, which gives a discomfort to the machine operator. Also,
The decrease in the rotation speed due to the lug down temporarily reduces the discharge flow rate of the hydraulic pump, and thus affects the workability and operability of the machine.

Conventionally, when a small engine is used, the drop in the lag-down rotation speed is small and the return time is short, so that the influence on workability and operability has not been a serious problem. However, in a hydraulic construction machine equipped with a large engine, the lug-down rotation speed is large as described above, so that the influence on workability and operability becomes a problem.

In the engine control device of the civil engineering construction machine disclosed in Japanese Patent Application Laid-Open No. 1-222419, a drag load is applied as described above to reduce lag down. However, in this method, a load is applied to the engine even when the engine is not operated, so that fuel efficiency is deteriorated and energy efficiency is deteriorated.

In order to prevent the engine lag down, a method of controlling the fuel supply amount to be rapidly increased when a sudden load is applied to the engine may be considered. However, since this method supplies wasteful fuel instantaneously,
As in the case of Japanese Patent Application Laid-Open No. 1-222419, fuel efficiency is deteriorated. Further, when the fuel supply amount is rapidly increased, a problem that black smoke is generated in the exhaust gas also occurs.

An object of the present invention is to provide an engine which is generated when a hydraulic actuator is suddenly operated from a non-operation state without deteriorating fuel consumption and increasing black smoke in a hydraulic construction machine employing a large engine as a prime mover. It is an object of the present invention to provide a device for preventing engine lag down of a hydraulic construction machine, which reduces the lag down of the engine.

[0014]

(1) In order to achieve the above object, the present invention provides an engine, a variable displacement hydraulic pump which is driven to rotate by the engine, and a pressure discharged by the hydraulic pump. A hydraulic actuator driven by oil, pump control means for controlling a capacity of the hydraulic pump so that an input torque of the hydraulic pump does not exceed a predetermined reference torque, and an exhaust turbine for supercharging the engine. In the engine lug down prevention device for a hydraulic construction machine, a pressure sensor for detecting a supercharging pressure by the exhaust turbine and a part of the pump control means are provided, and the supercharging pressure becomes equal to or less than a first predetermined value. Between the time when the hydraulic pump is increased to the second predetermined value and the time when the input torque of the hydraulic pump is reduced to be smaller than the reference torque to perform the torque reduction control. Shall and a torque control means.

[0015] The pressure sensor and the torque reduction control means are provided as described above, and the limit value of the input torque of the hydraulic pump is maintained between the time when the supercharging pressure becomes equal to or less than the first predetermined value and the time when the boost pressure increases to the second predetermined value. When the hydraulic actuator is suddenly operated from a non-operating state, the load applied to the engine is reduced by performing the torque reduction control with a value smaller than the reference torque. The return time of the rotation speed is also shortened, and the influence on the operability is reduced. In addition, the fuel supply amount during that period is also reduced, so that the fuel efficiency is improved and the generation of black smoke is reduced.

(2) In the above (1), preferably,
The reduction torque control means includes means for gradually increasing the limit value of the input torque to the reference torque when the boost pressure rises to the second predetermined value.

As a result, a good operation feeling can be obtained without a sudden change in the pump discharge flow rate.

(3) In the above (1), preferably, the pump control means is adapted to guide the discharge pressure of the hydraulic pump, and the discharge pressure does not cause the input torque of the hydraulic pump to exceed the reference torque. A hydraulic regulator for controlling the capacity of the hydraulic pump, wherein the torque reduction control means is configured to reduce the boost pressure from a first predetermined value to a second predetermined value. A controller that outputs a drive current for torque reduction control, an electromagnetic valve that operates by the drive current to generate a control pressure, and that when the control pressure is guided, the input torque limit value of the hydraulic pump is made smaller than the reference torque. Setting means for adjusting the set value of the hydraulic regulator so as to perform the setting.

Thus, the pump control means is constituted by a hydraulic regulator, and the torque reduction control can be performed as described in (1) above.

[0020]

Embodiments of the present invention will be described with reference to the drawings.

In FIG. 1, reference numeral 1 denotes a diesel engine, and a fuel injection amount of the engine 1 is controlled by a governor (fuel injection device) not shown. Two variable displacement hydraulic pumps 2 and 2 are connected to an output shaft 1a of the engine 1 via a power distribution mechanism 50, and the hydraulic pumps 2 and 2 are each driven by the engine 1 to discharge pressure oil.
The hydraulic oil discharged from the hydraulic pumps 2 and 2 is supplied to respective actuators, for example, hydraulic cylinders 5 via control valve units 3 and 3,
Drive. The control valves of the control valve units 3 and 3 are operated by operating lever devices 4 and 4 to control the flow rate and direction of the pressure oil supplied from the hydraulic pumps 2 and 2 to the respective actuators.

