JPH0758059B2 - Noise reduction device for multi-cylinder engine - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a noise suppression device for a multi-cylinder engine, and more particularly to a noise suppression device during acceleration.

(Prior Art) When a vehicle accelerates, unpleasant noise (hereinafter, referred to as “gurgling noise”) may occur, which may impair the feeling of acceleration, and it is a major issue to improve it. There is. This is because various noise deterioration factors are included in acceleration noise, and there are many unclear points regarding the physical characteristics that characterize these factors and their relationship with specific vibration phenomena.

For this reason, there are some that analyze the sound quality of Goro sound from the aspect of sound quality (see Nissan Technical Report Collection 1986, "Analysis of Effect of Power Plant Vibration on Sound Quality in Vehicle During Acceleration").

To explain this, Fig. 11 shows an example of measuring the frequency characteristics of the front seat noise of an FF 4-cylinder vehicle (displacement 1800cc class) with a pronounced gull noise (third gear position at full load constant rotation (3000 rpm)). According to the figure, there is a high-level band that is thought to be due to some resonance in the region of 200 to 500 Hz centered on 300 Hz, and the (n ± 0.5) -order component (n ± 0.5) such as 4.5 and 5.5 is present. Natural number) is high.

By the way, in the Goro sound, three adjacent engine rotations of 0.5th order
It is known that the ingredients are related. Therefore, in order to quantitatively grasp the gurgling sound, a synthesized sound having a frequency structure shown in FIG. 12 was made and a feeling evaluation experiment was conducted.
± 0.5) If the level difference between the nth order component and the nth order component is large (in the case shown in the upper part), there is no gurgling noise, but as shown in the lower part, there is a gurgling noise in the specified value (within 3-5 dB). Was revealed. In other words, it means that the feature of the spectral structure for the jumbled sound is extracted.

Next, in order to elucidate the specific vibration phenomenon that characterizes this spectral structure, we conducted an experiment on an actual power plant (engine).
It was confirmed that it was caused by the vibration phenomenon of the power plant. From this, the (n ± 0.5) -order component that affects the noise is a harmonic of the 0.5th-order component of the engine rotation, and the relative increase is due to the phenomenon that occurs once every two revolutions. Conceivable.

Therefore, it is presumed that the phenomenon is caused by either the combustion excitation force itself in each cylinder, or the difference in the vibration response of the power plant to it, but in conclusion it is the latter, that is, It is concluded that the vibration response of the crankshaft to the combustion exciting force of the cylinders is significantly different, and a large vibration is generated especially when the cylinder close to the flywheel (the last cylinder) is burned. This is because heavy objects such as flywheels and clutches are added to the rear end of the crankshaft. It is also clear from the fact that vibrations of much greater amplitude are observed than after the explosion of the other cylinders. The thirteenth
The figure is for a full load constant rotation (2000 rpm).

It can be said that the results of these analyzes reveal that the resonance phenomenon of the crankshaft is the main factor that causes the noise, and in this paper, the method of mounting the bearing beam and increasing the bulkhead thickness are used. It has been confirmed that by improving the support rigidity of the crankshaft, the noise can be improved. This is because the vibration of the crankshaft
In addition to the rigidity of the crankshaft itself, the supporting rigidity of the cylinder block plays an important role. (Problems to be solved by the invention) By the way, in such a device, if the supporting rigidity of the cylinder block is improved. I point out that it is good, but other improvement measures can be considered based on the analysis results.

For example, as a means of reducing the vibration of the crankshaft itself, (i) the resonance frequency of the crankshaft is removed from the sound generation region (200 to 500 Hz), (ii) the crankshaft vibration response to the combustion exciting force of the fourth cylinder. The combustion excitation force is suppressed so that the temperature becomes equal to or lower than the gurgling sound generation region.

Here, the vibration of the crankshaft is due to the fact that there is a bending vibration mode in which the fourth cylinder and the crankpin are antinodes (however, accompanied by surface runout vibration of the flywheel) in the vicinity of 300 Hz. , 1987 is one that reduces the resonance frequency by flexibly attaching the flywheel to the crankshaft.
It was announced at the year's motor show. This is a concrete measure for (i).

