Internal-combustion engines – Poppet valve operating mechanism – Rocker
Reexamination Certificate
2000-09-15
2001-11-06
Lo, Weilun (Department: 3748)
Internal-combustion engines
Poppet valve operating mechanism
Rocker
C123S090500, C384S565000, C384S568000, C029S898068, C074S569000
Reexamination Certificate
active
06311660
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a rolling-contact cylindrical element such as a tappet roller for use as a driven part such as a fuel injector, an intake or exhaust valve, or the like in an internal combustion engine.
2. Description of the Related Art
Conventionally, iron-based alloys such as a bearing steel and a tool steel, ceramics such as silicon nitride, and the like have been used as a rolling-contact cylindrical element such as a tappet roller. However,for example, there is the following problem. Because of the difference of parallelism between a cam and a contact surface, the deflection of the shaft of a fuel injection apparatus and intake and exhaust valves, there occurs partial contact of the cam with an end portion of the tappet roller and bearing pressure between the tappet roller and the cam increases. As a result, there occurs unstable rotation and the seizure, wear, pitching, and exfoliation of the contact surface.
Accordingly, a technique has been proposed to provide the contact surface of the tappet roller with crowning so as to alleviate the aforementioned partial contact due to a difference in parallelism and the deflection of a shaft, thereby suppressing the rise in bearing pressure and obtaining stable rotation. The shape of the bus of the crowning includes a so-called full crowning, a trapezoidal crowning, and a crowning combining circular arcs. For example, JP-U-5-36005 proposed that in order to overcome the problems of the trapezoidal crowning and the full crowning, a circular arc crowning having a large radius of curvature is provided in a central portion of the contact surface, while a circular arc crowning having a small radius of curvature is provided at an end portion thereof.
However, with tappet rollers in recent years, the bearing pressure with the cam is made high so as to effect control with higher accuracy by transmitting the rotation of the cam accurately to the fuel injector or the like. In addition, since fuel injection is effected under higher pressure as a countermeasure for controlling exhaust gases, the surface of contact with the cam has come to be subjected to extremely high contact pressure. For this reason, with the aforementioned crownings, even if they are able to transmit the rotation, excessively large bearing pressure occurs at the end portion, i.e., edge load occurs, due to misalignment during assembly, i.e., an inclination. Consequently, there are problems in that wear is promoted, variations occur in the transmission of rotation, the performance of the internal combustion engine declines, and the rolling life of the tappet roller decreases due to the exfoliation of the contact surface.
FIG. 9
shows a circular arc crowning of a general tappet roller. In this example, a half Le of the effective contact length is 8 mm, a circular arc crowning with a radius of curvature of 2, 000 mm is provided in its central portion, a circular arc crowning with a radius of curvature of 800 mm is provided in a 3-mm section ranging from an axial position, x=5 mm, with a center in the direction of the bus set as an origin to the end in such a manner as to continue therefrom.
FIG. 10
shows the distribution of bearing pressure when the tappet roller of this crowning shape and the cam are brought into contact with each other with an inclination of {fraction (5/1,000)}. The abscissa in the drawing shows the ratio of the aforementioned axial position x with the center in the direction of the bus set as the origin to the half L
e
of the effective contact length, while the ordinate shows the ratio of bearing pressure P to Hertz's maximum bearing pressure P
H
. However, in this case, it is assumed that the Hertz's maximum bearing pressure is defined as a maximum contact bearing pressure occurring in the center of the contact surface when circular cylinders are brought into contact with each other under ideal conditions in which there is no misalignment and no edge load. Then, as is apparent from the drawing, an extreme edge load occurs in the conventional case.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a rolling-contact cylindrical element such as a tappet roller capable of suppressing an increase in the bearing pressure and suppressing and preventing wear and exfoliation and of ensuring the performance of the internal combustion engine by clarifying specific numerical values of the shape of the circular-arcs combining crowning and numerical values of the shape of the partial crowning.
According to the present invention, a rolling-contact cylindrical element which abuts against a mating element having a surface with a radius of curvature and is axially supported rotatably so as to come into rolling contact with the mating element at its outer peripheral surface, wherein a crowning is provided on the outer peripheral surface for abutment against the mating element, and if it is assumed that a half of the effective contact length of the outer peripheral surface in a direction of a bus of the outer peripheral surface is L
e
, a shape of the bus of the crowning is provided such that an amount &dgr; of fall of the crowning at an axial position x toward an axial end of the rolling-contact cylindrical element from a center in a direction of the bus of the abutment surface of the rolling-contact cylindrical element set as an origin satisfies a following formula (1):
If−L
e
≦x≦L
e
,
-
8.6
×
10
6
E
′2
·
r
1
·
r
2
r
1
+
r
2
ln
{
1
-
(
1
-
1780
E
′
·
r
1
·
r
2
r
1
+
r
2
·
1
L
e
)
·
(
x
L
e
)
2
≤
δ
≤
-
45
×
10
6
E
′2
·
r
1
·
r
2
r
1
+
r
2
ln
{
1
-
(
1
-
3650
E
′
·
r
1
·
r
2
r
1
+
r
2
·
1
L
e
)
·
(
x
L
e
)
2
}
(
1
)
where,
1/E′=(1−&ngr;
1
2
)/E
1
+(1−&ngr;2
2
)/E
2
E
1
: modulus of longitudinal elasticity of the material of the rolling-contact cylinder (MPa)
E
2
: modulus of longitudinal elasticity of the material of the mating element (MPa)
&ngr;
1
: Poisson's ratio of the material of the rolling-contact cylinder
&ngr;
2
: Poisson's ratio of the material of the mating element
r
1
: outer radius of the rolling-contact cylindrical element of the mating surface abutting against the mating element (mm)
r
2
: minimum value of the radius of curvature of a projection portion of the mating element at its outer peripheral surface (mm)
ln: natural logarithmic function
In the present invention, as a result of analysis of the bearing pressure, a known logarithmic crowning (thesis by P. M. Johns and R. Gohar “Roller bearings under radial and eccentric loads” TRIBOLOGY International, vol. 14, 1981, pp. 131-136) was determined in which even if an inclination of {fraction (5/1,000)} or thereabouts has occurred, an excessive increase in the bearing pressure, i.e., the so-called edge load, does not occur. However, although the logarithmic crowning theoretically exhibits a long life, it is difficult to fabricate. Therefore, by focusing attention on the fact that a circular arc crowning also has a long life if its shape is close to a logarithmic crowning, the amount of fall of the crowning at ±L
e
from the center of the roller contact surface, i.e., up to both end points of the contact surface, is set between two logarithmic crowning profiles.
In addition, in the rolling-contact cylindrical element which abuts against a cam of a camshaft and is axially supported rotatably, a crowning is provided on a surface of contact with the cam, and if it is assumed that a half of the effective contact length of the contact surface in a direction of a bus of the contact surface is L
e
, the shape of the bus of the crowning may be provided such that an amount &dgr; of fall of the crowning at an axial position x with a center of the contact surface set as an origin satisfies a following formula:
If x=
Natsumeda Shinichi
Sahara Juntaro
Lo Weilun
NSK Ltd.
Sughrue Mion Zinn Macpeak & Seas, PLLC
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