JP3512449B2 - Ceramic cam rollers - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cam roller made of ceramic used as a driving part of a fuel injection device or a supply / exhaust valve of an internal combustion engine.

[0002]

2. Description of the Related Art Generally, a cam roller used in an internal combustion engine changes a rotational motion of a cam into a linear motion of a fuel injection device or a supply / exhaust valve of the internal combustion engine so that a fuel injection amount, a fuel injection pressure, an injection timing, a supply / exhaust gas are supplied. A rolling contact part is interposed between the fuel injection device and the supply / exhaust valve of the internal combustion engine to control timing and the like, and is incorporated in a transmission member to reduce sliding friction.

Conventionally, the above-mentioned rolling contact parts for driving and controlling a fuel injection device, a supply / exhaust valve and the like linked to a high-speed internal combustion engine include iron alloys such as bearing steel and tool steel. Metal cam rollers were used, but due to differences in the degree of parallelism in the contact surface between the rollers and the cam body and the deflection of the shafts of the fuel injection device and the supply / exhaust valve, etc. However, there has been a problem that the frictional coefficient between the cam and the cam roller becomes large, the roller cannot be stably rotated, and the contact surface is worn or seized.

Therefore, in order to solve the above problem, a crowning is provided on the outer peripheral end of the cam roller, and the outer diameter of the cam roller is tapered toward both outer peripheral ends of the cam roller to reduce the difference in the parallelism. It has been proposed that the cam roller be stably rotated without causing the cam roller to hit one side by alleviating the bending of the shaft and the like by crowning.

However, on the other hand, unless the reciprocating mass is made as small as possible and the inertia force applied to them is reduced as much as possible, the fuel injection device, the supply / exhaust valve and the like generate vibrations when operated at high speed and high load. In addition, there is a problem in that abrasion resistance is insufficient, stable rotation of the cam roller cannot be obtained, and normal control becomes difficult in a short period of time.

Therefore, it has been proposed to improve the durability by forming the cam roller from ceramics having a lower density and excellent wear resistance as compared with a metal cam roller, so as to eliminate the problems of vibration and wear resistance. (JP-A-4-152)
No. 96, Japanese Utility Model Application Laid-Open No. 59-121408).

[0007]

However, when a cylindrical cam roller is formed of ceramics as described above,
Since the end face of the cam roller is easily chipped and the durability is poor, as shown in FIGS. 3 and 4, the tapered crowning 9 on the outer peripheral end 8 of the ceramic cam roller 7 is used as a countermeasure. Although it is conceivable to provide a cam surface with a curved surface R, a recent cam roller requires a high surface pressure between the cam roller and the cam in order to accurately transmit the rotation of the cam to a fuel injection device or the like so as to further increase the control accuracy. It is built to generate, and furthermore, there is a tendency for high pressure injection to respond to exhaust gas regulation measures, etc., and the contact surface with the cam receives extremely high contact pressure .

As a result, if the above-mentioned crowning or curved surface is provided at the outer peripheral end of the ceramic cam roller, the cam does not hit one side, but if only the crowning or the curved surface is provided, the cam itself made of cast iron or cast steel is worn. The fuel injection volume and fuel injection pressure drop,
Fuel injection timing and supply / exhaust timing are shifted, and there is a problem that an increase in unburned gas, a decrease in fuel consumption, an increase in noise, and the like occur in terms of performance as an internal combustion engine.

[0009]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a ceramic cam roller which is less likely to be damaged or worn even under a high surface pressure with the cam, and does not wear the cam which comes into contact. It is another object of the present invention to provide a ceramic cam roller as a drive component of an internal combustion engine, which has improved durability without impairing the surfaces that come into contact with each other and requires no repair in a short period of time.

[0010]

According to the present invention, there is provided a ceramic cam roller comprising a rotatably supported substantially cylindrical cam roller having a radius of 1500 to 8500 mm at least at a surface where the cam comes into contact with the cam. Is provided.

[0011]

According to the ceramic cam roller of the present invention, at least 1500 to 850
Since the crowning having a radius of 0 mm is provided, the frictional resistance between the cam and the abutting surface of the ceramic cam roller is reduced, and the ceramic cam roller may cause cohesive wear of the cam or cause seizure. It becomes difficult to perform rotation and shows stable rotation.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a ceramic cam roller according to the present invention will be described in detail with reference to the drawings.

FIG. 1 is a sectional view showing an embodiment of a ceramic cam roller according to the present invention, and FIG. 2 is a view showing the configuration of a cam roller and a cam incorporated in a fuel injection device of an internal combustion engine.

In FIGS. 1 and 2, reference numeral 1 denotes a cam roller having a crowning 4 having a radius of 3 at least on a contact surface with the cam 2.

The cam roller 1 is in rolling contact with the crowning 4 with a high surface pressure in order to accurately transmit the rotational movement of the cam 2 made of cast iron or cast steel.
The cam roller 1 is converted into a linear motion by swinging the rotatably supported transmission member 5 with the rotation motion of the cam roller 1.
It is configured to control the fuel injection device 6 of the internal combustion engine.

As the ceramic cam roller, a non-oxide ceramic such as silicon nitride (Si ₃ N ₄ ) or silicon carbide (SiC) is preferable, but a nitride containing silicon nitride (Si ₃ N ₄ ) as a main component is preferable. A silicon-based sintered body is most preferable. In particular, the silicon nitride-based sintered body has a content of silicon nitride (Si ₃ N ₄ ) as a main component in view of sliding characteristics, wear resistance, and durability. 90% by weight or more, Rockwell hardness of _HRA 85 or more on A scale, fracture toughness value K _1C of 4.5 or more, and diameter of void formed in at least the contact surface with the cam 50
It is desirable that the thickness be 0 μm or less.

