JP2012233435A - Internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an internal combustion engine that includes a variable compression ratio mechanism and operates in a stable manner when a compression ratio is changed.SOLUTION: The internal combustion engine includes the variable compression ratio mechanism capable for changing a mechanical compression ratio, and a residual gas remaining in a combustion chamber while not being exhausted in the combustion cycle contains an unburnt gas and a burnt gas. The internal combustion engine estimates a ratio between the unburnt gas and the burnt gas contained in the residual gas upon a transient operation in which the mechanical compression ratio has been changed. The internal combustion engine regulates an amount of new gaseous mixture newly supplied to the combustion chamber in this combustion cycle so that an amount of unburnt gaseous mixture filling the combustion chamber in the combustion cycle is approximately equal to an amount upon a steady operation in which the mechanical compression ratio is substantially constant.

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 Application Laid-Open No. 2005-207273 discloses an internal combustion engine having an exhaust purification catalyst disposed in an exhaust passage and a compression ratio variable mechanism in which the compression ratio is changed by changing the volume of the combustion chamber. . This publication discloses that the fuel injection amount is corrected so that the air-fuel ratio of the air-fuel mixture in the cylinder becomes substantially equal to before and after the change of the compression ratio at the time of transition when the compression ratio is changed. It is disclosed that at the time of transition when the compression ratio is changed to a high compression ratio, correction for reducing the fuel injection amount injected from the fuel injection valve is performed as compared with the case where the compression ratio is constant.

  Japanese Patent Application Laid-Open No. 2009-114966 includes a variable compression ratio mechanism that can change the mechanical compression ratio and a variable valve timing mechanism that can control the closing timing of the intake valve, from a high compression ratio to a low compression ratio. An internal combustion engine that controls the amount of intake air into the combustion chamber by controlling the closing timing of the intake valve during the transition is disclosed.

  In Japanese Patent Application Laid-Open No. 2010-190193, in an internal combustion engine having a variable compression ratio mechanism and a variable valve mechanism, the closing timing for closing the intake valve in a low load range is controlled to be advanced from the bottom dead center. At the time of acceleration when the required load of the engine suddenly increases, the target intake valve closing timing is retarded to the knocking limit on the retarded side. At this time, the intake amount maximum intake valve closing timing at which the intake amount in the cylinder becomes maximum is passed, but during this period, the throttle valve opening is temporarily corrected to avoid transient knocking. It is disclosed.

JP-A-2005-207273 JP 2009-114966 A JP 2010-190193 A

  The compression ratio variable mechanism can change the mechanical compression ratio by including a mechanism for changing the volume of the combustion chamber when the piston reaches the compression top dead center, for example. During the transient operation in which the mechanical compression ratio is changed, the volume of the combustion chamber when the piston reaches top dead center gradually changes. For example, when the mechanical compression ratio is changed to be small, the volume of the combustion chamber when the piston reaches top dead center is increased.

  By the way, in the combustion chamber, when the air-fuel mixture is ignited, for example, a flame spreads around the spark plug. At this time, there is a region where the flame does not reach in the combustion chamber. When the air-fuel mixture burns in the combustion chamber, it remains as unburned gas in some areas without burning. The region where such combustion does not occur is called a quench zone. The size of the quench zone depends on the size of the combustion chamber. For this reason, if the mechanical compression ratio is changed by changing the size of the combustion chamber, the size of the quench zone changes, and as a result, the proportion of unburned gas also changes.

  On the other hand, in the exhaust stroke of the combustion cycle, not all of the gas burned in the expansion stroke is exhausted, and part of the burned gas remains until the next combustion cycle. This residual gas includes the above-mentioned unburned gas in addition to the already burned burned gas.

During the transient operation period in which the mechanical compression ratio is changed, the ratio of the unburned gas contained in the residual gas changes due to the change in the size of the quench zone. For this reason, an unexpectedly large torque may be output, or an unexpected amount of NO _X may be discharged. Further, when the output torque changes for a short time, there is a possibility that a torque shock, which is an impact caused by torque fluctuation, may occur.

