JP3146696B2 - Outer ring of cam follower device for engine valve train - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The outer ring of a cam follower device for an engine valve train according to the present invention is used, for example, in a state where it is incorporated in a valve train of an automobile engine.

[0002]

2. Description of the Related Art There are various types of engine for automobiles.
Except for the cycle engine, all are provided with an intake valve and an exhaust valve that open and close in synchronization with the rotation of the crankshaft.

There are various types of valve operating mechanisms for driving these intake valves and exhaust valves. For example, the SOHC type shown in FIG. / 2 speed (in the case of a four-cycle engine)
The intake valve 17 and the exhaust valve 18 are reciprocally driven via the rocker arms 16, 16. Cams 19, 19 fixed to a camshaft 15 that rotates in synchronization with the crankshaft 14 reciprocally drive the intake valve 17 and the exhaust valve 18 while slidingly contacting the ends of the rocker arms 16, 16.

In recent years, the frictional force between the peripheral surfaces of the cams 19, 19 and the opposing parts of the opposing members such as the rocker arms 16, 16 during engine operation has been reduced, and the fuel consumption rate during engine operation has been reduced. In order to reduce the size, a cam follower device which rotates in accordance with the rotation of the cams 19, 19 is provided in the opposed portion.

More specifically, as shown in FIGS. 4 to 6, a pair of support walls 20, 20 provided at an end of the rocker arm 16 facing the cam 19 at an interval from each other, are provided at both ends of a shaft 21. And a short cylindrical outer ring 23 around the shaft 21 via rollers 22, 22 or directly in contact with the shaft 21.
The outer diameter surface of the outer ring 23 and the outer diameter surface of the cam 19 are brought into contact with each other, so that the outer ring 23
However, it is configured to rotate around the shaft 21.

The fuel consumption rate is reduced by providing such an outer ring 23 and changing the friction between the cam 19 and the member opposed thereto from sliding friction to rolling friction.

When the above-described cam follower device is incorporated in the valve operating mechanism of the engine, the above-mentioned cam follower device is not subjected to the above-mentioned fluctuation due to the fluctuating load applied to the outer diameter surface of the cam 19 by the outer diameter surface of the outer ring 23. Damage such as pitching is likely to occur on the outer diameter surface of the cam 19.

For this reason, the magazine "Automotive Engineering", July 1989
As described on page 39 of the special issue "Roller Rocker Arm and Friction Reduction Effect" in the monthly issue,
9 is made of a high-strength and high-hardness metal material, such as quenched cast iron, chill cast iron, quenched steel, or a sintered alloy, having excellent pitching resistance. I have.

On the other hand, Japanese Patent Publication No. 1-30008 discloses
On the surface of the rolling surface with R _max form a random direction scratches at 0.3 to 1.5 .mu.m, it describes an invention relating to the bearing rolling elements to form a 50 kgf / mm ² or more residual stress layer in the surface portion I have.

Japanese Patent Application Laid-Open No. 3-117723-5 discloses that a large number of depressions are randomly formed on the surface by barrel processing so that the hardness of the surface layer is higher than the internal hardness and the surface layer is compressed. Inventions that produce residual stress are described.

Japanese Patent Application Laid-Open No. 3-199716 discloses that
A bearing is described in which a surface hardened layer is provided on a surface in contact with a mating member, and the depth of the peak value of the compressive residual stress matches the depth of the peak value of the shear stress distribution.

[0012] Further, JP-A-4-54312, by shot peening, the compressive residual stress and 100 kgf / mm ² or more in the surface portion, bearing component was 40 kgf / mm ² or more at a portion of the subsurface 300μm An invention is described.

Further, Japanese Patent Publication No. 2-17607 discloses that
On the surface of the metal product, a shot of 40 to 200 μm having a hardness equal to or higher than the product hardness is injected at an injection speed of 100 m /
injected above sec, increasing the temperature in the vicinity of the surface than A ₃ transformation point, the invention has been described for surface processing method.

[0014]

However, as described in the above-mentioned magazine "Automotive Engineering", the camshaft 15 including the cam 19 is simply made of a high-strength and high-hardness metal material such as quenched cast iron. In this case, peeling is likely to occur on the outer diameter surface of the outer ring 23 that comes into contact with the outer diameter surface of the cam 19.

