Buffer using a buffer lubricant composition

Abstract

This invention relates to a shock absorber lubricant composition, a shock absorber, and a friction adjustment method for the shock absorber lubricant composition, which can balance operational stability and ride comfort, particularly at low amplitudes. The shock absorber lubricant composition contains a base oil and a friction modifier, the friction modifier containing pentaerythritol ester, wherein the pentaerythritol ester contains pentaerythritol tetraester in a maximum proportion or at a proportion of 50% by mass or more, and the content of pentaerythritol ester is 0.5% by mass or more.

Description

[0001] This case is filed on the date of application. July 3, 2020 Application number is 202080070074.6 The invention is named Buffer Lubricating oil composition, shock absorber, and friction adjustment method for lubricating oil used in shock absorbers. A divisional application of the patent application. Technical Field

[0002] This invention relates to a lubricating oil composition for shock absorbers, a shock absorber, and a method for adjusting the friction of the lubricating oil for shock absorbers. Background Technology

[0003] It is known that the damping force of conventional shock absorbers is the resultant force of the hydraulic damping force generated by the valve and the frictional force generated by the piston rod and oil seal or the piston and cylinder sliding parts. Furthermore, when the shock absorber's damping force is large, operational stability increases, but ride comfort decreases; conversely, when the shock absorber's damping force is small, operational stability decreases, but ride comfort improves. Therefore, in recent years, with a focus on ride comfort, research has been conducted on reducing the shock absorber's damping force by adjusting the friction modifier added to the shock absorber's lubricating oil to reduce the friction of the lubricating oil (e.g., Non-Patent Literature 1).

[0004] Existing technical documents

[0005] Patent documents

[0006] Non-patent literature:

[0007] "Technological Trends and Tribology of Shock Absorbers" (Zhong Xibo, *TRIBOLOGIST*, 2009, Vol. 54, No. 9, p. 598) Summary of the Invention

[0008] The technical problem that the invention aims to solve

[0009] Buffers exhibit damping force through reciprocating motion, but hydraulic damping force takes time to build up. On the other hand, due to the high responsiveness of friction, friction is a significant factor in the damping force of buffers during the transition from a stationary to a sliding state, especially under micro-amplitude conditions. However, if ride comfort is prioritized as in the past, reducing the friction of the buffer lubricant also reduces the damping force, leading to deterioration in operational stability. Especially with the increase in road repairs in recent years, micro-amplitude vibrations are more frequent than normal amplitude vibrations; therefore, a buffer lubricant composition that can balance operational stability and ride comfort under micro-amplitude conditions is needed.

[0010] The present invention provides a buffer lubricant composition, a buffer, and a friction adjustment method for the buffer lubricant, which can balance operational stability and ride comfort, especially at low amplitude.

[0011] Technical means to solve technical problems

[0012] The present invention aims to describe the buffer lubricant compositions described in (1) to (8) below.

[0013] (1) A buffer lubricating oil composition, comprising a base oil and a friction modifier, wherein the friction modifier comprises pentaerythritol ester, wherein the pentaerythritol ester comprises pentaerythritol tetraester in a maximum proportion or at a proportion of 50% by mass or more, and the content of the pentaerythritol ester is 0.5% by mass or more.

[0014] (2) A buffer lubricating oil composition, comprising a base oil and a friction modifier, wherein the friction modifier comprises a pentaerythritol ester, wherein the average number of ester groups of the pentaerythritol ester is greater than 3, and the content of the pentaerythritol ester is 0.5% by mass or more.

[0015] (3) A buffer lubricating oil composition, comprising a base oil and a friction modifier, wherein the friction modifier comprises pentaerythritol ester, wherein the average number of hydroxyl groups of the pentaerythritol ester is less than 1, and wherein the content of the pentaerythritol ester is 0.5% by mass or more.

[0016] (4) A lubricating oil composition for a shock absorber, comprising a base oil and a friction modifier, wherein the friction modifier comprises pentaerythritol ester and the ratio (μ2 / μ1) of the coefficient of friction μ2 at micro amplitude to the coefficient of friction μ1 at normal amplitude is 0.8 or more.

[0017] (5) A lubricating oil composition for a shock absorber, comprising a base oil and a friction modifier, wherein the friction modifier comprises pentaerythritol ester, and the coefficient of friction μ3 of the lubricating oil before coming to a standstill or after just beginning to slide is greater than the coefficient of friction μ4 of the lubricating oil in the sliding state.

[0018] (6) The buffer lubricating oil composition according to any one of (1) to (5) above, wherein the hydroxyl value is 0.5 mg KOH / g or more.

[0019] (7) The buffer lubricating oil composition according to any one of (1) to (6) above, wherein the content of the above pentaerythritol ester is 5% by mass or more.

[0020] (8) The buffer lubricating oil composition according to any one of (1) to (7) above, wherein the friction modifier further contains zinc dithiophosphate.

[0021] In addition, the present invention also aims to describe the buffer described in (9) below.

[0022] (9) A buffer, wherein the buffer lubricating oil composition described in any one of (1) to (8) above is used.

