JPH0635873B2 - Hydraulic control equipment for construction machinery - Google Patents

Description

Detailed Description of the Invention A. BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydraulic control device for a construction machine represented by a hydraulic excavator, a wheel loader, etc., in which the horsepower of a prime mover and the flow rate of a hydraulic pump are controlled according to a load to improve a fuel consumption rate and the like. Is.

B. Conventional Technology A conventional technology will be described by taking a wheel hydraulic excavator as an example.

As shown in FIG. 8, the wheel-type hydraulic excavator includes a lower traveling body 2 having traveling wheels 1 and an upper traveling body 3 connected to the lower traveling body 2 via a traveling wheel. The upper turning body 3 is provided with an excavation attachment including a boom 7, an arm 8 and a bucket 9 which are driven by hydraulic cylinders 4 to 6, respectively.

Wheel type hydraulic excavators are allowed to run on general roads not limited to specific work sites, but there are flat roads and slopes on general roads, and the maximum legal speed of 35km / h is possible even under various road conditions. It is preferable to be able to drive.

Therefore, using an engine that can output a speed of 35km / h when climbing a slope with a certain required gradient will provide a solution to the running performance. In a wheel hydraulic excavator, one engine is generally used for both excavation and traveling, but the engine horsepower required for excavation work may be smaller than the engine horsepower required for traveling. For this reason, setting the engine to high horsepower with an emphasis on running performance when climbing slopes is wasteful in terms of excavation work in terms of fuel consumption, noise, cost, etc. When the engine is set to have a lower horsepower than the former, giving priority to fuel efficiency, noise, and cost, it will not be possible to obtain sufficient running performance when climbing a hill. In a wheel-type hydraulic excavator, excavation and running are limited as far as engine performance is concerned. Matching with will be bad.

Therefore, various ideas have been taken from the past, and one of the typical ideas is to satisfy the 35km / h stipulated by law only when driving on a flat road.

In this case, if the required flow rate for traveling on a flat road at 35 km / h is set to Q1 and the required pressure is set to P1 based on the specifications of the traveling hydraulic motor and the transmission to be used, for example, as shown in FIG. Required horsepower PS2 'is determined, and the maximum engine speed N1 and the maximum displacement volume q1 of the hydraulic pump are determined by this, and the engine speed-pump discharge amount diagram (N-Q diagram) is, for example, FIG. As shown in.

Considering the uphill traveling in the hydraulic traveling drive system having the NQ diagram shown in FIG. 10, FIG. 9 (a)
As shown in, the pump discharge pressure increases to P2 and the pump tilt angle decreases when climbing uphill, so the pump discharge rate decreases to Q2, and the speed is much slower than 35km / h (35km / h × Q2 / Q1), and satisfactory running performance cannot be obtained.

Therefore, when determining the specifications of the engine and hydraulic equipment, it is possible to obtain a speed of 35 km / h at a preset grade. With this setting,
As a matter of course, the speed of 35km / h can be obtained even when driving on the flat part.

Therefore, similar to the above, from the specifications of the hydraulic motor and the transmission to be used, the required flow rate when traveling at a certain grade uphill at 35 km / h is Q1, and the required pressure is P2 (> P).
1), the required horsepower PS2 of the engine is determined as shown in FIG. 9B, and the maximum engine speed N2 and the maximum displacement volume q2 of the hydraulic pump are determined. Pump discharge amount diagram (NQ diagram)
Is as shown in FIG. 11. Here, it is assumed that the performance of the engine in the hydraulic traveling drive system having the NQ diagram shown in FIG. 11 is determined as shown in FIG. As can be seen from the rotation speed-horsepower curve (N-PS curve) in FIG. 12, if PS2 is the pump absorption horsepower required for traveling on an uphill road having a certain slope at 35 km / h, the horsepower will be the engine rotation speed N2. You can get it at the time of. And the fuel consumption rate at that time [g /
It can be seen from the rotational speed-fuel consumption rate curve (N-g curve) that PSh] is g2. However, if PS2 '(<PS2) is the absorption horsepower of the pump when traveling on a flat road at 35 km / h with such a hydraulic traveling drive device, when the engine travels on a flat road with full throttle, It can be seen that the engine speed of the engine is N2 '(> N2) and the fuel consumption rate is g2'(> g2). That is,
With such engine and hydraulic system settings, running on a flat road at 35 km / h is not preferable because the engine is used in a region with a low fuel consumption rate. Also, because the engine is used in a region where the fuel consumption rate is high, when the throttle lever is operated and the engine speed is lowered, the pump discharge amount decreases and the specified speed (35km / h)
I can't put out.

