US1929831A - Composite piston - Google Patents

Description

Oct. 10, 1933. R. R. 'rEEToR 1,929,831

COMPOSITE PISTON Filed June 5,. 1931 2 Sheets-Sheet l Oct. 10, 1933. R, n. TEETOR l ACOMPOSITE PISToN Filed June 5. 1931 2 Sheets-Sheet 2 Patented Oct. 10, 1933 UNITED STATES PATENT OFFICE COMPOSITE PISTON Application June 5, 1931. Serial No. 542,232

2 Claims.

This invention relates to pistons and the like and more particularly7 to composite pistons for internal combustion engines and the like.

The principal object of my invention is to provide a piston having the head so assembled in alignment on the skirt that the head expands freely without distorting the skirt which is tted in the cylinder with minimum clearance. More specifically, I provide a piston having a head formed of light material, such as aluminum alloy, and a closely fitting skirt of harder material and having a lesser coecient of expansion, such as cast iron, and connect the head and skirt together so that the head may expand freely independently of the skirt while at the same time the head is maintained in proper alignment on the skirt during operation. l

The above and other objects of my invention will become apparent from the following description taken in conjunction with the accompanying drawings in which:

Fig. l is a longitudinal vertical section through a piston embodying one form of my invention.

Fig. 2 is a vertical section taken on the line 2-2 of Fig` 1;

Fig. 3 is a horizontal cross section taken on the line 3-3 of Fig. 1;

Fig. 4 is a longitudinal vertical section taken through a piston embodying another form of my invention;

Fig. 5 is a horizontal cross section taken on the line 5-5 of Fig. 4;

Fig. 6 is a side view of the head; and

Fig. 7 is a vertical section through the skirt, the section being taken at to that of Fig. 4.

The head 5, provided with the usual piston ring grooves 6, is formed of an aluminum alloy or other light material having a relatively .high coefcient of expansion. Depending from the head and integral with the depending wall of the head are two vertical, parallel hangers or supports 7 provided with aligned piston pin bosses 8 at their lower ends.

The cylindrical skirt 10 is formed of a harder material such as cast iron, having a lesser coefficient of expansion than that of the head. The skirt is provided with the usual strengthening ribs 11 and with diametrically opposed piston pin bosses 12. At one side of the skirt and to either side of one of the bosses 12 are vertical parallel ribs 13 forming a vertical groove between them. The skirt is fitted closely within the cylinder, the structure permitting a minimum clearance. The head has a greater clearance in the cylinder to permit of the greater expansion of the same.

the hanger positioned therein form, in eiect, a

tongue and groove arrangement. As is usual, the piston pin projects through the end of a connecting rod 14 and the pin may be of the full oating type or it may be fastened to the connecting rod or to one of the bosses, as desired. The head is supported on the wrist pin by the hangers 7 so that there is a slight gap or air space 16 between the upper end of the skirt and the lower edge of the depending wall of the head. The outer faces of the hangers 7 are spaced slightly from the inner ends of the bosses 12 as indicated at 12a when the engine is cold (Figs. 1 and 3).

In operation of the engine the head, which has a high coeiiicient of expansion and becomes highly heated, expands to a greater extent than the skirt. The air gap 16 prevents the direct transmission of heat from the head and but little heat is transmitted through the supports 7 and piston pin. During the expansion oi the head the hangers 7 separate slightly and this is accommodated for without imposing any stress or strain on the skirt by reason of the spaces 12a which normally exist between the hangers 7 and the ends of the bosses 12. Thus the skirt is not affected by the expansion of the head so that the skirt is permitted to maintain its true round form throughout without distortion. The one hanger 7 ts fairly snugly between the ribs 13 so that the head is properly centered, or aligned with the skirt at right angles to the piston pin.

In Figs. 4, 5, 6 and 7 I have illustrated another form of embodiment of my invention. As in the rst form, the head 20 is formed of aluminum or other metal having a high coeflicient of expansion and the separate skirt 2l is formed of cast iron or similar metal having a low coeicient of expansion. The head 20 is provided with depending hangers 22 having at their lower ends piston pin bosses 23v with arcuate horizontal ribs or tongues 26 on either side of each boss. The skirt is provided with piston pin bosses 24 and parallel, horizontal and arcuate ribs 25 on either side each boss to vform grooves 27.

