Construction machinery

Abstract

We aim to extend the replacement interval for biodegradable hydraulic fluid. [Solution] The controller calculates the cumulative flow rate of hydraulic fluid flowing into the acid removal filter as a first reference value when it is predicted that the rate of decrease in the concentration of the hydraulic fluid additive relative to the cumulative flow rate of hydraulic fluid flowing into the acid removal filter will decrease compared to the start of acid removal of the hydraulic fluid by the acid removal filter. When the cumulative flow rate of hydraulic fluid flowing into the acid removal filter is at the first reference value, the amount of additive contained in the hydraulic fluid is calculated as the minimum amount. The amount of additive contained in the hydraulic fluid where the amount of metal corrosion due to the additive is below the permissible value is calculated as the upper limit amount. The difference between the upper limit amount of additive and the minimum amount of additive is calculated as a second reference value. Before the cumulative flow rate of hydraulic fluid flowing into the acid removal filter reaches the first reference value, the controller opens the additive supply line with an on-off valve. When the cumulative flow rate of additive supplied from the additive tank to the hydraulic fluid tank reaches the second reference value, the controller closes the additive supply line with an on-off valve.

Description

Technical Field

[0001] The present invention relates to construction machines such as hydraulic excavators and wheel loaders.

Background Art

[0002] A construction machine includes a hydraulic oil tank for storing hydraulic oil, a hydraulic pump driven by an engine or an electric motor, etc., that pressurizes the hydraulic oil sucked from the hydraulic oil tank, a hydraulic actuator for work or traveling, and a control valve that controls the supply of the hydraulic oil flowing from the hydraulic pump to the hydraulic actuator and the discharge of the hydraulic oil flowing from the hydraulic actuator to the hydraulic oil tank. For example, in a construction machine, the control valve operates according to the operation of an operation lever by an operator, and the hydraulic actuator is driven.

[0003] The hydraulic oil of a construction machine is composed of a base oil and an additive. The base oil is obtained by refining crude oil, and mainly mineral oil is used. The additive improves the quality of the hydraulic oil, such as an antioxidant.

[0004] By the way, Patent Document 1 discloses a hydraulic oil regeneration device that removes acid and moisture contained in the hydraulic oil in order to regenerate the hydraulic oil. This hydraulic oil regeneration device is provided with an oil circulation path and a pump for circulating the hydraulic oil, an acid removal section that removes the acid contained in the hydraulic oil by an ion exchange resin, a moisture removal section that removes the moisture contained in the hydraulic oil by a moisture adsorption means mainly composed of zeolite, and a filtration section that filters the hydraulic oil by a filtration means. Further, Patent Document 1 discloses a hydraulic oil regeneration method that performs a filtration step of filtering the hydraulic oil, an acid removal step of removing the acid by bringing the hydraulic oil into contact with an ion exchange resin, and a moisture removal step of removing the moisture by bringing the hydraulic oil into contact with a moisture adsorption means mainly composed of zeolite.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

[0006] In recent years, hydraulic fluids used in construction machinery have been required to be environmentally friendly, and biodegradable hydraulic fluids that can be broken down by microorganisms in the natural environment even if they leak outside the construction machinery are increasingly being used.

[0007] However, the hydraulic fluid used in construction machinery deteriorates through oxidation due to the heat generated when pressure is applied and released. Biodegradable hydraulic fluid deteriorates more quickly through oxidation compared to conventional hydraulic fluids based on mineral oil. As the hydraulic fluid deteriorates through oxidation, antioxidants and other substances contained in the fluid are consumed, which can cause corrosion or leaching of hydraulic equipment and piping. Therefore, it is necessary to replace the hydraulic fluid stored in the hydraulic fluid tank periodically. This leads to the problem of having to shorten the replacement interval for biodegradable hydraulic fluid. The present invention has been made in view of the above matters, and its purpose is to provide a construction machine that can extend the interval between replacements of biodegradable hydraulic fluid. [Means for solving the problem]

[0008] To achieve the above objective, the present invention provides a construction machine comprising: a hydraulic oil tank for storing hydraulic oil; a hydraulic pump for pressurizing hydraulic oil drawn from the hydraulic oil tank; a hydraulic actuator; and a control valve for controlling the supply of hydraulic oil from the hydraulic pump to the hydraulic actuator and the discharge of hydraulic oil from the hydraulic actuator to the hydraulic oil tank, wherein the hydraulic oil is biodegradable hydraulic oil, and further comprising: an additive tank for storing additives; an additive supply line for supplying additives from the additive tank to the hydraulic oil tank; an on-off valve arranged in the additive supply line for opening and closing the additive supply line; an acid removal filter for removing acid from the hydraulic oil; a hydraulic oil flow meter for measuring the flow rate of hydraulic oil flowing into the acid removal filter; an additive flow meter for measuring the flow rate of additives supplied from the additive tank to the hydraulic oil tank; and a controller that controls the on-off valve based on the measurement results of the hydraulic oil flow meter and the measurement results of the additive flow meter, wherein the controller controls the acid removal filter The method is characterized by calculating the cumulative flow rate of hydraulic fluid flowing into the acid removal filter as a first reference value when it is predicted that the rate of decrease in the concentration of the hydraulic fluid additive relative to the cumulative flow rate of hydraulic fluid flowing into the acid removal filter will decrease compared to the start of the removal of acid from the hydraulic fluid by the method; calculating the minimum amount of additive contained in the hydraulic fluid when the cumulative flow rate of hydraulic fluid flowing into the acid removal filter is at the first reference value; calculating the upper limit amount of additive contained in the hydraulic fluid when the amount of metal corrosion due to the additive is below the permissible value; calculating the difference between the upper limit amount of additive and the minimum amount of additive as a second reference value; opening the additive supply line with an on-off valve before the cumulative flow rate of hydraulic fluid flowing into the acid removal filter reaches the first reference value based on the measurement results from the hydraulic fluid flow meter; and closing the additive supply line with an on-off valve when the cumulative flow rate of additive supplied from the additive tank to the hydraulic fluid tank reaches the second reference value based on the measurement results from the additive flow meter. [Effects of the Invention]

[0009] According to the present invention, it is possible to extend the interval between replacements of biodegradable hydraulic fluid. Further features related to the present invention will become apparent from the description herein and the accompanying drawings. Furthermore, problems, configurations, and effects other than those described above will be revealed by the following description of the embodiments. [Brief explanation of the drawing]

[0010] [Figure 1] A side view showing the structure of a construction machine in one embodiment of the present invention. [Figure 2] A diagram showing the configuration of the drive system of a construction machine in one embodiment of the present invention, along with related equipment. [Figure 3] A flowchart illustrating the controller's processing steps in one embodiment of the present invention. [Figure 4] This figure shows the relationship between the machine operating time, the additive concentration in the hydraulic fluid, and the cumulative flow rate of the hydraulic fluid flowing into the acid removal filter in one embodiment of the present invention. [Figure 5] This diagram shows the relationship between the cumulative flow rate of hydraulic fluid flowing into the acid removal filter and the concentration of additives in the hydraulic fluid. [Figure 6] This figure shows the relationship between the additive concentration, the amount of sliding part wear, and the amount of metal corrosion in Example 1 of the present invention. [Figure 7] A flowchart illustrating the process when the hydraulic fluid or acid removal filter shown in Figure 3 is replaced. [Figure 8] A diagram illustrating the additives used in Examples 1, 2, 3, and 4 of the present invention, and their effects. [Figure 9] A diagram illustrating the additives used in Comparative Example 1, Comparative Example 2, and Comparative Example 3, and their effects. [Figure 10] This figure shows the change in the total acid value of the hydraulic fluid in Example 1 and Comparative Example 3 of the present invention. [Modes for carrying out the invention]

[0011] Embodiments and examples will be described below with reference to the attached drawings. In the attached drawings, functionally identical elements are indicated by the same number. The attached drawings show embodiments and examples in accordance with the principles of this disclosure, but they are for the purpose of understanding this disclosure and are not to be used in any way to restrict the interpretation of this disclosure. The descriptions in this specification are merely typical examples and do not limit the claims or applications of this disclosure in any way.

