Supply assembly for a gaseous-fuel engine

Abstract

A supply assembly 1 for a gaseous-fuel engine (60,fig.5).The supply assembly comprises a fuel rail 12 for conveying a gaseous fuel to a plurality of injector units 13. Each injector unit comprising a fuel injector 20 that is at least indirectly connected to the fuel rail and is adapted to inject fuel into the engine. The supply assembly further comprises a lubricant-supply system 30 comprising at least one lubricant doser 31 with an outlet port (38,fig.2), the lubricant doser being adapted to controllably release a liquid lubricant through the outlet port into an injector unit and is mounted to the injector unit. The doser may be a volumetric doser comprising a pump chamber (35,fig.2) communicating with the outlet port and a pump plunger (34,fig.2) that is adapted to displace lubricant into the injector unit during a release process. The supply system may increase a fluid pressure at an inlet port 36 and decrease pressure at a control port (42,fig.2) to introduce lubricant from the inlet to the pump chamber, and decrease fluid pressure at the inlet and increase fluid pressure at the control port to eject lubricant from the chamber.

Description

TECHNICAL FIELD

[0001] The present invention relates to a supply assembly fora 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 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. 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 in particular 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 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 fuelsupply 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 comprising at least one lubricant doser with an outlet port, the lubricant doser being adapted to controllably release a liquid lubricant through the outlet port into an injector unit, and being mounted to the injector unit. 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, preferably a plurality of lubricant dosers, namely one for each injector unit. The lubricant doser comprises an outlet port and is adapted to controllably release a liquid lubricant through the outlet port. 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] The lubricant doser is mounted to the injector unit. Thus, it is in close proximity of the injector unit and a portion of the lubricant doser may even be disposed inside the injector unit. Preferably, the outlet port is disposed to release the lubricant into the injector unit. It may directly communicate with a cavity of the injector unit that is designed to contain gaseous fuel. In any case, a possible dead volume between the outlet port of the lubricant doser and the injector unit is greatly reduced, preferably to zero. Such a dead volume could potentially be the source of unwanted lubricant leakage since lubricant release from the dead volume cannot be directly controlled via the lubricant doser. Such unwanted lubricant release could potentially lead to over-lubrication of the fuel injector, which is highly improbable due to the inventive configuration. Also, it is beneficial that the lubricant is released into the injector unit rather than into the fuel rail. On the one hand, this prevents lubricant from remaining in the fuel rail, which does not require any lubrication. On the other hand, the inventive concept allows to provide lubricant to one specific fuel injector, which makes the lubrication more precise.

[0010] It is conceivable that a fuel injector is directly connected to the fuel rail, in which case the lubricant doser would release lubricant 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 lubricant doser is adapted to release lubricant into 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 that is adapted for containing fuel and guiding fuel from the fuel rail to the fuel injector. This may be referred to as a socket channel. The lubricant doser is adapted to release lubricant into the injector socket, e.g., directly into the socket channel. The socket may also comprise a socket-lubricant channel that is connected to the socket channel, and the lubricant doser may release lubricant into this socket-lubricant channel. Preferably, the lubricant doser is mounted to the injector socket. Thus, the fuel injector can be removed and replaced without the need to remove the lubricant doser.

[0011] The lubricant doser could work in a similar way as fuel injectors known in the art, i.e., it could comprise a 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. According to another 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 into the injector unit 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 by receiving a corresponding amount of lubricant. The latter process can be referred to as an intake process. 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. The volumetric doser can also be referred to as a pumping doser.

[0012] Preferably, the supply assembly is adapted to simultaneously initiate a release process in a plurality of lubricant dosers. In other words, the release process occurs simultaneously in a plurality of lubricant dosers. Preferably, this pertains to all lubricant dosers. This embodiment facilitates the lubrication process and its control. E.g., a time schedule for the release processes is simpler since it is the same for several (or all) dosers. Also, the number of components and / or the size of some components may be reduced as compared to an embodiment in which every doser has its own schedule. It should be noted that at least some control components, e.g., a control unit or a control software, may not be part of the lubricant-supply system but, e.g., could be part of a higher-level component that controls both the lubricant-supply system and the fuel-supply system.

