Brake control device and crane equipped with the same

Abstract

To provide a brake control device which can inhibit a brake response time from increasing when rapid brake operation is conducted, and to provide a crane including the brake control device.SOLUTION: A brake control device 10 includes: a brake unit 6 having a positive chamber 6b which generates force in a direction such that brake force exerted on a winch drum 11 is increased and a negative chamber 6c which generates force in a direction such that the brake force is decreased; an operation device 7 to which brake operation is provided; an electromagnetic proportional pressure reduction valve 2 which opens or closes so that a pressure of working fluid to be supplied to the positive chamber 6b can be adjusted according to a control amount of the brake operation; a selector valve 3 which switches its state between a pump connection state in which the negative chamber 6c is connected to a hydraulic pump 22 and a tank connection state in which the negative chamber 6c is connected to a tank 27; and a controller 4 which controls operation of the selector valve 3 so that the pump connection state is switched to the tank connection state when conditions of determination for determining that the rapid brake operation is provided are met.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present disclosure relates to a brake control device and a crane equipped with the same.

Background Art

[0002] Generally, a crane includes a self-propelled lower traveling body, an upper slewing body rotatably supported by the lower traveling body, a boom member including a boom attached to the upper slewing body so as to be able to rise and fall, a hook suspended from the tip of the boom member via a rope, and a winch for winding and unwinding the rope.

[0003] Patent Document 1 discloses a winch control device that controls the operation of a winch. This winch control device includes a winch, a state switching valve (state switching section), a pressure control valve, and a brake force adjustment section. The pressure control valve is a valve that converts the command of the brake force adjustment section into hydraulic pressure. The pressure control valve is a valve that controls (adjusts) the brake force when the winch is in a free state (when the switching position of the state switching valve is in the free position). The pressure control valve is, for example, an electromagnetic proportional pressure reducing valve. The winch includes a winch drum, a motor, a speed reducer, and a clutch.

[0004] The clutch switches the connection state (degree of connection) between the motor and the winch drum. The clutch applies a brake to the rotation of the winch drum. The clutch includes a housing, a clutch plate, a clutch cylinder, and a spring. The clutch cylinder includes a piston capable of pressing the clutch plate, a pressure contact chamber, and a separation chamber. In response to the command of the brake force adjustment section, the opening degree of the pressure control valve changes, and the pressure in the pressure contact chamber changes. The brake force of the winch (clutch) changes according to the pressure in the pressure contact chamber.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] By the way, when the pressure control valve is an electromagnetic proportional pressure reducing valve, due to its structure, while the electromagnetic proportional pressure reducing valve is good at controlling static pressure, it may not necessarily be suitable for operations that supply a large flow rate. Also, in order to ensure sufficient braking capacity in the clutch (brake unit), the pressure receiving areas of the pressure contact chamber (positive chamber) and the separation chamber (negative chamber), the stroke of the piston, and the piston volume (the product of the pressure receiving area and the stroke) become large. Therefore, when an emergency braking operation is performed by the operator, the flow rate of the hydraulic oil required in the brake unit (the value obtained by dividing the piston volume by the brake response time) becomes large. However, in the flow rate control by the pressure control valve constituted by the electromagnetic proportional pressure reducing valve, the flow rate of the hydraulic oil required in the brake unit may not be quickly supplied to the brake unit when an emergency braking operation is performed. In this case, the brake response time may become long.

Means for Solving the Problems

[0007] An object of the present disclosure is to provide a brake control device capable of suppressing an increase in the brake response time when an emergency braking operation is performed, and a crane equipped with the same.

[0008] The provided brake control device includes a tank for storing hydraulic oil, a hydraulic pump for discharging the hydraulic oil, a positive chamber that generates a force in a direction to increase the braking force on the winch drum by receiving the pressure of the hydraulic oil, and a negative chamber that generates a force in a direction to decrease the braking force by receiving the pressure of the hydraulic oil, a brake unit having the positive and negative chambers, an operating device to which a brake operation for adjusting the braking force is applied, an electromagnetic proportional pressure reducing valve that opens and closes so that the pressure of the hydraulic oil supplied to the positive chamber is adjusted according to the operation amount of the brake operation, a first switching valve that switches between a pump connection state in which the negative chamber is connected to the hydraulic pump and a tank connection state in which the negative chamber is connected to the tank, and a controller that controls the operation of the first switching valve so that the pump connection state switches to the tank connection state when a preset determination condition for determining that an emergency brake operation has been applied to the operating device is satisfied.

[0009] In this brake control device, when the determination condition is satisfied, the controller controls the operation of the first switching valve so that the pump connection state switches to the tank connection state. Therefore, the pressure in the negative chamber of the brake unit rapidly decreases from the pressure corresponding to the secondary pressure of the hydraulic pump to the pressure corresponding to the pressure of the tank. Accordingly, in this brake control device, compared to the case where the electromagnetic proportional pressure reducing valve operates in response to an emergency brake operation to generate a braking force, a braking force can be generated more rapidly. Thereby, it is suppressed that the brake response time becomes long when an emergency brake operation is performed.

[0010]

[0011] ​Preferably, the determination condition includes that the operation speed of the braking operation exceeds an operation speed threshold which is a preset value. In an emergency braking operation, the operation speed usually becomes relatively high. Therefore, with this configuration, the controller can determine whether an emergency braking operation is applied to the operating device by comparing the operation speed of the braking operation with the operation speed threshold.

[0012] The brake control device further includes a second switching valve that switches between a first state in which the positive chamber is connected to the hydraulic pump via the electromagnetic proportional pressure reducing valve and a second state in which the positive chamber is connected to the hydraulic pump bypassing the electromagnetic proportional pressure reducing valve. Preferably, the controller is configured to control the operation of the second switching valve such that the first state switches to the second state when the determination condition is satisfied. When the determination condition is satisfied, as the pump connection state switches to the tank connection state and the pressure in the negative chamber rapidly decreases to a pressure corresponding to the pressure in the tank, hydraulic oil flows into the positive chamber. In order to ensure the flow rate of the hydraulic oil into the positive chamber, the controller controls the operation of the second switching valve such that the positive chamber is connected to the hydraulic pump without passing through the electromagnetic proportional pressure reducing valve when the determination condition is satisfied. Therefore, it becomes easier to ensure the flow rate of the hydraulic oil into the positive chamber compared to the case where the hydraulic oil flows into the positive chamber through the electromagnetic proportional pressure reducing valve which is not suitable for an operation of supplying a large flow rate. Thereby, the possibility of cavitation occurring when the hydraulic oil flows into the positive chamber can be reduced.

