阅读说明：本技术 用于工程机械的动臂控制系统 (Boom control system for construction machine ) 是由 中岛秀树 于 2018-06-19 设计创作，主要内容包括：[问题]在配备有动臂的工程机械中,能够在动臂降低操作期间处理机器主体提升操作或突然操作,同时提高能量效率,并且实现部件数量的减少。[解决方案]其经配置使得在动臂降低操作期间在第一动臂控制阀16的操作位置处提供第一区域Y1和第二区域Y2,在第一区域Y1处打开回收阀通路16e并且关闭供应阀通路16f；在第二区域Y2处打开回收阀通路16e和供应阀通路16f,并且当在动臂降低操作期间既不执行机器主体提升操作也不执行突然操作时,第一动臂控制阀16位于第一区域Y1,并且当执行机器主体提升操作或突然操作时,第一动臂控制阀16位于区域Y2。([ problem ] to enable, in a construction machine equipped with a boom, processing of a machine body lifting operation or a sudden operation during a boom lowering operation while improving energy efficiency and achieving a reduction in the number of components. The solution is configured such that a first region Y1 and a second region Y2 are provided at the operation position of the first boom control valve 16 during the boom lowering operation, the recovery valve passage 16e is opened and the supply valve passage 16f is closed at the first region Y1; the recovery valve passage 16e and the supply valve passage 16f are opened at the second region Y2, and the first boom control valve 16 is located at the first region Y1 when neither the machine body lifting operation nor the sudden operation is performed during the boom lowering operation, and the first boom control valve 16 is located at the region Y2 when the machine body lifting operation or the sudden operation is performed.)

1. A boom control system in a construction machine configured to include a boom that moves vertically based on a telescopic operation of a boom cylinder, wherein a recovery oil passage allows oil discharged from a head-end oil chamber to be supplied to a rod-end oil chamber of the boom cylinder during a boom-down operation; a discharge oil passage allowing oil discharged from the head end oil chamber of the boom cylinder to flow into an oil tank; a supply oil passage that provides a fluid to allow a discharge oil of a hydraulic pump to be supplied to the rod-end oil chamber, and a supply valve passage that controls the flow rate of the supply oil passage is provided on a boom control valve that controls the flow rate of the recovery oil passage or the discharge oil passage; the pressure detection device is used for detecting the pressure in the head end oil chamber of the movable arm oil cylinder; an operation detection device for detecting an operation of the boom; and a controller for controlling the boom control valve based on input signals from the pressure detecting means and the operation detecting means; and the boom control valve provided with, in an operation position during a boom lowering operation, a first region that closes the supply valve passage and a second region that opens the supply valve passage on the one hand; on the other hand, the controller determines whether an operation is a machine body lifting operation for lifting a part of the machine body based on the pressure of the head end oil chamber during a boom-down operation, and the boom control valve is located in the first region if it is determined that the operation is not the machine body lifting operation, and the boom control valve is located in the second region if it is determined that the operation is the machine body lifting operation.

2. A boom control system in a construction machine configured to include a boom that moves vertically based on a telescopic operation of a boom cylinder, wherein a recovery oil passage allows oil discharged from a head-end oil chamber to be supplied to a rod-end oil chamber of the boom cylinder during a boom-down operation; a discharge oil passage allowing oil discharged from the head end oil chamber of the boom cylinder to flow into an oil tank; a supply oil passage that provides a flow rate that allows a discharge oil of a hydraulic pump to be supplied to the rod-end oil chamber, and a supply valve passage that controls a flow rate of the supply oil passage is provided on a boom control valve that controls a flow rate of the recovery oil passage or the discharge oil passage; the pressure detection device is used for detecting the pressure in the head end oil chamber of the movable arm oil cylinder; an operation detection device for detecting an operation of the boom; and a controller for controlling the boom control valve based on input signals from the pressure detecting means and the operation detecting means; and the boom control valve provided with, in an operation position during a boom lowering operation, a first region that closes the supply valve passage and a second region that opens the supply valve passage on the one hand; on the other hand, the controller determines whether the operation is a machine body lifting operation for lifting a part of the machine body based on the pressure of the head end oil chamber during a boom-down operation, and the boom control valve is located in the first region if it is determined that the operation is not a machine body lifting operation, and the boom control valve is located in the second region if it is determined that the operation is a machine body lifting operation.

3. The boom control system in a working machine according to claim 1 or 2, wherein the controller positions the boom control valve in the second region if the boom lowering operation is an abrupt operation regardless of whether the operation is a machine body lifting operation.

Technical Field

The present invention relates to a boom control system in a construction machine equipped with a boom that moves vertically by a telescopic operation of a boom cylinder.

Background

In general, among construction machines, there are some such as hydraulic excavators configured such that a front working implement mounted on a machine body includes a boom having a base end supported on the machine body in a vertically movable manner, a stick, and a working device; the rod is supported on the front end part of the movable arm in a longitudinally swinging mode; a working device (e.g., a bucket) is attached to a front end of the stick, and the boom is vertically moved based on a telescopic operation of the boom cylinder. In this construction machine, when the boom is lowered in the air (when the boom is lowered in a state where the working device does not contact the ground), the weight of the front work implement placed on the boom directly acts as a force for contracting the boom cylinder, and as a result, the oil pressure discharged from the head-end oil chamber becomes high, and the pressurized oil supplied to the rod-end oil chamber may be oil even at a low pressure. Therefore, conventionally, a technique of providing a recovery oil passage for supplying oil discharged from the head-end oil chamber of the boom cylinder to the rod-end oil chamber when the boom is lowered is widely used. By providing such a recovery oil passage, the flow rate of the pressurized oil supplied from the hydraulic pump to the rod-end oil chamber may be reduced or not required, thereby contributing to an improvement in energy efficiency. Further, if it is not necessary to supply pressurized oil from the hydraulic pump to the boom cylinder during the boom-down operation, when an interlock operation (combination operation) is performed between the boom cylinder and another hydraulic actuator (for example, an arm cylinder for swinging a stick), which uses the same hydraulic pump as the boom cylinder as the pressurized oil supply source, the influence of the pressurized oil supply to the boom cylinder on the behavior of the other hydraulic actuator can be reliably eliminated, and thus there is also an advantage of improving operability.

However, when the boom-down operation is performed, it is necessary to supply the high-pressure oil from the hydraulic pump to the rod-end oil chamber of the boom cylinder in some cases. For example, when a machine body lifting operation is performed (for example, in a hydraulic excavator, in the case of escaping from a dent or a soft ground, when an operation of relatively lowering the boom with respect to the machine body is performed by performing a boom lowering operation and the bucket contacts the ground to lift a part of the machine body), the boom cylinder contracts while resisting the weight of the machine body, and therefore, it is necessary to supply high-pressure oil to the rod-end oil chamber of the boom cylinder. Even when the boom is lowered in the air, the pressurized oil supply from the head-end oil chamber to the rod-end oil chamber using the recovery oil passage alone makes the acceleration of the boom cylinder slower than the case where the pressurized oil supply from the hydraulic pump is also performed. As a result, there arises a problem that responsiveness is poor when the operator suddenly operates the boom manipulating lever.

Therefore, conventionally, there is known a technique of providing a meter-in circuit (for example, see patent documents 1 and 2) in which recovered oil from only a head-end oil chamber is supplied to a rod-end oil chamber when a pressure of the head-end oil chamber of a boom cylinder is equal to or higher than a predetermined pressure during a boom-down operation, and discharged oil from a hydraulic pump is supplied to the rod-end oil chamber when the pressure of the head-end oil chamber is lower than the predetermined pressure. These construction machines are configured such that only recovered oil is used when the boom is lowered in the air, and pressurized oil from the hydraulic pump is also supplied to the rod-end oil chamber when the machine body is lifted.

