Patent Application
20240017972
The present invention relates to a work machine including a plurality of extension/contraction hydraulic cylinders that telescopes a multistage boom.
In the related art, there has been known a work machine (for example, a crane) including a plurality of extension/contraction hydraulic cylinders that telescopes a multistage boom. Patent Literature 1 discloses a telescopic boom-type high-place work vehicle provided with a limit switch that detects an amount of extension of an intermediate boom with respect to a proximal end boom, and configured to detect whether the intermediate boom is substantially fully contracted with respect to the proximal end boom.
However, in the crane, a state in which the boom is almost fully contracted, that is, a state in which the extension/contraction hydraulic cylinder is not completely fully contracted is not preferable. When the lifting load is hung in this state, the extension/contraction hydraulic cylinder receives a load originally to be received by the boom, and the extension/contraction hydraulic cylinder may be damaged. Therefore, in a crane including multistage booms, it is desired to completely fully contract the extension/contraction hydraulic cylinder.
However, in a crane including a plurality of extension/contraction hydraulic cylinders and capable of changing the extension/contraction order of the extension/contraction hydraulic cylinders, a state has occurred in which a predetermined extension/contraction hydraulic cylinder that should have been fully contracted is not fully contracted. For example, in the process of reducing the boom, even in a state in which the predetermined extension/contraction hydraulic cylinder that should have been fully contracted is not completely fully contracted, it may be determined as the fully contracted state. This is because, when the boom length detector is used, the detected length of the boom has a certain range due to variation and hysteresis of the boom length detector.
In addition, for example, is the extension process of the boom, the hydraulic oil may leak to the extension/contraction hydraulic cylinder not to be operated through the spool gap of the solenoid valve that switches the extension/contraction hydraulic cylinder to be operated, and the extension/contraction hydraulic cylinder not to be operated may extend.
An object of the present invention is to provide a work machine including a plurality of extension/contraction hydraulic cylinders that telescopes multistage booms, the work machine being capable of fully contracting a predetermined extension/contraction hydraulic cylinder.
An aspect of a work machine according to the present invention includes
According to the present invention, in a work machine including a plurality of extension/contraction hydraulic cylinders that telescopes multistage booms, a predetermined extension/contraction hydraulic cylinder can be completely fully contracted.
Hereinafter, a work machine according to an embodiment of the present invention will be described with reference to
First, an outline of a crane 1 which is an example of a work machine according to the present embodiment will be described. The crane 1 includes a first extension/contraction hydraulic cylinder 51 and a second extension/contraction hydraulic cylinder 52 that telescope a telescopic boom 4 on the basis of hydraulic oil supply and discharge, an extension/contraction cylinder pressure relief solenoid valve 88 provided on a pressure relief circuit that connects the first extension/contraction hydraulic cylinder 51 and the second extension/contraction hydraulic cylinder 52 to the tank 90, and a control unit 11 that causes the extension/contraction cylinder pressure relief solenoid valve 88 to connect one hydraulic cylinder to a tank 90 and releases a pressure in the one hydraulic cylinder when the other hydraulic cylinder of the first extension/contraction hydraulic cylinder 51 and the second extension/contraction hydraulic cylinder 52 is contracted or extended in a state where the one hydraulic cylinder of the first extension/contraction hydraulic cylinder 51 and the second extension/contraction hydraulic cylinder 52 is contracted. Hereinafter, a specific configuration of the crane 1 according to the present embodiment will be described.
[Configuration of Crane]
As illustrated in
The crane device 3 includes a boom 4 so as to protrude forward from a rear portion thereof. The boom 4 is configured to be turnable by a turning hydraulic motor (not illustrated). The boom 4 is configured to be telescoped by an extension/contraction hydraulic cylinder 5 (see
A wire rope 61 is stretched around the boom 4. A winch 62 around which the wire rope 61 is wound is disposed at the proximal end of the boom 4, and a hook 63 is suspended by the wire rope 61 at the distal end of the boom 4. The winch 62 is formed integrally with a winding hydraulic motor (not illustrated), and can wind in and out the wire rope 61. The hook 63 is configured to be movable up and down by a winding hydraulic motor. The lifting length and the lifting speed of the hook 63 are detected by a sensor (not illustrated).
