JPH0531247Y2 - - Google Patents

Description

[Detailed description of the invention] [Industrial application field] The present invention provides an air-fuel ratio sensor (herein, an oxygen concentration sensor (O ₂ sensor)) on the upstream side, downstream side, or both of the catalytic converter. The present invention relates to an air-fuel ratio control device for an internal combustion engine that performs air-fuel ratio feedback control using an O ₂ sensor.

[Conventional technology]

Generally, when controlling the air-fuel ratio of an internal combustion engine, the basic injection amount TAUP of the fuel injector is determined according to the intake air amount (or intake air pressure) and rotational speed of the engine.
The basic injection amount TAUP is corrected according to the air-fuel ratio correction coefficient FAF, which is calculated based on the detection signal of the O ₂ sensor that detects the concentration of a specific component in the engine exhaust gas, such as oxygen component. The amount of fuel actually supplied is controlled according to the corrected injection amount. This control is repeated until the air-fuel ratio of the engine is finally converged within a predetermined range. This type of air-fuel ratio feedback control allows the air-fuel ratio to be controlled within a very narrow range around the stoichiometric air-fuel ratio.
A three-way catalytic converter installed in the exhaust system, which converts CO, HC, and NOx contained in exhaust gas.
The purifying ability of the catalytic converter, which simultaneously purifies two harmful components, can be maintained at a high level.

[Problem that the invention attempts to solve]

In the above-mentioned air-fuel ratio feedback control, an O ₂ sensor that detects oxygen concentration is installed in the exhaust manifold assembly, but the change in the output characteristics of the O ₂ sensor over time poses an obstacle to improving the accuracy of air-fuel ratio control. It is occurring. For example, the exhaust gas hits the O ₂ sensor element poorly at the beginning due to poor permeability through coating parts, etc., but it becomes easier to hit the O 2 sensor element as time passes, so the Z output characteristic of the O ₂ sensor changes. Furthermore, the Z output characteristic of the O ₂ sensor deteriorates due to aging of the O ₂ sensor itself or the state of the engine.
Therefore, for example, as shown in FIG. 2A, in the Z output characteristic of the O ₂ sensor before deterioration, in order to obtain the stoichiometric air-fuel ratio (λ=1), the comparison voltage must be set to V _R
(for example, 0.45V), but the second B
As shown in the figure, even in the Z output characteristic of the O ₂ sensor after deterioration, when the comparison voltage is set to _V It deviates to the rich side by a larger amount than the fuel ratio (in the case of B). Therefore, in case A, it is necessary to set the comparative voltage V _R ′ high, and in case B, it is necessary to set the comparative voltage V _R ″ low. In other words, the degree of deterioration of the O ₂ sensor It is preferable to variably control the comparison voltage accordingly.

The conventional method of varying the comparison voltage according to the degree of deterioration of the O ₂ sensor is to adjust the voltage to 1/2 of the maximum or minimum value of the O ₂ sensor output during air-fuel ratio feedback control, or to change the comparison voltage to 1/2 of the maximum or minimum value of the O 2 sensor output during air-fuel ratio feedback control. _O2
The average value of the sensor output was used as the comparison voltage (see Japanese Patent Application Laid-open Nos. 55-445, 55-2932, and 57-13245).

However, during air-fuel ratio feedback control,
The maximum and minimum values of the O ₂ sensor output do not reflect the deterioration state of the O ₂ sensor well, and the comparison voltage obtained using these maximum and minimum values will not be an appropriate value. Therefore, there was a problem in that the air-fuel ratio could not be controlled to the stoichiometric air-fuel ratio and exhaust emissions were not sufficiently improved. In other words, the comparison voltage V _R for determining whether the air-fuel ratio is rich or lean is set to a predetermined value (for example, 0.45 V) based on the O ₂ sensor output characteristics before deterioration with no deviation in characteristics. ₂ Even if the sensor deteriorates and the output characteristics change as shown by the solid line (in the case of A) or the broken line (in the case of B) in Figure 2B, the air-fuel ratio feedback will still depend on the comparison voltage and the output of the O ₂ sensor. The air-fuel ratio will be controlled within a certain narrow air-fuel ratio range, centered around the air-fuel ratio corresponding to the point where these intersect. Therefore, in both cases A and B in Fig. 2B, the maximum value in the air-fuel ratio feedback,
The minimum values are almost the same, and it is not possible to obtain a comparison voltage that reflects the change in the characteristics of the O ₂ sensor from the maximum and minimum values in the air-fuel ratio feedback.

