JP2004278334A - Change control of compression ratio in internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technology for restraining the occurrence of self-ignition caused by residual gas in a combustion chamber in an internal combustion engine capable of changing the compression ratio. <P>SOLUTION: This internal combustion engine has a compression ratio changing part for changing the compression ratio by changing the volume of the combustion chamber, and a control part for controlling the compression ratio changing part according to an operation condition of the internal combustion engine. The internal combustion engine has a first operation mode of performing operation in the substantially stoichiometric air-fuel ratio, and a second operation mode of performing the operation in the air-fuel ratio higher than the stoichiometric air-fuel ratio, and can perform the operation in both two operation modes in a specific operation area relatively low in a load of the internal combustion engine. The control part sets the compression ratio to a relatively low value when the load and an engine speed of the internal combustion engine are relatively large in the second operation mode. <P>COPYRIGHT: (C)2005,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. The compression ratio is usually changed according to 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 combustion is performed at a lean air-fuel ratio, knocking is unlikely to occur because the combustion speed is low and the gas temperature during compression in the combustion chamber is low. Therefore, when performing combustion at a lean air-fuel ratio, a high compression ratio can be set.
[0004]
[Patent Document 1]
JP-A-63-159624
[Patent Document 2]
Japanese Utility Model Application Laid-Open No. 61-192541
[Patent Document 3]
JP-A-63-138443
[Patent Document 4]
Japanese Utility Model Publication No. 62-72450
[Patent Document 5]
JP-B-58-7816
[0005]
[Problems to be solved by the invention]
However, depending on the operating conditions, there is a problem that the gas temperature during compression in the combustion chamber becomes high due to the gas remaining in the combustion chamber. At this time, the end gas (unburned air-fuel mixture during combustion) rises to the self-ignition temperature and spontaneously ignites. As a result, abnormal combustion such as knocking occurs.
[0006]
The present invention has been made to solve the above-described problem in the related art, and is a technique capable of suppressing the occurrence of spontaneous ignition caused by residual gas in a combustion chamber in an internal combustion engine capable of changing a compression ratio. The purpose is to provide.
[0007]
[Means for Solving the Problems and Their Functions and Effects]
In order to solve at least a part of the above problems, a first device of 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 control unit for detecting operating conditions of the internal combustion engine, and controlling the compression ratio changing unit according to the detection result;
With
The internal combustion engine has a first operation mode in which operation is performed at substantially the stoichiometric air-fuel ratio, and a second operation mode in which operation is performed at an air-fuel ratio higher than the stoichiometric air-fuel ratio. In a specific operation region where the load of the engine is relatively low, the operation can be performed in both of the two operation modes,
The control unit includes:
In the second operation mode, the compression ratio is set to a relatively high value when the load and the rotation speed of the internal combustion engine are relatively small, and when the load and the rotation speed of the internal combustion engine are relatively large, The compression ratio is set to a relatively low value.
[0008]
In this device, in the second operation mode, the operation is performed at an air-fuel ratio higher than the stoichiometric air-fuel ratio, so that the gas temperature during compression in the combustion chamber can be reduced. However, if the amount of residual gas in the combustion chamber increases with an increase in the load and the number of revolutions of the internal combustion engine, the gas temperature during compression in the combustion chamber increases, and self-ignition may occur. However, in this device, when the load and the rotation speed of the internal combustion engine are relatively large, the compression ratio is set to a relatively low value, so that it is possible to suppress the occurrence of spontaneous ignition caused by the residual gas. Become.
[0009]
In the above device,
The control unit includes:
In the specific operation range, when it is determined that the gas temperature at the time of compression in the combustion chamber is relatively low based on a predetermined detection result other than the operation conditions of the internal combustion engine, the first operation mode is set. If it is determined that the gas temperature during compression is relatively high, the second operation mode may be selected.
[0010]
In this way, when it is determined that the gas temperature at the time of compression in the combustion chamber is relatively high, the operation is performed at an air-fuel ratio higher than the stoichiometric air-fuel ratio. It can be more suppressed.
[0011]
In the above device,
It is preferable that the control unit selects an operation mode based on a detection result of a temperature of cooling water for cooling the combustion chamber.
[0012]
This makes it possible to relatively easily determine the gas temperature at the time of compression in the combustion chamber.
[0013]
In the above device,
The control unit includes:
In the second operation mode, the air-fuel ratio is set to a relatively low value when the load and the rotation speed of the internal combustion engine are relatively small, and when the load and the rotation speed of the internal combustion engine are relatively large, Preferably, the air-fuel ratio is set to a relatively high value.