Disclosure of Invention

Problems to be solved by the invention

However, the construction machine of patent document 1 requires flow path changing means (a flow rate control valve and a center bypass switching valve) for switching the flow path between: in the case where a valve such as a jack switching valve is used to operate the flow path changing device, which supplies or does not supply the discharge oil from the hydraulic pump to the rod-end oil chamber of the boom cylinder, the circuit is complicated in addition to a direction switching valve for controlling the flow of the pressurized oil to the boom cylinder. Further, the construction machine of patent document 2 requires a direction switching valve for supplying discharge oil of the hydraulic pump to the rod-end oil chamber only when the machine body is lifted (at the time of jacking), and a valve such as a jack electromagnetic proportional valve for switching the direction switching valve, and has problems of a large number of parts, hindering cost reduction and space saving. Further, the construction machines in patent documents 1 and 2 have no check of responsiveness when the operator suddenly operates the boom manipulating lever to the boom-down side, and there are problems to be solved by the present invention in these respects.

Means for solving the problems

The object of the present invention is to solve these problems in view of the practical circumstances as described above. The invention of claim 1 is a boom control system in a construction machine configured to include a boom that moves vertically based on a telescopic operation of a boom cylinder, wherein a recovery oil passage allows oil discharged from a head-end oil chamber to be supplied to a rod-end oil chamber of the boom cylinder during a boom-down operation; the discharge oil path allows oil discharged from the head end oil chamber of the slave arm oil cylinder to flow into an oil tank; a supply oil passage that allows supply of discharge oil of the hydraulic pump to the rod-end oil chamber, and a supply valve passage for controlling a flow rate of the supply oil passage provided on a boom control valve for controlling a flow rate of the recovery oil passage or the discharge oil passage; the pressure detection device is used for detecting the pressure in the head end oil chamber of the movable arm oil cylinder; the operation detection device is used for detecting the operation of the movable arm; and a controller for controlling the boom control valve based on input signals from the pressure detecting means and the operation detecting means; and a boom control valve provided with, in an operation position during a boom lowering operation, a first region that closes the supply valve passage and a second region that opens the supply valve passage on the one hand; on the other hand, the controller determines whether the operation is a machine body lifting operation for lifting a part of the machine body based on the pressure of the head end oil chamber during the boom-down operation, and if the operation is determined not to be the machine body lifting operation, the boom control valve is located in the first region, and if the operation is determined to be the machine body lifting operation, the boom control valve is located in the second region.

The invention of claim 2 is a boom control system in a construction machine configured to include a boom that moves up and down based on a telescopic operation of a boom cylinder, wherein the recovery oil passage allows oil discharged from a head-end oil chamber to be supplied to a rod-end oil chamber of the boom cylinder during a boom-down operation; the discharge oil path allows oil discharged from the head end oil chamber of the slave arm oil cylinder to flow into an oil tank; a supply oil passage that allows supply of discharge oil of the hydraulic pump to the rod-end oil chamber, and a supply valve passage for controlling a flow rate of the supply oil passage provided on a boom control valve for controlling a flow rate of the recovery oil passage or the discharge oil passage; the pressure detection device is used for detecting the pressure in the head end oil chamber of the movable arm oil cylinder; the operation detection device is used for detecting the operation of the movable arm; and a controller for controlling the boom control valve based on input signals from the pressure detecting means and the operation detecting means; and a boom control valve provided with, in an operation position during a boom lowering operation, a first region that closes the supply valve passage and a second region that opens the supply valve passage on the one hand; on the other hand, the controller determines whether the operation is a machine body lifting operation for lifting a part of the machine body based on the pressure of the head end oil chamber during the boom-down operation, and if the operation is determined not to be the machine body lifting operation, the boom control valve is located in the first region, and if the operation is determined to be the machine body lifting operation, the boom control valve is located in the second region.

The invention of claim 3 is the boom control system in a working machine according to claim 1 or claim 2, wherein if the boom lowering operation is an abrupt operation, the controller positions the boom control valve in the second region regardless of whether the operation is a machine body lifting operation.

The invention has the advantages of

According to the first aspect of the invention, the boom control system can contribute to improvement of energy efficiency, and in addition to being able to smoothly perform the lifting operation of the machine main body, it is possible to perform switching between the case of supplying and the case of not supplying the discharge oil of the hydraulic pump to the rod-end oil chamber during the lowering operation of the boom, by providing the first region and the second region in the boom control valve which controls the flow rate of the recovery oil passage or the discharge oil passage during the lowering operation of the boom, thereby eliminating the need for a dedicated valve for performing the aforementioned switching, an electromagnetic valve for operating the valve, and the like, and thereby can contribute to reduction in the number of components and space saving.

According to the second aspect of the invention, the boom control system can contribute to improvement of energy efficiency, and in addition to being able to smoothly perform the lifting operation of the machine main body, it is possible to perform switching between the case of supplying and the case of not supplying the discharge oil of the hydraulic pump to the rod-end oil chamber during the lowering operation of the boom, by providing the first region and the second region in the boom control valve which controls the flow rate of the recovery oil passage or the discharge oil passage during the lowering operation of the boom, thereby eliminating the need for a dedicated valve for performing the aforementioned switching, an electromagnetic valve for operating the valve, and the like, and thereby can contribute to reduction in the number of components and space saving.

According to the third aspect of the present invention, the responsiveness of the boom control system is excellent in the case where the boom-down operation is suddenly operated.

Drawings

Fig. 1 is a side view of a hydraulic excavator.

Fig. 2 is a hydraulic control circuit diagram of the boom cylinder in the first embodiment.

Fig. 3A to 3C are diagrams showing the first embodiment, wherein fig. 3A is a diagram illustrating a first region at a lower side operation position of the first boom control valve; fig. 3B is a diagram illustrating a second region at a lower-side operation position of the first control valve for the boom; fig. 3C is a diagram illustrating a lowering operation position of the second boom control valve.

Fig. 4A and 4B are diagrams showing the first embodiment, wherein fig. 4A is a diagram illustrating opening characteristics of the first and second regions in the lowering side operation position of the first boom control valve; fig. 4B is a diagram illustrating the opening characteristic of the lowering-side operation position of the second boom control valve.

Fig. 5 is a hydraulic control circuit diagram of a boom cylinder in the second embodiment.

Fig. 6A to 6C are views showing the second embodiment, wherein fig. 6A is a view illustrating a lowering operation position of the first boom control valve; fig. 6B is a diagram illustrating a first region at a lowering-side operation position of the second control valve for the boom; and fig. 6C is a diagram illustrating a second region at the lowering-side operation position of the second boom control valve.

Fig. 7A and 7B are diagrams showing the second embodiment, wherein fig. 7A is a diagram explaining an opening characteristic of a lowering side operation position of the first boom control valve; fig. 7B is a diagram illustrating opening characteristics of the first and second regions in the lowering-side operation position of the second boom control valve.

Fig. 8 is a hydraulic control circuit diagram of a boom cylinder in the third embodiment.

Fig. 9A and 9B are diagrams showing the third embodiment, wherein fig. 9A is a diagram illustrating a first region at a lower side operation position of the boom control valve; fig. 9B is a diagram illustrating a second region at the lowering-side operation position of the boom control valve.

Fig. 10 is a diagram showing the third embodiment, and is a diagram explaining opening characteristics of the first and second regions at the lowering side operation position of the boom control valve.

