JPH0746061B2 - Knock detection device - Google Patents

Description

TECHNICAL FIELD The present invention relates to an engine knock detection device.

(Prior Art) As a conventional knock detection device, for example, there is one as shown in FIGS. 1 and 2 (see SAE paper 700061). First
In the figure, 1 is a cylinder block in which a cylinder 2 is formed, and a piston 3 is slidably inserted in the cylinder 2. A cylinder head 4 is fastened to the upper end of the cylinder block 1, and a combustion chamber 5 is defined by the cylinder block 1, the piston 3 and the cylinder head 4. An intake passage 7 communicating with the combustion chamber 5 via an intake valve 6 is formed in the cylinder head 4, and an ignition plug 8 for igniting an air-fuel mixture in the combustion chamber 5 is attached to the cylinder head 4. A knock sensor 9 for detecting knock vibration generated in the combustion chamber 5 is attached to the cylinder block 1. The knock sensor 9 converts the knock vibration into an electric signal to show the band bass filter shown in FIG. Outputting to 10.

The bandpass filter 10 is a filter of about 6 KHz (hereinafter 6 KHz) and detects only a knock signal having a frequency of 6 KHz. Knock vibrations around 6 KHz are detected in this way.Knock determination has traditionally been performed based on auditory standards, and human beings are most likely to hear 4 KHz sounds, and become less audible as the frequency increases. Therefore, the knock vibration is detected by the knock frequency that peaks near this frequency.

The knock signal from the bandpass filter 10 is a comparator
11 is directly input to the comparator 11 via the rectifier circuit 12 and the smoothing circuit 13, and the comparator 11 compares these two input signals to determine whether or not a knock has occurred. When it is present, it outputs a voltage signal of a predetermined value. The signal from the comparator 11 is input to the integrator 14, and the integrator 14 outputs a voltage signal according to the knock occurrence frequency to the ignition circuit 15. Ignition circuit 15 is an integrator 14
The ignition timing of the spark plug 8 is adjusted according to the magnitude of the voltage signal from the ignition plug 8. When the knock occurs, the ignition timing is delayed to avoid the occurrence of the knock.

However, in such a conventional knock detection device, since the generation of knock is detected based on knock vibration of a frequency around 6 KHz, the knock occurs anywhere in the cylinder (combustion chamber). Depending on whether or not the knock vibration is detected, there is a problem in that the knock vibration may or may not be detected, and the occurrence of knock cannot be stably detected.

That is, in the vicinity of 6 KHz, in the normal engine, the peripheral mode (resonance mode that produces a pressure gradient in the circumferential direction of the cylinder) of the knock's natural vibration modes is the first-order radial mode (which produces a pressure gradient in the radial direction of the cylinder). (Resonance mode) is the 0th order frequency, and in this mode of vibration, a node is formed in the circumferential direction of the cylinder, and the knock sensor may be located at this node depending on the place where knock occurs. When the knock sensor is located at the node, the vibration level becomes zero and the knock cannot be detected. On the other hand, when the knock sensor is located at the antinode of the amplitude, the knock is detected at a large vibration level. There are knocks with high strength to small knocks, but even with a big knock, the vibration level becomes zero when the position of the knock sensor is located at the vibration node,
On the other hand, even if the knock is small, the vibration level becomes large when the position of the knock sensor is located at the antinode of the vibration. Therefore, the magnitude of the knock does not correspond to the magnitude of the vibration level, and when determining the presence or absence of knock based on the magnitude of the vibration level, the knock to be detected is not detected,
There was a situation in which a minute knock that did not need to be detected was detected.

This will be explained in a little more detail. Waves are generally represented by the wave equation. Now, when p is pressure, ρ is density, and v is velocity, the velocity potential ψ with p = −ρ∂ψ / ∂t and v = gradψ is Where C is the speed of sound, where ψ = ψ ₀ e ^-jωt (2) where ω is the angular frequency, and ω is the angular frequency, and ω = ψ ₀ + kψ ₀ = 0 ... (3) However, k is wave number, k = ω / C = 2πf / C, and f is frequency.

