JP2014114742A - Internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an internal combustion engine for suppressing the resonance of a cylinder pressure sensor when abnormal combustion occurs.SOLUTION: The internal combustion engine includes a compression ratio varying mechanism for changing the capacity of a combustion chamber when a piston arrives at an upper dead center, to change a mechanical compression ratio, and the cylinder pressure sensor. Pressure vibration of gas in the combustion chamber at a time when the abnormal combustion occurs includes specified pressure vibration which resonates in the height direction of the combustion chamber. The compression ratio varying mechanism sets the mechanical compression ratio so that the frequency of the specified pressure vibration at the time when the abnormal combustion occurs deviates from the resonance frequency of the cylinder pressure sensor.

Description

  The present invention relates to an internal combustion engine.

  In the combustion chamber of the internal combustion engine, the air / fuel mixture is burned 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 that can change the compression ratio during an operation period is known.

  Japanese Patent Laid-Open No. 2007-92610 discloses a variable compression ratio mechanism, a knock sensor attached to a side surface of a cylinder block, and an ECU that detects that knocking has occurred in a cylinder of an internal combustion engine based on an output value of the knock sensor An internal combustion engine provided with (Electronic Control Unit) is disclosed. In this internal combustion engine, when the occurrence of knocking is detected, it is disclosed that control for changing the ignition timing is prohibited during at least a part of the period during the operation of changing the compression ratio.

  Japanese Unexamined Patent Application Publication No. 2010-190193 discloses an internal combustion engine including a variable compression ratio mechanism and a variable valve mechanism. This publication discloses that the acceleration is controlled to a low mechanical compression ratio. In addition, in order to avoid transient knocking due to response delay of the variable compression ratio mechanism during acceleration, the target intake valve closing timing is retarded to the knocking limit on the retarded side, and at the same time the throttle valve opening is increased. It is disclosed to decrease.

  Japanese Patent Laid-Open No. 2011-226302 discloses a spark ignition internal combustion engine including a variable compression ratio mechanism and a variable valve timing mechanism. In this publication, an operating point permission region is set so that a three-dimensional combustion abnormal region in which abnormal combustion occurs when an operating point consisting of a combination of a mechanical compression ratio, an intake valve closing timing, and an intake air amount enters is not entered. It is disclosed.

JP 2007-92610 A JP 2010-190193 A JP 2011-226302 A

  Abnormal combustion such as knocking occurs when combustion different from propagation of desired combustion occurs. When abnormal combustion occurs, the gas in the cylinder vibrates and a pressure wave having a predetermined frequency is generated. As a result, the engine body including the cylinder block vibrates. In the detection of abnormal combustion, vibration of the engine body caused by abnormal combustion can be detected by a knock sensor attached to the engine body. Alternatively, the occurrence of abnormal combustion can be detected by an in-cylinder pressure sensor that directly detects the pressure in the combustion chamber.

  However, when an in-cylinder pressure sensor is attached to a cylinder head or the like, if an abnormal combustion occurs, the in-cylinder pressure sensor may resonate due to gas vibration in the combustion chamber. Since the in-cylinder pressure sensor is small, the resonance frequency becomes high. However, for example, if abnormal combustion occurs when the volume of the combustion chamber is reduced by a variable compression ratio mechanism and the mechanical compression ratio is increased, the in-cylinder pressure sensor may resonate. If the in-cylinder pressure sensor resonates against the vibration of the gas during abnormal combustion, there is a risk of failure.

  An object of the present invention is to provide an internal combustion engine that suppresses resonance of an in-cylinder pressure sensor when abnormal combustion occurs.

  An internal combustion engine according to the present invention includes a variable compression ratio mechanism capable of changing a mechanical compression ratio by changing a volume of a combustion chamber when a piston reaches top dead center, and an in-cylinder pressure sensor that acquires pressure vibration in a cylinder. With. The compression ratio variable mechanism is formed to change the mechanical compression ratio according to the load. The pressure vibration of the gas in the combustion chamber when abnormal combustion occurs includes a specific pressure vibration having a frequency that resonates in the height direction of the combustion chamber and depends on the height of the combustion chamber. The compression ratio variable mechanism sets the mechanical compression ratio so that the frequency of the specific pressure vibration when abnormal combustion occurs deviates from the resonance frequency of the in-cylinder pressure sensor.

  In the above-mentioned invention, a load change range close to a mechanical compression ratio at which resonance is generated in the in-cylinder pressure sensor is provided in advance, including a required load detector that detects a required load of the internal combustion engine. Within the switching range, it is possible to maintain the mechanical compression ratio away from the mechanical compression ratio at which resonance occurs in the in-cylinder pressure sensor when the load changes.

  In the above invention, when the load decreases and reaches the switching range, the compression ratio variable mechanism increases the mechanical compression ratio to a mechanical compression ratio larger than the mechanical compression ratio at which resonance occurs in the in-cylinder pressure sensor. Internally, an elevated mechanical compression ratio can be maintained.

