JPH0634490A - Mbt detecting method utilizing ion current - Google Patents

Abstract

PURPOSE:To always control ignition timing so that the timing can conform to MBT (minimum spark advance for best torque) by making an ion current to flow to a cylinder immediately after ignition and calculating the time lag until a prescribed crank angle is reached after the current value becomes the maximum. CONSTITUTION:When a bias voltage is applied across a spark plug 18 from a bias power source 24 immediately after ignition, the ion current suddenly flows and again increases after once decreasing before reaching a top dead center when the combustion is normal. Then the ion current reaches the maximum value near a crank angle at which the combustion pressure becomes the highest. At the time of operation where the firing timing conforms to MBT, the peak of the ion current at which the combustion pressure becomes the highest coincides with a point which is delayed from the top dead center by a specific crank angle. Therefore, when the delayed or advancing angle of the peak of the ion current from the top dead center is detected by monitoring the ion current the peak of which becomes coincident with the combustion pressure, the degree of delayed or advancing angle of MBT can be detected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for detecting MBT by ion current mainly applied to automobile engines.

[0002]

2. Description of the Related Art In recent years, in a system in which an ignition timing is calculated by a computer and a signal is sent to an ignition coil based on the result, the ignition timing is set to MBT (Minimum
It is customary to comply with Spark Advance for Best Torque). This is because, generally, when the ignition timing is advanced under a constant operating condition, the axial torque rises and then descends as shown in FIG. 6, and the change is highest near the top. However, it is usually close to a flat state with a small change width and is insensitive to the ignition advance angle, but the NOx generation amount and the generation of knock are sensitive to the ignition timing, and it acts as a constraint condition when determining the ignition timing. is there. MBT above
Is detected by gradually advancing the ignition timing, retarding the ignition timing after the axial torque becomes flat, and detecting the time when the axial torque begins to decrease.

[0003]

By the way, the engine cannot always be operated if the ignition timing is determined by the MBT, and the knock limit may come before the MBT. In such a case, the ignition timing is set. If it is compatible with MBT, knocking will occur and operation is impossible. Therefore, if the MBT is adapted to the setting of the ignition timing as described above, the operation may not be possible. Therefore, as shown in FIG. 7, the knock margin including the variation factor is taken into consideration in consideration of the knock limit. It is necessary to set it in advance. However, in the case of detecting the MBT at the time when the shaft torque starts to decrease as in the above-described configuration, if the knock limit exists before that, it cannot be detected.

Further, for example, as in an internal combustion engine ion current detecting device described in Japanese Patent Publication No. 54-27277,
There is known a method of observing the combustion state by detecting that an ion current flows in the ions generated by the combustion after ignition by using a spark plug of an engine, but the MBT using the detected ion current is known. Was not to detect.

An object of the present invention is to eliminate such a problem.

[0006]

The present invention takes the following means in order to achieve such an object. That is, the MBT detection method using the ion current according to the present invention measures the time when the ion current is passed through the cylinder immediately after ignition and the current value becomes maximum, and the time difference between the measured time and the predetermined crank angle is calculated. It is characterized in that calculation is performed and the MBT is detected from the calculated time difference.

[0007]

With such a structure, in normal combustion, it is used that the elapsed time from ignition at which the ion current shows the maximum value is substantially equal to the elapsed time when the combustion pressure becomes maximum. is doing. Further, it is known that, in an operation in which the ignition timing is adapted to MBT, the timing at which the combustion pressure becomes maximum corresponds to a specific crank angle. Therefore, the elapsed time that is the maximum current value of the ion current is measured, subtracted from the predetermined crank angle that is set in accordance with the specific crank angle described above, and the MBT for the ignition timing at that time is determined as the crank angle from the time difference. It is possible to detect how many times the lead angle is advanced or retarded after conversion. Using the MBT detected in this way, the ignition timing is always M
It becomes possible to control so as to adapt to BT.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

An engine 100 schematically shown in FIG. 1 is a four-cylinder engine for an automobile, and its intake system 1 has a throttle valve 2 which opens and closes in response to an accelerator pedal (not shown).
Is provided, and the surge tank 3 is provided on the downstream side thereof. A fuel injection valve 5 is further provided near one end of the intake manifold 4 of the intake system 1 communicating with the surge tank 3 and communicating with the cylinder 10 via the intake valve 10a. The electronic control unit 6 controls each cylinder to inject independently. Further, in the exhaust system 20, an O ₂ sensor 21, which is an air-fuel ratio sensor for measuring the oxygen concentration in the exhaust gas, is provided upstream of a three-way catalyst 22 arranged in a pipe line leading to a muffler (not shown). Is installed in position.

