US2884919A - Fuel injection pumps for internal combustion engines - Google Patents

Description

May 5, 1959 s. M. BUTLER 2,884,919

FUEL INJECTION PUMPS FOR INTERNAL COMBUSTION ENGINES Filed July 31, 1957 I 2 Sheets+Sheet 1 ENGINE SUPERCHARGER AIR PRESSURE COMPRESSED F AIR RESEVOIR IN l/ENTO Q BY f ATTORNEY y 5, 1959 s. M; BUTLER 2,884,919

FUEL INJECTION PUMPS FOR INTERNAL COMBUSTION ENGINES Filed July s1, 195'! v 7 2 Sheets-Sheet 2 INVENTOR BY ATTORNEY FUEL..I NJECTIONP.UMPS FOR IN'IERNAL COM U T N EN NES :Stanley M. Butler, Hounslow, England, assignor to Alan Muntz & Company Limited, ;Hounslow, Middlesex, England Application July 31,1951, Serial No. 675,436 ,Claimspriority, applicationGreat Britain July 31, 1956 s laim to. 123-1139.)

The present invention relates to fuel injection pumps for internal combustion .engines employing high compression pressures. Such engines may vbe highly supercharged.crankshaftor freepiStonengines. By a free- ;piston engineinthisspecification and in the appended lclaims is meant either a free-piston gas generator or a ,free-piston gas-compressor. .In these free-piston ,en-

gines an engine piston operating in an engine cylinder is .directlyconnected-to a compressorpistonoperating in a :compressor cylinder, ,the .engine operates on the two- .stroke Diesel cycle, and energy accumulated 'by com- -pre,ssio n of air in a cushion on one side of the compressor derived wholly from the exhaust ports of ,the engine.

.In a gas-compressor the air compressed in the compressorcylinder or cylinders is delivered directly to the prime-mover without first passing through the engine.

It is well known to use with conventional crankshaft :Diesel engines operating with normal compression pressures what is known as a gas-operated fuel injection pump, that is -,to say a fuel injection pump which is driven by gas pressure from the :Diesel cylinder. Thus athe gas/pressure in the diesel cylinder may be applied to the-piston ofthefuel pump directly, and the fuel pres- ,sure is then proportional to the gas pressure. As the 'gas 'pressure risestduring the compression stroke the fuel pressure-rises until it :reaches the pressure to which the injectors are set. The fuel valves then open and the fuel is injected at a steadily increasing pressure, .until the ,wholeof the fuel inthe pump cylinder has been delivered. The quantity of fuel is controlled in the usual way by means of a spill port in the pump, which is closed at a pointin the stroke of the plunger at which .the required quantity of fuel is trapped in the pump barrel.

With .the injectors set at a panticular pressure, a pump working in this way will-theoretical1y start inject- ;ing ata point in the compression stroke at which the compression pressure reaches a value corresponding to the setting pressure of thejinjectors. The ratio-of areas of th g p s on an th p mp p un i usu y a ,about l :1 for a conventional diesel engine. Thismeans, for example, that with the injectors set at 1,800 .p.s.i. the start of injection will occur when the compression pressure reaches 180 psi, and if the maximum cylinder pressure is 1,000 p.s.i., the maximum fuel pressure will not exceed 10,000 p.s.i. Moreover, this maximum pressure will only be reached if the injection period is con- ,tinued until the maximum cylinder pressure is reached atabdut 'the inner dead centre.

United States Patent C) The design of a gas-operatedfuel-injeetionpump 'for a high compression ,pressure engine such as a freepiston engine presents ditficulties for the following rea sons. Firstly, the injector pressure setting is considerably higher than .in a conventional diesel engine, for

instance it may be about 2,800 p.s.i,, because of-the relatively high maximum cylinder pressures that are used in free-piston engines, particularly at full load. Secondly, the compression pressures-oceurringat thetime-when injection is required to start may vary from about 1150 p.s.i.g. when idling to about .250 ;p.s.i.g. at full ;l oa d.

These peculiarities of a high compression pressure engine give rise to the following objections:

Firstly a simple pump with a-ratio of'gas piston area to pump plunger areaof 10:1,,requiring a gas pressure of 280 p.s.i. to open thefuel-valves in the injectorswould give too late an injection under all conditions, and secondly, if the area ratio were chosen to give the correct injection timing at full load, it would still be much too late whenidling.

There is also the objection of t-he lateness -of-the; in-

jection at all loads, and means mustbe provided to overcome this objection.

