JPH08261047A - Lean limit sensing method - Google Patents

Abstract

PURPOSE: To precisely detect lean limit by generating ion current at every ignition in a combustion chamber, measuring time while the ion current is generated, computing a fluctuation ratio of the measured time, and determining lean limit when the fluctuation ratio is a target value. CONSTITUTION: An electronic control unit 6 determines a fuel injection valve opening time while correcting a base injection time through various correction factors determined according to an engine condition, for controlling a fuel injection valve 5. In a normal operation state, lean burn condition is obtained and feedback control is performed based on a voltage signal output from an deg.sensor 21. Ion current is generated at every ignition time inside a combustion chamber 10 of an engine 100. Time is measured while the ion current is generated, and a fluctuation rate of the measuring time is computed. When the fluctuation ratio is a target value which is previously set according to the operation condition of the engine 100, lean limit is detected.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art In recent years, in order to improve fuel efficiency, it is increasingly necessary to operate the engine with the air-fuel ratio leaner than the theoretical air-fuel ratio. In response to such needs, in this type of internal combustion engine, the engine load is detected and the engine is in a predetermined transient state, as in the air-fuel ratio control device disclosed in JP-A-62-162742. In this case, it is known that feedback control is performed by the stoichiometric air-fuel ratio, and in steady-state running, the fuel supply amount is controlled by the air-fuel ratio set leaner than the stoichiometric air-fuel ratio. Then, in such control of the air-fuel ratio on the lean side, the control is performed by using the output of the air-fuel ratio sensor so that the target air-fuel ratio (target air-fuel ratio) is obtained. The air-fuel ratio sensor is usually arranged upstream of the three-way catalyst in the exhaust system.

[0003]

By the way, it is known that the torque fluctuation occurs when the air-fuel ratio is increased, and therefore the upper limit of the lean burn region cannot be set to a certain value or more. Can not. Such torque characteristics are peculiar to the environment and engine, and the upper limit air-fuel ratio in the lean burn region is not always constant according to each torque characteristic, and is set according to the engine and 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 by the air-fuel ratio at that time to set the lean burn region.

Limit of Torque Fluctuation In other words, in order to detect the upper limit of the lean burn region, that is, the lean limit in which the vibration of the engine or the vehicle body feels uncomfortable due to the fluctuation of torque, for example, the ion current is maintained. Attempts have been made to detect variations in time.
In the detection method using the ion current, generally, the time from the time when the ion current is generated until the ion current disappears is measured, and the upper limit of the lean burn region is detected from the fluctuation state of the measured time.

In such a detection method, the ion current is detected for each ignition, and the variation rate of the generation time of the ion current is obtained, and the variation of the operating state is shown in FIG. As shown in (display), when the rate of change is equal to or greater than a predetermined limit value, the lean limit is detected as such a change in the generation time due to lean burn. However, the absolute value of this fluctuation rate changes depending on the operating condition of the engine.Therefore, if a predetermined limit value is set in this way and the lean limit is detected based on that limit value, it will always be in various operating conditions. Sometimes it was difficult to detect lean limits.

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, the lean limit detection method according to the present invention generates an ion current for each ignition in the combustion chamber of the internal combustion engine, measures the time during which the ion current is generated, and calculates the fluctuation rate of the measured time. , The operating condition of the internal combustion engine at the time of calculating the variation rate is detected, and the lean limit is set when the obtained variation rate in the detected operating state is the target variation rate set in advance according to the operating state of the internal combustion engine. It is characterized by detecting.

[0008]

With such a structure, the fluctuation rate of the time during which the measured ion current continues to flow is determined according to the operating state of the internal combustion engine. In other words, the lean limit is not detected as the lean limit at that time if the variation rate of the measured ion current generation time exceeds a certain variation rate, and the internal combustion engine of the time point when the variation rate is calculated is not detected. The operating state is detected, and the lean limit is detected by comparing the variation rate with the target variation rate for each operating state. Therefore, the lean limit can be reliably detected even when the operating state of the internal combustion engine is different.

