DK179875B1

DK179875B1 - Exhaust valve actuation system and large two-stroke internal combustion engine

Info

Publication number: DK179875B1
Application number: DKPA201870183A
Authority: DK
Inventors: Cenker Poul; Nørby Hansen Jens
Original assignee: MAN Energy Solutions
Priority date: 2018-03-22
Filing date: 2018-03-22
Publication date: 2019-08-14
Also published as: JP2019167952A; KR20190111771A; CN110295965B; KR102122224B1; JP6644926B2; CN110295965A; DK201870183A1

Abstract

An exhaust valve actuation system for a large two-stroke internal combustion engine, in particular a hydraulically powered exhaust valve actuation system that can be controlled electronically. The exhaust valve actuation system comprises a positive displacement pump (40) with a first shaft (43), a first port and a second port and capable of providing two flow directions. The system also comprises a hydraulic accumulator (28) fluidly connected to the first port. The second port is configured for fluidly connectingto a linear hydraulic actuator (70) acting on a spindle (23) of the exhaust valve (4). The system also comprises a motor-generator such as e.g. a variable displacement motor (30) with a second shaft (33), a third port and a fourth port and capable of two flow directions for one shaft rotation direction. The first shaft (43) is operably coupled to the second shaft (33).

Description

EXHAUST VALVE ACTUATION SYSTEM AND LARGE TWO-STROKE INTERNAL COMBUSTION ENGINE

TECHNICAL FIELD

The present disclosure relates to an exhaust valve actuation system for a large internal combustion engine, in particular to a hydraulically powered exhaust valve actuation system that can be controlled electronically. Hydraulically powered exhaust gas actuation systems are typically used in a large turbocharged two-stroke compression-ignition internal combustion engines. The present disclosure also related to a large two-stroke compression-ignition internal combustion engine with an exhaust valve actuation system.

BACKGROUND

Large turbocharged two-stroke compression-ignition internal combustion engines are typically used as prime movers in large ocean-going ships, such as container ships or in power plants.

The cylinders of these engines are provided with a single exhaust valve in the cylinder cover i.e. at the top of the cylinder and with a ring of piston controlled scavenge ports at the lower region of the cylinder liner.

Most modern engines are provided with an electronically controlled and hydraulically actuated exhaust valve actuation system. In comparison to an old-fashioned camshaft actuated exhaust valve actuation system the electronically controlled and hydraulically actuated system allows for a greatly improved flexibility and adjustability allowing optimization with respect to emissions and fuel consumption over the full range of operating conditions of the engine. The combustion process can thereby be better controlled resulting in a more efficient combustion and lower emission values allowing smokeless operation at all running speeds, reduced partload fuel consumption and lower minimum running speeds.

The hydraulic actuation system must open the exhaust valve against the pressure in the combustion chamber that acts on the valve disk of the exhaust valve and against the force of an air spring that urges the exhaust valve towards its seat.

Thus, initially a very large force is needed to open the exhaust valve and a considerable amount of the hydraulic energy is used for the opening stroke the exhaust valve.

A major portion of the energy delivered by the hydraulic actuator in the opening stroke of the exhaust valve is stored in the gas spring as potential energy. Instead, a major portion of the stored energy and of the energy of the exhaust gases acting on the exhaust valve in the closing stroke is wasted since there are no means to capture the energy coming back in the form of hydraulic energy from the hydraulic actuator. This hydraulic energy is wasted as return oil (hydraulic liquid) to the tank of the hydraulic system.

The amount of hydraulic energy that is used to actuate the exhaust valves on a large two-stroke diesel energy is quite significant, and a substantial part of the fuel savings obtained by the increased combustion control of the electronically controlled engine are lost in the hydraulically powered exhaust valve actuation system.

WO 01/20138 discloses the exhaust valve actuation system according to the preamble of claim 1.

SUMMARY

In view of the above it is an object to overcome or at least reduce the problem mentioned above.

The foregoing and other objects are achieved by the features of the independent claims. Further implementation forms are apparent from the dependent claims, the description and the figures.

