Supply assembly for a gaseous-fuel engine

Abstract

A supply assembly (fig.1,1) for a gaseous-fuel engine (fig.4,60). The assembly has a fuel-supply system (fig.1,10) comprising a fuel rail (fig.1,12) conveying a gaseous fuel and a plurality of injecto

Description

TECHNICAL FIELD

[0001] The present invention relates to a supply assembly for a gaseous-fuel engine. BACKGROUND OF INVENTION

[0002] For automotive applications, hydrogen engines are considered as a promising alternative to gasoline or diesel engines since the emissions from a hydrogen engine consist mainly of water. However, the usage of “dry” hydrogen, i.e., without any additional lubricant, may create a wear risk on the components of the engine system. All moving components in the system, e.g., pressure regulators, injectors etc., are prone to wear. Similar problems arise with internal combustion engines that uses other types of gaseous fuel, e.g., natural gas. Specifically, the service life and operational reliability of fuel injectors used with gaseous fuels may be seriously affected. The lack of lubrication is even more problematic for fuel injectors mounted for direct fuel injection, as they face higher temperatures, resulting in excessive wear, mainly at the pintle / seat interface of the injector nozzle. It has been proposed to provide a lubrication system that releases a liquid lubricant into a fuel-supply system upstream of the fuel injector or into the fuel injector itself. However, such lubricant release faces various challenges. Specifically, it is desirable to precisely control the amount of lubricant and to avoid any over-lubrication of the fuel injector, which could lead to sticking of the movable injector components. TECHNICAL PROBLEM

[0003] It is thus an object of the present invention to provide effective means for precise lubrication of a fuel injector for a gaseous-fuel engine.

[0004] This problem is solved by a supply assembly according to claim 1. GENERAL DESCRIPTION OF THE INVENTION

[0005] The invention provides a supply assembly for a gaseous-fuel engine as claimed in claim 1. In this context, a gaseous-fuel engine is an internal combustion engine that runs on a gaseous fuel, such as coal gas, producer gas, biogas, landfill gas, natural gas, or hydrogen. This may specifically be a hydrogen internal combustion engine. The engine can specifically be a drive engine for a vehicle, like a road vehicle, but other applications are also possible. As will be explained below, the supply assembly has the function to supply the engine and / or components associated with the engine with fuel and / or lubricant.

[0006] The supply assembly comprises a fuel-supply system a fuel-supply system comprising a fuel rail for conveying a gaseous fuel and a plurality of injector units, each injector unit comprising a fuel injector that is at least indirectly connected to the fuel rail and is adapted to inject fuel into the engine. Since the gaseous-fuel engine can be adapted for different gaseous fuels, the same is true for the fuel-supply system and the fuel rail. The material(s) for the fuel-supply system can be chosen depending on the characteristics of the gaseous fuel. In case of hydrogen fuel, stainless steel can be a preferred material. During operation, the gaseous fuel in the fuel-supply system may be under elevated pressure, e.g., up to 40 bar or more, in which case the mechanical stability of the fuel-supply system needs to be adapted accordingly. A plurality of injector units is connected to the fuel rail, each one comprising a fuel injector. Preferably, each injector unit comprises only one fuel injector. The fuel injector can be directly connected to the fuel rail or indirectly, i.e., via another element, specifically via an injector socket. One could say that these injector units branch off the fuel rail. The inside of the fuel rail is in fluid communication with each injector unit, wherefore it either directly or indirectly communicates with the inside of each fuel injector.

[0007] The fuel injector is adapted to inject gaseous fuel into the engine. This may in particular refer to a direct injection of the fuel, so that the fuel injector is adapted for direct injection of the fuel into a combustion chamber of a cylinder of the respective engine. However, the fuel injector could also be configured for other types of injection, i.e., for injection into an inlet manifold, inlet duct or any other element through which the engine is supplies with air. Fuel injectors for gaseous fuel, in particular for hydrogen-containing fuel are known in the art and the details of the fuel injector are not important in the context of the invention. By way of example, the fuel injector may extend along an injector axis from a proximal side to a distal side, which faces the engine. It may comprise an injector body defining a fuel passage, which fuel passage extends through the injector body and communicates with an outlet opening, which is disposed on the distal side of the injector body. As a rule, the outlet opening can be closed by a pintle that cooperates with a valve seat. It will be understood that the number of fuel injectors in the supply assembly may correspond to the number of cylinders in the engine, but there may also be a plurality of fuel injectors for a single cylinder. Preferably, all fuel injectors are identical. The same may apply to the injector units, if they comprise any additional elements apart from the fuel injectors.

