Construction machinery

Abstract

To suppress deterioration of hydraulic oil by suppressing contact with oxygen while suppressing pressure resistance required for a hydraulic oil tank.SOLUTION: A construction machine comprises: a vehicle body; a front work machine attached to the vehicle body; a hydraulic actuator driving the front work machine; a hydraulic oil tank storing hydraulic oil that drives the hydraulic actuator; a hydraulic pump sucking the hydraulic oil from the hydraulic oil tank and discharging as a pressure oil driving the hydraulic actuator; and a motor driving the hydraulic oil pump. The hydraulic oil tank is constituted so that outside air comes in / out via a breather according to ascend / descend of fluid level of the stored hydraulic oil. The construction machine comprises: a nitrogen gas generator that separates and generates nitrogen gas from air; and a nitrogen gas supply device that supplies the nitrogen gas from the nitrogen gas generator to the hydraulic oil tank.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to construction machinery such as hydraulic excavators.

Background Art

[0002] The hydraulic oil used in hydraulic-driven construction machinery such as hydraulic excavators oxidizes (deteriorates) due to contact with oxygen and temperature rise. Therefore, in order to suppress the deterioration of the hydraulic oil, it is important to suppress the temperature rise of the hydraulic oil and suppress the contact of the hydraulic oil with oxygen. However, in construction machinery, particularly in a hydraulic actuator driven at a high load, it is inevitable to increase the pressure of the hydraulic oil supplied thereto, and it is difficult to suppress the temperature rise of the hydraulic oil. On the other hand, there is a device called an air breaker whose volume changes according to the liquid level of the hydraulic oil tank provided in the hydraulic oil tank, and the hydraulic oil tank is structured to be airtight to suppress the contact between the hydraulic oil and oxygen (for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, the technique of Patent Document 1 has a structure in which pressure is applied to the air breaker using a weight, and the hydraulic oil tank is pressurized by receiving the internal pressure of the air breaker. Therefore, the hydraulic oil tank is required to have high pressure resistance.

[0005] An object of the present invention is to provide a construction machine that can suppress the deterioration of the hydraulic oil by suppressing the contact with oxygen while suppressing the pressure resistance required for the hydraulic oil tank.

Means for Solving the Problems

[0006] To achieve the above objective, the present invention provides a construction machine comprising a vehicle body, a front work implement attached to the vehicle body, a hydraulic actuator for driving the front work implement, a hydraulic oil tank for storing hydraulic oil for driving the hydraulic actuator, a hydraulic pump for drawing in the hydraulic oil tank and discharging it as pressurized oil for driving the hydraulic actuator, and a prime mover for driving the hydraulic pump, wherein the hydraulic oil tank is configured to allow outside air to enter and exit through a breather as the liquid level of the stored hydraulic oil rises and falls, and further comprising a nitrogen gas generator for separating and producing nitrogen gas from air, and a nitrogen gas supply device for supplying nitrogen gas from the nitrogen gas generator to the hydraulic oil tank. The nitrogen gas supply device comprises a nitrogen pipe connecting the nitrogen gas generator and the hydraulic fluid circuit; a container-shaped bubbling component having a plurality of pores and positioned inside the hydraulic fluid tank, to which the nitrogen pipe is connected, and configured to supply the nitrogen gas supplied from the nitrogen pipe to the internal space of the hydraulic fluid tank through the plurality of pores; a solenoid valve provided in the nitrogen pipe; a liquid level gauge provided inside the bubbling component; and a controller that controls the solenoid valve based on the output of the liquid level gauge to adjust the liquid level of the hydraulic fluid inside the bubbling component. We provide construction machinery. Furthermore, the present invention provides a construction machine comprising a vehicle body, a front work machine attached to the vehicle body, a hydraulic actuator for driving the front work machine, a hydraulic oil tank for storing hydraulic oil for driving the hydraulic actuator, a hydraulic pump for drawing in the hydraulic oil tank and discharging it as pressurized oil for driving the hydraulic actuator, and a prime mover for driving the hydraulic pump, wherein the hydraulic oil tank is configured to allow outside air to enter and exit through a breather as the liquid level of the stored hydraulic oil rises and falls, and further comprising a nitrogen gas generator for separating and producing nitrogen gas from air, and a nitrogen gas supply device for supplying nitrogen gas from the nitrogen gas generator to the hydraulic oil tank, wherein the nitrogen gas supply device comprises nitrogen piping connecting the nitrogen gas generator and the hydraulic oil circuit, and a booster pump for pressurizing the nitrogen gas produced by the nitrogen gas generator, and the nitrogen piping connects a return pipe connected to the inlet of the hydraulic oil tank and the booster pump. Furthermore, the present invention relates to a construction machine comprising a vehicle body, a front work machine attached to the vehicle body, a hydraulic actuator for driving the front work machine, a hydraulic oil tank for storing hydraulic oil for driving the hydraulic actuator, a hydraulic pump for drawing in the hydraulic oil tank and discharging it as pressurized oil for driving the hydraulic actuator, and a prime mover for driving the hydraulic pump, wherein the hydraulic oil tank is configured to allow outside air to enter and exit through a breather as the liquid level of the stored hydraulic oil rises and falls, and further comprising a nitrogen gas generator for separating and producing nitrogen gas from air, and a nitrogen gas supply device for supplying nitrogen gas from the nitrogen gas generator to the hydraulic oil tank, and the nitrogen gas supply device The present invention provides a construction machine comprising: a nitrogen pipe connecting the nitrogen gas generator and the hydraulic fluid circuit; an oxygen sensor for measuring the dissolved oxygen concentration in the hydraulic fluid; a solenoid valve provided in the nitrogen pipe; and a controller that controls the nitrogen gas generator and the solenoid valve based on the output of the oxygen sensor. The controller drives the nitrogen gas generator and opens the solenoid valve when the prime mover is started, continuously supplies the nitrogen gas to the hydraulic fluid while the prime mover is running, calculates the post-stop nitrogen supply time based on the output of the oxygen sensor when the prime mover stops, closes the solenoid valve after the post-stop nitrogen supply time has elapsed since the prime mover stopped, and stops the nitrogen gas generator. Furthermore, the present invention relates to a construction machine comprising a vehicle body, a front work machine attached to the vehicle body, a hydraulic actuator for driving the front work machine, a hydraulic oil tank for storing hydraulic oil for driving the hydraulic actuator, a hydraulic pump for drawing in the hydraulic oil tank and discharging it as pressurized oil for driving the hydraulic actuator, and a prime mover for driving the hydraulic pump, wherein the hydraulic oil tank is configured to allow outside air to enter and exit through a breather as the liquid level of the stored hydraulic oil rises and falls, and further comprising a nitrogen gas generator for separating and producing nitrogen gas from air, and a nitrogen gas supply device for supplying nitrogen gas from the nitrogen gas generator to the hydraulic oil tank, wherein the nitrogen gas supply device The present invention provides a construction machine comprising: a nitrogen pipe connecting the nitrogen gas generator and the hydraulic fluid circuit; a thermometer for measuring the temperature of the hydraulic fluid; a solenoid valve installed in the nitrogen pipe; and a controller that controls the nitrogen gas generator and the solenoid valve based on the output of the thermometer, wherein the controller drives the nitrogen gas generator and opens the solenoid valve when the prime mover is started, continuously supplies the nitrogen gas to the hydraulic fluid while the prime mover is running, calculates the time required for the temperature of the hydraulic fluid to drop to a predetermined temperature based on the output of the thermometer when the prime mover stops, closes the solenoid valve after the required time has elapsed since the prime mover stopped, and stops the nitrogen gas generator. [Effects of the Invention]

