Electronically controlled fuel injection system

Abstract: The fuel injectors (4) of an internal combustion engine (2) are connected to a pump (10) by means of fuel supply lines (12) which open into the high-pressure part (34) of the injectors (4). The cross-sectional area of the fuel connection (12, 34) between the pump (10) and the injection orifices of the injectors (4) is substantially bigger than the total cross-sectional area of all of the injection orifices of an injector (4). An unrestricted flow path for the pressurized fuel is provided between the pump (10) and the area immediately upstream of the injection orifices. Due to the small pressurized volume of the system, the transient behaviour of the injection system is fast and can easily be matched to the needs of a particular engine application.

Description: Technical Field The present invention relates to an accumulator type fuel injection system for an internal combustion engine as defined in the pre-characterizing clause of claim 1. Background of the Prior Art A fuel injection system of this type is disclosed in DE-A-32 27 742 and corresponding US-A-4,566,416. This known injection system employs injectors provided with an accumulator volume or chamber with a volume substantially larger than the maximum volume of fuel injected during each injection event. This accumulator chamber is located in the injector body upstream of the seat of the injector needle valve. The injection orifices are located downstream of this seat. These orifices communicate with the combustion chamber of the related internal combustion engine. The fuel stored in the accumulator chamber under high pressure is partly discharged through the injection orifices during each injection event with a simultaneous pressure drop in the accumulator chamber. Each accumulator chamber communicates with the high pressure fuel supply line of the injection system by means of a restricted passage or orifice. The orifice, due to its small cross-sectional flow area, prevents the formation of noticeable pressure waves in the fuel supply lines during each injection event. Such pressure waves would highly affect the uniform fuel distribution in a multicylinder engine and the stability of the injection events of a single injector from cycle to cycle. To obtain good engine performance with respect to engine power, efficiency and emissions, a very uniform fuel distribution from cylinder to cylinder must be achieved in a multicylinder engine at each engine operating point. The same holds true for each injector from cycle to cycle. In addition to said orifice between each accumulator chamber and the fuel supply line, a plenum fuel chamber communicating with the fuel supply lines of all injectors of the injection system is provided in order to achieve the desired uniform fuel distribution. Due to its relatively large volume, the plenum chamber evens out the pressure pulsations created by the high pressure fuel supply pump and thus creates a constant pressure level for all injectors. However, this relatively large volume of the plenum chamber does not allow to rapidly increase and drop the fuel pressure in the plenum chamber. Therefore, a quick adjustment of the fuel injection pressure to the varying engine operating conditions, in particular during transient speed and load conditions, is not possible. DE-A-26 47 744 discloses a fuel injection system which is provided with a pressure accumulator arranged downstream of a high pressure pump. A pressure relief valve keeps the pressure in the system constant for all operating conditions of the engine. In the fuel injection system as disclosed in US-A-4,258,674 the injection pressure in the injection lines is caused to drop during two subsequent strokes of the fuel pump and is built up to the actual fuel injection pressure only shortly before the beginning of an injection event. Summary of the Invention It is now the object of the present invention to provide an improved fuel injection system as defined in the precharacterizing part of new claim 1 in which the fuel injection pressure can be rapidly adjusted to the varying engine operating conditions, while maintaining a uniform fuel distribution at each engine operating point. According to the present invention this object is accomplished by the features mentioned in the characterizing part of claim 1. According to the present invention it is therefore possible to largely reduce the total high pressure volume of the injection system (by over an order of magnitude) compared to the prior art systems referred to earlier. This allows to rapidly adjust the injection pressure to the varying driver demands and thus to achieve a fast response during transient operation of the engine. This makes the injection system also suitable for use in passenger car engines without the need of an overdimensioned fuel injection pump or of a complex control scheme taking care of the transient engine operating conditions. These and further advantages of the invention will be readily apparent from the following detailed description of preferred embodiments of the present invention shown in the accompanying drawing. Brief Description of the Drawings Fig. 1 is a schematic view of an electronically