Now, considering the gas in the combustion chamber as a cylinder and converting equation (3) into cylinder coordinates, However, r is r = 0 to B / 2 (B is the diameter of the cylinder) in the radial direction of the cylinder, and ψ is ψ = 0 to 2π in the circumferential direction of the cylinder.

Generally, the height in the combustion chamber is smaller than the diameter B of the cylinder, so the component in the Z direction (axial direction of the cylinder) is ignored,
When the velocity potential ψ ₀ is represented by two harmonic vibrations of a radial component R (r) and a circumferential component θ (ψ), ψ ₀ = AR (r) θ (ψ) (5) where A Becomes a constant, and when the formula (5) is substituted into the formula (4) and arranged using the constant m for convenience, the following formula is obtained.

From the equation (6), since R (r) and θ (ψ) are independent, the following relationships are satisfied.

The following condition is obtained from the equation (7).

The equation (8) is a Bessel's differential equation, and r = 0
Since there is no inflow or outflow of combustion gas, the solution becomes the m-th order Bessel function of the first kind Jm (kr), and the following condition is obtained.

Then, the boundary condition of the equation (8) is that the cylinder surface (r = B /
In 2), the speed is ∂ψ ₀ / ∂r = 0, so Becomes

Therefore, the vibration mode of the gas in the combustion chamber is expressed by the following equation by substituting the equations (9) and (10) into the equation (5) using the velocity potential ψ ₀ .

ψ ₀ = AJm (kr) sin (mψ + ψ ₀ ) …… (12) where m = 0,1,2,3, ... And the value of kB / 2 (ξm that satisfies the boundary condition of equation (11).
n) is shown in the following Table 1 from the numerical table of the Bessel function.

Since the wave number k is k = ω / C = 2πf / C, the natural frequency fc of gas in the combustion chamber due to knock vibration is given by the following equation using the cylinder diameter B.

The sonic velocity C of the combustion gas is expressed by the following equation (14):
Determined only by the average temperature T of the combustion gas, However, To = 300 ° K, Co = 344 m / s The average temperature T of the combustion gas can be obtained by the following equation (15).

PV = GRT (15) where P: Pressure V: Volume G: Gas weight R: Gas constant T: Average temperature of combustion gas For example, for a 1800cc 4-cylinder (cylinder diameter 83mm) engine, the natural frequency of the knock In the case of this engine, T = 2500 ° K and C = 99 from the equation (14).
It will be 0 m / s. Therefore, when the natural frequency fc for each mode of ξ ₁₀ , ξ ₂₀ and ξ ₀₁ is calculated, C = 990 m / s
And from the equation (13), it becomes as follows.

fc (ξ ₁₀ ) = 7.0KHz fc (ξ ₂₀ ) = 11.6KHz fc (ξ ₀₁ ) = 14.5KHz Then, the calculation result is the actual measurement value shown in FIG. 3 (a) (the solid line in the figure indicates the time when knock occurs). The broken line shows the time when the knock does not occur.) Which is almost the same as the frequency spectrum of the natural vibration of the knock. However, the third
The solid line in FIG. 10A is the result of full knocking (full open throttle) at an engine speed of 1200 rpm and strong knocking (knocking when the ignition timing is advanced from the standard).

