CA1288014C - Piston of an internal combustion engine - Google Patents

Abstract

ABSTRACT
A piston of an internal combustion engine having a skirt with a hole to receive a piston pin the axis of which is perpendicular to the axis of the skirt the side surface of which is provided with two recesses arranged at the opposite sides of the piston pin hole axis and having cylindrical surfaces axes of which are parallel with the axis of the skirt, the pins receiving inserts having a cylindrical outer surface engageable with the surface of the cylinder of the internal combustion engine, this outer cylindrical surface having a radius of cur-vature equal to the radius of the cylinder of the engine, and having an inner cylindrical surface of a radius of curvature equal to the radius of curvature of the recess, and two springs each disposed between the insert and skirt to urge the corresponding insert to the cylinder.
the insert has in cross section the shape of a curvilinear wedge with the maximum angle not exceeding the angle of friction thereof.

Description

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 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 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 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 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.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY OR
PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
A piston of an internal combustion engine comprising:
- a skirt with two cylindrical portions of the same radius at the outer side surface having a common axis coincinding with the axis of said skirt;
- a hole to receive a piston pin provided in said skirt and having an axis perpendicular to the axis of said skirt;
- first and second recesses each provided at said corresponding cylindrical portion of said skirt at the opposite sides of the axis of` said piston pin hole hav-ing cylindrical surfaces axes of which are parallel with the axis of said skirt;
- first and second inserts received by said first and second recesses and having each an outer cylindrical surface for engagement with an inner surface of the cy-linder of the internal combustion engine of a radius of curvature equal to the radius of the cylinder of the internal combustion engine;
- said first and second inserts having each an inner cylindrical surface of a radius of curvature equal to the radius of curvature of said cylindrical surface of said corresponding recess and having in cross-section the shape of curvilinear wedge with the maximum angle thereof not exceeding its angle of friction;
- said cylindrical surface of each said recess the axis of which is offset from the axis of said skirt along the axis of said piston pin hole in the direction of taper of the wedge by a magnitude equal to the product of the radius of curvature of said inner surface of the cor-responding insert into the maximum angle of the wedge;
- first and second springs each disposed between said first and second inserts and said skirt to urge said corresponding insert to the cylinder of the internal com-bustion engine, the angle between the direction of the force produced by the spring and a tangent line to said inner surface of said corresponding insert at the point of application of this force toward the wedge taper being less than 90°.