[0009]

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 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).
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 communicating with the surge tank 3, and the fuel injection valve 5 is controlled to be opened and closed by an electronic control unit 6 based on a basic injection amount TP described later. ing. Then, at a position corresponding to the ceiling portion of the combustion chamber 10, the spark plug 1
8 is attached. Further, in the exhaust system 20, an O ₂ sensor 21 for measuring the oxygen concentration in the exhaust gas, a three-way catalyst 22 arranged in a pipe line leading to a muffler (not shown).
It is installed at a position 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
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. Intake pressure signal a output from the intake pressure sensor 13,
A cylinder determination signal G1, a crank angle reference position signal G2, an engine speed signal b output from a cam position sensor 14 for detecting the rotational state of the engine 100, and a vehicle speed output from a vehicle speed sensor 15 for detecting a vehicle speed. Signal c, LL signal d from idle switch 16 for detecting the open / closed state of throttle valve 2, engine 1
Water temperature signal e from the water temperature sensor 17 for detecting the cooling water temperature of 00, and 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. Although not shown, the electronic control unit 6 includes an A / D converter that converts an analog signal into a digital signal.

A bias power source 24 for measuring an ion current and an ion current measuring circuit 25 are connected to the spark plug 18 via a high voltage diode 23. As the ion current measuring circuit 25 itself including the bias power source 24, various circuits known in the art can be used. The bias power supply 24 applies a high voltage to the spark plug 18 via the high voltage diode 23 so as to generate an ion current after ignition in the combustion chamber 10. Further, the ionic current measuring circuit 25 is electrically connected to the input interface 9 of the electronic control unit 6, measures the ionic current generated by the high voltage application in an analog manner, and outputs an analog signal corresponding to the generated ionic 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.
The rotation speed signal b output from the main information is used as the main information, and the basic injection time TP is corrected by various correction factors determined according to the engine state to determine the fuel injection valve opening time, that is, the injector final energization time T, A program for controlling the fuel injection valve 5 according to the determined energization time and injecting fuel according to the engine load from the fuel injection valve 5 into the intake system 1 is built in. Further, in a steady operation state that is not during a transition such as acceleration, feedback control is performed based on the voltage signal output from the O ₂ sensor 21 in a lean burn state in which the air-fuel ratio is higher than the theoretical air-fuel ratio. It is programmed.

Further, in this program, the engine 10
When the ion current is generated in the combustion chamber 10 of 0 for each ignition, the time during which the ion current is generated is measured, the fluctuation rate F of the measured time is calculated, and the fluctuation rate F is calculated. It is programmed to detect an operating state of the engine 100 and detect a lean limit when the obtained variation rate F in the detected operating state is a target variation rate Ft preset according to the operating state of the engine 100. There is.
The target fluctuation rate Ft is, as shown in FIG.
The engine speed NE and the intake pressure PM indicating the operating state of are set as parameters, and are stored in the storage device 8 as a target fluctuation rate map. The target fluctuation rate Ft is
The lower the engine speed NE is and the higher the intake pressure PM is, the smaller the engine speed NE is set. When the intake pressure PM is the same, the engine speed NE is set to be substantially inversely proportional to the engine speed NE. The engine speed NE and the throttle opening, or the engine speed NE and the air flow rate may be set as the parameters indicating the operating state. That is, the item is not limited to these as long as the item reflects the magnitude of the load on the engine speed NE. Furthermore, the operating state of the engine may be detected by adding the engine temperature indicated by the cooling water temperature, the lubricating oil temperature, the intake air temperature, etc. to these parameters.

The outline of this lean limit detection program is as follows.
It is as shown in FIG.

Normally, when a bias voltage is applied to the spark plug 18 from the bias power source 24 immediately after ignition, the ionic current, in the case of normal combustion, as shown in FIG. It flows in the combustion chamber 10 so that it decreases before the dead center TDC and then increases again, and the current value reaches its peak value near the crank angle where the combustion pressure becomes maximum. The time during which the ionic current that exhibits such behavior flows for each ignition in a predetermined cylinder or each cylinder (the time during which it occurs)
Is measured from ignition until the ionic current disappears. The ion current generation time Ti is substantially equal to or proportional to the combustion time of the cylinder. The ion current is measured by A / D conversion cycle (unit based on crank angle) set according to the engine speed NE, for example, every 2.5 ° CA (crank angle), and A / D is measured immediately after ignition.
The conversion is started by converting the analog current value into a converted value which is 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 ignition. Then, the ion current generation time Ti converted into a crank angle is measured from the obtained number of converted values and the A / D conversion cycle.

