JP2009270460A - Engine combustion noise reducing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an engine combustion noise reducing method for improving sound quality in combustion noise generated from an engine. <P>SOLUTION: This engine combustion noise reducing method is provided for improving the sound quality in the combustion noise for reducing the combustion noise generated from the engine 1 by a change in cylinder internal pressure caused by the combustion operation of the engine 1. A frequency band high in human acoustic sensitivity is determined based on an equal loudness curve and is set as a target frequency band while the relationship between a groove frequency becomes minimum in a frequency component of the cylinder internal pressure in a frequency spectrum of the cylinder internal pressure of the engine 1, and a combustion period of the engine 1 is determined. When operating the engine 1 in combustion, a target combustion period in which the groove frequency is included in the target frequency band is determined, and the exhaust recirculation ratio of the engine 1 is controlled so that the combustion period of the engine 1 coincides with the target combustion period. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an engine combustion noise reduction method for improving the sound quality of combustion noise in order to reduce combustion noise generated from an engine.

  In general, when components contained in engine noise are distinguished by vibration sources, the engine structure is vibrated by the combustion noise generated by the vibration of the engine structure due to combustion and the movement of mechanical parts such as gears and pistons. Can be roughly divided into machine noise. Among these, in the diesel engine, the pressure in the cylinder (cylinder pressure) is high, so the combustion noise is larger than that in the gasoline engine.

  Therefore, in the development of diesel engine products, it is necessary to improve combustion noise, and measures are taken to suppress a sudden increase in in-cylinder pressure (combustion shock), and vibration transmission characteristics in engine structures are improved.

  Conventionally, when the overall engine noise level (hereinafter referred to as OA) is reduced by combustion improvement, the maximum value of the in-cylinder pressure increase rate (dP / dtmax or dP / dθmax) is aimed at mitigating the above-described combustion impact. Representing t is time and θ is a crank angle) (see, for example, Patent Document 1).

  FIG. 21 and FIG. 22 show the effect of reducing engine noise by measures for suppressing (reducing) the maximum value of the cylinder pressure increase rate. In FIG. 21, the horizontal axis represents time, and the vertical axis represents in-cylinder pressure and in-cylinder pressure increase rate (dP / dt). In addition, the thin line indicates before countermeasures and the thick line indicates after countermeasures. In FIG. 22, the horizontal axis represents frequency, the vertical axis represents sound pressure level, the thin line indicates before countermeasures, and the thick line indicates after countermeasures.

  As shown in FIG. 22, the above-mentioned countermeasure reduces the frequency component of 1 kHz to 2 kHz, which is the main component of combustion noise, in the automobile diesel engine, so that the noise level can be effectively reduced.

Japanese Patent Laid-Open No. 9-42034

  However, as described above, even when the maximum value of the in-cylinder pressure increase rate is the same, the sound quality (subjective evaluation) of the engine sound may be different.

  FIG. 23 shows the in-cylinder pressure and the in-cylinder pressure increase rate for two engine sounds having different sound qualities. FIG. 24 shows frequency components for the engine sound of FIG.

  The maximum value of the cylinder pressure increase rate is almost the same between the thick line and the thin line in FIG. 23, but the sound quality of the thin line is better than that of the thick line. Therefore, there may be no correlation between the maximum value of the in-cylinder pressure rise rate and the sound quality, and even if the maximum value of the in-cylinder pressure rise rate is suppressed, the sound quality may not be improved. I understand. The OA of the noise level (A characteristic sound pressure level) was almost the same for the thick line and the thin line.

  Thus, focusing on improving the sound quality of the engine sound, the frequency component may be different even if the OA of the noise level (and the maximum value of the in-cylinder pressure increase rate) is the same, and in that case, the sound quality is also different. Therefore, the conventional noise reduction method for reducing the noise level and the maximum value of the in-cylinder pressure rise rate has a problem that the sound quality cannot be sufficiently improved.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an engine combustion noise reduction method that solves the above problems and improves the quality of combustion noise generated from the engine.

  In order to achieve the above object, the present invention provides an engine combustion noise reduction method for improving the sound quality of combustion noise in order to reduce combustion noise generated from the engine due to a change in in-cylinder pressure accompanying engine combustion operation. A frequency band with high human auditory sensitivity is obtained based on an equal loudness curve, and the obtained frequency band is set as a target frequency band. On the other hand, the frequency component of the cylinder pressure is minimal in the frequency spectrum of the cylinder pressure of the engine. The relationship between the groove frequency and the combustion period of the engine is obtained, and the target combustion period in which the groove frequency is included in the target frequency band is determined from the relationship between the groove frequency and the combustion period when the engine is operated for combustion. And the exhaust gas recirculation rate of the engine is controlled so that the combustion period of the engine matches the target combustion period.

  Preferably, the target frequency band is 2 kHz to 5 kHz.

