JPH01187337A - Air-fuel ratio controller - Google Patents

Abstract

PURPOSE:To prevent any misjudgment of an active state from occurring by impressing more than two types of voltage of an oxygen sensor during open loop control at the time of judging whether the oxygen sensor outputs a limiting current value or not, and judging the active state of the oxygen sensor from a current deviation at the impression. CONSTITUTION:A controller bearing the above caption performs feedback control, controlling a mixture feeding means E according to a detection signal of an oxygen sensor D, or open loop control selectively by a control means F on the basis of output of an engine driving state detecting means C. In addition, it is provided with an oxygen sensor judging means G which judges on whether the oxygen sensor D outputs a specified limiting current value or not. In this case, the oxygen sensor judging means G impresses more than two types of voltage on the oxygen sensor with a voltage impressing part G1 while the air-fuel ratio is within the range and during the open loop control, while the deviation of a current flowing as corresponding to each voltage is detected by a current deviation detecting part G2, and when the deviation is less than the specified value, it is constituted so as to judge it as an oxygen sensor active state by an active state judging means G3.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Fields] The present invention relates to an air-fuel ratio control device that detects the oxygen concentration in exhaust gas using an oxygen concentration sensor and performs feedback control of the air-fuel ratio of the air-fuel mixture supplied to the engine. Specifically, it relates to an activity determination mechanism of an oxygen concentration sensor.

[Prior Art] Conventionally, in this type of air-fuel ratio control device, there has been one that uses a limiting current type oxygen sensor as a sensor for detecting the oxygen concentration in exhaust gas.
443 and JP-A-58-179351. This limiting current type oxygen sensor, for example, has an element substrate made of an oxygen ion-permeable solid electrolyte, electrode plates are provided on both sides of the element substrate, and one electrode plate (cathode) is connected to the other electrode plate (anode). It is formed by coating it with a thick porous ceramic layer. This limiting current type oxygen sensor is mounted at a predetermined position so that its detection element is in contact with the exhaust gas.

In such a limiting current type oxygen sensor, when a voltage is applied between both poles of the element at a predetermined element temperature, a limiting current flows through the element depending on the oxygen concentration of the exhaust gas, so this output current can be measured. This makes it possible to detect the oxygen concentration in exhaust gas. That is, such an oxygen sensor needs to be in a state in which it outputs a predetermined limiting current during use, that is, in an active state at a predetermined element temperature.

Conventionally, as a means for determining the activation state of such an oxygen sensor, for example, there is a method described in Japanese Patent Laid-Open No. 59-46350. In other words, when a fuel cut is performed while the vehicle is decelerating, the oxygen concentration at that time is almost equal to that of the atmosphere, so if the current value output from the oxygen concentration sensor is equal to or higher than a predetermined value, the sensor becomes activated. It has been determined that there is.

In addition, as another conventional technique, as described in Japanese Patent Application Laid-Open No. 60-90937, two types of voltages are applied to an oxygen concentration sensor, and the difference in the current value output corresponding to each voltage is calculated. There is also a known device that determines the active state when is below a predetermined range.

[Problems to be Solved by the Invention] However, when the former oxygen concentration sensor determination means is used in a vehicle equipped with an automatic transmission (hereinafter referred to as an A/T vehicle), the following problems occur. be. That is, A/T
In a car, when decelerating, the engine speed quickly drops to near the idle speed, making it impossible to maintain an engine speed range that satisfies the fuel cut conditions. However, there was a problem in that it was difficult to determine the sensor's activity when the fuel was cut off.

On the other hand, with the latter technology, if the engine operating state changes significantly between the first voltage application and the second voltage application and the air-fuel ratio changes, the current value of the sensor also changes significantly. In some cases, it was mistakenly assumed to be active.

The present invention has been made in order to solve the above-mentioned problems of the conventional technology, and is suitable for A/T vehicles where it is difficult to determine the activity of the oxygen concentration sensor during fuel cut. It is an object of the present invention to provide an air-fuel ratio control device that does not cause erroneous determination of the activation state of an oxygen concentration sensor.