[0012] Using a hydraulic excavator as an example of the application of the present invention, one embodiment of the present invention will be described with reference to the drawings. Figure 1 is a side view showing the structure of the construction machine 100 in this embodiment. As shown in Figure 1, the construction machine 100 of this embodiment is configured as a hydraulic excavator. The construction machine 100 of this embodiment comprises a drivable traveling body 1, a slewing body 2 rotatably mounted above the traveling body 1, and a work device 3 connected to the front side (left side in Figure 1) of the slewing body 2. The traveling body 1 and the slewing body 2 constitute the vehicle body. The traveling body 1 moves by the rotation of a traveling motor 4, and the slewing body 2 rotates by the rotation of a slewing motor (not shown).

[0013] The working device 3 comprises a boom 5 rotatably connected to the front of the slewing body 2, an arm 6 rotatably connected to the tip of the boom 5, and a bucket 7 rotatably connected to the tip of the arm 6. The boom 5 rotates by the extension and retraction of the boom cylinder 8, the arm 6 rotates by the extension and retraction of the arm cylinder 9, and the bucket 7 rotates by the extension and retraction of the bucket cylinder 10.

[0014] The rotating body 2 comprises a driver's cab 11 in which an operator can board, and a machine room 12 formed in the area other than the driver's cab 11. The driver's cab 11 is equipped with a number of operating devices (not shown) that can be operated by the operator, and a monitor (not shown). The monitor has, for example, a display for displaying messages, and buttons for inputting numerical values, etc.

[0015] The construction machine 100 of this embodiment includes a drive device 40 that drives a plurality of hydraulic actuators 30 according to the operations of a plurality of operating devices. The hydraulic actuators 30 include the traveling motor 4, swing motor, boom cylinder 8, arm cylinder 9, and bucket cylinder 10 described above. FIG. 2 is a diagram showing the configuration of the drive device 40 of the construction machine 100 in this embodiment together with related devices. In FIG. 2, for convenience, only the configuration related to the boom cylinder 8 as the hydraulic actuator 30 is shown among the configurations of the drive device 40.

[0016] As shown in FIG. 2, the drive device 40 of this embodiment includes a hydraulic oil tank 14, a hydraulic pump 16, a control valve 17, and an air-cooled or water-cooled cooler 19. The hydraulic oil tank 14 stores hydraulic oil. The hydraulic pump 16 is driven by the engine 15 and pressurizes the hydraulic oil sucked from the hydraulic oil tank 14. The control valve 17 operates according to the operation of the operating device and controls the supply of hydraulic oil from the hydraulic pump 16 to the hydraulic actuator 30 and the discharge of hydraulic oil from the hydraulic actuator 30 to the hydraulic oil tank 14. The cooler 19 is disposed in the discharge line 18 that discharges hydraulic oil from the control valve 17 to the hydraulic oil tank 14 and cools the hydraulic oil. The devices of the drive device 40 described above are disposed in the machine room 12 of the swing body 2.

[0017] The hydraulic oil tank 14 has an air breather 20, an air filter 21, and an oil filter 22. The air breather 20 takes in outside air into the tank and adjusts the pressure in the tank to the outside air pressure. The air filter 21 is connected to the air breather 20 and removes foreign matters from the outside air. The oil filter 22 is connected to the hydraulic pump 16 and the cooler 19 and removes foreign matters such as sludge from the hydraulic oil. The capacity of the hydraulic oil tank 14 is, for example, 200 L.

[0018] The hydraulic oil stored in the hydraulic oil tank 14 is biodegradable hydraulic oil. The hydraulic oil stored in the hydraulic oil tank 14 is composed of a base oil and an additive. The base oil is ester oil. The viscosity grade of the hydraulic oil is, for example, VG46.

[0019] Additives contained in hydraulic fluid include, for example, antioxidants, extreme pressure additives (load-bearing additives), detergents and dispersants, viscosity index improvers, defoamers, and anti-emulsifiers. Antioxidants include zinc dithiophosphate, organic sulfur compounds, hindered phenols, or aromatic amines. Extreme pressure additives (load-bearing additives) include higher fatty acids, higher alcohols, phosphate esters, phosphite esters, or thiophosphates. Detergents and dispersants include organic acid metal compounds, neutral and overbasic metals, overbasic metal sulfonates, overbasic metal phenates, overbasic metal sulfonates, succinimide, succinic acid esters, or benzylamines.

[0020] Viscosity index improvers include polymethacrylate, olefin copolymer, styrene-olefin copolymer, or polyisobutylene. Antifoaming agents include polymethylsiloxane, silicate, organofluorine compounds, metal soaps, fatty acid esters, phosphate esters, higher alcohols, or polyalkylene glycols. Antiemulsifiers include ethylene oxide adducts, ethylene oxide-propylene oxide block polymers, or quaternary ammonium salts.

[0021] Hydraulic fluid undergoes oxidative degradation due to the heat generated when pressure is applied and released. More specifically, the base oil that makes up hydraulic fluid is mainly composed of hydrocarbons. The thermal decomposition of hydrocarbons generates hydrocarbon radicals, which combine with oxygen to form peroxy radicals. Subsequently, the peroxy radicals combine with undecomposed base oil or hydroxyl radicals, etc., and are converted to alcohols or aldehydes, and finally to carboxylic acids. When the amount of carboxylic acid increases and the total acid number of the hydraulic fluid rises, it can cause corrosion or leaching of hydraulic equipment and piping. Therefore, it is necessary to periodically replace the hydraulic fluid stored in the hydraulic fluid tank 14. This leads to the problem of shortening the replacement interval for biodegradable hydraulic fluid.

[0022] Furthermore, if the acid removal filter 27 is used to remove the acid contained in the hydraulic fluid and extend the replacement interval, the wear suppression effect of the hydraulic fluid may decrease, potentially causing wear on the sliding parts of hydraulic equipment.

[0023] To explain in more detail, filters used to remove acids from hydraulic fluid may also remove extreme pressure additives, which are a type of additive added to the hydraulic fluid. Extreme pressure additives can suppress wear by reacting with metal surfaces and forming a film, but if they are removed by the filter and their concentration decreases, the wear-suppressing effect may decrease. Therefore, it is necessary to add extreme pressure additives in conjunction with the use of the acid removal filter 27 that removes acids from the hydraulic fluid.

