US2696786A - Fuel injection pump plunger - Google Patents

Description

United States Patent O FUEL INJECTION PUMP. BLUNGER Kenneth J. Fleck. and Stanley J; Kranc, Peoria, Ill. ass signors to. Caterpillar Tractor Co.., Beoria, Ill.,.a corpo ration. of California- Application January 21, 1952, Serial No. 267,486-

3" Claims. (@l. 103-41) The present invention relates to fuel injection for internal combustion engines and particularly to asystem of fuel injection by means of which an engine is caused tooperate efiiciently and quietly under all speed, and load conditions.

In an internal combustion engine employing solid fuel injection, as for example a compression ignition type engine, the speed and load capacity: of the engine are regulated by the volume of fuel injected into each cylinder on each power stroke of the piston therein. The most common method of injecting fuel into the cylinder includes the use of a fuel injection pump for eachof the engine cylinders. The injection pump is provided with a plunger reciprocated by cam action inti'medrel'atien to the operation of. the engine piston. The injection pump receives fuel from asuitable supply source and delivers a measured quantity of fuel under hi h pressure into the cylinder proper timing for the eflicient ignition and combustion therein. One of the most common types of. fuel injection pumps employs a fuel injection plunger having a constant length of, stroke. Such plu-ngers are usually provided with a cut-away portion in the plunger side with a: so-called scroll edge which is adapted to register with the intake passage of the pump so that upon angular adjustment of the plunger in the barrel the effective pumping stroke of the plunger may" bevaried' in response to engine speed and load conditions.

A characteristic of the operation of such aplunger is that as the engine is lugged or slowed down by overload the timing of the beginning of" fuel injection into the engine cylinder is advanced due to compressibility eiiects within the fuel line leading tothe cylinder. In addition, although the injection characteristics of the pump are satisfactory" for good combustion at normal speeds, at slower speeds under. high. load this rate offuel injection produces. undesirably high peak pressures within the cylinder resulting in decreased engine life and produces, an undesirable knocking; As engines of this: type, especially when employed in automotive vehicles, are frequently operated underslowspeed high load conditions the resulting' combustion noise and excessive peak pressures within the engine are undesirable.

It is, therefore, an object of the present invention to provide a method and apparatus for injecting fuel 'in an internal combustion engine wherein the injection rate is varied automatically to produce quiet and efficient combustion as the speed of the engine is decreased by overload. It is another object of this invention to provide means for automatically retarding the advance in timing that would otherwise occur with decreased speed of the engine which also contributes to the undesirable combustion characteristics within the engine cylinder.

Other objects and advantages of this invention will be made apparent in the following specification wherein reference is made to the accompanying drawings showing a preferred form of the invention.

In the drawings:

Fig. 1 is a vertical sectional view of the fuel pump and control mechanism therefor illustrating a typical arrangement with which the present invention is adapted for use;

Fig. 2 is an enlarged fragmentary sectional view of a portion of the pump illustrated in Fig. l to more clearly illustrate the invention; and

Fig. 3 is a sectional view taken on the line III-III of Fig. 2.

80 In Fig. 1 of the drawings a typical fuel injection pump 2,696,786 Patented Dec. 14, 1954 for compression ignition type engines is; illustrated as comprising a pump housing 10. The. pump. housing 10:- has: a central bore: containing a pump cylinder 11 and a valve. housing 12; which are. held in place within. the

housing 10 by an internal nut 13 urging them against'a,

and communicates. with a discharge. line 17 by means of' which fuel under high pressure is directed to, the combu'stion chamber of the engine. The valve housing con tains. a valve; 18; which, is seated against the upper end: of the cylinder 11 by a spring 19 so that the valve 18. acts in; the manner of a check valve and is. opened by' liquid pressure upon the. pressure. stroke of a. plunger within the cylinder 11.. This: plunger is shown at 20 and projects. downwardly beyond the open lower end of the cylinder 11- terminating in engagement with a cup 21 which is: mounted for reciprocal movement in an enlargcd bore 22 in the pump housing. A spring 23 disposed within. thisv bore engages a spring seat 24 resting on. a collar 25 formed on the. plunger and normally urges the plunger downwardly toward a retracted position A cam 26 fixed to! a shaft 27 which is rotated upon operation of the engine in. a conventional manner engages the bottom of cup 21 to effect its. reciprocation and con.

'scquently to impart reciprocation to the pump plunger against the action of the spring 23. As the plunger moves. inwardly past the intake shown at 15, the fluid above. the head end of the plunger is trapped in the cylinder 11 and exerts pressure on. the check valve 18 which is thereby opened discharging the fuel through line 17 into the combustion chamber of the engine. Ordinarily the full. stroke of the plunger would be effective but it is conventional practice to employ a metering structure which meters or regulates the volume of fuel injected into the engine inaccordance with the setting of the engine governor. This metering structure comprises an annular groove: 30: which circumscribes the plunger intermediate its ends a relatively short distance from its head or in ner end and which has an upper scroll edge 31 which: varies in its distance from the head of the plunger; A passage 32 formed in the side of the plunger between the inner end and the groove provides communicationv between the chamber above the head end of the plunger and the annular groove 30. On the inward or pressure stroke of the plunger the fuel in the cylinder is compressed inthe chamber above the head when the head of the plunger closes the intake port 15 and is retained under pressure until the scroll edge 31 passes and opens the intake port 15. At this instant the high pressure is relieved through the passage 32 and groove 30 and is thus communicated back to the relatively low pressure of the intake passage 15 which communicates with the transfer chamber (not shown). With this structure, although the plunger 20 is reciprocated through a full stroke upon each rotation of the cam shaft 27, the length of its effective stroke is determined by the distance between the edge of the scroll and the head of the plunger on the side which covers the intake port 15. This distance changes progressively around the plunger so that angular adjustment of the plunger is effective to increase or decrease the volume of fluid injected into the engine cylinder upon a full plunger stroke.

