WO2013132150A1

WO2013132150A1 - Hydraulic actuator

Info

Publication number: WO2013132150A1
Application number: PCT/FI2013/050214
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: EP2834481A1; CN104145092B; KR20140129362A; KR101990275B1; FI20125255A; FI124350B; CN104145092A; EP2834481B1

Abstract

The hydraulic actuator (35) for an internal combustion engine comprises a piston (7) that is arranged in a pressurizing chamber (9) for pressurizing hydraulic fluid. The piston (7) comprises a cylindrical part (7a) that is provided with at least one opening (13b) on its outer surface, through which opening (13b) the hydraulic fluid can be introduced from the inlet port (20a) into the input portion (9a) of the pressurizing chamber (9).

Description

HYDRAULIC ACTUATOR

Technical field of the invention

The present invention relates to a hydraulic actuator for an internal combustion engine, as defined in the preamble of claim 1. The invention also concerns the use of the hy- draulic actuator, as defined in the other independent claims.

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 conven- tional 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. Hydraulic actuators can also be used for actuating other devices of internal combustion engines, such as gas injection valves.

Summary of the invention

An object of the present invention is to provide an improved hydraulic actuator for an internal combustion engine. The characterizing features of the actuator according to the invention are given in the characterizing part of claim 1. The invention also concerns the use of such an actuator. The hydraulic actuator according to the invention comprises a pressurizing chamber for pressurizing hydraulic fluid, a reciprocating piston that is arranged in the pressurizing chamber and which piston divides the pressurizing chamber into at least one input portion and at least one output portion, at least one inlet port, which inlet port opens into the input portion of the pressurizing chamber for introducing pressurized hydraulic fluid into the input portion for moving the piston, and a fluid outlet for supplying hydraulic fluid from the output portion of the pressurizing chamber to the actuated device. The piston comprises a cylindrical part that is provided with at least one opening on its outer surface, through which opening the hydraulic fluid can be introduced from the inlet port into the input portion of the pressurizing chamber.

The construction of the hydraulic actuator provides good possibilities for throttling of the inflow into the pressurizing chamber and/or the outflow from the chamber. This makes the construction durable and allows smooth opening and closing curves of the actuated devices.

According to an embodiment of the invention, the cross-sectional flow area between the inlet port and the opening of the piston is smaller at the end of the movement of the piston from the input portion end of the pressurizing chamber to the output portion end than in the middle of the movement. This slows down the piston when it approaches the end of the pressurizing chamber at the end of the pressurizing stroke, and also at the beginning of the return stroke. The flow area can be smaller also at the beginning of the pressurizing stroke for slowing down the piston at the beginning of the pressurizing stroke and when the piston approaches the input portion end of the pressurizing chamber at the end of the return stroke.

The inlet can also be used for releasing hydraulic fluid from the inlet portion of the pressurizing chamber during the return stroke of the piston. A separate outlet port is thus not needed. However, the actuator can also comprise a separate outlet port into which outlet port hydraulic fluid can be introduced through the opening of the piston for releasing hydraulic fluid from the inlet portion of the pressurizing chamber during the return stroke of the piston.

According to an embodiment of the invention, the cross-sectional flow area between the outlet port and the opening of the piston is smaller at the end of the movement of the piston from the output portion end of the pressurizing chamber to the input portion end than in the middle of the movement. According to another embodiment, the cross- sectional flow area between the outlet port and the opening of the piston is smaller also at the beginning of the movement of the piston. According to an embodiment of the invention, the outer surface of the cylindrical part of the piston is provided with a circumferential groove that is in flow communication with the opening of the piston. According to another embodiment, the inner surface of the input portion of the pressurizing chamber is provided with a circumferential groove that is in flow communication with the inlet port. If the actuator is provided with a separate outlet port, the inner surface of the input portion of the pressurizing chamber can be provided with a circumferential groove that is in flow communication with the outlet port. The grooves enable different throttling effects at the end and/or at the beginning of the movements of the piston.

According to an embodiment of the invention, the groove of the piston or of the pressurizing chamber comprises at least one edge portion having a smaller depth than the middle part of the groove. According to another embodiment of the invention, the groove comprises a first edge portion, a second edge portion and a middle part that is arranged between the edge portions, each of the edge portions having a smaller depth than the middle part. If the grooves are provided with edge portions with smaller depths than the middle part of the groove, the flow into or out of the pressurizing chamber is very small at the beginning and at the end of the movement of the piston.

The hydraulic actuator can be used, for instance, for opening gas exchange valves or fuel injection valves, such as gas injection valves, of an internal combustion engine.

Brief description of the drawings

Fig. 1 shows a gas exchange valve arrangement comprising a valve actuator according to an embodiment of the invention.

