Transport vehicle

Abstract

A transport vehicle has: a cooling fan driven by a hydraulic motor; a heat exchanger disposed in the front of the vehicle body; a fan control valve that controls the flow of hydraulic oil supplied to the hydraulic motor; a cylinder control valve that controls the flow of hydraulic oil supplied to the hydraulic cylinder; and a control device. The fan control valve and the cylinder control valve are connected in series with the central bypass line. The fan control valve has: a neutral position in which the first hydraulic pump and the cylinder control valve communicate with each other, and the suction port and the discharge port of the hydraulic motor communicate with the working oil tank; and a rotation position in which the first hydraulic pump and the suction port of the hydraulic motor communicate with each other and the discharge port of the hydraulic motor and the hydraulic tank communicate with each other.

Description

Technical Field

[0001] The present invention relates to a transport vehicle such as a dump truck having a cooling fan. Background Art

[0002] A transport vehicle having a cooling fan is known (see Patent Document 1). The cooling wind generated by the cooling fan cools a cooling object such as engine cooling water. Patent Document 1 discloses a control device that performs a first control to set the rotation speed of the cooling fan according to the temperature of the cooling object when the temperature of the cooling object is higher than a lower threshold temperature, and performs a second control to set the rotation speed of the cooling fan to a minimum rotation speed and to reverse rotation when the temperature of the cooling object is lower than the lower threshold temperature.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Publication No. 2014-118902 Summary of the invention

[0006] Problems to be solved by the invention

[0007] Transport vehicles such as dump trucks are sometimes equipped with heat exchangers such as radiators and cooling fans at the front of the vehicle body. In addition, the load of the transport vehicle when traveling varies depending on whether there is cargo, the slope of the road, etc. For example, unloaded driving and flat driving are driving states with lower loads than driving with cargo or climbing a hill. If cooling air is continuously generated by the cooling fan in a low-load driving state, the cooling object (engine cooling water, etc.) may become overcooled due to the cooling air and the driving air. Here, in order to prevent overcooling, it is conceivable to stop the cooling fan. As a method of stopping the cooling fan, the following method is conceivable: cutting off the supply of working oil from a hydraulic source such as a hydraulic pump to a hydraulic motor used to drive the cooling fan.

[0008] In the vehicle described in Patent Document 1, a control valve (switching valve) is provided on the upstream side of a fan control valve that controls the rotation direction of a fan, which switches the supply destination of the working oil from the hydraulic source to the fan control valve or the loading and unloading device. That is, in the vehicle described in Patent Document 1, the hydraulic source of the hydraulic motor of the loading and unloading device and the cooling fan is shared.

[0009] Therefore, in the structure described in Patent Document 1, for example, in a low-load driving state, the cooling fan is stopped by switching the supply destination of the hydraulic oil from the hydraulic source to the loading and unloading device, thereby preventing overcooling. However, there is a problem that the structure of the hydraulic circuit becomes complicated by providing multiple control valves in the hydraulic circuit.

[0010] An object of the present invention is to provide a transport vehicle capable of preventing overcooling of a cooling object with a simple structure.

[0011] Means for solving problems

[0012] A transport vehicle according to one embodiment of the present invention comprises: at least one hydraulic pump driven by a prime mover; a hydraulic motor driven by working oil supplied from a first hydraulic pump of the at least one hydraulic pump; a cooling fan driven by the hydraulic motor; a heat exchanger arranged at the front of the vehicle body and cooling a cooling object by using cooling air generated by the cooling fan; a hydraulic cylinder driven by working oil supplied from the first hydraulic pump; a fan control valve controlling the flow of working oil supplied from the first hydraulic pump to the hydraulic motor; a cylinder control valve controlling the flow of working oil supplied from the first hydraulic pump to the hydraulic cylinder; and a control device controlling the fan control valve and the The discharge capacity of at least one hydraulic pump, wherein the fan control valve and the cylinder control valve are connected in series with the oil circuit connecting the first hydraulic pump and the working oil tank, the fan control valve is arranged on the upstream side of the cylinder control valve, and the fan control valve has the following positions: a neutral position, which connects the first hydraulic pump and the cylinder control valve, cuts off the connection between the first hydraulic pump and the hydraulic motor, and connects the suction port and the discharge port of the hydraulic motor with the working oil tank; and a rotation position, which cuts off the connection between the first hydraulic pump and the cylinder control valve, connects the first hydraulic pump with the suction port of the hydraulic motor, and connects the discharge port of the hydraulic motor with the working oil tank.

[0013] Effects of the Invention

[0014] According to the present invention, it is possible to provide a transport vehicle capable of preventing overcooling of a cooling target with a simple structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a perspective view showing the appearance of a dump truck.

[0016] Figure 2 It is a schematic plan view showing the structure of a dump truck.

[0017] Figure 3 It is a diagram showing a hydraulic system of a dump truck according to the first embodiment.

[0018] Figure 4 This is a functional block diagram of the control device according to the first embodiment.

[0019] Figure 5 This is a diagram showing the relationship between the discharge capacity q (tilt angle) and the discharge flow rate Q of the first hydraulic pump.

[0020] Figure 6 It is a diagram of a capacity control table which shows the relationship between the predetermined cooling water temperature Tc and the discharge capacity q.

[0021] Figure 7 This is a flowchart showing an example of a flow of fan control processing executed by the control device according to the first embodiment.

[0022] Figure 8 1 is a diagram showing 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.

[0023] Fig. 9 It is a diagram showing a hydraulic system of a dump truck according to a second embodiment.

[0024] Fig.10 This is a functional block diagram of a control device according to a third embodiment.

[0025] Fig.11 This is a flowchart showing an example of a processing flow of the loss reduction control at the time of engine startup executed by the control device according to the third embodiment.

[0026] Fig.12 This is a functional block diagram of a control device according to a fourth embodiment.

[0027] Fig.13 This is a table showing the relationship between the operating position of the operating device for the cargo box, the cooling water temperature, and the switching position of each control valve. DETAILED DESCRIPTION

[0028] <First embodiment>

[0029] A transport vehicle according to a first embodiment of the present invention will be described with reference to the drawings. Figure 1 The perspective view shows the appearance of a dump truck 100 as an example of a transport vehicle according to the first embodiment of the present invention. Unless otherwise specified in the following description, the front of the driver's seat (in the figure, the left front direction, see arrow) is set as the front of the vehicle body 101.

[0030] Figure 1 The dump truck 100 shown is a large dump truck used in mines and the like, and includes a vehicle body 101, a cab 103, a cargo container 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 of the vehicle body 101. The cab 103 is a cab for the operator of the dump truck 100 to get on and off, and is provided with a driver's seat, an accelerator pedal, a brake pedal, a steering wheel for steering (none of which are shown in the figure), and an operating device 91 for the cargo container (see FIG. 1 ). Figure 3 )wait.

[0031] The cargo box 104 can be mounted on the rear part of the vehicle body 101 in a manner that it can rise and fall. The cargo box 104 is rotatably supported on the rear part of the vehicle body 101 via a connecting pin, and is lifted by a lifting cylinder 10 (see Figure 3 ) and moves up and down with the connecting pin as a fulcrum. The front wheel 105 supports the vehicle body 101 at the front of the vehicle body 101 so that it can travel left and right, and the rear wheel 106 supports the vehicle body 101 at the rear of the vehicle body 101 so that it can travel left and right. The front wheel 105 constitutes a steering wheel for the operator of the dump truck 100 to steer (steering operation). The rear wheel 106 constitutes a driving wheel of the dump truck 100 and is rotationally driven by a travel drive device (not shown).

[0032] 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 vents for taking in external air into the vehicle body 101.

[0033] Figure 2 1 is a schematic plan view showing the structure of the dump truck 100. Figure 2 As shown, the vehicle body 101 is equipped with: 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 heat exchanger, i.e., a radiator 23, for cooling the engine cooling water using 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 object cooled by the cooling air generated by the cooling fan 9. Figure 2 In the figure, 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.

[0034] The engine 1 as the prime mover is constituted by, for example, a large diesel engine. The cooling fan 9 is driven by a fan motor 8 (see Figure 3 ) is driven. The cooling fan 9 draws in outside air from the front side of the vehicle body 101 through the front grille 107, and generates cooling air (see arrow F1) that flows from the front side to the rear side of the vehicle body 101. The radiator 23 is arranged on the rear side of the front grille 107, so the radiator 23 is cooled by the cooling air.

[0035] The radiator 23 exchanges heat with the cooling wind (air) generated by the cooling fan 9 to cool the engine cooling water heated by the engine 1. The engine cooling water cooled by the radiator 23 returns to the engine 1 to cool the engine 1. In addition, the radiator 23 is arranged at the front part of the vehicle body 101, and therefore receives the running wind (see arrow F2). Therefore, the engine cooling water in the radiator 23 is cooled by the running wind in addition to the cooling wind.

[0036] Reference Figure 3 , the hydraulic system 110 of the dump truck 100 is described. Figure 3 As shown, the hydraulic system 110 of the dump truck 100 includes a variable displacement hydraulic pump (hereinafter referred to as a first hydraulic pump) 2 driven by an engine 1 and a fixed displacement hydraulic pump (hereinafter referred to as a pilot pump) 4, a pair of lifting cylinders (in the embodiment of FIG. 1 ) driven by hydraulic oil supplied from the first hydraulic pump 2, and a pair of lifting cylinders (in the embodiment of FIG. 1 ). Figure 3 Only one is shown in the figure) 10, a fan motor 8 driven by the working oil supplied from the first hydraulic pump 2, a working oil tank 22 for storing the working oil, a fan control valve 5 and a lifting control valve 7 provided on the oil circuit connecting the first hydraulic pump 2 and the working oil tank 22, i.e., the central bypass line CL, and a control device 50 for controlling various parts of the dump truck 100.

[0037] The first hydraulic pump (main pump) 2 is driven by the engine 1, thereby sucking working oil from the working oil tank 22 and discharging high-pressure working oil (pressure oil). The discharge port of the first hydraulic pump 2 is connected to the working oil tank 22 via the central bypass line CL. The fan control valve 5 and the lifting control valve 7 are connected in series along the central bypass line CL. The fan control valve 5 controls the flow of working oil supplied from the first hydraulic pump 2 to the fan motor 8 and the flow of working oil ejected from the fan motor 8 to the working oil tank 22. The lifting control valve 7 is a cylinder control valve that controls the flow of working oil supplied from the first hydraulic pump 2 to the lifting cylinder 10 and the flow of working oil ejected from the lifting cylinder 10 to the working oil tank 22.

[0038] The fan control valve 5 is connected to a supply oil passage 61 branched from the central bypass line CL. The lifting control valve 7 is provided on the downstream side of the fan control valve 5 in the central bypass line CL. The lifting control valve 7 is connected to a supply oil passage 62 branched from the central bypass line CL. The return oil from the fan motor 8 is ejected to the working oil tank 22 through the return oil passage 68. The return oil from the lifting cylinder 10 is ejected to the working oil tank 22 through the return oil passage 69.

[0039] The fan motor 8 is a hydraulic motor that drives 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 through 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 via the fan control valve 5, respectively.

[0040] The motor oil circuit 81 is connected to a relief valve 11 that defines the maximum pressure of the motor oil circuit 81. The motor oil circuit 82 is provided with a relief valve 12 that defines the maximum pressure of the motor oil circuit 82. When the pressure in the pair of motor oil circuits 81 and 82 exceeds a specified value, the pair of relief valves 11 and 12 release the hydraulic oil to the hydraulic oil tank 22 to protect the hydraulic equipment of the fan circuit including the pair of motor oil circuits 81 and 82.

[0041] A pair of check valves 13 and 14 for replenishment are provided between the pair of motor oil passages 81 and 82 and the return oil passage 68. The check valve 13 is a check valve that allows the hydraulic oil to flow from the return oil passage 68 to the motor oil passage 81 and prohibits the hydraulic oil from flowing from the motor oil passage 81 to the return oil passage 68. The check valve 14 is a check valve that allows the hydraulic oil to flow from the return oil passage 68 to the motor oil passage 82 and prohibits the hydraulic oil from flowing from the motor oil passage 82 to the return oil passage 68.

[0042] When the fan motor 8 rotates by inertia or when the fan motor 8 rotates due to the traveling wind, if the motor oil circuit 81 or the motor oil circuit 82 becomes under negative pressure, the working oil in the working oil tank 22 is supplied to the motor oil circuits 81 and 82 under negative pressure through the return oil circuit 68.

[0043] The lifting cylinder 10 is installed on the vehicle body 101 (refer to Figure 1 ) and cargo box 104 (refer to Figure 1 ). The lifting cylinder 10 is a one-stage or multi-stage hydraulic cylinder that makes the cargo bucket 104 rise and fall. Figure 3 In FIG. 1 , a two-stage lifting cylinder 10 is shown. Figure 3 The lifting cylinder 10 shown comprises: an outer cylinder portion 10a on the outside; an inner cylinder portion 10b which is slidably arranged in the outer cylinder portion 10a and divides 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 which is telescopically arranged in the inner cylinder portion 10b.

