Hydraulic fluid supply device for industrial vehicles

Abstract

A hydraulic oil supply device for an industrial vehicle comprises a first hydraulic oil tank that stores hydraulic oil, a second hydraulic oil tank that stores hydraulic oil, an upper communication pipe through which the upper part of the first hydraulic oil tank and the upper part of the second hydraulic oil tank communicate, a lower communication pipe through which the lower part of the first hydraulic oil tank and the lower part of the second hydraulic oil tank communicate, a first hydraulic oil pipe through which the first hydraulic oil tank and a hydraulic oil supply target supplied with hydraulic oil communicate and which has a suction port in the first hydraulic oil tank, a second hydraulic oil pipe through which the second hydraulic oil tank and the hydraulic oil supply target communicate and which has a discharge port in the second hydraulic oil tank, and a hydraulic oil pump that pumps hydraulic oil from the first hydraulic oil tank. The second hydraulic oil tank is an airtight tank sealed from outside air, the upper communication pipe has a first open end provided in the first hydraulic oil tank and a second open end provided in the second hydraulic oil tank, the opening height of the first open end is above the opening height of the suction port, and the opening height of the second open end is above the opening height of the discharge port.

Description

Technical Field

[0001] The present disclosure relates to a hydraulic fluid supply device for an industrial vehicle.

Background Art

[0002] As a conventional technique of a hydraulic fluid supply device for an industrial vehicle, for example, the structure of a plurality of hydraulic fluid tanks disclosed in Patent Document 1 is known. The structure of the plurality of hydraulic fluid tanks disclosed in Patent Document 1 is a structure of a plurality of sealed and pressurized hydraulic fluid tanks attached to a plurality of hydraulic units. In this structure of the hydraulic fluid tank, a communication pipe for hydraulic fluid flow that connects the oil phase portions of the plurality of sealed and pressurized hydraulic fluid tanks to each other is provided by being joined to the lower surface of the hydraulic fluid tank. Further, a communication pipe for pressurized air flow that connects the gas phase portions to each other is provided by being joined near the upper surface of the hydraulic fluid tank. According to the structure of the plurality of hydraulic fluid tanks disclosed in Patent Document 1, even if there is a rapid inflow and outflow of oil in the hydraulic fluid tank, the pressurized air acting on each oil surface circulates with each other to maintain balance, so that the hydraulic fluid in the hydraulic fluid tank quickly flows in and out of each other through the communication pipe, and the oil level is always synchronized.

[0003] Further, as another conventional technique, for example, the vehicle body structure of an industrial vehicle disclosed in Patent Document 2 is known. In the vehicle body structure of the industrial vehicle of Patent Document 2, it is disclosed that a forklift is provided with a hydraulic fluid tank and a fuel tank on the left and right.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in the structure of the plurality of hydraulic fluid tanks disclosed in Patent Document 1, not only are communication pipes for hydraulic fluid flow that connect the oil phase portions to each other and communication pipes for compressed air flow that connect the gas phase portions to each other required, but also pneumatic equipment such as an air compressor and pneumatic piping are necessary. Further, the need for pneumatic equipment and pneumatic piping not only requires control of the pneumatic equipment, but also poses a problem that the structure of the apparatus becomes complicated. Further, in the vehicle body structure of the industrial vehicle disclosed in Patent Document 2, since one of the tanks is a fuel tank, nothing is suggested regarding the problems that may occur when a plurality of hydraulic fluid tanks are provided in the industrial vehicle.

[0006] An object of the present disclosure is to provide a hydraulic fluid supply device for an industrial vehicle that suppresses an increase in the difference in oil level between a plurality of hydraulic fluid tanks and suppresses hydraulic fluid leakage and air inflow into the hydraulic fluid suction port when the vehicle body is tilted.

Means for Solving the Problems

[0007] A hydraulic fluid supply device for an industrial vehicle according to an aspect of the present disclosure includes a first hydraulic fluid tank that stores hydraulic fluid, a second hydraulic fluid tank that stores hydraulic fluid, an upper communication pipe that communicates the upper part of the first hydraulic fluid tank and the upper part of the second hydraulic fluid tank, a lower communication pipe that communicates the lower part of the first hydraulic fluid tank and the lower part of the second hydraulic fluid tank and allows hydraulic fluid to pass through, a first hydraulic fluid pipe that communicates the first hydraulic fluid tank and a hydraulic fluid supply target that receives the supply of hydraulic fluid and has a suction port that sucks in hydraulic fluid in the first hydraulic fluid tank, a second hydraulic fluid pipe that communicates the hydraulic fluid supply target and the second hydraulic fluid tank and has a discharge port that discharges the hydraulic fluid returned to the second hydraulic fluid tank, and a hydraulic fluid pump that pumps up the hydraulic fluid in the first hydraulic fluid tank. The second hydraulic fluid tank is an airtight tank sealed against the outside air. The upper communication pipe has a first opening end provided inside the first hydraulic fluid tank and a second opening end provided inside the second hydraulic fluid tank. The opening height of the first opening end is higher than the opening height of the suction port, and the opening height of the second opening end is higher than the opening height of the discharge port.

[0008] In the hydraulic fluid supply device for an industrial vehicle according to one aspect of the present disclosure, when the hydraulic fluid pump pumps up the hydraulic fluid in the first hydraulic fluid tank, the oil level in the first hydraulic fluid tank decreases. Even when the oil level in the first hydraulic fluid tank decreases, when the oil level reaches the second opening end of the upper communication pipe, due to the increase in the internal pressure of the second hydraulic fluid tank, the flow rate of the hydraulic fluid from the second hydraulic fluid tank to the first hydraulic fluid tank increases. Therefore, an increase in the difference in the oil levels between the first hydraulic fluid tank and the second hydraulic fluid tank is suppressed. Further, even when the vehicle body is inclined such that the first hydraulic fluid tank is below the second hydraulic fluid tank, since the second hydraulic fluid tank is an airtight tank, when the first opening end Part is immersed in the oil surface, the displacement of the oil levels in the first hydraulic fluid tank and the second hydraulic fluid tank stops. Therefore, leakage of the hydraulic fluid from the first hydraulic fluid tank to the outside due to the inclination of the vehicle body is suppressed. On the other hand, even when the vehicle body is inclined such that the second hydraulic fluid tank is below the first hydraulic fluid tank, when the second opening end Part is immersed in the oil surface, the displacement of the oil levels in the first hydraulic fluid tank and the second hydraulic fluid tank stops. Therefore, it is possible to suppress the inflow of air into the suction port caused by the oil level in the first hydraulic fluid tank dropping below the suction port due to the inclination of the vehicle body.