[0014]
As described above, when the load and rotation speed of the internal combustion engine are relatively large, setting the air-fuel ratio to a relatively high value can further reduce the gas temperature during compression in the combustion chamber. The operation range that can be set to a relatively high value can be expanded, and as a result, the fuel consumption rate can be improved.
[0015]
A second device of 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 control unit for detecting operating conditions of the internal combustion engine, and controlling the compression ratio changing unit according to the detection result;
With
The internal combustion engine has a first operation mode in which operation is performed substantially at a stoichiometric air-fuel ratio, and a second operation mode in which operation is performed at an air-fuel ratio higher than the stoichiometric air-fuel ratio,
The control unit includes:
In the second operation mode, when the load and the rotation speed of the internal combustion engine are relatively small, the compression ratio is set to a relatively high value, and the air-fuel ratio is set to a relatively low value. When the load and the rotational speed are relatively large, the compression ratio is set to a relatively low value and the air-fuel ratio is set to a relatively high value.
[0016]
In this device, in the second operation mode, when the load and the rotation speed of the internal combustion engine are relatively large, the compression ratio is set to a relatively low value, so that the occurrence of spontaneous ignition caused by the residual gas is suppressed. be able to. Further, in the second operation mode, when the load and the rotation speed of the internal combustion engine are relatively large, the air-fuel ratio is set to a relatively high value, so that the gas temperature during compression in the combustion chamber can be further reduced. it can. As a result, the operation range in which the compression ratio can be set to a relatively high value can be set relatively large, and as a result, the fuel consumption rate can be improved.
[0017]
A third device of 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 control unit for controlling the compression ratio changing unit,
With
The control unit includes:
An estimator for estimating the residual gas amount in the combustion chamber,
The control unit includes:
When the residual gas amount is estimated to be relatively small, the compression ratio is set to a relatively high value, and when the residual gas amount is estimated to be relatively large, the compression ratio is set to a relatively low value. Is set.
[0018]
With this device, if the amount of residual gas in the combustion chamber is estimated to be relatively large, the compression ratio is set to a relatively low value, so that the occurrence of spontaneous ignition caused by the residual gas is reliably suppressed. Becomes possible.
[0019]
In the above device,
The estimating unit,
A detection unit for detecting a physical quantity related to the residual gas amount in the combustion chamber,
It is preferable that the estimation unit estimates the residual gas amount based on a detection result of the detection unit.
[0020]
This makes it possible to estimate the residual gas amount relatively accurately.
[0021]
Further, in the above device,
The internal combustion engine has a first operation mode in which operation is performed substantially at a stoichiometric air-fuel ratio, and a second operation mode in which operation is performed at an air-fuel ratio higher than the stoichiometric air-fuel ratio,
The control unit may set the compression ratio based on the residual gas amount in the second operation mode.
[0022]
A fourth device of 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 control unit for controlling the compression ratio changing unit,
With
The control unit includes:
An estimator for estimating a gas temperature during compression in the combustion chamber in which residual gas in the combustion chamber is considered,
The control unit includes:
If the gas temperature during the compression is estimated to be relatively low, the compression ratio is set to a relatively high value.If the gas temperature during the compression is estimated to be relatively high, the compression ratio is set to It is characterized in that it is set to a relatively low value.
[0023]
In this device, when the gas temperature during compression in the combustion chamber is estimated to be relatively high, the compression ratio is set to a relatively low value, so that the occurrence of spontaneous ignition caused by residual gas is reliably suppressed. It is possible to do.
[0024]
In the above device,
The estimating unit,
A first detector for detecting a physical quantity related to the residual gas in the combustion chamber;
A second detection unit for detecting a physical quantity related to air taken into the combustion chamber;
With
It is preferable that the estimating unit estimates the gas temperature at the time of the compression based on the detection results of the two detecting units.
[0025]
The gas temperature during compression in the combustion chamber depends on the residual gas in the combustion chamber and the air taken into the combustion chamber. For this reason, according to the above, the gas temperature at the time of compression in the combustion chamber can be estimated relatively accurately.
[0026]
In the above device,
The internal combustion engine has a first operation mode in which operation is performed substantially at a stoichiometric air-fuel ratio, and a second operation mode in which operation is performed at an air-fuel ratio higher than the stoichiometric air-fuel ratio,
The control unit may execute setting of a compression ratio based on a gas temperature during the compression in the second operation mode.
[0027]
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.
[0028]
BEST MODE FOR CARRYING OUT THE INVENTION
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 illustrating a schematic configuration of a gasoline engine 100 according to the first embodiment. The engine of this embodiment is mounted on a vehicle.
[0029]
The engine 100 includes an engine body 10, and the engine body 10 includes a cylinder head 20 and a cylinder block 30.
[0030]
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.
[0031]
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.
[0032]
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.
[0033]
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.
