Lubricant supply assembly

Abstract

A lubricant supply assembly for a gaseous fuel internal combustion engine comprising a pressure source module 10 and a lubricant dozer 31. The dozer includes a pumping chamber (35,fig.2) communicating

Description

Technical field The present invention generally relates to a lubricant supply assembly for a gaseous fuel internal combustion engine. It more specifically relates to a pressure source module for the control of delivery of lubricant. Background Art 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 towear. Similar problems arise with internal combustion engines that uses other types of gaseous fuel, e.g., natural gas or mixtures of hydrocarbon and hydrogen. 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. A lubricant supply assembly for gaseous fuel engine, as described e.g. in patent application GB 2317234.9, comprise a lubricant dozer and a lubricant pressure source. Currently, lubricant pressure source devices rely on a high-capacity pump connected to a directional valve which drives flow toward a system. Such architectures comes with high-cost and are not suitable for on-board lubrication systems in a vehicle. Technical problem It is an object of the present invention to provide a lubricant supply assembly which encapsulates pressure control for the delivery of lubricant, which is affordable and is suitable for on-board lubrication systems. General Description of the Invention This object is achieved by a lubricant supply assembly as claimed in claim 1. The invention provides a lubricant supply assembly for a gaseous fuel internal combustion engine, comprising a pressure source module and at least one lubricant dozer arranged to release lubricant into a gaseous fuel flow, the lubricant dozer including a pumping chamber communicating with a lubricant outlet port, and a pumping plunger that is adapted to displace lubricant from the pumping chamber in order to release a defined volume of lubricant during a delivery process, a supply port from which low-pressure lubricant is fed to the pumping chamber and a control port where high-pressure lubricant may be applied to actuate the pumping plunger. The pressure source module comprises: - a lubricant tank for storing liquid lubricant; - a first port fluidly coupled to the inlet port of the lubricant dozer; - a second port fluidly coupled to the control port of the lubricant dozer; - a pump in fluid communication with the lubricant tank, the first port and the second port, the pump being operable at a first pressure level Pi and at a second pressure level P2; - a shutoff valve arranged to selectively enable flow from the pump to the first port; and - a check valve configured to enable flow from the pump to the second port; the check valve having an opening pressure Pv, which is greater than the first pressure level Pi and smaller than the second pressure level P2. The proposed pressure source module allows the lubricant dozer to operate with two different pressure setups, low and high levels. Such pressure levels can be achieved by varying the supply power. With the lower pressure condition, current draw is minimized through low voltage application to the pump, while supplying lubricant to the dozers. In the high-pressure operation, the module allows actuating the dozer to perform lubricant release. Such operating modes allow the fuel pump to run continuously, minimizing wear effects due to intermittent operation, with a single pump and a controllable shutoff valve that diverts flow to the first or second port. The present invention has been particularly developed for engines operating on hydrogen fuel, or hydrogen fuel mixtures. The lubricant may be any appropriate lubricant adapted to protect and lubricate the fuel injectors, to maintain durability and functionality. The lubricant may be oil, in particular engine oil (e.g. 5W30 or 0W30), or a synthetic lubricant custom-formulated to be compatible with the particular gaseous fuel and the materials within the injectors. In embodiments, the pressure source module further comprises a first calibrated orifice arranged between the shutoff valve and the first port to enable return flow to the lubricant tank. In embodiments, the pressure source module further comprises a second calibrated orifice arranged between the check valve and the second port to enable return flow to the lubricant tank. In embodiments, the pressure source module further comprises a pressure regulator arranged between the check valve and the second port, and is configured to enable return flow to the lubricant tank when the pressure exceeds a predetermined threshold. Alternatively, the high-pressure side can be regulated in closed loop, by adjusting the pump voltage based on feedback from a pressure sensor and temperature sensor arranged downstream of the second port. Advantageously, the first port and the second port may be arranged on the lubricant tank, and the pump, shutoff valve and check valve may be arranged inside the lubricant tank. This provides a compact assembly in the form of a module with integrated functions. In practice, the various components may be appropriately connected with pipes, hoses and / or by means of