JP2005090299A - Internal combustion engine with variable compression ratio mechanism - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide technique for preventing exhaust efficiency deterioration and reducing exhaust loss in an internal combustion engine with a variable compression ratio mechanism. <P>SOLUTION: The internal combustion engine is equipped with the variable compression ratio mechanism for changing a compression ratio by varying volume of a combustion chamber. In this engine, when the compression ratio is increased by the variable compression ratio mechanism, valve closing timing of an exhaust valve is set after a top dead center in an exhaust stroke and valve opening timing of the exhaust valve is delayed to be more close to a bottom dead center in the exhaust stroke. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an internal combustion engine including a variable compression ratio mechanism that changes a compression ratio by changing the volume of a combustion chamber.

  In recent years, variable compression ratio mechanisms that change the compression ratio of an internal combustion engine have been developed for the purpose of improving the fuel efficiency performance and output performance of the internal combustion engine. For example, Patent Document 1 discloses a variable compression ratio mechanism in which a cylinder block and a crankcase are connected so as to be relatively movable and a camshaft is provided at the connecting portion. In this variable compression ratio mechanism, the compression ratio is changed by changing the volume of the combustion chamber by rotating the cam shaft so that the cylinder block and the crankcase approach or separate from each other.

  In addition, in an internal combustion engine equipped with a variable compression ratio mechanism, in order to improve thermal efficiency at low load and avoid occurrence of knocking at high load, the compression ratio is increased at low rotation and low load to increase engine rotation. A technique is known in which the compression ratio is continuously lowered as the number and the engine load increase (see, for example, Patent Document 2).

JP 2003-206871 A JP 2002-115571 A Japanese Patent Laid-Open No. 11-62648 JP 2001-140666 A JP 2000-73804 A

  In an internal combustion engine, in general, the opening timing of the exhaust valve is set before the bottom dead center of the exhaust stroke in order to suppress a decrease in exhaust efficiency. This is because when the exhaust efficiency decreases and the amount of burned gas remaining in the cylinder (hereinafter referred to as residual gas) increases, the ratio of the residual gas to the fresh air sucked into the cylinder in the next intake stroke ( (Hereinafter referred to as the residual gas ratio) increases and combustion becomes unstable.

  However, if the opening timing of the exhaust valve is set before the bottom dead center of the exhaust stroke, the exhaust valve is opened during the expansion stroke. There is a possibility that so-called exhaust loss discharged from the exhaust gas increases.

  Here, in the internal combustion engine provided with the variable compression ratio mechanism as described above, when the exhaust loss increases, there arises a problem that the effect of changing the compression ratio is reduced.

  The present invention has been made in view of the above problems, and provides a technique capable of reducing exhaust loss while suppressing a decrease in exhaust efficiency in an internal combustion engine equipped with a variable compression ratio mechanism. Is an issue.

The present invention employs the following means in order to solve the above problems.
That is, according to the present invention, in an internal combustion engine having a variable compression ratio mechanism, when the compression ratio is increased by the variable compression ratio mechanism, the opening timing of the exhaust valve is retarded, and the timing closer to the bottom dead center of the exhaust stroke. It is what.

More specifically, an internal combustion engine equipped with a variable compression ratio mechanism according to the present invention is:
An internal combustion engine having a variable compression ratio mechanism that changes the compression ratio by changing the volume of the combustion chamber,
When the compression ratio is increased by the variable compression ratio mechanism, the closing timing of the exhaust valve is set after the exhaust stroke top dead center, and the opening timing of the exhaust valve is retarded.

  When the compression ratio is increased by the variable compression ratio mechanism, the combustion chamber volume decreases. When the volume of the combustion chamber decreases and the exhaust valve closing timing is set after the exhaust stroke top dead center, the burned gas discharged from the combustion chamber when the piston reaches the exhaust top dead center The amount increases. Therefore, the residual gas amount is reduced.

  That is, if the combustion chamber volume is reduced to increase the compression ratio by the variable compression ratio mechanism, the exhaust efficiency of the internal combustion engine will be high if the exhaust valve closing timing is set after the top dead center of the exhaust stroke. .

