JP5079916B2 - Cam-driven exhaust valve actuation system for large two-cycle diesel engines - Google Patents

Description

  The present invention relates to a cam-driven hydraulic exhaust valve operation and a fuel injection system of a crosshead type large turbocharged two-cycle diesel engine.

Background of the Invention

  The crosshead type large turbocharged two-cycle diesel engine is used, for example, for propulsion of a large ocean-going vessel or as a main engine of a power plant. Not only because of its very large size, these two-cycle diesel engines are built differently from any other internal combustion engine. The two-cycle principle and the use of heavy oil with a viscosity of less than 700 cSt at 50 ° C. (ie non-flowable at room temperature) occupies a special position in the engine industry.

  Due to demands for performance improvement and emission reduction, common rail type electrohydraulic control type exhaust valve actuation system and electronic control type fuel injection system have been developed for these large two-cycle diesel engines. The advantage of these systems is their increased flexibility, and the timing of opening and closing the exhaust valves and the way in which fuel is supplied can be freely selected to suit the operating conditions of the engine. However, the common rail electrohydraulic system is relatively expensive, and the hydraulic energy used to open the exhaust valve opening process is lost without being recovered during the exhaust valve closing process. Even consumes a lot of energy.

  The hydraulic power source includes an electrically driven starter pump and a set of high pressure pumps having a predetermined constant outlet pressure obtained by stepless adjustment of capacity. The pump is driven by a single mechanical gear connected to the crankshaft.

  Long pipes are used to connect the hydraulically driven fuel injection pump and the high pressure system, and there are many pipe connections. This system has low redundancy for damage to gears, failure of the continuously variable capacity adjustment function, and damage to the rupture of the supply pipe or pipe connection that may occur due to sudden natural pressure fluctuations. The engine becomes inoperable, i.e. the engine stops completely.

  Furthermore, the efficiency of the continuously variable pump varies depending on the operating conditions, and it cannot be said that the efficiency is high under certain conditions. These disadvantages offset many of the advantages of electronically controlled engines.

  Against this background, it is an object of the present invention to provide an energy saving engine of the above type that overcomes or at least mitigates the above mentioned problems.

The object is to provide a plurality of cylinders each provided with at least one exhaust valve and at least one fuel injector, and each said at least one exhaust valve for any of said cylinders and a hydraulic push rod for said cylinder A crosshead large two-cycle diesel engine comprising at least one camshaft on which a plurality of exhaust cams for operating the engine are mounted:
The hydraulic push rod is a hydraulic piston pump provided for each actuator, the hydraulic piston pump driven by the corresponding cam on the cam shaft, and the exhaust valve for moving the corresponding exhaust valve in the opening direction. A hydraulic actuator provided on each exhaust valve for connecting the hydraulic piston pump of the associated actuator to the associated hydraulic actuator;
The exhaust cam has a shape that produces a lift amount that is greater than the lift amount required to open the exhaust valve, thereby providing additional hydraulic pressure supplied by the hydraulic piston pump and generated by the higher lift amount. This is accomplished by providing a large two-cycle diesel engine in which at least a portion of the oil is diverted from the hydraulic push rod and supplied to elements that use pressurized hydraulic oil with respect to the engine.

  By generating hydraulic fluid with the camshaft and the piston pump of the exhaust valve actuation system, it is possible to generate a certain amount of high pressure hydraulic fluid efficiently and with high redundancy. The additional hydraulic fluid can be used to drive other hydraulically driven components of the engine, such as fuel injection systems and cylinder lubrication systems. The portion of the additional hydraulic oil that cannot be used directly by the other hydraulically driven components is directed to the hydraulic push rod, increasing the opening stroke of the exhaust valve. The air spring that urges the exhaust valve to the closed position stores the energy contained in the portion of the additional hydraulic fluid and returns this energy to the camshaft by the return stroke of the exhaust valve.

  The element that uses the pressurized hydraulic fluid may be an engine fuel injection system.