[0008] The supply assembly also comprises a lubricant-supply system. At least one function of the lubricant-supply system is to provide lubrication for at least one fuel injector, preferably to all fuel injectors. Additionally, it could provide lubrication for other components. It comprises at least one lubricant doser that is adapted to controllably release a liquid lubricant through an outlet port. The lubricant doser comprises an outlet port and is adapted to controllably release lubricant therethrough. Normally, the liquid lubricant can also be referred to as a lubricating oil or simply oil. Its function is to provide lubrication to at least one component of the engine and / or the supply system. Various lubricants can be used in the inventive supply system, which may comprise natural and / or artificial components. While the lubricant is referred to as “liquid”, it is not ruled out that it may comprise minor amounts of solid particles, either as additives or as (unwanted) impurities. “Controllably” means that the design of the lubricant doser allows to control the timing and the amount of lubricant release, wherein the precision of the control may vary between different embodiments.

[0009] Further, the lubricant-supply system comprises at least one lubricant pipe connecting the lubricant doser to an injector unit, which lubricant pipe defines a lubricant passage having an inlet opening communicating with the outlet port, an outlet opening communicating with the injector unit, and a pipe channel extending from the inlet opening to the outlet opening. The lubricant pipe connects the lubricant doser with an injector unit, which refers to a mechanical connection, but more importantly to a fluid connection. I.e., lubricant can be transferred from the lubricant doser to the injector unit through the lubricant pipe. It will be understood that the connection can be indirect, e.g., via a fitting that connects the lubricant pipe to the lubricant doser or to the injector unit, respectively. On the other hand, such a fitting can also be regarded as part of the lubricant doser, the injector unit, or the lubricant pipe. The lubricant pipe either directly or indirectly communicates with a cavity of the injector unit that is designed to contain / receive gaseous fuel. The liquid lubricant can be supplied at least indirectly to the fuel injector, thereby avoiding the drawbacks associated with a “dry” gaseous fuel. The lubricant pipe is preferably tubular, i.e., tube-shaped. It comprises a pipe wall that surrounds or defines the pipe channel. The pipe channel is a portion of the lubricant passage and extends from an inlet opening to an outlet opening, which includes the possibility that the pipe channel extends beyond one of the openings. The pipe channel communicates through the openings with the outside of the lubricant pipe. The openings can be at opposite ends of the lubricant pipe, but at least one opening could be at a distance from one end. It is possible that the lubricant pipe comprises a plurality of inlet openings and / or outlet openings, but there is normally only one inlet opening and outlet opening, respectively. As will become apparent in the following, the lubricant-supply assembly may preferably comprise a plurality of lubricant pipes, each of which connects a lubricant doser to an injector unit.

[0010] According to the invention, the lubricant passage of at least one lubricant pipe at least locally has an inner diameter of not more than 0.3 mm. Here and in the following, “diameter” not only refers to a circular cross-section or the like but is meant to also include a non-circular geometry, in which case it refers to the minimum dimension of the crosssection, profile or the like. In case of a square cross-section, “diameter” refers to the edge length of the square. The lubricant passage of at least one lubricant pipe has, at least locally, an inner diameter of not more than 0.3 mm. In some embodiments, the inner diameter may be not more than 0.2 mm or not more than 0.1 mm. “At least locally” means that this pertains to at least a portion of the lubricant passage, which comprises the inlet opening, the pipe channel and the outlet opening. At least one of these three parts, or only a portion of one part, has an inner diameter of not more than 0.3 mm. Preferably, this pertains to a plurality of lubricant pipes and more preferably to all lubricant pipes.

[0011] The inventive supply assembly includes a lubricant pipe with an (at least locally) small inner diameter. It has been found that liquid lubricant may only traverse a section with such a small diameter in response to a significant pressure difference. In principle the lubricant pipe is part of the dead volume located downstream of the lubricant doser. Such a dead volume could potentially be the source of unwanted lubricant leakage since lubricant release from the dead volume cannot be fully controlled via the lubricant doser. I.e., even though the lubricant doser does not release any lubricant into the lubricant pipe, the lubricant doser cannot prevent lubricant draining from the lubricant pipe. Such unwanted lubricant release could potentially lead to over-lubrication of the fuel injector. However, lubricant is unlikely to traverse the small-diameter portion of the lubricant pipe, unless due to pressure exerted by the lubricant doser. Therefore, unwanted lubricant release can be minimized or even prevented. Moreover, any portion of the pipe channel with a small diameter has a small volume. Therefore, the dead volume is reduced, which reduces the amount of lubricant that could be released inadvertently in the worst case.