  In the above invention, the compression ratio variable mechanism resonates with the in-cylinder pressure sensor when the load increases and reaches the switching range when it is determined that the rapid acceleration is requested by the output of the required load detector. The mechanical compression ratio can be reduced to a smaller mechanical compression ratio, and the reduced mechanical compression ratio can be maintained within the switching range.

  According to the present invention, resonance of the in-cylinder pressure sensor when abnormal combustion occurs can be suppressed.

1 is a schematic cross-sectional view of an internal combustion engine in an 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. 4 is a graph showing the relationship between the crank angle and the height of the combustion chamber in the internal combustion engine of the embodiment. It is a graph explaining the relationship between the frequency and the intensity | strength of the pressure vibration in a cylinder when abnormal combustion generate | occur | produces. It is a graph of the resonant frequency of the specific pressure oscillation with respect to the crank angle in embodiment. It is a graph of the resonant frequency of the specific pressure vibration with respect to the mechanical compression ratio in embodiment. It is a 1st graph explaining the change of the mechanical compression ratio with respect to load. It is a 2nd graph explaining the change of the mechanical compression ratio with respect to load. It is a flowchart of the 1st operation control in an 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, a spark ignition type 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 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 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. The intake valve 6 opens and closes as the intake cam 51 rotates. The exhaust valve 8 opens and closes as the exhaust cam 52 rotates. 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 an in-cylinder pressure sensor 61 for detecting the pressure in the cylinder. The in-cylinder pressure sensor 61 acquires the pressure vibration of the gas inside the combustion chamber 5. The in-cylinder pressure sensor 61 is fixed to the cylinder head 4. The in-cylinder pressure sensor 61 is disposed on the top surface of the combustion chamber 5 that intersects the direction in which the piston 3 moves. In-cylinder pressure sensor 61 is disposed in the vicinity of spark plug 10. That is, the in-cylinder pressure sensor 61 is disposed at the central portion of the top surface of 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 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 functions as a required load detector that detects the required load. The load sensor 41 generates an output voltage corresponding 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 in-cylinder pressure sensor 61 generates an output signal corresponding to the pressure in the combustion chamber 5. The output signal of the in-cylinder pressure sensor 61 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 signal 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. 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 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 a cam shaft that supports the intake cam 51. The variable valve timing device 53 is controlled by the electronic control unit 31.

  The internal combustion engine in the present embodiment includes a variable compression ratio mechanism. In the present invention, a space in the cylinder surrounded by the crown surface of the piston and the cylinder head at an arbitrary position of the piston is referred to as a combustion chamber. The compression ratio of the internal combustion engine is determined depending on the volume of the combustion chamber when the piston reaches 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 when the piston reaches top dead center.

  FIG. 2 shows a first schematic cross-sectional view of the internal combustion engine variable compression ratio mechanism according to the present embodiment. FIG. 2 is a schematic view when a high compression ratio is achieved by the compression ratio variable mechanism. FIG. 3 shows a second schematic cross-sectional view of the compression ratio variable mechanism of the internal combustion engine in the present embodiment. FIG. 3 is a schematic view when the compression ratio is changed by the variable compression ratio mechanism. 2 and 3 show a state where the piston 3 has reached the top dead center.

  With reference to FIGS. 1 to 3, in the internal combustion engine in the present embodiment, the support structure including crankcase 79 and cylinder block 2 arranged on the upper side of the support structure relatively move. The support structure in the present embodiment supports the cylinder block 2 via a compression ratio variable mechanism. Further, the support structure in the present embodiment supports the crankshaft so as to be rotatable. The piston 3 is supported on the crankshaft via the connecting rod 23.

  A plurality of protrusions 80 are formed below the side walls on both sides of the cylinder block 2. A cam insertion hole having a circular cross section is formed in the projecting portion 80, and a circular cam 86 is rotatably disposed inside the cam insertion hole. A plurality of protrusions 82 are formed on the crankcase 79. The protrusion 82 is formed with a cam insertion hole having a circular cross-sectional shape, and a circular cam 88 is rotatably disposed inside the cam insertion hole. The protrusion 80 of the cylinder block 2 is fitted between the protrusions 82 of the crankcase 79.

  The circular cam 86 inserted into the protruding portion 80 of the cylinder block 2 and the circular cam 88 inserted into the protruding portion 82 of the crankcase 79 are connected to each other via an eccentric shaft 87. A plurality of circular cams 86 and a plurality of circular cams 88 are connected via an eccentric shaft 87 to form camshafts 84 and 85. In the present embodiment, a pair of camshafts 84 and 85 are formed. The compression ratio variable mechanism in the present embodiment includes a rotating device that rotates the pair of camshafts 84 and 85 in opposite directions. The circular cam 88 is arranged coaxially with the rotation axis of the cam shafts 84 and 85. The circular cam 86 is eccentric with respect to the rotation axis of the cam shafts 84 and 85. Further, the eccentric shaft 87 is eccentric with respect to the rotation axis of the camshafts 84 and 85.

