The invention is an improvement in a lightweight carbon-carbon composite piston, the improvement uses near-net shape knitted or warp-interlock preforms to improve the structural qualities of the piston. In its preferred embodiment, a one piece, tubular, closed-ended, knitted preform (a sock) of carbon fibers embedded within the matrix of the piston structure forms the crown, side wall, skirt and inner surface of the piston, and wrap-interlock preforms strengthen the piston crown and wrist pin bosses

Ransone, Philip O.

Taylor, Allan H.

English

NASA Technical Reports Server

United States Patent t191 [ii] Patent Number: 4,909,133 
Tavlor et al. r451 Date of Patent: Mar. 20, 1990 
LIGH"FXGHT PISTON ARCHITEcmTRE 
Inventors: Allan H. Taylor, Newport News; 
Philip 0. Ransone, Hayes, both of 
Va. 
The United States of America as 
represented by the Administrator of 
the National Aeronautics and Space 
Administration, Washington, D.C. 
Assignee: 
Appl. NO.: 250,469 
Filed: Sep. 28,1988 
Int. Cl.4 ................................................. F16J 1/04 
U.S. Cl. ........................................ 92/212; 92/213; 
92/222; 92/248; .123/193 P 29/888.046 
Field of Search ................. 92/212, 213, 222, 248, 
92/224, 214; 123/193 P; 29A56.5 R 
References Cited 
U.S. PATENT DOCUMENTS 
4,187,932 2/1980 Zarembka .......................... 188/73.2 
4,216,682 SA980 Ban et al. ....................... 29A56.5 R 
4,306,489 12/1981 Driver et al. ......................... 92/212 
4,329,915 5/1982 Schulz ................................... 92/212 
4,341,830 7/1982 Betts et al. ............................ 428/65 
4,354,804 10/1982 Cruzen ................................ 416/230 
4,363,602 12/1982 Martin ................................. 416/230 
4,440,069 4/1984 Holtzberg et al. .................... 92/224 
4,449,447 5/1984 Yanagi .................................. 92/248 
4,450,610 5/1984 Sch'aper ......................... 29A56.5 R 
A4 
4,466,399 8/1984 Him et al. ............................. 29/212 
4,518,640 5/1985 Wilkins ............................... 428/102 
4,651,631 3/1987 Avezou .......................... 29A56.5 R 
4,679,493 7/1987 Munro et al. ......................... 92/213 
4,683,809 8/1987 Taylor ................................... 92/208 
4,683,810 8/1987 Afimiwala ............................. 92/212 
4,736,676 4/1988 Taylor ................................... 92/212 
FOREIGN PATENT DOCUMENTS 
2912786 12/1986 Fed. Rep. of Germany . 
0238039 10/1987 Japan ............................. 29A56.5 R 
Primaly Exuminer-Edward K. Look 
Assistant Examiner-Thomas Denion 
Attorney, Agent, or Firm-George F. Helfrich; John R. 
Manning; Charles E. B. Glenn 
VI ABSTRACT 
The invention is an improvement in a lightweight car- 
bon-carbon composite piston, the improvement com- 
prehending the use of near-net shape knitted or warp- 
interlock pre-forms to improve the structural qualities 
of the piston. In its preferred embodiment, a one piece, 
tubular, closed-ended, knitted pre-form (a sock) of car- 
bon fibers (11) embedded within the matrix of the piston 
structure forms the crown (12), side wall (U), skirt (16) 
and inner surface (18) of the piston, and wrap-interlock 
pre-forms strengthen the piston crown and wrist pin 
bosses. 
4 Claims, 1 Drawing Sheet 
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https://ntrs.nasa.gov/search.jsp?R=19900012726 2020-03-24T03:16:09+00:00Z
US. Patent Mar. 20,1990 
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4,909,133 
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4,909,133 
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net shape knitted or warp-interlock pre-forms so as to 
reduce lay-up, material and molding expenses. 
An additional object is to reduce manufacturing time 
and expense for a carbon-carbon composite piston by 
The invention described herein was made by employ- 5 decreasing component thickness and thereby shortening 
the densification Processes. 
LIGHTWEIGHT PISTON ARCHITECTURE 
ORIGIN OF THE INVENTION 
ees of the United States Government and may be used 
by or for the Government for governmental purposes 
without payment of any royalties thereon or therefor. 
The invention relates to lightweight piston design, 
and more specifically to an improved structure for a 
carbon-carbon composite piston. 
BACKGROUND OF THE INVENTION 
BRIEF SUMMARY OF THE INVENTION 
According to the invention, the foregoing and addi- 
lo tional objects are attained by an improvement in prior 
lightweight piston art, with the improvement compris- 
ing the replacement of a woven fiber structure with the 
use of a knitted carbon fiber structure selectively rein- 
forced with directionally oriented fiber structural 
embodiment, the generalized form of 
OF THE INVENTION 
l5 shapes. 
Pistons for use in high performance internal combus- the 
tion engines must be light in weight, resistant to high 
temperatures and strong* Carbon-carbon 
the invention is realized as a closed-end tube or sock of 
knitted carbon fibers which is imbedded in the matrix of 
materials are tough, light, resistant to heat and have low the composite structure so as to form the crown, side 
