DK177695B1

DK177695B1 - A large slow running turbocharged two-stoke uniflow internal combustion engine with crosshead and a cam driven exhaust valve actuation system

Info

Publication number: DK177695B1
Application number: DK201200723A
Authority: DK
Inventors: Erik Due Pedersen; Kim Jensen; Daniel Jarnekrans
Original assignee: Man Diesel & Turbo Deutschland
Priority date: 2012-11-16
Filing date: 2012-11-16
Publication date: 2014-03-17
Also published as: CN103821622A; JP2014101878A; KR20140063471A; KR101438189B1; CN103821622B; JP5762495B2

Abstract

A large slow running multi cylinder turbocharged twostroke uniflow internal combustion engine (1) with cylinders with at least one exhaust valve (11), a least one camshaft (28) provided with exhaust cams (29) and a hydraulic push rod associated with the exhaust valve (11) of each of the cylinders (6), the engine is provided a device (50) configured for selectively adding a volume of hydraulic fluid to the hydraulic fluid in the hydraulic piston rod during the period where the closing flank (73) of the exhaust cam (29) is active for extending the opening time of the exhaust valve (11) and the device (50) is configured for removing the volume of hydraulic fluid that was added to the hydraulic piston rod from the hydraulic piston rod with a certain delay after the moment that the closing flank (73) has stopped being active for allowing the exhaust valve (11) to return to its seat (18) with a delay relative to the cam profile.

Description

i DK 177695 B1

A LARGE SLOW RUNNING TURBOCHARGED TWO-STROKE UNIFLOW INTERNAL COMBUSTION ENGINE WITH CROSSHEADS AND A CAM DRIVEN EXHAUST VALVE ACTUATION SYSTEM

5 FIELD OF THE INVENTION

The present invention relates to large slow running turbocharged two-stroke internal combustion engines with crossheads and a cam driven exhaust valve actuation 10 system.

BACKGROUND OF THE INVENTION

Large slow running turbocharged two-stroke internal 15 combustion engines with crossheads are engines with at least one cylinder and a reciprocating piston received therein. These engines have a crosshead disposed between the piston and the crankshaft. A combustion chamber is defined between the piston, the inner cylinder wall and 20 by a cylinder cover at one end of the cylinder. The cylinder cover includes an exhaust valve that is controllably and intermittently openable in order to expel combustion residues from the combustion chamber to an exhaust duct system. These engines also have means for 25 intermittently establishing an opening in the combustion chamber near the cylinder's second end prior to a combustion therein, for scavenging towards the first end by introduction through the opening of pressurized scavenge air comprising oxygen, and these engines 30 comprise means for fuel injection into the compressed scavenge air for internal combustion in the combustion chamber.

2 DK 177695 B1

Engines in accordance with the above definition are often referred to as "large turbocharged 2-stroke uniflow crosshead diesel engines", and are often embodied with a plurality of standing cylinders in line, their pistons 5 working on a single crankshaft; These engines can have a pure two-stroke working sequence and are normally of large physical size regarding cylinder diameter and piston stroke, often making such an engine as high as a house, in order to deliver at relatively low rotational 10 speed (approximately 80 rpm to 200 rpm) multiple megawatts of power for driving power plant generators or for propulsion of sea vessels in the MW+ range.

The desire for improved performance, energy efficiency 15 and reduced emissions has led to the development of common rail electro-hydraulically controlled exhaust valve actuation systems for these large two-stroke diesel engines. An advantage of these systems is their increased flexibility since the timing of the closing and opening 20 of the exhaust valve can be freely chosen to match the operating conditions of the engine. However, these common rail electrohydraulic systems are relatively expensive and consume more energy than conventional cam driven systems since more energy than required is consumed 25 during the opening process and without recovery during the closing process. These two drawbacks annihilate many of the advantages of the electronically controlled engine .

30 JP 2009203865 discloses a large two-stroke diesel engine with a camshaft driven exhaust valve actuating system of the type that uses a hydraulic pushrod. The hydraulic pushrod is connected to a volume control device that under command from an electronic control unit can absorb 3 DK 177695 B1 a volume of hydraulic fluid from the hydraulic pushrod.

The volume control device comprises a resiliently biased control piston that defines a volume control chamber. The characteristic of control piston can be influenced by the 5 electronic control unit via a hydraulic valve that selectively connects control chambers defined by the control piston to hydraulic accumulators. This system for flexibly controlling the timing of the opening and closing of the exhaust valve provides a solution large 10 two-stroke diesel engines with a camshaft operated exhaust valve actuation system. However, this solution is relatively complicated, reguires precise control, is not free of pressure peaks and still uses a significant amount of energy to establish the flexible timing for the 15 exhaust valve.

DE 10 2008 033 766, discloses an apparatus for variable control of gas exchange valves with a cam that has an opening flank, a closing flank and base diameter on a 20 camshaft and a hydraulic pushrod between the cam and the gas exchange valve. The gas exchange valve is biased to its closed position by a helical spring. An apparatus comprising a hydraulic accumulator and a throttling valve subjected to an electromagnetic field for changing the 25 viscosity of the fluid in the throttling valve is connected to the hydraulic push rod so as to remove a volume of hydraulic fluid from the hydraulic piston rod during the period where the opening flank is active. The removed amount of fluid is returned to the hydraulic push 30 rod before the active period of the closing flank ends and thus the gas exchange valve returns to its seat before or when the closing flank ends.

DISCLOSURE OF THE INVENTION

4 DK 177695 B1

On this background, it is an object of the present invention to provide large slow running turbocharged two-stroke internal combustion engines with crossheads and a 5 flexible but cam driven exhaust valve actuation system that is relatively simple and uses little energy.

