Industrial vehicles

Abstract

To improve the operability of an industrial vehicle at the start of operation.SOLUTION: A forklift 10 is powered by a battery 14. The forklift 10 comprises a brake housing with an oil chamber 81r filled with hydraulic oil formed therein, a brake mechanism that rotates in the oil chamber 81r together with the drive wheels, a storage tank 41 in which the hydraulic oil is stored, a circulation flow path 43 for circulating the hydraulic oil between the oil chamber 81r and the storage tank 41, a pump 42 that flows the hydraulic oil through the circulation flow path 43 by power supplied from the battery 14, a control unit 30 that controls the operation of the pump 42, and a temperature sensor 31 that detects the temperature of the hydraulic oil. The control unit 30 performs a drive process for driving the pump 42 when the temperature of the hydraulic oil is lower than a predetermined temperature while the battery 14 is stopped.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to an industrial vehicle.

Background Art

[0002] The industrial vehicle described in Patent Document 1 uses a battery as a drive source. Examples of the brake mechanism employed in such an industrial vehicle include the brake mechanism described in Patent Document 2. The brake mechanism described in Patent Document 2 is located in an oil chamber formed inside a housing.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] When the above brake mechanism is adopted in an industrial vehicle using a battery as a drive source, when the temperature of the hydraulic oil filled in the oil chamber decreases, the viscosity of the hydraulic oil increases. If the brake mechanism rotates together with the drive wheels of the industrial vehicle, it becomes difficult for the brake mechanism to rotate in the oil chamber due to the highly viscous hydraulic oil, making it difficult for the drive wheels to rotate. In the case of an industrial vehicle using an engine as a drive source, since the hydraulic oil is heated early using the engine as a heat source at the start of operation of the industrial vehicle, the decrease in the operability of the industrial vehicle due to the decrease in the temperature of the hydraulic oil can be eliminated in a short time. On the other hand, in an industrial vehicle using a battery as a drive source, since the hydraulic oil does not heat up using the engine as a heat source as described above, it takes time to heat up the hydraulic oil until it reaches the viscosity at which the drive wheels rotate normally. Therefore, in an industrial vehicle using a battery as a drive source, when the viscosity of the hydraulic oil increases due to a decrease in the temperature of the hydraulic oil, there is a risk that the operability of the industrial vehicle at the start of operation will decrease. [Means for solving the problem]

[0005] An industrial vehicle that solves the above problems is an industrial vehicle powered by a battery, comprising: a brake housing having an oil chamber filled with hydraulic fluid formed inside; a brake mechanism that rotates in the oil chamber together with the drive wheels; a storage tank for storing the hydraulic fluid; a circulation channel for circulating the hydraulic fluid between the oil chamber and the storage tank; a pump that flows the hydraulic fluid through the circulation channel by power supplied from the battery; a control unit that controls the drive of the pump; and a temperature sensor that detects the temperature of the hydraulic fluid, wherein the control unit performs a drive process to drive the pump when the temperature of the hydraulic fluid is below a predetermined temperature while the battery is not powered.

[0006] With the above configuration, when the battery is shut down, the hydraulic fluid circulates through the circulation channel due to the execution of the drive process. As the hydraulic fluid circulates between the oil chamber and the storage tank, its temperature rises during the execution of the drive process. By raising the temperature of the hydraulic fluid, the brake mechanism in the oil chamber rotates more easily. This makes it easier for the drive wheels, which rotate together with the brake mechanism, to rotate, thereby improving the operability of the industrial vehicle. With this configuration, the industrial vehicle can start operating with the hydraulic fluid at a higher temperature compared to a system where the pump is not always driven when the battery is shut down, regardless of the hydraulic fluid temperature. Therefore, the operability of the industrial vehicle at the start of operation can be improved.

