JPH023127B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for determining the optimum mounting position of a knock sensor mounted on an internal combustion engine body for detecting knocking.

2. Description of the Related Art There is a type of knock sensor that converts mechanical vibrations of an internal combustion engine into electrical vibrations. In this type of knock sensor, it is necessary to find a point where the amplitude of the engine body is large due to knocking occurring in each cylinder of the engine, and to install it at that point in order to improve the knocking detection accuracy. A conventional method for determining the installation position of a knock sensor is based on modal analysis. In this method, by calculating the vibration mode in the vicinity of the vibration frequency corresponding to knocking, several candidate points for installing the knock sensor are obtained, and a cylinder block with a boss for the knock sensor formed at these points is prototyped. Next, vibration in the knocking frequency band (for example, 6-8kHz) is applied to the cylinder block, the amplitude is measured at each candidate point, and the point with the best S/N ratio is determined as the knock sensor mounting position. . However, since this modal analysis method does not determine the location for installing the knock sensor by detecting knocking in the actual machine state, there are some concerns as to whether it is the optimal location for knocking detection. Furthermore, in modal analysis, the object is divided into meshes and the vibration mode at each point of the division is numerically calculated, but the number of divisions cannot be made very finely, so there is a problem in terms of accuracy.

Therefore, it is possible to apply vibration analysis using holography to detect knocking in an actual engine condition. That is, in vibration analysis using holography, a vibrating object is irradiated with laser light twice at intervals in the form of pulses. In this case, interference fringes (holograms) with a fringe interval corresponding to the displacement at two points in time are obtained on the dry plate. This allows vibration to be measured. However, the vibrations of an engine during actual operation are not only vibrations caused by knocking, but also consist of vibrations in various frequency bands caused by various other causes superimposed. Therefore,
Simply taking a hologram of a knocking engine cannot accurately detect knocking vibrations due to the influence of vibration components outside the knocking frequency band.

Problems to be Solved by the Invention The present invention is an improvement in engine vibration analysis using holography, and an object of the present invention is to provide a method that can isolate only the vibration caused by knocking and accurately detect knocking.

Means for Solving the Problems In the method of determining the mounting position of a knock sensor for an internal combustion engine according to the present invention, the engine is operated under operating conditions that cause knocking, and the engine is operated at a plurality of representative frequencies including the frequency that causes knocking. The vibration characteristics are measured with respect to time, two times t ₁ and t ₂ in one engine cycle at which the composite vibration displacement at a representative frequency other than the knocking frequency is substantially canceled are determined, and the times t ₁ and t ₂ are determined. A hologram is created by irradiating the engine with a light pulse, and the installation location of the knock sensor is determined from the resulting hologram.

Effect: At times t ₁ and t ₂ when the optical pulses are emitted, the amplitudes at representative frequencies other than the frequencies at which knocking occurs are substantially canceled. Therefore, only the hologram that is caused by the vibration caused by knocking can be obtained, and the knocking vibration can be accurately grasped.

Embodiment 10 is an engine to which the knock sensor mounting position is determined, and includes a fuel injection valve 12 and a spark plug 14.
Each cylinder (four cylinders in this case) is equipped with the following.
The fuel injection control device 16 controls the amount of fuel injected from the fuel injection valve 12, that is, the air-fuel ratio, while the ignition control device 18 independently controls the crank angle position of the engine at which discharge occurs at the electrode of the spark plug 14 for each cylinder. control. The fuel injection control device 16 and the ignition control device 18 themselves may have any known structure.

20 is a transmission, and 22 is a dynamometer.

Reference numeral 24 designates a two-pulse laser holography device as a whole, and includes a two-pulse laser light generator 26 . There is a beam splitter 28 in front of the laser beam generator 26, and the transmitted light is a signal beam.
L ₁ is supplied to a lens system 30 that illuminates the engine 10 . The reflected light from beam splitter 28 is supplied to a lens system 32 that produces reference light _L2 .
34 is a reflecting mirror that guides the reference light L ₂ onto the dry plate 36.

In the present invention, a plurality of sensors are provided to detect vibrations of each frequency component in engine vibrations. Reference numeral 38 denotes an accelerometer-type vibration meter, which is provided in the engine body 10 and is capable of detecting vibrations over all frequencies of the engine. Reference numeral 40 is a gap-type sensor installed at the top of the engine at a slight distance therefrom, and is capable of detecting vibrations in the low frequency range (100 Hz or less) associated with sideways shaking of the engine. As the gap sensor 40, a type that detects eddy current can be adopted. 4
2 is a high frequency equivalent to knocking (6-8kHz)
This is a resonance type accelerometer for detecting vibrations in the engine body 10, and is installed in the engine body 10.

