U.S. patent application number 09/939195 was filed with the patent office on 2003-02-27 for monobloc piston for diesel engines.
This patent application is currently assigned to Federal-Mogul World Wide, Inc.. Invention is credited to Gaiser, Randall R., Zhu, Xiluo.
Application Number | 20030037671 09/939195 |
Document ID | / |
Family ID | 25472714 |
Filed Date | 2003-02-27 |
United States Patent
Application |
20030037671 |
Kind Code |
A1 |
Zhu, Xiluo ; et al. |
February 27, 2003 |
MONOBLOC PISTON FOR DIESEL ENGINES
Abstract
A steel monobloc piston for diesel engines is formed with a
relatively short piston skirt whose lower edge resides below the
axis of the pin bores of the piston, but located at or above a
lowest tangent point of the pin bores. The piston body preferably
has a closed oil cooling gallery and the skirt is preferably joined
at its upper end to an outer wall of the piston in which a
plurality of ring grooves are formed.
Inventors: |
Zhu, Xiluo; (Ann Arbor,
MI) ; Gaiser, Randall R.; (Chelsea, MI) |
Correspondence
Address: |
Robert L. Stearns
5291 Colony Drive North
Saginaw
MI
48603
US
|
Assignee: |
Federal-Mogul World Wide,
Inc.
|
Family ID: |
25472714 |
Appl. No.: |
09/939195 |
Filed: |
August 24, 2001 |
Current U.S.
Class: |
92/231 |
Current CPC
Class: |
F02F 3/00 20130101; F02F
3/003 20130101; F02B 3/06 20130101 |
Class at
Publication: |
92/231 |
International
Class: |
F16J 001/04 |
Claims
What is claimed is:
1. A piston for diesel engines, comprising: a piston body
fabricated of steel; said piston body having an outer wall and a
closed oil gallery; a pair of pin bosses having pin bores formed
therein, said pin bores having a common pin bore axis and a lowest
tangency point; a skirt formed as one piece with the pin bosses,
said skirt coupled at an upper end to said outer wall; and said
piston skirt having a lower edge disposed below said pin bore axis
and located at or above said lowest tangency point of said pin
bores.
2. The piston of claim 1 wherein said piston body includes the
following dimensional ratios: (H/D)=0.5-0.75 (A/D)=0.3-0.6
(A/H)=0.7-1.2 where, H=compression height of the piston body
between a top of the piston and the axis of the pin bores, D=piston
diameter, and A=axial length between the lowest ring groove and the
lower edge of piston skirt.
3. The piston of claim 1 wherein said piston body is fabricated of
at least two separate parts which are connected across at least one
joint.
4. The piston of claim 3 wherein said at least one joint comprises
a friction weld joint.
5. A piston for a diesel engine, comprising: a piston body
fabricated of steel; a pair of pin bosses having aligned pin bores
disposed about a pin bore axis and having a lowest tangent point of
said pin bores; a skirt formed as one piece with said pin bores and
having a lower edge disposed below said pin bore axis and at or
above said lowest tangent point of said pin bores.
6. A diesel engine comprising: an engine block having at least one
cylinder bore; a monobloc piston disposed in said cylinder bore
having a piston body fabricated of steel and having a pair of pin
bosses with aligned pin bores disposed about a pin bore axis and
having a lowest tangent point of said pin bores; and a piston skirt
formed as one piece with said pin bosses, said skirt having a lower
edge disposed below said pin bore axis at or above said tangent
point of said pin bores.
7. The diesel engine of claim 6 wherein said piston body includes
the following dimensional ratios: (H/D)=0.5-0.75 (A/D)=0.3-0.6
(A/H)=0.7-1.2 where, H=compression height of the piston body
between a top of the piston and the axis of the pin bores, D=piston
diameter, and A=axial length between the lowest ring groove and the
lower edge of the piston skirt.
8. The diesel engine of claim 6 wherein the cylinder has a lower
edge and said lower edge of said piston skirt is disposed at or
above said lower edge of said cylinder when said piston is at a
lowest point of travel in said cylinder.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Technical Field
[0002] This invention relates generally to monobloc pistons for
diesel engine applications in which the piston skirt is formed as
one integral piece with the piston body, and more particularly to
the construction of the piston skirt.
[0003] 2. Related Art
[0004] Monobloc pistons for diesel engine applications are known
wherein the piston skirt is formed as an integral portion of the
piston body, as opposed as being articulated. Such pistons are
known to have piston skirts that are of such length and/or are
positioned such that the lower edge of the skirt extends well below
the bottom of the pin bosses to provide the desired support and
guidance to the piston as it reciprocates within the cylinder of
the engine. Such low lying skirts, however, can extend outside of
the cylinder liner at bottom dead center position of the piston and
can lead to scuffing of the piston skirt and/or liner due to the
sudden change in load and direction as the piston returns upwardly
in the cylinder. In addition, the low lying skirt interferes with
the location of oil injection nozzles which direct cooling oil up
into the piston, requiring the skirt to be notched in the area of
the nozzle to provide clearance. Examples of such monobloc pistons
are disclosed in U.S. Pat. Nos., 4,161,165 and 4,286,505, as well
as published international application WO 9620340. The piston
disclosed in the latter publication has a short, low lying piston
skirt which is uncoupled from the ring belt and, due to the wide
gap between the bottom of the ring belt and the top of the skirt as
well as the low, remote positioning of the skirt, transfers some of
the piston guidance duties to the ring lands near the top of the
piston, which is less efficient and could cause damage to the ring
lands as well as decrease the performance of the piston.