Therefore, an object of the present invention is to provide an air-fuel ratio control device for an internal combustion engine that compensates for output characteristics due to changes in characteristics of an O ₂ sensor.

[Means to solve the problem]

A means for solving the above-mentioned problems is shown in FIG. That is, the air-fuel ratio sensor is provided in the exhaust system of the internal combustion engine and detects the oxygen concentration in the exhaust gas. On the other hand, the condition determining means determines whether the engine satisfies the air-fuel ratio feedback condition or the open loop condition. As a result, when the engine satisfies the open loop condition and the air-fuel ratio is richer than the stoichiometric air-fuel ratio, the first storage means stores the output V _H of the air-fuel ratio sensor; When the air-fuel ratio satisfies the open loop condition and the air-fuel ratio is leaner than the stoichiometric air-fuel ratio, the second storage means stores the output V _L of the air-fuel ratio sensor. Further, the comparison voltage calculation means calculates the comparison voltage _VR by dividing each output V _H , V _L of the air-fuel ratio sensor stored in the first and second storage means at a predetermined ratio. For example, V _R
←(V _H +V _L )/2. When the engine satisfies the air-fuel ratio feedback conditions,
The comparison means compares the output V _OX of the air-fuel ratio sensor with the comparison voltage V _R
The air-fuel ratio adjusting means adjusts the air-fuel ratio of the engine according to the comparison result of the comparing means.

[Effect]

According to the above-mentioned means, when the engine is in an open loop and is operated at an air-fuel ratio on the rich side or lean side of the stoichiometric air-fuel ratio, _O2 sensors with the characteristics shown by the solid line (in case A) and the broken line (in case B) have greatly different outputs, so the first and second
The storage means stores outputs (V _H , V _L ) that well reflect the characteristic deviation of the O ₂ sensor.
Therefore, a comparison voltage _VR corresponding to a more accurate stoichiometric air-fuel ratio can be obtained from these values V _H and V _L.

〔Example〕

FIG. 3 is an overall schematic diagram showing an embodiment of an air-fuel ratio control device for an internal combustion engine according to the present invention. In FIG. 3, an air flow meter 3 is provided in the intake passage 2 of the engine body 1. As shown in FIG. air flow meter 3
The device directly measures the amount of intake air, and includes a built-in potentiometer to generate an analog voltage output signal proportional to the amount of intake air. This output signal is supplied to an A/D exchanger 101 with a built-in multiplexer of the control circuit 10. The distributor 4 also includes a crank angle sensor 5 whose shaft generates a pulse signal for detecting a reference position every 720 degrees in terms of crank angle, and a crank angle sensor 5 that detects an angular position every 30 degrees in terms of crank angle. A crank angle sensor 6 is provided which generates a pulse signal. The pulse signals of these crank angle sensors 5 and 6 are supplied to the input/output interface 102 of the control circuit 10, of which the output of the crank angle sensor 6 is
It is supplied to the interrupt terminal of the CPU 103.

Further, the intake passage 2 is provided with a fuel injection valve 7 for supplying pressurized fuel from a fuel supply system to the intake port for each cylinder.

Further, a water temperature sensor 8 for detecting the temperature of cooling water is provided in the water jacket of the cylinder block of the engine body 1. The water temperature sensor 8 generates an analog voltage electrical signal according to the temperature THW of the cooling water.

Furthermore, an O ₂ sensor 9 is provided in the exhaust manifold, that is, upstream of the catalytic converter (not shown), and this O ₂ sensor 9 generates an electrical signal according to the concentration of oxygen components in the exhaust gas. do. That is, the O ₂ sensor 9 generates different output voltages to the A/D converter 101 of the control circuit 10 depending on whether the air-fuel ratio is lean or rich with respect to the stoichiometric air-fuel ratio.