The acceleration sensor 38, which detects vibrations in all engine frequency ranges, is connected to a filter circuit 44, which serves to separate and transmit only engine vibrations in the intermediate frequency range (0.5-3kHz).

Sensors 38, 40, 42 are oscilloscope 50
are connected to respective input terminals 50-1, 50-2, and 50-3. A frequency generator 52 is used to find a sine wave approximate to each waveform observed on the oscilloscope, and is connected to an input terminal 50-4 of the oscilloscope 50. The oscilloscope 50 has an external synchronization terminal 50-5, and the terminal 50-5 is connected to a crank angle sensor 56 so that waveform observation can be performed in synchronization with the engine crank angle. engine 1
The crank angle sensor 56 is provided facing the rotary body on the crankshaft 10' of the crankshaft 10'.
When it reaches a predetermined position, a trigger signal is issued, and the waveform can be observed on the oscilloscope 50 in synchronization with the rotation of the engine crankshaft.

A frequency analysis device (FFT) 60 is used for frequency analysis of engine vibration.

The invention is based on the following facts. That is, the overall vibration characteristics of the engine with respect to time are expressed as shown in FIG. 2A. Here, the vertical axis is accelerating, but it is the same as vibration displacement. The region A in the figure corresponds to the time of ignition. Figure 2 A represents a signal containing all wavelength components of the vibration from the sensor 38 in Figure 1, and it is unclear from this graph how each frequency band contributes to engine vibration. be. FIG. 2B shows the result of decomposing the vibration waveform in A into components at each frequency by the frequency analyzer 60 of FIG. In other words, as is clear from (b), engine vibration mainly consists of three frequency bands: below 100Hz, 0.5-3kHz, and 6-8kHz, and the vibration in the lowest frequency band is the lateral vibration of the engine. It is thought that vibrations in the middle frequency band are caused by surface vibration of the cylinder block, and vibrations in the highest frequency band are caused by knocking. Therefore, in the present invention, we have focused on this fact, and have
Each sensor as described above is provided to independently detect a representative frequency of each component of the knocking vibration, and the vibration from each sensor is displayed on the oscilloscope 50. Two points at which vibrations at representative frequencies other than the knocking frequency are actually canceled out are determined from the observed pattern at the frequency, and a two-pulse laser is driven at these two points to obtain a hologram. This will be explained in more detail below.

In FIG. 1, the ignition control system 18 and the fuel injection control system 16 each adjust the ignition timing and mixture air/fuel ratio to cause knocking in one particular cylinder. As a result, knocking occurs due to the operation of the engine 10. The overall vibration characteristics at that time are represented by A in Figure 3 (this corresponds to the waveform at part A in Figure 2 A).
In this case, the horizontal axis is time and corresponds to the position of the engine crankshaft 10'. Vibration analysis by the frequency analyzer 60 results in engine vibration being divided into three frequency bands, low, medium, and high, as shown in Figure ₂ (b ₎ . ), and Notsking (L ₃ ). Representative frequencies in these three frequency bands (for example, frequencies ₁ , ₂ , and ₃ that cause vibration peaks in each frequency band) are selected as representative frequencies, and the sensor is configured to detect these representative frequencies. Characteristics are defined. That is, the gap sensor 40 has a frequency of ₁ ,
Further, the characteristics of the resonance type accelerometer 42 are expressed at frequency ₃ . Additionally, a sensor 38 that detects vibrations at all frequencies is connected to a filter 44, which is tuned to frequency ₂ . Therefore, vibration waveforms based on these selected representative frequencies ₁ , ₂ , and ₃ are displayed on the observation surface of the oscilloscope 50. That is, the gap sensor 40 displays vibrations at a typical frequency in the low frequency range of the engine, and the third
Shown in Figure B. Only the intermediate frequency range is passed through the filter 44, and the representative vibration in the frequency band based on the surface vibration of the cylinder block is observed on the oscilloscope 50 as shown in (c). Further, vibrations at representative frequencies in the high frequency range due to knocking are extracted by the resonant accelerometer 42 and observed on the oscilloscope 50. At this time, the oscilloscope 5
Each waveform observed on 0 is not a sine wave in the strict sense. Therefore, the function generator 5
2, a sine wave can be generated and corrected as a sine wave that matches well with the waveforms from each sensor observed on the oscilloscope. Alternatively, a sine wave closest to the actually measured waveform observed on the oscilloscope can be calculated.

