Patent Description:
The present invention preferably relates to an internal combustion engine like a large marine or ship engine or a stationary engine whose cylinders have an inner diameter of at least <NUM>. The engine preferably is a two-stroke engine or a two-stroke cross head engine. The engine can be a gas engine, a dual fuel or a multi fuel engine. Burning of liquid and or gaseous fuels in such engines is possible as well as self-igniting or forced igniting.

The internal combustion engine can be a longitudinally flushed two-stroke engine.

The term internal combustion engine also refers to large engines which can be operated not only in diesel mode, which is characterized by the self-ignition of the fuel, but also in Otto mode, which is characterized by the positive ignition of the fuel, or in mixtures of the two. Furthermore, the term internal combustion engine includes in particular dual-fuel engines and large engines in which the self-ignition of the fuel is used for the positive ignition of another fuel.

Engine speed is preferably below <NUM> RPM, especially for <NUM>-stroke engines, and more preferably below <NUM> RPM, especially for <NUM>-stroke engines, which indicates the designation of low speed engines.

Fuel can be diesel or marine diesel oils or heavy fuel oils or emulsions or slurries or methanol or ethanol as well as gases like liquid natural gas (LNG) liquid petrol gas (LPG) and so on.

Further possible fuels which might be added on request are: LBG (Liquefied Biogas), biological fuels (e. oil made from algae or seaweed), ammonia, hydrogen, synthetic fuels from CO2 (e.g. made by Power-To-Gas or Power-To-Liquid).

Large ships, in particular vessels for transport of goods, usually are powered by internal combustion engines, in particular diesel and/or gas engines, mostly two-stroke, cross head engines.

In a reciprocating piston combustion engine the compression ratio, i.e. the ratio between the volume of the cylinder and combustion chamber in the internal combustion engine at their maximum and minimum values, is an important parameter for the combustion, the thermal efficiency and for the exhaust gas emissions. The compression ratio is usually chosen to yield the best engine performance. Often the high load engine performance is the most relevant point for the choice. For optimal performance over the whole operating range a variable compression ratio would be desirable but due to complications with such a system a compromise is usually made defining a constant compression ratio.

<CIT> discloses large reciprocating piston combustion engines with a control apparatus for controlling the compression ratio of the reciprocating piston combustion machine.

<CIT> discloses a variable compression device for changing a compression ratio of an engine including a crosshead pin connected to the piston rod, the inside of the crosshead pin being provided with a fluid chamber in which the piston rod is moved in a direction of increasing the compression ratio by the pressure-increased working fluid being supplied into the fluid chamber. A pump increases the working fluid in pressure.

<CIT> discloses a compression ratio varying mechanism. The piston comprise an oil passage, which is formed inside the piston rod. The cooling oil enters the piston rod through communication hole. The communication hole includes a first opening opened in an outer peripheral side surface of the piston rod and a second opening, which is prevented from being opposed to the first opening in a radial direction of the piston rod and is connected to the oil passage at a position apart from the first opening in the stroke direction. The cooling oil is discharged through an axial return passage within the piston rod and to the outside of the crosshead pin through the outlet hole extending in the axial direction of the crosshead pin.

Variable Compression Ratio (VCR) systems can adjust the compression ratio continuously by a hydraulic cylinder located in the crosshead pin for moving the piston rod in vertical direction. The compression ratio can be adjusted during the normal engine running. The adjustment allows the optimization of the performance at part load without compromising the performance at high/full load. For the dual fuel engines, the compression ratio can be optimized for each fuel mode separately (high compression ratio for diesel mode, low compression ratio for gas mode). An optimization of the compression ratio depending on operational conditions (scavenge air temperature, methane number of fuel gas, wave load, etc.) is possible.

For a continuous reliable operation of a hydraulic VCR system low leakage from the hydraulic chamber/cylinder is important.

Beside the cylinder clearances, the oil viscosity plays an important role for the leakage. The oil viscosity is highly dependent from the temperature, so the lower the temperature of the oil in the fluid chamber of a VCR system the smaller the VCR chamber leakage is.

Piston cooling oil heated up in the piston and discharged from the piston rod via the crosshead pin may heat up the crosshead pin and the hydraulic oil in the fluid chamber.