The crane device 3 includes a cabin 32 on the side of the boom. 4. Inside the cabin 32, a turning operation tool, a telescopic operation tool, a derricking operation tool, a winding operation tool, and the like for operating the crane device 3 are provided.
[Boom]
The third boom 43 is a member that is disposed inside the second boom 42 and telescopes with respect to the second boom 42. The fourth boom 44 is disposed inside the third boom 43 and is a member that telescopes with respect to the third boom 43. The fifth boom 45 is an innermost, member disposed on the distal end side, disposed inside the fourth boom 44, and telescopes with respect to the fourth boom 44. The third boom 43, the fourth boom 44, and the fifth boom 45 are connected via a wire (not illustrated) or the like, and each of the booms 43, 44, and 45 is configured to telescope in conjunction at a constant rate. That is, in the third boom 43, the fourth boom 44, and the fifth boom 45 are in a fully contracted state at a time, and in a fully extended state at a time.
[Extension/Contraction Hydraulic Cylinder]
As shown in
[Boom Length Detector]
As illustrated in
[Configuration of Hydraulic Circuit Related to Extension/Contraction Hydraulic Cylinder]
The prime motor 81 is connected to the pump 82. The pump 82 corresponds to an example of a supply unit, is disposed between the tank 90 and the extension/contraction control valve 83, and pressure-feeds hydraulic oil from the tank 90 to the extension/contraction control valve 83.
The extension/contraction control valve 83 is disposed between the pump 82 and the extension/contraction cylinder operation switching solenoid valve 84. The extension/contraction control valve 83 is a four-way, four-port, three-position electromagnetic valve. The four ports are connected to the pump 82, the tank 90, the extension/contraction cylinder operation switching solenoid valve 84, a contraction circuit 51B of the first extension/contraction hydraulic cylinder 51 and a contraction circuit 525 of the second extension/contraction hydraulic cylinder 52, respectively.
The extension/contraction control valve 83 includes a first solenoid 831 and a second solenoid 832, and is configured to be switchable between a first position, a second position, and a third position by the first solenoid 831 and the second solenoid 832. Specifically, when the first solenoid 831 is turned on, and the second solenoid 832 is turned off, the extension/contraction control valve 83 is switched to the first position, and when the first solenoid 831 turned off, and the second solenoid 832 is turned on, the extension/contraction control valve 83 is switched to the second position, and when both the first solenoid 831 and the second solenoid 832 are turned off, the extension/contraction control valve 83 is switched to the third position.
In a state where the extension/contraction control valve 83 is switched co the third position, the port leading to the pump 82 is closed and the other three ports lead to the tank 90. In a state where the extension/contraction control valve 83 is switched to the first position, the pump 82 and the extension/contraction cylinder operation switching solenoid valve 84 are connected, and the contraction circuit 51B of the first extension/contraction hydraulic cylinder 51, the contraction circuit 52B of the second extension/contraction hydraulic cylinder 52, and the tank 90 are connected. In a state where the extension/contraction control valve 83 is switched to the first position, the hydraulic oil is supplied from the pump 82 to the extension/contraction cylinder operation switching solenoid valve 84.
In a state where the extension/contraction control valve 83 is switched to the second position, the pump 82, the contraction circuit 51B of the first extension/contraction hydraulic cylinder 51, and the contraction circuit 52B of the second extension/contraction hydraulic cylinder 52 are connected, and the extension/contraction cylinder operation switching solenoid valve 84 and the tank 90 are connected. In a state where the extension/contraction control valve 83 is switched to the second position, hydraulic oil is supplied from the pump 82 to the contraction circuit 51B of the first extension/contraction hydraulic cylinder 51 and the contraction circuit 52B of the second extension/contraction hydraulic cylinder 52.
