JP2004239175A - Control of internal combustion engine when two operation modes different in compression ratio and air fuel ratio are varied - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technology capable of suppression of the occurrence of abnormal combustion, such as knocking, and the rapid increase of output torque when operation modes are varied. <P>SOLUTION: An internal combustion engine has a first operation mode to execute operation in a high compression ratio and a lean air fuel ratio; and a second operation mode to execute operation in a low compression ratio and a theoretical air fuel ratio. In case of variation from the first operation mode to the second operation mode, first of all, operation of an intake valve is regulated such that an intake air amount in the initial stage of an operation mode variation period is decreased to a value lower than an intake air amount before variation of an operation mode, and as a result an air fuel ratio is decreased in a step-form state in the initial stage of the operation mode variation period. Then, the compression ratio is gradually lowered during a subsequent operation mode variation period, and in this case, operation of the intake valve is regulated such that an intake air amount is gradually increased, and a fuel feed amount is gradually increased. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an internal combustion engine capable of changing a compression ratio.
[0002]
[Prior art]
In recent years, various internal combustion engines having a mechanism capable of changing a compression ratio have been proposed. When the compression ratio is set high, power can be efficiently obtained, but knocking is likely to occur. Therefore, the compression ratio is changed according to the operating conditions. Specifically, when the load on the internal combustion engine is low (that is, when the accelerator opening is small), knocking is unlikely to occur, so the compression ratio is set to a high value. On the other hand, when the load of the internal combustion engine is high (that is, when the accelerator opening is large), knocking is likely to occur, so the compression ratio is set low.
[0003]
According to Patent Document 1, when the load on the internal combustion engine is low, the operation is performed at a high compression ratio and a lean air-fuel ratio (a state in which the air-fuel ratio of the air-fuel mixture is higher than the stoichiometric air-fuel ratio). Discloses a technique for performing an operation at a low compression ratio and a rich air-fuel ratio (the air-fuel ratio of the air-fuel mixture is lower than the stoichiometric air-fuel ratio). When changing from the operation mode in which the operation is performed with the high compression ratio and the lean air-fuel ratio to the operation mode in which the operation is performed with the low compression ratio and the rich air-fuel ratio, knocking may occur. In this technique, the change in the compression ratio and the change in the air-fuel ratio are simultaneously performed in a stepwise manner, thereby suppressing the occurrence of knocking. In addition, when the air-fuel ratio sharply decreases (enriched), the output torque sharply increases. However, in this technique, the air-fuel ratio is reduced and the compression ratio is reduced in a stepwise manner. The step (change amount) of the output torque is reduced.
[0004]
[Patent Document 1]
JP-A-63-159642 [0005]
[Problems to be solved by the invention]
However, it is difficult to simultaneously change the compression ratio and change the air-fuel ratio. If the change timing is shifted, there is a problem that the combustion state deteriorates. Specifically, if the change of the compression ratio is delayed, the operation is performed at a high compression ratio and a rich air-fuel ratio during the delay period, so that abnormal combustion such as knocking occurs. Further, a sharp increase in the output torque caused by a sharp decrease in the air-fuel ratio is mitigated by decreasing the compression ratio in a stepwise manner, but there is a problem that the step (change amount) of the output torque is relatively large. .
[0006]
The present invention has been made in order to solve the above-described problems in the related art, and is a technique capable of suppressing occurrence of abnormal combustion such as knocking and a sharp increase in output torque when changing operation modes. The purpose is to provide.
[0007]
[Means for Solving the Problems and Their Functions and Effects]
To solve at least part of the above-mentioned problems, an apparatus according to the present invention is an internal combustion engine,
Including a combustion chamber, a compression ratio changing unit for changing the compression ratio by changing the volume of the combustion chamber,
A variable valve train that includes a valve and that can adjust the amount of intake air drawn into the combustion chamber by adjusting the operation of the valve;
A fuel supply unit for supplying fuel to the combustion chamber,
A control unit for detecting operating conditions of the internal combustion engine, and controlling the compression ratio changing unit, the variable valve system, and the fuel supply unit according to the detection result,
With
The internal combustion engine has a first operation mode in which operation is performed at a relatively high compression ratio and a relatively high air-fuel ratio, and a second operation mode in which operation is performed at a relatively low compression ratio and a relatively low air-fuel ratio. , And
The control unit includes:
When changing from the first operation mode to the second operation mode according to the detection result,
(I) controlling at least the variable valve system so as to adjust the operation of the valve so that the intake air amount at the beginning of the operation mode change period is smaller than the intake air amount before the operation mode change period; At the beginning of the operation mode change period, the air-fuel ratio is reduced stepwise,
(Ii) During the operation mode change period after the air-fuel ratio decreases, the compression ratio changing unit is controlled to gradually reduce the compression ratio. At this time, the variable valve system is controlled to gradually increase the intake air amount. The operation of the valve is adjusted so as to increase, and the fuel supply unit is controlled to gradually increase the fuel supply amount.