  An object of the present invention is to provide an internal combustion engine that includes a variable compression ratio mechanism and can perform stable operation when the mechanical compression ratio is changed.

  The internal combustion engine of the present invention includes a compression ratio variable mechanism that can change the mechanical compression ratio, and the residual gas remaining in the combustion chamber without being discharged in the combustion cycle prior to the current combustion cycle includes unburned gas. And the already burned burned gas is included, and the unburned gas that is filled when the intake valve is closed by the new mixture supplied in the intake stroke of the combustion cycle and the unburned gas contained in the residual gas. A mixture is formed. The internal combustion engine estimates the ratio of unburned gas and burned gas contained in the residual gas during the transient operation and the mechanical compression ratio in the current combustion cycle during the transient operation in which the mechanical compression ratio is changed. Based on the estimated ratio of unburned gas to burned gas and the estimated mechanical compression ratio, the internal combustion engine determines the amount of unburned mixture or burned gas filled in the combustion chamber in the current combustion cycle. The amount of at least one of the amount of residual gas and the amount of new mixture in the current combustion cycle is set so that at least one of the amounts is substantially the same as the amount in steady operation where the mechanical compression ratio is substantially constant. Adjust.

  In the above-described invention, the variable valve mechanism that can change the closing timing of the intake valve is provided, and based on the amount of unburned gas and the mechanical compression ratio contained in the residual gas remaining in the combustion chamber, Estimating the closing timing of the intake valve where the amount of fuel mixture is almost the same as the amount of unburned mixture during steady operation, and controlling it to the estimated closing timing of the intake valve allows The amount of new mixture to be supplied can be adjusted.

  In the above invention, the burned gas included in the residual gas remaining in the combustion chamber is provided with a variable valve mechanism that can change the valve opening timing of the intake valve and a variable valve mechanism that can change the valve closing timing of the exhaust valve. The intake valve opening timing and exhaust valve closing timing when the amount of burned gas during transient operation is almost the same as the amount of burned gas during steady operation are estimated based on the amount of gas and the mechanical compression ratio. By controlling the estimated intake valve opening timing and the estimated exhaust valve closing timing, the amount of residual gas remaining in the combustion chamber can be adjusted.

  According to the present invention, it is possible to provide an internal combustion engine that includes a variable compression ratio mechanism and can perform stable operation when the mechanical compression ratio is changed.

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. In an internal combustion engine of an embodiment, it is a schematic diagram explaining a ratio of gas contained in residual gas when a mechanical compression ratio becomes a high compression ratio and when it becomes a low compression ratio. It is the schematic which shows the ratio of the gas with which it fills in the cylinder explaining the 1st operation control in embodiment. It is a flowchart of the 1st operation control in an embodiment. It is a graph explaining the relationship between the mechanical compression ratio in embodiment, and the ratio of burnt gas. It is a graph which estimates the cylinder temperature at the time of valve closing of the exhaust valve for calculating the amount of residual gas in embodiment. It is the schematic which shows the ratio of the gas with which it fills in the cylinder explaining the 2nd operation control in embodiment. It is a flowchart of the 2nd operation control in an embodiment.

  An internal combustion engine according to an 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 inside the cylinder block 2.

  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 spark plug 10 is formed to ignite fuel in the combustion chamber 5.

  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 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.

  Furthermore, the variable valve mechanism in the present embodiment includes a variable valve timing device 54 that changes the opening / closing timing of the exhaust valve 8. The variable valve timing device 54 is connected to the rotating shaft of the exhaust cam 52 and 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 piston 3 has reached the compression top dead center, and the volume of the combustion chamber 5 is reduced. When the intake air amount is always constant, the compression ratio becomes high. This state is a state where the mechanical compression ratio is high. On the other hand, in FIG. 4, the piston 3 reaches the compression top dead center, and the volume of the combustion chamber 5 is increased. When the intake air amount is always constant, the compression ratio becomes low. 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. Any variable compression ratio mechanism capable of changing the mechanical compression ratio by the mechanism can be employed.