According to a first aspect, there is provided an exhaust valve actuation system for a large two-stroke internal combustion engine, in particular a hydraulically powered exhaust valve actuation system that can be controlled electronically, the exhaust valve actuation system comprising:

a positive displacement pump with a first shaft, a first port and a second port and capable of providing two flow directions, a hydraulic accumulator fluidly connected to the first port, the second port being configured for fluidly connecting to a linear hydraulic actuator acting on a spindle of the exhaust valve, and a motor-generator with a second shaft, the first shaft being operably coupled to the second shaft.

By connecting an accumulator to the first port of the variable displacement pump, and by connecting the hydraulic exhaust valve actuator to the second port of the variable displacement pump, the hydraulic fluid is trapped between the hydraulic accumulator and the hydraulic actuator, and the mechanical energy supplied to the hydraulic actuator during the closing stroke of the exhaust valve by the return means (e.g. gas spring) and by the exhaust gases acting on the exhaust valve is transmitted to the hydraulic accumulator. Further, another part of the hydraulic energy coming from the hydraulic actuator during the return stoke is transmitted to the motor generator or variable displacement motor, that can momentarily act as a brake, i.e. act as a hydraulic pump and supply high pressure hydraulic liquid back into the hydraulic system that normally powers the hydraulic motor. Thus, a very large portion of the energy that is supplied to the exhaust valve during its closing stroke is recovered there by reducing the net amount of energy for actuating the exhaust valve significantly.

According to a possible implementation of the first aspect the hydraulic accumulator is connected to the first port to form a first closed hydraulic system.

According to a possible implementation of the first aspect the linear hydraulic actuator is connected to the second port to form a second closed hydraulic system.

According to a possible implementation of the first aspect the positive displacement pump is a variable displacement pump capable of providing two flow directions for one direction of rotation of the first shaft.

According to a possible implementation of the first aspect the motor-generator is configured to operate in two rotational directions of the second shaft.

According to a possible implementation of the first aspect the motor-generator is a variable displacement motor with a third port and a fourth port and capable of two rotation directions of the second shaft for one flow direction.

According to a possible implementation of the first aspect the motor-generator is an electric motor-generator.

According to a possible implementation of the first aspect the motor-generator is a variable displacement motor, with a third port and a fourth port and capable of two flow directions for one direction of rotation of said second shaft.

According to a possible implementation of the first aspect the third port is connected to a first source of a first high pressure hydraulic fluid, and wherein the fourth port is connected to a second source of a second high pressure, the first high pressure being higher than the second high pressure.

According to a possible implementation of the first aspect the exhaust valve actuation system comprises electronic control unit configured to control the rotary speed and displacement of the variable displacement motor and configured to control the displacement of the variable displacement pump.

According to a possible implementation of the first aspect the exhaust valve actuation system comprises a first sensor indicative of the position of the exhaust gas spindle.

According to a possible implementation of the first aspect the exhaust valve actuation system comprises a second sensor indicative of the rotary speed of the variable displacement motor.

According to a possible implementation of the first aspect the variable displacement pump is a radial piston pump and/or wherein the variable displacement hydraulic motor is a radial piston motor.

According to a possible implementation of the first aspect the exhaust valve actuation system comprises a first control valve fluidly connected to one or more control ports of the variable displacement pump, for controlling the displacement and direction flow of the first variable displacement pump the first control valve being electronically controlled by the electronic control unit.

According to a possible implementation of the first aspect the exhaust valve actuation system comprises a second control valve fluidly connected to one or more control ports of the variable displacement hydraulic motor, for controlling the displacement and direction flow of the variable displacement hydraulic motor the second control valve being electronically controlled by the electronic control unit.

According to a possible implementation of the first aspect the electronic control unit is configured to keep the rotary speed of the second shaft at a given rotary speed by controlling the displacement of the variable displacement hydraulic motor.

According to a possible implementation of the first aspect the electronic control unit is configured to control flow to and from the second port in accordance with a signal indicative of the desired position of the exhaust valve.

According to a possible implementation of the first aspect the exhaust valve actuation system comprises flywheel connected to said first shaft or to said second shaft.

