JP5516503B2 - Internal combustion engine - Google Patents

Description

  The present invention relates to an internal combustion engine.

  In the combustion chamber of the internal combustion engine, the air-fuel mixture is ignited in a compressed state. It is known that the compression ratio when compressing the air-fuel mixture affects the output torque and the fuel consumption. By increasing the compression ratio, the output torque can be increased or the fuel consumption can be reduced. On the other hand, it is known that if the compression ratio is too high, abnormal combustion such as knocking occurs. In the prior art, an internal combustion engine having a variable compression ratio mechanism capable of changing the compression ratio during an operation period is known. In addition to the compression ratio variable mechanism, there is known an internal combustion engine that includes a variable valve timing mechanism formed so that the opening / closing timing of the intake valve can be changed.

  Japanese Patent Laid-Open No. 2007-231824 discloses that in an internal combustion engine having a variable compression ratio mechanism, in a steady operation state, the target ignition timing is operated toward an optimal ignition timing that is advanced from the basic target ignition timing, and target compression is performed. A control device for an internal combustion engine is disclosed in which the ratio is operated to a higher compression ratio side than the basic target compression ratio. In this control device for an internal combustion engine, when knocking is detected during operation with the target compression ratio higher than the basic target compression ratio, the operation amount immediately before the occurrence of knocking is stored as a learned value, and the basic target for the next and subsequent times is stored. It is disclosed that it is reflected in the setting of the ignition timing and the basic target compression ratio.

  In JP-A-5-215004, an internal combustion engine having an exhaust gas recirculation passage from an engine exhaust system to an engine intake system and an EGR control valve whose opening degree is controlled is based on a signal from an in-cylinder pressure sensor. A combustion control device for an internal combustion engine that detects the maximum in-cylinder pressure timing, calculates a difference from a target value, increases or decreases the EGR rate correction amount of the external EGR, and corrects the EGR rate accordingly is disclosed. .

  Japanese Patent Laying-Open No. 2003-184588 discloses an internal combustion engine in which an intake valve is driven to open and close by a three-dimensional intake cam having a cam profile that changes in the axial direction. This publication discloses that internal exhaust gas recirculation is executed by steplessly adjusting the advance amount of the opening / closing timing of the intake valve based on the profile of the three-dimensional intake cam. In this publication, it is determined whether or not the internal EGR rate matches the target EGR rate obtained from the current engine operating state. If the internal EGR rate is smaller than the target internal EGR rate, the intake cam slides. Changing the amount is disclosed.

JP 2007-231824 A JP-A-5-215004 JP 2003-184588 A

  Even if the internal combustion engine continues to be used even when abnormal combustion such as knocking does not occur in one operating state at a predetermined time, the secular change occurs. As a result, even in the same operating state, abnormal combustion may occur if the use is continued. In an internal combustion engine equipped with a variable compression ratio mechanism, if abnormal combustion such as knocking occurs during the change of the operating state, in addition to changing the ignition timing, the occurrence of abnormal combustion is changed by changing the compression ratio. Can be suppressed. For example, the occurrence of abnormal combustion can be suppressed by reducing the target compression ratio to a compression ratio at which abnormal combustion can be avoided. Further, by performing the update to replace the calculated target compression ratio with the previous target compression ratio, it is possible to suppress the occurrence of abnormal combustion even when the same operation state is subsequently obtained.

However, in an internal combustion engine equipped with a variable compression ratio mechanism, when the target compression ratio is updated, the volume of the combustion chamber changes when the piston reaches top dead center. For example, when the target compression ratio is reduced, the volume of the combustion chamber is increased. The volume of the combustion chamber at the low compression ratio is larger than the volume of the combustion chamber at the high compression ratio. As a result, the combustion temperature when the fuel is burnt is changed, NO _X amount exhausted from the combustion chamber is disadvantageously increased. Thus, there has been a problem that the exhaust properties flowing out of the combustion chamber deteriorate when the target compression ratio is changed.

  An object of the present invention is to suppress deterioration of exhaust properties when changing a target mechanical compression ratio based on an operating state in an internal combustion engine having a variable compression ratio mechanism.

  The internal combustion engine of the present invention includes a compression ratio variable mechanism that can change the mechanical compression ratio, and a storage device that stores a target mechanical compression ratio and a target intake valve closing timing based on the operating state of the internal combustion engine. The gas sealed in the combustion chamber in the current combustion cycle includes residual gas that remains without being discharged in the previous combustion cycle. It is configured to detect the occurrence of abnormal combustion when the air-fuel mixture burns in the combustion chamber and perform learning control to update at least one target value of the target mechanical compression ratio and the target intake fresh air amount. When abnormal combustion occurs in learning control, the target mechanical compression ratio is updated to a smaller value, and the amount of residual gas contraction when the target mechanical compression ratio is reduced is estimated. Update to reduce the amount.

