JP3234418B2 - Lean limit detection method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lean limit detection method for detecting a limit at which a combustion failure occurs due to lean combustion in an internal combustion engine for an automobile.

[0002]

2. Description of the Related Art In recent years, it has become increasingly necessary to operate an engine with the air-fuel ratio leaner than the stoichiometric air-fuel ratio in order to improve fuel efficiency. In response to such needs, in this type of internal combustion engine, the load of the engine is detected and the engine is in a predetermined transient state, for example, as in an air-fuel ratio control device described in Japanese Patent Application Laid-Open No. 62-162742. In this case, feedback control based on a stoichiometric air-fuel ratio is performed in a case where the fuel supply amount is controlled at an air-fuel ratio set leaner than the stoichiometric air-fuel ratio in a steady running state. The control of the air-fuel ratio on the lean side is performed by using the output of the air-fuel ratio sensor so that the air-fuel ratio becomes a target air-fuel ratio (target air-fuel ratio). The air-fuel ratio sensor is usually disposed upstream of the three-way catalyst in the exhaust system.

[0003]

It is known that torque fluctuations occur as the air-fuel ratio is increased. Therefore, it is not possible to set the upper limit of the lean burn region to an air-fuel ratio equal to or higher than a certain value. Can not. Such torque characteristics are unique to the environment and the engine, and the upper limit air-fuel ratio in the lean burn region is not always constant according to such respective torque characteristics, and is set according to the engine and the operating environment. There is a need. Therefore, it has been proposed to detect the limit of torque fluctuation and set a target air-fuel ratio lower than the air-fuel ratio at that time to set a lean burn region.

In order to detect the upper limit of the lean burn region, for example, a method of detecting a change in the duration of the ion current has been attempted. In the detection method using the ionic current, generally, the time from when the ionic current is generated to when it disappears is measured, and the upper limit of the lean burn region is detected from the fluctuation state of the measured time. In this case, the timing is performed based on the cycle of A / D conversion performed to measure the ion current value. That is, since the A / D conversion cycle is determined according to the number of revolutions of the engine, the duration of the ion current can be measured by counting the number of data obtained by the A / D conversion. In such a case where the time is measured using the A / D conversion, if the A / D conversion cycle is long, the result of the time measurement increases, and the accuracy decreases.

[0005] Further, when trying to measure the time from the generation to the disappearance of the ion current, the processing time for A / D conversion of the ion current becomes longer, and the efficiency of the A / D conversion processing decreases. In view of this situation, for example, it is conceivable to measure the duration of the subsequent ion current with reference to top dead center, but the degree of variation with respect to the length of the measured time is large. In other words, when the measured time is long, the fluctuation rate is small, but when the measured time is short, the fluctuation rate becomes large as compared to when the measured time is long, and it is difficult to determine the limit.

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

[0007]

In order to achieve the above object, the present invention takes the following measures. That is, in the lean limit detection method according to the present invention, an ionic current is supplied to the combustion chamber of an internal combustion engine for each ignition, a time during which the ionic current is generated is measured, and a lean limit is detected based on the measured time. A method of detecting a lean limit, in which the ion current is continuously generated after a predetermined time determined according to the ignition timing from the ignition to the time when the ion current is generated in normal combustion. Is measured, and the predetermined time and the measured time are summed, and when the total time is equal to or less than a set time, a lean limit is determined.

[0008]

With such a configuration, the predetermined time is determined by the ignition timing, and therefore does not need to be measured. As a result, the time actually measured is determined by starting the measurement after the predetermined time has elapsed. Only during the continuation of the ion current.
In other words, not all time measurement is performed after the ion current is generated until it disappears, but the processing time required for the time measurement is reduced. Therefore, for example, when time measurement is performed using the cycle of the A / D conversion processing for measuring the ion current value, it is possible to improve the A / D conversion processing efficiency.

In addition, since the lean limit is determined based on the sum of the predetermined time and the continuation time of the ion current measured thereafter, the continuation of the ion current actually measured is continued. Even if the time is short, the measurement variation of the time is relatively small with respect to the total time, and the rate of the variation affecting the length of the measured time is small. Therefore, the determination accuracy of the lean limit can be increased.

[0010]

An embodiment of the present invention will be described below with reference to the drawings.

The engine 100 schematically shown in FIG. 1 is of a four-cylinder type 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).
, And a surge tank 3 is provided on the downstream side. A fuel injection valve 5 is further provided near one end communicating with the surge tank 3, and the electronic control unit 6 controls the opening of the fuel injection valve 5 based on a basic injection amount TP described later. ing. The spark plug 1 is located at a position corresponding to the ceiling of the combustion chamber 10.
8 is attached. In the exhaust system 20, an O ₂ sensor 21 for measuring the oxygen concentration in the exhaust gas is provided with a three-way catalyst 22 provided in a pipe leading to a muffler (not shown).
Installed upstream of Engine 100
Is not limited to four cylinders as in this embodiment, but may be six cylinders or twelve cylinders.