[0044] The lifting cylinder 10 extends by supplying the working oil (pressure oil) discharged from the first hydraulic pump 2 to the bottom oil chamber 10d, and spraying the working oil (return oil) from the rod side oil chamber 10e. As the lifting cylinder 10 extends, the cargo bucket 104 rotates upward with the connecting pin as a fulcrum. When the rotation action is completed, the cargo bucket 104 is in a discharge posture tilted downward and obliquely backward. The lifting cylinder 10 contracts by supplying the working oil (pressure oil) discharged from the first hydraulic pump 2 to the rod side oil chamber 10e, and spraying the working oil (return oil) from the bottom oil chamber 10d. As the lifting cylinder 10 contracts, the cargo bucket 104 rotates downward with the connecting pin as a fulcrum. When the rotation action is completed, the cargo bucket 104 is in a lying transport posture.

[0045] The bottom oil chamber 10d and the rod oil chamber 10e of the lifting cylinder 10 are connected to the lifting control valve 7 through 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 working oil tank 22 respectively via the lifting control valve 7. The actuator oil passage 71 is connected to the bottom oil chamber 10d of the lifting cylinder 10, and the actuator oil passage 72 is connected to the rod oil chamber 10e of the lifting cylinder 10.

[0046] The fan control valve 5 is constituted by, for example, a 6-port 3-position hydraulic pilot type directional control valve. The fan control valve 5 is constituted by a single directional control valve and has hydraulic pilot parts 5a and 5b on the left and right sides.

[0047] The fan control valve 5 is a switching valve that can switch the valve core (valve body) to a forward rotation position (5F), a reverse rotation position (5R) and a neutral position (5N). The fan control valve 5 is normally connected to the hydraulic pilot parts 5a and 5b of ... the hydraulic pilot parts 5a and the hydraulic pilot parts 5a and the hydraulic pilot parts 5a and the hydraulic pilot parts 5a and the hydraulic pilot parts 5a and the hydraulic pilot parts 5a

[0048] When the valve core of the fan control valve 5 is in the neutral position (5N), the upstream side and the downstream side of the fan control valve 5 of the central bypass line CL are connected, and the connection between the supply oil path 61 and the motor oil paths 81 and 82 is cut off. That is, in the neutral position (5N), the first hydraulic pump 2 is connected to the lifting control valve 7, and the connection between the first hydraulic pump 2 and the fan motor 8 is cut off. As a result, the working oil discharged from the first hydraulic pump 2 is supplied to the lifting control valve 7 through the fan control valve 5. In addition, when the valve core of the fan control valve 5 is in the neutral position (5N), a pair of motor oil paths 81 and 82 are connected to each other through the communication path 5c of the fan control valve 5, and a pair of motor oil paths 81 and 82 are connected to the return oil path 68. In the neutral position (5N), the suction port and the discharge port of the fan motor 8 are connected to the working oil tank 22 via the communication path 5c, and therefore, the rotation of the cooling fan 9 caused by the external force is allowed.

[0049] When the valve core of the fan control valve 5 is in the normal rotation position (5F), the supply oil path 61 is connected to the motor oil path 81, and the motor oil path 82 is connected to the return oil path 68. That is, in the normal rotation position (5F), the connection between the suction port and the discharge port of the fan motor 8 and the working oil tank 22 via the communication path 5c is cut off, the suction port of the fan motor 8 is connected to the first hydraulic pump 2, and the discharge port of the fan motor 8 is connected to the working oil tank 22. As a result, the working oil discharged from the first hydraulic pump 2 is supplied to the fan motor 8 through the supply oil path 61 and the motor oil path 81, and the fan motor 8 rotates in the normal rotation direction. The working oil ejected from the fan motor 8 is ejected to the working oil tank 22 through the motor oil path 82 and the return oil path 68. When the valve core of the fan control valve 5 is in the reverse rotation position (5R), the supply oil path 61 is connected to the motor oil path 82, and the motor oil path 81 is connected to the return oil path 68. That is, in the reverse position (5R), the connection between the suction port and the discharge port of the fan motor 8 and the working oil tank 22 via the communication path 5c is cut off, the suction port of the fan motor 8 is connected to the first hydraulic pump 2, and the discharge port of the fan motor 8 is connected to the working oil tank 22. As a result, the working oil discharged from the first hydraulic pump 2 is supplied to the fan motor 8 through the supply oil path 61 and the motor oil path 82, and the fan motor 8 rotates in the reverse direction, which is the opposite direction to the forward rotation direction. The working oil ejected from the fan motor 8 is ejected to the working oil tank 22 through the motor oil path 81 and the return oil path 68.

[0050] Thus, the forward rotation position (5F) and the reverse rotation position (5R) are rotation positions in which the first hydraulic pump 2 is connected to the fan motor 8 and the fan motor 8 is rotated by the hydraulic oil discharged from the first hydraulic pump 2. In addition, when the valve core of the fan control valve 5 is in the rotation position (5F) or (5R), the communication between the first hydraulic pump 2 and the lifting control valve 7 via the central bypass line CL is cut off.

[0051] The hoist control valve 7 is constituted by, for example, a 6-port 3-position hydraulic pilot type directional control valve. The hoist control valve 7 is constituted by a single directional control valve and has hydraulic pilot parts 7a and 7b on the left and right sides.

[0052] The lifting control valve 7 is a switching valve that can switch the valve core (valve body) to a rising position (7R), a falling position (7L) and a neutral position (7N). The lifting control valve 7 is normally connected to the hydraulic pilot parts 7a and 7b of the lifting control valve 7 with the hydraulic oil tank 22, and the valve core is held in the neutral position (7N) by a centering spring.

[0053] When the valve core of the lifting control valve 7 is in the neutral position (7N), the communication between the supply oil passage 62 and the return oil passage 69 and the actuator oil passages 71 and 72 is cut off. As a result, the supply of hydraulic oil to the lifting cylinder 10 and the ejection of hydraulic oil from the lifting cylinder 10 are stopped, and thus the movement of the lifting cylinder 10 is stopped. In addition, when the valve core of the lifting control valve 7 is in the neutral position (7N), the upstream side and the downstream side of the lifting control valve 7 of the center bypass line CL are connected.

[0054] When the valve core of the lifting control valve 7 is in the rising position (7R), the supply oil circuit 62 is connected to the actuator oil circuit 71, and the actuator oil circuit 72 is connected to the return oil circuit 69. In addition, the communication between the upstream side and the downstream side of the lifting control valve 7 of the central bypass line CL is cut off. Therefore, when the fan control valve 5 is in the neutral position (5N), the working oil discharged from the first hydraulic pump 2 is supplied to the bottom side oil chamber 10d of the lifting cylinder 10 through the supply oil circuit 62 and the actuator oil circuit 71. In addition, the working oil in the rod side oil chamber 10e is ejected to the working oil tank 22 through the actuator oil circuit 72 and the return oil circuit 69. As a result, the lifting cylinder 10 is driven in the extension direction, that is, the direction of lifting the cargo box 104.

[0055] When the valve core of the lifting control valve 7 is in the descending position (7L), the supply oil circuit 62 is connected to the actuator oil circuit 72, and the actuator oil circuit 71 is connected to the return oil circuit 69. In addition, the communication between the upstream side and the downstream side of the lifting control valve 7 of the central bypass line CL is cut off. Therefore, when the fan control valve 5 is in the neutral position (5N), the working oil discharged from the first hydraulic pump 2 is supplied to the rod side oil chamber 10e of the lifting cylinder 10 through the supply oil circuit 62 and the actuator oil circuit 72. In addition, the working oil in the bottom side oil chamber 10d is ejected to the working oil tank 22 through the actuator oil circuit 71 and the return oil circuit 69. As a result, the lifting cylinder 10 is driven in the direction of contraction, that is, the direction of descending the cargo box 104.

[0056] The pilot pump 4 is connected to a plurality of solenoid valves 16 to 19 via a pilot oil circuit. A pilot relief valve 15 that defines the pressure of the pilot oil circuit is provided in the pilot oil circuit between the pilot pump 4 and the plurality of solenoid valves 16 to 19. The plurality of solenoid valves 16 to 19 are pressure reducing valves that reduce the pressure (primary pressure) of the pilot oil circuit according to the control current from the control device 50 and output the reduced pressure (secondary pressure) as a pilot pressure. When a standby control current as an off signal is input to the solenoid valves 16 to 19, the hydraulic pilot parts 5a, 5b, 7a, 7b are connected to the working oil tank 22. When a driving control current as an on signal is input to the solenoid valves 16 to 19, the pilot pressure generated in the hydraulic pilot parts 5a, 5b, 7a, 7b is output.

[0057] The solenoid valves 16 and 17 for driving the fan control valve 5 are operated according to the control command (control current) outputted from the control device 50 corresponding to the temperature of the engine cooling water. The solenoid valves 18 and 19 for driving the lifting control valve 7 are operated according to the control command (control current) outputted from the control device 50 corresponding to the operation of the operating device 91 for the cargo box.

[0058] The control device 50 is composed of a computer having a processing device 51 such as a CPU (Central Processing Unit), an MPU (Micro Processing Unit), and a DSP (Digital Signal Processor), a non-volatile memory 52 such as a ROM (Read Only Memory), a flash memory, and a hard disk drive, a volatile memory 53 called a so-called RAM (Random Access Memory), an input / output interface, and other peripheral circuits. These hardware cooperate to make the software work and realize multiple functions. In addition, the control device 50 can be composed of one computer or multiple computers.

[0059] The nonvolatile memory 52 stores programs that can perform various operations and data (data tables, threshold values, mathematical expressions, etc.) used for various operations. That is, the nonvolatile memory 52 is a storage medium (storage device) that can read the program that realizes the functions of this embodiment. The volatile memory 53 is a storage medium (storage device) that temporarily stores the operation results of the processing device 51 and the signals input from the input / output interface. The processing device 51 is a device that expands the program stored in the nonvolatile memory 52 in the volatile memory 53 and performs operations, and performs prescribed operations on the data taken from the input / output interface, the nonvolatile memory 52, and the volatile memory 53 according to the program.

[0060] The operating device 91 for switching the lifting control valve 7 is connected to the input / output interface of the control device 50. The operating device 91 is composed of, for example, an electric rod 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, the rising position, and the falling position corresponding to each switching position of the lifting control valve 7, that is, the neutral position (7N), the rising position (7R), and the falling position (7L). The operating device 91 outputs an operation signal corresponding to the operation position to the control device 50.

[0061] The 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 cooling water flowing in the cooling water system 28 of the engine 1, and outputs a signal indicating the detection result to the control device 50. The cooling water system 28 is configured to include the following parts: a cooling water tank 27 that stores the engine cooling water, a cooling water circulation pump 24 that sucks and discharges the engine cooling water in the cooling water tank 27, and a radiator 23 that cools the engine cooling water by cooling air. The cooling water system 28 is a circulation system that can circulate the engine cooling water in the system by the cooling water circulation pump 24. The engine cooling water cools the cooling object 26 such as the engine 1 by absorbing heat from the cooling object 26. The temperature of the engine cooling water rises due to the heat received from the cooling object 26. The engine cooling water 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 provided in the cooling water tank 27 or the pipe on the suction side of the cooling water circulation pump 24, for example, and detects the temperature of the engine cooling water supplied to the radiator 23.

[0062] The input section of the input / output interface converts signals input from various devices (operating device 91, temperature sensor 25, etc.) into data that can be calculated by processing device 51. In addition, the output section of the input / output interface generates an output signal corresponding to the calculation result in processing device 51, and outputs the signal to various devices (solenoid valves 16 to 19, regulator 2a, etc.).

[0063] The control device 50 outputs a control signal to the regulator 2a of the first hydraulic pump 2. The regulator 2a is a capacity control device that variably controls the displacement (discharge capacity per rotation) of the first hydraulic pump 2. For example, when the first hydraulic pump 2 is a swash plate type piston pump, the regulator 2a has a tilting actuator that controls the tilting angle (displacement) of the swash plate of the first hydraulic pump 2 and an electromagnetic proportional valve that generates a control pressure of the tilting actuator using the discharge pressure of the first hydraulic pump 2 as an initial pressure.

[0064] When the operating device 91 is operated to the neutral position, the control device 50 controls the fan control valve 5 according to the engine cooling water temperature (hereinafter also referred to as the cooling water temperature) Tc detected by the temperature sensor 25. The control content of the fan control valve 5 will be described later.

[0065] When the operating device 91 is operated to the neutral position, the control device 50 maintains the hoist control valve 7 at the neutral position ( 7N). That is, the control device 50 outputs an OFF signal to both the solenoid valves 18 and 19 .

[0066] When the operating device 91 is operated to the rising position, the control device 50 controls the lifting control valve 7 to be switched to the rising position (7R). That is, the control device 50 outputs an on signal to the solenoid valve 18, and outputs 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 part 7a, and the lifting control valve 7 is switched to the rising position (7R). When the operating device 91 is operated to the falling position, the control device 50 controls the lifting control valve 7 to be switched to the falling position (7L). That is, the control device 50 outputs an off signal to the solenoid valve 18, and outputs 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 part 7b, and the lifting control valve 7 is switched to the falling position (7L).

[0067] The control device 50 controls the switching position of the fan control valve 5, controls the rotation and stop of the fan motor 8, and controls the rotation direction of the fan motor 8. In addition, the control device 50 controls the discharge capacity q of the first hydraulic pump 2 within the range from the minimum capacity qmin to the maximum capacity qmax via the regulator 2a, thereby controlling the rotation speed of the fan motor 8. Figure 4 , the function of the control device 50 related to the control of 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. Figure 4 As shown, 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 nonvolatile memory 52 .

