JPWO2012035647A1 - Apparatus for estimating heat release rate of internal combustion engine - Google Patents

Abstract

By determining the injection timing of the main injection, the “combustion field-in-cylinder pressure sensor distance” is acquired. The “combustion speed” is acquired from the combustion field-in-cylinder pressure sensor distance map, engine speed, and fuel injection pressure. The required minimum filter frequency map in which the “required minimum filter frequency” is acquired by the combustion speed map, the “distance between the combustion field and the in-cylinder pressure sensor”, and the “combustion speed” is stored in the ROM. The in-cylinder pressure data from the in-cylinder pressure sensor that detects the pressure in the combustion chamber is filtered by the “minimum required filter frequency” to estimate the heat release rate waveform, and the combustion start timing of the fuel injected in the main injection is calculated. recognize.

Description

  The present invention relates to an apparatus for estimating a heat generation rate of a compression self-ignition internal combustion engine represented by a diesel engine. In particular, the present invention relates to a measure for improving the heat generation rate estimation accuracy.

  As is well known in the art, in a diesel engine (hereinafter sometimes simply referred to as an engine) used as an automobile engine or the like, various kinds of power performance, combustion noise, exhaust emission, combustion stability, fuel consumption rate, etc. Complex control is performed so that characteristics and restrictions are within a predetermined target range (see, for example, Patent Document 1 and Patent Document 2 below).

  As one of means for realizing a combustion state in which the various characteristics and restrictions are within a predetermined target range, it is possible to optimize the ignition timing of the fuel in the combustion chamber. In other words, the fuel ignition timing is monitored, and the control parameters (fuel injection timing, fuel injection timing, etc.) are set so that the ignition timing becomes an appropriate timing (for example, diffusion combustion starts at the compression top dead center (TDC) of the piston). Fuel injection pressure and the like).

  In general, the ignition timing of the fuel in the combustion chamber can be obtained from a change in the heat generation rate (represented as a heat generation rate waveform) that changes with combustion of the air-fuel mixture. For this reason, in order to monitor the ignition timing of the fuel with high accuracy, it is indispensable to accurately acquire a change in heat generation rate (heat generation rate waveform).

  Since the heat generation rate has a correlation with the pressure in the combustion chamber (hereinafter sometimes referred to as “in-cylinder pressure”), an in-cylinder pressure sensor capable of detecting the in-cylinder pressure is provided, and the detected in-cylinder is detected. It is possible to estimate the heat release rate waveform according to the pressure change. That is, it is possible to obtain the heat generation rate waveform based on the in-cylinder pressure data acquired by this in-cylinder pressure sensor, and to determine the ignition timing of the fuel from this heat generation rate waveform.

  The heat generation rate waveform thus obtained is not only for determining the fuel ignition timing described above, but also for the combustion center of gravity, the peak value of the heat generation rate, the heat generation rate change gradient at the start of combustion, etc. It can be applied to the demands of a wide range of applications.

JP 2005-232990 A Japanese Patent Laid-Open No. 2004-3415 Republished patent WO2003 / 033896

  However, the in-cylinder pressure data acquired by the in-cylinder pressure sensor includes an error. As a cause of the error, in addition to electrical noise, noise due to air column vibration generated between the in-cylinder pressure sensor and the combustion chamber in accordance with a change in the in-cylinder pressure can be cited. In particular, the frequency of noise due to the air column vibration is close to the frequency component of the combustion pressure wave that is actually generated in the cylinder, which is a major obstacle for accurately obtaining the heat release rate waveform.

  As described above, since the in-cylinder pressure data acquired by the in-cylinder pressure sensor itself is not reliable, the heat generation rate waveform generated based on the data is also low in reliability. The current situation is that it cannot be obtained with high accuracy.

  The present invention has been made in view of such points, and the object of the present invention is to provide a reliable heat generation rate by performing appropriate processing on in-cylinder pressure data acquired by an in-cylinder pressure sensor. An object of the present invention is to provide a heat generation rate estimation device for an internal combustion engine capable of obtaining a waveform.

-Principle of solving the problem-
The solution principle of the present invention taken to achieve the above object is that the noise component (frequency component to be removed) included in the in-cylinder pressure data acquired by the in-cylinder pressure sensor is determined from the in-cylinder pressure sensor. And the pressure change rate in the combustion chamber (including the space where the in-cylinder pressure sensor is inserted) are correlated, and filtering is performed from this distance and the pressure change rate (correlation with the combustion speed). A frequency band (required minimum filter frequency: cut-off frequency) is set, thereby enabling removal of the noise component.

-Solution-
Specifically, the present invention relates to the pressure of the in-cylinder pressure sensor that can detect the in-cylinder pressure, and the heat generation rate when the fuel injected from the fuel injection valve burns into the combustion chamber of the compression ignition type internal combustion engine. A heat release rate estimation device for an internal combustion engine that estimates based on a detection signal is assumed. The heat generation rate estimation device is provided with combustion pressure wave transmission path acquisition means, combustion speed acquisition means, and necessary minimum filter frequency acquisition means. The combustion pressure wave transmission path acquisition means calculates the length of the transmission path of the combustion pressure wave between the combustion field and the in-cylinder pressure sensor based on the shape of the combustion chamber and the fuel injection timing from the fuel injection valve. Ask. The combustion speed acquisition means acquires a “combustion speed” by combustion of the air-fuel mixture in the combustion chamber. The necessary minimum filter frequency acquisition means is detected by the in-cylinder pressure sensor based on the length of the combustion pressure wave transmission path obtained by the combustion pressure transmission path acquisition means and the combustion speed obtained by the combustion speed acquisition means. The “required minimum filter frequency” for performing the filtering process on the obtained pressure data is obtained.

  Further, as a method of acquiring the combustion speed by the combustion speed acquisition means, specifically, the combustion speed is obtained based on the rotation speed of the internal combustion engine and the fuel injection pressure.