[0024] The drive unit 40 of the construction machine 100 in this embodiment includes an additive tank 23, an additive supply line 24, an on-off valve 25, an additive flow meter 26, an acid removal filter 27, a hydraulic fluid flow meter 29, a flow control valve 13, and a controller 28, as a configuration to extend the hydraulic fluid replacement interval. The additive tank 23 is located near the hydraulic fluid tank 14 and stores the additive. The additive supply line 24 supplies the additive from the additive tank 23 to the hydraulic fluid tank 14. The on-off valve 25 is located on the additive supply line 24 and opens and closes the additive supply line 24.

[0025] The additive flow meter 26 is located in the additive supply line 24 and measures and displays the flow rate of the additive from the additive tank 23 to the hydraulic oil tank 14. The acid removal filter 27 is located downstream of the cooler 19 in the discharge line 18 described above and removes acid from the hydraulic oil. The hydraulic oil flow meter 29 measures the flow rate of the hydraulic oil flowing into the acid removal filter 27. The flow control valve 13 controls the flow rate of the hydraulic oil flowing into the acid removal filter 27. The controller 28 controls the on / off valve 25 based on the measurement results of the hydraulic oil flow meter 29 and the measurement results of the additive flow meter 26.

[0026] As the acid removal filter 27 for removing acids from the hydraulic fluid, for example, an ion exchange resin, which is a synthetic resin having ion exchange groups, or activated carbon obtained by carbonizing carbon materials such as coconut shells, coal, wood, and sawdust and then treating them chemically or physically, can be used. Alternatively, as the acid removal filter 27, layered clay minerals such as montmorillonite and activated clay obtained by heat-treating layered clay minerals with sulfuric acid or hydrochloric acid can be used. In particular, it is preferable that the acid removal filter 27 consists of either an ion exchange resin or a layered clay mineral.

[0027] The additive tank 23 stores the additive. This additive includes an extreme pressure agent. Examples of extreme pressure agents include phosphate esters, phosphite esters, or thiophosphate salts. In particular, it is preferable that the extreme pressure agent includes either tricresyl phosphate or dioleyl hydrogen phosphite. The extreme pressure agent can be stored as a 100% concentrate or dissolved in the base oil. The material of the additive tank 23 can be resin or a metal container with the inner surface lined with resin. The capacity of the additive tank 23 is, for example, 5 L.

[0028] The controller 28 is a computer having a processor such as a CPU (Central Processing Unit) that executes processing according to a program, and memory for storing programs and data. The memory includes main memory and auxiliary memory. The main memory is used as the CPU's workspace and a storage area for computer programs and data. The main memory is formed by a combination of RAM (Random Access Memory) and ROM (Read Only Memory), for example. Computer programs such as the operating system and firmware are installed in the memory. The auxiliary memory is, for example, an SSD (Solid State Drive) and an HDD (Hard Disk Drive). The CPU may be composed of integrated circuits (ICs) and other digital circuits, or a part of it may be composed of analog circuits.

[0029] The controller 28 controls the on-off valve 25 based on the measurement results of the hydraulic fluid flow meter 29 and the additive flow meter 26. The processing details of the controller 28 will be explained using Figure 3. Figure 3 is a flowchart showing the processing details of the controller 28 in this embodiment.

[0030] As shown in Figure 3, in step S1, the controller 28 determines whether the drive unit 40 of the construction machine 100 is using the acid removal filter 27. If the drive unit 40 of the construction machine 100 is not using the acid removal filter 27, the controller 28 terminates the process. In step S2, the controller 28 receives input for the initial amount of hydraulic fluid, the initial additive concentration of the hydraulic fluid, and the upper limit concentration of the additive. These values ​​may be received, for example, by a monitor in the operator's cab 11. Alternatively, these values ​​may be pre-recorded in the controller 28's memory.

[0031] In step S3, the controller 28 determines whether the hydraulic fluid or the acid removal filter 27 has been replaced. If the hydraulic fluid or the acid removal filter 27 has not been replaced, the controller 28 proceeds to step S3. The case where the hydraulic fluid or the acid removal filter 27 has been replaced will be described later. In step S4, the controller 28 calculates the first reference value, the second reference value, the third reference value, the fourth reference value, the minimum amount of additive, and the maximum amount of additive.

[0032] The first reference value will now be explained. Figure 4 is a diagram showing the relationship between the machine operating time, the additive concentration in the hydraulic fluid, and the cumulative flow rate of the hydraulic fluid flowing into the acid removal filter 27 in one embodiment. Figure 5 is a diagram showing the relationship between the cumulative flow rate of the hydraulic fluid flowing into the acid removal filter 27 and the additive concentration in the hydraulic fluid. As shown in Figures 4 and 5, the acid removal filter 27 removes the extreme pressure additive contained in the hydraulic fluid. However, the amount of extreme pressure additive removed by the acid removal filter 27 is not proportional to the cumulative flow rate to the acid removal filter 27. As shown in Figures 4 and 5, until 20% (removal rate) of the additive contained in the hydraulic fluid is removed, the cumulative flow rate of the hydraulic fluid flowing into the acid removal filter 27 and the additive concentration in the hydraulic fluid are in a proportional relationship. However, after 20% of the additive contained in the hydraulic fluid has been removed, the additive concentration in the hydraulic fluid becomes almost constant.

[0033] In this embodiment, the first reference value is the cumulative flow rate of hydraulic fluid flowing into the acid removal filter 27 when it is predicted that the rate of decrease in the concentration of additives in the hydraulic fluid relative to the cumulative flow rate of hydraulic fluid flowing into the acid removal filter 27 will decrease compared to the start of acid removal of the hydraulic fluid by the acid removal filter 27. In the example of Figures 4 and 5, this is the cumulative flow rate of hydraulic fluid flowing into the acid removal filter 27 when it is predicted that 20% (removal rate) of the additives contained in the hydraulic fluid will be removed. The controller 28 calculates the first reference value as described above. For example, the controller 28 can pre-record graphs as shown in Figures 4 and 5 in memory for each hydraulic fluid and additive used, and calculate the first reference value from these graphs.

[0034] In this embodiment, the first reference value determines the timing of supplying the additive to the hydraulic fluid. That is, as described above, when the cumulative flow rate of the hydraulic fluid flowing into the acid removal filter 27 exceeds the first reference value, the additive concentration in the hydraulic fluid hardly changes. Therefore, before the cumulative flow rate of the hydraulic fluid flowing into the acid removal filter 27 exceeds the first reference value, the additive is supplied from the additive tank 23 to the hydraulic fluid tank 14 to avoid a prolonged state of low additive concentration.

[0035] The minimum amount, maximum amount, and second standard value of the additive will be explained. As shown in Figure 6, if the concentration of the extreme pressure additive in the hydraulic fluid is too low, wear resistance will decrease and wear may progress in sliding parts, etc. Conversely, if the concentration is too high, corrosiveness will increase, which can adversely affect metal parts, etc. Therefore, there is an appropriate concentration range for the extreme pressure additive in the hydraulic fluid. In the example in Figure 6, it is preferable that the concentration of the extreme pressure additive in the hydraulic fluid be between 0.5 wt% and 1.0 wt%. If the concentration of the extreme pressure additive in the hydraulic fluid is lower than 0.5 wt%, the amount of wear on sliding parts will increase. On the other hand, if the concentration of the extreme pressure additive in the hydraulic fluid is higher than 1.0 wt%, the amount of wear on sliding parts will decrease, but the amount of metal corrosion will increase.

