JP3072818B2 - Automatic sequential boosting system for hydraulic circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a safety valve which is firstly relieved at a first set pressure when an overload is applied to an actuator during operation, and then relieved at a second set pressure higher than the first set pressure after a predetermined time. , Regarding the automatic sequential boosting system of the hydraulic circuit to reduce the peak pressure at the time of relief,
In particular, when an overload is applied to the actuator during operation, the safety valve is first relief at the first set pressure, the discharge amount of the hydraulic pump is reduced after a predetermined time, and then the relief valve is released at the second set pressure higher than the first set pressure. By reducing the hydraulic energy and then relieving,
The present invention relates to an automatic sequential pressure boosting system for a hydraulic circuit that reduces the peak pressure at the time of relief to improve the durability of hydraulic equipment.

[0002]

2. Description of the Related Art FIGS. 5 to 9 show a prior art, FIG. 5 shows a control circuit of a hydraulic shovel according to the prior art (Japanese Patent Application No. 4-40519), and FIG. 6 shows the control of FIG. FIG. 7 is a diagram showing the relationship between the discharge pressure and the displacement of the hydraulic pump in the circuit, FIG. 7 is a diagram showing the relationship between the discharge pressure and the discharge flow rate of the hydraulic pump in the control circuit of FIG. 5, and FIG. 8 is a sudden load in the control circuit of FIG. FIG. 9 is a diagram showing the relationship between the discharge pressure of the hydraulic pump and the pump capacity during operation, and FIG. 9 is a diagram showing the change over time in the discharge pressure of the hydraulic pump in FIG.

Next, the control circuit shown in FIG. 5 will be described. 1 is an engine, 2 is a variable displacement hydraulic pump driven by the engine 1, 3 is a boom cylinder as one of actuators, 4 is an operation valve for controlling the boom cylinder 3, 5 is a discharge pressure of the hydraulic pump 2 , A cylinder for setting the pressure of the two-stage safety valve 5, 6 a control pressure pump driven by the engine 1, 7 a
Is a relief valve for keeping the discharge pressure of the control pressure pump 6 constant. Reference numeral 8 denotes a hydraulic pump displacement control device including a servo valve 8a and a servo cylinder 8b. Reference numeral 9 denotes a cutoff valve that regulates the maximum value of the discharge pressure of the hydraulic pump 2 before the two-stage safety valve 5 operates. 2, an absorption torque control valve, 10a is a solenoid for changing the absorption torque of the absorption torque control valve 10 in accordance with the input signal, 11 is a push button for increasing the excavating force, 12 is a power source, 13, 14 are solenoid on-off valves, 15 is a tank.

An operation when a slow load is applied in the prior art will be described with reference to FIGS. 6 and 7. FIG. When the hydraulic excavator performs a normal excavation operation with a prescribed excavation force, the voltage of the power supply 12 is not applied to the solenoids of the solenoid type on-off valves 13 and 14, so that the solenoid-type on-off valves 13 and 14 are set to the respective b positions. Operated. Therefore, the control source pressure P _C which is kept constant by the relief valve 7 of the control pressure pump 6, two-stage safety valve 5 and the cut-off valve 9 each pressure setting cylinder 5a, because it is not supplied to 9b, two-stage safety valve 5 Is P ₁ (for example, 325
kg / cm ² ), and the cut-off valve 9 is switched to the position “b” with a cut-off pressure lower than P ₁ to cut off the discharge pressure of the hydraulic pump.

Further, the constant held control source pressure P _C is the absorption torque control valve 10 of the control pressure pump 6, and discharge pressure P of the hydraulic pump 2, not shown in the controller 16 to be output to the solenoid 10a According to the setting signal from the absorption torque setting device, as shown in FIG. 6, the absorption torque T ₁ of the hydraulic pump 2 (P is the discharge pressure of the pump, V is the specific volume of the hydraulic pump, T is the absorption torque of the hydraulic pump, k Is assumed to be a proportional constant, T = kPV) is reduced so as to be constant, and is applied to the pilot cylinder of the servo valve 8a of the displacement control device 8 of the hydraulic pump 2 via the cutoff valve 9. Therefore, the servo valve 8a in response to the pilot pressure acting on pilot cylinder is operated, the control source pressure P _C of the control pressure pump 6 which is vacuum supplied to the servo cylinder 8b in accordance with the operation amount of the servo valve 8a Hydraulic pump 2
Is controlled.