[0005] U.S. Pat. No. 4,704,950 discloses a high performance
automotive piston for gasoline engines which is manufactured
entirely of aluminum and would be unsuitable for high compression
diesel applications to which the present invention is directed.
[0006] It is an object of the present invention to provide a
monobloc piston for diesel engines that overcomes or greatly
minimizes the deficiencies of the prior art pistons described
above.
SUMMARY OF THE INVENTION AND ADVANTAGES
[0007] A piston for diesel engines constructed according to a
presently preferred embodiment of the invention comprises a piston
body fabricated of steel having an outer wall and a closed oil
gallery. A pair of pin bosses have axially aligned pin bores and a
lowest tangency point of the pin bores. The piston body has a skirt
that is formed as one piece with the pin bosses and is coupled at
its upper end to the outer wall so as to form a continuous
extension of the outer wall. The piston skirt has a lower edge
spaced below the pin bore axis, but located at or above the lowest
tangency point of the pin bores.
[0008] The invention also contemplates a diesel engine which
includes an engine block having at least one cylinder bore and a
monobloc piston disposed in the cylinder bore having a piston body
fabricated of steel and including a pair of pin bosses with aligned
pin bores disposed about a pin bore axis and having a lowest
tangent point to the pin bores. A piston skirt is formed as one
piece with the pin bosses and has a lower edge disposed below the
pin bore axis at or above the lowest tangent point of the pin
bores.
[0009] The invention has the advantage of providing a steel
monobloc piston for diesel engine applications fitted with a short
skirt made of the same steel material of such size and location
relative to the remainder of the piston body to provide efficient
guidance to the piston during reciprocation in the cylinder bore to
reduce loading on the ring lands due to its high location relative
to the pin bores. The high location of the lower edge of the skirt
prevents the skirt from extending from the bottom of the cylinder
bore at bottom dead center of the piston, and thus minimizes or
eliminates scuffing of the skirt caused by a sudden change in load
or direction when the piston returns upwardly. The relatively high
location of the lower edge of the skirt also provides ample
clearance for the oil jet nozzles, eliminating the need for
clearance notches in the lower edge of the skirt so as to present a
continuous, non-interrupted lower leading edge of the skirt which
is stronger and easier to manufacture than notched skirts.
[0010] The overall reduction and the height of the skirt further
has the advantage of simplifying the manufacture of forged steel
pistons. The shorter length enables production of a relatively
thinner, more uniform thickness skirt wall as compared to forged
skirts of greater length which are generally thicker due to the
required draft angle to enable forging of the piston skirt.
THE DRAWINGS
[0011] These and other features and advantages of the present
invention will become more readily appreciated when considered in
connection with the following detailed description and appended
drawings, wherein:
[0012] FIG. 1 is a bottom perspective view of a piston constructed
according to the invention;
[0013] FIG. 2 is a side elevation view of the piston of FIG. 1;
[0014] FIG. 3 is a fragmentary elevation view like FIG. 2, but
shown partly in section; and
[0015] FIG. 4 is a schematic, fragmentary sectional view of a
diesel engine shown equipped with the piston of FIGS. 1-3.
DETAILED DESCRIPTION
[0016] A piston constructed according to the invention is shown
generally at 10 in FIGS. 1-3 and is shown installed as part of a
diesel engine 12 in FIG. 4.
[0017] The piston 10 includes a piston body 14 having a top wall 16
formed with a combustion bowl or crater 18 extending downwardly
from a top surface 20 of the top wall 16.
[0018] The piston body 14 includes an outer annular wall or ring
belt 22 having an outer surface 24 formed with a plurality of ring
grooves 26 for receiving piston rings (not shown). The outer wall
22 includes an annular inner surface 28 facing radially inwardly of
the piston body 14 opposite the outer surface 24.
[0019] The piston body 14 includes an annular inner wall 30
extending downwardly from the combustion bowl 18 having a radially
outwardly facing annular surface 32 spaced radially inwardly from
the inner surface 28 of the outer wall 22.
