Construction machinery

Abstract

The present invention provides a construction machine that can improve work efficiency by assisting the upward movement of the boom when moving a work tool along the ground using a float function. [Solution] The shovel 1 includes a float valve 22A provided in an oil passage 21A connecting the rod side of the boom cylinder 10 and the hydraulic oil tank 18, a float valve 22B provided in an oil passage 21B connecting the bottom side of the boom cylinder 10 and the hydraulic oil tank 18, an auxiliary valve 26 provided in an auxiliary oil passage 25 for extending the boom cylinder 10, and a control device 23. When the float function is effectively switched on by the float function switching device 20 and the arm 8 is instructed to be pushed out by the operating device 16B, the control device 23 performs auxiliary control to open the float valve 22A, close the float valve 22B, and open the auxiliary valve 26 according to the posture of the arm 8 detected by the arm posture sensor 24.

Description

Technical Field

[0001] The present invention relates to a construction machine having a float function.

Background Art

[0002] A construction machine such as an excavator includes a vehicle body, a boom rotatably connected to the vehicle body with the horizontal direction as a rotation axis, an arm rotatably connected to the boom with the horizontal direction as a rotation axis, a work tool connected to the distal end side of the arm, a boom cylinder that lowers the boom by contraction and raises the boom by extension, an arm cylinder that rotates the arm, and an arm operation device for instructing the operation (specifically, pushing out or retracting) of the arm.

[0003] Patent Document 1 discloses a float function mounted on the above-described construction machine. The construction machine of Patent Document 1 includes a float function switch that switches the float function on and off, and a float valve that communicates the rod side and the bottom side of the boom cylinder with a tank when the float function is switched on by the float function switch. By communicating the rod side and the bottom side of the boom cylinder with the tank, the boom enters a float state (a state operable by an external force).

[0004] When the boom is in the float state, the boom descends due to its own weight and the weights of the arm and the work tool, and the work tool comes into contact with the ground. Then, when the operator operates the arm operation device to push out or retract the arm, the boom rises or descends so that the work tool moves along the ground. Thereby, for example, if the work tool is a bucket, leveling work using the bucket can be easily performed.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

[0006] However, the above-mentioned conventional technology has room for improvement as follows. For example, when extending the arm from a retracted position using the float function, the arm cylinder requires a large driving force to not only extend the arm but also to raise the boom. Therefore, if the driving force of the arm cylinder is insufficient, the boom may not rise sufficiently, and the arm may not be able to be extended. As a result, even when the float function is operating, leveling work cannot be performed by arm operation alone, which may reduce work efficiency.

[0007] The present invention has been made in view of the above, and its purpose is to provide a construction machine that can improve work efficiency by assisting the upward movement of the boom when moving a work tool along the ground using a float function. [Means for solving the problem]

[0008] To achieve the above objective, the present invention provides a vehicle body, a boom rotatably connected to the vehicle body with the horizontal direction as the axis of rotation, an arm rotatably connected to the boom with the horizontal direction as the axis of rotation, a work tool connected to the tip of the arm, a boom cylinder that lowers the boom by retracting and raises the boom by extending, an arm cylinder that rotates the arm, an arm operating device for instructing the movement of the arm, a float function switching device for switching the float function on and off, a first float valve provided in an oil passage connecting the rod side of the boom cylinder and the hydraulic oil tank, and the bottom side of the boom cylinder and the hydraulic oil tank In a construction machine comprising a second float valve provided in an oil passage connecting the floats, and a control device that controls the first and second float valves in accordance with the switching of the float function switching device, the machine further comprises an arm attitude sensor for detecting the attitude of the arm, and an auxiliary valve provided in an auxiliary oil passage for extending the boom cylinder, wherein when the float function is effectively switched on by the float function switching device and the arm operation device instructs the arm to be pushed out, the control device performs corrective control to open the first float valve, close the second float valve, and open the auxiliary valve, according to the attitude of the arm detected by the arm attitude sensor. [Effects of the Invention]

[0009] According to the present invention, when using the float function to move a work tool along the ground or the like, the boom's upward movement can be assisted to improve work efficiency. [Brief explanation of the drawing]

