JPS604824A - Knocking detector - Google Patents

Abstract

PURPOSE:To enable accurate detection of possible knockings by providing a vibration selecting means of detecting the frequency which corresponds to the zero order in the circumferential mode of a cylinder among natural vibration modes of knockings. CONSTITUTION:A knocking sensor 9 converts a knocking vibration generated in a cylinder 2 into an electrical signal and outputs it to a band-pass filter 21. The band-pass filter 21 is so set as to pass only the frequency corresponding to zero order in the circumferential mode of the cylinder as well as in the diametrical mode among natural vibration modes of knockings generated in the cylinder and the frequency in the mode is, for example, 15kHz in the 4-cylinder engine with the displacement of 1,800cc. Such a setting of the band-pass filter 21 invariably enables always accurate detection of possible knockings regardless the position of knockings generated and the position of the knocking sensor 9 in the cylinder.

Description

[Detailed description of the invention] (Technical field) The present invention relates to an engine knock detection device.

(Prior Art) As a conventional knock detection device, for example, the one shown in FIG.
(see issue). In FIG. 1, l is a cylinder block in which a cylinder 2 is formed, and a piston 3 is slidably inserted into the cylinder 2. A cylinder head 4 is fixed to the upper end of the cylinder block 1, and the cylinder block 1, piston 3, and cylinder head 4 define a combustion chamber 5. The cylinder head 4 has an intake passage 7 that communicates with the combustion chamber 5 via an intake valve 6.
A spark plug 8 for igniting the air-fuel mixture in the combustion chamber 5 is also provided. A knock sensor 9 is attached to the cylinder block 1 to detect knock vibrations generated within the combustion chamber 5. The knock sensor 9 converts the knock vibrations into electrical signals and converts the knock vibrations into electrical signals through a bandpass filter shown in FIG. It is output to 10. The bandpass filter 10 is a 6KHz filter, and approximately 6K+
Only a knock signal with a frequency of lz is detected.

The reason why knock vibrations around 6 KHz are emitted is because knocks have traditionally been judged based on auditory standards, and humans are most likely to hear sounds at 4 K fiz.
As the frequency becomes higher, it becomes harder to hear, so knock vibrations are detected at the knock frequency that peaks around this frequency. The knock signal from the bandpass filter 10 is directly input to the comparator 11 and also input to the comparator 11 via the rectifier circuit 12 and the smoothing circuit 13, and the comparator 11 compares these two manual signals to determine whether knock has occurred. and outputs a voltage signal of a predetermined value when knocking occurs. The signal from the comparator 11 is input to the integrator 14, and the integrator 14 sends a voltage signal corresponding to the frequency of knock occurrence to the ignition circuit 15.
Output to. The ignition circuit 15 adjusts the ignition timing of the ignition plug 8 according to the magnitude of the voltage signal from the integrator 14, and when knocking occurs, the ignition timing is delayed to avoid the occurrence of knocking.

However, such conventional knock detection devices are configured to detect the occurrence of pack based on knock vibrations with a frequency of around 6 KHz, so it is difficult to determine where in the cylinder (combustion chamber) the knock occurs. Does it occur?
There is a problem in that it is sometimes possible to detect pack vibrations and sometimes not, and it is not possible to reliably detect the occurrence of knocking.

In other words, around 6 KHz, in a normal engine, among the natural vibration modes of knock, the circumferential mode (mode in the circumferential direction of the cylinder) is the first order and the radial mode (mode in the radial direction of the cylinder) is the zero order. This mode of vibration creates nodes in the circumferential direction of the cylinder, and depending on where the knock occurs, the knock sensor may be located at these nodes.

When the knock sensor is located at a node, the vibration rail is zero and knock cannot be detected.

To explain this in more detail, waves are generally expressed by a wave equation, where p is pressure, ρ is density, and ■ is velocity. where C is the speed of sound, and the velocity potential ψ is 8 rotations f and 1 rotation, and ψ
= ψo8−input element −−−−−(2, However, if ω is the angular frequency, the tlj formula becomes a number.

Now, if we consider the gas in the combustion chamber as a cylinder and convert equation (3) into circular If coordinates, we get In the direction r = 0~connection (B is the diameter of the cylinder), in the circumferential direction of yL and 'J', ψ-0~2
It is π.

Generally, the height inside the combustion chamber is the height of the cylinder.
Therefore, if we ignore the component in the Z direction (axial direction of the IJ counter) and express the velocity potential ψ0 by two harmonic oscillations: a component R(r) in the j51H direction and a component θ(ψ) in the circumferential direction, we get , ψo = AR (r) θ (I/) --- (51 However, A
is a constant, and by substituting this equation (5) into equation (4) and rearranging using the constant m for convenience, we get the following equation.

From equation (6), R(r), θ (1/) b, independent f and force 1 satisfy the following relationships.