It is an object of the present invention to avoid the drawbacks of the prior art and in particular to provide an internal combustion engine and a method of operating an internal combustion engine allowing a continuous reliable operation of a VCR system.

The object is achieved by the internal combustion engines and the method for running an internal combustion engine according to the independent claims.

The internal combustion engine has at least one cylinder. Preferably, the internal combustion engine is a large vessel engine with at least one cylinder having an inner diameter of at least <NUM>. The internal combustion engine may be a low pressure fuel gas engine or dual-fuel engine with.

The internal combustion engine has at least one piston which is movably arranged within the cylinder. For each cylinder the internal combustion engine further comprises a rotatably arranged crankshaft, with the piston being in each case connected to a crosshead via a piston rod, and with a crosshead pin connected to the piston rod. The crosshead is in each case connected to the crankshaft via a connecting rod to drive the crankshaft.

The engine comprises a variable compression ratio device for changing a compression ratio of an engine. The variable compression ratio device allows the volume above the piston at top dead centre to be changed.

The variable compression ratio device comprises a fluid chamber arranged in the inside of the crosshead pin, in which the piston rod is moveable relative to a bottom of the fluid chamber. The movement may be induced by a pressure-increased working fluid, for example a working oil, being supplied into and out of the fluid chamber.

The internal combustion engine may comprise a pumping device for transporting the working fluid into and out of the fluid chamber for changing the compression ratio.

Typically, the piston rod may include an end portion with a larger diameter at the end part of the piston rod close to the crosshead pin. The outer peripheral surface of the lower end portion of the piston rod close to the crosshead pin may protrude outward in the radial direction, and thus the diameter of the end portion is greater than that of the middle part of the piston rod.

Working fluid may be introduced into the fluid chamber below the end portion of the piston rod close to the crosshead pin. The end portion may comprise a sealing for holding the working fluid below the piston rod.

For the highest compression ratio the enlarged part of the end portion of the position rod may abut against an upper abutment member, for example an upper abutment face of the fluid chamber. For the smallest compression ratio the position rod may abut against the bottom of the fluid chamber.

The piston rod comprises cooling channels. The cooling channels for guiding a cooling fluid are formed inside the piston rod and extend in a stroke direction of the piston.

The crosshead pin comprises at least one first flow path for guiding a cooling fluid, for example a cooling oil, that is to be supplied to at least one of first cooling channels and at least one second flow path for guiding a cooling fluid that is to be discharged from at least one of second cooling channels.

The first flow path is arranged in a first distance to a bottom plane defined by the bottom of the fluid chamber and the second flow path is arranged in second distance to the bottom plane. The first distance is smaller than the second distance. Preferably, the bottom of the fluid chamber is flat and the bottom plane comprises the bottom of the fluid chamber.

Thus, the first flow path has a smaller distance to any working fluid which may be contained in the fluid chamber than the second flow path.

The first flow path comprises a plurality of first channels, which are, preferably uniformly, arranged in a first cross-section of the crosshead pin and parallel to the bottom plane.

The first flow path is for supplying a cooling fluid into the piston rod whereas the second flow path is for discharging the cooling fluid. Normally, cooling fluid transported via the first flow path is cooler than cooling fluid transported via the second flow path. The first flow path defines a cooling plane, which may shield working fluid in the fluid chamber from the second flow path. Hence, the warming of a working fluid, such as hydraulic oil, contained in the fluid chamber by cooling fluid which was heated up in the piston and is discharged from the piston rod via the second flow path is reduced or even prevented. As the working fluid keeps its temperature, the risk of leaking working fluid is reduced and the compression ration may be controlled very precisely.

The internal combustion engine may comprise a further pumping device for transporting the cooling fluid into the first flow path and out of the second flow path.

The second flow path may comprise at least one second channel arranged in a second cross-section of the crosshead pin parallel to the bottom plane. The second flow path may comprise a plurality of second channels, which preferably are uniformly arranged in the second cross-section.

The first flow path may comprise a first number of first channels and the second flow path comprises second number of second channels. The first number may be greater than the second number. A greater number of channels may be distributed more evenly, such that the shielding effect of the first flow path is optimized.

The diameter of first channels may be smaller than diameter of second channels.

Preferably the channels have a circular cross section. Otherwise, at the least the axial diameter of first channels may be smaller than axial diameter of second channels.