  Referring to FIG. 2, 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. Move. The circular cam 86 supporting the cylinder block 2 rotates in the opposite direction to the circular cam 88 as indicated by an arrow 96 inside the cam insertion hole. The cylinder block 2 moves in a direction away from the crankcase 79 as indicated by an arrow 98.

  As shown in FIG. 3, 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. 2 and 3, 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. As the distance between the central axis of the circular cam 86 and the central axis of the circular cam 88 increases, the cylinder block 2 moves away from the crankcase 79. The volume of the combustion chamber 5 increases as the cylinder block 2 moves away from the crankcase 79.

  In the compression ratio variable mechanism in the present embodiment, the volume of the combustion chamber 5 when the piston 3 reaches the top dead center is variably formed when the cylinder block 2 moves relative to the crankcase 79. ing. In the present embodiment, the 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 when the piston reaches the top dead center is referred to as a mechanical compression ratio. The mechanical compression ratio does not depend on the closing timing of the intake valve, and (mechanical compression ratio) = (volume of the combustion chamber when the piston reaches top dead center + stroke volume of the piston) / (volume of the combustion chamber) ).

  The internal combustion engine in the present embodiment includes a relative position sensor 89 that detects the relative position of the cylinder block 2 with respect to the crankcase 79. From the output of the relative position sensor 89, the relative position of the piston 3 with respect to the cylinder block 2 when the piston 3 is located at the top dead center can be acquired.

  In the state shown in FIG. 2, 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. In contrast, in the state shown in FIG. 3, 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.

  The compression ratio variable mechanism in the present embodiment is controlled by the electronic control unit 31. In the present embodiment, the motor that rotates the camshafts 84 and 85 is connected to the output port 37 via the corresponding drive circuit 39.

  Furthermore, the internal combustion engine in the present embodiment includes a variable valve mechanism that changes the closing timing of the intake valve. By changing the closing timing of the intake valve, the amount of intake air taken into the combustion chamber can be changed. The closing timing of the intake valve can be changed within a period in which the piston moves from the bottom dead center to the top dead center. In the internal combustion engine in the present embodiment, an actual compression ratio that is an actual compression ratio in the combustion chamber is set in addition to the mechanical compression ratio. The actual compression ratio depends on the closing timing of the intake valve. The actual compression ratio is (actual compression ratio) = (volume of the combustion chamber when the piston reaches top dead center + volume of the piston that moves while the intake valve is closed) / (volume of the combustion chamber) Is set. As the control of the internal combustion engine, it is possible to perform control to keep the actual compression ratio constant even when the load changes within a predetermined operating range. For example, as the load increases, control for lowering the mechanical compression ratio can be performed, and control for increasing the closing timing of the intake valve can be performed.

  The internal combustion engine of the present embodiment can detect the occurrence of abnormal combustion. Abnormal combustion occurs, for example, when combustion that spreads in order from the ignition part of the spark plug occurs and combustion that is different from the propagation of desired combustion occurs. Abnormal combustion includes a knocking phenomenon. In the present embodiment, the pressure vibration of the combustion chamber 5 can be acquired by the in-cylinder pressure sensor 61 to determine whether or not abnormal combustion has occurred.

  2 and 3, when the relative position of cylinder block 2 changes with respect to crankcase 79 by the variable compression ratio mechanism, height H of combustion chamber 5 changes. In the present invention, the length of the combustion chamber 5 in the direction in which the piston 3 moves is referred to as the height H of the combustion chamber 5. In the example shown in FIGS. 2 and 3, the top surface of the combustion chamber 5 is inclined, and the portion where the distance between the crown surface of the piston 3 and the top surface of the combustion chamber 5 is the largest is the height H of the combustion chamber 5. Called.

  FIG. 4 shows the relationship of the combustion chamber height H with respect to the crank angle when the mechanical compression ratio is changed. The crank angle on the horizontal axis is 0 ° at the position where the piston 3 reaches the compression top dead center. FIG. 4 shows a plurality of graphs when the mechanical compression ratio is changed. The mechanical compression ratio ε1 is the largest and the mechanical compression ratio ε5 is the smallest (ε1> ε2> ε3> ε4> ε5). In each of the mechanical compression ratios ε1 to ε5, the height H of the combustion chamber 5 increases as the crank angle CA increases. Further, when the mechanical compression ratios ε1 to ε5 are compared, the height H of the combustion chamber 5 decreases as the mechanical compression ratio increases. In the internal combustion engine of the present embodiment, when the mechanical compression ratio is changed, the diameter H of the combustion chamber 5 does not change and the height H of the combustion chamber 5 changes.

  By the way, when abnormal combustion occurs at a predetermined position of the piston 3, a pressure wave is generated. The pressure wave is propagated at the speed of sound, for example, and spreads in the combustion chamber 5. At this time, gas pressure oscillation depending on the shape of the combustion chamber 5 is generated inside the combustion chamber 5.