The cutoff valve 9 reduces the output pressure of the absorption torque control valve 10 in accordance with the sum of the downstream pressure of the cutoff valve 9 and the discharge pressure of the hydraulic pump 2 to control the capacity of the hydraulic pump 2. It is supplied to the pilot cylinder of the servo valve 8a of the device 8. Therefore, when the pump discharge pressure P in the pump delivery pressure P- pump capacity V curve on shown in FIG. 6 is raised, is controlled along the absorption torque T ₁ curve of the hydraulic pump, the discharge pressure P of the hydraulic pump bunk safety valve When than 5 set pressure P ₁ reaches slightly lower cutoff pressure, the cutoff valve 9 is in a state in which cutoff of the switched discharge pressure P in the b position bunk safety valve 5 acts increased to a set pressure P ₁ A hydraulic excavator operation is performed.

Further, the absorption torque T of the hydraulic pump 2
In the relational expression of kPV = constant, when both sides are multiplied by the engine speed N, the relational expression of TN = kP VN = constant is obtained, where TN = HP is the absorption horsepower of the hydraulic pump, and VN = Q
Is the discharge flow rate of the hydraulic pump, and if K is a constant, a relational expression of HP = KP · Q = constant is obtained. That is, P
· Q = becomes constant, the hyperbola as shown in HP ₁ to the absorption torque T ₁ in the same manner as FIG. 7 of the hydraulic pump in FIG. 6 the relationship between P and Q.

Next, when the operator wants to increase the excavating power during excavation work by the hydraulic excavator, when the push button 11 in FIG. 5 is pressed, the voltage of the power supply 12 is changed while the push button 11 is being pressed. 13. Since the voltage is applied to the solenoid of the cutoff switch 14, the solenoid type on-off valves 13 and 14 are operated to their respective a positions. Therefore, the control source pressure P _C which is kept constant by the relief valve 7 of the control pressure pump 6, the two-stage safety valve 5 and the cut-off valve 9 each pressure setting cylinder 5a, to be supplied to 9b, two-stage safety valve 5 From P ₁ (eg, 325 kg / cm ² ) to P ₂ (eg, 350 kg / c)
m ² ), the cut-off valve 9 switches to the position a via the spring 9c, and the cut-off function is released.

Further, the constant held control source pressure P _C is the absorption torque control valve 10 of the control pressure pump 6, and discharge pressure P of the hydraulic pump 2, not shown in the controller 16 to be output to the solenoid 10a by a setting signal from absorption torque setter and vacuum so that the absorption torque T ₂ of the hydraulic pump 2 as shown in FIG. 6 is constant, capacity control system for a hydraulic pump 2 through a cut-off valve 9 8 Act on the pilot cylinder of the servo valve 8a, the servo valve 8a is operated in accordance with the pilot pressure acting on the pilot cylinder, and the control source of the control pressure pump 6 is depressurized in accordance with the operation amount of the servo valve 8a. capacity of the hydraulic pump 2 is controlled by supplying the pressure P _C in the servo cylinder 8b.

As described above, when the cutoff valve 9 is switched to the position a by pressing the push button 11 to increase the excavating force, the cutoff function of the cutoff valve 9 is released, and Since the set pressure of the stage safety valve 5 increases from P ₁ to P ₂ , the absorption torque T ₂ (= kPV) of the hydraulic pump is increased to the set pressure P ₂ on the pump discharge pressure P-pump capacity V curve shown in FIG. It is controlled to be constant. Further, the hyperbola as shown in the same manner as the absorption torque T ₂ of the hydraulic pump in relation also Figure 6 of the discharge pressure P and the discharge flow rate Q of the hydraulic pump 7 in HP _2. Accordingly, while the push button 11 is being pressed, the torque proportional to the area of the hatched portion in FIG. 6 or the horsepower proportional to the area of the hatched portion in FIG. 7 increases. Hydraulic pump discharge volume Q
The working efficiency can be improved by increasing the discharge pressure P (excavation force) in the entire range of (working machine speed).