The operating lever devices 4 and 4 are of a hydraulic pilot type having an operating lever 4a and a pilot valve 4b in this example.
When the control lever 4a is operated, an operation pilot pressure corresponding to the operation direction and the operation amount is generated, whereby each control valve is switched. For example, when the control valve 3a is switched, the rod of the hydraulic cylinder 5 is moved. The flow rate according to the operation amount of the operation lever 4a is supplied to the side or the bottom side.

The hydraulic pump 2 has, for example, a swash plate 2a as a variable capacity member. The tilt angle of the swash plate 2a is controlled by a hydraulic regulator 51 having a power shift control function. That is, the pump displacement is controlled.

The engine 1 is a supercharged engine provided with an exhaust turbine 1b which pressurizes the intake air of the engine with the energy of exhaust gas. The supercharger pressurized by the exhaust turbine 1b is guided to an intake manifold 1c.
Inhaled into the engine cylinder.

The above-described hydraulic drive system is provided with the engine lag down prevention device of the present embodiment. The engine lag down prevention device is provided in the intake manifold 1c, detects a pressure of the supercharged air, a controller 53 that inputs a signal of the pressure sensor 52 and performs a predetermined arithmetic processing, and a controller 53 An electromagnetic proportional pressure-reducing valve 54 that operates by the output driving current and outputs a pressure corresponding to the driving current as a control pressure based on the pressure of the pilot hydraulic pressure source 6, and a control pressure output from the electromagnetic proportional pressure-reducing valve 54. And the above-described hydraulic regulator 51 that operates.

The details of the hydraulic regulator 51 are shown in FIG. The hydraulic regulator 51 is provided with the swash plate 2 of the hydraulic pump 2.
a tilt control actuator 31 for adjusting the tilt angle of a;
And a horsepower control servo valve 32 for controlling the operation of the tilt control actuator 31.

The tilt control actuator 31 has a servo piston 31a having a different pressure receiving area on both end faces, a pressure receiving chamber 31b in which the small diameter end face of the servo piston 31a is located, and a pressure receiving chamber 31c in which the large diameter end face is located. The pressure receiving chamber 31b on the smaller diameter end face is connected to the discharge path 2b of the hydraulic pump 2, and the pressure receiving chamber 31c on the larger diameter end face is connected to either the discharge path 2b of the hydraulic pump 2 or the tank via the servo valve 32. ing. When the pressure receiving chamber 31c on the large-diameter end face is connected to the tank under the control of the servo valve 32, the servo piston 3 is driven by the discharge pressure of the hydraulic pump 2 applied to the pressure receiving chamber 31b.
1a moves to the left in the figure to reduce the tilt angle (pump capacity) of the swash plate 2a of the hydraulic pump 2, and when the pressure receiving chamber 31c is connected to the discharge path 2b, the piston pressure receiving area in the pressure receiving chamber 31c decreases. Since it is larger than the piston pressure receiving area in the pressure receiving chamber 31b, the servo piston 1a moves rightward in the drawing, and increases the tilt angle (pump capacity) of the swash plate 2a of the hydraulic pump 2.

The servo valve 32 includes a spool 32a, a feedback sleeve 32b linked to a servo piston 31a via a feedback lever 33, and a spool 3a.
A setting spring 32c acting on one end of the spool 2a;
a hydraulic drive section 32d acting on the opposite end of the large-diameter piston 34, the hydraulic drive section 32d includes a large-diameter piston 34, and a small-diameter piston provided at the end of the large-diameter piston 34 opposite to the spool 32a. 36, a pressure receiving chamber 37 in which the end of the large-diameter piston 34 is located, and a pressure receiving chamber 39 in which the end of the small-diameter piston 36 is located.
The pump port 51a is connected to the discharge path 2b of the hydraulic pump 2, the pressure receiving chamber 39 has a reduced horsepower port 51b, and the reduced horsepower port 51b is connected to the secondary port of the electromagnetic proportional pressure reducing valve 54. ing.

When the electromagnetic proportional pressure reducing valve 54 is not operated, the spool 32a applies the force of the setting spring 32c to the pressure receiving chamber 37.
When the hydraulic pressure is smaller than the spring force, the pressure receiving chamber 31c of the tilt control actuator 31 is connected to the tank when the hydraulic pressure is smaller than the spring force. When the pump capacity is increased as described above and the hydraulic pressure becomes larger than the spring force, the pressure receiving chamber 31c of the tilt control actuator 31 is connected to the discharge path 2b, and the pump capacity is reduced as described above. The control is performed so that the input torque of the hydraulic pump 2 does not exceed the limit value determined by the setting spring 32c.

