WO2018002409A1

WO2018002409A1 - Gas exchange valve arrangement

Info

Publication number: WO2018002409A1
Application number: PCT/FI2016/050468
Authority: WO
Inventors: Edward Winter; Magnus Sundsten
Original assignee: Wärtsilä Finland Oy
Priority date: 2016-06-28
Filing date: 2016-06-28
Publication date: 2018-01-04

Abstract

The gas exchange valve arrangement for a piston en- gine comprises at least one gas exchange valve (1), a cam (2) for operating the valve (1), and force trans- mission means (3, 4, 5, 6, 7, 8, 9) between the cam (2) and the valve (1). The arrangement further comprises a piston (10) having a piston surface (11) delimiting a fluid chamber (12), the piston (10) being configured to be operated independently from the cam (2) by hy- draulic pressure applied to the piston surface (11) for creating opening force for additional opening of the gas exchange valve (1), a pressure medium source (13) for supplying pressure medium into the fluid chamber (12), means (14, 15, 15a) for controlling flow from the pressure medium source (13) into the fluid chamber (12), and means (14, 15, 15b) for controlling pressure release from the fluid chamber (12).

Description

Gas exchange valve arrangement Technical field of the invention

The present invention relates to a gas exchange valve arrangement in accordance with the preamble of claim 1 .

Background of the invention

Conventionally, the gas exchange valves, i.e. the intake and exhaust valves of piston engines have been cam-operated. With a cam-control the opening and closing timings of the gas exchange valves can be reliably controlled. To achieve more flexible valve timing, completely hydraulic systems have been developed. However, in hydraulic systems the reliability of completely mechanical systems cannot be achieved. Also gas exchange valve arrangements combining mechanical and hydraulic functions are known. For instance, the valve opening can be implemented by a conventional cam and mechanical or partly hydraulic force transmission means, whereas the closing of the valve can be controlled hydraulically. In arrangements where the valves are opened mechanically, the system typically comprises a fluid chamber, into which hydraulic fluid can be introduced during the opening movement of the gas exchange valve. By preventing or limiting outflow from the fluid chamber, closing of the gas exchange valve can be delayed. If the force transmission path between the cam and the gas exchange valve is at least partly hydraulic, the closing timing of the gas exchange valve can be advanced by releasing hydraulic fluid from a fluid chamber that forms part of the force transmission path. If the force transmission path between a cam and an exhaust valve is partly hydraulic, also an exhaust gas recirculation (EGR) function can be integrated to the gas exchange valve arrangement. The cam can be provided with an additional lobe opening the exhaust valve for EGR, and the opening can be disabled by utilizing hydraulic components of the gas exchange valve arrangement. Summary of the invention

The object of the present invention is to provide an improved gas exchange valve arrangement for a piston engine, the arrangement comprising at least one gas exchange valve, a cam for operating the gas exchange valve, and force transmission means for transforming rotational movement of the cam into linear movement of the gas exchange valve at least in the opening direction of the gas exchange valve for opening the gas exchange valve. The characterizing features of the arrangement according to the invention are given in the characterizing part of claim 1 . The gas exchange valve arrangement according to the invention comprises a first piston having a first piston surface delimiting a first fluid chamber, the first piston being configured to be operated independently from the cam by hydraulic pressure applied to the first piston surface for creating opening force for additional opening of the gas exchange valve, a first pressure medium source for supplying pressure medium into the first fluid chamber, means for controlling flow from the first pressure medium source into the first fluid chamber, and means for controlling pressure release from the first fluid chamber.

With the gas exchange valve arrangement according to the invention, the normal opening of the gas exchange valves, such as the opening of exhaust valves for exhaust stroke, can be cam-controlled, while additional opening of the gas exchange valves, for instance for internal EGR, can be controlled hy- draulically. Reliable operation of the gas exchange valves is thus ensured, but flexible additional opening of the valves is possible. With the piston the valve lift during an additional opening of the gas exchange valve can be limited. According to an embodiment of the invention, the arrangement comprises an actuating valve having a first position preventing flow from the first pressure medium source into the first fluid chamber and a second position allowing flow from the first pressure medium source into the first fluid chamber.