  By this specific matter, it is possible to effectively remove the frequency (frequency that is the cause of noise) such as air column vibration caused by the change in the in-cylinder pressure vibrating between the in-cylinder pressure sensor and the combustion chamber. It is possible to obtain the “required minimum filter frequency”. In other words, by eliminating the pressure data on the higher frequency side than this “necessary minimum filter frequency” (low-pass filter), it is possible to efficiently extract the combustion pressure wave resulting from the combustion in the combustion chamber and generate heat. The rate change can be estimated accurately. As a result, it is possible to accurately recognize the ignition timing of the fuel in the combustion chamber.

  As the arrangement structure of the in-cylinder pressure sensor, the in-cylinder pressure sensor is held in the in-cylinder pressure sensor mounting hole formed in the cylinder head via the sensor adapter. A pressure introduction hole is formed to communicate between the internal space of the cylinder and a sensing portion provided at the tip of the in-cylinder pressure sensor.

  In the case of such an in-cylinder pressure sensor arrangement structure, air column vibration generated in a space extending from the in-cylinder pressure sensor mounting hole to the pressure introduction hole causes the noise. According to the present invention, even for a structure in which noise due to air column vibration is likely to occur, according to the present invention, the combustion pressure wave caused by the combustion in the combustion chamber is efficiently reduced by the filtering process using the “required minimum filter frequency”. It becomes possible to extract.

  As a more specific configuration, the combustion pressure wave transmission path acquisition means is configured to calculate the length of the combustion pressure wave transmission path from the fuel injection timing of the fuel injection valve based on a combustion field-in-cylinder pressure sensor distance map. The length of the transmission path of the combustion pressure wave between the in-cylinder pressure sensor ”is acquired, and the combustion speed acquisition means obtains the“ combustion speed ”from the combustion speed map for determining the combustion speed from the rotational speed of the internal combustion engine and the fuel injection pressure. The necessary minimum filter frequency calculation means is calculated from the length of the combustion pressure wave transmission path acquired from the combustion field-in-cylinder pressure sensor distance map and the combustion speed acquired from the combustion speed map. Necessary minimum filter frequency from the necessary minimum filter frequency map for obtaining the necessary minimum filter frequency for filtering the pressure data detected by the in-cylinder pressure sensor And it has a configuration to get.

  In the present invention, the “required minimum filter frequency” is obtained based on “the length of the transmission path of the combustion pressure wave between the combustion field and the in-cylinder pressure sensor” and the “combustion speed”. The heat generation rate is estimated from the filtered pressure data. For this reason, the combustion pressure wave resulting from the combustion in the combustion chamber can be extracted efficiently, and the change in the heat generation rate can be accurately estimated.

FIG. 1 is a cross-sectional view illustrating a schematic configuration of a diesel engine and a control system thereof according to the embodiment. FIG. 2 is a block diagram showing a configuration of a control system such as an ECU. FIG. 3 is a cross-sectional view showing a mounting portion of the in-cylinder pressure sensor. FIG. 4 is a block diagram showing an outline of a heat generation rate calculation system. FIG. 5 is a diagram illustrating an example of a combustion field-in-cylinder pressure sensor distance map. FIG. 6 is a diagram illustrating an example of a combustion speed map. FIG. 7 is a diagram illustrating an example of a necessary minimum filter frequency map. FIG. 8 is a diagram showing an example of a heat release rate waveform obtained by performing data processing according to the present invention on in-cylinder pressure data. FIG. 9 shows an example of a heat generation rate waveform obtained by a conventional method, FIG. 9A shows a heat generation rate waveform obtained without a filter, and FIG. 9 is a heat release rate waveform obtained when the filter amount is small, and FIG. 9C is a heat release rate waveform obtained when the filter amount is larger than the appropriate amount.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In this embodiment, the heat release rate estimation device according to the present invention is applied to a common rail in-cylinder direct injection multi-cylinder (for example, in-line 4-cylinder) diesel engine (compression self-ignition internal combustion engine) mounted on an automobile. explain. In the present embodiment, various maps, which will be described later, are created by experiments with an engine performance experiment device, stored in the ROM of the ECU, and various map values are read from the ROM to execute arithmetic processing. The case where the heat release rate waveform is obtained by the above and the start timing of diffusion combustion is optimized will be described.

  Before describing the operation of creating the various maps and the operation of creating the heat release rate waveform by the calculation processing of the various map values, a schematic configuration of a diesel engine to which the present invention is applied will be described.

-Engine configuration-
FIG. 1 is a diagram showing a schematic configuration of an engine 1 and its control system according to the present embodiment.

  In this diesel engine 1, a piston 22 is housed in a cylinder 21 formed in a cylinder block 2, and the movement of the piston 22 that reciprocates in the cylinder 21 is transmitted as a rotational movement of the crankshaft 3 through a connecting rod 23. It has come to be.

  A cylinder head 5 that forms a combustion chamber 4 above the piston 22 is fixed to the upper end surface of the cylinder block 2. Specifically, the combustion chamber 4 is defined by a lower surface of the cylinder head 5 attached to the upper portion of the cylinder block 2 via a gasket 24, an inner wall surface of the cylinder 21, and a top surface 25 of the piston 22. Yes. A cavity (concave portion) 26 is formed in a substantially central portion of the top surface 25 of the piston 22, and the cavity 26 also constitutes a part of the combustion chamber 4.

  As for the shape of the cavity 26, the concave dimension is small in the central portion (on the cylinder center line P), and the concave dimension is increased toward the outer peripheral side. That is, when the piston 22 is in the vicinity of the compression top dead center, the combustion chamber 4 formed by the cavity 26 is a narrow space having a relatively small volume at the center portion, and the space is gradually enlarged toward the outer peripheral side. It is configured to be (expanded space).

  The piston 22 is connected to a small end portion 27 of the connecting rod 23 by a piston pin 28, and a large end portion of the connecting rod 23 is connected to a crankshaft 3 serving as an engine output shaft. As a result, the reciprocating movement of the piston 22 in the cylinder 21 is transmitted to the crankshaft 3 via the connecting rod 23, and the engine output is obtained by rotating the crankshaft 3.

