JP4657386B2 - Large two-cycle diesel engine with electronically controlled exhaust valve actuation system - Google Patents

Description

  The present invention relates to a crosshead large two-cycle diesel engine equipped with an electronically controlled exhaust valve actuation system, and more specifically, a crosshead large two-cycle diesel engine equipped with an energy efficient electronically controlled exhaust valve actuation system. About.

  Crosshead large two-cycle engines are commonly used in large ship propulsion systems or as power plant prime movers. This type of engine has recently evolved from a camshaft controlled engine to an electronically controlled engine. Electronic control makes it possible to control the timing and shape of combustion injection and the timing of the exhaust valve more flexibly. As a result, the combustion process can be suitably controlled at all driving speeds, resulting in effective combustion, reduction of exhaust load, improvement of partial load fuel consumption, and reduction of minimum driving speed.

  Japanese Unexamined Patent Application Publication No. 2004-084670 discloses an electronically controlled large two-cycle diesel engine. In this engine, the exhaust valve is operated by a hydraulic actuator powered by high pressure hydraulic fluid. By the actuator, the exhaust valve is biased in the opening direction against the pressure of the combustion chamber and the gas pressure of the air spring. Most of the energy supplied by the hydraulic actuator during the opening stroke of the exhaust valve is stored in the gas spring as potential energy. Unlike the camshaft driven engine, the energy stored in the gas spring is not reused in the closing stroke, but instead is discarded (dissipated) because there is no means to reuse the stored energy. The stored energy is converted into heat along with the return oil to the tank of the hydraulic system. In a large two-cycle diesel engine, the amount of hydraulic energy used to open the exhaust valve is very large, and a significant portion of the fuel savings resulting from improved combustion control in an electronically controlled engine is lost in the operation of the exhaust valve .

  DK148664B discloses a large two-cycle diesel engine with an electrohydraulic valve actuation system that applies two different hydraulic pressures to open an exhaust valve with a hydraulic actuator. A high pressure level is used during the initial stage of the opening stroke and a low pressure is used during the remainder of the exhaust valve opening stroke.

  W02006 / 108629 discloses an exhaust valve assembly for a large two-cycle diesel engine including an exhaust valve capable of double-acting operation between a closed position and an open position. A double-acting spring assembly is combined with the exhaust valve so that the exhaust valve can be controlled, and a mass-spring system with the mass of the exhaust valve and any other part that moves in unison with the exhaust valve Form. The double-acting spring assembly stores energy for subsequent reverse movement as the exhaust valve translates back and forth between the closed and open positions. The hydraulic means holds the exhaust valve in the closed position or the open position according to a command from the controller. This system requires that the actual position of the exhaust valve can be known and that the electronic controller emits a signal each time the exhaust valve needs to stop at its moving end. Also, the hydraulic system is relatively complex, and the configuration of the air spring and hydraulic actuator at the top of the valve stem is also significantly different from the corresponding configuration in conventional camshaft engines. This prior art configuration is relatively expensive and complex.

JP 2004-084670 A DK148664B W02006 / 108629

  From such a background, an object of the present invention is to provide a large two-cycle diesel engine that is flexible, energy efficient, has a simple structure, and has a reliable exhaust valve operation system.

The above object can be achieved according to claim 1 by providing the following large multi-cylinder two-cycle diesel engine.
This engine is a crosshead type large multi-cylinder two-cycle diesel engine equipped with an exhaust valve operating system,
An exhaust valve comprising a valve stem and a valve body, wherein the valve body is double-acting between a closed position where the valve body is seated on a valve seat and an open position;
An air spring comprising a spring piston housed in an air spring cylinder, connected to the valve rod so as to control the valve rod, and an air spring for urging the exhaust valve toward the closed position;
A hydraulic actuator having a pressure chamber, connected to the valve rod so as to control the valve rod of the exhaust valve, and hydraulic pressure for urging the exhaust valve in the opening direction when the pressure chamber is pressurized An actuator,
An electronically controlled hydraulic system;
For each cylinder. The electronically controlled hydraulic system includes the pressure chamber of the hydraulic actuator,
・ At the beginning of the opening process of the exhaust valve,
The period after the initial period until the exhaust valve reaches its open position, the intermediate pressure hydraulic accumulator
A period from the start of the closing stroke of the exhaust valve to immediately before the final stage of the closing stroke of the exhaust valve is in the intermediate pressure hydraulic accumulator,
In the final stage of the closing process of the exhaust valve,
Selectively connect.

