Shock absorbers and hydraulic oil for shock absorbers

Abstract

This shock absorber comprises: a cylindrical cylinder closed at the bottom; an oil sealing element containing an acrylonitrile butadiene rubber at an opening of the cylinder; and a hydraulic oil enclosed within the cylinder, wherein the hydraulic oil contains a base oil and an additive added to the base oil, and wherein the base oil is a first fluid having a first viscosity and is a vegetable-derived fat and oil, wherein the number of molecules of polyunsaturated fatty acid groups contained in the total triglyceride content is greater than the number of molecules of monounsaturated fatty acid groups, and a second fluid having a second viscosity lower than the first viscosity and containing a fatty acid ester.

Description

TECHNICAL AREA

[0001] The present invention relates to a shock absorber and a hydraulic oil for a shock absorber.

[0002] Priority is claimed by Japanese patent application No. 2023-087631, filed on May 29, 2023, the contents of which are incorporated herein by reference. STATE OF THE ART

[0003] Patent document 1 discloses a liquid composition useful as an insulating fluid, comprising: a mixture of a natural glyceride and at least one fatty acid ester other than triglycerides, wherein the fatty acids of the fatty acid ester comprise fatty acids derived from at least one vegetable oil or an equivalent natural source. Patent document 1 describes that 70% to 85% of the fatty acids comprising the mixture of the natural glyceride and the fatty acid ester are oleic acid, and that genetically modified high-oleic acid, rapeseed oil, soybean oil, sunflower oil, and the like may be used. Bibliography Patent document

[0004] Patent document 1: published Japanese translation No. 2014-534567 of the international PCT publication. SUMMARY OF THE INVENTION Technical Problem

[0005] In the prior art, there was a need for a hydraulic oil for a shock absorber that represents a low environmental impact, has outstanding lubrication and wear resistance, and does not cause problems such as oil leaks.

[0006] In the prior art, a mineral oil-based hydraulic oil has been used in shock absorbers. Considering the environmental impact, a plant-based hydraulic oil can be considered as an alternative. However, if acrylonitrile butadiene rubber is used as a sealing material for a shock absorber, the sealing material may swell because the polarity of a plant oil is closer to that of butadiene rubber than that of mineral oil. Furthermore, because a plant oil has a high viscosity, it cannot be used as a hydraulic oil on its own.

[0007] The present invention provides: a shock absorber containing a hydraulic oil that causes low environmental impact, is able to suppress the swelling of sealing elements, and has improved lubrication by reducing its viscosity; and a hydraulic oil for a shock absorber. Solution to the problem

[0008] According to one aspect of the present invention, a shock absorber comprises: a cylindrical cylinder closed at the bottom; an oil sealing element containing an acrylonitrile butadiene rubber at an opening region of the cylinder; and a hydraulic oil enclosed within the cylinder. The hydraulic oil comprises a base oil and an additive added to the base oil, and the base oil is a vegetable-derived fat and oil wherein the number of molecules of polyunsaturated fatty acid groups contained in the total triglycerides is greater than the number of molecules of monounsaturated fatty acid groups. This base oil comprises a first fluid having a first viscosity and a second fluid having a second viscosity lower than the first viscosity and containing a fatty acid ester. Advantageous effects of the invention

[0009] According to the disclosure, it is possible to provide a shock absorber comprising an acrylonitrile butadiene rubber oil seal material that suppresses swelling and exhibits outstanding sealing properties for hydraulic oil. Furthermore, by using a base oil comprising a first fluid consisting of a vegetable-derived fat and oil in which the number of molecules of polyunsaturated fatty acid groups contained in the total triglycerides is greater than the number of molecules of monounsaturated fatty acid groups, and a second fluid with a lower viscosity containing a fatty acid ester, it is possible to provide a shock absorber equipped with a hydraulic oil that exhibits outstanding lubricity and low environmental impact. BRIEF DESCRIPTION OF THE DRAWINGS [ Fig.1] A cross-sectional view showing an overall configuration of a hydraulic shock absorber according to a first embodiment of the present invention. DESCRIPTION OF EXECUTION FORMS

[0010] Below, a shock absorber will be described as a hydraulic shock absorber according to a first embodiment of the present invention.

