JP3154304B2 - Lean limit control method using ion current - 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 control method using an ionic current for controlling fuel at a lean burn limit when operating in a lean burn region where the air-fuel ratio is high, mainly in an internal combustion engine for an automobile. It is.

[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]

By the way, it is known that a torque fluctuation occurs when the air-fuel ratio is increased (FIG. 7 ). Therefore, the upper limit of the lean burn region is set to an air-fuel ratio exceeding a certain value. Cannot be set. As shown in FIG. 8 , such a torque characteristic is more specific to the environment and the engine, and the upper limit air-fuel ratio in the lean burn region is not always constant according to the respective torque characteristics. It must be set according to the driving environment. In response to such a situation, the value of the target air-fuel ratio is set with a certain safety factor (margin).

[0004] However, if the target air-fuel ratio is set including the above-mentioned safety factor, the fuel efficiency is deteriorated and NOx is increased, which is not preferable. In order to solve this, it is conceivable to detect the limit of the torque fluctuation, set the target air-fuel ratio lower than the air-fuel ratio at that time, and set the lean burn region. However, it was difficult to control the engine near the upper limit of the lean burn region. Also,
It was also difficult to attach an air-fuel ratio sensor to the exhaust manifold, detect the air-fuel ratio for each cylinder, and control the air-fuel ratio for each cylinder.

[0005] An object of the present invention is to solve such a problem.

[0006]

In order to achieve the above object, the present invention takes the following measures. That is, the lean limit control method using the ionic current according to the present invention measures the characteristics of the ionic current flowing in the cylinder immediately after ignition, and varies the measured characteristics of the ionic current.
If the lean limit is set based on the attachment rate , the fuel injection amount is increased.

The characteristics of the ion current in the present invention are as follows.
From ignition to the last moment when the ion current is greater than the set value
Shall refer to the result obtained by measuring the duration of the period at . Then, the lean limit is detected based on the variation rate of the duration. In addition, the present onset
The lean limit control method using bright ion current measures the duration of the ion current flowing in the cylinder immediately after ignition from the ignition to the final time when the ion current is greater than the set value, and measures the measured duration. It is characterized in that a lean limit is detected based on a time variation rate , and the fuel injection amount is increased when the lean limit is detected.

[0008]

With such a configuration, the lean burn region is determined based on the characteristic of the ion current, that is, the variation rate of the duration from the ignition to the final time when the ion current is larger than the set value. Detect operating limits at That is, when the air-fuel ratio exceeds the lean limit, the combustion is often slow, so that the characteristics of these ion currents are smaller than the set value compared to the case where the combustion time is normal. The period of the large current value becomes long,
Since the peak value of the ion current becomes lower, the lean limit is detected by determining the rate of the variation in the length of the period, which becomes longer according to the combustion time. When the lean limit is detected, the fuel injection amount is increased and corrected.
Control is performed so that the operation is continued at the air-fuel ratio immediately before the torque fluctuation occurs. If you have exceeded the lean limit,
Since the air-fuel ratio is so lean that normal combustion cannot be expected,
The fuel injection amount is increased and corrected. Thus, fuel efficiency and drivability do not deteriorate near the limit of torque fluctuation.

[0009]

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).
, And a surge tank 3 is provided on the downstream side. In the vicinity of 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, a fuel injection valve 5 is further provided. In addition, the electronic control unit 6 controls so as to perform independent injection for each cylinder. In the exhaust system 20, a lean sensor 21 as an air-fuel ratio sensor for measuring the oxygen concentration in the exhaust gas is provided at a position upstream of a three-way catalyst 22 provided in a pipe leading to a muffler (not shown). Attached to. This lean sensor 2
Reference numeral 1 has a configuration substantially similar to that of a normal O ₂ sensor. By applying a constant voltage between the atmosphere side electrode and the exhaust side electrode, lean burn is performed from the case of the stoichiometric air-fuel ratio at the time of feedback control. The 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
, A storage device 8, an input interface 9, and an output interface 11. The microcomputer system mainly includes a microcomputer system having an input interface 9 for detecting a pressure in the surge tank 3. The intake pressure signal a from the intake pressure sensor 13, the rotational speed signal b from the rotational speed sensor 14 for detecting the engine rotational speed NE, the vehicle speed signal c from the vehicle speed sensor 15 for detecting the vehicle speed, the throttle valve 2 An LL signal d from the idle switch 16 for detecting the open / close state, a water temperature signal e from the water temperature sensor 17 for detecting the cooling water temperature of the engine, a current signal h from the above-described lean sensor 21 and the like are input. On the other hand, the output interface 11
After that, the fuel injection signal f is output to the fuel injection valve 5 and the ignition pulse g is output to the spark plug 18. A bias power supply 24 for measuring an ion current is connected to the spark plug 18 via a high voltage diode 23. Various circuits known in the art can be used for the circuit for measuring the ion current including the bias power supply and the measuring method itself.