  The element using the pressurized hydraulic fluid may be an engine cylinder lubrication system.

  Preferably, the lift increment is generated by increasing the height of the exhaust lobe.

  At least a portion of the additional hydraulic oil may be diverted from the hydraulic push rod via a port of the hydraulic piston pump.

  The piston of the hydraulic piston pump may be provided with a hole connecting the upper surface of the piston to the side surface of the piston.

  A port for connecting the piston pump to an element that uses pressurized hydraulic oil may be provided on the wall surface of the piston pump.

  The port can be connected to the inlet of a pressure amplifier.

  The outlet of the pressure amplifier is connected to a common hydraulic conduit to which the elements using the hydraulic oil of each cylinder are connected.

  Preferably, the pressure amplifier is balanced by the pressure in the common regulating pressure conduit.

  The fuel injection system is operable with high pressure hydraulic fluid from a common hydraulic conduit.

  The fuel injection system may include, for each cylinder, a hydraulically driven intensifier that supplies fuel at an extremely high pressure to the fuel injection valve of each cylinder.

  Each of the intensifiers may be connected to the high pressure hydraulic conduit via a selection valve that selectively connects the intensifier to the high pressure common hydraulic conduit.

  The selection valve may be an electronically controlled or electrohydraulic controlled valve, preferably a proportional valve.

  At least a portion of the additional hydraulic oil generated by the higher lift amount supplied by the hydraulic piston pump and not diverted from the hydraulic push rod may be used to increase the opening stroke of the exhaust valve.

  The exhaust valve is provided with an air spring that biases the exhaust valve to the closed position, and the air spring stores the energy contained in the additional hydraulic oil in the air spring by responding to the increased opening stroke. The energy is returned to the camshaft during the exhaust valve closing stroke.

  Preferably, the hydraulic push rod is configured to be selectively connectable to a common high pressure hydraulic conduit to allow the exhaust valve to open prior to the profile defined by the cam shape.

  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.

In the following detailed portion of the present description, the present invention will be described in more detail with reference to exemplary embodiments shown in the drawings.
1 is a cross-sectional view of an engine according to the present invention. It is a longitudinal cross-sectional view regarding one cylinder division of the engine shown in FIG. 1 is a diagrammatic representation of a first embodiment of an exhaust valve actuation and fuel injection system according to the present invention. 3 is a bar graph illustrating the operation of the present invention. 3 is a bar graph illustrating the operation of the present invention. 3 is a bar graph illustrating the operation of the present invention. 3 is a bar graph illustrating the operation of the present invention. FIG. 3 is a diagrammatic representation of a second embodiment of an exhaust valve actuation and fuel injection system according to the present invention.

Detailed Description of the Preferred Embodiment

  FIGS. 1 and 2 are a cross-sectional view and a vertical cross-sectional view of one cylinder of the engine 1 according to a preferred embodiment of the present invention. The engine 1 is a crosshead uniflow 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 series. 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. Semi-assembled molds are manufactured from cast steel throws or forged steel throws that are connected to the main journal shaft by shrink fit.

  The base plate 2 may be manufactured as a single component, or may be manufactured by being divided into portions of an appropriate size according to the manufacturing facility. The base plate consists of side walls and welded cross grinders with bearing supports. 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 bearing 22. The cross head bearing 22 is guided between the vertical guide surfaces 23.

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

  A cylinder frame 5 is mounted on the top of the box frame 4. The retaining bolt 27 connects the base plate 2, the box frame 4, and the cylinder frame 5 to make the structure integral. The reserve bolt 27 is tightened with a hydraulic jack.

  The cylinder frame 5 is ultimately cast or welded into one or more parts having an integral camshaft housing 25. According to another embodiment (not shown), the camshaft 28 is housed in a separate camshaft housing that is attached to the cylinder frame.

  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 on the camshaft side. 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. At the bottom of the cylinder frame is a packing box for piston rods, which is equipped with a scavenging sealing ring and an oil ring that prevents exhaust products from entering the space of the box frame 4 and the base plate 2. In this way, all bearings existing in this space are protected.