The electronic control unit 6 includes a central processing unit 7
, A storage device 8, an input interface 9, and an output interface 11. The input / output interface 9 includes a microcomputer for detecting a pressure in the surge tank 3. An intake pressure signal a output from the intake pressure sensor 13;
A cylinder discrimination signal G1, a crank angle reference position signal G2, and an engine speed signal b output from a cam position sensor 14 for detecting a rotation state of the engine 100, and a vehicle speed output from a vehicle speed sensor 15 for detecting a vehicle speed. signal c, a water temperature signal e from LL signal d, the water temperature sensor 17 for detecting a cooling water temperature of the engine from an idle switch 16 for detecting the open or closed state of the throttle valve 2, the current from the O ₂ sensor 21 as described above The signal h and the like are input. On the other hand, from the output interface 11,
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. Although not shown, the electronic control unit 6 has an A for converting an analog signal into a digital signal.
A / D converter is built in.

The spark plug 18 is connected via a high voltage diode 23 to a bias power supply 24 for measuring an ion current and a circuit 25 for measuring an ion current. Various circuits known in the art can be used as the ion current measurement circuit 25 itself including the bias power supply 24. The bias power supply 24 applies a high voltage to the spark plug 18 via the high-voltage diode 23 so that an ion current after ignition flows into the combustion chamber 10. Further, the ion current measuring circuit 25 is electrically connected to the input interface 9 of the electronic control unit 6, measures the ion current generated by applying a high voltage in an analog manner, and outputs an analog signal corresponding to the generated ion current. Is input to the electronic control unit 6.

The electronic control unit 6 includes an intake pressure signal a output from the intake pressure sensor 13 and a cam position sensor 14.
And the rotation speed signal b output from the main engine as main information, the basic injection time TP is corrected by various correction coefficients determined according to the engine state, and the fuel injection valve opening time, that is, the injector final energization time T is determined. A program for controlling the fuel injection valve 5 based on the determined energization time and injecting fuel corresponding to the engine load from the fuel injection valve 5 to the intake system 1 is stored. Also, in this program,
An ion current flows through the combustion chamber 10 of the engine 100 for each ignition, and a time period during which the ion current is generated is measured.
It detects the lean limit based on the measured time,
After the lapse of a predetermined time determined according to the ignition timing from the ignition to the time when the ion current is generated in normal combustion, the time during which the ion current is continuously generated is measured, and the predetermined time is measured. The program is programmed to determine the lean limit when the total time is equal to or less than the set time.

The outline of the lean limit judgment program is as shown in FIG.

When a bias voltage is applied to the spark plug 18 from the bias power supply 24 immediately after ignition, as shown by a solid line in FIG. 3, in the case of normal combustion, the ion current flows rapidly and then immediately before the top dead center TDC. And then increase again,
In the vicinity of the crank angle at which the combustion pressure becomes maximum, the current flows into the combustion chamber 10 so that the current value becomes the peak value at which it becomes maximum. The ionic current exhibiting such a behavior is measured for the time during which the ionic current flows for each ignition in a predetermined cylinder. The ion current is measured from the top dead center TDC by the A / D conversion cycle (unit based on the crank angle) set in accordance with the engine speed NE, for example, 2.5 ° CA (crank angle).
/ D conversion is started, the analog current value is converted to digital data, and the obtained converted value is stored in the RAM of the storage device 8 with the data number DTn in ascending order from the top dead center TDC. Performed by A / D conversion is performed for a certain period of time from the top dead center TDC, for example, 80 ° CA in terms of crank angle.

In FIG. 2, in step S1, it is determined whether or not it is the timing of the top dead center TDC, which is the point in time when a predetermined time after ignition determined according to the ignition timing has elapsed. If there is, the process proceeds to step S2, and if it is not the timing of the top dead center TDC, this control ends.
That is, although the timing of the top dead center TDC is detected based on the signal from the cam position sensor 14, the ignition timing is set with reference to the top dead center TDC. The elapsed time until reaching the dead center can be expressed in terms of a crank angle. In step S2, an ion current value is measured for each A / D conversion cycle. In step S3, it is detected that the ion current value obtained by the A / D conversion is equal to or less than 0, and it is determined whether or not the A / D conversion end timing has been reached. Otherwise, this control is terminated.
In step S4, the number of conversion values obtained by the A / D conversion is multiplied by the A / D conversion cycle in terms of crank angle to determine the final ion generation timing as the combustion parameter NIONAFB.
Set to. In this step, the time during which the ion current from the top dead center TDC continuously flows is measured, and the time is converted into a crank angle and executed. In step S5, it is determined whether or not the combustion parameter NIONAFB is not 0. If not, the process proceeds to step S6,
If it is 0, the process moves to step S7. Step S6
Then, the combustion parameter NIONA is added to the ignition advance angle IGADV.
FB is added, and the final ion generation crank angle NIONA
Calculate F. In step S7, the final ion generation crank angle NIONAF is set to zero.

