Hydraulic system for excavating

Abstract

A hydraulic system (1A) for excavating according to an embodiment is mounted on an excavator having an excavating shaft with a telescopic structure, and includes a hydraulic motor (4) for rotating the excavating shaft, a directional switching valve (3) connected to the hydraulic motor (4) through a pair of supply and discharge lines (41, 42), and a hydraulic pump (2) connected to the directional switching valve (3) through a discharge line (22). In addition, the hydraulic system (1A) includes a pressure sensor (81) for measuring the discharge pressure of the hydraulic pump (2), a rotational speed sensor (73) for measuring the rotational speed of the hydraulic motor (4), and a control device (6) electrically connected to the pressure sensor (81) and the rotational speed sensor (73). The control device (6) determines that the excavating shaft (17) is twisted when the discharge pressure of the hydraulic pump (2) measured by the pressure sensor (81) is greater than a first threshold value and the rotational speed of the hydraulic motor (4) measured by the rotational speed sensor (73) is less than a second threshold value.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a hydraulic system for excavation loaded on an excavator. BACKGROUND

[0002] Conventionally, an excavator that excavates a vertical hole in a ground is known. The excavator includes an excavation shaft that extends in a vertical direction and a bucket that is provided at a lower end of the excavation shaft. For example, Japanese Patent Application Publication No. 2008-255765 discloses an excavator that rotates the excavation shaft using a hydraulic motor.

[0003] Further, the excavator disclosed in Japanese Patent Application Publication No. 2008-255765 includes a management device that detects an N value that indicates the strength of the ground during excavation. The management device calculates the N value from the inlet pressure and the rotational speed of the hydraulic motor. Then, the management device warns that an excavatable obstacle exists in the ground when the N value is an abnormal value.

[0004] When the bucket abuts against an excavatable obstacle such as a hard rock, the bucket is bent and the vertical hole can be formed obliquely. In this regard, if the presence of the excavatable obstacle in the ground is warned as described above, the oblique formation of the vertical hole can be prevented. SUMMARY

[0005] However, when a deep vertical hole is excavated in the ground, the excavation shaft is a telescopic structure. In such a long excavation shaft, when the excavation load increases due to the abutment of the bucket against an obstacle such as a hard rock, the hydraulic motor is stopped in a state in which the excavation shaft is greatly twisted. Therefore, when the operator reversely rotates the hydraulic motor, the hydraulic motor is reversely rotated at a high speed due to the twist of the excavation shaft, and excessive stress can be applied to the structural members of the hydraulic motor.

[0006] Therefore, an object of the present disclosure is to provide a hydraulic system for excavation that can detect the twist of a telescopic excavation shaft.

[0007] The present disclosure provides, from one aspect, a hydraulic system for excavation that is a hydraulic system for excavation loaded on an excavator having a telescopic excavation shaft, including: a hydraulic motor that rotates the excavation shaft; a directional switching valve that is connected to the hydraulic motor through a pair of supply and discharge lines; a hydraulic pump that is connected to the directional switching valve through a discharge line; a relief valve that is provided on a safety line branched from the discharge line; a pressure sensor that measures the discharge pressure of the hydraulic pump; a rotational speed sensor that measures the rotational speed of the hydraulic motor; and a control device that is electrically connected to the pressure sensor and the rotational speed sensor; wherein the control device determines that the excavation shaft is twisted when the discharge pressure of the hydraulic pump measured by the pressure sensor is greater than a first threshold value and the rotational speed of the hydraulic motor measured by the rotational speed sensor is less than a second threshold value.

[0008] Further, the present disclosure provides a hydraulic system for excavating from another aspect, which is a hydraulic system for excavating loaded on an excavator having an excavating shaft of a telescopic structure, and includes a hydraulic motor that rotates the excavating shaft, a directional switching valve connected to the hydraulic motor through a pair of supply and discharge lines, a hydraulic pump connected to the directional switching valve through a discharge line, a safety valve provided on a safety line branched from the discharge line, a pressure sensor that measures an inlet pressure of the hydraulic motor when the hydraulic motor is rotated in an excavating direction, a rotational speed sensor that measures a rotational speed of the hydraulic motor, and a control device electrically connected to the pressure sensor and the rotational speed sensor; the control device determines that the excavating shaft is twisted when the inlet pressure of the hydraulic motor measured by the pressure sensor is greater than a first threshold value and the rotational speed of the hydraulic motor measured by the rotational speed sensor is less than a second threshold value.