[0007] In an industrial vehicle, the control unit may perform the drive process while the battery is being charged. With the above configuration, during the drive process, battery power is used to drive the pump, but the battery is also charged at the same time, so the battery charge level does not decrease easily. Therefore, compared to the case where the drive process is performed regardless of whether the battery is charging or not, the decrease in the battery charge level associated with the execution of the drive process can be suppressed.

[0008] The industrial vehicle is equipped with a hydraulically driven cargo handling device and a cargo handling channel for circulating the hydraulic fluid between the cargo handling device and the storage tank, and in the industrial vehicle, the pump may supply power from the battery to flow the hydraulic fluid through the circulation channel and the cargo handling channel.

[0009] With the above configuration, during the drive process performed by the control unit, hydraulic fluid flows not only through the circulation channel but also through the cargo handling channel. Because the hydraulic fluid circulates between the cargo handling device and the storage tank, the hydraulic fluid temperature rises during the drive process. Therefore, compared to the case where the hydraulic fluid flows only through the circulation channel during the drive process, the hydraulic fluid can be heated up more quickly, further improving the operability of the industrial vehicle at the start of operation.

[0010] In an industrial vehicle, the control unit may perform a stop process to stop the pump's operation if the temperature of the hydraulic fluid is above a predetermined temperature during the execution of the drive process. According to the above configuration, if the drive process is terminated after a predetermined time has elapsed since the start of execution, the drive process may continue even after the hydraulic fluid temperature exceeds a predetermined temperature, depending on the length of the predetermined time. However, such continuation of the drive process does not occur. Therefore, the consumption of battery charge due to excessive time spent on the drive process can be suppressed.

[0011] The industrial vehicle is equipped with a heater for heating the hydraulic fluid, and in the industrial vehicle, the control unit heats the hydraulic fluid with the heater during the execution of the drive process and stops heating the hydraulic fluid with the heater during the execution of the stop process.

[0012] With the above configuration, the hydraulic fluid is heated by the heater, causing it to heat up more quickly during the drive process. Therefore, the operability of the industrial vehicle at the start of operation can be further improved. [Effects of the Invention]

[0013] This invention makes it possible to improve the operability of industrial vehicles at the start of operation. [Brief explanation of the drawing]

[0014] [Figure 1] This is a side view of a forklift. [Figure 2] This is a schematic diagram of a forklift. [Figure 3] This is a cross-sectional view showing the front axle. [Figure 4] This is a flowchart showing the processes performed by the control unit. [Modes for carrying out the invention]

[0015] The following describes one embodiment in which an industrial vehicle is converted into a forklift, with reference to the drawings. In the following description, "front," "rear," "down," "left," and "right" refer to the front, rear, down, left, and right when the operator driving the forklift is facing forward (in the direction of travel) of the forklift.

[0016] <Forklift Configuration> As shown in Figure 1, the forklift 10 comprises a body 11, two drive wheels 11f, two steering wheels 11r, a travel motor 13a, a load handling motor 13b, and a battery 14. Note that Figure 1 shows one drive wheel 11f and one steering wheel 11r. The two drive wheels 11f are located at the front lower part of the body 11. The two steering wheels 11r are located at the rear lower part of the body 11. The travel motor 13a, load handling motor 13b, and battery 14 are mounted on the body 11.

[0017] The forklift 10 is equipped with a hydraulically driven cargo handling device 12. The cargo handling device 12 is located at the front of the vehicle body 11. The battery 14 can be any rechargeable battery. For example, a secondary battery can be used as the battery 14. Examples of the secondary battery include a lead storage battery and a lithium ion secondary battery.

[0018] The traveling motor 13a is a motor that serves as a drive source for the drive wheels 11f. The cargo handling motor 13b is a motor for supplying hydraulic oil to the cargo handling device 12. The traveling motor 13a and the cargo handling motor 13b are driven by power supplied from the battery 14. When the traveling motor 13a is driven, the forklift 10 performs a traveling operation. When the cargo handling motor 13b is driven, the forklift 10 performs a cargo handling operation. That is, the forklift 10 uses the battery 14 as a power source.