  By the way, when the air-fuel mixture of fuel and air burns in the combustion chamber, there remains a portion that does not burn but becomes unburned gas. When the air-fuel mixture is ignited at the spark plug, a flame is generated, and the generated flame propagates toward the entire combustion chamber. At this time, a quench zone in which no flame reaches in the combustion chamber appears. For this reason, in addition to the burned gas in which the fuel is burned, the burned gas that has been burned includes unburned gas that remains without burning the fuel. Unburned gas includes fuel and air.

  In the internal combustion engine in the present embodiment, the piston rises to the compression top dead center in the exhaust stroke of the combustion cycle, but a part of the combustion gas does not flow into the engine exhaust passage but remains in the combustion chamber. Residual gas remains until the next combustion cycle. For this reason, the gas sealed in the combustion chamber in each combustion cycle includes a new mixture of fuel and air (fresh air) supplied from the engine intake passage and residual gas remaining in the previous combustion cycle. .

  The combustion gas includes burned gas and unburned gas, but when the mechanical compression ratio is changed, the size of the quench zone changes. For this reason, when the mechanical compression ratio changes, the ratio of burned gas and unburned gas contained in the residual gas changes.

  FIG. 5 is a schematic diagram illustrating the composition of residual gas remaining in the combustion chamber when the mechanical compression ratio changes. The piston 3 is supported on the crankshaft 59 via a connecting rod 58. As the crankshaft 59 rotates, the piston 3 reciprocates between the top dead center and the bottom dead center. FIG. 5 shows a case where the mechanical compression ratio ε is 20 as an example of the high compression ratio and a case where the mechanical compression ratio ε is 10 as the low compression ratio. Moreover, the example of the state of the steady operation in which each mechanical compression ratio is maintained constant is shown.

  In the variable compression ratio mechanism of the present embodiment, the cylinder block moves relative to the lower structure including the crankcase. For this reason, when the mechanical compression ratio changes, the size of the combustion chamber changes. In this embodiment, unless otherwise specified, the opening timing (IVO) of the intake valve is a top dead center (TDC) in the intake stroke, and the closing timing (IVC) of the intake valve is a bottom dead center in the intake stroke. (BDC). Further, the closing timing (EVC) of the exhaust valve is a top dead center (TDC) in the exhaust stroke. Further, it is assumed that there is no blowback.

  The gas remaining in the combustion chamber when the piston 3 reaches top dead center in the exhaust stroke corresponds to the residual gas 64. The residual gas 64 includes unburned gas 64a in which fuel remains without being burned and burned burned gas 64b. Further, the stroke volume in which the piston 3 moves from the top dead center to the bottom dead center corresponds to the new air-fuel mixture 63 that is newly supplied into the cylinder. The new air-fuel mixture 63 and the unburned gas 64a include the fuel 61 and the air 62, thereby forming an unburned air-fuel mixture.

  The quench zone becomes smaller as the mechanical compression ratio changes from a high compression ratio to a low compression ratio. As the mechanical compression ratio becomes smaller, the proportion of the unburned gas 64a contained in the residual gas 64 becomes smaller. Comparing the ratio r of the burned gas in the residual gas 64 between the case of the high compression ratio and the case of the low compression ratio, the ratio r (ε = 20) of the burned gas 64b having the high compression ratio is the same as that of the low compression ratio. It can be seen that the ratio is smaller than the ratio r (ε = 10) of the fuel gas 64b.

  FIG. 6 is a schematic diagram illustrating the ratio of gas in the cylinder in the first operation control of the present embodiment. Comparative Example 1 is an example when a steady operation is performed with the mechanical compression ratio ε maintained at 15. The ratio of the unburned gas 64a and the burned gas 64b in the residual gas 64 can be expressed as (1-r (ε = 15)): r (ε = 15).

  Comparative Example 2 is an example when the mechanical compression ratio ε decreases from 20 to 15. The mechanical compression ratio ε is the same as that in the comparative example 1, but in the comparative example 2, a transient operation in which the mechanical compression ratio is changed is performed. Since the ratio of the unburned gas 64a increases as the mechanical compression ratio increases, the transient operation that lowers the mechanical compression ratio is affected by the high ratio of the unburned gas 64a. For this reason, the ratio of the unburned gas 64a during the transient operation of the comparative example 2 is larger than that during the steady operation of the comparative example 1. In Comparative Example 2, the amount of the unburned air-fuel mixture in the cylinder including the unburned gas 64a and the new air-fuel mixture 63 is larger than that in Comparative Example 1. For this reason, the generated torque may increase or a torque shock may occur. Thus, even if the mechanical compression ratio is the same, the amount of unburned air-fuel mixture sealed in the combustion chamber during transient operation is greater than during steady operation, and thus the output torque may increase. is there.

