A uniflow scavenging two-cycle engine includes an scavenging port having a swirling guide portion that guides scavenging gas into a cylinder in a direction inclined with respect to a radial direction of the cylinder, and a center guide portion that is provided to be closer to a crank side of the cylinder than the swirling guide portion and guides the scavenging gas further toward the center side of the cylinder than the swirling guide portion. At least a part of the center guide portion faces a piston when the piston is positioned at bottom dead center during the high compression ratio mode, and the center guide portion and the piston do not face each other or an area of facing the piston is smaller than that during the high compression ratio mode when the piston is positioned at bottom dead center during the low compression ratio mode.

TECHNICAL FIELD

The present disclosure relates to a uniflow scavenging two-cycle engine in which a compression ratio is variable.

BACKGROUND ART

A uniflow scavenging two-cycle engine used as an engine in a ship is provided with an exhaust port on one end side and a scavenging port on the other end side of a cylinder. When active gas is suctioned from the scavenging port to a combustion chamber in an intake stroke, exhaust gas produced in combustion behavior is pushed and is exhausted from the exhaust port with the suctioned active gas.

For example, Patent Document 1 discloses a scavenging port inclined with respect to a radial direction of a cylinder. Since scavenging gas flowing into the cylinder from the scavenging port flows with swirl, the scavenging gas is easy to maintain a separation state from an exhaust gas layer in the cylinder, and scavenging efficiency is improved. In addition, Patent Document 2 discloses a configuration in which a scavenging port is a so-called skewed port. Here, the skewed port is a port having a portion on an exhaust port side that is inclined with respect to a radial direction of the cylinder and a portion on a side opposite to the exhaust port that is parallel to the radial direction of the cylinder. The scavenging port is the skewed port, and thereby leveling of a scavenging speed is achieved when the scavenging gas flow toward a combustion chamber.

CITATION LIST

Patent Document

SUMMARY

Incidentally, in a dual-fuel engine that uses a liquid fuel and fuel gas, a compression ratio is variable in some cases. In an engine in which the compression ratio is variable, when the scavenging port is the skewed port disclosed in Patent Document 2, blow-by of the fuel gas is reduced at a low compression ratio because the scavenging speed is leveled. On the other hand, since the liquid fuel is injected in a high compression ratio, the blow-by of the fuel gas does not occur and the scavenging speed does not need to be leveled. Therefore, in the high compression ratio, compared to a case where the scavenging port for producing the swirling flow which is disclosed in Patent Document 1 is used, the swirling flow is weak and the scavenging efficiency is likely to be lowered.

In consideration of such a problem, an object of the present disclosure is to provide a uniflow scavenging two-cycle engine that is capable of performing appropriate scavenging in response to a compression ratio.

A first aspect according to a uniflow scavenging two-cycle engine of the present disclosure relates to the uniflow scavenging two-cycle engine that includes an exhaust port formed on one end side of a cylinder in which a piston reciprocates and a scavenging port formed on the other end side of the cylinder, and that switches between at least two operation modes of a low compression ratio mode and a high compression ratio mode in which top dead center and bottom dead center of the piston is positioned to be closer to the exhaust port side than in the low compression ratio mode. The scavenging port has a swirling guide portion that guides scavenging gas from an outside to an inside of the cylinder in a direction inclined with respect to a radial direction of the cylinder, and a center guide portion that is provided to be closer to the other end side of the cylinder than the swirling guide portion and guides the scavenging gas further toward the center side of the cylinder than the swirling guide portion. At least a part of the center guide portion faces the piston in a case where the piston is positioned at bottom dead center during the high compression ratio mode, and the center guide portion and the piston does not face each other or an area of facing the piston is smaller than that during the high compression ratio mode in a case where the piston is positioned at bottom dead center during the low compression ratio mode.

According to the uniflow scavenging two-cycle engine of the present disclosure, it is possible to perform appropriate scavenging in response to a compression ratio.

DESCRIPTION OF EMBODIMENTS

Hereinafter, an embodiment according to the present disclosure will be described with reference to the accompanying figures. The dimensions, the materials, the specific numbers other than the dimensions and the materials, or the like are provided only as examples for easy understanding of the disclosure, and the disclosure is not limited thereto except for a case where a particular description is provided. Note that, in the present specification and the figures, an element having substantially the same function and configuration is assigned with the same reference sign and a repeated description thereof is omitted, and illustration of an element without a direct relationship with the present disclosure is omitted in the figures.

In the following embodiment, it is possible to execute by selecting one from a gas operation mode in which a fuel gas as a gaseous fuel is mainly combusted or a diesel operation mode in which fuel oil as the liquid fuel is combusted. The so-called dual-fuel type uniflow scavenging two-cycle engine is described. However, a type of engine is not limited to the dual fuel, and may be a uniflow scavenging two-cycle engine.

FIG. 1is a view showing an entire configuration of a uniflow scavenging two-cycle engine100. The uniflow scavenging two-cycle engine100of the embodiment is used in a ship or the like. The uniflow scavenging two-cycle engine100is configured to include a cylinder110, a piston112, a crosshead114, a connecting rod116, a crankshaft118, an exhaust port120, an exhaust valve driving device122, an exhaust valve124, a scavenging port126, a scavenging chamber128, a first fuel supply unit130, an auxiliary fuel supply unit132, a main combustion chamber134a, an auxiliary combustion chamber134b, a second fuel supply unit136, a rotary encoder138, a governor140(speed regulator), a fuel supply control unit142, and an exhaust control unit144.

In the uniflow scavenging two-cycle engine100, the piston112reciprocates in the cylinder110through four continuous strokes of intake (gas feeding), compression, combustion, and exhaust. One end of a piston rod112ais fixed to the piston112. The crosshead114is fixed to the other end of the piston rod112a, and the crosshead114reciprocates along with the piston112. A crosshead shoe114aregulates movement of the crosshead114in a direction (rightward-leftward direction inFIG. 1) perpendicular to a stroke direction of the piston112(hereinafter, abbreviated to the stroke direction) in the cylinder110.

One end of the connecting rod116is rotatably supported in the crosshead114. In addition, the other end of the connecting rod116is connected to the crankshaft118and the crankshaft118is structured to rotate with respect to the connecting rod116. As a result, when the crosshead114reciprocates in response to the reciprocating of the piston112, the crankshaft118rotates by interlocking with the reciprocating of the crosshead114.

In the uniflow scavenging two-cycle engine, since it is possible to form a relatively long stroke in the cylinder110and it is possible to cause the crosshead114to receive lateral pressure acting on the piston112, it is possible to achieve a high output of the uniflow scavenging two-cycle engine100.

The exhaust port120is provided in a cylinder head110apositioned on an upper side from a position of top dead center of the piston112inFIG. 1. In other words, the exhaust port120is formed on the one end side (upper end side inFIG. 1) of the cylinder110in the stroke direction of the piston112. The exhaust port120is opened and closed to discharge exhaust gas produced after combustion in the cylinder110. The exhaust valve driving device122opens and closes the exhaust port120by causing the exhaust valve124to slide vertically at a predetermined timing. In this manner, the exhaust gas discharged via the exhaust port120is discharged to the outside, for example, after the exhaust gas is supplied to a turbine side of a supercharger (not shown).

