PEDERSEN, Erik, Due (Vestersogade 48, 4tv, Copenhagen V, DK-1601, DK)
| CLAIMS : 1. A large two-stroke diesel engine of the crosshead type comprising: a number of cylinders, each cylinder being provided with at least one exhaust valve and with at least one fuel injector, at least one camshaft provided with exhaust cams for actuation of the at least one exhaust valve associated with each of the cylinders, and a hydraulic push rod associated which each of the cylinders, the hydraulic push rod comprises: a hydraulic piston pump per actuator, the hydraulic piston pumps being driven by respective cams on said camshaft, a hydraulic actuator per exhaust valve for moving the exhaust valve concerned in an opening direction, and a hydraulic conduit per exhaust valve for connecting the hydraulic piston pump of the actuator concerned with the hydraulic actuator concerned, characterized in that said exhaust cams are provided with a profile with an increased lift exceeding the lift required for opening the exhaust valve, whereby a least a portion of an additional volume of hydraulic fluid generated by the hydraulic piston pumps and caused by the increased lift is diverted from the hydraulic push rod and delivered to a consumer of pressurized hydraulic fluid that is associated with the engine. 2. A large two-stroke diesel engine according to claim 1, wherein a consumer of pressurized hydraulic fluid is the fuel injection system of the engine. 3. A large two-stroke diesel engine according to claim 1 or 2, wherein a consumer of pressurized hydraulic fluid is the cylinder lubrication system of the engine. 4. A large two-stroke diesel engine according to claim 1, wherein the extra lift is created by increasing the height of the exhaust lobe. 5. A large two-stroke diesel engine according to claim 1, wherein the portion of the additional volume of hydraulic is diverted from the hydraulic push rod via a port in the hydraulic piston pumps. 6. A large two-stroke diesel engine according to claim 5, wherein the pistons of the hydraulic piston pumps is provided with a bore connecting the top face of the piston to a side face of the piston. 7. A large two-stroke diesel engine according to claim 6, wherein the wall of the piston pumps is provided with a port connecting the piston pumps to the consumer of pressurized hydraulic fluid. 8. A large two-stroke diesel engine according to claim 7, wherein said port is connected to the inlet of a pressure amplifier. 9. A large two-stroke diesel engine according to claim 8, wherein the outlet of said pressure amplifier is connected to a common hydraulic conduit to which hydraulic pressure fluid consumers of each of the cylinders are connected. 10. A large two-stroke diesel engine according to claim 9, wherein said pressure amplifier is counterbalanced by the pressure in a common regulation pressure conduit. 11. A large two-stroke diesel engine according to claim 9 or 10, wherein the fuel injection system is operated with high pressure hydraulic fluid from said common hydraulic conduit. 12. A large two-stroke diesel engine according to claim 11, wherein said fuel injection system includes a hydraulically driven pressure booster per cylinder that delivers very high-pressure fuel to the fuel injection valves of each cylinder. 13. A large two-stroke diesel engine according to claim 11, wherein each of the pressure boosters is connected to the high-pressure, hydraulic conduit via a selection valve that selectively connects the pressure booster to the high-pressure common hydraulic conduit. 14. A large two-stroke diesel engine according to claim 13, wherein said selection valve is on electronic- or electro-hydraulic controlled valve, preferably a proportional valve. 15. A large two-stroke diesel engine according to any of the preceding claims, wherein the portion of the additional volume of hydraulic fluid generated by the hydraulic piston pumps and caused by the increased lift that is not diverted from the hydraulic push rod is used to create an additional length of opening stroke of the exhaust valve. 16. A large two-stroke diesel engine according to claim 15, wherein each of the exhaust valves is provided with an air spring urging the exhaust valve in to the closed position, and wherein air spring is configured to accommodate an said increased length of the opening stroke to thereby store the energy contained in the additional volume of hydraulic fluid in the air spring and return this energy to the camshaft during the closing stroke of the exhaust valve. 17. A large two-stroke diesel engine according to any of the preceding claims, wherein said hydraulic push rods are selectively connectable to the common high-pressure hydraulic conduit for allowing opening of the exhaust valve in advance of the profile defined by the cam profile . 18. A large two-stroke diesel engine according to any of the preceding claims, wherein said hydraulic push rods are selectively connectable to the common high-pressure hydraulic conduit for allowing closing of the exhaust valve in delay of the profile defined by the cam profile. |
FIELD OF THE INVENTION
The present invention relates to a cam driven hydraulic exhaust valve actuation and fuel injection system for a large turbocharged two-stroke diesel engine of the cross- head type.
