Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
12~F~014
PIS'rON OF AN INT~RNAL COMBU~TION
ENGINE
This invention relates to internal combustion engine
construction, and more particularly to improvement in a piston
of an internal combustion en~ine.
'~he herein proposed piston of an internal combustion
engine can be used in all types of internal combustion
engines, and in compressors.
It is known that wobblin~ of pistons in internal
combustion engines reduces the pressure sealing capacity of
piston rings which tend to be drawn together as the piston
wobbles and form clearances wherethrough gases rush from
the combustion chamber to the craKncase of the engine.
For obviating piston wobbling it is necessary to mi-
nimize the clearance between the piston skirt and cylinder
and thereby ensure that the piston moves inside thc cy-
linder so that the axes of the piston skirt and cylinaer would
align, that is the piston skirt would move without skewing.
~ here is known a piston of an internal combustion
engine, which ~rovides ooaxial movement of the piston skirt
in the cylinder through the use of a fluoroplastic inQert
secured between the skirt and cylinder in a recess made in
the side surface of the piston skirt (cf., US, A, 4,158,328).
The f`luoroplastic insert has in cross section the form of
a wedge tapering in a direction away from the piston head.
~he length of the re¢ess is greater than that of thc insert,
and the insert is therefore capable of moving axially of
the skirt from one extreme position to another. C~earances
are present between the end faces of the insert and recess
~b
in such extreme positions assumed by the inserts.
However, the clearance between the cylinder and
piston skirt is eliminated when the piston moves in a
direction from the bottom dead center to the top dead
center thus jaml~ng the insert in the clearance, whereas
the re~erse travel of thc piston from the top dead cen-
ter to the bottom dead center causes the insert to get
loose, whereby a clearance is formed between the piston
skirt, insert and cylinder to result in piston wobble,
faster wear and ~horter service life of the piston. In
addition, in the course of operation the insert te~ds to
wear in terms of' its thickness, and the clearance between
the insert and the lower end ~'ace of the recess gradually
diminishes. ln the absence of thi~ clearance the insert
fails to function, whereby it becomes impossible to eli-
minate the clearance between the piston skirt and cylinder.
'~here is also known a piston of an internal combus-
tion engine in which the insert acts to eliminate the
clearance between the pisto~ skirt and cylinder irrespec-
tive o~ the direction of movement of the piston (DE,
A, 393,755)-
'l'he piston comprises a skirt havin~ a piston pin holethe axis of which is perpendicular to the axis of the
skirt; the side surface of the skirt havi~g two recesses
at the opposite sides of the pin hole axis with cylindrical
surfaces the axes of which are parallel with the axis of
the piston skirt, each such recess accommodating an insert
having a cylindrical outer surface engageable with the
~ 28fi~
surface of the engine cylinder having a curvature radius
substantially equal to the r~dius of the cylinder and
with the inner cylin~rical surface of a curvature radius
egual to the curvature radius of the recess, and two
springs each disposed between the i~sert and piston
skirt for the spring force to urge the insert to the cy-
linder.
In cross section t~le insert has a continuous thick-
ness, since it is confined by the ~rcs of two concentric
circles. This insert is secured in a recess with a clea-
rance between its inner surface and the surface of the re-
cess. q'ne irlsert and I'~CeSS are of e~ual length, which
prevents the movement of the insert in the recess relative
to the piston skirt axially ther~of,. In ~ddition, the in-
sert is lin~ed with the piston skirt by a dowel to pre-
vent it fro~ turning about the axis of the piston skirt.
~ ach spring is accommodated in the respective recess
between the insert ~nd piston s~irt so that its ~xis runs
radially, whereby the radially directed spring force acts
to urge the insert to the wall of the cylinder.
In view o~ the aforedescribed, the insert is urged
by the spring exclusively in the radial direction thus
eliminating the clearance between the piston skirt and
cylinder and ensuring axial alignment during the travel
of the piston inside the cylinder with the aim of reduc-
ing piston wobble.
However, such an arrangement of the spring necessitates
a spring force exceedi~g the side pressure exerted on
12~3fiO14
the piston. Despite the fact that the side forces exer-
table on the piston amount to between one fourth and one
fifth of the axial (working) force imparted to the piston,
they are still guite high. It is therefore necessary to
use a spring of high co~pression force. As the piston
operates and as the insert wears out, the force imparted-
by the spring to the insert tends to reduce to result
in a shorter service life oY the piston. 'l'nis is accompa-
nied by an increase in the clearance between the insert
and the surface of the recess to result in disturbed co-
axiality of the movement of the piston inside the cy-
linder and conseguently in a tendency of the piston to
wobble.
It is therefore an object of the present invention
to provide a piston-of an internal combustion engine
having a longer service life.