  FIG. 5 shows a graph for explaining the relationship between the frequency of pressure vibration and the intensity of vibration inside the combustion chamber 5 when abnormal combustion occurs. The horizontal axis is the frequency of vibration, and the vertical axis is the intensity of vibration. The vibration detected by the in-cylinder pressure sensor 61 when abnormal combustion occurs includes a low-frequency pressure vibration VL and a high-frequency pressure vibration VH. The frequency of the low-frequency pressure vibration VL is, for example, 3 kHz to 15 kHz, and the high-frequency pressure vibration VH is, for example, 10 kHz to 100 kHz.

  Here, the inventors have found that the frequency of the pressure vibration VH on the high frequency side depends on the height H of the combustion chamber 5. The pressure vibration VH on the high frequency side is estimated to be vibration that resonates in the height direction of the combustion chamber 5. On the other hand, the pressure vibration VL on the low frequency side is estimated to be vibration that resonates in the radial direction of the combustion chamber 5. Although FIG. 5 shows the first-order resonance vibration and the second-order resonance vibration in the radial direction as the pressure vibration VL on the low frequency side, higher-order vibration may also occur. In the example shown in FIG. 5, it can be seen that the strength of the pressure vibration VH on the high frequency side is smaller than the strength of the pressure vibration VL on the low frequency side. Abnormal combustion can be detected using either the low-frequency pressure vibration VL or the high-frequency pressure vibration VH.

  Here, the frequency of the pressure vibration of the gas inside the combustion chamber 5 is not directly related to the natural frequency of the engine body 1 but depends on the shape of the combustion chamber 5 when a pressure wave is generated. To do. Further, the pressure vibration when the abnormal combustion occurs includes a high-frequency pressure vibration VH that resonates in the height direction of the combustion chamber 5. In the present invention, this high-frequency pressure vibration VH is referred to as specific pressure vibration. The specific pressure vibration is considered as vibration that resonates in the height direction of the combustion chamber, and has a high frequency as described above.

  FIG. 6 shows a graph for explaining the resonance frequency of the specific pressure vibration in the combustion chamber 5 with respect to the crank angle. The vertical axis represents the resonance frequency of the pressure wave in which vibration nodes are arranged in the height direction of the combustion chamber 5. That is, the resonance frequency of vibration in the height direction of the combustion chamber 5. In each of the mechanical compression ratios ε1 to ε5, the height H of the combustion chamber 5 increases as the crank angle CA increases, so the resonance frequency in the combustion chamber 5 decreases. In addition, in the plurality of mechanical compression ratios ε1 to ε5, the resonance frequency increases as the mechanical compression ratio increases.

  By the way, the in-cylinder pressure sensor 61 has a resonance frequency Fs according to the type and size. Further, the resonance frequency Fs of the in-cylinder pressure sensor 61 also depends on the internal structure and the like. The in-cylinder pressure sensor 61 is a small device, and the resonance frequency Fs is, for example, not less than 40 kHz and not more than 100 kHz. Referring to FIG. 5, the resonance frequency Fs of the in-cylinder pressure sensor 61 is higher than the frequency at which the low-frequency side pressure vibration VL occurs. However, the resonance frequency Fs of the in-cylinder pressure sensor 61 may coincide with the frequency of the pressure vibration VH on the high frequency side. When the resonance frequency Fs of the in-cylinder pressure sensor 61 coincides with the frequency of the specific pressure vibration, the in-cylinder pressure sensor 61 resonates, and there is a possibility that a large vibration occurs and breaks down.

  Referring to FIG. 6, when the mechanical compression ratio changes, the frequency of the specific pressure vibration caused by abnormal combustion changes. In particular, when the mechanical compression ratio is high, that is, when the height H of the combustion chamber 5 is small, the resonance frequency Fs of the in-cylinder pressure sensor 61 matches the resonance frequency of the specific pressure vibration. Here, it is difficult to specify the crank angle at which abnormal combustion occurs for each combustion cycle. Therefore, in the internal combustion engine in the present embodiment, a crank angle section SCA in which abnormal combustion occurs is set in advance. In this embodiment, a section where the crank angle is 5 ° or more and 10 ° or less is set as the crank angle section SCA in which abnormal combustion occurs.

  As shown in FIG. 6, in the crank angle section SCA where the abnormal combustion occurs, the mechanical compression ratio at which the resonance frequency Fs of the in-cylinder pressure sensor 61 and the resonance frequency of the specific pressure vibration in the combustion chamber 5 coincide is partially. Limited to range.

FIG. 7 shows a graph of the resonance frequency of the specific pressure vibration in the combustion chamber against the mechanical compression ratio. In FIG. 7, the resonance frequency of the specific pressure vibration at the crank angle position of 5 ° after the compression top dead center is shown by a solid line. Further, the resonance frequency of the specific pressure vibration at the position of the crank angle of 10 ° after the compression top dead center is shown by a broken line. As the crank angle after compression top dead center advances, the height H of the combustion chamber 5 increases and the resonance frequency decreases. Here, based on the crank angle section SCA where the abnormal combustion occurs and the resonance frequency Fs of the in-cylinder pressure sensor 61, a mechanical compression ratio range SCR in which the in-cylinder pressure sensor 61 resonates is determined. The mechanical compression ratio range SCR in which resonance occurs in the in-cylinder pressure sensor 61 is a range between the minimum mechanical compression ratio ε _SL and the maximum mechanical compression ratio ε _SH .