[0036] As shown in Figure 3, in step S4, the controller 28 calculates the minimum amount of additive contained in the hydraulic fluid when the cumulative flow rate of the hydraulic fluid flowing into the acid removal filter 27 is at a first reference value. The minimum amount of additive is calculated, for example, by multiplying the additive concentration of the hydraulic fluid when it is predicted that the rate of decrease in the concentration of the additive in the hydraulic fluid relative to the cumulative flow rate of the hydraulic fluid flowing into the acid removal filter 27 (Figure 5) will decrease by the initial oil amount input in step S2. As shown in Figure 3, in step S4, the controller 28 calculates the upper limit amount of additive contained in the hydraulic fluid when the amount of metal corrosion due to the additive is below the allowable value. The upper limit amount of additive is calculated, for example, by multiplying the upper limit concentration of 1.0 wt% (Figure 6) by the initial oil amount input in step S2.

[0037] As shown in Figure 3, in step S4, the controller 28 calculates the difference between the upper limit amount of additive and the lower limit amount of additive as the second reference value. In this embodiment, the second reference value represents the amount of additive supplied to the hydraulic fluid. In other words, the acid removal filter 27 reduces the amount of additive in the hydraulic fluid to the lower limit. Furthermore, if the amount of additive is below the upper limit, the amount of metal corrosion caused by the additive is below the permissible value. Therefore, in this embodiment, the amount by which the additive decreases from the initial amount to the lower limit is compensated for, and then the amount from the initial amount to the upper limit is compensated for. This makes it possible to maintain the concentration of the extreme pressure additive within an appropriate range. The second reference value is calculated by equation (6), obtained by substituting equations (2) to (5) into equation (1) below.

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[0038] In this embodiment, as described below, the controller 28 opens the additive supply line 24 with the on-off valve 25 before the cumulative flow rate of the hydraulic fluid flowing into the acid removal filter 27 reaches a first reference value, based on the measurement results from the hydraulic fluid flow meter 29. The controller 28 closes the additive supply line 24 with the on-off valve 25 when the cumulative flow rate of the additive from the additive tank 23 to the hydraulic fluid tank 14 reaches a second reference value, based on the measurement results from the additive flow meter 26.

[0039] The third reference value will now be explained. As shown in Figure 3, in step S4, the controller 28 calculates a third reference value that is smaller than the first reference value. As described above, before the cumulative flow rate of the hydraulic oil flowing into the acid removal filter 27 exceeds the first reference value, the additive is supplied from the additive tank 23 to the hydraulic oil tank 14 to avoid a prolonged state of low additive concentration. Therefore, the controller 28 calculates a third reference value that is smaller than the first reference value. The third reference value can be any value such as 1 / 2, 1 / 3, 2 / 3, 1 / 4, 3 / 4, 1 / 5, 2 / 5, 3 / 5, and 4 / 5 of the first reference value.

[0040] The fourth reference value will now be explained. As shown in Figure 3, in step S4, the controller 28 calculates a fourth reference value that is smaller than the second reference value. As described above, the second reference value is the amount of additive supplied to the hydraulic fluid, but by dividing the amount into the fourth reference value, which is smaller than the second reference value, and supplying the additive to the hydraulic fluid in this way, it is possible to avoid sudden fluctuations in the concentration of the additive in the hydraulic fluid and keep the hydraulic fluid in a stable state. The fourth reference value can be, for example, the value obtained by dividing the second reference value by an integer.

[0041] As shown in Figure 3, in step S5, the controller 28 determines whether the cumulative flow rate of the hydraulic fluid flowing into the acid removal filter 27 is equal to or greater than the third reference value. The controller 28 repeats the process in step S5 until the cumulative flow rate of the hydraulic fluid flowing into the acid removal filter 27 reaches the third reference value.

[0042] When the cumulative flow rate of the hydraulic fluid flowing into the acid removal filter 27 reaches the third reference value, in step S6, the controller 28 determines, based on the measurement results from the additive flow meter 26, whether the cumulative flow rate of the additive from the additive tank 23 to the hydraulic fluid tank 14 is equal to or greater than the second reference value. If the cumulative flow rate of the additive from the additive tank 23 to the hydraulic fluid tank 14 is equal to or greater than the second reference value, the controller 28 repeats steps S1 to S6. In this case, the controller 28 maintains the closure of the additive supply line 24 using the on-off valve 25.

[0043] If the cumulative flow rate of the additive from the additive tank 23 to the hydraulic oil tank 14 is not equal to or greater than the second reference value, in step S7, the controller 28 opens the on-off valve 25. In other words, the controller 28 opens the additive supply line 24 with the on-off valve 25 when the cumulative flow rate of the hydraulic oil flowing into the acid removal filter 27, based on the measurement results from the hydraulic oil flow meter 29, reaches the third reference value. In step S8, the controller 28 determines whether the cumulative flow rate since the opening of the on-off valve 25 is equal to or greater than the fourth reference value.

[0044] If the cumulative flow rate from the opening of the on-off valve 25 is not equal to or greater than the fourth reference value, the controller 28 proceeds to step S6. In step S6, the controller 28 determines, based on the measurement results from the additive flow meter 26, whether the cumulative flow rate of the additive from the additive tank 23 to the hydraulic oil tank 14 is equal to or greater than the second reference value. If the cumulative flow rate of the additive from the additive tank 23 to the hydraulic oil tank 14 is equal to or greater than the second reference value, the controller 28 repeats steps S1 to S6 and maintains the closure of the additive supply line 24 by the on-off valve 25.

[0045] In other words, based on the measurement results from the additive flow meter 26, when the cumulative flow rate of the additive from the additive tank 23 to the hydraulic oil tank 14 reaches the second reference value, the controller 28 closes the additive supply line 24 with the on / off valve 25.

[0046] If the cumulative flow rate of the additive from the additive tank 23 to the hydraulic oil tank 14 is not equal to or greater than the second reference value, in step S7, the controller 28 opens the on-off valve 25. In step S8, if the cumulative flow rate since the opening of the on-off valve 25 is equal to or greater than the fourth reference value, in step S9, the controller 28 closes the on-off valve 25. In step S10, the controller 28 sets (updates) the cumulative flow rate of the additive from the additive tank 23 to the hydraulic oil tank 14, based on the measurement results from the additive flow meter 26, to a value increased by the fourth reference value. The controller 28 repeats steps S1 to S10.

[0047] In other words, the controller 28 controls the opening and closing of the additive supply line 24 by the on-off valve 25 based on the measurement results from the additive flow meter 26, so that the cumulative flow rate of the additive from the additive tank 23 to the hydraulic oil tank 14 from the opening to the closing of the additive supply line 24 becomes the fourth reference value. When the cumulative flow rate of the additive from the additive tank 23 to the hydraulic oil tank 14 becomes the second reference value, the controller 28 closes the additive supply line 24 by the on-off valve 25.

[0048] Furthermore, the controller 28 may notify the operator via the monitor in the operator's cab 11 when the cumulative flow rate of the hydraulic fluid flowing into the acid removal filter 27 reaches the third reference value, when the cumulative flow rate of the additive since the opening of the on-off valve 25 reaches the fourth reference value, and when the cumulative flow rate of the additive reaches the second reference value, prompting the operator to take the necessary actions.