[0068] like Figure 4 As shown, the determination unit 54 determines whether the cooling water temperature Tc detected by the temperature sensor 25 is above the first threshold value Tc1. In addition, the determination unit 54 determines whether the cooling water temperature Tc detected by the temperature sensor 25 is above the second threshold value Tc2. The first threshold value Tc1 and the second threshold value Tc2 are pre-stored in the non-volatile memory 52. ​​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 met. 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.

[0069] The valve control unit 55 controls the switching position of the fan control valve 5 according to the determination result of the determination unit 54. 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 to switch 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 path 61 is connected to the motor oil path 81, and the motor oil path 82 is connected to the return oil path 68. Thus, the fan motor 8 is rotated by the working oil supplied from the first hydraulic pump 2.

[0070] In addition, when the determination unit 54 determines that the stop condition of the cooling fan 9 is met, the valve control unit 55 outputs a disconnection signal to the solenoid valves 16 and 17 to switch the fan control valve 5 to the neutral position (5N). When the fan control valve 5 is switched to the neutral position (5N), the connection between the supply oil circuit 61 and the motor oil circuits 81 and 82 is cut off. In addition, the motor oil circuit 81, the motor oil circuit 82 and the working oil tank 22 are connected via the connecting 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 rotates due to inertia, the working oil is replenished from the working oil tank 22 via the connecting passage 5c of the fan control valve 5 in the neutral position (5N) and the one-way valve 13 or the one-way valve 14. Therefore, cavitation can be prevented from occurring in the fan motor 8.

[0071] The pump control unit 56 controls the discharge flow rate Q of the first hydraulic pump 2 according to the cooling water temperature Tc detected by the temperature sensor 25. In addition, the discharge flow rate Q of the first hydraulic pump 2 is determined by the rotation speed of the engine 1 and the discharge capacity (volume) q of the first hydraulic pump 2. The pump control unit 56 of this embodiment controls the discharge flow rate Q of the first hydraulic pump 2 by controlling the discharge capacity q of the first hydraulic pump 2.

[0072] Figure 5 : is a diagram showing the relationship between the discharge capacity q (equivalent to the tilting angle of the swash plate) of the first hydraulic pump 2 and the discharge flow rate Q. Figure 5 As shown, 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 the minimum value (0%), the discharge flow rate Q is the minimum flow rate Qmin. When the discharge capacity q is the maximum value (100%), the discharge flow rate Q is the maximum flow rate Qmax.

[0073] The pump control unit 56 uses a capacity control table (see Figure 6 ), calculate the discharge capacity q of the first hydraulic pump 2. Figure 6 : is a diagram showing a capacity control table that specifies the relationship between the cooling water temperature Tc and the discharge capacity q. Figure 6As shown in FIG. 1 , the relationship between the cooling water temperature Tc and the discharge capacity q specified by the capacity control table is as follows. When the cooling water temperature Tc is less than the first threshold value Tc1, the discharge capacity q is the minimum capacity qmin. When the cooling water temperature Tc is greater than the first threshold value Tc1 and less than the second threshold value Tc2, the discharge capacity q increases proportionally with the increase in the cooling water temperature Tc. When the cooling water temperature Tc is greater than the second threshold value Tc2, the discharge capacity q is the maximum capacity qmax.

[0074] The pump control unit 56 refers to the capacity control table and calculates the discharge capacity q of the first hydraulic pump 2 according to the cooling water temperature Tc detected by the temperature sensor 25. Therefore, when the cooling water temperature Tc is less than the first threshold value Tc1, the pump control unit 56 controls the discharge capacity q of the first hydraulic pump 2 to the minimum capacity qmin. In addition, when the cooling water temperature Tc is greater than the first threshold value 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, when the cooling water temperature Tc is greater than the first threshold value Tc1 and less than the second threshold value Tc2, the higher the cooling water temperature Tc, the more the pump control unit 56 increases the discharge capacity q of the first hydraulic pump 2, and when the cooling water temperature Tc is greater than the second threshold value Tc2, the pump control unit 56 controls the discharge capacity q of the first hydraulic pump 2 to the maximum capacity qmax.

[0075] Reference Figure 7 , an example of a processing flow of fan control executed by the control device 50 is described. Figure 7 The process shown in the flowchart is started by turning on an ignition switch (not shown) and is repeatedly executed in a predetermined control cycle.

[0076] like Figure 7 As shown, in step S110, the control device 50 obtains the cooling water temperature Tc from the temperature sensor 25, and the process 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 the first threshold value Tc1. If it is determined in step S120 that the cooling water temperature Tc is greater than the first threshold value 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 value Tc1, the process proceeds to step S135.

[0077] 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, a pilot pressure is generated by the solenoid valve 16, and the generated pilot pressure is input to the hydraulic pilot portion 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 rotation direction by the hydraulic oil discharged from the first hydraulic pump 2.

[0078] When the processing of step S130 is completed, the processing 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 greater than the second threshold value Tc2. If it is determined in step S140 that the cooling water temperature Tc is greater than the second threshold value Tc2, the processing proceeds to step S150. If it is determined in step S140 that the cooling water temperature Tc is less than the second threshold value Tc2, the processing proceeds to step S155.

[0079] In step S150, the control device 50 outputs a control signal to the regulator 2a for making the discharge capacity q of the first hydraulic pump 2 the maximum capacity qmax, and the control cycle in this control cycle ends. Figure 7 In step S155, the control device 50 performs the processing according to the capacity control table (refer to Figure 6 ) and the cooling water temperature Tc obtained in step S110, determines the target value of the discharge capacity q of the first hydraulic pump 2. The control device 50 outputs a control signal to the regulator 2a for making the discharge capacity q of the first hydraulic pump 2 the target value corresponding to the cooling water temperature Tc, and ends the control cycle. Figure 7 The process is shown in the flowchart.

[0080] As described above, when it is determined in step S120 that the cooling water temperature Tc is less than the first threshold value Tc1, the process proceeds to step S135. In step S135, the control device 50 outputs a disconnection signal to the solenoid valves 16 and 17. When the disconnection signal is input to the solenoid valves 16 and 17, the hydraulic pilot parts 5a and 5b of the fan control valve 5 are connected to the working oil tank 22. As a result, the fan control valve 5 is switched to the neutral position (5N) by the force of the centering spring.

[0081] When the processing of step S135 is completed, the processing proceeds to the next step S137. In step S137, the control device 50 outputs a control signal to the regulator 2a for making the discharge capacity q of the first hydraulic pump 2 the minimum capacity qmin, and the control cycle in this control cycle ends. Figure 7 The process is shown in the flowchart.

[0082] Although not shown in the figure, the control device 50 determines whether the operating device 91 is operated to the neutral position, and executes the operation only when the operating device 91 is operated to the neutral position. Figure 7 That is, the control device 50 controls the fan control valve 5 to the neutral position (5N) regardless of the cooling water temperature Tc when the operating device 91 is not operated to the neutral position (that is, when the operating device 91 is operated to one of the rising position and the falling position).

[0083] In addition, Figure 7 In the flowchart of , an example is described in which the processing of step S137 is executed when a negative determination is made in step S120, the processing of step S150 is executed when a positive determination is made in step S140, and the processing of step S155 is executed when a negative determination is made in step S140. However, when the cooling water temperature Tc is less than the first threshold value Tc1 and when the cooling water temperature Tc is greater than the second threshold value Tc2, the control device 50 may also use the capacity control table (refer to Figure 6 ) to calculate the target value of the discharge volume q. For example, the processing of steps S137, S140, S150, and S155 may be omitted, and the processing equivalent to step S155 may be performed between steps S110 and S120.

[0084] Reference Figure 8 , the main operation of the hydraulic system 110 when the dump truck 100 of this embodiment is traveling will be described. In addition, during the traveling of the dump truck 100, the operating device 91 is operated to the neutral position, so the lifting control valve 7 is maintained in the neutral position (7N). Figure 8 1 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 corresponding to the cooling water temperature Tc. When the cooling water temperature Tc is equal to or higher than the first threshold value Tc1 during the travel of the dump truck 100, the control device 50 controls the fan control valve 5 to switch 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).

[0085] Here, for example, during unloaded driving after the discharge of transported objects such as sand and soil, if the cooling of the engine cooling water flowing in the radiator 23 continues by the cooling wind and the running wind, the cooling water temperature Tc decreases. In the range where the cooling water temperature Tc is above the first threshold value Tc1 and less than the second threshold value Tc2, the discharge capacity q of the first hydraulic pump 2 is controlled according to the cooling water temperature Tc. If the cooling water temperature Tc further decreases and the cooling water temperature Tc is less than the first threshold value Tc1, the control device 50 outputs a disconnection 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 and stops as time passes. Since the generation of cooling wind for the cooling fan 9 is stopped, overcooling of the engine cooling water can be prevented. In addition, the control device 50 controls the discharge flow rate Q of the first hydraulic pump 2 to the minimum flow rate Qmin. Thus, the hydraulic oil discharged from the first hydraulic pump 2 is ejected to the hydraulic oil tank 22 through the fan control valve 5 in the neutral position (5N) and the lifting 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 oil tank 22 can be reduced, and the discharge pressure of the first hydraulic pump 2 can be suppressed to be low. As a result, the load of the first hydraulic pump 2 is reduced, and the load of the engine 1 is reduced. Therefore, according to the present embodiment, the energy loss of the first hydraulic pump 2 can be reduced, and the fuel consumption can be suppressed.

[0086] According to the above-mentioned first embodiment, the following effects are achieved.

[0087] (1) The fan control valve 5 and the hoist control valve (cylinder control valve) 7 are connected in series to the central bypass line (oil path) CL connecting the first hydraulic pump 2 and the hydraulic oil tank 22, and the fan control valve 5 is arranged on the upstream side of the hoist control valve 7. The fan control valve 5 has a neutral position (5N) that connects the first hydraulic pump (hydraulic pump) 2 with the hoist control valve 7, cuts off the communication between the first hydraulic pump 2 and the fan motor (hydraulic motor) 8, and connects the suction port and the discharge port of the fan motor 8 with the hydraulic oil tank 22 via the communication path 5c; a forward rotation position (5F) and a reverse rotation position (5R) that cut off the communication between the first hydraulic pump 2 and the hoist control valve 7, connects the first hydraulic pump 2 with the suction port of the fan motor 8, and connects the discharge port of the fan motor 8 with the hydraulic oil tank 22. The control device 50 determines whether the cooling water temperature (temperature of the cooling object) Tc detected by the temperature sensor 25 is greater than the first threshold value Tc1. When the cooling water temperature Tc is higher than the first threshold value Tc1, the control device 50 switches the fan control valve 5 to the forward rotation position (5F), and controls the discharge capacity q of the first hydraulic pump 2 to a discharge capacity greater than the minimum capacity qmin. When the cooling water temperature Tc is lower than the first threshold value Tc1, the control device 50 switches the fan control valve 5 to the neutral position (5N), and controls the discharge capacity q of the first hydraulic pump 2 to the minimum capacity qmin.

[0088] The dump truck 100 of this embodiment is used as a hydraulic pump (first hydraulic pump 2) for supplying working oil to the lifting cylinder 10 and the fan motor 8 because the lifting cylinder 10 is used less frequently. In addition, the fan control valve 5 as a single control valve has the functions of switching the supply destination of the working oil discharged from the first hydraulic pump 2 to the lifting cylinder (hydraulic cylinder) 10 or the fan motor 8, and switching the rotation and stop of the fan motor 8. Therefore, there is no need to separately set a control valve for realizing each function, so the structure of the hydraulic circuit can be simplified. In addition, when the driving state with low load continues and the cooling water temperature Tc is less than the first threshold value Tc1 due to the cooling wind and the driving wind, the fan control valve 5 is switched to the neutral position (5N). As a result, the cooling wind generated by the cooling fan 9 is stopped, so that the overcooling of the engine cooling water can be prevented. That is, according to this embodiment, a dump truck (transport vehicle) 100 that can prevent the overcooling of the engine cooling water (cooling object) with a simple structure can be provided. Furthermore, by controlling the discharge capacity q of the first hydraulic pump 2 to the minimum capacity qmin, the load on the engine 1 is reduced, and therefore fuel consumption can be suppressed.

[0089] (2) When the cooling water temperature Tc is greater than or equal to the first threshold value Tc1 and less than the second threshold value Tc2, the higher the cooling water temperature Tc, the more the control device 50 increases the discharge capacity q of the first hydraulic pump 2. In addition, when the cooling water temperature Tc is greater than or equal to the second threshold value Tc2, the control device 50 controls the discharge capacity q of the first hydraulic pump 2 to the maximum capacity qmax.

[0090] According to this configuration, the higher the cooling water temperature Tc, the higher the rotation speed of the cooling fan 9 is, and the cooling effect on the engine cooling water can be improved. By controlling the rotation speed of the cooling fan 9 according to the cooling water temperature Tc, the engine cooling water can be prevented from becoming too low or too high.

