Boom lowering control system for work machine

Abstract

To perform a control for lowering a boom at a descending speed according to an operation tool operation amount in a stable condition even if a work attachment is replaced in a work machine in which a replaceable work attachment is attached to a tip of a work arm including a boom.SOLUTION: There is provided a monitor device 22 which inputs information regarding a weight of an attached work attachment 8 into a controller 21. The controller 21 is provided with a map 35 which shows a relationship between a weight of a replaceable work attachment 8 and a holding pressure of a boom cylinder head side oil chamber 14a. The controller 21 calculates a holding pressure estimation value according to the weight of the attached work attachment 8 based on the map 35, and controls an opening area of a contraction side discharge opening 18f of a control valve 18 based on the holding pressure estimation value.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to the technical field of boom lowering control systems for work machines such as hydraulic excavators. [Background technology]

[0002] Some work machines, such as hydraulic excavators, are equipped with a boom pivotally supported on the machine body so as to swing up and down, and a work arm composed of a stick or the like swingably supported at the tip of the boom. A work attachment, such as a bucket, breaker, or crusher, is interchangeably attached to the tip of the work arm, and the up and down movement of the boom is achieved by the extension and retraction of a boom cylinder, which extends when oil is supplied to a head-side oil chamber and contracts when oil is discharged from the head-side oil chamber. In such work machines, the weight of the work arm or the work attachment acts as a force to lower the boom, so the pressure in the head-side oil chamber of the boom cylinder is high. For this reason, the boom lowering speed is typically controlled by controlling the discharge flow rate (meter-out control) from the boom cylinder head-side oil chamber. In this case, for example, a control valve with a meter-out opening is provided in the discharge oil passage from the boom cylinder head-side oil chamber, and the boom lowering speed is controlled to correspond to the amount of operation of the boom operating tool by increasing or decreasing the meter-out opening area of ​​the control valve in accordance with the amount of operation of the operating tool. However, as mentioned above, when controlling the boom lowering speed by controlling the discharge flow rate from the boom cylinder head-side oil chamber, the discharge flow rate from the head-side oil chamber increases or decreases depending not only on the opening area of ​​the control valve's meter-out opening but also on the pressure in the boom cylinder head-side oil chamber, and the pressure in the boom cylinder head-side oil chamber varies greatly depending on the weight of the work attachment that acts as a force to lower the boom.As a result, even if the opening area of ​​the meter-out opening is the same, that is, even if the operation amount of the boom operating tool is the same, the boom lowering speed will change depending on the weight of the attached work attachment, making it impossible to accurately control the boom lowering speed and resulting in a problem of poor operability. Known technologies for ensuring a boom lowering speed that corresponds to the amount of operation of the operating tool even when the work attachment is replaced include, for example, a technology that provides a control valve (meter-out control valve) that controls the discharge flow rate from the boom cylinder head-side oil chamber, flow rate detection means that detects the flow rate passing through the control valve, and a pressure sensor that detects the holding pressure acting on the boom cylinder due to an external force, and controls the opening area of ​​the control valve based on the detected holding pressure and flow rate so that a pressure that counteracts the holding pressure is generated on the inlet side of the control valve (see, for example, Patent Document 1), and a technology that provides an electromagnetic proportional pressure reducing valve in a regeneration circuit that supplies discharged oil from the head-side oil chamber of the boom cylinder to the rod-side oil chamber when the boom is lowered, and controls the opening of the electromagnetic proportional pressure reducing valve based on the differential pressure between the pressure in the head-side oil chamber detected by a pressure sensor and a preset target pressure value for the head-side oil chamber (see, for example, Patent Document 2). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-106304 [Patent Document 2] Japanese Patent Application Laid-Open No. 2010-78035 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in both Patent Documents 1 and 2, the opening area of ​​the meter-out control valve and the opening of the electromagnetic proportional pressure reducing valve are controlled based on the pressure in the boom cylinder head-side oil chamber, which is input from a pressure sensor as needed. However, the pressure input from the pressure sensor as needed is a dynamic pressure, and depending on the usage conditions of the work attachment, there is a possibility that an unstable and unpredictable pressure value will be input. Using such dynamic pressure causes the control valve and electromagnetic proportional pressure reducing valve to move irregularly, making stable control impossible, and this is the problem that the present invention aims to solve. [Means for solving the problem]