In assembling the piston, the head is placed at 90 degrees to the skirt with respect to the position shown in Fig. 4 so that tongues 26 are in line with the grooves 27. The head is then rotated 90 degrees to bring the bossesy 23 and 24 into alignment and slide the tongues 26 into the grooves 25 to the position illustrated in Figs. 4 and 5. Then the piston pin is inserted into the bosses 23 and 24 and the opening through the connecting rod. As in the rst construction an air gap 30 is providedbetween the upper edge of the skirt and the lower edge of the depending Wall of the head.

It will be seen that the operation of the piston is much the same as that of the rst form above described. Normally, the outer faces of the lower ends of the hangers 22 are spaced from the inner faces of the bosses 23 and ribs 25, as indicated at 28 and 28a in Figs. 4 and 5, so that when the head expands to a greater extent than the skirt the hangers may separate freely Without distorting the skirt. As the tongues 26 tV in the grooves 27 the head is maintained in alignment on the skirt, and cannot rock, all the guiding that is necessary being performed by the skirt.

Cast iron pistons, such as are in wide use today, are necessarily heavy and must be loosely fitted in the cylinder when cold so that the piston will not seize in the cylinder or score the latter under high temperature operating conditions. The loose nt results in the familiar piston-slap, poor ol control and other defects. Further, the rate of heat conductivity of cast iron and metals having a similar coeiicient of expansion is not suiciently high to permit the engine to operate most efficiently. All-aluminum pistons, such as are now used to a considerable extent, answer the requirements of lightness and high rate of heat conductivity. In order to permit the skirt to be closely tted when the engine is cold it has been the custom to split the aluminum skirt with the intent of having it accommodate itself to the cylinder under operating conditions. It has been found by experience, however, that this leads to certain defects such as distorted skirts with attendant scoring, rocking in cylinder, undue Wear, excessive blow-by, etc. Such aluminum pistons have their head and skirt portions so coordinated that skirt distortion is caused by the higher expansion of the head portion. Also, they are limited because of the high coeflicient of expansion of the skirt. Composite pistons, having aluminum heads and cast iron skirts, have been proposed before, but as far as I am aware, none of the proposed structures have been very successful or satisfactory. It is evident that with my invention I have overcome the objections to which the prior art pistons have been subject. My piston is light in Weight, the heat is rapidly and efficiently conducted from the head to the cylinder walls through the piston rings, the skirt is not distorted in any way and may be tted normally With the minmum clearance, therefore eliminating rocking, and the means for connecting and properly centering the head and skirt are simple and eiective, because it assures the proper guiding of the piston rings.

I am aware that it has been proposed heretofore to support the head of a piston by means of hangers mounted on the piston pin and normally engaging the ends of the piston pin bosses on the skirt. In such construction the head is permitted and is intended to rock with respect to the skirt and at right anglesY to the piston pin, the head being guided by the cylinder. Such a structure is not satisfactory as it is subject to certain disadvantages, such as piston slap, distortion, excessive blow-by and wear, etc. I overcome these defects by preventing the head from rocking and permitting the skirt to do all of the guiding while at the same time permitting the head to expand freely without tending to distort the skirt in any way.

It will also be evident that my novel structures are extremely simple, cheap and easily assembled. The exterior of the pistons are machined on the outside, as with the conventional onepiece piston. With the form shown in Figs. 1, 2 and 3 it :'s only additionally necessary to face the sides of the ribs 13 and the sides and outer faces of the hangers. In finishing a piston of the second form it is only necessary to machine the outside and inside opposed faces on the lower ends of the hangers and the bosses 24 and ribs 25.

Changes may be made without departing from the spirit of the invention.

I claim:

l. In a composite piston, a head having a high coeicient of expansion and provided with depending hangers havng piston pin bosses, a skirt having a low coe'icient of expansion and provided With piston pin bosses, the hangers being spaced from the bosses on the skirt to permit the head to expand without aiecting the skirt and the hangers also maintaining the head in spaced relation from the skirt to provide an air gap, and vertical ribs on the skirt and engaging the opposite sides of one of said hangers.

2. In a composite piston, a head having a high coeicient of expansion and provided with depending hangers, a separate skirt having a low coeicient of expansion and provided with piston pin bosses, a piston pin projecting through said bosses and cooperating with said hangers, the head being permitted to expand freely independently of the skirt Without distortion of the skirt or head, and parallel vertical ribs on the skirt for engaging opposite sides of a portion of one of the hangers, said portion being slidable between the ribs while the piston is being assembled.

RALPH R. TEETOR.

Images