JPH0436255B2 - - Google Patents

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention determines the fuel injection amount according to the operating state of the engine, and calculates the amount of fuel to be injected according to the deviation between the air-fuel ratio detected by the air-fuel ratio sensor and the target air-fuel ratio. The present invention relates to an air-fuel ratio control device for an engine that performs feedback correction on fuel injection amount.

(Prior art) Conventionally, in engine air-fuel ratio control, in order to improve the control accuracy of the supplied air-fuel ratio, an air-fuel ratio sensor detects the supplied air-fuel ratio, and this detected air-fuel ratio is compared with a target air-fuel ratio. A technique is known in which the fuel injection amount is feedback-corrected in accordance with the deviation so that the supplied air-fuel ratio becomes the target air-fuel ratio. In particular, when a lean sensor that generates an output signal approximately proportional to the exhaust gas oxygen concentration is used as the air-fuel ratio sensor, and the air-fuel ratio is in a region leaner than the stoichiometric air-fuel ratio according to the output of the lean sensor. A technique is known in which the fuel efficiency is improved through feedback control (for example, see Japanese Unexamined Patent Publication No. 59-208141).

In the air-fuel ratio control described above, a map is used that sets the fuel injection amount or fuel injection pulse width according to the engine speed and engine load, and the basic fuel injection amount under the engine operating condition is determined and this value is determined. The actual fuel injection amount is determined by applying various corrections to the fuel injection amount. In addition, in order to obtain a feedback signal by comparing the air-fuel ratio sensor output with the target value, a map in which a reference value corresponding to the target air-fuel ratio corresponding to the operating condition is similarly set is used, and this reference value and the air-fuel ratio sensor are compared. The detected value is compared with the detected value, and the fuel injection amount is corrected and controlled based on the deviation. In this way, various control maps are required,
A large memory capacity is required to store it.

Furthermore, when creating the various maps mentioned above, when a new engine is developed, engine performance is changed, control characteristics are changed, injector is changed, etc., new maps must be created accordingly. It is something that cannot happen. In this case, in a map that registers the value of fuel injection pulse width as a map for calculating the fuel injection amount, it is necessary to reset the measurement settings of the optimal injection pulse width corresponding to the operating condition, which increases development man-hours. It will be huge.
In particular, the target air-fuel ratio, which depends on the engine operating condition, is almost unaffected by engine changes or injector changes. This requires many experiments over a period of time.

(Object of the Invention) In view of the above circumstances, the present invention simplifies the control system and reduces development man-hours in controlling the supply air-fuel ratio to the target air-fuel ratio based on the fuel injection amount depending on the operating state of the engine. It is an object of the present invention to provide an air-fuel ratio control device for an engine.

(Structure of the Invention) The air-fuel ratio control device of the present invention includes a basic injection amount calculation means that calculates a basic injection amount function corresponding to the stoichiometric air-fuel ratio according to the intake air amount based on a mathematical formula, and a basic injection amount calculation means that is determined in advance according to the operating state. a target air-fuel ratio calculation means for calculating a target air-fuel ratio corresponding to the operating state from a map storing the target air-fuel ratio determined by the target air-fuel ratio; and a reference value calculation means for calculating a reference value for comparison of the detection signal of the air-fuel ratio sensor using the target air-fuel ratio. and a feedback coefficient calculation means for comparing the detection signal of the air-fuel ratio sensor with the comparison reference value to obtain a feedback coefficient according to the deviation between the two, and a target air-fuel ratio calculated by the theoretical air-fuel ratio and the target air-fuel ratio calculation means. The present invention is characterized by comprising a final injection amount calculation means for correcting the basic injection amount using the ratio of 1 and the feedback coefficient to obtain a final injection amount.

FIG. 1 is an overall configuration diagram for clearly showing the configuration of the present invention. An air-fuel ratio adjusting means 4 is provided which injects and supplies a predetermined fuel from an injector 3 disposed in the intake passage 2 of the engine 1 to adjust the supplied air-fuel ratio. In response to this, a fuel injection pulse having a predetermined pulse width is output to the injector 3 at a predetermined timing. The final injection amount calculation means 5 receives signals from the basic injection amount calculation means 6, the target air-fuel ratio calculation means 7, and the feedback coefficient calculation means 8, respectively, and calculates the final injection amount.

The basic injection amount calculation means 6 receives a signal from the intake air amount detection means 9 that detects the intake air amount, and calculates the basic injection amount for the stoichiometric air-fuel ratio according to the intake air amount based on a functional formula. This functional expression matches the detection characteristics of the intake air amount detection means 9 and the injection characteristics of the injector 3 in response to changes in engine specifications. Further, the target air-fuel ratio calculating means 7 is provided with a map storing a target air-fuel ratio determined in advance according to the operating state, receives a signal from the operating state detecting means 10 for detecting the operating state of the engine, and responds according to the operating state. The target air-fuel ratio is determined from the above map. This map stores the target optimum air-fuel ratio for each operating state. The feedback coefficient calculating means 8 is
The signal Vr of the reference value calculation means 11 which calculates the comparison reference value using the target air-fuel ratio by the target air-fuel ratio calculation means 7, and the detection signal of the air-fuel ratio sensor 13 (lean sensor) installed in the exhaust passage 12 of the engine 1.
Vs, the detection signal Vs of the air-fuel ratio sensor 13 is compared with the reference signal Vr, and a feedback coefficient corresponding to the deviation between the two is calculated.