[0049] The following describes the process when the hydraulic fluid or the acid removal filter 27 is replaced. Figure 7 is a flowchart showing the process when the hydraulic fluid or the acid removal filter 27 in Figure 3 is replaced. In this embodiment, the process performed differs depending on whether the hydraulic fluid or the acid removal filter 27 is replaced. As shown in Figure 7, in step S101, the controller 28 determines whether the hydraulic fluid or the acid removal filter 27 has been replaced. This determination can be made, for example, by referring to the input received from the monitor in the driver's cab 11 indicating whether the hydraulic fluid or the acid removal filter 27 has been replaced.

[0050] If both the hydraulic fluid and the acid removal filter 27 have been replaced in step S101, the controller 28 resets the cumulative flow rate of hydraulic fluid flowing into the acid removal filter 27 to 0 in step S102, based on the measurement results from the hydraulic fluid flow meter 29. In step S103, the controller 28 resets the cumulative flow rate of additive from the additive tank 23 to the hydraulic fluid tank 14 to 0, based on the measurement results from the additive flow meter 26. In other words, because both the hydraulic fluid and the acid removal filter 27 have been replaced, the controller 28 resets the cumulative flow rate of hydraulic fluid flowing into the acid removal filter 27, which serves as the reference for the timing of supplying additives to the hydraulic fluid, to 0 and initializes itself. Also, because both the hydraulic fluid and the acid removal filter 27 have been replaced, the controller 28 resets the cumulative flow rate of additive to the hydraulic fluid tank 14, which serves as the reference for the amount of additive supplied to the hydraulic fluid, to 0 and initializes itself.

[0051] Subsequently, as shown in Figure 3, in step S5, the controller 28, based on the measurement results from the hydraulic fluid flow meter 29, opens the additive supply line 24 with the on-off valve 25 in step S7 when the cumulative flow rate of hydraulic fluid flowing into the acid removal filter 27, which has been reset to 0, reaches the third reference value. In step S6, the controller 28, based on the measurement results from the additive flow meter 26, closes the additive supply line 24 with the on-off valve 25 when the cumulative flow rate of additive from the additive tank 23, which has been reset to 0, to the hydraulic fluid tank 14 reaches the second reference value.

[0052] As shown in Figure 7, if the hydraulic fluid is replaced in step S101 but the acid removal filter 27 is not replaced, the controller 28 calculates the amount of additives removed by the acid removal filter 27 up to the time the hydraulic fluid is replaced, based on the cumulative flow rate of hydraulic fluid flowing into the acid removal filter 27 up to the time the hydraulic fluid is replaced, as determined from the measurement results by the hydraulic fluid flow meter 29, as the amount of additives removed. The amount of additives removed is calculated, for example, by calculating the difference between the value obtained by multiplying the initial additive concentration by the initial oil volume and the value obtained by multiplying the concentration of the additive in the hydraulic fluid by the initial oil volume relative to the cumulative flow rate of hydraulic fluid flowing into the acid removal filter 27 in Figure 5.

[0053] In step S105, the controller 28 calculates a new second reference value, which is the difference between the upper limit and the lower limit of the amount of additive, and the difference between the amount of additive that has been removed. In step S105, the controller 28 calculates a new third reference value that is smaller than the difference between the first reference value and the cumulative flow rate of hydraulic fluid flowing into the acid removal filter 27 up to the time the hydraulic fluid is replaced. However, if the hydraulic fluid is replaced late and the cumulative flow rate of hydraulic fluid flowing into the acid removal filter 27 up to the time the hydraulic fluid is replaced is greater than the first reference value, the difference between the first reference value and the cumulative flow rate of hydraulic fluid flowing into the acid removal filter 27 up to the time the hydraulic fluid is replaced will be a negative value. In this case, the controller 28 calculates a third reference value of that negative value.

[0054] In step S105, the controller 28 calculates a new fourth reference value that is smaller than the new second reference value. In step S106, the controller 28 resets the cumulative flow rate of hydraulic fluid flowing into the acid removal filter 27 to 0 based on the measurement results from the hydraulic fluid flow meter 29. In step S107, the controller 28 resets the cumulative flow rate of additive from the additive tank 23 to the hydraulic fluid tank 14 to 0 based on the measurement results from the additive flow meter 26.

[0055] In other words, when the hydraulic fluid is replaced but the acid removal filter 27 is not replaced, the amount of additive already removed from the hydraulic fluid before replacement by the acid removal filter 27 will not be removed from the replaced hydraulic fluid. Therefore, if this amount of removed additive is not subtracted from the second reference value before the hydraulic fluid was replaced, an excessive amount of additive will be supplied to the newly replaced hydraulic fluid. To address this, the controller 28 calculates a new second reference value by subtracting the amount of removed additive from the difference between the upper limit and the lower limit of the amount of additive.

[0056] Furthermore, the controller 28 recalculates the fourth reference value to match the second reference value. Also, because the hydraulic fluid has been replaced, the controller 28 recalculates the third reference value, which serves as the reference for the timing of supplying additives to the hydraulic fluid. Because the hydraulic fluid has been replaced, the controller 28 resets the cumulative flow rate of hydraulic fluid flowing into the acid removal filter 27, which serves as the reference for the timing of supplying additives to the hydraulic fluid, to 0. Because the hydraulic fluid has been replaced, the controller 28 resets the cumulative flow rate of additives from the additive tank 23 to the hydraulic fluid tank 14, which serves as the reference for the amount of additives supplied to the hydraulic fluid, to 0.

[0057] Subsequently, as shown in Figure 3, in step S5, the controller 28, based on the measurement results from the hydraulic fluid flow meter 29, opens the additive supply line 24 with the on-off valve 25 in step S7 when the cumulative flow rate of hydraulic fluid flowing into the acid removal filter 27, which has been reset to 0, reaches a new third reference value. If the new third reference value is a negative value, the controller 28 immediately opens the additive supply line 24 with the on-off valve 25 in step S7.

[0058] In steps S7, S8, S9, and S10, the controller 28 controls the opening and closing of the on-off valve 25 based on the measurement results from the additive flow meter 26, so that the cumulative flow rate of the additive from the additive tank 23 to the hydraulic oil tank 14 from the opening to the closing of the additive supply line 24 becomes a new fourth reference value.

[0059] In step S6, the controller 28, based on the measurement results from the additive flow meter 26, closes the additive supply line 24 with the on-off valve 25 when the cumulative flow rate of the additive from the additive tank 23, which has been reset to 0, to the hydraulic oil tank 14 reaches a new second reference value.

[0060] As shown in Figure 7, if the acid removal filter 27 is replaced in step S101 but the hydraulic oil is not replaced, the controller 28 calculates the amount of additive removed by the acid removal filter 27 up to the time the hydraulic oil is replaced, based on the cumulative flow rate of hydraulic oil flowing into the acid removal filter 27 up to the time the acid removal filter 27 is replaced, as the amount removed, in step S108. In step S109, the controller 28 calculates the cumulative flow rate of additive from the additive tank 23 to the hydraulic oil tank 14 up to the time the acid removal filter 27 is replaced, as the amount supplied, based on the measurement results of the additive flow meter 26.