  Therefore, when the combustion chamber volume is reduced to increase the compression ratio by the variable compression ratio mechanism, if the exhaust valve closing timing is set after the top dead center of the exhaust stroke, the opening timing of the exhaust valve is retarded. Even when the exhaust stroke is nearer to the bottom dead center, a decrease in exhaust efficiency is suppressed. As a result, exhaust loss can be reduced while suppressing a decrease in exhaust efficiency.

  In the present invention, when the opening timing of the exhaust valve is retarded, it may be gradually retarded as the compression ratio becomes higher, or may be retarded stepwise.

  In the present invention, when the compression ratio is increased by the variable compression ratio mechanism, the opening timing of the exhaust valve may be retarded to near the bottom dead center of the exhaust stroke.

  In this case, exhaust loss can be further reduced.

  When the operating state of the internal combustion engine is a high load operation, the exhaust efficiency becomes high even if the valve opening timing of the exhaust valve is not advanced. Therefore, in some internal combustion engines, the opening timing of the exhaust valve is retarded to the exhaust stroke bottom dead center side when the operation state is a high load operation regardless of the compression ratio.

  In such an internal combustion engine, when the compression ratio is increased by the variable compression ratio mechanism when the operation state is low load operation, if the valve opening timing of the exhaust valve is delayed, An effect of reducing exhaust loss while suppressing deterioration in efficiency can be obtained.

  Further, when the operation state of the internal combustion engine is low load operation, the exhaust efficiency becomes the highest when the exhaust valve closing timing is near the top dead center of the exhaust stroke.

  Therefore, in the present invention, when the compression ratio is increased by the variable compression ratio mechanism when the operation state of the internal combustion engine is low load operation, the valve closing timing of the exhaust valve is maintained near the top dead center of the exhaust stroke. However, it is preferable to retard the opening timing of the exhaust valve.

  By controlling the opening / closing timing of the exhaust valve in this way, it is possible to further suppress a decrease in exhaust efficiency.

The variable compression ratio internal combustion engine according to the present invention can reduce exhaust loss while suppressing a decrease in exhaust efficiency. Therefore, it is possible to improve thermal efficiency while ensuring stable combustion. As a result, fuel consumption can be improved.

  Hereinafter, specific embodiments of an internal combustion engine including a variable compression ratio mechanism according to the present invention will be described with reference to the drawings.

  FIG. 1 is a sectional view showing a schematic configuration of an internal combustion engine and a variable compression ratio mechanism according to the present embodiment. FIG. 2 is an external view showing a schematic configuration of the internal combustion engine and the variable compression ratio mechanism according to the present embodiment. FIG.

  The internal combustion engine 1 moves a cylinder block 3 having a cylinder 2 and a cylinder head 20 provided on the upper portion of the cylinder block 3 in the axial direction of the cylinder 2 with respect to a lower case 4 to which a piston 21 is connected. By changing the volume of the combustion chamber, the compression ratio is changed.

  As shown in FIG. 2, a plurality of cam storage portions 6 are formed at the lower portions on both sides of the cylinder block 3. A plurality of bearing storage portions 7 are formed at upper portions on both sides of the lower case 4 so as to be positioned between the cam storage portions 6.

  A cam storage hole 5 and a bearing storage hole 8 are formed in the cam storage part 6 of the cylinder block 3 and the bearing storage part 7 of the lower case 4, respectively. A cam shaft 9 is inserted through the cam storage holes 5 and the bearing storage holes 8 that are arranged in parallel on both sides of the cylinder 2 and are alternately arranged in each row.

  Here, the cam shaft 9 inserted through the cam housing hole 5 and the bearing housing hole 8 will be described with reference to FIG. The cam shaft 9 has the same outer shape as the cam portion 9a, a cam portion 9b having a circular cam profile fixed to the shaft portion 9a in a state of being eccentric with respect to the central axis of the shaft portion 9a, and the cam portion 9b. The movable bearing portions 9c that are rotatably attached to the holding shaft portion 9a are alternately arranged. The cam portion 9 b is housed in the cam housing hole 5, and the movable bearing portion 9 c is housed in the bearing housing hole 8. The movable bearing portion 9c is also eccentric with respect to the shaft portion 9a, and the amount of eccentricity is the same as that of the cam portion 9b. The eccentric directions of the plurality of cam portions 9b are the same. Further, since the outer shape of the movable bearing portion 9c is the same circle as the cam portion 9b, the outer surface of the cam portion 9b and the outer surface of the movable bearing portion 9c are made to coincide by rotating the movable bearing portion 9c. (State of FIG. 1). The pair of cam shafts 9 have a mirror image relationship.