[0012] It is conceivable that a fuel injector is directly connected to the fuel rail, in which case the lubricant doser would release lubricant through the lubricant pipe directly into the fuel injector. According to another embodiment, at least one injector unit comprises an injector socket through which the fuel injector is connected to the fuel rail, and the outlet opening of at least one lubricant pipe communicates with the injector socket. The injector socket can be fixed to the fuel rail, preferably in a non-detachable way, e.g., by welding. It may be made of the same material as the fuel rail, e.g., stainless steel. It is understood that the injector socket comprises a cavity or channel for containing fuel and guiding fuel from the fuel rail to the fuel injector. This may be referred to as a socket channel. The outlet opening of at least one lubricant pipe communicates with the injector socket, e.g., with the socket channel. Thus, the lubricant doser can release lubricant through the lubricant pipe into the injector socket, e.g., into the socket channel. The socket may also comprise a socketlubricant channel that is connected to the socket channel, and the outlet opening may communicate with this socket-lubricant channel.

[0013] One advantageous way to minimize or even prevent unwanted lubricant leaking through the lubricant pipe is to provide a small diameter at the outlet opening. In such an embodiment, the outlet opening of at least one lubricant pipe has an inner diameter of not more than 0.3 mm, preferably not more than 0.2 mm, more preferably not more than 0.1 mm. In this case, even if the diameter of the pipe channel is considerably larger, the small diameter at the outlet opening helps to retain lubricant inside the lubricant pipe. However, lubricant can be released from the lubricant pipe in case of a sufficiently high overpressure in the lubricant pipe, which can be generated by the lubricant doser.

[0014] The inner diameter of the pipe channel and the inner diameter of the outlet opening could be the same. However, pipes with very small inner diameter are difficult to produce. It can be easier from a manufacturing perspective to provide an outlet opening that is much smaller that the pipe channel. For such an embodiment, one end of the pipe channel can be closed by welding, brazing or the like, and then a small outlet opening can be produced by micro-drilling. One embodiment provides that the outlet opening of at least one lubricant pipe has an inner diameter corresponding to between 5% and 20% of an inner diameter of the pipe channel. In such an embodiment, retention of the lubricant inside the pipe cavity may largely be attributed to the small-diameter outlet opening. However, the inner diameter of the pipe channel may still be considered “small”, although it is much larger than that of the outlet opening, wherefore it can also contribute to the retention effect.

[0015] Irrespective of whether the outlet opening is much smaller than the pipe channel, as described above, it is preferred to have a pipe channel with a not too large diameter. Advantageously, the pipe channel of at least one lubricant pipe has an inner diameter of not more than 2 mm, preferably not more than 1,5 mm, more preferably not more than 1 mm. This pertains to the entire length of the pipe channel. On the one hand, a (still comparatively) small inner diameter may help to retain lubricant in the pipe cavity by capillary forces. On the other hand, with such a small inner diameter, the inner volume of the pipe cavity will be comparatively small, thereby minimizing the maximum amount of lubricant that could be released unintentionally. It should be appreciated that a portion of the pipe channel could still have a smaller inner diameter, e.g., not more than 0.3 mm.

[0016] Usually, each lubricant pipe is made of a single material, although different materials and / or a composite material could be used. Suitability of the material depends to some extent on the lubricant, but also on the gaseous fuel, because at least a portion of the lubricant pipe near the outlet opening will be subjected to the fuel. The material should be chemically resistant against the lubricant and the fuel. Also, especially in case of hydrogen fuel, it should reduce diffusion of the gaseous fuel to a minimum. Preferably, at least one lubricant pipe is made of metal, in particular stainless steel.

[0017] One embodiment provides that at least one lubricant pipe has an outer diameter of not more than 3 mm, preferably not more 2 mm, more preferably not more than 1,5 mm. On the one hand, this corresponds to a relatively thin tube wall, which helps to save material and weight. Preferably, the tube wall has a thickness of not more than 0.5 mm or not more than 0.2 mm. On the other hand, even in case of a lubricant tube made of relatively stiff material like stainless steel, such a thin tube can be bent into a variety of shapes to follow any desired route from the outlet port to the injector unit.

