Hydraulic control circuit for a construction machine

To make it possible to control supply, discharge, and recycled flow rates independently of each other for the boom cylinder in a construction machine comprising first and second boom spool valves respectively connected to first and second hydraulic pumps. When the boom cylinder is contracted, the first boom spool valve is configured to control the recycled flow rate from head side oil chamber to rod side oil chamber, the second boom spool valve is configured to control the discharge flow rate from head side oil chamber to oil tank, and both first and second boom spool valves are configured not to supply pressure oil from first and second hydraulic pumps to the boom cylinder.

This patent application is a 35 USC § 371 U.S. national stafe of International Application No. PCT/EP2019/025455 filed on Dec. 12, 2019, which claims the benefit and priority of Japanese Application No. 2018-233211 filed on Dec. 13, 2018, the disclosures of which are incorporated in their entirety by reference herein.

FIELD OF THE INVENTION

The present invention relates to a technical field of hydraulic control circuit used in construction machines such as a hydraulic excavator.

BACKGROUND ART

In general, some construction machines, such as a hydraulic excavator for example, have a boom vertically movably supported by a body and are configured to move the boom vertically with expansion and contraction operations of a boom cylinder. As for hydraulic control circuit for these construction machines, first and second hydraulic, pumps are installed as hydraulic pressure supply sources for multiple hydraulic actuators to be installed in these construction machines, and as for hydraulic actuator, such as the boom cylinder mentioned above for example, which needs a large flow rate corresponding to each work content, in order to enable pressure oil supply from both first and second hydraulic pumps, a circuit equipped with first and second spool valves connected to each of first and second hydraulic pumps has been ever widely used for controlling oil supply and discharge for hydraulic actuators (refer to FIG. 3 in PTL 1, for example).

Now, the spool valve mentioned above to be installed in conventional hydraulic control circuit for construction machine is configured to conduct a direction change-over control for changing over hydraulic oil supply/discharge direction for hydraulic actuator, a supply flow control for controlling supply flow rate from hydraulic pump to hydraulic actuator, and a discharge flow control for controlling discharge flow rate from hydraulic actuator to hydraulic pump simultaneously, so an opening areas for oil supply and oil discharge are uniquely determined according to a moved position of the spool valve. Furthermore, when recycling drain oil from one oil chamber in hydraulic actuator to another in order to reduce fuel consumption and when the spool valve mentioned above is to be used to control recycled flow rate as well, an opening area for oil recycle will be uniquely determined according to the moved position of the spool valve. Therefore, a relationship among a supply flow rate, discharge flow rate, and further recycled flow rate cannot be changed according to the content of various works, such as a stand-alone work to drive a boom cylinder alone, compound work to drive other hydraulic actuator as well, light load work, and heavy load work, for example, impeding an improvement of efficiency and operability. However, moving the boom vertically is a highly frequent manipulation in construction machine including hydraulic excavator and is often operated in combination with other hydraulic actuator, so it is required to improve efficiency and operability of the manipulation.

Therefore, it is disclosed in the PTL 1 that a control valve is installed for controlling pressure oil amount to be supplied to the first and second spool valves at upstream side of first and second spool valves controlling oil supply and discharge for hydraulic actuator. In this case, the control valve enables to change pressure oil supply amount to be supplied from first and second spool valves to hydraulic actuator according to the work content and others by changing pressure oil amount to be supplied to first and second spool valves even if the moved position of spool valve is a same.

Meanwhile, some technique controls supply and discharge flow rates for the hydraulic actuator with each valve individually by providing a flow control valve for controlling the supply flow rate from the hydraulic pump to the hydraulic actuator and a direction change-over valve arranged at a downstream side of the flow control valve for changing over a supply/discharge direction of hydraulic oil to the hydraulic actuator and controlling the discharge flow rate from the hydraulic actuator (refer to PTL 2, for example).

CITATION LIST

Patent Document

SUMMARY OF INVENTION

Problem to Be Solved by the Invention

However, in the PTL 1, a supply valve passage (second internal passage), which is installed in the spool valve in order to supply pressure oil to the hydraulic actuator, is configured to change the flow rate according to the spool position and a control unit for controlling a control valve is configured to satisfy opening areas of control valve and spool valve are the same extent as the opening of conventional spool. That is, since the control valve and spool valve installed in series with each other are configured to control the supply flow rate respectively separately when supplying delivery oil from hydraulic pump to hydraulic actuator, the control is complicated and it is hard to control the flow rate accurately.

Meanwhile, in PTL 2, since the flow control valve only controls the supply flow rate to the hydraulic actuator and a direction control valve does not control the supply flow rate, so this configuration will not cause a same problem as that of PTL 1. However a configuration of the PIT 2, first and second hydraulic pumps are installed as a hydraulic supply source for the boom cylinder, only one spool valve (direction change-over valve) is installed for the boom cylinder, and the delivery oil from first and second hydraulic pumps is merged after controlling the flow rate with a flow control valve and then supplied to the spool valve. Therefore, there are problems that the conventional circuit mentioned above, i.e., a circuit equipped with first and second spool valves connected to each of first and second hydraulic pumps for controlling oil supply/discharge of the boom cylinder, cannot be used as is, a new spool valve may be required in accordance with total flow rate from first and second hydraulic pumps, and a valve unit with a new circuit configuration needs to be manufactured, thereby causing higher cost.

In addition, as for a recycled flow control mentioned above, it has been requested to control the flow rate independently of supply/discharge flow controls by using the spool valve without using dedicated recycle valve separately; these are challenges to be solved by this invention.

Means for Solving the Problem

The present invention is created to solve these challenges; the invention of claim1is a hydraulic control circuit for a construction machine, comprising: a boom being vertically movably supported by a body and moving vertically in dependence upon extension and contraction operations of a boom cylinder; first and second hydraulic pumps as hydraulic supply source; and first and second boom spool valves being connected respectively to the first and second hydraulic pumps and controlling oil supply and discharge for the boom cylinder; wherein, when the boom cylinder is contracted, the first boom spool valve is configured to control recycled flow rate from a head side oil chamber of boom cylinder to a rod side oil chamber, the second boom spool valve is configured to control discharge flow rate from the head side oil chamber of the boom cylinder to an oil tank; and when the boom cylinder is contracted, both first and second boom spool valves are configured not to supply pressure oil from first and second hydraulic pumps to the boom cylinder.

