JP2619896B2 - Air-fuel ratio control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention detects an oxygen concentration in exhaust gas using an oxygen concentration sensor and feedback-controls an air-fuel ratio of an air-fuel mixture supplied to an engine. More specifically, the present invention relates to an activity determination mechanism of an oxygen concentration sensor.

2. Description of the Related Art Conventionally, in this type of air-fuel ratio control device, there is a device using a limiting current type oxygen sensor as a sensor for detecting an oxygen concentration in exhaust gas.
And JP-A-58-179351. In this limiting current type oxygen sensor, for example, an element substrate is formed of an oxygen ion-permeable solid electrolyte, electrodes are provided on both sides of the element substrate, and one electrode plate (cathode) is separated from the other electrode plate (anode). It is formed by coating with a thick porous ceramic layer. Then, 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 electrodes of the element at a predetermined element temperature, a limiting current flows to the element according to the oxygen concentration of the exhaust gas. Thereby, the oxygen concentration in the exhaust gas can be detected. That is, such an oxygen sensor needs to be in a state of outputting a predetermined limit 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 one described in Japanese Patent Application Laid-Open No. Sho 59-46350. That is, when the fuel cut is performed during the deceleration operation of the vehicle, the oxygen concentration at that time is substantially equal to the atmosphere, so that when the current value output from the oxygen concentration sensor is equal to or more than the predetermined value, the fuel cell is activated. It is determined that there is.

Further, 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 a difference between current values output corresponding to each voltage is applied. Is determined to be in the active state when is less than a predetermined range.

[Problems to be Solved by the Invention] However, vehicles equipped with an automatic transmission (hereinafter referred to as A / T
When the former means for determining the oxygen concentration sensor is used in a vehicle, there are the following problems. That is, A / T
In a car, when the vehicle is decelerating, the engine speed rapidly drops to near the idle speed, so it is not possible to maintain the engine speed region that satisfies the fuel cut condition, that is, there is a sufficient fuel cut state during deceleration Therefore, there is a problem that it is difficult to determine the activity of the sensor during fuel cut.

On the other hand, in the latter technology, when the engine operating state changes greatly between the time of the first voltage application and the time of the subsequent voltage application, and the air-fuel ratio changes, the sensor current value also greatly changes accordingly. In some cases, it was mistakenly regarded as an active state.

The present invention has been made in order to solve the above-described problems of the conventional technology, and is suitable for an A / T vehicle in which it is difficult to determine the activity of an oxygen concentration sensor at the time of a fuel cut. An object of the present invention is to provide an air-fuel ratio control device that does not erroneously determine the activation state of an oxygen concentration sensor.

[Means for Solving the Problems] The present invention made to solve the problems described above has an engine B that transmits driving force to an wheel side via an automatic transmission A as shown in FIG. An operating state detecting means C for detecting an operating state of the engine B; an oxygen concentration sensor D for detecting the oxygen concentration in the exhaust gas of the engine A based on a current value flowing according to the oxygen concentration by applying a predetermined voltage; An air-fuel mixture supply means E for supplying an air-fuel mixture having a desired air-fuel ratio to the engine A; a feedback control for controlling the air-fuel mixture supply means E according to a detection signal from the oxygen concentration sensor D; Control means F for switching between independent open-loop controls, and oxygen concentration sensor determining means G for determining whether the oxygen concentration sensor D outputs a predetermined limit current value. In the air-fuel ratio control device described above, the oxygen concentration sensor determining means G is configured such that the operating state from the operating state detecting means C and the air-fuel ratio from the control means F are within a predetermined range, and during open-loop control, The oxygen concentration sensor D has a predetermined different 2
A voltage application unit G1 for applying more than one kind of voltage, and a current deviation detection unit G2 for detecting a deviation of a current flowing corresponding to each voltage when the voltage is applied by the voltage application unit G1.
And an active state determination unit G3 for determining that the oxygen concentration sensor D is in an active state when the current deviation detected by the current deviation detection unit G2 is equal to or less than a predetermined value.

