WO2016008490A1

WO2016008490A1 - A lubrication system for main and/or crosshead bearings of a large turbocharged two-stroke internal combustion engine

Info

Publication number: WO2016008490A1
Application number: PCT/DK2015/050182
Authority: WO
Inventors: Martin Olsson; Henrik Bak WEIMAR
Original assignee: A.P. Møller - Mærsk A/S
Priority date: 2014-07-16
Filing date: 2015-06-24
Publication date: 2016-01-21

Abstract

A lubrication system for the main or crosshead bearings of a large slow-running turbocharged two-stroke internal combustion engine (1) with crossheads (5) and main bearings (8) for a crankshaft (7). The lubrication system comprises a source of lubrication oil configured to deliver a flow of lubrication oil to the main or crosshead bearings, the source of lubrication oil has a variable controllable output flow rate, an electronic control unit in receipt of a parameter indicative of the thermal load on the main or crosshead bearings. The electronic control unit is configured to adjust the output flow rate of the source of lubrication oil in response to the parameter. The electronic control unit (50) is configured to determine the flow rate of lubrication oil that needs to be delivered to the main or crosshead bearings in order to ensure that the temperature of the main or crosshead bearings does not exceed a threshold. The electronic control unit (50) controls the source of lubrication oil to deliver a flow rate of lubrication oil to the main or crosshead bearings that depends on the parameter, with a value of the parameter indicating a higher thermal load on the main or crosshead bearings resulting in higher lubrication oil flow rates to the main or crosshead bearings, a value of the parameter indicating a lower thermal load resulting in lower lubrication oil flow rates to the main lower lubrication bearings.

Description

A LUBRICATION SYSTEM FOR MAIN AND/OR CROSSHEAD BEARINGS OF A LARGE TURBOCHARGED TWO-STROKE INTERNAL COMBUSTION ENGINE TEHCNICAL FIELD

The present invention relates to a lubrication system for a large slow-running uniflow turbocharged two-stroke internal combustion engine with crossheads. BACKGROUND

Large two-stroke diesel engines with crossheads are typically used in propulsion systems of large ships. These engines have a crosshead disposed between the piston and the crankshaft and main bearings that supports the crankshaft. The main bearings and crosshead bearings of a large slow-running two-stroke internal combustion engine require constant supply of lubrication oil, in order to sustain the bearing oil film but also and foremost to cool the bearing and keep the temperature of the bearing at an acceptable level. Typically, one or more electrically driven lubrication pumps running at a constant speed have been used to supply these bearings with lubrication oil. JPS 60145406 discloses acylinder lubrication system according to the preamble of the independent claims.

SUMMARY

On this background, it is a first aspect to provide a lubrication system for the main bearings of a large slow- running turbocharged two-stroke internal combustion engine with crossheads and main bearings for a crankshaft, the lubrication system comprising a source of lubrication oil configured to deliver a flow of lubrication oil to the main bearings, the source of lubrication oil having a variable controllable output flow rate, an electronic control unit in receipt of a parameter indicative of the thermal load on the main bearings, the electronic control unit being configured to adjust the output flow rate of the source of lubrication oil in response to the parameter.

By controlling the flow rate of lubrication oil delivered to the main bearings the amount of energy used to pump the lubrication to the main bearings can be significantly reduced. This is especially true for slow steaming. Therefore, the present invention is particularly relevant for retrofit to existing engines that were originally dimensioned for higher steaming speeds of the ships in which they are installed than the speed at which the ships are presently operated, so-called slow steaming (running partial load) . During such slow steaming the amount of lubrication oil that is delivered to the main bearings is much higher than technically required, and pumping energy is thus wasted in the known lubrication systems .

In a first possible implementation of the lubrication system the electronic control unit is configured to determine the flow rate of lubrication oil that needs to be delivered to the main bearings in order to ensure that the temperature of the main bearings does not exceed a threshold .

In a second possible implementation form of the lubrication system the electronic control unit controls the source of lubrication oil to deliver a flow rate of lubrication oil to the main bearings that depends on the parameter, with a value of the parameter indicating a higher thermal load on the main bearings resulting in higher lubrication oil flow rates to the main bearings, a value of the parameter indicating a lower thermal load resulting in lower lubrication oil flow rates to the main bearings .

