EP3265668B1

EP3265668B1 - A fuel injection unit for an internal combustion engine

Info

Publication number: EP3265668B1
Application number: EP15710221.1A
Authority: EP
Inventors: Janne ENLUND; Antti VUOHIJOKI
Original assignee: Wartsila Finland Oy
Current assignee: Wartsila Finland Oy
Priority date: 2015-03-06
Filing date: 2015-03-06
Publication date: 2018-12-19
Anticipated expiration: 2035-03-06
Also published as: CN107110102B; CN107110102A; EP3265668A1; WO2016142570A1; KR20170102534A; KR101999908B1

Description

Technical field

The present invention relates to a fuel injection unit for an internal combustion engine having a plurality of cylinders and using a common rail fuel system in accordance with the preamble of claim 1. The present invention relates also to an internal combustion engine having a plurality of cylinders with cylinder heads and utilizing a common rail fuel system, each cylinder head being provided with the fuel injection unit in accordance with any one of claims 1-11.

Background art

In modern internal combustion engines fuel is injected by means of a fuel injection valve or an injector directly into the cylinders of an engine. Since the injection occurs at a relatively late phase at the end part of the compression stroke, a sufficiently high pressure is required for the injection. In a conventional fuel feeding system, each cylinder is provided with an injection pump of its own for pumping fuel through an injector into the combustion chamber of the cylinder. However, the use and control of the conventional system has significant limitations. The settings of the system cannot be adjusted easily. Additionally, the pressure in the injection pumps may vary, so that the injection into the different cylinders may take place under different pressures and may thus provide different amounts of fuel, respectively. Also, since the injection nozzles of prior art have been predominantly hydromechanical, i.e. opening at a certain predetermined fuel pressure and closing when the pressure decreases below the predetermined value, the control of the injection timing and duration should be able to take into account the wearing of the system components also during the use of the system, i.e. when the engine is running.
A more recent solution is the so called "common rail injection" or "common pressure injection", in which the provision of pressure and the injection of fuel are functionally separated from each other. Fuel is fed by means of at least one high pressure fuel pump into a common pressure supply, i.e. rail, from which it is led through separate pipes into the injector of each cylinder. In practice, the operation of an injector is electronically controlled, for instance by means of a solenoid or piezoelectric control valve, in order to obtain a sufficiently short and precise injection.
A number of the most obvious problem areas of traditional fuel feeding systems have been solved by the use of a high pressure (up to about 2200 bar) common fuel supply, and electronically controlled fuel injectors by means of which it is, for instance, possible to inject fuel into an engine cylinder several times during the same compression stroke. In other words, the timing of the injection, the duration of the injection and the quantity of injected fuel is in clearly better control than with the fuel injection pumps of prior art, whereby also the emission levels in normal operating conditions of an internal combustion engine have been drastically reduced.
The operation of the fuel injectors is nowadays controlled by an electronic control valve that is arranged in flow communication with the nozzle. The control valve and the nozzle function such that a full fuel rail pressure is provided in the cavity around the needle, i.e. in the needle cavity, the pressure tending to open the needle of the nozzle. However, the needle is provided with a spring that pushes the needle against its seat surface upstream of the injection nozzle openings. Furthermore, in connection with the end of the needle opposite to the nozzle openings a so-called needle control volume is arranged such that the pressure in the needle control volume pushes the needle in the same direction as the spring. The needle control volume and the needle cavity are arranged in flow communication with each other via one or mode well dimensioned openings or flow channels that restrict the flow between the two cavities, i.e. restrict the speed the pressure is able to raise in the needle control volume. The actual control of the needle takes place by opening the control valve electronically, whereby the pressurized fuel in the needle control volume is able to escape through the control valve to the low pressure fuel drain such that the full fuel pressure affects to the injector needle and lifts it off its seat surface opening the injection nozzle, and the injection starts. After a desired period of time the fuel injection is supposed to take, the control valve is closed, and the pressure in the needle control volume is raised, whereby the needle control volume pressure together with the spring closes the nozzle, i.e. pushes the needle against it seat.
This far the diesel engines have been optimized in view of their emissions at full load. However, the future emission legislation requires that the emission levels have to be minimized at all operating conditions. In other words, all loads spectrum tuning has to be performed. For instance, a case where even the use of modern common rail fuel system and electronic control of a fuel injector do not bring desired results relates to running an engine in low load, or, more generally, substantially far from its design load. The ultimate goal is to improve the injection of fuel such that the emissions of an engine throughout its operating conditions i.e. from low load to full load could be kept on minimal level.
This endeavour has led to the use of injection valves or injectors having two injection nozzles. For instance, US-B2-7,556,017 discusses a fuel injector having an injector body defining a hollow interior configured to receive pressurized fuel, a first nozzle configured for providing a first fuel spray pattern, and a second nozzle configured for providing a second fuel spray pattern different from the first fuel spray pattern. The first and second nozzles may be configured to inject fuel supplied from a common source into a combustion space. The nozzles may be used in separate stages during the compression stroke of piston such that the first nozzle injects a predetermined amount of fuel in an early stage of the compression stroke, and the second nozzle at a later stage or at the end of the compression stroke. The first nozzle is often called a pilot nozzle and the second one a main nozzle.
Prior art knows a device called a flow fuse or a flow-limiting valve that is arranged in communication with fuel injectors to take care of situations where the injector needle gets stuck in such a position that fuel is able to bleed in the cylinder. The flow fuse functions by detecting changes in fuel pressure and it affects the flow in case of abnormal pressure drop conditions. For example, if the injector needle is leaking the pressure after the flow fuse drops, whereby the flow fuse stops feeding fuel to the injector. The flow fuse is designed and dimensioned to allow an injection quantity corresponding to requirements set for the fuel quantity by the cylinder at full load, naturally with some margin, before shutting down the injector.
Such a flow fuse is for example disclosed in the document EP 2 646 674 A1 .
However, using the flow fuses in connection with an injector with two nozzles, i.e. pilot and main nozzles, sharing the same fuel volume is tricky. If a single flow fuse is arranged in the fuel line introducing pressurized fuel to the injector, it has to be, naturally, dimensioned for the main nozzle or needle. In other words, if the main needle fails, i.e. is stuck open, the flow fuse shuts down the oil introduction into the fuel volume shared by the both nozzles. However, as the injection quantity of the main needle, for which the flow fuse is dimensioned, is normally tens of times larger than that of the pilot needle, the failing of the pilot needle, for any reason, does not affect the operation of the flow fuse. In other words, as the injection quantity of the pilot needle is so small, the flow fuse is not able to detect the small variations the leaking pilot needle causes in the fuel pressure. As a result fuel may flow in the fuel volume and be injected from the nozzle openings to the engine cylinder without interruption.
The pilot needle may be leaking for two separate reasons. Firstly, the needle of the pilot nozzle may get stuck open, or secondly, the control valve may fail. The latter problem is now taken into closer consideration, as the prior art has not discussed that the control valve may also be a component that may fail. In other words, the pin of the control valve may not, for some reason, return on its seat after the time period the fuel injection via the pilot needle is supposed to take, but the control valve remains open and allows the fuel to drain into the low pressure fuel line through the control valve. In practice such a fuel drain means that the pressure, which would be normally raised in the needle control volume if the control valve is closed, is not raised, whereby the pilot needle remains open and fuel continues to be injected into the cylinder.