any appropriate fluid distribution structure. The fluid distribution structure may define a first channel that extends from a pump outlet to the first port. The shutoff valve may be is serially integrated in the first channel. The first calibrated orifice is arranged between the shutoff valve and the first port. The fluid distribution structure further defines a second channel that branches off from the first channel, upstream of the shutoff valve, and connects the second port. The check valve is integrated in the second channel such that lubricant can only flow downstream of the check valve if the pressure is above Pv. The first and second channels can be defined by individual pipes or hoses, or alternatively by a manifold component that defines the two channels and allows integrating the desired functions, e.g. the shutoff valve, check valve, pressure regulator, orifices. The manifold structure may be a plastic molded component, or other. Such manifold component can serve as a central hub, also allowing for compactness and serviceability. In embodiments, the lubricant supply assembly further comprises heating means selectively operable to heat up the lubricant and hence influence the viscosity of the lubricant. Such heating means may be arranged inside the tank and / or arranged on conduits connecting the pressure source module to the dozer(s). Electric (resistive) heating elements may be used. An electric heating element can be installed inside the tank. Additionally, or alternatively, an electric heating element can be combined with the piping connecting the pressure source module to the dozer, resp. the fuel rail. For example, resistive wires can be arranged inside the lubricant pipes connecting the pressure source module to the dozers. These and other aspects of the invention are recited in the appended claims. According to another aspect, the invention relates to a fuel delivery system comprising the lubricant supply assembly according to the present disclosure, a gaseous fuel tank connected to a fuel rail, and a plurality of gaseous fuel injectors arranged on said fuel rail. The at least one lubricant dozer of the lubricant supply assembly is configured to release lubricant into a gaseous fuel flow. In embodiments, the at least one lubricant dozer of the lubricant supply assembly is configured to release lubricant at an inlet of a fuel injector of the plurality of gaseous fuel injectors. In particular, the gaseous fuel injectors may be coupled to the fuel rail via respective sockets. One lubricant dozer is arranged on each socket such that lubricant can be selectively discharged via the lubricant outlet port into a socket channel connecting the fuel rail to a fuel injector inlet. In embodiments, a common supply pipe serially connects the supply ports of the lubricant dozers and is in communication with the first port of the pressure source module. A common control pipe serially connects the supply ports of the lubricant dozers and is in communication with the second port of the pressure source module. According to still another aspect, the invention relates to a method of operating a lubricant supply assembly according to the present invention, the method comprising an intake process and a delivery process; whereby, during the intake process, the shutoff valve is closed and the pump is operated at a first pressure level P1, such that pressure at the first port is greater than pressure at the second port; whereby, during the intake process, the shutoff valve is open and the pump is operated at a second pressure level P2, such that pressure at the second port is greater than pressure at the first port. According to still another aspect, the invention relates to a control unit comprising instructions which, when executed, cause the control unit to perform the present method of operating a lubricant supply assembly. Brief Description of the Drawings A preferred embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings in which: Fig. 1 is a schematic view of an embodiment of the lubricant supply assembly according to the invention; Fig. 2 is a cross sectional view of a lubricant dozer in the closed position; Fig. 3 is a cross sectional view of a lubricant dozer in the open position; Fig. 4 is a schematic view of a fuel delivery system comprising the present lubricant supply assembly; Fig. 5 is a schematic view showing the present lubricant supply assembly connected to the lubricant dozer, shown in cross-section integrated in the fuel rail; Fig.6 is another embodiment of the pressure source module of Fig. 1, which further includes heating means. Description of Preferred Embodiments Figure 1 shows a schematic drawing of the pressure source module 10 of the lubricant supply assembly according to the invention. The pressure source module 10 comprises a lubricant tank 12 with a first port 12a and a second port 12b. The tank is filled with lubricant 9 and closed by a cover 12c, in which the ports 12a and 12b are here integrated. Preferably, all of the hydraulic and electrical connections from the module 10 is done through the cover 12c that seals the module 10 to the environment. The pressure source module 10 further comprises a variable speed