WO2013132149A1

WO2013132149A1 - Hydraulic actuator and gas exchange valve arrangement

Info

Publication number: WO2013132149A1
Application number: PCT/FI2013/050213
Authority: WO
Inventors: Saku Niinikangas; Magnus Sundsten
Original assignee: Wärtsilä Finland Oy
Priority date: 2012-03-09
Filing date: 2013-02-26
Publication date: 2013-09-12
Also published as: FI124349B; CN104160119A; KR20140140571A; CN104160119B; EP2834480B1; FI20125254A; EP2834480A1; KR102032010B1

Abstract

The hydraulic actuator (35) for opening a gas exchange valve of an internal combustion engine comprises a drive piston (7) that is arranged in a pressurizing chamber (9) for pressurizing hydraulic fluid. A hydraulic valve (10) having two positions is used for operating the hydraulic actuator (35). The invention also concerns a gas exchange valve arrangement.

Description

HYDRAULIC ACTUATOR AND GAS EXCHANGE VALVE ARRANGEMENT

Technical field of the invention

The present invention relates to a hydraulic actuator for opening a gas exchange valve of an internal combustion engine according to the preamble of claim 1. The invention also concerns a gas exchange valve arrangement in accordance with the other independent claim.

Background of the invention

In large internal combustion engines, such as in ship or power plant engines, the gas exchange valves can be either mechanically or hydraulically actuated. The most conventional way to operate the intake and exhaust valves is to use cam-driven valve opening mechanisms, where the valves are opened by the lobe of a rotating cam and closed by valve springs. These kinds of arrangements are reliable, but also inflexible. Valve timing is difficult to adjust and if variable valve closing or opening timing is needed, valve mechanisms become complicated. In an electro-hydraulic systems valve timing can be changed easily. However, the flexibility is often achieved at the cost of reduced reliability.

Summary of the invention

An object of the present invention is to provide an improved hydraulic actuator for opening a gas exchange valve of an internal combustion engine. The characterizing features of the actuator according to the present invention are given in the characterizing part of claim 1. Another object of the invention is to provide an improved gas exchange valve arrangement. The characterizing features of the gas exchange valve arrangement according to the invention are given in the characterizing part of the other independent claim.

The hydraulic actuator according to the invention comprises a pressurizing chamber for pressurizing hydraulic fluid, a drive piston that is arranged in the pressurizing chamber and which drive piston divides the pressurizing chamber into at least one input portion and at least one output portion, an inlet duct for introducing pressurized hydraulic fluid into the input portion of the pressurizing chamber for moving the drive piston, a fluid outlet for supplying hydraulic fluid from the output portion of the pressurizing chamber to the gas exchange valve, and an outlet duct for releasing hydraulic fluid from the input portion of the pressurizing chamber. The actuator further comprises a hydraulic valve having a first position, in which position flow from the inlet duct to the input portion of the pressurizing chamber is allowed and flow from the input portion to the outlet duct is prevented, and a second position, in which position flow from the inlet duct to the input portion of the pressurizing chamber is prevented and flow from the input portion to the outlet duct is allowed.

The gas exchange valve arrangement according to the invention comprises at least one gas exchange valve for opening and closing flow communication between a gas exchange duct and a cylinder of the engine, the gas exchange valve comprising a valve head and a valve stem, a receiving chamber, a driven piston that is in mechanical connection with the valve stem and arranged in the receiving chamber, and a hydraulic actuator defined above.

With the hydraulic actuator and the gas exchange valve arrangement according to the invention, the number of electrical components in the gas exchange valve actuating mechanism can be minimized. The actuator and the arrangement thus combine the reliability of a mechanical valve opening system and the flexibility of an electro-hydraulic system. Since the valve lift is limited by the stroke of the drive piston, too high valve lifts are prevented.

According to an embodiment of the invention, the actuator comprises a control valve for actuating the hydraulic valve.