[0023] In addition, the present invention aims to explain the friction adjustment method of the buffer lubricating oil described in (10) to (13) below.

[0024] (10) A friction adjustment method for a buffer lubricating oil, wherein the friction adjustment method is for a buffer lubricating oil containing a base oil and a pentaerythritol ester, and the friction performance at micro-amplitude is adjusted by adjusting the average number of ester groups of the above-mentioned pentaerythritol ester.

[0025] (11) A friction adjustment method for a buffer lubricating oil, wherein the friction adjustment method is a buffer lubricating oil containing a base oil and a pentaerythritol ester, and the friction performance at micro amplitude is adjusted by adjusting the average number of hydroxyl groups of the pentaerythritol ester.

[0026] (12) A friction adjustment method for a buffer lubricant, wherein the friction adjustment method is a buffer lubricant composition containing a base oil and a pentaerythritol ester, wherein the reduction of the above-mentioned pentaerythritol ester is suppressed by adjusting the hydroxyl value of the buffer lubricant.

[0027] (13) A friction adjustment method for a buffer lubricant, wherein the friction adjustment method is a buffer lubricant composition containing a base oil and a pentaerythritol ester, and the friction coefficient of the buffer lubricant is adjusted by adjusting the number of carbon atoms of the fatty acid residues of the pentaerythritol ester.

[0028] Invention Effects

[0029] According to the present invention, a buffer lubricant composition, a buffer, and a method for adjusting friction of the buffer lubricant can be provided, particularly at low amplitudes, to balance operational stability and ride comfort. Attached Figure Description

[0030] Figure 1 This is a schematic diagram showing the relationship between the hydroxyl value of the buffer lubricating oil and the degree of degradation of the buffer oil (working oil).

[0031] Figure 2 A schematic diagram showing the relationship between the coefficient of friction of the buffer lubricant with added ZnDTP and the amount of pentaerythritol added.

[0032] Figure 3 This is a schematic diagram showing the relationship between the reduction rate of ZnDTP and the amount of pentaerythritol added.

[0033] Figure 4 This is a schematic diagram of an example of the friction testing apparatus in this embodiment.

[0034] Figure 5 A schematic diagram showing the relationship between the coefficient of friction of the lubricant used for a shock absorber without ZnDTP and the amount of various friction modifiers added.

[0035] Figure 6 A schematic diagram showing the relationship between the coefficient of friction of the buffer lubricant with added ZnDTP and the amount of various friction modifiers added.

[0036] Figure 7 This is a schematic diagram showing the results of a friction test (comparative example) using a buffer lubricant composition mainly containing pentaerythritol monoester, pentaerythritol dieester, or pentaerythritol triester.

[0037] Figure 8 This is a schematic diagram showing the results of a friction test (example) using a buffer lubricant composition that mainly contains pentaerythritol tetraester.

[0038] Figure 9 This is a schematic diagram showing the variation of the coefficient of friction in a friction test of existing shock absorber lubricating oil.

[0039] Figure 10 This is a graph used to illustrate the amplitude dependence index.

[0040] Figure 11 This is a graph used to illustrate the spike indicator.

[0041] Figure 12 A schematic diagram showing the frictional properties of a shock absorber lubricant corresponding to a ZnDTP type. Detailed Implementation

[0042] The friction adjustment method of the buffer lubricating oil composition, buffer, and buffer lubricating oil of the present invention will be described below with reference to the accompanying drawings. It should be noted that the present invention will be described below using the buffer lubricating oil composition as an example. Furthermore, the terms "micro-amplitude" or "normal amplitude" will be used in the following description. In the present invention, "micro-amplitude" refers to an amplitude of ±1.0 mm or less, and "normal amplitude" refers to an amplitude greater than ±1.0 mm.

[0043] The buffer lubricant according to this embodiment contains (A) a base oil and (B) a friction modifier, wherein (B) the friction modifier contains (B1) zinc dithiophosphate (hereinafter referred to as ZnDTP) and (B2) pentaerythritol.

[0044] (A) Base oil

[0045] The base oil in the buffer lubricant of this embodiment is mineral oil and / or synthetic oil. There are no particular limitations on the types of mineral oil and synthetic oil. Examples of mineral oils include paraffin-based mineral oils, intermediate mineral oils, or cycloalkane-based mineral oils obtained by conventional refining methods such as solvent refining and hydrogenation refining. Examples of synthetic oils include polybutene, polyolefins [α-olefin (co)polymers], various esters (e.g., polyol esters, diesters, phosphate esters, etc.), various ethers (e.g., polyphenylene ethers), alkylbenzenes, alkylnaphthalenes, etc.). In this invention, one of the above-mentioned mineral oils can be used as the base oil, or two or more can be used in combination. Furthermore, one of the above-mentioned synthetic oils can be used, or two or more can be used in combination. Additionally, one or more mineral oils and one or more synthetic oils can be used in combination.