The extension/contraction cylinder operation switching solenoid valve 84 is disposed between the extension/contraction control valve 83, the first counter balance valve 85, and the hose reel 87. The extension/contraction cylinder operation switching solenoid valve 84 is a 3-port single-acting electromagnetic valve, and is at the left side position when turned off, and is switched to the right side position when turned on. The three ports are connected to the extension/contraction control valve 83, the first counter balance valve 85, and the hose reel 87, respectively.
When the solenoid is turned off, the extension/contraction cylinder operation switching solenoid valve 84 connects the extension/contraction control valve 83 and the first counter balance valve 85 and closes the port connected to the hose reel 87. When the solenoid is turned on, the extension/contraction cylinder operation switching solenoid valve 84 connects the extension/contraction control valve 83 and the hose reel 87, and closes the port connected to the first counter balance valve 85.
The first counter balance valve 65 is disposed between the extension/contraction cylinder operation switching solenoid valve 84 and an extension circuit 51A of the first extension/contraction hydraulic cylinder 51. The second counter balance valve 86 is disposed between the hose reel 87 and an extension circuit 52A of the second extension/contraction hydraulic cylinder 52. The hose reel 87 is disposed between the extension/contraction cylinder operation switching solenoid valve 84 and the second counter balance valve 86.
The extension/contraction cylinder pressure relief solenoid valve 88 corresponds to an example of a switching valve, and is disposed between a circuit 91 connecting the first counter balance valve 85 and the extension/contraction cylinder operation switching solenoid valve 84 and the tank 90 and between a circuit. 92 connecting the hose reel 87 and the extension/contraction cylinder operation switching solenoid valve 84 and the tank 90. The extension/contraction cylinder pressure relief solenoid valve 88 is a four-direction, four-port, three-position electromagnetic valve, and includes a first extension/contraction cylinder pressure relief solenoid 881 on the left side and a second extension/contraction cylinder pressure relief solenoid 882 on the right side. The four ports are connected to the tank 90, the circuit 91, the circuit 92 and the closed circuit, respectively. Note that a circuit including the circuits 91 and 92 and connecting the first extension/contraction hydraulic cylinder 51, the second extension/contraction, hydraulic cylinder 52, and the pump 82 corresponds to an example of a supply circuit.
The extension/contraction cylinder pressure relief solenoid valve 88 is configured to be switchable between the first position, the second position, and the third position by the first extension/contraction cylinder pressure relief solenoid 881 and the second extension/contraction cylinder pressure relief solenoid 882. Specifically, when the first extension/contraction cylinder pressure relief solenoid 881 is turned on and the second extension/contraction cylinder pressure relief solenoid 882 is turned off, the extension/contraction cylinder pressure relief solenoid valve 88 is switched to the first positon. When the first extension/contraction cylinder pressure relief solenoid 881 is turned off and the second extension/contraction cylinder pressure relief solenoid 882 is turned on, the extension/contraction cylinder pressure relief solenoid valve 88 is switched to the second position. When both the first extension/contraction cylinder pressure relief solenoid 881 and the second extension/contraction cylinder pressure relief solenoid 882 are turned off, the extension/contraction cylinder pressure relief solenoid valve 88 is switched to the third position.
In a state where the extension/contraction cylinder Pressure relief solenoid valve 88 is switched to the third position, the four ports are closed, and the first circuit that does not connect the extension circuit 51A of the first extension/contraction hydraulic cylinder 51 and the extension circuit 52A of the second extension/contraction hydraulic cylinder 52 to the tank 90 is formed. That is, the first circuit includes the extension/contraction cylinder pressure relief solenoid valve 88 at the third position, a circuit that connects the extension circuit 51A of the first, extension/contraction hydraulic cylinder 51 and the extension/contraction cylinder pressure relief solenoid valve 88, and a circuit that connects the extension circuit 52A of the second extension/contraction hydraulic cylinder 52 and the extension/contraction cylinder pressure relief solenoid valve 88.