[Means for Solving the Problems] As shown in FIG. 1, the present invention, which has been made to solve the above problems, includes an engine B that transmits driving force to the wheels via an automatic transmission A, and an engine B that transmits driving force to the wheel side via an automatic transmission A. , an operating state detection means C that detects the operating state of this engine B, and an oxygen concentration sensor D that detects the oxygen concentration in the exhaust gas of the engine A based on the current value that flows in accordance with the oxygen concentration by applying a predetermined voltage. A mixture supplying means E that supplies a mixture having a desired air-fuel ratio to the engine A; a feedback control that controls the mixture supplying means E according to a detection signal of the oxygen concentration sensor D; and a feedback control that controls the mixture supplying means E according to a detection signal of the oxygen concentration sensor An air-fuel ratio control device comprising: a control means F that performs switching independent open loop control; and an oxygen concentration sensor determination means G that determines whether or not the oxygen concentration sensor D is outputting a predetermined limit current value. , The oxygen concentration sensor determining means G determines that the operating state from the operating state detecting means C and the air-fuel ratio from the controlling means F are within a predetermined range, and the oxygen concentration sensor D is detected during open loop control. A voltage application section G1 that applies two or more predetermined different voltages; and a current deviation detection 1dG that detects the deviation of the current flowing in accordance with each voltage when the voltage application section G1 applies a voltage.
2, and an active state determining section G3 that determines that the oxygen concentration sensor D is in an active state when the deviation of the current detected by the current deviation detecting section G2 is below a predetermined value. do.

[Function] The control means F of the air-fuel ratio control device in the present invention executes feedback control of the air-fuel ratio based on the detection signal corresponding to the oxygen concentration output from the oxygen concentration sensor D when the oxygen sensor D is in the active state. Furthermore, open loop control is executed when the oxygen concentration sensor D is in an inactive state.

In order to perform feedback control in this way, the oxygen concentration sensor D must be in an active state that outputs a predetermined limit current value, but the activation state of the oxygen concentration sensor D is determined by the oxygen temperature sensor. This is performed by the determining means G and the like. That is, the voltage application section G of the oxygen concentration sensor determination means G
1, the operating state of the engine detected by the operating state detection means C and the air-fuel ratio at that time are manually input from the control means F, and the voltage application section G1 determines that these values are within a predetermined range and that the engine is open. If it is determined that loop control is in progress,
Two or more types of predetermined voltages are applied to the oxygen concentration sensor D. A current corresponding to this voltage is output from the oxygen concentration sensor D, and is manually inputted to the current 1 deviation detection section G2. The current deviation detection unit G2 determines the deviation between the current values corresponding to the applied voltage, and outputs this to the active state determination unit G3. The active state determination unit G3 determines that the oxygen concentration sensor D is in the active state when the deviation of the manually input current value is less than or equal to a predetermined value.

This active state signal is used as a starting condition for air-fuel ratio feedback control.

Therefore, since the activity determination process of the oxygen concentration sensor D in the air-fuel ratio control device is executed during open-loop control, the process is reliably executed even in a vehicle equipped with an automatic transmission A, which is unlikely to occur during a fuel cut. . Also,
The determination process is executed only when the air-fuel ratio is within a predetermined range and the operating state of the engine is within a predetermined range, and is immediately stopped when the air-fuel ratio is outside the predetermined range.

[Example 1] An example of the present invention will be described below with reference to the drawings. FIG. 2 is a schematic configuration diagram showing an engine and its peripheral devices to which the air-fuel ratio control device of the embodiment is applied, and FIG. 3 is a block diagram mainly showing the electronic control device.

As shown in the figure, the engine 1 includes an intake system 7 that sucks air from the atmosphere, mixes fuel injected from a fuel injection valve 3 with air, and guides the mixture to an intake boat 5, and a spark plug 9.
The combustion chamber 11 extracts the energy of combustion of the air-fuel mixture ignited by the electric sparks formed by the piston 10 as rotational motion, and the exhaust system 13 discharges the gas after combustion through the exhaust port 12. It is composed of

The intake system 7 includes, from upstream, an air cleaner (not shown),
Throttle valve 16 that controls the amount of intake air, surge tank 1 that smoothes the pulsating flow of intake air, surge tank 1
Intake pressure sensor 19 provided at 8 to detect intake pipe negative pressure P
is provided.

The amount of intake air is normally controlled by the opening degree of a throttle valve 16 that is linked to an accelerator pedal (not shown).

In addition to the intake pressure sensor 19, the intake system 7 is provided with a throttle position sensor 23, an intake temperature sensor 24, and the like for detecting the operating state of the engine 1.

A mixture of air taken in through the throttle valve 16 and fuel injected from the fuel injection valve 3 is taken into the combustion chamber 11, compressed by the piston 10, and then compressed by an electric spark formed at the spark plug 9. ignited. The ignited air-fuel mixture is explosively combusted and drives the piston 10, and is then discharged into the exhaust system 13 as a gas, purified by a catalyst device (not shown), and then discharged into the atmosphere. This exhaust system 13 is provided with a so-called limiting current type oxygen concentration sensor 25 that detects the oxygen concentration in the exhaust gas, and this oxygen concentration sensor 25 is a lean sensor capable of controlling the air-fuel ratio in a lean state.