[0046] (B) Friction modifier

[0047] The buffer lubricant of this embodiment contains a friction modifier. The friction modifier is not particularly limited and may contain various anti-friction agents such as phosphorus compounds, amines, or esters. The coefficient of friction of the buffer lubricant can be adjusted by regulating the amount of lubricant added. Furthermore, the friction modifier according to this embodiment, as described below, contains at least (B1) zinc dithiophosphate and (B2) pentaerythritol ester.

[0048] (B1) Zinc dithiophosphate (ZnDTP)

[0049] ZnDTP is generally a compound represented by the following chemical formula 1, which has the function of assisting friction modifiers to adjust the coefficient of friction.

[0050]

[0051] In the above chemical formula 1, R represents a single hydrocarbon group, such as a straight-chain primary alkyl group, a branched secondary alkyl group, or an aryl group.

[0052] Thus, ZnDTP is known to have various types (structures) such as primary alkyl, secondary alkyl, or aryl. The buffer lubricant of this embodiment contains two types of ZnDTP described below.

[0053] That is, the buffer lubricating oil of this embodiment contains ZnDTP as the first type of ZnDTP, as shown in the following formula (1).

[0054]

[0055] In equation (1), R 11 ~R 14 It is an alkyl group, which has primary and secondary alkyl groups. That is, R 11 ~R 14One to three of them are primary alkyl groups, R 11 ~R 14 The remaining portion is a secondary alkyl group.

[0056] In the first type of ZnDTP, the primary alkyl group is not particularly limited, such as methyl, ethyl, n-propyl, n-butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl, n-nonyl, n-decyl, isopentyl, isobutyl, 2-methylbutyl, 2-ethylhexyl, 2,3-dimethylbutyl, 2-methylpentyl, etc., preferably an alkyl group with 4 to 12 carbon atoms (e.g., isobutyl (4 carbon atoms) or 2-ethylhexyl (8 carbon atoms)).

[0057] Furthermore, in the first type of ZnDTP, there are no particular restrictions on the secondary alkyl group, such as isopropyl, sec-butyl, 1-ethylpropyl, 4-methyl-2-pentyl, etc., but alkyl groups with 3 to 6 carbon atoms are preferred (e.g., isopropyl (3 carbon atoms)).

[0058] Furthermore, in the first type of ZnDTP, the ratio of primary alkyl to secondary alkyl groups is not particularly limited, but it is preferable that the ratio of primary alkyl groups is higher than that of secondary alkyl groups.

[0059] The content of the first type of ZnDTP is not particularly limited, but it is preferable to contain 0.1% by mass or more, more preferably 0.4% by mass or more, in the buffer lubricating oil. Furthermore, it is preferable that the content of the first type of ZnDTP in the buffer lubricating oil is 4.0% by mass or less, more preferably 2.0% by mass or less.

[0060] Thus, in the buffer lubricant of the present invention, because it contains a first type of ZnDTP having both primary and secondary alkyl groups, when a friction modifier is added, in addition to being able to easily adjust to a coefficient of friction suitable for ride comfort and handling stability, as described later (refer to friction test 3 and below). Figure 12 Compared to buffer lubricants containing only primary alkyl groups and / or only secondary alkyl groups, this product can suppress fluctuations in the coefficient of friction and further improve ride comfort.

[0061] Furthermore, the buffer lubricant according to this embodiment, as a friction modifier, includes a second type of ZnDTP with a structure different from the first type of ZnDTP. The second type of ZnDTP is represented by the following formula (2).

[0062]

[0063] In equation (2), R 21 ~R 24 It is a secondary alkyl group. That is, the second type of ZnDTP does not contain primary alkyl groups, only secondary alkyl groups.

[0064] The number of carbon atoms of the secondary alkyl group in the second type of ZnDTP is not particularly limited. Examples include isopropyl, sec-butyl, 1-ethylpropyl, 2-ethylhexyl, 4-methyl-2-pentyl, etc. As a secondary alkyl group, it is preferred to be an alkyl group with 3 to 8 carbon atoms (e.g., isopropyl (3 carbon atoms), 2-ethylhexyl (8 carbon atoms), or isobutyl (4 carbon atoms) etc).

[0065] Furthermore, the content of the second type of ZnDTP is not particularly limited, but is preferably less than that of the first type of ZnDTP, and is preferably less than 20% by weight relative to the amount of ZnDTP added (the total amount of the first type of ZnDTP and the second type of ZnDTP).

[0066] It should be noted that the type of alkyl group present in ZnDTP can be determined using known measurement methods. For example, C0.05 can be used. 13 The structure of ZnDTP can be determined by NMR or by FT-IR fingerprinting. Based on the characteristics of the absorption bands of POC and P=SP-S, the alkyl group can be analyzed to determine whether it is a primary or secondary alkyl group, thus determining the structure of ZnDTP.

[0067] Furthermore, as a dithiophosphate, the presence of a second type of ZnDTP having only secondary alkyl groups further improves ride comfort compared to the case containing only the first type of ZnDTP. Specifically, compared to the case containing only the first type of ZnDTP, slight vibrations during driving can be further reduced. Moreover, by using a second type of ZnDTP having secondary alkyl groups with 3 to 8 carbon atoms, the difference between the coefficient of friction at micro-amplitude (low speed) and normal amplitude (high speed) can be reduced, thereby improving ride comfort.

