US1497421A - Tappet - Google Patents

Description

flame w. 19-24. EAWAZE M. M. wmcox TAPPET Filed April 18. 1921 ATTORNEY Patented .lune 1G, *EJHL:

PATENT OFFICE.

MERRILL M. WILCOX, OF SAGINAW, MICHIGAN.

TAPPET.

Application fil ed April 18, 1921. Serial No. 462,424.

To all whom it may concern:

Be it known that I, MERRILL M. WiLoox, a citizen of the United States, residing at Saginaw, in the county of Saginaw and State of Michigan, have invented certain new and useful Improvements in Tappets; and I do hereby declare the following to be a full, clear, and exact description of the invention, such as will enable others skilled in the art to which it appertains to make and use the same.

This invention relates to cam followers i or tappets for use in internal combustion engines and the like and the improvement pertains more particularly to a new tappet construction w ereby the objects of my invention are attained.

These objects are, first, to provide a ta pet that is light in weight, yet exceeding y strong to resist the strains brought upon it .in use and capable of being manufactured I by the employment of a minimum number of operations.

A further object is to provide a tappet head made of material that is inexpensive and et admirably adapted to withstand the rapi l repeated impacts of the valve cam.

Wit these and certain other objects in view which will appear later in the specifications, my invention comprises the device's herein described and claimed and the equivalents thereof.

In the drawings, Fig. 1 is a vertical section through a tappet embodying one form of my improvement.

Fi 2 is a similar section through a modified o'rm of my improved tappet.

In the drawings, 1 is the tubular body or shell of the tappet. 2 is the head that receives the impact of the en ine cam, not shown. The end 3 of the lead may be flanged asshown, if desired, and the head is rovided with an axially extending cylindrical shank 4 adapted to be received in the end of the tubular body and to project into it a sufiicient distance to form an interior reinforcement for the tubular body 1, to prevent buckling or distortion of the body when the tappet is in action and is being rapidly reciprocated in the sliding bearing 'or guide in which a tappet is customarily mounted in an engine.

It has heretofore been common in the design and manufacture of tappets for high speed engines to make the tappet of a S11) is piece of metal; or of two pieces, as a tube ar body and a head; or sometimes of three pieces, as a tubular body, a plug at one end and a head at the other end. i

The purpose of the two-piece and threepiece tappets has been to enable the head to be made of alloy steel which is capable of being iven a great degree of hardness, while t e tubular body is made of softer and cheaper material.

Such multiple-piece tappets have required more operations for their manufacture and are ingeneral more expensive to make than the one-piece tappet, but on account of the advantage of lightness and because the design permits the heads to be made of alloy steel and case-hardened, the multiple-piece type of tappet has come into extensive use.

I have found however, in practice, that the alloy head has serious disadvantages in that it requires several incidental mechanical operations in its manufacture, thereby increasing its cost. I have also found by experience that the alloy steel heads have in erent disadvantages that detract from their usefulness and reduce the period of working life of the tappet. i

For example, an alloy steel head must be case-hardened on its working face and then ground to exact size. The case-hardening or carbonizing process, as is well known, consists in first electroplating the alloy steel head with copper, then grinding OK the copper from the face of the head and then carbonizin the head in the furnace, the cop-.

erplatin preventing the absor tion of caron by t. e surfaces that nee not necessarily be hardened, namely, all surfaces exce t the working face.

be head after hardening requires to be ground to its final shape, inserted in the tubular body and then spot-welded. The foregoing operations, while necessary in the construction of an alloy steel head tappet, are expensive.

In the commercial production of hardened allo steel tappets the face. of the head' is male extremely hard, but only for a short depth, and in the oil-quenching step of the hardeninw process there apparently is left sufficient heat in thebody of the head to result in slightly annealing that part of the metal of the head which lies directly back of the thin hard steel face.

Since alloy steel is intended for and particularly adapted to service requiring high tensile strength, and is not so well adapted to resist impact, it follows in practice that the constant hammering of the cam against the tappet produces a multitude of microscopic surface checks and imperfections in the thin hardened face. It is possible that this condition is aggravated by the shrinkage strains which are set up in the hardened surface when the heated metal of the body of the head cools subsequent to the initial chilling of the face, resulting in the minute temperature cracks on the surface. In any event, it has been proven that case-hardened alloy steel tappet heads are not sufficiently durable in practice to warrant the high expense that must be put into their manufacture.

To overcome these defects, while still preserving the general design, lightness and strength of multiple-piece tappets, I have devised the improvement herein illustrated.

I have discovered that a grey iron casting, which may preferably be chilled, and then ground, fitted and secured to the tubular body by welding produces a tappet head that is admirably adapted to withstand the impacts of the cam, that has a face which has no surface checks or cracks and which tends to become more dense with continued use, instead of developing cracks, as is the case with the hardened alloy heads previously referred to, and it also eliminates the necessity for employing the preliminary steps heretofore required for machining, electroplating and case-hardening; steps which constitute a considerable part of the entire cost of manufacturing tubular tappets.

In carrying out my invention in accordance with the construction of Fig. 2, I first make a tappet head of cast iron, grind the shank of the head to size, insert the shank in the tubular body and spot weld the tubular bod to the shank as indicated at 5, Fig. 2 and then grind the exterior of the tubular body and the face of the head to finished dimensions.

The working face of a ferrous casting so pre ared is almost perfectly smooth, highly polished and in use becomes glass hard without indentations. There are no apparcut surface checks or tension strains and the material becomes more and more dense with continued use under the hammering action of the engine cams.

There is no dificuity in spot welding the earner.

thin metal tappet 1 to the shank 2, a commercially perfect welded union being attained bv the use of the ordinary spot weldmg mac me.

In the type of tappet shown in Fig. 2, the tubular body 1 is made of a separate piece of metal, which may be cold rolled steel, or its equivalent, but the tappet may be made as shown in Fig. 1, where the entire tappet, including the head, is cast in one piece, the head may be cast in a chill and the tubular body being preferably cast in sand according to the methods of procedure which are well known in foundry practice.

By making the tappet head of either common grey iron or of chilled iron instead of alloy steel I have not only improved the wearing qualities of the tappet surface, but have reduced the cost of manufacture to a small part of the cost of a tubular tappet having a case-hardened head formed of alloy steel or similar material.

Having thus described my invention, what I claim and desire to secure by Letters Patent is:

1. As a new article of manufacture, a tappet comprising a hollow tubular stem and a ead formed of a chilled iron casting, said head and stem cast integral.

.7 2. As a new article of manufacture, a tappet comprisin a cast iron stem and a head formed of a c illed iron casting, said head and stem formed integral, for the purposes set forth.

3. As a new article of manufacture, a tappet formed of cast iron and having its camengaging face of chilled metal.

4. As a new article of manufacture, a tappet formed of cast iron and having a discous head formed with a cam-engaging face and also having a stem, said head portion being of chilled metal at and adjacent its cam-engaging face.

5. As a new article of manufacture, a tappet formed of cast iron and having a discous ead portion formed with a cam-engaging face and also having an integral stem ortion, said head portion being of chilled metal at and adjacent its cam-engaging face and the remainder of said tappet being unchilled.

In testimony whereof, I affix my signature.

MERRILL M. WILCOX.

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