JP7127663B2 - gear and drive unit - Google Patents

Description

The present disclosure relates to gears and drive units.

2. Description of the Related Art Conventionally, lubricating oil has been used in internal combustion engines, automatic transmissions, shock absorbers, power steering devices and other drive system devices, gears, and the like to facilitate their operation. Lubricating oil has mechanisms such as lubrication of various sliding parts, cooling inside the engine, cleaning of combustibles, rust prevention, and anticorrosion. Therefore, additives such as antiwear agents, metal detergents, and antioxidants are sometimes added to lubricating oils depending on the purpose.

For example, zinc dithiophosphate (ZnDTP), zinc dithiocarbamate (ZnDTC), molybdenum dithiocarbamate (MoDTC), molybdenum dithiophosphate (MoDTP), and the like are known as antiwear agents.

For example, MoDTC is known to produce MoS ₂ , which is a layered compound, on the sliding surface and exhibit low friction. In internal combustion engines such as engines, engine oils containing MoDTC are widely used in order to reduce the coefficient of friction of sliding parts to reduce friction loss. On the other hand, it is known that the effect of MoDTC varies greatly depending on other coexisting additives. Techniques using a combination of additives and the like have been proposed.

On the other hand, the lubricating oil used for gears, which have a surface pressure of more than 1 GPa at sliding parts and have a higher surface pressure than engines, is required to have higher wear resistance and seizure resistance than engine oils. Therefore, the composition of lubricating oil used for gears is different from the composition of engine oil. For example, the lubricating oil composition described in Patent Document 1 contains ZnDTP as an essential component. ZnDTP is not contained in gear oils such as transaxle fluids used in HVs or electric vehicles (EVs), and their compositions are different.

In gear oil with a different composition from engine oil, the effect of MoDTC is less likely to be exhibited than in engine oil, and gear oil in which the addition of MoDTC halves the friction coefficient like engine oil has not reached the market. For example, in Non-Patent Document 1, the effect of reducing friction by blending MoDTC is small, remaining at about 20%.

JP-A-6-336592

"Clarification of Friction Reduction Mechanism of Low Viscosity Differential Gear Oil" Tribology Conference 2018 Spring Tokyo Proceedings (2018), p.206-207, Nissan Motor Co., Ltd. Sachiko Okuda, Tomoo Kubo, Yuji Okamoto, Naoto Akie, Moena Ariyama, JXTG Energy , Hitoshi Komatsubara

In recent years, not only AT vehicles but also HVs and EVs have used gear type drive units (also referred to as gear drive units) to reduce the number of motor revolutions. In order to improve the fuel or electricity consumption of a vehicle using a gear drive unit, it is essential to reduce the friction coefficient of the gear sliding portion and reduce the friction loss of the gear drive unit. Conventionally, addition of an antiwear agent has been studied as one of the methods for increasing the effect of reducing the friction generated on the sliding surface of the gear sliding portion. However, it is difficult to say that the conventional technology is sufficiently effective in reducing friction, and there is a demand for the establishment of a technology that reduces the coefficient of friction in the sliding portion of the gear. ing.

The present disclosure has been made in view of the above.
A problem to be solved by an embodiment of the present disclosure is to provide a gear with a reduced coefficient of friction.
A problem to be solved by another embodiment of the present disclosure is to provide a drive unit with less friction loss.

Specific means for achieving the above object are as follows.
<1> A gear used in an automatic transmission or a transaxle,
Having a tribofilm on the carburized steel in the sliding area,
In the tribofilm, the peak area of the secondary ions detected by time-of-flight secondary ion mass spectrometry in which the surface of the tribofilm is irradiated with 30 keV Bi ⁺ ions as beam-like primary ions has the following (1a) to (4a): ) is a gear that satisfies the relationship
(1a) the ratio of the peak area of Mo ⁺ to the peak area of Fe ⁺ ≥ 0.05
(2a) the ratio of the Ca ⁺ peak area to the Fe ⁺ peak area ≥ 0.01
(3a) the ratio of the MoS ²⁻ peak area to the total peak area of the reference negative ions ≧0.0008;
(4a) the ratio of the peak area of C ₈ H ₇ SO ^3- to the total peak area of the reference negative ions ≤ 0.003;

In 3a and 4a above, the reference negative ions are C ⁻ (M/Z: 12.00), CH ⁻ (M/Z: 13.01), O ⁻ (M/Z: 16.00), OH ⁻ (M/Z: 17.00), C ₂ ⁻ (M/Z: 24.00), and C ₂ H ⁻ (M/Z: 25.01).
Note that M/Z represents the mass number, which is the value obtained by dividing the mass by the electric charge.

