EP3743602A1

EP3743602A1 - A safety actuator, a safety actuator assembly and a reciprocating internal combustion piston engine having such a safety actuator assembly

Info

Publication number: EP3743602A1
Application number: EP18703810.4A
Authority: EP
Inventors: Magnus Sundsten; Edward Winter
Original assignee: Wartsila Finland Oy
Current assignee: Wartsila Finland Oy
Priority date: 2018-01-26
Filing date: 2018-01-26
Publication date: 2020-12-02
Anticipated expiration: 2038-01-26
Also published as: EP3743602B1; WO2019145596A1

Abstract

The disclosure relates to a safety actuator (1) for operating a respective overhead valve (2) of a reciprocating internal combustion piston engine, comprising an operating configuration for operating the respective overhead valve (2) between a closed position and an open position during normal operating mode, and a safety configuration for operating the respective overhead valve between a closed position and a safety position during a safety operating mode. A safety actuator assembly comprising a operation control valve (6) for controlling the operating configuration, and a safety control valve (7) for controlling the safety configuration is also concerned. In addition, a reciprocating internal combustion engine having such a safety actuator assembly is also discussed.

Description

A SAFETY ACTUATOR, A SAFETY ACTUATOR ASSEMBLY AND A RECIPROCATING INTERNAL COMBUSTION PISTON ENGINE HAVING SUCH A SAFETY ACTUATOR ASSEMBLY

FIELD OF THE DISCLOSURE

The present disclosure relates to reciprocating internal combustion piston engines, and more particularly to a safety actuator for operating a respective overhead valve of such an engine. The present disclosure further concerns a safety actuator assembly and a reciprocating internal combustion piston engine equipped with such a safety actuator assembly.

BACKGROUND OF THE DISCLOSURE

Reciprocating internal combustion piston engines generally use overhead valves for controlling fluid communication between the combustion cylinder and an inlet port thereof, and respectively, between a combustion cylinder and an exhaust port thereof.

A typical way of operating overhead valves has been to use an overhead cam mechanically coupled to the overhead valves. A more precise control of the overhead valve has been obtained by replacing the overhead cam with a fluid operated piston for operating the overhead valve.

However, such configurations have been found to be more prone to malfunction than more conventional ones. Particularly, situations have occurred, where an overhead valve is unintentionally maintained in a closed position, which in turn may lead to significantly increased pressure and temperature levels within the combustion cylinder. Subsequently, this might cause further damage to the engine. Previously, an emergency shut down has been commenced in an occurrence of such an overhead valve malfunction in order to avoid further damage.

BRIEF DESCRIPTION OF THE DISCLOSURE

An object of the present disclosure is to provide a safety actuator for operating a respective overhead valve of a reciprocating internal combustion piston engine in safety mode, when there is a malfunction in the normal fluid powered piston actuation of overhead valve.

It is a further object of the present disclosure to provide a safety actuator assembly and a reciprocating internal combustion piston engine equipped with such a safety actuator assembly.

The objects of the disclosure are achieved by the safety actuator, safety actuator assembly and a reciprocating combustion piston engine which are characterized by what is stated in the independent claims. The preferred embodiments of the disclosure are disclosed in the dependent claims.

The disclosure is based on the idea of providing a safety configuration which can be independently operated so as to actuate the overhead valve into a safety position. Particularly, the having the overhead valve in a safety position prevents the rise of temperature and pressure levels by forcing the overhead valve sufficiently open to enable fluid communication from the combustion cylinder, while maintaining a sufficient clearance between the overhead valve and the combustion piston to avoid collision.

An advantage of the aspects according to the disclosure is that, in the occurrence of an overhead valve malfunction, the operation of the whole engine does not need to be shut down. Instead, the operation of the engine can be maintained using combustion cylinders with normally operating overhead valves, while the combustion cylinder with an overhead valve malfunction may be operated in a safety mode without risking further damage to the engine.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following the disclosure will be described in greater detail by means of preferred embodiments with reference to the accompanying drawings, in which

Fig. 1 shows a schematic cross-sectional illustration of a portion of a reciprocating internal combustion engine according to the disclosure, having an embodiment of the safety actuator where a safety piston actuates the overhead valve via an operating piston, and an embodiment of the safety actuator, where a safety piston actuates the overhead valve through an opening in an operating piston, and

Fig. 2 shows a schematic cross-sectional illustration of a portion of a reciprocating internal combustion engine according to the disclosure, having an embodiment of the safety actuator, where a safety piston actuates the overhead valve via a valve yoke.