Detailed Description

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

First, a first embodiment of the present invention will be discussed with reference to fig. 1 to 4. Fig. 1 is a view showing a hydraulic excavator 1 as an example of a working machine of the present invention, including various components such as a crawler type lower traveling body 2; an upper rotating body 3 rotatably supported above the lower traveling member 2; the front work implement 4 is attached to the upper swing structure 3. Further, the front work implement 4 includes a boom 5 having a base end portion supported on the upper swing body 3 so as to be vertically swingable; a rod 6 supported to a front end portion of the boom 5 so as to be longitudinally swingable; and a bucket 7 attached to the front end of the bar 6. The hydraulic excavator 1 is provided with various types of hydraulic actuators, such as a boom cylinder 8; a bucket rod cylinder 9; and a bucket cylinder 10 for causing the boom 5, the stick 6, and the bucket 7 to swing, respectively; a left and right traveling motor (not shown) for traveling the lower traveling body 2; a rotation motor (not shown) for rotating the upper rotating body 3. The configuration of hydraulic excavator 1 in the second and third embodiments described below is similar to that in the first embodiment, and fig. 1 is common to the first to third embodiments.

The boom cylinder 8 is configured to extend the cylinder to raise the boom 5 by supplying pressurized oil to the head-end oil chamber 8a and discharging oil from the rod-end oil chamber 8b, and to retract the cylinder to lower the boom 5 by supplying pressurized oil to the rod-end oil chamber 8b and discharging oil from the head-end oil chamber 8 a. Based on the hydraulic control circuit diagram shown in fig. 2, control of supplying pressurized oil to the boom cylinder 8 and discharging pressurized oil from the boom cylinder 8 will be discussed. In fig. 2, reference numerals 11 and 12 denote a first hydraulic pump and a second hydraulic pump serving as pressurized oil supply sources of the boom cylinder 8; reference numerals 13 and 14 denote first and second hydraulic pump oil passages to which discharge oil of the first and second hydraulic pumps 11 and 12 are supplied, respectively; reference numeral 15 denotes a fuel tank; 16 and 17 denote a first boom control valve and a second boom control valve for performing supply and discharge control of oil to and from the boom cylinder 8, and the first boom control valve 16 is connected to the first pump line 13 and the second boom control valve 17 is connected to the second pump line 14, respectively.

In fig. 2 described above, reference numerals 18, 19, and 20 respectively denote a left travel control valve, a bucket control valve, and a first stick control valve connected to the first pump oil passage 13; 21. 22 and 23 respectively represent a right travel control valve, a rotation control valve, and a second rod control valve connected to the second pump oil passage 14. These control valves 18 to 23 are switched from the neutral position to the operating position in response to the operation of the corresponding operating implement, and perform supply and discharge control of oil to and from the corresponding hydraulic actuators (left and right traveling motors, rotation motors, arm cylinder 9, and bucket cylinder 10), but detailed description of these control valves 18 to 23 will be omitted. Reference numerals 24 and 25 denote first and second center bypass control valves, and the first center bypass control valve 24 performs flow rate control of a first center bypass oil passage 26 extending from the first hydraulic pump 11 to the tank 15, which in turn passes through center bypass valve passages 18a, 16a, 19a, 20a formed in the respective control valves 18, 16, 19, and 20 connected to the first pump oil passage 13. Further, the second center bypass control valve 25 performs flow rate control of a second center bypass oil passage 27 extending from the second hydraulic pump 12 to the tank 15, which passes through the center bypass valve passages 21a, 22a, 17a, 23a formed in the respective control valves 21, 22, 17, 23 connected to the second pump oil passage 14 in sequence. Detailed description of the first and second center bypass control valves 24 and 25 will also be omitted.

The first boom control valve 16 is a four-position switching spool including lift-side and lower- side pilot ports 16b and 16 c. When the pilot pressure is not input to the two pilot ports 16b and 16c, the first boom control valve 16 is positioned at the neutral position N so as not to allow the pressurized oil to be supplied to the boom cylinder 8 or discharged from the boom cylinder 8. However, when the pilot pressure is input to the lift-side pilot port 16b, the first boom control valve 16 is switched to be positioned at the lift-side operation position X to allow the oil discharged from the first hydraulic pump 11 to be supplied to the head-end oil chamber 8a of the boom cylinder 8, and the oil discharged from the rod-end oil chamber 8b flows into the oil tank 15. When the pilot pressure is input to the lower side pilot port 16c, the first boom control valve 16 is switched to be positioned in the lower side operation position Y, but the first region Y1 and the second region Y2 are disposed in the lower side operation position Y. In this case, the second region Y2 is provided at a position where the displacement amount from the neutral position N is larger than the displacement amount of the first region Y1. In a state where the boom cylinder 8 is located in the first region Y1, the recovery valve passage 16e for supplying the oil discharged from the head-end oil chamber 8a of the boom cylinder 8 to the rod-end oil chamber 8b via the check valve 16d is opened; on the other hand, a supply valve passage 16f that allows the discharge oil of the first hydraulic pump 11 to be supplied to the rod-end oil chamber 8b is closed (see fig. 3A). In a state where the boom cylinder 8 is located in the second region Y2, the oil discharged from the head-end oil chamber 8a is allowed to be supplied to the recovery valve passage 16e of the rod-end oil chamber 8B via the check valve 16d, and the supply valve passage 16f, which allows the discharged oil of the first hydraulic pump 11 to be supplied to the rod-end oil chamber 8B, is opened (see fig. 3B).

On the other hand, the second boom control valve 17 is a three-position switching spool including the raising-side and lowering- side pilot ports 17b and 17 c. When the pilot pressure is not input to the two pilot ports 17b and 17c, the second boom control valve 17 is positioned at the neutral position N, and pressurized oil supply to the boom cylinder 8 or discharge from the boom cylinder 8 is not performed. When the pilot pressure is input to the lift-side pilot port 17b, the second boom control valve 17 is switched to be positioned at the lift-side operation position X to allow the oil discharged from the second hydraulic pump 12 to be supplied to the head-end oil chamber 8a of the boom cylinder 8. When the pilot pressure is input to the lower side pilot port 17c, the second boom control valve 17 is switched to be positioned at the lower side operation position Y. However, in the state where the second boom control valve 17 is positioned at the lowering side operation position Y, the discharge valve passage 17d that allows the oil discharged from the head end oil chamber 8a of the boom cylinder 8 to flow into the oil tank 15 is opened (see fig. 3C).

In the first embodiment, the first boom control valve 16 corresponds to a boom control valve of the present invention, and the second boom control valve does not correspond to a boom control valve of the present invention. In fig. 3A, 3B, and 3C described above, the oil passages connected to the central bypass valve passages 16a and 17a of the first and second boom control valves 16 and 17 will be omitted.

Here, the opening characteristics of the recovery valve passage 16e and the supply valve passage 16f when the first boom control valve 16 is located at the first region Y1 and the second region Y2 of the lowered side operation position Y are shown in fig. 4A. As shown in fig. 4A, in the first region Y1, only the recovery valve passage 16e is opened, and the opening area is set larger as the spool displacement amount is larger. Further, when the spool is further displaced beyond the first region Y1 to reach the second region Y2, the opening area of the recovery valve passage 16e is increased more and the supply valve passage 16f is opened, but the more the spool displacement amount is increased, the more the opening area of the supply valve passage 16f is set to be increased. The recovery flow rate from the head-end oil chamber 8a to the rod-end oil chamber 8b and the recovery flow rate from the first hydraulic pump 11 to the rod-end oil chamber 8b are controlled to increase or decrease in accordance with the increase or decrease in the opening areas of the recovery valve passage 16e and the supply valve passage 16f associated with these spool displacements.

When the opening characteristic of the discharge valve passage 17d when the second boom control valve 17 is located at the lower-side operation position Y is shown in fig. 4B, the more the displacement amount of the spool is increased, the more the opening area of the discharge valve passage 17d is set to be increased. The discharge flow rate from the head-end oil chamber 8a to the oil tank 15 is controlled to increase or decrease in accordance with an increase or decrease in the opening area of the discharge valve passage 17 d.

