JP2005220754A - Internal combustion engine equipped with variable compression ratio mechanism - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the heat efficiency while preventing the interference of a piston with a valve, in an internal combustion engine with a variable compression ratio by changing the relative distance of a cylinder head with a piston. <P>SOLUTION: In the internal combustion engine (1), the relative distance of the cylinder head (5) and the piston (8) at a top dead-center is changed to change the compression ratio. Provided that the piston (8) may interfere with valves (50, 51) at the exhaust gas top dead-center, the relative distance of the cylinder head (5) and the piston (8) at the exhaust gas top dead-center is made longer than the relative distance of the cylinder head (5) and the piston (8) at the compression top dead-center. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an internal combustion engine that changes a compression ratio by changing a relative distance between a cylinder head and a piston at a top dead center.

In recent years, internal combustion engines that can change the compression ratio have been developed for the purpose of improving thermal efficiency. As such an internal combustion engine, for example, one that changes the compression ratio by changing the relative distance between the cylinder head and the piston at the top dead center is known (see, for example, Non-Patent Document 1).
Kenichi Sugawara, “Research on Variable Strength Ratio (Variable Compression Ratio) Engine”, Automobile Engineering Society of Japan, Preprints 911, 1991-5 (pages 139-141)

  By the way, in the variable compression ratio mechanism that changes the relative distance between the cylinder head and the piston at the top dead center, the compression ratio cannot be inadvertently increased in order to avoid the interference between the valve and the piston at the exhaust top dead center. It was difficult to obtain a sufficient improvement effect.

  On the other hand, the technique disclosed in Non-Patent Document 1 described above changes the linkage ratio in the cycle, so that the exhaust top dead center is higher than the relative distance between the cylinder head and the piston at the compression top dead center. The relative distance between the cylinder head and piston is increased. However, the relative distance between the cylinder head and the piston at the exhaust top dead center becomes long even at a low / medium compression ratio where interference between the valve and the piston cannot occur, which may cause a decrease in exhaust efficiency.

  The present invention has been made in view of the various problems described above, and an object thereof is to improve exhaust efficiency in an internal combustion engine that changes the compression ratio by changing the relative distance between the cylinder head and the piston at the top dead center. It is in the point which improves a thermal efficiency suitably, without causing a fall etc.

The present invention employs the following means in order to solve the above problems.
The gist of the present invention is that, in an internal combustion engine that changes the compression ratio by changing the relative distance between the cylinder head and the piston at the top dead center, there is a possibility that interference between the piston and the valve at the exhaust top dead center may occur. The relative distance between the cylinder head and the piston at the exhaust top dead center is longer than the relative distance between the cylinder head and the piston at the compression top dead center.

  The interference between the piston and the valve at the exhaust top dead center is likely to occur at a high compression ratio in which the relative distance between the cylinder head and the piston is shortened. Conversely, at the time of low compression where the relative distance between the piston and the valve at the top dead center becomes long, the interference between the piston and the valve at the exhaust top dead center hardly occurs.

  Therefore, the variable compression ratio mechanism may be controlled so that the relative distance between the cylinder head and the piston at the exhaust top dead center is longer than the relative distance at the compression top dead center only when the compression ratio is equal to or greater than a predetermined value.

In this case, the relative distance between the cylinder head and the piston at the exhaust top dead center is increased only when the compression ratio is equal to or greater than a predetermined value. Therefore, the relative distance is not unnecessarily increased when the compression ratio is less than the predetermined value. As a result, a decrease in exhaust efficiency can be suppressed.

  In recent years, the development of valve opening characteristic changing means for making the valve opening characteristics of intake valves and exhaust valves variable has also been advanced. In an internal combustion engine provided with a valve opening characteristic changing means, the valve lift amount at the exhaust top dead center is changed by changing the valve opening / closing timing or the lift amount.

  For this reason, in an internal combustion engine having both valve opening characteristic changing means and a variable compression ratio mechanism, for example, if the valve lift amount at the exhaust top dead center is small even if the compression ratio is higher than the predetermined value, interference between the piston and the valve occurs. Absent. On the other hand, even if the compression ratio is lower than the predetermined value, if the valve lift amount at the exhaust top dead center is larger than the exhaust top dead center, interference between the piston and the valve may occur.

