HYDRAULIC SUPPLY SYSTEM OF A LARGE TWO-STROKE DIESEL ENGINE

The present application relates to a large two-stroke diesel engine with a hydraulic supply system, in particular to a large two-stroke diesel engine with a hydraulic supply system for providing hydraulic units such as exhaust valve actuators or pressure boosters for the fuel injection valves with high pressure hydraulic fluid.

BACKGROUND OF THE INVENTION

Large two-stroke diesel engines of the crosshead type are complicated machines that include a vast range of systems, such as, lubrication systems, cooling systems, hydraulic systems, pneumatic systems and electronic systems. The lubrication oil system provides various engine components with lubrication oil for lubrication and/or cooling purposes. The lubrication oil of large two-stroke diesel engines is also used as a source of hydraulic fluid for high-pressure hydraulic systems of the engine. In these systems, the purity lubrication oil is ensured by filters that provide the required level of purity for lubrication and cooling purposes in the low to medium pressure lubrication system. The lubrication oil that is transferred from the lubrication will system to the high-pressure hydraulic system is passed through a fine filter to achieve the required purity for the high- pressure hydraulic units. This purity level is substantially higher than the purity level required for lubrication purposes. Return fluid from the high-pressure system is returned to the lubrication system and thus the

full flow of hydraulic fluid that is used by the hydraulic units needs to be fine filtered.

DISCLOSURE OF THE INVENTION

On this background, it is an object of the present application to provide a large two-stroke diesel engine of the crosshead type with an improved oil supply system.

This object is achieved by providing a large two-stroke diesel engine of the crosshead type comprising a plurality of cylinders with an exhaust valve per cylinder, a hydraulic actuator for each exhaust valve for actuating the exhaust valve, a hydraulically driven fuel pressure booster for each cylinder, a low to medium pressure hydraulic system, a closed circuit high pressure hydraulic system for providing the hydraulic actuators and/or hydraulically driven pressure boosters for the fuel injection valves with high pressure hydraulic fluid, and a feed conduit including a flow filter and a feed pump, said feed conduit connecting the low to medium pressure hydraulic system to the closed loop high pressure hydraulic system.

By using a closed loop or closed circuit high-pressure hydraulic system that is fed with fluid from the low to medium pressure that has a purity that is lower than required for the closed loop high-pressure system only a small amount of fluid needs to be fine filtered through an additional filter. After initial filling up the closed loop high-pressure hydraulic system, only the amount of liquid that is needed to compensate for leakage losses in the closed circuit system needs to be fine filtered. This amount is significantly lower than the

amount of fluid that is circulated in the closed loop or closed circuit hydraulic system that needed to be filtered in the prior art systems. Thus, the present invention represents a significant reduction in the fine filtering capacity that is required.

The large two-stroke diesel may further comprise a high pressure hydraulic pump disposed in said closed loop or closed circuit high pressure hydraulic system for generating pressure in said closed loop hydraulic system.

The closed loop high pressure hydraulic circuit may be operated with a purity for the hydraulic fluid higher than the purity of the hydraulic fluid in the low to medium pressure system.

The feed conduit serves to refill said closed loop high pressure hydraulic system with hydraulic fluid to compensate for losses in the closed loop or closed circuit high pressure hydraulic system.

The low to medium pressure hydraulic system may be an engine lubrication oil system that is operated with lubrication oil.

The high pressure hydraulic pump may be cooled with hydraulic fluid from said low to medium pressure hydraulic system.

The high pressure hydraulic pump can be a variable displacement pump with axial pistons and a swashplate and the hydraulic fluid from the low to medium pressure hydraulic circuit for cooling the flowed through the pump housing in which the axial pistons rotate.

The closed loop high-pressure hydraulic system may be provided with a system that continuously or intermittently drains an amount of hydraulic fluid from the closed loop high-pressure system, passes the drained hydraulic fluid through the fine filter and returns the filtered hydraulic fluid to the closed circuit high- pressure hydraulic system.

