US1499073A - Piston - Google Patents

Description

.Hime 24 1924.

L. H. FOMEROY PISTON 111| l I 1 I I a Filed Sent. 4. 1919 Patented June 2d, 1324i-,

narra saai-fas satana casina.

LAURENCE HENRY POMEROY, F CLEVELAND', Omo, ASSIG'NOR T0' THE ALUMINUM COMPANY 0F AMERICA, 0F PITTSBURGH, PENNSYLVANIA, ACORPORATION OF PENNSYLVANIA.

PIs'roN.

Application led September 4, 1919. Serial No. 321,696.

To all 'whom t may concern.' vision of a piston that will wear evenly from 55 Be it lmown that l, LAURENCE HENRY end to end. oMERoY, a subject of the King of Great Another object of the invention is the at- Britain and Ireland, residing at Cleveland, tainment of the ends above mentioned in an 5 in the county of Cuyahoga and State of integrally cast piston.-

Ohio, have invented certain new and useful These and other more or less incidental e0 Improvements in Pistons, of which .the folobjects, are attained in the manner set forth lowing is a specification, reference being had in the follo-Wing description of the preferred therein to the accompanying drawings. form of construction. This invention relates more'particularly J Tn the drawings, v

to pistons adaptedj for use in internal com- Fig. 1 is a vlew partly in side elevation 65 bustion engines or under conditions in which and partly in section of a piston embodying the piston is subjected to considerable heat. the invention.

As is well known, the clearance with which' Fig. 2 is a section on the line 2-2, Fig. 1.

the pistons of internal combustion engines -My improvements are applicable to pisare fitted is determined in a large measure tons of various forms of construction but 70 by the difference' in thermal expansion of in the drawings, for purposes of explanation,

. the piston and the cylinder wall. This dif- I have shown the invention applied to the ference in thermal expansion is due to the slipper type of piston shown in United fact that the working temperature of the States Letters Patent No. 1,294,833, to H.

piston is somewhat higher than that of the R. Ricardo. 75 cylinder wall and, in some cases, to the use Referring in detail to the construction ilof dierent piston and cylinder materials lustrated, the piston has a head section 1 having diitl'erent cov-efficients of thermal concomprising a crown 1a and a side wall 1b ductivity'and expansion. Thus in the case which is formed with grooves to receive suitof pistons of aluminum or magnesium alloysable packing rings 2, 2. The guide sec-tion so working in iron cylinders the co-eflicient of of the piston comprises diametrically oppoeXpansion of the aluminum or the magnesite cylinder-engaging slippers 3 and 4:. a sium being higher than that o-f iron, it is pair of wrist pin bosses 5, 5 arranged benecessary to give the pistons a larger cleartween the slippers, and a pair of webs 6, 6

ance than is required for iron pistons workwhich join the slippers and bosses together 85 ing in iron cylinders. This larger clearand extend upward and mergel with the ance, with pistons as heretofore constructed, crown and side wall of the head section of results in piston slap or knock when the the piston, the entire piston being cast in engine is running cold at starting and, in one. Aside from the rings 2, 2, only the fact, whenever the thermal conditions of the slipper parts 3, 4.- are designed to contact 90 cylinder and piston are such that the large `with the cylinder wall, the piston differing clearance required to obviate seizure at high in this respect from the prior trunk or skirttemperatures exists between the piston and ed pistons which have a guide part in the cylinder wall. form of a continuous sleeve or skirt that One object 0f the present invention is the contacts with the cylinder wall on all sides. 95 provision of a piston of aluminum alloy or Tn the construction shown the slippers 3 other light weight metal, that will operate' and 4 arelnade unequal in size, the larger without piston slap. i slipper 3 being designed to take the angular Another object of the invention. is the thrust or reaction of the connecting rod durprovision of a piston so constructed that it ing theexplosion stroke of an internal com- 10o can be given a small workin clearance in.- -bustion engine, while the smaller slipper 4 dependent of diiferences of t ermaleXpanis designed to take the angular thrust dursion of the piston and the cylinder wall. ing the compression stroke of the engine.