According to another embodiment of the invention, the drive piston divides the output side of the pressurizing chamber into a first output portion that is provided with a first fluid outlet and into a second output portion that is provided with a second fluid outlet. Each of the fluid outlets can be used for supplying hydraulic fluid to one gas exchange valve. This guarantees simultaneous opening of both gas exchange valves. According to another embodiment of the invention, the output portion end of the drive piston is formed of a solid cylindrical part and the input portion end of the drive piston is formed of a hollow cylindrical part that comprises at least one opening in the sleeve for allowing flow into and out of the input portion of the pressurizing chamber. The opening can comprise a groove that is arranged around the outer circumference of the hollow cylindrical part and a boring connecting the groove to the space defined by the hollow cylindrical part. Because of the groove, flow into the input portion of the pressurizing chamber or out of it is allowed in any angular position of the drive piston.

According to another embodiment of the invention, the actuator comprises means for throttling the flow into the input portion of the pressurizing chamber and/or out of the input portion at the beginning and/or at the end of the movement of the drive piston. When the flow into and out of the input portion of the pressurizing chamber is limited, smooth acceleration and deceleration of the drive piston is ensured. The throttling effect can be achieved by arranging the opening of the piston to be only partially aligned with the end of an intermediate duct connecting the input portion of the pressurizing chamber to the hydraulic valve when the drive piston is at the input portion end and/or at the output portion end of the pressurizing chamber.

According to another embodiment of the invention, the inlet duct and the outlet duct are provided with adjustable throttles for regulating flow rates in the ducts. With adjustable throttles, gas exchange valve opening and closing speeds can be changed. According to another embodiment of the invention, the actuator comprises a second drive piston that has a larger diameter and a shorter stroke than the first drive piston and which second drive piston is arranged in the input portion of the pressurizing chamber for assisting the first drive piston at the beginning of the pressurizing stroke. With the second drive piston, the needed hydraulic pressure is lower and energy can be saved.

According to another embodiment of the invention, a fluid chamber that is in fluid communication with the inlet duct is arranged at one end of the spindle of the hydraulic valve, and a control valve is arranged to release pressure from the fluid chamber for actuating the hydraulic valve. No external fluid supply duct is thus needed for actuating the hydraulic valve.

According to an embodiment of the invention, the gas exchange valve arrangement is provided with a pressure accumulator that is connected to the outlet duct for recovering energy from the outlet duct, and to the inlet duct for supplying energy into the inlet duct.

According to an embodiment of the invention, the driven piston is arranged around the valve stem. This saves space compared to a construction where the driven piston is arranged at the end of the valve stem.

Brief description of the drawings

Fig. 1 shows a gas exchange valve arrangement according to an embodiment of the in- vention.

Fig. 2 shows the arrangement of Fig. 1 with open gas exchange valves.

Fig. 3 shows a gas exchange valve arrangement according to a second embodiment of the invention.

Fig. 4 shows a gas exchange valve arrangement according to a third embodiment of the invention.

Fig. 5 shows a gas exchange valve arrangement according to a fourth embodiment of the invention.

Fig. 6 shows a gas exchange valve arrangement according to a fifth embodiment of the invention.

Fig. 7 shows part of a valve actuator according to an embodiment of the invention.

Detailed description of the invention

Embodiments of the invention are now described in more detail with reference to the accompanying drawings.

The hydraulic actuator and the gas exchange valve arrangement according to the invention can be used in large internal combustion engines, such as in main or auxiliary en- gines of ships or in engines that are used at power plants for producing electricity. The arrangement comprises at least one gas exchange valve 1, , which opens and closes flow communication between a gas exchange duct 2 and a cylinder of the engine. The gas exchange valves 1, 1 ' can be either intake valves or exhaust valves, and the gas ex- change duct 2 is thus either an intake duct or an exhaust duct. In the embodiments shown in the accompanying figures, the arrangement comprises a first gas exchange valve 1 and a second gas exchange valve . In an engine, in which the arrangement is used, each cylinder of the engine is provided with a gas exchange valve arrangement according to the invention. Preferably, there is a similar arrangement for both the intake valves and the exhaust valves. The gas exchange valves 1, are arranged in the cylinder head 4 of the respective cylinder. Each gas exchange valve 1, 1 ' comprises a valve stem lb, lb' and a valve head la, la'. The valve head la, la' co-operates with a corresponding valve seat Id, Id'. A valve spring 16, 16' is arranged around the valve stem lb, lb' of each gas exchange valve 1, for closing the gas exchange valve 1, . The cylinder head 4 is provided with valve guides 17, 17' for accommodating the gas exchange valves 1, 1 '.