[0019] The cargo handling device 12 includes a mast 21, a lift bracket 22, two forks 23, a lift cylinder 24, and a tilt cylinder 25. The mast 21 includes an outer mast 21a and an inner mast 21b. The inner mast 21b is provided so as to be able to move up and down with respect to the outer mast 21a. The lift bracket 22 is attached to the inner mast 21b. The forks 23 are attached to the lift bracket 22. The lift bracket 22 and the forks 23 can move up and down together with the inner mast 21b. The lift cylinder 24 moves the inner mast 21b up and down. The tilt cylinder 25 tilts the mast 21 in the front-rear direction of the forklift 10. The lift cylinder 24 and the tilt cylinder 25 are hydraulic cylinders.

[0020] As shown in FIG. 2, the forklift 10 includes a power steering cylinder 26 and a power steering valve 27. The power steering valve 27 switches the supply and discharge of hydraulic oil to the power steering cylinder 26. The power steering cylinder 26 has a hydraulic oil chamber (not shown). With the supply and discharge of hydraulic oil to the power steering cylinder 26, the supply and discharge of hydraulic oil to the hydraulic oil chamber are performed. By the supply and discharge of hydraulic oil to the hydraulic oil chamber, a rod (not shown) connected to the steering wheel 11r is driven. By the drive of the rod, the steering wheel 11r is steered to face either the left or the right.

[0021] The handling device 12 includes a control valve 33. The control valve 33 is a hydraulic actuator that controls the flow rate of the hydraulic oil supplied to and discharged from each of the lift cylinder 24 and the tilt cylinder 25. Further, the hydraulic oil is supplied to and discharged from the power steering valve 27 via the control valve 33.

[0022] The opening and closing state of the control valve 33 is switched according to the operation of an operation member (not shown). The operation member is, for example, an operation lever for the driver to instruct the operations of each of the lift cylinder 24 and the tilt cylinder 25. When the control valve 33 is switched to the open state with the hydraulic oil supplied to the control valve 33, the hydraulic oil is supplied to the lift cylinder 24 and the tilt cylinder 25, and the hydraulic oil is discharged from the lift cylinder 24 and the tilt cylinder 25.

[0023] The forklift 10 is equipped with a storage tank 41 for storing hydraulic fluid, a circulation passage 43, and a pump 42. The circulation passage 43 has a first passage 43a, a second passage 43b, and a third passage 43c. The first passage 43a flows hydraulic fluid from the storage tank 41 to the pump 42. The second passage 43b flows hydraulic fluid from the pump 42 to the oil chamber 81r, which will be described later. The third passage 43c flows hydraulic fluid from the oil chamber 81r to the storage tank 41. By flowing hydraulic fluid through the first passage 43a, the second passage 43b, and the third passage 43c in this way, the circulation passage 43 circulates the hydraulic fluid between the oil chamber 81r and the storage tank 41.

[0024] Pump 42 is driven by a load-handling motor 13b powered by a battery 14. The hydraulic fluid stored in the storage tank 41 circulates through the circulation channel 43 as the pump 42 is driven. In other words, the pump 42 flows the hydraulic fluid into the circulation channel 43 using power supplied from the battery 14.

[0025] The forklift 10 is equipped with a cargo handling channel 44. The cargo handling channel 44 includes a supply channel 44a and a discharge channel 44b. The cargo handling channel 44 includes a first channel 43a. When the pump 42 is driven, the hydraulic fluid flows from the storage tank 41 to the pump 42 via the first channel 43a, and then is supplied from the pump 42 to the control valve 33 via the supply channel 44a. The hydraulic fluid is discharged from the control valve 33 to the storage tank 41 via the discharge channel 44b. In this way, the hydraulic fluid circulates between the control valve 33 and the storage tank 41 when the pump 42 is driven. The pump 42 flows the hydraulic fluid into the circulation channel 43 and the cargo handling channel 44 by power supplied from the battery 14. The cargo handling channel 44 circulates the hydraulic fluid between the cargo handling device 12 and the storage tank 41.