Example 1 shows an example when the first operation control in the present embodiment is performed. In the first operation control, the amount of residual gas remaining in the cylinder and the amount of unburned gas contained in the residual gas are estimated, and a new mixture is supplied to the cylinder based on the estimated amount of unburned gas. Control to adjust the amount of qi. Referring to Comparative Example 1 and Comparative Example 2, in Comparative Example 2, the amount of unburned air-fuel mixture including fuel 61 and air 62 is larger than Comparative Example 1 by the difference Δm _cyl . In the first operation control of the present embodiment, the amount of newly supplied air-fuel mixture is decreased, and the amount of unburned air-fuel mixture during transient operation is reduced to that of unburned air-fuel mixture during steady operation. Control to be the same as the amount.

In the first operation control of the present embodiment, the intake valve closing timing is advanced from the bottom dead center of the reference valve closing timing, thereby newly mixing the fuel 61 and air 62 supplied into the cylinder. Correction for reducing the amount of air 63 is performed. The amount of decrease in the air-fuel mixture corresponds to the difference Δm _cyl in the amount of the unburned gas 64a of the residual gas 64 between the comparative example 1 and the comparative example 2. By this control, the amount of the unburned mixture 65 in Comparative Example 1 and the amount of the unburned mixture 65 in Example 1 can be made substantially the same. The amount of combustible air-fuel mixture enclosed in the combustion chamber can be made the same. For this reason, even during the period when the mechanical compression ratio is changed, it is possible to suppress the output torque from changing greatly or causing a torque shock. The internal combustion engine in the present embodiment can perform stable operation even if the mechanical compression ratio is changed.

  Next, a specific example of the first operation control in the present embodiment will be described.

  FIG. 7 shows a flowchart of the first operation control in the present embodiment. The flowchart shown in FIG. 7 can be repeated, for example, while the mechanical compression ratio is being changed.

  First, in step 101, it is determined whether or not the piston is located at the top dead center (compression top dead center) of the compression stroke. If the piston is not at the top dead center of the compression stroke, this control is terminated. In step 101, when the piston is located at the top dead center of the compression stroke, the routine proceeds to step 102.

In step 102, the mechanical compression ratio ε _TDCfp when the piston is located at the top dead center of the compression stroke is detected. That is, the mechanical compression ratio at the top dead center when ignition is performed in the combustion chamber is detected.

Next, in step 103, it is determined whether or not the piston is located at the top dead center of the intake stroke (or the top dead center of the exhaust stroke). In step 103, when the piston is not located at the top dead center of the intake stroke, this control is repeated. That is, it waits until the piston reaches the top dead center of the intake stroke (until the crank angle rotates 360 °). In step 103, if the piston has reached the top dead center of the intake stroke, the routine proceeds to step 104. In step 104, the mechanical compression ratio ε _TDCvo at this time is detected.

Next, in step 105, the mechanical compression ratio ε _TDCivc when the piston reaches the bottom dead center of the intake stroke is estimated. The time when the piston reaches the bottom dead center of the intake stroke is a reference time for closing the intake valve, and the mechanical compression ratio when the intake valve opens is estimated. The mechanical compression ratio ε _BDCivc when the piston reaches the bottom dead center of the intake stroke can be estimated using the mechanical compression ratio ε _TDCfp detected in step 102 and the mechanical compression ratio ε _TDCvo detected in step 104. The mechanical compression ratio ε _BDCivc when the piston is located at the bottom dead center (intake bottom dead center) in the intake stroke can be estimated by the following equation 1.