  In the above invention, the internal EGR rate, which is the ratio of the residual gas amount to the total gas amount enclosed in the combustion chamber, is the same as the target mechanical compression ratio before update and the internal EGR rate at the target intake fresh air amount. Thus, it is preferable to determine the amount of decrease in the target intake fresh air amount.

  In the above invention, in the learning control, the occurrence of abnormal combustion is detected at a predetermined interval during the period in which the mechanical compression ratio is increasing, and the increase in the mechanical compression ratio based on the decrease amount of the target intake fresh air amount It is preferable to set the mechanical compression ratio obtained by adding the increased amount to the mechanical compression ratio immediately before the abnormal combustion is detected and calculating the updated target mechanical compression ratio.

  In the above invention, the variable valve mechanism that can change the closing timing of the intake valve is provided, and when abnormal combustion occurs in the learning control, the target intake valve is closed so as to correspond to the decrease amount of the target intake fresh air amount. The valve timing can be changed.

  According to the present invention, in an internal combustion engine provided with a variable compression ratio mechanism, it is possible to suppress the deterioration of exhaust properties when changing the target mechanical compression ratio based on the operating state.

1 is a schematic view of an internal combustion engine in an embodiment. It is a general | schematic disassembled perspective view of the compression ratio variable mechanism in embodiment. In the internal combustion engine of the embodiment, it is a schematic cross-sectional view of a cylinder block and a crankcase portion when the mechanical compression ratio is a high compression ratio. In the internal combustion engine of the embodiment, it is a schematic cross-sectional view of a cylinder block and a crankcase portion when the mechanical compression ratio is a low compression ratio. (A) is the schematic explaining the ratio of the fresh air and residual gas in a combustion chamber, when a mechanical compression ratio is a high compression ratio in a comparative example, (b) is an intake valve of this case It is the schematic explaining valve closing time. (A) is the schematic explaining the ratio of the fresh air and residual gas in a combustion chamber, when a mechanical compression ratio is a low compression ratio in a comparative example, (b) is an intake valve of this case It is the schematic explaining valve closing time. (A) is the schematic explaining the ratio of the fresh air and residual gas in a combustion chamber after performing learning control in an embodiment, and (b) is the valve closing time after performing learning control. FIG. It is a flowchart of learning control in an embodiment.

  The internal combustion engine in the embodiment will be described with reference to FIGS. In the present embodiment, an internal combustion engine disposed in a vehicle will be described as an example.

  FIG. 1 is a schematic view of an internal combustion engine in the present embodiment. The internal combustion engine in the present embodiment is a spark ignition type. The internal combustion engine includes an engine body 1. The engine body 1 includes a cylinder block 2 and a cylinder head 4. A piston 3 is disposed inside the cylinder block 2. The piston 3 reciprocates in the hole of the cylinder block 2.

  In the present embodiment, a space surrounded by the holes of the piston 3 and the cylinder block 2 and the cylinder head 4 when the piston 3 reaches the compression top dead center is referred to as a combustion chamber 5. The combustion chamber 5 is formed for each cylinder. An engine intake passage and an engine exhaust passage are connected to the combustion chamber 5. The engine intake passage is a passage for supplying air or a mixture of fuel and air to the combustion chamber 5. The engine exhaust passage is a passage for discharging exhaust gas generated by the combustion of fuel from the combustion chamber 5.

  An intake port 7 and an exhaust port 9 are formed in the cylinder head 4. The intake valve 6 is disposed at the end of the intake port 7 and is configured to be able to open and close the engine intake passage communicating with the combustion chamber 5. The exhaust valve 8 is disposed at the end of the exhaust port 9 and is configured to be able to open and close the engine exhaust passage communicating with the combustion chamber 5. A spark plug 10 as an ignition device is fixed to the cylinder head 4.

  The internal combustion engine in the present embodiment includes a fuel injection valve 11 for supplying fuel to the combustion chamber 5. The fuel injection valve 11 in the present embodiment is arranged so as to inject fuel into the intake port 7. The fuel injection valve 11 is not limited to this configuration, and may be arranged so that fuel can be supplied to the combustion chamber 5. For example, the fuel injection valve may be arranged to inject fuel directly into the combustion chamber.

  The fuel injection valve 11 is connected to the fuel tank 28 via an electronically controlled fuel pump 29 with variable discharge amount. The fuel stored in the fuel tank 28 is supplied to the fuel injection valve 11 by the fuel pump 29.