On the other hand, in fig. 2 described above, reference numeral 28 denotes a lift-side solenoid valve for outputting pilot pressure to the lift- side pilot ports 16b and 17b of the first and second boom control valves 16 and 17; reference numeral 29 denotes a decrease-side solenoid valve for outputting the pilot pressure to the decrease- side pilot ports 16c and 17 c. These rise-side solenoid valve 28 and fall-side solenoid valve 29 operate based on a control signal from a controller 30 described below to output a pilot pressure of the pressure in response to the control signal. The spools of the first and second boom control valves 16 and 17 are displaced by the pilot pressures output from the lift-side and lower- side solenoid valves 28 and 29 to the lift-side and lower- side pilot ports 16b, 17b, 16c, and 17c, and the first and second boom control valves 16 and 17 are switched to be located at the lift-side operation position X and the lower-side operation position Y. In this case, the displacement amount of the spool is controlled to be increased or decreased according to an increase or decrease of the pilot pressure, and the first boom control valve 16 is set to be positioned at the first region Y1, if the pilot pressure output from the lower side solenoid valve 29 is less than the predetermined pilot pressure Pp, and if the pilot pressure is higher than or equal to the predetermined pilot pressure Pp, the pilot pressure is set to be positioned at the second region Y2.

Reference numeral 31 denotes a pressure sensor (corresponding to a pressure detecting device of the present invention) for detecting the pressure of the head end oil chamber 8a of the boom cylinder 8; an operation detecting device for detecting an operation of a boom operation lever (not shown) is indicated at 32. Detection signals of the pressure sensor 31 and the operation detection device 32 are input to the controller 30. Based on these input signals, the controller 30 outputs control signals to the raising-side solenoid valve 28 and the lowering-side solenoid valve 29, thereby controlling the switching operation of the first boom control valve 16 and the second boom control valve 17.

The controller 30 is connected with operation detection means for detecting operations of the operating appliances of the hydraulic actuators (left and right traveling motor, rotation motor, arm cylinder 9, bucket cylinder 10) other than the boom cylinder 8, respectively, and an electromagnetic valve; the solenoid valves output pilot pressures to respective hydraulic actuator control valves (a first control valve for left travel, for the bucket, for the stick, and a second control valve for right travel, for the rotation, for the sticks 18 to 23) in response to control signals output from the controller 30 in accordance with detection signals of these operation detecting means and the like, which are not shown in the drawings, and the description thereof will be omitted.

Next, the control of the first and second boom control valves 16 and 17 performed by the controller 30 will be discussed. When a boom-up operation signal is input from the operation detection device 32, the controller 30 outputs a control signal of a pilot pressure output to the lift-side solenoid valve 28. In this case, the controller 30 outputs a control signal such that the pilot is increased or decreased according to an increase or decrease in the operation amount of the boom manipulation lever. As a result, the pilot pressure is input to the lift- side pilot ports 16b and 17b of the first and second boom control valves 16 and 17, and both the first and second boom control valves 16 and 17 are switched to be positioned at the lift-side operation position X. As described above, the first boom control valve 16 at the lift-side operation position X allows the discharge oil of the first hydraulic pump 11 to be supplied to the head-end oil chamber 8a of the boom cylinder 8, and allows the oil discharged from the rod-end oil chamber 8b to flow into the oil tank 15. The second boom control valve 17 at the lift-side operation position X allows the discharge oil of the second hydraulic pump 12 to be supplied to the head-end oil chamber 8a of the boom cylinder 8.

When the boom-up operation is performed, the discharge oil of the first and second hydraulic pumps 11 and 12 is supplied to the head-end oil chamber 8a of the boom cylinder 8 via the first and second boom control valves 16 and 17 at the lift-side operation position X. In other words, when the boom is lifted, the discharge oil of both the first hydraulic pump 11 and the second hydraulic pump 12 is supplied to the head-end oil chamber 8a, so that even the lifting operation of the boom 5 to which the weight of the front working implement 4 is applied can be quickly performed.

On the other hand, when a boom-down operation signal is input from the operation detection device 32, the controller 30 determines whether the operation is a machine body lifting operation (an operation of lowering the boom 5 with respect to the machine body by lowering the boom 5 when the bucket 7 contacts the ground, thereby lifting a part of the machine body) based on the pressure of the head end oil chamber 8a of the boom cylinder 8 input from the pressure sensor 31. Further, the controller 30 determines whether the operation speed of the boom manipulation lever is equal to or higher than a set speed preset as an abrupt operation based on the operation signal input from the operation detecting device 32.

Here, whether the operation is the machine body lifting operation is determined according to the pressure value of the head end oil chamber 8a of the boom cylinder 8 input from the pressure sensor 31. In other words, when the boom 5 is lowered in the air (when the bucket 7 is not in contact with the ground), the pressure of the head end oil chamber 8a is high because the total weight of the front work implement 4 is applied to the pressurized oil in the head end oil chamber 8a of the boom cylinder 8. On the other hand, when the boom 5 is lowered while acting against the force by which the boom 5 is lowered by the bucket 7 contacting the ground or the like, tension is applied to the boom cylinder 8 so that the pressure of the head end oil chamber 8a is lower than that in the air for boom lowering. However, during the machine body lifting operation, the boom 5 is lowered while resisting the weight of the machine body, so that a strong tensile force acts on the boom cylinder 8, and therefore the pressure in the head end oil chamber 8a becomes lower. Therefore, when the pressure of the head end oil chamber 8a of the boom cylinder 8 has decreased to be less than the predetermined set pressure Ps, it is determined that the operation is the machine body lifting operation, and when the pressure is higher than the set pressure Ps, it is determined that the operation is not the machine body lifting operation.

When a boom-down operation signal is input from the operation detecting device 32, the controller 30 outputs a control signal of a pilot pressure output to the lower-side solenoid valve 29, thereby inputting the pilot pressure to the lower- side pilot ports 16c and 17c of the first and second boom control valves 16 and 17, and the first and second boom control valves 16 and 17 are switched to be located at the lower-side operation position Y. In this case, if it is determined that the pressure of the head end oil chamber 8a of the boom cylinder 8 is higher than or equal to the set pressure Ps (not the machine body lifting operation) and the operation speed of the boom operation lever is less than the set speed (not the sudden operation), the controller 30 outputs a control signal to output a pilot pressure less than the above-described predetermined pilot pressure Pp, that is, a pilot pressure (a pilot pressure at which the spool displacement amount is located at the first region Y1) for the pressure at which the first boom control valve 16 is located at the first region Y1, to the lowering side solenoid valve 29. In this case, the controller 30 controls the output pilot pressure from the lower-side solenoid valve 29 such that the spool displacement amount is increased or decreased in accordance with an increase or decrease in the operation amount of the boom operation lever in a range smaller than the predetermined pilot pressure Pp (in a range where the first boom control valve 16 is located in the first region Y1). As a result, the first boom control valve 16 is located at the first region Y1, thereby opening the recovery valve passage 16e that allows the oil discharged from the head-end oil chamber 8a to be supplied to the rod-end oil chamber 8b of the boom cylinder 8. In addition, the second boom control valve 17 is switched to be positioned at the lowering-side operation position Y, thereby opening the discharge valve passage 17d that allows the oil discharged from the head-end oil chamber 8a of the boom cylinder 8 to flow into the oil tank 15.