A certain rate of cooling fluid guided through channels with a small diameter can be evenly distributed over the cross section of the crosshead pin. An even distribution is especially advantageous for the inflowing cooling fluid as it shields the heat of the outflowing cooling fluid.

The diameter of the second channels for the outflowing cooling fluid may be chosen larger.

The distance between the first channels may be smaller than the distance between the second channels. The first flow path having small distances between the first channels forms a shielding plane with a well distributed cooling fluid.

A first flow path with a great number of first channels having a small diameter and being arranged with a small distance provides for a homogeneous and therefore effective shielding plane.

The diameter of the first channels may be between <NUM> and <NUM>, preferably between <NUM> and <NUM>. Too small diameters may cause an increasing hydraulic resistance and manufacturing costs may get too high.

The number of first channels may be between <NUM> and <NUM>, preferably between <NUM> and <NUM>. The number may depend on the diameter of the first channels, preferably optimized with respect to hydraulic resistance and/or manufacturing costs, and the engine size.

The distance between first channels may be between <NUM> and <NUM>, preferably between <NUM> and <NUM>.

The distance corresponds to a wall thickness between the channels which provides for a sufficient stability and a convenient manufacturing.

The distance may depend on the diameter of the first channels, preferably optimized with respect to hydraulic resistance and/or manufacturing costs, and the engine size.

The crosshead pin may comprise a splitter ring.

The splitter ring may be fixedly arranged with respect to the crosshead pin, in particular above or within the fluid chamber.

The splitter ring may be arranged for defining a first annular cavity in fluid connection with at least one cooling channel for supplying cooling fluid to the piston rod. The splitter ring is arranged such that the first annular cavity is in fluid connection with the first flow path.

The splitter ring is arranged for defining a second annular cavity being in fluid connection with at least one cooling channel for discharging cooling fluid from the piston and being in fluid connection with the second flow path.

The first annular cavity and the second annular cavity are arranged around the piston rod, preferably around the end portion of the piston rod.

The first annular cavity and the second annular cavity may be separated from each other fluid tightly. Exchange between the first annular cavity and the second annular cavity shall be reduced or prevented.

The first annular cavity has a smaller distance to the bottom of fluid chamber than the second annular cavity.

The splitter ring provides for a separation of introduced cooling fluid and discharged cooling fluid and prevents mixing of the introduced cooling fluid and the discharged cooling fluid. The introduced cooling fluid which typically has a lower temperature than the cooling fluid which is discharged from the piston rod may provide for shielding the heat of the discharged cooling fluid form the working fluid contained in the fluid chamber below the piston rod.

At least a first seal member may be arranged on the outer peripheral surface of the end portion of the piston rod. The first seal member may at least partially be provided by a portion of the piston rod having an enlarged diameter and protruding radially outwards.

The first annular cavity may be bounded by the first seal member in stroke direction on the lower side which is closer to the bottom of the fluid chamber and by the splitter ring on the upper side.

Additionally a second seal member may be arranged on the outer peripheral surface of the end portion of the piston rod. The second seal member may at least partially be provided by a portion of the piston rod having an enlarged diameter and protruding radially outwards.

The second annular cavity may be bounded by the splitter ring on the lower side which is closer to the bottom of the fluid chamber and by the second seal member on the upper side.

The first and/or the second seal member may provide sliding ear faces between the piston rod and the crosshead pin.

The pair of the first seal member and a second seal member may be arranged apart from each other in the stroke direction of the piston rod. Preferably the first seal member and a second seal member are arranged on the outer peripheral side surface of a large-diameter end portion of the piston rod.

An annular groove may be formed between the first seal member and a second seal member. In the annular groove the exchange of cooling fluid takes place.

For the highest compression ratio, wherein the piston rod is pressed away from the bottom of the fluid chamber, most of the annular groove is used for the inflowing cooling fluid.

For the smallest compression ratio, wherein the piston rod is closest to the bottom of the fluid chamber, most of the annular groove is used for returning cooling fluid.

For higher compression ratios the first annular cavity has a smaller axial extension than for smaller compression ratios.

Analogously, for higher compression ratios the second annular cavity has a larger axial extension than for smaller compression ratios.

The splitter ring may comprise a seal member being in contact with the outer surface of the piston rod within the annular groove.