[0010] [Figure 1] This figure shows the configuration of the excavator drive system in the first embodiment of the present invention, along with the external structure of the excavator. [Figure 2] This figure illustrates a predetermined angle that serves as a criterion for determining the rotation angle of the arm in the first embodiment of the present invention. [Figure 3] This diagram illustrates the force required to raise the boom during the arm extension operation in the first embodiment of the present invention. [Figure 4] This is a flowchart illustrating the processing content of the control device in the first embodiment of the present invention. [Figure 5] This figure shows the configuration of the excavator drive system in a second embodiment of the present invention, along with the external structure of the excavator. [Figure 6] This is a flowchart illustrating the processing content of the control device in the second embodiment of the present invention. [Figure 7] This figure shows the characteristics of the pressure threshold, which is the criterion for determining the bottom pressure of the boom cylinder in the first modified example of the present invention. [Figure 8] This figure shows the characteristics of the opening degree of the auxiliary valve in a second modified example of the present invention. [Figure 9] This figure shows the configuration of the drive system of the shovel in a third modified example of the present invention, along with the external structure of the shovel. [Figure 10] This figure shows the configuration of the drive system for the shovel in a fourth modified example of the present invention, along with the external structure of the shovel. [Modes for carrying out the invention]

[0011] A first embodiment of the present invention will be described with reference to the drawings.

[0012] Figure 1 shows the configuration of the excavator drive system in this embodiment, along with the external structure of the excavator. In Figure 1 (and in Figures 5, 9, and 10 described later), the configuration of the excavator drive system shows only those related to the driving of the boom cylinder and arm cylinder, and omits those related to the driving of other hydraulic actuators.

[0013] Excavator 1 (construction machine) comprises a movable undercarriage 2 and a slewing body 3 that is rotatably mounted above the undercarriage 2, with the undercarriage 2 and slewing body 3 constituting the vehicle body. The undercarriage 2 moves by the drive of left and right undercarriage motors (not shown), and the slewing body 3 rotates by the drive of a slewing motor (not shown). The slewing body 3 has a machine room 4 and an operator's cab 5.

[0014] The shovel 1 includes a work device 6 coupled to a revolving structure 3. The work device 6 includes a boom 7 rotatably coupled to the revolving structure 3 with the horizontal direction as the rotation axis, an arm 8 rotatably coupled to the boom 7 with the horizontal direction as the rotation axis, and a work tool 9 (for example, the illustrated bucket) rotatably coupled to the distal end side of the arm 8 with the horizontal direction as the rotation axis. The boom 7 is rotated by the drive of a boom cylinder 10, the arm 8 is rotated by the drive of an arm cylinder 11, and the work tool 9 is rotated by the drive of a work tool cylinder 12.

[0015] The shovel 1 includes a drive system 13 that drives a plurality of hydraulic actuators (specifically, the traveling motor, revolving motor, boom cylinder 10, arm cylinder 11, and work tool cylinder 12 described above).

[0016] The drive system 13 of the shovel 1 includes a prime mover 14 (for example, the illustrated engine or electric motor), a main hydraulic pump 15 and a pilot hydraulic pump 30 driven by the prime mover 14, an operating device 16A (boom operating device) for instructing the operation (specifically, lowering or raising) of the boom 7, a control valve 17A (boom control valve) that controls the flow of pressure oil from the main hydraulic pump 15 to the boom cylinder 10 in response to the operation of the operating device 16A, an operating device 16B (arm operating device) for instructing the operation (specifically, pushing out or retracting) of the arm 8, and a control valve 17B (arm control valve) that controls the flow of pressure oil from the main hydraulic pump 15 to the arm cylinder 11 in response to the operation of the operating device 16B. The prime mover 14, main hydraulic pump 15, pilot hydraulic pump 30, and control valves 17A, 17B are mounted in the machine room 4 of the revolving structure 3, and the operating devices 16A, 16B are mounted in the cab 5 of the revolving structure 3.

[0017] Although not shown in detail, the operating device 16A includes an operation lever operable by an operator, a pilot valve on one side that uses the discharge pressure of the pilot hydraulic pump 30 as a source pressure to generate and output a pilot pressure corresponding to the operation amount on one side of the operation lever, and a pilot valve on the other side that uses the discharge pressure of the pilot hydraulic pump 30 as a source pressure to generate and output a pilot pressure corresponding to the operation amount on the other side of the operation lever.

