JPH05340213A - Cam contact part structure for valve system - Google Patents

Abstract

PURPOSE:To reduce the friction loss by improving the surface roughness of a cam in sliding, by properly setting the surface roughness of the sliding surface in the cam contact part, as for the cam contact part structure of a valve system which is applied with the covering by an abrasion-resistive material, at the cam contact part. CONSTITUTION:A valve lifter 2 for transmitting the force of a cam to a valve 3 which constitutes a suction valve, etc. is installed. A shim 7 is arranged on the sliding surface opposed to the cam 1 of the valve lifter 2. On the cam 1 side of the shim 7, a TIN-covered layer 6 is formed. The surface roughness of the covered layer 6 is set at 0.02-0.5muRz.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cam contact portion structure of a valve operating mechanism, and more particularly to a cam contact portion structure of a valve operating mechanism in which a cam contact portion sliding on a cam is coated with a wear resistant material.

[0002]

2. Description of the Related Art Since the cam contact portion of a valve mechanism of an internal combustion engine is used under extremely severe conditions where sliding and impact are combined, high durability is required for the cam contact portion of the valve mechanism. There is. As a cam contact structure that meets these requirements,
Conventionally, a sliding surface coated with a wear resistant material made of a ceramic material has been proposed, and for example, a material using chromium nitride (CrN) or a mixture of CrN and metallic chromium (Cr) as the ceramic material is known ( JP-A-3-1725
04).

According to the cam contact portion structure of the valve mechanism using the cam contact portion, the cam contact portion has high heat resistance and wear resistance, and the durability of the cam contact portion against problems such as wear and seizure is high. Remarkably improved.

[0004]

However, in the valve operating mechanism of the internal combustion engine, the cam and the cam contact portion are in contact with each other at a high surface pressure. Becomes higher and the oil film of the lubricating oil formed between the cam and the cam contact portion becomes thinner. Therefore, if the sliding surfaces of the cam and the cam contact portion are rough, solid contact will occur,
A large friction loss occurs when the cam and the cam contact portion slide.

Therefore, in the above-mentioned conventional cam contact portion structure, in order to reduce such friction loss and improve fuel efficiency of the internal combustion engine, it is necessary to surface-treat the sliding surface of the cam with high accuracy. there were. This surface treatment requires expensive equipment and a long processing time, which causes a significant increase in the cost of the conventional valve mechanism.

The present invention has been made in view of the above points, and optimizes the surface roughness of the sliding surface of the cam contact portion, and improves the surface roughness of the cam during sliding by its polishing action. An object of the present invention is to provide a cam contact portion structure of a valve mechanism that reduces friction loss.

[0007]

The above object is to provide a valve mechanism which slides on a cam which performs a predetermined rotary motion, converts the rotary motion of the cam into a linear reciprocating motion, and opens and closes a predetermined port. In the structure of the cam contact portion of the driven valve mechanism, the sliding surface of the cam contact portion that slides with the cam has a surface roughness of 0.0.
This can be solved by providing a titanium nitride coating layer having a thickness of 2 μRz to 0.7 μRz.

[0008]

According to the above structure, the titanium nitride coating layer of the cam contact portion slides on the cam to polish the sliding surface of the cam. For this reason, the surface roughness is improved even if the sliding surface on the cam side is not subjected to highly precise surface treatment in advance, and the friction loss at the cam and the cam contact portion is reduced.

On the other hand, the surface roughness of the coating layer is 0.7 μR.
If it is larger than z (the surface is rough), the cam causes great wear due to sliding, and the accuracy of the valve mechanism cannot be maintained.
When the surface roughness of the coating layer is smaller than 0.02 μRz (the surface is smooth), the surface treatment cost is high and the surface roughness of the cam is not improved so much.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a sectional view of a main portion of a direct drive type valve operating internal combustion engine incorporating an embodiment of a cam contact portion structure of a valve mechanism according to the present invention. In the figure, reference numeral 1 is a cam provided on a camshaft that rotates in synchronization with rotation of a crankshaft of an internal combustion engine (not shown).

Reference numeral 2 is a valve lifter, which is incorporated in a predetermined position of the cylinder block 5, and is provided with a cam shaft and a cam 1.
When is rotated, it is pressed by the nose of the cam 1 and presses the valve 3 downward. A valve body that constitutes an intake valve or an exhaust valve is provided at a tip end portion (not shown) of the valve 3,
When pressed downward by the cam 1, the valve body opens the intake port or the exhaust port. On the other hand, since the valve 3 is constantly urged upward by the valve spring 4 provided on the outer periphery thereof, the intake port or the exhaust port is closed except when it is pressed downward by the cam 1.

