JP2007056796A - Internal combustion engine equipped with variable compression ratio mechanism - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an internal combustion engine equipped with a variable compression ratio mechanism to obtain a proper compression ratio while suppressing occurrence of abnormal combustion. <P>SOLUTION: This internal combustion engine is provided with the variable compression ratio mechanism 20 for changing a compression ratio by changing volume of a clearance in a cylinder 2 and a suction air amount control means 10 for adjusting amount of air sucked into the cylinder 2. When increasing the compression ratio by the variable compression ratio mechanism 20, increase of the compression ratio by the variable compression ratio mechanism 20 is started after reduction of amount of suction air by the suction air amount control means 10 is started. First of all, the amount of suction air is reduced and pressure in the cylinder 2 is reduced to suppress occurrence of knocking. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an internal combustion engine that changes a compression ratio by changing a gap volume.

  An internal combustion engine that includes both a variable compression ratio mechanism and a variable valve timing mechanism is known. According to this internal combustion engine, the compression ratio and the expansion ratio can be changed by changing the clearance volume in the cylinder, and the thermal efficiency of the internal combustion engine can be improved. Moreover, the apparent stroke volume can be reduced by changing the opening / closing timing of the intake valve, and the thermal efficiency of the internal combustion engine can be improved.

  Here, the apparent stroke volume is a value obtained by multiplying the distance that the piston moves from the closed position of the intake valve to the top dead center by the cross-sectional area of the cylinder, and is hereinafter referred to as “execution stroke volume” or “actual displacement”. Called. Further, the apparent compression ratio is a value obtained by dividing the sum of the gap volume and the execution volume by the gap volume, and is hereinafter referred to as “actual compression ratio”. Furthermore, the expansion ratio is a value obtained by dividing the sum of the gap volume and the stroke volume in the expansion stroke by the gap volume.

  In other words, the execution volume changes by changing the closing timing of the intake valve by the variable valve timing mechanism. Further, the actual compression ratio changes even if the compression ratio is changed by the variable compression ratio mechanism, or the closing timing of the intake valve is changed by the variable valve timing mechanism. Further, the expansion ratio is changed by changing the compression ratio by the variable compression ratio mechanism.

  The execution volume, the actual compression ratio, and the expansion ratio that are changed by the variable compression ratio mechanism and the variable valve timing mechanism also affect the operating state and thermal efficiency of the internal combustion engine, that is, fuel consumption.

Here, a technique for controlling a variable compression ratio mechanism and a variable valve timing mechanism based on an engine speed and an engine load is known (see, for example, Patent Document 1). According to this prior art, when the load of the internal combustion engine increases, the closing timing of the intake valve is first advanced, and then the compression ratio of the combustion chamber is decreased when the load of the internal combustion engine further increases.
Japanese Patent Laid-Open No. 3-64649 JP 2002-276446 A JP 2003-328794 A JP 2003-232233 A

  By the way, when the compression ratio is increased by the variable compression ratio mechanism, if the amount of intake air suddenly increases due to the influence of intake pulsation or sudden operation of the throttle, the pressure in the cylinder may increase and knocking may occur. is there. In addition, when the compression ratio is changed by the variable compression ratio mechanism and when the intake valve closing timing is changed by the variable valve timing mechanism, the time taken from the start to the end is different. The balance between the ratio and the intake air amount may be lost and knocking may occur.

  The present invention has been made in view of the various problems as described above, and an object thereof is to obtain an appropriate compression ratio while suppressing the occurrence of abnormal combustion in an internal combustion engine equipped with a variable compression ratio mechanism. It is in.

  In order to achieve the above object, an internal combustion engine provided with a variable compression ratio mechanism according to the present invention is characterized by the following.

That is,
A variable compression ratio mechanism that changes the compression ratio by changing the gap volume in the cylinder;
Intake air amount control means for adjusting the amount of air sucked into the cylinder;
With
When the compression ratio is increased by the variable compression ratio mechanism, the increase of the compression ratio by the variable compression ratio mechanism is started after the reduction of the intake air amount by the intake air amount control means is started.