On the other hand, if it is determined that the pressure in the head end oil chamber 8a of the boom cylinder 8 is less than the set pressure Ps (machine body lifting operation) or the operation speed of the boom operating lever is equal to or higher than the set speed (sudden operation) when the signal of the boom lowering operation is input from the operation detecting device 32, then the controller 30 outputs a control signal to output a pilot pressure equal to or higher than a predetermined pilot pressure Pp, that is, a pilot pressure (pilot pressure when the spool displacement amount enters the second region Y2) for the pressure at which the first boom control valve 16 is positioned at the second region Y2, to the lowering side solenoid valve 29. In this case, the controller 30 controls the output pilot pressure from the lower-side solenoid valve 29 such that the spool displacement amount is increased or decreased in accordance with an increase or decrease in the operation amount of the boom operation lever in a range equal to or higher than the predetermined pilot pressure Pp (in a range where the first boom control valve 16 is located at the second region Y2). Therefore, the first boom control valve 16 is located at the second region Y2, and the recovery valve passage 16e that allows the oil discharged from the head-end oil chamber 8a to be supplied to the rod-end oil chamber 8b of the boom cylinder 8 is opened wider than the first region Y1, and the supply valve passage 16f that supplies the discharge oil of the first hydraulic pump 11 to the rod-end oil chamber 8b is opened. The second boom control valve 17 opens the discharge valve passage 17d, allowing the oil discharged from the head end oil chamber 8a of the boom cylinder 8 to flow into the oil tank 15, but the opening area of the discharge valve passage 17d becomes larger than when the output pilot pressure from the lowering side solenoid valve 29 is smaller than the predetermined pilot pressure Pp.

Therefore, when the boom-down operation is performed, if the boom cylinder 8 is not operated to lift the machine body (the pressure in the head-end oil chamber 8a of the boom cylinder 8 is equal to or higher than the set pressure Ps), and the boom operation lever is not operated suddenly, the oil discharged from the head-end oil chamber 8a of the boom cylinder 8 is supplied as recovered oil to the rod-end oil chamber 8b via the first boom control valve 16 at the first region Y1 of the lowering-side operation position Y, and the remaining oil discharged from the head-end oil chamber 8a is discharged to the oil tank 15 via the second boom control valve 17 at the lowering-side operation position Y. Therefore, the boom 5 is lowered using only the recovered oil from the head-end oil chamber 8a to the rod-end oil chamber 8b without using the discharge oil of the first hydraulic pump 11 and the second hydraulic pump 12, so that it is possible to contribute to improvement of energy efficiency. It should be noted that the boom cylinder 8 allows only the discharge amount from the head-end oil chamber 8a to cover the supply amount to the rod-end oil chamber 8b at the time of contraction (at the time of boom lowering), and the supply amount from the head-end oil chamber 8a is about twice as large as that from the rod-end oil chamber 8b due to the relationship of the pressure receiving area acting on the piston, and therefore a redundant portion will be generated.

On the other hand, when the boom-down operation is performed, if it is a machine body lifting operation (the pressure of the head-end oil chamber 8a of the boom cylinder 8 is less than the set pressure Ps) or if it is a boom operation lever suddenly operated, then the oil discharged from the head-end oil chamber 8a of the boom cylinder 8 is supplied to the rod-end oil chamber 8b via the first boom control valve 16 at the second region Y2 of the lowering side operation position Y (when the head-end oil chamber 8a is higher than the pressure of the rod-end oil chamber 8 b), and while the discharged oil from the first hydraulic pump 11 is supplied to the head-end oil chamber 8b, the remaining oil discharged from the head-end oil chamber 8a is discharged to the oil tank 15 at the lowering side boom operation position Y via the second boom control valve 17. Therefore, the discharge oil of the first hydraulic pump 11 is supplied to the rod-end oil chamber 8b of the boom cylinder 8, so that the machine body lifting operation for lowering the boom 5 while resisting the weight of the machine body can be smoothly performed. In addition, even if the boom manipulating lever is suddenly manipulated, the boom 5 can be quickly lowered in response without delay.

In the first embodiment, an oil passage extending from the head-end oil chamber 8a of the boom cylinder 8 to the rod-end oil chamber 8b that passes through the recovery valve passage 16e of the first boom control valve 16 is used as the recovery oil passage of the invention. An oil passage extending from the first hydraulic pump 11 to the rod-end oil chamber 8b of the boom cylinder 8 through the supply valve passage 16f of the first boom control valve 16 serves as a supply oil passage of the present invention. An oil passage extending from the head-end oil chamber 8a of the boom cylinder 8 to the oil tank 15 through the discharge valve passage 17d of the second boom control valve 17 serves as a discharge oil passage of the present invention. Further, in the first embodiment, the first hydraulic pump 11 corresponds to a hydraulic pump of the present invention.

In the first embodiment configured as described above, the vertical movement of the boom 5 is performed based on the telescopic operation of the boom cylinder 8, and the hydraulic circuit of the boom cylinder 8 includes the recovery oil passage that allows the oil discharged from the head-end oil chamber 8a to be supplied to the rod-end oil chamber 8b of the boom cylinder 8; the discharge oil passage allows oil discharged from the head-end oil chamber 8a of the boom cylinder 8 to flow into the oil tank 15, and the supply oil passage allows the discharged oil of the first hydraulic pump 11 to be supplied to the rod-end oil chamber 7 b. In the hydraulic circuit, when the supply valve passage 16f for controlling the flow rate of the supply flow passage is provided, a pressure sensor (pressure detection device) 31 for detecting the pressure of the head end oil chamber 8a is provided in the first boom control valve 16 for controlling the flow rate of the recovery oil passage; an operation detection device 32 for detecting an operation of the boom 5; and a controller 30 for providing a control signal for controlling the first boom control valve 16 based on input signals from the pressure sensor 31 and the operation detecting device 32, and the first boom control valve 16 includes a lowering-side operation position Y at the time of lowering the boom 5, which includes a first region Y1 where the supply valve passage 16f is closed and a second region Y2 where the supply valve passage 16f is open. The controller 30 determines whether the operation is a machine body lifting operation for lifting a part of the machine body according to the pressure of the head end oil chamber 8a during the lowering operation of the boom 5. If it is determined that the operation is not a machine body lifting operation, the first boom control valve 16 is located at the first region Y1, and if it is determined that the machine body lifting operation, the first boom control valve 16 is located at the second region Y2.

As a result, in the case where the machine body lifting operation is not performed during the lowering operation of the boom 5, the first boom control valve 16 is located at the first region Y1, and the supply valve passage 16f is closed. Therefore, only the recovered oil from the head-end oil chamber 8a is allowed to be used, and the discharged oil of the first hydraulic pump 11 is not allowed to be used, for supplying the pressurized oil to the rod-end oil chamber 8b of the boom cylinder 8, thereby contributing to improvement of energy efficiency, and to interlocking operability between the boom cylinder 8 and other hydraulic actuators (e.g., the arm cylinder 9 and the bucket cylinder 10) having the same pressurized oil supply source as the boom cylinder 8. On the other hand, when the lowering operation of the boom 5 is the machine body lifting operation, the first boom control valve 16 is located at the second region Y2 and will open the supply valve passage 16 f. Therefore, the discharge oil of the first hydraulic pump 11 will be supplied to the rod-end oil chamber 8a of the boom cylinder 8, so that the machine body lifting operation can be smoothly performed while resisting the machine body weight.

Further, in this hydraulic control circuit, when switching between the case of supplying the discharge oil of the first hydraulic pump 11 to the rod-end oil chamber 8b of the boom cylinder 8 and the case of not supplying the discharge oil of the first hydraulic pump 11, it is configured such that the first region Y1 and the second region Y2 are provided in the lowering-side operation position Y of the first boom control valve 16 for controlling the flow rate of the recovery oil passage during the boom lowering operation, and the supply valve passage 16f is closed at the first region Y1 and the supply valve passage 16f is open at the second region Y2. By using the first boom control valve 16 necessary to control the recovery flow rate when the boom 5 is lowered, it is possible to switch between a case where the oil discharged from the first hydraulic pump 11 is supplied to the rod-end oil chamber 8b and a case where the oil discharged from the first hydraulic pump 11 is not supplied. As a result, a dedicated valve for performing switching, a solenoid valve for operating the valve, and the like are not required, so that it is possible to contribute to a reduction in the number of parts and to a cost or space saving.

