Patent Description:
In a uniflow scavenging type two-cycle engine which is also used as an engine of a ship, a scavenging port is provided on one end side of a cylinder in the stroke direction of a piston, and an exhaust port is provided on a cylinder cover disposed on the other end side thereof. When fuel is burned in a combustion chamber and the piston pushed by combustion gas generated by the combustion moves to a position closer to the bottom dead center than the scavenging port, active gas is sucked into the inside of the cylinder from the opened scavenging port, and the exhaust gas after the fuel combustion is pushed out of the exhaust port by the active gas and is discharged.

Further, <CIT>- <CIT> describes a so-called dual-fuel type uniflow scavenging type two-cycle engine, which switches the fuel between liquid fuel and fuel gas.

<CIT> discloses a two-stroke engine. The two stroke engine has each piston engaging a slider sleeve with its lower edge of the piston skirt, in the downward stroke. The slider is depressed to open inlet slots for the inlet fuel-air mixture. The slider is connected to three push rods in the cylinder wall with each push rod connected to an exhaust valve in the cylinder head. The exhaust valves are spring loaded into the closed position. The inlet and exhaust are pushed open near the BDC of the piston movement. The valve springs include secondary springs which are engaged when the valves are pushed into the open setting, and thereby reinforce the normal valve springs. The top edge of the slider sleeve has a conical seal and a serrated lip which engages a similar profile on the bottom edge of the piston skirt, to prevent the piston from rotating.

<CIT> discloses an internal combustion engine with a scavenging control valve apparatus. A valve operating device drives a scavenging control valve according to an engine's crank angle. The valve operating device controls the scavenging control valve to synchronize the closing timing of a scavenging passage after a bottom dead position with the closing timing of an exhaust valve.

<CIT> discloses a low-pollution engine of the type that burns air and fuel to move a piston, wherein a separate combustion chamber is provided near one end of the cylinder and connected to the cylinder by a constricted passageway, the combustion chamber holding enough air to completely burn all of the fuel therein so that substantially only combustion products enter the cylinder. The walls of the combustion chamber are insulated so that they remain heated, and a perforated plate connects the combustion chamber to the cylinder so that the hot combustion products pass through the plate into the cylinder to heat extra air therein and move the piston. The combustion chamber and cylinder are both purged but by different amounts of air, and fuel is admitted to the combustion chamber by an injection nozzle whose fuel stream hits a target in the combustion chamber to further break up and disperse the fuel.

<CIT> discloses a diesel engine. The engine comprises a piston which works in a cylinder-liner. At the bottom end of the liner is a slide working with it to form a valve. This moves with the piston away from the liner so as to form with the latter an annular inlet port for scavenging air to the cylinder. The port shuts again with upward movement of the piston towards the top dead-centre position. The slide can be driven to and fro by the piston, while a first spring and-or damper unit is mounted between piston and slide. Further spring and-or damper units aid, restrict and-or damp movement of the slide.

<CIT> discloses an engine system that has an engine block that defines a cylinder bore, and a cylinder liner disposed within the cylinder bore. The engine system further has an air intake port radially formed within the cylinder liner, a piston within the cylinder liner to open and close the air intake port, a cylinder head to close off an end of the cylinder liner and form a combustion chamber, and an exhaust valve within the cylinder head.

In liquid fuel and fuel gas, in some cases, the optimum timing for causing the active gas to flow into the cylinder from the scavenging port may differ. Therefore, if the position of the scavenging port is designed in accordance with one of liquid fuel and fuel gas, in some cases, it is difficult to cause the active gas to flow into the cylinder at an appropriate timing when the other fuel is used.

Moreover, regardless of the presence or absence of fuel switching, the opening and closing timing of the scavenging port affects the efficiency of the engine. For example, if the scavenging port is close to the top dead center of the piston and the opening timing becomes earlier, there is a possibility that the expansion stroke will be shortened, thereby causing a decline in efficiency, and if the scavenging port is close to the bottom dead center of the piston and the closing timing becomes earlier, there is a possibility that the scavenging period of time will be shortened and a sufficient amount of active gas cannot be sucked.

