Shock absorbers and hydraulic fluid for shock absorbers

Abstract

This shock absorber: includes a bottomed-tubular cylinder and an acrylonitrile-butadiene-rubber-containing seal member disposed at the opening of said cylinder; and has hydraulic oil encapsulated in the cylinder. The shock absorber is characterized in that: the hydraulic oil comprises a base oil and an additive added to the base oil; and the base oil comprises a first fluid that has a first viscosity and that is a plant-derived oil or fat in which the number of molecules of polyunsaturated fatty acid groups included in the total amount of triglycerides contained in said oil or fat is greater than the number of molecules of monounsaturated fatty acid groups, and a second fluid that contains a fatty acid ester and that has a second viscosity lower than the first viscosity.

Description

Technical Field

[0001] The present invention relates to a shock absorber and a hydraulic oil for use in a shock absorber. This application claims priority based on Japanese Patent Application No. 2023-087631 filed in Japan on May 29, 2023, the content of which is incorporated herein by reference.

Background Art

[0002] Patent Document 1 discloses a liquid composition useful as an insulating fluid, which contains a mixture of a natural glyceride and at least one fatty acid ester different from triglyceride, and the fatty acid of the fatty acid ester contains a fatty acid derived from at least one vegetable oil or an equivalent natural resource. Patent Document 1 describes that 70 to 85% of the fatty acids constituting the mixture of the natural glyceride and the fatty acid ester is oleic acid, and it is possible to use genetically modified high-oleic acid, canola oil, soybean oil, sunflower oil, etc.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Conventionally, a hydraulic oil for a shock absorber that has a small environmental impact, excellent lubricity and wear resistance, and does not cause problems such as oil leakage has been desired. In shock absorbers, hydraulic oils based on mineral oil have conventionally been used. However, considering the environmental impact, vegetable-based hydraulic oils can be considered as alternative oils. However, when acrylonitrile-butadiene rubber is used for the seal material of the shock absorber, since the polarity of vegetable oil is closer to the polarity of butadiene rubber than the polarity of mineral oil, the seal material may swell. In addition, since vegetable oil has a high viscosity, it may not be directly applicable as a hydraulic oil.

[0005] The present invention provides a shock absorber and a shock absorber hydraulic fluid that have a low environmental impact, can suppress swelling of the oil seal member, and have good lubricity due to their low viscosity. [Means for solving the problem]

[0006] According to one aspect of the present invention, the buffer includes a bottomed cylindrical cylinder and an oil seal member containing acrylonitrile butadiene rubber at the opening of the cylinder, with hydraulic fluid sealed inside the cylinder. The hydraulic fluid includes a base oil and additives added to the base oil, the base oil being a plant-derived oil or fat in which the number of polyunsaturated fatty acid groups contained in the total amount of triglycerides is greater than the number of monounsaturated fatty acid groups. This base oil includes a first fluid having a first viscosity and a second fluid containing fatty acid esters and having a second viscosity lower than the first viscosity. [Effects of the Invention]

[0007] According to this disclosure, a buffer equipped with an acrylonitrile butadiene rubber oil seal material can be provided that can suppress swelling of the oil seal material and has excellent sealing properties for hydraulic fluid. Furthermore, by using a base oil that contains a first fluid of plant-derived oil or fat in which the number of polyunsaturated fatty acid groups in the total amount of triglycerides is greater than the number of monounsaturated fatty acid groups, and a second fluid with lower viscosity that contains fatty acid esters, a buffer equipped with hydraulic fluid that has excellent lubricity and low environmental impact can be provided. [Brief explanation of the drawing]

[0008] [Figure 1] This is a cross-sectional view showing the overall configuration of a hydraulic shock absorber according to the first embodiment of the present invention. [Modes for carrying out the invention]

[0009] The shock absorber as a hydraulic buffer according to the first embodiment of the present invention will be described below. The embodiments described below are provided to better illustrate the spirit of the invention and do not limit the present invention unless otherwise specified. Furthermore, the drawings used in the description of the embodiments below have been scaled appropriately to make each part easier to see.

