Hydraulic cylinder device

Abstract

Provided is a hydraulic cylinder device in which abrasion during initial friction of a sliding portion between a piston rod and a rod seal is suppressed, and durability of the sliding portion is improved as compared to the conventional device. A hydraulic cylinder device according to the present invention is characterized in that: the device comprises a cylinder tube, a piston capable of reciprocating inside the cylinder tube, a piston rod fixed to the piston, and a rod seal through which the piston rod slides; the rod seal includes a main lip part provided on the piston side and a dust lip part provided on the exterior side along the axial direction of the piston rod; an inter-lip space part not in contact with the piston rod is formed between the main lip part and the dust lip part; and the inter-lip space part is filled with grease containing at least one of an aliphatic diurea-based thickener, an alicyclic diurea-based thickener, and an aromatic diurea-based thickener.

Description

Hydraulic cylinder device

[0003]

[0001] The present invention relates to a hydraulic cylinder device.

[0002] A hydraulic cylinder device generally has a piston, a piston rod fixed to the piston, and hydraulic oil built into a cylinder tube. By taking in and discharging the hydraulic oil, the piston and the piston rod are reciprocated, or the reciprocating motion applied to the piston rod is attenuated by the flow resistance of the hydraulic oil.

[0003] When the piston and the piston rod reciprocate, a piston seal (also called a piston packing or a piston band) is disposed between the cylinder tube and the piston, and a rod seal (also called a rod packing or an oil seal) is disposed between the piston rod and the rod cover (also called a rod guide) to prevent unwanted pressure loss of the hydraulic oil and external leakage of the hydraulic oil. That is, the piston seal reciprocates while sliding with respect to the cylinder tube, and the piston rod reciprocates while sliding with respect to the rod seal.

[0004] Since the piston seal and the rod seal are members for preventing pressure loss / external leakage of the hydraulic oil, it is important to adhere closely to the sliding target. Usually, synthetic rubber or synthetic resin is used as the material of the piston seal and the rod seal. From these facts, a large frictional force is generated between the sealing material and the sliding target. On the other hand, from the viewpoints of smoothness of the reciprocating motion of the piston and the piston rod and durability of the sliding portion, reduction of the frictional force and ensuring of wear resistance at the sliding portion are required.

[0005] To address these conflicting requirements, for example, Patent Document 1 (JP-A-5-255683) provides a hydraulic fluid composition for shock absorbers characterized by containing (a) a base oil, (b) at least one compound selected from the group consisting of phosphate esters, phosphite esters, and phosphate ester amine salts, and (c) an alkanolamine. According to Patent Document 1, a hydraulic fluid for shock absorbers is provided that exhibits excellent friction characteristics even under conditions in which micro-vibrations and micro-amplitudes are applied to the shock absorber, and also shows good wear resistance and friction characteristics when used in a shock absorber using a sliding member made of polytetrafluoroethylene resin.

[0006] Japanese Patent Application Publication No. 5-255683

[0007] The inventors conducted research aimed at further improving the smoothness of the reciprocating motion of the piston and piston rod in a hydraulic cylinder device, as well as the durability of the sliding parts. In this research, it was found that dust and dirt adhering to the piston rod can unexpectedly reduce the durability of the sliding part between the piston rod and the rod seal.

[0008] Further research to elucidate the mechanism of this durability degradation revealed that the initial friction characteristics between the piston rod and the rod seal (sometimes referred to as "break-in") may be strongly related. Specifically, it was found that the rod seal may be damaged during the initial friction phase.

[0009] In this invention, initial friction and initial friction characteristics are defined as the friction and friction characteristics during the first 10 minutes after the hydraulic cylinder device has been inactive for a period of time (for example, stopped overnight or longer).

[0010] The sliding portion between the piston rod and the rod seal is basically lubricated with hydraulic fluid for hydraulic cylinder devices, as taught in Patent Document 1. Therefore, the idea of ​​taking any measures to address or address initial friction or initial friction characteristics (in other words, the very recognition that there is some kind of problem with initial friction or initial friction characteristics) has not existed until now.