[0009] According to the present disclosure, the twisting of the excavating shaft can be detected. BRIEF DESCRIPTION OF DRAWINGS

[0010] Figure 1 is a schematic configuration diagram of a hydraulic system for excavating of the first embodiment;

[0011] Figure 2 In the present disclosure, Figure 2 A is a side view of an excavator, Figure 2 B is an enlarged view of an excavating unit;

[0012] Figure 3 is a flowchart of control performed by the control device in the first embodiment;

[0013] Figure 4 is a schematic configuration diagram of a hydraulic system for excavating of the second embodiment;

[0014] Figure 5 is a flowchart of control performed by the control device in the second embodiment;

[0015] Figure 6 is a diagram showing a modification example of the directional switching valve;

[0016] Figure 7 is a diagram showing another modification example of the directional switching valve;

[0017] Figure 8 is a diagram showing still another modification example of the directional switching valve;

[0018] Figure 9 is a schematic configuration diagram of a hydraulic system for excavating of the modification example. DETAILED DESCRIPTION

[0019] (First Embodiment)

[0020] Figure 1 A hydraulic system 1A for excavating is shown. The hydraulic system 1A is mounted on an excavator 10 shown in Figure 2 A.

[0021] The excavator 10 includes a frame 11 extending in a vertical direction, on which a digging unit 15 is mounted. The digging unit 15 includes a base 16 combined with the frame 11, a digging shaft 17 extending in the vertical direction through the base 16, and a bucket 18 provided at a lower end of the digging shaft 17. The digging shaft 17 is rotatably and vertically slidably supported to the base 16.

[0022] Further, a reduction gear 19 is mounted on the base 16, on which a hydraulic motor 4 is mounted. The hydraulic motor 4 rotates the digging shaft 17 in a digging direction or a counter-digging direction via the reduction gear 19.

[0023] As shown in Figure 2 B, the digging shaft 17 is a telescopic structure. The digging shaft 17 is moved up and down and extended or contracted by a hoist unit 12 of the excavator 10 via a wire 13. In detail, the digging shaft 17 includes a plurality of tubular bodies having different diameters, and an nth tubular body from the outside is at least partially fitted in an (n-1)th tubular body. The number of the tubular bodies is three in the drawing, but is not particularly limited.

[0024] Returning to Figure 1 , the hydraulic system 1A includes the hydraulic motor 4 described above and a hydraulic pump 2 that supplies working fluid to the hydraulic motor 4 via a directional switching valve 3. The working fluid is typically working oil.

[0025] In detail, the hydraulic pump 2 is connected to a tank 20 via a suction line 21 and connected to the directional switching valve 3 via a discharge line 22. The directional switching valve 3 is connected to the tank 20 via a tank line 25.

[0026] A safety line 23 branches from the discharge line 22, and the safety line 23 is connected to the tank 20. The safety line 23 is provided with a safety valve 24.

[0027] The hydraulic motor 4 has a first port 4a as an inlet port when rotating in the digging direction and a second port 4b as an inlet port when rotating in the counter-digging direction. That is, the second port 4b is an outlet port when the hydraulic motor 4 rotates in the digging direction, and the first port 4a is an outlet port when the hydraulic motor 4 rotates in the counter-digging direction.

[0028] The first port 4a and the second port 4b of the hydraulic motor 4 are connected to the directional switching valve 3 via a pair of feed and discharge lines 41, 42. The feed and discharge line 41 is connected to the first port 4a, and the feed and discharge line 42 is connected to the second port 4b. The directional switching valve 3 has a neutral position between Figure 1 , a digging position, and a counter-digging position.Figure 1 The right side of the location is the excavation location and Figure 1 Switch between the left-hand position and the reverse rotation position.

