Transport vehicles

Abstract

To suppress energy loss when a cooling fan is stopped.SOLUTION: A transport vehicle comprises: a hydraulic motor and a hoist cylinder for a cooling fan driven with hydraulic oil from a first hydraulic pump; a steering circuit driven with the hydraulic oil from a second hydraulic pump; and a confluence control valve which merges the hydraulic oil from the first and second hydraulic pumps and leads the same to a hoist control valve. A fan control valve, the confluent control valve and the hoist control valve are connected in tandem to a center bypass line. The fan control valve has a neutral position to communicate the first hydraulic pump with the confluent control valve and a rotation position to communicate the first hydraulic pump with the hydraulic motor. The confluent control valve, when positioned at a non-confluence position, communicates the first hydraulic pump with the hoist control valve and the second hydraulic pump with the steering circuit through the fan control valve at the neutral position and cuts off communication between the second hydraulic pump and the hoist control valve.SELECTED DRAWING: Figure 3

Description

Technical Field

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[0001] The present invention relates to a transport vehicle such as a dump truck equipped with a cooling fan.

Background Art

[0002] Transport vehicles such as dump trucks equipped with a cooling fan are known (see Patent Document 1). The cooling air generated by the cooling fan cools a cooling target such as engine cooling water. Patent Document 1 discloses a transport vehicle including a work machine pump that supplies hydraulic oil to a hydraulic actuator, a fan pump that supplies hydraulic oil to a fan motor, and a confluence control valve (circuit switching valve) that switches and connects the discharge part of the fan pump between the hydraulic actuator and the fan motor for the purpose of miniaturization and cost reduction of the work machine pump.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In a transport vehicle, the load during travel varies depending on the presence or absence of a load, the road gradient, etc. For example, traveling with no load or on flat ground is a traveling state with a lower load compared to traveling with a load or climbing a slope. In a traveling state with a low load, cooling of the cooling target by the cooling fan may become unnecessary. However, in the configuration of the hydraulic circuit described in Patent Document 1, it is necessary to switch the confluence control valve to connect the discharge part of the fan pump and the hydraulic circuit for steering drive in order to stop the cooling fan. Therefore, in the transport vehicle described in Patent Document 1, the operating pressure of the steering cylinder, which has a high operating frequency during travel, acts on the fan pump. As a result, the load on the fan pump increases and energy loss occurs.

[0005] The present invention aims to provide a transport vehicle capable of suppressing energy loss when the cooling fan stops. [Means for solving the problem]

[0006] A transport vehicle according to one aspect of the present invention comprises: a cargo bed rotatably mounted on a vehicle body; a first hydraulic pump and a second hydraulic pump driven by a prime mover; a hydraulic motor driven by hydraulic fluid supplied from the first hydraulic pump; a cooling fan driven by the hydraulic motor; a heat exchanger that cools an object to be cooled by the cooling air generated by the cooling fan; a hoist cylinder that is extendable and retractable between the cargo bed and the vehicle body and driven by hydraulic fluid supplied from the first hydraulic pump; a fan control valve that controls the flow of hydraulic fluid supplied from the first hydraulic pump to the hydraulic motor; a hoist control valve that controls the flow of hydraulic fluid supplied from the first hydraulic pump to the hoist cylinder; and a steering circuit having a steering cylinder driven by hydraulic fluid supplied from the second hydraulic pump. In this transport vehicle, the hoist control valve includes a confluence position that combines the hydraulic fluid discharged from the second hydraulic pump with the hydraulic fluid discharged from the first hydraulic pump and guides it to the hoist control valve, and a steering circuit that guides the hydraulic fluid discharged from the first hydraulic pump to the hoist control valve and the hydraulic fluid discharged from the second hydraulic pump The system further comprises a merging control valve having a non-merging position that guides oil to the steering circuit, the fan control valve, the merging control valve and the hoist control valve are connected in tandem to an oil passage connecting the first hydraulic pump and the hydraulic oil tank, the fan control valve is positioned upstream of the merging control valve, the merging control valve is positioned upstream of the hoist control valve, the fan control valve has a neutral position that connects the first hydraulic pump and the merging control valve and blocks communication between the first hydraulic pump and the hydraulic motor, and a neutral position that blocks communication between the first hydraulic pump and the merging control valve. The confluence control valve has a rotational position that connects the first hydraulic pump and the hydraulic motor, and when the confluence control valve is in the confluence position, it connects the first hydraulic pump and the hoist control valve via the fan control valve in the neutral position, and connects the second hydraulic pump and the hoist control valve, and blocks communication between the second hydraulic pump and the steering circuit, and when the non-confluence position, it connects the first hydraulic pump and the hoist control valve via the fan control valve in the neutral position, and connects the second hydraulic pump and the steering circuit,The communication between the second hydraulic pump and the hoist control valve is cut off. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a transport vehicle that can suppress the occurrence of energy loss when the cooling fan stops. [Brief explanation of the drawing]

[0008] [Figure 1] Figure 1 is a perspective view showing the exterior of a dump truck. [Figure 2] Figure 2 is a schematic plan view showing the configuration of a dump truck. [Figure 3] Figure 3 shows the hydraulic system of a dump truck. [Figure 4] Figure 4 is a functional block diagram of the control device according to the first embodiment. [Figure 5] Figure 5 shows the relationship between the discharge capacity q (tilt angle) and the discharge flow rate Q of the first hydraulic pump. [Figure 6] Figure 6 shows a capacity control table that defines the relationship between the cooling water temperature Tc and the discharge capacity q. [Figure 7] Figure 7 is a flowchart showing an example of the processing flow for fan control performed by the control device according to the first embodiment. [Figure 8] Figure 8 shows the relationship between the switching position of the fan control valve and the discharge flow rate Q of the first hydraulic pump, according to the cooling water temperature Tc. [Figure 9] Figure 9 is a functional block diagram of the control device according to the second embodiment. [Figure 10] Figure 10 is a flowchart showing an example of the processing flow of loss reduction control during engine startup, which is performed by the control device according to the second embodiment. [Figure 11] Figure 11 is a functional block diagram of the control device according to the third embodiment. [Figure 12] Figure 12 is a table showing the relationship between the operating position and cooling water temperature of the control device for the cargo bed and the switching position of each control valve. [Modes for carrying out the invention]

[0009] <First Embodiment> A transport vehicle according to the first embodiment of the present invention will be described with reference to the drawings. Figure 1 is a perspective view showing the external appearance of a dump truck 100, which is an example of a transport vehicle according to the first embodiment of the present invention. In the following description, unless otherwise specified, the area in front of the driver's seat (to the left front in the figure, see arrow) is considered the front of the vehicle body 101.

[0010] The dump truck 100 shown in Figure 1 is a large vehicle used in mines and the like, and is equipped with a body 101, a cab 103, a cargo bed 104, front wheels 105, and rear wheels 106. The cab 103 is supported by a support base 102 and is located on the front and left side of the body 101. The cab 103 forms the driver's compartment from which the operator of the dump truck 100 enters and exits, and is equipped with a driver's seat, accelerator pedal, brake pedal, steering wheel 29 (see Figure 3), and cargo bed control device 91 (see Figure 3), etc.

[0011] The cargo bed 104 is mounted on the rear of the vehicle body 101 so as to be able to be raised and lowered. The cargo bed 104 is rotatably supported on the rear side of the vehicle body 101 via a connecting pin, and moves up and down with the connecting pin as a pivot point by the extension and retraction of the hoist cylinder 10 (see Figure 3). The front wheels 105 support the vehicle body 101 on the left and right sides of the front, and the rear wheels 106 support the vehicle body 101 on the left and right sides of the rear, respectively, so that the vehicle body 101 can move. The front wheels 105 constitute the steering wheels that are steered by the operator of the dump truck 100, and when the operator of the dump truck 100 operates the steering handle 29, steering is performed in conjunction with the extension and retraction of the left and right steering cylinders 34, 35 (see Figure 3), which will be described later. The rear wheels 106 constitute the drive wheels of the dump truck 100 and are rotationally driven by a driving device (not shown).

[0012] A front grille 107 is provided on the front surface of the vehicle body 101. The front grille 107 is provided with a plurality of ventilation holes for taking outside air into the interior of the vehicle body 101.

[0013] FIG. 2 is a schematic plan view showing the configuration of the dump truck 100. As shown in FIG. 2, inside the vehicle body 101, there are mounted an engine 1, a generator 80 connected to the engine 1, a plurality of hydraulic pumps connected to the engine 1, a cooling fan 9 for generating cooling air, and a radiator 23 which is a heat exchanger for cooling engine cooling water by the cooling air generated by the cooling fan 9. The engine cooling water is a refrigerant for cooling the engine 1 and is a cooling target cooled by the cooling air generated by the cooling fan 9. In FIG. 2, only the radiator 23 is shown as the heat exchanger, but there may be cases where heat exchangers such as an oil cooler for cooling hydraulic oil are mounted.

[0014] The engine 1 as a prime mover is constituted by, for example, a large diesel engine or the like. The cooling fan 9 is driven by a fan motor 8 (see FIG. 3) described later. The cooling fan 9 sucks outside air from the front side of the vehicle body 101 through the front grille 107 and generates cooling air flowing from the front side to the rear side of the vehicle body 101 (see arrow F1). Since the radiator 23 is disposed on the rear side of the front grille 107, the radiator 23 is cooled by the cooling air.

[0015] The radiator 23 exchanges heat with the cooling air (air) generated by the cooling fan 9 and cools the engine cooling water heated by the engine 1. The engine cooling water cooled by the radiator 23 returns to the engine 1 and cools the engine 1. Since the radiator 23 is disposed at the front part of the vehicle body 101, it receives traveling wind (see arrow F2). Therefore, the engine cooling water in the radiator 23 is cooled not only by the cooling air but also by the traveling wind.

[0016] Referring to FIG. 3, the hydraulic system 110 of the dump truck 100 will be described. As shown in FIG. 3, the hydraulic system 110 of the dump truck 100 includes a variable displacement type first hydraulic pump 2 and a second hydraulic pump 3 driven by an engine 1, and a fixed displacement type hydraulic pump (hereinafter referred to as a pilot pump) 4, a pair of hoist cylinders (only one is shown in FIG. 3) 10 provided between the cargo bed 104 and the vehicle body 101 and driven by hydraulic oil supplied from the first hydraulic pump 2, a fan motor 8 driven by hydraulic oil supplied from the first hydraulic pump 2, a steering circuit 33 having a pair of left and right steering cylinders 34, 35 driven by hydraulic oil supplied from the second hydraulic pump 3, a hydraulic oil tank 22 for storing hydraulic oil, a fan control valve 5, a confluence control valve 6, and a hoist control valve 7 provided on a center bypass line CL which is an oil passage connecting the first hydraulic pump 2 and the hydraulic oil tank 22, and a control device 50 for controlling each part of the dump truck 100.