[0011] The present invention has been made to solve such newly recognized problems, and its primary objective is to provide a hydraulic cylinder device that suppresses wear in the initial friction of the sliding portion between the piston rod and the rod seal, thereby improving the durability of the sliding portion compared to conventional devices.

[0012] One aspect of the present invention provides a hydraulic cylinder device comprising: a cylinder tube; a piston capable of reciprocating inside the cylinder tube; a piston rod fixed to the piston; and a rod seal on which the piston rod slides, wherein the rod seal has a main lip portion disposed on the piston side and a dust lip portion disposed on the external side along the axial direction of the piston rod, and a lip space portion is formed between the main lip portion and the dust lip portion that does not contact the piston rod, and the lip space portion is filled with grease containing at least one of an aliphatic diurea thickener, an alicyclic diurea thickener, and an aromatic diurea thickener.

[0013] The present invention allows for the following improvements and modifications to be freely combined in the above-described hydraulic cylinder device: (i) The rod seal is made of acrylonitrile butadiene nitrile rubber with a nitrile content of 30% by mass or less. (ii) The grease has a poly-alpha-olefin oil as its base oil. (iii) The piston rod has a chromium plating layer formed on its surface with an arithmetic mean roughness of 0.1 μm or less. (iv) The hydraulic cylinder device is a hydraulic shock absorber for automobiles.

[0014] According to the present invention, wear in the initial friction of the sliding portion between the piston rod and the rod seal can be suppressed, and a hydraulic cylinder device with improved durability of the sliding portion compared to conventional devices can be provided. Problems, configurations, and effects other than those mentioned above will be clarified by the description of the embodiments below.

[0015] This is an example of a hydraulic cylinder device according to the present invention, and is a schematic cross-sectional view of an automotive hydraulic shock absorber. This is an example of the rod seal configuration in the hydraulic cylinder device according to the present invention and a schematic cross-sectional view showing the vicinity of the sliding portion of the piston rod / rod seal.

[0016] Embodiments of the present invention will be described below with reference to the drawings. The drawings are exaggerated to aid in understanding the explanation. Furthermore, the present invention is not limited to the specific embodiments described, and it is possible to combine it with prior art or improve upon it without departing from the technical spirit of the invention.

[0017] (Basic Concept of the Invention) As mentioned above, the inventors conducted research aimed at further improving the smoothness of the reciprocating motion of the piston and piston rod in a hydraulic cylinder device and the durability of the sliding parts. In the process, they found that the durability of the sliding part between the piston rod and the rod seal could be unexpectedly reduced due to dust and dirt adhering to the piston rod. Further research was conducted to elucidate the mechanism of this reduction in durability, and it was found that the initial friction / initial friction characteristics between the piston rod and the rod seal may be strongly related.

[0018] Specifically, it was found that the frictional characteristics between the piston rod and the rod seal tend to have a high coefficient of friction during initial friction, and that the coefficient of friction tends to decrease as sliding is repeated. When the increase in the coefficient of friction during initial friction is large, and / or when it takes a long time for the coefficient of friction to decrease due to sliding, the high coefficient of friction state persists for a certain period of time. Therefore, if dust or dirt adheres to the surface of the piston rod, the surface of the rod seal is more likely to be scratched during initial friction, which is thought to induce external leakage of hydraulic fluid from the scratched area.

[0019] Therefore, the inventors diligently researched techniques to improve the initial friction characteristics of the sliding portion between the piston rod and the rod seal (reducing the degree of increase in the coefficient of friction during initial friction, and / or shortening the time it takes for the coefficient of friction to decrease due to sliding). As a result, they found that the desired effect can be obtained by forming a lip space between the main lip portion and the dust lip portion of the rod seal that does not come into contact with the piston rod, and filling this lip space with a predetermined grease. The present invention was completed based on this finding.

[0020] [Hydraulic Cylinder Device] An embodiment of the hydraulic cylinder device according to the present invention will be described below. Here, an automobile hydraulic shock absorber will be used as an example. Naturally, the hydraulic cylinder device of the present invention is not limited to automobile hydraulic shock absorbers.