It should be noted that, for the purpose of clarity, the appended drawings are illustrated in a simplified manner, and should not interpreted as restricting the scope of the present disclosure.

DETAILED DESCRIPTION OF THE DISCLOSURE

According to a first aspect of the present disclosure, a safety actuator 1 for operating a respective overhead valve 2 of a reciprocating internal combustion piston engine is provided. The overhead valve may be, for example an intake valve, or more suitably, an exhaust valve. Preferably, but not necessarily, the overhead valve is of the poppet valve -type.

Preferably, but not necessarily, the reciprocating internal combustion piston engine is a multi-piston engine.

The safety actuator comprises an operating configuration for operating the respective overhead valve 2 between a closed position and an open position during normal operating mode.

The operating configuration comprises an operating piston chamber 3a having an operating piston 3b movable between a first operating position and a second operating position within the operating piston chamber 3a, and

The operating configuration further comprises an operating fluid channel 3c for conducting operating fluid to the operating piston chamber 3a so as to actuate the operating piston 3b from the first operating position to the second operating position.

Particularly, the safety actuator further comprises a safety configuration for operating the respective overhead valve 2 between a closed position and a safety position during a safety operating mode, comprising:

The safety configuration further comprises a safety piston chamber 4a having a safety piston 4b movable between a first safety position and a second safety position within the safety piston chamber 4a.

The safety configuration further comprises a safety fluid channel 4c for conducting operating fluid to the safety piston chamber 4a so as to actuate the safety piston 4b from the first safety position to the second safety position.

The operating fluid used for the safety configuration may different from that used for the operating configuration. For example, the fluid itself may be of a different type, or it may be provided at a different pressure level. Alternatively, the operating fluid may be the same for both the operating configuration and the safety configuration.

The safety actuator 1 is configurable to be operationally coupled to the respective overhead valve 2 such that a movement of the operating piston 3b from the first operating position to the second operating position actuates the respective overhead valve 2 from the closed position to the open position. Moreover, a movement of the safety piston 4b from the first safety position to the second safety position actuates the respective overhead valve 2 from the closed position to the safety position.

The travel of the safety piston 4b between the first and second safety positions is shorter than the travel of the operating piston 3b between the first and second operating positions, and correspondingly, the travel of the overhead valve 2 between the closed position and the safety position is shorter than the travel between the closed position and the open position.

Most suitably, when the safety actuator 1 is operationally coupled to the respective overhead valve 2, the movement of the safety piston 4b from the first safety position to the second safety position actuates the respective overhead valve 2 from the closed position to the safety position such that there remains a clearance between the respective overhead valve in its safety position and a respective combustion piston in its top dead center position.

Most suitably, the travel of the safety piston 4b between the first and second safety positions is 5% - 50% of the travel of the operating piston 3b between the first and second operating positions. It has been considered that sufficient fluid communication is not achieved to prevent the rise of temperature and pressure levels, if the travel of the safety piston 4b between the first and second safety positions is less than 5% of the travel of the operating piston 3b between the first and second operating positions. On the other hand, the risk of the overhead valve colliding with a respective combustion piston becomes inevitable, if the travel of the safety piston 4b between the first and second safety positions more than 50% of the travel of the operating piston 3b between the first and second operating positions.

In an embodiment according to the first aspect of the disclosure, the safety piston 4b is operationally coupled to the operating piston 3b for actuating the operating piston, such that a movement of the safety piston 4b from the first safety position to the second safety position actuates the operating piston 3b from the first operating position towards the second operating position for a distance corresponding to the travel of the safety piston 4b between the first and second safety positions. Moreover, when the safety actuator is operationally coupled to the respective overhead valve 2, a movement of the operating piston 3b from the first operating position towards the second operating position for a distance corresponding to the travel of the safety piston 4b between the first and second safety positions actuates the respective overhead valve 2 from the closed position to the safety position.