The scavenging port126is a hole penetrating from an inner circumferential surface (inner circumferential surface of a cylinder block110b) to an outer circumferential surface of the cylinder110on the other end side (lower end side inFIG. 1) in the stroke direction of the piston112, and a plurality of scavenging ports are provided all around the cylinder110. The scavenging ports126suction active gas in the cylinder110in response to a sliding motion of the piston112. The active gas contains an oxidizing agent such as oxygen or ozone, or a mixture thereof (for example, air). The active gas (for example, air) pressurized by a compressor of the supercharger (not shown) is sealed in the scavenging chamber128, and the active gas is suctioned from the scavenging port126due to differential pressure between the scavenging chamber128and the cylinder110. The pressure in the scavenging chamber128can be substantially constant; however, a manometer may be provided in the scavenging port126in a case where the pressure in the scavenging chamber128changes, and other parameters such as an injection amount of the fuel gas according to a measurement value may be controlled.

The first fuel supply unit130is disposed on the outer circumferential side in the cylinder110from the scavenging port126, and causes the active gas and a premixture (fuel gas) to be suctioned from the scavenging port126into the cylinder110in the gas operation mode. Hereinafter, the first fuel supply unit130will be described in detail with reference toFIGS. 2A and 2B.

FIGS. 2A and 2Bare views showing the first fuel supply unit130, andFIG. 2Ais an enlarged view showing the vicinity of the first fuel supply unit130of a side view of the cylinder110. In addition,FIG. 2Bis an enlarged view of a portion in a dashed line inFIG. 2A.

As shown inFIG. 2A, the first fuel supply unit130has mixture pipes130aand130bwhich are separately formed from the cylinder110. The mixture pipes130aand130bare annular members surrounding the cylinder110from the outside in the radial direction along a circumferential direction. The mixture pipe130ais disposed on the one end side (upper side inFIG. 2A) of the piston112from the scavenging port126in the stroke direction, and the mixture pipe130bis disposed on the other end side (lower side inFIG. 2A) of the piston112from the scavenging port126in the stroke direction.

The mixture pipes130aand130bare provided with a mixture chamber that is formed in the inside thereof and extends to have an annular shape, and the fuel gas and the active gas are mixed in the mixture chamber such that the premixture is generated.

A plurality of circulation pipes130cthat extend in the stroke direction of the piston112are disposed between the mixture pipes130aand130bin the circumferential direction of the mixture pipes130aand130b. Of the adjacent circulation pipes130c, one pipe communicates with the mixture pipe130a, and the other pipe communicates with the mixture pipe130b. The premixture from the mixture pipe130aor the mixture pipe130bis circulated in the circulation pipe130c.

When the first fuel injecting valve (not shown) is opened, the premixture is ejected from an injection opening130dformed on the side surface of the circulation pipe130cshown inFIG. 2B. As a result, the premixture is sprayed from the injection opening130dof the first fuel supply unit130toward the active gas flowing toward the scavenging port126from the scavenging chamber128. Hereinafter, the premixture is simply referred to as the fuel gas except for a case where the premixture and the fuel gas are particularly distinguished.

Back toFIG. 1, the auxiliary fuel supply unit132is an injection valve provided in the cylinder head110a. The uniflow scavenging two-cycle engine100includes the main combustion chamber134aand the auxiliary combustion chamber134b, as the combustion chamber. The main combustion chamber134ais surrounded by the cylinder head110a, a cylinder liner in a cylinder block110b, and the piston112. The auxiliary combustion chamber134bis formed inside the cylinder head110aand has one end that projects from the cylinder head110atoward the main combustion chamber134aside.

FIGS. 3A to 3Care views for showing the auxiliary fuel supply unit132. InFIGS. 3A to 3C, the second fuel supply unit136is omitted for easy understanding. As shown inFIG. 3A, the auxiliary fuel supply unit132has the front end that is opened to the auxiliary combustion chamber134b, and the fuel oil is ejected toward the auxiliary combustion chamber134bin the gas operating mode.

The fuel oil ejected to the auxiliary combustion chamber134bignites with heat in the auxiliary combustion chamber134bas shown inFIG. 3B. As shown inFIG. 3C, the fuel gas and the exhaust gas combusted in the auxiliary combustion chamber134bis ejected along with flame to the main combustion chamber134a, and the fuel gas suctioned into the cylinder110from the scavenging port126is combusted.

Back toFIG. 1, the second fuel supply unit136is an ejecting valve provided in the cylinder head110a, has the front end that is opened to the main combustion chamber134a, and the fuel oil is injected toward the main combustion chamber134ain the diesel operation mode.

As described above, the fuel gas is supplied from the first fuel supply unit130into the cylinder110in the gas operation mode, and the fuel oil is supplied from the second fuel supply unit136into the cylinder110in the diesel operation mode. At this time, an appropriate compression ratio varies for the gas operation mode and the diesel operation mode. Specifically, the gas operation mode is performed at the low compression ratio, and the diesel operation mode is performed at the high compression ratio. In other words, the gas operation mode is equivalent to the low compression ratio mode, and the diesel operation mode is equivalent to the high compression ratio mode. In the embodiment, a variable compression ratio mechanism is provided in a connecting portion between the piston rod112aand the crosshead114in order to make the compression ratio variable.

FIGS. 4A and 4Bare views showing the variable compression ratio mechanism146, and show the connecting portion between the piston rod112aand the crosshead114. Since the gas operation mode is performed at the low compression ratio, as shown in FIG.4A, the piston rod112aand a crosshead pin114bare directly connected to each other.

On the other hand, since the diesel operation mode is performed at the high compression ratio, as shown inFIG. 4B, a shim plate148is interposed between the piston rod112aand the crosshead pin114b, and the positions of the top dead center and the bottom dead center of the piston112are shifted to the exhaust port120side. In this manner, the variable compression ratio mechanism146is capable of reducing the volume of the main combustion chamber134aat the top dead center so as to increase the compression ratio.

Back toFIG. 1, the rotary encoder138is provided in the crankshaft118and an angle signal of the crankshaft (hereinafter, referred to as a crank angle signal) is detected.

The governor140calculates a fuel injection amount, based on an engine output command value input from a higher control device and engine speed in response to a crank angle signal from the rotary encoder138, and outputs the calculated amount to the fuel supply control unit142.

The fuel supply control unit142controls the first fuel supply unit130and the second fuel supply unit136, based on information representing a fuel injection amount input from the governor140, information representing the operation mode, and the crank angle signal from the rotary encoder138.

The exhaust control unit144outputs an exhaust valve operation signal to the exhaust valve driving device122, based on information representing the fuel injection amount from the fuel supply control unit142, information representing the operation mode, and the crank angle signal from the rotary encoder138.

FIGS. 5A to 5Care views showing the scavenging port126,FIG. 5Ashows enlarged portion in the vicinity of the scavenging port126of a side view of the cylinder110,FIG. 5Bis a sectional view taken along line IV(b)-IV(b) inFIG. 5A, andFIG. 5Cis a sectional view taken along line IV(c)-IV(c) inFIG. 5A.