[0008]
In this device, when changing from the first operation mode to the second operation mode, first, the air-fuel ratio is reduced stepwise at the beginning of the operation mode change period. Therefore, at the beginning of the operation mode change period, the operation is performed with the compression ratio maintained at a relatively high state and the air-fuel ratio lowered. However, since the change of the air-fuel ratio is realized by reducing the intake air amount, the air-fuel mixture amount at the beginning of the operation mode change period is relatively small. As a result, at the beginning of the operation mode change period, the occurrence of abnormal combustion such as knocking can be suppressed, and the sudden increase in output torque can be suppressed. Then, during the subsequent operation mode change period, the compression ratio is gradually changed. At this time, the intake air amount and the fuel supply amount gradually increase, so that the air-fuel mixture amount gradually increases. As a result, during the operation mode change period, the occurrence of abnormal combustion such as knocking can be suppressed, and the output torque can be gradually increased.
[0009]
Here, it is preferable that the relatively high air-fuel ratio is set larger than the stoichiometric air-fuel ratio, and the relatively low air-fuel ratio is set substantially equal to the stoichiometric air-fuel ratio.
[0010]
In this way, the fuel consumption rate can be improved in the first operation mode, and the output torque can be improved in the second operation mode.
[0011]
In the above device,
The valve is an intake valve;
The control unit can change the actual compression ratio by changing the closing timing of the intake valve,
The actual compression ratio at the beginning of the operation mode change period is set lower than the actual compression ratio before the operation mode change,
The actual compression ratio during the operation mode change period is preferably set so as to gradually increase as the compression ratio decreases.
[0012]
Here, the actual compression ratio is a ratio between the volume of the combustion chamber at the timing of closing the intake valve and the minimum volume of the combustion chamber.
[0013]
By changing the actual compression ratio in this manner, the intake air amount can be reduced at the beginning of the operation mode change period, and the intake air amount can be gradually increased during the subsequent operation mode change period. Further, since the air-fuel mixture in the combustion chamber does not need to be strongly compressed, knocking during the operation mode change period can be reliably suppressed.
[0014]
The present invention relates to an internal combustion engine, a moving object equipped with the internal combustion engine, a control device and a control method for controlling the internal combustion engine, a computer program for realizing the functions of the control device, and a recording medium storing the computer program , Including the computer program, a data signal embodied in a carrier wave, and the like.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
A. Engine configuration:
Next, embodiments of the present invention will be described based on examples. FIG. 1 is an explanatory diagram showing a schematic configuration of the gasoline engine 100. The engine of this embodiment is mounted on a vehicle.
[0016]
The engine 100 includes an engine body 10, and the engine body 10 includes a cylinder head 20 and a cylinder block 30.
[0017]
The cylinder block 30 includes an upper block 31 functioning as a cylinder and a lower block 32 functioning as a crankcase. A piston 41 that reciprocates up and down is provided in the cylinder, and a crankshaft 43 that rotates is provided in the crankcase. The piston 41 and the crankshaft 43 are connected via a connecting rod 42. With this configuration, conversion between the reciprocating motion of the piston 41 and the rotational motion of the crankshaft 43 is performed. Note that a region surrounded by the cylinder head 20, the cylinder block 30, and the piston 41 forms a combustion chamber.
[0018]
An actuator 33 is provided between the upper block 31 and the lower block 32 to move the upper block 31 vertically with respect to the lower block 32. When the upper block 31 is moved upward, the cylinder head 20 is also moved upward. At this time, since the volume of the combustion chamber increases, the compression ratio decreases. Conversely, when the upper block 31 is moved downward, the cylinder head 20 also moves downward. At this time, since the volume of the combustion chamber is reduced, the compression ratio is increased. The compression ratio is expressed as Vb / Vt using the maximum volume Vb of the combustion chamber when the piston is located at the bottom dead center and the minimum volume Vt of the combustion chamber when the piston is located at the top dead center. You.
