Dump truck

Abstract

To prevent a period during which any brake is not activated from occurring when switching between a plurality of brakes.SOLUTION: A brake control device 22 outputs a first brake command to instruct application of braking force to a first brake device 32 when a select lever device 20 is operated and an operation signal designates switching from a second brake device 31 to the first brake device 32, and outputs a second brake release command to instruct release of braking force to the second brake device 31 after the hydraulic pressure supplied to the first brake device 32 reaches a predetermined pressure.SELECTED DRAWING: Figure 6

Description

Technical Field

[0001] The present invention relates to a dump truck.

Background Art

[0002] A dump truck, which is a large transport vehicle, includes a vessel (loading platform) provided on a vehicle body frame so as to be able to rise and fall. A large amount of cargo to be transported (for example, crushed stone or earth and sand) is loaded on the vessel to transport the cargo. The dump truck includes a front wheel brake unit, a rear wheel brake unit, and a rear wheel drive unit, and these are controlled by a control device to run. Further, the dump truck is equipped with a parking brake unit used when parking, similar to a general passenger car.

[0003] As a conventional technique related to the brake control of a dump truck equipped with a plurality of brakes, for example, Patent Document 1 is known. Patent Document 1 discloses a brake control device that controls the braking force of the front wheels and the rear wheels according to the operation amounts of a service brake pedal and a retarder brake lever.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Some dump trucks equipped with multiple brakes can switch the brake to be actuated from one brake to the other by an operating device. In this type of dump truck, when a problem occurs in the hydraulic system that drives the multiple brakes, when the brake to be actuated is switched by the operating device, the brake after switching may not be actuated immediately, and there may be a time when both brakes are not actuated. The brake control device disclosed in Patent Document 1 does not consider such problems at all, and there is room for improvement.

[0006] In view of the above circumstances, an object of the present invention is to prevent a time when none of the brakes are actuated from occurring when switching between multiple brakes.

Means for Solving the Problems

[0007] To solve the above problems, a dump truck of the present invention includes a plurality of brake devices and a brake control device that controls the operation of these brake devices. When the operating device for switching the brake device to be actuated is operated to switch from one brake device to the other, the brake control device releases the one brake device after confirming that the other brake device has applied a braking force.

[0008] Strictly speaking, the dump truck of the present invention includes a first brake device that applies a braking force for braking the rotation of a wheel to the wheel, a second brake device that applies a braking force to the wheel to hold the wheel in a stopped state, an operation device that outputs an operation signal for designating a brake device to be actuated to either the first brake device or the second brake device according to an operation, and a brake control device that outputs a command for braking or releasing the brake to the first brake device and the second brake device based on the operation signal output from the operation device. When the operation signal output from the operation device switches from an operation signal designating the second brake device to an operation signal designating the first brake device, the brake control device outputs a braking command to the first brake device, and after the first brake device applies a braking force of a predetermined magnitude to the wheel, outputs a release command to the second brake device.

Advantages of the Invention

[0009] According to the present invention, it is possible to prevent a time period during which none of the brakes is actuated from occurring when switching between a plurality of brakes.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Mode for Carrying Out the Invention

[0011] Hereinafter, embodiments of the present invention will be described with reference to the drawings. For components denoted by the same reference numerals in each embodiment, unless otherwise specified, each embodiment has similar components, and the description thereof will be omitted.

[0012] The configuration of the dump truck 1 will be described with reference to FIGS. 1 to 3. FIG. 1 is a side view of the dump truck 1. FIG. 2 is a diagram showing the configuration of the brake system of the dump truck 1 shown in FIG. 1. FIG. 3 is a diagram for explaining the select lever device 20 shown in FIG. 2.

[0013] As shown in FIG. 1, the dump truck 1, which is a large transport vehicle, includes a vessel 11 (loading platform) provided on the vehicle body frame 10 so as to be able to rise and fall. A large amount of cargo 12 to be transported (for example, crushed stone or earth and sand) is loaded on the vessel 11 and transported.