According to an embodiment of the invention, the arrangement comprises a pressure release valve having a first position allowing pressure release from the first fluid chamber and a second position preventing pressure release from the first fluid chamber. The actuating valve and the pressure release valve can be integrated into a single valve. A single actuating/pressure release valve can thus control both the opening and closing of the gas exchange valve. The actuating/pressure release valves can be electrically controlled valves, in which case a separate control valve is not needed. However, the actuating/pressure release valves could also be hydraulically controlled valves. The arrangement can thus further comprise an electrically controlled control valve for controlling control flow of pressure medium to the actuating/pressure release valves.

According to an embodiment of the invention, the force transmission means between the cam and the gas exchange valve are mechanical. Mechanical force transmission means allow very reliable operation of the gas exchange valves.

Instead of completely mechanical force transmission means, the cam can be arranged to operate a second piston, which pressurizes hydraulic fluid for cre- ating opening force for opening the gas exchange valve.

According to an embodiment of the invention, the arrangement comprises a pressure accumulator that is connected to a first fluid supply line between the first pressure medium source and the means for controlling flow from the first pressure medium source into the first fluid chamber. An additional pressure accumulator can be connected to a pressure release line of the first fluid chamber. The pressure accumulators can dampen sudden pressure pulses and lower energy consumption of the gas exchange valve arrangement.

According to an embodiment of the invention, the first piston is configured to throttle flow from the first pressure medium source into the first fluid chamber at the end of the movement of the first piston in the opening direction of the gas exchange valve. The gas exchange valve is thus smoothly opened.

The first piston can also be configured to throttle outflow from the first fluid chamber at the beginning and/or at the end of the movement of the first piston in the closing direction of the gas exchange valve. According to an embodiment of the invention, the arrangement comprises means for supplying pressure medium into the first fluid chamber at a lower pressure than the first pressure medium source. A pressure drop in the first fluid chamber can thus be limited in case the fluid supply from the first pressure medium source is suddenly cut. This reduces the risk of cavitation. The arrangement can comprise a second pressure medium source for supplying the pressure medium at the lower pressure.

According to an embodiment of the invention, the arrangement comprises a pressure accumulator that is connected to a fluid supply line between the second pressure medium source and the first fluid chamber. The pressure accumulator dampens pressure pulses and allows use of a smaller pump as the second pressure medium source.

A piston engine according to the invention comprises a gas exchange valve ar- rangement defined above.

Brief description of the drawings

Embodiments of the invention are described below in more detail with reference to the accompanying drawings, in which Fig. 1 shows a gas exchange valve arrangement according to a first embodiment of the invention,

Fig. 2 shows a gas exchange valve arrangement according to a second embodiment of the invention,

Fig. 3 shows a gas exchange valve arrangement according to a third embodi- ment of the invention,

Fig. 4 shows a gas exchange valve arrangement according to a fourth embodiment of the invention, and

Figs. 5 and 6 show cross-sectional views of a piston for the gas exchange valve arrangement according to the fourth embodiment of the invention.

Description of embodiments of the invention

Figure 1 shows schematically a gas exchange valve arrangement for a piston engine according to a first embodiment of the invention. The gas exchange valve arrangement can be used in large internal combustion engines, such as main or auxiliary engines of ships or engines that are used at power plants for producing electricity. Such engines typically have a cylinder bore of at least 150 mm and output power of at least 100 kW/cylinder. The expression "gas exchange valve" refers here to intake and exhaust valves of an engine. The gas exchange valve arrangement of figure 1 is used for controlling exhaust valves 1 of one cylinder of an engine. Each cylinder of the engine is provided with a similar arrangement for controlling the exhaust valves of that cylinder. The intake valves of the engine can be controlled with similar ar- rangements. Some of the components shown in figure 1 can be shared by the gas exchange valve arrangements of several cylinders.