Further, in this hydraulic control circuit, the controller 30 is configured such that, when the boom lowering operation is an abrupt operation, the first boom control valve 16 is positioned at the second region Y2 regardless of whether the operation is a machine body lifting operation, and the discharge oil of the first hydraulic pump 11 is supplied to the rod-end oil chamber 8b of the boom cylinder 8, and therefore, the responsiveness to the abrupt operation also becomes excellent.

In the first embodiment, as described above, two hydraulic pumps of the first hydraulic pump 11 and the second hydraulic pump 12 are provided as pressurized oil supply sources of the boom cylinder 8 and the aforementioned first boom control valve 16 and second boom control valve 17, which are switched together to be located at the lift-side position X when the boom-up operation is performed, and the discharge oils of the first hydraulic pump 11 and the second hydraulic pump 12 are supplied to the head-end oil chambers 8a of the boom cylinder 8, respectively.

Next, a second embodiment of the present invention will be discussed with reference to fig. 5 to 7. Fig. 5 shows a hydraulic control circuit diagram of the boom cylinder 8 of the second embodiment. The components in the second embodiment are the same as those in the first embodiment except for the first and second boom control valves 34 and 35, and thus the same reference numerals will be given thereto, and the description thereof will be omitted.

The first boom control valve 34 of the second embodiment described above is a three-position switching spool including the raising-side and lowering- side pilot ports 34b and 34 c. The first boom control valve 34 is configured to be positioned at a neutral position N where supply and discharge of pressurized oil to the boom cylinder 8 are not performed in a state where the pilot pressure is not input to both of the pilot ports 34b and 34c, and to be switched to be positioned at a lift-side operation position X when the pilot pressure is input to the lift-side pilot port 34b, to supply the discharge oil of the first hydraulic pump 11 to the head-end oil chamber 8a of the boom cylinder 8, and to allow the oil discharged from the rod-end oil chamber 8b to flow into the oil tank 15. The first boom control valve 34 is configured to switch to be positioned at the lowering-side operation position Y when the pilot pressure is input to the lowering-side pilot port 34c, but in a state of being positioned at the lowering-side operation position Y, open a recovery valve passage 34e (see fig. 6A) for supplying the oil discharged from the head-end oil chamber 8a of the boom cylinder 8 to the rod-end oil chamber 8b via a check valve 34 d.

The second boom control valve 35 of the second embodiment is a four-position switching spool including the raising-side and lowering- side pilot ports 35b and 35 c. In a state where the pilot pressure is not input to the two pilot ports 35b and 35c, the second boom control valve 35 is positioned at the neutral position N where the supply and discharge of the pressurized oil to the boom cylinder 8 are not performed, but is switched to be positioned at the raising-side operation position X when the pilot pressure is input to the raising-side pilot port 35b, and the discharge oil of the second hydraulic pump 12 is supplied to the head-end oil chamber 8a of the boom cylinder 8. Further, when the pilot pressure is input to the lower side pilot port 35c, the second boom control valve 35 is switched to be located at the lower side operation position Y, but the first region Y1 and the second region Y2 are provided in the lower side operation position Y. In this case, the second region Y2 is provided at a position where the displacement amount from the neutral position N is larger than the displacement amount of the first region Y1. Then, in the state of being located in the first region Y1, the discharge valve passage 35d that allows the oil discharged from the head-end oil chamber 8a of the boom cylinder 8 to flow into the oil tank 15 is opened, and on the other hand, the supply valve passage 35e for supplying the oil discharged from the second hydraulic pump 12 to the rod-end oil chamber 8B is closed (see fig. 6B). Further, the second boom control valve 35 is configured to open the discharge valve passage 35d in a state of being positioned at the second region Y2, the discharge valve passage 35d allows the oil discharged from the head-end oil chamber 8a of the boom cylinder 8 to flow into the oil tank 15, and the supply valve passage 35e allows the discharge oil of the second hydraulic pump 12 to be supplied to the rod-end oil chamber 8b (see fig. 6C).

In the second embodiment, the second boom control valve 35 corresponds to a boom control valve of the present invention, but the first boom control valve does not correspond to a boom control valve of the present invention. In fig. 5 and 6 described above, reference numerals 34a and 35a denote central bypass valve passages formed in the first and second boom control valves 34 and 35, respectively. In fig. 6, the oil passages connected to these central bypass valve passages 34a and 35a will be omitted.

Here, the opening characteristic of the recovery valve passage 34e when the first boom control valve 34 is located at the lower side operation position Y is shown in fig. 7A. The more the spool displacement amount increases, the more the opening area of the recovery valve passage 34e is set to increase. In response to an increase or decrease in the opening area of the recovery valve passage 34e, the recovery flow rate from the head-end oil chamber 8a to the rod-end oil chamber 8b is controlled to increase or decrease.

Further, the opening characteristics of the discharge valve passage 35d and the supply valve passage 35e when the second boom control valve 35 is located at the first region Y1 and the second region Y2 of the lowered side operation position Y are shown in fig. 7B. As shown in fig. 7B, at the first region Y1, only the discharge valve passage 35d is opened, and the more the spool displacement amount increases, the more the opening area is set to increase. Further, when the spool is further displaced beyond the first region Y1 to reach the second region Y2, the opening area of the discharge valve passage 35d becomes larger and the supply valve passage 35e is opened, but the more the spool displacement amount increases, the more the opening area of the supply valve passage 35e is set to increase. The discharge flow rate from the head-end oil chamber 8a to the tank 15 and the discharge flow rate from the second hydraulic pump 12 to the rod-end oil chamber 8b are controlled to increase or decrease in accordance with the increase or decrease in the opening areas of the discharge valve passage 35d and the supply valve passage 35e associated with these spool displacements.

Then, similar to the first embodiment, the first and second boom control valves 34 and 35 are controlled based on the control signal output from the controller 30, but when a signal of a boom-up operation is input from the operation detecting device 32, the controller 30 outputs a control signal of a pilot pressure output to the lift-side solenoid valve 28. Therefore, both the first and second boom control valves 34 and 35 are switched to be positioned at the raising-side operation position X, and the discharge oil of both the first and second hydraulic pumps 11 and 12 is supplied to the head-end oil chamber 8a, similarly to the first embodiment.

On the other hand, when a signal of a boom-down operation is input from the operation detecting device 32, the controller 30 determines whether the operation is a machine body lifting operation, and determines whether the boom-down operation is an abrupt operation, similarly to the first embodiment. If it is determined that the operation is neither a machine body lifting operation nor a sudden operation, the controller 30 outputs a control signal to output a pilot pressure equal to or higher than a predetermined pilot pressure Pp, that is, a pilot pressure for locating the second boom control valve 35 in the first region Y1 toward the lower side solenoid valve 29 (a pilot pressure at which the spool displacement amount enters the first region Y1). Therefore, the second boom control valve 35 located in the first region Y1 opens the discharge valve passage 35d, and the discharge valve passage 35d allows the oil discharged from the head end oil chamber 8a of the boom cylinder 8 to flow into the oil tank 15. The first boom control valve 34 is located at the lowering side operation position Y to open the recovery valve passage 34e that supplies the oil discharged from the head-end oil chamber 8a of the boom cylinder 8 to the rod-end oil chamber 8 b.

In contrast, when a signal of a boom-down operation is input from the operation detecting device 32, if it is determined that the operation is a machine body lifting operation or a sudden operation, the controller 30 outputs a control signal to output a pilot pressure equal to or higher than the predetermined pilot pressure Pp, that is, a pilot pressure for allowing the second boom control valve 35 to be positioned at the second region Y2 toward the lower side solenoid valve 29 (a pilot pressure at which the spool displacement amount enters the second region Y2). Therefore, the second boom control valve 35 is located at the second region Y2 and is opened wider than at the first region Y1, allowing the oil discharged from the head-end oil chamber 8a of the boom cylinder 8 to flow into the discharge valve passage 35d of the oil tank 15, opening the supply valve passage 35e, and the supply valve passage 35e allowing the discharge oil of the second hydraulic pump 12 to be supplied to the rod-end oil chamber 8 b. The first boom control valve 34 is located at the lowering side operation position Y to open the recovery valve passage 34e that allows the oil discharged from the head end oil chamber 8a to be supplied to the rod end oil chamber 8b of the boom cylinder 8, but the opening area of the recovery valve passage 34e becomes larger than that in the case where the output pilot pressure from the lowering side solenoid valve 29 is smaller than the predetermined pilot pressure Pp.