[0029] In the neutral position, discharge line 22, tank line 25, and feed / discharge lines 41 and 42 are blocked. In the excavation position, discharge line 22 is connected to feed / discharge line 41, and feed / discharge line 42 is connected to tank line 25. In the reverse rotation position, discharge line 22 is connected to feed / discharge line 42, and feed / discharge line 41 is connected to tank line 25.

[0030] In this embodiment, the directional switching valve 3 is driven by a pilot pressure. Specifically, the directional switching valve 3 includes a pair of pilot ports 31 and 32. However, the directional switching valve 3 can also be driven by an electrical signal.

[0031] Furthermore, the hydraulic system 1A includes an operating device 5 for switching the direction switching valve 3 from the neutral position to the digging position or from the neutral position to the reverse rotation position. The operating device 5 is located in the cab of the excavator 10. The operating device 5 includes an operating lever that tilts in the digging direction or the reverse digging direction.

[0032] In this embodiment, the operating device 5 is a pilot-operated valve that outputs a pilot pressure corresponding to the tilt angle of the operating lever. Therefore, the pilot ports 31 and 32 of the direction switching valve 3 are connected to the operating device 5 via pilot lines 51 and 52.

[0033] However, the operating device 5 can also be an electric joystick that outputs an electrical signal corresponding to the tilt angle of the operating lever. In this case, the pilot ports 31 and 32 of the direction switching valve 3 are respectively connected to a pair of electromagnetic proportional valves.

[0034] Furthermore, the hydraulic system 1A includes a control device 6. The control device 6 has a memory 61 capable of storing various data. Additionally, the control device 6 is electrically connected to a display 91 and an alarm 92.

[0035] As for the control device 6, the functions of the elements disclosed in this specification are executed by using a circuit or a processing circuit including a general-purpose processor, a dedicated processor, an integrated circuit, an ASIC (Application Specific Integrated Circuit), a conventional circuit, and / or a combination thereof, which are configured or programmed to execute the disclosed functions. The processor is considered as a processing circuit or a circuit because it includes transistors or other circuits. In this disclosure, a circuit, a unit, or a device is hardware that executes the listed functions or hardware that is programmed to execute the listed functions. The hardware can be the hardware disclosed in this specification or other known hardware that is programmed or configured to execute the listed functions. When the hardware is a processor that is considered as one of the circuits, the circuit, the device, or the unit is a combination of the hardware and software for the configuration of the hardware and / or the processor.

[0036] The control device 6 is also electrically connected to the pressure sensor 81 and the rotation speed sensors 71 to 73. For example, the rotation speed sensors 71 to 73 are magnetic speed sensors.

[0037] The pressure sensor 81 is provided in the discharge line 22 to measure the discharge pressure Pd of the hydraulic pump 2. The rotation speed sensor 71 is provided in the hoist unit 12 as shown in FIG. A to measure the hoist speed V of the cable 13 of the hoist unit 12. Also, the rotation speed sensor 72 is provided in a pulley provided at the upper end of the frame 11 to measure the digging depth Dp from the rotation speed of the pulley. The rotation speed sensor 73 is provided in the hydraulic motor 4 as shown in FIG. B to measure the rotation speed N of the hydraulic motor 4. Figure 2 Figure 2 Figure 2

[0038] However, either one of the rotation speed sensors 71 and 72 can be omitted. For example, the rotation speed sensor 72 can be omitted, and the digging depth Dp can be calculated by integrating the hoist speed V. Alternatively, both of the rotation speed sensors 71 and 72 can be omitted, and the control device 9 of the hydraulic system 1A can obtain the hoist speed V and the digging depth Dp of the cable 13 from the control device of the excavator 10.

[0039] Next, the control performed by the control device 6 will be described with reference to FIG. C. Figure 3

[0040] First, the control device 6 compares the discharge pressure Pd of the hydraulic pump 2 measured by the pressure sensor 81 with the first threshold value a in step S1 to determine whether the discharge pressure Pd of the hydraulic pump 2 is greater than the first threshold value a. The first threshold value a is a value slightly smaller than the set pressure of the safety valve 24, i.e., the safety pressure. For example, when the safety pressure is 34 MPa, the first threshold value a is 32 MPa.

