CN107435619B

CN107435619B - Fuel pump or lubricating pump for large two-stroke compression ignition internal combustion engine

Info

Publication number: CN107435619B
Application number: CN201710383002.7A
Authority: CN
Inventors: C·C·翁; J·霍尔斯特; R·B·尼耳森
Original assignee: Mannone Solutions Mannone Solutions Germany Branch
Current assignee: Mannone Solutions Mannone Solutions Germany Branch
Priority date: 2016-05-26
Filing date: 2017-05-26
Publication date: 2022-07-26
Anticipated expiration: 2037-05-26
Also published as: JP2019148264A; JP2017210962A; CN107435619A; KR20190086647A; JP6902066B2; CN115013112A; DK201670361A1; DK179219B1; KR102098753B1; KR20170134243A

Abstract

The present invention relates to a fuel or lubrication pump for a large two-stroke compression ignition internal combustion engine. A pump for supplying fuel or lubricant to a large two-stroke compression-ignition internal combustion engine. The pump (40) comprises two or more pump units (41,42, 43). Each pump unit (41,42,43) comprises a pump piston (62) slidably arranged in a pump cylinder (61) and a hydraulically driven drive piston (46) slidably arranged in a drive cylinder (45), wherein the drive piston (46) is coupled to the pump piston (62) for driving the pump piston (62).

Description

Fuel pump or lubricating pump for large two-stroke compression ignition internal combustion engine

Technical Field

The present invention relates to a fuel or lubricant pump for use in a large slow-running two-stroke single-flow compression-ignition internal combustion engine.

Background

Large two-stroke single-flow turbine supercharged compression-ignition internal combustion crosshead engines are commonly used as prime movers in propulsion systems for large vessels or in power plants. The enormous size, weight and power output of the above-described internal combustion engines has rendered them completely different from conventional internal combustion engines and has placed themselves in a class of large two-stroke turbocharged compression ignition internal combustion engines.

Conventionally, large two-stroke compression-ignition internal combustion engines have been operated on liquid fuels, such as fuel oil or heavy fuel oil. However, increased environmental concerns have led to a trend towards the use of alternative types of fuels, such as natural gas, methanol, coal slurries, petroleum coke, and the like.

Some of these alternative types of fuel have characteristics that are difficult to use in conventional fuel pumps. Some are abrasives, such as coal slurries, some have very poor lubricating properties, such as gasoline, and others require extremely low temperatures, such as liquefied gases.

WO2016/015732 discloses a cylinder lubrication system with multiple cylinder oil pumps. Each cylinder oil pump has a drive piston coupled to a plurality of dose plungers.

Therefore, it is desirable to provide a pump that can handle these alternative fuels.

Disclosure of Invention

It is an object of the present invention to provide a pump which overcomes or at least reduces the above mentioned problems.

The above and other objects are achieved by the features of the independent claims. Further embodiments are apparent from the dependent claims, the description and the drawings.

According to a first aspect, there is provided a pump comprising two or more pump units, each pump unit comprising a pump piston slidably disposed in a pump cylinder and a hydraulically driven drive piston slidably disposed in a drive cylinder, wherein the drive piston is coupled to the pump piston for driving the pump piston.

By providing a pump in which each pump piston is actuated by a linear hydraulic actuator, any suitable pump piston can be driven in a completely flexible manner, independent of the constraints and inertia of the crank, thereby allowing the operating parameters of the pump piston to be fully adjusted to suit the liquid to be pumped.

According to a first possible embodiment of the first aspect, the pump further comprises at least one hydraulic control valve connected to a source of high-pressure hydraulic fluid, preferably a source with a variable and controllable pressure level, and to a tank for controlling the flow of hydraulic fluid into and out of the drive cylinders of one or more of the pump units.

According to a second possible embodiment of the first aspect, the drive cylinder comprises a drive chamber and a return chamber.

According to a third possible embodiment of the first aspect, the drive chamber is connected to the hydraulic control valve and the return chamber is preferably permanently connected to a source of hydraulic fluid having a pressure lower than the pressure of the high pressure hydraulic fluid source.

According to a fourth possible implementation form of the first aspect, the drive cylinders have position sensors for sensing the position of the drive pistons in the respective drive cylinders.

According to a fifth possible embodiment of the first aspect, the fuel supply system further comprises an electronic control unit receiving signals from the position sensor, wherein the at least one hydraulic control valve is an electronic control valve coupled to the electronic control unit.

According to a sixth possible embodiment of the first aspect, the electronic control unit is configured to selectively connect the drive chamber of the pump unit to the high-pressure hydraulic fluid source or to a tank.