  The cylinder head 5 is formed with an intake port 51 and an exhaust port 52 that open to the combustion chamber 4.

  The intake port 51 and the exhaust port 52 are opened and closed by an intake valve 53 and an exhaust valve 54 driven by cams (not shown), respectively.

  The intake port 51 is connected to an intake pipe 6 for sucking outside air. During the intake stroke in which the intake valve 53 opens the intake port 51, the piston 22 descends in the cylinder 21 to generate a negative pressure in the cylinder. Then, the outside air sucked from the intake pipe 6 flows into the cylinder through the intake port 51.

  Further, the exhaust port 52 is connected to an exhaust pipe 7 for discharging combustion gas, and the exhaust valve 54 rises from the combustion chamber 4 (inside the cylinder) due to the piston 22 rising during the exhaust stroke in which the exhaust port 52 opens the exhaust port 52. The pushed combustion gas is discharged to the exhaust pipe 7 through the exhaust port 52.

  The fuel supply system includes a common rail 8 that accumulates high-pressure fuel, a fuel supply pump (not shown) that pumps high-pressure fuel to the common rail 8, and each of the high-pressure fuel accumulated in the common rail 8 that is injected into the combustion chamber 4. Each cylinder has an injector 81 and is controlled by an electronic control unit (hereinafter referred to as ECU 100).

  The common rail 8 stores the high-pressure fuel supplied from the fuel supply pump at a predetermined target rail pressure, and the stored high-pressure fuel is supplied to the injector 81 via the fuel pipe 82. The target rail pressure of the common rail 8 is set by the ECU 100. Specifically, the operating state of the engine 1 is detected from the accelerator opening (engine load) and the engine speed, and a target rail pressure suitable for the operating state is set.

  The injector 81 is disposed substantially vertically above the center of the combustion chamber 4 in a standing posture along the cylinder center line P, and injects fuel introduced from the common rail 8 toward the combustion chamber 4 at a predetermined timing. It has become.

-ECU-
As shown in FIG. 2, the ECU 100 includes a CPU 101, a ROM 102, a RAM 103, a backup RAM 104, and the like. The ROM 102 stores various control programs, maps that are referred to when the various control programs are executed, and the like. The CPU 101 executes various arithmetic processes based on various control programs and maps stored in the ROM 102. The RAM 103 is a memory that temporarily stores calculation results in the CPU 101, data input from each sensor, and the like. The backup RAM 104 is a non-volatile memory that stores data to be saved when the engine 1 is stopped, for example.

  The CPU 101, the ROM 102, the RAM 103, and the backup RAM 104 are connected to each other via the bus 107, and are connected to the input interface 105 and the output interface 106.

  The input interface 105 includes a crank position sensor 90, a rail pressure sensor 91, a throttle opening sensor 92, an air flow meter 93, an A / F sensor 94, a water temperature sensor 95, an accelerator opening sensor 96, an intake pressure sensor 97, an intake air temperature sensor. 98, an in-cylinder pressure sensor 99 and the like are connected.

  The crank position sensor 90 outputs a pulse signal at every predetermined crank angle (for example, 10 °). As an example of a method of detecting the crank angle by the crank position sensor 90, external teeth are formed every 10 ° on the outer peripheral surface of a rotor (NE rotor) 90a (see FIG. 1) integrally rotated with the crankshaft 3, The crank position sensor 90 made of an electromagnetic pickup is disposed to face the external teeth. When the external teeth pass in the vicinity of the crank position sensor 90 as the crankshaft 3 rotates, the crank position sensor 90 generates an output pulse.

  The rail pressure sensor 91 outputs a detection signal corresponding to the fuel pressure stored in the common rail 8. The throttle opening sensor 92 detects the opening of a throttle valve (diesel throttle) (not shown) provided in the intake pipe 6. The air flow meter 93 outputs a detection signal corresponding to the flow rate (intake air amount) of the intake air upstream of the throttle valve in the intake pipe 6. The A / F sensor 94 outputs a detection signal that continuously changes in accordance with the oxygen concentration in the exhaust gas on the downstream side of a catalyst (not shown) provided in the exhaust pipe 7. The water temperature sensor 95 outputs a detection signal corresponding to the cooling water temperature of the engine 1. The accelerator opening sensor 96 outputs a detection signal corresponding to the depression amount of the accelerator pedal. The intake pressure sensor 97 is disposed in the intake pipe 6 and outputs a detection signal corresponding to the intake air pressure. The intake air temperature sensor 98 is disposed in the intake pipe 6 and outputs a detection signal corresponding to the temperature of the intake air. The in-cylinder pressure sensor 99 is attached to the cylinder head 5 for each cylinder, detects the in-cylinder pressure of each cylinder, and outputs it to the ECU 100.

  On the other hand, the injector 81, the throttle valve 57, the EGR valve 58 provided in the EGR device (not shown), and the like are connected to the output interface 106.

  FIG. 3 is a cross-sectional view showing a portion where the in-cylinder pressure sensor 99 is attached. The in-cylinder pressure sensor 99 is held in the in-cylinder pressure sensor mounting hole 55 formed in the cylinder head 5 via a sensor adapter 56. Specifically, the in-cylinder pressure sensor mounting hole 55 is formed as a through hole having a circular cross section. The sensor adapter 56 has a substantially cylindrical shape whose outer diameter matches the inner diameter of the in-cylinder pressure sensor mounting hole 55, and a sensor insertion hole 56 a in which the in-cylinder pressure sensor 99 is mounted at the center. Is formed. At the tip of the sensor adapter 56, a plurality of (two in FIG. 3) pressure introduction holes 56b communicating between the internal space of the in-cylinder pressure sensor mounting hole 55 and the sensor insertion hole 56a, 56b is formed. An in-cylinder pressure sensor 99 is inserted into the sensor insertion hole 56a, and a sensing part (pressure receiving part) 99a provided at the tip of the in-cylinder pressure sensor 99 faces the pressure introduction holes 56b and 56b. For this reason, the combustion pressure generated in the combustion chamber 4 reaches the sensing unit 99a of the in-cylinder pressure sensor 99 from the combustion chamber 4 through the in-cylinder pressure sensor mounting hole 55 and the pressure introduction holes 56b and 56b. It is to be detected.

