JP6860521B2 - Construction machinery - Google Patents

Description

The present invention relates to a construction machine such as a hydraulic excavator equipped with a hydraulic system using a hydraulic closing circuit for directly driving a hydraulic actuator by a hydraulic pump, and particularly for construction equipped with a hydraulic system for driving a hydraulic cylinder with a hydraulic closing circuit. Regarding machinery.

In recent years, energy saving has become an important development item in construction machinery such as hydraulic excavators and wheel loaders. Energy saving of the hydraulic system itself is important for energy saving of construction machinery, and the application of a hydraulic system equipped with a hydraulic closing circuit that directly drives the hydraulic actuator by connecting the hydraulic actuator with a closed circuit by a hydraulic pump is being considered. There is. In this hydraulic system, there is no pressure loss due to the control valve, and there is no flow loss because the pump discharges only the required flow rate. It is also possible to regenerate the potential energy of the actuator and the energy during deceleration. Therefore, energy saving is possible.

As a conventional technique of a construction machine combined with a hydraulically closed circuit, there are those described in Patent Document 1 and Patent Document 2.

Patent Document 1 describes a hydraulic system in which a double tilting pump and a hydraulic cylinder are connected in a closed circuit, and a single tilting pump is connected to a cap chamber of the hydraulic cylinder via a switching valve. In the closed circuit, a charge pump for replenishing the leaked oil in the closed circuit is connected via the charge flow path, and a charge relief valve for regulating the charge pressure is arranged in the charge flow path. Further, the closed circuit is provided with a flushing valve for discharging excess oil to the tank, and the discharge side of the flushing valve is connected to the tank via a charge flow path and a charge relief valve.

In Patent Document 2, a double tilting pump and a hydraulic cylinder are connected in a closed circuit, and a single tilting pump provided separately from the double tilting pump is connected to both the cap chamber and the rod chamber of the hydraulic cylinder via a switching valve. The hydraulic system that can be connected is described. The closed circuit is provided with a flushing valve for discharging excess oil to the tank, and the discharge side of the flushing valve is connected to the tank via a low-pressure relief valve.

JP-A-2015-488999

Japanese Unexamined Patent Publication No. 2005-076781

In the hydraulic system described in Patent Document 1, a single tilting pump can be connected to the cap chamber of the hydraulic cylinder, whereby the hydraulic cylinder is driven only by the double tilting pump when the hydraulic cylinder is extended. The cylinder speed can be increased more than when the cylinder speed is increased.

In the hydraulic system described in Patent Document 2, since the unilateral tilting pump is connected to both the cap chamber and the rod chamber of the hydraulic cylinder via a switching valve, the unilateral tilting pump is used when the hydraulic cylinder is contracted. Can be increased in cylinder speed by connecting the above to the rod chamber of the hydraulic cylinder.

Also in Patent Document 1, as described in Patent Document 2, if the structure is such that it can be connected to both the cap chamber and the rod chamber of the hydraulic cylinder via a switching valve, when the hydraulic cylinder contracts. Can also increase the cylinder speed. However, in this case, an increase in the charge pressure due to an increase in excess oil discharged from the cap chamber generated when the one-side tilting pump is connected to the rod chamber of the hydraulic cylinder becomes a problem.

That is, in Patent Document 1, when the one-side tilting pump is connected to the rod chamber of the hydraulic cylinder, the contraction operation of the hydraulic cylinder can be accelerated as compared with the case where the hydraulic cylinder is driven only by the two-sided tilting pump. On the other hand, a large amount of excess oil discharged from the cap chamber flows into the charge flow path through the flushing valve and passes through the charge relief valve, so that the charge pressure rises due to the pressure loss of the charge relief valve. This increase in charge pressure increases the pressure on the low pressure side of the closed circuit (the pressure on the discharge side from the cap chamber of the hydraulic cylinder). When the back pressure of the hydraulic cylinder rises, the pushing pressure of the hydraulic cylinder rises, the load of the one-sided tilt pump and the charge pump increases, and the fuel consumption of the engine that drives the one-sided tilt pump is adversely affected. Further, since the maximum pressure of the hydraulic cylinder is defined by the main relief pressure, the pressure difference between the cap chamber and the rod chamber of the hydraulic cylinder is reduced, so that the thrust of the hydraulic cylinder is reduced and the operability is also deteriorated.

It is conceivable to change the charge relief valve to one with a large flow rate in order to suppress the rise in charge pressure when a large flow rate flows, but the flow rate passing through the charge relief valve fluctuates greatly depending on the drive speed of the hydraulic cylinder. There is no change in what is done, and even if an attempt is made to suppress a change in charge pressure, fluctuations in charge pressure are unavoidable due to the pressure override characteristics of the charge relief valve.

It is also conceivable to set the charge relief pressure low in order to suppress the influence on fuel efficiency and operability when the charge pressure rises, but the charge pressure becomes low when the flow rate passing through the charge relief valve is small. , Cavitation may occur and damage the equipment, resulting in reduced reliability. Further, since the volume elastic modulus of the hydraulic oil on the low pressure side decreases, the responsiveness deteriorates in the operation at the time of load reversal.

Also in Patent Document 2, since the discharge pressure of the flushing valve is limited by the low-pressure relief valve, there is a problem similar to that of the charge relief valve of Patent Document 1 in the contraction operation of the hydraulic cylinder.

In the hydraulic system of Patent Document 1, the extension operation of the hydraulic cylinder is increased by making it possible to connect an additional one-sided tilting pump in addition to the two-sided tilting pump and the one-sided tilting pump to the cap chamber of the hydraulic cylinder. Can be speeded up. The above-mentioned problem also occurs when the extension operation of the hydraulic cylinder is accelerated in such a hydraulic system.

The present invention has been made in view of the above problems, and an object of the present invention is to charge by changing the flow rate of the charge relief valve when the operation of the hydraulic cylinder is accelerated by a closed circuit pump and an open circuit pump. The purpose of the present invention is to provide a construction machine capable of suppressing pressure fluctuations, preventing deterioration of fuel efficiency, and obtaining good operability.

