JPH04166647A - Knocking detection device - Google Patents

Abstract

PURPOSE:To easily judge a knocking occurrence with composite judging for the knocking occurrence made possible by determining at least two resonance frequency components, included in the output of a vibration sensor, with the component range limited from a first crank angle to a second crank angle. CONSTITUTION:Vibration, produced by pressure variation following combustion in a combustion chamber, is caught with a knocking sensor 17 fitted in the vicinity of the combustion chamber, is outputted as an electric signal, and is inputted in a CPU in a control unit 9 via an amplifier and an AD converter. AD conversion is made at given time intervals in a given period, these AD conversion results are successively stored in a RAM, a frequency analysis requesting flag is sent to the CPU at the point of time when a converted number becomes (n), and frequency analysis is made with the CPU. Analyzed results including specific frequencies are selected and extracted from the frequency analysis result, and (m) results are added in order of the larger sizes of components. A knocking occurrence is recognized when an added result is compared with a mean value at the time of the knocking occurrence and found to have a ratio of a given value or more.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a knock detection device and method for internal combustion engines.

[Conventional technology]

If the engine's intake temperature, air-fuel ratio, compression ratio, ignition timing, etc. are not appropriate, knocking occurs in the engine, and vibrations with a unique resonant frequency component depending on the compression ratio and bore diameter occur.

Conventional knock detection devices use a bandpass filter to extract only the largest signal included in the knock vibration sensor signal among the resonant frequency components when a knock occurs, and rectify and integrate it only during a specific crank angle. An example of this type of device is Japanese Patent Application Laid-Open No. 60-204.
There is number 969. This device consisted entirely of analog circuits.

[Problems to be Solved by the Invention] In the above-mentioned conventional technology, the frequency bandwidth of the bandpass filter is relatively narrow and covers the majority of the characteristic frequencies that occur when knocking occurs. In reality, all characteristic frequencies are not single, but change depending on operating conditions such as load and rotation speed.

As shown in Fig. 2, according to Draper, there are several resonance modes along the circumferential direction and radial direction due to the resonance condition in the combustion chamber, and the characteristic frequency ranges from 7kHz to 18kHz.
Varies up to KHz.

Not only one of these frequencies occurs with each explosion, but multiple resonant frequencies may occur.

In particular, in the high rotation and high load operating range, the characteristic frequency is not constant, and it is difficult to detect knock using a single characteristic frequency detected by conventional technology. It is an object of the present invention to provide a device and a method that can sufficiently detect knocking even when the knocking frequency changes at high rotation speeds.

Further, in conventional knock detection circuits, the bandpass filter is constructed of an analog circuit, and frequency adjustment is complicated, and there are problems with drift due to aging and temperature changes.

[Means to solve the problem]

In order to achieve the above purpose, a vibration sensor that detects engine vibration or cylinder internal pressure vibration, a crank angle sensor that detects the engine crank angle, and a frequency band from the first crank angle to the second crank angle are used. We have provided a means to determine the ingredients.

Furthermore, in order to achieve the purpose of combating analog circuit drift, the invention further includes means for sampling the knock signal at predetermined time intervals, a memory for storing the sampling results, and frequency components included in the vibration sensor based on the memory contents. A means for analyzing and a means for determining the presence or absence of knocking for each of the five frequencies were provided.

[Effect]

By determining at least two resonance frequency components included in the output of the vibration sensor in a limited range from the first crank angle to the second crank angle, it is possible to determine whether or not knocking has occurred. Even under high load and high rotation, it is possible to distinguish between when knocking occurs and when knocking does not occur, making it easy to determine whether knocking has occurred.

In addition, by sampling the digital value of the output of the vibration sensor at predetermined time intervals and performing frequency analysis, the frequency can be easily selected, so that it can be adjusted to the resonant frequency at the time of knock occurrence.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG.

FIG. 1 is an overall configuration diagram of the present invention, in which an air cleaner 1. Inhalation air indicator 2. Throttle valve5. Air is guided into the combustion chamber through the intake manifold 6° intake valve.