[0018] As already pointed out, it is advantageous to minimize the dead volume between the lubricant doser and the injector unit. On the one hand, this can be achieved by minimizing the cross-section of the pipe channel. On the other hand, the length of the lubricant pipe can be limited. It is therefore preferred that at least one lubricant pipe has a length of not more than 350 mm. In some embodiments, the length may be not more than 250, 200 or 150 mm or not more than 100 mm. Alternatively or at the same time, it is preferred that at least one lubricant pipe has an inner volume of not more than 100 mm3. In case of a pipe length of 200 mm, this corresponds to a circular cross-section with an inner diameter of about 0.8 mm. Similarly, an inner volume of 100 mm3 can be obtained with a lubricant pipe having an inner diameter of 0.6 mm and a pipe length of 350 mm3. In some embodiments, the inner volume may be not more than 50 mm3 or not more than 20 mm3. The inner volume of the lubricant pipe, i.e., the volume of the pipe cavity, is at least approximately equivalent to the dead volume.

[0019] In embodiments, the lubricant pipe may have a length of up to 350 mm3 and an internal diameter of less than 1 mm, e.g. between 0.6 and 0.8 mm. The length and inner diameters can be adapted -depending on the application- to have an inner volume between 50 and 175 mm3, in particular between 90 and 130 mm3.

[0020] At least one lubricant doser can be connected to a plurality of injector units via a plurality of lubricant pipes. This is insofar advantageous as the number of lubricant dosers is reduced, possibly even to one. In other words, all injector units could be supplied by a single lubricant doser.

[0021] According to one embodiment, the supply assembly comprises a plurality of lubricant pipes, wherein the lengths of the individual lubricant pipes differ by not more than 10%. At the same time, the inner diameters of the individual lubricant pipes may differ by not more than 10%. The difference may be not more than 5% or not more than 2%. If the lubricant pipes have a comparable or even identical length and inner diameter, the transfer of lubricant through the different pipes will be very similar. Accordingly, if lubricant is introduced into two lubricant pipes under the same conditions, i.e., same pressure, same timing etc., lubricant will also exit the lubricant pipes under at least similar conditions. This may be particularly advantageous if lubricant pipes are connected to a single lubricant doser. It will be appreciated that even if the distance between a lubricant doser and a fuel injector connected thereto is usually different for each fuel injector, it is still possible to use lubricant pipes having the same length, since the routing of the individual pipes can be adapted to compensate for different distances.

[0022] The lubricant doser may be at least indirectly mounted to the fuel rail. It may be mounted directly or via an additional element like a bracket. This embodiment is particularly preferred if a plurality or even all injector units are supplied by a single lubricant doser. The lubricant doser may be mounted near the middle of the fuel rail, so that the distance to any of the injector units is not too great, thereby limiting the length of the lubricant pipes.

[0023] According to another embodiment, the supply assembly comprises a plurality of lubricant dosers, each lubricant doser being connected to a single fuel injector via a lubricant pipe. One could say that in this embodiment, there is a pairwise association between the lubricant dosers and the fuel injectors. This is normally an alternative to the abovementioned option of one lubricant doser being connected to a plurality of fuel injectors.

[0024] In embodiments with a plurality of lubricant dosers, there are various options how these can be arranged. One embodiment provides that the supply assembly comprises a doser assembly with a plurality of lubricant dosers, which doser assembly is disposed separately from the fuel rail. The doser assembly may comprise a common base or bracket to which all lubricants dosers are fixedly mounted. Them base can then be mounted in a suitable position, e.g., inside a vehicle. The lubricant pipes extend from the doser assembly to the various injector units.

[0025] Various types of lubricant dosers can be used with the inventive supply assembly, according to one embodiment, at least one lubricant doser is a volumetric doser comprising a pumping chamber communicating with the outlet port, and a pumping plunger that is adapted to displace lubricant from the pumping chamber in order to release a defined release volume of lubricant through the outlet port during a release process. During operation, the pumping chamber at least temporarily contains lubricant. During a release process, the pumping plunger displaces or expels lubricant from the pumping chamber, which communicates with the outlet port. Thus, the movement of the pumping plunger causes lubricant to get released from the outlet port. Specifically, a defined release volume can be released. In other words, the design of the volumetric doser allows only for release of a defined release volume of lubricant during one release process, which may also be referred to as a release event or the like. The pumping chamber is preferably adapted to receive and temporarily store lubricant between two release processes. I.e., the volumetric doser can perform a release process and can be reloaded or recharged afterwards, in a intake process, by receiving a corresponding amount of lubricant. It will be understood that a “defined” volume may vary to some extent depending on various factors. However, the volume preferably varies by less than 10% or less than 5% between different release processes. Release of this defined volume allows for a very precise lubrication, avoiding both over-lubrication and under-lubrication. If a plurality of lubricant dosers are volumetric dosers, it is preferred that the release volume is the same for every volumetric doser. Preferably, the release volume is less than 20 mm3, preferably less than 10 mm3, more preferably less than 5 mm3.