  By connecting the pressure chamber of the hydraulic actuator to an intermediate pressure hydraulic accumulator from immediately after the start of the opening stroke to the end, and connecting the pressure chamber to the same intermediate pressure hydraulic accumulator from the start to the end of the return stroke. Thus, most of the energy used to open the exhaust valve can be recovered and used for the next opening stroke. Thus, this exhaust valve actuation system provides the flexibility of an electronically controlled exhaust valve actuation system without the high energy consumption normally associated with an electronically controlled exhaust valve actuation system.

  The hydraulic system includes a first electronically controlled valve configured to connect the pressure chamber of the hydraulic actuator to the high pressure hydraulic fluid source for a short period of time at the start of an exhaust valve opening stroke. Also good.

  The hydraulic system connects the pressure chamber of the hydraulic actuator to the intermediate pressure hydraulic accumulator from the period when the first electronically controlled valve is open until the exhaust valve reaches its open position. A second electronically controlled valve configured as described above may be provided.

  The hydraulic system connects the pressure chamber of the hydraulic actuator to the intermediate pressure hydraulic accumulator from the start of the closing stroke of the exhaust valve to the start of the final short period at the end of the closing stroke of the exhaust valve. A third electronically controlled valve configured to do so may be provided.

  The hydraulic system may comprise a fourth electronically controlled valve configured to connect the pressure chamber of the hydraulic actuator to a tank during the final short period of the exhaust valve closing stroke.

  Since the check valve is controlled by hydraulic flow, it may be used to ensure a smooth transition between each phase of the cycle.

  The first electronically controlled valve and the fourth electronically controlled valve may be constituted by a single two-way valve.

  The second electronically controlled valve and the third electronically controlled valve may be constituted by a single two-way valve.

  The large two-cycle diesel engine may be provided with a first check valve that allows only a flow in a direction toward the intermediate pressure hydraulic accumulator in association with the second electronically controlled valve. A second check valve that permits only a flow away from the intermediate pressure hydraulic accumulator may be provided in association with the electronically controlled valve.

  By providing the first check valve and the second check valve, the first electronically controlled valve, the second electronically controlled valve, the third electronically controlled valve, and the second Substantial overlap is possible for opening of the four electronically controlled valves.

  The large two-cycle diesel engine may further include an electronic control unit configured to control a hydraulic connection between the pressure chamber, the high pressure hydraulic fluid source, the intermediate pressure hydraulic accumulator, and a tank.

  Further objects, features, advantages, and characteristics of the large two-cycle diesel engine according to the present invention will become apparent from the detailed description.

The invention will now be described in more detail with reference to exemplary embodiments depicted in the drawings.
1 is a cross-sectional view of an engine according to the present invention. It is a longitudinal cross-sectional view of one cylinder part of the engine shown in FIG. 1 is a schematic diagram of a first embodiment of an exhaust valve actuation system according to the present invention. It is a sequence diagram which shows the opening / closing timing of the electronically controlled valve of the exhaust valve operating system of FIG. The sequence diagram of FIG. 4 further shows the opening time that can be taken in an electronically controlled valve that utilizes the effect of a check valve It is a schematic diagram of 2nd Embodiment of the exhaust-valve operating system according to this invention.