  As shown in FIG. 2, a worm wheel 10 is attached to one end of each camshaft 9. The center of the worm wheel 10 is coincident with the center of the cam portion 9b. Worms 11a and 11b are engaged with the worm wheel 10, respectively. The worms 11 a and 11 b are attached to the output shaft of a single motor 12. The worms 11a and 11b have spiral grooves that rotate in opposite directions. For this reason, when the motor 12 is driven, the pair of cam shafts 9 rotate in opposite directions (directions indicated by arrows in FIG. 1) with the rotation of the worm wheel 10. The motor 12 is fixed to the cylinder block 3 and moves integrally with the cylinder block 3.

  Further, the cylinder head 20 also moves integrally with the cylinder block 3. The cylinder head 20 is provided with an intake port 22 and an exhaust port 23 formed so as to open to the combustion chamber. The intake port 22 is connected to an intake passage 28, and a throttle valve 34 is provided in the intake passage 28. On the other hand, the exhaust port 23 is connected to the exhaust passage 29.

  Openings to the combustion chamber of the intake port 22 and the exhaust port 23 are opened and closed by an intake valve 24 and an exhaust valve 25, respectively. The intake valve 24 and the exhaust valve 25 are provided with variable valve mechanisms 26 and 27, respectively.

  Further, the internal combustion engine 1 includes various sensors such as a pressure sensor 31 that detects the combustion pressure in the combustion chamber, a rotation angle sensor 32 that detects the rotation angle of the camshaft 9, and an accelerator opening sensor 33 that detects the accelerator opening. A sensor is provided.

  The internal combustion engine 1 is provided with an electronic control unit (ECU) 30 for controlling the internal combustion engine 1. The ECU 30 is a unit that controls the operation state of the internal combustion engine 1 in accordance with the operation conditions of the internal combustion engine 1 and the request of the driver. Various sensors such as a pressure sensor 31, a rotation angle sensor 32, and an accelerator opening sensor 33 are connected to the ECU 30 through electric wiring, and these output signals are input to the ECU 30. Further, the motor 30, the variable valve mechanisms 26 and 27, the throttle valve 34, and the like are electrically connected to the ECU 30, and these can be controlled. For example, the valve timing of the exhaust valve 25 can be changed by controlling the variable valve mechanism 27 by the ECU 30. As will be described later, the compression ratio can be changed by driving the motor 12 by the ECU 30 and controlling the rotation angle of the camshaft 9.

  Next, a method for controlling the compression ratio in the internal combustion engine 1 having the above-described configuration will be described. FIGS. 3A to 3C are cross-sectional views showing the relationship between the cylinder block 3, the lower case 4, and the camshaft 9 constructed between them. 3A to 3C, the central axis of the shaft portion 9a is indicated by a, the center of the cam portion 9b is indicated by b, and the center of the movable bearing portion 9c is indicated by c. FIG. 3A shows a state in which the outer circumferences of the cam portion 9b and the movable bearing portion 9c coincide with each other when viewed from the extension line of the shaft portion 9a. At this time, the pair of shaft portions 9 a are located outside the cam housing hole 5 and the bearing housing hole 8, respectively.

  When the motor 12 is driven from the state of FIG. 3A to rotate the cam shaft 9 in the direction of the arrow, the state of FIG. At this time, since the cam portion 9b and the movable bearing portion 9c are displaced in the eccentric direction with respect to the shaft portion 9a, the cylinder block 3 is slid toward the top dead center side with respect to the lower case 4. The sliding amount is maximum when the cam shaft 9 is rotated until a, b, and c are aligned in the axial direction of the cylinder 2 as shown in FIG. This is twice the amount of eccentricity of the portion 9b and the movable bearing portion 9c. The cam portion 9b and the movable bearing portion 9c rotate inside the cam housing hole 5 and the bearing housing hole 8, respectively, and allow the position of the shaft portion 9a to move inside the cam housing hole 5 and the bearing housing hole 8, respectively. doing.