An injector 16 is provided near the intake valve, and the opening time of the injector is changed by an engine control unit 9, which will be described later, to inject an appropriate amount of fuel for the amount of air taken into the combustion chamber.

The air and fuel taken into the combustion chamber are ignited by the spark plug 15 during the compression stroke and exploded, and are scavenged from the exhaust valve during the exhaust stroke and discharged into the atmosphere through the exhaust manifold 8, catalyst, and muffler.

A crank angle sensor 12 is attached to the crankshaft or camshaft of the engine, and outputs a position signal representing the crank angle and a reference signal for identifying the cylinder.

Furthermore, the engine control unit l-0 takes in signals from the crank angle sensor, intake air positioner signals, etc., calculates the valve opening time of the injector, and drives the injector. At the same time, the ignition timing is set at an appropriate timing.

A knock sensor is installed near the combustion chamber and detects vibrations caused by pressure fluctuations associated with combustion within the combustion chamber.
Convert to electrical signal.

Generally, a piezoelectric element is used for a knock sensor, but a magnetic type, variable resistance type, etc. can also be used.

The knock sensor may be a sensor that directly detects pressure fluctuations within the combustion chamber, such as one installed on the washer of the spark plug,
A device 19 that measures the pressure inside the combustion chamber with an inlet pipe may also be used.

It is desirable to install several knock sensors for each cylinder, but if the cylinder block has good transmission, even one knock sensor per multiple cylinders can save space.

The signal from the knock sensor is amplified by an amplifier to an input voltage range of an AD converter, which will be described later. The frequency characteristic of the amplifier is assumed to have a -like amplification over the frequency analysis range, or to have an inverse characteristic so as to correct the frequency characteristic of the knock sensor used. It is assumed that the amplification degree of the amplifier can be changed by an external instruction.

Cylinder identification and crank angle are determined by the signal from the crank angle sensor. For example, as shown in FIG. 3, the rise of the reference signal is assumed to be at a position of 110 degrees before the fifth dead center of each cylinder, and is maintained for a counter width that differs by a width corresponding to the cylinder number of each cylinder. By counting the number of positions during this period, the cylinder can be identified as the first cylinder when it is the largest.

In addition, the PoS counter counts position signals,
It is cleared at the rising edge of the reference signal and is compared with the conveyor register. When the PoS counter and the conveyor register match, AD conversion is started.

Then, the value of the conveyor register is set to the AD conversion end angle, and AD conversion is performed at predetermined time intervals during this period.

According to the sampling theorem, the conversion time interval of AD conversion is set to be equal to or less than the reciprocal of the sampling frequency fs, which is twice the upper limit frequency to be analyzed. For example, since the characteristic frequency shown in Fig. 2 is up to 18 KHz,
For example, fs may be 40 KHz, and τ is the reciprocal of 40 KHz, which is 25 psec.

The AD conversion results are stored one after another in the RAM 34, and when the number of conversions reaches n, a frequency analysis request flag is issued to the CPU. The CPU performs frequency analysis when the frequency analysis request flag is set.

Frequency analysis is performed using, for example, F 'fF "f (Fast F
This can be done using a digital filter or a digital filter.

The knock determination method is shown in FIG.

From the frequency analysis results, the analysis results including the specific frequencies shown in FIG. 2 are selected and extracted, and m components are added in descending order of magnitude. If the addition result is a ratio or difference of a predetermined constant amount I- compared to the average value when no knock occurs, it is recognized that a knock has occurred, and a knock flag is set.

In addition, as another knock determination method, the ratio or difference is determined for each frequency component, and m
There is also a method of adding up the numbers, and if the addition result is equal to or greater than a predetermined value, the occurrence of a knock is recognized and a knock flag is set.

As shown in the figure, the frequency component is selected so that it has a resonant frequency within its bandwidth and can be distinguished from other resonant modes.