BACKGROUND OF THE INVENTION
Large turbocharged two-stroke diesel engines of the cross-head type are for example used for propulsion of large oceangoing vessels or as primary mover in a power plant. Not only due to sheer size, these two-stroke diesel engines are constructed differently from any other combustion engines. The two-stroke principle and the use of heavy fuel oil with a viscosity below 70OcSt at 50 0 C (the oil does not flow at room temperatures) make them a class of their own in the engine world.
The desire for improved performance and reduced emissions has led to the development of common rail electro- hydraulically controlled exhaust valve actuation systems and electronically controlled fuel injection systems for these large two-stroke diesel engines. An advantage of these systems is their increased flexibility since the exhaust valve opening and closing timing and the fuel profiling can be freely chosen to match the operating conditions of the engine. However, these common rail electro-hydraulic systems are relatively expensive and consume more energy than conventional cam driven systems since the hydraulic energy that is used to open exhaust valve opening process is lost without recovery during the exhaust valve closing process. The hydraulic power supply is provided by an electrical driven starting up pump and a set of high pressure pumps with a given constant outlet pressure obtained by a stepless adjustment of the capacity. The pumps are driven by a single mechanical gear connected to the crank shaft. The hydraulic driven fuel injection pumps are connected to the high pressure system with long pipes and an extended number of pipe connections. This system has a low grade of redundancy as in case of damage of the gear or a failure of the stepless capacity adjustment or a fracture of the supply pipe or pipe connections caused by natural violent pressure vibrations and a failure will result in the engine not being operationable, i.e. total engine failure. Further, the efficiency of the stepless adjustable pumps varies with operating conditions and is in certain conditions far from high. These drawbacks annihilate many of the advantages of the electronically controlled engine.
DISCLOSURE OF THE INVENTION
On this background, it is an object of the present invention to provide an energy saving engine of the type described that overcomes or at least reduces the problems indicated above.
This object is achieved by providing a large two-stroke diesel engine of the crosshead type comprising a number of cylinders, each cylinder being provided with at least one exhaust valve and with at least one fuel injector, at least one camshaft provided with exhaust cams for actuation of the at least one exhaust valve associated with each of the cylinders, and a hydraulic push rod associated which each of the cylinders, the hydraulic push rod comprises a hydraulic piston pump per actuator, the hydraulic piston pumps being driven by respective cams on the camshaft, a hydraulic actuator per exhaust valve for moving the exhaust valve concerned in an opening direction, and a hydraulic conduit per exhaust valve for connecting the hydraulic piston pump of the actuator concerned with the hydraulic actuator concerned, whereby the exhaust cams are provided with a profile with an increased lift exceeding the lift required for opening the exhaust valve, whereby a least a portion of the additional volume of hydraulic fluid generated by the hydraulic piston pumps and caused by the increased lift is diverted from the hydraulic push rod and delivered to a consumer of pressurized hydraulic fluid that is associated with the engine.
By generating additional hydraulic fluid with the camshaft and the piston pump of the exhaust valve actuating system a volume of high pressure hydraulic fluid can be generated efficiently and with high redundancy. The additional volume of hydraulic fluid can be used to drive other fluid driven components of the engine, such as the fuel injection system or the cylinder lubrication system. Any portion of additional hydraulic fluid that cannot be directly used by the other fluid driven components is directed into the hydraulic push rod and results in increased opening stroke of the exhaust valve. The air spring that urges the exhaust valve to the closed position will store the energy contained in the portion of additional hydraulic fluid and return this energy to the camshaft with the return stroke of the exhaust valve. A consumer of pressurized hydraulic fluid can be the fuel injection system of the engine.
A consumer of pressurized hydraulic fluid can be the cylinder lubrication system of the engine.
Preferably, the extra lift is created by increasing the height of the exhaust lobe.
The portion of the additional volume of hydraulic can be diverted from the hydraulic push rod via a port in the hydraulic piston pumps.
The pistons of the hydraulic piston pumps can be provided with a bore connecting the top face of the piston to a side face of the piston.
The wall of the piston pumps can be provided with a port connecting the piston pumps to the consumer of pressurized hydraulic fluid.
