JP2013108156A - Member for valve drive system of internal combustion engine and method of using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a member for a valve drive system for an internal combustion engine, such as a valve lifter and a shim, which provides low friction and exerts steady slidability.SOLUTION: The member for a valve drive system for the internal combustion engine consists of a cam follower having a slide contact surface that is in slide-contact with a cam surface of a cam to follow the cam under a wet process condition where a lubricating oil lies. The slide contact surface of the cam follower is coated by a DLC film (DLC-B film) that consists of 5-25 atom% of H, 4-25 atom% of B, and the remainder of C when assuming the whole as 100 atom%. The slide contact surface that consists of the DLC-B film has high toughness and excellent impact resistance, and causes no lack, etc., even if received an impact force of 150-250 MPa/deg from the cam surface. Moreover, the cam follower exerts an excellent low friction coefficient when used under the wet process condition where the lubricating oil not containing molybdenum dialkyl dithiocarbamate (MoDTC) lies.

Description

  The present invention relates to a valve drive system member for an internal combustion engine comprising a cam follower excellent in slidability that stably exhibits low friction and a method of using the same.

  2. Description of the Related Art Internal combustion engines (referred to as “engines” as appropriate) mounted on automobiles and the like have been required to significantly reduce the coefficient of friction at each sliding portion in order to improve fuel efficiency. In order to realize this, for example, it has been proposed to form an amorphous carbon film called diamond-like carbon film (referred to as “DLC film” as appropriate) on the sliding surface, which can reduce the friction coefficient. There is a description related to this in the following Patent Document 1.

JP 2011-26591 A

  Patent Document 1 proposes a low friction sliding member in which an amorphous hard carbon film containing boron (B) is formed on a sliding portion. And it is described that the friction coefficient during sliding can be reduced by using the low friction sliding member under a specific lubricating oil not containing Mo.

  However, Patent Document 1 merely describes “low friction sliding member”, and does not describe any specific examples regarding the sliding member. Although a DLC film containing various additive elements is described, no specific evaluation has been made on what kind of DLC film is suitable for which sliding member.

  The present invention has been made in view of the above circumstances, and provides a valve drive system member for an internal combustion engine that is extremely effective for reducing power loss of an internal combustion engine and, in particular, for reducing fuel consumption, among sliding members. The purpose is to do.

  As a result of extensive research and trial and error, the inventor of the present invention has made a trial and error. When the crystalline carbon film (appropriately “DLC-B film”) is formed, it has been newly found that the friction coefficient is remarkably reduced, unlike the case of forming other DLC films or the like. In addition, unlike other DLC films, the DLC-B film formed on the slidable contact surface of the cam follower does not cause chipping or the like even when subjected to a high load from the slidable cam surface, and changes in engine operating conditions and operating time However, it has been newly found that the friction coefficient can be stably reduced. By developing these results, the present invention described below has been completed.

《Valve drive system member for internal combustion engine》
(1) The valve drive system member for an internal combustion engine of the present invention is interposed between a shaft end portion of a valve that controls intake or exhaust of the internal combustion engine and a cam that drives the valve to open and close, and lubricating oil is interposed. A valve drive system member for an internal combustion engine comprising a cam follower having a slidable contact surface that can slide and follow the cam surface of the cam under wet conditions, wherein the slidable contact surface of the cam follower has a total of 100 atoms. % (Simply referred to as “%”), an amorphous carbon film composed of 5 to 25% hydrogen (H), 4 to 25% boron (B), and the balance carbon (C). It is characterized by having.

(2) In the valve drive system member for an internal combustion engine of the present invention, the DLC-B film is provided on the sliding contact surface of the cam follower. As a result, the coefficient of friction between the cam surface and the sliding contact surface of the cam follower is significantly reduced. Moreover, the DLC-B film can stably maintain a good slidable contact surface without any chipping or cracking even when a very large impact force is applied at the start of contact with the cam surface. . Therefore, according to the present invention, the sliding or sliding contact between the cam follower and the cam surface is smoothly performed under a stable low friction, and the power loss of the engine and the fuel consumption can be greatly improved.

  The impact force applied to the sliding surface of the cam follower by the rotation of the cam is not easily specified. However, for example, 150 to 300 MPa / deg or 200 to 250 MPa / deg under severe high load (high load is instantaneous The valve drive system member for an internal combustion engine of the present invention can exhibit stable slidability even under high impact surface pressure applied to the internal combustion engine.

(3) The reason why the DLC-B film formed on the slidable contact surface of the cam follower can exhibit such excellent characteristics is not necessarily clear, but at present, it is considered as follows. The DLC-B film according to the present invention is harder than a cam follower base material and is excellent in wear resistance, etc., but its elastic modulus is lower than that of the base material (steel material) and rich in elasticity. Therefore, the DLC-B film according to the present invention has high toughness and excellent impact resistance. Therefore, the sliding contact surface of the cam follower coated with the DLC-B film according to the present invention is chipped even if a high impact force (or impact surface pressure) such as hitting with the cam surface is repeatedly applied immediately before the valve is opened. And no cracking. Even when the internal combustion engine is operated at various rotational speeds for a long period of time, a good sliding contact surface with low friction by the DLC-B film can be stably maintained.