Therefore, there is a demand for development of a technique for opening and closing the scavenging port at an appropriate timing depending on the operating conditions.

An object of the present disclosure is to provide a uniflow scavenging type two-cycle engine capable of opening and closing the scavenging port at an appropriate timing depending on the operating conditions.

This object is achieved by a uniflow scavenging type two-cycle engine having the features of claim <NUM>. Advantageous further developments are defined in the dependent claims.

According to the present disclosure, it is possible to open and close the scavenging port at an appropriate timing depending on the operating conditions.

Hereinafter, preferred embodiments of the present disclosure will be described in detail with reference to the attached drawings. Dimensions, materials, specific numerical values and the like of constituent elements shown in the present embodiment are merely examples for facilitating understanding of the invention, and do not limit the present disclosure unless otherwise specified. Further, in the specification and the drawings, by denoting elements having substantially the same functions and configurations by the same reference signs, repeated descriptions will be omitted, and elements not directly related to the present disclosure will not be shown.

<FIG> is an explanatory view showing an entire configuration of a uniflow scavenging type two-cycle engine <NUM>. The uniflow scavenging type two-cycle engine <NUM> is, for example, used in a ship or the like, and can selectively execute either one operation mode of a gas operation mode for mainly burning fuel gas that is gaseous fuel and a diesel operation mode for burning fuel oil that is liquid fuel. That is, the uniflow scavenging type two-cycle engine <NUM> is a dual-fuel type engine that switches the fuel between liquid fuel and fuel gas.

Specifically, the uniflow scavenging type two-cycle engine <NUM> is configured to include a cylinder <NUM>, a cylinder cover <NUM>, a piston <NUM>, a piston rod <NUM>, a scavenging port <NUM>, a scavenging reservoir <NUM>, a scavenging chamber <NUM>, a cooler <NUM>, a flow-adjusting plate <NUM>, a drain separator <NUM>, a combustion chamber <NUM>, an exhaust port <NUM>, an exhaust valve <NUM>, an exhaust valve drive device <NUM>, a liquid fuel injection valve <NUM>, a fuel gas main pipe <NUM>, a fuel injection device <NUM>, an annular pipe <NUM>, a fuel pipe <NUM>, a fuel injection port <NUM>, and a mover <NUM>. Hereinafter, in a central axis direction of the cylinder <NUM> (an up-down direction in the drawing of <FIG>), the cylinder cover <NUM>-side may be referred to as an upper side, and the scavenging chamber <NUM>-side may be referred to as a lower side.

In the uniflow scavenging type two-cycle engine <NUM>, the piston <NUM> slides inside the cylinder <NUM> (a cylinder liner 110a), and exhausting, intake, compression, combustion, and expansion are performed during two strokes of an up-stroke and a down-stroke of the piston <NUM>. One end of the piston rod <NUM> is fixed to the piston <NUM>. Further, a cross head (not shown) is connected to the other end of the piston rod <NUM>, and reciprocates with the piston <NUM>. When the cross head reciprocates with the reciprocation of the piston <NUM>, a crankshaft (not shown) rotates in conjunction with the reciprocation. Hereinafter, a direction in which the piston <NUM> reciprocates in the central axis direction of the cylinder <NUM> may be referred to as a stroke direction of the piston <NUM>.

The scavenging ports <NUM> are holes penetrating from an inner peripheral surface to an outer peripheral surface of the cylinder <NUM>, and the plurality of scavenging ports <NUM> are provided at intervals on the entire circumference of the cylinder <NUM>. Further, the scavenging ports <NUM> open in a process of movement of the piston <NUM> toward the bottom dead center, and cause active gas to flow into the cylinder <NUM>. The active gas contains oxygen, an oxidant such as ozone, or a mixture air thereof (for example, air). Although the scavenging port <NUM> of the present embodiment is formed in an oval shape extending in the stroke direction when viewed in the radial direction of the cylinder <NUM>, not being limited to such a shape, the scavenging port <NUM> may have, for example, a circular shape, an elliptical shape, a rectangular shape, a polygonal shape or the like. Hereinafter, the bottom dead center of the piston <NUM> may be referred to simply as a bottom dead center, and the top dead center of the piston <NUM> may be referred to simply as a top dead center.