Reference numeral 7 is a shim corresponding to a cam contact portion which is a main portion of the structure of this embodiment. The shim 7 is made of structural carbon steel, structural carbon steel, carbon tool steel, alloy tool steel, etc. as a base material, and has a coating layer 6 on the sliding surface that slides on the cam. The coating layer 6 is made of titanium nitride (Ti) having a film thickness of about 0.5 to 10 μm.
N) film, physical vapor deposition such as ion plating (PV
D) or chemical vapor deposition (CVD).

The shim 7 is fitted in the valve lifter 2 to act as a cam contact portion, and is also a member for adjusting the positional relationship between the cam 1 and the valve 3 in the height direction. That is, by adjusting the thickness of the shim 7, it is possible to cancel an error due to the processing accuracy of the cam 1 and the valve lifter 2, and the valve 3 can perform the opening / closing operation with high accuracy.

2 and 3 are views for explaining the proper range of the surface roughness of the shim. Hereinafter, the appropriate range of the surface roughness of the shim will be described based on each drawing.

FIG. 2 shows the relationship between the wear amount of the cam nose and the initial surface roughness of the shim when the cam and the shim are slid under predetermined conditions. In the figure, the points plotted with ◯ are the points obtained experimentally by sliding the cam and shim under predetermined sliding conditions. The sliding conditions of the cam and shim are as shown below.

Type of internal combustion engine: in-line 4-cylinder, 2000
cc, double overhead camshaft (DOH
C), 16 valves Engine speed: 1000 rpm Lubricating oil used: 5W-30 Oil temperature: 80 ° C Sliding time: 200 h The cam used in this test was made of alloy cast iron chill, and the surface roughness of its sliding surface was Is 3.2 μRz.

As shown in the figure, the wear amount of the cam nose becomes larger as the initial surface roughness of the shim becomes rougher, and the wear amount of the cam nose sharply increases when the surface roughness exceeds 0.7 μRz. The cam nose is a part that requires a certain degree of accuracy to open and close the supply / exhaust valve. Therefore, when the proper range of the initial surface roughness on the sliding surface of the shim of the present embodiment structure is obtained from the result of the cam nose wear test shown in the same figure, it becomes 0.7 μRz or less.

FIG. 3 shows the internal combustion engine used in the above test.
The relationship between the friction loss of the valve train when rotated at 000 rpm and the initial surface roughness of the shim is shown. In the figure, the solid line indicates the friction loss of the valve train using the shim of the present embodiment structure, and the two-dot chain line indicates the friction loss of the valve train using the conventional shim made of alloy cast iron with a phosphate coating. Indicates loss.

In this test, the camshaft of the valve train for which friction loss is to be measured is rotated by a motor via a torque meter, and when the camshaft reaches a predetermined rotation speed. The torque detected by the torque meter is used as the friction loss of the valve train.

As shown in the figure, the friction loss of the valve operating system using the shim of this embodiment becomes larger as the surface roughness of the shim becomes rougher, and the friction loss of the conventional valve operating system exceeds 0.7 μRz. Is equal to the friction loss at.

Therefore, in the shim of this embodiment, when the surface roughness of the sliding surface is 0.7 μRz or less, the cam nose is appropriately ground without excessive wear to reduce friction loss during sliding. Can be made

On the other hand, in order to make the sliding surface of the shim have a predetermined surface roughness, it is necessary to polish this sliding surface. This polishing requires highly accurate equipment and a long processing time to obtain a smooth surface, and thus increases the cost of the valve train. Therefore, in this embodiment, in particular, 0.02 μ
The surface roughness of Rz or less is removed as an excessive quality, and the surface roughness is limited to 0.02 μRz to 0.7 μRz.

The shims of the structure of this embodiment are ground to obtain a predetermined surface roughness. Also, TiN
Since this coating layer is thin, the surface roughness of the sliding surface is almost the same as the surface roughness of the base material even if this coating is performed. Therefore, polishing of the sliding surface may be performed on the base material before coating with TiN or on the coating layer after coating with TiN.

FIG. 4 is a diagram showing the relationship between the friction loss and the engine speed when the shim and the cam of the cam contact structure of the present embodiment and the conventional cam slide.

In the same figure, the broken line shows the case where a phosphate coating is used for the coating layer using the SMC15 carburized material as the base material of the shim, and the one-dot chain line and the two-dot chain line are known as the coating layers of conventional ceramic materials CrN and CrN
The case where a mixed film of Cr and Cr is used is shown. The solid line in the figure indicates the friction loss of the valve train in the valve train using the shim of the present embodiment.