Detailed Description of the Preferred Embodiment

  1 and 2 show an engine 1 according to a preferred embodiment of the present invention in a cross-sectional view and a longitudinal cross-sectional view (for one cylinder), respectively. The engine 1 is a crosshead uniflow type low-speed two-cycle diesel engine and can be a marine vessel propulsion system or a power plant prime mover. Such engines typically have 4 to a maximum of 14 cylinders in a row. The engine 1 is assembled from a base plate 2 having a main bearing of the crankshaft 3.

  The crankshaft 3 is a semi-assembled type. The semi-assembled mold is made from a cast steel throw or forged steel throw that is connected to the main journal shaft by a shrink fit connection.

  Although the base plate 2 can be manufactured from a single component, it can also be manufactured by dividing it into portions of an appropriate size according to the manufacturing facility. The base plate consists of a side wall and a cross grinder welded thereto. The cross beam has a bearing support. In the art, a cross beam is also referred to as a “transverse girder”. The oil receiver 58 is welded to the bottom of the base plate 2 and collects the return oil from the forced lubricating oil and cooling oil system.

  The connecting rod 8 connects the crankshaft 3 to the crosshead 22. The cross head 22 is guided between the vertical guide surfaces 23.

  A welded design A-shaped frame box 4 is mounted on the base plate 2. The frame box 4 is a welded design. The frame box 4 is provided with a relief valve for each cylinder on the exhaust side, while a large hinged door is provided for each cylinder on the opposite side. The crosshead guide surface 23 is integral with the frame box 4.

  The cylinder frame 5 is attached to the upper part of the frame box 4. The retaining bolt 27 connects the base plate 2, the frame box 4, and the cylinder frame 5, and supports the structure integrally. The reserve bolt 27 is tightened with a hydraulic jack.

  The cylinder frame 5 is cast as one or more parts or is weld designed.

  The cylinder frame 5 is provided with an access cover for cleaning the scavenging space and for checking the scavenging port and the piston ring. The cylinder frame forms a scavenging space together with the cylinder liner 6. The scavenging receiver 9 is bolted to the cylinder frame 5 on its open side. There is a piston rod stuffing box at the bottom of the cylinder frame, which prevents sealing products for scavenging and the exhaust products from entering the space of the frame box 4 and the base plate 2. An oil scraper ring is provided. These protect all bearings present in this space.

  The piston 13 includes a piston crown and a piston skirt. The piston crown is made of heat-resistant steel, has four ring grooves, and hard chrome is plated on the upper and lower surfaces of the groove portions.

  The piston rod 14 is connected to the crosshead 22 with four screws. The piston rod 14 has two coaxial holes (not visible in the drawing), and forms an inlet and an outlet for the cooling oil of the piston 13 together with the cooling oil pipe.

  The cylinder liner 6 is supported by the cylinder frame 5. The cylinder liner 6 is made of alloy cast iron and is suspended from the cylinder frame 5 by a flange at a low position. The top of the liner is surrounded by a cast iron cooling jacket. The cylinder liner 6 has a drill hole (not shown) for cylinder lubrication.

  The cylinder is a uniflow type and has a scavenging port 7 positioned in the air box, and this exhaust port is supplied with a scavenging receiver 9 (FIG. 1) to which scavenging air pressurized by a turbocharger 10 (FIG. 1) is supplied. ).

  The engine is equipped with one or more turbochargers 10. The turbocharger is disposed at the rear of the engine in the case of an engine having 4 to 9 cylinders and on the exhaust side in the case of an engine having 10 or more cylinders.

  Intake into the turbocharger 10 is performed directly from the engine room via an intake silencer (not shown) of the turbocharger. Air is guided from the turbocharger 10 to the scavenging port 7 of the cylinder liner 6 through an air supply pipe (not shown), an air cooler (not shown), and a scavenging receiver 9.

  The engine is provided with an electric scavenging blower (not shown). The suction side of the blower is connected to the scavenging space behind the air cooler. A check valve (not shown) is provided between the air cooler and the scavenger receiver, and this check valve automatically closes when the auxiliary blower supplies air. The auxiliary blower assists the turbocharger compressor in low and medium load conditions.