controlled injection system in accordance with the present invention; Fig. 2 is an enlarged fragmentary axial sectional view of an embodiment of an injector used in the injection system in accordance with the present invention, showing the design of the injector needle piston; and Fig. 3 is a schematic view of an alternate embodiment of the electronically controlled injection system shown in Fig. 1; and Detailed Description of the Preferred Embodiments Turning to the figures wherein like numerals are employed for identifying like parts, the disclosed electronically controlled fuel injection system is employed in a four cylinder engine 2. On the upper part of the engine 2 there are placed four electronically controlled injectors 4 to inject pressurized fuel into the combustion chamber (not shown) of the engine 2. The fuel comes from a fuel tank 6 and reaches through a low pressure pipe 6a a fuel filter 8 and, through another low pressure pipe 9, a high pressure pump 10. The drive shaft 5 of pump 10, which can be a one- or multicylinder pump, depending on the specific application, is driven by a shaft 3 of the engine 2 with a constant drive ratio, for example by means of a gear or a tooth-belt 11. As an important matter, the motion of the plunger or plungers of pump 10 shall be harmonic and each pumping event shall take place over a large angle of rotation of the pump drive shaft 5 and thus also of the engine crankshaft 7. Preferably, the maximum fuel delivery of the pump 10 per revolution of the engine crankshaft 7 shall be substantially equal to the maximum fuel quantity delivered to the engine and spilled back to the tank by the totality of the injectors 4 of the injection system in one revolution of the engine crankshaft 7. Furthermore the number of pumping strokes taking place shall be the same or an entire multiple of the number of injecticn events. In the case of the embodiment of Fig. 1, and where the engine 2 is a four cycle engine, two combustion events and thus two injection events take place during each revolution of the engine crankshaft 7. In this case one could use a two-plunger pump 10 driven by the engine 2 with a drive ratio of 1:1 in order to obtain the same number of pumping strokes and injection events. Each pumping event would then take place during an 180 degrees rotation of crankshaft 7. Since the pumping event takes place over a wide angle of rotation of the crank shaft 7 and the injection event is of a relatively short duration, there is no relationship between the momentary pumping rate of any of the pumping plungers of pump 10 and the injection rate of any of the injectors 4. Nevertheless, it is preferred that the injection event of each of the injectors 4 of the injection system takes place during the pumping stroke of any one of the pumping plungers of the pump 10. For the same four cylinder engine 2 as shown in Fig. 1, one could also use a single-plunger pump 10 driven by the engine 2 with a drive ratio between pump shaft 5 and crankshaft 7 of 2:1. Also a single-plunger pump 10 driven with a 1:1 drive ratio but with a construction providing two strokes of the plunger per revolution of the pump shaft 5 could be employed. The outlet of pump 10 is connected to a plurality of high pressure lines 12 wich belong to the high pressure section of the injection system. The fuel delivered by the pump 10 to this high pressure section of the injection system and to the high pressure lines 12 can be regulated, depending on the engine operating conditions, within the pump 10 in a manner known from already employed in-line or distributor type fuel injection pumps. As shown in the drawings, this regulating process is taken care of by an electronic control unit 20 and appropriate actuators 21 (not shown in detail) placed within the housing of the pump 10 and connected to the control unit 20 by means of an electrical connection 19. The control unit 20 also operates the solenoid 74 of each injector 4. The main input signals to the control unit 20 are the crankshaft angle position sensed by a pick-up sensor 22 and the position of the throttle pedal 24. Further input signals 26 such as engine coolant temperature, intake air or boost pressure etc. can be fed to the control unit 20 as well. The control unit 20 is powered by a battery 28. The control unit 20 comprises a one-chip microprocessor and the required input and output power modules. The desired relationships between the input signals and the output signals to the injector solenoids 74 and to the actuator 21 of the pump 10 are programmed into the microprocessor. The required data needed to determine the momentary value of the output signals as a function of the momentary input signals are stored in the microprocessor memory. The microprocessor can also be used to perform troubleshooting diagnostics of the combined engine and fuel-injection systems. The high pressure section of the injection system of Fig. 1 consists of the high pressure pipes 12 and the high pressure section 34 of each injector 4. From each injector 4 a low pressure spill pipe 38 and a low pressure pipe 40 connecting all pipes 38 returns low pressure fuel released form each injector 4 back to the fuel tank 6. The design of the