[0017] The first hydraulic pump 2 and the second hydraulic pump 3 are driven by the engine 1 to suck hydraulic oil from the hydraulic oil tank 22 and discharge high-pressure hydraulic oil (pressure oil). The discharge port of the first hydraulic pump 2 is connected to the hydraulic oil tank 22 via the center bypass line CL. The fan control valve 5, the confluence control valve 6, and the hoist control valve 7 are connected in tandem along the center bypass line CL. The fan control valve 5 controls the flow of hydraulic oil supplied from the first hydraulic pump 2 to the fan motor 8 and the flow of hydraulic oil discharged from the fan motor 8 to the hydraulic oil tank 22. The hoist control valve 7 controls the flow of hydraulic oil supplied from the first hydraulic pump 2 to the hoist cylinder 10 and the flow of hydraulic oil discharged from the hoist cylinder 10 to the hydraulic oil tank 22. The confluence control valve 6 functions as a circuit switching valve for switching the supply destination circuit of the hydraulic oil discharged from the second hydraulic pump 3.

[0018] A supply oil passage 61 branching from the center bypass line CL is connected to the fan control valve 5. The merging control valve 6 is located downstream of the fan control valve 5 in the center bypass line CL. A supply oil passage 63 extending from the discharge port of the second hydraulic pump 3 is connected to the merging control valve 6. The hoist control valve 7 is located downstream of the merging control valve 6 in the center bypass line CL. A supply oil passage 62 branching from the center bypass line CL is connected to the hoist control valve 7. Return oil from the fan motor 8 is discharged to the hydraulic oil tank 22 through the return oil passage 68. Return oil from the hoist cylinder 10 is discharged to the hydraulic oil tank 22 through the return oil passage 69.

[0019] The fan motor 8 is a hydraulic motor that rotates the cooling fan 9. The inlet and outlet (suction port and discharge port) of the fan motor 8 are connected to the fan control valve 5 by a pair of motor oil passages 81 and 82. The pair of motor oil passages 81 and 82 are connected to the first hydraulic pump 2 and the hydraulic oil tank 22, respectively, via the fan control valve 5.

[0020] A relief valve 11 is connected to the motor oil passage 81, which defines the maximum pressure in the motor oil passage 81. A relief valve 12 is provided in the motor oil passage 82, which defines the maximum pressure in the motor oil passage 82. The pair of relief valves 11 and 12 release the hydraulic fluid into the hydraulic fluid tank 22 when the pressure in the pair of motor oil passages 81 and 82 exceeds a predetermined value, protecting the hydraulic equipment of the fan circuit, including the pair of motor oil passages 81 and 82.

[0021] A pair of check valves 13 and 14 for makeup are provided between the pair of motor oil passages 81 and 82 and the return oil passage 68. Check valve 13 is a check valve that allows the flow of hydraulic fluid from the return oil passage 68 to the motor oil passage 81 and prohibits the flow of hydraulic fluid from the motor oil passage 81 to the return oil passage 68. Check valve 14 is a check valve that allows the flow of hydraulic fluid from the return oil passage 68 to the motor oil passage 82 and prohibits the flow of hydraulic fluid from the motor oil passage 82 to the return oil passage 68.

[0022] The pair of check valves 13 and 14 replenish the motor oil passages 81 and 82 with hydraulic fluid from the hydraulic fluid tank 22 via the return oil passage 68 when the motor oil passage 81 or 82 becomes negative pressure due to negative pressure when the fan motor 8 is rotating due to inertia or when the fan motor 8 is rotated by the airflow from the vehicle.

[0023] The hoist cylinder 10 is installed between the vehicle body 101 (see Figure 1) and the cargo bed 104 (see Figure 1). The hoist cylinder 10 is a single-stage or multi-stage hydraulic cylinder that raises and lowers the cargo bed 104. Figure 3 shows a two-stage hoist cylinder 10. The hoist cylinder 10 shown in Figure 3 has an outer cylinder portion 10a, an inner cylinder portion 10b that is slidably installed inside the outer cylinder portion 10a and divides the inside of the outer cylinder portion 10a into an upper bottom-side oil chamber 10d and a lower rod-side oil chamber 10e, and a piston rod 10c that is extendable and retractable inside the inner cylinder portion 10b.

[0024] The hoist cylinder 10 extends when hydraulic fluid (pressurized oil) discharged from the first hydraulic pump 2 is supplied to the bottom oil chamber 10d and hydraulic fluid (return oil) is discharged from the rod oil chamber 10e. As the hoist cylinder 10 extends, the platform 104 rotates upward around the connecting pin as a pivot point. Once the rotation is complete, the platform 104 assumes a downward-tilting position for unloading soil. The hoist cylinder 10 retracts when hydraulic fluid (pressurized oil) discharged from the first hydraulic pump 2 is supplied to the rod oil chamber 10e and hydraulic fluid (return oil) is discharged from the bottom oil chamber 10d. As the hoist cylinder 10 retracts, the platform 104 rotates downward around the connecting pin as a pivot point. Once the rotation is complete, the platform 104 assumes a tipped-over transport position.

[0025] The bottom oil chamber 10d and the rod oil chamber 10e of the hoist cylinder 10 are connected to the hoist control valve 7 by a pair of actuator oil passages 71 and 72. The pair of actuator oil passages 71 and 72 are connected to the first hydraulic pump 2 and the hydraulic oil tank 22, respectively, via the hoist control valve 7. Actuator oil passage 71 is connected to the bottom oil chamber 10d of the hoist cylinder 10, and actuator oil passage 72 is connected to the rod oil chamber 10e of the hoist cylinder 10.

[0026] The steering circuit 33 includes a pair of left and right steering cylinders 34 and 35, a steering control valve 31 that controls the flow of hydraulic fluid supplied from the second hydraulic pump 3 to the steering cylinders 34 and 35, steering oil passages 36 and 37 that connect the steering cylinders 34 and 35 to the steering control valve 31, a high-pressure oil passage 38 that connects the second hydraulic pump 3 to the steering control valve 31, and a low-pressure oil passage 39 that connects the steering control valve 31 to the hydraulic fluid tank 22.

[0027] The left and right steering cylinders 34 and 35 steer the left and right front wheels 105 by extending and retracting in response to the operation of the steering wheel 29. The left steering cylinder 34 is a hydraulic cylinder having a bottom oil chamber 34a and a rod oil chamber 34b. The right steering cylinder 35 is a hydraulic cylinder having a bottom oil chamber 35a and a rod oil chamber 35b. The bottom oil chamber 35a of the right steering cylinder 35 and the rod oil chamber 34b of the left steering cylinder 34 are connected via a steering oil passage 36. The bottom oil chamber 34a of the left steering cylinder 34 and the rod oil chamber 35b of the right steering cylinder 35 are connected via a steering oil passage 37. The steering oil passages 36 and 37 are connected to a high-pressure oil passage 38 and a low-pressure oil passage 39 via a steering control valve 31.

[0028] The handle 29 is located inside the cab 103. The handle 29 is rotated left and right by the operator to control the direction of travel of the dump truck 100. A hydraulic motor 30 is connected to the handle shaft of the handle 29, and the rotation of this hydraulic motor 30 reduces the operating force applied to the handle 29.

[0029] An accumulator 42 is connected to the high-pressure oil passage 38. The accumulator 42 stores the hydraulic fluid (pressurized oil) discharged from the second hydraulic pump 3. A relief valve 32 is provided between the high-pressure oil passage 38 and the low-pressure oil passage 39, which defines the maximum pressure of the high-pressure oil passage 38. Therefore, the high-pressure oil passage 38 is maintained at a predetermined pressure by the accumulator 42 and the relief valve 32. This allows the steering cylinders 34 and 35 to be driven appropriately when the steering wheel 29 is operated, and the vehicle body 101 to be turned in any direction. The accumulator 42 also functions as an emergency hydraulic power source for the left and right steering cylinders 34 and 35. That is, when hydraulic fluid is not supplied from the second hydraulic pump 3 to the supply oil passage 63 due to a failure of the second hydraulic pump 3, etc., the pressurized oil stored in the accumulator 42 is supplied to the left and right steering cylinders 34 and 35.

[0030] When the operator rotates the steering wheel 29, the steering control valve 31 switches from the neutral position (31N) to either the left or right steering position (31L) or (31R). As a result, the hydraulic fluid supplied from the second hydraulic pump 3 is supplied to the left and right steering cylinders 34 and 35 through the steering control valve 31, causing one of the steering cylinders 34 or 35 to extend and the other to contract. As a result, the left and right front wheels 105 of the dump truck 100 are steered in response to the rotation of the steering wheel 29.

[0031] The fan control valve 5 is configured, for example, as a hydraulic pilot-operated directional control valve with 6 ports and 3 positions. The fan control valve 5 is configured using a single directional control valve and has hydraulic pilot sections 5a and 5b on both the left and right sides.

[0032] The fan control valve 5 is a switching valve that can switch the spool (valve body) to a forward rotation position (5F), a reverse rotation position (5R), and a neutral position (5N). Under normal circumstances, both the hydraulic pilot sections 5a and 5b of the fan control valve 5 are connected to the hydraulic fluid tank 22, and the spool is held in the neutral position (5N) by a centering spring.

[0033] When the spool of the fan control valve 5 is in the neutral position (5N), the upstream and downstream sides of the fan control valve 5 in the center bypass line CL are in communication, and the communication between the supply oil passage 61 and the motor oil passages 81 and 82 is blocked. In other words, in the neutral position (5N), the first hydraulic pump 2 and the merging control valve 6 are in communication, and the communication between the first hydraulic pump 2 and the fan motor 8 is blocked. As a result, the hydraulic fluid discharged from the first hydraulic pump 2 is supplied to the merging control valve 6 through the fan control valve 5. Also, when the spool of the fan control valve 5 is in the neutral position (5N), the communication passage 5c of the fan control valve 5 connects the pair of motor oil passages 81 and 82 to each other, and the pair of motor oil passages 81 and 82 are connected to the return oil passage 68. In the neutral position (5N), the intake port and discharge port of the fan motor 8 and the hydraulic fluid tank 22 are in communication via the communication passage 5c, so the rotation of the cooling fan 9 due to external force is permitted.