[0011] The present embodiment described below is specifically described to facilitate a better understanding of the idea of ​​the invention, but does not limit the present invention unless otherwise stated. In addition, the scale of the drawing of the embodiment shown below, used in the description, has been appropriately modified to improve the visibility of each part.

[0012] Fig.Figure 1 is a vertical cross-sectional view showing a double-tube hydraulic shock absorber according to a first embodiment of the present invention. A hydraulic shock absorber 1 comprises a double-tube cylinder 4, which consists of a cylindrical outer tube 2 closed at its base and a cylindrical inner tube 3 closed at its base, which is provided coaxially within the outer tube 2. A piston rod 5, one end 5a of which is inserted into the inner tube 3 and the other end of which extends outwards from the cylinder 4 to a predetermined length, is inserted into the cylinder 4 such that it can move freely back and forth along the axial direction of the cylinder 4. A piston 6 is fixed to one end 5a of the piston rod 5, the piston 6 being able to slide along the inner surface of the inner tube 3 and to move within the inner tube 3 along the axial direction of the inner tube 3. Fig.Figure 1 shows the hydraulic shock absorber 1 in a state in which the axes of the outer tube 2, the inner tube 3 and the piston rod 5 are oriented in a vertical direction, with the bottom sides of the outer tube 2 and the inner tube 3 pointing downwards and the other end of the piston rod 5, which extends from the inner tube 3, pointing upwards.

[0013] The piston 6 has a function for dividing the interior of the inner tube 3 into an oil chamber A and an oil chamber B and is configured such that the volumes of oil chambers A and B change in accordance with the movement of the piston 6 within the inner tube 3. A reservoir chamber C is provided between the inner circumferential side of the outer tube 2 and the outer circumferential side of the inner tube 3, and is divided by the outer tube 2 and the inner tube 3. Oil chamber A, oil chamber B, and reservoir chamber C are filled with a hydraulic oil 7 for a shock absorber, which will be described in detail below.

[0014] The piston 6 comprises several flow paths connected to oil chambers A and B and is equipped with damping force-generating devices 8 and 9, each of which incorporates a valve mechanism in these flow paths. As the piston 6 moves within the inner tube 3 and the volumes of oil chambers A and B change, the hydraulic oil 7 for a shock absorber flows through the flow paths inside the piston 6 between oil chambers A and B. As a result, the piston 6 generates a damping force in response to the movement of the piston rod 5.

[0015] The bottom side of the in Fig.The inner tube 3 shown in Figure 1 is closed by a bottom wall element 12, which includes a bottom valve 11, and the bottom of the outer tube 2 is closed by a bottom wall 13. The bottom region of the inner tube 3 and the bottom region of the outer tube 2 are arranged close to each other, with the bottom wall element 12 installed so that it overlaps the bottom wall 13. A connecting chamber 14 is formed between the bottom wall element 12 and the bottom wall 13. This connecting chamber 14 is connected to the reservoir chamber C via a flow path element 15. The connecting chamber 14 is also connected to the oil chamber A via the bottom valve 11. The piston 6 is configured such that, as it moves closer to the bottom wall element 12, the hydraulic oil 7 for a shock absorber can flow from the oil chamber A to the reservoir chamber C via the bottom valve 11, the connecting chamber 14, and the flow path element 15.Furthermore, the piston 6 is configured such that when it moves in one direction away from the bottom wall element 12, the hydraulic oil 7 for a shock absorber can flow from the reservoir chamber C via the flow path element 15, the connecting chamber 14 and the bottom valve 11 into the oil chamber A.

[0016] An oil sealing element 17, containing an acrylonitrile butadiene rubber (NBR), is integrally provided with a cap 16 to seal a liquid-tight upper end region of the inner tube 3. A through-hole is formed in a central region of the cap 16, and the piston rod 5 is designed to extend through this opening. The annular oil sealing element 17 is located on the inner circumferential side of the through-hole and in a position in contact with the outer circumferential surface of the piston rod 5. In this description, acrylonitrile butadiene rubber may sometimes be referred to as nitrile rubber, and unless otherwise specified, the term "nitrile rubber" used in this description refers to acrylonitrile butadiene rubber.

