JPH0328577B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an air-fuel ratio control device for an engine.
In particular, the present invention relates to an engine in which the air-fuel ratio of an engine is feedback-controlled to a predetermined value using an air-fuel ratio sensor whose output changes linearly in accordance with the oxygen concentration in exhaust gas.

(Prior Art) It is widely known that the air-fuel ratio of the engine is detected based on the oxygen concentration in the exhaust gas of the engine, and the air-fuel ratio of the air-fuel mixture supplied to the engine is feedback-controlled to a predetermined value.

In this case, the air-fuel ratio sensor, which indirectly detects the air-fuel ratio by detecting the oxygen concentration in the exhaust gas, outputs (electromotive force) in steps at the oxygen concentration corresponding to the stoichiometric air-fuel ratio. There are so-called λ sensors that vary. This λ sensor is suitable for controlling the air-fuel ratio to the stoichiometric air-fuel ratio due to its output characteristics, but when high output is required, such as during acceleration or high-load operation, the air-fuel ratio is lower than the stoichiometric air-fuel ratio. When setting the air-fuel ratio to be richer, or when setting the air-fuel ratio leaner than the stoichiometric air-fuel ratio to improve fuel efficiency during steady high-speed driving, only the magnitude relative to the stoichiometric air-fuel ratio is determined as described above. , it is not possible to accurately detect air-fuel ratios that deviate from the stoichiometric air-fuel ratio to the lean or rich side, and it is not suitable for controlling the air-fuel ratio to an arbitrary value.

Therefore, the present applicant has developed an air-fuel ratio sensor to replace the above-mentioned λ sensor, which changes the output linearly according to the oxygen concentration in the exhaust gas, as shown in Japanese Patent Application Laid-Open No. 59-100854. We have proposed a so-called wide-range air-fuel ratio sensor that can continuously detect the air-fuel ratio from a rich region to a lean region, making it possible to control the air-fuel ratio to an arbitrary value. In other words, this wide-range air-fuel ratio sensor has porous electrodes formed on both sides of an oxygen ion-conducting solid electrolyte, and a semi-porous electrode mainly made of Pt etc. as the porous electrode on the side that comes into contact with the gas to be measured (exhaust gas). In addition to using a material with catalytic performance, a metal oxide such as SnO ₂ that oxidizes HC to generate CO is present near the three-phase point consisting of the electrode, solid electrolyte, and gas to be measured. It is what it is.

(Problem to be Solved by the Invention) However, due to its structure, the wide-range air-fuel ratio sensor as described above has a structure in which the catalytic activity of the porous electrode made of Pt or the like varies depending on the exhaust gas temperature, that is, the temperature of the wide-range air-fuel ratio sensor itself. The electromotive force characteristics change due to temperature changes (see Fig. 4). (This also applies to the λ sensor, but since the λ sensor only determines whether the air-fuel ratio is larger or smaller than the stoichiometric air-fuel ratio, there is no problem even if the electromotive force characteristics change slightly. ) Also, the electromotive force of the wide-range air-fuel ratio sensor is affected by the proportion of CO at the three-phase point, and this CO is controlled by the HC (hydrocarbon) concentration in the exhaust gas, so
The electromotive force characteristics change as the HC concentration changes (see Figure 5). Therefore, when using the above-mentioned wide-range air-fuel ratio sensor to feedback-control the air-fuel ratio of the engine to a predetermined value, the output value changes depending on the temperature of the wide-range air-fuel ratio sensor and the HC concentration in the exhaust gas, making it difficult to detect the air-fuel ratio. There is a problem that the air-fuel ratio cannot be controlled accurately due to the deviation. The same can be said of other wide-range air-fuel ratio sensors whose output varies linearly depending on the oxygen concentration in exhaust gas.

The present invention has been made in view of the above, and an object of the present invention is to set a target value as a comparison value to be compared with the output of the wide range air-fuel ratio sensor when controlling the air-fuel ratio using the wide range air-fuel ratio sensor. By correcting the fuel ratio sensor temperature (exhaust gas temperature) and the HC concentration in the exhaust gas, the above temperature and
The object of the present invention is to compensate for the deviation of the air-fuel ratio with respect to the HC concentration so that the air-fuel ratio can be controlled accurately.

