Hydraulic oil and work machine using it

Abstract

To provide a hydraulic operating oil excellent in both electrical conductivity and high-speed slidability, and a working machine utilizing the same.SOLUTION: A hydraulic operating oil comprises a base oil and an additive added to the base oil. The additive includes: a first compound that is a specific secondary amide compound or a tertiary amide compound; a second compound that is a specific phosphite ester compound; and at least one of a third compound that is a specific sorbitan fatty acid ester and a fourth compound that is a specific glyceride. A ratio of sum of a mass percent concentration of the third compound and the mass percent concentration of the fourth compound to a total value of the mass percent concentration of the first compound, the mass percent concentration of the second compound, the mass percent concentration of the third compound, and the mass percent concentration of the fourth compound falls within the range of 10% or more to less than 30%.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a hydraulic oil for use in a work machine and a work machine using the hydraulic oil. [Background technology]

[0002] Hydraulic excavators, wheel loaders, and other work machines use hydraulic pressure as a power source for work, and hydraulic fluid is used to transmit pressure. The hydraulic fluid is pressurized by a hydraulic pump, and the pressure and flow rate are adjusted by a hydraulic valve. After that, it is sent to hydraulic actuators, such as hydraulic cylinders and hydraulic motors, that drive the parts that perform the work and transmit power. After transmitting power, the hydraulic fluid is cooled in an oil cooler, has impurities filtered out by a hydraulic fluid filter, and then returns to the hydraulic fluid tank. In addition to being used for power transmission as described above, hydraulic fluid also functions as a lubricant to lubricate the sliding parts of each moving part.

[0003] Hydraulic fluids are composed of base oils, obtained by refining crude oil, and various additives added to the base oil. Base oils are broadly divided into mineral oils and synthetic oils, but mineral oils are primarily used for hydraulic fluids for work machinery. Additives include detergents, dispersants, antioxidants, load-bearing additives, rust inhibitors, corrosion inhibitors, metal deactivators, viscosity index improvers, pour point depressants, emulsifiers, demulsifiers, fungicides, and solid lubricants. These additives are used to improve performance. Some of these additives contain metal components. Metal components can cause sludge to form when hydraulic fluids deteriorate. Therefore, additives containing metal components are used in minimal amounts.

[0004] Furthermore, hydraulic fluids based on mineral oil typically have low electrical conductivity, ranging from several pS / m to several tens of pS / m at an oil temperature of 25°C. That is, hydraulic fluids based on mineral oil generally have insulating properties. Furthermore, hydraulic fluid filters that filter impurities from hydraulic fluids often use filter elements made of organic materials such as cellulose or insulating materials such as glass fiber. Therefore, the flow resistance (friction) of the hydraulic fluid as it passes through the hydraulic fluid filter causes the hydraulic fluid and the filter element of the hydraulic fluid to become slightly charged. However, considering the characteristics and reliability of the hydraulic fluid and hydraulic equipment, it is preferable to minimize the charging of the hydraulic fluid and the hydraulic fluid filter.

[0005] As a means for suppressing charging of hydraulic oil and hydraulic oil filters, additives that impart electrical conductivity have been proposed (see Patent Document 1).

[0006] Furthermore, for the purpose of improving the lubrication during high-speed sliding of hydraulic equipment having sliding parts such as hydraulic cylinders, hydraulic motors, and shock absorbers, there is a hydraulic oil for hydraulic equipment described in Patent Document 2. The hydraulic oil for hydraulic equipment described in Patent Document 2 contains a base oil, at least one of a phosphite ester compound and a phosphate ester compound, and a specific secondary amide compound (see Chemical Formula 1 in Patent Document 2) in order to obtain a small coefficient of friction and small fluctuations in the coefficient of friction due to temperature changes. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2020-132763 [Patent Document 2] Japanese Patent Application Publication No. 2018-2844 Summary of the Invention [Problem to be solved by the invention]

[0008] In working machines such as construction machines, hydraulic oils are required to have both the above-mentioned electrical conductivity and lubrication stability during high-speed operation of hydraulic motors. However, the inventors of the present application have found that, depending on the amounts and concentrations of additives for imparting electrical conductivity and additives for improving high-speed sliding properties, it may not be possible to obtain both the required electrical conductivity and high-speed sliding properties.

[0009] The present invention has been made based on the above circumstances, and an object of the present invention is to provide a hydraulic oil that is excellent in both electrical conductivity and high-speed sliding properties, and a work machine that uses the same. [Means for solving the problem]

[0010] The present invention includes multiple means for solving the above-mentioned problems. One example is a hydraulic oil containing a base oil and an additive added to the base oil, wherein the additive includes at least one compound selected from the group consisting of a first compound represented by the following chemical formula (1), a second compound represented by the following chemical formula (2), a third compound represented by the following chemical formula (3), and a fourth compound represented by the following chemical formula (4), and wherein the ratio of the sum of the mass percent concentrations of the third compound and the fourth compound to the total value obtained by adding together the mass percent concentrations of the first compound, the second compound, the third compound, and the fourth compound is in the range of 10% or more and less than 30%.

[0011] [ka]

[0012] In chemical formula (1), R 1 is an alkyl or alkenyl group having 8 to 24 carbon atoms, R 2 is an alkyl group or alkenyl group having 8 to 24 carbon atoms or a methyl group, R 3 Hame It is a methyl group.

[0013] [ka]

[0014] In chemical formula (2), R 4 and R 5 One of these is an alkyl or alkenyl group having 10 to 24 carbon atoms, and the other is a hydrogen atom or an alkyl or alkenyl group having 10 to 24 carbon atoms.

[0015] [ka]

[0016] In chemical formula (3), R 6 is an acyl group having an alkyl or alkenyl group having 8 to 18 carbon atoms, and two R 7 One of the R 7 The other is a hydrogen atom or an acyl group having an alkyl or alkenyl group having 8 to 18 carbon atoms.

[0017] [ka]

[0018] In chemical formula (4), two R 8 one of the R is an acyl group having an alkyl or alkenyl group having 8 to 18 carbon atoms, 8 The other is a hydrogen atom or an acyl group having an alkyl or alkenyl group having 8 to 18 carbon atoms. [Effects of the Invention]

[0019] According to the present invention, when the first compound, the second compound, and at least one of the third compound and the fourth compound are added as additives to a base oil, the ratio of the sum of the mass percent concentrations of the third compound and the fourth compound to the total mass percent concentration of all of these compounds is set to be 10% or more and less than 30%, thereby improving the electrical conductivity of the hydraulic oil and preventing the loss of the effect of improving the high-speed sliding properties of the hydraulic oil due to a high ratio of the sum to the total value. In other words, a hydraulic oil excellent in both electrical conductivity and high-speed sliding properties can be obtained. Problems, configurations, and effects other than those described above will become apparent from the following description of the embodiments. [Brief explanation of the drawings]

[0020] [Figure 1] 1 is a schematic diagram showing a work machine using the hydraulic fluid of the present invention; [Figure 2] 2 is a schematic diagram showing an example of the structure of a hydraulic motor that constitutes a part of the embodiment of the working machine of the present invention shown in FIG. 1. FIG. [Figure 3] 2 is a cross-sectional view showing an example of the structure of a hydraulic oil filter that constitutes a part of the embodiment of the working machine of the present invention shown in FIG. 1. FIG. [Figure 4] FIG. 2 is a characteristic diagram showing the test results (limit rotation speed) of a block-on-ring test with respect to changes in the mass percent concentration ratio of a specific additive in one embodiment of the hydraulic oil of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0021] Hereinafter, an embodiment of the hydraulic oil of the present invention and a working machine using the same will be described with reference to the drawings. In this embodiment, a hydraulic excavator will be taken as an example of the working machine.

[0022] [One embodiment] First, the configuration of a work machine that uses the hydraulic oil of the present invention will be described with reference to Figure 1. Figure 1 is a schematic diagram showing a work machine that uses the hydraulic oil of the present invention. In Figure 1, thick arrows indicate the flow direction of the hydraulic oil.

[0023] In Fig. 1, a hydraulic excavator 1 serving as a work machine includes a self-propelled lower traveling body 2, an upper rotating body 3 mounted on the lower traveling body 2 so as to be able to rotate freely, and a front work unit 4 attached to the front of the upper rotating body 3 so as to be able to move up and down (rotate). The hydraulic excavator 1 is one of construction machines and mining machines, along with wheel loaders, dump trucks, etc. The upper rotating body 3 is driven to rotate relative to the lower traveling body by a swing hydraulic motor 6 serving as a hydraulic actuator.

[0024] The lower traveling body 2 has crawler-type traveling devices 8 (only the left one is shown in FIG. 1) on both the left and right sides. The left and right traveling devices 8 are each driven by a traveling hydraulic motor 9 serving as a hydraulic actuator.

[0025] The front work device 4 is an articulated work device for performing work such as excavation work, and is composed of, for example, a boom 11, an arm 12, and a bucket 13 as a work implement. The base end of the boom 11 is rotatably attached to the front of the upper rotating body 3. The base end of an arm 12 is rotatably attached to the tip of the boom 11. The base end of the bucket 13 is rotatably attached to the tip of the arm 12. The boom 11, arm 12, and bucket 13 are driven by a boom cylinder 15, an arm cylinder 16, and a bucket cylinder 17, which serve as hydraulic actuators, respectively.