[0009] In one embodiment, the hydraulic fluid supply device for an industrial vehicle may include a breather connected to the first hydraulic fluid tank. In order to return the hydraulic fluid sent from the first hydraulic fluid tank to the second hydraulic fluid tank via the hydraulic fluid supply target to the first hydraulic fluid tank from the second hydraulic fluid tank, it is necessary to pressurize the inside of the second hydraulic fluid tank. Therefore, the second hydraulic fluid tank is not suitable as a place to provide a breather. By providing a breather in the first hydraulic fluid tank, it is not necessary to provide a breather in the second hydraulic fluid tank.

[0010] In one embodiment, the hydraulic oil supply device of the industrial vehicle may include a pressure regulating valve that is connected to the first hydraulic oil tank and communicates the inside of the first hydraulic oil tank with the outside air when the pressure in the space of the first hydraulic oil tank becomes equal to or higher than a predetermined pressure. In this case, the pressure in the space of the first hydraulic oil tank can be made higher than the atmospheric pressure. As a result, it becomes easier for the hydraulic oil pump to suck up the hydraulic oil in the first hydraulic oil tank. It becomes possible to extend the service life of the hydraulic oil pump.

[0011] In one embodiment, the opening height of the second opening end portion may be lower than the opening height of the first opening end portion, or may be the same as the opening height of the first opening end portion. In this case, it is possible to suppress the oil level in the second hydraulic oil tank from rising above the second opening end portion. In particular, when the opening height of the second opening end portion is the same as the opening height of the first opening end portion, it is difficult for a difference in the oil levels of the first hydraulic oil tank and the second hydraulic oil tank to occur even when the vehicle body is tilted.

[0012] In one embodiment, the hydraulic oil supply device of the industrial vehicle may include a third hydraulic oil pipe that communicates the second hydraulic oil tank with the hydraulic oil supply target and has a suction port for sucking hydraulic oil in the second hydraulic oil tank, and a second hydraulic oil pump for pumping up the hydraulic oil in the second hydraulic oil tank. In this case, since the third hydraulic oil pipe and the second hydraulic oil pump are provided, it is possible to suck up hydraulic oil not only from the first hydraulic oil tank but also from the second hydraulic oil tank. Therefore, it is possible to sufficiently supply the necessary hydraulic oil to the hydraulic oil supply target, and it is possible to improve the operating speed of the hydraulic oil supply target.

Advantages of the Invention

[0013] According to the present disclosure, it is possible to provide a hydraulic oil supply device for an industrial vehicle that suppresses an increase in the difference in oil levels in a plurality of hydraulic oil tanks, and suppresses hydraulic oil leakage and air inflow into the hydraulic oil suction port when the vehicle body is tilted.

Brief Description of the Drawings

[0014]

Figure 1

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Mode for Carrying Out the Invention

[0015] [First Embodiment] Hereinafter, the hydraulic oil supply device of the industrial vehicle according to the first embodiment will be described with reference to the drawings. In this embodiment, the hydraulic oil supply device of the forklift will be exemplified and described. Note that the "front and rear", "left and right", and "up and down" for specifying directions correspond to the directions based on the state where the operator of the forklift is seated on the driver's seat of the driver's cab and facing the forward side of the forklift.

[0016] First, the outline of the forklift will be described. As shown in FIG. 1, the forklift 10 includes a cargo handling device 12 at the front of the vehicle body 11. A driver's cab 13 is provided near the center of the vehicle body 11. Drive wheels (not shown) as front wheels are provided at the front of the vehicle body 11. Steering wheels (not shown) as rear wheels are provided at the rear of the vehicle body 11. A counterweight 14 is arranged at the rear of the vehicle body 11. The counterweight 14 is provided for adjusting the vehicle weight and achieving weight balance in the vehicle body 11. The forklift 10 of this embodiment is a battery-powered forklift with a traveling electric motor (not shown) and a battery (not shown) mounted on the vehicle body 11.

[0017] A driver's seat 15 is provided on the driver's cab 13 in the vehicle body 11. The driver's seat 15 is a seat on which the operator of the forklift 10 sits. An instrument panel 16 is provided in front of the driver's seat 15. A steering column 17 is provided on the instrument panel 16. A steering wheel 18 is provided on the steering column 17.

[0018] The handling device 12 has a mast 19 including an outer mast 20 and an inner mast 21. A pair of left and right outer masts 20 are provided with an inner mast 21 that is slidable inside the outer mast 20. A tilt cylinder (not shown) that operates by hydraulic pressure is installed between the vehicle body 11 and the outer mast 20. The mast 19 tilts in the front-rear direction with the lower end as a fulcrum by the operation of the tilt cylinder. The mast 19 is provided with a lift cylinder (not shown) that operates by hydraulic pressure. By the operation of the lift cylinder, the inner mast 21 slides up and down inside the outer mast 20.

[0019] A pair of left and right forks 23 are provided on the mast 19 via lift brackets 22. The lift brackets 22 are provided so as to move up and down together with the inner mast 21. That is, the lift brackets 22 are movable up and down with respect to the outer mast 20. Note that the left and right forks 23 have the same configuration.

[0020] The vehicle body 11 is provided with a head guard 24 that covers the upper part of the driver's seat 13. The head guard 24 is supported by a pair of left and right front pillars 25 erected from the front part of the vehicle body 11 and a pair of left and right rear pillars 26 erected from the rear part of the vehicle body 11.

[0021] Incidentally, in the present embodiment, the vehicle body 11 is equipped with a hydraulic oil supply device 30 (hydraulic oil supply device of an industrial vehicle) for the forklift 10. In the following description, the hydraulic oil supply device 30 of the forklift 10 is simply referred to as "hydraulic oil supply device 30". As shown in FIG. 2, the hydraulic oil supply device 30 includes a first hydraulic oil tank 31, a second hydraulic oil tank 32, a lower communication pipe 33, a hydraulic oil supply target 34, a first hydraulic oil pipe 35, a second hydraulic oil pipe 36, a hydraulic oil pump 37, and an upper communication pipe 38.