  Therefore, in the internal combustion engine having both the valve opening characteristic changing means and the variable compression ratio mechanism, the predetermined value is preferably made variable according to the valve lift amount at the exhaust top dead center. In this case, the control for making the relative distance between the cylinder head and the piston at the exhaust top dead center different from the relative distance at the compression top dead center is not executed unnecessarily, and the interference between the piston and the valve is surely prevented. Is possible.

  Also, how long is the relative distance between the cylinder head and the piston at the exhaust top dead center relative to the relative distance at the compression top dead center, that is, the difference between the relative distance at the exhaust top dead center and the relative distance at the compression top dead center. The compression ratio may be determined as a parameter.

This is because the relative distance between the cylinder head and the piston at the top dead center increases or decreases in inverse proportion to the compression ratio.
For example, since the relative distance between the cylinder head and the piston at the top dead center becomes shorter as the compression ratio becomes higher, the difference may be made larger as the compression ratio becomes higher.

In the internal combustion engine having both the valve opening characteristic changing means and the variable compression ratio mechanism, it is preferable to determine the above difference in consideration of the valve opening characteristic in addition to the compression ratio.
For example, when the valve opening characteristic increases the valve lift amount at the exhaust top dead center, the above difference becomes larger than when the valve lift amount at the exhaust top dead center decreases, and the valve lift amount at the exhaust top dead center decreases. The above difference may be made smaller than when the valve lift amount at the exhaust top dead center increases.

In this case, since the difference described above can be set to a minimum value at which the piston and the valve do not interfere with each other, a decrease in exhaust efficiency or the like can be minimized.
Even in an internal combustion engine having both the valve opening characteristic changing means and the variable compression ratio mechanism, the above difference may be determined using only the compression ratio as a parameter to simplify the control. However, in this case, it is necessary to determine the above difference assuming the maximum lift amount that the valve can take at the exhaust top dead center.

  According to the internal combustion engine equipped with the variable compression ratio mechanism according to the present invention, it is possible to achieve a desired compression ratio while preventing interference between the piston and the valve, and to suppress a decrease in exhaust efficiency to a minimum. Therefore, the effect of improving the thermal efficiency can be suitably obtained.

Specific embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine according to the present invention. FIG. 1 shows a single-cylinder internal combustion engine for the sake of simplicity.

  The internal combustion engine 1 shown in FIG. 1 is of a reciprocating type in which the compression ratio (compression ratio = (stroke volume + combustion chamber volume) / combustion chamber volume) is variable by increasing / decreasing the combustion chamber volume while keeping the stroke volume constant. It is an internal combustion engine.

  The internal combustion engine 1 includes a crankcase 3 in which a crankshaft 2 is rotatably mounted, a cylinder block 4 slidably attached to the crankcase 3 in the cylinder axial direction, and an upper portion of the cylinder block 4. A cylinder head 5 and an oil pan case 6 attached to the bottom of the crankcase 3 are provided.

  A cylinder 7 is formed in the cylinder block 4. A piston 8 is fitted to the cylinder 7 so as to be slidable in the cylinder axial direction. The piston 8 is connected to the crankshaft 2 via a connecting rod 9.

  The cylinder head 5 is provided with an intake valve 50 and an exhaust valve 51, and these valves are respectively driven to open and close by an intake camshaft and an exhaust camshaft (not shown).

  A drive mechanism 10 that displaces the cylinder block 4 toward the top dead center side or the bottom dead center side in the cylinder axial direction is provided at the engaging portion between the cylinder block 4 and the crankcase 3. As the drive mechanism 10, for example, a mechanism disclosed in Japanese Patent Application Laid-Open No. 2003-206761 can be used.

  Further, a crank position sensor 11, a water temperature sensor 12, and an accelerator position sensor 13 are attached to the internal combustion engine 1, and these are electrically connected to an ECU 14 (Electronic Control Unit).

  The ECU 14 is an arithmetic logic operation circuit including a CPU, a ROM, a RAM, a backup RAM, and the like. The ECU 14 inputs output signals from the various sensors described above, and calculates the control value of the drive mechanism 10 using these input signals as parameters.