A further object ofthe-invention is the The abo-ve described features of the conprovision'of a piston capable of adjusting struction are characteristic of the Ricardo 105 itself to the cylinder as wear occurs of the slipper piston.` i piston or cylinder or both. My improvements constituting the present Another object of the invention is the proinvention are effected by forming the piston so that some part of the guide structure is capable of resiliently yielding at points between the cylinder-engaging surfaces on opposite sides of the wrist pin to compensate for differences in thermal expansion of the piston and cylinder and I prefer to make the guide structure so that it will yield more readily between the wrist pin bosses and the .-yiinder-engaging surface which takes the thrustl during the compression stroke ot the piston, than between said bosses and the cylinder-engaging surface which takes the thrust during the explosion stroke. The means, when applied to the` slipper type of piston illustrated, that the major yield shall occur between the pin bosses 5 and the cylinder-engaging surface of the slipper 4, and in the construction illustrated I have made provision for a resilient yielding in the webs 6, 6 which permits movement of the slipper 4 toward and from the slipper 3. To secure relative movement of the slipper 4 in parallelism, the web structure is formed to yield in two separated sections, which are preferably adjacent the respective ends of the slipper.

In the constructionillustrated this is accomplished by forming each of the webs G with two parallel slots 7 and the slot 7 being open at its upper end and closed at its lower end, while the slot 8 is closed at its upper end and open at its lowerend. The slots 7 and 8 terminate at their closed ends with enlarged cylindrical aperatures 7n and 8a, respectively. @Thus it will be seen that the slipper 4 is supported by elongated strips or sections 9 of the webs 6, and each of the sections 9 has reduced and weakened cross sections at 9a and 9b, so that any yielding of the web structure is localized at these points 9L and 9b. i

My improved form of construction can be app-lied to pistons cast of any suitable metal but it. is especially useful in connection with pistons of aluminum alloy or other light metals having high co-efticients of thermal expansion in comparison with iron as it makes it possible to tit such pistons with as small a clearance as is possible with iron pistons of prior forms of construction. ron pistons of internal combustion engines iitted with a clearance of 0.00075 inch per inch of piston diameter are found to operate with substantial freedom from piston slap, and pistons of aluminum alloy made in accordance with my invention can readily be operated with similar clearances. Indeed a still smaller clearance is made possible by my invention.

In the operation of aluminum pistons of my improved form of construction, asuming a cold \working clearance of 0.00075 inch per inch of piston diameter, or less, to insure freedom. from piston slap when starting, as the engine heats up the excess expansion of the piston as compared with th'e surrounding cylinder wall of iron will reduce this clearance; but as the clearance approaches zero the construction of the piston webs permits them to yield so as to compensate for the excess expansion of the guide section of the piston and all danger of the seizing of the piston is obviated. ll'hen the engine is stopped and the parts again cool down the resilience of the web structure causes it to return to normal form and a suitable small clearance between the piston guide and the cylinder wall is maintained. It will. of course, be understood that the piston head proper is given a smaller diameter than the guide and does not function as a guide. -\s has been explained the yielding of the web structure occurs at the points 9 and 9h adjacent to the upper and lower parts of the slipper 4 so that the slipper 4 is maintained in parallelism with the axis of the cylinder. This insures uniform contact and wear throughout the full length of the slippers. As only a relatively light thrust, incident to the compression of the combustible charge in the engine cylinder, is applied to the smaller slipper 4, the resilient web structure is able to sustain the stresses to which it is suhjected, it being possible, of course, to make the guide structure between the wrist pin bosses and the cylinder-engaging surface ot the slipper 3 adequately strong to sustain the heavy thrust due to the explosion of the engine charge. This is an important feature of my invention since in most, if not all, cases it is found that a construction that is capable of. yielding sufficiently to adequately compensate for differences of expansion, will fail if subjected to the angular thrust of the connecting rod in the working or explosion stroke of the piston.

lt is to be understood that the dimensions of the yieldable web sections, as at 9a and 9", will be determined by the diameter of the piston and other factors such as the compression pressure and the maximum engine speed, the requirements being that the web sections 9a and 9b yield suiliciently to prevent seizing under theJ pressure set up between the cylinder wall and the piston due to thermal expansion, but do not yield too much under the thrust due to compression and inertia, and that they yield, whether under said expansion pressure or under the thrust due to compression and inertia, in a manner to maintain the slipper 4 parallel to the piston axis.