high pressure section 34 of each injector 4 will be discussed later in connection with Fig. 2. It is important to note at this point that each high pressure pipe 12 provides for a direct flow path without any restriction from the high pressure pump 10 to each injector 4. As shown in the detail A of one of the injectors 4, a direct and unrestricted hydraulic connection is made between the outlet side of the high pressure pump 10 to the region around the seat of the injector needle valve in the tip of each injector 4 by means of the high pressure pipes 12 and the high pressure section 34 of the injector 4. With the above-mentioned layout of the high pressure section of the injection system of Fig. 1 consisting of high pressure pipes 12 and of one high pressure section 34 in each injector 4 it is possible to eliminate any fuel plenum chambers as well as an accumulator volume placed within the injector's body as described in DE-A-37 27 742 (corresponding to US-A-4,566,416) and DE-A-31 26 393. The essential features of the fuel injection system of the present invention are as follows: the entire fuel volume enclosed under high pressure in the lines 12 and sections 34 of each injector 4 hydraulically communicates within this high pressure section in an unhindered, unrestricted way, the cross sectional areas of all high pressure passages leading from the outlet of the pump 10 to the region around the seat of the injectors 4 of the injection system is substantially bigger preferably at least 10 times bigger than the combined cross sectional area of all injection orifices of one injector 4, during engine operation the entire high pressure section is permanently pressurized to a pressure substantially equal to the injection pressure suitable at given engine running conditions. The reduction of the total high pressure volume of the injection system (by over an order of magnitude) compared to the prior art systems referred to earlier allows to achieve a fast response during transient operation of the engine 2, which allows to employ the injection system also for example for passenger car engines without the need of an overdimensioned pump 10 or of a complex control scheme taking care of the transient engine operating conditions. However, due to pressure waves arising in a system as just described, an injector design insensitive to pressure waves must be used in conjunction with this system in order to maintain the desired uniformity of fuel delivery of the injectors 4. A preferred design of such an injector 4 is shown in Fig. 2. If the injection system of the present invention is used in an engine with a wide speed range, such as a passenger car engine, it is important that each pumping event takes place over a large angle of rotation of the engine crankshaft 7. In the discussed arrangement of Fig. 1 with a two plunger pump, driven by the engine with a drive ratio of 1:1, each pumping event takes place over 180 degrees of rotation of the crankshaft 7. The slow, harmonic pumping motion makes it possible to avoid high pressure peaks at a high engine speed, which would be detrimental to the mechanical durability of the components of the injection system. At the same time, due to the fact that there is no relationship between the momentary pumping rate of the pumping plungers and the injection rate of any of the injectors 4, the injection pressure can be maintained at a high level when the engine speed is slow. Both attributes allow to optimise the engine performance with respect to power, noise and emissions. It is furthermore important that, as shown in Fig. 1, the injection system's high pressure section is built in such a way that it is symmetrical with respect to the arrangement of the fuel lines 12. Accordingly, the time for a pressure wave to travel from anyone of the injectors 4 to the outlet side of the pump 10 or vice-versa will be the same for all injectors 4 employed. In an alternate arrangement of the injection system according to the present invention (not shown in Fig. 1), each injector 4 is connected by fuel lines 12 of equal length directly to the housing of the pump 10. In this case a hydraulic connection between the fuel lines 12 would also be provided within the housing of the pump 10. Fig. 2 shows the main portion of an injector 4 of preferred design, which can be employed advantageously in conjunction with the injection system of Fig. 1. The pressurized fuel coming from one of the high pressure lines 12 shown in Fig. 1 enters the injector 4 through bore 42, which is machined into the housing 44 of the injector 4. The bore 42 is connected to a bore 54 which extends downwards in axial direction to the needle valve seat 56. An injector needle valve 52 is arranged within the bore 54 and extends downwards into the injector neck 55 and to the needle valve seat 56. As shown in Fig. 2 the tip of the needle valve 52 is engaged with the valve seat 56 and closes the injection orifices 58, thus preventing pressurized fuel to be injected from the bore 54 through the seat 56 and the injection orifices 58 into the combustion chamber of the related internal combustion engine (not shown). As already mentioned, the cross-sections of the flow passages from bore 42 to the valve