[0014] The dump truck 1 includes front wheels 13 and rear wheels 15, and a prime mover (an electric motor in the present embodiment) for driving these is controlled by a control device 19. In the dump truck 1 of the present embodiment, the front wheels 13 are driven wheels and the rear wheels 15 are driving wheels, but it is not limited thereto.

[0015] As shown in FIG. 2, the braking system of the dump truck 1 includes a select lever device 20, a brake pedal device 21, a control device 19 including a brake control device 22, a front wheel brake device 36, a rear wheel brake device 37, and a parking brake device 38 (hereinafter also referred to as "P brake device 38").

[0016] The brake pedal device 21 is an operating device for operating the front wheel brake device 36 and the rear wheel brake device 37 of the dump truck 1. The brake pedal device 21 includes a brake pedal that is depressed by an operator and a sensor that detects the depression amount of the brake pedal. The brake pedal device 21 outputs an operation signal corresponding to the depression amount of the brake pedal by the operator to the brake control device 22 of the control device 19.

[0017] The select lever device 20 is an operating device for designating the traveling direction of the dump truck 1. Further, the select lever device 20 is an operating device for operating the parking brake (hereinafter also referred to as "P brake") or the load dump brake (hereinafter also referred to as "LD brake") of the dump truck 1.

[0018] The P brake is a brake used when the dump truck 1 is parked. The P brake is a brake that holds the wheels in a stopped state, similar to a general passenger car. The LD brake is a brake used when loading or unloading the cargo 12 on the dump truck 1. The LD brake is mounted on the dump truck 1 for the purpose of preventing the wheels from rotating due to an impact applied to the vessel 11 during loading of the cargo 12, etc., and is a brake that brakes the rotation of the rear wheels 15.

[0019] The select lever device 20 includes a select lever 20a operated by an operator and a sensor that detects the position of the select lever 20a. The operator can operate the select lever 20a to alternatively select the position of the select lever 20a at an arbitrary position. The select lever device 20 outputs an operation signal corresponding to the selected position of the select lever 20a by the operator to the control device 19.

[0020] Specifically, as shown in FIG. 3, the select lever 20a is attached to the select lever device 20 so as to be movable to a forward position 33, a neutral position 34, and a reverse position 35. When the forward position 33 is selected as the position of the select lever 20a, the select lever device 20 outputs an operation signal for designating the gear of the transmission to the control device 19 so as to move the dump truck 1 forward. When the select lever 20a moves to the neutral position 34, the select lever device 20 outputs an operation signal for stopping the power supply to the traveling motor to the control device 19. When the select lever 20a moves to the reverse position 35, the select lever device 20 outputs an operation signal for designating the gear of the transmission to the control device 19 so as to move the dump truck 1 backward.

[0021] Furthermore, the select lever 20a can also move to a P brake position 31 and an LD brake position 32. The brake device that operates changes depending on the position to which the select lever 20a moves. That is, when the select lever 20a moves to the P brake position 31, the select lever device 20 outputs an operation signal for designating the brake device (the brake device to be operated) that applies a braking force to the wheels to the brake control device 22 of the control device 19 as the P brake device 38. On the other hand, when the LD brake position 32 is selected, the select lever device 20 outputs an operation signal for designating the brake device (the brake device to be operated) that applies a braking force to the wheels to the brake control device 22 of the control device 19 as the rear wheel brake device 37.

[0022] The main pump 29 supplies hydraulic pressure for driving the front-wheel brake device 36, the rear-wheel brake device 37, and the P-brake device 38. The pilot pump 30 supplies hydraulic pressure (pilot pressure) for controlling the front-wheel brake device 36, the rear-wheel brake device 37, and the P-brake device 38.