In theory, this objection could be overcome by sufficiently increasing the .ratio of the area of the gas piston to the area of the pump plunger. This, however, results in maximum fuel line pressures which are too high for many purposes. For example, with a ratioof 18 .or 2011 which mightbe required, and a maximum cylinderrpressure of 1,800 p.s.i., the maximum :fuel line pressure would be 33,000 to 36,000 psi The present invention has for its main object ,-to provide a gas-operated fuel-injection system for highcom- 'pression pressure engines in which excessive fuel line pressures are avoided.

According tothe main feature of the invention, therefore, in a gas-operated fuel-injection system for a high compression pressure engine there is provided an accumulator adapted to receive fuel from the gas-operated fuel pump when the delivery pressureof the pump tends to exceed a predetermined pressure, the accumulator being arranged to supply accumulated fuelto the injector means.

The present invention has for a subsidiary object to provide a fuel injection system for ahigh compression pressure engine in which the relation between the timing at full load and when idling can be varied in an appropriate manner.

According to a subsidiary feature of the present invention, therefore, a high compression pressure engine has a gas-operated fuel injection pump comprising a pump piston operating ;in a pump cylinder, the gas pressure from the combustion chamber of the engine cylinder beingapplied to one side of the said pump piston, and means being provided for applying to the other side of the pump piston a gas pressure which increases as the supercharge pressure increases. This gas pressure may be derived from a suitable part of the engine, or machine driven thereby,

such that the delivery pressure of the fuel pump at ,full

load is reduced in comparison withthat whenidling. The said part may for example be the cushion cylinder or'the engine case in a gas-generator, or the scavengepressure in adiesel. When the .said part is the cushion cylinder the maximum cushion pressure is preferably employed. The effect is thus to retard the injection at full load, whereas little effect is produced at no load, and hence a relative change in timing between full load and no load is produced in the required sense.

The invention will be described, by way of example, with reference to the accompanying drawings in which-- Fig. 1 shows somewhat diagrammatically and input a preferred form that the fuel pump and accumu lator according to the invention may take,

Fig. 2 is a. diagram showing the combination of components of Fig.1 in an engine, 'Fig. 3 shows a modified form of the fuel pump and Fig. 4 shows a modified form of the accumulator. '{Referring to Figs. 1 and 2, a fuel pump comprises a casing 11 having its upper portion formed as a cylinder '12 in which works a piston 13. The upper end of the 'cylinder 12 is connected by a pipe 14, as shown in Fig. 2,

to a diesel cylinder 15. The piston 13 has a piston rod 16' connected thereto and the lower end of the piston rod constitutes a plunger working in a cylinder 17. The piston 13 is biased upwards by a spring 24 engaging a -member 25 fixed to the piston rod 16.

Fuel enters the pump through a pipe 18 and passes into the cylinder 17 through an inlet valve 19 and a port 20.

-Fuel is forced out of the cylinder 17 by the pump plunger 16 through an outlet port 21 and a spring-loaded nonreturn valve 22 into an outlet pipe 23.

- The inlet valve 19 controls the quantity of fuel ejected from the pump at each stroke of the piston assembly 13,

16 in the following way. The valve 19 is biased to its closed position by a spring 26 and the upper end of its stem is acted upon by a cam 27 forming one arm of a bell-crank lever rockably mounted upon an eccentric fulcrum 28. The other arm of the lever has a slot in which engages a pin 29 fixed to the piston rod 16. The movements of the cam 27 produced by the reciprocation of the piston assembly 13, 16- serve to open and close the valve 19. The closing of the inlet valve is delayed by an amount which is variable by means of a lever 30 which rotates the eccentric fulcrum 28, thereby controlling the quantity of fuel ejected.

Gas pressure from a suitable part of the engine or its associated'equipment is applied through a pipe 31 to the underside of the piston 13. The point from which this gas pressure is derived can be chosen according to circumstances but must be such that its value is higher at gas pressure applied at 31 is derived from the cushion of a. free-piston engine and that the maximum cushion pressure is to be used. For this purpose a non-return valve 32 is provided between the pipe 31 and the interior of the casing 11. In this way a steady pressure approximately equal to the maximum cushion pressure is applied to the under side of the piston 13. A small leak 33 is also provided around the non-return valve 32 in order to allow the pressure applied to the piston 13 to drop when the cushion pressure drops.

As shown in Fig. 2, the fuel from the pump 10 passes through the outlet pipe 23 to an accumulator 34 and thence by a pipe 35 to an injector 36.