  In the internal combustion engine 1 configured as described above, the ECU 14 obtains the target compression ratio from the output signals of the crank position sensor 11 and the accelerator position sensor 13, and the relative position between the cylinder block 4 and the crankcase 3 corresponds to the target compression ratio. The drive mechanism 10 is controlled so as to be in the position.

  The drive mechanism 10 displaces the cylinder block 4 toward the top dead center side or the bottom dead center side in the cylinder axis direction in accordance with a control signal from the ECU 14. When the cylinder block 4 is displaced toward the top dead center side or the bottom dead center side in the cylinder axial direction, the cylinder block 4 and the cylinder head 5 approach or separate from the crankcase 3.

  As described above, when the cylinder block 4 and the cylinder head 5 approach or separate from the crankcase 3, the combustion chamber volume increases or decreases. At this time, since the stroke volume does not change, the sum of the stroke volume and the combustion chamber volume with respect to the combustion chamber volume, that is, the compression ratio changes.

  For example, when the cylinder block 4 is displaced toward the bottom dead center, the cylinder block 4 and the cylinder head 5 are relatively close to the crankcase 3 to reduce the combustion chamber volume. As a result, the compression ratio of the internal combustion engine 1 increases.

When the cylinder block 4 and the cylinder head 5 are displaced to the displacement end on the bottom dead center side (when the cylinder block 4 and the cylinder head 5 are closest to the crankcase 3), the combustion chamber volume is minimized. The compression ratio of the internal combustion engine 1 is the highest.

  On the other hand, when the cylinder block 4 is displaced toward the top dead center, the cylinder block 4 and the cylinder head 5 are relatively separated from the crankcase 3 to increase the combustion chamber volume. As a result, the compression ratio of the internal combustion engine 1 is reduced.

  When the cylinder block 4 and the cylinder head 5 are displaced to the displacement end on the top dead center side (when the cylinder block 4 and the cylinder head 5 are farthest from the crankcase 3), the combustion chamber volume is maximized and The compression ratio is the lowest.

  Therefore, the ECU 14 can continuously change the compression ratio of the internal combustion engine 1 by continuously displacing the cylinder block 4 between the top dead center side displacement end and the bottom dead center side displacement end.

  By the way, in the internal combustion engine 1 described above, the combustion chamber volume at the compression top dead center decreases as the compression ratio increases, and this also applies to the exhaust top dead center. For this reason, when the compression ratio is increased to some extent, the relative distance between the cylinder head 5 and the piston 8 at the exhaust top dead center is shortened, and the intake valve 50 and / or the exhaust valve 51 may interfere with the piston 8.

  Generally, the opening timing of the intake valve 50 is set to advance from the exhaust top dead center, and the closing timing of the exhaust valve 51 is set to be retarded from the exhaust top dead center. At this point, the intake / exhaust valves 50 and 51 are lifted. If the compression ratio is increased to some extent under such conditions, the intake valve 50 and / or the exhaust valve 51 interfere with the piston 8 at the exhaust top dead center, as shown in FIG.

  In order to solve the above problem, a method of changing the set value of the valve timing or restricting the bottom dead center side displacement end of the cylinder block 4 is conceivable. However, either method causes a decrease in the efficiency of the internal combustion engine 1. It is not preferable because it is obtained.

  Therefore, in the internal combustion engine 1 according to the present embodiment, the minimum value of the compression ratio at which the intake valve 50 and / or the exhaust valve 51 interfere with the piston 8 is obtained in advance, and the target compression ratio has a predetermined margin to the minimum value. When the added value (hereinafter referred to as interference limit compression ratio) is exceeded, the cylinder block 4 is temporarily displaced toward the top dead center at the exhaust top dead center, and the relative distance between the cylinder head 5 and the piston 8 is increased. I tried to do it.

  According to this method, it is possible to prevent interference between the intake and exhaust valves 50 and 51 and the piston 8 at the exhaust top dead center while setting the combustion chamber volume at the compression top dead center to a target volume. Further, when the target compression ratio is equal to or less than the interference limit compression ratio, the cylinder block 4 is not displaced toward the top dead center at the exhaust top dead center, so that the combustion chamber volume at the exhaust top dead center is unnecessary. There is no increase in exhaust efficiency.