[0026] A hydraulic oil tank 21, a hydraulic pump 22, a prime mover 23, a hydraulic valve unit 24, an oil cooler 25, a hydraulic oil filter 40, etc. are arranged inside the upper rotating body 3. The hydraulic oil tank 21 is connected to the suction side of the hydraulic pump 22, and the hydraulic valve unit 24 is connected to the discharge side of the hydraulic pump 22. The hydraulic oil filter 40 is arranged upstream of the hydraulic oil tank 21, and the oil cooler 25 is arranged upstream of the hydraulic oil filter 40. The hydraulic oil tank 21, hydraulic pump 22, hydraulic valve unit 24, hydraulic actuator, oil cooler 25, hydraulic oil filter 40, etc. make up a hydraulic circuit.

[0027] The hydraulic oil tank 21 stores hydraulic oil and can be fitted with an oil level gauge, air breather, etc. The hydraulic oil is supplied as pressurized oil to the hydraulic actuator to transmit power. In addition to being used for power transmission, the hydraulic oil also functions as a lubricant that lubricates the sliding parts of the hydraulic pump 22 and the hydraulic actuator.

[0028] The hydraulic pump 22 is a mechanism that applies pressure to hydraulic oil and discharges it as pressurized oil. Typical types of the hydraulic pump 22 include piston pumps, gear pumps, vane pumps, screw pumps, swash plate axial piston pumps, bent axis axial piston pumps, and radial piston pumps. The prime mover 23 is the power source of the hydraulic pump 22, and an engine, an electric motor, or the like can be used.

[0029] The hydraulic valve unit 24 is an assembly of multiple valves, and controls the direction and flow rate of the pressure oil supplied from the hydraulic pump 22 to each of the hydraulic actuators 6, 9, 15, 16, and 17. The hydraulic valve unit 24 can be configured by combining hydraulic control valves, flow control valves, directional control valves, etc.

[0030] The hydraulic actuators are driven by the supply of pressurized oil (hydraulic oil) discharged from the hydraulic pump 22. As described above, the hydraulic actuators include the hydraulic cylinders of the boom cylinder 15, arm cylinder 16, and bucket cylinder 17 that operate the work elements 11, 12, and 13 of the front work unit 4, the swing hydraulic motor 6 that swings the upper swing body 3, and the traveling hydraulic motor 9 that travels the hydraulic excavator 1.

[0031] The hydraulic motors that constitute the swing hydraulic motor 6 and the traveling hydraulic motor 9 are mechanisms that convert hydraulic energy stored in the hydraulic oil supplied from the hydraulic pump 22 into mechanical energy. Hydraulic motors are generally classified into gear motors, vane motors, piston motors, etc., and have the same basic structure as hydraulic pumps. The structure of the hydraulic motors used as the swing hydraulic motor 6 and the traveling hydraulic motor 9 (see Figure 2 below) will be described later.

[0032] The oil cooler 25 cools hydraulic oil. The oil cooler 25 may be an air-cooled type or a water-cooled type, and is configured to perform heat exchange via tubes and fins made of metal such as copper or aluminum.

[0033] The hydraulic oil filter 40 is a mechanism that filters out impurities contained in the hydraulic oil to ensure its cleanliness. An appropriate hydraulic oil filter can be selected depending on the amount of hydraulic oil used and the oil pressure. The structure of the hydraulic oil filter 40 (see Figure 3 below) will be described later.

[0034] Next, an example of the structure of a hydraulic motor in an embodiment of the work machine of the present invention will be described with reference to Figure 2. Figure 2 is a schematic diagram showing an example of the structure of a hydraulic motor that constitutes part of the embodiment of the work machine of the present invention shown in Figure 1.

[0035] In FIG. 2, the hydraulic motor 30 used as the traveling hydraulic motor 9 or swing hydraulic motor 6 shown in FIG. 1 is, for example, a variable displacement swash plate type. The hydraulic motor 30 includes a motor casing 31, an output shaft 32 rotatably supported within the motor casing 31, and a cylinder block 33 disposed within the motor casing 31 and rotating integrally with the output shaft 32. A plurality of plungers 34 are housed within the cylinder block 33 so that they can reciprocate. A shoe 35 is provided at one end of each plunger 34 so that it can swing. Each shoe 35 is configured to slide against a swash plate 36 disposed within the motor casing 31. The hydraulic motor 30 further includes a variable displacement mechanism that changes the displacement of the hydraulic motor 30. The variable displacement mechanism changes the stroke amount of the plungers 34 by changing the inclination angle of the swash plate 36.

[0036] The hydraulic motor 30 further includes a parking brake 37. The parking brake 37 includes a plurality of brake rotors 37a attached to the cylinder block 33, a plurality of friction plates 37b arranged opposite each of the brake rotors 37a, and a brake piston 37c that displaces the plurality of friction plates 37b. The parking brake 37 is configured as a negative brake in which, for example, the brake piston 37c is displaced by the supply of pressurized oil, thereby separating the friction plates 37b from the brake rotor 37a. Note that the parking brake can also be configured as a positive brake in which the brake piston 37c is displaced by the supply of pressurized oil, thereby pressing the friction plates 37b against the brake rotor 37a.

[0037] Next, an example of the structure of a hydraulic oil filter in an embodiment of the work machine of the present invention will be described with reference to Figure 3. Figure 3 is a schematic cross-sectional view showing an example of the structure of a hydraulic oil filter that constitutes part of the embodiment of the work machine of the present invention shown in Figure 1. In Figure 3, thick arrows indicate the flow direction of hydraulic oil.

[0038] In Figure 3, the hydraulic oil filter 40 includes a filter element 41 that filters hydraulic oil. The filter element 41 is generally made of an organic material such as cellulose. The filter element 41 is, for example, a cylindrical element with numerous pleats formed by folding cellulose filter paper. The filtering performance of the filter element 41 can be changed by selecting the density and coarseness of the filter paper.

[0039] The hydraulic oil filter 40 is, for example, a cartridge type. Specifically, the filter element 41 is held by an element case 42 and element case lids 43 provided on one and the other sides of the element case 42, and forms an integrated structure with the element case 42 and the element case lid 43. The filter element 41, element case 42, and element case lid 43 as an integrated structure are housed in a filter case 44. The filter case 44 is, for example, a cylindrical container with a bottom and an opening on one side, and the opening is closed by a filter case lid 45. The filter case 44 forms a flow path through which hydraulic oil flows. The filter case 44 is provided with an inlet 46 through which hydraulic oil flows in. The filter case lid 45 is provided with an outlet 47 through which hydraulic oil that has passed through the filter element 41 and been purified flows out. The filter element 41 can be replaced by removing the element case 42 from the filter case 44.

[0040] Next, the flow of hydraulic oil in one embodiment of the work machine of the present invention will be described with reference to FIGS. 1 to 3. Hydraulic oil in a hydraulic oil tank 21 shown in FIG. 1 is sucked in and pressurized by a hydraulic pump 22 driven by a prime mover 23. The hydraulic oil as pressurized oil discharged from the hydraulic pump 22 is controlled in direction and flow rate by each valve in a hydraulic valve unit 24, and then supplied to hydraulic actuators such as the boom cylinder 15, arm cylinder 16, bucket cylinder 17, swing hydraulic motor 6, and traveling hydraulic motor 9. The hydraulic actuators are driven by the supply of pressurized oil (hydraulic oil), thereby performing various operations of the hydraulic excavator 1. For example, the front work unit 4 is operated by supplying pressurized oil to the three hydraulic cylinders, namely the boom cylinder 15, arm cylinder 16, and bucket cylinder 17. The upper rotating body 3 is rotated left and right by supplying pressurized oil to the swing hydraulic motor 6. The hydraulic excavator 1 travels by supplying pressurized oil to the traveling hydraulic motor 9.

[0041] In the hydraulic motor 30 shown in FIG. 2 as the swing hydraulic motor 6 or the traveling hydraulic motor 9, pressure oil supplied from the hydraulic pump 22 applies torque in the rotational direction to the cylinder block 33 when each plunger 34 slides on the swash plate 36 against which it is in contact via the shoe 35. This torque causes the cylinder block 33 to rotate, and the output shaft 32 also rotates integrally with the cylinder block 33. The hydraulic motor 30 changes the rotation speed of the output shaft 32 by a variable displacement mechanism. The rotation of the output shaft 32 causes the upper swing body 3 to swing and drives the traveling device 8 of the lower traveling body 2.

[0042] When each plunger 34 reciprocates within the cylinder block 33 due to the pressure oil from the hydraulic pump 22, the outer circumferential surface of each plunger 34 slides against the inner wall surface of the cylinder block 33, and each shoe 35 slides against the swash plate 36. The pressure oil (hydraulic oil) supplied from the hydraulic pump 22 functions as a lubricant for these sliding parts.

[0043] Pressurized oil (hydraulic oil) discharged from the hydraulic actuator is cooled by the oil cooler 25 and then purified by the hydraulic oil filter 40. Specifically, the hydraulic oil flows into a filter case 44 via an inlet 46 of the hydraulic oil filter 40 shown in FIG. 3, and passes from the primary side to the secondary side of a filter element 41 arranged in the filter case 44. This removes impurities such as sludge contained in the hydraulic oil. The hydraulic oil that has passed through the filter element 41 flows out from an outlet 47 of the hydraulic oil filter 40, returns to the hydraulic oil tank 21 shown in FIG. 1, and is then sucked into the hydraulic pump 22 again.

[0044] In this way, the hydraulic oil circulates through the hydraulic circuit of the hydraulic excavator 1 to transmit power to the hydraulic actuators 6, 9, 15, 16, and 17. The hydraulic oil also functions as a lubricant that lubricates the sliding parts of the hydraulic pump 22 and the hydraulic actuators 6, 9, 15, 16, and 17.