  In the internal combustion engine described above, the compression ratio is changed by changing the elements involved in the compression ratio of the internal combustion engine, such as the piston stroke and the combustion chamber volume, by the variable compression ratio mechanism. Further, the expansion ratio is also changed by changing the gap volume. Here, the smaller the gap volume, the higher the compression ratio and the expansion ratio, and the higher the thermal efficiency. However, if the compression ratio becomes too high, knocking may occur. Further, when the actual compression ratio is increased by the variable compression ratio mechanism, the expansion ratio is also increased.

  On the other hand, when the intake air amount is decreased by the intake air amount control means, the air amount with respect to the gap volume decreases, so the pressure of the compressed air becomes low. Thereby, occurrence of knocking is suppressed.

  Here, when the actual compression ratio is increased, the thermal efficiency is increased. However, when the actual compression ratio is increased too much, knocking occurs. Therefore, if the variable compression ratio mechanism and the intake air amount are controlled so that the actual compression ratio is close to the upper limit, the thermal efficiency is increased. In addition, since the expansion ratio is increased by setting the actual compression ratio near the upper limit, the thermal efficiency is also increased in this respect.

  Thus, if the actual compression ratio and the expansion ratio are changed by the variable compression ratio mechanism and the intake air amount is changed by the intake air amount control means, the thermal efficiency of the internal combustion engine changes. And since a thermal efficiency becomes high by making an actual compression ratio and the amount of intake air into an appropriate value, a fuel consumption can be improved.

  In the present invention, when the compression ratio is increased, the intake air amount is first decreased by the intake air amount control means. Thereby, the pressure in the cylinder after compression falls. Thereafter, the compression ratio is increased by the variable compression ratio mechanism. In this way, by first reducing the pressure in the cylinder after compression, even if the intake air amount suddenly increases during the increase of the compression ratio, it is suppressed from increasing to the pressure at which knocking occurs. Thereby, occurrence of knocking can be suppressed.

  In the present invention, the increase in the compression ratio may be started before the reduction of the intake air amount is completed, that is, in the middle of the reduction of the intake air amount. Further, the increase in the compression ratio may be started after the intake air amount has decreased until the pressure in the cylinder reaches a pressure that can suppress the occurrence of knocking. Furthermore, the relationship between the compression ratio, which is the in-cylinder pressure that can suppress the occurrence of knocking, and the intake air amount may be obtained in advance, and the compression ratio and the intake air amount may be changed while maintaining this relationship.

In order to achieve the above object, an internal combustion engine provided with a variable compression ratio mechanism according to the present invention may be characterized as follows. That is,
A variable compression ratio mechanism that changes the compression ratio by changing the gap volume in the cylinder;
Intake air amount control means for adjusting the amount of air sucked into the cylinder;
With
When the compression ratio is lowered by the variable compression ratio mechanism, the intake air amount may be increased by the intake air amount control means after the compression ratio is lowered by the variable compression ratio mechanism. . Further, the increase in the intake air amount may be started after the compression ratio is lowered until the pressure in the cylinder becomes a pressure that can suppress the occurrence of knocking.

  When the compression ratio is decreased, the intake air amount is increased by the intake air amount control means, and the compression ratio is decreased by the variable compression ratio mechanism. Here, when reducing the compression ratio, if the intake air amount is increased while the compression ratio is still high, the pressure in the cylinder becomes too high, and knocking may occur. Therefore, before the intake air amount is increased, the compression ratio is first reduced to reduce the pressure in the cylinder. Thereafter, by increasing the intake air amount, it is possible to suppress the pressure in the cylinder from becoming too high. Thereby, occurrence of knocking can be suppressed.

