US2139387A - Accelerating pump - Google Patents

Description

1933 v J. scHwgrss 2,139,387

ACCELERATING PUMP Filed Dec. 5, 1935 JOSEPH SCHWEISS INVENTOR A TTORNE Y Patented Dec. 6, 1938 UNITED STATES PATENT oFFicE ACCELERATING PUMP Joseph Schweiss, St. Louis, Mo., assignor to Carter Carburetor Corporation, St. Louis, Mo., a

corporation of Delaware l Application December 3, 1935 Serial No. 52,651

'1 Claim. (Cl. 309-33) This invention relates to piston or plunger devices particularly adapted for use in carburetor pump chamber wall. In other cases solid metal pistons have been provided and usually these are formed of the same kind of metal as the chamberwall or of metal having a similar coefiicient of expansion in order toequalize thermal strains in the piston and chamber 'due to frictionor the temperature changes of an asso: ciated engine, I

Whereleather pistons are used there is great difficulty in maintaining uniformityin the Size 3') and texture of the leather parts due to varia .tions in the hides from which the leathers are made and for other reasons. A' leather piston, being absorbent, swells when immersed in liquid with the result that such a pistonyif fitted to its chamber whensaturated, may not function proption with the chamber wall and parts may be dissolved or washed away by the fluid'resulting 30 in loss of compression even though thepiston apparently fitstightly within its chamber] Solid metal pistons are subject to the objection.

of being rigid in contour and thus unable to yield so as to conform with the shape of the chamber, particularly when the piston and chamber are worn or do not exactly fit together for any other reason. Such a piston also embodies a ing pumps, a clearance between'a solid metal pis- 7'.) ton and the chamber wall of aproxlmately .001

inch in excess of thenormal working clearance ordinarily results in loss of pressure and 'im-;

proper functioning of the carburetor, particularly during acceleration. Pistons of leather, even ter wearing properties than rigid pistons.

An object of the present invention is to provide a piston particularly adapted for use in a carburetor accelerating pump, which will function 60 satisfactorily for a substantially greater period of Carburetor accelerating pumps have frequently erly when allowed to dry out. Leather pistons also are subject to substantial wear due to fric u. though expansible, do not have substantially betoperation than previous pistons of thistype, and ordinarily for the lifeof the automobile on which the carburetor is used.

Another object is to provide a metal piston adapted to function properly within wider clearance limitsthan previous metal pistons.

Another object is to provide a metal piston which is substantially easier and cheaper to manufacture wlthin extremely close limits of variation than previous metal pistons.

Another object is to produce a piston capable of automatic expansion to take up its own wear. Another object is to provide a piston of the above type adapted to conform with a chamber wall which isworn or otherwise out of shape so as to maintain a sealing fit therein. I

Another object is to provide a resilient. expansibleyandpliable metal piston.

Another object is to providea new method of manufacturing metal pistons.

These objects and other more detailed objects hereafter appearing are attained by the structures illustrated in the accompanying drawing in which:

stem embodying the invention.

Figure 2 is a section taken on the longitudinal center line of the device in Figure 1.

Figure 3 is an end view of the piston disassembled from-the stem.

Figures 4 and 5 are exaggerated diagrammatic sections showing the piston assembled with a pump chamber but under different operating conditions.

f Figure 6 is an exaggerated top view and section showing the novel piston assembled with a cylinder worn out of round.

Figure 7 is a view similar toFig ure 6 but showing the cylinder worn evenly all around.

The embodiment illustrated in the figures comprises a piston rod or stem 1 having an aperture 2 at one end for attachment to associated mechanism and a reduced portion 3 at the other end threaded for a nut 4. Mounted on the reduced end of stem l is an air dome member including a cup-shaped portion 5 extending beyond nut 4 and a bushing portion 6 directly receiving portion 3 of the stem. Secured between the upper end of bushing portionli which in effect forms ashouldered part ofthe stem structure, and a shoulder 1 at the end of portion 3 of the stem is a washer 9 and'a piston member generally designated at Ill. The piston and stenimay be as;- sembled in any suitable manner, and the air dome structure may be varied as desired, or omitted.

Air dome portioni extends slightly within cupshaped piston member Ill and serves as a protector for the free edge of the piston member. A small clearance is provided between the piston member and air dome portion 5 to permit flexing Figure 1 is aside View of a piston and piston ill) ' during the application of pressure through stem I. End wall Ii is flattened and the periphery of the piston skirt as described hereafter. Pis-, ton member II is formed conveniently though not necessarily, by the stamp drawing process from a piece of sheet aluminum of approximately .006 inch thickness and comprises a disk-like end wall II and a cylindrical side wall portion forming a skirt I 2. The side and end wall portions are preferably Joined by a fillet as at It and the end wall portion is inclined slightly outwardly from the apertured center thereof (Fig. ures 2 and 4). In the assembled device, the clamping washer I and bushing portion. 6 are drawn together tightly against the flattened center portion of the generally dome-like or frustoconical end wall of the piston.