[0005] The present invention has been made in view of the above-mentioned circumstances and with the aim of solving these problems. The invention of claim 1 relates to a work machine comprising a work arm including at least a boom pivotally supported on a machine body so as to be able to swing up and down, a replaceable work attachment attached to the tip of the work arm, a boom cylinder that swings the boom up and down by extending when oil is supplied to a head-side oil chamber and by contracting when oil is discharged from the head-side oil chamber, a control valve having a meter-out opening that controls the discharge flow rate from the head-side oil chamber of the boom cylinder, control means for controlling the operation of the control valve, and an operating tool that is operated to move the boom up and down. a control means for controlling the boom lowering of a work machine, the control means including an information input means for inputting information relating to the weight of the attached work attachment to the control means, the control means including a map showing the relationship between the weight of the interchangeable work attachment and the holding pressure of the boom cylinder head-side oil chamber, determining an estimated holding pressure value corresponding to the weight of the attached work attachment based on the map, and controlling the meter-out opening area of ​​the control valve based on the estimated holding pressure value so that the discharge flow rate from the boom cylinder head-side oil chamber during boom lowering will be a target discharge flow rate that is set in accordance with the amount of operation of the operating tool. The invention of claim 2 is a boom lowering control system for a work machine, as set forth in claim 1, characterized in that, when determining an estimated holding pressure value corresponding to the weight of the attached work attachment based on the map, the control means divides the map values ​​of the holding pressure in the boom cylinder head side oil chamber into a plurality of groups according to the magnitude of the holding pressure map values, sets a representative holding pressure value for each group in advance, and sets the representative holding pressure value of the group to which the holding pressure map value corresponding to the weight of the attached work attachment belongs as the estimated holding pressure value corresponding to the weight of the attached work attachment. The invention of claim 3 is a boom lowering control system for a work machine according to claim 1, characterized in that, when determining an estimated holding pressure value corresponding to the weight of the attached work attachment based on the map, the control means divides the work attachments into a plurality of groups according to the weight of the work attachments, sets a representative holding pressure value in advance for each group, and uses the representative holding pressure value of the group to which the attached work attachment belongs as the estimated holding pressure value corresponding to the weight of the attached work attachment. The invention of claim 4 is a boom lowering control system for a work machine according to any one of claims 1 to 3, characterized in that the map represents a linear relationship between the weight of the work attachment and the holding pressure of the boom cylinder head-side oil chamber based on the moment around the support shaft that supports the boom so that it can swing freely on the machine body. The invention of claim 5 is a boom lowering control system for a work machine, characterized in that in claim 1, the weight of the work attachment includes the weight of a coupler used to attach the work attachment to the tip of the work arm. The invention of claim 6 is a boom lowering control system for a work machine, characterized in that, in claim 1, the work arm is composed of a boom and a stick pivotally supported at the tip of the boom so that it can swing freely, the work attachment is either attached to the tip of the boom or to the tip of the stick, and separate maps are provided for when the work attachment is attached to the tip of the boom and when it is attached to the tip of the stick. [Effects of the Invention]

[0006] By adopting the invention of claim 1, even if the work attachment is replaced, control can be performed in a stable state to lower the boom at a lowering speed according to the amount of operation of the boom operating device, which greatly contributes to improving operability. By adopting the inventions of claims 2 and 3, more stable boom lowering control can be performed and tuning is also excellent. According to the invention as defined in claim 4, it is possible to easily obtain holding pressure map values ​​corresponding to the weights of various work attachments. According to the invention of claim 5, the weight of the coupler is also taken into consideration when calculating the estimated holding pressure, making it possible to obtain an appropriate estimated holding pressure. By adopting the invention as defined in claim 6, whether the work arm component to which the work attachment is attached is a boom or a stick, an appropriate estimated holding pressure value can be obtained. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 2 is a schematic side view of the hydraulic excavator in the maximum reach position. [Figure 2] FIG. 2 is a hydraulic circuit diagram of a boost cylinder. [Figure 3] FIG. 2 is a control block diagram of a boom lowering control system. [Figure 4] (A) shows the map for the stick mount, and (B) shows the map for the boom mount. [Figure 5] FIG. 10 is a table showing groupings of work attachments. DETAILED DESCRIPTION OF THE INVENTION

[0008] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a schematic side view of a hydraulic excavator 1, which is an example of a work machine of the present invention. The hydraulic excavator 1 is made up of various parts such as a crawler-type lower traveling body 2, an upper rotating body (corresponding to the machine body of the present invention) 3 that is rotatably supported above the lower traveling body 2, and a front working implement 4 that is attached to the upper rotating body 3. The front working implement 4 is further made up of various members such as a boom 5 whose base end is supported on the upper rotating body 3 via a boom support shaft 5a so that it can swing up and down, and a work arm 7 that is made up of a stick 6 that is supported at the tip of the boom 5 via a stick support shaft 6a so that it can swing back and forth, a work attachment 8 that is movably attached to the tip of the stick 6 via an attachment support shaft 8a, a stick cylinder 10 that extends and retracts to swing the stick 6, a bucket cylinder 11 that extends and retracts to swing the work attachment 8, and first and second links 12 and 13 that respectively connect the tip of the bucket cylinder 11 to the stick 6 and the work attachment 8.

[0009] Furthermore, reference numeral 14 denotes a boom cylinder that extends and retracts to swing the boom 5 up and down. The boom cylinder 14 has its head side end supported so as to be freely swingable at the front of the upper rotating body 3 via a head side support shaft 14c, and its rod side end supported so as to be freely swingable at the middle of the length of the boom 5 via a rod side support shaft 14d. The boom cylinder 14 is configured so that it extends when oil is supplied to a head side oil chamber 14a (not shown in Figure 1) of the boom cylinder 14, thereby raising the boom 5, and contracts when oil is discharged from the head side oil chamber 14a, thereby lowering the boom 5.