In order to solve this problem, the present invention has a single-rod type hydraulic cylinder having a cap chamber and a rod chamber, and two discharge ports capable of discharging in both directions, and the two discharge ports are of the hydraulic cylinder. It has a closed circuit pump connected to each of the cap chamber and the rod chamber so as to form a closed circuit, a suction port for sucking hydraulic oil from an oil tank, and a discharge port for discharging hydraulic oil. The pressure of the charge flow path is adjusted with an open circuit pump connected to at least one of the cap chamber and the rod chamber via a switching valve, a charge pump connected to the closed circuit via a supply check valve and a charge flow path. A charge relief valve, a flushing valve connected to the closed circuit and discharging excess oil in the closed circuit to the charge flow path, an operation lever device for instructing the operation of the hydraulic cylinder, and the operation lever device. In a construction machine including the closed circuit pump, the open circuit pump, and a controller that controls the switching valve according to the lever operation amount, the charge relief valve is a variable relief valve that can change the set pressure, and the controller. , the accordance passing flow of charge relief valve is increased, have a charge relief valve control unit that adjusts an opening degree of the charge relief valve as set pressure of the charge relief valve is reduced, the charge flowpath The charge relief valve control unit further includes a pressure sensor for detecting pressure, and the charge relief valve control unit includes a setting information storage unit that stores upper and lower limit values that are thresholds of a permissible range of the target pressure of the charge flow path, and the pressure sensor. The charge relief valve for holding the pressure of the charge flow path at the target pressure based on the detected pressure of the charge flow path and the threshold value of the allowable range of the target pressure stored in the setting information storage unit. It calculates a command current shall have a a relief valve command calculating unit for changing the set pressure of the by command current by adjusting an opening degree of the charge relief valve the charge relief valve.
Further, in the present invention, the charge relief valve control unit is calculated by the charge flow rate calculation unit that calculates the charge flow rate flowing into the charge flow path based on the lever operation amount of the operation lever device, and the charge flow rate calculation unit. At least one map used in the calculation of the command current of the charge relief valve for holding the pressure of the charge flow path at the target pressure with respect to the charged flow rate, and the allowable range of the target pressure of the charge flow path. The charge flow path of the charge flow path is based on the setting information storage unit that stores the upper limit value and the lower limit value, which are the threshold values of the above, and the charge flow rate calculated by the charge flow rate calculation unit and the map stored in the setting information storage unit. The set pressure or command current of the charge relief valve for holding the pressure at the target pressure is calculated, and the pressure of the charge flow path detected by the pressure sensor and the target stored in the setting information storage unit. The set pressure of the charge relief valve or the correction value of the command current for holding the pressure of the charge flow path at the target pressure is calculated based on the threshold value of the allowable pressure range, and the set pressure of the charge relief valve or the set pressure of the charge relief valve is calculated. A relief valve command calculation unit that corrects the command current with the correction value, calculates the command current of the charge relief valve, adjusts the opening degree of the charge relief valve by this command current, and changes the set pressure of the charge relief valve. And shall have.

By changing the set pressure of the charge relief valve in this way, when the operation of the hydraulic cylinder is accelerated by the closed circuit pump and the open circuit pump, the fluctuation of the charge pressure due to the change in the passing flow rate of the charge relief valve is suppressed. However, deterioration of fuel efficiency can be prevented and good operability can be obtained.

According to the present invention, when the operation of the hydraulic cylinder is accelerated by the closed circuit pump and the open circuit pump, the fluctuation of the charge pressure due to the change of the passing flow rate of the charge relief valve is suppressed, and the deterioration of fuel efficiency is prevented and good. Operability can be obtained.

It is a side view which shows the appearance of the hydraulic excavator which is the construction machine to which this invention is applied. It is a figure which shows the hydraulic system of the construction machine which concerns on the basic embodiment of this invention provided in the hydraulic excavator shown in FIG. It is a figure which shows the circuit state when the arm cylinder is driven by the pressure oil of a closed circuit pump, and the arm dump operation is performed. It is a figure which shows the circuit state at the time of performing the arm dump operation by driving the arm cylinder by the pressure oil of a closed circuit pump and the pressure oil of an open circuit pump at an accelerated speed. It is a figure which shows the relationship between the set pressure of the charge relief valve and the charge pressure when the passing flow rate of the charge relief valve increases, and the one-point chain line is the charge pressure when the set pressure of the charge relief valve is constant (conventional). The change is shown, and the solid line is a diagram showing the change in the charge pressure when the set pressure of the charge relief valve is adjusted (the present invention). It is a figure which shows the relationship between the set pressure of the charge relief valve and the charge pressure when the passing flow rate of the charge relief valve decreases, and the one-point chain line is the charge pressure when the set pressure of the charge relief valve is constant (conventional). The change is shown, and the solid line is a diagram showing the change in the charge pressure when the set pressure of the charge relief valve is adjusted (the present invention). It is a functional block diagram which shows the processing content of the controller which concerns on the basic embodiment of this invention. It is a flowchart which shows the process flow of a controller. It is a figure which shows the map of the passing flow rate of a charge relief valve, and the set pressure of a charge relief valve. It is a figure which shows the map of the set pressure of a charge relief valve and the command current of a charge relief valve. It is a figure which shows the map of the passing flow rate of a charge relief valve, and the command current of a charge relief valve. It is a flowchart which shows the process flow of the controller when the map shown in FIG. 9A is used. It is a figure which shows the hydraulic system of the construction machine which concerns on 1st Embodiment of this invention. It is a functional block diagram which shows the processing content of the controller which concerns on 1st Embodiment of this invention. It is a flowchart which shows the process flow of a controller. It is a flowchart which shows the processing flow of the controller in the modification which directly calculates the command current of a charge relief valve. It is a functional block diagram which shows the processing content of the controller of the construction machine which concerns on the 2nd Embodiment of this invention. It is a flowchart which shows the process flow of a controller. It is a figure which shows the hydraulic system of the construction machine which concerns on 3rd Embodiment of this invention. It is a figure which shows the circuit state at the time of performing the arm cloud operation by driving the arm cylinder by the pressure oil of a closed circuit pump and the pressure oil of two open circuit pumps at an accelerated speed.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

< Basic form >
The basic embodiment of the present invention will be described.

FIG. 1 is a side view showing the appearance of a hydraulic excavator, which is a construction machine to which the present invention is applied.

In FIG. 1, the hydraulic excavator includes a front device 101A, an upper swing body 101B, and a lower traveling body 101C. The front device 101A includes a boom 102, an arm 103, and a bucket 104. Further, a boom cylinder 105 for operating the boom 102, an arm cylinder 106 for operating the arm 103, a bucket cylinder 107 for operating the bucket 104, and a swivel motor (not shown) for swiveling the upper swivel body 101B. A traveling motor (not shown) for traveling the lower traveling body 101C is provided.

The upper swing body 101B is provided with a cabin 110 forming a driver's cab, and in the cabin 110, an electric lever type that is operated by an operator to command the operation of the boom 102, the arm 103, the bucket 104, and the upper swing body 101B. Operating lever devices 111 and 112 (see FIG. 2) are provided.

FIG. 2 is a diagram showing a hydraulic system provided in the hydraulic excavator shown in FIG.

The hydraulic system according to this basic embodiment includes a closed circuit pump 7 which is a bi-tilt variable displacement pump having two discharge ports capable of discharging in both directions, a suction port for sucking hydraulic oil from an oil tank 11, and a hydraulic oil discharge. It is provided with an open circuit pump 8 which is a unidirectional tilting variable capacity pump having a discharge port, a charge pump 9 which is a unilateral tilting fixed capacity pump, and a single rod type hydraulic cylinder 10. The closed circuit pump 7, the open circuit pump 8, and the charge pump 9 are driven by a prime mover (for example, a diesel engine) (not shown).

