JP2008019873A - Control of internal combustion engine during compression ratio changing period - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide technology capable of suppressing abnormal combustion such as knocking which may occur during a change period from high compression ratio to low compression ratio. <P>SOLUTION: An internal combustion engine is provided with a compression ratio change part for changing compression ratio by changing volume of a combustion chamber, a fuel supply part for supplying fuel into the combustion chamber, and a control part detecting an operation condition of the internal combustion engine and controlling the compression ratio change part and the duel supply part according to the detection results. When the control part controls the compression ratio control part to change compression ratio from a relatively high first condition to a relatively low second condition, the control part controls the fuel supply part to establish air fuel ratio during a predetermined period of time including an initial stage of the change period larger than air fuel ratio under the second condition. Fuel supply quantity under the second condition during the change period is established larger than fuel supply quantity under the first condition. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an internal combustion engine capable of changing a compression ratio.

  In recent years, various internal combustion engines having mechanisms capable of changing the compression ratio have been proposed. If the compression ratio is set high, power can be obtained efficiently, but knocking is likely to occur. For this reason, 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 hardly occurs, so the compression ratio is set high. On the other hand, when the load on 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.

  Incidentally, it is necessary to suppress the occurrence of knocking even in the change period in which the compression ratio of the internal combustion engine is changed. Knocking is likely to occur when the compression ratio is changed from a high compression ratio to a low compression ratio. In Patent Document 1, in order to suppress knocking that may occur during the change period from the high compression ratio to the low compression ratio, the ignition timing and / or the amount of fuel to be supplied are set to values suitable for the high compression ratio during the change period. The technique to hold is disclosed.

Japanese Utility Model Publication No. 3-108833

  However, the conventional technique has a problem that it is sometimes difficult to suppress the occurrence of knocking. This is because it is difficult to quickly change the compression ratio according to changes in operating conditions. That is, when the required load of the internal combustion engine increases rapidly, the amount of air and the amount of fuel supplied to the combustion chamber usually increase rapidly, but the compression ratio is not changed rapidly. At this time, in the combustion chamber, the combustion temperature becomes high, and the end gas (unburned mixture at the time of combustion) is strongly compressed. Then, the end gas rises to the self-ignition temperature and self-ignites, and as a result, knocking occurs.

  The present invention has been made to solve the above-described problems in the prior art, and can further suppress abnormal combustion such as knocking that may occur during a change period from a high compression ratio to a low compression ratio. The purpose is to provide.

In order to solve at least a part of the above problems, a first device of the present invention is an internal combustion engine,
A compression ratio changing unit for changing the compression ratio by changing the volume of the combustion chamber, including a combustion chamber;
A fuel supply unit for supplying fuel into the combustion chamber;
A control unit for detecting an operating condition of the internal combustion engine and controlling the compression ratio changing unit and the fuel supply unit according to a detection result;
With
The controller is
When the compression ratio changing unit is controlled to change the compression ratio from the relatively high first state to the relatively low second state, the fuel supply unit is controlled to include a predetermined period including an initial period of change. Setting the air-fuel ratio in the period to be larger than the air-fuel ratio in the second state;
The fuel supply amount in the change period and the second state is set to be larger than the fuel supply amount in the first state.

  In the first device, the fuel supply amount in the change period and the second state is set to be larger than the fuel supply amount in the first state. However, since the air-fuel ratio in the predetermined period including the initial period of the change period is set to be larger than the air-fuel ratio in the second state, the combustion temperature in the predetermined period can be relatively lowered. As a result, the change period Thus, it is possible to further suppress abnormal combustion such as knocking that may occur.

In the first device,
It is preferable that the air-fuel ratio in the predetermined period is set so as to become gradually smaller as the compression ratio is changed.

  In this way, it is possible to improve the output of the internal combustion engine in the latter period of the predetermined period.

A second device of the present invention is an internal combustion engine,
A compression ratio changing unit for changing the compression ratio by changing the volume of the combustion chamber, including a combustion chamber;
A fuel injection section for injecting fuel into an intake passage through which air introduced into the combustion chamber passes to supply fuel into the combustion chamber;
A control unit for detecting an operating condition of the internal combustion engine and controlling the compression ratio changing unit and the fuel injection unit according to a detection result;
With
The controller is
When the compression ratio changing unit is controlled to change the compression ratio from the relatively high first state to the relatively low second state, the fuel injection unit is controlled to include a predetermined period including an initial period of change. The overlapping period of the fuel injection period in the period and the intake stroke period of the internal combustion engine is set larger than the overlapping period in the second state.

  In the second device, in a predetermined period including the initial period of the change period, more fuel is injected in the intake stroke period than in the second state. For this reason, it is possible to make the temperature of the combustion chamber relatively low by using latent heat when the fuel is vaporized, and as a result, it is possible to further suppress abnormal combustion such as knocking that may occur during the change period. Become.

In the second device,
The fuel injection period in the predetermined period is preferably set so that all fuel is injected within the intake stroke period of the internal combustion engine.

  If it carries out like this, the temperature of a combustion chamber can be made lower and it will become possible to suppress abnormal combustion, such as knocking, more reliably.

In the second device,
The fuel injection period in the second state is preferably set so that fuel is not injected during the intake stroke period of the internal combustion engine and fuel is injected during another stroke period.

  In this case, in the second state, it is not necessary to lower the temperature of the combustion chamber, so that the pressure during combustion can be increased, and as a result, the output of the internal combustion engine can be improved.

In the second device,
It is preferable that the overlapping period in the predetermined period is set so as to become gradually smaller as the compression ratio is changed.

  In this way, it is possible to improve the output of the internal combustion engine in the latter period of the predetermined period.

