DK177410B1

DK177410B1 - Valve actuation system for a large two stroke diesel engine

Info

Publication number: DK177410B1
Application number: DKPA201000154A
Authority: DK
Inventors: Poul Cenker
Original assignee: Man Diesel & Turbo Deutschland
Priority date: 2010-02-24
Filing date: 2010-02-24
Publication date: 2013-04-02
Also published as: CN102162383B; KR20110097674A; JP5130378B2; CN102162383A; KR101248424B1; JP2011174461A; DK201000154A

Abstract

A valve actuation system for a large two-stroke diesel engine with a valve arrangement that provides for controlled return flow from the pressure pipe (10) that connects the top of the exhaust valve actuator to the electro hydraulic control valve (5) placed on the top of the cylinder housing much below the top of the exhaust valve. Thereby, formation of air pockets and subsequent cavitation can be avoided when the pressure pipe (10) is depressurized without the need of using a pressure booster or separator between the e control valve (5) and the pressure pipe (10)

Description

± DK 177410 B1

VALVE ACTUATION SYSTEM FOR A LARGE TWO STROKE DIESEL ENGINE

5 The present disclosure relates to an electro-hydraulically controlled exhaust valve actuation system for a large two-stroke diesel engine with.

•BACKGROUND OF THE INVENTION

10

Large two-stroke diesel engines are typically used as prime movers in large ocean going ships, such as container ships or in power plants.

15 Electro-hydraulically controlled valve actuation systems in large two-stroke diesel engines allow for flexible operation and profiling of the exhaust valve, allowing improved emission control and fuel efficiency.

20 However, enormous forces are required to open an exhaust valve weighing up to 400 kg against the pressure in the combustion chamber and in the gas spring that urges the exhaust valve in the closing direction. Thus, a high pressure and high power hydraulic system is required for 25 the opening of the exhaust valves of a large tow-stroke diesel engine.

A conventional electronically controlled (electro-hydraulic) exhaust valve actuation system for a large 30 two-stroke diesel engine will include high-pressure pumps delivering a hydraulic fluid (hydraulic oil or lubrication oil) via a common rail to valve blocks located near or on the top plate of the cylinder housing.

The valve blocks carry hydraulic accumulators and 2 DK 177410 B1 proportional electro-hydraulic control valves that control the flow of hydraulic fluid for operating the fuel injectors and the exhaust valves.

5 A pressure pipe connects each of the valve blocks to their respective exhaust valve. The valve blocks are typically placed on the top of the cylinder housing, and thus, the pressure pipes have to bridge a considerable distance and height difference between the valve blocks 10 and the top of the exhaust valve actuator. This difference in height can be several meters.

A pressure booster (basically a piston with a large and a small active surface on either end) is mounted at the top 15 of the valve block. One end of the pressure pipe connects to the pressure booster whilst the other end of the pressure pipe connects to the top of the exhaust valve.

Thus, pressure pipe extends from the valve block to the top of the exhaust valve.

20

Due to the size of these engines the difference in height between the top of the exhaust valve and the valve block can be significant, i.e. several meters.

25 When the exhaust valve is in the closed position the pressure in the pressure pipe should be close to zero.

The pressure booster between the valve block and the lower end of the pressure pipe prevents the hydraulic 30 fluid in the pressure pipe from being drained and avoids that the pressure pipe is filled with air as opposed to hydraulic fluid.

3 DK 177410 B1

When it is time to close the exhaust valve, the electro-hydraulic control valve connects the pressure pipe to tank. Due to the inertia of the exhaust valve air pockets may form in the pressure pipe. These air pockets 5 may result in cavitation when pressure increases again and therefore it is necessary to place a pressure booster or pressure separator between the electro-hydraulic control valve and the pressure pipe.

10 DISCLOSURE OF THE INVENTION

On this background, it is an object of the present application to provide an exhaust valve actuating system that avoids or at least reduces the drawbacks mentioned 15 above.

This object is achieved by providing an exhaust valve actuation system for large two-stroke diesel engine of the crosshead type according to claim 1.