[0021] Figure 1 is an example of a hydraulic cylinder device according to the present invention, and is a schematic cross-sectional view of an automotive hydraulic shock absorber. The automotive hydraulic shock absorber 100 shown in Figure 1 is a rod-extendable, double-tube type hydraulic shock absorber, and the cylindrical section 10 has a double structure consisting of an outer cylinder 12 and an inner cylinder 14 (also called a cylinder tube). A piston 20 is disposed inside the inner cylinder 14, and one end of the piston rod 30 is fixed to the piston 20 and the other end is arranged to protrude from the cylindrical section 10 (outer cylinder 12, inner cylinder 14), and hydraulic fluid 40 is sealed so as to fill the inner cylinder 14.

[0022] On the side of the cylindrical portion 10 from which the piston rod 30 protrudes, a rod guide 50 and a guide bush 52 are provided to suppress the radial movement of the piston rod 30, and a rod seal 54 is provided to prevent unwanted external leakage of the hydraulic fluid 40.

[0023] The piston 20 is equipped with a piston valve 22 that generates damping force by utilizing the flow resistance of the hydraulic fluid 40, and a piston seal 24 that prevents unwanted pressure leakage of the hydraulic fluid 40.

[0024] Due to the extension and retraction of the piston rod 30 (and the resulting reciprocating motion of the piston 20), the hydraulic fluid 40 enters and exits the piston upper chamber A and piston lower chamber B within the inner cylinder 14 through the piston valve 22 provided on the piston 20, and also enters and exits the reservoir chamber C between the inner cylinder 14 and the outer cylinder 12 through the base valve 16 provided at the bottom of the inner cylinder 14.

[0025] A rod-extendable, twin-tube hydraulic shock absorber generates damping force by utilizing the flow resistance of the hydraulic fluid 40 as it passes through the piston valve 22 and the base valve 16. In a rod-extendable, twin-tube hydraulic shock absorber, the damping force in the compression direction is generally controlled by the base valve 16, and the damping force in the extension direction is controlled by the piston valve 22.

[0026] As described above, the automotive hydraulic shock absorber 100 has three main sliding parts (inner cylinder 14 / piston seal 24, piston rod 30 / guide bush 52, and piston rod 30 / rod seal 54). Ensuring wear resistance is important for all sliding parts, but if the rod seal 54 is damaged at the sliding part of the piston rod 30 / rod seal 54, external leakage of hydraulic fluid 40 is likely to occur from the damaged area.

[0027] (Rod Seal) The hydraulic cylinder device 100 according to the present invention is characterized by the configuration of the rod seal 54, which can improve the initial friction characteristics at the sliding portion of the piston rod 30 / rod seal 54. Figure 2 is a schematic cross-sectional view showing an example of the rod seal configuration in the hydraulic cylinder device according to the present invention and the vicinity of the sliding portion of the piston rod / rod seal.

[0028] The rod seal 54 shown in Figure 2 has a main lip portion 54m that is disposed on the piston 20 side along the axial direction of the piston rod 30 and contacts the piston rod 30, and a dust lip portion 54d that is disposed on the external side and contacts the piston rod 30. A lip space portion 54s that does not contact the piston rod 30 is formed between the main lip portion 54m and the dust lip portion 54d, and a predetermined grease 54g is filled into the lip space portion 54s.

[0029] The entire rod seal 54 is held in place by a stay 55, the main lip portion 54m is in close contact with the piston rod 30 by a main lip portion spring 56, and the dust lip portion 54d is in close contact with the piston rod 30 by a dust lip portion spring 57. The close contact between the main lip portion 54m and the dust lip portion 54d with the piston rod 30 allows the grease 54g to be held in the space between the lips 54s. The presence of the grease 54g improves the initial friction characteristics and suppresses wear of the rod seal 54 during initial friction.

[0030] There are no particular limitations on the material of the rod seal 54, and conventional synthetic rubber or resin can be used. For example, in the case of the automotive hydraulic shock absorber 100 described above, from the viewpoint of oil resistance, sealing performance and cold resistance, acrylonitrile butadiene rubber (NBR) with an acrylonitrile content of 30% by mass or less is preferably used as the material for the rod seal 54. NBR with an acrylonitrile content of 24% by mass or less is more preferable. In addition, the Shore A hardness of the rod seal 54 at 20°C is preferably 75 to 90.

