CN108291462B

CN108291462B - Pressure regulation arrangement and method and lubrication system

Info

Publication number: CN108291462B
Application number: CN201580084595.6A
Authority: CN
Inventors: I·霍蒂
Original assignee: Wartsila Finland Oy
Current assignee: Wartsila Finland Oy
Priority date: 2015-11-19
Filing date: 2015-11-19
Publication date: 2020-05-15
Anticipated expiration: 2035-11-19
Also published as: KR20180084096A; KR102084873B1; EP3377737A1; CN108291462A; EP3377737B1; WO2017085354A1

Abstract

Pressure regulation arrangement and method and lubrication system. A pressure regulation arrangement for a lubrication system of a piston engine comprises: a pressure regulating valve (16) for releasing pressure from the lubricating oil line (4); a first control valve (19) configured to open when the control pressure at said valve (19) exceeds a first predetermined limit value; and a second control valve (20) configured to open when the control pressure exceeds a second predetermined limit value, which is lower than the first predetermined limit value, wherein the opening of the control valve (19, 20) is configured to allow the opening of the pressure regulating valve (16). The arrangement further comprises: a control line (17) for conveying a control pressure from the lubrication oil line (4) to the first control valve (19), and an actively controllable valve (25) for opening and closing a fluid communication between the control line (17) and the second control valve (20).

Description

Pressure regulation arrangement and method and lubrication system

Technical Field

The invention relates to a pressure regulating arrangement for a lubrication system of a piston engine. The invention also relates to a method for regulating the pressure in a lubrication system of a piston engine.

Background

Large internal combustion engines, such as marine engines or power plant engines, are often required to operate under very different operating conditions. To ensure adequate lubrication of the various components of the engine, the lubrication system needs to be designed to manage even the harshest operating conditions. This means that the capacity of the oil pump is over-dimensioned for easier operating conditions. Due to the over-dimensioning, both the flow rate and the lubricating oil pressure are higher than necessary for most engine operation times. The power required for operating the lubrication oil pump is proportional to the flow rate and pressure in the lubrication system, which means that energy is wasted by excessive flow rates and pressures.

Disclosure of Invention

It is an object of the present invention to provide an improved pressure regulating arrangement for a lubrication system of a piston engine. The pressure regulating arrangement comprises a pressure regulating valve having: an inlet that may be placed in fluid communication with a lubrication line requiring pressure regulation; an outlet that may be disposed in fluid communication with a pressure relief line; and a valve member movable between a closed position preventing flow between the inlet and the outlet and an open position allowing flow between the inlet and the outlet; a first pressure controlled control valve configured to move from a closed position to an open position when a control pressure at the first control valve exceeds a first predetermined limit value, wherein opening of the first control valve is configured to allow the valve member of the pressure regulating valve to move from the closed position to the open position, and a control line that may be disposed in fluid communication with the lubrication line to communicate a control pressure to the first control valve. It is a further object of the invention to provide an improved method of regulating the pressure in a lubrication system of a piston engine, the lubrication system comprising: a pressure regulating valve for releasing pressure from the lube line into the pressure relief line; at least two pressure controlled control valves, each of the control valves configured to open when a control pressure at the valve exceeds a single (individual) predetermined limit value, wherein the opening of any one of the control valves is configured to open the pressure regulating valve.

According to the invention, the pressure regulating arrangement comprises a second pressure controlled control valve configured to move from a closed position to an open position when the control pressure at the second control valve exceeds a second predetermined limit value, which is lower than the first predetermined limit value, wherein the opening of the second control valve is configured to allow the valve member of the pressure regulating valve to move from the closed position to the open position, and the pressure regulating arrangement further comprises an actively controllable valve for opening and closing a fluid communication between the control line and the second control valve.

The method according to the invention comprises the following steps: determining a parameter or a set of parameters describing the operating conditions of the engine, determining at least two different operating conditions requiring different lubricating oil pressures based on said parameters, detecting said operating conditions of the engine, and in each detected operating condition of the engine, transmitting a control pressure from the lubricating oil line to at least that control valve having a lowest predetermined limit value corresponding to at least the required lubricating oil pressure, and preventing transmission of control pressure to those control valves in which the predetermined limit value is lower than the required lubricating oil pressure.