The center of the piston112is represented by a dashed line inFIG. 5A. A swirling guide portion126ais formed on one end side (upper side inFIG. 5A) of the scavenging port126in the stroke direction from the center of the stroke direction. In addition, a center guide portion126bis formed on the other end side (lower side inFIG. 5A) in the stroke direction of the cylinder110from the swirling guide portion126a.

As shown inFIG. 5B, the swirling guide portion126ahas a shape that guides the scavenging gas from an outside to an inside of the cylinder110in a direction inclined with respect to a radial direction of the cylinder110. Specifically, the swirling guide portion126aextends in a direction inclined with respect to the radial direction of the cylinder110. In addition, any scavenging port126provided over the entire circumference of the cylinder110is also inclined substantially to the equal extent that the swirling guide portion126ais inclined. As a result, as shown with an arrow inFIG. 5B, the scavenging gas forms swirling flow, and rises in the cylinder110so as to flow to the exhaust port120side.

As shown with an arrow inFIG. 5C, the center guide portion126bhas a shape that guides the scavenging gas toward the center side of the cylinder110from the swirling guide portion126a. Specifically, the center guide portion126bis an opening toward the center of the cylinder110and extends in the radial direction of the cylinder110. As a result, as shown with an arrow inFIG. 5C, while the scavenging gas flows toward the center side of the cylinder110in the radial direction thereof, the scavenging gas rises in the cylinder110and flows to the exhaust port120side.

In this manner, the scavenging port126is a so-called skewed port. Operations performed and problems arising in the case where the scavenging port126is the skewed port are described with reference toFIGS. 6A and 6B.

FIGS. 6A and 6Bare views showing flow of scavenging gas in a comparative example.FIG. 6Ashows flow of scavenging gas in a first comparative example, andFIG. 6Bshows flow of scavenging gas in a second comparative example, in a state in which the piston112is positioned at the bottom dead center. In the first comparative example, a scavenging port S1entirely becomes a swirling guide portion S1a, and, in the second comparative example, a scavenging port S2becomes a skewed port.

As shown inFIG. 6A, in the first comparative example, since the scavenging port S1entirely becomes the swirling guide portion S1a, a swirling flow (represented by an arrow inFIG. 6A) is strong in the flow of scavenging gas, the scavenging gas is likely to maintain a separation state from an exhaust gas layer in the cylinder110, and thus scavenging efficiency is improved.

On the other hand, as understood when speed distribution of the scavenging gas to the exhaust port120side which is shown in a dashed line inFIG. 6A, the speed is likely to decrease in the central portion in the radial direction of the cylinder110. At this time, since the fuel gas is mixed in the scavenging gas in the case of the gas operation mode (low compression ratio mode), there is a possibility that blow-by of the fuel gas which is not combusted from the exhaust port120is likely to be performed when uneven speed distribution of the scavenging gas is existed.

In contrast, when the scavenging port S2is the skewed port as in the second comparative example, since the scavenging gas flows toward the center side of the cylinder110in the radial direction by a center guide portion S2b, a speed on the center side of the cylinder110in the radial direction increases toward the exhaust port120. As a result, as shown with dashed line inFIG. 6B, the speed distribution of the scavenging gas toward the exhaust port120side is more leveled than in the first comparative example, and the blow-by of the fuel gas are reduced.

However, as shown with an arrow inFIG. 6B, when the scavenging port S2is the skewed port, the swirling flow is likely to be weaker than in the first comparative example due to the extent that the center guide portion S2bis provided. For example, in the case of the diesel operation mode (high compression ratio mode), since the fuel gas is not injected from the first fuel supply unit130as in the gas operation mode, a priority is given to maintaining of the separation state between the scavenging gas and the exhaust gas without a concern of an occurrence of the blow-by of the fuel gas. However, since the swirling flow is weak in the second modification example, the scavenging efficiency is likely to be lowered.

FIGS. 7A and 7Bare views showing the flow of scavenging gas in the embodiment.FIG. 7Ashows a state in which the piston112is positioned at the bottom dead center in the gas operation mode, andFIG. 7Bshows a state in which the piston112is positioned at the bottom dead center in the diesel operation mode.

As shown inFIG. 7A, in the gas operation mode (low compression ratio mode), similar to the second comparative example, the center guide portion126bcauses the scavenging gas to flow toward the center side of the cylinder110in the radial direction. Therefore, as shown with a dashed line inFIG. 7A, the speed distribution of the scavenging gas toward the exhaust port120side is more leveled than in the first comparative example, and the blow-by of the fuel gas are reduced.

On the other hand, as shown inFIG. 7B, in the diesel operation mode (high compression ratio mode), the position of the top dead center and the bottom dead center of the piston112are more shifted to the exhaust port120side than in the gas operation mode (low compression ratio mode). When the piston112is positioned at the bottom dead center in the diesel operation mode (high compression mode), the center guide portion126bhas a positional relationship of facing the piston112(side wall of the piston112) in the radial direction of the piston112by this shift. Therefore, the scavenging gas does not almost flow in the cylinder110from the center guide portion126b, and the majority of scavenging gas flows in the cylinder110from the swirling guide portion126a. As a result, as shown with an arrow inFIG. 7B, the swirling flow becomes strong and the scavenging efficiency in improved.

As described above, actual opening conditions of the center guide portion126bof the scavenging port126(skewed port) are adjusted by the position of the bottom dead center of the piston112, and thereby it is possible to perform appropriate scavenging in response to the compression ratio.

In the embodiment described above, in the case where the piston112is positioned at the bottom dead center in the low compression ratio mode, a case where the center guide portion126band the piston112do not face each other is described. However, the center guide portion126bmay have a smaller area of facing the piston112in the low compression ratio mode than at least in the high compression ratio mode.

In addition, in the embodiment described above, the case where the swirling guide portion126aand the center guide portion126bform one scavenging port126is described. However, the swirling guide portion126aand the center guide portion126bmay individually form ports, or two ports may have a part in which the two ports are connected.

In addition, in the embodiment described above, the case where the first fuel supply unit130ejects, from the injection opening130d, the premixture obtained by mixing the fuel gas and the active gas, is described. However, instead of the premixture, the fuel gas may be injected from the injection opening130d.

In addition, in the embodiment described above, the case where the first fuel supply unit130is disposed on the outer circumferential side in the cylinder110from the scavenging port126, and causes the fuel gas to be suctioned from the scavenging port126into the cylinder110is described. However, the first fuel supply unit130may be disposed at any position as long as the first fuel supply unit supplies the fuel gas into the cylinder110.

In addition, in the embodiment described above, the case where the variable compression ratio mechanism146has the configuration in which the positions of the top dead center and the bottom dead center of the piston112are variable depending on the presence and absence of the shim plate148is described. However, as long as there is provided a mechanism in which the compression ratio is variable, another configuration, such as a length of the piston112or the piston rod112amay be hydraulically adjusted, may be employed. An example of the other configuration of the variable compression ratio mechanism will be described below in detail.