The above-mentioned circumferential mode and diameter mode are respectively referred to as “ci
rcumferential ”,“ radial mode ”(for example,“ ENGI
NE NOISE ", PLENUM Publication 1993, P18, 19). The primary circumferential mode is the mode in which the pressure distribution in the cylinder changes in the circumferential direction. Looking at, when the phase angle ψ ₀ rotates in the circumferential direction starting from O,
There is a pressure change for one cycle of sin (mψ + ψ ₀ ) in the above equation (12), and the pressure change is always 0 in the diameter direction passing through ψ ₀ = 0. Similarly, in the second-order circumferential mode, si in the previous equation (12)
Since n (mψ + ψ ₀ ) appears for two cycles, the pressure change in the two diametrical directions becomes zero. On the other hand, the radial mode is a mode in which the pressure distribution changes in the radial direction, and the pressure distribution is given by the Bessel function Jm (kr) of the equation (12). As described above, since the circumferential mode and the radial mode generate different frequencies, the pressure distribution observed at each frequency is as shown in FIG. 4, and many modes coexist.

The generation state of the node in the cylinder for each mode is as shown in FIG. The numerical value in FIG. 5 is the value of ξmn.

In the conventional example, the vibration around 6 KHz detected by the knock sensor and the bandpass filter is the vibration of the mode of ξ ₁₀ . The vibration of this ξ ₁₀ mode, that is, the diameter of 0
As shown in FIG. 3 (b), the vibration in the next mode has a node (indicated by a broken line for convenience) in the circumferential direction of the cylinder, and depending on the knock occurrence location and the knock sensor attachment location. , The knock sensor may coincide with this section (note that I, II, and III in FIG. 3 (b) correspond to the frequencies of I, II, and III in FIG. 3 (a). ).

In this case, since the amplitude of knock vibration is zero at the node, the knock sensor cannot detect knock vibration. In other words, as long as vibrations in the first or higher modes in the circumferential direction are detected, even a large knock to be detected may not be detected when it is located at the node of vibration of the knock sensor. Even a small knock that should not be performed may be detected when the knock sensor is located at the antinode of vibration. Therefore, there is a problem that the occurrence of knock cannot be detected stably.

(Object of the Invention) Therefore, an object of the present invention is to stably detect the occurrence of knock by detecting only the zero-order vibration of the mode in the circumferential direction of the cylinder among the natural vibration modes of the knock. .

(Structure of the Invention) The knock detection device of the present invention comprises a knock detection means for detecting knock vibration generated in a cylinder of an engine, a vibration selection means for detecting a predetermined frequency of the knock vibration, and a vibration of a predetermined frequency. In the knock detection device including knock determination means for determining the magnitude of knock from the level of, the vibration selection means selects only the zero-order frequency in the circumferential mode of the cylinder among the natural vibration modes of the knock. By detecting it, the occurrence of knock is stably detected.

(Examples) Examples of the present invention will be described below with reference to the drawings.

6 to 8 are views showing an embodiment of the present invention.

First, the structure will be described. In FIG. 6, reference numeral 1 is a cylinder block in which a cylinder 2 is formed.
A piston 3 is slidably inserted therein. A cylinder head 4 is fastened to the upper end of the cylinder block 1, and a combustion chamber 5 is defined by the cylinder block 1, the piston 3 and the cylinder head 4. An intake passage 7 communicating with the combustion chamber 5 via an intake valve 6 is formed in the cylinder head 4, and an ignition plug 8 for igniting an air-fuel mixture in the combustion chamber 5 is attached to the cylinder head 4. A knock sensor (knock detecting means) 9 for detecting knock vibration generated in the combustion chamber 5 is attached to the cylinder block 1. The knock sensor 9 converts the knock vibration generated in the cylinder 2 into an electric signal. It is converted and output to the bandpass filter (vibration selection means) 21 shown in FIG.

In the bandpass filter 21, among the natural vibration modes of the knock generated in the cylinder 2, the mode in the circumferential direction of the cylinder (circumferential mode) is the 0th order, and the mode in the radial direction of the cylinder (radial mode) is the 1st order. It is set so that only the frequency fc (ξ ₀₁ ) which is is passed, and the frequency of this mode ξ ₀₁ varies depending on the type of engine.
In the case of a cc 4-cylinder engine, about 15
Since it is KHz, the bandpass filter 21 of the present embodiment is 1
Only a knock signal having a frequency of 5 KHz ± 2 KHz is extracted and directly output to the comparator 11, and also output to the comparator 11 via the rectifying circuit 12 and the smoothing circuit 13.