[0011]

However, in the above-mentioned prior art, the horsepower in the hatched portion in FIG. 7 can be used, and the working machine power can be increased over the entire range of the working machine speed. while it is, since the set pressure of the safety valve is switched from P ₁ to P _2, the discharge amount Q of the hydraulic pump is large (fast drilling rate)
In the work in the range, a sudden load acts and the set pressure P ₂
When the pressure relief is performed, a large peak pressure is generated to shorten the life of the hydraulic device, and also increase the noise, thereby deteriorating the working environment of the operator. This will be described with reference to FIG. 8. When the bucket of the hydraulic shovel collides with a large stone and a sudden overload is applied when working in Q-A where the pump capacity V is the maximum, the hydraulic pump capacity V is absorbed. instead of moving the N-point from the point a via the upper torque curve T _2, the pressure remains maximum capacity of the hydraulic pump capacity V is the point Q rises from point a to point L P _2, two-stage safety valve 5 Then, the pressure rises to the peak pressure M while relief, and then moves to the point N. That is, the hydraulic pump 2 at maximum capacity, and for relief at the maximum discharge pressure state (the maximum energy state), problems such as the peak pressure P ₃ is also increased the has occurred. FIG. 9 is a diagram showing a change with time during which the discharge pressure P of the hydraulic pump 2 in FIG. 8 moves to the point N after rising to the peak pressure P ₃ (point M).

[0012]

SUMMARY OF THE INVENTION The present invention has been made to solve the problems in the prior art, the first shot
Akira is a variable displacement hydraulic for driving the actuator
Pump and displacement control device for this hydraulic pump and this displacement
A control pressure source of a control device and a discharge pressure detector of the hydraulic pump
And the predetermined absorption torque signal, this discharge pressure detection
Hydraulic pump discharge pressure
The first absorption torque curve that determines the pump capacity
Function, and switches the predetermined absorption torque signal.
The same discharge pressure of the hydraulic pump
A capacity smaller than the capacity in one absorption torque curve by a predetermined amount
Therefore, the uniquely determined second absorption torque curve has a monotonically decreasing function.
The source pressure of the control pressure source is reduced so that
An absorption torque control valve to be supplied to the quantity control device;
A two-stage safety valve that sets the maximum set pressure of the
Pressure switching device for a two-stage safety valve, and the absorption torque control valve
Supply to the solenoid and the set pressure switch of the two-stage safety valve
A hydraulic circuit consisting of a controller that controls the switching signal
In the control device, the controller is a discharge pressure detector.
When a pressure signal less than the first maximum set pressure is input from the
The specified absorption torque signal that draws the first absorption torque curve is
Switch to a reduced absorption torque signal that draws a second absorption torque curve
When the pressure signal of the first set pressure is input,
After a fixed period of time, the controller
Configured to output the second set pressure setting signal higher than the constant pressure
It was done. Each of the two monotonically decreasing functions is a hydraulic pump
Of constant product of pump capacity and hydraulic pump discharge pressure
May be.

[0013] The second invention is based on the configuration mainly based on the first invention.
Then, the reduced absorption torque signal is released to release the specified absorption torque.
Release switch for returning to the
The controller inputs the release signal from the switch
During this time, the controller controls the absorption torque control valve.
Release the reduced absorption torque signal to the solenoid and absorb it as specified
It is configured to output a torque signal.

According to a third aspect of the invention, there is provided a configuration mainly comprising the first aspect of the invention.
The two monotonic functions are the capacity of the hydraulic circuit and the oil.
The product is constant with the discharge pressure of the pressure pump
Things.

[0015] A fourth invention is directed to a configuration mainly based on the first invention.
In this case, the solenoid of the absorption torque control valve of the hydraulic pump is
In the predetermined absorption torque signal supplied to the
The discharge flow rate is uniquely determined with respect to the discharge pressure of the pressure pump
The first horsepower curve becomes a monotonically decreasing function, and the predetermined absorption
By switching the torque signal, the same discharge of the hydraulic pump
From the discharge flow rate in the first horsepower curve for the output pressure
A second horsepower curve that is uniquely determined by a predetermined small discharge flow rate
The source pressure of the control pressure source is adjusted so that the line becomes a monotonically decreasing function.
The pressure is reduced and supplied to the capacity control device.
Things.