This object is achieved by providing a large slow running multi-cylinder turbocharged two-stroke uniflow internal 10 combustion engine with crossheads, the engine comprising: a plurality of cylinders with at least one exhaust valve and one exhaust valve seat per cylinder, the exhaust valve being configured to be movable between a closed 15 position where it rests on the seat and an open position, a pneumatic spring associated with each exhaust valve, the pneumatic spring being arranged to bias the exhaust valve associated therewith in a closing direction towards 20 and onto the valve seat, at least one camshaft provided with exhaust cams, the exhaust cams being provided with a cam profile for actuating the exhaust valve associated with the exhaust 25 cam concerned, the cam profile including an opening flank, a closing flank, a dwell segment connecting the opening flank to the closing flank and a base diameter segment connecting the 30 closing flank to the opening flank, a hydraulic push rod associated with the exhaust valve of each of the cylinders, 5 DK 177695 B1 the hydraulic push rod comprising a hydraulic piston pump, the hydraulic piston pump comprising a pump piston driven 5 by an exhaust cam of the camshaft, a hydraulic actuator including an actuation piston acting on the exhaust valve for moving the exhaust valve concerned in an opening direction, and 10 a hydraulic conduit connecting the hydraulic piston pump with the hydraulic actuator, and hydraulic fluid in the hydraulic push rod between the pump piston and the actuation piston, 15 the engine further comprising a device configured for selectively adding a volume of hydraulic fluid to the hydraulic fluid in the hydraulic piston rod during the period where the closing flank is active for extending 20 the opening time of the exhaust valve and the device being configured for removing the volume of hydraulic fluid that was added to the hydraulic piston rod from the hydraulic piston rod with a certain delay after the moment that the closing flank has stopped being active 25 for allowing the exhaust valve to return to its seat with a delay relative to the closing moment as defined by the cam profile.

The pneumatic spring is configured to be sufficiently 30 "strong" or "stiff" to avoid the cam roller jumping-off the cam during deceleration at the end of the opening stroke. Thus, the pressure in the hydraulic push rod during the dwell phase is high since the pneumatic spring is fully compressed. This means that adding hydraulic 6 DK 177695 B1 fluid during the dwell phase requires a high pressure and accordingly a large amount of energy that is lost when the volume of hydraulic fluid is removed from the hydraulic push rod unless a special arrangement is 5 provided for storing the energy in the volume of hydraulic fluid that is removed, like in the relatively complicated solution in the prior art. When the closing flank is active the pressure in the hydraulic push rod falls significantly and by adding the volume of hydraulic 10 fluid during this phase the additional volume can be added at a substantially lower pressure, which requires substantially less energy so that a complicated energy storage system is not required.

15 In an embodiment compression of the pneumatic spring causes a dwell pressure in the hydraulic fluid in the hydraulic push rod when the exhaust valve dwells in its open position and the dwell segment of the exhaust cam is active, and wherein the device is configured to urge the 20 volume of hydraulic fluid into the pushrod with a pressure that is lower than the dwell pressure.

By urging the volume of hydraulic fluid to be added with a certain pressure that corresponds to a pressure in the 25 hydraulic push rod during the exhaust valve closing phase, the flow into the hydraulic push rod starts smoothly, thereby avoiding pressure oscillations in the system.

30 In an embodiment the device comprises a regulation piston having a stroke between a fully retracted position and a fully extended position with a regulation chamber at one side of the regulation piston, the regulation chamber being in fluid communication with the hydraulic fluid in 7 DK 177695 B1 the hydraulic push rod, and an electronically controlled actuating system acting on the regulation piston, the electronically controlled actuating system being configured to start to urge the regulation piston from 5 the fully retracted position to the extended position from a point in time during the period where the dwell segment is active and with a force that corresponds to a pressure in the regulating chamber that is lower than the dwell pressure so that the regulation piston does not 10 start to move towards its extended position before the pressure in the hydraulic fluid in the hydraulic push rod has fallen below the dwell pressure due to the closing flank becoming active.

15 By allowing the regulation piston to start from its fully retracted position it becomes possible to urge the regulation piston with a force that is substantially lower than the force required to overcome the dwell pressure without any risk that hydraulic fluid flowing 20 backwards.

In another embodiment the electronically controlled actuating system is configured to start urging the regulation piston from its fully retracted position 25 towards its extended position during the period where the dwell segment is active, and the electronically controlled actuating system is configured to continue to urge the regulation piston towards its extended position until the certain delay has elapsed and thereafter to 30 urge or allow the regulation piston to move back to its fully retracted position.

Thus, the timing of the start of the flow of hydraulic fluid to the hydraulic piston rod regulates itself 8 DK 177695 B1 automatically and complicated and accurate control systems are not required. Further, this feature ensures a soft start of the flow into the hydraulic rush rod and harmful pressure peaks are thus avoided.

5

In an embodiment the regulation piston is connected to an extension piston for urging the regulation piston towards its extended position and the regulation piston is connected to a return piston for urging the regulation 10 piston towards its retracted position.

In an embodiment the extension piston has an operating chamber associated therewith and wherein the operating chamber is connected to an electronically controlled 15 hydraulic valve that connects the operating chamber either to a source of pressure or to tank.

In an embodiment the device comprises the extension piston, the return piston and the electronically 20 controlled hydraulic valve.

In an embodiment the electronically controlled valve is connected to an electronic control unit.

25 In an embodiment the return piston has a smaller diameter than the extension piston and wherein the return piston has an operating chamber associated therewith that is continually connected to the source of pressure. Thus the control system can be kept simple.

30

In an embodiment the engine further comprises a position sensor indicative of the angular position of the crankshaft or of the camshaft and wherein the electronically controlled hydraulic valve is activated to 9 DK 177695 B1 delay the closing of the exhaust valve by a controlled delay on the basis of a conversion map that is based on a desired compression pressure to scavenging pressure ratio map .

5

In an embodiment the electronic control unit is configured to instruct the electronically controlled valve to connect the operating chamber to tank with a certain delay after the moment that the closing flank has 10 stopped to be active so that the exhaust valve returns to its seat and the regulation piston returns to a seat that coincides with its retracted position.

The object above is also achieved by providing a method 15 for operating a large slow running multi-cylinder turbocharged two-stroke uniflow internal combustion engine with crossheads, the engine comprising: a plurality of cylinders with at least one exhaust valve 20 and one exhaust valve seat per cylinder, a pneumatic spring associated with each exhaust valve, the pneumatic spring being arranged to bias the exhaust valve associated therewith in a closing direction towards 25 and onto the valve seat, at least one camshaft provided with exhaust cams, the exhaust cams being provided with a cam profile for actuating the exhaust valve associated with the exhaust 30 cam concerned, a hydraulic push rod associated with the exhaust valve of each of the cylinders for transmitting the cam profile to the exhaust valve, 5 10 DK 177695 B1 the hydraulic push rod containing a hydraulic fluid, the exhaust valves having an operating sequence controlled by the cam profile, the cam profile including an opening flank, a closing flank, a dwell segment connecting the opening flank to the closing flank and base diameter segment connecting the closing flank to the opening flank, the bias of the 10 air spring causing a given predetermined dwell pressure in the hydraulic fluid in the hydraulic push rod during the dwell period, the method comprising: adding an amount of hydraulic fluid to the hydraulic fluid in the hydraulic push rod during the period that the closing 15 flank is active with a pressure that is lower than the pressure that is present in the volume of hydraulic rod during the dwell period, and removing the amount of hydraulic fluid from the volume of hydraulic fluid in the hydraulic push rod with a certain delay after the moment 20 that the closing flank has stopped being active.