  The intake port 7 of each cylinder is connected to a surge tank 14 via a corresponding intake branch pipe 13. The surge tank 14 is connected to an air cleaner (not shown) through the intake duct 15. An air flow meter 16 that detects the amount of intake air is disposed inside the intake duct 15. A throttle valve 18 driven by a step motor 17 is disposed inside the intake duct 15. On the other hand, the exhaust port 9 of each cylinder is connected to a corresponding exhaust branch pipe 19. The exhaust branch pipe 19 is connected to the exhaust treatment device 21. The exhaust treatment device 21 in the present embodiment includes a three-way catalyst 20. The exhaust treatment device 21 is connected to the exhaust pipe 22.

  The internal combustion engine in the present embodiment includes an electronic control unit 31. The electronic control unit 31 in the present embodiment includes a digital computer. The electronic control unit 31 includes a RAM (random access memory) 33, a ROM (read only memory) 34, a CPU (microprocessor) 35, an input port 36 and an output port 37 which are connected to each other via a bidirectional bus 32. .

  The output signal of the air flow meter 16 is input to the input port 36 via the corresponding AD converter 38. A load sensor 41 is connected to the accelerator pedal 40. The load sensor 41 generates an output voltage proportional to the depression amount of the accelerator pedal 40. This output voltage is input to the input port 36 via the corresponding AD converter 38. The required load can be detected from the output of the load sensor 41.

  The crank angle sensor 42 generates an output pulse each time the crankshaft rotates, for example, a predetermined angle, and this output pulse is input to the input port 36. The engine speed can be detected from the output of the crank angle sensor 42. Further, the crank angle can be detected from the output of the crank angle sensor 42. In the engine exhaust passage, a temperature sensor 43 as a temperature detector that detects the temperature of the exhaust treatment device 21 is disposed downstream of the exhaust treatment device 21. The output of the temperature sensor 43 is input to the input port 36 via the corresponding AD converter 38.

  The output port 37 of the electronic control unit 31 is connected to the fuel injection valve 11 and the spark plug 10 via the corresponding drive circuits 39. The electronic control unit 31 in the present embodiment is formed to perform fuel injection control and ignition control. That is, the fuel injection timing and the fuel injection amount are controlled by the electronic control unit 31. Further, the ignition timing of the spark plug 10 is controlled by the electronic control unit 31. The output port 37 is connected to a step motor 17 and a fuel pump 29 that drive the throttle valve 18 via a corresponding drive circuit 39. These devices are controlled by the electronic control unit 31.

  The intake valve 6 is formed to open and close as the intake cam 51 rotates. The exhaust valve 8 is formed to open and close as the exhaust cam 52 rotates. The internal combustion engine in the present embodiment includes a variable valve mechanism. The variable valve mechanism includes a variable valve timing device 53 that changes the opening / closing timing of the intake valve 6. The variable valve timing device 53 in the present embodiment is connected to the rotation shaft of the intake cam 51. The variable valve timing device 53 is controlled by the electronic control unit 31.

  The variable valve timing device according to the present embodiment is configured such that the operating angle from when the valve starts to open until it closes is substantially constant, and the phase at the center of the operating angle can be changed. The variable valve timing device is not limited to this form, and the operating angle may be variably formed. Also, any variable valve timing device that can change the opening / closing timing of the intake valve or the exhaust valve can be adopted.

  The internal combustion engine in the present embodiment includes a variable compression ratio mechanism. The compression ratio of the internal combustion engine is determined depending on the volume of the combustion chamber when the piston reaches the compression top dead center. The variable compression ratio mechanism in the present embodiment is formed to change the compression ratio by changing the volume of the combustion chamber. The actual compression ratio, which is the actual compression ratio in the combustion chamber, is expressed by (actual compression ratio) = (combustion chamber volume + piston stroke volume when the intake valve is closed) / (combustion chamber volume).

  FIG. 2 is an exploded perspective view of the compression ratio variable mechanism of the internal combustion engine in the present embodiment. FIG. 3 is a first schematic cross-sectional view of the combustion chamber portion of the internal combustion engine. FIG. 3 is a schematic diagram when a high compression ratio is obtained by the variable compression ratio mechanism. In the internal combustion engine in the present embodiment, the lower structure including the crankcase and the cylinder block arranged on the upper side of the lower structure move relative to each other. The substructure in the present embodiment supports the cylinder block via a compression ratio variable mechanism. Further, the lower structure in the present embodiment supports the crankshaft.

  2 and 3, a plurality of protrusions 80 are formed below the side walls on both sides of the cylinder block 2. The protrusion 80 is formed with a cam insertion hole 81 having a circular cross section. A plurality of protrusions 82 are formed on the upper wall of the crankcase 79. The protrusion 82 is formed with a cam insertion hole 83 having a circular cross-sectional shape. The protrusion 82 of the crankcase 79 is fitted between the protrusions 80 of the cylinder block 2.