[0041] ​​​​When the discharge pressure Pd of the hydraulic pump 2 is smaller than the first threshold value α, the control device 6 repeats the comparison of the discharge pressure Pd of the hydraulic pump 2 and the first threshold value α. On the contrary, when the discharge pressure Pd of the hydraulic pump 2 is larger than the first threshold value α, the control device 6 proceeds to Step S2. In the present embodiment, Step S1 is repeated when Pd = α, but Step S2 can be entered when Pd = α.

[0042] In Step S2, the control device 6 compares the rotational speed N of the hydraulic motor 4 measured by the rotational speed sensor 73 with the second threshold value β, and judges whether the rotational speed N of the hydraulic motor 4 is smaller than the second threshold value β. The second threshold value β is an index whether the hydraulic motor 4 is considered to be stopped, and is, for example, 100 rpm.

[0043] When the rotational speed N of the hydraulic motor 4 is larger than the second threshold value β, the control device 6 returns to Step S1. On the contrary, when the rotational speed N of the hydraulic motor 4 is smaller than the second threshold value β, the control device 6 proceeds to Step S3. In the present embodiment, Step S1 is returned to when N = β, but Step S3 can be entered when N = β.

[0044] In Step S3, the control device 6 compares the digging depth Dp measured by the rotational speed sensor 72 with the third threshold value γ, and judges whether the digging depth Dp is larger than the third threshold value γ. The third threshold value γ is, for example, 10 m. When the digging depth Dp is smaller than the third threshold value γ, the control device 6 returns to Step S1. On the contrary, when the digging depth Dp is larger than the third threshold value γ, the control device 6 proceeds to Step S4. In the present embodiment, Step S1 is returned to when Dp = γ, but Step S4 can be entered when Dp = γ.

[0045] In Step S4, the control device 6 compares the hoisting speed V of the cable 13 measured by the rotational speed sensor 71 with the fourth threshold value ε, and judges whether the hoisting speed V of the cable 13 is smaller than the fourth threshold value ε. The fourth threshold value ε is, for example, 0.5 m / s. When the hoisting speed V of the cable 13 is larger than the fourth threshold value ε, the control device 6 returns to Step S1. On the contrary, when the hoisting speed V of the cable 13 is smaller than the fourth threshold value ε, the control device 6 proceeds to Step S5. In the present embodiment, Step S1 is returned to when V = ε, but Step S5 can be entered when V = ε. Further, the specific condition is satisfied when Yes in Step S3 and Yes in Step S4.

[0046] In Step S5, the control device 6 judges that the excavating shaft 17 is twisted. On the other hand, during a period in which Step S5 is not entered, for example, during a period in which the above-described specific condition is not satisfied, the control device 6 judges that the excavating shaft 17 is not twisted. Further, the control device 6 performs a specific action in Step S5.

[0047] In the present embodiment, the operation performed by the control device 6 includes an operation of causing the display 91 to display that an abnormality has occurred and an operation of causing the alarm 92 to sound an alarm. However, the control device 6 can perform either of the operation of causing the display 91 to display that an abnormality has occurred and the operation of causing the alarm 92 to sound an alarm.

[0048] Further, the control device 6 can cause the display 91 to display that an abnormality has occurred and cause the display 91 to display a warning. The warning can be, for example, a warning that the operation lever cannot be tilted immediately in the anti-digging direction, or it can be a warning of the time during which the operation lever should be secured to a neutral state to some extent.

[0049] Further, the control device 6 stores, in the memory 61, the date and time when the digging shaft 17 is twisted, the discharge pressure Pd of the hydraulic pump 2, the rotational speed N of the hydraulic motor 4, the digging depth Dp, and the hoisting speed V of the cable 13 when the digging shaft 17 is twisted, when it is determined that the digging shaft 17 is twisted. Thus, if the shovel 10 is abnormal, the cause of the abnormality can be investigated.