With the pressure regulating arrangement and method according to the invention, the pressure level in the lubrication system can easily be reduced from a certain pressure level to a lower pressure level. The pressure level can be adjusted so that the oil pressure in the lubrication system can meet the requirements of difficult operating conditions of the engine when the first control valve is responsible for the pressure regulation. On the other hand, when a lower oil pressure is sufficient, the second control valve may regulate this pressure and reduce the energy consumption of the lubrication system.

According to an embodiment of the invention, the pressure regulating arrangement comprises a third pressure controlled control valve configured to open when the control pressure at the third control valve exceeds a third predetermined limit value, which is lower than the second predetermined limit value, wherein the opening of the third control valve is configured to allow the valve member of the pressure regulating valve to move from the closed position to the open position, and the pressure regulating arrangement further comprises an actively controllable valve for opening and closing a fluid communication between the control line and the third control valve.

With the third control valve, the pressure in the lubrication system may be reduced to a third pressure level, which is lower than the second pressure level. The lubrication system can thus be operated at three different pressure levels depending on the operating conditions of the engine.

The valve for opening and closing the fluid communication between the control line and the second control valve and/or the third control valve may be, for example, a solenoid valve. A single valve may also be used to select which control valve is in fluid communication with the control line.

Drawings

Embodiments of the present invention will now be described in more detail with reference to the accompanying drawings, in which,

fig. 1 shows an example of a lubrication system of a piston engine, an

Fig. 2 shows a pressure regulating arrangement for a lubrication system of a piston engine according to an embodiment of the present invention.

Detailed Description

The lubrication system of a piston engine is shown in fig. 1. The engine is a large internal combustion engine such as a main engine or an auxiliary engine of a ship or an engine used for power generation at a power plant. The cylinder bore of the engine is at least 150 mm. The engine is rated for at least 150kW per cylinder. In the embodiment of FIG. 1, the engine includes six cylinders arranged in a row, but the engine may include any reasonable number of cylinders. These cylinders may also be arranged, for example, in a V-shaped configuration. The lubrication system is configured to deliver lubrication oil to components of the engine for lubrication and/or cooling purposes. The lubrication system supplies, for example, lubricating oil to the main bearing 2 of the engine, but lubricating oil may also be supplied to various other places.

The lubrication system comprises an oil pump 1 which pressurizes and feeds lubricating oil into a lubricating oil line 4, where the lubricating oil is led to the components that need lubricating oil. The lubricating oil is taken out of the oil reservoir 6. In the embodiment of fig. 1, the oil sump is a wet oil sump 6. However, the engine may also be provided with a dry oil sump, in which case oil will be taken out of a separate oil tank into which oil is led from the dry oil sump. The oil pump 1 produces a constant flow rate at a constant engine speed. The oil pump 1 may be a screw pump, for example. The lubrication system is also provided with a pre-lubrication pump 7 which ensures that a flow of lubricating oil is also available at the start of the engine. The pre-lubrication pump 7 is arranged in parallel with the oil pump 1. The pre-lubrication pump 7 is electrically driven.

An oil cooler 8 is provided downstream of the oil pump 1 for cooling the pressurized lubricating oil. A bypass conduit 9 is arranged in parallel with the oil cooler 8 for allowing the oil cooler 8 to be bypassed when the temperature of the lubricating oil is low, for example, at the time of engine start-up. A bypass valve 10 connects the bypass line 9 to the lubricating oil line 4 downstream of the oil cooler 8. The bypass valve 10 is used to selectively direct the lubrication flow from the oil pump 1 through the oil cooler 8 or through the bypass line 9. The bypass valve 10 may be temperature controlled to automatically maintain the temperature of the lubrication oil within a suitable temperature range.