(Means for Solving the Problems) In order to achieve the above object, the solving means of the present invention is provided in the exhaust passage of an engine, as shown in FIG. An air-fuel ratio sensor 8 whose output changes, and the air-fuel ratio sensor 8 corresponding to the air-fuel ratio of the air-fuel mixture described in advance.
a target value setting means 15 for setting a target value, and a comparison means 17 for comparing the output of the air-fuel ratio sensor 8 with the target value set by the target value setting means 15.
and an air-fuel ratio control means 18 which receives the output of the comparison means 17 and controls the air-fuel ratio of the air-fuel mixture supplied to the engine to the target value. In addition to this, detecting means 9 and 10 for detecting the temperature of the air-fuel ratio sensor 8 and the hydrocarbon concentration in the exhaust gas, and receiving the outputs of the detecting means 9 and 10,
A correction means 16 is provided for correcting the target value of the target value setting means 15 according to the temperature of the air-fuel ratio sensor 8 and the hydrocarbon concentration in the exhaust gas.

(Function) With the above configuration, in the present invention, the output changes linearly according to the oxygen concentration in the exhaust gas.
When feedback controlling the air-fuel ratio to a set value using a so-called wide-range air-fuel ratio sensor, the air-fuel ratio corresponding to the set air-fuel ratio is determined according to the temperature of the air-fuel ratio sensor (exhaust gas temperature) and the HC concentration in the exhaust gas. By correcting the target value of the sensor, the target value corresponds to the change in the output value of the air-fuel ratio sensor due to the temperature and HC concentration, and the deviation in the air-fuel ratio is compensated for.

(Example) Hereinafter, an example of the present invention will be described based on the drawings from FIG. 2 onwards.

FIG. 2 shows a schematic configuration of an engine air-fuel ratio control system according to an embodiment of the present invention, in which 1 is an engine, 2 is an intake passage for supplying intake air to the engine 1, and 3 is an exhaust gas from the engine 1. This is an exhaust passage for discharging. A throttle valve 4 for controlling the amount of intake air supplied to the engine 1 is disposed in the intake passage 2, and a fuel injection valve 5 for injecting fuel to the engine 1 is disposed in the intake passage 2 downstream of the throttle valve 4. It is arranged.

Further, upstream of the throttle valve 4 in the intake passage 2, an air flow sensor 6 for detecting the amount of intake air and an intake temperature sensor 7 for detecting the temperature of intake air are provided. On the other hand, the exhaust passage 3 includes an air-fuel ratio sensor 8 that detects the air-fuel ratio based on the oxygen concentration in the exhaust gas, an HC sensor 9 that detects the hydrocarbon (HC) concentration in the exhaust gas, and an air-fuel ratio sensor 9 that detects the air-fuel ratio based on the exhaust gas temperature. An exhaust temperature sensor 10 is provided to detect the temperature of the sensor 8, and the outputs of these sensors 6 to 10 are input to an air-fuel ratio controller 11 that controls the fuel injection valve 5. Also, 12 is a spark plug, 13 is an ignition coil, 14
is an igniter, and the ignition signal from the igniter 14 is inputted to the air-fuel ratio controller 11 as an engine rotational speed signal or the like.

The air-fuel ratio sensor 8 has porous electrodes formed on both sides of an oxygen ion conductive solid electrolyte as described above, and a semi-catalyst such as Pt as the porous electrode on the side that contacts the gas to be measured (exhaust gas). SnO ₂ , In ₂ O ₃ , which oxidizes HC to generate CO, are used near the three-phase point consisting of the electrode, solid electrolyte, and gas to be measured (exhaust gas).
It is made up of metal oxides such as NiO, Co ₃ O ₄ , CnO, etc., and its electromotive force characteristics are such that, as shown in Figure 3, the output of the electromotive force is linear depending on the oxygen concentration in the exhaust gas. It is a so-called wide-range air-fuel ratio sensor that has basic characteristics that allow it to continuously detect the air-fuel ratio from a rich region to a lean region.
The electromotive force characteristic of this air-fuel ratio sensor 8 is the fourth
As shown in the figure, it has a temperature characteristic that changes depending on the temperature of the air-fuel ratio sensor 8 (exhaust gas temperature), and as the temperature increases, the electromotive force decreases on the lean side compared to the stoichiometric air-fuel ratio, and on the rich side , the electromotive force increases. Furthermore, as shown in FIG. 5, the electromotive force of the air-fuel ratio sensor 8 has an HC concentration characteristic that changes depending on the HC concentration in the exhaust gas, and as the HC concentration increases on the lean side of the stoichiometric air-fuel ratio. The electromotive force increases (note that since the HC concentration is originally high on the rich side, there is almost no change in the electromotive force).

