JPH01170738A - Air-fuel ratio controller - Google Patents

Abstract

PURPOSE:To prevent exhaust emission from degradation or the like by stopping air-fuel ratio feed-back control when the element temperature of an O2 sensor falls out of a predetermined range in the feed-back control of air-fuel ratio on the basis of the output of O2 sensor provided in an exhaust system. CONSTITUTION:An air-fuel ratio controller is provided with an air-fuel ratio controlling means D for comparing a desired air-fuel ratio set by a desired air-fuel ratio setting means B on the basis of the running condition of engine A with the output of an O2 sensor C for generating current value according to oxygen(O2) concentration in exhaust gas. According to the result of comparation is carried out air-fuel ratio feed-back control for adjusting a fuel injection amount. Then, a temperature detecting means E for detecting the element temperature of O2 sensor C is provided to send the output signal to the input of a deviation commanding means F. When the element temperature falls outside a predetermined range, said means F sends the signal to an air-fuel ratio control means D to change voltage applied to the O2 sensor C or stop the feed-back control.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to an air-fuel ratio control device that detects the oxygen concentration in the exhaust gas of an engine by sensing the oxygen concentration, and controls the air-fuel ratio based on the detected value. It is related to.

[Prior art and its problems] Conventionally, in this type of air-fuel ratio control device, a limiting current type oxygen sensor has been used as a sensor for detecting the oxygen concentration in exhaust gas. -172
443 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, electrode plates are provided on both sides of this element substrate, and one electrode plate (cathode) is used as the other electrode plate (anode). It is formed by coating it with a thicker porous ceramic layer. Then, when this limiting current type oxygen sensor is installed in a predetermined position so that its detection element is in contact with the exhaust gas and a voltage is applied between both poles of the element, a limiting current flows through the element depending on the oxygen concentration of the exhaust gas.
By measuring this output current, the oxygen concentration in the exhaust gas can be detected.

As shown in Fig. 8, such an oxygen concentration sensor has
There is a temperature-dependent relationship between the voltage VLS applied to the element and the current value ILS. That is, as is clear from the figure, the limiting current type oxygen sensor, for example, has an air-fuel ratio (A/
F) In 19, the applied voltage VLS is 0. 4-0.
When the voltage is 8V (7), a limiting current IL is generated in the element temperature range of 650° C. to 700° C., and the current value ILS increases as the temperature rises.

Therefore, for example, when the current value ILS is detected by setting the voltage applied to the element to VLSti - 0°8v,
When the temperature rises to 00° C. or higher, the current value ILS increases out of the range of the limiting current IL. Therefore, when air-fuel ratio control is executed with such an increased current value ILS,
The air-fuel ratio will be controlled on the rich side, and Co, HC
There is a problem in that the amount increases.

The present invention has been made in order to solve the problems of the above-mentioned conventional technology, and can prevent incorrect air-fuel ratio control from being performed even when the element temperature of the oxygen concentration sensor is high. The purpose of the present invention is to provide an air-fuel ratio control device that can improve emissions and fuel efficiency.

[Means for Solving the Problems] The present invention has been made to solve the above problems, as shown in FIG. B, an oxygen concentration sensor C that outputs a current value according to the oxygen concentration in the exhaust gas while a voltage is applied, and a voltage is applied to this oxygen concentration sensor C, and a current value from the oxygen concentration sensor C and the above target are output. In the air-fuel ratio side'a device, which includes an air-fuel ratio control means for feedback controlling the fuel injection amount based on the air-fuel ratio, an element temperature of the oxygen concentration sensor C or temperature data corresponding to this element temperature is detected. Temperature detection means E; If the element temperature from this temperature detection means E is outside a predetermined range, a signal is sent to the air-fuel ratio control means to change the voltage applied to the oxygen concentration sensor C or perform feedback control. It is characterized by comprising a change command means F for canceling.

Here, the above-mentioned temperature detection means E refers to one that directly measures the element temperature of the oxygen concentration sensor C with a thermocouple or the like, or one that measures the internal resistance of the element of the oxygen concentration sensor C and directly calculates it from this internal resistance. In addition, it also includes indirect measurements based on the operating state of engine A, such as the engine rotation speed, output torque, and vehicle speed.

