Internal-combustion engines – Poppet valve operating mechanism – Rocker
Reexamination Certificate
2002-04-23
2003-07-29
Denion, Thomas (Department: 3748)
Internal-combustion engines
Poppet valve operating mechanism
Rocker
C123S090250, C123S090390, C074S559000
Reexamination Certificate
active
06598571
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a cam follower with roller, and more particularly, to a cam follower with roller that is incorporated into a valve mechanism of an internal combustion engine of a vehicle.
2. Description of the Background Art
To increase durability and maintenability of an engine valve system, it is necessary to address the problems related to abrasion and insufficient lubrication of a cam and a follower on a cam shaft.
To prevent abrasion of the valve system, a hydraulic lash adjuster has been practically utilized in an OHV-type engine, and recently, use of a rolling bearing for the follower has rapidly increased in order to reduce abrasion and friction loss of the cam and follower.
A cam is a portion where lubrication easily dies away among other engine components, and a contact surface thereof is called a boundary lubrication area. In a cam follower with roller used under such circumstances, the cam is in contact with the roller basically by rolling contact. However, the rolling contact involves sliding, since absolute rolling movement is hindered by abrupt variations in the load applied onto the roller and by changes in the rolling speed of the roller due to the shape of the cam. Thus, peeling or smearing, i.e. surface damage, occurs on an outer diameter rolling surface of the roller in connection with the lubricating conditions (amount and temperature of oil, debris) and surface roughness of the opposing cam, resulting in a short life.
Moreover, a supporting shaft rotatably supporting the roller is limited in the loaded zone, and thus a very large pressure is applied onto the surface of the supporting shaft, resulting in shorter rolling fatigue life compared to that of the roller or a bearing. Therefore, increase of rolling fatigue life has been desired.
The bearing rotatably supporting the roller is generally a full type roller bearing, which generates skew and relative sliding, so that the bearing is also subjected to surface damage such as peeling and smearing.
It is noted that SUJ2 has conventionally been used for the material of such roller, supporting shaft and bearing.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a cam follower with roller having a roller, a supporting shaft rotatably supporting the roller and a rolling element that are made of heat-resisting, peeling-resisting and smearing-resisting materials, and capable of increasing rolling fatigue life and reducing surface damage under high temperature conditions.
According to the present invention, in a cam follower with roller including a cam follower body having a roller supporting portion integrated into the cam follower body, a supporting shaft of which both ends are fixed to the roller supporting portion, and a roller rotatably supported on the supporting shaft with a plurality of needle rollers interposed; at least one of the supporting shaft, needle roller and roller is formed of heat-resisting steel.
According to a cam follower with roller of the present invention, at least one of the supporting shaft, needle roller and roller is formed of the heat-resisting steel, so that the heat resistance can be improved and surface damage such as smearing and peeling can be prevented, resulting in increase of rolling fatigue life under high temperature conditions.
In the cam follower with roller, preferably, the both ends of the supporting shaft is caulked to be fixed to the roller supporting portion.
Thus, the both ends of the supporting shaft are caulked to be fixed to the roller supporting portion, and this caulking and fixing work can be performed merely by notching an end surface of the supporting shaft. Therefore, no impact is applied onto the roller supporting portion, so that the cam follower would not be deformed at assembling.
In the cam follower with roller, preferably, a rolling contact surface on which the needle roller rolls, of an outer circumferential surface of the supporting shaft, is subjected to high frequency quenching so as to have a surface hardness of at least HV 650, and the both ends of the supporting shaft is subjected to no quenching so as to have a surface hardness of at least HV 200 and at most HV 280.
Since the rolling contact surface has a surface hardness of at least HV 650, it can remain intact when the needle roller rolls, without the supporting shaft being deformed due to abrasion. Furthermore, both end surfaces of the supporting shaft has a surface hardness in the range between HV 200 and HV 280, so that the end surfaces can be notched at assembling to enlarge the edge portion. Such a caulking process generates no crack at the ends, allowing the supporting shaft to be easily and firmly fixed to the cam follower body.
In the cam follower with roller, preferably, the supporting shaft is through-quenched and is press-fit to the roller supporting portion.
Thus, the supporting shaft is through-quenched, allowing the hardness to be higher. Furthermore, the supporting shaft is press-fit to the roller supporting portion, so that the supporting shaft can be fixed to the roller supporting portion even if the supporting shaft is produced by the through quenching which allows no caulking for fixing.
In the cam follower with roller, preferably, the supporting shaft is through-quenched and is fixed to the roller supporting portion in the axial direction of the supporting shaft with a snap ring interposed.
Thus, the supporting shaft is through-quenched, allowing the hardness to be higher. Furthermore, the supporting shaft is fixed by the snap ring, so that the supporting shaft can be fixed to the roller supporting portion without press-fitting or caulking work.
In the cam follower with roller, preferably, the roller is made of heat-resisting steel.
In particular, the roller is in rolling-contact with the cam while sliding, and thus the sliding or tangential stress may act onto the roller to increase the temperature on the roller surface, or shear heating occurs in lubrication oil to reduce the thickness of an oil film. This may easily cause surface damage such as peeling and smearing. Such surface damage can, however, be prevented by using the heat-resisting steel for the roller.
In the cam follower with roller, preferably, the heat-resistant steel is made of a steel material at least containing as alloy elements in a matrix, by mass %, at least 0.6% and at most 1.3% of C(carbon), at least 0.3% and at most 3.0% of Si(silicon), at least 0.2% and at most 1.5% of Mn(manganese), at most 0.03% of P(phosphorus), at most 0.03% of S(sulfur), at least 0.3% and at most 5.0% of Cr(chromium), at least 0.1% and at most 3.0% of Ni(nickel), at most 0.050% of Al(aluminum), at most 0.003% of Ti(titanium), at most 0.0015% of O(oxygen) and at most 0.015% of N(nitrogen), and a remaining part of Fe(iron) and an unavoidable impurity.
The use of the steel material allows rolling fatigue life to be elongated by quenching and tempering, under the environment contaminated with debris, without a carbonitriding process. Thus, carbonitriding can be dispensed with, reducing the manufacturing cost. Moreover, the steel material is superior in its heat resistance, peeling-resisting property and smearing-resisting property, so that rolling fatigue life can be increased and surface damage can be reduced under high temperature conditions.
The reasons for limitations of each component indicated above will be described below.
(1) C Content (at Least 0.6% and at Most 1.3%)
C is a requisite element for securing the strength as a rolling bearing, and at least 0.6% of the C content is required to maintain the hardness after a prescribed heat treatment. Thus, the lower limit of the C content is set to be 0.6%. Moreover, if the content of C exceeds 1.3%, large carbide appears, resulting in shorter rolling fatigue life. Therefore, the upper limit of the C content is set to be 1.3%.
(2) Si Content (at Least 0.3% and at Most 3.0%)
Si is preferably added because it has a function of suppressing softening in a high temperature range and impr
Harimoto Kazuyoshi
Kasahara Nobuhiro
Kitagawa Masaru
Nakano Yoshiyasu
Chang Ching
NTN Corporation
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