JPH06159208A - Mbt control method by ion current - Google Patents

Abstract

PURPOSE:To prevent ignition timing from being corrected erroneously by prohibiting conforming work when combustion fluctuation is detected in the case of passing an ion current through a cylinder immediately after ignition and conforming ignition timing to Minimum Spark Advance for Best Torque(MBT) based on the characteristics of the ion current and the position of the MBT. CONSTITUTION:In the electronic control unit 6 of an engine 100, respective detected signals from an intake air pressure sensor 13, a rotational speed sensor 14, a vehicle speed sensor 15, an idle switch 16, a water temperature sensor 17 and a lean sensor 21 are inputted respectively in an input interface 9. From the output interface 11, respective control signals are outputted respectively in a fuel injection valve 5 and a spark plug 18. An ion current is passed through a cylinder 10 immediately after ignition, and ignition timing is conformed to MBT based on the characteristics of the ion current and the position of MBT. In this case, combustion fluctuation is detected based on the characteristics of the ion current. It is possible to prohibit ignition timing from being conformed to MBT when the combustion fluctuation is detected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an MBT control method based on an ion current, which controls the ignition timing mainly by detecting a change in the ion current flowing immediately after combustion in an automobile engine.

[0002]

2. Description of the Related Art Conventionally, as a technique using an ionic current, for example, an internal combustion engine ionic current detecting device disclosed in Japanese Patent Laid-Open No. 54-27277, a spark plug of an engine is used and after ignition. There is known a method of observing a combustion state by detecting that an ion current flows through ions generated by combustion. Utilizing such an ion current detection technique, the applicant previously noted that the peak position of the ion current and the peak position of the combustion pressure (converted to the crank angle) substantially coincide with each other. By detecting the peak position and adjusting the ignition timing, it is possible to obtain the maximum torque at the peak position by the so-called MBT (Minimum Sp
The MBT control method by the ion current for controlling the position of ark Advance for Best Torque) is proposed.

[0003]

In the above control method, there are cases where combustion becomes unstable by adjusting the ignition timing to the retard side. That is,
The engine cannot always be operated if the ignition timing is determined by the MBT, and the knock limit may come before the MBT. For that reason, the knock limit is taken into consideration and the knock margin including the variation factor is provided for ignition. Set the time. In this way, if the ignition timing is changed in consideration of the knock limit, sometimes the ignition timing is adjusted excessively, the combustion becomes unstable and the ion current fluctuates, and the ignition timing cannot be detected because the peak cannot be detected. In some cases, control could not be performed so as to comply with MBT.

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

[0005]

The present invention takes the following means in order to achieve such an object. That is, according to the MBT control method by the ionic current according to the present invention, the ionic current is caused to flow in the cylinder immediately after ignition to measure its characteristic, and the measured ionic current characteristic
Is a MBT control method using an ion current for adjusting the ignition timing to the MBT based on the position of, and detecting combustion variations based on the characteristics of the measured ion current,
It is characterized in that the ignition timing is prohibited from being adapted to the MBT when variations in combustion are detected.

The characteristics of the ionic current in the present invention are the time length from the flow of the ionic current to the peak position where the current value is maximum, the total time length of the time when the current value is above a predetermined value, and from ignition. The time length until the final time when the current value exceeds the predetermined value, the degree of variation in the maximum value of the current value, the degree of variation in the integrated value of the ion current until the final point, and the like.

[0007]

With such a structure, the combustion becomes unstable by adjusting the ignition timing to the retard side in order to generate the maximum torque, and the variation is detected based on the characteristics of the ion current. Then, the control that matches the ignition timing with the MBT is prohibited. In other words, taking the peak position that has the strongest correlation with the ignition timing in the characteristics of the ionic current as an example, when the peak position of the ionic current is detected, it means that there is no variation in combustion. In this case, based on the detected peak position, control is performed so that the peak position of the ion current of combustion at the next ignition timing comes to the MBT position. On the other hand, when the peak position of the ion current is not detected, it means that the combustion is unstable and there are variations, and the peak position required to determine the ignition timing is unknown, so the ignition timing is set to MBT. It is prohibited to control to comply with. This can prevent the ignition timing from being erroneously corrected.