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

Figs. 3-6 show different gas exchange valve arrangements with a valve actuator according to 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 according to the invention can be used in large internal combustion engines, such as in main or auxiliary engines of ships or in engines that are used at power plants for producing electricity. The hydraulic actuator can be used, for instance, for opening gas exchange valves or fuel injection valves, such as gas injection valves, of an engine. In figures 2-6 are shown different gas exchange valve arrangements, which comprise a hydraulic actuator 35 according to the invention. Each gas exchange valve arrangement comprises gas exchange valves 1, Γ, which open and close 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 exchange duct 2 is thus either an intake duct or an exhaust duct. In the accompanying figures, the arrange- ment 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. Preferably, there is a similar arrangement for both the intake valves and the exhaust valves. The gas exchange valves 1, 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, 1 '. The cylinder head 4 is provided with valve guides 17, 17' for accommodating the gas exchange valves 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 actuator 35. The hydraulic actuator 35 comprises a pressurizing chamber 9, in which a piston 7 is arranged. The piston 7 divides the pressurizing chamber 9 into at least one input portion 9a and at least one output portion 9b. In the arrangements 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 piston 7 can reciprocate in the pressurizing chamber 9. When pressure medium is introduced into the input portion 9a of the pressurizing chamber 9, the 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 piston 7 towards the input portion 9a of the pressurizing chamber 9. Instead of the returning spring 18, the return stroke of the piston 7 can be implemented by using hydraulic fluid that is introduced into the output portion 9b of the pressurizing chamber 9. The gas exchange valve arrangement 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 prevents 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, 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, 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 exchange 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 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 exchange valves 1, are opened. When hydraulic fluid is released from the input portion 9a of the pressurizing chamber 9, the 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 arrangement 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. An inlet port 20a connects the intermediate duct 20 to the input portion 9a of the pressurizing chamber 9. 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 commu- nication 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 arrangement is provided with a control valve 11. The control valve 11 is a hydraulic valve that is operated with a solenoid. The control valve 11 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 arrangement 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 piston 7 is formed a solid cylindrical part 7b and the input portion end of the 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 fluid is applied. The hydraulic fluid is introduced into the input portion 9a of the pressurizing chamber 9 through the surface of the hollow cylindrical part 7a. The hollow cylindrical part 7a is therefore provided with at least one opening 13b. In figures 1-6 the piston 7 is also provided with a circumferential groove 13a that is in fluid communication with the opening 13b of the piston 7. The inlet port 20a of the hydraulic actuator 35 is thus in fluid communication with the opening 13b through the groove 13 a. Because of the groove 13a that is arranged around the whole outer circumference of the hollow cylindrical part 7a, flow through the drillings 13b is allowed in any angular position of the piston 7. The groove 13a widens towards the outer surface of the hollow cylindrical part 7a and is only partially aligned with the inlet port 20a when the piston 7 is at the input portion end of the pressurizing chamber 9. The cross-sectional flow area between the inlet port 20a and the opening 13b of the piston 7 is smaller at the beginning of the movement of the piston 7 from the input portion end of the pressurizing chamber 9 to the output por- tion end than in the middle of the movement. 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 piston 7 accelerates smoothly. When the 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 piston 7 approaches the output portion end of the pressurizing chamber 9, the groove 13a becomes again partly overlapping with the inlet port 20a, and the cross- sectional flow area between the inlet port 20a and the opening 13b of the piston 7 is again smaller than in the middle of the pressurizing stroke. The flow into the input portion 9a of the pressurizing chamber 9 is thus limited and the piston 7 slows down. The movement of the 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 be- ginning and at the end of the movement of the piston 7, both the acceleration and deceleration of the piston 7 is smooth.

The 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 arrangement shown in figure 3 differs from the arrangement 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 interme- diate 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. An outlet port 28a connects the input portion 9a of the pressurizing chamber 9 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 outlet port 28a and the second intermediate duct 28. In the arrangement 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 arrangement of figure 3, the driven piston lc, lc' is ar- ranged at the end of the valve stem lb, lb'.

In the arrangement of figure 4, the hydraulic valve 10 is identical to the hydraulic valve 10 of figure 3. In this arrangement, 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 pressurizing chamber 9 is allowed. The third intermediate duct 37 is located so that when the piston 7 is at the input portion end of the pressurizing chamber 9, the groove 13a of the 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 piston 7 is at the output portion end of the pressurizing chamber 9, the opening 13a of the 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 pre- vented. Flow speed is thus restricted at the beginning and at the end of the stroke of the piston 7 and smooth acceleration and deceleration is achieved. In the arrangement 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 piston 7'. The se- cond piston 7' has larger diameter and a shorter stroke than the first piston 7. Since the second piston 7' assists the first piston 7, smaller hydraulic pressure is needed at the beginning of the stroke of the first piston 7. Smaller hydraulic pressure decreases energy consumption of the arrangement. The arrangement of figure 5 differs from the arrangement of figure 4 in that the arrangement 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 return stroke of the piston 7, energy can be recovered from the outlet duct 21 into the pressure accu- mulator 32. The first hydraulic pump 12 supplies hydraulic fluid at a smaller pressure level than is needed for operating the 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 arrangement 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. In figure 7 is shown one option for limiting the cross-sectional flow area between the inlet port 20a and the opening 13b of the piston 7. In this embodiment, the input portion 9a of the pressurizing chamber 9 is provided with a circumferential groove 13c that is in fluid communication with the inlet port 20a. The groove 13c is provided with a first edge portion 13d, a second edge portion 13e and a middle part 13f that is arranged between the edge portions 13d, 13e. Each of the edge portions 13d, 13e has a smaller depth than the middle part 13f. At the end and the beginning of the stroke of the piston 7 the cross-sectional flow area between the inlet port 20a and the opening 13 of the piston is thus very small, and the flow is effectively throttled. The same shape of the groove could also be applied to a groove 13a that is arranged around the piston 7. If the hydraulic actuator 35 is provided with a separate outlet port 28a, there could be a groove in connection with the outlet port 28a.