The comparator 11 compares these two input signals to determine whether knock has occurred, and when the knock has occurred, outputs a voltage signal of a predetermined value to the integrator 14. The integrator 14 calculates the knock occurrence frequency based on the signal from the comparator 11 and outputs a voltage signal corresponding to the knock occurrence frequency to the ignition circuit 15
Output to. The ignition circuit 15 adjusts the ignition timing of the spark plug 8 according to the magnitude of the voltage signal from the integrator 14,
When a knock occurs, the ignition timing is delayed to avoid the knock. The rectifying circuit 12, the smoothing circuit 13, and the comparator 11 constitute knock determining means 22 for determining the magnitude of knock from the level of a predetermined frequency.

Next, the operation will be described.

The knocks generated in the cylinder 2 do not have the same place in the cylinder 2. For example, when a knock occurs at the position N _{1 in} the upper part of FIG. 8, a vibration node of mode ξ ₁₀ (indicated by a solid line in the cylinder 2 in FIG. 8) is formed at the mounting position of the knock sensor 9, and the knock sensor In 9 mode ξ ₁₀
Vibration is transmitted through a distant transmission path, and is attenuated and felt as the magnitude of ψ ₁ . However, when a knock occurs at the position of N _{2 in} the lower part of FIG. 8, the transmission path is shorter than that of N ₁ , so that the user feels that the magnitude of ω ₃ is larger than ω ₁ .

Thus, in mode ξ ₁₀ , knocks N _{1 of} the same magnitude,
Even if N ₂ occurs, there is an inconvenience that the magnitude of vibration transmitted to knock sensor 9 varies depending on the position where N ₂ occurs. In this embodiment, the mode ξ ₀₁ is used instead of the mode ξ ₁₀ . Specifically, the bandpass filter 21 is set to the knock frequency of the mode ξ ₀₁ of this engine, and the knock vibration of the mode ξ ₀₁ is detected.

The vibration of the mode ξ ₀₁ causes a node at a fixed position in the cylinder 2. Therefore, no matter where the knock occurs,
Alternatively, no matter where the knock sensor 9 is attached, the occurrence of knock can always be detected stably. For example, even if a knock occurs at the N ₂ position in the lower part of FIG. 8, the vibration is transmitted through the same transmission path as N ₁ , so that the occurrence of the knock can be stably detected.

In FIG. 8, ω ₁ , ω ₂ , ω ₃ , and ω ₄ indicate the waveforms of knock vibrations in each mode ξ ₁₀ and ξ ₀₁ detected by the knock sensor 9. Of the knock vibrations, ω ₁ and ω ₃ are detected at different levels depending on the position of the knock sensor 9. When such a vibration is used for knock detection, there is a situation in which a knock of a magnitude that should be detected is not detected because the strength of the knock and the strength of the vibration level do not correspond, and a minute knock that is unnecessary for detection is detected. Occurs. On the other hand, knock vibration ω
₂ and ω ₄ are detected at the same level regardless of the position of the knock sensor 9. Therefore, when such vibration is used for knock detection, the strength of the knock corresponds to the strength of the vibration level, and the knock of the magnitude to be detected is detected, and the detection of minute knock that is unnecessary for detection is eliminated. It becomes possible to do.

Here, the distribution of pressure values in the cylinder at a certain time is shown as in FIG. 4 described above. The distribution of pressure values fluctuates about ± 1 atmospheric pressure during pressure oscillation with the equilibrium pressure P ₀ (for example, 50 atmospheric pressure) as the center with the passage of time. In the case of vibration of which the circumferential direction is the 0th order and the radial direction is the 1st order, a pressure gradient does not occur in the circumferential direction, but when the radial direction is the 1st order, a pressure gradient occurs in the radial direction at the same time. Moreover, as shown in the schematic drawing in the column of n = 1, pressure vibration occurs in which the middle side and the outer side change in opposite phases at the boundary of the circle.