[0026] The forklift 10 is equipped with a heater 35 for heating the hydraulic fluid. The hydraulic fluid stored in the storage tank 41 is heated by the operation of the heater 35. The forklift 10 is equipped with a temperature sensor 31 and an ignition switch 32. The temperature sensor 31 detects the temperature T of the hydraulic fluid. Specifically, the temperature sensor 31 detects the temperature T of the hydraulic fluid stored in the storage tank 41.

[0027] <Front Axle> As shown in Figure 3, the forklift 10 is equipped with a front axle 50. The front axle 50 comprises an axle shaft 51, an axle bracket 60, an axle housing 70 in which the axle shaft 51 is housed, a brake device 80, and a hub 15. The front axle 50 rotates the drive wheel 11f. The axle housing 70 is connected to the axle bracket 60.

[0028] The axle shaft 51 comprises a shaft body 53 and a shaft flange 55. Hereinafter, the direction in which the axis of the shaft body 53 extends is referred to as the axial direction Z. The shaft flange 55 is provided at the first end 54 of the shaft body 53 in the axial direction Z. The shaft flange 55 is connected to the hub 15. The wheel 17 of the drive wheel 11f is fixed to the hub 15. As the axle shaft 51 rotates, the hub 15 and the drive wheel 11f rotate together. This causes the forklift 10 to move.

[0029] The front axle 50 is equipped with a bearing 95. The bearing 95 rotatably supports the hub 15. The axle bracket 60 is cylindrical. The axle bracket 60 is positioned near the second end 58, which is the end of the shaft body 53 opposite to the first end 54. The axle bracket 60 is positioned so that the direction in which the axis of the axle bracket 60 extends coincides with the axial direction Z. A first insertion hole 61 is formed in the axle bracket 60. The shaft body 53 is inserted through the first insertion hole 61. The axle bracket 60 also has a mounting part (not shown). The front axle 50 is attached to the forklift 10 by attaching this mounting part to the vehicle body 11.

[0030] The axle housing 70 comprises a cylindrical body 71. The axle housing 70 is positioned such that the direction in which the axis of the body 71 extends coincides with the axial direction Z. The axle housing 70 is provided alongside the axle bracket 60 in the axial direction Z. The axle housing 70 is positioned closer to the first end 54 than the axle bracket 60 in the axial direction Z. A second through hole 73 is formed in the body 71 of the axle housing 70. The shaft body 53 is inserted through the second through hole 73.

[0031] The brake system 80 comprises a brake housing 81 and a brake mechanism 90 housed within the brake housing 81. In other words, the forklift 10 comprises a brake housing 81 and a brake mechanism 90. The brake housing 81 is connected to the axle housing 70.

[0032] The brake housing 81 is cylindrical in shape so as to cover the axle housing 70. The brake housing 81 is positioned such that the direction in which its axis extends coincides with the axial direction Z. The brake housing 81 comprises a first housing 82 and a second housing 83.

[0033] The first housing 82 comprises a cylindrical portion 84 and a wall portion 85 extending from the cylindrical portion 84 toward the axis of the cylindrical portion 84. An axle insertion hole 86 is formed in the wall portion 85 through which the axle housing 70 is inserted. The second housing 83 is cylindrical. The second housing 83 is connected to the cylindrical portion 84.

[0034] An oil chamber 81r filled with hydraulic fluid is formed inside the brake housing 81. The oil chamber 81r is formed by the first housing 82, the second housing 83, the hub 15, and the axle housing 70. The oil chamber 81r is located along the outer circumferential surface of the axle housing 70.

[0035] The brake mechanism 90 is located in the oil chamber 81r. The brake mechanism 90 in this embodiment is a wet multi-plate brake. The brake mechanism 90 comprises a friction plate 91, a mate plate 92, and a piston 93. The friction plate 91 is fixed to the hub 15. As a result, the friction plate 91 rotates together with the hub 15, and is able to rotate together with the drive wheel 11f. Therefore, the brake mechanism 90 rotates together with the drive wheel 11f in the oil chamber 81r. The mate plate 92 is fixed to the inner circumferential surface of the second housing 83. The piston 93 is housed in the first housing 82.

