JP2010203308A - Cylinder block for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To compatibly achieve both of cooling loss reduction at the time of a high compression ratio and knocking prevention at the time of a low compression ratio without causing bore deformation. <P>SOLUTION: In a cylinder block 20 for the internal combustion engine 1 including a variable compression ratio mechanism changing engine compression ratio by changing top dead center position of a piston 22, and a water jacket 29 disposed around a cylinder for making liquid cooling medium flow therein, at least a section surrounding the water jacket 29 is formed out of single material, and a section 142a corresponding to a piston ring position at the time of top dead center in a low compression ratio state in a cylinder axial direction has higher heat radiation properties from an inside of the cylinder to the cooling medium than a section 142b corresponding to a piston ring position at the time of top dead center in a high compression ratio state. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a cylinder block of an internal combustion engine, and more particularly to a cooling water passage in the cylinder block.

  2. Description of the Related Art A variable compression ratio internal combustion engine having a mechanism capable of changing an engine compression ratio by changing a top dead center position of a piston is known. In such a variable compression ratio internal combustion engine, in a situation where knocking is unlikely to occur during low load operation or the like, the output is improved by controlling to a high compression ratio. Also, in situations where knocking is likely to occur, such as during high-load operation, knocking is prevented by controlling to a low compression ratio. Therefore, at the time of a high compression ratio, it is required to insulate the inside of the cylinder, reduce the cooling loss, and increase the thermal efficiency as much as possible. However, if heat insulation in the cylinder is achieved at a low compression ratio, knocking is likely to occur, and the effect of lowering the compression ratio cannot be obtained, for example, the charging efficiency is reduced.

  Thus, in conventional variable compression ratio internal combustion engines, whether to focus on reducing cooling loss at high compression ratios or to focus on preventing knocking at low compression ratios is an alternative. There was a problem of being unable to achieve both.

  Therefore, a low thermal conductivity member is used for the part facing the piston ring at the top dead center of the piston when the compression ratio is high, and a high thermal conductivity member is used for the part corresponding to the low compression ratio. The cylinder block which comprises is disclosed by patent document 1. FIG.

JP 2007-247446 A

  However, since the cylinder liner is made of different materials, the deformation amount of the bore becomes non-uniform due to the difference in the linear expansion coefficient of each member, so-called bore deformation occurs. As a result, there is a problem that friction when the piston slides increases.

  Therefore, an object of the present invention is to achieve both a reduction in cooling loss at a high compression ratio and prevention of knocking at a low compression ratio, and suppress bore deformation.

  The cylinder block of the internal combustion engine of the present invention includes a variable compression ratio mechanism that changes the engine compression ratio by changing the top dead center position of the piston, a water jacket for flowing a liquid cooling medium provided around the cylinder, It is a cylinder block of an internal combustion engine provided with. And at least the part surrounding the water jacket is formed of a single material, and the part corresponding to the piston ring position at the top dead center in the low compression ratio state in the cylinder axis direction is at the top dead center in the high compression ratio state. The heat dissipation from the cylinder to the cooling medium is higher than the portion corresponding to the piston ring position.

  According to the present invention, it is possible to reduce the cooling loss at the time of a high compression ratio and to prevent knocking at the time of a low compression ratio. Moreover, since the site | part surrounding a cylinder liner and at least a water jacket is formed with a single material, a bore deformation | transformation can be suppressed.