The control circuit 10 is configured as a microcomputer, for example, and includes an A/D converter 101, an input/output interface 102, a CPU 103, and
ROM104, RAM105, backup RAM
106, a clock generation circuit 107, etc. are provided. Note that the backup RAM 106 is directly connected to a backup battery (not shown), so even if the ignition switch is turned off, the contents stored in the backup RAM 106 will not be erased.

Further, a throttle sensor 12 is provided on the shaft of the throttle valve 11 in the intake passage 2 to detect the opening degree TA of the throttle valve 11.
2, the throttle valve 11 is opened at a predetermined opening, for example.
It has a built-in power-on switch (VL) that turns on when the angle is 50° or more, and an idle switch (LL) that turns on when the throttle valve 11 is fully closed.
These outputs are supplied to an input/output interface 102 of the control circuit 10.

Further, in the control circuit 10, a down counter 108, a flip-flop 109, and a drive circuit 110 are for controlling the fuel injection valve 7. That is, in the routine described later, when the fuel injection amount TAU is calculated, the fuel injection amount TAU is preset in the down counter 108 and the flip-flop 109 is also set. As a result, the drive circuit 110 starts energizing the fuel injection valve 7. On the other hand, when the down counter 108 counts the clock signal (not shown) and finally its carrier out terminal reaches the "1" level, the flip-flop 109 is reset and the drive circuit 110 is reset.
stops the energization of the fuel injection valve 7. In other words, the fuel injection valve 7 is energized by the above-mentioned fuel injection amount TAU,
Therefore, an amount of fuel corresponding to the fuel injection amount TAU is sent to the combustion chamber of the engine body 1.

Furthermore, an interrupt occurs in the CPU 103 when the A/D converter 101 finishes A/D conversion, when the input/output interface 102 receives a pulse signal from the crank angle sensor 6, and so on.

The intake air amount data Q of the air flow meter 3 and the water temperature data THW of the water temperature sensor 8 are taken in by an A/D conversion routine executed at predetermined time intervals and stored in a predetermined area of the RAM 105. In other words, data Q and THW in RAM105
is updated at predetermined intervals. Further, the rotational speed data Ne is calculated by an interrupt of the crank angle sensor 6 every 30° CA, and is stored in a predetermined area of the RAM 105. The operation of the control circuit shown in FIG. 3 will be explained below.

FIG. 4 shows a fuel cut setting routine, which is executed every predetermined period of time, for example, every 4 ms. This routine uses the fuel cut flag XFC as shown in Figure 5.
This is for setting. In addition, in Fig. 5, Nc indicates the fuel cut rotation speed, and N _R indicates the fuel cut return rotation speed, both of which are determined by the engine cooling water temperature.
Updated by THW.

In step 401, it is determined whether the output signal LL of the idle switch of the slot sensor 12 is "1", that is, whether the throttle valve 11 is fully closed. If it is not fully closed, the process proceeds to step 404; on the other hand, if it is fully closed, the process proceeds to step 402. In step 402, the rotation speed Ne is read from the RAM 105 and compared with the fuel cut rotation speed Nc, and in step 403, it is compared with the fuel cut return rotation speed _NR . As a result, when Ne≦N _R , the step
Set the fuel cut flag XFC to “0” at 404,
When Ne≧Nc, the process proceeds to step 405, and the fuel cut flag XFC is set to "1". N _R ＜Ne＜Nc
When , flag XFC will be kept in its previous state.

The routine then ends at step 406.

FIG. 6 shows a comparison voltage calculation routine for calculating a comparison voltage, which is executed every predetermined period of time, for example, every 4ms. That is, in step 601, the O ₂ sensor 9
It is determined whether a closed loop (feedback) condition for the air-fuel ratio is satisfied. While starting the engine,
During fuel increase operation after startup, warm-up increase operation, power increase operation (VL="1"), lean control, fuel cut (XFC="1"), inactive state of O ₂ sensor 9, etc. The closed-loop condition is not satisfied in all cases, and the closed-loop condition is satisfied in all other cases. In addition,
RAM1 determines whether the _O2 sensor 9 is active or inactive.
Read water temperature data THW from 05 and set THW once.
Determine whether the temperature has reached ≧70℃ or
This is done by determining whether the output level of the O ₂ sensor 9 has increased or decreased once. If the closed loop condition is satisfied, proceed directly to step 610;
If the closed-loop condition is not satisfied, that is, if the open-loop condition is satisfied, the process advances to step 602.