[0036] The friction plate 91 and the mating plate 92 are arranged alternately in the axial direction Z. The piston 93 is movable in the axial direction Z. By moving in the axial direction Z, the piston 93 can be displaced between a pressing position in which it presses against the mating plate 92 and a release position in which it releases pressure on the mating plate 92.

[0037] <Department Head> As shown in Figure 2, the forklift 10 is equipped with a control unit 30. The control unit 30 is electrically connected to a temperature sensor 31 and an ignition switch 32. The control unit 30 receives the hydraulic fluid temperature T detected by the temperature sensor 31 as input. When the ignition switch 32 is operated by the driver of the forklift 10, the ignition switch 32 outputs an operation signal to the control unit 30.

[0038] The control unit 30 comprises a processor (not shown), such as a CPU or GPU, and a storage unit (not shown), such as RAM and ROM. The storage unit stores program code or instructions configured to cause the processor to execute processing. The storage unit, i.e., the computer-readable medium, includes any available medium accessible by a general-purpose or dedicated computer. The control unit 30 may be composed of hardware circuits such as an ASIC (Application Specific Integrated Circuit) or an FPGA (Field Programmable Gate Array). The control unit 30, which is a processing circuit, may include one or more processors that operate according to a computer program, one or more hardware circuits such as an ASIC or FPGA, or a combination thereof.

[0039] The control unit 30 can switch between driving and stopping the load handling motor 13b. That is, the control unit 30 controls the driving of the pump 42 by controlling the load handling motor 13b. The control unit 30 can switch between driving and stopping the pump 42. The control unit 30 can switch between driving and stopping the heater 35.

[0040] <Drive and stop processes> The control unit 30 performs a drive process to drive the pump 42 when the hydraulic fluid temperature T is below a predetermined temperature Tp while the battery 14 is not powered. Specifically, the control unit 30 performs the drive process assuming that the battery 14 is not powered during the period between when the ignition switch 32 is turned off and when it is turned on. In the drive process, the control unit 30 drives the pump 42 by driving the load handling motor 13b. The predetermined temperature Tp is the temperature at which, if the hydraulic fluid temperature is below the predetermined temperature Tp, the viscosity of the hydraulic fluid may increase, potentially causing a decrease in the rotation of the drive wheel 11f. The predetermined temperature Tp is a value that has been set in advance through experiments or other means. The predetermined temperature Tp is, for example, 0 degrees. In addition, the control unit 30 in this embodiment performs the drive process while the battery 14 is charging.

[0041] The control unit 30 performs a stop process to stop the pump 42 if the temperature T of the hydraulic fluid is above a predetermined temperature Tp during the execution of the drive process. Specifically, in the stop process, the control unit 30 stops the pump 42 by stopping the drive of the load handling motor 13b.

[0042] The control unit 30 heats the hydraulic fluid with the heater 35 while the drive process is being executed. The control unit 30 stops heating the hydraulic fluid with the heater 35 while the stop process is being executed. Next, an example of the procedure for processing performed by the control unit 30 will be described. This process is repeatedly performed by the control unit 30 at predetermined intervals when the battery 14 is not powered.

[0043] As shown in Figure 4, once processing begins, the control unit 30 determines whether or not the battery 14 is being charged (step S110). If it determines that the battery 14 is not being charged (step S110: NO), the control unit 30 terminates the process.

[0044] If the control unit 30 determines that the battery 14 is being charged (step S110: YES), it determines whether the hydraulic fluid temperature T is lower than a predetermined temperature Tp (step S120). If the control unit 30 determines that the hydraulic fluid temperature T is equal to or higher than the predetermined temperature Tp (step S120: NO), it terminates this process.