[0091] (3) The fan control valve 5 has a forward position (5F) and a reverse position (5R) as rotation positions, wherein the forward position (5F) is used to rotate the fan motor 8 in the forward direction, and the reverse position (5R) is used to rotate the fan motor 8 in the reverse direction opposite to the forward direction. When the fan control valve 5 is switched to the reverse position (5R), cooling air is generated to flow forward from the cooling fan 9, and dust attached to the filter of the air vent of the front grille 107, the gap of the radiator (heat exchanger) 23, etc. is removed. Therefore, according to the present embodiment, the cooling performance of the radiator 23 reduced by dust can be easily restored.

[0092] In addition, the control device 50 can be configured to temporarily switch the fan control valve 5 to the reverse position (5R) during maintenance of the dump truck 100 or regularly. If a service person operates the input device during maintenance and inputs a reverse command of the cooling fan 9 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 specified time. In addition, the control device 50 measures the operating time of the dump truck 100 by a timing function, and switches the fan control valve 5 to the reverse position (5R) for a specified time every time the operating time exceeds a specified operating time. In addition, the control device 50 can also temporarily switch the fan control valve 5 to the reverse position (5R) when the engine 1 is started or when the engine 1 is stopped.

[0093] (4) The hydraulic system 110 includes: a pair of motor oil passages 81 and 82 connecting the fan control valve 5 to 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 structure, when the fan control valve 5 is switched to the neutral position (5N), for example, when the cooling fan 9 is rotated by the running wind, hydraulic oil is supplied from the hydraulic oil tank 22 to the suction port of the fan motor 8 through the check valves 13 and 14, and hydraulic oil is supplied from the hydraulic oil tank 22 to the suction port of the fan motor 8 through the fan control valve 5. Therefore, it is possible to suppress the suction port of the fan motor 8 from becoming a negative pressure, thereby preventing 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 oil is also supplied from the hydraulic oil tank 22 to the suction port of the fan motor 8 through the fan control valve 5, so that it is possible to effectively prevent the occurrence of cavitation compared to the case where hydraulic oil is supplied only through the check valves 13 and 14. In addition, the same is true when the fan control valve 5 is switched to the neutral position (5N) when the cooling fan 9 rotates forward or reversely, and the cooling fan 9 continues to rotate due to inertia. That is, when the cooling fan 9 rotates due to inertia, the working oil is supplied from the working oil tank 22 to the suction port of the fan motor 8 through the connecting path 5c of the fan control valve 5 and the one-way valve 13 or the one-way valve 14, so that the suction side of the fan motor 8 can be suppressed from becoming negative pressure.

[0094] In addition, when the valve core of the fan control valve 5 is in the neutral position (5N), the motor oil circuit 81 is connected to the motor oil circuit 82. That is, the fan control valve 5 of the present embodiment is a so-called neutral free-style directional switching valve. Therefore, the working oil of the motor oil circuit on the discharge side is also supplied to the motor oil circuit on the suction side through the fan control valve 5. Therefore, according to the present embodiment, compared with the case where the pair of motor oil circuits 81 and 82 are not connected to each other in the neutral position (5N) (the case of a neutral blocking directional switching valve), the occurrence of cavitation can be effectively prevented.

[0095] <Second embodiment>

[0096] A transport vehicle according to a second embodiment of the present invention will be described with reference to the drawings. Configurations identical or corresponding to those described in the first embodiment are denoted by the same reference numerals, and the description will focus on differences.

[0097] In transport vehicles, in order to miniaturize and reduce the cost of the hydraulic pump used to drive the hydraulic actuator, there are sometimes: a hydraulic pump that supplies working oil to the hydraulic actuator (lifting cylinder and steering cylinder); a fan pump that supplies working oil to the fan motor; and a confluence control valve (circuit switching valve) that switches the discharge part of the fan pump between the hydraulic actuator and the fan motor.

[0098] In a transport vehicle, the load during driving varies depending on whether or not there is cargo, the slope of the road, and the like. For example, unloaded driving and driving on flat ground are driving states with lower loads than driving with cargo or driving uphill. In a driving state with a low load, cooling of the cooling object by a cooling fan is sometimes not necessary. When the confluence control valve (circuit switching valve) is switched to connect the discharge portion of the fan pump to the hydraulic circuit for steering drive in order to stop the cooling fan, the working pressure of the steering cylinder with a high operating frequency during driving acts on the fan pump. As a result, the load of the fan pump increases, resulting in energy loss. Therefore, a transport vehicle that can suppress energy loss when the cooling fan is stopped is desired.

[0099] Reference Fig. 9 , the hydraulic system 110 of the dump truck 100 according to the second embodiment will be described. Fig. 9 As shown, the hydraulic system 110 of the dump truck 100 of the second embodiment includes: a variable capacity first hydraulic pump 2 and a second hydraulic pump 3 and a pilot pump 4, which are driven by an engine 1; a pair of lifting cylinders (in Fig. 9 Only one is shown in the figure) 10, which can be telescopically arranged between the cargo box 104 and the vehicle body 101, and is driven by the working oil supplied from the first hydraulic pump 2; a fan motor 8, which is driven by the working oil supplied from the first hydraulic pump 2; a steering circuit 33, which has a pair of left and right steering cylinders 34, 35 driven by the working oil supplied from the second hydraulic pump 3; a working oil tank 22, which accumulates working oil; a fan control valve 5, a confluence control valve 6 and a lifting control valve 7, which are arranged on the oil circuit connecting the first hydraulic pump 2 and the working oil tank 22, that is, the central bypass pipeline CL; a control device 50, which controls various parts of the dump truck 100. In addition, the relationship between the discharge capacity q of the second hydraulic pump 3 and the discharge flow rate Q and the relationship between the discharge capacity q of the first hydraulic pump 2 and the discharge flow rate Q (refer to Figure 5 ) and therefore the description is omitted.

[0100] The first hydraulic pump 2 and the second hydraulic pump 3 are driven by the engine 1, thereby sucking working oil from the working oil tank 22 and discharging high-pressure working oil (pressure oil). The discharge port of the first hydraulic pump 2 is connected to the working oil tank 22 via the central bypass line CL. The fan control valve 5, the confluence control valve 6 and the lifting control valve 7 are connected in series along the central bypass line CL. The fan control valve 5 controls the flow of working oil supplied from the first hydraulic pump 2 to the fan motor 8 and the flow of working oil ejected from the fan motor 8 to the working oil tank 22. The lifting control valve 7 controls the flow of working oil supplied from the first hydraulic pump 2 to the lifting cylinder 10 and the flow of working oil ejected from the lifting cylinder 10 to the working oil tank 22. The confluence control valve 6 functions as a circuit switching valve for switching the circuit of the supply destination of the working oil discharged from the second hydraulic pump 3.

[0101] The fan control valve 5 is connected to a supply oil path 61 branched from the central bypass line CL. The confluence control valve 6 is provided on the downstream side of the fan control valve 5 in the central bypass line CL. The confluence control valve 6 is connected to a supply oil path 63 extending from the discharge port of the second hydraulic pump 3. The lifting control valve 7 is provided on the downstream side of the confluence control valve 6 in the central bypass line CL. The lifting control valve 7 is connected to a supply oil path 62 branched from the central bypass line CL. The return oil from the fan motor 8 is ejected to the working oil tank 22 through the return oil path 68. The return oil from the lifting cylinder 10 is ejected to the working oil tank 22 through the return oil path 69.

[0102] The steering circuit 33 includes: a pair of left and right steering cylinders 34, 35; a steering control valve 31 for controlling the flow of the working oil supplied from the second hydraulic pump 3 to the steering cylinders 34, 35; steering oil passages 36, 37 connecting the steering cylinders 34, 35 and the steering control valve 31; a high-pressure side oil passage 38 connecting the second hydraulic pump 3 and the steering control valve 31; and a low-pressure side oil passage 39 connecting the steering control valve 31 and the working oil tank 22. Front wheel 105 (refer to Figure 1 ) constitutes a steering wheel for steering (steering operation) by the operator of the dump truck 100. When the operator of the dump truck 100 operates the steering wheel 29, the control operation is performed along with the extension and retraction action of the left and right steering cylinders 34 and 35.

[0103] The left and right steering cylinders 34 and 35 extend and retract according to the operation of the steering wheel 29, thereby steering the left and right front wheels 105. The left steering cylinder 34 is a hydraulic cylinder having a bottom side oil chamber 34a and a rod side oil chamber 34b. The right steering cylinder 35 is a hydraulic cylinder having a bottom side oil chamber 35a and a rod side oil chamber 35b. The bottom side oil chamber 35a of the right steering cylinder 35 is connected to the rod side oil chamber 34b of the left steering cylinder 34 via a steering oil passage 36. The bottom side oil chamber 34a of the left steering cylinder 34 is connected to the rod side oil chamber 35b of the right steering cylinder 35 via a steering oil passage 37. The steering oil passages 36 and 37 are connected to a high pressure side oil passage 38 and a low pressure side oil passage 39 via a steering control valve 31.

[0104] The steering wheel 29 is provided in the cab 103. The steering wheel 29 is rotated left and right by the operator to control the travel direction of the dump truck 100. A hydraulic motor 30 is connected to the steering shaft of the steering wheel 29, and the rotation of the hydraulic motor 30 reduces the operating force on the steering wheel 29.

[0105] The accumulator 42 is connected to the high-pressure side oil circuit 38. The accumulator 42 accumulates the working oil (pressure oil) discharged from the second hydraulic pump 3. A relief valve 32 that specifies the maximum pressure of the high-pressure side oil circuit 38 is provided between the high-pressure side oil circuit 38 and the low-pressure side oil circuit 39. Therefore, the high-pressure side oil circuit 38 is maintained at a specified pressure by the accumulator 42 and the relief valve 32. As a result, the steering cylinders 34 and 35 can be appropriately driven when the steering wheel 29 is operated, so that the vehicle body 101 can be rotated in any direction. In addition, the accumulator 42 also functions as a temporary hydraulic source for the left and right steering cylinders 34 and 35. That is, when the working oil is not supplied from the second hydraulic pump 3 to the supply oil circuit 63 due to a failure of the second hydraulic pump 3 or the like, the pressure oil accumulated in the accumulator 42 is supplied to the left and right steering cylinders 34 and 35.

[0106] When the operator rotates the steering wheel 29, the steering control valve 31 is switched from the neutral position (31N) to one of the left and right steering positions (31L) and (31R). As a result, the hydraulic oil 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, and one of the steering cylinders 34 and 35 is extended and the other is contracted. As a result, the left and right front wheels 105 of the dump truck 100 are steered according to the rotation operation of the steering wheel 29.

[0107] The fan control valve 5 is constituted by, for example, a 6-port 3-position hydraulic pilot type directional control valve. The fan control valve 5 is constituted by a single directional control valve and has hydraulic pilot parts 5a and 5b on the left and right sides.

[0108] The fan control valve 5 is a switching valve that can switch the valve core (valve body) to a forward rotation position (5F), a reverse rotation position (5R) and a neutral position (5N). The fan control valve 5 is normally connected to the hydraulic pilot parts 5a and 5b of ... the hydraulic pilot parts 5a and the hydraulic pilot parts 5a and the hydraulic pilot parts 5a and the hydraulic pilot parts 5a and the hydraulic pilot parts 5a and the hydraulic pilot parts 5a

[0109] When the valve core of the fan control valve 5 is in the neutral position (5N), the upstream side and the downstream side of the fan control valve 5 of the center bypass line CL are connected, and the connection between the supply oil path 61 and the motor oil paths 81 and 82 is cut off. That is, in the neutral position (5N), the first hydraulic pump 2 is connected to the confluence control valve 6, and the connection between the first hydraulic pump 2 and the fan motor 8 is cut off. As a result, the hydraulic oil discharged from the first hydraulic pump 2 is supplied to the confluence control valve 6 through the fan control valve 5. In addition, when the valve core of the fan control valve 5 is in the neutral position (5N), the pair of motor oil paths 81 and 82 are connected to each other through the communication path 5c of the fan control valve 5, and the pair of motor oil paths 81 and 82 are connected to the return oil path 68. In the neutral position (5N), the suction port and the discharge port of the fan motor 8 are connected to the hydraulic oil tank 22 via the communication path 5c, so that the rotation of the cooling fan 9 caused by the external force is allowed.

[0110] When the valve core of the fan control valve 5 is in the normal rotation position (5F), the supply oil path 61 is connected to the motor oil path 81, and the motor oil path 82 is connected to the return oil path 68. That is, in the normal rotation position (5F), the connection between the suction port and the discharge port of the fan motor 8 and the working oil tank 22 via the communication path 5c is cut off, the suction port of the fan motor 8 is connected to the first hydraulic pump 2, and the discharge port of the fan motor 8 is connected to the working oil tank 22. As a result, the working oil discharged from the first hydraulic pump 2 is supplied to the fan motor 8 through the supply oil path 61 and the motor oil path 81, and the fan motor 8 rotates in the normal rotation direction. The working oil ejected from the fan motor 8 is ejected to the working oil tank 22 through the motor oil path 82 and the return oil path 68. When the valve core of the fan control valve 5 is in the reverse rotation position (5R), the supply oil path 61 is connected to the motor oil path 82, and the motor oil path 81 is connected to the return oil path 68. That is, in the reverse position (5R), the connection between the suction port and the discharge port of the fan motor 8 and the working oil tank 22 via the communication path 5c is cut off, the suction port of the fan motor 8 is connected to the first hydraulic pump 2, and the discharge port of the fan motor 8 is connected to the working oil tank 22. As a result, the working oil discharged from the first hydraulic pump 2 is supplied to the fan motor 8 through the supply oil path 61 and the motor oil path 82, and the fan motor 8 rotates in the reverse direction, which is the opposite direction to the forward rotation direction. The working oil ejected from the fan motor 8 is ejected to the working oil tank 22 through the motor oil path 81 and the return oil path 68.