  The pressure information (pressure data) detected by the sensing unit 99a includes noise due to air column vibration generated between the combustion chamber 4 and the in-cylinder pressure sensor 99 as the in-cylinder pressure changes. ing. This noise removal will be described later.

  The ECU 100 executes various controls of the engine 1 based on the outputs of the various sensors described above. For example, the ECU 100 executes pilot injection (sub-injection) and main injection (main injection) as fuel injection control of the injector 81.

  The pilot injection is an operation for injecting a small amount of fuel in advance prior to the main injection from the injector 81. The pilot injection is an injection operation for suppressing the ignition delay of fuel due to the main injection and leading to stable diffusion combustion, and is also referred to as sub-injection. Further, the pilot injection in the present embodiment has not only a function of suppressing the initial combustion speed by the main injection described above but also a preheating function of increasing the in-cylinder temperature. That is, after the pilot injection is performed, the fuel injection is temporarily interrupted, and the compressed gas temperature (in-cylinder temperature) is sufficiently increased until the main injection is started to reach the fuel self-ignition temperature. This ensures good ignitability of the fuel injected in the main injection.

  The main injection is an injection operation (torque generation fuel supply operation) for generating torque of the engine 1. The injection amount in the main injection is basically determined so as to obtain the required torque according to the operation state such as the engine speed, the accelerator operation amount, the coolant temperature, the intake air temperature, and the like. For example, the higher the engine speed (the engine speed calculated based on the detection value of the crank position sensor 90), the greater the accelerator operation amount (the accelerator pedal depression amount detected by the accelerator opening sensor 96). As the accelerator opening becomes larger, the required torque value of the engine 1 is higher, and accordingly, the fuel injection amount in the main injection is also set higher.

  In addition to the pilot injection and main injection described above, after injection and post injection are performed as necessary. This after-injection is an injection operation for increasing the exhaust gas temperature. Further, the post-injection is an injection operation for directly introducing fuel into the exhaust system to increase the temperature of the catalyst.

  The pressure control of the fuel injected from the injector 81 controls the fuel pressure accumulated in the common rail 8 and supplies the fuel so that the actual rail pressure detected by the rail pressure sensor 91 matches the target rail pressure. The pump discharge amount (pump discharge amount) is feedback controlled.

  Specifically, the target value of the fuel pressure supplied from the common rail 8 to the injector 81, that is, the target rail pressure, as the common rail internal pressure is generally increased as the engine load (engine load) increases. The higher the number, the higher. That is, when the engine load is high, the amount of air sucked into the combustion chamber 4 is large, so that a large amount of fuel must be injected from the injector 81 into the combustion chamber 4. The pressure needs to be high. Also, when the engine speed is high, the injection period is short, so the amount of fuel injected per unit time must be increased, and therefore the injection pressure from the injector 81 must be increased. . Thus, the target rail pressure is generally set based on the engine load and the engine speed. The target rail pressure is set according to a fuel pressure setting map stored in the ROM 102, for example. That is, by determining the fuel pressure according to this fuel pressure setting map, the valve opening period (injection rate waveform) of the injector 81 is controlled, and the fuel injection amount during the valve opening period can be defined.

  The injection amount control of the injector 81 controls the injection amount and the injection timing injected from the injector 81, calculates the optimal injection amount and injection timing according to the operating state of the engine 1, and according to the calculation result. The solenoid valve of the injector 81 is driven.

-Heat release rate estimation operation-
Next, the heat generation rate estimation operation, which is an operation characteristic of the present embodiment, will be described. This heat generation rate estimation operation generates a heat generation rate waveform by calculating a change in the heat generation rate (heat generation amount per unit rotation angle of the crankshaft 3) in the combustion chamber 4, and based on this, for example, This is useful for estimating the combustion start time (diffuse combustion start time) of the fuel injected in the main injection. More specifically, since the heat generation rate associated with the combustion in the combustion chamber 4 is correlated with the in-cylinder pressure, this is used to generate heat from the in-cylinder pressure detected by the in-cylinder pressure sensor 99. The rate is estimated.

  An outline of the heat generation rate estimation operation will be described. FIG. 4 is a block diagram showing an outline of the heat generation rate calculation system according to the present embodiment. As shown in FIG. 4, first, raw pressure data from the in-cylinder pressure sensor 99 is acquired. This raw pressure data is in-cylinder pressure data detected by the in-cylinder pressure sensor 99 every predetermined time (for example, every several msec) or every predetermined rotation angle of the crankshaft 3 (for example, every 0.2 ° CA).

  The raw pressure data is subjected to frequency analysis by FFT (Fast Fourier Transform) to obtain an in-cylinder pressure spectrum for each frequency band. After that, by the filter that is a feature of the present invention (details of this filter will be described later), only the band (frequency band) necessary for heat generation rate estimation is extracted by eliminating the frequency band causing the noise, This is subjected to IFFT (Inverse Fast Fourier Transform) to calculate filtered in-cylinder pressure data (filtered pressure data). The heat generation rate is calculated from the post-filter pressure data.

  Specifically, various maps, which will be described later, are created from various data acquired through experiments with an engine performance experiment device and stored in the ROM 102 of the ECU 100.

  Hereinafter, a procedure for creating various maps including a necessary minimum filter frequency map in which a necessary minimum filter frequency for extracting only a band necessary for heat generation rate estimation by the above filter is set will be described. The various maps are created in the order of (1) creation of a combustion field-in-cylinder pressure sensor distance map, (2) creation of a combustion speed map, and (3) creation of a necessary minimum filter frequency map.