The splitter ring may comprise at least two half rings or four quarter rings, preferably being screwed together.

The splitter ring may be radially pressed to the wall of the fluid chamber and/or may be axially pressed into a groove or step within or above the fluid chamber. The splitter ring may be prevented from an axial movement, preferably in the direction towards the bottom of the fluid chamber, by an abutment face of the groove or step.

The splitter ring may be fixed by a locking device, for example a cylindrical shaped spring element, to avoid a rotational and/or axial movement.

The splitter ring may be prevented from an axial movement, preferably in the direction away from the bottom of the fluid chamber, by an abutment face of the spring element.

The piston rod may comprises at least one supply channel for supplying cooling fluid into cooling channels and/or may comprise at least one discharge channel for discharging cooling fluid from cooling channels.

Preferably, the supply channel is in fluid connection with the first annular cavity and/or the discharge channel is in fluid connection to the second annular cavity defined by the splitter ring.

Preferably, the supply channel has a smaller distance to the bottom of fluid chamber than the discharge channel.

Thus, the first flow path, the first annular chamber and the supply channel form a supply system, as well as a the second flow path, the second annular chamber and the discharge channel form a discharge system, wherein the supply system is arranged in a closer distance to the bottom plane than the discharge system.

The working fluid thus is completely shielded from the heat of the discharged cooling fluid by the supply system transporting cooling fluid of a lower temperature.

The internal combustion engine may comprise at least one first knee lever connected to the crosshead pin for providing and/or releasing the cooling fluid. The first knee lever may comprise pipes which are fluidly connected to the first and to the second flow path.

Alternatively or additionally the internal combustion engine may comprise at least one second knee lever connected to the crosshead pin for providing and/or releasing the working fluid. The second knee lever may comprise at least one pipe which is fluidly connected to the fluid chamber.

According to the invention a method for running an internal combustion engine as described above comprises the following steps.

A pressure-increased working fluid is provided in a fluid chamber in which the piston rod is moveable relative to a bottom of the fluid chamber.

When working fluid is supplied into the fluid chamber, the piston rod moves upwardly in a direction away from the bottom of the fluid chamber to increase the compression ratio.

The piston is cooled by guiding a cooling fluid through cooling channels arranged in the piston rod.

The cooling fluid is supplied to at least one of the cooling channels through at least one first flow path in the crosshead pin and the cooling fluid is discharged from at least one of the cooling channels through at least one second flow path in the crosshead pin.

The supplied cooling fluid shields the working fluid from the heat of the discharged cooling fluid.

Shielding may be achieved by the discharged cooling fluid being guided in greater distance to the working fluid in the fluid chamber than the supplied cooling fluid.

According to the invention, the cooling fluid is suppliable to at least one of the cooling channels in an area between the bottom plane and the area where the cooling fluid is discharged from the at least one of the cooling channels.

The working fluid may keep a temperature below <NUM>, preferably below <NUM>, more preferably below <NUM>.

The piston rod may be moved relative to the bottom of the fluid chamber by supplying working fluid into the fluid chamber or discharging supplying working fluid from the fluid chamber.

According to the invention a crosshead pin for an internal combustion engine, as described above, comprises a fluid chamber for guiding a piston rod which is moveable relative to a bottom of the fluid chamber. The fluid chamber may receive a working fluid.

The crosshead pin comprises at least one first flow path for guiding a cooling fluid that is to be supplied to at least one of the cooling channels of the piston rod and at least one second flow path for guiding a cooling fluid that is to be discharged from at least one of the cooling channels of the piston rod.

The first flow path is arranged in a first distance to the bottom plane defined by the bottom of the fluid chamber and the second flow path is arranged in a second distance to the bottom plane. The first distance is smaller than the second distance. The first flow path comprises first channels, preferably uniformly, arranged in a first cross-section of the crosshead pin parallel to the bottom plane.

In the following, the invention is further explained in embodiments by means of figures. Same reference numbers refer to functionally corresponding features.

<FIG> shows a schematic view of an internal combustion engine <NUM> having a cylinder <NUM>. The engine <NUM> has a piston <NUM> which is movably arranged within the cylinder <NUM>. The piston <NUM> is connected to a crosshead pin <NUM> arranged in a crosshead <NUM> via a piston rod <NUM>. The crosshead <NUM> is connected to a crankshaft <NUM> via a connecting rod <NUM> to drive the crankshaft <NUM>.