[0010] Figure 1 is a longitudinal cross-sectional view showing a twin-tube hydraulic shock absorber according to the first embodiment of the present invention. The hydraulic shock absorber 1 has a twin-tube cylinder 4 consisting of a bottomed cylindrical outer cylinder 2 and a bottomed cylindrical inner cylinder 3 coaxially provided inside the outer cylinder 2. A piston rod 5 is inserted into the cylinder 4 so as to be able to reciprocate along the axial direction of the cylinder 4, with one end 5a inserted into the inner cylinder 3 and the other end protruding outward from the cylinder 4 by a predetermined length. A piston 6 is fixed to one end 5a of the piston rod 5 so as to be able to move within the inner cylinder 3 in the axial direction of the inner cylinder 3 while sliding along the inner surface of the inner cylinder 3. Figure 1 shows the hydraulic shock absorber 1 with the axes of the outer cylinder 2, inner cylinder 3, and piston rod 5 oriented vertically, the bottoms of the outer cylinder 2 and inner cylinder 3 drawn downwards, and the other end of the piston rod 5 protruding outward from the inner cylinder 3 drawn upwards.

[0011] The piston 6 has the function of dividing the inside of the inner cylinder 3 into oil chamber A and oil chamber B, and is configured such that the volumes of oil chamber A and oil chamber B change in accordance with the movement of the piston 6 inside the inner cylinder 3. A reservoir chamber C is provided on the inner circumference side of the outer cylinder 2 and the outer circumference side of the inner cylinder 3, which is defined by the outer cylinder 2 and the inner cylinder 3. Oil chamber A, oil chamber B, and reservoir chamber C are filled with hydraulic fluid 7 for the shock absorber, which will be described in detail later. The piston 6 has multiple passages that communicate with oil chamber A and oil chamber B, and damping force generating devices 8 and 9 incorporating valve mechanisms are provided in these passages. As the piston 6 moves within the inner cylinder 3 and the volumes of oil chamber A and oil chamber B change, the hydraulic fluid 7 for the shock absorber moves between oil chamber A and oil chamber B through the passages inside the piston. As a result, the piston 6 generates a damping force against the movement of the piston rod 5.

[0012] As shown in Figure 1, the bottom of the inner cylinder 3 is closed by a bottom wall member 12 containing a bottom valve 11, and the bottom of the outer cylinder 2 is closed by a bottom wall 13. The bottoms of the inner cylinder 3 and the outer cylinder 2 are positioned close together, and the bottom wall member 12 is installed so as to overlap the bottom wall 13. A communication chamber 14 is formed between the bottom wall member 12 and the bottom wall 13. This communication chamber 14 is connected to the reservoir chamber C via a flow path member 15. The communication chamber 14 is also connected to the oil chamber A via the bottom valve 11. When the piston 6 moves towards the bottom wall member 12, the system is configured so that the buffer hydraulic fluid 7 can move from the oil chamber A to the reservoir chamber C via the bottom valve 11, the communication chamber 14, and the flow path member 15. Furthermore, when the piston 6 moves away from the bottom wall member 12, the system is configured so that the buffer hydraulic fluid 7 can move from the reservoir chamber C to the oil chamber A via the flow path member 15, the connecting chamber 14, and the bottom valve 11.

[0013] The upper end of the inner cylinder 3 is sealed liquid-tightly by an oil seal member 17 containing acrylonitrile butadiene rubber (NBR) which is integrated with the lid 16. A through-hole is formed in the center of the lid 16, and a piston rod 5 is provided so as to pass through this through-hole. An annular oil seal member 17 is provided on the inner circumference side of the through-hole, in contact with the outer surface of the piston rod 5. In this specification, acrylonitrile butadiene rubber may be referred to as nitrile rubber, and unless otherwise specified, the term "nitrile rubber" in this specification refers to acrylonitrile butadiene rubber. In the configuration shown in Figure 1, a rod guide 10 is provided inside the oil seal member 17 and within the upper end of the inner cylinder 3. The rod guide 10 has a cylindrical inner circumference 10a and a cylindrical outer circumference 10b, and is positioned so that the inner circumference 10a contacts the outer surface of the piston rod 5 and the outer circumference 10b contacts the inner circumference of the upper end of the outer cylinder 2. The rod guide 10 is in liquid-tight contact with the piston rod 5 at the inner circumference 10a but allows the piston rod 5 to reciprocate.

[0014] A ring-shaped cover 16 and an oil seal member 17 are integrally attached to the upper end of the outer cylinder 2 shown in Figure 1. The rod guide 10 is held in place by this cover 16. The piston rod 5 passes through the cover 16 and protrudes to the outside of the inner cylinder 3. An oil seal member 17 is integrally provided with the cover 16 to close the gap between the inner circumference of the cover 16 and the outer circumference of the piston rod 5.