  By the way, the reason why the DLC-B film according to the present invention exerts the optimum characteristics (particularly, low friction) on the sliding surface of the cam follower as described above is not necessarily certain among the DLC films. It seems like. According to the research conducted by the inventor, it is found that the DLC-B film suitable for the sliding contact surface of the cam follower not only has an amorphous structure but also has no carbides formed and is non-oriented. ing. For this reason, the entire DLC-B film is very homogeneous not only macroscopically but also microscopically. Lubricating oil, especially various additives contained therein, are easily adsorbed uniformly on the surface of the DLC-B film forming the sliding surface of the cam follower. As a result, it is considered that a special boundary film having a very large friction reducing effect is formed between the DLC-B film and the cam surface of the mating member in sliding contact. Thus, when the cam follower according to the present invention is used, it is considered that the power loss of the valve drive system is greatly reduced and the fuel efficiency of the internal combustion engine is improved.

<< Usage of valve drive system member for internal combustion engine >>
(1) The present invention is understood not only as a valve drive system member for an internal combustion engine but also as a method of using the same. For example, the present invention is used in a valve drive system member for an internal combustion engine, characterized in that it is used under wet conditions in which a lubricating oil containing 100 ppm or less of molybdenum (Mo) and not containing molybdenum dialkyldithiocarbamate (MoDTC) is present. It can be grasped as a method.

(2) The valve drive system member for an internal combustion engine of the present invention is premised on being used under wet conditions in which lubricating oil (engine oil) is present. As long as general engine oil is used, regardless of the type, the valve drive system member for an internal combustion engine of the present invention can exhibit the effects described above.

  However, in recent years when environmental load reduction is required, lubricating oils that do not contain molybdenum dialkyldithiocarbamate (MoDTC), which has been conventionally used as a friction modifier or the like (referred to as “MoDTC-free oil” as appropriate) are being used. When such an oil containing no MoDTC is used, the coefficient of friction between the sliding surface of the cam follower and the cam surface is higher than when using a conventional lubricating oil containing MoDTC (referred to as “MoDTC-containing oil” as appropriate). Can be expensive. In particular, the friction coefficient tends to increase when the sliding surface of the cam follower remains in the conventional Lubrite process or is covered with another DLC film.

  However, when the sliding surface of the cam follower is coated with the DLC-B film according to the present invention, the friction coefficient is greatly reduced regardless of whether the lubricating oil is an oil containing MoDTC or not containing MoDTC. Is done. In particular, it has been confirmed that the reduction rate of the coefficient of friction by the DLC-B film under the wet conditions of the MoDTC-free oil is significantly higher than that of other DLC films or conventional surface treatment layers. Therefore, it can be said that the valve drive system member for an internal combustion engine of the present invention is more preferable when it is used under wet conditions in which MoDTC-free oil is interposed. The reason why such an excellent effect is obtained is not necessarily clear, but it is considered that the above-described special boundary film is formed on the sliding portion.

<Others>
(1) The “amorphous carbon film” referred to in the present specification may contain elements effective for improving the characteristics of the amorphous carbon film other than C, H, and B (and O). The type of property to be improved is not limited. Of course, “inevitable impurities” that are difficult to remove due to cost or technical reasons, such as impurities contained in the raw material or impurities mixed during film formation, are also contained in the amorphous carbon film according to the present invention. obtain.

(2) When the valve drive system member for an internal combustion engine of the present invention is used, the friction coefficient between the sliding surface of the cam follower and the cam surface can be greatly reduced, but the absolute value of the friction coefficient is not limited. The coefficient of friction itself may vary depending on the type of lubricating oil, the material and properties of the cam surface that is the sliding contact. For this reason, it should be noted that the friction reduction effect referred to in this specification is a relative evaluation in the case where the situation except the sliding contact surface of the cam follower is the same. The friction coefficient when the cam follower according to the present invention is used under wet conditions is, for example, 0.03 to 0.05.

(3) Unless otherwise specified, “x to y” in this specification includes a lower limit value x and an upper limit value y. Any numerical value included in the various numerical values or numerical ranges described in the present specification can be newly established as a new lower limit value or upper limit value such as “ab”.