Active gas (for example, air) compressed by a supercharger, a blower or the like (not shown) is cooled by the cooler <NUM> and is sealed in the scavenging reservoir <NUM>. The active gas flows in the scavenging reservoir <NUM> from the cooler <NUM> to the scavenging chamber <NUM>. The compressed and cooled active gas is flow direction-adjusted by the flow-adjusting plates <NUM> disposed in the scavenging reservoir <NUM>, and then water is removed therefrom by the drain separator <NUM>.

The scavenging chamber <NUM> communicates with the scavenging reservoir <NUM> and surrounds one end side (a lower side in <FIG>) of the cylinder <NUM> in the stroke direction of the piston <NUM> (hereinafter simply referred to as the stroke direction). The active gas subjected to compression, cooling, and removal of water is guided to the scavenging chamber <NUM> from the scavenging reservoir <NUM>.

The scavenging ports <NUM> open in the scavenging chamber <NUM>. When the piston <NUM> descends below the scavenging ports <NUM>, the inside of the cylinder <NUM> and the scavenging chamber <NUM> communicate with each other through the scavenging ports <NUM>, and the scavenging ports <NUM> suck the active gas into the cylinder <NUM> from the scavenging chamber <NUM> due to a pressure difference between the scavenging chamber <NUM> and the inside of the cylinder <NUM>.

When the piston <NUM> is close to the top dead center, the combustion chamber <NUM> is surrounded by the cylinder cover <NUM> (a cylinder head) disposed to cover an upper end opening portion of the cylinder <NUM>, the cylinder liner 110a, and the piston <NUM> and thus is formed inside the cylinder <NUM>. The active gas and the fuel gas sucked into the cylinder <NUM> are guided to the combustion chamber <NUM> by the piston <NUM>.

The exhaust port <NUM> is formed on the upper side of the combustion chamber <NUM> in <FIG> and is opened and closed to discharge the exhaust gas generated by burning the fuel gas in the cylinder <NUM> outward of the cylinder <NUM>. The exhaust valve <NUM> is slid up and down by the exhaust valve drive device <NUM> at predetermined timings to open and close the exhaust port <NUM>. After combustion of the fuel gas, when the exhaust valve <NUM> is opened, the exhaust gas in the cylinder <NUM> is pushed out of the exhaust port <NUM> by the active gas (scavenging air) flowing in from the scavenging ports <NUM>.

Further, as described above, a diesel operation mode and a gas operation mode are provided in the uniflow scavenging type two-cycle engine <NUM> of the present embodiment. A liquid fuel supply mechanism to be mainly used in the diesel operation mode and a fuel gas supply mechanism to be mainly used in the gas operation mode will be described below.

The liquid fuel injection valve <NUM> is provided on the cylinder cover <NUM>, and a tip thereof protrudes into the combustion chamber <NUM>, and the liquid fuel injection valve <NUM> injects the fuel oil from the tip into the combustion chamber <NUM> in the diesel operation mode.

The fuel gas main pipe <NUM> communicates with a fuel tank (not shown) and communicates with the annular pipe <NUM> via the fuel injection device <NUM>. The fuel gas is guided from the fuel tank to the fuel gas main pipe <NUM>, and when the fuel injection device <NUM> is operated, the fuel gas in the fuel gas main pipe <NUM> flows into the annular pipe <NUM>.

Here, the fuel gas is, for example, a gas generated by gasifying LNG (Liquefied Natural Gas). Further, the fuel gas is not limited to LNG, and it is possible to use a gas obtained by gasifying, for example, LPG (Liquefied Petroleum Gas), light oil, heavy oil or the like.