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 hydraulic pressure fluid consumers of each of the cylinders are connected.
Preferably, the pressure amplifier is counterbalanced by the pressure in a common regulation pressure conduit. The fuel injection system can be operated with high pressure hydraulic fluid from the common hydraulic conduit .
The fuel injection system may include a hydraulically driven pressure booster per cylinder that delivers very high-pressure fuel to the fuel injection valves of each cylinder.
Each of the pressure boosters can be connected to the high-pressure, hydraulic conduit via a selection valve that selectively connects the pressure booster to the high-pressure common hydraulic conduit.
The selection valve can be on electronic- or electro- hydraulic controlled valve, preferably a proportional valve .
The portion of the additional volume of hydraulic fluid generated by the hydraulic piston pumps and caused by the increased lift that is not diverted from the hydraulic push rod can be used to create an additional length of opening stroke of the exhaust valve.
The exhaust valves is provided with an air spring urging the exhaust valve in to the closed position, and wherein air spring is configured to accommodate an the increased length of the opening stroke to thereby store the energy contained in the additional volume of hydraulic fluid in the air spring and return this energy to the camshaft during the closing stroke of the exhaust valve.
Preferably, the hydraulic push rods are selectively connectable to the common high-pressure hydraulic conduit for allowing opening of the exhaust valve in advance of the profile defined by the cam profile.
Further objects, features, advantages and properties of the large two-stroke diesel engine according to the invention will become apparent from the detailed description.
BRIEF DESCRIPTION OF THE DRAWINGS
In the following detailed portion of the present description, the invention will be explained in more detail with reference to the exemplary embodiments shown in the drawings, in which figure 1 is a cross-sectional view of an engine according to the present invention, figure 2 is a longitudinal-sectional view of one cylinder section of the engine shown in figure 1, figure 3 is a symbolic representation of a first embodiment of the exhaust valve actuation and fuel injection system according to the present invention, figures 4 to 7 bar graphs illustrating the operation of the invention, and figure 8 is a symbolic representation of a second embodiment of the exhaust valve actuation and fuel injection system according to the present invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
Figures 1 and 2 show an engine 1 according to a preferred embodiment of the invention in cross-sectional view and longitudinal-sectional view (for one cylinder) respectively. The engine 1 is a uniflow low-speed two- stroke crosshead diesel engine of the crosshead type, which may be a propulsion system in a ship or a prime mover in a power plant. These engines have typically from 4 up to 14 cylinders in line. The engine 1 is built up from a bedplate 2 with the main bearings for the crankshaft 3.
The crankshaft 3 is of the semi-built type. The semi- built type is made from forged or cast steel throws that are connected with the main journals by shrink fit connections .
The bedplate 2 can be made in one part or be divided into sections of suitable size in accordance with production facilities. The bedplate consists of side walls and welded cross girders with bearing supports. The cross girders are in the art also referred to as "transverse girders". The oil pan 58 is welded to the bottom of the bedplate 2 and collects the return oil from the forced lubricating and cooling oil system.
The connecting rods 8 connect the crankshaft 3 to the crosshead bearings 22. The crosshead bearings 22 are guided between vertical guide planes 23.
A welded design A-shaped frame box 4 is mounted on the bedplate 2. The frame box 4 is a welded design. On the exhaust side the frame box 4 is provided with relief valves for each cylinder, while on the camshaft side the frame box 4 is provided with a large hinged door for each cylinder. The crosshead guide planes 23 are integrated in the frame box 4.
A cylinder frame 5 is mounted on top of the frame box 4. Staybolts 27 connect the bedplate 2, the frame box 4 and the cylinder frame 5 and keep the structure together. The staybolts 27 are tightened with hydraulic jacks.
The cylinder frame 5 is cast in one or more pieces eventually with an integrated camshaft housing 25, or it is a welded design. 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 access covers for cleaning the scavenge air space and for inspection of scavenge ports and piston rings from the camshaft side. Together with the cylinder liner 6 it forms the scavenge air space. The scavenge air receiver 9, is bolted with its open side to the cylinder frame 5. At the bottom of the cylinder frame there is a piston rod stuffing box, which is provided with sealing rings for scavenge air, and with oil scraper rings which prevent exhaust products to penetrate into the space of the frame box 4 and the bedplate 2 and in this way protects all the bearings which are present in this space.
