Work vehicle and fan control method for a work vehicle

Abstract

To improve a power saving property in the time of engine startup.SOLUTION: A control method of a fan for a work vehicle makes hydraulic oil flow by a first flow rate in an oil passage by making a current in a first magnitude flow in a solenoid of a variable relief valve provided in the oil passage to which the hydraulic oil is output from a hydraulic pump driven by an engine in the time of engine startup, rotates a fan connected to a hydraulic motor by rotating the hydraulic motor connected to the oil passage. The control method reduces a rotational speed of the fan by making the hydraulic oil flow by a second flow rate smaller than the first flow rate in the oil passage by making the current in the second magnitude larger than the first magnitude flow in the solenoid when the rotational speed of the engine is larger than the first rotational speed threshold. The control method changes the rotational speed of the fan by making the current according to a temperature of liquid flowing in the work vehicle flow in the solenoid when the rotational speed of the engine is larger than the second rotational speed threshold larger than the first rotational speed threshold.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a work vehicle and a method for controlling a fan for a work vehicle. [Background technology]

[0002] Patent Document 1 discloses a work vehicle in which a hydraulic motor for rotating an engine cooling fan when the engine is started is controlled so that the motor rotation speed is fixed at a predetermined speed or lower until the start of the engine is confirmed, thereby reducing the influence of the hydraulic motor on the engine. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 4312681 Summary of the Invention [Problem to be solved by the invention]

[0004] In the work vehicle of Patent Document 1, a control valve for controlling an oil passage between a hydraulic motor for rotating the fan and a hydraulic pump must be closed or drained in order to limit the motor rotation speed while the engine is being started. Generally, since the time during which a work vehicle is in operation is overwhelmingly longer than the time during which the engine is started, the vehicle is designed to pass a current through a solenoid when the control valve is closed or drained in order to reduce power consumption. For this reason, in the work vehicle of Patent Document 1, a considerable amount of current must be passed through the solenoid of the control valve while the engine start is being confirmed.

[0005] An object of the technology disclosed in the present application is to provide a work vehicle and a fan control method for a work vehicle that reduces the current flowing through a solenoid when the engine is started, thereby improving power saving when the engine is started. [Means for solving the problem]

[0006] A method for controlling a fan for a work vehicle according to a first aspect of the present disclosure includes, at engine start, passing a current of a first magnitude through a solenoid of a variable relief valve provided in an oil passage through which hydraulic oil is output from a hydraulic pump driven by the engine, thereby causing hydraulic oil to flow through the oil passage at a first flow rate, thereby rotating a hydraulic motor connected to the oil passage, thereby rotating a fan connected to the hydraulic motor. When the rotation speed of the engine becomes higher than a first rotation speed threshold, the control method passes a current of a second magnitude larger than the first magnitude through the solenoid, thereby causing hydraulic oil to flow through the oil passage at a second flow rate smaller than the first flow rate, thereby reducing the rotation speed of the fan. When the rotation speed of the engine becomes higher than a second rotation speed threshold that is higher than the first rotation speed threshold, the control method passes a current according to the temperature of a liquid flowing inside the work vehicle through the solenoid, thereby changing the rotation speed of the fan.

[0007] A work vehicle according to a second aspect of the present disclosure includes an engine, a hydraulic pump driven by the engine, an oil passage connected by the hydraulic pump, a hydraulic motor provided in the oil passage and configured to rotate with hydraulic oil supplied by the hydraulic pump, a fan connected to the hydraulic motor and configured to rotate together with the hydraulic motor, a variable relief valve provided in the oil passage, having a solenoid, and configured to control the flow rate of hydraulic oil flowing in the oil passage in accordance with a current passed through the solenoid, and an electronic circuit that controls the magnitude of the current passed through the solenoid and controls the rotation speed of the fan. The electronic circuit is configured to: pass a current of a first magnitude through the solenoid when the engine is started, thereby causing hydraulic oil to flow through the oil passage at a first flow rate and rotating a fan connected to the oil passage; when the engine rotation speed becomes greater than a first rotation speed threshold, pass a current of a second magnitude greater than the first magnitude through the solenoid, thereby causing hydraulic oil to flow through the oil passage at a second flow rate smaller than the first flow rate, thereby reducing the rotation speed of the fan; and when the engine rotation speed becomes greater than a second rotation speed threshold that is greater than the first rotation speed threshold, pass a current corresponding to the temperature of the liquid flowing within the work vehicle through the solenoid, thereby changing the rotation speed of the fan. Effect of the Invention

[0008] The technology disclosed in the present application provides a work vehicle and a control method for a fan for a work vehicle that improves power saving during the period from engine start to confirmation of engine start. For example, a work vehicle and a control method for a fan for a work vehicle that improves power saving during engine start can be provided by reducing the current flowing through a solenoid during a portion of the period until engine start is confirmed. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is an overall side view of a work vehicle. [Diagram 2] FIG. 2 is a schematic diagram showing a hydraulic circuit of the work vehicle. [Diagram 3] FIG. 3 is a diagram showing the relationship among the engine rotation speed, the current flowing through the solenoid, and the flow rate of hydraulic oil flowing through the first partial oil passage. [Figure 4] FIG. 4 is a flowchart showing the process flow of the fan control method for the work vehicle. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings, in which like reference numerals indicate corresponding or identical components in each drawing.