A third device of the present invention is an internal combustion engine,
A compression ratio changing unit for changing the compression ratio by changing the volume of the combustion chamber, including a combustion chamber;
A fuel injection section for supplying fuel into the combustion chamber, a first injection section for injecting fuel into an intake passage through which air introduced into the combustion chamber passes; and fuel in the combustion chamber A second injection unit for direct injection, and the fuel injection unit,
A control unit for detecting an operating condition of the internal combustion engine and controlling the compression ratio changing unit and the fuel injection unit according to a detection result;
With
The controller is
When the compression ratio changing unit is controlled to change the compression ratio from the relatively high first state to the relatively low second state, the fuel injection unit is controlled to include a predetermined period including an initial period of change. The ratio of the fuel amount by the second injection unit in the period is set to be larger than the ratio in the second state.

  In the third device, in the predetermined period including the initial period of the change period, the ratio of the fuel directly injected into the combustion chamber is larger than that in the second state. For this reason, it is possible to make the temperature of the combustion chamber relatively low by using latent heat when the fuel is vaporized, and as a result, it is possible to further suppress abnormal combustion such as knocking that may occur during the change period. Become.

In the third device,
It is preferable that the ratio in the predetermined period is set so as to become gradually smaller as the compression ratio is changed.

  In this way, it is possible to improve the output of the internal combustion engine in the latter period of the predetermined period.

A fourth device of the present invention is an internal combustion engine,
A compression ratio changing unit for changing the compression ratio by changing the volume of the combustion chamber, including a combustion chamber;
A stratification degree changing unit capable of changing a stratification degree of the air-fuel mixture in the combustion chamber;
A control unit for detecting an operating condition of the internal combustion engine and controlling the compression ratio changing unit and the stratification degree changing unit according to a detection result;
With
The controller is
When the compression ratio changing unit is controlled to change the compression ratio from the relatively high first state to the relatively low second state, the stratification degree changing unit is controlled to include an initial change period. The stratification degree in a predetermined period is set higher than the stratification degree in the second state.

  Here, the stratification degree of the air-fuel mixture is an index indicating the distribution of the fuel concentration in the air-fuel mixture, and the air-fuel mixture having a high stratification degree has a relatively high fuel concentration in a partial region in the combustion chamber. This means an air-fuel mixture with a relatively low fuel concentration in the surrounding area.

  In the fourth device, the stratification degree of the air-fuel mixture in a predetermined period including the initial period of the change period is set higher than the stratification degree of the air-fuel mixture in the second state. For this reason, the flame propagation distance can be shortened to shorten the combustion time, and as a result, it is possible to further suppress abnormal combustion such as knocking that may occur during the change period.

In the fourth device,
The stratification degree changing unit is
You may make it contain the eddy current formation part for generating or increasing a vortex | eddy_current in the said combustion chamber.

In the fourth device,
The stratification degree changing unit is
A fuel injection portion for supplying fuel into the combustion chamber during an intake stroke period of the internal combustion engine;
The fuel injection end timing in the predetermined period may be set to be retarded from the fuel injection end timing in the second state.

Alternatively, in the fourth device,
The stratification degree changing unit is
Including a fuel injection section for directly injecting fuel into the combustion chamber;
The fuel injection period in the predetermined period is set within the compression stroke period of the internal combustion engine, and the fuel injection period in the second state is set within the intake stroke period of the internal combustion engine. Also good.

  In this way, the stratification degree of the air-fuel mixture can be increased in a predetermined period.

In the fourth device,
It is preferable that the stratification degree in the predetermined period is set so as to gradually become lower as the compression ratio is changed.

  In this way, it is possible to improve the output of the internal combustion engine in the latter period of the predetermined period.

In the above first to fourth devices,
The predetermined period is preferably substantially equal to the change period.

  By so doing, it is possible to reliably suppress the occurrence of knocking during the change period.

  The present invention relates to an internal combustion engine, a moving body 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 function of the control device, and a recording medium on which the computer program is recorded. It can be realized in various modes such as a data signal including the computer program and embodied in a carrier wave.

A. First embodiment:
A-1. 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 a gasoline engine 100 in the first embodiment. Note that the engine of this embodiment is mounted on a vehicle.

  The engine 100 includes an engine body 10, and the engine body 10 includes a cylinder head 20 and a cylinder block 30.

  The cylinder block 30 includes an upper block 31 that functions as a cylinder and a lower block 32 that functions 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.

  In addition, an actuator 33 is provided between the upper block 31 and the lower block 32 to move the upper block 31 in the vertical direction 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 is also moved downward. At this time, since the volume of the combustion chamber is reduced, the compression ratio is increased.

  An intake port 23 and an exhaust port 24 are formed in the cylinder head 20. An intake valve 21 is disposed in the intake port 23, and an exhaust valve 22 is disposed in the exhaust port 24. The intake valve 21 and the exhaust valve 22 are driven by valve mechanisms (cam mechanisms) 25 and 26 that operate according to the reciprocating motion of the piston 41, respectively.

  An intake pipe 50 is connected to the intake port 23, and the intake port 23 and the intake pipe 50 form an intake passage. An exhaust pipe 58 is connected to the exhaust port 24, and the exhaust port 24 and the exhaust pipe 58 form an exhaust passage. The intake pipe 50 is provided with a throttle valve 52 and a fuel injection valve 55. Air is supplied from the 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 (port injection). As a result, an air-fuel mixture is generated. After the air-fuel 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.

  The engine 100 also 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 that are connected to each other via a bus. The ECU 60 is connected to 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. The ECU 60 controls the actuator 33, the fuel injection valve 55, the spark plug 27, and the like based on these detection results.

A-2. Engine control:
FIG. 2 is a flowchart showing an outline of engine control. In addition, ECU60 repeatedly performs the process of step S101, S102.

  In step S101, engine operating conditions are detected. Specifically, the ECU 60 detects the engine speed and the accelerator opening as operating conditions. The engine speed is determined based on the detection result of the crank angle sensor 61, and the accelerator opening is determined based on the detection result of the accelerator opening sensor 62.

  In step S102, various controls are executed based on the operating conditions detected in step S101.

