WO2012175794A2

WO2012175794A2 - Supercharging system for an internal combustion piston engine and method of operating an internal combustion piston engine

Info

Publication number: WO2012175794A2
Application number: PCT/FI2012/050587
Authority: WO
Inventors: Gösta Liljenfeldt; Håkan NYNÄS
Original assignee: Wärtsilä Finland Oy
Priority date: 2011-06-23
Filing date: 2012-06-12
Publication date: 2012-12-27
Also published as: WO2012175794A3; FI20115651A; FI123325B; FI20115651A0; EP2724008A2

Abstract

Invention relates to a supercharging system for an internal combustion piston engine (100) comprising a turbocharger unit (101) having a compressor part (102) and a turbine part (103) mechanically connected with each other, and a gas flow system connecting the compressor part (102) and the turbine part (103) of turbocharger unit (101) with the engine, which gas flow system comprises at least one fluid flow control device arranged to control the flow of gas between the compressor part (102), the turbine part (103) and the engine (100). At least one fluid flow control device (22) comprises at least two parallel valve units (22.1 - 22. N) each having two operational positions.

Description

Supercharging system for an internal combustion piston engine and method of operating an internal combustion piston engine

Technical field

[001 ] The present invention relates to a supercharging system for an internal combustion piston engine comprising a turbocharger unit having a compressor part and a turbine part mechanically connected with each other, and a gas flow system connecting the compressor part and the turbine part of turbocharger unit with the engine, which gas flow system comprises at least one fluid flow control device arranged to control the flow of gas between the compressor part, the turbine part and the engine according to the preamble of claim 1 . [002] The present invention relates also to a method of operating an internal combustion engine in which the combustion air is pressurized by means of a compressor part of a turbocharger unit and the compressor part is driven by a turbine part of the turbocharger unit, and exhaust gas is conducted from the engine to the turbine part of the turbocharger unit and the exhaust gas flow is controlled by at least one fluid flow control device.

Background art

[003] A combustion engine, particularly an internal combustion piston engine comprises several fluid circuits having specific devices for controlling the fluid flows in the circuits of the engine. For example a cooling system of an engine is typically controlled in order to maintain the temperature of the engine and its components within required limits. There are also other fluid flows in connection with which at least some kind of flow rate control is per- formed, such as fuel injection, charge air / exhaust gas flow, just to mention a few. Typically, controlling such fluid flows is practised by adjusting the flow rate to at least some extent. Basically all fluid flows in an internal combustion piston engine have an impact to its operation, some of the fluid flows requiring very accurate control due to their strong effect on the operation.

[004] The operational requirements of combustion engines are becoming more and more demanding and thus the accuracy and reliability of control systems is ever more important. This relates, not only to the fuel system the importance of which has been recognized a long ago, but to practically all fluid flow systems in an internal combustion piston engine, which have an influence on the overall performance of the engine.

[005] An extremely important fluid flow system in connection with an internal combustion piston engine is the charge air - exhaust gas flow system. In the efficiently operating internal combustion piston engines, it is almost a rule to use air compressors, typically turbochargers, in connection with the engines. In order to operate the engine properly and efficiently over a wide load range means to control of the gas flow is need at least to some extent. Therefore the turbo charger is often provided with a so called waste gate. The waste gate is a by-pass channel over the turbine part of the turbo- charger through which a controllable amount of exhaust gas may be led without performing work in the turbine part. The waste gate is typically provided with a mechanical valve, the opening/closure of which is depending of the charge air pressure or the engine load. The valve is operating in a very harsh environment, where it is exposed to temperatures of several hundreds of Celsius degrees in exhaust gases flowing at very high velocities. Also in transient load stages the control on the turbocharger has considerable impact on the engine performance. [006] An object of the invention is to provide a fluid flow arrangement for an internal combustion piston engine in which the control performance is considerably improved compared to the prior art solutions.

[007] It is a still particular object of an embodiment of the invention to pro- vide a charging system for an internal combustion piston engine in which the control performance is considerably improved compared to the prior art solutions.

Disclosure of the Invention

[008] The objects of the invention are substantially met by a supercharging system for an internal combustion piston engine comprising a turbocharger unit having a compressor part and a turbine part mechanically connected with each other, and a gas flow system which connects the compressor part and the turbine part of turbocharger unit with the engine, which gas flow system comprises at least one fluid flow control device arranged to control the flow of gas between the compressor part, the turbine part and the engine. It is characteristic to the invention that the at least one fluid flow control device comprises at least two parallel valve units each having two op- erational positions.