Preferably, but not necessarily, the safety piston 4b comprises a safety stem 4d’ extending up to the operating piston 3b, whereby the safety piston 4b, safety stem 4d’ and the operating piston 3b are configured such that, when the safety piston 4b is in the second safety position, the safety stem 4d’ restricts movement of the operating piston 3b to the first operating position. An advantage of this arrangement is that a relatively simple construction is achieved for the safety configuration and the operating configuration while requiring relatively little space, as compared to providing the safety and operating configurations as completely separate entities.

An arrangement according to this embodiment has been illustrated in Fig. 1 as the safety actuator 1 operationally coupled to the overhead valve 2 on the left.

In another embodiment according to the first aspect of the disclosure, the safety piston 4b comprises a safety stem 4d” extending through an opening on the operating piston 3b. The safety piston 4b, safety stem 4d” and the operating piston 3b are configured such that, when the safety actuator 1 is operationally coupled to the respective overhead valve 2 and the safety piston 4b is in the second safety position, the safety stem 4d” extends up to said overhead valve 2, thereby restricting movement of the overhead valve 2 to the closed position.

An advantage of this arrangement is that the safety configuration may be operated independently of the operating configuration, while requiring relatively little space as compared to providing the safety and operating configurations completely separate.

An arrangement according to this embodiment has been illustrated in Fig. 1 as the safety actuator 1 operationally coupled to the overhead valve 2 on the right

In a further embodiment according to the first aspect of the disclosure, the safety actuator 1 comprises a valve yoke 5 for conveying movements of the operating piston 3b and the safety piston 4d to a respective overhead valve 2. The valve yoke 5 is positioned between said overhead valve 2, and both the operating piston 3b and the safety piston 4b, when the safety actuator 1 is operationally coupled to said respective overhead valve 2.

Preferably, but not necessarily, when the safety actuator 1 is operationally coupled to two or more respective overhead valves 2, the valve yoke 5 extends over said two or more overhead valves 2, thereby conveying movements of the operating piston 3b and the safety piston 4b to said two or more overhead valves 2.

An advantage of this arrangement is that a single safety actuator 1 may be used to actuate multiple overhead valves. Moreover, this enables the operating configuration and the safety configuration to be constructed as completely separate entities, thus ensuring more robust operation of the safety configuration. Preferably, but not necessarily, the operating piston chamber 3a and the safety piston chamber 4a are positioned side-by-side in a direction transverse to the movement of both the operating piston 3b and the safety piston 4b.

An arrangement according to this embodiment has been illustrated in Fig. 2.

According to a second aspect of the disclosure, a safety actuator assembly is provided. The safety actuator assembly comprises a safety actuator 1 according to any embodiment, or variations thereof, according to the first aspect of the present disclosure.

The safety actuator assembly further comprises an operating control valve 6 for selectively coupling the operating fluid channel 3c between an operating fluid supply and an operating fluid discharge.

The safety actuator assembly further comprises a safety control valve 7 for selectively coupling the safety fluid channel 4c between a safety fluid supply and a safety fluid discharge. Instead, the operation of the engine can be maintained using combustion cylinders with normally operating overhead valves, while the combustion cylinder with an overhead valve malfunction may be operated in a safety mode without risking further damage to the engine.

The fluid supply and the fluid discharge of used for the safety configuration may different from those used for the operating configuration. For example, the fluid itself may be of a different type, or it may be provided at a different pressure level. Alternatively, the fluid supply and fluid discharge may be the same for both the operating configuration and the safety configuration.

In an embodiment according to the second aspect of the present disclosure, the safety actuator assembly further comprises a drainage channel for conducting operating fluid from the operating piston chamber 3c, and a drainage control valve for selectively enabling or disabling fluid communication via said drainage channel.

This enables movement of the operating piston 3b towards the first operating position even in a situation where, the operating control valve 7 has malfunctioned such that a fluid communication with the operating fluid discharge cannot be established.