  The compression ratio variable mechanism in the present embodiment includes a pair of camshafts 84 and 85 as support shafts for the cylinder block. A circular cam 88 that is rotatably inserted into each cam insertion hole 83 is fixed to the cam shafts 84 and 85. The circular cam 88 is arranged coaxially with the rotation axis of each camshaft 84, 85. On the other hand, eccentric shafts 87 arranged eccentrically with respect to the rotation axis of the cam shafts 84 and 85 extend on both sides of each circular cam 88. On the eccentric shaft 87, another circular cam 86 is eccentrically attached to be rotatable. These circular cams 86 are arranged on both sides of the circular cam 88. The circular cam 86 is rotatably inserted into the corresponding cam insertion hole 81.

  The compression ratio variable mechanism includes a motor 89. Two worms 91 and 92 having spiral directions opposite to each other are attached to the rotating shaft 90 of the motor 89. Worm wheels 93 and 94 are fixed to the end portions of the camshafts 84 and 85, respectively. The worm wheels 93 and 94 are arranged so as to mesh with the worms 91 and 92. When the motor 89 rotates the rotating shaft 90, the camshafts 84 and 85 can be rotated in directions opposite to each other.

  Referring to FIG. 3, when the circular cams 88 arranged on the respective camshafts 84 and 85 are rotated in opposite directions as indicated by arrows 97, the eccentric shaft 87 faces the upper end of the circular cam 88. Moving. The circular cam 86 rotates in the opposite direction to the circular cam 88 as indicated by an arrow 96 in the cam insertion hole 81.

  FIG. 4 shows a second schematic cross-sectional view of the combustion chamber portion of the internal combustion engine in the present embodiment. FIG. 4 is a schematic diagram when a low compression ratio is achieved by the compression ratio variable mechanism. As shown in FIG. 4, when the eccentric shaft 87 moves to the upper end of the circular cam 88, the central axis of the circular cam 88 moves below the eccentric shaft 87. Referring to FIGS. 3 and 4, the relative position between crankcase 79 and cylinder block 2 is determined by the distance between the central axis of circular cam 86 and the central axis of circular cam 88. The cylinder block 2 moves away from the crankcase 79 as the distance between the central axis of the circular cam 86 and the central axis of the circular cam 88 increases. As the cylinder block 2 moves away from the crankcase 79 as indicated by an arrow 98, the volume of the combustion chamber 5 when the piston 3 reaches the compression top dead center increases.

  In the variable compression ratio mechanism in the present embodiment, the volume of the combustion chamber is variably formed by moving the cylinder block relative to the crankcase. In the present embodiment, a compression ratio determined only from the stroke volume of the piston from the bottom dead center to the top dead center and the volume of the combustion chamber is referred to as a mechanical compression ratio. In FIG. 3, the volume of the combustion chamber 5 is small, and the compression ratio is high when the intake air amount is always constant. This state is a state where the mechanical compression ratio is high. On the other hand, in FIG. 4, the volume of the combustion chamber 5 is large, and the compression ratio is low when the intake air amount is always constant. This state is a state where the mechanical compression ratio is low. Thus, the internal combustion engine in the present embodiment can change the compression ratio during the operation period. For example, the compression ratio can be changed by a variable compression ratio mechanism according to the operating state of the internal combustion engine.

  Referring to FIG. 3, a relative position sensor 95 for detecting a relative position between crankcase 79 and cylinder block 2 is attached to a boundary portion between crankcase 79 and cylinder block 2. The relative position sensor 95 can detect the relative position between the crankcase 79 and the cylinder block 2 to detect the mechanical compression ratio. The output signal of the relative position sensor 95 is input to the electronic control unit.

  The variable compression ratio mechanism according to the present embodiment moves the cylinder block relative to the crankcase by rotating a circular cam having an eccentric rotation shaft, but is not limited to this form. Any compression ratio variable mechanism capable of changing the ratio can be employed.

  Referring to FIG. 1, in the internal combustion engine of the present embodiment, a temperature sensor 55 for detecting the temperature of intake air is arranged inside intake duct 15 of the engine intake passage. In the cylinder block 2, an engine coolant flow path 54 is formed around a hole where the piston 3 is disposed. The engine cooling water channel 54 is formed so as to be able to supply engine cooling water. The engine main body 1 can be cooled by circulating the engine cooling water through the engine cooling water flow path 54. In the present embodiment, a temperature sensor 56 that detects the temperature of the engine cooling water is disposed. Further, in the present embodiment, an in-cylinder temperature sensor (not shown) for detecting the temperature in the combustion chamber 5 is arranged. Outputs of these temperature sensors 55 and 56 and the in-cylinder temperature sensor are input to the electronic control unit 31.