[009] According to another embodiment of the invention the fluid flow control device comprises more than two parallel valve units. [0010] According to a further embodiment of the invention the fluid flow control device comprises parallel valve units having different flow characteristics.

[001 1 ] According to still another embodiment of the invention at least one of the valve units is provided with a removable/exchangable restriction element influencing on the flow characteristics of the valve unit. [0012] According to another embodiment of the invention all valve units are provided with a removably assembled restriction elements influencing on the flow characteristics of the valve unit.

[0013] According to another embodiment of the invention the valve units are identical to each other and the restriction elements are different from each other. [0014] According to another embodiment of the invention the restriction element comprises a removable flange.

[0015] According to another embodiment of the invention the restriction element comprises a pin element arranged removably in to the valve unit.

[0016] According to another embodiment of the invention the restriction element comprises a stop to limit movement range of a valve member of the valve unit. [0017] According to another embodiment of the invention the valve unit is an on-off valve.

[0018] According to another embodiment of the invention the valve unit is a flow dividing unit having two operational positions.

[0019] According to another embodiment of the invention at least one fluid flow control device is arranged to the exhaust gas conduit and a bypass channel to control an amount of exhaust gases bypassing the turbine part. [0020] According to another embodiment of the invention at least one fluid flow control device is arranged the inlet conduit and to a second bypass channel to control an amount of gases bypassing the engine. [0021 ] The objects of the invention are substantially met by a method of operating an internal combustion engine in which the combustion air is supercharged by pressurizing the air in a compressor part of a turbocharger unit and the compressor part is driven by a turbine part of the turbocharger unit, exhaust gas is led from the engine to the turbine part of the turbocharger unit and the the exhaust gas flow is controlled by at least one fluid flow control device. It is characteristic to the invention that the conducting of the exhaust gas is practised by controlling the exhaust gas flow to selectively flow through one or more of several parallel valve units arranged in the at least one fluid flow control device.

[0022] According to another embodiment of the invention the pressure prevailing upstream the compressor part is measured and the operational position of each of the one or more of several parallel valve units is determined and changed if needed.

[0023] According to another embodiment of the invention one or more out of several parallel valve units has only two operational positions between which its state is selected each time the steps of, monitoring the pressure prevailing upstream the compressor part and determining the operational position of each of the one or more of several parallel valve units and changing if needed, are practised.

[0024] According to another embodiment of the invention the conducting of the exhaust gas is controlled by arranging a part of the combustion air to bypass the engine.

[0025] According to another embodiment of the invention the conducting of the exhaust gas is controlled by arranging a part of the exhaust gas to by- pass the turbine part. Brief Description of Drawings

[0026] In the following, the invention will be described with reference to the accompanying exemplary, schematic drawings, in which

Figure 1 illustrates a fluid flow system in an internal combustion piston engine according to an embodiment of the invention,

Figure 2 illustrates an advantageous embodiment of a fluid flow control device according to the invention,

Figure 3 illustrates an embodiment of a valve unit according to the invention,

Figure 4 illustrates an embodiment of another valve unit for a fluid flow con- trol device according to the invention,

Figure 5 illustrates an embodiment of another valve unit for a fluid flow control device according to the invention,

Figure 6 illustrates a fluid flow system in an internal combustion piston engine according to another embodiment of the invention,

Figure 7 illustrates a still another embodiment of a valve unit for a fluid flow control device according to the invention, and

Figure 8 illustrates a fluid flow system in an internal combustion piston engine according to still another embodiment of the invention.