It is an electron beam diffraction image of the DLC-B film concerning the present invention. It is a TEM image of the section of the DLC-B film. It is an analysis spectrum figure by the EELS of the DLC-B film. It is the graph which analyzed the intensity | strength of the electron diffraction pattern of the DLC-B film | membrane in two directions. It is the graph which analyzed the intensity | strength of the electron diffraction pattern of a DLC-Si film in two directions. It is a graph which shows the amount of B of DLC-B film, and the relation of hardness. It is the bar graph which compared the friction coefficient of various DLC films. It is a graph which shows the relationship between B amount of a DLC-B film | membrane, and a friction coefficient. It is a schematic diagram which shows the contact locus | trajectory of the slidable contact surface and cam surface on the slidable contact surface of a shim (cam follower). It is a graph which shows the relationship between a cam angle and the contact load which acts on the sliding contact surface of a shim. It is a bar graph which shows the friction coefficient of each film in the wet conditions of MoDTC non-containing oil. It is a bar graph which shows the friction coefficient of each film in the wet conditions of MoDTC containing oil. It is a graph which shows the friction coefficient of each film in the wet conditions of MoDTC non-containing oil. It is a graph which shows the friction coefficient of each film in the wet conditions of MoDTC containing oil. It is a photograph which shows the mode after the sliding test of the shim surface coat | covered with the DLC-B film | membrane. It is a photograph which shows the mode after the sliding test of the shim surface coat | covered with the DLC-Si film | membrane.

  The present invention will be described in more detail with reference to embodiments of the invention. One or two or more configurations arbitrarily selected from the present specification may be added to the configuration of the present invention described above. The contents described in the present specification can be applied not only to the valve drive system member for an internal combustion engine according to the present invention, but also to its usage and manufacturing method. A configuration related to a manufacturing method can be a configuration related to an object if understood as a product-by-process. Note that which embodiment is the best depends on the target, required performance, and the like.

《Valve drive system member for internal combustion engine》
<Cam follower>
(1) The cam follower is driven by a cam driven by an engine or the like, and pushes a shaft end portion (valve end) of an intake valve or exhaust valve of the engine (referred to as “engine valve” as appropriate). Thus, the engine valve is opened and closed through the cam follower. The cam follower may be a direct hit type in which the opening and closing movement of the engine valve is directly performed by a cam, or a rocker arm type in which the opening and closing movement of the engine valve is indirectly performed through a rocker arm.

  In the case of direct hitting, the cam follower may be a valve lifter itself that guides the reciprocating movement of the valve end, or a shim interposed between the valve lifter and the cam surface to adjust the valve clearance. Such a slidable contact surface of the valve lifter or shim is likely to receive a large impact force or contact surface pressure from the cam surface. Even in such a case, the DLC-B film according to the present invention that covers the sliding contact surface exhibits a stable friction reducing effect. Therefore, a valve lifter or shim having a severe use environment is suitable as the cam follower according to the present invention.

(2) The cam follower covered with the DLC-B film is not limited to the material (base material), but is usually made of steel (carbon steel or alloy steel). Incidentally, the cam is made of cast iron or steel. Note that the cam surface of the cam is often subjected to surface modification such as carburizing to improve wear resistance.

  The cam follower before coating with the DLC-B film preferably has a surface roughness Ra (centerline average roughness / JIS) of 0.1 μm or less, 0.04 μm or less, and further 0.01 μm or less. In order to improve the adhesion between the substrate surface of the cam follower and the DLC-B film, it is preferable that one or more intermediate layers made of Cr, CrC or the like be formed between them.

<Amorphous carbon film (DLC-B film)>
(1) Composition The DLC-B film constituting the slidable contact surface of the cam follower contains B, H and the balance (main component) C as essential elements.

  The amount of B is 4 to 25%, 5 to 23%, 6 to 21%, 6.5 to 20%, or 7 to 18% when the entire film is 100 atomic% (referred to as “%” as appropriate). Is preferable. If B is too small, the coefficient of friction and hardness of the DLC-B film will be excessive, which is not preferable. When B is excessive, it becomes difficult to form a good DLC-B film.

  The amount of H is preferably 5 to 25%, 10 to 23%, and more preferably 15 to 22% when the entire film is 100%. When H is too small, the DLC-B film becomes excessively hard and the toughness can be lowered. When H is excessive, the DLC-B film becomes excessively soft and wear resistance decreases.

  The amount of O is preferably less than 6% or even less than 3% when the entire film is taken as 100%. An excessive amount of O is not preferable because the DLC-B film is excessively softened or a good film formation is difficult.

  In addition to the elements described above, the DLC-B film according to the present invention may contain a modifying element or an unavoidable impurity that improves its sliding characteristics. Examples of such elements include Al, Mn, Mo, Si, Ti, Cr, W, V, and Ni. The content of these elements is not limited, but it is preferably less than 8 atomic% or even less than 4 atomic%.

  Note that the composition of the amorphous carbon film may be homogeneous, slightly changed, or may be inclined with respect to the thickness direction of the DLC-B film.

(2) Structure / Organization The DLC-B film according to the present invention has an amorphous structure as in the conventional DLC film. However, the DLC-B film does not substantially contain carbides and has a non-oriented structure. It turns out to be preferable.