In a third possible implementation form of the lubrication system the electronic control unit is configured to use a lookup table or an equation to determine the appropriate lubrication oil flow rate to the main bearings in relation to the parameter.

In a fourth possible implementation form of the lubrication system the source of lubrication oil comprises fixed displacement pumps that are driven by variable speed electric drive motors, and wherein to the electronic control unit is configured to adapt and control the speed of the electric drive motors.

In a first possible implementation form of the lubrication system the source of lubrication oil comprises a plurality of pumps, and wherein the electronic control unit is configured to selectively activate a number of the plurality of pumps in order to control the amount of lubrication oil delivered to the main bearings .

In a sixth possible implementation form of the lubrication system the source of lubrication oil comprises a variable displacement pump, and wherein the electronic control unit is configured to control the amount of lubrication oil delivered to the main bearings by changing the setting of the variable displacement pump .

According to a second aspect, there is provided a method for controlling of lubrication oil flow to the main bearings of a large slow-running turbocharged two-stroke internal combustion engine with crossheads and main bearings for a crankshaft, the method comprising adjusting the flow rate of lubrication oil delivered to the main bearings in response to a parameter indicative of the thermal load on the main bearings in order to ensure that the temperature of the main bearings does not exceed a threshold. In a first possible implementation form of the second aspect the method further comprises decreasing the flow of lubrication to the main bearings when the parameter indicates thermal load is below a second threshold, increasing the flow of lubrication oil to the main bearings when the parameter indicates thermal load above a first given threshold and maintaining a present flow rate of lubrication oil to the main bearings when the parameter has a value between the first and second threshold .

In a first possible implementation form of the second aspect the method further comprises using a lookup table or an equation to determine the appropriate lubrication oil flow rate to the main bearings in relation to the parameter.

On this background, it is a third aspect to provide a lubrication system for the crosshead bearings of a large slow-running turbocharged two-stroke internal combustion engine with crosshead bearings for crossheads connecting the piston rods to the big ends and main bearings for a crankshaft, said lubrication system comprising: a source of lubrication oil configured to deliver a flow of lubrication oil to said crosshead bearings, said source of lubrication oil having a variable controllable output flow rate, an electronic control unit in receipt of a parameter indicative of the thermal load on said crosshead bearings, said electronic control unit being configured to adjust the output flow rate of said source of lubrication oil in response to said parameter.

By controlling the flow rate of lubrication oil delivered to the crosshead bearings the amount of energy used to pump the lubrication to the crosshead bearings can be significantly reduced. This is especially true for slow steaming. Therefore, the present invention is particularly relevant for retrofit to existing engines that were originally dimensioned for higher steaming speeds of the ships in which they are installed than the speed at which the ships are presently operated, so- called slow steaming (running partial load) . During such slow steaming the amount of lubrication oil that is delivered to the crosshead bearings is much higher than technically required, and pumping energy is thus wasted in the known lubrication systems.

In a first possible implementation of the lubrication system according to the third aspect the electronic control unit is configured is configured to determine the flow rate of lubrication oil that needs to be delivered to the crosshead bearings in order to ensure that the temperature of the crosshead bearings does not exceed a threshold . In a second possible implementation of the lubrication system according to the third aspect the electronic control unit controls said source of lubrication oil to deliver a flow rate of lubrication oil to the crosshead bearings that depends on said parameter, with a value of said parameter indicating a higher thermal load on the crosshead bearings resulting in higher lubrication oil flow rates to said crosshead bearings a value of said parameter indicating a lower thermal load resulting in lower lubrication oil flow rates to said crosshead bearings .

In a third possible implementation of the lubrication system according to the third aspect the electronic control unit is configured to use a lookup table or an equation to determine the appropriate lubrication oil flow rate to said crosshead bearings in relation to said parameter .

In a fourth possible implementation of the lubrication system according to the third aspect the source of lubrication oil comprises fixed displacement pumps that are driven by variable speed electric drive motors, and wherein said electronic control unit is configured to adapt and control the speed of said electric drive motors .

