JPH0681945B2 - Maximum cylinder pressure detection device for internal combustion engine - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a device for detecting a crank angle position where the pressure in a combustion chamber of an internal combustion engine such as an automobile is maximum.

(Prior Art) Recently, ignition timing is controlled (so-called knock control) in order to prevent engine knock, and at the same time,
The ignition timing is controlled (hereinafter referred to as MBT control) to obtain the maximum torque.

At the time of MBT control, it is necessary to detect the crank angle (hereinafter, referred to as combustion peak position) θ _{pmax at} which the pressure in the combustion chamber (hereinafter, referred to as in-cylinder pressure) becomes maximum, and as a conventional detection of this kind, For example, there is an ignition timing control device described in JP-A-59-39974.

In this device, the in-cylinder pressure sensor is used to detect the in-cylinder pressure, and the in-cylinder pressure signal from the sensor is converted to a voltage in order to obtain the combustion peak position θ _pmax.
The crank angle at which the converted value becomes the maximum is θ _pmax .

(Problems to be Solved by the Invention) However, in such a conventional device, in order to ensure the accuracy of θ _pmax when performing digital processing of the sensor output and detecting θ _pmax based on the result, there are many Since a high-speed A / D converter and CPU were indispensable to obtain the in-cylinder pressure sample, it became a costly device, and the conventional control unit generally used for electronic control of the engine has θ _pmax Was difficult to detect.

(Object of the Invention) Therefore, the present invention compares the in-cylinder pressure with a predetermined value given by the operating condition at that time, and detects θ _pmax from the values of a plurality of crank angles when the magnitude relationship is reversed, By simplifying the system configuration required to detect θ _pmax , it is possible to detect θ _pmax sufficiently at the component level of a conventional control unit without using a high-performance device. The purpose is to provide a time detection device.

(Structure of the Invention) As shown in the basic conceptual diagram of the apparatus for detecting the maximum cylinder pressure in an internal combustion engine according to the present invention, a pressure detecting means a for detecting the combustion pressure of the engine and an operating state of the engine are detected. Operating state detecting means b, reference value setting means c for setting a comparison reference value for determining the combustion peak position according to the operating state, and comparing means d for comparing the combustion pressure and the comparison reference value.
The crank angle is calculated from the output of the comparison means when the magnitude relationship between the combustion pressure and the comparison reference value changes, the direction of change of the combustion pressure at that time is detected, and the combination is set from these values. Peak position calculating means e for calculating the combustion peak position based on a crank angle section excluding a crank angle section of a predetermined angle or less
And are provided to simplify the system configuration required for detecting the combustion peak position θ _pmax .

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

2 to 8 are diagrams showing an embodiment of the present invention, which is an example in which the present invention is applied to an ignition timing control device.

First, the configuration will be described. In FIG. 2, reference numeral 1 denotes an in-cylinder pressure sensor (pressure detecting means), and the in-cylinder pressure sensor 1 converts the combustion pressure in the cylinder into an electric charge by a piezoelectric element, and outputs the electric charge.
Output S ₁ . Specifically, the in-cylinder pressure sensor 1 is screwed to the cylinder head 2 and formed as a washer for the ignition plug 3, as shown in detail in FIGS. 3 (A) and 3 (B).
Tightening part of the spark plug 3 in the outer recess of the cylinder head 2.
It is pressed and fixed by 3a.

The sensor output S ₁ is input to the charge amplifier 4, and the charge amplifier 4 operates as shown in FIG. 4 in detail.
OP1, OP2, resistors R1 to R8, capacitor C1 and diode
A so-called charge-voltage conversion amplifier including D1 to D3 is configured to convert the sensor pressure S ₁ into a voltage signal S ₂ and output the voltage signal S ₂ to the comparator 5. Comparator 5 determines the magnitude relation by comparing the voltage signal S ₂ comparison reference value from the D / A converter 6 (the slice level) SL _A, and outputs a determination signal Sh to the control unit 7. The D / A converter 6 is a slice level output as a digital value from the control unit.
D / A converts SL _D to an analog value and outputs it to the comparator 5. The comparator 5 and the D / A converter 6 form a comparison means 8.