A filter 11 is arranged downstream of the bypass valve 10. The filter 11 is an automatic backflush filter which is connected to a backflush line 12. The automatic back flushing of the filter 11 ensures that the filter 11 functions properly and minimises the need for maintenance. The backflush line 12 is provided with a centrifugal filter 13 which removes particles from the lubricating oil before the oil is returned to the oil sump 6. The backflush line 12 is also provided with a three-way valve 14 which allows bypassing the centrifugal filter 13 when required.

A pressure relief line 15 is connected to the lubricating oil line 4 between the oil pump 1 and the oil cooler 8. In the example of fig. 1, the pressure relief line 15 is connected to the lubricating oil line 4 just after the oil pump 1. The pressure relief line 15 is provided with a pressure regulating valve 16, which is controlled on the basis of the pressure in the lubricating oil line 4. When the pressure in the lubrication line 4 exceeds a predetermined limit value, the pressure regulating valve 16 opens and allows the flow of lubrication oil from the lubrication line 4 to flow into the oil sump 6 via the pressure relief line 15, thereby reducing the pressure in the lubrication line 4. The control pressure is transmitted to the pressure regulating valve 16 via a control line 17. In the example of fig. 1, the control line 17 is connected to the lubrication oil line 4 downstream of the main bearing 2 of the engine. The pressure in the lubrication system is thus controlled based on the pressure detected in the lubrication oil line 4 after the main bearing 2. The point at which the control line 17 is connected to the lube line 4 is a pressure monitoring point. Due to the flow resistance in the lubrication system, the pressure behind the main bearing 2 (i.e. the pressure at the pressure monitoring point) is lower than the pressure just behind the oil pump 1. The pressure of the lubrication system may also be monitored at some other point in the lubrication system than the point shown in fig. 1. The most suitable connection point of the control line 17 depends on the configuration of the lubrication system and the lubrication and/or cooling needs of the different components of the lubrication system.

It should be noted that the lubrication system described above is only an example of a lubrication system in which the pressure regulating device according to the present invention may be used. All of the components listed above are not required and, on the other hand, the lubrication system may include many additional components. Lubricating oil may also be used for cooling purposes, e.g. injection cooling of the pistons of an engine.

Fig. 2 shows a pressure regulating arrangement according to an embodiment of the invention. The pressure regulating valve 16 of the lubrication system forms part of the pressure regulating arrangement. The pressure regulating valve 16 includes an inlet 22 and an outlet 23. The inlet 22 of the pressure regulating valve 16 is in fluid communication with the lubrication line 4. The outlet 23 of the pressure regulating valve 16 is in fluid communication with the pressure relief line 15. When the pressure regulating valve 16 is open, pressure can thus be released from the lubrication oil line 4 into the pressure relief line 15 and the pressure in the lubrication system can be controlled. The pressure regulating valve 16 includes a valve member 24 having a closed position and an open position. In the closed position shown in fig. 2, flow is prevented from flowing from the inlet 22 of the pressure regulating valve 16 to the outlet of the pressure regulating valve 16. In the open position of the valve member 24, flow is allowed from the inlet 22 to the outlet 23. The pressure regulating valve 16 is configured such that fluid pressure in the inlet 22 of the pressure regulating valve 16 urges the valve member 24 toward the open position. In the embodiment of fig. 2, the end surface of the valve member 24 forms a first piston surface 29, on which first piston surface 29 the pressure in the inlet 22 of the pressure regulating valve 16 is exerted. An opposite end of the valve member 24 forms a second piston surface 30, the second piston surface 30 defining a fluid chamber 27 disposed within the pressure regulator valve 16. The pressure regulating valve 16 includes a spring 28, the spring 28 urging the valve member 24 toward the closed position. Thus, the pressure in the fluid chamber 27 together with the force of the spring 28 generates a closing force, and the pressure regulating valve 16 opens when the force generated by the fluid pressure acting on the first piston surface 29 exceeds the combined closing force of the spring 28 and the hydraulic force acting on the second piston surface 30. When the pressure in the fluid chamber 27 is released, the valve member 24 of the pressure regulating valve 16 is thus allowed to move from the closed position to the open position.