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

To execute such feedback control, the oxygen concentration sensor D needs to be in an active state to output a predetermined limit current value. The determination is performed by the determination means G or the like. That is, the voltage application unit of the oxygen concentration sensor determination unit G
The operating state of the engine detected by the operating state detecting means C and the air-fuel ratio at that time are input to G1 from the control means F, and these values are within a predetermined range by the voltage applying section G1 and are open. If it is determined that loop control is being performed,
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 input to the current deviation detection unit G2. The current deviation detection unit G2 calculates a deviation between current values corresponding to the applied voltage,
This is output to the active state determination unit G3. Active state judgment unit G3
Determines that the oxygen concentration sensor D is in the active state when the deviation of the input current value is equal to or less than a predetermined value. And
The signal in the active state is used as a condition for starting the air-fuel ratio feedback control.

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

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

As shown in the figure, the engine 1 draws air from the atmosphere, mixes fuel and air injected from a fuel injection valve 3 and guides the mixture to an intake port 5, and electricity formed in a spark plug 9. It is provided with a combustion chamber 11 that takes out the energy of combustion of the air-fuel mixture ignited by the spark as a rotational motion through a piston 10 and an exhaust system 13 that exhausts the burned gas through an exhaust port 12. .

An air cleaner (not shown), a throttle valve 16 for controlling the amount of intake air, a surge tank 18 for smoothing the pulsating flow of the intake air, a surge tank
An intake pressure sensor 19 for detecting an intake pipe negative pressure P is provided at 18. Normally, the intake air amount is controlled by the opening of a throttle valve 16 linked to an accelerator pedal (not shown). In addition, the intake system 7 is provided with a throttle position sensor 23, an intake temperature sensor 24, and the like for detecting an operating state of the engine 1 in addition to the intake pressure sensor 19.

A mixture of air sucked through the throttle valve 16 and fuel injected from the fuel injection valve 3 is sucked into the combustion chamber 11, compressed by the piston 10, and then compressed by an electric spark formed in the spark plug 9. Ignite. The ignited air-fuel mixture explosively burns, drives the piston 10, becomes exhaust gas, is discharged to the exhaust system 13, is purified by a catalyst device (not shown), and is released to the atmosphere. This exhaust system 13
Is provided with a so-called limiting current type oxygen concentration sensor 25 for detecting the oxygen concentration in the exhaust gas.
Is a return sensor that can perform lean air-fuel ratio control.

A spark plug 9 provided in each cylinder of the engine 1 is connected to a distributor 29 for distributing a high voltage generated in an igniter 27 in synchronization with rotation of a crankshaft (not shown) by a high pressure cord (not shown). Have been. In the distributor 29, a rotation speed sensor 32 for generating a pulse corresponding to the rotation speed NE of the engine 1 and a cylinder discrimination sensor 34 are provided. The cylinder block 38 of the engine 1 is cooled by circulating cooling water, and the temperature of the 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. You.

The output signal of each sensor that detects the operating state of the engine 1 is input to the electronic control unit 40, and is used for fuel injection amount control, ignition timing control, and the like. As shown in FIG. 3, the electronic control unit 40 is mainly composed of a one-chip microcomputer 41 having a built-in CPU, ROM, RAM and the like and having an input / output port. This one-chip microcomputer 41
One-chip microcomputer for input / output ports
41 External speed sensor 32, cylinder discriminating sensor 34, and igniter 27 are directly connected.
An A / D conversion input circuit 43 in the inside, a heater energization control circuit 46 for controlling electric power supplied to the heater 25b of the oxygen concentration sensor 25 using a battery 45 as a power supply, and a drive circuit 48 for driving the fuel injection valve 3 are provided. It is connected. The oxygen concentration sensor
A voltage application circuit 49 is connected to the 25 detection elements 25a, and applies a predetermined voltage VLS for detection to the detection elements 25a.