[0013] The brake control device further includes a second switching valve that switches between a first state in which the positive chamber is connected to the hydraulic pump via the electromagnetic proportional pressure reducing valve and a second state in which the positive chamber bypasses the electromagnetic proportional pressure reducing valve and is connected to the tank. The controller may be configured to control the operation of the second switching valve so that the first state switches to the second state when the determination condition is satisfied. When the determination condition is satisfied, as the pump connection state switches to the tank connection state and the pressure in the negative chamber rapidly decreases to a pressure corresponding to the pressure in the tank, hydraulic oil flows into the positive chamber. In order to ensure the flow rate of the hydraulic oil into the positive chamber, the controller controls the operation of the second switching valve so that the positive chamber is connected to the tank without passing through the electromagnetic proportional pressure reducing valve when the determination condition is satisfied. Therefore, it becomes easier to ensure the flow rate of the hydraulic oil into the positive chamber compared to the case where hydraulic oil flows into the positive chamber through the electromagnetic proportional pressure reducing valve, which is not suitable for operations that supply a large flow rate. Thereby, the possibility of cavitation occurring when hydraulic oil flows into the positive chamber can be reduced.

[0014] The provided crane includes a machine body, a lifting member attached to the machine body so as to be able to lift and lower, a winch drum for winding and unwinding a rope hanging from the lifting member, and the above-described brake control device capable of adjusting the braking force on the winch drum. With this crane, it is possible to suppress an increase in the brake response time when an emergency braking operation is performed.

Effects of the Invention

[0015] According to the present disclosure, there are provided a brake control device capable of suppressing an increase in the brake response time when an emergency braking operation is performed and a crane equipped with the same.

Brief Description of the Drawings

[0016]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Mode for Carrying Out the Invention

[0017] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings.

[0018] FIG. 1 is a side view showing a crane 100 according to an embodiment of the present disclosure. As shown in FIG. 1, the crane 100 includes a self-propelled lower traveling body 101, an upper slewing body 103 rotatably supported about an axis on the lower traveling body 101, a boom member attached to the upper slewing body 103 so as to be able to rise and fall, a hook 105 suspended from the tip of the boom member via a rope R, a gantry 107 attached to the upper slewing body 103, and a winch drum 11. The lower traveling body 101 and the upper slewing body 103 are examples of the machine body. In the crane 100 shown in FIG. 1, the boom member is constituted by a boom 104, but the boom member may further include a jib (not shown) attached to the tip of the boom 104. Further, the crane 100 may be provided with a mast instead of the gantry 107.

[0019] The winch drum 11 causes the hook 105 to perform a lifting and lowering operation for lifting work by winding or unwinding the rope R connected to the hook 105. The rope R is fed out from the winch drum 11, passes through the tip of the undulating member, and is arranged to hang down from the tip of the undulating member to suspend the hook 105. A suspended load 106 is suspended from the hook 105. The winch drum 11 is arranged such that its rotation axis coincides with the width direction of the upper slewing body 103. In the present embodiment, the winch drum 11 is supported by the upper slewing body 103, but it may be supported by the boom 104.

[0020] As shown in FIG. 2, the crane 100 further includes a main pump 21, a winch motor 23, a winch control valve 24, a winch operating device 25, and a speed reducer 28.

[0021] The main pump 21 discharges hydraulic oil by being driven by a drive source (not shown) such as an engine.

[0022] The winch motor 23 is a hydraulic motor for rotationally driving the winch drum 11. In the present embodiment, the winch motor 23 has an output shaft 23a that rotates by receiving the supply of hydraulic oil from the main pump 21. The winch motor 23 has a first port and a second port, and when it receives the supply of hydraulic oil to one of these ports, the output shaft 23a rotates in the direction corresponding to the one port and operates to discharge the hydraulic oil from the other port.

[0023] The winch control valve 24 is interposed between the main pump 21 and the winch motor 23, selectively guides the hydraulic oil for driving the winch motor 23 from the main pump 21 to one of the first port and the second port of the winch motor 23 to control the direction of the hydraulic oil supplied to the winch motor 23, and controls the flow rate of the hydraulic oil supplied to the winch motor 23. The winch control valve 24 has a first pilot port and a second pilot port.

[0024] The winch operating device 25 has a winch operating lever 25a and a pilot valve 25b (remote control valve). The winch operating lever 25a rotates in the direction in which a winch operation is applied by an operator to the winch operating lever 25a. The pilot valve 25b has an inlet port connected to a pilot pump (not shown) and a pair of outlet ports. The pair of outlet ports are respectively connected to a first pilot port and a second pilot port of the winch control valve 24 via pilot lines. The pilot valve 25b opens to allow a pilot pressure corresponding to the magnitude of the winch operation to be supplied from the pilot pump to the pilot port corresponding to the direction of the winch operation applied to the winch operating lever 25a among the first and second pilot ports. Note that the pilot pump may be a control pump 22 described later, or may be a pump different from the control pump 22.

[0025] When no pilot pressure is input to either the first or second pilot port, the winch control valve 24 is held in a neutral position (the central position in FIG. 2). In this neutral position, the connection between the main pump 21 and the winch motor 23 is blocked and the center bypass line is opened, so that the hydraulic oil from the main pump 21 returns directly to the tank 27 through the center bypass line.

[0026] When a pilot pressure equal to or higher than a certain level is supplied to the first pilot port, the winch control valve 24 shifts from the neutral position to a first drive position (the upper position in FIG. 2) with a stroke corresponding to the magnitude of the pilot pressure. In this first drive position, the hydraulic oil from the main pump 21 is supplied to the first port of the winch motor 23 at a flow rate corresponding to the stroke, and the hydraulic oil is discharged from the second port. Thereby, the output shaft 23a of the winch motor 23 rotates in the first direction. The discharged hydraulic oil returns to the tank 27.

[0027] When a pilot pressure equal to or higher than a certain level is supplied to the second pilot port, the winch control valve 24 shifts from the neutral position to the second drive position (the lower position in Fig. 2) with a stroke corresponding to the magnitude of the pilot pressure. In this second drive position, the hydraulic oil from the main pump 21 is supplied to the second port of the winch motor 23 at a flow rate corresponding to the stroke, and the hydraulic oil is discharged from the first port. As a result, the output shaft 23a of the winch motor 23 rotates in the second direction. The discharged hydraulic oil returns to the tank 27.

[0028] The speed reducer 28 is interposed between the output shaft 23a of the winch motor 23 and the winch drum 11 to transmit the power of the winch motor 23 to the winch drum 11. The speed reducer 28 is constituted by, for example, a planetary gear mechanism. A plate 6e in the brake unit 6 described later is connected to the carrier shaft of the speed reducer 28.