In addition, in the embodiment described above, the configuration, in which the main combustion chamber134aand the auxiliary combustion chamber134bare provided as the combustion chamber, and the fuel gas combusted in the auxiliary combustion chamber134bis injected into the main combustion chamber134ain the gas operation mode, is described. However, a small amount of fuel oil may be injected in the main combustion chamber134ato ignite the fuel gas suctioned from the scavenging port126without providing the auxiliary combustion chamber134b.

In addition, in the embodiment described above, the case where a small amount of the fuel oil is injected into the auxiliary combustion chamber134bsuch that the fuel gas in the auxiliary combustion chamber134bignites is described. However, the fuel gas in the auxiliary combustion chamber134bmay ignite with a spark plug.

In addition, in the embodiment described above, the case where two modes of the low compression ratio mode and the high compression ratio mode are provided is described. however, three or more modes having different compression ratios may be provided, and at least two modes of the three or more modes may correspond to the low compression ratio mode and the high compression ratio mode.

Here, an example of the other configuration of the variable compression ratio mechanism which can be applied to the present disclosure is described below in detail.

In the related art, a configuration of a four-cycle engine including a piston that is provided with a cylindrical piston outer having the sealed top surface, and a piston inner that is provided to freely slide inside the piston outer and is connected to a connecting rod via a piston pin in which a variable compression ratio mechanism is provided between the piston outer and the piston inner is disclosed (for example, see Japanese Unexamined Patent Application, First Publication No. 2005-54619 and Japanese Patent No. 4657162).

The variable compression ratio mechanism of the related art which is disclosed in the documents described above is configured to include a first rotary cam plate that is provided on the top surface of the piston inner and is configured to have a first projecting portion and a first recessed portion, a second rotary cam plate that is provided on a surface of the piston outer which faces the first rotary cam plate, and is configured to have a second recessed portion and a second projecting portion which mesh with the first projecting portion and the first recessed portion, and an actuator that causes the first rotary cam plate to rotate. The actuator is configured to include a hydraulic mechanism that causes the first rotary cam plate to rotate in one rotating direction, and a return spring that biases the first rotary cam plate in the other rotating direction; and a plunger of the hydraulic mechanism and the return spring are embedded in the piston inner.

In the variable compression ratio mechanism of the related art, the hydraulic mechanism of the actuator causes the first rotary cam plate to rotate against a bias force of the return spring, thereby the first projecting portion and the second projecting portion come into contact with each other, a relative distance between the piston inner and the piston outer increases such that a high compression ratio is obtained. Furthermore, the first projecting portion and the first recessed portion are caused to mesh with the second recessed portion and the second projecting portion, and a relative distance between the piston inner and the piston outer decreases such that a low compression ratio is obtained.

As described above, in the variable compression ratio mechanism of the related art, since the actuator for causing the first rotary cam plate to rotate is embedded in the piston inner, a problem arises in that the piston has a complicated shape and thus manufacturing costs of the piston are likely to increase.

In addition, since the first rotary cam plate is biased by the return spring usually in other rotating directions, a shear force is applied to the first projecting portion, the first recessed portion, the second recessed portion, and the second projecting portion. Hence, a problem arises in that members which configure the variable compression ratio mechanism need to have high stiffness and costs of material increase.

In consideration of such problems, a variable compression ratio mechanism, in which a compression ratio varies in a simplified structure and at low costs, is proposed as follows.

In order to solve the problems described above, the variable compression ratio mechanism is provided in an engine in which a piston slides in a cylinder due to explosion pressure produced in a combustion chamber, and the compression ratio varies by changing a position of a stroke of the piston. The variable compression ratio mechanism includes a first member that is provided with a plurality of tooth portions, which face a tooth surface thereof on the combustion chamber side, and which are provided on a circular circumference with the center axis of the piston as the axis, and that integrally reciprocates with the piston in a stroke direction of the piston, a second member that is provided with a plurality of meshing portions aligned on the same circular circumference with the tooth portions of the first member, that freely moves between a meshing position at which the meshing portions mesh with the tooth portions and a non-meshing position which is on the combustion chamber side from the meshing position and at which a meshing relationship between the meshing portions and the tooth portions is released, that freely rotates around the center axis of the piston at the non-meshing position, and that has different depths of meshing between the tooth portions and the meshing portions depending on a relative rotating position with respect to the first member at the meshing position, a contact portion that is provided in the second member and faces the first member side, a contact target portion that is provided on the first member side from the contact portion and is disposed to face the contact portion, and a driving unit that causes the contact portion and the contact target portion to approach each other in the stroke direction and causes both to come into contact with each other, and that causes the contact portion and the contact target portion to be separated from each other in the stroke direction after a pressing force is applied to the second member in the stroke direction via the contact portion. In addition, at least one of the contact portion and the contact target portion is configured of an inclined surface having an inclined angle in the rotating direction of the second member. When the contact portion and the contact target portion come into contact with each other by the driving unit in the state in which the second member is disposed at the meshing position, the pressing force generated by the driving unit is distributed along the inclined surface in the stroke direction and the rotating direction and is transmitted to the second member, the second member moves from the meshing position to the non-meshing position due to the pressing force in the stroke direction, the second member rotates due to a component force acting on the rotating direction such that the relative rotating position with respect to the first member changes, and then the second member moves to the meshing position when the contact portion and the contact target portion are separated from each other after the rotation of the second member.

As a result, it is possible to change the compression ratio in a simplified structure and at low costs.

In addition, the contact target portion may be provided with a plurality of tooth members facing the tooth surfaces on the combustion chamber side, on the circular circumference with the center axis of the piston as the axis, the contact portion may be provided with a plurality of meshing members disposed on the same circular circumference with the tooth members of the contact target portion, the meshing members may mesh with the tooth members, and the inclined surface may be provided on the tooth members and the meshing members.

In addition, the driving unit causes the contact target portion to move in a direction in which the contact target portion approaches the combustion chamber, thereby, causing the contact target portion to come into contact with the contact portion, and causes the contact target portion to move in a direction in which the contact target portion is separated from the combustion chamber, thereby, causing the contact target portion to be separated from the contact portion.

In addition, the contact portion is provided in the circumferential direction of the second member and the contact target portion is provided in the circumferential direction of the first member.

In addition, the meshing portion of the second member has an apex, a first bottom portion that is positioned on the one side in the rotating direction of the second member with the apex as the boundary, and a second bottom portion that is positioned on the other side in the rotating direction of the second member with the apex as the boundary and has a larger depth from the apex than the first bottom portion. The distance between the apexes of the meshing members of the contact portion and the distance between the apexes of the tooth members of the contact target portion are longer than the distance between the apex of the meshing portion of the second member and the second bottom portion adjacent in the apex in the rotating direction, and is shorter than the distance between the first bottom portion and the second bottom portion in the rotating direction.

In addition, the driving unit may cause the contact portion and the contact target portion to approach each other in the stroke direction such that both come into contact with each other, when the piston reaches the bottom dead center, and may cause the contact portion and the contact target portion to be separated from each other in the stroke direction after the pressing force is applied to the second member in the stroke direction via the contact portion.