[0034]
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 includes 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 a water temperature sensor provided on the engine body 10. 70 are connected. Then, the ECU 60 controls the actuator 33, the fuel injection valve 55, the spark plug 27 and the like based on these detection results.
[0035]
Note that the engine body 10 in the present embodiment corresponds to a compression ratio changing unit in the present invention. Further, the ECU 60, the crank angle sensor 61, the accelerator opening sensor 62, the intake pressure sensor 56, and the water temperature sensor 70 correspond to a control unit in the present invention.
[0036]
A-2. Control of engine in comparative example:
FIG. 2 is a flowchart illustrating an outline of control of the engine in the comparative example. Note that the ECU 60 repeatedly executes the processing of steps S101 and S102.
[0037]
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.
[0038]
In step S102, various controls are executed based on the operating conditions detected in step S101.
[0039]
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.
[0040]
In step S102b, control of fuel injection is executed. Specifically, the ECU 60 first determines a target air-fuel ratio based on the detected operating conditions (engine speed and required torque).
[0041]
In the comparative example, 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 of a target compression ratio and a target air-fuel ratio used in the comparative example. In the comparative example, as shown in FIG. 3A, the target compression ratio is set to a relatively high value when the required torque is relatively low. Conversely, under conditions where the required torque is relatively high, the target compression ratio is set to a relatively low value. Further, in the comparative example, as shown in FIG. 3B, the air-fuel ratio of the air-fuel mixture is set to substantially the stoichiometric air-fuel ratio regardless of the operating conditions (required torque and engine speed).
[0042]
By using the map of FIG. 3A, it is possible to execute the operation at a 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. Therefore, in the map of FIG. 3A, when the engine load is high, the target compression ratio is set low.
[0043]
When the target air-fuel ratio (substantially the stoichiometric air-fuel ratio) is determined, the ECU 60 determines the amount of air taken into the combustion chamber, and determines the fuel supply amount based on the amount of intake air and the target air-fuel ratio. Note that the intake air amount is obtained based on the detection result of the intake pressure sensor 56. Usually, 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.
[0044]
In step S102c, ignition timing control is performed. Specifically, the ECU 60 determines the ignition timing using a map stored in the ROM and indicating the target ignition timing according to the operating conditions. The ignition by the ignition plug 27 is executed at an appropriate timing based on the detection result from the crank angle sensor 61.
[0045]
A-3. Control of Engine in First Embodiment:
By the way, in the comparative example (FIG. 3), when the compression ratio is high and the engine speed is high, there is a possibility that spontaneous ignition may occur due to residual gas in the combustion chamber. That is, when the compression ratio is high, the gas temperature during compression in the combustion chamber (hereinafter, also referred to as “in-cylinder gas temperature”) increases. In addition, when the engine speed is high, it is difficult to efficiently discharge the burned gas in the exhaust stroke, and the exhaust gas tends to remain in the combustion chamber. At this time, the residual gas in the combustion chamber raises the in-cylinder gas temperature, and as a result, the end gas (unburned air-fuel mixture during combustion) ignites spontaneously. Here, the in-cylinder gas temperature means, for example, a temperature (compression end temperature) when the gas in the combustion chamber is most compressed in the combustion chamber, and a temperature of the gas in the combustion chamber when the intake valve is closed.
[0046]
In the comparative example, the air-fuel ratio of the air-fuel mixture is set to substantially the stoichiometric air-fuel ratio. Instead, when the air-fuel ratio of the air-fuel mixture is set to the lean air-fuel ratio, the above problem is reduced. That is, when combustion is performed at a lean air-fuel ratio, spontaneous ignition is relatively unlikely to occur because the combustion speed is relatively low and the in-cylinder gas temperature is relatively low. However, even when combustion is performed with a lean air-fuel mixture, if the compression ratio is set to a high value and the required torque and the engine speed are large, residual gas will increase, and self-ignition may occur.
[0047]
Therefore, in the present embodiment, a device is devised so that the occurrence of spontaneous ignition caused by the residual gas can be suppressed. Specifically, in this embodiment, two operation modes are prepared, and one of the two operation modes is selected according to the state of the engine. In the first operation mode, the air-fuel ratio of the air-fuel mixture is set to substantially the stoichiometric air-fuel ratio. In the second operation mode, the air-fuel ratio of the air-fuel mixture is set to a lean air-fuel ratio.
[0048]
FIG. 4 is a flowchart showing an outline of engine control in the first embodiment. FIG. 4 is almost the same as FIG. 2 except that step S101A is changed.