[0011] Referring to FIG. 1, a work vehicle 1, for example, a compact track loader, includes a vehicle body frame 2, a traveling device 3, a working device 4, and a cabin 5. The vehicle body frame 2 supports the traveling device 3, the working device 4, and the cabin 5. In the illustrated embodiment, the traveling device 3 is a track-type traveling device. Therefore, the traveling device 3 includes a driving wheel 31, driven wheels 32 and 33, and a roller 34. However, the traveling device 3 is not limited to a track-type traveling device. The traveling device 3 may be, for example, a front-wheel / rear-wheel traveling device, or a traveling device having front wheels and a rear crawler. As shown in FIG. 2, the traveling device 3 is provided on the vehicle body frame 2. The working device 4 includes a work equipment (bucket) 41 at the distal end of the working device 4. The proximal end of the working device 4 is attached to the rear of the vehicle body frame 2. The working device 4 includes a pair of arms 42 for rotatably supporting a bucket 41 via a bucket pivot shaft 43. Each of the pair of arms 42 includes a lift link 44 and a boom 45.

[0012] The lift link 44 is rotatable relative to the vehicle body frame 2 around a fulcrum shaft 46. The boom 45 is rotatable relative to the lift link 44 around a joint shaft 47. The working device 4 further includes a plurality of boom cylinders 48 and at least one equipment cylinder 49. Each of the plurality of boom cylinders 48 is rotatably connected to the vehicle body frame 2 and the boom 45, and moves the lift link 44 and the boom 45 to lift and lower the bucket 41. The at least one equipment cylinder 49 is configured to tilt the bucket 41. The cabin 5 is attached to the front of the vehicle body frame 2. The work vehicle 1 includes a front door 51 in front of the cabin 5, and includes a driver's seat 52 and an operating device (described later) in the cabin 5. The interior space of the cabin 5 is defined by a cab frame 53.

[0013] Referring to FIG. 1, the work vehicle 1 further includes an engine 6 and a heat exchanger 7 provided at the rear of the body frame 2. The engine 6 is configured to provide driving force to the traveling device 3 and the working device 4. The heat exchanger 7 includes a radiator that cools the coolant of the engine 6. Furthermore, preferably, the heat exchanger 7 includes an oil cooler configured to cool hydraulic oil used in the hydraulic system (e.g., the boom cylinder 48 and at least one tool cylinder 49) of the work vehicle 1. The work vehicle 1 includes a fan 71 for air-cooling the heat exchanger 7. The fan 71 is provided below the heat exchanger 7. The engine 6 and the heat exchanger 7 are provided between a pair of arms 42. The work vehicle 1 further includes a bonnet cover 9 provided at the rear end of the body frame 2. The bonnet cover 9 can be opened and closed, allowing a maintenance worker to perform maintenance work on the engine 6 and the like. The work vehicle 1 further includes a cover 8 that covers the heat exchanger 7 and the engine 6. The cover 8 is provided with an air suction port 8 a for taking in cooling air generated by a fan 71 inside the cover 8 .

[0014] Fig. 2 is a schematic diagram showing a hydraulic circuit 10 of the work vehicle 1. Referring to Fig. 2, the hydraulic circuit 10 includes the engine 6, a hydraulic pump 11, an oil passage 20, a hydraulic motor 12, a fan 71, a variable relief valve 13, an unloading valve 14, a rotational direction switching valve 15, a hydraulic oil tank 16, and a controller 17. The hydraulic pump 11 is driven by the engine 6. That is, the rotating elements of the hydraulic pump 11 are configured to be rotated by the driving force of the engine 6 and to discharge hydraulic oil. Therefore, when the engine 6 starts, the rotating elements of the hydraulic pump 11 are also rotated and hydraulic oil is discharged.

[0015] The oil passage 20 connects the hydraulic pump 11 and the hydraulic oil tank 16 via the hydraulic motor 12. The hydraulic circuit 10 is provided with a first bypass oil passage 23 and a second bypass oil passage 24 that branch off from the oil passage 20 at a branch point J1 and merge with the oil passage 20 at a junction J2. For ease of explanation, the oil passage 20 between the branch point J1 and the hydraulic motor 12 is called a first partial oil passage 21. That is, the first bypass oil passage 23 and the second bypass oil passage 24 are connected in parallel to the oil passage 20 (first partial oil passage 21). The first bypass oil passage 23 and the second bypass oil passage 24 merge at a junction J3, and the first bypass oil passage 23 and the second bypass oil passage 24 are configured as one oil passage from the junction J3 to the junction J2, but are not limited to this configuration. The first bypass oil passage 23 and the second bypass oil passage 24 do not have to be joined until they join the oil passage 20, and the branch point between the oil passage 20 and the first bypass oil passage 23 and the branch point between the oil passage 20 and the second bypass oil passage 24 do not have to be a common branch point J1. When the branch point between the oil passage 20 and the first bypass oil passage 23 and the branch point between the oil passage 20 and the second bypass oil passage 24 are not a common branch point J1, the starting point of the first partial oil passage 21 is the branch point closer to the hydraulic motor 12 among the branch point between the oil passage 20 and the first bypass oil passage 23 and the branch point between the oil passage 20 and the second bypass oil passage 24. When the junction point of the oil passage 20 and the first bypass oil passage 23 and the junction point of the oil passage 20 and the second bypass oil passage 24 are not a common junction point J3, the end point of the first partial oil passage 21 is the junction point of the oil passage 20 and the first bypass oil passage 23 or the junction point of the oil passage 20 and the second bypass oil passage 24 that is closer to the hydraulic motor 12. The second bypass oil passage 24 may be referred to as an additional oil passage.