<2> The gear according to <1>, satisfying the following relationships (1b) to (4b).
(1b) the ratio of the peak area of Mo ⁺ to the peak area of Fe ⁺ ≥ 0.30
(2b) the ratio of the Ca ⁺ peak area to the Fe ⁺ peak area ≥ 0.02
(3b) the ratio of the MoS ²⁻ peak area to the total peak area of the reference negative ions ≧0.0009
(4b) the ratio of the peak area of C ₈ H ₇ SO ³⁻ to the total peak area of the reference negative ions ≦0.002;

<3> The gear according to <1> or <2>, further satisfying the following relationship (5a).
(5a) the ratio of the peak area of Zn ⁺ to the peak area of Fe ⁺ ≤ 0.10

<4> The gear according to any one of <1> to <3>, further satisfying the following relationship (6a).
(6a) the ratio of the peak area of PO ²⁻ to the total peak area of reference negative ions ≤ 0.08

<5> A drive unit comprising: the gear according to any one of <1> to <4>; and a mechanism for distributing power to at least one of an internal combustion engine and a motor by the gear.

According to one embodiment of the present disclosure, a gear with a reduced coefficient of friction is provided.
According to another embodiment of the present disclosure, a drive unit with low frictional losses is provided.

FIG. 4 is a TOF-SIMS spectrum showing MoS ₂ ⁻ peaks; FIG. FIG. 3 is a TOF-SIMS spectrum showing the PO ₂ ⁻ peak. FIG. 1 is a TOF-SIMS spectrum showing the C ₈ H ₇ SO ₃ ^— peak. TOF-SIMS spectra showing Mo ^{2 +} peaks. TOF-SIMS spectra showing Ca ⁺ peaks. FIG. 3 is a TOF-SIMS spectrum showing Fe ⁺ peaks. FIG. FIG. 4 is a TOF-SIMS spectrum showing Zn ⁺ peaks; FIG. It is a schematic diagram showing a block-on-ring type abrasion tester used for abrasion testing. It is a TOF-SIMS spectrum of negative ions at M/Z=158-168. It is a TOF-SIMS spectrum of negative ions at M/Z=158-168. It is a TOF-SIMS spectrum of negative ions at M/Z=20-80. It is a TOF-SIMS spectrum of negative ions at M/Z=20-80. It is a TOF-SIMS spectrum of positive ions at M/Z=30-120. It is a TOF-SIMS spectrum of positive ions at M/Z=30-120.

The content of the present disclosure will be described in detail below.
The description of the constituent elements described below may be made based on representative embodiments of the present disclosure, but the present disclosure is not limited to such embodiments.

In the present disclosure, the term "to" indicating a numerical range is used to include the numerical values before and after it as lower and upper limits. In the numerical ranges described step by step in the present disclosure, the upper limit or lower limit described in one numerical range may be replaced with the upper limit or lower limit of another numerical range described step by step. Also, in the numerical ranges described in the present disclosure, the upper or lower limits of the numerical ranges may be replaced with the values shown in the examples.

In this specification, when referring to the amount of each component in the composition, if there are multiple substances corresponding to each component in the composition, unless otherwise specified, multiple components present in the composition means the total amount of

In addition, in the present disclosure, a combination of preferred aspects is a more preferred aspect.