In a fifth possible implementation of the lubrication system according to the third aspect the source of lubrication oil comprises a plurality of pumps, and wherein said electronic control unit is configured to selectively activate a number of said plurality of pumps in order to control the amount of lubrication oil delivered to the crosshead bearings.

In a sixth possible implementation of the lubrication system according to the third aspect the source of lubrication oil comprises a variable displacement pump, and wherein said electronic control unit is configured to control the amount of lubrication oil delivered to the croshead bearings by changing the setting of the variable displacement pump.

On this background, it is a fourth aspect to provide a method for controlling of lubrication oil flow to the croshead bearings of a large slow-running turbocharged two-stroke internal combustion engine with crosshead bearings for crossheads connecting the piston rods to the big ends and main bearings for a crankshaft, said method comprising adjusting the flow rate of lubrication oil delivered to said crosshead bearings in response to a parameter indicative of the thermal load on said crosshead bearings in order to ensure that the temperature of the crosshead bearings does not exceed a threshold . In a first possible implementation the method according to the fourth aspect further comprises decreasing the flow of lubrication to crosshead bearings when said parameter indicates thermal load is below a second threshold, increasing the flow of lubrication oil to said crosshead bearings when said parameter indicates thermal load is above a first given threshold and maintaining a present flow rate of lubrication oil to said crosshead bearings when said parameter has a value between said first and second threshold. In a second possible implementation the method according to the fourth aspect further comprises using a lookup table or an equation to determine the appropriate lubrication oil flow rate to said crosshead bearings in relation to said parameter.

These and other aspects of the invention will be apparent from and the example embodiments described below.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following detailed portion of the present description, the invention will be explained in more detail with reference to the exemplary embodiments shown in the drawings, in which:

Fig. 1 is a diagrammatic sectional view of a lubrication system for a large two-stroke diesel engine according to an example embodiment, and

Fig. 2 is a diagrammatic sectional view of a lubrication system for a large two-stroke diesel engine according to another example embodiment. DETAILED DESCRIPTION

In the following detailed description, the lubrication system for a large low speed two stroke engine will be described by the example embodiments. Fig. 1 diagrammatically shows a large low speed turbocharged two-stroke diesel engine 1 with a crankshaft 7 and crossheads 5 sectional view. Large turbocharged two- stroke diesel engines typically have between four and sixteen cylinders in line, carried by an engine frame 10. The engine 1 may e.g. be used as the main engine in an ocean going vessel. The total output of the engine may, for example, range from 5,000 to 110,000 kW.

The engine is a diesel engine of the two-stroke uniflow type with scavenge ports 14 at the lower region of the cylinders 1 and an exhaust valve 12 at the top of the cylinders 1. The engine can be operated on various types of fuel, such as e.g. marine diesel, heavy fuel, or gas. The scavenge air is passed from the scavenge air receiver 11 to the scavenge ports 14 of the individual cylinders 2. A piston 3 in the cylinder 2 compresses the scavenge air, fuel is injected and combustion follows and exhaust gas is generated. When an exhaust valve 12 is opened, the exhaust gas flows through an exhaust duct associated with the cylinder 2 concerned into the exhaust gas receiver 13 and onwards through a first exhaust conduit to a turbocharger (not shown) , from which the exhaust gas flows away from the atmosphere. The turbocharger delivers pressurized scavenge air to a scavenge air conduit leading to the scavenge air receiver 11.