The control unit 7 further includes an operating state detecting means 9
Is inputted, and the operating state detecting means 9 is composed of a crank angle sensor 10 and an air flow meter 11. Crank angle sensor 10 explosive interval (120 ° crank angle for 6 cylinder engine, 180 ° for 4 cylinder engine)
A reference position signal that becomes a pulse of [H] level at a predetermined position before the compression top dead center (TDC) of each cylinder, for example, BTDC 70 °
Unit signal C ₁ that outputs Ca and becomes a pulse of [H] level for each unit angle (for example, 2 °) of the crank angle
Is output. The engine speed can be known by counting the pulses of the signal Ca. Further, the air flow meter 11 detects the intake air amount Qa of the engine and outputs an analog signal Sa.

The control unit 7 has a function as a reference value setting means and a peak position calculating means, and has CPU21, ROM22, RAM2.
3, A / D converter 24 and I / O port 25. C
PU21 I / O according to the program written in ROM22
Θ while taking in the required external data from port 25 and exchanging data with RAM23
Processing values required for _pmax detection and ignition timing control are calculated, and the processed data are output to the I / O port 25 as needed. Together with the signal from the operating condition detecting means 9 and the comparator 5 is input to the I / O port 25, the slice level signal SL _D and the ignition signal Sp digital value is output from the I / O port 25. The A / D converter 24 A / D converts the external signal input to the I / O port 25 according to the instruction of the CPU 21. Further, the ROM 22 stores the calculation program in the CPU 21, and the RAM 23 stores the data used for the calculation in the form of a map or the like.

The ignition signal Sp is input to the ignition means 26, and the ignition means 26
Is composed of an ignition coil, a distributor, an ignition plug, etc., and generates a high voltage based on the ignition signal Sp to ignite the air-fuel mixture.

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

FIG. 5 (a) shows a standard in-cylinder pressure waveform. The crank angle θ _pmax when the in-cylinder pressure reaches the maximum P _max is set to a predetermined position (ATDC 10 ° to 15 °) that maximizes the torque generated by the engine.
When the ignition timing is controlled by MBT so that the temperature reaches (°), combustion efficiency is improved, and fuel efficiency and driving performance are improved by improving the torque characteristics. In order to execute the MBT control having such an advantage, it is necessary to detect θ _pmax . FIG. 5 (b) shows a conventional detection method in which the in-cylinder pressure waveform is digitally processed in order to detect the θ _pmax .

By the way, Pmax fluctuates greatly depending on the operating conditions, but since it is a peak value, it is clear that it exists between two when the pressure is increasing and when it is decreasing. Therefore, the in-cylinder pressure is sliced at a predetermined level SL in order to capture a peak waveform in which the pressure rises and falls above a predetermined level in the narrowest possible portion. Then, the peak value Pmax is obtained between the two sliced values.

The slice level SL is determined according to the operating conditions by taking into consideration that Pmax varies greatly depending on the operating conditions, with the engine speed, the intake air amount, etc. as parameters. The value is selected to be smaller than Pmax and larger than the in-cylinder pressure at the start of detection. Further, the slice level SL is compared with the in-cylinder pressure, and the crank angle and the direction of change (large → small or small → large) when the magnitude relationship changes are stored. For example, when the waveform of FIG. 5 (a) is sliced,
As shown in (c) of the same figure, the crank angle and the direction of change are determined as shown in Table 1 below at the time points indicated by the circles and the crosses.

And from these two values of ATDC 7 ° and 23 °, θ _pmax
Calculate the position of. As an example of the calculation method, there is a method of averaging two angles.

However, in general, the in-cylinder pressure waveform is not a clean waveform as shown in FIG. 5 (a), and noise is superimposed or the combustion state is poor and two peaks appear due to various factors. FIG. 6 (a) shows an example thereof. The first and last peaks are noise, the second peak is due to motoring and the third peak is due to combustion. Such a waveform occurs when the ignition timing is late. The slice mode in this case is shown in FIG. 6 (b), and is as follows according to the order of change.