[0007] According to the present invention, it is possible to suppress the deterioration of the hydraulic fluid by reducing contact with oxygen while keeping the pressure resistance required for the hydraulic fluid tank down. [Brief explanation of the drawing]

[0008] [Figure 1] A perspective view showing the external appearance and main components of a hydraulic excavator, which is an example of a construction machine according to the first embodiment of the present invention. [Figure 2] Figure 1 shows a diagram illustrating the essential components of the hydraulic circuit of the hydraulic system of a hydraulic excavator. [Figure 3] Schematic diagram of a hydraulic oil tank provided in a construction machine according to a second embodiment of the present invention. [Figure 4] Schematic diagram of a hydraulic oil tank provided in a construction machine according to the third embodiment of the present invention. [Figure 5] Schematic diagram of a hydraulic oil tank provided in a construction machine according to the fourth embodiment of the present invention. [Figure 6] A flowchart illustrating the control procedure for supplying nitrogen gas to the hydraulic fluid by a controller provided in a construction machine according to a fifth embodiment of the present invention. [Figure 7] A flowchart illustrating the control procedure for supplying nitrogen gas to the hydraulic fluid by a controller provided in a construction machine according to the sixth embodiment of the present invention. [Figure 8] A flowchart illustrating the control procedure for supplying nitrogen gas to the hydraulic fluid by a controller provided in a construction machine according to the seventh embodiment of the present invention. [Modes for carrying out the invention]

[0009] Embodiments of the present invention will be described below with reference to the drawings.

[0010] (First Embodiment) -Construction machinery- Figure 1 is a perspective view showing the main components of a hydraulic excavator, which is an example of a construction machine according to the first embodiment of the present invention, along with its external appearance. In this embodiment, a hydraulic excavator with a bucket 23 attached as an attachment to the front workpiece 20 is described as an example of a construction machine. However, the present invention can also be applied to hydraulic excavators with attachments other than buckets, or to other types of construction machines such as wheel loaders and bulldozers. In this specification, the front of the driver's cab 16 (upper left side in Figure 1) is defined as the front of the slewing body of the construction machine.

[0011] The construction machine shown in the figure comprises a vehicle body 10 and a front work implement 20. The vehicle body 10 comprises a traveling body 11 and a rotating body 12.

[0012] -Vehicle- In this embodiment, the vehicle 11 is equipped with crawler-type left and right running gears 13 having continuous track tracks, and the vehicle moves by driving the left and right running gears 13 respectively with left and right running motors 14. Hydraulic motors are used for the running motors 14.

[0013] -Rotating body- The revolving body 12 is provided rotatably on the upper part of the traveling body 11 via a slewing device 15. A cab 16 for an operator to board is provided at the front part (the left front part in this embodiment) of the revolving body 12. A machine room 17 housing an engine 35 etc. is provided on the rear side of the cab 16 in the revolving body 12, and a counterweight (not shown) for balancing the weight with the front working machine 20 is mounted on the rear end. The slewing device 15 connecting the revolving body 12 to the traveling body 11 includes a slewing motor 34 (FIG. 2), and when the slewing motor 34 is driven, the revolving body 12 revolves with respect to the traveling body 11. A hydraulic motor is used as the slewing motor 34.

[0014] Also, the revolving body 12 is equipped with a fuel tank 18, an exhaust gas purification device 19, a hydraulic pump 36, a hydraulic oil tank 38, a nitrogen gas generator 41, a booster pump 42, and a storage battery 43. Further, the revolving body 12 includes a nitrogen gas supply device 40 for supplying nitrogen gas from the nitrogen gas generator 41 to the hydraulic oil tank 38. In this embodiment, the nitrogen gas supply device 40 includes the booster pump 42 and a nitrogen pipe 44.

[0015] The fuel tank 18 is arranged on the front side of the machine room 17 in the right part of the revolving body 12. The fuel stored in this fuel tank 18 is supplied to the engine 35, and the engine 35 is driven by the energy of the fuel. The exhaust gas purification device 19 is housed in the machine room 17 and purifies the exhaust of the engine 35.

[0016] The hydraulic oil tank 38 is a tank for storing hydraulic oil for driving hydraulic actuators (such as boom cylinders 31 etc.), and in this embodiment, it is mounted on the front side of the fuel tank 18 in the revolving body 12. The hydraulic oil tank 38 is provided with a breather (vent valve) 38b, and is configured such that outside air enters and exits through the breather 38b as the liquid level of the stored hydraulic oil rises and falls.

[0017] The hydraulic pump 36 is housed in the machine room 17 adjacent to the engine 35. The drive shaft of the hydraulic pump 36 is connected to the output shaft of the engine 35 and driven by the engine 35. It draws hydraulic fluid from the hydraulic fluid tank 38 and discharges it as pressurized oil to drive hydraulic actuators (boom cylinder 31, etc.). In this embodiment, the case in which the engine 35 is used as the prime mover to drive the hydraulic pump 36 is given as an example, but an electric motor may be used as the prime mover instead of the engine 35.

[0018] The nitrogen gas generator 41 is a device that separates and generates nitrogen gas from air (outside air around the hydraulic excavator), and in this embodiment, it is mounted in front of the hydraulic oil tank 38 on the rotating body 12. Nitrogen gas and oxygen gas in the air have different molecular sizes, resulting in a difference in their adsorption rates to the carbon molecular sieve (not shown), which is an adsorbent. The nitrogen gas generator 41 utilizes this difference in molecular size to generate high-concentration nitrogen gas. Specifically, oxygen gas molecules are adsorbed onto the carbon molecular sieve faster than nitrogen gas molecules, and the amount of adsorption is particularly large under high pressure. Therefore, by pressurizing the air and sending it into a tank (not shown) filled with carbon molecular sieves, oxygen gas, carbon dioxide gas, moisture, etc. in the compressed air are adsorbed in a short time and discharged before nitrogen gas is adsorbed. In this way, the nitrogen gas generator 41 stably and continuously generates high-purity nitrogen gas.

[0019] The nitrogen gas generated by the nitrogen gas generator 41 is a gas whose main component is nitrogen (for example, a gas with a nitrogen content of 95% or more), and is not limited to a gas with a nitrogen content of 100%.

[0020] The booster pump 42 is a compressor that increases the pressure of nitrogen gas, for example, about 0.5 MPa, generated by the nitrogen gas generator 41 to a predetermined pressure, and is mounted on the swivel body 12 adjacent to the nitrogen gas generator 41.

[0021] The nitrogen gas generator 41 and the booster pump 42 are powered by electricity supplied from a battery 43. The battery 43 is located in the rotating body 12 (e.g., the machine room 17).

[0022] -Front work equipment- The front work implement 20 is a multi-jointed work arm for performing tasks such as excavating earth and sand, and is attached to the front of the slewing body 12 (to the right of the driver's cab 16 in this embodiment). This front work implement 20 consists of a boom 21, an arm 22, and a bucket 23. The boom 21 is connected to the base frame of the slewing body 12, called the slewing frame, by pins (not shown) extending to the left and right, and rotates up and down relative to the slewing body 12 as the boom cylinder 31 extends and retracts. Both ends of the boom cylinder 31 are rotatably connected to the boom 21 and the slewing body 12 via pins (not shown) extending to the left and right. The arm 22 is connected to the tip of the boom 21 by pins (not shown) extending to the left and right, and rotates back and forth relative to the boom 21 as the arm cylinder 32 extends and retracts. Both ends of the arm cylinder 32 are rotatably connected to the arm 22 and the boom 21 via pins (not shown) extending to the left and right. The bucket 23 is connected to the tip of the arm 22 by pins (not shown) extending horizontally to the left and right, and rotates relative to the arm 22 as the bucket cylinder 33 extends and retracts. The base end of the bucket cylinder 33 is connected to the arm 22, and the tip is connected to the bucket via a link. The boom cylinder 31, arm cylinder 32, and bucket cylinder 33 are hydraulic actuators that drive the front work implement 20.