In an embodiment of the method the amount of fluid is added by a regulation piston having a stroke between a fully retracted position and a fully extended position 25 with a regulation chamber at one side of the regulation piston, and the regulation chamber being in fluid communication with the hydraulic fluid in the hydraulic push rod, the method comprising urging the regulation piston from the fully retracted position towards the 30 fully extended position from a point in time during the period where the dwell segment is active with a force on the regulation piston that should result in a pressure in the regulation chamber that is lower than the dwell pressure, so that the regulation piston does not start to 11 DK 177695 B1 move towards its extended position before the pressure in the hydraulic fluid in the hydraulic push rod has fallen below the dwell pressure due to the closing flank becoming active.

5

In an embodiment of the method the point in time where for starting to remove the amount of hydraulic fluid from the volume of hydraulic fluid in the hydraulic push rod is determined on the basis of a signal indicative of the 10 angular position of the crankshaft.

In an embodiment of the method the point in time where for starting to remove the amount of hydraulic fluid from the volume of hydraulic fluid in the hydraulic push rod 15 is used to control compression pressure in the combustion chamber of the cylinder concerned.

Further objects, features, advantages and properties of the large slow running turbocharged two-stroke internal 20 combustion engines with crossheads and a cam driven exhaust valve actuation system and method according to the invention will become apparent from the detailed description .

25 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 30 in the drawings, in which figure 1 is a cross-sectional view of an engine according to an exemplary embodiment of the present invention, figure 2 is a longitudinal-sectional view of one cylinder section of the engine shown in figure. 1, 12 DK 177695 B1 figure 3 is a detailed cross sectional view of the top of the engine shown in figure 1, this view showing an exemplary embodiment of the exhaust valve and the exhaust valve actuation system, 5 figure 4 is a sectional view of the exhaust valve, the hydraulic piston rod, the camshaft and the device for selectively adding a volume of hydraulic fluid to the hydraulic fluid in the hydraulic piston rod of the engine shown in Figure 1, 10 figure 5 is a sectional view of a detail of figure 4 showing an exemplary embodiment of a device for extending the opening time of the exhaust valve relative to the cam profile, figure 6 is a symbolic representation of an exemplary 15 embodiment of the exhaust valve actuating system of the engine shown in figure 1, figure 7 is a detailed view of an exemplary embodiment of a cam profile, figure 8 shows a graph of the valve lift profile of the 20 engine shown in figure 1 with conventional cam driven valve actuation, figure 9 shows a graph of the valve lift profile of the engine shown in figure 1 with conventional cam driven valve actuation and the device for extending the opening 25 time of the exhaust valve relative to the cam profile being active, figure 10 shows a detail focusing on the exhaust valve closing profile of the graph shown in figure 10, and figure 11 shows a graph of figure 9 that also shows the 30 pressure of the hydraulic fluid in the exhaust valve actuator and in the hydraulic push rod.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

13 DK 177695 B1

Figures 1 and 2 show an engine 1 according to an exemplary embodiment of the invention in cross-sectional view and longitudinal-sectional view (for practical reasons only a section of the length of the engine 5 covering one cylinder is shown, but is understood that there will be at least four cylinders in an engine) 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 10 mover in a power plant. These engines have typically from four up to fourteen cylinders in line. The engine may e.g. be used as the main engine in an ocean-going vessel or as a stationary engine for operating a generator in a power station. The total output of the engine may, for example, 15 range from 5,000 to 110,000 kW.

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-20 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 25 with bearing supports. The cross girders are in the art also referred to as "transverse girders". The oil pan 43 welded to the bottom of the bedplate 2 and collects the return oil from the forced lubricating and cooling oil system.

30

The connecting rods 8 connect the crankshaft 3 to the crosshead bearings 22. The crosshead bearings 22 are guided between vertical guide planes 23.

14 DK 177695 B1 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 5 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.

10 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 15 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 5.

20 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 25 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 penetrating into the space of the frame box 4 and the 30 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 15 DK 177695 B1 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 5 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.

10 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 15 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 20 air receiver 9 (Fig. 1), is supplied with scavenge air pressurized by a turbocharger 10 (Fig. 1).

The engine 1 is fitted with one or more turbochargers 10 arranged on the aft end of the engine for 4-9 cylinder 25 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 30 (not shown) 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.

16 DK 177695 B1

The engine 1 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 5 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.

10 Fuel valves 40 are mounted concentrically in a cylinder cover 12. At the end of the compression stroke the injection valves 40 inject fuel at high pressure through their injection nozzles as a fine mist into the combustion chamber 15. An exhaust valve 11 is mounted 15 centrally in the top of the cylinder in the cylinder cover 12 and rests when it is closed on a valve seat 18 that is provided in the top plate of the cylinder liner 6 concerned. At the end of the expansion stroke the exhaust valve 11 opens before the engine piston 13 passes down 20 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 gas receiver 17 and the pressure in the combustion chamber 15 is relieved. The exhaust valve 11 25 closes again during the upward movement of the piston 13.

The exhaust valves 11 are actuated by a hydraulic push rod that connects each exhaust valve 11 to a respective exhaust cam 29 on the camshaft 28. An air spring 38 ensures that the exhaust valve follows the closing flank 30 on the exhaust cam 29 and returns to the valve seat 18.

Figures 3 to 7 illustrate an example embodiment of the exhaust valve actuating system according to the present invention. The exhaust valve actuating system is for all 17 DK 177695 B1 of the embodiments illustrated with respect to a single cylinder. In a multi-cylinder engine there will be the same provisions for each cylinder, though with a single camshaft 28 that carries multiple exhaust cams 29. The 5 exhaust valve actuating system includes the camshaft 28 with multiple cams 29 (only one is shown) . A roller 30 follows the surface of the cam (cam profile) and is connected to the piston 32 of a piston pump 31. The piston pump 31 is connected to an exhaust valve actuator 10 34 via a conduit 36. The exhaust valve actuator 34 is mounted on the top of the exhaust valve 11 and includes a actuation piston 35 that acts on the top of the stem of the exhaust valve 11. A gas spring 38 is also connected to the stem of the exhaust valve 11 and the gas pressure 15 in the pressure chamber of the gas spring 38 urges the exhaust valve 11 in the closing direction and onto its seat 18. The gas spring 38 is configured to be stiff enough to ensure that the roller 30 stays in contact with the closing flank 73 on the surface of the cam profile.