According to a seventh possible embodiment of the first aspect, the electronic control unit is configured to start the pump stroke of one drive piston as the pump stroke of the other drive piston approaches its end, such that there is a small overlap between the ending pump stroke and the starting pump stroke. Thus, a substantially steady flow of fuel or lubricant out of the pump may be achieved without significant pressure fluctuations.

According to an eighth possible embodiment of the first aspect, the electronic control unit is configured to take into account the dynamics of the ending pump stroke and the dynamics of the starting pump stroke in order to obtain a substantially constant flow of high pressure fuel or lubricant from the pump.

According to a ninth possible embodiment of the first aspect, the electronic control unit is configured to determine when the pump stroke of one of the drive cylinders/units has to start and when the pump stroke of any one of the drive cylinders has to end. Thus, the point at which the pump stroke starts and in particular the point at which the pump stroke ends can be accurately controlled.

According to a tenth possible embodiment of the first aspect, the electronic control unit is configured to activate the individual drive cylinders substantially successively, preferably in such a way that there is a small overlap.

According to an eleventh possible embodiment of the first aspect, the electronic control unit is configured to operate the drive pistons of the remaining functioning pump units in case of failure of one of the pump units. Thus, redundancy is obtained and the pumping action can be continued if one of the pump units fails.

According to a twelfth possible embodiment of the first aspect, the electronic control unit is configured to operate the drive pistons of the remaining active pump units so as to activate the drive cylinders of the remaining active pump units substantially successively, preferably with a small overlap.

According to a thirteenth possible embodiment of the first aspect, the electronic control unit is configured to adjust the position of the drive piston when the drive chamber is disconnected from the source of high pressure hydraulic fluid according to the size of the flow of liquefied gas from the high pressure pump to the high pressure evaporator. The position at which the pump stroke is diverted can thus be kept the same, irrespective of the speeds and resulting inertia of the pump piston and the drive piston.

According to a fourteenth possible embodiment of the first aspect, the electronic control unit is configured to: when the flow of fuel or lubricant from the pump increases, the position of the respective drive piston at which the drive chamber of the drive piston is disconnected from the high pressure fluid source is adjusted in a direction opposite to the direction of the drive stroke.

According to a fifteenth possible implementation form of the first aspect, the electronic control unit is configured to: when the flow of fuel or lubricant from the pump decreases, the position of the drive chamber of the drive piston is adjusted in the direction of the drive stroke from the corresponding drive piston at which the high pressure fluid source is disconnected.

According to a sixteenth possible embodiment of the first aspect, the electronic control unit is configured to adjust the position of the respective drive piston when the drive chamber of the drive piston is disconnected from the high pressure fluid source according to an algorithm, plan or randomly, so as to distribute the positions to which the pump piston is steered over the stroke area of the pump piston, thereby reducing wear of the pump cylinder.

According to a seventeenth possible embodiment of the first aspect, the electronic control unit is configured to control the pressure of the fuel or lubricant pumped by the pump by controlling the pressure of the hydraulic fluid supplied to the drive chamber. Thus, an effective and immediately responsive control of the pressure of the pumped fuel or lubricant is achieved.

According to an eighteenth possible implementation of the first aspect, the electronic control unit is configured to use a desired pressure of the pumped fuel or lubricant in a feed forward function to control the pressure of the hydraulic fluid supplied to the drive chamber. By using feed forward control of the liquefied gas pressure by hydraulic pressure, an even faster and smoother control of the pressure of the pumped fuel or lubricant can be achieved.

According to a nineteenth possible implementation of the first aspect, the electronic control unit is configured to use the measured pressure of the pumped fuel or lubricant in a feedback function to control the pressure of the hydraulic fluid supplied to the drive chamber. Thus, non-linearity and transients can be satisfied by the control system.

According to a twentieth possible embodiment of the first aspect, the electronic control unit is configured to control the activation and deactivation of each drive piston independently of the control of the pressure of the hydraulic fluid supplied to the drive chamber. The control strategy for activating the drive piston can thus be optimized independently of the pressure control by the electronic control unit.

According to a twenty-first possible implementation form of the first aspect, the electronic control unit is configured to use the information representative of the position of the drive piston to control the activation and deactivation of the drive piston.

According to a second aspect there is provided a large two-stroke turbocharged compression ignition internal combustion engine having a pump according to the first aspect and any possible embodiment thereof.

According to a third aspect, a cargo vessel is provided comprising the internal combustion engine according to the second aspect.