lubricant pump 14, which is configured to be operable at a first pressure level P1 or at a second pressure level P2. This is typically done by varying the pump supply voltage. The pump 14 may be high-flow brushed or brushless pump. The lubricant pump 14 is arranged inside the lubricant tank 12, such that an inlet 14.1 of the lubricant pump 14 is in fluid communication with lubricant 9 stored inside the lubricant tank 12. The outlet 14.2 of the lubricant pump 14 is fluidly coupled to the first port 12a via a controllable shutoff valve 16. The outlet of the lubricant pump 14 is also fluidly coupled to the second port 12b via a check valve 18 having a minimum opening pressure Pv which is greater than the first pressure level P1 and smaller than the second pressure level P2. The pressure source module 10 further comprises a first calibrated orifice 20 arranged between the shutoff valve 16 and the first port 12a, and a second calibrated orifice 22 arranged between the check valve 18 and the second port 12b. The first and second calibrated orifices 20, 22 enable return flow to the lubricant tank 12 at a controlled rate. Optionally, a pressure regulator may be 24 is arranged between the check valve 18 and the second port 12b to enable return flow to the lubricant tank 12 when the pressure exceeds a safety threshold (above P2). In practice, a first duct or hose 7 may extend from the pump outlet 14.2 to the first port 12a. The shutoff valve 16 is serially integrated on the first duct 7. The calibrated orifice 20 is arranged between the shutoff valve 16 and the first port 12a. It can be a hole or aperture of calibrated size (inferior to the cross-section of the duct 7) in the first duct 7 itself, or such hole / aperture at the end of a duct portion branched off from the first duct 7 and that opens in the inner tank volume. A second duct or hose 8 may be branched off from the first duct 7, upstream of the shutoff valve 16, and connect the second port 12b. The check valve 18 is integrated in the second duct 8 such that lubricant can only flow downstream of check valve 18 if the pressure is above Pv. The calibrated orifice 22 is arranged between the check valve 18 and the second port 12b. Similar to the other calibrated orifice 20, it can be a hole or aperture of calibrated size in the second duct 8 itself, or such hole / aperture at the end of a duct portion branched off from the second duct and that opens in the inner tank volume. Likewise, the pressure regulator 18, which may be a simple check valve, is arranged in communication with the second duct downstream of the check valve either directly on the second duct 8, or in a branched off duct portion that opens in the inner tank volume. The shutoff valve 16 may be an electromechanics valve, e.g. a solenoid actuated valve that can be selectively operated by energizing the solenoid. It may be a normally open valve. As will be explained below, the pressure source module 10 enables hydraulic control of lubricant dozers 31 in a gaseous fuel delivery system 100. Such a gaseous fuel delivery system 100 is shown on figure 4. The gaseous fuel delivery system 100 comprises a gaseous fuel tank 102, a pressure regulator 104, and a fuel rail 106 coupled to a plurality of fuel injectors 110, here four, adapted for fuel gas injection. The pressure regulator 104 is serially connected between the gaseous fuel tank 102 and the fuel rail 106 by means of piping 108. The pressure regulator 104 is configured to decreases the flow pressure upstream thereof to a nominal working pressure range, e.g. around 5 to 40 bar. The gaseous fuel tank 102 is typically configured to store pressurized gaseous fuel at pressures of up to 700 bars. The gaseous fuel delivery system 100 is adapted to supply a gaseous fuel, in this case hydrogen, to the engine. The engine comprises a plurality of cylinders (not shown), each of which can receive fuel from a single fuel injector 110. In other words, there is one fuel injector for each cylinder, in this case a total of four. Each fuel injector 110 is connected to the fuel rail 106 via an injector socket 105, which is fixedly connected to the fuel rail 106 (or could be manufactured in one piece with fuel rail), (better seen in Fig.5). During operation of the engine, pressurized fuel (having a fuel pressure of, e.g., 40 bar) is supplied through a piping 108 to the fuel rail 106 and from there to each injector 110. The exact working principle of the fuel injector 110 is not here relevant and will not be described in detail. The fuel injector 110 may be of conventional design. It may typically comprise an injector body which defines a fuel passage that extends from an inlet opening 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 a magnetic field generated by a solenoid. As is known to those skilled in the art, the fuel rail 106 generally comprises a tubular body 106.1 defining an accumulator volume 106.2 (or chamber) for the fuel gas, and there is one outlet passage 106.3 per injector trough the tubular body wall. One socket 105 is provided per outlet channel, for direct coupling of the fuel injectors to the fuel rail. The injector socket 105 hence comprises a socket channel 105.1 that fluidly