The object is attained by that in a piston of an
inter~al combustion engine comprisin~ a skirt with a
hole to receive a piston pin the axis of' which is per-
pendicular to the axis of the skirt the side surface of`
which is provided with two recesses arranged at the oppo-
site sides of the piston pin hole axis and having cylindric-
al surfaces with axos thereof parallel with the axis of the
skirt, each pin receiving an insert having an outer cy-
lindrical surface engageable with the surface of the cy-
linder of the internal combustion engine, this outer cy-
lindrical surface having a radius of curvature equal to
the radius of the cylinder of the internal combustion
`` ~l2~ 14
engine, and havin~ an inner cylindrical surface of a ra-
dius o~ curvature equal to the radius of curvature of the
recess, and two springs each disposed between the corres-
ponding insert and skirt for the force of the spring to
urge tne insert to the cylinder, according to the inven-
tion, cross-sectionally the insert has the form of a
curvilinear wedge having a maximum angle not exceeding
the angle o~ Iriction thereof, the inner surf`ace of the
insert en~a~ing with the the cylindrical surface of the
recess the axis of which is ofiset from the axis of the
skirt axially of the piston pin hole axis in the direction
of taper of the wed~e by a magnitude equal to the product
of the radius Or curvature o~ the inner surface of the
insert by the maximum angle oI the wedge, the spring being
so disposed that the angle between the direction of force
produced by the sprin~ and a tangent line to the inner
surface of the corresponding insert at the point of app-
lication of this ~`orce toward the Wedge taper is less
than 90.
~ le arran~ement of the insert in the f`orm of a cur-
vilinear wedge makes it possible to completely eliminate
the clearanc~ between the piston skirt and cylinder irres-
pective of the extent o~ wear of the insert and cylindcr.
since in the course of wear the insert is caused to turn
about the axis of the skirt on the surface of` the recess
under the action of the spring thus eliminating the clea-
rance, which prevents the tendency of the piston to wobble.
By ~irtue of the fact that the maximum wedge angle of the
12~80~4
-- 6
insert is less than the angle of friction thereof, turn-
in~ oi' the insert requires a relatively small force. It
i.s therel'ore possible to use a spring of` low compression
1orce. Another advanta~e is less rigid requirements to
the strength of the material of' the insert accompanied
~y ~ore pron~unc~d antifriction properties, whereas the
piston can be f~bricated from a stron~er heat-resista~t
material.
~ e afore~escribed enables to extend i'ive-fold the
service life o~` the piston of an in-ernal combustion
engine.
The invention will now be described in ~reater detail
with rel~erence to a preI'erred embodiment thereof taken
in conjunctio~ with the accompanying drawings, in which:
~ ig. l is a partially sectional view of a piston of an
internal co~bustion en~ine accordiug to the invention; and
~ ig. ~ is a section taken along the line II-II in
Fig. l.
A piston of an internal co~bu~tion engine comprises
a skirt l (Fi~. l) with a head 2 an outside surface of
which has two portions of cylindrical shape wi th a com-
mon axis "O" coinciding with the axis of the skirt l. Pro-
vided in the midportion of t.he skirt l is a hole 3 to re-
ceive a piston pin (not shown) with an axis "l" thereof
bein~ perpendicùlar to the axis 1tO~1 Of the skirt l. Arran-
~ed at the outer sur~'ace of the skirt l at the opposi te
sides of the axis "1" are two recesses which receive
inserts 5, the length of each such insert 5 being equal
`` ~2~014
-- 7
to the length of the recess 4.
~ ;he insert5 (Fig. 2) has aconvex cylindrical outer
s,urface engageable with the inner surface o~' a cylinder 6
( shown schematically in Figs. 1 and ~) of the internal
combustion engine. R - radius of curvature oI the outer
surface of the insert 5 is the same as the radius of the
cylin~er 6 of tne engine. ~he inner surface Ol' the insert 5
en~ageable with tne suri`ace Or the recess 4 is concave,
whereas r - radius of curvature o~` the inner sur~`ace of
the insert 5 is equal to the radius ol` curvature of the
sur~ace of the recess 4.
A compression spring 7 (Fig. ~) is provided between
each insert 5 and skirt l, this spring 7 being thrust
by one end a~ainst a shoulder ~ provided on the skirt l
and by the other end a~ainst a shoulaer 9 provided on the
insert 5.
T~e insert 5 has in cross-section the form of a cur-
vilinear wedge, the maximum angle o~ of this wedge not
exceeding the an~le o~ I`riction o~' the insert 5. This
an~le ~ is generally an angle betwee~ ~angent lines "m"
and "n" to t~le outer ~nd inner surYaces Or the insert 5, res-
pecti~ely, at a point ~ of application o~ the lateral com-
ponent N of the f'orce P (Fig. l) exerted on the piston
along the axis "O".