Further, in a wheel type hydraulic excavator equipped with a traveling hydraulic drive device, as described above, a single engine and a single hydraulic pump mounted on the upper rotating body are used to provide an excavation actuator and a traveling hydraulic motor. However, the required absorption horsepower PS2 of the hydraulic pump when traveling uphill is considerably larger than the required absorption horsepower PS3 of the hydraulic pump during excavation.

Therefore, in the engine having the characteristics shown in FIG. 12, when excavating work at the throttle lever position of the maximum engine speed N2, the required absorption horsepower of the hydraulic pump is P
If S3 (<PS2), the engine speed increases to N3 and the fuel consumption rate becomes g3 (> g2). If the engine speed is lowered by operating the throttle lever, the pump discharge amount will decrease and the work speed will slow down.

Such a problem also applies to the relationship between heavy load work and light load work in the crawler hydraulic excavator.
In other words, setting the engine to high horsepower with an emphasis on heavy load work is wasteful from the viewpoint of light load work in terms of fuel consumption, noise, cost, etc. On the other hand, placing importance on light load work. If the engine is set to low horsepower, sufficient excavation performance will not be obtained during light load work. If the engine is set to high horsepower and the engine speed is lowered during light load work, the pump discharge amount will decrease, and the desired work speed cannot be obtained. Similar problems occur in other construction machines such as wheel loaders where the work load changes greatly.

Therefore, the present applicant previously proposed a hydraulic control device that solves the above-mentioned problems in the specification of Japanese Patent Application No. 60-239897.

That is, in the hydraulic control device, the prime mover and the hydraulic pump can be operated in at least two types of modes, and in the operation mode with a larger load (hereinafter referred to as the power mode), the pump maximum displacement volume is set small and the prime mover is set. Is operated in a higher rotational speed range, and in the operation mode with a light load (hereinafter referred to as economy mode), the maximum displacement of the pump is increased and the maximum rotational speed of the prime mover is limited to a certain smaller value. ing. More specifically, referring to the NQ diagram in FIG. 14, when the power mode is selected, the maximum displacement of the hydraulic pump is set to a small value q _P , and the prime mover has its maximum rotation speed N _P.
When the economy mode is selected, the maximum displacement of the hydraulic pump is set to a large value q _E , and the prime mover is limited to a rotational speed N _E smaller than N _P. Then, the engine speed N _{E to} N when the power mode is selected
The discharge flow rate Q ₀ of the hydraulic pump in the region _P is set to be substantially equal to the discharge flow rate Q ₀ of the hydraulic pump at the prime mover rotation speed N _E when the economy mode is selected.

C. Problems to be Solved by the Invention However, the hydraulic control device proposed in Japanese Patent Application No. 60-239897 mentioned above has the following problems.

That is, the time of the power mode, the control method of the motor speed during economy mode, because a method of limiting the maximum rotational speed is taken, in the region speed is lower than N _E of the engine, even if switched mode The speed cannot be controlled. On the other hand, since the maximum displacement volume can be switched, when switching from the power mode to the economy mode, the discharge flow rate Q of the hydraulic pump increases, the work speed changes, and the operating performance may be adversely affected. On the contrary, when switching from the economy mode to the power mode, the discharge oil flow rate Q decreases.