[0010] 1 illustrates a bucket as the work attachment 8 attached to the tip of the work arm 7, but various work tools such as a breaker (hammer), compactor, tilt bucket, clamshell bucket, thumb bucket, grapple, and crusher (none of which are shown) can be interchangeably attached to the tip of the work arm 7 depending on the type of work to be performed by the hydraulic excavator 1. Furthermore, when attaching these work tools to the tip of the work arm 7, a coupler may not be used as in the case of the bucket shown in FIG. 1, but various couplers not shown (pin-fixed couplers, quick couplers, hook-equipped couplers, couplers that allow the work tool to tilt or rotate relative to the work arm, etc.) may also be used. Furthermore, when a coupler is used, the combination of the work tool and coupler can be selected appropriately depending on the function of the coupler, etc. In this embodiment, when a coupler is used, the work tool and coupler are referred to as the work attachment 8, and when a coupler is not used, the work tool is referred to as the work attachment 8. 1 illustrates a boom 5 and a stick 6 as the arm members that make up the working arm 7 of the present invention, with a work attachment 8 attached to the tip of the stick 6, however, some of the various work attachments 8 described above are attached to the tip of the boom 5, in which case the stick 6 is not included in the working arm 7. Furthermore, the working arm 7 includes at least the boom 5 that is pivotally supported on the machine body so that it can swing up and down, but if there is another arm member that makes up the working arm 7 in addition to the boom 5, the arm member is not limited to the stick 6, and arm members of various shapes and numbers may be used.

[0011] Next, oil supply / discharge control for the boom cylinder 14 will be explained based on the schematic hydraulic circuit diagram of Figure 2. In Figure 2, reference numeral 15 denotes a hydraulic pump that serves as a hydraulic pressure supply source for the boom cylinder 14, 16 denotes a pilot pump that serves as a pilot pressure supply source, 17 denotes an oil tank, and 18 denotes a control valve that controls oil supply / discharge for the boom cylinder 14. The hydraulic circuit of the hydraulic excavator 1 also includes control circuits for hydraulic actuators other than the boom cylinder 14 (such as the stick cylinder 10 and bucket cylinder 11, or a swing motor (not shown) that swings the upper swing body 3, and a travel motor (not shown)), as well as a circuit for controlling the discharge flow rate of the hydraulic pump, but these will not be shown or described here.

[0012] The control valve (corresponding to the control valve of the present invention) 18 is a pilot-operated three-position switching spool valve having extension-side and retraction-side pilot ports 18a, 18b. When pilot pressure is not input to both pilot ports 18a, 18b, the control valve is located in a neutral position N where oil is not supplied to or discharged from the boom cylinder 14. However, when pilot pressure is input to the extension-side pilot port 18a, the control valve switches to the extension-side position X, and oil supplied from the hydraulic pump 15 is supplied to the boom cylinder 14 via the extension-side supply opening 18c. Oil is supplied to head-side oil chamber 14a, and oil discharged from rod-side oil chamber 14b flows into oil tank 17 via extension-side discharge opening 18d, while pilot pressure is input to retraction-side pilot port 18b, switching to retraction-side position Y causes oil from hydraulic pump 15 to be supplied to rod-side oil chamber 14b of boom cylinder 14 via retraction-side supply opening 18e, and oil discharged from head-side oil chamber 14a to flow into oil tank 17 via retraction-side discharge opening 18f (corresponding to the meter-out opening of the present invention). The opening areas of extension-side supply and discharge openings 18c, 18d and retraction-side supply and discharge openings 18e, 18f are controlled to increase or decrease by the movement stroke of the spool, which moves in response to pilot pressure input to extension-side and retraction-side pilot ports 18a, 18b.

[0013] 2, reference numerals 19 and 20 denote extension and reduction side electromagnetic proportional valves, which output pilot pressures to extension and reduction side pilot ports 18a and 18b of the control valve 18, respectively, based on control signals output from a controller 21, which will be described later. The spool movement stroke of the control valve 18 increases or decreases with an increase or decrease in the pilot pressures output from the extension and reduction side electromagnetic proportional valves 19 and 20, thereby controlling the increase or decrease in the opening areas of the extension side supply and discharge openings 18c and 18d and the reduction side supply and discharge openings 18e and 18f.

[0014] When the boom 5 is lowered in the air (when the boom 5 is lowered with the work attachment 8 not on the ground), the weight of the front work implement 4 (the work arm 7, work attachment 8, etc.) acts as a force that retracts the boom cylinder 14, so the pressure in the head-side oil chamber 14a of the boom cylinder 14 is sufficiently higher than the pressure in the rod-side oil chamber 14b. For this reason, the descent speed of the boom 5 is controlled by controlling the discharge flow rate (meter-out control) from the boom cylinder head-side oil chamber 14a.