The annular pipe <NUM> is disposed radially outward of the cylinder <NUM> and above the scavenging ports <NUM> in <FIG> and extends annularly in the circumferential direction of the cylinder <NUM> to surround the cylinder <NUM>. A plurality of fuel pipes <NUM> are fixed to the scavenging port <NUM>-side of the annular pipe <NUM> in the stroke direction (that is, the lower side in <FIG>). One fuel pipe <NUM> is disposed for each scavenging port <NUM> and extends in the stroke direction. Hereinafter, the radial direction of the cylinder <NUM> may be referred to simply as a radial direction, and the circumferential direction of the cylinder <NUM> may be referred to simply as a circumferential direction.

The fuel pipe <NUM> faces a wall surface of the cylinder <NUM> between scavenging ports <NUM> adjacent to each other in the circumferential direction, and the fuel injection port <NUM> is formed on a portion of the fuel pipe <NUM> facing the wall surface. Here, since a plurality of scavenging ports <NUM> are provided on the entire circumference of the cylinder <NUM>, a plurality of fuel pipes <NUM> (the fuel injection ports <NUM>) are also provided in the circumferential direction of the cylinder <NUM> in accordance with the scavenging ports <NUM>.

The fuel injection ports <NUM> inject the fuel gas flowed into the annular pipe <NUM> into the active gas to be sucked into the scavenging ports <NUM>. As a result, the fuel gas joins the flow of the active gas and is sucked into the cylinder <NUM> from the scavenging ports <NUM> together with the active gas.

At a desired time point in the engine cycle, a suitable amount of the fuel oil (an amount smaller than in the diesel operation mode) is injected from the liquid fuel injection valve <NUM>. The fuel oil is vaporized by heat of the combustion chamber <NUM>. Further, the fuel oil is vaporized and spontaneously ignited and burns in a short time, the temperature of the combustion chamber <NUM> becomes extremely high, and the fuel gas guided to the combustion chamber <NUM> and compressed is burned. The piston <NUM> is reciprocated mainly by the expansion pressure due to the combustion of the fuel gas.

In the fuel gas and the fuel oil, that is, in the gas operation mode and the diesel operation mode, in some cases, the optimum timings for causing the active gas to flow into the cylinder <NUM> from the scavenging port <NUM> may be different. Therefore, if the position of the scavenging port <NUM> is designed in accordance with either one of the fuel gas and the fuel oil, in some cases, it may be difficult to cause the active gas to flow into the cylinder <NUM> at an appropriate timing when the other fuel is used.

Therefore, the uniflow scavenging type two-cycle engine <NUM> is provided with the mover <NUM> that changes the position of the scavenging port <NUM> in the stroke direction.

<FIG>, <FIG> are explanatory views showing the structure of the mover <NUM>. <FIG> extracts and shows the vicinity of the scavenging ports <NUM> in <FIG>, <FIG> shows a cross section taken along a line 3A-3A of <FIG>, and <FIG> shows a cross section taken along a line 3B-3B of <FIG>. Here, <FIG> show cross-sectional views each including the central axis of the cylinder <NUM>.

As shown in <FIG>, the cylinder <NUM> (the cylinder liner 110a) is configured to include an upper cylinder <NUM> on an upper side (the cylinder cover <NUM>-side of <FIG>) in <FIG>, and a lower cylinder <NUM> disposed below (the piston <NUM>'s bottom dead center-side of) the upper cylinder <NUM> in <FIG>. The upper cylinder <NUM> is positioned to be closer to the piston <NUM>'s top dead center than the lower cylinder <NUM>, and the scavenging ports <NUM> are formed in the lower cylinder <NUM>.

On an inner peripheral surface of the lower end portion on the lower side (the lower cylinder <NUM>-side) of the upper cylinder <NUM> in <FIG>, an upper groove 152a recessed radially outward from the inner peripheral surface is provided. As shown in <FIG>, a plurality of upper grooves 152a are provided at intervals in the circumferential direction, and extend in the stroke direction. The upper grooves 152a open downward of the upper cylinder <NUM>.