[0023] - Hydraulic System - Figure 2 is a diagram showing the essential parts of the hydraulic circuit of the hydraulic system of the hydraulic excavator shown in Figure 1. In Figure 2, elements that have already been explained are given the same reference numerals as in the previously shown drawings, and their explanations are omitted.

[0024] The hydraulic system shown in Figure 2 is a device that drives the driven components of a hydraulic excavator and is mainly housed in the machine room 17. The driven components are, for example, the front work equipment 20 (boom 21, arm 22, and bucket 23) and the vehicle body 10 (traveling body 11 and slewing body 12). In addition to the engine 35, hydraulic pump 36, and hydraulic oil tank 38 mentioned above, this hydraulic system also includes a control valve unit 37, various piping, wiring, etc.

[0025] The control valve unit 37 is comprised of multiple directional control valves that control the direction and flow rate of pressurized oil supplied from the hydraulic pump 36 to the hydraulic actuator (e.g., boom cylinder 31) via the discharge pipe 36a. Each directional control valve constituting the control valve unit 37 is operated by a pilot pressure acting on the pressure receiving chamber in response to operator operation, which drives the spool. In Figure 2, only the boom cylinder 31, arm cylinder 32, bucket cylinder 33, and swing motor 34 are shown as hydraulic actuators, but the travel motor 14 (Figure 1), etc., can also be controlled by the control valve unit 37. Return oil from the hydraulic actuator is returned from the control valve unit 37 to the hydraulic oil tank 38 via the return pipe 38a. The discharge pipe 36a of the hydraulic pump 36 is provided with a relief valve 39 that defines the maximum pressure (relief pressure) of the discharge pipe 36a.

[0026] As mentioned above, the nitrogen gas supply device 40 is composed of a booster pump 42 and nitrogen piping 44. The booster pump 42 is connected to the hydraulic fluid circuit shown in Figure 2 (hydraulic fluid tank 38 in the example of Figure 2) via nitrogen piping 44, and the nitrogen gas generator 41 is connected via nitrogen piping 44 and the booster pump 42. This configuration allows nitrogen gas generated by the nitrogen gas generator 41 to be injected into the hydraulic fluid flowing through the hydraulic circuit.

[0027] -effect- (1) According to this embodiment, by driving the nitrogen gas generator 41 and the booster pump 42 to inject nitrogen gas into the hydraulic fluid in the hydraulic circuit via the nitrogen piping 44, dissolved oxygen in the hydraulic fluid can be purged, and the dissolved oxygen concentration in the hydraulic fluid can be reduced. Furthermore, since only nitrogen gas is injected into the hydraulic fluid circuit, for example, the hydraulic fluid tank 38 equipped with the breather 38b is not excessively pressurized. Therefore, according to this embodiment, the deterioration of the hydraulic fluid can be suppressed by reducing contact with oxygen while keeping the pressure resistance required of the hydraulic fluid tank 38 down. Consequently, not only can the manufacturing cost of the hydraulic fluid tank 38 be reduced, but the operating cost of the hydraulic excavator can also be reduced by extending the lifespan of the hydraulic fluid.

[0028] Furthermore, the system is simple and inexpensive, consisting of a nitrogen gas generator 41 and a booster pump 42 installed on the hydraulic excavator and nitrogen piping 44 connected to the hydraulic fluid circuit. As mentioned above, there is no need to replace the hydraulic fluid tank 38 with one that has higher pressure resistance. Therefore, the oxygen purging system of this embodiment can be easily applied to existing hydraulic excavators.

[0029] Currently, mineral-based hydraulic fluids are the mainstream, but there is a possibility that the demand for biodegradable hydraulic fluids, which have a lower environmental impact, will increase in the future. This embodiment is effective for both mineral-based and biodegradable hydraulic fluids, but biodegradable hydraulic fluids are more prone to oxidation and are more expensive than mineral-based hydraulic fluids, resulting in a significant cost burden for users. From this perspective, this embodiment can extend the lifespan of the hydraulic fluid, thus reducing operating costs even when using biodegradable hydraulic fluids, and can contribute to the widespread adoption of biodegradable hydraulic fluids.

[0030] Here, the ratio of the volume concentrations of dissolved oxygen and nitrogen gases in the purchased biodegradable hydraulic fluid was measured and found to be approximately 1:4. This ratio is equivalent to the ratio of the volume concentrations of oxygen and nitrogen gases in air. From this, the inventors of the present invention realized that the source of the dissolved gases in the hydraulic fluid is air, and that the hydraulic fluid incorporates the air it comes into contact with.

[0031] Furthermore, when nitrogen gas was injected into the biodegradable hydraulic fluid at a predetermined flow rate for several hours and measurements were taken, it was found that the dissolved oxygen concentration in the hydraulic fluid decreased by approximately 60%, potentially doubling the operating time limit in hydraulic excavators. Further effects can be expected depending on the nitrogen gas flow rate and injection time.

[0032] (2) In this embodiment, the nitrogen gas generator 41 and the booster pump 42 are powered by the battery 43, so that nitrogen gas can be injected into the hydraulic fluid even when the engine 35 is stopped. Therefore, the nitrogen gas generator 41 and the booster pump 42 can be driven not only when the hydraulic excavator is in operation (for example, when the engine 35 is running) but also when it is stopped.

[0033] (Second Embodiment) Figure 3 is a schematic diagram of a hydraulic oil tank provided in a construction machine according to a second embodiment of the present invention. In Figure 3, elements already described in the first embodiment are denoted by the same reference numerals as in the previously shown drawings, and their descriptions are omitted.

[0034] This embodiment is an example of a configuration that efficiently reduces the dissolved oxygen concentration in the hydraulic fluid using nitrogen gas. In this example, a bubbling component 50 is placed inside the hydraulic fluid tank 38, and the bubbling component 50 is connected to a booster pump 42 via nitrogen piping 44. The nitrogen gas supply device 40 in this embodiment consists of a booster pump 42 and nitrogen piping 44, as well as a solenoid valve 45, a bubbling component 50, a liquid level gauge 55, and a controller 60. The configuration is described below.

[0035] -Hydraulic oil tank- The hydraulic oil tank 38 is a container-shaped component with a lid, and in addition to the breather 38b mentioned above, it has a hydraulic oil inlet 38c, an outlet 38d, a lid 38e, and the like.

[0036] The breather 38b is a vent valve that connects the inside and outside of the hydraulic oil tank 38. The hydraulic excavator performs various operations such as traveling and digging, and the amount of hydraulic oil inside the hydraulic oil tank 38 increases or decreases depending on the flow rate of pressurized oil supplied to the hydraulic actuator. The breather 38b is adjusted so that the inside of the hydraulic oil tank 38 is kept at positive pressure even when the amount of hydraulic oil in the hydraulic oil tank 38 increases or decreases, or when the internal pressure of the hydraulic oil tank 38 changes due to filling with nitrogen gas. For example, if the liquid level L rises, the air (e.g., nitrogen or a small amount of oxygen) inside the hydraulic oil tank 38 is discharged to the outside of the hydraulic oil tank 38 via the breather 38b.