A spark plug 9 provided in each cylinder of the engine 1 is connected to a distributor 29 that distributes high voltage generated to an igniter 27 in synchronization with the rotation of a crankshaft (not shown).
It is connected by a high voltage cord (not shown). Inside this distributor 29, there is a rotation speed N of the engine 1.
A rotation speed sensor 32 that generates a pulse according to E and a cylinder discrimination sensor 34 are provided. In addition, engine 1
The cylinder block 38 is cooled by circulating cooling water, and the temperature of this cooling water, which is one of the operating states of the engine 1, is detected by a cooling water temperature sensor 39 provided in the cylinder block 38.

Output signals from each sensor that detects the operating state of the engine 1 are input to the electronic control device 40 and used for fuel injection amount control, ignition timing control, and the like. The electronic control device 40, as shown in FIG.
It is mainly composed of. A rotation speed sensor 32, a cylinder discrimination sensor 34, and an igniter 27 external to the one-chip microcomputer 41 are directly connected to the human output board of the one-chip microcomputer 41. Conversion input circuit 4
3, a heater energization control circuit 46 that controls the power supplied to the heater 25b of the oxygen concentration sensor 25 using the dispersion 45 as a power source, and a drive circuit 4 that drives the fuel injection valve 3 are connected. Note that a voltage application circuit 49 is connected to the detection element 25a of the oxygen/temperature sensor 25, and applies a predetermined voltage VLS for detection to the detection element 25a.

Connected to the A/D conversion input circuit 43 are sensors that output analog signals, such as an intake pressure sensor 19, a throttle position sensor 23, an intake air temperature sensor 24, and a coolant temperature sensor 39. Therefore, the CPU can read various parameters reflecting the operating state of the engine 1 via the A/D conversion input circuit 43 and know them one by one. The A/D conversion input circuit 43 also includes the output of a heater energization control circuit 46 that applies voltage to the heater 25b of the oxygen concentration sensor 25, the output of an amplifier 54 that amplifies the terminal voltage of the current detection resistor 52, and The terminals of the current detection resistor 50 are connected, and the applied voltage VLS of the heater 25b,
The electric current im I LS flowing through the detection element 25a and the electric current flowing through the heater 25b of the oxygen concentration sensor 25 can be detected.

On the other hand, the one-chip microcomputer 41 outputs a drive signal directly to the igniter 27 or outputs a control signal to the fuel injection valve 3 etc. via the drive circuit 4, etc.
Drive these actuators.

The electronic control device 40 having such a configuration has the engine 1
Various controls are performed by reading the operating status of the oxygen concentration sensor 25, but in order to perform lean feedback control using the oxygen concentration in the exhaust gas, the oxygen concentration sensor 25 must be in an active state outputting a limit current value. However, the activity determination process of the oxygen concentration sensor 25 is performed by the electronic Faj device 40 according to the flowcharts shown in FIGS. 4(A) and 4(B). First, by turning on the ignition key, a flag indicating the active state of the oxygen concentration sensor 25,
After initial settings including initialization of counters and the like are performed, the processes from step 101 onwards are executed.

First, in steps 101 to 107, various conditions are determined as to whether or not the activity determination process of the oxygen concentration sensor 25 should be executed. That is, step 1
01, the feedback (F/B) control permission flag FF is used to determine whether lean feedback control of the air-fuel ratio is being performed.
This is done by determining the set/reset status of. This flag FF is in a reset state when the program is started, and the following activity determination process of the oxygen concentration sensor 25 is performed as follows:
Since this is to determine the conditions for transitioning from open loop control to lean feedback control, in this first activation, open loop control is determined and the process proceeds to the next step 103. In step 103, a determination is made as to whether or not there is a fuel cut state. This fuel cut state is determined by a fuel cut flag that is set and reset by other routines. For example, when the idle switch built into the throttle position sensor 23 is turned on and the engine speed NE is above a predetermined value, the fuel cut flag is set.

In the next step 105, it is determined whether the operating state of the engine 1 is suitable for determining the activity of the oxygen moisture sensor 25.

The conditions for this establishment include, for example, the following conditions.

(2) A condition in which the difference in change in intake pipe pressure PM based on the detection signal output from the intake pressure sensor 19 is 6° lmmHg or less.