[0015] On the other hand, the controller (corresponding to the control means of the present invention) 21 controls the control valves for the various hydraulic actuators and controls the discharge flow rate of the hydraulic pump 15, etc., based on the operation of the operating tools for the various hydraulic actuators, and of the controls performed by the controller 21, the portion relating to the control of lowering of the boom 5 will be explained with reference to the control block diagram of Figure 3. On the input side of the controller 21, a monitor device 22 and boom operation detection means 23 that detects the operation direction and operation amount of a boom operating tool 23a (corresponding to the operating tool of the present invention) that is operated to move the boom 5 up and down are connected, and on the output side, the reduction side solenoid proportional valve 20 is connected, and various sections are also provided, such as an attachment arm member determination section 25, a work attachment weight calculation section 26, a holding pressure map section 27, a grouping section 28, a holding pressure estimated value setting section 29, a target discharge flow rate setting section 30, an opening area calculation section 32, a valve control section 33, etc.

[0016] The monitor device 22 corresponds to the information input means of the present invention, and in this embodiment is disposed inside the cab 3a mounted on the upper rotating body 3. It has a display screen (not shown) that displays information about the various interchangeable work attachments 8, operation means (not shown) such as a keyboard or touch panel, and stores information about the weight of the various work attachments 8. When the operator operates the monitor device 22, weight information about the attached work attachment 8 is input to the controller 21. For example, the work tools T1-Tn and couplers C1-Cn of the interchangeable work attachment 8 are displayed on the display screen of the monitor device 22, and by selecting the work tool T and coupler C (if a coupler is used) of the attached work attachment 8 from among these work tools T1-Tn and couplers C1-Cn using the operation means, the weights Wt and Wc of the attached work tool T and coupler C are input to the controller 21. In this case, for a particular work tool that is subjected to a heavy load, such as carrying a heavy object, information on not only the weight of the work tool itself but also the load weight corresponding to the work tool (for example, 1 / 2 of the maximum estimated load weight) is stored in the monitor device 22, and the weight obtained by adding the load weight to the weight of the work tool itself is output to the controller 21 as the weight Wt of the work tool. Furthermore, the monitor device 22 is configured so that information on which arm member, the boom 5 or the stick 6, the work attachment 8 is attached to can be selected using an operating means, and information on the attached arm member is also input to the controller 21. In this embodiment, information relating to the weight of each work attachment 8 is stored in the monitor device 22, but it is also possible to store this information in the controller 21 and perform only the selection operation on the monitor device 22. Even in this case, information relating to the weight of the attached work attachment 8 is input to the controller 21 based on the operation of the monitor device 22.

[0017] Next, the lowering control of the boom 5 performed by the controller 21 will be explained with reference to FIG. 3. The controller 21 inputs the information output from the monitor device 22 to the attachment arm member determination unit 25 and the work attachment weight calculation unit 26. The attachment arm member determination unit 25 determines whether the work attachment 8 is attached to the boom 5 or the stick 6 based on information input from the monitor device 22, and outputs the determination result to the holding pressure map unit 27. The work attachment weight calculation unit 26 also calculates the weight W of the work attachment 8 based on information input from the monitor device 22. The weight W of the work attachment 8 is calculated by adding the weight Wt of the work tool T selected by the monitor device 22 and the weight Wc of the coupler C (W = Wt + Wc). The calculated weight W of the work attachment 8 is then output to the holding pressure map unit 27.

[0018] The holding pressure map section 27 is provided with a map 35 that shows the relationship between the weight of the attachable work attachment 8 and the holding pressure of the head-side oil chamber 14a of the boom cylinder 14. The map 35 is provided with separate boom mount map 35a for when the work attachment 8 is attached to the tip of the boom 5, and stick mount map 35b for when the work attachment 8 is attached to the tip of the stick 6, and either the boom mount map 35a or the stick mount map 35b is selected based on the determination result of the attachment arm member determination section 25. Then, using the selected boom mount map 35a or stick mount map 35b, the holding pressure map section 27 determines the map value Pm of the holding pressure corresponding to the weight W of the work attachment 8 calculated by the work attachment weight calculation section 26. Then, the holding pressure map value Pm is output to the grouping section 28.