[0111] Thus, the forward rotation position (5F) and the reverse rotation position (5R) are rotation positions in which the first hydraulic pump 2 is connected to the fan motor 8 and the fan motor 8 is rotated by the hydraulic oil discharged from the first hydraulic pump 2. In addition, when the valve core of the fan control valve 5 is in the rotation position (5F) or (5R), the connection between the first hydraulic pump 2 and the confluence control valve 6 via the central bypass line CL is cut off.

[0112] The merging control valve 6 is constituted by, for example, a 6-port 3-position hydraulic pilot type directional control valve. The merging control valve 6 is constituted by a single directional control valve and has hydraulic pilot parts 6a and 6b on both left and right sides.

[0113] The merging control valve 6 is a switching valve that can switch the valve core (valve body) to a merging position (6C), a diverging position (6D), and a neutral position (6N). The merging control valve 6 is normally connected to the hydraulic pilot parts 6a and 6b of the hydraulic pilot part 6 to the hydraulic oil tank 22, and the valve core is held in the neutral position (6N) by a centering spring.

[0114] When the valve core of the merging control valve 6 is in the merging position (6C), the supply oil passage 63 is connected to the center bypass line CL, and the connection between the supply oil passage 63 and the high-pressure side oil passage 38 of the steering circuit 33 is cut off. Therefore, when the merging control valve 6 is in the merging position (6C), the first hydraulic pump 2 is connected to the lifting control valve 7 via the fan control valve 5 in the neutral position (5N), and the second hydraulic pump 3 is connected to the lifting control valve 7, and the connection between the second hydraulic pump 3 and the steering circuit 33 is cut off. Therefore, when the merging control valve 6 is in the merging position (6C) and the fan control valve 5 is in the neutral position (5N), the hydraulic oil discharged from the first hydraulic pump 2 and the hydraulic oil discharged from the second hydraulic pump 3 are combined and guided to the lifting control valve 7.

[0115] When the valve core of the merging control valve 6 is in the neutral position (6N), the supply oil passage 63 is connected to the high-pressure side oil passage 38 of the steering circuit 33. In addition, when the valve core of the merging control valve 6 is in the neutral position (6N), the upstream side and the downstream side of the merging control valve 6 of the center bypass line CL are connected. That is, in the neutral position (6N), the fan control valve 5 is connected to the lifting control valve 7. Therefore, when the merging control valve 6 is in the neutral position (6N), the first hydraulic pump 2 is connected to the lifting control valve 7 via the fan control valve 5 in the neutral position (5N), and the second hydraulic pump 3 is connected to the steering circuit 33, and the connection between the second hydraulic pump 3 and the lifting control valve 7 is cut off. Thus, when the merging control valve 6 is in the neutral position (6N), when the fan control valve 5 is in the neutral position (5N), the hydraulic oil discharged from the first hydraulic pump 2 is guided to the lifting control valve 7 through the fan control valve 5 and the merging control valve 6, and the hydraulic oil discharged from the second hydraulic pump 3 is guided to the steering circuit 33. That is, the neutral position (6N) is a non-merging position in which the hydraulic oil discharged from the first hydraulic pump 2 and the hydraulic oil discharged from the second hydraulic pump 3 are not merged.

[0116] When the valve core of the confluence control valve 6 is in the diverting position (6D), the supply oil path 63 is connected to the high-pressure side oil path 38 of the steering circuit 33 and the actuator oil path 85. As a result, the hydraulic oil discharged from the second hydraulic pump 3 is diverted and guided to the steering circuit 33 and the actuator oil path 85. Therefore, the accessory actuator 86 connected to the actuator oil path 85 can be operated during driving. In addition, the diverting position (6D) is a non-confluence position in which the hydraulic oil discharged from the first hydraulic pump 2 and the hydraulic oil discharged from the second hydraulic pump 3 are not merged, as in the neutral position (6N).

[0117] The hoist control valve 7 is constituted by, for example, a 6-port 4-position hydraulic pilot type directional control valve. The hoist control valve 7 is constituted by a single directional control valve and has hydraulic pilot parts 7a and 7b on the left and right sides.

[0118] As a plurality of switching positions, the lifting control valve 7 has: a rising position (7R) in which the lifting cylinder 10 is extended by supplying and spraying the working oil to rotate the cargo bucket 104 upward; a descending position (7L) in which the lifting cylinder 10 is contracted by supplying and spraying the working oil to rotate the cargo bucket 104 downward; a floating position (7F) in which the lifting cylinder 10 is contracted by the dead weight of the cargo bucket 104 to allow the dead weight of the cargo bucket 104 to fall; and a neutral position (7N) in which the supply and spraying of the working oil are stopped to maintain the cargo bucket 104. The lifting control valve 7 is a switching valve that can switch the valve core (valve body) to a rising position (7R), a descending position (7L), a floating position (7F) and a neutral position (7N). Normally, both the hydraulic pilot parts 7a and 7b of the lifting control valve 7 are connected to the working oil tank 22, and the valve core is maintained in the neutral position (7N) by a centering spring.

[0119] When the valve core of the lifting control valve 7 is in the neutral position (7N), the communication between the supply oil passage 62 and the return oil passage 69 and the actuator oil passages 71 and 72 is cut off. As a result, the supply of hydraulic oil to the lifting cylinder 10 and the ejection of hydraulic oil from the lifting cylinder 10 are stopped, and thus the movement of the lifting cylinder 10 is stopped. In addition, when the valve core of the lifting control valve 7 is in the neutral position (7N), the upstream side and the downstream side of the lifting control valve 7 of the center bypass line CL are connected.

[0120] When the valve core of the lifting control valve 7 is in the rising position (7R), the supply oil circuit 62 is connected to the actuator oil circuit 71, and the actuator oil circuit 72 is connected to the return oil circuit 69. In addition, the communication between the upstream side and the downstream side of the lifting control valve 7 of the central bypass line CL is cut off. Therefore, when the fan control valve 5 is in the neutral position (5N), the working oil discharged from the first hydraulic pump 2 is supplied to the bottom side oil chamber 10d of the lifting cylinder 10 through the supply oil circuit 62 and the actuator oil circuit 71. In addition, the working oil in the rod side oil chamber 10e is ejected to the working oil tank 22 through the actuator oil circuit 72 and the return oil circuit 69. As a result, the lifting cylinder 10 is driven in the extension direction, that is, the direction of lifting the cargo box 104.

[0121] When the valve core of the lifting control valve 7 is in the descending position (7L), the supply oil circuit 62 is connected to the actuator oil circuit 72, and the actuator oil circuit 71 is connected to the return oil circuit 69. In addition, the communication between the upstream side and the downstream side of the lifting control valve 7 of the central bypass line CL is cut off. Therefore, when the fan control valve 5 is in the neutral position (5N), the working oil discharged from the first hydraulic pump 2 is supplied to the rod side oil chamber 10e of the lifting cylinder 10 through the supply oil circuit 62 and the actuator oil circuit 72. In addition, the working oil in the bottom side oil chamber 10d is ejected to the working oil tank 22 through the actuator oil circuit 71 and the return oil circuit 69. As a result, the lifting cylinder 10 is driven in the direction of contraction, that is, the direction of descending the cargo box 104.

[0122] When the valve core of the lifting control valve 7 is in the floating position (7F), the supply oil passage 62 is connected to the center bypass line CL on the downstream side of the lifting control valve 7. In addition, when the valve core of the lifting control valve 7 is in the floating position (7F), the actuator oil passage 71 is connected to the return oil passage 69. As a result, the lifting cylinder 10 ejects the working oil in the bottom side oil chamber 10d to the working oil tank 22, and supplies the working oil in the working oil tank 22 to the rod side oil chamber 10e through the oil passage not shown. Therefore, when the lifting control valve 7 is in the floating position (7F), the lifting cylinder 10 can be retracted by the dead weight of the cargo box 104 side.

[0123] The pilot pump 4 is connected to a plurality of solenoid valves 16 to 21 via a pilot oil circuit. A pilot relief valve 15 that defines the pressure of the pilot oil circuit is provided in the pilot oil circuit between the pilot pump 4 and the plurality of solenoid valves 16 to 21. The plurality of solenoid valves 16 to 21 are pressure reducing valves that reduce the pressure (primary pressure) of the pilot oil circuit according to the control current from the control device 50 and output the reduced pressure (secondary pressure) as a pilot pressure. When a standby control current as an off signal is input to the solenoid valves 16 to 21, the hydraulic pilot parts 5a, 5b, 6a, 6b, 7a, 7b are connected to the working oil tank 22. When a driving control current as an on signal is input to the solenoid valves 16 to 21, the pilot pressure generated in the hydraulic pilot parts 5a, 5b, 6a, 6b, 7a, 7b is output.

[0124] The solenoid valves 16 and 17 for driving the fan control valve 5 are operated according to the control command (control current) output from the control device 50 corresponding to the temperature of the engine cooling water. The solenoid valves 18 and 19 for driving the lifting control valve 7 are operated according to the control command (control current) output from the control device 50 corresponding to the operation of the operating device 91 for the cargo box. The solenoid valves 20 and 21 for driving the confluence control valve 6 are operated according to the control command (control current) output from the control device 50 corresponding to the operation of the operating device 91 for the cargo box and the operating device of the accessory actuator 86 (not shown).

[0125] An operating device 91 for switching the lifting control valve 7, i.e., operating the lifting cylinder 10, is connected to the input / output interface of the control device 50. The operating device 91 is composed of, for example, 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 switching positions of the lifting control valve 7, i.e., the neutral position (7N), the rising position (7R), the floating position (7F), and the lowering position (7L), corresponding to the neutral position, the rising position, the floating position, and the lowering position. The operating device 91 outputs an operating signal corresponding to the operating position to the control device 50.

[0126] The input section of the input / output interface converts signals input from various devices (operating device 91, temperature sensor 25, etc.) into data that can be calculated by processing device 51. In addition, the output section of the input / output interface generates an output signal corresponding to the calculation result in processing device 51, and outputs the signal to various devices (solenoid valves 16 to 21, regulators 2a, 3a, etc.).

[0127] 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. The regulator 2a is a capacity control device that variably controls the displacement (discharge capacity per rotation) of the first hydraulic pump 2, and the regulator 3a is a capacity control device that variably controls the displacement (discharge capacity per rotation) of the second hydraulic pump 3. For example, in the case where the hydraulic pump is a swash plate type piston pump, the regulator has: a tilting actuator that controls the tilting angle (discharge capacity) of the swash plate of the hydraulic pump; and an electromagnetic proportional valve that generates a control pressure of the tilting actuator using the discharge pressure of the hydraulic pump as an initial pressure.

[0128] When the operating device 91 is operated to the neutral position, the control device 50 controls the fan control valve 5 according to the engine cooling water temperature (hereinafter also referred to as the cooling water temperature) Tc detected by the temperature sensor 25. The control content of the fan control valve 5 will be described later.

[0129] 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). That is, the control device 50 outputs a disconnection signal to both the 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 be switched to the floating position (7F). That is, the control device 50 outputs a disconnection signal to the solenoid valve 18 and outputs a first connection signal to the solenoid valve 19. As a result, the pilot pressure generated by the solenoid valve 19 acts on the hydraulic pilot portion 7b, and the hoist control valve 7 is switched to the floating position (7F).

[0130] When the operating device 91 is operated to the rising position, the control device 50 controls the lifting control valve 7 to be switched to the rising position (7R). That is, the control device 50 outputs an on signal to the solenoid valve 18, and outputs 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 part 7a, and the lifting control valve 7 is switched to the rising position (7R). When the operating device 91 is operated to the descending position, the control device 50 controls the lifting control valve 7 to be switched to the descending position (7L). That is, the control device 50 outputs an off signal to the solenoid valve 18, and outputs a second on signal to the solenoid valve 19. The current value of the second on signal is larger than that of the first signal. As a result, the pilot pressure generated by the solenoid valve 19 acts on the hydraulic pilot part 7b, and the lifting control valve 7 is switched to the descending position (7L).

[0131] When the operating device 91 is operated to the raised position, the control device 50 controls the merging control valve 6 to switch to the merging position (6C). That is, 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 portion 6a, and the merging control valve 6 is switched to the merging position (6C).

[0132] Therefore, when the operating device 91 is operated to the raised position, the hydraulic oil discharged from both the first hydraulic pump 2 and the second hydraulic pump 3 is supplied to the lifting cylinder 10. As a result, the lifting cylinder 10 with a large capacity can be smoothly extended to discharge cargo such as sand and soil from the cargo box 104. According to this embodiment, compared with a structure in which the extension action of the lifting cylinder 10 is performed using only the hydraulic oil discharged from the first hydraulic pump 2, the first hydraulic pump 2 can be miniaturized.