According to a fourth aspect, there is provided a method for pumping fuel or lubricant to an internal combustion engine for injection of high pressure gas into the internal combustion engine, the method comprising:

storing the fuel or lubricant in a storage tank; and

pumping the fuel or lubricant to the internal combustion engine with a pump, wherein the pump comprises two or more pump units, each pump unit comprising a pump piston slidably disposed in a pump cylinder and a hydraulically driven drive piston coupled to the pump piston for driving the pump piston,

the method further comprises the following steps:

supplying high pressure hydraulic fluid to the drive cylinder to drive the drive piston; and

the pressure of the fuel or lubricant exiting the high pressure pump is controlled by controlling the pressure of the hydraulic fluid fed to the drive cylinder.

According to a first possible embodiment of the fourth aspect, the method further comprises: one of the drive pistons is activated for a drive stroke and thereafter deactivated for a return stroke.

According to a second possible embodiment of the fourth aspect, the pump piston and the drive piston are connected to each other to move in full unison.

According to a third possible embodiment of the fourth aspect, the method further comprises: the pump stroke of one drive piston is started as the pump stroke of the other drive piston approaches its end, so that there is a small overlap between the ending pump stroke and the starting pump stroke.

According to a fourth possible embodiment of the fourth aspect, the method further comprises: the dynamics of the ending pump stroke and the dynamics of the starting pump stroke are taken into account in order to obtain a substantially constant flow of fuel or lubricant from the pump to the internal combustion engine.

According to a fifth possible embodiment of the fourth aspect, the method further comprises: the individual drive cylinders are activated substantially one after the other, preferably in such a way that there is a small overlap.

These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.

Drawings

In the following detailed part of the invention, the invention will be described in more detail with reference to exemplary embodiments shown in the drawings, in which:

FIG. 1 is an elevational view of a large two-stroke diesel internal combustion engine according to an exemplary embodiment;

FIG. 2 is a schematic representation of a fuel supply system for supplying high pressure natural gas from an LNG storage tank to a large two-stroke diesel internal combustion engine according to FIG. 1;

FIG. 3 is an elevation view of a high pressure pump in the fuel supply system of FIG. 2;

FIG. 4 is a diagrammatic view of the high pressure pump of FIG. 3;

FIG. 5 is a detailed cross-sectional view of a pump unit of the high pressure pump of FIG. 3;

fig. 6 to 8 are diagrams illustrating an operation of the high-pressure pump of fig. 3;

FIG. 9 is a diagrammatic view of a control system for controlling the high pressure pump of FIG. 3;

fig. 10 and 11 are graphs showing piston movement at various speeds for the high pressure pump of fig. 3.

Detailed Description

In the following detailed description, a fuel supply system for a large two-stroke, low-speed turbocharged, compression-ignition internal combustion engine with crosshead will be described with reference to an exemplary embodiment, but it will be appreciated that the internal combustion engine may be of another type, for example a two-stroke otto type, a four-stroke otto type or a diesel type with or without turbocharging, with or without exhaust gas recirculation or selective catalytic reduction. Also, a pump for supplying fuel or lubricant to a large two-stroke, low-speed turbocharged, compression-ignition internal combustion engine with crosshead will be described with reference to an exemplary embodiment, but it will be appreciated that the internal combustion engine may be of another type, for example a two-stroke otto type, a four-stroke otto type or a diesel type with or without turbocharging, with or without exhaust gas recirculation or selective catalytic reduction.

Figure 1 shows a large, low speed turbocharged two-stroke diesel internal combustion engine with a runner and crosshead. In this exemplary embodiment, the internal combustion engine has six cylinders in a row. Large low speed turbocharged two-stroke diesel internal combustion engines typically have four to fourteen cylinders in a row, which are carried by a cylinder frame carried by an engine frame 6. The internal combustion engine may for example be used as a main internal combustion engine in a marine vessel or as a stationary internal combustion engine for operating a generator in a power plant. The total output of the internal combustion engine may be, for example, in the range of 1000kW to 110000 kW.

In this exemplary embodiment the internal combustion engine is a two stroke single flow type compression ignition internal combustion engine with a scavenging port at the lower region of the cylinder 1 and a central exhaust valve 4 at the top of the cylinder liner 1. Scavenging air is delivered from the scavenging air container 2 to the scavenging port of each cylinder 1. The pistons in the cylinder liner 1 compress the scavenging gas, injecting high pressure fuel, such as gaseous fuel, through fuel valves in the cylinder head, and combustion occurs and exhaust gases are produced.