[0019] Here, the maps 35 (boom mount map 35a, stick mount map 35b) represent the linear relationship between the weight W of the work attachment 8 and the holding pressure P of the boom cylinder head side oil chamber 14a. The method for creating the maps 35 will be explained below using the stick mount map 35b as an example when an interchangeable work attachment 8 is attached to the tip of the stick 6. FIG. 1 shows the hydraulic excavator 1 when a work attachment 8 (bucket) is attached to the tip of the stick 6 via an attachment spindle 8a, and the attitude of the work arm 7 (boom 5 and stick 6) is such that the height of the shaft centre of the attachment spindle 8a is the same as the height of the shaft centre of the boom spindle 5a (positioned on the same horizontal line H), and the shaft centre of the attachment spindle 8a is at the farthest position from the shaft centre of the boom spindle 5a, and this maximum reach attitude is the attitude in which the moment M about the boom spindle 5a due to the weight of the front work implement 4 is at its maximum, and the moment M due to the weight of the front work implement 4 in this maximum reach attitude can be calculated using the following equation (1). M=(W×L×g)+Σ(Wi×Li×g) ···(1) In the above equation (1) and the following equations (3) and (4), W is the weight of the work attachment 8, L is the horizontal distance from the axis of the boom spindle 5a to the center of gravity of the work attachment 8 in the maximum reach posture, Wi (i = 1, 2, 3, . . . x) is the weight of each of the members A1, A2, A3, . . . Ax that make up the front work implement 4 other than the work attachment 8 (in the front work implement 4 shown in FIG. 1 , this includes the boom 5, stick cylinder 10, stick 6, bucket cylinder 11, first link 12, second link 13, etc.), Li (i = 1, 2, 3, . . . x) is the horizontal distance from the axis of the boom spindle 5a in the maximum reach posture to the center of gravity of each of the members A1, A2, A3, . . . Ax other than the work attachment 8, and g is the acceleration due to gravity. In addition, Figure 1 shows the horizontal distances L, L1, L2, L3, L4, L5, and L6 from the axis position of the boom support shaft 5a to the axis positions of the work attachment 8, boom 5, stick cylinder 10, stick 6, bucket cylinder 11, first link 12, and second link 13. On the other hand, the moment M around the boom support shaft 5a due to the holding pressure P in the head side oil chamber 14a of the boom cylinder 14 is calculated by the following formula (2). M = P × S × R (2) In the above equation (2) and the following equations (3) and (4), P is the holding pressure of the head-side oil chamber 14a of the boom cylinder 14, S is the head-side pressure-receiving area of ​​the piston of the boom cylinder 14, and R is the moment arm, which is the length of the perpendicular line from the axis of the boom support shaft 5a to the line of action of the boom cylinder 14 (the straight line connecting the head-side support shaft 14c and the rod-side support shaft 14d of the boom cylinder 14). Then, from the equation for balancing the moment M around the boom spindle 5a due to the weight of the front working implement 4 and the moment M around the boom spindle 5a due to the holding pressure P in the head-side oil chamber 14a of the boom cylinder 14, the holding pressure P in the head-side oil chamber 14a of the boom cylinder 14 when the front working implement 4 is in the maximum reach position is expressed by the following equation (3). P={(W×L×g) / (S×R)}+{Σ(Wi×Li×g) / (S×R)} ···(3) Furthermore, "Σ(Wi×Li×g) / (S×R)" in the above formula (3) is an element other than the work attachment 8 and is a constant value regardless of the work attachment 8 that is attached ({Σ(Wi×Li×g) / (S×R)}=b: constant), and further, if the horizontal distance L from the axis position of the boom spindle 5a to the center of gravity position of the work attachment 8 is considered to be constant even if the work attachment 8 is replaced, then "(L×g) / (S×R)" in the above formula (3) also becomes a constant value ({(L×g) / (S×R)}=a: constant), and therefore formula (3) can be expressed as the following formula (4). P = (a × W) + b (4) Then, by calculating "a" and "b" in the above formula (4) based on known data or measurement data of each member constituting the front work implement 4 and the boom cylinder 14, a stick mount map 35b (see FIG. 4(A)) is created that linearly represents the relationship between the weight W of the work attachment 8 and the holding pressure P of the boom cylinder head-side oil chamber 14a. Also, when the work attachment 8 is attached to the tip of the boom 5, although the values of "a" and "b" in the above formula (4) are different, similarly, a boom map 35a (see Fig. 4(B)) representing the relationship between the weight W of the work attachment 8 and the holding pressure P in the oil chamber 14a on the boom cylinder head side in a linear relationship is created. In this case, the attachment pivot 8a is provided at the tip of the boom 5, and the maximum reach position is such that the axial height of the attachment pivot 8a is the same as the axial height of the boom pivot 5a (located on the same horizontal line), and the axis of the attachment pivot 8a is at the farthest position from the axis of the boom pivot 5a.

[0020] Then, as described above, using the map 35 (boom mount map 35a or stick mount map 35b), the map value Pm of the holding pressure corresponding to the weight W of the work attachment 8 mounted in the holding pressure map section 27 is obtained, and the holding pressure map value Pm is output to the grouping section 28. In the grouping section 28, the map value Pm of the holding pressure is grouped into a plurality of groups (in this embodiment, three groups: the first, second, and third groups G1, G2, G3) according to the magnitude of the holding pressure map value Pm. In this case, in the threshold setting section 28a, the same number of holding pressure thresholds Pt as the number of groups are set (in this embodiment, the first, second, and third holding pressure thresholds Pt1, Pt2, Pt3 (Pt1 ≦ Pt2 ≦ Pt3)), and grouping is performed using these holding pressure thresholds. In this embodiment, when the holding pressure map value Pm is less than or equal to the first holding pressure threshold Pt1 (Pm ≦ Pt1), it is set as the first group G1, when it exceeds the first holding pressure threshold Pt1 and is less than or equal to the second holding pressure threshold Pt2 (Pt1 < Pm ≦ Pt2), it is set as the second group G2, and when it exceeds the second holding pressure threshold Pt2 and is less than or equal to the third holding pressure threshold Pt3 (Pt2 < Pm ≦ Pt3), it is set as the third group G3. The values of these holding pressure thresholds can be appropriately changed, for example, using an external input means such as the monitor device 22 according to the size and specifications of the hydraulic excavator 1. Then, the grouping section 28 outputs the result of the grouping, that is, to which of the first, second, and third groups the holding pressure map value Pm belongs, to the holding pressure estimation value setting section 29.