In this case, in the shim of this embodiment shown by the solid line in the figure, SKD11 was used as the base material, the surface corresponding to the sliding surface was polished to 0.1 μRz, and then 4 μm TiN was formed by ion plating. It is a covered structure. Before the test shown in FIG. 4 is performed, the cam and shim are rubbed together under the conditions shown in FIG. 5, so the result shown in FIG.
This is the result with the cams and shims fully smoothed.

As described above, the shim TiN coating film of the structure of this embodiment is excellent in mechanical strength such as abrasion resistance, and the sliding cam is polished to reduce friction during sliding. To work. Therefore, as is clear from FIG. 4, the shim of the present embodiment structure is
Friction loss generated in the valve train can be suppressed to be small in the entire engine speed range.

Therefore, according to the structure of this embodiment, it is possible to improve the fuel consumption of the internal combustion engine, and at the same time, the generation and wear of frictional heat on the sliding surfaces of the cam and shim are suppressed.
It is possible to maintain the accuracy and improve the durability of the valve mechanism.

In the present embodiment, the coating film is formed on the shim only on the sliding surface, but the present invention is not limited to this. The outer peripheral surface of the shim and the surface on the side opposite to the sliding surface are coated. You may. As a result, both sides of the shim can be treated as sliding surfaces, and front / back determination at the time of assembly is unnecessary.

In the case where only one surface of the shim is coated with TiN and only one surface is used as the sliding surface as in the above-mentioned embodiment, a mechanism for preventing wrong mounting on the front and back sides may be provided.

FIG. 6 shows an example of this front and back wrong assembly mechanism. A recess 14 is provided at a portion of the shim 11 opposite to the clothing layer 12 and fitted with the valve lifter 13.
At a portion of the valve lifter 13 that fits with the shim 11, a convex portion 15 that fits with the concave portion 14 is provided. For this reason,
If you try to assemble the front and back of the shim 11 by mistake,
The shim 11 and the valve lifter 13 do not fit well, which prevents wrong mounting of the shim on the front and back.

In the above embodiment, the shim is used as the cam contact portion, but the cam contact portion is not limited to this. For example, the top surface of the valve lifter or the rocker arm without the shim is not used. Any portion, such as a pad surface, that slides on the cam, similar to the shim, may be used.

[0033]

As described above, according to the present invention, the sliding surface of the cam contact portion has a surface roughness of 0.02 μRz to 0.5 μR.
Since it is TiN of z, the surface roughness of the cam is improved by sliding. Therefore, the friction loss in the valve mechanism is significantly reduced, and the fuel economy of the internal combustion engine is improved. Further, since wear and frictional heat are suppressed during sliding between the cam contact portion and the cam of the structure according to the present invention, durability of the cam contact portion is improved and on-off valve timing accuracy is maintained for a long period of time. Can be planned.

[Brief description of drawings]

FIG. 1 is a sectional view of a main part of a direct-acting valve-operated internal combustion engine incorporating an embodiment of a cam contact portion structure of a valve mechanism according to the present invention.

FIG. 2 is a diagram showing the relationship between the surface roughness of the shim and the wear amount of the cam nose of the structure of this embodiment.

FIG. 3 is a diagram showing the relationship between the surface roughness of the shim and the friction loss of the valve train in the structure of the present embodiment.

FIG. 4 is a graph showing the relationship between friction loss and engine speed in shims of this embodiment and a conventional structure.

FIG. 5 is a chart showing a condition for adjusting a shim and a cam in the structure of the present embodiment.

FIG. 6 is another embodiment of the shim of the present embodiment structure.

[Explanation of symbols]

 1 cam 2,13 valve lifter 3 valve 4 valve spring 6,12 coating layer 7,11 shim

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Koji Harada 1 Toyota Town, Toyota City, Aichi Prefecture, Toyota Motor Co., Ltd. (72) Inventor, Hitoshi Ozawa 1 Toyota Town, Toyota City, Aichi Prefecture, Toyota Motor Co., Ltd. ( 72) Inventor Yoshito Moriya 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Co., Ltd.

Claims (1)

[Claims] 1. A cam contact portion of a valve mechanism that slides on a cam that performs a predetermined rotary motion to convert the rotary motion of the cam into a linear reciprocating motion and drive a valve mechanism that opens and closes a predetermined port. In the structure, on the sliding surface of the cam contact portion that slides on the cam, a titanium nitride coating layer having a surface roughness of 0.02 μRz to 0.7 μRz is provided, and the cam contact portion of the valve operating mechanism is characterized. Construction.