  By using the mechanism as described above, the cylinder block 3 and the cylinder head 20 can be moved relative to the lower case 4 in the axial direction of the cylinder 2, and the compression ratio is changed by changing the volume of the combustion chamber. can do.

  Next, the relationship among the throttle valve opening, the compression ratio, the exhaust valve opening timing, the residual gas ratio, and the fuel consumption in this embodiment will be described. FIG. 4 is a time chart showing the relationship among the throttle valve opening, the compression ratio, the exhaust valve opening timing, the residual gas ratio, and the fuel consumption. In FIG. 4, the throttle valve opening indicates the opening of the throttle valve 34, and the exhaust valve opening timing indicates the opening timing of the exhaust valve 25. FIG. 4 is a diagram for explaining the relationship among the throttle valve opening, the compression ratio, the exhaust valve opening timing, the residual gas ratio, and the fuel consumption. The actual control of the ratio and the opening timing of the exhaust valve 25 is not limited to the order shown in the time chart.

  Further, in this embodiment, the opening timing of the exhaust valve 25 is before the exhaust stroke bottom dead center, and delaying the opening timing of the exhaust valve 25 is closer to the exhaust stroke bottom dead center. It is. The valve closing timing of the exhaust valve 25 is set after the top dead center of the exhaust stroke regardless of the valve opening timing.

  When the internal combustion engine 1 is operated at a high load, that is, when the opening of the throttle valve 34 is large, even if the opening timing of the exhaust valve 25 is not advanced so much from the bottom dead center of the exhaust stroke, in the intake stroke Since the amount of fresh air to be sucked is large and the exhaust efficiency is high, the residual gas ratio is difficult to increase. Therefore, the valve opening timing of the exhaust valve 25 is late (timing near the bottom dead center of the exhaust stroke).

  When the operating state of the internal combustion engine 1 shifts from a high load to a low load, the opening degree of the throttle valve 34 is reduced during the period (1) to (3). When the operating state of the internal combustion engine 1 shifts from a high load to a low load, the residual gas ratio is likely to increase. Therefore, the opening timing of the exhaust valve 25 is advanced during the period from (2) to (4). When the valve opening timing of the exhaust valve 25 is advanced, the exhaust gas efficiency is increased and the residual gas ratio is decreased.

  After the operating state of the internal combustion engine 1 is shifted to a low load, during the period from (5) to (6), the volume of the combustion chamber is reduced and the compression ratio is increased. In this embodiment, the closing timing of the exhaust valve 25 is set after the exhaust stroke top dead center. Therefore, when the compression chamber is increased by reducing the volume of the combustion chamber, the piston 21 is brought to the exhaust stroke top dead center. When it reaches, the amount of burned gas discharged from the combustion chamber increases. Accordingly, the residual gas ratio is further reduced. Further, when the compression ratio is increased, the combustion efficiency is increased, so that fuel efficiency is improved.

  After increasing the compression ratio, the valve opening timing of the exhaust valve 25 is retarded during the period from (7) to (8). If the opening timing of the exhaust valve 25 is retarded, the exhaust efficiency is lowered, and the residual gas ratio increases. However, as described above, when the compression ratio is high, the burnt gas is easily discharged from the combustion chamber, so that a reduction in exhaust efficiency is suppressed. Therefore, it is possible to retard the valve opening timing of the exhaust valve 25 while suppressing the residual gas ratio to a value smaller than a value that causes deterioration of combustion (a value indicated by a dashed line A in FIG. 4). If the opening timing of the exhaust valve 25 is retarded in a state where the compression ratio is high, the exhaust efficiency is further increased because the exhaust loss is suppressed. Therefore, the fuel consumption is further improved.

  According to the control of the compression ratio and the opening timing of the exhaust valve as described above, the exhaust efficiency is improved by retarding the opening timing of the exhaust valve toward the top dead center side when the compression ratio is increased. Exhaust loss can be reduced while suppressing the decrease.

  Next, the control of the compression ratio and the opening timing of the exhaust valve 25 in this embodiment will be described. FIG. 5 is a flowchart showing a control routine for the compression ratio and the opening timing of the exhaust valve 25 in this embodiment. This routine is stored in advance in the ECU 30 and is executed every predetermined time during the operation of the internal combustion engine 1.