[0015] The buffer hydraulic fluid 7 of the first embodiment is a plant-derived oil in which the number of polyunsaturated fatty acid groups contained in the total amount of triglycerides is 30% or more. The buffer hydraulic fluid 7 is mainly composed of a base oil consisting of a first fluid having a first viscosity and a second fluid containing fatty acid esters and having a second viscosity lower than the first viscosity. The fatty acid ester contained in the second fluid is a fatty acid ester derived from fatty acids that constitute the triglycerides contained in plant-derived oils and fats. Preferably, the plant-derived oils and fats that constitute the first and second fluids are the same plant oil. The ratio of the first fluid to the second fluid is such that the kinematic viscosity (at 40°C) of the base oil is between 8 mPaS and 15 mPaS. The ratio of the first fluid to the second fluid is, for example, in the range of 70:30 to 50:50.

[0016] The first fluid is a vegetable oil containing 50% or more polyunsaturated fatty acids (such as linoleic acid and leleic acid) that have two or more double bonds, meaning that the polyunsaturated fatty acid content is greater than the total content of other fatty acids. For example, soybean oil and sunflower oil are more desirable. Soybean oil and sunflower oil have lower viscosity than other vegetable oils, making it possible to reduce the amount of fatty acid esters used for viscosity adjustment, as described later. As a result, swelling of the oil seal material 17 can be suppressed, and a buffer 1 that is less prone to oil leakage can be made. For example, soybean oil contains approximately 51% by mass of linoleic acid and 8.5% by mass of linolenic acid, as well as approximately 24% by mass of oleic acid, 11% by mass of palmitic acid, and 2-3% by mass of myristic acid and stearic acid. For example, sunflower oil contains approximately 70% by mass of linoleic acid and 1% by mass of linolenic acid, as well as approximately 18% by mass of oleic acid, 7% by mass of palmitic acid, and 4% by mass of stearic acid. As such, soybean oil and sunflower oil are rich in polyunsaturated fatty acids. In other words, they contain less of other fatty acids, such as monounsaturated fatty acids like oleic acid and saturated fatty acids. Therefore, the first fluid is a fluid that contains more polyunsaturated fatty acids than other fatty acids. Furthermore, the first fluid is not limited to soybean oil or sunflower oil; it may contain some or all of other oils, such as waste oil, as long as the polyunsaturated fatty acid content is higher than the other content. In other words, it is possible to blend an oil in which the polyunsaturated fatty acid content is higher than the total content of other fatty acids with an oil in which the polyunsaturated fatty acid content is lower than the total content of other fatty acids, i.e., waste oil. The blending ratio can be determined arbitrarily. Generally, the swelling resistance of nitrile rubber improves as the nitrile content increases, so increasing the ester in the second fluid allows for the use of more waste oil, etc. (= viscosity can be maintained), but cold resistance decreases, so the ratio can be determined arbitrarily considering the expected usage conditions. The fatty acid esters contained in the second fluid are plant-derived, just like vegetable oils such as soybean oil and sunflower oil, which have low viscosity, and fatty acid esters with 10 to 20 carbon atoms can be used. The second fluid has lower viscosity than the first fluid, which has the viscosity of the first fluid. Therefore, by adding the second fluid to the first fluid, the viscosity of the buffer hydraulic fluid 7 can be further reduced.

[0017] The reason for limiting the kinematic viscosity at 40°C as described above is that if the kinematic viscosity is less than 8 mPa-sec, the viscosity decreases at high temperatures, making it impossible to obtain the desired damping force characteristics. Furthermore, if the kinematic viscosity exceeds 15 mPa-sec, the damping force characteristics during operation deteriorate, particularly affecting the ride comfort of the vehicle to which the shock absorber 1 is applied, especially at low temperatures. The hydraulic fluid 7 for the shock absorber according to this embodiment may further be added with any one of metal detergents, dispersants, antiwear agents, antioxidants, corrosion inhibitors, friction modifiers, pour point depressants, defoamers, oiliness improvers, viscosity index improvers, rust preventives, etc. that are added to general hydraulic fluids for shock absorbers.