[0029] The crane 100 is provided with a brake control device 10. As shown in Fig. 2, the brake control device 10 includes the tank 27, the control pump 22, the brake unit 6, the brake operation device 7, the operation amount sensor 5, the mode switching valve 1, the electromagnetic proportional pressure reducing valve 2, the emergency brake switching valve 3, the relief valve 9, and the controller 4. The emergency brake switching valve 3 is an example of the first switching valve in the present disclosure, and the mode switching valve 1 is an example of the second switching valve in the present disclosure. The tank 27 stores the hydraulic oil.

[0030] The control pump 22 discharges the hydraulic oil by being driven by a drive source (not shown) such as an engine. The control pump 22 is an example of the hydraulic pump in the present disclosure.

[0031] The brake unit 6 is configured to be able to generate a braking force on the winch drum 11 by receiving the supply of the hydraulic oil discharged from the control pump 22.

[0032] The brake unit 6 is configured to be operable to switch between a clutch-on state in which the power of the winch motor 23 is transmitted to the winch drum 11 and a clutch-off state in which the winch drum 11 is disconnected from the winch motor 23 and free rotation of the winch drum 11 is allowed.

[0033] The brake unit 6 has a piston 6a, a spring 6d, a plurality of plates 6e including an inner plate and an outer plate, and a unit case 6f that houses these components. Inside the unit case 6f is partitioned into a positive clutch chamber 6b, a negative clutch chamber 6c, and a plate chamber in which the plurality of plates 6e are arranged. The piston 6a is displaceable with respect to the unit case 6f in its axial direction. The axial direction is the direction in which the piston 6a approaches the plurality of plates 6e or the direction in which the piston 6a moves away from the plurality of plates 6e.

[0034] By receiving the pressure of the hydraulic oil from the control pump 22, the positive clutch chamber 6b generates a force in the direction of increasing the braking force on the winch drum 11, that is, a force in the direction in which the piston 6a approaches the plurality of plates 6e. The positive clutch chamber 6b is an example of the positive chamber in the present disclosure. By receiving the pressure of the hydraulic oil from the control pump 22, the negative clutch chamber 6c generates a force in the direction of decreasing the braking force on the winch drum 11, that is, a force in the direction in which the piston 6a moves away from the plurality of plates 6e. The negative clutch chamber 6c is an example of the negative chamber in the present disclosure.

[0035] When the piston 6a moves in the axial direction, the state of the brake unit 6 switches between the clutch-on state (the state in which the brake is applied) and the clutch-off state (the state in which the brake is released). Specifically, when the piston 6a moves in a direction approaching the plurality of plates 6e, a pressing force is applied to the plurality of plates 6e so that the inner plate and the outer plate in the plurality of plates 6e are in contact with each other. As a result, the state of the brake unit 6 becomes the clutch-on state. On the other hand, when the piston 6a moves in a direction away from the plurality of plates 6e, the inner plate and the outer plate are separated. As a result, the state of the brake unit 6 becomes the clutch-off state. The spring 6d biases the piston 6a in a direction in which the state of the brake unit 6 becomes the clutch-on state, that is, in a direction in which the piston 6a approaches the plurality of plates 6e.

[0036] In the present embodiment, when the pressure in the positive clutch chamber 6b and the pressure in the negative clutch chamber 6c are the same, the state of the brake unit 6 becomes the clutch-on state due to the biasing force of the spring 6d. On the other hand, when the pressure in the negative clutch chamber 6c becomes greater than the pressure in the positive clutch chamber 6b, and the force generated due to this differential pressure (that is, the force in the direction of moving the piston 6a away from the plurality of plates 6e) becomes greater than the biasing force of the spring 6d, the state of the brake unit 6 becomes the clutch-off state.

[0037] The brake operating device 7 is given a brake operation by the operator to adjust the braking force on the winch drum 11. The brake operating device 7 is an example of the operating device in the present disclosure. The brake operating device 7 has a brake pedal 7a (foot pedal) as an operating member.

[0038] When a brake operation (pedal operation) by the operator is applied to the brake pedal 7a of the brake operating device 7, the operation amount sensor 5 detects the operation amount of the pedal operation and inputs a brake detection signal, which is a detection signal corresponding to the detected operation amount, to the controller 4.

[0039] The mode switching valve 1 is interposed between the control pump 22 and the brake unit 6. The mode switching valve 1 switches between a first state (the right position in FIG. 2) in which the control pump 22 and the brake unit 6 are connected via the electromagnetic proportional pressure reducing valve 2, and a second state (the left position in FIG. 2) in which the control pump 22 and the brake unit 6 are connected bypassing the electromagnetic proportional pressure reducing valve 2 (without passing through the electromagnetic proportional pressure reducing valve 2). Specifically, in the first state, the positive clutch chamber 6b of the brake unit 6 is connected to the control pump 22 via the electromagnetic proportional pressure reducing valve 2. In the second state, the positive clutch chamber 6b of the brake unit 6 is connected to the control pump 22 bypassing the electromagnetic proportional pressure reducing valve 2. In the present embodiment, when the state of the mode switching valve 1 is the first state, the control pump 22, the electromagnetic proportional pressure reducing valve 2, the mode switching valve 1, and the positive clutch chamber 6b of the brake unit 6 are connected in this order. When the state of the mode switching valve 1 is the second state, the control pump 22, the mode switching valve 1, and the positive clutch chamber 6b of the brake unit 6 are connected in this order, and the electromagnetic proportional pressure reducing valve 2 is not interposed between the control pump 22 and the mode switching valve 1.

[0040] The mode switching valve 1 is an electromagnetic switching valve that switches between the first state and the second state in response to a mode command signal from the controller 4. Specifically, in the present embodiment, when the solenoid of the mode switching valve 1 is in a non-excited state, the state of the mode switching valve 1 is the second state (the left position in FIG. 2), and when the solenoid of the mode switching valve 1 is in an excited state, the state of the mode switching valve 1 is the first state (the right position in FIG. 2).

[0041] The electromagnetic proportional pressure reducing valve 2 opens and closes so that, in the free mode described later, the pressure of the hydraulic oil supplied to the brake unit 6 is adjusted according to the operation amount of the brake operation (pedal operation). Specifically, in the present embodiment, the controller 4 outputs a brake command signal to the electromagnetic proportional pressure reducing valve 2 according to the operation amount of the brake operation (pedal operation), and the electromagnetic proportional pressure reducing valve 2 opens and closes so that the pressure of the hydraulic oil supplied to the positive clutch chamber 6b of the brake unit 6 is adjusted according to the brake command signal from the controller 4.