[0049]
In step S101A, the operating conditions (requested torque and engine speed) are detected as described with reference to FIG. In step S101A, one of the two operation modes is selected according to the state of the engine. Specifically, the ECU 60 determines whether the temperature of the engine cooling water is equal to or lower than a predetermined value based on the detection result of the water temperature sensor 70, and selects one of the operation modes. When it is determined that the cooling water temperature is equal to or lower than the predetermined value, the first operation mode is selected, and the operation is performed at substantially the stoichiometric air-fuel ratio. Conversely, when it is determined that the cooling water temperature exceeds the predetermined value, the second operation mode is selected, and the operation is performed with the lean air-fuel ratio.
[0050]
FIG. 5 is an explanatory diagram schematically showing a map of a target compression ratio and a target air-fuel ratio used in the first and second operation modes of the first embodiment. FIGS. 5 (A-1) and 5 (B-1) show maps of the target compression ratio and the target air-fuel ratio used in the first operation mode, respectively. B-2) shows a map of the target compression ratio and the target air-fuel ratio used in the second operation mode, respectively. FIGS. 5A-1 and 5B-1 are the same as FIGS. 3A and 3B.
[0051]
When the cooling water temperature is relatively low and the first operation mode is selected, the process of step S102 is performed using the maps shown in FIGS. 5A-1 and 5B-1.
[0052]
In the first operation mode, the operation is performed substantially at the stoichiometric air-fuel ratio. When the required torque is relatively low, a high compression ratio is set. At this time, when the engine speed increases, exhaust gas remains in the combustion chamber, and as a result, the in-cylinder gas temperature increases. However, the first operation mode is selected when it is determined that the coolant temperature is relatively low, in other words, when it is determined that the in-cylinder gas temperature is relatively low. For this reason, even when the engine speed is high, the occurrence of spontaneous ignition due to the residual gas is suppressed.
[0053]
On the other hand, when the cooling water temperature is relatively high and the second operation mode is selected, the process of step S102 is executed using the maps shown in FIGS. 5 (A-2) and (B-2). You. As shown in the drawing, in the second operation mode, as the required torque and the engine speed increase (that is, as the intake air amount per unit time increases), in other words, the in-cylinder gas temperature Tc increases. The compression ratio is set to a lower value. Further, the air-fuel ratio of the air-fuel mixture is set to a lean air-fuel ratio in the entire operation range, but the value of the air-fuel ratio is changed according to the operating conditions. Specifically, the air-fuel ratio is set to a lower value as the required torque or the engine speed increases.
[0054]
In the second operation mode, the operation is performed at the lean air-fuel ratio, so that the in-cylinder gas temperature can be lowered. Further, when the required torque and the engine speed increase, exhaust gas remains in the combustion chamber, but since the compression ratio is set to a relatively low compression ratio, an increase in the in-cylinder gas temperature is moderated. Thereby, even when the required torque and the engine speed are large, it is possible to suppress the occurrence of spontaneous ignition caused by the residual gas.
[0055]
By the way, as can be seen by comparing FIGS. 5 (A-1) and 5 (A-2), in a part of the operating range, specifically, in the operating range where the required torque is relatively low, the engine 100 has two Operation can be performed in both operation modes. In the present embodiment, as described above, the operation mode is selected based on the detection result of the water temperature sensor 70. Thus, regardless of which operation mode is selected, it is possible to suppress the occurrence of spontaneous ignition caused by the residual gas as described above.
[0056]
In the present embodiment, the coolant temperature is detected in order to estimate the in-cylinder gas temperature. However, instead of this, the temperature of the wall of the combustion chamber or the catalyst provided downstream of the combustion chamber may be used. The temperature of an apparatus (not shown) may be detected. Further, a temperature sensor may be provided in the combustion chamber to directly detect the in-cylinder gas temperature. That is, the selection of the operation mode only needs to be performed in an operation region where the required torque is relatively low, based on a predetermined detection result other than the operating conditions (the required torque and the engine speed). However, if the operation mode is selected based on the detection result of the water temperature sensor 70 as in the present embodiment, the advantage that the in-cylinder gas temperature can be determined relatively easily and relatively accurately. There is.
[0057]
Further, in this embodiment, when the first operation mode is selected, a map divided into a low compression ratio region and a high compression ratio region is used as shown in FIG. However, the high compression ratio region may be divided into a plurality of small regions. For example, the high compression ratio region may be divided into three small regions of a high compression ratio region, a medium compression ratio region, and a low compression ratio region, as in FIG. 5A-2. This has the advantage that in the first operation mode, the occurrence of spontaneous ignition caused by the residual gas can be suppressed more reliably.
[0058]
Further, in the present embodiment, when the second operation mode is selected, as shown in FIG. 5B-2, the air-fuel ratio is changed according to the operation conditions. Alternatively, the air-fuel ratio may be kept constant at a predetermined air-fuel ratio higher than the stoichiometric air-fuel ratio regardless of the operating conditions.