The invention of claim2is the hydraulic control circuit for a construction machine of claim1, wherein, when the boom cylinder is extended, first boom spool valve is configured to control a supply flow rate from first hydraulic pump to a head oil chamber of boom cylinder and a discharge flow rate from a rod side oil chamber to an oil tank, and second boom spool valve is configured to control the supply flow rate from second hydraulic pump to the head side oil chamber of boom cylinder.

The invention of claim3is the hydraulic control circuit for a construction machine of claim1or2, providing a means to determine whether it is a body lift-up operation for lifting up a part of the body based on a pressure in the head side oil chamber when the boom cylinder is contracted, wherein the first boom spool valve is configured to control the supply flow rate from first hydraulic pump to the rod side oil chamber of boom cylinder when it is determined a body lift-up operation by the determination means.

The invention of claim4is the hydraulic control circuit for a construction machine of any of claims1to3, comprising first and second bypass valves respectively controlling a flow rate of first and second bypass oil passages for feeding delivery oil of first and second hydraulic pumps to oil tank.

Effects of the Invention

According to the invention of claim1, recycle and discharge flow rates for the boom cylinder can be controlled independently of each other by using first and second boom spool valves when the boom cylinder is contracted, and in addition, pressure oil supply from first and second hydraulic pumps to the boom cylinder is no longer needed, thereby contributing high efficiency, improvement of operability, and cost suppression.

According to the invention of claim2, when the boom cylinder is contracted, supply/discharge flow rates for the boom cylinder can be controlled independently of each other by using first and second boom spool valves.

According to the invention of claim3, the body lift-up operation can be performed smoothly, and in addition, the supply flow rate to the boom cylinder can be controlled independently when lifting up the body.

According to the invention of claim4, the delivery flow rate of first and second hydraulic pumps can be controlled accurately.

DESCRIPTION OF EMBODIMENTS

Now, an explanation is provided below about embodiments of the present invention based on drawings.

First of all, an explanation about first embodiment of the present invention is provided based onFIGS.1to6;FIG.1is a drawing illustrating hydraulic excavator1as an example of construction machine according to this invention, wherein the hydraulic excavator1is composed of a crawler type lower traveling body2, an upper swiveling body3swivelably supported on the lower traveling body2, a front working machine4mounted on the upper swiveling body3, and others; and furthermore, the front working machine4is composed of a boom5whose base end part is supported vertically swingably by upper swiveling body3, a stick6longitudinally swingably supported at an end part of the boom5, a bucket7swivelably mounted at an end part of the stick6, and others; wherein the hydraulic excavator1is provided with various hydraulic actuators, such as a boom cylinder8, stick cylinder9, and bucket cylinder10for swinging the boom5, stick6, and bucket7respectively; left and right traveling motors (not shown) for moving the lower traveling body2; a swiveling motor (not shown) for swiveling the upper swiveling body3. Note that the constitution of hydraulic excavator1is similar to those according to second and third embodiments mentioned later andFIG.1is common to first to third embodiments. Also, in description below, a swing of stick6bringing the end part of stick close to the body is assumed to be stick-in (in-side swing) and the swing of stick6moving the end part of stick away from the body is assumed to be stick-out (out-side swing).

When oil is supplied into head side oil chamber8aand discharged from rod side oil chamber8b, the boom cylinder8is configured to extend and the boom5is configured to rise; meanwhile, when the oil is supplied into the rod side oil chamber8band discharged from the head side oil chamber8a, the boom5is configured to lower. When the oil is supplied into the head side oil chamber9aand discharged from the rod side oil chamber9b, the stick cylinder9is configured to extend and the stick6is configured to swing toward in-side; meanwhile, when oil is supplied into the rod side oil chamber9band discharged from the head side oil chamber9a, the stick cylinder9is configured to contract and the stick6is configured to swing toward out-side; now based onFIG.2, an explanation is provided about oil feed/discharge control for these boom cylinder8and stick cylinder9; inFIG.2, reference numbers11,12denote first and second hydraulic pumps as hydraulic supply source for various hydraulic actuators installed on the hydraulic excavator excavator1mentioned above, reference numbers13,14denote first and second oil passages through which delivery oil is supplied from first and second hydraulic pumps11,12, reference number15denotes an oil tank, reference numbers16,17denote first and second boom spool valves for controlling oil supply and discharge for the boom cylinder8, reference numbers18,19denote first and second stick spool valves for controlling oil supply and discharge for the stick cylinder9; the first boom spool valve16and first stick spool valve18are connected to the first pump oil passage13, and the second boom spool valve17and second stick spool valve19are connected to the second pump oil passage14respectively. Furthermore, at an upstream side of the first stick spool valve18, a poppet valve20mentioned later is disposed, which controls the supply flow rate from first hydraulic pump11to first stick spool valve18.

In addition, since the boom cylinder8and stick cylinder9are hydraulic actuator which requires large flow rate, the first and second boom spool valves16,17and the first and second stick spool valves18,19are installed so that pressure oil can be supplied from both the first and second hydraulic pumps11,12. Also, in theFIG.2, reference numbers21,22denote a left travel spool valve and bucket spool valve both connected to first pump oil passage13, reference numbers23,24denote a right travel spool valve and rotation spool valve both connected to second pump oil passage14, wherein these spool valves21to24change over between neutral and operation position according to operations of corresponding manipulator to control oil supply and discharge for corresponding hydraulic actuator (left travel motor, bucket cylinder10, right travel motor, and rotation motor); but detailed description about these spool valves21to24is omitted.