The gas exchange valves 1, are electro-hydraulically operated. For operating the gas exchange valves 1, 1 ', each gas exchange valve arrangement comprises a hydraulic ac- tuator 35. The hydraulic actuator 35 comprises a pressurizing chamber 9, in which a drive piston 7 is arranged. The drive piston 7 divides the pressurizing chamber 9 into at least one input portion 9a and at least one output portion 9b. In the embodiment of the figures, the pressurizing chamber 9 is divided into one input portion 9a and into a first and a second output portion 9b, 9b'. The drive piston 7 can reciprocate in the pressuriz- ing chamber 9. When pressure medium is introduced into the input portion 9a of the pressurizing chamber 9, the drive piston 7 pressurizes hydraulic fluid on the output side 9b, 9b' of the pressurizing chamber 9. A returning spring 18 is arranged in the pressurizing chamber 9 for pushing the drive piston 7 towards the input portion 9a of the pressurizing chamber 9. However, the return stroke of the drive piston 7 could also be im- plemented by introducing hydraulic fluid into the output portion 9b of the pressurizing chamber 9. The hydraulic actuator 35 comprises a hydraulic valve 10 for opening and closing flow communication between a pressure source, such as a hydraulic pump 12, and the input portion 9a of the pressurizing chamber 9. The hydraulic valve 10 also pre- vents and allows outflow from the input portion 9a of the pressurizing chamber 9. The hydraulic valve 10 is arranged between a hydraulic pump 12 and the input portion 9a of the pressurizing chamber 9. In a first position of the hydraulic valve 10, flow from an inlet duct 15 into the input portion 9a of the pressurizing chamber 9 is allowed and flow from the input portion 9a into an outlet duct 21 is prevented, as shown in figure 2. In a second position of the hydraulic valve 10, flow from the inlet duct 15 into the input portion 9a of the pressurizing chamber 9 is prevented and flow from the input portion 9a into the outlet duct 21 is allowed, as shown in figure 1. The same hydraulic valve 10 is thus used for controlling valve opening and closing timing of both gas exchange valves 1, . The hydraulic actuator 35 further comprises fluid outlets 9d, 9d' for supplying hydraulic fluid from the output portions 9b, 9b' of the pressurizing chamber 9 to the gas exchange valves 1, .

A driven piston lc, lc' is arranged in mechanical connection with the valve stem lb, lb' of each gas exchange valve 1, . The gas exchange valve 1, is thus moved together with the driven piston lc, lc'. The driven piston lc, lc' is arranged in a receiving chamber 5, 5 ' that is in fluid communication with the output portion 9b, 9b' of the pressurizing chamber 9. The first output portion 9b of the pressurizing chamber 9 is connected with a first connecting duct 6 to the receiving chamber 5 of the first gas ex- change valve 1, and the second output portion 9b' of the pressurizing chamber 9 is connected with a second connecting duct 6' to the receiving chamber 5' of the second gas exchange valve . Since the hydraulic actuator 35 is provided with an own output portion 9b, 9b' for each of the gas exchange valves 1 , , the pressurized hydraulic fluid is supplied simultaneously to both of the gas exchange valves 1, 1 '.

When hydraulic fluid is introduced into the input portion 9a of the pressurizing chamber 9, the drive piston 7 moves and pressurizes hydraulic fluid in the output portions 9b, 9b' of the pressurizing chamber 9. From the output portions 9b, 9b' of the pressurizing chamber 9, the hydraulic fluid flows into the receiving chambers 5, 5' and the gas ex- change valves 1, are opened. When hydraulic fluid is released from the input portion 9a of the pressurizing chamber 9, the drive piston 7 can be moved backwards by the returning spring 18. Hydraulic fluid can thus flow from the receiving chambers 5, 5' back into the output portions 9b, 9b' of the pressurizing chamber 9 and the gas exchange valves 1, 1 ' can be closed by the valve springs 16, 16'.