  Thus, when the type or the like of the in-cylinder pressure sensor 61 is determined, the resonance frequency Fs of the in-cylinder pressure sensor is determined, and further, a mechanical compression ratio range SCR in which the in-cylinder pressure sensor 61 is resonated is determined. In the internal combustion engine of the present embodiment, the mechanical compression ratio is changed so as to avoid the mechanical compression ratio range SCR in which resonance occurs in the in-cylinder pressure sensor 61.

  FIG. 8 is a graph for explaining a change in the mechanical compression ratio when the load is reduced in the first operational control of the present embodiment. The operating range of the internal combustion engine of the present embodiment includes a range in which control is performed to increase the mechanical compression ratio as the load decreases. That is, when the load is shifted from the large region to the small region, as shown by an arrow 91, control is performed to reduce the load and increase the mechanical compression ratio.

Here, a mechanical compression ratio range SCR in which resonance occurs in the in-cylinder pressure sensor 61 is set. If abnormal combustion occurs in a region where the mechanical compression ratio ε _{SL is} equal to or greater than the mechanical compression ratio ε _SH , resonance of the in-cylinder pressure sensor 61 may occur. Therefore, when the mechanical compression ratio is close to the mechanical compression ratio range SCR where resonance occurs in the in-cylinder pressure sensor 61, the mechanical compression ratio is greatly increased beyond the mechanical compression ratio range SCR as indicated by an arrow 92. . After the mechanical compression ratio is increased to a predetermined value, the mechanical compression ratio is maintained substantially constant even when the load is reduced. And when it falls to the predetermined load, as shown by the arrow 93, control which raises a mechanical compression ratio with the fall of a load is performed.

A mechanical compression ratio that greatly increases the mechanical compression ratio as indicated by an arrow 92 can be set in advance. For example, it is possible when it reaches the mechanical compression ratio obtained by subtracting a predetermined margin Δε from mechanical compression ratio epsilon _SL, significantly increase the mechanical compression ratio. Further, the mechanical compression ratio ε _SH can be increased to a mechanical compression ratio obtained by adding a predetermined margin Δε. The range from the mechanical compression ratio (ε _SL −Δε) to the mechanical compression ratio (ε _SH + Δε) is equal to the range close to the mechanical compression ratio range SCR where resonance occurs in the in-cylinder pressure sensor 61.

  In the present embodiment, the load switching range RL is set in advance corresponding to the mechanical compression ratio range close to the mechanical compression ratio range SCR where resonance occurs in the in-cylinder pressure sensor 61. Until reaching the switching range RL, the mechanical compression ratio can be increased as the load decreases. When the load reaches the switching range RL, the mechanical compression ratio can be maintained substantially constant after the mechanical compression ratio is greatly increased. Further, when the load is reduced and deviated from the switching range RL, the mechanical compression ratio can be increased as the load is reduced. In the present embodiment, the operation line maintained at a higher mechanical compression ratio than the mechanical compression ratio range SCR in which resonance occurs in the in-cylinder pressure sensor 61 is referred to as an operation line a.

  In FIG. 8, the control of the mechanical compression ratio of the comparative example is shown by a broken line. In the control of the comparative example, the load is reduced and the mechanical compression ratio is increased in the load switching range RL. In particular, as indicated by an arrow 94, control is performed to gradually increase the mechanical compression ratio as the load decreases even in the mechanical compression ratio range SCR where resonance occurs in the in-cylinder pressure sensor 61 and in the vicinity of the range. In the internal combustion engine of the comparative example, the cylinder pressure sensor 61 may gradually pass through the mechanical compression ratio range SCR in which resonance occurs. Alternatively, the mechanical compression ratio may be maintained within the mechanical compression ratio range SCR where resonance occurs in the in-cylinder pressure sensor 61. If abnormal combustion occurs in such a case, the in-cylinder pressure sensor 61 may resonate with the pressure vibration of the abnormal combustion, and the in-cylinder pressure sensor 61 may fail.

  In contrast, in the present embodiment, when the in-cylinder pressure sensor 61 approaches the mechanical compression ratio range SCR in which resonance occurs, the mechanical compression ratio is increased so as to greatly exceed the mechanical compression ratio range SCR. For this reason, the range SCR of the mechanical compression ratio in which resonance occurs in the in-cylinder pressure sensor 61 can be crossed. The time existing in the mechanical compression ratio range SCR is short, and the resonance of the in-cylinder pressure sensor 61 can be suppressed even if abnormal combustion occurs. Further, in the switching range RL, the in-cylinder pressure is maintained even when abnormal combustion occurs in order to maintain the mechanical compression ratio far from the mechanical compression ratio range SCR where resonance occurs in the in-cylinder pressure sensor 61 even when the load changes. It is possible to avoid the resonance of the sensor 61.