[0018] Although not shown in detail, the control valve 17A is a three-position proportional control valve having a neutral position, a switching position on one side, and a switching position on the other side. When the operation lever of the operating device 16A is not operated, no pilot pressure is output from the operating device 16A to the pressure receiving portions on one side and the other side of the control valve 17A, and the control valve 17A is in the neutral position. At this time, the control valve 17A blocks the flow of pressure oil from the main hydraulic pump 15 to the boom cylinder 10, and blocks the flow of pressure oil from the boom cylinder 10 to the hydraulic oil tank 18.

[0019] When the operation lever of the operating device 16A is operated to one side (in other words, when the lowering of the boom 7 is instructed by the operating device 16A), a pilot pressure (in other words, a pilot pressure for boom lowering) is output from the operating device 16A to the pressure receiving portion on one side of the control valve 17A, and the control valve 17A is set to the switching position on the one side. At this time, the control valve 17A supplies pressure oil from the main hydraulic pump 15 to the rod side of the boom cylinder 10, discharges pressure oil from the bottom side of the boom cylinder 10 to the hydraulic oil tank 18, and controls the flow rates thereof to increase in accordance with the increase of the pilot pressure. As a result, the boom cylinder 10 is contracted, and the boom 7 is lowered.

[0020] When the operating lever of the operating device 16A is operated to the other side (in other words, the operating device 16A instructs the boom 7 to rise), pilot pressure (in other words, pilot pressure for boom raising) is output from the operating device 16A to the pressure receiving part on the other side of the control valve 17A, and the control valve 17A moves to the other side switching position. At this time, the control valve 17A supplies pressurized oil from the main hydraulic pump 15 to the bottom side of the boom cylinder 10 and discharges pressurized oil from the rod side of the boom cylinder 10 to the hydraulic oil tank 18, and controls the flow rates of these to increase in accordance with the increase in pilot pressure. As a result, the boom cylinder 10 extends and the boom 7 rises.

[0021] Although not shown in detail, the operating device 16B includes an operating lever that can be operated by an operator, a pilot valve on one side that uses the discharge pressure of the pilot hydraulic pump 30 as the base pressure to generate and output a pilot pressure corresponding to the amount of operation on one side of the operating lever, and a pilot valve on the other side that uses the discharge pressure of the pilot hydraulic pump 30 as the base pressure to generate and output a pilot pressure corresponding to the amount of operation on the other side of the operating lever.

[0022] Although not shown in detail, the control valve 17B is a three-position proportional control valve having a neutral position, a switching position for one side, and a switching position for the other side. When the operating lever of the operating device 16B is not operated, no pilot pressure is output from the operating device 16B to the pressure receiving parts on one side and the other side of the control valve 17B, and the control valve 17B returns to the neutral position. At this time, the control valve 17B shuts off the flow of pressurized oil from the main hydraulic pump 15 to the arm cylinder 11 and shuts off the flow of pressurized oil from the arm cylinder 11 to the hydraulic oil tank 18.

[0023] When the operating lever of the operating device 16B is operated to one side (in other words, when the operating device 16B instructs the arm 8 to be pushed out), pilot pressure (in other words, pilot pressure for pushing out the arm) is output from the operating device 16B to the pressure receiving part on one side of the control valve 17B, and the control valve 17B moves to the one-side switching position. At this time, the control valve 17B supplies pressurized oil from the main hydraulic pump 15 to the rod side of the arm cylinder 11 and discharges pressurized oil from the bottom side of the arm cylinder 11 to the hydraulic oil tank 18, and controls the flow rate of these to increase in accordance with the increase in pilot pressure. As a result, the arm cylinder 11 is retracted and the arm 8 is pushed out (in other words, the arm 8 rotates so that the tip of the arm 8 moves away from the vehicle body). In this embodiment, a pilot pressure sensor 19 is provided to detect the pilot pressure for pushing out the arm output from the operating device 16B.

[0024] When the operating lever of the operating device 16B is operated to the other side (in other words, when the operating device 16B instructs the retraction of the arm 8), pilot pressure (in other words, pilot pressure for arm retraction) is output from the operating device 16B to the pressure receiving part on the other side of the control valve 17B, and the control valve 17B moves to the other side switching position. At this time, the control valve 17B supplies pressurized oil from the main hydraulic pump 15 to the bottom side of the arm cylinder 11 and discharges pressurized oil from the rod side of the arm cylinder 11 to the hydraulic oil tank 18, and controls the flow rates of these to increase in accordance with the increase in pilot pressure. As a result, the arm cylinder 11 extends and the arm 8 is retracted (in other words, the arm 8 rotates so that the tip of the arm 8 approaches the vehicle body).