[0021] Figure 5 shows examples of the results of determining the holding pressure map value Pm corresponding to the weight W of the work attachment 8 (work tool T and coupler C) using map 35 (boom mount map 35a or stick mount map 35b) in each case where interchangeable work tools T1 to T25 of various types and sizes (bucket, breaker (hammer), compactor, tilt bucket, clamshell bucket, thumb bucket, grapple, crusher, etc.) are attached to the tip of the stick 6 or boom 5 without a coupler or via couplers C1 to C9 that can be combined with the work tools T1 to T25, and then grouping the holding pressure map values ​​Pm (first, second, and third groups G1, G2, and G3).

[0022] On the other hand, when the group to which the holding pressure map value Pm belongs is input from the grouping unit 28, the holding pressure estimated value setting unit 29 sets a predetermined holding pressure representative value for each group as the holding pressure estimated value P corresponding to the attached work attachment 8, and outputs the holding pressure estimated value P to the opening area calculation unit 32. In this embodiment, the holding pressure representative value for each group is set to the maximum holding pressure map value Pm of the group, that is, the first group G1 is set to the first holding pressure threshold value Pt1, the second group G2 is set to the second holding pressure threshold value Pt2, and the third group G3 is set to the third holding pressure threshold value Pt3, and these first, second, and third holding pressure threshold values ​​Pt1, Pt2, and Pt3 become the holding pressure estimated values ​​P of the work attachments 8 belonging to the first, second, and third groups G1, G2, and G3, respectively.

[0023] Meanwhile, as described above, the input side of the controller 21 is connected to the boom operation detection means 23 that detects the operation of the boom operation tool 23a, and the operation signal output from the boom operation detection means 23 is input to the target discharge flow rate setting unit 30 of the controller 21. When a boom lowering operation signal is input from the boom operation detection means 23, the target discharge flow rate setting unit 30 sets the target discharge flow rate Qt from the head-side oil chamber 14a of the boom cylinder 14 in accordance with the operation amount of the boom operation tool 23a, so as to achieve a boom lowering speed in accordance with the operation amount of the boom operation tool 23a. The target discharge flow rate Qt is then output to the opening area calculation unit 32.

[0024] The opening area calculation unit 32 calculates the opening area of ​​the reduction-side discharge opening 18f of the control valve 18 based on the holding pressure estimated value P input from the holding pressure estimated value setting unit 29 and the target discharge flow rate Qt input from the target discharge flow rate setting unit 30, using equation (6) derived from the orifice equation (5) shown below. Q=C×A×√(ΔP / ρ) (5) A=(√ρ / C)×(Qt / √P) ···(6) In the above formula (5), Q is the flow rate through the orifice, A is the opening area of ​​the orifice, ΔP is the differential pressure across the orifice, C is the flow coefficient, and ρ is the fluid density. In the above equation (6), A is the opening area of ​​the reduction-side discharge opening 18f of the control valve 18, Qt is the target discharge flow rate set by the target discharge flow rate setting unit 30, P is the estimated holding pressure value set by the estimated holding pressure value setting unit 29, C is the flow coefficient, and ρ is the fluid density. In equation (6), the pressure (tank pressure) downstream of the reduction-side discharge opening 18f is considered to be "0 (zero)." The value of "√ρ / C" in equation (6) is considered to be a constant, and the value of "√ρ / C" is set by the constant setting unit 32a using an external input means such as the monitor device 22, and is input to the opening area calculation unit 32. The opening area of ​​the reduction-side discharge opening 18f of the control valve 18 calculated using the above formula (6) is then output to the valve control unit 33.

[0025] The valve control unit 33 calculates the spool movement stroke of the control valve 18 that will result in the opening area of ​​the reduction-side discharge opening 18f, based on the opening area of ​​the reduction-side discharge opening 18f input from the opening area calculation unit 32. The valve control unit 33 then calculates an input pilot pressure to the reduction-side pilot port 18b for moving the spool to that stroke, calculates a current command value to the reduction-side electromagnetic proportional valve 20 for outputting the pilot pressure, and outputs the current command value as a control signal to the reduction-side electromagnetic proportional valve 20. In this way, the reduction-side discharge opening 18f of the control valve 18 is controlled to have the opening area calculated by the opening area calculation unit 32. By controlling the opening area of ​​the reduction-side discharge opening 18f of the control valve 18 in this manner, the discharge flow rate from the head-side oil chamber 14a of the boom cylinder 14 can be controlled to be the target discharge flow rate Qt that is set in response to the operation of the boom operating device 23a.