The electronic control unit 6 uses the intake pressure signal a output from the intake pressure sensor 13 and the rotational speed signal b output from the rotational speed sensor 14 as main information, and various kinds of information determined according to the engine conditions. The basic injection time is corrected by the correction coefficient to determine the fuel injection valve opening time, that is, the injector final energization time T. The fuel injection valve 5 is controlled based on the determined energization time, and the fuel corresponding to the engine load is supplied to the fuel. A program for injecting the fuel from the injection valve 5 to the intake system 1 is incorporated. In this program, the value of the ion current flowing in the cylinder immediately after the ignition is compared with a set value, and the ion current is larger than the set value from the ignition of the ion current.
It is programmed to measure the duration of the period up to the end point , detect the lean limit based on the variation rate of the measured duration, and increase the fuel injection amount when the lean limit is detected. is there.

The outline of the lean limit control program is as shown in FIGS. However, the program itself for calculating the effective injection time TAU in consideration of various correction coefficients and thereafter calculating the injector final energization time T can be a conventionally known program, and therefore, illustration and description thereof are omitted. The control switching determination between the feedback control for operating near the stoichiometric air-fuel ratio and the control in the lean burn region is performed based on the engine speed, the magnitude of the load, the cooling water temperature, and the like, and the engine is being started. It is assumed that the engine is operated in the lean burn region when the engine is in a steady state, except for a case where the engine is in a steady state, except for a case where a warm-up operation is being performed during a warm-up operation, or a transient state such as during acceleration.

The lean limit is detected by the ionic current. When a bias voltage is applied from the bias power supply 24 to the spark plug 18 immediately after ignition, as shown in FIG. This is performed based on the fact that the ion current decreases before the top dead center TDC and then increases again, and reaches a peak value at which the value of the ion current becomes maximum near the crank angle at which the combustion pressure becomes maximum. On the other hand, in the case of unstable combustion, as shown in FIG. 5, the ion current value does not increase as a whole and the peak value does not appear clearly because of slow combustion in the latter half of combustion as compared with the case of normal combustion. It is. An ion current exhibiting such characteristics is measured at predetermined time intervals, and a combustion state detection level PIONA is set as a set value.
The lean limit is detected based on the time during which the state exceeding F is maintained (duration).

Specifically, first, in step 51b , a point
From the fire, the ion current MADCx becomes the combustion state detection level P
The period c up to the final point which is larger than IONAF (see FIG. 6)
), The combustion duration CNION
Measure AF. Measurement of the combustion duration time between CNIONAF
A / D converts the ion current MADCx and converts the converted data.
Data and calculate the combustion duration from the calculated data
Calculate NIONAF. The A / D conversion is performed only during a predetermined crank angle (for example, 80 °) from the ignition, and is not converted thereafter, and the ion current MADCx is larger than the combustion state detection level PIONAF the latest in this period. A certain point is adopted as the last point. The calculation in this case is based on the A / D conversion period (for example, 2.5
° CA) is known, so that A /
This is performed by multiplying by the D conversion period. Ion current M
ADCx is A / D set according to the engine speed.
A / D conversion is started from the top dead center TDC in the conversion cycle, and the obtained conversion value is stored in the RAM of the storage device 8 and measured.

Next, in step 52b, the current ignition
Including the combustion duration NIONAF
The combustion duration NIONAF (for example, 3
Divided by the average value of the standard deviation of
Calculate the number NIONHDK. The standard deviation calculation is generally
And may be performed in a manner well known to those skilled in the art.
Next, in step 53b, the obtained variation coefficient NION
HDK _n is set to the fuel limit set to detect the lean limit.
If the value exceeds the grilling variation coefficient determination level OVIONHDK
In that case, it is determined that the combustion at that time was at the lean limit.
You. That is, coefficient of variation NIONHDK _n combustion variation coefficient
If the judgment level OVIONHDK is exceeded, the
NIONAF varies in duration due to misfire or slow burning
Due to that. In addition, instead of standard deviation, statistics
Alternatively, a dispersion may be used.

As described above, since the detection of the lean limit is performed by the ion current measured after one ignition, it can be performed for each ignition and for each cylinder.