That is, finishing of the outer diameter surface of the cam 19 made of a hard metal material such as quenched cast iron is more difficult than finishing of ordinary cast iron. As shown in FIG. 8, a large number of minute projections are formed on the outer diameter surface of the cam 19, and the outer diameter surface has a relatively rough surface roughness of about 0.4 μm Ra to 0.8 μm Ra. . On the other hand, the outer race 23 is made of bearing steel which is harder than the cam 19, but since its shape is simpler than that of the camshaft 15 provided with the cam 19, it is easy to super finish the surface, and therefore, The outer diameter surface of the outer ring 23 is shown in FIGS.
As shown in FIG. 8, the surface roughness is as smooth as about 0.05 μmRa. For this reason, the amount of the lubricating oil 24 held on the outer diameter surface of the outer ring 23 is limited.

Thus, when the amount of the lubricating oil 24 is limited,
In the case of an outer ring that constitutes a cam follower device and that makes rolling contact with the outer diameter surface of the cam while operating the engine, the life may be shortened due to the occurrence of peeling. That is, S
When a valve train is located above the engine, as in an OHC or DOHC engine, lubricating oil is not always sufficiently supplied to the valve train, and lubrication conditions during operation become severe. Under such conditions, when the outer diameter surface of the outer ring 23 and the outer diameter surface of the cam 19 come into rolling contact with each other while sliding, peeling having a depth of 2 to 10 μm occurs on the outer diameter surface of the outer ring 23. However, the life of the outer diameter surface of the outer ring 23 is shortened.

In this case, even if the invention relating to the bearing component described in JP-A-4-54312 is applied to the outer ring 23, if the lubrication conditions are severe, the peeling resistance is insufficient regardless of the friction conditions. Becomes Also, Japanese Patent Laid-Open No. 3-19971
No. 6 describes no problem when the friction condition is only rolling friction, but when sliding friction occurs, the peeling resistance becomes poor. Also, 1-30
008 and JP-A-3-117723-5 also have severe lubricating conditions and severe peeling resistance under severe operating conditions such as a large load at the contact portion. Also, the one described in Japanese Patent Publication No. 2-17607 cannot obtain sufficient peeling resistance as it is.

Furthermore, in addition to the above publications,
JP-A-7525, JP-A-56-150622 and JP-B-63-44505 disclose inventions relating to a processing method or a workpiece in which a shot having a small particle diameter is jetted onto a surface to be processed at high speed. However, none of these publications describes a technique for obtaining an outer ring having sufficient peeling resistance.

In view of such circumstances, the inventor of the present invention has previously set the maximum compressive residual stress of this surface layer in the range of 0 to 50 μm to 50 to 110 kgf /
mm ² , hardness of Hv 830 to Hv 960, average surface roughness of 25 μm or less, and a ratio of retained austenite in the surface layer portion of more than 7% by volume (refer to Japanese Patent Application No. 4-113196). No.).

If the rolling sliding component according to the invention is used as an outer ring constituting the cam follower device, it is possible to prevent peeling having a depth of 2 to 10 μm from occurring,
While the life of the outer diameter surface of the outer ring can be increased, the following new problems to be solved arise.

That is, when the entire surface of the outer ring whose outer diameter surface is in contact with the cam 19 and whose inner diameter surface is in contact with the shaft 21 or the roller 22 is made to have the above-mentioned properties, the outer diameter surface of the cam 19 and Although it is possible to prevent the occurrence of peeling on the outer diameter surface portion of the outer ring, the surface is smoothed by barrel processing or super finish processing. Also makes the surface smooth
The outer diameter surface of the shaft 21 is easily worn.

The outer ring of the cam follower device for a valve train of an engine according to the present invention has been invented in view of the above-mentioned circumstances.

[0023]

An outer ring of a cam follower device for a valve operating mechanism of an engine according to the present invention includes a metal cam fixed to a camshaft that rotates in synchronization with a crankshaft of the engine, and a cam facing the cam. A pair of support wall portions formed at intervals on a member that receives the movement of the cam, a shaft fixed in a state of being bridged between the pair of support wall portions, A cam follower device for an engine valve operating mechanism comprising an outer ring rotatably supported on the periphery.

In particular, the outer ring of the cam follower device for the valve train of the engine according to the present invention has a depth from the outer diameter surface of 0 to 5 mm.
When the range of 0 μm is the surface layer, the maximum compressive residual stress of the surface layer is 50 to 110 kgf / mm ² , the hardness of the surface layer is Hv 830 to Hv 960, and the average wavelength of the surface roughness is 25 μm or less. The ratio of the retained austenite in the surface layer portion exceeds 7% by volume, and the inner diameter surface is super-finished.