Brief summary of the Invention

An object of the present invention is to solve the above discussed problem.
Another object of the present invention is to increase safety in the common rail fuel-injection system.
A further object of the present invention is to prevent excessive fuel injection to an engine cylinder.
A still further object of the present invention is to reduce emissions created by the internal combustion engine.
At least an object of the invention is met by a fuel injection unit as defined in claim 1.
At least one object of the invention is met by the large internal combustion engine having a plurality of cylinders with cylinder heads and utilizing a common rail fuel system, wherein each cylinder head is provided with a fuel injection unit in accordance with any one of claims 1 - 10.
Other characteristic features of the fuel injection unit of the present invention will become apparent from the appended dependent claims.
The present invention, when solving at least one of the above-mentioned problems, also brings about, in case of control pin failure, a number of advantages, of which a few has been listed in the following:

Eliminates the risk of too high a cylinder pressure caused by excessive fuel injection,
Reduces emissions,
Reduces the amount of circulated fluid, and
Reduces the energy needed for pressurizing the fuel.

Brief Description of the Drawings

In the following, the fuel injection unit of the present invention is explained in more detail in reference to the accompanying Figures, of which

Figure 1 illustrates schematically a cross sectional view of the fuel injection unit in accordance with a preferred embodiment of the present invention, and
Figure 2 illustrates schematically a detail of the fuel feeding arrangement of Figure 1 in an enlarged scale.