[0019]
An intake port 23 and an exhaust port 24 are formed in the cylinder head 20. An intake valve 21 is arranged at the intake port 23, and an exhaust valve 22 is arranged at the exhaust port 24. The intake valve 21 and the exhaust valve 22 are driven by valve operating mechanisms (cam mechanisms) 25 and 26 that operate according to the reciprocating motion of the piston 41, respectively. The valve operating mechanism 25 that drives the intake valve 21 is a variable valve operating mechanism.
[0020]
An intake pipe 50 is connected to the intake port 23, and an exhaust pipe 58 is connected to the exhaust port 24. The intake pipe 50 is provided with a throttle valve 52 and a fuel injection valve 55. Air is supplied from an upstream side of the intake pipe 50 via an air cleaner 51. The throttle valve 52 controlled by the electric actuator 53 adjusts the amount of air guided to the combustion chamber. The fuel injection valve 55 injects fuel (gasoline) supplied from a fuel pump (not shown) into the intake port 23. Thus, a mixture of air and fuel is generated. After the mixture is supplied into the combustion chamber, it is burned by the electric spark formed by the spark plug 27. The burned exhaust gas is discharged from the combustion chamber.
[0021]
Further, the engine 100 includes an electronic control unit (ECU) 60 for controlling the entire engine. The ECU 60 includes a CPU, a ROM, a RAM, and an input / output circuit connected to each other by a bus. The ECU 60 is connected with a crank angle sensor 61 provided on the crankshaft 43, an accelerator opening sensor 62 provided on the accelerator pedal, an intake pressure sensor 56 provided on the intake pipe 50, and the like. Then, the ECU 60 controls the actuator 33, the variable valve mechanism 25, the spark plug 27, the fuel injection valve 55, and the like based on these detection results.
[0022]
Note that the engine body 10 in the present embodiment corresponds to a compression ratio changing unit in the present invention. Further, the intake valve 21 and the variable valve mechanism 25 correspond to a variable valve system in the present invention, and the fuel injection valve 55 corresponds to a fuel supply unit in the present invention. Further, the ECU 60, the crank angle sensor 61, and the accelerator opening sensor 62 correspond to a control unit in the present invention.
[0023]
B. Engine control:
FIG. 2 is a flowchart showing an outline of control of the engine. Note that the ECU 60 repeatedly executes the processing of steps S101 and S102.
[0024]
In step S101, operating conditions of the engine are detected. Specifically, the ECU 60 detects an engine speed and a required torque as operating conditions. The engine speed is determined based on the detection result of the crank angle sensor 61, and the required torque is determined based on the detection result of the accelerator opening sensor 62.
[0025]
In step S102, various controls are executed based on the operating conditions detected in step S101.
[0026]
In step S102a, control of the compression ratio is executed. Specifically, the ECU 60 determines a target compression ratio based on the detected operating conditions (engine speed and required torque). The ECU 60 sets the compression ratio of the engine to the target compression ratio by driving the actuator 33.
[0027]
In step S102b, control of the air-fuel ratio is performed. Specifically, the ECU 60 determines a target air-fuel ratio based on the detected operating conditions (engine speed and required torque).
[0028]
The control of the air-fuel ratio includes control of the operation of the intake valve (step S102b1) and control of the fuel injection (step S102b2). The control of the operation of the intake valve is executed to adjust the amount of intake air taken into the combustion chamber. Specifically, the ECU 60 controls the variable valve mechanism 25 to adjust the operation of the intake valve 21, and as a result, the amount of intake air actually sucked into the combustion chamber is adjusted. Here, the “intake air amount” means the amount of air that is compressed in the combustion chamber during the compression stroke. The control of the operation of the intake valve will be further described later.
[0029]
The intake air amount is obtained based on the detection result of the intake pressure sensor 56. Then, the fuel supply amount is determined based on the target air-fuel ratio and the intake air amount. In the present embodiment, the fuel injection amount per unit time and the fuel injection end timing are predetermined. For this reason, the fuel supply amount is changed by adjusting the fuel injection start timing. The fuel injection by the fuel injection valve 55 is executed at an appropriate timing based on the detection result from the crank angle sensor 61.
