JPH0715422B2 - Cylinder pressure sensor abnormality determination device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a device for determining an abnormality of an in-cylinder pressure sensor that detects combustion pressure oscillation occurring in an internal combustion engine of an automobile or the like.

(Prior Art) In recent years, there is a tendency for the engine to require fuel economy and drivability of other fields, and from this point of view, the combustion state is optimally controlled by applying a microcomputer or the like.

As one of the methods for monitoring the combustion state, there is a method for detecting the pressure of the combustion gas in the cylinder (hereinafter referred to as the cylinder pressure).
There is an in-cylinder pressure sensor (vibration sensor) using a piezoelectric ceramic as described in Japanese Patent Laid-Open Publication. This piezoelectric ceramic tends to be widely used because of its advantages such as high mechanical-electrical conversion dynamics, simple sensor structure, and small size.

(Problems to be Solved by the Invention) By the way, since such a piezoelectric ceramic is used as a so-called sensor, reliability of the sensor information is required. When such reliability is lacking, that is, when the sensor is abnormal, for example, it is determined that knocking has occurred but it has not occurred, and it is difficult to control the ignition timing of the engine normally.

In order to solve such a problem, for example, an abnormality determination device for an in-cylinder pressure sensor as shown in FIG. 6 can be considered (the contents of the following comparative examples are the prior application by the applicant (Japanese Patent Application No. 60). -117913)).

In the figure, reference numeral 1 denotes an in-cylinder pressure sensor for detecting combustion pressure oscillation of the engine. The in-cylinder pressure sensor 1 converts the combustion pressure in the cylinder into an electric charge by a piezoelectric ceramic and outputs an electric charge output S ₁ . Specifically, the in-cylinder pressure sensor 1 is tightened as a washer of an ignition plug screwed to a cylinder head of an engine,
Fixed. In addition, in-cylinder pressure sensor 1 is connected in parallel with resistor R1,
R2 is inserted, and the power source Vcc is provided to the midpoint of each of the resistors R1 and R2 via the resistor R3. This is equivalent to lowering the DC impedance of the in-cylinder pressure sensor 1 by inserting the resistors R1 and R2, disconnection of the output signal line of the in-cylinder pressure sensor 1, short circuit to the ground side, short circuit to the power supply Vcc, etc. This is because the abnormal state of is detected by the potential at point A in the figure.

The sensor output S ₁ is input to the charge amplifier 2. The charge amplifier 2 constitutes a so-called charge-voltage conversion amplifier including an operational amplifier OP and resistors R4 and R5, and the potential of the sensor output S ₁ and the point A is converted into a voltage signal S. _It is converted to ₂ and output to the bandpass filter (BPE) 3 and the microcomputer 4. The band-pass filter 3 is an extracting unit that passes only a signal in the frequency band (for example, 6 KHz to 19 KHz) corresponding to knocking vibration in the signal S ₂ , and outputs it as the signal S ₃ to the rectifying integrator 5. The rectification integrator 5 rectifies the extracted signal S ₃ and integrates the rectified value to output a signal S corresponding to the combustion vibration energy amount (the energy amount of the vibration component of the predetermined frequency band) to the microcomputer 4. . The microcomputer 4 determines the occurrence of knocking based on the signal S from the rectifier / integrator 5, and directly monitors the signal S ₂ from the charge amplifier 2 to detect an abnormality in the cylinder pressure sensor 1. For example, when the in-cylinder pressure sensor 1 is short-circuited to the ground side, the input signal S ₁ of the charge amplifier 2 becomes 0 [V], so that the abnormal state is detected.

However, even such a conventional in-cylinder pressure sensor abnormality determination device has the following unsolved problems. That is, in this device, since the output S ₂ of the charge amplifier 2 is constantly monitored by the microcomputer 4 to determine the abnormality of the sensor, the short-circuit state of the in-cylinder pressure sensor 1 can be accurately detected, but the open state is not detected. It cannot always be detected accurately. Further, it is difficult to detect when the sensor sensitivity is abnormally deteriorated.