  FIG. 9 shows a graph for explaining a change in the mechanical compression ratio when the load is reduced in the first operation control of the present embodiment. When the load is shifted from a small state to a large state, as indicated by an arrow 101, it is possible to perform control for decreasing the mechanical compression ratio as the load increases. When the load increases and the in-cylinder pressure sensor 61 approaches the mechanical compression ratio range SCR in which resonance occurs, as shown by the arrow 102, the mechanical compression ratio is greatly reduced so as to be less than the mechanical compression ratio range SCR. To control. In this example, when the load reaches the preset switching range RL, the mechanical compression ratio is greatly reduced. Control is performed to keep the mechanical compression ratio constant after the mechanical compression ratio is lowered to a predetermined value. In this example, control for maintaining the mechanical compression ratio is performed within the switching range RL. Further, when the load increases and deviates from the switching range RL, as shown by an arrow 103, it is possible to perform control to decrease the mechanical compression ratio as the load increases. In the present embodiment, the operation line maintained at a lower mechanical compression ratio than the mechanical compression ratio range SCR in which resonance occurs in the in-cylinder pressure sensor 61 is referred to as an operation line b.

Here, as the mechanical compression ratio when the mechanical compression ratio is greatly reduced, a value obtained by adding a predetermined margin Δε to the mechanical compression ratio ε _SH can be employed. Further, it is possible to reduce to a mechanical compression ratio by subtracting a predetermined margin Δε from mechanical compression ratio epsilon _SL. Further, the mechanical compression ratio can be kept low so that the cylinder pressure sensor 61 does not enter the range close to the mechanical compression ratio range SCR where resonance occurs.

  In FIG. 9, the control of the internal combustion engine of the comparative example is shown by a broken line. In the internal combustion engine of the comparative example, in the mechanical compression ratio range SCR where resonance occurs in the in-cylinder pressure sensor 61 and in the vicinity of the range, the load increases and the mechanical compression ratio is gradually reduced. For this reason, as in the comparative example (see FIG. 8) in the case of reducing the load, the time existing in the mechanical compression ratio range SCR in which resonance occurs in the in-cylinder pressure sensor 61 becomes longer, and the in-cylinder pressure sensor 61 resonates. May occur.

  On the other hand, in the control of the present embodiment, as indicated by an arrow 102, when approaching the mechanical compression ratio range SCR where resonance occurs in the in-cylinder pressure sensor 61, the mechanical compression ratio range SCR is crossed. In order to reduce the mechanical compression ratio, the mechanical compression ratio range SCR in which resonance of the in-cylinder pressure sensor 61 occurs can be passed in a short time. For this reason, resonance of the in-cylinder pressure sensor 61 when abnormal combustion occurs can be suppressed. Within the switching range RL, the in-cylinder pressure sensor 61 is maintained even when abnormal combustion occurs in order to maintain the mechanical compression ratio far from the mechanical compression ratio range SCR where resonance occurs in the in-cylinder pressure sensor 61 even when the load changes. Resonance can be prevented from occurring.

  The relationship of the mechanical compression ratio with respect to the load as shown in FIGS. 8 and 9 can be stored in the electronic control unit 31 in advance. In operation control, knocking or the like is less likely to occur as the engine speed increases. Therefore, the mechanical compression ratio may be set higher as the engine speed increases. That is, the mechanical compression ratio may be set based on the load and the engine speed. In this case, a map of the mechanical compression ratio having the load and the engine speed as a function can be stored in the electronic control unit 31 in advance. In the present embodiment, the relationship of the mechanical compression ratio with respect to the load outside the load switching range RL is the same when the load is lowered and when the load is raised.

  Referring to FIGS. 8 and 9, in the first operation control, in the load switching range RL, when the load is reduced, the machine is higher than the mechanical compression ratio range SCR in which resonance occurs in the in-cylinder pressure sensor 61. The compression ratio is kept constant. Further, when the load is increased, the mechanical pressure ratio is kept constant at a lower mechanical compression ratio than the mechanical compression ratio range SCR in which resonance occurs in the in-cylinder pressure sensor 61. By controlling the hysteresis with different operation lines for the load increase and the load decrease, the operation frequency at which the mechanical compression ratio changes before and after the change point of the mechanical compression ratio can be reduced. That is, it is possible to suppress the mechanical compression ratio from increasing or decreasing across the change point of the mechanical compression ratio.

  FIG. 10 shows a flowchart of the first operation control in the present embodiment. The control shown in FIG. 10 can be repeatedly performed by interrupt control or the like.

  In step 111, the amount of depression of the accelerator pedal is detected. In step 112, the required load desired by the user is detected. The amount of depression of the accelerator pedal 40 can be detected by the load sensor 41. Further, the required load can be calculated based on the depression amount of the accelerator pedal 40.

  Next, in step 113, it is determined whether or not the required load has entered the range from outside the switching range RL. That is, it is determined whether or not the load has reached the switching range RL. If the required load has not entered the switching range RL, the process proceeds to step 117, and the target mechanical compression ratio is set by the current operation line. For example, when the required load is maintained in the switching range RL from the previous operation control, or in the previous operation control, the required load was within the switching range RL, but in the current operation control, the range of the switching range RL If it is outside, control is performed with the current operation line.