Preferably, the relationship between the combustion period and the groove frequency is represented by the following formula: T = (2.59 ± 0.06) × where T is the combustion period, f _{0 is} the groove frequency, and Ne is the engine speed of the engine. 6 x Ne / f ₀
When the engine is burned, the engine speed is detected and substituted into the engine speed Ne of the above equation, and the predetermined frequency selected from the target frequency band is set to the groove frequency of the above equation. By substituting into f ₀ , the target combustion period is obtained.

  In order to achieve the above object, the present invention provides an engine combustion noise reduction method for improving the sound quality of combustion noise in order to reduce combustion noise generated from the engine due to a change in in-cylinder pressure accompanying engine combustion operation. The resonance frequency of the combustion chamber of the engine or the resonance frequency of the engine structural parts forming the combustion chamber is obtained as a target frequency. On the other hand, in the frequency spectrum of the cylinder pressure of the engine, the frequency component of the cylinder pressure is The relationship between the minimum groove frequency and the combustion period of the engine is obtained, and the target combustion period in which the groove frequency matches the target frequency based on the relationship between the groove frequency and the combustion period when the engine is operated for combustion. And the exhaust gas recirculation rate of the engine is controlled so that the combustion period of the engine matches the target combustion period. That.

  The control of the exhaust gas recirculation rate of the engine is performed when the actual combustion period of the engine is detected and the combustion period is shorter than the target combustion period in order to make the detected combustion period coincide with the target combustion period. May be performed by increasing the exhaust gas recirculation rate and decreasing the exhaust gas recirculation rate when the combustion period is longer than the target combustion period.

  According to the present invention, an excellent effect of improving the sound quality of combustion noise generated from an engine is exhibited.

  Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

  The engine combustion noise reduction method of the present embodiment is applied to, for example, a diesel engine (hereinafter referred to as an engine) mounted on a vehicle such as a truck.

  Based on FIG. 1, the schematic structure of the engine of this embodiment is demonstrated.

  As shown in FIG. 1, the engine 1 is a common rail diesel engine using electronic control, and an engine main body 2 in which a combustion chamber 21 is formed, and fuel injection for supplying fuel to the combustion chamber 21 of the engine main body 2. Device 3, intake passage 4 for supplying intake air to engine body 2, exhaust passage 5 for discharging exhaust from engine body 2, and exhaust gas recirculation device for returning a part of the exhaust of engine body 2 to the intake system (Hereinafter referred to as an EGR device) 6, a turbocharger 7, and an engine control unit (hereinafter referred to as an ECU) 8 for controlling the fuel injection device 3 and the EGR device 6.

  The engine body 2 has a plurality (four in the illustrated example) of combustion chambers 21. An in-cylinder pressure sensor 22 that detects the pressure in the combustion chamber 21 is attached to the combustion chamber 21 (in the illustrated example, it is attached only to the leftmost combustion chamber 21). The in-cylinder pressure sensor 22 is connected to the ECU 8 and outputs a detection signal (in-cylinder pressure value). As will be described in detail later, the in-cylinder pressure sensor 22 is used to refer to (detect) the actual combustion period.

  The fuel injection device 3 includes a plurality of injectors 31 that are respectively attached to the engine body 2 so as to face the combustion chambers 21, a common rail 32 in which fuel supplied to the injectors 31 is stored, and fuel to the common rail 32. And a fuel pump 33 that boosts and pumps pressure. The injector 31 is connected to the ECU 8, and command signals for controlling the fuel injection timing (start timing), the fuel injection period, and the fuel injection amount are input from the ECU 8.

  An intake manifold 41 communicating with each combustion chamber 21 is provided at the end of the intake passage 4 on the engine body 2 side. Upstream of the intake manifold 41 in the intake passage 4, the intake throttle 42 for adjusting the flow rate of intake air passing through the intake passage 4, the intercooler 43, the compressor 71 of the turbocharger 7, and the intake passage 4, in order from the intake manifold 41 side. An intake flow rate sensor 44 is provided for detecting the flow rate of the intake air passing through the inside.

  The intake throttle 42 has a throttle body 421 disposed in the intake passage 4 upstream of the branch portion of the intake manifold 41 and a throttle actuator 422 that drives the throttle body 421. The throttle body 421 is configured such that the valve opening can be continuously adjusted between fully open and fully closed. The throttle actuator 422 is connected to the ECU 8 and opens / closes the throttle body 421 based on a command signal (valve opening signal) input from the ECU 8.

  An exhaust manifold 51 communicating with each combustion chamber 21 is provided at an end of the exhaust passage 5 on the engine body 2 side, and a turbine 72 of the turbocharger 7 is provided downstream of the exhaust manifold 51.

  The EGR device 6 includes an EGR passage 61 that connects the intake passage 4 and the exhaust passage 5, an EGR valve 62 that adjusts the flow rate of EGR gas (exhaust gas) that flows through the EGR passage 61, And an EGR cooler 63 for cooling the EGR gas. In the illustrated example, one end (upstream end) of the EGR passage 61 is connected to the exhaust manifold 51 and the other end (downstream end) is connected to the intake manifold 41.