[0030]
Incidentally, the target compression ratio and the target air-fuel ratio are determined using a map stored in the ROM of the ECU 60. FIG. 3 is an explanatory diagram schematically showing a map indicating a target compression ratio and a target air-fuel ratio according to operating conditions. As shown in the figure, in the present embodiment, the target compression ratio is set to a relatively high value and the target air-fuel ratio is set to a relatively high value (lean air-fuel ratio) under the condition that the required torque is relatively small (the lean air-fuel ratio). 1 operation mode). Further, under the condition that the required torque is relatively large, the target compression ratio is set to a relatively low value, and the target air-fuel ratio is set to a relatively low value (the stoichiometric air-fuel ratio) (second operation mode).
[0031]
By using the map of FIG. 3, it is possible to execute the operation at a relatively high compression ratio while suppressing the occurrence of knocking. That is, when the engine load is high, knocking is likely to occur. The occurrence of knocking can be suppressed by lowering the compression ratio. For this reason, in the map of FIG. 3, when the engine load is high, the target compression ratio is set low. In addition, when the map in FIG. 3 is used, when the engine load is low, the operation is performed at the lean air-fuel ratio, so that the fuel consumption rate can be improved. Conversely, when the engine load is high, the operation is performed at the stoichiometric air-fuel ratio, so that the output torque can be improved.
[0032]
In step S102c (FIG. 2), control of the ignition timing is executed according to the detected operating condition. In the present embodiment, the ignition timing is determined using a map indicating a target ignition timing according to the operating conditions stored in the ROM of the ECU 60. The ignition by the ignition plug 27 is executed at an appropriate timing based on the detection result from the crank angle sensor 61.
[0033]
C. Control when changing operation mode:
By the way, when changing from the first operation mode to the second operation mode, abnormal combustion such as knocking may occur. For this reason, the present embodiment is devised so as to suppress the occurrence of knocking when the operation mode is changed. However, in the following, prior to the description of the control content when the operation mode is changed in the present embodiment, the control content in the comparative example will be described.
[0034]
FIG. 4 is an explanatory diagram schematically showing control contents when the operation mode is changed in the comparative example. This control is executed, for example, when the required torque increases in the map of FIG. 3 and the operating condition changes from the point Ca to the point Cc.
[0035]
FIG. 4A illustrates a change in the required torque. FIG. 4B shows a change in the air-fuel ratio of the air-fuel mixture, and FIGS. 4C and 4D show a change in the intake air amount and a change in the fuel supply amount, respectively. FIG. 4E shows a change in the compression ratio. FIG. 4F shows a change in the output torque.
[0036]
As shown in FIG. 4A, during a period Ta in which the required torque is relatively small, the air-fuel ratio is set to a relatively high value (lean air-fuel ratio) as shown in FIGS. 4B and 4E. Therefore, the compression ratio is set to a relatively high value. That is, in the period Ta, the operation is performed in the first operation mode shown in FIG. When the required torque sharply increases at time t1, the air-fuel ratio and the compression ratio are changed in a step-like manner. Specifically, during a period Tc where the required torque is relatively large, the air-fuel ratio is set to a relatively low value (theoretical air-fuel ratio), and the compression ratio is set to a relatively low value. That is, in the period Tc, the operation is performed in the second operation mode shown in FIG.
[0037]
The reason why the air-fuel ratio is changed stepwise as shown in FIG. 4B is to suppress the emission of nitrogen oxides (NOx). That is, the emission amount of NOx becomes maximum when the air-fuel ratio is slightly higher than the stoichiometric air-fuel ratio (when the air-fuel ratio is about 16). Therefore, in this embodiment, the air-fuel ratio is changed stepwise from a lean air-fuel ratio (for example, about 22) to a stoichiometric air-fuel ratio (about 14.7). When combustion is performed at a relatively high compression ratio when the air-fuel ratio is set to the stoichiometric air-fuel ratio, knocking occurs. For this reason, in the comparative example, the air-fuel ratio is changed stepwise, and at the same time, the compression ratio is reduced stepwise.
[0038]
When the required torque rapidly increases, the throttle opening also rapidly increases (FIG. 4A). At this time, as shown in FIG. 4C, the amount of intake air also increases rapidly. Then, in order to realize the air-fuel ratio after changing the operation mode (that is, the stoichiometric air-fuel ratio), the fuel supply amount is rapidly increased as shown in FIG. As a result, the output torque sharply increases, as shown in FIG.