[0050] In the hydraulic system 1A described above, the following effects can be obtained. When the digging load increases because the bucket 18 contacts an obstacle such as a hard rock, the hydraulic motor 4 rotates while the digging shaft 17 is twisted, and thus the discharge pressure Pd of the hydraulic pump 2 rises to the set pressure of the safety valve 24, whereby the safety valve 24 opens and the hydraulic motor 4 stops. Thus, the twisting of the digging shaft 17 can be detected on the basis of the discharge pressure Pd of the hydraulic pump 2 and the rotational speed N of the hydraulic motor 4.

[0051] Further, in the present embodiment, it is determined that the digging shaft 17 is not twisted when the specific conditions are not satisfied, and thus the following situations are excluded from the situations in which it is determined that the digging shaft 17 is twisted: a situation in which the digging depth Dp is smaller than the third threshold value γ, such as a dump soil operation in which the digging shaft 17 is rotated in the reverse direction while the bucket 18 is raised, and a situation in which the hoisting speed V of the cable 13 is larger than the fourth threshold value ε, such as during hoisting.

[0052] (Second Embodiment)

[0053] Figure 4 A digging hydraulic system 1B according to a second embodiment is shown. Also, in the present embodiment, the same reference numerals are assigned to the same structural elements as those of the first embodiment, and repeated description is omitted.

[0054] In the present embodiment, a pressure sensor 82 that measures the inlet pressure Pi of the hydraulic motor 4 when the hydraulic motor 4 is rotated in the digging direction is used. The pressure sensor 82 is provided on the feed / discharge line 41 connected to the first port 4a of the hydraulic motor 4 and is electrically connected to the control device 6. Also, in the present embodiment, the rotational speed sensors 71, 72 are not needed.

[0055] Next, the operation of the hydraulic system 1B according to the second embodiment will be described with reference to FIG. 6. Figure 5The control performed by the control device 6 will be described.

[0056] First, the control device 6 compares the inlet pressure Pi of the hydraulic motor 4 measured by the pressure sensor 82 with the first threshold value ζ in step S11, and determines whether the inlet pressure Pi of the hydraulic motor 4 is greater than the first threshold value ζ. The first threshold value ζ is a value slightly smaller than the set pressure of the safety valve 24, i.e., the safety pressure. For example, when the safety pressure is 34 MPa, the first threshold value ζ is 32 MPa.

[0057] When the inlet pressure Pi of the hydraulic motor 4 is smaller than the first threshold value ζ, the control device 6 repeats the comparison of the inlet pressure Pi of the hydraulic motor 4 with the first threshold value ζ. In contrast, when the inlet pressure Pi of the hydraulic motor 4 is greater than the first threshold value ζ, the control device 6 proceeds to step S12. In the present embodiment, step S11 is repeated when Pi = ζ, but step S2 can be entered when Pi = ζ.

[0058] Step S12 is the same as step S2 described in the first embodiment. That is, the control device 6 returns to step S11 when the rotational speed N of the hydraulic motor 4 is greater than the second threshold value β, and proceeds to step S13 when the rotational speed N of the hydraulic motor 4 is smaller than the second threshold value β. In the present embodiment, step S11 is returned to when N = β, but step S13 can be entered when N = β.

[0059] In step S13, the control device 6 determines that the excavating shaft 17 is twisted. On the other hand, during a period in which step S13 is not entered, the control device 6 determines that the excavating shaft 17 is not twisted. Further, the control device 6 performs a specific action in step S13. The action is the same as the action described in the first embodiment.

[0060] Further, the control device 6 stores the date and time when the excavating shaft 17 is twisted, the inlet pressure Pi of the hydraulic motor 4, and the rotational speed N of the hydraulic motor 4 in the memory 61 when it is determined that the excavating shaft 17 is twisted. Therefore, if the shovel 10 is abnormal, the cause of the abnormality can be investigated.

[0061] In the hydraulic system IB of the present embodiment, the following effects can be obtained. When the digging load increases because the bucket 18 contacts an obstacle such as a hard rock, the excavating shaft 17 is twisted while the hydraulic motor 4 rotates, so that the inlet pressure Pi of the hydraulic motor 4 rises to the set pressure of the safety valve 24, whereby the safety valve 24 opens and the hydraulic motor 4 stops. Therefore, the twisting of the excavating shaft 17 can be detected based on the inlet pressure Pi of the hydraulic motor 4 and the rotational speed N of the hydraulic motor 4.