In step 602, it is determined whether the power-on switch of the throttle sensor 12 is on (VL="1") or not.
That is, it is determined whether the opening degree of the throttle valve 11 is 50 degrees or more, and in step 603, it is determined whether or not fuel is being cut (XFC="1"). As a result, when the power-on switch is on (VL="1")
The process proceeds to steps 604-606, and if fuel is being cut (XFC="1"), the process proceeds to steps 607-609; otherwise, the process proceeds to step 610. In other words, VL
If = “1”, the power is being increased, and therefore,
It is clear rich control, in this case, proceed to steps 604 to 606, and if XFC="1", it is clear lean control, in this case, proceed to step 607.
Proceed to ~609.

In step 604, the output V _OX of the O ₂ sensor 9 is A/D converted and taken in, and in step 605, V _H ←
The high level value _VH is updated as _VOX . and,
At step 606, back up _VH again to RAM1.
Store in 06.

On the other hand, in step 607, the output of the O ₂ sensor 9
V _OX is A/D converted and imported, and in step 608
Update the low level value V _L as V _L ← V _OX . Then, in step 609, back up V _L again.
Store in RAM 106.

Then, in step 610, the average value of the high level value V _H and the low level value V _L is calculated as the comparison voltage V _R , that is, V _R ← (V _H + V _L )/2, and in step 611, this routine is ends.
Note that in step 610, x and y (x≠y) may be appropriately determined as V _R ←x·V _H +y·V _L /x+y.

In this way, the comparison voltage V _R is calculated based on the output V _OX of the O ₂ sensor 9 during open loop.

FIG. 7 shows an air-fuel ratio feedback control routine for calculating an air-fuel ratio correction coefficient FAF based on the output of the O ₂ sensor 9.
executed every time.

In step 701, similarly to step 601 in FIG. 6, it is determined whether a closed loop (feedback) condition for the air-fuel ratio by the O ₂ sensor 9 is satisfied. If the closed-loop condition does not hold, the step
Proceed to 727 and set the air-fuel ratio correction coefficient FAF to 1.0. In this case, the FAF value immediately before the closed loop control is stopped or its average value may be used. On the other hand, if the closed loop condition is met, the process advances to step 702.

In step 702, the output V _OX of the O ₂ sensor 9 is A/D converted and taken in, and in step 703 it is determined whether V _OX is less than the comparison voltage V _R , for example, 0.45V, that is, whether the air-fuel ratio is rich or not. Determine if it is lean. If lean (V _OX ≦ V _R ), step 704
It is determined whether the delay counter CDLY is positive or not at step 705. If CDLY>0, CDLY is set at step 705.
is set to 0 and the process proceeds to step 706. In step 706, the delay counter CDLY is decremented by 1, and then in step 707 it is determined whether CDLY<TDL. Note that TDL is a lean delay time for maintaining the determination that the rich state is present even if the output of the O ₂ sensor 9 changes from rich to lean, and is defined as a negative value. Therefore,
Only when CDLY<TDL, at step 708
CDLY is set to TDL, and the air-fuel ratio flag F is set to "0" (lean) in step 709. On the other hand, if it is rich (V _OX > V _R ), it is determined in step 710 whether the delay counter CDLY is negative or not, and CDLY < 0.
If so, CDLY is set to 0 in step 711 and the process proceeds to step 712. In step 712, the delay counter CDLY is incremented by 1, and then in step 713 it is determined whether CDLY<TDR. In addition,
TDR is a rich delay time for maintaining the determination that the engine is in a lean state even if the output of the O ₂ sensor 9 changes from lean to rich, and is defined as a positive value. Therefore, only when CDLY>TDR, CDLY is set to TDR in step 714, and the air-fuel ratio flag F is set to "1" (rich) in step 715.