The piston 13 includes a piston crown and piston skirt. The piston crown is made of heat-resistant steel and has four ring grooves which are hard-chrome plated on both the upper and the lower surfaces of the grooves.
The piston rod 14 is connected to the crosshead 22 with four screws. The piston rod 14 has two coaxial bores (not visible in the drawings) which, in conjunction with a cooling oil pipe, forms the inlet and outlet for cooling oil for the piston 13. The cylinder liners 6 are carried by the cylinder frame 5. The cylinder liners 6 are made of alloyed cast iron and are suspended in the cylinder frame 5 by means of a low situated flange. The uppermost part of the liner is surrounded by cast iron cooling jacket. The cylinder liners 6 have drilled holes (not shown) for cylinder lubrication.
The cylinders are of the uniflow type and has scavenge air ports 7 located in an airbox, which from a scavenge air receiver 9 (Fig. 1), is supplied with scavenge air pressurized by a turbocharger 10 (Fig. 1) .
The engine is fitted with one or more turbochargers 10 arranged on the aft end of the engine for 4-9 cylinder engines and on the exhaust side for 10 or more cylinder engines .
The air intake to the turbocharger 10 takes place directly from the engine room through an intake silencer of the turbocharger. From the turbocharger 10, the air is led via a charging air pipe (not shown) , air cooler (not shown) and scavenge air receiver 9 to the scavenge ports 7 of the cylinder liners 6.
The engine is provided with electrically-driven scavenge air blowers (not shown) . The suction side of the blowers is connected to the scavenge air space after the air cooler. Between the air cooler and the scavenge air receiver non-return valves (not shown) are fitted which automatically close when the auxiliary blowers supply the air. The auxiliary blowers assist the turbocharger compressor at low and medium load conditions. Fuel valves 48 are mounted concentrically in a cylinder cover 12. At the end of the compression stroke the injection valves 48 inject fuel at high pressure through their injection nozzles as a fine mist into the combustion chamber 15. An exhaust valve 11 is mounted centrally in the top of the cylinder in the cylinder cover 12. At the end of the expansion stroke the exhaust valve 11 opens before the engine piston 13 passes down past the scavenge air ports 7, whereby the combustion gases in the combustion chamber 15 above the piston 13 flow out through an exhaust passage 16 opening into an exhaust receiver 17 and the pressure in the combustion chamber 15 is relieved. The exhaust valve 11 closes again during the upward movement of the piston 13. The exhaust valve 11 is hydraulically activated.
Figure 3 shows a first embodiment- of the exhaust valve actuating system according to the present invention. The exhaust valve actuating system is for all of the embodiments illustrated with respect for a single cylinder. In a multi-cylinder engine there will be the same provisions for each cylinder. The exhaust valve actuation system includes the camshaft 28 with exhaust cams 29 with increased lift 30 (only one of each is shown since only one cylinder is illustrated) . A roller 31 follows the surface of the cam 29 and is connected to the piston of a positive displacement pump 32. The positive displacement pump 32 is connected to an exhaust valve actuator 34 via a pressure pipe 36. The positive displacement pump 32, the pressure pipe 36 and the exhaust valve actuator 34 form together a hydraulic pushrod. The exhaust valve actuator 34 is a positive displacement linear actuator is capable of applying a force in the opening direction of the exhaust valve 11. The exhaust valve is also 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 the engine control unit (ECU) .
The additional lift of the exhaust cam 29 is indicated by the hatched area 30. The cam profile of the exhaust cam 29 would only need to extend until the hatched area 34 for providing enough stroke of the positive displacement pump 32 to obtain inadequate opening stroke of the exhaust valve 11. The additional stroke of the positive displacement pump 32 that is created by the additional height of the cam 29 causes the positive displacement pump 32 to have a stroke that exceeds the requirement for sufficiently opening the exhaust valve 11.
The piston of the positive displacement pump 32 is provided with a bore 35 that is in communication with a port 37 during a predetermined portion of the stroke of the piston.
When the pressure in port 37 is lower than the pressure in the pressure chamber of the positive displacement pump 32 a portion of the additional volume of hydraulic fluid generated by the hydraulic piston pump 32 and caused by the increased lift is diverted to port 37.