[0062] (Other Embodiments)

[0063] The present disclosure is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present disclosure.

[0064] For example, the directional switching valve 3 need not necessarily block the delivery line 22, the tank line 25, and the charge / discharge lines 41, 42 in the neutral position. For example, as shown in Figure 6 the directional switching valve 3 can also communicate the charge / discharge lines 41, 42 with the tank line 25 through a throttle portion in the neutral position. If so configured, when the directional switching valve 3 returns to the neutral position after the excavation load increases and the hydraulic motor 4 stops, the hydraulic motor 4 can slowly rotate in the reverse direction to gradually eliminate the twist of the excavation shaft 17.

[0065] Alternatively, the pilot lines 51, 52 can also be configured as shown in Figure 7 the directional switching valve 3 slowly returns to the neutral position. Specifically, the pilot lines 51, 52 are each provided with a throttle portion 53, and a bypass line 54 connected to the pilot line 51 or 52 bypasses the throttle portion 53. The bypass line 54 is provided with a check valve 55 that allows flow toward the pilot port 31 or 32 but prohibits flow in the opposite direction.

[0066] Alternatively, the control device 6, upon determining that the excavation shaft 17 has twisted, can perform the operation of maintaining the directional switching valve 3 in the neutral position for a prescribed time instead of one or both of the operations of causing the display 91 to display that an abnormality has occurred and causing the alarm 92 to sound an alarm after the directional switching valve 3 is switched to the neutral position. The prescribed time is, for example, until the delivery pressure of the hydraulic pump 2 is below a prescribed value in the first embodiment, or until the inlet pressure of the hydraulic motor 4 is below a prescribed value in the second embodiment. Alternatively, the operation of maintaining the directional switching valve 3 in the neutral position for a prescribed time can be performed together with one or both of the operations of causing the display 91 to display that an abnormality has occurred and causing the alarm 92 to sound an alarm.

[0067] For example, as shown in Figure 8 the control device 6, upon determining that the excavation shaft 17 has twisted, can close the electromagnetic on / off valve 56 only for a prescribed time.

[0068] Alternatively, as in the modified example of the excavation hydraulic system 1C shown in Figure 9 when the directional switching valve 3 is driven by an electric signal, the control device 6 can switch the directional switching valve 3 to the reverse rotation position after maintaining the directional switching valve 3 in the neutral position for a prescribed time when the lever of the operation device 5 as an electric joystick is tilted from the excavation direction to the reverse excavation direction.

[0069] Further, if either of the operation of causing the display 91 to display that an abnormality has occurred and the operation of causing the alarm 92 to sound an alarm is performed, the operator can be caused to perform the operation of stopping the hydraulic motor 4 immediately after the excavation load is increased and the hydraulic motor 4 is stopped and then reversing the hydraulic motor 4. On the other hand, if the operation of maintaining the directional switching valve 3 in the neutral position for a prescribed time is performed when the directional switching valve 3 is switched to the neutral position, the twist of the excavation shaft 17 can be eliminated during the period in which the directional switching valve 3 is maintained in the neutral position.

[0070] Further, it can also be that the control device 6, after determining that the twist of the excavation shaft 17 has occurred, causes the operation lever of the operation device 5 to be tilted in the reverse excavation direction and the hydraulic motor 4 to be reversed, and causes the display 91 to display that a malfunction can occur and the alarm 92 to sound an alarm when the rotational speed N of the hydraulic motor 4 exceeds the threshold value.

[0071] Further, it can also be that the hydraulic motor 4 includes a rotating unit composed of a plurality of pistons and cylinders and the like and a housing that accommodates the rotating unit, the pressure in the housing is measured by a pressure sensor, and the display 91 is caused to display that a breakage has occurred and the alarm 92 is caused to sound an alarm when the pressure in the housing exceeds a threshold value.