Detailed Description of Drawings

Figure 1 illustrates schematically a cross sectional view of the fuel injection unit of the present invention. The fuel injection unit 10 comprises a fuel accumulator 12 receiving fuel at a desired pressure from a common rail (not shown), a main flow fuse 14, a first control valve 16, a second control valve 18, and a fuel injector 20. The fuel injector 20 comprises a first or pilot nozzle 22 with a first needle 24 and a second or main nozzle 26 with a second needle 28. The first and the second nozzles 22, 26 have a common needle cavity 30. Both nozzles have seat surfaces and nozzle openings at an end of the injection unit 10 facing the engine cylinder. The ends of the needles, i.e. the first ends thereof, facing the engine cylinder rest against the seat surfaces closing the flow communication from the needle cavity 30 to the nozzle openings 32. At the opposite end, i.e. the end facing away from the engine cylinder or the second end, of the first needle 24 there is a first needle control volume 34, and at the upper end, i.e. the end facing away from the engine cylinder or the second end, of the second needle 28 there is a second needle control volume 36. The needle control volumes 34 and 36 are arranged in flow communication with the common needle cavity 30 via first restricted flow passages 38 and 40, respectively. The first and the second needles 26 and 28 are maintained in their closed position, i.e. pressed on their seat surfaces at a first end of the needles facing the cylinder of the engine, by means of the springs 42 and 44 and the fuel pressure acting in the needle control volumes 34 and 36. What has been this far described is a prior art fuel injection unit.
For describing how a prior art fuel injection unit works the first nozzle 22 is taken as an example. The starting point is that the full fuel rail pressure is present in the accumulator 12 and in the needle cavity 30 acting on all surfaces of the first needle 26 including the surfaces, when subjected to the fuel pressure, tending to lift the first needle 28 off its seat surface. However, as the first control valve 16 is closed the same rail pressure affects in the first needle control volume 34, too, whereby the fuel pressure in the needle control volume 34 and the force of the compressed spring 42 are able to keep the first needle 26 against its seat surface, whereby the first nozzle 22 is closed. Now that the electronic control unit of the engine instructs the first control valve 16 to open a direct flow path for pressurized fuel from the first needle control volume 34 to the low pressure fuel outlet drain 46 is formed via the flow passage 48 between the first needle control volume 34 and the first control valve 16. Simultaneously, the pressure in the first needle control volume 34 drops and since the spring 42 is not alone capable of keeping the first needle 26 against its seat surface, the full fuel pressure lifts the first needle 26 off its seat surface and a high pressure fuel jet is sprayed into the cylinder via the first nozzle 22. Next the electronic control unit of the engine instructs the first control valve 16 to close and thereby also to close the direct flow path from the needle control volume 34 to the low pressure fuel outlet drain 46. Simultaneously, the pressure in the needle control volume 34 starts to raise, whereby the pressure together with the spring 42 are capable of pushing the first needle 26 against its seat surface to cease the spraying action. The function of the second nozzle 24 is exactly the same.
However, the above discussed injector unit, and especially its first nozzle 22 has a weakness, and it is the first control valve 16. If the control valve 16 fails, i.e. it is not able to close the direct flow path for pressurized fuel from the first needle control volume 34 to the low pressure fuel outlet drain 46, the pressure in the first needle control volume 34 is not raised, and the first needle 26 remains in its lifted state so that fuel is sprayed continuously in the cylinder of the engine. At the same time there is a continuous flow from the needle control volume 34 via the flow passage 48 and the first control valve 16 to the low pressure fuel outlet drain 46. In order to solve the apparent problem in the injector unit, the present invention suggest an improvement in the injection unit.
The improvement the present invention introduces to the above discussed prior art injector unit may be seen in Figure 1 where the injector unit 10 is provided with a flow fuse 50 arranged in the flow passage 48 between the first needle control volume 34 at the second end of the first needle 26 and the first control valve 16.