According to a possible implementation of the first aspect the exhaust first shaft is coupled to the second shaft to rotate in unison therewith.

According to a possible implementation of the first aspect the variable displacement pump and the variable displacement motor are constructed as a single unit with a single common shaft.

According to a possible implementation of the first aspect the variable displacement hydraulic motor is configured to temporality act as a pump and/or wherein the variable displacement pump is configured to temporarily act as a motor.

According to a second aspect there is provided a large turbocharged two-stroke self-igniting internal combustion engine, the engine comprising:

a plurality of cylinders with scavenge ports at their lower region and an exhaust valve at their top, an exhaust valve with a valve stem and a valve disc, the exhaust valve being movable in opposite directions between a closed position in which the valve disk rests on a valve seat and an open position allowing evacuation of gas in the cylinder, a single acting fluid-operated means operably connected to the valve stem for urging the exhaust valve towards its closed position, a linear hydraulic actuator operably connected to the valve stem and the hydraulic actuator being configured to urge the exhaust valve towards its open position when the linear hydraulic actuator is pressurized, and an exhaust valve auction system according to the first aspect and any one possible implementation thereof.

According to a possible implementation of the second aspect the electronic control unit (50) is configured to control the position and/or speed of the exhaust valve in a closed loop manner by comparing the signal from the first sensor (62) with a desired position for the exhaust valve (4).

According to a possible implementation of the second aspect a conduit connecting the first port to the accumulator is connected to the first source of high pressure via an orifice.

These and other aspects of the invention will be apparent from the embodiment(s) described below.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following detailed portion of the present disclosure, the invention will be explained in more detail with reference to the example embodiments shown in the drawings, in which:

Fig. 1 is an elevated view showing the fore end and one side of a large two-stroke self-igniting turbocharged engine according to an example embodiment,

Fig. 2 is an elevated view showing the aft end and the other side of the engine of Fig. 1,

Fig. 3 is a diagrammatic representation the engine according to Fig. 1 with its intake and exhaust systems, Fig. 4 is a diagram illustrating a first embodiment of the electrohydraulic exhaust valve actuation system of the engine of Fig. 1,

Fig. 4A is a diagram illustrating another embodiment the electrohydraulic exhaust valve actuation system of the engine of Fig. 1,

Fig. 5 is a graph illustrating the opening movement of the exhaust valve, and

Fig. 6 is a graph illustrating motor torque and motor speed.

DETAILED DESCRIPTION

In the following detailed description, the large two stroke engine will be described by the example embodiments. Figs. 1 to 3 show a large low speed turbocharged two-stroke diesel engine with a crankshaft 42 and crossheads 44. Figure 3 shows a diagrammatic representation of a large low speed turbocharged two-stroke diesel engine with its intake and exhaust systems. In this example embodiment the engine has six cylinders 1 in line. Large turbocharged two-stroke diesel engines have typically between five and sixteen cylinders in line, carried by an engine frame 45. The engine may e.g. be used as the main engine in an ocean-going vessel or as a stationary engine for operating a generator in a power station. The total output of the engine may, for example, range from 5,000 to 110,000 kW.

The engine is a diesel (self-igniting) engine of the twostroke uniflow type with scavenge ports 22 in the form a ring of piston-controlled ports at the lower region of the cylinders 1 and an exhaust valve 4 at the top of the cylinders 1. Thus, the flow in the combustion chamber is always from the bottom to the top and thus the engine is of the so called uniflow type. The scavenging air is passed from the scavenging air receiver 2 to the scavenging air ports 22 of the individual cylinders 1. A reciprocating piston 7 in the cylinder 1 compresses the scavenging air, fuel is injected, combustion follows, and exhaust gas is generated. When an exhaust valve 4 is opened, the exhaust gas flows through an exhaust duct 35 associated with the cylinder 1 concerned into an exhaust gas receiver 3 and onwards through a first exhaust conduit 18 to a turbine 6 of the turbocharger 5, from which the exhaust gas flows away through a second exhaust conduit 7. Through a shaft 8, the turbine 6 drives a compressor 9 supplied via an air inlet 10.