A piston rod 4 extends from the bottom of the piston rod to the crosshead 5. A connecting rod 6 connects the crosshead 5 to one of the throws of the crankshaft 7. The crankshaft 7 is rotation suspended in the engine frame and bedplate by the main bearings 8. A thrust bearing (not shown) is provided at the aft of the engine to accommodate the thrust created by a propeller (not shown) driven by the engine 1. The thrust bearing is supplied with lubrication oil by the same conduit that supplies the main bearings 8. The main bearings 8 for the crankshaft 7 are machined to have a circular cylindrical bearing surface and in the bore there is provided an upper shell and a lower shell defining a bearing surface for supporting a corresponding bearing journal of the crankshaft. The hydrodynamic effects of the rotational movement of the journal create a pressure build up in the oil film between the bearing surface and the journal with a pressure that lifts the journal from the bearing surface. The circular cylindrical bearing surface is formed by the inner surfaces of the upper and lower shells abutting each other at two partition faces. The shells are made of steel supporting material, on the inner side of which bearing metal has been deposited. A lower bearing housing part can be shaped directly in the engine bedplate (not shown) and the lower shell is placed directly in the bearing boring of the bedplate. An upper bearing housing part is tightened towards the bedplate (not shown) by means of bearing studs. A crankshaft journal rotates in the mainly circular cylindrical space formed by the two shells. An oil film between the bearing surface and the journal surface carries the journal and prevents substantially any direct contact between the journal surface and the inside surface of the shells and provides lubrication. A flow of lubrication oil is supplied to the bearing surface. The lubrication oil film assists in cooling the main bearing.

Large two-stroke diesel engines include many components that are for lubrication and/or cooling purposes supplied with lubrication oil. For example, the crankshaft 7 is placed in an oil pan that is provided in the lower part of the engine 1 and supplied with lubrication oil under pressure that is circulated through the oil pan. Other lubrication positions, such as bearings, etc. are separately provided with lubrication oil, as will be described in greater detail further below. The surplus leakage oil is collected in the oil pan. A lubrication oil supply loop is provided for supplying lubrication oil to all lubrication oil consumers. The lubrication oil supply loop includes a supply conduit 15 that starts at a lubrication oil tank and a return conduit connecting the oil sump 9 to the lubrication oil tank. The supply conduit 15 includes two low-pressure pumps 16 arranged in parallel with respective electric drive motors for arranging the oil transport (although it is understood that there could be any other number of supply pumps) . The supply conduit 15 also includes a cooler for cooling the lubrication oil and a filter 17 for filtering out contamination. This can in embodiment be a ΒσΚ 50μ filter .

The supply conduit splits downstream of the filter 17 into an oil sump supply conduit, a bearing supply conduit 20 and a hydraulic system supply conduit 18. The oil sump supply conduit delivers filtered and cooled lubrication oil to the oil sump 9. The hydraulic system supply conduit 18 includes an additional fine filter 19 (this can in embodiment be a ΒσΚ 6μ filter) and downstream thereof a plurality of high-pressure pumps 30 for providing the hydraulic system with high-pressure hydraulic fluid, i.e. the hydraulic system uses filtered lubrication oil that has been filtered in extra time as hydraulic fluid. The hydraulic fluid from the hydraulic system is again returned to the lubrication oil tank (return conduits not shown) . The bearing supply conduit 20 branches into a main bearing supply conduit 23 and a crosshead bearing supply conduit 26. The main bearing supply conduit 23 also provides the thrust bearing the aft of the engine 1 with lubrication oil.

The main bearing supply conduit 23 includes an electronically controlled valve 21 for controlling the flow. The main bearing supply conduit 23 also includes a feed pump 22. In the present embodiment a pair of parallel feed pumps are shown, but it is understood that any number of pumps could be used, although a plurality of pumps is preferred for redundancy reasons. The feed pump 22 is driven by one or more electric drive motors. The main bearing supply conduit 23 delivers a substantially constant flow of lubrication oil to the main bearings .

The crosshead bearing supply conduit 26 includes an electronically controlled valve 24 for controlling the flow. The crosshead bearing supply conduit 26 also includes a feed pump 25. In the present embodiment a pair of parallel feed pumps are shown, but it is understood that any number of pumps could be used, although a plurality of pumps is preferred for redundancy reasons. The feed pump 25 is driven by one or more electric drive motors. The crosshead bearing supply conduit 26 delivers a substantially constant flow of lubrication oil to the crosshead bearings.

The electronic control unit 50 receives signals that contain information about the engine, such as specific temperatures and pressures, and operating conditions, such as the engine load and speed. The electronic control unit 50 is also connected via signal cables to the feed pumps 22 for the main bearings, the control valve 21 in the main bearing supply conduit 23, the feed pumps 25 for the crosshead banks, control valve 24 in the crosshead bearing supply conduit 26 and to the control valve 24 in the crosshead bearing supply conduit 26.