The flow fuse 50, which is discussed in more detail in Figure 2, is formed of a cylindrical cavity 52 having an inside wall 54 and a bottom surface 56, the flow passage 48 has an opening 48' therein. A cup-shaped piston 58 formed of a bottom 60 facing the first needle control volume 34 and a skirt 62 facing away from the first needle control volume 34 and extending from the bottom 60 is arranged in the cylindrical cavity 52 such that a spring 64 is arranged inside the piston skirt 62 between the bottom 60 of the piston 58 and the bottom surface 56 of the cylindrical cavity 52.The bottom 60 and the skirt 62 of the piston 58 leave at least one restricted flow passage 66 between themselves and the inside wall 54 of the cylindrical cavity 52. The flow fuse 50 functions such that in normal operating condition, i.e. when the first control valve 16 opens in the manner it is supposed to work allowing the oil flow from the first needle control volume 34 to the first control valve 16, the piston 58 of the flow fuse 50 moves away from the first needle control volume 34, i.e. the pressure in the first needle control volume 34 compresses the spring 64 and moves the piston 58. A prerequisite for this kind of an operation is that the flow resistance of the first control valve 16 is lower than that of the at least one restricted flow passage 66, whereby the volume flow via the control valve 16 is higher than that via the at least one restricted flow passage 66. Thereby, the results is that the pressure in the first needle control volume 34 is relieved so that the first needle 26 is lifted off its seat surface, and the fuel injection may take place. And after the first control valve 16 is closed the needle control volume 34 is quickly filled with pressurized fuel via the at least one first restricted flow passage 38, whereby the first needle 26 is pushed back against its seat surface. Now, when the first control valve 16 is closed, the spring 64 pushes the piston 58 towards the needle control volume 34 as some of the fuel in the needle control volume 34 is able to pass the piston 58 along the at least one second restricted flow passage 66 so that the fuel pressure on both sides of the piston 58 is equalized. The piston 58, its skirt 62 and the cylindrical cavity 52, as well as the at least one second restricted flow passage 66, are dimensioned such that when the piston 58 moves in a direction away from the needle control volume 34 the released space is sufficient for reducing the pressure in the space below the pressure needed to keep the first needle 28 against its seat surface. In other words, the flow resistance of the first restricted flow passage 38 is higher than that of the second restricted flow passage 66.
In an abnormal operating condition, i.e. when the first control valve 16 has not closed after a predetermined period of time equalling to a certain volume of oil flown to the low pressure fuel drain 46, but remains open, the piston 58 of the flow fuse 50 moves away from the needle control volume 34 until the skirt 62 of the piston 58 meets the bottom surface 56 of the cylindrical cavity 52 and blocks the flow connection from the first needle control volume 34 to the low pressure fuel outlet drain 46 via flow passage 48. In other words, as the flow passage 48 opens to the bottom surface 56 of the cylindrical cavity 52 inside the skirt 62, the only connection to the needle control volume 34 via the at least one second restricted flow passage 66 is blocked. Thereafter, the pressure in the first needle control volume 34 may be raised as it normally does when the first control valve 16 is closed so that the first needle 26 will be pushed back against its seat surface. However, now that the fuel pressure in the first needle control volume 34 is not able to enter the interior of the piston 58, there is no pressure inside the piston 58 aiding in returning the piston 58 back towards the needle control volume 34, whereby the first needle 28 remains closed until the first control valve 16 is closed.
It should be understood that the above is only an exemplary description of a novel and inventive fuel injection unit of an internal combustion engine. It should be understood that though the specification above discusses a certain position of a flow fuse, its position does not limit the invention to the position discussed. The same applies to the type of the flow fuse, i.e. for instance, the detailed construction of the flow fuse is only limited to such that functions as discussed above. Thus, the flow fuse can be a ball-type, piston-type, or any other type of floating valve. Similarly, the flow fuse may be positioned wherever along the length of the flow passage between the first needle control volume at the second end of the first needle and the first control valve. Thus, the flow fuse may be arranged, not only in direct communication with the first needle control volume, but upstream thereof all the way up to the control valve. The above explanation should not be understood as limiting the invention by any means but the entire scope of the invention is defined by the appended claims only.

