Transport vehicles

Abstract

To prevent supercooling of an object with a simple configuration.SOLUTION: A transport vehicle comprises: a cooling fan driven with a hydraulic motor; a heat exchanger arranged in a front section of a vehicle body; a fan control valve controlling a flow of hydraulic oil supplied to the hydraulic motor; a cylinder control valve controlling the flow of the hydraulic oil supplied to the hydraulic cylinder; and a control device. The fan control valve and the cylinder control valve are connected in tandem to a center bypass line. The fan control valve has a neutral position to communicate the hydraulic pump with the cylinder control valve and intake and discharge ports of the hydraulic motor with a hydraulic oil tank and a rotation position to communicate the hydraulic pump with the intake port of the hydraulic motor and the discharge port of the hydraulic motor with the hydraulic oil tank. The control device switches the fan control valve to the rotation position when a temperature of a cooling object is equal to or higher than a first threshold. The control device switches the fan control valve to the neutral position when the temperature thereof is less than the first threshold and adjusts a discharge capacity of the hydraulic pump to a minimum capacity.SELECTED DRAWING: Figure 3

Description

Technical Field

[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 control device that performs a first control for setting the rotational speed of the cooling fan according to the temperature of the cooling target when the temperature of the cooling target is higher than the lower threshold temperature, and a second control for setting the rotational speed of the cooling fan to the minimum rotational speed and performing reverse rotation when the temperature of the cooling target is lower than the lower threshold temperature.

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 such as a dump truck, a heat exchanger such as a radiator and a cooling fan may be arranged at the front of the vehicle body. Also, the load during traveling of the transport vehicle changes depending on the presence or absence of a load, the road gradient, etc. For example, traveling with no load, traveling on flat ground, etc. are traveling states with a lower load compared to traveling with a load, traveling uphill, etc. If cooling air continues to be generated by the cooling fan in a traveling state with a low load, there is a risk that the cooling target (engine cooling water, etc.) will be overcooled by the cooling air and the traveling wind. Here, in order to prevent overcooling, it is conceivable to stop the cooling fan. As a method of stopping the cooling fan, a method of shutting off the supply of hydraulic oil from a hydraulic source such as a hydraulic pump to a hydraulic motor that drives the cooling fan can be considered.

[0005] In the vehicle described in Patent Document 1, a control valve (switching valve) is provided upstream of the fan control valve that controls the rotation direction of the fan, which switches the destination of the hydraulic fluid supply from the hydraulic power source to either the fan control valve or the cargo handling device. In other words, in the vehicle described in Patent Document 1, the hydraulic power source for the cargo handling device and the hydraulic motor of the cooling fan are shared.

[0006] Therefore, in the configuration described in Patent Document 1, for example, under low-load driving conditions, overcooling can be prevented by switching the supply destination of the hydraulic fluid from the hydraulic source to the cargo handling device, thereby stopping the cooling fan. However, there is a problem in that the hydraulic circuit is equipped with multiple control valves, making the configuration of the hydraulic circuit complex.

[0007] The present invention aims to provide a transport vehicle that can prevent overcooling of the object being cooled with a simple configuration. [Means for solving the problem]