[0034] When the spool of the fan control valve 5 is in the forward rotation position (5F), the supply oil passage 61 and the motor oil passage 81 are in communication, and the motor oil passage 82 and the return oil passage 68 are in communication. In other words, in the forward rotation position (5F), the communication between the intake and discharge ports of the fan motor 8 and the hydraulic oil tank 22 via the communication passage 5c is blocked, while the intake port of the fan motor 8 is in communication with the first hydraulic pump 2, and the discharge port of the fan motor 8 is in communication with the hydraulic oil tank 22. As a result, the hydraulic oil discharged from the first hydraulic pump 2 is supplied to the fan motor 8 through the supply oil passage 61 and the motor oil passage 81, causing the fan motor 8 to rotate in the forward direction. The hydraulic oil discharged from the fan motor 8 is discharged to the hydraulic oil tank 22 through the motor oil passage 82 and the return oil passage 68. When the spool of the fan control valve 5 is in the reverse position (5R), the supply oil passage 61 and the motor oil passage 82 are in communication, and the motor oil passage 81 is in communication with the return oil passage 68. In other words, in the reverse position (5R), the communication between the intake and discharge ports of the fan motor 8 and the hydraulic oil tank 22 via the communication passage 5c is blocked, while the intake port of the fan motor 8 is in communication with the first hydraulic pump 2, and the discharge port of the fan motor 8 is in communication with the hydraulic oil tank 22. As a result, the hydraulic oil discharged from the first hydraulic pump 2 is supplied to the fan motor 8 through the supply oil passage 61 and the motor oil passage 82, causing the fan motor 8 to rotate in the reverse direction, which is the opposite direction to the forward direction. The hydraulic oil discharged from the fan motor 8 is discharged to the hydraulic oil tank 22 through the motor oil passage 81 and the return oil passage 68.

[0035] Thus, the forward rotation position (5F) and the reverse rotation position (5R) are rotational positions that connect the first hydraulic pump 2 and the fan motor 8, and rotate the fan motor 8 with the hydraulic fluid discharged from the first hydraulic pump 2. When the spool of the fan control valve 5 is in the rotational position (5F) or (5R), the communication between the first hydraulic pump 2 and the merging control valve 6 via the center bypass line CL is interrupted.

[0036] The merging control valve 6 is configured, for example, by a hydraulic pilot-operated directional control valve with 6 ports and 3 positions. The merging control valve 6 is configured using a single directional control valve and has hydraulic pilot sections 6a and 6b on both the left and right sides.

[0037] The confluence control valve 6 is a switching valve that can switch the spool (valve body) to the confluence position (6C), the diversion position (6D), and the neutral position (6N). Under normal circumstances, both the hydraulic pilot sections 6a and 6b of the confluence control valve 6 are connected to the hydraulic fluid tank 22, and the spool is held in the neutral position (6N) by a centering spring.

[0038] When the spool of the confluence control valve 6 is in the confluence position (6C), the supply oil passage 63 and the center bypass line CL are connected, and the connection between the supply oil passage 63 and the high-pressure side oil passage 38 of the steering circuit 33 is blocked. Therefore, when the confluence control valve 6 is in the confluence position (6C), the first hydraulic pump 2 and the hoist control valve 7 are connected via the fan control valve 5, which is in the neutral position (5N), and the second hydraulic pump 3 and the hoist control valve 7 are connected, while the connection between the second hydraulic pump 3 and the steering circuit 33 is blocked. As a result, when the confluence control valve 6 is in the confluence position (6C) and the fan control valve 5 is in the neutral position (5N), the hydraulic fluid discharged from the first hydraulic pump 2 and the hydraulic fluid discharged from the second hydraulic pump 3 are combined and led to the hoist control valve 7.

[0039] When the spool of the confluence control valve 6 is in the neutral position (6N), the supply oil passage 63 and the high-pressure oil passage 38 of the steering circuit 33 are in communication. Also, when the spool of the confluence control valve 6 is in the neutral position (6N), the upstream and downstream sides of the confluence control valve 6 of the center bypass line CL are in communication. In other words, in the neutral position (6N), the fan control valve 5 and the hoist control valve 7 are in communication. Therefore, when the confluence control valve 6 is in the neutral position (6N), the first hydraulic pump 2 and the hoist control valve 7 are in communication via the fan control valve 5, which is in the neutral position (5N), and the second hydraulic pump 3 and the steering circuit 33 are in communication, while the communication between the second hydraulic pump 3 and the hoist control valve 7 is interrupted. As a result, when the merging control valve 6 is in the neutral position (6N) and the fan control valve 5 is in the neutral position (5N), the hydraulic fluid discharged from the first hydraulic pump 2 is guided to the hoist control valve 7 through the fan control valve 5 and the merging control valve 6, and the hydraulic fluid discharged from the second hydraulic pump 3 is guided to the steering circuit 33. In other words, the neutral position (6N) is a non-merging position in which the hydraulic fluid discharged from the first hydraulic pump 2 and the hydraulic fluid discharged from the second hydraulic pump 3 are not merged.

[0040] When the spool of the merging control valve 6 is in the diversion position (6D), the supply oil passage 63 communicates with the high-pressure oil passage 38 of the steering circuit 33 and the actuator oil passage 85. As a result, the hydraulic fluid discharged from the second hydraulic pump 3 is divided and directed to the steering circuit 33 and the actuator oil passage 85. Therefore, the attachment actuator 86 connected to the actuator oil passage 85 can be operated while driving. The diversion position (6D), like the neutral position (6N), is a non-merging position in which the hydraulic fluid discharged from the first hydraulic pump 2 and the hydraulic fluid discharged from the second hydraulic pump 3 are not merged.

[0041] The hoist control valve 7 is configured, for example, as a hydraulic pilot-operated directional control valve with 6 ports and 4 positions. The hoist control valve 7 is configured using a single directional control valve and has hydraulic pilot sections 7a and 7b on both the left and right sides.

[0042] The hoist control valve 7 has multiple switching positions, including a raised position (7R) in which the hoist cylinder 10 is extended by supplying and discharging hydraulic fluid to rotate the platform 104 upward, a lowered position (7L) in which the hoist cylinder 10 is retracted by supplying and discharging hydraulic fluid to rotate the platform 104 downward, a floating position (7F) in which the hoist cylinder 10 is retracted by the weight of the platform 104 to allow the platform 104 to fall under its own weight, and a neutral position (7N) in which the supply and discharge of hydraulic fluid is stopped to hold the platform 104 in place. The hoist control valve 7 is a switching valve in which the spool (valve body) can be switched between the raised position (7R), the lowered position (7L), the floating position (7F), and the neutral position (7N). Under normal circumstances, both the hydraulic pilot sections 7a and 7b of the hoist control valve 7 are connected to the hydraulic fluid tank 22, and the spool is held in the neutral position (7N) by a centering spring.

[0043] When the spool of the hoist control valve 7 is in the neutral position (7N), communication between the supply oil passage 62 and the return oil passage 69 and the actuator oil passages 71 and 72 is blocked. As a result, the supply of hydraulic fluid to the hoist cylinder 10 and the discharge of hydraulic fluid from the hoist cylinder 10 are stopped, and the movement of the hoist cylinder 10 stops. Also, when the spool of the hoist control valve 7 is in the neutral position (7N), the upstream and downstream sides of the hoist control valve 7 of the center bypass line CL are in communication.

[0044] When the spool of the hoist control valve 7 is in the raised position (7R), the supply oil passage 62 and the actuator oil passage 71 are in communication, and the actuator oil passage 72 and the return oil passage 69 are in communication. However, communication between the upstream and downstream sides of the hoist control valve 7 on the center bypass line CL is blocked. As a result, when the fan control valve 5 is in the neutral position (5N), the hydraulic fluid discharged from the first hydraulic pump 2 is supplied to the bottom oil chamber 10d of the hoist cylinder 10 through the supply oil passage 62 and the actuator oil passage 71. In addition, the hydraulic fluid in the rod-side oil chamber 10e is discharged to the hydraulic fluid tank 22 through the actuator oil passage 72 and the return oil passage 69. As a result, the hoist cylinder 10 is driven in the direction of extension, that is, in the direction of lifting the loading platform 104.

[0045] When the spool of the hoist control valve 7 is in the lowered position (7L), the supply oil passage 62 and the actuator oil passage 72 are in communication, and the actuator oil passage 71 and the return oil passage 69 are in communication. However, communication between the upstream and downstream sides of the hoist control valve 7 on the center bypass line CL is blocked. As a result, when the fan control valve 5 is in the neutral position (5N), the hydraulic fluid discharged from the first hydraulic pump 2 is supplied to the rod-side oil chamber 10e of the hoist cylinder 10 through the supply oil passage 62 and the actuator oil passage 72. In addition, the hydraulic fluid in the bottom-side oil chamber 10d is discharged to the hydraulic fluid tank 22 through the actuator oil passage 71 and the return oil passage 69. As a result, the hoist cylinder 10 is driven in the direction of contraction, that is, in the direction of lowering the loading platform 104.

[0046] When the spool of the hoist control valve 7 is in the floating position (7F), the supply oil passage 62 and the center bypass line CL downstream of the hoist control valve 7 are in communication. Also, when the spool of the hoist control valve 7 is in the floating position (7F), the actuator oil passage 71 and the return oil passage 69 are in communication. As a result, the hydraulic fluid in the bottom oil chamber 10d of the hoist cylinder 10 is discharged to the hydraulic fluid tank 22, and the hydraulic fluid in the rod oil chamber 10e is supplied from the hydraulic fluid tank 22 via an oil passage (not shown). Therefore, when the hoist control valve 7 is in the floating position (7F), the hoist cylinder 10 can be retracted by the weight of the loading platform 104.

[0047] The pilot pump 4 is connected to a plurality of solenoid valves 16-21 via a pilot oil passage. A pilot relief valve 15 is provided in the pilot oil passage between the pilot pump 4 and the plurality of solenoid valves 16-21 to regulate the pressure in the pilot oil passage. The plurality of solenoid valves 16-21 are pressure reducing valves that reduce the pressure (primary pressure) in the pilot oil passage according to the control current from the control device 50 and output the reduced pressure (secondary pressure) as the pilot pressure. When a standby control current is input as an off signal, the solenoid valves 16-21 communicate with the hydraulic pilot units 5a, 5b, 6a, 6b, 7a, 7b and the hydraulic oil tank 22. When a drive control current is input as an on signal, the solenoid valves 16-21 output the generated pilot pressure to the hydraulic pilot units 5a, 5b, 6a, 6b, 7a, 7b.

[0048] The solenoid valves 16 and 17 for driving the fan control valve 5 operate in accordance with the control command (control current) output from the control device 50 according to the engine coolant temperature. The solenoid valves 18 and 19 for driving the hoist control valve 7 operate in accordance with the control command (control current) output from the control device 50 in accordance with the operation of the operating device 91 for the cargo bed. The solenoid valves 20 and 21 for driving the merging control valve 6 operate in accordance with the control command (control current) output from the control device 50 in accordance with the operation of the operating device 91 for the cargo bed and the operating device of an attachment actuator 86 (not shown).

[0049] The control unit 50 consists of a computer equipped with processing units 51 such as a CPU (Central Processing Unit), MPU (Micro Processing Unit), and DSP (Digital Signal Processor), non-volatile memory 52 such as ROM (Read Only Memory), flash memory, and hard disk drive, volatile memory 53 known as RAM (Random Access Memory), an input / output interface, and other peripheral circuits. These hardware components work together to run software and realize multiple functions. The control unit 50 may consist of one computer or multiple computers.