[0045] If the control unit determines that the hydraulic fluid temperature T is lower than a predetermined temperature Tp (step S120: YES), it drives the pump 42 (step S130) and then drives the heater 35 (step S140).

[0046] Next, the control unit 30 determines whether the temperature T of the hydraulic fluid is equal to or greater than a predetermined temperature Tp (step S150). If it determines that the temperature T of the hydraulic fluid is lower than the predetermined temperature Tp (step S150: NO), the control unit 30 repeats the process in step S150. The control unit 30 repeatedly performs the process in step S150 as long as it determines in step S150 that the temperature T of the hydraulic fluid is lower than the predetermined temperature Tp.

[0047] If the control unit determines that the hydraulic fluid temperature T is above a predetermined temperature Tp (step S150: YES), it stops the pump 42 from running (step S160), and then stops the heater 35 from running (step S170). After that, the control unit 30 terminates this process.

[0048] [Effect of the Embodiment] The operation of the embodiment will now be described. When a forklift 10 is parked for a long period of time in a low-temperature environment, the viscosity of the hydraulic fluid may increase due to a decrease in its temperature.

[0049] As shown in Figure 3, the brake mechanism 90 rotates in the oil chamber 81r together with the drive wheel 11f. Therefore, as the viscosity of the hydraulic fluid increases with the decrease in temperature, the hydraulic fluid in the oil chamber 81r makes it difficult for the brake mechanism 90 to rotate, which in turn makes it difficult for the drive wheel 11f, which rotates together with the brake mechanism 90, to rotate.

[0050] According to this embodiment, the control unit 30 performs a drive process to drive the pump 42 when the temperature T of the hydraulic fluid is lower than a predetermined temperature Tp while the battery 14 is not running. In this embodiment, steps S120, S130, and S140 in Figure 4 correspond to the drive process.

[0051] The drive process allows the pump 42 to be driven even when the battery 14 is stopped. As a result, the hydraulic fluid flows through the circulation channel 43 during the drive process, causing the hydraulic fluid to circulate between the oil chamber 81r and the storage tank 41. During the drive process, the hydraulic fluid flows through the circulation channel 43, causing friction with the components in the path through which the hydraulic fluid flows, which in turn raises the temperature of the hydraulic fluid. In this case, the components in the path through which the hydraulic fluid flows include, for example, the channel walls that form the circulation channel 43 internally, and the brake housing 81 as a component that partitions the oil chamber 81r.

[0052] In this embodiment, the pump 42 supplies hydraulic fluid to the cargo handling channel 44 in addition to the circulation channel 43 by power supplied from the battery 14. Therefore, while the control unit 30 is performing the drive process, hydraulic fluid flows to the cargo handling channel 44 in addition to the circulation channel 43. As a result, hydraulic fluid circulates between the control valve 33, which is part of the cargo handling device 12, and the storage tank 41. During the drive process, the hydraulic fluid flows through the cargo handling channel 44, and the friction of the hydraulic fluid against the components in the path through which the hydraulic fluid flows causes the hydraulic fluid to heat up. In this case, the components in the path through which the hydraulic fluid flows are, for example, the channel walls that form the cargo handling channel 44 inside, and the control valve 33, which is a component of the cargo handling device 12.

[0053] The control unit 30 performs a stop process to stop the pump 42 if the temperature T of the hydraulic fluid is above a predetermined temperature Tp during the execution of the drive process. In this embodiment, steps S150, S160, and S170 in Figure 4 correspond to the stop process. The execution of the drive process continues until the control unit 30 performs the stop process. As a result, the hydraulic fluid continues to flow through the circulation channel 43 and the cargo handling channel 44 during the execution of the drive process, allowing the hydraulic fluid to be heated up until its temperature T is above the predetermined temperature Tp.

