Material for valve-actuating mechanism of internal combustion engine

A material, and a process for producing same, for fabricating components of valve-actuating mechanisms of internal combustion engines, the material comprising an iron-base sintered alloy, which comprises, by weight: 2-7% Cr (chromium); 0.1-1.5% Mo (molybdenum); 0.5-7% W (tungsten); 0.1-3% V (vanadium); and 0.5-3% C (carbon). Upon being subjected to a slide-contact with another member, the material exhibits a high degree of abrasion resistance and at the same time is capable of effectively protecting the material of a member operatively cooperating therewith in slide-contact. The material is thus highly suitable for very frequent slide-contact with a cam member or the like.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a material, and a process for producing 
same, which is suitable for use in fabricating components of the 
valve-actuating mechanism of an internal combustion engine. More 
particularly, the invention relates to a material suitable for fabricating 
members subjected to very frequent slide-contact with a cam member, i.e., 
for members such as rocker arms and valve lifters which make up the 
valve-actuating mechanism of an internal combustion engine. 
2. Description of Relevant Art 
Valve-actuating mechanism components of internal combustion engines, 
particularly members such as rocker arms and valve lifters which are 
repeatedly subjected to very frequent slide-contact with a cam, require 
for their fabrication a material having special properties. 
With reference to the accompanying drawings, the general structure of 
valve-actuating mechanisms of internal combustion engines will be 
described. 
An example of an OHC-type valve-actuating mechanism of an internal 
combustion engine is shown in FIG. 1. In response to rotation of a cam 2, 
a rocker arm 1 undergoes a seesaw motion, and thereby the rocker arm 1 
alternatingly opens and closes a valve 5. In a valve-actuating mechanism 
of this type, the abrasion resistance of the working face of the rocker 
arm 1, which working face is brought into frequent slide-contact with the 
cam 2, becomes the most critically important feature. 
With reference to FIG. 2, there is shown an example of a valve-actuating 
mechanism of the push rod type. A valve lifter 3 and push rod 4 are 
interposed between the cam 2 and rocker arm 1, thereby transmitting the 
motion of the cam 2 to the valve 5. In a valve-actuating mechanism of such 
type, the most critical feature resides in the abrasion resistance of the 
working face of the valve lifter 3, which working face is brought into 
frequent slide-contact with the cam 2. 
In each of the above-described types of valve-actuating mechanisms, it is 
of course important that the aforesaid working faces have superior 
abrasion resistance as mentioned above. In addition, it is also important 
that the working face does not wear or abrade the cam 2, which is the 
member operatively cooperating with the working face. 
The aforesaid members have heretofore been fabricated generally of an 
iron-base material such as a steel or alloyed cast iron. In order to 
enhance their abrasion resistance, prior to their use, the working faces 
cooperating with the cam 2 have been subjected to a treatment such as 
surface hardening through heat treatment, chilling, hard chromium plating 
or flame spraying of an autogeneous alloy. 
However, such treated prior art materials have attendant problems, such as 
that carburized steel is poor in durability, and a hard chromium plated 
material is likely to be subject to chipping-off due to localized contacts 
or abrasion. On the other hand, where an autogeneous alloy is 
flame-sprayed, there arises another disadvantage with regard to 
fabrication cost due to increased fabrication steps and use of expensive 
raw materials as well as uncertainty in providing quality assurance, due 
to the inclusion of the flame-spraying step. 
In view of the foregoing problems, there has developed a desideratum for 
superior materials for use in fabricating components of valve-actuating 
mechanisms of internal combustion engines. The present invention eminently 
fulfills such desideratum, and effectively overcomes the foregoing 
problems attendant prior art materials used in fabricating components of 
valve-actuating mechanisms of internal combustion engines. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide a material for fabricating 
components of valve-actuating mechanisms of internal combustion engines, 
which material exhibits a high degree of abrasion resistance even when 
subjected to very frequent slide-contact and at the same time is capable 
of effectively protecting the material of a member operatively cooperating 
therewith. Thus, the material in accordance with the present invention is 
highly suitable for very frequent slide-contact with a cam member or the 
like. 
Another object of the present invention is to provide a process for 
producing a material which per se has a high degree of abrasion 
resistance, but on the other hand has an extremely low degree of 
wearing-off of material operatively cooperating therewith in 
slide-contact. The material produced in accordance with the present 
invention is thus highly suitable for use in fabricating components of 
valve-actuating mechanisms of internal combustion engines or the like, 
which components are subjected to very frequent slide-contact. 