[0026] In the embodiment configured as described above, the hydraulic excavator 1 is equipped with a work arm 7 including at least a boom 5 pivotally supported on an upper rotating body (machine body) so as to be able to swing up and down freely, a replaceable work attachment 8 attached to the tip of the work arm 7, a boom cylinder 14 that extends when oil is supplied to a head-side oil chamber 14a and retracts when oil is discharged from the head-side oil chamber 14b, thereby swinging the boom 5 up and down, a control valve (control valve) 18 having a retraction-side discharge opening (meter-out opening) 18f that controls the discharge flow rate from the head-side oil chamber 14a of the boom cylinder 14, a controller (control means) 21 that controls the operation of the control valve 18, and a boom operating tool 23a that is operated to move the boom 5 up and down. The hydraulic excavator 1 is further equipped with a monitor device (information input means) 22 that inputs information related to the weight of the attached work attachment 8 to the controller 21. The controller 21 is provided with a map 35 that shows the relationship between the weight of the replaceable work attachment 8 and the holding pressure of the boom cylinder head side oil chamber 14a, and determines an estimated holding pressure value that corresponds to the weight of the attached work attachment 8 based on the map 35, and controls the opening area of ​​the reduction side discharge opening 18f of the control valve 18 based on the estimated holding pressure value so that the discharge flow rate from the boom cylinder head side oil chamber 14a when the boom 5 is lowered becomes a target discharge flow rate that is set in accordance with the amount of operation of the boom operating device 23a.

[0027] As described above, in the embodiment of the present invention, by controlling the opening area of ​​retraction-side discharge opening 18f of control valve 18 when boom 5 is lowered based on the estimated holding pressure value corresponding to the weight of work attachment 8, even if the weight of work attachment 8 changes when work attachment 8 is replaced, it is possible to control the discharge flow rate from boom cylinder 14 to be the target discharge flow rate set in accordance with the amount of operation of boom operating device 23a, that is, to control so that boom 5 can be lowered at a lowering speed in accordance with the amount of operation of boom operating device 23a. In this case, the estimated holding pressure value is a fixed value calculated in accordance with the weight of the attached work attachment 8 based on map 35 provided in controller 21. Therefore, as is the case when discharge flow rate control is performed using the detected pressure value of boom cylinder head-side oil chamber 14a input at any time from a pressure sensor as the holding pressure, there is no problem such as the opening area of ​​retraction-side discharge opening 18f changing irregularly in accordance with the detected pressure value, which would make control unstable, and stable discharge flow rate control can be performed. As a result, even if the work attachment 8 is replaced, the boom 5 can be lowered in a stable state at a lowering speed according to the amount of operation of the boom operating tool 23a, which greatly contributes to improving operability.

[0028] Furthermore, in this device, when controller 21 determines the holding pressure estimated value corresponding to the weight of the attached work attachment 8 based on map 35, it divides the map values ​​of the holding pressure of the boom cylinder head side oil chamber 14a into a plurality of groups (in this embodiment, three groups: first, second and third groups G1, G2 and G3) according to the magnitude of the holding pressure map values, and presets a representative holding pressure value for each group (in this embodiment, first, second and third holding pressure thresholds Pt1, Pt2 and Pt3). It also uses the representative holding pressure value of the group to which the holding pressure map value corresponding to the weight of the attached work attachment 8 belongs as the holding pressure estimated value corresponding to the weight of the attached work attachment 8. By dividing the holding pressure map values ​​into groups in this way and using the representative holding pressure value of each group as the holding pressure estimated value to be used for discharge flow rate control, more stable boom lowering control can be performed and tuning is also excellent.

[0029] Furthermore, the map 35 expresses the relationship between the weight of the work attachment 8 and the holding pressure of the boom cylinder head side oil chamber 14a as a linear relationship based on the moment around the support shaft (boom support shaft 5a) that supports the boom 5 on the machine body so that it can swing freely.By using map 35 that expresses this linear relationship, it is possible to easily determine holding pressure map values ​​that correspond to various weights of the work attachment 8.

[0030] Furthermore, in this device, the weight of the work attachment 8 includes the weight of the coupler used to attach the work attachment 8 to the tip of the work arm 7. As a result, even when a coupler is used, the weight of the coupler is taken into account when calculating the estimated holding pressure, making it possible to obtain an appropriate estimated holding pressure value.

[0031] Furthermore, in this embodiment, the work arm 7 is made up of a boom 5 and a stick 6 that is pivotally supported at the tip of the boom 5 so that it can swing freely, while the work attachment 8 is either attached to the tip of the boom 5 or to the tip of the stick 6, and the map 35 showing the relationship between the weight and holding pressure of the interchangeable work attachment 8 is provided separately as a map (boom mount map 35a) for when the work attachment 8 is attached to the tip of the boom 5, and a map (stick mount map 35b) for when it is attached to the tip of the stick 6. In this way, by providing individual maps 35 according to the work arm component (boom 5, stick 6) to which the work attachment 7 is attached, it is possible to obtain appropriate estimated holding pressure values ​​whether the work arm component to which the work attachment 8 is attached is the boom 5 or the stick 6.