[0013] 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 , and the outlet port communicates with the pumping chamber through an outlet valve. The doser body may comprise one or several components that are connected, preferably fixedly connected. Within the doser body, there is a doser cavity. The pumping plunger is movably disposed inside the doser cavity. To facilitate movement of the pumping plunger along the plunger axis, it may be guided by the inner wall of the doser body that defines the doser cavity. At least a portion of the doser cavity can be regarded as a cylinder cavity in which the pumping plunger is disposed. The pumping plunger can be moved between a proximal position and a distal position, which are positions with respect to the plunger axis. As the pumping plunger moves from the proximal to the distal position, the volume of the pumping chamber is reduced. When the pumping plunger moves from the distal position to the proximal position, the volume is increased. This pumping chamber, which may at least partially be formed by the doser cavity, is partially defined by a distal portion of the pumping plunger. As a rule, it is also partially defined by the doser body. Since the pumping plunger is movable within the doser cavity, a gap between the pumping plunger and the wall of the doser cavity is a potential leakage point. This problem can be alleviated if an elastomeric element is connected to the pumping plunger and is interposed between the pumping plunger and the doser body. Such an elastomeric element may be an elastomeric O-ring disposed circumferentially around the pumping plunger. It may be made of rubber or another suitable elastomeric material. Although the elastomeric element may increase friction, it provides a sealing effect which would otherwise only be achievable by increasing the length of the pumping plunger along the plunger axis, thereby increasing the length of a possible leakage path. However, an increased length of the pumping plunger would also increase the total size of the lubricant doser.

[0014] In this embodiment, the lubricant doser also comprises an inlet port which communicates with the pumping chamber, and the outlet port communicates with the pumping chamber through an outlet valve. The inlet port is adapted for a connection to a lubricant source or lubricant supply, i.e., the lubricant doser can receive lubricant through the inlet port. Lubricant transfer from the inlet port to the pumping chamber may be controlled in various ways, as will be discussed below. Lubricant transfer from the inlet port into the pumping chamber coincides with a volume increase of the pumping chamber and thus with a movement of the pumping plunger from the distal position to the proximal position. Lubricant transfer from the pumping chamber to the outlet port is controlled by an outlet valve. Generally, the outlet valve may be any kind of valve. Preferably, it defines at least a closed position in which lubricant transfer from the pumping chamber to the outlet port is prevented, and an open position in which lubricant transfer is enabled. Lubricant transfer from the pumping chamber into the outlet port coincides with a volume decrease of the pumping chamber and thus with a movement of the pumping plunger from the proximal position to the distal position. It will be appreciated that the lubricant doser described here can be a volumetric doser. During a release process, the outlet valve is open, while the pumping plunger moves to the distal position and expels lubricant from the pumping chamber. If the proximal position and the distal position are well-defined, the movement of the pumping plunger leads to the release of a defined release volume. Similarly, when the outlet valve is closed and the pumping plunger moves to the proximal position, a lubricant quantity corresponding to the release volume can be transferred from the inlet port to the pumping chamber.

[0015] In one embodiment, the inlet port communicates with the pumping chamber through an inlet valve. In this case, lubricant transfer from the inlet port to the pumping chamber is controlled by an inlet valve. Generally, the inlet valve may be any kind of valve. Preferably, it defines at least a closed position in which lubricant transfer from the inlet port to the pumping chamber is prevented, and an open position in which lubricant transfer is enabled. In another embodiment, the inlet port communicates with the pumping chamber through an inflow opening which is disposed adjacent to the pumping chamber so that the pumping plunger blocks the inflow opening in the distal position and uncovers the inflow opening in the proximal position. In this embodiment, there is no dedicated “inlet valve”, but the function of the inlet valve is performed by the pumping plunger. As the pumping plunger moves between the proximal position and the distal position, the inflow opening is alternatingly blocked and uncovered by the pumping plunger. The inflow opening is disposed adjacent to the pumping chamber so that the pumping plunger, or a portion thereof, can block the inflow opening. Possibly, the inflow opening may represent a constriction or narrow between the inlet port and the pumping chamber. I.e., a cross-section of the inflow opening may be reduced with respect to an adjacent cavity that communicates with, or constitutes, the inlet port. In particular, the inflow opening may be realized by a micro bore, which may have a diameter of a few micrometers up to a few hundred micrometers. However, a larger diameter is also possible.