In such a configuration, after the ignition, in other words, after the ion current is generated, if the piston has not reached the top dead center TDC, the control for detecting the lean limit is executed by completing step S1. Thereafter, when the piston reaches the top dead center TDC, the control proceeds to steps S1 → S2 → S3.
A / D conversion is started to measure the ion current value,
The above steps are repeatedly executed until the timing to end the A / D conversion. Next, when the measurement of the ion current value is continued and the A / D conversion ends, that is, when the ion current value becomes 0, the control proceeds from step S1 to step S1.
The process proceeds from 2 to S3 to S4 to S5, and if the obtained combustion parameter NIONAFB is not 0, the final ion generation crank angle NIONAF is calculated. That is, as shown in FIG. 3, the combustion parameter NIONAFB does not become 0 when the combustion is normal, but becomes shorter as the combustion worsens. Therefore, in the combustion at the lean limit, the ion current may not flow near the top dead center TDC, in which case the ion current did not flow before reaching the top dead center TDC. Assuming that it is in the state, the combustion parameter NIONAFB becomes 0 without being measured. If the combustion parameter NIONAFB is 0, the control proceeds from step S5 to S7, and the final ion generation crank angle NIONAF is set to 0.

The determination of the lean limit is made based on the value of the final ion generation crank angle NIONAF. As described above, in the normal combustion, since the ion current exists even after the top dead center TDC, the combustion parameter NIONAF
B is detected, but TDC
There is no ion current nearby. In other words, when the combustion is degraded, that is, when the air-fuel ratio is lean and the lean limit is reached, the ion current has disappeared at the timing of the top dead center TDC. It becomes 0, and the final ion generation crank angle NIONAF is set to 0, and it is determined that a misfire has occurred completely. Therefore, the combustion parameter NIONA
Even if the value of FB is small, the final generated crank angle NION
AF is the ignition advance angle IGADV and the combustion parameter NIONA
Since it is the sum with FB, the combustion parameter NIONAFB
Of the value due to the A / D conversion cycle has a small effect on the final ion generation crank angle NIONAF. Therefore, it is possible to accurately measure the duration from the generation of the ion current to the disappearance of the ion current, and as a result, the accuracy of detecting the lean limit is improved.

The present invention is not limited to the embodiment described above. In the above embodiment, the A / D conversion is started based on the top dead center TDC. However, the time when the A / D conversion starts, that is, the time when a predetermined time after ignition determined according to the ignition timing has elapsed, is For example, BT before top dead center
It may be set as DC 10 ° CA or ATDC 5 ° CA after top dead center.

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

[0022]

According to the present invention, as described in detail above, the predetermined time determined from the ignition timing and the actual time when the measurement is started after the lapse of the predetermined time are summed to maintain the ion current. Since the combustion time, that is, the lean limit is determined from the calculated time, the processing time required for time measurement can be reduced. In addition, the time is measured from the time when a certain time has elapsed since the generation of the ionic current, and the time for performing the determination is a predetermined time and the subsequent measurement compared to the case where the lean limit is determined based on the time. Since the total time is used, regardless of the length of the measured time,
The measurement variation at that time is substantially equal to the total time, and as a result, data substantially equal to the combustion state of the internal combustion engine is obtained, and the accuracy of obtaining the lean limit can be improved.

[Brief description of the drawings]

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

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

FIG. 3 is an operation explanatory view of the embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 5 ... Fuel injection valve 6 ... Electronic control unit 7 ... Central processing unit 8 ... Storage device 9 ... Input interface 10 ... Combustion chamber 11 ... Output interface 24 ... Power supply for bias 25 ... Circuit for ion current measurement

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-5-332194 (JP, A) JP-A-6-42384 (JP, A) JP-A-6-207575 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) F02D 45/00 F02D 41/04-41/14 F02P 17/12 G01M 15/00

Claims (1)

(57) [Claims] 1. A lean limit detection method for flowing an ion current into a combustion chamber of an internal combustion engine for each ignition, measuring a period of time during which the ion current is generated, and detecting a lean limit based on the measured time. After a lapse of a predetermined time determined according to the ignition timing from the ignition to the time when the ionic current is generated in normal combustion, the time during which the ionic current is continuously generated is measured, and the predetermined time is measured. A lean limit is determined when the total time is less than or equal to a set time.