connects the fuel rail outlet channel 106.3 with the injector inlet opening. The socket channel 105.1 opens into a sleeve-like coupling member 105.3 that receives the injector inlet portion. Gas-tight connexion is achieved by means of sealing elements mounted around the injector inlet portion. In the presented embodiment, one lubricant dozer 31 is provided per socket / injector. A socket-lubricant channel 105.2 branches off the socket channel 105.1. A lubricant dozer 31 is mounted on each injector socket, such that its outlet port is fluidly coupled with the socket-lubricant channel 105.2. During a lubricant delivery process, each lubricant dozer 31 thus releases lubricant in the socket-lubricant channel of their respective injector socket, which then flows towards the inlet opening of the fuel injector through the socket channel. In the shown embodiment, each lubricant dozer 31 is arranged in a housing 105.4 that is part of the socket 105. Housing 105.4 can be in one piece with the socket 105 or assembled thereto, e.g. by brazing. A control unit 112, typically an Engine Control Unit, is configured to control operation of the fuel injectors 110, the pressure regulator 104 and here further the pressure source module 10. Specifically, the control unit 112 may control operation of the shutoff valve 16 and the lubricant pump 14. Figure 2 and 3 show cross sectional views of a lubricant dozer 31. More specifically figure 2 shows a lubricant dozer 31 in its closed position, while figure 3 shows the lubricant dozer 31 in its open position. Flow of lubricant through the lubricant dozer 31 is represented by solid arrow L. The lubricant dozer 31 comprises a dozer body 32 that defines a dozer cavity 33. Within the dozer cavity 33, a pumping plunger 34 is movable along a plunger axis A. The distal side of the pumping plunger 34 defines a pumping chamber 35 which is part of the dozer cavity 33. The pumping chamber 35 communicates with an inlet / supply port 36 - here via an inlet check valve 37- and with an outlet port 38 via an outlet check valve 39. The outlet port 38 enables delivery of lubricant to a fuel injector 110. The pumping plunger 34 is movable along plunger axis A between a proximal position (as shown in figure 2) and a distal position (as shown in figure 3). The terms proximal / distal are used to indicate relative positioning in the drawings. Specifically, the term proximal refers to positions toward the top of the drawing sheet, while distal refers to positions toward the bottom of drawing sheet. 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. The movement of the pumping plunger 34 towards the distal position corresponds to a lubricant delivery process whereby lubricant is released through the outlet port 38, as shown on figure 3. As the lubricant in the pumping chamber 35 is compressed by the pumping plunger 34, the increased pressure opens the outlet valve 39 and enables flow from the pumping chamber 35 to the outlet port 38. The plunger 34 is advantageously dimensioned to provide a multiplying effect, by which the lubricant pressure at the control port is sufficient to overcome hydrogen fuel rail pressure. The lubricant dozer 31 further comprises control port 42 which communicates with a control chamber 41. The control chamber 41 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. In use, lubricant pressure in the control chamber 41 acts on the proximal portion 34.3 of the pumping plunger 34, thereby biasing the pumping plunger 34 towards the distal position. At the same time, pressure in the pumping chamber 35 act on the distal portion 34.1 of the pumping plunger 34, and pressure in an intermediate chamber 40 of the dozer cavity 33 acts on an intermediate portion 34.2 of the pumping plunger 34, thereby biasing the pumping plunger 34 towards the proximal position. The intermediate chamber 40 communicates with the inlet port 36 through a channel 43. Hence, movement of the pumping plunger 34 is controlled by the pressure differences between the control chamber 41, the intermediate chamber 40 and the pumping chamber 35. In use, hydraulic pressure applied at the control port 40 is typically higher than that of the lubricant at inlet port 36. The pressure source module 12 is configured to supply lubricant to the dozers 31 and to selectively actuate them to release / discharge lubricant. Accordingly, the first port 12a of the pressure source module 12 is fluidly coupled with the inlet ports 36 of each lubricant dozer 31, preferably via a common supply pipe 45. Likewise, the second port 12b of the pressure source module 12 is fluidly coupled with the control ports 42 of each lubricant dozer 31, preferably via a common control pipe 47. As can be understood from the figures, the common pipes 45 and 47 can be rigid pipes integrated to the common rail, that connect each housing 105.4, respectively communicating with the supply and control ports. Connection of the rigid common pipes 45 and 47 to the pressure source 10 can be done via rigid pipes or flexible hoses. The operation of the pressure source module 12 for the control of lubricant dozers 31 will now be described. The operation comprises a low-pressure intake process and a high-pressure