The A / D conversion input circuit 43 is connected to sensors that output analog signals, such as the intake pressure sensor 19, the throttle position sensor 23, the intake temperature sensor 24, and the 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 can successively know it. The A / D conversion input circuit 43 includes an output of a heater energization control circuit 46 for applying a voltage to the heater 25b of the oxygen concentration sensor 25, an output of an amplifier 54 for amplifying a terminal voltage of the current detection resistor 52, and The terminal of the current detecting resistor 50 is connected, and the voltage VLS applied to the heater 25b, the current ILS flowing through the detecting element 25a, and the current flowing through the heater 25b of the oxygen concentration sensor 25 can be detected.

On the other hand, the one-chip microcomputer 41 drives these actuators by directly outputting a drive signal to the igniter 27 or outputting a control signal to the fuel injection valve 3 and the like via the drive circuit 48.

The electronic control unit 40 having such a configuration is used for the engine 1
The operation state is read and various controls are performed, 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 in which the limit current value is output. However, the activity determination process of the oxygen concentration sensor 25 is performed by the electronic control unit 40 in accordance with the flowcharts of FIGS. First, by turning on the ignition key,
After the initial setting including the flag indicating the activation state of the oxygen concentration sensor 25 and the initialization of the counter, etc., is performed,
Execute the processing of 101 and below.

First, in steps 101 to 107, various conditions for determining whether or not to execute the activity determination process of the oxygen concentration sensor 25 are determined. That is, in step 101, it is determined whether or not the lean feedback control of the air-fuel ratio is being performed based on the determination of the set / reset state of the feedback (F / B) control permission flag FF. This flag FF
Is in the reset state when the program starts, and
The following activity determination process of the oxygen concentration sensor 25 is for determining a condition for shifting from the open loop control to the lean feedback control. Therefore, in the first activation, it is determined that the control is the open loop control, and the next step 103
Proceed to. In step 103, it is determined whether or not the vehicle is in the fuel cut state. This fuel cut state is
The determination is made by determining a fuel cut flag set / reset by another routine. For example, when the engine speed NE is equal to or higher than a predetermined value when the idle switch built in the throttle position sensor 23 is turned on, the fuel cut flag is set.

In the next step 105, it is determined whether or not the operating state of the engine 1 is in a state suitable for determining the activation of the oxygen concentration sensor 25.

The conditions to be satisfied include, for example, the following conditions.

The condition that the change difference ΔPM of the intake pipe pressure PM based on the detection signal output from the intake pressure sensor 19 is 6.1 mmHg or less.

3 from the start of energization of the heater 25b of the oxygen concentration sensor 25
Conditions under which the element temperature 25a is estimated to be equal to or higher than a predetermined temperature after elapse of 20 minutes or more.

A condition in which the coolant temperature is 55 ° C. or higher based on the detection signal output from the coolant temperature sensor 39.

 Condition where the idle switch is off.

Conditions where the engine speed NE is in the range of 1000 rpm to 3000 rpm.

In the next step 107, it is determined whether or not the air-fuel ratio A / F is near the predetermined air-fuel ratio α. Here, α is generally assumed to be an air-fuel ratio slightly darker than that during the lean field back, for example, 19.

The activity determination conditions (steps) of these oxygen concentration sensors 25
If 101 to 107) hold, the process proceeds to step 111. In step 111, the activation determination permission flag FAO is determined. Since the flag FAO has been reset to 1 at the time of initialization, first, the case of proceeding to step 113 will be described.

In the processing after step 113, a predetermined voltage is applied to the oxygen concentration sensor 25, and the current value In (i1 to
i3) is measured. This will be schematically described with reference to FIG. 5. First, a voltage V1 is applied to the detection element 25a, and a voltage V2 is applied when a predetermined time has elapsed. Apply voltage V1 and output current values i1 to
If the deviation of i3 is within a predetermined range, it is determined to be in the active state.