20

By providing a valve arrangement that controls the flow back to tank the formation of air pockets and the occurrence of cavitation are substantially reduced.

25 According to an embodiment, the valve arrangement comprises a fixed flow restriction.

Preferably, the valve arrangement comprises movable valve member in a bore downstream of the fixed flow 30 restriction.

In an embodiment the movable valve member is provided with a first effective pressure surface on one side and a second effective pressure surface on its other side, «j 4 DK 177410 B1 whereby the first effective pressure surface is larger than the second effective pressure surface and the first effective pressure surface faces a first pressure chamber disposed between the first effective pressure surface and 5 the flow restriction and the second effective surface faces a second pressure chamber.

Preferably, said second effective pressure chamber is kept at a relatively low pressure. The pressure in the 10 pressure pipe will migrate towards this pressure.

In an embodiment the first pressure chamber is connected to said second pressure chamber via a bore in said movable valve member.

15

In another embodiment the pressure in the first pressure chamber urges the movable valve member towards a position where the first pressure chamber is connected to an outlet port of the valve arrangement that is connected to 20 tank.

Preferably, the movable valve member defines a control edge together with an edge of a bore in which the movable valve member is received.

25

Further objects, features, advantages and properties of the exhaust valve actuation system according to the present disclosure will become apparent from the detailed 30 description.

5 DK 177410 B1

BRIEF DESCRIPTION OF THE DRAWINGS

In the following detailed portion of the present description, the invention will be explained in more 5 detail with reference to the exemplary embodiments shown in the drawings, in which:

Fig. 1 is a diagrammatic and partially cross-sectional view of the exhaust valve actuation system according to 10 an exemplary embodiment,

Fig. 2 is a diagram illustrating the hydraulic scheme of the valve actuation system shown in Fig. 1, and Fig. 3 is a detailed cross-sectional view of a valve arrangement in the exhaust valve actuation system shown 15 in Fig. 1.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Fig. 1 is a partially cross-sectional view of the exhaust 20 valve actuation system according to an exemplary embodiment of the disclosure. The exhaust valve actuation system is part of a large two stroke diesel engine, such as a large turbocharged uniflow diesel engine of the cross-head type. The construction and operation of large 25 two stroke diesel engines is well known and therefore not described in detail here.

A valve block 3 is mounted on the top plate of the cylinder housing of a large two stroke diesel engine. The 30 valve block carries an electronically controlled proportional hydraulic control valve 5. The electronically controlled proportional hydraulic control valve 5 is connected to an electronic control unit (not shown) of the engine. The valve block 3 also carries one 6 DK 177410 B1 or more accumulators 8 and a valve arrangement 20. One end of a pressure pipe 10 is connected to a port in the valve block 3. The difference in height covered by the pressure pipe 10 can be several meters, and without 5 countermeasures gravity could cause the pressure pipe 10 to be drained and filled with air when the pressure pipe 10 is de-pressurized for allowing the exhaust valve to return to its seat.

10 A bore 7 in the valve block 3 connects the pressure pipe 10 to a port of the proportional hydraulic control valve 5, a bore 11 connects the a valve arrangement 20 to another port of the proportional hydraulic control valve 5 and another bore 9 connects the proportional hydraulic 15 control valve 5 to a source of high pressure which is in this case a common rail.

The other end of the pressure pipe 10 is connected to the top of the exhaust valve housing 12. Only the spindle 14 20 of the exhaust valve is shown in the figures. A hydraulic actuator for opening of the exhaust valve is placed at the top of the spindle 14. The hydraulic actuator includes at least one pressure chamber 16 and one piston 18 and when the hydraulic actuator is pressurized it 25 urges the exhaust valve in the opening direction. An air spring (not shown) is used to urge the exhaust valve in the closing direction in a well-known manner.

Fig. 2 is a diagram illustrating the hydraulic scheme of 30 the valve actuation system shown in Fig. 1. The system includes a high-pressure common rail of 32 that is fed by one or more high pressure pumping stations of the engine.