In the closed circuit pump 7, two discharge ports are connected to the cap chamber and the rod chamber of the hydraulic cylinder 10 so as to suck the pressure oil from one of the cap chamber or the rod chamber of the hydraulic cylinder 10 and discharge it to the other, respectively, and the hydraulic cylinder A closed circuit is formed for 10. The open circuit pump 8 sucks pressure oil from the oil tank 11 and discharges the pressure oil sucked through the switching valves 12a and 12b that perform on / off operation to the cap chamber or rod chamber of the hydraulic cylinder. It is connected to the cap chamber and the rod chamber of the 10 via switching valves 12a and 12b, and constitutes an open circuit with respect to the hydraulic cylinder 10.

In the present basic embodiment , the hydraulic cylinder 10 is, for example, an arm cylinder 106 that operates the arm 103, and the operation of the arm 103 is instructed by the operation lever device 112.

The hydraulic system according to this basic embodiment also includes a bleed-off valve 13 provided in a flow path branched from the discharge flow path of the open circuit pump 8, a flushing valve 14 for adjusting excess or deficiency of pressure oil in the closed circuit, and replenishment. It is provided with check valves (replenishment check valves) 15a and 15b as valves, main relief valves 16a and 16b, and a charge relief valve 17.

The bleed-off valve 13 continuously changes the opening area according to the lever operation amount of the operation lever device 111 to increase the speed of the hydraulic cylinder 10. The charge pump 9 is connected to the flushing valve 14, the check valves 15a and 15b, and the main relief valves 16a and 16b via the charge flow path 9a, and the charge relief valve 17 is connected to the charge flow path 9a. The charge pump 9 sucks oil from the oil tank 11 and replenishes the closed circuit with pressure oil via the charge flow path 9a and the check valves 15a and 15b. When excess oil is generated in the closed circuit, the flushing valve 14 discharges the excess oil to the oil tank 11 via the charge flow path 9a and the charge relief valve 17. The main relief valves 16a and 16b set the maximum pressure of the closed circuit, and the charge relief valve 17 sets the pressure of the charge flow path 9a (charge pressure), that is, the maximum discharge pressure of the charge pump 9.

The operation signals (electrical signals) of the operation lever devices 111 and 112 are input to the controller 22. The controller 22 controls the regulator 37 of the closed circuit pump 7, the regulator 38 of the open circuit pump 8, the switching valves 12a and 12b, and the bleed-off valve 13 according to the operation signal (operation amount) of the operation lever device 112.

The regulators 37 and 38 of the closed circuit pump 7 and the open circuit pump 8 operate by the control signals from the controller 22, respectively, the regulator 37 controls the discharge direction and the discharge flow rate of the closed circuit pump 7, and the regulator 38 operates the open circuit. The discharge flow rate of the pump 8 is controlled.

The switching valves 12a and 12b and the bleed-off valve 13 are solenoid valves, the switching valves 12a and 12b operate on / off (open / close operation) by a control signal from the controller 22, and the bleed-off valve 13 opens by a control signal from the controller 22. Change the area.

As shown in FIG. 2, the switching valves 12a and 12b are in the closed position in the standby state, and hold the pressure in the cap chamber and the rod chamber of the hydraulic cylinder 10. Further, the bleed-off valve 13 is in the open position in the standby state, and the standby flow rate of the open circuit pump 8 is released to the oil tank 11 to prevent the pressure from rising.

Further, the charge relief valve 17 is a variable relief valve capable of changing the set pressure, and has a setting adjusting unit 17a for changing the set pressure. The controller 22 outputs a command current to the setting adjustment unit 17a of the charge relief valve 17, and adjusts the opening degree of the charge relief valve 17 so that the set pressure of the charge relief valve 17 decreases as the passing flow rate of the charge relief valve 17 increases. adjust.

Next, the operation of the hydraulic system according to this basic embodiment will be described by taking as an example an arm dump operation in which the arm 103 is driven and rotated forward.

The arm dump operation is performed by operating the operation lever of the operation lever device 112 in the arm dump direction and contracting the arm cylinder 10 (106 in FIG. 1). Further, when the arm dump operation is performed, the closed circuit pump 7 sucks the pressure oil from the flow path on the cap chamber side of the arm cylinder 10 and discharges it to the flow path on the rod chamber side. At this time, the switching valve 12a connecting the open circuit pump 8 and the cap chamber of the arm cylinder 10 is opened, the switching valve 12b connecting the open circuit pump 8 and the rod chamber is closed, and the lever operating amount of the operating lever device 112 is adjusted. The bleed-off valve 13 is opened accordingly. Further, when the flow path on the rod chamber side has a higher pressure than the flow path on the cap chamber side of the arm cylinder 10, the flushing valve 14 switches to the position on the left side in the drawing, and the charge flow path 9a has a low pressure on the arm cylinder 10. It is connected to the flow path on the side. As a result, the circuit state shown in FIG. 3 is obtained. Assuming that the discharge flow rate of the closed circuit pump 7 is Qcp and the pressure receiving area of the rod chamber of the arm cylinder 10 is Ar, the flow rate of the pressure oil flowing into the rod chamber of the arm cylinder 10 is Qcp. Since the rod chamber has a higher pressure than the cap chamber, the cylinder speed v1 is v1 = Qcp / Ar. At this time, the amount of the pressure oil flowing out from the cap chamber of the arm cylinder 10 excluding the amount sucked by the closed circuit pump 8 returns to the oil tank 11 through the bleed-off valve 13, so that the charge relief is performed through the flushing valve 14. The flow rate through the valve 17 is almost zero.

Next, when increasing the lever operation amount of the operation lever device 112 and increasing the cylinder speed, the switching valve 12a connecting the open circuit pump 8 and the cap chamber of the arm cylinder 10 is closed, and the open circuit pump 8 and the arm cylinder are closed. The switching valve 12b connecting to the rod chamber of 10 is opened, the bleed-off valve 13 is closed, and the open circuit pump 8 sucks pressure oil from the oil tank 11 and discharges it to the flow path on the rod chamber side of the arm cylinder 10. As a result, the circuit state shown in FIG. 4 is obtained, and assuming that the discharge flow rate of the open circuit pump 8 is Qop, the flow rate of the pressure oil flowing into the rod chamber of the arm cylinder 10 is Qcp + Qop, and the cylinder speed v2 is v2 =. It becomes (Qcp + Qop) / Ar. At this time, the pressure oil flowing out of the cap chamber of the arm cylinder 10 passes through the charge relief valve 17 via the flushing valve 14 and returns to the oil tank 11 except for the pressure oil sucked into the closed circuit pump 7. Since the flow rate of the pressure oil flowing out of the cap chamber of the arm cylinder 10 is Ac / Ar (Qcp + Qop), the flow rate passing through the charge relief valve 17 via the flushing valve 14 is (Ac-Ar) / Ar × Qcp + Ac. / Ar × Qop. Since the discharge flow rate of the charge pump 9 is very small, it can be ignored here. When considering the discharge flow rate of the charge pump 9, the discharge flow rate may be added to (Ac-Ar) / Ar × Qcp + Ac / Ar × Qop.