[0022] The first hydraulic oil tank 31 is a tank for storing hydraulic oil L. The first hydraulic oil tank 31 is arranged on the left side of the driver's seat 13 in the vehicle body 11 (see FIG. 1). The first hydraulic oil tank 31 has a bottom plate 41, a top plate 42, and side plates 43. The side plates 43 are provided between the bottom plate 41 and the top plate 42. The first hydraulic oil tank 31 is an airtight tank with high airtightness. A breather 44 is connected to the top plate 42. In the example of FIG. 2, the breather 44 is directly connected to the top plate 42 of the first hydraulic oil tank 31. The breather 44 discharges air to the outside when the pressure in the space of the first hydraulic oil tank 31 becomes higher than the atmospheric pressure. The breather 44 takes in air from the outside when the pressure in the space of the first hydraulic oil tank 31 becomes lower than the atmospheric pressure. A first hydraulic oil pipe 35 is inserted through the top plate 42. An upper communication pipe 38 is inserted through the top plate 42.

[0023] The second hydraulic oil tank 32 is a tank for storing hydraulic oil L. The second hydraulic oil tank 32 is arranged on the right side of the driver's seat 13 in the vehicle body 11 (see FIG. 1). The second hydraulic oil tank 32, like the first hydraulic oil tank 31, has a bottom plate 45, a top plate 46, and side plates 47. The side plates 47 are provided between the bottom plate 45 and the top plate 46. The second hydraulic oil tank 32 is an airtight tank with high airtightness. A second hydraulic oil pipe 36 is inserted through the top plate 46. An upper communication pipe 38 is inserted through the top plate 46. The bottom plate 45 is at the same height as the bottom plate 41 of the first hydraulic oil tank 31 in the vertical direction of the vehicle body 11. The top plate 42 is at the same height as the top plate 42 of the first hydraulic oil tank 31 in the vertical direction of the vehicle body 11. In this embodiment, the vehicle body of the engine-type forklift is diverted to the vehicle body 11 of the battery-type forklift, and the fuel tank of the engine-type forklift is utilized as the first hydraulic oil tank 31.

[0024] The lower communication pipe 33 is a pipe that connects the lower part of the first hydraulic oil tank 31 and the lower part of the second hydraulic oil tank 32. Specifically, one end 51 of the lower communication pipe 33 is connected near the lower part of the side plate 43 in the first hydraulic oil tank 31. The other end 52 of the lower communication pipe 33 is connected near the lower part of the side plate 47 in the second hydraulic oil tank 32. Therefore, the hydraulic oil L stored in the first hydraulic oil tank 31 and the second hydraulic oil tank 32 can move through the lower communication pipe 33.

[0025] The hydraulic oil supply target 34 is various hydraulic circuits and hydraulic equipment that require hydraulic oil. The hydraulic oil supply target 34 is, for example, a cargo handling system hydraulic circuit including the lift cylinder and tilt cylinder of the cargo handling device 12. The hydraulic oil supply target 34 may also be other braking system hydraulic circuits and steering system hydraulic circuits. The first hydraulic oil pipe 35 is a pipe for hydraulic oil that connects the first hydraulic oil tank 31 and the hydraulic oil supply target 34. The end of the first hydraulic oil pipe 35 on the side of the first hydraulic oil tank 31 is the suction port 53. The suction port 53 is provided close to the bottom plate 41 so as to be fully immersed in the stored hydraulic oil L when the vehicle body 11 is not tilted. The end 54 of the first hydraulic oil pipe 35 on the side opposite to the suction port 53 is connected to the hydraulic oil supply target 34.

[0026] The first hydraulic oil pipe 35 is provided with a hydraulic oil pump 37. The hydraulic oil pump 37 is a pump capable of pumping up the hydraulic oil L stored in the first hydraulic oil tank 31. The hydraulic oil pump 37 is, for example, a gear pump. The hydraulic oil pump 37 is driven by the drive of an electric motor (not shown) for the pump. The hydraulic oil pump 37 supplies the hydraulic oil L pumped up through the first hydraulic oil pipe 35 to the hydraulic oil supply target 34.

[0027] The second hydraulic oil pipe 36 is a pipe for hydraulic oil that connects the hydraulic oil supply target 34 and the second hydraulic oil tank 32. The end 55 of the second hydraulic oil pipe 36 is connected to the hydraulic oil supply target 34. The end of the second hydraulic oil pipe 36 on the side of the second hydraulic oil tank 32 is the discharge port 56. The discharge port 56 is provided close to the bottom plate 45 so as to be fully immersed in the stored hydraulic oil L when the vehicle body 11 is not tilted. The opening height of the discharge port 56 of the second hydraulic oil pipe 36 is the same as the opening height of the suction port 53 of the first hydraulic oil pipe 35. Therefore, the hydraulic oil L supplied to the hydraulic oil supply target 34 returns to the second hydraulic oil tank 32 through the second hydraulic oil pipe 36.

[0028] The upper communication pipe 38 is a pipe that communicates the upper part of the first hydraulic oil tank 31 and the upper part of the second hydraulic oil tank 32. Incidentally, in the present embodiment, the upper communication pipe 38 is provided so as to cross above an electric motor for cargo handling (not shown). The upper communication pipe 38 penetrates the top plate 42 of the first hydraulic oil tank 31. The opening height of the first opening end 57 of the upper communication pipe 38 on the side of the first hydraulic oil tank 31 is higher than the opening height of the suction port 53 of the first hydraulic oil pipe 35. The upper communication pipe 38 penetrates the top plate 46 of the second hydraulic oil tank 32. The opening height of the second opening end 58 of the upper communication pipe 38 on the side of the second hydraulic oil tank 32 is higher than the opening height of the discharge port 56 of the second hydraulic oil pipe 36. The pipe diameter of the upper communication pipe 38 is smaller than the pipe diameter of the lower communication pipe 33.

[0029] In the hydraulic oil supply device 30 of the present embodiment, with the vehicle body 11 not tilted, the hydraulic oil L is stored to such an extent that the oil level S1, S2 of the hydraulic oil L stored in the first hydraulic oil tank 31 and the second hydraulic oil tank 32 do not reach the first opening end 57 and the second opening end 58 of the upper communication pipe 38 (see FIG. 2). The state where the vehicle body 11 is not tilted is, for example, a state where the forklift 10 is stationary on a horizontal road surface.