Next, among the representative frequency vibrations in each frequency band corrected as a sine wave in this way, there are two points where the combined vibrations of the representative frequencies in the low frequency band and intermediate frequency band, which are unrelated to knocking, are canceled out. It is determined. For example, in Fig. 3, at time t ₁ , the wave height of B is Δ ₁ and the wave height of C is Δ ₁ ′, Δ ₁ + Δ ₁ ′ = 0, while at time t ₂ , the wave height of B is Δ ₂ , and the wave height of C is Δ 1 ′. Δ ₂ ′ and Δ ₂ + Δ ₂ ′=
It is 0. Two times selected in this way
At t ₁ and t ₂ , the composite vibration of the representative frequency in frequency bands other than the knocking band is canceled, so
If a hologram is taken at times t ₁ and t ₂ , it is possible to observe the magnitude of the times based only on notching. The meaning of the cancellation of the composite time here does not necessarily mean that the composite vibration does not exist at all, but that the knocking vibration can be observed to be sufficiently larger than other vibrations, or that vibrations other than the knocking vibration are due to the sensitivity of holography. This means that it does not exceed λ/4 (λ: laser light wavelength). In addition, although the representative frequency in each frequency band is selected as the frequency that produces a vibration peak in each frequency band in this embodiment, it is considered that a frequency in the vicinity thereof may be used. in this way,
By canceling components other than knocking frequencies at representative frequencies of each frequency band, vibration components other than knocking can also be canceled at frequencies other than the representative frequencies of each frequency band.

The laser emission timing control 63 of the two-pulse laser generator is adjusted so that two pulses are generated with a time difference calculated from the above-mentioned times t ₁ and t ₂ . Further, in synchronization with a predetermined crankshaft signal from the crank angle sensor 56, the times t ₁ and t ₂ in FIG.
A laser pulse will be generated at a crank angle corresponding to .

Direct light L ₁ from the laser beam generator 26 hits the engine body 10 causing knocking at time t ₁ ,
It is emitted at t ₂ and the diffracted light is collected on a dry plate 36 . At times t ₁ and t ₂ , there is a difference in the vibration displacement due to notching, as shown in x in Figure 3 D (choosing t ₁ and t ₂ so that this difference x becomes large is a good way to improve the hologram). ), interference fringes for each half of the wavelength of the laser beam are formed on the dry plate 36 in accordance with this vibration displacement difference x. Reproduction of such interference fringes can be performed by a well-known hologram reproduction method.

FIG. 4 schematically shows the state of interference fringes resulting from hologram reproduction when knocking is caused independently in each of cylinders #1, #2, #3, and #4. The position where interference fringes appear, that is, the position where knocking vibration appears greatly, changes depending on which cylinder is knocking, but the common position where knocking is likely to occur is P, the 4th bearing on the crankshaft of the 4th cylinder. It is determined that the position between the fifth bearing and the fifth bearing is preferable.

Effects of the Invention According to the present invention, engine vibrations in vibration bands other than the knocking band are canceled out2.
Vibration analysis is performed by generating a laser pulse at one point in time and obtaining a hologram. Therefore, only the vibration component due to knocking can be detected accurately and quickly without repeating trial-and-error prototyping. Furthermore, by measuring the displacement based on knocking when knocking occurs in each cylinder, it is possible to specify a common location where knocking is likely to occur. Therefore, highly accurate knocking detection can be performed with a single knock sensor.

[Brief explanation of drawings]

Fig. 1 is an overall diagram of the system that realizes the method of the present invention, Fig. 2 is a comprehensive engine vibration A and its frequency analysis diagram B, Fig. 3 is a diagram showing vibration at each representative frequency, and Fig. 4 is a diagram showing the overall vibration of the engine and its frequency analysis. The figure is a diagram schematically showing the position of interference fringes on the engine body when the hologram is reproduced by causing knocking in each cylinder and obtaining a hologram by the method of the present invention. DESCRIPTION OF SYMBOLS 10... Engine body, 24... Holographic device, 38... Accelerometer, 40... Gap sensor, 42... Resonance type accelerometer, 44... Filter, 50... Oscilloscope, 60... Frequency analysis device.

Claims (1)

[Claims] 1. A method for determining the mounting position of a knock sensor in an internal combustion engine, which comprises operating the engine under operating conditions that cause knocking, and measuring engine vibration characteristics over time at a plurality of representative frequencies, including the frequency that causes knocking. , and determine two times t ₁ and t ₂ in one engine cycle at which the resultant vibration displacement at a representative frequency other than the knocking frequency is substantially canceled, and irradiate the engine with light pulses at the times t ₁ and t ₂ . This method involves creating a hologram by doing this, and determining the installation location of the knock sensor from the resulting hologram.