Fuel injection systems for internal combustion engines

Abstract: A fuel injection system for a stratified charge hybrid internal combustion engine includes a main combustion chamber and a precombustion chamber, and fuel injectors (56, 54) in both the main chamber and the precombustion chamber which open at higher and lower pressure levels respectively to sequentially inject fuel into the precombustion chamber and main chamber. The system also includes a timed-spark ignition trigger (58) in the precombustion chamber, and an engine-driven and timed fuel injection pump (12) having a variable output capacity which varies with the engine power level requirements, the injection pump (12) being supplied by a low pressure charge pump (26). The injection system further includes a shuttle valve (30) with a shuttle spool (36) positioned therein defining a precombustion chamber supply chamber (40) on one side thereof and a spool activation chamber (38) on the opposite side. An initial charge from the injection pump (12) displaces the spool (36) from its first (right-hand) to its second (left-hand) position. The initial part of this displacement valves-off the supply of fuel into the supply chamber (40), and further displacement causes the spool (36) to supply a charge of fuel to the prechamber injector (54) until the spool reaches its second position defined by a stop (61). Thereafter, the fuel pressure from the injection pump (12) acting in the spool actuation chamber (38) rises to the opening pressure level of the main injector (56), and fuel flows through the spool actuation chamber to the main injector. The trigger (58) positioned in the shuttle valve fires the ignition means as the spool moves from its first position.

Description: This invention relates in general to fuel injection systems in internal combustion piston engines. More particularly, it relates to a stratified charge hybrid-type engine having dual injectors, one in the pilot or precombustion chamber and the other one in the main combustion chamber, a single engine-driven and-timed injection pump supplying both injectors in sequential order, and a trigger for timed spark ignition. The engine is hybrid in the sense of having transitional combustion modes from spark-ignited stratified charge mode at lower power, to a spark-assisted compression ignition at higher power loads, and a compression ignition mode at maximum power loads. The engine is a low compression engine which burns turbine fuels and has no specific octane or cetane requirements. The engine is described in further detail in US-A-4,594,976 and in US-A-4,765,293. Stratified charge engines which include pilot chambers and main chambers have been in existence for over 50 years as exemplified by the Ricardo, US-A-2,191,042. These type of engines, in isolated cases, have successfully operated with turbine fuels, however, they have been in ground transportation applications of low specific power output types. A number of prior patents utilize dual injectors which are ignited by an electrical spark, as typified by Hoffman, US-A-2,902,011 and Loyd, US-A-4,141,940. Both of the latter mentioned engines are low specific power output engines that require wide injection timing spreads between pilot and main chambers of approximately 40° which limits the power and speed capabilities of the engine. Nallinger, US-A-2,914,043 also teaches a stratified charge dual injector system which is supplied by a single pump. This engine is strictly a gasoline engine with the fuel injection system operating at low pressures, and is not configured to operate in a diesel or hybrid mode. The Nallinger engine is of an early injection timing type, and requires fuels that provide a measure of detonation or autoignition control on combustion, and therefore require octane rated fuels. The Nallinger engine is clearly not configured to operate in a diesel or hybrid mode. The injection system embodying the present invention is considered a late injection system (main injection starts at approximately 10° BTDC (before top dead centre), while pilot injection starts at approximately 30° BTDC). Later injection, of course, requires higher injection pressures, as in convention diesel engines. US-A-4,239,023 to Simko describes a dual injection system utilised in a pilot or prechamber and main chamber. However, this early injection timing engine is a strictly spark-ignition low output engine based on turbulent flow conditions in both the prechamber and main chamber cavities, while the late-timed engine embodying the present invention depends upon well organized swirl conditions in both chambers. The engine embodying the present invention and the Simko engine are similar in that they both utilise a shuttle valve between the injectors in the prechamber and main chamber. However, the response time with applicant's shuttle valve is shorter and more precise than Simko which includes a variety of slow moving check valves which affect the overall reaction time and timing precision of the system. A similar stratified charge low-compression turbine fueled experimental engine is being developed by White Engines, Inc. and Texaco, Inc. referred to as the L-163-ST engine (Road and Track, November 1979, pages 39 and 40). The