WO2004106724A1

WO2004106724A1 - Fuel injector

Info

Publication number: WO2004106724A1
Application number: PCT/SE2004/000821
Authority: WO
Inventors: Vesa Hokkanen
Original assignee: Scania Cv Ab (Publ)
Priority date: 2003-05-27
Filing date: 2004-05-27
Publication date: 2004-12-09
Also published as: SE525208C2; SE0301556L; SE0301556D0

Abstract

The invention relates to a fuel injector 8, a method for injection of fuel, and a combustion engine with a fuel injector 8. The fuel injector 8 comprises a connection 22 for pressurised fuel 12, an accumulator space 26 for fuel 12, and a nozzle needle 28 which intermittently blocks apertures 30,32 to a combustion chamber 18, while the injector 8 further comprises a piston 46 which is connected to the high-pressure space 26 via a duct 58 and is movable within a space 47 and which, when moved directly or indirectly under the influence of a control unit 67 before the beginning of an injection period, can assume a position such that pressurised fuel is supplied to the space 47, whereby the fuel column 73 from the connection 22 for pressurised fuel 12 is set in motion before injection takes place. The dynamic energy, i.e. the mass moment of inertia, in the fuel flow can thereby be used for the injection into the combustion chamber, making it possible to achieve a high injection pressure throughout the injection period.

Description

FUEL INJECTOR

Technical field

The present invention relates to a fuel injector for combustion engines, a method for injection of fuel, and a combustion engine comprising a fuel injector.

Background

Fuel injectors are used in combustion engines for introducing fuel into the latter's combustion chambers.

A conventional fuel injector for combustion engines usually comprises a high-pressure connection for fuel via which fuel under pressure is led to the injector and out from the latter partly via the injector's atomiser to the engine's combustion chamber and partly via a combined fuel return and nozzle needle guide duct. The injector is controlled by a control valve in the combined fuel return and nozzle needle guide duct being opened to enable fuel to flow out via the latter. This results in a decrease in the pressure at the end of the nozzle needle which is situated near to the combined fuel return and nozzle needle guide duct, and in the nozzle needle thereby being moved axially away from the combustion chamber so that pressurised fuel can flow into the combustion chamber. When the control valve closes, the pressure at said end of the nozzle needle increases, causing the nozzle needle to move axially towards the combustion chamber and shut off the flow of fuel.

As it is desired to inject a relatively large amount of fuel during a relatively short period of time in order to reduce fuel consumption and exhaust emissions, the greatest possible pressure and flow are desirable throughout the injection period. One problem with fuel injectors of the known kind mentioned above is that the injection pressure in them is lower at the beginning of the injection period than just before the end of the injection period, resulting in non-optimum fuel consumption and exhaust emissions. Brief description of the invention

The problem of the injection pressure being lower at the beginning of the injection period than just before the end of the injection period is solved according to the invention by a fuel injector according to the preamble of claim 1 being provided with the characteristics indicated in the characterising part of claim 1.

The fuel injector having the characteristics of claim 1 affords the advantage that the dynamic energy, i.e. the mass moment of inertia, in the fuel flow can be used for the injection into the combustion chamber, thereby making it possible to achieve a high injection pressure throughout the injection period. The fuel column is set in motion before the injection process begins, resulting in higher injection pressure and greater injection flow at the beginning of the injection period as compared with known systems.

The characteristics in the dependent claims afford the following further advantages:

- shorter needle opening time, since the mass of the control mechanism comprises only the nozzle needle, resulting in higher pressure and greater flow at the beginning and end of the injection period. - shorter reaction times than the reaction times of previous known systems, since the control system according to the invention works even with unrestricted flows.

- no fuel leakage flow past the needle guide between injection periods, with consequent reduction of the energy consumption of the high-pressure pump and the fuel cooling requirement.

