JP3169166B2 - Control device for hydraulic drive machine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a control device for a hydraulic drive machine.

[0002]

2. Description of the Related Art When a warm-up operation is to be performed in a conventional hydraulically driven machine, an operator fixes a hydraulic actuator for driving a working machine by a predetermined method.
An operation is performed to hold the operation lever fully operated. As a result, a pressure loss of the hydraulic oil supplied to the hydraulic actuator occurs, and the temperature of the hydraulic oil rises.

There is an operating valve operated and operated by an operating lever between a hydraulic pump driven by an engine and a hydraulic actuator, and the spool of the operating valve is provided at each switching position. Has a variable orifice. The flow rate of the pressure oil supplied to the hydraulic actuator is determined by changing the opening cross-sectional area of the variable orifice. The size of the cross-sectional area of the variable orifice is determined by the operation amount of the operation lever (operation lever stroke amount).
It will be decided according to. Normally, when the stroke of the operating lever is small, the cross-sectional area of the variable orifice is adjusted to the hydraulic actuator until the stroke reaches a predetermined value.
It is not large enough to drive the data. For this reason, even if the operation lever is operated while the stroke amount of the operation lever is small, there is a dead stroke range of the operation lever in which the hydraulic actuator does not operate. In addition, as the cross-sectional area of the variable orifice changes, the flow rate of the pressure oil drained to the tank also changes.

[0004]

As described above, the size of the pressure oil supplied to the hydraulic actuator is determined by the opening sectional area of the variable orifice incorporated in the operation valve, and the opening sectional area of the variable orifice is determined. Is determined by the stroke of the operation lever. Here, the magnitude of the pressure of the pressure oil supplied to the hydraulic actuator is determined by the rotation speed of the engine that drives the hydraulic pump. For this reason, when the engine speed is low and the engine speed is low, when the engine speed is low, the pressure of the discharge oil of the hydraulic pump becomes low, and the operating lever in which the hydraulic actuator is not driven is operated.
Will increase the dead stroke range. Conversely, when the engine speed is high, the pressure of the oil discharged from the hydraulic pump becomes high, and the dead stroke range of the operation lever becomes small. Such a difference in the dead stroke range affects the sensual operation feeling of the operation lever. If the operation feeling of the operation lever differs depending on the size of the engine speed,
Cannot give a stable operation feeling to the operator, and cannot perform a stable operation. SUMMARY OF THE INVENTION It is an object of the present invention to provide a device which can always provide a stable operation feeling to an operator regardless of the size of the engine speed.

[0005]

Accordingly, in the present invention, a hydraulic pump driven by an engine and a first hydraulic oil supply passage communicating between the hydraulic pump, an operating valve operated by an operating lever, and a hydraulic actuator are provided. A hydraulic drive machine configured to supply hydraulic oil discharged from the hydraulic pump to the hydraulic actuator in accordance with an operation amount of the operation lever to drive the hydraulic actuator; The second to communicate with
And a variable orifice disposed in the second pressure oil supply path for varying the cross-sectional area of the second pressure oil supply path, and a signal for detecting a signal indicating the number of revolutions of the engine. Detecting means for controlling the cross-sectional area of the second pressure oil supply path to decrease as the engine speed decreases based on the output of the signal detecting means so that the range of the dead stroke of the operating lever becomes constant. Variable orifice control means.

[0006]

The present invention focuses on the following points. That is, the lower the engine speed, the lower the pressure of the hydraulic pump discharge oil, thereby increasing the dead stroke range of the operating lever. Conversely, the higher the engine speed, the higher the discharge pressure oil of the hydraulic pump. And the dead stroke range of the operation lever is reduced. Here, if the cross-sectional area of the second pressure oil supply path is reduced, the pressure of the pressure oil supplied from the hydraulic pump to the hydraulic actuator increases, and the dead stroke range of the operation lever can be reduced. . Therefore, the variable orifice is controlled so as to reduce the cross-sectional area of the second pressure oil supply path as the engine speed decreases, so that the dead-stroke range of the operating lever is kept constant irrespective of the engine speed. I do.

[0007]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing a control apparatus for a hydraulic drive machine according to the present invention.

FIG. 1 shows a hydraulically driven machine such as a power machine.
1 shows a configuration of an embodiment apparatus applied to a shovel.