When the exhaust valve 4 is open, the exhaust gas flows into the exhaust gas container 3 through the exhaust duct connected to the cylinder 1 and goes to the turbine of the turbocharger 5, through which the exhaust gas leaves the turbine and enters the atmosphere. The turbine of the turbocharger 5 drives a compressor which is supplied with fresh air via an air intake. The compressor delivers pressurized scavenging gas into a scavenging line leading to the scavenging gas container 2. The scavenging gas in the scavenging line passes through an intercooler 7 for cooling the scavenging gas.

FIG. 2 is a schematic diagram of a fuel or lubricant supply system for an internal combustion engine. The fuel supply system may be mounted on a marine vessel, such as an LNG carrier or a container ship.

The fuel supply system comprises a fuel tank 8, in which fuel tank 8 lubricant or fuel, such as fuel oil, is stored. Alternatively, the fuel is a liquefied gas stored under cryogenic conditions.

A feed conduit 9 connects the outlet of the fuel or lubricant reservoir 8 to the inlet of the high pressure pump 40. The feed pump 10 assists in transporting fuel or lubricant from the reservoir 8 to the inlet of the pump 40.

The pump 40 pumps fuel or lubricant gas to the internal combustion engine through the supply conduit 18. The valve means 19 controls the connection between the fuel/lubricant supply system and the large two-stroke diesel combustion engine.

The pump 40 has two or

more pump units

41,42,43 (3 pump units are shown in this embodiment). Each

pump unit

41,42,43 comprises: a pump piston 62 slidably disposed in the pump cylinder 61; and a hydraulically driven drive piston 46 slidably arranged in the drive cylinder 45, wherein the drive piston 46 is coupled to the pump piston 62 for driving said pump piston 62.

The pump piston 62 and the pump cylinder 61 form a positive displacement pump. In an embodiment, the pump piston 62 and the pump cylinder 61 form a so-called cold end of a cryogenic pump unit having a pump chamber 63 for pumping liquefied gas.

The pump cylinder 61 is connected to the drive pistons of the

pump units

41,42,43 by means of a piston rod 49. The drive piston 46 divides the interior of the drive cylinder 45 into a drive chamber 48 and a return chamber 47.

The drive cylinder 45 is connected to a source of high pressure hydraulic liquid 20, such as a pump or pumping station, by means of a high pressure hydraulic liquid supply conduit 23. In the embodiment shown, the high-pressure hydraulic fluid source 20 comprises an electric drive motor 21, which drives a high-pressure pump 22. The high-pressure pump 22 may be, for example, a positive displacement pump, preferably a variable displacement positive displacement pump. In an embodiment, the source of high pressure hydraulic fluid comprises two high pressure hydraulic pumps 22 for redundancy purposes, each high pressure hydraulic pump 22 being driven by its own electric drive motor 21.

Fig. 3 is an elevation view of the high-pressure pump 40, the high-pressure pump 40 having three

pump units

41,42,43, which have a pump cylinder 61, a drive cylinder 45 and a control valve 24 and are supported by a frame 35, the high-pressure pump 40 also having an accumulator 53 for equalizing the higher pressure of the high-pressure pump 40 and for equalizing the lower pressure of the return chamber. The pump unit 41, the pump unit 42, the pump unit 43 are arranged in a compact manner on the frame 35 and the components on the frame 35 have no spark generating components and only ATEX certified electronic components, allowing the unit to be installed in an ATEX environment without problems.

Fig. 4 is a diagram of high-pressure pump 40 with pump unit 41, pump unit 42, and pump unit 43. Each

pump unit

41,42,43 is connected to a tank by means of a hydraulic liquid return line 26 and to a source of high pressure hydraulic liquid comprising a variable displacement positive displacement pump 22 connected to each

pump unit

41,42 and 43 by means of a hydraulic liquid supply conduit 23. Each of the

pump units

41,42 and 43 is connected to the supply pipe 18.

Each

pump unit

41,42,43 comprises a hydraulic control valve 24, which hydraulic control valve 24 is configured to selectively connect each drive chamber 48 to a source of high pressure hydraulic liquid or to a tank by means of a control conduit 25.