Y:L,,),/;! (r)+,? +(fl-mtsuQ
(F−)=D −−−−−t8, the following condition is satisfied from equation (7).

Further, equation (8) is a Bessel differential equation table, and since there is no inflow or outflow of combustion gas at r-0, the solution becomes the m-th order Heso cell function of the first kind Jm (kr), and the following conditions are satisfied.

1'm (徾) = 0--- (11).

Therefore, ζ, the vibration mode of the gas in the combustion chamber is expressed by the following equation by substituting equations (9) and 00) into equation (5) using velocity potential ψ0.

ψo = AJm ('k r) sin (m+/+ψ
0)---(12> However, it is shown as m=Q, 1.2.3,----1-. Also, since the wave number is = w = xxf,
The natural frequency fc of the gas in the combustion chamber due to knock vibration is given by the following equation using the cylinder diameter B.

Engineering --- (13) fc-3m n -+B Note that the sound speed C of the combustion gas is determined only by the average temperature T of the combustion gas, as shown in the following equation (14), and C=Co stone i--
1--(14) Here, T o =300''K, G o =34
4 m/J The average temperature T of the combustion gas can be calculated from the following equation (15).

1)■=GRT--- (15) Here, P: pressure, ■=volume, G: gas weight, R: gas constant, T: average temperature of combustion gas, for example, 1800cc
Let's look at the natural frequency of knock for a 4-cylinder engine (cylinder diameter: 83 dragons).

For this corn gin, T = 2500°K,
From equation (14), C=990m/8. Therefore, mouth 2. , ζ, , , ζ9 When the natural frequency is calculated for each mode, Table 1 and C = 990 m, Equation (13)
It becomes as follows.

kQ,, ) =7. OKl(z fcc3w) -11,6K l1zkc5 bo
) = 14.5K HzThe results of this calculation are the actual measured values shown in Figure 3a (the solid line in the figure indicates when knocking occurs;
The broken line indicates when no knock occurs. ), which almost matches the frequency spectrum of the natural vibration of knock. Furthermore, the generation state of knots within the cylinder for each mode is as shown in FIG.

Note that the numerical values in FIG. 4 are the values of ζmn.

In other words, the vibration of about 6 KIIz (near 4 is ζ
, D mode vibration. And ζ,
The D mode vibration, that is, the first circumferential and zero radial mode vibration, has nodes in the circumferential direction of the cylinder, as shown in Figure 3. Depending on the location, the knock sensor may be located at this node. In addition, in Figure 3 [, ■, ■ are Figure 3 a]
These correspond to the middle ■, ■, and ■ frequencies. In this case, since the amplitude of the knock vibration at the node is zero, the knock sensor cannot detect the knock vibration. That is, as long as vibrations in the first or second mode in the circumferential direction are detected, knocking may not be detected, and there is a problem in that the occurrence of knocking cannot be reliably detected.

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

(Structure of the Invention) The knock detection device of the present invention includes a knock detection means for detecting knock vibration generated within the 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, the vibration sorting means detects a frequency in which the mode in the circumferential direction of the cylinder is zero-order among the natural vibration modes of the knock. By doing so, the occurrence of knocking can be detected reliably.

(Example) Hereinafter, the present invention will be described in detail with reference to the drawings.

5 to 7 are diagrams showing one embodiment of the present invention.

First, to explain the configuration, in FIG. 5, 1 is a cylinder block in which a cylinder 2 is formed;
A piston 3 is slidably inserted therein. A cylinder head 4 is fixed to the upper end of the cylinder block 1, and the cylinder block 1, piston 3, and cylinder head 4 define a combustion chamber 5. 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 the air-fuel mixture in the combustion chamber 5 is attached. and,
A knock sensor (knock detection means) 9 is attached to the cylinder block 1 to detect knock vibrations generated within the combustion chamber 5. The knock sensor 9 converts the knock vibrations generated within the cylinder 2 into electrical signals. Then, it is output to a bandpass filter (vibration selection means) 21 shown in FIG. The bandpass filter 21 is configured such that among the natural vibration modes of knock occurring within the cylinder 2, the moat 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 0th order. A certain frequency fc (ζoo)
This mode is set to pass only ζ
The frequency of Oo varies depending on the type of engine, but is 1
In the case of an 800cc, 4-cylinder engine, as mentioned above,
15 is +lz, so the bandpass filter 21 is 1
It is set to 5KHz. The bandpass filter 21 outputs only a knock signal with a frequency of 15Kt (z±2KHz) directly to the comparator 11, and
and a smoothing circuit I3 to the comparator 11, and the comparator 11 compares these two human power signals to determine whether or not a knock has occurred. It is output to 14. The integrator 14 calculates the frequency of knock occurrence based on the signal from the comparator 11 and outputs a voltage signal corresponding to the frequency of knock occurrence to the ignition circuit 15. The ignition circuit 15 is an integrator 1
The ignition timing of the spark plug 8 is adjusted according to the magnitude of the voltage signal from the spark plug 4, and when knock occurs, the ignition timing is delayed to avoid the occurrence of knock. The rectifier circuit 12, smoothing circuit 13, and comparator 11 constitute a knock determining means 22 that determines the magnitude of knock from the level of a predetermined frequency.