In a state where the extension/contraction cylinder pressure relief solenoid valve 88 is switched to the first position, the circuit 91 and the tank 90 are connected, and the circuit 92 is connected to a closed circuit. That is, in a state in which the extension/contraction cylinder pressure relief solenoid valve 88 is switched to the first position, the second circuit that connects the extension circuit 51A of the first extension/contraction hydraulic cylinder 51 to the tank 90, and does not connect the extension circuit 52A of the second extension/contraction hydraulic cylinder 52 to the tank 90 is formed. That is, the second circuit includes the extension/contraction cylinder pressure relief solenoid valve 88 at the first position, a circuit that connects the extension circuit 51A of the first extension/contraction hydraulic cylinder 51 and the tank 90, a circuit that connects the extension circuit 52A of the second extension/contraction hydraulic cylinder 52 and the extension/contraction cylinder pressure relief solenoid valve 88, and a closed circuit.
In a state where the extension/contraction cylinder pressure relief solenoid valve 88 is switched to the second position, the circuit 92 and the tank 90 are connected, and the circuit 91 connected to a closed, circuit. That is, in a state in which the extension/contraction cylinder pressure relief solenoid valve 88 is switched to the second position, the third circuit that does not connect the extension circuit 51A of the first extension/contraction hydraulic cylinder 51 to the tank 90 and connects the extension circuit 52A of the second extension/contraction hydraulic cylinder 52 to the tank 90 is formed. That is, the third circuit includes the extension/contraction cylinder pressure relief solenoid valve 88 at the second position, a circuit that connects the extension circuit 52A of the second extension/contraction, hydraulic cylinder 52 and the tank 90, a circuit that connects the extension circuit 51A of the first extension/contraction, hydraulic cylinder 51 and the extension/contraction cylinder pressure relief solenoid valve 88, and a closed circuit.
As described above, the extension/contraction cylinder pressure relief solenoid valve 88 is an electromagnetic valve that switches between the first circuit, the second circuit, and the third circuit. It can be said that the first circuit, the second circuit, and the third circuit constitute a pressure relief circuit.
The relief valve 89 is disposed between the delivery side of the pump 82 and the tank 90, and is a valve that returns surplus hydraulic oil delivered from the pump 82 to the tank 90. The tank 90 stores hydraulic oil used in a hydraulic circuit.
In addition, the first solenoid 831 and the second solenoid 832 of the extension/contraction control valve 83, the solenoid of the extension/contraction cylinder operation, switching solenoid valve 84, and the first extension/contraction cylinder pressure relief solenoid 881 and the second extension/contraction cylinder pressure relief solenoid 882 of the extension/contraction cylinder pressure relief solenoid valve 88 are connected to the control unit 11.
The boom length detector 7 and an extension/contraction operation lever 12 are also connected to the control unit 11. The extension/contraction operation lever 12 operates extension/contraction of the first extension/contraction hydraulic cylinder 51 and the second extension/contraction hydraulic cylinder 52 according to the operation direction (extension direction and contraction direction) and the operation amount of the lever.
The control unit 11 includes a control device such as a CPU and a storage device such as a random access memory (RAM) and a read only memory (ROM). The control unit 11 controls the extension/contraction control valve 83, the extension/contraction cylinder operation, switching solenoid valve 84, and the extension/contraction cylinder pressure relief solenoid valve 88 according to inputs from the boom length detector 7 and the extension/contraction operation lever 12.