  First, if there is a carbide in the DLC-B film, the additives contained in the lubricating oil easily aggregate near the carbide. Therefore, if the carbide is not substantially contained in the DLC-B film, a uniform boundary film is easily formed on the DLC-B film that is in sliding contact with the cam surface, and the friction coefficient is stably reduced. Although details will be described later, the presence or absence of carbide is determined based on an electron beam diffraction image obtained by observing the DLC-B film with a transmission electron microscope (TEM).

  In addition, even when the DLC-B film has orientation, the formation of the above-described uniform boundary film is inhibited, so that the DLC-B film according to the present invention is not substantially oriented. Preferably it consists of. This orientation is also determined from the shape of the diffraction ring (substantially a perfect circle) belonging to the graphite (002) plane of the electron diffraction image.

(3) Characteristics The DLC-B film forming the sliding contact surface of the cam follower is preferably harder than the steel (carbon steel or alloy steel) base material constituting the cam follower, and preferably has a smaller elastic modulus than this steel base material. Thereby, the DLC-B film according to the present invention can exhibit high wear resistance and high toughness or high impact resistance.

  The hardness of the DLC-B film is preferably, for example, 10 GPa or more, 12 GPa or more, and further 14 GPa or more. However, if the hardness is excessive, cracking of the DLC-B film is likely to occur, and therefore it is preferably 30 GPa or less, more preferably 25 GPa or less. Incidentally, the steel substrate can be improved in hardness to about 8 GPa by performing heat treatment.

  The elastic modulus of the DLC-B film is preferably 200 GPa or less, 190 GPa or less, and further 170 GPa or less, for example. However, when the elastic modulus is too small, the hardness is also lowered, and therefore the elastic modulus is preferably 100 GPa or more and further 120 GPa.

  From the viewpoint of maintaining stable wear resistance, for example, the adhesion of the DLC-B film is preferably 20 N or more, and more preferably 25 N or more in a scratch test (REVETEST manufactured by CSM).

  The DLC-B film preferably has a surface roughness Ra of 0.05 μm or less, 0.02 μm or less, and further 0.01 μm or less. If Ra is excessive, the friction coefficient may increase and the wear resistance may decrease. The lower limit of the surface roughness is not limited, but when Ra is 0.001 μm or more, further 0.005 μm or more, the additive in the lubricating oil is easily adsorbed on the surface of the DLC-B film and a boundary film is easily formed. It is preferable.

  Although the film thickness of a DLC-B film | membrane is not ask | required, it is preferable in it being 0.5-3 micrometers further 0.7-2 micrometers. If the film thickness is too small, the durability becomes insufficient, which is not preferable.

<< Usage of valve drive system member for internal combustion engine >>
<Lubricant>
The valve drive system member for an internal combustion engine of the present invention exhibits excellent sliding characteristics when used under wet conditions where lubricating oil is present. In the present invention, the type of lubricating oil is not limited, but when the lubricating oil is a MoDTC-free oil, the DLC-B film according to the present invention exhibits particularly superior characteristics than other surface treatment films and the like.

  This MoDTC-free oil is composed of one or more of sulfur (S) or phosphorus (P), zinc (Zn), calcium (Ca), magnesium (Mg), sodium (Na) when the total amount is 100% by mass. It is preferable that 500 ppm or more in total of at least one of barium (Ba) and copper (Cu) is contained.

  Elements that become negative ions such as S and P are preferentially adsorbed on the surface of the DLC-B film in cooperation with elements that become positive ions such as Zn, Ca, Mg, Na, Ba, Cu, and friction. A boundary film effective for reducing the coefficient can be formed. When these elements are 500 ppm or more, further 1000 ppm or more, even if the friction modifier MoDTC is not contained, a friction reduction effect equivalent to or higher than that of the conventional one is more easily exhibited.

  Even in the case of MoDTC-free oil, Mo may be included in a form different from that of MoDTC. For example, Mo is effective as an antioxidant and the like, and MoDTC-free oil preferably contains 100 ppm or less of Mo.

<< Method for Manufacturing Valve Drive System Member for Internal Combustion Engine (DLC-B Film Formation Method) >>
The valve drive system member for an internal combustion engine of the present invention is obtained by forming a DLC-B film on the surface of the cam follower (and the surface of the intermediate layer). Here, a method for forming a DLC-B film will be described in detail.

  The method for forming the DLC-B film is not limited, but, for example, a sputtering method, particularly an unbalanced magnetron sputtering (UBMS) method, is preferable because a dense DLC-B film is efficiently formed.

Before forming the DLC-B film, it is preferable to evacuate the chamber to 10 ⁻⁵ Pa or less, or introduce hydrogen gas into the chamber to remove oxygen and moisture remaining in the chamber before film formation. . The amount of hydrogen gas introduced may be adjusted according to the amount of H in the DLC-B film.

