Information
-
Patent Grant
-
6685193
-
Patent Number
6,685,193
-
Date Filed
Thursday, August 30, 200122 years ago
-
Date Issued
Tuesday, February 3, 200420 years ago
-
Inventors
-
Original Assignees
-
Examiners
- Miller; William
- Ho; Thomas
Agents
- Soltis; Lisa M.
- Croll; Mark W.
- Breh; Donald J.
-
CPC
-
US Classifications
Field of Search
US
- 277 459
- 277 436
- 277 447
- 277 448
- 277 460
- 277 464
- 277 465
- 277 461
- 277 462
- 277 463
-
International Classifications
-
Abstract
A non-sealing, lubricating piston ring for lubricating the cylinder wall of a piston housing in a combustion tool is disclosed. The lubricating piston ring is made from a lubricating material such as polytetrofluroethylene (PTFE). The shape of the PTFE ring is designed to optimize the lubricity of the piston housing, while allowing enough friction for the piston to operate properly within the piston housing during reciprocating cycling movement. The PTFE ring may have radial fins extending from an outer surface thereof that are angled to promote ring rotations, such that the ring moves easily along and efficiently lubricates the inner cylinder wall of the piston housing. The PTFE ring does not form a seal between the piston and the housing. Instead, the PTFE ring is positioned above or below a sealing ring, such as a steel piston ring which forms the seal between the piston and the piston housing.
Description
TECHNICAL FIELD
The present invention generally relates to piston rings for lubricating a cylinder wall of a piston housing in a combustion tool and, more particularly, to piston rings made of self lubricating materials.
BACKGROUND ART
It is well known that commercially available piston rings can be molded from a wearable low friction, e.g. self-lubricating, material in a shape to act as self-lubricating, sealing piston rings. Typically, such piston rings are made of PTFE (polytetraflouroethylene) which have extraordinarily low coefficients of sliding friction, high thermal stability and satisfactory wear properties. In fact, these PTFE rings are used in the vast majority of cordless, internal combustion engine-driven pneumatic nailers and air compressors. The presence of a PTFE ring in the piston assembly of an internal combustion engine would negate the need for an external lubricant, and allows the engine to run on lubricant-free fuel which is less costly than lubricant-added fuel. However, it has been observed that the use of PTFE rings to perform both self-lubricating and sealing functions has certain disadvantages.
More particularly, when the PTFE rings are used as a direct replacement for steel sealing rings, the natural lubricity of the PTFE rings is so excellent that it makes the cylinder wall too slippery. As a result, the piston will not retain its position at the top of the stroke (TDC). This causes problems in fuel-air mixture and in the pre-travel of the driver blade.
While it has been proposed to solve the above problem by forming additional grooves in the cylinder to physically hold the piston at TDC, arrangements of such grooves or the like have necessitated the reconstruction of the piston from several points at high costs. This, in turn, can adversely affect the marketability of the tool.
SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention to provide a piston ring assembly for use in internal combustion engine-driven tools in which the aforementioned disadvantages are avoided.
It is another object of the present invention to provide a piston ring assembly for use in an internal combustion engine of a cordless tool which is capable of efficiently lubricating the cylinder wall of a piston housing while allowing enough friction for the piston to operate properly within the piston housing during cycling, especially when the piston is at the top-of-the-stroke position.
It is a further object of the present invention to provide a non-sealing, self-lubricating ring for use in the inventive piston ring assembly. The non-sealing, self-lubricating ring is configured to optimize the lubricity of the piston housing by uniformly transferring the self-lubricating material onto the cylinder wall.
These and other objects of the present invention are achieved by separating the sealing and lubricating functions of the piston ring assembly in an internal combustion engine.
In accordance with an aspect of the present invention, a piston assembly comprises a reciprocating piston axially movable within a cylinder, and a piston ring assembly. The piston ring assembly includes at least one sealing ring, for sealing between an inner wall of the cylinder and the piston, and a non-sealing, self-lubricating ring positioned between the inner wall of the cylinder and the piston and axially spaced from the sealing ring. The non-sealing, self-lubricating ring is made at least partially of a low-friction wearable material.