The working machine hydraulic circuit shown in FIG. 1 is configured as follows. That is, the variable displacement hydraulic pump 1 is driven by the engine 2 and the swash plate driving servo valve 3
The discharge flow rate per rotation is changed by changing the tilt angle of the swash plate 1a. The pressure of the pipe on the discharge side of the hydraulic pump 1 and the pressure of the jet sensor orifice 6 are applied to the swash plate driving servo valve 3 as pilot pressure. The valve 3 selects the smaller one of these and tilts the swash plate 1a. The discharge pressure oil of the pump 1 passes through a first pressure oil supply passage T1 that connects the hydraulic pump 1, the operation valve 4, the cylinder chamber of the hydraulic cylinder 8, and the drain tank 7, and the hydraulic pump 1 and the operation valve 4 And the variable pressure orifice 5, the jet sensor orifice 6, and the drain tank 7 through a second pressure oil supply path T2.

Here, the variable orifice 5 is connected to the pressure oil supply passage T
2, but instead of the pressure oil supply path T2, a pressure oil supply that does not communicate with the discharge port of the hydraulic pump 1, the jet sensor orifice 6, and the drain tank 7 (does not pass through the operation valve 4). A passage may be provided, and the variable orifice 5 may be provided on the pressure oil supply passage. In short, the variable orifice 5 may be provided on a pressure oil supply path that connects the hydraulic pump 1 and the drain tank 7.

The electric operation lever 9 is an operation lever for switching the operation valve 4. The operation stroke amount of the lever 9 is detected by a lever stroke amount detection sensor 9a, and the detection signal is transmitted to a hydraulic device control. Added to LA10. The operating valve solenoid 11 is energized in response to a signal applied from the hydraulic controller 10 to drive the spool of the operating valve 4. The variable orifice 5 is a variable orifice that varies the cross-sectional area of the pipe of the second pressure oil supply passage T2, and the cross-sectional area is changed according to a signal applied to the solenoid 5a.

The hydraulic oil temperature sensor 12 is a temperature sensor disposed at an appropriate position in the hydraulic oil pipeline to detect the temperature of the hydraulic oil supplied to the hydraulic cylinder 8, and the temperature detection signal of the sensor 12 is controlled by the hydraulic device control. -Added to la 10;

The engine 2 is provided with a fuel injection pump 13 and a governor 14. Governor 14 fuel control
The lever lever 14a is driven by a stepping motor 15,
The driving position of the lever 14a is detected by a potentiometer 16. The throttle dial 17 is a dial for setting a target engine speed, and a throttle signal set by the dial 17 is applied to the hydraulic controller 10. The rotation sensor 18 is a sensor for detecting the rotation speed of the output shaft of the engine 2, and the rotation signal detected by the sensor 18 is transmitted to the hydraulic controller 10 and the governor controller.
Added to LA19.

The governor controller 19 includes a rotation sensor 18.
Engine speed and hydraulic device controller 1 detected by
The output torque of the engine 2 is regulated to a predetermined value based on the throttle signal of the throttle dial 17 added from 0, that is, the target rotation speed of the engine 2 and the driving position of the governor 14 detected by the potentiometer 16. The driving position of the governor 14 is controlled so as to move along the line. It should be noted that such a governor control technique is well-known and has no direct relation to the gist of the present application, so that further detailed description will be avoided.

The hydraulic pump discharge oil pressure sensor 20 is a pressure sensor which is provided in a pipeline on the discharge side of the hydraulic pump 1 and detects the pressure of the discharge pressure oil of the hydraulic pump 1. -Added to la 10; Further, the mode changeover switch 21 is used for the operation mode as described later.
A signal for selecting the operation mode, and a signal indicating the selected operation mode is applied to the hydraulic controller 10.

Hereinafter, the following first to fourth controls are executed in the hydraulic controller 10.

1) First control (warm-up operation control) This first control automatically and automatically sets the temperature of the pressure oil supplied to the hydraulic cylinder 8 shown in FIG. This is a control for quickly shifting.

FIGS. 2 and 3 show flowcharts of the first control.