[0037] The inlet 38c of the hydraulic oil tank 38 is provided by penetrating the side plate or top plate (top plate) of the hydraulic oil tank 38 at a high position. The return pipe 38a described above is connected to this inlet 38c. The outlet 38d of the hydraulic oil tank 38 is provided by penetrating the bottom plate of the hydraulic oil tank 38. This outlet 38d is connected to the intake port (not shown) of the hydraulic pump 36 via piping (not shown). The hydraulic oil that drives the hydraulic actuator such as the boom cylinder 31 flows from the return pipe 38a through the inlet 38c into the hydraulic oil tank 38. At that time, the hydraulic oil that flows from the return pipe 38a into the hydraulic oil tank 38 passes through the filter F1 to remove foreign matter and air bubbles before being stored in the hydraulic oil tank 38. The hydraulic oil stored in the hydraulic oil tank 38 is then discharged from the outlet 38d and sucked into the hydraulic pump 36, and discharged from the hydraulic pump 36 as pressurized oil to drive the hydraulic actuator. At that time, the hydraulic fluid discharged from the hydraulic fluid tank 38 passes through the filter F2 to remove foreign matter and air bubbles before being drawn into the hydraulic pump 36. When changing or replenishing the hydraulic fluid, the lid 38e is opened and hydraulic fluid is poured in through the top opening of the hydraulic fluid tank 38.

[0038] -Bubbling parts- In this embodiment, the bubbling component 50 is fixedly installed on the floor inside the hydraulic oil tank 38 so that it is completely immersed in the hydraulic oil stored in the hydraulic oil tank 38 while the hydraulic excavator is in operation. Furthermore, the bubbling component 50 in this embodiment is a container-shaped member and is composed of numerous small holes 51, inlets and outlets 52, guides 53, etc.

[0039] The pores 51 are preferably located in the upper half of the bubbling component 50. In this embodiment, the top plate of the bubbling component 50 is formed in a mesh shape, and numerous pores 51 are provided in the top plate of the bubbling component 50. The nitrogen pipe 44 is inserted into the lower half of the bubbling component 50 and fixedly connected, and nitrogen gas supplied from the nitrogen pipe 44 is introduced into the internal space of the bubbling component 50. The nitrogen gas introduced into the bubbling component 50 is ejected from the bubbling component 50 through the numerous pores 51 and supplied into the internal space of the hydraulic oil tank 38, where it floats in the hydraulic oil as fine bubbles B. In other words, the bubbling component 50 supplies nitrogen gas to the internal space of the hydraulic oil tank 38 via the pores 51.

[0040] The inlet / outlet 52 is an opening that connects the internal and external spaces of the bubbling component 50, separate from the pores 51. While the pores 51 are located in the upper half of the bubbling component 50, the inlet / outlet 52 is located in the lower half. During operation of the nitrogen gas generator 41 and the booster pump 42, a gas reservoir is formed in the upper part of the internal space of the bubbling component 50 by nitrogen gas supplied from the nitrogen piping 44, and the nitrogen gas in this reservoir is ejected from the pores 51 as bubbles B. The volume of this gas reservoir increases or decreases depending on the flow rate of nitrogen gas into the bubbling component 50 and the kinematic viscosity of the hydraulic fluid. At that time, the liquid level S of the hydraulic fluid formed inside the bubbling component 50 rises and falls as hydraulic fluid is allowed to enter and exit the bubbling component 50 through the inlet / outlet 52.

[0041] The guide 53 is a guide member that guides the nitrogen gas bubbles B ejected from the numerous pores 51 in a direction away from the outlet 38d of the hydraulic oil tank 38. In this embodiment, the pores 51 are provided on the upper surface of the bubbling component 50, and the guide 53 is formed in a cylindrical shape so as to surround the area where these pores 51 are provided. The guide 53 extends vertically and guides the nitrogen gas bubbles B ejected from the pores 51 in the direction of their buoyancy. Since the outlet 38d of the hydraulic oil tank 38 is provided on the bottom plate of the tank, the nitrogen gas bubbles B ejected from the pores 51 are not sucked into the outlet 38d but are guided by the guide 53 and float upward.

[0042] -Sensor- The hydraulic fluid tank 38 is equipped with sensors such as an oxygen sensor 54, a liquid level gauge 55, and a thermometer 56.

[0043] The oxygen sensor 54 is, for example, a fluorescent sensor that measures the dissolved oxygen concentration in the hydraulic fluid. It is fixed to the lower half of the inner wall of the hydraulic fluid tank 38 via a bracket so that it remains immersed in the hydraulic fluid even when the hydraulic fluid level L in the hydraulic fluid tank 38 drops. The oxygen sensor 54 is connected to the controller 60 via lead wires. The oxygen sensor 54 does not necessarily have to be a fluorescent sensor; any sensor capable of measuring dissolved oxygen in the hydraulic fluid is applicable, and there are no particular limitations on the measurement principle or configuration.

[0044] The liquid level gauge 55 is a sensor that measures the height of the hydraulic fluid level S inside the bubbling component 50, and is located inside the bubbling component 50. This liquid level gauge 55 is connected to the controller 60 via a lead wire 55a. The lead wire 55a of the liquid level gauge 55 is wired through the nitrogen piping 44, and the nitrogen piping 44, bubbling component 50, liquid level gauge 55, and lead wire 55a constitute one unit (bubbling unit). In addition to the nitrogen piping 44, bubbling component 50, liquid level gauge 55, and lead wire 55a, a solenoid valve 45 and its lead wire may also be added to form a bubbling unit.

[0045] The thermometer 56 is a sensor that measures the temperature of the hydraulic fluid. It is fixed to the lower half of the inner wall of the hydraulic fluid tank 38 via a bracket, together with the oxygen sensor 54, so that it remains immersed in the hydraulic fluid even if the hydraulic fluid level L in the hydraulic fluid tank 38 drops. The thermometer 56 is also connected to the controller 60 via lead wires.

[0046] -controller- The outputs of the oxygen sensor 54, liquid level gauge 55, and thermometer 56 are each input to the controller 60 via lead wires. The controller 60 is an on-board computer mounted on the hydraulic excavator and consists of an input unit (e.g., AD converter), memory (e.g., RAM, ROM, HDD, etc.), processing unit (e.g., CPU), output unit (e.g., DA converter), etc. The controller 60 has a function to adjust the height of the hydraulic fluid level S inside the bubbling component 50 by controlling the solenoid valve 45 based on the output of the liquid level gauge 55. This function is executed by the CPU according to the program loaded into RAM, for example, by loading a program stored in ROM into RAM.

[0047] The solenoid valve 45 described above is an electromagnetically driven proportional valve installed in the nitrogen piping 44. By adjusting the opening of this solenoid valve 45, the supply of nitrogen gas to the hydraulic oil tank 38 can be shut off or the flow rate adjusted. The solenoid of the solenoid valve 45 is connected to the output of the controller 60 via a lead wire and is driven by a command signal from the controller 60. While the hydraulic excavator is in operation, the solenoid valve 45 is opened with the nitrogen gas generator 41 and booster pump 42 running, and nitrogen gas is constantly supplied to the hydraulic oil tank 38 to prevent the hydraulic oil tank 38 from becoming negative pressure even if the liquid level L of the hydraulic oil in the hydraulic oil tank 38 drops. During this time, the controller 60 controls the opening of the solenoid valve 45 based on the output of the liquid level gauge 55, adjusting the height of the liquid level S of the hydraulic oil inside the bubbling component 50. Specifically, the controller 60 stores a predetermined setting range for the height of the liquid level gauge in memory and provides feedback control to the solenoid valve 45 so that the output of the liquid level gauge 55 falls within the set range.

