Construction machine

Abstract

The present application provides a kind of engineering machinery, with electromagnetic valve, it reduces pressure to boom lowering pilot pressure for second direction control valve;And controller, it controls the electromagnetic valve, the controller calculates first opening degree command value with the communication area of boom lowering pressure reducing valve and the pressure chamber of second direction control valve decreases with the bottom pressure of boom cylinder, calculates second opening degree command value with the communication area increases with the increase of boom lowering operation amount, minimum opening degree command value is determined as the opening degree command value of the electromagnetic valve in the elapsed time after boom lifting operation is less than set time, the minimum selection value of the first and the second opening degree command value is determined as the opening degree command value of the electromagnetic valve in the elapsed time is above the set time, and the opening degree command value corresponding to the determined command signal is output to the electromagnetic valve.

Description

TECHNICAL FIELD

[0001] The present application relates to a hydraulic excavator or the like construction machine. BACKGROUND

[0002] In a hydraulic excavator or the like construction machine, various operations such as a tamping operation, a grading operation, and the like are performed in addition to a digging operation. The flow rate and pressure of hydraulic oil required for driving a boom cylinder differ depending on the operation. For example, in a boom raising operation, the discharge oil of a plurality of hydraulic pumps is merged, and the like, to increase the inlet throttle flow rate to the boom cylinder. In contrast, in a case where a boom lowering operation is performed in a state where a bucket is suspended, the inlet throttle flow rate to the boom cylinder is limited to suppress energy loss. Also, in a case where a boom lowering operation is performed in a state where the bucket is in contact with the ground, the inlet throttle flow rate to the boom cylinder can be increased to perform a lifting action.

[0003] Such control of the inlet throttle flow rate to the boom cylinder is performed, for example, by controlling the supply flow rate of hydraulic oil to the boom cylinder using a solenoid valve in accordance with the bottom pressure of the boom cylinder (Patent Literature 1).

[0004] PRIOR ART DOCUMENTS

[0005] PATENT LITERATURE

[0006] Patent Literature 1: Japanese Patent Application Publication No. 2010-275818 SUMMARY

[0007] PROBLEMS TO BE SOLVED BY THE INVENTION

[0008] For a boom lowering action performed in a state where the bucket is suspended, or a lifting action performed by pressing the bottom surface of the bucket against the ground and lowering the boom, the bottom pressure of the boom cylinder does not change drastically, and thus the inlet throttle flow rate can be appropriately controlled by the technique disclosed in Patent Literature 1.

[0009] However, in a tamping operation where the boom is repeatedly raised and lowered, for example, the control of the inlet throttle flow rate can act against the operator's intention due to drastic changes in the bottom pressure of the boom cylinder. In a boom lowering operation in a state where the bucket is suspended, the control is performed in a manner that the bottom pressure of the boom cylinder becomes high, the rod pressure of the boom cylinder becomes low, and the inlet throttle flow rate becomes small. On the other hand, in a lifting operation where the bucket is pressed against the ground, the control is performed in a manner that the bottom pressure of the boom cylinder becomes low, the rod pressure of the boom cylinder becomes high, and the inlet throttle flow rate becomes large. However, in a tamping operation where the boom is repeatedly raised and lowered in a short period of time, after switching from a boom raising operation to a boom lowering operation, the inlet throttle flow rate corresponding to the lifting operation can be selected, and the state where the inlet throttle flow rate is large can continue. As a result, a state where the required boom action speed does not match can occur, and the operability is affected.

[0010] The present application provides a construction machine capable of matching the speed of a boom to a required speed and improving operability.

[0011] Means for solving the problem

[0012] To achieve the above object, the present application provides a construction machine including a vehicle body, a front work machine coupled to the vehicle body, a boom cylinder that drives the front work machine up and down, a prime mover, a first hydraulic pump driven by the prime mover, a second hydraulic pump driven by the prime mover, a first directional control valve that controls hydraulic oil flowing from the first hydraulic pump to the boom cylinder, a second directional control valve that controls hydraulic oil flowing from the second hydraulic pump to the boom cylinder, a pilot pump that discharges pilot oil for driving the first directional control valve and the second directional control valve, a boom lowering pressure-reducing valve that sets the pilot oil to an initial pressure and outputs a boom lowering pilot pressure for driving the first directional control valve and the second directional control valve in a boom lowering direction, a boom raising pressure-reducing valve that sets the pilot oil to an initial pressure and outputs a boom raising pilot pressure for driving the first directional control valve and the second directional control valve in a boom raising direction, and a boom operation lever that operates the boom lowering pressure-reducing valve and the boom raising pressure-reducing valve. The construction machine includes a bottom pressure sensor that measures a bottom pressure of the boom cylinder, an operation amount sensor that measures an operation amount of the boom operation lever, a solenoid valve provided in a pilot oil path connecting the boom lowering pressure-reducing valve and a pressure-receiving chamber of the second directional control valve and reducing the boom lowering pilot pressure for the second directional control valve, and a controller that controls the solenoid valve based on the bottom pressure measured by the bottom pressure sensor and the operation amount measured by the operation amount sensor. The controller calculates a first opening degree command value in such a manner that a communication area of the pressure-receiving chamber of the boom lowering pressure-reducing valve and the second directional control valve decreases as the bottom pressure increases based on the bottom pressure measured by the bottom pressure sensor, calculates a second opening degree command value in such a manner that the communication area increases as the boom lowering operation amount increases based on the boom lowering operation amount measured by the operation amount sensor, determines a minimum opening degree command value that makes the communication area minimum as the opening degree command value of the solenoid valve in a case where an elapsed time after a boom raising operation is less than a set time, determines a minimum selection value of the first opening degree command value and the second opening degree command value as the opening degree command value of the solenoid valve in a case where the elapsed time is the set time or more, and outputs a command signal corresponding to the determined opening degree command value to the solenoid valve.