The compressor 9 delivers pressurized charging air to a charging air conduit 11 leading to the charging air receiver 2. The scavenging air in the conduit 11 passes through an intercooler 12 for cooling the charging air. The cooled charging air passes via an auxiliary blower 16 driven by an electric motor 17 that pressurizes the charging air flow in low or partial load conditions to the charging air receiver 2. At higher loads the turbocharger compressor 9 delivers sufficient compressed scavenging air and then the auxiliary blower 16 is bypassed via a nonreturn valve 15.

The cylinders are formed in a cylinder liner 52. The cylinder liners 52 are carried by a cylinder frame that is supported by the engine frame 45.

As shown in the first embodiment of Fig. 4, the exhaust valve 4 comprises a valve spindle 23 with a valve disk 25 at one end. The valve spindle 23 is slidably and sealingly received in a bore in a valve housing. At its lower end the valve housing defines a circumferential valve seat 26 on which the valve disc 25 rests when the exhaust valve 4 is in its closed position.

An air spring 67 that includes a plunger 61 that is configured to resiliently urge the exhaust valve 4 to its closed position. The plunger 61 is secured to the valve stem 23 and the plunger 61 is slidably and sealingly received in a bore in the housing. A spring chamber 66 is located below the plunger 61 and when pressurized urges the plunger 61 upwards. The spring chamber 66 is connected to a source of pneumatic pressure 63 via a nonreturn valve, to ensure correct pressurization of the spring chamber 66.

Alternatively, the air spring can be replaced by a liquidbased return-biased system, in which the chamber 66 is filled with a pressurized liquid that is allowed to escape from the chamber 69 but kept at a given, preferably constant, pressure by a connection to a source of pressure.

The top of the valve spindle 23 is connected to plunger 61 that is slidably and sealingly received in a bore in the valve housing. A pressure chamber 60 is formed in the bore above the plunger 61 and chamber 60 is in fluid communication with a port that connected to a second hydraulic conduit 35.

The pressure chamber 60 and the plunger 61 are received in a housing and is a part of a linear exhaust valve actuator 70. When the pressure chamber 60 is pressurized the plunger 61 urges the exhaust valve 4 towards its open position, i.e. in a downward direction (downward as in the orientation of Fig. 4). Then, the exhaust valve 4 is opened hydraulically against the force of an air spring 67 and the force of the combustion pressure in the combustion chamber acting on the valve disk 25. The air spring 67 comprises the spring chamber 66 that is connected to the source of high-pressure air 63 via a nonreturn valve.

The valve actuation system is provided with a variable displacement pump 40 with a first shaft 43 that is of the type that can deliver two flow directions without reversing the direction of rotation of the first shaft 43. The variable displacement pump 40 has a first port connected to a hydraulic accumulator 28 via a first hydraulic conduit 34 and a second port connected to the pressure chamber 60 of the linear actuator of the exhaust valve 4 via a second hydraulic conduit 35. The first hydraulic conduit 34 is connected to a first source of first high pressure via an orifice 36, merely to compensate leak losses in the variable displacement pump 40 and in the linear hydraulic exhaust valve actuator 70, and to ensure that the accumulator 28 is kept pressurized at the first high pressure, and thus stores a significant amount of hydraulic energy. However, only a small flow of hydraulic liquid is possible though the orifice 36, in order to compensate for the leak losses over a longer period of time. Thus, the hydraulic liquid flowing through the orifice 36 is insufficient to influence dynamic changes in pressure in the first hydraulic conduit 34 that occurs during the opening stroke and the closing stroke of the exhaust valve 4, i.e. the hydraulic accumulator 28 is connected to the first port to form a first closed hydraulic system.

The variable displacement pump 40 is in an embodiment a radial piston pump. In an embodiment the radial piston pump is of the type that has radial pistons in a cylinder block that run against a stroke ring, with the position of the stroke ring relative to the cylinder block being adjustable in order to adjust the displacement of the variable displacement pump. The eccentric position of the stroke ring is controlled by two diametrically opposed control pistons and a compensator (when the position of the stroke ring is centric the displacement is zero).