In the embodiment of figure 1 , the gas exchange valve arrangement controls two exhaust valves 1 . However, each cylinder of the engine could also be provided with a different number of exhaust valves 1 , for instance with one or three exhaust valves, in which case the gas exchange valve arrangement could control one or three exhaust valves 1 . Preferably, all the exhaust valves of one cylinder are controlled by the same gas exchange valve arrangement.

In the embodiment of figure 1 , the exhaust valves 1 are opened for the exhaust stroke in a conventional way using a cam 2. The cam 2 is attached to a camshaft and the rotating movement of the cam 2 is transformed into linear movement of the exhaust valve 1 via mechanical force transmission means. The force transmission means comprise a cam follower 3, which is engaged with the cam 2. The cam 2 comprises a base circle 2a and a lobe 2b. When the cam follower 3 becomes engaged with the lobe 2b of the cam 2, the cam follower 3 is pushed outwards from the center of rotation of the cam 2. The cam follower 3 is connected to a push rod 4, which is arranged to rotate a rocker arm 5 around a pivot point. The rocker arm 5 pushes a yoke 6, which is connected to the exhaust valves 1 . The exhaust valves 1 are thus moved from a closed position to an open position and outflow from the cylinder into an exhaust duct is allowed. When the cam follower 3 enters the descending ramp of the lobe 2b, closing movement of the exhaust valves 1 is allowed. The exhaust valves 1 are provided with valve springs 27, which push the exhaust valves 1 towards the closed position. In the embodiment of figure 1 , mechanical springs are shown, but also pneumatic springs could be used. Mechanical force transmission connection between the cam 2 and the exhaust valves 1 could also be implemented in many other ways. For instance, the cam 2 could be located above the exhaust valves 1 , in which case the rocker arm 5 would not be needed. By operating the exhaust valves 1 by the cam 2, reliable normal opening of the exhaust valves 1 is ensured. In certain operating conditions of the engine, there may be a need for an additional opening of the gas exchange valves 1 . For instance, in the case of exhaust valves 1 , the exhaust valves 1 can be opened during an intake stroke for exhaust gas recirculation (EGR). Such an opening of the exhaust valves 1 allows flow of exhaust gas from the exhaust duct into the cylinder. The additional opening could be implemented with an additional lobe arranged on the cam 2. However, according to the invention, the additional opening of the gas exchange valves 1 is implemented electro-hydraulically.

For the additional opening, the gas exchange valve arrangement is provided with a first pressure medium source 13, which supplies pressurized liquid, such as hydraulic fluid, for opening the gas exchange valves 1 . The first pressure medium source 13 is a hydraulic pump, which is connected to a tank 28. The hydraulic pump 13 can be common for all the gas exchange valves 1 of the engine. For exerting an opening force on the exhaust valves 1 , the gas exchange valve arrangement of figure 1 is provided with a first piston 10. The first piston 10 comprises a first piston surface 1 1 , which delimits a first fluid chamber 12. The first fluid chamber 12 has a first end and a second end. When hydraulic pressure is applied to the first piston surface 1 1 , the first piston 10 is pushed towards the second end of the first fluid chamber 12 and exerts via the rocker arm 5 and the yoke 6 a force to the exhaust valves 1 . When the force exceeds the closing force of the valve springs 27, the exhaust valves 1 are moved from the closed position towards an open position. The moving direction of the first piston 10 from the first end towards the second end of the fluid chamber 12 is therefore called the opening direction of the gas exchange valves 1 . A first fluid supply line 18 connects the first pressure medium source 13 to the first fluid chamber 12. When pressure is released from the first fluid chamber 12, the valve springs 27 can push the first piston 10 back to the first end of the first fluid chamber 12 and the exhaust valves 1 are closed. The fluid released from the first fluid chamber 12 is conducted via a pressure release line 20 back into the tank 28. The fluid could also be conducted to another tank. For controlling the additional opening of the exhaust valves 1 , the gas exchange valve arrangement is provided with means for controlling the flow from the first pressure medium source 13 into the first fluid chamber 12 and with means for controlling pressure release from the first fluid chamber 12. In the embodiment of figure 1 , both the flow into the first fluid chamber 12 and pressure release from the first fluid chamber 12 is controlled by a combined actuating valve / pressure release valve 14, which is hereinafter called shortly actuating valve 14. The actuating valve 14 is a hydraulically controlled valve. The actuating valve 14 has a first position and a second position. In the first position of the actuating valve 14, which is shown in figure 1 , flow from the first pressure medium source 13 into the first fluid chamber 12 is prevented and flow in the pressure release line 20 is allowed. In the second position of the actuating valve 14, flow from the first pressure medium source 13 into the first fluid chamber 12 is allowed and outflow from the first fluid chamber 12 is prevented.