On the other hand, the present application proposes a measure for (ii), that is, an attempt to improve the noise caused by engine control. In a multi-cylinder engine, the air-fuel mixture is evenly distributed to each cylinder in order to obtain uniform combustion in each cylinder, and the ignition timing is often the same for all cylinders (Actual No. 59-100973). This is because the present situation is that the combustion control for improving the noise is not performed.

The present invention has been made in view of such a conventional problem, and provides a device that suppresses the combustion excitation force of only the cylinder closest to the flywheel under the condition that the noise is generated during acceleration. The purpose is to do.

(Means for Solving Problems) As shown in FIG. 1, the present invention is a means for controlling combustion pressure in an engine cylinder (for example, ignition timing control means or intake air amount control means) 1 and engine vibration (for example, A sensor (vibration accelerometer or displacement meter) 2 that detects vibrations of the engine mount bracket and surface wobbling displacement of the flywheel, etc., and it is determined based on the detected engine vibrations whether or not the condition is such that a thump sound is generated. Means 3 and means 4 for instructing the combustion pressure control means 1 to reduce the combustion pressure of the cylinder closest to the flywheel (4th cylinder in a 4-cylinder engine) when this condition is determined are provided. . Reference numeral 5 is a means for determining whether or not the cylinder is the closest to the flywheel.

(Operation) According to the combustion pressure control of the engine, each cylinder is ignited at the same ignition timing, and the same amount of intake air is distributed and supplied to each cylinder.

On the other hand, when it is determined by the detection of the engine vibration that the condition is to generate a noise, the ignition timing of the cylinder closest to the flywheel is delayed or the intake air amount is throttled more than other cylinders. . For this reason, combustion is delayed in the cylinder, and the peak value of the combustion pressure, that is, the combustion excitation force is reduced, and the vibration of the crankshaft that causes a rattling noise during acceleration is reduced. It

(Embodiment) FIG. 2 is an embodiment in which the present invention is applied to an electronically controlled in-line four-cylinder engine, and FIG. 2 shows a system diagram of an ignition timing control system. Here, in the four-cylinder engine, the cylinder closest to the flywheel is the rearmost cylinder, the fourth cylinder.

Reference numeral 13 is a crank angle sensor that outputs a signal for each unit angle of the crank angle and a signal for each reference position. The engine speed (N) is measured from the signal for each unit angle, and is the fourth from the signal for each reference position. It is determined whether or not it is a cylinder.
Reference numeral 14 is a sensor that outputs according to the suction negative pressure (P), and P and N are parameters for determining a common ignition timing for each air.

On the other hand, a vibration accelerometer 15 for detecting engine vibration is attached to an engine mount bracket 12 for connecting the engine body 11 to the vehicle body, and a signal from the accelerometer 15 is input to a frequency analyzer 16.

The control unit 18 to which the signals from the analyzer 16 and the operating condition signals (N and P) are input performs the operations shown in FIGS. 3 and 4 based on these signals to output the ignition timing (ignition timing). (Advance value) is determined, and an ignition signal corresponding to the ignition advance value is generated and output to the ignition device 19. The control unit 18 is mainly an I / 0, CPU and storage device (ROM or RAM).
It is composed of a microcomputer consisting of.

FIG. 3 is a program for setting the ignition advance value (Θ) for each cylinder. The operating condition signals at that time, that is, N and P are read, and the basic ignition advance value (Θ ₀ ) is calculated according to these detected values. To do. For example, Θ ₀ with N and P as parameters
The table is stored in the ROM and read out by table lookup according to N and P at that time (steps 21 to 23). Note that Θ ₀ is set as a common value so that the same combustion state can be obtained in each cylinder.

Now, in order to reduce the combustion exciting force of the fourth cylinder, it is necessary to retard the ignition timing so that the combustion is delayed.
Here, we introduce ΔΘ as the retard correction amount of the ignition timing,
The value obtained by correcting the basic ignition advance retard Θ ₀ by the following equation (Θ ₀ −Δ
Θ) is the ignition advance value (Θ) to be output (step 2)
5,26).

Θ = Θ ₀ −ΔΘ For example, if a numerical value representing the crank angle before compression top dead center is adopted as Θ ₀ , by giving a positive value to ΔΘ,
For the fourth cylinder, the ignition timing is retarded from Θ ₀ by ΔΘ. The retard correction is not performed for cylinders other than the fourth cylinder (steps 24 and 28).