[0020] The piston body 14 preferably includes a bottom wall 34
which extends between and interconnects the lower end regions of
the outer wall 22 and inner wall 30 in spaced relation to the top
wall 16. The top wall 16 and outer wall 22 and inner walls 30 bound
an annular cooling chamber or gallery 36 for receiving cooling oil
which is preferably closed at the bottom by the bottom wall 34. By
"closed", it is not meant that the gallery is entirely self
contained, but includes provision for openings and passages for
introducing oil into and draining oil from the gallery 36. A
representative oil inlet opening 38 is shown in FIG. 3, as is a
representative oil drainage passage 40 according to convention. The
bottom wall 34 is formed as one piece with the lower regions of the
outer wall 22 and inner wall 30 and serves, in addition to closing
the gallery 36, as a structural web or bridge between the outer and
inner walls 22, 30.
[0021] The piston body 14 includes a pair of pin bosses 42. The pin
bosses 42 are formed of one piece with the inner wall 30 and
preferably extend downwardly from the bottom wall 34 and are set
radially inwardly from the outer surface 24 of the outer wall 22.
The pin bosses 42 are formed with pin bores 44 which receive a
wrist pin (not shown) for connecting the piston 10 to a connecting
rod (not shown) of the engine 12. The pin bores 44 are aligned
about a common pin bore axis A, which represents a center line of
the pin bores with respect to a longitudinal axis B of the piston
body 14. The pin bores 14 have a lowest tangent point 46, which
represents the lowest part of the pin bores 44 in the longitudinal
direction, with the tangency point 46 determined by passing a plane
P through the piston body 14 perpendicular to the longitudinal axis
B which contains the lowest point of the pin bore surfaces 48 of
the pin bores 44, as illustrated in FIG. 2.
[0022] The piston body 14 includes a piston skirt 50 that is formed
as one piece with the pin bores 44, such that the piston body 14
has a monobloc structure with a fixed skirt, rather than a separate
skirt articulated to the pin bosses by the wrist pin (not shown).
The skirt 50 is further preferably formed with an upper end region
52 coupled directly to the outer wall 22, such that the piston
skirt 50 is formed as continuous downward extension of the outer
wall 22 below the bottom wall 34. As such, the piston skirt 50 is
also interconnected as one piece with the bottom wall 34, as
illustrated best in FIG. 3.
[0023] The piston skirt 50 has a lower, marginal free edge 54 which
defines the lowest part of the skirt 50 in the longitudinal
direction of the piston body 14. According to the invention, the
location of the lower edge 54 is such that is provides a relatively
short piston skirt 50 as compared to conventional piston skirts.
Particularly, the lower edge 54 of the piston skirt 50 is disposed
at a location which is below the level of the pin bore axis A but
which is at or above the lowest tangent point 46 of the pin bores
44, and more preferably above the lowest tangent point 46.
[0024] In addition to the longitudinal relationship of the lower
edge 54 of the piston skirt 50 relative to the pin bores 44, the
piston body 14 has the following dimensional ratios: H/D=0.5-0.75,
A/D=0.3-0.6, and A/H=0.7-1.2, where H is the compression height of
the piston body 14 measured between the top surface 20 of the
piston body and the axis A of the pin bores 44, D equals the piston
diameter and A equals the axial length between the lowest ring
groove 26 and the lower edge 54 of the piston skirt 50, as shown
best in FIG. 2.
[0025] As shown best in FIGS. 1 and 2, the lower edge 54 of the
piston skirt 50 is relatively smooth and continuous and free of any
clearance notches for oil nozzles or the like.
[0026] The piston body 14 is preferably fabricated of at least two
separate parts which are separately formed and then subsequently
joined to one another across a joint or joints 56. In the
illustrated embodiment, the piston body 14 includes an upper part
58 and a lower part 60 which, when joined together, form the
enclosed cooling gallery 36. The joint 56 of the preferred
embodiment is preferably a friction weld joint. However, the
invention contemplates other approaches to joining separately
formed piston parts, such as bonding, brazing, bolting, joint
threads, etc. which would operate to unite the separately formed
parts as a single, unified structure once joined for service as a
piston body 14. In the present embodiment, the lower part 60
includes the pin bosses 42, piston skirt 50, bottom wall 34, and
lower portions of the outer and inner walls 24, 30, with the
friction weld joint 56 provided in the outer and inner walls 22,
30. The lower part 60 is preferably forged from steel. The upper
part 60 includes the top wall 16, the bowl 18, and upper portions
of the outer walls 22 and inner wall 30 which are joined across the
joint 56 to the lower portions of the outer wall 22 and inner wall
30 to unite the structure.
[0027] FIG. 4 illustrates the piston 10 described above installed
in the diesel engine 12 for reciprocation within at least one
associated cylinder 62 of the engine 12. The piston 14 is
illustrated in its bottom dead center position, which is the lowest
point that the piston 10 travels in the cylinder 62. It will be
seen that the piston skirt 50 is contained within the cylinder 62,
such that the lower edge 52 of the skirt 50 does not extend below
the lower edge 64 of the cylinder 62 in which it reciprocates.
[0028] Obviously, many modifications and variation of the present
invention are possible in light of the above teachings. It is,
therefore, to be understood that within the scope of the appended
claims, the invention may be practiced otherwise than as
specifically described. The invention is defined by the claims.
* * * * *