  In step S102a, the compression ratio is controlled. Specifically, the ECU 60 first determines a target compression ratio based on the detected operating conditions (engine speed and accelerator opening). Further, the ECU 60 drives the actuator 33 to set the compression ratio of the engine to the determined target compression ratio.

  In this embodiment, the target compression ratio is determined using a map stored in the ROM of the ECU 60. FIG. 3 is an explanatory diagram schematically showing a map showing the target compression ratio according to the operating conditions. As shown in the drawing, the target compression ratio is set to a relatively low value under a condition where the accelerator opening is relatively large (that is, a condition where the engine load is relatively high). On the other hand, the target compression ratio is set to a relatively high value under a condition where the accelerator opening is relatively small (that is, a condition where the engine load is relatively low). Further, the target compression ratio is set to a relatively low value under a condition where the engine speed is relatively low.

  If the map of FIG. 3 is used, it will become possible to perform the operation | movement by a comparatively high compression ratio while suppressing generation | occurrence | production of knocking. That is, knocking is likely to occur when the engine load is high. The occurrence of knocking can be suppressed by lowering the compression ratio. For this reason, in the map of FIG. 3, the target compression ratio is set lower as the engine load becomes higher. Further, knocking is likely to occur even when the engine speed is low. For this reason, in the map of FIG. 3, the target compression ratio is set lower as the rotational speed becomes lower.

  In step S102b (FIG. 2), fuel injection control according to the set compression ratio is executed. Specifically, the ECU 60 obtains the amount of air taken into the combustion chamber and determines the fuel supply amount based on the intake air amount.

  In this embodiment, the intake air amount is obtained based on the detection result of the intake pressure sensor 56. The fuel supply amount is determined so that the air-fuel ratio of the air-fuel mixture becomes a predetermined air-fuel ratio. In this embodiment, the predetermined air-fuel ratio is determined using a map stored in the ROM of the ECU 60. Specifically, a map indicating the target air-fuel ratio corresponding to the operating conditions is stored in the ROM for each compression ratio. Then, the target air-fuel ratio is determined using a map corresponding to the set compression ratio. When the target air-fuel ratio is determined, the fuel supply amount is determined using the intake air amount. In this embodiment, the fuel injection amount per unit time and the fuel injection end timing are determined in advance. 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.

  In step S102c, the ignition timing is controlled according to the set compression ratio. In this embodiment, the ignition timing is determined using a map stored in the ROM of the ECU 60. Specifically, a map indicating the target ignition timing corresponding to the operating conditions is stored in the ROM for each compression ratio. Then, the target ignition timing is determined using a map corresponding to the set compression ratio. The ignition by the spark plug 27 is executed at an appropriate timing based on the detection result from the crank angle sensor 61.

A-3. Control of compression ratio change period:
By the way, when the compression ratio is changed from a relatively high state to a relatively low state, knocking is likely to occur during the change period. This is because the change of the compression ratio is delayed with respect to the change of the operating condition. Specifically, when the user suddenly increases the accelerator opening, the throttle opening is also rapidly increased. At this time, the amount of intake air sucked into the combustion chamber suddenly increases, and accordingly, the amount of fuel supplied to the combustion chamber is also set rapidly large. However, the compression ratio is not changed quickly. At this time, in the combustion chamber, the combustion temperature becomes high, and the end gas (unburned mixture at the time of combustion) is strongly compressed. Then, the end gas rises to the self-ignition temperature and self-ignites, and as a result, knocking occurs.

  If a large actuator is used, the compression ratio can be quickly changed as the operating conditions change. However, in order to drive a large actuator, a large amount of energy is required, and as a result, the fuel consumption rate deteriorates.

  In this embodiment, therefore, the occurrence of knocking during the change period is suppressed by adjusting the air-fuel ratio of the air-fuel mixture in step S102b of FIG.

  In the change period, the ignition timing control in step 102c of FIG. 2 may be executed with a setting suitable for a relatively high compression ratio before the change, for example, or a relatively low compression ratio after the change. It may be executed with a suitable setting. Further, it may be executed with a setting suitable for the current compression ratio being changed. The current compression ratio in the middle of the change is obtained from the control amount for the actuator 33, for example.

  FIG. 4 is an explanatory diagram showing the control content of the compression ratio change period in the first embodiment. FIG. 4A shows the change in the throttle opening, and FIG. 4B shows the change in the compression ratio. FIG. 4C shows a change in the air-fuel ratio of the air-fuel mixture, and FIG. 4D shows a change in the amount of fuel supplied to the combustion chamber.

  As shown in FIG. 4B, in the period Ta, the compression ratio is set to a relatively high value, and in the period Tc, the compression ratio is set to a relatively low value. In the period Tb, the value of the compression ratio is gradually changed. Such a change in the compression ratio is executed, for example, when the accelerator opening is increased and the operating condition is changed from the point Ca to the point Cc in the map of FIG.

  When the accelerator opening is rapidly increased, the throttle opening is also rapidly increased as shown in FIG. At this time, in step S102a of FIG. 2, the target compression ratio is determined to be a relatively small value. However, as shown in FIG. 4B, the compression ratio is changed after a relatively long period Tb. That is, the change in the compression ratio is delayed with respect to the change in the operating condition.

  For this reason, in this embodiment, as shown in FIG. 4C, the air-fuel ratio is changed in the change period Tb. Specifically, the air-fuel ratios in the periods Ta and Tc are set to be approximately equal, but the air-fuel ratio in the period Tb is set to be larger (that is, on the lean side) than the air-fuel ratio in the periods Ta and Tc. . However, the intake air amount in the periods Tb and Tc is larger than the intake air amount in the period Ta. For this reason, as shown in FIG. 4D, the fuel supply amount in the periods Tb and Tc is set larger than the fuel supply amount in the period Ta. Note that the fuel supply amount in the period Tb is set smaller than the fuel supply amount in the period Tc, and as a result, changes in the air-fuel ratio in the periods Tb and Tc in FIG. 4C are realized.