[0016] The doser body may comprise an outer part, which may also be referred to as a doser housing. This outer part may comprise two elements, which may at least in some embodiments be referred to as a housing shell and a housing lid. These two parts may be connected e.g., by a screw connection. The doser housing may contain an inner assembly, which may comprise inner parts of the doser body, as well as the pumping plunger and other elements, like the inlet valve and / or the outlet valve. The doser cavity may at least partially be disposed within the inner assembly, but partially also between the inner assembly and the doser housing. The inner assembly may comprise at least two parts which are connected, e.g., by press-fitting. A first part may be referred to as a plunger part and may define at a portion of the doser chamber, specifically a portion in which the pumping plunger is disposed. A second part may be referred to as a seat part and may constitute a seat of the outlet valve. The inner assembly may be pre-assembled before it is placed inside a part of the doser housing, e.g., the housing shell, whereafter the parts of the housing are connected so that the inner assembly is enclosed.

[0017] In order to promote lubricant distribution in the injector unit, a porous outlet cap may be provided at the outlet port. The outlet cap is disposed so that lubricant can only be released from the outlet port through the outlet cap. The outlet cap is porous, which means that it comprises a plurality of pores or through-openings through which the lubricant is released. Thus, formation of small-size droplets can be promoted, which helps to distribute the lubricant in the gaseous fuel. The outlet cap could be e.g., a single metal body with a plurality of through-holes, or a mesh of metal wires.

[0018] Preferably, a pumping volume, which is displaced by the pumping plunger between the proximal position and the distal position, is less than 20 mm3, preferably less than 10 mm3, more preferably less than 5 mm3. The pumping volume is the volume that the pumping plunger displaces when it moves from the proximal position to the distal position. It corresponds to the distance between these positions multiplied by the cross-section of the pumping plunger adjacent to the pumping chamber. Apart from volume variations due to compressibility of the lubricant, the pumping volume may be identical to the release volume. In other words, in this embodiment, each movement of the pumping plunger leads to a release process in which only a small amount of lubricant is released. Such small amounts are considered optimal for lubrication of the fuel injector.

[0019] One embodiment provides that 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. Each check valve may comprise a stationary valve seat and a movable valve member that sealingly engages the valve seat in a closed position of the check valve. The valve member is elastically biased towards the closed position, e.g., by a spring element. At least one of the valve seat and the valve element may comprise an elastomeric sealing portion that engages the other element in the closed position to provide an improved seal. It will be understood that each of the inlet valve and the outlet valve can be adapted to open only when the respective overpressure exceeds a defined opening threshold. When the pumping plunger moves to the distal position, the pressure in the pumping chamber increases and may exceed the pressure at the inlet port, wherefore the inlet valve will close or stay closed. The outlet valve, on the other hand, opens due to the pressure increase. In this context, it should be appreciated that the outlet port is in fluid communication with the injector unit, wherefore it is usually subjected to a considerable pressure by the fuel gas. In other words, for the outlet valve to open, the pressure in the pumping chamber at least has to be greater than the gas pressure at the outlet port. On the other hand, if the pressure at the inlet port exceeds the pressure in the pumping chamber (plus the abovementioned opening threshold), the inlet valve opens. At this time, the outlet valve should be closed, so the opening threshold of the outlet valve has to be set accordingly. In order to open the inlet valve, it is possible to increase the pressure at the inlet port, in which case the pumping plunger may be “passively” moved to the proximal position by the fluid pressure in the pumping chamber. Alternatively, the pressure in the pumping chamber can be decreased by actively moving pumping plunger to the proximal position.

[0020] There are various possible ways to effect the movement of the pumping plunger towards the distal position. E.g., the plunger could be moved by a magnetic field that is generated by a magnetic coil in the doser body. One preferred embodiment provides that wherein the doser cavity comprises a control chamber on a proximal side of the pumping plunger, which control chamber communicates with a control port, and the pumping plunger is movable to the distal position by a fluid pressure at the control port. This embodiment relies on fluid actuation of the pumping plunger. The control chamber (which could also be referred to as a control portion) is a portion of the doser cavity that is disposed on a proximal side of the pumping plunger, i.e., on an opposite side with respect to the pumping chamber. The control chamber may be partially defined by the doser body and by the pumping plunger. It communicates with a control port, which may at least in some embodiments also be regarded as a part of the control chamber. When the fluid pressure at the control port changes, a pressure force acting on the proximal side of the pumping plunger also changes. For instance, if the pressure in the pumping chamber remains unchanged while the pressure in the control chamber is increased, this may result in a force difference that moves the pumping plunger to the distal position. This fluid actuation of the plunger may simplify the layout of the lubricant doser. Specifically, there is no need for a dedicated actuator, e.g., an electromagnetic actuator and thus no need for an electric connection or the like. Also, fluid actuation may lead to a more robust lubricant doser that is less prone to failure.

