US 1469087 A
Description (OCR text may contain errors)
E. R. HEWETT INTERNAL COMBUSTION ENGINE Filed May 2, 1918 Z MW 5 m a a m? m S 9W w Patented Sept. 25, 1923.
EDWARD HEWITT, OF IDVALE, NEW JERSEY. v
. m'raanaL-conausrron Enema Application filed may 2,
To all whom it may concern -Be it known'that I, EDWARD R. HEWITT citizen of the United States, resident oi idvale, county of Passaic, and State of New Jersey, have invented certain new and useful Improvements in- Internal-Combustion Engines, of which the following isa specification, reference being had to the accompanying drawings, illustrative of one particular embodiment of my invention.
This invention relates to internal combustion engines, and more particularly a most essential factor involved in their successful operation, namely, the relation of cylinder and the fit of the piston under the heat conditions to which the interior of the cylinder is subjected.
Owing to the character of an internal combustion engine, the head of the piston is in contact withzfthe products of combustion and the re it of combustion of the explosive mixture "s manifest in heat and expansion. The temperature in the combustion space is dependent upon the rate of expansion and with a very quick expansion of the products of combustion advantages are realized owing. to various conditions. A uniform temperature under work ing conditions, if maintained in the combustion space, is advantageous, and if this ismaintained with certainty below the oint of premature ignition, maximum a vanta es of operation-result.
y invention aims to dissipate the heat from the head of the piston, by conductivity ina manner which will insure a coordination of the best conditions of operation with maximum power and efliciency and reliability.'
While the practice of my invention may lead to many variations in construction and design, I have illustrated and will hereinafter describe a specific embodiment which has proven most eflicacious.
In the particular embodiment of my invention shown in the accompanying draw in ig. I is a longitudinal section of piston,
with surrounding cylinder parts in fragmentary view.
Fig. II is a side elevation of the piston. Fig. III is a bottom view of the piston. The cylinder has the inner wall A uniform in diameter, and the piston B adapted to move longitudinally within the wall. The
1918. Serial Ho.,282,014. piston has the grooves C--C'-C" adapted to receive the piston rings near the head end of the cylin er,while the groove D is adapted to receive a Scraper rm ,the
rings being shown incross-section, ig. I.
On the inside of the piston are bosses 1B for the connecting rod low these are slits F- piston connecting at f with a slit G extending to the lower edge or toe and of the piston.
These slits permit a slight yield of the p ston walls from a point close to the connectmg rod pin bosses to the toe edge, for the purpose as. will hereinafter appear. On
' the inside of the piston close to the toe end is a groove H adapted to receive a split sprlng ring J, having a normal size slightly greater than the groove H, so that upon insertion it will have a tendency to expand the toe end of the piston to effect the desired pressure.
To illustrate in a specific case, the normal diameter of an aluminum alloy piston is less than the normal interior diameter 'of the cylinder wall, to an extent of 12 thousandths of an inch adjacent to the roove C, while between groove 0' and G- it is about 10 thousandths, and below C" the clearance is reduced to 8 thousandths, and half way from there to the end, 6 thousandths, while close to the end or toe is only 3 thousandths.
pin support, and bein the wall of the These dimensions have proven satisfactory eral way to lth of an inch in thickness at,
It will thus be seen that as shown, the iston B has a head sufiicient for the requlred strength and embodying a sutlicient mass of metal to conduct away the heat which it absorbs by contact of its end with the hot products of combustion. The walls of the piston near the head are of sufiicient thickness to conduct in turn the required amount of heat away from the head and along the walls of the piston, and particularly to the surfige of the piston between the grooves C" an With the heat absorbed by the metal of the piston, which, for high speed and light alloy, the expansion of the head is'greater than the expansion of the inside diameter of the cylinder wall. The latter is cooled by the water-'acket, and its increase in temperature is t erefore not as rent as the increase in temperature of tie metal at the head of the piston, in addition to the difi'erence in coefiicient of expansion ofthe different metals of which they are constructed. Sufiicient difference in diameter is provided as above mentioned, so-that expansion due to the greater heating of the piston head will, under operating conditions, avoid the chance of the head of the piston equaling the diameter of the interior of the piston walls,-therefore avoiding what is generally called seizing. In so providing for the avoidance of seizing, there is aplay or discrepancy in size which would cause a looseness of fit except for the piston rings, and in the construction of pistons heretofore such looseness has involved the entire piston with the result that in operation the reaction or thrust on the piston forces it against one side of the cylinder wall so that practically one-half, or the semi-circumference of the piston wall-is in contact with the wall of the cylinder and the heat conducted by the metal of the cylinder wall only thru this area of contact of the piston wall with the cylinder.