[0013] Effects of the invention

[0014] According to the present application, the speed of a boom can be matched to a required speed, and operability can be improved.BRIEF DESCRIPTION OF DRAWINGS BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 is a side view of a construction machine representing an embodiment of the present application.

[0016] Figure 2 is a circuit diagram representing a main part of a hydraulic system mounted on a construction machine of an embodiment of the present application.

[0017] Figure 3 is a flowchart representing a control step of a controller of a construction machine of an embodiment of the present application.

[0018] Figure 4 is a diagram representing an example of a functional block of a controller for executing Figure 3 a flow. DETAILED DESCRIPTION

[0019] Hereinafter, an embodiment of the present application will be described using the drawings.

[0020] CONSTRUCTION MACHINE

[0021] Figure 1 is a side view of a construction machine representing an embodiment of the present application. In this drawing, a hydraulic excavator 1 is exemplified as the construction machine, but the present application can be applied to other kinds of construction machines for various works such as civil engineering works, construction works, dismantling works, and the like. The hydraulic excavator 1 is of a crawler type, but the present application can also be applied to a construction machine of a wheel type.

[0022] The hydraulic excavator 1 is constituted by including a vehicle body 4 and a front working machine 10 mounted to the vehicle body 4. The vehicle body 4 is constituted by including a traveling body 2 and a swing body 3 swingably provided on the traveling body 2. The traveling body 2 travels by driving left and right crawlers with a traveling hydraulic motor. The swing body 3 has a cab 7 in which an operator rides, and is swingably driven with respect to the traveling body 2 by a swing hydraulic motor provided to the vehicle body 4. Inside the cab 7, in addition to the above-mentioned traveling hydraulic motor and swing hydraulic motor, there are provided various operation devices for operating various hydraulic actuators mounted to the hydraulic excavator 1, such as a boom cylinder 15, a stick cylinder 16, and a bucket cylinder 17, which will be described later.

[0023] The front working machine 10 is a working machine in which a multi-joint type working arm 11 is mounted with a bucket 14 as an accessory device corresponding to a work, and is linked to the swing body 3. The working arm 11 includes a boom 12 linked to a front portion of the swing body 3 so as to be able to turn up and down, and a stick 13 linked to a front end of the boom 12 so as to be able to turn back and forth. The boom 12 is driven by the boom cylinder 15, the stick 13 is driven by the stick cylinder 16, and the bucket 14 is driven by the bucket cylinder 17. In the working arm 11, the boom 12, the stick 13, and the bucket 14 are linked to each other so as to be able to turn in a horizontal plane. Figure 1The bucket 14 is exemplified as the attachment mounted to the working arm 11, but the bucket 14 can be replaced with another attachment such as a grab.

[0024] Hydraulic system

[0025] Figure 2 is a circuit diagram of a main part of a hydraulic system of the construction machine shown in Figure 1 is a circuit diagram of a main part of a hydraulic system of the construction machine shown in Figure 2 The driving circuit of the boom cylinder 14 is extracted in The hydraulic system shown in the drawing has a prime mover 51, a first hydraulic pump 52, a second hydraulic pump 53, a first directional control valve 54, a second directional control valve 55, a pilot pump 56, an operation lever device 57, a solenoid valve 58, and a controller 60.

[0026] Hydraulic pump

[0027] The first hydraulic pump 52 and the second hydraulic pump 53 are variable capacity type pumps that discharge working oil for driving hydraulic actuators mounted to the hydraulic excavator 1, and are driven by the prime mover 51. The prime mover 51 in the present embodiment is an engine that converts combustion energy of an internal combustion engine or the like into power, but an electric motor is sometimes used as the prime mover 51. In the present embodiment, only one of the first hydraulic pump 52 and the second hydraulic pump 53 is illustrated, but at least one of the first hydraulic pump 52 and the second hydraulic pump 53 is sometimes provided as a plurality of pumps. Figure 2 Hydraulic oil taken in from the working oil tank 59 and discharged from the first hydraulic pump 52 is supplied to the boom cylinder 14 via the first directional control valve 54. Hydraulic oil taken in from the working oil tank 59 and discharged from the second hydraulic pump 53 is supplied to the boom cylinder 14 via the second directional control valve 55. Return oil from the boom cylinder 14 is returned to the working oil tank 59 via the first directional control valve 54 and the second directional control valve 55.

[0028] Pilot pump

[0029] The pilot pump 56 is a fixed capacity type pump that discharges pilot oil for driving hydraulic drive type control valves such as the first directional control valve 54 and the second directional control valve 55. Like the first hydraulic pump 52 and the second hydraulic pump 53, the pilot pump 56 is driven by the prime mover 51. It is also possible to configure so that the pilot pump 56 is driven by a power source different from the prime mover 51. The discharge passage 56m of the pilot pump 56 is branched and connected to the boom lowering pressure reducing valve 57d, the boom raising pressure reducing valve 57u, and the like of the operation lever device 57. The discharge pressure of the pilot pump 56 is input as a pilot pressure primary pressure to the boom lowering pressure reducing valve 57d, the boom raising pressure reducing valve 57u, and the like via the discharge line 57a.