[0017] In the Fig.In the configuration shown in Figure 1, a rod guide 10 is provided within the oil sealing element 17 and within the upper end region of the inner tube 3. The rod guide 10 has a tubular inner circumferential section 10a and a tubular outer circumferential section 10b and is arranged such that the inner circumferential section 10a is in contact with the outer circumferential surface of the piston rod 5 and the outer circumferential section 10b is in contact with the inner circumferential surface of the upper end region of the outer tube 2. The rod guide 10 is in fluid-tight contact with the piston rod 5 above the inner circumferential section 10a, while allowing reciprocating movement of the piston rod 5.

[0018] The ring-shaped cap 16 and the oil sealing element 17 are integral to the upper end section of the in Fig.The rod guide 10 is attached to the outer tube 2 shown in Figure 1. The rod guide 10 is held at the bottom by the cap 16. The piston rod 5 passes through the cover 16 and extends to the outside of the inner cylinder 3. The oil sealing element 17, which closes a gap between the inner circumferential area of ​​the cap 16 and the outer circumferential area of ​​the piston rod 5, is integrally formed with the cap 16.

[0019] The hydraulic oil 7 for a shock absorber of the first embodiment is a grease and oil derived from plants, wherein the number of molecules of polyunsaturated fatty acid groups contained in the total triglyceride content is 30% or more. The hydraulic oil 7 for a shock absorber essentially comprises a base oil consisting of a first fluid with a first viscosity and a second fluid with a second viscosity lower than the first viscosity, and containing a fatty acid ester.

[0020] The fatty acid ester contained in the second fluid is a fatty acid ester derived from a fatty acid that forms a triglyceride contained in a fat and oil derived from plants. The plant-derived fat and oil that form the first and second fluids are preferably the same fat and oil.

[0021] The ratio of the first fluid to the second fluid is a ratio where the kinematic viscosity (at 40°C) of the base oil is 8 mPa·s to 15 mPa·s.

[0022] The ratio of the first fluid to the second fluid, for example, is in the range of 70:30 to 50:50.

[0023] The first fluid is a vegetable oil in which the proportion of polyunsaturated fatty acids (such as linoleic acid and linolenic acid) containing two or more double bonds is 50% or more; that is, the proportion of polyunsaturated fatty acids is greater than the total content of other fatty acids. Soybean oil or sunflower oil is particularly preferred.

[0024] Soybean oil and sunflower oil have a lower viscosity than other vegetable oils, which makes it possible to reduce the content of the fatty acid ester used for viscosity adjustment, as will be described below. Therefore, it is possible to suppress swelling of the oil sealing material 17 and to provide a shock absorber 1 in which oil leakage is less likely to occur.

[0025] For example, soybean oil contains about 51% by mass of linoleic acid and about 8.5% by mass of linolenic acid, and additionally contains about 24% by mass of oleic acid, about 11% by mass of palmitic acid and about 2 to 3% by mass of myristic acid and stearic acid.

[0026] For example, sunflower oil contains about 70% by mass of linoleic acid and about 1% by mass of linolenic acid, and additionally it contains about 18% by mass of oleic acid, about 7% by mass of palmitic acid and about 4% by mass of stearic acid.

[0027] As described above, soybean oil and sunflower oil contain a large amount of polyunsaturated fatty acids. In other words, the content of other fatty acids, such as oleic acid, which is a monounsaturated fatty acid, and of saturated fatty acids is low. Thus, the first oil is a fluid that has a higher amount of polyunsaturated fatty acids than other fatty acids.