Preferably, but not necessarily the drainage control valve is provided as the safety control valve 7. In such an arrangement, the drainage channel is coupled to the safety control valve 7. The safety control valve 7 is further configured to enable fluid communication via the drainage channel when the safety fluid channel 4c is coupled with the safety fluid supply, and respectively, disable fluid communication via the drainage channel when the safety fluid channel 4c is coupled with the safety fluid discharge.

Alternatively, the drainage control valve may be provided in connection with the safety stem 4d, 4d’, 4d”. In such an arrangement, the drainage channel extends through an opening in which the safety stem 4d, 4d’, 4d” is received. The safety stem 4d, 4d’, 4d” is further configured to enable fluid communication via the drainage channel when the safety piston 4b is in the second safety position, and respectively, disable fluid communication via the drainage channel when the safety piston 4b is in the first safety position.

According to a third aspect of the present disclosure, a reciprocating internal combustion piston engine is provided. Preferably, but not necessarily, a multi-piston a reciprocating internal combustion piston engine is provided.

The reciprocating internal combustion piston engine comprises a safety actuator assembly according to any of embodiments, or variants thereof, according to the second aspect of the present disclosure. Particularly, the safety actuator 1 being operationally coupled to a respective overhead valve 2 of said engine. Naturally, more than one safety actuators 1 may be provided.

The engine further comprises sensor means 8 for providing information indicative of an overhead valve operating malfunction.

The engine further comprises a control unit 9 coupled to the operating control valve 6 for selectively actuating the overhead valve 2 from the closed position to the open position, by operating said operating control valve 6. The control unit 9 is further coupled to the safety control valve 7 for selectively actuating the overhead valve 2 from the closed position to the safety position, by operating said safety control valve 7. Moreover, the control unit 9 is further coupled to the sensor means 8 for receiving information indicative of an overhead valve operating malfunction.

The control unit 9 is configured to determine normal operation mode when information indicative of an overhead valve malfunction is not received from the sensor means 8. Respectively, the control unit is configured to determine safety operation mode when information indicative of an overhead valve malfunction is received from the sensor means 8

During normal operating mode, the control unit 9 is further configured to operate the operating control valve 6 so as to actuate the operating piston 3b between the first operating position and the second operating position, thereby moving the overhead valve 2 respectively from the closed position to the open position in accordance with a predefined operating sequence. Moreover, during normal operating mode, the control unit 9 is configured to operate the safety control valve 7 so as to actuate the safety piston 4b into the first safety position.

During safety operating mode, the control unit 9 is further configured to operate the safety control valve 7 so as to actuate the safety piston 4b into the second safety position, thereby restricting the movement of the overhead valve 2 towards the closed position at the safety position.

Suitably, during safety operating mode, the control unit 9 is further configured to operate the operating control valve 6 so as to enable fluid communication between the operating fluid discharge and the operating fluid channel 3c. This prevents the operating piston 3b from restricting the movement of the overhead valve 2 towards its closed position, even when no drainage channel is provided for the operating piston chamber 3a.

Preferably, but not necessarily, the engine is a multi-piston internal combustion engine. This enables maintaining operation of the engine using combustion cylinders with normally operating overhead valves, while the combustion cylinder with an overhead valve malfunction may be operated in a safety mode without risking further damage to the engine.

Suitably, said overhead valve 2 is an intake valve, and more suitably, said overhead valve 2 is an exhaust valve. Preferably, but not necessarily said overhead valve is of the poppet -type.

An overhead valve malfunction may be caused by a plurality of different reasons. For example, the operating control valve 6 may not be operating correctly due to a malfunctioning solenoid or a return spring, or the operating control valve engaging member, such as a valve spool, may be jammed. Moreover, the operating control piston 3b itself may be jammed or the operating fluid channel 3c may be blocked, for example. A further cause which may result in an overhead valve malfunction, is that the overhead valve 2 itself may be jammed. Nevertheless, any one or more suitable sensor for indicating an overhead valve malfunction may be used as the sensor means 8.