Therefore, when the boom-down operation is performed, if the operation is not the machine body lifting operation and the boom manipulation lever is not suddenly operated, the oil discharged from the head-end oil chamber 8a of the boom cylinder 8 is supplied as the recovered oil to the rod-end oil chamber 8b via the first boom control valve 34 at the lowering-side operation position Y, and the remaining oil discharged from the head-end oil chamber 8a is discharged to the oil tank 15 via the second boom control valve 35 at the first region in the lowering-side operation position Y. On the other hand, when the boom-down operation is performed, if the operation is the machine body lifting operation or the abrupt operation, the oil discharged from the head-end oil chamber 8a of the boom cylinder 8 is supplied to the rod-end oil chamber 8b via the first boom control valve 34 at the lowering-side operation position Y, and the discharged oil from the second hydraulic pump 12 is supplied to the rod-end oil chamber 8b via the second boom control valve 35 at the second region Y2 in the lowering-side operation position Y. Further, in the lowering-side operation position Y, the surplus oil discharged from the head end oil chamber 8a is discharged to the tank 15 via the second boom control valve 35 at the second region Y2.

In the second embodiment, an oil passage extending from the head-end oil chamber 8a of the boom cylinder 8 to the rod-end oil chamber 8b that passes through the recovery valve passage 34e of the first boom control valve 34 is used as the recovery oil passage of the invention. Further, an oil passage extending from the second hydraulic pump 12 to the rod-end oil chamber 8b of the boom cylinder 8 through the supply valve passage 35e of the second boom control valve 35 serves as a supply oil passage of the present invention. Further, an oil passage extending from the head-end oil chamber 8a of the boom cylinder 8 to the oil tank 15 through the discharge valve passage 35d of the second boom control valve 35 serves as a discharge oil passage of the present invention. Further, in the second embodiment, the second hydraulic pump 12 corresponds to a hydraulic pump of the present invention.

Further, in the hydraulic control circuit of the second embodiment constructed as described above, similarly to the above-described first embodiment, when the lowering operation of the boom 5 is neither the machine body lifting operation nor the sudden operation, only the recovered oil from the head-end oil chamber 8a is used to supply the pressurized oil to the rod-end oil chamber 8b of the boom cylinder 8. On the other hand, when the lowering operation of the boom 5 is the machine body lifting operation or the abrupt operation, the discharge oil of the second hydraulic pump 12 is supplied to the rod-end oil chamber 8b in addition to the recovery of the oil from the head-end oil chamber 8a, and therefore the same operational effect as the first embodiment is exhibited. However, in the hydraulic control circuit of the second embodiment, configured to allow switching between the case where the discharge oil of the second hydraulic pump 12 is supplied to the rod-end oil chamber 8b and the case where the discharge oil of the second hydraulic pump 12 is not supplied to the rod-end oil chamber 8b, which is performed by setting the first region Y1 and the second region Y2 at the lowering-side operation position Y of the second boom control valve 35, the second boom control valve 35 controls the flow rate of the discharge oil path when the boom 5 is lowered. Therefore, also in the hydraulic control circuit of the second embodiment, a dedicated valve for performing switching, an electromagnetic valve for operating the valve, and the like are not required, so that it is possible to contribute to a reduction in the number of components and to a saving in cost and space.

Next, a third embodiment of the present invention will be discussed with reference to fig. 8 and 9. Fig. 8 shows a hydraulic control circuit diagram of the boom cylinder 8 of the third embodiment. However, in the third embodiment, only one hydraulic pump 36 is used as the hydraulic pressure supply source of the boom cylinder 8. A boom control valve 38 for controlling supply and discharge of oil to and from the boom cylinder 8 is connected to the pump oil passage 37, and the discharge oil of the hydraulic pump 36 is supplied to the pump oil passage 37.

In fig. 8, reference numerals 39 to 43 denote for left and right travel, respectively; for rotation; for a stick; and a control valve of the bucket for performing control of supplying and discharging oil to and from the left and right traveling motors, the rotating motor, the arm cylinder 9, and the bucket cylinder 10. Reference numeral 44 denotes a center bypass control valve 44 for controlling the flow rate of the center bypass oil passage 45, but the description thereof will be omitted. In the third embodiment, the same reference numerals are assigned to parts similar to those in the first embodiment, and thus the description thereof will be omitted.

The boom control valve 38 of the third embodiment is a four-position switching spool that includes the raising-side and lowering- side pilot ports 38b and 38 c. In a state where the pilot pressure is input to the two pilot ports 38b and 38c, the boom control valve 38 is configured to be positioned at the neutral position N where the supply of the pressurized oil to the boom cylinder 8 and the discharge of the pressurized oil from the boom cylinder 8 are not performed, but to be positioned at the raising-side operation position X when the pilot pressure is input to the raising-side pilot port 38b, and to supply the discharge oil of the hydraulic pump 36 to the head-end oil chamber 8a of the boom cylinder 8, and to allow the oil discharged from the rod-end oil chamber 8b to flow into the oil tank 15. Further, when the pilot pressure is input to the lower side pilot port 38c, the boom control valve 38 is switched to be located at the lower side operation position Y, but the first region Y1 and the second region Y2 are provided in the lower side operation position Y. In this case, the second region Y2 is provided at a position where the displacement amount from the neutral position N is larger than the displacement amount provided at the first region Y1. The boom control valve 38 opens the recovery valve passage 38e in the state of being located in the first region Y1, the recovery valve passage 38e allows the oil discharged from the head-end oil chamber 8a to be supplied to the rod-end oil chamber 8b of the boom cylinder 8 via the check valve 38d, and opens the discharge valve passage 38a to flow the surplus oil discharged from the head-end oil chamber 8a into the oil tank 15, while closing the supply valve passage 38g that supplies the discharged oil of the hydraulic pump 36 to the rod-end oil chamber 8b (see fig. 9A). Further, the boom control valve 38 is configured to open the recovery valve passage 38e and the discharge valve passage 38f in a state of being positioned at the second region Y2, the recovery valve passage 38e allowing the oil discharged from the head-end oil chamber 8a to be supplied to the rod-end oil chamber 8b via the check valve 38 d; the discharge valve passage 38f allows the remaining oil discharged from the head-end oil chamber 8a to flow into the oil tank 15, and opens the supply valve passage 38g, which allows the oil discharged from the hydraulic pump 36 to be supplied to the rod-end oil chamber 8B (see fig. 9B).

In fig. 8 and 9 described above, reference numeral 38a denotes a central bypass valve passage formed in the boom control valve 38. In fig. 9, the oil passage connected to the central bypass valve passage 38a is omitted.

Here, the opening characteristics of the recovery valve passage 38e, the discharge valve passage 38f, and the supply valve passage 38g when the boom control valve 38 is located at the first region Y1 and the second region Y2 of the lowering-side operation position Y are shown in fig. 10. As shown in fig. 10, in the first region Y1, the recovery valve passage 38e and the discharge valve passage 38f are opened, and the more the spool displacement amount increases, the more the opening area is set to increase. When the spool is further displaced beyond the first region Y1 to reach the second region Y2, the opening areas of the recovery valve passage 38e and the discharge valve passage 38f still increase, and the supply valve passage 38g opens, but the more the spool displacement amount increases, the more the opening area of the supply valve passage 38g is set to increase. The increase or decrease of the recovery flow rate from the head-end oil chamber 8a to the rod-end oil chamber 8b, the discharge flow rate from the side oil chamber 8a to the oil tank 15, and the supply flow rate from the hydraulic pump 36 to the rod-end oil chamber 8b are performed in accordance with the increase or decrease of the opening areas of the recovery valve passage 38e, the discharge valve passage 38f, and the supply valve passage 38g associated with these spool displacements.