[0133] Furthermore, the control device 50 controls the merging control valve 6 to switch to the diverting position (6D) when the operating device (not shown) of the accessory actuator 86 is operated. Furthermore, the control device 50 controls the merging control valve 6 to maintain the neutral position (6N) when the operating device 91 is operated to any one of the neutral position, the floating position, and the lowered position and the operating device of the accessory actuator 86 is not operated.

[0134] The control device 50 controls the switching position of the fan control valve 5, for example, according to the cooling water temperature Tc, thereby controlling the rotation and stop of the fan motor 8 and the rotation direction of the fan motor 8. In addition, the control device 50 controls the discharge capacity q of the first hydraulic pump 2 within the range from the minimum capacity qmin to the maximum capacity qmax via the regulator 2a, for example, according to the cooling water temperature Tc, thereby controlling the rotation speed of the fan motor 8.

[0135] In addition, the control device 50 controls the discharge capacity q of the second hydraulic pump 3 within the range from the minimum capacity qmin to the maximum capacity qmax via the regulator 3a, for example, based on the pressure of the accumulator 42 detected by the pressure sensor (not shown). The minimum capacity qmin and the maximum capacity qmax of the discharge capacity q of the second hydraulic pump 3 may be different values ​​from those of the first hydraulic pump 2, or may be the same value.

[0136] The functions of the control device 50 of the second embodiment and the fan control process executed by the control device 50 are the same as those of the first embodiment. In addition, although not shown in the figure, the control device 50 determines whether the operating device 91 is operated to the neutral position or the floating position, and executes the fan control process when the operating device 91 is operated to the neutral position or the floating position. Figure 7 When 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. That is, when the operating device 91 is operated to the raised position or the lowered position, the control device 50 gives priority to the operation of the lifting cylinder 10.

[0137] Reference Figure 8 , the main operation of the hydraulic system 110 when the dump truck 100 of the second embodiment is traveling will be described. In addition, during the travel of the dump truck 100, the operating device 91 is operated to the neutral position, so the lifting control valve 7 is maintained in the neutral position (7N). In addition, the confluence control valve 6 is in the neutral position (6N) or the diversion position (6D). Figure 8 1 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 corresponding to the cooling water temperature Tc. When the cooling water temperature Tc is equal to or higher than the first threshold value Tc1 during the travel of the dump truck 100, the control device 50 controls the fan control valve 5 to switch 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).

[0138] Here, for example, during unloaded driving after the discharge of transported objects such as sand and soil, if the cooling of the engine cooling water flowing in the radiator 23 continues by the cooling wind and the running wind, the cooling water temperature Tc decreases. In the range where the cooling water temperature Tc is above the first threshold value Tc1 and less than the second threshold value Tc2, the discharge capacity q of the first hydraulic pump 2 is controlled according to the cooling water temperature Tc. If the cooling water temperature Tc further decreases and the cooling water temperature Tc is less than the first threshold value Tc1, the control device 50 outputs a disconnection 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 and stops as time passes. By stopping the generation of cooling wind for the cooling fan 9, overcooling of the engine cooling water can be prevented. In addition, the control device 50 controls the discharge flow rate Q of the first hydraulic pump 2 to the minimum flow rate Qmin. Thus, the hydraulic oil discharged from the first hydraulic pump 2 is ejected to the hydraulic oil tank 22 through the fan control valve 5 in the neutral position (5N), the confluence control valve 6 in the neutral position (6N) or the diversion position (6D), and the lifting 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 oil tank 22 can be reduced, and the discharge pressure of the first hydraulic pump 2 can be suppressed to be low. As a result, the load of the first hydraulic pump 2 is reduced, and the load of the engine 1 is reduced. Therefore, according to the present embodiment, the energy loss of the first hydraulic pump 2 can be reduced, and the fuel consumption can be suppressed.

[0139] According to the second embodiment described above, the following effects are achieved.

[0140] (1) The fan control valve 5, the confluence control valve 6, and the lifting control valve 7 are connected in series to the central bypass line (oil path) CL connecting the first hydraulic pump 2 and the hydraulic oil tank 22. On the central bypass line CL, the fan control valve 5 is arranged on the upstream side of the confluence control valve 6, and the confluence control valve 6 is arranged on the upstream side of the lifting control valve 7. The confluence control valve 6 has: a confluence position (6C) that causes the hydraulic oil discharged from the second hydraulic pump 3 to merge with the hydraulic oil discharged from the first hydraulic pump 2 and guide them to the lifting control valve 7; a neutral position (6N) as a non-confluence position; and a divergence position (6D) that guides the hydraulic oil discharged from the first hydraulic pump 2 to the lifting control valve 7 and guides the hydraulic oil discharged from the second hydraulic pump 3 to the steering circuit 33.

[0141] The fan control valve 5 has: a neutral position (5N), which connects the first hydraulic pump 2 with the confluence control valve 6 and cuts off the connection between the first hydraulic pump 2 and the fan motor (hydraulic motor) 8; a forward position (5F) and a reverse position (5R) as rotation positions, which cut off the connection between the first hydraulic pump 2 and the confluence control valve 6 and connect the first hydraulic pump 2 with the fan motor 8.

[0142] When the merging control valve 6 is in the merging position (6C), the first hydraulic pump 2 is connected to the lifting control valve 7 via the fan control valve 5 in the neutral position (5N), and the second hydraulic pump 3 is connected to the lifting control valve 7, and the connection between the second hydraulic pump 3 and the steering circuit 33 is cut off. When the merging control valve 6 is in the non-merging position (6N) or (6D), the first hydraulic pump 2 is connected to the lifting control valve 7 via the fan control valve 5 in the neutral position (5N), and the second hydraulic pump 3 is connected to the steering circuit 33, and the connection between the second hydraulic pump 3 and the lifting control valve 7 is cut off.

[0143] According to this structure, when the lifting cylinder 10 is not driven during driving, when the fan control valve 5 is switched to the neutral position (5N), the hydraulic oil discharged from the first hydraulic pump 2 is guided to the hydraulic oil tank 22 through the fan control valve 5, the confluence control valve 6, and the lifting control valve 7. Therefore, it is possible to suppress the generation of 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. In addition, the hydraulic oil discharged from the second hydraulic pump 3 is guided to the steering circuit 33 through the confluence control valve 6, so that it can rotate in any direction during driving.

[0144] The steering circuit 33 operates at a high frequency during driving. Here, when the cooling fan 9 is stopped, the working oil of the first hydraulic pump 2 and the working oil of the second hydraulic pump 3 are combined and guided to the steering circuit 33, and the working pressure of the steering circuit 33 is generated on the first hydraulic pump 2. In contrast, in the present embodiment, when the cooling fan 9 is stopped during driving of the dump truck 100, the working pressure of the steering circuit 33 does not act on the first hydraulic pump 2, and therefore, the life of the first hydraulic pump 2 can be increased.

[0145] (2) The control device 50 determines whether the cooling water temperature (temperature of the cooling object) Tc detected by the temperature sensor 25 is greater than the first threshold value Tc1. When the cooling water temperature Tc is greater than the first threshold value Tc1, the control device 50 switches the fan control valve 5 to the forward rotation position (rotation position) 5F. When the cooling water temperature Tc is less than the first threshold value Tc1, the control device 50 switches the fan control valve 5 to the neutral position (5N).

[0146] The dump truck 100 of this embodiment is used as a hydraulic pump (first hydraulic pump 2) for supplying working oil to the lifting cylinder 10 and the fan motor 8 because the lifting cylinder 10 is used less frequently. In addition, the fan control valve 5, which is a single control valve, has both the function of switching the supply destination of the working oil discharged from the first hydraulic pump 2 to the lifting cylinder 10 or the fan motor 8 and the function of switching the rotation and stop of the fan motor 8. Therefore, there is no need to separately set a control valve for realizing each function, so the structure of the hydraulic circuit can be simplified. In addition, when the low-load driving state continues and the cooling water temperature Tc is less than the first threshold value Tc1 due to the cooling wind and the driving wind, the fan control valve 5 is switched to the neutral position (5N). As a result, the generation of cooling wind of the cooling fan 9 is stopped, so that the overcooling of the engine cooling water can be prevented. That is, according to this embodiment, a dump truck (transport vehicle) 100 that can prevent the overcooling of the engine cooling water (cooling object) with a simple structure can be provided.

[0147] (3) When the cooling water temperature Tc is equal to or higher than the first threshold value 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 cooling water temperature Tc is less than the first threshold value Tc1, the control device 50 controls the discharge capacity q of the first hydraulic pump 2 to the minimum capacity qmin. According to this structure, during driving, if the cooling water temperature Tc is less than the first threshold value Tc1, 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 of the engine 1 is reduced, so that fuel consumption during driving can be suppressed.

[0148] (4) When the cooling water temperature Tc is greater than or equal to the first threshold value Tc1 and less than the second threshold value Tc2, the higher the cooling water temperature Tc, the more the control device 50 increases the discharge capacity q of the first hydraulic pump 2. In addition, when the cooling water temperature Tc is greater than or equal to the second threshold value Tc2, the control device 50 controls the discharge capacity q of the first hydraulic pump 2 to the maximum capacity qmax.

[0149] According to this configuration, the higher the cooling water temperature Tc, the higher the rotation speed of the cooling fan 9 is, and the cooling effect on the engine cooling water can be improved. By controlling the rotation speed of the cooling fan 9 according to the cooling water temperature Tc, the engine cooling water can be prevented from becoming too low or too high.

[0150] (5) As non-merging positions, the merging control valve 6 has: a neutral position (6N) that guides the hydraulic oil discharged from the first hydraulic pump 2 to the hoist control valve 7 and guides the hydraulic oil discharged from the second hydraulic pump 3 to the steering circuit 33; and a diverting position (6D) that guides the hydraulic oil discharged from the first hydraulic pump 2 to the hoist control valve 7 and diverts the hydraulic oil discharged from the second hydraulic pump 3 to the steering circuit 33 and the accessory actuator 86. According to this structure, when the cooling fan 9 stops while the dump truck 100 is traveling, the load on the engine 1 can be reduced even when the merging control valve 6 is switched to either the neutral position (6N) or the diverting position (6D).

[0151] (6) As rotation positions, the fan control valve 5 has: a forward rotation position (5F) for rotating the fan motor 8 in the forward rotation direction; and a reverse rotation position (5R) for rotating the fan motor 8 in the reverse rotation direction opposite to the forward rotation direction. When the fan control valve 5 is switched to the reverse rotation position (5R), cooling air is generated to flow forward from the cooling fan 9, and dust adhering to the filter of the air vent of the front grille 107, the gap of the radiator (heat exchanger) 23, etc. is removed. Therefore, according to the present embodiment, the cooling performance of the radiator 23 reduced by dust can be easily restored.

[0152] In addition, the control device 50 can be configured to temporarily switch the fan control valve 5 to the reverse position (5R), for example, during maintenance of the dump truck 100 or periodically. If a service person operates the input device during maintenance and inputs a reverse command of the cooling fan 9 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 specified time. In addition, the control device 50 measures the operating time of the dump truck 100 by a timing function, and switches the fan control valve 5 to the reverse position (5R) for a specified time each time the operating time exceeds a specified operating time. In addition, the control device 50 can also temporarily switch the fan control valve 5 to the reverse position (5R) when the engine 1 is started or when the engine 1 is stopped.

[0153] (7) The hydraulic system 110 includes: a pair of motor oil passages 81 and 82 connecting the fan control valve 5 to 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 structure, when the fan control valve 5 is switched to the neutral position (5N), for example, when the cooling fan 9 is rotated by the running wind, hydraulic oil is supplied from the hydraulic oil tank 22 to the suction port of the fan motor 8 through the check valves 13 and 14, and hydraulic oil is supplied from the hydraulic oil tank 22 to the suction port of the fan motor 8 through the fan control valve 5. Therefore, it is possible to suppress the suction port of the fan motor 8 from becoming a negative pressure, thereby preventing 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 oil is also supplied from the hydraulic oil tank 22 to the suction port of the fan motor 8 through the fan control valve 5, so that it is possible to effectively prevent the occurrence of cavitation compared to the case where hydraulic oil is supplied only through the check valves 13 and 14. In addition, the same is true when the fan control valve 5 is switched to the neutral position (5N) when the cooling fan 9 rotates forward or reversely, and the cooling fan 9 continues to rotate due to inertia. That is, when the cooling fan 9 rotates due to inertia, the working oil is supplied from the working oil tank 22 to the suction port of the fan motor 8 through the connecting path 5c of the fan control valve 5 and the one-way valve 13 or the one-way valve 14, so that the suction side of the fan motor 8 can be suppressed from becoming negative pressure.

[0154] In addition, when the valve core of the fan control valve 5 is in the neutral position (5N), the motor oil circuit 81 is connected to the motor oil circuit 82. That is, the fan control valve 5 of the present embodiment is a so-called neutral free-style directional switching valve. Therefore, the working oil of the motor oil circuit on the discharge side is also supplied to the motor oil circuit on the suction side through the fan control valve 5. Therefore, according to the present embodiment, compared with the case where the pair of motor oil circuits 81 and 82 are not connected to each other in the neutral position (5N) (the case of a neutral blocking directional switching valve), the occurrence of cavitation can be effectively prevented.