As shown in FIG. 2, first, a detection signal t of the hydraulic oil temperature sensor 12 is taken in (step 10).
1) It is determined whether the detected temperature t is equal to or higher than a predetermined temperature Tset. Here, it is assumed that the predetermined temperature Tset is set as the temperature of the pressure oil suitable for the operation of the hydraulic drive machine (step 102). The determination result of step 102 is NO
In other words, if it is determined that the temperature t of the pressure oil supplied to the hydraulic cylinder 8 is lower than the predetermined temperature Tset, the sectional area of the second pressure oil supply passage T2 with respect to the solenoid 5a of the variable orifice 5 The signal for minimizing is output. As a result, the opening degree of the throttle portion of the variable orifice 5 becomes minimum, and the second pressure oil supply passage T2 has the minimum cross-sectional area.
Here, as the cross-sectional area of the second pressure oil supply passage T2 becomes smaller, the pressure difference before and after the variable orifice 5 becomes larger, so that the calorific value increases and the temperature of the pressure oil rises. Therefore, the oil temperature t quickly rises above the threshold value Tset by reducing the opening of the throttle portion of the variable orifice 5 to the minimum (step 104). On the other hand, if the result of the determination in step 102 is YES, the oil temperature t has already reached the warm-up temperature, so there is no need to raise the oil temperature t any longer, but rather the energy loss due to heat generation becomes large. . Therefore, a signal for maximizing the sectional area of the second pressure oil supply passage T2 is output to the solenoid 5a of the variable orifice 5 in order to reduce energy loss. As a result, the opening of the throttle portion of the variable orifice 5 is opened to the maximum, and the second pressure oil supply passage T2 has the largest cross-sectional area (step 103).

The processes of steps 101 to 104 may be performed before the hydraulically driven machine performs a work.
Here, it is possible to automatically detect that the hydraulic drive machine is in a state before the start of the work and raise the operating oil temperature by the procedure as shown in FIG. That is, in steps 201, 203, 204, and 205 in FIG. 3, the same processing as steps 101, 102, 103, and 104 in FIG. 2 is executed, and the operation lever 9 is moved to the neutral position (new) before step 203. (Tral), that is, whether or not the hydraulically driven machine has not started to perform any work before starting the work. This determination process is performed based on the detection signal of the sensor 9a input to the hydraulic controller 10 (step 202). Step 20
Only when it is determined that the operation lever 9 is set to the neutral position in Step 2 and that the work is not started before the start of the work in which no work is performed, the process proceeds to the next Step 203, and Step 2 is executed.
In 03, the warm-up operation process of increasing the oil temperature is performed only when the hydraulic oil temperature t is lower than the predetermined temperature Tset (steps 203 to 205).

Here, since the judgment processing of step 202 is a processing for judging whether or not the operation lever 9 is set to the neutral position, if the operation lever 9 is at the neutral position, it is only before the start of work. This also includes the case where the hydraulic drive machine is not working, so that the opening of the restrictor of the variable orifice 5 is also performed when the working oil temperature t has not reached the predetermined temperature Tset. The process of minimizing the cross-sectional area and raising the hydraulic oil temperature to a predetermined temperature Tset or higher is performed.

For this reason, the warm-up operation can be performed in parallel with the excavation work and the like, and the work efficiency is dramatically improved.

The above is the contents of the first control.

2) Second control (dead-stroke control) In this second control, the range of the stroke of the operating lever 9 in which the hydraulic cylinder 8 does not operate is fixed regardless of the rotation speed of the engine 2. This is a control for improving the operation feeling of the operation lever 9 within the range. FIG. 11 shows the relationship between the stroke of the operating lever and the equivalent opening area of the variable orifice in the conventional working machine hydraulic circuit having no variable orifice 5, and FIG. 12 shows the operating lever in the prior art.
The relationship between the stroke amount and the operating speed of the hydraulic cylinder is shown. Here, the equivalent opening area of the orifice existing at each switching position of the operation valve is determined by the first stroke according to the stroke of the operation lever.
It changes as shown by L'1 and L'2 in FIG. That is, the equivalent opening area of the second pressure oil supply passage that connects the hydraulic pump and the drain tank changes as L'1 according to the magnitude of the stroke of the operating lever. This characteristic L '
1 is uniquely determined by the type of the operation valve.
Similarly, the equivalent opening area of the first pressure oil supply passage connecting the hydraulic pump and the hydraulic cylinder also changes as indicated by L'2 according to the stroke of the operating lever. As shown in FIG. 12, there is a dead stroke range in which the hydraulic cylinder does not operate (the speed of the cylinder rod becomes zero) while the stroke of the operation lever is small. This dead stroke range is determined by the equivalent opening area of the second pressure oil supply passage. That is, the second
The smaller the equivalent opening area of the pressure oil supply passage, the smaller the dead stroke range. On the other hand, the lower the rotation speed of the engine, the lower the pressure of the oil discharged from the hydraulic pump, and the larger the dead stroke range of the operating lever. In addition, the dead stroke depends on the engine speed.
Range is different. L'3 in FIG. 12 indicates the relationship between the operating lever and the operating speed of the hydraulic cylinder when the engine speed is high, and L'4 indicates the relationship between the operating lever and the hydraulic cylinder when the engine speed is low. The relationship with the operation speed is shown. This clearly shows that the lower the engine speed, the larger the dead-stroke range and the different the feeling of lever operation. Therefore, in the second control, the opening area of the throttle section of the variable orifice 5 is reduced as the engine speed decreases, thereby canceling the increase of the dead-stroke range as the engine speed decreases. Thus, the dead-stroke range is always kept constant regardless of the engine speed.