[0059]
Generally, in the second operation mode in which the operation is performed at an air-fuel ratio higher than the stoichiometric air-fuel ratio, when the required torque and the engine speed are relatively large, the compression ratio may be set to a relatively low value. .
[0060]
B. Second embodiment:
FIG. 6 is an explanatory diagram schematically showing a map of a target compression ratio and a target air-fuel ratio used in the second operation mode of the second embodiment. The present embodiment is almost the same as the first embodiment, but uses the maps of FIGS. 6A and 6B instead of the maps of FIGS. 5A-2 and 5B-2. Can be
[0061]
As can be seen by comparing FIG. 6B with FIG. 5B-2, the distribution of the air-fuel ratio is changed in FIG. 6B. In FIG. 6A, the region where the compression ratio is set to a relatively high compression ratio is expanded with the change in the distribution of the air-fuel ratio. In FIG. 6A, for comparison, the boundary line of the high compression ratio region in FIG. 5A-2 is indicated by a broken line.
[0062]
Specifically, in FIG. 5B-2, the air-fuel ratio is set to a lower value as the required torque or the engine speed increases. On the other hand, in FIG. 6B, as in FIG. 5B-2, the air-fuel ratio of the air-fuel mixture is set to a lean air-fuel ratio in the entire region, but as the required torque and the engine speed increase (that is, the engine speed increases). The air-fuel ratio is set to a higher value as the in-cylinder gas temperature Tc increases.
[0063]
If the configuration of this embodiment is adopted, as in the first embodiment, in the second operation mode, the compression ratio is set to a relatively low value when the required torque and the engine speed are relatively large. In addition, the occurrence of spontaneous ignition caused by the residual gas can be suppressed. Further, as shown in FIG. 6B, when the required torque and the engine speed are relatively large, the air-fuel ratio is set to a relatively high value (the air-fuel ratio on the leaner side). Can be relatively low. By making the in-cylinder gas temperature relatively low, the region in which the compression ratio can be set to a relatively high value can be expanded to a relatively large required torque and engine speed. Can be improved.
[0064]
In this embodiment, as in the first embodiment, in the operation region where the required torque is relatively low, the operation can be performed in both the first and second operation modes. The operation may be performed only in the second operation mode. Specifically, the operation may be performed at substantially the stoichiometric air-fuel ratio in the operation region where the required torque is relatively high, and the operation may be performed at the lean air-fuel ratio in the operation region where the required torque is relatively low.
[0065]
Generally, in the second operation mode in which the operation is performed with a lean air-fuel ratio, when the required torque and the engine speed are relatively large, the compression ratio is set to a relatively low value and the air-fuel ratio is set to a relatively high value. Set it to a value.
[0066]
C. Third embodiment:
In the first embodiment, as shown in FIG. 5A-2, the target compression ratio in the second operation mode is changed based on the operating conditions (required torque and engine speed). Is changed based on the amount of exhaust gas remaining in the combustion chamber (residual gas amount). That is, the present embodiment is almost the same as the first embodiment, but another map is used instead of the map of FIG.
[0067]
FIG. 7 is an explanatory diagram showing a schematic configuration of a gasoline engine 100C in the third embodiment. FIG. 7 is substantially the same as FIG. 1, except that a back pressure sensor 72 is added. The back pressure sensor 72 is provided in the exhaust pipe 58 and detects the pressure (back pressure) in the exhaust pipe forming the exhaust passage.
[0068]
The residual gas amount is almost proportional to the back pressure. This is because the higher the back pressure, the more difficult it is to discharge the burned gas in the combustion chamber. In the present embodiment, the ECU 60 estimates the residual gas amount based on the detection result of the back pressure from the back pressure sensor 72. Then, the compression ratio is changed according to the estimated residual gas amount.
[0069]
Note that the back pressure sensor 72 corresponds to a detection unit in the present invention. Further, the ECU 60 and the back pressure sensor 72 correspond to an estimation unit in the present invention.
[0070]
FIG. 8 is an explanatory diagram schematically showing a map of a target compression ratio used in the second operation mode of the third embodiment. As shown, in the present embodiment, when the residual gas amount is relatively small, the compression ratio is set to a relatively high value, and when the residual gas amount is relatively large, the compression ratio is set to a relatively low value. Is set to As described above, if the compression ratio is reduced when the residual gas amount is large, it is possible to reliably suppress the occurrence of spontaneous ignition caused by the residual gas.
[0071]
If the compression ratio map according to the residual gas amount shown in FIG. 8 is converted into a compression ratio map according to the operating conditions, the first and second embodiments (FIG. 5 (A-2), FIG. 6 (A)) It is considered that a map similar to the above can be obtained. However, in this embodiment, since the compression ratio is determined based on the residual gas amount closely related to the occurrence of spontaneous ignition, a relatively high compression ratio can be set as compared with the first and second embodiments. There is an advantage that a special area can be expanded.