[0030] Next, the operation of the hydraulic oil supply device 30 of the present embodiment will be described. First, in the hydraulic oil supply device 30 in a state where the vehicle body 11 is not inclined, when the hydraulic oil pump 37 operates, the hydraulic oil L in the first hydraulic oil tank 31 is pumped up. The pumped-up hydraulic oil L is supplied to the hydraulic oil supply target 34. As shown in FIG. 3(a), the oil level S1 in the first hydraulic oil tank 31 decreases due to the pumping up of the hydraulic oil L by the hydraulic oil pump 37. Therefore, the pressure in the space in the first hydraulic oil tank 31 tends to decrease.

[0031] On the other hand, the hydraulic oil L from the hydraulic oil supply target 34 is recovered to the second hydraulic oil tank 32 through the second hydraulic oil pipe 36. Therefore, as shown in FIG. 3(a), the oil level S2 in the second hydraulic oil tank 32 rises. Therefore, the pressure in the space in the second hydraulic oil tank 32 tends to increase. However, the pressure in the space in the second hydraulic oil tank 32 is released to the space in the first hydraulic oil tank 31 through the upper communication pipe 38. Further, due to the drive of the hydraulic oil pump 37, the difference between the oil level S1 in the first hydraulic oil tank 31 and the oil level S2 in the second hydraulic oil tank 32 tends to increase. Due to the head difference △H, the hydraulic oil L in the second hydraulic oil tank 32 flows to the first hydraulic oil tank 31 through the lower communication pipe 33. The flow rate of the hydraulic oil flowing through the lower communication pipe 33 depends on the head difference △H. When the flow rate in the lower communication pipe 33 increases and matches the flow rate in the second hydraulic oil pipe 36, the head difference △H becomes constant. In this state, the oil level S1 in the first hydraulic oil tank 31 and the oil level S2 in the second hydraulic oil tank 32 are maintained together with the head difference △H during the drive of the hydraulic oil pump 37.

[0032] Incidentally, when the head difference ΔH increases, as shown in FIG. 3(b), it is conceivable that the oil level S2 in the second hydraulic oil tank 32 becomes higher than the second opening end 58 of the upper communication pipe 38. In this case, the pressure in the space of the second hydraulic oil tank 32 increases, and the hydraulic oil L in the second hydraulic oil tank 32 flows through the upper communication pipe 38 and into the first hydraulic oil tank 31. Further, in the lower communication pipe 33, the flow rate of the hydraulic oil L flowing into the first hydraulic oil tank 31 increases due to the increase in the pressure in the space of the second hydraulic oil tank 32. That is, the second opening end 58 defines the upper limit of the oil level S2. For this reason, an increase in the difference between the oil level S1 in the first hydraulic oil tank 31 and the oil level S2 in the second hydraulic oil tank 32 is suppressed. In FIGS. 3(a) and 3(b), the oil level Sm in a state where there is no difference from each other is indicated by a dashed-dotted line.

[0033] Next, as shown in FIG. 4(a), the operation of the hydraulic oil supply device 30 in a state where the right side of the vehicle body 11 is upward and the left side is downward and inclined will be described. Incidentally, a case where the hydraulic oil pump 37 is not driven during the inclination will be described. Immediately after the vehicle body 11 is inclined as in the example of FIG. 4(a), the difference between the oil level S1 of the hydraulic oil L in the first hydraulic oil tank 31 and the oil level S2 of the hydraulic oil L in the second hydraulic oil tank 32 is large. Specifically, the oil level S1 of the hydraulic oil L in the first hydraulic oil tank 31 is low, and the oil level S2 of the hydraulic oil L in the second hydraulic oil tank 32 is high. For this reason, due to the head difference ΔH, the hydraulic oil L in the second hydraulic oil tank 32 flows into the first hydraulic oil tank 31 through the lower communication pipe 33. When the hydraulic oil L in the second hydraulic oil tank 32 flows into the first hydraulic oil tank 31, the oil level S1 in the first hydraulic oil tank 31 rises, and the oil level S1 in the second hydraulic oil tank 32 drops. When the oil level S1 in the first hydraulic oil tank 31 rises, the pressure in the space of the first hydraulic oil tank 31 tends to rise. The pressure in the space of the first hydraulic oil tank 31 is released into the space of the second hydraulic oil tank 32 through the upper communication pipe 38.

[0034] As shown in FIG. 4(b), when the rise of the oil level S1 in the first hydraulic oil tank 31 continues and the first opening end 57 of the upper communication pipe 38 is immersed in the hydraulic oil L, air cannot pass through the upper communication pipe 38. Therefore, the hydraulic oil L in the second hydraulic oil tank 32 cannot move to the first hydraulic oil tank 31 through the lower communication pipe 33. The rise of the oil level S1 in the first hydraulic oil tank 31 stops. That is, the difference between the oil level S1 of the hydraulic oil L in the first hydraulic oil tank 31 and the oil level S2 of the hydraulic oil L in the second hydraulic oil tank 32 is not eliminated. The rise of the oil level S1 of the hydraulic oil L in the first hydraulic oil tank 31 stops when the first opening end 57 of the upper communication pipe 38 is immersed in the hydraulic oil L. Therefore, leakage of the hydraulic oil L from the breather 44 is suppressed. In FIGS. 4(a) and 4(b), the oil level Sm in a state without difference from each other is indicated by a dashed-dotted line.

[0035] Next, as shown in FIG. 5(a), the operation of the hydraulic oil supply device 30 in a state where the left side of the vehicle body 11 is upward and the right side is downward and inclined will be described. Note that the case where the hydraulic oil pump 37 is not driven during the inclination will be described. Immediately after the vehicle body 11 is inclined as in the example of FIG. 5(a), the difference between the oil level S1 of the hydraulic oil L in the first hydraulic oil tank 31 and the oil level S2 of the hydraulic oil L in the second hydraulic oil tank 32 is large. Specifically, the oil level S1 of the hydraulic oil L in the first hydraulic oil tank 31 is high, and the oil level S2 of the hydraulic oil L in the second hydraulic oil tank 32 is low. Therefore, due to the head difference △H, the hydraulic oil in the first hydraulic oil tank 31 flows to the second hydraulic oil tank 32 through the lower communication pipe 33. When the hydraulic oil in the first hydraulic oil tank 31 flows to the second hydraulic oil tank 32, the oil level S2 in the second hydraulic oil tank 32 rises, and the oil level S1 in the first hydraulic oil tank 31 drops. As the oil level S2 in the second hydraulic oil tank 32 rises, the pressure in the space of the second hydraulic oil tank 32 tends to rise. The pressure in the space of the second hydraulic oil tank 32 is released to the space of the first hydraulic oil tank 31 through the upper communication pipe 38.