[0026] According to one preferred embodiment, the lubricant doser comprises a doser body with a doser cavity in which the pumping plunger is movable along a plunger axis between a proximal position and a distal position so that a volume of the pumping chamber, which is partially defined by a distal portion of the pumping plunger, is greater in a proximal position of the pumping plunger than in a distal position, and the lubricant doser further comprises an inlet port which communicates with the pumping chamber through an inlet valve, and an outlet port which communicates with the pumping chamber through an outlet valve. Preferably, the inlet valve and the outlet valve are check valves, the inlet valve is adapted to open in response to an overpressure at the inlet port with respect to the pumping chamber and the outlet valve is adapted to open in response to an overpressure in the pumping chamber with respect to the outlet port. The plunger could be moved by a magnetic field that is generated by a magnetic coil in the doser body. However, it could also be moved by fluid pressure, which acts on a proximal side of the pumping plunger. In fact, the entire movement of the pumping plunger could be effected by alternatingly increasing the fluid pressure at the inlet port and at a control port that communicates with the proximal side of the plunger. The fluid acting on the proximal side may even be the same lubricant that is used for the fuel injectors.

[0027] Normally as an alternative to at least one volumetric doser, at least one lubricant doser can be a valve doser that is adapted to continuously release lubricant through the outlet port while it is in an open state. Such a valve doser can work in a similar way as fuel injectors known in the art, i.e., it may comprisea single valve that allows for lubricant release while it remains open. In such a case, the amount or volume of released lubricant depends mostly on the opening time of the respective valve, which necessitates a precisely timed control of this valve. The doser may comprise a pintle that is movable in a doser cavity that corresponds to the fuel passage describe above for a fuel injector. The pintle cooperates with a valve seat at the outlet port. The doser cavity extends from an inlet port to the outlet port. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Preferred embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which: Fig. 1 is a perspective view of a first embodiment of an inventive supply assembly; Fig.2 is a sectional view of a lubricant doser and a lubricant pipe of the supply assembly from fig.1; Fig.3 is a sectional view of a detail of the lubricant pipe from fig.2; Fig.4 is a schematic view of a second embodiment of an inventive supply assembly and an engine. Fig.5 is a sectional view of a lubricant doser of the supply assembly from fig.4; and Fig.6 is a partially sectional view of a part of the supply assembly from fig.4. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0029] Fig. 1 shows a perspective view of parts of a first embodiment of an inventive supply assembly 1 for a gaseous-fuel engine 60. Accordingly, as the fuel is gaseous, the terms fuel and gas are considered as synonyms. The supply assembly 1 comprises a fuel-supply system 10, which is adapted to supply a gaseous fuel, in this case hydrogen, to the engine 60, which is only shown schematically in fig.4. It comprises a plurality of cylinders (not shown), each of which can receive fuel from fuel injectors 17 of the fuel-supply system 10. In other words, there is one fuel injector 17 for each cylinder, in this case a total of four. Reference 12 designates a fuel rail, which conventionally comprises an tubular main body defining an elongate internal cavity that communicates with an inlet port and a plurality of outlet ports distributed along the length of the fuel rail 12. Each fuel injector 17 (or gas injector) is connected to a fuel rail 12 via an injector socket 14, which is fixedly connected to the fuel rail 12. The injector socket 14 is a solid body fixedly and sealingly attached to the rail 12, and comprises an internal channel, referred to as socket channel, that communicates at one end with a rail outlet port and at the other end with the injector. The socket thus forms a connector for supplying gas to the fuel injector 17. The fuel injector 17 and the injector socket 14 together constitute an injector unit 13. During operation of the engine 60, pressurized fuel (having a fuel pressure of, e.g., 40 bar) is supplied (e.g., through a connecting pipe 11 as shown in fig.6) to the fuel rail 12 and from there to each injector unit 13. The exact working principle of the fuel injector 17 is not the focus of the invention and will not be described in detail. By way of example, the fuel injector 17 comprises an injector body which defines a fuel passage that extends from an injector inlet to an injector outlet. The injector outlet can be closed by a pintle that cooperates with a valve seat. The pintle may be moved by an armature that is movable by an electric field generated by a magnetic coil.