It is a figure which shows a variable compression ratio internal combustion engine. It is explanatory drawing which shows the state which made the variable compression ratio internal combustion engine the high compression ratio. It is explanatory drawing which shows the state made into the low compression ratio similarly. The piston stroke characteristic obtained by a variable compression ratio internal combustion engine and a single link type piston stroke mechanism is shown. It is a figure shown about heat transfer coefficient (alpha) of the inner wall part of a water jacket. 6A and 6B are diagrams showing a surface of a portion having a high heat transfer coefficient α, in which FIG. 5A is a plan view, and FIG. It is a figure which shows the relationship between the depth of the water jacket surrounding a cylinder liner, and the heat transfer coefficient (alpha) of a coolant. It is a figure for demonstrating the fine particle in a coolant, a rod-like micelle, and a spherical micelle. It is a figure showing the heat transfer rate distribution of an inner wall part, the heat transfer rate distribution of a coolant, the heat transmissivity distribution, the heat quantity distribution which flows in through a piston ring from a cylinder, and block wall temperature distribution from the left side. It is the figure which showed an example of the engine compression ratio, the coolant temperature near a water jacket, and the saturation temperature of a coolant when a water pump is driven with a crankshaft.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  The internal combustion engine according to the present invention is, for example, an in-line four-cylinder spark ignition gasoline engine, which is a variable compression ratio internal combustion engine using a multi-link type piston stroke mechanism that variably controls the compression ratio.

  FIG. 1 is a diagram showing the variable compression ratio internal combustion engine 1. First, this will be described with reference to FIG.

  In the variable compression ratio internal combustion engine 1, the piston 22 and the crankshaft 21 are connected via two links, an upper link 11 and a lower link 12, so that the compression ratio can be variably controlled. Is connected to a control link 13 that restricts its behavior, and the control link 13 can be changed in its compression ratio by changing its rotation (swing) center by a control shaft 14 having an eccentric shaft portion 15. It has become.

  The structure of the compression ratio control means will be described in more detail. The crankshaft 21 has a plurality of journals 21a and crank pins 21b. The journal 21 a is rotatably supported by the main bearing of the cylinder block 20. The cylinder block 20 is provided with a water jacket 29 through which cooling water circulates. The crank pin 21b is eccentric by a predetermined amount from the journal 21a, and the lower link 12 is rotatably connected thereto. The lower link 12 is configured to be split into two members, and the crank pin 21b is fitted into a substantially central connecting hole.

  The lower end of the upper link 11 is rotatably connected to one end of the lower link 12 by a connecting pin 25, and the upper end is rotatably connected to the piston 22 by a piston pin 24.

  The piston 22 is slidably fitted to a cylinder liner 27 fitted to the cylinder block 20. The piston 22 receives the combustion pressure and reciprocates in the cylinder 23. A piston ring (top ring) 28 is inserted into the piston 22. The piston ring 28 transfers the heat received by the piston 22 to the cylinder liner 27. The cylinder liner 27 may be formed by plating or the like.

  The upper end side of the control link 13 is rotatably connected to the other end of the lower link 12 by a connecting pin 26, and the lower end side is rotatable about the eccentric shaft portion 15 of the control shaft 14.

  The control shaft 14 is rotated by a pinion 32 attached to the tip of the actuator 31. When the control shaft 14 rotates, the eccentric shaft portion 15 moves up and down, and the control link 13 moves up and down accordingly.

  Here, the adjustment method of the piston top dead center position of the variable compression ratio internal combustion engine 1 will be described with reference to FIGS. FIG. 2 shows a case where the piston top dead center position is at a high compression ratio, and FIG. 3 shows a case where the piston top dead center position is at a low compression ratio.

  When increasing the compression ratio, as shown in FIG. 2, the actuator 31 is driven to lower the eccentric shaft portion 15 of the control shaft 14. Then, the lower link 12 moves clockwise and the connecting pin 25 is raised, so that the position of the top dead center of the piston 22 rises.

  When the compression ratio is lowered, the eccentric shaft portion 15 of the control shaft 14 is raised by driving the actuator 31 as shown in FIG. Then, the lower link 12 moves counterclockwise and the connecting pin 25 is lowered, so that the position of the top dead center of the piston 22 is lowered.

  2 and 3 representatively show the high compression ratio state and the low compression ratio state, but the compression ratio can be continuously changed between them.

  FIG. 4 is obtained by a conventional single link type piston stroke mechanism in which the piston stroke characteristic obtained by the variable compression ratio internal combustion engine 1 and the piston and the crank pin of the crankshaft are connected by a single link (connecting rod). The piston stroke characteristics are shown.