In this way, when the open circuit pump 8 is connected to the rod chamber of the arm cylinder 10, the bleed-off valve 13 is closed, and the discharge flow rate of the open circuit pump 8 is increased, the cylinder speed increases from v1 to v2. However, the flow rate passing through the charge relief valve 17 via the flushing valve 14 also increases. At this time, when the set pressure Ps of the charge relief valve 17 is a constant value as shown by the alternate long and short dash line A1 in FIG. 5A, the passing flow rate Qr of the charge relief valve 17 increases due to the pressure override characteristic of the charge relief valve 17. The upstream pressure of the charge relief valve 17, that is, the pressure (charge pressure) Pc of the charge flow path 9a increases as shown by the alternate long and short dash line B1. Here, the set pressure Ps of the charge relief valve 17 is the upstream pressure of the charge relief valve 17 when a certain fixed flow rate is passed through the charge relief valve 17. The charge pressure Pc needs to be maintained at a predetermined target pressure so as not to adversely affect the fuel consumption of the engine (not shown) for driving the closed circuit pump 7 and the open circuit pump 8 and the operability of the arm 103 by the operation lever device 112. However, when the set pressure Ps of the charge relief valve 17 is constant, the charge pressure Pc also rises as the passing flow rate QR of the charge relief valve 17 increases as described above, and the charge pressure increases as the increase in the passing flow rate Qr increases. Pc also rises significantly. Therefore, the fuel consumption is deteriorated. Further, since the maximum pressure of the arm cylinder 10 is defined by the set pressures of the main relief valves 16a and 16b, when the charge pressure Pc rises, the pressure difference between the cap chamber and the rod chamber of the arm cylinder 10 decreases, which causes the arm. The thrust of the cylinder 10 is reduced, and the operability is also deteriorated.

In this basic embodiment , in order to solve such a problem, the charge relief valve 17 is a variable relief valve whose set pressure can be changed, and the opening degree of the charge relief valve 17 is adjusted by the controller 22 to change the set pressure Ps. Therefore, the pressure Pc of the charge flow path 9a is controlled so as not to exceed a predetermined target pressure.

FIG. 6 is a functional block diagram showing the processing contents of the controller 22 according to this basic embodiment. FIG. 7 is a flowchart showing a processing flow of the controller 22.

The controller 22 has the functions of the valve / pump command generation unit 22a and the charge relief valve control unit 22A. The charge relief valve control unit 22A reduces the set pressure Ps of the charge relief valve 17 so that the pressure Pc of the charge flow path 9a does not exceed the target pressure, that is, as the passing flow rate Qr of the charge relief valve 17 increases. It adjusts the opening degree of the charge relief valve 17 and changes the set pressure of the charge relief valve 17, and has the functions of the charge flow rate calculation unit 22b, the setting information storage unit 22c, and the relief valve command calculation unit 22d. There is. Further, in the present basic embodiment , the charge relief valve control unit 22A adjusts the set pressure Ps of the charge relief valve 17 so that the pressure Pc of the charge flow path 9a does not exceed the target pressure by feedforward control.

The setting information storage unit 22c sets the passing flow rate Qr of the charge relief valve 17 and the charge relief valve 17 for holding the pressure of the charge flow path 9a at the target pressure with respect to the fluctuation of the passing flow rate Qr of the charge relief valve 17. A map (table) of the pressure Ps and a map (table) of the set pressure Ps of the charge relief valve 17 and the command current (relief valve command current) i of the charge relief valve 17 are stored. The relief valve command calculation unit 22d adjusts the set pressure Ps of the charge relief valve 17 by feedforward control using those maps.

The details of the function of the controller 22 will be described below with reference to FIG. 7.

In the controller 22, the valve / pump command generation unit 22a inputs the operation signal (electric signal) of the operation lever device 112, and generates the valve command and the pump command according to the lever operation amount (step F1 in FIG. 7). The generated valve command is output to the switching valves 12a and 12b and the bleed-off valve 13, and the pump command is output to the regulators 37 and 38 of the closed circuit pump 7 and the open circuit pump 8. As a result, the switching valves 12a and 12b, the closed circuit pump 7, and the open circuit pump 8 are controlled so that the operation corresponding to the lever operation amount can be obtained.

The charge flow rate calculation unit 22b flows into the charge flow path 9a via the flushing valve 14 based on the processing result of the valve / pump command generation unit 22a, and the flow rate of the pressure oil passing through the charge relief valve 17 (charge flow rate). Calculate Qr (step F2 in FIG. 7). As described above, the passing flow rate QR of the charge relief valve 17 is a value represented by (Ac-Ar) / Ar × Qcp + Ac / Ar × Qop, and is closed from the pump command calculated by the valve / pump command generator 22a. By obtaining the discharge flow rate Qcp of the pump 7 and the discharge flow rate Qop of the open circuit pump 8, the passing flow rate Qr of the charge relief valve 17 can be calculated.

The relief valve command calculation unit 22d first reads a map of the passing flow rate Qr of the charge relief valve 17 and the set pressure Ps of the charge relief valve 17 stored in the setting information storage unit 22c, and calculates the charge flow rate based on the map. The set pressure Ps of the charge relief valve 17 corresponding to the passing flow rate of the charge relief valve 17 calculated in the part 22b is calculated (step F3 in FIG. 7).

FIG. 8A is a diagram showing a map of the passing flow rate (relief valve passing flow rate) Qr of the charge relief valve 17 and the set pressure (relief valve set pressure) Ps of the charge relief valve 17 stored in the setting information storage unit 22c. In this map, the relationship between the passing flow rate Qr of the charge relief valve 17 and the set pressure Ps is that the set pressure Ps decreases as the passing flow rate Qr of the charge relief valve 17 increases (the opening degree of the charge relief valve 17 increases). ) Is set.

Next, the relief valve command calculation unit 22d reads a map of the set pressure Ps of the charge relief valve 17 and the command current (relief valve command current) i of the charge relief valve 17 stored in the setting information storage unit 22c, and the map is read. The relief valve command current i corresponding to the set pressure Ps of the charge relief valve 17 calculated in step F3 is calculated based on the above, and this relief valve command current i is output to the setting adjustment unit 17a of the charge relief valve 17 (FIG. Step 7 F4).