[0050] The non-volatile memory 52 stores programs capable of performing various calculations and data used in those calculations (data tables, thresholds, formulas, etc.). In other words, the non-volatile memory 52 is a storage medium (device) from which programs realizing the functions of this embodiment can be read. The volatile memory 53 is a storage medium (device) that temporarily stores the calculation results from the processing unit 51 and signals input from the input / output interface. The processing unit 51 is a device that expands the programs stored in the non-volatile memory 52 into the volatile memory 53 and performs calculations, and performs predetermined calculation processing on data taken from the input / output interface, the non-volatile memory 52 and the volatile memory 53 according to the program.

[0051] An operating device 91, which controls the switching operation of the hoist control valve 7, i.e., the operation of the hoist cylinder 10, is connected to the input / output interface of the control device 50. The operating device 91 is configured, for example, by an electric lever device and has an operating lever 91a that is manually tilted by an operator in the cab 103. The operating device 91 is operated to one of the neutral position, raised position, raised position, or lowered position, which corresponds to each switching position of the hoist control valve 7, i.e., the neutral position (7N), raised position (7R), floating position (7F), and lowered position (7L). The operating device 91 outputs an operation signal to the control device 50 according to the operating position.

[0052] A temperature sensor 25 is connected to the input / output interface of the control device 50. The temperature sensor 25 detects the temperature of the engine coolant flowing through the engine coolant system 28 of the engine 1 and outputs a signal representing the detection result to the control device 50. The coolant system 28 consists of a coolant tank 27 that stores engine coolant, a coolant circulation pump 24 that draws in and discharges engine coolant from the coolant tank 27, and a radiator 23 that cools the engine coolant with cooling air. The coolant system 28 is a circulation system that can circulate engine coolant within the system by the coolant circulation pump 24. The engine coolant cools the object to be cooled 26, such as the engine 1, by absorbing heat from the object to be cooled 26. The temperature of the engine coolant rises as it receives heat from the object to be cooled 26. The engine coolant, whose temperature has risen, is cooled by the cooling air generated by the cooling fan 9 in the radiator 23. The temperature sensor 25 is installed, for example, in the intake line of the coolant tank 27 or the coolant circulation pump 24, and detects the temperature of the engine coolant supplied to the radiator 23.

[0053] The input section of the input / output interface converts signals received from various devices (operating device 91, temperature sensor 25, etc.) into data that can be processed by the processing unit 51. The output section of the input / output interface generates output signals according to the calculation results of the processing unit 51 and outputs these signals to various devices (solenoid valves 16-21, regulators 2a, 3a, etc.).

[0054] The control device 50 outputs control signals to the regulator 2a of the first hydraulic pump 2 and the regulator 3a of the second hydraulic pump 3. Regulator 2a is a capacity control device that variably controls the displacement volume (discharge volume per revolution) of the first hydraulic pump 2, and regulator 3a is a capacity control device that variably controls the displacement volume (discharge volume per revolution) of the second hydraulic pump 3. For example, if the hydraulic pump is a swashplate piston pump, the regulator has a tilt actuator that controls the tilt angle (displacement volume) of the swashplate of the hydraulic pump, and an electromagnetic proportional valve that generates a control pressure for the tilt actuator using the discharge pressure of the hydraulic pump as the source pressure.

[0055] When the operating device 91 is operated to the neutral position, the control device 50 controls the fan control valve 5 based on the engine coolant temperature (hereinafter also referred to as coolant temperature) Tc detected by the temperature sensor 25. The control details of the fan control valve 5 will be described later.

[0056] When the operating device 91 is operated to the neutral position, the control device 50 keeps the hoist control valve 7 in the neutral position (7N). In other words, the control device 50 outputs an off signal to both solenoid valves 18 and 19. When the operating device 91 is operated to the floating position, the control device 50 controls the hoist control valve 7 to switch to the floating position (7F). In other words, the control device 50 outputs an off signal to solenoid valve 18 and a first on signal to solenoid valve 19. As a result, the pilot pressure generated by solenoid valve 19 acts on the hydraulic pilot unit 7b, and the hoist control valve 7 is switched to the floating position (7F).

[0057] When the operating device 91 is operated to the raised position, the control device 50 controls the hoist control valve 7 to switch to the raised position (7R). In other words, the control device 50 outputs an ON signal to the solenoid valve 18 and an OFF signal to the solenoid valve 19. As a result, the pilot pressure generated by the solenoid valve 18 acts on the hydraulic pilot unit 7a, and the hoist control valve 7 is switched to the raised position (7R). When the operating device 91 is operated to the lowering position, the control device 50 controls the hoist control valve 7 to switch to the lowering position (7L). In other words, the control device 50 outputs an OFF signal to the solenoid valve 18 and a second ON signal to the solenoid valve 19. The second ON signal has a larger current value than the first signal. As a result, the pilot pressure generated by the solenoid valve 19 acts on the hydraulic pilot unit 7b, and the hoist control valve 7 is switched to the lowering position (7L).

[0058] When the operating device 91 is operated to the raised position, the control device 50 controls the merging control valve 6 to the merging position (6C). In other words, the control device 50 outputs an ON signal to the solenoid valve 20 and an OFF signal to the solenoid valve 21. As a result, the pilot pressure generated by the solenoid valve 20 acts on the hydraulic pilot unit 6a, and the merging control valve 6 is switched to the merging position (6C).

[0059] Therefore, when the operating device 91 is operated to the raised position, hydraulic fluid discharged from both the first hydraulic pump 2 and the second hydraulic pump 3 is supplied to the hoist cylinder 10. This allows the large-capacity hoist cylinder 10 to extend smoothly, enabling the release of cargo such as soil from the loading platform 104. According to this embodiment, the first hydraulic pump 2 can be made smaller compared to a configuration in which the extension operation of the hoist cylinder 10 is performed using only the hydraulic fluid discharged from the first hydraulic pump 2.

[0060] Furthermore, the control device 50 controls the confluence control valve 6 to the diversion position (6D) when the operating device (not shown) of the attachment actuator 86 is operated. In addition, the control device 50 holds the confluence control valve 6 in the neutral position (6N) when the operating device 91 is operated to the neutral position, floating position, or lowered position, and the operating device of the attachment actuator 86 is not operated.

[0061] The control device 50 controls the rotation and stopping of the fan motor 8 and the direction of rotation of the fan motor 8 by controlling the switching position of the fan control valve 5 based on the cooling water temperature Tc, for example. The control device 50 also controls the rotational speed of the fan motor 8 by controlling the discharge capacity q of the first hydraulic pump 2 via the regulator 2a within a range from a minimum capacity qmin to a maximum capacity qmax, based on the cooling water temperature Tc, for example.

[0062] The control device 50 controls the discharge capacity q of the second hydraulic pump 3 via the regulator 3a within a range from a minimum capacity qmin to a maximum capacity qmax, based on the pressure of the accumulator 42 detected by, for example, a pressure sensor (not shown). The minimum capacity qmin and maximum capacity qmax of the discharge capacity q of the second hydraulic pump 3 may be different from or the same as those of the first hydraulic pump 2.

[0063] Referring to Figure 4, the functions of the control device 50 for controlling the cooling fan 9 and the first hydraulic pump 2 will be described. Figure 4 is a functional block diagram of the control device 50. As shown in Figure 4, the control device 50 functions as a determination unit 54, a valve control unit 55, and a pump control unit 56 by executing a program stored in the non-volatile memory 52.

[0064] As shown in FIG. 4, the determination unit 54 determines whether the cooling water temperature Tc detected by the temperature sensor 25 is equal to or higher than a first threshold value Tc1. Further, the determination unit 54 determines whether the cooling water temperature Tc detected by the temperature sensor 25 is equal to or higher than a second threshold value Tc2. The first threshold value Tc1 and the second threshold value Tc2 are stored in the non-volatile memory 52 in advance. The magnitude relationship between the first threshold value Tc1 and the second threshold value Tc2 is Tc1 < Tc2. When the cooling water temperature Tc is less than the first threshold value Tc1, the determination unit 54 determines that the stop condition for the cooling fan 9 is satisfied. Therefore, it can be said that the first threshold value Tc1 is a threshold value for determining whether to stop driving the cooling fan 9.

[0065] Based on the determination result of the determination unit 54, the valve control unit 55 controls the switching position of the fan control valve 5. When the determination unit 54 determines that the stop condition for the cooling fan 9 is not satisfied, the valve control unit 55 outputs an on signal to the solenoid valve 16 and an off signal to the solenoid valve 17, and switches the fan control valve 5 to the forward rotation position (5F). When the fan control valve 5 is switched to the forward rotation position (5F), the supply oil passage 61 and the motor oil passage 81 communicate with each other, and the motor oil passage 82 and the return oil passage 68 communicate with each other. As a result, the fan motor 8 rotates by the hydraulic oil supplied from the first hydraulic pump 2.

[0066] When the determination unit 54 determines that the stop condition for the cooling fan 9 is satisfied, the valve control unit 55 outputs an off signal to the solenoid valves 16 and 17, and switches the fan control valve 5 to the neutral position (5N). When the fan control valve 5 is switched to the neutral position (5N), the communication between the supply oil passage 61 and the motor oil passages 81 and 82 is blocked. Further, the motor oil passage 81, the motor oil passage 82, and the hydraulic oil tank 22 communicate with each other through the communication passage 5c of the fan control valve 5. As a result, the fan motor 8 decelerates and stops over time. While the fan motor 8 is rotating due to inertia, the hydraulic oil is supplied from the hydraulic oil tank 22 through the communication passage 5c of the fan control valve 5 in the neutral position (5N) and the check valve 13 or the check valve 14. Therefore, it is possible to prevent the occurrence of cavitation in the fan motor 8.

[0067] The pump control unit 56 controls the discharge flow rate Q of the first hydraulic pump 2 based on the cooling water temperature Tc detected by the temperature sensor 25. The discharge flow rate Q of the first hydraulic pump 2 is determined by the rotational speed of the engine 1 and the discharge capacity (volume) q of the first hydraulic pump 2. In this embodiment, the pump control unit 56 controls the discharge flow rate Q of the first hydraulic pump 2 by controlling the discharge capacity q of the first hydraulic pump 2.

[0068] Figure 5 shows the relationship between the discharge capacity q (corresponding to the tilt angle of the swash plate) and the discharge flow rate Q of the first hydraulic pump 2. The relationship between the discharge capacity q and the discharge flow rate Q of the second hydraulic pump 3 is the same as shown in Figure 5, so no explanation is given. As shown in Figure 5, when the engine rotation speed is constant, the discharge flow rate Q of the first hydraulic pump 2 increases proportionally with the increase in the discharge capacity q of the first hydraulic pump 2. When the discharge capacity q is at its minimum value (0%), the discharge flow rate Q is the minimum flow rate Qmin. When the discharge capacity q is at its maximum value (100%), the discharge flow rate Q is the maximum flow rate Qmax.