delivery process. During the intake process, the shutoff valve 16 is open and the lubricant pump 14 is operated at a first voltage V1 to output lubricant at the first pressure level P1, thereby enabling flow of pressurized lubricant towards the first port 12a and the inlet ports 36 of the lubricant dozers 31. Since the check valve 18 has an opening pressure Pv which is greater than the first pressure level P1, flow of pressurized lubricant from the lubricant pump 14 to the second port 12b is prevented. Due to the second calibrated orifice 22, the pressure at the second port 12b and at the control port 42 of the lubricant dozers 31 is similar to the pressure in the lubricant tank 12 and is thus smaller than P1. Hence, during the intake process, the pressure at the inlet port 36 of the lubricant dozers 31 is greater than the pressure at their control port 42. In turn, the pressure in the intermediate chamber 40 and the pumping chamber 35 is greater than the pressure in the control chamber 41, thereby causing the pumping plunger 34 to move to its proximal position. This in turns increase the volume of the pumping chamber 35, thereby decreasing the pressure therein, which opens the inlet check valve 37 and enables filling of the control chamber 35. During the delivery process, the shutoff valve 16 is closed and the lubricant pump 14 is operated at a second voltage V2 to output lubricant at the second pressure level P2, thereby preventing flow of pressurized lubricant towards the first port 12a and the inlet ports 36 of the lubricant dozers 31. Since the check valve 18 has an opening pressure Pv which is lower than the second pressure level P2, flow of pressurized lubricant from the lubricant pump 14 to the second port 12b is enabled. Due to the first calibrated orifice 20, the pressure at the first port 12a and at the inlet port 36 of the lubricant dozers 31 decreases to a level similar to that of the lubricant tank 12 and is thus smaller than P2. Hence, during the delivery process, the pressure at the inlet port 36 of the lubricant dozers 31 is smaller than the pressure at their control port 42. In turn, the pressure in the intermediate chamber 40 and the pumping chamber 35 is smaller than the pressure in the control chamber 35, thereby causing the pumping plunger 34 to move to its distal position. This in turns decreases the volume of the pumping chamber 35, thereby increasing the pressure therein, which opens the outlet valve 39 and enables delivery of lubricant to the injectors 110. In summary, the intake process is performed by operating the lubricant pump 14 at a low-pressure level P1 and opening the shutoff valve 16, and results in a proximal movement of the pumping plunger 34 and refilling of the pumping chamber 35. Conversely, the delivery process is performed by operating the lubricant pump 14 at a high-pressure level P2 and closing the shutoff valve 16, and results in a distal movement of the pumping plunger 34 and delivery of lubricant from the pumping chamber 35 to the injectors 110. These intake and delivery processes may be repeated to provide lubricant to the fuel injectors 110 as required. The required lubricant volumes, per release process, are rather small. In embodiments, the pumping chamber 35 and the pumping plunger 34 may be designed such that a pumping volume, which is displaced by the pumping plunger 34 as it moves from the proximal position to the distal position, is less than 20 mm3, preferably less than 10 mm3, more preferably less than 5 mm3. This volume is approximately identical to a defined release volume that is released from each lubricant dozer 34. The pressure source module 10 thus forms a single lubricant source that is used for both lubricant supply for the purpose of injector lubrication, as well as hydraulic pressure source for actuation of the lubricant dozers 31. Hence a single volume of lubricant is necessary. Any suitable lubricant may be used. For example, the lubricant can be engine oil such as 5W30 or 0W30, which allows for a wide operating range. The terms low-pressure and high-pressure are here used as relative terms, meaning that the pressure at the control port is higher than at the supply port. In practice, a pressure differential of 1 to 3 bars is sufficient. The supply pressure may be of a few bars, e.g. between 1 and 6 bar(g). The high pressure may, e.g., be of 4 to 7 bar(g). In embodiments, heating means may be provided to heat up the lubricant, to influence the viscosity of the lubricant. This allows extending the temperature operating range of the lubrication pressure source 10. This guarantees that the system is less subject to environmental temperature limitations, notably in cold weather conditions, in which lubricants viscosity would prevent the pump to run optimally. The heating means may comprise a resistive heater 50, which can be arranged vertically in the tank, or in the bottom, as indicated by the dashed line boxes in Fig.6. Such heater 50 could operate with or without a temperature sensor 52 positioned near the bottom and / or in the cover of the lubricant reservoir, in order to provide 5 feedback to the control unit to determine when the resistive heater 50 shall be operated.