Brief description of the drawings

The invention is explained in more detail below with reference to the attached drawings, in which : Figure 1 depicts schematically a fuel injection system for a combustion engine in a vehicle,

Figure 2 depicts schematically a previous known fuel injector in a state of rest,

Figure 3 depicts schematically a fuel injector according to the invention in a state of rest,

Figure 4 depicts schematically the fuel injector according to Figure 3 in a situation just before the beginning of an injection period, and

Figure 5 depicts schematically the fuel injector according to Figure 3 in a situation just after the beginning of an injection period.

Description of preferred embodiments

The same reference notations are used to denote items which are similar, albeit not identical, in the various drawings.

Figure 1 depicts schematically a fuel injection system 2 for a combustion engine, e.g. a diesel engine or a gasoline engine, in a vehicle. The fuel injection system 2 comprises a fuel tank 4, at least one high-pressure pump 6 connected to the fuel tank 4 by a low- pressure line 14, at least one injector 8 connected to the high-pressure pump 6 by a high-pressure pipe 16, and preferably also at least one pressure and volume accumulator 10 connected between the high-pressure pump 6 and the injector 8 in the form of, for example, a fuel rail, which accumulator has a fixed volume, i.e. the volume of the accumulator 10 does not vary.

The fuel injection system 2 functions as follows: fuel 12 is drawn by the high-pressure pump 6 via the low-pressure line 14 from the fuel tank 4 to the high-pressure pump 6 which pressurises the fuel 12 to the pressure level desired as system pressure, followed by the fuel 12 being led via the high-pressure pipe 16 either directly 18, or via 20 the accumulator 10, to the injector 8 and from the latter to the combustion chamber 18 of the combustion engine and also via the combined fuel return and nozzle needle guide duct 20 back to the fuel tank 4.

Preferably, only one high-pressure pump 6 is used for pressurising the fuel 12, followed by the fuel 12 being led to a single accumulator 10 from which one or more high-pressure pipes 16 lead the fuel 12 to one or more nozzles 8 which themselves lead into one or more combustion chambers 18, whereby the number of high-pressure pipes 16 leading from the accumulator 10 depends on the number of nozzles 8. It is also possible to arrange one high-pressure pump 6 for each nozzle 8, with or without intermediate accumulator 10. The accumulator 10 may be arranged in such a way that the high-pressure pipes 16 leading from the accumulator 10 are always pressurised or in such a way that the accumulator 10 applies, i.e. distributes, pressure to each of the high-pressure pipes 16 at the time when the respective associated injector 8 is intended to inject pressurised fuel 12 into the respective combustion chamber 18.

Figure 2 depicts schematically a previous known fuel injector in a state of rest. The injector 8 comprises a high-pressure connection 22 through which pressurised fuel 12 is led into the injector 8 from a high-pressure pipe 16. The fuel 12 is thereafter led partly via a duct 24 to a pressure and volume accumulator space 26 and from the latter to a combustion chamber 18 of the combustion engine via one or more apertures 30,32 which are intermittently blocked by a nozzle needle 28, and partly via a duct 34, a control space 36 and a combined fuel return and nozzle needle guide duct 20 back to the fuel tank 4. The accumulator space 26 has a fixed volume.

This prior known injector 8 is controlled by a control valve 38 in the combined fuel return and nozzle needle guide duct 20 being opened so that fuel 12 can flow out. This reduces the pressure at the end of the nozzle needle 28 which is situated near to the combined fuel return and nozzle needle guide duct 20, thereby causing the nozzle needle 28 to move axially away from the apertures 30,32 so that pressurised fuel 12 can flow into the combustion chamber 18 via the apertures 30,32. When the control valve 38 closes, the pressure at the end of the nozzle needle 28 which is situated near to the combined fuel return and nozzle needle guide duct 20 increases, whereupon a return spring 40 causes the nozzle needle 28 to move axially towards the apertures 30,32 and shut off the flow of fuel 12 by blocking said apertures 30,32. In previously known injectors 8 of this kind, the injection pressure is lower at the beginning of the injection period than just before the end of the injection period. The flow in the combined fuel return and nozzle needle guide duct 20, which depends on, for example, constrictions 42,44, is usually 15 to 20% of the flow through the apertures 30,32.