Detailed Description of Drawings

[0027] In figure 1 there is schematically shown a fluid flow system 10 in an internal combustion piston engine 100 according to an embodiment of the invention. The internal combustion piston engine 100 includes a turbo- charger unit 101 with a compressor part 102 and a turbine part 103. In this embodiment the fluid flow system is a gas exchange system in connection with the engine 100. [0028] The gas exchange system includes a main fluid channel which in this embodiment includes an exhaust gas conduit 12. The exhaust gas conduit 12 is at its first end in connection with the exhaust manifold and further with the cylinders 16 of the engine. In the cylinders the pressure and temperature of the exhaust gases is increased by means of cyclic combustion of fuel in the cylinders of the engine. The exhaust gas conduit is connected at its second end to the inlet of the turbine part 103 in which energy of the exhaust gas is partially used for driving the compressor part 102. The compressor part 102 is connected to an inlet manifold of the engine by an inlet conduit 1 1 . The turbocharger unit 101 may be of a type known as such. The gas exchange system or the turbocharger unit 101 is provided with a bypass channel 12.2, which connects the engine's exhaust gas conduit 12 directly to the outlet side of the turbocharger unit, particularly the turbine part 103 thereof. [0029] The exhaust gas conduit 12 is provided with a fluid flow control device 22 arranged upstream the turbine part. The flow control device 22 controls the flow of exhaust gas to the turbine part 103 and/or passing by the turbine part via the bypass channel 12.2. Thus The control device is and works as a waste gate of the turbo charger unit 101 . The flow control device 22 i.e. the waste gate comprises several parallel valve units 22.1 , ... 22. N. The valve units are in connection with the exhaust gas conduit 12 at their inlet sides. Each of the valve unit 22.1 , ... 22. N has two operational positions to which the valve units may be switched. In the first operational position of the valve unit it is set to connect the engines exhaust gas conduit to the inlet side of the turbine part 103 and in the second operational position of the valve unit it is set to connect the engine to the outlet side of the tur- bine part 103. Each of the valve unit is independently controllable/set to either of its operational positions.

[0030] Thus the combustion air is supercharged by means of pressurizing the inlet air in the compressor 102 part. The compressor part is driven by the turbine part 103 of the turbocharger unit 101 which in turn is driven by exhaust gas generated in the engine. The exhaust gas is conducted through the exhaust gas conduit 12 from the engine to the turbine part 103 of the turbocharger unit. The conducting of the exhaust gas is controlled 30 by at least one fluid flow control device 22 so that the conducting of the exhaust gas is controlled to selectively flow through one or more of several parallel valve units 22.1 -22. N arranged in the at least one fluid flow control device. [0031 ] Each of the valve units has different flow characteristics. In practise this means preferably that the flow areas of the valve units differ from each other. There is also a control system 30 provided in connection with the control device 22. The control system 30 is arranged to set the operational position of each valve unit 22.1 , 22. N into one of the two operational po- sitions between which the valve unit may be switched. The control system is preferably provided with a sensor system 32 transmitting the control information of the operation of the engine. Based on the control information the control system 30 defines the state of each valve unit and sets their operational positions accordingly. The control system is preferably provided also with a sensor system 32 transmitting the information of at least the charge pressure directly or indirectly.

[0032] When the engine is running the control system receives information relating to the operation and/or performance of the engine. Based on the information and/or other information stored to be available to the control system 30 it sets each individual valve unit 22.1 , 22. N into one of its two operational positions. In this way and depending on the running conditions of the engine the control system 30 sets the control device 22 into different combinations of operational positions of the valve units. This way the operation of the turbocharger may be controlled very efficiently. [0033] The valve units have two operational positions. In the first operational position the valve units connect the flow of exhaust gas to the turbine part 103 and in the second operational position the valve units connect the exhaust gas flow to pass the turbine part via the bypass channel 12.2. The control device operates as a waste gate of the turbo charger unit 101 .

[0034] The valve units i.e. the number of valve units and the flow characteristics of the valve units in the engine are preferably selected so that substantially equal total flow characteristics of the control device 22 may be achieved with at least two different combinations of operational positions of the valve units. This way the control device and the engine may be used at least temporarily or until next service shutdown even if at least one of the valve units is defective.

[0035] With the present invention it is possible to efficiently control the op- eration of the turbocharger by means of setting the amount exhaust gas bypassing the turbine part 103 with respective selection of operational positions of the parallel valve units. The control device 22 operating as the waste gate comprises minimum two but, preferably, at least four parallel valve units.