[0025]

In the case of the outer race according to the present invention, it is possible to effectively prevent the occurrence of peeling having a depth of about 2 to 10 μm on the outer diameter surface, and to improve the durability.

More specifically, when used under severe lubrication conditions, the outer diameter surface of the outer ring is only at the tip of the minute projection formed on the surface, and does not intervene through the oil film, but with the surface of the mating part. Direct contact (metal contact). At this time,
Most of the load applied to the outer diameter surface of the outer ring is supported by a small number of small projections in contact with the surface of the mating component, and a large stress is concentrated and a tangential force is applied to each small projection.

[0027] Then, based on the stress concentration and the tangential force, minute cracks are generated on the outer diameter surface of the outer ring, and the cracks develop and peel. In order to simply prevent wear, it is sufficient to increase the hardness of the surface of the component. However, if the hardness is increased, cracks associated with peeling are likely to occur due to stress concentration.

In the case of the present invention, the hardness of the surface layer is Hv 830 to Hv 830.
Since the range of Hv 960 is regulated, it is possible to prevent the occurrence of cracks that lead to peeling while suppressing wear. When the hardness is less than Hv 830, cracks do not occur but wear becomes remarkable. Conversely, when the hardness exceeds Hv 960, cracks tend to occur instead of suppressing wear, and in any case, the life becomes longer. Comes down.

Also, increasing the maximum compressive residual stress is as follows.
It is important to prevent the generated crack from further evolving and to prevent the crack from leading to peeling. However, the maximum compressive residual stress on the outer ring surface is 110 kg
When the working exceeds f / mm ² , the hardness of this surface exceeds Hv960, so the maximum value of the maximum compressive residual stress was set to 110 kgf / mm ² . Conversely, if the maximum compressive residual stress is less than 50 kgf / mm ² , the effect of preventing the crack from developing is too small, so the minimum value of the maximum compressive residual stress was set to 50 kgf / mm ² .

The surface roughness affects the ability to form an oil film between the outer ring surface and the mating component surface, and the pitch (wavelength) of the roughness
The finer the particle, the better the oil film forming ability.
Experiments conducted by the present inventors have confirmed that the ability to form an oil film is significantly improved when the thickness is 5 μm or less. Therefore, the average wavelength of the roughness is regulated to 25 μm or less. Incidentally, in the present specification, the mean wavelength lambda _a surface roughness, lambda _a =
Represented by 2π · R _a / θ _a. However, R _a is the average roughness of the surface, the theta _a is the average of the absolute value of the inclination angle of the minute protrusions on the surface.

[0031] between a result of shortening the mean wavelength lambda _a surface roughness as improves the ability to retain lubricant between the large number of fine projections on the surface, the outer ring surface and the mating part surface Oil film forming ability is improved, and cracks such as those associated with peeling are less likely to occur.

Further, when a large amount of ductile austenite remains, the effect of preventing the occurrence of cracks can be expected, but when the residual ratio is 7% by volume or less, the effect of preventing the occurrence of cracks can be expected too much. Absent. Further, in order to keep the values of the maximum compressive residual stress and the hardness in the above-mentioned ranges, it is necessary to set the residual ratio of austenite to a value exceeding 7% by volume.

That is, as a sufficient condition that the maximum compressive residual stress and the hardness of the surface layer do not exceed the upper limits, ie, 110 kgf / mm ² and Hv 960, the austenite decomposition rate ( (A rate at which austenite decreases with processing) may be suppressed to 30% or less. On the other hand, before surface processing, the ratio of austenite contained in bearing steel such as SUJ2 is about 11% by volume. Therefore, in order to prevent the maximum compressive residual stress and the hardness from exceeding the upper limit values, the ratio of austenite after processing should be 7%.
It is necessary to exceed the capacity%. When the processing by shot peening is too weak, the maximum compressive residual stress and the hardness are respectively lower limit values, that is, 50 kgf / mm ² , Hv83
Does not reach zero.

On the other hand, the oil film parameter Λ (= h / σ, where h / σ is the value between the inner diameter surface of the super-finished outer ring and the outer diameter surface of the roller or shaft also subjected to the barrel processing or the super-finish processing. h: EHL oil film thickness, σ: synthetic roughness) are sufficiently large. As a result, lubrication between the inner diameter surface of the outer ring and the outer diameter surface of the roller or the shaft is sufficiently performed, and peeling occurs on the rolling surface of the roller, or the outer diameter surface of the shaft is worn. Can be prevented. As a result, the durability of the entire cam follower device incorporating the outer ring can be improved.