Further, the change command means F determines that the element temperature of the oxygen concentration sensor C detected by the temperature detection means E has become above a predetermined temperature or below a predetermined temperature, that is, the oxygen concentration sensor C has become outside the range in which the limit current value flows. It sends a signal to the air-fuel ratio control means when

[Operation] According to the configuration of the air-fuel ratio control device described above, the target air-fuel ratio is set by the target air-fuel ratio setting means B based on the operating state of the engine A, for example, parameters such as the intake air amount and the engine rotation speed. Ru. This target air-fuel ratio is manually inputted by the air-fuel ratio control means, and is compared with the oxygen concentration in the exhaust gas from the oxygen concentration sensor C to perform feedback control so that the fuel injection amount becomes the target air-fuel ratio.

Further, the oxygen concentration sensor C outputs a current value corresponding to the oxygen concentration when the voltage output from the air-fuel ratio control means is applied. It has properties that fluctuate greatly when it is out of this range. In order to compensate for this, the present invention is provided with temperature detection means E that directly detects the element temperature of the oxygen concentration sensor C or detects temperature data that can be estimated indirectly. The signal from this temperature detection means E is the change command means F.
If it is manually determined that the element temperature is outside the predetermined range, a signal is output to the air-fuel ratio control means. One of the preferable aspects of the control carried out by the air-fuel ratio control means D that receives this signal is to stop the air-fuel ratio control, thereby preventing an incorrect oxygen concentration from being taken in from the oxygen concentration sensor C.
Fuel injection control is performed using another method, or as another preferred embodiment, the voltage applied to the oxygen concentration sensor C is changed so that the oxygen concentration detected from the oxygen concentration sensor C becomes an accurate detection value. .

[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 the combustion of the air-fuel mixture ignited by the electric spark formed by the piston 10 as rotational motion, and the exhaust system 13 discharges the gas after combustion through the exhaust boat 12. It is composed of

The intake system 7 includes, from upstream, an air cleaner (not shown),
A throttle valve 16 that controls the amount of intake air, a surge tank 18 that smoothes the pulsating flow of intake air, and a surge tank 1
An intake pressure sensor 19 is provided on the day and detects the 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 an electric spark is formed at the spark plug 9. ignited by. The ignited air-fuel mixture is explosively combusted and drives the piston 10, and then is discharged into the exhaust system 13 as exhaust 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 time control, and the like. As shown in FIG. 3, the electronic control device 40 is a one-chip microcomputer 41 that has a built-in CPU, ROM, RAM, etc., and is equipped with an input/output board.
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 uses the battery 45 as a power source to control the power supplied to the heater 25b of the oxygen concentration sensor 25, and a drive circuit 4 that drives the fuel injection valve 3. Note that a voltage application circuit 49 is connected to the detection element 25a of the oxygen concentration 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 current ILS flowing through the detection 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 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 state of the engine 1, and the oxygen concentration in the exhaust gas of the engine 1 is detected for use in fuel injection control, air-fuel ratio control, etc.

The processing executed by this electronic control unit 40 will be explained according to the flowchart of FIG.

When the electronic control unit 40 is started by turning on the ignition key, first, the activation determination flag FA and high temperature determination flag FT, which indicate the state of the oxygen concentration sensor 25, and the feedback (F/B) control permission flag FF are activated. The first Xi process including each flag process is executed, and then the first step 100 is executed. first step 1
At 00, it is determined 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.

Next, when it is determined in step 100 that the fuel is in the fuel cut state, in step 105, the activity determination process of the oxygen concentration sensor 25 is executed. This activity determination process is performed when the oxygen concentration in the exhaust gas at the time of fuel cut is approximately equal to the oxygen concentration in the atmosphere of 20%, and when a predetermined voltage is applied, the oxygen concentration sensor 25 This is based on the fact that a large current is output, and the active state is determined when the current is greater than a predetermined value. If it is determined in this step 105 that the oxygen concentration sensor 25 is in the active state, the activation determination flag FA is set to 1 in step 110. On the other hand, if it is determined that the oxygen concentration sensor 25 is not in the active state , the activation determination flag is reset to O in step 115.