[0039]
In the comparative example, since the air-fuel ratio and the compression ratio are simultaneously changed stepwise, it is possible to suppress the occurrence of knocking. However, by changing the air-fuel ratio stepwise, the output torque sharply increases, and as a result, drivability is impaired. In the comparative example, the rapid increase in the output torque due to the rapid decrease (enrichment) of the air-fuel ratio is somewhat alleviated by decreasing the compression ratio stepwise at the same time as the change in the air-fuel ratio. However, the step (change amount) of the output torque is still relatively large.
[0040]
By the way, in the comparative example, the air-fuel ratio and the compression ratio are simultaneously changed stepwise, but such a change is usually difficult. That is, the change timing between the air-fuel ratio and the compression ratio is usually shifted. In this case, it is difficult to maintain normal combustion.
[0041]
Specifically, when the change of the compression ratio is delayed, combustion is performed at a high compression ratio and a stoichiometric air-fuel ratio during the delay period, so that abnormal combustion such as knocking occurs. Although the occurrence of knocking can be suppressed by greatly retarding the ignition timing, the fuel consumption rate is deteriorated. Conversely, when the change of the air-fuel ratio is delayed, combustion is performed at a low compression ratio and a lean air-fuel ratio during the delay period, which causes misfiring and emission deterioration.
[0042]
It is usually difficult to change the compression ratio quickly. If a large-sized actuator is used, the compression ratio can be quickly changed according to a change in operating conditions. However, driving a large actuator requires a large amount of energy, and as a result, the fuel consumption rate deteriorates.
[0043]
Therefore, in the present embodiment, the occurrence of abnormal combustion such as knocking and the sudden increase in output torque are suppressed by devising a procedure for changing the operation mode. Specifically, when the operation mode is changed, the compression ratio is changed after a relatively long period, and the intake air amount is adjusted by devising the operation of the intake valve.
[0044]
In this embodiment, the adjustment of the intake air amount is realized by changing the phase of the intake valve. As can be seen from this description, the variable valve mechanism 25 of the present embodiment employs a variable valve timing system. In this method, the opening / closing timing of the intake valve 21 is changed by changing the phase of the cam.
[0045]
FIG. 5 is a flowchart illustrating a processing procedure when the operation mode is changed in the present embodiment. However, FIG. 5 shows a specific process of step S102 (FIG. 2) when the operation mode is changed, focusing on changes in the air-fuel ratio and the compression ratio. That is, the process in FIG. 5 is executed when an increase in the required torque is detected in step S101 in FIG. 2 and the operation mode is changed in step S102.
[0046]
FIG. 6 is an explanatory diagram schematically showing the control contents when the operation mode is changed in the present embodiment. FIGS. 6A to 6F correspond to FIGS. 4A to 4F, respectively. FIG. 6G shows a change in the phase of the intake valve. FIGS. 6A and 6B are the same as FIGS. 4A and 4B.
[0047]
In step S201 of FIG. 5, first, the air-fuel ratio of the air-fuel mixture is changed stepwise from the lean air-fuel ratio to the stoichiometric air-fuel ratio. This is realized by changing the phase of the intake valve to the retard side in a stepwise manner, as shown in FIG. Specifically, by changing the phase of the intake valve, the intake air amount decreases stepwise (FIG. 6C), and as a result, the air-fuel ratio of the air-fuel mixture is set to the stoichiometric air-fuel ratio. That is, in this embodiment, when the air-fuel ratio is changed, the fuel supply amount is not changed as shown in FIG. When the air-fuel ratio is changed, the compression ratio is not changed as shown in FIG. Therefore, immediately after the change of the air-fuel ratio, combustion is performed at a relatively high compression ratio and a stoichiometric air-fuel ratio. However, at this time, the amount of air-fuel mixture is decreasing with a decrease in the amount of intake air. For this reason, when the air-fuel ratio is changed, occurrence of abnormal combustion such as knocking and a sudden increase in output torque due to a sudden decrease in the air-fuel ratio are suppressed.