[0008] A transport vehicle according to one aspect of the present invention includes a hydraulic pump driven by a prime mover, a hydraulic motor driven by hydraulic fluid supplied from the hydraulic pump, a cooling fan driven by the hydraulic motor, and a heat exchanger located at the front of the vehicle body that cools the object to be cooled by the cooling air generated by the cooling fan. A cargo bed is provided at the rear of the vehicle body so as to be able to be raised and lowered, A temperature sensor that detects the temperature of the object to be cooled, and a hydraulic pump that is driven by the hydraulic fluid supplied from the hydraulic pump. , the aforementioned cargo bed is raised and lowered A hydraulic cylinder, and a fan control valve that controls the flow of hydraulic fluid supplied from the hydraulic pump to the hydraulic motor, The hydraulic cylinder has a raised position in which it is driven to lift the loading platform, a lowered position in which it is driven to lower the loading platform, and a neutral position in which the supply of hydraulic fluid to the hydraulic cylinder is cut off. A cylinder control valve that controls the flow of hydraulic fluid supplied from the hydraulic pump to the hydraulic cylinder, An operating device for switching the cylinder control valve to the raised position, the lowered position, and the neutral position, A transport vehicle comprising the fan control valve and a control device for controlling the discharge capacity of the hydraulic pump, wherein the fan control valve and the cylinder control valve and The oil passage connecting the hydraulic pump and the hydraulic oil tank at The fan control valve is connected in tandem and positioned upstream of the cylinder control valve. And , Through the aforementioned fan control valveThe hydraulic pump and the cylinder control valve are connected, the connection between the hydraulic pump and the hydraulic motor is blocked, and the suction port and discharge port of the hydraulic motor are connected to the hydraulic oil tank in a neutral position, and the hydraulic pump and the cylinder control valve are connected Through the aforementioned fan control valve The control device has a rotation position that blocks communication, connects the hydraulic pump and the suction port of the hydraulic motor, and connects the discharge port of the hydraulic motor and the hydraulic oil tank. The control device determines whether the temperature of the object to be cooled, as detected by the temperature sensor, is above a first threshold. If the temperature of the object to be cooled is above the first threshold, the control device switches the fan control valve to the rotation position and controls the discharge capacity of the hydraulic pump to a discharge capacity greater than the minimum capacity. If the temperature of the object to be cooled is below the first threshold, the control device switches the fan control valve to the neutral position and controls the discharge capacity of the hydraulic pump to the minimum capacity. Furthermore, if the cylinder control valve is operated to the raised position or the lowered position by the operating device, the fan control valve is controlled to the neutral position regardless of the temperature of the object to be cooled. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a transport vehicle that can prevent overcooling of the object to be cooled with a simple configuration. [Brief explanation of the drawing]

[0010] [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. [Figure 5] Figure 5 shows the relationship between the discharge capacity q (tilt angle) and the discharge flow rate Q of the main 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. [Figure 8] FIG. 8 is a diagram showing the relationship between the switching position of the fan control valve and the discharge flow rate Q of the main pump according to the cooling water temperature Tc.

Mode for Carrying Out the Invention

[0011] Referring to the drawings, a transport vehicle according to an embodiment of the present invention will be described. FIG. 1 is a perspective view showing the appearance of a dump truck 100 which is an example of the transport vehicle according to the embodiment of the present invention. In the following description, unless otherwise specified, the front of the driver's seat (in the figure, the front left direction, see the arrow) is taken as the front of the vehicle body 101.

[0012] The dump truck 100 shown in FIG. 1 is a large one operating in a mine or the like, and includes a vehicle body 101, a cab 103, a loading platform 104, front wheels 105 and rear wheels 106. The cab 103 is supported by a support base 102 and is located on the front side and the left side on the vehicle body 101. The cab 103 forms a driver's cab for the operator of the dump truck 100 to get on and off, and inside it, a driver's seat, an accelerator pedal, a brake pedal, a steering wheel (not shown in any of them), an operating device 91 for the loading platform (see FIG. 3), etc. are provided.

[0013] The loading platform 104 is mounted on the rear part of the vehicle body 101 so as to be able to rise and fall. The loading platform 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 fulcrum by the telescopic operation of a hoist cylinder 10 (see FIG. 3). The front wheels 105 are respectively provided on the left and right of the front part of the vehicle body 101, and the rear wheels 106 are provided on the left and right of the rear part of the vehicle body 101 to support the vehicle body 101 so as to be able to run. The front wheels 105 constitute a steering wheel that is steered (steering operation) by the operator of the dump truck 100. The rear wheels 106 constitute the drive wheels of the dump truck 100 and are rotationally driven by a traveling drive device (not shown).

[0014] A front grill 107 is provided on the front surface of the vehicle body 101. The front grill 107 is provided with a plurality of ventilation holes for taking outside air into the inside of the vehicle body 101.

[0015] 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, 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 the engine cooling water by the cooling air generated by the cooling fan 9 are mounted. 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 a heat exchanger such as an oil cooler for cooling the hydraulic oil may be mounted.

[0016] The engine 1 as the 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.

[0017] The radiator 23 performs heat exchange 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 portion 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.