In the embodiment of figures 1 and 2, an intermediate duct 20 is arranged between the hydraulic valve 10 and the pressurizing chamber 9 for connecting the input portion 9a of the pressurizing chamber 9 to the hydraulic valve 10. The hydraulic valve 10 is a hydraulically actuated slide valve. The hydraulic valve 10 is a three-way valve that comprises a first port 10a that is connected to the inlet duct 15, a second port 10b that is connected to the outlet duct 21, and a third port 10c that is connected to the intermediate duct 20. The hydraulic valve 10 comprises a spindle 22 that has a first position and a second position. In the first position of the spindle 22, flow communication between the first port 10a and the third port 10c is closed and flow communication between the second port 10b and the third port 10c is open. Hydraulic fluid can thus flow from the inlet duct 15 into the intermediate duct 20, but flow from the intermediate duct 20 into the outlet duct 21 is prevented. In the second position of the spindle 22, flow communication between the first port 10a and the third port 10c is open and the flow communication between the second port 10b and the third port 10c is closed. Hydraulic fluid can thus flow from the intermediate duct 20 into the outlet duct 21, but flow from the inlet duct 15 into the intermediate duct 20 is prevented. The hydraulic valve 10 is provided with a spring 19 that keeps the spindle 22 in the first position when the hydraulic valve 10 is not actuated. When an external force is applied to the spindle 22, the spindle 22 is moved to the second position. For applying the force on the spindle 22, the hydraulic actuator 35 is provided with a control valve 11. The control valve 11 is a hydraulic valve that is operated with a solenoid. The control valve 1 1 could also be some other kind of electrically actuated valve. When the control valve 11 is in the position of figure 2, hydraulic fluid is introduced onto a pressure surface 23 of the spindle 22 for moving the spindle 22. In the embodiment of figures 1 and 2, the receiving chamber 5, 5' is arranged around the valve stem lb, lb' and the driven piston lc, lc' is a projection of the valve stem lb, lb'. This arrangement enables compact design of the cylinder head 4.

The output portion end of the drive piston 7 is formed a solid cylindrical part 7b and the input portion end of the drive piston 7 is formed of a hollow cylindrical part 7a. The input portion end of the solid cylinder 7b forms a surface onto which the pressure of the hydraulic fiuid is applied. The hydraulic fiuid is introduced into the input portion 9a of the pressurizing chamber 9 through the sleeve of the hollow cylinder 7a. The sleeve is therefore provided with at least one opening, which consists of a groove 13a and a drilling 13b. In the embodiment of the figures, two drillings 13b are in connection with the groove 13a. Because of the groove 13a that is arranged around the whole outer circumference of the hollow cylinder, flow through the drillings 13b is allowed in any angular position of the drive piston 7. The groove 13a widens towards the outer surface of the hollow cylinder and is only partially aligned with the intermediate duct 20 when the drive piston 7 is at the input portion end of the pressurizing chamber 9. Therefore, the flow into the input portion 9a of the pressurizing chamber 9 is throttled when the hydraulic valve 10 is moved into the second position and fluid supply from the hydraulic pump 12 into the pressurizing chamber 9 is allowed. Consequently, the drive piston 7 accelerates smoothly. When the drive piston 7 moves forward, the groove 13a becomes fully aligned with the intermediate duct 20 and maximum flow into the input portion 9a of the pressurizing chamber 9 is allowed. When the drive piston 7 approaches the output portion end of the pressurizing chamber 9, the groove 13a becomes again partly overlapping with the walls of the pressurizing chamber 9. The flow into the input portion 9a of the pressurizing chamber 9 is thus limited and the drive piston 7 slows down. The movement of the drive piston 7 in the opposite direction works in a similar way. Since the outflow from the input portion 9a of the pressurizing chamber 9 is throttled at the beginning and at the end of the movement of the drive piston 7, both the acceleration and deceleration of the drive piston 7 is smooth.

