JPH0343417Y2 - - Google Patents

Description

[Detailed explanation of the idea]

(Field of Industrial Application) The present invention relates to an ignition timing control device that suppresses knocking in an internal combustion engine such as an automobile and performs MBT control to improve drivability. (Prior Art) The ignition timing of an internal combustion engine needs to be determined depending on the state of the engine so that the engine can be operated optimally.
Generally speaking, when considering engine efficiency and fuel consumption, it is known that it is best to ignite at the minimum advance angle at maximum torque, so-called MBT control (Minimum advance for Best Torque), and depending on the engine condition, the ignition timing is controlled by MBT. The so-called change
MBT control is performed. However, in certain engine conditions, advancing the ignition timing causes knocking, making it impossible to operate the engine stably. For example, at low speeds and low loads, the knocking limit is reached before the MBT. Furthermore, the knocking limit is easily affected by atmospheric conditions such as temperature and humidity. Therefore, the MBT described above uses so-called knock control, which controls the ignition timing depending on the presence or absence of knocking.
A system that can be used in conjunction with control has been developed; for example, such a system is disclosed in
There is a device described in Publication No. 39974. This device detects the cylinder pressure using a cylinder pressure sensor, and fires the ignition so that the crank angle at which the pressure is maximum (hereinafter referred to as the combustion peak position) θ _pnax is at a predetermined position that maximizes the torque generated by the engine. MBT controls the timing. In this case, in order to obtain θ _pnax , the in-cylinder pressure is A/D converted every 1° from TDC to ATDC60°. (Problems to be solved by the invention) However, in such _conventional ignition timing control devices for internal combustion engines, high-speed Since the configuration required an A/D converter and a CPU, it was an expensive device, and it was difficult to implement MBT control with conventional control units commonly used for electronic engine control. . (Purpose of the invention) Therefore, the present invention sets two crank angles θ ₁ and θ ₂ with the target value θ _T of MBT control in between, and determines the combustion peak position from the difference in detected combustion pressure for each crank angle. By determining the positional relationship between θ _pnax and the above target value, it is possible to reduce the number of times the cylinder pressure is taken in, eliminate the need for a high-speed A/D converter or a high-performance microcomputer, and make it effective even with an inexpensive system configuration. The purpose of this invention is to provide an ignition timing control device that can perform MBT control. (Structure of the invention) The ignition timing control device for an internal combustion engine according to the invention, as shown in the basic conceptual diagram in FIG. a state detection means b, a first crank angle that is on the leading side of the target value of the crank angle at which the combustion pressure is maximum and located after the top dead center, and a first crank angle that is on the lag side of the target value and located after the top dead center. The output from the pressure detection means is taken in at the timing of the second crank angle located after the point, and the output is taken in at the third crank angle corresponding to the target value, or at the fourth crank angle that is later than the second crank angle. The difference between the combustion pressure intake means c that captures combustion pressure even at the timing of the first crank angle and the timing of the second crank angle is determined, and the value of the difference is determined as an allowable value. a correction amount calculation means d for calculating a correction amount for correcting the basic ignition timing so that the basic ignition timing is within the range of the correction amount; ignition timing setting means e for igniting the air-fuel mixture based on the output of the ignition timing setting means; The difference between the combustion pressure and the combustion pressure taken at the timing of the first crank angle, and the difference between the combustion pressure taken at the timing of the third or fourth crank angle and the second crank angle. The present invention is characterized by comprising abnormality determining means g for determining abnormal combustion in the engine when the difference between the combustion pressure and the combustion pressure taken in at the timing of is both smaller than a predetermined value, and prohibiting the correction operation of the correction amount calculating means. There are things. Here, the detection of the cylinder pressure in such a configuration is performed at predetermined small timing points such as the first crank angle, the second crank angle, the third crank angle, or the fourth crank angle. Therefore, the number of sampling times can be reduced and the system configuration required for MBT control can be simplified. (Example) Hereinafter, the present invention will be explained based on the drawings. 2 to 7 are diagrams showing an embodiment of the present invention. First, the configuration will be explained. In FIG. 2, reference numeral 1 denotes a cylinder pressure sensor (pressure detection means), and the cylinder pressure sensor 1 converts the combustion pressure in the cylinder into an electric charge using a piezoelectric element, and outputs an electric charge output _S1 . Specifically, as shown in detail in FIGS. 3A and 3B, the cylinder pressure sensor 1 is screwed onto a cylinder head 2 and formed as a washer for a spark plug 3, and the spark plug is mounted in a recess on the outside of the cylinder head 2. It is pressed and fixed by the tightening portion 3a of No.3. The sensor output _S1 is input to a charge amplifier 4, and the charge amplifier 4 includes operational amplifiers OP1 and OP2 and resistors R1 to R, as shown in detail in Figure 4.
8. Capacitor C1 and diodes D1-D3
A so-called charge-to-voltage conversion amplifier is configured, which converts the sensor output _S1 into a voltage signal _S2 and outputs it to the control unit 5. The control unit 5 further receives a signal from an operating state detecting means 6, and the operating state detecting means 6 is composed of a crank angle sensor 7 and an air flow meter 8. The crank angle sensor 7 indicates the explosion interval (in a 6-cylinder engine, the crank angle
A predetermined position before compression top dead center (TDC) of each cylinder every 120° (180° for a four-cylinder engine), e.g.
It outputs a reference position signal Ca that becomes a [H] level pulse at 70° BTDC, and outputs a unit signal _C1 that becomes an [H] level pulse for every unit angle of the crank angle (for example, 2°). Note that the engine rotation speed can be determined by counting the pulses of the signal Ca. In addition, the air flow meter 8 detects the intake air amount θ _a of the engine and outputs an analog signal.