When the electromagnetic proportional pressure reducing valve 54 operates, a control pressure is introduced into the pressure receiving chamber 39, and the hydraulic pressure by the control pressure is applied to the end of the small-diameter piston 36 in the same direction as the oil pressure by the pump discharge pressure of the pressure receiving chamber 37. Additionally acts on the spool 32a so that the oil pressure by the pump discharge pressure in the pressure receiving chamber 37 is balanced with the force obtained by subtracting the additional hydraulic pressure in the pressure receiving chamber 39 from the force of the setting spring 32c. For this reason, the hydraulic pump 2 can output a smaller flow rate for the same pump discharge pressure than when the electromagnetic proportional pressure reducing valve 23 is not operated, and the limit value of the input torque of the hydraulic pump 2 is reduced. Is controlled. This control is called torque reduction control.

FIG. 3 shows the relationship between the output control pressure of the electromagnetic proportional pressure reducing valve 54 and the limit value of the input torque of the hydraulic pump 2. FIG. 4 shows a change in the horsepower characteristic corresponding to a change in the limit value of the input torque of the hydraulic pump 2. In the drawing, T0 is a limit value of the input torque set by the setting spring 32c, and is referred to as a rated torque (reference torque). T1 is a limit value of the input torque at the time of the torque reduction control. Electromagnetic proportional pressure reducing valve 5
4, when the output control pressure is 0 or near 0, the limit value of the input torque of the hydraulic pump 2 is set to the rated torque T0. As the control pressure increases, the limit value of the input torque of the hydraulic pump decreases, and the control pressure becomes the maximum. When the pressure increases to near high pressure, the limit value of the input torque of the hydraulic pump 2 decreases to T1. The horsepower control characteristic of the hydraulic pump changes as shown in FIG. 4 according to the decrease in the input torque limit value.

The controller 53 performs a calculation process as shown in the flowchart of FIG. In FIG. 5, P is the supercharging pressure,
T is a pump input torque limit value, F is a determination flag indicating that the supercharging pressure has dropped to P1 or less, and ΔT is a torque increment value.

Hereinafter, the operation of the present embodiment will be described while explaining the processing contents of the controller 53 with reference to FIG.

When the power of the controller 53 is turned on,
First, in a procedure 200 as initialization processing, the determination flag F is set to F
Let a = 0. Next, after reading the supercharging pressure P detected by the pressure sensor 52 in step 201, the supercharging pressure P is read in step 202.
Is less than or equal to a first predetermined value P1 (for example, 0.2 kgf / cm ² ). When the controller 53 is powered on, the operation lever 4a is not operated, the load on the engine 1 is small, the engine is at a high idle speed, and the exhaust turbine 1
Since the supercharging pressure by b is low, the judgment result is Yes,
Proceed to step 203. In step 203, the determination flag F is set to F
= 1, and then in step 204, the input torque limit value T of the hydraulic pump 2 is set to T = T1, and the corresponding drive current is output to the electromagnetic proportional pressure reducing valve 54. Here, T1 is a limit value of the input torque at the time of the torque reduction control in which the output pressure of the electromagnetic proportional pressure reducing valve 54 is obtained at the highest level as described above,
A drive current with the output pressure at the highest level is output to the electromagnetic proportional pressure reducing valve 54. Thus, the hydraulic pump 2 is subjected to torque reduction control so that the input torque does not exceed the limit value T1.

While the operation lever 4a of the operation lever device 4 is not operated, the above procedures 201 to 204 are repeated, and the torque reduction control is continued. Thus, when the operation lever 4a is not operated, the load applied to the engine 1 is reduced.

When the operating lever 4a of the operating lever device 4 is operated and a load is applied to the hydraulic pump 2, the engine 1
, The fuel supply amount to the engine 1 increases, and the supercharging pressure by the exhaust turbine 1b increases. Pressure sensor 5
When the supercharging pressure P detected in Step 2 becomes higher than P1, Step 20
The determination result of No. 2 is No, and the procedure proceeds to Step 210. Step 2
At 10, it is determined whether the determination flag F is F = 1.
In this case, since F = 1 was set in the previous step 203, the determination result is Yes, and the procedure proceeds to step 220. In step 220, the supercharging pressure P is changed to the second predetermined value P2 (for example, 1.0 kgf
/ Cm ² ; P2> P1) It is determined whether it is less than or equal to. At first, since the supercharging pressure P is P1 <P <P2, the determination result is Yes, and the process proceeds to Step 221.
The limit value T of the input torque of the hydraulic pump 2 is set as T = T1, and the torque reduction control is performed.