[0023] The front-wheel brake device 36 includes a front-wheel brake valve 23 and a front-wheel brake unit 24. The front-wheel brake valve 23 adjusts the valve opening degree of the front-wheel brake valve 23 based on the hydraulic pressure supplied from the main pump 29 and the pilot pump 30 and the front-wheel brake command described later output from the brake control device 22, and controls the hydraulic pressure supplied to the front-wheel brake unit 24.

[0024] The front-wheel brake unit 24 applies a braking force for braking the rotation of the front wheels 13 to the front wheels 13 by the hydraulic pressure supplied through the front-wheel brake valve 23. The front-wheel brake unit 24 is constituted by a wet multi-disc brake or the like.

[0025] The rear-wheel brake device 37 includes a rear-wheel brake valve 25 and a rear-wheel brake unit 26. The rear-wheel brake valve 25 adjusts the valve opening degree of the rear-wheel brake valve 25 based on the hydraulic pressure supplied from the main pump 29 and the pilot pump 30 and the rear-wheel brake command described later output from the brake control device 22, and controls the hydraulic pressure supplied to the rear-wheel brake unit 26.

[0026] The rear wheel brake unit 26 applies a braking force to the rear wheel 15 to brake the rotation of the rear wheel 15 by the hydraulic pressure supplied through the rear wheel brake valve 25. Strictly speaking, the braking force by the rear wheel brake unit 26 becomes stronger as the supplied hydraulic pressure increases, and then is maintained at a certain magnitude. The rear wheel brake unit 26 is constituted by a wet multi-disc brake or the like. The rear wheel brake unit 26 includes a sensor 26a that detects the hydraulic pressure (hereinafter also referred to as "rear wheel brake pressure") supplied to the rear wheel brake unit 26. The sensor 26a outputs the detected hydraulic pressure (rear wheel brake pressure) to the brake control device 22.

[0027] The P-brake device 38 includes a P-brake valve 27 and a P-brake unit 28. The P-brake valve 27 adjusts the valve opening degree of the P-brake valve 27 based on the hydraulic pressure supplied from the main pump 29 and the pilot pump 30 and the P-brake release command described below output from the brake control device 22, and controls the hydraulic pressure supplied to the P-brake unit 28.

[0028] The P-brake unit 28 is a negative-actuated brake unit. The P-brake unit 28 releases the braking force applied to the rear wheel 15 to hold the wheel in a stopped state by supplying hydraulic pressure through the P-brake valve 27. Strictly speaking, the braking force by the P-brake unit 28 becomes weaker as the supplied hydraulic pressure increases, and is finally released. The P-brake unit 28 includes a sensor 28a that detects the hydraulic pressure (hereinafter also referred to as "P-brake release pressure") supplied to the P-brake unit 28. The sensor 28a outputs the detected hydraulic pressure (P-brake release pressure) to the brake control device 22.

[0029] The control device 19 is a device that comprehensively controls each component of the dump truck 1. In particular, the control device 19 controls components related to the running of the dump truck 1, such as the prime mover and transmission of the dump truck 1. The control device 19 includes a processor such as a CPU, and memories such as a ROM and a RAM. The functions of the control device 19 are realized by the processor executing the programs stored in the memories.

[0030] The control device 19 includes a brake control device 22 that controls components related to the braking of the dump truck 1. The brake control device 22 includes a processor such as a CPU, and memories such as a ROM and a RAM. The functions of the brake control device 22 are realized by the processor executing the programs stored in the memories. The brake control device 22 may be provided integrally with the control device 19 or may be provided separately from the control device 19.

[0031] When an operation signal corresponding to the depression amount of the brake pedal is output from the brake pedal device 21, the brake control device 22 generates a front-wheel brake command and a rear-wheel brake command corresponding to the operation signal. The brake control device 22 outputs the generated front-wheel brake command and rear-wheel brake command to the front-wheel brake device 36 and the rear-wheel brake device 37, respectively.