Further, on the upper end surface 154a on the upper side (the upper cylinder <NUM>-side) of the lower cylinder <NUM> in <FIG>, a lower protrusion 154b protruding toward the upper cylinder <NUM> is provided. The lower protrusion 154b is provided in a portion on the radially inner side of the upper end surface 154a. As shown in <FIG>, a plurality of lower protrusions 154b are provided to be spaced apart from each other in the circumferential direction at the same intervals as the upper grooves 152a, and the length (height) in the stroke direction of the lower protrusion 154b is substantially equal to the length in the stroke direction of the upper groove 152a.

Further, the upper end surface 154a (end portion) of the lower cylinder <NUM> is inserted through (into) the upper cylinder <NUM> in the stroke direction, and the plurality of lower protrusions 154b of the lower cylinder <NUM> are inserted into the plurality of upper grooves 152a of the upper cylinder <NUM> in the stroke direction. That is, the upper end portion of the lower cylinder <NUM> other than the lower protrusions 154b is closely inserted into the lower end portion of the upper cylinder <NUM> below the upper grooves 152a to be slidable in the stroke direction. By fitting the lower protrusion 154b into the upper groove 152a, circumferential rotation of the lower cylinder <NUM> with respect to the upper cylinder <NUM> is restricted. In addition, the lower protrusion 154b can slide in the upper groove 152a in the stroke direction, and the lower cylinder <NUM> can relatively move with respect to the upper cylinder <NUM> in the stroke direction.

Further, the inner diameter of the upper cylinder <NUM> (the inner diameter of the portion of the upper cylinder <NUM> above the upper grooves 152a) and the inner diameter of the lower cylinder <NUM> are substantially equal to each other, and portions in which the lower protrusions 154b are inserted into the upper grooves 152a are designed such that there are almost no steps in the circumferential direction.

The mover <NUM> is provided in a connection portion between the upper cylinder <NUM> and the lower cylinder <NUM>, and moves the lower cylinder <NUM> in the stroke direction with respect to the upper cylinder <NUM>. Specifically, the mover <NUM> is configured of a hydraulic mechanism, and includes a hydraulic piston <NUM> and a hydraulic chamber <NUM>. However, the mover <NUM> is not limited to a hydraulic mechanism, and may have any configuration as long as the lower cylinder <NUM> can be moved in the stroke direction with respect to the upper cylinder <NUM>.

A hollow portion 152c is provided in a portion of the lower end portion of the upper cylinder <NUM>, which is radially outward of the upper grooves 152a. A plurality (for example, four in this case) of hollow portions 152c are disposed to be spaced apart from each other in the circumferential direction of the upper cylinder <NUM>, and symmetrically with respect to the central axis of the upper cylinder <NUM>. That is, the hollow portions 152c are disposed at equal intervals in the circumferential direction of the upper cylinder <NUM>. The hydraulic piston <NUM> is disposed inside the hollow portion 152c to be slidable in the stroke direction, and divides the hollow portion 152c into two spaces in the stroke direction.

The hydraulic chamber <NUM> is a space on the lower side (the lower cylinder <NUM>-side) of the hollow portion 152c in <FIG>, which is partitioned by the hydraulic piston <NUM>. The hydraulic chamber <NUM> communicates with an oil pump (not shown), and pressure-increased hydraulic oil is supplied from the oil pump to the hydraulic chamber <NUM>.

When the hydraulic oil is supplied to the hydraulic chamber <NUM>, the hydraulic piston <NUM> is moved upward in <FIG> by the hydraulic pressure of the hydraulic oil supplied to the hydraulic chamber <NUM>. Further, when the hydraulic oil is discharged from the hydraulic chamber <NUM>, the hydraulic piston <NUM> moves downward in <FIG> by gravity. Further, for example, a configuration in which the pressure-increased hydraulic oil is alternately supplied to the two spaces divided by the hydraulic piston <NUM> in the hollow portion 152c and the hydraulic piston <NUM> reciprocates in the stroke direction may be provided. The movement of the hydraulic piston <NUM> to either one side in the stroke direction may be performed by the hydraulic oil, and the movement to the other side may be performed by another external force (gravity or a pushing force of a spring or the like).