Output Sa. The control unit 5 has functions as a combustion pressure intake means, a correction amount calculation means, an ignition timing setting means, and an abnormality determination means, and includes a CPU 11, a ROM
12, RAM 13, A/D converter 14 and I/
It is composed of an O port 15. CPUR11 is
It takes in necessary external data from the I/O port 15 according to the program written in the ROM 12, and calculates processing values necessary for ignition timing control while exchanging data with the RAM 13. It processes the data and outputs the processed data to the I/O port 15 as necessary. I/O port 1
Signals from the operating state detection means 6 and the charge amplifier 4 are input to the I/O port 15, and an ignition signal Sp is output from the I/O port 15. A/D
The converter 14 A/D converts the external signal input to the I/O port 15 according to instructions from the CPU 11. Further, the ROM 12 stores calculation programs for the CPU 11, and the RAM 13 stores data used in calculations in the form of a map or the like. The ignition signal Sp is input to the ignition means 16,
The ignition means 16 includes an ignition coil, a distributor, a spark plug, etc., and generates a high voltage based on the ignition signal Sp to ignite the air-fuel mixture. Next, the operation will be explained, but first, the basic principle of the present invention will be described. FIGS. 5A to 5D are diagrams showing general changes in cylinder pressure. In the figure, θ _T is the target value of the combustion peak position θ _pnax , and θ _{1 and} θ ₂ are the two crank angles at which the in- _cylinder pressure is detected. This corresponds to the second crank angle θ ₂ . Assuming that the cylinder pressures at θ ₁ and θ ₂ are Pθ ₁ and Pθ ₂ , respectively, FIG. 5a is an example of θ _pnax =θ _T , and in this case, Pθ ₁ =Pθ ₂ . FIG. 5b is an example of θ _pnax <θ _T , in which case Pθ ₁ >Pθ ₂ . Also, the fifth
Figure c is an example of θ _pnax > θ _T , in which case Pθ ₁ < Pθ ₂
It is. From the above facts, the cylinder pressure at two points sandwiching θ _T is
By detecting Pθ ₁ and Pθ ₂ , the positional relationship between θ _pnax and θ _T can be determined. That is, by analyzing the state of change in the cylinder pressure in each of the aspects shown in Fig. 5 a to c, the positional relationship between θ _pnax and θ _T can be found, and Pθ 1 = Pθ ₁ =
By controlling the ignition timing so that Pθ ₂
MBT control is achieved. In addition, in order to control the ignition timing so that Pθ ₁ = Pθ ₂ in actual control, the difference ΔP between Pθ ₁ and Pθ ₂ must be
=|Pθ ₁ −Pθ ₂ | is controlled so that it falls within a predetermined tolerance range. At this time, since the magnitude of the cylinder pressure changes considerably depending on the operating conditions, control accuracy can be improved by changing the allowable range of ΔP depending on the operating conditions. Furthermore, if the combustion condition is poor and the engine is on the verge of ignition or misfire, ΔP becomes small and appropriate control becomes difficult. FIG. 5d shows an example of changes in cylinder pressure in such a case. Therefore, in order to determine such abnormal combustion, in addition to θ ₁ and θ ₂ , one more
The cylinder pressure is also detected at a crank angle such as θ _T or θ ₃ (corresponding to the fourth crank angle). In the case of abnormal combustion, there is not much of a pressure difference between the in-cylinder pressure at θ _T or θ ₃ compared to the pressures at the other two points, so abnormality can be determined by detecting the difference. Generally, the slope of the change in cylinder pressure is steeper when the pressure increases than when the pressure decreases, so θ ₁ and θ ₂ should be set at slightly shifted positions rather than symmetrical with respect to θ _T. is appropriate. Next, we will introduce MTB control based on the basic principle described above.
The explanation will be given according to the program shown in the figure. When this program detects the [H] pulse of the reference position signal Ca of the crank angle sensor 7, it changes the [H] pulse of the unit signal _C1.
Pulses are counted a predetermined number of times and start when the crank angle θ reaches a predetermined value. First, compare the crank angle θ with θ ₁ at P ₁ , and find that θ<θ ₁
When θ≧θ ₁ , _the voltage signal _{S 2 at} this time (that is, the charge amplifier output corresponding to the combustion pressure) is taken in and A/D converted. Next, in P ₃ , the crank angle θ is compared with the target value θ _T , and if θ < θ _T , it waits, and θ≧
When θ _T is reached, the voltage signal S ₂ at this time is taken in at P ₄ and A/D converted. Similarly, at P ₅ and P ₆ , the voltage signal S ₂ at the time when θ≧θ ₂ is taken in and A/D converted. As a result, the voltage signals at θ ₁ , θ _T , θ ₂
S ₂ , that is, the cylinder pressure, is each digitally processed. These processed values are then stored in a predetermined area of the RAM 13. Here, the combustion pressure of the engine is θ ₁ , θ ₂ and θ _T or θ ₃ for abnormality determination.
It is captured at the timing of a total of three points. Therefore, it is not necessary to take data in chronological order at an extremely high frequency as in the conventional example, so the number of sampling times can be greatly reduced, eliminating the need for high-speed A/D converters and high-performance microcomputers, etc. Effective MBT control can be achieved with a relatively inexpensive and simple system configuration. In addition, in the above, when signal processing of the signal S ₂ is performed at a different crank angle of θ ₃ shown in the embodiment of FIG. 5 d instead of θ _T , the order of A/D conversion may be different. . Furthermore, the A/D conversion of the signal S ₂ may be executed in the form of an interrupt, and in this case, other processing can be executed from the start of this program to θ ₂ , which burdens the CPU 11. becomes lighter. Next, abnormal combustion is detected in _P7 . The method is ΔP′=|Pθ ₁ −Pθ _T |, ΔP″=|Pθ ₂
−Pθ _T | The pressure difference ΔP′, ΔP′ is obtained from the engine speed, intake air amount, etc. The pressure difference ΔP is recognized as normal according to the operating conditions at that time. When the conditions ΔP _N >ΔP' and ΔP _N >ΔP'' are satisfied for _N , the current combustion is determined to be abnormal combustion.In this case, θ ₁ , θ ₂ are used as information for the following control. The cylinder pressure Pθ ₁ corresponding to
Suppose that Pθ ₂ is not used. Note that the above-mentioned abnormality determination function can also be used as a device for detecting misfire, and in that case, it can be performed with a simpler configuration than conventional ones. In addition, when detecting a misfire, the voltage signal S ₂
As the crank angles for digitally processing, θ ₁ , θ ₂ , θ _T , and θ ₃ may be used as described above. On the other hand, if normal combustion is determined at P ₇ instead of abnormal, the positional relationship between the combustion peak position θ _pnax and the target value θ _T is detected at P ₈ . Specifically, first, ΔP=|
Pθ ₁ −Pθ ₂ | is calculated, and the allowable pressure difference ΔP ₀ corresponding to the operating conditions at that time is calculated, and these are compared to determine the positional relationship between the two as shown in Table 1 below.