[0016] The hydraulic motor 12 is provided in an oil passage 20, and is configured to be rotated by hydraulic oil supplied by a hydraulic pump 11. The fan 71 is connected to the hydraulic motor 12, and is configured to rotate together with a rotating shaft of the hydraulic motor 12. The variable relief valve 13 is connected to the oil passage 20. More specifically, the variable relief valve 13 is provided in a first bypass oil passage 23. The variable relief valve 13 has a solenoid 13s, and is configured to control the flow rate of hydraulic oil flowing in the oil passage 20 (first partial oil passage 21) in response to a current passed through the solenoid 13s. In other words, the variable relief valve 13 is configured to control the flow rate of hydraulic oil flowing to the hydraulic motor 12 in response to a current passed through the solenoid 13s. The variable relief valve 13 is configured to increase the flow rate of hydraulic oil passing through the first bypass oil passage 23 as the current passed through the solenoid 13s increases. Therefore, the variable relief valve 13 is configured so that the flow rate of the hydraulic oil flowing through the first partial oil passage 21 decreases as the current flowing through the solenoid 13s increases.

[0017] The unloading valve 14 is provided in parallel with the variable relief valve 13 on the second bypass oil passage 24. The unloading valve 14 has an additional solenoid 14s, and is configured to control the flow rate of the hydraulic oil flowing through the second bypass oil passage 24 in response to a current applied to the additional solenoid 14s. Specifically, the unloading valve 14 is configured to be switchable between a first position 14A and a second position 14B. When the unloading valve 14 is switched to the first position 14A by applying a current exceeding the unloading current S to the additional solenoid 14s, the unloading valve 14 is configured to flow a larger volume of hydraulic oil than the variable relief valve 13. At this time, the unloading valve 14 can eliminate the load of hydraulic oil on the hydraulic motor 12 by flowing all of the hydraulic oil from the hydraulic pump 11 to the junction J2 via the second bypass oil passage 24. When a current not exceeding the unload current threshold is applied to the additional solenoid 14s, the unload valve 14 is switched to the second position 14B and is configured not to allow hydraulic oil to flow from the branch point J1 to the junction point J3 on the second bypass oil passage 24.

[0018] The rotation direction switching valve 15 can be switched between a forward rotation position 15A and a reverse rotation position 15B by operating a switching valve solenoid 15s. When the rotation direction switching valve 15 is switched to the forward rotation position 15A shown in Fig. 2, the hydraulic oil discharged from the hydraulic pump 11 flows in the forward direction through the hydraulic motor 12, causing the hydraulic motor 12 to rotate in the forward direction. Conversely, when the rotation direction switching valve 15 is switched to the reverse position 15B, the hydraulic oil flows in the reverse direction through the hydraulic motor 12, causing the hydraulic motor 12 to rotate in the reverse direction.

[0019] The controller 17 is configured to be connected to a rotation speed sensor 6s for detecting the rotation speed of the engine 6 and to acquire the rotation speed of the engine 6 from the rotation speed sensor 6s. The rotation speed sensor 6s is, for example, a hardware such as an encoder or a potentiometer connected to a rotating element (such as a crankshaft) of the engine 6 or a rotating element of a reducer connected to the rotating element. The controller 17 is configured to be connected to a temperature sensor 20s for detecting the temperature of the hydraulic oil in the oil passage 20 and to acquire the temperature of the hydraulic oil in the oil passage 20. The controller 17 is configured to be connected to a temperature sensor 7s for detecting the temperature of the cooling water that cools the engine 6 and to acquire the temperature of the cooling water. Note that, although the temperature sensor 7s is provided in the heat exchanger 7 that cools the cooling water in FIG. 2, it may be provided in another location.

[0020] The controller 17 is an electronic circuit that controls the magnitude of the current flowing through the solenoid 13s and controls the rotation speed of the fan 71. This electronic circuit includes a hardware processor 18 and a memory 19, and the control described in this embodiment may be realized by the hardware processor 18 executing a program stored in the memory 19. This program may be installed in the controller 17 via a computer-readable storage medium such as a CD-ROM. Alternatively, the electronic circuit may be an ASIC (Application Specific Integrated Circuit) that executes the control described in this embodiment.

[0021] Specifically, referring to FIG. 3, the controller 17 is configured to cause the solenoid 13s to pass a current of a first magnitude i1 when the engine 6 is started, thereby causing the hydraulic oil to flow at a first flow rate FR1 through the oil passage 20 (first partial oil passage 21) to rotate the fan 71 connected to the oil passage 20 (first partial oil passage 21). The current of the first magnitude i1 is preferably zero. On the other hand, the controller 17 is configured to cause the unloading valve 14 to cut off the second bypass oil passage 24 (additional oil passage) by passing a current of a third magnitude i3 through the additional solenoid 14s of the unloading valve 14 from the time the engine 6 is started until the rotation speed of the engine 6 exceeds a third rotation speed threshold RS3 that is equal to or higher than the first rotation speed threshold RS1. The current of the third magnitude i3 is preferably zero. In FIG. 3, the current of the third magnitude i3 is illustrated as being larger than the current of the first magnitude i1, but the current of the third magnitude i3 is determined independently of the current of the first magnitude i1. Since the second bypass oil passage 24 is blocked, the first flow rate FR1 is a value obtained by subtracting the flow rate of hydraulic oil flowing to the first bypass oil passage 23 via the variable relief valve 13 from the discharge rate of the hydraulic pump 11. Since the discharge rate of the hydraulic pump 11 increases according to the rotation speed of the engine 6, the first flow rate FR1 increases according to the rotation speed of the engine 6. In Fig. 3, the first flow rate FR1 changes as if it were proportional to the rotation speed of the engine 6, but this is merely a schematic illustration and may change non-linearly. Except for the case where the flow rate is zero, the other flow rates change in the same manner.