[0028] The first fluid is not limited to soybean or sunflower oil, as long as the polyunsaturated fatty acid content is greater than that of other fatty acids, and it may contain other oils, such as waste oil, either partially or entirely. In other words, it is also possible to mix a fat and oil (i.e., waste oil) in which the polyunsaturated fatty acid content is less than the total content of other fatty acids with a fat and oil in which the polyunsaturated fatty acid content is greater than the total content of other fatty acids. The mixing ratio can be determined arbitrarily. Generally, resistance to swelling improves when the nitrile content of the nitrile rubber is increased; therefore, it is possible to use a larger quantity of waste oil or the like (i.e., maintain the viscosity) by increasing the amount of ester in the second fluid.However, because cold resistance decreases, the ratio can be determined arbitrarily, taking into account the expected operating conditions.

[0029] The fatty acid ester contained in the second fluid is also derived from plants, such as vegetable oils like soybean and sunflower oil, which have low viscosities, and a fatty acid ester with a carbon number of approximately 10 to 20 can be used. The second fluid has a lower viscosity than the first fluid. Therefore, by adding the second fluid to the first fluid, the viscosity of the hydraulic oil 7 for a shock absorber can be further reduced.

[0030] The reason for limiting the kinematic viscosity at 40°C, as described above, is that if the kinematic viscosity is less than 8 mPa·s, the viscosity decreases at high temperatures, and the desired damping characteristics cannot be achieved. Furthermore, if the kinematic viscosity exceeds 15 mPa·s, the damping characteristics deteriorate during operation, which particularly affects the ride comfort of a car equipped with shock absorber 1 at low temperatures.

[0031] The hydraulic oil 7 for a shock absorber of the present embodiment may further comprise any of a metal detergent, a dispersant, an anti-wear agent, an antioxidant, a corrosion inhibitor, a friction modifier, a pour point reducer, an antifoaming agent, an oiliness improver, a viscosity index improver and a rust inhibitor, which are generally added to hydraulic oils for shock absorbers.

[0032] As in Fig. As shown in Figure 1, a mounting eyelet 20 is attached to an outer side of the bottom wall 13. The hydraulic shock absorber 1 is installed by mounting the distal section on the outer side of the piston rod 5 and the mounting eyelet 20 between the relative movable parts on which it is to be mounted.

[0033] In an automotive application, for example, the hydraulic shock absorber 1 is used by connecting the outer end of the piston rod 5 to the body side of a vehicle and connecting the mounting eyelet 20 to the wheel side of the vehicle.

[0034] In the hydraulic shock absorber 1, the piston rod 5 and the piston 6 slide integrally within the cylinder 4, thereby changing the volumes of the oil chambers A and B. At this point, it is possible to generate a damping force through the flow resistance of the fluid, which acts on the damping force-generating mechanisms 8 and 9 of the piston 6 and the bottom valve 11.

[0035] The hydraulic shock absorber 1 is configured during vehicle operation such that the piston rod 5 and the outer tube 2 repeatedly receive external impact forces in the axial direction. Each time an impact force is received, the piston rod 5 moves in a compression or extension direction, and a damping force is exerted at that time. In this way, the hydraulic shock absorber 1 demonstrates its function as a shock absorber in the strut suspension of an automobile.

[0036] With the hydraulic oil 7 for a shock absorber of the present embodiment, it is possible to contribute to carbon neutrality because a vegetable oil is used without using a mineral oil.

[0037] Furthermore, because the hydraulic oil 7 for a shock absorber is derived from plants and is biodegradable, contamination treatment of soil or the like is simple, even if it spills or leaks, and environmental impact is significantly reduced. Moreover, because the hydraulic oil 7 for a shock absorber of the present embodiment can reduce the proportion of fatty acid esters used for viscosity adjustment, there is less tendency for the NBR, which forms the oil sealing element 17, to swell, and it does not diminish the sealing properties, thus making it possible to avoid problems such as oil leakage. Examples

[0038] Examples included soybean oil composed of polyunsaturated fatty acids in a proportion of 59.7% by mass, sunflower oil composed of polyunsaturated fatty acids with a mass fraction of 70.7% by mass, and esterified soybean oil, and the base oils were prepared with the proportions described in Examples 1 to 5 below.