The gas exchange valve arrangement of figure 1 is further provided with a control valve 16. The control valve 16 is a solenoid valve, which is used for controlling control pressure at the actuating valve 14. The control valve 16 has a first position and a second position. In the first position of the control valve 16, flow from the first pressure medium source 13 into a control line 29 of the actuating line is prevented and flow from the control line 29 into a pressure release line 20 is allowed. In the second position of the control valve 16, flow from the first pressure medium source 13 into the control line 29 of the actuating valve 14 is allowed and flow from the control line 29 into the pressure release line 20 is prevented. When the control valve 14 is switched from the first position to the second position, the hydraulic pressure in the control line 29 pushes the actuating valve 14 to the second position and flow from the first pressure medium source 13 into the first fluid chamber 12 is allowed. When the control valve 14 is switched from the second position back to the first position, the pressure in the control line 29 is released and the actuating valve 14 is allowed to move by spring force back to the first position. Pressure is thus released from the first fluid chamber 12 via the pressure release line 20 into the tank 28.

A first pressure accumulator 17 is connected to the first fluid supply line 18 between the first pressure medium source 13 and the actuating valve 14. A sec- ond pressure accumulator 19 is connected to the pressure release line 20 between the actuating valve 14 and the tank 28. The pressure accumulators 17, 19 can receive sudden flow pulses and help lowering energy consumption of the gas exchange valve arrangement. The pressure accumulators 17, 19 can be common to all the gas exchange valves 1 of the engine.

The gas exchange valve arrangement further comprises a second pressure medium source 24, which has a lower pressure than the first pressure medium source 13. The second pressure medium source is a hydraulic pump 24. The second pressure medium source 24 is connected to the first fluid chamber 12 via a second fluid supply line 26. The second fluid supply line 26 is provided with a check valve 30, which prevents flow from the first fluid chamber 12 to the second pressure medium source 24. A third pressure accumulator 25 is connected to the second fluid supply line 26. In case the pressure in the first fluid chamber 12 drops below the pressure in the second fluid supply line 26, the check valve 30 opens and hydraulic fluid is supplied via the second fluid supply line 26 into the first fluid chamber 12. Because of the third pressure ac- cumulator 25, the capacity of the hydraulic pump 24 does not need to be large, but the pressure accumulator 25 can handle sudden flow demand. Due to the second pressure medium source 24, excessive pressure drop in the first fluid chamber 12 is avoided and cavitation can be prevented. In case the actuating valve 14 is switched from the second position to the first position in the middle of the opening movement of the exhaust valves 1 , the first piston 10 can continue moving in the opening direction due to inertia forces. Without the second pressure medium source 24, this could cause cavitation, but the second pressure medium source 24 ensures that the pressure does not drop too much. The pressure of the second pressure medium source 24 is configured to be lower than the pressure of the first pressure medium source 13. When the first pressure medium source 13 is connected to the first fluid chamber 12, the check valve 30 thus remains closed and the opening force exerted on the exhaust valves 1 is determined by the pressure of the first pressure medium source 13. Instead of the second pressure medium source 24, also the first pressure medium source 13 could be used for supplying pressure medium into the first fluid chamber 12 via the second fluid supply line 26. For example a pressure reducer valve could be arranged between the first pressure medium source 13 and the first fluid chamber 12 for lowering the pressure to a suitable level. With the gas exchange valve arrangement according to the invention, the timing and duration of the additional opening of the gas exchange valves 1 can be controlled flexibly. Because of the first piston 10 that is used for opening the gas exchange valves 1 , the maximum valve lift is limited to a desired maximum value. The second pressure medium source 24 allows interruption of the additional gas exchange valve opening without risk of cavitation in the first fluid chamber 12.