[Table] This judgment is based on the basic principle mentioned above.
This can be easily done from digitally processed values of θ ₁ , θ ₂ , θ _T , and the in-cylinder pressure at these values. Next, in _P9 , MBT control of the ignition timing is performed using the above determination result and the pressure difference ΔP so that the combustion peak position θ _pnax comes to a predetermined position where the generated torque is maximized. The details of MBT control are well known and are described in, for example, Japanese Unexamined Patent Publication No. 82074/1982, so they will not be described here. The ignition timing correction amount m is calculated by MBT control, and the previous ignition timing correction amount M' and the current correction amount m are calculated.
The sum M′+m becomes the current ignition timing correction amount M M=M′+m. In addition, the basic ignition timing N (represented by an advance value in the figure) is determined from the data table shown in Fig. 7 based on the operating conditions such as engine speed and intake air amount, and the final ignition timing is determined from this N and the above M. The timing (N+M) is determined, and when the timing arrives, the ignition signal Sp is output and the ignition means 16 ignites the air-fuel mixture. In this way, by detecting multiple low cylinder pressures, it is possible to easily and at low cost use the capabilities of conventional systems.
MBT control becomes possible. As a result, it is possible to increase the combustion efficiency of the engine, improve torque characteristics, and achieve improvements in fuel efficiency and driving performance. Moreover, if the above-described ignition timing control is performed including abnormal information such as misfire, it becomes possible to further improve the driving performance. (Effects) According to the present invention, the configuration of the system required for MBT control is simplified, and MBT control can be performed easily and at low cost using the capabilities of conventional systems, thereby improving engine operating performance. I can do it.