Also inFIG.2, reference numbers25,26denote first and second bypass valves; the first bypass valve25controls a flow rate of first center bypass oil passage27passing through center bypass passages21a,16a,22a, and18ain order, which are formed by spool valves21,16,22, and18and connected to first pump oil passage13, and leading to first hydraulic pump11and oil tank15, and the second bypass bypass valve26controls a flow rate of second center bypass oil passage28passing through center bypass passages23a,24a,171, and19ain order, which are formed by spool valves23,24,17, and19and connected to second pump oil passage14, and leading to second hydraulic pump12and the oil tank15. In this case, the center bypass passages21a,16a,22a,18a,23a,24a,17a, and19aformed by the spool valves21,16,22,18,23,24,17, and19have roughly a certain opening area regardless of change-over position or spool's displaced amount of spool valves21,16,22,13,23,24,17, and19, and in addition, the first and second bypass valves25,26are configured to control increase or decrease of the flow rate of first and second center bypass oil passages27,28, i.e. bypass flow rate feeding from first and second hydraulic pumps11,12, to oil tank15, by controlling increase or decrease of opening area based on control signal output by control unit30mentioned later to first and second bypass valve solenoid valves49,50. As the bypass flow rate is controlled to be increased or decreased by the first and second bypass valves25,26, the delivery flow rate from first and second hydraulic pumps11,12is controlled to be increased or decreased, and thus, the delivery flow rate from first and second hydraulic pumps11,12can be supplied to spool valves21,16,22,18,23,24,17, and19in just proportion.

In addition, according to this embodiment, as first and second bypass oil passages of this invention, first and second center bypass oil passages are provided passing through each spool's center bypass passage, at its lowermost stream, first and second bypass valves are disposed, but at uppermost stream of these spools, first and second bypass oil passages can be provided for feeding the oil from first and second hydraulic pumps to the oil tank and first and second bypass valves can be disposed in the first and second bypass oil passages. In this case, center bypass passage formed on each spool valve can be abolished.

Next, an explanation is provided in detail about oil supply and discharge control for the boom cylinder8.

First of all, the first boom spool valve16is a three position change-over valve having pilot ports16b,16cat lowering (contracted) and raising (extended) sides, wherein, when a pilot pressure is not input into both pilot ports16b,16c, the valve is positioned at neutral position N, where pressure oil is not supplied to nor discharged from the boom cylinder8, but when the pilot pressure is input into the lowering side pilot port16b, the valve switches to a lowering side operation position V to open a recycle valve passage16dfor supplying the discharge oil from head side oil chamber8aof boom cylinder8to rod side oil chamber8b. Also, the first boom spool valve16is configured, when the pilot pressure is input into raising side pilot port16c, to switch to raising side operation position W and open head side supply valve passage16efor supplying the delivery oil from first hydraulic pump11to head side oil chamber8aof boom cylinder8and open rod side discharge valve passage16ffor feeding the discharge oil from the rod side oil chamber8bof boom cylinder8to the oil tank15. Note that, in the recycle valve passage16d, a check valve to block an oil flow from rod side oil chamber8bto head side oil chamber8a.

Also, the second boom spool valve17is the three position change-over valve having pilot ports17b,17cat lowering (contracted) and raising (extended) sides, wherein, when the pilot pressure is not input into both pilot ports17b,17c, the valve17is positioned at neutral position N, where the pressure oil is not supplied to nor discharged from the boom cylinder8, but when the pilot pressure is input into the lowering side pilot port17b, the valve17switches to the lowering side operation position V to open a head side discharge valve passage17dfor feeding the discharge oil from head side oil chamber8aof boom cylinder8to oil tank15. Also, the second boom spool valve17is configured, when the pilot pressure is input into raising side pilot port17c, to switch to the raising side operation position W and open the head side supply valve passage17efor supplying the delivery oil from second hydraulic pump12to head side oil chamber8aof boom cylinder8.

Furthermore, in theFIG.2, reference numbers31,32denote first and second lowering side solenoid valves for outputting the pilot pressures to the lowering side pilot ports16b,17bfor the first and second boom spool valves16,17, reference numbers33,34denote first and second raising side solenoid valves for outputting the pilot pressure to raising side pilot ports16c,17c, wherein these first and second lowering and raising side solenoid valves31to34start to output the pilot pressure corresponding to the control signal based on the control signal from the control unit30mentioned later. Then, the spool of first and second boom spool valves16,17is changed by the pilot pressure to be output from first and second lowering and raising side solenoid valves31to34to lowering and raising side pilot ports16b,17b,16c, and17cof first and second boom spool valves16,17, so that the valves16,17switch to the lowering and raising side operation positions V, W; in this case, a spool's displaced amount is controlled to be increased or decreased according to increase or decrease of pilot pressure.

Here,FIG.3illustrates the opening characteristics of recycle valve passage16dof the first boom spool valve16at lowering side operation position V, the head side supply valve passage16eand rod side discharge valve passage16fat raising side operation position W, and the head side discharge valve passage17dof the second boom spool valve17at lowering side operation position V and head side supply valve passage17eat raising side operation position W; as shown in theFIG.3, the opening area of these valve passages16d,16e,16f,17d, and17eis set to be large as the spool's displaced amount becomes large. As the opening area of valve passages16d,16e,16f,17d, and17eincreases or decreases in coordination with spool's displacement, the recycled flow rate from head side oil chamber8aof boom cylinder8to rod side oil chamber8b, the supply flow rate from first hydraulic pump11to head side oil chamber8a, the discharge flow rate from rod side oil chamber8bto oil tank15, the discharge flow rate from head side oil chamber8ato oil tank15, and the supply flow rate from second hydraulic pump12to head side oil chamber8aare controlled to be increased or decreased.

That is to say, when first and second boom spool valves16,17are located at lowering side operation position V, the recycle valve passage16dof first boom spool valve16controls the recycled flow rate from head side oil chamber8ato rod side oil chamber8band the head side discharge valve passage17dof second boom spool valve17controls the discharge flow rate from head side oil chamber8ato oil tank15, Meanwhile, when first and second boom spool valves16,17are located at raising side operation position W, the head side supply valve passage16eand rod side discharge valve passage16fof first boom spool valve16control the supply flow rate from first hydraulic pump11to head side oil chamber8aand the discharge flow rate from rod side oil chamber8bto oil tank15, and also, the head side supply valve passage17eof second boom spool valve17controls the supply flow rate from second hydraulic pump12to head side oil chamber8a.