(Creation of distance map between combustion field and in-cylinder pressure sensor)
The distance map between the combustion field and the in-cylinder pressure sensor shows the injection timing of the main injection and the center of the combustion field when the fuel injected by the main injection is diffusely burned (ignition position of the representative combustion field: for example, FIG. The distance between the point X) and the sensing part 99a of the in-cylinder pressure sensor 99 (the length of the combustion pressure wave transmission path between the combustion field and the in-cylinder pressure sensor 99: hereinafter, “the distance between the combustion field and the in-cylinder pressure sensor”) It may also be referred to as “)”. The distance between the combustion field and the in-cylinder pressure sensor is such that the combustion pressure wave generated by the combustion in the combustion chamber 4 passes through the combustion chamber 4, the in-cylinder pressure sensor mounting hole 55, and the pressure introduction hole 56b. Since the route reaches the sensing unit 99a, the length varies depending on the shape of the combustion chamber 4. That is, the distance between the combustion field and the in-cylinder pressure sensor is defined based on the shape of the combustion chamber 4 (including the in-cylinder pressure sensor mounting hole 55 and the pressure introduction hole 56b) and the fuel injection timing of the injector 81. .

  FIG. 5 shows an example of the distance map between the combustion field and the in-cylinder pressure sensor. According to the combustion field-cylinder pressure sensor distance map, the "combustion field-cylinder pressure sensor distance" can be acquired by determining the injection timing of the main injection. This combustion field-in-cylinder pressure sensor distance map is created by experiment (or simulation) as described above, and when combustion is started with a chemical time delay from the time when fuel is injected in the main injection. The distance between the center of the combustion field (point X in FIG. 1) and the sensing part 99a of the in-cylinder pressure sensor 99 (for example, the shortest distance between them). That is, the length of the pressure propagation path until the pressure wave (combustion pressure wave) from the combustion field reaches the sensing unit 99a of the in-cylinder pressure sensor 99 is obtained.

  When the fuel injection timing is a value between the values shown on the combustion field-in-cylinder pressure sensor distance map, the "combustion field-in-cylinder pressure sensor distance" is determined by a predetermined interpolation calculation. "Is calculated.

(Create combustion speed map)
The combustion speed map is a map for obtaining the combustion speed in the combustion chamber 4 using the engine speed and the fuel injection pressure as parameters.

  FIG. 6 shows an example of this combustion speed map. According to this combustion speed map, combustion is performed from the engine speed calculated based on the detection value of the crank position sensor 90 and the internal pressure of the common rail 8 (corresponding to the fuel injection pressure) detected by the rail pressure sensor 91. The combustion speed in the chamber 4 is required. This combustion speed map is also created by experiment (or simulation) as described above, and is a map obtained with a higher combustion speed as the engine speed is higher and the fuel injection pressure is higher. .

  When the engine speed and the fuel injection pressure are values between values shown on the combustion speed map, the combustion speed is calculated by a predetermined interpolation calculation.

(Create minimum filter frequency map)
The necessary minimum filter frequency map uses the “combustion field-in-cylinder pressure sensor distance” acquired by the combustion field-in-cylinder pressure sensor distance map and the “combustion speed” acquired by the combustion speed map as parameters. 7 is a map for obtaining a “necessary minimum filter frequency” for performing filtering on in-cylinder pressure data acquired from the in-cylinder pressure sensor 99; This is because the noise component (frequency component to be removed) included in the in-cylinder pressure data acquired by the in-cylinder pressure sensor 99 is the distance from the combustion field to the in-cylinder pressure sensor 99 and the combustion speed in the combustion chamber 4. Is defined as a map for obtaining a “required minimum filter frequency” for removing the noise component by defining a frequency band to be filtered from the distance and the combustion speed. That is, by eliminating pressure data on a higher frequency side than the “necessary minimum filter frequency”, it is possible to efficiently extract a combustion pressure wave resulting from combustion in the combustion chamber 4. .

  FIG. 7 shows an example of the necessary minimum filter frequency map. According to the necessary minimum filter frequency map, the “required minimum filter frequency” is obtained based on the “distance between the combustion field and the in-cylinder pressure sensor” and the “combustion speed”. This necessary minimum filter frequency map is also created by experiment (or simulation) as described above. The longer the “distance between the combustion field and the in-cylinder pressure sensor” and the higher the “combustion speed”, the “necessary The “minimum filter frequency” is set to a high frequency.

  In addition, when the “distance between the combustion field and the in-cylinder pressure sensor” and the “combustion speed” are values between the values shown on the necessary minimum filter frequency map, the “necessary” is calculated by a predetermined interpolation calculation. The “minimum filter frequency” is calculated.

  Hereinafter, a specific heat generation rate estimation operation will be described. As already described with reference to FIG. 4, first, raw pressure data acquisition operation is performed in the cylinder that is in the combustion stroke. That is, the in-cylinder pressure is detected by the in-cylinder pressure sensor 99. The raw pressure data acquisition period (sampling period) is, for example, the rotation angle of the crankshaft 3 and 30 ° before the compression top dead center of the piston 22 (BTDC 30 ° CA) to 50 ° after the compression top dead center of the piston 22 ( ATDC 50 ° CA). These values are not limited to this, and can be set arbitrarily. This period is recognized based on the detection signal from the crank position sensor 90. Further, the interval (sampling timing) of the detection timing of the raw pressure data is set, for example, every 0.2 ° CA or every predetermined time (for example, every several msec) as the rotation angle of the crankshaft 3. These values are not limited to this, and are appropriately set according to the arithmetic processing capability of the ECU 100.

  A plurality of in-cylinder pressure data detected during the period is subjected to frequency analysis by FFT to obtain an in-cylinder pressure spectrum for each frequency band.

  On the other hand, by applying the current fuel injection timing to the combustion field-in-cylinder pressure sensor distance map, the "combustion field-in-cylinder pressure sensor distance" is acquired (combustion field and cylinder by the combustion pressure wave transmission path acquisition means). Along with the acquisition of the length of the transmission path of the combustion pressure wave between the internal pressure sensor and the current engine speed and the fuel injection pressure are applied to the combustion speed map, the “combustion speed” is acquired (combustion speed). Acquisition of combustion speed by acquisition means). Then, the “required minimum filter frequency” is obtained by fitting these “combustion field-in-cylinder pressure sensor distance” and “combustion speed” to the required minimum filter frequency map (required minimum filter frequency acquisition means required minimum). (Acquisition of filter frequency), among the frequencies analyzed by the FFT, only the frequency band defined by the “required minimum filter frequency” (lower frequency side than the minimum required filter frequency) is extracted.