[0045] Incidentally, when hydraulic oil passes through the filter element 41 of the hydraulic oil filter 40, it becomes slightly charged due to flow resistance (friction). In addition, as the hydraulic oil becomes charged, the filter element 41 also becomes slightly charged. In a work machine such as a construction machine, including the hydraulic excavator 1, there is a concern that the amount of charge on the hydraulic oil will increase.

[0046] More specifically, in recent years, efforts have been made to increase the rated pressure of the hydraulic pump 22 and to reduce the size of the hydraulic oil tank 21. As the hydraulic pressure increases, it is necessary to consider the impact of foreign matter mixed in the hydraulic oil on hydraulic equipment such as the hydraulic pump 22, hydraulic valve unit 24, and hydraulic actuators 6, 9, 15, 16, and 17. Therefore, for example, the mesh size of the filter element 41 of the hydraulic oil filter 40 is made finer to further prevent foreign matter from mixing in the hydraulic oil.

[0047] However, as the mesh size of the filter element 41 becomes finer, the flow resistance (friction) of the hydraulic oil as it passes through the filter element 41 increases, raising concerns about an increase in the amount of static electricity on the hydraulic oil and the filter element 41. Furthermore, as the hydraulic oil tank 21 becomes smaller, the amount of hydraulic oil stored decreases, which tends to speed up the circulation of the hydraulic oil. As a result, the amount of static electricity per unit amount of hydraulic oil tends to increase.

[0048] In particular, when the hydraulic excavator 1 is used in a low-temperature environment, the kinetic viscosity of the hydraulic oil increases with a decrease in temperature, which tends to increase the flow resistance of the hydraulic oil and the amount of charge on the hydraulic oil and the filter element 41.

[0049] On the other hand, in the hydraulic excavator 1 as a work machine, the traveling hydraulic motor 9 may be driven at a speed exceeding the rated rotation speed when climbing a slope or traveling on rough roads. At this time, the plungers 34 of the hydraulic motor 30 (traveling hydraulic motor 9) shown in Fig. 3 slide at high speed, making it difficult for hydraulic oil to be supplied to the sliding parts between the plungers 34 and the inner wall surfaces of the cylinder block 33, and the lubrication state of these sliding parts deteriorates.

[0050] Therefore, the hydraulic oil according to this embodiment is configured to contain an additive of a compound different from the additives of conventional hydraulic oils in order to simultaneously suppress charging and improve the lubrication of sliding parts during high-speed sliding.

[0051] Next, the composition of one embodiment of the hydraulic oil of the present invention will be described. The hydraulic oil is composed of a base oil and a plurality of additives added to the base oil.

[0052] As the base oil, mineral oil obtained by refining crude oil and synthetic oil synthesized using crude oil as a raw material can be used. Generally, mineral oil is used from the viewpoint of cost, etc. Mineral oils are classified into Group I to Group III (classification by the American Petroleum Institute (API)) based on the refining method from crude oil, the amount of residual sulfur, the proportion of saturated hydrocarbons, etc. Examples of mineral oils include paraffin-based mineral oil and naphthene-based mineral oil. Mineral oil has low electrical conductivity and is insulating.

[0053] The hydraulic oil according to the present embodiment contains, as additives, a first compound represented by the following chemical formula (1), a second compound represented by the following chemical formula (2), and at least one compound selected from a third compound represented by the following chemical formula (3) and a fourth compound represented by the following chemical formula (4).

[0054] [ka]

[0055] In chemical formula (1), R 1 is an alkyl or alkenyl group having 8 to 24 carbon atoms, R 2 is an alkyl group or alkenyl group having 8 to 24 carbon atoms or a methyl group, R 3 is hydrogen or a methyl group.

[0056] [ka]

[0057] In chemical formula (2), R 4 and R 5 One of these is an alkyl or alkenyl group having 10 to 24 carbon atoms, and the other is a hydrogen atom or an alkyl or alkenyl group having 10 to 24 carbon atoms.

[0058] [ka]

[0059] In chemical formula (3), R 6 is an acyl group having an alkyl or alkenyl group having 8 to 18 carbon atoms, and two R 7 One of the R 7 The other is a hydrogen atom or an acyl group having an alkyl or alkenyl group having 8 to 18 carbon atoms.

[0060] [ka]

[0061] In chemical formula (4), two R 8 one of the R is an acyl group having an alkyl or alkenyl group having 8 to 18 carbon atoms, 8 The other is a hydrogen atom or an acyl group having an alkyl or alkenyl group having 8 to 18 carbon atoms.

[0062] The hydraulic oil according to this embodiment is further configured so that the ratio of the sum of the mass percentage concentrations of the third compound and the fourth compound to the total sum of the mass percentage concentrations of the first compound (compound represented by chemical formula (1)), the second compound (compound represented by chemical formula (2)), the third compound (compound represented by chemical formula (3)), and the fourth compound (compound represented by chemical formula (4)) is within the range of 10% or more and less than 30%.

[0063] According to this configuration, when the first compound, the second compound, and / or the third and fourth compounds are added to a base oil as additives, the ratio of the sum of the mass percent concentrations of the third and fourth compounds to the total mass percent concentration of all of these compounds is set to 10% or more and less than 30%. This improves the electrical conductivity of the hydraulic oil and prevents the loss of the effect of improving the high-speed sliding properties of the hydraulic oil due to a high ratio of the sum to the total. In other words, a hydraulic oil with excellent both electrical conductivity and high-speed sliding properties can be obtained. This effect will be clarified from the experimental results of the examples and comparative examples described below.

[0064] R in the compound represented by chemical formula (1) 1 and R 2 Examples of the alkyl group include lauryl, myristyl, cetyl, and stearyl. 1 and R 2 Examples of the alkenyl group of R include an oleyl group and an erucyl group. 1 and R 2 may be the same alkyl or alkenyl group, or may be different alkyl or alkenyl groups. 1 and R 2 R may be a combination of an alkyl group and an alkenyl group. 2 and R 3 Both of R may be methyl groups. 3 can also be hydrogen.

[0065] Specific examples of the compound (first compound) represented by chemical formula (1) include N-lauryl lauric acid amide, N-lauryl stearic acid amide, N-lauryl oleic acid amide, N-lauryl erucic acid amide, N-stearyl lauric acid amide, N-stearyl stearic acid amide, N-stearyl oleic acid amide, N-stearyl erucic acid amide, N-oleyl lauric acid amide, N-oleyl stearic acid amide, N-oleyl oleic acid amide, N-oleyl erucic acid amide, and N,N-dimethyldecanamide. The first compound is called a secondary amide compound or a tertiary amide compound.

[0066] R in the compound represented by chemical formula (2) 4 and R 5 Examples of the alkyl group include lauryl, myristyl, cetyl, and stearyl. 4 and R 5 Examples of the alkenyl group of R include an oleyl group and an erucyl group. 4 and R 5 may be the same alkyl or alkenyl group, or may be different alkyl or alkenyl groups. 4 and R 5 may be a combination of alkyl and alkenyl groups.

[0067] The compound (second compound) represented by chemical formula (2) can be composed of only one type of phosphite ester compound or a mixture of multiple types of phosphite ester compounds. Specific examples of the second compound include dilauryl hydrogen phosphite, distearyl hydrogen phosphite, and dioleyl hydrogen phosphite. The second compound is called a phosphite ester compound.

[0068] R in the compound represented by chemical formula (3) 6 and R 7Examples of the acyl group include an octanoyl group (an acyl group having an alkyl group with 8 carbon atoms), a lauroyl group (an acyl group having an alkyl group with 12 carbon atoms), a myristoyl group (an acyl group having an alkyl group with 14 carbon atoms), a palmitoyl group (an acyl group having an alkyl group with 16 carbon atoms), a palmitoleoyl group (an acyl group having an alkenyl group with 16 carbon atoms), a stearoyl group (an acyl group having an alkyl group with 18 carbon atoms), and an oleoyl group (an acyl group having an alkenyl group with 18 carbon atoms). 6 and R 7 may be the same acyl group or different acyl groups.

[0069] Specific examples of the compound (third compound) represented by chemical formula (3) include sorbitan monooctanoate, sorbitan dioctanoate, sorbitan sesquioctanoate, sorbitan monolaurate, sorbitan dilaurate, sorbitan sesquilaurate, sorbitan monostearate, sorbitan distearate, sorbitan sesquistearate, sorbitan monooleate, sorbitan dioleate, sorbitan sesquioleate, etc. The third compound is called a sorbitan fatty acid ester.

[0070] R in the compound represented by chemical formula (4) 8 The acyl group in the compound represented by chemical formula (3) is R 6 and R 7 The acyl group is the same as that of the compound represented by chemical formula (4) (fourth compound). Specific examples of the compound represented by chemical formula (4) (fourth compound) include monostearate glyceride, distearate glyceride, sesquistearate glyceride, monooleate glyceride, dioleate glyceride, and sesquioleate glyceride. The fourth compound is called a glyceride.

[0071] The compounds represented by the above chemical formulas (1) to (4) are all organic substances, which is intended to prevent them from containing metal components that are sources of sludge generation.

[0072] In this embodiment, it is assumed that the compound (second compound) represented by the above chemical formula (2) releases protons through catalytic action, and is thereby adsorbed onto the metal surface of the plunger 34 of the hydraulic motor 30 and the metal surface of the inner wall surface of the cylinder block 33, thereby forming a stable adsorption film. It is believed that this adsorption film improves the sliding properties (lubricity) between the plunger 34 and the cylinder block 33.