[0048] In other respects, this embodiment is the same as the first embodiment.

[0049] -effect- In this embodiment as well, the same effects as in the first embodiment can be obtained by injecting nitrogen gas into the hydraulic fluid to purge the oxygen.

[0050] Furthermore, in this embodiment, a bubbling component 50 is installed at the bottom of the hydraulic oil tank 38, and nitrogen gas is supplied through this bubbling component 50, so that the nitrogen gas is supplied to the hydraulic oil as a large number of fine bubbles B. As a result, the specific surface area of ​​the nitrogen gas is increased, and the dissolved oxygen concentration in the hydraulic oil can be reduced more efficiently.

[0051] Furthermore, the kinematic viscosity of the hydraulic fluid changes with temperature. For example, if the kinematic viscosity of the hydraulic fluid increases, it becomes more difficult for nitrogen gas to be ejected from the bubbling component 50, and if the kinematic viscosity decreases, it becomes easier for nitrogen gas to be ejected from the bubbling component 50. Therefore, if the supply flow rate of nitrogen gas to the bubbling component 50 is constant, the liquid level S of the hydraulic fluid inside the bubbling component 50 will decrease, and nitrogen gas can be discharged from the bubbling component 50 through the inlet / outlet 52 without passing through the pores 51.

[0052] Therefore, in this embodiment, the liquid inside the bubbling member 50 is determined based on the output of the liquid level gauge 55. rank By controlling this, nitrogen gas can be supplied to the hydraulic fluid in the correct amount, neither too much nor too little. This prevents nitrogen gas from being discharged from the bubbling component 50 without passing through the pores 51 due to an excess supply of nitrogen gas, and allows all of the nitrogen gas to be efficiently ejected from the bubbling component 50 as fine bubbles B through the pores 51.

[0053] Furthermore, similar to the bubbling component 50, a flow of hydraulic fluid is formed near the outlet 38d located at the bottom of the hydraulic fluid tank 38, which is then drawn into the hydraulic pump 36. If nitrogen gas bubbles B are carried along with this flow and drawn into the hydraulic pump 36, the hydraulic fluid mixed with bubbles B will be sent to the hydraulic actuator, potentially affecting the operational stability of the hydraulic actuator due to cavitation.

[0054] In contrast, in this embodiment, by providing a guide 53 on the bubbling component 50, the flow of hydraulic fluid toward the outlet 38d of the hydraulic fluid tank 38 is separated from the air bubbles B, thereby preventing the air bubbles B from being sent to the hydraulic actuator.

[0055] Furthermore, by passing the lead wire 55a of the liquid level gauge 55 installed inside the bubbling component 50 through the nitrogen piping 44, and unitizing the nitrogen piping 44, bubbling component 50, liquid level gauge 55, and lead wire 55a, the bubbling unit is easy to handle. Therefore, this bubbling unit can be easily retrofitted to construction machinery already in operation at the customer's site after delivery.

[0056] (Third embodiment) Figure 4 is a schematic diagram of a hydraulic oil tank provided in a construction machine according to the third embodiment of the present invention. In Figure 4, elements already described in the first and second embodiments are denoted by the same reference numerals as in the previously shown drawings, and their descriptions are omitted.

[0057] -composition- The difference between this embodiment and the second embodiment is that it includes a heater 57 located inside the bubbling component 50. The nitrogen gas supply device 40 in this embodiment includes a booster pump 42 and nitrogen piping 44, as well as a solenoid valve 45, a bubbling component 50, a thermometer 56, a heater 57, and a controller 60. In Figure 4, the inlet / outlet 52 and liquid level gauge 55 of the bubbling component 50 are omitted, but the inlet / outlet 52 and liquid level gauge 55 may be provided as needed.

[0058] The heater 57 is located inside the bubbling component 50. This heater 57 is connected to the controller 60 via a lead wire 57a and is powered by electricity supplied from the controller 60 to heat the hydraulic fluid inside the bubbling component 50. The controller 60 is programmed to activate the heater 57 when, for example, the temperature of the hydraulic fluid measured by a thermometer 56 falls below a set value. The lead wire 57a of the heater 57 is also routed through the nitrogen piping 44, and the nitrogen piping 44, bubbling component 50, heater 57, and lead wire 57a constitute a single unit (bubbling unit). In addition to the nitrogen piping 44, bubbling component 50, heater 57, and lead wire 57a, a solenoid valve 45 and its lead wire may also be added to form a bubbling unit.

[0059] In other respects, this embodiment shown in Figure 4 is the same as the second embodiment described in Figure 3.

[0060] -effect- In this embodiment as well, the same effects as in the first embodiment can be obtained by injecting nitrogen gas into the hydraulic fluid to purge the oxygen.

[0061] In addition, in this embodiment, by placing the heater 57 inside the bubbling component 50, the kinematic viscosity of the hydraulic fluid can be reduced by the heater 57 when the kinematic viscosity of the hydraulic fluid is high, such as immediately after starting the hydraulic excavator or during operation in winter or cold regions. This allows an appropriate amount of nitrogen gas to be smoothly ejected from the bubbling component 50 even if the pressure of the nitrogen gas supplied to the hydraulic fluid is low. Furthermore, even if the hydraulic excavator is stopped for a certain period and the inside of the bubbling component 50 is filled with hydraulic fluid due to the cessation of nitrogen gas supply, nitrogen gas can be easily supplied to the inside of the bubbling component 50 by reducing the kinematic viscosity of the hydraulic fluid with the heater 57. In this case, nitrogen gas can be supplied to the inside of the bubbling component 50 even if the pressure of the nitrogen gas is low (for example, even at around 0.2 MPa), and the hydraulic fluid can be pushed out of the bubbling component 50 in a short time.

[0062] (Fourth Embodiment) Figure 5 is a schematic diagram of a hydraulic oil tank provided in a construction machine according to the fourth embodiment of the present invention. In Figure 5, elements already described in the first to third embodiments are denoted by the same reference numerals as in the previously shown drawings, and their descriptions are omitted.

[0063] -composition- The difference between this embodiment and the second embodiment is that the nitrogen piping 44 connects the return piping 38a, which is connected to the inlet 38c of the hydraulic oil tank 38, to the booster pump 42. The nitrogen gas supply device 40 in this embodiment consists of the booster pump 42 and the nitrogen piping 44, as well as the return piping 38a, solenoid valve 45, pressure gauge 58, and controller 60. In Figure 5, the bubbling component 50 and liquid level gauge 55 are omitted.

[0064] In this embodiment, since the nitrogen piping 44 is connected to the return piping 38a, the minimum required nitrogen gas pressure is higher than when the nitrogen piping 44 is connected to the hydraulic oil tank 38. This is because the pressure of the hydraulic oil flowing through the return piping 38a is slightly higher than the pressure of the hydraulic oil in the hydraulic oil tank 38. For example, in the second or third embodiment, a nitrogen gas pressure of about 0.2 MPa was sufficient, but in this embodiment, it is desirable that the nitrogen gas pressure supplied to the return piping 38a be about 3 MPa.