An object of the present invention is to provide a hydraulic control device for a construction machine that sets a prime mover rotation speed and a displacement volume according to a load so as not to largely change the flow rate of a hydraulic pump in order to obtain an output horsepower suitable for the load. To provide.

D. Means for Solving the Problems To achieve such an object, the present invention provides a prime mover, operating means for changing the rotation speed of the prime mover, a variable displacement hydraulic pump driven by the prime mover, A hydraulic actuator driven by the oil discharged from the variable displacement hydraulic pump, a detection unit for detecting the load of the hydraulic actuator, and when the detected load exceeds a predetermined value, based on the operation of the operation unit. Rotation speed setting means for increasing the rotation speed of the rotating prime mover by a predetermined amount, and displacement volume setting means for reducing the displacement volume by a predetermined amount when the detected load exceeds a predetermined value. It is equipped with.

In the device according to claim 1, the discharge flow rate of the hydraulic pump, which is determined by the displacement volume and the prime mover rotation speed set by the rotation speed setting means and the displacement volume setting means, respectively, is higher than that of the prime mover. It is preferable that each of the setting means sets the number of revolutions of the prime mover and the maximum displacement to be substantially constant in the rotation range.

Further, in the device according to claim 2, when the prime mover rotation speed is the maximum value, the discharge flow rate of the hydraulic pump is equal to or smaller than the detected load, whether the detected load exceeds or falls below the predetermined value. It is preferable that the rotation speed setting means and the displacement volume setting means set the prime mover rotation speed and the maximum displacement volume so that they are equal to each other.

Further, in the device according to any one of claims 1 to 3, the change of the prime mover rotational speed and the displacement volume in response to the detected load is performed with a delay time. You can also

E. The prime mover rotation speed set in accordance with the operation of the operation operation means is set higher by a predetermined amount when the detected load is equal to or higher than a predetermined value under the control of the rotation speed setting means. At that time, the displacement volume of the variable displacement hydraulic pump is set smaller by a predetermined amount by the control of the displacement volume setting means.
Therefore, the discharge flow rate of the variable displacement hydraulic pump does not fluctuate significantly when the engine speed is increased or decreased in accordance with the fluctuating load.

F. Embodiment FIG. 1 shows an embodiment of the present invention, which is a variable displacement hydraulic pump 13 driven by an engine 11 which constitutes a prime mover.
The discharge port of is connected to the actuator 19 including the traveling hydraulic motor, the excavating cylinders (hydraulic cylinders 4 to 6 in FIG. 8), and the turning motor via the control valve 15. The control valve 15 is switch-controlled by a traveling operation lever (not shown) and an excavation operation lever (not shown).

The discharge flow rate of the variable displacement hydraulic pump 13 is controlled by the pump regulator according to the circuit pressure, for example, as shown in the PQ diagram of FIG. 5, and its maximum displacement volume constitutes maximum displacement volume setting means. Maximum tilt angle setting device 21
It is variable by. The setting device 21 has a hydraulic cylinder 211, and the expansion / contraction of the hydraulic cylinder 211 controls the maximum displacement per rotation of the pump in two stages. The hydraulic cylinder 211 is connected to the pressure source 70 and the tank 26 via the solenoid valve 23.

Further, reference numeral 25 is a device constituting a rotation speed setting means, and as shown in FIGS. 2 (a) to (c), an engine control lever 32 provided in a driver's seat and a governor throttle lever 33 of the engine 11 are provided. And the intermediate lever 35 between them. The engine control lever 3
2, governor throttle lever 33, intermediate lever 35, 2
The rotation speed control means is constituted by 52. Referring to FIG. 2 (a), the engine control lever 32 is pivotally supported by the console box 37 in the driver's seat, and is attached to one end of the first intermediate lever 35 pivotally supported at a predetermined portion of the vehicle. They are connected via a push-pull cable 39. The first intermediate lever 35 is formed in a substantially V shape, and the hydraulic cylinder 251 is fixed to the other end. A second intermediate lever 252 is pivotally supported coaxially with the first intermediate lever 35, and the rotation of the first intermediate lever 35 is transmitted to the second intermediate lever 252 via a hydraulic cylinder 251. The second intermediate lever 252 is connected to the governor throttle lever 33 via the push-pull cable 41. Here, the hydraulic cylinder 251 and the intermediate lever 252 constitute a rotation speed setting means, and the hydraulic cylinder 251 is connected to the hydraulic power source 70 and the tank 26 via the electromagnetic valve 27.