Next, the operation of the air-fuel ratio controller 11 will be explained with reference to _the flowchart shown in FIG.
Fzone (“0” on the lean side, “1” on the rich side) is set to “0”, and delay flags Fl and Fr (not in delay) on the lean side and rich side are used to distinguish whether fuel injection is delayed or not. Initial setting is ``0'' during the injection period and ``1'' during the delay period), and a feedback coefficient Cfb, which determines the relationship between the engine speed and the injection time, is initially set to ``1''. Furthermore, in step _S2 , a basic timer that determines a fixed period for calculating engine speed, etc. is reset, and in the next step _S3 , the basic timer is set to a fixed period Ti.
Wait until the time has elapsed, and when the predetermined time Ti has elapsed, the basic timer is reset again in step _S4 .
Note that this basic timer is a counter that counts up the time from the moment it is reset.

Next, in step _S5 , the engine speed Ne is determined by the ignition pulse signal from the igniter 14.
Calculate the airflow sensor ₆ in step S6.
And the intake air flow rate Ue is calculated based on the signal from the intake temperature sensor 7.

Next, in step _S7 , the electromotive force Vs signal as an output signal from the air-fuel ratio sensor 8, the HC concentration signal from the HC sensor 9, and the exhaust gas temperature signal from the exhaust temperature sensor 10 (air-fuel ratio sensor temperature signal) are input. Later, in step _S8 , the target air-fuel ratio, HC
The concentration and exhaust gas temperature are input into a data table as shown in FIG. 7, and the slice level median value Vref as the target value of the air-fuel ratio sensor 8 corresponding to the target air-fuel ratio is determined.

Here, the target air-fuel ratio is set, for example, based on the map shown in FIG. 8, depending on the engine operating state due to engine speed and engine load. F=12), and lean (A/F=18) during high-speed steady driving. Furthermore, in the data table shown in Fig. 7 above, the slice level median value Vref corresponding to the exhaust gas temperature and HC concentration is written for each target air-fuel ratio, and Fig. 9 shows the slice level median value Vref corresponding to the exhaust gas temperature and HC concentration. The median slice level Vref is determined from the map shown, and Vref increases as the temperature increases on the rich side (for example, A/F = 12), and as the temperature increases on the lean side (for example, A/F = 18). As a result, Vref decreases and the stoichiometric air-fuel ratio (A/
F=14.7), Vref remains almost constant with respect to temperature changes (in Fig. 9, it is assumed that the HC concentration is constant). In addition, for the HC concentration, the slice level median value Vref is determined from the map shown in Figure 10, and on the lean side (A/F = 18), Vref increases as the HC concentration increases, and the stoichiometric air-fuel ratio ( A/F
= 14.7) and HC on the rich side (A/F = 12)
Vref remains almost constant with respect to concentration changes (in addition,
In Fig. 10, the exhaust gas temperature is assumed to be constant).

After that, in the following steps _S9 to _S29 ,
Feedback control is executed to adjust the air-fuel ratio to the target air-fuel ratio using the correspondence between the output characteristics of the air-fuel ratio sensor 8 and the average fuel injection amount from the fuel injection valve 5 as shown in FIG. That is, first, in step _S9 , in order to determine the hysteresis (dead zone) of the target electromotive force of the air-fuel ratio sensor 8 for noise resistance, it is determined whether the zone flag Fzone is "0" or "1".
When Fzone = 0 on the lean side, in step _S10 the slice level median value V'ref is set to Vref + Vhl (Vhl:
When Fzone is on the rich side with Fzone = 1, the slice level median value V'ref is set as Vref - Vhr (Vhr: dead zone width on the rich side) in step _S11 , and the process proceeds to step _S12 . . Then, in step _S12 , the actually measured electromotive force Vs from the air-fuel ratio sensor 8 is compared with the slice level median value V'ref determined in step _S10 or _S11 .

If the determination in step _S12 is that Vs≧V'ref, the zone flag Fzone is determined in step _S13 , and if Fzone=1, which is on the rich side, it is determined that the air-fuel ratio is richer than the target value. step
In step _S14 , the feedback coefficient Cfb is set to Cfb-Cr (Cr: integral constant) to lean the air-fuel ratio, that is, to reduce the fuel injection amount, and in step _S15 , the fuel injection time τ is calculated from the formula K, Cfb, Ue/Ne. Then return to step _S3 .