[0061] In step S110, the controller 28 calculates a new second reference value as the sum of the difference between the upper limit and the lower limit of the amount of additive, and the difference between the amount of additive removed and the amount of additive supplied. In step S110, the controller 28 calculates a new fourth reference value that is smaller than the new second reference value. In other words, when the acid removal filter 27 is replaced but the hydraulic fluid is not replaced, the replaced acid removal filter 27 removes an even larger amount of additive from the hydraulic fluid in addition to the amount of additive already removed by the acid removal filter 27 before replacement. Therefore, if the second and fourth reference values ​​are not newly calculated based on the amount of additive removed and the amount of additive supplied, there will be a shortage of additive supplied to the hydraulic fluid.

[0062] Therefore, the controller 28 calculates a new second reference value as the sum of the difference between the upper limit and the lower limit of the amount of additive, and the difference between the amount of additive removed and the amount of additive supplied. The controller 28 also newly calculates a fourth reference value in accordance with the second reference value. On the other hand, since the hydraulic oil has not been changed, the controller 28 does not reset the cumulative flow rate of hydraulic oil flowing into the acid removal filter 27, which is the reference for the timing of supplying additives to the hydraulic oil, to zero. Also, since the hydraulic oil has not been changed, the controller 28 does not reset the cumulative flow rate of additives to the hydraulic oil tank 14, which is the reference for the amount of additives supplied to the hydraulic oil, to zero.

[0063] Subsequently, as shown in Figure 3, in step S5, the controller 28, based on the measurement results from the hydraulic fluid flow meter 29, opens the additive supply line 24 with the on-off valve 25 in step S7 when the cumulative flow rate of hydraulic fluid flowing into the acid removal filter 27 reaches the third reference value. In step S5, if the cumulative flow rate of hydraulic fluid flowing into the acid removal filter 27 is already equal to or greater than the third reference value based on the measurement results from the hydraulic fluid flow meter 29, the controller 28 immediately opens the additive supply line 24 with the on-off valve 25.

[0064] In steps S7, S8, S9, and S10, the controller 28 controls the opening and closing of the on-off valve 25 based on the measurement results from the additive flow meter 26, so that the cumulative flow rate of the additive from the additive tank 23 to the hydraulic oil tank 14 from the opening to the closing of the additive supply line 24 becomes a new fourth reference value.

[0065] In step S6, the controller 28 closes the additive supply line 24 with the on-off valve 25 when the cumulative flow rate of the additive from the additive tank 23 to the hydraulic oil tank 14 reaches a new second reference value, based on the measurement results from the additive flow meter 26.

[0066] As described above, in this embodiment, by supplying additives from the additive tank 23 to the hydraulic oil tank 14 via the additive supply line 24, a decrease in the concentration of extreme pressure additives in the hydraulic oil can be suppressed, and a decrease in wear resistance can be suppressed even when using the acid removal filter 27 in the hydraulic oil. Therefore, it is possible to extend the hydraulic oil replacement interval while maintaining the wear resistance of the hydraulic oil.

[0067] Furthermore, in this embodiment, if the rate of change in the oxidation degree of the hydraulic fluid exceeds a predetermined value, the timing of additive supply is notified or controlled. Also, if the rate of change in the oxidation degree of the hydraulic fluid is below a predetermined value, the timing of additive supply is notified or controlled when the machine operating time reaches a predetermined value. As a result, deterioration of the hydraulic fluid can be suppressed, and the interval between additive replenishment can be extended.

[0068] Examples of the additives stored in the additive tank 23 and their effects will be described below with reference to Figures 8, 9, and 10.

[0069] As shown in Figure 8, the material of the acid removal filter 27 in Example 1 is an ion exchange resin, and the extreme pressure agent is tricresyl phosphate (0.5 wt%). The extreme pressure agent is supplied as appropriate up to the upper limit concentration (1.0 wt%).

[0070] As shown in Figure 8, the material of the acid removal filter 27 in Example 2 is layered clay mineral, and the extreme pressure agent is tricresyl phosphate (0.5 wt%). The extreme pressure agent is supplied as appropriate up to the upper limit concentration (1.0 wt%).

[0071] As shown in Figure 8, the material of the acid removal filter 27 in Example 3 is an ion exchange resin, and the extreme pressure agent is dioryl hydrogen phosphite (0.5 wt%). The extreme pressure agent is supplied as appropriate up to the upper limit concentration (1.0 wt%).

[0072] As shown in Figure 8, the material of the acid removal filter 27 in Example 4 is layered clay mineral, and the extreme pressure agent is dioryl hydrogen phosphite (0.5 wt%). The extreme pressure agent is supplied as appropriate up to the upper limit concentration (1.0 wt%).

[0073] On the other hand, as shown in Figure 9, the material of the acid removal filter 27 in Comparative Example 1 is ion exchange resin, and the extreme pressure agent is tricresyl phosphate (0.5 wt%). No extreme pressure agent is supplied.

[0074] As shown in Figure 9, the material of the acid removal filter 27 in Comparative Example 2 is layered clay mineral, and the extreme pressure agent is dioryl hydrogen phosphite (0.5 wt%). No extreme pressure agent is supplied.

[0075] As shown in Figure 9, in Comparative Example 3, the acid removal filter 27 is not applied, and the extreme pressure agent is tricresyl phosphate (0.5 wt%). The extreme pressure agent is not supplied.

[0076] As shown in Figure 10, in Comparative Example 3 (in other words, when the acid removal filter 27 in the hydraulic fluid is not used), the total acid value of the hydraulic fluid increases significantly as the machine operating time increases. On the other hand, in Example 1, the increase in the total acid value of the hydraulic fluid can be suppressed even when the machine operating time is extended. Therefore, as shown in Figure 8, the hydraulic fluid replacement interval can be extended to 4.3 to 5.1 times that of Comparative Example 3. Furthermore, by adding an extreme pressure additive whose concentration is reduced by the use of the acid removal filter 27 that captures acid, the amount of wear on the sliding parts can be kept low. In addition, by keeping the amount of extreme pressure additive below the upper limit concentration, the amount of metal corrosion can also be kept low.

[0077] On the other hand, as shown in Figure 9, in Comparative Examples 1 and 2, where the acid removal filter 27 was applied, the increase in the total acid value of the hydraulic fluid was suppressed. However, in Comparative Examples 1 and 2, since no extreme pressure additive whose concentration is reduced by the use of the acid removal filter 27 was added, the amount of wear on the sliding parts was increased. As a result, the hydraulic fluid replacement interval in Comparative Examples 1 and 2 was shorter than that in Examples 1 to 4.

[0078] As shown in Figure 6, the concentration of the extreme pressure additive added to the hydraulic fluid is preferably between 0.5 and 1.0 wt%. If it is lower than 0.5 wt%, the amount of wear on the sliding parts increases, and if it is higher than 1.0 wt%, the amount of wear on the sliding parts decreases, but the amount of metal corrosion increases.

[0079] Furthermore, in the above embodiment, the controller 28 was described as notifying by displaying a message on the monitor indicating that the on-off valve 25 should be opened, but it is not limited to this. The controller 28 may, for example, notify by outputting an audio message through a speaker indicating that the on-off valve 25 should be opened.