  As described above, if the air-fuel ratio in the period Tb is set larger than the air-fuel ratio in the period Tc (that is, on the lean side), the combustion temperature in the change period can be made relatively low. For this reason, the temperature of the end gas (unburned mixture at the time of combustion) can be made relatively low, and as a result, the occurrence of abnormal combustion such as knocking during the change period can be suppressed.

  FIG. 5 is an explanatory diagram showing the control content of the compression ratio change period in the first modification of the first embodiment. FIG. 5 is almost the same as FIG. 4, but FIG. 5C is changed, and FIG. 5D is changed in accordance with this change.

  Specifically, the air-fuel ratio in the period Tb is set substantially equal to the air-fuel ratio in the period Ta, and the air-fuel ratio in the period Tb is set larger than the air-fuel ratio in the period Tc. Further, the fuel supply amount in the periods Tb and Tc is set larger than the fuel supply amount in the period Ta, and the fuel supply amount in the period Tb is set smaller than the fuel supply amount in the period Tc.

  Also in FIG. 5, as in FIG. 4, the air-fuel ratio in the period Tb is set larger than the air-fuel ratio in the period Tc (that is, on the lean side), so the combustion temperature in the change period is relatively low. As a result, it is possible to suppress the occurrence of abnormal combustion such as knocking during the change period.

  FIG. 6 is an explanatory diagram showing the control content of the compression ratio change period in the second modification of the first embodiment. FIG. 6 is substantially the same as FIG. 5, but FIG. 6C is changed, and FIG. 6D is changed with this change.

  Specifically, as in FIG. 5, the air-fuel ratio in the period Tb is set larger than the air-fuel ratio in the period Tc. However, the air-fuel ratio in the period Tb is set smaller than the air-fuel ratio in the period Ta. Similarly to FIG. 5, the fuel supply amount in the periods Tb and Tc is set larger than the fuel supply amount in the period Ta, and the fuel supply amount in the period Tb is set smaller than the fuel supply amount in the period Tc. Has been.

  Also in FIG. 6, as in FIGS. 4 and 5, the air-fuel ratio in the period Tb is set larger than the air-fuel ratio in the period Tc (that is, on the lean side), so abnormal combustion such as knocking in the change period Can be suppressed.

  FIG. 7 is an explanatory diagram showing the control content of the compression ratio change period in the third modification of the first embodiment. FIG. 7 is almost the same as FIG. 4, but FIG. 7C is changed, and FIG. 7D is changed in accordance with this change.

  Specifically, in FIG. 4C, the air-fuel ratio in the period Tb is kept substantially constant, but in FIG. 7C, it is gradually set smaller as the compression ratio decreases. Further, as shown in FIG. 7 (d), the fuel supply amount is gradually set to increase with a decrease in the compression ratio in the period Tb.

  As described above, when the compression ratio is changed from a relatively high state to a relatively low state, knocking is likely to occur during the change period, but knocking is likely to occur particularly at the beginning of the change period. This is because, in the initial period of the change period, the combustion temperature becomes high even though the compression ratio is relatively high. On the other hand, since the compression ratio is relatively low in the later stage of the change period, knocking is relatively difficult to occur. Therefore, as shown in FIG. 7, if the air-fuel ratio is gradually decreased (that is, to the rich side) in the period Tb, the engine output in the period Tb can be gradually improved. In other words, the occurrence of knocking can be suppressed by setting the air-fuel ratio at the initial stage of the change period to be relatively large, and the engine output can be improved by setting the air-fuel ratio at the latter stage of the change period to be relatively small. Can be made.

  As can be seen from FIGS. 4 to 7, in general, the air-fuel ratio in the change period only needs to be set larger than the air-fuel ratio in the changed state.

  As can be seen from the above description, the engine body 10 corresponds to the compression ratio changing unit in the present invention, and the fuel injection valve 55 corresponds to the fuel supply unit. The ECU 60, the crank angle sensor 61, and the accelerator opening sensor 62 correspond to the control unit in the present invention.

B. Second embodiment:
FIG. 8 is an explanatory diagram showing the control content of the compression ratio change period in the second embodiment. FIGS. 8A to 8C show a change in throttle opening, a change in compression ratio, and a change in fuel injection end timing, respectively. 8A and 8B are the same as FIGS. 4A and 4B. The configuration of the engine is the same as that shown in FIG.

  FIG. 9 is an explanatory diagram showing a fuel injection period in the second embodiment. 9A to 9C show the fuel injection periods in the periods Ta, Tb, and Tc, respectively. In FIG. 9, four strokes are shown, and each stroke is divided into a top dead center (TDC) and a bottom dead center (BDC) of the piston.

  As shown in FIGS. 8C and 9, in the periods Ta and Tc, the fuel injection is performed in the exhaust stroke period preceding the intake stroke. The fuel injection end time is set at the end of the exhaust stroke (that is, when the piston is located at the top dead center). The fuel injected from the fuel injection valve 55 adheres to the inner wall surface of the intake port 23, is vaporized by the heat of the engine body 10 in the exhaust stroke and the intake stroke, and is supplied into the combustion chamber in the intake stroke. On the other hand, in the period Tb, the fuel injection is executed in the intake stroke period. The fuel injection end timing is set to the middle of the intake stroke (that is, when the piston is located between the top dead center and the bottom dead center). The fuel injected from the fuel injection valve 55 is supplied into the combustion chamber together with the intake air.

  As shown in FIG. 9, the fuel injection period in the periods Tb and Tc is set longer than the fuel injection period in the period Ta. This is because the amount of fuel to be supplied to the combustion chamber increases as the accelerator opening increases.

  Thus, if the fuel injection period in the period Tb is set so as to overlap the intake stroke period, the fuel can be vaporized in the combustion chamber. For this reason, the temperature in the combustion chamber can be made relatively low by using latent heat when the fuel is vaporized, and as a result, it is possible to suppress the occurrence of abnormal combustion such as knocking during the change period.