In contrast, as shown inFIG.5, the control unit30is configured to be input signals from boom actuator, stick manipulator, operation detection means36for detecting each operation of various manipulators including manipulators for other hydraulic actuators installed on the hydraulic excavator1(according to this embodiment, the right/left traveling motors, bucket cylinder10, swiveling motor), first and second pump pressure sensors37,38for respectively detecting delivery pressure from first and second hydraulic pumps11,12, head side/rod side boom pressure sensors39,40for respectively detecting pressure in head/rod side oil chambers8a,8bof boom cylinder8, head side/rod side stick pressure sensors41,42for detecting pressure in head/rod side oil chambers9a,9bof stick cylinder9, various pressure detection sensors for other hydraulic actuators (not shown, but pressure sensors for respectively detecting pressure in head/rod side oil chambers of bucket cylinder10, for example), engine controller43, and others, and based on these input signals, output control signals to first and second lowering/rising side solenoid valves31to34for outputting pilot pressure to the first and second boom spool valves16,17, first and second in-side/out-side solenoid valves45to48mentioned later for outputting pilot pressure to first and second stick spool valves18,19, poppet valve solenoid valve29for outputting pilot pressure to poppet valve20, various solenoid valves (not shown) for outputting pilot pressure to spool valves for other hydraulic actuators (in this embodiment, left travel spool valve21, bucket spool valve22, right travel spool valve23, and swiveling spool valve24), first bypass valve solenoid valve49for outputting pilot pressure to the first bypass valve25, and second bypass valve solenoid valve50for outputting pilot pressure to second bypass valve26.

Then, an explanation is provided about a control of first and second boom spool valves16,17conducted by the control unit30; when a signal of boom lowering operation is input from operation detection means36, the control unit30outputs the control signal to first and second lowering side solenoid valves31,32. Thus, the pilot pressure is input into the lowering side pilot ports16b,17bof first and second boom spool valves16,17to switch both first and second boom spool valves16,17to lowering side operation position V. Then, as mentioned above, the first boom spool valve16at the lowering side operation position V controls the recycled flow rate from head side oil chamber8aof boom cylinder8to rod side oil chamber8band the second boom spool valve17at the lowering side operation position V controls the discharge flow rate from head side oil chamber8ato oil tank15. Thus, the oil is discharged from head side oil chamber $a and supplied into rod side oil chamber8bto contract the boom cylinder8and lower the boom5; here, based on the various signals (signal and others from the operation detection means36and various pressure sensors37to42) input into the control unit30, the control unit30calculates the recycle and discharge flow rates required to the boom cylinder8and outputs respective control signals to first and second lowering side solenoid valves31,32in order to control them independently of each other. These independent controls of recycle and discharge flow rates are enabled since the first boom spool valve16controls only the recycled flow rate during lowering operation of boom5(contraction of boom cylinder8) and the second boom spool valve17controls only the discharge flow rate.

Here, when the boom5is lowering, both first and second boom spool valves16,17are configured not to supply the delivery oil from first and second hydraulic pumps11,12to rod side oil chamber8bof boom cylinder8. That is because, during lowering operation of boom5(contraction of boom cylinder8), a discharge amount from head side oil chamber8aof boom cylinder8is remarkably large compared with a supply amount to rod side oil chamber8b(about twice, for example) based on the relationship of piston's pressured area, in addition, the head side oil chamber8ais highly pressured as whole weight of front working machine4is applied, and therefore, recycle oil from head side oil chamber8ais enough for the oil supply to rod side oil chamber8b. Then, during the lowering of boom5, first and second hydraulic pumps11,12can be configured not to supply the delivery oil to boom cylinder8, contributing to energy saving.

Meanwhile, when a signal of boom raising operation is input from operation detection means36, the control unit30outputs the control signal for outputting pilot pressure to first and second raising side solenoid valves33,34.

Thus, the pilot pressure is input into raising side pilot ports16c,17cof first and second boom spool valves16,17to switch both first and second boom spool valves16,17to raising side operation position W. Then, as mentioned above, the first boom spool valve16at the raising side operation position W controls the supply flow rate from first hydraulic pump11to head side oil chamber8aand the discharge flow rate from rod side oil chamber8bto oil tank15, and the second boom spool valve17at the raising side operation position W controls the supply flow rate from second hydraulic pump12to head side oil chamber8a. Thus, the oil is supplied into head side oil chamber8aand discharged from rod side oil chamber8bto extend the boom cylinder8and raise the boom5; here, based on the various signals (signal and others from operation detection means36and various pressure sensors37to42, and engine controller43) input into the control unit30, the control unit30calculates the supply and discharge flow rates required to the boom cylinder8and outputs the control signal to each of first and second raising side solenoid valves33,34in order to control them independently. These independent controls of supply and discharge flow rates are enabled since the first boom spool valve16controls the supply and discharge flow rates from first hydraulic pump11during raising operation of boom5(extension of boom cylinder8) and the second boom spool valve17controls the supply flow rate from second hydraulic pump12.

Note that, as for first boom spool valve16during raising of boom5, the relationship between the opening areas of head side supply valve passage16eand rod side discharge valve passage16fis uniquely decided with a spool displaced amount; the supply/discharge flow rates for boom cylinder8can be controlled independently of each other by controlling the increase and decrease of opening area of head side supply valve passage17e, which is connected to second boom spool valve17that controls the supply flow rate only, so that total supply flow rate from first and second boom spool valves (first and second hydraulic pumps11,12)16,17will be the supply flow rate required by boom cylinder8.

Next, an explanation is provided in detail about oil supply and discharge control for the stick cylinder9.

First, the poppet valve20has a check function, is capable of metering, and is provided at an upstream side of first stick spool valve18, i.e. at a supply oil passage from first hydraulic pump11to first stick spool valve18. Also, the poppet valve20is started by pilot pressure output from the poppet valve solenoid valve29based on the control signal output by the control unit30to the poppet valve solenoid valve29to control the supply flow rate from first hydraulic pump11to first stick spool valve18. The supply flow rate of first hydraulic pump11supplied from poppet valve20to first stick spool valve18is, as mentioned later, configured to be supplied as-is to stick cylinder9without being increased or decreased by the first stick spool valve18.