[0073] In this embodiment, it is assumed that the compound (first compound) represented by the above chemical formula (1) promotes a reaction in which the compound represented by the above chemical formula (2) releases a proton. As a result, the compound represented by the chemical formula (2) that has released a proton and become ionized is believed to be stably adsorbed onto the metal surfaces of the plunger 34 and the cylinder block 33, forming an adsorption film. In other words, the first compound and the second compound are additives for improving lubricity during high-speed sliding in hydraulic equipment.

[0074] Furthermore, in this embodiment, the compound represented by the chemical formula (3) and the compound represented by the chemical formula (4) have both an acyl group that functions as a lipophilic group and a hydroxyl group that functions as a hydrophilic group, thereby improving the solubility in the base oil and simultaneously improving the electrical conductivity (electrical conductivity). In other words, the third compound and the fourth compound are additives that impart electrical conductivity to the hydraulic oil. This reduces the amount of charge in the hydraulic oil. Note that, according to the results described below, it is sufficient to add at least one of the third compound and the fourth compound.

[0075] However, it was found that adding at least one of the first compound, the second compound, the third compound, and the fourth compound to a base oil without considering their mass percent concentrations may not improve the high-speed sliding properties of the hydraulic fluid. Therefore, in this embodiment, as described above, the ratio of the sum of the mass percent concentrations of the third compound and the fourth compound to the total mass percent concentration of these compounds is limited to a predetermined range (10% or more and less than 30%), thereby improving electrical conductivity and reliably improving the high-speed sliding properties of the hydraulic fluid. The method for determining the range of the ratio of the sum to the total will be clarified from the experimental results of the examples and comparative examples described below.

[0076] In this embodiment, R in the above chemical formula (1) 1 and R 2 At least one of these is preferably an alkyl group or an alkenyl group having a carbon number of 10 to 24. This improves the solubility of the compound represented by chemical formula (1) in the base oil.

[0077] Furthermore, in this embodiment, R 1 and R 2 At least one of these is preferably an alkyl group or an alkenyl group having from 12 to 18 carbon atoms, which further improves the solubility of the compound represented by chemical formula (1) in the base oil.

[0078] In this embodiment, R 4 and R 5 At least one of these is preferably an alkyl group or an alkenyl group having a carbon number of 12 to 18. This improves the solubility of the compound represented by chemical formula (2) in the base oil.

[0079] In this embodiment, the two R 7 and a third compound in which both R 8It is preferable to add at least one compound of the fourth compounds in which one of the groups is a hydrogen atom. When there are many OH groups as hydrophilic groups in chemical formula (3) and chemical formula (4), the electrical conductivity of the hydraulic oil tends to be high.

[0080] Furthermore, the hydraulic oil according to this embodiment preferably has an electrical conductivity of 400 pS / m or more at an oil temperature of 25° C. This is because with hydraulic oil having an electrical conductivity of 400 pS / m or more at an oil temperature of 25° C., the amount of charge in the hydraulic oil is considered to be within a range that has almost no effect on the hydraulic equipment or hydraulic oil filter even when the hydraulic excavator 1 (work machine) is operated in a low-temperature environment.

[0081] Incidentally, the hydraulic oil used in the hydraulic excavator 1 is repeatedly heated by pressurization in a hydraulic pump 22 and flow rate control in a hydraulic valve unit 24, and cooled in an oil cooler 25, as shown in Fig. 1. It has been confirmed that hydraulic oil containing at least one of the compounds represented by chemical formula (3) and chemical formula (4) does not experience a significant decrease in electrical conductivity due to repeated heating and cooling.

[0082] The hydraulic oil according to this embodiment may contain additives to compensate for various functions that are lacking in the base oil alone, provided that the effects of the above four additives are not impaired. Typical examples include detergents and dispersants, antioxidants, load-bearing additives, rust inhibitors, corrosion inhibitors, metal deactivators, viscosity index improvers, pour point depressants, emulsifiers, antifoaming agents, demulsifiers, fungicides, and solid lubricants.

[0083] As the detergent dispersant, organic acid metal compounds, neutral / overbased metals, overbased metal sulfonates, overbased metal phenates, overbased metal sulfonates, succinimides, succinic acid esters, benzylamines, etc. can be used.

[0084] As the antioxidant, zinc dithiophosphate, organic sulfur compounds, hindered phenols, aromatic amines, etc. can be used.

[0085] As the rust inhibitor, carboxylic acids, sulfonates, phosphates, alcohols, esters, etc. can be used.

[0086] As the corrosion inhibitor, nitrogen-containing compounds, zinc dithiophosphate, etc. can be used.

[0087] As the metal deactivator, a nitrogen-containing compound can be used.

[0088] As the viscosity index improver, polymethacrylate, olefin copolymer, styrene olefin copolymer, polyisobutylene, etc. can be used.

[0089] Pour point depressants that can be used include polymethacrylates, alkylated aromatic compounds, fumarate-vinyl acetate copolymers, and ethylene-vinyl acetate copolymers.

[0090] As the emulsifier, ethylene oxide adducts, esters, carboxylates, sulfates, sulfonates, phosphates, amine derivatives, quaternary ammonium salts, etc. can be used.

[0091] Examples of the antifoaming agent that can be used include polymethylsiloxane, silicate, organic fluorine compounds, metal soaps, fatty acid esters, phosphate esters, higher alcohols, and polyalkylene glycols.

[0092] Examples of demulsifiers that can be used include ethylene oxide adducts, ethylene oxide-propylene oxide block polymers, and quaternary ammonium salts.

[0093] As the mildew inhibitor, phenol compounds, formaldehyde donor compounds, salicylianilide compounds, etc. can be used.

[0094] As the solid lubricant, molybdenum disulfide, tungsten disulfide, graphite, boron nitride, tetrafluoroethylene polymer, graphite fluoride, fullerene, or the like can be used.

[0095] Next, the compositions and effects of the hydraulic oils of Examples 1 to 17 according to the present invention will be explained in comparison with the hydraulic oils of Comparative Examples 1 to 8. First, the compositions and effects of the hydraulic oils of Examples 1 to 12 will be explained using Tables 1 to 3 in comparison with the hydraulic oils of Comparative Examples 1 to 6. Table 1 shows the compositions of the hydraulic oils of Comparative Examples 1 to 6 compared to Examples 1 to 12, the results of the hydraulic motor seizure test, the results of electrical conductivity measurements, and the results of the hydraulic oil filter damage test. Table 2 shows the compositions of the hydraulic oils of Examples 1 to 6, the results of the hydraulic motor seizure test, the results of electrical conductivity measurements, and the results of the hydraulic oil filter damage test. Table 3 shows the compositions of the hydraulic oils of Examples 7 to 12, the results of the hydraulic motor seizure test, the results of electrical conductivity measurements, and the results of the hydraulic oil filter damage test.

[0096] [Table 1]

[0097] [Table 2]

[0098] [Table 3]

[0099] First, a seizure test of a hydraulic motor was conducted to test the high-speed slidability of the hydraulic oils of Comparative Examples 1 to 6 and Examples 1 to 12. Specifically, the hydraulic oils of Comparative Examples 1 to 6 and Examples 1 to 12 were used in an actual hydraulic excavator to rotate and drive the hydraulic motor. The rotational speed at which the hydraulic motor seized was measured when the rotational speed was gradually increased (hereinafter referred to as the limit rotational speed). When the limit rotational speed of the hydraulic motor was equal to or greater than twice the rated rotational speed of the hydraulic motor, the high-speed slidability of the hydraulic oil was judged to be good (◯). When the limit rotational speed was equal to or greater than 1.5 times but less than 2.0 times the rated rotational speed, the high-speed slidability of the hydraulic oil was judged to be insufficient (△). Furthermore, when the limit rotational speed was less than 1.5 times the rated rotational speed, the high-speed slidability of the hydraulic oil was judged to be insufficient (×). The seizure test of the hydraulic motor was conducted using the same hydraulic excavator. That is, the test was conducted using the same type of hydraulic motor with the same hydraulic circuit configuration.

[0100] Second, the electrical conductivity of the hydraulic oils of Comparative Examples 1 to 6 and Examples 1 to 12 was measured. The specific measurement method is as follows. The volume resistivity of the hydraulic oil was measured by a method based on the electrical insulating oil test method described in JIS C2101. However, the measurement temperature was 25°C instead of 80°C. The electrical conductivity of each hydraulic oil was calculated from the reciprocal of the volume resistivity of the measurement result.

[0101] Third, a damage test was conducted on the hydraulic oil filter when the hydraulic oils of Comparative Examples 1 to 6 and Examples 1 to 12 were used in an actual hydraulic excavator and operated. When the outside air temperature is low and the temperature of the hydraulic oil is low, there is a concern that the hydraulic oil filter may be damaged by discharge. Therefore, as a test condition, the work machine was started (the hydraulic pump was started) five times from a state in which the temperature of the hydraulic oil was low in a low-temperature environment where the outside air temperature was 0°C or below. After the five starts, the presence or absence of damage to the hydraulic oil filter was confirmed. The hydraulic oil filter damage test was conducted using the same work machine. In other words, the test was conducted under the same conditions, with the same rated pressure of the hydraulic pump, the same capacity of the hydraulic oil tank, the same configuration and structure of the hydraulic oil filter, and the same configuration of the hydraulic circuit.