[0030] The injector inlet communicates with the socket channel 15 of the socket 14. A socket-lubricant channel 16, which will be explained later, branches off the socket channel 15. These channels are only shown only in fig.5, which relates to another embodiment, but the principal arrangement is the same.

[0031] Further, the supply assembly 1 comprises a lubricant-supply system 20, which is adapted to provide a liquid lubricant L to the fuel injectors 17. It comprises in this case a single lubricant doser 21, which is mounted to the fuel rail 12 via a doser bracket 19. The lubricant doser 21 can also be referred to as a valve doser. It works in a similar way as the fuel injectors 17 in that it comprises a lubricant passage (corresponding to the fuel passage) with an inlet port 26 and an outlet port 28. The lubricant doser 21 receives lubricant L from a lubricant reservoir (not shown here) through the inlet port 26. Near the outlet port 28, it comprises a valve that can be controlled by movement of a pintle that cooperates with an armature that is movable by the magnetic field of a magnetic coil. The lubricant doser 21 will release lubricant L while the valve is open. Near the outlet port 28, four fittings 34 are connected to the lubricant doser 21, and each fitting 34 is connected to a lubricant pipe 35 made of stainless steel. Each lubricant pipe 35 connects the lubricant doser 21 to one of the injector sockets 14. Specifically, it is connected to the injector socket 14 via another fitting 34 so that a lubricant passage 36 of the lubricant pipe 35 communicates with the socket-lubricant channel 16. The lubricant doser 21 is supplied with a lubricant L with a pressure that is higher than the fuel pressure in the socket-lubricant channel 16. When the valve of the lubricant doser 21 is open, lubricant L is released through the outlet port 28 and the lubricant pipe 35 into the socket-lubricant channel 16, from where it reaches the fuel injector 17 through the socket channel 15. When the valve is closed, a certain amount of lubricant L remains inside the lubricant passage 36 of the lubricant pipe 35, which represents a “dead volume”.

[0032] An end portion of the lubricant pipe 35 is shown in detail in fig.3. On the one hand, the dead volume is minimized by the dimensions of the lubricant pipe 35. Each lubricant pipe 35 has a length of, e.g., 120 mm and a channel inner diameter du of the pipe channel 37 is, e.g., 1.0 mm. Of course, these values and other values mentioned in the following are just exemplary and there are other possible choices. The inner volume of the lubricant passage 36 corresponds to about 94 mm3 or 0.094 ml. Moreover, an outlet inner diameter dj2 of the outlet opening 39 is, e.g., 0.1 mm, corresponding to only 10 % of the channel inner diameter du. Even in case of a small underpressure in the socket-lubricant channel 16 with respect to the lubricant passage 36, liquid lubricant L is unlikely to traverse this smalldiameter opening, which can at least partially be attributed to capillary force. Accordingly, unwanted lubricant release from the lubricant pipe 35 is unlikely. Even if it occurs, its amount is limited by the small inner volume of the lubricant passage 36. An outer diameter d0 of the lubricant pipe 35 may be, e.g., 1.5 mm, wherefore the lubricant pipe 35 can easily be bent according to any desired route from the lubricant doser 21 to the injector socket 14. This property is useful also because all lubricant pipes 35 have the same length, regardless of the distance between the lubricant doser 21 to the injector socket 14. The equal length guarantees that lubricant L will behave similarly in every lubricant pipe 35 and a similar or identical amount of lubricant L is supplied to every injector unit 13.

[0033] Fig. 4 shows a second embodiment of an inventive supply system 1, which comprises four lubricant dosers 21 that are mounted to a doser carrier 41 as parts of a doser assembly 40. The doser assembly 40 is mounted separately from the fuel rail 12. Each lubricant doser 21 is connected to an injector socket 14 via a lubricant pipe 35. The lubricant pipes 35 may have the same dimensions as in the first embodiment. This supply system 1 employs a different kind of lubricant doser 21 that is shown in detail in fig.5. The lubricant doser 21 comprises a doser body 22 that defines a doser cavity 23. Within the doser cavity 23, a pumping plunger 24 is movable along a plunger axis A. On a distal side of the pumping plunger 24, there is a pumping chamber 25 which is partof the doser cavity 23. The pumping chamber 25 communicates with the inlet port 26 through an inlet valve 27 and with the outlet port 28 through an outlet valve 29. The outlet port 28, in turn, communicates with the lubricant passage 36 of a lubricant pipe 35. socket-lubricant channel 15. Accordingly, lubricant L that is released from the outlet port 27 can traverse the socket-lubricant channel 16 and the socket channel 15 and enter the injector 17.