  In FIG. 9, the fuel injection period in the period Tb is set so that all the fuel is injected within the intake stroke period. However, some of the fuel may be injected within an exhaust period preceding the intake stroke. Also in this case, the temperature in the combustion chamber can be lowered by using latent heat accompanying the vaporization of the fuel. However, if the fuel injection period in the period Tb is set as shown in FIG. 9, the temperature of the combustion chamber can be lowered, so that the occurrence of abnormal combustion such as knocking can be more reliably suppressed. There is.

  In FIG. 9, the fuel injection periods in the periods Ta and Tc are set so that fuel is not injected within the intake stroke period, in other words, all fuel is injected within the exhaust stroke period. . However, some fuel may be injected within the intake stroke period. However, if the fuel injection periods in the periods Ta and Tc are set as shown in FIG. 9, it is not necessary to reduce the temperature of the combustion chamber in the periods Ta and Tc, so that the pressure during combustion can be increased, As a result, there is an advantage that the output of the engine can be improved. In FIG. 9, the fuel injection period in the periods Ta and Tc is set to the exhaust stroke period, but may be set to another period, for example, an expansion stroke period preceding the intake stroke.

  In the present embodiment, the overlapping period between the fuel injection period and the intake stroke period in the change period is kept substantially constant. Instead, the overlapping period is gradually reduced as the compression ratio decreases. You may make it do. Specifically, in FIG. 8C, the fuel injection end timing may be gradually shifted to the advance side (top dead center side) as the compression ratio decreases. In this way, as in FIG. 7, it is possible to suppress the occurrence of knocking at the initial stage of the change period in which knocking is relatively likely to occur, and to output the engine in the latter period of the change period in which knocking is relatively difficult to occur. There is an advantage that can be improved.

  In general, the overlap period between the fuel injection period and the intake stroke period in the change period may be set to be longer than the overlap period between the fuel injection period and the intake stroke period in the changed state.

C. Third embodiment:
FIG. 10 is an explanatory diagram showing a schematic configuration of a gasoline engine 100C in the third embodiment. FIG. 10 is substantially the same as FIG. 1 except that a second fuel injection valve 57 is added. The first fuel injection valve 55 injects fuel into the intake port 23 that forms the intake passage (port injection). The second fuel injection valve 57 directly injects fuel into the combustion chamber (in-cylinder injection).

  In the present embodiment, the first fuel injection valve 55 injects fuel, for example, in a period preceding the intake stroke (for example, the exhaust stroke). On the other hand, the second fuel injection valve 57 injects fuel in the intake stroke or the subsequent compression stroke. In the combustion chamber, combustion is performed using the fuel injected from the two fuel injection valves 55 and 57.

  FIG. 11 is an explanatory diagram showing the control content of the compression ratio change period in the third embodiment. 11A to 11C show a change in the throttle opening, a change in the compression ratio, and a change in the ratio of the fuel amount due to the in-cylinder injection, respectively. 11A and 11B are the same as FIGS. 4A and 4B. “0%” shown in FIG. 11C means that all of the fuel supplied into the combustion chamber is injected from the first fuel injection valve 55, and “100%” means that the fuel is injected into the combustion chamber. This means that all of the supplied fuel is injected from the second fuel injection valve 57.

  As shown in FIG. 11 (c), in the periods Ta and Tc, about 20% of the fuel supplied to the combustion chamber is injected from the second fuel injection valve 57. On the other hand, in the period Tb, about 50% of the fuel is injected from the second fuel injection valve 57.

  Thus, if the ratio of the fuel amount by in-cylinder injection is increased in the change period Tb, a relatively large amount of fuel can be vaporized in the combustion chamber. For this reason, it is possible to reduce the temperature in the combustion chamber using latent heat when the fuel is vaporized, and as a result, it is possible to suppress the occurrence of abnormal combustion such as knocking during the change period.

  In FIG. 11, the ratio of the fuel amount by in-cylinder injection in the period Tb is kept substantially constant. Instead, the ratio is gradually set smaller as the compression ratio decreases. May be. By doing so, it is possible to suppress the occurrence of knocking in the early stage of the change period in which knocking is relatively likely to occur, and to improve the engine output in the later stage of the change period in which knocking is relatively difficult to occur. There is an advantage.

  In general, the ratio of the fuel injection amount by the second fuel injection valve in the change period may be set to be larger than the ratio in the state after the change.

D. Fourth embodiment:
FIG. 12 is an explanatory diagram showing a schematic configuration of a gasoline engine 100D in the fourth embodiment. FIG. 12 is substantially the same as FIG. 1, but the fuel injection valve is changed. Specifically, in FIG. 1, a fuel injection valve 55 that injects fuel into the intake port 23 that forms the intake passage is used, but in FIG. 12, a fuel injection valve 57 that directly injects fuel into the combustion chamber. Is used.

  FIG. 13 is an explanatory diagram showing the control content of the compression ratio change period in the fourth embodiment. FIGS. 13A to 13C show the change in the throttle opening, the change in the compression ratio, and the change in the stratification degree of the air-fuel mixture, respectively. FIGS. 13A and 13B are the same as FIGS. 4A and 4B.

  Here, the stratification degree of the air-fuel mixture is an index indicating the distribution of the fuel concentration in the air-fuel mixture. The air-fuel mixture having a high stratification means an air-fuel mixture having a relatively high fuel concentration in the region near the spark plug 27 and a relatively low fuel concentration in the surrounding region in the combustion chamber. On the other hand, an air-fuel mixture with a low stratification means an air-fuel mixture with a substantially uniform fuel concentration in the combustion chamber.

  As shown in FIG. 13C, the stratification degree is set relatively low in the periods Ta and Tc, but the stratification degree is set relatively high in the period Tb.