[0022] The controller 17 is configured to, when the rotation speed of the engine 6 becomes higher than the first rotation speed threshold RS1, pass a current of a second magnitude i2 larger than the first magnitude i1 to the solenoid 13s, thereby causing the hydraulic oil to flow to the oil passage 20 (first partial oil passage 21) at a second flow rate FR2 smaller than the first flow rate FR1, thereby reducing the rotation speed of the fan 71. On the other hand, when the rotation speed of the engine 6 exceeds the third rotation speed threshold RS3, the controller 17 is configured to, when the rotation speed of the engine 6 exceeds the third rotation speed threshold RS3, pass a current of a fourth magnitude i4 larger than the current of the third magnitude i3 to the additional solenoid 14s, thereby opening the unload valve 14 and causing the hydraulic oil from the hydraulic pump 11 to flow to the second bypass oil passage 24 (additional oil passage) via the second bypass oil passage 24 (additional oil passage). When the unloading valve 14 is opened, the hydraulic oil discharged from the hydraulic pump 11 is discharged to the hydraulic oil tank 16 via the second bypass oil passage 24 (additional oil passage), so that the flow rate of the hydraulic oil flowing through the oil passage 20 (first partial oil passage 21) becomes approximately zero. Preferably, the first rotational speed threshold value RS1 and the third rotational speed threshold value RS3 are equal, so that the second flow rate FR2 becomes approximately zero.

[0023] The controller 17 is configured to change the flow rate of hydraulic oil flowing through the second bypass oil passage 24 (additional oil passage) by passing a current according to the temperature of the liquid flowing inside the work vehicle 1 through the additional solenoid 14s when the rotation speed of the engine 6 exceeds the fourth rotation speed threshold RS4, which is equal to or higher than the third rotation speed threshold RS3. Specifically, the controller 17 is configured to pass a current of a third magnitude i3 through the additional solenoid 14s of the unloading valve 14 to close the unloading valve 14 when the rotation speed of the engine 6 is higher than the fourth rotation speed threshold RS4 and the temperature of the hydraulic oil exceeds the first threshold temperature T1. Alternatively, the controller 17 may be configured to pass a current of the third magnitude i3 through the additional solenoid 14s of the unloading valve 14 to close the unloading valve 14 when the rotation speed of the engine 6 is higher than the fourth rotation speed threshold RS4 and the temperature of the cooling water exceeds the second threshold temperature T2. Preferably, the third rotation speed threshold RS3 is equal to the fourth rotation speed threshold RS4.

[0024] In Fig. 3, the solid line indicates the current of the additional solenoid 14s and the flow rate of the hydraulic oil flowing through (the first partial oil passage 21) when the temperature of the hydraulic oil exceeds the first threshold temperature T1 at a rotation speed RS4a of the engine 6 that is greater than the fourth rotation speed threshold RS4 and less than the second rotation speed threshold RS2. In Fig. 3, the two-dot chain line indicates the current of the additional solenoid 14s and the flow rate of the hydraulic oil flowing through (the first partial oil passage 21) when the temperature of the hydraulic oil exceeds the first threshold temperature T1 at a rotation speed RS4b of the engine 6 that is greater than the second rotation speed threshold RS2. Note that, because the changes in both are the same until the rotation speed of the engine 6 reaches the rotation speed RS4a, the two-dot chain line is displayed only in the range where the rotation speed of the engine 6 is equal to or greater than the rotation speed RS4a. Preferably, the second rotational speed threshold RS2 makes it easier to reach the low idle target rotational speed of the engine 6 by making the third rotational speed threshold RS4, which is approximately equal to the low idle target rotational speed of the engine 6, smaller than the second rotational speed threshold RS2.

[0025] The controller 17 is configured to change the rotation speed of the fan 71 by passing a current corresponding to the temperature of the liquid flowing inside the work vehicle 1 to the solenoid 13s when the rotation speed of the engine 6 becomes higher than the second rotation speed threshold RS2 that is equal to or higher than the fourth rotation speed threshold RS4. Specifically, the controller 17 is configured to pass a current of a fifth magnitude i5, which is equal to or lower than the first magnitude i1, to the solenoid 13s of the variable relief valve 13 to close the variable relief valve 13 when the rotation speed of the engine 6 becomes higher than the second rotation speed threshold RS2 and the temperature of the working oil exceeds the first threshold temperature T1. Alternatively, the controller 17 may be configured to pass a current of a fifth magnitude i5 to the solenoid 13s of the variable relief valve 13 to close the variable relief valve 13 when the rotation speed of the engine 6 becomes higher than the second rotation speed threshold RS2 and the temperature of the cooling water exceeds the second threshold temperature T2.

[0026] In Fig. 3, the solid line represents the current of the solenoid 13s when the temperature of the hydraulic oil exceeds the first threshold temperature T1 at a rotation speed RS4a of the engine 6 that is greater than the fourth rotation speed threshold RS4 and less than the second rotation speed threshold RS2. In Fig. 3, the dashed-dotted line represents the current of the solenoid 13s when the temperature of the hydraulic oil exceeds the first threshold temperature T1 at a rotation speed RS4b of the engine 6 that is greater than the second rotation speed threshold RS2. Note that, because all the changes are the same until the rotation speed of the engine 6 reaches the rotation speed RS4a, the dashed-dotted line is displayed only in the range where the rotation speed of the engine 6 is equal to or greater than the rotation speed RS4a.

[0027] The above-mentioned first rotation speed threshold RS1 to fourth rotation speed threshold RS4 are smaller than the idling rotation speed RSi of the engine 6. This idling rotation speed RSi is the minimum rotation speed of the engine 6 that can be set by the accelerator for setting the rotation speed of the engine 6. With the above control, when the engine rotation speed exceeds the first rotation speed threshold RS1, a large flow rate of hydraulic oil is not sent to the hydraulic motor 12 until the viscosity of the hydraulic oil is deemed to have decreased so that the temperature of the hydraulic oil exceeds a predetermined temperature, thereby improving the durability of the hydraulic motor 12.

