US2674950A - Fuel injection pump - Google Patents

Description

A ril 13, 1954 A. F. UNDERWOOD FUEL INJECTION PUMP Filed Aug. 26, 1948 Patented Apr. 13 1954 UNITED STATES PATENT OFFICE FUEL INJECTION PUMP Arthur Underwood, Grosse Pointe, Mich, as-

vs'ignor to General Motors Corporation, Detroit, Mich, a corporation of Delaware Application August 26, 1948, Serial No.46g247 12 Claims.

1 This invention relates to :fuel injection pumps and more particularly to improvements in the aplungers thereo Conventional fuel injection pumps make use of a plunger closely fitted to a cylinder bore to reduce the leakage "of fuel between the cylinder and plunger when the latter moves on the fuel pressure discharge stroke. In order to accurately .control the clearance between the cylinder and plunger it .is necessary that the :entire length of the cylinder :bore and plunger be-made extremely straight and round and by selective fitting of adjacent the leading edge or the working face through which the plunger moves sothat the ad- .jacent plunger and cylinder surfaces are maintained concentric and properly lubricated.

The means by which this objectand other features of the invention is accomplished will become apparent by reference to the following detailed description of and drawings illustrating a form of the invention which isparticularly adapted for high pressure fuel injection pumps for compression ignition'internal combustion engines.

Figure 1 is a longitudinal cross section of a fuel injection pump incorporating my improved plunger with parts shown broken :away and in section.

igure's'2 and 3 are enlargedviews of a portion of Figure 1 with parts shown broken away and in section to illustrate the plunger before and after expansion, Figure 3 illustrating the plunger expanded.

Figure i is a viewsimilarito Figures 12 and 3 of :amodifiedforin of plunger.

As best illustrated. in Figure 1 the fuel dis- :charge portion of a well known type of fuel injection pump is provided withmy improved pump plunger. This pump includes a hollow pump body 1 having (a fuel spray nozzle '3 seated on an internal flange 5 of the body by means of a hollow spacer 1 held in fluid tight engagement between 'the end faces of the spray nozzle 3 and a hollow pump cylinder 9 by suitabl clamping "means, not shown. The space H between the body 1 and cylindersleeve as supplied with fuel and ports l3-.-l5 are provided in the sleeve and communicate with the fuel space I l. The fuel spray nozzle 3 is provided 'wi h a recess adjacent the hollow spacer l in which apcheck yalve mechanism is located. This mechanism includes a valve disk I1 retained seated on the outer end face of the hollow spacer l by a helical ;compres sion spring [9. An axial bore Q21 leads from the recess in the spray nozzle 3 to fuel discharge openings 23 in the nozzle tip projecting outwardly of the body I.

Aplunger 125 is reciprocal in the hollow cylinder 9 in conventional manner. The plunger is provided with an axialrecess 21 in the innercend face 29 of the plunger ofsubstantially ellipsoidal form and forms the inner end-of a :fuel pumping chamber generally indicatedby thecharacter ref erence 3|, the outer endsurface of this chamber being formed by the inner :face of the valve disk I! seated on the outercface of the hollow spacer i. Communicating axial {and radial-passages :3.2-'32 in the plunger establish communication between the plunger recess 21 and the :bottom of anexternal groove 33 of the plunger '25. The edges of the plunger groove 33 cooperate with the two cylinder ports l3;|-5 upon reciprocation of the plunger in .a well known :manner to provide fuel :inlet to the pumping chamber ,31l vupon outward [movement of the plunger on the fuel filling stroke and to provide fuel by-pass, :pressure dischargeandpressure relief from the pumpring (chamber upon inward movement 'of (the plunger on the fuel discharge stroke, fuel dis charge taking place :past the valve disk 1:1 and through the fuel discharge openings 23 :in the spray nozzle 3.

It will be evident with ithe above described structure upon anincrease in the fuel pressure in .the pumping chamber 3| by inwardmovement of the plunger 25 on the fuel discharge stroke,

causing closure of both cylinder ports -l3-l5,

that uniform pressure will'be applied to the internal surface of the plunger-recess 21. As this recess is of substantially ellipsoidal form the'wall portions at opposite ends of the recess are reinforced against expansion and by having a thicker wall at the ends with the wall thickness decreasing to a smaller value at a point intermediate the ends to allow greater expansion by pressure so that the outer surface of the wallat this point closely conforms to the internal sur face of thecylinder-9, as bestshown exaggerated in Figure 3, to reduce the fuel leakage between the plunger and cylinder. 'It'will be noted that the reinforced or thicker wall portions at-th "end pump Plunger having of the recess expand less than the wall portion intermediate the ends and an annular wedge shaped lubricating film of compressed fuel is formed between the internal surface of the cylinder and outer surface of the plunger adjacent the leading edge or end face 29 through which the plunger moves to provide improved lubrication of these surfaces and to retain the plunger concentric to the cylinder.

As best shown in Figure 4 if it is desired to decrease the volume of the plunger recess 2'! a plug 35 is threaded into an enlargementin the axial plunger passage 32 and axial and radial passages 3t-3l are provided in the plug for establishing communication with the axial and radial plunger passages 32-32. The diameter of the plug is less than thatof the outer end of the plunger recess 2'! so that an annular recess is provided between the ellipsoidal surface of the recess and the outer surface of the plug therein.

It will be evident that the advantages of the plunger structures disclosed may be obtained by providing recesses in the working face of different forms and by reinforcement of the plunger walls adjacent the recesses by other means than by varying the thickness of the wall.

Iclaim:

inner end of the plunger upon inward movement thereof on the pressure discharge stroke.