  The EGR valve 62 includes a valve body 621 that is provided in the exhaust manifold 51 and opens and closes the downstream end of the EGR passage 61, and a valve actuator 622 that drives the valve body 621. The valve body 621 is configured such that the valve opening can be continuously adjusted between fully open and fully closed. The valve actuator 622 is connected to the ECU 8 and opens and closes the valve body 621 based on a command signal (valve opening signal) input from the ECU 8.

  The ECU 8 is connected to various sensors such as the in-cylinder pressure sensor 22, the intake flow rate sensor 44, the accelerator sensor 23, the engine rotation sensor 24, and a common rail pressure sensor (not shown) that detects the fluid pressure in the common rail 32. , Detection signals from these sensors are input.

  The ECU 8 is connected to various actuators such as the injector 31, the throttle actuator 422 of the intake throttle 42, the valve actuator 622 of the EGR valve 62, and the SVC (not shown) for adjusting the discharge pressure of the fuel pump 33, and these actuators. A command signal is output to.

  The fuel injection device 3 (injector 31, common rail 32, fuel pump 33), EGR valve 62, and intake throttle 42 are controlled by a command from the ECU 8, and the combustion state of the engine body 2 is controlled.

  As will be described in detail later, the ECU 8 adjusts the combustion period of the initial combustion part in normal diesel combustion or the combustion period in PCI combustion in order to improve the sound quality of combustion noise. Note that PCI combustion refers to a combustion mode in which fuel injected into the combustion chamber 21 ignites after a premixing period.

  Specifically, the combustion period is adjusted by the EGR rate (EGR amount and / or intake air amount), and adjustment of the EGR amount and / or intake air amount is performed by adjusting the opening degrees of the EGR valve 62 and the intake throttle 42. . These electronic control parameters (the valve opening degrees of the EGR valve 62 and the intake throttle 42) are determined by calculation in the ECU 8.

  Next, the engine combustion noise reduction method of this embodiment will be described.

  The engine combustion noise reduction method of the present embodiment improves the quality of combustion noise so as to reduce the combustion noise generated from the engine 1 due to the change in the in-cylinder pressure accompanying the combustion operation of the engine 1.

  First, in the engine combustion noise reduction method, before operating the engine 1, a frequency band with high auditory sensitivity is obtained in advance based on an equal loudness curve (according to ISO 226: 2003) and set as a target frequency band. Although described later in detail, the target frequency band is 2 kHz to 5 kHz. In addition, the relationship between the groove frequency at which the frequency component of the in-cylinder pressure is minimized in the frequency spectrum of the in-cylinder pressure of the engine 1 (hereinafter referred to as the in-cylinder pressure spectrum) and the combustion period of the engine 1 is shown by simulation and experiment. Ask.

  Next, when the engine 1 is in a combustion operation, the ECU 8 obtains a target combustion period in which the groove frequency is included in the target frequency band 2 kHz to 5 kHz from the relationship between the groove frequency and the combustion period, and the engine 1 is in the target combustion period. The EGR rate of the engine 1 is controlled so that the combustion periods coincide.

  The EGR rate of the engine 1 is controlled by detecting an actual combustion period (hereinafter referred to as an actual combustion period) of the engine 1 by the in-cylinder pressure sensor 22 and matching the detected actual combustion period with the target combustion period by the ECU 8. Therefore, the EGR rate is increased when the actual combustion period is shorter than the target combustion period, and the EGR rate is decreased when the actual combustion period is longer than the target combustion period.

  As a result, in the present embodiment, in the electronically controlled diesel engine 1 described above, the combustion state of the engine 1 is controlled by adapting the EGR rate (that is, the EGR amount and / or the intake air amount) that is a control parameter. By adjusting the initial combustion part in diesel combustion or the combustion period in PCI combustion, the frequency component of in-cylinder pressure that is the excitation source of combustion noise has a frequency band of 2k to 5kHz that is highly sensitive in the equal loudness curve Can be reduced, and the engine sound quality can be improved.

  This point will be described in detail below.

  First, the target frequency band 2 kHz to 5 kHz will be described with reference to FIGS. 3 to 5.

  In order to improve the sound quality, an evaluation index capable of quantitatively evaluating the sound quality is required in addition to the noise level, and an evaluation based on a psychoacoustic evaluation amount such as loudness and sharpness is considered necessary.

  Among the psychoacoustic evaluation amounts, the loudness level representing the “volume” of the sound is an important evaluation amount used as a basis for calculating other psychoacoustic evaluation amounts.

  FIG. 3 shows a comparison of an equal loudness curve (equal loudness level curve) used for calculating the loudness level and an auditory correction (A characteristic according to JIS C1505-1988) used for calculating the noise level.

  The thick line in FIG. 3 is an example of an equal loudness curve standardized by ISO 226: 2003 (when a 1 kHz sound is 40 dB), and is an equal loudness curve with a loudness level of 40 phon.