[0068] (B2) Pentaerythritol Ester

[0069] Pentaerythritol esters are tetravalent sugar alcohols, compounds obtained by forming ester bonds between the hydroxyl groups of the terminal substituents of pentaerythritol and fatty acid residues. Pentaerythritol esters include pentaerythritol tetraesters, in which all four terminal substituents form ester bonds with fatty acid residues, and partially esterified pentaerythritol monoesters, pentaerythritol diesters, and pentaerythritol triesters, in which any terminal substituent forms ester bonds with fatty acid residues.

[0070] In the pentaerythritol ester of the present invention, the fatty acid residues are not particularly limited, and may be, for example, C6 to C22 fatty acid residues such as stearic acid residues and oleic acid residues. Furthermore, examples of fatty acid residues include caprylic acid, capric acid, oleic acid, stearic acid, myristic acid, palmitic acid, linoleic acid, adipic acid, nonanoic acid, tall oil fatty acid, palm fatty acid, coconut oil fatty acid, and tallow fatty acid.

[0071] The coefficient of friction of shock absorber lubricants can be adjusted by regulating the number of carbon atoms in the fatty acid residues of pentaerythritol esters. Specifically, the more carbon atoms in the fatty acid residues of pentaerythritol esters, the lower the coefficient of friction of the shock absorber lubricant tends to be; conversely, the fewer carbon atoms in the fatty acid residues, the higher the coefficient of friction. Therefore, to achieve the desired coefficient of friction in shock absorber lubricants, pentaerythritol esters can be selected based on the number of carbon atoms in their fatty acid residues. Furthermore, the coefficient of friction of shock absorber lubricants can be adjusted by combining multiple pentaerythritol esters with different numbers of carbon atoms in their fatty acid residues. For example, the coefficient of friction of shock absorber lubricants can also be adjusted by regulating the proportions of pentaerythritol esters with fewer carbon atoms and pentaerythritol tetraesters with more carbon atoms in their fatty acid residues.

[0072] In the buffer lubricant of the present invention, pentaerythritol ester is characterized by being "primarily pentaerythritol tetraester". Here, "primarily pentaerythritol tetraester" means that among pentaerythritol monoester, pentaerythritol diester, pentaerythritol triester, and pentaerythritol tetraester, pentaerythritol tetraester, the proportion of pentaerythritol tetraester is the highest, or the content of pentaerythritol tetraester is 50% or more.

[0073] Furthermore, in the manufacture of pentaerythritol tetraester, it is technically difficult to produce only pentaerythritol tetraester; it is often mixed with pentaerythritol monoester, pentaerythritol diester, pentaerythritol triester, etc. Therefore, in practice, even products commercially available as "pentaerythritol tetraester" are not composed solely of pentaerythritol tetraester, but rather primarily contain pentaerythritol tetraester, but also pentaerythritol triester, pentaerythritol diester, or pentaerythritol monoester, etc. Therefore, pentaerythritol esters commercially available as "pentaerythritol tetraester" can be defined as pentaerythritol esters that are "primarily pentaerythritol tetraester" in this invention.

[0074] Furthermore, pentaerythritol esters that are "primarily pentaerythritol tetraesters" can also be defined as follows: For pentaerythritol esters that, in addition to pentaerythritol tetraesters, also contain pentaerythritol triesters, pentaerythritol diesters, pentaerythritol monoesters, etc., the number of ester groups can be measured. Pentaerythritol esters with an average number of ester groups greater than 3 are considered to be pentaerythritol esters that are "primarily pentaerythritol tetraesters." Additionally, for pentaerythritol esters, the number of hydroxyl groups can also be measured. Pentaerythritol esters with an average number of hydroxyl groups less than 1 are considered to be pentaerythritol esters that are "primarily pentaerythritol tetraesters." The average number of ester groups or hydroxyl groups in pentaerythritol esters can be determined using, for example, gas chromatography-mass spectrometry (GC-MS) or liquid chromatography-mass spectrometry (LC-MS).

[0075] Furthermore, the buffer lubricant of this embodiment, as a pentaerythritol ester, mainly contains pentaerythritol tetraester without hydroxyl groups, but also contains a portion of pentaerythritol triester, pentaerythritol diester, and pentaerythritol monoester containing hydroxyl groups. The hydroxyl value of the pentaerythritol containing these hydroxyl groups is preferably 0.5 mg KOH / g or more, more preferably 1.0 mg KOH / g or more, and even more preferably 1.5 mg KOH / g or more.