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, which show:

Fig. 1 a large two-stroke diesel engine with hydraulic and lubrication supply systems according to an embodiment of the invention, Fig. 2 a part of the hydraulic supply system shown in figure 1 in detail, and

Fig. 3 a part of a hydraulic system according to another embodiment .

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Figure 1 shows an engine 1 according to a preferred embodiment of the invention. The engine 1 is a

turbocharged uniflow low-speed two-stroke crosshead diesel engine, which may be a propulsion engine in a ship or a prime mover in a power plant. These engines have typically from 3 up to 14 cylinders in line. The principal construction and operation of such large two- stroke diesel engines is well known and does in the present context not require any further explanation.

Large two-stroke diesel engines of the present kind include many components that are for lubrication and/or cooling purposes supplied with lubrication oil. For example, the crankshaft is placed in an oil pan 3 that is provided in the lower part of the engine 1 and supplied with lubrication oil under pressure that is circulated through the oil pan 3. Other lubrication positions, such as bearings, etc. are separately provided with lubrication oil. The surplus leakage oil is collected in the oil pan 3. The amount of lubrication oil in the oil pan 3 is indicated by the oil sump 4.

A lubrication oil supply loop is provided for supplying lubrication oil to all lubrication oil consumers. The lubrication oil supply loop includes a supply conduit 6 that starts at an oil tank 5 and a return conduit 7 connecting the oil sump 4 to the oil tank 5. The supply conduit 6 includes two low-pressure pumps 8 arranged in parallel with respective drive motors for arranging the oil transport. The supply conduit 6 so includes a cooling device 9 for cooling the lubrication oil and a filter 10 for filtering out contamination. The filter can have a mesh size of 34 or 48 μ. The return conduit 7 is constructed as a non-pressurized return pipe.

The present large two-stroke diesel engine 1 also includes components that are actuated by hydraulic power units. Examples of such components are the fuel injection pressure boosters 11 and the cylinder-piston linear actuator 12 that is associated with each exhaust valve.

These hydraulic power units 11,12 are supplied with high- pressure hydraulic fluid, which is in the present invention taken from the lubrication oil. The hydraulic fluid for the hydraulic power units 11,12 is branched off at connection point 13 at which a feed conduit 14 starts.

These hydraulic power units 11,12 require a contamination level of the hydraulic fluid that is much lower than the contamination level that is acceptable for the lubrication oil in the lubrication system.

Therefore, the feed conduit 14 includes a fine filter 16. Filter 16 is provided with a smaller mesh size than the filter 10, which can thus be considered as a pre-filter. The feed conduit 14 includes a feed pump 18 with an associated drive motor downstream of the filter 16. The outlet of the feed pump 18 is connected to a closed loop high-pressure system via a selection valve 19.

The high pressure closed loop system provides the hydraulic power units 11,12 with high pressure hydraulic fluid that is taken from the engine lubrication system. The closed loop high pressure system circulates the hydraulic fluid and tfie "fluid .delivered by the feed conduit 14 is only needed for the initial filling of the closed loop system and for compensating for leakage losses. Normally leakage losses are relatively low and thus the feed conduit only needs to deliver a small

amount of hydraulic fluid when compared to the flow rate of fluid that is circulated. The filter 16 can correspondingly be dimensioned relatively small since it will only need to clean small amounts of fluid.

The fluid flow in closed loop high pressure hydraulic is driven by a bi-directional variable pressure pump 15 with an associated drive motor that is capable of generating a high pressure, e.g. 300 bar.