[0072]
In the present embodiment, the residual gas amount is estimated based on the detection result of the back pressure sensor 72, but may be estimated based on the detection result of the intake pressure sensor 56 instead. Good. That is, the residual gas amount affects the intake pressure. This is because when the residual gas amount is large, it is difficult for air to be sucked into the combustion chamber. Therefore, the residual gas amount can be estimated based on the detection result of the intake pressure from the intake pressure sensor 56. Generally, a physical quantity related to the amount of residual gas in the combustion chamber may be detected. This makes it possible to estimate the residual gas amount relatively accurately.
[0073]
Further, in this embodiment, as shown in FIG. 8, in a region where the residual gas amount is relatively small, the compression ratio is maintained at a high value, but instead, the compression ratio is gradually increased with the increase in the residual gas amount. May be reduced. However, if the map of FIG. 8 is used, the high compression ratio region can be set large, and there is an advantage that the fuel consumption rate can be improved.
[0074]
Further, in the present embodiment, when the second operation mode is selected, the air-fuel ratio is changed according to the operating conditions, as in the first embodiment (FIG. 5B-2). Alternatively, the air-fuel ratio may be kept constant at a predetermined air-fuel ratio higher than the stoichiometric air-fuel ratio regardless of the operating conditions.
[0075]
In this embodiment, as in the first embodiment, in the operation region where the required torque is relatively low, the operation can be performed in both the first and second operation modes. The operation may be performed in the second operation mode.
[0076]
Further, in the present embodiment, as in the first embodiment, two operation modes are prepared. However, only an operation mode in which operation is always performed at a lean air-fuel ratio may be prepared, or almost always. Only the operation mode in which the operation is performed at the stoichiometric air-fuel ratio may be prepared.
[0077]
Generally, the residual gas amount in the combustion chamber is estimated based on a predetermined detection result, and when the residual gas amount is estimated to be relatively large, the compression ratio may be set to a relatively low value.
[0078]
D. Fourth embodiment:
In the third embodiment, the target compression ratio in the second operation mode is changed according to the residual gas amount, but in the fourth embodiment, the target compression ratio is changed according to the in-cylinder gas temperature. That is, the present embodiment is almost the same as the third embodiment, but uses another map instead of the map of FIG.
[0079]
FIG. 9 is an explanatory diagram illustrating a schematic configuration of a gasoline engine 100D according to the fourth embodiment. FIG. 9 is substantially the same as FIG. 7, except that two temperature sensors 74 and 76 are added. The first temperature sensor 74 is provided in the intake pipe 50 and detects a gas temperature (intake temperature) in the intake pipe forming the intake passage. The second temperature sensor 76 is provided in the exhaust pipe 58 and detects a gas temperature (exhaust temperature) in the exhaust pipe forming the exhaust passage.
[0080]
The in-cylinder gas temperature changes according to the residual gas amount and the intake air amount. The in-cylinder gas temperature changes according to the temperature of the residual gas and the temperature of the intake air. More specifically, the in-cylinder gas temperature changes according to the sum of the product of the residual gas amount and the residual gas temperature and the product of the intake air amount and the intake air temperature. In the present embodiment, the ECU 60 estimates the in-cylinder gas temperature using two sensors 72 and 76 provided in the exhaust pipe 58 and two sensors 56 and 74 provided in the intake pipe 50. Note that, as described above, the residual gas amount can be estimated based on the detection result of the back pressure sensor 72, and the intake air amount can be estimated based on the detection result of the intake pressure sensor 56. The exhaust gas temperature detected by the second temperature sensor 76 is used as the residual gas temperature, and the intake air temperature detected by the first temperature sensor 74 is used as the intake air temperature. The ECU 60 estimates the in-cylinder gas temperature based on the detection results of the four sensors, and changes the compression ratio according to the estimated in-cylinder gas temperature.
[0081]
Note that the two sensors 72 and 76 provided in the exhaust pipe correspond to the first detection unit in the present invention, and the two sensors 56 and 74 provided in the intake pipe correspond to the second detection unit in the present invention. Equivalent to. Further, the ECU 60 and the four sensors 72, 76, 56, 74 correspond to an estimation unit in the present invention.
[0082]
FIG. 10 is an explanatory diagram schematically showing a map of a target compression ratio used in the second operation mode of the fourth embodiment. As shown, in the present embodiment, the target compression ratio is determined according to the in-cylinder gas temperature. Specifically, when the in-cylinder gas temperature is relatively low, the compression ratio is set to a relatively high value, and when the in-cylinder gas temperature is relatively high, the compression ratio is set to a relatively low value. You. As described above, if the compression ratio is reduced when the in-cylinder gas temperature is high, it is possible to more reliably suppress the occurrence of spontaneous ignition caused by the residual gas.