[0069] The pump control unit 56 calculates the discharge capacity q of the first hydraulic pump 2 using a capacity control table (see Figure 6) that is pre-stored in the non-volatile memory 52. ​​Figure 6 is a diagram showing the capacity control table that defines the relationship between the cooling water temperature Tc and the discharge capacity q. As shown in Figure 6, the relationship between the cooling water temperature Tc and the discharge capacity q defined by the capacity control table is as follows: When the cooling water temperature Tc is less than the first threshold Tc1, the discharge capacity q is the minimum capacity qmin. When the cooling water temperature Tc is between the first threshold Tc1 and the second threshold Tc2, the discharge capacity q increases proportionally with the increase in cooling water temperature Tc. When the cooling water temperature Tc is above the second threshold Tc2, the discharge capacity q is the maximum capacity qmax.

[0070] The pump control unit 56 refers to the capacity control table and calculates the discharge capacity q of the first hydraulic pump 2 based on the cooling water temperature Tc detected by the temperature sensor 25. Therefore, if the cooling water temperature Tc is less than the first threshold Tc1, the pump control unit 56 controls the discharge capacity q of the first hydraulic pump 2 to the minimum capacity qmin. Also, if the cooling water temperature Tc is greater than or equal to the first threshold Tc1, the pump control unit 56 controls the discharge capacity q of the first hydraulic pump 2 to a discharge capacity q greater than the minimum capacity qmin. Specifically, if the cooling water temperature Tc is greater than or equal to the first threshold Tc1 and less than the second threshold Tc2, the pump control unit 56 increases the discharge capacity q of the first hydraulic pump 2 as the cooling water temperature Tc increases, and if the cooling water temperature Tc is greater than or equal to the second threshold Tc2, the pump control unit 56 controls the discharge capacity q of the first hydraulic pump 2 to the maximum capacity qmax.

[0071] Referring to Figure 7, an example of the processing flow for fan control performed by the control device 50 will be described. The processing shown in the flowchart of Figure 7 is started when the ignition switch (not shown) is turned on and is repeatedly executed at a predetermined control cycle.

[0072] As shown in Figure 7, in step S110, the control device 50 obtains the cooling water temperature Tc from the temperature sensor 25 and proceeds to step S120. In step S120, the control device 50 determines whether the cooling water temperature Tc obtained in step S110 is greater than or equal to the first threshold Tc1. If it is determined in step S120 that the cooling water temperature Tc is greater than or equal to the first threshold Tc1, the process proceeds to step S130. If it is determined in step S120 that the cooling water temperature Tc is less than the first threshold Tc1, the process proceeds to step S135.

[0073] In step S130, the control device 50 outputs an ON signal to the solenoid valve 16 and an OFF signal to the solenoid valve 17. When the ON signal is input to the solenoid valve 16, pilot pressure is generated by the solenoid valve 16, and the generated pilot pressure is input to the hydraulic pilot section 5a of the fan control valve 5. As a result, the fan control valve 5 is switched to the forward rotation position (5F), and the fan motor 8 rotates in the forward direction by the hydraulic fluid discharged from the first hydraulic pump 2.

[0074] When the processing in step S130 is completed, the process proceeds to the next step S140. In step S140, the control device 50 determines whether the cooling water temperature Tc obtained in step S110 is equal to or greater than the second threshold Tc2. If it is determined in step S140 that the cooling water temperature Tc is equal to or greater than the second threshold Tc2, the process proceeds to step S150. If it is determined in step S140 that the cooling water temperature Tc is less than the second threshold Tc2, the process proceeds to step S155.

[0075] In step S150, the control device 50 outputs a control signal to the regulator 2a to set the discharge capacity q of the first hydraulic pump 2 to its maximum capacity qmax, and terminates the process shown in the flowchart of Figure 7 for this control cycle. In step S155, the control device 50 determines a target value for the discharge capacity q of the first hydraulic pump 2 based on the capacity control table (see Figure 6) and the cooling water temperature Tc acquired in step S110. The control device 50 outputs a control signal to the regulator 2a to set the discharge capacity q of the first hydraulic pump 2 to a target value corresponding to the cooling water temperature Tc, and terminates the process shown in the flowchart of Figure 7 for this control cycle.

[0076] As described above, if it is determined in step S120 that the cooling water temperature Tc is less than the first threshold Tc1, the process proceeds to step S135. In step S135, the control device 50 outputs an off signal to the solenoid valves 16 and 17. When the off signal is input to the solenoid valves 16 and 17, the hydraulic pilot sections 5a and 5b of the fan control valve 5 are connected to the hydraulic oil tank 22. As a result, the fan control valve 5 is switched to the neutral position (5N) by the biasing force of the centering spring.

[0077] When the process in step S135 is completed, the process proceeds to the next step, S137. In step S137, the control device 50 outputs a control signal to the regulator 2a to set the discharge capacity q of the first hydraulic pump 2 to its minimum capacity qmin, thereby ending the process shown in the flowchart of Figure 7 for this control cycle.

[0078] Although not shown in the diagram, the control device 50 determines whether the operating device 91 is operated to the neutral position or the floating position, and if the operating device 91 is operated to the neutral position or the floating position, it executes the control shown in the flowchart of Figure 7. If the operating device 91 is operated to the raised position or the lowered position, the control device 50 controls the fan control valve 5 to the neutral position (5N), regardless of the cooling water temperature Tc. In other words, if the operating device 91 is operated to the raised position or the lowered position, the control device 50 prioritizes the operation of the hoist cylinder 10.

[0079] Furthermore, the flowchart in Figure 7 illustrates an example in which, if a negative determination is made in step S120, the process in step S137 is executed; if a positive determination is made in step S140, the process in step S150 is executed; and if a negative determination is made in step S140, the process in step S155 is executed. However, the control device 50 may also calculate the target value of the discharge capacity q using the capacity control table (see Figure 6) when the cooling water temperature Tc is less than the first threshold Tc1, and when the cooling water temperature Tc is equal to or greater than the second threshold Tc2. For example, the processes in steps S137, S140, S150, and S155 may be omitted, and a process equivalent to step S155 may be executed between steps S110 and S120.

[0080] Referring to Figure 8, the main operations of the hydraulic system 110 when the dump truck 100 according to this embodiment is in motion will be described. Note that while the dump truck 100 is in motion, the operating device 91 is operated to the neutral position, so the hoist control valve 7 is held in the neutral position (7N). Also, the confluence control valve 6 is in the neutral position (6N) or the diversion position (6D). Figure 8 is a diagram showing the relationship between the switching position of the fan control valve 5 and the discharge flow rate Q of the first hydraulic pump 2 according to the cooling water temperature Tc. While the dump truck 100 is in motion, if the cooling water temperature Tc is equal to or greater than the first threshold Tc1, the control device 50 controls the fan control valve 5 to the forward rotation position (5F). That is, the control device 50 outputs an ON signal to the solenoid valve 16 and an OFF signal to the solenoid valve 17. As a result, the fan control valve 5 is switched to the forward rotation position (5F).

[0081] Here, for example, during unloaded driving after the operation of unloading transported materials such as soil, the cooling of the engine coolant flowing through the radiator 23 continues due to the cooling air and the airflow from driving, causing the coolant temperature Tc to decrease. When the coolant temperature Tc is in the range of 1st threshold Tc1 or higher and less than the 2nd threshold Tc2, the discharge capacity q of the first hydraulic pump 2 is controlled according to the coolant temperature Tc. When the coolant temperature Tc further decreases and falls below the 1st threshold Tc1, the control device 50 outputs an off signal to the solenoid valve 16 and the solenoid valve 17, respectively. As a result, the fan control valve 5 is switched to the neutral position (5N). Therefore, the rotation of the cooling fan 9 slows down over time and stops. Since the generation of cooling air by the cooling fan 9 stops, overcooling of the engine coolant can be prevented. The control device 50 also controls the discharge flow rate Q of the first hydraulic pump 2 to the minimum flow rate Qmin. As a result, the hydraulic fluid discharged from the first hydraulic pump 2 is discharged into the hydraulic fluid tank 22 through the fan control valve 5 in the neutral position (5N), the merging control valve 6 in the neutral position (6N) or the diversion position (6D), and the hoist control valve 7 in the neutral position (7N). Therefore, the pressure loss in the center bypass line CL connecting the first hydraulic pump 2 and the hydraulic fluid tank 22 is reduced, and the discharge pressure of the first hydraulic pump 2 can be kept low. As a result, the load on the first hydraulic pump 2 is reduced, and the load on the engine 1 is reduced. Therefore, according to this embodiment, the energy loss of the first hydraulic pump 2 can be reduced, and fuel consumption can be suppressed.

[0082] According to the above-described embodiment, the following effects are achieved.

[0083] (1) The fan control valve 5, the confluence control valve 6, and the hoist control valve 7 are connected in tandem to the center bypass line (oil passage) CL that connects the first hydraulic pump 2 and the hydraulic oil tank 22. On the center bypass line CL, the fan control valve 5 is positioned upstream of the confluence control valve 6, and the confluence control valve 6 is positioned upstream of the hoist control valve 7. The confluence control valve 6 has a confluence position (6C) in which the hydraulic oil discharged from the second hydraulic pump 3 is combined with the hydraulic oil discharged from the first hydraulic pump 2 and guided to the hoist control valve 7, and a neutral position (6N) and a diversion position (6D) in which the hydraulic oil discharged from the first hydraulic pump 2 is guided to the hoist control valve 7 and the hydraulic oil discharged from the second hydraulic pump 3 is guided to the steering circuit 33.

[0084] The fan control valve 5 has a neutral position (5N) that connects the first hydraulic pump 2 and the merging control valve 6 and blocks communication between the first hydraulic pump 2 and the fan motor (hydraulic motor) 8, and a forward rotation position (5F) and a reverse rotation position (5R) that block communication between the first hydraulic pump 2 and the merging control valve 6 and connect the first hydraulic pump 2 and the fan motor 8.

[0085] When the merging control valve 6 is in the merging position (6C), it connects the first hydraulic pump 2 and the hoist control valve 7 via the fan control valve 5 in the neutral position (5N), and also connects the second hydraulic pump 3 and the hoist control valve 7, while blocking communication between the second hydraulic pump 3 and the steering circuit 33. When the merging control valve 6 is in the non-merging position (6N) or (6D), it connects the first hydraulic pump 2 and the hoist control valve 7 via the fan control valve 5 in the neutral position (5N), and also connects the second hydraulic pump 3 and the steering circuit 33, while blocking communication between the second hydraulic pump 3 and the hoist control valve 7.

[0086] With this configuration, when the hoist cylinder 10 is not being driven, such as during driving, and the fan control valve 5 is switched to the neutral position (5N), the hydraulic fluid discharged from the first hydraulic pump 2 is guided to the hydraulic fluid tank 22 through the fan control valve 5, the merging control valve 6, and the hoist control valve 7. This suppresses energy loss when the cooling fan 9 is stopped during driving. As a result, the fuel consumption of the dump truck 100 can be reduced. Furthermore, since the hydraulic fluid discharged from the second hydraulic pump 3 is guided to the steering circuit 33 through the merging control valve 6, the truck can be turned in any direction while driving.