[0048]
In step S202 in FIG. 5, as shown in FIG. 6E, the compression ratio is gradually reduced. In step S203, the air-fuel mixture amount is gradually increased. Specifically, by gradually shifting the phase of the intake valve to the advance side (FIG. 6 (g)), the intake air amount is gradually increased (FIG. 6 (c)). Then, the fuel supply amount is gradually increased so that the air-fuel ratio of the air-fuel mixture is maintained at the stoichiometric air-fuel ratio (FIG. 6D). In this way, if the air-fuel ratio of the air-fuel mixture is maintained at the stoichiometric air-fuel ratio and the compression ratio is gradually reduced and the air-fuel mixture amount is gradually increased, abnormal combustion such as knocking during the change period of the compression ratio can be achieved. Generation can be suppressed, and the output torque can be gradually increased (FIG. 6F).
[0049]
In the present embodiment, the processing of steps S202 and S203 is set to end almost simultaneously. Specifically, the process of step S202 is executed such that the compression ratio reaches the target compression ratio after a predetermined period Tb. Further, the process of step S203 is executed such that the phase of the intake valve returns to the phase before the operation mode change after a predetermined period Tb. The predetermined period Tb may be determined based on, for example, a change amount of the required torque per unit time. In other words, it can be determined that the required torque increases relatively quickly as the change amount is relatively large, so that the predetermined period may be set relatively short. Alternatively, the predetermined period Tb may be set to a fixed period regardless of the amount of change in the required torque per unit time.
[0050]
It is preferable that the control of the ignition timing in the period Tb is executed at a timing suitable for the current compression ratio. The current compression ratio in the period Tb is obtained, for example, from the control amount for the actuator 33.
[0051]
FIG. 7 is an explanatory diagram showing a specific operation of the intake valve in each of the periods Ta, Tb, and Tc in FIG. FIG. 7 shows the operation of the exhaust valve 22 together with the operation of the intake valve 21. As can be seen from the change in the lift amount, the exhaust valve 22 is set to the open state during the exhaust stroke, and the intake valve 21 is set to the open state during the intake stroke. The operation of the intake valve during the period Ta is represented by a curve V1a, and the operation of the intake valve during the period Tc is represented by a curve V1c. Note that the curve V1a and the curve V1c are the same. The operation of the intake valve during the period Tb is represented by a curve V1b. Specifically, the phase of the intake valve during the period Tb is first changed stepwise from the curve V1a to the retard side, and then gradually changed to the advance side to reach the curve V1c.
[0052]
As shown in the figure, the operating angles (that is, the periods during which the intake valve is open) in each of the periods Ta, Tb, and Tc are set to be equal. I have. More specifically, in the period Tb, the opening and closing timing of the intake valve is set to be more retarded than the opening and closing timing in the periods Ta and Tc. At this time, the angle difference between the closing timing of the intake valve and the bottom dead center in the period Tb is set to be larger than the angle difference between the closing timing of the intake valve and the bottom dead center in the periods Ta and Tc. That is, by changing the phase of the intake valve as shown in FIG. 7, the actual compression ratio in the period Tb can be set lower than the actual compression ratio in the periods Ta and Tc. Note that the actual compression ratio means a volume ratio based on the closing timing of the intake valve, and the volume Vm of the combustion chamber at the closing timing of the intake valve and the volume Vm of the combustion chamber when the piston is located at the top dead center. It is expressed by Vm / Vt using the minimum volume Vt.
[0053]
By changing the phase of the intake valve as described above, in other words, by changing the actual compression ratio, the throttle opening degrees in the periods Tb and Tc are the same (FIG. 6A). In addition, the intake air amount at the beginning of the period Tb can be set smaller than the intake air amount in the period Ta, and the intake air amount can be gradually increased in the period Tb (FIG. 6C). Further, since the actual compression ratio in the period Tb is set relatively low, the air-fuel mixture in the combustion chamber does not need to be strongly compressed in the compression stroke. This makes it possible to more reliably suppress abnormal combustion such as knocking that may occur in the period Tb.
[0054]
As described above, by employing the configuration of the present embodiment, it is possible to suppress the occurrence of abnormal combustion such as knocking at the beginning of the operation mode change period, and to suppress the rapid increase in output torque. it can. Further, during the operation mode change period after the air-fuel ratio decreases, the occurrence of abnormal combustion such as knocking can be suppressed, and the output torque can be gradually increased.
[0055]
In the present embodiment, the phase of the intake valve in the period Ta and the phase of the intake valve in the period Tc are set to be substantially the same, but may be set to different phases.