[0032] The front-wheel brake command is a control command for controlling the operation of the front-wheel brake device 36 so as to apply a braking force that brakes the rotation of the front wheels 13 to the front wheels 13. That is, the front-wheel brake command is a control command that commands the front-wheel brake device 36 to apply a braking force to the front wheels 13. The rear-wheel brake command is a control command for controlling the operation of the rear-wheel brake device 37 so as to apply a braking force that brakes the rotation of the rear wheels 15 to the rear wheels 15. That is, the rear-wheel brake command is a control command that commands the rear-wheel brake device 37 to apply a braking force to the rear wheels 15.

[0033] When the LD brake position 32 is selected as the position of the select lever 20a and an operation signal designating the rear wheel brake device 37 is output from the select lever device 20, the brake control device 22 generates an LD brake command which is a rear wheel brake command corresponding to the operation signal. The brake control device 22 outputs the generated LD brake command to the rear wheel brake device 37. Further, based on the LD brake pressure detected by the sensor 26a, the brake control device 22 determines the state of the LD brake, that is, whether or not the rear wheel brake device 37 has applied a braking force to the rear wheels 15 in response to the output of the LD brake command.

[0034] In the present embodiment, among the rear wheel brake commands, the rear wheel brake command generated in response to the operation signal output from the select lever device 20 when the LD brake position 32 is selected is also referred to as the "LD brake command". In the present embodiment, among the rear wheel brake pressures which are the hydraulic pressures supplied to the rear wheel brake unit 26, the rear wheel brake pressure related to the LD brake is also referred to as the "LD brake pressure". The LD brake command is a control command for instructing the rear wheel brake device 37 to apply a braking force to the rear wheels 15.

[0035] Also, when the select lever 20a at the P brake position 31 is selected other than the P brake position 31 and the operation signal from the select lever device 20 no longer designates the P brake device 38, the brake control device 22 generates a P brake release command. The brake control device 22 outputs the generated P brake release command to the P brake device 38. Then, when the P brake position 31 is selected as the position of the select lever 20a and an operation signal designating the P brake device 38 is output from the select lever device 20, the brake control device 22 stops the output of the P brake release command. Further, based on the P brake release pressure detected by the sensor 28a, the brake control device 22 determines the state of the P brake, that is, whether or not the braking force applied to the rear wheels 15 by the P brake device 38 has been released in response to the output of the P brake release command.

[0036] In this embodiment, a control command generated in response to an operation signal output from the select lever device 20 when the select lever 20a at the P-brake position 31 selects a position other than the P-brake position 31 is also referred to as a "P-brake release command". In this embodiment, the hydraulic pressure supplied to the P-brake unit 28 to release the braking force applied by the P-brake device 38 to the rear wheels 15 is also referred to as the "P-brake release pressure" as described above. The P-brake release command is a control command that commands the P-brake device 38 to release the braking force applied to the rear wheels 15.

[0037] Control commands output from the brake control device 22, such as a front-wheel brake command, a rear-wheel brake command, an LD-brake command, or a P-brake release command, may be generated as pulse signals. When outputting these control commands, the brake control device 22 sets the pulse signal to ON (high level), and when stopping the output of these control commands, sets the pulse signal to OFF (low level).

[0038] The operation of the dump truck 1 will be described with reference to FIGS. 4 to 8. FIG. 4 is a timing chart 41 for explaining the operation of a conventional dump truck when the position of the select lever 20a is switched from the P-brake position 31 to the LD-brake position 32.

[0039] As shown in the timing chart 41 of FIG. 4, in a conventional dump truck, at the timing 42 when the position of the select lever 20a is switched from the P-brake position 31 to the LD-brake position 32, the brake control device 22 outputs (turns on) a P-brake release command and outputs (turns on) an LD-brake command.

[0040] When the P-brake release command is output (turned on), the P-brake release pressure increases. When the P-brake release pressure reaches a predetermined pressure Pa, the brake control device 22 determines that the applied braking force has been released. That is, at the timing 43 when the P-brake release pressure detected by the sensor 28a reaches the predetermined pressure Pa, the brake control device 22 determines that the operation of the P-brake has stopped (turned off).

