crane

Abstract

To stably wind down a bucket.SOLUTION: A crane comprises a first winch (6), a first hydraulic motor (31) to drive the first winch, a second winch (7), a second hydraulic motor (13) to drive the second winch, and an attachment (16). In the case that the first winch and the second winch are wound down simultaneously and that the attachment load does not exceed a threshold, the crane executes a first control (S7) to change motor capacity of the first hydraulic motor to maintain a prescribed value when the load pressure of the first hydraulic motor exceeds the prescribed value or to change the motor capacity of the second hydraulic motor to maintain the prescribed value when the load pressure of the second hydraulic motor exceeds the prescribed value. In the case that the first winch and the second winch are wound down simultaneously and that the attachment load exceeds the threshold, the crane executes a second control (S8) different from the first control to control the motor capacity.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a crane. [Background technology]

[0002] A known crane uses a variable displacement hydraulic motor as the winch drive motor, and controls the motor displacement (motor tilt) according to the circuit pressure of the hydraulic motor (see, for example, Patent Document 1). This type of prior art reduces the motor displacement as the operating pressure increases, and when the motor circuit pressure reaches the set pressure (cutoff pressure) of the servo valve, the servo valve is switched to prevent further reduction in motor displacement, thereby preventing the circuit pressure from exceeding the predetermined cutoff pressure. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 4291110 Summary of the Invention [Problem to be solved by the invention]

[0004] Crane operations sometimes involve driving two winches simultaneously to operate a bucket and perform excavation work. In this case, if the load balance between the two winches is lost during lowering, the hydraulic motor is variable displacement, so the load on one winch decreases, causing the hydraulic motor to be controlled to a small tilt position, increasing the lowering speed. However, if the load on the other winch increases and exceeds a predetermined value, the hydraulic motor is automatically controlled to a large tilt position, slowing the lowering speed. Therefore, with the above-mentioned conventional technology, once the load balance between the two winches is lost, the two winches cannot be synchronized, making it difficult to stably lower the bucket.

[0005] The present invention has been devised with the object of providing a crane that can stably hoist and lower a bucket while maintaining work efficiency when multiple winches are driven simultaneously. [Means for solving the problem]

[0006] In order to achieve the above object, a representative aspect of the present invention is a crane including a first winch, a first rope wound around the first winch, a first variable displacement hydraulic motor that drives the first winch, a second winch, a second rope wound around the second winch, a second variable displacement hydraulic motor that drives the second winch, and an attachment suspended by the first rope and the second rope, wherein, when the first winch and the second winch are performing a lowering operation simultaneously and the load of the attachment does not exceed a threshold value, if the load pressure of the first hydraulic motor exceeds a predetermined value, a first control is executed to vary the motor displacement of the first hydraulic motor so as to maintain the predetermined value, and when the load pressure of the second hydraulic motor exceeds the predetermined value, a second control different from the first control is executed instead of the first control, when the first winch and the second winch are performing a lowering operation simultaneously and the load of the attachment exceeds a threshold value. The first hydraulic motor and the second hydraulic motor are driven at the same speed so that the lowering speeds of the first hydraulic motor and the second hydraulic motor are synchronized. The motor displacement of the first hydraulic motor and the second hydraulic motor is controlled.

[0007] According to the present invention, when multiple winches are driven simultaneously, the bucket can be stably hoisted down while maintaining work efficiency. Note that problems, configurations, and effects other than those described above will become clear from the description of the following embodiments. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a side view of a crane according to an embodiment of the present invention. [Figure 2] FIG. 1 is an overall configuration diagram (hydraulic circuit diagram) of a drive device for a main hoisting winch. [Figure 3]10 is a flowchart showing a processing procedure for motor displacement control of a hydraulic motor by a controller. [Figure 4] FIG. 10 is a diagram showing the relationship between the hanging load and the motor holding pressure. [Figure 5] 10 is a flowchart showing details of motor displacement synchronization control. DETAILED DESCRIPTION OF THE INVENTION

[0009] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of a crane according to the present invention will be described with reference to the drawings.