  In the conventional single link type piston stroke mechanism, the piston moves fast (high acceleration) near the top dead center, and dull (low acceleration) near the bottom dead center. On the other hand, in the case of the multi-link type piston stroke mechanism 1, a piston stroke characteristic close to simple vibration can be obtained by appropriately setting the link configuration. Therefore, the piston acceleration is leveled, and the piston speed near the top dead center becomes slower than the conventional one. In the vicinity of the top dead center, scavenging, filling, and air-fuel mixture formation are performed by high-pressure fresh air supplied from the intake valve, and ignition is also performed. Thus, by reducing the piston speed near the top dead center where the stroke is concentrated by the multi-link mechanism, it is possible to increase the rotation speed that can be output. However, if the piston speed near the top dead center decreases, the cooling loss increases accordingly.

  By the way, in an internal combustion engine, when the compression ratio is increased, the thermal efficiency is increased accordingly. This is because increasing the compression ratio also increases the expansion ratio. Here, the high thermal efficiency means that when the same thermal energy is applied, more work is performed, that is, the output is large. Further, if the thermal efficiency is increased, the fuel consumption rate is also reduced, so that the fuel consumption is improved.

  Therefore, in a situation where knocking is unlikely to occur during low load operation, it is desirable to increase the compression ratio to the limit in order to improve output and fuel consumption.

  However, as the compression ratio is increased, the ratio of the surface area (S) to the volume (V) of the combustion chamber (hereinafter referred to as “S / V ratio”) increases and the cooling loss increases. This is because when the surface area of the combustion chamber is large, the generated thermal energy is absorbed by the wall surface of the combustion chamber and the thermal energy that can be used for expansion of the combustion gas is reduced. Therefore, when the compression ratio exceeds 15, sufficient thermal efficiency improvement effect cannot be obtained, and conversely, the thermal efficiency decreases.

  As an effective method for reducing such an increase in cooling loss due to an increase in S / V ratio due to high compression and an increase in cooling loss due to a decrease in piston speed near the top dead center, a cylinder liner 27 is used. For example, it is conceivable to increase the heat insulating property by using a heat insulating material such as zirconia. Most of the heat received by the piston 22 is transferred to the cylinder liner 27 via the piston ring 28. Then, the heat is finally radiated to the cooling water flowing through the water jacket 29. This is because if the cylinder liner is made of a heat insulating material, the heat radiation to the cooling water can be suppressed, and a decrease in thermal energy that can be used for expansion of the combustion gas can be suppressed.

  Thus, the heat transfer amount from the piston ring 28 to the cylinder liner 27 can be reduced by configuring the cylinder liner 27 with a heat insulating material. As a result, the amount of heat transfer from the combustion gas to the piston can be reduced, and the decrease in thermal energy that can be used for the expansion of the combustion gas can be suppressed. Therefore, the cooling loss is reduced, the thermal efficiency is improved, and the fuel consumption is also improved.

  In other words, when the variable compression ratio internal combustion engine 1 is set to a high compression ratio, such as during low load operation, it is required to reduce the amount of heat transferred to the cylinder liner 27 as much as possible in order to reduce cooling loss.

  On the other hand, during high load operation, the combustion chamber wall surface becomes hot and knocking is likely to occur, so it is necessary to lower the compression ratio than during low load operation. At this time, it is easier to prevent knocking by increasing the amount of heat transfer to the cylinder liner 27. This is because the amount of heat received by the piston 22 can be transferred to the cylinder liner 27 via the piston ring 28 and radiated to the cooling water flowing through the water jacket 29. Thereby, the temperature in a cylinder can be lowered efficiently. Further, by reducing the temperature in the cylinder, the expansion of the intake air can be suppressed, and the charging efficiency is also improved.

  That is, in a state where the variable compression ratio internal combustion engine 1 is set to a low compression ratio, such as during high load operation, it is required to increase the amount of heat transfer to the cylinder liner 27 as much as possible in order to prevent knocking and improve charging efficiency.