(Object of the Invention) Therefore, the present invention focuses on the fact that knocking is a stochastic phenomenon by nature and the value of the energy amount equivalent signal S has a predetermined dispersion tendency, and appropriately determines the degree of this dispersion. The purpose of the present invention is to improve the accuracy of the abnormality determination by accurately determining the abnormality regardless of the abnormal state of the sensor.

(Structure of the Invention) As shown in the basic conceptual diagram of the apparatus for discriminating an abnormality of an in-cylinder pressure sensor according to the present invention, a vibration detecting means a for detecting combustion pressure vibration of an engine and a predetermined output from the vibration detecting means. Extraction means b for extracting the vibration component of the frequency band, and for each combustion cycle of the engine based on the output of the extraction means, a first value corresponding to the energy amount of the vibration component in a predetermined period during the combustion cycle is set. A calculating means c for calculating and a second value obtained by averaging the first value,
The fluctuation state calculating means d for calculating the variance value of the first value based on the first value and the second value, and it is determined that the vibration detecting means is abnormal when the variance value is smaller than a predetermined reference value. Abnormality determining means e and operating state detecting means f for detecting that the operating state of the engine is low rotation and low load operation
And a prohibiting means g for prohibiting the abnormality determination when the operating state is low rotation and low load operation, and accurately determines the abnormality of the sensor.

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

2 to 5 are views showing an embodiment of the present invention.

First, the configuration will be described. In FIG. 2, 1-3 are 6th.
The same components as those of the conventional example shown in the figure are shown, and the same numbers are assigned. In the present embodiment, the in-cylinder pressure sensor 1 has a function as a vibration detecting means, and the bandpass filter 3 has a function as an extracting means.

The output S ₃ of the bandpass filter 3 is input to the calculating means 11, and the calculating means 11 is composed of a rectifying circuit 12, an integrator 13, a crank angle sensor 14 and an integration timing controller 15. The crank angle sensor 14 detects the crank angle of the engine. For example, in the case of a 6-cylinder engine, the crank angle sensor 14 outputs a reference signal Ci for each 120 ° of the crank angle and a position signal C ₁ for each 1 ° of the crank angle. The integration timing controller 15 sets an integration timing for each combustion cycle based on the signals Ci and C ₁ from the crank angle sensor 14 and outputs a section signal S _k to the integrator 13. This preferably corresponds to a section where knocking may occur, for example 10 ° to 45 ° after top dead center.
Set to °. The rectifier circuit 12 rectifies the signal S ₃ and integrator 13
Then, the integrator 13 integrates this rectified signal during the input of the section signal S _k , that is, in the section of 10 ° to 45 ° after top dead center, and outputs it as an integrated value S to the microcomputer 16. The signals Ci and C ₁ from the crank angle sensor 14 are further input to the microcomputer 16. The microcomputer 16 has a function as an operating state detection means and a prohibition means in addition to a function as a fluctuation state calculation means and an abnormality determination means, and performs abnormality determination of the in-cylinder pressure sensor 1 and prohibition of the determination according to an internal program. At the same time, ignition control is performed to suppress knocking. It should be noted that the microcomputer 16 is adapted to detect the operating state of the engine based on detection information from the crank angle sensor 14 and known means such as water temperature and air flow meter (not shown).

Next, the operation will be described. First, the basic principle of the present invention will be described.

During operation of the engine, a vibration component in a predetermined frequency band is extracted from the output of the in-cylinder pressure sensor 1 by the bandpass filter 3, and the integrated value is obtained as a value corresponding to the energy amount of the vibration component for each combustion cycle of the engine. S (first value) is calculated, and this S is distributed as shown in FIG. 3 according to its mode. That is, when knocking does not occur, the value of S concentrates on a relatively small value as indicated by the broken line in the figure. On the other hand, when knocking occurs, S having a large value appears as shown by the solid line in the figure, and for example, the value of S shown by the shaded portion is determined to be knocking. Further, when an abnormality such as an open or short state of the sensor occurs, the value of S has only a component such as electrical noise and has a distribution as shown by the alternate long and short dash line in the figure.