[0010] Figure 1 is a side view of a crane according to an embodiment of the present invention. The crane 1 shown in Figure 1 is a crawler crane and includes a running body 2, a rotating body 4 rotatably mounted on the running body 2 via a rotating device 3, a boom 5 attached to the tip of the rotating body 4 so that it can be raised and lowered, and sheaves 10, 11 and sheaves 17, 18 provided at the tip of the boom 5. A bucket 16, which is an example of an attachment, is suspended by a main hoisting rope (first rope) 12 that passes through sheaves 10 and 17, and an auxiliary hoisting rope (second rope) 13 that passes through sheaves 11 and 18.

[0011] A cab 9 is provided on the rotating body 4, and an operator operates control levers 25, 26 (described later) in the cab 9 to perform lifting and excavation work with the crane 1. Incidentally, the control levers 25, 26 are in a neutral position when not in operation, and the operator can tilt the control levers 25, 26 in a specified direction to perform the desired operation.

[0012] The main hoisting rope 12 and auxiliary hoisting rope 13 are wound around a main hoisting winch (first winch) 6 and an auxiliary hoisting winch (second winch) 7 mounted on the rotating body 4, and the ropes 12 and 13 are wound up or let out by driving the winches 6 and 7, thereby raising or lowering the suspended load. The bucket 16 is then suspended by the main hoisting rope 12 and auxiliary hoisting rope 13, and the main hoisting winch 6 and auxiliary hoisting winch 7 are driven simultaneously, allowing the bucket 16 to be lowered. As will be described in more detail below, the lowering speeds of the winches 6 and 7 are controlled to be synchronized in order to stably lower the bucket 16.

[0013] A pendant rope 14 is connected to the tip of the boom 5, and when the boom hoisting rope 15 is wound or unwound by driving the boom hoisting winch 8 mounted on the rotating body 4, the boom 5 is raised or lowered via the pendant rope 14.

[0014] Fig. 2 is an overall configuration diagram (hydraulic circuit diagram) of the drive device for the main hoisting winch 6. As shown in Fig. 2, the drive device for the main hoisting winch 6 includes a variable displacement hydraulic pump 30, a variable displacement hydraulic motor (first hydraulic motor) 31 driven by pressurized oil from the hydraulic pump 30 supplied via a pair of main pipelines 37, 38, a directional control valve 32 that controls the flow of pressurized oil from the hydraulic pump 30 to the hydraulic motor 31, a counterbalance valve 33 interposed between the directional control valve 32 and the hydraulic motor 31, a relief valve (not shown) that limits the pump discharge pressure, an electric operation lever 25 that commands the drive of the main hoisting winch 6, and a motor capacity control device 40 that controls the motor capacity (also referred to as motor displacement or motor absorption amount) of the hydraulic motor 31.

[0015] The output shaft of the hydraulic motor 31 is connected to the drum 6a of the main hoisting winch 6, and the drum 6a rotates in conjunction with the rotation of the hydraulic motor 31, thereby winding or unwinding the main hoisting rope 12. The hydraulic pump 30 is driven by an engine (not shown) provided inside the revolving unit 4. The pump capacity of the hydraulic pump 30 is controlled in accordance with the pump discharge pressure by so-called horsepower control, and the motor capacity of the hydraulic motor 31 is also controlled by horsepower control in a similar manner.

[0016] An operation signal from the operating lever 25 is input to the solenoid directional control valves 55, 56 via the controller 60. The solenoid directional control valves 55, 56 are normally in position P1. When the operator operates the operating lever 25, an operation signal is input from the controller 60 to the solenoid directional control valves 55, 56, and the solenoid directional control valves 55, 56 switch from position P1 to position P2. This causes pressure oil (pilot pressure) from the pilot pump 47, which serves as a hydraulic source, to be introduced into the pressure receiving portion 32a or 32b of the directional control valve 32, switching the directional control valve 32 from position A0 to position A1 or position A2. When the directional control valve 32 switches to position A1, the main hoisting winch 6 is hoisted up, and when the directional control valve 32 switches to position A2, the main hoisting winch 6 is lowered. In FIG. 2, symbols E1 to E5 indicate electrical wiring.

[0017] Here, a hydraulic operating lever may be used instead of the electric operating lever 25. In this case, pilot pressure from a hydraulic source may be introduced directly to the pressure receiving portions 32a, 32b of the directional control valve 32 by operating the hydraulic operating lever. Also, an electromagnetic proportional directional control valve may be used instead of the directional control valve 32. In this case, there is no need to introduce pilot pressure to the directional control valve, which simplifies the hydraulic piping.