  By the way, the internal combustion engine in the present embodiment is configured to detect an operating state and control the mechanical compression ratio and the intake fresh air amount based on the detected operating state. In the present embodiment, the intake fresh air amount can be adjusted by changing the closing timing of the intake valve. By changing the closing timing of the intake valve, the amount of new air-fuel mixture (new air) flowing into the cylinder through the engine intake passage can be adjusted.

  For example, the engine speed and the required load can be selected as the operating state for determining the mechanical compression ratio and the closing timing of the intake valve. In this case, a map of the target mechanical compression ratio and a map of the target intake valve closing timing as functions of the engine speed and the required load can be created in advance and stored in the electronic control unit. During the normal operation period, the engine speed and the required load are detected, and the target mechanical compression ratio and the target intake valve closing timing are read from the stored map. The internal combustion engine can be controlled with the read target mechanical compression ratio and target intake valve closing timing.

  By the way, in an internal combustion engine, even if abnormal combustion does not occur in one operating state, aging may occur if the use is continued. If aging occurs, abnormal combustion may occur even in the same operating state.

  The control apparatus for an internal combustion engine in the present embodiment obtains a target mechanical compression ratio and a target intake valve closing timing at which abnormal combustion can be avoided when abnormal combustion occurs, and performs learning control for updating these target values. Shaped to do. In the present embodiment, an operating state in which abnormal combustion occurs is detected, and the target mechanical compression ratio and the target intake fresh air amount are updated based on the detected operating state.

  In the cylinder, a space as a combustion chamber remains even when the piston reaches top dead center. Even if the piston reaches top dead center in the exhaust stroke of the combustion cycle, a predetermined amount of exhaust gas remains in the combustion chamber. Alternatively, the exhaust gas of the previous cycle remains depending on the opening / closing timing of the intake valve and the exhaust valve. That is, the exhaust gas generated in the previous combustion cycle remains in the current combustion cycle. In the present embodiment, exhaust gas remaining in the combustion chamber is used as residual gas. The residual gas includes burned gas and unburned mixture.

  Thus, internal exhaust gas recirculation (internal EGR) occurs in the internal combustion engine. The internal EGR rate indicating the ratio of residual gas can be defined as the ratio of the amount of residual gas to the total amount of gas enclosed in the combustion chamber. For example, the internal EGR rate is (internal EGR rate) = (residual gas amount from the previous combustion cycle) / ((new air amount in the current combustion cycle) + (residual gas amount from the previous combustion cycle)). Can be represented.

In learning control, when knocking occurs during a period in which the mechanical compression ratio is increased toward a predetermined target mechanical compression ratio, for example, control for updating the target mechanical compression ratio to a smaller value can be performed. However, reducing the target mechanical compression ratio increases the volume of the combustion chamber. For this reason, the amount of fresh intake air increases when the mechanical compression ratio is lower than when the mechanical compression ratio is high. When fresh air is drawn into the cylinder, the residual gas is cooled, and the residual gas contracts. As a result, the amount of fresh air that is inhaled increases. Therefore, the combustion temperature when the air-fuel mixture is burned in the combustion chamber becomes high, the problem of generation amount of the NO _X is increased occurs.

Thus, when the target mechanical compression ratio is changed, there is a problem that the internal EGR rate changes, the combustion temperature changes, and the exhaust properties change. In particular, when updating small target mechanical compression ratio is _the amount of NO _X is increased higher combustion temperature, there is a problem that the exhaust characteristics worse.

  FIG. 5 is a schematic diagram for explaining the ratio of the residual gas and the closing timing of the intake valve when the mechanical compression ratio is a high compression ratio as a comparative example. FIG. 5A is a schematic diagram illustrating the ratio of fresh air and residual gas at a high compression ratio in the comparative example. FIG. 5B is a schematic diagram illustrating the closing timing of the intake valve. FIG. 5 corresponds to the mechanical compression ratio before the target value is updated and the intake valve closing timing in one operating state.

  With reference to FIG. 5A, the piston 3 is supported by the crankshaft 58. The piston 3 has reached the top dead center of the compression stroke. The gas contained in the combustion chamber includes residual gas (EGR gas) 64 remaining from the previous combustion cycle and new air 63 which is a new air-fuel mixture flowing from the engine intake passage in the intake stroke. At the low compression ratio, since the amount of fresh air 63 that is sucked is small, the contraction amount of the residual gas 64 is small. Referring to FIG. 5B, the intake valve in the present embodiment maintains the intake valve open state as indicated by arrow 101, and at the valve closing timing 65 when the piston exceeds the bottom dead center. Closes when reached.