After that, as the fuel injection amount decreases in step _S15 , the air-fuel ratio becomes lean as shown in FIG. 11, and when the determination in step _S12 becomes Vs<V'ref,
In step _S16 , the zone flag Fzone is determined,
Since it is still the rich side with Fzone=1, in the next step _S17 it is determined whether the lean side delay flag Fl is "1". When Fl=0 (NO), it is determined that the rich side has changed to the lean side, and after setting the delay flag Fl to "1" in step _S18 ,
In step _S19 , the delay timer is reset (note that, like the basic timer described above, this delay timer is a timer that counts up the time from the moment it is reset.) Then, YES of Fl=1.
During the delay, the delay timer determines whether or not a predetermined delay time tdl has elapsed in the next step _S20 . If the delay time has not elapsed, the process moves to step _S14 to prevent the influence of noise, and the feedback coefficient Cfb is set. is maintained at Cfb-Cr, and the process returns to step _S3 while reducing the fuel injection amount in step _S15 . On the other hand, when the delay time tdl has elapsed, the zone flag Fzone is set to " ₀ " and the delay flag Fl is set to "0" in step S21, and then the feedback coefficient Cfb is set to Cfb+Csl (Cfb+Csl) in order to enrich the air-fuel ratio in step _S22 . Csl: proportionality constant), the fuel injection amount is increased in step _S15 , and the process returns to step _S3 .

Next, even with this increase in the fuel injection amount, the determination in step _S12 is still that Vs<V'ref, so in step _S16 it is determined that the zone flag Fzone is on the lean side of 0, and in step _S23 To enrich the air-fuel ratio, change the feedback coefficient Cfb to Cfb + Cl.
(Cl: integral constant), the fuel injection amount is further increased in step _S15 , and the process returns to step _S3 .

After that, this increase in fuel injection amount causes the step
The determination in S ₁₂ is Vs≧V′ref, but step S ₁₃
Since the judgment is on the lean side with the zone flag Fzone = 0, it is determined in step _S24 whether the rich side delay flag Fr is "1" or not, and if it is NO with Fr = 0, it is reversed from the lean side to the rich side. Judging that this is the case, set the delay flag Fr to “1” in step S ₂₅ .
After that, the day delay timer is reset in step _S26 . Then, during the delay of YES with Fr=1, in the next step _S27 , the delay timer determines whether or not a predetermined delay time tdr has elapsed, and if it has not elapsed, a step is executed to prevent the influence of noise. The process moves to _S23 , and the feedback coefficient Cfb is maintained at Cfb+Cl, and the process returns to step _S3 while increasing the fuel injection amount in step _S15 . on the other hand,
When the delay time tdr has elapsed, the zone flag Fzone is set to "1" and the delay flag Fr is set to "0" in step _S28 , and then the feedback coefficient Cfb is set in order to make the air-fuel ratio leaner in step _S29 .
As Cfb−Csr (Csr: constant of proportionality), step
At _S15 , the fuel injection amount is decreased and the process returns to step _S3 .
Thereafter, the determination in step _S12 is that Vs≧V'ref, and the determination in step _S13 is that Fzone=1, and the same operation as above is repeated thereafter.

Incidentally, the injection timing of the fuel injection valve 5 is the 12th injection timing.
As shown in the figure, the main flow of the air-fuel ratio controller 11 is interrupted by the rise of the ignition pulse from the igniter 14,
First, the injection timer is set to the fuel injection time τ (this injection timer is a counter that counts down the set time and generates an injection end interrupt signal (described later) at the moment it reaches zero), and then starts the fuel injection. Turn on the current to valve 5 and start fuel injection. Then, the end of the fuel injection is interrupted by the injection end interrupt signal from the injection timer, as shown in FIG. 13, and the current to the fuel injection valve 5 is turned off.

Therefore, in the operation flow of the air-fuel ratio controller 11, in step S8, the target value setting is performed to set the target value (slice level median value Vref) of the air-fuel ratio sensor ₈ corresponding to the preset air-fuel ratio of the air-fuel mixture. The target value setting means 1 is configured according to the temperature of the air-fuel ratio sensor 8 (exhaust gas temperature) and the HC concentration in the exhaust gas.
A correction means 16 for correcting the target value of No. 5 is configured. Also, in step _S12 , the air-fuel ratio sensor 8
output (electromotive force Vs) and the target value set by the target value setting means 15 (slice level median value
It constitutes a comparison means 17 for comparing with V'ref). Furthermore, in steps _S13 to _S29 , the air-fuel ratio is controlled to receive the output of the comparison means 17 and control the fuel injection amount of the fuel injection valve 5 to control the air-fuel ratio of the air-fuel mixture supplied to the engine 1 to the target value. It constitutes a fuel ratio control means 18.