Next, the action will be explained.

The location of the knock occurring within the cylinder 2 is not constant within the cylinder 2. For example, if a knock occurs at position N in the upper row of FIG. 7, the knock sensor 9 is installed in position mode ζ.

A node of vibration (indicated by a solid line inside the cylinder 2 in FIG. 7) is formed, and the knock sensor 9 cannot detect vibration in this mode. However, in this embodiment, since the bandpass filter 21 is set to the knock frequency of the mode ζoo of this engine, the knock vibration of the mode ζ00 can be detected.

Since the vibration of this mode ζoo does not produce any nodes in the cylinder 2, no matter where the knock occurs,
No matter where the knock sensor 9 is installed, the occurrence of knock can always be reliably detected. Therefore, even if a knock occurs at the position N2 in the lower row of FIG. 7, the occurrence of knock can be reliably detected. ω in Figure 7
1, ω2, ω3, and ω- are each mode ζ detected by the knock sensor 9. , ζ00.

In addition, in the above embodiment, the knock sensor is equipped with 15Kl.
(A sensor having a resonance point near z may be used and the bandpass filter may be omitted. In this case, the knock sensor will serve as both a knock detection means and a vibration selection means.

It goes without saying that in addition to using such a knock sensor, a bandpass filter may also be used.

Figure 8.9 shows another embodiment of the invention.

In FIG. 8, 31 is a cylinder pressure sensor (knock detection means) disposed between the washer 8a of the spark plug 8 and the cylinder head 4, and the cylinder pressure sensor 3I is composed of a piezoelectric element. The pressure change within the combustion chamber 5) is converted into a voltage signal and output to the bandpass filter 2I.

Therefore, in this embodiment as well, mode ζ. Even when the knock cannot be detected in the above-mentioned case, as shown in FIG. 9, since the vibration of the mode ζoo is detected, the occurrence of knock can be detected very reliably. In addition, N3 and N in Figure 9
', l indicate the knock occurrence location, and indicate the waveform of knock vibration detected by the ω5 to ω8 cylinder pressure sensor IJ-31.

In each of the above embodiments, vibrations in the 0th circumferential mode and the 0th radial mode are detected, but as long as the circumferential mode is 0th order, the radial mode does not need to be 0th order. However, the vibration frequency becomes higher.

(Effects) According to the present invention, it is possible to detect zero-order vibration in the circumferential direction of the cylinder, so that - Regardless of the knock occurrence position or the installation position of the knock sensor, knock occurrence can be reliably detected. can be detected.

[BRIEF DESCRIPTION OF THE DRAWINGS] Fig. 1.2 shows a conventional knock detection device, Fig. 1 is a sectional view of the engine to which the knock sensor is installed, and Fig. 2 is its overall configuration. , Fig. 3 is a diagram showing actual measured values of engine vibration, Fig. 3 a shows the frequency Svek 1-ram of the natural vibration of the cylinder internal pressure;
Figure 4 schematically shows the formation of nodes in the cylinder in the natural vibration mode that reaches the peak level of Fig. 4. Figure 4 schematically shows the formation of nodes in the cylinder in each natural vibration mode of knock. Figures 5 to 7 are diagrams showing one embodiment of the knock detection device of the present invention, Figure 5 is a sectional view of an engine to which the knock sensor is installed, and Figure 6 is its overall configuration. Figure 7 is an explanatory diagram of its operation, and Figures 8 and 9 are diagrams showing other embodiments of the knock detection device of the present invention.
FIG. 8 is an overall configuration diagram thereof, and FIG. 9 is an explanatory diagram of its operation. 2------Cylinder, 9.31---Knock detection means, 21---Vibration selection means, 22--- Knock discrimination means. Patent Applicant Nissan Motor Co., Ltd. Representative Patent Attorney JJtx by Ugagun Parts Figure 3 [English] (TL) (S) Figure 4 Figure 7 Figure 8

Claims (1)

[Claims] Knock detection means for detecting knock vibrations occurring within the cylinders of an engine; Vibration sorting means for detecting a predetermined frequency of knock vibration; and Knock discrimination means for determining the magnitude of knock from the vibration level of the predetermined frequency. A knock detection device comprising: the vibration selection means detects a frequency in which the mode in the circumferential direction of the cylinder is zero order among the natural vibration modes of the knock.