[0021] As explained, the fluid actuation relies on a force difference between the proximal side and the distal side of the plunger. On the one hand, this force difference can be due to a pressure difference. On the other hand, it can be due to a different effective area on which the pressure is acting. According to one embodiment, a proximal portion of the pumping plunger, which is disposed adjacent to the control chamber, has a greater cross-section perpendicular to the plunger axis than the distal portion. It will be understood that regarding a movement of the plunger parallel to the plunger axis, the cross-section perpendicular to the plunger axis represents the effective area regarding the pressure force. In this embodiment, the cross-section of the proximal portion, which is subjected to the pressure in the control chamber, is greater than the cross-section of the distal portion. The ratio between these two cross-sections can also be referred to as a plunger ratio or piston-to-plunger ratio (wherein the proximal portion represents the “piston” and the distal portion represents the “plunger”), which in this embodiment is greater than 1, e.g., between 5 and 50 or between 10 and 30. Accordingly, the pressure force on the proximal portion is increased in relation to the fluid pressure acting thereon. Thus, during a release process, it is possible to generate a fluid pressure in the pumping chamber that is sufficiently high to open the outlet valve (against the gas pressure in the injector unit) without the need to apply an equally high pressure to the control chamber and the control port.

[0022] The doser cavity may comprise an intermediate chamber in which an intermediate portion of the pumping plunger is disposed, and which communicates with the inlet port through a bypass channel that bypasses the inlet valve. This intermediate portion is preferably disposed in a position between the proximal portion and the distal portion with respect to the plunger axis, although it is conceivable that there is at least some positional overlap. With the pumping plunger disposed in the doser cavity, fluid exchange and pressure exchange between the intermediate chamber and the control chamber is prevented or at least hindered. However, the intermediate chamber communicates with the inlet port via the bypass channel. Accordingly, irrespective of the state of the inlet valve, the pressure in the intermediate chamber at least approximately corresponds to that at the inlet port. This pressure acts against the intermediate portion of the pumping plunger and can lead to a force that acts in the proximal direction. Thus, the pressure at the inlet port can be used to assist the movement of the pumping plunger to the proximal position.

[0023] One embodiment provides that the lubricant-supply system is adapted to increase a fluid pressure at the inlet port and decrease a fluid pressure at the control port to introduce lubricant through the inlet port into the pumping chamber, and to decrease the fluid pressure at the inlet port and increase the fluid pressure at the control port to eject lubricant from the pumping chamber through the outlet port during the release process. Accordingly, two different processes and different phases can be distinguished. One phase, corresponding to an intake process, serves to introduce lubricant into the pumping chamber, which necessitates opening the inlet valve. If the inlet valve is a check valve, the pressure at the inlet port needs to be greater than the pressure in the pumping chamber. Thus, it makes sense to increase the pressure at the inlet port. On the other hand, the pumping chamber should have its maximum volume, wherefore the pumping plunger should be in its proximal position. Thus, the pressure at the inlet port should be decreased. The other phase represents the release process, which needs the outlet valve to be open and the pumping plunger to move to the distal position. During this process, the pressure at the control port should be increased. It would be conceivable to maintain the pressure at the inlet port at a high level, but this would increase the chance of the inlet valve opening during the release process. I.e., lubricant would flow into the pumping chamber during the release process, making it impossible to control the release volume of the lubricant. Therefore, this embodiment provides that the pressure at the inlet port is reduced for the release process. If there is an intermediate chamber that communicates with the inlet port as described above, it will be appreciated that the increased pressure at the inlet port helps to move the pumping plunger to the proximal position, while the reduced pressure at inlet port facilitates the movement of the plunger to the distal position.

[0024] Preferably, the lubricant supply system comprises a supply piping, which is connected to the inlet port of at least one lubricant doser, and / or a control piping, which is connected to the control port of at least one lubricant doser. The supply piping can supply lubricant to the at least one inlet port. It can be connected, either directly or indirectly, to a lubricant reservoir. Specifically, the supply piping may be connected to the lubricant reservoir via at least one valve and / or it may comprise at least one valve. The control piping can supply a fluid to the at least one control port. In particular, it may supply lubricant and may be at least indirectly to a lubricant reservoir, e.g., the same lubricant reservoir as the supply piping. The control piping may be connected to the lubricant reservoir via at least one valve and / or it may comprise at least one valve.