Preferably, but not necessarily, the sensor means 8 comprise at least one of

a feedback loop of the operating control valve 6 for determining position of the operating control valve 6;

an overhead valve position sensor for determining position the overhead valve 2; an overhead valve motion sensor for determining movement of the overhead valve 2; an operating piston chamber pressure sensor for determining an operating pressure of the operating piston chamber 3a;

a combustion cylinder pressure sensor for determining a cylinder pressure of an combustion cylinder associated to the overhead valve 2, and

an exhaust temperature sensor for determining exhaust temperature in an exhaust port associated to the overhead valve.

When a feedback loop of the operating control valve 7 for determining position of the operating control valve is be used as the sensor means 8, an overhead valve malfunction may be indicated if the determined position of the operating control valve 7 does not correspond to the desired position thereof.

When an overhead valve position sensor for determining position of the overhead valve is used as the sensor means 8, an overhead valve malfunction may be indicated if the determined position of the overhead valve 2 does not correspond to the desired position thereof, i.e the position does not match that defined in accordance with a predefined operating sequence during normal operating mode.

When an overhead valve motion sensor for determining movement of the overhead valve 2 is used as the sensor means 8, an overhead valve malfunction may be indicated if no motion of the overhead valve 2 is determined during normal operation mode, or when the determined motion of the overhead valve 2 does not correspond to the motion that should result from a predefined operating sequence of the overhead valve 2 during normal operating mode.

When an operating piston chamber pressure sensor for determining an operating pressure is used as the sensor means 8, an overhead valve malfunction may be indicated if the determined operating pressure of the operating piston chamber 3a exceeds a predefined threshold. In other words, an overhead valve malfunction may be indicated when the operating pressure of the operating piston chamber 3a exceeds a pressure level expected during normal operation mode.

When a combustion cylinder pressure sensor for determining a cylinder pressure of a combustion cylinder associated to the overhead valve is used as the sensor means 8, an overhead valve malfunction may be indicated if the determined combustion cylinder pressure exceeds a predefined threshold. In other words, an overhead valve malfunction may be indicated when the combustion cylinder pressure exceeds a pressure level expected during normal operation mode. When an exhaust temperature sensor for determining exhaust temperature in an exhaust port associated to the overhead valve 2 is used as the sensor means 8, an overhead valve malfunction may be indicated if the determined exhaust temperature in an exhaust port associated to the overhead valve 2 does not exceed a predefined threshold. In other words, an overhead valve malfunction may be indicated when the exhaust temperature is lower than a temperature level expected during normal operation mode.

Fig. 1 shows a cross-sectional view of a portion of a cylinder head associated to an internal combustion piston engine according to an embodiment of the present disclosure. The cylinder head has two exhaust ports, each equipped with a respective overhead valve 2 of the poppet type. Both of the overhead valves 2 are spring biased towards their respective closed positions, although other biasing means may naturally be used. Such biasing enables that the overhead valve 2 only needs to be actuated towards its open position, while movement towards the closed position is achieved by the biasing when the overhead valve 2 is not actuated.

The overhead valve 2 on the left side is operationally coupled with an embodiment of a safety actuator 1 according to the present disclosure. This safety actuator comprises an operating piston chamber 3a, in which an operating piston 3b is movably arranged. The An end of operating piston 3b not facing the operating piston chamber 3a lies against the overhead valve 2, thus enabling movement of the operating piston 3b to be directly transferred to the overhead valve 2. An operating fluid channel 3c is provided for conducting operating fluid to the operating piston chamber 3a so as to actuate the operating piston 3b. A safety piston chamber 4a, in which a safety piston 4b is movably arranged, is provided above the operating piston chamber 3a and the operating piston 3b, i.e. in a direction away from the overhead valve 2. Accordingly, a safety fluid channel 4c is provided for conducting operating fluid to the safety piston chamber 4a so as to actuate the safety piston 4b. In the situation of Fig. 1 , i.e.. the overhead valve 2 being in its closed position, the operating piston 3b being in its first operating position and the safety piston 4b being in its first safety position, a safety stem 4d’ of the safety piston 4b extends up to, and lies against, the operating piston, so as to directly transfer movement of the safety piston 4b to the operating piston 3b. That is, movement of the safety piston 4b actuates the overhead valve 2 via the operating piston 3b.

