JP3147538B2 - Cam follower and manufacturing method thereof - 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 follower used for a valve train of an internal combustion engine.

[0002]

2. Description of the Related Art Since the oil crisis, automobile manufacturers have been making efforts to improve fuel efficiency for energy saving. However, in recent years, efforts to reduce CO ₂ emissions and other global environmental measures have been strengthened worldwide. There is a demand for even greater fuel economy.

[0003] As a countermeasure, reduction of power loss of an engine and the like has become an important issue along with weight reduction of a vehicle and high efficiency of an engine. Among the power loss of the engine, for the reduction of the loss by the valve train, reduction of the weight of parts and reduction of the friction of the sliding portion, mainly for the purpose of reducing the inertial weight, are being studied.

FIG. 1 shows various valve operating mechanisms of an automobile engine. At present, from the viewpoint of engine performance, an OHC (overhead cam) system having excellent valve motion characteristics is mainly used.

FIG. 2 shows an example of a direct drive type valve operating mechanism of the OHC system, wherein 1 is an engine cylinder head, 2 is a cam, 3 is a valve lifter, 4 is an adjusting shim, and 5 is intake and exhaust. A valve, 6 is a valve seat, and 7 is a valve spring. In the one shown in FIG.
Thus, the valve lifter 3 is driven, and the displacement of the cam 2 is transmitted to the intake / exhaust valve 5. In this case, the adjusting gym 4 is a cam follower, and in another method shown in FIG.
The swing arm and the rocker arm correspond to a cam follower. In a direct drive system, a tappet shim integrated with a valve lifter may be used for a cam follower.

Conventionally, these cam followers are usually made of steel, but some are made of ceramics to reduce the weight and reduce the friction loss.

However, when ceramics are used for the cam follower in order to reduce the weight, in the direct drive system, the ratio of the cam follower to the inertial weight of the valve train is very small, so that the actual power loss is hardly improved. In addition, in other systems (swing arm, rocker arm system), it is difficult to ceramicize the entire cam follower because of the strength of the cam follower, and a method of partially using it on the contact surface with the cam is adopted. There has been a problem that the contribution to weight reduction is small, and similarly, the effect of improving power loss is not recognized.

Further, when ceramics are used for the cam follower for the purpose of reducing friction loss due to sliding between the cam and the cam follower, there is a problem that the aggressiveness to the cam is increased and the cam is worn hard.

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to provide a cam follower capable of reducing frictional loss due to sliding and greatly reducing power loss.

[0010]

That SUMMARY OF THE INVENTION The present invention is gold
The surface of the base metal is 0.2 μm in ten-point average roughness (Rz) in advance.
After finishing below, at least the side that comes in contact with the cam
Has a Vickers hardness of 1000 k on the surface on the metal substrate.
gf / mm ² or more, Young's modulus is 25,000 kgf / mm ²
The above ceramic or metal layer is coated,
Ten-point average roughness (Rz) of the surface is 0.2 μm or less
A method for manufacturing a cam follower characterized by the following.

In the present invention, at least the surface roughness of the surface in contact with the cam has a ten-point average roughness (Rz) of 0.2 μm or less, preferably less than 0.1 μm, and the Vickers hardness of the surface is 1000 kgf / mm. ² or more, preferably 12
By using a cam follower of 00 kgf / mm ² or more, the sliding friction loss with the cam is greatly reduced, the power loss of the engine can be reduced, the aggressiveness to the cam is reduced, and the cam wear is improved. be able to.

If the surface roughness exceeds 0.2 μm, the sliding friction resistance with the cam increases, the effect of reducing the power loss decreases, and the aggressiveness to the cam becomes unfavorable. Further, the Vickers hardness of the surface is 1000 kgf /
If it is less than ² mm, on the other hand, the surface roughness is deteriorated by the attack from the cam, and in some cases, local wear occurs to change the clearance with the cam, so that the frictional resistance with the cam similarly increases. Therefore, the power loss increases with time as the engine operates, so that the life and durability are particularly problems.

In general, the power loss of the engine increases in proportion to the engine speed, but the power loss due to the valve train usually takes a substantially constant value regardless of the engine speed. In the low rotation speed range during low-speed running, the ratio of the power loss of the valve train to the power loss of the engine increases.