Similar to the first and second embodiments, the boom control valve 38 is controlled based on the control signal output from the controller 30. However, when a signal of a boom-up operation is input from the operation detecting device 32, the controller 30 outputs a control signal of the pilot pressure output from the lift-side solenoid valve 28. Therefore, the boom control valve 38 is switched to be located at the raising-side operation position X, and the discharge oil of the hydraulic pump 36 is supplied to the head-end oil chamber 8 a.

On the other hand, when a signal of a boom-down operation is input from the operation detecting device 32, the controller 30 determines whether the operation is a machine body lifting operation and determines whether the boom-down operation is an abrupt operation, similarly to the first and second embodiments. If it is determined that neither the machine body lifting operation nor the abrupt operation is performed, the controller 30 outputs a control signal to output a pilot pressure that is a pressure less than the predetermined pilot pressure Pp, that is, a pilot pressure for positioning the boom control valve 38 at the first region Y1 toward the reduction-side solenoid valve 29 (a pilot pressure at which the spool displacement amount enters the first region Y1). Therefore, the boom control valve 38 is located in the first region Y1 to open the recovery valve passage 38e that allows the oil discharged from the head-end oil chamber 8a to be supplied to the rod-end oil chamber 8b of the boom cylinder 8, and the discharge valve passage 38f that allows the oil discharged from the head-end oil chamber 8a to flow into the oil tank 15.

In contrast, when a signal for a boom-down operation is input from the operation detecting device 32, if it is determined as a machine body lifting operation or a sudden operation, the controller 30 outputs a control signal to output a pilot pressure equal to or higher than a predetermined pilot pressure Pp, that is, a pilot pressure for shifting the pressure at which the boom control valve 38 is located at the second region Y2 to the lowering-side solenoid valve 29 (a pilot pressure at which the spool displacement amount enters the second region Y2). Therefore, the boom control valve 38 is located in the second region Y2 and is opened wider than the first region Y1, the recovery valve passage 38e allows the oil discharged from the head-end oil chamber 8a to be supplied to the rod-end oil chamber 8b of the boom cylinder 8, the discharge valve passage 38f allows the oil discharged from the head-end oil chamber 8a to flow into the oil tank 15, and the supply valve passage 38g is opened, the supply valve passage 38g allows the discharge oil of the hydraulic pump 36 to be supplied to the rod-end oil chamber 8 b.

When the boom lowering operation is performed, if the operation is not the machine body lifting operation and the boom operation lever is not suddenly operated, the oil discharged from the head-end oil chamber 8a of the boom cylinder 8 is supplied as the recovered oil to the rod-end oil chamber 8b via the boom control valve 38 at the first region Y1 in the lowering-side operation position Y, and the remaining oil discharged from the head-end oil chamber 8a is discharged into the oil tank 15. On the other hand, when the boom-down operation is performed, if the operation is a machine body lifting operation or an abrupt operation, the oil discharged from the head-end oil chamber 8a of the boom cylinder 8 is supplied to the rod-end oil chamber 8b via the boom control valve 38 at the second region Y2 in the lowering-side operation position Y, and further the discharged oil from the hydraulic pump 36 is supplied to the rod-end oil chamber 8b, and the remaining oil discharged from the head-end oil chamber 8a is discharged to the oil tank 15.

In the third embodiment, an oil passage extending from the head-end oil chamber 8a of the boom cylinder 8 to the rod-end oil chamber 8b through the recovery valve passage 38e of the boom control valve 38 serves as a recovery oil passage of the invention; and an oil passage extending from the hydraulic pump 36 to the rod-end oil chamber 8b of the boom cylinder 8 through the supply valve passage 38g of the boom control valve 38 serves as a supply oil passage of the invention; and an oil passage extending from the head end oil chamber 8a of the boom cylinder 8 to the oil tank 15 through the discharge valve passage 38f of the boom control valve 38 serves as a discharge oil passage of the present invention.

Further, in the hydraulic control circuit of the third embodiment constructed as described above, similarly to the first and second embodiments described above, if the lowering operation of the boom 5 is neither the machine body lifting operation nor the sudden operation, only the recovered oil from the head-end oil chamber 8a is used to supply the pressurized oil to the rod-end oil chamber 8b of the boom cylinder 8. On the other hand, if the operation is a machine body lifting operation or an abrupt operation, the discharge oil of the hydraulic pump 36 is supplied to the rod-end oil chamber 8b in addition to the recovery of the oil from the head-end oil chamber 8a, and therefore, the similar action and effect to those of the first and second embodiments are exhibited.

However, in the hydraulic control circuit of the third embodiment, by providing two regions in the first region Y1 and the second region Y2 in the lowering-side operation position Y of the boom control valve 38, switching between supply of the discharge oil of the hydraulic pump 36 to the rod-end oil chamber 8b and non-supply of the discharge oil of the hydraulic pump 36 to the rod-end oil chamber 8b is performed for controlling the flow rates of the recovery oil passage and the supply oil passage during the lowering operation of the boom 5. Therefore, in the hydraulic control circuit of the third embodiment, a dedicated valve for performing the above switching, a solenoid valve for operating the valve, and the like are also not required, thereby contributing to a reduction in the number of components and to cost and space savings.

It goes without saying that the present invention is not limited to the first to third embodiments. For example, the first boom control valve 16, the second boom control valve 17, the first boom control valve 34, the second boom control valve 35, and the boom control valve 38 provided in the first to third embodiments are all pilot operation spools switched according to pilot pressure, but these control valves may also be configured by using an electromagnetic proportional type spool in which a control signal from a controller is directly input.

Further, in the first and second embodiments, the first and second boom control valves 16 and 17 (or 34 and 35) are provided as control valves for controlling the supply of oil to the boom cylinder 8 and the discharge of oil from the boom cylinder 8, and are configured such that pilot pressures are output from the common raising-side, lowering- side solenoid valves 28 and 29 to the raising-side, lowering- side pilot ports 16b, 16c, 17b, 17c (or 34b, 34c, 35b, 35c) of the first and second control valves 16, 17 (or 34, 35). However, in the case where a plurality of boom control valves are provided in this manner, it may be configured to provide a raising-side, lowering-side solenoid valve individually for each control valve.

In the first to third embodiments, when it is determined whether the operation is the machine body lifting operation according to the pressure of the head end oil chamber during the boom lowering operation, the operation is determined according to the pressure value of the head end oil chamber of the boom cylinder. However, it may be configured to detect not only the pressure in the head-end oil chamber but also the pressure in the rod-end oil chamber, and determine whether the operation is a machine body lifting operation from the pressure difference between the two oil chambers.

Further, it is needless to say that the present invention can be applied not only to a hydraulic excavator but also to various construction machines equipped with a boom.

Industrial applicability

The present invention may be applied to a boom control system of a construction machine such as a hydraulic excavator equipped with a boom.

List of reference numerals

5 Movable arm

8 swing arm cylinder

8a head end oil chamber

8b rod end oil chamber

11 first hydraulic pump

12 second hydraulic pump

15 oil tank

16 first boom control valve

16e recovery valve passage

16f supply valve passage

30 controller

31 pressure sensor

32 operation detection device

35 second boom control valve

35d discharge valve passage

35e supply valve passage

36 hydraulic pump

38 boom control valve

38e recovery valve passage

38f discharge valve passage

38g supply valve passage

First region of Y1

Second region of Y2