[0155] <Third Embodiment>

[0156] Reference Fig.10 and Fig.11 , a dump truck (transport vehicle) according to a third embodiment of the present invention will be described. In addition, the same reference numerals are given to the same or corresponding structures as those described in the second embodiment, and mainly the differences will be described.

[0157] The control device 50 of the third embodiment has the functions described below in addition to the functions described in the second embodiment. Fig.10 is a functional block diagram of the control device 50 of the third embodiment. Fig.10As shown, the rotation speed sensor 41 is connected to the control device 50. The rotation speed sensor 41 detects the rotation speed N of the engine 1 (hereinafter also referred to as the engine rotation speed) and outputs a signal indicating the detection result to the control device 50.

[0158] The determination unit 54 determines the state of the engine 1 based on the detection result of the rotation speed sensor 41. The valve control unit 55 controls the switching position of the confluence control valve 6 based on the determination result of the determination unit 54. The pump control unit 56 controls the discharge capacities q of the first hydraulic pump 2 and the second hydraulic pump 3 based on the determination result of the determination unit 54.

[0159] Fig.11 This is a flowchart showing an example of a processing flow of the loss reduction control at the time of engine startup executed by the control device 50 according to the third embodiment. Fig.11 The process shown in the flowchart is started by turning on an ignition switch (not shown), that is, turning on an ignition power supply. In addition, 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 supply is turned on. That is, power is supplied to the control device 50, and the control device 50 is started. When the ignition switch is operated from the on position to the start position, the engine 1 is started by the starter motor 40.

[0160] In step S220, the determination unit 54 determines whether the engine 1 is being started, 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. The determination unit 54 determines, for example, whether the engine rotation speed N is greater than 0. When the engine rotation speed N is 0, the determination unit 54 determines that the engine 1 is not being started. When the engine rotation speed N is greater than 0, the determination unit 54 determines that the engine 1 is being started, and the process proceeds to step S230. The determination unit 54 repeatedly performs the process of step S220 in a predetermined control cycle until it is determined that the engine 1 is being started.

[0161] In step S230 , the pump control unit 56 outputs a control signal for setting the discharge capacity q of the first hydraulic pump 2 to the minimum capacity qmin to the regulators 2 a and 3 a , and the process proceeds to step S240 .

[0162] 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). In addition, although not shown, the valve control unit 55 outputs an off signal to the solenoid valves 16 to 19. As a result, the lifting control valve 7 is maintained in the neutral position (7N), and the fan control valve 5 is maintained in the neutral position (5N). When the process (S240) of switching the merging control valve 6 to the merging position (6C) is completed, the process proceeds to step S250.

[0163] In step S250, the determination unit 54 determines whether the start of the engine 1 is completed based on the engine rotation speed N detected by the rotation speed sensor 41. For example, when the engine rotation speed N is greater than the idle rotation speed (speed threshold) Ni, the determination unit 54 determines that the start of the engine 1 is completed, and the process proceeds to step S270. When the engine rotation speed N is less than the idle rotation speed (speed threshold) Ni, the determination unit 54 determines that the start of the engine 1 is not completed, and the process returns to step S230. In addition, the speed threshold for whether the start of the engine 1 is completed can also be set to a value slightly lower than the idle rotation speed Ni.

[0164] In addition, the method for determining whether the start of the engine 1 is completed is not limited to the above method, and the following determination method may be used. For example, when the state of the engine rotation speed N being above the speed threshold continues for a predetermined time, the determination unit 54 determines that the start of the engine 1 is completed. When the state of the engine rotation speed N being above the speed threshold does not continue for a predetermined time, the determination unit 54 determines that the start of the engine 1 is not completed.

[0165] In step S270, the valve control unit 55 outputs a disconnection signal to the solenoid valve 20 and outputs a disconnection signal to the solenoid valve 21, switching the confluence control valve 6 to the neutral position (6N), and the process ends. Fig.11 In addition, if Fig.11 When the processing shown in the flowchart is completed, the control device 50 transfers to Figure 7 The process is shown in the flowchart.

[0166] In the dump truck 100 of the third embodiment, the main operation of the hydraulic system 110 when the engine 1 is started by the starter motor 40 is described. When the operator operates the ignition switch from the off position to the start position via the on position, power is supplied to the starter motor 40, and the starter motor 40 is driven. As a result, the cranking of the engine 1 by the starter motor 40 starts. During the cranking operation, the rotation speed of the engine 1 does not reach the minimum rotation speed after the engine start is completed, that is, the idle rotation speed.

[0167] The control device 50 determines whether the engine (prime mover) 1 is being started. When it is determined that the engine 1 is being started, the control signal (the on signal to the solenoid valve 20) (S220, S240) is output to switch the confluence control valve 6 to the confluence position (6C). In addition, the fan control valve 5 and the lifting control valve 7 are respectively maintained in the neutral position (5N) and (7N). As a result, the first hydraulic pump 2 and the working oil tank 22 are connected via the fan control valve 5, the confluence control valve 6 and the lifting control valve 7. When the engine 1 is started by the starter motor 40, the confluence control valve 6 is switched to the confluence position (6C), and the working oil discharged from the first hydraulic pump 2 and the working oil discharged from the second hydraulic pump 3 are combined and ejected to the working oil tank 22 through the central bypass line CL. Therefore, according to the present embodiment, compared with the case where the engine 1 is started with the confluence control valve 6 in the neutral position (6N), the load of the second hydraulic pump 3 can be reduced. This can reduce the load on the engine 1 , thereby improving the startability of the engine 1 by the starter motor 40 .

[0168] Furthermore, when the control device 50 determines that the engine 1 is being started, the discharge capacity q of the first hydraulic pump 2 and the second hydraulic pump 3 is controlled to the minimum capacity qmin (S220, S230). According to this configuration, for example, when the discharge capacity q of the first hydraulic pump 2 is controlled to a value corresponding to the cooling water temperature Tc at the time of engine starting, the load acting on the engine 1 can be reduced compared to the case where the discharge capacity q of the first hydraulic pump 2 and the second hydraulic pump 3 is larger than the minimum capacity qmin. As a result, the startability of the engine 1 can be further improved.

[0169] Thus, according to the third embodiment, in addition to the effects described in the second embodiment, the engine startability can be improved. In particular, in a low temperature environment such as winter or cold regions where the working oil is low temperature, the load of the hydraulic pump is likely to increase. According to the third embodiment, a dump truck 100 having good engine startability even in a low temperature environment can be provided.

[0170] <Fourth embodiment>

[0171] Reference Fig.12 and Fig.13 , a dump truck (transport vehicle) according to a fourth embodiment of the present invention will be described. In addition, the same reference numerals are given to the same or corresponding structures as those described in the second embodiment, and mainly the differences will be described.

[0172] The control device 50 of the second embodiment keeps the fan control valve 5 in the neutral position (5N) regardless of the cooling water temperature Tc when the operating position of the operating device 91 for the cargo box is in the raised position or the lowered position. In contrast, the control device 50 of the fourth embodiment switches the fan control valve 5 to the forward position (5F) when the cooling water temperature Tc rises to near the alarm temperature even when the operating position of the operating device 91 for the cargo box is in the raised position or the lowered position. The alarm temperature refers to the temperature at which an alarm is output to prevent overheating of the engine 1.

[0173] The control device 50 of the fourth embodiment gives priority to the operation of the lifting cylinder 10 when the operating device 91 is operated to the raised position or the lowered position when the cooling water temperature Tc is lower than the third threshold value Tc3 higher than the second threshold value Tc2, and gives priority to the operation of the fan motor 8 when the operating device 91 is operated to the raised position or the lowered position when the cooling water temperature Tc is higher than the third threshold value Tc3. The third threshold value Tc3 corresponds to a temperature slightly lower than the alarm temperature, for example, and is pre-stored in the non-volatile memory 52.

[0174] Fig.12 4 is a functional block diagram of the control device 50 according to the fourth embodiment. The determination unit 54 determines whether the cooling water temperature Tc detected by the temperature sensor 25 is equal to or higher than a third threshold value Tc3.

[0175] The determination unit 54 determines the operation position of the operation device 91, that is, what kind of operation is performed on the lifting cylinder 10, based on the signal indicating the operation position output from the operation device 91. Specifically, the determination unit 54 determines whether the lifting operation for switching the lifting control valve 7 to the rising position (7R) is being performed by the operation device 91. The determination unit 54 determines whether the lifting operation for switching the lifting control valve 7 to the lowering position (7L) is being performed by the operation device 91. The determination unit 54 determines whether the floating operation for switching the lifting control valve 7 to the floating position (7F) is being performed by the operation device 91.

[0176] Fig.13 TABLE 9 is a table showing the relationship between the operating position of the operating device 91 for the cargo box, the cooling water temperature Tc, and the switching position of each control valve 5 to 7. Fig.13 As shown, the valve control unit 55 outputs control signals to the electromagnetic valves 16 to 21 based on the determination result of the determination unit 54 , thereby controlling the hoist control valve 7 , the confluence control valve 6 , and the fan control valve 5 .

[0177] When the operating position of the operating device 91 is the neutral position, that is, when the operating device 91 is in the non-operating state (initial state), the valve control unit 55 maintains the hoist control valve 7 in the neutral position (7N) and maintains the merging control valve 6 in the neutral position (6N). When the operating position of the operating device 91 is the raising position, that is, when the hoist raising operation is being performed by the operating device 91, the valve control unit 55 switches the hoist control valve 7 to the raising position (7R) and switches the merging control valve 6 to the merging position (6C). When the operating position of the operating device 91 is the lowering position, that is, when the hoist lowering operation is being performed by the operating device 91, the valve control unit 55 maintains the merging control valve 6 in the neutral position (6N) and switches the hoist control valve 7 to the lowering 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 maintains the merging control valve 6 in the neutral position (6N) and switches the hoist control valve 7 to the floating position (7F).

[0178] When the operating position of the operating device 91 is the neutral position or the floating position, as in the second embodiment, the valve control unit 55 maintains the fan control valve 5 in the neutral position (5N) when the cooling water temperature Tc is less than the first threshold value Tc1, and switches the fan control valve 5 to the forward rotation position (5F) when the cooling water temperature Tc is greater than the first threshold value Tc1.

[0179] On the other hand, when the operating position of the operating device 91 is the rising position or the falling position, the valve control unit 55 maintains the fan control valve 5 in the neutral position (5N) when the cooling water temperature Tc is less than the third threshold value Tc3, and switches the fan control valve 5 to the forward position (5F) when the cooling water temperature Tc is above the third threshold value Tc3.

[0180] As described above, the control device 50 of the fourth embodiment switches the lifting control valve 7 to the raising position and switches the merging control valve 6 to the merging position (6C) when the lifting operation is performed by the operating device 91. In addition, when the lifting operation is performed when the cooling water temperature Tc is less than the third threshold value Tc3, the control device 50 switches the fan control valve 5 to the neutral position (5N) even if the cooling water temperature Tc is greater than the first threshold value Tc1. As a result, the hydraulic oil discharged from both the first hydraulic pump 2 and the second hydraulic pump 3 merges at the merging control valve 6 and is supplied to the lifting cylinder 10. As a result, the lifting cylinder 10 can be smoothly extended.

[0181] On the other hand, when the lifting operation is performed when the cooling water temperature Tc is equal to or higher than the third threshold value Tc3, the control device 50 switches the fan control valve 5 to the forward rotation position (5F). As a result, the hydraulic oil discharged from the first hydraulic pump 2 is supplied to the fan motor 8 through the fan control valve 5, and the hydraulic oil discharged from the second hydraulic pump 3 is supplied to the lifting cylinder 10 through the confluence control valve 6. As a result, the cooling air generated by the cooling fan 9 can be used to cool the engine cooling water, and the lifting cylinder 10 can be extended. Therefore, according to the fourth embodiment, overheating of the engine 1 can be prevented.

[0182] The following modifications are also within the scope of the present invention. The structure shown in the modification may be combined with the structure described in the above embodiment, or the structures described in the above different embodiments may be combined with each other, or the structures described in the following different modifications may be combined with each other.

[0183] <Variation 1>

[0184] In the above embodiment, an example is described in which the pump control unit 56 controls the discharge capacity q of the first hydraulic pump 2 according to the capacity control table that specifies 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 according to a mathematical formula (function) that specifies the relationship between the cooling water temperature Tc and the discharge capacity q of the first hydraulic pump 2.

[0185] In addition, the pump control unit 56 may control the discharge capacity q according to the determination result of the determination unit 54 without using the capacity control table and the mathematical formula. For example, when it is determined that the cooling water temperature Tc is less than the first threshold value Tc1, the pump control unit 56 controls the discharge capacity q to the minimum capacity qmin, and when it is determined that the cooling water temperature Tc is greater than the second threshold value Tc2, the pump control unit 56 controls the discharge capacity q to the maximum capacity qmax. In this case, in the process of the cooling water temperature Tc rising from the state less than the first threshold value Tc1 to the second threshold value Tc2, the discharge capacity q is controlled to the minimum capacity qmin, and when the cooling water temperature Tc exceeds the second threshold value Tc2, the discharge capacity q is controlled to the maximum capacity qmax. In addition, in the process of the cooling water temperature Tc decreasing from the state greater than the second threshold value Tc2 to the first threshold value Tc1, the discharge capacity q is controlled to the maximum capacity qmax, and when the cooling water temperature Tc is less than the first threshold value Tc1, the discharge capacity q is controlled to the minimum capacity qmin.