[0018] The hoisting speed and lowering speed of the main hoisting winch 6 are controlled by a motor capacity control device 40. The motor capacity control device 40 is a device for changing the motor displacement of the hydraulic motor 31, and is specifically configured as follows: The hoisting speed and lowering speed of the main hoisting winch 6 are also controlled by the discharge flow rate of the hydraulic pump 30 and the opening degrees of various valves, but a description of this will be omitted here.

[0019] The hydraulic motor 31 is provided with a piston 41 that changes the angle of the swash plate (motor tilt). Pressurized oil from the main pipe 38 is introduced into one oil chamber 41a of the piston 41, and pressurized oil from the main pipe 38 is introduced into the other oil chamber 41b via a load pressure control spool 42, which is a control valve, a tilt control spool 44, which is also a control valve, and a throttle 50. The diameter of the piston in the oil chamber 41b is larger than the diameter of the piston in the oil chamber 41a.

[0020] Therefore, the piston 41 moves in direction a or direction b depending on the magnitude relationship between value X, which is the pressure of the pressurized oil introduced into oil chamber 41a multiplied by the cross-sectional area of ​​the piston, and value Y, which is the pressure of the pressurized oil introduced into oil chamber 41b multiplied by the cross-sectional area of ​​the piston. Specifically, when value X is greater than value Y, the piston 41 moves in direction a, and the motor displacement increases. As a result, the rotational speed of the hydraulic motor 31 decreases (becomes slower). On the other hand, when value X is less than value Y, the piston 41 moves in direction b, and the motor displacement decreases. As a result, the rotational speed of the hydraulic motor 31 increases (becomes faster).

[0021] The load pressure control spool 42 includes a piston 43. One oil chamber 43a of the piston 43 receives pressurized oil from the main line 38, and the other oil chamber 43b receives pressurized oil from the main line 37. The load pressure control spool 42 switches from position B0 to position B1 or B2 depending on the balance between the difference in force acting on oil chamber 43a and the force acting on oil chamber 43b and the biasing force of spring 42a.

[0022] The tilt control spool 44 is equipped with a piston 45. Pressurized oil (pilot pressure) from a fixed displacement pilot pump 47 is introduced into an oil chamber 45a of the piston 45 via an electromagnetic proportional valve 46. The pilot pump 47 is driven by an engine (not shown). The opening of the electromagnetic proportional valve 46 is controlled in response to a control signal from a controller 60. The tilt control spool 44 switches from position C0 to position C1 or C2 depending on the balance between the force acting on the oil chamber 45a and the biasing force of the spring 44a.

[0023] When the load pressure control spool 42 is switched to position B1 and the tilt control spool 44 is switched to position C1, pressure oil from the main conduit 38 flows through the conduit 51 and is introduced into the oil chamber 41b. Note that a throttle 50 is provided in the conduit 51, which limits the flow rate of pressure oil to prevent a sudden increase in the flow rate of pressure oil from being supplied to the oil chamber 41b.

[0024] On the other hand, when the tilt control spool 44 switches to position C2, the oil chamber 41b and the tank 34 communicate with each other, and the pressure oil in the oil chamber 41b returns to the tank 34.

[0025] When the load pressure control spool 42 is switched to position B0 or ​​the tilt control spool 44 is switched to position C0, the motor tilt becomes stable.

[0026] Although the configuration of the hydraulic circuit for driving the auxiliary winch 7 is omitted in FIG. 2 , in reality, a configuration similar to that of the main winch 6 is provided. By operating the control lever 26, the hydraulic motor (second hydraulic motor) 131 of the auxiliary winch 7 rotates, and the motor displacement of the hydraulic motor 131 is controlled by a motor capacity control device 140 for the hydraulic motor 131 of the auxiliary winch 7. Then, by simultaneously operating the control levers 25 and 26, the bucket 16 can be lowered to perform excavation work. In this embodiment, the hydraulic motor 31 of the main winch 6 and the hydraulic motor 131 of the auxiliary winch 7 are connected in series to the hydraulic pump 30 to form a series circuit. In other words, pressure oil discharged from the hydraulic pump 30 is supplied to the hydraulic motor 131 and then supplied to the hydraulic motor 31. Of course, the present invention is not limited to such a series circuit.