[0030] First directional control valve

[0031] The first direction control valve 54 is a hydraulic drive type direction switching valve that controls the flow (direction and flow rate) of hydraulic oil supplied from the first hydraulic pump 52 to the boom cylinder 15, and is driven by a pilot pressure input to a pressure-receiving chamber. The first direction control valve 54 is a proportional three-position switching valve having a boom lowering position 54d, a boom raising position 54u, and a neutral position 54n. In a state where no pilot pressure is acting, the spool of the first direction control valve 54 is located at the neutral position 54n by spring force.

[0032] In a case where the first direction control valve 54 is in the neutral position 54n, the first hydraulic pump 52 is connected to the working oil tank 59 bypassing the boom cylinder 15, and the rod-side oil chamber and the bottom-side oil chamber of the boom cylinder 15 are closed. Thus, the boom cylinder 15 is kept from extending and contracting.

[0033] In a case where the first direction control valve 54 is in the boom lowering position 54d, the first hydraulic pump 52 is connected to the working oil tank 59 bypassing the boom cylinder 15, and the bottom-side oil chamber of the boom cylinder 15 is connected to the rod-side oil chamber and the working oil tank 59. Thus, a part of hydraulic oil pushed out of the bottom-side oil chamber by the weight of the front working machine 10 is supplied to the rod-side oil chamber, and the boom cylinder 15 contracts.

[0034] In a case where the first direction control valve 54 is in the boom raising position 54u, the first hydraulic pump 52 is connected to the bottom-side oil chamber of the boom cylinder 15, and the rod-side oil chamber of the boom cylinder 15 is connected to the working oil tank 59. Thus, the boom cylinder 15 extends by hydraulic oil discharged from the first hydraulic pump 52.

[0035] • Second direction control valve

[0036] The second direction control valve 55 is a hydraulic drive type direction switching valve that controls the flow (direction and flow rate) of hydraulic oil supplied from the second hydraulic pump 53 to the boom cylinder 15, and is driven by a pilot pressure input to a pressure-receiving chamber. The second direction control valve 55 is a proportional three-position switching valve having a boom lowering position 55d, a boom raising position 55u, and a neutral position 55n. In a state where no pilot pressure is acting, the spool of the second direction control valve 55 is located at the neutral position 55n by spring force.

[0037] In a case where the second direction control valve 55 is in the neutral position 55n, the second hydraulic pump 53 is connected to the working oil tank 59 bypassing the boom cylinder 15, and the rod-side oil chamber and the bottom-side oil chamber of the boom cylinder 15 are closed. Thus, the boom cylinder 15 is kept from extending and contracting.

[0038] In a case where the second direction control valve 55 is in the boom lowering position 55d, the second hydraulic pump 53 is connected to the rod-side oil chamber of the boom cylinder 15, and the bottom-side oil chamber of the boom cylinder 15 is connected to the working oil tank 59. Thus, the boom cylinder 15 contracts by hydraulic oil discharged from the second hydraulic pump 53.

[0039] With the second directional control valve 55 in the boom-raised position 55u, the second hydraulic pump 53 is connected to the bottom oil chamber of the boom cylinder 15, and the rod-side oil chamber of the boom cylinder 15 is connected to the working oil tank 59. Thus, the boom cylinder 15 extends using the hydraulic oil discharged from the second hydraulic pump 53.

[0040] • Boom lowering pressure relief valve

[0041] The pressure chambers on the boom lowering side of the first directional control valve 54 and the second directional control valve 55 are respectively connected to the boom lowering pressure relief valve 57d via pilot oil passages 56a and 56b, and are also connected to the pilot pump 56 via the boom lowering pressure relief valve 57d. The boom lowering pressure relief valve 57d is operated by the boom operating lever 57l. When the boom operating lever 57l is moved in the boom lowering direction (in... Figure 2 When operating in the left direction (center to left), the boom lowering pressure relief valve 57d operates according to the operating amount of the boom operating lever 57l. Consequently, the discharge oil passage 56m of the pilot pump 56 is connected to the pilot oil passages 56a and 56b, and the pressure of the pilot oil from the pilot pump 56 is used as the initial pressure to output a boom lowering pilot pressure corresponding to the boom lowering operating amount of the boom operating lever 57l. When this pilot pressure acts on the pressure chambers of the first directional control valve 54 and the second directional control valve 55 on the boom lowering side, the first directional control valve 54 and the second directional control valve 55 are driven from the neutral positions 54n and 55n in the boom lowering direction, switching to the boom lowering positions 54d and 55d.

[0042] • Boom lifting pressure reducing valve

[0043] The pressure chambers on the boom lifting side of the first directional control valve 54 and the second directional control valve 55 are connected to the boom lifting pressure reducing valve 57u via pilot oil lines 56c and 56d, respectively, and are also connected to the pilot pump 56 via the boom lifting pressure reducing valve 57u. The boom lifting pressure reducing valve 57u is also operated by the boom lowering pressure reducing valve 57d, similar to the boom operating lever 57l. When the boom operating lever 57l is moved in the boom lifting direction (in... Figure 2 When operating in the right direction (center to right), the boom lifting pressure relief valve 57u operates according to the operating amount of the boom operating lever 57l. Consequently, the discharge oil passage 56m of the pilot pump 56 is connected to the pilot oil passages 56c and 56d, using the pressure of the pilot oil from the pilot pump 56 as the initial pressure to output a boom lifting pilot pressure corresponding to the boom lifting operation amount of the boom operating lever 57l. When this pilot pressure acts on the pressure chambers of the first directional control valve 54 and the second directional control valve 55 on the boom lifting side, the first directional control valve 54 and the second directional control valve 55 are driven from the neutral positions 54n and 55n in the boom lifting direction, switching to the boom lifting positions 54u and 55u.