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 an internal combustion engine, which hydraulic actuator (35) comprises

a pressurizing chamber (9) for pressurizing hydraulic fluid,

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

at least one inlet port (20a), which inlet port (20a) opens into the input portion (9a) of the pressurizing chamber (9) for introducing pressurized hydraulic fluid into the input portion (9a) for moving the piston (7), and

a fluid outlet (9d) for supplying hydraulic fluid from the output portion (9b) of the pressurizing chamber (9) to the actuated device (1, 1 '),

characterized in that the piston (7) comprises a cylindrical part (7a) that is provided with at least one opening (13b) on its outer surface, through which opening (13b) the hydraulic fluid can be introduced from the inlet port (20a) into the input portion (9a) of the pressurizing chamber (9).

2. An actuator (35) according to claim 1, characterized in that the cross-sectional flow area between the inlet port (20a) and the opening (13b) of the piston (7) is smaller at the end of the movement of the piston (7) from the input portion end of the pressurizing chamber (9) to the output portion end than in the middle of the movement.

3. An actuator (35) according to claim 1 or 2, characterized in that the cross- sectional flow area between the inlet port (20a) and the opening (13b) of the piston (7) is smaller at the beginning of the movement of the piston (7) from the input portion end of the pressurizing chamber (9) to the output portion end than in the middle of the movement.

4. An actuator (35) according to any of claims 1-3, characterized in that the inlet port (20a) is also used for releasing hydraulic fluid from the inlet portion (9a) of the pressurizing chamber (9) during the return stroke of the piston (7).

5. An actuator (35) according to any of claims 1-3, characterized in that the actuator (35) comprises a separate outlet port (28a) into which outlet port (28a) hydraulic fluid can be introduced through the opening (13b) of the piston (7) for releasing hydraulic fluid from the inlet portion of the pressurizing chamber (9) during the return stroke of the piston (7).

6. An actuator (35) according to claim 5, characterized in that the cross-sectional flow area between the outlet port (28a) and the opening (13b) of the piston (7) is smaller at the end of the movement of the piston (7) from the output portion end of the pressur- izing chamber (9) to the input portion end than in the middle of the movement.

7. An actuator (35) according to claim 5 or 6, characterized in that the cross- sectional flow area between the outlet port (28) and the opening (13b) of the piston (7) is smaller at the beginning of the movement of the piston (7) from the output portion end of the pressurizing chamber (9) to the input portion end than in the middle of the movement.

8. An actuator (35) according to any of the preceding claims, characterized in that the outer surface of the cylindrical part (7a) of the piston (7) is provided with a circum- ferential groove (13a) that is in flow communication with the opening (13b) of the piston (7).

9. An actuator (35) according to any of the preceding claims, characterized in that the inner surface of the input portion (9a) of the pressurizing chamber (9) is provided with a circumferential groove (13c) that is in flow communication with the inlet port (20a).

10. An actuator (35) according to any of claims 5-7, characterized in that the inner surface of the input portion (9a) of the pressurizing chamber (9) is provided with a cir- cumferential groove that is in flow communication with the outlet port (28a).

11. An actuator (35) according to any of claims 8-10, characterized in that the groove (13a, 13c) of the piston (7) or the pressurizing chamber (9) comprises at least one edge portion (13d, 13e) having a smaller depth than the middle part (13f) of the groove (13a, 13c).

12. An actuator (35) according to claim 11, characterized in that the groove (13a, 13c) comprises a first edge portion (13d), a second edge portion (13e) and a middle part

(13f) that is arranged between the edge portions (13d, 13e), each of the edge portions (13d, 13e) having a smaller depth than the middle part (13f).

13. The use of a hydraulic actuator (35) according to any of claims 1-12 for actuat- ing a gas exchange valve (1, 1 ') of an internal combustion engine.

14. The use of a hydraulic actuator (35) according to any of claims 1-12 for actuating a fuel injection valve of an internal combustion engine.

15. The use of a hydraulic actuator (35) according to claim 14, characterized in that the fuel injection valve is a gas injection valve.