The embodiment of figure 2 is similar to the embodiment of figure 1 . The only difference between the two embodiments is that in the embodiment of figure 2 the hydraulically controlled actuating/pressure release valve 14 and the electrically controlled control valve 16 are replaced by an electrically controlled actu- ating valve / pressure release valve 15. The actuating valve 15 is a solenoid valve. As in the embodiment of figure 1 , the actuating valve 15 has a first position preventing flow from the first pressure medium source 13 into the first fluid chamber 12 and a second position for releasing pressure from the first fluid chamber 12 into the tank 28. In the first position of the actuating valve 15, flow in the pressure release line 20 is allowed, and in the second position of the actuating valve 15, flow in the pressure release line 20 is prevented. An advantage of this embodiment is that the additional opening and closing of the gas exchange valve 1 can be controlled with a single valve.

Figure 3 shows a third embodiment of the invention. This embodiment is simi- lar to the embodiment of figure 2, but instead of an integrated actuating and pressure release valve 15, the arrangement comprises a separate actuating valve 15a and a pressure release valve 15b. Both valves 15a, 15 have a first position and a second position. In figure 3, both valves 15a and 15b are in their first positions. In the first position of the actuating valve 15a flow from the first pressure medium source 13 into the first fluid chamber 12 is prevented, and in the second position the flow is allowed. In the first position of the pressure release valve 15b, flow from the first fluid chamber 12 into the pressure release line 20 is allowed. In the second position of the pressure release valve 15b, flow from the first fluid chamber 12 into the pressure release line 20 is prevent- ed. Both valves 15a, 15b need to be in the second positions to allow additional opening of the gas exchange valves 1 . In the embodiment of figure 3, the actuating valve 15a and the pressure release valve 15b are electrically controlled valves. However, they could also be hydraulically controlled valves in a similar way as the actuating/pressure release valve 14 of the embodiment of figure 1 . Figure 4 shows a fourth embodiment of the invention. This embodiment is similar to the embodiment of figure 1 , but the force transmission connection between the cam 2 and the gas exchange valve 1 is partly hydraulic. Because of the partly hydraulic force transmission means, also the first piston 10 is hy- draulically connected to the gas exchange valves 1 . The first piston 10 comprises a second piston surface 31 , which delimits a second fluid chamber 32. The second fluid chamber 32 is in fluid communication with a third fluid chamber 33. A second fluid supply duct 35 is used for establishing fluid communication between the second fluid chamber 32 and the third fluid chamber 33. A third piston 9, which delimits the third fluid chamber 33, is attached to the gas exchange valve 1 . When pressurized hydraulic fluid is introduced into the third fluid chamber 33, the gas exchange valve 1 is pushed towards an open position. The moving of the first piston 10 is controlled in the same way as in the embodiment of figure 1 . When the first piston 10 is pushed by hydraulic pres- sure towards the second end of the first fluid chamber 12, hydraulic fluid in the second fluid chamber 32 is pressurized. The hydraulic pressure is transmitted from the second fluid chamber 32 into the third fluid chamber 33, and an opening force is thus exerted on the gas exchange valve 1 . The second fluid chamber 32 and the third fluid chamber 33 are part of a closed hydraulic system. However, for compensating leakages from the system, the system is provided with a third pressure medium source 37, which can be used for refilling the system.