Then, this retard correction may be performed only under the condition that a gurgling sound is generated. Here, the gurgling sound generation condition is the nth-order component of the engine rotation and (n ± 0.
5) The case where the difference (energy difference) in the sound pressure level from the next component is less than or equal to a predetermined value (E ₀ ).

Fig. 4 shows a program for setting ΔΘ, which is used by the frequency analyzer 16
From the frequency data obtained in step 1, the n-th order component of the engine rotation in the region where the noise is generated (for example, 300 to 500 Hz) and (n ±
0.5) Select only the next-order component, the energy sum E ₁ and E _{2 of} each component is calculated, and the energy difference ΔE (= E ₁
-E ₂ ) and E ₀ (about 3 dB in the 1800cc class) are compared, and when ΔE ≤ E ₀ , a predetermined value δ (1800
cc class is set to about 4 °) (steps 31 to 3)
7). Then, this value of ΔΘ is used in the main routine of FIG. 3 (step 25). When ΔE> E ₀ , retard correction is not performed (steps 36, 3).
9).

The specific numerical values of E ₀ and δ must be individually determined according to the type of engine.

Next, the operation of this example will be described with reference to FIG. 5. During normal operation, the same ignition is performed in each cylinder as shown in FIG.

On the other hand, when it is determined by the detection of the engine vibration that the condition is that of a sound-blowing sound generation condition, the ignition timing is delayed as compared with the other cylinders including only the fourth cylinder, as shown in FIG. (Steps 24-27).

Here, there is a correlation between the combustion excitation force of the cylinder closest to the flywheel (4th cylinder) and the bending vibration of the crankshaft accompanied by the surface wobbling vibration of the flywheel, and the vibration of this crankshaft produces a smashing noise. Is causing
As pointed out in the above-mentioned paper, therefore, when the ignition timing of the fourth cylinder is retarded, the combustion is delayed and the peak value of the combustion pressure, the combustion exciting force becomes small,
As a result, the occurrence of a rattling noise during acceleration is prevented.

In other words, in order to reduce crankshaft vibration, it is possible to approach from the viewpoint of combustion control.By taking measures from this aspect, there is no need to change the design of the crankshaft or the engine body, so the cost is reduced. Up can be minimized.

However, retarding the ignition timing wastes the engine output corresponding to the correction amount, and therefore the engine output should not be significantly reduced by the retard correction. Therefore, it is necessary to determine the amount by which the ignition timing is retarded, that is, δ, in view of the influence on the engine output.

For example, in order to confirm the effect of vibration reduction by retardation correction, the experimental results when the ignition timing of the fourth cylinder is changed are shown in FIGS. 6 to 8, and from FIG. It can be seen that a further retardation of 4 ° has a sufficient effect (indicated by □ −− □). Further, since the vibration level is greatly reduced, the stability of the engine is not disturbed, and therefore the influence of the torque fluctuation on the muffled noise and the like can be reduced.

Then, the reduction of the shaft torque at this time is only about 0.2 kgm (about 1% of the engine output) as shown in FIGS. 7 and 8, and if it is about this level, the acceleration performance may be impaired in practical use. Is not the value of. Note that FIG. 6 shows the characteristics at a constant rotation (4000 rpm) at full load, and FIGS. 7 and 8 show the characteristics at full load.

Next, FIG. 9 is another embodiment applied to an in-line four-cylinder engine, like the above-mentioned embodiment, which limits the intake air amount to the fourth cylinder downstream of the intake throttle valve 41. It is a thing. If the intake air amount is decreased, the cylinder compression ratio is lowered, so that the combustion speed is delayed, and this suppresses the combustion exciting force of the fourth cylinder.

A second intake throttle valve 45, which is different from the other cylinders, is provided at a branch portion 43 of the intake manifold 42 connected to the throttle chamber to the fourth cylinder, which is different from the other cylinders. It is driven by a stepping motor, etc.) 46 that rotates about 3 ° with one signal input.

On the other hand, a flywheel 48 is provided on the side 47 of the cylinder block.
A non-contact type and a displacement meter 49 for measuring the surface runout are attached, and the signal from this displacement meter 49 is passed through an amplifier 52 and a bandpass filter 53 that passes only the frequency component in the Goro sound region (200 to 500 Hz). Input to the I / O of the control unit 51. The displacement meter 49 may be one that picks up the vibration of either one of the two bearing caps that support the cylinder closest to the flywheel 48 (cylinder No. 4). It can also be configured by using what is detected.