20

The operational connection between the cam 29 and the exhaust valve 11 is called a hydraulic push rod. The hydraulic push rod includes the hydraulic piston pump 31, the hydraulic actuator 34 including an actuation piston 25 35 acting on the exhaust valve 11 for moving the exhaust valve and the hydraulic conduit 36 connecting the hydraulic piston pump 31 with the hydraulic actuator 34, and hydraulic fluid in the hydraulic push rod between said pump piston 32 and said actuation piston 35.

30

When the valve actuator 34 is pressurized it urges the exhaust valve 11 in the opening direction. The position of the exhaust valve 11 is measured by the sensor (not shown) that is connected to an electronic control unit 90 18 DK 177695 B1 of the engine. In operation, the camshaft 28 rotates in unison with the crankshaft 3. The profile of the cam 29 determines the movement of the piston pump 31 and the cam profile includes an opening flank 71, a closing flank 73, 5 a dwell segment 72 connecting the opening flank 71 to the closing flank 73 and a base diameter segment 70 connecting the closing flank 73 to the opening flank 71.

The camshaft 28 rotates in the direction indicated by the 10 arrow A. The transition between the base segment 70 and the opening flank 71 is marked by interrupted line I. The transition between opening flank 71 and the dwell segment 72 is marked by interrupted line II. The transition between the dwell segment 72 and the closing flank 73 is 15 marked by interrupted line III and the transition between the closing flank 73 and the base segment 70 is marked by interrupted line IV. The camshaft 28 rotates in the direction indicated by the arrow A and the opening flank 71 is active after the base segment 70, the dwell segment 20 72 is active after the opening flank 71, the closing flank 73 is active after the dwell segment 72 and the base segment 70 is active after the closing flank 73. Corresponding interrupted lines are shown in figure 8 that shows a graph of the opening profile of the exhaust 25 valve 11 as defined by the cam profile.

In the period that the base segment 7 0 is active the exhaust valve 11 rests on its seat and the pressure in the hydraulic push rod is at a low level since the gas 30 spring 38 is not much compressed. This period is referred to in figure 8 that shows a graph with the opening profile of the exhaust valve 11 purely based on the cam profile as the seated period between interrupted lines IV and I. In the period that the opening flank 71 is active 19 DK 177695 B1 the exhaust valve 11 moves from its closed position on its seat 18 to its open position and the pressure in the hydraulic push rod increases to a high level due to increasing compression of the gas spring 38. This period 5 is referred to in figure 8 as the opening period between interrupted lines I and II. In the period where the dwell segment 72 is active the pressure in the hydraulic push rod is substantially constant (except for at the start of this period (see figure 11)) and at the high level 10 because the gas spring 38 is fully compressed. This period is referred to in figure 8 as the dwell period between interrupted lines II and III. In the period where the closing flank 73 is active the pressure in the hydraulic push rod decreases from the high level to the 15 low level. This period is referred to in figure 8 as the closing period between interrupted lines III and IV.

The pressure of the hydraulic fluid is not only determined by the effect of the gas spring 38; 20 acceleration and deceleration of masses involved also have an influence, as can be seen in figure 11, but overall the pressure development is as described above.

When the positive displacement pump piston 32 moves 25 upwards, a hydraulic fluid is forced into the valve actuator 34 via conduit 36. The actuator 34 forces the exhaust valve 11 to open against the pressure in the combustion chamber and in the gas spring 38. When the positive displacement pump piston 32 moves downwards, the 30 gas spring 38 urges the exhaust valve 11 and the exhaust valve actuator 34 to move upwards and thereby the fluid in the exhaust valve actuator 34 flows back to the positive displacement pump 31. Most of the energy that was transferred to the exhaust valve actuator 34 during 20 DK 177695 B1 the opening movement of the exhaust valve 11 was stored in the gas spring and is returned to the camshaft 28 by the pressure that is created in the positive displacement pump 31 during the return stroke of the exhaust valve 5 actuator 34. Thus, only a small portion of the hydraulic energy that is needed to open the exhaust valve 11 is dissipated.

The exhaust valve actuation system according to the 10 present embodiment includes a device 50 for adding a volume of fluid to the hydraulic push rod and for removing the added volume again. The volume of hydraulic fluid is added to the hydraulic push rod with the purpose of delaying the moment that the exhaust valve 11 closes 15 (rests with its head on seat 18) relative to the closing moment defined by the cam profile (the closing moment defined by the cam profile corresponds to the position where line IV intersects with the cam profile and to the intersection of interrupted line IV with the time scale 20 in figure 8) .

The delay of the closing moment, i.e. the length in time of the delay, is used to variably control the compression pressure of the scavenging air in the cylinder 6. The 25 required delay is determined by the electronic control unit 90 in on the basis of the operating conditions, such as e.g. engine load, scavenge air pressure and rpm and other parameters relating to the operating conditions as communicated by various sensors to the electronic control 30 unit 90 and by the use of e.g. data in an engine map for the specific type of engine concerned. The engine map can contain tables for the desired compression pressure to scavenge air pressure ratios (this ratio is a dimensionless measure of the exhaust valve closing 21 DK 177695 B1 angle). The determination by the electronic control unit 90 for the delay can also depend on an operating mode selected by a human operator or automatically selected on the basis of a geographical position of the engine, so as 5 to switch e.g. between a fuel saving optimized mode of operation and an NOx optimized mode of operation.

In the present embodiment the device 50 is attached to the piston pump 31 and communicates with the hydraulic 10 fluid in the hydraulic push rod via a conduit 63 that is in part formed in the housing of the piston pump 31. It is noted that the device 50 could be 1 elsewhere, though preferably near the hydraulic piston rod, e.g. at the exhaust valve actuator 34.