Of these eight data, the direction of change in cylinder pressure is (small →
If a pair is made so that (large) and (large → small), it becomes four sections (a) to (d) as described above, and each of these sections is represented by a crank angle [-16, -16], [-
3, 6], [15, 50], [53, 54]. In addition, TDC
The front is represented by a negative angle.

Of the above four pairs, a section where the combustion pressure has a peak θ _pmax is searched. First, when the width of the section is equal to or less than a predetermined angle, for example, 2 ° or less, this is determined as noise and the data is removed from the candidates. Normally, this operation narrows down the candidates to two or less. However, when the number of candidates is 1 as a result of the narrowing down, the candidate section is determined as an existing section of the combustion peak position θ _pmax , but when the number of candidates is 2, for example, as in the above example, When the section (a) and the section (d) are below a predetermined angle (2 ° or less) and the two sections (b) and (c) excluding these are candidates, the section that appears later, that is, The section (C) is determined as the existence section of the combustion peak position θ _pmax . The reason is that, as described above, the above-mentioned peak is generally caused by motoring. In the example shown in FIG. 6 (a) by such treatment, it is determined that there is a peak in the cylinder pressure between ATDC 15 ° and ATDC 50 °, and the peak position θ is determined from the two values of 15 ° and 50 °. Calculate _pmax . In this way, θ _pmax can be detected by a simple calculation such as comparison processing without digitally processing the in-cylinder pressure at high speed.

Next, the MBT control based on the above basic principle will be described according to the program shown in FIG.

When the program detects the [H] pulse of the reference position signal Ca of the crank angle sensor 10, it starts counting the [H] pulse of the unit signal C ₁ and counts a predetermined number of times to determine the crank angle θ.
Start when the value reaches a predetermined value (for example, θ = BTDC20 °).

First, at P ₁ , the engine speed and the intake air amount are used as pulses to determine the slice level SL _D (digital value) according to the operating conditions at that time, and output to the D / A converter 6. Therefore, SL _D is converted to an analog value SL _A by the D / A converter 6 and input to the comparator 5, and the voltage signal S ₂ is compared with the slice level SL _A by the comparator 5 and the magnitude relationship is determined. The comparison signal Sh is output. At P ₂ , the crank angle θ is detected. The detection end value θ _D end (for example, θ _D end = ATDC60
)), When θ <θ _D end, proceed to P ₃ and θ ≧ θ _D e
When it comes to nd, proceed to p ₅ .

It is determined whether or not the change in P ₃ In comparison signal Sh occurs, change stores P ₄ by the crank angle θ at that time the state of the change in the RAM23, if any. On the other hand, when there is no change, it returns to P ₂ . Therefore, the output Sh of the comparator 5 is monitored by the control unit 7 in the section from BTDC 20 ° to ATDC 60 °, and the crank angle θ when the in-cylinder pressure crosses the slice level SL _A and the changing direction thereof are stored.

Next, of the data stored in the RAM 23 in P ₅ , the section including the peak of the in-cylinder pressure due to combustion is determined according to the basic principle described above, and θ _pmax is detected. When the section including the peak is discriminated, θ _pmax is calculated as follows.

(I) Since the in-cylinder pressure waveform is substantially symmetrical in that section, the center of the section is set to θ _pmax .

(II) Alternatively, since the gradient when the in-cylinder pressure increases is slightly steeper than when the in-cylinder pressure decreases, the point that internally _{divides the} section into a predetermined ratio is θ _pmax . For example, when θ _pmax is experimentally obtained from the inclinations in both directions, it is found that 4: 5 is preferable for a model engine having an internal division point.

If the engine misfires, the peak due to motoring may be mistaken for the combustion peak position in the above _method.In such a case, the ignition timing and θ _pmax
It is possible to judge the misfire from the relationship with. Then, in this case, θ _pmax at the time of misfire is not used as the information for performing the MBT control.