[0083]
If the compression ratio map according to the in-cylinder gas temperature shown in FIG. 10 is converted into a compression ratio map according to the operating conditions, the first and second embodiments (FIG. 5 (A-2), FIG. 6 (A)) It is thought that a map similar to that of ()) can be obtained. However, in the present embodiment, since the compression ratio is determined based on the in-cylinder gas temperature which is closely related to the occurrence of spontaneous ignition, a relatively high compression ratio is set as compared with the first to third embodiments. The advantage is that the possible area can be further extended.
[0084]
In the present embodiment, the in-cylinder gas temperature is estimated using the residual gas amount, the residual gas temperature, the intake air amount, and the intake air temperature. May be used to estimate the in-cylinder gas temperature, or the in-cylinder gas temperature may be estimated using the residual gas temperature and the intake air temperature. Generally, a physical quantity related to the residual gas in the combustion chamber and a physical quantity related to the air drawn into the combustion chamber may be detected. This makes it possible to estimate the in-cylinder gas temperature relatively accurately.
[0085]
Further, in the present embodiment, as shown in FIG. 10, in a region where the in-cylinder gas temperature is relatively low, the compression ratio is maintained at a high value. May be gradually reduced. However, if the map of FIG. 10 is used, the high compression ratio region can be set large, and there is an advantage that the fuel consumption rate can be improved.
[0086]
Further, in the present embodiment, when the second operation mode is selected, the air-fuel ratio is changed according to the operating conditions, as in the first embodiment (FIG. 5B-2). Alternatively, the air-fuel ratio may be kept constant at a predetermined air-fuel ratio higher than the stoichiometric air-fuel ratio regardless of the operating conditions.
[0087]
In this embodiment, as in the first embodiment, in the operation region where the required torque is relatively low, the operation can be performed in both the first and second operation modes. The operation may be performed in the second operation mode.
[0088]
Further, in the present embodiment, as in the first embodiment, two operation modes are prepared. However, only an operation mode in which operation is always performed at a lean air-fuel ratio may be prepared, or almost always. Only the operation mode in which the operation is performed at the stoichiometric air-fuel ratio may be prepared.
[0089]
In general, based on a predetermined detection result, the in-cylinder gas temperature in which the residual gas in the combustion chamber is considered is estimated, and when it is estimated that the in-cylinder gas temperature is relatively high, the compression ratio is relatively low. Set it to a value.
[0090]
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.
[0091]
(1) In the first and second embodiments, the compression ratio can be set to any one of a plurality of predetermined values. However, the compression ratio continuously changes between a predetermined maximum value and a predetermined minimum value. May be settable. In the third and fourth embodiments, the compression ratio can be set continuously between a predetermined maximum value and a predetermined minimum value. However, the compression ratio can be set to any one of a plurality of predetermined values. It may be settable.
[0092]
In the above embodiment, the compression ratio is changed by moving the upper block 31 in the vertical direction with respect to the lower block 32, but may be changed by another method.
[0093]
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.
[0094]
(2) 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.
[0095]
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 illustrating a schematic configuration of a gasoline engine 100 according to a first embodiment.
FIG. 2 is a flowchart illustrating an outline of control of an engine in a comparative example.
FIG. 3 is an explanatory diagram schematically showing a map of a target compression ratio and a target air-fuel ratio used in a comparative example.
FIG. 4 is a flowchart illustrating an outline of engine control in the first embodiment.
FIG. 5 is an explanatory diagram schematically showing a map of a target compression ratio and a target air-fuel ratio used in first and second operation modes of the first embodiment.
FIG. 6 is an explanatory diagram schematically showing a map of a target compression ratio and a target air-fuel ratio used in a second operation mode of the second embodiment.
FIG. 7 is an explanatory diagram illustrating a schematic configuration of a gasoline engine 100C according to a third embodiment.
FIG. 8 is an explanatory diagram schematically showing a map of a target compression ratio used in a second operation mode of the third embodiment.
FIG. 9 is an explanatory diagram illustrating a schematic configuration of a gasoline engine 100D according to a fourth embodiment.
FIG. 10 is an explanatory diagram schematically showing a map of a target compression ratio used in a second operation mode of the fourth embodiment.