  The equal loudness curve is a characteristic that reproduces the frequency characteristics of human hearing, and is a contour line that connects sound pressure levels at which the “volume” of the sound for each frequency sounds the same. The equal loudness curve is a characteristic in which a sound pressure level (dB value measured by a machine) that humans feel that the “volume” of the sound is the same is examined and plotted for each frequency. For example, in FIG. 3, since it feels the same volume as a sound of 40 dB at 1 kHz, at 3 Hz, it becomes 36 dB which is smaller than 40 dB. The graph of FIG. 3 shows that a person with a smaller dB value is more audible.

  The thin line in FIG. 3 is a curve related to the A characteristic. The A characteristic was determined based on an equal loudness curve, but the detailed frequency characteristic has not been reproduced, and there is a clear difference between 1 and 5 kHz, which is important for diesel engine 1 noise. The A characteristic is created on the basis of an equal loudness curve, but is simplified in consideration of simulation in an electronic circuit. There is a difference between the A characteristic and the equal loudness curve at 1 to 16 kHz, and the equal loudness curve is a more complex curve that expresses hearing in more detail than the A characteristic.

  Furthermore, according to the equal loudness curve, it can be seen that the dB value is small in the frequency band of 2 k to 5 kHz, and this frequency band is sensitive to human hearing. Therefore, sound quality can be improved by reducing the frequency components of the sensitive frequency band 2k to 5 kHz in the combustion noise of the engine 1.

  A method for quantitatively evaluating the “volume” of the sound in consideration of such frequency sensitivity characteristics is the loudness level (ISO 532B) shown in FIGS. The loudness level is roughly considered to be a characteristic obtained by subtracting the numerical value of the equal loudness curve for each frequency band from the frequency analysis result (dB value) of the sound (the amount to be subtracted as the frequency band has a smaller dB value of the equal loudness curve). Because it is small, the numerical value (influence) becomes large).

  FIG. 4 shows a loudness spectrum for two engine sounds having different sound qualities, with a fine line indicating a good sound quality and a thick line indicating a bad sound. The left graph of FIG. 5 shows the OA of the noise level for the two engine sounds of FIG. 4, and the right graph shows the total loudness (the total value of the loudness spectrum).

  As shown in FIGS. 4 and 5, the inventors of the present invention evaluated the two engine sounds having the same noise level (A characteristic sound pressure level) but different sound quality by subjective evaluation using the loudness level. Differences in sound quality were also detected with respect to the levels (loudness spectrum and total loudness), and it was found that the evaluation based on the loudness level gave a result consistent with the qualitative tendency in the subjective evaluation (listening comparison).

  From the above, improvement of the sound quality is one of the effective means for improving the loudness level, and it is effective to reduce the component of the frequency band 2k to 5 kHz having high sensitivity (small numerical value) in the equal loudness curve. It can be said that there is.

  Therefore, in this embodiment, the frequency band 2k to 5 kHz is set as the target frequency band.

  Next, the target frequency band 2k to 5 kHz and the in-cylinder pressure will be described with reference to FIGS.

  As described above, since the excitation source (cause) of the combustion noise of the engine 1 is mainly the in-cylinder pressure, in order to reduce the combustion noise in the target frequency band 2k to 5 kHz, basically the in-cylinder pressure What is necessary is just to reduce the frequency component of 2 to 5 kHz.

  Accordingly, the inventors of the present application have conducted a numerical simulation shown in FIGS. 6 to 9 and studied a method for reducing the frequency component of 2 k to 5 kHz of the in-cylinder pressure.

  In the numerical simulations of FIGS. 6 to 9, the heat generation rate is expressed by a Wiebe function, and the heat generation period in the expression is defined as a combustion period. In addition, since the relationship between the heat generation rate, pressure, and volume is defined by the first law of thermodynamics, the in-cylinder pressure was calculated from the heat generation rate. In FIG. 10, the combustion period is defined as a pressure increase period due to combustion (see reference symbol T in FIG. 10) other than the pressure change due to compression at the rate of increase dP / dθ in the cylinder.

  FIG. 6 shows the case where the in-cylinder pressure waveform is calculated by changing the maximum value dp / dθmax (hereinafter referred to as the maximum increase rate) of the in-cylinder pressure increase rate with a constant combustion period. Is what we asked for. FIG. 7 shows the frequency component of the in-cylinder pressure (in-cylinder pressure spectrum) obtained by Fourier transforming the in-cylinder pressure waveform calculated in FIG.

  8 and 9 show the in-cylinder pressure increase rate (dP / dθ) and the in-cylinder pressure spectrum in the same manner as in FIG. 6 and FIG. 7 when the maximum increase rate dp / dθmax is constant and the combustion period is changed. Each is what I have found.

  Since the frequency f [Hz] is the reciprocal of time [Hz] = [1 / s], the frequency increases as the variation time (cycle) decreases. In the engine 1, when the combustion period is shortened, the rate of increase of the in-cylinder pressure increases, and the in-cylinder pressure spectrum obtained by Fourier transforming the in-cylinder pressure includes a high frequency component.