Also, the first stick spool valve18is the three position change-over valve having in-side (extended side) and out-side (contracted side) pilot ports18b,18c; wherein, when the pilot pressure is not input into both pilot ports18b,18c, the valve18is positioned at neutral position N, where the pressure oil is not supplied to nor discharged from the stick cylinder9, but when the pilot pressure is input into in-side pilot port18b, the valve18switches to an inside operation position X to open the head side supply valve passage18dfor supplying the delivery oil from first hydraulic pump11supplied through poppet valve20to head side oil chamber9aof stick cylinder9and open recycle valve passage18efor supplying the delivery oil from the rod side oil chamber9bto head side oil chamber9a. Also, the first stick spool valve18is configured, when the pilot pressure is input into out-side pilot port18c, to switch to out-side operation position Y and open rod side supply valve passage18ffor supplying the delivery oil from first hydraulic pump11supplied through the poppet valve20to rod side oil chamber9band open head side discharge valve passage18gfor feeding delivery oil from head side oil chamber9ato oil tank15; as mentioned later, the head side supply valve passage18dand rod side supply valve passage18fare configured to supply the supply flow rate as-is from poppet valve20to stick cylinder9without increasing or decreasing the flow rate. Note that, in the recycle valve passage18e, a check valve to block the oil flow from head side oil chamber9ato rod side oil chamber9b.

Also, the second stick spool valve19is the three position change-over valve having in-side (extended side) and out-side (contracted side) pilot ports19b,19c; wherein, when the pilot pressure is not input into both pilot ports19b,19c, the valve19is positioned at neutral position N, where the pressure oil is not supplied to nor discharged from stick cylinder9, but when the pilot pressure is input into in-side pilot port19b, the valve19switches to the in-side operation position X to open the head side supply valve passage19dfor supplying the delivery oil from second hydraulic pump12to head side oil chamber9aof stick cylinder9and open rod side discharge valve passage19efor feeding the discharge oil from rod side oil chamber9bto oil tank15. Also, the second stick spool valve19is configured, when the pilot pressure is input into out-side pilot port19c, to switch to out-side operation position Y and open rod side supply valve passage19ffor supplying delivery oil from second hydraulic pump12to rod side oil chamber9band open head side discharge valve passage19gfor feeding the discharge oil from head side oil chamber9ato oil tank15.

Here, as an allocation structure of poppet valve20is shown inFIG.6, the poppet valve20is, in a valve block where first and second stick spool valves18,19are incorporated, incorporated in a pump port connected to first hydraulic pump11for supplying the delivery oil from first hydraulic pump11to first stick spool valve18. Also, inFIG.6, a reference number35denotes the check valve incorporated in the pump port connected to second hydraulic pump12for supplying the delivery oil from second hydraulic pump12to second stick spool valve19; wherein the check valve35is configured to block a backflow from second stick spool valve19to second hydraulic pump12, That is to say, in the pump port in the valve block where spool valves such as first and second stick spool valves18,19are incorporated, in general, the check valve such as the check valve35mentioned above is incorporated to block the backflow from spool valve to hydraulic pump; according to this embodiment, in place of this check valve, a pocket valve20having a check function and being capable of metering is configured to be incorporated in the pump port; thus, there is no need to ensure a space for the poppet valve20separately and it is easy to dispose the poppet valve20there.

Furthermore, in theFIG.2, reference numbers45,46denote first and second in-side solenoid valves for outputting pilot pressures to the inside pilot ports18b,19bof first and second stick spool valves18,19, reference numbers47,48denote first and second out-side solenoid valves for outputting pilot pressure to out-side pilot ports18c,19c; wherein these first and second in-side/out-side solenoid valves45to48start to output pilot pressure corresponding to the control signal based on the control signal from the control unit30. Then, the pilot pressure output from first and second in-side/out-side solenoid valves45to48to the in-side and out-side pilot ports18b,19b,18c,19cof first and second stick spool valves18,19displace each spool of first and second stick spool valves18,19, so that the valves18,19switch to in-side and out-side operation positions X, Y; in this case, each spool's displaced amount is controlled to be increased or decreased according to a change of pilot pressure.

Here,FIG.4illustrates the opening characteristics of head side supply valve passage18dand recycle valve passage18eat in-side operation position X of the first stick spool valve18, rod side supply valve passage18fand head side discharge valve passage18gat out-side operation position Y, head side supply valve passage19dand rod side discharge valve passage19eat in-side operation position X of second stick spool valve19, and rod side supply valve passage19fand head side discharge valve passage19gat out-side operation position Y; as shown in theFIG.4, in the head side and rod side supply valve passages18d,18fand rod side supply valve passage18fof the first stick spool valve18, the opening area is set to become maximum just when the spool displaces from the neutral position N. i.e. even when the spool's displaced amount is small. Thus, the first stick spool valve18is configured to supply the supply flow rate as-is from first hydraulic pump11supplied through poppet valve20to the head side and rod side oil chambers9a,9bof stick cylinder9without increasing or decreasing the flow rate. That is, the supply flow rate from the first hydraulic pump11to the stick cylinder9is not controlled at first stick spool valve18, and the supply flow rate controlled at the poppet valve20is supplied as-is to the stick cylinder9.

Meanwhile, the opening area of recycle valve passage18eof first stick spool valve18and head side discharge valve passage18g, head side supply valve passage19dof second stick spool valve19, rod side discharge valve passage19e, rod side supply valve passage19f, and head side discharge valve passage19gis configured to become larger as the spool's displaced amount gets large. As the opening area of valve passages18e,18g,19d,19e,19f, and19gincreases or decreases in coordination with the spool's displacement, the recycled flow rate from rod side oil chamber9bof stick cylinder9to head side oil chamber9a, the discharge flow rate from head side oil chamber9ato oil tank15, the supply flow rate from second hydraulic pump12to head side oil chamber9a, the discharge flow rate from rod side oil chamber9bto oil tank15, the supply flow rate from second hydraulic pump12to rod side oil chamber9b, and the discharge flow rate from head side oil chamber9ato oil tank15are controlled to be increased or decreased.