The engine <NUM> comprises a variable compression ratio device <NUM> for changing a compression ratio of an engine.

As can be seen in <FIG>, the variable compression ratio device <NUM> comprises a fluid chamber <NUM> arranged in the inside of the crosshead pin <NUM>. The piston rod <NUM> is moveable relative to a bottom <NUM> of the fluid chamber <NUM> by a pressure-increased working fluid being supplied into the fluid chamber <NUM>.

A knee lever <NUM> is connected to the crosshead pin <NUM> for providing and/or releasing the working fluid.

The end portion <NUM> of the piston rod <NUM> has an enlarged radial diameter as compared to the middle portion <NUM> of the piston rod.

The overall length <NUM> of the piston rod <NUM> and the crosshead pin <NUM> a in the stroke direction changes in accordance with the separation distance <NUM> between the stepped surface <NUM> of the end portion <NUM> of the piston rod <NUM> and the stepped surface <NUM> of the crosshead pin <NUM> in the stroke direction, here an upper abutment face of the fluid chamber <NUM>.

<FIG> shows a further schematic view of the variable compression ratio device <NUM>.

The piston rod <NUM> comprises cooling channels 14a, 14b for guiding a cooling fluid to the piston <NUM>. The cooling fluid may be provided by a knee lever <NUM> which is connected to the crosshead pin <NUM> (see <FIG>).

The crosshead pin <NUM> comprises a first flow path <NUM> for guiding a cooling fluid that is to be supplied to first cooling channels 14a and at least one second flow path <NUM> for guiding a cooling fluid that is to be discharged from a second cooling channel 14b.

The first flow path <NUM> is arranged in first distance d1 to a bottom plane <NUM> comprising the bottom <NUM> of the fluid chamber <NUM> and the second flow path <NUM> is arranged in a second distance d2 to the bottom plane <NUM>. The first distance d1 is smaller than the second distance d2.

As can be seen in <FIG> the first flow path <NUM> comprises a plurality of first channels <NUM>, which are uniformly arranged in a first cross-section <NUM> of the crosshead pin <NUM> parallel to the bottom plane <NUM>. The first channels <NUM> are open towards the fluid chamber <NUM>. The first seal member <NUM> of the piston rod <NUM> (see <FIG>) prevents the cooling fluid from mixing with the working fluid.

<FIG> shows a schematic partial sectional view of a crosshead pin <NUM>. The second flow path <NUM> comprises a plurality of second channels <NUM> arranged in a second cross-section <NUM> of the crosshead pin <NUM> parallel to the bottom plane <NUM>. The first number of first channels <NUM> is greater than a second number of second channels <NUM>.

The diameter D1 of the first channels <NUM> is smaller than the diameter D2 of the second channels <NUM>.

The distance d3 between the first channels <NUM> is smaller than the distance d4 between the second channels <NUM>.

The cooling fluid is supplied to at least one of the cooling channels 14a (see <FIG>) in an area <NUM> between the bottom plane <NUM> and the area <NUM> where the cooling fluid is discharged from the cooling channel 14b (see <FIG>).

<FIG> shows a schematic partial sectional view of the crosshead pin <NUM> and the piston rod <NUM>.

The end portion <NUM> of the piston rod comprises a first seal member <NUM> and a second seal member <NUM> provided by portions of the piston rod <NUM> having an enlarged diameter and protruding radially outwards.

The crosshead pin <NUM> comprises a splitter ring <NUM>.

The splitter ring <NUM> defines a first annular cavity <NUM> below the splitter ring <NUM>. The first annular cavity <NUM> is in fluid connection with a cooling channel 14a for supplying cooling fluid to the piston <NUM> via supply channels <NUM>. The first annular cavity <NUM> is also in fluid connection with the first flow path <NUM>.

The splitter ring <NUM> also defines a second annular cavity <NUM> above the splitter ring <NUM>. The second annular cavity <NUM> is in fluid connection with at least one cooling channel 14b for discharging cooling fluid from the piston rod <NUM> via discharge channels <NUM>. The second annular cavity <NUM> is also in fluid connection with the second flow path <NUM>.