The electronic control unit 6 includes a central processing unit 7
And a memory device 8, an input interface 9, and an output interface 11 are mainly configured, and the input interface 9 is for detecting the pressure in the surge tank 3. The intake pressure signal a from the intake pressure sensor 13, the rotation speed signal b from the rotation speed sensor 14 for detecting the engine rotation speed NE, the vehicle speed signal c from the vehicle speed sensor 15 for detecting the vehicle speed, the throttle valve 2 The LL signal d from the idle switch 16 for detecting the open / closed state, the water temperature signal e from the water temperature sensor 17 for detecting the cooling water temperature of the engine, the voltage signal h from the O ₂ sensor 21 described above.
Is entered. On the other hand, the output interface 11 outputs a fuel injection signal f to the fuel injection valve 5 and an ignition pulse g to the spark plug 18. In the spark plug 18,
A bias power supply 24 for measuring an ion current is connected via the high voltage diode 23. As the circuit for measuring the ionic current including the bias power supply and the measuring method itself, various methods known in the art can be used.

The electronic control unit 6 has an intake pressure signal a output from the intake pressure sensor 13 and a rotation speed signal b output from the rotation speed sensor 14 as main information, and various kinds of information are determined depending on the engine condition. The fuel injection valve opening time, that is, the injector final energization time T is determined by correcting the basic injection time with the correction coefficient, and the fuel injection valve 5 is controlled according to the determined energization time to supply the fuel according to the engine load. A program for injecting from the injection valve 5 to the intake system 1 is built in. In this program, an ion current is passed through the cylinder immediately after ignition, the time when the current value becomes maximum is measured, the difference between the measured time and a predetermined crank angle is calculated, and the MBT is calculated from the calculated time difference. It has been programmed to detect.

An outline of this MBT detection control program is as shown in FIG.

To detect MBT by ionic current, when a bias voltage is applied to the spark plug 18 from the bias power source 24 immediately after ignition, as shown in FIG. 4, in the case of normal combustion, the ionic current rapidly flows and then rises. This is performed based on the fact that the ion current value reaches a peak value near the crank angle at which the combustion pressure is maximized, after decreasing before the dead center TDC and then increasing again. Generally, the ignition timing is MB
During operation that is compatible with T, the peak of the maximum combustion pressure is at a specific crank angle, such as 1 from the top dead center TDC.
It is known to coincide with a point delayed by 5 ° CA (crank angle). Therefore, by monitoring the ion current whose peak is almost the same as the peak of the combustion pressure to detect how much the ion current peak is retarded or advanced from the top dead center TDC, the MBT can detect the current time. It is possible to detect how much the ignition timing is retarded or advanced. If the ignition timing is adjusted so that the peak of the ion current is 15 ° CA retarded from the top dead center TDC by utilizing the degree of the retarded angle or advanced angle of the detected MBT, The constant ignition timing can be adapted to MBT. In this embodiment, as the predetermined crank angle set for detecting the MBT, an angle delayed by 15 ° CA from the top dead center TDC is set.

Specifically, first, in step 51, the maximum value MAD of the measured ion current MADCx after ignition is set.
Detect CMAX. The ion current MADCx is a conversion value which is an analog current value converted into digital data by starting A / D conversion from the top dead center TDC at an A / D conversion cycle (unit based on crank angle) set according to the engine speed. Then, the obtained converted values are stored in the RAM of the storage device 8 with the data numbers in ascending order from the top dead center TDC and measured. Next, in step 52, the detected maximum value MA
The data number DTMBTn attached to DCMAX is detected. Since the A / D conversion cycle is determined from the crank angle, the crank angle between the top dead center TDC and the MBT can be determined by multiplying the data number DTMBT _n by the conversion cycle. In step 53, the detected data number DTMBT _n is smoothed by the following equation (1), and the smoothed value MBTAV is calculated.

MBTAV _n = MBTAV _n−1 + (DTMBT _n −MBTAV _n−1 ) / 8 (1) After that, in step 54, the obtained smoothed value MBTA is obtained.
The ion current MA measured this time from the top dead center TDC by multiplying V _n by the A / D conversion period (unit based on crank angle)
The elapsed time BRNTIME until the crank angle of the peak where the maximum value MDCMAX of DCx is reached is calculated. Then, in step 55, the calculated elapsed time BRNTIME is calculated.
The amount of deviation MBTPOS between MBT and MBT is calculated by the following equation (2). MBTPOS = BRNTIME-15 ° CA (2) In this way, when the ignition timing does not match the MBT, the MBT is detected because it is retarded or advanced from the predetermined crank angle. Is. In other words, at each ignition, it is detected how much the ignition timing at that time is advanced or retarded by converting from MBT to a crank angle. The above steps are performed for each cylinder for each ignition.