(2) A condition in which the element temperature 25a is estimated to be equal to or higher than a predetermined temperature after 3 minutes and 20 seconds or more have passed since the start of energization to the heater 25b of the oxygen moisture sensor 25.

(2) A condition in which the cooling water temperature based on the detection signal output from the cooling water temperature sensor 39 is 55°C or higher.

■ Condition that the idle switch is OFF.

■ Engine speed NE from 100Orpm to 300O
Conditions in the rpm range.

In the next step 107, the air-fuel ratio A/F is set to a predetermined air-fuel ratio α
A determination is made as to whether or not it is in the vicinity of .

Here, α is generally slightly higher than in lean feedback)
The air-fuel ratio on the tremor side is, for example, 19.

If these conditions for determining the activity of the oxygen temperature sensor 25 (steps 101 to 107) are satisfied, the process proceeds to step 111.
Move to. In step 111, the activation determination permission flag FAO is determined, but since the flag FAO was set to 1 at the time of initialization, step 1 is first performed.
The case of proceeding to step 13 will be explained.

In the process after step 113, a predetermined voltage is applied to the oxygen concentration sensor 25, and the current value In(
if~i3) is measured, and this will be schematically explained using FIG.
2 is applied, and a voltage V1 is further applied, and if the deviation of the current values 11 to i3 output at that time is within a predetermined range, it is determined that the active state is present.

That is, from step 113 to step 119, the first current value 11 is read, and step 121
From step 127 to step 127 is the second reading of the current value 12, and from step 129 to step 135 is the third reading.
The process of reading the current value i3 for the second time is performed. That is, when the counter CA is within 0.2 seconds (step 11
3) Apply voltage V1 to the oxygen concentration sensor 25 (step 115), measure the current value 11 when counter CA has elapsed for 0.2 seconds (step 117), and set this value to R.
It is stored in AM (step 119). Similarly, counter CA is set between 0.2 seconds and 0.4 seconds (step 1
21), apply voltage v2 (step 123), counter CA is 0.4v/! i! (Step 12)
5), measure the current value 12 and store this value in the RAM (step 127). Further, the voltage V1 is applied to the counter CA from 0.4 seconds to 0.6 seconds (step 129), and when the counter CA reaches 0.6 seconds (step 133), the current f [Measure i3 and store this value in RA (VH) (step 135
).

The current values 11 to 13 measured in this way are determined to be active based on their deviations in the step shown in FIG. The activation determination permission flag FAO shown is reset (step 137), and a counter CB, which will be described later, is cleared (step 139).

The determination based on the ig difference between the current values 11 to 13 is performed in steps 141 to 145. First, in step 141, the difference between the current (1Mi 1) and the current value 12 is calculated, and it is determined whether the difference is within 0.7 mA. It is determined whether the deviation of 13 is within 0.4 mA, and in step 145, the current values 11 to 13 are all 5 mA to 10 mA.
A determination is made as to whether it is within the range of , and if both results are affirmative, an activation determination flag FA is set to 1.

As described later, this activation determination flag FA is used in another routine shown in FIG. 6, and it is determined whether or not it is possible to switch from open loop control to lean feedback control by adding other conditions. . On the other hand, if a negative determination is made in any of steps 141 to 145, the activity determination flag FA of the oxygen moisture sensor 25 is reset to O (step 149), and the F/B control permission flag FF is reset to 0. (step 151), thereby prohibiting execution of air-fuel ratio control and providing open-loop control.

In this way, the activity determination process of the oxygen moisture sensor 25 is performed, and in steps 141 to 145, the current ffi
When it is determined that the deviation of i1 to i3 is outside the predetermined range, the activation determination process is performed again after a predetermined period of time has elapsed. That is, since the activation determination permission flag FAO is reset to 0 and the counter CO is cleared in step 137, in the next process, the flag determination in step 111 is negative, and the process moves to step 159. When the counter CB has elapsed for 16 seconds or more, the activation determination permission flag FAO is set to 1 in step 161, and the counter CA starts counting in step 163. Then, in the next repeated process, when the flag determination process in step 111 makes an affirmative determination, the process moves to step 113 and the above-described activity determination process for the oxygen concentration sensor 25 is executed.

If the activation determination condition is no longer satisfied in steps 101 to 107, the process moves to step 153, resets the activation determination permission flag FAO to O, clears the counter CO, and roughly resets the counter CA. clear. As a result, a negative determination is made in the flag determination process in step 111, and when it is determined in step 159 that 16 seconds have elapsed by the counter CB, the activation determination process is executed again.