In view of this, the cam follower is further composed of a material having a Young's modulus of 25,000 kgf / mm ² or more, and at least the surface roughness and Vickers hardness of the surface in contact with the cam are controlled within the range of the present invention. Thereby, the sliding frictional resistance with the cam in the low engine speed range can be reduced, and the power loss of the engine can be further reduced.

On the other hand, the Young's modulus is 25,000 kgf / mm
^When a material less than ² is used, a low rotation range, particularly 1000
The engine power loss reduction effect at ２０００2000 rotations or less is reduced.

In the present invention, the Vickers hardness of at least the surface of the cam follower that contacts the cam is 1000 kgf.
/ Mm ² or more can be produced by coating the surface of a low-hardness material such as steel with a high-hardness ceramic or metal. For example, in ceramics, Cr, Zr, Ta, Nb, W, Hf,
There is a method of coating a nitride, carbide, or oxide such as Mo, V, Ti, or Si by a vapor deposition method such as physical vapor deposition (PVD), chemical vapor deposition (CVD), or a plasma reaction method, or by thermal spraying. In metal coating, mainly C
Examples of the method include vapor deposition and plating of r.

Further, a method of improving the surface hardness by ion implantation of N, C, Si, B, Ti or the like into steel or ceramics or the above-mentioned coating layer can be used.

The surface roughness of at least the surface of the cam follower contacting the cam of the cam follower manufactured by these methods is as described above.
Before performing the grinding process, the surface of the metal base material may be previously processed to have an Rz of 0.2 μm or less by grinding, polishing, etching, or the like , or may be processed before and after the process. but when a thin coating layer thickness, when the surface roughness before treatment keep control within the scope of the present invention
Good.

When performing ion implantation, it is desirable to control the surface roughness within the scope of the present invention in advance.

In a valve train of an internal combustion engine such as an automobile engine, lubrication with oil is basically performed. Ideally, sliding material does not come into solid contact with each other through an oil film made of lubricating oil without causing solid contact. In this case, the frictional resistance of the sliding surface can be reduced by causing the fluid to slide, that is, by generating the fluid lubrication. In this state, the frictional force is very small because it is based on the shear stress of the fluid, and the sliding surface does not wear.

The thickness of the oil film formed between the cam and the cam follower changes depending on the engine speed and the surface pressure if the characteristics of the lubricating oil are constant. With respect to the oil film thickness formed at this time, in the conventional cam follower, since the surface roughness Rz of the surface in contact with the cam is relatively large, the convex portion of the contact surface of the cam follower causes solid contact with the cam. It is considered that the sliding frictional resistance of the sample increased. On the other hand, in the present invention, the surface viscosity Rz of the contact surface of the cam follower with the cam is
Is assumed to be a smooth surface of 0.2 μm or less, it is considered that unevenness of the surface is smaller than the formed oil film thickness, and that sliding frictional resistance is greatly reduced.

On the other hand, at the start of the engine and in the low rotation speed range, the increase in the surface pressure and the supply of the lubricating oil are restricted, so that the sliding surface between the cam and the cam follower decreases with the decrease in the oil film thickness formed. The rate of solid contact increases (boundary lubrication area). Conventionally, since the cam follower is usually made of steel, and the cam has been subjected to a surface hardening treatment by nitriding, in such a state, the surface roughness of the cam follower is deteriorated by the attack from the cam, and the sliding friction is increased. Resistance increases.

On the other hand, by increasing the Vickers hardness of the contact surface with the cam to 1000 kgf / mm ² or more as in the present invention, the surface roughness of the cam follower can be easily changed even when attacked by the cam. And a stable sliding friction resistance reducing effect is obtained. At this time, if the surface roughness of the contact surface of the cam follower with the cam exceeds 0.2 μm, on the contrary, the attack on the cam surface becomes conspicuous and the cam is worn.

Further, in the low engine speed range, the cam follower elastically deforms due to an increase in surface pressure,
When a material having a low Young's modulus is used for the cam follower, the degree of deformation increases, so that the solid contact area with the cam increases as in the case where the surface roughness of the contact surface with the cam increases,
The sliding friction resistance increases.