The overhead valve 2 on the right side, in turn, is operationally coupled with another embodiment of a safety actuator 1 according to the present disclosure. Particularly, the safety actuator arrangement on the right side differs from that on the left side by having a safety stem 4d” extending through an opening in the operating piston 3b directly up to the overhead valve 2, so that the safety stem 4d” lies against the overhead valve. Accordingly, the movement of the safety piston actuates the overhead valve 2 directly.

Although Fig. 1 shows, for illustrative purposes, different embodiments of a safety actuator 1 according to the disclosure, it is clear for the skilled person, that both overhead valves 2 may utilize identical safety actuators 1 . Moreover, either of the safety actuators of Fig. 1 may be used in an arrangement where only a single overhead valve 2 is operationally coupled to a safety actuator 1 .

The safety actuator assembly of Fig. 1 also shows an operating control valve 6 selectively coupling the operating fluid channel 3c between an operating fluid supply and an operating fluid discharge. Correspondingly, a safety control valve 7 is provided to selectively couple the safety fluid channel 4c between a safety fluid supply and a safety fluid discharge. Both the operating control valve 6 and the safety control valve 7 are shown as solenoid controlled valves biased to positions coupling the operating fluid channel 3c and the safety fluid channel 4c to their respective discharges. Naturally, other types of valves may be used. Although Fig. 1 illustrates both safety actuators 1 coupled to a common operating control valve 6 and a common safety control valve 7, separate respective valves may be used for each safety actuator.

Moreover, the portion of the internal combustion piston engine illustrated in Fig. 1 has a control unit 9 operationally coupled to the operating control valve 6 and the safety control valve 7 so as to actuate them. Moreover, sensor means 8 are provided as motion sensor for determining motion of each overhead valve 2. As discussed earlier, other types of sensors may be used instead, or in addition, to the motion sensors 8 illustrated in Fig. 1 .

During normal operation, the control unit 9 operates the safety control valve 7 so that the safety fluid channel 4c is in fluid communication with the safety fluid discharge, i.e. no force is exerted on the safety piston 4b. Moreover, the control unit 9 operates the operating control valve 6 to couple the operating fluid supply with the operating fluid channel 3c when the overhead valve 2 is required to be opened in accordance with a predetermined operating sequence. The operating piston 3b then moves from its first operating position to its second operating position, thereby pushing the overhead valve 2 to its open position. When the overhead valve is required to close in accordance with a predetermined operating sequence, the control unit 9 operates the operating control valve 6 so as to couple the operating fluid channel 3c with operating fluid discharge, thus enabling the overhead valve to move into its closed position, pushed by the biasing spring. When an overhead valve malfunction is determined by the control unit 9, for example, when the sensor means 8 detects that the overhead valve 2 is not moving in a manner corresponding to the predefined operating sequence, safety operation mode is applied for the safety actuator 1 corresponding to the malfunctioning overhead valve 2. The control unit 9 then operates the safety control valve 7 so as to couple the safety fluid supply in fluid communication with the safety fluid channel 4c, thereby causing the safety piston 4b to move from its first safety position to its second safety position and pushing the overhead valve 2 to its respective safety position.

Suitably, during safety operation mode, the control unit 9 operates the operating control valve 6 so that the operating fluid channel 3c is in fluid communication with the operating fluid discharge, i.e. no force is exerted on the operating piston 3b. However, this is not necessary, if a separate drainage channel (not illustrated) is provided such that a fluid communication is established between operating piston chamber 3a and the drainage channel during safety operation mode, as discussed earlier.

Fig. 2 illustrates a similar arrangement to that of Fig. 1 with the exception of the safety actuator 1 being provided as one according to a further embodiment of the present disclosure. Particularly, the operating piston chamber 3a and the safety piston chamber 4a, and their respective pistons 3b, 4b, are arranged side by side. Moreover, a valve yoke 5 is situated between the overhead valves 2 and both the operating piston 3b and the safety piston 4b. The end of the operating piston 3b not facing the safety piston chamber 3a, and respectively, the end of the safety piston 4b, namely the safety stem 4d, both lie against the valve yoke 5, so that movement of the pistons 3b, 4b are transferred to the overhead valve 2 via the valve yoke 5.