[0018] Referring to Figure 3, the hydraulic system 110 of the dump truck 100 will be described. As shown in Figure 3, the hydraulic system 110 of the dump truck 100 includes a variable displacement hydraulic pump (hereinafter referred to as the main pump) 2 and a fixed displacement hydraulic pump (hereinafter referred to as the pilot pump) 4 driven by the engine 1, a pair of hoist cylinders (only one is shown in Figure 3) 10 driven by the hydraulic fluid supplied from the main pump 2, a fan motor 8 driven by the hydraulic fluid supplied from the main pump 2, a hydraulic fluid tank 22 in which the hydraulic fluid is stored, a fan control valve 5 and a cylinder control valve 7 provided on the center bypass line CL, which is an oil passage connecting the main pump 2 and the hydraulic fluid tank 22, and a control device 50 that controls various parts of the dump truck 100.

[0019] The main pump 2, driven by the engine 1, draws hydraulic fluid from the hydraulic fluid tank 22 and discharges high-pressure hydraulic fluid (pressurized oil). The discharge port of the main pump 2 is connected to the hydraulic fluid tank 22 via the center bypass line CL. The fan control valve 5 and the cylinder control valve 7 are connected in tandem along the center bypass line CL. The fan control valve 5 controls the flow of hydraulic fluid supplied from the main pump 2 to the fan motor 8 and the flow of hydraulic fluid discharged from the fan motor 8 to the hydraulic fluid tank 22. The cylinder control valve 7 controls the flow of hydraulic fluid supplied from the main pump 2 to the hoist cylinder 10 and the flow of hydraulic fluid discharged from the hoist cylinder 10 to the hydraulic fluid tank 22.

[0020] A supply oil passage 61, branching from the center bypass line CL, is connected to the fan control valve 5. The cylinder control valve 7 is located downstream of the fan control valve 5 in the center bypass line CL. A supply oil passage 62, branching from the center bypass line CL, is connected to the cylinder 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.

[0021] 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 main pump 2 and the hydraulic oil tank 22, respectively, via the fan control valve 5.

[0022] 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.

[0023] 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.

[0024] 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 motor oil passage 82 becomes 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.

[0025] 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.

[0026] The hoist cylinder 10 extends when hydraulic fluid (pressurized oil) discharged from the main 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 releasing soil. The hoist cylinder 10 retracts when hydraulic fluid (pressurized oil) discharged from the main 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.

[0027] The bottom oil chamber 10d and the rod oil chamber 10e of the hoist cylinder 10 are connected to the cylinder 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 main pump 2 and the hydraulic oil tank 22, respectively, via the cylinder 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.

[0028] 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.

[0029] 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.

[0030] 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 main pump 2 and the cylinder control valve 7 are in communication, and the communication between the main pump 2 and the fan motor 8 is blocked. As a result, the hydraulic fluid discharged from the main pump 2 is supplied to the cylinder control valve 7 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.

[0031] 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 main 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 main 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 main 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 main 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 rotation 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.

[0032] Thus, the forward rotation position (5F) and the reverse rotation position (5R) are rotational positions that connect the main pump 2 and the fan motor 8, and rotate the fan motor 8 using the hydraulic fluid discharged from the main pump 2. When the spool of the fan control valve 5 is in the rotational position (5F) or (5R), the communication between the main pump 2 and the cylinder control valve 7 via the center bypass line CL is interrupted.

[0033] The cylinder control valve 7 is configured, for example, as a hydraulic pilot-operated directional control valve with 6 ports and 3 positions. The cylinder 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.

[0034] The cylinder control valve 7 is a switching valve that can switch the spool (valve body) to the raised position (7R), the lowered position (7L), and the neutral position (7N). Under normal circumstances, both the hydraulic pilot sections 7a and 7b of the cylinder 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.

[0035] When the spool of the cylinder 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 cylinder control valve 7 is in the neutral position (7N), the upstream and downstream sides of the cylinder control valve 7 of the center bypass line CL are in communication.

[0036] When the spool of the cylinder 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 cylinder control valve 7 in 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 main 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.

[0037] When the spool of the cylinder 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 cylinder control valve 7 in 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 main 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.

[0038] The pilot pump 4 is connected to a plurality of solenoid valves 16-19 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 16-19 to regulate the pressure in the pilot oil passage. The plurality of solenoid valves 16-19 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 16-19 communicate the hydraulic pilot units 5a, 5b, 7a, 7b with the hydraulic oil tank 22. When a drive control current is input as an on signal, the solenoid valves 16-19 output the generated pilot pressure to the hydraulic pilot units 5a, 5b, 7a, 7b.

[0039] 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 cylinder control valve 7 operate in accordance with the control command (control current) output from the control device 50 in response to the operation of the cargo bed operating device 91.