The activation determination flag FA of the oxygen concentration sensor 25, which is set◆reset in the flowchart of FIG. 4, is used in the process shown in the flowchart of FIG.

This flowchart shows conditions for starting switching from open loop control to lean feedback control. In FIG. 6, first, the activation determination flag FA is determined in step 201, and then step 203
Based on the detection signal from the idle switch, it is determined whether the idle switch is in the on state. When an affirmative judgment is made in any of these steps 201 and 203, the F/B control permission flag FF is set to 1, and lean feedback control is started in another routine using this flag FF. Ru.

Therefore, according to the present embodiment, the activity determination process of the oxygen concentration sensor 25 is carried out during open loop control other than when the fuel is cut off, so it is particularly suitable for application to AZT vehicles where it is difficult to maintain the fuel cut state for a long time. It is valid.

Also, during the activation determination process, the air-fuel ratio A/F and intake pipe pressure P
If the operating state of the engine 1 such as M changes greatly, the determination process is immediately stopped, so that an erroneous activation determination is not made. Therefore, the reliability of the determination process is improved.

Furthermore, since the activity determination process that was stopped once will not be restarted until a relatively long period of 16 seconds has elapsed,
Since the voltage for determination is not applied to the oxygen moisture sensor 25 more than necessary, there is also the effect that the life of the oxygen concentration sensor 25 is not shortened.

In the above embodiment, the active state is determined when the determination condition of the oxygen concentration sensor 25 is satisfied only once, but it is determined that the oxygen concentration sensor 25 is in the active state only when the activation determination condition is satisfied twice or more. An embodiment may also be used in which it is determined that the sensor 25 is in an active state, thereby further increasing reliability.

[Effects of the Invention] As explained above, according to the air-fuel ratio side TA device of the present invention, since the activity determination process is performed during open loop control,
Suitable for A/T vehicles where it is difficult to determine the activity of the oxygen moisture sensor during fuel cut, and in order to immediately interrupt the diagnosis when the engine operating condition changes significantly, it is possible to falsely determine the activation state of the oxygen (agriculture) sensor. There is no.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing an example of an air-fuel ratio control device according to the present invention, FIG. 2 is a configuration diagram showing an engine and its peripheral equipment equipped with an air-fuel ratio control device according to an embodiment of the present invention, and FIG. Block diagram mainly showing the electronic control unit, Part 4
Figures (A) and (B) are flowcharts showing the air-fuel ratio control of the same example, Figure 5 is a graph showing the relationship between the applied voltage and current value in the oxygen moisture sensor, and Figure 6 is the switch to lean feedback control. It is a flowchart showing conditions. A... Automatic transmission B... Engine C...
Operating state detection means D...Oxygen humidity sensor E...Mixture supply means F
... Control means G ... Oxygen moisture sensor judgment means G1 ... Voltage application section G2 ... Current deviation detection section G
3...Activity state determination unit 1...Engine 3...Fuel injection valve 7...
Intake system 13...Exhaust system 19...-Intake pressure sensor 25...Oxygen moisture sensor 25a...Detection element 25b...-Heater 32...Rotation speed sensor 40
...Electronic control device agent Patent attorney Tsutomu Sadatsu Hka ≠ Wife ≠ Figure 1 Figure 4 (B) Figure 5 Applied voltage Vts of oxygen concentration sensor Figure 6

Claims (1)

[Scope of Claims] An engine that transmits driving force to the wheels via an automatic transmission; an operating state detection means that detects the operating state of the engine; an oxygen concentration sensor that detects the oxygen concentration in engine exhaust gas based on a flowing current value; an air-fuel mixture supply means that supplies the engine with an air-fuel mixture at a desired air-fuel ratio; A control means that performs switching between feedback control that controls the supply means and open loop control that does not depend on the detection signal of the oxygen concentration sensor; and an oxygen concentration sensor that determines whether or not the oxygen concentration sensor is outputting a predetermined limit current value. In the air-fuel ratio control device, the oxygen concentration sensor determines that the operating state from the operating state detection means and the air-fuel ratio from the control means are within a predetermined range, and the oxygen concentration sensor determines that the operating state is within a predetermined range, and It includes a voltage application section that applies two or more predetermined different voltages to the oxygen concentration sensor, and a current deviation detection section that detects the deviation of the current flowing corresponding to each voltage when the voltage application section applies voltage. and an active state determining section that determines that the oxygen concentration sensor is in an active state when the deviation of the current detected by the current deviation detecting section is below a predetermined value. Device.