[0035]

EXAMPLE Next, an example of a method of processing an outer diameter surface into a predetermined property in order to produce an outer ring of the present invention and an experiment conducted by the present inventor to confirm the effect of the present invention will be described. I will explain this.

With respect to conducting the experiment, as shown in the table below,
A total of 12 types of test pieces were prepared, including four types of the present invention and eight types of comparative products. All test piece materials are bearing steel (SU
J2), prior to subjecting the surface to the desired treatment, the same quenching treatment as usual (heating at 800 to 850 ° C. followed by oil cooling) and tempering treatment (150 to 200 ° C.) are performed. did. The size of the test piece was 20 mm in outer diameter and 13 in inner diameter.
mm and a short cylindrical shape having a thickness (width) of 8 mm.

[0037]

[Table 1]

[0038] Among the comparative products, the test piece 1 was not polished by polishing the surface thereof with a polishing cloth, and thus was not subjected to shot peening for hardening the surface. In addition, test pieces 2 to 12 belonging to the comparative product and the product of the present invention.
Japanese Patent Application Laid-Open No. 4-54
As in the case of the invention described in Japanese Patent Publication No. 312, shot peening was performed using an apparatus as shown in FIG. 1 to harden the surface and generate a large compressive residual stress in the surface layer. .

The structure and operation of the shot peening apparatus shown in FIG. 1 will be briefly described. Fine shot grains 3 put into a pressurized tank 2 from a hopper 1 It is pushed into the mixer 5 by being pushed by the compressed air sent into the pressure tank 2. Then, the air is pushed to the nozzle 7 by the compressed air sent to the mixer 5 through the branch pipe 6, and is blasted from the nozzle 7 toward the surface to be processed. As a result, the work surface is hardened, a compressive residual stress is generated on the work surface, and minute unevenness is formed on the work surface.

As the shot grains 3, test pieces 2 to 1
2, the average particle size is 0.03 to 0.7 mm,
The average hardness using a steel ball of H _R C 61. The projection speed of the shot particles 3 (the initial speed of the shot particles 3 ejected from the nozzle 7) is 32 to 120 m / sec (average projection speed = 80 m / sec).
sec). The adjustment of the projection speed is performed by adjusting the opening of the adjustment valve 8 provided in the middle of the branch pipe 6, and based on the adjustment of the projection speed, the compressive residual stress generated on the surface of each of the test pieces 2 to 12 is adjusted. Was adjusted.

Further, the inner diameter surfaces of the test piece 1 and the test pieces 9 to 12 are subjected to super finishing after the shot peening. The test pieces 2 to 8 were only subjected to shot peening on the inner diameter surfaces. In addition, the shot peening process is performed 8 pieces at a time, and the hardness of the surface layer portion,
Approximately eight test pieces were prepared for all of the residual stress in the surface layer, the amount of retained austenite in the surface layer, and the average wavelength of the roughness.

Each of the 12 kinds of 8 pieces obtained in this way,
A durability test was performed on all of the 96 test pieces 1 to 12 using a test apparatus as shown in FIG.

Two mating rings 10 and 10 are fixed at two positions on the outer diameter surface of a rotating shaft 9 driven to rotate by a motor with an interval therebetween. This partner ring 10,
A pair of support pieces 12, 12 provided on one surface of the pressing piece 11 at intervals of 10, one test piece 1 each.
Each of the test pieces 13 and 13 is rotatably supported by a plurality of rollers.
The outer diameter surfaces 0 and 10 are in contact with each other. As a result, the rollers are rolled with the rotation of the rotation shaft 9,
Each test piece 13 rotates. Therefore, in the test apparatus shown in FIG. 2, the durability test of two test pieces 13, 13 is performed at the same time.

The rotation speed of the rotating shaft 9 is determined for each test piece 1.
The rotation speeds of 3, 13 were adjusted to be 5100 rpm. The pressing piece 11 is 356 kg toward the rotating shaft 9.
Pressed with force f. Therefore, the contact portions between the outer diameter surfaces of the test pieces 13 and 13 and the outer diameter surfaces of the mating rings 10 and 10 are
A radial load of 178 kgf is applied to each. Further, the outer diameter surface of the properties of each party rings 10 and 10, in the before starting the test, the surface hardness H _R C 60-61, the average roughness R _a of the surface is 0.38 to 0.45 met Was. Further, the lubrication of the contact portion was performed by splashing a mineral oil of 10W-30.

