Cylinder liner formed with cross-hatching grooves

Details Cylinder liner formed with cross-hatching grooves Cylinder liner formed with cross-hatching grooves

2000-03-29

2001-04-24

McMahon, Marguerite (Department: 3747)

Internal-combustion engines

Particular piston and enclosing cylinder construction

Cylinder detail

Reexamination Certificate

active

06220214

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a cylinder liner, and more particularly, to a type thereof fitted in a cylinder wall of a cylinder block.
Conventionally, a cylinder block is formed of an aluminum alloy and a cylinder liner formed of cast iron is fitted in the cylinder block in order to reduce overall weight and to improve thermal conductivity of an automobile engine. An inner peripheral surface of the cylinder liner is subjected to honing in order to exhibit lubrication oil controllability and an initial break-in property.
For the honing process, a honing tool having a honing head
5
is employed as shown in FIG.
6
. The honing head
5
has a body
6
in which a push rod
7
provided integrally with a taper cone
8
is disposed movably in an axial direction of the body
6
. An elongated grindstone or a hone
10
extending in an axial direction of the body
6
is fixed to a stone holder
9
provided at an outer peripheral surface of the body
6
. Several parts of the stone holder
9
radially inwardly protrude toward an axis of the body
6
, and a tapered surface
9
a
in mating relation to the taper cone
8
is formed at each inner end of the protruding part.
If the push rod
7
is moved downwardly by a hydraulic drive means (not shown), the stone holder
9
is moved radially outwardly by the taper cone
8
, so that the grindstone
10
is pressed onto a surface of a workpiece
1
, i.e., an inner peripheral surface
4
of the cylinder liner. The body
6
is connected to a drive motor (not shown) for rotating motion and to a hydraulic device (not shown) for reciprocating motion. Thus, the honing head
5
is reciprocatingly movable in a direction indicated by an arrow Va, while the honing head
5
is rotated in a direction indicated by an arrow Vr. Thus, honing is imparted on the inner surface
4
of the workpiece
1
.
As a result of the honing, cross-hatching grooves “A” having a predetermined cross-hatching angle and surface roughness are formed in the inner surface
4
of the workpiece
1
. A portion sectioned by the cross-hatching grooves is referred to as a plateau. A desired function of the cylinder liner such as the above-mentioned oil controllability and initial break-in property is provided by the cross-hatching grooves. Thus, the cylinder liner can provide a sufficient scuffing resistance.
In order to improve scuffing resistance, a typical grindstone for honing is GC800K or a low hardness grindstone formed of a resin or a cork. The roughness attendant to the cross-hatching is relatively large such as from 0.8 to 2.0 &mgr;mR
3Z
even in case of the plateau honing. Incidentally, R
3Z
implies surface roughness measurement amount. In case of a mean surface roughness R
Z
defined in DIN4768, a test piece is subdivided into five individual cross-sections, and a distance between the highest peak and the deepest score with respect to each cross-section is obtained to obtain a mean value. On the other hand, R
3Z
implies a functional surface roughness in which 2 outliers in the top and bottom ranges are not taken into consideration in each of the 5 individual sections. Incidentally GC800K is defined in JIS R6211-1980 or ISO 525. “GC” implies material of grindstone particle, i.e., silicon carbide, “800” implies particle size, i.e., extremely fine, and “K” implies binding force of a binder for binding together the grindstone particles.
SUMMARY OF THE INVENTION
FIG. 7
shows a graphical representation showing the relationship between the surface roughness attendant to the cross-hatching grooves and lubrication oil consumption amount. As is apparent from the graph, oil consumption amount increases in accordance with an increase in roughness. If the roughness decreases, the oil consumption amount is deemed to be decreased.
According to a conventional cylinder liner, since the surface roughness is relatively large such as from 0.8 to 2.0 &mgr;mR
3Z
, greater oil consumption amount resulted. An attempt was made to lower the surface roughness of the cylinder liner to not more than 0.8 &mgr;mR
3Z
in order to reduce the oil consumption amount. However, honing performance is insufficient, and “plastic flows” may occur in an inner peripheral surface of the cylinder liner if fine surface roughness is desired. The plastic flows may plug or close an opening of graphite existing or exposing at the inner peripheral surface of the cylinder liner. The graphite opening inherently provides oil retaining property. However, due to the plugging, this property may be lowered. Further, due to excessive honing, “open phase rate of graphite” may be low. This rate is the rate of the non-damaged graphite precipitated at the inner peripheral surface of the cylinder liner, the graphite being not damaged by the honing. Due to the lowering of the rate, a supplemental lubrication property because of the self-lubricating characteristic of the graphite cannot be performed, and therefore, scuffing may easily occur if an oil film is not uniformly provided or disappears in the inner surface of the cylinder liner.
It is therefore an object of the present invention to provide a cylinder liner providing high scuffing resistance yet providing a low oil consumption efficiency.
This and other objects of the present invention will be attained by providing a cylinder liner fixed to a cylinder bore and in relative sliding contact with a piston, the liner having an inner peripheral surface whose surface roughness ranges from 0.4 &mgr;mR
3Z
to 0.8 &mgr;mR
3Z
. Graphite is precipitated on the surface, and an open phase rate of graphite is not less than 80%.


REFERENCES:
patent: 5560283 (1996-10-01), Hannig
patent: 6158407 (2000-12-01), Mizutani
patent: 7-54706 (1995-02-01), None

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