The insert 5 can be fabricated f'rom a material f'eatur-
ing high anti~'riction properties, such as metal ceramics,
~'luoroplastic, or other known material generally employed
for making piston inserts.
12~38014
-- 8
As is known, for most of` the materials the maximum
angle of f'riction is approximately 6. The angle of fric-
tion is determined from tables ~ound in re~erence litera-
t~re, and depends on the material ol' ~riction pairs and
other factors, such as lubricants, surface cleanness, type
and character o~' loads -exerted thereon, etc.
'l'ne maximum wedge angle c~ (Fig. 2) of the insert 5
is not to exceed the angle of friction of the insert 5,
and should preferably ensure its self-braking in the
recess 4 unaer the action of the component N of the force P.
If the wed~e angle ~ is greater than the an~le of fric-
tion, then under the action of the com~onent N the in-
sert 5 will tend to be arbitrarily pushed i`rom the recess 4
to necessitate spring 7 of' a higher rigidity.
When selecting the wedge angle of the insert 5, it
is desirable to take into consideration the type (uni-
i'ormly distributed or concentrated) and character (con-
tin~ous, oscillatin~, variable-sign) of load.
Favourably, this angle is less than the angle of
friction. ~or example, with respect to the "piston-cylin-
der" friction pair the f'riction coefficient should pre-
ferably range from 0.07 to 0.85, which corresponds to an
angle of friction of 4 to 5
If for structural consi~erations it is necessary
to have a difl'erent angle of friction, conditions of
lubrication, surface roughness and the spring force di-
rection should be such as that self-braking of the in-
sert 5 in the recess 4 would be ensured during operation
~ 12l~3014
of the piston unuer load.
The inner surf~ces of the inserts 5 are in con~ct
with the cylindrical surfaces of the recesses 4 having
a common axis "0~" parallel with the axis "O" of the
skirt 1. The axis "2" of the recesses 4 is offset from
the axis "O" of the sKirt 1 alon~ the axis "l" of the
piston pin hole 3 in the direction of the taper of the
wedge by a magnitude equal to the product of r - radius
of the recess by o~ - the maximum angle of the wedge, that
is the distance 2 = r d, where ~ is expressed in
radians, since for small angles within the angle of
friction tg o~ ~C. Therefore, the recess 4 has in
cross section a shape conforming to the shape of the in-
sert ~. 'l'he spring 7 is so disposed that tne angle ~ bet-
ween the direction of force of the spring 7 coinciding
with its axis ~ e and tangent line "k" to the inner
surface of the insert 5 at the point of application of
this force, viz., at the point "C" o~ contact of the
spring 7 with the inner surface of the insert 5, is always
less tha~ 90, which provides for the movement of the
insert 5 toward its taper as it wears out in the re-
cess 4.
~ `he proposed piston o~ an internal combustione engine
operates in the following manner.
During reciprocating motion of the skirt 1 (Figs. 1
and 2) of the piston inside the cylinder 6 of the in-
ternal combustion engine bhe insert ~ received by the
recess 4 is caused under the ~ction of the spring 7 to
1288014
-- 10
eliminate the clearance between the skirt 1 of the piston
and cylinder 6 and engages by the entire outer surface
thereof with the inner sur~ace o~` the cylinder 6, and by
tne entire inner surface with the surface of` the recess 4
of the skirt 1.
lherewith, the insert 5 fails to move in the recess 4
longitudinally, that is along the axis "O" of the skirt 1,
~hereby only the outer surface thereof is subject to wear,
this surface tending to move relative to the inner sur-
~ace of the cylinder 6 in the course of movement of the
piston.
As the insert ~ wears out, the clearance between
the insert 5 and cylinder 6 fails to appear, since the
spring 7 actsto continuously lorce the insert 5 in the
recess 4 to~ard its taper, and ur~e the insert 5 to the
cylinder 6 thereby ensuring t~e movement oL the piston in
the cylinder 6 without wobbling. The force of the spring 7
is preferably to be grea~er than the force of friction
between the insert 5 and skirt 1 of the piston, this
latter friction force being negli~eable compared with the
~`orce of friction between ~he cylinder ~ ~nd outer sur-
f`ace of the in~ert 5. In view of the at`oredescribed, the
proposed construction of the piston o* an internal com-
bustion engine enables to virtually completely eliminate
a clearance between the skirt 1 and cylinder 6 through-
out the service life of the piston regardless of the
extent of wear of the insert 5 and cylinder 6 of the
internal co~bustion engine. This eventually results in
a longer ser~ice life of the piston.