The displacement of the variable displacement pump 40 is controlled with a first control valve 41, which is in the present embodiment a solenoid proportional control valve. The first control valve 41 is operably connected to the variable displacement pump 40 for hydraulically adjusting the displacement of the variable displacement pump 40, e.g. by controlling the hydraulic pressure delivered by the first control valve 41 to the diametrically opposed control pistons. The second first valve 41 is electronically controlled by an electronic control unit 50.

The first shaft 43 of the variable displacement pump 40 is coupled to a second shaft 33 of a motor-generator 30, in the present embodiment via a coupling 53 that causes the first shaft 43 and the second shaft 33 to rotate in unison. However, in an embodiment the first shaft 43 and the second shaft 33 are coupled by gear with ratio of 1 to 1 or different from 1 to 1.

A pressure relief valve 39 connects the second hydraulic conduit 35 to tank T in order to protect the system from excessive pressures. Thus, the linear hydraulic actuator is 70 connected to the second port to form a second closed hydraulic system.

The motor-generator is in an embodiment an electric motorgenerator and is in the shown embodiment a variable displacement hydraulic motor 30 that can be supplied with a flow of hydraulic liquid in two flow directions without changing the direction of rotation of the second shaft 33. The variable displacement hydraulic motor 30 has a third port and a fourth port. The third port is connected to the first source 29 of the first high pressure and the fourth port is connected to a second source 19 of a second high pressure. The second high pressure is lower than the first high pressure, preferably significantly lower, but well above zero or normal tech pressure.

The variable displacement motor 30 is in an embodiment a radial piston motor. In an embodiment the radial piston motor is of the type that has radial pistons in a cylinder block that run against a stroke ring, with the position of the stroke ring relative to the cylinder block being adjustable in order to adjust the displacement of the variable displacement motor. The eccentric position of the stroke ring is controlled by two diametrically opposed control pistons and a compensator (when the position of the stroke ring is not eccentric the displacement is zero).

The displacement of the variable displacement motor 30 is controlled with a second control valve 31, which is in the present embodiment a solenoid proportional control valve. The second control valve 31 is operably connected to the variable displacement motor 30 for hydraulically adjusting the displacement of the variable displacement motor 30 e.g. by controlling the hydraulic pressure delivered by the first control valve 41 to the diametrically opposed control pistons. The second control valve 31 is electronically controlled by the electronic control unit 50.

The rotary speed of the motor 30, i.e. the rotary speed of the second shaft 33 is captured by a second sensor 32.

The signal of the second sensor 32 is communicated to the electronic control unit 50, e.g. by a signal cable.

The electronic control unit 50 issues a signal to the second control valve 31 via a signal cable to thereby control the rotary speed of the first shaft/hydraulic motor 30. The first control valve controls the displacement and the direction of flow of the variable displacement pump 40.

The exhaust valve 4 is provided with a first sensor 62 for measuring the position and speed of the exhaust valve 4.

The first sensor 62 generates a signal representative of the position and/or speed of the exhaust valve 4. The sensor 62 is connected to the electronic control unit 50, e.g. via signal cable so that the electronic control unit 50 is thus informed of the position and speed of the exhaust valve 4.

The electronic control unit 50 issues a signal to the first control valve second via a signal cable to thereby control the displacement of the variable displacement pump 40, and thereby the speed of the exhaust valve 4.

The electronic control unit 50 monitors the speed of the exhaust valve 4. The electronic control unit 50 is in an embodiment configured to determine the appropriate speed/profile for the exhaust valve 4 to follow. This profile is in an embodiment continuously adapted according to engine operation conditions.

The electronic control unit 50 is informed about the crank angle of the engine and controls the actuation of the valve 4 so that the profile of the exhaust valve actuation is synchronized with the engine cycle.

The electronic control unit 50 can be provided with a lookup table based on calibrated data from engine running tests or with an equation that uses calibrated data from engine running tests in order to determine the appropriate desired profile for the exhaust valve 4. The desired profile for the exhaust valve 4 is chosen such that the system is optimized for emissions, power, and/or the fuel efficiency, with these factors being weighed in accordance with circumstances.