  As described above, the cylinder liner 27 is required to have a heat dissipation property that is contradictory between a state where the variable compression ratio internal combustion engine 1 is set to a high compression ratio and a state where the variable compression ratio internal combustion engine 1 is set to a low compression ratio. In order to satisfy these requirements, it is also conceivable to form a cylinder liner using members having different thermal conductivities. That is, the cylinder liner 27 is configured by using a low thermal conductivity member at a portion corresponding to the highest piston position at the time of high compression ratio and using a high thermal conductivity member at a portion corresponding to the highest piston position at the time of low compression ratio. To do.

  However, in such a configuration, the deformation amount of the bore diameter of the cylinder liner 27 becomes non-uniform due to the difference in the coefficient of linear expansion of the member, so-called bore deformation occurs, and the friction when the piston slides increases. .

  Therefore, in the present embodiment, the configuration described below suppresses bore deformation while achieving both a cooling loss reduction at a high compression ratio and a knocking prevention at a low compression ratio.

  FIG. 5 is a view showing the heat transfer coefficient α of the inner wall 142 of the water jacket 29. As shown in FIG. 5, the heat transfer coefficient α is locally high at the portion 142a corresponding to the position of the piston ring 28 at the top dead center at the time of the low compression ratio, and the top dead center at the time of the high compression ratio. Other portions including the portion 142b corresponding to the position of the piston ring 28 in the position are constant values.

  The part corresponding to the position of the piston ring 28 means a part including at least the top ring position in the range from the top ring to the bottom ring when a plurality of rings are used.

  6A and 6B are diagrams showing the surface of the portion having the high heat transfer coefficient α, where FIG. 6A is a plan view and FIG. 6B is a cross-sectional view taken along line AA in FIG.

  A variable heat transfer layer 144 is formed on the surface of the inner wall 142 of the portion. The variable heat transfer layer 144 faces the interface of heat exchange with the cooling water, and the amount of heat transfer per unit area from the inner wall 142 to the cooling water determined by the temperature difference between the cooling water and the inner wall 142 is low. , It has a specific characteristic that increases on the boundary of the difference between the wall surface temperature and the saturation temperature of the cooling water. For this reason, the heat transfer amount of the inner wall part 142 changes with use conditions, without providing a special apparatus with energy consumption.

  The variable heat transfer layer 144 has a plurality of fine cylindrical holes 146, and the cylindrical holes 146 have a predetermined average diameter and a predetermined average depth. Based on the predetermined average diameter and average depth, it is possible to determine the difference between the specific wall surface temperature and the saturation temperature of the cooling water. By providing such a cylindrical hole 146, the surface area for taking in the coolant is increased, so that the coolant temperature in the vicinity of the surface is likely to rise, and bubbles are likely to grow in the coolant. The heat transfer rate is improved by the action of promoting the separation of the bubbles.

  In order to reliably increase the amount of heat transfer with a specific temperature difference as a boundary, it is desirable to appropriately change the average diameter and the average depth of the cylindrical hole 146 according to the composition of the cooling medium. For example, when the cooling medium is a liquid, the average diameter is preferably 25 nm to 1 μm, and the average depth is preferably 100 nm to 25 mm. Furthermore, in the case of water containing an additive in the cooling medium, it is desirable that the average diameter is 40 nm to 450 nm and the average depth is 280 nm to 4.5 mm.

  The heat insulating layer 148 is made of an oxide film made of a material constituting the cylinder block 20 and is integrated with the inner wall portion 142. Note that the cross-sectional shape of the cylindrical hole 146 is not limited to a circular shape, and may be a square or a hexagon, for example.

  Here, a method for forming the variable heat transfer layer 144 will be described. Here, it is assumed that the cylinder block 20 is formed of an aluminum alloy.

  The process of forming the variable heat transfer layer 144 includes a polishing process, an anodizing process, and an etching process.

  In the polishing process, the inner wall 142 of the water jacket 29 is subjected to buffing and electrolytic polishing to adjust the surface shape. Either buffing or electropolishing can be omitted as appropriate.