In addition, the engine may include a piston rod having one end fixed to the piston, and a crosshead that is connected to the other end side of the piston rod and integrally reciprocates with the piston. The first member and the second member may be provided in any one of the piston, the piston rod, or the crosshead.

Hereinafter, an embodiment of the variable compression ratio mechanism described above will be described in detail with reference to the accompanying figures. The dimensions, materials, the specific numbers other than the dimensions and the materials, or the like is provided only as an example for easy understanding of the disclosure, and the disclosure is not limited thereto except for a case where a particular description is provided. Note that, in the following description, an element having substantially the same function and configuration is assigned with the same reference sign and a repeated description thereof is omitted, and illustration of an element without a direct relationship with the present disclosure is omitted in the figures.

In the following embodiment, first, the engine that is provided with the variable compression ratio mechanism will be described, and then the variable compression ratio mechanism will be described in detail. Note that, in the embodiment, as the engine that is provided with the variable compression ratio mechanism, a uniflow scavenging type of engine in which one period is constituted of two cycles (strokes) and gas flows in one direction inside the cylinder. However, as long as the engine provided with the variable compression ratio mechanism is an engine in which the piston slides in the cylinder due to the explosion pressure produced in the combustion chamber, the number of cycles and the flowing direction of gas are not limited thereto.

FIG. 8is a view showing an entire configuration of a uniflow scavenging two-cycle engine1100. The uniflow scavenging two-cycle engine1100of the embodiment is used in a ship or the like.

In addition, the uniflow scavenging two-cycle engine1100of the embodiment is a so-called dual-fuel type engine, in which it is possible to execute by selecting one from the gas operation mode in which the fuel gas as the gaseous fuel is mainly combusted or the diesel operation mode in which fuel oil as the liquid fuel is combusted. Specifically, the uniflow scavenging two-cycle engine1100is configured to include a cylinder1110, a piston1112, a crosshead1114, a connecting rod1116, a crankshaft1118, an exhaust port1120, an exhaust valve1122, a scavenging port1124, a scavenging reservoir1126, a cooler1128, a scavenging chamber1130, and a combustion chamber1132.

In the uniflow scavenging two-cycle engine1100, exhaust, intake, compression, and combustion are performed during two strokes of an ascending stroke and a descending stroke of the piston1112and the piston1112reciprocates in the cylinder1110. One end of a piston rod1112ais fixed to the piston1112. In addition, a crosshead pin1114aof the crosshead1114is fixed to the other end of the piston rod1112a, and the crosshead1114reciprocates along with the piston1112. A crosshead shoe1114bregulates movement of the crosshead1114in a direction (rightward-leftward direction inFIG. 8) perpendicular to a stroke direction of the piston1112.

The crosshead pin1114ais inserted into a hole provided at one end of the connecting rod1116, and supports the one end of the connecting rod1116. In addition, the other end of the connecting rod1116is connected to the crankshaft1118and the crankshaft1118is structured to rotate with respect to the connecting rod1116. As a result, when the crosshead1114reciprocates in response to the reciprocating of the piston1112, the crankshaft1118rotates by interlocking with the reciprocating.

The exhaust port1120is an opening provided in a cylinder head1110apositioned above the top dead center of the piston1112, and is opened and closed to discharge exhaust gas produced after combustion in the cylinder1110. The exhaust valve1122slides vertically at a predetermined timing by an exhaust valve driving device (not shown) and opens and closes the exhaust port1120. In this manner, the exhaust gas discharged via the exhaust port1120is discharged to the outside, for example, after the exhaust gas is supplied to a turbine side of a supercharger C via an exhaust pipe1120a.

The scavenging port1124is a hole penetrating from an inner circumferential surface (inner circumferential surface of a cylinder liner1110b) to an outer circumferential surface of the cylinder1110on the lower end side, and a plurality of scavenging ports are provided all around the cylinder1110. The scavenging ports1124suction active gas in the cylinder1110in response to a sliding motion of the piston1112. The active gas contains an oxidizing agent such as oxygen or ozone, or a mixture thereof (for example, air).

The active gas (for example, air) pressurized by a compressor of the supercharger C is sealed in the scavenging reservoir1126, and the active gas is cooled by the cooler1128. The cooled active gas is pressed into the scavenging chamber1130formed in a cylinder jacket1110c. The active gas is suctioned from the scavenging port1124into the cylinder1110due to differential pressure between the scavenging chamber1130and the cylinder1110.

In addition, a pilot injection valve (not shown) is provided in the cylinder head1110a. An appropriate amount of fuel oil is injected from the pilot injection valve at a predetermined time point in the engine cycle in the gas operation mode. The fuel oil is vaporized into fuel gas with heat in the combustion chamber1132surrounded by the cylinder head1110a, the cylinder liner1110b, and the piston1112and the fuel gas spontaneously ignites, is combusted in a short time, and the temperature of the combustion chamber1132rises to be very high. As a result, it is possible to reliably combust the fuel gas flowing in the cylinder1110at a predetermined timing. The piston1112reciprocates using expansion pressure mainly produced from the combustion of the fuel gas.

Here, the fuel gas is generated, for example, by gasifying liquefied natural gas (LNG). In addition, the fuel gas is not limited to the LNG, and, for example, gas generated by gasifying liquefied petroleum gas (LPG), gas oil, heavy oil, or the like can be applied to the fuel gas.

On the other hand, a larger amount of fuel oil is injected from the pilot injection valve in the diesel operation mode than an injection amount of the fuel oil in the gas operation mode. The piston1112reciprocates without using the fuel gas but using expansion pressure produced from the combustion of the fuel gas.

In addition, the uniflow scavenging two-cycle engine1100is provided with the variable compression ratio mechanism that changes the stroke positions of the piston1112and thereby changing the compression ratio. Hereinafter, the variable compression ratio mechanism will be described in detail.

FIG. 9is a view showing a variable compression ratio mechanism1200, and a sectional view showing the piston1112and the vicinity of the piston1112. As shown inFIG. 9, the piston1112of the embodiment is configured to include a first member1210connected to the piston rod1112aby using a bolt1112b, and a second member1240disposed on the combustion chamber1132side from the first member1210.

The variable compression ratio mechanism1200is configured to include the first member1210, a press member1220, the driving unit1230, the second member1240, and a press target member1250.

The first member1210has a cylindrical shape and is provided with tooth portions1212on a surface on the combustion chamber1132side. In addition, the first member1210is provided with an annular groove1210aformed outwardly in the radial direction from the tooth portions1212, and the press member1220is positioned in the annular groove1210aso as to freely move in the stroke direction. The press member1220is provided with a contact target portion1222on a surface on the combustion chamber1132side.

The driving unit1230is configured to include rods1232that communicate with the annular groove1210a, are inserted into insertion holes1210bformed at intervals in the circumferential direction of the annular groove1210a, and are connected to a back surface of the contact target portion1222of the press member1220, a spring1234that biases the rods1232to the second member1240side, and an actuator (for example, a hydraulic mechanism or a motor) not shown which presses the rods1232to the combustion chamber1132side. The driving unit causes the press member1220to move in the stroke direction. Note that a plurality of rods1232are connected to the press member1220and regulates the movement of the press member1220in the rotating direction.