[0027] Next, a description will be given of the motor displacement control (motor capacity control) of the hydraulic motors 31, 131. Fig. 3 is a flowchart showing the processing procedure of the motor displacement control of the hydraulic motors 31, 131 by the controller 60.

[0028] The controller 60 is configured to include an arithmetic processing unit having a CPU, memory devices such as ROM and RAM, and other peripheral circuits. The controller 60 is connected to the operation levers 25, 26 via electrical wiring E1, and is also electrically connected to a line pull detector 61 that detects the rope tension (load of the suspended load) of the derricking rope 15 via electrical wiring E2 (see FIG. 2). Based on detection signals input from these devices, the controller 60 controls the operation of the solenoid switching valves 55, 56 or the operation of the solenoid proportional valve 46.

[0029] First, in order to detect the load on the bucket 16, the controller 60 acquires data on the rope tension T of the hoisting rope 15 from the line pull detector 61 (Step S1), performs a threshold determination to determine whether the rope tension T exceeds the threshold value Tr, and stores the determination result (Step S2). Next, the controller 60 determines whether the operating lever 25 of the main hoisting winch 6 is being operated (Step S3). If the operating lever 25 is being operated (Step S3 / Yes), the controller 60 determines whether the operating lever 26 of the auxiliary hoisting winch 7 is being operated (Step S4). If the operating lever 26 is being operated (Step S4 / Yes), the controller 60 determines whether the main hoisting winch 6 and auxiliary hoisting winch 7 are simultaneously performing a hoisting operation (Step S5).

[0030] If the main winch 6 and auxiliary winch 7 are not simultaneously performing a lowering operation (step S5 / No), the controller 60 executes motor tilt independent control to independently control the hoisting speed / lowering speed of the main winch 6 and auxiliary winch 7 (step S7). On the other hand, if the main winch 6 and auxiliary winch 7 are simultaneously performing a lowering operation (step S5 / Yes), the controller 60 checks the result of the threshold determination in step S2. That is, the controller 60 determines whether the rope tension T of the hoisting ropes 15 exceeds the threshold Tr (step S6).

[0031] If it is determined that the rope tension T exceeds the threshold value Tr (step S6 / Yes), the controller 60 executes motor tilt synchronization control to synchronize the winding-down speeds of the main hoisting winch 6 and the auxiliary hoisting winch 7 (step S8). On the other hand, if it is determined that the rope tension T is equal to or less than the threshold value Tr (step S6 / No), the controller 60 executes motor tilt independent control to independently control the winding-down speeds of the main hoisting winch 6 and the auxiliary hoisting winch 7 (step S7). Note that if the operating lever 25 is not operated and if the operating lever 26 is not operated (step S3 / No, step S4 / No), the process ends.

[0032] Here, in step S1, instead of obtaining data on the rope tension T of the hoisting ropes 15, it is also possible to obtain the rope tension T1 of the main hoisting rope 12 and the rope tension T2 of the auxiliary hoisting rope 13, and determine whether their sum (T1 + T2) exceeds a threshold value. In other words, any detection means can be used as long as it can detect the load of the bucket 16, which is the suspended load. Note that the load of the bucket 16 refers to a load that includes the weight of the contents when the bucket 16 is holding contents.

[0033] Next, the motor displacement only control (first control) executed in step S7 will be described. Motor displacement only control is a commonly performed control of a variable displacement hydraulic motor, and is a control that automatically changes the motor displacement from small to large displacement when the motor holding pressure (load pressure) exceeds a predetermined value. This will be described in detail below using FIG. 4.

[0034] Figure 4 is a diagram showing the relationship between the hanging load and the motor holding pressure. As shown in Figure 4, with the hanging load (rope tension) on the horizontal axis and the motor holding pressure on the vertical axis, when the hydraulic motor 31, 131 is operated at a small tilt, the motor holding pressure changes linearly from point A to point B as the hanging load increases, and when the hydraulic motor 31, 131 is operated at a large tilt, the motor holding pressure changes linearly from point C to point D. The slope of the increase in motor holding pressure with an increase in the hanging load is greater when the hydraulic motor is operated at a small tilt than when it is operated at a large tilt.