On the other hand, if it is determined in step 100 that the fuel is not in the fuel cut state, that is, if it is determined that the current is in the energized operation state, the process proceeds to step 120 and subsequent steps.
A process is executed to deal with changes in the element temperature of the oxygen concentration sensor 25 to be estimated from the engine speed NE. Here, the element temperature of the oxygen concentration sensor 25 is estimated from the engine rotation speed NE based on an experimental example. If the relationship between the engine rotation speed NE and the element temperature of the oxygen concentration sensor 25 is expressed as a time chart, FIG. This is based on the fact that if the engine speed NE continues to be higher than a predetermined time for a predetermined time or longer, the temperature of the engine element also increases accordingly.

In the following step 120, it is determined based on the detection signal of the rotation speed sensor 32 whether or not the engine rotation speed NE continues to be 4000 rpm for 4 minutes or more.If the judgment is affirmative, the high temperature determination flag F is set in step 125. Tt
If the determination is negative, the process proceeds to step 130. In step 130, it is determined whether the engine speed NE has been below 250 rpm for more than 1 minute, and if the determination is negative, the process directly proceeds to the next step 140, while if the determination is affirmative, step 135 After setting the high temperature determination flag FT to 1 in step 140, the process proceeds to step 140.

In step 140 and step 145, a process is performed to determine whether or not feedback control should be executed based on the state of each of the flags FAS FT. That is, first, the activation determination flag FA is determined in step 140, and the high temperature determination flag FT is determined in step 145, and if both flags FA and FT are set to 1, that is, , oxygen concentration sensor 2
5 is in an active state and the temperature is determined to be below a predetermined temperature, the F/B control permission flag F is set in step 150.
Set F to 1. Using this F/B control permission flag in another routine, feedback control is executed to match the target air-fuel ratio. On the other hand, any flag FA
, FT has been reset, step 155
The F/B permission flag FF is reset to O, thereby prohibiting execution of air-fuel ratio control and changing to open-loop control.

In this flowchart, the above-mentioned series of processes are executed, and this process will be explained in a case where the driving state of the vehicle changes from normal driving to high-speed driving and then to normal driving.

If the fuel is not in the fuel cut state and the oxygen concentration sensor 25 is active and the vehicle is running normally, steps 100, 120, 130, and 135 are performed, and then steps 140, 145, and 150 are repeated. , feedback control is performed, but if high-speed driving continues for a long time, that is, if the engine speed NE of 400 rpm continues for more than 4 minutes, step 120 is performed.
An affirmative determination is made in step 125, and the high temperature determination flag FT is reset (step 125). By resetting the flag FT, a negative determination is made in the flag determination process of step 145, and the F/B permission flag FF is reset (step 155), thereby stopping the air-fuel ratio control. Then, when the vehicle shifts to normal driving again and the engine speed NE decreases and such a state continues for a predetermined period of time, that is, when it is determined that the engine speed NE of 2500 rpm or less has continued for more than 1 minute, (Step 130), the high temperature determination flag FT is set (Step 135), and this causes the determination in Step 145 and the F temperature in Step 150.
Feedback control is restarted by setting the /B control permission flag FF.

If the element temperature of the oxygen concentration sensor 25 is determined to be equal to or higher than the predetermined value by performing this process as in case B, the air-fuel ratio control will not be performed due to the incorrect output of the oxygen moisture sensor 25.
Therefore, since feedback control is not erroneously performed to the rich side, deterioration of exhaust gas emissions is not caused.

Further, in the above embodiment, the engine rotation speed NE is 4000.
Feedback control is not restarted immediately even when the rpm drops, but feedback control is resumed after the low rotational speed state continues for a predetermined period of time, so feedback control is executed using an incorrect oxygen concentration signal. You can avoid that.

-Next, a second embodiment of the present invention will be described based on the flowchart of FIG. In this embodiment, even if it is determined that the element temperature of the oxygen temperature sensor 25 has increased, the feedback control is not canceled but the oxygen concentration sensor 25
By performing a process of changing the voltage VLS applied to the oxygen sensor 5, the current ILS from the oxygen air conditioner sensor 25 is output as a consolidated one.