[0102] [Comparative Example 1] For the hydraulic fluid of Comparative Example 1, a Group III mineral oil was used as the base oil, as shown in Table 1. To the base oil, N-oleylstearamide was added as an additive at a concentration of 0.1 mass% (the mass ratio of the first compound to the total mass of the hydraulic fluid) as a compound represented by chemical formula (1) (first compound), and dioleylhydrogen phosphite was added as a compound represented by chemical formula (2) (second compound) at a concentration of 1.0 mass%. Furthermore, detergent-dispersant, antioxidant, load-bearing additive, viscosity index improver, antifoaming agent, and demulsifier were used as other additives. The hydraulic fluid of Comparative Example 1 did not contain the compound represented by chemical formula (3) (third compound) or the compound represented by chemical formula (4) (fourth compound). In this case, the ratio of the sum of the mass percent concentrations of the third compound and the fourth compound to the total sum of the mass percent concentrations of the first compound, the second compound, the third compound, and the fourth compound (hereinafter sometimes referred to as the mass percent concentration ratio of the specific additive) is 0.0%.

[0103] The measurement result of the limit rotation speed of the hydraulic motor using the hydraulic oil of Comparative Example 1 was more than twice the rated rotation speed of the hydraulic motor. In other words, the high-speed sliding properties of the hydraulic oil of Comparative Example 1 were judged to be good (◯). The measurement result of the electrical conductivity of the hydraulic oil of Comparative Example 1 was 75 pS / m. Furthermore, in a damage test of a hydraulic oil filter using the hydraulic oil of Comparative Example 1, damage occurred to the hydraulic oil filter. From these results, it was judged that the hydraulic oil of Comparative Example 1 had good high-speed sliding properties but low electrical conductivity.

[0104] Comparative Example 2 For the hydraulic fluid of Comparative Example 2, as shown in Table 1, a Group II mineral oil was used as the base oil. To the base oil, N-oleyl stearic acid amide, a compound represented by chemical formula (1), was added at a concentration of 0.1 mass %, and sorbitan monooleate, a compound represented by chemical formula (3), was added at a concentration of 0.3 mass %. Furthermore, the same types of additives as those used in Comparative Example 1 (detergent-dispersant, antioxidant, load-bearing additive, viscosity index improver, antifoaming agent, and demulsifier) ​​were used as other additives. Note that the compound represented by chemical formula (2) and the compound represented by chemical formula (4) were not added to the hydraulic fluid of Comparative Example 2. In this case, the mass % concentration of the specific additives was 75.0%.

[0105] The measurement result of the limit rotation speed of the hydraulic motor using the hydraulic oil of Comparative Example 2 was less than 1.5 times the rated rotation speed of the hydraulic motor. In other words, the hydraulic oil of Comparative Example 2 was judged to have insufficient high-speed sliding properties (×). Furthermore, the measurement result of the electrical conductivity of the hydraulic oil of Comparative Example 2 was 550 pS / m. Furthermore, in a damage test of a hydraulic oil filter using the hydraulic oil of Comparative Example 2, no damage occurred to the hydraulic oil filter. From these results, it was judged that the hydraulic oil of Comparative Example 2 had insufficient high-speed sliding properties but high electrical conductivity.

[0106] Comparative Example 3 For the hydraulic fluid of Comparative Example 3, as shown in Table 1, a Group III mineral oil was used as the base oil. To the base oil, dioleylhydrogen phosphite as a compound represented by chemical formula (2) was added at a concentration of 0.3 mass%, and sorbitan dioleate as a compound represented by chemical formula (3) was added at a concentration of 0.4 mass%. Furthermore, the same types of additives as those used in Comparative Example 1 were used as other additives. Note that the compound represented by chemical formula (1) and the compound represented by chemical formula (4) were not added to the hydraulic fluid of Comparative Example 3. In this case, the mass% concentration of the specific additives was 57.1%.

[0107] The measurement result of the limit rotation speed of the hydraulic motor using the hydraulic oil of Comparative Example 3 was 1.5 times or more and less than 2.0 times the rated rotation speed of the hydraulic motor. In other words, the high-speed sliding properties of the hydraulic oil of Comparative Example 1 were judged to be insufficient (△). The measurement result of the electrical conductivity of the hydraulic oil of Comparative Example 3 was 400 pS / m. Furthermore, in a damage test of a hydraulic oil filter using the hydraulic oil of Comparative Example 3, no damage occurred to the hydraulic oil filter. From these results, it was judged that the hydraulic oil of Comparative Example 3 had insufficient high-speed sliding properties but high electrical conductivity.

[0108] Comparative Example 4 In the hydraulic oil of Comparative Example 3, a Group II mineral oil was used as the base oil, as shown in Table 1. To the base oil, N-oleyl stearic acid amide as a compound represented by chemical formula (1) was added at a concentration of 0.1 mass%, and dilauryl hydrogen phosphite as a compound represented by chemical formula (2) was added at a concentration of 1.0 mass%. Furthermore, the same types of additives as those used in Comparative Example 1 were used as other additives. Note that the hydraulic oil of Comparative Example 4 did not contain the compound represented by chemical formula (3) or the compound represented by chemical formula (4). In this case, the mass% concentration of the specific additive was 0.0%.

[0109] The measurement result of the limit rotation speed of the hydraulic motor using the hydraulic oil of Comparative Example 4 was more than twice the rated rotation speed of the hydraulic motor. In other words, the high-speed sliding properties of the hydraulic oil of Comparative Example 4 were judged to be good (◯). The measurement result of the electrical conductivity of the hydraulic oil of Comparative Example 4 was 80 pS / m. Furthermore, in a damage test of a hydraulic oil filter using the hydraulic oil of Comparative Example 4, damage occurred to the hydraulic oil filter. From these results, it was judged that the hydraulic oil of Comparative Example 4 had good high-speed sliding properties but low electrical conductivity.

[0110] Comparative Example 5 For the hydraulic fluid of Comparative Example 5, a Group III mineral oil was used as the base oil, as shown in Table 1. To the base oil, N-oleyl stearic acid amide as a compound represented by chemical formula (1) was added at a concentration of 0.1 mass %, and sorbitan monostearate as a compound represented by chemical formula (3) was added at a concentration of 0.2 mass %. Furthermore, the same types of additives as those used in Comparative Example 1 were used as other additives. Note that the compound represented by chemical formula (2) and the compound represented by chemical formula (4) were not added to the hydraulic fluid of Comparative Example 5. In this case, the mass % concentration of the specific additives was 66.7%.

[0111] The measurement result of the limit rotation speed of the hydraulic motor using the hydraulic oil of Comparative Example 5 was less than 1.5 times the rated rotation speed of the hydraulic motor. In other words, the hydraulic oil of Comparative Example 5 was judged to have insufficient high-speed sliding properties (×). The measurement result of the electrical conductivity of the hydraulic oil of Comparative Example 5 was 540 pS / m. Furthermore, in a damage test of a hydraulic oil filter using the hydraulic oil of Comparative Example 5, no damage occurred to the hydraulic oil filter. From these results, it was judged that the hydraulic oil of Comparative Example 5 had insufficient high-speed sliding properties but high electrical conductivity.

[0112] Comparative Example 6 For the hydraulic oil of Comparative Example 6, a Group II mineral oil was used as the base oil, as shown in Table 1. To the base oil, as additives, dilauryl hydrogen phosphite as a compound represented by chemical formula (2) was added at a concentration of 0.3 mass%, and sorbitan sesquistearate as a compound represented by chemical formula (3) was added at a concentration of 0.3 mass%. Furthermore, the same types of additives as those used in Comparative Example 1 were used as other additives. Note that the compound represented by chemical formula (1) and the compound represented by chemical formula (4) were not added to the hydraulic oil of Comparative Example 6. In this case, the mass% concentration of the specific additives was 50.0%.

[0113] The measurement result of the limit rotation speed of the hydraulic motor using the hydraulic oil of Comparative Example 6 was 1.5 times or more and less than 2.0 times the rated rotation speed of the hydraulic motor. In other words, the high-speed sliding property of the hydraulic oil of Comparative Example 1 was judged to be insufficient (△). Furthermore, the measurement result of the electrical conductivity of the hydraulic oil of Comparative Example 6 was 450 pS / m. Furthermore, in a damage test of a hydraulic oil filter using the hydraulic oil of Comparative Example 6, no damage occurred to the hydraulic oil filter. From these results, it was judged that the hydraulic oil of Comparative Example 6 had insufficient high-speed sliding property but high electrical conductivity.

[0114] [Example 1] For the hydraulic fluid of Example 1, a Group III mineral oil was used as the base oil, as shown in Table 2. To the base oil, the following additives were added: N-oleyl stearic acid amide (a compound represented by chemical formula (1)) at a concentration of 0.1 mass%, dioleyl hydrogen phosphite (a compound represented by chemical formula (2)) at a concentration of 1.0 mass%, and sorbitan monooleate (a compound represented by chemical formula (3)) at a concentration of 0.15 mass%. In this case, the mass% concentration of the specific additives was 12.0%. Furthermore, the same types of additives as those used in Comparative Example 1 (detergent-dispersant, antioxidant, load-bearing additive, viscosity index improver, antifoaming agent, and demulsifier) ​​were added as other additives.

[0115] The measurement result of the limit rotation speed of the hydraulic motor using the hydraulic oil of Example 1 was more than twice the rated rotation speed of the hydraulic motor. In other words, the high-speed sliding properties of the hydraulic oil of Example 1 were judged to be good (◯). Furthermore, the measurement result of the electrical conductivity of the hydraulic oil of Example 1 was 550 pS / m. Furthermore, in a damage test of a hydraulic oil filter using the hydraulic oil of Example 1, no damage occurred to the hydraulic oil filter. From these results, the hydraulic oil of Example 1 was judged to have good high-speed sliding properties and high electrical conductivity.