[0035] When the hydraulic motor 31, 131 is operating at a small tilt, if the motor holding pressure reaches a predetermined value Pa, a regulator (not shown) mounted on the hydraulic motor 31, 131 automatically shifts the motor tilt toward a large tilt to prevent the motor holding pressure from increasing any further. In other words, between points E and F in FIG. 4 (between rope tensions Ta and Tb), the motor tilt shifts from a small tilt to a large tilt, so the motor holding pressure is maintained at the predetermined value Pa even if the lifted load increases. With this function, during motor tilt-only control, the hydraulic motor 31, 131 is controlled so that the motor holding pressure increases along the line connecting points A, E, F, and D as the lifted load increases.

[0036] As described above, between points E and F, the motor tilt automatically shifts toward the large tilt side so that the motor holding pressure does not exceed the predetermined value Pa. Therefore, the motor tilt of the hydraulic motors 31, 131 automatically varies in response to the motor load. Therefore, during this period, if the lifting load changes, the rotation speed also changes. Therefore, if the main winch 6 and the auxiliary winch 7 are simultaneously lowered between points E and F, it becomes difficult to synchronize the lowering speeds if the load balance between the winches 6, 7 changes. Therefore, in this embodiment, when the main winch 6 and the auxiliary winch 7 are simultaneously lowered (step S3 / Yes in FIG. 3 ) and the rope tension T exceeds a threshold value Tr (step S6 / Yes in FIG. 3 ), which is slightly smaller than the rope tension Ta corresponding to point E (the rope tension at which the motor tilt automatically starts shifting toward the large tilt side), the motor tilt synchronization control (second control / step S8 in FIG. 3 ) is executed. The motor tilt synchronization control will be described below with reference to FIG. 5 .

[0037] Fig. 5 is a flowchart showing the details of the motor displacement synchronization control according to this embodiment. As shown in Fig. 5, when the motor displacement synchronization control is started, the controller 60 controls the motor capacity control devices 40, 141 to fix the hydraulic motor 31 of the main hoisting winch 6 and the hydraulic motor 131 of the auxiliary hoisting winch 7 to the maximum displacement (specific capacity) (step S81).

[0038] Specifically, the controller 60 switches the solenoid proportional valve 46 to return the pilot pressure in the oil chamber 45a to the tank 34. Then, the biasing force of the spring 44a switches the tilt control spool 44 to position C2, and the pressure oil in the oil chamber 41b flows through the conduit 51 and is returned to the tank 34. At this time, because pressure oil is introduced into the oil chamber 41a from the main conduit 38, the piston 41 moves in the direction a, and the motor tilt θ1 of the hydraulic motor 31 is fixed at the maximum tilt. In other words, the hydraulic motor 31 is controlled to a specific displacement corresponding to the maximum tilt. Through similar control, the motor tilt θ2 of the hydraulic motor 131 is also fixed at the maximum tilt. In this way, the main winch 6 and the auxiliary winch 7 rotate at the same lowering speed, and the bucket 16 descends slowly and steadily.

[0039] Then, in step S82, the controller 60 determines whether the operating levers 25, 26 are being operated, and if the operating levers 25, 26 are being operated (S82 / Yes), the process returns to step S81 and the motor rotations θ1, θ2 remain fixed at the maximum rotations. On the other hand, if it is determined that the operating levers 26, 26 are not being operated, in other words, if it is determined that the operating levers 25, 26 are in the neutral position, the controller 60 releases the fixation of the motor rotations (step S83) and ends the process.

[0040] The motor displacement synchronization control according to this embodiment will be further explained with reference to Fig. 4. When the motor displacement synchronization control is executed, the motor displacement of the hydraulic motors 31, 131 is fixed to the maximum displacement (maximum motor capacity). Therefore, in this embodiment, the motor displacement of the hydraulic motors 31, 131 is controlled along the line from point A to point E' to point G to point F to point D.

[0041] Therefore, in the past, it was difficult to synchronize the lowering speeds of both winches 6, 7 because the motor tilt was changing from small tilt to large tilt between points E and F. However, in the second embodiment, the motor tilt is controlled to be fixed at large tilt from point E', so it is possible to avoid operating the hydraulic motors 31, 131 between points E and F. Therefore, even when the main winch 6 and auxiliary winch 7 are driven simultaneously to lower the bucket 16, the bucket 16 can be lowered (lowered) stably.