That is, the silicon nitride (S
When the content of i ₃ N ₄ ) is 90% by weight or more, a sintered body having high hardness is easily obtained, and the wear resistance is improved.

[0018] The iron-based alloy which has been conventionally employed has a low hardness and a high toughness, so that the cam roller and the cam to which a high contact surface pressure acts are liable to cause cohesive wear, while The hardness of the sintered body is A of Rockwell hardness
When the _{HRA is} 85 or more on a scale, the adhesive wear is less likely to occur.

On the other hand, even in the case of a silicon nitride-based sintered body, if the fracture toughness value K _1C is 4.5 or more, further degranulation of ceramic particles, which is a problem when the ceramic material is worn, occurs. If the diameter of the void formed in at least the contact surface with the cam is not more than 500 μm, it tends to be difficult to be a starting point of the ceramic particle shedding phenomenon.

Next, when evaluating the ceramic cam roller of the present invention, at least 90% by weight of high-purity α-silicon nitride powder having a composition shown in Table 1 was added to yttrium oxide (Y ₂ ) as a sintering aid. O ₃ ) and aluminum oxide (A
l ₂ O ₃ ) is added to the raw material powder obtained by adding a predetermined amount and pulverized and mixed,
A binder comprising an organic substance such as PVA is added, and a cylindrical body having through holes is pressure-formed using a granulated body produced by means such as spray drying, and the molded body is heated in a vacuum furnace. After debinding, 1750 in a nitrogen gas atmosphere
The resultant was fired at a temperature of １1800 ° C. for 5 hours to obtain a silicon nitride sintered body which was densified to 95% or more of the theoretical density.

Next, the silicon nitride-based sintered body is polished to obtain an outer diameter of about 4 mm with various crownings.
A ceramic cam roller for evaluation having 0 mm, an inner diameter of about 15 mm, and a height of about 25 mm was produced.

Prior to the durability evaluation test of the thus obtained ceramic cam roller, the composition of the ceramic cam roller was analyzed using a fluorescent X-ray analyzer with a ceramic cam roller for evaluation having the same specifications.

Next, the hardness at the surface in contact with the cam was measured with a Rockwell hardness meter, and the contact surface was also measured with a Vickers hardness meter at an indenter load of 20 kg and a load time of 15 kg.
A minute crack is developed in seconds, the length of the crack is measured, K _1C is measured by Miyoshi's formula, and the maximum diameter of a void formed in the surface is further measured from an electron micrograph,
The results shown in Table 1 were obtained.

[0024]

[Table 1]

Next, the radius of the crowning of the ceramic cam roller for evaluation was determined by using a surface roughness meter so that the contact surface with the cam was moved by 0.3 mm per second from the peripheral edge of one end face to the peripheral edge of the other end face. Then, the measurement mode was set to Ra, the measurement magnification was increased to 2000 times, and the measurement was performed. The result was recorded by a recorder, and the recorded result was analyzed to obtain the crowning radius.

Thereafter, the ceramic cam roller for evaluation is incorporated into a transmission member using a carburized cast iron pin, and the transmission member is mounted on a bench test apparatus for a diesel engine using a FCD standard cast steel cam. At 100,000 km, 200,000 km
m, the amount of change in the outer diameter of the cam from the initial value, and the amount of change in the outer diameter of the ceramic cam roller from the initial value for each rolling contact distance of 300,000 km. The amount of change from the initial value of the clearance was measured, and the integrated value of の of each average value was evaluated as the amount of wear, and the external appearance of the pin and the cam was visually inspected.

A conventional example is a cam roller made of SUJ standard high carbon chromium bearing steel. Table 2 shows the above results.

[0028]

[Table 2]

[0029]

According to the ceramic cam roller of the present invention, at least the surface of the cam contacting roller has a radius of 1500-8.
The 500mm crowning provides stable rotation even under high surface pressure, high speed, and high load conditions, making it difficult for the ceramic cam roller itself to be damaged or worn, and for the cam itself to be in contact with. A highly durable ceramic cam roller which is hardly damaged and does not require repair in a short period of time is obtained.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an embodiment of a ceramic cam roller according to the present invention.

FIG. 2 is a diagram showing a configuration of a cam roller and a cam incorporated in a fuel injection device of an internal combustion engine.

FIG. 3 is a sectional view showing a conventional cam roller.

FIG. 4 is a sectional view showing a conventional cam roller.

[Explanation of symbols]

1 cam roller 2 cam 3 radius 4 Crowning

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) F16H 51/00-55/30

Claims (1)

(57) [Claims] 1. A cam roller consisting rotatably axially supported by a ceramic with abuts against the cam, the cell
Lamix added 90 % silicon nitride (Si ₃ N ₄ )
Contains at least weight%, Rockwell hardness H _RA 85 or more
From a silicon nitride sintered body having a fracture toughness of K _1C 4.5 or more.
At least the voids opened in the contact surface with the cam.
The diameter is 500 μm or less, and one end is
A ceramic cam roller having a crowning with a radius of 1500 to 8500 mm when measured from the peripheral edge of the surface to the peripheral edge of the other end surface .