That is to say, when first and second stick spool valves18,19are positioned at in-side operation position X, the supply flow rate from first hydraulic pump11to head side oil chamber9ais controlled with the poppet valve20, the recycled flow rate from rod side oil chamber9bto head side oil chamber9ais controlled with recycle valve passage18eof first stick spool valve18, and the supply flow rate from second hydraulic pump12to head side oil chamber9aand the discharge flow rate from rod side oil chamber9bto oil tank15are controlled with head side supply valve passage19dand rod side discharge valve passage19eof second stick spool valve19. Meanwhile, when first and second stick spool valves18,19are positioned at out-side operation position Y, the supply flow rate from first hydraulic, pump11to rod side oil chamber9bis controlled with poppet valve20, the discharge flow rate from head side oil chamber9ato oil tank15is controlled with head side discharge valve passage18gof first stick spool valve18, and the supply flow rate from second hydraulic pump12to rod side oil chamber9band the discharge flow rate from head side oil chamber9ato oil tank15are controlled with rod side supply valve passage19fof second stick spool valve19and head side discharge valve passage19g.

Thereafter, an explanation is provided about a control of poppet valve20and first and second stick spool valves18,19conducted by the control unit30; when a stick-in signal is input from operation detection means36, the control unit30outputs the control signal to poppet valve solenoid valve29for outputting pilot pressure. Thus, the poppet valve20starts to supply the delivery oil from first hydraulic pump11to first stick spool valve18while the flow rate of delivery oil is controlled. Furthermore, the control unit30outputs the control signal to first and second in-side solenoid valves45,46for outputting pilot pressure. Thus, the pilot pressure is input into in-side pilot ports18b,19bof first and second stick spool valves18,19to switch both first and second stick spool valves18,19to in-side operation position X. Then, as mentioned above, the poppet valve20controls the supply flow rate from first hydraulic pump11to head side oil chamber9a, the first stick spool valve18at in-side operation position X controls the recycled flow rate from rod side oil chamber9bto head side oil chamber9a, and the second stick spool valve19at in-side operation position X controls the supply flow rate from second hydraulic pump12to head side oil chamber9aand the discharge flow rate from rod side oil chamber9bto oil tank15. Thus, the oil is supplied into head side oil chamber9aand discharged from rod side oil chamber9bto extend the stick cylinder9and swing the stick6to in-side; here, based on the various signals (signal and others from the operation detection means36, various pressure sensors37to42, and engine controller43) input into the control unit30, the control unit30calculates the supply, recycle, and discharge flow rates required to stick cylinder9and outputs respective control signals to poppet valve solenoid valve29and first and second in-side solenoid valves45,46in order to control them independently of each other. These independent controls of supply, recycle, and discharge flow rates are enabled since, during in-side operation of stick6(extension of stick cylinder9), the poppet valve20controls the supply flow rate from first hydraulic pump11, the first stick spool valve18controls the recycled low rate, and the second stick spool valve19controls the supply and discharge flow rates from second hydraulic pump12.

Note that, during the in-side operation of stick6, the relationship between opening areas of head side supply valve passage19dand rod side discharge valve passage19eof second stick spool valve19is uniquely decided with the spool displaced amount; the supply/discharge flow rates for the stick cylinder9can be controlled independently of each other by controlling the increase and decrease of opening area of poppet valve20, which controls only the supply flow rate, so that total supply flow rate from the poppet valve20(supply flow rate from first hydraulic pump11) and second stick spool valve19(supply flow rate from second hydraulic pump12) is controlled to be the supply flow rate required by stick cylinder9.

Meanwhile, when a stick-out operation signal is input from operation detection means36, the control unit30outputs the control signal to poppet valve solenoid valve29for outputting pilot pressure. Thus, the poppet valve20starts to supply the delivery oil from first hydraulic pump11to first stick spool valve18while the flow rate of delivery oil is controlled. Furthermore, the control unit30outputs the control signal to first and second out-side solenoid valves47,48for outputting the pilot pressure. Thus, the pilot pressure is input into out-side pilot ports18c,19cof first and second stick spool valves18,19to switch both first and second stick spool valves18,19to out-side operation position Y. Then, as mentioned above, the poppet valve20controls the supply flow rate from first hydraulic pump11to rod side oil chamber9b, the first stick spool valve18at out-side operation position Y controls the discharge flow rate from head side oil chamber9ato oil tank15, and the second stick spool valve19at out-side operation position Y controls the supply flow rate from second hydraulic pump12to rod side oil chamber9band the discharge flow rate from head side oil chamber9ato oil tank15. Thus, the oil is supplied into rod side oil chamber9band discharged from head side oil chamber9ato contract stick cylinder9and swing stick6to out-side; here, based on the various signals (signal and others from the operation detection means36, various pressure sensors37to42, and engine controller43) input into the control unit30, the control unit30calculates the supply and discharge flow rates required to stick cylinder9and outputs respective control signals to poppet valve solenoid valve29and first and second out-side solenoid valves47,48in order to control them independently of each other. These independent controls of supply and discharge flow rates are enabled since, during out-side operation of stick6(contraction of stick cylinder9), the poppet valve20controls the supply flow rate from first hydraulic pump11, the first stick spool valve18controls the discharge flow rate, and the second stick spool valve19controls the supply and discharge flow rates from second hydraulic pump12.

Note that, during the out-side operation of stick6, the relationship between opening areas of rod side supply valve passage19fand head side discharge valve passage19gof second stick spool valve19is uniquely decided with the spool displaced amount; the supply/discharge flow rates for stick cylinder9can be controlled independently of each other by controlling the increase and decrease of opening area of poppet valve20, which controls only the supply flow rate, so that total supply flow rate from poppet valve20(supply flow rate from first hydraulic pump11) and second stick spool valve19(supply flow rate from second hydraulic pump12) is controlled to be the supply flow rate required by stick cylinder9or by controlling the increase and decrease of opening area of head side discharge valve passage18gof first stick spool valve18, which controls only the discharge flow rate, so that total discharge flow rate from first stick spool valve18and second stick spool valve19is controlled to be the discharge flow rate required to stick cylinder9.