The second member1240has a cylindrical shape and is provided with meshing portions1242on a surface facing the first member1210. In addition, the second member1240is provided with an annular groove1240aformed outwardly in the radial direction from the meshing portions1242, and the press target member1250is fitted into the annular groove1240a. The press target member1250is fixed to the second member1240with a pin1240b. Hence, the press target member1250moves along with the second member1240. The press target member1250is provided with a contact portion1252on a surface on the first member1210side.

Note that, in the embodiment, the first member1210and the contact target portion1222(press member1220) move only in the stroke direction, and the second member1240and the contact portion1252(press target member1250) move in the stroke direction, and moves around a center axis P of the piston1112, which will be described below in detail.

FIGS. 10A, 10B, and 11A to 11Fare views showing the first member1210, the press member1220, the second member1240, and the press target member1250.FIGS. 10A and 10Bare perspective views showing a portion surrounded in a dashed line inFIG. 9.FIG. 11Ais a plan view showing the second member1240and the contact portion1252of the portion surrounded in the dashed line inFIG. 9.FIG. 11Bis a view showing the unrolled contact portion1252in a circumferential direction.FIG. 11Cis a view showing the unrolled second member1240in the circumferential direction.FIG. 11Dis a plan view showing the first member1210and the contact target portion1222in the portion surrounded in the dashed line inFIG. 9.FIG. 11Eis a view showing the unrolled first member1210in the circumferential direction.FIG. 11Fis a view showing the unrolled contact target portion1222in the circumferential direction.

As shown inFIG. 10A, the first member1210is provided with a plurality of tooth portions1212having a tooth surface on the combustion chamber1132(refer toFIG. 9) on the circular circumference with the center axis P of the piston1112(refer toFIG. 9) as the axis and reciprocates in the stroke direction.

In addition, as shown inFIGS. 11D and 11E, the tooth portion1212of the first member1210has an apex1212aand a bottom portion1212bwhich are disposed at equal intervals from each other in the rotating direction. In addition, the tooth portion1212of the first member1210is provided with an inclined surface1212cthat has an inclined angle in the circumferential direction (rotating direction of the second member1240, hereinafter, simply referred to as a “rotating direction”) with the center axis P as the axis, from the apex1212ato the bottom portion1212b, and an inclined surface1212dthat has an inclined angle from the bottom portion1212bto the apex1212ain the rotating direction. Note that the heights of the tooth portions1212of the first member1210are all the same.

As shown inFIG. 10B, the second member1240has a plurality of meshing portions1242aligned in the same circular circumference with the tooth portions1212of the first member1210. In addition, as shown inFIGS. 11A and 11C, the meshing portion1242has an apex1242a, and bottom portions1242band1242cwhich have different depths from the apex1242ain the stroke direction. Specifically, the depth from the apex1242ato the bottom portion1242b(second bottom portion) in the rotating direction is larger by a width D than a depth from the apex1242ato the bottom portion1242c(first bottom portion).

In addition, the meshing portions1242of the second member1240are aligned such that the bottom portion1242band the bottom portion1242care alternately disposed to interpose the apex1242atherebetween. In addition, the meshing portion1242of the second member1240is provided with an inclined surface1242dthat has an inclined angle in the rotating direction from the apex1242ato the bottom portion1242b, an inclined surface1242ethat has an inclined angle in the rotating direction from the bottom portion1242bto the apex1242a, an inclined surface1242fthat has an inclined angle in the rotating direction from the apex1242ato the bottom portion1242c, and an inclined surface1242gthat has an inclined angle in the rotating direction from the bottom portion1242cto the apex1242a.

In addition, the second member1240freely moves between a meshing position at which the meshing portions1242and the tooth portions1212mesh each other and a non-meshing position which is on the combustion chamber1132side from the meshing position and at which a meshing relationship between the meshing portions1242and the tooth portions1212is released, and freely rotates around the center axis P of the piston1112at the non-meshing position, which will be described below in detail. At the meshing position, the apexes1212aof the tooth portions1212mesh with the bottom portions1242bof the meshing portions1242, or the apexes1212aof the tooth portions1212mesh with the bottom portions1242cof the meshing portions1242, depending on the relative rotating position with respect to the first member1210.

In other words, depths of meshing between the tooth portions1212and the meshing portions1242are different depending on a relative rotating position of the second member1240and the first member1210.

As shown inFIG. 10A, the contact target portion1222is configured to have the plurality of tooth members1224provided in the circumferential direction of the first member1210and the tooth member1224has a tooth surface on the combustion chamber1132(refer toFIG. 9) side. The contact target portion1222is provided in the press member1220so as to freely move with respect to the first member1210, and moves in the stroke direction in response to the press member1220by the driving unit1230.

In addition, as shown inFIGS. 11D and 11F, the tooth members1224of the contact target portion1222are disposed such that the apexes1224aare disposed at equal intervals in the rotating direction, that is, the bottom portions1224bare disposed at equal intervals in the rotating direction. In addition, the tooth member1224of the contact target portion1222is provided with an inclined surface1224cthat has an inclined angle in the rotating direction from the apex1224ato the bottom portion1224band a perpendicular surface1224dthat stands upright from the bottom portion1224bto the apex1224a.

As shown inFIG. 10B, the contact portion1252is configured to have the plurality of meshing members1254provided in the second member1240in the circumferential direction of the second member1240and are aligned on the same circular circumference with the tooth members1224of the contact target portion1222, and the meshing members1254mesh with the tooth members1224. As described above, in the embodiment, the contact portion1252is provided on the press target member1250, and the press target member1250is fixed to the second member1240with the pin1240b. Therefore, the contact portion1252integrally rotates with the second member1240or integrally reciprocates with the second member1240in the stroke direction.

In addition, as shown inFIGS. 11A and 11B, the meshing members1254of the contact portion1252are disposed such that the apexes1254aare disposed at equal intervals in the rotating direction, that is, the bottom portions1254bare disposed at equal intervals in the rotating direction. In addition, the meshing member1254of the contact portion1252is provided with an inclined surface1254cthat has an inclined angle in the rotating direction from the apex1254ato the bottom portion1254band a perpendicular surface1254dthat stands upright from the bottom portion1254bto the apex1254a.

Subsequently, a dimensional relationship between the tooth portion1212of the first member1210, the tooth member1224of the contact target portion1222, the meshing portion1242of the second member1240, and the meshing member1254of the contact portion1252will be described.

FIG. 12is a view showing the dimensional relationship between the tooth portion1212of the first member1210, the tooth member1224of the contact target portion1222, the meshing portion1242of the second member1240, and the meshing member1254of the contact portion1252. As shown inFIG. 12, a distance (rotating angle) between the apexes1254aof the contact portion1252in the rotating direction, that is, a distance (rotating angle) between the apexes1224aof the contact target portion1222in the rotating direction, is referred to as a distance L1, the distance (rotating angle) between the apexes1242aof the second member1240and the bottom portion1242badjacent to the apex1242ain the rotating direction is referred to as a distance L2, a distance (rotating angle) between the bottom portion1242band the bottom portion1242cof the second member1240in the rotating direction is referred to as a distance L3, and a distance (rotating angle) between the bottom portions1242bin the rotating direction and a distance (rotating angle) between the bottom portions1242cin the rotating direction is referred to as a distance L4.