  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, together with the cooling oil pipe, forms an inlet and an outlet for the cooling oil of the piston 13.

  The cylinder liner 6 is carried 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 located near the air box. The exhaust port is supplied with scavenged air pressurized by the turbocharger 10 (FIG. 1) from the scavenging receiver 9 (FIG. 1).

  The engine is equipped with one or more turbochargers 10. This turbocharger is disposed at the rear 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 to the turbocharger 10 is generated directly from the engine compartment 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 electrically driven scavenging blower (not shown). The suction side of the blower is connected to the scavenging space after air cooling. 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 compression by the turbocharger under low and medium load conditions.

  The fuel valve 48 is concentrically mounted on the cylinder cover 12. At the end of the compression stroke, the injection valve 48 injects fine mist-like fuel into the combustion chamber 15 through the injection nozzle at a high pressure. The exhaust valve 11 is attached to the center of the cylinder upper portion of the cylinder cover 12.

  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. The exhaust valve actuation system relates to all of the illustrated embodiments for a single cylinder. Even in a multi-cylinder engine, the same equipment is provided for each cylinder. The exhaust valve actuation system comprises a camshaft 28 fitted with an exhaust cam 29 having an increased lift amount 30 (only one is shown because only one cylinder is shown). The roller 31 follows the surface of the cam 29 and is connected to the piston of the positive displacement pump 32. The positive displacement pump 32 is connected to the exhaust valve actuator 34 via the pressure pipe 36. The positive displacement pump 32, the pressure pipe 36, and the exhaust valve actuator 34 together form a hydraulic push rod. The exhaust valve actuator 34 is a positive displacement linear actuator that can apply a force in the opening direction of the exhaust valve 11.

  The exhaust valve is provided with an air spring 33 that urges the exhaust valve 11 to the closed position. The position of the exhaust valve 11 is measured and communicated to an engine control unit (ECU).

  The increment of the lift amount by the exhaust cam 29 is indicated by the hatched portion 30. The cam profile of the exhaust cam 29 need only swell to the bottom of the shaded portion 30 in order to provide a sufficient stroke for the positive displacement pump 32 to obtain an insufficient opening stroke of the exhaust valve 11. Due to the incremental stroke of the positive displacement pump 32 produced by further bulging of the cam 29, the positive displacement pump 32 will have a stroke that exceeds the need for full opening of the exhaust valve 11.

  The piston of the positive displacement pump 32 is provided with a hole 35 that communicates with the port 37 during a predetermined portion of the piston stroke.

  If the pressure at the port 37 is lower than the pressure in the pressure chamber of the positive displacement pump 32, a portion of the additional hydraulic oil generated from the hydraulic piston pump 32 and resulting from the increased lift is diverted to the port 37. .

  If the pressure at the port 37 is higher than the pressure in the pressure chamber of the positive displacement pump 32, some of the additional hydraulic oil generated from the hydraulic piston pump 32 and due to increased lift of the cam 29 will be routed through the pressure pipe 36. To the exhaust valve actuator 34. This causes an increase in the opening stroke of the exhaust valve 11, i.e. an opening stroke that exceeds the length of the normally required opening stroke.

  The air spring 33 is configured to cope with an increase in the opening stroke of the exhaust valve 11, whereby the air spring 33 is included in a part of the additional hydraulic oil generated by the increase in the lift amount. Store and store energy. In some embodiments, the air spring 33 may be provided with advanced features to increase the amount of energy that the air spring can store. The energy stored in the air spring 33 is returned to the camshaft 28 in the subsequent return stroke of the exhaust valve 11.

  The pressure port 37 is connected to an intermediate intensifier 38. The intermediate pressure booster 38 increases the pressure at the port 37 and supplies the increased hydraulic oil via the conduit 39 to the common high pressure hydraulic conduit 18 connected to all of the cylinders.