FIG. 8B is a diagram showing a map of the set pressure Ps of the charge relief valve 17 and the command current (relief valve command current) i of the charge relief valve 17 stored in the setting information storage unit 22c. In this map, the relationship between the set pressure Ps of the charge relief valve 17 and the relief valve command current i is set so that the relief valve command current i increases as the set pressure increases.

By controlling the charge relief valve 17 using the maps shown in FIGS. 8A and 8B in this way, the charge relief valve 17 increases as the passing flow rate Qr of the charge relief valve 17 increases as shown by the solid line A2 in FIG. 5A. The set pressure Ps of is lowered (the opening degree of the charge relief valve 17 is increased), and as shown by the solid line B2 in FIG. 5A, the pressure (charge pressure) Pc of the charge flow path 9a is controlled so as to be substantially constant, and the charge is charged. The increase in pressure Pc can be suppressed.

Further, when the operation of the operation lever device 112 is stopped from the state where the speed of the arm cylinder 10 is increased, the discharge flow rates of the closed circuit pump 7 and the open circuit pump 8 gradually decrease to zero. At this time, as shown by the alternate long and short dash line C1 in FIG. 5B, if the set pressure Ps of the relief valve remains lowered in order to suppress the increase in the charge pressure Pc, as shown by the alternate long and short dash line D1 in FIG. 5B. The charge pressure Pc decreases as the passing flow rate Qr of the charge relief valve 17 decreases.

In this basic embodiment , since the charge relief valve 17 is controlled by using the maps shown in FIGS. 8A and 8B, the charge relief valve is charged as the passing flow rate Qr of the charge relief valve 17 decreases as shown by the solid line C2 in FIG. 5B. The set pressure Ps of 17 is increased (the opening degree of the charge relief valve 17 is decreased), and the pressure (charge pressure) Pc of the charge flow path 9a is controlled to be substantially constant as shown by the solid line D2 in FIG. 5B. It is possible to suppress a decrease in the charge pressure Pc.

As described above , according to the present basic embodiment , not only the pressure oil discharged by the closed circuit pump 7 but also the pressure oil discharged by the open circuit pump 8 can be supplied to the rod chamber of the arm cylinder 10 during the arm dump operation. It is possible to accelerate not only the extension operation of the arm cylinder 10 (hydraulic cylinder) but also the contraction operation. Further, at that time, it is possible to suppress an increase in the charge pressure due to an increase in the passing flow rate QR of the charge relief valve 17, thereby preventing deterioration of fuel consumption and obtaining good operability without reducing the thrust of the arm cylinder 10. be able to. Further, in the case of an operation in which the passing flow rate QR of the charge relief valve 17 decreases, the opening degree of the charge relief valve 17 is controlled to decrease and the set pressure is increased, so that the decrease in the charge pressure is suppressed and the charge is charged. It is possible to suppress a decrease in reliability and a deterioration in responsiveness due to a decrease in pressure.

In the above embodiment, the command current i of the charge relief valve 17 is calculated using two maps, but the two maps are combined into one, and the command current i of the charge relief valve 17 is calculated using the map. It may be calculated. FIG. 9A is a diagram showing the map. In this map, the relationship between the charge flow rate QR and the relief valve command current i is that the relief valve command current i decreases as the charge flow rate Qr increases (the charge relief valve 17). The opening is increased). FIG. 9B is a flowchart showing the processing flow of the controller 22 in that case. In the controller 22, the relief valve command calculation unit 22d uses the map shown in FIG. 9A to command the charge relief valve 17 corresponding to the flow rate Qr from the passing flow rate Qr of the charge relief valve 17 calculated by the charge flow rate calculation unit 22b. The current i is directly calculated, and this command current i is output to the setting adjustment unit 17a of the charge relief valve 17 (step F34 in FIG. 9B). Even in such a configuration, the same actions and effects as those in the above-described embodiment can be obtained.

< First Embodiment >
The first embodiment of the present invention will be described.

FIG. 10 is a diagram showing a hydraulic system according to the first embodiment of the present invention. The difference from the hydraulic system according to the basic form shown in FIG. 2 is that a pressure sensor 21 for detecting the pressure of the charge flow path 9a is provided in the charge flow path 9a, and the detection signal of the pressure sensor 21 and the operating lever devices 111, 112 The operation signal (electric signal) of the above is input to the controller 122, and the controller 122 adjusts the set pressure of the charge relief valve 17 by using the detection signal (pressure sensor information) of the pressure sensor 21.

FIG. 11 is a functional block diagram showing the processing contents of the controller 122 according to the present embodiment. FIG. 12 is a flowchart showing a processing flow of the controller 122.

The controller 122 has the functions of the valve / pump command generation unit 22a and the charge relief valve control unit 122A. The charge relief valve control unit 122A has the functions of the setting information storage unit 122c and the relief valve command calculation unit 122d. Further, in the present embodiment, the charge relief valve control unit 122A receives the charge relief valve so that the pressure of the charge flow path 9a does not exceed the target pressure by feedback control, that is, as the passing flow rate Qr of the charge relief valve 17 increases. The opening degree of the charge relief valve 17 is adjusted so that the set pressure Ps of the charge relief valve 17 is reduced, and the set pressure of the charge relief valve 17 is changed.

In the setting information storage unit 122c, the upper limit value E1 and the lower limit value E2, which are the threshold values of the allowable range of the target pressure with the target pressure of the charge flow path 9a as the median value, and the charge relief valve 17 shown in FIG. A map (table) of the set pressure Ps and the command current (relief valve command current) i of the charge relief valve 17 is stored. The relief valve command calculation unit 122d uses the upper limit value E1 and the lower limit value E2 of the target pressure to adjust the opening degree of the charge relief valve 17 by feedback control and change the set pressure.

The details of the function of the controller 122 will be described below with reference to FIG.

In the controller 122, the function of the valve / pump command generation unit 22a is the same as that of the basic form, and the operation signal (electric signal) of the operation lever device 112 is input, and as described in the basic form , according to the lever operation amount. A valve command and a pump command are generated, and the switching valves 12a and 12b, the closed circuit pump 7, and the open circuit pump 8 are controlled so that the operation corresponding to the lever operation amount can be obtained by the valve command and the pump command.

The relief valve command calculation unit 122d inputs the detection signal (electrical signal) of the pressure sensor 21, reads the upper limit value E1 and the lower limit value E2 of the target pressure of the charge flow path 9a stored in the setting information storage unit 122c, and reads the pressure sensor 21. It is determined whether or not the pressure (charge pressure) Pc of the charge flow path 9a detected by the above is within the range of the upper limit value E1 and the lower limit value E2 of the target pressure (step F10 in FIG. 12).