FIG. 4 shows the relationship between the stroke of the operating lever 9 and the equivalent opening area of the variable orifice in the embodiment, and FIG. 5 shows the stroke of the operating lever 9 and the operation of the hydraulic cylinder 8. This shows the relationship with speed. Here, the equivalent opening area of the variable orifice means an opening area obtained by combining the orifice of the operation valve 4 and the variable orifice 5.

In the hydraulic device controller 10, an operation lever is provided.
The relationship between 9 and the equivalent opening area is set as characteristic lines l1, l'1,... Such that the equivalent opening area decreases as the engine speed decreases, as shown by the broken line in FIG.
Therefore, the hydraulic controller 10 selects a line corresponding to the current rotation speed of the engine 2 from the lines l1, l'1... Based on the output of the rotation sensor 18 and the output of the sensor 9a. In step (1), an urging signal is output to the solenoid 5a to control the opening of the throttle of the variable orifice 5 so that an equivalent opening area corresponding to the operation stroke of the operation lever 9 is obtained. As a result, as shown in FIG. 5, the dead-stroke range is constant irrespective of the high (line L3) or low (line L4) rotational speed of the engine 2. Therefore, even if the engine speed changes, a constant operation feeling can always be obtained in the operation lever 9, so that a stable operation can be performed.

In this control, a signal indicating the engine speed is used as an output of a rotation sensor 18 for detecting the speed of the output shaft of the engine 2 and as a set throttle signal of a throttle dial 17 for setting an engine target speed. Also, the fuel control lever 14 of the governor 14
It can be obtained as the output of the potentiometer 16 that detects the drive position of “a”.

The above is the contents of the second control.

(3) Third Control (Work Mode Switching Control) This third control is a control for reducing the energy loss due to the drainage of the pressure oil to the tank 7 according to the work state.

As described above, the equivalent opening area of the orifice at each switching position of the operating valve in the conventional working machine hydraulic circuit in which the variable orifice 5 does not exist is uniquely determined according to the type of the operating valve (FIG. 11). L'1).
The way of setting the line L'1 in FIG. 11 is as follows. In order to reduce the energy loss, when the load pressure increases during the reverse stroke, the discharge oil of the hydraulic pump is completely discharged and the second hydraulic oil supply path is set. And the operation of the hydraulic cylinder was stopped. By the way, when an excessive load is applied to the hydraulic cylinder in a certain work type, the discharge oil of the hydraulic pump may be entirely drained in order to stop the operation of the hydraulic cylinder. From the viewpoint of improvement, it is desirable that the flow rate of the discharge oil flowing from the hydraulic pump to the tank 7 does not drain completely. Therefore, in this embodiment, the type of work performed by the hydraulic drive machine is the work mode 1 in which it is desirable to drain the entire discharge oil of the hydraulic pump 1 and the work mode in which it is desirable to drain a part of the discharge oil of the hydraulic pump 1. C2
The discharge oil of the hydraulic pump 1 is entirely drained or partially drained by making the opening of the throttle portion of the variable orifice 5 different depending on each operation mode. FIG. 6 shows the relationship between the stroke of the operating lever and the equivalent opening area of the variable orifice in the embodiment. Here, the equivalent opening area of the variable orifice means an opening area obtained by combining the orifice of the operation valve 4 and the variable orifice 5. In the mode change switch 21, the work mode 1 and the work mode 2 are selected by switching the switch 21 on and off. In FIG. 6, lines L5 and L6 are set according to the work mode 1 and the work mode 2. Here, the line 5 is a characteristic in which the opening of the throttle portion of the variable orifice 5 is maximized, and the line L6 is a characteristic in which the opening of the throttle portion of the variable orifice 5 is narrowed by a predetermined amount. Therefore, the hydraulic controller 10 sets lines L5 and L6 in accordance with the operation mode selected based on the output of the mode changeover switch 21 and the output of the operation lever 9.
And outputs an energizing signal to the solenoid 5a so that an equivalent opening area corresponding to the operation stroke of the operation lever 9 is obtained on the selected line to open the throttle section of the variable orifice 5. Control the degree. As a result,
When the work mode 1 is selected, the entire discharge oil of the hydraulic pump 1 can be drained, and when the work mode 2 is selected, only a part of the discharge oil of the hydraulic pump 1 is drained. It can be drained, and an increase in energy loss can be avoided.