[0036] As shown in FIG. 5(b), as the oil level S2 in the second hydraulic oil tank 32 continues to rise and the second opening end 58 of the upper communication pipe 38 is immersed in the hydraulic oil, air cannot pass through the upper communication pipe 38. For this reason, the hydraulic oil in the first hydraulic oil tank 31 cannot move to the second hydraulic oil tank 32 through the lower communication pipe 33. The rise in the oil level S2 in the second hydraulic oil tank 32 stops. That is, the difference between the oil level S1 of the hydraulic oil L in the first hydraulic oil tank 31 and the oil level S2 of the hydraulic oil L in the second hydraulic oil tank 32 is not eliminated. The rise in the oil level S2 of the hydraulic oil L in the second hydraulic oil tank 32 stops when the second opening end 58 of the upper communication pipe 38 is immersed in the hydraulic oil L. The oil level S1 of the hydraulic oil L in the first hydraulic oil tank 31 also stops without decreasing. For this reason, even if the vehicle body 11 is tilted as in the example of FIG. 5(b), it is possible to prevent the oil level S1 of the hydraulic oil L in the first hydraulic oil tank 31 from dropping too much and the suction port 53 of the first hydraulic oil pipe 35 from being exposed to the space. As a result, even if the hydraulic oil pump 37 is driven with the vehicle body 11 tilted as in the example of FIG. 5(b), it is possible to suppress the immediate intake of air from the suction port 53. In FIGS. 5(a) and 5(b), the oil level Sm in the state where there is no difference from each other is indicated by a dashed-dotted line.

[0037] The hydraulic oil supply device 30 of this embodiment has the following effects. When the hydraulic oil pump 37 pumps up the hydraulic oil in the first hydraulic oil tank 31, the oil level S1 in the first hydraulic oil tank 31 drops. Even when the oil level S1 in the first hydraulic oil tank 31 drops, when the oil level reaches the second opening end 58 of the upper communication pipe 38, due to the increase in the pressure in the space of the second hydraulic oil tank 32, the flow rate of the hydraulic oil from the second hydraulic oil tank 32 to the first hydraulic oil tank 31 increases. For this reason, an increase in the difference between the oil levels S1 and S2 of the first hydraulic oil tank 31 and the second hydraulic oil tank 32 is suppressed. Even when the first hydraulic oil tank 31 is below the second hydraulic oil tank 32 and the vehicle body 11 is tilted, when the first opening end 57 is immersed in the hydraulic oil L, the displacement of the oil levels S1 and S2 of the first hydraulic oil tank 31 and the second hydraulic oil tank 32 stops. That is, the first opening end 57 defines the upper limit of the oil level S1. Therefore, leakage of the hydraulic oil L from the first hydraulic oil tank 31 to the outside due to the tilt of the vehicle body 11 is suppressed. On the other hand, even when the vehicle body 11 is tilted so that the second hydraulic oil tank 32 is below the first hydraulic oil tank 31, when the second opening end 58 is immersed in the hydraulic oil L, the displacement of the oil levels S1 and S2 of the first hydraulic oil tank 31 and the second hydraulic oil tank 32 stops. That is, the second opening end 58 defines the upper limit of the oil level S2. Therefore, it is possible to suppress the inflow of air into the suction port 53 caused by the oil level S1 in the first hydraulic oil tank 31 dropping below the suction port 53 due to the tilt of the vehicle body 11.

[0038] In order to return the hydraulic oil sent from the first hydraulic oil tank 31 to the second hydraulic oil tank 32 via the hydraulic oil supply target 34 from the second hydraulic oil tank 32 to the first hydraulic oil tank 31, it is necessary to pressurize the inside of the second hydraulic oil tank 32. Therefore, the second hydraulic oil tank 32 is not suitable as a place to provide a breather. By providing the breather 44 in the first hydraulic oil tank 31, it is not necessary to provide the breather 44 in the second hydraulic oil tank 32.

[0039] In addition, in the present embodiment, the opening heights of the first opening end portion 57 and the second opening end portion 58 of the upper communication pipe 38 are set to be substantially the same height. However, as shown in FIG. 6, the opening height of the second opening end portion 58 may be set lower than the opening height of the first opening end portion 57. For example, by setting the opening height of the second opening end portion 58 to be slightly higher than the opening height of the discharge port 56, it becomes possible to reduce the amount of the hydraulic oil L stored in the second hydraulic oil tank 32.

[0040] [Second Embodiment] Next, a hydraulic oil supply device according to the second embodiment will be described. This embodiment is different from the first embodiment in that a hydraulic oil pipe and a hydraulic pump for pumping up the hydraulic oil in the second hydraulic oil tank are provided. In this embodiment, for the same configuration as that of the first embodiment, the description of the first embodiment is incorporated and common reference numerals are used.

[0041] As shown in FIG. 7, the hydraulic oil supply device 60 includes a third hydraulic oil pipe 61 and a second hydraulic oil pump 62. The third hydraulic oil pipe 61 is a hydraulic oil pipe that connects the second hydraulic oil tank 32 and the hydraulic oil supply target 34. The end portion of the third hydraulic oil pipe 61 on the second hydraulic oil tank 32 side is a suction port 63. The suction port 63 is provided close to the bottom plate 45 so as to be sufficiently immersed in the stored hydraulic oil L in a state where the vehicle body 11 is not inclined. The end portion 64 of the third hydraulic oil pipe 61 on the side opposite to the suction port 63 is connected to the hydraulic oil supply target 34.

[0042] The third hydraulic oil pipe 61 is provided with a second hydraulic oil pump 62. The second hydraulic oil pump 62 is a pump capable of pumping up the hydraulic oil L stored in the second hydraulic oil tank 32. The second hydraulic oil pump 62 is, for example, a gear pump. The second hydraulic oil pump 62 is driven by driving an electric motor (not shown) for the pump. The second hydraulic oil pump 62 supplies the hydraulic oil L pumped up through the third hydraulic oil pipe 61 to the hydraulic oil supply target 34.

[0043] According to this embodiment, the same operational effects as those of the first embodiment can be achieved. Further, in this embodiment, since the third hydraulic oil pipe 61 and the second hydraulic oil pump 62 are provided, the hydraulic oil L can be pumped up not only from the first hydraulic oil tank 31 but also from the second hydraulic oil tank 32. Therefore, even when the hydraulic oil supply target 34 requires a large flow rate of the hydraulic oil L, the necessary hydraulic oil L can be sufficiently supplied to the hydraulic oil supply target 34, and the operating speed of the hydraulic oil supply target 34 can be improved.