On the other hand, in the present invention, the Young's modulus is 25
It is considered that by using a material of 000 kgf / mm ² or more for the cam follower, the amount of elastic deformation is reduced, and an increase in sliding frictional resistance is avoided, so that the power loss of the engine can be further reduced.

Incidentally, portions other than the contact surface with the cam described above,
For example, by applying the present invention to a contact surface with a lifter in a direct drive system, the sliding friction resistance can be further reduced.

Hereinafter, embodiments of the present invention will be described.
The present invention is not limited to this.

[0028]

EXAMPLE 1 An adjusting shim (cam follower) shown in FIG. 3 using various ceramics sintered bodies and steel (Cr-Mo steel).
Was prepared. Here, as for the steel adjusting shim , the steel contact shim (the surface denoted by reference numeral 8 in FIG. 3) was manufactured by ceramic coating, chromium plating, and ion implantation with nitrogen.

Before the surface treatment, the contact surfaces of the steel and various ceramics sintered bodies with the cam were finished under various conditions to have the surface roughness shown in Table 1. Table 1 shows the surface roughness of the surface-treated steel adjusting shim after the surface treatment. Table 1 shows measured values of Vickers hardness of the contact surface with the cam.

The adjusting shim produced in this manner was diverted from a commercially available 2000 cc automotive gasoline engine shown in FIG. 4 and a motoring device equipped with a direct drive OHC valve mechanism (cylinder head) was used to convert the adjusting shim to an engine equivalent. At 2000 rpm, and the torque of the camshaft was measured. The same measurement was performed for a conventional steel adjusting shim, and the camshaft torque reduction rates of various adjusting shims were calculated based on the measured values by the following equation.

[0031]

## EQU1 ## Camshaft torque reduction rate = [1-{(camshaft torque of various adjusting shims) / (camshaft torque of conventional steel adjusting shims)}} × 100 (%) The surface roughness of the adjusting shim and the amount of wear on the cam surface after continuous operation at several thousand rpm for 160 hours were measured.

Table 1 shows the above results. As is clear from Table 1, by using the adjusting shim (cam follower) of the present invention, a significant reduction effect of the camshaft torque due to the reduction of the sliding friction resistance was recognized. No deterioration in the surface roughness of the contact surface is observed.

[0033]

[Table 1]

[0034]

The effect of the present invention is not limited to the direct drive type cam follower (adjusting shim) of the present embodiment, and the same effect can be obtained in a car follower of another valve train.

[0036]

[0037]

As described above, the cam follower according to the present invention makes it possible to greatly reduce the power loss of the valve train of an internal combustion engine such as an engine and to improve the wear resistance, thereby improving the fuel economy, performance and durability of the internal combustion engine. Performance can be improved.

[Brief description of the drawings]

FIG. 1 is an explanatory view of various valve operating mechanisms of an automobile engine.

FIG. 2 is a longitudinal sectional view of a direct drive type valve train.

FIG. 3 is a longitudinal sectional view of an adjusting shim.

FIG. 4 is a longitudinal sectional view of a motoring test apparatus.

[Explanation of symbols]

 1 Cylinder Head 2 Cam 3 Valve Lifter 4 Adjusting Shim 5 Valve 6 Valve Seat 7 Valve Spring A Cam Lifter B Swing Arm C Rocker Arm D Rod

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-3-16971 (JP, A) JP-A-1-229198 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) F16H 53/00-53/06 F01L 1/14-1/20

Claims (2)

(57) [Claims] The surface of a metal substrate is preliminarily made to have a ten-point average roughness (R
After finishing the 0.2μm or less z), on the surface on at least said metal base of the side material in contact with the cam, the Vickers hardness of 1000 kgf / mm ² or more, a Young's modulus of 250
Coated with a layer made of 00kgf / mm ² or more ceramic or metal, ten-point average roughness of said surface (Rz) is 0.2
Manufacturing method of cam follower characterized in that it is less than μm
Law . 2. The method according to claim 1, wherein at least a surface in contact with the cam is modified by an ion implantation method.