  In this routine, first, in S101, the ECU 30 determines whether or not the operating state of the internal combustion engine 1 is a low load. When it is determined in S101 that the operating state of the internal combustion engine 1 is not low load, the ECU 30 once ends the execution of this routine. On the other hand, when it is determined in S101 that the operating state of the internal combustion engine 1 is a low load, the ECU 30 proceeds to S102.

In S102, the ECU 30 increases the compression ratio. At this time, the compression ratio is calculated from MAP based on the engine load of the internal combustion engine 1, the engine speed, and the like. Then, the ECU 30 drives the motor 12 to rotate the camshaft 9 so that the compression ratio of the internal combustion engine 1 becomes the compression ratio calculated from the MAP.

  Next, the ECU 30 proceeds to S103, and detects the accelerator opening from the output value of the accelerator opening sensor 33. Further, the compression ratio is detected from the output value of the rotation angle sensor 32.

  Next, the ECU 30 proceeds to S104, and calculates a target exhaust valve opening timing based on the accelerator opening and the compression ratio detected in S103, and further on the engine speed of the internal combustion engine 1. Here, the target exhaust valve opening timing is calculated from MAP as shown in FIG. In the MAP, the vertical axis represents the accelerator opening, and the horizontal axis represents the compression ratio. A plurality of such MAPs are provided according to the engine speed of the internal combustion engine 1 and stored in advance in the ECU 30.

  In the MAP, the target exhaust valve opening timing is set so that the residual gas ratio becomes a value smaller than a value causing deterioration of combustion, and is as late as possible. Therefore, as shown in FIG. 6, the target exhaust valve opening timing is retarded as the accelerator opening is larger, that is, as the engine load of the internal combustion engine 1 is higher, and as the compression ratio is higher. The target exhaust valve opening timing is always before the exhaust stroke bottom dead center.

  Next, the ECU 30 proceeds to S105 and controls the variable valve mechanism 27 to adjust the valve opening timing of the exhaust valve 25 to the target exhaust valve opening timing.

  Next, the ECU 30 proceeds to S106, and calculates the combustion pressure fluctuation amount during the combustion cycle from the output value of the pressure sensor 31. The target exhaust valve opening timing is set to a timing that does not cause combustion deterioration due to residual gas, but the residual gas amount and the amount of new air sucked in during the intake stroke vary. The ratio increases, combustion becomes unstable, and combustion pressure fluctuations may increase. When the combustion pressure fluctuation is large, the rotation fluctuation of the internal combustion engine 1 also becomes large.

  The ECU 30 having calculated the combustion pressure fluctuation amount in S106 proceeds to S107, and determines whether or not the calculated combustion pressure fluctuation amount is equal to or less than a specified amount. The prescribed amount here is a threshold value within which the rotational fluctuation of the internal combustion engine 1 is within an allowable range, and is a predetermined fixed value.

  If it is determined in S107 that the combustion pressure fluctuation amount is larger than the specified value, the ECU 30 proceeds to S108. In S108, the ECU 30 advances the valve opening timing of the exhaust valve 25 by one step. Here, to advance one step means to advance by a predetermined fixed angle. For example, one step may be 0.5 to 1 °. When the opening timing of the exhaust valve 25 is advanced, the burned gas is easily discharged and the residual gas ratio is reduced. As a result, the combustion pressure fluctuation amount can be reduced. In S108, the ECU 30 that advanced the valve opening timing of the exhaust valve 25 by one step returns to S106.

  On the other hand, when it is determined in S107 that the combustion pressure fluctuation amount is equal to or less than the specified amount, the ECU 30 once ends the execution of this routine.

  According to the control described above, when the compression ratio is increased, the valve opening timing of the exhaust valve 25 is retarded to the target valve opening timing, thereby suppressing the residual gas amount and ensuring stable combustion. Exhaust loss can be suppressed.

  In the present embodiment, when the opening timing of the exhaust valve 25 is retarded toward the top dead center side of the exhaust stroke, it may be gradually retarded as the compression ratio becomes higher, or it is retarded stepwise. You may do it.