Figure 3 depicts schematically a fuel injector 8 according to the invention, i.e. an injector 8 whereby the fuel flow to and in the injector is in motion before the injection period begins. The injector 8 comprises a high-pressure connection 22 through which pressurised fuel 12 is led into the injector 8 from a high-pressure pipe 16. Thereafter the fuel 12 is led via a duct 24 to a high-pressure space 26 for fuel, e.g. a pressure and volume accumulator space and/or a high-pressure duct, and from there to a combustion chamber 18 of the combustion engine via one or more apertures 30,32 which are intermittently blocked by a nozzle needle 28.

The injector 8 also comprises, in addition to a nozzle needle 28, a piston 46 arranged in a space 47. The space 47 is connected to the high-pressure connection 22 via a duct 58, the accumulator space 26 and the duct 24. As the accumulator space 26 and one end 56 of the piston 46 (the end situated furthest away from the spring 54) are thus linked to the duct 58, a larger amount of fuel can flow into the injector 8 via the high- pressure connection 22 when the piston 46 moves downwards (according to the drawing), since part of the space 47 is thereby filled with pressurised fuel. Both the piston 46 and the nozzle needle 28 are held in their first end-positions 50,52 by a common spring 54. The space 60 between the nozzle needle 28 and the piston 46 (i.e. the space 60 which houses the spring 54) has running from it a duct 62 leading to a preferably free-standing three-way control valve 64, preferably a solenoid valve, which is operated by an electronic control unit 67, preferably via a magnetic coil 66. The electronic control unit 67 operates both the high-pressure pump 6 and the piston 46.

The injection process is described below with reference to Figures 4 and 5. Figure 4 depicts schematically the fuel injector 8 according to Figure 3 in a situation just before an injection period begins. The control unit 67 delivers an electrical pulse to the three-way control valve 64 which accordingly assumes a position whereby the space 60 between the nozzle needle 28 and the piston 46 is connected to the fuel return duct 20, thereby causing fuel situated in the space 60 to drain from the space 60 to the fuel tank 4. As the area of the upper side of the piston 46 which is exposed to pressurised fuel is greater than the area in the accumulator space 26 which pushes the nozzle needle upwards, the result is a pressure drop above the piston 46, thereby setting the latter in motion, i.e. moving it, towards its lower end-position as depicted in the drawing. As the fuel volume 71 in the portion 70 of the injector 8 which is being subjected to high pressure thereby increases, the fuel columns 72,73 in the high- pressure portion 70 are set in motion from the high-pressure pipe 16 and the connection 22 for pressurised fuel 12 to the first end of the piston 46 via the accumulator space 26. The whole fuel volume from the high-pressure pump 6 onwards is thereby set in motion. When the piston 46 reaches its lower end-position, the pressure in the space 60 between the nozzle needle 28 and the piston 46 drops quickly while at the same time a pressure pulse is caused by the pressure column 72 being forced to decelerate when the movement of the piston 46 ceases. The piston 46 thereby assumes a position such that pressurised fuel is supplied to the space 47, whereby the fuel column 73 from the connection 22 for pressurised fuel 12 is set in motion before injection takes place.

Figure 5 depicts schematically the fuel injector 8 according to Figure 3 in a situation just after the beginning of an injection period. When the movement of the piston 46 ceases and the pressure in the space 60 between the nozzle needle 28 and the piston 46 drops, the pressure prevailing in the accumulator space 26 causes the nozzle needle 28 to begin to move towards its upper end-position, as may be seen in the drawing, thereby opening the connection 30,32 to the combustion chamber, whereupon injection of fuel 12 to the combustion chamber 18 begins at a pressure corresponding to the pressure in the high-pressure pipe 16 plus the pressure pulse from the decelerated fuel column 72. The dynamic energy, i.e. the mass moment of inertia, of the fuel flow in all of the fuel both in the injector 8 and in the high-pressure pipe 16 can be used for the injection into the combustion chamber 18, making it possible to maintain a high average injection pressure during the whole injection period.