[0018] [[ID= 4]] As shown in FIG. 1, the mounting eye 20 is attached to the outside of the bottom wall 13. The hydraulic shock absorber 1 is used by attaching the tip of the outside of the piston rod 5 and the mounting eye 20 between the relative moving members that are the mounting targets. For example, in the case of automotive applications, the hydraulic shock absorber 1 is used by connecting the outer end of the piston rod 5 to the vehicle body side of the vehicle and connecting the mounting eye 20 to the vehicle wheel side of the vehicle. In the hydraulic shock absorber 1, the piston rod 5 and the piston 6 slide integrally within the cylinder 4, changing the volumes of the oil chambers A and B. At that time, the damping force can be generated by the flow resistance of the liquid acting on the damping force generating mechanisms 8, 9 and the bottom valve 11 of the piston 6.

[0019] The hydraulic shock absorber 1 during vehicle travel is configured such that the piston rod 5 or the outer cylinder 2 repeatedly receives an external impact force in their axial directions. Each time an impact force is received, the piston rod 5 moves to the contraction side or the extension side, and at that time, a damping force acts. In this way, the hydraulic shock absorber 1 functions as a shock absorber used in a strut-type suspension of an automobile.

[0020] According to the hydraulic fluid 7 for the shock absorber of this embodiment, since vegetable oil is used without using mineral oil, it can contribute to carbon neutrality. In addition, since the hydraulic fluid 7 for the shock absorber is plant-derived and biodegradable, even if it spills or leaks around, it is easy to treat soil contamination and so on, and the environmental load is very small. Further, the hydraulic fluid 7 for the shock absorber of this embodiment can reduce the ratio of the fatty acid ester that adjusts the viscosity, so it is difficult to swell the NBR constituting the oil seal member 17 and does not reduce the tightening force, so problems such as oil leakage can be prevented.

Example

[0021] As examples, soybean oil with a polyunsaturated fatty acid content of 59.7% by mass, sunflower oil with a polyunsaturated fatty acid content of 70.7% by mass, and esterified soybean oil were prepared, and base oils were made in the proportions described in Examples 1 to 5 below. Next, dispersants, anti-wear agents, antioxidants, friction modifiers, pour point depressants, defoamers, oiliness improvers, rust inhibitors, etc., were added to the base oils described in Examples 1 to 5 to prepare hydraulic fluid for shock absorbers. Comparative Examples 1 to 5 were prepared in the same manner. Example 1 involved a formulation with a composition of 70% soybean oil and 30% ester, with a polyunsaturated fatty acid content of 59.7% by mass, and was adjusted to a kinematic viscosity of 14.8 mPa·S at 40°C. Example 2 involved a mixture of soybean oil and ester in a ratio of 60:40, adjusted to a kinematic viscosity of 12.1 mPa·S at 40°C.

[0022] Example 3 was formulated with a ratio of 50 parts soybean oil to 50 parts ester, and adjusted to a kinematic viscosity of 9.4 mPa·S at 40°C. Example 4 involved a formulation with a ratio of 60% sunflower oil to 40% ester, where the proportion of polyunsaturated fatty acids was 70.7% by mass, and the kinematic viscosity at 40°C was adjusted to 14.3 mPa·S. Example 5 involved a mixture of sunflower oil and ester in a 50:50 ratio, adjusted to a kinematic viscosity of 11.9 mPa·S at 40°C. Nitrile rubber with a nitrile content of 27%, suitable for use at -30°C, a temperature typically required for automobiles, was immersed in the oils of Examples 1-5. The volume change was measured after being left at 100°C for 70 hours. The pour point was also measured. Note that -30°C is even lower than the average minimum temperature of subarctic regions such as Winnipeg, Canada, and Moscow, Russia, and was set as a temperature at which the material would function adequately in the environment in which a typical automobile is used.

[0023] As a comparative example, a new rapeseed oil with a polyunsaturated fatty acid content of 33.0% was prepared and processed as shown in Comparative Examples 1 to 5. Comparative Example 1 was formulated with a ratio of 80 parts soybean oil to 20 parts ester, and adjusted to a kinematic viscosity of 18.1 mPa·S at 40°C. Comparative Example 2 was formulated with a ratio of 40 parts soybean oil to 60 parts ester, and adjusted to a kinematic viscosity of 7.5 mPa·S at 40°C. Comparative Example 3 was formulated with a ratio of 70 parts sunflower oil to 30 parts ester, and adjusted to a kinematic viscosity of 17.8 mPa·S at 40°C. Comparative Example 4 was formulated with a ratio of 50 parts rapeseed oil to 50 parts ester, and adjusted to a kinematic viscosity of 18.7 mPa·S at 40°C. Comparative Example 5 was formulated with a ratio of 40 parts rapeseed oil to 60 parts ester, and adjusted to a kinematic viscosity of 9.5 mPa·S at 40°C.