15

In the present embodiment the device 50 includes a housing 51 and is provided with a regulation piston 52 that is received in a cylinder formed inside the housing 51. The cylinder and the regulation piston 52 define 20 together a regulation chamber 53 on one side of the regulation piston 52 and the regulation chamber 53 is during operation filled with hydraulic fluid. The regulation piston 52 has a stroke between a fully retracted position and a fully extended position. The 25 fully retracted and extended positions are limited by physical end stops such as by e.g. the regulation piston abutting with the respective end of the cylinder in which it is received. The end stops ensure that the maximum volume of hydraulic fluid added to the hydraulic push rod 30 cannot exceed a predetermined small amount. The regulation chamber 53 is in fluid communication with the hydraulic fluid in said hydraulic push rod, via conduit 63.

22 DK 177695 B1

The regulation piston 52 is operably connected to an extension piston 54 for urging the regulation piston 52 towards its extended position and the regulation piston 52 is operably connected to a return piston 56 for urging 5 the regulation piston 52 towards its retracted position.

The extension piston 54 has an operating chamber 55 associated therewith. The operating chamber 55 is connected to an electronically controlled 3/2 hydraulic valve 69 that selectively connects the operating chamber 10 55 either to a source of hydraulic pressure 80 or to tank, depending on the position of the electronically controlled hydraulic valve 69. The source of pressure is preferably a constant pressure that is chosen to match the forces required to be applied to the regulation 15 piston 52. In an embodiment the dimensions (diameters) of regulation piston 52 and extension piston 54 are chosen with a constant reference pressure and the hydraulic pressure source is not used for means of compression pressure control.

20

The electronically controlled valve 69 is connected to the electronic control unit 90 and the electronic control unit 90 determines the position of the electronically controlled valve 69.

25

The return piston 56 has a smaller diameter than the extension piston 54. The return piston 56 has an operating chamber 57 associated therewith that is continuously connected by a conduit 60 to the source of 30 hydraulic pressure 80. The difference in diameter between the extension piston 54 and the return piston 56 causes a force urging the regulation piston 52 towards its extended position when both operating chamber 55 and 57 are pressurized, i.e. when the electrically controlled 23 DK 177695 B1 valve connects the operating chamber 55 to the source of hydraulic pressure 80. The magnitude of the force urging the regulation piston 52 towards its extended position determines the pressure with which hydraulic fluid is 5 urged into the hydraulic push rod. As can be seen in figures 8 to 11 the pressure corresponding to this force is chosen such that the hydraulic fluid starts moving into the hydraulic push rod approximately in the middle of the period where the closing flank is active and with 10 a pressure that is approximately one third of the stable pressure during the dwell phase.

If it has been determined by the electronic control unit 90 that the opening time of the exhaust valve 11 needs to 15 be extended, the electronic control unit 90 will start to urge said regulation piston 52 from said fully retracted position to said extended position from a point in time during said period where said dwell segment 72 is active (dwell phase) , as can be seen form the signal to the 20 electrically controlled valve in figures 9 and 11. The extract activation point of the electronically controlled hydraulic valve 69 is not critical, as long as it is before the point in time where the pressure in the hydraulic push rod has not yet dropped below the pressure 25 generated by the regulation piston 52. Since the force that urges the regulation piston 52 to its extended position corresponds to a pressure in said regulating chamber 53 that is lower than the dwell pressure the regulation piston 52 does not start to move towards its 30 extended position before the pressure in the hydraulic fluid in said hydraulic push rod has fallen well below to said dwell pressure due to the closing flank 73 becoming active, as can be seen from the graphs in figures 9 to 11.

24 DK 177695 B1

The electronic control unit 90 is configured to start urging the regulation piston 52 from its fully retracted position towards its extended position during the period 5 where the dwell segment 70 is active so that the regulation piston cannot move backwards due to the high pressure in the hydraulic push rod since the mechanical end stop prevents the regulation piston 52 from moving backwards .

10

As can be seen from figures 9 to 11 the electronic control unit 90 is configured to continue to urge the regulation piston 52 towards its extended position until certain delay has elapsed after the end of the closing 15 period defined by the cam profile (corresponding to interrupted line IV) . Then, the electronic control unit 90 urges the regulation piston 52 to move back to its fully retracted position by switching the electronically controlled valve 69 to the position where the operating 20 chamber 55 is connected to tank so that the pressure of the hydraulic fluid in operating chamber 57 acting on the return piston 56 causes a force acting on the regulating piston 52 towards its retracted position. The return movement of the regulation piston 52 is assisted by the 25 pressure in the regulation chamber 53. The movement of the regulating piston 52 to its retracted position removes the volume of hydraulic fluid that was earlier added thereto and thereby allows the exhaust valve 11 to return to close and return to its seat 18.

30

The length of the delay of the closing of the exhaust valve 11 has a significant influence on the compression pressure in the engine cylinder 6 and the length of the delay is therefore critical and is controlled accurately.

25 DK 177695 B1

The determination of the desired length for the delay for the closing of the exhaust valve 11 is as described above and can include the use of a conversion map that is based on a desired compression pressure to scavenging pressure 5 ratio map.

The device 50 can be constructed differently than described in the embodiments above. Any device constructed so as to be able to urge a volume of 10 hydraulic fluid into the hydraulic push rod with a pressure that corresponds to a pressure below the dwell pressure and above the base pressure, and being configured for starting to urge the volume of hydraulic fluid into the hydraulic push rod during the dwell phase 15 (before the closing flank becomes active) and being configured to remove the volume from the hydraulic push rod with a controlled delay after the moment in time where the closing flank stops being active (corresponding to the position where line IV intersects with the cam 20 profile) is suitable for use in the present invention.

The term "comprising" as used in the claims does not exclude other elements. The term "a" or "an" as used in the claims does not exclude a plurality.

25

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 30 departing from the scope of the invention.