It will be seen that the amount of yielding in the piston webs will be determined` for the most part, by the cold working clearance of the piston. By making this clearance sufficiently small the clearance will be rendered nil when the parts heat up in operation and a resilient pressure of the slippers against 4the cylinder wall will be secured.

Under these conditions the resiliency of the piston web structure will insure the maintenance of close workin contacts between the slippers and the cylinder wall as wear of these parts occurs and, as above noted, the movement of the slipper 4 parallel to the piston axis will insure a uniform contact and wear of the parts throughout the full lengths of the slippers. In other words, my resiliently yieldable piston structure, by compensating for excess expansion of the piston, secures an automatic adjustment of the piston to the cylinder as wear occurs.

My improvements, while applicable in their broader aspects to other types of pistons, are especially applicable to the slipper type of piston illustrated and it will be seen that this is due, in part at least, to the fact that the yieldable web parts have no contact with the cylinderwall and thus are free, in so far as the cylinder is concerned, to accommodate themselves to the movement of those parts which do engage the cylinder.

It is obvious that my invention can be embodied in various forms of construction and it is to be understood that it is not limu ited to the particular construction illustrated inthe drawing except as specified in the following claims.

What I claim is:

1. An integrally cast piston comprising a head, diametrically opposite guide slippers, a pair of wrist pinbosses between the slippers and a pair of webs joining the head, slippers and bosses together, said webs being formed at points between the bosses and one of the slippers so as to resiliently yield and'permit movement of said slipper toward and from the other slipper.

2. An integrally cast piston com rising a head, diametrically opposite gui e slippers, a rpair of wrist pin bosses between the slippers and a pair of webs joining the head,

slippers and bosses together, said webs bein formed at points between the bosses an one ofthe slippers so yas to resilientl yield and permit movement of said slipper 1n paralle lism toward and from thekother slipper. 3. An integrally cast piston comprising a a pair of wrist. pinvbosses between the slippers anda pair of webs joiningthe head, slippers and bosses together, said 'webs being formed between the bosses and one of the slippers each with a pair of parallel slots of which one is open at its. end adjacent Athe of head, diametrically opposite guide slippers',

5. A piston having a head and a guide l structure connected thereto, said guide struc- ,ture comprising diametrically opposite parts having cylinder-engaging surfaces, wrist pin bosses, between said opposite parts, and means for joining said bosses and cylinderengaging parts, said joining means being arranged not to engage the cylinder and the guide structure being adapted to resiliently yield to a greater extent between the pin bosses and one of said cylinder-engaging surfaces than between the said pin bosses and the other cylinder-engaging surface.

6. A piston having a head and a guide structure connected thereto, said guide structure comprising diametrically opposite slippers having cylinder-engaging surfaces, wrist pin bosses between the slippers and means joining said bosses and sllppers together, the guide structure being adapted to resiliently yleld to a greater extent at points between the pin bosses and the cylinderengaging surfaces of one slipper than between the said pin bosses and the cylinderengaging surfaces of the other slipper.

7. A piston having a head and a guide structure connected thereto which comprises diametrically opposite cylinder-engaging parts, wrist pin bosses between the cylinderengaging parts, and means joining said bosses and cylinder-engaging parts together,

the said joining means being resilientlyyieldable to a greater extent on one side of the wrist pin bosses than on the other side,

thereof.

8. A piston having a head and a guide structure connected thereto'which comprises v diametrically opposite slippers, wrist pin bosses between the slippers and means joining said bosses and slippers together, the said joining means being resiliently yieldlable to a greater extent on one side of the wrist pin bosses thanon the other side therev`9. A piston as claimed in claim 4 characterized by being integrally cast.

10. lA piston as claimed in claim 5 characterized by being integrally cast.

11. A piston as claimed in claim 6 characterized by being integrally cast.

j 12. A piston as claimed in claim 7 characterized by being integrally cast.

13. A piston as claimed in claim 8 characterized by bein integrally cast.

In testimony whereof, I hereunto ax my signature.

LAURENCE HENRY POMEROY.

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