The accumulator 34 'as shown in Fig. 1, comprises a piston 37 within a cylinder 38, the upper face of the piston 37 being loaded by compressed air from any convenient source applied through a pipe 39. The underside of the piston 37 is open to the atmosphere through a vent 40. The piston 37 bears upon the upper end of a plunger 41 on a cylinder 42 in communication with the fuel pipe through a port 43 in the side of the cylinder 42 and through a non-return valve 44 in the bottom of the cylinder 42. Downward movement of the plunger 41 is limited by the cushioning effect of the fuel trapped beyond the port 43 before it reaches the surface 45.

In operation, when the delivery pressure of the fuel .pump' 10 acting upon the underside of the plunger 41 tends to exceed the pressure applied through the pipe 39 multiplied by the square of the ratio of the diameter of the piston 37 to that of theplunger 41, the plunger rises and fuel is received in the cylinder 42. When the force exerted upon the upper end of the plunger 41 by the piston 37 is greater than that exerted upon the lower end by the fuel pressure the plunger 41 falls thereby delivering fuel to the injector. The end of injection will occur when the plunger 41 over-rides the port 43, provided that the plunger 16 of the injection pump 10 has at this time completed its downward stroke.

The passage including the non-return valve 44 is provided to allow fuel to enter the cylinder 42 as rapidly as is required, even when the plunger 41 has over-run the port 43, and to prevent fuel from leaving the cylinder 42 excepting through the port 43, thereby providing a hydraulic buffer for the accumulator plunger.

Instead of loading the piston of the accumulator by means ofair pressure, as described, it may be loaded by means of fuel oil under pressure derived from the injection system through a non-return valve and a slow leak. The pressure required when starting the engine may then be provided by a single stroke pump plunger driven by the compressed air used for starting the engine. Air pressure would not then be 48. The upper face of the piston 47 is open to the atmosphere through vents 49. It is assumed in this example that the pressure applied to the lower face of the piston 47 is not the maximum cushion pressure but some other pressure such as the average cushion pressure, the engine-case pressure, or a control pressure derived from the speed governor of the associated turbine. Thus the non-return valve 32 and restricted passage 33 is not required and has been omitted from Fig. 3.

The control of the accumulator piston 37 may be effected as disclosed in the specification of British Patent No. 628,132. Thus as shown in Fig. 4, instead of the dash-pot arrangement, the under face of the plunger 41 is in direct communication with the fuel pipe 23 and a spring butter, such as a pile of Belleville washers 50, and a shoulder 51 acting as a stop are provided to limit the downward movement of the piston 37. The spring buffer 50 prevents impacts of the piston 37 against the stop 51.

' I claim:

1. A high-compression supercharged internal combustion engine, fuel injector means for said engine, a fuel pump having a piston operating in a cylinder, means coupling the combustion chamber of said engine to said cylinder at one side of said piston to apply gas pressure to operate said piston, a pressure source yielding a pressure which increases as said supercharge pressure in creases, means connecting said cylinder on the other side of said piston to said pressure source, fuel feed means connecting said pump to said fuel injector means, and a fuel accumulator in said fuel feed means, said accumulator having means responsive to a pressure exceeding a predetermined pressure to admit fuel from said fuel pump to said accumulator.

2. An engine according to claim 1, wherein said accumulator comprises a plunger operating in a plunger cylinder, means applying pressure to said plunger cylinder on one side of said plunger to urge said plunger in one direction, and a port in said plunger cylinder on the other side of said plunger connecting with said fuel feed means and applying fuel pressure to urge said plunger in the other direction, said port being positioned to be closed by said plunger.

3. An engine according to claim 2, comprising a nonreturn valve in said plunger cylinder on said other side of said plunger connecting said plunger cylinder with said fuel feed means and admitting fuel to said plunger cylinder.

4. A high-compression supercharged internal combustion engine, fuel injector means for said engine, a fuel pump having a piston operating in a cylinder, means coupling the combustion chamber of said engine to said cylinder on one side of said piston, a pressure source yielding a pressure which increases as said supercharge pressure increases, means connecting said cylinder on the other side of said piston to said pressure source, and fuel feed means connecting said fuel pump to said fuel injector means.

5. An engine according to claim 4, wherein said piston is a stepped piston, the said one side thereof being the smaller.

References Cited in the file of this patent UNITED STATES PATENTS 2,246,701 Steiner June 24, 1941

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