[0025] The drive system 13 of the shovel 1 includes a float function switching device 20 for switching the float function on and off, a float valve 22A (first float valve) provided in the oil passage 21A connecting the rod side of the boom cylinder 10 and the hydraulic oil tank 18, a float valve 22B (second float valve) provided in the oil passage 21B connecting the bottom side of the boom cylinder 10 and the hydraulic oil tank 18, and a control device 23 that controls the float valves 22A and 22B in accordance with the switching of the float function switching device 20. The float function switching device 20 is mounted in the operator's cab 5 of the slewing body 3 and is, for example, a switch that can be operated by the operator.

[0026] Although not shown in detail, the control device 23 includes a processor that executes processing according to a program, and memory for storing programs and data. When the float function is switched to disabled by the float function switching device 20, the control device 23 controls the float valves 22A and 22B to a closed state. On the other hand, when the float function is switched to enabled by the float function switching device 20, it normally controls the float valves 22A and 22B to a connected state. This connects the rod side and bottom side of the boom cylinder 10 to the hydraulic oil tank 18, causing the boom 7 to float (become operable by external force).

[0027] When the boom 7 is in a floating state, the boom 7 lowers due to the weight of the work device 6, and the work tool 9 comes into contact with the ground. Then, when the operator operates the control device 16B to push out or retract the arm 8, the floating boom 7 rises or lowers so that the work tool 9 moves along the ground. As a result, if the work tool 9 is the bucket shown in the figure, leveling work using the bucket can be easily performed.

[0028] However, for example, when using the float function to push out arm 8 from a retracted position, a large driving force is required to push out arm 8 and raise boom 7 at the same time. Therefore, if the driving force of arm cylinder 11 is insufficient, boom 7 may not rise sufficiently, and arm 8 may not be able to be pushed out. As a result, even when the float function is operating, leveling work cannot be performed by arm operation alone, which may reduce work efficiency.

[0029] Therefore, a feature of this embodiment is that the drive system 13 of the shovel 1 includes an arm attitude sensor 24 for detecting the attitude of the arm 8 and an auxiliary valve 26 provided in an auxiliary oil passage 25 for extending the boom cylinder 10 (more specifically, an oil passage connecting the bottom side of the boom cylinder 10 and the rod side of the arm cylinder 11). The arm attitude sensor 24 may be a sensor that detects the rotation angle of the arm 8 with respect to the boom 7 (more specifically, the angle between the straight line connecting the rotation center of the boom 7 and the rotation center of the arm 8 and the straight line connecting the rotation center of the arm 8 and the rotation center of the work tool 9, as shown in Figures 2(a) and 2(b) described later), or it may be a sensor that detects the rotation angle (absolute angle) of the arm 8 with respect to the ground.

[0030] A feature of this embodiment is that when the float function is effectively switched on by the float function switching device 20 and the arm 8 is instructed to be pushed out by the operating device 16B, the control device 23 performs corrective control to open the float valve 22A, close the float valve 22B, and open the auxiliary valve 26 according to the posture (rotation angle) of the arm 8 detected by the arm posture sensor 24. As a result, a portion of the pressurized oil supplied from the main hydraulic pump 15 to the rod side of the arm cylinder 11 via the control valve 17B is supplied to the bottom side of the boom cylinder 10 via the auxiliary valve 26. Therefore, the boom cylinder 10 can be extended to assist in the raising operation of the boom 7.

[0031] To explain in more detail, the control device 23 performs the above-described auxiliary control when the float function is effectively switched on by the float function switching device 20 and the operation device 16B instructs the arm 8 to be extended, and the tip of the arm 8 is closer to the vehicle body than the position in which the arm 8 extends perpendicularly to the ground when the work tool 9 is on the ground (more specifically, when the rotation angle of the arm 8 detected by the arm posture sensor 24 is less than a predetermined angle). The aforementioned predetermined angle is the rotation angle θ1 of the arm 8 when the arm 8 extends perpendicularly to the ground when the work tool 9 is on the ground (in other words, when the boom 7 is at its highest position when the work tool 9 is on the ground) (see Figure 2(a)), or a smaller angle (see Figure 2(b)). The details will be explained below.