[0039] Next, additives such as a dispersant, an anti-wear agent, an antioxidant, a friction modifier, a pour point reducer, an antifoaming agent, an oiliness improver, and a rust inhibitor were added to the oils described in Examples 1 to 5 to produce hydraulic oils for shock absorbers. Similarly, the following comparative examples 1 to 5 were prepared.

[0040] In Example 1, soybean oil, composed of polyunsaturated fatty acids in a proportion of 59.7 wt%, and an ester in a ratio of 70:30 were mixed, and the kinematic viscosity at 40°C was adjusted to 14.8 mPa·s.

[0041] In Example 2, soybean oil and an ester were mixed in a ratio of 60:40, and the kinematic viscosity at 40°C was adjusted to 12.1 mPa·s.

[0042] In Example 3, soybean oil and an ester were mixed in a 50:50 ratio, and the kinematic viscosity at 40°C was adjusted to 9.4 mPa·s.

[0043] In Example 4, sunflower oil, composed of polyunsaturated fatty acids in a proportion of 70.7 wt%, and an ester in a ratio of 60:40 were mixed, and the kinematic viscosity at 40°C was adjusted to 14.3 mPa·s.

[0044] In Example 5, sunflower oil and an ester were mixed in a ratio of 50:50, and the kinematic viscosity at 40°C was adjusted to 11.9 mPa·s.

[0045] A nitrile rubber with a nitrile content of 27%, usable down to -30°C as generally required for automobiles, was immersed in the oils of Examples 1 to 5, and the change in volume after standing at 100°C for 70 hours was measured. Additionally, the pour point was measured. -30°C is a temperature lower than the mean minimum temperature in Winnipeg, Canada, and Moscow, Russia, which are located in the subarctic zone, and was chosen as a temperature at which normal automobiles can function adequately under typical operating conditions.

[0046] For comparison, rapeseed oil, composed of polyunsaturated fatty acids in a proportion of 33.0%, was freshly produced, and the oils shown in comparison examples 1 to 5 were produced.

[0047] In comparative example 1, soybean oil and an ester were mixed in a ratio of 80:20, and the kinematic viscosity at 40°C was adjusted to 18.1 mPa·s.

[0048] In comparative example 2, soybean oil and an ester were mixed in a ratio of 40:60, and the kinematic viscosity at 40°C was adjusted to 7.5 mPa·s.

[0049] In comparative example 3, sunflower oil and an ester were mixed in a ratio of 70:30, and the kinematic viscosity at 40°C was adjusted to 17.8 mPa·s.

[0050] In comparative example 4, rapeseed oil and an ester were mixed in a ratio of 50:50, and the kinematic viscosity at 40°C was adjusted to 18.7 mPa·s.

[0051] In comparative example 5, rapeseed oil and an ester were mixed in a ratio of 40:60, and the kinematic viscosity at 40°C was adjusted to 9.5 mPa·s. [Table 1] Example 1 Example 2 Example 3 Example 5 Example 6 Soybean oil 70 60 50 Sunflower oil 60 50 Ester 30 40 50 40 50 Viscosity (mPa·s: 40°C) 8 to 15 14,8 12,1 9,4 14,3 11,9 Pour point (°C) -30 or lower -33 -36 -40 -44 -46 Volume change of medium nitrile rubber (%) 10 or less 6, 8 8 9, 8 7, 8 9, 4 [Table 2] See example 1 See example 2 See example 3 See example 4 See example 5 Soybean oil 80 40 Sunflower oil 70 rapeseed oil 50 40 Ester 20 60 30 50 60 Viscosity (mPa.s: 40°C) 8 to 15 18,1 7,5 17,8 18,7 9,5 Pour point (°C) -30 or lower -30 -43 -41 -20 -23 Volume change of medium nitrile rubber (%) 10 or less 4,9 12,1 6,5 10,2 13,5

[0052] As can be seen from the comparison between Tables 1 and 2, it was found that comparison examples 1 to 5 did not meet some of the properties with regard to viscosity, pour point and volume changes.

[0053] In contrast, the viscosities of examples 1 to 5 were within the desired range of 8 to 15, the pour points were within the desired range of -30°C or lower, and the volume changes of the nitrile rubber were also small.