[0042] Due to its structure, the electromagnetic proportional pressure reducing valve 2 is not necessarily suitable for operations that supply a large flow rate. One of the reasons is that, for example, the cross-sectional area of the flow path through which the hydraulic oil flows in the electromagnetic proportional pressure reducing valve 2 is smaller than the cross-sectional area of the flow path through which the hydraulic oil flows in the mode switching valve 1 and the cross-sectional area of the flow path through which the hydraulic oil flows in the emergency brake switching valve 3.

[0043] The emergency brake switching valve 3 is configured to be switchable between a supply position (the left position in FIG. 2) that allows the hydraulic oil from the control pump 22 to be supplied to the negative clutch chamber 6c and a discharge position (the right position in FIG. 2) that allows the hydraulic oil in the negative clutch chamber 6c to be discharged from the negative clutch chamber 6c to the tank 27. In other words, the emergency brake switching valve 3 switches between a pump connection state in which the negative clutch chamber 6c is connected to the control pump 22 and a tank connection state in which the negative clutch chamber 6c is connected to the tank 27. In the pump connection state, the pressure of the hydraulic oil from the control pump 22 is supplied to the negative clutch chamber 6c. In the present embodiment, the emergency brake switching valve 3 is constituted by an electromagnetic valve (electromagnetic switching valve).

[0044] In this embodiment, the solenoid of the emergency brake switching valve 3 is in a non-energized state as shown in FIG. 2 during normal times. The spool of the emergency brake switching valve 3 is set at the supply position, and the state of the emergency brake switching valve 3 is set to the pump connection state. When the state of the mode switching valve 1 is in the first state (the solenoid is in the energized state), for example, when a failure such as a disconnection occurs and the secondary pressure of the electromagnetic proportional pressure reducing valve 2 decreases, the controller 4 switches the solenoid of the emergency brake switching valve 3 to the energized state. As a result, the spool of the emergency brake switching valve 3 switches from the supply position to the discharge position. That is, the state of the emergency brake switching valve 3 switches from the pump connection state to the tank connection state, and the negative clutch chamber 6c is connected to the tank 27. Thereby, a braking force is generated on the winch drum 11, that is, a state where a brake is applied to the winch drum 11 is obtained.

[0045] The brake control device 10 may further include a schematic pressure sensor that detects the secondary pressure of the electromagnetic proportional pressure reducing valve 2. The controller 4 may determine whether a failure such as a disconnection has occurred based on the pressure detection signal input from the pressure sensor and the brake detection signal.

[0046] When the state of the mode switching valve 1 is in the second state (the solenoid is in the non-energized state), since pressures corresponding to the secondary pressure of the control pump 22 are supplied to both the positive clutch chamber 6b and the negative clutch chamber 6c, the state of the brake unit 6 becomes the clutch-on state by the biasing force of the spring 6d. Hereinafter, the mode of the brake control device 10 when the state of the mode switching valve 1 is in the second state (the solenoid is in the non-energized state) may be referred to as the brake mode.

[0047] In this braking mode, a braking force is always generated on the winch drum 11, that is, the winch drum 11 is in a braked state (clutch-on state). In this clutch-on state, the power of the winch motor 23 is transmitted to the winch drum 11. Therefore, in response to the winch operation by the operator applied to the winch operation lever 25a, the winch drum 11 rotates by the power of the winch motor 23, and the rope R is wound or unwound.

[0048] When the state of the mode switching valve 1 is the first state (the solenoid is in the excited state), the secondary pressure of the electromagnetic proportional pressure reducing valve 2 is applied to the positive clutch chamber 6b. Hereinafter, the mode of the braking control device 10 when the state of the mode switching valve 1 is the first state (the solenoid is in the excited state) may be referred to as the free mode.

[0049] In this free mode, according to the output from the electromagnetic proportional pressure reducing valve 2, the balance between the pressure in the positive clutch chamber 6b and the pressure in the negative clutch chamber 6c changes, and the piston 6a is displaced in its axial direction with respect to the unit case 6f. When a brake detection signal corresponding to the operation amount of the brake operation is input from the operation amount sensor 5 to the controller 4, the controller 4 outputs a brake command signal corresponding to the brake detection signal to the electromagnetic proportional pressure reducing valve 2, and the electromagnetic proportional pressure reducing valve 2 outputs a secondary pressure corresponding to the brake command signal input from the controller 4. That is, the electromagnetic proportional pressure reducing valve 2 outputs a secondary pressure corresponding to the operation amount of the brake operation. Specifically, the electromagnetic proportional pressure reducing valve 2 outputs a larger secondary pressure as the operation amount of the brake operation increases. When the output (secondary pressure) of the electromagnetic proportional pressure reducing valve 2 increases, the braking force on the winch drum 11 also increases, and the winch drum 11 is in a braked state. When the output (secondary pressure) of the electromagnetic proportional pressure reducing valve 2 decreases, the braking force on the winch drum 11 also decreases, and the brake on the winch drum 11 is released. Therefore, in the free mode, the operator can switch between the state of applying a brake to the winch drum 11 and the state of releasing the brake by adjusting the operation amount of the brake operation. In the state where the brake is released in the free mode, the suspended load 106 can freely fall by its own weight. The speed of this free fall can be increased or decreased according to the operation amount of the brake pedal 7a.

[0050] The crane 100 may further include a mode changeover switch 30. The mode changeover switch 30 is a switch for switching the mode of the brake control device 10 between the brake mode and the free mode. The mode changeover switch 30 is configured to be operable by the operator, for example, by being provided inside the cab of the crane.

[0051] When the mode changeover switch 30 receives a free mode operation by an operator, it inputs a free mode signal to the controller 4, and the controller 4 controls the operation of the mode changeover valve 1 so that the state of the mode changeover valve 1 becomes the first state (the right position in FIG. 2). Thereby, the mode of the brake control device 10 is switched to the free mode. On the other hand, when the mode changeover switch 30 receives a brake mode operation by an operator, it inputs a brake mode signal to the controller 4, and the controller 4 controls the operation of the mode changeover valve 1 so that the state of the mode changeover valve 1 becomes the second state (the left position in FIG. 2). Thereby, the mode of the brake control device 10 is switched to the brake mode.

[0052] When the pressure of the discharge line (the discharge line from which the hydraulic oil is discharged from the control pump 22) connected to the control pump 22 exceeds a predetermined value, the relief valve 9 opens so that at least a part of the hydraulic oil flows to the tank 27.

[0053] In order to prevent seizure of the plurality of plates 6e due to friction generated between the inner plate and the outer plate, as shown in FIG. 2, the brake unit 6 is configured such that cooling oil is supplied to the plate chamber.