In a preferred embodiment, the non-sealing, self-lubricating ring is made of PTFE while the sealing ring is a steel sealing ring. Thus, the non-sealing, PTFE ring is used in conjunction with the steel ring wherein the PTFE ring will be used solely to lubricate the cylinder wall and the steel ring will perform the sealing function of the piston to the cylinder wall. By not utilizing the PTFE ring as a seal, many different shapes and geometries of the PTFE ring are possible to achieve-maximum lubrication results.
The foregoing objects of the present invention are also achieved by a non-sealing, self-lubricating ring configured to be in contact with the cylinder wall and rotate about the piston during engine operation, thereby evenly transferring the self-lubricating material onto the cylinder wall.
In accordance with an aspect of the present invention, the non-sealing, self-lubricating ring has an outer circumferential portion which forms a plurality of obliquely extending gas passages communicating upper and lower surfaces of the non-sealing, self-lubricating ring. As a result, gases or fluids contained in the cylinder are free to move through the outer circumferential portion to promote rotation of the non-sealing, self-lubricating ring about the piston during axial movements thereof within the cylinder.
In accordance with another aspect of the present invention, the non-sealing, self-lubricating ring comprises an annular cylindrical body adapted to be mounted on and carried by a piston axially movable within a cylinder, and a plurality of fins of a low-friction wearable material formed on the outer circumferential surface of the annular body and adapted to be in constant contact with an inner wall of the cylinder. The radial fins extend obliquely between the end faces of the annular body to promote rotation of the non-sealing, self-lubricating ring about the piston during axial movements of the piston within the cylinder. As a result, the low-friction wearable material, which is preferably PTFE, will transfer itself easily and uniformly to the inner wall of the cylinder.
Still other objects and advantages of the present invention will become readily apparent to those skilled in the art from the following detailed description, wherein the preferred embodiments of the invention are shown and described, simply by way of illustration of the best mode contemplated of carrying out the invention. As will be realized, the invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, all without departing from the invention. Accordingly, the drawings and description thereof are to be regarded as illustrative in nature, and not as restrictive.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention is illustrated by way of example, and not by limitation, in the figures of the accompanying drawings, wherein elements having the same reference numeral designations represent like elements throughout, and wherein:
FIG. 1
is a schematic sectional view showing a piston assembly of an internal combustion engine utilizing a non-sealing, self-lubricating ring of the present invention;
FIG. 2
is a plan view of a non-sealing, self-lubricating ring in accordance with an embodiment of the present invention;
FIG. 3
is a side view of the non-sealing, self-lubricating ring of
FIG. 2
;
FIG. 4
is an enlarged fragmentary view of a split opening of the non-sealing, self-lubricating ring shown in
FIG. 2
;
FIG. 5
is a perspective view of a non-sealing, self-lubricating ring in accordance with another embodiment of the present invention; and
FIG. 6
is a perspective view of a non-sealing, self-lubricating ring in accordance with yet another embodiment of the present invention.
BEST MODE FOR CARRYING OUT THE INVENTION
A non-sealing, self-lubricating ring, a piston assembly utilizing the non-sealing, self-lubricating ring, and an internal combustion engine utilizing the piston assembly according to the present invention are described. In the following detailed description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be apparent, however, that the present invention may be practiced without these specific details. In other instances, well-known structures and devices are schematically shown in order to simplify the drawing.
Referring now to
FIG. 1
, an internal combustion engine
10
is shown. The internal combustion engine
10
comprises a cylinder and a reciprocating piston
12
. The cylinder includes a cylinder wall
11
and a cylinder head (not shown). The cylinder head, cylinder wall
11
and piston
12
together define a combustion chamber
19
into which fuel is infected for ignition or self-ignition. Piston
12
may be connected by a piston rod (not shown) to a crankshaft (not shown) to transmit power to the outside. It should be understood that the invention is equally suitable for use in any type of internal combustion engine where it is desirable to prevent combustion gases from leaking into other parts of the engine and/or to prevent contaminants from entering combustion chamber
19
.
Piston rings
13
,
14
are provided to seal between piston
12
and cylinder wall
11
during engine operation. Piston rings
13
,
14
seal in the combustion gases and the compression pressures generated at the end of the ignition stroke. Furthermore, the interface between cylinder wall
11
and piston rings
13
,
14
prevents the leakage of contaminants, such as crankcase oil, into combustion chamber
19
during engine operation.