The aim of this invention is to so proportion the head of the piston and a part close to the head, that the chance of seizing is avoided, but to proportion the remainder of the piston wall, and in particular a sujiicient extent of the piston wall from its thinnest end toward the head, so that when heated and consequently expanded under predetermined conditions of operation, all of that area of the piston Wall, instead of half or less, will be in contact with the cylinder wall. This condition results in having double the area of piston and cylinder wall contact, and therefore double the area of heat conduction from the metal of the piston to the wall of the cylinder, with the consequent insurance of carrying away the heat of the piston in so much greater volume as to insure maintenance of low temperature at the head of the piston and consequently greatly improved conditions of operation, for the reasons above stated.
In order to obtain this result the clearance or differential in size of piston and cylinder between the groove C" and the toe end is such that the predetermined increase in temperature of the metal will'expand the piston to the extent of a perfect fit, allowing only for the infinitesimal oil film. The slight variations of condition in operation which must still be compensated, when this piston wall contact position is desired, are accommodated b a slotting of the piston, as shown at '-F and G, which permits a piston is conducted to the recaps? slight Jyielding. lln additiomit desired, the
ressure to maintain the condition whichw 1S desired for this advantageous result.
With the taperingthickness of the walls of the piston from the head to the toe, which is desired to meet the conditions of strength, and also with the varying distance from the head subjected to the maximum heat, the expansion of the Walls of the piston at different oints will vary proportionally from the dlstance from the head.
It will thus be seen that fora predetermined distance from the head the piston has a diameter which will, under all conditions, prevent seizing,-and beyond that point to the toe the diameter is so proportioned that with the operating conditions when they reach their fixed temperature of operation, there will be the substantially complete contact of the piston walls with the cylinder Walls, and the resultant doubling, or more than doubling of contact for dissipation of the heat from the piston thru the cylinder.
This extended contact throughout an extent ofpiston from the toe upwards, involves the metal throughout thatportion which structurally will yield before seizing, and in addition it aifords a bearing which .maintains a true axial reciprocation of the reality scraper rings and not packing rings,
and this in addition to the fit maintained over a considerable area inoperation results in a more perfect maintenance of packing so far as the piston as a whole is concerned.
In actual operation the advantages set forth have been proven beyond question, and have resulted in most successful operation at extremely high speeds with maintenance of uniform and low temperature in the combustion space. These conditions of piston construction consequently aid in numerous ways in the perfection of control and operation of the engine, which could not be obtained, or in no case reliably obtained with entire dependence or assurance of unity of operation with other constructions. With the entire assurance of low, uniform temperature in the combustion space, higher pressures of mixture and resulting higher mean-effective pressures become a matter of certain and ractical realization. Other advantages Wlll be evident, which those familiar with the art will see are attributable to the use of construction and design in conformity with my invention.
What I claim and desire to secure by Letters Patent is:
1. In an internal combustion engine, a cylinder, a piston, a series of piston rings fitting under 'all conditions a space between the piston surface and the cylinder surface, a head portion of the piston having an outside diameter which under all operating conditions of expansion will remain less than the interior diameter of the cylinder,
and the remainder of the wall: of the piston having a diameter which under heat conditions of operation will expand to a spring contact-fit with the walls of the cylinder, and a plurality of slits from the toe' upward through the wall of the piston and extending laterally near their upper end, to provide for said spring contact fit.
2. In an internal combustion engine, a cylinder wall, a piston, a series of piston rings at all times contacting with the cylinder surface and bridging the gap between it and the piston wall, a major portion of the pis ton'wall extending from the toe end having a diameter which under normal conditions of operation wil'l have a yielding bearingfit on the cylinder Wall, and a minor portion of the piston extending from the head end having a diameter which under all conditions of operation will maintain a cle'ar-' to the boss, to provide for said yielding bearing fit.