The above described shaping of the piston side and end walls is readily attained by the stamp drawing process in which the 'sheetmetal is forced into a cylindrical die, the re-shaping of the metal under pressure resulting in slight bowing or "cupping in the disk-like center portion of the blank which forms the end wall of the cup. Where thin resilient metal is used, as in the present case, the end wall forms, in effect, a flexible diaphragm and the offset center portion thereof may be flexed under axial pressure and upon release of the pressurewill re-assume its original position provided the flexing does not exceed the elastic limit of the material. During inward flexing, the metal yields in a direction parallel to its surface and the peripheral portion thereof is expanded. w

In the piston described above, substantially the entire end wall ii of the cup including the fillet I! may flex, as described, during the application of pressure coaxially of stem l, or only a portion thereof may be cupped so as to function in this manner. The side wall or skirt of the piston or a portion thereof, preferably, though not necessarily, is inclined slightly outwardly from the end wall po on as at It and this shaping also is readily fo ed by the stamp drawing process where resilient metal is used.

Figures 4 and 5 illustrate on a greatly exaggerated scale, the manner in which the novel piston functions-to seal a cylinder or chamber. In Figure 4 the piston end wall is contracted and cupped, as is the case whensubstantially no pressure is applied thereto through stem l. A

portion of skirt I2 is shown as spaced from the chamber wall H. Inpractice only very. slight clearance is provided" between the skirt and chamber wall and the skirt throughout its depth may engage the chamber wall.

Figure 5 illustrates the condition of the parts thereof expanded towards the chamber wall, resulting in the application of pressure transversely against the chamber wall through piston skirt it. The skirt is thus forcedagainst the chamber wall and into sealing engagement therewith.

The skirt, being. laterally flexible, can yield to conform with the crossv sectional shape of the chamber wall. Figure 6 illustrates, in great exaggeration, a condition in which the piston chamber is non-circular in cross section due to wear. or for any other reason, the piston skirt being distorted correspondingly. Such a condition may exist due to production the chamber is worn by use.

In Figure '1, the chamber, while cylindrical, is

tolerances or after aisassr slightly larger all around than the piston. In this case, the piston expands uniformly all around when pressure is applied to stem I to force the'piston skirt into sealing engagement not necessarily, formed of aluminum, or other material which has a great r coefficient of thermal expansion than the chamber wall, ordinarily brass. in carburetor accelerating pumps, so that the seal will be improved when the piston becomes heated. The piston will function propcrly for a period of time longer than non-flexing pistons, even though formed of softer material than the chamber wall, or vice versa, due to its ability to'expand and to conform with a noncircular chamber. Aluminum is a satisfactory material for forming the piston due to its resistance to corrosion, lightness, strength, resilience, and workability.

The piston need expand or distort only a very small amount and no actual expansion may occur where the piston closely fits within its chamber. The pressure developed in a carburetor accelerating pumpduring each stroke of the piston is not very great, but this pressure, in addition to the friction between the piston skirt and chamber wall,'oflers sufflcient resistance to forces applied through the piston stem to insure slight flexing of the piston end wall provided the cupping or bowing of this portion of the piston is not too great.

The novel sheet metal piston has important advantages .even though the end wall portion thereof is formed flat instead of being slightly cupped. The yielding skirt portion will readily conform with cylinder wall irregularities or imperfections and may be easily stretched or shaped,

particularly at its freeedge by a suitable tool or instrument. It has been found that the pressure developed by the piston and consequently the rate of ejection of fuel from a carburetor accelerating pump in which the piston is used may be increased by merely expanding the piston skirt. This in particular, facilitates servicing of used carburetors. The facility and cheapness of manufacture, durability and uniformity of such a piston also constitute distinct advantages not attained in other types of metal and leather pistons.

Obviously the shaping and proportion of various parts of the illustrated embodiment may be varied and certain parts may be eliminated without departing from the spirit of the invention. Also the piston may be formed by a process other than stamp drawing. The exclusive use of all such modifications as come within the scope of the appended claims is contemplated. I claim:

A piston comprising a thin sheet metal cup having an annular rim with a substantially smooth surface both inside and out, at least a portion of the end wall of the cup being substantially of frusto-conical shape whereby pressure exerted at the center of said end wall in one direction will tend to cause expansion of the outer wall of the cup.

JOSEPH SCHWEISS.

Images