  The fuel valve 40 is concentrically mounted on the cylinder cover 12. At the end of the compression stroke, the injection valve 40 injects fine mist-like fuel into the combustion chamber 15 through the injection nozzle at a high pressure. The exhaust valve 11 is mounted at the center of the cylinder cover 12 at the top of the cylinder. At the end of the expansion stroke, before the piston 13 of the engine descends beyond the scavenging port 7, the exhaust valve 11 is opened, so that the combustion gas in the combustion chamber 15 on the piston 13 is released to the exhaust receiver 17. The exhaust gas flows out through the exhaust passage 16 and the pressure in the combustion chamber 15 is released. The exhaust valve 11 closes again during the upward movement of the piston 13. The exhaust valve 11 is hydraulically operated.

  FIG. 3 shows a first embodiment of an exhaust valve actuation system according to the present invention. Although only one cylinder is depicted, this exhaust valve actuation system is for all embodiments. In a multi-cylinder engine, the same thing is provided for each cylinder.

  The exhaust valve actuation system includes an exhaust valve 11 with a valve stem 31 and a valve disk 32. In the closed position shown in FIG. 3, the valve body 32 is seated on a valve seat provided at the upper part of the cylinder 6. The open position of the exhaust valve 11 is shown in FIG.

  The air spring 34 biases the exhaust valve 11 toward the closed position. The air spring 34 is provided with an air piston 35 coupled to the valve rod 31, so that the air spring 34 can cooperate with the exhaust valve 11.

  The position sensor 33 measures the position of the exhaust valve 11 by either an analog type or a digital type. A signal from the position sensor 33 is communicated to an engine control unit (for example, a computer) 42 via a signal cable. The engine control unit 42 also receives a position signal related to the crankshaft from a crankshaft sensor (not shown).

  The exhaust valve actuator 37 is disposed above the valve rod 31. The exhaust valve actuator 37 has a cylindrical valve housing, and a hydraulic piston 38 is accommodated in the cylindrical housing. A hydraulic piston 38 is connected to the valve stem 31 so that the hydraulic actuator 37 can control the exhaust valve 11. A pressure chamber 39 is defined on the hydraulic piston 38.

  A pressure conduit 40 connects the pressure chamber 39 of the hydraulic actuator 38 to the hydraulic system of the exhaust valve actuation system.

  The hydraulic system of the exhaust valve actuation system includes a high pressure hydraulic fluid source such as a pump station (not shown). The pump station may be dedicated to the exhaust valve actuation system or may be used for other purposes (system pressure) such as providing pressure to the combustion injection system or cylinder lubrication system. Typically, the system pressure is a few hundred bars. In implementation, the hydraulic system and hydraulic actuator 37 are often isolated by equipment such as a pressure intensifier to avoid contamination between systems.

  A first electronically controlled valve 44, such as a hydraulic on / off valve, allows the pressure conduit 40 to be selectively connected to a high pressure hydraulic fluid source.

  The pressure conduit 40 is also connected to the branch conduit 41.

  The branch conduit 41 is connected to the intermediate hydraulic accumulator 43 via a first check valve 45 and a second electronically controlled valve 46 (for example, a hydraulic on / off valve).

  The intermediate pressure hydraulic accumulator 43 is preferably of a type in which an elastic film that divides the accumulator is provided in a portion filled with pressurized hydraulic fluid and a portion filled with pressurized gas.

  The branch conduit 41 is connected to the hydraulic accumulator 43 via a second check valve 47 and a third electronically controlled valve 48 (for example, a hydraulic on / off valve).

  Furthermore, the branch conduit 41 is connected to the tank via a fourth electronically controlled valve 50 (eg, a hydraulic on / off valve).

  The flow direction of the first check valve 45 and the second check valve 47 is opposite to each other.