[0044] Solenoid valve

[0045] The electromagnetic valve 58 is a proportional electromagnetic pressure-reducing valve that reduces the boom lowering pilot pressure output from the boom lowering pressure-reducing valve 57d and outputs a corrected boom lowering pilot pressure (a corrected boom lowering pilot pressure) to the pressure-receiving chamber on the boom lowering side of the second directional control valve 55. The electromagnetic valve 58 is provided to the pilot oil passage 56b that connects the boom lowering pressure-reducing valve 57d and the pressure-receiving chamber on the boom lowering side of the second directional control valve 55. The electromagnetic valve 58 has an open position 58a and a shut position 58b. In the present embodiment, the spool of the electromagnetic valve 58 is pressed to the shut position 58b side by the spring force in a state where the solenoid is demagnetized, and moves to the open position 58a side against the spring force if the solenoid is excited. However, it can also be configured such that the spool is pressed to the open position 58a in the demagnetized state, and moves to the shut position 58b side when excited.

[0046] The electromagnetic valve 58 is a two-position valve configured to be switched to the open position 58a and the shut position 58b. When the electromagnetic valve 58 is switched to the open position 58a, the pressure-receiving chamber on the boom lowering side of the second directional control valve 55 is connected to the boom lowering pressure-reducing valve 57d. When the electromagnetic valve 58 is switched to the shut position 58b, the pressure-receiving chamber on the boom lowering side of the second directional control valve 55 is connected to the working oil tank 59. The position of the spool is adjusted by the excitation current to the solenoid of the electromagnetic valve 58, whereby the proportion of the open area of the pressure-receiving chamber of the second directional control valve 55 connected to the boom lowering pressure-reducing valve 57d and the open area of the pressure-receiving chamber connected to the working oil tank 59 is changed. The amount of pressure reduction of the boom lowering pilot pressure is adjusted by the proportion of the open area, and the corrected boom lowering pilot pressure to the second directional control valve 55 is controlled. The greater the amount of pressure reduction of the boom lowering pilot pressure to the second directional control valve 55 based on the electromagnetic valve 58 (the smaller the corrected boom lowering pilot pressure), the smaller the amount of movement of the second directional control valve 55 to the boom lowering direction even if the same boom lowering operation amount is performed. Also, the amount of supply of hydraulic oil flowing from the second hydraulic pump 53 to the rod-side oil chamber of the boom cylinder 15 is reduced. As a result, the inlet throttling flow rate from the second hydraulic pump 53 to the rod-side oil chamber of the boom cylinder 15 is reduced even if the same boom lowering operation amount is performed.

[0047] In the present embodiment, when the electromagnetic valve 58 is completely switched to the shut position 58b, the boom lowering pilot pressure does not act on the second directional control valve 55, and hydraulic oil is not supplied from the second hydraulic pump 53 to the rod-side oil chamber of the boom cylinder 15 even if the boom lowering operation is performed. On the other hand, when the electromagnetic valve 58 is completely switched to the open position 58a, the amount of pressure reduction of the boom lowering pilot pressure is the smallest. Thus, the second directional control valve 55 operates in accordance with the boom lowering operation amount to the same extent as the first directional control valve 54, and hydraulic oil is supplied from the second hydraulic pump 53 to the rod-side oil chamber of the boom cylinder 15.

[0048] • sensor

[0049] The operation amount of the boom operation lever 57l is measured by the operation amount sensors S3, S4. The operation amount sensor S3 measures the boom lowering operation amount Ad, and the operation amount sensor S4 measures the boom raising operation amount Au. The operation amount sensors S3, S4 are pressure sensors. The operation amount sensor S3 is provided to a pilot oil passage 56a or 56b (for example, an output port of the boom lowering pressure reducing valve 57d or immediately downstream thereof) that connects the boom lowering pressure reducing valve 57d and a pressure-receiving chamber on the boom lowering side of the first directional control valve 54 and the solenoid valve 58. The boom lowering pilot pressure is measured by the operation amount sensor S3, whereby the boom lowering operation amount Ad is measured. The operation amount sensor S4 is provided to a pilot oil passage 56c or 56d (for example, an output port of the boom raising pressure reducing valve 57u or immediately downstream thereof) that connects the boom raising pressure reducing valve 57u and pressure-receiving chambers on the boom raising side of the first directional control valve 54 and the second directional control valve 55. The boom raising pilot pressure is measured by the operation amount sensor S4, whereby the boom raising operation amount Au is measured. Further, instead of the pressure sensors, a potentiometer or the like can be used as the operation amount sensors S3, S4 to measure the angle of the boom operation lever 57l, thereby measuring the boom lowering operation amount Ad and the boom raising operation amount Au.

[0050] The bottom pressure Pb (pressure of the bottom side oil chamber) of the boom cylinder 15 is measured by the bottom pressure sensor S1. The bottom pressure sensor S1 is a pressure sensor provided to an oil passage (for example, an input / output port of the bottom side oil chamber or the vicinity thereof) that connects the bottom side oil chamber of the boom cylinder 15 and the first directional control valve 54 and the second directional control valve 55.