[0065] Therefore, in this example, in addition to the solenoid valve 45, a pressure gauge 58 for measuring the pressure in the nitrogen pipe 44 is installed in the nitrogen pipe 44, and the controller 60 controls the opening degree of the solenoid valve 45 based on the output of the pressure gauge 58 to maintain the pressure in the nitrogen pipe 44 at or above a set pressure (for example, 3 MPa). The controller 60 performs feedback control, for example, by increasing (opening) the opening degree of the solenoid valve 45 if the output of the pressure gauge 58 is higher than a predetermined value determined based on the set pressure, and decreasing (throttling) the opening degree of the solenoid valve 45 if the output of the pressure gauge 58 is lower than the predetermined value.

[0066] In other respects, this embodiment shown in Figure 5 is the same as the second embodiment described in Figure 3.

[0067] -effect- In this embodiment as well, the same effects as in the first embodiment can be obtained by injecting nitrogen gas into the hydraulic fluid to purge the oxygen.

[0068] In addition, in this embodiment, by supplying nitrogen gas to the flow of hydraulic fluid returning to the hydraulic fluid tank 38, the nitrogen gas can be brought into uniform contact with the hydraulic fluid, thereby suppressing unevenness in the dissolved oxygen concentration of the hydraulic fluid.

[0069] (Fifth embodiment) Figure 6 is a flowchart illustrating the control procedure for supplying nitrogen gas to the hydraulic fluid by a controller provided in a construction machine according to the fifth embodiment of the present invention.

[0070] -Control Procedure- In this embodiment, an example is described in which the supply of nitrogen gas to the hydraulic fluid is continued for a predetermined post-stop nitrogen supply time T1 after the hydraulic excavator has stopped (for example, after the engine has stopped). The post-stop nitrogen supply time T1 is the nitrogen supply time required to reduce the dissolved oxygen concentration in the hydraulic fluid to a target concentration set from the viewpoint of suppressing oxidation of the hydraulic fluid, and is calculated based on the output of the oxygen sensor 54. Specifically, for example, a data table that defines the relationship between the output value of the oxygen sensor 54 and the post-stop nitrogen supply time T1 is stored in the memory of the controller 60. When the hydraulic excavator stops, the controller 60 refers to the data table to calculate the post-stop nitrogen supply time T1 according to the output of the oxygen sensor 54, and continues to supply nitrogen to the hydraulic fluid for a time T1 from the time the hydraulic excavator stops. Except for the above points, the hardware configuration of this embodiment is the same as any of the first to fourth embodiments.

[0071] The flow shown in Figure 6 is explained below. When the controller 60 starts the engine 35 based on a signal from, for example, a key switch (not shown) located in the operator's cab 16, the flow shown in Figure 6 begins. Once the flow shown in the figure has started, the controller 60 drives the nitrogen gas generator 41 and the booster pump 42 and opens the solenoid valve 45, continuously supplying nitrogen gas to the hydraulic fluid while the engine 35 is running (step S11). During this time, the operator operates the front work implement 20, the traveling body 11, and the slewing body 12 to perform excavation work, travel, etc.

[0072] While the engine 35 is running, the controller 60 determines whether the engine 35 has been instructed to stop based on the signal from the key switch (not shown) (step S12). If the key has not been turned off, the controller 60 continues to run the engine 35 and continue to supply nitrogen gas to the hydraulic fluid. Conversely, if the key has been turned off, the controller 60 stops the engine 35 (step S13). Accordingly, the controller 60 calculates the nitrogen supply time T1 after stopping based on the output of the oxygen sensor 54 (step S14), and continues to supply nitrogen gas to the hydraulic fluid for the duration of the nitrogen supply time T1 after the engine 35 has stopped (step S15). Then, after the nitrogen supply time T1 has elapsed since the engine 35 stopped (at the time of elapsed time), the controller 60 closes the solenoid valve 45, stops the nitrogen gas generator 41 and the booster pump 42, stops the supply of nitrogen gas, and ends the flow shown in Figure 6 (step S16).

[0073] -effect- In this embodiment as well, the same effects as in the first embodiment can be obtained by injecting nitrogen gas into the hydraulic fluid to purge the oxygen.

[0074] In addition, in this embodiment, when the hydraulic excavator stops, the supply of nitrogen gas to the hydraulic fluid is continued for a predetermined time even after the engine 35 has stopped, thereby reducing the dissolved oxygen concentration in the stopped hydraulic fluid to a predetermined value, and thus the dissolved oxygen concentration in the hydraulic fluid can be continuously suppressed for a long period of time.

[0075] (Sixth Embodiment) Figure 7 is a flowchart illustrating the control procedure for supplying nitrogen gas to the hydraulic fluid by a controller provided in a construction machine according to the sixth embodiment of the present invention.

[0076] -Control Procedure- In this embodiment, an example is described in which nitrogen gas is continuously supplied to the hydraulic fluid for a period of time T2 required until the hydraulic fluid temperature drops to a predetermined temperature after the hydraulic excavator has stopped (for example, after the engine has stopped). The required time T2 is the time required for the hydraulic fluid, which has risen in temperature during operation, to cool down and for the temperature difference between the inside and outside of the hydraulic fluid tank 38 to decrease, and is calculated based on the output value of the thermometer 56. The assumed temperature of the hydraulic fluid after the required time T2 has elapsed since the hydraulic excavator has stopped operating may be a value set by statistically analyzing past ambient temperature data of the site where the hydraulic excavator is operating, or it may be the ambient temperature at the time the hydraulic excavator has stopped operating. The ambient temperature at the time the hydraulic excavator has stopped operating may be obtained by using a thermometer (not shown) installed on the hydraulic excavator to measure the ambient temperature, or by using ambient temperature data received from a server in the site office. For example, a data table defining the relationship between the output value of the thermometer 56 (or the temperature difference between the hydraulic fluid temperature measured by the thermometer 56 and the ambient temperature) and the required time T2 is stored in the memory of the controller 60. When the hydraulic excavator stops, the controller 60 refers to a data table to calculate the required time T2 according to the output of the thermometer 56, and continues to supply nitrogen to the hydraulic fluid for time T2 from the time the hydraulic excavator stops. Except for the above, this embodiment is the same as any of the first to fourth embodiments.

[0077] The flow shown in Figure 7 will be explained. When the controller 60 starts the engine 35 based on a signal from, for example, a key switch (not shown) located in the operator's cab 16, the flow shown in Figure 7 begins. Once the flow shown in the figure has started, the controller 60 drives the nitrogen gas generator 41 and the booster pump 42 and opens the solenoid valve 45, continuously supplying nitrogen gas to the hydraulic fluid while the engine 35 is running (step S21). During this time, the operator operates the front work implement 20, the traveling body 11, and the slewing body 12 to perform excavation work, travel, etc.

[0078] While the engine 35 is running, the controller 60 determines whether the engine 35 has been instructed to stop based on the signal from the key switch (not shown) (step S22). If the key has not been turned off, the controller 60 continues to run the engine 35 and continue to supply nitrogen gas to the hydraulic fluid. Conversely, if the key has been turned off, the controller 60 stops the engine 35 (step S23). Accordingly, the controller 60 calculates the time T2 required for the hydraulic fluid temperature to drop to a predetermined temperature based on the output of the thermometer 56 (step S24), and continues to supply nitrogen gas to the hydraulic fluid for the required time T2 after the engine 35 has stopped (step S25). Then, after the required time T2 has elapsed since the engine 35 stopped (at the time of elapsed time), the controller 60 closes the solenoid valve 45, stops the nitrogen gas generator 41 and the booster pump 42, stops the supply of nitrogen gas, and ends the flow shown in Figure 7 (step S26).