[0031] (Grease) Grease consists of three elements: base oil, thickener, and additives. The grease used in the present invention is characterized by its thickener, which is preferably contained in an amount of 10% to 30% by mass relative to the total grease. As the thickener, a diurea-based thickener having two urea bonds in its molecular structure is preferred, and specifically, it is preferable to include one or more selected from aliphatic diurea-based thickeners, alicyclic diurea-based thickeners, and aromatic diurea-based thickeners. Diurea-based thickeners are characterized by excellent adhesion to metal surfaces, water resistance, oxidation stability, and lubrication life.

[0032] Furthermore, the grease thickener used in the present invention may be mixed with metal soap thickeners (e.g., lithium soap thickeners, calcium soap thickeners) or complex thickeners (e.g., calcium complex thickeners, aluminum complex thickeners, lithium complex thickeners) as long as its main component (more than 50% of the thickener) is a diurea-based thickener.

[0033] As the base oil, conventionally used mineral oils and / or synthetic oils can be used as appropriate. The base oil may be one type of mineral oil or synthetic oil used alone, or a combination of multiple types of mineral oils and synthetic oils may be used.

[0034] Examples of mineral oils used as base oils include paraffinic mineral oils and naphthenic mineral oils. Examples of synthetic oils include polybutene-based synthetic oils, polypropylene-based synthetic oils, poly-α-olefin-based synthetic oils, ester-based synthetic oils, polyalkylene glycol-based synthetic oils, polyphenyl ether-based synthetic oils, alkylbenzene-based synthetic oils, synthetic naphthenic synthetic oils, silicone-based synthetic oils, and fluorine-based synthetic oils. From the viewpoint of viscosity index and temperature characteristics, poly-α-olefin-based synthetic oils are preferred.

[0035] There are no particular restrictions on the additives used; conventionally used additives (for example, rust inhibitors, antioxidants, load-bearing additives) can be used as appropriate.

[0036] (Histon Rod) The piston rod 30 is chromium plated on its surface for rust prevention and wear resistance. Preferably, the surface roughness (arithmetic mean roughness Ra) of the chromium plating layer is 0.1 μm or less. If the Ra of the chromium plating layer exceeds 0.1 μm, the frictional force increases at the sliding parts of the piston rod 30 / guide bush 52 and the piston rod 30 / rod seal 54, which reduces the smoothness of the reciprocating motion. Furthermore, the average thickness of the chromium plating layer is preferably in the range of 10 μm to 30 μm. If the average thickness falls outside this range, it becomes difficult to control Ra, or excessive time is required for film formation.

[0037] The present invention will be described in more detail below through various experiments. However, the present invention is not limited to the configurations and structures described in these experiments.

[0038] [Experiment 1] (Preparation of sealing samples) For sealing samples for various experiments, NBR plates with a low nitrile composition (acrylonitrile content of 24% by mass or less) used in automotive hydraulic shock absorbers (thickness 2 mm, manufactured by NOK Corporation, A437) were prepared.

[0039] (Preparation of dust-mixed hydraulic fluid) To simulate the adhesion of dust and dirt to the sliding surface of the seal sample, a dust-mixed hydraulic fluid was prepared. Specifically, a dust-mixed hydraulic fluid was prepared by mixing and dispersing test dust (JIS Z 8901 Test Powder 1 No. 7, Kanto loam) at a concentration of 1% by mass into automotive hydraulic shock absorber hydraulic fluid.

[0040] [Experiment 2] (Scratch resistance evaluation by rotational sliding test using dust-mixed hydraulic fluid) In this experiment, a rotational sliding test was performed using dust-mixed hydraulic fluid to evaluate whether or not the sealing material was scratched (scratch resistance). The rotational sliding test was performed using a ball-on-disk friction and wear tester (PCS Instruments, UK, MTM traction tester).