Furthermore, since the resonant frequency when a knock occurs drifts depending on the rotational speed and load, the bandwidth is set to include the drift.

In this way, the bandwidth is divided into several bands within the frequency range in which frequency analysis is performed, and it is also possible to perform knock detection for each band.

Add m pieces in descending order of size. The addition result is compared with the average value (BGl,,) when no knock occurs.

If there is a difference or ratio (sr,) greater than a predetermined threshold, it is recognized that a knock has been detected and a knock flag is set.

If it is determined that there is no knock, use B G L as the coefficient α and SL
Correct using.

Another knock determination method is to find the difference or ratio SLi for each frequency component and add m to the larger 1@ of the difference or ratio 54E=S Li as shown in Figure 5. , if the addition result is above a predetermined threshold,
There is also a method of recognizing that a knock has been detected and setting a knock flag.

If it is determined that there is no knock, BGL is displayed for each frequency component.
Correct i using coefficients α and SLi, respectively.

As shown in FIG. 6, the frequency component is selected so that it has a resonant frequency within its bandwidth and can be distinguished from other resonant modes.

Furthermore, since the resonant frequency when a knock occurs drifts depending on the rotational speed and load, the bandwidth is set to include the drift.

In this manner, the bandwidth is divided into several bands within the frequency range for frequency analysis, and knock detection can be performed for each band.

〔Effect of the invention〕

According to the present invention, knock determination can be performed by selecting an arbitrary frequency component included in the vibration sensor, so that it is possible to determine whether knocking has occurred using an appropriate resonance frequency component depending on the operating state of the engine. can. Therefore, knocking can be determined over the entire operating range of the engine.

Furthermore, since the bandwidth for performing frequency analysis can be specified and narrowed from among the entire frequency analysis range, there is an effect that the calculation load on the CPU can be reduced.

[Brief explanation of drawings]

Fig. 1 is a main configuration diagram of one embodiment of the present invention, Fig. 2 is an explanatory diagram of the resonance vibration mode when a knock occurs, Fig. 3 is a timing chart for sampling a knock signal, and Fig. 4 is for knock detection. FIG. 5 is a flowchart of another means for knock detection, and FIG. 6 is an explanatory diagram of band division of the frequency analysis range. 1... Air cleaner, 2... Air flow rate 4.3... Duct, 6... Intake manifold, 7... Engine block 58... Exhaust manifold, 7
...Control unit, 12...Crank angle sensor, 17...Knock sensor, ]8... Seat pressure sensor,
19... Cylinder pressure needle 3

Claims (1)

[Claims] 1. A knock vibration sensor installed near the combustion chamber of an internal combustion engine or a cylinder pressure sensor that detects pressure changes in the combustion chamber is provided, and within the vibration energy band including the resonance frequency that occurs when knock occurs. Within a band with energy of a given proportion of
1. A knock detection device comprising means for detecting knock vibrations for each band width that is continuously divided into predetermined bands. 2. In the knock detection device according to claim 1, a plurality of components with large vibration components are selected and calculated, and a knock is detected when a predetermined condition is satisfied by comparing the calculation results with the calculation results when no knock occurs. A knock detection device characterized by comprising means. 3. In the knock detection device according to claim 1, the signal ratio or difference for each vibration component is calculated by comparing each vibration component with the average value when no knock occurs, and when the calculation result is equal to or higher than a predetermined value, A knock detection device characterized in that it is provided with means for performing knock detection. 4. The knock detection device according to claim 1, characterized in that the vibration energy band including the resonance frequency is limited to have 90% or more energy between the first frequency and the second frequency. Knock detection device. 5. In the knock detection device according to claims 1, 2, 3, and 4,
A knock detection device comprising means for selecting and calculating a vibration component according to the rotational speed and load of an internal combustion engine. 6. The knock detection device according to claim 1, 2, 3, 4, or 5, further comprising means for detecting knock by overlapping part of the frequency bands for detecting knock vibration components.