  Thereafter, the in-cylinder pressure data in the extracted frequency band is acquired as filtered in-cylinder pressure data (filtered pressure data) by IFFT. Then, a heat generation rate for each crank angle is calculated from the post-filter pressure data, thereby creating a heat generation rate waveform of the combustion performed in the combustion chamber 4.

  FIG. 8 is a diagram showing an example of the heat release rate waveform obtained in this way. As shown in FIG. 8, a heat generation rate waveform that almost contains noise and reflects the combustion state in the combustion chamber 4 substantially accurately is obtained. This can be verified by the fact that a decrease in the heat generation rate due to the endothermic reaction appears at the start of pilot injection and main injection. With this heat generation rate waveform, the start timing of the combustion (diffusion combustion) in the main injection performed in the combustion chamber 4 (when the heat generation rate shifts from negative to positive) is the timing Tm in the figure. Presumed. In addition, with this heat generation rate waveform, it is also possible to estimate the start timing of combustion (premixed combustion) in pilot injection (when the heat generation rate has shifted from negative to positive). It is the inside timing Tp.

  FIG. 9 shows an example of a heat generation rate waveform obtained by a conventional method, FIG. 9A shows a heat generation rate waveform obtained without a filter, and FIG. 9B shows an appropriate amount of filter. FIG. 9C shows a heat generation rate waveform obtained when the filter amount is larger than the appropriate amount.

  In the heat generation rate waveform shown in FIG. 9A, there is a lot of noise due to air column vibration generated between the in-cylinder pressure sensor 99 and the combustion chamber 4 with the change in the in-cylinder pressure, and the change in the heat generation rate is recognized. It is impossible to do.

  In the heat generation rate waveform shown in FIG. 9B, the noise component remains, and it is difficult to accurately recognize the change in the heat generation rate (particularly, the combustion start timing).

  In the heat generation rate waveform shown in FIG. 9C, the noise component does not remain, but a part of the combustion pressure wave caused by combustion (combustion pressure wave in the frequency band to be reflected in the heat generation rate waveform) is filtered. Therefore, a heat release rate waveform that accurately reflects the combustion state is not obtained. This can be confirmed by almost no decrease in the heat generation rate due to the endothermic reaction at the initial start of the pilot injection and the main injection.

  As described above, in the present embodiment, the frequency (frequency that causes noise) such as air column vibration generated between the in-cylinder pressure sensor 99 and the combustion chamber 4 in accordance with the change in the in-cylinder pressure is effective. It is possible to obtain the “required minimum filter frequency” that can be removed by the process, and to obtain the heat release rate waveform based on the pressure data filtered by this “required minimum filter frequency”. For this reason, the combustion pressure wave resulting from the combustion in the combustion chamber 4 can be extracted efficiently, the change in the heat generation rate can be accurately estimated, and the ignition timing of the fuel in the combustion chamber 4 Can be accurately recognized.

  When the ignition timing of the fuel is recognized in this way and the ignition timing is delayed from the target ignition timing, the fuel injection timing from the injector 81 is corrected to the advance side. Then, control is performed such that the ignition timing approaches the target ignition timing by correcting the target rail pressure to be high. Conversely, when the recognized ignition timing is advanced from the target ignition timing, the fuel injection timing from the injector 81 is corrected to the retard side, or the target rail pressure is corrected to be lowered. As a result, control is performed so that the ignition timing approaches the target ignition timing.

-Other embodiments-
In the embodiment described above, the case where the present invention is applied to the common rail in-cylinder direct injection multi-cylinder diesel engine 1 mounted on an automobile has been described. The present invention is not limited to this, and can also be applied to a diesel engine mounted other than an automobile. Further, the present invention is applicable not only to diesel engines but also to gasoline engines.

  In the above embodiment, the cylinder pressure sensor 99 is supported by the cylinder head 5 through the sensor adapter 56 having the pressure introducing hole 56 b as the arrangement structure of the cylinder pressure sensor 99. The arrangement structure of the in-cylinder pressure sensor 99 is not limited to this, and the in-cylinder pressure sensor may be inserted into and supported by the in-cylinder pressure sensor mounting hole 55 formed in the cylinder head 5 without using an adapter. Good.

  In addition, the heat generation rate estimation device according to the present invention is not limited to the estimation of the heat generation rate in pilot injection or main injection, but can be applied to the estimation of the heat generation rate in the above-mentioned after injection or post injection. Is possible.

  In addition, the heat generation rate waveform obtained in the above embodiment obtains not only the fuel ignition timing, but also the combustion center of gravity, the peak value of the heat generation rate, the heat generation rate change gradient at the start of combustion, etc. The present invention is applicable to any case, and its use is not particularly limited.

  Further, in the above-described embodiment, various maps (combustion field-in-cylinder pressure sensor distance map, combustion speed map, necessary minimum filter frequency map) are created by experiments in the engine performance experiment apparatus, and these are stored in the ROM 102 of the ECU 100. The heat generation rate waveform is obtained by reading out various map values from the ROM 102 and executing arithmetic processing in the engine operating state on the actual machine. The present invention is not limited to this, and the required minimum filter frequency may be obtained by calculation from the fuel injection timing, fuel injection pressure, and engine speed, and the heat release rate waveform may be obtained by a filtering process based on it. That is, the heat release rate waveform is obtained by calculation processing on an actual machine without creating a map in advance.

  INDUSTRIAL APPLICABILITY The present invention is applicable to heat generation rate estimation for obtaining a heat generation rate waveform that can accurately recognize the ignition timing of combustion in a common rail in-cylinder direct injection multi-cylinder diesel engine mounted on an automobile.