When the pressure in port 37 is not lower than the pressure in the pressure chamber of the positive displacement pump 32, a portion of the additional volume of hydraulic fluid generated by the hydraulic piston pump 32 and caused by the increased lift of the cam 29 is delivered to the exhaust valve actuator 34 via pressure pipe 36 thereby causing an increased opening stroke of the exhaust valve 11, i.e. an opening stroke that exceeds length of the normally required opening stroke.
The air spring 33 has been adapted to accommodate the increased opening stroke of the exhaust valve 11 and the air spring 33 thereby accumulates and stores the energy that was contained in the portion of the additional volume of hydraulic fluid generated by the increased lift. The air spring 33 can in an embodiment be provided with a progressive characteristic for increasing 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 following return stroke of the exhaust valve 11.
Pressure port 37 is in communication with an intermediate pressure booster 38. Intermediate pressure booster a 38 increases the pressure at port 37 and delivers hydraulic fluid with the increased pressure via conduit 39 to a common high-pressure hydraulic conduit 18 that is connected to all of the cylinders.
The common high-pressure hydraulic conduit 18 is during engine operation kept in a high pressure, e.g. at a level that is set between approximately 200 and 600 bar. At engine startup in the pressure in the common high- pressure hydraulic conduit 18 is generated by an electrically driven pump 9. During engine operation the pressure in the common high-pressure hydraulic conduit 18 is delivered by the intermediate booster (s) 38.
The intermediate booster 38 is provided with two pressure chambers. The first pressure chamber delivers the high pressure hydraulic fluid to the common high-pressure hydraulic conduit 18. The second pressure chamber is connected via conduit 41 to common control pressure conduit 42. The pressure in the common control pressure conduit 42 is kept at approximately 100 to 200 bar and is controlled by the engine control unit (ECU) in the following way. The engine control unit receives a signal representing the pressure in the common high-pressure hydraulic conduit 18. The engine control unit controls a pressure regulating valve 44 that is connected to the pressure control conduit 42 and thereby the engine control unit controls the pressure in the common high- pressure hydraulic conduit 18.
When the engine control unit detects that the pressure in the common high-pressure hydraulic conduit 18 is lower than desired the engine control unit lowers the pressure in the pressure control conduit 42. Thereby, the intermediate booster 38 receives a reduced amount of counterpressure and will deliver an increased amount of high-pressure hydraulic fluid to the common high-pressure hydraulic conduit 18.
When the engine control unit detects that the pressure in the common high-pressure hydraulic control unit is higher than desired the engine control unit increases the pressure in the pressure control unit 42. Thereby, the intermediate booster 38 receives an increased amount of counterpressure and will deliver a reduced amount of high pressure hydraulic fluid 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 booster 38. The intermediate booster 38 is connected to a low- pressure (approximately 3 bar) feeding pressure conduit 43 via conduit 40 replenishing the pressure chamber of the pressure booster 38.
The portion of additional volume of hydraulic fluid that is generated by the extra lift of the exhaust cam 29 that is not that diverted to a consumer of pressurized hydraulic fluid that is associated with the engine fluctuates with differing engine operation conditions. When the engine operates under high load a relatively high amount of fuel needs to be injected for each cycle and only little or no portion of the additional volume of hydraulic fluid is used to create an increased lift of the exhaust valve 11.
When the engine operates under little or medium load conditions, a relatively low amount of fuel needs to be injected for each cycle and a relatively large portion of the additional volume of hydraulic fluid is used to create an increased lift of the exhaust valve 11. The energy that is contained in this non-diverted portion of the additional hydraulic fluid is stored in the gas spring 33 and returned to the camshaft 28 during the closing stroke off the exhaust valve 11.
The pressure in the control pressure conduit 42 acting on the intermediate pressure booster 38 regulates the amount of high-pressure hydraulic fluid that is delivered by the intermediate booster 38 to the common high-pressure conduit 18. Thus, the engine control unit can ensure that the desired pressure is available in the common high-pressure conduit 18 Each cylinder is provided with two or more fuel injection valves 48 that include an injection nozzle. The fuel injection valves 48 receive high pressure fuel from a pressure booster 46. The fuel is typically heavy fuel oil that needs to be heated in order to have a viscosity that is low enough to render it liquid. The pressure booster 46 is driven with the high-pressure hydraulic fluid from the common high-pressure fluid conduit 18. Hereto, the pressure booster 46 is connected to the common high-pressure hydraulic conduit 18 via conduit 45 and proportional valve 49. A hydraulic accumulator 47 is connected to conduit 45 in order to minimize any pressure fluctuations. The proportional valve 49 is electronically or electro-hydraulically controlled by the engine control unit and operates in an as such well-known manner.