[0051] In addition, in the present embodiment, it is not necessarily required, but the rod pressure Pr (pressure of the rod side oil chamber) of the boom cylinder 15 is measured by the rod pressure sensor S2. The rod pressure sensor S2 is a pressure sensor provided to an oil passage (for example, an input / output port of the rod side oil chamber or the vicinity thereof) that connects the rod side oil chamber of the boom cylinder 15 and the first directional control valve 54 and the second directional control valve 55.

[0052] The measured values of the above-mentioned bottom pressure sensor S1, rod pressure sensor S2, and operation amount sensors S3, S4 are input to the controller 60.

[0053] - controller -

[0054] The operation of the electromagnetic valve 58 is controlled by the controller 60 in accordance with the bottom pressure Pb of the boom cylinder 15 and the operation amount of the boom operation lever 57l. The controller 60 is a vehicle-mounted computer configured by including a CPU, a memory, a timer, and the like, and performs various processes by the CPU executing a program stored in advance in the memory. In the present embodiment, the controller 60 has a characteristic function of controlling the electromagnetic valve 58 in accordance with the bottom pressure measured by the bottom pressure sensor S1, the boom lowering operation amount measured by the operation amount sensor S3, and the elapsed time after the boom raising operation, at the time of boom lowering operation. This function will be described below.

[0055] Figure 3 is a flowchart showing the control steps of the controller 60 on the electromagnetic valve 58. The controller 60 repeatedly executes the flow of Figure 3 at a short cycle time (for example, 0.1 s) at the time of power-on (for example, at the time of key switch-on).

[0056] When the flow of the figure is started, the controller 60 first inputs the measured values (output signals) of the bottom pressure sensor S1 and the operation amount sensors S3, S4 (step S01).

[0057] Next, the controller 60 determines whether the boom lowering operation is being performed (whether the boom lowering operation amount Ad is > 0) in accordance with the measured value of the operation amount sensor S3 (step S02). In the case where the boom lowering operation is being performed, the controller 60 transfers the step from step S02 to step S03. In the case where the boom lowering operation is not being performed, the controller 60 transfers the step from step S02 to step S07.

[0058] In the case where the boom lowering operation is being performed, the controller 60 calculates the first opening command value V1 of the electromagnetic valve 58 in accordance with the bottom pressure Pb of the boom cylinder 15 measured by the bottom pressure sensor S1 (step S03). The first opening command value V1 is calculated in accordance with a control table set in such a manner that the communication area of the boom lowering pressure reducing valve 57d with the pressure-receiving chamber of the second directional control valve 55 (the opening area of the oil passage of the opening position 58a) decreases as the bottom pressure Pb increases.

[0059] Next, the controller 60 calculates the second opening command value V2 of the electromagnetic valve 58 in accordance with the boom lowering operation amount Ad measured by the operation amount sensor S3 (step S04). The order of steps S03, S04 can be reversed, or they can be performed simultaneously. The second opening command value V2 is calculated in accordance with a control table set in such a manner that the communication area of the boom lowering pressure reducing valve 57d with the pressure-receiving chamber of the second directional control valve 55 (the opening area of the oil passage of the opening position 58a) increases as the boom lowering operation amount Ad increases.

[0060] Next, the controller 60 calculates the elapsed time T since the boom raising operation, based on the measured value of the operation amount sensor S4, and determines whether the elapsed time T is equal to or greater than a predetermined set time Ts (step S05). The elapsed time T is, for example, the time from the time when the last input boom raising operation amount Au (> 0) becomes 0 to the current time. Further, the start of the elapsed time T can be the time when the boom raising operation amount reaches a predetermined pilot pressure. In the case where the elapsed time T is equal to or greater than the set time Ts, the controller 60 shifts the step from step S05 to step S06. In the case where the elapsed time T is less than the set time Ts, the controller 60 shifts the step from step S05 to step S07.

[0061] In the case where the elapsed time T since the boom raising operation is equal to or greater than the set time Ts, the controller 60 determines the minimum selected value (the smaller one of the values) of the first opening degree command value V1 and the second opening degree command value V2 as the final opening degree command value V (step S06).

[0062] In the case where the elapsed time T since the boom raising operation is less than the set time Ts, the controller 60 determines the minimum opening degree command value Vmin as the final opening degree command value V (step S07). The same applies to the case where it is determined in step S02 that the boom lowering operation is not performed. The minimum opening degree command value Vmin is a value that minimizes the communication area (the opening area of the oil passage of the open position 58a) of the boom lowering pressure reducing valve 57d and the pressure-receiving chamber of the second directional control valve 55. The minimum value of the communication area (the opening area of the oil passage of the open position 58a) is, for example, 0, in which case the pressure-receiving chamber of the boom lowering side of the second directional control valve 55 is cut off between the boom lowering pressure reducing valve 57d and is connected only to the working oil tank 59.

[0063] If the opening degree command value V is determined in step S06 or S07, the controller 60 generates a command signal (current or voltage) corresponding to the determined opening degree command value V, and outputs the generated command signal to the electromagnetic valve 58 (applied to the solenoid) to return the step to step S01 (step S08).

[0064] The electromagnetic valve 58 is controlled as described above, whereby the operation of the second directional control valve 55 at the time of the boom lowering operation is conditionally limited. If the operation of the second directional control valve 55 is limited, the inlet throttling flow rate from the second hydraulic pump 53 to the bottom side oil chamber of the boom cylinder 15 decreases even for the same boom lowering operation amount Ad.