As mentioned in the above discussion, if piston rings
13
,
14
possess high lubricity, cylinder wall
11
may be made so slippery that piston
12
may not retain its position at the top of the stroke (TDC). This in turn causes problems in fuel-air mixture and in the pre-travel of the driver blade. Therefore, it is important to configure piston rings
13
,
14
to supply the necessary friction to keep piston
12
at the top of its stroke. Without this friction, piston
12
will slide down and not be ready for the next combustion cycle.
It should be understood that piston rings
13
,
14
of the present invention serve two functions i) to act as the main seal during combustion, and ii) to supply the necessary friction between cylinder wall
11
and piston
12
. Any arrangement of piston rings
13
,
14
which meets the above two requirements will be suitable for the purpose of the present invention. Preferably, piston rings
13
,
14
are made of steel though other materials are not excluded. Likewise, the present invention is not limited to the double-ring configuration shown in
FIG. 1
, i.e. any other number of piston rings may be used.
In addition to piston rings
13
,
14
, the piston assembly of the present invention is further provided with a ring
15
for lubricating cylinder wall
11
. As can be seen in
FIG. 1
, non-sealing, self-lubricating ring
15
of the invention is placed below piston rings
13
,
14
with respect to combustion chamber
19
. However, other arrangements are not excluded. For example, non-sealing, self-lubricating ring
15
can be positioned closer to combustion chamber
19
, e.g. above at least one of piston rings
13
,
14
.
Since a gap
18
inherent between cylinder wall
11
and piston
12
has been completely sealed by piston rings
13
,
14
, there is no need to configure ring
15
to form a seal. In accordance with the present invention, ring
15
is a non-sealing, self-lubricating ring. Apparently, non-sealing, self-lubricating ring
15
is not necessarily subject to strict requirements of a seal, and its configuration could be more flexible than those of self-lubricating sealing rings known in the art which function as both a seal and a self-lubricating element. The configuration, i.e. material and shape, of non-sealing, self-lubricating ring
15
can be selected to exclusively optimize the lubricity of cylinder wall
11
.
According to one aspect of the present invention, non-sealing, self-lubricating ring
15
, or at least its outer portion which contacts with cylinder wall
11
, is made of a wearable low-friction material. The wearable (self-lubricating) low-friction material should be capable of transferring itself to cylinder wall
11
during axial movements of piston
12
within the cylinder, thereby allowing non-sealing, self-lubricating ring
15
to move easily along and efficiently lubricate cylinder wall
11
. Preferably, non-sealing, self-lubricating ring
15
is made of a synthetic-resin material with low friction coefficient and self-lubricating properties, such as polytetrafluoroethylene (PTFE).
According to another aspect of the present invention, non-sealing, self-lubricating ring
15
is configured to ensure uniform distribution of the wearable low-friction material on, and hence uniform lubrication of, the entire cylinder wall
11
. This can best be done if non-sealing, self-lubricating ring
15
is, for instance, caused to rotate during axial movements of piston
12
within the cylinder. For this purpose, non-sealing, self-lubricating ring
15
is provided with surfaces which are slanted with respect to the axial direction of the cylinder. When piston
12
moves up and down within the cylinder, pressure of gases or other fluids contained in the cylinder will act upon the slanted surfaces causing non-sealing, self-lubricating ring
15
to rotate.
FIGS. 2-4
,
5
and
6
illustrate exemplary embodiments of a non-sealing, self-lubricating ring having such slanted surfaces in accordance with the present invention.
As can be seen in
FIG. 2
, a non-sealing, self-lubricating ring
20
includes an annular body
21
, and a plurality of radial fins
22
formed on the outer surface of annular body
21
. As can be seen in
FIG. 3
, fins
22
obliquely extend between upper and lower end faces
31
,
32
of annular body
21
. More particularly, fins
22
extend from upper end face
31
of annular body
21
to the lower end face
32
thereof. Each adjacent pair of fins
22
forms in between a channel
23
which also obliquely extends between upper and lower end faces
31
,
32
of annular body
21
. Upper and under sides
33
,
34
of each of fins
22
are slanted with respect to the axial direction of the cylinder, and will be acted upon by gases or fluids contained in the cylinder during engine operation (movements of piston
12
). Non-sealing self-lubricating ring
20
is thus caused to rotate.