Each

pump unit

41,42,43 comprises a drive unit 44 in the form of a linear hydraulic actuator, which drive unit 44 is formed by a drive cylinder 45, in which drive cylinder 45 a drive piston 46 is slidably arranged. The return chamber 47 is permanently connected to a hydraulic pressure source comprising a hydraulic pump 30 (e.g. a variable displacement positive displacement pump) by means of a return chamber supply line 31, which return chamber supply line 31 preferably comprises a flow restrictor 33 and is coupled to an accumulator 32, which accumulator 32 serves to ensure a steady supply of pressurized hydraulic liquid to the return chamber 47. Alternatively, the low-pressure source is obtained from a high-pressure hydraulic system by means of a pressure reducing valve. In one embodiment, the hydraulic fluid supplied to the return chamber is at a substantially lower pressure than the hydraulic fluid supplied to the drive chamber 48. Alternatively, the effective pressure surface of the side of the drive piston 46 facing the return chamber 47 may be arranged to be significantly smaller than the effective pressure surface of the drive piston facing the drive chamber 48. In the latter case, the pressure of the hydraulic fluid in the return chamber 47 may be substantially equal to the pressure of the hydraulic fluid supplied to the drive chamber 48.

Each

pump unit

41,42,43 comprises a pump 60 in the form of a linear positive displacement pump, which pump 60 is formed by a pump cylinder 61, which pump cylinder 61 accommodates a pump piston 62 to form a pump chamber 63. The pump chamber 63 is connected to the feed conduit 9 by means of a first one-way valve 51, which first one-way valve 51 only allows a flow to the pressure chamber 63. The pump chamber 63 is connected to the supply line 18 by means of a second one-way valve 52, which second one-way valve 52 only allows flow out of the pressure chamber 63.

Fig. 5 is a detailed cross-sectional view of pump unit 41, pump unit 42, and pump unit 43 of high-pressure pump 40. The

pump units

41,42,43 comprise a hydraulic linear actuator 44, which hydraulic linear actuator 44 comprises a cylinder 45, in which cylinder 45 a drive piston 46 is arranged. The drive piston 46 is connected to a piston shaft 47, preferably both formed as one unit. The piston rod 49 and the drive piston 46 have a bore 58 for receiving a rod 57 of a position sensor 56. The signal of the position sensor 56 is transmitted to the electronic control unit 70. The driving piston 46 divides the interior of the driving cylinder 45 into a driving chamber 48 and a return chamber 47. In fig. 5, the return chamber is not discernable because the drive piston 46 has reached the end of its drive stroke. The drive chamber 48 is connected to the hydraulic control valve 24 via the hole 25. The return chamber 47 is permanently connected to the hydraulic pressure source by means of the bore 31.

The piston rod 47 of the linear hydraulic actuator 44 is connected to the piston rod 62 of the cryogenic pump 60 (although the pump 60 could also be a conventional linear positive displacement pump for pumping non-cryogenic liquids). The connection between the piston rod 47 and the piston rod 62 is established by the connector block 54 in the following manner: causing piston rod 47 and piston rod 62 to move in unison. The drive cylinder 45 is connected to the pump cylinder 61 by a bolt connection 55. The cryopump 60 has an outlet that connects the pump chamber 63 to the delivery conduit 50.

Fig. 9 is a diagrammatic view of a control system in the form of an electronic control unit 70 for controlling the operation of the high pressure pump 40.

The electronic control unit 70 receives a fuel or lubricant pressure set point 71. The pressure set point 71 is transmitted to a summing point 72. At a first summing point 72, the measured pressure is subtracted and the difference between the set point and the measured pressure at the outlet of the pump 40 is transmitted to a PI (proportional integral) controller 74, which PI controller 74 is part of a feedback control loop.

The pressure set point is transmitted to the feed forward piston proportional gain unit 78. At a second summing point 76, the signal from the feed forward piston proportional gain unit 78 is compared to the signal from the PI controller 74.

The measured pressure of the fuel or lubricant that is sent to the first summing point 72 may be based on a measurement of the pressure in the tube space at the internal combustion engine, i.e. downstream of the valve arrangement 19. The valve means 19 is a double-shut valve means receiving a flow of fuel or lubricant from the supply conduit 18. The fuel or lubricant is filtered in a filter 86 to measure pressure.

The result of the comparison at the second summing point 76 is transmitted to the source 20 of high pressure hydraulic liquid. Based on the signal, the high-pressure hydraulic liquid source 20 delivers hydraulic liquid having an appropriate pressure to the high-pressure pump unit 40.

The electronic control unit 70 receives a signal indicative of the position of the drive piston and processes the position signal in the piston monitoring unit 92. A piston monitoring unit 92 is coupled to the piston activation strategy unit 90. The details of the operation of the piston monitoring unit 92 and the piston activation strategy unit 90 will be shown and described in further detail below. The signal of the piston activation strategy unit 90 is transmitted to the control valve 24 of the high-pressure pump 40 for activating the drive piston 46.

Activation of the drive piston 46 causes fuel or lubricant to be pumped through the supply conduit 18.

The main pressure control of the electronic control unit 70 is of the forward type. The PI controller compensates for non-linearity and assists transients.