The valve yoke 5 extends over the two overhead valves 2, such that a single safety actuator may be used for controlling both overhead valves 2. It should be noted, however, that a valve yoke 5 may be used to operationally couple a single safety actuator 1 to a single overhead valve 2. That is, a or each overhead valve 2 may be provided with a respective safety actuator 1 equipped with its respective valve yoke 5, thus enabling said or each overhead valve to be operated separately.

Claims

1 . A safety actuator (1 ) for operating a respective overhead valve (2) of a reciprocating internal combustion piston engine, comprising:

an operating configuration for operating the respective overhead valve (2) between a closed position and an open position during normal operating mode, comprising

- an operating piston chamber (3a) having an operating piston (3b) movable between a first operating position and a second operating position within the operating piston chamber, and

- an operating fluid channel (3c) for conducting operating fluid to the operating piston chamber (3a) so as to actuate the operating piston (3b) from the first operating position to the second operating position,

characterized by the safety actuator further comprising a safety configuration for operating the respective overhead valve between a closed position and a safety position during a safety operating mode, comprising:

- a safety piston chamber (4a) having a safety piston (4b) movable between a first safety position and a second safety position within the safety piston chamber, and

- a safety fluid channel (4c) for conducting operating fluid to the safety piston chamber (4a) so as to actuate the safety piston (4b) from the first safety position to the second safety position,

wherein the safety actuator (1 ) is configurable to be operationally coupled to the respective overhead valve (2) such that:

- a movement of the operating piston (3b) from the first operating position to the second operating position actuates the respective overhead valve (2) from the closed position to the open position,

- a movement of the safety piston (4b) from the first safety position to the second safety position actuates the respective overhead valve (2) from the closed position to the safety position, and

wherein the travel of the safety piston (4b) between the first and second safety positions is shorter than the travel of the operating piston (3b) between the first and second operating positions, and correspondingly, the travel of the overhead valve (2) between the closed position and the safety position is shorter than the travel between the closed position and the open position.

2. The safety actuator according to Claim 1 , characterized in that the travel of the safety piston (4b) between the first and second safety positions is 5% - 50% of the travel of the operating piston (3b) between the first and second operating positions.

3. The safety actuator according to Claim 1 or 2, characterized in that the safety piston (4b) is operationally coupled to the operating piston (3b) for actuating the operating piston, such that:

a movement of the safety piston (4b) from the first safety position to the second safety position actuates the operating piston (3b) from the first operating position towards the second operating position for a distance corresponding to the travel of the safety piston (4b) between the first and second safety positions, and

a movement of the operating piston (3b) from the first operating position towards the second operating position for a distance corresponding to the travel of the safety piston (4b) between the first and second safety positions actuates the respective overhead valve (2) from the closed position to the safety position.

4. The safety actuator according to Claim 3, characterized the safety piston (4b) comprises a safety stem (4d’) extending up to the operating piston (3b),

wherein the safety piston (4b), safety stem (4d’) and the operating piston (3b) are configured such that, when the safety piston (4b) is in the second safety position, the safety stem (4d’) restricts movement of the operating piston (3b) to the first operating position.

5. The safety actuator according to Claim 1 or 2, characterized in that the safety piston (4b) comprises a safety stem (4d”) extending through an opening on the operating piston (3b),

wherein the safety piston (4b), safety stem (4d”) and the operating piston (3b) are configured such that, when the safety actuator (1 ) is operationally coupled to the respective overhead valve (2) and the safety piston (4b) is in the second safety position, the safety stem (4d”) extends up to said overhead valve (2) thereby restricting movement of the overhead valve (2) to the closed position.

6. The safety actuator (1 ) according to any of the preceding Claims 1 -5, characterized by comprising a valve yoke (5) for conveying movements of the operating piston (3b) and the safety piston (4d) to a respective overhead valve (2), the valve yoke (5) being positioned between said overhead valve (2), and both the operating piston (3b) and the safety piston (4b), when the safety actuator (1 ) is operationally coupled to said respective overhead valve (2).