  In the anodic oxidation process, the inner wall 142 whose surface properties are adjusted is immersed in an electrolytic solution, and a voltage is applied to form an anodic oxide film. The electrolytic solution is, for example, an acid system. The applied voltage is, for example, 70 to 80 [V]. The anodic oxide film is an oxide film made of alumina and has fine pores. These fine holes and the oxide film function as the cylindrical hole 146 and the heat insulating layer 148 described above.

  In the etching process, the inner wall 142 on which the oxide film is formed is immersed in an etching solution in order to expose the clean surface. The etching solution is, for example, acid-based. The immersion time is about 15 minutes, for example.

  Note that the average diameter and the average depth of the micropores can be adjusted by controlling the selection of the component composition of the aluminum substrate, the selection of the component composition of the electrolytic solution, the anodic oxidation conditions, and the like.

  In this embodiment, the heat transfer layer 144 is formed of an anodic oxide film. However, the method of forming the heat transfer layer 144 is not limited to this, and may be formed by mechanical processing such as press working. Therefore, the heat transfer layer 144 (148) does not necessarily need to be a heat insulating layer.

  Next, the cooling medium flowing in the water jacket 29 will be described. Here, a coolant added with a surfactant that forms rod-like micelles is used as the cooling medium.

  FIG. 7 is a diagram showing the relationship between the depth of the water jacket 29 surrounding the cylinder liner 27 and the heat transfer coefficient α of the coolant. FIG. 8 is a view for explaining fine particles, rod-like micelles and spherical micelles in the coolant.

  Normally, the heat transfer coefficient of the coolant in the water jacket 29 has a strong correlation with the flow velocity, and as shown in FIG. 7, the heat transfer coefficient is the largest at the central portion where the flow velocity is relatively high.

  On the other hand, when a surfactant is added, the rod-like micelle structure of the surfactant becomes dominant. By forming rod-like micelles, the coolant flow becomes laminar. It is known that the laminar flow reduces the flow resistance but reduces the heat transfer coefficient. By the way, the coolant contains fine particles (such as microcapsules) having a diameter of several tens to several hundreds μm, that is, larger than the average diameter of the cylindrical holes 146, and the fine particles are uneven on the wall surface of the water jacket 29. When agitated by the above, the connection of the rod-like micelles near the wall surface is broken to change to spherical micelles. In particular, the higher the coolant temperature, the easier it is to change from rod-like micelles to spherical micelles. And since the degree of laminar flow falls by changing from a rod-like micelle to a spherical micelle, a heat transfer rate increases. On the other hand, since the fine particles and the rod-like micelles are both on the coolant mainstream when they are separated from the wall surface, the fine particles do not break the bond of the rod-like micelles.

  In other words, by using a coolant containing a surfactant, the rod-like micelles change to spherical micelles and the heat transfer coefficient increases at parts where the amount of heat flowing in is large and the cooling demand is strong, such as the cylinder liner side wall surface. In this part, laminar flow is maintained, and the flow resistance becomes small.

  Here, since the coolant temperature decreases as it goes down the cylinder, the heat transfer coefficient gradually decreases as the jacket becomes deeper, as shown in FIG. However, since the piston speed decreases near the bottom dead center of the piston, the amount of heat flowing in from the piston increases and the coolant temperature increases, so the heat transfer coefficient also increases.

  FIG. 9 is a diagram for explaining the temperature (block wall temperature) of the inner wall 142 when a coolant containing a surfactant is passed through the water jacket 29 including the variable heat transfer layer 144 described above. 9, from the left side, the heat transfer coefficient distribution of the inner wall 142 (similar to FIG. 5), the heat transfer coefficient distribution of the coolant (similar to FIG. 7), the heat transmissivity distribution, and flows from the cylinder through the piston ring 28. It represents the heat distribution and block wall temperature distribution. For comparison, a combination of a general water jacket and a coolant that does not include a surfactant is also indicated by a broken line.

  The heat transmissibility distribution is obtained by combining the heat transfer coefficient of the inner wall 142 and the heat transfer coefficient of the coolant described above.