There are also other ways for achieving the throttling effect. In figure 7 is shown part of a valve actuator 35, where the opening of the drive piston is a straight drilling 13b. The intermediate duct 20 between the hydraulic valve 10 and the input portion 9a of the pressurizing chamber 9 is connected to a groove 13c that encircles the inner surface of the pressurizing chamber 9. When the drive piston 7 is at the output portion end of the pressurizing chamber 9, as shown in figure 7, or at the input portion end of the pressur- izing chamber 9, the drilling 13b of the drive piston 7 is only partially aligned with the groove 13c of the input portion 9a of the pressurizing chamber 9. The flow out of the input portion 9a of the pressurizing chamber 9 or into it is thus throttled. The groove 13c is chamfered so that the flow area is very small at the beginning and at the end of the movement of the drive piston 7.

The drive piston 7 further comprises a boring 39, which connects the input portion 9a of the pressurizing chamber 9 to the output portion 9b. A second boring 40 connects the input portion 9a to the second output portion 9b'. Through the borings 39, 40, leakages from the output side of the valve actuator 35 can be compensated. The diameters of the borings 39, 40 are small, and flow through the borings 39, 40 does thus not disturb the functioning of the hydraulic actuator 35. The input portion 9a and the output portions 9b, 9b' of the pressurizing chamber 9 are also provided with air removal ports 41, 42, 43 for removing air from the hydraulic system. The diameters of the air removal ports 41, 42, 43 are small for preventing excessive leakage of the hydraulic fluid. The air removal ports 41, 42, 43 can also be provided with throttles 41a, 42a, 43a for reducing leaking of the hydraulic fluid, as shown in figure 4.

The embodiment shown in figure 3 differs from the embodiment of figures 1 and 2 in terms of the construction of the hydraulic valve 10. The hydraulic valve 10 of figure 3 comprises a fourth port lOd. The hydraulic actuator 35 comprises a first intermediate duct 20 and a second intermediate duct 28. The first port 10a of the hydraulic valve 10 is connected to the inlet duct 15 and the third port 10c is connected to the first intermediate duct 20. The second port 10b is connected to the outlet duct 21 and the fourth port lOd is connected to the second intermediate duct 28. In the first position of the hydraulic valve 10, the spindle 22 allows flow from the inlet duct 15 into the first intermediate duct 20 and prevents flow from the second intermediate duct 28 into the outlet duct 21. In the second position of the hydraulic valve 10, the spindle 22 allows flow from the second intermediate duct 28 into the outlet duct 21 and prevents flow from the inlet duct 15 into the second intermediate duct 28. Hydraulic fluid is introduced into the input portion 9a of the pressurizing chamber 9 through the first intermediate duct 20. The hydraulic fluid is released from the input portion 9a of the pressurizing chamber 9 through the second intermediate duct 28. In the embodiment of figure 3, separate fluid supply to the control valve 11 is not needed. The inlet duct 15 is connected with a control duct 26 to a fluid chamber 27 that is arranged at one end of the spindle 22. Together with the spring 19 of the hydraulic valve 10, the pressure in the fluid chamber 27 keeps the hydraulic valve 10 in the first position, when the control valve 11 is closed. When the control valve 11 is opened, hydraulic fluid is released from the fluid chamber 27 and the hydraulic valve 10 is switched into the second position. In the embodiment of figure 3, the driven piston lc, lc' is arranged at the end of the valve stem lb, lb'.