  Here, when the in-cylinder pressure waveform is a time function g (t), the Fourier transform G (f) is a frequency function including a trigonometric function. Since the trigonometric function is a periodic function, it takes a numerical value between -1 and 1, and its square repeats periodically between 0 and 1. Since the in-cylinder pressure waveform g (t) cannot be mathematically expressed, G (f) cannot also be mathematically expressed. However, due to the nature of Fourier transform, a trigonometric function is included, and it is considered that the increase / decrease is repeated periodically. Therefore, increase / decrease (crests and grooves) appear in the frequency data (in-cylinder pressure spectrum) after Fourier transform.

In the illustrated example, as shown in FIGS. 7 and 9, the in-cylinder pressure spectrum includes at least one groove frequency (hereinafter referred to as a groove frequency) f ₀ at which the in-cylinder pressure is minimized.

  As shown in FIG. 9, the groove frequency shifts to the low frequency side when the combustion period is lengthened, and shifts to the high frequency side when the combustion period is shortened. Therefore, even if the maximum increase rate dP / dθmax is the same, in FIG. 9, the groove frequency is shifted to the low frequency side by shifting the groove frequency to the target frequency band (target frequency band) of 2 k to 5 kHz. It was found that it can be reduced.

  That is, the frequency component of the target frequency band 2k to 5 kHz can be effectively reduced by matching the groove frequency with the target frequency band 2k to 5 kHz by adjusting the combustion period.

  Next, the relationship between the combustion period and the groove frequency will be described with reference to FIGS.

  11 to 12 show the relationship between the combustion period and the frequency component of in-cylinder pressure by numerical simulation. In the numerical simulations of FIGS. 11 to 12, the same analysis model as that of the numerical simulations of FIGS. 6 to 9 was used.

  FIG. 11 shows the relationship between the in-cylinder pressure and the crank angle. FIG. 12 shows the relationship between the in-cylinder pressure increase rate obtained by differentiating the in-cylinder pressure with respect to the crank angle (time) and the crank angle. FIG. 13 shows an in-cylinder pressure spectrum obtained by Fourier transform of the in-cylinder pressure.

  In the numerical simulations of FIGS. 11 to 13, the combustion period is changed with the total heat generation amount (fuel injection amount) due to combustion being constant. Therefore, as shown in FIGS. 12 and 13, both the combustion period and the maximum rate of increase dP / dθ change, but as described above, the change in the target frequency band 2k to 5 kHz of the in-cylinder pressure spectrum is The influence of the burning period is strong.

  In FIG. 13, the groove frequency is a frequency corresponding to the first groove (the groove on the lowest frequency side) in the in-cylinder pressure spectrum. The groove frequency was found to have the following relationship with the combustion period and engine speed in the numerical simulation.

The groove frequency f ₀ obtained from the in-cylinder pressure spectrum after Fourier transform and the reciprocal of the numerical value obtained by converting the combustion period T [degCA] into time [s] (referred to as 6 · Ne / T, combustion frequency) [1 / s] = [Hz], the relationship shown in FIG. 14 was obtained.

According to the graph of FIG. 14, the relationship between the combustion frequency (6 · Ne / T) and the groove frequency f ₀ is expressed by the approximate expression (1).

f ₀ = (2.59 ± 3σ) × (6 × Ne / T) (1)
Here, σ is a standard deviation, and 3σ = 0.06.

Thus, in the in-cylinder pressure spectrum, the frequency f ₀ [Hz] (groove frequency) at which the frequency component sharply decreases and the groove is formed is assumed that the combustion period is T [degCA] and the engine speed is Ne [rpm]. And represented by the above formula (1).

When this equation (1) is rewritten with respect to the combustion period T, a relational expression between the combustion period T and the groove frequency f ₀ is given by the following equation (2) using the rotational speed Ne of the engine 1 as a parameter.

T = (2.59 ± 0.06) × 6 Ne / f ₀ (2)
Next, a method for determining the target combustion period using these equations (1) or (2) will be described.

  In this embodiment, the target combustion period with respect to the groove frequency, which is set according to the engine speed, is determined by Equation (1). By setting the target groove frequency to 2 kHz basically, the frequency component of the cylinder pressure higher than that can be reduced, and the frequency component of 2 k to 5 kHz can be reduced.

In other words, the target combustion period is obtained by substituting the actual engine speed for the speed Ne in the equation (2), and at the predetermined frequency selected from the target frequency band for the groove frequency f ₀ (in the present embodiment, as described above). To 2 kHz).

  Next, an example of the control logic according to the engine combustion noise reduction method of the present embodiment will be described based on FIG.

  FIG. 2 shows a control logic of ECU calculation for determining the combustion period. This control logic is executed by the ECU 8 during the combustion operation of the engine 1, for example.

  As shown in FIG. 2, the ECU 8 obtains the target combustion period determined by the equation (2) according to the engine speed, and the actual combustion period (hereinafter referred to as the actual combustion period) coincides with the target combustion period. Thus, the EGR rate (EGR amount and / or intake air amount) determined by the fuel injection amount is controlled. In the control of the combustion period, the ECU 8 of the present embodiment calculates the actual combustion period from dP / dθ obtained by differentiating the output of the in-cylinder pressure sensor 22 and uses it as a reference signal for control.