[0041] For the test samples, we prepared seal samples without grease application and seal samples with grease (100 mg) applied to the surface. As for the greases, we prepared grease A, which used a poly-α-olefin synthetic oil as the base oil and an aliphatic diurea thickener (23% by mass), and grease B, which used a poly-α-olefin synthetic oil as the base oil and an aromatic diurea thickener (23% by mass).

[0042] The conditions of the rotational sliding test are as follows. A SUJ2 (high-carbon chromium bearing steel) with a diameter of 3 / 4 inch was used as the ball test piece, and the test samples prepared above (NBR plate without grease, NBR plate with grease) were used as the disk test pieces. The sliding load during sliding was 5 or 30 N, the sliding speed was 0.5 m / s, and the sliding time was 5 hours. The dust-mixed working oil was filled until the sliding surface was immersed. The oil temperature of the dust-mixed working oil was carried out at two types of 10°C and 80°C.

[0043] After the rotational sliding test, the surface of the NBR plate was observed with an optical microscope, and the presence or absence of scratches in the sliding direction and the length of the scratches in the case of scratches were measured. Those in which scratches in the sliding direction could not be observed or confirmed were judged as "no scratches", those in which scratches with a length of less than 10 mm were observed or confirmed in the sliding direction were judged as "with minor scratches", and those in which scratches with a length of 10 mm or more were observed or confirmed in the sliding direction were judged as "with major scratches". The test results of Experiment 1 are summarized in Table 1.

[0044]

[0045] As shown in Table 1, in the rotational sliding tests of the NBR plates without grease application (Test Nos. 1 to 3), large and small scratches were observed and confirmed on the surface of the NBR plates after the test, indicating that the anti-scratch property of the seal sample could not be ensured. The reason why the anti-scratch property in the rotational sliding test at an oil temperature of 80°C was relatively better than that at 10°C is considered to be that due to the high temperature, the deformation amount of the NBR plate, which is the disk test piece, became larger, the contact area with the ball test piece increased, and the contact pressure with the ball test piece decreased. The same reason is considered for the fact that the anti-scratch property in the rotational sliding test with a sliding load of 30 N was better than that in the case of 5 N.

[0046] In contrast, in the rotational sliding tests of the NBR plates with grease application (Test Nos. 4 to 9), no scratches were observed on the surface of the NBR plates after the test, and it was confirmed that good anti-scratch property was ensured.

[0047] [Experiment 3] (Test evaluation of initial friction characteristics) In this experiment, in order to evaluate the initial friction characteristics in the reciprocating sliding of the piston rod and the rod seal, an experiment was conducted using a reciprocating friction tester (Bruker Japan Co., Ltd., UMT TriboLab).

[0048] For the fixed test piece, the same test samples as in Experiment 2 (NBR plate without grease, NBR plate coated with Grease A, NBR plate coated with Grease B) were used. For the movable test piece, an S45C piece (S45C is carbon steel for machine structures, and the arithmetic mean roughness Ra of the surface of the hard chromium plating is about 0.08 μm) with hard chromium plating on the surface was used.

[0049] The other conditions of the reciprocating sliding test are as follows. The sliding load during sliding was 50 N, the sliding stroke was 10 mm, the frequency was 5 Hz, and the total sliding time was 10 hours. An operating oil (100 μL) without dust mixed was dropped on the sliding surface. Also, the temperature of the movable test piece was carried out at two types, 40 °C and 80 °C.

[0050] As evaluation items, the average friction coefficients at 0 - 10 minutes, 10 minutes - 1 hour, 1 - 2 hours, 4 - 5 hours, and 9 - 10 hours from the start of sliding were measured. Note that the data of the friction coefficient are accumulated in the control PC at intervals of 1 second.

[0051] Also, the wear amount of the NBR plate of the test sample was evaluated as follows. After the 10 - hour reciprocating sliding test, the operating oil remaining in the test sample and the testing machine was recovered, the recovered operating oil was washed with toluene, and the washed liquid was filtered through a membrane filter (pore diameter 0.8 μm), and the residue was taken as the NBR wear amount. The test results of Experiment 3 are summarized in Table 2.