In the embodiment of figure 4, the hydraulic valve 10 is identical to the hydraulic valve 10 of figure 3. In this embodiment, the first and the second intermediate ducts 20, 28 are merged into a combined intermediate duct 36 before the pressurizing chamber 9. A third intermediate duct 37 and a fourth intermediate duct 38 are branched from the combined intermediate duct 36 and connected to the input portion 9a of the pressurizing chamber 9. The diameters of the third intermediate duct 37 and the fourth intermediate duct 38 are smaller than the diameter of the combined intermediate duct 36. The third and the fourth intermediate ducts 37, 38 are provided with check valves 24, 25. Through the third intermediate duct 37, flow from the combined intermediate duct 36 into the pres- surizing chamber 9 is allowed. The third intermediate duct 37 is located so that when the drive piston 7 is at the input portion end of the pressurizing chamber 9, the groove 13a of the drive piston 7 is aligned with the end of the third intermediate duct 37 and direct flow from the combined intermediate duct 36 into the pressurizing chamber 9 is prevented. Through the fourth intermediate duct 38, flow from the pressurizing chamber 9 into the combined intermediate duct 36 is allowed. The fourth intermediate duct 38 is located so that when the drive piston 7 is at the output portion end of the pressurizing chamber 9, the opening 13a of the drive piston 7 is aligned with the fourth intermediate duct 38 and direct flow from the pressurizing chamber 9 into the combined intermediate duct 36 is prevented. Flow speed is thus restricted at the beginning and at the end of the stroke of the drive piston 7 and smooth acceleration and deceleration is achieved. In the embodiment of figure 4, the inlet duct 15 is provided with an adjustable throttle 30. Also the outlet duct 21 is provided with an adjustable throttle 31. With the throttles 30, 31, the flow in the inlet duct 15 and the outlet duct 21 can be restricted and the opening and closing curves of the gas exchange valves 1, can be affected. Smaller flow gives slower gas exchange valve opening/closing and faster flow gives quicker opening/closing. The input portion 9a of the pressurizing chamber 9 is provided with a second drive piston 7'. The second drive piston 7' has larger diameter and a shorter stroke than the first drive piston 7. Since the second drive piston 7' assists the first drive piston 7, smaller hydraulic pressure is needed at the beginning of the stroke of the first drive piston 7. Smaller hydraulic pressure decreases energy consumption of the arrangement.

The embodiment of figure 5 differs from the embodiment of figure 4 in that the ar- rangement is provided with a pressure accumulator 32 for energy recovery. The pressure accumulator 32 is connected to the outlet duct 21 upstream from the throttle 31. The pressure accumulator 32 is also connected to the inlet duct 15 upstream from the throttle 30 and downstream from the hydraulic pump 12 and the pressure accumulator 32. A second hydraulic pump 12b is arranged downstream from the hydraulic pump 12 and from the pressure accumulator 32 A check valve 33 is arranged between the pressure accumulator 32 and the outlet duct 21 for preventing flow from the first hydraulic pump 12 or the pressure accumulator 32 into the outlet duct 21. During the backwards stroke of the drive piston 7, energy can be recovered from the outlet duct 21 into the pressure accumulator 32. The first hydraulic pump 12 supplies hydraulic fluid at a smaller pressure level than is needed for operating the drive piston 7. The pressure of the flow from the first hydraulic pump 12 and from the pressure accumulator 32 is raised to the sufficient level by the second hydraulic pump 12b.

In the embodiment of figure 6, the hydraulic valve 10 is a solenoid valve. Since the flow capacity of a single solenoid valve is small, the arrangement is provided with a second solenoid valve 10b that is arranged in parallel with the first solenoid valve 10. The valves 10, 10b could also be other electrically actuated valves.

It will be appreciated by a person skilled in the art that the invention is not limited to the embodiments described above, but may vary within the scope of the appended claims. For instance, it is possible to combine features of the different embodiments.

Claims

1. A hydraulic actuator (35) for opening a gas exchange valve (1, ) of an internal combustion engine, which hydraulic actuator (35) comprises

a pressurizing chamber (9) for pressurizing hydraulic fluid,

- a drive piston (7) that is arranged in the pressurizing chamber (9) and which drive piston (7) divides the pressurizing chamber (9) into at least one input portion (9a) and at least one output portion (9b),

an inlet duct (15) for introducing pressurized hydraulic fluid into the input portion (9a) of the pressurizing chamber (9) for moving the drive piston (7), - a fluid outlet (9d) for supplying hydraulic fluid from the output portion (9b) of the pressurizing chamber (9) to the gas exchange valve (1, 1 '), and

an outlet duct (21) for releasing hydraulic fluid from the input portion (9a) of the pressurizing chamber (9),

characterized in that the actuator (35) comprises a hydraulic valve (10) having

- a first position, in which position flow from the inlet duct (15) to the input portion (9a) of the pressurizing chamber (9) is allowed and flow from the input portion (9a) to the outlet duct (21) is prevented, and

a second position, in which position flow from the inlet duct (15) to the input portion (9a) of the pressurizing chamber (9) is prevented and flow from the input portion (9a) to the outlet duct (21) is allowed.