[0016]

Next, the operation of the above configuration will be described. Hydraulic port
Input the first set pressure signal from the pump discharge pressure detector
After a predetermined time, the controller outputs a second set pressure signal higher than the first set pressure to the set pressure switch to increase the set pressure of the two-stage safety valve . For this reason, when an overload acts on the actuator during the operation, while the two-stage safety valve is relieved for a predetermined time at the lower first set pressure,
The hydraulic pump is controlled by the absorption torque control valve that reduces the source pressure of the control pressure source and supplies the displacement to the displacement control device so that the displacement of the hydraulic pump becomes a monotonically decreasing function with respect to the discharge pressure. It decreases to the volume corresponding to the first set pressure in the monotonically decreasing function within a time. Therefore, even when the hydraulic pump is suddenly overloaded and the hydraulic pump is instantaneously increased to the first set pressure while the large capacity during the operation is being started and the relief is started, the first set pressure is equal to the second set pressure. Since the pressure is lower than the set pressure, the hydraulic energy for relief is reduced, so that the peak pressure can be kept small.
Further, even if the relief set pressure is increased from the first set pressure to the second set pressure higher than the first set pressure after a predetermined time from the start of the relief by rising to the first set pressure, the capacity of the hydraulic pump decreases. Therefore, the hydraulic energy to be relieved is reduced, and the temporal change rate of the pressure increase is small. Therefore, the peak pressure when the two-stage safety valve is increased to the second set pressure can be reduced.

Further , when the controller inputs a pressure signal equal to or less than the first set pressure from the discharge pressure detector of the hydraulic pump, a second absorption torque curve smaller than the first absorption torque curve drawn on the discharge pressure-capacity coordinate of the hydraulic pump is obtained. When the controller outputs the reduced absorption torque signal for switching to the absorption torque curve from the controller to the solenoid of the absorption torque control valve and when the controller inputs the first set pressure signal from the discharge pressure detector, the controller sets the set pressure switch after a predetermined time. And outputs a second set pressure signal higher than the first set pressure to increase the set pressure of the two-stage safety valve.

Accordingly, when an overload is applied to the actuator during the operation, the absorption torque control valve starts the absorption on the discharge pressure-capacity curve of the hydraulic pump from the pressure equal to or lower than the first set pressure. While being switched to the smaller second absorption torque curve, and while the two-stage safety valve is relieving at the lower first set pressure for a predetermined time, the hydraulic pump operates at the first set pressure on the second absorption torque curve. To the corresponding capacity.

As described above, after the hydraulic pump has decreased to the capacity corresponding to the first set pressure in the second absorption torque curve, the relief set pressure is increased from the first set pressure to a second set pressure higher than the first set pressure. Even when the capacity of the hydraulic pump is larger than the second absorption torque curve, the capacity corresponding to the first set pressure in the first absorption torque curve, and the relief set pressure from the first set pressure to the second set pressure higher than that. As compared with the case where the pressure is increased, the hydraulic energy to be relieved is further reduced, and the peak pressure when the two-stage safety valve is raised to the second set pressure can be further reduced. In addition, each of the monotone decreasing functions is generally set such that the product of the capacity of the hydraulic pump and the discharge pressure is constant or approximated.

Further, a release switch for releasing the reduced absorption torque signal and returning to the specified absorption torque signal, and while the release signal from the release switch is being input to the controller, the controller may output the absorption torque signal. If the control valve solenoid is configured to release the reduced absorption torque signal and output the specified absorption torque signal,
If the operator wants to work at a slightly higher speed while performing relief at the second set pressure on the second absorption torque curve due to overload during work, the release switch is used to release the second set pressure on the first absorption torque curve. Can work with.

With respect to the discharge pressure of the hydraulic pump detected by the discharge pressure detector, the discharge flow rate of the hydraulic pump is univocal.
1st horsepower curve and 2nd horsepower curve monotonously decrease
If it is configured to be a function, the absorption horsepower of the hydraulic pump can be controlled to a predetermined value in the same manner as the absorption torque of the hydraulic pump.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. 1 to 4 show the embodiment of the present invention. The same reference numerals are given to the same components as those in the conventional technique, and the description of the configuration and operation will be omitted. FIG. 1 is a diagram showing a control circuit of a hydraulic shovel according to an embodiment of the present invention, and FIG.
FIG. 3 shows details of a controller in the control circuit of FIG.
FIG. 4 is a diagram showing the relationship between the discharge pressure P of the hydraulic pump and the pump capacity V in the control circuit of FIG. 1, and FIG. 4 is a diagram showing the change over time of the discharge pressure P of the hydraulic pump when a sudden load acts in FIG. is there.