If the charge pressure Pc is not within the range of the upper limit value E1 and the lower limit value E2 of the target pressure, the relief valve command calculation unit 122d keeps the charge pressure Pc within the range of the upper limit value E1 and the lower limit value E2 of the target pressure. Calculate the set pressure Ps of the charge relief valve 17 for this purpose (step F11 in FIG. 12). This operation can be performed, for example, as follows. The deviation ΔP (= charge pressure Pc (current value) -upper limit value E1 or lower limit value E2) between the current value of the charge pressure Pc and the upper limit value E1 or the lower limit value E2 is calculated, and this pressure deviation ΔP is used for the charge relief valve 17. The increment of the set pressure Ps is converted to ΔPs, and this increment is added to the set pressure Ps one control cycle before to calculate a new set pressure Ps. Next, the relief valve command calculation unit 122d maps the set pressure Ps of the charge relief valve 17 and the command current (relief valve command current) i of the charge relief valve 17 stored in the setting information storage unit 122c as shown in FIG. 8B. Is read, the relief valve command current i corresponding to the set pressure Ps of the charge relief valve 17 calculated in step F11 is calculated based on the map, and this relief valve command current i is used as the setting adjustment unit 17a of the charge relief valve 17. (Step F12 in FIG. 12).

With this configuration, the passing flow rate Qr of the charge relief valve 17 increases when the speed of the arm cylinder 10 that supplies the discharge oil of both the closed circuit pump 7 and the open circuit pump 8 to the rod chamber of the arm cylinder 10 is increased. When the charge pressure Pc tries to exceed the upper limit value E1 of the target pressure, the set pressure Ps of the charge relief valve 17 is corrected to a small value as shown by the solid line A2 in FIG. 5A, and the solid line B2 in FIG. 5A is used. As shown, the charge pressure Pc can be suppressed so as not to exceed the upper limit value E1 of the target pressure.

Further, when the operation of the operation lever device 112 is stopped from the state where the cylinder speed is increased, the discharge flow rates of the closed circuit pump 7 and the open circuit pump 8 gradually decrease to zero. At this time, as shown by the alternate long and short dash line C1 in FIG. 5B, if the set pressure Ps of the relief valve remains lowered in order to suppress the increase in the charge pressure Pc, as shown by the alternate long and short dash line D1 in FIG. 5B. The charge pressure Pc decreases as the passing flow rate Qr of the charge relief valve 17 decreases. Therefore, the relief valve command calculation unit 122d performs the process in the same manner as when suppressing the increase in the charge pressure Pc.

That is, it is determined from the information of the pressure sensor 21 whether the charge pressure Pc is lower than the lower limit value E2 of the target pressure, and if it is lower, the set pressure Ps of the charge relief valve 17 is large as shown by the solid line C2 in FIG. 5B. It is corrected to a value, and as shown by the solid line D2 in FIG. 5B, the charge pressure Pc can be suppressed so as not to fall below the lower limit value E2 of the target pressure.

Here, the upper and lower limit values E1 and E2 of the target pressure are determined based on the following ideas.

When the charge pressure, that is, the pressure on the low pressure side of the closed circuit rises, the load on the open circuit pump 8 and the charge pump 9 increases, which adversely affects fuel efficiency. Further, since the maximum pressure of the hydraulic cylinder 10 is defined by the relief pressure of the main relief valve 16a or 16b, the pressure difference between the cap chamber and the rod chamber of the hydraulic cylinder 10 is reduced, so that the thrust of the hydraulic cylinder 10 is reduced and the operation is performed. The sex also gets worse. The upper limit value E1 of the target pressure is set within a range that does not affect the above fuel efficiency and operability. In addition, when the charge pressure Pc becomes low, cavitation occurs and damages the equipment, resulting in a decrease in reliability. Further, since the volume elastic modulus of the hydraulic oil on the low pressure side of the closed circuit decreases, the responsiveness deteriorates in the operation at the time of load reversal. The lower limit value E2 of the target pressure is predetermined and stored in the memory within the range that minimizes the influence on the reliability and operability described above. For example, the upper limit value E1 is 3 MPa and the lower limit value E2 is 1 MPa.

The same effect as that of the basic embodiment can be obtained in the present embodiment configured as described above. Further, in the present embodiment, since the pressure of the charge flow path 9a is controlled so as not to exceed the target pressure by feedback control, the charge pressure can be controlled more accurately.

In the above embodiment, the command current i of the charge relief valve 17 is calculated using the two steps F11 and F12, but the two steps F11 and F12 are combined into one and the command current i of the charge relief valve 17 is combined. May be calculated. FIG. 13 is a flowchart showing a processing flow of the controller 122 in that case. In the controller 122, the relief valve command calculation unit 122d calculates the deviation ΔP (= charge pressure Pc (current value) -upper limit value E1 or lower limit value E2) between the current value of the charge pressure Pc and the upper limit value E1 or the lower limit value E2. Then, this pressure deviation ΔP is directly converted into the increment Δi of the command current i of the charge relief valve 17, and this increment Δi is added to the command current i one control cycle before to calculate a new command current i, and this command is obtained. The current i is output to the setting adjustment unit 17a of the charge relief valve 17 (step F112 in FIG. 13). Even with this configuration, the same actions and effects as those of the above-described embodiment can be obtained.

< Second embodiment >
A second embodiment of the present invention will be described.

The configuration of the hydraulic system according to the second embodiment of the present invention is the same as the hydraulic system according to the first embodiment shown in FIG. 10, except that the controller 22 is replaced with the controller 222 in FIG. Is.

FIG. 14 is a functional block diagram showing the processing contents of the controller 222 according to the present embodiment. FIG. 15 is a flowchart showing a processing flow of the controller 222.

The controller 222 has the functions of the valve / pump command generation unit 22a and the charge relief valve control unit 222A. The charge relief valve control unit 222A has the functions of the charge flow rate calculation unit 22b, the setting information storage unit 222c, and the relief valve command calculation unit 222d. Further, in the present embodiment, the charge relief valve control unit 222A prevents the pressure of the charge flow path 9a from exceeding the target pressure by the combination of feedforward control and feedback control, that is, the passing flow rate Qr of the charge relief valve 17 increases. As a result, the opening degree of the charge relief valve 17 is adjusted and the set pressure of the charge relief valve 17 is changed so that the set pressure Ps of the charge relief valve 17 decreases. The function of the valve / pump command generation unit 22a is the same as that of the basic form.

The details of the function of the charge relief valve control unit 222A of the controller 222 will be described below with reference to FIG.

In the charge relief valve control unit 222A, the charge flow rate calculation unit 22b performs the processing of step F2 in FIG. 15, and the relief valve command calculation unit 222d performs the processing of steps F3, F10, F20, F21, and F22 in FIG. The processing of steps F2 and F3 is the same as the processing of steps F2 and F3 in the basic form shown in FIG. 7, and the processing of step F10 is the same as the processing of step F10 shown in FIG. The setting information storage unit 222c stores the setting information stored in the setting information storage unit 22c (FIG. 6) of the basic embodiment and the setting information stored in the setting information storage unit 122c (FIG. 11) of the first embodiment. ing.