[0040] 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.

[0041] 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.

[0042] An operating device 91 for switching the cylinder control valve 7 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 (7N), raised position (7R), or lowered position (7L), which correspond to each switching position of the cylinder control valve 7. The operating device 91 outputs an operating signal to the control device 50 according to the operating position.

[0043] 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.

[0044] 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 16-19, regulator 2a, etc.).

[0045] The control device 50 outputs a control signal to the regulator 2a of the main pump 2. The regulator 2a is a capacity control device that variably controls the displacement volume (discharge volume per revolution) of the main pump 2. For example, if the main pump 2 is a swashplate piston pump, the regulator 2a has a tilt actuator that controls the tilt angle (displacement volume) of the swashplate of the main pump 2, and an electromagnetic proportional valve that generates a control pressure for the tilt actuator using the discharge pressure of the main pump 2 as the source pressure.

[0046] 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.

[0047] When the operating device 91 is operated to the neutral position, the control device 50 causes the cylinder control valve 7 to be held in the neutral position (7N). In other words, the control device 50 outputs an off signal to both solenoid valves 18 and 19.

[0048] When the operating device 91 is operated to the raised position, the control device 50 controls the cylinder control valve 7 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 cylinder control valve 7 is switched to the raised position (7R). When the operating device 91 is operated to the lowered position, the control device 50 controls the cylinder control valve 7 to the lowered position (7L). In other words, the control device 50 outputs an OFF signal to the solenoid valve 18 and an ON signal to the solenoid valve 19. As a result, the pilot pressure generated by the solenoid valve 19 acts on the hydraulic pilot unit 7b, and the cylinder control valve 7 is switched to the lowered position (7L).

[0049] The control device 50 controls the switching position of the fan control valve 5 to control the rotation and stopping of the fan motor 8 and the direction of rotation of the fan motor 8. The control device 50 also controls the rotational speed of the fan motor 8 by controlling the discharge capacity q of the main pump 2 via the regulator 2a within a range from a minimum capacity qmin to a maximum capacity qmax. The functions of the control device 50 related to the control of the cooling fan 9 and the main pump 2 will be explained with reference to Figure 4. 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.

[0050] 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 the 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 the 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 of 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.

[0051] 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 of 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 main pump 2.

[0052] When the determination unit 54 determines that the stop condition of 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 via 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, the occurrence of cavitation in the fan motor 8 can be prevented.

[0053] The pump control unit 56 controls the discharge flow rate Q of the main pump 2 based on the cooling water temperature Tc detected by the temperature sensor 25. The discharge flow rate Q of the main pump 2 is determined by the rotational speed of the engine 1 and the discharge capacity (volume) q of the main pump 2. In this embodiment, the pump control unit 56 controls the discharge flow rate Q of the main pump 2 by controlling the discharge capacity q of the main pump 2.

[0054] 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 main pump 2. As shown in Figure 5, when the engine rotation speed is constant, the discharge flow rate Q of the main pump 2 increases proportionally with the increase in the discharge capacity q of the main pump 2. When the discharge capacity q is at its minimum value (0%), the discharge flow rate Q becomes the minimum flow rate Qmin. When the discharge capacity q is at its maximum value (100%), the discharge flow rate Q becomes the maximum flow rate Qmax.

[0055] The pump control unit 56 calculates the discharge capacity q of the main 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.

[0056] The pump control unit 56 refers to the capacity control table and calculates the discharge capacity q of the main 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 main 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 main 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 main 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 main pump 2 to the maximum capacity qmax.

[0057] 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.

[0058] 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.

[0059] 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 main pump 2.

[0060] 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.

[0061] In step S150, the control device 50 outputs a control signal to the regulator 2a to set the discharge capacity q of the main 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 main 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 main 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.

[0062] 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.

[0063] When the processing 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 main pump 2 to the minimum capacity qmin, and the process shown in the flowchart of Figure 7 for this control cycle is completed.

[0064] Although not shown in the diagram, the control device 50 determines whether the operating device 91 is operated to the neutral position, and only if the operating device 91 is operated to the neutral position, it executes the control shown in the flowchart of Figure 7. In other words, if the operating device 91 is not operated to the neutral position (i.e., if the operating device 91 is operated to either 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.

[0065] 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.