[0116] [Example 2] For the hydraulic fluid of Example 2, a Group II mineral oil was used as the base oil, as shown in Table 2. To the base oil, as additives, N-oleyl stearic acid amide as a compound represented by chemical formula (1) was added at a concentration of 0.1 mass%, dioleyl hydrogen phosphite as a compound represented by chemical formula (2) was added at a concentration of 0.5 mass%, and sorbitan sesquioleate as a compound represented by chemical formula (3) was added at a concentration of 0.2 mass%. In this case, the mass% concentration of the specific additives was 25.0%. Furthermore, the same types of additives as those in Comparative Example 1 were added as other additives.

[0117] The measurement result of the limit rotation speed of the hydraulic motor using the hydraulic oil of Example 2 was more than twice the rated rotation speed of the hydraulic motor. In other words, the high-speed sliding properties of the hydraulic oil of Example 2 were judged to be good (◯). Furthermore, the measurement result of the electrical conductivity of the hydraulic oil of Example 2 was 460 pS / m. Furthermore, in a damage test of a hydraulic oil filter using the hydraulic oil of Example 2, no damage occurred to the hydraulic oil filter. From these results, the hydraulic oil of Example 2 was judged to have good high-speed sliding properties and high electrical conductivity.

[0118] [Example 3] For the hydraulic fluid of Example 3, a Group III mineral oil was used as the base oil, as shown in Table 2. To the base oil, as additives, N-oleylstearamide as a compound represented by chemical formula (1) was added at a concentration of 0.1 mass%, dioleyl hydrogen phosphite as a compound represented by chemical formula (2) was added at a concentration of 0.4 mass%, and sorbitan dioleate as a compound represented by chemical formula (3) was added at a concentration of 0.2 mass%. In this case, the mass% concentration of the specific additives was 28.6%. Furthermore, the same types of additives as those in Comparative Example 1 were added as other additives.

[0119] The measurement result of the limit rotation speed of the hydraulic motor using the hydraulic oil of Example 3 was more than twice the rated rotation speed of the hydraulic motor. In other words, the high-speed sliding properties of the hydraulic oil of Example 3 were judged to be good (◯). Furthermore, the measurement result of the electrical conductivity of the hydraulic oil of Example 3 was 400 pS / m. Furthermore, in a damage test of a hydraulic oil filter using the hydraulic oil of Example 3, no damage occurred to the hydraulic oil filter. From these results, the hydraulic oil of Example 3 was judged to have good high-speed sliding properties and high electrical conductivity.

[0120] [Example 4] For the hydraulic fluid of Example 4, a Group II mineral oil was used as the base oil, as shown in Table 2. To the base oil, as additives, N-oleyl stearic acid amide as a compound represented by chemical formula (1) was added at a concentration of 0.1 mass%, dilauryl hydrogen phosphite as a compound represented by chemical formula (2) was added at a concentration of 1.0 mass%, and monooleic acid glyceride as a compound represented by chemical formula (4) was added at a concentration of 0.3 mass%. In this case, the mass% concentration of the specific additives was 21.4%. Furthermore, the same types of additives as those in Comparative Example 1 were added as other additives.

[0121] The measurement result of the limit rotation speed of the hydraulic motor using the hydraulic oil of Example 4 was more than twice the rated rotation speed of the hydraulic motor. In other words, the high-speed sliding properties of the hydraulic oil of Example 4 were judged to be good (◯). The measurement result of the electrical conductivity of the hydraulic oil of Example 4 was 480 pS / m. Furthermore, in a damage test of a hydraulic oil filter using the hydraulic oil of Example 4, no damage occurred to the hydraulic oil filter. From these results, the hydraulic oil of Example 4 was judged to have good high-speed sliding properties and high electrical conductivity.

[0122] [Example 5] For the hydraulic fluid of Example 5, a Group III mineral oil was used as the base oil, as shown in Table 2. To the base oil, as additives, N-oleyl stearic acid amide as a compound represented by chemical formula (1) was added at a concentration of 0.1 mass%, dilauryl hydrogen phosphite as a compound represented by chemical formula (2) was added at a concentration of 0.5 mass%, and sorbitan monostearate as a compound represented by chemical formula (3) was added at a concentration of 0.2 mass%. In this case, the mass% concentration of the specific additives was 25.0%. Furthermore, the same types of additives as those in Comparative Example 1 were added as other additives.

[0123] The measurement result of the limit rotation speed of the hydraulic motor using the hydraulic oil of Example 5 was more than twice the rated rotation speed of the hydraulic motor. In other words, the high-speed sliding properties of the hydraulic oil of Example 5 were judged to be good (◯). Furthermore, the measurement result of the electrical conductivity of the hydraulic oil of Example 5 was 540 pS / m. Furthermore, in a damage test of a hydraulic oil filter using the hydraulic oil of Example 5, no damage occurred to the hydraulic oil filter. From these results, the hydraulic oil of Example 5 was judged to have good high-speed sliding properties and high electrical conductivity.

[0124] [Example 6] For the hydraulic fluid of Example 6, a Group II mineral oil was used as the base oil, as shown in Table 2. To the base oil, as additives, N-oleyl stearic acid amide as a compound represented by chemical formula (1) was added at a concentration of 0.1 mass%, dilauryl hydrogen phosphite as a compound represented by chemical formula (2) was added at a concentration of 0.4 mass%, and sorbitan sesquistearate as a compound represented by chemical formula (3) was added at a concentration of 0.2 mass%. In this case, the mass% concentration of the specific additives was 28.6%. Furthermore, the same types of additives as those in Comparative Example 1 were added as other additives.

[0125] The measurement result of the limit rotation speed of the hydraulic motor using the hydraulic oil of Example 6 was more than twice the rated rotation speed of the hydraulic motor. In other words, the high-speed sliding properties of the hydraulic oil of Example 6 were judged to be good (◯). Furthermore, the measurement result of the electrical conductivity of the hydraulic oil of Example 6 was 450 pS / m. Furthermore, in a damage test of a hydraulic oil filter using the hydraulic oil of Example 6, no damage occurred to the hydraulic oil filter. From these results, the hydraulic oil of Example 6 was judged to have good high-speed sliding properties and high electrical conductivity.

[0126] [Example 7] For the hydraulic fluid of Example 7, a Group III mineral oil was used as the base oil, as shown in Table 3. To the base oil, as additives, N-oleyl erucic acid amide as a compound represented by chemical formula (1) was added at a concentration of 0.1 mass%, dioleyl hydrogen phosphite as a compound represented by chemical formula (2) was added at a concentration of 1.0 mass%, and sorbitan monooleate as a compound represented by chemical formula (3) was added at a concentration of 0.2 mass%. In this case, the mass% concentration of the specific additives was 15.4%. Furthermore, the same type of additive as in Comparative Example 1 was added as other additives.

[0127] The measurement result of the limit rotation speed of the hydraulic motor using the hydraulic oil of Example 7 was more than twice the rated rotation speed of the hydraulic motor. In other words, the high-speed sliding properties of the hydraulic oil of Example 7 were judged to be good (◯). Furthermore, the measurement result of the electrical conductivity of the hydraulic oil of Example 7 was 550 pS / m. Furthermore, in a damage test of a hydraulic oil filter using the hydraulic oil of Example 7, no damage occurred to the hydraulic oil filter. From these results, the hydraulic oil of Example 7 was judged to have good high-speed sliding properties and high electrical conductivity.

[0128] [Example 8] For the hydraulic fluid of Example 8, a Group II mineral oil was used as the base oil, as shown in Table 3. To the base oil, as additives, N-oleyl erucic acid amide as a compound represented by chemical formula (1) was added at a concentration of 0.1 mass%, dioleyl hydrogen phosphite as a compound represented by chemical formula (2) was added at a concentration of 0.5 mass%, and sorbitan sesquioleate as a compound represented by chemical formula (3) was added at a concentration of 0.2 mass%. In this case, the mass% concentration of the specific additives was 25.0%. Furthermore, the same types of additives as those in Comparative Example 1 were added as other additives.

[0129] The measurement result of the limit rotation speed of the hydraulic motor using the hydraulic oil of Example 8 was more than twice the rated rotation speed of the hydraulic motor. In other words, the high-speed sliding properties of the hydraulic oil of Example 8 were judged to be good (◯). Furthermore, the measurement result of the electrical conductivity of the hydraulic oil of Example 8 was 460 pS / m. Furthermore, in a damage test of a hydraulic oil filter using the hydraulic oil of Example 8, no damage occurred to the hydraulic oil filter. From these results, the hydraulic oil of Example 8 was judged to have good high-speed sliding properties and high electrical conductivity.

[0130] [Example 9] For the hydraulic fluid of Example 9, a Group III mineral oil was used as the base oil, as shown in Table 3. To the base oil, additives were added: N-oleyl erucic acid amide as a compound represented by chemical formula (1) at a concentration of 0.1 mass%, dioleyl hydrogen phosphite as a compound represented by chemical formula (2) at a concentration of 0.4 mass%, and sorbitan distearate as a compound represented by chemical formula (3) at a concentration of 0.2 mass%. In this case, the mass% concentration of the specific additives was 28.6%. Furthermore, the same additives as those used in Comparative Example 1 were added as other additives.

[0131] The measurement result of the limit rotation speed of the hydraulic motor using the hydraulic oil of Example 9 was more than twice the rated rotation speed of the hydraulic motor. In other words, the high-speed sliding properties of the hydraulic oil of Example 9 were judged to be good (◯). Furthermore, the measurement result of the electrical conductivity of the hydraulic oil of Example 9 was 410 pS / m. Furthermore, in a damage test of a hydraulic oil filter using the hydraulic oil of Example 9, no damage occurred to the hydraulic oil filter. From these results, it was judged that the hydraulic oil of Example 9 has good high-speed sliding properties and high electrical conductivity.