1 engine (internal combustion engine)
4 Combustion chamber 5 Cylinder head 55 Cylinder pressure sensor mounting hole 56 Sensor adapter 56a Sensor insertion hole 56b Pressure introduction hole 81 Injector (fuel injection valve)
90 Crank position sensor 91 Rail pressure sensor 99 In-cylinder pressure sensor 99a Sensing unit 100 ECU

-Principle of solving the problem-
The solution principle of the present invention taken to achieve the above object is that the noise component (frequency component to be removed) included in the in-cylinder pressure data acquired by the in-cylinder pressure sensor is determined from the in-cylinder pressure sensor. And the pressure change rate in the combustion chamber (including the space where the in-cylinder pressure sensor is inserted) are correlated, and filtering is performed from this distance and the pressure change rate (correlation with the combustion speed). set the frequency band (cutoff frequency), thereby, enabling the removal of the noise component.

-Solution-
Specifically, the present invention relates to the pressure of the in-cylinder pressure sensor that can detect the in-cylinder pressure, and the heat generation rate when the fuel injected from the fuel injection valve burns into the combustion chamber of the compression ignition type internal combustion engine. A heat release rate estimation device for an internal combustion engine that estimates based on a detection signal is assumed. The heat generation rate estimation device includes a combustion pressure wave transmission path acquisition unit, a combustion speed acquisition unit, and a unit for obtaining a cutoff frequency . The combustion pressure wave transmission path acquisition means includes: a cylinder head lower surface, a cylinder inner wall surface, a piston top surface, a space defined by a recess formed in the piston top surface, and the space and the in-cylinder pressure sensor the shape of the space between the sensing portion of, based on the fuel injection timing from the fuel injection valve, "fuel ignition position and the cylinder pressure sensor of the fuel in the central position of the combustion chamber at the time of combustion The length of the combustion pressure wave transmission path, which is the shortest distance to the sensing unit, is obtained . The combustion speed acquisition means acquires a “combustion speed” by the combustion of fuel in the combustion chamber. The means for obtaining the cut-off frequency is detected by the in-cylinder pressure sensor based on the length of the combustion pressure wave transmission path obtained by the combustion pressure transmission path obtaining means and the combustion speed obtained by the combustion speed obtaining means. A cut-off frequency, which is a lower limit frequency of the pressure data on the high frequency side to be excluded by filtering processing, is obtained for the obtained pressure data .

By this specific matter, it is possible to effectively remove the frequency (frequency that is the cause of noise) such as air column vibration caused by the change in the in-cylinder pressure vibrating between the in-cylinder pressure sensor and the combustion chamber. It is possible to obtain the “ cutoff frequency ”. In other words, by eliminating pressure data on the higher frequency side than this “ cut-off frequency ” (low-pass filter), it is possible to efficiently extract the combustion pressure wave caused by combustion in the combustion chamber, and the heat generation rate It is possible to accurately estimate the change in. As a result, it is possible to accurately recognize the ignition timing of the fuel in the combustion chamber.

As a more specific configuration, the combustion pressure wave transmission path acquisition means, combustion field determine the length of the combustion pressure wave transmission path from the fuel injection timing of the fuel injection valve - "combustion pressure by the cylinder pressure sensor distance map get the length "of the wave of the transmission path, the combustion speed acquiring means acquires a more" burn rate "in burning rate map for determining the combustion rate from the rotational speed and the fuel injection pressure of an internal combustion engine, the cut-off frequency means for determining, said combustion field - the length of the cylinder pressure sensor distance map obtained from the combustion pressure wave transmission path, from an acquisition combustion rate from the combustion speed map, which is detected by the cylinder pressure sensor cutoff by the cutoff frequency map for determining the cut-off frequency is a lower limit frequency of the pressure data of the high-frequency side to eliminate by filtering the pressure data And it has a configuration to get the frequency.

In the present invention, based on the "length of the transmission path of the combustion pressure wave" and "burn rate" seek "cutoff frequency", the heat generation rate from the filtering pressure data by the "cut-off frequency" I try to estimate. For this reason, the combustion pressure wave resulting from the combustion in the combustion chamber can be extracted efficiently, and the change in the heat generation rate can be accurately estimated.

FIG. 1 is a cross-sectional view illustrating a schematic configuration of a diesel engine and a control system thereof according to the embodiment. FIG. 2 is a block diagram showing a configuration of a control system such as an ECU. FIG. 3 is a cross-sectional view showing a mounting portion of the in-cylinder pressure sensor. FIG. 4 is a block diagram showing an outline of a heat generation rate calculation system. FIG. 5 is a diagram illustrating an example of a combustion field-in-cylinder pressure sensor distance map. FIG. 6 is a diagram illustrating an example of a combustion speed map. FIG. 7 is a diagram illustrating an example of a cutoff frequency map. FIG. 8 is a diagram showing an example of a heat release rate waveform obtained by performing data processing according to the present invention on in-cylinder pressure data. FIG. 9 shows an example of a heat generation rate waveform obtained by a conventional method, FIG. 9A shows a heat generation rate waveform obtained without a filter, and FIG. FIG. 9C shows the heat generation rate waveform obtained when the filter amount is larger than the appropriate amount.

Hereinafter, various maps creation procedures described comprising a cut-off frequency map configured only cut-off frequency for extracting the band required for heat generation rate estimated by the filter. The various maps are created in the order of (1) creation of a combustion field-in-cylinder pressure sensor distance map, (2) creation of a combustion speed map, and (3) creation of a cutoff frequency map.

(Creation of cutoff frequency map)
The cutoff frequency map uses the “combustion field-in-cylinder pressure sensor distance” acquired by the combustion field-in-cylinder pressure sensor distance map and the “combustion speed” acquired by the combustion speed map as parameters. 7 is a map for obtaining a “ cut-off frequency ” for performing filtering on in-cylinder pressure data acquired from the in-cylinder pressure sensor 99; This is because the noise component (frequency component to be removed) included in the in-cylinder pressure data acquired by the in-cylinder pressure sensor 99 is the distance from the combustion field to the in-cylinder pressure sensor 99 and the combustion speed in the combustion chamber 4. Is defined as a map for obtaining a “ cut-off frequency ” for removing the noise component by defining a frequency band to be filtered from the distance and the combustion speed. In other words, by eliminating the pressure data on the higher frequency side than the “ cut-off frequency ”, it is possible to efficiently extract the combustion pressure wave caused by the combustion in the combustion chamber 4.