coefficients of friction and thermal expansion. The de- 20 wall, skirt and inside surface of a piston. Additional 
by structures such as those described in U.S. Pat. No. 
4,683,809. 
qualities of carbon-carbon composite is fiber orienta- 
tion. When the composite structure is composed of 
randomly directed fibers (mat or N-D structure) the 
qualities thereof vary as fiber length and homogeneity 
vary. Failure to adequately control these additional 3 0  and crown- 
parameters can induce errors which will negatively 
influence structural strength and consistency of manu- 
facturing results. 
When a composite structure is composed of ran- 
domly directed fibers, there is no way to increase 35 
strength in a specific area to accomodate localized 
stresses except to thicken the structure. This exacts a 
serious penalty in increased weight. Alternatively, the 
selective orientation of fibers prior to their embedding 
in the matrix serves to reinforce orientation of fibers 40 
prior to their embedding in the matrix serves to rein- 
force high-stress areas without greatly increasing over- 
all weight. 
Carbon-carbon composite structures are relatively 
Of piston design and the qualities Of carbon-car- 
as evidenced pre-formed crown and wrist pin boss reinforcements of warp interlocked cabon fibers are added to strengthen are therefore 
these stress areas. 
One parameter affecting several of the structural 25 BRIEF DESCRIPTION OF THE DRAWINGS 
FIG. l is a side view of a carbon-carbon composite 
piston according to the present invention showing a 
longitudinal Cross section through the wrist Pin boss 
FIG. 2 is a side view of a carbon-carbon composite 
piston according to the present invention showing a 
longitudinal cross section through the piston skirt, side 
wall and crown. 
FIG. 3 is a bottom view of a carbon-carbon compos- 
ite piston according to the present invention taken along 
line A-A of FIG. 1 showing a lateral cross section 
through the wrist pin boss and piston skirt. 
DETAILED DESCRIPTION OF THE 
INVENTION 
The invention comprises an improvement in the 
structure of lightweight carbon-carbon composite pis- 
tons for use in internal combustion engines. U.S. pat. 
expensive to form because of the high raw material 45 No. 4,683,809 by Taylor discloses details of the method 
costs of certain components such as pobacdonitde of molding, curing and densification, including details 
Plus the lengthy and energy intensive re- of materials and processes to be used in conjunction 
and re-pyrolization steps required to Ob- with this improvement. The essence of the present in- 
tain a structure of sufficient strength and density to vention is the use of knitted or warp interlock pre-forms withstand the operating environment inside an internal 50 which are embedded in the composite matrix so as to 
combustion engine. The time required to complete this comprise structural components of the completed pis- densification process increases exponentially as the sec- ton. The particular quality which the knitting and warp- tional thickness of the composite structure increases. 
a knitted fiber architecture, which enables the interlock fabrication methods have in common is that 
fiber directions to be controllable, results in increased 55 when thay are used to components for 
and better controlled interlaminar strength properties composite structures, the orientation of the fibers in 
than cloth or mat layups. Consequently, the incre& them are more controllable than the orientation of the 
strength savings from econom- fibers in a mat-type layup. By controllable orientation is 
ical use of materials, decreased difficulty of machining, meant the PreT1-g of how the fiber bundles will 
shorter fabrication times, and reduced energy consump- 60 in the completed composite material, thereby giving 
tion. the pre-forms tailorable mechanical qualities dependent 
Therefore, an object of the present invention is to upon their geometry. 
increase the strength per unit weight of a carbon-carbon When the Pre-forms have been fabricated into the 
composite piston by wing knitted or warp-interlock shape of the piston structure by methods such a knitting 
pre-forms of structural shapes to control internal fiber 65 or warp interlock, they are then impregnated with a 
orientation. carbonaceous resin system such as furfuryl alcohol, and 
An additional object is to reduce manufacturing costs laid in a compression mold. Subsequent curing and 
for a carbon-carbon composite piston by the use of near densification is carried out by processes standard in the 
n 
4,909,133 
3 
art of carbon-carbon composite materials such as pres- 
sure infrltration or carbon vapor deposition (CVD). 
Referring now to FIGS. 1,2 and 3, the present inven- 
tion is shown in the preferred embodiment, which com- 
prises a one piece, tabular, closed-ended, knitted pre- 
form (a sock) of carbon fibers (11) used to form the 
crown (12), side wall (14), skirt (16) and inner surface 
(18) of a lightweight carbon-carbon piston. The sock is 
impregnated with a suitable carbonaceous resin system 
(e.g., furfuryl alcohol), and then the closed end is in- 