[0042] Furthermore, the motor tilts θ1 and θ2 are fixed to the maximum tilts only when the rope tension T of the derricking ropes 15 exceeds the threshold value Tr, thereby preventing a decrease in work efficiency. That is, in this embodiment, the bucket 16 is controlled to have the maximum tilt (specific capacity) only when it is gripping and lowering a heavy load of contents, and when the contents are sufficiently light, such as when no contents are gripped, it can operate at high speed with small tilts, allowing for lowering in a stable posture while minimizing a decrease in work efficiency.

[0043] Furthermore, once the motor tilting synchronization control is started, this control continues until the operating levers 25, 26 are not operated (until step S82 returns No), so the operation of lowering the bucket 16 can be performed stably.

[0044] Here, the effects of this embodiment will be further explained. For example, a configuration is conceivable in which the motor load pressure of the hydraulic motor 31 or the hydraulic motor 131, whichever is higher, is used to control the motor rotation of the hydraulic motors 31, 131. However, with this configuration, when the rope tensions of the two ropes 12, 13 are equal in the initial state, the pressure at which the motor rotation is variable is not reached. Furthermore, if simultaneous variable control of the motor rotation begins at a stage when the rope tensions of the two ropes 12, 13 become unbalanced, the bucket 16 will descend while the load balance between the main hoisting winch 6 and the auxiliary hoisting winch 7 remains unbalanced.

[0045] In contrast to this, according to this embodiment, when the main winch 6 and auxiliary winch 7 are simultaneously performing a hoisting operation and the load on the bucket 16 exceeds a threshold value, the motor tilting synchronization control is executed, so that hoisting can be performed in a stable posture while minimizing any decrease in work efficiency.

[0046] Furthermore, for example, if the configuration is such that control is performed to fix the motor capacity (motor tilt) to a specific value only during lowering operation, the winch speed of winches 6 and 7 will always be operated at a low speed during lowering, which will reduce work efficiency.

[0047] In contrast, according to this embodiment, whether or not to perform motor tilt synchronization control is determined depending on whether or not the load of bucket 16 exceeds a threshold value, so a decrease in work efficiency can be prevented. As described above, according to this embodiment, when multiple winches 6, 7 are driven simultaneously, bucket 16 can be stably lowered while maintaining work efficiency.

[0048] (Reference to other embodiments) The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the gist of the present invention. The present invention covers all technical matters included in the technical ideas described in the claims. The above-described embodiments are preferred examples, but a person skilled in the art can realize various alternatives, modifications, variations, or improvements from the contents disclosed in this specification, and these are included in the technical scope described in the appended claims.

[0049] For example, in this embodiment, the rope tension T of the derrick ropes 15 is detected using the line pull detector 61 to measure the load of the bucket 16 (suspended load), but other sensors may be used to detect the load of the bucket 16. Also, a pressure sensor may be provided to detect the circuit pressure of the hydraulic circuit, and if the circuit pressure detected by this pressure sensor exceeds a predetermined value (for example, 60% of the relief pressure), it may be determined that the load of the bucket 16 (which is an attachment) has exceeded a threshold value, and the motor tilt angles θ1 and θ2 may be fixed at the maximum tilt angles.

[0050] Furthermore, if the pressure of the hydraulic motor for the hoisting winch 8 exceeds a predetermined threshold when the hoisting winch 8 is driven to raise the boom 5 with the bucket 16 suspended, the controller 60 can determine that the bucket 16, which is a heavy load, is suspended. In this case, the controller 60 may, for example, set a flag to store the fact that the pressure of the hydraulic motor for the hoisting winch 8 has exceeded the predetermined threshold, and when the operating levers 25, 26 are simultaneously operated to lower the bucket 16, the controller 60 may control the hydraulic motors 31, 131 to fix the maximum tilt based on the fact that the flag has been set. In this case, the bucket 16 can also be lowered stably.

[0051] In this embodiment, the motor tilts θ1 and θ2 may be fixed to a motor tilt slightly smaller than the maximum tilt (for example, approximately 80% of the maximum tilt), or may be set arbitrarily based on the detected tension. That is, when the bucket 16 is suspended by the main hoisting rope 12 and the auxiliary hoisting rope 13 and the main hoisting winch 6 and the auxiliary hoisting winch 7 are simultaneously lowered, the motor tilt angle is not important as long as operation of the hydraulic motors 31 and 131 can be avoided between points E and F (see FIG. 4). It is sufficient to reduce the rotational speed of the hydraulic motors 31 and 131 to a level that allows the bucket 16 to be stably lowered. In this case, any means may be used to fix the motor tilt. The swash plates of the hydraulic motors 31 and 131 may be physically fixed, or the swash plates may be fixed at the desired angle under the control of the motor displacement control devices 40 and 140.