The fluid chamber 27 of the pressure regulating valve 16 is in fluid communication with the lubrication oil line 4 via an actuation line 34. When there is no flow in the actuation line 34, the pressure in the fluid chamber 27 is thus substantially the same as the pressure in the lubrication line 4. The inlet 22 of the pressure regulating valve 16 and the actuation line 34 are connected to the same point of the lubricating oil line 4, so that the pressure in the actuation line 34 is substantially the same as the pressure in the inlet 22. The area of the second piston surface 30 is larger than the area of the first piston surface 29 of the valve member 24. In a static condition, the closing force applied to the valve member 24 by the spring 28 and the fluid pressure in the fluid chamber 27 thus exceeds the opening force 16 applied to the valve member 24 by the fluid pressure in the inlet 22 of the pressure regulating valve 16, so that the pressure regulating valve 16 remains in the closed position.

The actuation line 34 is provided with a first control valve 19 which is arranged downstream of a connecting line 35 connecting the fluid chamber 27 of the pressure regulating valve 16 to the actuation line 34. A first control valve 19 may be used to control the opening of the pressure regulating valve 16. The downstream side of the first control valve 19 is connected to the relief line 15. The first control valve 19 is a pressure control valve, which is held in a closed position by a spring force. The first control valve 19 is in fluid communication with the lube line 4 via the control line 17. The control line 17 delivers a control pressure to a first control valve 19. In the embodiment of the figure, the control line 17 is connected to the lubricating oil line 4 close to the main bearing 2 of the engine. Therefore, the pressure regulating valve 16 is controlled based on the lubricant pressure in the main bearing 2. The first control valve 19 is configured to open when the pressure in the control line 17 exceeds a first predetermined limit value. The opening pressure of the first control valve 19 is adjustable. The first control valve 19 is adjusted to open at a pressure equal to the maximum oil pressure required for the main bearings 2 of the engine. The pressure may be, for example, 5 bar (bar). When the pressure in the control line 17 exceeds a first predetermined limit value, the first pressure regulating valve 19 opens. Thus allowing fluid flow from the fluid chamber 27 into the relief line 15. As a result, the closing force applied to the valve member 24 of the pressure regulating valve 24 by the fluid pressure in the fluid chamber 27 is reduced, and the hydraulic force acting on the first piston surface 29 of the valve member 24 may push the valve member 24 towards the open position, allowing flow from the lubrication line 4 into the relief line 15. Flow is allowed to flow from the lubrication oil line 4 into the fluid chamber 27 via the actuation line 34. However, the actuation line 34 is provided with a first throttle 31, the first throttle 31 being configured to cause a pressure drop when the lubricating oil flows through the first throttle 31. This pressure drop allows the pressure in fluid chamber 27 to decrease and valve member 24 to move toward the open position. A second throttle 32 is arranged in the connecting line 35. The throttle 35 limits the speed of movement of the valve member 24.

The actuation line 34 is provided with a branch 36, the branch 36 being connected to the control line 17. The branch 36 is provided with a check valve 33, the check valve 33 allowing flow from the actuation line 34 to the control line 17 when a predetermined pressure difference of the check valve 33 is exceeded. The predetermined pressure difference may be, for example, 3 bar. This arrangement ensures that in the event of the pressure in the lubricating oil line 4 at the connection point of the pressure regulating valve 16 exceeding a limit value (for example due to clogging of the filter 11), the pressure regulating valve 16 opens and prevents an overpressure at the oil pump 1. The control line 17 is provided with a third throttle valve 37, which ensures that the pressure in the branch 36 does not disappear via the control line 17 when the check valve 33 is open, but that the pressure in the lubricating oil line 4 at the point where the pressure regulating valve 16 is connected to the lubricating oil line 4 becomes the control pressure of the first control valve 19. The third throttle valve 37 also prevents pulsations in the control line 17.