White engine above-mentioned does not include a separate prechamber but rather locates the spark plug in the main chamber and achieves stratification by closely locating the injector to the spark plug. SAE Technical Paper No. 830666 titled "The Pencil Nozzle - Past, Present and Future" dated February 28-March 4, 1983, illustrates the concept of an ignition-triggering nozzle on page 24, wherein the opening of the nozzle due to pressure rises within the nozzle electrically fires the ignition system in place of a separate ignition distribution system. Poore, US-A-4,681,073 also teaches a stratified charge internal combustion engine with a dual injection system utilizing a pilot and main chamber injector. Poore also utilizes a shuttle valve between the injectors; however, they both appear to open up at the same pressure level which does not provide any sort of precise overlap between the pilot injection and main injection. This injection system clearly does not operate in a hybrid mode nor is the ignition triggered by the shuttle spool position. The present invention is directed to a fuel injection system for a stratified charge hybrid internal combustion engine, generally of the type disclosed in US-A-4,239,023, and as defined in the precharacterising clause of claim 1. The injection system embodying the present invention includes a novel ignition triggering means in the shuttle valve which fires the spark plug in the prechamber, which is not taught by any of the above-mentioned prior art. It is an object of the present invention to provide a fuel injection system for combined precombustion injection and main chamber injection in sequential order with a spark ignition means timed to the actuation of a fuel shuttle valve supplying the respective injectors. The present invention consists in a fuel injection system, as defined in the characterising clause of claim 1. The engine to which the invention may be applied is a hybrid internal combustion engine which uses a stratified charge OTTO cycle during starting, idle, and low specific power operations, while gradually converting to a time-spark assisted or a non-assisted compression ignition (diesel) mode as the specific engine outputs increase. The engine can utilise a wide range of fuels, with the preferred fuel being turbine fuels, with relatively low compression ratios and high specific power outputs. The precombustion or pilot chamber located in the cylinder head includes a pilot fuel injector and spark plug. The prechamber is connected to the main combustion chamber by means of a passage or orifice located in such a manner as to induce swirling airflows within the prechamber during the compression stroke. During the compression stroke, the prechamber fuel injection and ignition begins at approximately 30° BTDC which is then ignited by the spark plug initiating the combustion process. At approximately 10° BTDC, the main injector begins to inject as ignition commences from the torch flames emanating from the prechamber. The system is generally considered a late injection system. Prechamber pilot injection basically precedes main injection in a sequential order at timings from top dead center. The system embodying the present invention incorporates a shuttle valve which sequentially supplies the prechamber injector followed by the main injector, the shuttle being provided with ignition trigger means. The system is a dual fuel injection nozzle system supplied by a single pump through the shuttle valve, which allows a wide range of nozzle operating pressures and nozzle differential operating pressures. The shuttle valve has decreased and precise reaction times, and the ignition trigger in the shuttle valve allows precise relative timings of fuel injection and ignition events. The fuel delivery to the prechamber or pilot injector via the shuttle valve is controlled by the position of a power lever of the engine, or one or more other power sensitive functions of the engine. The shuttle valve includes a positive valve closure to the main injector in the initial or first position of the shuttle spool. The spool of the shuttle valve may be stepped to provide pressure amplification functions between the pilot to main fuel injection pressure ratios, including main injection pressures lower than pilot injection pressures. In order that the invention may be more readily understood, reference will now be made to the accompanying drawings, in which:- Figure 1 is a schematic view of the fuel injection system embodying the present invention; Figure 2 is a symbolic view of the shuttle valve of a modified form which allows a variable pilot delivery; Figure 3 is a symbolic view of the shuttle valve of a further modified form; Figure 4 is a symbolic view of the shuttle valve of a still further modified form; and Figure 5 is a graph illustrating the operating flows of the injection pump through a complete injection cycle. The injection system embodying the present invention is generally designated by reference numeral 10 as seen in Fig. 1, without most of the various engine parts which it controls. The engine which the present system 10 controls, is set forth in US-A-4,594,976 and 4,765,293. The pilot or prechamber injector 564 and main chamber