[Basic Operation of Hydraulic Circuit]
According to the hydraulic circuit of
At this time, when the first extension/contraction hydraulic Cylinder 51 is operated, the extension/contraction cylinder operation switching solenoid valve 84 is turned off (state in which the extension/contraction control valve 83 and the first extension/contraction hydraulic cylinder 51 are connected). On the other hand, when the second extension/contraction hydraulic cylinder 52 is operated, the extension/contraction cylinder operation switching solenoid valve 84 is turned on (a state in which the extension/contraction control valve 83 and the second extension/contraction hydraulic cylinder 52 are connected). That is, the extension/contraction control valve 83 controls the operation direction and the operation speed of the first extension/contraction hydraulic cylinder 51 or the second extension/contraction hydraulic cylinder 52, and the extension/contraction cylinder operation switching solenoid valve 84 switches between the first extension/contraction hydraulic cylinder 51 or the second extension/contraction hydraulic cylinder 52 to be operated.
[Extension/Contraction Mode]
The control unit 11 can execute a plurality of extension/contraction modes having different extension/contraction orders of the first extension/contraction hydraulic cylinder 51 and the second extension/contraction hydraulic cylinder 52, and controls the extension/contraction control valve 83, the extension/contraction cylinder operation switching solenoid valve 84, and the extension/contraction cylinder pressure relief solenoid valve 88 in each extension/contraction mode. In the present embodiment, the plurality of extension/contraction modes are the first extension/contraction mode and the second extension/contraction mode. The first extension/contraction mode and the second extension/contraction mode can be selected (can be set) by operating an operation unit (not illustrated), and can be selected and operated in either the fully contracted state or the fully extended state of the boom 4. In other states, the last selected extension/contraction, mode is held.
(First Extension/Contraction Mode)
The first extension/contraction mode is a mode for performing control so as to be able to obtain a first state (state illustrated in
That is, the first extension/contraction mode is a mode that transitions between the first state and the second, state by the first extension/contraction hydraulic cylinder 51 extending and contracting, and that transitions between the second state and the third state by the second extension/contraction hydraulic cylinder 52 extending and contracting.
Table 1 is a table illustrating a state of each solenoid in the first extension/contraction mode.
As shown in Table 1, when transitioning between the first state and the second state, the control unit 11 causes the extension/contraction cylinder operation switching solenoid valve 84 to be turned off, the first extension/contraction cylinder pressure relief solenoid 881 to be turned off, and the second extension/contraction cylinder pressure relief solenoid 882 to be turned on. When transitioning between the second state and the third state, the control unit 11 causes the extension/contraction cylinder operation switching solenoid valve 84 to be turned on, the first extension/contraction cylinder pressure relief solenoid 861 to be turned off, and the second extension/contraction cylinder pressure relief solenoid 882 to be turned off.
Here, the control unit 11 determines the first state, the second state, and the third state from the detection result (detection value) of the boom length detector 7. However, the length of the boom 4 detected by the boom length detector 7 has a certain range due to variation and hysteresis of the boom length detector 7. Therefore, within this range, the second extension/contraction hydraulic cylinder 52 at the time of transitioning from the third state to the second state may not be completely fully contracted.
In this regard, a process of reducing the boom 4 from the fully extended state to the fully contracted state in the first extension/contraction mode will be described as an example. When the boom 4 is in the fully extended state, the first extension/contraction hydraulic cylinder 51 and the second extension/contraction hydraulic cylinder 52 are in the third state of being fully extended. When the second extension/contraction hydraulic cylinder 52 is reduced from this state, the length of the boom 4 detected by the boom length detector 7 is reduced, and it is determined that the second state is reached, the second extension/contraction hydraulic cylinder 52 may not be completely fully contracted.
When it is determined that the second state is reached, the extension/contraction cylinder operation switching solenoid valve 84 is switched off, the first extension/contraction hydraulic cylinder 51 starts to contract, the second extension/contraction cylinder pressure relief solenoid 882 is turned on, and the extension circuit 52A of the second extension/contraction hydraulic cylinder 52 is connected to the tank 90. Therefore, when the first extension/contraction hydraulic cylinder 51 contracts, the second extension/contraction hydraulic cylinder 52 also contracts at the same time. As a result, there is no stroke (amount of extension) remaining in the second extension/contraction hydraulic cylinder 52, and the second extension/contraction, hydraulic cylinder 52 is completely contracted.