  In the present invention, the increase in the intake air amount may be started before the reduction of the compression ratio is completed, that is, in the middle of the reduction of the compression ratio. Further, the increase in the intake air amount may be started after the compression ratio is lowered until the pressure in the cylinder becomes a pressure that can suppress the occurrence of knocking. Furthermore, the relationship between the compression ratio, which is the in-cylinder pressure that can suppress the occurrence of knocking, and the intake air amount may be obtained in advance, and the compression ratio and the intake air amount may be changed while maintaining this relationship.

  In the present invention, the intake air amount control means may comprise a variable valve timing mechanism that changes the valve timing of the intake valve.

  The variable valve timing mechanism controls the advance angle and retard angle of the valve timing. Here, since the intake air amount becomes the largest when the intake valve is closed near the bottom dead center of intake, the intake air amount decreases even if the closing timing of the intake valve is made earlier or later. . For example, if the closing timing of the intake valve is delayed so that the intake valve closes in the middle of the compression stroke, the air once sucked into the cylinder is pushed out to the intake passage as the piston rises. Therefore, since the amount of air in the cylinder is reduced, the pressure of the compressed air is also reduced. As a result, the same effect as when the compression ratio is decreased can be obtained. That is, the execution volume is smaller than the gap volume.

  Here, in the low-load operation region of the internal combustion engine, if the closing timing of the intake valve is delayed, the actual effective displacement becomes smaller and the average effective pressure becomes higher, which increases the thermal efficiency. However, delaying the closing timing of the intake valve causes a decrease in thermal efficiency in that the actual compression ratio is reduced.

  When the actual compression ratio is increased, the thermal efficiency increases, but the upper limit of the compression ratio is determined by the occurrence of knocking. Therefore, if the variable compression ratio mechanism and the variable valve timing mechanism are controlled so that the actual compression ratio is near the upper limit, the thermal efficiency is increased. Further, since the expansion ratio can be made extremely high by setting the actual compression ratio in the vicinity of the upper limit, the thermal efficiency is also increased in this respect.

  On the other hand, the actual displacement has an optimum value according to the operation state at that time, and the thermal efficiency is lowered even if it is larger or smaller than this. Therefore, if the variable valve timing mechanism is controlled so that the actual displacement becomes an optimum value, the thermal efficiency becomes high.

As described above, when the actual compression ratio and the expansion ratio are changed by the variable compression ratio mechanism, and the actual compression ratio and the actual displacement are changed by the variable valve timing mechanism, the thermal efficiency of the internal combustion engine changes. Then, by setting the actual compression ratio and the actual displacement to appropriate values, the thermal efficiency is increased and the fuel consumption can be improved.

  According to the internal combustion engine provided with the variable compression ratio mechanism according to the present invention, it is possible to obtain an appropriate compression ratio while suppressing the occurrence of abnormal combustion, so that fuel efficiency can be improved.

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

  FIG. 1 is a diagram showing a schematic configuration of a variable compression ratio internal combustion engine (hereinafter simply referred to as “internal combustion engine”) 1 in which the compression ratio is variable. In this embodiment, in order to display the internal combustion engine 1 in a concise manner, some components are not shown.

  The internal combustion engine 1 is a gasoline engine having four cylinders 2.

  The internal combustion engine 1 includes a cylinder head 3, a cylinder block 4, and a crankcase 5. Each cylinder 2 is provided with a piston 6.

  In the internal combustion engine 1 according to the present embodiment, for example, as described in Japanese Patent Application Laid-Open No. 2003-206871, the cylinder block 4 is arranged in the cylinder axial direction (hereinafter also referred to as the vertical direction) with respect to the crankcase 5. A variable compression ratio mechanism 20 is provided which is attached so as to be able to move forward and backward, and is provided with a double eccentric shaft at the connecting portion between them, and the cylinder block 4 is driven to move forward and backward by swinging and rotating the double eccentric shaft.