The first control valve 19 keeps the pressure at the pressure monitoring point of the lube line 4 around a first predetermined limit value. The first predetermined limit value is chosen such that the lubrication of the main bearings 2 of the engine is sufficient even in poor operating conditions of the engine. However, such oil pressure is only occasionally required, and energy is wasted by maintaining the oil pressure at this level. The pressure regulating arrangement according to the invention therefore even comprises a second control valve 20. The second control valve 20 is also a pressure control valve. The second control valve 20 is configured to open when the control pressure at the second control valve 20 exceeds a second predetermined limit value, which is lower than the first limit value. Also, the opening pressure of the second control valve 20 is adjustable. The second predetermined limit value may be 4 bar, for example. By means of the second control valve 20 the pressure of the lubricating oil at the main bearing 2 of the engine can thus be adjusted to a lower level than the pressure selected by the first control valve 19.

A second control line 38 connects the second control valve 20 to the control line 17. The second control line 38 is provided with an actively controllable valve 25 which can be used to open and close fluid communication between the control line 17 and the second control valve 20. Thus, the control pressure is only delivered to the second control valve 20 when the valve 25 is open. In the embodiment of the figures, the valve 25 is a solenoid valve. Valve 25 is a normally closed valve. When the solenoid of the valve 25 is not energized, the valve 25 is thus held in the closed position, preventing flow from the control line 17 to the second control valve 20. A second connecting line 39 connects the second control valve 20 to the actuating line 34. When the valve 25 is switched to the open position, flow is allowed from the control line 17 to the second control valve 20. The downstream side of the second control valve 20 is connected to the relief line 15. When the pressure in the control line 17 exceeds a second predetermined limit value, the second control valve 20 opens, allowing flow from the fluid chamber 27 of the pressure regulating valve 16 into the pressure relief line 15. The pressure regulating valve 16 thus opens and keeps the pressure in the lubricating oil line 4 at the pressure monitoring point around the second predetermined limit value. The first control valve 19 receives the same control pressure as the second control valve 20, but the first control valve 19 does not open because the first predetermined limit value is greater than the second predetermined limit value. The second control line 38 is provided with a filter 40, which filter 40 protects the solenoid valve 25. In the embodiment of fig. 2, valve 25 is an 3/2 valve. When the valve 25 is in the closed position, the volume between the valve 25 and the second control valve 20 is connected to the tank. This ensures that a possible leakage through the valve 25 does not increase the pressure in the second control line 38 downstream of the valve 25 and that the second control valve 20 remains closed.

In the embodiment of fig. 2, the pressure regulating arrangement even comprises a third control valve 21. The third control valve 21 is also a pressure control valve. The third control valve 21 is configured to open when the control pressure at the third control valve 21 exceeds a third predetermined limit value, which is lower than the second limit value. The opening pressure of the third control valve 21 is also adjustable. The third predetermined limit value may be, for example, 3 bar. By means of the third control valve 21, the lubricating oil pressure at the engine main bearing 2 can thus be adjusted to a lower level than the pressure selected by the first control valve 19 or the second control valve 20.

A third control line 41 connects the third control valve 21 to the control line 17. In the embodiment of fig. 2, the third control valve 21 is connected to the second control line 38 upstream of the solenoid valve 25, but the third control line 41 may also be connected directly to the control line 17. The third control line 41 is provided with an actively controllable valve 26 which can be used to open and close fluid communication between the control line 17 and the third control valve 21. Thus, the control pressure is only transmitted from the control line 17 to the third control valve 21 when the valve 26 is open. In the embodiment of the figures, the valve 26 is a solenoid valve. Valve 26 is a normally closed valve. When the solenoid of the valve 26 is not energized, the valve 26 is thus held in the closed position, preventing flow from the control line 17 to the third control valve 21. A third connecting line 42 connects the third control valve 21 to the actuating line 34. When the valve 26 is switched to the open position, flow is allowed to flow from the control line 17 to the third control valve 21. The downstream side of the third control valve 21 is connected to the relief line 15. When the pressure in the control line 17 exceeds a third predetermined limit value, the third control valve 21 opens, allowing flow from the fluid chamber 27 of the pressure regulating valve 16 into the relief line 15. Thus, the pressure regulating valve 16 opens and keeps the pressure in the lubrication oil line 4 at the pressure monitoring point around the third predetermined limit value. If the valve 25 in the second control line 38 is open, the first control valve 19 and the second control valve 20 receive the same control pressure as the third control valve 21, but the first control valve 19 and the second control valve 20 do not open, since the first predetermined limit value and the second predetermined limit value are greater than the third predetermined limit value. The third control line 41 is connected to the second control line 38 downstream of the filter 40, which therefore also protects the solenoid valve 26 in the third control line 41. In the embodiment of fig. 2, the valve 26 in the third control line 41 is also an 3/2 valve. When the valve 26 is in the closed position, the volume between the valve 26 and the third control valve 21 is connected to the tank. This ensures that a possible leakage through the valve 26 does not increase the pressure in the third control line 41 downstream of the valve 26 and that the third control valve 21 remains closed.