[0025] While it is possible to connect the supply piping or the control piping only to a single lubricant doser, it is highly preferred that the supply piping is connected to a plurality of inlet ports and / or the control piping is connected to a plurality of control ports. One could say that the respective piping has a branching structure that supplies a plurality of lubricant dosers. Thus, by controlling the pressure in the supply piping, it is possible to control the pressure at the inlet ports of several lubricant dosers at the same time. Likewise, by controlling the pressure in the control piping, it is possible to control the pressure at the control ports of several lubricant dosers simultaneously. This greatly facilitates a synchronized operation of several - and possibly all - lubricant dosers. The synchronization is “automatically” achieved by all dosers being subjected to the same pressure present in the supply piping, or the control piping, respectively.

[0026] According to one embodiment, the lubricant-supply system comprises a high-pressure pipe connected to a lubricant reservoir and a low-pressure pipe connected to the lubricant reservoir and is adapted to generate a higher pressure in the high-pressure pipe than in the low-pressure pipe. The lubricant reservoir can be a lubricant tank or the like. It may be open for pressure exchange with the surrounding atmosphere. Both the high-pressure pipe and the low-pressure pipe are connected to the lubricant reservoir. However, during operation, the pressure in the high-pressure pipe is increased. For this purpose, the high-pressure pipe may comprise a pressure pump. Preferably, the pressure in the low-pressure pipe corresponds to atmospheric pressure (i.e., about 1 bar) while the pressure in the high-pressure pipe can be considerably higher, e.g., by a factor of between 5 and 20 or between 7 and 15.

[0027] Preferably, the lubricant supply system comprises a valve device which is adapted to fluidly connect the supply piping to the high-pressure pipe in a first state and to fluidly connect the supply piping to the low-pressure pipe in a second state. The valve device can be a single valve, e.g., a multiway valve, but it may also comprise a plurality of valves. In a first state, which may be used for the intake process, it connects the supply piping to the high-pressure pipe, thus increasing the pressure at the inlet port and enabling lubricant to flow into the pumping chamber while moving the pumping plunger to the proximal position. In a second phase, which may be used for the release process, it connects the supply piping to the low-pressure pipe, thus decreasing the pressure at the inlet port. If the inlet valve is a check valve, it will close due to the decreasing pressure at the inlet port, wherefore a higher pressure can be maintained inside the pumping chamber.

[0028] Preferably, the valve device is adapted to fluidly connect the control piping to the low-pressure pipe in the first state and to fluidly connect the control piping to the high-pressure pipe in the second state. In other words, in this embodiment, the valve devices alternatingly connects the supply piping and the control piping to the high-pressure pipe (or the low-pressure pipe, respectively). On the other hand, it alternatingly connects the high-pressure pipe and the low-pressure supply piping to the control piping (or the supply piping, respectively). In the first state, the control piping is connected to the low-pressure line, thus lowering the pressure at the control port, which facilitates moving the pumping plunger to the proximal position. In the second state, the control piping is connected to the high-pressure line, thus increasing the pressure at the control port, which facilitates moving the pumping plunger to the distal position, increasing the pressure in the pumping chamber and opening the outlet valve (if it is a check valve). This embodiment enables actuation of the pumping plunger by using the same lubricant that is used for lubricating the fuel injector(s). There is no need for an additional fluid supply. The different processes - refill process, release process - are initiated by changing the state of the valve device. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] 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 parts of an inventive supply assembly; Fig.2 is a sectional view of a lubricant doser and an injector unit of the supply assembly from fig.1; Fig.3 is a sectional view the lubricant doser from fig.2 in a first state; Fig.4 is a sectional view the lubricant doser from fig.2 in a second state; Fig.5 is a schematic view of the supply assembly from fig. 1. and an engine Fig.6 is a sectional view of another embodiment of lubricant doser in a first state; and Fig.7 is a sectional view of the lubricant doser from fig.6 in a second state. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0030] Fig. 1 shows a perspective view of parts of an inventive supply assembly 1 for a gaseous-fuel engine 60, while fig. 5 is a schematic representation of the supply assembly 1 and the engine 60. The supply assembly 1 comprises a fuel-supply system 10, which is adapted to supply a gaseous fuel, in this case hydrogen fuel, to the engine 60, which is only shown schematically in fig.5. It comprises a plurality of cylinders (not shown), each of which can receive fuel from fuel injectors 20 of the fuel-supply system. In other words, there is one fuel injector 20 for each cylinder, in this case a total of four. Each fuel injector 20 is connected to a fuel rail 12 via an injector socket 14, which is fixedly connected to the fuel rail 12. The fuel injector 20 and the injector socket 14 together form an injector unit 13. During operation of the engine 60, pressurized fuel (having a fuel pressure of, e.g., 40 bar) is supplied through a connecting pipe 11 to the fuel rail 12 and from there to each injector unit 13. The exact working principle of the fuel injector 20 is not important and will not be described in detail. As shown in fig.2, the fuel injector 20 comprises an injector body 21 which defines a fuel passage 22 that extends from an inlet opening 23 to an outlet opening (not shown). The outlet opening 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. The inlet opening 23 communicates with a socket channel 15 of the socket 14. A socket-lubricant channel 16, which will be explained later, branches off the socket channel 15.