  More specifically, first, the engine speed sensor 24 detects the actual engine speed and outputs it to the ECU 8. The ECU 8 sets the target based on the engine speed from the engine speed sensor 24 and the above equation (2). Find the burning period. Expression (2) is stored in the ECU 8 as a mathematical expression (program) or as a map (data) with the engine speed as a parameter.

  The in-cylinder pressure sensor 22 detects the actual in-cylinder pressure and outputs the detected in-cylinder pressure to the ECU 8. The ECU 8 obtains the actual combustion period based on the in-cylinder pressure from the in-cylinder pressure sensor 22. For example, the ECU 8 obtains the actual combustion period as shown in FIG. 10 based on the in-cylinder pressure increase rate calculated from the detected in-cylinder pressure.

  Next, the ECU 8 obtains a target EGR amount and / or a target intake air amount such that the actual combustion period matches the target combustion period based on the target combustion period and the actual combustion period, and the target EGR amount and / or Alternatively, the EGR valve opening and the intake throttle opening are controlled based on the target intake air amount.

  For example, the ECU 8 corrects the EGR amount and / or the intake air amount obtained from the fuel injection amount with a correction value obtained from the difference between the actual combustion period and the target combustion period, and the target EGR amount and / or the target intake air. Find the air volume. The fuel injection amount is calculated by the ECU 8 from the accelerator opening and the engine speed.

  When the actual combustion period coincides with the target combustion period by the above control, the actual groove frequency in the in-cylinder pressure spectrum becomes 2 kHz, and the frequency component of 2 k to 5 kHz in the in-cylinder pressure is reduced.

  As a result, according to the present embodiment, the in-cylinder pressure and the frequency components of combustion noise generated by the in-cylinder pressure in the frequency band of 2 k to 5 kHz where the sensitivity of hearing is high can be reduced. Can improve the sound quality of combustion noise.

  As described above, the inventors of the present application have different sound quality when the frequency component is different even if the maximum value of the cylinder pressure increase rate dP / dθ and the OA of the noise level are the same (see FIGS. 4 and 5), and 2k. The reduction of the frequency component of ˜5 kHz is found to be effective for improving sound quality, and the relationship between the frequency component of combustion noise (in-cylinder pressure) and the combustion period is expressed by equation (1) or equation (2). The sound quality was improved by aggressive control of the combustion period.

  Next, the evaluation experiment result of the engine combustion noise reduction method of this embodiment will be described with reference to FIGS. 15 and 16.

  In the experiment, the actual engine 1 was used to confirm the effect of improving the loudness level by changing the combustion period. Table 1 shows the specifications of the engine 1 used.

The engine rotation speed was 1500 rpm, the fuel injection amount was 15 mm ³ / stroke, and the combustion period of PCI combustion was changed.

  FIG. 15 shows the measurement results of the loudness level for the combustion periods A to E, and the horizontal axis represents the combustion period [deg. CA], and the vertical axis is the loudness level [phon]. FIG. 16 shows measurement results of dynamo torque for each combustion period A to E, and the vertical axis represents dynamo torque [Nm]. 15 and 16, the groove frequencies corresponding to the combustion periods A to E are shown in Table 2.

  As shown in FIG. 15, it was confirmed that the loudness level was improved by extending the combustion period. Further, as shown in FIG. 16, it was confirmed that there was almost no change in the output torque of the engine 1 even if the combustion period was changed.

  In addition, this invention is not limited to the above-mentioned embodiment, Various modifications and application examples can be considered.

  For example, in the above-described embodiment, the target frequency is appropriately selected from the frequency band with high human auditory sensitivity based on the equal loudness curve. However, the present invention is not limited to this, and the target frequency is the resonance frequency of the combustion chamber 21 or the cylinder block. The resonance frequency of engine structural parts such as

  More specifically, as shown in FIG. 13, peaks and grooves appear in the frequency analysis result of the in-cylinder pressure. As an applied method for determining the combustion period, when aiming to reduce the resonance frequency of the combustion chamber 21 and the resonance frequency of engine structural parts (cylinder block, etc.), the groove frequency with a low in-cylinder pressure level is selected as the resonance frequency. It is effective to match the resonance frequency.

Further, since the level once rises (becomes a crest) at a frequency higher than the groove frequency, when the crest matches the frequency of the resonance or the resonance phenomenon, the excitation force that excites them becomes larger than f _0. End up. Aiming to reduce in-cylinder pressure at a specific frequency (resonance frequency, resonance frequency), so that the frequency at which the sound pressure level increases once at a frequency slightly higher than the groove frequency does not coincide with the resonance frequency or resonance frequency aimed at reduction. By setting the groove frequency of equation (2) (setting the target combustion period), effective sound quality improvement can be achieved.

  Another embodiment will be described based on FIGS. 17 and 18.

  This embodiment is different from the above-described embodiment in that the resonance frequency of the combustion chamber is a target frequency.