During P1 <P <P2, the above procedure 201,
202, 210, 220, 221 are repeated, and T = T
1 is continued.

When the amount of fuel supplied to the engine 1 further increases and the supercharging pressure P becomes higher than the second predetermined value P2, the procedure proceeds to step 220.
Is No, and the procedure goes to step 230. Step 2
At 30, the limit value T of the pump input torque is set to T = T + ΔT
It is determined in step 231 whether or not the limit value T has reached T0. If the determination result is No, steps 201 and 20 are performed.
2, 210, 220, 230 and 231 are repeated. In step 230, since T = T + ΔT, a drive current is generated and output so that the output control pressure of the electromagnetic proportional pressure reducing valve 54 gradually decreases. As a result, the pump input torque T
Gradually increases. Limit value T of pump input torque is T0
Is reached, the result of the determination in step 231 is Yes,
After rewriting the determination flag F to F = 1 in step 232, the process returns to step 201.

First step 210 after returning to step 201
Is No, and the procedure proceeds to step 240. Step 2
At 40, the input torque limit value T of the hydraulic pump 2 is set to T =
T0 is set, and the corresponding drive current is output to the electromagnetic proportional pressure reducing valve 54. Here, T0 is a limit value of the torque reduction control obtained when the output pressure of the electromagnetic proportional pressure reducing valve 54 is near 0 as described above, and the drive current output to the electromagnetic proportional pressure reducing valve 54 is set to 0. As a result, the input torque of the hydraulic pump 2 is limited to the limit value T.
The rated torque is controlled so as not to exceed zero.

While the operating lever 4a is in the operating state and the supercharging pressure P is P> P1, the procedures 201, 202, 21
Steps 0 and 240 are repeated, and the rated torque control is continued.

In the above, the hydraulic regulator 51
Constitutes pump control means for controlling the capacity of the hydraulic pump 2 so that the input torque of the hydraulic pump 2 does not exceed a predetermined reference torque (rated torque) T0.
3, the electromagnetic proportional pressure reducing valve 54, the small-diameter piston 36 of the hydraulic regulator 51, the pressure receiving chamber 39, and the horsepower reduction port 51b.
Is provided as a part of the pump control means, and is provided with a second predetermined value P2 after the supercharging pressure becomes equal to or less than the first predetermined value P1.
Until the hydraulic pump 2 rises, the limiting value of the input torque of the hydraulic pump 2 is made smaller than the reference torque T0 to constitute a torque reduction control means for performing torque reduction control.

The engine load, supercharging pressure,
FIG. 6 is a time chart showing changes in the limit value of the pump input torque.

When the operating lever 4a is in the operating state, the engine load and the supercharging pressure are high, and the limit value of the pump input torque is at the rated torque T0. When the operation lever 4a is returned to the neutral state and is in the non-operation state, both the engine load and the supercharging pressure decrease, and when the supercharging pressure decreases to a first predetermined value P1 or less,
When the electromagnetic proportional pressure reducing valve 54 is excited, the limit value of the pump input torque is reduced to the limit value T1 of the torque reduction control. This state continues while the operation lever 4a is in the non-operation state.

When the operation lever 4a is operated from this state, the engine load and the supercharging pressure increase. Supercharging pressure is 2nd
Is less than or equal to the predetermined value P2, the pump input torque limit value is held at the torque reduction control limit value T1. When the supercharging pressure rises to a second predetermined value P2 (> P1), the limit value of the pump input torque is changed from T1 to the normal set torque T with time.
It gradually increases to zero.

When a sudden operation is performed from a state where the load of the engine 1 is low and the supercharging pressure is equal to or lower than P1, the input torque of the hydraulic pump 2 is limited to a low value T1 until the supercharging pressure reaches P2. Since the load applied to the engine 1 is limited, it is possible to prevent a sudden decrease in engine speed.

Therefore, according to this embodiment, a hydraulic construction machine employing an engine with a large lag down
When the operating lever 4a is in a non-operating state and the operating lever 4a is suddenly operated from a state in which the engine 1 is at a high idle speed, a drop in the rotating speed of the engine 1 due to a lag down can be reduced, and the return time can be shortened. The effect of engine lag down on operability can be reduced. Further, when a sudden load is applied from the state where the engine 1 is at the idling speed, the fuel supply amount is not rapidly increased, so that deterioration of fuel efficiency can be prevented and generation of black smoke can be reduced. Further, discomfort of the operator is reduced, and a comfortable operation can be performed.