As the sputtering gas, for example, one or more of rare gases such as argon (Ar) gas, helium (He) gas, and nitrogen (N 2) gas can be used. As the H-containing gas, one or more hydrocarbon-based gases such as methane (CH ₄ ), acetylene (C ₂ H ₂ ), and benzene (C ₆ H ₆ ) can be used.

The gas flow rate may be, for example, noble gas: 200 to 500 sccm and hydrocarbon gas: 10 to 25 sccm. In addition to these, H ₂ gas: 1 to 25 sccm may be introduced to reduce the amount of O and impurities in the film. The unit: sccm is a flow rate at room temperature of atmospheric pressure (1013 hPa).

  The film forming temperature of the DLC-B film is preferably 150 to 300 ° C., because the formation of carbides can be suppressed. The film formation temperature is the surface temperature of the base material during film formation, and can be measured by a thermocouple or a heat radiation thermometer.

  In addition, it is preferable to perform sputtering with a gas pressure of 0.5 to 1.5 Pa, a power applied to the target of 1 kW to 3 kW, and a magnetic field strength in the vicinity of the cam follower (base material) of 6 to 10 mT. Further, a negative bias voltage of 100 to 500 V may be applied to the substrate.

  In addition to the sputtering method, the DLC-B film may be formed by an arc ion plating (AIP) method. The AIP method is a method of forming a DLC-B film on the surface of a substrate by causing arc discharge in a vacuum and reacting C and B evaporated from each target with a processing gas in a reaction vessel. is there.

The present invention will be described more specifically with reference to examples.
《Amorphous carbon film》
First, in order to select an amorphous carbon film (DLC film) suitable for a valve drive system member for an internal combustion engine, samples in which various coatings shown in Table 1 were formed on the test substrate surface were manufactured.

<Base material>
A steel material (martensitic stainless steel: SUS440C) of 6.3 mm × 15.7 mm × 10.1 mm was prepared as a base material. The surface hardness before film formation was HRC60, and the surface roughness Ra (centerline average roughness / JIS) was 0.005 μm.

<Film formation>
The DLC film was formed on the substrate surface using an unbalanced magnetron sputtering apparatus (UBMS504 manufactured by Kobe Steel, Ltd.). Specifically, it is as follows.

(1) Formation of intermediate layer Before forming the DLC film, an intermediate layer was formed on the surface of the substrate in advance. Specifically, the inside of the sputtering apparatus was evacuated to 1 × 10 ⁻⁵ Pa, and a pure chromium target arranged to face the substrate surface was sputtered with Ar gas. Thus, a columnar Cr film was formed on the substrate surface. Subsequently, CH ₄ gas was introduced into the apparatus to form a Cr—C film on the surface of the Cr film. Thus, an intermediate layer having a total thickness of about 0.8 μm was formed. Throughout this example, the distance between the substrate surface and the target surface was adjusted to 100 to 800 mm. In addition, the film thickness was specified by Caltest made by CMS (hereinafter the same).

(2) Formation of DLC-B film (Sample Nos. 1 to 7)
In the same manner as described above, a B ₄ C target and a graphite target, which are boron sources arranged opposite to the substrate surface, were sputtered with Ar gas. Subsequently, 200 sccm of Ar gas, 10 sccm of CH ₄ gas (hydrocarbon gas) and 1 sccm of H ₂ gas were introduced into the apparatus. At this time, the gas pressure in the apparatus was 0.7 Pa. In this way, a sample was obtained in which the coating composed of the intermediate layer and the DLC-B film was formed on the surface of the substrate. The thickness of the DLC-B film was about 1.5 μm.

(3) Other DLC films (Sample Nos. C1 to C4)
A sample on which a DLC film other than the DLC-B film was formed was also prepared. In either case, a DLC film was formed on the surface of the base material on which the intermediate layer was formed. Specifically, the sample No. shown in Table 1 was used. The C1 DLC-Si film was formed by the DC plasma CVD method described in Japanese Patent No. 4372663. Sample No. The C2 DLC-Ti film was formed by the same method as in the case of the DLC-B film by changing the target from B ₄ C to Ti. Sample No. The C3 DLC-H film was formed by changing the target to C and introducing CH ₄ gas. Sample No. The hydrogen free DLC film of C4 was formed by the arc ion plating method described in Japanese Patent Application Laid-Open No. 2004-115826.

<Measurement / Evaluation>
For each DLC film shown in Table 1, the film composition, film structure, orientation, surface hardness (nano hardness), elastic modulus, surface roughness and friction coefficient were measured.

(1) Film composition B, Si, Ti and O in the film are electron probe microanalysis (EPMA), X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), or Rutherford backscattering (RBS). ). H was quantified by elastic recoil detection method (ERDA). ERDA is a method of measuring the hydrogen concentration by irradiating the surface of a film with a 2 MeV helium ion beam, detecting hydrogen ejected from the film with a semiconductor detector. The composition of the DLC film thus obtained is also shown in Table 1.