  FIG. 6 is a schematic diagram for explaining the ratio of residual gas and the closing timing of the intake valve when the mechanical compression ratio of the internal combustion engine as a comparative example is a low compression ratio. FIG. 6A is a schematic diagram for explaining the ratio of fresh air and residual gas at a low compression ratio in the comparative example. FIG. 6B is a schematic diagram for explaining the closing timing of the intake valve. FIG. 6 corresponds to the mechanical compression ratio and the intake valve closing timing in the same operation state after the learning control of the comparative example is performed and the target value is updated.

  With reference to FIGS. 6B and 5B, in the comparative example, even when the mechanical compression ratio becomes a low compression ratio, the intake valve closing timing 65 is the intake air in the case of the high compression ratio. This is the same as the valve closing timing 65 of the valve. Even when the learning control of the comparative example is performed, the closing timing of the intake valve is the same as in the case of the high compression ratio.

Referring to FIGS. 6A and 5A, when the mechanical compression ratio is low, the volume of the combustion chamber is larger than when the mechanical compression ratio is high. The amount of fresh air 63 flowing into the combustion chamber increases. The residual gas 64 is cooled by the fresh air 63 and contracts, and the contracted portion 64a becomes large. The volume of the residual gas 64 is reduced. It can be seen that the shrinkage rate of the residual gas 64 increases by shifting to a state where the mechanical compression ratio is low. For this reason, it turns out that an internal EGR rate becomes low. Thus, when the target mechanical compression ratio is changed, the internal EGR rate changes. In particular, when the internal EGR rate decreases, the amount of NO _x contained in the exhaust gas increases and the exhaust properties deteriorate.

  FIG. 7 shows a schematic diagram after performing learning control in the present embodiment. FIG. 7A is a schematic diagram illustrating the ratio of fresh air and residual gas in the combustion chamber when the learning control in the present embodiment is performed and the target mechanical compression ratio becomes low. FIG. 7B is a schematic diagram for explaining the closing timing of the intake valve when the learning control in the present embodiment is performed and the target mechanical compression ratio becomes low.

  In the present embodiment, when knocking is detected during the learning control period, the target mechanical compression ratio is decreased and updated, and the target intake valve closing timing is retarded and updated. With reference to FIG. 7B, as shown by an arrow 102, the closing timing of the intake valve is retarded from the closing timing 65 to the closing timing 66. By performing this control, the amount of fresh air 63 sucked into the cylinder during the intake stroke can be reduced.

  In the present embodiment, control is performed so that the internal EGR rate is substantially the same as before the update by changing the closing timing of the intake valve to reduce the amount of the fresh air 63. For example, the target intake valve closing timing is updated so that the internal EGR rate in the state shown in FIG. 5A and the internal EGR rate in the state shown in FIG. By this control, it is possible to suppress the deterioration of the exhaust properties after performing the learning control.

  FIG. 8 shows an example of a flowchart of learning control for suppressing knocking in the present embodiment. The learning control in the present embodiment can be performed during a normal operation period. Further, the learning control shown in FIG. 8 can be repeatedly performed at predetermined time intervals, for example.

  In step 111, it is determined whether or not a knocking learning condition for performing learning control is satisfied in the operation of the internal combustion engine. That is, it is determined whether or not the internal combustion engine is in an operating state in which learning control for suppressing knocking can be performed. Examples of the knocking learning condition are that the engine speed is within a predetermined range, the charging efficiency is within a predetermined range, and the temperature of the engine cooling water is equal to or higher than a predetermined temperature. Can do. Furthermore, it can be exemplified that the throttle valve opening is substantially constant within a predetermined range.

  In step 111, if the knocking learning condition is not satisfied, this control is terminated. In step 111, when the knocking learning condition is satisfied, the routine proceeds to step 112.

  In step 112, when the required operating state of the internal combustion engine changes, the target mechanical compression ratio εt and the target intake valve closing timing ξt at that time are read. For example, when the engine speed and the required load of the internal combustion engine change, the target mechanical compression ratio εt and the target intake valve closing timing ξt at this time are read.

  Next, in step 113, the mechanical compression ratio ε and the intake valve closing timing ξ are changed toward the target mechanical compression ratio εt and the target intake valve closing timing ξt.

  Next, at step 114, every time a predetermined time elapses, the actual mechanical compression ratio and the actual closing timing of the intake valve are detected and stored. The actual mechanical compression ratio can be detected by the relative position sensor 95. Further, the actual closing timing of the intake valve can be detected by the driving state of the variable valve timing device 53.