A further object of the present invention is to provide members for 
valve-actuating mechanisms of internal combustion engines, which members 
are fabricated of a material having a high degree of abrasion resistance 
and excellent anti-friction characteristics with respect to members 
operatively cooperating therewith, and thus being highly suitable for very 
frequent slide-contact. 
In accordance with the present invention there is provided a material for 
fabricating components of valve-actuating mechanisms of internal 
combustion engines, comprising an iron-base sintered alloy which comprises 
by weight: 2-7% Cr (chromium); 0.1-1.5% Mo (Molybdenum); 0.5-7% W 
(tungsten); 0.1-3% V (vanadium); and 1.5-3% C (carbon). 
The present invention also provides a process for producing iron-base 
alloys comprising the steps of: mixing powdery raw materials to obtain a 
weight composition comprising 2-7% CR (chromium), 0.1-1.5% Mo 
(molybdenum), 0.5-7% W (tungsten), 0.1-3% V (vanadium), 0.5-3% C (carbon), 
0.1-2% P (phosphorus), and the remainder FE (iron) and unavoidable 
impurities; pressing the thus mixed raw materials to shape them into the 
configuration of a desired member; sintering the thus-shaped raw materials 
under predetermined conditions; and subjecting the thus-sintered raw 
materials to a heat treatment so as to obtain a predetermined iron-base 
alloy structure. 
The present invention also provides a rocker arm or valve lifter for a 
valve-actuating mechanism of an internal combustion engine, the mechanism 
being adapted to drive the rocker arm either directly or through the valve 
lifter and a push rod by a cam. The working face portion of the rocker arm 
or valve lifter in accordance with the invention, which working face 
portion is adapted to be brought into slide-contact with the cam, is 
formed of an iron-base sintered alloy comprising by weight: 2-7% Cr; 
0.1-1.5% Mo; 0.5-7% W; 0.1-3% V; 1.5-3% C; 0.1-2% P; and the remainder Fe 
and unavoidable impurities. 
Other objects, details and features of the present invention will become 
apparent from the following detailed description of preferred embodiments 
thereof.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
The following detailed description relates to an embodiment of the present 
invention as applied to a rocker arm. 
As illustrated in FIG. 3, the main body 1a of the rocker arm, other than 
its working face which operatively cooperates with a cam, was fabricated 
of a low-alloy steel. A pad 1b made of an alloy according to the present 
invention was bonded to a portion corresponding to the working face. The 
thus fabricated rocker arm was subjected to various measurements and 
tests. 
Example: Iron powder, graphite powder, iron-phosphorus powder, alloy steel 
powder, etc., were proportioned and mixed to obtain substantially the 
following compositions by weight: 
Sample 1: 4.3% Cr, 5.0% W, 1.7% C, 1.0% Mo, 0.3% V, 0.4% P, and the 
remainder Fe. 
Sample 2: 5.4% Cr, 1.8% W, 2.0% C, 0.5% Mo, 0.2% V, 0.5% P, and the 
remainder Fe. 
The materials were then pressed under a forming pressure of 6 tons/cm.sup.2 
into the configuration of a desired pad, and sintered and heat-treated 
under the following conditions, thereby preparing Sample 1 and Sample 2: 
______________________________________ 
Sample 1 Sample 2 
______________________________________ 
Sintering vacuum vacuum 
atmosphere (1 .times. 10.sup.-3 mmHg) 
Sintering 1200.degree. C. 
1200.degree. C. 
temperature 
Hardening in Ar gas in quenching oil 
conditions 
Hardening 1200.degree. C. 
900.degree. C. 
temperatures 
Tempering 550.degree. C. 
200.degree. C. 
temperatures 
______________________________________ 
The resultant samples had a structure containing a martensite matrix and a 
hardened material distributed in a network pattern throughout the matrix. 
The densities of the sinters and their hardnesses were as follows: 
______________________________________ 
Sample 1 
Sample 2 
______________________________________ 
Density of 7.4 7.5 
sinter (g/cm.sup.3) 
Hardness (H.sub.R C) 
50-65 55-70 
______________________________________ 
Thereafter, each of the pads 1b was bonded to the rocker arm 1a and 
assembled in a water-cooled 1800 cc engine with four cylinders arranged in 
a line. The state of abrasion of the pad 1b and cam 2 were compared 
through a bench test with those of a pad and cam which were made of a 
conventional material. In the test, the engine was continuously operated 
at 2000 rpm while maintaining its motor oil (SAE 10W-30) at 
45.+-.5.degree. C. After a lapse of 250 hours, the engine was disassembled 
and the amount of abrasion of each material was measured. 