Angular adjustment of the plunger may be accomplished through a segment gear 34 which is fixed by a. cap screw 35 to the end of the pump plunger below the collar 25 and is received within the cup 21. The side wall of the cup 21 is cut away as illustrated to permit a gear 36 to mesh with gear 34. The gear 36 is carried by shaft 37 which, through conventional mechanism not disclosed, is connected with an engine governor. The setting of the governor controls the angular position of the plunger and the relationship of the scroll edge 31 to the intake port 15 to vary the volume of fluid injected into the cylinder.

With the type of injection pump illustrated, the same volume of fuel is delivered to the engine cylinder for any given setting of the metering plunger. The rate of injection will, therefore, depend upon the speed of engine operation. It has been found that when the engine is slowed down by overload this rate of injection is not satisfactory for optimum combustion and results in ex cessive peak pressures and audible knocking within the engine cylinder. To eliminate this condition it is desirable to decrease the rate of injection during the initial part of the injection stroke. Another characteristic of the conventional metering structure is that compressibility effects within the pump and fuel line connecting the pump to the cylinder produce a time lag between the time the inlet port is closed by the plunger and the actual beginning of injection of fuel into the engine cylinder. This time lag is relatively constant throughout the speed range of the engine and therefore produces an advance in the cyclic timing or of the actual beginning of injection into the engine cylinder relative to the other engine events when the engine is operating slowly due to overload. This advance in cyclic timing of course results in less efficient combustion conditions within the engine cylinder and in some cases aggravates the peak pressures and knocking of the engine.

To overcome these undesirable conditions the head end of the plunger is provided with a relatively small groove or relief 40 extending part of the way around the periphery of the plunger. The relief 40 is positioned to delay the complete closing of port 15 when the plunger is adjusted for high load or large volume of fuel delivery. It has, however, no effect on the injection characteristics when the plunger is positioned for light loads or small volume fuel delivery and therefore does not interfere with idling of the engine. In actual practice the size of the relief employed on a plunger having a diameter of 4 tenths of an inch is on the order of 2 one-thousandths deep and twenty-five one-thousandths wide. Because of its small size the relief has substantially no effect on the injection characteristics of the plunger during normal operating speeds, however, as the speed of the engine is decreased by overloading so that the plunger is held in its maximum delivery position, the effect of the relief becomes more pronounced. This occurs due to the relief remaining in registry with the port 15 for a longer period of time permitting a greater quantity of fuel to leak out of the pressure chamber than would otherwise occur. This results in a slower build-up of pressure within the fuel line decreasing the initial rate of fuel injection into the engine cylinder as well as retarding the timing of this initial injection. By retarding the initial rate of injection and delaying the beginning of injection, the combustion of the fuel within the engine cylinder is accomplished more efiiciently with lower peak pressures which in turn eliminates the undesirable knocking.

We claim:

1. In combination with a fuel injection pump having a cylinder with a fuel intake port in its wall, a reciprocable angularly adjustable plunger with a head operating past said port and a circumscribing groove intermediate the ends of the plunger and having a scroll edge of varying distance from the head, and a communicating axial- 1y disposed channel between the head of the plunger and said groove to relieve pressure toward the intake port when the scroll edge registers with the port whereby angular adjustment of the plunger will vary its effective stroke, a rabbet in the plunger between the groove and the head extending into the head and of small axial extent as compared with the solid portion of said plunger where the groove joins said channel and extending less than half of the circumference of said plunger, said rabbet stopping short of said channel by a distance greater than the width of said intake port, said rabbet communicating with said port only when the plunger is operating with a long effective stroke and presenting a small cross section limiting the bleeding back of fuel after the head of the plunger passes the port to a quantity that will effect a reduction in the rate of fuel injection during the initial part of the injection stroke.

2. In combination with a fuel injection pump having a cylinder with a fuel intake port in its wall, a reciprocable angularly adjustable plunger with a head operating past the said port, and a circumscribing groove intermediate the ends of the plunger and having a scroll edge of varying distance from the head, and a channel in the side of the plunger opening at one end through the head of the plunger and communicating at its other end with said groove to relieve pressure through the intake port when the scroll edge registers with the port whereby angular adjustment of the plunger will vary its effective stroke, a rabbet in the plunger between the groove and the head extending into the head and of small axial extent as compared with the solid portion of said plunger where the groove joins said channel, said channel having a side wall spaced circumferentially of the plunger from one end of said rabbet a distance at least equal to the width of the intake port, the rabbet having a circumferential extent materially greater than the distance between the said one end thereof and the said wall of the channel, said rabbet communicating with said port only when the plunger has been angularly adjusted to operate with a long effective stroke and presenting a small cross section to said port limiting the bleeding back of fuel therethrough after the head of the plunger passes the port to a quantity that will effect a reduction in the rate of fuel injection during the initial part of the injection stroke.

3. The invention according to claim 2, wherein the end of the scroll edge nearest to the head terminates at the said side wall of the channel.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,050,134 Thomas Aug. 4, 1936 2,118,578 Trapp May 24, 1938 2,516,521 MacDonald July 25, 1950 2,535,535 Fleck Dec. 26, 1950

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