Next, the hydraulic control circuit in FIG. 1 will be described. FIG. 1 omits the components related to the cutoff valve 9, the push button 11, and the controller 16, and replaces the cutoff release switch 17, the discharge pressure detector 18, the monitor 19, and the controller 20 with respect to the conventional technology shown in FIG. 5. It is the same as FIG. 5 except that it is added. In FIG. 1, the controller 20 includes a discharge pressure signal Pi from the discharge pressure detector 18 and
A work mode signal for heavy excavation work, excavation work, etc., from the monitor 20, and a cutoff release signal IC from the cutoff release switch 17 are input to the solenoid 10a of the torque variable valve 10 to reduce the torque signal I0 or the prescribed torque signal I.
1 is output to the solenoid of the solenoid on-off valve 13 as a boost signal IR.

FIG. 2 is a diagram showing the details of the controller 20. Reference numeral 21 denotes a comparator, which compares the discharge pressure signal Pi from the discharge pressure detector 18 with, for example, a set pressure P2 = 350 kg / cm ² to obtain Pi ≧ P2. If so, a YES signal “Y” is output; otherwise, a NO signal “N” is output. Reference numeral 22 denotes a timer which outputs a YES signal "Y" after, for example, Tt = 0.5 seconds from the input of the YES signal "Y" from the comparator 21, and receives the NO signal "N" from the comparator 21. Reset. Reference numeral 23 denotes a switch. When a YES signal "Y" from the timer 22 is inputted, a boost signal IR for setting the ^two -stage safety valve 5 to P2 = 350 kg / cm2 is output from the power supply 24 to the solenoid on-off valve 13. When the YES signal "Y" from the timer 22 is not input, the boosting signal IR is cut. Reference numeral 25 denotes a comparator which outputs a discharge pressure signal Pi from the discharge pressure detector 18 to, for example, P ₀ = 315 kg /
Compared cm ^2, and outputs a YES signal "Y" when Pi ≧ P _0.

Reference numeral 26 denotes a switch which outputs a reduced torque signal I0 from a reduced torque signal generator 27 to the solenoid 10a of the absorption torque control valve 10 when a YES signal "Y" of the comparator 25 is input. When the NO signal "N" is input or the cut-off release signal IC from the cut-off release switch 11 is input, the specified torque signal I1 from the specified torque signal generator 28 is supplied to the absorption torque control valve 1.
0 is output to the solenoid 10a. As the reduced torque signal I0 output from the reduced torque signal generator 27, the discharge pressure signal Pi is inputted, and the product of the discharge pressure P and the pump displacement V is calculated as shown in FIG.
The specified torque signal I1 output from the specified torque signal generator 28 receives the discharge pressure signal Pi, and the product of the discharge pressure P and the pump displacement V is calculated as follows. This is a value such that the prescribed torque curve T1 shown in FIG. 3 is constant.

Next, the operation of FIGS. 1 and 2 will be described with reference to FIG.
It is explained together with. Hydraulic pump 2 by discharge pressure detector 18
The discharge pressure signal Pi is detected by the controller 2
When output to 0, the comparator 21 calculates P2 = 350 kg / cm.
^If the discharge pressure P is lower than 350 kg / cm ² , an “N” signal is output to the timer 22 and the switch 26 to reset the timer 22 and to switch the specified torque signal generator 27 from the switch 26. To output the specified torque signal I1. Accordingly, the hydraulic pump 2 operates on the specified torque curve T1 in FIG.

For example, when the hydraulic pressure in FIG.
When the bucket is hitting a large stone or the like and a sudden load is applied during the excavation work with the maximum pump capacity up to the point, the relief does not reach the point D via the specified torque curve T1 but instantaneously. Is P at point B via point F
Start relief at 1 = 325 kg / cm ² . Also,
At the point F, the discharge pressure P becomes P0 = 315 kg / cm ² , so that the signal “Y” output from the comparator 25 causes the reduced torque generator 27 to output the reduced torque signal I0 via the switch 26 to the torque variable valve 10. Is output to the solenoid 10a. Accordingly, the discharge pressure P which instantaneously reaches the point B moves to the point J through the points C and D at which the peak pressure P4 is reached while being relieved at the set pressure P1 = 325 kg / cm ² .