Further, as shown in FIG. 7, the opening degree of the throttle portion of the variable orifice 5 is made constant irrespective of the stroke amount of the operating lever 9, and the characteristics of the working mode 1 and the working mode 2 are set. L8 and L9 may be set.

The above is the content of the third control.

4) Fourth Control (Damping Characteristics Control) The purpose of this fourth control is to eliminate the possibility that the operation of the hydraulic cylinder 8 becomes oscillating when the operation lever is suddenly operated, thereby impairing stability. This is the control to be performed. As described above, in the conventional working machine hydraulic circuit in which the variable orifice 5 does not exist, the equivalent opening area of the second pressure oil supply path changes in accordance with the magnitude of the stroke of the operating lever, which is changed by the operation. It is uniquely determined by the type of valve. For this reason, when the operation lever is suddenly operated, the operation of the hydraulic cylinder is vibrated due to the inertia of the hydraulic cylinder and the elasticity of the oil, and the stability is impaired (the damping characteristic is poor). Here, in order to improve the stability during operation of the operation lever, it is better to increase the opening amount of the orifice, but there is a problem that the energy loss increases. By the way, it is known that the above damping characteristics deteriorate as the pressure of the oil discharged from the hydraulic pump 1 increases.

FIG. 9 shows the pressure PP of the oil discharged from the hydraulic pump 1.
And the opening area AD of the orifice. In the figure, solid lines indicate lines L10 (when the operation lever stroke amount is small), L11 (when the operation lever stroke amount is medium) and L12 (operation lever stroke) in the embodiment.
(In the case where the lock amount is large), and the dotted line indicates the conventional line L'1
0 (when the operation lever stroke amount is small), L'11
(When the operation lever stroke amount is medium), L'12
(When the amount of operation lever stroke is large). Here, in the embodiment, the opening degree of the throttle portion of the variable orifice 5 is increased in a predetermined relationship as the pressure PP of the discharge oil of the hydraulic pump 1 increases.

The hydraulic controller 10 changes the line corresponding to the current operation amount of the operation lever 9 to the line L based on the output of the hydraulic pump discharge oil pressure sensor 20 and the output of the sensor 9a.
10, L11 and L12, and outputs an energizing signal to the solenoid 5a so that an equivalent opening area corresponding to the pressure PP of the discharge oil of the hydraulic pump 1 is obtained on the selected line. The degree of opening of the throttle is controlled. FIG. 10 shows the pressure PP of the oil discharged from the hydraulic pump 1.
The relationship between the flow rate and the flow rate QD passing through the orifice is indicated by the line L'13 in the related art, and by the line L13 in the embodiment. As can be seen from the figure, the flow rate QD of the pump discharge pressure PP passing through the variable orifice 5 at P1 is QD2, which is much lower than the conventional flow rate QD1. Even if the discharge pressure of the hydraulic pump 1 is further increased, the flow rate passing through the variable orifice 5 is much smaller than the conventional flow rate, so that the energy loss can be reduced.

The conventional line L 'at pressure PP
The inclination of the tangent line 13 of 13 is the same as the inclination of the line L13 of the embodiment, but the inclination of the tangent line decreases as the discharge pressure PP of the hydraulic pump 1 increases (tangent line 13), and the damping characteristics are deteriorated. However, the line L13 of the embodiment
Does not change and does not decrease even if the discharge pressure of the hydraulic pump 1 increases. Therefore, the damping characteristics are greatly improved as compared with the conventional one.

It is also possible to calculate the differential value of the discharge pressure of the hydraulic pump 1 and increase the sectional area of the variable orifice 5 by an amount proportional thereto. According to this technique, the damping characteristic is improved at a frequency higher than the predetermined frequency, and the average hydraulic pressure loss does not change.

The above is the contents of the fourth control.