A shaft <NUM> is fixed to the lower side of the hydraulic piston <NUM> in <FIG>. The shaft <NUM> penetrates a wall portion of the upper cylinder <NUM> below the hydraulic chamber <NUM> in <FIG> and extends to a position below the scavenging port <NUM> in the stroke direction. The lower end portion of the shaft <NUM> is fixed to a protrusion 154c provided on the outer peripheral surface of the lower cylinder <NUM>.

<FIG> is an explanatory view showing the operation of the mover <NUM>. The part (a) of <FIG> shown on the upper side of the drawing of <FIG> shows a state in which the lower cylinder <NUM> is at the uppermost position (a position at which the lower cylinder <NUM> is closest to the top dead center of the piston <NUM>, and a position at which the lower cylinder <NUM> is closest to the upper cylinder <NUM>). The part (b) of <FIG> shown on the lower side of the drawing of <FIG> shows a state in which the lower cylinder <NUM> is at the lowermost position (a position at which the lower cylinder <NUM> is farthest away from the top dead center of the piston <NUM> in the stroke direction, and a position at which the lower cylinder <NUM> is farthest away from the upper cylinder <NUM> in the stroke direction). As shown in the parts (a) and (b) of <FIG>, when the hydraulic piston <NUM> moves upward in <FIG> by hydraulic pressure or the like, the lower cylinder <NUM> connected to the hydraulic piston <NUM> via the shaft <NUM> also moves upward. Similarly, when the hydraulic piston <NUM> moves downward in <FIG> by hydraulic pressure or the like, the lower cylinder <NUM> also moves downward.

In this way, a configuration in which the position of the lower cylinder <NUM> with respect to the upper cylinder <NUM> is displaced in the stroke direction by the mover <NUM> is provided. As a result, the position of the scavenging port <NUM> provided in the lower cylinder <NUM> is also displaced in the stroke direction. That is, the opening position 118a on the piston <NUM>'s top dead center-side of the scavenging port <NUM> is displaced in the stroke direction. In other words, the position of the opening edge on the piston <NUM>'s top dead center-side of the scavenging port <NUM> (the position of the opening edge closest to the top dead center of the piston <NUM>, the position of the opening edge closest to the upper cylinder <NUM>) can be changed in the stroke direction by the mover <NUM>.

As described above, in the fuel gas and the fuel oil, in some cases, the optimum timings for causing the active gas to flow into the cylinder <NUM> from the scavenging port <NUM> may differ. Specifically, in the case of using the fuel oil, in some cases, it may be preferable that the scavenging port <NUM> be disposed at a position away from the top dead center (the lower side in <FIG>) to secure a long expansion stroke after the fuel combustion. On the other hand, in the case of using the fuel gas, in some cases, in order to discharge a large amount of high-temperature exhaust gas in the combustion chamber <NUM> which causes preignition, it may be preferable that the scavenging port <NUM> be disposed to be close to the top dead center (the upper side in <FIG>) to start the scavenging by the active gas early.

In the diesel operation mode using the fuel oil, as shown in the part (b) of <FIG>, by moving the lower cylinder <NUM> downward, and in the gas operation mode using the fuel gas, as shown in the part (a) of <FIG>, by moving the lower cylinder <NUM> upward, it is possible to cause the active gas to flow into the cylinder <NUM> from the scavenging port <NUM> at an appropriate timing. As a result, in the diesel operation mode, a long expansion stroke can be secured to improve the efficiency, and in the gas operation mode, it is possible to increase the injection amount of the fuel gas and to raise the output because the occurrence of preignition is limited.

Further, as shown in the part (a) of <FIG>, in a state in which the lower cylinder <NUM> is displaced to the closemost positon to the top dead center, the opening position 118a on the top dead center-side of the scavenging port <NUM> is to be closer to the bottom dead center than the lower end surface 152b of the upper cylinder <NUM> (the end portion on the bottom dead center-side).