  Next, in step 115, it is determined whether or not knocking has been detected. In the present embodiment, it is possible to determine whether or not knocking has occurred by a knocking sensor 57 attached to the engine body 1. If knocking is not detected in step 115, the process proceeds to step 116.

  In step 116, it is determined whether or not the actual mechanical compression ratio has reached the target mechanical compression ratio εt. Further, it is determined whether or not the closing timing of the intake valve has reached the target intake valve closing timing ξt. If at least one of the mechanical compression ratio and the intake valve closing timing has not reached the target value, the process returns to step 114.

  In step 116, when the actual mechanical compression ratio has reached the target mechanical compression ratio and the intake valve closing timing has reached the target intake valve closing timing, this control is terminated. In this case, it is possible to determine that knocking has not occurred even if the mechanical compression ratio and the closing timing of the intake valve are changed, and that aged deterioration has not occurred in the current learning control range.

If knocking is detected in step 115, the process proceeds to step 117. In step 117, the operating state of the internal combustion engine when knocking is detected is detected. In the present embodiment, when knocking is detected, the intake air temperature (Ta) is detected by the temperature sensor 55 disposed in the engine intake passage. Further, the engine coolant temperature (Tc) is detected by a temperature sensor 56 attached to the engine body 1. Further, the compression end temperature (Tp) of the combustion chamber when the piston reaches the compression top dead center is detected. The compression end temperature (Tp) can be detected by an in-cylinder temperature sensor attached to the combustion chamber. Alternatively, the compression end temperature (Tp) may be estimated based on the operating state. Further, the internal EGR rate (R _EGR ) when knocking occurs is estimated. The internal EGR rate can be estimated by an arbitrary method based on the operating state of the internal combustion engine.

  Further, in step 117, the actual mechanical compression ratio and the actual intake valve closing timing immediately before the occurrence of knocking are read out of the mechanical compression ratio and the intake valve closing timing stored in step 114.

Next, in step 118, the internal EGR rate after the residual gas contracts when the target mechanical compression ratio is reduced is estimated using the operating state variable detected in step 117. The estimated internal EGR rate after the residual gas contracts can be estimated by the following equation (1), for example. In the present embodiment, the variable of the operating state immediately before the occurrence of knocking is used.

Here, the variable S _EGR is the estimated internal EGR rate after the residual gas contracts, and the item (Tp−Ta) is the temperature difference between the compression end temperature and the intake air temperature, and the larger this temperature difference is, the more the variable S _EGR is. The amount of shrinkage of the residual gas increases. Further, the item (Tp−Tc) is a temperature difference between the compression end temperature and the engine cooling water, and the amount of contraction of the residual gas increases as the temperature difference increases. Further, the constant K ₁ and the constant K ₂ is a pre-adapted coefficients.

Next, in step 119, the corrected target mechanical compression ratio and the corrected target intake valve closing timing are calculated. The corrected target mechanical compression ratio can be calculated by the following equation (2), for example. Further, the corrected target intake valve closing timing can be calculated by the following equation (3), for example.

Here, the variable (S _EGR / R _EGR ) is a variable related to the contraction rate of the residual gas. The subscript i indicates when knocking occurs, and the subscript (i-1) indicates immediately before knocking occurs. The subscript (i + 1) indicates a value after correction. In the present embodiment, as will be described later, the target mechanical compression ratio εt is also corrected in consideration of the contraction rate of the residual gas. In the expression (3), a plus sign indicates an advance side, and a minus sign indicates a retard side.

  Next, in step 120, the target mechanical compression ratio and the target intake valve closing timing are updated. The corrected target mechanical compression ratio and the corrected target intake valve closing timing value calculated in step 119 are set to the updated target mechanical compression ratio and the updated target intake valve closing timing. In the present embodiment, the map value of the target mechanical compression ratio stored in the electronic control unit is updated. Further, the target intake valve closing timing map stored in the electronic control unit is updated.

  Even after the learning control in this embodiment is performed, even when the same engine speed and required load as this time are reached, the target mechanical compression ratio and the target intake valve closing timing are updated, so that knocking is suppressed. In addition, the operation can be performed while suppressing the deterioration of the exhaust properties.

  In the learning control of the present embodiment, the target intake fresh air amount is determined so as to be substantially the same as the target mechanical compression ratio before update and the internal EGR rate in the target intake fresh air amount before update. By performing this control, the internal EGR rate can be made substantially the same before and after the update, and deterioration of exhaust properties can be suppressed. The learning control is not limited to this mode, and control for updating the target intake fresh air amount to be smaller can be performed based on the contraction amount of the residual gas when the target mechanical compression ratio is reduced.