  If the required load enters the switching range RL in step 113, the process proceeds to step 114. That is, when the mechanical compression ratio approaches the mechanical compression ratio range SCR in which resonance occurs in the in-cylinder pressure sensor 61, the routine proceeds to step 114.

  In step 114, it is determined whether or not the required load has increased. By comparing the required load in the previous control with the required load in the current control, it can be determined whether or not the required load has increased.

  In step 114, if the required load has increased, the process proceeds to step 115. In step 115, the relationship of the mechanical compression ratio with respect to the load of the operation line b shown in FIG. 9 is selected. Control close to the mechanical compression ratio range SCR where the resonance of the in-cylinder pressure sensor 61 is generated can be selected to maintain the mechanical compression ratio lower than the mechanical compression ratio range SCR.

  In step 114, if the required load has not increased, the process proceeds to step 116. In this case, the load is reduced. In step 116, the relationship of the mechanical compression ratio with respect to the load of the operation line a shown in FIG. 8 is selected. Control that maintains a mechanical compression ratio higher than the mechanical compression ratio range SCR in which the resonance of the in-cylinder pressure sensor 61 occurs when the mechanical compression ratio range SCR in which the in-cylinder pressure sensor 61 causes resonance can be selected. .

  Next, in step 117, a target mechanical compression ratio is set based on the required load. A target mechanical compression ratio can be set based on the operation line a or the operation line b. In step 118, the target mechanical compression ratio is changed by the variable compression ratio mechanism. Thus, when the required load enters the switching range RL from outside the switching range RL, the operation line of the compression ratio variable mechanism can be selected.

  In the first operation control, when the load is increased, the mechanical compression ratio is controlled by the operation line b. However, the present invention is not limited to this mode, and the mechanical compression ratio is controlled by the operation line a. It doesn't matter. For example, as shown by an arrow 105 in FIG. 8, when the load is increased, in the load switching range RL, the mechanical compression ratio is maintained higher than the mechanical compression ratio range SCR in which resonance occurs in the in-cylinder pressure sensor 61. It doesn't matter. In addition, when the load increases and deviates from the switching range RL, control for greatly reducing the mechanical compression ratio may be performed.

  As described above, in both cases of increasing the load and decreasing the load, the load switching range RL is maintained at a mechanical compression ratio higher than the mechanical compression ratio range SCR in which resonance occurs in the in-cylinder pressure sensor 61. Control may be performed. By this control, the time for setting the mechanical compression ratio to be high can be lengthened, and the theoretical thermal efficiency can be improved.

  When the mechanical compression ratio is maintained higher than the mechanical compression ratio range SCR in which resonance of the in-cylinder pressure sensor 61 occurs based on the operation line a, the intake valve closing timing is delayed as compared with the control of the comparative example. be able to. When the valve closing timing of the intake valve is delayed by the variable valve timing device 53, the actual compression ratio in the combustion chamber 5 can be maintained substantially constant. For this reason, abnormal combustion such as knocking can be suppressed. Moreover, pump loss (pumping loss) can be suppressed by delaying the closing timing of the intake valve.

  The operation line a and the operation line b of the mechanical compression ratio described above maintain the mechanical compression ratio substantially constant within the range of the switching range RL. However, the present invention is not limited to this form, and the specific pressure vibration when abnormal combustion occurs. The mechanical compression ratio can be set so that this frequency deviates from the resonance frequency of the in-cylinder pressure sensor. For example, the mechanical compression ratio may change within the switching range RL. However, it is preferable to control to a mechanical compression ratio sufficiently distant from the mechanical compression ratio range SCR where resonance occurs in the in-cylinder pressure sensor 61.

  Next, the second operation control in the present embodiment will be described. In the second operation control, the mechanical compression ratio is higher than the mechanical compression ratio range SCR in which the resonance of the in-cylinder pressure sensor 61 occurs when the load increases or decreases within the load switching range RL. Control to maintain. However, there is a case where rapid acceleration of the internal combustion engine is necessary according to the desire of the user. In the second operation control, the range of the mechanical compression ratio in which resonance occurs in the in-cylinder pressure sensor 61 when the rapid acceleration of the internal combustion engine is necessary. Control is performed to maintain a mechanical compression ratio lower than that of the SCR.

  Referring to FIG. 8, in operation control other than the case where rapid acceleration of the internal combustion engine is required, the mechanical compression ratio is changed along operation line a as shown by arrows 92 and 105. However, when rapid acceleration of the internal combustion engine is required, the mechanical compression ratio is selected along the operation line b as shown by an arrow 102 as shown in FIG.

  When the internal combustion engine is accelerated rapidly, the mechanical compression ratio is changed using the operation line b, so that the mechanical compression ratio is set lower than the operation line a and the amount of intake air flowing into the combustion chamber 5 is increased. Can do. For example, when a variable valve timing device is used to control the actual compression ratio to be constant, the mechanical compression ratio becomes low, so that the intake valve closes earlier and the intake air amount becomes larger. Become. Further, when the air-fuel ratio is controlled to be constant, the fuel injection amount is also increased. For this reason, the output of the internal combustion engine can be increased, and the user can obtain a great feeling of acceleration.