The relief valve command calculation unit 222d repeats the process of step F10 when the charge pressure Pc is within the range of the upper limit value E1 and the lower limit value E2 of the target pressure. If the charge pressure Pc is not within the range of the upper limit value E1 and the lower limit value E2 of the target pressure, the relief valve command calculation unit 222d determines that the deviation ΔP between the current value of the charge pressure Pc and the upper limit value E1 or the lower limit value E2 ( = Charge pressure Pc (current value) -upper limit value E1 or lower limit value E2) is calculated, and this pressure deviation ΔP is converted into an increment ΔPs of the set pressure Ps of the charge relief valve 17 (step F21 in FIG. 15).

Further, the relief valve command calculation unit 222d uses the increment ΔPs of the set pressure Ps of the feedback control charge relief valve 17 obtained in step F21 as a correction value, and sets the feedforward control charge relief valve 17 obtained in step F3. The pressure Ps is corrected and the set pressure Ps for control is calculated. This correction can be performed, for example, by adding the increment ΔPs to the set pressure Ps.

In addition, instead of obtaining the increment ΔPs of the set pressure Ps of the feedback control in step F21, the charge pressure Pc is set to the upper limit value E1 and the lower limit value E2 of the target pressure as in step F11 shown in FIG. 12 in the first embodiment. The set pressure Ps of the charge relief valve 17 to be kept within the range is calculated, and this set pressure Ps and the set pressure Ps of the feedforward control charge relief valve 17 obtained in step F3 are combined to form the set pressure Ps for control. May be calculated. This synthesis can be performed, for example, by obtaining the average value of the set pressure Ps of the feedforward control and the set pressure Ps of the feedback control (((set pressure Ps of feedforward control + set pressure Ps of feedback control) / 2)). ..

Next, the relief valve command calculation unit 222d uses the map shown in FIG. 8B read from the setting information storage unit 222c, and the relief valve command corresponding to the set pressure Ps for control of the charge relief valve 17 calculated in step F20. The current i is calculated, and the relief valve command current i is output to the setting adjustment unit 17a of the charge relief valve 17 (step F22 in FIG. 15).

According to the present embodiment configured in this way, the effects of both good responsiveness of feedforward control and improvement of control accuracy of feedback control can be obtained.

Also in the present embodiment, the set pressure Ps of the charge relief valve 17 or the increment ΔPs of the set pressure Ps is set as in the modified examples shown in FIGS. 9A, 9B and 17 of the basic embodiment and the first embodiment. Instead of obtaining the charge relief valve 17, the command current i of the charge relief valve 17 or the increment Δi of the command current i may be directly calculated to calculate the command current i of the charge relief valve 17. Even with this configuration, the same actions and effects as those of the above-described embodiment can be obtained.

< Third embodiment >
A third embodiment of the present invention will be described.

FIG. 16 is a diagram showing a hydraulic system according to a third embodiment of the present invention. In the figure, the same elements as those related to the basic embodiment to the second embodiment shown in FIGS. 2 and 10 are designated by the same reference numerals.

The hydraulic system according to the present embodiment has two closed circuit pumps 7 and 47 equipped with regulators 37 and 57, respectively, and two open circuit pumps 8 and 48 equipped with regulators 38 and 58, respectively. These pumps 7, 47, 8 and 48 are connected to two hydraulic cylinders 10 and 50 via switching valves 12a to 12l, respectively.

In the present embodiment, the hydraulic cylinder 10 is, for example, an arm cylinder 106 that operates an arm 103 (see FIG. 1), and the hydraulic cylinder 50 is, for example, a boom cylinder that operates a boom 102 (see FIG. 1). The operation of the arm 103 is instructed by the operating lever device 112 (see FIG. 2), and the operation of the boom 102 is instructed by the operating lever device 111 (see FIG. 2). In FIG. 16, the control system including the operation lever devices 111 and 112 and the controller is not shown.

The hydraulic system according to the present embodiment also adjusts the excess and deficiency of the pressure oil in the closed circuit with the bleed-off valves 13 and 53 provided in the flow path branched from the discharge flow path of the open circuit pumps 8 and 48. Flushing valves 14, 54, check valves 15a, 15b, 15c, 15d as replenishment valves, main relief valves 16a, 16b, 16c, 16d, one charge pump 9 and one charge relief valve 17 (variable relief valve). ) Is provided. The charge pump 9 is connected to any of the two hydraulic cylinders 10 and 50 via the check valves 15a to 15d, and the pressure (charge pressure) of the charge flow path 9a is maintained by one charge relief valve 17. ..

In such a configuration, the operation lever of the operation lever device 112 is operated in the direction of the arm cloud, and pressure oil is supplied to the cap chamber of one of the two hydraulic cylinders 10 and 50, which is the hydraulic cylinder 10, to operate the hydraulic cylinder 10. It is assumed that the arm cloud operation to extend is performed. At this time, the switching valve 12i connecting the closed circuit pump 7 and the hydraulic cylinder 10 and the switching valve 12a connecting the open circuit pump 8 and the cap chamber of the hydraulic cylinder 10 are opened, and the other switching valves are closed. Assuming that the discharge flow rate of the closed circuit pump 7 is Qcp1, the flow rate balance in the closed circuit can be maintained by setting the discharge flow rate of the open circuit pump 8 to the flow rate Qop1 that compensates for the difference in the pressure receiving area between the rod chamber and the cap chamber of the hydraulic cylinder 10. , The flow rate passing through the charge relief valve 17 via the flushing valve 14 becomes zero.

Here, assuming that the pressure receiving area of the rod chamber of the hydraulic cylinder 10 is Ar1 and the pressure receiving area of the cap chamber is Ac1, the cylinder speed v1 is v1 = (Qcpl + Qop1) / Ac1 when the cap chamber is high pressure.

Next, when the operating amount of the operating lever is increased and the cylinder speed is increased, as shown in FIG. 17, there is an operation pattern in which the switching valve 12h connecting the open circuit pump 48 and the cap chamber of the hydraulic cylinder 10 is also opened. .. At this time, assuming that the discharge flow rate of the closed circuit pump 7 is Qcpl, the discharge flow rate of the open circuit pump 8 is Qop1, and the discharge flow rate of the open circuit pump 48 is Qop2, the inflow flow rate of the cap chamber of the hydraulic cylinder 10 is Qcp1 + Qop1 + Qop2. , The outflow flow rate from the rod chamber of the hydraulic cylinder 10 becomes Ar1 / Ac1 × (Qcp1 + Qop1 + Qop2), and the surplus flow rate (Ar1 / Ac1-1) × Qcp1 + Ar1 / Ac1 × Qop1 + Ar1 / Ac1 × Qop2 is flushed. It is discharged from the charge relief valve 17 via the valve 14. At this time, the cylinder speed v2 is v2 = (Qcp1 + Qop1 + Qop2) / Ac1.