When the electrical pulse from the control unit 67 ceases, the three-way control valve 64 reverts to the position (see the position of the valve 64 depicted in Figure 3) whereby the space 60 between the nozzle needle 28 and the piston 46 is connected to the high-pressure portion of the injector 8. The space 60 is pressurised to at least the same pressure as in the accumulator space 26 for fuel 12, whereupon the spring force causes the nozzle needle 28 to revert to its lower end-position, followed by the piston 46 reverting to its upper end-position, i.e. the piston 46 remains in its lower end- position until the nozzle needle 28 reaches its lower end-position. The nozzle needle 28 thus closes the connection 30,32 to the combustion chamber 18, and the injection of fuel 12 to the combustion chamber 18 is shut off. The injection process is thus completed and the injector 8 has returned to the state of rest depicted in Figure 3.

Claims

1. A fuel injector comprising a connection (22) for pressurised fuel (12), a high- pressure space (26) for fuel (12), and a nozzle needle (28) which intermittently blocks apertures (30,32) to a combustion chamber (18), characterised in that the injector (8) further comprises a piston (46) which is connected to the high-pressure space (26) by a duct (58) and is movable within a space (47) and which, when moved directly or indirectly under the influence of a control unit (67) before the beginning of an injection period, can assume a position such that pressurised fuel is supplied to the space (47), whereby the fuel column (73) from the connection (22) for pressurised fuel (12) is set in motion before injection takes place.

2. A fuel injector according to claim 1, characterised in that the high-pressure space (26) for fuel (12) and the end (56) of the piston (46) which is situated furthest away from the nozzle needle (28) are linked to the duct (58).

3. A fuel injector according to any one of the foregoing claims, characterised in that a duct (62) runs from a space (60) between the nozzle needle (28) and the piston (46) to a three-way control valve (64) which is itself connected to a fuel return duct (20).

4. A fuel injector according to any one of the foregoing claims, characterised in that the piston (46) and the nozzle needle (28) are held in their first end-positions (50 and 52 respectively) by a common spring (54).

5. A fuel injector according to claim 4, characterised in that the spring (54) is housed in the space (60) between the nozzle needle (28) and the piston (46).

6. A method for injection of fuel to a combustion chamber (18) of a combustion engine using a fuel injector comprising a connection (22) for pressurised fuel (12), a high-pressure space (26) for fuel (12), and a nozzle needle (28) intermittently blocking apertures (30,32) to the combustion chamber (18), characterised by steps whereby: - draining of pressurised fuel out from a space (60) between the nozzle needle (28) and a movable piston (46) (the latter being connected to the high-pressure space (26) via a duct (58)) commences, whereupon the piston (46) is set in motion by a pressure drop which occurs above the piston (46), the fuel volume in the injector (8) increases and the fuel column (73) from the connection (22) for pressurised fuel (12) is set in motion,

- the movement of the piston (46) ceases, whereupon the nozzle needle (28) opens the connection (30,32) to the combustion chamber (18) because the pressure in the space (60) between the nozzle needle (28) and the piston (46) drops, whereupon the injection of fuel (12) to the combustion chamber (18) begins, and

- the space (60) between the nozzle needle (28) and the piston (46) becomes pressurised to at least the same pressure as in the high-pressure space (26) for fuel (12), whereupon the nozzle needle (28) closes the connection (30,32) to the combustion chamber (18) and the injection of fuel (12) to the combustion chamber (18) is shut off.

7. A method for injection of fuel according to claim 6, characterised in that pressurised fuel from the space (60) between the nozzle needle (28) and the movable piston (46) is drained out via a three-way control valve (64).

8. A method for injection of fuel according to claim 7, characterised in that the control valve (64) is controlled by an electronic control unit (67).

9. A combustion engine characterised in that it comprises a fuel injector according to any one of claims 1 to 5.