  FIG. 11 shows a flowchart of the second operational control of the present embodiment. Steps 111 to 114 are the same as the first operation control in the present embodiment (see FIG. 10). If the load drops in step 114, the process proceeds to step 116 and the operation line a is selected. If the load increases in step 114, the process proceeds to step 119.

  In step 119, it is determined whether or not rapid acceleration of the internal combustion engine is required. In the present embodiment, it is determined whether or not the amount of depression of the accelerator pedal is greater than a predetermined determination value. When the amount of depression of the accelerator pedal is larger than a predetermined determination value, it can be determined that rapid acceleration is required.

  The method for determining whether or not rapid acceleration of the internal combustion engine is required is not limited to this form. For example, the increase amount of the accelerator pedal depression amount in the previous operation control and the current operation control is calculated and calculated. It may be determined whether or not rapid acceleration of the internal combustion engine is required based on the increased amount. Alternatively, the acceleration of the depression amount of the accelerator pedal may be calculated, and it may be determined whether or not the rapid acceleration of the internal combustion engine is requested based on the calculated acceleration.

  If it is determined in step 119 that the depression amount of the accelerator pedal 40 is equal to or smaller than a predetermined determination value, the process proceeds to step 116. In this case, it can be determined that a moderate load increase is required. In step 116, the operation line a is selected.

  In step 119, when the depression amount of the accelerator pedal 40 is larger than a predetermined determination value, the process proceeds to step 115. In step 115, the operation line b is selected.

  Step 117 and step 118 are the same as the first operation control (see FIG. 10). The mechanical compression ratio can be changed by setting a target mechanical compression ratio based on the operation line a or the operation line b.

  In the second operational control of the present embodiment, the output of the internal combustion engine can be increased when the internal combustion engine is accelerated rapidly. Further, similarly to the first operation control, the operation can be performed while avoiding the range of the mechanical compression ratio in which the resonance of the in-cylinder pressure sensor 61 occurs.

  The variable compression ratio mechanism in the present embodiment changes the mechanical compression ratio by moving the cylinder block relative to the crankcase, but is not limited to this form, and the piston has reached top dead center. Any variable compression ratio mechanism capable of changing the height of the combustion chamber at the time can be employed.

  The internal combustion engine in the present embodiment includes a variable valve mechanism. However, the present invention is not limited to this form, and the present invention can also be applied to an internal combustion engine that does not include a variable valve mechanism. The mechanical compression ratio can be changed so as to avoid the mechanical compression ratio in which resonance of the in-cylinder pressure sensor occurs when abnormal combustion occurs.

  The above embodiments can be combined as appropriate. In the above control, the order of steps can be changed as appropriate within the same range of operation and function. In the respective drawings described above, the same or equivalent 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 31 Electronic control unit 40 Accelerator pedal 41 Load sensor 51 Intake cam 61 In-cylinder pressure sensor 79 Crankcase 84, 85 Camshaft 86, 88 Circular cam 87 Eccentric shaft

Claims (4)

A variable compression ratio mechanism capable of changing the mechanical compression ratio by changing the volume of the combustion chamber when the piston reaches top dead center;
An in-cylinder pressure sensor for acquiring pressure vibration in the cylinder,
The compression ratio variable mechanism is formed to change the mechanical compression ratio according to the load,
The pressure vibration of the gas in the combustion chamber when abnormal combustion occurs includes a specific pressure vibration having a frequency that resonates in the height direction of the combustion chamber and depends on the height of the combustion chamber,
The internal combustion engine, wherein the variable compression ratio mechanism sets the mechanical compression ratio so that the frequency of the specific pressure vibration when abnormal combustion occurs deviates from the resonance frequency of the in-cylinder pressure sensor. A required load detector for detecting the required load of the internal combustion engine;
A load switching range close to the mechanical compression ratio at which resonance occurs in the in-cylinder pressure sensor is predetermined,
2. The internal combustion engine according to claim 1, wherein the variable compression ratio mechanism maintains a mechanical compression ratio separated from a mechanical compression ratio at which resonance occurs in the in-cylinder pressure sensor when the load changes within the switching range.   When the load decreases and reaches the switching range, the variable compression ratio mechanism increases the mechanical compression ratio to a mechanical compression ratio larger than the mechanical compression ratio at which resonance occurs in the in-cylinder pressure sensor, and raises it within the switching range. The internal combustion engine of claim 2, wherein the internal combustion engine is maintained at a high mechanical compression ratio.   The compression ratio variable mechanism is a mechanical compression ratio that causes resonance in the in-cylinder pressure sensor when the load increases and reaches the switching range when it is determined that rapid acceleration is required by the output of the required load detector. 4. The internal combustion engine according to claim 2, wherein the internal combustion engine is reduced to a smaller mechanical compression ratio and maintained at the reduced mechanical compression ratio within the switching range. 5.

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