Next, in step 106, the ratio r (ε _TDCfp ) of burned gas in the residual gas when the piston is located at the top dead center of the compression stroke and the residual when the piston is located at the bottom dead center of the intake stroke. The ratio r (ε _BDCivc ) of burned gas in the gas is estimated.

In FIG. 8, the graph explaining the ratio of the burned gas contained in the residual gas in each mechanical compression ratio is shown. As the mechanical compression ratio ε increases, the ratio r of the burned gas in the residual gas decreases. The relationship between the mechanical compression ratio and the ratio of burned gas shown in FIG. 8 can be stored as a map in advance in an electronic control unit or the like. In step 106 of FIG. 7, it can be read between the mechanical compression ratio epsilon _TDCfp detected at step 102, by the mechanical compression ratio epsilon _TDCvo detected at step 104, the ratio r of the burned gas in each state from the map .

Next, in step 107, the residual gas amount m _res (ε _BDCivc ) when the piston reaches the bottom dead center of the intake stroke is calculated. When the piston reaches the bottom dead center of the intake stroke, that is, the residual gas amount corresponding to the mechanical compression ratio at the reference valve closing timing of the intake valve is estimated. The residual gas amount m _{res at} each mechanical compression ratio can be calculated by the following equation 2.

Here, the variable P _EVC is the pressure in the cylinder when the exhaust valve is closed. The variable _VEVC is the volume in the cylinder when the exhaust valve is closed, and varies depending on the respective mechanical compression ratios. The constant R is a gas constant, and the variable _TEVC is the temperature in the cylinder when the exhaust valve is closed.

The variable P _EVC can be detected by arranging an in-cylinder pressure sensor for detecting the pressure in the cylinder. Or it can estimate using the output of a crank angle sensor, etc. The variable V _EVC can be calculated from the following Expression 3, for example.

Here, the variable V _cyl indicates the displacement, the variable n _cyl indicates the number of cylinders, the variable EVC is the closing timing of the exhaust valve, and the unit is [rad ATDC].

In addition, the variable _TEVC can store, for example, a map in which the operating state of the internal combustion engine is a function in advance in an electronic control unit or the like. The variable _TEVC can be estimated by detecting the operating state of the internal combustion engine and reading it from the stored map. The variable T _EVC can be expressed by the following Equation 4.

  Here, the variable NE is the engine speed, the variable KL is the charging efficiency, and the variable SA is the ignition timing.

FIG. 9 shows a graph for explaining a map for estimating the temperature _TEVC in the cylinder when the exhaust valve is closed. The temperature T _EVC is, for example, monotonically increasing with respect to the engine speed NE and monotonically increasing with respect to the charging efficiency KL. On the other hand, the temperature T _EVC decreases monotonously with respect to the ignition timing SA. The temperature T _EVC can be estimated from the map having such a relationship. In this way, the residual gas amount m _res at each mechanical compression ratio can be calculated from the above Equation 2.

Referring to FIG. 7, in step 107, after estimating the residual gas amount m _res (ε _BDCivc ) when the piston reaches the bottom dead center of the intake stroke, the _{routine proceeds} to step 108. In step 108, a decrease amount Δm _cyl for reducing the newly supplied air-fuel mixture in the cylinder is calculated. The reduction amount Δm _cyl of the gas in the cylinder can be calculated by the following formula 5.

In Equation 5, the proportion of unburned gas definitive mechanical compression ratio at the compression top dead center _{(1-r (ε TDCfp)} ) ratio of the unburned gas in the bottom dead center of the intake stroke from (1-r (ε _BDCivc) ) _{Is subtracted} and multiplied by the residual gas amount m _res (ε _BDCivc ) calculated in step 107.

Next, in step 109, it estimates the newly supplied new air-fuel mixture amount _{m new new} into the cylinder. The new air-fuel mixture amount m _new supplied into the cylinder can be estimated from the output of an air flow meter, for example. Alternatively, the new mixture amount in the current combustion cycle can be estimated from the new mixture amount filled in the previous combustion cycle.

Next, at step 110, the valve closing timing of the intake valve is calculated by the following equation (6). Here, a plus sign indicates an advance angle. That is, in the present embodiment, the closing timing of the intake valve is advanced.