[0032] Figures 3(a) and 3(b) illustrate the force F required to raise the boom 7 during the extension operation of the arm 8. As shown in Figure 3(a), the force F required to raise the boom 7 (i.e., the working device 6) corresponds to the reaction force from the ground and can be calculated using the formula F = W × r / r', where W is the weight of the working device 6, r is the distance from the pivot point of the boom 7 to the center of gravity of the working device 6, and r' is the horizontal distance from the pivot point of the boom 7 to the point where the work tool 9 touches the ground. The horizontal distance r' changes significantly compared to the distance r, depending on the rotation angle of the arm 8. Therefore, as shown in Figure 3(b), as the rotation angle of the arm 8 decreases (the tip of the arm 8 approaches the vehicle body), the force F required to raise the boom 7 increases, and the driving force of the arm cylinder 11 required for this also increases. Therefore, if the driving force of the arm cylinder 11 is insufficient when the rotation angle of the arm 8 is < θ1, the predetermined angle should be set to θ1, and if the driving force of the arm cylinder 11 is insufficient when the rotation angle of the arm 8 is < θ2, the predetermined angle should be set to θ2. Note that when the arm 8 is being pushed out, if the rotation angle of the arm 8 is ≥ θ1, the boom 7 will descend so that the work tool 9 moves along the ground, so the force F required to raise the boom 7 is unnecessary. Also, if the arm 8 is instructed to be pushed out from the position where the arm 8 extends perpendicular to the ground with the work tool 9 on the ground, the boom 7 must descend in response to the pushing out of the arm 8, otherwise the work tool 9 will be lifted off the ground. Therefore, the predetermined angle is set to be less than or equal to the angle (θ1) when the arm 8 is in the position where the arm 8 extends perpendicular to the ground with the work tool 9 on the ground.

[0033] The processing details of the control device 23 in this embodiment will be explained using Figure 4. Figure 4 is a flowchart showing the processing details of the control device in this embodiment.

[0034] In step S1, the control device 23 determines whether the float function has been switched to enabled by the float function switching device 20. If the float function has been switched to disabled by the float function switching device 20, the process proceeds to step S2. In step S2, the control device 23 controls the float valves 22A, 22B and the auxiliary valve 26 to a closed state.

[0035] If the float function is switched to active by the float function switching device 20, the process proceeds to step S3. In step S3, the control device 23 determines whether the operating device 16B has instructed the arm 8 to be pushed out, based on whether the pilot pressure detected by the pilot pressure sensor 19 is above a threshold. If the operating device 16B has instructed the arm 8 to be pushed out, the process proceeds to step S4. In step S4, the control device 23 determines whether the rotation angle of the arm 8 detected by the arm attitude sensor 24 is less than a predetermined angle.

[0036] If the operating device 16B does not instruct the extension of the arm 8, or if the rotation angle of the arm 8 detected by the arm attitude sensor 24 is greater than or equal to a predetermined angle, the process proceeds to step S5. In step S5, the control device 23 controls the float valves 22A and 22B to the open state and the auxiliary valve 26 to the closed state. As a result, the boom 7 becomes a floating state.

[0037] If the operating device 16B instructs the extension of the arm 8, and the rotation angle of the arm 8 detected by the arm attitude sensor 24 is less than a predetermined angle, the process proceeds to step S6. In step S6, the control device 23 controls the float valve 22A to be open, the float valve 22B to be closed, and the auxiliary valve 26 to be open (auxiliary control). This extends the boom cylinder 10 and assists in the upward movement of the boom 7. As a result, when using the float function to move the work tool 9 along the ground, the upward movement of the boom 7 is assisted, thereby improving work efficiency.

[0038] A second embodiment of the present invention will be described with reference to the drawings. In this embodiment, parts equivalent to those in the first embodiment are denoted by the same reference numerals, and their descriptions are omitted as appropriate.

[0039] Figure 5 is a diagram showing the configuration of the excavator drive system in this embodiment, along with the external structure of the excavator.