(2) Film structure Sample No. An electron beam diffraction image obtained by irradiating an electron beam to the central portion of the cross section in the thickness direction of the DLC-B film No. 5 is shown in FIG. 1A. This electron beam diffraction image is obtained by using a transmission electron microscope (TEM)) to obtain a micro region No. 1 of the TEM image shown in FIG. 3 is observed. From this electron beam diffraction image, a halo-like pattern is observed. 5 shows that the DLC-B film of No. 5 has an amorphous structure. In addition, similar electron beam diffraction images were observed in the DLC films of other samples, and they had an amorphous structure.

  Further, from the TEM image shown in FIG. 5 shows that the DLC-B film 5 is uniformly formed with a thickness of about 1 μm on the Cr-based intermediate layer composed of the Cr layer and the CrC layer.

  The adhesion of the DLC-B film was 30 N or more when examined by a scratch test (REVETEST manufactured by CSM). Therefore, it was found that the DLC-B film has high adhesion by interposing the intermediate layer.

  Moreover, the spectrum image regarding C and B obtained by analyzing the four minute regions shown in FIG. 1B by electron energy loss spectroscopy (EELS) is shown in FIG. 1C. First, regarding C, a peak (π * edge) indicating a π bond was recognized, but a peak (σ * edge) indicating a σ bond was not recognized and was broad. From this, it is considered that the DLC-B film of this example also has a covalent bond.

  Next, when it observed about B, although it detected, the spectrum was broad broadly and the detection of the carbide | carbonized_material was not recognized. This tendency was the same for other samples with a large amount of B. Therefore, it was found that the DLC-B film of this example substantially does not contain carbide. Note that the above description applies to all four regions subjected to EELS analysis, and the DLC-B film of this example was homogeneous in the film thickness direction.

(3) Orientation Sample No. FIG. 2A shows the result of analyzing the orientation of the DLC-B film No. 5 based on the electron diffraction pattern (FIG. 1A) described above. Sample No. FIG. 2B shows the result of the same analysis on the C4 DLC ₀ film. This result shows that the intensity of the electron diffraction pattern is measured along two orthogonal directions (horizontal direction (H direction) and vertical direction (V direction) in FIG. 1A) extending in the radial direction of the diffraction ring. Is processed by analysis software. 2A and 2B, the horizontal axis is the distance between the transmitted wave and the diffracted wave (r: unit is nm ⁻¹ ), and the vertical axis is the intensity.

  In the graph of FIG. 2A, the intensity gradually decreased as the r value increased in both the V direction and the H direction, and there was no intensity difference in the electron diffraction pattern between the two. This indicates that the DLC-B film does not contain carbide and is not oriented (consists of a non-oriented structure). On the other hand, in the graph of FIG. 2B, an intensity difference appears in the electron diffraction pattern between the V direction and the H direction (r = 2.803 (1 / nm) vicinity), and it is clear that the films are oriented. Incidentally, when the r value was compared with the face spacing described in the JCPDS card, it was found to be (002) orientation because it belonged to the graphite (002) face. A similar orientation was obtained for sample no. The C1 DLC-Si film has also been confirmed.

(4) Mechanical properties The surface hardness and elastic modulus of each DLC film were determined from the measured values with a nanoindenter testing machine (MTS manufactured by Toyo Corporation). The surface roughness was measured with a non-contact surface shape measuring instrument (New View 5000, manufactured by Zygo). The properties of the DLC film thus obtained are also shown in Table 1.

  Based on the results in Table 1, the relationship between the amount of B and the hardness regarding the DLC-B film is shown in FIG. As can be seen, the hardness of the DLC-B film decreases with an increase in the amount of B, but the hardness is stabilized in the range of 14 to 17 GPa when the amount of B is 5% or more, further 6% or more. This hardness is the same as Sample No. Although it is equivalent to the hardness of the CLC DLC-Si film, it is sufficiently larger than the hardness of the substrate (6 GPa).

  As is clear from Table 1, the same tendency as hardness was observed for the elastic modulus of the DLC-B film. The elastic modulus of the DLC-B film was smaller than that of the base material (elastic modulus 200 GPa) regardless of the amount of B. In particular, it was revealed that a DLC-B film having a B content of 4% or more has a low elastic modulus of 160 to 120 GPa and is rich in elasticity.