[0031] Further, the supply assembly 1 comprises a lubricant-supply system 30, which is adapted to provide a liquid lubricant L to the fuel injectors 20. It comprises in this case a total of four lubricant dosers 31, each of which is mounted to an injector socket 14. Each lubricant doser 31 can also be referred to as a volumetric doser or pumping doser. It comprises a doser body 32 that defines a doser cavity 33. Within the doser cavity 33, a pumping plunger 34 is movable along a plunger axis A. On a distal side of the pumping plunger 34, there is a pumping chamber 35 which is part of the doser cavity 33. The pumping chamber 35 communicates with an inlet port 36 through an inlet valve 37 and with an outlet port 38 through an outlet valve 39. The outlet port 38, in turn, communicates with the socketlubricant channel 15. Accordingly, lubricant L that is released from the outlet port 37 can traverse the socket-lubricant channel 16 and the socket channel 15 and enter the injector 20.

[0032] The operation of the lubricant doser 31 will now be explained with reference to figs. 3-5. The pumping plunger 34 is movable along the plunger axis A between a proximal position that is shown inf fig.3 and a distal position that is shown in fig.4. A volume of the pumping chamber 35, which is partially defined by a distal portion 33.1 of the pumping plunger 33, is greater in the proximal position than in the distal position. The movement of the pumping plunger 33 to the distal position corresponds to a release process in which lubricant L is released through the outlet port 38, as indicated in fig.4. The lubricant L in the pumping chamber 35 is compressed, and the increased pressure opens the outlet valve 39, which is a check valve. On the other hand, the inlet valve 37, which is also a check valve, is closed at this time, due to an overpressure in the pumping chamber 35 relative to the inlet port 36. This overpressure is partially due to a reduction in pressure at the inlet port 36. As can be seen in fig.5, the inlet ports 36 of all lubricant dosers 31 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.5). 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.

[0033] 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 65 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 42 of each lubricant doser 31. As can be seen in figs. 3 and 4, the control port 42 communicates with a control chamber 41, which is disposed on a proximal side of the pumping plunger 34 and is partially delimited by a proximal portion 34.3 of the pumping plunger 34. As the control piping 46 is connected to the high-pressure pipe 49, an elevated pressure acts on the proximal portion 34.3. At the same time, the considerably lower pressure of the low-pressure pipe 51 acts on an intermediate portion 34.2 of the pumping plunger 34 which is disposed in an intermediate chamber 40 of the doser cavity 33. This is because the intermediate chamber 40 communicates with the inlet port 36 through a bypass channel 43 that bypasses the inlet valve 37. A force resulting from this pressure acting on the intermediate portion 34.2 is much smaller than the force acting on the proximal portion 34.3. Also, although the pressure in the pumping chamber 35 is as high or even higher than the pressure in the control chamber 41, the resulting force is much smaller, since the proximal portion 34.3 has a considerably greater cross-section perpendicular to the plunger axis A than the distal portion 34.1. Thus results the movement of the pumping plunger 34 to the distal position and the release process, which is effected in all lubricant dosers 31 simultaneously. The pumping chamber 35 and the pumping plunger 34 are designed so that a pumping volume, which is displaced by the pumping plunger between the proximal position and the distal position, is less than 20 mm3, preferably less than 10 mm3, more preferably less than 5 mm3. This pumping volume is at least approximately identical to a defined release volume that is released from each lubricant doser 34.