  The distribution of the amount of heat flowing from the cylinder through the piston ring is the largest at the part where the piston ring 28 contacts, and otherwise, the part becomes larger at the part where the piston speed becomes slower. That is, it increases from the uppermost part of the water jacket 29 to the piston ring position, gradually decreases from there to the deep part of the jacket, and increases again in the vicinity of the piston bottom dead center position.

  Thus, since the heat transmissivity distribution and the distribution of the amount of heat flowing in are substantially the same, the block wall temperature approaches a constant regardless of the depth direction position of the water jacket 29. Further, since the heat transfer coefficient of the inner wall portion 142 described above is realized by the single material cylinder block 20, the equalization of the block wall temperature leads to suppression of bore deformation.

  On the other hand, in a combination of a general water jacket and a coolant that does not contain a surfactant, the heat transmissivity of the portion where the inflowing heat is large is small, and the heat transmissivity of the portion where the inflowing heat is small is large. For this reason, the distribution of the block wall temperature increases from the uppermost part of the water jacket 29 to the piston ring position in the same manner as the inflowing heat quantity distribution, and gradually decreases from there to the deep part of the jacket, and near the piston bottom dead center position. It grows again. That is, the degree of expansion of the bore diameter becomes non-uniform in the depth direction of the water jacket 29, leading to an increase in friction.

  FIG. 10 is a diagram illustrating an example of the engine compression ratio, the coolant temperature near the water jacket, and the coolant saturation temperature when the water pump is driven by the crankshaft. The horizontal axis is the heat load that can be almost equated with the amount of heat released from the coolant.

  In this case, since the pressure in the water jacket is determined by the engine speed, the saturation temperature is one value for the engine speed.

  For example, in a low rotation range such as 2000 rpm, the coolant does not boil because the coolant temperature is lower than the saturation temperature even under full load conditions. However, in a medium rotation range such as 4000 rpm and a high rotation range such as 6000 rpm, boiling occurs because the coolant temperature exceeds the saturation temperature in a region where the engine compression ratio is low, that is, in a high load region.

  In the present embodiment, the heat transfer coefficient of the inner wall surface 142 at the piston ring position at the top dead center at the time of the high compression ratio is relatively low, and the heat transfer coefficient is also relatively low as shown in FIG. For this reason, overcooling in a low load region can be prevented, and as a result, fuel efficiency can be improved.

  On the other hand, the heat transfer coefficient of the inner wall surface 142 at the piston ring position at the top dead center at the time of the low compression ratio is relatively high, and the heat transfer coefficient is also relatively high as shown in FIG. For this reason, at the time of a high load with a low compression ratio, heat is reliably transferred from the engine to the coolant, and the occurrence of knocking can be prevented.

  Further, in an operation region that is frequently used in general operation, such as a high compression ratio, the number of times of boiling is reduced by suppressing the temperature rise of the coolant. Thereby, the lifetime improvement of a coolant can be achieved.

  In addition to the above-mentioned means, the radiator cap pressure is variably controlled according to the compression ratio as a means for reliably radiating heat from the engine to the coolant at the low compression ratio and reducing the cooling loss at the high compression ratio. May be. This lowers the coolant pressure so that nucleate boiling of the coolant on the surface of the water jacket is likely to occur at a low compression ratio. Such control of the coolant pressure can also be performed by controlling the water pump rotation speed in accordance with the compression ratio using an electric water pump that can rotate independently of the engine rotation.

  As described above, in the present embodiment, the following effects can be obtained.

  (1) In the cylinder block of the variable compression ratio internal combustion engine 1 in which the engine compression ratio is changed by changing the top dead center position of the piston, at least a portion surrounding the water jacket is formed of a single material, and the cylinder axial direction The portion 142a corresponding to the piston ring position at the top dead center in the low compression ratio state is more heat radiating from the inside of the cylinder to the coolant than the portion 142b corresponding to the piston ring position at the top dead center in the high compression ratio state. Therefore, it is possible to reduce the cooling loss at the time of the high compression ratio and prevent knocking at the time of the low compression ratio.