The high-pressure common rail 32 is kept at a pressure of a couple of hundred bar. There is also a low-pressure 7 DK 177410 B1 common rail 34 that is kept at approximately 2,2 bar. A common rail 36 connects to tank at substantially atmospheric pressure.

5 A conduit 9 (formed by a bore in valve block 3) connects the proportional electro-hydraulic control valve 5 to the high-pressure common rail 32. The proportional electro-hydraulic control valve 5 includes a pilot stage that uses pressure from conduit 9 to move the spool of the 10 proportional electro-hydraulic control valve 5 in a desired position. Conduit 9 as a branch that connects to several hydraulic accumulators 8 that serve to maintain/stabilize pressure when flow rates suddenly increase.

15 A conduit 13 connects an outlet port of the proportional electro-hydraulic control valve 5 that is associated with the fuel injection system to the low-pressure common rail 34. A conduit 11 connects an outlet port of the 20 proportional electro-hydraulic control valve 5 that is associated with the exhaust valve actuation system to the low-pressure common rail 34 via a valve arrangement 20.

The valve arrangement 20 includes a flow restriction, a non-return function and maintains and minimum pressure in 25 conduit 11.

The proportional electro-hydraulic control valve 5 is connected to the fuel injection system 30 with its pressure booster and injectors 37 and the proportional 30 electro-hydraulic control valve 5 is also connected to the exhaust valve actuator. The fuel injection system is as such well known and will not be described in greater detail here.

p DK 177410 B1

The hydraulic diagram shows the pressure pipe 10 connected to the exhaust valve actuator housing 12 with a piston 18 airs ping the exhaust valve spindle 14. A source of pressurized air 19 also connects to the exhaust 5 valve housing 12 for supplying the pressurized air for the air spring that urges the exhaust valve in the closing direction. Further, a position sensor that determines the position of the exhaust valve is associated with the exhaust valve actuator.

10

During engine operation the proportional electro-hydraulic control valve 5 is commanded by the electronic control unit of the engine to connect either the exhaust valve actuation system or the fuel injection system to 15 the high-pressure common rail at appropriate times in the engine cycle. Thus, when it is time to open the exhaust valve the electronic control unit of the engine will command the proportional electro-hydraulic control valve 5 to establish a connection between the high pressure 20 common rail 32 and the pressure pipe 10. Thereupon, the exhaust valve will open against the pressure in the combustion chamber and against the force of the air spring. When it is time to close the exhaust valve again the electronic control unit will command the proportional 25 electro-hydraulic control valve 5 to connect the pressure pipe 10 to the low-pressure common rail 34 via valve arrangement 20. The exhaust valve and the exhaust valve actuator associated therewith have a considerable inertia and the closing of the exhaust valve will be much slower 30 than the pressure drop in the pressure pipe 10 if the pressure pipe 10 and was directly connected to tank when the proportional electro-hydraulic control valve 5 established the connection. The valve arrangement 20 includes a flow restriction that assures that the 9 DK 177410 B1 pressure drop is not too rapid and the valve arrangement 20 will maintain a minimum pressure on its upstream side. Thereby, it is avoided that the pressure in the pressure pipe 10 will drop too rapid and too low. This will avoid 5 the formation of air pockets in the pressure pipe 10 and will avoid subsequent cavitation.

Fig. 3 shows the valve arrangement 20 in greater detail.

In this exemplary embodiment the valve arrangement 10 includes a housing with a through going bore. The valve arrangement 20 includes a fixed flow restriction 21 disposed at or near the inlet port of the valve arrangement 20 at one end of the through going bore. The inlet port of the valve arrangement 20 can be connected 15 to the proportional electro-hydraulic control valve 5 via a bore 11.

A movable valve member 22 with a substantially cylindrical body is slidably received in the through 20 going bore. The movable valve member 22 is provided with a pressure surface on each end. A first pressure surface is disposed on the side of the movable valve member 22 that faces the inlet port and the flow restriction 21. A first pressure chamber 23 is formed in the bore between 25 the flow restriction 21 and the first pressure surface.