[0052] It goes without saying that in the present invention, any type of hydraulic motor can be used as long as it is a variable displacement type.

[0053] Furthermore, the operation levers for each winch, such as operation levers 25, 26, may be located not in the cab 9 of the crane 1 but, for example, in a remote control room that is remote from the crane 1. Furthermore, instead of the operation levers 25, 26, a device such as an operation dial may be used, or the hoisting / lowering speed of the winches 6, 7, etc. may be input from an operation unit such as a touch panel or a mobile terminal, and the controller 60 may output a current command value corresponding to the input value (speed value) to the solenoid directional control valves 55, 56. In other words, as a means for specifying the rotation speed of the winches 6, 7, etc., in addition to a means in which the operator gives an instruction using the amount of operation of the operation levers 25, 26, any means may be used, such as an instruction using an operation dial or an instruction by directly inputting a speed value.

[0054] Furthermore, while a crawler crane has been given as an example of a crane, the present invention is not limited to this and can be applied to any type of cranes, including other mobile cranes such as wheel cranes, truck cranes, rough terrain cranes, and all-terrain cranes, as well as foundation machines such as tower cranes, overhead cranes, jib cranes, retractable cranes, stacker cranes, gantry cranes, unloaders, and earth drills. Furthermore, while a grab bucket 16 as shown in Figure 1 has been given as an example of an attachment, the present invention can be applied to any type of attachment that operates with multiple winches, and can also be applied to, for example, clamshells, hammer grabs, and diaphragm wall equipment. [Explanation of symbols]

[0055] 1 crane 2. Running body 3 Swivel device 4 Rotating body 5. Boom 6 Main winch (No. 1 winch) 7 Auxiliary winch (second winch) 8. Hoisting winch 9 Cab 10,11 Sheaves 12 Main winding rope (first rope) 13 Auxiliary rope (second rope) 14 Pendant Rope 15. Descending rope 16 Bucket (attachment) 17,18 Sheaves 25,26 Control lever 30 Hydraulic pump 31 Hydraulic motor (first hydraulic motor) 32 Directional control valve 32a,23b Pressure receiving part 33 Counterbalance valve 34 Tank 37,38 Main pipeline 40 Motor capacity control device 41 Piston 41a,41b Oil room 42 Load pressure control spool 42a Spring 43 Piston 43a,43b Oil room 44 Tilt control spool 44a Spring 45 piston 45a Oil room 46 Solenoid proportional valve 47 Pilot Pump 50 apertures 51 Pipeline 55,56 Solenoid valve 60 Controller 61,62 Line pull detector 131 Hydraulic motor (second hydraulic motor) 140 Motor capacity control device E1~E5 Electrical wiring

Claims

1. a first winch, a first rope wound around the first winch, and a variable displacement first hydraulic motor that drives the first winch; a second winch, a second rope wound around the second winch, and a variable displacement second hydraulic motor that drives the second winch; an attachment suspended by the first rope and the second rope, a first control is executed in which, when the first winch and the second winch are simultaneously performing a winch lowering operation and the load of the attachment does not exceed a threshold value, the motor displacement of the first hydraulic motor is varied so as to maintain the predetermined value when the load pressure of the first hydraulic motor exceeds a predetermined value, and when the load pressure of the second hydraulic motor exceeds the predetermined value, the motor displacement of the second hydraulic motor is varied so as to maintain the predetermined value; a crane comprising: when the first winch and the second winch perform a winch lowering operation simultaneously and the load of the attachment exceeds a threshold value, a second control different from the first control is performed instead of the first control, and the motor capacities of the first hydraulic motor and the second hydraulic motor are controlled so that the winch lowering speeds of the first hydraulic motor and the second hydraulic motor are synchronized.

2. The crane of claim 1, When the second control is executed, the motor displacement of the first hydraulic motor and the motor displacement of the second hydraulic motor are fixed to specific displacements.

3. The crane according to claim 1 or 2, The crane, wherein, once the second control is executed, the second control is maintained until the first winch and the second winch are not operated.

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