  (2) The inner wall surface 142 on the cylinder side of the water jacket 29 has a portion corresponding to the piston ring position at the top dead center in the low compression ratio state in the cylinder axial direction. The heat transfer coefficient is higher than the part corresponding to the position. Since such a difference in heat dissipation is realized by such a configuration, it is not necessary to combine different materials with the cylinder portion, and the occurrence of bore deformation is suppressed.

  (3) The surface of the inner wall surface 142 corresponding to the piston ring position at the top dead center in the low compression ratio state in the cylinder axial direction is subjected to surface processing so as to promote bubble separation in the coolant. Growth and separation of bubbles due to bubbles and nucleate boiling are promoted to improve the heat transfer rate.

  (4) By controlling the coolant pressure so that the nucleate boiling of the coolant is likely to occur on the surface of the water jacket in the low compression ratio state, the bubble growth and detachment due to the nucleate boiling is further promoted.

  (5) Since the coolant contains a surfactant that forms rod-like micelles, the coolant temperature distribution in the depth direction of the water jacket is as shown in FIG. 7, and the temperature of the inner wall surface 142 in the direction of the water jacket The distribution approaches uniform.

  (6) Since the coolant contains fine particles having a diameter larger than the average diameter of the cylindrical hole 146, when the fine particles are stirred by bubbles, the change from rod-like micelles to spherical micelles is promoted. . Since the detachment of the bubbles is promoted at the low compression ratio, the change from the rod-like micelle to the spherical micelle by the stirring of the fine particles is also promoted, and as a result, the heat transfer coefficient is improved.

  The present invention is not limited to the above-described embodiments, and it goes without saying that various modifications can be made within the scope of the technical idea described in the claims.

DESCRIPTION OF SYMBOLS 1 Variable compression ratio internal combustion engine 11 Upper link 12 Lower link 13 Control link 14 Control shaft 29 Water jacket 31 Actuator 32 Pinion 144 Variable heat transfer layer 146 Cylindrical hole 148 Heat insulation layer

Claims (7)

In a cylinder block of an internal combustion engine having a variable compression ratio mechanism that changes the engine compression ratio by changing the top dead center position of the piston,
A water jacket for flowing a liquid coolant around the cylinder
At least a portion surrounding the water jacket is formed of a single material,
The portion corresponding to the piston ring position at the top dead center in the low compression ratio state in the cylinder axial direction is more from the inside of the cylinder to the cooling medium than the portion corresponding to the piston ring position at the top dead center in the high compression ratio state. A cylinder block of an internal combustion engine characterized by having a high heat dissipation property.   The cylinder inner wall surface of the water jacket has a portion corresponding to the piston ring position at the top dead center in the low compression ratio state in the cylinder axial direction, a portion corresponding to the piston ring position at the top dead center in the high compression ratio state. 2. The cylinder block of the internal combustion engine according to claim 1, wherein the heat transfer coefficient is higher than that of the internal combustion engine.   The surface of the cylinder side inner wall surface corresponding to the piston ring position at the top dead center in the low compression ratio state in the cylinder axial direction is subjected to surface processing that promotes bubble separation in the cooling medium, thereby increasing the heat transfer coefficient. The cylinder block of the internal combustion engine according to claim 2, wherein the cylinder block is raised.   The cylinder block of the internal combustion engine according to claim 3, wherein the surface processing is processing to form a plurality of minute columnar recesses.   The cooling medium pressure control means for controlling the pressure of the cooling medium so as to easily cause nucleate boiling of the cooling medium on the surface of the water jacket when in a low compression ratio state. The cylinder block of the internal combustion engine as described in any one.   The cylinder block of the internal combustion engine according to any one of claims 1 to 5, wherein the cooling medium includes a surfactant that forms rod-like micelles.   The cylinder block of the internal combustion engine according to any one of claims 4 to 6, wherein the cooling medium contains fine particles having a diameter larger than an average diameter of the columnar recesses.