According to first embodiment as configured above, the hydraulic control circuit of hydraulic excavator1comprises first and second hydraulic pumps11,12as hydraulic supply source and first and second boom spool valves16,17being connected respectively to the first and second hydraulic pumps11,12and controlling oil supply and discharge for boom cylinder8; wherein, when the boom cylinder8is contracted (lowering operation of boom5), the first boom spool valve16controls the recycled flow rate from head side oil chamber8aof boom cylinder8to rod side oil chamber8b, the second boom spool valve17controls the discharge flow rate from head side oil chamber8aof boom cylinder8to oil tank15, and both first and second boom spool valves16,17do not to supply pressure oil from first and second hydraulic pumps11,12to boom cylinder8when the boom cylinder8is contracted.

That is to say, during the contraction of boom cylinder8, the first boom spool valve16controls only the recycled flow rate from head side oil chamber8ato rod side oil chamber8b, so the first boom spool valve16can control the recycled flow rate independently. Also, the second boom spool valve17controls only the discharge flow rate from head side oil chamber8ato oil tank15, so the second boom spool valve17can control the discharge flow rate independently.

As the result, during the contraction of boom cylinder8, the recycle and discharge flow rates for the boom cylinder8can be controlled independently of each other, and according to various work contents of stand-alone work for driving the boom cylinder8alone, compound work for driving other hydraulic actuator (stick cylinder9, bucket cylinder10, for example) as well, light load work, heavy load work, and others, the relationship between the supply and discharge flow rates can be changed, contributing high efficiency and improvement of operability. Furthermore, this control is done by making use of first and second boom spool valves16,17, which are generally used in hydraulic control circuit of hydraulic excavator1conventionally, so the valve unit for conventional circuit configuration can be used as-is, attaining cost reduction. Furthermore, during the contraction of boom cylinder8, both first and second boom spool valves16,17do not supply pressure oil from first and second hydraulic pumps11,12to boom cylinder8, contributing energy conservation. In addition, during the contraction of boom cylinder8(lowering operation of boom5), the discharge amount from head side oil chamber8aof boom cylinder8is remarkably large compared to the supply amount to rod side oil chamber8bbecause of relationship of piston's pressured area, and in addition, the head side oil chamber8ais highly pressured by whole weight of front working machine4, so the recycle oil from head side oil chamber8ais enough for the oil supply to rod side oil chamber8b.

Furthermore in in this regard, during the extension of boom cylinder8(raising of boom5), the first boom spool valve16controls the supply flow rate from first hydraulic pump11to head oil chamber8aof boom cylinder8and the discharge flow rate from rod side oil chamber8bto oil tank15, and the second boom spool valve17controls the supply flow rate from second hydraulic pump12to head side oil chamber8aof boom cylinder8.

That is to say, during the extension of boom cylinder8, the second boom spool valve17controls only the supply flow rate from second hydraulic pump12to head side oil chamber8a, so the second boom spool valve17can control the supply flow rate from second hydraulic pump12independently. Also, the first boom spool valve16controls the supply flow rate from first hydraulic pump11to head side oil chamber8aand the discharge flow rate from rod side oil chamber8bto oil tank15; in this case, the discharge flow rate can be controlled independently with the first boom spool valve16by giving precedence to the discharge flow rate control. Furthermore, the first boom spool valve16cannot control the supply flow rate independently, but the first boom spool valve16can control total supply flow rate from both first and second hydraulic pumps11,12independently when the second boom spool valve17also controls to increase or decrease the supply flow rate from second hydraulic pump12. As the result, even when the boom cylinder8is extended, the supply and discharge flow rates for the boom cylinder8can also be controlled independently, contributing high efficiency and improvement of operability largely.

Furthermore in this regard, the hydraulic control circuit of hydraulic excavator1comprises the first and second bypass valves25,26that control the flow rate of first and second bypass oil passages27,28respectively for feeding the delivery oil from first and second hydraulic pumps11,12to oil tank15. Thus, the first and second bypass valves25,26can control the flow rate from first and second hydraulic pumps11,12to oil tank15so that the delivery flow rate from first and second hydraulic pumps11,12can be controlled accurately.

In addition, according to this embodiment, the stick cylinder9as well as boom cylinder8is configured to be able to control the supply; discharge, and recycled flow rates independently of each other by making use of first and second stick spool valves18,19, thus both the boom cylinder8and stick cylinder9, which are installed in the hydraulic excavator1and are hydraulic actuator needing large flow rates, can control the supply, discharge, and recycled flow rates independently of each other by utilizing first and second spool valves (first and second boom spool valves16,17and first and second stick spool valves18,19), contributing high efficiency, improvement of operability, and cost suppression.

Next, second embodiment of the present invention is described in reference to hydraulic control circuit diagram shown inFIG.7; since anything other than first boom spool valve55mentioned later is the same as first embodiment, an explanation is omitted about it.

First boom spool valve55according to the second embodiment comprises, similar to first boom spool valve16according to first embodiment, lowering and raising side pilot ports55b,55c, wherein the valve55switches from neutral position N to the lowering side and raising side operation positions V, W when the pilot pressure is input into lowering side and raising side pilot ports55b,55c, wherein first and second areas V1, V2are provided in the lowering side operation position V of first boom spool valve55according to second embodiment. In this case, spool's displaced amount of second area V2from neutral position N is set larger than that of first area V1. Then, when the valve55is positioned in first area V1, the recycle valve passage55dis opened for supplying the discharge oil from head side oil chamber8aof boom cylinder8to rod side oil chamber8b. Also, when the valve55is positioned in second area V2, it is configured to open the recycle valve passage55dand the rod side supply valve passage55gfor supplying delivery oil from first hydraulic pump11to rod side oil chamber8b. Note that, inFIG.7, reference number55adenotes a center bypass passage installed on first boom spool valve55.

Here,FIG.8aillustrates opening characteristics of recycle valve passage55dand rod side supply valve passage55gin first and second areas V1, V2at the lowering side operation position V; the opening characteristics of recycle valve passage55dare same as those of recycle valve passage16dwhen the first boom spool valve16according to the first embodiment is at lowering side operation position V and the opening characteristics of rod side supply valve passage55gare configured to be closed in first area V1and have lamer opening area just after entering into second area V2. Also, since the opening area of the rod side supply valve passage55gbecomes larger soon, when the first boom spool valve55is positioned in second area V2, the valve passage55gis configured to supply delivery oil from first hydraulic pump11quickly to rod side oil chamber8bof boom cylinder8.