[0186] <Variation 2>

[0187] In the third embodiment, an example is described in which the determination unit 54 determines whether the engine 1 is being started based on the detection result of the rotation speed sensor 41. However, the method for determining whether the engine 1 is being started is not limited to this. For example, the determination unit 54 may determine that the engine 1 is being started when the ignition switch (engine key switch) is operated to the start position, and determine that the engine 1 is not being started when the ignition switch (engine key switch) is not operated to the start position.

[0188] <Variation 3>

[0189] In the third embodiment, an example is described in which the discharge capacities q of the first hydraulic pump 2 and the second hydraulic pump 3 are controlled to the minimum capacities qmin during the start of the engine 1. However, this may be omitted. Fig.11 The process of step S230.

[0190] <Variation 4>

[0191] In the above embodiment, an example in which the prime mover that drives the first hydraulic pump 2 and the second hydraulic pump 3 is the engine 1 has been described, but the prime mover may be an electric motor.

[0192] <Variant 5>

[0193] In the above embodiment, the cooling object of the cooling air is described as an example of engine cooling water for cooling the engine 1, but the cooling object of the cooling air is not limited to this. For example, the cooling object of the cooling air may also be cooling oil for cooling the brake device. In addition, as a driving source of a travel device for driving the vehicle body 101, in the case of a travel electric motor and a travel inverter for controlling the travel electric motor, the cooling water for cooling the travel inverter may also be the cooling object of the cooling air.

[0194] Furthermore, the cooling object may also be working oil. The oil cooler cools the working oil by exchanging heat between the working oil and the cooling air. In this case, the circulation system of the cooling object is composed of a hydraulic circuit including a working oil tank 22 and a hydraulic pump (a first hydraulic pump 2, a second hydraulic pump 3). The viscosity of the working oil increases as the temperature of the working oil decreases. Therefore, when the working oil is in an overcooled state, the high-viscosity working oil is discharged from the hydraulic pump, and the pressure loss in the oil circuit becomes higher. As a result, the load on the hydraulic pump increases and fuel consumption deteriorates. However, according to a modified example of the present embodiment, when the temperature of the working oil is less than the first threshold value Tc1, the rotation of the cooling fan 9 stops to prevent overcooling of the working oil, thereby preventing the load on the hydraulic pump from increasing.

[0195] <Variant 6>

[0196] In the above-mentioned embodiment, as a case where the cooling fan 9 is not required for cooling, a case where the temperature of the engine cooling water is less than the first threshold value Tc1 due to the running wind and the cooling wind in a low-load running state is described. However, the case where the engine cooling water cooling is not required is not limited to this. For example, in a low-temperature environment, even if the radiator 23 is not arranged in a position directly exposed to the running wind, sometimes the cooling of the engine cooling water is not required. That is, the heat exchanger such as the radiator 23 is not limited to the case where it is arranged at the front part of the vehicle body 101. The present invention can also be applied to a transport vehicle in which a heat exchanger is arranged at the side or rear part of the vehicle body 101.

[0197] <Variant 7>

[0198] In the second to fourth embodiments, the example in which the merging control valve 6 is a 6-port 3-position directional control valve is described. However, the merging control valve 6 may be a 6-port 2-position directional control valve without a branching position (6D).

[0199] As described above, the transport vehicle of the above embodiment has: at least one hydraulic pump driven by a prime mover; a hydraulic motor driven by working oil supplied from a first hydraulic pump of at least one hydraulic pump; a cooling fan driven by the hydraulic motor; a heat exchanger arranged at the front of the vehicle body and cooling the cooling object by the cooling wind generated by the cooling fan; a hydraulic cylinder driven by working oil supplied from the first hydraulic pump; a fan control valve controlling the flow of working oil supplied from the first hydraulic pump to the hydraulic motor; a cylinder control valve controlling the flow of working oil supplied from the first hydraulic pump to the hydraulic cylinder; and a control device controlling the discharge capacity of the fan control valve and at least one hydraulic pump. The fan control valve and the cylinder control valve are connected in series to the oil circuit connecting the first hydraulic pump and the working oil tank. The fan control valve is arranged on the upstream side of the cylinder control valve. The invention has the following positions: a neutral position, which connects the first hydraulic pump and the cylinder control valve, cuts off the connection between the first hydraulic pump and the hydraulic motor, and connects the suction port and the discharge port of the hydraulic motor with the working oil tank; a rotation position, which cuts off the connection between the first hydraulic pump and the cylinder control valve, connects the first hydraulic pump and the suction port of the hydraulic motor, and connects the discharge port of the hydraulic motor with the working oil tank. Thus, a transport vehicle can be provided, which can prevent overcooling of the cooling object with a simple structure.

[0200] Although the embodiments of the present invention have been described above, the above embodiments merely represent a part of application examples of the present invention, and the technical scope of the present invention is not limited to the specific structures of the above embodiments.

[0201] Explanation of symbols

[0202] 1…Engine (prime mover), 2…1st hydraulic pump (hydraulic pump), 2a…Regulator, 3…2nd hydraulic pump (hydraulic pump), 3a…Regulator, 4…Pilot pump, 5…Fan control valve, 5a, 5b…Hydraulic pilot, 5F…Forward position (rotation position), 5N…Neutral position, 5R…Reverse position (rotation position), 6…Merging control valve, 6a, 6b…Hydraulic pilot, 6C…Merging position, 6D…Diverting position (non-merging position), 6N…Neutral position (non-merging position), 7…Lifting control valve (cylinder control valve), 7a, 7b…Hydraulic pilot, 7F…Floating position, 7L…Lowering position, 7N…Neutral position, 7… R…Lifting position, 8…Fan motor (hydraulic motor), 9…Cooling fan, 10…Lifting cylinder (hydraulic cylinder), 10a…Outer cylinder, 10b…Inner cylinder, 10c…Piston rod, 10d…Bottom oil chamber, 10e…Rod oil chamber, 11, 12…Relief valve, 13, 14…Check valve, 15…Pilot relief valve, 16 to 21…Solenoid valve, 22…Working oil tank, 23…Radiator (heat exchanger), 24…Cooling water circulation pump, 25…Temperature sensor, 26…Cooling object, 27…Cooling water tank, 28…Cooling water system (circulation system), 29…Steering wheel, 30…Hydraulic motor, 31…Steering control valve, 33…Steering return 34, 35…steering cylinder, 36, 37…steering oil circuit, 38…high pressure side oil circuit, 39…low pressure side oil circuit, 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 circuit, 68, 69…return oil circuit, 71, 72…actuator oil circuit, 80…generator, 81, 82…motor oil circuit, 85…actuator oil circuit, 86…accessory actuator, 91…operating device, 91a…operating working rod, 100…dump truck (transport vehicle), 101…body, 102…support base, 103…cab, 104…cargo box, 105…front wheel, 106…rear wheel, 107…front grille, 110…hydraulic system, CL…central bypass line (oil circuit), N…engine rotation speed, Ni…idling rotation speed (speed threshold), q…discharge capacity (displacement), Q…discharge flow rate, qmax…maximum capacity, Qmax…maximum flow rate, qmin…minimum capacity, Qmin…minimum flow rate, Tc…cooling water temperature (temperature of cooling object), Tc1…first threshold, Tc2…second threshold, Tc3…third threshold.

Claims

1. A transport vehicle having: at least one hydraulic pump driven by the prime mover; a hydraulic motor driven by hydraulic oil supplied from a first hydraulic pump among the at least one hydraulic pump; a cooling fan driven by the hydraulic motor; a heat exchanger disposed at the front portion of the vehicle body and cooling a cooling object using cooling air generated by the cooling fan; a hydraulic cylinder driven by hydraulic oil supplied from the first hydraulic pump; a fan control valve that controls the flow of hydraulic oil supplied from the first hydraulic pump to the hydraulic motor; a cylinder control valve that controls the flow of hydraulic oil supplied from the first hydraulic pump to the hydraulic cylinder; and a control device for controlling the fan control valve and the discharge capacity of the at least one hydraulic pump, It is characterized in that The fan control valve and the cylinder control valve are connected in series with an oil circuit connecting the first hydraulic pump and the working oil tank. The fan control valve is arranged on the upstream side of the cylinder control valve. The fan control valve has the following positions: a neutral position, which connects the first hydraulic pump and the cylinder control valve, disconnects the first hydraulic pump from the hydraulic motor, and connects the suction port and the discharge port of the hydraulic motor to the working oil tank; and The rotation position cuts off the communication between the first hydraulic pump and the cylinder control valve, connects the first hydraulic pump with the suction port of the hydraulic motor, and connects the discharge port of the hydraulic motor with the hydraulic oil tank.

2. The transport vehicle according to claim 1, characterized in that: The transport vehicle comprises: a cargo box, which is arranged to be rotatable relative to the vehicle body; The at least one hydraulic pump includes the first hydraulic pump and the second hydraulic pump, The hydraulic cylinder is a lifting cylinder that can be telescopically arranged between the cargo box and the vehicle body. The cylinder control valve is a lifting control valve that controls the flow of hydraulic oil supplied from the first hydraulic pump to the lifting cylinder. The transport vehicle also has: a steering circuit having a steering cylinder driven by hydraulic oil supplied from the second hydraulic pump; and A combining control valve with the following positions: a merging position at which the hydraulic oil discharged from the second hydraulic pump merges with the hydraulic oil discharged from the first hydraulic pump and is guided to the hoist control valve; as well as a non-merging position that guides the hydraulic oil discharged from the first hydraulic pump to the hoist control valve and guides the hydraulic oil discharged from the second hydraulic pump to the steering circuit, The fan control valve, the confluence control valve, and the lifting control valve are connected in series with an oil circuit connecting the first hydraulic pump and the working oil tank. The fan control valve is arranged on the upstream side of the confluence control valve. The confluence control valve is arranged on the upstream side of the lifting control valve. The fan control valve has the following positions: a neutral position that connects the first hydraulic pump to the confluence control valve and disconnects the first hydraulic pump from the hydraulic motor; and a rotation position that cuts off the communication between the first hydraulic pump and the confluence control valve and connects the first hydraulic pump to the hydraulic motor, When the merging control valve is in the merging position, the first hydraulic pump is connected to the lifting control valve via the fan control valve in the neutral position, and the second hydraulic pump is connected to the lifting control valve, and the connection between the second hydraulic pump and the steering circuit is cut off. When the merging control valve is in the non-merging position, the first hydraulic pump is connected to the lifting control valve via the fan control valve in the neutral position, and the second hydraulic pump is connected to the steering circuit, and the connection between the second hydraulic pump and the lifting control valve is cut off.

3. The transport vehicle according to claim 2, characterized in that: The prime mover is an engine started by a starter motor, The control device determines whether the engine is being started. The control device outputs a control signal for switching the merging control valve to the merging position when it is determined that the engine is being started.

4. The transport vehicle according to claim 3, characterized in that: The control device controls the discharge capacities of the first hydraulic pump and the second hydraulic pump to minimum capacities when determining that the engine is being started.

5. The transport vehicle according to claim 2, characterized in that: The transport vehicle has a temperature sensor for detecting the temperature of the cooling object. The control device determines whether the temperature of the cooling object detected by the temperature sensor is equal to or higher than a first threshold value. When the temperature of the cooling object is equal to or higher than the first threshold, the control device switches the fan control valve to the rotation position. The control device switches the fan control valve to the neutral position when the temperature of the cooling object is lower than the first threshold value.

6. The transport vehicle according to claim 5, characterized in that: When the temperature of the cooling object is equal to or higher than the first threshold value, the control device controls the discharge capacity of the first hydraulic pump to a discharge capacity greater than a minimum capacity. The control device controls the discharge capacity of the first hydraulic pump to the minimum capacity when the temperature of the cooling target is lower than the first threshold value.

7. The transport vehicle according to claim 6, characterized in that: When the temperature of the cooling object is equal to or higher than the first threshold value and lower than a second threshold value, the control device increases the discharge capacity of the first hydraulic pump as the temperature of the cooling object increases. The control device controls the discharge capacity of the first hydraulic pump to a maximum capacity when the temperature of the cooling target is equal to or higher than the second threshold value.

8. The transport vehicle according to claim 7, characterized in that: The transport vehicle has: an operating device, which operates the lifting cylinder, The lifting control valve has the following positions: a raised position, which causes the lifting cylinder to extend and the cargo bucket to rotate upward; a descending position, which causes the lifting cylinder to retract and the cargo bucket to rotate downward; as well as A neutral position, which holds the cargo bed, The control device determines whether the temperature of the cooling object detected by the temperature sensor is equal to or higher than a third threshold value higher than the second threshold value, the control device determines whether a hoist raising operation for switching the hoist control valve to the raising position is being performed by the operating device, When the lifting operation is performed by the operating device, the control device switches the lifting control valve to the lifting position and switches the merging control valve to the merging position. When the lifting operation is performed when the temperature of the cooling object is less than the third threshold value, the control device switches the fan control valve to the neutral position even if the temperature of the cooling object is greater than the first threshold value. When the lifting operation is performed when the temperature of the cooling target is equal to or higher than the third threshold value, the control device switches the fan control valve to the rotation position.

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