FIG. 2A shows a case where the engine control lever 32 is in the off position and the hydraulic cylinder 251 is contracted, and the engine 11 is stopped at this time. Even if the hydraulic cylinder 251 extends, the second intermediate lever 252 does not rotate. 2 (b) shows that the engine control lever 32 is operated to the maximum position and the hydraulic cylinder 25
1 shows the case where 1 is reduced, and at this time, the engine 11 rotates at the rotation speed N _E. FIG. 2 (c) shows a case where the hydraulic cylinder 251 is extended from the state of FIG. 2 (b), and the second intermediate lever 252 rotates by the amount of extension of the hydraulic cylinder 251 and the maximum rotation speed N _P Then the engine rotates.

The operation amount of the engine control lever 32, the engine speed, and the discharge flow rate of the hydraulic pump will be described in detail with reference to FIG.

In the economy mode in which the hydraulic cylinder 251 is contracted, the engine is stopped when the engine control lever 32 is set to the "OFF E" position in the figure. Then, if the engine speed at the “OFF E” position is considered to be zero, the maximum position (second
The engine speed can be controlled from zero to N _E by operating the engine control lever 32 up to (b) in FIG. At this time, if the pump displacement volume is constant at q _E , the hydraulic pump discharge flow rate can be controlled from ₀ to Q ₀ as shown by the chain line E. In addition, FIG.
(a) shows that the engine control lever 32 is "off P".
However, as can be seen from FIGS. 2 (a) and 3, the range from "OFF E" to "OFF P" is in the state where the hydraulic cylinder 251 is contracted. It becomes the play of the engine control lever 32.

In the power mode in which the hydraulic cylinder 251 is extended, the engine is stopped when the engine control lever 32 is set to the "OFF P" position in FIG. Then, if the engine speed at the “OFF P” position is considered to be zero, the maximum position (second
By operating the engine control lever 32 to FIG. (C) refer), capable of controlling the engine rotational speed from zero to N _P. At this time, if the pump displacement volume is constant at q _P , the hydraulic pump discharge flow rate can be controlled from ₀ to Q ₀ as shown by the solid line P.

Here, the engine speed N _E is determined so that 35 km / h can be obtained when traveling on a flat road with a minimum required horsepower corresponding to the tilt angle of the pump, and is a speed suitable for a light load of the engine. is there. Further, the maximum engine speed N _P is determined so that 35 km / h can be obtained when traveling on an uphill road at a desired gradient with a minimum required horsepower corresponding to the tilt angle of the pump, and is suitable for a heavy load on the engine. It is the number of revolutions.

In FIG. 1 again, reference numeral 29 is a controller composed of, for example, a microcomputer, and the input port thereof has a mode selector switch 31 and a load detection sensor 22.
And the automatic control selection switch 24 are connected. The mode switch 31 is a switch that can switch between the power mode position (P) and the economy mode position (E), and for example, a toggle switch can be used.

The load detection sensor 22 constituting the detection means detects the load of the actuator 19, and the automatic control selection switch 24 switches between the power mode operation and the economy mode operation by manually switching the mode switch 31. It is switched between a manual position and an automatic position which is automatically switched according to the load detected by the sensor 22. Then, at the output port of the controller 29, the solenoid valve 23 connected to the maximum tilt angle setting hydraulic cylinder 211,
An electromagnetic valve 27 connected to the engine speed increasing / decreasing hydraulic cylinder 251 is connected. Solenoid valves 23 and 27
Are switched according to the program shown in FIG.