  The first electronic control valve 44, the second electronic control valve 46, the third electronic control valve 48, and the fourth electronic control valve 50 are connected to the engine control unit 42 via a signal cable. These valves are opened and closed according to commands from the engine control unit 42.

  The electronic control unit 42 determines the end of the period “1” based on the time, but also uses the signal from the sensor 33 to determine the valve lift and to obtain the requested valve lift: Correct the length of “1” in the cycle.

  Here, the operation of the electrohydraulic valve actuation system will be described with reference to the sequence diagram shown in FIG.

  In the sequence diagram, the operation of the exhaust valve 11 is divided into six sequential periods. In the first period “0”, since the exhaust valve 11 is closed, the first to fourth electronically controlled valves 44, 46, 48, 50 are also closed.

  The electronic control unit 42 determines the end of the period “0” and the start of the period “1” of the exhaust valve 11 based on the crankshaft signal. This determination may also be based on other operating conditions of the engine. At the start of this short period at the start of the opening stroke of the exhaust valve 11, the first electronically controlled valve 44 is opened and the high pressure hydraulic fluid can flow into the pressure chamber 39. The high pressure hydraulic fluid in the pressure chamber 39 allows the exhaust valve 11 to be opened with respect to the pressure of the combustion gas in the combustion chamber 15. Since the high pressure of the gas in the combustion chamber presses the exhaust valve 11 against its seat, the hydraulic actuator 37 needs to provide a strong opening force at the very start of the opening stroke of the exhaust valve 11.

  When the exhaust valve 11 is slightly opened, the combustion gas does not urge the exhaust valve 11 to the seat side, and the hydraulic actuator 37 does not need to provide a strong force. Thus, at the end of the first short period “1” at the start of the opening stroke of the exhaust valve 11, the electronic control unit 42 commands the first electronically controlled valve 44 to be closed and the second electronic Command controlled valve 46 to open. The electronic control unit 42 uses the signal from the position sensor 33 to determine the end of the period “1” and corrects the timing based on the result of the final cycle.

  The remaining period of the opening stroke of the exhaust valve 11 is represented as a period “2” in the sequence diagram of FIG. 4.

  The hydraulic accumulator 43 holds an intermediate pressure, for example 10-30 bar hydraulic fluid. Therefore, when the second electronically controlled valve 46 is opened, intermediate hydraulic fluid flows into the pressure chamber 39 and can be advanced until the exhaust valve 11 completes its opening stroke. By using an intermediate pressure for the majority of the opening stroke, the amount of energy used to open the exhaust valve 11 is relatively low and the opening is controlled more smoothly and smoothed by the weaker force. At the end of the opening stroke, the sum of inertia and acting force of the valve and actuator is reduced to zero, and the aerodynamic force in the spring chamber of the air spring 34 acting on the air piston 35 pushes the exhaust valve 11 back. start. However, the return movement is blocked by the check valve 45 and the exhaust valve 11 stops in its open position. Part of the hydraulic energy used to open the exhaust valve 11 is stored here in the air spring 34.

  At this point, the period “2” ends and the period “3” starts. The electronic control unit 42 commands the second electronically controlled valve 46 to close, and the exhaust valve 11 remains open for the period “3”. The electronic control unit 42 can determine the end of the period “2” based on the signal from the position sensor 33.

  Based on the signal from the crankshaft sensor (based on other operating parameters in some embodiments), the electronic control unit 42 determines when the period “3” ends and when the period “4” starts. The period “4” includes the start of the closing stroke of the exhaust valve 11 and most of it.