[0080] Furthermore, in the above embodiment, the controller 28 was described as executing both a control to notify that the on-off valve 25 should be opened and a control to open the on-off valve 25, but it is not limited to this. The controller 28 may execute only one of the two controls: a control to notify that the on-off valve 25 should be opened and a control to open the on-off valve 25.

[0081] In the above description, the present invention has been explained using the application of a hydraulic excavator as an example, but it is not limited to this. That is, the present invention may also be applied to other construction machinery 100, such as a wheel loader.

[0082] In the above embodiment, the controller 28 calculates the cumulative flow rate of hydraulic fluid flowing into the acid removal filter 27 as a first reference value when it is predicted that the rate of decrease in the concentration of the hydraulic fluid additive relative to the cumulative flow rate of hydraulic fluid flowing into the acid removal filter 27 will decrease compared to the start of acid removal of the hydraulic fluid by the acid removal filter 27. The controller 28 calculates the minimum amount of additive contained in the hydraulic fluid when the cumulative flow rate of hydraulic fluid flowing into the acid removal filter 27 is at the first reference value. The controller 28 calculates the upper limit amount of additive contained in the hydraulic fluid when the amount of metal corrosion due to the additive is below the permissible value. The controller 28 calculates the difference between the upper limit amount of additive and the minimum amount of additive as a second reference value.

[0083] Based on the measurement results from the hydraulic fluid flow meter 29, the controller 28 opens the additive supply line 24 using the on-off valve 25 before the cumulative flow rate of hydraulic fluid flowing into the acid removal filter 27 reaches a first reference value. This allows the additive to be supplied to the hydraulic fluid before the concentration of the additive decreases due to the acid removal filter 27. Furthermore, based on the measurement results from the additive flow meter 26, the controller 28 closes the additive supply line 24 using the on-off valve 25 when the cumulative flow rate of the additive from the additive tank 23 to the hydraulic fluid tank 14 reaches a second reference value. This prevents excessive supply of additive to the hydraulic fluid, which would lead to increased metal corrosion.

[0084] Furthermore, in the above embodiment, the controller 28 calculates a third reference value smaller than the first reference value, and a fourth reference value smaller than the second reference value. Based on the measurement results from the hydraulic fluid flow meter 29, the controller 28 opens the additive supply line 24 with the on-off valve 25 when the cumulative flow rate of hydraulic fluid flowing into the acid removal filter 27 reaches the third reference value. Based on the measurement results from the additive flow meter 26, the controller 28 controls the opening and closing of the on-off valve 25 so that the cumulative flow rate of additive from the additive tank 23 to the hydraulic fluid tank 14 from the opening to the closing of the additive supply line 24 by the on-off valve 25 reaches the fourth reference value. As a result, the acid removal filter 27 supplies the additive to the hydraulic fluid in small increments before the additive concentration decreases, and the concentration of the additive in the hydraulic fluid can be appropriately maintained.

[0085] Furthermore, in the above embodiment, the controller 28 closes the additive supply line 24 with the on-off valve 25 when the cumulative flow rate of the additive from the additive tank 23 to the hydraulic oil tank 14 reaches a second reference value, based on the measurement results from the additive flow meter 26. This prevents excessive supply of additives to the hydraulic oil, which would lead to increased metal corrosion.

[0086] Furthermore, in the above embodiment, when the hydraulic fluid and acid removal filter 27 are replaced, the controller 28 resets the cumulative flow rate of hydraulic fluid flowing into the acid removal filter 27 to 0 based on the measurement results from the hydraulic fluid flow meter 29, and resets the cumulative flow rate of additives to the hydraulic fluid tank 14 to 0 based on the measurement results from the additive flow meter 26. The controller 28 performs the above control based on the cumulative flow rate of hydraulic fluid flowing into the acid removal filter 27, which has been reset to 0, and the cumulative flow rate of additives to the hydraulic fluid tank 14, which has been reset to 0. Therefore, even when the hydraulic fluid and acid removal filter 27 are replaced, an appropriate amount of additives can be supplied to the hydraulic fluid.

[0087] Furthermore, in the above embodiment, when the hydraulic fluid has been replaced but the acid removal filter 27 has not been replaced, the controller 28 calculates new second, third, and fourth reference values. The controller 28 resets the cumulative flow rate of hydraulic fluid flowing into the acid removal filter 27 to 0 based on the measurement results from the hydraulic fluid flow meter 29, and resets the cumulative flow rate of additives to the hydraulic fluid tank 14 to 0 based on the measurement results from the additive flow meter 26. The controller 28 performs the above control based on the new second reference value, new third reference value, new fourth reference value, the cumulative flow rate of hydraulic fluid flowing into the acid removal filter 27 which has been reset to 0, and the cumulative flow rate of additives to the hydraulic fluid tank 14 which has been reset to 0. Therefore, even when the hydraulic fluid has been replaced but the acid removal filter 27 has not been replaced, an appropriate amount of additives can be supplied to the hydraulic fluid.

[0088] Furthermore, in the above embodiment, the controller 28 calculates new second and fourth reference values ​​when the acid removal filter 27 has been replaced but the hydraulic fluid has not been replaced. The controller 28 then performs the above control based on the new second and fourth reference values. Therefore, even when the acid removal filter 27 has been replaced but the hydraulic fluid has not been replaced, an appropriate amount of additive can be supplied to the hydraulic fluid.

[0089] Furthermore, in the above embodiment, the additive includes an extreme pressure agent. Therefore, it is possible to prevent both an increase in wear of the sliding parts due to a decrease in the concentration of the extreme pressure agent by the acid removal filter 27 and an increase in metal corrosion due to an excessive supply of the extreme pressure agent.

[0090] Furthermore, in the above embodiment, the extreme pressure agent includes either tricresyl phosphate or dioleyl hydrogen phosphate. Thus, the above embodiment can also be applied to typical extreme pressure agents.

[0091] Furthermore, in the above embodiment, the acid removal filter 27 is made of either an ion exchange resin or a layered clay mineral. Thus, the above embodiment can also be applied to a typical acid removal filter 27.

[0092] Although several embodiments of the present invention have been described above, the invention is not limited to the embodiments described above and can be realized in various configurations without departing from the spirit of the invention. For example, configurations in which the components of the embodiments are arbitrarily changed or omitted can easily be conceivable. These variations are included within the scope of the invention and its equivalents as described in the claims. [Explanation of Symbols]

[0093] 1. Running body 2. Rotating body 3. Working equipment 4. Driving motor 5 Boom 6 Arms 7 buckets 8 Boom Cylinder 9 Arm Cylinder 10 Bucket Cylinders 11 Driver's cab 12 Machine room 13 Flow control valve 14. Hydraulic oil tank 15 Engine 16 Hydraulic pump 17 Control valve 18 Discharge Line 19 Cooler 20 Air Breather 21 Air filter 22 Oil filter 23 Coating Tank 24 Additive supply line 25 Shut-off valves 26 Additive flow meter 27 Acid removal filter 28 Controllers 29 Hydraulic oil flow meter 30 Hydraulic Actuator 40 Drive unit 100 Construction Machinery