  Hereinafter, the compression ratio control in the present embodiment will be described with reference to FIGS. When executing the compression ratio control, the ECU 14 executes a compression control routine shown in FIG. This compression ratio control routine is a routine that is repeatedly executed every predetermined time (for example, every time the crank position sensor 11 outputs a pulse signal).

In the compression ratio control routine, the ECU 14 first reads the engine speed and the accelerator opening in S301.
In S302, the ECU 14 calculates a target compression ratio: εt from the engine speed and the accelerator opening read in S301.

In S303, the ECU 14 determines whether or not the target compression ratio: εt is equal to or less than the interference limit compression ratio: ε0.
If it is determined in S303 that the target compression ratio: εt is equal to or less than the interference limit compression ratio: ε0, the ECU 14 proceeds to S304 and controls the drive mechanism 10 according to the target compression ratio: εt.

  Specifically, as shown in FIG. 4, the ECU 14 controls the drive mechanism 10 so that the cylinder block 4 is displaced to the target position of the cylinder block 4 that achieves the target compression ratio: εt. In this case, since the cylinder block 4 is not displaced toward the top dead center at the exhaust top dead center, the position of the cylinder block 4 at the compression top dead center and the position of the cylinder block 4 at the exhaust top dead center are the same. The interference limit position shown in FIG. 4 indicates the position of the cylinder block 4 that realizes the interference limit compression ratio: ε0.

  If it is determined in S303 that the target compression ratio: εt exceeds the interference limit compression ratio: ε0, the ECU 14 proceeds to S305 and determines whether or not the cylinder 7 is in the exhaust stroke.

  If it is determined in S305 that the cylinder 7 is in the exhaust stroke, the ECU 14 proceeds to S306 and controls the drive mechanism 10 to displace the cylinder block 4 to the interference limit position. In S305, the cylinder 7 is in the exhaust stroke. If not, the process proceeds to S307, and the drive mechanism 10 is controlled to displace the cylinder block 4 to a target position corresponding to the target compression ratio: εt.

  That is, when the target compression ratio: εt exceeds the interference limit compression ratio: ε0, the ECU 14 causes the cylinder block 4 to be at the interference limit position at the exhaust top dead center, as shown in FIG. The drive mechanism 10 is controlled so that 4 is a target position corresponding to the target compression ratio: εt.

  If the cylinder block 4 is displaced to the interference limit position at the exhaust top dead center, the relative distance between the piston 8 and the cylinder head 5 becomes longer, and therefore the interference between the intake / exhaust valves 50 and 51 and the piston 8 is prevented. Further, since the cylinder block 4 is displaced to the target position except at the exhaust top dead center, a desired compression ratio is realized at the compression top dead center.

  Therefore, according to the above compression ratio control, in the operation region where the target compression ratio: εt exceeds the interference limit compression ratio: ε0, interference between the piston 8 and the intake / exhaust valves 50 and 51 at the exhaust top dead center can be prevented. At the same time, a desired target compression ratio: εt can be realized at the compression top dead center. As a result, the thermal efficiency of the internal combustion engine 1 can be sufficiently improved.

  Further, in the operation region where the target compression ratio: εt is equal to or less than the interference limit compression ratio: ε0, the position of the cylinder block 4 becomes the target position in all strokes, so the combustion chamber volume is unnecessarily expanded at the exhaust top dead center. This prevents a decrease in exhaust efficiency.

  In the present embodiment, an internal combustion engine having a valve operating system in which the valve opening characteristics of the intake and exhaust valves 50 and 51 are constant has been described as an example. However, the opening / closing timing, the lift amount, the working angle, etc. When the present invention is applied to an internal combustion engine having a valve operating system with variable valve opening characteristics, the interference limit compression ratio: ε0 and the interference limit position are variable according to the lift amount of the intake and exhaust valves at the exhaust top dead center. It is good.

For example, in an internal combustion engine having a valve operating system that makes the intake valve opening / closing timing variable, the interference limit compression ratio: ε0 is lowered and the interference limit is reduced as the intake valve opening timing is advanced from the exhaust top dead center. Change the position to the top dead center.