[0054] [Effects of the Embodiment] The effects of this embodiment will be described. (1) The control unit 30 performs a drive process to drive the pump 42 when the temperature T of the hydraulic fluid is lower than a predetermined temperature Tp while the battery 14 is stopped. As a result, while the battery 14 is stopped, the hydraulic fluid flows through the circulation channel 43 due to the execution of the drive process. As the hydraulic fluid circulates between the oil chamber 81r and the storage tank 41, the hydraulic fluid temperature rises while the drive process is being executed. By raising the temperature of the hydraulic fluid, the brake mechanism 90 rotates more easily in the oil chamber 81r. This makes it easier for the drive wheels 11f, which rotate together with the brake mechanism 90, to rotate, thereby improving the operability of the forklift 10. According to this embodiment, compared to the case where the pump 42 is not driven at all when the battery 14 is stopped, regardless of the temperature T of the hydraulic fluid, the operation of the forklift 10 can be started with the hydraulic fluid temperature raised. Therefore, the operability of the forklift 10 at the start of operation can be improved.

[0055] (2) The control unit 30 performs the drive process while the battery 14 is charging. Therefore, in the drive process, power from the battery 14 is used to drive the pump 42, but the battery 14 is also charged at the same time, so the charge level of the battery 14 does not decrease easily. Thus, compared to the case where the drive process is performed regardless of whether the battery 14 is charging or not, the decrease in the charge level of the battery 14 that occurs when the drive process is performed can be suppressed.

[0056] (3) The pump 42 supplies hydraulic fluid to the circulation channel 43 and the cargo handling channel 44 by power supplied from the battery 14. Therefore, while the control unit 30 is performing the drive process, hydraulic fluid flows not only through the circulation channel 43 but also through the cargo handling channel 44. Because the hydraulic fluid circulates between the control valve 33, which is part of the cargo handling device 12, and the storage tank 41, the hydraulic fluid is heated up while the drive process is being performed. Therefore, compared to the case where the hydraulic fluid flows only through the circulation channel 43 during the drive process, the hydraulic fluid can be heated up more quickly, which further improves the operability of the forklift 10 at the start of operation.

[0057] (4) The control unit 30 performs a stop operation to stop the pump 42 if the temperature T of the hydraulic fluid is above a predetermined temperature Tp while the drive operation is in progress. Therefore, if the drive operation is to be terminated after a predetermined time has elapsed since the start of the drive operation, the drive operation will continue even after the hydraulic fluid temperature T reaches above the predetermined temperature Tp, depending on the length of the predetermined time, but such continuation of the drive operation will not occur. Thus, the consumption of the battery 14 due to the drive operation being performed for an excessive amount of time can be suppressed.

[0058] (5) The control unit 30 heats the hydraulic fluid with the heater 35 while the drive process is being executed. The control unit 30 stops heating the hydraulic fluid with the heater 35 while the stop process is being executed. As a result, the hydraulic fluid heats up earlier during the drive process by the amount that the heater 35 heats the hydraulic fluid. Therefore, the operability of the forklift 10 at the start of operation can be further improved.

[0059] [Example of changes] The embodiment can be implemented with the following modifications. The embodiment and the following modifications can be combined with each other to the extent that they do not contradict the technical principles.

[0060] ○ Pump 42 does not necessarily have to be powered by the battery 14 to supply hydraulic fluid to the cargo handling channel 44. In this case, the forklift 10 may have a separate cargo handling pump for supplying hydraulic fluid to the cargo handling channel 44, in addition to pump 42.

[0061] ○ The heater 35 may heat hydraulic fluid other than the hydraulic fluid stored in the storage tank 41. In this case, the heater 35 may, for example, heat the hydraulic fluid in the circulation passage 43, or heat the hydraulic fluid filling the oil chamber 81r.

[0062] ○ The heater 35 may be omitted from the forklift 10. ○ The temperature sensor 31 may also detect the temperature T of hydraulic fluid other than the hydraulic fluid stored in the storage tank 41. In this case, the temperature sensor 31 may, for example, detect the temperature T of the hydraulic fluid in the circulation channel 43, or it may detect the temperature T of the hydraulic fluid filling the oil chamber 81r.