<Gear>
A gear of the present disclosure (hereinafter also referred to as a gear) is a gear used in an automatic transmission or transaxle that is a gear drive unit (gear drive unit), and has a tribofilm on the carburized steel material in the sliding area. . In the tribofilm in the gear of the present disclosure, the peak area of the secondary ions detected by time-of-flight secondary ion mass spectrometry in which the surface of the tribofilm is irradiated with 30 keV Bi ⁺ ions as beam-like primary ions is as follows ( Satisfy 1a) to (4a).
(1a) the ratio of the Mo ⁺ peak area S ^Mo to the Fe ⁺ peak area S ^Fe ≥ 0.05
(2a) the ratio of the Ca ⁺ peak area S ^Ca to the Fe ⁺ peak area S ^Fe ≥ 0.01
(3a) the ratio of the peak area S ^MoS of MoS ²⁻ to the total peak area S ^t of the standard negative ions ≧0.0008
(4a) the ratio of the peak area S ^CSO of C ₈ H ₇ SO ^3- to the total peak area S ^t of the standard negative ions ≤ 0.003;

The above “reference negative ions” are C ⁻ (M/Z: 12.00), CH ⁻ (M/Z: 13.01), O ⁻ (M/Z: 16.00), OH ⁻ (M/ Z: 17.00), C ₂ ⁻ (M/Z: 24.00), and C ₂ H ⁻ (M/Z: 25.01).

In order to improve the fuel or electricity consumption of a vehicle using a gear type drive unit (gear drive unit), it is effective to reduce the coefficient of friction in the gear sliding portion. Conventionally, the addition of an antiwear agent has been considered as one of the methods of reducing friction. However, it is difficult to say that the conventional technology is sufficiently effective in reducing the friction generated on the sliding surface of the gear sliding portion, and there is a need to establish a technology that effectively reduces the friction coefficient of the gear sliding portion. .

Conventionally, many AT vehicles employ a wet multi-disc clutch that transmits power to the transmission mechanism by friction. In the clutch part, it is necessary to secure a friction coefficient of a certain value or more, and therefore the ATF does not use a low friction coefficient like MoDTC-containing engine oil.

When the gear of the present disclosure is installed in a gear drive unit, a tribofilm having a specific composition is formed on the gear surface by gear oil such as automatic transmission fluid (ATF) or transaxle fluid. A tribofilm having a specific composition can significantly reduce the coefficient of friction, especially on the gear sliding surface of a gear drive unit.
Thereby, the friction loss of the gear drive unit can be effectively reduced.

The gear of the present disclosure has a carburized steel and a tribofilm formed on the carburized steel. Gears of the present disclosure may also have other membranes as desired.

(Carburized steel)
Carburized steel is a base material that forms the skeleton structure of gears.
Carburized steel refers to steel manufactured by adding carbon to harden the surface.

As the carburized steel material, any carburized steel material may be used. Carburizing treatment refers to a treatment for hardening by diffusing carbon into the surface layer of low-carbon steel having workability. For example, it may be a steel material obtained by infiltrating and diffusing carbon on the surface of a low-carbon steel to increase the carbon content of the surface and then quenching to harden the surface. Since the interior of the steel material remains low-carbon steel, it retains its toughness when it is made into a product, and in addition to being hardened by quenching, it has excellent wear resistance due to the action between the surface layer and the interior.

The shape, size, and other properties of the carburized steel material may be appropriately selected according to the purpose, etc., and are not particularly limited.

(Tribofilm)
The gear of the present disclosure has a tribofilm formed on a carburized steel material. A tribofilm refers to a protective film formed on the gear surface when the gear is used.

A tribofilm refers to a film (also called a tribofilm) formed by an additive contained in a lubricating oil adhering to the surface of a sliding part where friction occurs. It is a protective film formed by additives adsorbing or chemically reacting on the surface of sliding parts.

In the tribofilm in the present disclosure, the peak area of the secondary ions detected by time-of-flight secondary ion mass spectrometry in which the surface of the tribofilm is irradiated with 30 keV Bi ⁺ ions as beam-like primary ions is as described above. , satisfy the following relationships (1a) to (4a).
(1a) ^SMo / ^SFe ≧0.05
(2a) S ^Ca /S ^Fe ≧0.01
(3a) S ^MoS /S ^t ≧0.0008
(4a) S ^CSO /S ^t ≤ 0.003

“Reference negative ions” at St refer to negative ^ions at each M/Z, C ⁻ (M/Z: 12.00), CH ⁻ (M/Z: 13.01), O ⁻ (M /Z: 16.00), OH ⁻ (M/Z: 17.00), C ₂ ⁻ (M/Z: 24.00), and C ₂ H ⁻ (M/Z: 25.01).