In the shown embodiment, the feed pump 22 is driven by variable speed electric drive motors, such as e.g. VLT drives. The speed of the electric drive motors that drive the feed pump 22 is controlled by the control signal that is issued by the electronic control unit 50. Thus, the electronic control unit 50 is configured to adapt and control the speed of the electric drive motors and thereby the speed of the feed pump 22. The flow rate of lubrication oil delivered by the feed pump 22 is essentially proportional to the speed of the pump 22. Thus, by adjusting the speed of the electric motor the electronic control unit 50 can adjust the flow rate of lubrication oil delivered by the pump 22 to the main bearings 8 via conduit 23.

The electronic control unit is configured to determine the amount (flow rate) lubrication oil that needs to be delivered to the main bearings 8 in order to ensure that the temperature of the main bearings does not reach undesirable high levels. Various parameters are indicative of the need for the main bearings 8 to receive lubrication oil for cooling purposes. Examples of such parameters are engine load, main bearing temperature, engine speed and lubrication oil temperature in the oil sump (this is a non-exhaustive list) . In an embodiment the electronic control unit 50 is configured to decrease the flow of lubrication to the main bearings 8 when the parameter indicates thermal load below a second threshold and configured to increase the flow of lubrication oil to the main bearings 8 when the parameter indicates thermal load is above a first given threshold and configured to maintain a present flow rate of lubrication oil to the main bearings 8 when the parameter has a value between the first and second threshold. The first and second threshold can be determined empirically, by tests or by experience values.

In embodiment, the electronic control unit 50 uses the engine load to determine the amount of lubrication oil that needs to be delivered to the main bearings 8. Thus, electronic control unit 50 will control the feed pump 22 to deliver a flow rate of lubrication oil to the main bearings 8 that depends on the engine load. Higher engine loads result in higher flow rates and lower engine loads result in lower flow rates. The electronic control unit 50 may use a lookup table or an equation to determine the appropriate flow rate in relation to the engine load.

In another embodiment the electronic control unit 50 receives a signal from one or more temperature sensors that are configured to measure the temperature of the main bearings. In this embodiment the electronic control unit 50 is configured to control the feed pump 22 to deliver a flow rate of lubrication oil to the main bearings 8 that depends on the temperature of the main bearings. Higher main bearing temperatures result in higher flow rates and lower main bearing temperatures result in lower flow rates. The electronic control unit 50 may use a lookup table or an equation to determine the appropriate flow rate in relation to the main bearing temperature .

In yet another embodiment the electronic control unit 50 receives a signal indicative of the engine speed. In this embodiment the electronic control unit 50 is configured to control the feed pump 22 to deliver a flow rate of lubrication oil to the main bearings 8 that depends on the engine speed. Higher engine speeds result in higher flow rates and lower engine speeds result in lower flow rates. The electronic control unit 50 may use a lookup table or an equation to determine the appropriate flow rate in relation to the engine speed.

In yet another embodiment the electronic control unit 50 receives a signal indicative of lubrication oil temperature in the oil sump 9. In this embodiment the electronic control unit 50 is configured to control the feed pump 22 to deliver a flow rate of lubrication oil to the main bearings 8 that depends on the lubrication oil temperature in the oil sump 9. Higher lubrication oil temperatures result in higher oil temperatures and lower lubrication oil temperatures result in lower flow rates. The electronic control unit 50 may use a lookup table or an equation to determine the appropriate flow rate in relation to lubrication oil temperature.

In yet another embodiment the electronic control unit 50 is configured to use a combination of the parameters listed above that are indicative of need for the main bearings to receive lubrication oil for controlling the temperature of the main bearings. In embodiments where there is a plurality of pumps that form the feed pump 22, the flow rate delivered by the pump 22 can also be adapted by the electronic control unit (50) activating different numbers of pumps. Thus, in an embodiment with two parallel pumps the electronic control unit 50 will activate only one pump when there is a low need for lubrication oil to the main bearings 8 and the electronic control unit 50 will activate both pumps when there is a high need for lubrication oil to the main bearings 8.