That is, first, the first reading of the current value i1 is performed in steps 113 to 119, the second reading of the current value i2 is performed in steps 121 to 127, and the third reading of the current value i2 is performed in steps 129 to 135. The reading process of the value i3 is performed. That is, when the counter CA is within 0.2 seconds (step 113), the voltage V
When 1 is applied (step 115) and the counter CA has elapsed 0.2 seconds (step 117), the current value i1 is measured and this value is stored in the RAM (step 119). Similarly, when the counter CA is between 0.2 and 0.4 seconds (step 121), the voltage
V2 is applied (step 123), and when 0.4 seconds has elapsed in the counter CA (step 125), the current value i2 is measured and this value is stored in the RAM (step 127). Further, the counter CA counts the voltage V1 from 0.4 seconds to 0.6 seconds (step 129).
Is applied (step 131), and when the counter CA has elapsed 0.6 seconds (step 133), the current value i3 is measured and this value is stored in the RAM (step 135).

The current values i1 to i3 measured in this way are determined to be active based on the deviation in the step shown in FIG. 4 (B), but it is necessary to read the data of the current values i1 to i3 before that. The activation determination permission flag FAO shown is reset (step 137), and the counter CB described later is cleared (step 139).

The determination based on the deviation between the current values i1 to i3 is performed in step 141.
Performed at ~ 145. First, in step 141, the current value i1
The difference between the current value i2 and the current value i3 is calculated, and it is determined whether the difference is within 0.7 mA. Then, in step 143, it is determined whether the deviation between the current value i1 and the current value i3 is within 0.4 mA. I,
Then, in step 145, it is determined whether or not all the current values i1 to i3 are in the range of 5 mA to 10 mA. If all the determinations are affirmative, the activation determination flag FA is set to 1. The activation determination flag FA is used in another routine shown in FIG. 6, as will be described later, and it is determined whether switching from open loop control to lean feedback control is possible in addition to other conditions. . Meanwhile, one of the steps
If a negative determination is made in 141-145, the oxygen concentration sensor
The 25 activation determination flag FAO is reset (step 149), and the F / B control permission flag FF is reset to 0 (step 151), whereby the execution of the air-fuel ratio control is prohibited and the open-loop control and the Become.

As described above, the activity determination process of the oxygen concentration sensor 25 is performed. However, when the deviation or the like of the current values i1 to i3 is determined to be out of the predetermined range in steps 141 to 145, the renewed activity determination process is performed in a predetermined manner. Executed after a lapse of time. That is, in step 137, the activation determination permission flag FAO is reset to 0 and the counter CB is cleared. Therefore, in the next process, a negative determination is made based on the flag determination in step 111, and the process proceeds to step 159 to proceed to step 159. CB
If 16 seconds have elapsed, the activation determination permission flag FAO is set to 1 in step 161 and the measurement of the counter CA is started in step 163. Then, in the next repetitive processing, when the affirmative determination is made in the flag determination processing of step 111, the processing shifts to step 113 to execute the above-described activity determination processing of the oxygen concentration sensor 25.

If the activation determination condition is not satisfied in steps 101 to 107, the process proceeds to step 153, where the activation determination permission flag FAO is reset to 0, the counter CB is cleared, and the counter CA is further cleared. I do. As a result, a negative determination is made in the flag determination processing in step 111, and when it is determined in step 159 that 16 seconds have elapsed by the counter CB, the activation determination processing is executed again.

The activation determination flag FA of the oxygen concentration sensor 25 set / reset in the flowchart of FIG. 4 is used in the processing shown in the flowchart of FIG. This flowchart shows a condition for starting switching from open loop control to lean feedback control. In FIG. 6, first, at step 201, the determination of the activation determination flag FA is performed, and then, at step 203, it is determined whether or not the idle switch is on based on the detection signal from the idle switch. . When an affirmative determination is made in both 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.