[0028] Furthermore, the controller 17 is configured to, when the rotation speed of the engine 6 exceeds the first rotation speed threshold RS1, pass a current of the second magnitude i2 to the solenoid 13s until the rotation speed falls below the fifth rotation speed threshold RS5, which is smaller than the first rotation speed threshold RS1, even if the rotation speed falls below the first rotation speed threshold RS1 again. When the rotation speed falls below the fifth rotation speed threshold RS5, for example, the engine stalls. Therefore, the fifth rotation speed threshold RS5 may be the same as the threshold for determining whether the engine stalls or not. In FIG. 3, the current value and the flow rate of the hydraulic oil flowing through the oil passage 20 (first partial oil passage 21) when the rotation speed falls below the first rotation speed threshold RS1 again after exceeding the first rotation speed threshold RS1 are shown by dotted lines. In this case, the current value passed through the additional solenoid 14s may be maintained at the fourth magnitude i4, and the flow rate of the hydraulic oil flowing through the oil passage 20 (first partial oil passage 21) may be set to zero. This makes it possible to prevent engine stall even if the engine load temporarily increases when the rotation speed of the engine 6 exceeds the first rotation speed threshold RS1. Note that the controller 17 is configured to pass a current of the first magnitude i1 through the solenoid 13s when the rotation speed of the engine 6 exceeds the first rotation speed threshold RS1 and then falls below RS5.

[0029] 4 is a flowchart showing a process flow of a method for controlling the fan 71 of the work vehicle 1 according to this embodiment. This flowchart is started by a trigger when the ignition key of the engine 6 is turned or the start button of the engine 6 is pressed, and the engine 6 is started. In this control method, in step S1, when the engine 6 is started, the controller 17 causes a current of a third magnitude i3 to flow through the additional solenoid 14s of the unloading valve 14, thereby causing the unloading valve 14 to block the second bypass oil passage 24 (additional oil passage). In step S2, when the engine 6 is started, the controller 17 causes a current of a first magnitude i1 to flow through the solenoid 13s of the variable relief valve 13, thereby causing the hydraulic oil to flow through the oil passage 20 (first partial oil passage 21) at a first flow rate FR1, and the hydraulic motor 12 is rotated to rotate the fan 71.

[0030] In step S3, the controller 17 determines whether the rotation speed of the engine 6 acquired from the rotation speed sensor 6s has become greater than the first rotation speed threshold RS1. If the rotation speed of the engine 6 has not become greater than the first rotation speed threshold RS1 (NO in step S3), the controller 17 repeats the process of step S3. If the rotation speed of the engine 6 becomes greater than the first rotation speed threshold RS1 (YES in step S3), in step S4, the controller 17 applies a current of a second magnitude i2 greater than the first magnitude i1 to the solenoid 13s, thereby causing the hydraulic oil to flow through the oil passage 20 (first partial oil passage 21) at a second flow rate FR2 smaller than the first flow rate FR1, thereby reducing the rotation speed of the fan 71.

[0031] In step S5, the controller 17 determines whether or not the rotation speed of the engine 6 acquired from the rotation speed sensor 6s is below the fifth rotation speed threshold RS5. If the rotation speed of the engine 6 is not below the fifth rotation speed threshold RS5 (NO in step S3), the process of step S4 continues and proceeds to step S6. If the rotation speed of the engine 6 is below the fifth rotation speed threshold RS5 (YES in step S3), the controller 17 executes the process of step S2. The process from step S2 onwards is as shown in the flowchart.

[0032] In step S6, the controller 17 judges whether or not the rotation speed of the engine 6 acquired from the rotation speed sensor 6s exceeds the third rotation speed threshold RS3. If the rotation speed of the engine 6 exceeds the third rotation speed threshold RS3 (YES in step S6), the controller 17 opens the unloading valve 14 by passing a current of a fourth magnitude i4, which is greater than the third magnitude i3, to the additional solenoid 14s in step S7, and causes the hydraulic oil from the hydraulic pump 11 to flow through the second bypass oil passage 24 (additional oil passage) to the second bypass oil passage 24 (additional oil passage). If the rotation speed of the engine 6 does not exceed the third rotation speed threshold RS3 (YES in step S6), the process returns to step S5, and the controller 17 executes the process of step S5 again.

[0033] In step S8, the controller 17 determines whether the rotation speed of the engine 6 acquired from the rotation speed sensor 6s exceeds the fourth rotation speed threshold RS4. When the rotation speed of the engine 6 exceeds the fourth rotation speed threshold RS4, a current according to the temperature of the liquid (hydraulic oil, coolant) is passed through the additional solenoid 14s to change the flow rate of the hydraulic oil passed through the second bypass oil passage 24 (additional oil passage). Specifically, in step S8, the controller 17 further acquires the oil temperature of the hydraulic oil in the oil passage 20 from the temperature sensor 20s, or the temperature of the coolant from the temperature sensor 7s, and determines whether the temperature of the hydraulic oil exceeds the first threshold temperature T1. Then, when the temperature of the hydraulic oil exceeds the first threshold temperature T1 and the rotation speed of the engine 6 exceeds the fourth rotation speed threshold RS4 (YES in step S8), the controller 17 passes a current of a third magnitude i3 through the additional solenoid 14s of the unloading valve 14 to close the unloading valve 14 in step S9. When the rotation speed of the engine 6 does not exceed the fourth rotation speed threshold RS4 or none of the temperatures determined in step S8 exceed the threshold (NO in step S8), the controller 17 repeats the process of step S8.