2. In a fluid pump, a Dump cylinder having a closed end and a pressure discharge passage leading outwardly therethrough, a cylindrical and more closely conform to the internal surface of the cylinder.

3. In a fluid pump, a pump cylinder having a closed end and a pressure discharge passage extending outwardly therethrough, a cylindrical pump plunger having a resilient wall formed by an annular recess in the inner end of the plunger, said resilient wall having thick end wall portions and a thinner intermediate wall portion ance and fluid leakage past the outer surface of the intermediate wall portion and for maintaining the plunger coaxially with the cylinder upon movement of the plunger on the fluid discharge stroke.

4. In a fluid pump, a pump cylinder having a closed end and a fluid pressure discharge passage leading outwardly therefrom, a cylindrical a resilient Wall formed by an axial recess in the inner end of the plunger, the inner surface of the resilient wall decreasing in diameter from the outer end of the recess toward the transverse midplane of the recess in order to limit expansion of the wall portion adjacent the inner end of the plunger and to cause the outer surface of the wall to increas in diameter from the inner end of the plunger toward the intermediate portion of the wall by the pressure in the recess.

5. In a fluid pump, a pump cylinder having a closed end and a fluid pressure discharge passage, a pump plunger having an externally cylindrical surface slidably fitting the cylinder and having an axial recess in the inner end of the plunger subjected to fluid pressure, said recess and cylindrical surface cooperating to form an expansible plunger wall of variable expansibility,

said wall having a thickened portion surrounding the pressure entrance of said recess to reduce the expansion of said inner end of the plunger relative to remaining portion of said wall.

6. In a fluid pump, a pump cylinder having a closed end and a fluid discharge passage, a pump plungerhaving an externally cylindrical surface slidably fitting cylinder and having an axial recess of circular cross section in th inner end of the plunger subjected to fluid pressure, said recess and cylindrical surface being in cooperative relation to provide an annular, pressure expansible plunger wall of variable expansibility, said wall having thickened end portions to reduce the expansion of the end portions relative to the portion of the wall intermediate said end portions.

7. In a fluid pump, a pump cylinder having a closed end and a fluid discharge passage, a pump plunger having an externally cylindrical external surface slidably fitting the cylinder and having an axial recess of circular cross section in the inner end of th plunger subjected to fluid pressure, said recess and cylindrical surface being in cooperative relation to provide an annular, pressure expansible plunger wall of variable expansibility, the thickness of said expansible wall being a minimum at a distance inwardly of said recess from said plunger end.

8. In a fluid pump, a pump cylinder having a closed end and a fluid pressure discharge passage, a pump plunger slidable in the cylinder and having an axial recess in the inner end of the plunger subjected to fluid pressure and forming an annular plunger wall of variable expansibility, the internal surface of said plunger wall having an inwardly curved portion surrounding the entrance to the recess to reduce pressure expansion of said wall portion relative that of the plunger wall inwardly of the recess from said portion.

9. In a fluid pump, a pump cylinder having a closed end and a fluid pressure discharge passage extending outwardly therethrough, a plunger slidable in the cylinder and having an axially disposed recess of annular form in the inner end of the plunger subjected to fluid pressure and forming a pressure expansible, annular plunger wall of variable expansibility cooperating with the cylinder wall and a central plunger portion extending axially with respect to said wall, said wall having reinforced end portions adjacent the ends to reduce the expansion by fluid pressure of said end portions relative to the wall portion intermediate said end portions and thereby maintain greater clearance between the cylinder wall and the external surface portions of the plunger Wall adjacent said reinforced end portions thereof than between the cylinder wall and the external surface portion of the plunger wall intermediate said reinforced end portions.

10. In a fluid pump, a cylinder having a closed end and a fluid pressure discharge passage eX- tending outwardly therefrom, a pump plunger slidable in the cylinder and having an annular recess disposed axially in the inner end of the plunger subjected to fluid pressure to form an annular plunger wall of variabl expansibility cooperating with the cylinder wall and a plunger portion disposed axially with respect to said plunger wall, the internal surface of said plunger wall having inwardly curved end portions to reinforce said wall and decrease the expansion thereof by pressure relative to the wall portion intermediate the ends and thereby provide an annular wedge shaped clearance spac between the cylinder wall and the end portions of the plunger wall and less clearance between the cylinder wall and the portion of the plunger wall intermediate the ends to reduce fluid leakage.

11. In a fluid pump having a pumping cylinder with a side port, a plunger reciprocable in the cylinder having an end subjected to cylinder pressure below said port and an external groove spaced from said end for controlling said port during plunger reciprocation, said plunger having a recess extending into said end and terminating below said groove, said recess being of sufiicient depth and transverse dimension that th transversely surrounding plunger walls will expand under the force of fluid pressure within said recess during the pumping stroke, the walls of said plunger defining said recess being of different thicknesses longitudinally of the plunger axis whereby the rate of said expansion of said walls by fluid pressure varies longitudinally of the plunger axis.

12. The combination set forth in claim 11, together with means for reducing the volume of the recess and extending thereinto coaxially of the plunger axis and spaced from the sides of the recess.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,005,457 Oberhansli Oct. 10, 1911 1,498,273 Hesselman June 1'7, 1924 1,611,526 l-Icsselman Dec. 2 1925 1,759,160 Lang H May 20, 1930 1,759,162 Lang May 20, 1930 2,195,946 Uccusic et al. Apr. 2, 1940 2,357,563 Truxell, Jr. l Sept. 5, 1944 FOREIGN PATENTS Number Country Date 75,433 Switzerland 1935 422,952 Great Britain 1935 521,122 Great Britain 1940 530,775

Great Britain 1940

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