In FIG. 6, in step S1, the signals of the sensor 22 and the switches 24, 31 are read, and in step S2,
It is determined whether the switch 24 is in the manual position or the automatic position. If it is the manual position, it is determined in step S3 whether the switch 31 is in the power mode position or the economy mode position. If it is in the power mode position, in step S4, the solenoid valves 23, 27
Are both turned on (excited). If it is in the economy mode position, both solenoid valves 23 and 27 are turned off (demagnetized) in step S5. On the other hand, if the switch 24 is in the automatic position, in step S6 it is determined whether the detected load is equal to or greater than a predetermined value,
If it is greater than or equal to the predetermined value, the process proceeds to step S4, and if it is less than the predetermined value, the process proceeds to step S5.

The operation of the present embodiment configured as described above will be described below.

(1) Power mode position When the mode selector switch 31 is switched to the power mode position, or when the automatic control of mode switching is selected and the detected load is equal to or greater than a predetermined value, the solenoid valve 23 is excited and the hydraulic pressure is increased. The cylinder 211 is connected to the pressure source 24, whereby the illustrated maximum tilt angle setting device 21 operates and the maximum tilt angle is set to the displacement volume q _P. At this time, the electromagnetic valve 27 for increasing / decreasing the engine speed is also excited and the hydraulic cylinder 251 is expanded. Therefore, if the engine control lever 32 at the driver's seat is fully pulled, the second cylinder as shown in FIG. The engine can be rotated up to the maximum rotation speed N _P via the intermediate lever 252.

Therefore, as long as the tilt angle of the hydraulic pump 13 becomes the maximum value in the power mode and the displacement volume is q _P in the low pressure region (pressure P2 or less: see FIG. 5), the solid line in FIG. As shown, the pump discharge flow rate increases in proportion to the increase of the engine speed, and the maximum discharge flow rate Q ₀ is obtained at the maximum engine speed N _P. In this case, the PQ diagram of the pump at the engine speed N _P is as shown by the solid line P in FIG.

(2) Economy mode operation When the mode selector switch 31 is switched to the economy mode position or when the automatic control of mode switching is selected and the detected load is less than the predetermined value, the solenoid valve 23 is demagnetized and the hydraulic cylinder is deactivated. 211 is connected to the tank 26,
As a result, the maximum tilt angle setting device 21 shown operates to set the maximum tilt angle to the displacement volume q _E (> q _P ).
At this time, the solenoid valve 27 is demagnetized and the hydraulic cylinder 251 is contracted. Therefore, even if the engine control lever 32 in the driver's seat is fully pulled, as shown in FIG.
Since the rotation of the intermediate lever 252 is reduced by the reduction of the hydraulic cylinder 251, the maximum engine speed is N _E (<N _P ).
Limited by.

Therefore, as long as the tilt angle of the hydraulic pump 13 becomes the maximum value in the economy mode in the low pressure region (pressure P1 or less: see FIG. 5) and the displacement volume is q _E ,
As indicated by the one-dot chain line E in the figure, the pump discharge flow rate increases in proportion to the increase in the engine speed, and the maximum discharge flow rate Q ₀ is obtained at the maximum engine speed N _E. In this case, the PQ diagram of the pump at the engine speed N _E is shown by the one-dot chain line E in FIG.

The curve shown by the broken line in FIG. 5 is the maximum displacement volume q _E
9 shows a PQ diagram when the maximum engine speed rises to N _P when switching to.