In addition, it is conceivable that, in the process of extending the boom 4, the hydraulic oil leaks to the extension/contraction hydraulic cylinder not to be operated via the spool gap of the extension/contraction cylinder operation switching solenoid valve 84, and the extension/contraction hydraulic cylinder not to be operated extends.
In this regard, a process of extending the boom 4 from the fully contracted state to the fully extended state in the first extension/contraction mode will be described as an example. When the boom 4 is in the fully contracted state, the first extension/contraction hydraulic cylinder 51 and the second extension/contraction hydraulic cylinder 52 are in the first state of being fully contracted. While the first extension/contraction hydraulic cylinder 51 extends from this state to the second state, a high Pressure acts on the extension circuit 51A of the first extension/contraction hydraulic cylinder 51 in order to move the cylinder.
At this time, since the second extension/contraction, hydraulic cylinder 52 is not operating and only low pressure is applied, the hydraulic oil may leak toward the extension circuit 52A of the second extension/contraction hydraulic cylinder 52 via the spool gap of the extension/contraction cylinder operation switching solenoid, valve 84 due to the pressure difference.
However, since the second extension/contraction cylinder pressure relief solenoid 882 is turned on and the extension circuit 52A of the second extension/contraction hydraulic cylinder 52 is connected to the tank 90, the leaked hydraulic oil return to the tank 90 through the second extension/contraction cylinder pressure relief solenoid 882 before reaching the extension circuit 52A of the second extension/contraction hydraulic cylinder 52. As a result, the second extension/contraction hydraulic cylinder 52 does not extend and can maintain a completely fully contracted state.
As described above, the control unit 11 controls each solenoid such that the pressure relief circuit is the third circuit when the first extension/contraction mode transitions between the first state and the second state. As a result, when the first extension/contraction mode transitions between the first state and the second state, the second extension/contraction hydraulic cylinder 52 can be completely fully contracted.
(Second Extension/Contraction Mode)
The second extension/contraction, mode is a mode for performing control so as to be able to obtain a first state (state illustrated in
That is, the second extension/contraction mode is a mode that transitions between the first state and the fourth state by the second extension/contraction hydraulic cylinder 52 extending and contracting, and that transitions between the fourth state and the third state by the first extension/contraction hydraulic cylinder 51 extending and contracting.
Table 2 is a table illustrating a state of each solenoid in the second extension/contraction mode.
As shown in Table 2, when transitioning between the first state and the fourth state, the control unit 11 causes the extension/contraction cylinder operation switching solenoid valve 84 to be turned on, the first extension/contraction cylinder pressure relief solenoid 881 to be turned on, and the second extension/contraction cylinder pressure relief solenoid 882 to be turned off. When transitioning between the fourth state and the third state, the control unit 11 causes the extension/contraction cylinder operation switching solenoid valve 84 to be turned, off, the first extension/contraction cylinder pressure relief solenoid 881 to be turned off, and the second extension/contraction cylinder pressure relief solenoid 882 to be turned off.
As in the first extension/contraction mode, the control unit 11 determines the first state, the third state, and the fourth state from the detection result of boom length detector 7. Therefore, for the same reason as in the first extension/contraction mode, the first extension/contraction hydraulic cylinder 51 at the time of transition from the third state to the fourth state may not be completely fully contracted.
In this regard, a process of reducing the boom 4 from the fully extended, state to the fully contracted state in the second extension/contraction mode will be described as an example. When the boom 4 is in the fully extended state, the first extension/contraction hydraulic cylinder 51 and the second extension/contraction hydraulic cylinder 52 are in, the third state of being fully extended. When the first extension/contraction hydraulic cylinder 51 contracts from this state, the length of the boom 4 detected by the boom length, detector 7 is she and it is determined that the fourth state is reached, the first extension/contraction hydraulic cylinder 51 may not be completely fully contracted.