[0087] The steering circuit 33 operates frequently while driving. If the configuration is such that the hydraulic fluid from the first hydraulic pump 2 is merged with the hydraulic fluid from the second hydraulic pump 3 and directed to the steering circuit 33 when the cooling fan 9 stops, then the operating pressure of the steering circuit 33 will be generated on the first hydraulic pump 2. In contrast, in this embodiment, when the cooling fan 9 stops while the dump truck 100 is driving, the operating pressure of the steering circuit 33 does not act on the first hydraulic pump 2, thus improving the lifespan of the first hydraulic pump 2.

[0088] (2) The control device 50 determines whether the cooling water temperature (temperature of the object to be cooled) Tc detected by the temperature sensor 25 is equal to or greater than the first threshold Tc1. If the cooling water temperature Tc is equal to or greater than the first threshold Tc1, the control device 50 switches the fan control valve 5 to the forward rotation position (rotation position) 5F. If the cooling water temperature Tc is less than the first threshold Tc1, the control device 50 switches the fan control valve 5 to the neutral position (5N).

[0089] In this embodiment, the dump truck 100 uses the same hydraulic pump (first hydraulic pump 2) to supply hydraulic fluid to both the hoist cylinder 10 and the fan motor 8, as the hoist cylinder 10 is used infrequently. Furthermore, a single control valve, the fan control valve 5, has both the function of switching the supply destination of the hydraulic fluid discharged from the first hydraulic pump 2 to either the hoist cylinder 10 or the fan motor 8, and the function of switching the rotation and stopping of the fan motor 8. Therefore, it is not necessary to provide separate control valves to realize each function, thus simplifying the configuration of the hydraulic circuit. In addition, if a low-load driving state continues and the cooling water temperature Tc falls below the first threshold Tc1 due to the cooling air and driving airflow, the fan control valve 5 is switched to the neutral position (5N). As a result, the generation of cooling air by the cooling fan 9 stops, thus preventing overcooling of the engine coolant. In other words, according to this embodiment, a dump truck (transport vehicle) 100 can be provided that prevents overcooling of the engine coolant (the object to be cooled) with a simple configuration.

[0090] (3) When the coolant temperature Tc is equal to or greater than the first threshold Tc1, the control device 50 controls the discharge capacity q of the first hydraulic pump 2 to a discharge capacity greater than the minimum capacity qmin, and when the coolant temperature Tc is less than the first threshold Tc1, it controls the discharge capacity q of the first hydraulic pump 2 to the minimum capacity qmin. With this configuration, when the coolant temperature Tc falls below the first threshold Tc1 during driving, the fan control valve 5 is switched to the neutral position (5N), and the discharge capacity q of the first hydraulic pump 2 is reduced. As a result, the load on the engine 1 is reduced, and fuel consumption during driving can be suppressed.

[0091] (4) When the cooling water temperature Tc is greater than or equal to the first threshold Tc1 and less than the second threshold Tc2, the control device 50 increases the discharge capacity q of the first hydraulic pump 2 as the cooling water temperature Tc increases. Also, when the cooling water temperature Tc is greater than or equal to the second threshold Tc2, the control device 50 controls the discharge capacity q of the first hydraulic pump 2 to its maximum capacity qmax.

[0092] With this configuration, the higher the coolant temperature Tc, the faster the cooling fan 9 rotates, thereby increasing the cooling effect on the engine coolant. By controlling the rotation speed of the cooling fan 9 according to the coolant temperature Tc, it is possible to prevent the engine coolant temperature from becoming too low or too high.

[0093] (5) The merging control valve 6 has a neutral position (6N) in which the hydraulic fluid discharged from the first hydraulic pump 2 is directed to the hoist control valve 7 and the hydraulic fluid discharged from the second hydraulic pump 3 is directed to the steering circuit 33, and a diversion position (6D) in which the hydraulic fluid discharged from the first hydraulic pump 2 is directed to the hoist control valve 7 and the hydraulic fluid discharged from the second hydraulic pump 3 is diverted and directed to the steering circuit 33 and the attachment actuator 86. With this configuration, when the cooling fan 9 is stopped while the dump truck 100 is in motion, the load on the engine 1 can be reduced regardless of whether the merging control valve 6 is switched to the neutral position (6N) or the diversion position (6D).

[0094] (6) The fan control valve 5 has two rotational positions: a forward rotation position (5F) for rotating the fan motor 8 in the forward direction, and a reverse rotation position (5R) for rotating the fan motor 8 in the reverse direction opposite to the forward direction. When the fan control valve 5 is switched to the reverse rotation position (5R), cooling air is generated that flows forward from the cooling fan 9, removing dust and debris adhering to the filters of the vents in the front grille 107 and the gaps in the radiator (heat exchanger) 23. Therefore, according to this embodiment, the cooling performance of the radiator 23, which has been reduced by dust and debris, can be easily restored.

[0095] The control device 50 can be configured to temporarily switch the fan control valve 5 to the reverse position (5R) for a predetermined period, for example, during maintenance of the dump truck 100 or periodically. When a service technician operates the input device during maintenance and a command to reverse the cooling fan 9 is input from the input device to the control device 50, the control device 50 switches the fan control valve 5 to the reverse position (5R) for a predetermined time. The control device 50 also measures the operating time of the dump truck 100 using a timer function and switches the fan control valve 5 to the reverse position (5R) for a predetermined time each time a predetermined operating time has elapsed. The control device 50 may also temporarily switch the fan control valve 5 to the reverse position (5R) when the engine 1 is started or stopped.

[0096] (7) The hydraulic system 110 includes a pair of motor oil passages 81 and 82 connecting the fan control valve 5 and the fan motor 8, and a pair of check valves 13 and 14 provided between the pair of motor oil passages 81 and 82 and the hydraulic oil tank 22. In this configuration, when the fan control valve 5 is switched to the neutral position (5N), for example, when the cooling fan 9 rotates due to the airflow from the vehicle, hydraulic oil is supplied from the hydraulic oil tank 22 to the intake port of the fan motor 8 through the check valves 13 and 14, and also from the hydraulic oil tank 22 to the intake port of the fan motor 8 through the fan control valve 5. Therefore, it is possible to suppress negative pressure at the intake port of the fan motor 8 and prevent the occurrence of cavitation. In other words, it is possible to prevent damage to the fan motor 8 caused by cavitation. In addition to the check valves 13 and 14, hydraulic fluid is supplied from the hydraulic fluid tank 22 to the intake port of the fan motor 8 through the fan control valve 5. Therefore, compared to the case where hydraulic fluid is supplied only through the check valves 13 and 14, cavitation can be effectively prevented. The same applies when the fan control valve 5 is switched to the neutral position (5N) when the cooling fan 9 is rotating in the forward or reverse direction, and the cooling fan 9 continues to rotate due to inertia. In other words, when the cooling fan 9 rotates due to inertia, hydraulic fluid is supplied from the hydraulic fluid tank 22 to the intake port of the fan motor 8 through the communication passage 5c of the fan control valve 5 and the check valve 13 or check valve 14, thereby suppressing negative pressure on the intake side of the fan motor 8.

[0097] Furthermore, when the spool of the fan control valve 5 is in the neutral position (5N), the motor oil passage 81 and the motor oil passage 82 are in communication. In other words, the fan control valve 5 according to this embodiment is a so-called neutral-free type directional control valve. Therefore, the hydraulic fluid from the discharge-side motor oil passage is also supplied to the suction-side motor oil passage through the fan control valve 5. Accordingly, according to this embodiment, cavitation can be prevented more effectively than when the pair of motor oil passages 81 and 82 are not in communication in the neutral position (5N) (when a neutral-block type directional control valve is provided).

[0098] <Second Embodiment> A dump truck (transport vehicle) according to the second embodiment of the present invention will be described with reference to Figures 9 and 10. Components identical or equivalent to those described in the first embodiment will be given the same reference numerals, and the differences will be primarily explained.

[0099] The control device 50 according to the second embodiment has the functions described below in addition to the functions described in the first embodiment. Figure 9 is a functional block diagram of the control device 50 according to the second embodiment. As shown in Figure 9, a rotational speed sensor 41 is connected to the control device 50. The rotational speed sensor 41 detects the rotational speed N of the engine 1 (hereinafter also referred to as engine rotational speed) and outputs a signal representing the detection result to the control device 50.

[0100] The determination unit 54 determines the state of the engine 1 based on the detection result of the rotational speed sensor 41. The valve control unit 55 controls the switching position of the merging control valve 6 based on the determination result of the determination unit 54. The pump control unit 56 controls the discharge capacity q of the first hydraulic pump 2 and the second hydraulic pump 3 based on the determination result of the determination unit 54.

[0101] Figure 10 is a flowchart showing an example of the processing flow of loss reduction control during engine startup, which is performed by the control device 50 according to the second embodiment. The process shown in the flowchart of Figure 10 starts when the ignition switch (not shown) is turned on, that is, when the ignition power is supplied. The ignition switch is, for example, an engine key switch having an off position, an on position and a start position. When the ignition switch is operated from the off position to the on position, the ignition power is turned on. That is, power is supplied to the control device 50, and the control device 50 starts up. When the ignition switch is operated from the on position to the start position, the engine 1 is started by the starter motor 40.

[0102] In step S220, the determination unit 54 determines whether the engine 1 is running, that is, whether the engine 1 is being cranked by the starter motor 40, based on the engine rotation speed N detected by the rotation speed sensor 41. For example, the determination unit 54 determines whether the engine rotation speed N is greater than 0. If the engine rotation speed N is 0, the determination unit 54 determines that the engine 1 is not running. If the engine rotation speed N is greater than 0, the determination unit 54 determines that the engine 1 is running and proceeds to step S230. The determination unit 54 repeatedly executes the process in step S220 at a predetermined control cycle until it is determined that the engine 1 is running.

[0103] In step S230, the pump control unit 56 outputs control signals to the regulators 2a and 3a to set the discharge capacity q of the first hydraulic pump 2 to the minimum capacity qmin, and proceeds to step S240.

[0104] In step S240, the valve control unit 55 outputs an ON signal to the solenoid valve 20 and an OFF signal to the solenoid valve 21, switching the merging control valve 6 to the merging position (6C). Although not shown in the diagram, the valve control unit 55 also outputs OFF signals to the solenoid valves 16-19. As a result, the hoist control valve 7 is held in the neutral position (7N), and the fan control valve 5 is held in the neutral position (5N). Once the process of switching the merging control valve 6 to the merging position (6C) (S240) is completed, the process proceeds to step S250.

[0105] In step S250, the determination unit 54 determines whether or not the engine 1 has started based on the engine rotation speed N detected by the rotation speed sensor 41. For example, if the engine rotation speed N is greater than or equal to the idling rotation speed (speed threshold) Ni, the determination unit 54 determines that the engine 1 has started and proceeds to step S270. If the engine rotation speed N is less than the idling rotation speed (speed threshold) Ni, the determination unit 54 determines that the engine 1 has not started and returns to step S230. The speed threshold for determining whether or not the engine 1 has started may be slightly lower than the idling rotation speed Ni.