[0044] [Third Embodiment] Next, the hydraulic oil supply device according to the third embodiment will be described. The hydraulic oil supply device 30A of this embodiment is different from the first embodiment in that it includes a pressure regulating valve 70 instead of the breather 44 that discharges air to the outside when the pressure in the space of the first hydraulic oil tank 31 becomes higher than the atmospheric pressure. The pressure regulating valve is a valve configured to communicate the inside of the first hydraulic oil tank 31 with the outside air when the pressure in the space of the first hydraulic oil tank 31 becomes a predetermined pressure or higher. The predetermined pressure may be, for example, an atmospheric pressure that is higher than the standard atmospheric pressure (1 atm: 101.33 kPa) by a predetermined set differential pressure. The set differential pressure may be a differential pressure that assists the hydraulic oil pump 37 in pumping up the hydraulic oil L in the first hydraulic oil tank 31. The set differential pressure may be a differential pressure that releases the pressure in the space of the first hydraulic oil tank 31 when the hydraulic oil L in the first hydraulic oil tank 31 becomes hot. Specifically, when the temperature of the hydraulic oil L in the first hydraulic oil tank 31 rises, the temperature of the air layer in the first hydraulic oil tank 31 rises due to heat transfer from the hydraulic oil L, and the pressure of the air layer rises based on Boyle's law. The set differential pressure is set such that the pressure regulating valve 70 opens at the pressure of the air layer corresponding to the temperature of the hydraulic oil when the pressure in the space of the first hydraulic oil tank 31 is released when the temperature of the predetermined hydraulic oil reaches a certain level. In this embodiment, for the same configurations as those of the first embodiment, the description of the first embodiment is incorporated by reference, and common reference numerals are used.

[0045] FIG. 8 is a configuration diagram schematically showing an operating oil supply device of a forklift according to a third embodiment. FIG. 9 is a schematic partial cross-sectional view showing an example of a valve structure of a pressure regulating valve. As shown in FIG. 8, a pressure regulating valve 70 is connected to the top plate 42 of the first hydraulic oil tank 31. In the example of FIG. 8, the pressure regulating valve 70 is directly connected to the top plate 42 of the first hydraulic oil tank 31. The pressure regulating valve 70 has a valve structure 70A including a housing 71, a first plunger 72, a second plunger 73, a first spring 74, a second spring 75, a retainer 76, a fastening member 78, and a snap ring 77. The pressure regulating valve 70 is connected to the first hydraulic oil tank 31 such that the upper part of the valve structure 70A above the paper surface of FIG. 9 is on the atmosphere side and the lower part of the valve structure 70A below the paper surface of FIG. 9 is on the inner side of the first hydraulic oil tank 31.

[0046] The housing 71 is a cylindrical (for example, circular cylindrical) member that supports the internal components of the valve structure 70A. The housing 71 includes a side wall portion 71a and a bottom portion 71b. An opening 71c is formed in the side wall portion 71a on the side of the first hydraulic oil tank 31. The opening 71c opens, for example, in a circular shape. The side opposite to the first hydraulic oil tank 31 of the side wall portion 71a is continuous with the bottom portion 71b. An opening 71d is formed in the central portion of the bottom portion 71b.

[0047] The first plunger 72 is a cylindrical (for example, circular cylindrical) member that functions as a valve body. The first plunger 72 includes a main body portion 72a and a flange 72b formed at one end of the main body portion 72a. The flange 72b is, for example, a disk-shaped with an outer diameter larger than the opening diameter of the opening 71d. The first plunger 72 is disposed in the housing 71 with one end of the main body portion 72a facing away from the first hydraulic oil tank 31. In FIG. 9, the flange 72b abuts against the inner surface of the bottom portion 71b of the housing 71 inside the housing 71. A through hole through which a bolt 78a of the fastening member 78 described later can be inserted is formed in the center of the first plunger 72.

[0048] The second plunger 73 is a cylindrical (e.g., circular cylinder) member that functions as a valve body. The second plunger 73 is, for example, disc-shaped with a smaller diameter than the outer diameter of the flange 72b of the first plunger 72. The second plunger 73 is arranged on the side opposite to the first hydraulic oil tank 31 with respect to the first plunger 72. In FIG. 9, the surface of the second plunger 73 on the side of the first hydraulic oil tank 31 is in contact with the surface of the flange 72b on the side opposite to the first hydraulic oil tank 31. A through-hole through which the bolt 78a of the fastening member 78 described later can be inserted is formed at the center of the second plunger 73.

[0049] The first spring 74 is a spring for intake of the pressure regulating valve 70. The first spring 74 is, for example, a coil spring. The first spring 74 has an inner diameter larger than the outer diameter of the main body portion 72a of the first plunger 72. The first spring 74 has an outer diameter smaller than the outer diameter of the flange 72b of the first plunger 72. The first spring 74 is arranged such that one end of the first spring 74 seats on the surface 72c of the flange 72b on the side of the first hydraulic oil tank 31.

[0050] The second spring 75 is a spring for exhaust of the pressure regulating valve 70. The second spring 75 is, for example, a coil spring thinner than the first spring 74. The second spring 75 has an inner diameter larger than the outer diameter of the bolt 78a of the fastening member 78. The second spring 75 has an outer diameter smaller than the outer diameter of the main body portion 72a of the first plunger 72. The second spring 75 is arranged such that one end of the second spring 75 seats on the end surface 72d of the main body portion 72a on the side of the first hydraulic oil tank 31.

[0051] The retainer 76 is a cylindrical (e.g., circular cylinder) member for integrally holding the first plunger 72 and the first spring 74. The retainer 76 includes a main body portion 76a and a flange 76b formed at one end of the main body portion 76a. The main body portion 76a is, for example, cylindrical with an outer diameter smaller than the inner diameter of the first spring 74. The flange 76b is, for example, disc-shaped with an outer diameter slightly smaller than the inner diameter of the housing 71. A through-hole through which the second spring 75 can be inserted is formed at the center of the retainer 76.

[0052] The retainer 76 is disposed in the housing 71 with one end of the main body 76a facing the first hydraulic oil tank 31 side. In FIG. 9, after the first plunger 72, the first spring 74, and the second spring 75 are disposed inside the housing 71, the retainer 76 is inserted from the opening 71c of the housing 71. The retainer 76 is fixed by the snap ring 77 in a state where the other end of the first spring 74 is seated on the surface 76c of the flange 76b opposite to the first hydraulic oil tank 31, compressing the first spring 74. The snap ring 77 is fitted into a groove 71e formed on the inner wall surface on the opening 71c side of the housing 71.