In step 716, it is determined whether the sign of the air-fuel ratio flag F has been inverted. That is, it is determined whether the air-fuel ratio after the delay process has been reversed. If the air-fuel ratio is reversed, it is determined in step 717 whether the reversal is from rich to lean or from lean to rich. Reversal from rich to lean (F=
“0”), in step 718 FAF←FAF+
RSR is increased in a skip manner, and conversely, if there is a reversal from lean to rich (F="1"), in step 719, FAF←FAF+RSL is decreased in a skip manner. In other words, skip processing is performed.

If the sign of the air-fuel ratio flag F is not inverted in step 716, integration processing is performed in steps 720, 721, and 722. That is, at step 720, F=
If “0” (lean), FAF← in step 721
On the other hand, if F=“1” (rich), then in step 722, FAF←FAF−KIL is set. Here, the integral constants KIR and KIL are skip constants
It is set smaller than RSR and RSL. Therefore, step 721 gradually increases the fuel injection amount in the lean state (F="0"), and step 722 gradually decreases the fuel injection amount in the rich state (F="1").

The air-fuel ratio correction coefficient FAF calculated in steps 718, 719, 721, 722 is calculated in steps 723, 724, 725,
726 with minimum value e.g. 0.8 and maximum value e.g.
1.2, and as a result, if the air-fuel ratio correction coefficient FAF becomes too large or too small for some reason, the engine's air-fuel ratio is controlled using that value to prevent over-rich or over-lean conditions.

The FAF calculated as described above is stored in the RAM 105, and the routine ends at step 728.

FIG. 8 shows an injection amount calculation routine, which is executed at every predetermined crank angle, for example, 360° CA. At step 801, the fuel cut flag XFC is set to “0”.
As a result, if XFC="1", the process directly advances to step 808 and executes fuel cut. On the other hand, if XFC="0", the process advances to step 802. In step 802, the RAM 105 reads out the intake air amount data Q and the rotational speed data Ne to calculate the basic injection amount TAUP. for example
Let TAUP←α・Q/Ne (α is a constant). Cooling water temperature data from RAM105 in step 803
THW is read and a one-dimensional map stored in the ROM 104 is used to interpolate the warm-up increase value FWL.
As shown in the figure, this warm-up increase value FWL is set to decrease as the current cooling water temperature THW increases.

In step 804, the power increase value is set in accordance with VL="1" and Q/Ne in order to make the output air-fuel ratio sufficiently rich with respect to the air-fuel ratio during feedback.
FPOWER is calculated by interpolation using a two-dimensional map stored in the ROM 104.

In step 805, the final injection amount TAU is
←TAUP・FAF・(FWL+β+1)・(FPOWER
+γ+1)+δ. Note that β, γ,
δ is a correction amount determined by other operating state parameters, such as a signal from a throttle sensor, a signal from an intake air temperature sensor, battery voltage, etc.
It is stored in RAM105. Next, in step 807, the injection amount TAU is counted down by the down counter 108.
At the same time, the flip-flop 109 is set to start fuel injection. The routine then ends at step 808. As mentioned above, when the time corresponding to the injection amount TAU has elapsed, the flip-flop 109 is reset by the carry-out signal of the down counter 108, and the fuel injection ends.

FIG. 9 is a timing diagram illustrating the O ₂ sensor output waveform according to the present invention. As shown in FIG. 9A, the vehicle speed SPD changes, power increase is executed from time _t1 to _t2 (VL="1"), and fuel cut (XFC="1") occurs from time _t3 to _t4 . ”) shall be executed. Therefore, times t ₁ to t ₂ and t ₃ to _{t 4} are both open-loop, and in other cases air-fuel ratio feedback control (F/B) is in progress.

If the O ₂ sensor 9 has not deteriorated (see FIG. 2A), it will exhibit a relatively large high level value V _H when VL="1", and will exhibit a relatively small low level value V _L when XFC="1". Also, the O ₂ sensor 9
If the characteristics change as shown in A in diagram B, VL=
Although it shows a relatively large high level value V _H when it is "1", it also shows a relatively large low level value V _L when XFC="1". Furthermore, the O ₂ sensor 9
If the characteristics change as shown in B in the diagram, VL = “1”
Although it sometimes shows a relatively small high level value V _H , it also shows a relatively small low level value V _L when XFC="1". In either case, the amplitude is larger than that during air-fuel ratio feedback.