[0032] It should be noted that this embodiment is not limited to the above embodiment, and for example, when determining the estimated holding pressure value corresponding to the weight of the attached work attachment based on the map, the work attachments can be divided into a plurality of groups according to the weight of the work attachment, a representative holding pressure value can be set in advance for each group, and the representative holding pressure value for the group to which the attached work attachment belongs can be determined using the map, and this representative holding pressure value can be used as the estimated holding pressure value corresponding to the weight of the attached work attachment. By dividing the work attachments into groups in this way and using the representative holding pressure value as the estimated holding pressure value, more stable boom lowering control can be performed and tuning is also excellent, as in the above embodiment. Furthermore, in the above embodiment, when the opening area calculation unit 32 of the controller 21 calculates the opening area of ​​the reduction-side discharge opening (meter-out opening) 18f, the calculation is performed using equation (6) as described above. However, by adding a correction value that takes into account the pressure loss of the control valve 18 and the hydraulic piping to this calculation, more accurate opening area control can be performed. Furthermore, in the above embodiment, the map showing the relationship between the weight of the work attachment and the holding pressure in the boom cylinder head-side oil chamber is created assuming that the work arm is in the maximum reach position. This is because it is assumed that the holding pressure is highest when the work arm is in the maximum reach position, and by performing control assuming that the holding pressure is at its highest, it is possible to reliably prevent the boom lowering speed from being faster than the expected speed. However, it is conceivable that the holding pressure may become higher depending on the type of work being performed by the work machine, and a correction value can be added to the map to prepare for such cases. Furthermore, the present invention is not limited to hydraulic excavators, but can be applied to boom lowering control systems for various types of work machines in which an interchangeable work attachment is attached to the tip of a work arm including a boom. [Industrial Applicability]

[0033] The present invention can be used in a boom lowering control system when the work attachment is replaced in a work machine such as a hydraulic excavator. [Explanation of symbols]

[0034] 5. Boom 5a Boom support shaft 6 sticks 7 Working Arm 8 Work attachments 14 Boom cylinder 14a Head side oil chamber 18 Control Valve 18f Reduction side discharge opening 21 Controller 22 Monitor Device 23a Boom control equipment 27 Holding pressure map section 28 Group Division 30 Target discharge flow rate setting section 32 Opening area calculation section 35 Maps 35a Boom Mount Map 35b Stick Mount Map

Claims

1. a boom cylinder that extends when oil is supplied to a head-side oil chamber and contracts when oil is discharged from the head-side oil chamber, thereby causing the boom to swing up and down; a control valve having a meter-out opening that controls the flow rate of oil discharged from the head-side oil chamber of the boom cylinder; control means for controlling the operation of the control valve; and an operating tool that is operated to move the boom up and down. The boom lowering control system for a work machine is characterized in that: an information input means is provided for inputting information related to the weight of the attached work attachment to the control means; the control means has a map that shows the relationship between the weight of the exchangeable work attachment and the holding pressure of the boom cylinder head-side oil chamber, and determines an estimated holding pressure value that corresponds to the weight of the attached work attachment based on the map; and controls the meter-out opening area of ​​the control valve based on the estimated holding pressure value so that the flow rate of oil discharged from the boom cylinder head-side oil chamber when the boom is lowered reaches a target flow rate that is set in accordance with the amount of operation of the operating tool.

2. 2. A boom lowering control system for a work machine according to claim 1, wherein the control means, when determining the holding pressure estimated value corresponding to the weight of the attached work attachment based on the map, divides the map values ​​of the holding pressure of the boom cylinder head side oil chamber into a plurality of groups according to the magnitude of the holding pressure map values, sets in advance a representative holding pressure value for each group, and uses the holding pressure representative value of the group to which the holding pressure map value corresponding to the weight of the attached work attachment belongs as the holding pressure estimated value corresponding to the weight of the attached work attachment.

3. 2. A boom lowering control system for a work machine according to claim 1, wherein the control means, when determining the estimated holding pressure value corresponding to the weight of the attached work attachment based on the map, divides the work attachments into a plurality of groups according to the magnitude of the weight of the work attachment, sets in advance a representative holding pressure value for each group, and uses the representative holding pressure value of the group to which the attached work attachment belongs as the estimated holding pressure value corresponding to the weight of the attached work attachment.

4. 4. A boom lowering control system for a work machine according to claim 1, wherein the map represents a linear relationship between the weight of the work attachment and the holding pressure of the boom cylinder head-side oil chamber, based on a moment about a support shaft that pivotally supports the boom to the machine body so that it can swing freely.

5. 2. A boom lowering control system for a work machine according to claim 1, wherein the weight of the work attachment includes the weight of a coupler used to attach the work attachment to the tip of the work arm.

6. 2. A boom lowering control system for a work machine according to claim 1, wherein the work arm comprises a boom and a stick pivotally supported at the tip of the boom so as to be able to swing freely, the work attachment is either attached to the tip of the boom or to the tip of the stick, and the maps are separately provided for when the work attachment is attached to the tip of the boom and when it is attached to the tip of the stick.

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