In this case, the contact target portion1222, the second member1240and the contact portion1252are disposed such that the distance L1is longer than the distance L2, and is shorter than the distance L3. In addition, the first member1210is disposed such that the distance between the apexes1212abecomes the distance L4.

Subsequently, a change in compression ratio by the variable compression ratio mechanism1200is described.FIGS. 13A to 13C and 14A and 14Bare views showing changes in compression ratio by the variable compression ratio mechanism1200. Note that, for easy understanding, the first member1210, the contact target portion1222, the second member1240, and the contact portion1252are shown in a simplified manner, and the driving unit1230is omitted inFIGS. 13A to 13C and 14A and 14B. In addition, the first member1210and the second member1240are represented by hatched regions, the contact target portion1222is represented by a black region, and the contact portion1252is represented by a white region. In addition, movement in the stroke direction is represented by a white arrow, and the movement in the rotating direction is represented by a black arrow inFIGS. 13A to 13C, 14A, and 14B.

At the meshing position in which the tooth portions1212of the first member1210mesh with the meshing portions1242of the second member1240, the contact portion1252and the contact target portion1222are separated in the stroke direction as shown inFIG. 13A. Note that, at a meshing position shown inFIG. 13A, the apexes1212aof the first members1210mesh with the bottom portions1242bof the second member1240. In addition, at the meshing position, the apexes1254aof the contact portion1252and the bottom portions1224bof the contact target portion1222are disposed at different positions from each other in the circumferential direction. In other words, the apexes1224aof the contact target portion1222have a positional relationship of facing the inclined surface1254cof the contact portion1252.

In a case where the compression ratio changes, the driving unit1230causes the contact target portion1222(press member1220) to move in the stroke direction toward the contact portion1252(press target member1250) side (direction of approaching to the combustion chamber1132), and causes the contact target portion1222to come into contact with the contact portion1252as shown inFIG. 13B, and the pressing force is applied to the second member1240via the contact portion1252. As described above, since the apex1224aof the contact target portion1222has a positional relationship to face the inclined surface1254cof the contact portion1252, the press force generated by the driving unit1230is distributed on the inclined surface1254cin the stroke direction and the rotating direction and is transported to the second member1240.

In this manner, as shown inFIG. 13C, the contact portion1252and the second member1240rotate, and the second member1240moves from the meshing position to the non-meshing position due to the press force in the stroke direction. When the apexes1224aof the contact target portion1222mesh with the bottom portions1254bof the press target member1250, the relative rotating position (position in the circumferential direction) of the second member1240with respect to the first member1210is changed, and a positional relationship, in which the apexes1212aof the first member1210and the inclined surfaces1242eor the inclined surfaces1242g(here, the inclined surfaces1242g) of the second member1240face each other, is achieved.

In other words, the apexes1212aof the first member1210mesh with the bottom portions1242bof the second member1240at the meshing position shown inFIG. 13A, and the positional relationship in which the apexes1212aof the first member1210and the inclined surface1242eor the inclined surface1242g(here, the inclined surfaces1242g) of the second member1240face each other, is achieved at the non-meshing position shown inFIG. 13C.

Subsequently, as shown inFIG. 14A, the driving unit1230causes the contact target portion1222(press member1220) to move in a direction in which the contact target portion is separated from the combustion chamber1132such that the contact portion1252and the contact target portion1222are separated in the stroke direction. In the uniflow scavenging two-cycle engine1100, since a force from the combustion chamber1132to the crankshaft1118is applied to the second member1240at all times, the contact target portion1222is caused to move in the direction in which the contact target portion1222is separated from the combustion chamber1132, and thereby the second member1240and the contact portion1252move on the first member1210side.

Here, as described above, since a positional relationship in which the apexes1212aof the first member1210face the inclined surface1242gof the meshing portion1242of the second member1240is achieved, the force from the combustion chamber1132to the crankshaft1118is applied to the inclined surface1212cof the first member1210and the inclined surface1242eof the second member1240in the rotating direction when the second member1240comes into contact with the first member1210. In this manner, as shown inFIG. 14B, the second member1240further rotate in a process of meshing with the first member1210, and moves to the meshing position at which the apexes1212aof the first member1210mesh with the bottom portions1242cof the second member1240. In addition, the contact portion1252rotates in response to the rotation of the second member1240, and thereby the positional relationship, that is, practically the same positional relationship as shown inFIG. 13A, in which the apexes1224aof the tooth members1224of the contact target portion1222face the inclined surface1254cof the meshing members1254of the contact portion1252is again achieved.

FIGS. 15A and 15Bare views showing a positional relationship between the first member1210and the second member1240which have different meshing positions, respectively.FIG. 15Ais a perspective view of the first member1210and the second member1240at the meshing position shown inFIG. 13A, andFIG. 15Bis a perspective view of the first member1210and the second member1240at the meshing position shown inFIG. 14B.

As described above, the driving unit1230causes the contact target portion1222(press member1220) to move in an approach direction to the combustion chamber1132and to come into contact with the contact portion1252, and the pressing force is applied to the second member1240via the contact portion1252in the stroke direction. Then, the driving unit causes the contact portion1252to move in a separated direction from the combustion chamber1132such that the contact portion1252and the contact target portion1222are separated from each other in the stroke direction, and thereby the apex1212aof the first member1210shift from the meshing position (refer toFIGS. 13A and 15A) at which the apexes mesh with the bottom portions1242bof the second member1240to the meshing position (refer toFIGS. 14B and 15B) at which the apexes mesh with the bottom portions1242cof the second member1240. In this manner, a height H of the first member1210and the second member1240increases by a width D as a difference in depth of the bottom portion1242cfrom the apex1242a. In other words, the first member1210projects from the second member1240to the combustion chamber1132side by the width D as the difference in depth of the bottom portion1242band the bottom portion1242cfrom the apex1242a. As described above, the stroke position of the piston1112changes and it is possible to change the compression ratio from the low compression ratio to the high compression ratio.

As described above, in the variable compression ratio mechanism1200according to the embodiment, only the contact target portion1222is pressed in the stroke direction, and then it is possible to rotate the second member1240. Therefore, the actuator for rotating the second member1240does not need to be embedded in the piston1112, and thus it is possible to simplify the shape of the piston1112. As described above, it is possible to reduce an increase in the manufacturing costs of the piston1112.

In addition, since the second member1240rotates during a period when the contact target portion1222presses the contact portion1252, that is, while the first member1210is separated from the second member1240, the shear force does not act in the rotating direction while the tooth portions1212of the first member1210mesh with the meshing portions1242of the second member1240. Hence, the first member1210and the meshing portions1242may not have very high stiffness such that it is possible to reduce an increase in costs of materials.