The second pressure surface is disposed on the opposite side of the movable valve member 22. The second pressure surface faces a second pressure chamber 25, also disposed 30 in the through going bore. The second pressure chamber is connected to a source of relatively low pressure, such as the low pressure common rail 34.

10 DK 177410 B1

The diameter of the through going bore is larger in the section where it forms the first pressure chamber than in the section where it forms the second pressure chamber.

Thus, the effective surface of the first pressure surface 5 is larger than the effective surface of the second pressure surface. The movable valve member 22 is provided with a bore 26 that connects the first and second pressure chambers. The diameter of the bore 26 is relatively small so that throttles the flow between the 10 two pressure chambers.

An outlet port 27 connects tank 36. The outlet port 27 is closed off by the movable valve member 22 in a range of positions of the movable valve member 22 and open in 15 another range of positions of the movable valve member 22 to thereby connect the first pressure chamber to said outlet port 27. In the range of open positions of the movable valve member 22 the first pressure chamber 23 is connected to outlet port 27.

20

With reference to the orientation of the valve arrangement in Fig. 3, the movable valve member 22 closes off the connection between the first pressure chamber 23 and the outlet port 27 when the movable valve member 22 25 is in its lower range of positions and opens up for connection between the first pressure chamber 23 and the outlet port 27 when the movable valve member 22 is in its upper range of positions.

30 The larger first effective pressure area urges the movable valve member 22 towards the range of positions where the outlet port 27 is connected to the first pressure chamber 23 and the smaller second effective pressure area urges the movable valve member 22 towards λ1 DK 177410 B1 the range of positions where the connection between the first pressure 23 chamber and the outlet port 27 is closed.

5 The movable valve member 22 is provided with a side bore 28 that connects to an overflow port 29 in the housing of the valve arrangement 20 when said movable valve member 22 is moved upwards (upwards with reference to the orientation of the valve arrangement in Fig. 3) to a 10 large extent so that the side bore 28 overlaps with the overflow port 29. Thus, the second pressure chamber 25 is connected to tank 34 thereby allowing the movable valve member 22 open up completely the output port 27 to relieve pressure in the first pressure chamber 23 during 15 pressure peaks in the latter pressure chamber.

When there is no flow though the restriction 21 into the first pressure chamber the pressure in the latter chamber is lower than the pressure in the second pressure chamber 20 by a factor that is equal to the ratio between the size of the effective pressure surfaces. Thus, when the pressure is for example 2.2 bar in the second pressure chamber the pressure could be 1.5 bar in the first pressure chamber. When the proportional electro-25 hydraulic control valve 5 connects the pressure pipe 10 to the valve arrangement 20, there will be a substantial flow through the restriction 21 and the pressure in the first pressure chamber will become high enough to urge the movable valve member 22 towards a position where a 30 connection between the first pressure chamber 21 and the outlet port 27 is established so that hydraulic fluid can be evacuated to tank. The position of the movable valve member 22 will be balanced between the pressure in the pressure chambers.

12 DK 177410 B1

The position of the valve 22 is decided by the following forces. The first effective pressure area at the first pressure chamber 23 x pressure in the first pressure 5 chamber 23 against second effective valve area in the second pressure chamber 25 x pressure in the second pressure chamber 25. When exhaust valve is closed, the pressure in the second pressure chamber 25 is about 2 bar. The force balancing pressure in the first pressure 10 chamber 23 can be 1,5 bar. The pressure difference between the first pressure chamber 23 and the second pressure chamber 25 will lead to a fluid flow through orifice 26, into the first pressure chamber 23.

15 A pressure increase in the first chamber 23 will move the valve member 22 upward and the increased opening to the outlet port 27 will limit the pressure again to the value balancing the forces acting on the movable valve member 22.

20

Thus, the flow through orifice 26 will be the same as the flow from chamber 23 to outlet port 27. The opening area from the first pressure chamber 23 to the outlet port 27 will be a flow through the orifice 26 at dP (the pressure 25 difference) between the first pressure chamber 23 and the second pressure chamber 25. The moveable valve member 22 will thus "float" and adapt its position to the operating conditions.