injector 6 are comparable to injectors 22 and 25 of the last-mentioned patent, and are standard type diesel injectors. Pilot injector 54 extends into a spherical prechamber which in turn is tangentially joined to the main chamber, as seen in the various figures of the above-mentioned patent. The pair of injectors 54 and 56 are supplied by a single fuel injection pump 12 which is a standard type fuel injection pump, either of the rotary distributor type or the inline type, both of which are well known in the prior art. Fig. 1 illustrates the injection system for a single cylinder, and therefore with a multiple cylinder engine there will be duplicate systems, as shown in Fig. 1, for each cylinder of the engine. Typically a standard distributor type injection pump would have 4 to 8 separate cylinders, and 4 to 8 pistons 18 as shown in Fig. 1. Injection pump 12 is a piston type pump driven by a cam 16 which is attached to an engine driven shaft 14 and rotates at, typically, half the engine speed. Typically, a single upward stroke of piston 18 provides the fuel charge for one firing cycle of pilot injector 54 and main injector 56. The fuel injection system 10 also includes a low pressure charging circuit 27, including a feed pump 26 which refills the pump 12 and a chamber 40 of a shuttle valve 30 on their corresponding suction strokes. Feed pump 26 is a positive displacement pump of any type, and includes a relief valve 28 in the charging circuit which allows the pump discharge to return to the inlet of feed pump 26 or to a fuel reservoir 25, and maintains constant pressures ranging from 69x10³ to 4136.9x10³ Pa (10 to 60 PSI) in the circuit depending on fuel types and system applications. Feed pump 26 also recharges supply chamber 40, as a shuttle spool 36 of the shuttle valve 30 moves rightwardly and expands the chamber 40. Shuttle valve 30 comprises the shuttle spool 36 slidably positioned in a bore with a spool actuation chamber 38 on its right end and prechamber supply chamber 40 on its left end. Maximum movement of shuttle spool 36 in the left direction is limited by an adjustment screw 61, while maximum movement in the right direction is limited by an ignition trigger pin 58. In the absence of pressure, shuttle spool 36 is moved in the right direction by the bias of a return spring 41, while movement in the left direction is caused by a greater fuel pressure differential in chamber 38 over chamber 40. Shuttle spool 36 has a first position to the far right with the right end of spool 30 in contact with ignition trigger pin 58. Shuttle spool 36 has a second position to the far left with the left end of spool 36 in contact with adjustment screw 61. Low pressure feed pump 26 refills chamber 40 on the left end of spool 36 via line 34 with low pressure fuel as return spring 41 moves spool 36 in a rightward direction. Positioned in the injector supply conduit 48 is a delivery valve 52 which is symbolically shown as a check valve spring-biased to a closed position. Actually, the poppet or closure element in the delivery valve closes its lateral valving port before the poppet reaches the end of its stroke so that there is an additional downward travel after the lateral flow passage closes so as to relieve the pressure in supply conduit 48. A similar delivery valve 50 is positioned in the main injector supply conduit 46 which supplies main injector 56. The purpose of these delivery valves 50 and 52 is to prevent the injectors from dribbling after the injectors close and keep the injection lines 46 and 48 primed with fuel for the next injection event. Injector 56, which supplies the main combustion chamber of the engine, can have any set prearranged opening pressure. However, in a typical instance it would be higher than that of the pilot injector 54 and, for example, might be 3000 PSI, while the pilot injector 54 may open at 1200 PSI. The particular structures of injector nozzles 54 and 56 are standard in the trade and are therefore not shown in detail. Standard type injection pump 12 previously mentioned, must have some form of variable output to accommodate variable fuel demands of the engine. To symbolically show this variable feature of pump 12, a vertically slidable sleeve 22 is shown in the drawing, which has an inlet valving port 20 supplied by charging fluid from the charging circuit 27. While piston 18 always has the same stroke, the displacement per single stroke of pump 12 may be varied by moving sleeve 22 up or down so that point at which the compression stroke begins can be varied. The pumping stroke will begin approximately at the point as illustrated in FIG. 1 wherein the edge of piston 18 passes over and closes inlet valving port 20, thereby preventing any further back flow in low pressure line 34. Once valving port 20 is closed, the additional upward stroke of piston 18 will be the total displacement of fluid forced through injectors 54 and 56. Spring 24 in the pump returns the piston 18 to the bottom of its stroke as cam 16 shortens it contacting radius. At idle power settings of the engine, sleeve 22 would be moved upwardly to its illustrated position, so that valving port 20 closes just prior to the end of its stroke, so that the main injection charge would be very small