The peak area of ions detected by time-of-flight secondary ion mass spectrometry is detected by irradiating the surface of the tribofilm with a beam of primary ions by the TOF-SIMS (Time Of Flight Secondary Ion Mass Spectrometry) method. It refers to the area of the peak waveform for each ion in an intensity spectrum represented on a two-dimensional coordinate system with the intensity of secondary ions as the ordinate and the mass number (M/Z) as the abscissa.
Note that the mass number represented by M/Z is an amount corresponding to a value obtained by dividing the mass by the electric charge.

In detection by time-of-flight secondary ion mass spectrometry (TOF-SIMS), the surface of a solid gear is irradiated with Bi ⁺ ions in the form of a beam of primary ions, and secondary ions generated by collisions between the Bi ⁺ ions and the gear surface are generated. Ions are detected with a time-of-flight mass spectrometer (TOF-MS).

In the present disclosure, the surface of the tribofilm is irradiated with 30 keV Bi ⁺ ions as a beam of primary ions. This identifies the composition of the tribofilm formed on the surface of the steel gear. At this time, the secondary ion spectrum obtained is mostly a group of fragment ions of hydrocarbons derived from the base oil and its degraded substances. A characteristic ion derived from a component of is detected. By detecting this, the composition of the tribofilm can be identified.

For detection using the TOF-SIMS method, for example, a time-of-flight secondary ion mass spectrometer TOF-SIMS ⁵ manufactured by Ion-Tof can be used.

(1a) Mo ⁺ strength The ratio of the peak area S ^Mo of Mo ⁺ to the peak area S ^Fe of Fe ⁺ (S ^Mo /S ^Fe ) is 0.05 or more. An ^SMo / ^SFe ratio of 0.05 or more is effective in reducing the friction coefficient.
The ^SMo / ^SFe ratio is preferably 0.30 or more, more preferably 0.35 or more, and even more preferably 0.40 or more. Moreover, the upper limit of the ^SMo / ^SFe ratio is not particularly limited.

(2a) Ca ⁺ strength The ratio of the Ca ⁺ peak area S ^Ca to the Fe ⁺ peak area S ^Fe (S ^Ca /S ^Fe ) is 0.01 or more. When the S ^Ca /S ^Fe ratio is 0.01 or more, the wear resistance is improved.
The S ^Ca /S ^Fe ratio is preferably 0.02 or more, more preferably 0.025 or more. Moreover, the upper limit of the S ^Ca /S ^Fe ratio can be set to 0.5 or less, preferably 0.1 or less, from the viewpoint of reducing the coefficient of friction.

(3a) MoS ^2- strength The ratio of the peak area S ^MoS of MoS ^2- to the total peak area S ^t of reference negative ions (S ^MoS /S ^t ) is 0.0008 or more. An S ^MoS /S ^t ratio of 0.0008 or more is effective in reducing the friction coefficient.
The S ^MoS /S ^t ratio is preferably 0.0009 or more. Also, the upper limit of the S ^MoS /S ^t ratio is not particularly limited.

(4a) C ₈ H ₇ SO ^3- strength The ratio of the peak area S ^CSO of C ₈ H ₇ SO ^3- to the total peak area S ^t of the standard negative ions (S ^CSO /S ^t ) is 0.003 or less. is. An S ^CSO /S ^t ratio of 0.003 or less is effective in reducing the friction coefficient.
The S ^CSO /S ^t ratio is preferably 0.002 or less, more preferably 0.0015 or less. Moreover, the lower limit of the S ^CSO /S ^t ratio is not particularly limited, and can be 0.00005 or more.