[0076] By ensuring the hydroxyl value of the buffer lubricant is above 0.5 mg KOH / g, the decomposition of pentaerythritol (which leads to the deterioration of the buffer lubricant) can be inhibited, thus improving the wear resistance of the buffer lubricant. Figure 1 This is a schematic diagram showing the relationship between the hydroxyl value of the buffer lubricating oil and the degree of degradation of the buffer lubricating oil. It should be noted that... Figure 1 In the examples, by adjusting the amount of pentaerythritol ester added, as shown in Table 1 below, the deterioration degree of buffer lubricants with a hydroxyl value of 0 mg KOH / g (sample 1), 0.58 mg KOH / g (sample 2), 1.16 mg KOH / g (sample 3), and 1.74 mg KOH / g (sample 4) was measured. The deterioration degree of the buffer lubricants was determined using a FALEX-LFW1 block-on-ring friction and wear testing machine. 250 ml of each of the above buffer lubricants was supplied to the sliding part, and the parts were slid under conditions of 0.6 m / s speed and 6581 N load. After performing the equivalent of 2 million buffer operations, the sludge was removed using a centrifuge, and the lubricant of each buffer was measured.

[0077] [Table 1]

[0078]

[0079] like Figure 1 As shown in Table 1 above, increasing the amount of pentaerythritol ester to achieve a hydroxyl value of 0.58 mgKOH / g for the buffer lubricant allows for a 55% reduction in degradation even after 2 million buffer operations. Furthermore, further increasing the amount of pentaerythritol ester to achieve a hydroxyl value of 1.74 mgKOH / g results in a degradation rate of 9.1% (less than 10%) after 2 million buffer operations. This demonstrates that a higher hydroxyl value in the buffer lubricant leads to lower degradation. Specifically, from the perspective of suppressing degradation, a hydroxyl value of 0.5 mgKOH / g or higher is preferred, more preferably 1.0 mgKOH / g or higher, and even more preferably 1.5 mgKOH / g or higher.

[0080] Next, the content of pentaerythritol ester will be explained. In the buffer lubricating oil of this embodiment, pentaerythritol ester is contained at least 0.5% by mass, more preferably at least 1.0% by mass. Here, Figure 2 This is a schematic diagram showing the relationship between the coefficient of friction of a buffer lubricant with added ZnDTP and the content of pentaerythritol ester. (Example) Figure 2 As shown, when the content of pentaerythritol ester is 0.2% by mass or more, the coefficient of friction of the buffer lubricant containing ZnDTP remains unchanged and converges to the range of 0.02 to 0.05. Thus, by ensuring the content of pentaerythritol ester is 0.2% by mass or more, changes in the coefficient of friction of the buffer lubricant containing ZnDTP can be suppressed. Therefore, in the buffer lubricant of this embodiment, considering the decomposition of pentaerythritol ester, the content of pentaerythritol ester is 0.5% by mass or more, preferably 1.0% by mass or more.

[0081] Furthermore, the lubricating oil for the shock absorber is more preferably composed of pentaerythritol ester at 2.0% by mass or more. When pentaerythritol ester is absent, ZnDTP decreases due to decomposition, etc., thus increasing the coefficient of friction of the shock absorber lubricating oil and leading to wear. Here, Figure 3 This is a schematic diagram showing the relationship between the reduction rate of ZnDTP and the amount of pentaerythritol ester added. Additionally, in... Figure 3 In the example, with Figure 1 Similarly, using a FALEX-LFW1 ring-block friction and wear testing machine, 250 ml of lubricating oil additive was provided to the sliding part. The part was slid under conditions of 0.6 m / s speed and 6581 N load. After performing the equivalent of 2 million shock cycles, the sludge was removed using a centrifuge, and the ZnDTP content was measured using FT-IR. Figure 3 As shown, without the addition of pentaerythritol ester, ZnDTP was found to decrease by approximately 80% in the equivalent of 2 million buffer operations. In contrast, with the addition of 0.5% by mass of pentaerythritol ester, the reduction of ZnDTP was suppressed to approximately 55% in the equivalent of 2 million buffer operations; with the addition of 1.0% by mass of pentaerythritol ester, the reduction was suppressed to approximately 25% in the equivalent of 2 million buffer operations; and with the addition of 2.0% by mass of pentaerythritol ester, the reduction was suppressed to approximately 9% in the equivalent of 2 million buffer operations. Thus, by including more than 2.0% by mass of pentaerythritol ester in the buffer lubricant, the reduction of ZnDTP can be effectively suppressed, thereby inhibiting the deterioration of the buffer lubricant.

[0082] Furthermore, the lubricating oil for the buffer in this embodiment preferably contains 5.0% by mass or more pentaerythritol ester. For example... Figure 1 As illustrated, in order to suppress the deterioration of the buffer lubricating oil, the hydroxyl value of the buffer lubricating oil is preferably 0.5 mg KOH / g or more. However, the pentaerythritol ester contained in the buffer lubricating oil of this embodiment is mainly pentaerythritol tetraester without hydroxyl groups. In order to make the hydroxyl value of the buffer lubricating oil 0.5 mg KOH / g or more, the content of pentaerythritol ester is preferably 5% by mass or more.

[0083] Example

[0084] Next, an example of the buffer lubricant of this embodiment will be described.