Figure 4 is a graph 42 illustrating the exhaust cam lift. The hatched area illustrates the additional lift that exceeds the amount of lift that would be required for normal opening of the exhaust valve 11. Only approximately 60% of the lift is required to open the exhaust valve 11. The reminder of the lift (the hatched are) is used to generate the additional volume of pressurized hydraulic fluid.
Figure 5 is a graph illustrating the exhaust valve lift in operating conditions with a medium engine load, so that a portion of the additional hydraulic fluid generated by the piston pump 32 results in additional lengths of the opening stroke (lift) of the exhaust of 11. The additional opening stroke (lift) of the exhaust valve 11 indicated by the hatched area. Figure 6 is a graph illustrating the opening area in the actuator port 37.
Figure 7 is a graph illustrating the displacement of the intermediate booster 38. Phase A is a delivery face, phase B is an equilibrium face with force/pressure balance and phase C is the return/suction stroke.
Figure 8 illustrates a second embodiment of the invention, which is essentially identical with the first embodiment except that this embodiment is provided with means to add an additional amount of hydraulic fluid from the control pressure conduit 42 to the hydraulic push rod. Further, the cylinder lubricators 52 are operated with hydraulic fluid from the common high-pressure hydraulic conduit 18.
The means for delivering an additional amount of hydraulic fluid to the hydraulic push rod include a conduit 50 that connects the pressure chamber of the piston pump 32 to the common high-pressure hydraulic conduit 18 (or alternatively to the control pressure conduit 42) via a modified version of the proportional valve 49. The proportional valve 49 is in this embodiment provided with two further positions for controlling the flow of hydraulic fluid 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 unit can control the timing and the amount of the hydraulic fluid that is delivered to the hydraulic pushrod. By delivering a controlled amount of hydraulic fluid in a timely manner to the hydraulic pushrod the engine control unit can advance the opening of the exhaust valve 11 to thereby regulate the blowback pressure. Control of cylinder compression pressure is achieved by delivering a controlled amount of hydraulic fluid to the hydraulic pushrod just before closing of the exhaust valve 11 is initiated. The exhaust valve actuating system according to this embodiment offers the possibility for profiling, i.e. changing the timing of the opening of the exhaust valve 11 and changing the timing of the closing of the exhaust valve 11.
The engine control unit is also in command of the cylinder lubrication unit 52 that is operated with high- pressure hydraulic fluid from the common high-pressure hydraulic conduit 18 and delivers cylinder lubrication oil to the cylinder.
Thus, in the second embodiment both the fuel injection system and the cylinder lubrication system are operated with high-pressure hydraulic fluid that has been generated by means of the increased lift of the exhaust valve cam 29.
In other embodiments, (not shown) there could be other (further) hydraulically operated engine components that are driven by the additional volume of hydraulic fluid generated by the additional lift of the camshaft. An example of such another hydraulically operated engine component are the auxiliary blowers, which can be driven by hydraulic motors that receive their hydraulic power from the common high-pressure hydraulic conduit 18. Since the auxiliary blowers are active only during low to medium engine load there will typically a surplus of hydraulic fluid available from the intermediate booster 38, which can be directly used for driving the auxiliary blowers .
The invention has numerous advantages. Different embodiments or implementations may yield one or more of the following advantages. It should be noted that this is not an exhaustive list and there may be other advantages which are not described herein. One advantage of the invention is that it provides for a large two-stroke diesel engine with a flexible and energy-efficient exhaust valve actuation and fuel injection system. It is another advantage of the present invention that it provides for a large two-stroke diesel engine with a flexible electronically controlled fuel injection system that does not require high pressure pumping stations or pumps. It is a further advantage of the invention that mainly high-efficiency components are used for the valve actuation and the fuel injection. It is a further advantage of the invention that it provides excellent redundancy for power supply with proven reliability. It is another advantage of the present invention that existing engines with camshaft operated exhaust valve actuation can be refitted with the system according to the present invention.
The term "comprising" as used in the claims does not exclude other elements. The term "a" oi the claims does not exclude a plurality. Although the present invention has been described in detail for purpose of illustration, it is understood that such detail is solely for that purpose, and variations can be made therein by those skilled in the art without departing from the scope of the invention.
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