A similar non-sealing, self-lubricating ring
50
is illustrated in FIG.
5
. Non-sealing self-lubricating ring
50
comprises an annular body
51
and radial fins
52
formed on the outer surface of annular body
51
. Ring
50
differs from ring
20
in that ring
50
has channels
53
smaller than fins
52
while in ring
20
, channels
23
are larger than fins
22
. Furthermore, fins
52
of ring
50
are slanted at a steeper angle than that of fins
22
in ring
20
. However, both rings
20
and
50
are formed with a plurality of gas/fluid passages (in the form of channels
23
,
53
) which communicate upper and lower end faces of the rings. Therefore, during engine operation, i.e. up-and-down movements of piston
12
, gases or fluids contained in the cylinder are free to move from one of the upper and lower end faces to the other via the slanted passages, thereby facilitating rotation of the non-sealing, self-lubricating ring
20
or
50
. It is worthwhile noting that presence of channels
23
,
53
excludes the use of rings
20
,
50
as a sealing element between cylinder wall
11
and piston
12
.
It should be understood that though channels
23
,
53
have been shown and described to be formed at the interface of cylinder wall
11
and non-sealing, self-lubricating ring
20
,
50
, other arrangements can be contemplated. For example, the gas/fluid passages can be formed inside the non-sealing, self-lubricating ring itself (not shown). It should also be understood that the non-sealing, self-lubricating ring of the present invention does not necessarily have the “open” configurations with gas/fluid passages as depicted in
FIGS. 2-3
and
5
. A “closed” configuration may be available as illustrated in FIG.
6
.
As can be seen in
FIG. 6
, non-sealing, self-lubricating ring
60
has an inner annular body
61
and a plurality of slanted primary fins
62
. Ring
60
further includes a plurality of secondary fins
63
extending between the end faces of annular body
61
and connecting adjacent primary fins
62
with each other. When ring
60
is mounted on piston
12
, secondary fins
63
extend substantially in the axial direction of the cylinder and therefore will not impede rotation of ring
60
. As in the case of rings
20
,
50
, the slanted upper and under sides of primary fins
62
will be acted upon by gasses and fluids contained in the cylinder thereby causing ring
60
to rotate.
Besides specific shape and geometry of the non-sealing, self-lubricating ring, the manner in which the ring is installed may also contribute to promotion of the ring rotation. As can be seen in
FIG. 1
, non-sealing, self-lubricating ring
15
loosely fits in an annular groove
16
formed in a wall of piston
12
. An inner portion of ring
15
, such as annular body
21
or
51
of rings
20
,
50
, is at least partially received within groove
16
. The non-sealing, loose fit between cylinder wall
11
and ring
15
allows ring
15
to rotate and distribute its lubricity evenly on cylinder wall
11
.
Furthermore, ring
15
needs to be in constant contact with cylinder wall
11
. For this purpose, an O-ring
70
or other type ring is preferably placed behind, or partially embedded in, non-sealing, self-lubricating ring
15
to maintain a certain contact force to cylinder wall
11
, so that the transfer of the wearable low-friction material is maintained. It should be noted that in accordance with the present invention, the contact force exercised by O-ring
70
and non-sealing, self-lubricating ring
15
on cylinder wall
11
is not necessarily as large as a sealing force required to seal between e.g. piston rings
13
,
14
and cylinder wall
11
. Instead, the contact force should be sufficiently small to not impede rotation of ring
15
. Alternatively, ring
15
can be molded directly over a spring steel ring or a wire spring ring (not shown) by, e.g., an insert molding process. In this manner, ring
15
can have more controlled and longer lasting spring properties.
In an embodiment, it is preferable to position the gas/fluid passages of the non-sealing, self-lubricating ring, such as channels
23
,
53
of rings
20
,
50
, completely in gap
18
between cylinder wall
11
and piston
12
, as shown in FIG.
1
. Then, the gas/fluid passages will not be limited, at least partially, by the piston wall immediately above and below groove
16
.