[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, a lean sensor 21, which is an air-fuel ratio sensor for measuring the oxygen concentration in the exhaust gas, is provided at a position upstream of the three-way catalyst 22 arranged in a pipe line leading to a muffler (not shown). Is attached to. This lean sensor 2
No. 1 has a configuration similar to that of a normal O ₂ sensor, and by applying a constant voltage between the atmosphere side electrode and the exhaust side electrode, lean burn from the case of the theoretical air-fuel ratio during feedback control is performed. Current is output according to the oxygen concentration in the exhaust gas over the air-fuel ratio in the region.

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 current signal h from the lean sensor 21 and the like are input. On the other hand, the output interface 11
From the above, a fuel injection signal f is output to the fuel injection valve 5, and an ignition pulse g is output to the spark plug 18 to an igniter (not shown). A bias power supply 24 for measuring an ion current is connected to the spark plug 18 via a 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 MBT control method using an ionic current that causes an ion current to flow in the cylinder immediately after ignition, measures its characteristics, and adjusts the ignition timing to the MBT based on the measured ion current characteristics and the MBT position. It is programmed to detect combustion variation based on the characteristic of the measured ion current, and to prohibit at least adjusting ignition timing to MBT when combustion variation is detected. Is. The outline of this MBT control control program is as shown in FIGS. However, the program itself that calculates the effective injection time TAU in consideration of various correction factors and then calculates the injector final energization time T is
Since a conventionally known one can be used, illustration and description thereof will be omitted. Further, the engine 100 is operated by both control methods of feedback control for operating in the vicinity of the ideal air-fuel ratio and control in the lean burn region, and the control switching determination is engine speed, load magnitude, and cooling. When the engine is in a steady state except when the engine is starting, warming up during warm-up, increasing the amount of warm-up, or in a transient state such as during acceleration, etc. It shall be operated in the lean burn area.

First, regarding the ionic current, if a bias voltage is applied to the spark plug 18 from the bias power source 24 immediately after ignition, as shown in FIG. 3, in the case of normal combustion, the ionic current rapidly flows like a pulse. The characteristic is that it decreases before the top dead center TDC, then increases again, and reaches a peak value where the current value becomes maximum near the crank angle where the combustion pressure becomes maximum. On the contrary, if the combustion is unstable,
As shown in FIG. 4, the characteristic is that the current continues to flow at a low current value during the combustion period without forming a remarkable peak as in normal combustion. Generally, the ignition timing is MB during normal combustion.
It is known that the peak of the maximum combustion pressure at the time of operation conforming to T coincides with a point that is retarded by 15 ° CA (crank angle) from the top dead center TDC. Then, the peak of the ionic current substantially coincides with the peak of the combustion pressure during normal combustion.

Considering such characteristics of the ion current,
First, in step 51, it is determined whether or not a knock has occurred. If a knock is detected, the process proceeds to step 61, and if no knock is detected, the process proceeds to step 52. Knock detection is performed by extracting a knock current having a high frequency characteristic generated by knock that is superimposed on the detected ion current from a low frequency frequency characteristic ion current with, for example, a bandpass filter, and determining the maximum absolute value of the knock current. This is done by detecting the value. Normally, the knock is detected during a predetermined period based on the ignition timing, and if it is not detected within that period, the occurrence of the knock is not detected.

In step 52, the variation of combustion is determined. When the variation is detected, the process proceeds to step 71, and when it is determined that there is no variation, the process proceeds to step 53. This variation detection determines that the current value of the ion current fluctuates multiple times during the measurement period of the ion current, and normalizes when a simple rise and fall is made excluding the fluctuation at the initial measurement. Judge that it is burning. As described above, in the case of normal combustion, as shown in FIG. 3, the peak of the combustion pressure is almost the same, so the peak of the ion current is about 15 ° CA (crank angle) after the top dead center TDC. Although it is located in the vicinity, when the combustion varies, as shown in FIG. 4, the ion current does not form a peak and rises and falls at a low current value, and at which time the current value is the peak value. It cannot be determined and the peak position cannot be detected.

