US2335183A - Fuel injection system for compression-ignition engines - Google Patents

Description

Nov. 23, 1943. s. HHNQHCMFFE FUEL INJECTION SYSTEM FOR COMPRESSION IGNITON ENGINES Filed Feb. 13, lllzl Patented Nov. 23, 1943 FUEL INJECTION SYSTEM FR COMPRES SIGN-IGNITION ENGINES Sydney lHinchclie, Wylam-on-Tyne, England Application February 13, 1941, Serial No. 378,832`

In Great Britain January 29, 1940 Y claims (o1. 12a-139) Y This invention relates to fuel injection systems for compression ignition engines.

In the conventional fuel injection 4sy'stems the' fuel oil in the systemfrom the injection pump to the injection valve-is stationary up to the point of opening of the injection valve. The result is that when the injection valve does open there is a substantial drop in the Ipressure of the oil at the injection nozzle, so that provision has to be made for compensating for this. Otherwise the reduced pressure will result in poor atomisation and thereiore'delayed ignition, with the iur` ther result that additional oil is being forced into the combustion chamber without being ignited, 'so 'that when ignition'does occurthere is an excessively rapid rise of cylinder pressure which 'produces excessive maximum pressures and temperatures in the engine. This compensation has -been effected by increasing the pressure generated by the pump to impart the necessary high acceleration `.to the stationary oil in'order to build up andmaintain the pressure at the injection nozzle at that necessary for atomisation. However, as is well known, such pump pressures are of excessive magnitudey and require pumps of such superlative precision that their `production can be undertaken only by manufacturers possessing special facilities. l

`It is thefobject of the present invention to provide means whereby such excessive pump pressures may be obviated, while at the same time the necessary injection 'pressure may be maintained under precise control and so the point of ignition more 'accurately determined, with theY further `result `that'engines may be run morey smoothly` with reduced maximum-pressures and temperatures withthe still further result of increased power/weight ratio. Another object is simultaneously to provide means whereby a substantially finer. degree of atomisation is attained than hitherto,fso that engines may be run eiectively on'a wider range of fueloils than has been hitherto possible with conventional fuel injection systems. A further object is to provide means which will nullify the eiect of the expansion and contraction of the fuel oil pipe owing to the high pressures which have to be generated by the pump. Y

`A number of proposals have been made which included the use of an accumulator piston which was adapted to move under the increasing oil pressure on the pressure stroke of the fuel pump until a predetermined oil pressure was attained, whereupon ther injection valveopened and injection took place, the accumulator piston being free to continue its movement so that the'injection pressure-thus depending solely on the static pressure in the oil system-remained substantially constant. Such proposals included the use `of an injection valve connected to the accumulatcr piston through a lost motion arrangement, so that after a predetermined movement of the said piston the injection valve wasopenedand continued to open in accordance with the difierence between the increasing oil pressure and the pressure drop due to the opening of the injec tion valve.

`'Ihe fuel'injecton system according to the invention comprises an injection valve adapted to be maintained on its seating by the fuel oil pressure, a fuel pipe, a pressure accumulator comprisin g a cylinder and a piston in said cylinder, said piston being adapted to be subjected to the pressure of the oil in the system, the area of said piston being greater thanithat of the injection valve subjected to the fuel oil pressure, means for ar-A resting the movement of said piston at about the timewhencommencement of injection is due, and

lost motion means operatively interposed between said accumulator piston and said injection valve for opening said injection valve after the `said piston has moved for a predetermined distance under the rising oil pressure, the arrangement being such that subsequent movement of the said piston before its arrest is only suflicient to lift the fuel injection valve the requisite amount ior Aefficient fuel injection.

The invention will now be `described by way of example with reference to the accompanying drawing. Y

`In the said drawing:

Fig. l is a diagrammatic longitudinal sectional view of a form of the invention comprising a combined pressure accumulator and cylinder.

Fig.. 2 is a diagrammatic longitudinal section of an alternative form of pump to be used instead of the pump shown in Fig. 1.

Referring more particularly to Fig. 1, I is an vaccumulator cylinder, and 2 the accumulator piston. Sis an enlarged cylinder communicating and in axial alignment with the cylinder I. The cylinder 3 houses a compression spring 4 whose lower end abuts against the piston 2. The upper end of the cylinder 3 has a vent 3a to prevent the building up of pressure.

The piston 2 is adaptedto abut against an adjustable abutment screw 5 to limit its upwardV The lower end of the piston 2 projectsV travel.

into an enlarged cavity 6, and is T-slotted at 2a to receive the headed end 1a of the valve stem 1 hand is slightly less than the distance between the end of theV abutment screw and the upper end of the piston 2, by an amount equal to the lift necessary for the valve 1b.

' The spring 8 is purely supplementary, and ensures the valve lb being retained on its seating when the engine is stopped and there ls no oil prg-ESSUIE.

Oil is forced by the pump B through the pipe I0 into the cavity B below the piston 2, and the resulting oil pressure causes the piston 2 tomove upwards; but it maintains the valve lb on its seating until, after moving-upwards for a certain distance, the shoulder 2b of the piston 2 abuts against the under side of the head la, and so begins to lift thevalve 1b, lifting continuing until the movement of the piston 2 is arrested by the abutment screw 5.