FIG. 10 shows a program for controlling the second throttle valve 45, in which two engine revolutions (one cycle) are sent by a signal from a sensor 50 which detects a crank angle reference position (for example, a top dead center position). divided into the combustion section of each cylinder (4 sections), the maximum value of the amplitude obtained in the combustion section of the fourth cylinder (f _MAX1) and the maximum value of the amplitude obtained in the other three intervals of one cycle of (f _MAX2) It is memorized for a while (steps 61 and 62). Then, if Δf (= f _Max1 −f _Max2 ) below the two maximum values exceeds the reference value (f ₀ ), the throttle valve 45 is closed and another reference value (f ₁ , where f ₀ > f ₁ ) If it is smaller than that, a signal to open is sent from the control unit 51 to the actuator 46 (steps 63, 64, 63, 65, 66).

The dead zone is provided by making f ₀ (for example, 15 dB) slightly larger than f ₁ (for example, 10 dB) because the throttle valve 45 repeatedly opens and closes every cycle to reduce the torque fluctuation that becomes a noise vibration source. This is to prevent it from going up and down.

No experiment was performed to confirm the vibration reduction effect for this example, but the second throttle valve 45 was used to obtain the combustion pressure equivalent to that when the ignition timing is retarded by 4 ° for the fourth cylinder.
By determining the angle of, the same result as the above-mentioned embodiment can be obtained. It is assumed that this throttle valve angle is slightly closed rather than fully opened.

(Effect of the Invention) As described above, according to the present invention, a sensor for detecting engine vibration is provided, and it is determined whether or not there is a sound-causing sound based on the detected engine vibration. In this case, the combustion pressure of the cylinder closest to the flywheel is reduced, so that it is possible to reduce the noise caused by acceleration and improve the feeling of acceleration.

[Brief description of drawings]

FIG. 1 is a diagram corresponding to the claims of the present invention, FIG. 2 is a system diagram of an ignition timing control system according to an embodiment of the present invention, and FIGS.
FIG. 5 is a flow chart for explaining the operation of this embodiment, FIG. 5 is a waveform diagram showing the ignition timing characteristic of this embodiment, FIG. 6 is a vibration acceleration amplitude level characteristic diagram according to this embodiment, FIG. 7 and FIG. FIG. 8 is a characteristic diagram of the shaft torque and the corrected shaft torque according to this embodiment, respectively. FIG. 9 is a system diagram of a control system of another embodiment of the present invention,
FIG. 10 is a flow chart for explaining the operation of this embodiment,
Figures 11 to 13 are characteristic diagrams of the sound pressure level, frequency structure, and surface runout vibration of the flywheel shown in the collection of papers that are conventional examples. 1 ... Combustion pressure control means, 2 ... Engine vibration detection sensor, 3 ... Blow noise generation condition determination means, 4 ... Combustion pressure reduction instruction means, 11 ... Engine body, 12 ... Engine mount bracket, 13 ... … Crank angle sensor, 14 …… Suction negative pressure sensor, 15 …… Vibration accelerometer, 16 …… Frequency analyzer,
18 …… Control unit, 19 …… Ignition device, 41 ……
Intake throttle valve, 42 ... Intake manifold, 43 ... Branch section, 45 ... Second intake throttle valve, 46 ... Actuator, 50 ... Reference position sensor, 51 ... Control unit, 52 ... Amplifier, 53 …… Band pass filter.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁶ Identification number Internal reference number FI Technical indication location F02P 5/153 (72) Inventor Yoshiharu Nakaji 2 Takaracho, Kanagawa-ku, Yokohama, Kanagawa Nissan Motor Co., Ltd. (56) References JP-A 61-38142 (JP, A) JP-A 60-184966 (JP, A)

Claims (1)

[Claims] 1. A means for controlling a combustion pressure in an engine cylinder, a sensor for detecting engine vibration, a means for judging whether or not a condition for generating a noise is generated based on the detected engine vibration, and A noise suppressing device for a multi-cylinder engine, comprising: means for instructing the combustion pressure control means to reduce the combustion pressure of a cylinder closest to the flywheel when a condition is determined.