[0066] 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 cylinder control valve 7 is held in the neutral position (7N). 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 main pump 2 according to the cooling water temperature Tc. When the cooling water temperature Tc is above the first threshold Tc1 while the dump truck 100 is in motion, 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).

[0067] 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 a first threshold Tc1 or higher and less than a second threshold Tc2, the discharge capacity q of the main pump 2 is controlled according to the coolant temperature Tc. When the coolant temperature Tc further decreases and falls below the first 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). Consequently, 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 main pump 2 to the minimum flow rate Qmin. As a result, the hydraulic fluid discharged from the main pump 2 is discharged into the hydraulic fluid tank 22 through the fan control valve 5 in the neutral position (5N) and the cylinder control valve 7 in the neutral position (7N). Therefore, the pressure loss in the center bypass line CL connecting the main pump 2 and the hydraulic fluid tank 22 is reduced, and the discharge pressure of the main pump 2 can be kept low. As a result, the load on the main pump 2 is reduced, and the load on the engine 1 is reduced. Therefore, according to this embodiment, the energy loss of the main pump 2 can be reduced, and fuel consumption can be suppressed.

[0068] According to the above-described embodiment, the following effects are achieved.

[0069] (1) The fan control valve 5 and the cylinder control valve 7 are connected in tandem to the center bypass line (oil passage) CL that connects the main pump 2 and the hydraulic oil tank 22, and the fan control valve 5 is positioned upstream of the cylinder control valve 7. The fan control valve 5 has a neutral position (5N) that connects the main pump (hydraulic pump) 2 and the cylinder control valve 7, blocks communication between the main pump 2 and the fan motor (hydraulic motor) 8, and connects the inlet and outlet of the fan motor 8 to the hydraulic oil tank 22 via a communication passage 5c, and a forward rotation position (5F) and a reverse rotation position (5R) that block communication between the main pump 2 and the cylinder control valve 7, connects the main pump 2 and the inlet of the fan motor 8, and connects the outlet of the fan motor 8 to the hydraulic oil tank 22. 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. When 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 position (5F) and controls the discharge capacity q of the main pump 2 to a discharge capacity greater than the minimum capacity qmin. When 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) and controls the discharge capacity q of the main pump 2 to the minimum capacity qmin.

[0070] In this embodiment, the dump truck 100 uses the same hydraulic pump (main 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, serves both to switch the supply destination of the hydraulic fluid discharged from the main pump 2 to either the hoist cylinder (hydraulic cylinder) 10 or the fan motor 8, and to switch the fan motor 8 between rotation and stopping. Therefore, there is no need to provide separate control valves for each function, simplifying the hydraulic circuit configuration. Additionally, if low-load driving conditions persist and the cooling water temperature Tc falls below a first threshold Tc1 due to cooling air and driving airflow, the fan control valve 5 is switched to the neutral position (5N). This stops the generation of cooling air by the cooling fan 9, preventing overcooling of the engine coolant. In short, this embodiment provides a dump truck (transport vehicle) 100 with a simple configuration that can prevent overcooling of the engine coolant (the object to be cooled). Furthermore, by controlling the discharge capacity q of the main pump 2 to the minimum capacity qmin, the load on the engine 1 is reduced, thereby suppressing fuel consumption.

[0071] (2) 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 main 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 main pump 2 to its maximum capacity qmax.

[0072] 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.

[0073] (3) 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 that has been reduced by dust and debris can be easily restored.

[0074] 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.

[0075] (4) 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.

[0076] 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).

[0077] 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 following different modifications.

[0078] <Example 1> In the above embodiment, an example was described in which the pump control unit 56 controls the discharge capacity q of the main 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 main pump 2. However, the method for controlling the discharge capacity q of the main 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 main 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 main pump 2.

[0079] 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.

[0080] <Modification 2> In the above embodiment, an example was described in which the prime mover driving the main pump 2 is an engine 1, but the prime mover may also be an electric motor.

[0081] <Variation 3> 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.

[0082] Furthermore, the object 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 object to be cooled is composed of a hydraulic circuit including a hydraulic fluid tank 22 and a main pump 2. 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 main pump 2, resulting in a high pressure loss in the oil passage. As a result, the load on the main pump 2 increases, and fuel consumption worsens. 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 main pump 2.