The tribofilms in the present disclosure are formed on gear surfaces through the use of lubricated gears. At this time, the additive contained in the lubricating oil forms a protective film by adsorption or chemical reaction on the surface of the carburized steel material, so by adjusting the composition of the lubricating oil to be used, the above (a1) to (a4) can be adjusted within a range that satisfies

From the viewpoint of more effectively exhibiting the effects of the present disclosure, it is preferable that the relationships (1a) to (4a) satisfy the following relationships (1b) to (4b).
(1b) ^SMo / ^SFe ≧0.30
(2b) S ^Ca /S ^Fe ≧0.02
(3b) S ^MoS /S ^t ≧0.0009
(4b) S ^CSO /S ^t ≤ 0.002

Furthermore, the relationships (1a) to (4a) above are more preferably in a range that satisfies the relationships (1c) to (4c) below.
(1c) ^SMo / ^SFe ≧0.40
(2c) S ^Ca /S ^Fe ≧0.025
(3c) S ^MoS /S ^t ≧0.0009
(4c) S ^CSO /S ^t ≤ 0.0015

Further, since zinc (Zn) compounds are known to cause clogging of wet clutches in automatic transmissions, it is preferable that the following relationship (5a) is satisfied.
(5a) the ratio of the Zn ⁺ peak area S ^Zn to the Fe ⁺ peak area S ^Fe ≤ 0.10
Furthermore, since it is known that zinc (Zn) compounds clog wet clutches in automatic transmissions, the relationship (5a) above is preferably within the range of the relationship (5b) below.
(5b) ^SZn / ^SFe≤0.01

Moreover, from the viewpoint of increasing the proportion of the Mo compound in the friction surface and effectively reducing the coefficient of friction, it is preferable that the following relationship (6a) is satisfied.
(6a) the ratio of the peak area S ^PO2 of PO ₂ ⁻ to the total peak area S ^t of the standard negative ions ≤ 0.08
Further, the relationship (6a) is preferably within the range of the relationship (6b) below from the viewpoint of increasing the proportion of the Mo compound in the friction surface and reducing the coefficient of friction more effectively.
(6b) S ^PO2 /S ^t ≤ 0.07
Furthermore, the relationship (6a) above is preferably within the range of the relationship (6c) below for the same reason as above.
(6c) 0.02≦S ^PO2 /S ^t ≦0.07

Quantification of the TOF-SIMS spectrum shall be performed by the following method.
Since the quantification value may differ slightly depending on the selected range of peaks in the spectrum, the method of assigning the peaks of each ion and calculating the area when performing quantification is shown below.
Peaks in TOF-SIMS spectra may increase or decrease in two decimal places for each analysis. Therefore, for quantitative comparison of samples (test pieces), the range of M/Z for each peak is not constant, and the peak range is determined from the shape of the peak for each sample according to the following criteria. In addition, in the present disclosure, in consideration of the increase and decrease of the above numerical values, normalization is performed by taking the ratios as in (1a) to (4a) described above.

MoS ₂ ⁻ shown in FIG. 1A is judged as follows.
The MoS ₂ ⁻ count number shown in FIG. 1A presents a complex peak shape in which multiple peaks overlap. This is because MoS ₂ on the analysis surface (outermost surface) is easily oxidized, and after the friction test and before being inserted into the analysis equipment, it was washed and exposed to the atmosphere, and a part of it was converted to MoSO ₂ and MoO ₄ . This is probably due to oxidation. Measurement of the standard MoS ₂ spectrum also tends to give similar peak shapes. Therefore, the MoS ₂ ⁻ (M/Z: 161.850) peak is the area of the colored region containing MoO ₄ ⁻ , that is, the fine peak top is in the range of M/Z = 161.840 to 161.880. Find the total peak area of a certain peak.

On the other hand, as shown in FIGS. 1B to 1G, the counts of PO ₂ ⁻ , C ₈ H ₇ SO ₃ ⁻ , Mo ⁺ , Ca ⁺ , Fe ⁺ , and Zn ⁺ all exhibit sharp peaks. there is
For these ions, the peak top obtained by analyzing the friction surface (outermost surface) of each test piece in the same manner as described above is in the range of M / Z = 62.960 to 62.970 for PO ₂ ^- , M/Z=182.992-183.035 for C ₈ H ₇ SO ₃ ⁻ , M/Z=97.897-97.912 for Mo ⁺ , M/Z=39.957 for Ca ⁺ Determine the peak area in the range ∼39.966. Also, as shown in FIG. 1G, although no peak was observed in the count number of Zn ⁺ , the area in the range of M/Z=93.920 to 93.936 is determined.