serted into an outer die which forms the outside surface 
of the piston. Next the crown reinforcement (24) and 
wrist pin boss reinforcemens (22) are resin impregnated 
and inserted into the interior of the sock as it lies in the 
outer die. This material can be unidirectional fibers as 
described in U.S. Pat. No. 4,683,809 or may be knitted 
or warp-interlock preforms as disclosed herein. Finally, 
the open end of the sock is folded inward, and arranged 
within the outer die so as to cover all reinforcing pieces. 
In this configuration it then forms the inner surface (18) 
of the piston, the shape of which is defined by the inner 
die which applies pressure for consolidation of the com- 
posite materials during curing. After initial curing, re- 
moval from the dies and pyrolyzation, the composite 
structure is relatively porous and must be densified 
before use. This can be effectively accomplished by two 
cycles of pressure infiltration and re-pyrolyzation with 
carbonaceous resin, followed by a final step of CVD. 
Because of the shape of the sock and its orientation 
within the inner and outer dies, a near-net shape form is 
obtained and very little machining of the finished piston 
is required. Generally this is limited to boring wrist pin 
holes (28) in the wrist pin bosses (20), cutting retaining 
clip grooves (26) and final surface grinding of the outer 
circumferential surface (15). Additionally, the elimina- 
tion of piston rings allows the skirt (13) of the piston to 
be short and thin. The knitted architecture, which in- 
herently uses a continuous filament to form a compliant 
preform, conforms more readily to a complex piston 
shape than a woven architecture. Moreover, the knitted 
structure has much greater strength than woven struc- 
tures, and is further strengthened by directionally ori- 
ented fiber structural shapes within the carbon-carbon 
composite. The combination of all of these design ad- 
vantages allows the piston structure to be very thin in 
most spots, concomitantly reducing overall cost, weight 
and densification times. 
As described in U.S. Pat. No. 4,683,809, the proper- 
ties of carbon-carbon can eliminate the necessity for 
sealing piston rings in some applications. Conversely, 
although no piston ring grooves are displayed in the 
figures, it is understood that ringed pistons could be 
4 
manufactured without departing from the practice of 
this invention. 
Optimum qualities of molded carbon-carbon com- 
posities are obtained when subsequent machining steps 
5 avoid cutting the embedded fibers. Therefore, the dies 
for forming the piston should be slightly undersized and 
the densification steps should deposit sufficient resin to 
allow for finishing the outer surface of the piston with- 
out cutting the sock fibers. For this reason, also, better 
10 results are obtained if an oversized wrist pin hole is 
formed in the piston after the initial cure so that subse- 
quent densification steps can re-imbed the cut fiber ends 
in this region and the final finishing of the wrist pin 
bearing surface can be carried out without exposing cut 
Although specific embodiments of the invention have 
been described herein, they are to be considered exem- 
plary of the novel features thereof and are not exhaus- 
tive. There are obviously many variations and modifica- 
2o tions of these specific examples that will be readily 
apparent to those skilled in the art in light of the above 
teachings without departing from the spirit or scope of 
the appended claims. It is, therefore, to be understood 
that the invention may be practiced otherwise than is 
What is claimed as new and desired to be secured by 
1. In combination with a lightweight piston having a 
3o crown, side wall, skirt, inner surface and a reinforced 
wrist pin boss area, said lightweight piston being com- 
posed of carbon-carbon composite, the improvement 
which comprises a one-piece, closed-end, single knitted 
fiber structural shape forming an exterior surface of the 
35 carbon-carbon composite, said knitted structural shape 
forming the crown, side wall, skirt and inner surfaces of 
the piston. 
2. A lightweight piston as in claim 1 wherein the 
improvement comprises directionally oriented fiber 
40 structural shapes within the carbon-carbon composite 
to improve the mechanical properties of the piston. 
3. A lightweight piston as in claim 1 wherein the 
improvement comprises a selective reinforcement of the 
wrist pin boss area with a warp-interlock fiber shape 
45 formed to near-net shape dimensions prior to its imbed- 
ding within the carbon-carbon composite. 
4. A lightweight piston as in claim 1 wherein the 
improvement comprises a selective reinforcement of the 
piston crown with a warp-interlock fiber shape formed 
50 to near-net shape dimensions prior to the embedding 
thereof within the carbon-carbon composite. 
l5 fiber ends. 
25 specifically described. 
Letters Patent of the United States is: 
* * * * *  
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60 
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Lightweight piston architecture

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