As described above, sufficient pressure of the hydraulic liquid in the pressure chamber 60 causes the exhaust valve 4 to open against the pressure in the combustion chamber and against the force of the air spring 67. When the electronic control unit 50 determines that the exhaust valve 4 needs to be opened, the electronic control unit 50 issues a command to the first control valve 41 to adjust the displacement and flow direction of the variable displacement pump 40 accordingly. Thereupon, hydraulic liquid is pumped from the hydraulic actuator 28 to the pressure chamber 60 of the exhaust valve actuator 70, thereby urging the exhaust valve to open against the pressure of the air spring 67 and the pressure in the combustion chamber. The pumping action is substantially assisted by the high pressure of the hydraulic liquid stored in the hydraulic accumulator 28 and thus, the variable displacement pump 40 needs to supply only little if any power to support this flow. In an embodiment the pressure in the hydraulic actuator 28 is high enough to force the variable displacement variable displacement pump 40 to be operated as a hydraulic motor and simultaneously for the variable displacement motor 30 to be operated as a pump. Hereto, the electronic control unit 50 controls the displacement and flow direction of the variable displacement hydraulic motor 30 accordingly, in order to maintain the desired rotational speed of the second shaft 33. When the exhaust valve 4 has reached the end of the opening stroke the electronic control unit 50 instructs the first control valve 41 to adjust the displacement of the variable displacement pump 40 to 0 and thereby stop the movement of the exhaust valve 4.

When the electronic control unit 50 determines that the exhaust valve needs to be closed, the process is reversed and the electronic control unit 50 instructs the first control valve 41 to adjust the displacement flow direction of the variable displacement pump 40 accordingly to thereby pump hydraulic liquid from the second conduit 35 into the first hydraulic conduit 34 and into the hydraulic accumulator 28. This flow is assisted by the exhaust gas acting on the exhaust valve and by the air spring 67 but is against the pressure in the hydraulic accumulator 28. Thus, depending on the pressure in the accumulator 28 and the assistance from the pressure in the pressure chamber 60, the variable displacement pump 40 requires to be driven by the variable displacement motor 30. Hereto, the electronic control unit 50 adjusts the displacement and flow direction of variable displacement motor 30 in order to maintain a constant speed of the second shaft 33. The accurate control of the electronic control unit 50 over the displacement of the variable displacement pump 40 allows for a soft-close of the exhaust valve disk 25 on its seat 26, and thus the exhaust valve actuator can be constructed without a damper for the closing stroke.

Fig. 5 is a graph illustrating the opening movement of an exhaust valve 4 against time. The shown profile is merely an example and the shape of the profile and the size of the opening stroke can be freely controlled by the electronic control unit 50. The electronic control unit 50 determines the profile for opening the exhaust valve 4 and controls the displacement of the variable displacement pump 40 accordingly. The electronic control unit 50 is informed of the position of the exhaust valve 4 by a signal from the position sensor 62. The result being that the electronic control unit 50 can determine the position of the exhaust valve in accordance with any desired profile.

Fig. 6 is a graph illustrating torque and rotational speed of the first shaft of the motor 30. The graph illustrates that the motor torque becomes negative, i.e. the motor 30 acts as a break/pump during initial phase of the opening stroke of the exhaust valve 4. Simultaneously, the speed of the second shaft 33 of the hydraulic motor 30 slightly increases and then returns to its set speed. The negative torque is created because the pressure in the hydraulic accumulator 28 is higher than the pressure in the linear hydraulic actuator 70 of the exhaust valve and thus, the flow from the hydraulic actuator 28 to the linear hydraulic actuator 70 drives the variable displacement pump 40, i.e. the variable displacement pump 40 acts in this phase like a motor. The situation is reversed when the exhaust 4 valve returns to its seat 26. During the initial phase of the return stroke the electronic control unit changes the displacement of the variable displacement pump 40 in order to pump hydraulic liquid from the linear hydraulic actuator 70 to the hydraulic accumulator 28. This pumping action requires breaking torque from the variable displacement motor 30 to the arrow displacement pump 40, which shows in the graph as a positive torque for the variable displacement motor 30 and a slight dip in the rotational speed of the second shaft 33 of the motor 30. The electronic control unit 50 is configured to maintain the rotational speed of the second shaft 33 at a constant desired level and adjusts the displacement of the variable displacement motor 30 accordingly.