[0132] [Example 10] For the hydraulic fluid of Example 10, a Group II mineral oil was used as the base oil, as shown in Table 3. To the base oil, as additives, N-oleyl erucic acid amide as a compound represented by chemical formula (1) was added at a concentration of 0.1 mass%, dilauryl hydrogen phosphite as a compound represented by chemical formula (2) was added at a concentration of 1.0 mass%, and monostearate glyceride as a compound represented by chemical formula (4) was added at a concentration of 0.3 mass%. In this case, the mass% concentration of the specific additives was 21.4%. Furthermore, the same types of additives as those in Comparative Example 1 were added as other additives.

[0133] The measurement result of the limit rotation speed of the hydraulic motor using the hydraulic oil of Example 10 was more than twice the rated rotation speed of the hydraulic motor. In other words, the high-speed sliding properties of the hydraulic oil of Example 10 were judged to be good (◯). Furthermore, the measurement result of the electrical conductivity of the hydraulic oil of Example 10 was 470 pS / m. Furthermore, in a damage test of a hydraulic oil filter using the hydraulic oil of Example 10, no damage occurred to the hydraulic oil filter. From these results, the hydraulic oil of Example 10 was judged to have good high-speed sliding properties and high electrical conductivity.

[0134] [Example 11] For the hydraulic fluid of Example 11, a Group III mineral oil was used as the base oil, as shown in Table 3. To the base oil, as additives, N-oleyl erucic acid amide as a compound represented by chemical formula (1) was added at a concentration of 0.1 mass%, dilauryl hydrogen phosphite as a compound represented by chemical formula (2) was added at a concentration of 0.5 mass%, and sorbitan monolaurate as a compound represented by chemical formula (3) was added at a concentration of 0.2 mass%. In this case, the mass% concentration of the specific additives was 25.0%. Furthermore, the same types of additives as those in Comparative Example 1 were added as other additives.

[0135] The measurement result of the limit rotation speed of the hydraulic motor using the hydraulic oil of Example 11 was more than twice the rated rotation speed of the hydraulic motor. In other words, the high-speed sliding properties of the hydraulic oil of Example 11 were judged to be good (◯). Furthermore, the measurement result of the electrical conductivity of the hydraulic oil of Example 11 was 530 pS / m. Furthermore, in a damage test of a hydraulic oil filter using the hydraulic oil of Example 11, no damage occurred to the hydraulic oil filter. From these results, the hydraulic oil of Example 11 was judged to have good high-speed sliding properties and high electrical conductivity.

[0136] [Example 12] For the hydraulic fluid of Example 12, a Group II mineral oil was used as the base oil, as shown in Table 3. To the base oil, as additives, N-oleyl erucic acid amide as a compound represented by chemical formula (1) was added at a concentration of 0.1 mass%, dilauryl hydrogen phosphite as a compound represented by chemical formula (2) was added at a concentration of 0.4 mass%, and sorbitan monooctanoate as a compound represented by chemical formula (3) was added at a concentration of 0.2 mass%. In this case, the mass% concentration of the specific additives was 28.6%. Furthermore, the same type of additive as in Comparative Example 1 was added as other additives.

[0137] The measurement result of the limit rotation speed of the hydraulic motor using the hydraulic oil of Example 12 was more than twice the rated rotation speed of the hydraulic motor. In other words, the high-speed sliding properties of the hydraulic oil of Example 12 were judged to be good (◯). Furthermore, the measurement result of the electrical conductivity of the hydraulic oil of Example 12 was 530 pS / m. Furthermore, in a damage test of a hydraulic oil filter using the hydraulic oil of Example 12, no damage occurred to the hydraulic oil filter. From these results, the hydraulic oil of Example 12 was judged to have good high-speed sliding properties and high electrical conductivity.

[0138] Next, the compositions and effects of the hydraulic oils of Examples 13 to 17 according to the present invention will be explained using Table 4, in comparison with the hydraulic oils of Comparative Examples 7 and 8. Table 4 shows the compositions of the hydraulic oils of Examples 13 to 17 and the hydraulic oils of Comparative Examples 7 and 8 for these examples, the results of a seizure test on a hydraulic motor, the results of electrical conductivity measurements, and the results of a damage test on a hydraulic oil filter.

[0139] [Table 4]

[0140] As a test for the high-speed sliding properties of the hydraulic oils of Examples 13 to 17 and Comparative Examples 7 and 8, a block-on-ring test was conducted to simulate a seizure test of a hydraulic motor in an actual work machine. In the block-on-ring test, a block test piece was pressed against a rotating ring test piece. As test conditions, the load of the block test piece pressed against the ring test piece was set to 50 N. 1 mg of each hydraulic oil was supplied to the sliding portion between the ring test piece and the block test piece. The rotation speed of the ring test piece was increased at a rate of 0.25 m / s, and the rotation speed of the ring test piece at which seizure of both test pieces occurred (hereinafter referred to as the limit rotation speed of the block-on-ring test) was measured. When the limit rotation speed of the block-on-ring test was converted to the limit rotation speed of the above-mentioned hydraulic motor seizure test, if it was more than twice the rated rotation speed of the hydraulic motor, the high-speed sliding properties of the hydraulic oil were judged to be good (good). If the converted value of the limit rotation speed in the block-on-ring test was 1.5 times or more but less than 2.0 times the rated rotation speed, the hydraulic oil was judged to have insufficient high-speed sliding properties (△). Also, if the converted value was less than 1.5 times the rated rotation speed, the hydraulic oil was judged to have insufficient high-speed sliding properties (×). The conversion of the limit rotation speed in the block-on-ring test can be derived, for example, from the correlation between the limit rotation speed in the block-on-ring test and the limit rotation speed in the hydraulic motor seizure test when the same hydraulic oil is used.

[0141] [Example 13] For the hydraulic fluid of Example 13, a Group III mineral oil was used as the base oil, as shown in Table 4. To the base oil, additives were added: N,N-dimethyldecanamide (a compound represented by chemical formula (1)) at a concentration of 0.1 mass%, dioleylhydrogen phosphite (a compound represented by chemical formula (2)) at a concentration of 0.4 mass%, and sorbitan monooleate (a compound represented by chemical formula (3)) at a concentration of 0.2 mass%. In this case, the mass% concentration of the specific additives was 28.6%. Furthermore, detergent-dispersant, antioxidant, load-bearing additive, viscosity index improver, antifoaming agent, and demulsifier were used as other additives.

[0142] The measurement result of the limit rotation speed in the block-on-ring test using the hydraulic oil of Example 13 was 4.58 m / s. This corresponds to a converted value of the limit rotation speed in the block-on-ring test that is more than twice the rated rotation speed of the hydraulic motor. In other words, the high-speed sliding properties of the hydraulic oil of Example 13 were judged to be good (◯).

[0143] [Example 14] For the hydraulic fluid of Example 14, a Group III mineral oil was used as the base oil, as shown in Table 4. To the base oil, additives were added: N,N-dimethyldecanamide (a compound represented by chemical formula (1)) at a concentration of 0.2 mass%, dioleylhydrogen phosphite (a compound represented by chemical formula (2)) at a concentration of 0.8 mass%, and sorbitan monooleate (a compound represented by chemical formula (3)) at a concentration of 0.2 mass%. In this case, the mass% concentration of the specific additives was 16.7%. Furthermore, the same additives as in Example 13 were used as other additives.

[0144] The measurement result of the limit rotation speed in the block-on-ring test using the hydraulic oil of Example 14 was 6.41 m / s. This corresponds to a converted value of the limit rotation speed in the block-on-ring test that is more than twice the rated rotation speed of the hydraulic motor. In other words, the high-speed sliding properties of the hydraulic oil of Example 14 were judged to be good (◯).

[0145] [Example 15] For the hydraulic fluid of Example 15, a Group III mineral oil was used as the base oil, as shown in Table 4. To the base oil, additives were added: N,N-dimethyldecanamide (a compound represented by chemical formula (1)) at a concentration of 0.2 mass%, dioleylhydrogen phosphite (a compound represented by chemical formula (2)) at a concentration of 0.8 mass%, and sorbitan monooleate (a compound represented by chemical formula (3)) at a concentration of 0.4 mass%. In this case, the mass% concentration of the specific additives was 28.6%. Furthermore, the same additives as in Example 13 were used as other additives.

[0146] The measurement result of the limit rotation speed in the block-on-ring test using the hydraulic oil of Example 15 was 5.04 m / s. This corresponds to a converted value of the limit rotation speed in the block-on-ring test that is more than twice the rated rotation speed of the hydraulic motor. In other words, the high-speed sliding properties of the hydraulic oil of Example 15 were judged to be good (◯).

[0147] [Example 16] For the hydraulic fluid of Example 16, a Group III mineral oil was used as the base oil, as shown in Table 4. To the base oil, additives were added: N,N-dimethyldecaneamide (a compound represented by chemical formula (1)) at a concentration of 0.3 mass%, dioleylhydrogen phosphite (a compound represented by chemical formula (2)) at a concentration of 1.2 mass%, and sorbitan monooleate (a compound represented by chemical formula (3)) at a concentration of 0.2 mass%. In this case, the mass% concentration of the specific additives was 11.8%. Furthermore, the same additives as in Example 13 were used as other additives.