[0036] According to a preferred embodiment of the invention each of the valve units is provided with a base part 25 and a restriction element 24. Preferably the restriction element 24 is arranged into the valve unit so that it throttles the fluid flow. The restriction element 24 advantageously is remov- ably inserted into the base part 25. The restriction element is a member affecting the flow characteristics of the valve unit in throttling manner. More specifically the restriction element 24 influences on the flow resistance of the valve unit, preferably by forming a locally constricted flow area. This is depicted in figure 1 as a circle. Additionally it is advantageous that the base parts 25 of valve units 22.1 , 22.2, ... 22. N are substantially identical, and particularly with respect to joining elements by means of which the re- 5 striction element 24 joins to the valve unit. The number of valve units may vary but preferably there are at least four units. The restriction element includes means for choosing the flow characteristics of the valve unit when assembling it, which means that the restriction elements are preferably different in different valve units. This way the valve units are modularized ali o lowing their flow characteristics to be changed simply by changing only the only restriction element 24 in the valve unit.

[0037] The restriction elements 24 are preferably selected so that when the first valve unit has a relative effective flow area of 1 , the corresponding flow

15 area of a second valve unit is 1/2, the area of a third valve unit is 1/4 etc. i.e. their flow areas are arranged so that the area "next" valve unit is half of the flow area of the previous one. In case the fluid flow control device comprises four on/off valve units the relations between the combination of operational positions and flow rate is shown in the following table, which clearly

20 shows the accuracy which can be achieved with 4 valve units.

Total relative

Valve unit 1 Valve unit 2 Valve unit 3 Valve unit 4

flow rate

0 0 0 0 0,000

0 0 0 1 0, 125

0 0 1 0 0,250

0 0 1 1 0,375

0 1 0 0 0,500

0 1 0 1 0,625

0 1 1 0 0,750

0 1 1 1 0,875

1 0 0 0 1.000

1 0 0 1 1 , 125

1 0 1 0 1 ,250

1 0 1 1 1 ,375

1 1 0 0 1 ,500

1 1 0 1 1 ,625

1 1 1 0 1 ,750

1 1 1 1 ,875

[0038] In this embodiment the valve unit 1 provides a relative flow rate 1 , valve unit 2 provides a relative flow rate 0,5 an so on. It can be seen that 16 different flow rates can be obtained with four valve units. Correspondingly, 32 and 64 different flow rates may be obtained with 5 and 6 valve units respectively. [0039] As each of the valve units may be independently switched between two operational positions it is possible to set practically any required fluid flow situations that may be needed by arranging and combining of the operational positions of individual valve units suitably. Depending on the type of the valve units the operational positions may be "on" or "off or positions guiding the flow to either of two possible directions. In the case of Figure 1 the valve units have two selectable positions guiding the flow to either of two possible directions. [0040] In Figure 2 there is shown an advantageous embodiment of the fluid flow control device 22 according to the invention. The fluid flow control device 22 comprises a base part 25 into which the other part of the fluid flow control device are arranged. The base part is provided with a fluid inlet manifold 4 to which the main fluid channel is to be connected. The base part 25 comprises also several valve spaces 6. The valve spaces 6 are cylindrical in the embodiment of figure 6. The first end 8 of each space is connected to the fluid inlet manifold 4. The valve spaces are substantially iden- tical to each other. The valve space is provided with a first outlet 210 and a second outlet 212 in its cylindrical portion. The first outlet 210 of each valve space is connected to a first outlet manifold 214 common to the first outlets. Respectively the second outlet 212 of each valve space is connected to a second outlet manifold 216 common to the second outlets.

[0041 ] There is valve member 218 arranged in each valve space. The valve member and the valve space form a valve unit in this embodiment. The valve member is arranged movable in the valve space 6 so that the position of the valve member rules the operational position of the valve unit. The valve member 18' is shown at its position where the fluid inlet manifold 4 is in flow connection with the first outlet manifold 214. With the reference 218 there are shown valve members at their other position where the fluid inlet manifold 4 is in flow connection with the second outlet manifold 216. [0042] To be more specific, the valve member 218 shown in the Figure 2 is a cylindrical substantially hollow sleeve which covers a portion of the valve space 6. As the position of the sleeve is changed it either covers the first outlet 210 or the second outlet 212, which makes it possible to guide the fluid inside the valve member 218. The valve member and valve space both have cylindrical cross section and common centre line 18'. In this case the movement of the valve member takes place in the direction of the centre line 18'. [0043] The valve member is arranged such that only one of the first outlet 210 and the second outlet 212 may be in flow connection with the fluid inlet manifold 4.