[0085] [Friction Testing Apparatus 10]

[0086] Figure 4 This is a structural diagram of the friction testing apparatus 10 used in the friction test in this embodiment. The friction testing apparatus 10 is a pin-on-disc friction testing apparatus. An electromagnetic vibrator 3 causes a disc-shaped test piece 2 fixed on a sliding bearing 1 to reciprocate, and a strain gauge 6 mounted on a fixed shaft 5 of the pin-shaped test piece 4 measures the frictional force generated when the pin-shaped test piece 4 slides under pressure. Furthermore, since the combination of the buffer lubricant and oil seal is a factor affecting the friction performance of the buffer, therefore, in Figure 4 In the friction testing apparatus 10 shown, acrylonitrile-butadiene rubber (NBR) used as an oil seal is applied to the needle-shaped test piece 4 in the buffer. The top of the needle-shaped test piece 4 is cut at a 140° angle to match the shape of the oil lip. Furthermore, the disc-shaped test piece 2 uses the same hard chrome plating applied to the piston rod surface. It should be noted that, in this embodiment, although the frictional force (coefficient of friction) between the NBR needle-shaped test piece 4 and the chrome-plated disc-shaped test piece 2 is measured, the frictional force (coefficient of friction) between the copper ball and the chrome-plated disc-shaped test piece 2 can also be measured.

[0087] [Friction Test 1]

[0088] First, in friction test 1, using friction testing apparatus 10, under conditions of amplitude ±0.2 mm, frequency 1.5 Hz, load 20 N, and temperature 30 °C, the average coefficient of friction was measured by reciprocating the needle-type test piece 4 and the disc-type test piece 2. Furthermore, in friction test 1, the coefficient of friction was measured in buffer lubricating oil with various friction modifiers such as phosphorus, amine, or ester, with and without the addition of 1% ZnDTP. Figure 5 The coefficient of friction for the shock absorber with lubricant but without added ZnDTP is shown. Figure 6The coefficient of friction of the shock absorber lubricant with added ZnDTP is shown. When the coefficient of friction of the shock absorber lubricant is too low, operational stability deteriorates; when the coefficient of friction is too high, ride comfort deteriorates. Therefore, the coefficient of friction is preferably adjusted to the range of 0.02 to 0.05. Conventionally, the coefficient of friction is adjusted by adjusting the amount of friction modifier added, but... Figure 5 As shown, without the addition of ZnDTP, it is difficult to adjust the coefficient of friction using friction modifiers alone. In contrast, as... Figure 6 As shown, with the addition of ZnDTP, the coefficient of friction can be easily adjusted according to the amount of friction modifier added, and the coefficient of friction can be adjusted to the target value range of 0.02 to 0.05.

[0089] Thus, in the shock absorber lubricant of the present invention, since the friction modifier contains ZnDTP, the coefficient of friction of the shock absorber lubricant can be adjusted to a range of 0.02 to 0.05 that can balance operational stability and ride comfort, thereby making it possible to balance operational stability and ride comfort.

[0090] [Friction Test 2]

[0091] In friction test 2, using the aforementioned friction testing apparatus 10, the friction coefficient of the buffer lubricating oil was measured under the following conditions: two amplitudes (micro-amplitude ±0.2 mm) and normal amplitude (amplitude ±2.0 mm), a frequency of 1.5 Hz, a load of 20 N, and a temperature of 30 °C. Furthermore, in friction test 2, a test was conducted where only the type of pentaerythritol ester added to the buffer lubricating oil was changed. The test results are shown below. Figure 7 and Figure 8 It should be noted that, in Figure 7 (A) to (C) show the test results (comparative examples) of buffer lubricants containing pentaerythritol esters, primarily pentaerythritol monoester, pentaerythritol dieester, or pentaerythritol triester. Furthermore, Figure 8 (D) to (F) show the results (examples) of adding pentaerythritol ester, which mainly contains pentaerythritol tetraester, to the buffer lubricant of this embodiment. It should be noted that... Figure 7 and Figure 8 In the reciprocating sliding of the buffer, the buffer in the outward sliding direction is represented by positive values ​​for the frictional force of the lubricating oil and the amplitude of the buffer, while the buffer in the return sliding direction is represented by negative values ​​for the frictional force of the lubricating oil and the amplitude of the buffer. Typically, such as... Figure 9 The frictional properties of the buffer with lubricating oil shown are represented by a cyclic graph.

[0092] like Figure 7As shown in (A) to (C), in the shock absorber lubricant (comparative example) that does not primarily contain pentaerythritol tetraester, the coefficient of friction is relatively small at micro-amplitude and relatively large at normal amplitude. This indicates that in the shock absorber lubricant (comparative example) that does not primarily contain pentaerythritol tetraester, the coefficient of friction tends to increase with the amplitude. This means that at micro-amplitude, sufficient operational stability cannot be achieved due to the low friction; on the other hand, at normal amplitude, excessive friction may reduce ride comfort.

[0093] In comparison, such as Figure 8 As shown in (D) to (F), in the buffer lubricant of this embodiment, which mainly contains pentaerythritol tetraester, the coefficient of friction at micro-amplitude is the same as that at normal amplitude. Therefore, in the buffer lubricant of this embodiment (Example), which mainly contains pentaerythritol tetraester, since the same frictional force as at normal amplitude can be obtained even at micro-amplitude, the operational stability at micro-amplitude can be improved. Furthermore, at micro-amplitude, since the vibration input to the buffer itself is small, even if the frictional force is larger than that of the comparative example, riding comfort can be ensured. That is, in the buffer lubricant of this embodiment (Example), which mainly contains pentaerythritol tetraester, both operational stability and riding comfort can be taken into account at micro-amplitude.