The energy consumption for the exhaust valve actuation is low when the exhaust valve is not moving, since the variable displacement pump 40 will have zero displacement. During the opening stroke the hydraulic energy in the hydraulic actuator 28 drives the linear exhaust valve actuator 70 and actually drives the variable displacement pump 40. The energy going into the variable displacement pump 40 is partially recovered during this phase by the variable displacement motor 30 acting as a pump and delivering hydraulic energy back into the hydraulic system of the engine. During the closing stroke the forces acting on the linear exhaust valve actuator 70, from the gas spring and from the gases in the combustion chamber acting on the exhaust valve disk 25 and shaft 23 transmitted to the plunger 61 and pressurize the hydraulic liquid in the pressure chamber 60. This pressure assists the variable displacement pump 40 in recharging the hydraulic accumulator 28 for the next stroke. Thus, the energy in the exhaust gas and in the air spring is recovered during the return stroke by transmitting and storing this energy in the hydraulic accumulator 28.

Fig. 4A shows another embodiment of the exhaust valve actuation system, that is essentially identical to the first embodiment shown in Fig. 4, except for the hydraulic pump 40 being a fixed displacement pump instead of a variable displacement pump. The fixed displacement pump 40 is configured to operate in two directions of rotation in order to provide flow in two directions.

Accordingly, the motor generator, in this the embodiment in the form of a variable displacement hydraulic motor 30 will need to operate its drive shaft 33 (second shaft) in different directions in order to control the flow pump 40 in opposite directions. Thus, in this embodiment positive displacement pump 40 and the variable displacement motor 30 are operated in one direction of rotation of their respective shafts 33, 43 for discharging the hydraulic accumulator 28 and pressurizing the linear hydraulic actuator 70 for opening the exhaust valve 4, and the positive displacement pump 40 and the variable displacement motor 30 are operated in the opposite direction of rotation of the respective shafts 33, 43 in order to replenish the hydraulic accumulator 28 evacuate the linear hydraulic actuator 70 (specifically evacuate the pressure chamber 60) for closing the exhaust valve 4.

The control of the exhaust valve actuation system by the electronic control unit 50 is through the first control valve 31 to thereby control the operation of the variable displacement motor 30. Since the fixed displacement pump 40 itself does not have any hydraulic control inputs the hydraulic and control system according to the embodiment of Fig. 4A is less complicated compared to the embodiment of Fig. 4.

In an embodiment the variable displacement motor 30 and the variable displacement pump 40 or constructed as a single unit with a common shaft. This single unit is in an embodiment directly attached to the exhaust valve housing.

The invention has been described in conjunction with various embodiments herein. However, other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word comprising does not exclude other elements or steps, and the indefinite article a or an does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. A computer program may be stored/distributed on a suitable medium, such as an optical storage medium or a solid-state medium supplied together with or as part of other hardware, but may also be distributed in other forms, such as via the Internet or other wired or wireless telecommunication systems. The electronic control unit has been represented as a single unit but can be realized by a combination of multiple connected electronic control units.

The reference signs used in the claims shall not be construed as limiting the scope.

Claims

Exhaust valve actuation system for a large two-stroke internal combustion engine, in particular an electronically controlled hydraulic exhaust valve actuation system, the exhaust valve actuation system comprising:

a displacement pump (40) having a first shaft (43), a first port and a second port, characterized in that the displacement pump (40) is capable of providing two flow directions, a hydraulic accumulator (28) fluidly connected to the first port, the second port being configured for fluid connection to a linear hydraulic actuator (70) acting on a spindle (23) of the exhaust valve (4), and a motor generator with a second shaft (33), wherein the first shaft (43) is operatively coupled to the second shaft (33).

The exhaust valve actuation system of claim 1, wherein the hydraulic accumulator is connected to the first port to form a first closed hydraulic system.