[0056]
In the present embodiment, in the period Tb, the actual compression ratio is lowered by shifting the phase of the intake valve 21 to the retard side, but instead, the phase of the intake valve 21 is shifted to the advance side. More specifically, the actual compression ratio may be reduced by setting the closing timing of the intake valve before the bottom dead center.
[0057]
Generally, by changing the closing timing of the intake valve, the actual compression ratio at the beginning of the operation mode change period is set lower than the actual compression ratio before the operation mode change, and the actual compression ratio during the operation mode change period is What is necessary is just to set so that it may increase gradually as the compression ratio decreases.
[0058]
The present invention is not limited to the above-described examples and embodiments, but can be implemented in various modes without departing from the gist of the invention, and for example, the following modifications are possible.
[0059]
(1) In the above embodiment, the change of the compression ratio and the change of the air-fuel mixture (steps S202 and S203 in FIG. 5) during the operation mode change period after the air-fuel ratio is reduced are set to end almost at the same time. However, the end times of the two processes may be shifted. However, according to the above-described embodiment, during the operation mode change period after the air-fuel ratio decreases, the occurrence of abnormal combustion such as knocking can be reliably suppressed, and the output torque can be smoothly increased. There is an advantage.
[0060]
In general, during the operation mode change period after the air-fuel ratio is reduced stepwise, the compression ratio may be gradually reduced, and the intake air amount and the fuel supply amount may be gradually increased.
[0061]
(2) In the above embodiment, the change of the air-fuel ratio at the beginning of the operation mode change period is realized by changing only the intake air amount. Instead, the fuel supply amount is changed together with the intake air amount. You may make it. For example, at the beginning of the operation mode change period, the change amount (decrease amount) of the intake air amount may be set slightly smaller, and the fuel supply amount may be slightly increased. Conversely, at the beginning of the operation mode change period, the amount of change (decrease) in the amount of intake air may be set to be slightly large, and the fuel supply amount may be slightly reduced. Even in this manner, at the beginning of the operation mode change period, the air-fuel ratio can be changed from the lean air-fuel ratio to the stoichiometric air-fuel ratio. However, according to the above-described embodiment, there is an advantage that occurrence of abnormal combustion such as knocking and a sudden increase in output torque can be further suppressed.
[0062]
Further, in the above embodiment, the air-fuel ratio is changed stepwise from the lean air-fuel ratio to the stoichiometric air-fuel ratio at the beginning of the operation mode change period, and thereafter, the stoichiometric air-fuel ratio is maintained. However, instead of this, the air-fuel ratio may be gradually changed during the operation mode change period after the air-fuel ratio is reduced stepwise. For example, at the beginning of the operation mode change period, the air-fuel ratio is changed stepwise from the lean air-fuel ratio to the rich air-fuel ratio, and during the subsequent operation mode change period, the air-fuel ratio is gradually changed from the rich air-fuel ratio to the stoichiometric air-fuel ratio. You may do so.
[0063]
Generally, at the beginning of the operation mode change period, the air-fuel ratio may be reduced stepwise by adjusting at least the intake air amount.
[0064]
(3) In the above embodiment, the compression ratio can be set to one of two predetermined values (FIG. 3), but is set to one of three or more predetermined values. It may be possible. Further, the compression ratio may be set continuously between a predetermined maximum value and minimum value.
[0065]
Further, in the above embodiment, the air-fuel ratio in the second operation mode is set to the stoichiometric air-fuel ratio. Alternatively, for example, the air-fuel ratio may be set to the rich air-fuel ratio.
[0066]
In general, an internal combustion engine has a first operation mode in which operation is performed at a relatively high compression ratio and a relatively high air-fuel ratio, and a second operation mode in which operation is performed at a relatively low compression ratio and a relatively low air-fuel ratio. And the mode.
[0067]
(4) In the above embodiment, the compression ratio is changed by moving the upper block 31 vertically with respect to the lower block 32, but may be changed by another method.
[0068]
In general, the compression ratio changing unit includes a combustion chamber, and by changing the volume of the combustion chamber, more specifically, by changing at least one of the maximum volume and the minimum volume of the combustion chamber, What is necessary is just to change a compression ratio.
[0069]
(5) Although the variable valve mechanism 25 of the above embodiment employs a variable valve timing system capable of changing the phase of the cam, another system may be employed. For example, a variable valve timing and lift system that can change the cam phase and lift amount, a variable valve lift system that can change only the cam lift amount, a variable valve operating angle system that can change only the cam operation angle, etc. Can be adopted.