Here, for example, considering the average value of S, the average value a ₁ of S at the time of abnormality and the average value a ₂ without knocking are very close to each other, and the average value a ₃ at the time of knocking occurs. Are large values far apart. Therefore, in consideration of changes in the output sensitivity of the sensor over time, it is expected that it will be considerably difficult to distinguish between the abnormal state and the case without knock.

Therefore, in order to make the above-mentioned discrimination appropriate, when attention is paid to the value (S−) ² , for example, as shown in FIG. 4, their average values b ₁ , b ₂ in each mode are shown. , B ₃
A big difference appears. Furthermore, the weighted average value (S) of (S-) ² , that is, the variance of S represents the degree of variation in the value of S. Therefore, according to (▲), the output sensitivity of the sensor is not affected by changes over time. It is possible to determine each aspect.

In the present invention, the above-mentioned discrimination function is realized by the program shown in FIG. 5 based on such a principle. This program is executed once every predetermined time, and Pi (i = 1, 2, 3 ...
...) indicates each step of the flow.

P ₁ reads the rectified integral value S of the high frequency component caused by knocking for each combustion cycle, and P ₂ reads the difference value according to the following equation.
Ask for SW.

SW = S- However ,: the average value of S up to the previous routine, then P ₃
Then, the value SF {SF = (S−) ² } obtained by squaring the difference value SW is obtained with
_{In step 4} , the weighted average value ▲ ▼ of SF is calculated according to the following equation as a parameter representing the time-series fluctuation state of the rectified integral value S.

However, ▲ ▼: In ▲ ▼ and P ₅ of the previous routine, the difference value SW is compared with the slice level SL for determining the presence or absence of knock. Since the difference value SW has the distribution characteristics shown in FIG. 3, the slice level is shown in the shaded area in FIG.
This is because if SL is set, it can be determined whether or not there is a knock.
When SW> SL, it is determined that knock has occurred, and the ignition timing is corrected to the retard side in P ₆ , and when SW ≤ SL, it is determined that there is no knock and P ₇
After the ignition timing is corrected to the advanced side with, the average value S of S at this time is calculated according to the following equation at P ₈ .

However, ▲ ▼: Average value of the previous routine This allows the engine to be operated at the optimum ignition timing while suppressing knocking.

Note that the average value of S is calculated only when knocking does not occur at P _{8 because} the value of adding a large value of S when knocking occurs to the data for calculating the average value becomes excessively large. This is because normal knocking cannot be detected.

Then, it is determined whether or not the engine at P ₉ is operated at a predetermined operating condition. When the engine is operating in the low rotation speed and low load region, the routine of this time is ended without determining the abnormality of the sensor. This is because in such an operating range, the value of S is so small that it is difficult to determine even in a normal state, and because knocking hardly occurs in this range, it is not necessary to determine the abnormality of the sensor. On the other hand, low rotation at P _9, when it is driven at a driving range other than the low load region
At P ₁₀ , the weighted average value ▲ ▼ is compared with the predetermined value AL. Since this ▲ ▼ has the distribution characteristics shown in FIG. 4, if the value of ▲ ▼ is compared with a predetermined value, the cylinder pressure sensor 1
This is because it is possible to determine the abnormality. When ▲ ▼ <AL, it is determined that the cylinder pressure sensor 1 is abnormal, and the abnormality flag ALF is set (ALF = 1) at P ₁₁ and the routine of this time is ended. By setting the abnormality flag ALF, for example, an external alarm display or the like may be displayed, whereby appropriate processing can be performed in response to the abnormality of the in-cylinder pressure sensor 1. In addition, at the time of this abnormality, the ignition timing may be corrected to the retard side to ensure the safety of the ignition timing control. On the other hand, when P ₁₀ is ▲ ▼ ≧ AL, it is judged that the in-cylinder pressure sensor 1 is not abnormal, and the routine jumps to P ₁₁ to end the routine of this time.