[0052]

[0053] As shown in Table 2, in the reciprocating sliding test of the NBR plate without grease coating (Test Nos. 10 - 11), the average friction coefficient in the initial friction at 0 - 10 minutes from the start of sliding is high, and although the average friction coefficient gradually decreases with the passage of time, it is confirmed that it changes at a relatively high level. As a result, it is confirmed that the NBR plate wear amount is also relatively large.

[0054] In contrast, in the reciprocating sliding test of the NBR plate coated with grease (Test Nos. 12 - 15), it is confirmed that the average friction coefficient is low from the initial friction and changes stably. As a result, it is confirmed that the NBR plate wear amount is also significantly reduced.

[0055] Furthermore, when the mass change of the movable test specimen (an S45C specimen with hard chrome plating on its surface) was measured using a precision electronic balance to confirm the amount of wear on the movable test specimen, no mass change was observed in any of the tests No. 10 to 15. In other words, no wear was observed on the movable test specimen in this experiment.

[0056] From the experimental results described above, it was confirmed that the hydraulic cylinder device according to the present invention can suppress wear during the initial friction of the sliding portion between the piston rod and the rod seal (improve the initial friction characteristics). Reducing the amount of wear on the sliding portion leads to improved durability of the sliding portion.

[0057] The embodiments and experiments described above are explained to aid in understanding the present invention, and the present invention is not limited to the specific configurations described. For example, it is possible to replace some of the configurations of the embodiments with configurations that are common knowledge to those skilled in the art, and it is also possible to add configurations that are common knowledge to those skilled in the art to the configurations of the embodiments. In other words, the present invention allows for the deletion, substitution, and addition of some of the configurations of the embodiments and experiments specified herein, as long as it does not depart from the technical spirit of the invention.

[0058] 100...Automotive hydraulic shock absorber, 10...Cylinder section, 12...Outer cylinder, 14...Inner cylinder, 16...Base valve, 20...Piston, 22...Piston valve, 24...Piston seal, 30...Piston rod, 40...Hydraulic fluid, 50...Rod guide, 52...Guide bush, 54...Rod seal, 54m...Main lip section, 54d...Dust lip section, 54s...Space between lips, 54g...Grease, 55...Stay, 56...Main lip section spring, 57...Dust lip section spring.

Claims

1. A hydraulic cylinder device comprising: a cylinder tube; a piston capable of reciprocating inside the cylinder tube; a piston rod fixed to the piston; and a rod seal on which the piston rod slides, wherein the rod seal has a main lip portion disposed on the piston side and a dust lip portion disposed on the external side along the axial direction of the piston rod, and a lip space portion is formed between the main lip portion and the dust lip portion that does not contact the piston rod, and the lip space portion is filled with grease containing at least one of an aliphatic diurea thickener, an alicyclic diurea thickener, and an aromatic diurea thickener.

2. A hydraulic cylinder device according to claim 1, characterized in that the rod seal is made of acrylonitrile butadiene nitrile rubber with a nitrile content of 30% by mass or less.

3. A hydraulic cylinder device according to claim 1, characterized in that the grease has a poly-alpha-olefin oil as its base oil.

4. A hydraulic cylinder device according to claim 2, characterized in that the grease has a base oil of poly-alpha-olefin oil.

5. A hydraulic cylinder device according to claim 1, characterized in that the piston rod has a chromium plating layer with an arithmetic mean roughness of 0.1 μm or less formed on its surface.

6. A hydraulic cylinder device according to claim 2, characterized in that the piston rod has a chromium plating layer with an arithmetic mean roughness of 0.1 μm or less formed on its surface.

7. A hydraulic cylinder device according to claim 3, characterized in that the piston rod has a chromium plating layer with an arithmetic mean roughness of 0.1 μm or less formed on its surface.

8. A hydraulic cylinder device according to claim 4, characterized in that the piston rod has a chromium plating layer with an arithmetic mean roughness of 0.1 μm or less formed on its surface.

9. A hydraulic cylinder device according to any one of claims 1 to 8, characterized in that the hydraulic cylinder device is an automobile hydraulic shock absorber.

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