Note that, when the first boom spool valve55according to second embodiment is in raising side operation position W, similar to the case where first boom spool valve16according to first embodiment is in raising side operation position W, the valve55opens head side supply valve passage55efor supplying delivery oil from first hydraulic pump11to head side oil chamber8aof boom cylinder8and rod side discharge valve passage55ffor feeding discharge oil from rod side oil chamber8bof boom cylinder8to oil tank15; opening characteristics of these head side supply valve passage55eand rod side discharge valve passage55fare configured to be same as those of head side supply valve passage16eand rod side discharge valve passage16fof first boom spool valve16according to first embodiment (refer toFIG.8b).

Meanwhile, according to second embodiment, when a boom lowering operation signal is input from operation detection means36, the control unit30decides whether the signal denotes the body lift-up operation (lowers boom5while the bucket7is on earth to lower the boom5relatively against the body so that a part of the body is lifted up) based on a pressure in head side oil chamber8aof boom cylinder8input from head side boom pressure sensor39. Note that, according to second embodiment, the control unit30configures a judgment means for the present invention.

Here, the judgment whether the signal denotes the body lift-up operation or not is conducted based on the pressure value in head side oil chamber8aof boom cylinder8input from head side boom pressure sensor39. That is to say, when lowering the boom5in air (lowering boom5while the bucket7is not on earth), the pressure in head side oil chamber8aof boom cylinder8is high since total weight of front working machine4is applied on pressure oil in head side oil chamber8a. Meanwhile, when lowering boom5while a force resisting the lowering of boom5is acting due to the bucket7being on earth, and others, a tensile force is applied on boom cylinder8so that the pressure in head side oil chamber8ais reduced more than when lowering the boom5in air; during the body lift-up operation, a strong tensile force acts on the boom cylinder8since the boom5is lowered against the body weight so that the pressure in head side oil chamber8is reduced further. Therefore, when the pressure in head side oil chamber8aof boom cylinder8is reduced to less than predefined setting value Ps, the signal is deemed a body lift-up operation; also, when the pressure is not less than setting value Ps, the signal is not deemed the body lift-up operation.

Furthermore, when an operation signal for lowering boom is input from operation detection means36, similar to first embodiment, the control unit30outputs control signal to first and second lowering side solenoid valves31,32for outputting pilot pressure to switch first and second boom spool valves55,17to lowering side operation position V; in this case, when the operation signal is not deemed the body lift-up operation (the pressure in head side oil chamber8aof boom cylinder8is not less than predefined setting value Ps), the control signal is output to first lowering side solenoid valve31to output pilot pressure for positioning first boom spool valve55in first area V1(spool's displaced amount for entering into first area V1). Thus, the first boom spool valve55is positioned in first area V1and opens recycle valve passage55dfor supplying the discharge oil from head side oil chamber8aof boom cylinder8to rod side oil chamber8b.

On the other hand, when an operation signal for lowering boom is input from operation detection means36and when the operation signal is deemed the body lift-up operation (the pressure in head side oil chamber8aof boom cylinder8is less than setting value Ps), the control unit30outputs control signal to first lowering side solenoid valve31to output pilot pressure for positioning first boom spool valve55in second area V2(spool's displaced amount for entering into second area V2). Thus, the first boom spool valve55is positioned in second area V2, opens recycle valve passage55dwider than when sitting in first area V1for supplying the discharge oil from head side oil chamber8aof boom cylinder8to rod side oil chamber8b, and opens rod side supply valve passage55gfor supplying delivery oil from first hydraulic pump11to rod side oil chamber8b. Note that, when the first boom spool valve55is positioned in second area V2, the first boom spool valve55opens recycle valve passage55dfor supplying the discharge oil from head side oil chamber8ato rod side oil chamber8b, but during the body lift-up operation, since the pressure in rod side oil chamber8bis higher than head side oil chamber8a, the oil is not recycled and the check valve provided in recycle valve passage55dprevents a backflow (oil flow from rod side oil chamber Sb to head side oil chamber8a).

As such, according to second embodiment, when lifting up the body during the boom's lowering operation (contraction of boom cylinder8), the first boom spool valve55is positioned in second area V2and opens rod side supply valve passage55g. Thus, the delivery oil is to be supplied from first hydraulic pump11to rod side oil chamber8bof boom cylinder8, enabling a smooth body lift-up operation against the weight of the body by lowering the boom5.

In addition, when the first boom spool valve55is positioned in first area V1at lowering side operation position V, similar to when the first boom spool valve16according to first embodiment is positioned in the lowering side operation position V, the recycle valve passage55dcontrols the recycled flow rate from head side oil chamber8ato rod side oil chamber8b. Also, when the first boom spool valve55is positioned in second area V2at lowering side operation position V, the rod side supply valve passage55gcontrols the supply flow rate from first hydraulic pump11to rod side oil chamber8b(as mentioned above, the oil is not recycled from head side oil chamber8ato rod side oil chamber8b). That is, when the first boom spool valve55at lowering side operation position V is positioned in first area V1, the valve55is configured to control the recycled flow rate only, and also, when located in second area V2, the valve55is configured to control the supply flow rate only. Furthermore, similar to when the first boom spool valve16according to first embodiment is positioned at raising side operation position W, the first boom spool valve55sitting at raising side operation position W controls the supply and discharge flow rates from first hydraulic pump11. Also, since the second boom spool valve17is similar to that of first embodiment, when located at lowering side operation position V, the valve17controls the discharge flow rate only, and when positioned at raising side operation position W, the valve17controls the supply flow rate only from second hydraulic pump12. Thus, also according to the second embodiment, the first and second boom spool valves16,17can control the supply, recycle, and discharge flow rates independently of each other, causing the same effect as the first embodiment.

Note that it is to be understood that the present invention is not confined to the first and second embodiments; for instance, both the first and second stick spool valves provided in each of the embodiments are a spool valve of pilot operated type changing with the pilot pressure; these first and second stick spool valves can be configured with a spool valve of electromagnetic proportional type where the control signal is directly input from control unit.

INDUSTRIAL APPLICABILITY

The present invention can be used in a hydraulic control circuit for construction machines such as hydraulic excavator comprising the booms vertically movably supported by the body.