seat 56 are big compared to the total cross-sectional flow area of all injection orifices 58. The needle valve 52 can be momentarily shifted axially in order to open the injection orifices 58 and to allow injection of a desired quantity of fuel. On the end opposite to its tip, the injector needle valve 52 is provided with a needle valve piston 60 with two sections of different outer diameters. The outer diameter of the lower section 63 is tightly matched to the inner diameter of a guide-piece 62. The latter has an enlarged portion which, together with a sealing ring 64, is pressed against a shoulder 44a of the injector housing 44 by an internal hexagon-screw 66, thus sealing the high pressure section of the injector 4. The outer diameter of the upper section 69 of the needle valve piston 60 is larger than the outer diameter of the lower section 63. The needle valve piston 60 with its two sections 63, 69 of different outer diameters is firmly connected to the injector needle valve 52, either because it is made of one piece with the injector needle valve 52 as shown on Fig. 2, or by firmly connecting the two parts 52, 60 to one another, for example by press-fitting or by welding the parts together. A bore 65 machined in the inner part of the needle valve piston 60 is connected at one end to the bore 54 of the injector 4. The other end of bore 65 is connected to a restricted orifice 67 with a substantially smaller flow cross-sectional area compared to the cross-sectional area of bore 65. The other end of the orifice 67 extends through the upper end surface 69a of the thicker section 69 of the needle valve piston 60. The outer diameter of the thicker section 69 is tightly matched to the inner bore 71a of a cylindrical piece 71 which is closed at one end and provided with an orifice 70 opening into a chamber or space 72. The latter is defined by the piece 71 and by the thicker section 69 of the needle valve piston 60. Both orifices 67 and 70 are axially aligned and extend along the longitudinal axis 4a of the injector 4. A solenoid valve S is provided having a solenoid 74 which actuates a valve stem 76. As shown in Fig. 2, the valve stem 76 is closing the outlet of the orifice 70, thus preventing fuel to flow through the orifice 70 into the neighbouring low pressure region 78 which is connected the return line 38 (see also in Fig. 1). The piece 71 will be pushed by the fuel pressure in the chamber 72 against a flat surface 79a of a support 79, which determines the axial position of the piece 71 and at the same time guides the valve stem 76. As an important matter, the piece 71 is guided in a tight fit relationship at an inner surface 71a only by the thicker section 69 of the needle valve piston 60. The outer surface 71b of the piece 71 is not guided. This allows a substantially seal-tight, leak-free design and an unhindered axial motion of the injector needle valve 52 during the injection event. If the piece 71 had to be guided also at its outer surface 71b, due to the tight fits needed for reasons of fluid seal tightness, jammming of the neddle valve piston 60 or at least undesired high frictional forces could occur in case the tight fits needed for a tight seal are not perfectly concentrical to one another. The mode of operation of the injector 4 is as follows: When at a desired point in time the solenoid 74 is energized by an electric pulse of a predetermined duration coming from the control unit 20, the valve stem 76 is retracted from its seat and the outlet of the orifice 70 is opened. The pressure in the chamber 72 will abruptly drop, due to the formation of a single fuel jet in the two aligned orifices 67 and 70. The fuel pressure acting on the underside 63a of the lower section 63 of the injector needle valve piston 60 can now shift the needle valve 52 in its opened position and the injection event begins by discharging fuel through the injection orifices 58. The release of fuel results in a negative pressure wave which propagates from the injector 4 into the high pressure section of the injection system of Fig. 1. If the electric pulse to the solenoid 74 is interrupted, the solenoid valve 76 is shifted back to its seat at the outlet of the orifice 70 by the spring 78. The pressure in the space 72 will abruptly rise. Since the upper surface 69a of the upper, thicker section 69 is greater than the lower surface 63a of the lower, thinner section 63 of the needle valve piston 60, a force to quickly reseat the injector needle valve 52 and thus terminate the injection event results, even if the fuel pressure in the bore 54 is equal to the pressure in the space 72. Even a pressure wave in the system does not noticeably disturb the closing of the injector needle valve. This is not the case in the solution disclosed in DE-A-32 27 742 where the injector needle valve piston is of a uniform outer diameter. In this case, a pressure wave acting on the underside of the needle valve piston would drastically affect the closing behaviour of the injector needle valve and thus the uniformity of fuel delivery. For this reason an accumulator chamber within the injector housing and an orifice between this accumulator and the fuel supply line had to be provided in this prior art system