The

control valves

19, 20, 21 and the

solenoid valves

25, 26 may be integrated in the valve module 18.

When the engine is running, the pressure required by the lubrication system varies according to the operating conditions of the engine. The pressure in the lubrication system comprising the pressure regulating device according to the invention can be regulated such that the use of excessive lubrication oil pressure can be avoided.

The desired oil pressure may depend on several different factors, such as engine load, engine speed, and the use of variable intake valve closing timing (VIC). For example, higher lubricant pressure may be required when the VIC function is used or when the engine load is high and greater cooling oil flow rate is required for injection cooling of the engine pistons. In order to achieve an optimal pressure regulation in the lubrication system, a parameter or a set of parameters describing the operating conditions of the engine may be determined. The parameters may include, for example, engine load, engine speed, and the condition (on/off) of the VIC function. Based on the parameter, different engine operating conditions are determined. For each operating condition, a corresponding required lubrication oil pressure is determined. While the engine is running, the operating conditions of the engine are monitored.

Based on the detected operating conditions, the control pressure from the lubricating oil line 4 is transmitted to the

control valve

19, 20, 21, which sets the lubricating oil pressure at the pressure monitoring point to the lowest possible level corresponding to at least the required lubricating oil pressure. The control pressure is prevented from being transmitted to the

control valves

19, 20, 21 having an operating pressure lower than the required lubricating oil pressure.

As an example, the status of VIC functions may be monitored. When the VIC function is switched on, it can be regarded as an indication of an operating condition requiring a lubricant pressure of 5 bar. The first control valve 19 is regulated to open when the control pressure is 5 bar, the second control valve 20 is regulated to open when the control pressure is 4 bar, and the third control valve 21 is regulated to open when the control pressure is 3 bar. Therefore, only the first control valve 19 can maintain the pressure at the pressure monitoring point at a desired level. Thereby preventing the control pressure from being transmitted to the second control valve 20 and the third control valve 21 and the first control valve 19 regulates the pressure.

As another example, the load of the engine may be monitored. The specific load is taken as an indication of the operating conditions, wherein a lubricant pressure of 4 bar is sufficient. At this point, the valve 25 in the second control line 38 may be opened to communicate the control pressure from the control line 17 to the second control valve 20. The valve 26 in the third control line 41 remains closed. The second control valve 20 thus regulates the pressure at which a pressure of about 4 bar is maintained at the pressure monitoring point.

If the operating conditions of the engine require only a lubricating oil pressure of 3 bar, the control pressure can be transmitted to the third control valve 21 by opening the valve 26 in the third control line 41. The valve 25 in the second control line 38 may be opened or closed. Now the third control valve 21 regulates the pressure, keeping the pressure at the pressure monitoring point around 3 bar.

It should be clear to a person skilled in the art that the present invention is not limited to the embodiments discussed above, but that it can be varied within the scope of the appended claims. For example, the opening pressure of the control valve need not be adjustable. Instead of three control valves, the pressure regulating arrangement may comprise four or more control valves or only two control valves. Instead of the solenoid valve presented in fig. 2, for example, a pneumatically controlled valve may be used. Instead of two or more solenoid valves, the pressure regulating arrangement may also be provided with a single valve for selecting which control valve is connected to the control line.