  The common high pressure hydraulic conduit 18 is maintained at a high pressure during engine operation, for example, at a level set between about 200 bar and 600 bar. At engine start-up, the pressure in the common high-pressure hydraulic conduit 18 is generated by the electrically driven pump 9. During engine operation, the pressure in the common high pressure hydraulic conduit 18 is supplied by an intermediate intensifier 38.

  The intermediate pressure intensifier 38 is provided with two pressure chambers. The first pressure chamber supplies high pressure hydraulic oil to the common high pressure hydraulic conduit 18. The second pressure chamber is connected to a common control pressure conduit 42 via conduit 41. The pressure in the common control pressure conduit 42 is maintained between about 100 bar and 200 bar and is controlled by an engine control unit (ECU) as follows. The engine controller receives a signal representative of the pressure in the common high pressure hydraulic conduit 18. The engine controller controls a pressure regulating valve 44 connected to the pressure control conduit 42, whereby the engine controller controls the pressure in the common high pressure hydraulic conduit 18.

  When the engine controller detects that the pressure in the common high pressure hydraulic conduit 18 is lower than desired, the engine controller reduces the pressure in the pressure control conduit 42. Thereby, the intermediate pressure booster 38 receives a reduced amount of counter pressure and increases the amount of high pressure hydraulic fluid supplied to the common high pressure hydraulic conduit 18.

  When the engine control device detects that the pressure in the common high pressure hydraulic unit is higher than desired, the engine control device increases the pressure in the pressure control unit 42. This causes the intermediate pressure booster 38 to receive an increased amount of counter pressure and reduce the amount of high pressure hydraulic oil supplied to the common high pressure hydraulic conduit 18.

  The pressurized fluid from the pressure control conduit 42 also powers the return / suction stroke of the intermediate intensifier 38. The intermediate intensifier 38 is connected to a low pressure (approximately 3 bar) supply pressure conduit 43 via a conduit 40 that assists the pressure chamber of the intensifier 38.

  The amount of additional hydraulic oil produced by the lift amount increase of the exhaust cam 29 that is not diverted to elements that use pressurized hydraulic oil with respect to the engine will vary depending on various engine operating conditions. When the engine operates under a high load, it is necessary to inject a relatively large amount of fuel every stroke, and is there a small part of the additional hydraulic oil used to increase the lift amount of the exhaust valve 11? Not at all.

  When the engine is operating under low or intermediate loads, the amount of fuel injected per stroke is relatively small and a relatively large portion of additional hydraulic oil is used to increase the lift of the exhaust valve 11. . The energy contained in this non-split portion of additional hydraulic oil is stored in the gas spring 33 and returned to the camshaft 28 during the exhaust valve 11 closing stroke.

  The pressure in the control pressure conduit 42 acting on the intermediate intensifier 38 adjusts the amount of high pressure hydraulic oil supplied to the common high pressure conduit 18 by the intermediate intensifier 38. Thus, it can be ensured that the desired pressure can be obtained in the common high-pressure conduit 18 by the engine control device.

  Each cylinder is provided with two or more fuel injection valves 48 including injection nozzles. The fuel injection valve 48 receives high pressure fuel from the pressure intensifier 46. Fuel is usually heavy oil that needs to be heated to liquefy due to its very low viscosity. The intensifier 46 is driven by high pressure hydraulic oil from the common high pressure fluid conduit 18. Here, the pressure booster 46 is connected to the common high-pressure hydraulic conduit 18 via a conduit 45 and a proportional valve 49. A hydraulic accumulator 47 is connected to the conduit 45 to minimize pressure fluctuations. The proportional valve 49 is electronically or electrohydraulically controlled by the engine control device and operates in a known manner.

  FIG. 4 is a graph 42 illustrating the state of the lift of the exhaust cam. The shaded area illustrates an increased amount of lift that exceeds the amount of lift that may be required for normal opening of the exhaust valve 11. Only about 60% of the lift is required to open the exhaust valve 11. The remaining lift (shaded area) is used to produce an additional amount of pressurized hydraulic fluid.