[0065] Figure 4 is a flow of the controller 60 that is an example of a functional block that represents a function of Figure 3 Figure 4 ​In the example shown, the controller 60 has a function that performs the processes of the first opening command value operation 61, the second opening command value operation 62, the boom-raising operation elapsed time operation 63, the third opening command value operation 64, and the opening command value decision 65.

[0066] The first opening command value operation 61 is a process that operates the first opening command value V1 from the base pressure Pb measured by the base pressure sensor S1 according to a control line (control table) stored in the memory. As shown in the block of the first opening command value operation 61, the control line is defined such that, in a Pb-V1 coordinate system that takes Pb on the horizontal axis and V1 on the vertical axis, V1 decreases as Pb increases. The first opening command value V1 corresponds to a value that indicates the communication area of the boom lowering pressure reducing valve 57d and the pressure-receiving chamber on the boom lowering side of the second direction control valve 55, and the larger V1 is, the larger the communication area is. V1 operated under the control line shown in the block of the first opening command value operation 61 decreases as the base pressure Pb increases.

[0067] At this time, in the present embodiment, the control line referred to in the first opening command value operation 61 includes a first control line L1 and a second control line L2. The first control line L1 is a control line referred to when the base pressure Pb increases, and the second control line L2 is a control line referred to when the base pressure Pb decreases. P1 to P4 shown in the block of the first opening command value operation 61 are set values for Pb (P1

[0068] The first control line L1 is defined such that, in a region where Pb

[0069] The value of Vl calculated by the controller 60 along with the increase and decrease of Pb under the control line will be described in detail. In the case where Pb rises from a value below P2 (i.e., Vl takes a value of Vmax), the controller 60 decreases Vl along the first control line LI (Vl corresponding to Pb is calculated on the first control line LI). On the contrary, in the case where Pb falls from a value above P3 (i.e., Vl takes a value of Vmin), the controller 60 increases Vl along the second control line L2 (Vl corresponding to Pb is calculated on the second control line L2). Thus, for example, in the case where Pb rises from PI to P4 and then falls to PI, Vl simply decreases from Vmax to Vmin along the first control line LI with the rise of Pb, and then increases from Vmin to Vmax along the second control line L2 with the fall of Pb.

[0070] On the contrary, in the case where Pb rises from a value below P2 to P4 and then falls to Px (P2

[0071] In the case where Pb falls from a value above P3 to PI and then falls to Px (P3

[0072] The second opening command value calculation 62 is a process of calculating the second opening command value V2 from the boom lowering operation amount Ad measured by the operation amount sensor S3 in accordance with the control line (control table) stored in the memory. As shown in the block of the second opening command value calculation 62, the control line is defined such that V2 increases with the increase of Ad in the Ad-V2 coordinate system in which the horizontal axis takes Ad and the vertical axis takes V2. The second opening command value V2 also corresponds to a value indicative of the communication area of the boom lowering pressure reducing valve 57d and the boom lowering side of the pressure chamber of the second directional control valve 55, and the larger V2 is, the larger the communication area is. V2 calculated under the control line shown in the block of the second opening command value calculation 62 increases with the increase of Ad.

[0073] A1, A2 shown in the block of the second opening degree command value operation 62 are set values with respect to Ad (0 < A1 < A2). The control line referred to in the second opening degree command value operation 62 is defined such that V2 = Vmin in a region where Ad < A1, V2 monotonously increases from Vmin to Vmax as Ad increases in a region where A1 ≤ Ad ≤ A2, and V2 = Vmax in a region where Ad > A2. Unlike the control line referred to in the first opening degree command value operation 61, the control line referred to in the second opening degree command value operation 62 is single, and the value on the control line is always operated as V2 with respect to Ad.

[0074] The boom-raising operation elapsed time operation 63 is a process of operating the elapsed time T from the stop of the most recent boom-raising operation to the current time, based on the boom-raising operation amount Au measured by the operation amount sensor S4 and the measured time of the timer. The start of the elapsed time T is the time when the most recent boom-raising operation amount Au (> 0) becomes 0. The time when the boom-raising operation amount Au becomes 0 can be determined, for example, from the log data of the boom-raising operation amount Au stored in the memory, and the boom-raising operation elapsed time T is operated as the difference between the determined time and the current time.

[0075] The third opening degree command value operation 64 is a process of operating the third opening degree command value V3 of the electromagnetic valve 58 based on the boom-raising operation elapsed time T. In the process of the third opening degree command value operation 64, in the case where the boom-raising operation elapsed time T is less than the set time Ts, the third opening degree command value V3 of the electromagnetic valve 58 is operated in such a manner that the communication area of the boom lowering pressure reducing valve 57d and the pressure-receiving chamber on the boom lowering side of the second directional control valve 55 is the minimum value (V3 = Vmin). In addition, in the case where the boom-raising operation elapsed time T is the set time Ts or more, the third opening degree command value V3 of the electromagnetic valve 58 is operated in such a manner that the communication area of the boom lowering pressure reducing valve 57d and the pressure-receiving chamber on the boom lowering side of the second directional control valve 55 is the maximum value (V3 = Vmax).