[Brief explanation of the drawing]

Fig. 1 is a basic conceptual diagram of the present invention, Figs. 2 to 7 are diagrams showing an embodiment of the present invention, Fig. 2 is a block diagram thereof, and Fig. 3A is an installation state of the cylinder pressure sensor. 3B is a plan view of only the cylinder pressure sensor, Figure 4 is a detailed circuit diagram of the charge amplifier, and Figures 5a to 5d show changes in cylinder pressure to explain its operation. FIG. 6 is a flowchart showing the MBT control program, and FIG. 7 is a diagram showing the basic ignition timing characteristics. 1... Cylinder pressure sensor (pressure detection means), 5...
Control unit (combustion pressure intake means,
correction amount calculation means, ignition timing setting means, abnormality determination means), 6... operating state detection means, 16... ignition means.

Claims (1)

[Scope of Claim for Utility Model Registration] a. Pressure detecting means for detecting the combustion pressure of the engine; b. Operating state detecting means for detecting the operating state of the engine; c. output from the pressure detection means at the timing of a first crank angle located on the side and after top dead center, and a second crank angle that is on the lag side than the target value and located after top dead center. At the same time, the third value corresponding to the target value is
combustion pressure intake means that captures combustion pressure even at a timing of a crank angle of or a fourth crank angle that is delayed than the second crank angle; d the first crank angle and the second crank angle; a correction amount calculating means for calculating a correction amount for correcting the basic ignition timing so that the value of the difference is within an allowable value by determining the difference in combustion pressure taken in at the timing of the e engine; ignition timing setting means for setting ignition timing and correcting the basic ignition timing according to the correction amount; f ignition means for igniting the air-fuel mixture based on the output of the ignition timing setting means, and g The difference between the combustion pressure taken at the timing of the third crank angle or the fourth crank angle and the combustion pressure taken at the timing of the first crank angle, and the third crank angle, or Abnormal combustion in the engine is determined when the difference between the combustion pressure taken in at the timing of the fourth crank angle and the combustion pressure taken in at the timing of the second crank angle are both smaller than a predetermined value, and the correction amount is calculated. An ignition timing control device for an internal combustion engine, comprising an abnormality determining means for prohibiting a correction operation of the means.