  FIG. 5 is a graph illustrating the state of the exhaust valve lift under operating conditions due to an intermediate engine load. A portion of the additional hydraulic fluid produced by the piston pump 32 provides an additional length of eleven exhaust open strokes (lifts). The additional opening stroke (lift) of the exhaust valve 11 is indicated by the shaded area.

  FIG. 6 is a graph illustrating the open area at the actuator port 37.

  FIG. 7 is a graph illustrating the displacement of the intermediate intensifier 38. Stage A is the supply plane, Stage B is the balance plane with force / pressure balance, and Stage C is the return / suction stroke.

  FIG. 8 illustrates a second embodiment of the present invention. This embodiment is essentially the same as the first embodiment, except that this embodiment is provided with means for adding an additional amount of hydraulic oil from the control pressure conduit 42 to the hydraulic push rod. Further, the cylinder lubricator 52 operates with hydraulic oil from the common high pressure hydraulic conduit 18.

  Means for supplying an additional amount of hydraulic oil to the hydraulic push rod may connect the pressure chamber of the piston pump 32 via the modified proportional valve 49 to the common high pressure hydraulic conduit 18 (or alternatively, the control pressure conduit 42). A conduit 50 connected to the. In this embodiment, the proportional valve 49 is provided with two further positions for controlling the flow of hydraulic oil from the common high pressure hydraulic conduit 18 to the pressure chamber of the piston pump 32. Through the proportional valve 49, the engine control device can control the timing and amount of hydraulic fluid supplied to the hydraulic push rod. By supplying a controlled amount of hydraulic oil to the hydraulic push rod in a timely manner, the engine controller can adjust the blowback pressure by expediting the opening of the exhaust valve 11. Control of the cylinder compression pressure is achieved by supplying a controlled amount of hydraulic fluid to the hydraulic push rod just before the exhaust valve 11 starts to close. The exhaust valve actuation system according to the present embodiment provides the possibility of profiling, that is, changing the timing of opening the exhaust valve 11 and changing the timing of closing the exhaust valve 11.

  The engine control device also controls the cylinder lubrication unit 52 that operates with the high-pressure hydraulic oil from the common high-pressure hydraulic conduit 18 to supply the cylinder lubricant to the cylinder.

  Therefore, in the second embodiment, both the fuel injection system and the cylinder lubrication system operate with high-pressure hydraulic oil generated by increasing the lift of the exhaust valve cam 29.

  In other embodiments (not shown), there may be other (further) hydraulically operated engine components that are driven by an additional amount of hydraulic oil produced by an additional lift of the camshaft. An example of such another hydraulically operated engine component is an auxiliary blower that can be driven by a hydraulic motor that receives its hydraulic power from a common high-pressure hydraulic conduit 18. The auxiliary blower operates only during low to medium engine loads. In the meantime, there is usually extra hydraulic oil available from the intermediate intensifier 38, which can be used directly for driving the auxiliary blower.

  The present invention has a number of advantages. Different embodiments or implementations may provide one or more of the following advantages. It should be noted that this is not a comprehensive list and there may be other advantages not described herein. One advantage of the present invention is that it provides a flexible, energy efficient exhaust valve actuation and fuel injection system for large two-cycle diesel engines. Another advantage of the present invention is that it provides a large two-cycle diesel engine with a flexible electronically controlled fuel injection system that does not require a high pressure pump station or pump. A further advantage of the present invention is the use of primarily highly efficient components for valve actuation and fuel injection. A further advantage of the present invention is that it provides excellent power supply redundancy with proven reliability. Another advantage of the present invention is that existing engines with camshaft-operated exhaust valves can be modified and used with a system according to the present invention.

  The term “comprising”, when used in the claims, does not exclude other elements. The singular terms in the claims do not exclude the plural.