[0054] The controller 4 includes a computer including an arithmetic processing device such as an MPU and a memory. When a determination condition preset to determine that an emergency braking operation has been applied to the brake operation device 7 is satisfied, the controller 4 controls the operation of the emergency brake changeover valve 3 so that the pump connection state is switched to the tank connection state.

[0055] In this embodiment, the determination condition is a condition (first determination condition) that the operation amount of the braking operation exceeds an operation amount threshold value which is a preset threshold value. The operation amount in an emergency braking operation usually becomes the maximum operation amount that can be applied to the brake pedal 7a of the braking operation device 7 or a large operation amount close thereto. Therefore, in this embodiment, the controller 4 can determine whether an emergency braking operation is applied to the brake pedal 7a by comparing the operation amount of the braking operation with the operation amount threshold value.

[0056] FIG. 3 is a graph showing an example of the relationship between the operation amount (pedal operation amount) of the braking operation and the pressure (clutch pressure) in the braking control device 10 according to this embodiment. In FIG. 3, the horizontal axis represents the ratio (unit: %) of the operation amount (pedal operation amount) of the braking operation applied to the brake pedal 7a when the maximum operation amount is 100, and the vertical axis represents the pressure (unit: MPa). In FIG. 3, the solid line indicates the pressure (positive clutch pressure) supplied to the positive clutch chamber 6b of the brake unit 6. The broken line indicates the pressure (negative clutch pressure) supplied to the negative clutch chamber 6c of the brake unit 6. The alternate long and short dash line is the differential pressure (negative clutch pressure - positive clutch pressure) which is the value obtained by subtracting the pressure supplied to the positive clutch chamber 6b from the pressure supplied to the negative clutch chamber 6c. In FIG. 3, the vertical straight line indicated by the double-dashed line represents the operation amount threshold value.

[0057] In the free mode in which the braking force on the winch drum 11 is adjusted according to the braking operation applied to the brake pedal 7a of the braking operation device 7, the state of the mode switching valve 1 is set to the first state, and the state of the emergency brake switching valve 3 is set to the pump connection state.

[0058] In this free mode, in the specific example shown in FIG. 3, the positive clutch pressure exhibits the following behavior. The minimum value of the positive clutch pressure is the positive clutch pressure when the pedal operation amount is zero, and it is the pressure corresponding to the pressure of the tank 27. The maximum value of the positive clutch pressure is the pressure corresponding to the secondary pressure of the control pump 22. As shown in FIG. 3, as the pedal operation amount increases from zero, the opening area of the electromagnetic proportional pressure reducing valve 2 also increases. Therefore, as the pedal operation amount increases as shown in FIG. 3, the positive clutch pressure also increases. When the pedal operation amount increases to a certain value (the value corresponding to the pump pressure), the positive clutch pressure reaches the pressure corresponding to the secondary pressure of the control pump 22. Therefore, even if the pedal operation amount becomes even larger than the value corresponding to the pump pressure, the positive clutch pressure remains constant at the pressure corresponding to the secondary pressure of the control pump 22. In the specific example of FIG. 3, the value corresponding to the pump pressure is a value smaller than the operation amount threshold, and even if the pedal operation amount becomes even larger than the operation amount threshold, the positive clutch pressure remains constant at the pressure corresponding to the secondary pressure of the control pump 22.

[0059] On the other hand, the negative clutch pressure exhibits the following behavior. In the region from when the pedal operation amount is zero to the operation amount threshold (pump connection region), the spool of the emergency brake switching valve 3 is held at the supply position, and the state of the emergency brake switching valve 3 is maintained in the pump connection state. Therefore, the negative clutch pressure is held at the pressure corresponding to the secondary pressure of the control pump 22. Therefore, in this pump connection region, the differential pressure between the negative clutch pressure and the positive clutch pressure (negative clutch pressure - positive clutch pressure) gradually decreases as the pedal operation amount increases from zero, and becomes approximately 0 MPa when the pedal operation amount reaches the value corresponding to the pump pressure. The differential pressure is held at a constant value (approximately 0 MPa) in the region where the pedal operation amount is between the value corresponding to the pump pressure and the operation amount threshold. In the region where this differential pressure is a constant value (approximately 0 MPa), a braking force sufficient to stop the rotation of the winch drum 11 by the biasing force of the spring 6d (a braking force capable of stopping the suspended load from descending) can be generated. Therefore, a braking force sufficient to stop the rotation of the winch drum 11 can be generated before the pedal operation amount reaches the operation amount threshold.

[0060] In this embodiment, when the pedal operation amount exceeds the operation amount threshold value, the controller 4 controls the operation of the emergency brake switching valve 3 so that the pump connection state is switched to the tank connection state. As a result, the negative clutch chamber 6c is connected to the tank 27. Therefore, as shown in FIG. 3, the negative clutch pressure instantaneously decreases from the pressure corresponding to the secondary pressure of the control pump 22 to the pressure corresponding to the pressure of the tank 27 (pressure near 0 MPa). At this time, since the positive clutch pressure is maintained at the pressure corresponding to the secondary pressure of the control pump 22, the differential pressure (negative clutch pressure - positive clutch pressure) becomes a negative value. When the differential pressure becomes a negative value, a larger braking force is generated compared to the region where the differential pressure is a constant value (substantially 0 MPa). In the region where the pedal operation amount is larger than the operation amount threshold value, the state in which the negative clutch chamber 6c is connected to the tank 27 is maintained, so the differential pressure remains a negative value.

[0061] When the pedal operation amount gradually increases, as shown in FIG. 3, the differential pressure decreases from the state where a sufficient braking force is generated at a constant value (substantially 0 MPa) to a negative value. In this case, it is assumed that the winch drum 11 has already stopped when the differential pressure decreases to a negative value.

[0062] On the other hand, when the operator performs an emergency braking operation such as quickly and deeply stepping on the brake pedal 7a, the pedal operation amount exceeds the operation amount threshold value almost simultaneously with the start of the pedal operation, and the state of the emergency brake switching valve 3 switches from the pump connection state to the tank connection state. That is, when an emergency braking operation is applied to the brake pedal 7a of the brake operating device 7, the negative clutch pressure instantaneously decreases from the pressure corresponding to the secondary pressure of the control pump 22 to the pressure corresponding to the pressure of the tank 27. Therefore, it is possible to quickly generate a sufficient braking force without being affected by the time caused by the electromagnetic proportional pressure reducing valve 2 when the emergency braking operation is performed. As a result, it is possible to suppress an increase in the brake response time when the emergency braking operation is performed.

[0063] Next, while referring to FIG. 4, the operation of the brake control device 10 according to the present embodiment will be described. FIG. 4 is a flowchart showing an example of arithmetic processing by the controller 4.