In this way, since the MBT of the ignition timing can be detected every time without modifying the engine periphery, the control for adjusting the ignition timing to match the MBT can be easily performed.

Next, in order to utilize the above MBT detection, the MBT is detected based on the detected shift amount MBTPOS.
The control for setting the ignition timing that complies with will be described with reference to the flowchart shown in FIG.

First, at step 61, it is judged whether or not it is the first cylinder by a cylinder discrimination signal from a cam position sensor (not shown). If it is the first cylinder, the routine proceeds to step 62. If it is not the first cylinder, the second cylinder is discriminated. Proceed to the process for any one of the three, four, and cylinders. The processing for each cylinder is the same as the processing for the first cylinder, and thus the description thereof is omitted. In step 62, the deviation amount MBT of the first cylinder out of the deviation amounts MBTPOSn obtained this time in steps 51 to 55
The POS 1 is read from the storage device 8. In step 63, the read deviation amount MBTPOS1 is adjusted to the previous ignition timing AESA1 _n-1 of the first cylinder to calculate the present ignition timing AESA1 _n {Equation (3)}. AESA1 _n = AESA1 _n-1 − (± MBTPOS1) (3) In the control for adjusting the ignition timing as described above, the ignition of the first cylinder is started when the operation is performed in the lean burn region. When the ion current MADCx is measured, the control first proceeds from step 51 to step 55 in order to detect MBT, detects the MBT of this ignition, and the ignition timing of this time becomes MBT. Detect how much it is deviated. This deviation is the deviation amount M
The BTPOS code may be retarded or advanced.
In this embodiment, the predetermined crank angle is set to a position that is retarded by 15 ° CA from the top dead center TDC, but it is not limited to this value. Then, the detected deviation amount MB
TPOS1 is stored and used when determining the next ignition timing. The determination of the ignition timing is performed from step 61 to step 63. After the cylinder is discriminated, the deviation amount MBTPOS _{n of the} cylinder is set to the previous ignition timing AES.
It is added to A1 _n-1 to determine the next ignition timing AESA1 _n . In this case, as shown in FIG.
When OS shows a negative value and retards by 5 ° CA, the peak of the ion current MADCx will be MBT due to the next ignition.
The previous ignition timing AESA1 _n-1 is set to a value advanced by the deviation amount MBTPOS so as to overlap with.

As described above, the deviation of the ignition timing that does not conform to the MBT can be detected for each ignition, and the ignition timing can be corrected for each detection and for each cylinder, so that the ignition timing of each cylinder is always maintained. It can be in a state suitable for MBT, and by combining with knock feedback control or the like, engine variations can be absorbed, and it becomes possible to operate at an optimal ignition timing in consideration of the knock limit. Therefore, deterioration of drivability and emission can be prevented.

The present invention is not limited to the embodiment described above.

In addition, the configuration of each part is not limited to the illustrated example, and various modifications can be made without departing from the spirit of the present invention.

[0022]

INDUSTRIAL APPLICABILITY As described in detail above, the present invention provides MB
Since T can be detected for each ignition, it is possible to easily create a state in which it is possible to easily adjust the ignition timing to the optimum ignition timing suitable for MBT.

[Brief description of drawings]

FIG. 1 is a schematic configuration explanatory view showing an embodiment of the present invention.

FIG. 2 is a flowchart showing a control procedure of the embodiment.

FIG. 3 is a flowchart showing a control procedure of the embodiment.

FIG. 4 is a graph showing changes in combustion pressure and ion current with respect to a crank angle in the example.

FIG. 5 is an operation explanatory view of the same embodiment.

FIG. 6 is a graph showing the relationship between ignition timing and shaft torque.

FIG. 7 is a graph showing the relationship between knock limit and MBT in the conventional example.

[Explanation of symbols]

 6 ... Electronic control device 7 ... Central processing unit 8 ... Storage device 9 ... Input interface 10 ... Cylinder 11 ... Output interface 18 ... Spark plug

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Sadao Takagi 2-1-1 Taoyuan, Ikeda-shi, Osaka Daihatsu Industry Co., Ltd. (72) Manabu Takeuchi 1-15-27 Tsukamoto, Yodogawa-ku, Osaka Diamond Within Mondo Electric Co., Ltd.

Claims (1)

[Claims] 1. An ion current is caused to flow in a cylinder immediately after ignition, the time at which the current value becomes maximum is measured, the time difference between the measured time and a predetermined crank angle is calculated, and the MBT is calculated from the calculated time difference. A method for detecting MBT by ionic current, which comprises detecting