In another embodiment, it is preferable to form the non-sealing, self-lubricating ring of the present invention as a split annulus for easy fit on piston
12
. As can be seen in
FIG. 2
, ring
20
may be discontinuous and have a split
23
which is shown in larger detail in FIG.
4
. As can be seen in
FIG. 4
, ring
20
has first and second circumferential end portions
41
,
42
overlapping each other. A similar arrangement can also be seen in
FIG. 6
where ring
60
has first and second circumferential end portions
64
,
65
overlapping each other. The difference between ring
20
and
60
resides in that circumferential end portions
64
,
65
of ring
60
further include projections
66
,
67
, respectively, extending toward one another. Thus, a step lock is formed to keep ring
60
in place after ring
60
has been installed on piston
12
.
Another split annulus arrangement for the non-sealing, self-lubricating ring of the present invention is depicted in
FIG. 5
at
54
. As can bee seen in
FIG. 5
, ring
50
extends circumferentially for less than 360 degree, and has a first end
55
stopping short of a second end
56
. Spacing
54
between first and second ends
55
,
56
is approximately of the same size as channels
53
formed between fins
52
.
It should now be apparent that a non-sealing, self-lubricating ring, a piston assembly utilizing the non-sealing, self-lubricating ring, and an internal combustion engine utilizing the piston assembly according to the present invention have been described. In accordance with the present invention, the sealing and lubricating functions of a piston ring assembly are separately performed by one or more sealing rings and a non-sealing, self-lubricating ring, respectively.
On one hand, the sealing rings are not required to be made of a material with high self-lubricating properties, and can be configured to provide sufficient friction with the cylinder wall to retain the piston at the top of the stroke.
On the other hand, the non-sealing, self-lubricating ring is not required to function as a seal between the piston and the cylinder. Therefore, the non-sealing, self-lubricating ring may have many different shapes and geometries to achieve optimal lubrication of the cylinder wall. The non-sealing, self-lubricating ring may be even configured to rotate about the piston during engine operation to uniformly transfer the self-lubricating material on the cylinder wall. The service life of the non-sealing, self-lubricating ring is thus prolonged. These advantages would not be observed where a self-lubricating ring is configured to also form a complete seal between the piston and the cylinder because such a self-lubricating sealing ring would not be able to rotate and evenly distribute its lubricity to the cylinder wall. The service life of the self-lubricating sealing ring is also shortened.
While there have been described and illustrated specific embodiments of the invention, it will be clear that variations in the details of the embodiments specifically illustrated and described may be made without departing from the true spirit and scope of the invention as defined in the appended claims.
Claims
- 1. A piston assembly, comprising:a reciprocating piston axially movable within a cylinder; at least one sealing ring for sealing between an inner wall of the cylinder and the piston; and means for lubricating the inner wall of the cylinder, said means consisting essentially of a non-sealing ring positioned between the inner wall of the cylinder and the piston and axially spaced from said at least one sealing ring, said non-sealing ring being made at least partially of a low-friction wearable material transferable onto the inner wall of the cylinder during relative movement of said non-sealing ring and said inner wall of the cylinder wherein the non-sealing ring comprises first and second end faces spaced from each other by a thickness of said non-sealing ring in an axial direction of said piston assembly, the non-sealing ring further comprising an inner portion at least partially received in a groove formed on the piston; and an outer portion being made of said low-friction wearable material and extending radially from the inner portion, wherein said outer portion has a plurality of obliquely extending gas passages that connect the first and second end faces and extend through the entire thickness of said ring, thereby allowing gases contained in the cylinder to move through said outer portion to promote rotation of said non-sealing ring about the piston during axial movements of the piston within the cylinder.
- 2. The piston assembly of claim 1, wherein said outer portion comprises a plurality of obliquely extending fins defining said gas passages, said fins extending from the first end face to the second end face.
- 3. The piston assembly of claim 2, wherein said non-sealing ring is formed as a split annulus extending circumferentially for less than 360 degrees and having first and second ends circumferentially spaced from each other by a circumferential spacing which is about the same size as a width of a channel defined between adjacent ones of said fins.
US Referenced Citations (39)
Foreign Referenced Citations (2)
Number |
Date |
Country |
1918690 |
Oct 1970 |
DE |
3520668 |
Jun 1986 |
DE |