[0034] For an intake process, the control unit 65 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 36 and in the intermediate chamber, while the pressure at the control port is decreased. Accordingly, the pumping plunger 34 moves to the proximal position. Also, the inlet valve 46 opens so that lubricant L flows into the pumping chamber 35, which is now ready for another release process.

[0035] Figs. 6 and 7 show another embodiment of a lubricant doser 31, which may be used instead of the embodiment shown in figs. 2-4. This second embodiment will only be described insofar as it differs from the first embodiment. In this case, the doser body 32 comprises two outer parts, namely a cup-like housing shell 53 and a housing lid 54, which together form a doser housing. The doser housing contains an inner assembly 55, which comprises inner parts of the doser body 32, which are connected, e.g., by press-fitting. A plunger part 56 defines the pumping chamber 35 and a major portion of the doser cavity 33. A seat part 57, which is connected to a distal end of the plunger part 56, forms a seat of the outlet valve 39. The inner assembly 55 also comprises the pumping plunger 34. The inner assembly 55 may be pre-assembled before it is placed the housing shell 53. Afterwards, the housing lid 54 may be assembled to the housing shell 53 and connected thereto by screwing. Thus, the inner assembly 55 is enclosed between the housing shell 53 and the housing lid 54.

[0036] An elastomeric O-ring 44 is disposed circumferentially around the pumping plunger 34. It provides a reliable seal between the control chamber 41 and the intermediate chamber 40 while the length of the pumping plunger 34, as well as its stroke length (i.e., the distance between the proximal position and the distal position) can be kept small. This helps to limit the total size of the lubricant doser 31.

[0037] In contrast to the first embodiment, the lubricant doser 31 does not comprise an inlet valve. Instead, the inlet port 36 communicates with the pumping chamber 35 through an inflow opening 59, which may be formed as a micro bore. It is disposed adjacent to the pumping chamber 35. When the pumping plunger 34 is in the proximal position, as shown in fig.6, the inflow opening 59 is uncovered by the pumping plunger 34, wherefore lubricant L may flow into the pumping chamber 35, as indicated by the arrow. As pressure in the control chamber 41 is increased, the pumping plunger 34 moves towards the distal position and blocks the inflow opening 59, thereby preventing lubricant L from escaping towards the inlet port 36. Instead, the lubricant L is expelled through the outlet valve 39 and the outlet port 38. In order to promote lubricant distribution, a porous outlet cap 58 is disposed at the outlet port 38. It comprises a plurality of through-openings through which the lubricant L is released. The through-openings are too small to be shown in the figures. In this embodiment, the outlet cap 58 is a single metal body with a plurality of through-holes.

[0038] As the pressure at the control port 42 is decreased and the pressure at the inlet port 36 is decreased as described above, the pumping plunger 34 moves towards the proximal position, finally uncovering the inflow opening 59 again so that the pumping chamber 35 is again fluidly connected to the inlet port 36. As in the previous embodiment, a bypass channel 43 is arranged so that movement of the pumping plunger 34 into the proximal position can be promoted by lubricant pressure in the intermediate chamber 40 while the inflow opening 59 is blocked by the pumping plunger 34. 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 20 fuel injector 21 injector body 22 fuel passage 23 inlet opening 30 lubricant-supply system 31 lubricant doser 32 doser body 33 doser cavity 34 pumping plunger 34.1 distal portion 34.2 intermediate portion 34.3 proximal portion 35 pumping chamber 36 inlet port 37 inlet valve 38 outlet port 39 outlet valve 40 intermediate chamber 41 control chamber 42 control port 43 bypass channel 44 O-ring 45 supply piping 46 control piping 47 valve device lubricant reservoir high-pressure pipe pressure pump low-pressure pipe relief valve housing shell housing lid inner assembly plunger part seat part outlet cap inflow opening engine control unit plunger axis 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 (20) that is at least indirectly connected to the fuel rail (12) and is adapted to inject fuel into the engine (60), anda lubricant-supply system (30) comprising at least one lubricant doser (31) with an outlet port (38), the lubricant doser (31) being adapted to controllably release a liquid lubricant (L) through the outlet port (38) into an injector unit (13), and being mounted to the injector unit (13).

2. The supply assembly according to claim 1, wherein at least one injector unit (13) comprises an injector socket (14) through which the fuel injector (20) is connected to the fuel rail (12), and the lubricant doser (31) is adapted to release lubricant (L) through the outlet port (38) into the injector socket (14).