Each cylinder of the engine is provided with one or more hydraulically driven pressure boosters 11 and an exhaust valve (not shown) with an associated hydraulic exhaust valve actuator 12 of the type that includes a cylinder with a piston received therein. The pressure boosters 11 include a pressure amplifier (a piston with two different effective areas at its opposing sides) that is driven by the high pressure fluid of the closed circuit high pressure system and the pressure boosters 11 deliver fuel at very high pressure to the fuel injection valves with their injection nozzles. Each cylinder of the engine 1 is provided with one or more fuel injection valves in the cylinder cover that are supplied with very high pressure fuel from the respective pressure booster 11. In an embodiment (not shown) in which the pressure in the high pressure hydraulic closed circuit is high enough to drive the fuel valves without boosting, the pressure booster 11 can be a simple piston with a 1 to 1 boost ratio, i.e. the pressure booster 11 will still fulfill the function of separating the hydraulic oil from the (heavy) fuel oil and the limited stroke of this piston still limits the maximum amount of fuel than can be fed to the cylinder but there is no boost or increase of pressure.

The pressure booster 11 and the exhaust valve actuator 12 of each single cylinder are connected by a hydraulic valve 20 to the closed loop or closed circuit high pressure hydraulic system.

As shown in figure 2, the closed loop high-pressure hydraulic system includes a high-pressure conduit 24, which is operated with the pressure of approximately 300 bar and a low-pressure conduit 26 that is operated with approximately 10 bar. The electromagnetically actuated selection valve 19 can selectively connect the feed conduit 14 to either of the two conduits 24,26 of the closed loop high-pressure hydraulic system. The selection valve 19 is connected to the electronic control unit (not shown) of the engine 1. During initial filling of the closed-circuit high-pressure hydraulic system before engine startup the selection valve 19 connects the outlet of pump 14 to the high-pressure conduit 24. During engine operation the selection valve 19 connects the outlet of pump 14 to the high-pressure conduit 26 to compensate for leakage losses.

The high-pressure conduit is connected to the respective hydraulic valves 20 via a conduits 23. Each conduit 23 is connected to a hydraulic accumulator 29 for equalizing the supply pressure in conduit 23. The low-pressure conduit 26 is connected to the hydraulic valves 20 via conduits 27. The hydraulic valve 20 is a pressure actuated proportional 5/3 way valve. The hydraulic pressure that controls the position of the hydraulic valve 20 is controlled by an electromagnetically actuated control valve ^' 21. The control valve 21 is connected to the electronic control unit (not shown) of the engine 1.

The engine control unit receives signals with information about the operating conditions of the engine 1 including a signal of the crankshaft position and on the basis of this signal and possibly also only basis other engine operating conditions the electronic control unit determines the timing of the fuel injection inclusive rate shaping and the profile of the opening of the exhaust valve by issuing command signals to the respective control valves 21.

The hydraulic valve 20 has three positions of which one is a central neutral position in which neither the pressure booster 11 nor the exhaust valve actuator 12 is pressurized: both hydraulic units are connected to the low-pressure conduit 26. In one of the two other positions the hydraulic valve 20 connects the high- pressure conduit 24 to the pressure booster 11 via conduit 33, whereby the pressure amplifier 35 is pressurized. In this position the exhaust valve actuator 12 is connected to the low-pressure conduit 26 via conduit 31 and 27. In another of the three positions the hydraulic valve 20 connects the high-pressure conduit 24 to the exhaust valve actuator 12 via conduit 31, whereby the pressure chamber above the piston 36 of the exhaust valve actuator 12 is pressurized. In this position the pressure booster 11 is connected to the low-pressure conduit 26 via conduits 33 and 27.

The fuel pressure boosters 11 and the hydraulic actuators 12 are connected to the return conduit 7 to collect leakage oil of these hydraulic units.