[0034] In step S10, the controller 17 determines whether or not the rotation speed of the engine 6 acquired from the rotation speed sensor 6s exceeds the second rotation speed threshold RS2. When the rotation speed of the engine 6 exceeds the second rotation speed threshold RS2, a current corresponding to the temperature of the liquid (hydraulic oil, coolant) is passed through the solenoid 13s to change the rotation speed of the fan 71. Specifically, in step S8, the controller 17 further acquires the oil temperature of the hydraulic oil in the oil passage 20 from the temperature sensor 20s, and determines whether or not the temperature of the hydraulic oil exceeds the first threshold temperature T1. Then, when the temperature of the hydraulic oil exceeds the first threshold temperature T1 and the rotation speed of the engine 6 exceeds the second rotation speed threshold RS2 (YES in step S10), in step S11, the controller 17 passes a current of a fifth magnitude i5, which is equal to or smaller than the first magnitude i3, through the solenoid 13s of the variable relief valve 13 to close the variable relief valve 13. When the rotation speed of the engine 6 does not exceed the fourth rotation speed threshold RS4, or when none of the temperatures determined in step S10 exceed the threshold (NO in step S10), the controller 17 repeats the process of step S10. <Effects of this embodiment>

[0035] The work vehicle 1, the control method for the fan 71 of the work vehicle 1, the controller 17 of the work vehicle 1, and the program stored in the controller 17 according to this embodiment pass a current of a first magnitude i1 to the solenoid 13s of the variable relief valve 13 when the engine 6 is started, and pass a current of a second magnitude i2 larger than the first magnitude i1 to the solenoid 13s when the rotation speed of the engine 6 becomes higher than a first rotation speed threshold RS1. When the engine 6 is started, the rotation speed is low, and therefore the amount of hydraulic oil discharged from the hydraulic pump 11 is also small. For this reason, even if the flow rate of the hydraulic oil discharged from the variable relief valve 13 to the first bypass oil passage 23 is small, a large amount of low-viscosity hydraulic oil is not sent to the hydraulic motor 12. On the other hand, when the rotation speed of the engine 6 becomes higher than the first rotation speed threshold RS1, the flow rate of the hydraulic oil discharged from the variable relief valve 13 to the first bypass oil passage 23 is increased, so that even if the discharge rate of the hydraulic oil from the hydraulic pump 11 increases, a large amount of low-viscosity hydraulic oil is not sent to the hydraulic motor 12. Therefore, the risk of low-viscosity hydraulic oil damaging the hydraulic motor 12 is reduced, while the current supplied to the solenoid 13s is reduced, thereby improving power saving.

[0036] Furthermore, the control method for the fan 71 of the work vehicle 1, the controller 17 of the work vehicle 1, and the program stored in the controller 17 cause the unloading valve 14 to cut off the second bypass oil passage 24 by passing a current of a third magnitude i3 to the additional solenoid 14s of the unloading valve 14 when the engine 6 is started, and when the rotation speed of the engine 6 exceeds a third rotation speed threshold RS3, cause a current of a fourth magnitude i4 larger than the third magnitude i3 to pass through the additional solenoid 14s to open the unloading valve 14. When the engine 6 is started, the rotation speed is low, so the amount of hydraulic oil discharged from the hydraulic pump 11 is also small. Therefore, even if the hydraulic oil is not discharged from the unloading valve 14 to the second bypass oil passage 24, a large amount of low-viscosity hydraulic oil is not sent to the hydraulic motor 12. On the other hand, when the rotation speed of the engine 6 becomes higher than the second rotation speed threshold RS2, the unload valve 14 discharges the hydraulic oil into the second bypass oil passage 24, so that even if the discharge amount of hydraulic oil from the hydraulic pump 11 increases, low-viscosity hydraulic oil is not sent to the hydraulic motor 12. Therefore, the risk of low-viscosity hydraulic oil damaging the hydraulic motor 12 is reduced, and power saving can be improved by reducing the current supplied to the additional solenoid 14s.

[0037] Furthermore, the control method for the fan 71 of the work vehicle 1, the controller 17 of the work vehicle 1, and the program stored in the controller 17 change the flow rate of the hydraulic oil flowing through the second bypass oil passage 24 by passing a current according to the temperature of the liquid (hydraulic oil, cooling water) through the additional solenoid 14s when the rotation speed of the engine 6 exceeds the fourth rotation speed threshold RS4. Specifically, when the rotation speed of the engine 6 is higher than the fourth rotation speed threshold RS4 and the temperature of the hydraulic oil exceeds the first threshold temperature T1, a current of a third magnitude i3 is passed through the additional solenoid 14s to close the unloading valve 14. When the unloading valve 14 is closed, the flow rate of the hydraulic oil flowing through the oil passage 20 (first partial oil passage 21) increases, but the viscosity of the hydraulic oil is reduced because the temperature of the hydraulic oil exceeds the first threshold temperature T1. This reduces the risk of damaging the hydraulic motor 12. Furthermore, when the rotation speed of the engine 6 is greater than the fourth rotation speed threshold RS4 and the coolant temperature exceeds the second threshold temperature T2, a current of a third magnitude i3 may be passed through the additional solenoid 14s to close the unloading valve 14.

[0038] Furthermore, the control method for the fan 71 of the work vehicle 1, the controller 17 of the work vehicle 1, and the program stored in the controller 17 change the rotation speed of the fan 71 by passing a current according to the temperature of the liquid (hydraulic oil, cooling water) to the solenoid 13s when the rotation speed of the engine 6 exceeds the second rotation speed threshold RS2. Specifically, when the rotation speed of the engine 6 is higher than the second rotation speed threshold RS2 and the temperature of the hydraulic oil exceeds the first threshold temperature T1, a current of a fifth magnitude i5 equal to or smaller than the first magnitude i1 is passed to the solenoid 13s of the variable relief valve 13 to close the variable relief valve 13. When the variable relief valve 13 is closed, the flow rate of the hydraulic oil flowing through the oil passage 20 (first partial oil passage 21) increases, but the viscosity of the hydraulic oil is reduced because the temperature of the hydraulic oil exceeds the first threshold temperature T1. This reduces the risk of damaging the hydraulic motor 12. Furthermore, when the rotation speed of the engine 6 is greater than the second rotation speed threshold RS2 and the coolant temperature exceeds the second threshold temperature T2, a current of a fifth magnitude i5 less than the first magnitude i3 may be passed through the solenoid 13s of the variable relief valve 13 to close the variable relief valve 13.