[0041] On the one hand, when the LD brake command is output (ON), the LD brake pressure increases. When the LD brake pressure reaches a predetermined pressure Pb, the brake control device 22 determines that sufficient braking force has been applied to the rear wheels 15. That is, at the timing 44 when the LD brake pressure detected by the sensor 26a reaches the predetermined pressure Pb, the brake control device 22 determines that the LD brake has been activated (ON).

[0042] Here, due to aging deterioration or the like, problems may occur in the hydraulic system that drives the P-brake device 38 and the rear-wheel brake device 37. In such a case, a time lag occurs between the timing 43 when the P-brake release pressure reaches the predetermined pressure Pa and the timing 44 when the LD brake pressure reaches the predetermined pressure Pb. As shown by reference numeral 57 in FIG. 4, there may be a time when both the P-brake and the LD brake are not activated. This problem can also occur when the position of the select lever 20a is switched from the LD brake position 32 to the P-brake position 31.

[0043] FIG. 5 is a timing chart 45 for explaining the operation of a conventional dump truck when the position of the select lever 20a is switched from the LD brake position 32 to the P-brake position 31.

[0044] As shown in the timing chart 45 of FIG. 5, in a conventional dump truck, at the timing 46 when the position of the select lever 20a is switched from the LD brake position 32 to the P-brake position 31, the brake control device 22 stops (OFF) the output of the LD brake command and stops (OFF) the output of the P-brake release command.

[0045] When the output of the LD brake command stops (turns OFF), the LD brake pressure decreases. When the LD brake pressure reaches a predetermined pressure Pd, the brake control device 22 determines that the applied braking force has been released. That is, at the timing 47 when the LD brake pressure detected by the sensor 26a reaches the predetermined pressure Pd, the brake control device 22 determines that the operation of the LD brake has stopped (turned OFF).

[0046] On the other hand, when the output of the P-brake release command stops (turns OFF), the P-brake release pressure decreases. When the P-brake release pressure reaches a predetermined pressure Pc, the brake control device 22 determines that a braking force has been applied to the rear wheels 15. That is, at the timing 48 when the P-brake release pressure detected by the sensor 28a reaches the predetermined pressure Pc, the brake control device 22 determines that the P-brake has been actuated (turned ON).

[0047] Similar to the case shown in FIG. 4, in the case shown in FIG. 5, a time lag occurs between the timing 47 when the LD brake pressure reaches the predetermined pressure Pd and the timing 48 when the P-brake release pressure reaches the predetermined pressure Pc. As indicated by reference numeral 58 in FIG. 5, there may be a time when both the P-brake and the LD brake are not actuated.

[0048] Therefore, the brake control device 22 of the present embodiment controls the timing of the output or output stop of the P-brake release command and the LD brake command to prevent a time when both the P-brake and the LD brake are not actuated from occurring.

[0049] FIG. 6 is a timing chart 49 for explaining the operation of the dump truck 1 of the present embodiment when the position of the select lever 20a is switched from the P-brake position 31 to the LD-brake position 32.

[0050] As shown in the timing chart 49 of FIG. 6, in the dump truck 1 of the present embodiment, at the timing 50 when the position of the select lever 20a is switched from the P-brake position 31 to the LD-brake position 32, the brake control device 22 outputs (turns on) an LD-brake command and holds the output (turns on) of the P-brake release command.

[0051] When the LD-brake command is output (turned on), the LD-brake pressure increases. When the LD-brake pressure reaches a predetermined pressure Pb, the brake control device 22 determines that sufficient braking force has been applied to the rear wheels 15. That is, at the timing 51 when the LD-brake pressure detected by the sensor 26a reaches the predetermined pressure Pb, the brake control device 22 determines that the LD-brake has been actuated (turned on).

[0052] Then, after the timing 51 when the LD-brake pressure reaches the predetermined pressure Pb in response to the output of the LD-brake command, the brake control device 22 outputs (turns on) a P-brake release command.