Claims

A fuel injection unit suitable for assembly to a cylinder head and for injecting fuel to a cylinder of an internal combustion engine having a common rail fuel system with at least one high pressure fuel pump, the fuel injection unit (10) being connectable to the common rail fuel system, the fuel injection unit (10) comprising a pilot nozzle (22) and a main nozzle (24), the pilot nozzle (22) having a pilot needle (26) and a pilot needle control volume (34) connected by means of a flow passage (48) with a pilot control valve (16), the pilot nozzle (22) and the main nozzle (24) having a common needle cavity (30), characterized in a flow fuse (50) arranged in connection with the flow passage (48) connecting the pilot needle control volume (34) to the pilot control valve (16).
The fuel injection unit as recited in claim 1, characterized in that the flow fuse (50) comprises means for closing a flow connection from the pilot needle control volume (34) to the pilot control valve (16).
The fuel injection unit as recited in claim 1 or 2, characterized in that the flow fuse (50) is a ball-type, or a piston-type floating valve.
The fuel injection unit as recited in claim 2 or 3, characterized in that the flow connection closing means is a piston (58) arranged in a cylindrical cavity (52) between the needle control volume (34) and the first control valve (16).
The fuel injection unit as recited in claim 4, characterized in that the piston (58) has a bottom (60) and a skirt (62), the bottom (60) facing the needle control volume (34) and the skirt (62) extending from the bottom (60) in a direction away from the needle control volume (34).
The fuel injection unit as recited in claim 4, characterized in the cylindrical cavity (52) having a bottom surface (56) and a spring (64) arranged in connection with the piston (58) between the bottom (60) of the piston (58) and the bottom surface (56) of the cylindrical cavity (52).
The fuel injection unit as recited in claims 1, 5 and 6, characterized in an opening (48') for the flow passage (48) in the bottom surface (56) of the cylindrical cavity (52) positioned and dimensioned such that the skirt (62) of the piston (58), when pressed against the bottom surface (56), surrounds the opening (48') and blocks the flow connection from around the piston (58) to the flow passage (48).
The fuel injection unit as recited in any one of the preceding claims, characterized in at least one first restricted flow passage (38) having a first flow resistance between the common needle cavity (30) and the needle control volume (34).
The fuel injection unit as recited in claim 5, characterized in at least one second restricted flow passage (66) having a second flow resistance between the piston (58) and the side wall (54) of the cylindrical cavity (52).
The fuel injection unit as recited in claims 8 and 9, characterized in that the first flow resistance is higher than the second flow resistance.
The fuel injection unit as recited in claims 1 and 9, characterized in that the pilot control valve (16) has a flow resistance, and that the flow resistance of the pilot control valve (16) is lower than the second flow resistance.
An internal combustion engine having a plurality of cylinders with cylinder heads and utilizing a common rail fuel system, characterized in that each cylinder head is provided with a fuel injection unit (10) in accordance with any one of claims 1 - 11.