The fuel or lubricant pressure is self-controlled by the hydraulic feed pressure provided to the pump unit 41, the pump unit 42, the pump unit 43. The pressure is controlled on the hydraulic side and does not need to be applied on the gas side. When the hydraulic pressure is properly controlled, the system cannot reach excessively high fuel or lubricant pressures.

The drive piston 46 is controlled by means of a control strategy which is not an active part of the pressure control.

Each

pump unit

41,42,43 is individually controllable. Thus, different piston strategies and various operating conditions may be operated. In addition, the possibility of operating the

pump units

41,42,43 separately provides redundancy, since it is possible to change from three

pump units

41,42,43 to two pump units between two strokes.

The return speed may be greater than the forward (pump) speed, so that there may be overlap when only two pump units are running. The overlap between

pump units

41,42,43 may be adjusted as required to reduce pressure spikes.

The end position of the pump stroke may be varied over time to distribute wear over the area of the pump cylinder 61, as opposed to having high wear at a fixed location of the cylinder.

This system allows little or no pressure overshoot, even at sudden shut-offs (piston stops), due to very low inertia or other factors that negatively impact dynamic response.

The control valve 24 may be a hydraulic control valve or an electrically controlled valve. In embodiments where the control valve 24 is a hydraulic control valve, an electrically controlled solenoid valve (not shown) is provided that controls a hydraulic control signal to the control valve 24. The electrically controlled solenoid valve receives an electronic control signal from the electronic control unit 70.

Electronic control unit 70 (in particular piston activation strategy unit 90) is configured to selectively connect pump unit 41, pump unit 42, drive chamber 48 of pump unit 43 to high pressure hydraulic liquid source 20 or to a tank.

The electronic control unit 70, in particular the piston activation strategy unit 90, is configured to start the pump stroke of one drive piston 47 when the pump stroke of the other drive piston 47 is near its end, so that there is little overlap between the finished pump stroke and the started pump stroke. In one embodiment, the electronic control unit 70 is configured to activate the individual drive cylinders substantially sequentially, preferably with a small overlap.

Thus, as shown in fig. 6 and 7, a substantially steady flow of LNG to the high-pressure vaporizer 14 can be achieved without significant pressure fluctuations.

Fig. 6, 7 and 8 illustrate typical operation of the high pressure pump 40. The thin solid line represents the pump unit 41, the thick solid line represents the pump unit 42, and the broken line represents the pump unit 43. Fig. 6 is a diagram showing the movement of the drive piston 46/pump piston 62. As shown, the beginning of the pump stroke of the next pump unit starts just before the end of the pump stroke of the currently active pump unit. Fig. 7 shows the final pressure which is composed of the pressure outputs from the three

pump units

41,42,43 by means of the delivery line 50. The final pressure is substantially constant and free of fluctuations.

Fig. 8 shows a speed profile of the pump units, wherein it can clearly be seen that the speed of the return stroke is significantly higher than the speed of the pump stroke, allowing for an overlap between the pump units, even if only two of the three or more pump units are in use.

In an embodiment, the electronic control unit 70 (in particular the piston activation strategy unit 90) is configured to take into account the dynamics of the ending pump stroke and the dynamics of the starting pump stroke in order to obtain a substantially constant flow of high pressure liquefied gas from the high pressure pump to the high pressure evaporator 14.

In an embodiment, the electronic control unit 70 (in particular the piston activation strategy unit 90) is configured to determine when a pump stroke of one of the

pump units

41,42,43 has to start and to determine when a pump stroke of one of the

pump units

41,42,43 has to end. Thus, the point at which the pump stroke starts and in particular the point at which the pump stroke ends can be accurately controlled by the piston strategy unit 90 (preferably together with the piston monitoring unit 92).

In an embodiment, the electronic control unit 70 is configured to operate the driving pistons of the remaining

functioning pump units

41,42,43 upon failure of one of the

pump units

41,42, 43. Thus, redundancy is obtained and the pumping action may be continued if one of the

pump units

41,42,43 fails.

In an embodiment, the electronic control unit 70 is configured to adjust the position of the drive piston 46 when the drive chamber 48 is disconnected from the high pressure hydraulic liquid source in dependence on the magnitude of the flow of liquefied gas from the high pressure pump 40 to the high pressure evaporator. Thus, the position at which the pump stroke is steered may be controlled regardless of the velocity and resulting inertia of the drive piston 46 and the pump piston 62.