  A resonance phenomenon occurs in a space having a volume such as a combustion chamber. In this resonance, a resonance mode that is a distribution of a high sound pressure portion and a low sound pressure portion is determined by the size of the space.

  FIG. 17 shows the lowest frequency (low order) mode shape among resonance modes generated in the combustion chamber space (including the gap between the piston upper surface and the cylinder head lower surface) of the engine. In FIG. 17, a portion where the sound pressure is high and a portion where the sound pressure is low are distributed in the left-right direction on the paper. The resonance frequency was determined by the size of the space and the density of the fluid (gas) filling the space, and was calculated to be 4885 Hz.

  FIG. 18 shows the result of frequency analysis after measuring the pressure in the combustion chamber (cylinder pressure). Here, when resonance occurs, the pressure at that frequency increases, so a resonance peak is observed in the measurement result. When a pressure peak due to resonance occurs in the combustion chamber, the engine is vibrated at the frequency of the peak and noise is generated.

  17 and 18 show that a peak occurs at a specific frequency in the in-cylinder pressure, which is an excitation source of combustion noise, and an example of an analysis result in which the cause is resonance of the combustion chamber due to the coincidence of resonance frequencies. Is shown.

  The engine combustion noise reduction method according to the present embodiment obtains the resonance frequency of the combustion chamber 21 of the engine 1 as a target frequency, and on the other hand, the groove frequency at which the frequency component of the in-cylinder pressure is minimized in the frequency spectrum of the in-cylinder pressure of the engine. The combustion period of the engine 1 is determined, and when the engine 1 is burned, the target combustion period in which the groove frequency matches the target frequency is determined from the relationship between the groove frequency and the combustion period. The exhaust gas recirculation rate of the engine 1 is controlled so as to coincide with the target combustion period.

  As shown in FIG. 18, the resonance frequency of the combustion chamber 21 of the engine 1 is measured in advance by experiments or the like.

  In this embodiment, resonance of the combustion chamber 21 due to fluctuations in the in-cylinder pressure can be suppressed, thereby improving the quality of combustion noise.

  Another embodiment will be described based on FIGS. 19 and 20.

  This embodiment is different from the above-described embodiment in that the resonance frequency of the engine structural component in the combustion noise transmission path is set as a target frequency.

  FIG. 19 is a schematic configuration diagram of the engine body 2. In the engine body 2, 23 is a cylinder head, 24 is a cylinder block, 25 is a piston, 26 is a connecting rod, 27 is a crankshaft, and 28 is an oil pan.

  FIG. 20 shows transfer characteristics in the combustion noise transmission path in the engine main body 2 of FIG. 19, where the vertical axis represents the transfer function (mobility) and the horizontal axis represents the frequency.

The transfer function (mobility) is defined by vibration velocity V [m / s ² ] / excitation force F [N]. In the present embodiment, the target engine structural component is the cylinder block 24, the excitation force (in-cylinder pressure) is measured (or calculated) in the combustion chamber 21, and the vibration speed is at the lower end of the cylinder block 24. Measured (or calculated). The target engine structural component is not limited to the cylinder block 24 but may be the cylinder head 23 or the like.

  In the engine combustion noise reduction method of the present embodiment, the resonance frequency of the cylinder block 24 forming the combustion chamber 21 of the engine 1 is obtained as a target frequency, and on the other hand, the frequency component of the cylinder pressure in the frequency spectrum of the cylinder pressure of the engine. The relationship between the groove frequency at which the groove is minimized and the combustion period of the engine 1 is obtained, and when the engine 1 is burned, the target combustion period in which the groove frequency matches the target frequency is obtained from the relationship between the groove frequency and the combustion period. The exhaust gas recirculation rate of the engine 1 is controlled so that the combustion period of the engine coincides with the target combustion period.

  As shown in FIG. 20, the resonance frequency of the cylinder block 24 is obtained in advance by experiments or numerical simulations.

  In the present embodiment, resonance of the cylinder block 24 due to fluctuations in the in-cylinder pressure can be suppressed, thereby improving the quality of combustion noise.