Since the time from the point B to the point J is set to be shorter than 0.5 second, the discharge pressure P becomes equal to the set pressure P1 =
0.5 seconds after the pressure reaches 325 kg / cm ² , a “Y” signal is input from the timer 22 to the switch 23, and the controller 20 sets the two-stage safety valve 5 to P 2 = 350 kg / cm 2.
^When the boost signal IR for setting to ² is output to the solenoid on-off valve 13, the source pressure PC kg / cm ^{2 of the} control pressure source is output.
Is supplied to the pressure setting cylinder 5a of the two-stage safety valve 5, so that the pressure of the two-stage safety valve 5 is set to 350 kg / cm ² . Accordingly, in FIG. 3, from the point J, the set pressure P2 = 35.
Peak pressure PK while relief at K point of 0 kg / cm ²
After the pressure rises and the pressure vibrates, a relief state is established at point K. In this state, the hydraulic energy is reduced due to a decrease in the discharge amount of the pump, and therefore, compared to the peak pressure P3 shown in FIG. Low peak pressure.

As described above, when the cut-off release switch 17 is pressed in the relief state at the point K, the cut-off release signal IC is applied to the switch 26 while the cut-off release switch 17 is being pressed. The specified torque signal I from the signal generator 28 via the switch 26
1 is output to the solenoid 10a of the absorption torque control valve 10. Therefore, in FIG. 3, the set pressure P2 = 350 kg
/ Cm ² to move to point E from point K with relief, although the peak pressure PE is generated can improve the working efficiency by increasing the drilling speed if the bucket is in the movable state. While relief at set pressure P2 = 350kg / cm ² if the hand is released from the cut-off release switch 11 returns the point K from point E, it is possible to reduce the relief losses. In FIG. 3, the product is controlled so that the product of the discharge pressure P of the hydraulic pump and the pump displacement V is constant.
= A monotonically decreasing function approximated by a plurality of straight lines to a constant hyperbola. FIG. 4 shows the peak pressure P ₄ in FIG.
It is a diagram showing a state of aging of P _E.

As described above, in the embodiment shown in FIGS.
At point F where P = P0, the pump absorption torque is controlled to decrease from the specified absorption torque T1 to the reduced absorption torque T0. However, if similar control is performed with the specified absorption torque T1, points A to G will be used. And P1 = 325 kg / cm
^It moves to the point D via the point H at which the peak pressure becomes P5 while being relieved by ² , and P2 = 350k by the boost signal PC.
When it moves to the point E where g / cm ² is reached, a peak pressure PE is generated. This peak pressure PE is higher than the peak pressure PK because the relief hydraulic energy is higher than in the above embodiment. Also, the discharge pressure P of the hydraulic pump is detected, and P · V
= Absorbing torque T of the pump that controls the pump capacity V so as to be constant = constant control. However, by detecting the rotational speed N of the pump 2 and outputting this rotational speed signal Ni to the controller 20, Similarly to the relationship between FIGS. 6 and 7 showing the technique described above, it is also possible to control the absorption horsepower HP of the pump to be constant.

[0031]

Since the present invention is constructed as described above, the following effects can be obtained. (1) When an overload is applied to the actuator during operation
The two-stage safety valve starts relief at the first set pressure on the low pressure side
At the specified time from when the pressure changes to the second set pressure on the high pressure side
In the meantime, the capacity of the hydraulic pump decreases,
Hydraulic energy that relieves even if the pressure is raised to a high second set pressure
The relief at the second set pressure at once.
Significantly reduces the peak pressure during relief compared to when
To improve the durability of hydraulic equipment,
The effect of reducing noise and improving the working environment is remarkable. ( 2 ) If an overload is applied to the actuator during the work, if the absorption torque or absorption horsepower of the hydraulic pump is reduced by a predetermined amount from the discharge pressure below the first set pressure of the two-stage safety valve, the two-stage safety valve Since the capacity of the hydraulic pump is further reduced after a predetermined time from the start of the relief at the first set pressure, even if the pressure is increased to the second set pressure higher than the first set pressure, the relief hydraulic energy is further reduced. Therefore, the effect of reducing the peak pressure at the time of relief to improve the durability of the hydraulic equipment and reducing the noise to improve the working environment is further remarkable. ( 3 ) When an overload is applied to the actuator during the operation, the actuator is relieved with a second absorption torque curve larger than the first absorption torque curve or the absorption horsepower curve or a second set pressure on the absorption horsepower curve. If you want to work at a slightly higher speed while operating, operate the release switch to release the work on the first absorption torque curve or the absorption horsepower curve, and during the operation, use the second absorption torque curve ,
Alternatively, since the work can be performed at the second set pressure on the absorption horsepower curve, the work efficiency can be improved.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a control circuit of a hydraulic shovel according to an embodiment of the present invention.