Claims

1. Stor, langsomtgående, flercylindret, turboladet totaktsmotor (1) med længdeskylning, indvendig 5 forbrænding og krydshoveder (22), hvilken motor (1) omfatter: en flerhed af cylindre med i det mindste en udstødningsventil (11) og et udstødningsventilsæde (18) 10 for hver cylinder, hvilken udstødningsventil (11) er dimensioneret således, at den bevæges mellem en lukket stilling, hvor den hviler på sædet (18) og en åben stilling, 15 en pneumatisk fjeder (38), der er forbundet med hver enkelt udstødningsventil (11), hvilken pneumatisk fjeder (38) er udformet således, at den forspænder udstødningsventilen (11), der er forbundet med denne, i en lukkeretning hen mod og hen på ventilsædet (18), 20 i det mindste en knastaksel (28), der er forsynet med udstødningsknaster (29), hvilke udstødningsknaster (29) er forsynet med en knastprofil til aktivering af udstødningsventilen (11), der er forbundet med den 25 vedkommende udstødningsknast (29), hvilken knastprofil indeholder en åbningsflanke (71), en lukkeflanke (73), et holdesegment (72), der forbinder åbningsflanken (71) med lukkeflanken (73), og et 30 grunddiametersegment (70), der forbinder lukkeflanken (73) med åbningsflanken (71), 2 DK 177695 B1 en hydraulisk stødstang, der er forbundet med udstødningsventilen (11) på hver cylinder (6), hvilken hydraulisk stødstang omfatter: 5 en hydraulisk stempelpumpe (31), hvilken hydraulisk stempelpumpe (31) omfatter et pumpestempel (32), der drives af en udstødningsknast (29) på knastakslen (28) , 10 en hydraulisk aktuator (34), der indeholder et aktiveringsstempel (35), der virker på udstødningsventilen (11) til bevægelse af den vedkommende udstødningsventil i en åbningsretning, og 15 en hydraulisk ledning (36) , der forbinder den hydrauliske stempelpumpe (31) med den hydrauliske aktuator (34), og 20 hydraulikvæske i den hydrauliske stødstang mellem pumpestemplet (32) og aktiveringsstemplet (35), kendetegnet ved, at 25 motoren desuden omfatter en anordning (50), der er dimensioneret til en selektiv tilførsel af en mængde hydraulikvæske til hydraulikvæsken i den hydrauliske stempelstang i løbet af tidsrummet, hvor lukkeflanken (73) er aktiv, til forlængelse af åbningstiden for 30 udstødningsventilen (11), hvilken anordning (50) er dimensioneret til at fjerne mængden af hydraulikvæske, der blev tilført den hydrauliske stempelstang, fra den hydrauliske stempelstang med en given forsinkelse efter tidspunktet, hvor lukkeflanken (73) er blevet inaktiv, 3 DK 177695 B1 således at udstødningsventilen (11) kan vende tilbage til sit sæde (18) med en forsinkelse i forhold til lukkemomentet, der defineres af knastprofilen.A large, slow-moving, multi-cylinder, two-stroke turbocharged engine (1) with longitudinal flushing, internal combustion and cross-heads (22), comprising: a plurality of cylinders having at least one exhaust valve (11) and an exhaust valve seat (18) 10 for each cylinder, which exhaust valve (11) is dimensioned to move between a closed position where it rests on the seat (18) and an open position, 15 a pneumatic spring (38) connected to each an exhaust valve (11), said pneumatic spring (38) being designed to bias the exhaust valve (11) connected thereto in a closing direction toward and on the valve seat (18), at least one camshaft (28 ) provided with exhaust knobs (29), which exhaust knobs (29) are provided with a cam profile for actuating the exhaust valve (11) connected to the respective exhaust cam (29), said cam profile. holding an opening flange (71), a closing flange (73), a holding segment (72) connecting the opening flange (71) to the closing flange (73), and a 30 diameter diameter segment (70) connecting the closing flank (73) to the opening flange (71) A hydraulic shock bar connected to the exhaust valve (11) on each cylinder (6), comprising: a hydraulic piston pump (31), said hydraulic piston pump (31) comprising a pump piston (32); driven by an exhaust cam (29) on the camshaft (28), a hydraulic actuator (34) containing an actuating piston (35) acting on the exhaust valve (11) for moving the respective exhaust valve in an opening direction, and a hydraulic line (36) connecting the hydraulic piston pump (31) to the hydraulic actuator (34), and 20 hydraulic fluid in the hydraulic shock bar between the pump piston (32) and the actuating piston (35), characterized in that 25 the engine further comprises a device (50) dimensioned for selectively supplying an amount of hydraulic fluid to the hydraulic fluid in the hydraulic piston rod during the period of time in which the closing flange (73) is active to extend the opening time of the exhaust valve (11), which means (50) is sized to remove the amount of hydraulic fluid supplied to the hydraulic piston rod from the hydraulic piston rod with a given delay after the time when the closing flange (73) has become inactive, so that the exhaust valve (11) ) can return to its seat (18) with a delay relative to the closing torque defined by the cam profile.

2. Motor ifølge krav 1, ved hvilken sammentrykningen af den pneumatiske fjeder (38) forårsager et holdetryk i hydraulikvæsken i den hydrauliske stødstang, når udstødningsventilen (11) hviler i sin åbne stilling og holdesegmentet (72) på udstødningsknasten (29) er aktivt, 10 og ved hvilken anordningen (50) er dimensioneret til at presse mængden af hydraulikvæske ind i stødstangen med et tryk, der er lavere end holdetrykket.The engine of claim 1, wherein the compression of the pneumatic spring (38) causes a holding pressure in the hydraulic fluid of the hydraulic thrust bar when the exhaust valve (11) rests in its open position and the holding segment (72) of the exhaust cam (29) is active. 10 and wherein the device (50) is sized to press the amount of hydraulic fluid into the thrust bar at a pressure lower than the holding pressure.

3. Motor ifølge krav 1, ved hvilken anordningen (50) 15 omfatter: et reguleringsstempel (52), der har et slag mellem en fuldstændigt indtrukket og en fuldstændigt udkørt stilling, med et reguleringskammer (53) på den ene side 20 af reguleringsstemplet (52), hvilket reguleringskammer (53) har en væskeforbindelse til hydraulikvæsken i den hydrauliske trykstang, et elektronisk styret aktiveringssystem, der virker på 25 reguleringsstemplet (52), hvilket elektronisk styrede aktiveringssystem er dimensioneret til at påbegynde bevægelsen af reguleringsstemplet (52) fra den fuldstændigt indtrukne stilling til den udkørte stilling fra et tidspunkt inden for det tidsrum, hvor 30 holdesegmentet (72) er aktivt, og med en kraft, der svarer til et tryk i reguleringskammeret (53) , der er lavere end holdetrykket, således at reguleringsstemplet (52) ikke begynder at bevæge sig mod sin udkørte stilling, før trykket i hydraulikvæsken i den hydrauliske 4 DK 177695 B1 trykstang er faldet til et niveau, der er lavere end holdetrykket, fordi lukkeflanken (73) er blevet aktiv.The engine of claim 1, wherein the device (50) comprises: a regulating piston (52) having a stroke between a fully retracted and fully extended position, with a regulating chamber (53) on one side 20 of the regulating plunger ( 52), which regulating chamber (53) has a fluid connection to the hydraulic fluid in the hydraulic pressure rod, an electronically controlled actuating system acting on the regulating piston (52), which electronically controlled actuating system is designed to initiate the movement of the regulating piston (52) from the completely retracted position to the extended position from a point within the time period in which the holding segment (72) is active and with a force corresponding to a pressure in the control chamber (53) lower than the holding pressure, such that the control piston (52 ) does not begin to move towards its extended position until the pressure in the hydraulic fluid in the hydraulic 4 DK 177695 B1 push rod is decreased to a level lower than the holding pressure because the closing flank (73) has become active.