Further, according to the present embodiment, since the pump input torque limit value is increased with time, the pump discharge flow rate does not suddenly change, and the operation feeling is also good in this respect.

In the above embodiment, the present invention is applied to the hydraulic drive system including the hydraulic regulator having the input torque control function. However, the input torque limit values T0 and T1 are stored in the controller. The drive current is output to the electromagnetic proportional pressure reducing valve so that the input torque limit value corresponding to the change of the supercharging pressure is obtained, and the tilt control actuator is driven by the output pressure from the electromagnetic proportional pressure reducing valve to reduce the capacity of the hydraulic pump. You may make it control.

[0049]

According to the present invention, in a hydraulic construction machine employing an engine having a large lag down, a decrease in the number of revolutions of the engine lag down which occurs when the hydraulic actuator is suddenly operated from the non-operation state is reduced. It can be made smaller and the return time can be shorter. Therefore, the influence of engine lag down on operability is reduced. Further, when a sudden load is applied to the engine, the supply amount of fuel is not rapidly increased, so that deterioration of fuel efficiency can be prevented and generation of black smoke can be reduced.
Further, since the discomfort of the operator is reduced, a comfortable operation can be performed.

[Brief description of the drawings]

FIG. 1 is a diagram showing a hydraulic drive system including an engine lag down prevention device according to a first embodiment of the present invention.

FIG. 2 is a diagram showing details of a hydraulic regulator of the hydraulic pump shown in FIG.

FIG. 3 is a diagram showing a relationship between an output pressure of an electromagnetic proportional pressure reducing valve and a limit value of a pump input torque adjusted by the output pressure.

FIG. 4 is a diagram showing changes in horsepower control characteristics when the pump input torque changes as shown in FIG. 3;

FIG. 5 is a flowchart showing a process performed by a controller shown in FIG. 1;

FIG. 6 shows an engine load according to an operation state of an operation lever,
6 is a time chart showing changes in the limit values of the supercharging pressure and the pump input torque.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Engine 2 Hydraulic pump 3 Control unit 3a Control valve 4 Operation lever device 4a Operation lever 5 Hydraulic cylinder 6 Pilot hydraulic power source 31 Tilt control actuator (Pump control means) 32 Horsepower control servo valve (Pump control means) 32a Spool (Pump control) Means) 32b Feedback sleeve (pump control means) 32c Setting spring (pump control means) 32d Hydraulic drive unit (pump control means; reduced torque control means) 34 Large diameter piston (pump control means) 36 Small diameter piston (reduced torque control means) 37 pressure receiving chamber (pump control means) 39 pressure receiving chamber (reduced torque control means) 51 hydraulic regulator (pump control means) 52 pressure sensor 53 controller (pump control means; reduced torque control means) 54 electromagnetic proportional pressure reducing valve (reduced torque control) means)

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Claims (3)

[Claims] 1. An engine, a variable displacement hydraulic pump rotationally driven by the engine, a hydraulic actuator driven by pressure oil discharged by the hydraulic pump, and an input torque of the hydraulic pump being predetermined. An engine lug down prevention device for a hydraulic construction machine, comprising: a pump control unit that controls a capacity of the hydraulic pump so as not to exceed a reference torque; and an exhaust turbine that supercharges the engine. And a pressure sensor provided as a part of the pump control means, and the input of the hydraulic pump during a period from the time when the supercharging pressure becomes equal to or less than a first predetermined value to a time when the pressure increases to a second predetermined value. And a torque reduction control means for performing torque reduction control by making the torque limit value smaller than the reference torque. Jinragudaun prevention device. 2. An engine lag down prevention device for a hydraulic construction machine according to claim 1, wherein said torque reduction control means comprises:
An engine lag down prevention device for a hydraulic construction machine, comprising: means for gradually increasing the limit value of the input torque to the reference torque when the boost pressure rises to the second predetermined value. 3. The engine lag down prevention device for a hydraulic construction machine according to claim 1, wherein said pump control means guides a discharge pressure of said hydraulic pump, and the discharge pressure controls an input torque of said hydraulic pump to said reference. A hydraulic regulator for controlling the capacity of the hydraulic pump so as not to exceed a torque, wherein the torque reduction control means controls the supercharged pressure from a first predetermined value to a second predetermined value. A controller that outputs a drive current for torque reduction control, a solenoid valve that is operated by the drive current and outputs a control pressure, and a limit value of an input torque of the hydraulic pump when the control pressure is guided. And a setting adjusting means for adjusting a set value of the hydraulic regulator so as to be smaller than a torque.