The thickness of the tribofilm is not particularly limited, and may be in the range of 1 nm to 1000 nm, and may be in the range of 10 nm to 400 nm.

The elemental composition of the tribofilm can be controlled by selecting the type of lubricating oil and the type of additive contained in the lubricating oil so that the peak waveform appearing in the TOF-SIMS spectrum becomes the desired waveform.
The lubricating oil is not particularly limited, and commercially available automatic transmission fluid (ATF (automatic transmission fluid), etc.) can be used.

<Drive unit>
The drive unit of the present disclosure comprises the gears of the present disclosure described above and a mechanism for distributing engine power and motor power through the gears. Since the tribofilm satisfying the above-described relationships (1a) to (4a) is formed on the sliding surface of the gear, friction loss in the drive unit can be greatly reduced.

A mechanism that distributes the power of at least one of an internal combustion engine and a motor by means of gears refers to a power distributor that distributes power to a plurality of mechanisms as needed. For example, the power from the engine is distributed between the motor generator and the counter gear. gear mechanism etc. can be mentioned.

An internal combustion engine is a prime mover that obtains mechanical work using combustion gas generated by burning fuel in an engine such as a cylinder, and includes, for example, an engine.

A motor is a device that converts electrical energy into mechanical energy and includes, for example, electric motors.

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples as long as the gist of the present invention is not exceeded. Unless otherwise specified, "parts" are based on mass, and M/Z may be expressed as "m/z".

-Preparation of sample oil-
(1) Commercially available automatic transmission fluid (ATF (automatic transmission fluid); S element: 600 ppm, N element: 2100 ppm, B element: 70 ppm, P element: 300 ppm, Ca element: 120 ppm), shown in Table 1 below Sample oil 1 was prepared by blending commercially available additives to give the elemental composition shown.

(2) Molybdenum dithiocarbamate (MoDTC) is added to commercially available automatic transmission fluid (ATF (automatic transmission fluid); S element: 600 ppm, N element: 2100 ppm, B element: 70 ppm, P element: 300 ppm, Ca element: 120 ppm). ) to prepare sample oil 2 having the elemental composition shown in Table 1 below.

(3) By adding MoDTC to ATF containing S element: 1700 ppm, N element: 1700 ppm, B element: 100 ppm, P element: 500 ppm, and Ca element: 200 ppm, sample oil 3 having the elemental composition shown in Table 1 below was obtained. prepared.

(4) By adding MoDTC to sample oil 1, sample oil 4 having the elemental composition shown in Table 1 below was prepared.

The above sample oils 1 to 4 were subjected to a block-on-ring friction test (LFW-1 tester manufactured by FALEX) to evaluate the friction reduction effect.
The element content of each sample oil was measured by inductively coupled plasma (ICP) emission spectrometry for metal elements and sulfur content, and the nitrogen content was measured by trace nitrogen analysis by chemiluminescence.

－Block-on-ring friction test－
Using the block-on-ring type wear tester shown in FIG. 2, the sample oils 1 to 4 described above were sequentially charged into the container, and the ring test piece was arranged so that a portion of the test piece was immersed in the sample oil. A block test piece was arranged at a position facing the ring test piece and in contact with the ring outer peripheral surface of the ring test piece. By rotating the ring test piece, the ring outer peripheral surface of the ring test piece and the surface of the block test piece slide against each other.
SCM420 steel (chromium molybdenum steel) was used as the steel material for the block test piece, and the carburized steel was carburized so that the surface hardness was HV750 or higher. The surface of the block test piece was mirror-finished with a surface roughness (Ra) of 0.1 μm or less, and the width of the friction surface was 6.3 mm.
As the ring test piece, an S-10 standard test piece made of AISI4620 carburized steel (manufactured by FALEX; hardness HV800, surface roughness (Ra) 0.26 μm, outer diameter φ35 mm, width 8.8 mm) was used.