Therefore, according to the present embodiment, the activity determination process of the oxygen concentration sensor 25 is performed at the time of open loop control other than the time of the fuel cut, so that it is particularly applied to an A / T vehicle in which the fuel cut state is difficult to secure for a long time. It is valid.

Also, during the activity determination process, the air-fuel ratio A / F and the intake pipe pressure PM
If the operating state of the engine 1 greatly fluctuates,
Since the determination process is immediately stopped, erroneous activation determination is not performed. Therefore, the reliability of the determination processing is improved.

Furthermore, once stopped activity determination processing, since it does not resume unless a relatively long time of 16 seconds elapses,
Since the voltage for determination is not applied to the oxygen concentration sensor 25 more than necessary, there is also an effect that the life of the oxygen concentration sensor 25 is not shortened.

In the above embodiment, the activation state is determined when the determination condition of the oxygen concentration sensor 25 is satisfied only once. However, the oxygen concentration sensor 25 is first determined when the activation determination condition is satisfied two or more times. The embodiment may be such that the active state is determined, whereby the reliability can be further improved.

[Effects of the Invention] As described above, according to the air-fuel ratio control device of the present invention, the activity determination process is performed during open loop control.
Suitable for A / T vehicles where it is difficult to determine the activation of the oxygen concentration sensor during fuel cut.In addition, when the operating state of the engine fluctuates greatly, diagnosis is interrupted immediately, so there is no erroneous determination of the activation state of the oxygen concentration sensor. .

[Brief description of the drawings]

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 equipped with an air-fuel ratio control device according to one embodiment of the present invention, and peripheral devices thereof, and FIG. FIG. 4 is a block diagram mainly showing the electronic control device.
5A and 5B are flow charts showing the air-fuel ratio control of the embodiment, FIG. 5 is a graph showing the relationship between the applied voltage and the current value in the oxygen concentration sensor, and FIG. 6 is a condition for switching to lean feedback control. It is a flowchart which shows. A: automatic transmission, B: engine C: operating state detecting means D: oxygen concentration sensor, E: mixture supply means F: control means G: oxygen concentration sensor determining means G1: voltage application Section, G2: current deviation detection section G3: activation state determination section 1 ... engine, 3 ... fuel injection valve 7 ... intake system, 13 ... exhaust system 19 ... intake pressure sensor, 25 ... oxygen concentration Sensor 25a: detection element, 25b: heater 32: rotation speed sensor, 40: electronic control unit

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-60-90937 (JP, A) JP-A-63-53462 (JP, A) JP-B-62-40537 (JP, B2)

Claims (1)

(57) [Claims] An engine for transmitting a driving force to an wheel through an automatic transmission, an operating state detecting means for detecting an operating state of the engine, and a flow corresponding to the oxygen concentration by applying a predetermined voltage. An oxygen concentration sensor for detecting the oxygen concentration in the exhaust gas of the engine based on the current value; an air / fuel mixture supply means for supplying an air / fuel mixture to the engine with a desired air / fuel ratio; Control means for switching between feedback control for controlling the means and open-loop control independent of the detection signal of the oxygen concentration sensor; and oxygen concentration sensor determination for determining whether the oxygen concentration sensor outputs a predetermined limit current value. And an air-fuel ratio control device comprising: an oxygen concentration sensor determining unit configured to determine an operating state from the operating state detecting unit; A voltage application unit that applies a predetermined two or more different voltages to the oxygen concentration sensor during the open-loop control when the air-fuel ratio is within a predetermined range, and when the voltage application unit applies a voltage, A current deviation detecting unit for detecting a deviation of a current flowing according to the voltage; and an activity for determining that the oxygen concentration sensor is in an active state when the deviation of the current detected by the current deviation detecting unit is equal to or less than a predetermined value. An air-fuel ratio control device, comprising: a state determination unit.