[0063] ○ The control unit 30 may perform the drive process on the condition that the charge level of the battery 14 is equal to or greater than a predetermined charge level. In this case, for example, in Figure 4, a process for determining whether or not the charge level of the battery 14 is equal to or greater than a predetermined charge level may be added before step S120. If the additional process determines that the charge level of the battery 14 is less than the predetermined charge level, the control unit 30 terminates the process shown in Figure 4. If the additional process determines that the charge level of the battery 14 is equal to or greater than a predetermined charge level, the control unit 30 performs the process from the additional step onward.

[0064] ○ The control unit 30 may perform the drive process regardless of whether the battery 14 is being charged or not. In this case, step S110 may be omitted from the process shown in Figure 4. ○ The stop process performed by the control unit 30 does not have to be performed only when the temperature T of the hydraulic fluid is above a predetermined temperature Tp during the execution of the drive process. For example, the control unit 30 may perform a stop process that stops the drive of the pump 42 after a predetermined time has elapsed since the start of the drive process. In this case, it is preferable that the predetermined time is set to the time after the start of the drive process when the temperature T of the hydraulic fluid will be above a predetermined temperature Tp, regardless of the temperature T of the hydraulic fluid before the start of the drive process.

[0065] ○ The control unit 30 does not have to perform a stop process. In this case, the control unit 30 may, for example, perform a drive process while the battery 14 is stopped, and then continue the drive process until the battery 14 is started to run again.

[0066] ○ In the process shown in Figure 4, the order of steps S160 and S170 may be reversed. [Explanation of symbols]

[0067] T...Temperature, Tp...Specified temperature, 10...Forklift as an industrial vehicle, 11f...Drive wheel, 12...Cargo handling equipment, 14...Battery, 30...Control unit, 31...Temperature sensor, 35...Heater, 41...Storage tank, 42...Pump, 43...Circulation channel, 44...Cargo handling channel, 81...Brake housing, 81r...Oil chamber, 90...Brake mechanism.

Claims

1. Industrial vehicles powered by batteries, A brake housing with an oil chamber filled with hydraulic fluid formed inside, A brake mechanism that rotates in the oil chamber together with the drive wheels, A storage tank in which the aforementioned hydraulic fluid is stored, A circulation channel for circulating the hydraulic fluid between the oil chamber and the storage tank, A travel motor and a cargo handling motor, which are driven by power supplied from the aforementioned battery, A pump that flows the hydraulic fluid through the circulation channel, A control unit controls the drive of the drive wheels by controlling the drive of the travel motor, and controls the drive of the pump by controlling the drive of the cargo handling motor, The system includes a temperature sensor for detecting the temperature of the hydraulic fluid, The control unit performs drive processing assuming that the battery is not being driven between the time the ignition switch is turned off and when it is turned on. In the aforementioned drive process, the industrial vehicle is characterized in that, when the temperature of the hydraulic fluid is lower than a predetermined temperature, the pump is driven by the load handling motor powered by the battery.

2. The industrial vehicle according to claim 1, wherein the control unit performs the drive processing while the battery is being charged.

3. The industrial vehicle is equipped with a hydraulically driven cargo handling device and a cargo handling passage for circulating the hydraulic fluid between the cargo handling device and the storage tank. The industrial vehicle according to claim 1 or 2, wherein the pump flows the hydraulic fluid through the circulation channel and the cargo handling channel while the control unit is performing the drive process.

4. The industrial vehicle according to claim 1 or 2, wherein the control unit performs a stop operation to stop the pump's operation if the temperature of the hydraulic fluid is above a predetermined temperature during the execution of the drive process.

5. The industrial vehicle is equipped with a heater for heating the hydraulic fluid, The industrial vehicle according to claim 4, wherein the control unit heats the hydraulic fluid with the heater during the execution of the drive process and stops heating the hydraulic fluid with the heater during the execution of the stop process.

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