[0094] Furthermore, in the buffer lubricant of this embodiment (Example), which mainly contains pentaerythritol tetraester, with... Figure 7 Compared to the buffer lubricant shown (comparative example), the coefficient of friction is lower under normal amplitude conditions. This is because, in the buffer lubricant (example) which mainly contains pentaerythritol tetraester, when driving on roads with poor conditions or other conditions that generate large amplitude, the friction is lower than in the comparative example, which means that the damping force can be reduced and the ride comfort can be improved.

[0095] Furthermore, in the buffer lubricating oil of this embodiment, which mainly contains pentaerythritol tetraester, such as Figure 10As shown, when the coefficient of friction under micro-amplitude is set as μ2 and the coefficient of friction under normal amplitude is set as μ1, the ratio (μ2 / μ1) of the coefficient of friction under micro-amplitude to the coefficient of friction under normal amplitude is close to 1. In this invention, this ratio (μ2 / μ1) is called the amplitude dependence index. For various shock absorber lubricants that mainly contain pentaerythritol tetraester, the calculated amplitude dependence index (μ2 / μ1) is 0.8 or higher, more preferably 0.8 to 1.2. Therefore, as a shock absorber lubricant containing pentaerythritol, as long as the amplitude dependence index is 0.8 or higher, more preferably 0.8 to 1.2, the operational stability under micro-amplitude can be improved, and the ride comfort under normal amplitude can also be improved.

[0096] Furthermore, friction test 2 shows that the lubricating oil for the shock absorber in this embodiment can improve operational stability by increasing tire grip. That is, compared with... Figure 7 Compared to the buffer shown, which was lubricated with oil (comparative example), in... Figure 8 The buffer lubricant of this embodiment (Example) mainly contains pentaerythritol tetraester, as shown in the example. Figure 11 As shown in P1 to P4, under normal amplitude, the frictional force is higher at P1 and P3 before the transition from the sliding state to the stationary state, and at P2 and P4 immediately after the transition from the stationary state to the sliding state than it is in the sliding state. Thus, by setting the amplitude dependence index to 0.8 or higher, more preferably 1 or higher, the frictional force at P1 and P3 before the transition from the sliding state to the stationary state, and at P2 and P4 immediately after the transition from the stationary state to the sliding state, can be increased, thereby improving the damping force during the state transition process. Furthermore, since the frictional force of the damper with lubricating oil increases before the transition to stationary state and immediately after the start of sliding, the damping force can take effect immediately even if the sliding direction changes, thereby enabling the tire's grip to be effective and improving tire traction.

[0097] [Friction Test 3]

[0098] Furthermore, in friction test 3, under conditions of amplitude ±0.1 mm, frequency 5 Hz, 20 N, and 30 °C, the needle-shaped test piece 4 and the disc-shaped test piece 2 were reciprocated, and the coefficient of friction of the buffer lubricating oil was measured. Furthermore, in friction test 3, such as... Figure 12As shown, in addition to Example 1, which is a buffer lubricant (a buffer lubricant containing a first type of ZnDTP having primary and secondary alkyl groups) according to this embodiment, the coefficients of friction of Comparative Examples 1 to 4 were also measured. Comparative Example 1 is an example of a buffer lubricant containing ZnDTP having only primary alkyl groups with 3 or 5 carbon atoms; Comparative Example 2 is an example of a buffer lubricant containing ZnDTP having only secondary alkyl groups with 3 or 5 carbon atoms; Comparative Example 3 is an example of a buffer lubricant containing ZnDTP having only secondary alkyl groups with 6 or 8 carbon atoms; and Comparative Example 4 is an example of a buffer lubricant containing ZnDTP having only primary alkyl groups with 8 carbon atoms. Furthermore, Comparative Example 5 is an example of a buffer lubricant containing a mixture of ZnDTP having only secondary alkyl groups with 3 or 6 carbon atoms and ZnDTP having only primary alkyl groups with 8 carbon atoms in a 1:1 ratio.

[0099] Furthermore, in friction test 3, the maximum and average coefficients of friction for Examples 1 and Comparative Examples 1-5 were measured at various ZnDTP addition amounts (wt%). The maximum / average coefficient of friction was calculated, and the calculated values ​​were plotted based on the ZnDTP addition amount (wt%).

[0100] Figure 12 The results of friction test 3 are illustrated below. The closer the ratio of maximum friction coefficient to average friction coefficient is to 1, the smaller the fluctuation rate of the friction coefficient, which can be considered an indication of good ride comfort. According to... Figure 12 The results show that in Comparative Examples 1-5, when the amount of ZnDTP added was 1.0 wt% or less, the value of the maximum friction coefficient / average friction coefficient was significantly increased compared to Example 1. Even when the amount of ZnDTP added was 1.0 wt% or more, the value of the maximum friction coefficient / average friction coefficient was still higher than that of Example 1. In contrast, in Example 1, compared to Comparative Examples 1-5, the ratio of the maximum friction coefficient to the average friction coefficient generally tended to decrease, especially when the amount of ZnDTP added was 0.5-1.0 wt%, the value of the maximum friction coefficient / average friction coefficient was significantly reduced compared to Comparative Examples 1-5.