[0076] The opening degree command value decision 65 is a process of deciding the minimum selected value of the first opening degree command value V1, the second opening degree command value V2, and the third opening degree command value V3 as the opening degree command value V, and generating and outputting the command signal to the electromagnetic valve 58 based on the decided opening degree command value V. If the boom-raising operation elapsed time T is less than the set time Ts, the third opening degree command value V3 is the minimum opening degree command value Vmin, and therefore, if T < Ts, it is necessarily V = Vmin. In addition, if the boom-raising operation elapsed time T is the set time Ts or more, V3 = Vmax, and therefore, if T ≥ Ts, the minimum selected value of V1 and V2 is necessarily V.

[0077] The electromagnetic valve 58 is controlled by the above-described processes, and therefore, as in the example shown in FIG. 6, the communication area of the boom lowering pressure reducing valve 57d and the pressure-receiving chamber on the boom lowering side of the second directional control valve 55 is the minimum value (V3 = Vmin) immediately after the boom-raising operation, and the communication area of the boom lowering pressure reducing valve 57d and the pressure-receiving chamber on the boom lowering side of the second directional control valve 55 is the maximum value (V3 = Vmax) after the boom-raising operation elapsed time T reaches the set time Ts.Figure 3 The amount of restriction of the inlet throttle flow to the bottom side oil chamber of the boom cylinder 15 at the time of the boom lowering operation is appropriately controlled as explained above.

[0078] In the present embodiment, in the case where the boom lowering operation amount Ad is small and the bottom pressure Pb is high, the operation of the second directional control valve 55 is restricted (operation restriction is enhanced), and the inlet throttle flow to the rod side oil chamber of the boom cylinder 15 is reduced. In the case where the boom lowering operation amount Ad is small and the bottom pressure Pb is high, it is presumed that the boom lowering operation is performed in a state where the bucket 14 is suspended, and in such a scenario, unnecessary inlet throttle flow for boom lowering is suppressed, whereby energy loss can be suppressed.

[0079] In addition, in the case where the boom lowering operation amount Ad is large and the bottom pressure Pb is low, the operation restriction of the second directional control valve 55 is released (operation restriction is weakened), and the inlet throttle flow to the rod side oil chamber of the boom cylinder 15 is increased. In the case where the boom lowering operation amount Ad is large and the bottom pressure Pb is low, it is presumed that the bucket 14 is forcibly pressed into the ground as in a lifting operation, and in such a scenario of high load work, the inlet throttle flow for boom lowering can be ensured.

[0080] Further, during the elapsed time T after the recent boom raising operation reaches the set time Ts, the operation of the second directional control valve 55 is prohibited (operation restriction is maximum), and even if the boom lowering operation is performed, the inlet throttle flow to the rod side oil chamber of the boom cylinder 15 does not immediately increase. For example, in the case where the boom raising operation and the boom lowering operation are alternately repeated at a short cycle as in a tamping work, for example, at the time of switching back from the boom raising to the boom lowering, the bottom pressure Pb of the boom cylinder 15 sometimes greatly fluctuates. In such a case, if the control condition of the solenoid valve 58 is accidentally satisfied, the solenoid valve 58 operates in an undesirable scenario, and the operability can deteriorate, but the solenoid valve 58 does not operate from the boom raising operation to the set time Ts, and thus, deterioration of the operability can be suppressed.

[0081] -Effects-

[0082] (1) As described above, according to the present embodiment, in the scenario of the low-load boom lowering operation presumed to be performed in the state where the bucket 14 is suspended, the energy loss can be suppressed by suppressing the inlet throttle flow for the boom lowering. In addition, in the scenario of the high-load boom lowering operation presumed to be performed such that the bucket 14 is strongly pressed against the ground like the lifting operation, the inlet throttle flow for the boom lowering can be increased to secure the required output. Also, in the scenario where the solenoid valve 58 can operate in an undesirable manner in the case where the boom raising operation and the boom lowering operation are repeatedly performed like the tamping work, the operation of the solenoid valve 58 is suppressed from the boom raising operation until the lapse of the set time Ts, whereby the excessive inlet throttle flow at the time of the boom lowering can be suppressed, and the deterioration of the operability can be suppressed.

[0083] As described above, according to the present embodiment, the operation speed of the boom can be made to coincide with the required speed, and the reduction of the energy loss and the improvement of the operability can be both taken into account.

[0084] (2) For example, in the case where the bucket 14 shifts from the suspended state to the lifting operation, or the boom cylinder 15 is rapidly contracted by the emergency operation in the boom lowering operation, there is a moment where the bottom pressure Pb increases and decreases in the operation of the front working machine 10. If the first opening command value V1 is increased and decreased in accordance with the increase and decrease of the bottom pressure Pb at such a moment, the solenoid valve 58 can operate excessively sensitively to affect the operability.

[0085] In contrast to this, in the present embodiment, the first control line L1 and the second control line L2 are prepared, and the first opening command value V1 is calculated under the first control line L1 at the time of the increase of the Pb, and the first opening command value V1 is calculated under the second control line L2 at the time of the decrease of the Pb. The first control line L1 and the second control line L2 are offset by ΔPb in the Pb-V1 coordinate system in the direction of the Pb axis, and therefore, at the time when the value of the Pb changes from the increase to the decrease (or from the decrease to the increase), the first opening command value V1 does not change until the change of the Pb exceeds a certain amount (ΔPb). Therefore, the solenoid valve 58 can be suppressed from operating excessively sensitively in the scenario where the bottom pressure Pb increases and decreases as described above.