[Explanation of symbols]
10 Engine body
20 ... Cylinder head
21 ... intake valve
22 ... Exhaust valve
23 ... intake port
24… 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 ... Fuel injection valve
56 ... intake pressure sensor
58 ... exhaust pipe
60 ... ECU
61 ... Crank angle sensor
62 ... accelerator opening sensor
70 ... Water temperature sensor
72 ... Back pressure sensor
74, 76… Temperature sensor
100,100C, 100D ... Engine

Claims (11)

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 control unit for detecting operating conditions of the internal combustion engine, and controlling the compression ratio changing unit according to the detection result;
With
The internal combustion engine has a first operation mode in which operation is performed at substantially the stoichiometric air-fuel ratio, and a second operation mode in which operation is performed at an air-fuel ratio higher than the stoichiometric air-fuel ratio. In a specific operation region where the load of the engine is relatively low, the operation can be performed in both of the two operation modes,
The control unit includes:
In the second operation mode, the compression ratio is set to a relatively high value when the load and the rotation speed of the internal combustion engine are relatively small, and when the load and the rotation speed of the internal combustion engine are relatively large, An internal combustion engine, wherein the compression ratio is set to a relatively low value. The internal combustion engine according to claim 1,
The control unit includes:
In the specific operation range, when it is determined that the gas temperature at the time of compression in the combustion chamber is relatively low based on a predetermined detection result other than the operation conditions of the internal combustion engine, the first operation mode is set. An internal combustion engine that selects the second operation mode when it is determined that the gas temperature at the time of compression is relatively high. The internal combustion engine according to claim 2,
The control unit performs selection of an operation mode based on a detection result of a temperature of cooling water for cooling the combustion chamber, an internal combustion engine, The internal combustion engine according to any one of claims 1 to 3, wherein
The control unit includes:
In the second operation mode, the air-fuel ratio is set to a relatively low value when the load and the rotation speed of the internal combustion engine are relatively small, and when the load and the rotation speed of the internal combustion engine are relatively large, An internal combustion engine that sets the air-fuel ratio to a relatively high value. 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 control unit for detecting operating conditions of the internal combustion engine, and controlling the compression ratio changing unit according to the detection result;
With
The internal combustion engine has a first operation mode in which operation is performed substantially at a stoichiometric air-fuel ratio, and a second operation mode in which operation is performed at an air-fuel ratio higher than the stoichiometric air-fuel ratio,
The control unit includes:
In the second operation mode, when the load and the rotation speed of the internal combustion engine are relatively small, the compression ratio is set to a relatively high value, and the air-fuel ratio is set to a relatively low value. An internal combustion engine, wherein when the load and the rotational speed are relatively large, the compression ratio is set to a relatively low value and the air-fuel ratio is set to a relatively high value. 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 control unit for controlling the compression ratio changing unit,
With
The control unit includes:
An estimator for estimating the residual gas amount in the combustion chamber,
The control unit includes:
When the residual gas amount is estimated to be relatively small, the compression ratio is set to a relatively high value, and when the residual gas amount is estimated to be relatively large, the compression ratio is set to a relatively low value. An internal combustion engine characterized in that: The internal combustion engine according to claim 6, wherein
The estimating unit,
A detection unit for detecting a physical quantity related to the residual gas amount in the combustion chamber,
The internal combustion engine, wherein the estimation unit estimates the residual gas amount based on a detection result of the detection unit. The internal combustion engine according to claim 6 or 7,
The internal combustion engine has a first operation mode in which operation is performed substantially at a stoichiometric air-fuel ratio, and a second operation mode in which operation is performed at an air-fuel ratio higher than the stoichiometric air-fuel ratio,
The internal combustion engine, wherein the control unit executes the setting of a compression ratio based on the residual gas amount in the second operation mode. 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 control unit for controlling the compression ratio changing unit,
With
The control unit includes:
An estimator for estimating a gas temperature during compression in the combustion chamber in which residual gas in the combustion chamber is considered,
The control unit includes:
If the gas temperature during the compression is estimated to be relatively low, the compression ratio is set to a relatively high value.If the gas temperature during the compression is estimated to be relatively high, the compression ratio is set to An internal combustion engine characterized by being set to a relatively low value. The internal combustion engine according to claim 9,
The estimating unit,
A first detector for detecting a physical quantity related to the residual gas in the combustion chamber;
A second detection unit for detecting a physical quantity related to air taken into the combustion chamber;
With
The internal combustion engine, wherein the estimating unit estimates a gas temperature at the time of the compression based on a detection result of the two detecting units. The internal combustion engine according to claim 9 or 10,
The internal combustion engine has a first operation mode in which operation is performed substantially at a stoichiometric air-fuel ratio, and a second operation mode in which operation is performed at an air-fuel ratio higher than the stoichiometric air-fuel ratio,
The internal combustion engine, wherein the control unit executes a setting of a compression ratio based on a gas temperature during the compression in the second operation mode.

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