Further, although the variable compression ratio mechanism1200of the embodiment has only a simple configuration in which the contact target portion1222is pressed or the pressing is released, it is possible to separate the first member1210from the second member1240, and to perform rotation of the second member1240. Therefore, it is possible to change the compression ratio of not only the uniflow scavenging two-cycle engine1100, but also a four-cycle engine. Note that, the four-cycle engine has not only a period when the force is applied from the combustion chamber1132to the crankshaft1118, but also a period when the force is applied from the crankshaft1118to the combustion chamber1132. Hence, in a case where the variable compression ratio mechanism1200of the embodiment is applied to the four-cycle engine, a structure in which the first member1210is not separated from the second member1240may be employed. For example, the first member1210may be biased to the second member1240with an elastic member such as a spring.

In addition, it is possible to change the compression ratio at all times, during driving of the engine, during stopping of the engine, and regardless of the strokes during the driving of the engine.

Note that it is possible to change the compression ratio; however, the change is performed when the piston1112reaches the bottom dead center, that is, when the piston1112reaches the bottom dead center, the driving unit1230causes the contact portion1252to approach the contact target portion1222such that both come into contact with each other, and causes the contact portion1252to be separated from the contact target portion1222in the stroke direction after the pressing force is applied to the second member1240in the stroke direction via the contact portion1252.

Since the minimum force is applied to the second member1240from the combustion chamber1132to the crankshaft1118when the piston1112reaches the bottom dead center, the pressing force from the driving unit1230to the contact target portion1222can be minimized. Hence, the compression ratio is changed when the piston1112reaches the bottom dead center, and thereby it is possible to reduce the driving force of the driving unit1230and it is possible to reduce operation costs of the driving unit1230.

In addition, the variable compression ratio mechanism1200may change the compression ratio depending on the operation mode or may change the compression ratio depending on a load of the engine.

Further, the dimensional relationship between the tooth portion1212of the first member1210, the tooth member1224of the contact target portion1222, the meshing portion1242of the second member1240, and the meshing member1254of the contact portion1252is set as described above, and thereby it is possible to cause the contact portion1252(second member1240) not only to rotate with the pressing force of the contact target portion1222shown inFIG. 13C, but also to cause the second member1240(contact portion1252) to further rotate, as shown inFIG. 14A. The additional rotation makes it possible to maintain the constant relative positional relationship between the first member1210and the second member1240at all times. Hence, whenever the contact target portion1222presses the contact portion1252, it is possible to shift, by one tooth, a position at which the tooth portions1212of the first member1210meshes with the meshing portions1242of the second member1240. As described above, since the second member1240of the embodiment have the bottom portions1242band1242cwhich are alternately provided, that is, the meshing depths of the first member1210and the second member1240are alternately different by one tooth at the meshing position, it is possible to change the meshing position with the pressing by the contact target portion1222once.

In the embodiment described above, the variable compression ratio mechanism1200that is capable of changing the compression ratio in two steps is described above. However, in the variable compression ratio mechanism, it is possible to change the compression ratio in three or more steps, by devising the tooth portion of the first member and the meshing portion of the second member.

FIG. 16is a view showing a second member1340of the variable compression ratio mechanism1200according to a modification example. As shown inFIG. 16, the meshing portion1342of the second member1340is configured to have four apexes1342b,1342d,1342f, and1342h, and four bottom portions1342a,1342c,1342e, and1342g, which have different depths from the apex1342bdisposed to be closest to the first member1210side. By designing the meshing portions1342in this manner, it is possible to change the compression ratio in four steps.

Note that, in this case, the distance L1between the apexes1254aof the contact portion1252in the rotating direction may be determined, based on the longest distance of a distance L5between the bottom portion1342gand the apex1342hin the rotating direction, that is, the distance between the bottom portion and the apex of the meshing portion1342of the second member1340in the rotating direction.

Note that, in the embodiment described above, an example of the configuration in which the driving unit1230causes the contact target portion1222to move is described above. However, the driving unit1230may cause the contact portion1252and the contact target portion1222to approach each other in the stroke direction such that both come into contact with each other, and may cause the contact portion1252and the contact target portion1222to be separated from each other in the stroke direction after the pressing force is applied to the second member1240in the stroke direction via the contact portion1252. For example, the driving unit1230may cause the contact portion1252to move or may cause the contact portion1252and the contact target portion1222to move.

In addition, in the embodiment described above, an example of the case where the contact target portion1222is provided outwardly in the radial direction from the tooth portion1212of the first member1210is described above. However, the contact target portion1222may be provided in the circumferential direction of the first member1210. For example, the contact target portion1222may be provided inwardly in the radial direction from the tooth portion1212of the first member1210.

In addition, in the embodiment described above, an example of the case where the contact portion1252is provided outwardly in the radial direction from the meshing portion1242of the second member1240is described above. However, the contact portion1252may be provided in the circumferential direction of the second member1240. For example, the contact portion1252may be provided inwardly in the radial direction from the meshing portion1242of the second member1240.

In addition, in the embodiment described above, an example of the configuration in which the apexes1212aof the first member1210have a constant height, the depths of the bottom portions1242band1242c(a distance from the apex1212aof the first member1210) of the second member1240are caused to be different from each other, and thereby the meshing depths between the tooth portions1212and the meshing portions1242are different from each other is described above. However, as long as it is possible to cause the meshing depths of the tooth portions1212and the meshing portions1242to be different from each other, there is no limitation to the configuration. For example, the apexes1242aof the second member1240may have a constant height, the depths of the bottom portions1212bof the first member1210may be caused to be different from each other, and thereby the meshing depths between the tooth portions1212and the meshing portions1242may be caused to be different from each other is described.

In addition, in the embodiment described above, an example of the configuration in which the tooth portion1212and the meshing portion1242have inclined surfaces1212cand1242dto1242gis described above. However, the tooth portion1212and the meshing portion1242may not have the inclined surface. In this case, when the driving unit1230causes the contact portion1252and the contact target portion1222to come into contact with each other in a state in which second member1240is disposed at the meshing position, the second member1240moves from the meshing position to the non-meshing position with the pressing force in the stroke direction, and the second member1240rotates with the component force applied in the rotating direction such that the relative rotating position with respect to the first member1210changes, when the meshing relationship between the tooth portion1212and the meshing portion1242is released.

In addition, in the embodiment described above, an example of the configuration in which the meshing member1254of the contact portion1252and the tooth member1224of the contact target portion1222have the inclined surfaces1224cand1254cis described above. However, the inclined surface having the inclined angle in the rotating direction of the second member1240may be provided at least one of the contact portion1252and the contact target portion1222.

In addition, in the embodiment described above, an example of the configuration in which the first member1210and the second member1240of the variable compression ratio mechanism1200are provided in the piston1112is described above. However, the first member1210and the second member1240may be provided in the piston rod1112aor the crosshead1114.

As described above, the embodiment of the present disclosure is described with reference to the accompanying figures; however, it is needless to say that the present disclosure is not limited to the embodiment. It is obvious for those skilled in the art to conceive various modification examples or alteration examples within the range of the claims, and thus it is understood that the examples are included within the technical scope of the present disclosure.

INDUSTRIAL APPLICABILITY

The present disclosure can use an engine in which a compression ratio is variable.