Under the following sliding wear conditions, a load is applied to the block test piece and the block test piece is pressed against a rotating ring test piece to perform a friction test for 30 minutes under continuous sliding conditions in the form of line contact. evaluated. The sliding wear condition is a condition that imitates the gear sliding condition of an automotive drive train unit.
The coefficient of friction was read for one minute immediately before the end of the 30-minute test. Each of the sample oils 1 to 4 was tested twice, and the average value was taken as the coefficient of friction.
<Sliding wear conditions>
・Load (W): 1179 N (Maximum Hertz surface pressure: 611 MPa)
・Sliding speed (v): 0.9m/sec
・Oil temperature (T): 80°C
・Test time (t): 30 min

Regarding the results of the above friction test, the coefficient of friction for each sample oil is shown in Table 2 below.
In addition, when sliding under the sliding wear conditions described above, it is considered that the lubrication state is boundary lubrication. Boundary lubrication is a severe lubrication condition in which a sufficient oil film is not formed and contact between solids occurs.

-Sliding surface analysis-
The composition of the tribofilm formed on the steel material surface of the test piece in the block-on-ring friction test was analyzed by the following method.
Specifically, it is as follows.
After the block-on-ring friction test, the secondary ion spectrum of the surface of the block test piece was measured by TOF-SIMS (time-of-flight secondary ion mass spectrometry) to analyze the composition. Analysis conditions are shown below.
<Analysis conditions>
Apparatus: TOF-SIMS ⁵ (manufactured by Ion-Tof)
Primary ion species: Bi ⁺
Irradiation voltage: 30 keV
Mode: High current bunched mode
Scan area: 200 μm square (128 pixels × 128 pixels)
Number of scans: 10scans

Regarding the coefficient of friction (μ), as shown in Table 2 above, the coefficient of friction ( μ) was observed. Among them, the sample oils 3 to 4, which satisfy the relationships (1a) to (4a) described above, showed good coefficients of friction (μ). In particular, when sample oil 4 having the elemental composition shown in Table 2 was used, the μ value was 0.050, and the desired excellent friction reduction effect was obtained in a friction test simulating the sliding state of a gear. Got.
From the above results, it is assumed that each sample oil forms a tribofilm on the surface of the steel material of the test piece. proved to be significantly different. In particular, the elemental composition of the tribofilm formed when sample oils 3 and 4 are used significantly lowers the coefficient of friction, making it possible to effectively reduce friction loss in the drive unit.

Next, the spectra of the tribofilms formed using the above sample oils 1 to 4 are shown in FIGS. 3 to 8. FIG.

3 and 4 are TOF-SIMS spectra of negative ions at M/Z=158-168.
Among the spectra shown in FIGS. 3 and 4, MoS ₂ ^- ions were detected near the mass number (M/Z) of 161.86 in the tribofilms formed using sample oils 2 to 4 to which MoDTC was added. . It was confirmed that MoS ₂ was generated on the surface of the steel material.

5 and 6 are TOF-SIMS spectra of negative ions at M/Z=20-80.
In the spectra shown in FIGS. 5 and 6, the presence of phosphoric acid compounds, such as PO ^2- and PO ^3- , which are considered to be generated from phosphorus-based additives blended as anti-wear agents, were recognized.

7 and 8 are TOF-SIMS spectra of positive ions at M/Z=30-120.
In the spectra shown in FIGS. 7 and 8, Ca ⁺ ions thought to be derived from the additive Ca-sulfonate (rust inhibitor) were observed, confirming the formation of a tribofilm containing a Ca compound. . On the other hand, no Zn ⁺ ions were detected, confirming the absence of Zn compounds.
Moreover, the above-mentioned Fe ⁺ is derived from the steel material of the block test piece. By calculating the ratio of the peak area of Fe ⁺ ions to the peak area of each compound ion, it was possible to quantitatively compare the component compositions of the tribofilms.

Table 2 shows the ratio of the peak areas of the positive ions and the reference negative ions.
C ₈ H ₇ SO ₃ ^— is presumed to be an adsorbed component of sulfonate groups derived from Ca-sulfonate.