In this way, θ _pmax can be easily detected by comparing and discriminating several points of the in-cylinder pressure and performing digital processing.

This kind of signal processing is different from the conventional method of digitally processing changes in the cylinder pressure continuously one by one, and it is possible to sufficiently cope with the conventional control unit component level and high-speed A / D conversion. No vessel is needed.

Note that, with the same circuit configuration, a change in the output Sh of the comparator 5 may be used as a trigger to interrupt the CPU 21 and execute the same program. If so, θ
_The CPU 21 can execute other programs even during the _pmax detection period, _reducing the load on the CPU 21.

Next, at P ₆ , MBT control is performed based on the detection information of θ _pmax . The following is performed as an example of the MBT control.

While calculating the average value of the latest predetermined number of θ _pmax ,
It is compared with a target value, and the ignition timing correction amount m is calculated according to the result. Next, the previous ignition timing correction amount M ′ and the current correction amount m (M ′ + m) are set as the current ignition timing correction amount M (M = M ′ + m). Further, the basic ignition timing N (represented by an advance angle value in the figure) N is obtained from the operating conditions such as the engine speed and the intake air amount, for example, from the data table shown in FIG. Ignition signal when timing (N + M) is determined and the timing is reached
Sp is output and the air-fuel mixture is ignited by the ignition means 26. As a result, the ignition timing is controlled so as to maximize the generated torque. As a result, it is possible to improve the combustion efficiency of the engine and improve the torque characteristics, and it is possible to achieve improvements in fuel consumption and driving performance.

(Effect) According to the present invention, the system configuration required for detecting θ _pmax can be simplified, and θ _pmax can be easily and low cost at the component level of the conventional control unit.
Can be detected.

[Brief description of drawings]

FIG. 1 is a basic conceptual diagram of the present invention, FIGS. 2 to 8 are diagrams showing an embodiment of the present invention, and FIG. 2 is a block configuration diagram thereof.
3 (A) is a sectional view showing the mounting state of the cylinder pressure sensor, FIG. 3 (B) is a plan view of only the cylinder pressure sensor, and FIG. 4 is a detailed circuit diagram of the charge amplifier. FIGS. 6A to 6C are first timing charts for explaining the action, FIGS. 6A and 6B are second timing charts for explaining the action, and FIG. That
FIG. 8 is a flowchart showing the MBT control program, and FIG. 8 is a diagram showing the characteristic of the basic ignition timing. 1 ... In-cylinder pressure sensor (pressure detection means), 7 ... Control unit (reference value setting means, peak position calculation means), 8 ... Comparison means, 9 ... Operating state detection means.

Claims (2)

[Claims] 1. A) pressure detection means for detecting the combustion pressure of the engine, b) operating state detection means for detecting the operating state of the engine, and c) a comparison reference for determining the combustion peak position according to the operating state. Reference value setting means for setting a value, d) comparing means for comparing the combustion pressure with the comparison reference value, and e) calculating the crank angle when the magnitude relationship between the combustion pressure and the comparison reference value changes from the output of the comparing means. The combustion peak position is detected based on the crank angle section, which detects the direction of change of the combustion pressure at that time, and which is set from the combination of these values, and excludes the crank angle section equal to or less than the predetermined angle. A peak position calculating means for calculating the following, and an internal cylinder pressure maximum timing detecting device for an internal combustion engine, characterized in that: 2. 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, and c) a comparison reference for determining the combustion peak position according to the operating state. Reference value setting means for setting a value, d) comparing means for comparing the combustion pressure with the comparison reference value, and e) calculating the crank angle when the magnitude relationship between the combustion pressure and the comparison reference value changes from the output of the comparing means. In addition, when the direction of change of the combustion pressure at that time is detected, and there are two remaining crank angle sections other than the crank angle section of a predetermined angle or less among the crank angle sections set from the combination of these values. Is a peak position calculating means for calculating a combustion peak position based on a crank angle section appearing later, and a cylinder pressure maximum timing detecting device for an internal combustion engine.