  At the start of period “4”, electronic control unit 42 commands to open third electronically controlled valve 48. As a result, the hydraulic chamber 39 is connected again to the hydraulic accumulator 43. The air spring 34 urges the exhaust valve 11 in the closing direction, and the hydraulic accumulator 43 is filled with the energy previously stored in the gas spring 34 by the hydraulic fluid flowing out from the hydraulic chamber 39 and stored. Here, the energy stored in the hydraulic accumulator 43 can be used for the next opening stroke of the exhaust valve 11. At the end of period “4” and at the beginning of period “5”, electronic control unit 42 commands to close third electronically controlled valve 48 and opens fourth electronically controlled valve 50. To order. The period “5” includes the final short period of the closing stroke of the exhaust valve 11. During this period, the pressure chamber 39 is connected to the tank, so that the exhaust valve 11 can be pressed against its seat by the remaining pressure of the air spring 34. The start of the period “5” is determined by the electronic control unit 42 based on the signal from the position sensor 33 and based on the pressure in the accumulator 43. In this embodiment, the signal from the pressure sensor connected to the accumulator 43 is supplied to the engine control unit 42. The control unit adapts the start timing of the period “5” based on the result in the previous cycle so as to maintain the predetermined pressure in the accumulator 43. Therefore, when the pressure in the accumulator 43 increases, the start of the period “5” is advanced, and when the pressure in the accumulator 43 decreases, the start of the period “5” is delayed.

  At the end of period “5”, the exhaust valve 11 sits in its seat (completely closed) and the electronic control unit 42 commands the fourth electronically controlled valve 50 to close. The end of the period “5” and the start of the period “0” are determined by the electronic control unit 42 based on the signal from the sensor 33. During the period “0”, the exhaust valve 11 is closed until the next cycle starts.

  This valve actuation system allows a portion of the energy stored in the air spring 34 to be reused during the next cycle. This can significantly reduce the overall energy consumption of the exhaust valve actuation system compared to conventional electrohydraulic valve actuation systems where the energy stored in the air spring 34 is dissipated during the return stroke.

  FIG. 5 is a diagram in which a number of lines are added to the sequence diagram of FIG. 4 to represent additional periods during which the electronically controlled valves 46, 48, and 50 can be opened. These overlaps are made possible by providing a first check valve 45 and a second check valve 47. The overlap facilitates ensuring that each electronically controlled valve 46, 48, 50 is opened when the preceding valve is still closed. For example, the second electronically controlled valve 46 can be opened during period “1”, thereby eliminating the need to open just during the transition from period “1” to period “2”. Accordingly, the line area in the figure indicates that the corresponding valve can be opened or closed.

  FIG. 6 shows another embodiment of an electromechanical valve actuation system in which the first electronically controlled valve 44 and the fourth electronically controlled valve 50 are combined into a single three-way valve. The second electronically controlled valve 46 and the third electronically controlled valve 48 are combined into a single two-way valve (cartridge valve). According to a modification (not shown) of the present embodiment, the first check valve 45, the second electronically controlled valve 46, the second check valve 47, and the third electronically controlled valve 48 are: The connection between the conduit 41 and the hydraulic accumulator 43 is combined into a single three-way valve having a central position at which the connection is broken. Switching between the first valve and the fourth valve can be realized by one signal from the electronic control unit, and switching between the second valve and the third valve is performed from the electronic control unit. Since it can be realized by one signal, the number of control signals required by the present embodiment is reduced.

  According to an embodiment (not shown), one hydraulic accumulator 43 can be shared by several cylinders or all cylinders of the engine.

  The teachings of the present invention have a number of advantages. Depending on the embodiment or implementation, one or more of the following advantages may be provided. Note that this is not an exclusive list and there may be other advantages not described herein. One advantage of the teachings of the present application is to provide an electrohydraulic valve actuation system that uses relatively little energy for a large two-cycle diesel engine. Another advantage of the teachings of this application is that it uses a simple (non-stage) hydraulic actuator to actuate the valve stem and uses a conventional air spring to bias the exhaust valve to the closed position. It is an object to provide an electrohydraulic valve actuation system that can be installed in a large two-cycle diesel engine having a known existing exhaust valve configuration. Yet another advantage of the teachings of the present application is to provide a reliable electrohydraulic valve actuation system. Another advantage of the present invention is to reduce energy loss.