or zero. For maximum power settings, sleeve 22 would be moved downwardly, so that valving port 20 closes sooner, and the full stroke of fluid, as indicated by arrows A,would be delivered to the pilot and main injectors 54 and 56 respectively. As piston 18 moves upward, closing valving port 20, fluid thereabove is forced through pump output line 32 into spool actuation chamber 38. This increased pressure in chamber 38 forces shuttle spool 36 to move in a leftward direction, enlarging chamber 38 while supply chamber 40 reduces in volume at a similar rate. Once the left end of shuttle spool 36 passes over valving port 42, back flow stops in low pressure charging line 34 and the fluid trapped in chamber 40 begins to rise in pressure. This increasing pressure causes the poppet in delivery valve 52 to lift against its biasing spring and open chamber 40 into injector supply conduit 48. As the rising pressure reaches the opening pressure of injector 54, the nozzle opens and the pilot charge of fuel is sprayed into the engine prechamber (which is not shown in the drawings). The flow to the prechamber stops when spool 36 contacts adjustment screw 61, and injector 54 closes. After injector 54 closes, delivery valve 52 seats its poppet and further drops the pressure in conduit 48. With spool 36 stopped by screw 61, the increasing pressure in chamber 38 due to movement of piston 18 will force the remaining fluid from its stroke to main injector 56 through valving port 44 and delivery valve 50. Before main injector 56 opens, the pressure in main injector supply conduit 46 must rise to the opening pressure of the injector. The amount of fuel injected in the main injector varies with the prearranged position of valving sleeve 22 in pump 12 as previously discussed. In the embodiments of FIGS. 1, 2 and 4, the valving port 44 is permanently open. However, in the embodiment of FIG. 3, the valving port 44' to the main injector 56 is not opened until spool 36 moves to its second position. OPERATION The fuel injection system embodying the present invention is illustrated in FIG. 1 with a single cylinder. However, in most applications there will be multiple cylinders of varying numbers, each of which will have a complete circuit, as shown in FIG. 1. The cams 16, one for each cylinder, will all be on a common shaft 14 with different angular positions as determined by their firing orders. Charging circuit 27, which includes the low pressure feed pump 26 and relief valve 28, constantly supplies a low pressure to both the charge lines 34 to injection pump 12 and also to chamber 40 in shuttle valve 30. As the injection pump 12 begins its compression stroke, piston 18 moves upward, displacing fluid from the pump cylinder which back flows in charge line 34 until valving port 20 is closed by piston 18. Further movement of piston 18 displaces its fluid through pump output line 32 into spool actuation chamber 38. Rising pressure in chamber 38 causes shuttle spool 36 to move in a leftward direction, closing valving port 42. The measured amount of fuel trapped in chamber 40 is forced through delivery valve 52 and out of prechamber injector 54 once the opening pressure of the injector is reached. When spool 36 contacts screw 61, the pressure in chamber 38 rises further to the opening pressure of main injector 56. The duration and amount of fuel flow to main injector 56 varies with the setting of movable sleeve 22 in pump 12. After leftward movement of spool 36 away from ignition trigger 58, the spark plug 53 in the prechamber of the engine is fired by the ignition system 11, thus igniting the pilot flow as it is injected through prechamber injector 54. The spark may be a single or series of sparks. Once shuttle spool 36 ends its leftward movement, pilot injector 54 closes with the assistance of delivery valve 52. As the injector pump piston 18 reaches the end of its stroke, pressure drops in chamber 38 and line 46, and main injector 56 closes. Spring 24 in injector pump 12 returns piston 18 to its next compression stroke while spring 41 returns shuttle spool 36 to its far right first position before the next pump delivery stroke. If it is desirable to vary the prechamber charge, a variable stop means 61' can be utilised, as shown in FIG. 2, which can be connected to or incorporate the power lever, or can be arranged to be adjusted in dependence upon some other related engine function. In a modified valving arrangement, valving port 44' can be moved to the left, as shown in FIG. 3, so that chamber 38 is closed to injector 56 until spool 36 moves leftward towards its second position. The shuttle spool 36 can be constructed in a stepped fashion 36', as shown in FIG. 4, so that the pressure in the prechamber or pilot circuit can be amplified above that in the main injector circuit if desired, so as to provide a wide range of pilot-to-main fuel injection pressure ratios. FIG. 5 illustrates the fuel injector line pressures and pump discharge pressures during crankshaft rotation or injection pump rotation. The flow changes 62 of the pilot delivery shown in FIG. 5, can be made by the previously described adjustable means 61, 61', whilst lower main injection pressures 64 can be achieved with the stepped spool 36' of FIG. 4.