2. An actuator (35) according to claim 1, characterized in that the actuator (35) comprises a control valve (11) for actuating the hydraulic valve (10).

3. An actuator (35) according to claim 1 or 2, characterized in that the drive piston (7) divides the output side of the pressurizing chamber (9) into a first output portion (9b) that is provided with a first fluid outlet (9d) and into a second output portion (9b') that is provided with a second fluid outlet (9d').

4. An actuator (35) according to any of claims 1-3, characterized in that the actuator (35) comprises means for throttling the flow into the input portion (9a) of the pres- surizing chamber (9) and/or out of the input portion (9a) at the beginning and/or at the end of the movement of the drive piston (7).

5. An actuator (35) according to any of the preceding claims, characterized in that the output portion end of the drive piston (7) is formed of a solid cylindrical part (7b) and the input portion end of the drive piston (7) is formed of a hollow cylindrical part (7a) that comprises at least one opening (13a, 13b) in the sleeve for allowing flow into and out of the input portion (9a) of the pressurizing chamber (9).

6. An actuator (35) according to claim 5, characterized in that the opening (13a, 13b) comprises a groove (13a) that is arranged around the outer circumference of the hollow cylindrical part (7a) and a boring (13b) connecting the groove (13a) to the space defined by the hollow cylindrical part (7a).

7. An actuator (35) according to claim 5 or 6, characterized in that the opening (13a, 13b) in the sleeve of the drive piston (7) widen towards the outer surface of the sleeve.

8. An actuator (35) according to any of claims 5-7, characterized in that the open- ing (13a, 13b) in the sleeve of the drive piston (7) is only partially aligned with the end of an intermediate duct (20, 28) connecting the input portion (9a) of the pressurizing chamber (9) to the hydraulic valve (10) when the drive piston (7) is at the input portion end of the pressurizing chamber (9).

9. An actuator (35) according to any of claims 5-8, characterized in that the opening (13a, 13b) in the sleeve of the drive piston (7) is only partially aligned with the end of an intermediate duct (20, 28) when the drive piston (7) is at the output portion end of the pressurizing chamber (9).

10. An actuator (35) according to any of the preceding claims, characterized in that the inlet duct (15) and the outlet duct (21) are provided with adjustable throttles (30, 31) for regulating flow rates in the ducts (15, 21).

11. An actuator (35) according to any of the preceding claims, characterized in that the actuator (35) comprises a second drive piston (7') that has a larger diameter and a shorter stroke than the first drive piston (7) and which second drive piston (7') is arranged in the input portion (9a) of the pressurizing chamber (9) for assisting the first drive piston (7) at the beginning of the pressurizing stroke.

12. An actuator (35) according to any of the preceding claims, characterized in that a fluid chamber (27) that is in fluid communication with the inlet duct (15) is arranged at one end of the spindle (22) of the hydraulic valve (10), and a control valve (11) is arranged to release pressure from the fluid chamber (27) for actuating the hydraulic valve (10).

13. A gas exchange valve arrangement for an internal combustion engine, which arrangement comprises

- at least one gas exchange valve (1, 1 ') for opening and closing flow communication between a gas exchange duct (2) and a cylinder of the engine, the gas exchange valve (1, ) comprising a valve head (la, la') and a valve stem (lb, lb'),

a receiving chamber (5, 5'), and

- a driven piston (lc, lc') that is in mechanical connection with the valve stem

(lb) and arranged in the receiving chamber (5, 5'),

characterized in that the arrangement comprises a hydraulic actuator (35) according to any of claims 1-12.

14. An arrangement according to claim 13, characterized in that the arrangement is provided with a pressure accumulator (32) that is connected to the outlet duct (21) for recovering energy from the outlet duct (21), and to the inlet duct (15) for supplying energy into the inlet duct (15).

15. An arrangement according to claim 13 or 14, characterized in that the driven piston (lc, lc') is arranged around the valve stem (lb, lb').