3. A piston having a relatively thick section of metal at its head, and a substantial equivalent of metal in its wall adjacent to the head tapering to a relatively thinsection near the toe end, and a parting in the wall extending from the toe end to close proximity to the connecting rod pin boss and there diverging to both sides of the boss, whereby a yielding wall throughout the circumference is provided for the purpose described.
4. A piston having a relatively thick section of metal at its head, and a substantial equivalent of metal in its wall adjacent to the head tapering to a relatively thin section near the toe end, a boss for the connecting rod pin, a slot severing the wall of the cylinder from the toe end to adjacent the boss and branching into two slots extending obliquely in opposite directions from the main slot, an internal groove near the toe end and a spring ring in said groove, and a slot in the wall of the piston extend ing from the toe toward the head and in general diverging laterally into two slots in the neighborhood of the middle of the piston.
5. A piston for an internal combustion surface, the major one of which extending from the toe of the piston having a normaloutside diameter which under operating heat conditions will assume a substantially said major section to permit said yielding,
and a'complementary oppositely oblique slot and the minor portion of the surface extending from the head end having an outside diametervwhich under all heat conditions of operation will maintain a lesser diameter than the major portion,
6. In an internal combustion engine, a cylinder wall, a piston of metal having a greater ooefiicient of'expansion' of the cylinder'wall, a major portion of the surface of said piston extending from the toe and having a diameter which under operating heat conditions will assume a spring bear ing-fit with the walls of the cylinder, a pluralit of slot-s extending from the. toe towar the head branching into lateral diverg-' ing portions about the middle ofthe piston,
a minor ortion of the surface extendand ingfrom theead end of the piston having a 1 ameter which under all heat conditions of operation will maintain a ,clearance with the walls of the cylinder. i V
7. A piston comprising walls having a cross-section suflicient to conduct the heat acquired at the head to the side walls, said wa ls having an outside diameter whereby conducting contact is assured on both sides, including means whereby the sides act as a spring and maintain at all times contact with the adjacent walls of the cylinder, said means including a plurality of oblique slots about the middle of the piston and extensions to said slots cut through the toe.
8. A piston, walls of said piston proportioned to conduct the heat acquired by the head to the side walls, said side walls havingoutside diameters whereby under conditions of operation contact of the side walls is maintained with the Walls of the c linder in the direction of oscillation o the connecting rod at both sides at once, including means whereby the lower portion'of the piston acts as a spring, said means involv ing slots generally in a plane normal to the oscillation of the connecting rod extending from the toe of the piston toward the head and'branohing obliquely in proximity to the.
heavier portions of the piston wall.
9. In 'an internal combustion engine, a cylinder, a piston, cross-head bosses in said piston, means in the Walls of said piston whereby integral portions of said wall below the cross-head bosses constitute a springsection, slots dividing the lower portion ofthepiston wall to form said integral portions of greater circumference at the toe than the circumference of the section at the inte ral connection with the head portion of t e piston, a portion of each'slot extending in a line obli ue to the elements of the piston wall, where y both sides of the piston walls are'maintained in contact ,with the cylinder walls in the direction of oscillation of the connecting rod.
10. In an internal combustion engine, a piston with a relatively heavier sectional mass of metal at its head tapering to and with relation to the relatively lighter sectional mass at the toe, slots severing thetoe end of the piston into a plurality of secions with integral portions connected with 15 the head end of lesser extent than the circumference of each section at its toe ex- -tremity, a plurality of piston packing rings bridgin a clearance of the head of the piston wit the cylinder walls and a scraper ring at thetoeend of the plural sections permitting contact of the ends of the section with the walls.
11. A piston for an internal combustion engine, havin a plurality of slots in the skirt of the piston extendingfrcm the edge toward the head, a part of each slot extend-' ing in a direction oblique to the elements recaps? of the piston cylinder, each of said oblique slot parts having a complementary oppositely oblique slot.
12. A piston for an internal combustion engine, comprising integral head and skirt portions, a pair of oblique slots in the skirt portion symmetrical with respect to the elements of the piston and an extremity of the slot severing the edge of the skirt.
13. A piston for an internal combustion engine, comprising head and skirt portions, and having pairs of oblique slots in said a skirt portion, symmetrical with respect to EDWARD R. HEWITT.
Witnesses i I HELEN F. Awm, M. MUCHMOBE.