The splitter ring <NUM> provides for a fluid tight separation between the first annular cavity <NUM> and the second annular cavity <NUM>.

The first annular cavity <NUM> is arranged below the second annular cavity <NUM> and has a smaller distance to the bottom <NUM> of fluid chamber <NUM> than second annular cavity <NUM>.

The first annular cavity <NUM> is limited by the first seal member <NUM> in stroke direction on the lower side which is closer to the bottom <NUM> and by the splitter ring <NUM> on the upper side.

The second annular cavity <NUM> is limited by the second seal member <NUM> in stroke direction on the upper side by the splitter ring <NUM> on the lower side.

<FIG> shows a further schematic partial sectional view of the crosshead pin <NUM>.

The splitter ring <NUM> is fixed to the crosshead pin <NUM> by a locking device, in this case a cylindrical shaped spring element <NUM>.

<FIG> shows half sectional views of the crosshead pin <NUM> with the piston rod <NUM> in two different positions.

In the figure on the left the piston rod <NUM> is in the uppermost position which corresponds to the largest possible compression ratio. The second annular cavity <NUM> above the splitter ring <NUM> has its maximal axial extension.

In the figure on the right the piston rod <NUM> is in the lowermost position which corresponds to the smallest possible compression ratio. The first annular cavity <NUM> below the splitter ring <NUM> has its maximal axial extension.

In both cases the second annular cavity <NUM> is in fluid contact with the discharge channel <NUM> and second channels <NUM> of the second flow path <NUM>, whereas the first annular cavity <NUM> is in fluid contact with the supply channel <NUM> and first channels <NUM> of the first flow path <NUM>.

The supply system comprising the first flow path <NUM>, the first annular cavity <NUM> and the supply channels <NUM> is arranged below the discharge system comprising the second flow path <NUM>, the second annular cavity <NUM> and the discharge channel <NUM> for all axial positions of the piston rod <NUM>.

Claim 1:
Internal combustion engine (<NUM>) having at least one cylinder (<NUM>), preferably a large vessel engine with at least one cylinder (<NUM>) having an inner diameter of at least <NUM>, preferably a low pressure fuel gas engine, a dual-fuel or multi-fuel engine,
having at least one piston (<NUM>) which is movably arranged within the cylinder (<NUM>),
having a rotatably arranged crankshaft (<NUM>), with the piston (<NUM>) being connected to a crosshead (<NUM>) via a piston rod (<NUM>), and with a crosshead pin (<NUM>) connected to the piston rod (<NUM>), and with the crosshead (<NUM>) being connected to the crankshaft (<NUM>) via a connecting rod (<NUM>) to drive the crankshaft (<NUM>),
the engine comprising a variable compression ratio device (<NUM>) for changing a compression ratio of an engine (<NUM>), the variable compression ratio device (<NUM>) being provided with a fluid chamber (<NUM>) arranged in the inside of the crosshead pin (<NUM>), in which the piston rod (<NUM>) is moveable relative to a bottom (<NUM>) of the fluid chamber (<NUM>) by a pressure-increased working fluid being supplied into the fluid chamber (<NUM>),
the piston rod (<NUM>) comprising cooling channels (14a, 14b), the crosshead pin (<NUM>) comprising at least one first flow path (<NUM>) for guiding a cooling fluid that is to be supplied to at least one of the cooling channels (14a) and at least one second flow path (<NUM>) for guiding a cooling fluid that is to be discharged from at least one of the cooling channels (14b),
characterized in that,
the first flow path (<NUM>) is arranged in a first distance (d1) to a bottom plane (<NUM>) defined by a bottom (<NUM>) of the fluid chamber (<NUM>) and the second flow path (<NUM>) is arranged in a second distance (d2) to the bottom plane (<NUM>), the first distance (d1) being smaller than the second distance (d2), such that the cooling fluid is suppliable to at least one of the cooling channels (14a) in an area (<NUM>) between the plane (<NUM>) defined by the bottom (<NUM>) of the fluid chamber (<NUM>) and the area (<NUM>) where the cooling fluid is dischargeable from the at least one of the cooling channels (14b), wherein the first flow path (<NUM>) comprises a plurality of first channels (<NUM>), preferably uniformly, arranged in a first cross-section (<NUM>) of the crosshead pin (<NUM>) parallel to the bottom plane (<NUM>).