  Although the teachings of this application have been described in detail for purposes of illustration, such details are merely for that purpose and modifications may be made to the teachings by those skilled in the art without departing from the scope of the teachings of this application. I hope you understand.

  It should also be noted that there are many alternative ways of implementing an apparatus based on the teachings of the present invention.

  The term “comprising”, used in the claims, does not exclude other elements or steps. The singular terms used in the claims do not exclude the plural. A single processor or other unit may fulfill the functions of several means recited in the claims.

Claims (10)

A crosshead large multi-cylinder two-cycle diesel engine equipped with an exhaust valve operating system,
An exhaust valve comprising a valve stem and a valve body, wherein the valve body is double-acting between a closed position where the valve body is seated on a valve seat and an open position;
An air spring comprising a spring piston housed in an air spring cylinder, connected to the valve rod so as to control the valve rod, and an air spring for urging the exhaust valve toward the closed position;
A hydraulic actuator having a pressure chamber, connected to the valve rod so as to control the valve rod of the exhaust valve, and hydraulic pressure for urging the exhaust valve in the opening direction when the pressure chamber is pressurized An actuator,
An intermediate pressure hydraulic accumulator that accumulates energy released from the air spring during a return stroke of the exhaust valve and supplies energy to the hydraulic actuator during an open stroke of the exhaust valve;
The pressure chamber of the hydraulic actuator;
・ At the beginning of the opening process of the exhaust valve,
A period after the initial period until the exhaust valve reaches its open position, the intermediate pressure hydraulic accumulator
· Period until immediately before the final stage of the closing stroke from the start of the closing stroke of the exhaust valve the exhaust valve, the intermediate pressure hydraulic accumulator,
In the final stage of the closing process of the exhaust valve,
An electronically controlled hydraulic system for selective connection;
Is a large multi-cylinder two-cycle diesel engine provided for each cylinder.   The hydraulic system comprises a first electronically controlled valve configured to connect the pressure chamber of the hydraulic actuator to the high pressure hydraulic fluid source at the beginning of the opening stroke of the exhaust valve. Item 2. A large two-cycle diesel engine according to Item 1.   The hydraulic system transfers the pressure chamber of the hydraulic actuator to the intermediate pressure hydraulic accumulator during a period after the initial start of the opening of the first electronically controlled valve until the exhaust valve reaches its open position. The large two-cycle diesel engine of claim 2, comprising a second electronically controlled valve configured to connect.   The hydraulic system is configured to connect the pressure chamber of the hydraulic actuator to the intermediate pressure hydraulic accumulator from the start of the closing stroke of the exhaust valve to before the final phase of the closing stroke of the exhaust valve begins. A large two-cycle diesel engine according to claim 3, comprising a third electronically controlled valve.   The hydraulic system comprises a fourth electronically controlled valve configured to connect the pressure chamber of the hydraulic actuator to a tank during the final phase of the closing stroke of the exhaust valve. The large two-cycle diesel engine described.   The large two-cycle diesel engine according to claim 5, wherein the first electronically controlled valve and the fourth electronically controlled valve are constituted by a single two-way valve.   The large two-cycle diesel engine according to claim 4, wherein the second electronically controlled valve and the third electronically controlled valve are constituted by a single two-way valve.   A first check valve that only allows flow in a direction toward the intermediate pressure hydraulic accumulator is associated with the second electronically controlled valve and a second that only allows flow in a direction away from the intermediate pressure hydraulic accumulator. A large two-stroke diesel engine according to any of claims 4 to 7, wherein a non-return valve is associated with the third electronically controlled valve.   A substantial overlap exists at the opening time of the first to fourth electronically controlled valves, and the overlap is enabled by the presence of the first and second check valves. Item 9. The large two-cycle diesel engine according to Item 8.   The large size according to any one of claims 1 to 9, further comprising an electronic control unit configured to control a hydraulic connection between the pressure chamber, the high pressure hydraulic fluid source, the intermediate pressure hydraulic accumulator, and a tank. 2-cycle diesel engine.

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