[0148] The measurement result of the limit rotation speed in the block-on-ring test using the hydraulic oil of Example 16 was 8.25 m / s. This corresponds to a converted value of the limit rotation speed in the block-on-ring test that is more than twice the rated rotation speed of the hydraulic motor. In other words, the high-speed sliding properties of the hydraulic oil of Example 16 were judged to be good (◯).

[0149] [Example 17] For the hydraulic fluid of Example 17, a Group III mineral oil was used as the base oil, as shown in Table 4. To the base oil, additives were added: N,N-dimethyldecaneamide (a compound represented by chemical formula (1)) at a concentration of 0.3 mass%, dioleylhydrogen phosphite (a compound represented by chemical formula (2)) at a concentration of 1.2 mass%, and sorbitan monooleate (a compound represented by chemical formula (3)) at a concentration of 0.4 mass%. In this case, the mass% concentration of the specific additives was 21.1%. Furthermore, the same additives as in Example 13 were used as other additives.

[0150] The measurement result of the limit rotation speed in the block-on-ring test using the hydraulic oil of Example 17 was 6.41 m / s. This corresponds to a converted value of the limit rotation speed in the block-on-ring test that is more than twice the rated rotation speed of the hydraulic motor. In other words, the high-speed sliding properties of the hydraulic oil of Example 17 were judged to be good (◯).

[0151] Comparative Example 7 For the hydraulic fluid of Comparative Example 7, as shown in Table 4, a Group III mineral oil was used as the base oil. To the base oil, N,N-dimethyldecanamide, a compound represented by chemical formula (1), was added at a concentration of 0.1 mass%, and dioleylhydrogen phosphite, a compound represented by chemical formula (2), was added at a concentration of 0.4 mass%. Furthermore, the same types of additives as those used in Example 13 were used as other additives. Note that the compound represented by chemical formula (3) and the compound represented by chemical formula (4) were not added to the hydraulic fluid of Comparative Example 7. In this case, the mass% concentration of the specific additives was 0.0%.

[0152] The measurement result of the limit rotation speed in the block-on-ring test using the hydraulic oil of Comparative Example 7 was 5.47 m / s. This corresponds to a converted value of the limit rotation speed in the block-on-ring test that is more than twice the rated rotation speed of the hydraulic motor. In other words, the high-speed slidability of the hydraulic oil of Comparative Example 7 was judged to be good (◯). The hydraulic oil of Comparative Example 7 contains the first and second compounds that improve high-speed slidability, but does not contain the third and fourth compounds that improve electrical conductivity, so that the high-speed slidability is improved.

[0153] [Comparative Example 8] For the hydraulic fluid of Comparative Example 8, a Group III mineral oil was used as the base oil, as shown in Table 4. To the base oil, additives were added: N,N-dimethyldecanamide (a compound represented by chemical formula (1)) at a concentration of 0.1 mass%, dioleylhydrogen phosphite (a compound represented by chemical formula (2)) at a concentration of 0.4 mass%, and sorbitan monooleate (a compound represented by chemical formula (3)) at a concentration of 0.4 mass%. In this case, the mass% concentration of the specific additives was 44.4%. Furthermore, the same types of additives as in Example 13 were used as other additives.

[0154] The measurement result of the limit rotation speed in the block-on-ring test using the hydraulic oil of Comparative Example 8 was 3.21 m / s. This corresponds to a converted value of the limit rotation speed in the block-on-ring test that is less than 1.5 times the rated rotation speed of the hydraulic motor. In other words, the hydraulic oil of Comparative Example 8 was judged to have insufficient high-speed slidability (×). The hydraulic oil of Comparative Example 8 had a higher mass % concentration of the specific additive than the hydraulic oils of Examples 13 to 17. From this, it was judged that even if the first compound and second compound that improve high-speed slidability were added, the effect of improving high-speed slidability would be lost if the mass % concentrations of the third compound and fourth compound that improve electrical conductivity were increased.

[0155] It is possible to set the mass % concentration ratio of the specific additive that improves both electrical conductivity and high-speed sliding properties based on the results of the block-on-ring test using the hydraulic oils of Examples 13 to 17 and Comparative Examples 7 and 8. Fig. 4 is a characteristic diagram showing the test results (limit rotation speed) of the block-on-ring test with respect to changes in the mass % concentration ratio of the specific additives, i.e., the first compound, the second compound, the third compound, and the fourth compound.

[0156] When the ratio of the sum of the mass percent concentrations of the third compound and the fourth compound to the total mass percent concentration of the first compound, the second compound, the third compound, and the fourth compound is in the range of 10% or more and less than 30%, the hydraulic oil has good high-speed sliding properties, as shown in Figure 4. Furthermore, in the hydraulic oils of Examples 1 to 12, the ratio of the mass percent concentration of each hydraulic oil is in the range of 10% or more and less than 30%, and both the electrical conductivity and the high-speed sliding properties are excellent.

[0157] On the other hand, if the mass percent concentration is 30% or more, it is expected that the high-speed sliding properties of the hydraulic oil will be insufficient or insufficient, taking into account the hydraulic oil of Comparative Example 8. Also, if the mass percent concentration is less than 10%, there is a concern that even if the high-speed sliding properties of the hydraulic oil are good, it will not be possible to reliably improve the electrical conductivity.

[0158] Therefore, in this embodiment, the ratio of the sum of the mass percentage concentrations of the third compound and the fourth compound to the total sum of the mass percentage concentrations of the first compound, the second compound, the third compound, and the fourth compound is limited to a range of 10% or more and less than 30%, thereby reliably improving both the high-speed sliding properties and the electrical conductivity of the hydraulic oil.

[0159] [Other embodiments] It should be noted that the present invention is not limited to the present embodiment, but includes various modifications. The above-described embodiment has been described in detail to clearly explain the present invention, and the present invention is not necessarily limited to an embodiment having all of the described configurations. It is also possible to add, delete, or replace part of the configuration of the above-described embodiment with other configurations.

[0160] Although an example in which the present invention is applied to a hydraulic excavator has been shown, the present invention can be widely applied to various types of work machines such as hydraulic cranes and wheel loaders in which a hydraulic motor is driven to rotate at high speed by hydraulic oil.

[0161] In the above-described embodiment, an example was shown in which the filter element 41 of the hydraulic oil filter 40 was formed in a cylindrical shape, but a hydraulic oil filter having a plate-shaped filter element is also possible. Also, although an example was shown in which cellulose was used as the material for the filter element 41, various materials such as glass fiber can also be used. [Explanation of symbols]

[0162] 1...hydraulic excavator (work machine), 6...swing hydraulic motor (hydraulic motor), 9...travel hydraulic motor (hydraulic motor), 30...hydraulic motor, 40...hydraulic oil filter

Claims

1. A base oil, A hydraulic oil containing an additive added to the base oil, The additive is a first compound represented by the following chemical formula (1); a second compound represented by the following chemical formula (2); The compound includes at least one compound selected from a third compound represented by the following chemical formula (3) and a fourth compound represented by the following chemical formula (4), a ratio of the sum of the mass percent concentration of the third compound and the mass percent concentration of the fourth compound to the total sum of the mass percent concentration of the first compound, the mass percent concentration of the second compound, the mass percent concentration of the third compound, and the mass percent concentration of the fourth compound is in the range of 10% or more and less than 30%. A hydraulic oil characterized by: 【Chemistry 1】 (In chemical formula (1), R １ is an alkyl or alkenyl group having 8 to 24 carbon atoms, R ２ is an alkyl group or alkenyl group having 8 to 24 carbon atoms or a methyl group, R ３ is a methyl group) 【Chemistry 2】 (In chemical formula (2), R ４ and R ５ one of which is an alkyl or alkenyl group having from 10 to 24 carbon atoms, and the other is a hydrogen atom or an alkyl or alkenyl group having from 10 to 24 carbon atoms. 【Transformation 3】 (In chemical formula (3), R ６ is an acyl group having an alkyl group or an alkenyl group having 8 to 18 carbon atoms, and two R ７ One of the R ７ the other is a hydrogen atom or an acyl group having an alkyl or alkenyl group having 8 to 18 carbon atoms. 【Chemistry 4】 (In the chemical formula (4), two R ８ one of the R is an acyl group having an alkyl or alkenyl group having 8 to 18 carbon atoms, ８ the other is a hydrogen atom or an acyl group having an alkyl or alkenyl group having 8 to 18 carbon atoms.

2. 2. The hydraulic oil of claim 1, R in the chemical formula (1) １ and R ２ At least one of the groups is an alkyl group or an alkenyl group having 10 to 24 carbon atoms. A hydraulic oil characterized by:

3. The hydraulic oil of claim 2, R in the chemical formula (1) １ and R ２ At least one of the groups is an alkyl group or an alkenyl group having 12 to 18 carbon atoms. A hydraulic oil characterized by:

4. 2. The hydraulic oil of claim 1, R in the chemical formula (2) ４ and R ５ At least one of the groups is an alkyl group or an alkenyl group having 12 to 18 carbon atoms. A hydraulic oil characterized by:

5. 2. The hydraulic oil of claim 1, The third compound is a compound represented by the formula (3) ７ are hydrogen atoms, The fourth compound is a compound represented by the formula (4) ８ One of the atoms is a hydrogen atom. A hydraulic oil characterized by:

6. 2. The hydraulic oil of claim 1, Electrical conductivity at an oil temperature of 25°C is 400 pS / m or more A hydraulic oil characterized by:

7. a hydraulic motor that is rotationally driven by the supply of hydraulic oil; a hydraulic oil filter that cleans the hydraulic oil, The hydraulic fluid is the hydraulic fluid according to claim 1. A work machine characterized by:

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