[0039] Furthermore, the control method for the fan 71 of the work vehicle 1, the controller 17 of the work vehicle 1, and the program stored in the controller 17, when the rotation speed of the engine 6 exceeds the first rotation speed threshold RS1, flow a current of the second magnitude i2 to the solenoid 13s until it falls below the fifth rotation speed threshold RS5 that is smaller than the first rotation speed threshold RS1, and when the rotation speed of the engine 6 exceeds the first rotation speed threshold RS1 and falls below the fifth rotation speed threshold RS5, flow a current of the first magnitude i2 to the solenoid 13s. As a result, even if the rotation speed of the engine 6 temporarily decelerates after the rotation speed of the engine 6 exceeds the first rotation speed threshold RS1, the opening degree of the variable relief valve 13 is maintained, thereby suppressing an increase in the load on the engine 6. As a result, it is possible to suppress engine stall. Also, when the rotation speed of the engine 6 falls below the fifth rotation speed threshold RS5, it is in a state where the engine has substantially reached a stall. Therefore, in such a case, power saving can be realized by reducing the current flowing to the solenoid 13s. <Modifications of the embodiment>

[0040] In the above-described embodiment, the unloading valve 14 and the rotational direction switching valve 15 may be omitted. One of the temperature sensor 7s and the temperature sensor 20s may be omitted. When the unloading valve 14 is omitted, the flow rate of the hydraulic oil flowing through the oil passage 20 (first partial oil passage 21) from the rotation speed of the engine 8 from the first rotation speed threshold RS1 to the rotation speed RS4a changes as shown by the dashed line in FIG. 3. When the rotation speed of the engine 6 is lower than the second rotation speed threshold RS2, and the temperature of the hydraulic oil exceeds the first threshold temperature T1, the rotation speed of the engine 6 changes as shown by the straight line at the second rotation speed threshold RS2.

[0041] In addition, for the above-mentioned changes and other changes, FIG. 3 shows a schematic example in which the flow rate of the hydraulic oil flowing through the oil passage 20 (first partial oil passage 21) changes linearly, but the flow rate may change non-linearly.

[0042] The process of step S4 in Fig. 4 may be executed between steps S6 and S7. In this case, if the result of step S4 is NO, the process returns to step S1.

[0043] In this application, the term "comprises" and its derivatives are open-ended terms that describe the presence of elements and do not exclude the presence of other elements not listed. This also applies to the terms "have", "include" and their derivatives.

[0044] The terms "member," "part," "element," "body," and "structure" may have multiple meanings, such as a single part or multiple parts.

[0045] Ordinal numbers such as "first" and "second" are merely terms used to identify a structure and do not have any other meaning (such as a particular order). For example, the presence of a "first element" does not imply the presence of a "second element," and the presence of a "second element" does not imply the presence of a "first element."

[0046] Words expressing degree, such as "substantially," "about," and "approximately," may mean a reasonable deviation that does not significantly change the final result, unless otherwise specified in the embodiment. All numerical values ​​described in this application may be interpreted to include words such as "substantially," "about," and "approximately."

[0047] In this application, the phrase "at least one of A and B" should be interpreted as including A only, B only, and both A and B.

[0048] It is apparent that various changes and modifications of the present invention are possible in light of the above disclosure, and therefore, the present invention may be practiced otherwise than as specifically disclosed herein without departing from the spirit and scope of the present invention.

Claims

1. At the start of the engine, a first magnitude of current is passed through a solenoid of a variable relief valve connected to an oil passage through which hydraulic oil is output from a hydraulic pump driven by the engine, thereby rotating a hydraulic motor connected to the oil passage, thereby rotating a fan connected to the hydraulic motor and configured to air-cool a heat exchanger configured to cool at least one of the hydraulic oil and a cooling water of the engine; when the rotation speed of the engine becomes greater than a first rotation speed threshold, a current having a second magnitude greater than the first magnitude is caused to flow through the solenoid, thereby controlling the flow rate so as to reduce a ratio of the flow rate of hydraulic oil flowing through the oil passage to the rotation speed compared to when a current of the first magnitude is caused to flow through the solenoid, thereby changing the rotation speed of the fan; When the rotation speed of the engine becomes higher than a second rotation speed threshold value that is higher than the first rotation speed threshold value, a current flowing through the solenoid is controlled so as to increase the ratio when the temperature of the hydraulic oil or the cooling water becomes high, thereby changing the rotation speed of the fan. A method for controlling a fan for a work vehicle.

2. from the start of the engine until the rotation speed of the engine exceeds a third rotation speed threshold value that is equal to or higher than the first rotation speed threshold value, a current of a third magnitude is applied to an additional solenoid of an unloading valve that is provided in parallel with the variable relief valve in an additional oil passage connected in parallel to the oil passage, thereby blocking the additional oil passage with the unloading valve; When the rotation speed of the engine exceeds the third rotation speed threshold, a current having a fourth magnitude greater than the third magnitude is applied to the additional solenoid to open the unload valve and allow hydraulic oil from the hydraulic pump to flow into the additional oil passage; When the rotation speed of the engine is equal to or higher than the third rotation speed threshold and exceeds a fourth rotation speed threshold which is equal to or lower than the second rotation speed threshold, the flow rate of the hydraulic oil flowing through the additional oil passage is changed by controlling the current flowing through the additional solenoid so as to increase the ratio when the temperature of the hydraulic oil or the cooling water becomes high. The control method according to claim 1 .