Note that in the above embodiment, the high level value V _H during power increase and the low level value V _L during fuel cut are used, but the high level value V _H during catalyst overheat prevention increase (FOTP) under heavy load, The low level value V _L during partial lean at light load may be used.

Furthermore, the present invention can be applied to a single O ₂ sensor system in which an O ₂ sensor is provided downstream of the catalyst, and a double O ₂ sensor system in which O ₂ sensors are provided upstream and downstream of the catalyst, respectively.

Furthermore, instead of the air flow meter, a Karman vortex sensor, a heat wire sensor, or the like may be used as the intake air amount sensor.

Furthermore, in the above embodiment, the fuel injection amount is calculated according to the intake air amount and the engine rotation speed, but the fuel injection amount is calculated according to the intake air pressure and the engine rotation speed, or the throttle valve opening and the engine rotation speed. The fuel injection amount may also be calculated.

Furthermore, although the above-described embodiment shows an internal combustion engine in which the amount of fuel injected into the intake system is controlled by a fuel injection valve, the present invention can also be applied to a carburetor type internal combustion engine. For example, an electric air control valve (EACV) adjusts the intake air amount of the engine to control the air-fuel ratio, and an electric bleed air control valve adjusts the air bleed amount of the carburetor to control the main system. The present invention can be applied to devices that control the air-fuel ratio by introducing atmospheric air into passages and slow system passages, those that adjust the amount of secondary air sent to the exhaust system of an engine, and the like. In this case, the basic fuel injection amount corresponding to the basic injection amount TAUP in step 802 is determined by the carburetor itself, that is, it is determined according to the intake pipe negative pressure according to the intake air amount and the engine rotation speed, Final fuel injection amount TAU at step 805
The amount of supplied air corresponding to is calculated.

Further, although the above-described embodiments are constructed using a microcomputer, that is, a digital circuit, it may also be constructed using an analog circuit.

[Effect of idea]

As explained above, according to the present invention, since the comparison voltage corresponding to the stoichiometric air-fuel ratio can be appropriately set,
Changes in the output characteristics of the air-fuel ratio sensor are compensated for, thus helping to prevent deterioration of exhaust emissions.

[Brief explanation of the drawing]

Figure 1 is an overall block diagram for explaining the configuration of the present invention, Figures 2A and 2B are graphs for explaining the output characteristics of the O ₂ sensor, and Figure 3 is an internal combustion engine air conditioner according to the present invention. Overall schematic diagram showing one embodiment of the fuel ratio control device, FIGS. 4, 5, 6, and 7
8 is a flowchart for explaining the operation of the control circuit of FIG. 3, and FIG. 9 is a timing diagram for supplementary explanation of the flowchart of FIG. 6. 1... Engine body, 3... Air flow meter, 4
... Distributor, 5, 6 ... Crank angle sensor, 9 ... O ₂ sensor, 10 ... Control circuit,
12...Throttle sensor.

Claims (1)

[Scope of Claim for Utility Model Registration] An air-fuel ratio sensor that detects oxygen concentration in exhaust gas of an internal combustion engine and whose output changes rapidly with an air-fuel ratio near the stoichiometric air-fuel ratio; a condition determining means for determining whether an air-fuel ratio feedback condition based on output is satisfied or an open loop condition; and when the engine satisfies the open loop condition, the engine a first storage means for storing the output of the air-fuel ratio sensor when the engine is operated at an air-fuel ratio richer than the stoichiometric air-fuel ratio; a second storage means for storing the output of the air-fuel ratio sensor when the engine is operated at an air-fuel ratio leaner than the stoichiometric air-fuel ratio; a comparison voltage calculation means for calculating a comparison voltage by dividing each output of the air-fuel ratio sensor by a predetermined division ratio; An air-fuel ratio control device for an internal combustion engine, comprising: means for comparing with a voltage; and an air-fuel ratio adjusting means for adjusting an air-fuel ratio of the engine according to a comparison result of the comparing means.