In the flowchart shown in FIG. 3, first, in step S1, it is determined whether or not feedback control is being performed in the lean burn region. When the feedback control is not executed, this lean limit detection program is stopped. On the contrary, if the feedback control is being performed, the control proceeds to step S2, and the target variation rate Ft is obtained from the target variation rate map from the engine speed NE and the intake pressure PM at this time. Then, the control proceeds to step S3, and the fluctuation rate F of this time is calculated by the following equation using the ion current generation time Ti measured at this time. In other words, this fluctuation rate F is the moving average of Ti ion current generation time Ti from the time the measured ionic current generation time Ti _n and seven ion current generating time measured it previously Ti
calculates the _av, calculates the deviation .DELTA.Ti between the absolute value and the moving average _{Ti av} the difference between the moving average _{Ti av} and the current ion current generation time Ti _n, the moving average and the deviation .DELTA.Ti Ti
_The fluctuation rate F is calculated from _av and _av .

[0018] _{Ti av = (Ti n + Ti} n-1 + ...... + Ti n-7) / 8 ΔTi = (| Ti av -Ti n |) / 8 F = ΔTi / Ti av However, Ti _n is the current ion Value of current generation time is 1
_Let the value measured before the number of times be T in _-1 and the value measured 8 times before be the number of T in _-7 .

If the obtained current fluctuation rate F _n substantially matches the target fluctuation rate Ft, it is determined that the operating state is the lean limit. If the current fluctuation rate F _n exceeds the target fluctuation rate Ft, it is determined that the lean limit has already been exceeded. On the other hand, if it is below the target, it is determined that there is a margin to the lean limit. In this way, the lean limit can be detected based on the target fluctuation rate Ft in various operating states of the engine 100 defined by the engine speed NE and the intake pressure PM.

As described above, during the feedback control in the lean burn, when the operating state at that time exceeds the lean limit and the ion current generation time T fluctuates, the air-fuel ratio becomes too lean. Therefore, the fuel injection amount is increased and the air-fuel ratio is controlled to become rich. On the contrary, when it is detected that the lean limit has a margin, the fuel injection amount is reduced and the air-fuel ratio is controlled to be lean. Therefore, the air-fuel ratio can be made lean to an appropriate lean limit depending on the operating state, and when it exceeds the lean limit, it can be quickly returned to an air-fuel ratio in which combustion fluctuation does not occur. As a result, fuel efficiency can be improved and drivability can be improved.

The present invention is not limited to the embodiment described above. For example, in the above-described embodiment, the ion current generation time Ti is obtained by measuring from immediately after ignition to when it disappears, but it is measured by starting the A / D conversion with the top dead center TDC as a reference. May be. Further, the time to start the A / D conversion may be, for example, a time after a predetermined time after ignition, which is determined according to the ignition timing, e.g., BTDC 10 ° CA before top dead center or ATDC 5 after top dead center. It may be set as in CA.

The fluctuation rate F is the ion current generation time T
It may be calculated from the quotient obtained by dividing the average value, variance or standard deviation of i by the average value. In this case, the average value, standard deviation, and variance may be obtained by a calculation method that is generally well known in statistical processing.

In the above embodiment, the moving average Ti _av
Although eight samples were used for calculating, the number of samples is not limited to eight, and may be 16, for example. Further, the moving average Ti _av and the deviation ΔTi may be subjected to an averaging calculation process in order to make the state of change gentle.

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.

[0025]

As described in detail above, according to the present invention, the fluctuation rate of the measured time during which the ion current continues to flow is determined according to the operating state of the internal combustion engine. The lean limit in the state can be detected. Therefore, it is possible to improve fuel efficiency, improve drivability in the entire driving range, and prevent emission from decreasing.

[Brief description of drawings]

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

FIG. 2 is a graph schematically showing the contents of a target variation rate map of the same example.

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

FIG. 4 is a graph schematically showing a generation state of an ion current in the same example.

FIG. 5 is a graph showing a relationship between an air-fuel ratio and a fluctuation rate in a conventional example.

[Explanation of symbols]

 5 ... Fuel injection valve 6 ... Electronic control device 7 ... Central processing unit 8 ... Memory device 9 ... Input interface 10 ... Combustion chamber 11 ... Output interface 24 ... Bias power supply 25 ... Ion current measurement circuit

Claims (1)

[Claims] 1. An ion current is generated for each ignition in the combustion chamber of an internal combustion engine, the time during which the ion current is generated is measured, the fluctuation rate of the measured time is calculated, and the fluctuation rate is calculated. It is characterized by detecting the operating state of the internal combustion engine at that time and detecting the lean limit when the obtained variation rate in the detected operating state is a target variation rate preset according to the operating state of the internal combustion engine. Lean limit control method.