[0086] - Modified Examples -

[0087] The embodiment of the present application has been described above, but the embodiment of the present application is not limited to the above-described mode, and various modifications can be made within the scope of the gist of the present application. Several modified examples will be exemplified below.

[0088] For example, the case where the first opening command value V1 is calculated only from the bottom pressure Pb of the boom cylinder 15 has been described. In this regard, the controller 60 can be configured to calculate the difference between the rod pressure Pr measured by the rod pressure sensor S2 and the bottom pressure Pb, and calculate the first opening command value V1 from the difference.

[0089] In addition, the operation lever device 57 having the boom operation lever 57l mechanically linked with the boom lowering pressure reducing valve 57d and the boom raising pressure reducing valve 57u is described, but the operation lever device 57 can also adopt an electric lever device. In this case, the boom lowering pressure reducing valve 57d and the boom raising pressure reducing valve 57u are provided as electromagnetic drive types, and the boom lowering pressure reducing valve 57d and the boom raising pressure reducing valve 57u are operated by an instruction signal output from the controller 60 according to an operation signal of the electric lever device. Even in the case where the operation lever device 57 adopts the electric lever device, the operation amount of the boom operation lever 57l can be detected by a potentiometer or the like, and the present application can be applied.

[0090] In addition, the case where the first hydraulic pump 52 and the second hydraulic pump 53 are each one is described, but at least one of the first hydraulic pump 52 and the second hydraulic pump 53 can be provided as a plurality of pumps.

[0091] Symbol Description

[0092] 1...hydraulic shovel (construction machine), 4...vehicle body, 10...front working machine, 15...boom cylinder, 51...prime mover, 52...first hydraulic pump, 53...second hydraulic pump, 54...first directional control valve, 55...second directional control valve, 56...pilot pump, 56b...pilot oil passage, 57d...boom lowering pressure reducing valve, 57l...boom operation lever, 57u...boom raising pressure reducing valve, 58...solenoid valve, 60...controller, Ad...boom lowering operation amount (operation amount), Au...boom raising operation amount (operation amount), L1...first control line, L2...second control line, Pb...bottom pressure, Pr...rod pressure, S1...bottom pressure sensor, S2...rod pressure sensor, S3, S4...operation amount sensor, T...elapsed time, Ts...set time, V...opening degree command value, V1...first opening degree command value, V2...second opening degree command value, V3...third opening degree command value, Vmax...maximum opening degree command value, Vmin...minimum opening degree command value.

Claims

1. An engineering machine, comprising: a vehicle body; a front work machine connected to the vehicle body; a boom cylinder for driving the front work machine up and down; a prime mover; a first hydraulic pump driven by the prime mover; a second hydraulic pump driven by the prime mover; a first directional control valve for controlling hydraulic oil flowing from the first hydraulic pump to the boom cylinder; a second directional control valve for controlling hydraulic oil flowing from the second hydraulic pump to the boom cylinder; a pilot pump for discharging pilot oil that drives the first and second directional control valves; a boom lowering pressure relief valve for setting the pilot oil to an initial pressure and outputting a boom lowering pilot pressure that drives the first and second directional control valves in a boom lowering direction; a boom lifting pressure relief valve for setting the pilot oil to an initial pressure and outputting a boom lifting pilot pressure that drives the first and second directional control valves in a boom lifting direction; and a boom operating lever for operating the boom lowering pressure relief valve and the boom lifting pressure relief valve, characterized in that... The engineering machinery has the following features: A bottom pressure sensor that measures the bottom pressure of the boom cylinder; An operation quantity sensor measures the operation quantity of the boom control lever; A solenoid valve, disposed in the pilot oil circuit connecting the boom lowering pressure reducing valve to the pressure receiving chamber of the second directional control valve, reduces the pilot pressure for boom lowering relative to the second directional control valve; and The controller controls the solenoid valve based on the bottom pressure measured by the bottom pressure sensor and the operating amount measured by the operating amount sensor. The controller calculates the first opening command value based on the bottom pressure measured by the bottom pressure sensor, in a manner that the communication area between the pressure chambers of the boom lowering pressure reducing valve and the second directional control valve decreases as the bottom pressure increases. The controller calculates a second opening command value based on the boom lowering operation amount measured by the operation amount sensor, in a manner that the connected area increases with the increase of the boom lowering operation amount. The controller determines the opening command value of the solenoid valve based on the elapsed time after the boom lifting operation. If the elapsed time is less than a set time, the controller sets the minimum opening command value that minimizes the connected area as the opening command value of the solenoid valve. If the elapsed time is greater than the set time, the controller sets the minimum value between the first opening command value and the second opening command value as the opening command value of the solenoid valve. The controller outputs a command signal corresponding to the determined opening command value to the solenoid valve.

2. The engineering machinery according to claim 1, characterized in that, The controller stores a first control line and a second control line. In a coordinate system where the horizontal axis represents the base pressure and the vertical axis represents the first opening command value, the first opening command value decreases as the base pressure increases, and the second control line is offset in the direction of the horizontal axis. When the bottom pressure rises, the controller calculates the first opening command value with reference to the first control line; when the bottom pressure falls, the controller calculates the first opening command value with reference to the second control line.

3. The engineering machinery according to claim 1, characterized in that, The construction machinery includes: a rod pressure sensor, which measures the rod pressure of the boom cylinder. The controller calculates the difference between the bottom pressure measured by the bottom pressure sensor and the rod pressure measured by the rod pressure sensor, and calculates the first opening command value based on the difference.

Images