  When the compression ratio is high, the closing timing of the exhaust valve 25 may be retarded to near the exhaust stroke bottom dead center. In this case, exhaust loss can be further suppressed.

  In the present embodiment, when the operation state of the internal combustion engine 1 is a low load operation, when the compression ratio is increased and the opening timing of the exhaust valve 25 is retarded, the closing timing of the exhaust valve 25 is exhausted. It is preferable that the stroke is fixed near the top dead center. By doing in this way, the fall of the exhaust efficiency by the valve opening timing of the exhaust valve 25 being delayed can be suppressed more. Further, the lift amount of the exhaust valve 25 is preferably fixed to a specified lift amount regardless of the opening timing.

  In this embodiment, as shown in the control routine of FIG. 5 described above, after the operating state of the internal combustion engine 1 shifts to a low load, the compression ratio is increased, and further, the compression ratio is increased, Although the opening timing of the exhaust valve 25 is retarded, the compression ratio and the opening timing of the exhaust valve 25 may be changed as the operating state of the internal combustion engine 1 shifts to a low load.

  In the embodiment described above, an example in which the opening timing of the exhaust valve 25 is retarded when the compression ratio is increased only when the operating state of the internal combustion engine 1 is a low load has been described. Even when the operation state is a high load, the opening timing of the exhaust valve 25 may be retarded when the compression ratio is increased.

1 is a cross-sectional view showing a schematic configuration of an internal combustion engine and a variable compression ratio mechanism according to the present invention. 1 is an external view showing a schematic configuration of an internal combustion engine and a variable compression ratio mechanism according to the present invention. Sectional drawing which showed the relationship between a cylinder block, a lower case, and a cam shaft. FIG. 3A is a diagram illustrating a state in which the outer circumferences of all the cam portions and the movable bearing portion are coincident when viewed from the extension line of the shaft portion. The figure (b) is a figure which shows the state which rotated the axial part in the arrow direction from the state of the figure (a). FIG. 3C is a diagram showing a state where the movement amount of the cylinder block is maximized. The time chart figure which shows the relationship between throttle valve opening degree, compression ratio, exhaust valve opening timing, residual gas ratio, and fuel consumption. The flowchart figure which shows the control routine of the compression ratio and the valve opening timing of an exhaust valve. MAP showing the relationship between the accelerator opening, the compression ratio, and the target exhaust valve opening timing.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 2 ... Cylinder 3 ... Cylinder block 4 ... Lower case 5 ... Cam storage hole 6 ... Cam storage part 7 ... Bearing storage part 8 ... Bearing storage hole 9 ... Cam shaft 9a ... Shaft 9b ... Cam 9c ... Movable bearing 10 ... Worm wheel 11a ... Worm 11b ... Worm 12 ... Motor 20 ... Cylinder head 21 ... Piston 22 ... · Intake port 23 · · exhaust port 24 · · intake valve 25 · · exhaust valve 26 · · variable valve mechanism 27 · · variable valve mechanism 28 · · intake passage 29 · · exhaust passage 30 · · ECU
31..Pressure sensor 32..Rotation angle sensor 33..Accelerator opening sensor 34..Throttle valve

Claims (4)

An internal combustion engine having a variable compression ratio mechanism that changes the compression ratio by changing the volume of the combustion chamber,
When the compression ratio is increased by the variable compression ratio mechanism, the exhaust valve closing timing is set after the exhaust stroke top dead center, and the exhaust valve opening timing is retarded. An internal combustion engine equipped with a compression ratio mechanism.   2. The variable compression ratio mechanism according to claim 1, wherein when the compression ratio is increased by the variable compression ratio mechanism, the valve opening timing of the exhaust valve is retarded to near the bottom dead center of the exhaust stroke. Internal combustion engine.   When the compression state is increased by the variable compression ratio mechanism when the operating state of the internal combustion engine is low load operation, the exhaust valve closing timing is set after the exhaust stroke top dead center, and the exhaust 3. An internal combustion engine having a variable compression ratio mechanism according to claim 1, wherein the valve opening timing is retarded.   4. An internal combustion engine having a variable compression ratio mechanism according to claim 3, wherein the valve closing timing of the exhaust valve is maintained near the top dead center of the exhaust stroke, and the valve opening timing of the exhaust valve is retarded. .

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