[0024] [Table 1]

[0025] [Table 2]

[0026] As is clear from the comparison in Tables 1 and 2, Comparative Examples 1-5 were found to be partially unsatisfactory in terms of viscosity, pour point, and volume change. In contrast, the viscosity of Examples 1-5 was within the desirable range of 8-15, the pour point was below -30°C, and the volume change of the nitrile rubber was minimal. As mentioned above, this table assumes a nitrile rubber with a nitrile content of 27%, which is usable at -30°C, a common requirement for automobiles. If this requirement is not met, the nitrile content can be increased and the proportion of the second fluid can be increased. For example, if the nitrile content is 50%, the viscosity, pour point, and volume change can be satisfied if the polyunsaturated fatty acids in the first fluid make up 30 percent or more. [Industrial applicability]

[0027] According to this disclosure, a buffer equipped with an acrylonitrile butadiene rubber oil seal material can be provided that can suppress swelling of the oil seal material and has excellent sealing properties for hydraulic fluid. Furthermore, by using a base oil that contains a first fluid of plant-derived oil or fat in which the number of polyunsaturated fatty acid groups in the total amount of triglycerides is greater than the number of monounsaturated fatty acid groups, and a second fluid with lower viscosity that contains fatty acid esters, a buffer equipped with hydraulic fluid that has excellent lubricity and low environmental impact can be provided. [Explanation of Symbols]

[0028] 1. Hydraulic shock absorber 2 Outer cylinder 3 Inner cylinder 4 cylinders 5 Piston rod 6 pistons 7 Hydraulic oil for shock absorbers 8, 9 Damping force generation mechanism 10 Rod Guides 11 Bottom valve 17 Oil seal component A, B oil chamber C Reservoir Room

Claims

1. A bottomed cylindrical cylinder and an oil seal member containing acrylonitrile butadiene rubber are included in the opening of the cylinder. A buffer in which hydraulic fluid is sealed inside the cylinder, The aforementioned hydraulic fluid is It comprises a base oil and an additive added to the base oil, The aforementioned base oil is At least a portion of the mixture contains oils derived from plants, in which the number of polyunsaturated fatty acid groups in the total amount of triglycerides is greater than the number of other fatty acid groups, and a first fluid having a first viscosity, A second fluid containing a fatty acid ester and having a second viscosity lower than the first viscosity, It is a base oil that contains buffer.

2. The aforementioned buffer is, A gas that contains virtually no oxygen is then sealed inside. The shock absorber according to claim 1.

3. The cylinder is provided with a piston that slides against the cylinder, The piston rod is connected to the piston and reciprocates in the axial direction of the cylinder while in contact with the oil seal member relative to the cylinder, A shock absorber according to claim 1 or claim 2.

4. A hydraulic fluid for a shock absorber, comprising a base oil and additives added to the base oil, used in an environment exposed to acrylonitrile butadiene rubber, The aforementioned base oil is A plant-derived oil or fat in which the total amount of triglycerides contains 30 percent or more of polyunsaturated fatty acid groups, and a first fluid having a first viscosity, A second fluid containing a fatty acid ester and having a second viscosity lower than the first viscosity, It is a base oil that contains Hydraulic oil for shock absorbers.

5. The fatty acid ester contained in the second fluid is It is a fatty acid ester derived from fatty acids that constitute the triglycerides contained in plant-derived oils and fats. The hydraulic fluid for a shock absorber according to claim 4.

6. The oils and fats derived from plants that constitute the first and second fluids are the same oil. The hydraulic fluid for a shock absorber according to claim 4.

7. The base oil is obtained by mixing the first fluid and the second fluid. The hydraulic fluid for a shock absorber according to claim 4.

8. The base oil is obtained by modifying a portion of the first fluid into the second fluid. The hydraulic fluid for a shock absorber according to claim 4.

9. The proportion of the first fluid is greater than the proportion of the second fluid. The hydraulic fluid for a shock absorber according to claim 4.

10. The ratio of the first fluid to the second fluid is, The ratio is such that the viscosity of the base oil is 8 mPa seconds or more and 14 mPa seconds or less. The hydraulic fluid for shock absorbers according to any one of claims 4 to 9.

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