As described above, the SF having the distribution characteristic as shown in FIG.
By using (= (S−) ² ), it is possible to prevent an erroneous determination regarding a decrease in sensitivity of the in-cylinder pressure sensor 1, and by using the average value ▲ ▼ (dispersion of the first value),
It is possible to prevent erroneous determination even when the result of one SF calculation becomes less than or equal to a predetermined value due to variations in sensor sensitivity. As a result, it is possible to accurately and accurately determine all abnormal states that cannot fulfill the normal function of the sensor, such as the open and short states of the in-cylinder pressure sensor 1 or the abnormal reduction of the output sensitivity due to the aging of the sensor.
Further, since the abnormal state of the in-cylinder pressure sensor 1 is not discriminated when the operating state of the engine is low rotation and low load operation, the above-mentioned abnormal state of the in-cylinder pressure sensor 1 can be discriminated more accurately. You can That is, in a region where the engine operating condition is low rotation and low load operation, even if the average value is a normal value, it becomes very small, and the calculated weighted average value ▲ ▼ becomes very small, making it difficult to determine. It becomes impossible to accurately determine the abnormal state of the sensor 1. In the present embodiment, the engine operating condition is set so as not to determine the abnormality of the in-cylinder pressure sensor 1 at the time of low rotation and low load operation in which the weighted average value ▲ ▼ becomes small. It can be determined more accurately.

(Effect) According to the present invention, the vibration component in the predetermined frequency band is extracted, and for each combustion cycle of the engine, the first amount corresponding to the energy amount of the vibration component in the predetermined period in the combustion cycle is extracted.
Of the second value obtained by averaging this first value
Is calculated, and the variance value of the first value is calculated based on the first value and the second value. If the variance value is smaller than a predetermined reference value, it means that the vibration detecting means is abnormal. Since it is discriminated, all abnormal states that cannot fulfill the normal function of the vibration detecting means, such as open or short state of the vibration detecting means or abnormal decrease of output sensitivity due to deterioration of the vibration detecting means over time, etc., are accurately identified. Can be accurately determined.

Further, since the abnormality determination is prohibited when the engine operating condition is low rotation and low load operation, the vibration detection means is short-circuited in the low rotation and low load operation range where the variance value is calculated and the variance value becomes small. It is possible to prevent a situation in which it becomes impossible to determine an abnormal state such as an open state. As a result, it is possible to more accurately determine the abnormal state of the vibration detecting means.

[Brief description of drawings]

FIG. 1 is a basic conceptual diagram of the present invention, FIGS. 2 to 5 are diagrams showing an embodiment of the present invention, and FIG. 2 is a block configuration diagram thereof.
FIG. 3 is a diagram showing the distribution characteristic of the integrated value S, FIG. 4 is a diagram showing the distribution characteristic of (S-) ² thereof, FIG. 5 is a flow chart showing the program for the sensor abnormality determination, and FIG. It is the circuit diagram which shows the conventional abnormality determination device of the cylinder pressure sensor. 1 ... In-cylinder pressure sensor, 3 ... Bandpass filter (extracting means), 11 ... Computing means, 16 ... Microcomputer (fluctuation state computing means, abnormality determining means, operating state detecting means, inhibiting means).

Claims (1)

[Claims] 1. A vibration detection means for detecting combustion pressure vibration of an engine; b) extraction means for extracting a vibration component of a predetermined frequency band from the output of the vibration detection means; and c) based on the output of the extraction means. Calculating means for calculating, for each combustion cycle of the engine, a first value corresponding to the energy amount of the vibration component in a predetermined period during the combustion cycle; and d) a second value obtained by averaging the first value. Fluctuation state calculating means for calculating a value and calculating a variance value of the first value based on the first value and the second value; and e) vibration detection when the variance value is smaller than a predetermined reference value. Abnormality determining means for determining that the means is abnormal; f) operating state detecting means for detecting that the operating state of the engine is low rotation and low load operation; and g) operating state is low rotation and low load operation. If it is Abnormality determination device of the in-cylinder pressure sensor, characterized in that it comprises a prohibiting means for stopping, the.