30 This balance in combination with the flow restrictor 21 will provide for a suitable flow rate and maintain an overpressure upstream of the valve arrangment (i.e. in the pressure pipe if the valve arrangement is used in an exhaust valve actuation system) . These effects ensure 13 DK 177410 B1 that the flow rate is controlled and that there is no ingress of air.

The exhaust valve actuation system has been described 5 with reference to a single cylinder of a large two-stroke diesel engine. In a multi-cylinder engine such an exhaust valve actuation system has to be provided for each cylinder (or at least for each exhaust valve), except for the common rails that can be used for a 10 plurality of cylinders.

The teaching of this disclosure has numerous advantages. Different embodiments or implementations may yield one or more of the following advantages. It should be noted that 15 this is not an exhaustive list and there may be other advantages which are not described herein. One advantage of the teaching of this disclosure is that it provides for an exhaust valve actuation system that can do without a pressure booster or separator at the bottom of the 20 pressure pipe. It is another advantage of the teaching of this disclosure that it provides for a valve arrangement that allows return to tank at controlled conditions thereby avoiding creation of air pockets and cavitation.

It is yet another advantage of the teaching of this 25 disclosure that it provides for an exhaust valve actuation system that allows a pressure booster for the hydraulic exhaust valve actuator to be located at the top of the exhaust valve. It is another advantage of the present disclosure that it provides for a valve 30 arrangement that can take the function of a check valve in harsh environments where conventional check valves that operate with a valve member that abuts with a seat cannot be used.

14 DK 177410 B1

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 5 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 10 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.

Claims

An actuator system for exhaust valve for large two-stroke diesel engine of the crosshead type comprising: a hydraulic actuator suitable for mounting 10 on top of an exhaust valve for the large two-stroke diesel engine and which hydraulic actuator is configured to move the exhaust valve in the opening direction 15, a pressure tube (10) connecting the hydraulic actuator to a hydraulic control valve (5) located at a substantial distance from and below the hydraulic actuator, 20 which hydraulic control valve (5) has a position for bringing the pressure tube ( 10) in direct fluid communication with a source of a high-pressure fluid (32) for moving the exhaust valve to an open position, and which hydraulic control valve (5) has a second position for bringing the pressure tube (10) into contact with the tank (36) via a valve system (20) to enable the exhaust valve to close and remain on its seat, characterized in that the valve assembly (20) is connected shown to throttle the flow back to the tank (36) and to maintain a minimum pressure on the upstream side of the valve assembly (20).

Exhaust valve actuating system according to claim 1, wherein the valve device comprises a fixed flow restriction (21).

2 DK 177410 B1

3 DK 177410 B1 (23) is connected to an outlet opening (27) in the valve device which is connected to the tank.

Exhaust valve actuating system according to claim 2, wherein the valve device (20) comprises a movable valve member (22) in a downstream bore of the fixed flow constraint (21).

Exhaust valve actuating system according to claim 3, wherein the movable valve member (22) has a first effective pressure surface on one side and a second effective pressure surface on its other side, the first effective pressure surface being larger than the second effective pressure surface and the first the effective pressure face faces a first pressure chamber (23) located between the first effective pressure face and the flow restriction (21), and the second effective face faces a second pressure chamber (25). 20

Exhaust valve actuation system according to claim 4, which exhaust valve actuation system is configured to hold the second effective pressure chamber at a relatively low pressure. 25

Exhaust valve activation system according to claim 5, wherein the first pressure chamber (23) is connected to the second pressure chamber (25) via a bore (26) in the movable valve member (22). 30

Exhaust valve actuating system according to claim 6, wherein the first pressure chamber (23), when pressurized, is configured to force the movable valve member (22) in a position where the first pressure chamber

Exhaust valve actuation system according to claims 1, 5, wherein the movable valve member (22) defines a guide edge together with an edge of a bore in which the movable valve member (22) is received.

Exhaust valve actuation system according to claim 3, 10, wherein an air spring is configured to force the exhaust valve in the closing direction.