FIG. 7 shows an example of this cutoff frequency map. According to this cutoff frequency map, the “ cutoff frequency ” is obtained based on the “distance between the combustion field and the in-cylinder pressure sensor” and the “combustion speed”. This cut-off frequency map also, have been prepared by the above-described as experimental (or simulated), - as "Combustion cylinder pressure sensor distance" is long, also as "burn rate" is high, "cut-off “ Frequency ” is set to a high frequency.

Incidentally, "Combustion - cylinder pressure sensor distance" and "burn rate" is, in the case of values between the values between which are shown in the cut-off frequency map on the "cut-off by the predetermined interpolation calculation The “ frequency ” is calculated.

On the other hand, the combustion field of timing current fuel injection - cylinder pressure sensor distance map to fit it in the "Combustion - cylinder pressure sensor distance" to get (by that combustion in the combustion pressure wave transmission path acquisition means (Acquisition of length of pressure wave transmission path) and acquisition of the "combustion speed" by applying the current engine speed and fuel injection pressure to the combustion speed map (acquisition of combustion speed by the combustion speed acquisition means) ). Then, by applying these “combustion field-in-cylinder pressure sensor distance” and “combustion speed” to the cut-off frequency map, the “ cut-off frequency ” is obtained (the cut-off frequency of the cut-off frequency by means for obtaining the cut-off frequency ). Acquisition), only the frequency band (lower frequency side than the cutoff frequency) defined by the “ cutoff frequency ” is extracted from the frequencies analyzed by the FFT.

As described above, in the present embodiment, the frequency (frequency that causes noise) such as air column vibration generated between the in-cylinder pressure sensor 99 and the combustion chamber 4 in accordance with the change in the in-cylinder pressure is effective. It is possible to obtain a “ cut-off frequency ” that can be removed, and it is possible to obtain a heat release rate waveform based on the pressure data filtered by this “ cut-off frequency ”. For this reason, the combustion pressure wave resulting from the combustion in the combustion chamber 4 can be extracted efficiently, the change in the heat generation rate can be accurately estimated, and the ignition timing of the fuel in the combustion chamber 4 Can be accurately recognized.

Furthermore, in the above-described embodiment, various maps (combustion field-in-cylinder pressure sensor distance map, combustion speed map, cutoff frequency map) are created by experiments in the engine performance experiment apparatus, and these are stored in the ROM 102 of the ECU 100. In addition, in the engine operating state on the actual machine, various map values are read from the ROM 102 and the calculation process is executed to obtain the heat release rate waveform. The present invention is not limited to this, and the cut-off frequency may be obtained by calculation from the fuel injection timing, fuel injection pressure, and engine speed, and the heat release rate waveform may be obtained by filtering processing based on the cut-off frequency . That is, the heat release rate waveform is obtained by calculation processing on an actual machine without creating a map in advance.

Claims (4)

An internal combustion engine that estimates a heat generation rate when fuel injected from a fuel injection valve burns into a combustion chamber of a compression self-ignition internal combustion engine based on a pressure detection signal of an in-cylinder pressure sensor capable of detecting the in-cylinder pressure. In an engine heat release rate estimation device,
Combustion pressure wave transmission path acquisition means for obtaining “the length of the combustion pressure wave transmission path between the combustion field and the in-cylinder pressure sensor” based on the shape of the combustion chamber and the fuel injection timing from the fuel injection valve; ,
Combustion speed acquisition means for obtaining a "combustion speed" by combustion of the air-fuel mixture in the combustion chamber;
For the pressure data detected by the in-cylinder pressure sensor based on the length of the combustion pressure wave transmission path obtained by the combustion pressure wave transmission path obtaining means and the combustion speed obtained by the combustion speed obtaining means. An apparatus for estimating a heat release rate of an internal combustion engine, comprising: a necessary minimum filter frequency obtaining means for obtaining a “required minimum filter frequency” for performing a filtering process. In the internal combustion engine heat release rate estimation apparatus according to claim 1,
An internal combustion engine heat release rate estimation device, wherein the combustion speed acquisition means is configured to obtain a combustion speed based on a rotational speed of the internal combustion engine and a fuel injection pressure. The heat release rate estimation device for an internal combustion engine according to claim 1 or 2,
The in-cylinder pressure sensor is held in a cylinder pressure sensor mounting hole formed in the cylinder head via a sensor adapter, and the sensor adapter includes an internal space of the cylinder pressure sensor mounting hole and a tip of the cylinder pressure sensor. A heat release rate estimation device for an internal combustion engine, characterized in that a pressure introduction hole is formed to communicate with a sensing unit provided in the internal combustion engine. The heat generation rate estimation device for an internal combustion engine according to claim 1, 2, or 3,
The combustion pressure wave transmission path acquisition means is configured to calculate the length of the combustion pressure wave transmission path from the fuel injection timing of the fuel injection valve based on a distance map between the combustion field and the in-cylinder pressure sensor. Get the length of the combustion pressure wave transmission path,
The combustion speed acquisition means acquires a "combustion speed" from a combustion speed map for obtaining a combustion speed from the rotational speed of the internal combustion engine and the fuel injection pressure,
The necessary minimum filter frequency acquisition means includes the in-cylinder pressure sensor based on the length of the combustion pressure wave transmission path acquired from the combustion field-in-cylinder pressure sensor distance map and the combustion speed acquired from the combustion speed map. A heat release rate estimation device for an internal combustion engine, characterized in that a required minimum filter frequency is obtained from a required minimum filter frequency map for obtaining a required minimum filter frequency for performing filtering processing on pressure data detected by .

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