(3) Mode switching operation When the mode switching switch 31 is switched to the economy mode position during the power mode operation, or when the automatic control of mode switching is selected and the actuator load of a predetermined value or more becomes less than the predetermined value, the solenoid valve 23, 27 is demagnetized. As a result, the hydraulic cylinder 211 is reduced, the maximum tilt angle of the hydraulic pump 13 is increased, and the maximum displacement volume is q _E
Becomes Further, the hydraulic cylinder 251 contracts, the second intermediate lever 252 follows it, and it rotates counterclockwise in FIG. 2 (c), so that the engine speed decreases by a predetermined value. Therefore, no matter what range the engine speed is,
While keeping the discharge flow rate of the hydraulic pump substantially constant, arrow A in FIG.
The power mode is changed to the economy mode on the NQ diagram. Conversely, when the economy mode is switched to the power mode, each device operates in reverse. Therefore, while the discharge flow rate of the hydraulic pump remains substantially constant over the entire range of engine speed, NQ along the arrow B in FIG. The economy mode is switched to the power mode on the diagram.

In the present embodiment, in economy mode, the maximum displacement of the pump is increased to q _E (> q _P ), the maximum engine speed is limited to N _E (<N _P ), and the maximum pump discharge flow rate is set to Q _o. As a result, the working speed including the traveling speed in the economy mode and the power mode at the maximum pump discharge flow rate is made the same. Therefore, as shown in FIG. 12, the required horsepower P at the engine speed N _E
S2 'can be obtained and the fuel consumption rate can be reduced to g _E. On the other hand, when the pump discharge flow rate is Q ₀ , the maximum speed is 35 km.
Considering that / h is output, as can be seen from FIG. 5, the pump discharge pressure is P1 in economy mode.
(For example, pressure required for running on a flat road) Can run at 35km / h If the pump discharge pressure exceeds P1 as when climbing uphill, 35km / h cannot run, but in power mode the pump discharge pressure is P2 (eg It is possible to drive up to 35km / h up to the pressure required when traveling uphill at θ.

By the way, a conventional pump, for example, N- as shown in FIG.
In the pump having the Q diagram, when the engine speed is reduced from N2 to N1 to reduce the pump absorption horsepower to increase fuel consumption as in this embodiment, the maximum displacement volume of the pump is constant. The P-Q diagram is as shown by the broken line in FIG. 13, and the pump discharge amount decreases to Q ₁ and a predetermined speed cannot be obtained.

In the automatic mode switching operation by the program of FIG. 6, hunting may occur if the load of the actuator fluctuates in the vicinity of the reference value. FIG. 7 shows a program for preventing such hunting.

In FIG. 7, when the solenoid valves 23 and 27 are switch-controlled according to the load change of the actuator, the state is maintained regardless of the load change until a predetermined time elapses.
This prevents hunting. That is, the procedure S
In 9 and 10, the time t after switching the solenoid valve is the predetermined time T
It is determined whether or not a and Tb have been exceeded, and the procedure is exited only when an affirmative determination is made.

In the above description, q _P , N _P , q _E , and N _E are set so that the pump maximum discharge flow rate Q ₀ (= q _P × N _P = q _E × N _E ) in each mode is equal. The two do not have to be the same as long as they are substantially equal, and as a guideline, they may differ so that the maximum traveling speed in each mode is 30 km / h to 35 km / h. Further, in the above description, the maximum tilt angle of the pump and the increase / decrease in the engine speed are controlled by the hydraulic cylinder, but an electromagnetic type may be used.
Furthermore, it is possible to set the maximum tilt angle in three or more stages using linear renoid or using multiple hydraulic cylinders.
You may control the increase and decrease of the engine speed according to it,
In this case, the engine and the hydraulic system are set so as to be optimal for various engine loads, and fuel efficiency can be further improved. The present invention can also be applied to the case where the hydraulic pump 13 is driven by an electric motor instead of the engine. Further, the engine speed may be increased or decreased by increasing or decreasing the fuel injection amount using the electronically controlled governor. In this case, the hydraulic cylinder 251 and the second intermediate lever 252 are unnecessary. Furthermore, although the wheel type hydraulic excavator has been described above, the present invention can be applied to other construction machines having large load fluctuations.