[0079] -effect- In this embodiment as well, the same effects as in the first embodiment can be obtained by injecting nitrogen gas into the hydraulic fluid to purge the oxygen.

[0080] In addition, after the hydraulic excavator has been operated (for example, after excavation work), the hydraulic fluid, which has been heated during operation, cools down, and consequently the pressure in the gas reservoir inside the hydraulic fluid tank 38 decreases. During the cooling process of this gas reservoir, outside air may be drawn into the hydraulic fluid tank 38 through the breather 38b. Therefore, in this embodiment, by supplying nitrogen gas to the hydraulic fluid tank 38 during this time, the drawing of outside air into the hydraulic fluid tank 38 through the breather 38b is suppressed, reducing the opportunity for contact between the hydraulic fluid and air and suppressing oxidation of the hydraulic fluid. Furthermore, since the differential pressure between the inside and outside of the hydraulic fluid tank 38 can be suppressed, the pressure resistance required of the hydraulic fluid tank 38 can also be reduced.

[0081] (Seventh Embodiment) Figure 8 is a flowchart illustrating the control procedure for supplying nitrogen gas to the hydraulic fluid by a controller provided in a construction machine according to the seventh embodiment of the present invention.

[0082] -Control Procedure- In this embodiment, an example of supplying nitrogen gas to the hydraulic fluid when necessary will be described. When necessary means, for example, when changing the hydraulic fluid or when the dissolved oxygen concentration in the hydraulic fluid exceeds a specified value.

[0083] For example, the dissolved oxygen concentration of hydraulic fluid may be related to the brand and manufacturing lot number of the hydraulic fluid. For instance, the necessity of nitrogen supply can be defined for each brand and manufacturing lot number of hydraulic fluid, and this data table can be stored in the memory of the controller 60. In this case, by having the operator input a trigger that identifies that the hydraulic fluid has been changed, along with the brand and manufacturing lot number of the new hydraulic fluid to be used, into the controller 60, the controller 60 can determine whether or not nitrogen supply is necessary. It is also conceivable to install a barcode reader or similar device on the hydraulic excavator and read the data of the new hydraulic fluid using the reader. Furthermore, even for brands of hydraulic fluid that require nitrogen gas supply, if the hydraulic fluid has undergone a process to reduce the dissolved oxygen concentration before being used in the hydraulic excavator, it is not necessary to supply nitrogen gas in the hydraulic excavator when changing the hydraulic fluid. In this case, by inputting information into the controller 60 that the hydraulic fluid has undergone a process to reduce the dissolved oxygen concentration, the controller 60 can identify that nitrogen gas supply is unnecessary.

[0084] Furthermore, regardless of the type, brand, or manufacturing lot number of the hydraulic fluid, it is also possible to monitor the dissolved oxygen concentration of the hydraulic fluid and determine whether or not nitrogen gas needs to be supplied. In this case, for example, a predetermined value for the dissolved oxygen concentration of the hydraulic fluid is set in advance and stored in memory. This allows the controller 60 to compare the dissolved oxygen concentration of the hydraulic fluid calculated based on the output of the oxygen sensor 54 with the predetermined value, and determine that nitrogen gas supply is necessary if the dissolved oxygen concentration is equal to or greater than the predetermined value. Except for the points mentioned above, this embodiment is the same as any of the first to fourth embodiments.

[0085] The flow shown in Figure 8 is explained below. The controller 60 starts the free flow shown in Figure 8 as soon as power is turned on. Once the flow shown in the figure has started, the controller 60 determines whether or not nitrogen gas needs to be supplied to the hydraulic fluid as described above (step S31). If nitrogen gas supply is not needed, the controller 60 repeats the procedure in step S31 and waits until it becomes necessary to supply nitrogen gas to the hydraulic fluid. If it is necessary to supply nitrogen gas to the hydraulic fluid, the controller 60 drives the nitrogen gas generator 41 and the booster pump 42 to open the solenoid valve 45 and starts supplying nitrogen gas to the hydraulic fluid (step S32).

[0086] While nitrogen gas is being supplied, the controller 60 calculates the dissolved oxygen concentration in the hydraulic fluid in real time based on the output of the oxygen sensor 54 and determines whether the calculated dissolved oxygen concentration is below a specified value (step S33). If the dissolved oxygen concentration in the hydraulic fluid is below the specified value, the controller 60 closes the solenoid valve 45 to stop the nitrogen gas generator 41 and the booster pump 42, stops the supply of nitrogen gas to the hydraulic fluid (step S35), and returns to step S31. Conversely, if the dissolved oxygen concentration in the hydraulic fluid is above the specified value, the controller 60 determines whether the elapsed time since the start of nitrogen gas supply has reached a predetermined time (step S34). If the predetermined time has not yet elapsed, the controller 60 continues the supply of nitrogen gas and returns to step S33; if the predetermined time has been reached, it moves to step S35, stops the supply of nitrogen gas to the hydraulic fluid, and returns to step S31. The controller 60 starts the free operation shown in Figure 8 when power is turned on.

[0087] In this way, the controller 60 repeatedly executes the flow shown in the figure while power is supplied. Furthermore, the flow shown in Figure 8 can be configured to be executed not only during the operation of the hydraulic excavator, but also when necessary while the hydraulic excavator is stopped, for example, by power supply from the storage battery 43.

[0088] -effect- In this embodiment as well, the same effects as in the first embodiment can be obtained by injecting nitrogen gas into the hydraulic fluid to purge the oxygen.

[0089] In addition, in this embodiment, nitrogen gas can be supplied to the hydraulic fluid only when needed and in the required amount, thereby suppressing the excessive supply of nitrogen gas to the hydraulic fluid and improving energy efficiency.

[0090] Furthermore, even if the dissolved oxygen concentration in the hydraulic fluid does not fall below a specified value, temporarily stopping the supply of nitrogen gas after a certain period of time can suppress energy waste in cases where a decrease in the dissolved oxygen concentration cannot be expected even if nitrogen gas is supplied due to the properties of the hydraulic fluid. However, even if this limitation on the supply time of nitrogen gas (step S34) is omitted, the flow shown in Figure 8 will still be valid.

[0091] Furthermore, if the need to supply nitrogen gas is determined in step S31 based on the brand of the new hydraulic fluid to be used rather than the measured dissolved oxygen concentration, then measuring the dissolved oxygen concentration is unnecessary for this determination, and therefore the oxygen sensor 54 is not required. In this case, if the flow is set to stop supplying nitrogen gas after supplying it for a certain period of time (flow of steps S32 → S34 → S35), the oxygen sensor 54 can also be omitted.

[0092] (modified version) The above embodiments are particularly effective when applied to biodegradable hydraulic fluids that are susceptible to oxidation, but they can also be effective when applied to mineral-based hydraulic fluids.

[0093] Furthermore, although the above embodiments have described a hydraulic excavator equipped with a booster pump 42 as an example, the booster pump 42 is not necessarily required. For example, if a nitrogen pipe 44 is connected to the hydraulic oil tank 38 as in the second and third embodiments, nitrogen gas can be supplied to the hydraulic oil even at a low pressure of about 0.2 MPa. Since the nitrogen gas generated by the nitrogen gas generator 41 is generally at about 0.5 MPa, if the pressure of the nitrogen gas supplied to the hydraulic oil tank 38 can be kept at 0.2 MPa or higher while suppressing pressure loss in the flow path, the booster pump 42 can be omitted.