  Thus, if the stratification degree is increased during the change period, it is possible to suppress the occurrence of abnormal combustion such as knocking during the change period. Specifically, when the degree of stratification is increased, the flame propagation distance is shortened, and as a result, the combustion time is shortened. Further, since the air-fuel ratio of the air-fuel mixture in the vicinity of the spark plug is relatively small (that is, the air-fuel ratio becomes rich), the combustion temperature is lowered. Further, since the air-fuel ratio of the surrounding air-fuel mixture becomes relatively large (that is, the air-fuel ratio becomes lean), the surrounding air-fuel mixture becomes difficult to burn. Due to these phenomena, the end gas (unburned mixture at the time of combustion) does not need to be ignited, and as a result, the occurrence of abnormal combustion such as knocking is suppressed.

  FIG. 14 is an explanatory diagram showing a first example for changing the stratification degree of the air-fuel mixture. In the first example, the stratification degree of the air-fuel mixture is changed by changing the fuel injection period. 14A to 14C show the fuel injection periods in the periods Ta, Tb, and Tc, respectively.

  As shown in the figure, during the periods Ta, Tb, and Tc, fuel is injected during the intake stroke. However, in the periods Ta and Tc, the fuel injection is executed in the first half of the intake stroke. The fuel injection end timing is set to the middle of the intake stroke (that is, when the piston is located between the top dead center and the bottom dead center). On the other hand, the fuel injection in the period Tb is performed in the latter half of the intake stroke. The fuel injection end timing is set to the end of the intake stroke (that is, when the piston is located at the top dead center). That is, the fuel injection end timing in the period Tb is changed to the retard side from the fuel injection end timing in the periods Ta and Tc.

  As shown in FIG. 14, if the fuel injection end timing is retarded in the change period Tb, before the fuel directly injected from the fuel injection valve 57 into the combustion chamber is sufficiently diffused in the combustion chamber, in other words, The air-fuel mixture can be combusted in a state where the degree of stratification of the air-fuel mixture is relatively high.

  FIG. 15 is an explanatory diagram showing a second example for changing the stratification degree of the air-fuel mixture. FIGS. 15A to 15C correspond to FIGS. 14A to 14C, respectively. In the second example, as in the first example, the stratification degree of the air-fuel mixture is changed by changing the fuel injection period.

  As shown in the drawing, the fuel injection in the periods Ta and Tc is executed in the intake stroke period. The fuel injection end timing is set to the end of the intake stroke (that is, when the piston is located at the top dead center). On the other hand, the fuel injection in the period Tb is performed in the compression stroke period. The fuel injection end timing is set in the middle of the compression stroke (that is, when the piston is located between the bottom dead center and the top dead center). That is, also in the second example, the fuel injection end timing in the period Tb is changed to the retard side with respect to the fuel injection end timing in the periods Ta and Tc.

  As shown in FIG. 15, if the fuel injection end timing is retarded in the change period Tb, the air-fuel mixture can be combusted in a state where the degree of stratification of the air-fuel mixture is relatively high, as in FIG. If the second example (FIG. 15) is adopted, there is an advantage that the stratification degree of the air-fuel mixture in the change period can be set higher than that of the first example (FIG. 14).

  In the first and second examples (FIGS. 14 and 15), the stratification degree is increased by changing the fuel injection end timing to the retard side in the change period. In the example, the stratification is increased by generating a vortex in the combustion chamber during the change period. That is, in the third and fourth examples, the control for executing the fuel injection in the presence of the vortex is also included in the control of the fuel injection in step S102b of FIG.

  FIG. 16 is an explanatory diagram showing a third example for changing the stratification degree of the air-fuel mixture. FIG. 16 is drawn with attention paid to the engine body. FIG. 16 is substantially the same as FIG. 12, but the intake port 23 is provided with a flow control valve 71. The opening / closing operation of the flow control valve 71 is controlled by the ECU 60 driving the electric actuator 73.

  More specifically, the flow control valve 71 is provided in a region below the intake port 23 so as to block a partial region of the intake port 23. For this reason, when the flow control valve 71 is set to the closed state, the air is mainly supplied into the combustion chamber through the upper region in the intake port 23.

  In the third example, the flow control valve 71 is set in the open state during the periods Ta and Tc. On the other hand, in the period Tb, the flow control valve 71 is set to a closed state. Thus, when the flow control valve 71 is set to the closed state in the period Tb, a tumble flow is generated in the combustion chamber. Here, the tumble flow is a flow swirling around the direction perpendicular to the cylinder axis in the combustion chamber, as shown in FIG.

  As shown in FIG. 16, if the tumble flow is generated in the change period Tb, the fuel directly injected from the fuel injection valve 57 into the combustion chamber can be unevenly distributed in the vicinity of the spark plug 27. As a result, as a result, A state in which the degree of stratification is relatively high can be formed.

  In FIG. 16, the tumble flow is formed in the combustion chamber, but instead, a reverse tumble flow having a reverse swirl direction may be formed.

  FIG. 17 is an explanatory diagram showing a fourth example for changing the stratification degree of the air-fuel mixture. FIG. 17 schematically shows a state when the combustion chamber is viewed from above with respect to the engine that is substantially the same as FIG. As shown in the figure, the cylinder head is provided with two intake ports 23a and 23b and two exhaust ports 24a and 24b. A flow control valve 81 is provided in the second intake port 23b. Note that the opening / closing operation of the flow control valve 81 is controlled by driving the electric actuator 83 by the ECU 60 as in the third example.

  In the fourth example, as in the third example, the flow control valve 81 is set to the open state during the periods Ta and Tc, and is set to the closed state during the period Tb. Thus, when the flow control valve 81 is set to the closed state in the period Tb, a swirl flow is generated in the combustion chamber. Here, the swirl flow is a flow swirling around the axis of the cylinder in the combustion chamber as shown in FIG.

  As shown in FIG. 17, even if the swirl flow is generated in the change period Tb, the fuel directly injected from the fuel injection valve 57 into the combustion chamber can be unevenly distributed in the vicinity of the spark plug 27, as in FIG. As a result, a state where the degree of stratification of the air-fuel mixture is relatively high can be formed.