[0083] 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]

[0084] 1…Engine, 2…Main pump (hydraulic pump), 2a…Regulator, 4…Pilot pump, 5…Fan control valve, 5a, 5b…Hydraulic pilot section, 5F…Forward position (rotation position), 5N…Neutral position, 5R…Reverse position (rotation position), 7…Cylinder control valve, 7a, 7b…Hydraulic pilot section, 7L…Lower position, 7N…Neutral position, 7R…Raised position, 8…Fan motor (hydraulic motor), 9…Cooling fan, 10… Hoist cylinder (hydraulic cylinder), 10a...tube, 10b...piston, 10c...piston rod, 10d...bottom oil chamber, 10e...rod side oil chamber, 11,12...relief valve, 13,14...check valve, 15...pilot relief valve, 16~19...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, 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, 61,62...Supply oil passage, 68,69...Return oil passage, 71,72...Actuator oil passage, 80...Generator, 81,82...Motor oil passage, 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), q...discharge capacity (displacement volume), Q...discharge flow rate, qmax...maximum capacity, Qmax...maximum flow rate, qmin...minimum capacity, Qmin...minimum flow rate, Tc...cooling water temperature (temperature of the object being cooled), Tc1...first threshold, Tc2...second threshold

Claims

1. A hydraulic pump driven by a prime mover, A hydraulic motor driven by hydraulic fluid supplied from the aforementioned hydraulic pump, A cooling fan driven by the aforementioned hydraulic motor, A heat exchanger is located at the front of the vehicle body and cools the object to be cooled by the cooling air generated by the cooling fan, A cargo bed is provided at the rear of the vehicle body so as to be able to be raised and lowered, A temperature sensor for detecting the temperature of the object to be cooled, A hydraulic cylinder driven by hydraulic fluid supplied from the aforementioned hydraulic pump raises and lowers the cargo bed, A fan control valve that controls the flow of hydraulic fluid supplied from the hydraulic pump to the hydraulic motor, The hydraulic cylinder has a raised position in which it is driven to lift the loading platform, a lowered position in which it is driven to lower the loading platform, and a neutral position in which the supply of hydraulic fluid to the hydraulic cylinder is cut off, and a cylinder control valve that controls the flow of hydraulic fluid supplied from the hydraulic pump to the hydraulic cylinder, An operating device for switching the cylinder control valve to the raised position, the lowered position, and the neutral position, A transport vehicle comprising a control device for controlling the discharge capacity of the fan control valve and the hydraulic pump, The fan control valve and the cylinder control valve are connected in tandem in the oil passage connecting the hydraulic pump and the hydraulic oil tank. The aforementioned fan control valve is It is located upstream of the cylinder control valve, The fan control valve connects the hydraulic pump and the cylinder control valve, disconnects the hydraulic pump and the hydraulic motor, and connects the intake port and discharge port of the hydraulic motor to the hydraulic oil tank in a neutral position, The fan control valve has a rotational position that blocks communication between the hydraulic pump and the cylinder control valve, connects the hydraulic pump and the intake port of the hydraulic motor, and connects the discharge port of the hydraulic motor and the hydraulic oil tank. 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, and the discharge capacity of the 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 fan control valve is switched to the neutral position, and the discharge capacity of the hydraulic pump is controlled to the minimum capacity. When the cylinder control valve is operated to the raised or lowered position by the operating device, the fan control valve is controlled to the neutral position regardless of the temperature of the object being cooled. A transport vehicle characterized by the following features.

2. In the transport vehicle described in claim 1, 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 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 hydraulic pump is controlled to its maximum capacity. A transport vehicle characterized by the following features.

3. In the transport vehicle described in claim 1, The fan control valve has a forward rotation position for rotating the hydraulic motor in the forward direction and a reverse rotation position for rotating the hydraulic motor in the reverse direction opposite to the forward direction. A transport vehicle characterized by the following features.

4. In the transport vehicle described in claim 1, A pair of motor oil passages connecting the fan control valve and the hydraulic motor, The system includes a pair of check valves provided between the pair of motor oil passages and the hydraulic oil tank, When the fan control valve is switched to the neutral position, when the cooling fan rotates, hydraulic fluid is supplied from the hydraulic fluid tank to the intake port of the hydraulic motor through the check valve, and hydraulic fluid is supplied from the hydraulic fluid tank to the intake port of the hydraulic motor through the fan control valve. A transport vehicle characterized by the following features.

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