G. According to the present invention, the engine speed set according to the operation of the operating means is set higher by a predetermined amount when the detected load exceeds a predetermined value, and the displacement of the variable displacement hydraulic pump is removed. Since the volume is set small,
Even if the prime mover rotational speed is increased or decreased in accordance with the fluctuating load, the discharge flow rate of the variable displacement hydraulic pump does not fluctuate significantly, so that the speed of the actuator does not fluctuate and the operating performance improves.

In addition, the operator judges the magnitude of the load and, for example, H
Compared to the case of selecting the mode or the E mode, the prime mover rotation speed and the displacement volume suitable for the load are automatically set, so that the operation suitable for the load can be surely performed even if the mode switching is forgotten.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG.
(a)-(c) is a front view showing an example of an engine speed control device and an increasing / decreasing device, FIG. 2 (a) is a state in which the engine control lever is in the off position, and FIG. 2 (b) is an economy mode. Fig. 2 (c) shows the engine control lever operated to the maximum position under power mode, Fig. 2 (c) shows the engine control lever operated to the maximum position under power mode, and Fig. 3 shows the engine control lever operation amount and pump discharge. FIG. 4 is a graph showing the relationship between the engine speed N and the pump discharge amount Q in the present embodiment, and FIG. 5 is a PQ line of the pump in the present embodiment. FIG. 6 is a flow chart showing an example of a procedure for controlling the rotation speed and the maximum displacement, and FIG. 7 is a flow chart showing another example thereof.
The figure is a side view showing an example of a wheel-type hydraulic excavator, the ninth
10 (a) and 10 (b) are views showing two examples of the conventional PQ diagram,
11 and 11 are graphs respectively showing the relationship between the engine speed N and the pump discharge flow rate Q in a conventional wheel hydraulic excavator, FIG. 12 is a diagram showing an engine performance curve, and FIG. 13 is a conventional wheel hydraulic. The figure which shows the PQ diagram in the pump of a shovel, FIG. 14 is a NQ diagram of the hydraulic control apparatus proposed previously. 1: Running wheels 2: Lower running body 3: Upper running body 4-9: Attachment for excavation 11: Engine 13: Variable displacement hydraulic pump 15: Control valve 19: Actuator 21: Maximum tilt angle setting device 22: Load detection sensor, 23, 27: Solenoid valve 24: Automatic control selection switch 25: Rotation speed increasing / decreasing device, 29: Controller 31: Mode selection switch 32: Engine control lever 35: Intermediate lever 211: Maximum tilt angle setting hydraulic cylinder 251: Hydraulic cylinder, 252: Intermediate lever

Claims (4)

[Claims] 1. A prime mover, operating means for changing the number of revolutions of the prime mover, a variable displacement hydraulic pump driven by the prime mover, and a hydraulic pressure driven by oil discharged from the variable displacement hydraulic pump. An actuator, a detection means for detecting the load of the hydraulic actuator, and, when the detected load exceeds a predetermined value, increases the rotation speed of the prime mover rotating based on the operation of the operation means by a predetermined amount. A hydraulic control device for a construction machine, comprising: a rotation speed setting means; and a displacement volume setting means for reducing the displacement volume by a predetermined amount when the detected load exceeds a predetermined value. 2. An apparatus according to claim 1, wherein the discharge of the hydraulic pump is determined by the displacement volume and the prime mover rotational speed set by the rotation speed setting means and the displacement volume setting means, respectively. A hydraulic control device for a construction machine, wherein a prime mover rotation speed and a maximum displacement volume are set so that the flow rate is substantially constant in a high rotation range of the prime mover. 3. The device according to claim 2, wherein when the prime mover rotational speed is the maximum value, whether the detected load exceeds or falls below the predetermined value, the hydraulic pump A hydraulic control device for a construction machine, wherein the rotation speed setting means and the displacement volume setting means set the prime mover rotation speed and the maximum displacement volume so that the discharge flow rates become equal. 4. The apparatus according to any one of claims 1 to 3, wherein a delay time is set for changing the engine speed and the displacement volume in response to the detected load. A hydraulic control device for a construction machine, which is characterized in that