7. The safety actuator (1 ) according to Claim 6, characterized in that, when the safety actuator (1 ) is operationally coupled to two or more respective overhead valves (2), the valve yoke (5) extends over said two or more overhead valves (2), thereby conveying movements of the operating piston (3b) and the safety piston (4b) to said two or more overhead valves (2).

8. The safety actuator (1 ) according to Claim 6 or 7, characterized in that the operating piston chamber (3a) and the safety piston chamber (4a) are positioned side-by-side in a direction transverse to the movement of both the operating piston (3b) and the safety piston (4b).

9. A safety actuator assembly, characterized by comprising

the safety actuator (1 ) according to any of the preceding Claims 1 -8;

an operating control valve (6) for selectively coupling the operating fluid channel (3c) between an operating fluid supply and an operating fluid discharge, and

a safety control valve (7) for selectively coupling the safety fluid channel (4c) between a safety fluid supply and a safety fluid discharge.

10. The safety actuator assembly according to Claim 9, characterized by further comprising

a drainage channel for conducting operating fluid from the operating piston chamber (3c), and

a drainage control valve for selectively enabling or disabling fluid communication via said drainage channel.

1 1 . The safety actuator assembly according to Claim 10, characterized in that the drainage control valve is provided as the safety control valve (7),

whereby the drainage channel is coupled to the safety control valve (7) and the safety control valve (7) is configured to enable fluid communication via the drainage channel when the safety fluid channel (4c) is coupled with the safety fluid supply, and respectively, disable fluid communication via the drainage channel when the safety fluid channel (4c) is coupled with the safety fluid discharge.

12. The safety actuator assembly according to Claim 10 characterized in that the drainage control valve is provided in connection with the safety stem (4d, 4d’, 4d”) whereby the drainage channel extends through an opening in which the safety stem (4d, 4d’, 4d”) is received, and

the safety stem (4d, 4d’, 4d”) being is configured to enable fluid communication via the drainage channel when the safety piston (4b) is in the second safety position, and respectively, disable fluid communication via the drainage channel when the safety piston is in the first safety position.

13. A reciprocating internal combustion piston engine, characterized by comprising: the safety actuator assembly according to any of the preceding Claims 9-12, wherein the safety actuator is operationally coupled to a respective overhead valve (2) of said engine;

sensor means (8) for providing information indicative of an overhead valve operating malfunction, and

a control unit (9) coupled to:

- the operating control valve (6) for selectively actuating the overhead valve (2) from the closed position to the open position, by operating said operating control valve (6);

- the safety control valve (7) for selectively actuating the overhead valve (2) from the closed position to the safety position, by operating said safety control valve (7), and

- the sensor means (8) for receiving information indicative of an overhead valve operating malfunction, and

the control unit (9) being configured to determine normal operation mode when information indicative of an overhead valve malfunction is not received from the sensor means (8), and respectively, determine safety operation mode when information indicative of an overhead valve malfunction is received from the sensor means (8), wherein, during normal operating mode, the control unit (9) is further configured to:

- operate the operating control valve (6) so as to actuate the operating piston (3b) between the first operating position and the second operating position, thereby moving the overhead valve (2) respectively from the closed position to the open position, in accordance with a predefined operating sequence, and - operate the safety control valve (7) so as to actuate the safety piston (4b) into the first safety position, and

wherein, during safety operating mode, the control unit (9) is further configured to:

- operate the safety control valve (7) so as to actuate the safety piston (4b) into the second safety position, thereby restricting the movement of the overhead valve

(2) towards the closed position at the safety position.

14. The piston engine according to Claim 13, characterized in that said overhead valve (2) is an exhaust valve or an intake valve.

15. The piston engine according to Claim 13 or 14, characterized in that the sensor means (8) comprise at least one of

- a feedback loop of the operating control valve (6) for determining position of the operating control valve (6);

- an overhead valve position sensor for position the overhead valve (2);

- an overhead valve motion sensor for determining movement of the overhead valve (2);

- an operating piston chamber pressure sensor for determining an operating pressure of the operating piston chamber (3a);

- a combustion cylinder pressure sensor for determining a cylinder pressure of a combustion cylinder associated to the overhead valve (2);

- an exhaust temperature sensor for determining exhaust temperature in an exhaust port associated to the overhead valve (2).