[0106] Furthermore, the method for determining when engine 1 has started is not limited to the method described above, and the following determination methods may also be adopted. For example, the determination unit 54 determines that engine 1 has started if the state in which the engine rotational speed N is equal to or greater than the speed threshold continues for a predetermined time. The determination unit 54 determines that engine 1 has not started if the state in which the engine rotational speed N is equal to or greater than the speed threshold does not continue for a predetermined time.

[0107] In step S270, the valve control unit 55 outputs an off signal to the solenoid valve 20 and an off signal to the solenoid valve 21, switching the merging control valve 6 to the neutral position (6N), and ending the process shown in the flowchart of Figure 10. After the process shown in the flowchart of Figure 10 is completed, the control device 50 proceeds to the process shown in the flowchart of Figure 7.

[0108] In the dump truck 100 according to this second embodiment, the main operation of the hydraulic system 110 when the engine 1 is started by the starter motor 40 will be described. When the operator moves the ignition switch from the off position to the on position and then to the start position, power is supplied to the starter motor 40, and the starter motor 40 is driven. This starts the cranking of the engine 1 by the starter motor 40. During the cranking operation, the rotational speed of the engine 1 has not reached the idling speed, which is the minimum rotational speed after the engine has finished starting.

[0109] The control device 50 determines whether or not the engine (prime mover) 1 is running, and if it determines that the engine 1 is running, it outputs a control signal (an ON signal to the solenoid valve 20) to switch the merging control valve 6 to the merging position (6C) (S220, S240). The fan control valve 5 and the hoist control valve 7 are held in the neutral positions (5N) and (7N), respectively. As a result, the first hydraulic pump 2 and the hydraulic oil tank 22 are in communication via the fan control valve 5, the merging control valve 6, and the hoist control valve 7. When the engine 1 is started by the starter motor 40, the merging control valve 6 is switched to the merging position (6C), and the hydraulic oil discharged from the first hydraulic pump 2 and the hydraulic oil discharged from the second hydraulic pump 3 merge and are discharged into the hydraulic oil tank 22 through the center bypass line CL. Therefore, according to this embodiment, the load on the second hydraulic pump 3 can be reduced compared to when the engine 1 is started with the merging control valve 6 in the neutral position (6N). As a result, the load acting on the engine 1 can be reduced, and thus the starting performance of the engine 1 by the starter motor 40 can be improved.

[0110] Furthermore, when the control device 50 determines that the engine 1 is starting, it controls the discharge capacity q of the first hydraulic pump 2 and the second hydraulic pump 3 to the minimum capacity qmin (S220, S230). With this configuration, for example, when the discharge capacity q of the first hydraulic pump 2 is controlled to a value corresponding to the coolant temperature Tc during engine startup, the load acting on the engine 1 can be reduced compared to when the engine 1 is started with the discharge capacity q of the first hydraulic pump 2 and the second hydraulic pump 3 greater than the minimum capacity qmin. This further improves the starting performance of the engine 1.

[0111] Thus, according to this second embodiment, in addition to the effects and advantages described in the first embodiment, engine starting performance can be improved. In particular, in winter when the hydraulic fluid is cold, or in cold climates and other low-temperature environments, the load on the hydraulic pump tends to increase. According to this second embodiment, a dump truck 100 with good engine starting performance even in low-temperature environments can be provided.

[0112] <Third Embodiment> A dump truck (transport vehicle) according to the third embodiment of the present invention will be described with reference to Figures 11 and 12. Components identical or equivalent to those described in the first embodiment will be given the same reference numerals, and the differences will be primarily explained.

[0113] In the control device 50 according to the first embodiment, when the operating position of the operating device 91 for the cargo bed was in the raised or lowered position, the fan control valve 5 was kept in the neutral position (5N) regardless of the coolant temperature Tc. In contrast, in the control device 50 according to the third embodiment, when the coolant temperature Tc rises to near the alarm temperature, the fan control valve 5 is switched to the forward rotation position (5F) even when the operating position of the operating device 91 for the cargo bed is in the raised or lowered position. The alarm temperature is the temperature at which an alarm is output to prevent the engine 1 from overheating.

[0114] In the control device 50 according to the third embodiment, when the operating device 91 is operated to the raised or lowered position while the cooling water temperature Tc is less than the third threshold Tc3 which is higher than the second threshold Tc2, the control device 50 prioritizes the operation of the hoist cylinder 10, and when the operating device 91 is operated to the raised or lowered position while the cooling water temperature Tc is equal to or greater than the third threshold Tc3, the control device 50 prioritizes the operation of the fan motor 8. The third threshold Tc3 corresponds to, for example, a temperature slightly lower than the alarm temperature and is stored in advance in the non-volatile memory 52.

[0115] Figure 11 is a functional block diagram of the control device 50 according to the third embodiment. The determination unit 54 determines whether the cooling water temperature Tc detected by the temperature sensor 25 is equal to or greater than the third threshold Tc3.

[0116] The determination unit 54 determines the operating position of the operating device 91, i.e., what kind of operation was performed on the hoist cylinder 10, based on the signal representing the operating position output from the operating device 91. Specifically, the determination unit 54 determines whether or not a hoist raising operation is performed by the operating device 91 to switch the hoist control valve 7 to the raised position (7R). The determination unit 54 determines whether or not a hoist lowering operation is performed by the operating device 91 to switch the hoist control valve 7 to the lowered position (7L). The determination unit 54 determines whether or not a floating operation is performed by the operating device 91 to switch the hoist control valve 7 to the floating position (7F).

[0117] Figure 12 is a table showing the relationship between the operating position of the loading platform control device 91, the cooling water temperature Tc, and the switching positions of each control valve 5 to 7. As shown in Figure 12, the valve control unit 55 controls the hoist control valve 7, the merging control valve 6, and the fan control valve 5 by outputting control signals to the solenoid valves 16 to 21 based on the determination result of the determination unit 54.

[0118] When the operating position of the operating device 91 is in the neutral position, i.e., when the operating device 91 is in a non-operated state (initial state), the valve control unit 55 holds the hoist control valve 7 in the neutral position (7N) and holds the junction control valve 6 in the neutral position (6N). When the operating position of the operating device 91 is in the raised position, i.e., when the operating device 91 is performing a hoist raising operation, the valve control unit 55 switches the hoist control valve 7 to the raised position (7R) and switches the junction control valve 6 to the junction position (6C). When the operating position of the operating device 91 is in the lowered position, i.e., when the operating device 91 is performing a hoist lowering operation, the valve control unit 55 holds the junction control valve 6 in the neutral position (6N) and switches the hoist control valve 7 to the lowered position (7L). When the operating position of the operating device 91 is the floating position, that is, when the floating operation is being performed by the operating device 91, the valve control unit 55 holds the junction control valve 6 in the neutral position (6N) and switches the hoist control valve 7 to the floating position (7F).

[0119] When the operating position of the operating device 91 is in the neutral position or floating position, the valve control unit 55, as in the first embodiment, holds the fan control valve 5 in the neutral position (5N) when the cooling water temperature Tc is less than the first threshold Tc1, and switches the fan control valve 5 to the forward position (5F) when the cooling water temperature Tc is equal to or greater than the first threshold Tc1.

[0120] On the other hand, when the operating position of the operating device 91 is in the raised or lowered position, the valve control unit 5 holds the fan control valve 5 in the neutral position (5N) when the cooling water temperature Tc is less than the third threshold Tc3, and switches the fan control valve 5 to the forward rotation position (5F) when the cooling water temperature Tc is equal to or greater than the third threshold Tc3.

[0121] As described above, in this third embodiment, when a hoist raising operation is performed by the operating device 91, the control device 50 switches the hoist control valve 7 to the raised position and switches the confluence control valve 6 to the confluence position (6C). Furthermore, if a hoist raising operation is performed when the cooling water temperature Tc is less than the third threshold Tc3, the control device 50 switches the fan control valve 5 to the neutral position (5N) even if the cooling water temperature Tc is equal to or greater than the first threshold Tc1. As a result, the hydraulic fluid discharged from both the first hydraulic pump 2 and the second hydraulic pump 3 merges at the confluence control valve 6 and is supplied to the hoist cylinder 10. Consequently, the hoist cylinder 10 can be extended smoothly.

[0122] On the other hand, when the hoist raising operation is performed while the cooling water temperature Tc is equal to or greater than the third threshold Tc3, the control device 50 switches the fan control valve 5 to the forward rotation position (5F). As a result, the hydraulic fluid discharged from the first hydraulic pump 2 is supplied to the fan motor 8 through the fan control valve 5, and the hydraulic fluid discharged from the second hydraulic pump 3 is supplied to the hoist cylinder 10 through the merging control valve 6. As a result, the hoist cylinder 10 can be extended while the cooling fan 9 generates cooling air to cool the engine cooling water. Therefore, according to this third embodiment, overheating of the engine 1 can be prevented.

[0123] The following modifications are also within the scope of the present invention, and it is possible to combine the configurations shown in the modifications with the configurations described in the embodiments described above, or to combine the configurations described in the different embodiments described above, or to combine the configurations described in the following different modifications.

[0124] <Example 1> In the above embodiment, an example was described in which the pump control unit 56 controls the discharge capacity q of the first hydraulic pump 2 based on a capacity control table that defines the relationship between the cooling water temperature Tc and the discharge capacity q of the first hydraulic pump 2. However, the method for controlling the discharge capacity q of the first hydraulic pump 2 is not limited to the method described in the above embodiment. For example, the pump control unit 56 may control the discharge capacity q of the first hydraulic pump 2 based on a mathematical formula (function) that defines the relationship between the cooling water temperature Tc and the discharge capacity q of the first hydraulic pump 2.

[0125] Furthermore, the pump control unit 56 may control the discharge capacity q based on the determination result of the determination unit 54 without using a capacity control table and mathematical formulas. For example, if the pump control unit 56 determines that the cooling water temperature Tc is less than the first threshold Tc1, it controls the discharge capacity q to the minimum capacity qmin, and if it determines that the cooling water temperature Tc is equal to or greater than the second threshold Tc2, it controls the discharge capacity q to the maximum capacity qmax. In this case, during the process of the cooling water temperature Tc rising from a state where it is less than the first threshold Tc1 to the second threshold Tc2, the discharge capacity q is controlled to the minimum capacity qmin, and when the cooling water temperature Tc exceeds the second threshold Tc2, the discharge capacity q is controlled to the maximum capacity qmax. Also, during the process of the cooling water temperature Tc falling from a state where it is equal to or greater than the second threshold Tc2 to the first threshold Tc1, the discharge capacity q is controlled to the maximum capacity qmax, and when the cooling water temperature Tc falls below the first threshold Tc1, the discharge capacity q is controlled to the minimum capacity qmin.