According to an embodiment, the electronic control unit 70 is configured to: when the flow rate of fuel or lubricant from the high pressure pump to the internal combustion engine increases, the position of the respective drive piston 46 at which the drive chamber 48 of the drive piston 46 is disconnected from the source 20 of high pressure liquid is adjusted in a direction opposite to the direction of the drive stroke, and the electronic control unit 70 is configured to: when the flow of fuel or lubricant from the high pressure pump to the internal combustion engine decreases, the position of the drive chamber 48 of the drive piston 46 is adjusted in the direction of the drive stroke with the corresponding drive piston 46 when the high pressure liquid source 20 is disconnected. This is shown in fig. 10 and 11.

Fig. 10 illustrates the effect of the increased velocity of the drive piston 46 and the pump piston 62 at the end position of the drive/pump stroke. The thin solid line represents the pump unit 41, the thick solid line represents the pump unit 42, and the broken line represents the pump unit 43. When the drive piston has reached a stroke of 80mm, the electronic control unit 70 signals the hydraulic control valve 24 to connect the drive chamber 48 to the tank, regardless of the load/magnitude of the flow of liquefied gas delivered by the high-pressure pump 40. Due to inertia and higher speed, the stop/steer position of the drive piston 46 varies from 85mm at 25% load to 89mm at 50% load to 98mm at 100% load.

Fig. 11 is a graph showing the effect of the electronic control unit 70 compensating for the increased speed of the drive piston 46/pump piston 62 by connecting the drive chamber 48 to the tank for a shorter stroke (when the load is high) and for a longer stroke (when the load is low). As can be seen from the figure, the electronic control unit 70 can accurately control the end position of the driving/pump stroke in this manner.

In the example of the figure, when the previous cylinder enters the drive chamber 75mm, a signal for connecting the drive chamber 48 to the tank is issued for 25% load (i.e. 25% of the maximum capacity of the high pressure pump 40) for the next drive cylinder. When the drive chamber is 93mm, the drive chamber of the "previous" drive cylinder is connected to the reservoir. The connection of the next driving cylinder to the high pressure source "signal on" and the connection of the "previous" cylinder to the reservoir "signal off" are shown in table 1 below.

	25% load	45% load	70% load	100% load
					Signal switch-on	75mm	75mm	75mm	75mm
Signal turn-off	93mm	86mm	83mm	80mm
					Stop position	97mm	97mm	97mm	97mm

TABLE 1

Of course, the electronic control unit 72 can still be programmed to deliberately change the starting position in order to reduce wear of the pump cylinder 61.

In an embodiment, the electronic control unit 70 is configured to adjust the position of the respective drive piston 46 when the drive chamber 48 of the drive piston 46 is disconnected from the high pressure fluid source 20 according to an algorithm, schedule or randomly in order to distribute the positions at which the pump piston 62 is turned over the stroke area of the pump piston 62, thereby reducing wear of the pump cylinder 61. It is known that wear on the pump cylinder 61 is highest at the position where the pump stroke ends. By changing the position of the end of the pump stroke, the wear of the pump cylinder 61 can be spread over a larger area, and therefore the lifetime of the pump cylinder 61 can be significantly increased.

In one embodiment, the electronic control unit 70 is configured to control the activation and deactivation of each drive piston 46 independently of the pressure control of the hydraulic fluid supplied to the drive chamber 48. The control strategy for activating the drive piston can thus be optimized by the electronic control unit 70, independently of the pressure control.

The invention has been described in connection with various embodiments herein. However, other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the term "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. The electronic control unit may be formed by a combination of independent electronic control units. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Reference signs used in the claims shall not be construed as limiting the scope.

Claims

1. A cryogenic fuel pump (40) for pumping cryogenic fuel to a large two-stroke turbocharged compression-ignition internal combustion engine, the cryogenic fuel pump comprising: two or more pump units (41,42,43), each pump unit (41,42,43) comprising a pump piston (62) slidably arranged in a single pump cylinder (61) and a hydraulically driven drive piston (46) slidably arranged in a single drive cylinder (45), wherein the drive piston (46) is coupled to the pump piston (62) for driving the pump piston (62); the pump piston (62) and the pump cylinder (61) forming a cold end of a cryogenic pump unit comprising a pump chamber for pumping the cryogenic fuel,

a feed pump (10) for assisting in conveying the cryogenic fuel from a storage tank (8) to an inlet of the cold end of the cryogenic fuel pump (40),

a first source of high pressure hydraulic fluid (22),

a second source of hydraulic fluid (30), the second source of hydraulic fluid (30) having a pressure lower than the first pressure of the first source of high pressure hydraulic fluid (22), and at least one electronic control valve (24), the electronic control valve (24) being connected to the first source of high pressure hydraulic fluid (22) and to a tank for controlling the flow of hydraulic fluid into and out of the drive cylinders (45) of two or more of the pump units (41,42,43),