Also in the fourth embodiment, the force transmission means between the cam 2 and the gas exchange valve 1 comprise a cam follower 3 and a push rod 4. However, the push rod 4 is not connected to a rocker arm but to a piston 7. This second piston 7 is used for pressurizing hydraulic fluid, which is used for the normal opening of the gas exchange valve 1 . The second piston 7 delimits a fourth fluid chamber 34, and when the second piston 7 is pushed by the cam 2 in the fourth fluid chamber 34, the hydraulic fluid is pressurized. The pressurized hydraulic fluid is introduced via a third fluid supply duct 8 into the third fluid chamber 33 for opening the gas exchange valve 1 . In the embodiment of figure 2, the second fluid supply duct 35 is connected to the fourth fluid chamber 34. The second fluid chamber 32 is thus in fluid communication with the third fluid chamber 33 via the second fluid supply duct 35 and the third fluid supply duct 8. In the embodiment of figure 4, a hydraulically controlled actuating / pressure release valve 14 and an electrically controlled control valve 16 are used for controlling the additional opening of the gas exchange valve 1 in the same way as in the embodiment of figure 1 . However, instead of the two valves 14, 16, a single electrically controlled actuating/pressure release valve 15 could be used in a similar way as in the embodiment of figure 2, or separate actuating and pressure release valves 15a, 15b could be used in the same way as in the embodiment of figure 3.

Figures 5 and 6 show cross-sectional views of a piston 10 that can be used as the first piston 10 in the embodiment of figure 4. The first fluid chamber 12 is connected to the first pressure medium source 13 via a first inlet 21 . The first fluid chamber 12 is connected to the pressure release line 20 via an outlet 22. The first fluid chamber 12 also comprises a second inlet 36 for connecting the first fluid chamber 12 to the second pressure medium source 24.

The first fluid chamber 12 has a first end and a second end. In figures 5 and 6, the lower end is the first end. When pressurized hydraulic fluid is introduced in- to the first fluid chamber 12, the first piston 10 moves from the first end towards the second end of the fluid chamber 12. When the first piston 10 is at the first end of the first fluid chamber 12, as shown in figure 5, the first inlet 21 is open and the second inlet 36 is closed. Hydraulic fluid can thus be introduced into the first fluid chamber 12 from the first pressure medium source 13 but not from the second pressure medium source 24. The outlet 22 is closed. When the first piston 10 is at the second end of the first fluid chamber 12, as shown in figure 6, the first inlet 21 is only partially open. The second inlet 36 is open. The outlet 22 is partially open. Flow from the first fluid chamber 12 into the pressure release line 20 is thus throttled. This ensures that the movement of the first piston 10 is smooth at the beginning of the closing movement and the gas exchange valves 1 are closed smoothly. In an intermediate position of the first piston 10 between the first and the second ends of the first fluid chamber 12, the first and the second inlets 21 , 36 are open. The outlet 22 is open. Quick movement of the first piston 10 is thus allowed. As the first piston 10 ap- proaches the first end of the first fluid chamber 1 2, the outlet 22 is partially closed. The outflow of the hydraulic fluid is thus limited and the first piston 10 arrives smoothly at the first end of the first fluid chamber 12 and also the gas exchange valves 1 are closed smoothly. Figures 5 and 6 also show the second fluid chamber 32. In the gas exchange valve arrangements of figures 1 and 2 a similar first piston 10 could be used, but the second fluid chamber 32 would be replaced by an open end for engaging the first piston 10 with the rocker arm 5. The second inlet 36 remains open almost over the whole moving range of the first piston 10. If the fluid communication between the first pressure medium source 13 and the first fluid chamber 12 is abruptly cut, the second inlet 36 ensures that fluid is supplied into the first fluid chamber 12 from the second pres- sure medium source 24. If the first piston 10 is moving towards the second end of the first fluid chamber 12, its movement may continue regardless of cut fluid supply from the first pressure medium source 13. In such a case, the fluid supply from the second pressure medium source 24 prevents cavitation.

It will be appreciated by a person skilled in the art that the invention is not lim- ited to the embodiments described above, but may vary within the scope of the appended claims. For instance, the gas exchange valves could also be intake valves instead of exhaust valves.