[0072] (SUMMARY)

[0073] The present disclosure provides, from one aspect, a hydraulic system for excavation, which is a hydraulic system for excavation loaded on an excavator having an excavation shaft of a telescopic structure, and includes a hydraulic motor that rotates the excavation shaft, a directional switching valve connected to the hydraulic motor through a pair of supply and discharge lines, a hydraulic pump connected to the directional switching valve through a discharge line, a safety valve provided on a safety line branched from the discharge line, a pressure sensor that measures the discharge pressure of the hydraulic pump, a rotational speed sensor that measures the rotational speed of the hydraulic motor, and a control device electrically connected to the pressure sensor and the rotational speed sensor; the control device determines that the twist of the excavation shaft has occurred when the discharge pressure of the hydraulic pump measured by the pressure sensor is greater than a first threshold value and the rotational speed of the hydraulic motor measured by the rotational speed sensor is less than a second threshold value.

[0074] When the excavation load is increased due to the contact of the bucket with an obstacle such as a harder rock, the excavation shaft is twisted and the hydraulic motor is rotated, and thus the discharge pressure of the hydraulic pump rises to the set pressure of the safety valve, and the safety valve is opened and the hydraulic motor is stopped. Therefore, the twist of the excavation shaft can be detected based on the discharge pressure of the hydraulic pump and the rotational speed of the hydraulic motor.

[0075] Also, the control device can determine that the excavating shaft is twisted when the discharge pressure of the hydraulic pump measured by the pressure sensor is greater than the first threshold value and the rotational speed of the hydraulic motor measured by the rotational speed sensor is less than the second threshold value. In this case, the control device can determine that the excavating shaft is twisted when the excavating depth is greater than a third threshold value and the hoisting speed of a cable of a hoisting unit that moves the excavating shaft up and down via the cable is less than a fourth threshold value. According to this configuration, the determination that the excavating shaft is twisted can be excluded from a situation in which the excavating depth is less than the third threshold value, such as a dump operation in which the excavating shaft is reversely rotated in a state in which the bucket is raised, and a situation in which the hoisting speed of the cable is greater than the fourth threshold value, such as during hoisting.

[0076] Also, the control device can determine that the excavating shaft is twisted when the discharge pressure of the hydraulic pump measured by the pressure sensor is greater than the first threshold value and the rotational speed of the hydraulic motor measured by the rotational speed sensor is less than the second threshold value. In this case, the control device can determine that the excavating shaft is twisted when the excavating depth is greater than a third threshold value and the hoisting speed of a cable of a hoisting unit that moves the excavating shaft up and down via the cable is less than a fourth threshold value. According to this configuration, the determination that the excavating shaft is twisted can be excluded from a situation in which the excavating depth is less than the third threshold value, such as a dump operation in which the excavating shaft is reversely rotated in a state in which the bucket is raised, and a situation in which the hoisting speed of the cable is greater than the fourth threshold value, such as during hoisting.

[0077] When the excavating load increases due to contact of the bucket with an obstacle such as a hard rock, the excavating shaft is twisted while the hydraulic motor is rotated, and thus the discharge pressure of the hydraulic pump increases to the set pressure of the safety valve. As a result, the safety valve is opened, and the hydraulic motor is stopped. Therefore, the twisting of the excavating shaft can be detected based on the inlet pressure of the hydraulic motor and the rotational speed of the hydraulic motor.

[0078] Also, the control device can perform at least one of displaying an abnormality on a display and sounding an alarm when it is determined that the excavating shaft is twisted. According to this configuration, the operator can be caused to stop the operation of reversely rotating the hydraulic motor immediately after the hydraulic motor is stopped due to an increase in the excavating load.

[0079] Also, the control device can maintain the directional switching valve in the neutral position for a predetermined time after the directional switching valve is switched to the neutral position when it is determined that the excavating shaft is twisted. According to this configuration, the twisting of the excavating shaft can be resolved during the period in which the directional switching valve is maintained in the neutral position for the predetermined time.