The test was terminated for 400 hours, and interrupted a plurality of times (20 hours, 50 hours, 100 hours, hereinafter every 50 hours after the start of the test), and the outer surfaces of the test pieces 13 and 13 and the outside of the rollers were stopped. The diameter surface (rolling surface) was observed, and the presence or absence of peeling was inspected. When the occurrence of peeling was observed, the durability test on the test pieces 13 was terminated at that time.

As a result, 40 samples were obtained for all eight test pieces.
Until the elapse of 0 hours, ◎ indicates that no peeling occurred on the outer surface of the outer ring, ○ indicates that peeling occurred on 1 to 3 pieces, and △ indicates peeling occurred on 4 to 7 pieces. , And those in which peeling occurred in all eight pieces were evaluated as x, and are described in the column of outer diameter portion evaluation in the above table. If even one roller was peeled, it was marked as x as a roller peeling bearing, and ◎ indicates that no peeling occurred until 400 hours passed, and each was described in the column of roller rolling surface evaluation. .

As is apparent from the above table showing the results of the durability test, the outer diameter surface of the outer race of the present invention can obtain sufficient peeling resistance even under severe lubrication conditions.
In addition, it is possible to sufficiently secure the peeling resistance of the rolling surface of the roller or the abrasion resistance of the outer diameter surface of the shaft, which is in contact with the inner diameter surface of the outer ring of the present invention. In addition, among the symbols described after each numerical value in the above table, ○ indicates that the numerical value is included in the limited range of the present invention, and x (excluding the column of evaluation) indicates that the numerical value is limited to the present invention. Each is out of range. Further, of the maximum residual stress in the surface layer portion, + represents a tensile residual stress, and − represents a compressive residual stress.

[0048]

As described above, the outer ring of the cam follower device for the valve train of the engine according to the present invention is constructed as described above. However, the outer diameter surface of the outer ring is strengthened and the outer ring has a rough shape having excellent oil film forming ability. Due to the formation, peeling can be prevented from occurring on the outer diameter surface of the outer ring, and the durability of the outer ring can be improved. Also, the inner surface has a small roughness due to super finishing.
Also, since the oil film parameter between the rolling surface of the roller smoothed by barrel processing or superfinishing or the outer diameter surface of the shaft increases, the life of these rollers or the shaft can be extended. Therefore, the durability of the entire cam follower device incorporating the outer ring can be improved.

[Brief description of the drawings]

FIG. 1 is a schematic vertical sectional view of a shot peening apparatus.

FIG. 2 is a half vertical sectional view of the durability test apparatus.

FIG. 3 is a perspective view showing an example of an engine valve mechanism.

FIG. 4 is a side view of a cam follower device incorporated in the valve train shown in FIG. 3;

FIG. 5 is a sectional view taken along line AA of FIG. 4 (in the case of a rolling bearing).

FIG. 6 is a sectional view taken along line AA of FIG. 4 (in the case of a sliding bearing).

FIG. 7 is a schematic view showing processing marks formed on the outer diameter surface of a conventional outer ring.

FIG. 8 is a partially enlarged sectional view of FIG. 7;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Hopper 2 Pressurized tank 3 Shot grain 4 Air supply pipe 5 Mixer 6 Branch pipe 7 Nozzle 8 Adjusting valve 9 Rotating shaft 10 Mating ring 11 Pressing piece 12 Supporting piece 13 Test piece 14 Crankshaft 15 Camshaft 16 Rocker arm 17 Intake valve 18 Exhaust valve 19 Cam 20 Support wall 21 Shaft 22 Roller 23 Outer ring 24 Lubricating oil

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int. Cl. ⁷ , DB name) F16C 33/34 F01L 1/18

Claims (1)

(57) [Claims] 1. A metal cam fixed to a camshaft that rotates in synchronization with a crankshaft of an engine, and a member provided opposite to the cam and receiving the movement of the cam, with a gap therebetween. A cam follower for a valve train of an engine, comprising: a pair of support walls; a shaft fixedly spanned between the pair of support walls; and an outer ring rotatably supported around the shaft. In the above outer ring constituting the device, when the surface layer has a depth of 0 to 50 μm from the surface of the outer diameter surface, the maximum compressive residual stress of the surface layer is 50 to 110 kgf / mm ² . Similarly, the hardness of the surface layer portion is Hv830 to Hv960, the average wavelength of the surface roughness is 25 μm or less, the ratio of the retained austenite in the surface layer portion exceeds 7% by volume, and the inner surface is super-finished. It is characterized by being given The outer ring of the valve operating mechanism for the cam follower of an engine.