[0064] When the mode of the brake control device 10 is set to the brake mode, that is, when the state of the mode switching valve 1 is the second state, the controller 4 determines whether an operation by the operator has been applied to the mode switching switch 30 (step S1). When a free mode signal is input from the mode switching switch 30 (YES in step S1), the controller 4 controls the operation of the mode switching valve 1 so that the mode switching valve 1 switches from the second state to the first state (that is, so that the solenoid of the mode switching valve 1 is in an excited state), and switches the mode of the brake control device 10 to the free mode (step S2).

[0065] Next, the controller 4 determines whether the operation amount of the brake operation applied to the brake pedal 7a of the brake operation device 7 exceeds the operation amount threshold based on the detection signal input from the operation amount sensor 5 (step S3). When the operation amount of the brake operation is equal to or less than the operation amount threshold (NO in step S3), the state of the emergency brake switching valve 3 is maintained in the pump connection state (step S5). When the free mode switches to the brake mode while the processes of step S3 and step S5 are being repeated, the controller 4 ends the process shown in FIG. 4.

[0066] On the other hand, when the operation amount of the brake operation exceeds the operation amount threshold value (YES in step S3), the controller 4 controls the operation of the emergency brake switching valve 3 so that the state of the emergency brake switching valve 3 switches from the pump connection state to the tank connection state (that is, the solenoid of the emergency brake switching valve 3 is in the excited state) (step S4). As a result, the negative clutch chamber 6c is connected to the tank 27, and the negative clutch pressure instantaneously decreases from the pressure corresponding to the secondary pressure of the control pump 22 (pump pressure) to the pressure corresponding to the pressure of the tank 27 (tank pressure). At this time, since the positive clutch chamber 6b is maintained in a state of being connected to the control pump 22, the positive clutch pressure is held at the pressure corresponding to the secondary pressure of the control pump 22 (pump pressure). Therefore, the differential pressure (negative clutch pressure - positive clutch pressure) becomes a negative value, and a large brake pressure is generated rapidly. Thereby, it is suppressed that the brake response time becomes long when an emergency brake operation is performed.

[0067] Moreover, when the determination condition is satisfied, the controller 4 according to the present embodiment preferably controls the operation of the emergency brake switching valve 3 so that the pump connection state switches to the tank connection state, and controls the operation of the mode switching valve 1 so that the first state switches to the second state in order to suppress the occurrence of cavitation. Specifically, it is as follows.

[0068] When the determination condition is satisfied, the pump connection state is switched to the tank connection state, and as the pressure in the negative clutch chamber 6c instantaneously drops to the tank pressure, at least a part of the hydraulic oil in the negative clutch chamber 6c is discharged outside the negative clutch chamber 6c, and the hydraulic oil flows into the positive clutch chamber 6b. In order to ensure the flow rate of the hydraulic oil to the positive clutch chamber 6b, when the determination condition is satisfied, the controller 4 controls the operation of the mode switching valve 1 so that the first state (the right position in FIG. 2) is switched to the second state (the left position in FIG. 2). Thereby, the positive clutch chamber 6b is connected to the control pump 22 bypassing the electromagnetic proportional pressure reducing valve 2 (without passing through the electromagnetic proportional pressure reducing valve 2). This makes it easier to ensure the flow rate of the hydraulic oil to the positive clutch chamber 6b compared to the case where the hydraulic oil flows into the positive clutch chamber 6b through the electromagnetic proportional pressure reducing valve 2 which is not suitable for an operation to supply a large flow rate. Thereby, the possibility of cavitation occurring when the hydraulic oil flows into the positive clutch chamber 6b can be reduced.

[0069] FIG. 5 is a graph showing an example of the relationship between the operation speed and pressure of the brake operation in the brake control device 10 according to Modification 1 of the present embodiment. In the brake control device 10 according to this Modification 1, the determination condition is different from the determination condition of the brake control device 10 shown in FIG. 3. Other configurations of the brake control device 10 according to Modification 1 are the same as those of the brake control device 10 shown in FIG. 2. Hereinafter, Modification 1 will be described with reference to FIGS. 2 and 5.

[0070] In Modification 1, the determination condition is a condition (second determination condition) that the operation speed of the brake operation exceeds an operation speed threshold value which is a preset threshold value. The operation speed in an emergency braking operation (that is, the pedal operation speed for depressing the brake pedal 7a in the emergency braking operation) usually becomes a large operation speed. Therefore, in this Modification 1, the controller 4 can determine whether an emergency braking operation is applied to the brake pedal 7a of the brake operation device 7 by comparing the operation speed of the brake operation with the operation speed threshold value.

[0071] In this Modification 1, when the second determination condition is satisfied, the controller 4 controls the operation of the emergency brake switching valve 3 so that the state of the emergency brake switching valve 3 switches from the pump connection state to the tank connection state.

[0072] In FIG. 5, the horizontal axis represents the operation speed (pedal operation speed) of the brake operation, and the vertical axis represents the pressure (unit: MPa). In FIG. 5, the solid line represents the pressure (positive clutch pressure) supplied to the positive clutch chamber 6b of the brake unit 6. The broken line represents the pressure (negative clutch pressure) supplied to the negative clutch chamber 6c. The one-dot chain line represents the state of the emergency brake switching valve 3. The notation "Emergency brake valve OFF" indicates that the state of the emergency brake switching valve 3 is the pump connection state, and the notation "Emergency brake valve ON" indicates that the state of the emergency brake switching valve 3 is the tank connection state. The vertical straight line indicated by the two-dot chain line represents the operation speed threshold.

[0073] Also in Modification 1 shown in FIG. 5, similar to the above-described embodiment shown in FIG. 3, in the free mode, the state of the mode switching valve 1 is set to the first state, and the state of the emergency brake switching valve 3 is set to the pump connection state.

[0074] As shown in FIG. 5, in the free mode, the positive clutch pressure becomes a value corresponding to the secondary pressure of the electromagnetic proportional pressure reducing valve 2 regardless of the pedal operation speed, that is, a value corresponding to the pedal operation amount.

[0075] On the other hand, the negative clutch pressure shows the following behavior. In the free mode, in the region where the pedal operation speed is from zero to the operation speed threshold (pump connection region), the spool of the emergency brake switching valve 3 is held at the supply position, and the state of the emergency brake switching valve 3 is maintained in the pump connection state. Therefore, the negative clutch pressure is held at the pressure (pump pressure) corresponding to the secondary pressure of the control pump 22.