FIG. 1 is a schematic configuration diagram of an engine targeted by an engine combustion noise reduction method according to an embodiment of the present invention. FIG. 2 is an example of a control block of the engine combustion noise reduction method according to the present embodiment. FIG. 3 is a diagram comparing the A characteristic and the equal loudness curve. FIG. 4 is a diagram comparing the loudness spectra of two engine sounds having different sound quality. FIG. 5 is a diagram comparing the noise level OA and the total loudness for the two engine sounds of FIG. FIG. 6 is a graph showing the relationship between the increase rate of the in-cylinder pressure and the crank angle when the combustion period is constant and the maximum value of the increase rate of the in-cylinder pressure is changed. FIG. 7 is a graph showing a frequency spectrum of the in-cylinder pressure in FIG. FIG. 8 is a graph showing the relationship between the increase rate of the in-cylinder pressure and the crank angle when the maximum value of the increase rate of the in-cylinder pressure is constant and the combustion period is changed. FIG. 9 is a graph showing the frequency spectrum of the in-cylinder pressure in FIG. FIG. 10 is a diagram for explaining the definition of the combustion period. FIG. 11 is a graph showing the relationship between the combustion period and the in-cylinder pressure. FIG. 12 is a graph showing the relationship between the combustion period and the in-cylinder pressure increase rate. FIG. 13 is a graph showing the relationship between the combustion period and the in-cylinder pressure spectrum (frequency spectrum of the in-cylinder pressure). FIG. 14 is a graph showing the relationship between the groove frequency, the combustion period, and the engine speed. FIG. 15 is a diagram for explaining the effect of improving the loudness level with respect to the combustion period by the engine combustion noise reduction method according to the present embodiment, and shows experimental results. FIG. 16 is a diagram for explaining the influence on the torque with respect to the combustion period by the engine combustion noise reduction method according to the present embodiment. FIG. 17 is a diagram for explaining the resonance of the combustion chamber, and shows the analysis result of the resonance mode. FIG. 18 is a diagram for explaining resonance in the combustion chamber, and shows an in-cylinder pressure spectrum (frequency spectrum of in-cylinder pressure). FIG. 19 is a schematic configuration diagram of engine structural components in the combustion noise transmission path. FIG. 20 is a diagram for explaining the transmission characteristics in the combustion noise transmission path. FIG. 21 is a diagram for explaining the noise reduction effect due to the reduction of the maximum value of the cylinder pressure increase rate according to the conventional noise reduction method, and the cylinder pressure and cylinder pressure increase rate for two different engine sounds. The result of comparing with the maximum value of is shown. FIG. 22 shows the result of comparing engine noise levels in FIG. FIG. 23 is a diagram for explaining an example in which the maximum value of the in-cylinder pressure increase rate and the OA of the noise level are the same and the sound quality is different. For the two engine sounds having different sound qualities, the in-cylinder pressure and the in-cylinder pressure increase are illustrated. The result of comparing with the maximum value of the rate is shown. FIG. 24 shows the result of comparing engine noise levels in FIG.

Explanation of symbols

8 ECU (Engine Control Unit)
6 EGR device (exhaust gas recirculation device)
22 In-cylinder pressure sensor 23 Accelerator opening sensor 24 Engine rotation sensor 42 Intake throttle 62 EGR valve

Claims (5)

In the engine combustion noise reduction method for improving the sound quality of the combustion noise in order to reduce the combustion noise generated from the engine due to a change in in-cylinder pressure accompanying the combustion operation of the engine,
Based on the equal loudness curve, a frequency band with high human auditory sensitivity is obtained, and the obtained frequency band is set as a target frequency band.
On the other hand, in the frequency spectrum of the in-cylinder pressure of the engine, a relationship between the groove frequency at which the frequency component of the in-cylinder pressure is minimized and the combustion period of the engine is obtained.
When burning the engine,
From the relationship between the groove frequency and the combustion period, the target combustion period in which the groove frequency is included in the target frequency band is obtained,
An engine combustion noise reduction method characterized by controlling an exhaust gas recirculation rate of the engine so that a combustion period of the engine coincides with the target combustion period.   The engine combustion noise reduction method according to claim 1, wherein the target frequency band is 2 kHz to 5 kHz. The relationship between the combustion period and the groove frequency is as follows: T = (2.59 ± 0.06) × 6 × Ne, where T is the combustion period, f _{0 is} the groove frequency, and Ne is the engine speed of the engine. / F ₀
Sought in
When burning the engine,
The engine speed is detected and substituted for the engine speed Ne of the above formula, and a predetermined frequency selected from the target frequency band is substituted for the groove frequency f _{0 of the} formula, and the target combustion period is calculated. The engine combustion noise reduction method according to claim 1 or 2. In the engine combustion noise reduction method for improving the sound quality of the combustion noise in order to reduce the combustion noise generated from the engine due to a change in in-cylinder pressure accompanying the combustion operation of the engine,
The resonance frequency of the combustion chamber of the engine or the resonance frequency of engine structural parts forming the combustion chamber is determined as a target frequency,
On the other hand, in the frequency spectrum of the in-cylinder pressure of the engine, a relationship between the groove frequency at which the frequency component of the in-cylinder pressure is minimized and the combustion period of the engine is obtained.
When burning the engine,
From the relationship between the groove frequency and the combustion period, obtain a target combustion period in which the groove frequency matches the target frequency,
An engine combustion noise reduction method characterized by controlling an exhaust gas recirculation rate of the engine so that a combustion period of the engine coincides with the target combustion period. Control of the exhaust gas recirculation rate of the engine
In order to detect the actual combustion period of the engine and to make the detected combustion period coincide with the target combustion period, when the combustion period is shorter than the target combustion period, the exhaust gas recirculation rate is increased, The engine combustion noise reduction method according to any one of claims 1 to 4, wherein the exhaust gas recirculation rate is decreased when the combustion period is longer than the target combustion period.

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