  In the third and fourth examples (FIGS. 16 and 17), the flow control valves 71 and 81 are set in the open state during the periods Ta and Tc. A large intermediate opening state may be set. Moreover, although the flow control valves 71 and 81 are set in the closed state in the period Tb, the flow control valves 71 and 81 may be set in an intermediate opening state having a relatively small opening instead. By doing this, it is possible to generate a relatively weak eddy current (that is, a relatively low flow velocity) in the periods Ta and Tc, and to increase the vortex flow in the period Tb to be relatively strong (ie, the flow velocity is relatively large). ) Can generate eddy currents. Even in this case, the stratification degree of the air-fuel mixture in the change period can be increased.

  Further, a vortex flow may always be generated in the combustion chamber by devising the shape of the intake port. Also in this case, if the strength of the vortex is increased during the change period using the flow control valve, the stratification degree of the air-fuel mixture during the change period can be increased.

  Further, in the third and fourth examples, fuel is supplied into the combustion chamber by in-cylinder injection, but fuel may be supplied into the combustion chamber by port injection. Also in this case, the stratification degree of the air-fuel mixture can be increased by generating a vortex.

  In the third and fourth examples, the flow control valve is used to generate the vortex, but instead, the vortex may be generated by controlling the operation of the intake valve. For example, when two intake valves are provided in the combustion chamber, eddy current can be generated by setting one intake valve to an open state and setting the other intake valve to a closed state.

  FIG. 18 is an explanatory diagram showing the control content of the compression ratio change period in the modification of the fourth embodiment. FIG. 18 is substantially the same as FIG. 13, but FIG. 18 (c) is modified.

  Specifically, in FIG. 18, the stratification degree is set to be relatively high in the period Ta where the compression ratio is relatively high, and the stratification degree is set to be relatively low in the period Tc where the compression ratio is relatively low. . In the change period Tb, the degree of stratification is set lower than the period Ta and higher than the period Tc. That is, in FIG. 18, when the compression ratio is relatively high, the degree of stratification is increased and lean combustion is performed.

  Even in this case, since the stratification degree in the period Tb is set to be relatively high, occurrence of abnormal combustion such as knocking can be suppressed.

  In FIGS. 13 and 18, the stratification degree in the period Tb is kept substantially constant, but instead, the stratification degree may be set gradually lower as the compression ratio decreases. . By doing so, it is possible to suppress the occurrence of knocking in the early stage of the change period in which knocking is relatively likely to occur, and to improve the engine output in the later stage of the change period in which knocking is relatively difficult to occur. There is an advantage.

  In general, the stratification degree in the compression ratio change period may be set higher than the stratification degree in the state after the change.

  As can be seen from the above description, the fuel injection valve 57 in the first and second examples (FIGS. 14 and 15) corresponds to the stratification degree changing unit and the fuel injection unit in the present invention. Further, the flow control valves 71 and 81 and the electric actuators 73 and 83 in the third and fourth examples (FIGS. 16 and 17) correspond to the stratification degree changing unit and the vortex forming unit in the present invention.

  The present invention is not limited to the above-described examples and embodiments, and can be implemented in various modes without departing from the gist thereof. For example, the following modifications are possible.

(1) In the above embodiment, the compression ratio can be set to any one of a plurality of predetermined values (four values in FIG. 3). It may be possible to set continuously between the minimum value or only one of the maximum value and the minimum value.

  Moreover, in the said Example, although the compression ratio is changed by moving the upper block 31 to an up-down direction with respect to the lower block 32, you may change by another method.

  Generally, 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.

(2) In the above embodiment, knocking countermeasures are taken in all periods of the compression ratio change period, but instead, only in a part of the period including the initial period of the compression ratio change period, You may make it take a countermeasure against knocking. For example, in FIG. 4, the air-fuel ratio may be set large in the first half period of the period Tb, and the air-fuel ratio may be returned in the second half period. In this way, knocking can be efficiently suppressed at the beginning of the change period in which knocking is relatively likely to occur. However, there is an advantage that abnormal combustion such as knocking can be reliably suppressed if the period during which the countermeasure against knocking is applied and the change period are set to be substantially equal as in the above embodiment.

  In general, when the control unit changes the compression ratio from the relatively high first state to the relatively low second state, it is only necessary that a countermeasure against knocking is taken in a predetermined period including the initial period of the change period. .

(3) In the above embodiment, the engine is mounted on the vehicle, but may be mounted on a moving body such as a ship. Moreover, you may mount in the stationary apparatus.

  In general, the present invention is applicable to an internal combustion engine including a compression ratio changing unit.

It is explanatory drawing which shows schematic structure of the gasoline engine 100 in 1st Example. It is a flowchart which shows the outline | summary of control of an engine. It is explanatory drawing which shows typically the map which shows the target compression ratio according to an operating condition. It is explanatory drawing which shows the control content of the compression ratio change period in 1st Example. It is explanatory drawing which shows the control content of the compression ratio change period in the 1st modification of 1st Example. It is explanatory drawing which shows the control content of the compression ratio change period in the 2nd modification of 1st Example. It is explanatory drawing which shows the control content of the compression ratio change period in the 3rd modification of 1st Example. It is explanatory drawing which shows the control content of the compression ratio change period in 2nd Example. It is explanatory drawing which shows the fuel-injection period in 2nd Example. It is explanatory drawing which shows schematic structure of the gasoline engine 100C in 3rd Example. It is explanatory drawing which shows the control content of the compression ratio change period in 3rd Example. It is explanatory drawing which shows schematic structure of gasoline engine 100D in 4th Example. It is explanatory drawing which shows the control content of the compression ratio change period in 4th Example. It is explanatory drawing which shows the 1st example for changing the stratification degree of air-fuel | gaseous mixture. It is explanatory drawing which shows the 2nd example for changing the stratification degree of air-fuel | gaseous mixture. It is explanatory drawing which shows the 3rd example for changing the stratification degree of air-fuel | gaseous mixture. It is explanatory drawing which shows the 4th example for changing the stratification degree of air-fuel | gaseous mixture. It is explanatory drawing which shows the control content of the compression ratio change period in the modification of 4th Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Engine main body 20 ... Cylinder head 21 ... Intake valve 22 ... Exhaust valve 23 ... Intake port 24 ... Exhaust port 23a, 23b ... Intake port 24a, 24b ... Exhaust port 25, 26 ... Valve mechanism 27 ... Spark plug 30 ... Cylinder Block 31 ... Upper block 32 ... Lower block 33 ... Actuator 41 ... Piston 42 ... Connecting rod 43 ... Crankshaft 50 ... Intake pipe 51 ... Air cleaner 52 ... Throttle valve 53 ... Electric actuator 55, 57 ... Fuel injection valve 56 ... Intake pressure sensor 58 ... exhaust pipe 60 ... ECU
61 ... Crank angle sensor 62 ... Accelerator opening sensor 71, 81 ... Flow control valve 73, 83 ... Electric actuator 100, 100C, D ... Engine