  According to the variable compression ratio mechanism 20, the cylinder head 3 together with the cylinder block 4 is moved relative to the crankcase 5 in the axial direction of the cylinder 2. As a result, the volume of the combustion chamber constituted by the cylinder block 4, the cylinder head 3 and the piston 6 is changed. As a result, the compression ratio of the internal combustion engine 1 is variably controlled. For example, when the cylinder block 4 is relatively moved away from the crankcase 5, the combustion chamber volume increases and the compression ratio decreases.

  In the internal combustion engine 1, the intake valve 7 is opened and closed by the intake camshaft 8. An intake pulley 9 is attached to the intake camshaft 8. Further, a variable valve timing mechanism (hereinafter referred to as “VVT”) 10 that can change the relative rotational phase between the intake camshaft 8 and the intake pulley 9 is provided. The VVT 10 controls the relative rotation phase between the intake side camshaft 8 and the intake side pulley 9 in accordance with a command from the ECU 90.

  Then, the rotational drive of the intake pulley 9 is performed by the driving force of the crankshaft 11. As a result, the intake side camshaft 8 is rotationally driven, and the intake valve 7 is opened and closed.

  An intake pipe 30 is connected to the internal combustion engine 1, and a throttle 31 is attached in the middle of the intake pipe 30.

  Here, the internal combustion engine 1 is provided with an ECU 90 that is an electronic control unit for controlling the internal combustion engine 1. The ECU 90 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.

  Here, the crank position sensor 91 is electrically connected to the ECU 90, and the ECU 90 receives a signal corresponding to the rotation angle of the output shaft of the internal combustion engine 1, and determines the engine rotation speed of the internal combustion engine 1 and the engine rotation speed. The vehicle speed and the like of the vehicle on which the internal combustion engine 1 is mounted are calculated from the gear ratio and the like. An accelerator opening sensor 92 is electrically connected to the ECU 90, and the ECU 90 receives a signal corresponding to the accelerator opening, and calculates an engine load required for the internal combustion engine 1 according to this signal.

  Further, a motor that constitutes the variable compression ratio mechanism 20 is electrically connected to the ECU 90. Then, the motor is driven by a command from the ECU 90, and the compression ratio of the internal combustion engine 1 is changed by the variable compression ratio mechanism 20.

  In this embodiment, in the low load operation region of the internal combustion engine 1, the closing timing of the intake valve 7 is delayed by the VVT 10, and the compression ratio is increased by the variable compression ratio mechanism 20. The variable compression ratio mechanism 20 is controlled so that the actual compression ratio at which knocking may occur unless the valve closing timing of the intake valve 7 is delayed by the VVT 10. That is, the cylinder block 4 is moved in a direction that shortens the relative distance between the cylinder block 4 and the crankcase 5. Further, the VVT 10 delays the closing timing of the intake valve 7 to lower the actual compression ratio. Finally, the valve closing timing of the intake valve 7 is set by the VVT 10 so as to achieve an actual compression ratio that is unlikely to cause knocking.

  By doing so, the actual compression ratio can be set high within a range where knocking does not occur in the low load operation region, and the expansion ratio can be made very high. As a result, thermal efficiency can be improved. On the other hand, in the high load operation region, the amount of air flowing into the cylinder 2 can be increased by reducing the actual compression ratio and the expansion ratio, and the output can be improved.

  In this embodiment, the compression ratio of the internal combustion engine 1 is increased when shifting from the high load operation state to the low load operation state. At this time, first, the closing timing of the intake valve 7 is delayed by the VVT 10. Thereafter, the actual compression ratio is increased by the variable compression ratio mechanism 20.

  By first operating the VVT 10, the pressure in the cylinder 2 decreases. Therefore, even if the intake air amount suddenly increases due to a sudden operation of the throttle 31 or the like, an excessive increase in the pressure in the cylinder 2 is suppressed. Thereby, occurrence of knocking can be suppressed.