[0053] When the P-brake release command is output (turned on), the P-brake release pressure increases. When the P-brake release pressure reaches a predetermined pressure Pa, the brake control device 22 determines that the applied braking force has been released. That is, at the timing 52 when the P-brake release pressure detected by the sensor 28a reaches the predetermined pressure Pa, the brake control device 22 determines that the operation of the P-brake has stopped (turned off).

[0054] As a result, when switching from the P-brake to the LD-brake, the brake control device 22 of the present embodiment can stop the operation of the P-brake after confirming that the LD-brake has been activated. Therefore, even if a time lag occurs between the timing 52 at which the P-brake release pressure reaches the predetermined pressure Pa and the timing 51 at which the LD-brake pressure reaches the predetermined pressure Pb, as shown by reference numeral 59 in FIG. 6, it is possible to prevent a period during which both the P-brake and the LD-brake are inoperative. Thus, the brake control device 22 can improve the robustness of the brakes of the dump truck 1.

[0055] FIG. 7 is a timing chart 53 for explaining the operation of the dump truck 1 of the present embodiment when the position of the select lever 20a is switched from the LD-brake position 32 to the P-brake position 31.

[0056] As shown in the timing chart 53 of FIG. 7, in the dump truck 1 of the present embodiment, at the timing 54 when the position of the select lever 20a is switched from the LD-brake position 32 to the P-brake position 31, the brake control device 22 stops (turns OFF) the output of the P-brake release command, but holds off on stopping (turning OFF) the output of the LD-brake command.

[0057] When the output of the P-brake release command is stopped (turned OFF), the P-brake release pressure decreases. When the P-brake release pressure reaches the predetermined pressure Pc, the brake control device 22 determines that sufficient braking force has been applied to the rear wheels 15. That is, at the timing 55 when the P-brake release pressure detected by the sensor 28a reaches the predetermined pressure Pc, the brake control device 22 determines that the P-brake is operating (ON).

[0058] Then, after the timing 55 at which the P-brake release pressure reaches the predetermined pressure Pc in response to the stop of the output of the P-brake release command, the brake control device 22 stops (turns OFF) the output of the LD-brake command.

[0059] When the output of the LD brake command stops (turns OFF), the LD brake pressure decreases. When the LD brake pressure reaches a predetermined pressure Pd, the brake control device 22 determines that the applied braking force has been released. That is, at the timing 56 when the LD brake pressure detected by the sensor 26a reaches the predetermined pressure Pd, the brake control device 22 determines that the operation of the LD brake has stopped (turned OFF).

[0060] As a result, when switching from the LD brake to the P brake, the brake control device 22 of the present embodiment can stop the operation of the LD brake after confirming that the P brake has been actuated. Therefore, even if a time lag occurs between the timing 55 when the P brake release pressure reaches the predetermined pressure Pc and the timing 56 when the LD brake pressure reaches the predetermined pressure Pd, as shown by reference numeral 60 in FIG. 7, it is possible to prevent a time when both the P brake and the LD brake are not operating from occurring. Thus, the brake control device 22 can improve the robustness regarding the brakes of the dump truck 1.

[0061] Note that the predetermined pressure Pb, the predetermined pressure Pa, the predetermined pressure Pd, and the predetermined pressure Pc can each be arbitrarily set. However, the predetermined pressure Pb, the predetermined pressure Pa, the predetermined pressure Pd, and the predetermined pressure Pc are preferably set as follows based on the brake performance of the dump truck 1.

[0062] The predetermined pressure Pb is set based on the LD brake performance based on the specifications of the rear wheel brake device 37. The predetermined pressure Pb is preferably set to a value greater than a value that can apply sufficient braking force to the rear wheels 15.

[0063] The predetermined pressure Pa is set based on the P brake performance based on the specifications of the P brake device 38. The predetermined pressure Pa is preferably set to a value at which the braking force applied to the rear wheels 15 becomes zero and is smaller than a value at which there is no risk of the P brake unit 28 being damaged by the reaction force of the braking force.