[0094] Furthermore, the supply of nitrogen gas to the hydraulic fluid is automatically performed by controlling the nitrogen gas generator 41, booster pump 42, and solenoid valve 45 with the controller 60, but it may also be performed manually based on the judgment of an operator or other human. [Explanation of Symbols]

[0095] 10...Vehicle body, 20...Front work implement, 31...Boom cylinder (hydraulic actuator), 32...Arm cylinder (hydraulic actuator), 33...Bucket cylinder (hydraulic actuator), 35...Engine (prime mover), 36...Hydraulic pump, 38...Hydraulic oil tank (hydraulic oil circuit), 38a...Return piping (hydraulic oil circuit), 38b...Breather, 38d...Hydraulic oil tank outlet, 40...Nitrogen gas supply device, 41...Nitrogen gas generator, 42...Booster pump, 44...Nitrogen piping, 45...Solenoid valve, 50...Bubbling component, 51...Pore, 53...Guide, 54...Oxygen sensor, 55...Liquid level gauge, 55a...Lead wire, 56...Thermometer, 57...Heater, 58...Pressure gauge, 60...Controller, L...Hydraulic oil level, S...Hydraulic oil level inside the bubbling component, T1...Nitrogen supply time after stopping, T2...Time required for the hydraulic oil temperature to drop to a predetermined temperature

Claims

1. A construction machine comprising a vehicle body, a front work implement attached to the vehicle body, a hydraulic actuator for driving the front work implement, a hydraulic oil tank for storing hydraulic oil for driving the hydraulic actuator, a hydraulic pump for drawing in the hydraulic oil tank and discharging it as pressurized oil for driving the hydraulic actuator, and a prime mover for driving the hydraulic pump, wherein the hydraulic oil tank is configured to allow outside air to enter and exit through a breather as the liquid level of the stored hydraulic oil rises and falls, A nitrogen gas generator that separates and produces nitrogen gas from air, The system includes a nitrogen gas supply device that supplies nitrogen gas from the nitrogen gas generator to the hydraulic oil tank, The nitrogen gas supply device is A nitrogen piping connecting the nitrogen gas generator and the hydraulic fluid circuit, A container-shaped bubbling component having multiple pores and positioned inside the hydraulic oil tank, to which the nitrogen piping is connected, and configured to supply the nitrogen gas supplied from the nitrogen piping to the internal space of the hydraulic oil tank through the multiple pores, A solenoid valve installed in the nitrogen piping, A liquid level gauge is provided inside the aforementioned bubbling component, A controller that controls the solenoid valve based on the output of the liquid level gauge and adjusts the liquid level of the hydraulic fluid inside the bubbling component. A construction machine characterized by being equipped with the following features.

2. In the construction machine described in claim 1, The construction machine is characterized in that the bubbling component is provided with a guide that directs the nitrogen gas ejected from the plurality of pores toward a direction away from the outlet of the hydraulic oil tank.

3. In the construction machine described in claim 1, A construction machine characterized in that the lead wires of the liquid level gauge are routed through the nitrogen piping, and the nitrogen piping, the bubbling component, the liquid level gauge, and the lead wires are configured as a single unit.

4. In the construction machine described in claim 1, The construction machine is characterized in that the nitrogen gas supply device includes a heater located inside the bubbling component.

5. A construction machine comprising a vehicle body, a front work implement attached to the vehicle body, a hydraulic actuator for driving the front work implement, a hydraulic oil tank for storing hydraulic oil for driving the hydraulic actuator, a hydraulic pump for drawing in the hydraulic oil tank and discharging it as pressurized oil for driving the hydraulic actuator, and a prime mover for driving the hydraulic pump, wherein the hydraulic oil tank is configured to allow outside air to enter and exit through a breather as the liquid level of the stored hydraulic oil rises and falls, A nitrogen gas generator that separates and produces nitrogen gas from air, The system includes a nitrogen gas supply device that supplies nitrogen gas from the nitrogen gas generator to the hydraulic oil tank, The nitrogen gas supply device is A nitrogen piping connecting the nitrogen gas generator and the hydraulic fluid circuit, The system includes a booster pump for pressurizing the nitrogen gas generated by the nitrogen gas generator, The nitrogen piping connects the return piping, which is connected to the inlet of the hydraulic oil tank, to the booster pump. A construction machine characterized by the following features.

6. In the construction machine described in claim 5, The nitrogen gas supply device is A solenoid valve installed in the nitrogen piping, A pressure gauge for measuring the pressure in the aforementioned nitrogen piping, A controller that controls the solenoid valve based on the output of the pressure gauge to maintain the pressure in the nitrogen piping at or above a set pressure. A construction machine characterized by being equipped with the following features.

7. A construction machine comprising a vehicle body, a front work implement attached to the vehicle body, a hydraulic actuator for driving the front work implement, a hydraulic oil tank for storing hydraulic oil for driving the hydraulic actuator, a hydraulic pump for drawing in the hydraulic oil tank and discharging it as pressurized oil for driving the hydraulic actuator, and a prime mover for driving the hydraulic pump, wherein the hydraulic oil tank is configured to allow outside air to enter and exit through a breather as the liquid level of the stored hydraulic oil rises and falls, A nitrogen gas generator that separates and produces nitrogen gas from air, The system includes a nitrogen gas supply device that supplies nitrogen gas from the nitrogen gas generator to the hydraulic oil tank, The nitrogen gas supply device is A nitrogen piping connecting the nitrogen gas generator and the hydraulic fluid circuit, An oxygen sensor for measuring the dissolved oxygen concentration in the hydraulic fluid, A solenoid valve installed in the nitrogen piping, The system includes a controller that controls the nitrogen gas generator and the solenoid valve based on the output of the oxygen sensor, The aforementioned controller, The nitrogen gas generator is driven and the solenoid valve is opened when the prime mover is started, and the nitrogen gas is continuously supplied to the hydraulic fluid while the prime mover is running. Upon stopping the prime mover, the nitrogen supply time after stopping is calculated based on the output of the oxygen sensor, and the solenoid valve is closed and the nitrogen gas generator is stopped after the nitrogen supply time has elapsed since the prime mover stopped. A construction machine characterized by the following features.

8. A construction machine comprising a vehicle body, a front work implement attached to the vehicle body, a hydraulic actuator for driving the front work implement, a hydraulic oil tank for storing hydraulic oil for driving the hydraulic actuator, a hydraulic pump for drawing in the hydraulic oil tank and discharging it as pressurized oil for driving the hydraulic actuator, and a prime mover for driving the hydraulic pump, wherein the hydraulic oil tank is configured to allow outside air to enter and exit through a breather as the liquid level of the stored hydraulic oil rises and falls, A nitrogen gas generator that separates and produces nitrogen gas from air, The system includes a nitrogen gas supply device that supplies nitrogen gas from the nitrogen gas generator to the hydraulic oil tank, The nitrogen gas supply device is A nitrogen piping connecting the nitrogen gas generator and the hydraulic fluid circuit, A thermometer for measuring the temperature of the hydraulic fluid, A solenoid valve installed in the nitrogen piping, The system includes a controller that controls the nitrogen gas generator and the solenoid valve based on the output of the thermometer, The aforementioned controller, The nitrogen gas generator is driven and the solenoid valve is opened when the prime mover is started, and the nitrogen gas is continuously supplied to the hydraulic fluid while the prime mover is running. Upon stopping the prime mover, the time required for the temperature of the hydraulic fluid to drop to a predetermined temperature is calculated based on the output of the thermometer. After the prime mover stops and the required time has elapsed, the solenoid valve is closed, and the nitrogen gas generator is stopped. A construction machine characterized by the following features.

Images