[0040] In this embodiment, the drive system 13 of the shovel 1 is equipped with a pressure sensor 27 that detects the bottom pressure of the boom cylinder 10. While the control device 23 is performing auxiliary control, if the bottom pressure of the boom cylinder 10 detected by the pressure sensor 27 is equal to or greater than a pressure threshold, the control device 23 switches the auxiliary valve 26 from the open state to the closed state.

[0041] The processing details of the control device 23 in this embodiment will be explained using Figure 6. Figure 6 is a flowchart showing the processing details of the control device in this embodiment.

[0042] Similar to the first embodiment, when the float function is effectively switched on by the float function switching device 20, and the operating device 16B instructs the arm 8 to be pushed out, and the rotation angle of the arm 8 detected by the arm attitude sensor 24 is less than a predetermined angle, the process proceeds to step S6 via steps S1, S3, and S4. In step S6, the control device 23 controls the float valve 22A to be in the open state, the float valve 22B to be in the closed state, and the auxiliary valve 26 to be in the open state (auxiliary control).

[0043] Subsequently, the process proceeds to step S7, where the control device 23 determines whether the bottom pressure of the boom cylinder 10 detected by the pressure sensor 27 is equal to or greater than the pressure threshold P. The pressure threshold P corresponds to the bottom pressure of the boom cylinder 10 just before the work tool 9 leaves the ground, and the control device 23 can determine whether or not the work tool 9 leaves the ground based on the aforementioned determination.

[0044] If the bottom pressure of the boom cylinder 10 detected by the pressure sensor 27 is less than the pressure threshold P, the control device 23 terminates the process with the auxiliary valve 26 in the open state. On the other hand, if the bottom pressure of the boom cylinder 10 detected by the pressure sensor 27 is equal to or greater than the pressure threshold P, the process proceeds to step S8, and the control device 23 switches the auxiliary valve 26 from the open state to the closed state. This limits the assistance for raising the boom 7 so that the work tool 9 does not leave the ground.

[0045] In the second embodiment, the control device 23 was described using a fixed pressure threshold P as an example, but it is not limited to this. The control device 23 may vary the pressure threshold P according to the rotation angle of the arm 8 detected by the arm attitude sensor 24. To explain in more detail, the bottom pressure of the boom cylinder 10 just before the work tool 9 leaves the ground changes according to the rotation angle of the arm 8. Therefore, the control device 23 stores the characteristics of the pressure threshold P that change according to the rotation angle of the arm 8, for example, as shown in Figure 7. In this characteristic, the pressure threshold P increases as the rotation angle of the arm 8 increases. The control device 23 uses the pressure threshold P corresponding to the rotation angle of the arm 8 detected by the arm attitude sensor 24. In other words, based on the attitude of the arm 8 detected by the arm attitude sensor 24, the control device 23 sets the pressure threshold P to be larger as the tip of the arm 8 moves further away from the vehicle body. In this modified example, the accuracy of the control can be improved.

[0046] Furthermore, in the second embodiment and the above modified examples, the control device 23 was described using the case where the opening degree of the auxiliary valve 26 in the open state is fixed, but it is not limited to this. The control device 23 may vary the opening degree of the auxiliary valve 26 according to the bottom-side pressure of the boom cylinder 10 detected by the pressure sensor 27. To explain in more detail, the control device 23 stores the characteristics of the opening degree of the auxiliary valve 26 that change according to the bottom-side pressure of the boom cylinder 10, for example, as shown in Figure 8. In this characteristic, when the bottom-side pressure of the boom cylinder 10 is 0, the auxiliary valve 26 is in a fully open state (opening degree 100%). Also, when the bottom-side pressure of the boom cylinder 10 is at the pressure threshold P, the auxiliary valve 26 is in a fully closed state (opening degree 0%). Also, when the bottom-side pressure of the boom cylinder 10 is greater than 0 and less than the pressure threshold P, the opening degree of the auxiliary valve 26 decreases in accordance with the increase in the bottom-side pressure of the boom cylinder 10. The control device 23 controls the auxiliary valve 26 so that its opening degree corresponds to the bottom pressure of the boom cylinder 10 detected by the pressure sensor 27. In other words, the control device 23 sets the opening degree of the auxiliary valve 26 smaller the greater the bottom pressure of the boom cylinder 10 detected by the pressure sensor 27. In this modified example, the accuracy of the control can be improved.