Therefore, in the above embodiment, the air-fuel ratio is detected by the air-fuel ratio sensor 8 whose output (electromotive force) changes depending on the oxygen concentration in the exhaust gas of the engine 1, and the output of the air-fuel ratio sensor 8 and The air-fuel mixture supplied to the engine 1 is compared with the target value of the air-fuel ratio sensor 8 corresponding to a preset air-fuel ratio, and the fuel injection amount from the fuel injection valve 5 is controlled according to the deviation. The air-fuel ratio will be feedback-controlled to the target value.

In this case, the electromotive force characteristics of the air-fuel ratio sensor 8 change as shown in FIGS. 4 and 5 depending on the temperature of the air-fuel ratio sensor 8 (exhaust gas temperature) and the HC concentration in the exhaust gas. The target value (slice level median value) corresponding to the set air-fuel ratio is corrected according to the temperature and HC concentration, so that it corresponds to the change in the electromotive force characteristics. in gas
The deviation of the air-fuel ratio with respect to the HC concentration is compensated for, and the air-fuel ratio can be accurately controlled using the wide-range air-fuel ratio sensor 8.

It should be noted that the present invention is not limited to the above-mentioned embodiments, but also includes various other modifications. For example, in the above embodiment, the air-fuel ratio is controlled by controlling the fuel injection amount in the fuel injection method, but the air-fuel ratio may be controlled by controlling the air bleed amount in the carburetor method.

(Effects of the Invention) As explained above, according to the present invention, the air-fuel ratio of the engine is feedback-controlled to the set air-fuel ratio using an air-fuel ratio sensor whose output changes according to the oxygen concentration in the exhaust gas of the engine. In this case, the target value of the air-fuel ratio sensor corresponding to the above-mentioned set air-fuel ratio is corrected according to the temperature of the air-fuel ratio sensor (exhaust gas temperature) and the HC concentration in the exhaust gas, and the target value of the air-fuel ratio sensor corresponding to the set air-fuel ratio is corrected to
Since the change in the output characteristic of the air-fuel ratio sensor is made to correspond to the concentration, it is possible to compensate for the deviation of the air-fuel ratio with respect to the temperature and HC concentration, and to perform the air-fuel ratio control accurately.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of the present invention. Figures 2 to 13 illustrate embodiments of the present invention, Figure 2 is a schematic configuration diagram of an engine air-fuel ratio control system, and Figures 3 to 5 illustrate electromotive force characteristics of the air-fuel ratio sensor. Characteristic diagram showing basic characteristics, temperature characteristics and HC concentration characteristics, Figure 6 is a flowchart diagram showing the operation of the air-fuel ratio controller, Figure 7
The figure shows an example of a data table, Figure 8 shows a map for setting the target air-fuel ratio, Figure 9 shows a map of the median slice level versus temperature, and Figure 10 shows the slice level versus HC concentration. A diagram showing a map of the median value, Figure 11 is an explanatory diagram showing the correspondence between the output characteristics of the air-fuel ratio sensor and the average fuel injection amount, and Figures 12 and 13 are interrupts at the start and end of fuel injection, respectively. It is a figure which shows a process. 1... Engine, 3... Exhaust passage, 5... Fuel injection valve, 8... Air-fuel ratio sensor, 9... HC sensor, 10... Exhaust temperature sensor, 11... Air-fuel ratio controller, 15... Target value Setting means, 16... Correction means, 17... Comparison means, 18... Air-fuel ratio control means.

Claims (1)

[Claims] 1. An air-fuel ratio sensor that is installed in the exhaust passage of the engine and whose output changes linearly according to the oxygen concentration in the exhaust gas, and a target value of the air-fuel ratio sensor that corresponds to a preset air-fuel ratio of the air-fuel mixture. a target value setting means for setting the air-fuel ratio sensor; a comparison means for comparing the output of the air-fuel ratio sensor with the target value set by the target value setting means; an air-fuel ratio control means for controlling the fuel ratio to the target value; a detection means for detecting the temperature of the air-fuel ratio sensor and the hydrocarbon concentration in the exhaust gas; An air-fuel ratio control device for an engine, comprising: a correction means for correcting the target value of the target value setting means according to the concentration of hydrocarbons in the gas.