3. The temperature is a temperature of hydraulic oil flowing between the hydraulic pump and the hydraulic motor, 3. The control method of claim 2, further comprising: when the engine speed is greater than the fourth engine speed threshold and the temperature of the hydraulic oil exceeds a first threshold temperature, passing a current of the third magnitude through the additional solenoid to close the unload valve.

4. 4. The control method according to claim 3, wherein when the engine rotational speed is greater than the second rotational speed threshold and the temperature of the hydraulic oil exceeds the first threshold temperature, a current of a fifth magnitude less than the first magnitude is passed through the solenoid of the variable relief valve to close the variable relief valve.

5. 5. The control method according to claim 1, wherein when the engine rotational speed exceeds the first rotational speed threshold, the second magnitude of current is passed through the solenoid until the engine rotational speed falls below a fifth rotational speed threshold that is lower than the first rotational speed threshold.

6. The control method according to claim 5 , further comprising the step of: causing a current of the first magnitude to flow through the solenoid when the engine speed exceeds the first rotational speed threshold and then falls below a fifth rotational speed threshold that is lower than the first rotational speed threshold.

7. The second rotational speed threshold is less than an idling rotational speed of the engine. A control method according to any one of claims 1 to 6.

8. The engine, a hydraulic pump driven by the engine; An oil passage connected by the hydraulic pump; a hydraulic motor provided in the oil passage and configured to be rotated by hydraulic oil supplied by the hydraulic pump; a heat exchanger configured to cool at least one of the hydraulic oil and the engine cooling water; a fan connected to the hydraulic motor and configured to rotate together with the hydraulic motor to air-cool the heat exchanger; a variable relief valve connected to the oil passage, having a solenoid, and configured to control a flow rate of hydraulic oil flowing through the oil passage in response to a current applied to the solenoid; an electronic circuit for controlling the magnitude of a current flowing through the solenoid and controlling the rotation speed of the fan; The electronic circuit includes: a first amount of hydraulic oil is caused to flow through the oil passage by a first flow rate by passing a current of a first magnitude through the solenoid at the start of the engine, thereby rotating a fan connected to the oil passage; when the rotation speed of the engine becomes greater than a first rotation speed threshold, a current having a second magnitude greater than the first magnitude is passed through the solenoid, thereby controlling the flow rate so as to reduce a ratio of the flow rate of the hydraulic oil passed through the oil passage to the rotation speed compared to when a current of the first magnitude is passed through the solenoid, thereby changing the rotation speed of the fan; When the rotation speed of the engine becomes higher than a second rotation speed threshold value that is higher than the first rotation speed threshold value, the current flowing through the solenoid is controlled so as to increase the ratio when the temperature of the hydraulic oil or the cooling water becomes high, thereby changing the rotation speed of the fan. Work vehicle.

9. An additional oil passage connected in parallel to the oil passage; an unloading valve that is provided in parallel with the variable relief valve in the additional oil passage, has an additional solenoid, and is configured to control the flow rate of hydraulic oil flowing through the additional oil passage in response to a current applied to the additional solenoid; Further equipped with The electronic circuit includes: from the start of the engine until the rotation speed of the engine exceeds a third rotation speed threshold value that is equal to or higher than the first rotation speed threshold value, a current of a third magnitude is applied to the additional solenoid of the unloading valve, thereby blocking the additional oil path by the unloading valve; When the rotation speed of the engine exceeds the third rotation speed threshold, a current having a fourth magnitude greater than the third magnitude is applied to the additional solenoid to open the unload valve and allow hydraulic oil from the hydraulic pump to flow into the additional oil passage; When the rotation speed of the engine is equal to or higher than the third rotation speed threshold and exceeds a fourth rotation speed threshold which is equal to or lower than the second rotation speed threshold, the flow rate of the hydraulic oil flowing through the additional oil passage is changed by controlling a current flowing through the additional solenoid so as to increase the ratio when the temperature of the hydraulic oil or the cooling water becomes high. A work vehicle according to claim 8.

10. The temperature is a temperature of hydraulic oil flowing between the hydraulic pump and the hydraulic motor, the electronic circuit is configured to, when the engine speed is greater than the fourth engine speed threshold and the temperature of the hydraulic oil exceeds a first threshold temperature, pass a current of the third magnitude through the additional solenoid to close the unload valve. A work vehicle according to claim 9.

11. the electronic circuit is configured to, when the engine rotation speed is greater than the second rotation speed threshold and the temperature of the hydraulic oil exceeds the first threshold temperature, apply a current of a fifth magnitude, which is less than or equal to the first magnitude, to the solenoid of the variable relief valve to close the variable relief valve. A work vehicle according to claim 10.

12. The electronic circuit is configured to cause the second magnitude of current to flow through the solenoid when the engine rotational speed exceeds the first rotational speed threshold until the engine rotational speed falls below a fifth rotational speed threshold that is lower than the first rotational speed threshold. A work vehicle according to any one of claims 8 to 11.

13. the electronic circuit is configured to cause the first magnitude of current to flow through the solenoid when the engine rotational speed exceeds the first rotational speed threshold and then falls below a fifth rotational speed threshold that is lower than the first rotational speed threshold. A work vehicle as claimed in claim 12.

14. The second rotational speed threshold is less than an idling rotational speed of the engine. A work vehicle according to any one of claims 8 to 13.

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