[0044] In the embodiment shown in figure 2 the inner surface of the valve space 6 is covered with a sleeve 220 inside of which the valve member 218 is arranged. The inner surface of the sleeve 220 and the counter surface of the valve member 218 form a cylindrical sealing by means of which the fluid flow is directed to the direction ruled by the position of the valve member. The sleeve is provided with openings at the location of the first outlet 210 and the second outlet 212. The sleeve 220 is removably assembled and exchangeable so that after a period of use and/or when damaged or worn it may be replaced in a non-destructive manner.

[0045] In the first end of the valve space 8 there is a restriction element 24. The valve spaces of valve units 22.1 , 22.2, ... 22. N are substantially identical particularly with respect to other parts except the restriction element 24. The restriction element is arranged immediately upstream the sleeve 220, before the valve member. The restriction element 24 is advantageously a flange having an orifice. Here, the orifice may be centrally located in the flange. In each of the valve units the orifice is of different diameter. This way the flange effects on the flow characteristics of the valve unit. The valve units may be modularized allowing their flow characteristics to be changed by simply changing only the flanged restriction element 24 in the valve unit. The restriction element may also be an element, such as a plate, with one or several holes located centrally or offset from centreline of the element. [0046] According to an embodiment of the invention at least two of the the orifices in the valve units are of same diameter. [0047] Each valve unit valve unit 22.1 , 22.2, ... 22. N is provided with an actuator 225, which is arranged to move the valve member in the valve space. The actuator is in the embodiment of figure 5 a dual action actuator capable of acting on the valve member 218 in two directions in order to actively move the valve member between it two operational positions. The actuator may be a solenoid operated or hydraulically operated device or a combination thereof in which case a solenoid system controls the hydraulic pressure applied to the actuator 225. Each of the actuators 225 are in connection with a control device (not shown).

[0048] In figure 3 there is shown an embodiment of a valve unit 22.1 in which the fluid is passed outside the valve member 318 along the recess 319 arranged in to the valve member. In the fluid flow control device there are several valve units 22.1 parallel coupled. The valve space 306 is pro- vided with a first outlet 310 and a second outlet 312 in its cylindrical portion connected to the first outlet manifold 314 and to the second outlet manifold 316 respectively. In this embodiment the actuator 327 is a single action actuator which is capable of acting on the valve member 318 only in one direction. In order to move the valve member between it two operational posi- tions there is a spring element 327' arranged in the opposite end to the actuator 327 of the valve member 318. The actuator 327 is of hydraulic/pneumatic type and it is capable of moving the valve member 318 in a direction against the spring and after releasing the work pressure the spring returns the valve member back to its initial position.

[0049] There is also a restriction element 24 arranged in the valve unit 22.1 of figure 3. The restriction element is arranged immediately upstream the valve member. The restriction element 24 is in this embodiment a sleeve having a central opening. This way the sleeve effects on the flow character- istics of the valve unit. The valve units may be modularized allowing their flow characteristics to be changed by simply changing only the sleeve in the valve unit. [0050] The restriction element may be realized in many ways. As is depicted in figure 4, instead of a flange or a sleeve the restriction element could be a replaceable pin 24 extending into the fluid flow channel of the valve unit. The valve unit in figure 4 corresponds to the valve unit in figure 3 except to the details relating to the restriction element. The effect of the restriction element may be changed by changing the pin having different dimensions as depicted by the dash-dot line 24'. [0051 ] In figure 5 there is shown still another embodiment of the invention which mainly corresponds to that of figure 3. In the figure 5 there is shown a restriction element 24, which is accomplished by means of the stop 24" against which the valve member 318 is pushed at a position in which the fluid is directed into the first outlet 610. Due to the stop 24 the valve mem- ber movement is restricted so that it restricts the flow in to the first outlet 310. The valve unit may comprise a stop also at its other end to limit the movement of the valve member to its other operational position (not shown). This kind of a stop may be used in various kinds of valve configurations.

[0052] Figure 6 illustrates another embodiment of the invention in which the internal combustion piston engine 100 includes a turbo charger unit 101 with a compressor part 102 and a turbine part 103. In this embodiment the fluid flow system is a gas exchange system in connection with the engine 100.