Therefore, it is possible to avoid a situation in which the upper cylinder <NUM> covers part of the scavenging port <NUM> and the inflow of the active gas from the scavenging port <NUM> is disturbed by the upper cylinder <NUM>, and it is possible to perform inflow of the active gas at an appropriate timing.

<FIG> is an explanatory view showing an entire configuration of a uniflow scavenging type two-cycle engine <NUM> of a modified example of the above embodiment. In the embodiment described above, the case in which the fuel injection port <NUM> of the fuel gas supply mechanism injects the fuel gas into the active gas to be sucked into the scavenging port <NUM> has been described. In the present modified example, a fuel injection port <NUM> of the fuel gas supply mechanism is provided in a portion of the cylinder <NUM> between the scavenging port <NUM> and the exhaust port <NUM>.

A plurality of fuel injection ports <NUM> are provided at intervals in the circumferential direction of the cylinder <NUM>. A fuel injection valve <NUM> is disposed at each fuel injection port <NUM>. The fuel injection valve <NUM> communicates with a fuel pipe <NUM> and injects the fuel gas guided from the fuel pipe <NUM> into the cylinder <NUM> through the fuel injection port <NUM>.

In this way, the fuel gas supply mechanism is not limited to the configuration in which the fuel injection port <NUM> injects the fuel gas into the active gas to be sucked into the scavenging port <NUM>, and may have a configuration in which the fuel injection port <NUM> is provided in the cylinder <NUM> and the fuel gas is supplied from the fuel injection port <NUM> into the cylinder <NUM>.

Although the embodiments of the present disclosure have been described above with reference to the attached drawings, the present disclosure is not limited to the above-described embodiments. The shapes, combinations, and the like of the constituent members described in the above embodiments are merely examples, and addition, omission, substitution, and other changes of the configuration can be adopted based on design requirements and the like within the technical scope of the present disclosure.

For example, in the embodiment and the modified example described above, a case has been described in which the cylinder <NUM> is configured to include the upper cylinder <NUM> and the lower cylinder <NUM>, and the mover <NUM> displaces the lower cylinder <NUM> with respect to the upper cylinder <NUM> in the stroke direction, thereby allowing the displacement of the entire scavenging port <NUM> in the stroke direction. That is, a configuration in which the position of the opening edge on the top dead center-side of the scavenging port <NUM> changes in the stroke direction may be adopted, and a configuration in which the entire scavenging port <NUM> is displaced in the stroke direction may be adopted.

Further, in the embodiment and the modified example described above, the case in which the uniflow scavenging type two-cycle engines <NUM> and <NUM> are dual-fuel type engines that switch fuel between the liquid fuel and the fuel gas has been described. However, the uniflow scavenging type two-cycle engines <NUM> and <NUM> are not limited to the dual-fuel types, and may be engines that use only one of the liquid fuel and the fuel gas. However, when the uniflow scavenging type two-cycle engine is a dual-fuel type, in each of the gas operation mode and the diesel operation mode, the scavenging port <NUM> can be opened at an appropriate timing, and the active gas can be allowed to flow into the cylinder <NUM>.

Further, in the embodiment and the modified example described above, the case in which the lower cylinder <NUM> is displaced in the stroke direction in accordance with the operation mode has been described. However, the lower cylinder <NUM> is not displaced in accordance with the operation mode but may be displaced in the stroke direction in accordance with the stroke of the engine. For example, in the expansion stroke, when the lower cylinder <NUM> is positioned to be close to the bottom dead center as shown in the part (b) of <FIG>, the timing at which the scavenging port <NUM> starts to open is delayed, and the expansion stroke is lengthened, thereby making it possible to improve the efficiency.

On the other hand, in the compression stroke, when the lower cylinder <NUM> is positioned to be close to the top dead center as shown in the part (a) of <FIG>, the timing at which the scavenging port <NUM> is closed is delayed, and the scavenging (intake) period of time is lengthened, thereby making it possible to efficiently perform the inflow of the active gas and the discharge of the exhaust gas.