Claims

1. In a construction machine comprising a hydraulic oil tank for storing hydraulic oil, a hydraulic pump for pressurizing the hydraulic oil drawn from the hydraulic oil tank, a hydraulic actuator, and a control valve for controlling the supply of hydraulic oil from the hydraulic pump to the hydraulic actuator and the discharge of hydraulic oil from the hydraulic actuator to the hydraulic oil tank, The hydraulic fluid is a biodegradable hydraulic fluid. An additive tank for storing additives, An additive supply line that supplies additives from the additive tank to the hydraulic oil tank, A shut-off valve is placed in the additive supply line and opens and closes the additive supply line, An acid removal filter to remove acid from the hydraulic fluid, A hydraulic fluid flow meter for measuring the flow rate of hydraulic fluid flowing into the acid removal filter, An additive flow meter for measuring the flow rate of the additive supplied from the additive tank to the hydraulic fluid tank, The system includes a controller that controls the on / off valve based on the measurement results of the hydraulic fluid flow meter and the measurement results of the additive flow meter, The aforementioned controller, The cumulative flow rate of hydraulic fluid flowing into the acid removal filter is calculated as a first reference value when it is predicted that the rate of decrease in the concentration of the hydraulic fluid additive relative to the cumulative flow rate of hydraulic fluid into the acid removal filter will decrease compared to the start of acid removal of the hydraulic fluid by the acid removal filter. The amount of additives contained in the hydraulic fluid is calculated as the minimum amount when the cumulative flow rate of the hydraulic fluid flowing into the acid removal filter is equal to the first reference value. The amount of additives in the hydraulic fluid that causes metal corrosion below the permissible limit is calculated as the upper limit. The difference between the aforementioned upper limit amount of the additive and the aforementioned lower limit amount of the additive is calculated as the second reference value. Based on the measurement results from the hydraulic fluid flow meter, before the cumulative flow rate of the hydraulic fluid flowing into the acid removal filter reaches the first reference value, the additive supply line is opened by the on / off valve. Based on the measurement results from the additive flow meter, when the cumulative flow rate of the additive supplied from the additive tank to the hydraulic oil tank reaches the second reference value, the on / off valve closes the additive supply line. A construction machine characterized by the following features.

2. The aforementioned controller, A third reference value smaller than the first reference value is calculated, A fourth reference value smaller than the second reference value is calculated, Based on the measurement results from the hydraulic fluid flow meter, when the cumulative flow rate of the hydraulic fluid flowing into the acid removal filter reaches the third reference value, the on / off valve opens the additive supply line. Based on the measurement results from the additive flow meter, the opening and closing of the on-off valve is controlled so that the cumulative flow rate of the additive supplied from the additive tank to the hydraulic oil tank becomes the fourth reference value. Based on the measurement results from the additive flow meter, when the cumulative flow rate of the additive supplied from the additive tank to the hydraulic oil tank reaches the second reference value, the on / off valve closes the additive supply line. The construction machine according to feature 1.

3. The aforementioned controller, When the hydraulic fluid and the acid removal filter are replaced, The cumulative flow rate of the hydraulic fluid flowing into the acid removal filter, based on the measurement results from the hydraulic fluid flow meter, is reset to 0. Based on the measurement results from the additive flow meter, the cumulative flow rate of the additive supplied from the additive tank to the hydraulic oil tank is reset to 0. Based on the measurement results from the hydraulic fluid flow meter, when the cumulative flow rate of the hydraulic fluid flowing into the acid removal filter, which has been reset to zero, reaches the third reference value, the on / off valve opens the additive supply line. Based on the measurement results from the additive flow meter, when the cumulative flow rate of the additive supplied from the additive tank (which has been reset to zero) to the hydraulic fluid tank reaches the second reference value, the on-off valve closes the additive supply line. The construction machine according to feature 2.

4. The aforementioned controller, When the hydraulic fluid has been replaced but the acid removal filter has not been replaced, Based on the cumulative flow rate of hydraulic fluid flowing into the acid removal filter up to the time the hydraulic fluid is replaced, which is determined from the measurement results of the hydraulic fluid flow meter, the amount of additives removed by the acid removal filter up to the time the hydraulic fluid is replaced is calculated as the amount removed. The difference between the upper limit amount of the additive and the lower limit amount of the additive, minus the difference between the amount of the additive removed and the lower limit amount of the additive, is calculated as the new second reference value. A new third reference value is calculated that is smaller than the difference between the first reference value and the cumulative flow rate of the hydraulic fluid flowing into the acid removal filter until the hydraulic fluid is replaced. A new fourth reference value smaller than the new second reference value is calculated, The cumulative flow rate of the hydraulic fluid flowing into the acid removal filter, based on the measurement results from the hydraulic fluid flow meter, is reset to 0. Based on the measurement results from the additive flow meter, the cumulative flow rate of the additive supplied from the additive tank to the hydraulic oil tank is reset to 0. Based on the measurement results from the hydraulic fluid flow meter, when the cumulative flow rate of the hydraulic fluid flowing into the acid removal filter, which has been reset to zero, reaches the new third reference value, the on / off valve opens the additive supply line. Based on the measurement results from the additive flow meter, the opening and closing of the valve is controlled so that the cumulative flow rate of the additive supplied from the additive tank to the hydraulic oil tank from the opening to the closing of the additive supply line by the valve becomes a new fourth reference value. Based on the measurement results from the additive flow meter, when the cumulative flow rate of the additive supplied from the additive tank (which has been reset to 0) to the hydraulic oil tank reaches a new second reference value, the on-off valve closes the additive supply line. The construction machine according to feature 3.

5. The aforementioned controller, When the acid removal filter has been replaced but the hydraulic fluid has not been replaced, Based on the cumulative flow rate of hydraulic fluid flowing into the acid removal filter up to the time the acid removal filter is replaced, which is determined from the measurement results of the hydraulic fluid flow meter, the amount of additives removed by the acid removal filter up to the time the hydraulic fluid is replaced is calculated as the amount removed. Based on the measurement results from the additive flow meter, the cumulative flow rate of the additive supplied from the additive tank to the hydraulic oil tank up to the time the acid removal filter is replaced is calculated as the amount supplied. The difference between the upper limit amount of the additive and the lower limit amount of the additive, and the sum of the difference between the amount of the additive removed and the amount of the additive supplied, are calculated as the new second reference value. A new fourth reference value smaller than the new second reference value is calculated, Based on the measurement results from the hydraulic fluid flow meter, when the cumulative flow rate of the hydraulic fluid flowing into the acid removal filter reaches a new third reference value, the on / off valve opens the additive supply line. Based on the measurement results from the additive flow meter, the opening and closing of the valve is controlled so that the cumulative flow rate of the additive supplied from the additive tank to the hydraulic oil tank from the opening to the closing of the additive supply line by the valve becomes a new fourth reference value. Based on the measurement results from the additive flow meter, when the cumulative flow rate of the additive supplied from the additive tank to the hydraulic oil tank reaches a new second reference value, the on-off valve closes the additive supply line. The construction machinery according to feature 4.

6. The construction machine according to claim 5, characterized in that the additive is an extreme pressure agent.

7. The construction machine according to claim 6, characterized in that the extreme pressure agent comprises either tricresyl phosphate or diorylhydrogen phosphite.

8. The construction machine according to claim 7, characterized in that the acid removal filter is made of either an ion exchange resin or a layered clay mineral.

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