  Next, the intake valve is closed at the valve closing timing calculated in step 111. By performing this control, even during the period when the mechanical compression ratio is changed, the amount of new mixture is corrected so that the total amount of mixture of fuel and air is almost the same as during steady operation. Can do. The first operation control of the present embodiment can be repeatedly performed during the period when the mechanical compression ratio is changed. For this reason, it is possible to suppress the occurrence of unexpected torque or the occurrence of torque shock during the transient operation in which the mechanical compression ratio is changed.

  In the first operation control in the present embodiment, the amount of unburned air-fuel mixture during transient operation is determined as steady operation based on the amount of unburned gas contained in the residual gas remaining in the combustion chamber and the mechanical compression ratio. Estimate the closing timing of the intake valve that is almost the same as the amount of unburned air-fuel mixture at the time. By controlling the estimated intake valve closing timing, the amount of new air-fuel mixture supplied to the combustion chamber can be adjusted, and stable operation can be performed.

  In this embodiment, correction is performed to advance the closing timing of the intake valve. However, the present invention is not limited to this configuration, and control for adjusting the new mixture amount by retarding the closing timing of the intake valve. You may do. Alternatively, any control or any device that adjusts the amount of new mixture to be filled in the combustion chamber can be employed.

Next, the second operation control in the present embodiment will be described. In transient operation state, not only variations in torque output, may vary the amount of the NO _X discharged from the combustion chamber. For example, there are cases where the amount of the NO _X discharged from the combustion chamber increases. In the second operation control of the present embodiment, control is performed to suppress an increase in the amount of NO _X that occurs in the transient operation state.

  FIG. 10 is a schematic diagram for explaining the ratio of gas in the cylinder in the second operation control of the present embodiment. Comparative Example 1 and Comparative Example 2 are the same as Comparative Example 1 and Comparative Example 2 in the description of the first operation control (see FIG. 6). Example 2 shows the ratio of gas in the cylinder when the second operation control in the present embodiment is performed.

Referring to Comparative Example 2, the amount of burnt gas 64b during transient operation is smaller than the amount of burnt gas 64b during steady operation even if the mechanical compression ratio is the same. That is, the ratio of the burned gas 64b in the cylinder is reduced. For this, the temperature at which the air-fuel mixture is burnt is increased, the amount of the NO _X increases. Even when the mechanical compression ratio ε is substantially the same, the amount of NO _X generated during the transient operation is larger than the amount of NO _X generated during the steady operation.

In the second operation control of the present embodiment, by increasing the amount of burned gas 64b at the time of transient operation, it performs control to suppress the amount of generated NO _X. In the second operation control of the present embodiment, control is performed so that the amount of burnt gas 64b contained in the residual gas 64 during transient operation is substantially the same as the amount of burnt gas 64b during steady operation.

In the second operation control of the present embodiment, control is performed to advance the valve opening timing of the intake valve. Furthermore, control is performed to retard the closing timing of the exhaust valve. By performing this control, the residual gas amount m _res during transient operation can be increased. For this reason, it is possible to correct a large amount of burned gas 64b contained in the residual gas 64. In Example 2, the amount of burned gas 64b during transient operation is adjusted to be the same as the amount of burned gas 64b of Comparative Example 1 during steady operation. By performing this control, it is possible to suppress the amount of generated NO _X. To be able to suppress the amount of NO _X is changed at the time of transient operation, it is possible to perform stable operation of the internal combustion engine.

  FIG. 11 shows a flowchart of the second operational control in the present embodiment. The second operation control of the present embodiment can be repeatedly performed during the period when the mechanical compression ratio is changed.

Step 121 and step 122 are the same as step 101 and step 102 of the first operation control (see FIG. 7). The mechanical compression ratio ε _TDCfp when the piston is located at the top dead center of the compression stroke is detected.

Next, in step 123, it is determined whether or not the piston is located at the bottom dead center of the exhaust stroke (bottom dead center of the expansion stroke). In step 123, the process waits until the piston reaches the bottom dead center of the exhaust stroke (until the crank angle rotates 180 °). In step 123, if the piston has reached the bottom dead center of the exhaust stroke, the routine proceeds to step 124. In step 124, the mechanical compression ratio _εBDCevo when the piston is located at the bottom dead center of the exhaust stroke is detected. The mechanical compression ratio ε _BDCevo when the exhaust valve _opens is detected.