(5) Friction characteristics The friction coefficient of the DLC film shown in Table 1 was measured using a ring-on-block friction tester (LFW-1, manufactured by FALEX). This friction test is performed by sliding the DLC film and the counterpart material (ring) on the surface of the base material (block) described above under a certain friction condition under wet conditions in which lubricating oil is present. A ring (φ 35 mm, width 8 mm) made of carburized steel (SAE 4620) and having a surface roughness Rz (10-point average roughness / JIS) of 13 μm was used as the counterpart material. As the lubricating oil, an engine oil (Toyota Castle SM 5W-30 (SAE viscosity standard) / ILSAC standard: GF-4) not containing MoDTC (molybdenum dialkyldithiocarbamate) as a friction modifier was used. The friction conditions were as follows: load: 130 N (maximum Hertz surface pressure: 210 MPa), sliding speed: 0.3 m / s (rotation speed: 160 rpm), oil temperature: 80 ° C., sliding time: 30 minutes. Lubricating oil was supplied to the sliding part of the block and the ring by rotating the ring in a half bath state in the lubricating oil. The friction coefficients of the respective DLC films thus obtained are shown in FIGS. 4A and 4B. In addition, the friction coefficient shown here is a value measured immediately before the end of the test.

  First, as apparent from FIG. 4A, the coefficient of friction with respect to the steel material under wet conditions was significantly lower in the DLC-B film than in other DLC films. Specifically, the friction coefficient of the DLC-B film was lower by about 40 to 50% than the other DLC films.

  Next, as apparent from FIG. 4B, the coefficient of friction with respect to the steel material under wet conditions also changed depending on the amount of B in the DLC-B film. Specifically, the friction coefficient of the DLC-B film decreased with an increase in the B amount, and stabilized at a low value of about 0.03 to 0.05 when the B amount was 4% or more.

《Valve drive system member for internal combustion engine》
The frictional sliding characteristics of a shim (cam follower) having the above-described various DLC films formed on the surface thereof were measured using an engine valve system test device. The shim used is an outer shim having a shim diameter of φ25 mm.

<Test equipment>
The test apparatus consisted of a valve system part constituting an actual small gasoline engine (displacement: 1600 cc), and a camshaft as a part thereof was driven by a motor. When the camshaft rotates, the cam surface slides on the shim DLC film to which a predetermined load (spring load) is applied by the valve spring. Sim then follows the cam profile.

  The cam used here is made of material: cast iron, base circle: φ28 mm, cam width: 9.5 mm, opening angle: 110 ° (crank angle is 220 °), and the cam profile is almost symmetrical between the open side and the closed side. there were. The mounting load of the valve spring was 220N.

  When this test apparatus was operated, the contact locus with the cam surface on the shim surface (DLC film surface) is shown in FIG. 5A, and the contact load fluctuation at the contact position between them is shown in FIG. 5B. As can be seen from FIG. 5A, the cam surface starts contact from a position about 1 mm away from the center of the shim (contact start point), and then changes the contact position in the order of section I → section II → section III, From the shim at a position (disengagement point) about 1 mm away from the shim. Here, as can be seen from FIG. 5B, the contact load acting between both surfaces changes suddenly in the vicinity of the contact start point or the separation point. Specifically, at that time, the contact load changes by about 220 N during the cam angle of about 1 deg. For this reason, it can be seen that a large impact force acts between both in the vicinity of the contact start point.

<Friction sliding test>
Shim (surface roughness Rz: 0.3 μm) coated with a DLC-B film (sample No. 5), shim (surface roughness Rz: coated with a DLC-Si film (sample No. C1)) 1.1 μm) and current shims (surface roughness Rz: 2.9 μm) actually used in the above-described small engine (commercially available) were sequentially assembled and the respective frictional sliding characteristics were examined. Each shim is made of SCM material (JIS). In addition, the current shim has been subjected to a rubrite treatment on its base material.

  All of these tests were performed under wet conditions in the presence of lubricating oil. For the lubricating oil, use engine oil that does not contain MoDTC (Toyota Castle SN 0W-20 / ILSAC standard: GF-5) or engine oil that contains MoDTC (Toyota Castle SM 0W-20 / ILSAC standard: GF-4) It was. The former is called MoDTC-free oil, and the latter is called MoDTC-containing oil. The friction coefficient of each shim when each lubricant was used was determined. The results are shown in FIGS. 6A and 6B (both are appropriately referred to as “FIG. 6”) and FIGS. 7A and 7B (both are appropriately referred to as “FIG. 7”). The friction coefficient was the average value during the valve opening period (110 ° cam angle). In all cases, the test time was 20 hours or longer.

<Evaluation>
(1) Friction coefficient The friction coefficient shown in FIG. 6 is a value when the camshaft rotation speed is 500 rpm (engine rotation speed: equivalent to 1000 rpm) and the lubricating oil temperature is 80 ° C. When a shim coated with a DLC-B film was used, the friction coefficient was 0.04 or less regardless of the type of lubricating oil, and the friction coefficient was lower than any other shim. As can be seen from FIG. 6A in particular, when MoDTC-free oil is used, it is clear that the friction coefficient is remarkably lowered when a DLC-B film is provided on the sliding surface of the shim. Specifically, the coefficient of friction decreased by about 60% compared with the current shim.