In yet another embodiment, the feed pump 22, is a variable displacement pump, controlled by the electronic control unit 50, and the flow rate of lubrication oil to the main bearings is adapted by changing the displacement of the pump.

In the shown embodiment, the feed pump 25 is driven by variable speed electric drive motors, such as e.g. VLT drives. The speed of the electric drive motors that drive the feed pump 25 is controlled by the control signal that is issued by the electronic control unit 50. Thus, the electronic control unit 50 is configured to adapt and control the speed of the electric drive motors and thereby the speed of the feed pump 25. The flow rate of lubrication oil delivered by the feed pump 25 is essentially proportional to the speed of the pump 25. Thus, by adjusting the speed of the electric motor the electronic control unit 50 can adjust the flow rate of lubrication oil delivered by the pump 25 to the crosshead bearings 8 via conduit 26.

The electronic control unit 50 is configured to determine the amount (flow rate) lubrication oil that needs to be delivered to the crosshead bearings in order to ensure that the temperature of the crosshead bearings does not reach undesirable high levels. Various parameters are indicative of the need for the crosshead bearings to receive lubrication oil for cooling purposes. Examples of such parameters are engine load, crosshead bearing temperature, engine speed and lubrication oil temperature in the oil sump (this is a non-exhaustive list) .

In an embodiment the electronic control unit 50 is configured to decrease the flow of lubrication to the crosshead bearings hen the parameter indicates thermal load is below a second threshold and configured to increase the flow of lubrication oil to the crosshead bearings when the parameter indicates thermal load is above a first given threshold and configured to maintain a present flow rate of lubrication oil to the crosshead bearings when the parameter has a value between the first and second threshold. The first and second threshold can be determined empirically, by tests or by experience values .

In embodiment, the electronic control unit 50 uses the engine load to determine the amount of lubrication oil that needs to be delivered to the crosshead bearings. Thus, electronic control unit 50 will control the feed pump 25 to deliver a flow rate of lubrication oil to the crosshead bearings that depends on the engine load. Higher engine loads result in higher flow rates and lower engine loads result in lower flow rates. The electronic control unit 50 may use a lookup table or an equation to determine the appropriate flow rate in relation to the engine load. In another embodiment the electronic control unit 50 receives a signal from one or more temperature sensors that are configured to measure the temperature of the crosshead bearings. In this embodiment the electronic control unit 50 is configured to control the feed pump 25 to deliver a flow rate of lubrication oil to the crosshead bearings that depends on the temperature of the crosshead bearings. Higher crosshead bearing temperatures result in higher flow rates and lower crosshead bearing temperatures result in lower flow rates. The electronic control unit 50 may use a lookup table or an equation to determine the appropriate flow rate in relation to the crosshead bearing temperature. In yet another embodiment the electronic control unit 50 receives a signal indicative of the engine speed. In this embodiment the electronic control unit 50 is configured to control the feed pump 25 to deliver a flow rate of lubrication oil to the crosshead bearings that depends on the engine speed. Higher engine speeds result in higher flow rates and lower engine speeds result in lower flow rates. The electronic control unit 50 may use a lookup table or an equation to determine the appropriate flow rate in relation to the engine speed.

In yet another embodiment the electronic control unit 50 receives a signal indicative of lubrication oil temperature in the oil sump 9. In this embodiment the electronic control unit 50 is configured to control the feed pump 25 to deliver a flow rate of lubrication oil to the crosshead bearings that depends on the lubrication oil temperature in the oil sump 9. Higher lubrication oil temperatures result in higher oil temperatures and lower lubrication oil temperatures result in lower flow rates. The electronic control unit 50 may use a lookup table or an equation to determine the appropriate flow rate in relation to lubrication oil temperature.

In yet another embodiment the electronic control unit 50 is configured to use a combination of the parameters listed above that are indicative of need for the crosshead bearings to receive lubrication oil for controlling the temperature of the crosshead bearings.

In embodiments where there is a plurality of pumps that form the feed pump 25, the flow rate delivered by the pump 25 can also be adapted by the electronic control unit (50) activating different numbers of pumps. Thus, in an embodiment with two parallel pumps the electronic control unit 50 will activate only one pump when there is a low need for lubrication oil to the crosshead bearings and the electronicl control unit 50 will activate both pumps when there is a high need for lubrication oil to the crosshead bearings.