4. Motor ifølge krav 3, ved hvilken det elektronisk 5 styrede aktiveringssystem er dimensioneret til at påbegynde bevægelsen af reguleringsstemplet (52) fra dets fuldstændigt indtrukne stilling mod dets udkørte stilling i løbet af det tidsrum, hvor holdesegmentet (70) er aktivt, og det elektronisk styrede aktiveringssystem er 10 dimensioneret til at fortsætte bevægelsen af reguleringsstemplet mod dets udkørte stilling, indtil den givne forsinkelse er udløbet og derefter at bevæge reguleringsstemplet eller gøre det muligt for reguleringsstemplet (52) at bevæge sig tilbage til dets 15 fuldstændigt indtrukne stilling.The motor of claim 3, wherein the electronically controlled actuating system is sized to initiate movement of the control piston (52) from its fully retracted position toward its extended position during the period of time in which the retaining segment (70) is active and the electronically controlled actuating system 10 is dimensioned to continue movement of the regulating piston toward its extended position until the given delay has expired and then to move the regulating piston or allowing the regulating piston (52) to move back to its fully retracted position.

5. Motor ifølge krav 3, ved hvilken reguleringsstemplet (52) er forbundet med et udkøringsstempel (54) til at bevæge reguleringsstemplet (52) mod dets udkørte 20 stilling, og ved hvilken reguleringsstemplet (52) er forbundet med et returstempel (56) til at bevæge reguleringsstemplet (52) mod dets indtrukne stilling.The engine of claim 3, wherein the regulating piston (52) is connected to an exit piston (54) for moving the regulating piston (52) to its extended position, and wherein the regulating piston (52) is connected to a return piston (56) for moving the control piston (52) to its retracted position.

6. Motor ifølge krav 5, ved hvilken udkøringsstemplet 25 (54) har et driftskammer (55), der er forbundet med dette, og ved hvilken driftskammeret (55) er forbundet med en elektronisk styret hydraulisk ventil (69), der selektivt forbinder driftskammeret (55) enten med en trykkilde (80) eller med tanken.The engine of claim 5, wherein the ejector piston 25 (54) has an operating chamber (55) connected thereto and wherein the operating chamber (55) is connected to an electronically controlled hydraulic valve (69) which selectively connects the operating chamber (55) either with a pressure source (80) or with the tank.

7. Motor ifølge krav 6, ved hvilken anordningen (50) omfatter udkøringsstemplet (54), returstemplet og den elektronisk styrede hydrauliske ventil (69). 5 DK 177695 B1An engine according to claim 6, wherein the device (50) comprises the exit piston (54), the return piston and the electronically controlled hydraulic valve (69). 5 DK 177695 B1

8. Motor ifølge krav 7, ved hvilken den elektronisk styrede ventil (69) er forbundet med en elektronisk styreenhed (90).The motor of claim 7, wherein the electronically controlled valve (69) is connected to an electronic control unit (90).

9. Motor ifølge krav 6, ved hvilken returstemplet (56) har en mindre diameter end udkøringsstemplet (55), og ved hvilken returstemplet (56) har et driftskammer (57), som er forbundet med dette, og som er forbundet permanent med trykkilden (80). 10The engine of claim 6, wherein the return piston (56) has a smaller diameter than the exit piston (55) and wherein the return piston (56) has an operating chamber (57) connected thereto and permanently connected to the pressure source. (80). 10

10. Motor ifølge krav 8, som desuden omfatter en positionssensor, der viser en vinkelposition for krumtapakslen (3) eller for knastakslen (28), og ved hvilken den elektronisk styrede hydrauliske ventil (69) 15 aktiveres for at forsinke lukningen af udstødningsventilen ved en reguleret forsinkelse på baggrund af et omregningsskema, der er baseret på et skema over ønsket forhold mellem kompressionstryk og skylletryk. 20An engine according to claim 8, further comprising a position sensor showing an angular position of the crankshaft (3) or of the camshaft (28), wherein the electronically controlled hydraulic valve (69) is actuated to delay the closing of the exhaust valve by a controlled delay based on a conversion scheme based on a diagram of the desired relationship between compression pressure and rinse pressure. 20

11. Motor ifølge krav 9, ved hvilken den elektronisk styrede styreenhed (90) er dimensioneret til at bevirke, at den elektronisk regulerede ventil (69) forbinder driftskammeret (55) med tanken med en given forsinkelse 25 efter det tidspunkt, hvor lukkeflanken (73) er blevet inaktiv, således at udstødningsventilen (11) vender tilbage til sit sæde (18) og reguleringsstemplet (52) vender tilbage til et leje, der falder sammen med dets indtrukne stilling. 30An engine according to claim 9, wherein the electronically controlled control unit (90) is dimensioned to cause the electronically controlled valve (69) to connect the operating chamber (55) to the tank with a given delay 25 after the time when the closing flank (73) ) has become inactive so that the exhaust valve (11) returns to its seat (18) and the control piston (52) returns to a bearing that coincides with its retracted position. 30