[0034] The operation of the lubricant doser 21 will now be explained with reference to figs. 4 and 5. The pumping plunger 24 is movable along the plunger axis A between a proximal position that is shown inf fig.5 and a distal position (not shown). The movement of the pumping plunger 23 to the distal position corresponds to a release process in which lubricant L is released through the outlet port 28. The lubricant L in the pumping chamber 25 is compressed, and the increased pressure opens the outlet valve 29, which is a check valve. On the other hand, the inlet valve 27, which is also a check valve, is closed at this time, due to an overpressure in the pumping chamber 25 relative to the inlet port 26. This overpressure is partially due to a reduction in pressure at the inlet port 26. As can be seen in fig.4, the inlet ports 26 of all lubricant dosers 21 are connected to a supply piping 45. The supply piping 45 is connected to a valve device 47 (in this case a multi-port valve), which connects the supply piping 45 to a high-pressure pipe 49 in a first state and to a low-pressure pipe 51 in a second state (which is shown in fig.4). while the lower-pressure pipe 51 is directly connected to a lubricant reservoir 48, the higher-pressure pipe 49 is connected to the lubricant reservoir 48 via a pressure pump 50 that increases the lubricant pressure from 1 bar at the reservoir 48 to, e.g., between 2 and 5 bar.

[0035] The high-pressure pipe 49 and the low-pressure pipe 51 are connected via a relief valve 52 that bypasses the pressure pump 50. A control unit 55 controls the switching state of the valve device 47. For the release process, the supply piping 45 is connected to the low-pressure pipe 51. A control piping 46, on the other hand, is connected to the high-pressure pipe 49. The control piping 46 is connected to a control port 32 of each lubricant doser 21. As can be seen in fig. 5, the control port 32 communicates with a control chamber 31, which is disposed on a proximal side of the pumping plunger 24 and is partially delimited by a proximal portion 24.3 of the pumping plunger 24. As the control piping 46 is connected to the high-pressure pipe 49, an elevated pressure acts on the proximal portion 24.3. At the same time, the considerably lower pressure of the low-pressure pipe 51 acts on an intermediate portion 24.2 of the pumping plunger 24 which is disposed in an intermediate chamber 30 of the doser cavity 23. This is because the intermediate chamber 30 communicates with the inlet port 26 through a bypass channel 33 that bypasses the inlet valve 27. A force resulting from this pressure acting on the intermediate portion 24.2 is much smaller than the force acting on the proximal portion 24.3. Also, although the pressure in the pumping chamber 25 is as high or even higher than the pressure in the control chamber 31, the resulting force is much smaller, since the proximal portion 24.3 has a considerably greater cross-section perpendicular to the plunger axis A than the distal portion 24.1. Thus results the movement of the pumping plunger 24 to the distal position and the release process, which is effected in all lubricant dosers 21 simultaneously. For an intake process, the control unit 55 connects the supply piping 45 to the high-pressure pipe 49 and the control piping 46 to the low-pressure pipe 51. This results in a pressure increase at the inlet port 26 and in the intermediate chamber, while the pressure at the control port is decreased. Accordingly, the pumping plunger 24 moves to the proximal position. Also, the inlet valve 46 opens so that lubricant L flows into the pumping chamber 25, which is now ready for another release process.