Next, in step 125, the mechanical compression ratio ε _TDCvo when the piston reaches the top dead center of the intake stroke (top dead center of the exhaust stroke) is estimated. A mechanical compression ratio is estimated at a reference valve opening timing for opening the intake valve or a reference valve closing timing for closing the exhaust valve. The mechanical compression ratio when the piston reaches the top dead center of the intake stroke can be estimated using the mechanical compression ratio ε _TDCfp detected in step 122 and the mechanical compression ratio ε _BDCevo detected in step 124. The mechanical compression ratio ε _TDCvo when the piston is located at the top dead center in the intake stroke can be estimated by the following equation (7).

Next, in step 126, the ratio r (ε _TDCfp ) of burned gas contained in the residual gas when the piston is located at the top dead center of the compression stroke and the residual when the piston is located at the top dead center of the intake stroke The ratio r (ε _TDCvo ) of burned gas contained in the gas is read. These ratios r can be estimated by creating a map in advance and reading from the map, as in the first operation control step 106 (see FIG. 7) in the present embodiment.

Next, in step 127, a residual gas amount m _res (ε _TDCvo ) serving as a reference when the piston is positioned at the top dead center of the intake stroke (a reference valve opening timing for opening the intake valve) is calculated. . As the residual gas amount here, for example, the residual gas amount of the previous combustion cycle can be adopted by using the same method as in step 107 (see FIG. 7) of the first operation control in the present embodiment. . Or you may estimate based on the amount of residual gas of a previous combustion cycle.

Next, in step 128, a target residual gas amount m _{res, t} that is a target value when the exhaust valve is closed is calculated. The target residual gas amount m _{res, t} is the reference residual gas amount m _res when the piston reaches the top dead center of the intake stroke, _{and the} residual gas amount m _{res, t} when the piston reaches the top dead center of the compression stroke. It can be calculated by using the ratio r (ε _TDCfp ) of the fuel gas and the ratio r (ε _TDCvo ) of the burned gas in the mechanical compression ratio when the piston is located at the top dead center of the intake stroke. The target residual gas amount m _{res, t} can be calculated by the following equation 8.

Next, in step 129, a new air-fuel mixture amount m _new supplied into the cylinder is estimated. The new air-fuel mixture amount m _new can be estimated from the output of the air flow meter, for example, in the same manner as in the first operation control.

Next, in step 130, the intake air amount m _new and the target residual gas amount m _{res, t in} the cylinder, and the residual gas amount m _res (ε _TDCvo ) at the top dead center of the intake stroke are used. The opening timing (IVO) and the exhaust valve closing timing (EVC) can be calculated. The opening timing (IVO) of the intake valve can be calculated by the following equation (9). The exhaust valve closing timing (EVC) can be calculated by the following equation (10).

Next, in step 131, control is performed to open the intake valve at the calculated valve opening timing. Further, control is performed to close the exhaust valve at the calculated valve closing timing. By performing this control, it is possible to the amount of burnt gas of the residual gas in the transient operation, it can be made substantially same as the amount of burned gas during normal operation, to suppress the increase of the NO _X .

In the second operation control of the present embodiment, the amount of burned gas during transient operation is the same as that during steady operation based on the amount of burned gas contained in the residual gas remaining in the combustion chamber and the mechanical compression ratio. The intake valve opening timing and exhaust valve closing timing, which are almost the same as the amount of fuel gas, are estimated. By controlling the closing timing of the valve-opening timing of the estimated intake valve and the estimated exhaust valve to adjust the amount of residual gas remaining in the combustion chamber, the amount of released amount of NO _X is prevented from being increased Can do. Further, it is possible to suppress the NO _X amount flowing out from the combustion chamber varies greatly.

  In the second operational control of the present embodiment, the timing for opening the intake valve is advanced, and further, the timing for closing the exhaust valve is retarded. However, the present invention is not limited to this configuration, and the residual remaining in the combustion chamber. Any control or any device capable of adjusting the amount of burnt gas contained in the gas can be employed.