[0047] Furthermore, in the first embodiment, the second embodiment, and the above-described modifications, the control device 23 was described as executing the float mode (i.e., steps S4 and later described above) when the float function was effectively switched on by the float function switching device 20, but it is not limited to this. The control device 23 may, for example, execute the float mode when the float function was effectively switched on by the float function switching device 20 and the lowering of the boom 7 was instructed by the operating device 16A. Such modifications will be explained using Figure 9. Figure 9 is a diagram showing the configuration of the excavator drive system in this embodiment, along with the external structure of the excavator.

[0048] In this modified example, the drive system 13 of the shovel 1 includes a pilot pressure sensor 28 that detects the pilot pressure for lowering the boom output from the operating device 16A, and an on / off valve 29 provided in the oil passage between the operating device 16A and the pressure receiving part on one side of the control valve 17A.

[0049] When the float function is disabled by the float function switching device 20, the control device 23 controls the on-off valve 29 to the open state. On the other hand, when the float function is enabled by the float function switching device 20, the control device 23 determines whether the operating device 16A has instructed the lowering of the boom 7 based on whether the pilot pressure detected by the pilot pressure sensor 28 is above a threshold. If the lowering of the boom 7 is instructed, the control device 23 controls the on-off valve 29 to the closed state (i.e., sets the control valve 17A to the neutral position) and executes the float mode (i.e., steps S4 and onward described above).

[0050] In this modified configuration, the float mode is not activated simply by switching the float function to active using the float function switching device 20. Furthermore, the float mode is activated when the operator instructs the lowering of the boom 7 using the control device 16A. Therefore, the likelihood of the operator executing the float mode as intended can be increased. In addition, when the float function is active, the boom 7 can be raised by instructing the operator to raise the boom 7 using the control device 16A.

[0051] Furthermore, in the first embodiment, the second embodiment, and the above-described modifications, the auxiliary oil passage 25 for extending the boom cylinder was described as an example of an oil passage connecting the bottom side of the boom cylinder 10 and the rod side of the arm cylinder 11, but it is not limited to this. For example, as shown in Figure 10, the auxiliary oil passage 25A for extending the boom cylinder may be an oil passage connecting the pressure receiving part on the other side of the control valve 17A and the pilot hydraulic pump 30. When the auxiliary valve 26A provided in the auxiliary oil passage 25A is controlled to the open state by the control device 23, it uses the discharge pressure of the pilot hydraulic pump 30 as the source pressure to generate and output pilot pressure. As a result, the control valve 17A becomes the other-side switching position, and pressurized oil is supplied from the main hydraulic pump 15 to the bottom side of the boom cylinder 10 via the control valve 17A. Therefore, the boom cylinder 10 can be extended to assist in the upward movement of the boom 7. As a result, when using the float function to move the work tool 9 along the ground, the upward movement of the boom 7 can be assisted to improve work efficiency.

[0052] Furthermore, in the first embodiment, the second embodiment, and the above-described modifications, the operating devices 16A and 16B were described as being configured to generate and output pilot pressure corresponding to the amount of operation of the operating lever, but the invention is not limited to this. The operating devices 16A and 16B may also be configured to generate and output operation signals (electrical signals) corresponding to the amount of operation of the operating lever. The control device 23 generates drive signals corresponding to the operation signals of the operating devices 16A and 16B and outputs them to a plurality of electromagnetic proportional valves (not shown). The plurality of electromagnetic proportional valves generate pilot pressure corresponding to the drive signals and output them to the pressure receiving sections of the control valves 17A and 17B. In this case, instead of pilot pressure, the control device 23 can determine, based on the operation signal, whether the operating device 16B has instructed the arm 8 to be pushed out, or whether the operating device 16A has instructed the boom 7 to be lowered.

[0053] Furthermore, in the first embodiment, the second embodiment, and the above-described modifications, the working tool 9 was described using the example of a bucket, but it is not limited to this, and may be a sweeper or a compactor, for example.

[0054] In the above description, the present invention has been explained using the application of the present invention to an excavator as an example, but it is not limited to this and may be applied to other construction machinery. In other words, the present invention can be applied to any construction machine that comprises a vehicle body, a boom rotatably connected to the vehicle body with the horizontal direction as the axis of rotation, an arm rotatably connected to the boom with the horizontal direction as the axis of rotation, a work tool connected to the tip of the arm, a boom cylinder that lowers the boom by retracting and raises the boom by extending, an arm cylinder that rotates the arm, and an arm operating device for instructing the operation of the arm cylinder.