The peak area (unit: cps) of the detected negative ions is likely to change depending on the state of the analytical instrument. Hydrocarbon groups, and C ⁻ (M/Z: 12.00), CH ⁻ (M/Z: 13.01), O ⁻ (M/Z: 16.00), OH ⁻ (M/Z: 17.00), C ₂ ⁻ (M/Z: 24.00), and C ₂ H ⁻ (M/Z: 25.01) detected amounts (reference negative (total value of peak areas of ions). Specifically, the ratio of the peak area (unit: cps) of the detected negative ions to the total peak area of the reference negative ions is shown.
In addition, positive ions are shown as a relative ratio to the peak area of Fe ⁺ ions originating from the steel material.

As shown in Table 2 above, in the tribofilms (tribofilms formed using sample oils 2 to 4) in which a low μ value (friction coefficient) was observed, it can be seen that a large amount of MoS ₂ ⁻ was generated. . However, the order of the MoS ₂ ^- amount and the μ value does not completely match, and it is considered that the friction characteristics cannot be determined only by the MoS ₂ amount on the surface.

Focusing on the tribofilms formed using sample oils 2 to 4 to which MoDTC was added, C ₈ H ₇ SO ₃ ⁻ derived from the additive Ca-sulfonate and Ca ⁺ differ in the order of production amounts. It is recognized that the lower the friction, the more MoS ₂ ^- is produced and the smaller the amount of C ₈ H ₇ SO ₃ ^- adsorbed, the better. Under the circumstances where Ca-sulfonate is also an essential component for securing various properties of ATF, it is considered that a friction surface that suppresses adsorption of sulfonate groups is effective in reducing friction.

It is generally known that the formation of phosphorus-based compounds on sliding surfaces is important for ensuring wear resistance and seizure resistance. Comparing the tribofilms formed using sample oil 3 or sample oil 4 in Table 2, it can be seen that the lower the PO ₂ ^- amount, the lower the μ value.
Since none of the ATFs used in this example contained a Zn-based additive, no Zn component was detected from the sliding surface.

Claims (4)

A gear used in an automatic transmission or transaxle,
Having a tribofilm on the carburized steel in the sliding area,
In the tribofilm, the peak area of the secondary ions detected by time-of-flight secondary ion mass spectrometry in which the surface of the tribofilm is irradiated with 30 keV Bi ⁺ ions as beam-like primary ions has the following (1a) to (5a ): ) that satisfies the relationship of gears.
(1a) the ratio of the peak area of Mo ⁺ to the peak area of Fe ⁺ ≥ 0.05
(2a) the ratio of the Ca ⁺ peak area to the Fe ⁺ peak area ≥ 0.01
(3a) the ratio of the MoS ₂ ⁻ peak area to the total peak area of the reference negative ions ≧0.0008;
(4a) the ratio of the peak area of C ₈ H ₇ SO ₃ ⁻ to the total peak area of the reference negative ions ≦0.003;
(5a) the ratio of the peak area of Zn ⁺ to the peak area of Fe ⁺ ≤ 0.10
In 3a and 4a, the reference negative ions are C ⁻ (M/Z: 12.00), CH ⁻ (M/Z: 13.01), O ⁻ (M/Z: 16.00), OH ⁻ (M/Z: 17.00), C ₂ ⁻ (M/Z: 24.00), and C ₂ H ⁻ (M/Z: 25.01). M/Z represents mass number, which is mass divided by charge. The gear according to claim 1, which satisfies the following relationships (1b) to (4b).
(1b) the ratio of the peak area of Mo ⁺ to the peak area of Fe ⁺ ≥ 0.30
(2b) the ratio of the Ca ⁺ peak area to the Fe ⁺ peak area ≥ 0.02
(3b) the ratio of the MoS ₂ ⁻ peak area to the total peak area of the reference negative ions ≧0.0009;
(4b) the ratio of the peak area of C ₈ H ₇ SO ₃ ⁻ to the total peak area of the reference negative ions ≦0.002; 3. The gear according to claim 1 or 2 , further satisfying the following relationship (6a).
(6a) the ratio of the peak area of PO ₂ ⁻ to the total peak area of reference negative ions ≦0.08; A gear according to any one of claims 1 to 3 ,
a mechanism for distributing power to at least one of an internal combustion engine and a motor by the gear;
drive unit with

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