Claims: A fuel injection system, for a stratified charge hybrid internal combustion engine, including: a main combustion chamber; a precombustion chamber connected with the main chamber, fuel injectors (56, 54) in the main combustion chamber and precombustion chamber which open at different pressure levels to sequentially inject fuel into the precombustion chamber and the main chamber; timed spark ignition means (53) in the precombustion chamber for ignition of the fuel-air mixture therein; an engine driven and timed fuel injection pump (12) having a variable output capacity that varies with variations in power level, the injection pump being supplied by a low pressure charging pump (26); a shuttle valve (30) including a bore therein, shuttle spool means (36) positioned within the bore defining a precombustion chamber supply chamber (40) on one side thereof and a spool actuation chamber (38) on the opposite side thereof, said spool means having a first and a second position; biasing means (41) urging the spool means (36) towards its first position with the spool actuation chamber (38) at its minimum volume; first conduit means (34) connecting fuel under charging pressure to the precombustion chamber supply chamber (40) in the first position of the spool means (36); second conduit means (32) connecting the pressure side of the injection pump (12) to the spool actuation chamber (38); third conduit means (46) connecting the spool actuation chamber (38) with the main injector (56); and fourth conduit means (48) connecting the precombustion chamber supply chamber (40) with the precombustion chamber injector (54); the arrangement being such that, in operation of the system, an initial charge from the injection pump (12) actuates the spool means (36) from its first to its second position, valving closed the first conduit means (34) and displacing the spool means (36) into the precombustion chamber supply chamber (40) until the spool means reaches its second position, thereby displacing the required amount of fuel to the precombustion chamber injector (54), whereupon the pressure of the fuel from the injection pump (12), flowing through the spool actuation chamber (38), rises to the opening level of the main injector (56); characterised by: electrical ignition trigger means (58) being provided in the shuttle valve (30) for triggering the ignition means (53) as the spool means (36) moves from its first position. A fuel injection system as claimed in claim 1, wherein the spool means (36) valves-closed a valving port (44') of the third conduit means (46) from the spool actuation chamber (38) in the first position of the spool means (36). A fuel injection system as claimed in claim 1 or 2, wherein the ignition trigger means (58) comprises an electrical contact positioned in the spool actuation chamber (38), and directly contacted by the spool means (36) in the first position of the spool, the contact, in turn, being electrically connected to the ignition means (53) of the engine whereby, when electrical contact is broken between the contact and the spool means, the ignition means is triggered. A fuel injection system as claimed in claim 3, wherein the contact (58) comprises an insulated electrical terminal (58) which acts as a stop for the spool means (36), the latter being urged against the terminal in contacting relation therewith by said biasing means (41) in the first position of the spool means (36). A fuel injection system as claimed in any preceding claim, including limit stop means (61, 61') in the precombustion chamber supply chamber (40) which determines the second position of the spool means (36), the stop means being adjustable to vary the extent of travel of the spool means (36), whereby the amount of fuel injected into the precombustion chamber can be varied. A fuel injection system as claimed in claim 5, wherein the limit stop means (61'), and therefore the second position of the spool means (36), is adjustable so that the amount of fuel injected into the precombustion chamber can be varied as a function of one or more power-related functions. A fuel injection system as claimed in claim 6, wherein the limit stop means (61') is adjustable as a function of the position of a power control lever of an engine.

Inventors: GONZALEZ CESAR, GONZALEZ, CESAR
Applicants: CESSNA AIRCRAFT CO, THE CESSNA AIRCRAFT COMPANY
Application year: 1991
Main classification: F02B19
IPC codes: F02B1, F02M59, F02M63, F02M45, F02B19