FIG. 2 is a diagram showing details of a controller in the control circuit of FIG. 1;

FIG. 3 shows a discharge pressure P of a hydraulic pump in the control circuit of FIG.
FIG. 4 is a diagram showing a relationship between the pump capacity and the pump capacity.

FIG. 4 is a diagram showing a change over time of a discharge pressure P of a hydraulic pump in FIG. 3;

FIG. 5 is a diagram showing a control circuit of a hydraulic shovel according to a conventional technique (Japanese Patent Application No. 4-40519).

6 is a diagram showing a relationship between a discharge pressure of a hydraulic pump and a displacement in the control circuit of FIG. 5;

FIG. 7 is a diagram showing a relationship between a discharge pressure of a hydraulic pump and a pump displacement in the control circuit of FIG. 5;

8 is a diagram showing a relationship between a discharge pressure and a discharge flow rate of a hydraulic pump when a sudden load is applied in the control circuit of FIG. 5;

9 is a diagram showing a change over time of the discharge pressure of the hydraulic pump in FIG.

[Explanation of symbols]

1 ... Engine 21, 25
... Comparator 2 ... Variable displacement hydraulic pump 22 ...
Timer 3 ・ ・ ・ Boom cylinder 23, 26
... Switch 4 ... Operating valve 24 ...
Power supply 5 ... two-stage safety valve 27 ...
Reduced torque generator 5a: Pressure setting cylinder 28:
Specified torque generator 6 Control pressure pump 7 Relief valve 8 Capacity control device 8a Servo valve 8b Servo cylinder 10 Absorption torque control valve 10a Solenoid 12 ... Power supply 13 ... Solenoid open / close valve 15 ... Tank 17 ... Cutoff release switch 18 ... Discharge pressure detector 19 ... Controller 20 ... Monitor

Claims (4)

(57) [Claims] 1. A variable displacement hydraulic pump for driving an actuator, a displacement control device for the hydraulic pump,
In the control pressure source of the displacement control device, the discharge pressure detector of the hydraulic pump, and the predetermined absorption torque signal, the capacity of the hydraulic pump is determined by the discharge pressure of the hydraulic pump detected by the discharge pressure detector. The uniquely determined first absorption torque curve becomes a monotonically decreasing function, and by switching the predetermined absorption torque signal, a capacity smaller by a predetermined amount than the capacity in the first absorption torque curve for the same discharge pressure of the hydraulic pump. An absorption torque control valve for reducing the original pressure of the control pressure source and supplying the reduced pressure to the displacement control device so that the uniquely determined second absorption torque curve becomes a monotonically decreasing function; A two-stage safety valve for setting the pressure in two stages, a set pressure switch for the two-stage safety valve, a switching signal supplied to the solenoid of the absorption torque control valve and a set pressure switch for the two-stage safety valve In the control device of the hydraulic circuit comprising a controller to control, when the controller receives a pressure signal equal to or less than the first maximum set pressure from the discharge pressure detector, the specified absorption torque signal that draws the first absorption torque curve, When the pressure is switched to the reduced absorption torque signal that draws the second absorption torque curve and the pressure signal of the first set pressure is input, after a predetermined time, the controller sets the second set pressure higher than the first set pressure to the set pressure switch. An automatic sequential boosting system for a hydraulic circuit, which outputs a signal. 2. A release switch for releasing the reduced absorption torque signal and returning to the specified absorption torque signal, and the controller controls the absorption torque while the controller receives a release signal from the release switch. the solenoid of the control valve, and outputs a prescribed absorption torque signal to release the reduced absorption torque signal according to claim 1
Automatic sequential boosting system of hydraulic circuit. 3. An automatic sequential boosting system of a hydraulic circuit of claim 1 product is constant between the two monotonic decreasing function capacity and the hydraulic pump discharge pressure of the hydraulic circuit. 4. A predetermined absorption torque signal supplied to a solenoid of an absorption torque control valve of the hydraulic pump,
The first horsepower curve whose discharge flow rate is uniquely determined with respect to the discharge pressure of the hydraulic pump is a monotonically decreasing function, and the first absorption torque signal is switched to switch the first horsepower curve for the same discharge pressure of the hydraulic pump. With the discharge flow rate smaller than the discharge flow rate in the horsepower curve by a predetermined amount, the original pressure of the control pressure source is reduced and supplied to the displacement control device so that the uniquely determined second horsepower curve becomes a monotonically decreasing function. The automatic sequential boosting system for a hydraulic circuit according to claim 1 .