  The friction coefficient shown in FIG. 7 is a value when the lubricating oil temperature is 80 ° C. and the rotational speed of the camshaft is changed between 250 to 1000 rpm (equivalent to the engine rotational speed: 500 to 2000 rpm). In this case as well, as in the case of FIG. 6, when a shim coated with a DLC-B film is used, the friction coefficient becomes almost 0.04 or less at any rotational speed regardless of the type of lubricating oil. The friction coefficient was lower than any of the shims. In particular, compared with the current shim, the friction coefficient of the shim coated with the DLC-B film was about 1/3 in the low rotation range and about 1/2 in the high rotation range, which was a very low value.

(2) Slidability After performing the above test under the wet condition of MoDTC-containing oil, the surface of each DLC-B film (sample No. 5) and the surface of the DLC-Si film (sample No. C1) It observed with the optical three-dimensional shape measuring machine (New View by Zygo). The external appearance photographs thereof are shown in FIGS. 8A and 8B, respectively. On the sliding contact surface of the shim made of the DLC-B film, no chipping or the like was observed to the extent that a minute sliding mark was observed at a position about 1 mm away from the center of the shim (near the contact start point). . On the other hand, on the slidable contact surface of the shim made of the DLC-Si film, a large sliding mark was observed at a position about 1 mm away from the center of the shim (near the contact start point), and chipping was also observed.

  The same tendency appeared when using a MoDTC-free oil. Further, when the shim mounting load (valve spring mounting load) was changed from 220N to 100N or 300N, the same tendency was confirmed. That is, the DLC-B film formed on the shim surface did not cause damage such as chipping in any case, and the DLC-B film maintained a stable shim sliding surface with low friction.

  The reason why the contact surface of the shim covered with the DLC-B film is stable despite receiving a large impact force is that the DLC-B film has both the above-mentioned appropriate hardness and elasticity, and the DLC. This is considered to be due to the much higher toughness (high impact resistance) than the Si film or the like.

  Incidentally, the impact force generated at the contact start point is, for example, 100 to 300 N / deg (150 to 250 MPa / deg), and is 220 N / deg (230 MPa / deg) in the case shown in FIG. 5B. The surface pressure acting between the shims was calculated from the contact circle radius and contact width of the cam, the mounting load of the valve spring, the longitudinal elastic modulus of each member, and the like.

Claims (11)

The cam is interposed between a shaft end portion of a valve for controlling intake or exhaust of the internal combustion engine and a cam for driving the valve to open and close, and is in sliding contact with the cam surface of the cam under a wet condition in which lubricating oil is interposed. A valve drive system member for an internal combustion engine comprising a cam follower having a sliding contact surface that can be driven,
The sliding surface of the cam follower is 5 to 25% hydrogen (H), 4 to 25% boron (B), and the balance carbon (100% by mass). A valve drive system member for an internal combustion engine having an amorphous carbon film made of C) on the surface.   The valve drive system member for an internal combustion engine according to claim 1, wherein an impact force of 150 to 300 MPa / deg can act on the sliding contact surface of the cam follower by the rotation of the cam.   The valve drive system member for an internal combustion engine according to claim 1, wherein the amorphous carbon film is made of a non-oriented structure.   The valve drive system member for an internal combustion engine according to claim 1, wherein the amorphous carbon film does not substantially contain carbide.   The valve drive system member for an internal combustion engine according to any one of claims 1 to 4, wherein the amorphous carbon film is harder than a steel base constituting the cam follower and has a smaller elastic modulus than the steel base.   The valve drive system member for an internal combustion engine according to claim 1, wherein boron in the amorphous carbon film is 6.5 to 20%.   The valve drive system member for an internal combustion engine according to any one of claims 1 to 6, wherein the amorphous carbon film has an oxygen (O) content of less than 6%.   The valve drive system member for an internal combustion engine according to any one of claims 1 to 7, wherein the amorphous carbon film is formed on an intermediate layer formed on a surface of a base material of the cam follower.   The valve drive system member for an internal combustion engine according to any one of claims 1 to 8, wherein the cam is made of cast iron.   The valve drive system member for an internal combustion engine according to any one of claims 1 to 9, under a wet condition in which a lubricating oil containing 100 ppm or less of molybdenum (Mo) and substantially free of molybdenum dialkyldithiocarbamate (MoDTC) is interposed. A method of using a valve drive system member for an internal combustion engine, characterized in that   The lubricating oil is composed of at least one of sulfur (S) and phosphorus (P), zinc (Zn), calcium (Ca), magnesium (Mg), sodium (Na), and barium when the total amount is 100% by mass. The usage method of the valve drive system member for internal combustion engines of Claim 10 which contains 500 ppm or more in total of 1 or more types of (Ba) or copper (Cu).