3. The supply assembly according to any of the preceding claims, wherein at least one lubricant doser (31) is a volumetric doser comprising a pumping chamber (35) communicating with the outlet port (38), and a pumping plunger (34) that is adapted to displace lubricant (L) from the pumping chamber (35) in order to release a defined release volume of lubricant (L) into the injector unit (13) during a release process.

4. The supply assembly according to any of the preceding claims, being adapted to simultaneously initiate a release process in a plurality of lubricant dosers (31).

5. The supply assembly according to any of the preceding claims, wherein the lubricant doser (31) comprises a doser body (32) with a doser cavity (33) in which the pumping plunger (34) is movable along a plunger axis (A) between a proximal position and a distal position so that a volume of the pumping chamber (35), which is partially defined by a distal portion (34.1) of the pumping plunger (34), is greater in the proximal position than in the distal position, and the lubricant doser (31) further comprises an inlet port (36) which communicates with the pumping chamber (35), and the outlet port (38) communicates with the pumping chamber (35) through an outlet valve (39).

6. The supply assembly according to any of the preceding claims, wherein the inlet port (36) communicates with the pumping chamber (35) through an inlet valve (37), orthrough an inflow opening (59) which is disposed adjacent to the pumping chamber (35) so that the pumping plunger (34) blocks the inflow opening (59) in the distal position and uncovers the inflow opening (59) in the proximal position.

7. The supply assembly according to any of the preceding claims, wherein at least one of the inlet valve (37) and the outlet valve (39) is a check valve, the inlet valve (37) is adapted to open in response to an overpressure at the inlet port (36) with respect to the pumping chamber (35) and / or the outlet valve (39) is adapted to open in response to an overpressure in the pumping chamber (35) with respect to the outlet port (38).

8. The supply assembly according to any of the preceding claims, wherein the doser cavity (33) comprises a control chamber (41) on a proximal side of the pumping plunger (34), which control chamber (41) communicates with a control port (42), and the pumping plunger (34) is movable to the distal position by a fluid pressure at the control port (42).

9. The supply assembly according to any of the preceding claims, wherein a proximal portion (34.3) of the pumping plunger (34), which is disposed adjacent to the control chamber (41), has a greater cross-section perpendicular to the plunger axis (A) than the distal portion (34.1).

10. The supply assembly according to any of the preceding claims, wherein the doser cavity (33) comprises an intermediate chamber (40) in which an intermediate portion (34.2) of the pumping plunger (34) is disposed, and which communicates with the inlet port (36) through a bypass channel (43) that bypasses the inlet valve (37).

11. The supply assembly according to any of the preceding claims, wherein the lubricantsupply system (30) is adapted to increase a fluid pressure at the inlet port (36) and decrease a fluid pressure at the control port (42) to introduce lubricant through the inlet port (36) into the pumping chamber (35), and to decrease the fluid pressure at the inlet port (36) and increase the fluid pressure at the control port (42) to eject lubricant from the pumping chamber (35) through the outlet port (38) during the release process.

12. The supply assembly according to any of the preceding claims, wherein the lubricant supply system (30) comprises a supply piping (45), which is connected to the inlet port (36) of at least one lubricant doser (31), and / or a control piping (46), which is connected to the control port (42) of at least one lubricant doser (31).

13. The supply assembly according to any of the preceding claims, wherein the supply piping (45) is connected to a plurality of inlet ports (36) and / or the control piping (46) is connected to a plurality of control ports (42).

14. The supply assembly according to any of the preceding claims, wherein the lubricantsupply system (30) comprises a high-pressure pipe (49) connected to a lubricant reservoir (48) and a low-pressure pipe (51) connected to the lubricant reservoir (48) and is adapted to generate a higher pressure in the high-pressure pipe (49) than in the low-pressure pipe (51).

15. The supply assembly according to any of the preceding claims, wherein the lubricant supply system (30) comprises a valve device (47) which is adapted to fluidly connect the supply piping (45) to the high-pressure pipe (49) in a first state and to fluidly connect the supply piping (45) to the low-pressure pipe (51) in a second state, wherein preferably the valve device (47) is adapted to fluidly connect the control piping (46) to the low-pressure pipe (51) in the first state and to fluidly connect the control piping (46) to the high-pressure pipe (49) in the second state.

Images