Claims

1 . A gas exchange valve arrangement for a piston engine, the arrangement comprising at least one gas exchange valve (1 ), a cam (2) for operating the gas exchange valve (1 ), and force transmission means (3, 4, 5, 6, 7, 8, 9) for transforming rotational movement of the cam (2) into linear movement of the gas exchange valve (1 ) at least in the opening direction of the gas exchange valve (1 ) for opening the gas exchange valve (1 ), characterized in that the arrangement comprises

- a first piston (10) having a first piston surface (1 1 ) delimiting a first fluid chamber (12), the first piston (10) being configured to be operated independently from the cam (2) by hydraulic pressure applied to the first piston surface (1 1 ) for creating opening force for additional opening of the gas exchange valve (1 ),

- a first pressure medium source (13) for supplying pressure medium into the first fluid chamber (12),

- means (14, 15, 15a) for controlling flow from the first pressure medium source (13) into the first fluid chamber (12), and

- means (14, 15, 15b) for controlling pressure release from the first fluid chamber (12).

2. An arrangement according to claim 1 , wherein the arrangement comprises an actuating valve (14, 15, 15a) having a first position preventing flow from the first pressure medium source (13) into the first fluid chamber (12) and a second position allowing flow from the first pressure medium source (13) into the first fluid chamber (12).

3. An arrangement according to claim 1 or 2, wherein the arrangement comprises a pressure release valve (14, 15, 15b) having a first position allowing pressure release from the first fluid chamber (12) and a second position preventing pressure release from the first fluid chamber (12).

4. An arrangement according to claim 2 and 3, wherein the actuating valve 14, 15, 15a) and the pressure release valve (14, 15, 15b) are integrated into a single valve (14, 15).

5. An arrangement according to claim 2 or 4, wherein the actuating valve (14, 15, 15a) is an electrically controlled valve (15, 15a).

6. An arrangement according to claim 3 or 4, wherein the pressure release valve (14, 15, 15b) is an electrically controlled valve (15, 15b).

7. An arrangement according to claim 2 or 4, wherein the actuating valve (14, 15, 15a) is a hydraulically controlled valve (14).

8. An arrangement according to claim 3 or 4, wherein the pressure release valve (14, 15, 15b) is a hydraulically controlled valve (14).

9. An arrangement according to claim 7 or 8, wherein the arrangement comprises an electrically controlled control valve (16) for controlling control flow of pressure medium to the actuating valve and/or pressure release valve (14).

10. An arrangement according to any of the preceding claims, wherein the force transmission means (3, 4, 5, 6) between the cam (2) and the gas exchange valve (1 ) are mechanical.

1 1 . An arrangement according to any of claims 1 to 9, wherein the cam (2) is arranged to operate a second piston (7), which pressurizes hydraulic fluid for creating opening force for opening the gas exchange valve (1 ).

12. An arrangement according to any of the preceding claims, wherein the arrangement comprises a pressure accumulator (17) that is connected to a first fluid supply line (18) between the first pressure medium source (13) and the means (14, 15, 15a) for controlling flow from the first pressure medium source (13) into the first fluid chamber (12).

13. An arrangement according to any of the preceding claims, wherein the arrangement comprises a pressure accumulator (19) that is connected to a pressure release line (20) of the first fluid chamber (12).

14. An arrangement according to any of the preceding claims, wherein the first piston (10) is configured to throttle flow from the first pressure medium source (13) into the first fluid chamber (12) at the end of the movement of the first piston (10) in the opening direction of the gas exchange valve (1 ).

15. An arrangement according to any of the preceding claims, wherein the first piston (10) is configured to throttle outflow from the first fluid chamber (12) at the beginning of the movement of the first piston (10) in the closing direction of the gas exchange valve (1 ).

16. An arrangement according to any of the preceding claims, wherein the first piston (10) is configured to throttle outflow from the first fluid chamber (12) at the end of the movement of the first piston (10) in the closing direction of the gas exchange valve (1 ).

17. An arrangement according to any of the preceding claims, wherein the arrangement comprises means (24, 26) for supplying pressure medium into the first fluid chamber (12) at a lower pressure than the first pressure medium source (13).

18. An arrangement according to claim 17, wherein the arrangement comprises a pressure accumulator (25) that is connected to a fluid supply line (26) between the first fluid chamber (12) and a second pressure medium source (24) that is arranged to supply pressure medium into the first fluid chamber (12) at a lower pressure than the first pressure medium source (13).

19. A piston engine comprising a gas exchange valve arrangement according to any of the preceding claims.