[0126] <Modification 2> In the second embodiment, an example was described in which the determination unit 54 determines whether or not the engine 1 is running based on the detection result of the rotational speed sensor 41. However, the method for determining whether or not the engine 1 is running is not limited to this. For example, the determination unit 54 may determine that the engine 1 is running if the ignition switch (engine key switch) is operated to the start position, and determine that the engine 1 is not running if it is not operated to the start position.

[0127] <Variation 3> In the second embodiment, an example was described in which the discharge capacity q of the first hydraulic pump 2 and the second hydraulic pump 3 is controlled to the minimum capacity qmin while the engine 1 is running. However, the process in step S230 of Figure 10 may be omitted.

[0128] <Modification 4> In the first embodiment, an example was described in which the prime mover driving the first hydraulic pump 2 and the second hydraulic pump 3 is an engine 1, but the prime mover may be an electric motor.

[0129] <Modification 5> In the above embodiment, an example was described in which the object to be cooled by the cooling air is the engine coolant that cools the engine 1, but the object to be cooled by the cooling air is not limited to this. For example, the object to be cooled by the cooling air may be the coolant that cools the brake system. Also, if the driving source of the running gear that moves the vehicle body 101 is a running electric motor and a running inverter that controls the running electric motor, the object to be cooled by the cooling air may be the coolant that cools the running inverter.

[0130] Furthermore, the substance to be cooled may be hydraulic fluid. An oil cooler cools hydraulic fluid by exchanging heat between the hydraulic fluid and cooling air. In this case, the circulation system for the substance to be cooled is composed of a hydraulic circuit including a hydraulic fluid tank 22, a first hydraulic pump 2, and a second hydraulic pump 3. The viscosity of the hydraulic fluid increases as the temperature of the hydraulic fluid decreases. Therefore, if the hydraulic fluid becomes supercooled, high-viscosity hydraulic fluid will be discharged from the first hydraulic pump 2 and the second hydraulic pump 3, resulting in a high pressure loss in the oil passage. As a result, the load on the first hydraulic pump 2 and the second hydraulic pump 3 increases, worsening fuel consumption. However, according to a modified version of this embodiment, when the temperature of the hydraulic fluid falls below a first threshold Tc1, the rotation of the cooling fan 9 stops, preventing supercooling of the hydraulic fluid, and thus preventing an increase in the load on the first hydraulic pump 2 and the second hydraulic pump 3.

[0131] <Variation 6> In the above embodiment, the case in which cooling using the cooling fan 9 becomes unnecessary was described as when, under low-load driving conditions, the temperature of the engine coolant falls below the first threshold Tc1 due to the airflow from driving and the cooling airflow. However, the cases in which engine coolant cooling becomes unnecessary are not limited to this. For example, in low-temperature environments, engine coolant cooling may become unnecessary even if the radiator 23 is not positioned to directly receive the airflow from driving. In other words, the heat exchanger such as the radiator 23 is not limited to being located at the front of the vehicle body 101. The present invention can also be applied to transport vehicles in which heat exchangers are located at the sides or rear of the vehicle body 101.

[0132] <Example 7> In the above embodiment, an example was described in which the confluence control valve 6 is a directional control valve with 6 ports and 3 positions. However, the confluence control valve 6 may also be a directional control valve with 6 ports and 2 positions that does not have a diversion position (6D).

[0133] Although embodiments of the present invention have been described above, these embodiments only represent a part of the application examples of the present invention, and are not intended to limit the technical scope of the present invention to the specific configurations of the above embodiments. [Explanation of symbols]

[0134] 1...Engine (prime mover), 2...First hydraulic pump, 2a...Regulator, 3...Second hydraulic pump, 3a...Regulator, 4...Pilot pump, 5...Fan control valve, 5a, 5b...Hydraulic pilot section, 5F...Forward position (rotation position), 5N...Neutral position, 5R...Reverse position, 6...Merge control valve, 6a, 6b...Hydraulic pilot section, 6C...Merge position, 6D...Dividing position (non-merging position), 6N...Neutral position (non-merging position), 7...Hoist control valve, 7a, 7b...Hydraulic pilot section, 7F...Floating position, 7L...Lowered position, 7N...Neutral position, 7R...Raised position, 8...F 9... Cooling fan, 10... Hoist cylinder (hydraulic cylinder), 11,12... Relief valve, 13,14... Check valve, 15... Pilot relief valve, 16~21... Solenoid valve, 22... Hydraulic oil tank, 23... Radiator (heat exchanger), 24... Cooling water circulation pump, 25... Temperature sensor, 26... Object to be cooled, 27... Cooling water tank, 28... Cooling water system (circulation system), 29... Handle, 30... Hydraulic motor, 31... Steering control valve, 33... Steering circuit, 34,35... Steering cylinder, 36,37... Steering 38…High-pressure oil passage, 39…Low-pressure oil passage, 40…Starter motor, 41…Rotation speed sensor, 42…Accumulator, 50…Control device, 51…Processing device, 52…Non-volatile memory (storage device), 53…Volatile memory (storage device), 54…Determination unit, 55…Valve control unit, 56…Pump control unit, 61~63…Supply oil passage, 68,69…Return oil passage, 71,72…Actuator oil passage, 80…Generator, 81,82…Motor oil passage, 85…Actuator oil passage, 86…Attachment actuator, 91…Operating device, 91a…Operating lever, 100 ...dump truck (transport vehicle), 101...body, 102...support base, 103...cab, 104...cargo bed, 105...front wheels, 106...rear wheels, 107...front grille, 110...hydraulic system, CL...center bypass line (oil passage), N...engine rotational speed, Ni...idling rotational speed (speed threshold), q...discharge volume (displacement volume), Q...discharge flow rate, qmax...maximum volume, Qmax...maximum flow rate, qmin...minimum volume, Qmin...minimum flow rate, Tc...cooling water temperature (temperature of the object being cooled), Tc1...first threshold, Tc2...second threshold, Tc3...third threshold

Claims

1. A cargo bed that is rotatably mounted on the vehicle body, A first hydraulic pump and a second hydraulic pump driven by a prime mover, A hydraulic motor driven by hydraulic fluid supplied from the first hydraulic pump, A cooling fan driven by the aforementioned hydraulic motor, A heat exchanger that cools the object to be cooled by the cooling air generated by the aforementioned cooling fan, A hoist cylinder is provided between the cargo bed and the vehicle body so as to be extendable and retractable, and is driven by hydraulic fluid supplied from the first hydraulic pump, A fan control valve controls the flow of hydraulic fluid supplied from the first hydraulic pump to the hydraulic motor, A hoist control valve controls the flow of hydraulic fluid supplied from the first hydraulic pump to the hoist cylinder, A transport vehicle comprising a steering circuit having a steering cylinder driven by hydraulic fluid supplied from the second hydraulic pump, The system further includes a merging control valve having a merging position that merges the hydraulic fluid discharged from the second hydraulic pump with the hydraulic fluid discharged from the first hydraulic pump and guides it to the hoist control valve, and a non-merging position that guides the hydraulic fluid discharged from the first hydraulic pump to the hoist control valve and the hydraulic fluid discharged from the second hydraulic pump to the steering circuit. The fan control valve, the merging control valve, and the hoist control valve are connected in tandem to the oil passage connecting the first hydraulic pump and the hydraulic oil tank. The fan control valve is located upstream of the merging control valve. The aforementioned merging control valve is located upstream of the hoist control valve. The aforementioned fan control valve is A neutral position that connects the first hydraulic pump and the merging control valve, and disconnects the communication between the first hydraulic pump and the hydraulic motor, It has a rotational position that disconnects the communication between the first hydraulic pump and the merging control valve, and connects the first hydraulic pump and the hydraulic motor, The aforementioned merging control valve is When in the aforementioned merging position, the first hydraulic pump and the hoist control valve are connected via the fan control valve in the neutral position, and the second hydraulic pump and the hoist control valve are connected, while the communication between the second hydraulic pump and the steering circuit is interrupted. When in the non-merging position, the first hydraulic pump and the hoist control valve are connected via the fan control valve in the neutral position, the second hydraulic pump and the steering circuit are connected, and the connection between the second hydraulic pump and the hoist control valve is blocked. A transport vehicle characterized by the following features.

2. In the transport vehicle described in claim 1, The prime mover is an engine that is started by a starter motor. The control device includes a device that determines whether the engine is running or not, and if it is determined that the engine is running, outputs a control signal to switch the merging control valve to the merging position. A transport vehicle characterized by the following features.

3. In the transport vehicle described in claim 2, When the control device determines that the engine is running, it controls the discharge capacity of the first hydraulic pump and the second hydraulic pump to the minimum capacity. A transport vehicle characterized by the following features.

4. In the transport vehicle described in claim 1, A temperature sensor for detecting the temperature of the object to be cooled, The system includes a control device that controls the fan control valve based on the detection result of the temperature sensor, The control device is The temperature of the object to be cooled, as detected by the temperature sensor, is determined to be equal to or greater than a first threshold. If the temperature of the object to be cooled is equal to or greater than the first threshold, the fan control valve is switched to the rotation position. If the temperature of the object to be cooled is below the first threshold, the fan control valve is switched to the neutral position. A transport vehicle characterized by the following features.

5. In the transport vehicle described in claim 4, The control device is If the temperature of the object to be cooled is equal to or greater than the first threshold, the discharge capacity of the first hydraulic pump is controlled to a discharge capacity greater than the minimum capacity. If the temperature of the object to be cooled is below the first threshold, the discharge capacity of the first hydraulic pump is controlled to the minimum capacity. A transport vehicle characterized by the following features.

6. In the transport vehicle described in claim 5, The control device is If the temperature of the object to be cooled is above the first threshold and below the second threshold, the discharge capacity of the first hydraulic pump is increased as the temperature of the object to be cooled increases. If the temperature of the object to be cooled is equal to or greater than the second threshold, the discharge capacity of the first hydraulic pump is controlled to its maximum capacity. A transport vehicle characterized by the following features.

7. In the transport vehicle described in claim 6, The hoist cylinder is equipped with an operating device for operating the hoist cylinder, The hoist control valve has a raised position in which the hoist cylinder is extended and the platform is rotated upward, a lowered position in which the hoist cylinder is retracted and the platform is rotated downward, and a neutral position in which the platform is held. The control device is It is determined whether the temperature of the object to be cooled, as detected by the temperature sensor, is above a third threshold, which is higher than the second threshold. The operating device determines whether or not a hoist raising operation is being performed to switch the hoist control valve to the raised position. When the hoist raising operation is performed by the operating device, the hoist control valve is switched to the raised position and the merging control valve is switched to the merging position. If the hoist lifting operation is performed when the temperature of the object to be cooled is below the third threshold, the fan control valve is switched to the neutral position even if the temperature of the object to be cooled is above the first threshold. If the hoisting operation is performed when the temperature of the object to be cooled is equal to or greater than the third threshold, the fan control valve is switched to the rotation position. A transport vehicle characterized by the following features.

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