Claims

1. A pressure regulation arrangement for a lubrication system of a piston engine, the pressure regulation arrangement comprising:

-a pressure regulating valve (16) having: an inlet (22) that can be placed in fluid communication with a lubricating oil line (4) requiring pressure regulation; an outlet (23) that can be placed in fluid communication with a pressure relief line (15); and a valve member (24) movable between a closed position preventing flow between the inlet (22) and the outlet (23) and an open position allowing flow between the inlet (22) and the outlet (23),

-a first pressure controlled control valve (19) configured to move from a closed position to an open position when a control pressure at the first pressure controlled control valve (19) exceeds a first predetermined limit value, wherein the opening of the first pressure controlled control valve (19) is configured to allow the valve member (24) of the pressure regulating valve (16) to move from the closed position to the open position,

-a control line (17) which can be placed in fluid communication with the lubricating oil line (4) for delivering a control pressure to the first pressure controlled control valve (19), and

-a second pressure controlled control valve (20) configured to move from a closed position to an open position when a control pressure at the second pressure controlled control valve (20) exceeds a second predetermined limit value, which is lower than the first predetermined limit value, wherein the opening of the second pressure controlled control valve (20) is configured to allow the valve member (24) of the pressure regulating valve (16) to move from the closed position to the open position,

characterized in that the pressure regulating arrangement further comprises an actively controllable normally closed valve (25) for opening and closing fluid communication between the control line (17) and the second pressure controlled control valve (20), wherein a control pressure is transmitted to the second pressure controlled control valve (20) only when the actively controllable normally closed valve (25) is open.

2. An arrangement according to claim 1, wherein the valve (25) for opening and closing fluid communication between the control line (17) and the second pressure controlled control valve (20) is a solenoid valve.

3. An arrangement according to claim 1 or 2, wherein the pressure regulating arrangement comprises a third pressure controlled control valve (21) configured to open when the control pressure at the third pressure controlled control valve (21) exceeds a third predetermined limit value, which is lower than the second predetermined limit value, wherein the opening of the third pressure controlled control valve (21) is configured to allow the valve member (24) of the pressure regulating valve (16) to move from the closed position to the open position, and the pressure regulating arrangement further comprises an actively controllable valve (26) for opening and closing a fluid communication between the control line (17) and the third pressure controlled control valve (21).

4. An arrangement according to claim 3, wherein the valve (26) for opening and closing fluid communication between the control line (17) and the third pressure controlled control valve (21) is a solenoid valve.

5. A lubrication system of a piston engine, wherein the lubrication system comprises a pressure regulating arrangement according to any of claims 1-4.

6. A method of regulating pressure in a lubrication system of a piston engine, the lubrication system comprising:

-a pressure regulating valve (16) for releasing pressure from the lubricating oil line (4) into the pressure relief line (15),

-at least two pressure controlled control valves (19, 20, 21), each of the at least two pressure controlled control valves (19, 20, 21) being configured to open when the control pressure at the at least two pressure controlled control valves (19, 20, 21) exceeds a single predetermined limit value, wherein the opening of any one of the at least two pressure controlled control valves (19, 20, 21) is configured to open the pressure regulating valve (16),

the method comprises the following steps:

-determining a parameter or a set of parameters describing the operating conditions of the engine,

-determining at least two different operating conditions requiring different lubricating oil pressures based on said parameters,

-monitoring the operating conditions of the engine, and

-in each detected operating condition of the engine, transferring a control pressure from the lubricating oil line (4) to at least that pressure controlled control valve (19, 20, 21) having a lowest predetermined limit value corresponding to at least a required lubricating oil pressure,

wherein the transmission of the control pressure to those pressure controlled control valves (19, 20, 21) having a predetermined limit value below the required lubricating oil pressure is prevented by actively controllable normally closed valves (25, 26), wherein the actively controllable normally closed valves (25, 26) transmit the control pressure to the respective pressure controlled control valve (19, 20, 21) only when the actively controllable normally closed valves (25, 26) are open.

7. A method according to claim 6, wherein the lubrication system comprises at least three pressure controlled control valves (19, 20, 21).