Claims

1. A lubricant supply assembly for a gaseous fuel internal combustion engine, comprising a pressure source module (10) and at least one lubricant dozer (31) arranged to release lubricant into a gaseous fuel flow, the lubricant dozer including a pumping chamber (35) communicating with a lubricant outlet port (38), and a pumping plunger (34) that is adapted to displace lubricant from the pumping chamber in order to release a defined volume of lubricant during a delivery process, a supply port (36) from which low-pressure lubricant is fed to the pumping chamber and a control port (42) where high-pressure lubricant may be applied to actuate the pumping plunger, wherein the pressure source module comprises:- a lubricant tank (12) for storing liquid lubricant;- a first port (12a) fluidly coupled to the inlet port of the lubricant dozer;- a second port (12b) fluidly coupled to the control port of the lubricant dozer;- a pump (14) in fluid communication with the lubricant tank, the first port and the second port, the pump being operable at a first pressure level Pi and at a second pressure level P2;- a shutoff valve (16) arranged to selectively enable flow from the pump to the first port; and- a check valve (18) configured to enable flow from the pump to the second port; the check valve having an opening pressure Pv, which is greater than the first pressure level Pi and smaller than the second pressure level P2.

2. The lubricant supply assembly according to any of the preceding claims, wherein the pressure source module further comprises a first calibrated orifice (20) arranged between the shutoff valve and the first port to enable return flow to the lubricant tank.

3. The lubricant supply assembly according to any of the preceding claims, wherein the pressure source module further comprises a second calibrated orifice (22) arranged between the check valve and the second port to enable return flow to the lubricant tank.

4. The lubricant supply assembly according to any of the preceding claims, wherein the pressure source module further comprises a pressure regulator (24) arranged between the check valve and the second port, and is configured to enable return flow to the lubricant tank when the pressure exceeds a predetermined threshold.

5. The lubricant supply assembly according to any of the preceding claims, wherein the first port and the second port are arranged on the lubricant tank, and wherein the pump, shutoff valve and check valve are arranged inside the lubricant tank.

6. The lubricant supply assembly according to any of the preceding claims, further comprising heating means (50) selectively operable to heat up the lubricant.

7. The lubricant supply assembly according to claim 6, wherein the heating means is arranged inside the tank and / or arranged in or on conduits connecting the pressure source module to the dozer(s).

8. The lubricant supply assembly according to claim 7, wherein the heating means include resistive elements and / or resistive wires.

9. The lubricant supply assembly according to any of the preceding claims comprising a fluid distribution structure defininga first channel (7) connecting a pump outlet to the first port, the shutoff valve being is serially mounted in the first channel; anda second channel (8) that branches off from the first channel, upstream of the shutoff valve, and connects the second port, check valve being integrated in the second channel such that lubricant can only flow downstream of the check valve if the pressure is above Pv.

10. A fuel delivery system comprising the lubricant supply assembly according to any of the preceding claims, a gaseous fuel tank connected to a fuel rail (106), and a plurality of gaseous fuel injectors arranged on said fuel rail;wherein the at least one lubricant dozer (31) of the lubricant supply assembly is configured to release lubricant into a gaseous fuel flow.

11. The fuel delivery system according to claim 10, wherein the at least one lubricant dozer of the lubricant supply assembly is configured to release lubricant at an inlet of a fuel injector of the plurality of gaseous fuel injectors.

12. The fuel delivery system according to claim 10 or 11, whereinthe gaseous fuel injectors are coupled to the fuel rail via respective sockets (105);one lubricant dozer is arranged on each socket such that lubricant can be selectively discharged via the lubricant outlet port into a socket channel (105.1) connecting the fuel rail to a fuel injector inlet.

13. The fuel delivery system according to any of claims 10 to 12, whereina common supply pipe serially connects the supply ports of the lubricant dozers and is in communication with the first port of the pressure source module; anda common control pipe serially connects the supply ports of the lubricant dozers and is in communication with the second port of the pressure source module.

14. A method of operating a lubricant supply assembly according to any of claims 1 to 9, or a fuel delivery system according to any of claims 10 to 13, the method comprising an intake process and a delivery process;whereby, during the intake process, the shutoff valve is closed and the pump is operated at a first pressure level P1, such that pressure at the first port is greater than pressure at the second port;whereby, during the intake process, the shutoff valve is open and the pump is operated at a second pressure level P2, such that pressure at the second port is greater than pressure at the first port.

15. Control unit comprising instructions which, when executed, cause the control unit to perform the method according to claim 14.A

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