[0076] In this Modification 1, when the pedal operation speed exceeds the operation speed threshold, that is, when the second determination condition is satisfied, the controller 4 controls the operation of the emergency brake switching valve 3 so that the state of the emergency brake switching valve 3 switches from the pump connection state to the tank connection state. As a result, the negative clutch chamber 6c is connected to the tank 27, so that as shown in FIG. 5, the negative clutch pressure instantaneously drops from the pump pressure to the pressure corresponding to the pressure of the tank 27 (tank pressure). At this time, the positive clutch pressure is the pressure corresponding to the secondary pressure of the electromagnetic proportional pressure reducing valve 2 (the pressure corresponding to the operation amount of the pedal operation). Therefore, the differential pressure between the negative clutch pressure and the positive clutch pressure (negative clutch pressure - positive clutch pressure) becomes a negative value, and a large braking force is generated.

[0077] When the determination condition is the first determination condition (the condition using the operation amount threshold), even if the operator intends to perform a braking operation that exceeds the operation amount threshold, but in actuality, the brake pedal 7a is not depressed sufficiently, the state of the emergency brake switching valve 3 is maintained in the pump connection state. On the other hand, in Modification 1 described above, even if the operation amount does not exceed the operation amount threshold, if the pedal operation speed exceeds the operation speed threshold, the state of the emergency brake switching valve 3 switches from the pump connection state to the tank connection state. Therefore, the second determination condition in Modification 1 is a condition that is more responsive to the braking operation (fast pedal operation) that the operator often performs in a scenario where the operator wants to apply the brake instantaneously. Thus, in Modification 1, it is possible to more appropriately determine whether an emergency braking operation has been applied.

[0078] FIG. 6 is a diagram showing the hydraulic circuit and the controller 4 of the brake control device 10 according to Modification 2 of the present embodiment. The brake control device 10 according to this Modification 2 is different from the brake control device 10 shown in FIG. 2 in that both the positive clutch chamber 6b and the negative clutch chamber 6c are connected to the tank 27 when the determination condition is satisfied. Other configurations of the brake control device 10 according to Modification 2 are the same as those of the brake control device 10 shown in FIG. 2.

[0079] As shown in FIG. 6, the mode switching valve 1 switches between a first state (right-side position in FIG. 6) in which the positive clutch chamber 6b is connected to the control pump 22 or the tank 27 via the electromagnetic proportional pressure reducing valve 2, and a second state (left-side position in FIG. 6) in which the positive clutch chamber 6b bypasses the electromagnetic proportional pressure reducing valve 2 and is connected to the control pump 22 or the tank 27.

[0080] When the state of the mode switching valve 1 is the first state (right-side position in FIG. 6) and the state of the emergency brake switching valve 3 is the pump connection state (left-side position in FIG. 6), the positive clutch chamber 6b is connected to at least one of the control pump 22 and the tank 27 via the electromagnetic proportional pressure reducing valve 2. When the state of the mode switching valve 1 is the first state (right-side position in FIG. 6) and the state of the emergency brake switching valve 3 is the tank connection state (right-side position in FIG. 6), the positive clutch chamber 6b is connected to at least one of the control pump 22 and the tank 27 via the electromagnetic proportional pressure reducing valve 2.

[0081] When the state of the mode switching valve 1 is the second state (left-side position in FIG. 6) and the state of the emergency brake switching valve 3 is the pump connection state (left-side position in FIG. 6), the positive clutch chamber 6b is connected to the control pump 22 by bypassing the electromagnetic proportional pressure reducing valve 2 (without passing through the electromagnetic proportional pressure reducing valve 2). When the state of the mode switching valve 1 is the second state (left-side position in FIG. 6) and the state of the emergency brake switching valve 3 is the tank connection state (right-side position in FIG. 6), the positive clutch chamber 6b is connected to the tank 27 by bypassing the electromagnetic proportional pressure reducing valve 2 (without passing through the electromagnetic proportional pressure reducing valve 2).

[0082] Also in Modification 2 shown in FIG. 6, as in the above-described embodiment shown in FIG. 3, in the free mode, the state of the mode switching valve 1 is set to the first state (right-side position in FIG. 6), and the state of the emergency brake switching valve 3 is set to the pump connection state (left-side position in FIG. 6). Therefore, in the free mode, the pressure (positive clutch pressure) supplied to the positive clutch chamber 6b becomes a value corresponding to the secondary pressure of the electromagnetic proportional pressure reducing valve 2, that is, a value corresponding to the pedal operation amount.

[0083] In the free mode, when the determination condition (the first determination condition or the second determination condition) is not satisfied, that is, in the region where the pedal operation amount is from zero to the operation amount threshold (pump connection region) or the region where the pedal operation speed is from zero to the operation speed threshold (pump connection region), the spool of the emergency brake switching valve 3 is held at the supply position, and the state of the emergency brake switching valve 3 is maintained in the pump connection state. Therefore, the pressure supplied to the negative clutch chamber 6c (negative clutch pressure) is held at the pressure corresponding to the secondary pressure of the control pump 22 (pump pressure).

[0084] When the determination condition is satisfied, the controller 4 controls the operation of the emergency brake switching valve 3 so that the state of the emergency brake switching valve 3 switches from the pump connection state (the left position in FIG. 6) to the tank connection state (the right position in FIG. 6), and at the same time, controls the operation of the mode switching valve 1 so that the state of the mode switching valve 1 switches from the first state (the right position in FIG. 6) to the second state (the left position in FIG. 6). As a result, both the positive clutch chamber 6b and the negative clutch chamber 6c are connected to the tank 27. As a result, the pressure in the positive clutch chamber 6b instantaneously drops from the value corresponding to the secondary pressure of the electromagnetic proportional pressure reducing valve 2 (that is, the value corresponding to the pedal operation amount) to the pressure corresponding to the pressure of the tank 27 (tank pressure), and the pressure in the negative clutch chamber 6c instantaneously drops from the pump pressure to the pressure corresponding to the pressure of the tank 27 (tank pressure). As a result, the piston 6a is moved in the direction approaching the plurality of plates 6e by the biasing force of the spring 6d, and a braking force sufficient to stop the rotation of the winch drum 11 can be rapidly generated. Thereby, it is suppressed that the braking response time becomes long when an emergency braking operation is performed.

[0085] As the piston 6a moves in a direction approaching the plurality of plates 6e, at least a part of the hydraulic oil in the negative clutch chamber 6c is discharged outside the negative clutch chamber 6c, and the hydraulic oil flows into the positive clutch chamber 6b. In this Modification 2, when the determination condition is satisfied, not only is the negative clutch chamber 6c connected to the tank 27, but also the positive clutch chamber 6b is connected to the tank 27 without passing through the electromagnetic proportional pressure reducing valve 2. This makes it easier to ensure the flow rate of the hydraulic oil into the positive clutch chamber 6b compared to the case where the hydraulic oil flows into the positive clutch chamber 6b through the electromagnetic proportional pressure reducing valve 2. Thereby, the possibility of cavitation occurring when the hydraulic oil flows into the positive clutch chamber 6b can be reduced.