  FIG. 2 is a time chart showing transitions of the opening degree of the throttle 31, the control amount of the VVT 10, and the control amount of the variable compression ratio mechanism 20 when the required load of the internal combustion engine shifts from a high load to a low load. . The upper stage is the throttle opening, the middle stage is the closing timing of the intake valve 7, that is, the retard amount by the VVT 10, and the lower stage is the compression ratio set by the variable compression ratio mechanism 20 (referred to as the mechanical compression ratio in FIG. 2). Each shows.

  There is a low load demand at the time indicated by A, the VVT 10 starts operating at the time indicated by B, and the variable compression ratio mechanism 20 starts operating at the time indicated by C. Thus, after the required load of the internal combustion engine 1 starts to decrease, the amount of retardation of the VVT 10 starts to increase, and thereafter, the compression ratio increase by the variable compression ratio mechanism 20 is started. That is, the compression ratio is increased by the variable compression ratio mechanism 20 after the intake air amount is decreased by increasing the retard amount of the intake valve 7.

Next, the control flow of the VVT 10 and the variable compression ratio mechanism 20 according to this embodiment will be described.

  FIG. 3 is a flowchart showing a control flow of the VVT 10 and the variable compression ratio mechanism when the internal combustion engine shifts from the high load operation state to the low load operation state. This routine is repeatedly executed every predetermined time.

  In step S101, it is determined whether there is a low load request. That is, it is determined whether or not the actual compression ratio is increased. In this step, it is determined that there is a low load request when the accelerator depression amount obtained by the accelerator opening sensor 92 changes to a smaller side.

  If an affirmative determination is made in step S101, the process proceeds to step S102. On the other hand, if a negative determination is made, this routine is temporarily terminated.

  In step S102, the amount by which the valve closing timing of the intake valve 7 is changed by the VVT 10 and the amount by which the cylinder block 4 is moved by the variable compression ratio mechanism 20 are determined. That is, the control amounts of the VVT 10 and the variable compression ratio mechanism 20 are determined.

  For example, the relationship between the opening degree of the throttle 31, the closing timing of the intake valve 7, and the compression ratio set by the variable compression ratio mechanism 20 is obtained in advance through experiments or the like and mapped and stored. Then, the closing timing of the intake valve 7 from the closing timing of the intake valve 7 corresponding to the current opening of the throttle 31 and the closing timing of the intake valve 7 corresponding to the opening of the throttle 31 before the change is made. The amount of change is calculated. In order to obtain this amount of change, the amount by which the VVT 10 operates is determined as the control amount. The control amount of the variable compression ratio mechanism 20 is determined in the same manner.

  In step S103, control of the VVT 10 is started. That is, the delay of the closing timing of the intake valve 7 is started.

  In step S104, control of the variable compression ratio mechanism 20 is started. That is, the cylinder block 4 is moved to the crankcase 5 side. The time from the start of the control of the VVT 10 to the start of the control of the variable compression ratio mechanism 20 is obtained in advance through experiments or the like as values corresponding to these control values and stored in the ECU 90.

  In this manner, when the internal combustion engine 1 shifts from the high load operation state to the low load operation state, the delay of the closing timing of the intake valve 7 is first started, so the intake air amount is temporarily reduced. That is, since the compression ratio is increased by the variable compression ratio mechanism 20 after the pressure in the cylinder is once reduced, it is possible to suppress an excessive increase in pressure even if the throttle 31 is suddenly operated. Therefore, the occurrence of knocking can be suppressed.

  In the present embodiment, control of the VVT 10 and the variable compression ratio mechanism 20 when the internal combustion engine 1 shifts from the low load operation state to the high load operation state will be described.

  In this embodiment, when the internal combustion engine 1 shifts from the low load operation state to the high load operation state, the compression ratio of the internal combustion engine 1 is lowered. At this time, the actual compression ratio is first lowered by the variable compression ratio mechanism 20. Then, the closing timing of the intake valve 7 is advanced by the VVT 10 to increase the intake air amount.