At step 53, MBT control is executed so as to match the ignition timing with MBT. In the MBT control, as shown in FIG. 3, the peak of the ionic current is M during normal combustion.
Since it is in the vicinity of BT, it is detected how much the ion current peak is retarded or advanced from the top dead center TDC, and the ion current peak is determined from the top dead center based on the degree of the retard angle. Adjust the ignition timing so that the ignition timing is delayed by 15 ° CA. By this adjustment, the ignition timing can always match the MBT. As shown in FIG. 5, the ignition timing and the peak position of the ion current are converted into crank angles, and when the ignition timing is before the top dead center TDC (BTDC), the peaks are generated as the ignition timing is retarded. The position also moves from before the top dead center TDC and beyond the top dead center TDC. However, when the ignition timing is between 10 ° CA (BTDC) and the top dead center TDC, the peak position becomes unstable as shown by the dotted line in the figure, indicating that the combustion varies. The relationship between the combustion variation and the ignition timing is shown in FIG. 6, where the ignition timing is 10 ° CA (BTD).
The variation of combustion rapidly increases from C) to the retard angle side. The lean limit parameter may be determined from this relationship. In this embodiment, the position of MBT is set to the top dead center TD.
Although the position is set to be retarded by 15 ° CA from C, it is not limited to this value.

At step 61, since it is detected at step 52 that knock has occurred, knock feedback control is performed. This knock feedback control may employ a method known in the art, in which the knock is detected by a knock sensor and the engine is controlled to a state immediately before the knock occurs. As an example, the ignition timing is retarded until the knock is no longer detected in response to the detection of the knock. In step 71, because the combustion varies, the MBT control is not performed, but
Ignition timing is open control. That is, since the combustion varies due to the ignition timing being adjusted to the retard side, the ignition timing is returned to the basic ignition timing (base ignition timing) according to the engine speed, and the MBT control is not performed at all.

In the above structure, when normal combustion continues, the control proceeds to steps 51 → 52 → 53 to execute the MBT control. When the MBT control is executed in this way and a knock occurs due to an advance,
The control repeats steps 51 → 61 until the knock is eliminated by adjusting the ignition timing.
Knock feedback control is executed instead of T control. By performing this knock feedback control, the ignition timing is advanced regardless of MBT. Then, when the knock is not generated, if the combustion state is normal again, M
The BT control is executed and the engine 100 is operated at the optimum ignition timing. On the other hand, if the combustion fluctuates during execution of the MBT control or knock feedback control, the control proceeds to steps 51 → 52 → 71, and the ignition timing open control is executed without executing (prohibiting) the MBT control.
Also in this case, as in the case of knock feedback control, the main purpose is to return to a normal operating state, and the ignition timing is adjusted to the base ignition timing without adapting to the MBT.

As described above, since the combustion variation is detected by the ion current, the combustion state can be grasped for each ignition in each cylinder, and the ignition timing is adapted to MBT during normal combustion, so that the maximum torque can be obtained. The operating state can be maintained, and if the combustion varies, the ignition timing is open-controlled without performing MBT control.
The ignition timing will not be erroneously corrected due to erroneous detection of BT. Then, even if the combustion is normal, if knocking occurs, knock feedback control is performed without performing MBT control as in the case of variation in combustion. The driving condition does not become unstable. Therefore, smooth rotation can be obtained, and deterioration of drivability and emission can be prevented.

The present invention is not limited to the embodiment described above. For example, when detecting the variation of combustion, not only the peak of the ion current is determined, but also the time when the current value of the ion current exceeds a predetermined value is measured,
When the time is longer than the set time, the peak may be detected or the combustion may be determined to vary. In this case, the measured time is the total time during which the current value exceeds the predetermined value, and from ignition,
It may be any time until the final time when the current value exceeds the predetermined value.

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.

[0021]

As described above in detail, according to the present invention, when the combustion varies, the ignition timing is prohibited from being controlled in conformity with the MBT, so that the ignition timing can be prevented from being erroneously corrected. Therefore, the ignition timing can be surely adapted to the MBT, and the operation near the maximum torque can always be maintained.

[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 waveform diagram showing a waveform of an ion current during normal combustion detected in the same example.

FIG. 4 is a waveform diagram showing a waveform of an ion current when the combustion detected in the example varies.

FIG. 5 is a graph showing the relationship between the ignition timing and the peak position of the ion current in the example.

FIG. 6 is a graph showing a relationship between ignition timing and combustion variation in the 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

Claims (1)

[Claims] 1. An ionic current is caused to flow in a cylinder immediately after ignition to measure its characteristics, and the measured ionic current characteristics and MB are measured.
An MBT control method using an ionic current, which adjusts ignition timing to MBT based on the position of T, in which combustion variation is detected based on the characteristics of the measured ion current, and combustion variation is detected. Is a method of MBT control by ion current, which is adapted to prohibit the ignition timing from being adapted to MBT.