[0086] [Modification] The present disclosure is not limited to the embodiments described above. The present disclosure includes, for example, the following forms.

[0087] (A) Regarding the determination condition In the above-described embodiment, the determination condition is that the operation amount of the braking operation exceeds the operation amount threshold value (first determination condition). In Modification 1 of the above-described embodiment, the determination condition is that the operation speed of the braking operation exceeds the operation speed threshold value (second determination condition). However, the determination condition according to the present disclosure includes both the first determination condition and the second determination condition. The controller may control the operation of the emergency brake switching valve (first switching valve) so that the pump connection state switches to the tank connection state when the first determination condition is satisfied and the second determination condition is satisfied. When the determination condition includes both the first determination condition and the second determination condition in this way, it is possible to more appropriately determine whether an emergency braking operation has been applied compared to the case where the determination condition is the second determination condition. Specifically, for example, when the suspended load 106 is freely falling due to its own weight, the operator may perform a braking operation to reduce the falling speed of the suspended load 106 instead of an emergency braking operation to stop the falling operation of the suspended load 106. In such a case, for example, even if the operation amount of the braking operation does not exceed the operation amount threshold value (even if the first determination condition is not satisfied), when the operation speed of the braking operation exceeds the operation speed threshold value (when the second determination condition is satisfied), the state of the emergency brake switching valve 3 switches from the pump connection state to the tank connection state. In this case, an emergency brake for stopping the falling operation of the suspended load 106 is applied, and this emergency brake may not match the operator's feeling. On the other hand, when the determination condition includes both the first determination condition and the second determination condition, the state of the emergency brake switching valve 3 switches from the pump connection state to the tank connection state only when both the first determination condition and the second determination condition are satisfied. Thereby, the determination of whether an emergency braking operation has been applied becomes closer to the operator's feeling.

[0088] (B) Regarding the switching valve In the above-described specific example, the emergency brake switching valve 3 is configured such that when the solenoid is in the non-energized state, the state of the switching valve 3 becomes the pump connection state, and when the solenoid is in the energized state, the state of the switching valve 3 becomes the tank connection state. However, the emergency brake switching valve 3 may be configured such that when the solenoid is in the non-energized state, the state of the switching valve 3 becomes the tank connection state, and when the solenoid is in the energized state, the state of the switching valve 3 becomes the pump connection state.

[0089] Also, the mode switching valve 1 is configured such that when the solenoid is in the non-energized state, the state of the switching valve becomes the second state, and when the solenoid is in the energized state, the state of the switching valve becomes the first state. However, the mode switching valve 1 may be configured such that when the solenoid is in the non-energized state, the state of the switching valve becomes the first state, and when the solenoid is in the energized state, the state of the switching valve becomes the second state.

Explanation of Reference Numerals

[0090] 1: Mode switching valve (an example of the second switching valve) 2: Electro-hydraulic proportional pressure reducing valve 3: Emergency brake switching valve (an example of the first switching valve) 4: Controller 5: Operation amount sensor 6: Brake unit 6b: Positive clutch chamber 6c: Negative clutch chamber 7: Brake operating device (an example of the operating device) 10: Brake control device 11: Winch drum 22: Control pump (an example of the hydraulic pump) 27: Tank 100: Crane 101: Lower traveling body (an example of the machine body) 103: Upper slewing body (an example of the machine body) 104: Boom (an example of the lifting member) R: Rope

Claims

1. A tank for storing hydraulic oil, a hydraulic pump for discharging the hydraulic oil, a brake unit having a positive chamber that generates a force in a direction to increase the braking force on the winch drum by receiving the pressure of the hydraulic oil and a negative chamber that generates a force in a direction to decrease the braking force by receiving the pressure of the hydraulic oil, an operating device to which a braking operation for adjusting the braking force is applied, an electromagnetic proportional pressure reducing valve that opens and closes so that the pressure of the hydraulic oil supplied to the positive chamber is adjusted according to the operation amount of the braking operation, a first switching valve that switches between a pump connection state in which the negative chamber is connected to the hydraulic pump and a tank connection state in which the negative chamber is connected to the tank, a controller that controls the operation of the first switching valve so that the pump connection state switches to the tank connection state when a preset determination condition for determining that an emergency braking operation has been applied to the operating device is satisfied, a second switching valve that switches between a first state in which the positive chamber is connected to the hydraulic pump via the electromagnetic proportional pressure reducing valve and a second state in which the positive chamber is connected to the hydraulic pump bypassing the electromagnetic proportional pressure reducing valve, and the controller controls the operation of the second switching valve so that the first state switches to the second state when the determination condition is satisfied, a brake control device.

2. A tank for storing hydraulic oil, a hydraulic pump for discharging the hydraulic oil, a brake unit having a positive chamber that generates a force in a direction to increase the braking force on the winch drum by receiving the pressure of the hydraulic oil and a negative chamber that generates a force in a direction to decrease the braking force by receiving the pressure of the hydraulic oil, an operating device to which a braking operation for adjusting the braking force is applied, an electromagnetic proportional pressure reducing valve that opens and closes so that the pressure of the hydraulic oil supplied to the positive chamber is adjusted according to the operation amount of the braking operation, a first switching valve that switches between a pump connection state in which the negative chamber is connected to the hydraulic pump and a tank connection state in which the negative chamber is connected to the tank, a controller that controls the operation of the first switching valve so that the pump connection state switches to the tank connection state when a preset determination condition for determining that an emergency braking operation has been applied to the operating device is satisfied, a second switching valve that switches between a first state in which the positive chamber is connected to the hydraulic pump via the electromagnetic proportional pressure reducing valve and a second state in which the positive chamber is connected to the tank, bypassing the electromagnetic proportional pressure reducing valve; The controller controls an operation of the second switching valve so that the first state is switched to the second state when the determination condition is satisfied.

3. The brake control device according to claim 1 or 2, wherein the determination condition includes a condition that the operation amount of the brake operation exceeds a preset operation amount threshold.

4. 4. The brake control device according to claim 1, wherein the determination condition includes a condition that an operation speed of the brake operation exceeds an operation speed threshold that is a preset threshold.

5. The aircraft and A lifting member attached to the airframe in a liftable manner; The winch drum is for winding and unwinding the rope hanging from the hoisting member; A crane comprising: the brake control device according to any one of claims 1 to 4, which is capable of adjusting the braking force applied to the winch drum.

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