In yet another embodiment, shown in Fig. 2 at least one of the feed pumps, 25, is a variable displacement pump, controlled by the electronic control unit 50, and the flow rate of lubrication oil to the crosshead bearings is adapted by changing the displacement of the pump25. In this embodiment the feed pump 22 can also comprise at least one variable displacement pump, controlled by the electronic control unit 50 and the flow rate of lubrication oil to the main bearings being adapted by changing the displacement of pump 22. It is understood that it is possible to have either the feed pumps 22 or the feed pumps 25 including a variable displacement pump. It is also understood that both pumps 22 or both feed pumps 25 can be variable displacement pumps. An advantage of using variable displacement pumps is that a fixed speed electric drive can be used. The embodiments above have been described with reference to controlling the supply of lubrication oil (system oil or crankcase oil) to the main bearings and to the crosshead bearings. However, since the other consumers of lubrication oil (system oil) of the engine are arranged downstream of the crosshead, the amount of oil supplied to the other consumers of lubrication oil is also adjusted when the amount of lubrication oil to the crosshead is adjusted. Thus, the lubrication system also adjusts the amount of oil delivered to the other consumers of lubrication oil of the engine. Examples of such other consumers of lubrication oil of the engine are the pistons for cooling, the camshaft bearings and followers, and the chain or gear drive. The invention has been described in conjunction 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 word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. A single processor or other unit may fulfil the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measured cannot be used to advantage. The reference signs used in the claims shall not be construed as limiting the scope.

Claims

CLAIMS :

1. A lubrication system for the main bearings of a large slow-running turbocharged two-stroke internal combustion engine (1) with crossheads (5) and main bearings (8) for a crankshaft (7), said lubrication system comprising: a source of lubrication oil configured to deliver a flow of lubrication oil to said main bearings (8), characterized by said source of lubrication oil having a variable controllable output flow rate, an electronic control unit (50) in receipt of a parameter indicative of the thermal load on said main bearings (8), and said electronic control unit being configured to adjust the output flow rate of said source of lubrication oil in response to said parameter.

2. A lubrication system according to claim 1, wherein said electronic control unit (50) is configured to determine the flow rate of lubrication oil that needs to be delivered to the main bearings (8) in order to ensure that the temperature of the main bearings (8) does not exceed a threshold.

3. A lubrication system according to claim 1 or 2, wherein said electronic control unit (50) controls said source of lubrication oil to deliver a flow rate of lubrication oil to the main bearings (8) that depends on said parameter, with a value of said parameter indicating a higher thermal load on the main bearings resulting in higher lubrication oil flow rates to said main bearings (8) a value of said parameter indicating a lower thermal load resulting in lower lubrication oil flow rates to said main bearings (8) .

4. A lubrication system according to any one of claims 1 to 3, wherein said electronic control unit (50) is configured to use a lookup table or an equation to determine the appropriate lubrication oil flow rate to said main bearings (8) in relation to said parameter.

5. A lubrication system according to any one of claims 1 to 4, wherein said source of lubrication oil comprises fixed displacement pumps (22) that are driven by variable speed electric drive motors, and wherein said electronic control unit (50) is configured to adapt and control the speed of said electric drive motors.

6. A lubrication system according to any one of claims 1 to 4, wherein said source of lubrication oil comprises a plurality of pumps (22), and wherein said electronic control unit (50) is configured to selectively activate a number of said plurality of pumps in order to control the amount of lubrication oil delivered to the main bearings

7. A lubrication system according to any one of claims 1 to 4, wherein said source of lubrication oil comprises a variable displacement pump (22), and wherein said electronic control unit (50) is configured to control the amount of lubrication oil delivered to the main bearings (8) by changing the setting of the variable displacement pump .

8. A lubrication system according to any one of claims 1 to 7, wherein said source of lubrication oil also delivers lubrication oil to the crosshead and/or the connecting rod and/or the piston and/or the thrust bearings .