[0070]
In the above embodiment, the operation of the intake valve is controlled by a variable valve mechanism having a cam. Alternatively, the operation of the intake valve may be controlled by an electromagnetic drive mechanism having a solenoid coil. This has the advantage that the phase, lift amount, operating angle, and the like of the intake valve can be arbitrarily changed.
[0071]
Further, in the above embodiment, the intake air amount is adjusted by changing the operation of the intake valve, but instead or together with the operation of the exhaust valve, the intake air amount is adjusted. May be adjusted.
[0072]
In general, the variable valve train may include a valve, and may adjust the operation of the valve so that the amount of intake air drawn into the combustion chamber can be adjusted.
[0073]
(6) In the above embodiment, the engine is mounted on the vehicle, but may be mounted on a moving body such as a ship. Further, it may be mounted on a stationary device.
[0074]
Generally, the present invention is applicable to an internal combustion engine including a compression ratio changing unit.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram showing a schematic configuration of a gasoline engine 100.
FIG. 2 is a flowchart showing an outline of engine control.
FIG. 3 is an explanatory diagram schematically showing a map indicating a target compression ratio and a target air-fuel ratio according to operating conditions.
FIG. 4 is an explanatory diagram schematically showing control contents when an operation mode is changed in a comparative example.
FIG. 5 is a flowchart illustrating a processing procedure when the operation mode is changed in the embodiment.
FIG. 6 is an explanatory diagram schematically showing control contents when the operation mode is changed in the embodiment.
FIG. 7 is an explanatory diagram showing a specific operation of the intake valve in each of the periods Ta, Tb, and Tc in FIG. 6;
[Explanation of symbols]
Reference Signs List 10 engine body 20 cylinder head 21 intake valve 22 exhaust valve 23 intake port 24 exhaust port 25 variable valve mechanism 26 valve actuation mechanism 27 spark plug 30 cylinder block 31 upper block 32 lower part Block 33 Actuator 41 Piston 42 Connecting rod 43 Crankshaft 50 Intake pipe 51 Air cleaner 52 Throttle valve 53 Electric actuator 55 Fuel injection valve 56 Intake pressure sensor 58 Exhaust pipe 60 ECU
61 ... Crank angle sensor 62 ... Accelerator opening sensor 100 ... Engine

Claims (3)

An internal combustion engine,
Including a combustion chamber, a compression ratio changing unit for changing the compression ratio by changing the volume of the combustion chamber,
A variable valve train that includes a valve and that can adjust the amount of intake air drawn into the combustion chamber by adjusting the operation of the valve;
A fuel supply unit for supplying fuel to the combustion chamber,
A control unit for detecting operating conditions of the internal combustion engine, and controlling the compression ratio changing unit, the variable valve system, and the fuel supply unit according to the detection result,
With
The internal combustion engine has a first operation mode in which operation is performed at a relatively high compression ratio and a relatively high air-fuel ratio, and a second operation mode in which operation is performed at a relatively low compression ratio and a relatively low air-fuel ratio. , And
The control unit includes:
When changing from the first operation mode to the second operation mode according to the detection result,
(I) controlling at least the variable valve system so as to adjust the operation of the valve so that the intake air amount at the beginning of the operation mode change period is smaller than the intake air amount before the operation mode change period; At the beginning of the operation mode change period, the air-fuel ratio is reduced stepwise,
(Ii) During the operation mode change period after the air-fuel ratio decreases, the compression ratio changing unit is controlled to gradually reduce the compression ratio. At this time, the variable valve system is controlled to gradually increase the intake air amount. An internal combustion engine wherein the operation of the valve is adjusted so as to increase, and the fuel supply unit is controlled to gradually increase the fuel supply amount. The internal combustion engine according to claim 1,
The relatively high air-fuel ratio is set larger than the stoichiometric air-fuel ratio,
The internal combustion engine, wherein the relatively low air-fuel ratio is set substantially equal to a stoichiometric air-fuel ratio. The internal combustion engine according to claim 1,
The valve is an intake valve;
The control unit can change the actual compression ratio by changing the closing timing of the intake valve,
The actual compression ratio at the beginning of the operation mode change period is set lower than the actual compression ratio before the operation mode change,
The internal combustion engine, wherein the actual compression ratio during the operation mode change period is set to gradually increase as the compression ratio decreases.

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