[0064] The predetermined pressure Pd is set based on the LD brake performance according to the specifications of the rear-wheel brake device 37. The predetermined pressure Pd is preferably set to a value smaller than the value at which the braking force applied to the rear wheel 15 becomes zero.

[0065] The predetermined pressure Pc is set based on the P-brake performance according to the specifications of the P-brake device 38. The predetermined pressure Pc is preferably set to a value larger than the value at which a braking force of sufficient magnitude can be applied to the rear wheel 15.

[0066] By setting the predetermined pressures Pb, Pa, Pd, and Pc in this way, the brake control device 22 can stop the operation of the P-brake after confirming that the LD-brake has operated reliably, and can stop the operation of the LD-brake after confirming that the P-brake has operated reliably. Therefore, the brake control device 22 can surely prevent a situation where the times when both the P-brake and the LD-brake are not operating occur. Thus, the brake control device 22 can further improve the robustness regarding the brakes of the dump truck 1.

[0067] FIG. 8 is a flowchart showing the processing of the brake control device 22 in the cases shown in FIGS. 6 and 7. Steps S501 to S505 in FIG. 8 show the processing of the brake control device 22 in the case shown in FIG. 7. Steps S511 to S515 in FIG. 8 show the processing of the brake control device 22 in the case shown in FIG. 6. The brake control device 22 executes the processing shown in FIG. 8 every time a predetermined control cycle elapses.

[0068] In step S501, the brake control device 22 determines whether the position of the select lever 20a has been switched from the LD brake position 32 to the P brake position 31 based on the operation signal from the select lever device 20. If the position of the select lever 20a has been switched from the LD brake position 32 to the P brake position 31, the brake control device 22 proceeds to step S502. If the position of the select lever 20a has not been switched from the LD brake position 32 to the P brake position 31, the brake control device 22 proceeds to step S511.

[0069] In step S502, the brake control device 22 stops (turns OFF) the output of the P brake release command.

[0070] In step S503, the brake control device 22 determines whether the P brake release pressure detected by the sensor 28a has reached a predetermined pressure Pc or less. If the P brake release pressure has reached a predetermined pressure Pc or less, the brake control device 22 proceeds to step S504. If the P brake release pressure is greater than the predetermined pressure Pc, the brake control device 22 proceeds to step S505.

[0071] In step S504, the brake control device 22 stops (turns OFF) the output of the LD brake command. Thereafter, the brake control device 22 ends the process shown in FIG. 8.

[0072] In step S505, the brake control device 22 maintains the output (ON) of the LD brake command. Thereafter, the brake control device 22 ends the process shown in FIG. 8.

[0073] In step S511, the brake control device 22 determines whether the position of the select lever 20a has been switched from the P-brake position 31 to the LD-brake position 32 based on the operation signal from the select lever device 20. If the position of the select lever 20a has been switched from the P-brake position 31 to the LD-brake position 32, the brake control device 22 proceeds to step S512. If the position of the select lever 20a has not been switched from the P-brake position 31 to the LD-brake position 32, the brake control device 22 ends the process shown in FIG. 8.

[0074] In step S512, the brake control device 22 outputs (turns on) an LD-brake command.

[0075] In step S513, the brake control device 22 determines whether the LD-brake pressure detected by the sensor 26a has reached a predetermined pressure Pb or more. If the LD-brake pressure has reached a predetermined pressure Pb or more, the brake control device 22 proceeds to step S514. If the LD-brake pressure is less than the predetermined pressure Pb, the brake control device 22 proceeds to step S515.

[0076] In step S514, the brake control device 22 outputs (turns on) a P-brake release command. Then, the brake control device 22 ends the process shown in FIG. 8.

[0077] In step S515, the brake control device 22 maintains the output stop (turns off) of the P-brake release command. Then, the brake control device 22 ends the process shown in FIG. 8.