The bi-directional variable pressure pump 15 is a variable displacement pump with axial pistons and a

swashplate. In this type of pump the pistons rotate inside a pump housing (these details are not shown but well known for this type of pump) . The bi-directional variable pressure pump 15 is provided with a cooling arrangement. This cooling arrangement includes coolant supply conduit 40 and a coolant return conduit 42. The cooling supply conduit 40 connects the feed conduit 14 upstream or downstream (not shown) of the fine filter 16 to the bi-directional variable pressure pump 15. The cooling supply conduit 14 includes a restriction for 41 to reduce the flow rate at which the coolant is delivered to the bi-directional variable pressure pump 15. Other forms of flow rate reduction/control than a restriction could also be used, for example a flow control valve. The coolant is lubrication oil from the lubrication system and the coolant is flowed through the pump housing of the bi-directional variable pressure pump 15. The coolant leaves the pump housing via a coolant return conduit 42 that connects the pump housing to the return conduit 7. This cooling arrangement causes the pistons of the bidirectional variable pressure pump 15 to be submerged into the lubrication oil. The pistons of the bidirectional variable pressure pump 15 rotate inside the pump housing. Since the pump housing is filled with relatively cool lubrication oil the pistons (and their corresponding cylinders) of the bi-directional variable pressure pump 15 rotate in a bath of cool oil. Due to the rotation of the pistons and their associated cylinders they are exposed to a great amount of surface contact with the cool lubrication oil and the pistons and their cylinders are thereby cooled in a very effective way.

The bi-directional variable pressure pump 15 is thereby kept cool and the hydraulic fluid in the high-pressure closed loop system is cooled when it passes through the bi-directional variable pressure pump 15. Therefore, the system can operate without a separate oil cooler for the closed loop high-pressure hydraulic system.

Figure 3 discloses another embodiment of the closed loop high-pressure hydraulic system according to the invention. This embodiment is essentially identical to the embodiment of figure 2, except that the hydraulic exhaust valve actuators are operated with hydraulic pressure on both sides of piston 36. Thus, the chamber below the piston 36 is permanently connected to the high- pressure conduit 24 via conduits 45. This construction has the advantage that it eliminates the need to provide a pneumatic system with conduits leading to each of the cylinders. Further, the size of the hydraulic piston for driving the return stroke can be significantly smaller than the piston of an air spring since the pressure at which the hydraulic system is operated is significantly higher than that of a pneumatic system.

Further, the low-pressure conduit 26 is provided with a branch conduit 49 that connects the low-pressure conduit 26 to the feed conduit 14. The branch conduit 49 includes a restriction 50. This construction ensures that a small amount of hydraulic oil is constantly drained from the closed loop hydraulic system, passed thought the fine filter 16 and fed back to the closed loop hydraulic system under the action of pump 14, i.e. an off-line filtering of the oil in the closed loop system The action of the feed pump 14 and the selection valve 19 is controlled by the electronic control unit

(not shown) of the engine 1. The filtered oil is returned with the selection valve 19 connecting the outlet of the feed pump 14 to the low pressure conduit 26. The restriction 50 ensures that a small amount of hydraulic oil is continuously drained from the high pressure closed circuit. Alternatively, an electronically controlled valve (not shown) instead of a restriction could periodically drain an amount of hydraulic oil from the closed circuit high-pressure hydraulic system for being filtered though the fine filter 16 and returned to the closed circuit high-pressure hydraulic system.

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 teaching of this application is that it provides for a large two-stroke diesel engine with high-pressure hydraulic system that uses oil from the engine lubrication system that does not require a large filter capacity for the closed loop system. Another advantage of the teaching of this application is that it provides for the closed loop high-pressure hydraulic system for large two-stroke diesel engine that does not require a separate cooling arrangement. It is another advantage of the invention that it creates less drain oil. It is a further advantage of the invention that the high pressure hydraulic system is separated from contamination generated by the engine lubrication system. The contamination generated by the engine can be significant in particular as a result of an engine failure.

Although the teaching of this application 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 teaching of this application.

The term "comprising" as used in the claims does not exclude other elements or steps. The term "a" or "an" as used in the claims does not exclude a plurality. The single processor or other unit may fulfill the functions of several means recited in the claims.