[0080] The control device can include a memory, and the control device can save the date and time when the excavating shaft is twisted, the discharge pressure of the hydraulic pump, the inlet pressure of the hydraulic motor, and the rotational speed of the hydraulic motor in the memory when it is determined that the excavating shaft is twisted. According to this configuration, if an abnormality occurs in the excavator, the cause of the abnormality can be investigated.

Claims

1. A hydraulic system for excavating, which is mounted on an excavator having an excavating shaft with a telescopic structure, comprising: a hydraulic motor that rotates the excavating shaft; a directional switching valve connected to the hydraulic motor through a pair of supply and discharge lines; a hydraulic pump connected to the directional switching valve through a discharge line; a safety valve provided on a safety line branched from the discharge line; a pressure sensor that measures a discharge pressure of the hydraulic pump; a rotational speed sensor that measures a rotational speed of the hydraulic motor; and a control device electrically connected to the pressure sensor and the rotational speed sensor; wherein the control device determines that the excavating shaft is twisted when the discharge pressure of the hydraulic pump measured by the pressure sensor is greater than a first threshold value and the rotational speed of the hydraulic motor measured by the rotational speed sensor is less than a second threshold value.

2. The hydraulic system for excavating according to claim 1, wherein the control device determines that the excavating shaft is twisted when the discharge pressure of the hydraulic pump measured by the pressure sensor is greater than the first threshold value and the rotational speed of the hydraulic motor measured by the rotational speed sensor is less than the second threshold value, in a case where a specific condition is satisfied; and the specific condition is that a digging depth is greater than a third threshold value and a hoisting speed of a cable of a hoisting unit that moves the excavating shaft up and down by the cable is less than a fourth threshold value.

3. The hydraulic system for excavating according to claim 1 or 2, wherein the control device performs at least one of displaying an abnormality on a display and sounding an alarm when it is determined that the excavating shaft is twisted.

4. The hydraulic system for excavating according to claim 1 or 2, wherein the control device maintains the directional switching valve in a neutral position for a predetermined time after the directional switching valve is switched to the neutral position when it is determined that the excavating shaft is twisted, to eliminate the twist of the excavating shaft.

5. The hydraulic system for excavating according to claim 1 or 2, wherein the control device includes a memory; and the control device stores a date and time when the excavating shaft is twisted, a discharge pressure of the hydraulic pump or an inlet pressure of the hydraulic motor, and a rotational speed of the hydraulic motor in the memory when it is determined that the excavating shaft is twisted.

6. A hydraulic system for excavating, which is mounted on an excavator having an excavating shaft with a telescopic structure, comprising: a hydraulic motor that rotates the excavating shaft; a directional switching valve connected to the hydraulic motor through a pair of supply and discharge lines; a hydraulic pump connected to the directional switching valve through a discharge line; a safety valve provided on a safety line branched from the discharge line; a pressure sensor that measures an inlet pressure of the hydraulic motor when the hydraulic motor is rotated in a digging direction; a rotational speed sensor that measures a rotational speed of the hydraulic motor; and a control device electrically connected to the pressure sensor and the rotational speed sensor; wherein the control device determines that the excavating shaft is twisted when the inlet pressure of the hydraulic motor measured by the pressure sensor is greater than a first threshold value and the rotational speed of the hydraulic motor measured by the rotational speed sensor is less than a second threshold value. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 7. The hydraulic system for excavating according to claim 6, wherein the control device performs at least one of displaying an abnormality has occurred on a display and sounding an alarm by an alarm when it is determined that the twisting of the excavating shaft has occurred.

8. The hydraulic system for excavating according to claim 6 or 7, wherein the control device maintains the direction switching valve in the neutral position for a prescribed time after the direction switching valve is switched to the neutral position when it is determined that the twisting of the excavating shaft has occurred, and eliminates the twisting of the excavating shaft.

9. The hydraulic system for excavating according to claim 6 or 7, wherein the control device includes a memory; the control device saves a date and time when the twisting of the excavating shaft has occurred, a discharge pressure of the hydraulic pump or an inlet pressure of the hydraulic motor, and a rotational speed of the hydraulic motor in the memory when it is determined that the twisting of the excavating shaft has occurred.

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