[0101] Furthermore, in Example 1, when the amount of ZnDTP added was 0.1 to 4.0% by weight, the ratio of the maximum coefficient of friction to the average coefficient of friction was 1.3 or less, and when it was 0.25 to 2.0% by weight, the ratio was even lower, down to 1.22 or less. Therefore, it can be seen that in the shock absorber lubricant containing the first type of ZnDTP having primary and secondary alkyl groups in this embodiment, by adding 0.25 to 2.0% by weight of ZnDTP, ride comfort is further improved.

[0102] Furthermore, friction test 3 showed that in Comparative Examples 1-5, compared to Example 1, the maximum friction coefficient / average friction coefficient ratio tended to change when the amount of ZnDTP added changed. In contrast, in Example 1, the maximum friction coefficient / average friction coefficient ratio did not easily change even when the amount of ZnDTP added changed. For example, in Example 1, the maximum friction coefficient / average friction coefficient ratio remained below 1.24 even when the amount of ZnDTP added was between 0.2% and 4.0% by weight. Therefore, it can be concluded that in the first type of ZnDTP containing primary and secondary alkyl groups in this embodiment, even when the ZnDTP content decreases due to prolonged use and deterioration (decomposition), the ride comfort remains relatively stable compared to Comparative Examples 1-5.

[0103] Furthermore, in order to improve ride comfort, in the buffer lubricant of the present invention (Example 1), in order to clarify whether it is necessary to use a buffer lubricant containing both primary and secondary alkyl ZnDTP (first type ZnDTP), or whether a buffer lubricant containing a mixture of primary and secondary alkyl ZnDTP can be used, a friction test was conducted using a buffer lubricant containing a mixture of primary and secondary alkyl ZnDTP as Comparative Example 5. The results showed that in Comparative Example 5, the value of the maximum coefficient of friction / average coefficient of friction could not be reduced as in Example 1, and ride comfort could not be improved. Therefore, it can be concluded that the effect of the buffer lubricant containing both primary and secondary alkyl ZnDTP (first type ZnDTP) of the buffer lubricant of this embodiment (Example 1) cannot be achieved by simply using a buffer lubricant containing both primary and secondary alkyl ZnDTP.

[0104] Thus, in the shock absorber lubricant of this embodiment, there is (A) a base oil and (B) a friction modifier. The (B) friction modifier contains a first type of ZnDTP having primary and secondary alkyl groups (C). In addition to being easily adjustable to a coefficient of friction suitable for ride comfort and handling stability when the friction modifier is added, the friction modifier can suppress fluctuations in the coefficient of friction and further improve ride comfort compared to shock absorber lubricants having only primary alkyl groups and / or only secondary alkyl groups.

[0105] [Driving Test 1]

[0106] In addition, a comparison was conducted between a vehicle equipped with a shock absorber lubricant that does not primarily contain pentaerythritol tetraester (comparative example) and a vehicle equipped with a shock absorber lubricant that primarily contains pentaerythritol tetraester (example), with all conditions except the shock absorbers being the same and driving along the same driving path, by a professional driver and an ordinary driver.

[0107] The results show that on roads with minimal bumps, compared to the comparative example, using a shock absorber lubricant primarily containing pentaerythritol tetraester (Example) resulted in improved tire and chassis system performance, tire grip, and maneuverability. This improvement is noticeable not only to professional drivers but also to ordinary drivers. Furthermore, when using a shock absorber lubricant primarily containing pentaerythritol tetraester (Example), the increased damping force allows for easier transmission of information about minor road imperfections to the driver, providing a greater range of information.

[0108] The preferred embodiments of the present invention have been described above, but the technical scope of the present invention is not limited to the embodiments described above. Various changes and modifications can be made to the above embodiments, and forms with such changes or modifications are also included within the technical scope of the present invention.

Claims

1. A buffer using a buffer lubricating oil composition, wherein, The buffer lubricating oil composition contains a base oil and a friction modifier. The friction modifier contains pentaerythritol ester and zinc dithiophosphate. The pentaerythritol ester contains pentaerythritol tetraester in the highest proportion or at a content of more than 50% by mass. The content of the pentaerythritol ester is 5% by mass or more.

2. The buffer using a buffer lubricating oil composition according to claim 1, wherein, The pentaerythritol ester has an average number of ester groups greater than 3.

3. The buffer using a buffer lubricating oil composition according to claim 1, wherein, The average number of hydroxyl groups in the pentaerythritol ester is less than 1.

4. The buffer using a buffer lubricating oil composition according to claim 1, wherein, The hydroxyl value of the lubricating oil composition for the buffer is 0.5 mg KOH / g or higher.

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