FIG. 4 depicts the results of the above test in the form of a bar graph, 
wherein in each histogram the white and dotted or the white and hatched 
sections represent respectively the amount of abrasion of the cam top 
portion and that of the working face of the rocker arm. The histograms 
bearing dots relate to materials according to the present invention, while 
the histogram including hatchings relates to the conventional material. 
The working face of each of the rocker arms and the material or surface 
treatment of its corresponding cam were combined as follows: 
______________________________________ 
Sample Cam Working face (pad) 
______________________________________ 
Conventional 
Chilled low- Hard chromium 
example alloy steel plating 
No. 1 Chilled low- Sample No. 1 
alloy steel 
No. 2 Chilled low- Sample No. 2 
alloy steel 
______________________________________ 
As apparent from the graph of FIG. 4, when the material of Sample 1 was 
used as the pad material, the amount of overall abrasion of the cam and 
working face was decreased to about 36% of that of the conventional 
material. 
As shown by the above test results, the material according to the present 
invention is capable of considerably reducing the abrasion of both a cam 
and the member which is brought into operatively cooperating slide-contact 
with the cam, as well as improving their overall abrasion characteristics. 
Accordingly, the present invention is extremely useful in prolonging the 
service life of a valve-actuating mechanism. 
The weight composition of a material according to the present invention 
will hereinafter be described in detail. The abrasion resistance of a 
material according to the present invention has been increased, 
principally, by causing a hard phase of metal carbides to be dispersed 
throughout its martensite matrix. At the same time, the improved abrasion 
resistance of a cam is attributed to an appropriate selection of types of 
metal carbides, the amounts thereof, and the combination thereof. 
The particulars of the weight composition of the material according to the 
invention are as follows: 
Cr: While reinforcing the martensite matrix, it reacts with C to form a 
hard carbide, thereby improving the abrasion resistance. However, when 
used in an amount less than 2%, its specific effect would not be attained. 
On the other hand, an amount greater than 7% results in disadvantages such 
as brittleness of the material and lower machinability thereof. 
Mo: Similar to Cr, while reinforcing the martensite matrix, it reacts with 
C to form a hard carbide, thereby improving the abrasion resistance. 
However, an amount less than 0.1% does not bring about the desired 
particular effect, while an amount greater than 1.5% renders the 
operatively cooperating material susceptible to damage. 
W: Also similar to Cr, it reinforces the martensite matrix and, at the same 
time, reacts with C to form a hard carbide, thereby improving the abrasion 
resistance. However, when added in an amount less than 0.5%, the desired 
specific effect is not attained. On the other hand, an amount greater than 
7% results in brittleness of the material. 
V: It reacts with C to form a carbide, thereby contributing to an 
improvement of the abrasion resistance. However, an addition of less than 
0.1% does not bring about the desired specific effect, while an amount 
greater than 3% lowers the machinability of the material and renders the 
operatively cooperating material susceptible to damage. 
C: While reinforcing the martensite matrix, it reacts, as described above, 
with Cr and other additive components to cause a hard phase to be 
deposited, thereby improving the abrasion resistance. However, when added 
in an amount less than 1.5%, its desired effect may not be fully attained. 
On the other hand, if added in an amount greater than 3%, the toughness of 
the material would be impaired. 
P: P is a sintering agent, by which the raw material mixture is allowed to 
undergo liquid phase sintering so as to highly densify the iron-base 
sintered alloy. An addition of less than 0.1% does not bring about the 
desired effect. On the other hand, an addition beyond 2% is not preferred 
because the liquid phase is produced to too great an extent and its 
dimensional stability is considerably lowered during sintering work. 
Although there have been described what are at present considered to be the 
preferred embodiments of the invention, it will be understood that the 
present invention may be embodied in other specific forms without 
departing from the spirit or essential characteristics thereof. The 
present embodiments are therefore to be considered in all respects as 
illustrative, and not restrictive. The scope of the invention is indicated 
by the appended claims rather than by the foregoing description.