Exhaust valve actuation system according to claim 1 or 2, wherein the linear hydraulic actuator (70) is connected to the second port to form a second closed hydraulic system.

Exhaust valve actuation system according to any one of claims 1 to 3, wherein the displacement pump is a variable displacement pump (40) capable of providing two flow directions for one direction of rotation of the first shaft.

Exhaust valve actuation system according to any one of claims 1 to 4, wherein the motor generator is designed to operate in two directions of rotation for the second shaft (33).

Exhaust valve actuation system according to claim 4 or 5, wherein the engine generator is a variable cylinder volume engine (30) having a third port and a fourth port and capable of two directions of rotation for the second shaft (33) for one flow direction.

An exhaust valve actuation system according to any one of claims 1 to 5, wherein the motor generator is an electric motor generator.

Exhaust valve actuation system according to one of claims 1 to 5, wherein the engine generator is a variable cylinder volume engine (30) having a third port and a fourth port and capable of two flow directions for one direction of rotation of the second shaft (33).

The exhaust valve actuation system of claim 8, wherein the third port is connected to a first source of a first high pressure hydraulic fluid, and wherein the fourth port

2 4 is connected to a second high pressure source, the first high pressure being higher than the second high pressure.

The exhaust valve actuation system of claim 8 or 9, further comprising an electronic control unit (50) configured to control the rotational speed and cylinder volume of the variable cylinder engine (30) and configured to control the cylinder volume of the variable cylinder volume pump (40). .

An exhaust valve actuation system according to any one of claims 1 to 10, comprising a first sensor (62) indicating the position of the spindle (23).

Exhaust valve actuation system according to any one of claims 1 to 11, comprising a second sensor (32) indicating the rotational speed of the engine generator.

Exhaust valve actuation system according to any one of claims 1 to 12, wherein the variable cylinder volume pump is a radial piston pump and / or the variable cylinder volume motor (30) is a radial piston engine.

Exhaust valve actuation system according to any one of claims 4 to 13, comprising a first control valve (41) fluidly connected to one or more control ports of the variable cylinder volume pump (40), for controlling the cylinder volume and the flow direction of the variable flow pump (40I). cylinder volume, which first control valve (41) is electronically controlled by the electronic control unit (50).

Exhaust valve actuation system according to any one of claims 4 to 14, comprising a second control valve (31) fluidly connected to one or more control ports for the variable cylinder hydraulic motor (30), for controlling the cylinder volume and the flow direction of the hydraulic motor (3) with variable cylinder volume, the second control valve (31) being electronically controlled by the electronic control unit (50).

Exhaust valve actuation system according to any one

any of the requirements 4 to 15, where the electronic control unit (50) is configured to to keep the rotational speed for the other shaft (33) at a given

rotational speed when controlling the cylinder volume of the hydraulic motor (30) with variable cylinder volume.

Exhaust valve actuation system according to any one of claims 1 to 16, wherein the electronic control unit (50) is configured to control flow to and from the second port relative to a signal indicating the desired position of the exhaust valve (4).

Large turbocharged self-igniting two-stroke internal combustion engine, which engine includes:

a plurality of cylinders (1) having flush ports (22) at their lower region and an exhaust valve (4) at their top, said exhaust valve (4) having a valve stem (23) and a valve disc (25), and wherein the exhaust valve (4) can be moved in opposite directions between a closed position, in which the valve disc rests (25) on a valve seat (26), and an open position, single-acting fluid-driven means operatively connected to the valve stem (23) to force the exhaust valve (4) towards its closed position, a linear hydraulic actuator (70) operatively connected to the valve stem (23), which hydraulic actuator (70) is designed to force the exhaust valve (4) toward its open position when the linear hydraulic actuator is pressurized, and an exhaust valve actuation system according to any preferably one of claims 1 to 17.

The engine of claim 18, wherein the electronic control unit (50) is configured to control the position and / or speed of the exhaust valve as in a closed loop by comparing the signal from the first sensor (62) with a desired position of the exhaust valve (4).

An engine according to claim 18 or 19, wherein a first channel connecting the first port to the accumulator (28) is connected to the first high pressure source via an opening (36).