[0053] The fastening member 78 is a member for integrally holding the first plunger 72, the second plunger 73, and the second spring 75. The fastening member 78 includes a bolt 78a, a washer 78b, and a lock nut 78c. The bolt 78a is inserted from the second plunger 73 side through the through hole of the second plunger 73, the through hole of the first plunger 72, and the second spring 75 in a state where the retainer 76 is fixed by the snap ring 77 as described above. The lock nut 78c is screwed onto the bolt 78a with the other end of the second spring 75 seated on the washer 78b. When the lock nut 78c is tightened, the second spring 75 is compressed. The fastening member 78 is operable integrally with the second plunger 73. When the pressure regulating valve 70 opens, mainly the pressure in the space of the first hydraulic oil tank 31 acts on the lower surface of the second plunger 73, and the second plunger 73 moves upward, pushing up the head of the bolt 78a, and the second plunger 73 and the bolt 78a move upward integrally. When the pressure regulating valve 70 closes, as the pressure in the space of the first hydraulic oil tank 31 decreases, the bolt 78a moves downward as the second spring 75 extends, and the second plunger 73 is pushed down by the bolt 78a. Note that the head of the bolt 78a and the second plunger 73 may be integrated by adhesion or the like.

[0054] FIG. 10 is a partial cross-sectional view showing an operation example of the pressure regulating valve of FIG. 9. As shown in FIG. 10, in the pressure regulating valve 70 configured as described above, when the pressure in the space of the first hydraulic oil tank 31 increases, a force that pushes up the second plunger 73 in the direction from the first hydraulic oil tank 31 side toward the upper side of the paper surface of FIG. 10 acts on the fastening member 78 and the second plunger 73. The bolt 78a, the washer 78b, and the lock nut 78c are pushed up, and the second spring 75 is compressed. The contact (sealing) between the first plunger 72 and the second plunger 73 is released. That is, when the pressure in the space of the first hydraulic oil tank 31 becomes equal to or higher than a predetermined pressure, the inside of the first hydraulic oil tank 31 communicates with the outside air. As a result, the air inside the first hydraulic oil tank 31 is discharged to the outside. The pressure regulating valve 70 has a cap 79 provided so as to cover the valve structure 70A (see FIG. 11). The air discharged from the inside of the first hydraulic oil tank 31 through the pressure regulating valve 70 is discharged to the outside of the pressure regulating valve 70 through the space between the housing 71 of the valve structure 70A and the cap 79.

[0055] According to the present embodiment, the same operational effects as those of the first embodiment are achieved. Further, in the present embodiment, since the pressure regulating valve 70 is provided instead of the breather 44, when the pressure in the space of the first hydraulic oil tank 31 becomes equal to or higher than a predetermined pressure, the inside of the first hydraulic oil tank 31 communicates with the outside air. As a result, the pressure in the space of the first hydraulic oil tank 31 can be made higher than the atmospheric pressure. As a result, it becomes easier for the hydraulic pump 37 to suck up the hydraulic oil L in the first hydraulic oil tank 31. The service life of the hydraulic pump 37 can be extended.

[0056] The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the gist of the invention. For example, the following modifications may be made.

[0057] In the above-described embodiment, the breather 44 and the pressure regulating valve 70 were directly connected to the top plate 42 of the first hydraulic oil tank 31, but the present invention is not limited thereto. The breather 44 and the pressure regulating valve 70 may be indirectly connected to the top plate 42 of the first hydraulic oil tank 31 via a pipe. For example, FIG. 11 is a schematic perspective view showing an example of an attachment configuration of the breather and the pressure regulating valve to the first hydraulic oil tank. FIG. 12 is a configuration diagram schematically showing a hydraulic oil supply device of a forklift having the attachment configuration of FIG. 11. In the hydraulic oil supply device 30B shown in FIGS. 11 and 12, the pressure regulating valve 70 disposed inside the cap 79 is indirectly connected to the top plate 42 of the first hydraulic oil tank 31 via a pipe 80. The pipe 80 may include, for example, a tank-side pipe 81, a rubber hose 82, and a mounting block 83. The rubber hose 82 may be bent or linear according to the shapes of the first hydraulic oil tank 31 and the second hydraulic oil tank 32. The mounting block 83 may be omitted. According to the indirect connection via a pipe as shown in FIGS. 11 and 12, the degree of freedom in arranging the breather 44 and the pressure regulating valve 70 increases. It becomes difficult to be restricted by the layout of the components around the first hydraulic oil tank 31, and it becomes possible to easily arrange the breather 44 and the pressure regulating valve 70.

[0058] In the above-described embodiment, the first hydraulic oil tank and the second hydraulic oil tank were arranged to be a pair on the left and right in the vehicle body, but the present invention is not limited thereto. The first hydraulic oil tank and the second hydraulic oil tank may be arranged, for example, to be a pair in the front and rear in the vehicle body. In this case, the inclination of the vehicle body corresponds to an inclination in which the front side of the vehicle body is upward and the rear side is downward, or an inclination in which the front side of the vehicle body is downward and the rear side is upward.

[0059] In the above-described embodiment, the hydraulic oil supply device of a forklift as an industrial vehicle has been described, but the present invention is not limited thereto. The industrial vehicle may be, for example, an automated guided vehicle, a towing tractor, or a construction vehicle in addition to the forklift.

[0060] In the above-described embodiment, the hydraulic oil is stored in the first hydraulic oil tank and the second hydraulic oil tank such that there is a space between the first opening end portion and the second opening end portion of the upper communication pipe and the oil level. However, the present invention is not limited to this. For example, the hydraulic oil may be stored such that the oil level is the same as the opening height of the first opening end portion and the opening height of the second opening end portion. The hydraulic oil may be stored such that the first opening end portion and the second opening end portion interfere with or are immersed in the hydraulic oil. In this case, when the vehicle body is in a horizontal state, immediately after the rotation of the hydraulic oil pump starts, the oil level in the second hydraulic oil tank hardly rises above the second opening end portion. Even when the vehicle body is inclined, the oil level hardly changes.

[0061] In the above-described embodiment, the first hydraulic oil tank and the second hydraulic oil tank had substantially the same configuration. However, the present invention is not limited to this. The first hydraulic oil tank and the second hydraulic oil tank may have different shapes or capacities from each other.