In FIG. 1, a variable orifice 5 is provided in the pressure oil supply path T2, and the size of the equivalent opening area is changed by changing the degree of opening of the throttle portion. As shown in the figure, a pressure control valve 22 is disposed in the second pressure oil supply passage T2 instead of the variable orifice 5, and the equivalent opening area is changed according to a pressure setting signal applied to a solenoid 22a of the pressure control valve 22. May be changed to perform the above-described first to fourth controls.

[0040]

As described above, according to the present invention, a stable operation feeling can always be given to the operator irrespective of the rotational speed of the engine, and a stable operation can be performed.

[Brief description of the drawings]

FIG. 1 is a diagram conceptually showing a configuration of an embodiment of a control device for a hydraulic drive machine according to the present invention.

FIG. 2 is a flowchart illustrating a processing procedure performed by a hydraulic device controller shown in FIG. 1;

FIG. 3 is a flowchart illustrating a processing procedure performed by the hydraulic device controller shown in FIG. 1;

FIG. 4 is a graph showing a relationship between a stroke amount of an operation lever set by a hydraulic device controller shown in FIG. 1 and an equivalent opening area of an orifice.

FIG. 5 is an operation lever when the equivalent opening area of the orifice changes according to the relationship shown in FIG.
5 is a graph showing the relationship between the stroke amount and the operating speed of the hydraulic cylinder.

FIG. 6 is a graph showing a relationship between a stroke amount of an operation lever set by a hydraulic device controller shown in FIG. 1 and an equivalent opening area of an orifice.

FIG. 7 is a graph showing a relationship between a stroke amount of an operation lever set by the hydraulic controller shown in FIG. 1 and an equivalent opening area of the orifice.

FIG. 8 is a view used to explain that a pressure control valve can be used instead of the variable orifice shown in FIG. 1;

FIG. 9 is a graph showing the relationship between the pressure of the discharge oil of the hydraulic pump and the opening area of the orifice.

FIG. 10 is a graph showing the relationship between the pressure of hydraulic oil discharged from a hydraulic pump and the flow rate of hydraulic oil passing through an orifice.

FIG. 11 is a graph showing a relationship between a stroke amount of an operation lever and an equivalent opening area of an orifice in a conventional technique.

FIG. 12 is a graph showing the relationship between the stroke of the operating lever and the operating speed of the hydraulic cylinder when the equivalent opening area of the orifice changes according to the relationship shown in FIG.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Hydraulic pump, 2 ... Engine, 4 ... Operating valve, 5 ... Variable orifice, 7 ... Drain tank, 8 ... Hydraulic cylinder,
9: Electric operation lever, 9a: Operation stroke amount detection sensor, 10: Hydraulic device controller, 11: Solenoid for operation valve, 12: Hydraulic oil temperature sensor, 18: Rotation sensor, 2
0: hydraulic pump discharge oil pressure sensor, 21: mode changeover switch, T1: first pressure oil supply path, T2: second pressure oil supply path.

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-1-141203 (JP, A) JP-A-59-4002 (JP, A) JP-A-63-101504 (JP, A) 73401 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) F15B 11/00 E02F 9/22

Claims (5)

(57) [Claims] A hydraulic pump that is driven by an engine; and a first pressure oil supply path that communicates a hydraulic actuator with an operation valve that is operated by the hydraulic pump, an operation lever, and an operation of the operation lever. In a hydraulic drive machine configured to supply hydraulic oil discharged from the hydraulic pump to the hydraulic actuator in accordance with an amount to drive the hydraulic actuator, a second pressure that communicates the hydraulic pump with a drain tank is provided. An oil supply path, a variable orifice disposed in the second pressure oil supply path, for varying a cross-sectional area of the second pressure oil supply path, and a signal detection means for detecting a signal indicating the engine speed. Disconnecting the second pressure oil supply path as the engine speed decreases based on the output of the signal detection means so that the range of the dead stroke of the operation lever becomes constant. Hydraulic drive machine controller, characterized in that it comprises a variable orifice control means for controlling to reduce the product. 2. The control device for a hydraulically driven machine according to claim 1, wherein said variable orifice control means performs said control when an operation amount of said operation lever is equal to or less than a predetermined value. 3. The control device for a hydraulically driven machine according to claim 1, wherein the signal detection unit is a rotation sensor that detects an actual rotation speed of an output shaft of the engine. 4. The control device for a hydraulically driven machine according to claim 1, wherein said signal detection means is a sensor for detecting a set position of a setting device for setting a target rotation speed of said engine. 5. The control device for a hydraulic drive machine according to claim 1, wherein said signal detection means is a sensor for detecting a drive position of a governor provided in said engine.