[0053] The gas exchange system includes a main fluid channel which in this embodiment includes an exhaust gas conduit 12. The exhaust gas conduit 12 is at its first end in connection with the exhaust manifold and further with the cylinders 16 of the engine. In the cylinders the pressure and temperature of the exhaust gases is increased by means of cyclic combustion of fuel in the cylinders of the engine. The exhaust gas conduit is connected at its second end to the inlet of the turbine part 103 in which energy of the exhaust gas is partially used for driving the compressor part 102. The turbo charger unit 101 may be of a type known as such. The gas exchange system or the turbocharger unit 101 is provided with a bypass channel 12.2, which connects the engine's exhaust gas conduit 12 directly to the outlet side of the turbocharger unit, particularly the turbine part 103 thereof.

[0054] The exhaust gas conduit 12 is provided with a fluid flow control device 22' arranged upstream the turbine part in the bypass channel 12.2. So, the flow control device 22' controls the flow of exhaust gas via the bypass channel 12.2 i.e. allows some of the gas from the engine to by-pass the turbine section and thus it also controls the flow of exhaust gas in to the turbine part. [0055] There is also a second bypass channel 613 connecting the pressure side of the compressor part 102 directly to the engine's exhaust gas conduit 12. The junction of the second bypass channel 613 is provided with a fluid flow control device 22". The fluid flow control device 22 is arranged to allow a portion of the charge air to flow directly to the turbine part under control of the control system 30. In other respects the fluid flow control device and its operation corresponds to that described in figure 1 .

[0056] In Figure 7 there is shown an advantageous embodiment of the fluid flow control device 22 according to the invention. The fluid flow control de- vice 22 comprises a base part 25 into which the other parts of the fluid flow control device are arranged. The base part is provided with a fluid inlet manifold 4 to which the main fluid channel is to be connected. The base part is also provided with a fluid outlet manifold 716. [0057] The base part 25 comprises also several valve members 18 separating the inlet manifold and the outlet manifold. There is a valve member 318 arranged in each valve space. The valve member is movable so that the position of the valve member determines the operational position of the valve unit.

[0058] To be more specific, the valve member 718 shown in the Figure 7 is a disk valve. As the position of the disk is changed it either closes or opens the connection between the inlet and outlet manifold.

[0059] In figure 7 there is also schematic illustration of a further embodiment of the invention according to which each of the valve unit 22.1 , 22.2, ... 22. N is provided with a manual locking system 719 by means of which the valve member in each valve unit may be locked to either of their operational positions, The manual locking system 719 comprises locking means in connection with each valve unit so that for example in the case of malfunction of the valve unit may be locked. The locking means is also ar- ranged to allow the manual change of the operational position. Even if this is depicted here with the reference to the figure 7 the manual locking system may be naturally arranged in other embodiments of the valve units according to the invention.

[0060] There is a restriction element 24 arranged to the fluid flow control device 22 in connection with each valve member. The restriction element 24 is also arranged to operate as a valve seat mating with a control surface of the valve member. The valves are substantially identical particularly with respect to other parts except the restriction element 24. It is clear that the restriction element may also be separate to the valve seat. The valve units may be modularized allowing their flow characteristics to be changed by simply changing only the restriction element 24 in the valve unit. [0061 ] Each valve unit valve member is provided with an actuator, here a common actuator system 727 is arranged, which is arranged to move each valve member in the valve space independently. [0062] In figure 8 there is shown a still another embodiment of the invention in which the internal combustion piston engine 100 includes a turbo charger unit 101 with a compressor part 102 and a turbine part 103. In this embod- iment the fluid flow system is also gas exchange system in connection with the engine 100.

[0063] The gas exchange system includes a main fluid channel which in this embodiment includes an exhaust gas conduit 12. The exhaust gas conduit 12 is at its first end in connection with the exhaust manifold and further with the cylinders 16 of the engine. In the cylinders the pressure and temperature of the exhaust gases is increased by means of cyclic combustion of fuel in the cylinders of the engine. The exhaust gas conduit is connected at its second end to the inlet of the turbine part 103 in which energy of the ex- haust gas is partially used for driving the compressor part 102. The turbo charger unit 101 may be of a type known as such. The gas exchange system or the turbocharger unit 101 is provided with a recycling channel 12.1 which connects the engine's exhaust gas conduit 12 directly to the inlet side of the engine. The recycling channel 12.1 is provided with a fluid flow con- trol device 22"' arranged. So, the flow control device 22"' controls the portion of exhaust gas via the recycling channel 12.1 to the inlet side of the engine i.e. allows some of the exhaust gas from the engine to be recycled back to the engine. [0064] In other respects the fluid flow control device and its operation corresponds to that described in figure 1 .