First, the process from step 200 to step 230 is the same process as step 100 to step 115 and step 140 to 155 in the flowchart of FIG.
The determination process No. 5 and the determination process of whether or not feedback control should be executed are performed.

On the other hand, in the processing from step 235 to step 260, processing different from that in the flowchart of FIG. 4 is performed. That is, if it is determined in step 200 that the fuel is not in the fuel cut state, the presence or absence of the active state of the oxygen moisture sensor 25 is determined by the flag FA (step 23
5) If the inactive state is determined, the applied voltage VLS of the oxygen temperature sensor 25 is set to Ov (step 240), and the engine speed NE is set to 400Orp.
If it is determined that the applied voltage is greater than m and continues for more than 4 minutes (step 245), the applied voltage VLS is set to 0°6■ (step 250), and furthermore, if the engine speed NE is less than 250 orpm and it continues for more than 4 minutes, the applied voltage VLS is set to 0°6■ (step 250). If it is determined that the above continues (step 255), the applied voltage increases to 0.85.
V (step 260).

Therefore, according to the above embodiment, the oxygen concentration sensor 25
Based on the element temperature of the oxygen concentration sensor 25, the current I
By changing the applied voltage VLS so that LS falls within the limiting current range, the oxygen concentration can be accurately detected even if the element temperature of the oxygen concentration sensor 25 changes. Therefore, since the range in which feedback control can be performed is wider than in the first embodiment, fuel efficiency can be improved.

In Embodiment 1.2, the element temperature of the oxygen concentration sensor 25 is controlled by predicting it from the engine rotation speed NE as the operating state of the engine 1.
A thermocouple is attached to the detection element 25a of the oxygen concentration sensor 25 to directly detect the temperature, or the internal resistance of the detection element 25a of the oxygen concentration sensor 25 is measured and the temperature is determined from the measured internal resistance, as shown in FIG. The applied voltage may be changed continuously as shown in FIG.

Furthermore, instead of changing the voltage VLS applied to the oxygen concentration sensor 25, the voltage VLS applied to the oxygen) preparation sensor 25 can be changed.
The electronic control device 4 can be stopped by changing LS to OV to stop feedback control, or by stopping feedback control with applied voltage VLS applied.
0 can be simplified and costs can be reduced.

[Effects of the Invention] As explained above, according to the air-fuel ratio control device according to the present invention, even when the element temperature of the oxygen concentration sensor is high, the air-fuel ratio control device according to the present invention prevents the air from being emptied due to an incorrect oxygen concentration due to the output from the oxygen concentration sensor. It is possible to prevent the fuel ratio from being controlled, and it is possible to improve emissions and fuel efficiency.

[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
The figure is a flowchart showing air-fuel ratio control in the same embodiment.
The figure is a graph showing the relationship between the engine speed and the element temperature of the oxygen concentration sensor in the same example, Figure 6 is a flowchart showing a modification of Figure 4, and Figure 7 is the relationship between the voltage applied to the oxygen concentration sensor and the element temperature. A graph showing the relationship with temperature, and FIG. 8 is a graph showing the relationship between the current value of the oxygen concentration sensor and the applied voltage. A...Engine B...Target air-fuel ratio setting means C...Oxygen concentration sensor D...Air-fuel ratio control device E.
...Temperature detection means F...Change command means 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 device agent Patent attorney Tsutomu Sadatsu (and one other person) Fig. 1 Fig. 5/'C Time Fig. 7 Element temperature of oxygen concentration sensor ( °C)

Claims (1)

[Scope of Claims] A target air-fuel ratio setting means that sets a target air-fuel ratio in advance according to the operating state of the engine; an oxygen concentration sensor that outputs a current value according to the oxygen concentration in exhaust gas while applying a voltage; The air-fuel ratio control device includes an air-fuel ratio control means that applies voltage to the oxygen concentration sensor and feedback-controls the fuel injection amount based on the current value from the oxygen concentration sensor and the target air-fuel ratio, the oxygen concentration sensor temperature detection means for detecting the element temperature or temperature data corresponding to the element temperature; and when the element temperature from the temperature detection means is outside a predetermined range, a signal is sent to the air-fuel ratio control means to the oxygen concentration sensor. an air-fuel ratio control device, comprising: change command means for changing the applied voltage or canceling feedback control.