When it is determined that the fourth state is reached, the extension/contraction cylinder operation switching solenoid valve 84 is switched on, the second extension/contraction hydraulic cylinder 52 starts to contract, the first extension/contraction cylinder pressure relief solenoid 881 is turned on, and the extension circuit 51A of the first extension/contraction hydraulic cylinder 51 is connected to the tank 90. Therefore, when the second extension/contraction hydraulic cylinder 52 contracts, the first extension/contraction hydraulic cylinder 51 also contracts at the same time. As a result, there is no stroke (amount of extension) remaining in the first extension/contraction hydraulic cylinder 51, and the first extension/contraction hydraulic cylinder 51 is completely fully contracted.
As in the first extension/contraction mode, it is conceivable that the hydraulic oil leaks to the extension/contraction hydraulic cylinder not to be operated through the spool gap of the extension/contraction cylinder operation switching solenoid valve 84 in the extension, process of the boom 4, and the extension/contraction hydraulic cylinder not to be operated extends.
In this regard, a process of extending the boom 4 from the fully contracted state to the fully extended state in the second extension/contraction mode will be described as an example. When the boom 4 in the fully contracted state, the first extension/contraction hydraulic cylinder 51 and the second extension/contraction hydraulic cylinder 52 are in the first state of being fully contracted. Until the second extension/contraction hydraulic cylinder 52 extends from this state to the fourth state, a high pressure acts on the extension circuit 52A of the second extension/contraction hydraulic cylinder 52 in order to move the cylinder.
At this time, since the first extension/contraction, hydraulic cylinder 51 is not operating and only low pressure is applied, the hydraulic oil may leak toward the extension, circuit 51A of the first extension/contraction hydraulic cylinder 51 via the spool gap of the extension/contraction cylinder operation switching solenoid valve 84 due to the pressure difference.
However, since the first extension/contraction cylinder pressure relief solenoid 881 is turned on and the extension circuit 51A of the first extension/contraction hydraulic cylinder 51 is connected to the tank 90, the leaked hydraulic oil return to the tank 90 through the first extension/contraction cylinder pressure relief solenoid 881 before reaching the extension circuit 51A of the first extension/contraction hydraulic cylinder 51. As a result, the first extension/contraction hydraulic cylinder 51 does not extend and, can, maintain a completely fully contracted state.
As described above, when the second extension/contraction mode transitions between the first state and the fourth state, the control unit 11 controls each solenoid such that the extension/contraction cylinder pressure relief solenoid valve 88, which is a pressure relief circuit, is the second circuit. As a result, when the second extension/contraction mode transitions between the first state and the fourth state, the first extension/contraction hydraulic cylinder 51 can be completely fully contracted.
According to the crane 1 of the above embodiment, during extension and contraction of one of the first extension/contraction hydraulic cylinder 51 and the second extension/contraction hydraulic cylinder 52, the other is connected to the tank 90 through the pressure relief circuit, so that the pressure of the other extension circuit is released, and the other can be fully contracted. As a result, when the lifting load is suspended in a state where the other extension/contraction hydraulic cylinder is completely fully contracted, the load of the lifting load can be received by the cross section of the boom 4 without being received by the other extension/contraction hydraulic cylinder, so that damage to the other extension/contraction hydraulic cylinder can be suppressed.
When the number of stages of the booms increases and the number of extension/contraction cylinders increases accordingly, the extension/contraction cylinder operation switching solenoid valve 84 and the extension/contraction cylinder pressure relief solenoid valve 88 are increased according to the number of extension/contraction cylinders and similarly controlled, so that similar actions and effects can be obtained.
The entire disclosure of the specification, drawings, and abstract included in Japanese Patent Application No. 2020-196126 filed on Nov. 26, 2020 is incorporated herein by reference.
The present invention can be applied to various work machines having a telescopic boom.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2020-196126 | Nov 2020 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2021/042460 | 11/18/2021 | WO |