A schematic drawing of this situation is shown in Figure 8 as ξ ₀₁ (ξ ₀₀
It is a double circle (⊚) figure in the column (corrected). Therefore, the pressure in the portion of the cylinder 2 is the same at any time at the same time, and it vibrates up and down. Up and down of the pressure are transmitted through the cylinder head 4 to the knock sensor 9 as indicated by an arrow (see an arrow in FIG. 8).

In the ξ ₀₁ mode, no matter which knock occurs in N ₁ or N ₂ , the pressure distribution of the same ⊚ figure can be made, so that it is possible to detect with the same size.

It is preferable to use a knock sensor having a resonance point near 15 Hz for the knock sensor of the above-described embodiment, because a bandpass filter becomes unnecessary. In this case, the knock sensor serves as both the knock detecting means and the vibration selecting means. Needless to say, a bandpass filter may be used in addition to the knock sensor.

9 and 10 show another embodiment of the present invention.

In FIG. 9, 31 is an in-cylinder pressure sensor (knock detection means) arranged between the washer 8a of the ignition plug 8 and the cylinder head 4, and the in-cylinder pressure sensor 31 is composed of a piezoelectric element.
The pressure change in the cylinder 2 (combustion chamber 5) is converted into a voltage signal and output to the bandpass filter 21.

Also in this embodiment, the mode ξ is set by the bandpass filter 21.
_Since the vibration of ₀₁ is detected (see Fig. 10), the occurrence of knock can always be detected stably. The tenth
N ₃ and N ₄ in the figure respectively indicate the knock occurrence location. Further, ω _{5 to} ω ₈ indicate the waveform of knock vibration detected by the in-cylinder pressure sensor 31.

In each of the above-described embodiments, vibrations in the 0th-order and 1st-order modes are detected, but if the mode in the circumferential direction is 0th-order,
The radial mode does not have to be the primary mode (however, the frequency becomes higher).

(Effect) According to the present invention, since only the 0th order vibration frequency of the cylinder in the circumferential direction can be detected, the magnitude of the knock and the vibration level are irrespective of the knock generation position and the knock sensor mounting position. The magnitudes of the knocks correspond to each other, and it is possible to eliminate the detection of a minute knock that is unnecessary for detection and always stably detect the occurrence of the knock.

[Brief description of drawings]

1 and 2 are views showing a conventional knock detection device. FIG. 1 is a sectional view of an engine having the knock sensor attached, FIG. 2 is an overall configuration diagram thereof, and FIG. 3 is vibration of the engine. Fig. 4 is a diagram showing the actual measurement value of Fig. 4, Fig. 4 is a diagram schematically showing the knock natural vibration mode of pressure, and Fig. 5 is a diagram schematically showing the generation state of the node in the cylinder in each natural vibration mode of the knock. 6 to 8 are views showing an embodiment of the knock detecting device of the present invention. FIG. 6 is a sectional view of an engine to which the knock sensor is attached, FIG. 7 is its overall configuration diagram, and FIG. 9 and 10 are diagrams showing another embodiment of the knock detection device of the present invention, FIG. 9 is an overall configuration diagram thereof, and FIG. 10 is an action explanation diagram thereof. 2 ... Cylinder, 9, 31 ... Knock detection means, 21 ... Vibration selection means, 22 ... Knock discrimination means.

Claims (1)

[Claims] 1. A knock detection means for detecting knock vibration generated in a cylinder of an engine, a vibration selection means for detecting a predetermined frequency of the knock vibration, and a knock magnitude from a vibration level of the predetermined frequency. In a knock detection device provided with knock determination means for determining, the vibration selection means detects only the frequency in which the mode in the circumferential direction of the cylinder is the 0th order among the natural vibration modes of the knock. Knock detection device.