[0078] Note that the rear wheel brake device 37 described in this embodiment is an example of the "first brake device" described in the claims. The P-brake device 38 is an example of the "second brake device" described in the claims. The select lever device 20 is an example of the "operation device" described in the claims. The brake control device 22 is an example of the "brake control device" described in the claims. The LD brake command is an example of the "first brake command" described in the claims. The P-brake release command is an example of the "second brake release command" described in the claims.

[0079] As described above in detail with respect to the embodiments of the present invention, the present invention is not limited to each embodiment, and various changes can be made without departing from the spirit of the present invention. The present invention can add the components of one embodiment to the components of another embodiment, replace the components of one embodiment with the components of another embodiment, or delete a part of the components of one embodiment.

[0080] For example, in the above embodiment, the P-brake device 38 is a negative brake that applies braking force when no working oil is supplied, and the rear wheel brake device 37 is a positive brake that applies braking force when working oil is supplied. However, either brake device can adopt both positive and negative brakes. Also, the way of selection regarding which brake device adopts which type of brake is arbitrary.

Explanation of Reference Numerals

[0081] 1…Dump truck, 10…Vehicle body frame, 11…Vessel, 12…Cargo, 13…Front wheel, 15…Rear wheel, 19…Control device, 20…Select lever device (operating device), 20a…Select lever, 21…Brake pedal device, 22…Brake control device, 23…Front wheel brake valve, 24…Front wheel brake unit, 25…Rear wheel brake valve, 26…Rear wheel brake unit, 26a…Sensor (first sensor), 27…P brake valve, 28…P brake unit, 28a…Sensor (second sensor), 29…Main pump, 30…Pilot pump, 31…P brake position, 32…LD brake position, 33…Forward position, 34…Neutral position, 35…Reverse position, 36…Front wheel brake device, 37…Rear wheel brake device (first brake device), 38…P brake device (second brake device), Pa…Predetermined pressure, Pb…Predetermined pressure (first predetermined pressure), Pc…Predetermined pressure (second predetermined pressure), Pd…Predetermined pressure

Claims

1. A first braking device that applies a braking force for braking the rotation of a wheel to the wheel; A second braking device that applies a braking force to the wheel to keep the wheel in a stopped state; An operating device that outputs an operation signal for designating, according to an operation, a braking device to be actuated to either the first braking device or the second braking device; A brake control device that outputs a command for braking or releasing braking to the first braking device and the second braking device based on the operation signal output from the operating device; and when the operation signal output from the operating device switches from an operation signal designating the second braking device to an operation signal designating the first braking device, the brake control device outputs a braking command to the first braking device, and after the first braking device applies a braking force of a predetermined magnitude to the wheel, outputs a release command to the second braking device A dump truck characterized by the above.

2. Having a first sensor that detects the hydraulic pressure supplied to the first braking device; The first braking device is a positive-type brake that exerts a braking force by supplying hydraulic pressure; The second braking device is a negative-type brake that normally exerts a braking force by spring force and releases the braking force by supplying hydraulic pressure; when the operation signal output from the operating device switches from an operation signal designating the second braking device to an operation signal designating the first braking device, the brake control device outputs a first brake command for commanding braking to the first braking device, and outputs a second brake release command for commanding release of braking to the second braking device when a first predetermined pressure is detected by the first sensor The dump truck according to claim 1, characterized by the above.

3. Having a second sensor that detects the hydraulic pressure supplied to the second braking device; when the operation signal output from the operating device switches from an operation signal designating the first braking device to an operation signal designating the second braking device, and when the brake control device detects that the hydraulic pressure as a brake release signal is lower than a second predetermined pressure by the second sensor, the brake control device stops outputting the first brake command The dump truck according to claim 2, characterized by the above.

4. The first braking device is a load dump brake used when loading or unloading the cargo on the dump truck, The second braking device is a parking brake used when the dump truck is parked The dump truck according to claim 1, characterized in that.

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