to ensure a repeatable closing behaviour of the injector needle valve. The mentioned pressure waves have an influence on the shape of the injection rate during the injection event. To make sure that all injectors of a multicylinder engine do have the same performance it is preferable to build the high pressure section of the injection system of Fig. 1 symmetrically. In an alternative layout of the fuel injection system according to the present invention shown in Fig. 3, the electronic control unit 20 controls an electrically driven high-to-low pressure spill valve 80. The electrical connection 19 and the actuator 21 within the housing of the pump 10 in the embodiment of Fig. 1 can be eliminated. In this case the high pressure pump 10 will have a constant fuel delivery per revolution of the pump shaft 5, which will be entirely pumped into the high pressure lines 12 (except for some leakage of the pump 10). The spill valve 80 is of the on/off type valve, timed by the control unit 20 in a suitable way to release the excess fuel delivered by the pump 10 in a return line 30 and establish the desired pressure in the lines 12 according to the operating conditions of the engine 2. An electrical connection 82 connects the control unit 20 with the electrically driven on/off spill valve 80. The valve 80 could also be a very sensitive adjustable pressure regulator valve capable to even out to some extent any undesired pressure pulsations generated by the fuel pump 10 or induced by the injectors 4. The power demand of the pump 10 for part-load running conditions of engine 2 will in this case be somewhat higher compared to the design of Fig. 1, since fuel in excess must be pressurized. However, the layout of Fig. 3 allows to achieve another advantage as explained below. If the spill valve 80 is an electrically driven on/off valve, when it is switched on by means of an electric signal of the control unit 20 fuel will flow in the line section 12a from the pump 10 to the valve 80. When the valve 80 is switched off, the moving fuel column in line 12a will be stopped and a positive dynamic pressure wave will propagate upstream of the valve 80 into the line 12a as well as into the remaining lines 12 leading to the injectors. After a given travel time this positive dynamic pressure wave will reach the seat 56 (see also Fig. 2) of one or more injectors 4. By timing the off-signal of the valve 80 appropriately by means of the control unit 20 in such a way that the positive dynamic pressure wave arrives at an injector 4 when the injection event begins, it is possible to obtain a higher effective injection pressure (in the range of 20 to 30%) compared to the static pressure without the positive dynamic pressure wave. This allows to increase the effective injection pressure at full load engine running conditions, when a high injection pressure is required. Also, since in this case the pump 10 must generate a lower pressure, less mechanical input power at shaft 5 is required. Since the timing of the off-signal of the valve 80 is determined by the electronic control unit 20, it can be governed flexibly to obtain the desired effect for all injectors 4 employed in the injection system as well as, if needed, at different engine running speeds and load conditions. It has to be noted that the essential criteria of the injection system of the present invention, as explained earlier while describing Fig. 1, must still apply in order to obtain the benefit of the advantage of said positive dynamic pressure wave.

Claims: Accumulator type fuel injection system for an internal combustion engine (2) a) comprising a plurality of electromagnetically operated fuel injectors (4) for intermittently injecting pressurized fuel into the combustion chamber of the internal combustion engine (2), b) each of said fuel injectors (4) having a body portion (44) with a valve seat (56), at least one discharge orifice (58) and an elongated injector valve member (52) mounted within said body portion (44) for engagement with said valve seat (56) for closing the discharge orifice (58), said injector valve member (52) being momentarily shiftable in its axial direction to be lifted from said valve seat (56) for opening the discharge orifice (58), c) further comprising a high pressure fuel pump (10) common to all injectors (4) and driven by the internal combustion engine (2) and delivering fuel to a fuel flow path (12, 42) at a substantially uniform pressure level which is adjustable according to the engine operating conditions, d) said fuel flow path (12, 42) leading from the outlet side of said pump (10) to a region (54) immediately upstream of said valve seat (56) of each fuel injector (4), and forming a volume of permanently pressurized fuel common to all injectors (4) and being constituted by fuel lines (12) connecting the outlet side of said high pressure pump (10) with passages (42) in the injectors (4) leading to the regions (54) immediately upstream of said valve seat (54), e) said fuel injectors (4) being provided with a control chamber (72) connectable with said fuel flow path (12, 42), the fuel pressure in said control chamber (72) acting upon said injector valve member (52) forcing the latter against said valve