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

Claims (14)

A plurality of cylinders each provided with at least one exhaust valve and at least one fuel injector;
At least one camshaft, each mounted with a plurality of exhaust cams for actuating the at least one exhaust valve for any of the cylinders and a hydraulic push rod for the cylinders;
A crosshead type large two-cycle diesel engine comprising:
The hydraulic push rod is
A hydraulic piston pump provided for each actuator and driven by a corresponding exhaust cam on the camshaft;
A hydraulic actuator provided for each exhaust valve and moving the corresponding exhaust valve in the opening direction;
A hydraulic conduit provided for each exhaust valve and connected to the hydraulic piston pump via a port of the hydraulic piston pump, the hydraulic conduit connecting the hydraulic piston pump to the corresponding hydraulic actuator;
With
The exhaust cam has a shape that produces a lift amount that is greater than the lift amount required to open the exhaust valve, thereby providing additional hydraulic pressure supplied by the hydraulic piston pump and generated by the higher lift amount. At least a portion of the oil is diverted from the hydraulic push rod and supplied to an element that uses pressurized hydraulic oil with respect to the engine, and the at least a portion of the additional hydraulic oil is another part of the hydraulic piston pump. Diverted from the hydraulic pushrod through a port , but the lift increment is generated by increasing the height of the exhaust lobe,
The piston of the hydraulic piston pump is provided with a hole that connects the upper surface of the piston to the side surface of the piston, and the other port that connects the hydraulic piston pump to the element that uses the pressurized hydraulic oil includes: Provided on the wall surface of the hydraulic piston pump,
This is a large two-cycle diesel engine.   The large two-stroke diesel engine according to claim 1, wherein the element using the pressurized hydraulic oil is a cylinder lubrication system of the engine. The large two-cycle diesel engine according to claim 1 or 2 , wherein the another port is connected to an inlet of a pressure amplifier. The large two-cycle diesel engine according to claim 3 , wherein the outlet of the pressure amplifier is connected to a common hydraulic conduit to which elements using the pressurized hydraulic oil of each cylinder are connected. The large two-stroke diesel engine of claim 4 , wherein the pressure amplifier is balanced by pressure in a common control pressure conduit. The large two-cycle diesel engine according to claim 4 or 5 , wherein the element using the pressurized hydraulic oil is a fuel injection system of the engine. The large two-cycle diesel engine of claim 6 , wherein the fuel injection system operates with high pressure hydraulic fluid from the common hydraulic conduit. The large-sized two-cycle diesel engine according to claim 6 or 7 , wherein the fuel injection system includes, for each cylinder, a hydraulically driven intensifier that supplies fuel of extremely high pressure to the fuel injector of the cylinder. The large two-cycle diesel engine of claim 8 , wherein each of the boosters is connected to the common hydraulic conduit via a selection valve that selectively connects the booster to the common hydraulic conduit. The large-sized two-cycle diesel engine according to claim 9 , wherein the selection valve is an electronic control type or an electrohydraulic control type valve . At least a portion of the additional hydraulic oil generated by the higher lift amount supplied by the hydraulic piston pump and not diverted from the hydraulic push rod is used to increase the opening stroke of the exhaust valve. A large two-cycle diesel engine according to any one of claims 1 to 10 . Each of the exhaust valves is provided with an air spring that biases the exhaust valve to a closed position, the air spring responding to the increased opening stroke, thereby allowing the portion of the additional hydraulic oil to The large two-cycle diesel engine of claim 11 , configured to store the energy contained in the air spring in the air spring and return the energy to the camshaft during a closing stroke of the exhaust valve. The hydraulic push rod, in order to allow the opening of the exhaust valve before the profile defined by the shape of the exhaust cam, selectively connectable configured in a common hydraulic conduit to claim 1 The large two-cycle diesel engine described. The hydraulic push rod, in order to allow the closing of the exhaust cams of the shape the exhaust valve later than the profile defined by selectively connectable configured in a common hydraulic conduit to claim 1 The large two-cycle diesel engine described.

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