[0054] As described above, the tables are based on the assumption of using a nitrile rubber with a nitrile content of 27%, usable down to -30°C, as is generally required for automobiles. If it is not necessary to meet this requirement, the nitrile content can be increased and the proportion of the second fluid can be decreased. For example, if the nitrile content is set to 50%, the viscosity, pour point, and volume change can be satisfied if the polyunsaturated fatty acid content in the first fluid is 30% or higher. INDUSTRIAL APPLICABILITY

[0055] According to the disclosure, it is possible to provide a shock absorber comprising an acrylonitrile butadiene rubber oil seal material, which reduces the swelling of the oil seal material and exhibits outstanding sealing performance for a hydraulic oil. By using a base oil comprising a first fluid, which is a vegetable-derived grease and oil in which the number of molecules of polyunsaturated fatty acid groups contained in the total triglyceride content is greater than the number of molecules of monounsaturated fatty acid groups, and a second fluid with a lower viscosity and containing a fatty acid ester, it is possible to provide a shock absorber equipped with a hydraulic oil that offers outstanding lubrication properties and low environmental impact. LIST OF REFERENCE MARKS 1 Hydraulic shock absorber (shock absorber) 2 outer pipe 3 inner tube 4 cylinders 5 piston rod 6 pistons 7 Hydraulic oil for one shock absorber 8, 9 Damping force generating mechanisms 10 Staff Leadership 11 Bottom valve 17 Oil sealing element A, B Oil chamber C Reservoir chamber QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] JP 2023-087631

[0002] JP 2014-534567

[0004]

Claims

[1] Shock absorber, comprising: a cylindrical cylinder closed at the bottom; an oil sealing element containing an acrylonitrile butadiene rubber, at an opening area of ​​the cylinder; and a hydraulic oil that is enclosed inside the cylinder, containing the hydraulic oil a base oil and an additive added to the base oil, and containing the base oil a first fluid having a first viscosity and formulated at least partially from a plant-derived fat and oil, wherein the number of molecules of polyunsaturated fatty acid groups contained in the total triglyceride content is greater than the number of molecules of other fatty acid groups, and a second fluid that has a second viscosity which is lower than the first viscosity and which contains a fatty acid ester. [2] Shock absorber according to claim 1, wherein furthermore a gas which contains substantially no oxygen is enclosed in the shock absorber. [3] Shock absorber according to claim 1 or 2, further comprising: a piston that is provided inside the cylinder and that slides relative to the cylinder; and a piston rod that is connected to the piston and is configured to move back and forth in the axial direction of the cylinder relative to the cylinder while in contact with the oil sealing element. [4] Hydraulic oil for a shock absorber, comprising: a base oil; and an additive added to the base oil, wherein the hydraulic oil for a shock absorber is used in an environment exposed to acrylonitrile butadiene rubber, and containing the base oil a first fluid having a first viscosity and being a vegetable-derived fat and oil, wherein the number of molecules of polyunsaturated fatty acid groups contained in the total triglyceride content is 30% or more, and a second fluid that has a second viscosity which is lower than the first viscosity and which contains a fatty acid ester. [5] Hydraulic oil for a shock absorber according to claim 4, wherein the fatty acid ester contained in the second fluid is derived from a fatty acid forming a triglyceride contained in a fat and oil derived from plants. [6] Hydraulic oil for a shock absorber according to claim 4, wherein the plant-derived grease and oil comprising the first fluid and the second fluid are the same grease and oil. [7] Hydraulic oil for a shock absorber according to claim 4, wherein the base oil is obtained by mixing the first fluid with the second fluid. [8] Hydraulic oil for a shock absorber according to claim 4, wherein the base oil is obtained by modifying a portion of the first fluid to form the second fluid. [9] Hydraulic oil for a shock absorber according to claim 4, wherein the proportion of the first fluid is greater than the proportion of the second fluid. [10] Hydraulic oil for a shock absorber according to any one of claims 4 to 9, wherein the ratio of the first fluid to the second fluid is a ratio in which the viscosity of the base oil is 8 mPa·s to 14 mPa·s.

Images