[0036] It should be noted that the lubricant dosers 21 in this embodiment could be replaced by lubricant dosers 21 like the one in the first embodiment. Also, the lubricant doser 21 of the first embodiment could be replaced by a lubricant doser of the second embodiment. Also, although the pumping plunger 24 in the second embodiment is moved by hydraulic forces that necessitate the control port 32 and the control piping 46, it would be conceivable to change the design so that the pumping plunger 24 is moved magnetically by a magnetic coil in the lubricant doser 21. Legend of Reference Numbers: 1 supply assembly 10 fuel-supply system 11 connecting pipe 12 fuel rail 13 injector unit 14 injector socket 15 socket channel 16 socket-lubricant channel 17 fuel injector 19 doser bracket 20 lubricant-supply system 21 lubricant doser 22 doser body 23 doser cavity 24 pumping plunger 24.1 distal portion 24.2 intermediate portion 24.3 proximal portion 25 pumping chamber 26 inlet port 27 inlet valve 28 outlet port 29 outlet valve 30 intermediate chamber 31 control chamber 32 control port 33 bypass channel 34 fitting 35 lubricant pipe 36 lubricant passage 37 inlet opening 38 outlet opening 39 pipe channel doser assembly doser carrier supply piping control piping valve device lubricant reservoir high-pressure pipe pressure pump low-pressure pipe relief valve control unit engine plunger axis inner diameter outer diameter lubricant

Claims

1. A supply assembly (1) for a gaseous-fuel engine (60), comprising:- a fuel-supply system (10) comprising a fuel rail (12) for conveying a gaseous fuel and a plurality of injector units (13), each injector unit (13) comprising a fuel injector (17) that is at least indirectly connected to the fuel rail (12) and is adapted to inject fuel into the engine (60), and- a lubricant-supply system (20) comprising at least one lubricant doser (21) that is adapted to controllably release a liquid lubricant (L) through an outlet port (28), and at least one lubricant pipe (35) connecting the lubricant doser (21) to an injector unit (13), which lubricant pipe (35) defines a lubricant passage (36) having an inlet opening (38) communicating with the outlet port (28), an outlet opening (39) communicating with the injector unit (13), and a pipe channel (37) extending from the inlet opening (38) to the outlet opening (39),wherein at least a portion of the lubricant passage (36) of at least one lubricant pipe (35) has an inner diameter (du, djz) of not more than 0,3 mm and said at least one lubricant pipe (35) has an inner volume of not more than 100 mm3.

2. The supply assembly according to claim 1, wherein at least one injector unit comprises an injector socket (14) through which the fuel injector (17) is connected to the fuel rail (12), and the outlet opening (39) of at least one lubricant pipe (35) communicates with the injector socket (14).

3. The supply assembly according to claim 1, wherein the outlet opening (39) of at least one lubricant pipe (35) has an inner diameter (diz) of not more than 0,3 mm.

4. The supply assembly according to any of the preceding claims, wherein the outlet opening (39) of at least one lubricant pipe (35) has an inner diameter (di2) corresponding to between 5% and 20% of an inner diameter (du) of the pipe channel (37).

5. The supply assembly according to any of the preceding claims, wherein the pipe channel (37) of at least one lubricant pipe (35) has an inner diameter (du) of not more than 2 mm.

6. The supply assembly according to any of the preceding claims, wherein at least one lubricant pipe (35) is made of stainless steel.

7. The supply assembly according to any of the preceding claims, wherein at least one lubricant pipe (35) has an outer diameter (d0) of not more than 3 mm.

8. The supply assembly according to any of the preceding claims, wherein at least one lubricant pipe (35) has a length of not more than 200 mm.

9. The supply assembly according to any of the preceding claims, wherein at least one lubricant doser (21) is connected to a plurality of injector units (13) via a plurality of lubricant pipes (35).

10. The supply assembly according to any of the preceding claims, comprising a plurality of lubricant pipes (35), wherein the lengths of the individual lubricant pipes (35) differ by not more than 10%.

11. The supply assembly according to any of the preceding claims, wherein the lubricant doser (21) is at least indirectly mounted to the fuel rail (12).

12. The supply assembly according to any of the preceding claims, comprising a plurality of lubricant dosers (21), each lubricant doser (21) being connected to a single fuel injector (17) via a lubricant pipe (35).

13. The supply assembly according to any of the preceding claims, comprising a doser assembly (40) with a plurality of lubricant dosers (21), which doser assembly (40) is disposed separately from the fuel rail (12).

14. The supply assembly according to any of the preceding claims, wherein at least one lubricant doser (21) is a volumetric doser comprising a pumping chamber (25) communicating with the outlet port (28), and a pumping plunger (24) that is adapted to displace lubricant (L) from the pumping chamber (25) in order to release a defined release volume of lubricant (L) through the outlet port (28) during a release process.

15. The supply assembly according to any of the preceding claims, wherein at least one lubricant doser (21) is a valve doser that is adapted to continuously release lubricant (L) through the outlet port (28) while it is in an open state.

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