In this way, when one closed circuit pump 7 and two open circuit pumps 8 and 48 are connected to the cap chamber of the hydraulic cylinder 10 and the discharge flow rate is increased, the cylinder speed increases from v1 to v2. However, the flow rate passing through the charge relief valve 17 via the flushing valve 14 also increases. At this time, as in the basic form , as shown in FIG. 5A, when the set pressure of the charge relief valve 17 is constant 18, the charge pressure 20 rises as the passing flow rate increases due to the pressure override characteristic of the charge relief valve 17. I will do it.

Therefore, also in the present embodiment, the increase in the charge pressure can be suppressed by performing the processing by the relief valve command calculation units 22d, 122d, 222d as in the basic embodiment to the second embodiment.

Further, even when the operation of the operation lever is stopped, the decrease in the charge pressure is suppressed by performing the processing by the relief valve command calculation units 22d, 122d, 222d as in the basic embodiment to the second embodiment. Can be done.

In addition to the operation examples shown in the basic embodiment to the third embodiment , the adverse effects on fuel efficiency, operability, and reliability due to the fluctuation of the charge pressure due to the change in the flow rate passing through the charge relief valve 17 , By applying the present invention in the same manner, the effect of improving them can be obtained.

101A ... Front device 101B ... Upper swivel body 101C ... Lower traveling body 102 ... Boom 103 ... Arm 104 ... Bucket 105 ... Boom cylinder 106 ... Arm cylinder 107 ... Bucket cylinder 111, 112 ... Operating lever devices 7, 47 ... Closed circuit pump 8 , 48 ... Open circuit pump 9 ... Charge pump 9a ... Charge flow path 10, 50 ... Hydraulic cylinder 11 ... Oil tank 12a, 12b, 12c-12l ... Switching valve 13, 53 ... Bleed-off valve 14, 54 ... Flushing valve 15a, 15b, 15c, 15d, ... Check valve (replenishment check valve)
16a, 16b, 16c, 16d ... Main relief valve 17 ... Charge relief valve 17a ... Setting adjustment unit 21 ... Pressure sensor 22, 122, 222 ... Controller 22a ... Valve / pump command generation unit 22A, 122A, 222A ... Charge relief valve control Unit 22b ... Charge flow rate calculation unit 22c, 122c, 222c ... Setting information storage unit 22d, 122d, 222d ... Relief valve command calculation unit

Claims (2)

A single-rod type hydraulic cylinder with a cap chamber and a rod chamber,
A closed circuit pump having two discharge ports capable of discharging in both directions and connecting the two discharge ports to the cap chamber and the rod chamber of the hydraulic cylinder so as to form a closed circuit, respectively.
An open circuit pump having a suction port for sucking hydraulic oil from an oil tank and a discharge port for discharging hydraulic oil, and the discharge port connected to at least one of a cap chamber and a rod chamber of the hydraulic cylinder via a switching valve. ,
A charge pump connected to the closed circuit via a replenishment check valve and a charge flow path,
A charge relief valve that adjusts the pressure in the charge flow path and
A flushing valve connected to the closed circuit and discharging excess oil in the closed circuit to the charge flow path,
An operation lever device that commands the operation of the hydraulic cylinder, and
In a construction machine including the closed circuit pump, the open circuit pump, and a controller for controlling the switching valve according to the lever operating amount of the operating lever device.
The charge relief valve is a variable relief valve whose set pressure can be changed.
The controller has a charge relief valve control unit that adjusts the opening degree of the charge relief valve so that the set pressure of the charge relief valve decreases as the passing flow rate of the charge relief valve increases.
A pressure sensor for detecting the pressure in the charge flow path is further provided.
The charge relief valve control unit
A setting information storage unit that stores an upper limit value and a lower limit value, which are threshold values of an allowable range of the target pressure of the charge flow path, and
To hold the pressure of the charge flow path at the target pressure based on the pressure of the charge flow path detected by the pressure sensor and the threshold value of the allowable range of the target pressure stored in the setting information storage unit. A construction machine having a relief valve command calculation unit that calculates a command current of the charge relief valve, adjusts the opening degree of the charge relief valve by the command current, and changes the set pressure of the charge relief valve. .. A single-rod type hydraulic cylinder with a cap chamber and a rod chamber,
A closed circuit pump having two discharge ports capable of discharging in both directions and connecting the two discharge ports to the cap chamber and the rod chamber of the hydraulic cylinder so as to form a closed circuit, respectively.
An open circuit pump having a suction port for sucking hydraulic oil from an oil tank and a discharge port for discharging hydraulic oil, and the discharge port connected to at least one of a cap chamber and a rod chamber of the hydraulic cylinder via a switching valve. ,
A charge pump connected to the closed circuit via a replenishment check valve and a charge flow path,
A charge relief valve that adjusts the pressure in the charge flow path and
A flushing valve connected to the closed circuit and discharging excess oil in the closed circuit to the charge flow path,
An operation lever device that commands the operation of the hydraulic cylinder, and
In a construction machine including the closed circuit pump, the open circuit pump, and a controller for controlling the switching valve according to the lever operating amount of the operating lever device.
The charge relief valve is a variable relief valve whose set pressure can be changed.
The controller has a charge relief valve control unit that adjusts the opening degree of the charge relief valve so that the set pressure of the charge relief valve decreases as the passing flow rate of the charge relief valve increases.
A pressure sensor for detecting the pressure in the charge flow path is further provided.
The charge relief valve control unit
A charge flow rate calculation unit that calculates the charge flow rate flowing into the charge flow path based on the lever operation amount of the operation lever device, and a charge flow rate calculation unit.
At least one map used for calculating the command current of the charge relief valve for holding the pressure of the charge flow path at the target pressure with respect to the charge flow rate calculated by the charge flow rate calculation unit , and the charge flow. A setting information storage unit that stores the upper and lower limits, which are the thresholds of the allowable range of the target pressure of the road, and
Based on the charge flow rate calculated by the charge flow rate calculation unit and the map stored in the setting information storage unit, the set pressure of the charge relief valve for holding the pressure of the charge flow path at the target pressure or While calculating the command current, the pressure of the charge flow path is calculated based on the pressure of the charge flow path detected by the pressure sensor and the threshold value of the allowable range of the target pressure stored in the setting information storage unit. The correction value of the set pressure or command current of the charge relief valve for holding at the target pressure is calculated, and the set pressure or command current of the charge relief valve is corrected by the correction value to obtain the command current of the charge relief valve. A construction machine having a relief valve command calculation unit that calculates and adjusts the opening degree of the charge relief valve by the command current to change the set pressure of the charge relief valve.

Images