[0062] In the above-described embodiment, the opening height of the discharge port 56 of the second hydraulic oil pipe 36 was set to the same opening height as the suction port 53 of the first hydraulic oil pipe 35. However, the present invention is not limited to this. The opening height of the discharge port 56 may be higher than the suction port 53. The opening height of the discharge port 56 may be lower than the suction port.

[0063] Note that a valve that opens under a predetermined condition (for example, when the vehicle body 11 is inclined at a predetermined inclination angle or more based on an inclination angle sensor) may be provided in the upper communication pipe 38. In this case, depending on whether or not air can flow in the upper communication pipe 38, for example, when the vehicle body 11 is inclined at a predetermined inclination angle or more, the movement of the hydraulic oil from the second hydraulic oil tank to the first hydraulic oil tank can be allowed at a desired timing.

[0064] Hereinafter, the constituent elements of various aspects of the present disclosure will be described. <Invention 1> A first hydraulic oil tank for storing hydraulic oil, A second hydraulic oil tank for storing hydraulic oil, An upper communication pipe that communicates the upper part of the first hydraulic oil tank and the upper part of the second hydraulic oil tank, A lower communication pipe that connects the lower part of the first hydraulic oil tank and the lower part of the second hydraulic oil tank and allows hydraulic oil to pass through; A first hydraulic oil pipe that connects the first hydraulic oil tank and a hydraulic oil supply target that receives the supply of hydraulic oil and has a suction port for sucking hydraulic oil in the first hydraulic oil tank; A second hydraulic oil pipe that connects the hydraulic oil supply target and the second hydraulic oil tank and has a discharge port for discharging the hydraulic oil returned to the second hydraulic oil tank; A hydraulic oil pump for pumping up the hydraulic oil in the first hydraulic oil tank, and is provided with; The second hydraulic oil tank is an airtight tank sealed against the outside air, The upper communication pipe, A first opening end provided inside the first hydraulic oil tank, A second opening end provided inside the second hydraulic oil tank, and has; The opening height of the first opening end is higher than the opening height of the suction port, The opening height of the second opening end is higher than the opening height of the discharge port, and an operating oil supply device for an industrial vehicle. <Invention 2> The operating oil supply device for an industrial vehicle according to Invention 1, further comprising a breather connected to the first hydraulic oil tank. <Invention 3> The operating oil supply device for an industrial vehicle according to Invention 1, further comprising a pressure regulating valve connected to the first hydraulic oil tank and communicating the inside of the first hydraulic oil tank with the outside air when the pressure in the space of the first hydraulic oil tank becomes a predetermined pressure or more. <Invention 4> The opening height of the second opening end is lower than the opening height of the first opening end, or is the same as the opening height of the first opening end. The operating oil supply device for an industrial vehicle according to any one of Inventions 1 to 3. <Invention 5> A third hydraulic oil pipe that connects the second hydraulic oil tank and the hydraulic oil supply target and has a suction port for sucking hydraulic oil in the second hydraulic oil tank; The operating oil supply device for an industrial vehicle according to any one of Inventions 1 to 4, further comprising a second hydraulic oil pump for pumping up the hydraulic oil in the second hydraulic oil tank.

Explanation of Symbols

[0065] 10... Forklift, 11... Vehicle body, 12... Handling device, 13... Driver's seat, 15... Driving seat, 18... Steering wheel, 22... Lift bracket, 23... Fork, 30, 30A, 30B, 60... Hydraulic oil supply device for industrial vehicles, 31... First hydraulic oil tank, 32... Second hydraulic oil tank, 33... Lower communication pipe, 34... Hydraulic oil supply target, 35... First hydraulic oil pipe, 36... Second hydraulic oil pipe, 37... Hydraulic oil pump, 38... Upper communication pipe, 44... Breather, 53, 63... Suction ports, 56... Discharge port, 57... First opening end, 58... Second opening end, 61... Third hydraulic oil pipe, 62... Second hydraulic oil pump, 70... Pressure regulating valve, L... Hydraulic oil, S1, S2, Sm... Oil levels, △H... Head difference.

Claims

1. A first hydraulic oil tank for storing hydraulic oil, A second hydraulic oil tank for storing hydraulic oil, An upper communication pipe that communicates the upper part of the first hydraulic oil tank and the upper part of the second hydraulic oil tank, A lower communication pipe that communicates the lower part of the first hydraulic oil tank and the lower part of the second hydraulic oil tank and allows hydraulic oil to pass through, A first hydraulic oil pipe that communicates the first hydraulic oil tank and a hydraulic oil supply target that receives the supply of hydraulic oil and has a suction port for sucking hydraulic oil in the first hydraulic oil tank, A second hydraulic oil pipe that communicates the hydraulic oil supply target and the second hydraulic oil tank and has a discharge port for discharging the hydraulic oil returned to the second hydraulic oil tank, A hydraulic oil pump for pumping up the hydraulic oil in the first hydraulic oil tank, and The second hydraulic oil tank is an airtight tank sealed against the outside air, The upper communication pipe, A first opening end provided inside the first hydraulic oil tank for defining the upper limit of the oil level in the first hydraulic oil tank, A second opening end provided inside the second hydraulic oil tank for defining the upper limit of the oil level in the second hydraulic oil tank, and The opening height of the first opening end is higher than the opening height of the suction port, The opening height of the second opening end is higher than the opening height of the discharge port. A hydraulic oil supply device for an industrial vehicle.

2. The hydraulic oil supply device for an industrial vehicle according to claim 1, comprising a breather connected to the first hydraulic oil tank.

3. The hydraulic oil supply device for an industrial vehicle according to claim 1, comprising a pressure regulating valve connected to the first hydraulic oil tank and communicating the inside of the first hydraulic oil tank with the outside air when the pressure in the space of the first hydraulic oil tank becomes a predetermined pressure or more.

4. The hydraulic oil supply device for an industrial vehicle according to claim 1 or 2, wherein the opening height of the second opening end is lower than the opening height of the first opening end or the same as the opening height of the first opening end.

5. A third hydraulic oil pipe that communicates the second hydraulic oil tank and the hydraulic oil supply target and has a suction port for sucking hydraulic oil in the second hydraulic oil tank, The hydraulic oil supply device for an industrial vehicle according to claim 1 or 2, comprising a second hydraulic oil pump for pumping up the hydraulic oil in the second hydraulic oil tank.

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