This is because, as shown in FIG. 6, the lift amount of the intake valve at the exhaust top dead center increases as the opening timing of the intake valve is advanced from the exhaust top dead center.
Further, in an internal combustion engine having a valve operating system in which the opening / closing timing of the exhaust valve is variable, the interference limit compression ratio: ε0 is lowered and the interference limit is reduced as the exhaust valve closing timing is delayed from the exhaust top dead center. Change the position to the top dead center.

This is because the lift amount of the exhaust valve at the exhaust top dead center increases as the valve closing timing of the exhaust valve is retarded from the exhaust top dead center, as shown in FIG.
Thus, by making the interference limit compression ratio and the interference limit position variable according to the valve opening characteristics of the intake and exhaust valves, it is possible to minimize the temporary expansion of the combustion chamber volume at the exhaust top dead center. Become.

  However, when the compression ratio control is simplified, the interference limit compression ratio and the interference limit position may be fixed values. In that case, the interference limit compression ratio and the interference limit position may be determined assuming the maximum lift amount that the intake and exhaust valves can take at the exhaust top dead center.

  The compression ratio control according to the present embodiment can also be applied to a multi-cylinder internal combustion engine. For example, when applied to a V-type 6-cylinder or V-type 8-cylinder internal combustion engine, a variable compression ratio mechanism is provided for each bank so that the relative distance between the cylinder head and the piston at the exhaust top dead center is relative to the compression top dead center. It can be longer than the distance.

  When applied to an in-line four-cylinder internal combustion engine, it is necessary to provide a variable compression ratio mechanism for each cylinder. This is because, in an in-line four-cylinder internal combustion engine, the exhaust top dead center of one cylinder is at the same time as the compression top dead center of the other cylinder, so the relative distance at the exhaust top dead center of one cylinder is This is because, if an attempt is made to make it longer than the relative distance at the compression top dead center, the relative distance at the compression top dead center of the other cylinders is also increased in conjunction.

  In the present embodiment, the variable compression ratio mechanism for displacing the cylinder block and the cylinder head relative to the crankcase has been described as an example. However, the present invention is not limited to this, and the large end of the connecting rod and the crank A mechanism that changes the top dead center position of the piston by interposing an eccentric bearing between the pins and controlling the rotational position of the eccentric bearing, and a lever ratio between the crankshaft and the connecting rod using a folding connecting rod It may be a mechanism for changing

The figure which shows schematic structure of the internal combustion engine in embodiment The figure which shows the operating state of an internal combustion engine when the compression ratio more than an interference limit compression ratio is implement | achieved in exhaust top dead center Flow chart showing the compression ratio control routine The figure which shows the displacement state of a cylinder block when a target compression ratio is below an interference limit compression ratio Diagram showing displacement of cylinder block when target compression ratio exceeds interference limit compression ratio The figure which shows the relationship between the valve opening timing of the intake valve and the lift amount at the exhaust top dead center The figure which shows the relationship between the valve closing timing of the exhaust valve and the lift amount at the exhaust top dead center

Explanation of symbols

5 ... cylinder head, 8 ... piston, 10 ... drive mechanism, 14 ... ECU, 50 ... intake valve, 51 ... exhaust valve

Claims (3)

In an internal combustion engine equipped with a variable compression ratio mechanism that changes the compression ratio by changing the relative distance between the cylinder head and the piston at the top dead center,
Provided with a relative distance control means for controlling the variable compression ratio mechanism so that the relative distance between the cylinder head and the piston at the exhaust top dead center is longer than the relative distance at the compression top dead center when the compression ratio exceeds a predetermined value. An internal combustion engine provided with a variable compression ratio mechanism. A valve opening characteristic changing means for changing the valve opening characteristic of the valve;
The internal combustion engine having a variable compression ratio mechanism according to claim 1, wherein the predetermined value is changed to a lower value as the valve lift amount at the exhaust top dead center is increased. A valve opening characteristic changing means for changing the valve opening characteristic of the valve;
The internal combustion engine having the variable compression ratio mechanism according to claim 1 or 2, wherein the relative distance between the cylinder head and the piston at the exhaust top dead center is increased as the valve lift amount at the exhaust top dead center is increased.

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