seat (56), and being further provided with control means (67, 74, 76) controlling a low pressure outlet (70) of said control chamber (72) to quickly reduce the fuel pressure in said control chamber (72) to allow for the momentary axial movement of said injector valve member (52) in its opening direction by the fuel pressure acting upon said injector valve member (52) and for quickly restoring the fuel pressure in said control chamber (72) for moving said injector valve member (52) in its closing direction, characterised in that f) said common volume of permanently pressurized fuel is solely constituted by said fuel flow path (12, 42) g) said fuel flow path (12, 42) is designed in such a manner that the cross-sectional area of said fuel flow path (12, 42) is substantially larger than the total cross-sectional area of all injection orifices (58) of one of the fuel injectors (4), that said fuel flow path (12, 42) is substantially free of flow restrictions which would result in substantial pressure drops compared with the fuel pressure level and allows a substantially unhindered fuel communication between the outlet side of said pump (10) and said region (54) around and immediately upstream of said valve seat (56), and that the total volume of permanently pressurized fuel in said fuel flow path (12, 42) is at one hand so small that a rapid change of the adjustable fuel pressure level in said fuel flow path (12, 42) during transient operation of the internal combustion engine (2) is achieved, and on the other hand big enough to ensure that the fuel pressure in said fuel flow path (12, 42) before, during , and after an injection event, as well as in the time interval between any two subsequent injection events is substantially equal to the demanded fuel injection pressure at a given running condition, h) the high pressure section formed by said fuel lines (12) and the high pressure section (34) of each injector (4) is built in such a way that the effects of pressure waves generated in the high pressure section during every injection event are the same for all injectors (4). Fuel injection system according to claim 1, wherein said injector valve member (52) is provided with a first surface (69a) subject to the fuel pressure in said control chamber (72) and a second surface (63a) upon which the pressure of the fuel in said fuel flow path (12, 14, 42) acts, the area of said first surface (69a) being greater than the area of said second surface (63a). Fuel injection system according to claim 1; wherein the frequency of the pumping strokes of said fuel pressure pump (10) is the same or an entire mutiple of the frequency of the injection events of the totality of the injectors (4). Fuel injection system according to claim 1, wherein said fuel pump (10) is provided with a drive shaft (5) driven by the crankshaft (7) of the internal combustion engine (2), the drive ratio between said crankshaft (7) and said drive shaft (5) being 1:1 or an entire multiple of 1:1. Fuel injection system according to claim 1, wherein said fuel pump (10) comprises pumping plungers, said pumping plungers are movable according to a harmonic function. Fuel injection system according to claim 5, wherein anyone of the injection events takes places during part of a pumping stroke of anyone of said pumping plungers. Fuel injection system according to claim 1, further comprising an electrically operated spill valve (80) connected to said high pressure injection line (12, 42) and a low pressure return line (30), and a control unit (20) for controlling the opening and closing of said spill valve (80) for spilling fuel delivered by said fuel pump (10) into said return line (30) in order to adjust the quantity of fuel delivered by said pump (10) to said injectors (4). Fuel injection system according to claim 7, wherein said fuel pump (10) delivers a constant amount of fuel per pumping stroke. Fuel injection system according to the claim 7; wherein the timing for the signal to close the spill valve (80) is choosen by the control unit (20) in such a way that the pressure wave induced in said injection line (12, 42) by closing said spill valve (80) reaches the region (54) immediately around and upstream of said valve seat (56) of an injector (4) immediately before orduring the momentary opening of said discharge orifice (58) of said injector (4). Fuel injection system according to claim 1, comprising at least four fuel injectors (4) arranged in groups of at least two fuel injectors (4), the injectors (4) of each group being connected to one another by means of fuel connection lines (12) providing an unrestricted fuel flow path, the injectors (4) of each group being further connected to a common fuel supply line (12, 12a) connected to the outlet side of said fuel pump (10). Fuel injection system according to claim 1, wherein the length of the fuel flow path from the outlet side of said fuel pump (10) to said region (54) immediately upstream of said valve seat (56) is the same for all of said fuel injectors (4).

Inventors: GANSER MARCO ALFREDO, GANSER, MARCO ALFREDO
Applicants: GANSER HYDROMAG, GANSER-HYDROMAG
Application year: 1987
Main classification: F02M63
IPC codes: F02M65, F02M47, F02M55, F02M63, F02M59, F02M51