[0055] Furthermore, although the example given was the operation to push out the arm 8 using the float function from the position in which the arm 8 is retracted, the system is not limited to this. In the operation of retracting the arm 8 from the position in which it is retracted to the position in which it extends perpendicular to the ground, if the driving force of the arm cylinder 11 is insufficient, the system may be configured to assist the upward movement of the boom 7 when an instruction is given to retract the arm 8. [Explanation of Symbols]

[0056] 1. Excavator (construction machinery) 2. Running body (vehicle body) 3. Rotating body (vehicle body) 7 Boom 8 Arms 9. Work Tools 10 Boom Cylinder 11 Arm Cylinder 15 Main hydraulic pump 16B Operating device (arm operating device) 17A Control valve (Boom control valve) 18. Hydraulic oil tank 20. Float function switching device 21A,21B oil passage 22A Float valve (first float valve) 22B Float valve (second float valve) 23 Control device 24 Arm posture sensor 25,25A Auxiliary oil path 26,26A Auxiliary valve 27 Pressure Sensor 30 Pilot Hydraulic Pumps

Claims

1. The car body and, A boom rotatably connected to the vehicle body with the horizontal direction as the axis of rotation, An arm rotatably connected to the boom with the horizontal direction as the axis of rotation, A work tool connected to the tip of the aforementioned arm, A boom cylinder that lowers the boom by shortening it and raises the boom by extending it, An arm cylinder that rotates the aforementioned arm, An arm operating device for instructing the movement of the aforementioned arm, A float function switching device that switches the float function on and off, A first float valve is provided in the oil passage connecting the rod side of the boom cylinder and the hydraulic oil tank, A second float valve is provided in the oil passage connecting the bottom side of the boom cylinder and the hydraulic oil tank, A construction machine comprising a control device that controls the first and second float valves in accordance with the switching of the float function switching device, An arm posture sensor for detecting the posture of the arm, The system includes an auxiliary valve provided in an auxiliary oil passage for extending the boom cylinder, The control device is characterized in that, when the float function is effectively switched on by the float function switching device and the arm is instructed to be pushed out by the arm operating device, the control device performs auxiliary control to open the first float valve, close the second float valve, and open the auxiliary valve, according to the posture of the arm detected by the arm posture sensor.

2. In the construction machine described in claim 1, The boom cylinder is equipped with a pressure sensor that detects the pressure on the bottom side, The control device is characterized in that, while performing the auxiliary control, if the bottom pressure of the boom cylinder detected by the pressure sensor is equal to or greater than a pressure threshold, the auxiliary valve is switched from an open state to a closed state.

3. In the construction machine described in claim 2, The control device is characterized in that, based on the posture of the arm detected by the arm posture sensor, the pressure threshold is set to be larger as the tip of the arm moves further away from the vehicle body.

4. In the construction machine described in claim 2, The control device is characterized in that the opening degree of the auxiliary valve is set to be smaller the greater the bottom-side pressure of the boom cylinder detected by the pressure sensor.

5. In the construction machine described in claim 1, The construction machine is characterized in that the auxiliary oil passage is an oil passage connecting the bottom side of the boom cylinder and the rod side of the arm cylinder.

6. In the construction machine described in claim 1, A main hydraulic pump that discharges pressurized oil supplied to the boom cylinder, A boom control valve that controls the flow of pressurized oil from the main hydraulic pump to the boom cylinder, A pilot hydraulic pump that discharges pressurized oil supplied to the pressure receiving section of the boom control valve, The construction machine is characterized in that the auxiliary oil passage is an oil passage connecting the pressure receiving section of the boom control valve and the pilot hydraulic pump.

7. In the construction machine described in claim 1, The control device is A construction machine characterized in that, when the float function is effectively switched on by the float function switching device and the arm operating device instructs the arm to be pushed out, the auxiliary control is performed when the posture of the arm detected by the arm posture sensor is such that the tip of the arm is closer to the vehicle body than the posture in which the arm extends perpendicularly to the ground when the work tool is in contact with the ground.

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