  Further, referring to the above equation (2), in the learning control of the present embodiment, immediately before the abnormal combustion is detected by calculating the increase amount of the mechanical compression ratio based on the decrease amount of the target intake fresh air amount. The mechanical compression ratio is calculated by adding the increase amount to the mechanical compression ratio. Control is performed to set the added mechanical compression ratio to the updated target mechanical compression ratio. By retarding the closing timing of the intake valve, the amount of fresh air is reduced. For this reason, the actual compression ratio when actually compressed is lowered. In the present embodiment, control is performed to correct the target mechanical compression ratio to the larger side so as to compensate for the decrease in the actual compression ratio. As a result, for example, the actual compression ratio can be made substantially the same before and after the update of the target mechanical compression ratio. When the amount of fresh intake air decreases, the actual compression ratio decreases and the output decreases. However, in the learning control of the present embodiment, the decrease in the actual compression ratio can be suppressed to suppress the output from decreasing. As described above, in the learning control according to the present embodiment, the target mechanical compression ratio that avoids the occurrence of knocking is further corrected. However, the present invention is not limited to this mode, and this correction may not be performed.

  In the present embodiment, control is performed to reduce the amount of fresh intake air by delaying the closing timing of the intake valve. That is, the target intake valve closing timing is changed so as to correspond to the decrease amount of the target intake fresh air amount. By performing this control, the amount of fresh intake air can be easily reduced. Control for reducing the amount of fresh intake air is not limited to this form, and any control for reducing the amount of fresh intake air can be performed. For example, when control is performed to close the intake valve before the piston reaches bottom dead center, the intake valve closing timing is advanced (accelerated) in order to reduce the amount of fresh intake air. ) To reduce the amount of fresh intake air. Alternatively, the intake fresh air amount may be adjusted by adjusting the opening of the throttle valve.

  In the present embodiment, knocking is exemplified and described as abnormal combustion. However, the present invention is not limited to this form, and the present invention can be applied to abnormal combustion other than a desired combustion state. Examples of abnormal combustion include detonation and pre-ignition in addition to knocking.

  In the present embodiment, the internal combustion engine disposed in the vehicle has been described as an example. However, the present invention is not limited to this embodiment, and the present invention can be applied to any internal combustion engine.

  In the respective drawings described above, the same or corresponding parts are denoted by the same reference numerals. In addition, said embodiment is an illustration and does not limit invention. In the embodiment, the change shown in a claim is included.

2 Cylinder block 3 Piston 5 Combustion chamber 6 Intake valve 21 Exhaust processing device 31 Electronic control unit 40 Accelerator pedal 41 Load sensor 53 Variable valve timing device 54 Engine cooling water flow path 55 Temperature sensor 56 Temperature sensor 57 Knock sensor 63 Fresh air 64 Residual gas (EGR gas)
64a Contraction part 65, 66 Valve closing timing 79 Crankcase 84, 85 Camshaft 86 Circular cam 87 Eccentric shaft 88 Circular cam 89 Motor 95 Relative position sensor

Claims (4)

A variable compression ratio mechanism capable of changing the mechanical compression ratio;
A storage device for storing a target mechanical compression ratio and a target intake valve closing timing based on the operating state of the internal combustion engine,
The gas enclosed in the combustion chamber in this combustion cycle contains residual gas that remains without being discharged in the previous combustion cycle.
It is configured to detect the occurrence of abnormal combustion when the air-fuel mixture burns in the combustion chamber, and to perform learning control to update at least one target value of the target mechanical compression ratio and the target intake fresh air amount,
When abnormal combustion occurs in learning control, the target mechanical compression ratio is updated to a smaller value, and the amount of residual gas contraction when the target mechanical compression ratio is reduced is estimated. An internal combustion engine characterized by performing an update to reduce the amount.   Target intake so that the internal EGR rate, which is the ratio of the amount of residual gas to the total amount of gas sealed in the combustion chamber, becomes the same as the internal EGR rate in the target mechanical compression ratio and the target intake fresh air amount before the update. The internal combustion engine according to claim 1, wherein a decrease amount of the fresh air amount is determined.   In the learning control, the occurrence of abnormal combustion is detected at a predetermined interval during the period when the mechanical compression ratio is increasing, and the increase amount of the mechanical compression ratio is calculated based on the decrease amount of the target intake fresh air amount. 3. The internal combustion engine according to claim 1, wherein a mechanical compression ratio obtained by adding the increase amount to a mechanical compression ratio immediately before the detection of abnormal combustion is set as an updated target mechanical compression ratio. 4. Equipped with a variable valve mechanism that can change the closing timing of the intake valve,
4. The target intake valve closing timing is changed so as to correspond to a decrease amount of the target intake fresh air amount when abnormal combustion occurs in the learning control. 4. The internal combustion engine described.

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