Next, the correction for increasing the fuel injection amount when the lean limit is detected will be described. In FIG. 3, first, in step 61, it is determined whether or not the cylinder is the first cylinder based on a cylinder determination signal from a cam position sensor (not shown).
If it is the first cylinder, the process proceeds to step 62. If it is not the first cylinder, the process proceeds to one of the second, third, and fourth cylinders. The processing for each cylinder is the same as that for the first cylinder, and a description thereof will be omitted. In step 62, it is determined whether or not the lean limit has been detected. If the lean limit has been detected, the process proceeds to step 63; otherwise, the process proceeds to step 64. In step 63, the injection correction coefficient FTAULN1 based on the lean limit is calculated by the following equation (2). In equation (2), the current injection correction coefficient FT
AULN1 _n is obtained from the last injection correction coefficient FTAULN _n-1 by adding the correction addition amount during the lean limit.

FTAULN1 _n = FTAULN _n-1 + KTAULN1A (2) On the other hand, in step 64, the injection correction coefficient FTAULN1 is calculated by the following equation (3). In Expression (3), KTAULN1D is a correction subtraction amount in the lean burn region until the lean limit is reached.

FTAULN1 _n = FTAULN _n−1 −KTAULN1D (3) In step 65, the calculated injection correction coefficient FAULN
1, the effective injection time T for the fuel injection amount of the first cylinder
AU1 is calculated.

TAU1 = TAUBSE1 × FAULN1 (4) Here, TAUBSE1 is obtained by multiplying the basic injection time TP by various correction coefficients required at the time of calculation.

In the above configuration, when the operation is performed in the lean burn region, the measurement of the ion current is performed for each ignition, and the lean limit is detected from the combustion duration NINONAF of the measured ion current. . In this case, control proceeds to steps 51 b → 52 b → 53 b , the combustion duration NIONAF _n of the current measured ion current
By calculating the coefficient of variation NIONHDK _n indicating the variation rate, is to determine whether the operating state at the lean limit by the result. That is, in the change of the ionic current at the time of instability shown in FIG. 5, the fuel burns without showing a peak as compared with the normal state, and the burning duration is longer than that of the normal state. When the lean limit is detected in this manner, the control proceeds to step 61 to correct the fuel injection amount at the lean limit. If the cylinder at the detected lean limit is the first cylinder, the control
The process proceeds from step 61 → 62 → 63 → 65, and the fuel injection amount of the first cylinder is increased and corrected. Thereafter, if the operating state of the same first cylinder is not the lean limit, the control proceeds to steps 61 → 62 → 64 → 65, the fuel injection amount is corrected to be reduced, and the air-fuel ratio is further shifted to the lean side. It is.

As described above, since the lean limit can be detected for each ignition and for each cylinder, and the fuel injection amount can be corrected for each detection, it is possible to flexibly respond to changes in the operating environment. The same is true for individual engines, and therefore, it is possible to operate with lean burn in a region sufficiently close to the non-constant lean limit, and to improve fuel economy because of the lean operation at the limit. In addition, it is possible to suppress the occurrence of torque fluctuation and prevent deterioration of drivability and emission.

The present invention is not limited to the embodiment described above, and may be controlled by simultaneous injection in a multi-cylinder engine.

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.

[0026]

As described in detail above, the present invention detects the lean limit of the air-fuel ratio based on the characteristics of the ion current, that is, based on the variation rate of the length of the duration of the ion current. At this point, the fuel injection amount is increased and the operation is continued at the air-fuel ratio immediately before the torque fluctuation occurs.Therefore, lean combustion at a high air-fuel ratio near the limit of the lean burn region without deteriorating fuel efficiency Can be.

[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 a flowchart showing a control procedure of the embodiment.

FIG. 4 is a graph showing a change in a combustion pressure and an ion current with respect to a crank angle in the embodiment.

FIG. 5 is a graph showing changes in the ion current during stable combustion and the ion current during unstable combustion with respect to the crank angle in the embodiment.

[6] operation explanatory view showing the burning duration in step 51 b of the embodiment.

FIG. 7 is a graph showing a change in torque fluctuation with respect to an air-fuel ratio .
H.

FIG. 8 is a graph showing a variation in a lean limit in a conventional example .
rough.

[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

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Katsuyuki Kajiya 2-1-1, Taoyuan, Ikeda-shi, Osaka Dai-Hatsu Kogyo Co., Ltd. (56) References JP-A-5-65864 (JP, A) JP-A Heisei 5-312081 (JP, A) JP-A-5-18297 (JP, A)

Claims (1)

(57) [Claims] 1. Ion current flowing in a cylinder immediately after ignition
The last time the ion current is greater than the set value from ignition
Measuring the duration of the period up to the point , detecting the lean limit based on the variation rate of the measured duration, and increasing the fuel injection amount when the lean limit is detected. Limit control method.