9. A method for controlling of lubrication oil flow to the main bearings of a large slow-running turbocharged two-stroke internal combustion engine (1) with crossheads (5) and main bearings (8) for a crankshaft (7), characterized by said method comprising adjusting the flow rate of lubrication oil delivered to said main bearings in response to a parameter indicative of the thermal load on said main bearings in order to ensure that the temperature of the main bearings (8) does not exceed a threshold.

10. A method according to claim 9, further comprising decreasing the flow of lubrication to said main bearings when said parameter indicates thermal load is below a second threshold, increasing the flow of lubrication oil to said main bearings (8) when said parameter indicates thermal load is above a first given threshold and maintaining a present flow rate of lubrication oil to said main bearings (8) when said parameter has a value between said first and second threshold.

11. A method according to claim 9 or 10, further comprising using a lookup table or an equation to determine the appropriate lubrication oil flow rate to said main bearings (8) in relation to said parameter.

12. A lubrication system for the crosshead bearings of a large slow-running turbocharged two-stroke internal combustion engine (1) with crosshead bearings for crossheads (5) connecting the piston rods (4) to the big ends (6) and main bearings (8) for a crankshaft (7), said lubrication system comprising: a source of lubrication oil configured to deliver a flow of lubrication oil to said crosshead bearings, characterized by said source of lubrication oil having a variable controllable output flow rate, an electronic control unit (50) in receipt of a parameter indicative of the thermal load on said crosshead bearings (8), and said electronic control unit (50) being configured to adjust the output flow rate of said source of lubrication oil in response to said parameter.

13. A lubrication system according to claim 12, wherein said electronic control unit (50) is configured to determine the flow rate of lubrication oil that needs to be delivered to the crosshead bearings in order to ensure that the temperature of the crosshead bearings does not exceed a threshold.

14. A lubrication system according to claim 12 or 13, wherein said electronic control unit (50) controls said source of lubrication oil to deliver a flow rate of lubrication oil to the crosshead bearings that depends on said parameter, with a value of said parameter indicating a higher thermal load on the crosshead bearings resulting in higher lubrication oil flow rates to said crosshead bearings a value of said parameter indicating a lower thermal load resulting in lower lubrication flow rates to said crosshead bearings (8) .

15. A lubrication system according to any one of claims 12 to 14, wherein said electronic control unit (50) is configured to use a lookup table or an equation to determine the appropriate lubrication oil flow rate to said crosshead bearings in relation to said parameter.

16. A lubrication system according to any one of claims 12 to 15, wherein said source of lubrication oil comprises fixed displacement pumps (22) that are driven by variable speed electric drive motors, and wherein said electronic control unit (50) is configured to adapt and control the speed of said electric drive motors.

17. A lubrication system according to any one of claims 12 to 15, wherein said source of lubrication oil comprises a plurality of pumps (22), and wherein said electronic control unit (50) is configured to selectively activate a number of said plurality of pumps in order to control the amount of lubrication oil delivered to the crosshead bearings.

18. A lubrication system according to any one of claims 12 to 15, wherein said source of lubrication oil comprises a variable displacement pump (22), and wherein said electronic control unit (50) is configured to control the amount of lubrication oil delivered to the croshead bearings by changing the setting of the variable displacement pump.

19. A method for controlling of lubrication oil flow to the croshead bearings of a large slow-running turbocharged two-stroke internal combustion engine (1) with crosshead bearings for crossheads (5) connecting the piston rods (4) to the big ends (6) and main bearings (8) for a crankshaft (7), characterized by said method comprising adjusting the flow rate of lubrication oil delivered to said crosshead bearings in response to a parameter indicative of the thermal load on said crosshead bearings in order to ensure that the temperature of the crosshead bearings does not exceed a threshold .

20. A method according to claim 19, further comprising decreasing the flow of lubrication to crosshead bearings when said parameter indicates thermal load is below a second threshold, increasing the flow of lubrication oil to said crosshead bearings when said parameter indicates thermal load is above a first given threshold and maintaining a present flow rate of lubrication oil to said crosshead bearings when said parameter has a value between said first and second threshold.

21. A method according to claim 19 or 20, further comprising using a lookup table or an equation to determine the appropriate lubrication oil flow rate to said crosshead bearings in relation to said parameter.