the first source of high pressure hydraulic fluid (22) comprises a positive displacement pump and is configured to provide hydraulic fluid at a first pressure,

the drive cylinder (45) comprising a drive chamber (48) and a return chamber (47), the drive chamber (48) being connected to the control valve (24), and the return chamber (47) is permanently connected to the second hydraulic fluid source (30), the drive cylinders having position sensors (56), the position sensors (56) being for sensing the position of the drive pistons (46) in the respective drive cylinders (45), the signals from the position sensors (56) being received by an electronic control unit (70), wherein the electronic control valves (24) are coupled to the electronic control units (70), at least one of the electronic control units (70) being configured to selectively connect the drive chamber (48) of the drive cylinder (45) of the pump unit (41,42,43) to the first high pressure hydraulic fluid source (22) or to a tank by operating the electronic control valve (24).

2. A cryogenic fuel pump (40) as claimed in claim 1, wherein the first source of high pressure hydraulic fluid (22) has a variable and controllable pressure rating.

3. A cryogenic fuel pump (40) according to claim 1, wherein the electronic control unit (70) is configured to start the pump stroke of one drive piston as the pump stroke of the other drive piston approaches the end of the pump stroke such that there is a small overlap between the ending pump stroke and the starting pump stroke.

4. A cryogenic fuel pump (40) according to claim 3, wherein the electronic control unit (70) is configured to take into account the dynamics of the ending pump stroke and the dynamics of the starting pump stroke in order to obtain a substantially constant flow of fuel from the cryogenic fuel pump.

5. The cryogenic fuel pump (40) of claim 4, wherein the electronic control unit (70) is configured to activate the individual drive cylinders sequentially, activating the individual drive cylinders with a small overlap.

6. The cryogenic fuel pump (40) of claim 1, wherein the electronic control unit (70) is configured to adjust the position of the drive piston (46) when the drive chamber (48) is disconnected from the first source (22) of high pressure hydraulic fluid in accordance with the magnitude of the flow of fuel pumped by the cryogenic fuel pump.

7. The cryogenic fuel pump (40) of claim 6, wherein the electronic control unit (70) is configured to: when the flow rate of the fuel pumped by the low-temperature fuel pump (40) increases, the position of the corresponding drive piston at which the drive chamber of the drive piston is disconnected from the first high-pressure hydraulic fluid source is adjusted in a direction opposite to the direction of the drive stroke.

8. The cryogenic fuel pump (40) of claim 6, wherein the electronic control unit (70) is configured to: when the flow rate of the fuel from the low-temperature fuel pump decreases, the position of the corresponding drive piston at which the drive chamber of the drive piston is disconnected from the first high-pressure hydraulic fluid source is adjusted in the direction of the drive stroke.

9. Cryogenic fuel pump (40) according to claim 1, wherein the electronic control unit (70) is configured to adjust the position of the drive piston according to an algorithm, plan or randomly in order to distribute the position of the pump piston steering over a part of the stroke of the pump piston, thereby reducing wear of the pump cylinder.

10. The cryogenic fuel pump (40) of claim 1, wherein the electronic control unit (70) is configured to control the pressure of the fuel exiting the cryogenic fuel pump by controlling the pressure of the hydraulic fluid fed to the drive chamber.

11. The cryogenic fuel pump (40) of claim 10, wherein the electronic control unit (70) is configured to use a desired pressure of fuel exiting the cryogenic fuel pump in a feed forward function to control the pressure of hydraulic fluid supplied to the drive piston.

12. The cryogenic fuel pump (40) of claim 10, wherein the electronic control unit (70) is configured to use the measured pressure of the fuel exiting the cryogenic fuel pump in a feedback function to control the pressure of the hydraulic fluid fed to the drive piston.

13. The cryogenic fuel pump (40) of claim 10, wherein the electronic control unit (70) is configured to control activation and deactivation of each drive piston (46) independently of pressure control of hydraulic fluid supplied to the drive chamber.

14. The cryogenic fuel pump (40) of claim 10, wherein the electronic control unit (70) is configured to use a signal indicative of the position of the drive piston (46) to control activation and deactivation of the drive piston.

15. A large two-stroke turbocharged compression ignition internal combustion engine comprising a cryogenic fuel pump (40) according to any one of claims 1 to 14, the cryogenic fuel pump (40) being for pumping cryogenic fuel to the large two-stroke turbocharged compression ignition internal combustion engine.