In addition, a configuration may be adopted in which when either one of the gas operation mode and the diesel operation mode is performed, the position of the opening edge on the top dead center-side of the scavenging port <NUM> or the position of the entire scavenging port <NUM> is changed in the stroke direction depending on the operating conditions (the time of accelerating or decelerating) or the rotational speed of the engine in order to improve the engine efficiency.

In the embodiment and the modified example described above, the case in which the end portion (the upper end portion) of the lower cylinder <NUM> is inserted through (into) the inside of the upper cylinder <NUM> (the inside of the lower end portion thereof) has been described. However, the end portion (the lower end portion) of the upper cylinder <NUM> may be inserted into the inside of the lower cylinder <NUM> (the inside of the upper end portion thereof). However, when the end portion of the lower cylinder <NUM> is inserted into the inside of the upper cylinder <NUM>, the outer diameter of the lower cylinder <NUM> can be reduced to reduce the weight thereof, and the driving force required for the mover <NUM> can be reduced.

Further, in the embodiment and the modified example described above, the case has been described in which in a state where the lower cylinder <NUM> is displaced to the closemost position to the top dead center, the opening position 118a on the top dead center-side of the scavenging port <NUM> is to be closer to the bottom dead center than the end portion on the bottom dead center-side of the upper cylinder <NUM>. However, the opening position on the top dead center-side of the scavenging port <NUM> may be the same as the end portion on the bottom dead center-side of the upper cylinder <NUM> or may be positioned to be closer to the top dead center than the end portion.

Moreover, although the case in which the plurality of upper grooves 152a and the plurality of lower protrusions 154b are each provided at intervals in the circumferential direction has been described in the embodiment and modified example described above, the upper grooves 152a and the lower protrusions 154b are not essential structures. However, by providing the upper grooves 152a and the lower protrusions 154b, the circumferential rotation of the lower cylinder <NUM> with respect to the upper cylinder <NUM> can be restricted by a simple configuration. Further, by providing the plurality of upper grooves 152a and the plurality of lower protrusions 154b, it is possible to limit the abutment of a piston ring (the end portion forming the abutment) provided in the piston <NUM> from catching in the upper groove 152a or in the portion between lower protrusions 154b adjacent to each other in the circumferential direction, and the piston <NUM> can slide smoothly on the inner peripheral surface of the cylinder <NUM>. If the number of the upper grooves 152a and the lower protrusions 154b provided in the circumferential direction is increased, it is possible to further limit the abutment of the piston ring provided in the piston <NUM> from catching in the upper grooves 152a or the like.

In the embodiment and the modified example described above, although the cylinder cover <NUM>-side is referred to as the upper side and the scavenging chamber <NUM>-side is referred to as the lower side in the central axis direction of the cylinder <NUM>, this description does not limit the posture of the uniflow scavenging type two-cycle engines <NUM> and <NUM> in actual use, and they may be used in any posture as long as suitable operation can be ensured.

Claim 1:
A uniflow scavenging type two-cycle engine (<NUM>, <NUM>) being a dual-fuel type which switches fuel between liquid fuel and fuel gas, comprising:
a cylinder (<NUM>) including a lower cylinder (<NUM>), and an upper cylinder (<NUM>) disposed to be closer to a top dead center of a piston (<NUM>) than the lower cylinder (<NUM>);
a scavenging port (<NUM>) which is formed in the lower cylinder (<NUM>), is a hole penetrating from an inner peripheral surface to an outer peripheral surface of the lower cylinder (<NUM>), opens in a process of movement of the piston (<NUM>) toward a bottom dead center, and causes active gas to flow into the cylinder (<NUM>); and
a mover (<NUM>) which displaces an opening position (118a) on a piston top dead center-side of the scavenging port (<NUM>) in a stroke direction of the piston (<NUM>), wherein
the mover (<NUM>) is configured to displace the lower cylinder (<NUM>) with respect to the upper cylinder (<NUM>) in the stroke direction of the piston (<NUM>) so as to open and close the scavenging port (<NUM>) at an appropriate timing depending on the fuel used.