  Furthermore, in the operation control of the internal combustion engine, the second operation control can be performed in addition to the first operation control. That is, control is performed so that the amount of new mixture supplied into the cylinder of the first operation control is substantially the same as that in the steady operation, and the residual gas amount in the second operation control is substantially the same as that in the steady operation. be able to. In this case, in addition to the variable valve timing device that changes the opening and closing timing of the intake valve, an intake angle adjustment mechanism that can adjust the length of time that the intake valve is open (operating angle) is adopted. The valve opening timing and the intake valve closing timing can be individually adjusted.

  As shown in the first operation control and the second operation control described above, the internal combustion engine in the present embodiment has the ratio of the unburned gas and the burned gas contained in the residual gas during the transient operation, and this time The mechanical compression ratio in the combustion cycle is estimated, and based on the estimated ratio of unburned gas to burned gas and the estimated mechanical compression ratio, the unburned mixture filled in the combustion chamber in the current combustion cycle In the current combustion cycle, control can be performed so that at least one of the amount of air and the amount of burned gas is approximately the same as the amount during steady operation where the mechanical compression ratio is substantially constant. At least one of the amount of the residual gas and the amount of the new gas mixture can be adjusted.

  In the present embodiment, of the transient operations in which the mechanical compression ratio is changed, the transient operation in which the mechanical compression ratio is reduced is illustrated. However, the present invention is not limited to this embodiment, and the present invention is also applied to a transient operation in which the mechanical compression ratio is increased. Can be applied.

  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 including a variable compression ratio mechanism.

  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 8 Exhaust valve 31 Electronic control unit 51 Intake cam 52 Exhaust cam 53 Variable valve timing device 54 Variable valve timing device 61 Fuel 62 Air 63 New mixture 64 Residual gas 64a Unburned gas 64b Burned gas 65 Unburned mixture 79 Crankcase 86 Circular cam 87 Eccentric shaft 88 Circular cam 89 Motor 95 Relative position sensor

Claims (3)

Equipped with a variable compression ratio mechanism that can change the mechanical compression ratio.
Residual gas remaining in the combustion chamber without being discharged in the combustion cycle prior to the current combustion cycle includes unburned gas and burned burned gas,
A new mixture supplied in the intake stroke of the combustion cycle and an unburned gas included in the residual gas constitute an unburned mixture that is filled when the intake valve is closed,
At the time of transient operation where the mechanical compression ratio is changed, the ratio of unburned gas and burned gas contained in the residual gas during transient operation and the mechanical compression ratio in this combustion cycle are estimated,
Based on the estimated ratio of unburned gas to burned gas and the estimated mechanical compression ratio, at least of the amount of unburned mixture or burned gas filled in the combustion chamber in the current combustion cycle Adjust the amount of at least one of the amount of residual gas and the amount of new mixture in the current combustion cycle so that one amount is almost the same as the amount in steady operation where the mechanical compression ratio is almost constant. An internal combustion engine characterized by Equipped with a variable valve mechanism that can change the closing timing of the intake valve,
Based on the amount of unburned gas contained in the residual gas remaining in the combustion chamber and the mechanical compression ratio, the amount of unburned mixture during transient operation is almost the same as the amount of unburned mixture during steady operation. Estimate the closing timing of the intake valve
2. The internal combustion engine according to claim 1, wherein the amount of new air-fuel mixture supplied to the combustion chamber is adjusted by controlling the estimated closing timing of the intake valve. A variable valve mechanism that can change the valve opening timing of the intake valve and a variable valve mechanism that can change the valve closing timing of the exhaust valve,
Based on the amount of burned gas contained in the residual gas remaining in the combustion chamber and the mechanical compression ratio, the amount of burned gas during transient operation is almost the same as the amount of burned gas during steady operation. Estimate valve opening timing and exhaust valve closing timing,
3. The internal combustion engine according to claim 1, wherein the amount of residual gas remaining in the combustion chamber is adjusted by controlling the estimated opening timing of the intake valve and the estimated closing timing of the exhaust valve. organ.

Images