12. Fremgangsmåde til drift af en stor, langsomtgående, flercylindret, turboladet totaktsmotor (1) med længdeskylning, indvendig forbrænding og krydshoveder (22), hvilken motor (1) omfatter: DK 177695 B1 5 6 en flerhed af cylindre (6) med i det mindste en udstødningsventil (11) og et udstødningsventilsæde (18) for hver cylinder, en pneumatisk fjeder (38) , der er forbundet med hver enkelt ventil (11), hvilken pneumatisk fjeder (38) er udformet således, at den forspænder udstødningsventilen (11), der er forbundet med denne, i en lukkeretning hen 10 mod og hen på ventilsædet (18), i det mindste en knastaksel (28), der er forsynet med udstødningsknaster (29) , hvilke udstødningsknaster (29) er forsynet med en knastprofil til aktivering af 15 udstødningsventilen (11), der er forbundet med den vedkommende udstødningsknast (29), en hydraulisk stødstang, der er forbundet med udstødningsventilen (11) på hver cylinder (6) til 20 overførsel af knastprofilen til udstødningsventilen (11), hvilken hydraulisk stødstang indeholder en hydraulikvæske, hvilke udstødningsventiler (11) har en driftssekvens, der 25 reguleres af knastprofilen, hvilken knastprofil indeholder en åbningsflanke (71), en lukkeflanke (73) og et holdesegment (72), der forbinder åbningsflanken (71) med lukkeflanken (73), og et grunddiametersegment (70) , der forbinder lukkeflanken (73) med åbningsflanken (71), idet forspændingen af luftfjederen (38) forårsager et givet, på forhånd fastlagt holdetryk i hydraulikvæsken i den hydrauliske trykstang i løbet af holdetiden, 30 7 DK 177695 B1 hvilken fremgangsmåde omfatter: tilførsel af en mængde hydraulikvæske til hydraulikvæsken i den hydrauliske trykstang i løbet af tidsrummet, hvor 5 lukkeflanken (73) er aktiv, med et tryk, der er lavere end trykket, der foreligger i volumenet af den hydrauliske stang under holdetiden, og fjernelse af mængden af hydraulikvæske fra volumenet af 10 hydraulikvæske i den hydrauliske trykstang med en given forsinkelse, efter tidspunktet, hvor lukkeflanken (73) er blevet inaktiv.A method of operating a large, slow-moving, multi-cylinder, two-stroke turbocharged engine (1) with longitudinal flushing, internal combustion and cross-heads (22), comprising: (a) a plurality of cylinders (6) including at least one exhaust valve (11) and one exhaust valve seat (18) for each cylinder, a pneumatic spring (38) connected to each valve (11), said pneumatic spring (38) being designed to bias the exhaust valve ( 11) connected thereto, in a closing direction towards and toward the valve seat (18), at least one camshaft (28) provided with exhaust knobs (29), which exhaust knobs (29) are provided with a cam profile for actuating the exhaust valve (11) connected to the respective exhaust cam (29), a hydraulic thrust bar connected to the exhaust valve (11) on each cylinder (6) for transferring the cam profile to exhaust the exhaust valve (11), which hydraulic thrust bar contains a hydraulic fluid, which exhaust valves (11) have an operating sequence controlled by the cam profile, which cam profile includes an opening flange (71), a closing flank (73) and a holding segment (72) connecting the opening flange (71) with the closing flank (73) and a base diameter segment (70) connecting the closing flank (73) to the opening flank (71), the biasing of the air spring (38) causing a given predetermined holding pressure in the hydraulic fluid in the hydraulic pressure rod during holding time, which method comprises: supplying an amount of hydraulic fluid to the hydraulic fluid in the hydraulic pressure rod during the period of time in which the closing flange (73) is active, at a pressure lower than the pressure which is is present in the volume of the hydraulic rod during the holding time, and the removal of the amount of hydraulic fluid from the volume of 10 hydraulic fluid in the hydra non-linear pressure rod with a given delay, after the time when the closing flange (73) has become inactive.

13. Fremgangsmåde ifølge krav 12, ved hvilken mængden af 15 væske tilføres ved hjælp af et reguleringsstempel (52), der har et slag mellem en fuldstændigt indtrukket og en fuldstændigt udkørt stilling, med et reguleringskammer (53) på den ene side af reguleringsstemplet (52), hvilket reguleringskammer (53) har en væskeforbindelse til 20 hydraulikvæsken i den hydrauliske trykstang, hvilken fremgangsmåde omfatter en bevægelse af reguleringsstemplet (52) fra den fuldstændigt indtrukne stilling mod den fuldstændigt udkørte stilling fra et tidspunkt inden for det tidsrum, hvor holdesegmentet (72) 25 er aktivt, med en kraft på reguleringsstemplet (52), der skal resultere i et tryk i reguleringskammeret (53) , der er lavere end holdetrykket, således at reguleringsstemplet (52) ikke begynder at bevæge sig mod sin udkørte stilling, før trykket i hydraulikvæsken i den 30 hydrauliske trykstang er faldet til et niveau, der er lavere end holdetrykket, fordi lukkeflanken (73) er blevet aktiv. 8 DK 177695 B1The method of claim 12, wherein the amount of liquid is supplied by means of a regulating piston (52) having a stroke between a fully retracted and a fully extended position, with a regulating chamber (53) on one side of the regulating piston (52). 52), which control chamber (53) has a fluid connection to the hydraulic fluid in the hydraulic pressure rod, comprising a movement of the control piston (52) from the fully retracted position toward the fully extended position from a time within the period of the holding segment ( 72) 25 is active, with a force on the regulating piston (52) which results in a pressure in the regulating chamber (53) lower than the holding pressure, so that the regulating piston (52) does not begin to move towards its extended position before the pressure in the hydraulic fluid in the 30 hydraulic pressure rod has dropped to a level lower than the holding pressure because the closing flange (73 ) has become active. 8 DK 177695 B1

14. Fremgangsmåde ifølge krav 12, ved hvilken tidspunktet for påbegyndelsen af fjernelsen af mængden af hydraulikvæske fra volumenet af hydraulikvæske i den hydrauliske trykstang bestemmes på baggrund af et signal, 5 der viser en vinkelposition for krumtapakslen.The method of claim 12, wherein the time of commencing removal of the amount of hydraulic fluid from the volume of hydraulic fluid in the hydraulic pressure rod is determined on the basis of a signal showing an angular position of the crankshaft.

15. Fremgangsmåde ifølge krav 14, ved hvilken tidspunktet for påbegyndelsen af fjernelsen af mængden af hydraulikvæske fra volumenet af hydraulikvæske i den 10 hydrauliske trykstang anvendes til at regulere kompressionstrykket i forbrændingskammeret (15) i den vedkommende cylinder (6).The method of claim 14, wherein the time of starting the removal of the amount of hydraulic fluid from the volume of hydraulic fluid in the hydraulic pressure rod is used to control the compression pressure in the combustion chamber (15) of the respective cylinder (6).