[0065] While the invention has been described herein by means of examples in connection with what are, at present, considered to be the most pre- ferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but is intended to cover various combinations or modifications of its features, and several other applications included within the scope of the invention, as defined in the appended claims. The details mentioned in connection with any embodiment above may be used in connection with another embodiment when such combination is technically feasible.

Claims

1 . A supercharging system for an internal combustion piston engine (100) comprising a turbocharger unit (101 ) having a compressor part (102) and a turbine part (103) mechanically connected with each other, and a gas flow system connecting the compressor part (102) and the turbine part (103) of turbocharger unit (101 ) with the engine, which gas flow system comprises at least one fluid flow control device arranged to control the flow of gas between the compressor part (102), the turbine part (103) and the engine (100), characterized in that the at least one fluid flow control device (22) comprises at least two parallel valve units (22.1 - 22. N) each having two operational positions.

2. A supercharging system for an internal combustion piston engine according to claim 1 , characterized in that the valve units (22.1 - 22. N) have different flow characteristics.

3. A supercharging system for an internal combustion piston engine according to claim 1 or 2, characterized in that the fluid flow control device (22) comprises more than two parallel valve units (22.1 - 22. N).

4. A supercharging system for an internal combustion piston engine according to claim 1 , characterized in that at least one of the valve units is provided with a replaceable restriction element (24,) influencing on the flow characteristics of the valve unit.

5. A supercharging system for an internal combustion piston engine according to claim 4, characterized in that all valve units are provided with a replaceable restriction element (24) influencing on the flow characteristics of the valve unit.

6. A supercharging system for an internal combustion piston engine according to claim 4, characterized in that the valve units (22.1 - 22. N) are identical to each other, and the restriction elements (24) are different from each other.

7. A supercharging system for an internal combustion piston engine according to claim 4, characterized in that the restriction element (24) comprises a replaceable flange.

8. A supercharging system for an internal combustion piston engine according to claim 4, characterized in that the restriction element (24) comprises a replaceable pin element arranged into the valve unit.

9. A supercharging system for an internal combustion piston engine according to claim 4, characterized in that the restriction element (24) comprises a sliding stop (24') to limit movement range of a valve member (318) of the valve unit.

10. A supercharging system for an internal combustion piston engine according to claim 1 , characterized in that at least one fluid flow control device is arranged to the exhaust gas conduit and a bypass channel (12.2) to control an amount of exhaust gases bypassing the turbine part (103).

1 1 . A supercharging system for an internal combustion piston engine according to claim 1 , characterized in that at least one fluid flow control device is arranged the inlet conduit (1 1 ) and to a second bypass channel (613) to control an amount of gases bypassing the engine (100).

12. A method of operating an internal combustion engine (100) in which the combustion air is supercharged by pressurizing the air in a compressor (102) part of a turbocharger unit (101 ) and the compressor part is driven by a turbine part (103) of the turbocharger unit (101 ), exhaust gas is conduct- ed from the engine to the turbine part (103) of the turbocharger unit and the conducting of the exhaust gas is controlled (22) by at least one fluid flow control device, characterized in that the conducting of the exhaust gas is practised by guiding (22) the exhaust gas flow to selectively flow through one or more of several parallel valve units (22.1 -22. N) arranged in the at least one fluid flow control device (22,22',22").

13. A method of operating an internal combustion engine (100) according to claim 12, characterized in that the pressure prevailing upstream the compressor part is monitored and the operational position of each of the one or more of several parallel valve units (22.1 -22. N) is determined and changed if needed.

14. A method of operating an internal combustion engine (100) according to claim 13, characterized in that each of the one or more of several parallel valve units (22.1 - 22. N) has only two operational positions between which its state is selected each time the step of claim 13 is practised.

15. A method of operating an internal combustion engine (100) according to claim 12, characterized in that the conducting of the exhaust gas is controlled (22) by arranging a part of the combustion air to bypass the en- gine.

16. A method of operating an internal combustion engine (100) according to claim 12, characterized in that the conducting of the exhaust gas is controlled (22) by arranging a part of the exhaust gas to bypass the turbine part (103).