Owing to the movement of the piston 2, the oil .is able to gain momentum through the pipe I0,

to that of the piston portion I2a is moved along the pipe I0 before the piston 2 begins to lift the valve lb. Thus the oil in the pipe I0 is accelerated before injection starts, and so has been allowed to gain momentum.

It will be observed that the oil pressure except I when injection is taking place is forcingfthe injection valve 'Ib on to its seat, thus tending to prevent leakage.l I

In the conventional arrangement there is a delay between the commencement of pump delivery and the opening of the injection valve due to the expansion of the pipes and other parts from a small pressure to the high pressure necesceiving the oil. The said oil receiving means may comprise, as shown, a spill v'alve II,' the oilpassing from the passage IU to the discharge port B of the pump B where the spill valve I I will have been lifted, thus allowing the oil toescape to the suction chamber B2 of the pump B.

An injector as shown in Fig. 1 may be used,

if desired, with fuel pumps such as that Vshown in Fig. 2, that is to say pumps which spill from the Vpump cylinders, and not from the delivery pas- *sagev as is the case with the pump B of Fig. 1.

The delivery valve I2 of the pump C shown in Fig. 2 may have a portion of it arranged to act as a piston I2a as shown. With such an arrangement the fuel pump now delivers oil to the accumulator cylinder until the accumulator piston has reached its stop 5. mences and continues until the spill valve I3 opens. At this point the delivery valve I2 closes, but owing to its piston portion I 2a there is displaced along the pump delivery pipe by the piston 2 a volume of oil equalto the volume of the said piston portion, thus allowing the valve 'Ib to seat and the piston 2 to maintain a pressure on the oil. l

The motion of the accumulator piston 2 is nally Yarrested by the valve head 'Ia or by the oil trapped in the system when the delivery valve reaches its seat, according to the relative volumes displaced by the accumulator piston 2 and the piston portion I2a of the delivery valve I2. By keeping the volume of the piston portion I2a less than the maximum displacement of the accumulator piston, the delivery valve I2 seats before the accumulator piston reaches the valve head la, and the pressure is thusY maintained on the oil system between consecutive periods of injection. When the succeeding delivery of the pump begins, a Avolume of oil approximately equal Injection then com-Y sary to open the injection valve. This causes variations ln the actual point of injection and reduces the engine efficiency.

With the smaller -pressure increases required by the arrangement according to the invention this drawback is obviated and a more delicate control of the fuel ignition point may be effected.

Again, owing to ytherfact that' the suitability of Diesel engine oils depends on the rapidity with which they ignite, and aslgnition is a function of initial atomisation', vthe invention permits the use of a'wider range offfuels than hitherto.

The advantages above set forth are more marked in contrast .with the conventional fuel injection Vsystems at high engine speeds. The operation ofthe system according to the invention is practically independent` of the engine speedf and therefore isvof specialadvantage for variable speed engines. 1

Another result of the system according to the invention effects the fuel nozzle. 'lhel size of nozzle orifcevi's chiefly a function of the fuel quantity, the duration of the injection and the mean pressure of the fuel. As the system according to tne'invention reduces the mean fuel pressure, the'siae of orifice can be increased. The nozzle is therefore'cheaper to make but also makes possible the use o f orifice shapes other than circular or annular-`-which are not necessarily the best-for atornising'. This effect is progressive because by using a more efficient atomismg shape the pressure can again be reduced and so on.

What I claim as my invention and desire to secure by Letters Patent of the United States is:

l. A fuel injection system comprising an injection valve adapted to bemaintained on its seating by the fuel oil pressure, a fuel pipe, a pressure accumulator comprisingva cylinder VVVand a piston in said cylinder, said piston being adapted to be subjected to the pressureof the oil in the system, the area of said piston being greater than that of the injection valve subjected to the fuel oil pressure, means for arresting. the movement of said piston at about the time when commencement of injection is due, and lost motion means operatively interposed between saidaccumulator piston and said injection valve for opening said injection valve after said piston has moved for a predetermined distance under the oil pressure, the arrangement being such that subsequent movement of the said piston vbefore its arrest is only sufficient to lift the fuel injection valve the requisite amount for efllclent fuel injection. v

2. A fuel injection system according to claim 1, a shoulder on the accumulatorpiston, said shoulder beingV adapted to engage an abutment on the assunse injection valve after the predetermined amount of movement oi' said piston has taken place.

3. A fuel injection system according to claim 1. wherein the accumulator piston has formed thereon a T-slot, an abutment screw adapted to abut against the inner end of the accumulator piston, a valve stem integral with the injection valve, a, head on the end of said valve stem, said head engaging with the T-slot in the accumulator piston, a spring adapted to press the inner wall of said T-s1ot against the outer face of said head, while the lower face of said head is adapted to abut against the shoulder formed by said T-slot, the diierence between the lengths of said head and the distance between the inner face of said lo slot and the inner face of said shoulder, being pump.

slightly less than the distance between said abutment screw and the piston when the injection valve is closed, by an amount equal to the lift necessary for the injection valve.

4. A fuel injection system according to claim 1, comprising means for maintaining the pressure during the period between consecutive injections in the fuel oil pipe line at a value approximating that required for injection, said means comprising a fuel pump delivery valve having a piston portion thereon which allows its ownvoluxne of oil to move along the fuel pipe before opening and closing of the said delivery yalve, and a. spill valve betweensaid delivery valve and the fuel SYDNEY HINCHCLIFFE.

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