By operating the variable compression ratio mechanism 20 first, the compression ratio is lowered. Therefore, even if the intake air amount suddenly increases due to a sudden operation of the throttle 31 or the like, an excessive increase in the pressure in the cylinder 2 is suppressed. Thereby, the occurrence of knocking can be suppressed.

  FIG. 4 is a flowchart showing a control flow of the VVT 10 and the variable compression ratio mechanism when the internal combustion engine shifts from the low load operation state to the high load operation state. This routine is repeatedly executed every predetermined time. Steps in which the same processing as in FIG. 3 is performed are denoted by the same reference numerals and description thereof is omitted.

  In step S201, it is determined whether there is a high load request. That is, it is determined whether or not the actual compression ratio is in a reduced state. In this step, it is determined that there is a high load request when the accelerator depression amount obtained by the accelerator opening sensor 92 is changed to a larger side.

  If an affirmative determination is made in step S201, the process proceeds to step S102. On the other hand, if a negative determination is made, this routine is temporarily terminated.

  In step S202, control of the variable compression ratio mechanism 20 is started. That is, the cylinder block 4 is moved in a direction away from the crankcase 5.

  In step S203, control of the VVT 10 is started. That is, the advance angle of the closing timing of the intake valve 7 is started. The time from the start of the control of the variable compression ratio mechanism 20 to the start of the control of the VVT 10 is obtained in advance through experiments or the like as values corresponding to these control values and stored in the ECU 90.

  In this way, when the internal combustion engine 1 shifts from the low load operation state to the high load operation state, the compression ratio reduction by the variable compression ratio mechanism 20 is first started, so the pressure in the cylinder is temporarily reduced. . Thereafter, the amount of intake air is increased by the VVT 10, so that even if the throttle 31 is suddenly operated, it is possible to suppress an excessive increase in pressure, thereby suppressing the occurrence of knocking. it can.

It is a figure showing the schematic structure of the variable compression ratio internal combustion engine which makes a compression ratio variable. 6 is a time chart showing changes in throttle opening, VVT control amount, and variable compression ratio mechanism control amount when the required load of the internal combustion engine shifts from a high load to a low load. It is the flowchart which showed the control flow of VVT and a variable compression ratio mechanism at the time of an internal combustion engine shifting from a high load driving | running state to a low load driving | running state. It is the flowchart which showed the control flow of VVT and a variable compression ratio mechanism when an internal combustion engine transfers from a low load driving | running state to a high load driving | running state.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Internal combustion engine 2 Cylinder 3 Cylinder head 4 Cylinder block 5 Crankcase 6 Piston 7 Intake valve 8 Intake side camshaft 9 Intake side pulley 10 Variable valve timing mechanism 11 Crankshaft 20 Variable compression ratio mechanism 30 Intake pipe 31 Throttle 90 ECU
91 Crank position sensor 92 Accelerator opening sensor

Claims (3)

A variable compression ratio mechanism that changes the compression ratio by changing the gap volume in the cylinder;
Intake air amount control means for adjusting the amount of air sucked into the cylinder;
With
When the compression ratio is increased by the variable compression ratio mechanism, the variable compression ratio mechanism starts increasing the compression ratio after the intake air amount control means starts decreasing the intake air amount. An internal combustion engine equipped with a compression ratio mechanism. A variable compression ratio mechanism that changes the compression ratio by changing the gap volume in the cylinder;
Intake air amount control means for adjusting the amount of air sucked into the cylinder;
With
When the compression ratio is lowered by the variable compression ratio mechanism, the intake air amount is increased by the intake air amount control means after the compression ratio is lowered by the variable compression ratio mechanism. An internal combustion engine equipped with a compression ratio mechanism.   The internal combustion engine having a variable compression ratio mechanism according to claim 1 or 2, wherein the intake air amount control means includes a variable valve timing mechanism for changing a valve timing of the intake valve.

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