Claims (14)

An internal combustion engine,
A compression ratio changing unit for changing the compression ratio by changing the volume of the combustion chamber, including a combustion chamber;
A fuel supply unit for supplying fuel into the combustion chamber;
A control unit for detecting an operating condition of the internal combustion engine and controlling the compression ratio changing unit and the fuel supply unit according to a detection result;
With
The controller is
When the compression ratio changing unit is controlled to change the compression ratio from the relatively high first state to the relatively low second state, the fuel supply unit is controlled to include a predetermined period including an initial period of change. Setting the air-fuel ratio in the period to be larger than the air-fuel ratio in the second state;
The internal combustion engine, wherein the fuel supply amount in the change period and the second state is set to be larger than the fuel supply amount in the first state. The internal combustion engine according to claim 1,
An internal combustion engine in which the air-fuel ratio in the predetermined period is set so as to gradually decrease as the compression ratio is changed. An internal combustion engine,
A compression ratio changing unit for changing the compression ratio by changing the volume of the combustion chamber, including a combustion chamber;
A fuel injection section for injecting fuel into an intake passage through which air introduced into the combustion chamber passes to supply fuel into the combustion chamber;
A control unit for detecting an operating condition of the internal combustion engine and controlling the compression ratio changing unit and the fuel injection unit according to a detection result;
With
The controller is
When the compression ratio changing unit is controlled to change the compression ratio from the relatively high first state to the relatively low second state, the fuel injection unit is controlled to include a predetermined period including an initial period of change. An internal combustion engine characterized in that an overlap period between a fuel injection period and an intake stroke period of the internal combustion engine is set to be larger than the overlap period in the second state. An internal combustion engine according to claim 3,
The internal combustion engine, wherein the fuel injection period in the predetermined period is set so that all fuel is injected within an intake stroke period of the internal combustion engine. An internal combustion engine according to claim 3,
The internal combustion engine in which the fuel injection period in the second state is set so that fuel is not injected during the intake stroke period of the internal combustion engine and fuel is injected during another stroke period. An internal combustion engine according to claim 3,
The internal combustion engine, wherein the overlap period in the predetermined period is set so as to gradually become smaller as the compression ratio is changed. An internal combustion engine,
A compression ratio changing unit for changing the compression ratio by changing the volume of the combustion chamber, including a combustion chamber;
A fuel injection section for supplying fuel into the combustion chamber, a first injection section for injecting fuel into an intake passage through which air introduced into the combustion chamber passes; and fuel in the combustion chamber A second injection unit for direct injection, and the fuel injection unit,
A control unit for detecting an operating condition of the internal combustion engine and controlling the compression ratio changing unit and the fuel injection unit according to a detection result;
With
The controller is
When the compression ratio changing unit is controlled to change the compression ratio from the relatively high first state to the relatively low second state, the fuel injection unit is controlled to include a predetermined period including an initial period of change. An internal combustion engine characterized in that a ratio of a fuel amount by the second injection unit in a period is set larger than the ratio in the second state. An internal combustion engine according to claim 7,
The internal combustion engine, wherein the ratio in the predetermined period is set so as to gradually decrease as the compression ratio is changed. An internal combustion engine,
A compression ratio changing unit for changing the compression ratio by changing the volume of the combustion chamber, including a combustion chamber;
A stratification degree changing unit capable of changing a stratification degree of the air-fuel mixture in the combustion chamber;
A control unit for detecting an operating condition of the internal combustion engine and controlling the compression ratio changing unit and the stratification degree changing unit according to a detection result;
With
The controller is
When the compression ratio changing unit is controlled to change the compression ratio from the relatively high first state to the relatively low second state, the stratification degree changing unit is controlled to include an initial change period. An internal combustion engine characterized in that the stratification degree in a predetermined period is set higher than the stratification degree in the second state. An internal combustion engine according to claim 9,
The stratification degree changing unit is
An internal combustion engine including a vortex generator for generating or increasing a vortex in the combustion chamber. An internal combustion engine according to claim 9,
The stratification degree changing unit is
A fuel injection portion for supplying fuel into the combustion chamber during an intake stroke period of the internal combustion engine;
The internal combustion engine, wherein the fuel injection end timing in the predetermined period is set to be retarded from the fuel injection end timing in the second state. An internal combustion engine according to claim 9,
The stratification degree changing unit is
Including a fuel injection section for directly injecting fuel into the combustion chamber;
The fuel injection period in the predetermined period is set within the compression stroke period of the internal combustion engine, and the fuel injection period in the second state is set within the intake stroke period of the internal combustion engine. . An internal combustion engine according to claim 9,
The internal combustion engine, wherein the stratification degree in the predetermined period is set so as to gradually become lower as the compression ratio is changed. An internal combustion engine according to any one of claims 1, 3, 7, and 9,
The internal combustion engine, wherein the predetermined period is substantially equal to the change period.

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