The final injection amount calculation means 5 receives the signals from the respective means 6 to 8, and calculates the basic injection amount corresponding to the stoichiometric air-fuel ratio from the basic injection amount calculation means 6, and calculates the basic injection amount corresponding to the stoichiometric air-fuel ratio and the target air-fuel ratio calculation means 7. The fuel injection amount corresponding to the target air-fuel ratio is determined by correcting the fuel injection amount by the ratio between the target air-fuel ratio and the target air-fuel ratio according to the operating condition from The final injection amount is determined so that the detection signal of the air-fuel ratio sensor 13 corresponding to the fuel ratio matches the reference value corresponding to the target air-fuel ratio.

(Effects of the Invention) According to the present invention, in calculating the fuel injection amount,
The target air-fuel ratio calculated from the air-fuel ratio map according to the operating state by the target air-fuel ratio calculation means is used by both the final injection amount calculation means and the reference value calculation means for the feedback coefficient calculation means, so that the maps can be shared. The aim is to simplify the control system and make effective use of storage capacity. Furthermore, when setting control characteristics due to changes in engine specifications, etc., there is almost no change in the map that stores the target air-fuel ratio according to the operating condition and its calculation process, and the function formula for calculating the basic injection amount is changed. , it is sufficient to find the matching with the engine in the final injection amount calculation means, so
The number of development steps can be reduced.

In particular, the basic injection amount is calculated using different functional formulas depending on the engine specifications, etc., so that the stoichiometric air-fuel ratio is achieved with respect to the intake air amount, while the target air-fuel ratio is calculated from a map corresponding to the operating condition. The optimum target air-fuel ratio is determined according to the different required air-fuel ratios in each operating region, and the basic injection amount based on the stoichiometric air-fuel ratio is adjusted to the injection amount corresponding to the target air-fuel ratio. By correcting based on the ratio of the two, changes in engine specifications etc. can be dealt with mainly by changing the function formula for determining the basic injection amount.
Changes in engine performance in each operating state can be handled by modifying the map of the target air-fuel ratio, and compared to setting the basic injection amount according to the target air-fuel ratio, calculation processing inside the controller during operation is more efficient. Even if the process is somewhat complicated, it will be easier to process when changing engine specifications, etc.

In other words, if you set a map in which the fuel injection amount corresponding to the target air-fuel ratio according to the operating condition is directly registered, it will take a lot of effort to modify it because there is a lot of information gathered in this map. This requires experimental measurements. Further, the reference signal for the feedback coefficient calculation means also requires similar processing in order to be set in accordance with the target air-fuel ratio depending on the operating state, and this can be simplified.

(Example) Examples of the present invention will be described below with reference to the drawings. FIG. 2 is an overall configuration diagram of an engine equipped with an air-fuel ratio control device.

An injector 3 is disposed in an intake passage 2 that supplies intake air to a combustion chamber 15 of the engine 1, and fuel is supplied thereto. In this intake passage 2, an air cleaner 16, an intake air amount sensor 17 that measures the amount of intake air, and a throttle valve 18 that controls the amount of intake air are arranged in this order from the upstream side. On the other hand, a catalyst device 19 is provided in the exhaust passage 12 that discharges exhaust gas from the combustion chamber 15.
is installed to purify harmful components of exhaust gas including NOx. An air-fuel ratio sensor 13 (lean sensor) is disposed in the exhaust passage 12 upstream of the catalyst device 19.

The air-fuel ratio supplied to the combustion chamber 15 of the engine 1 is adjusted by the amount of fuel injected from the injector 3, and the fuel injection by the injector 3 is controlled by a control signal output from the controller 20. . The controller 20 includes a throttle sensor 21 that detects the intake air amount signal from the intake air amount sensor 17 and the opening degree of the throttle valve 18 in order to detect the operating state of the engine 1.
A detection signal from the engine rotation signal (crank angle signal) based on the ignition signal from the distributor 22 and the igniter 23, an intake air temperature signal from the intake air temperature sensor 24 disposed in the air cleaner 16, and a water temperature sensor that detects the cooling water temperature. The water temperature signal from 25 and the air-fuel ratio signal from the air-fuel ratio sensor 13 are respectively input, and the fuel injection amount and injection timing are controlled according to the operating state of the engine. Note that 26 is a battery.

The controller 20 has the functions of each of the means shown in FIG. Determine the fuel ratio, and in the case of feedback conditions in the lean region, determine the feedback coefficient from the reference value corresponding to the target air-fuel ratio and the air-fuel ratio sensor output, and calculate the final injection pulse width by determining other various correction coefficients. It is something to do.

FIG. 3 is a control block diagram of the controller 20. The intake air amount signal Tp from the intake air amount sensor 17 is
After the intake temperature is corrected by the intake temperature correction coefficient Cair based on the intake air temperature sensor 24, the basic injection pulse
In addition to being used to calculate Tp×Ck, the first air-fuel ratio AF1 is read from a first map _M1 that is preset according to the engine rotational speed Ne based on the crank angle and the intake air amount signal Tp. On the other hand, the throttle opening degree Ta and engine speed detected by the throttle sensor 21
A second air-fuel ratio AF2 is read from a second map _M2 preset according to Ne, and the first air-fuel ratio
A target air-fuel ratio AF is calculated based on AF1.

This target air-fuel ratio AF is used to correct the basic injection pulse and calculate the reference signal Vr after water temperature correction is performed using the water temperature correction coefficient Cw for warm-up increase based on the water temperature sensor 25.

The signal from the air-fuel ratio sensor 13 is amplified, and the output signal is compared with the reference value Vr by a comparator to determine a feedback correction coefficient Cfb based on PI control.
Furthermore, the learning correction coefficient Cstdy is determined by averaging the peak values at the time of signal inversion in the PI control. Further, the acceleration state and deceleration state are detected from the rate of change of the intake air amount signal Tb or the throttle speed of the throttle opening Ta, and an acceleration increase correction coefficient Cacc and a deceleration increase correction coefficient Cdec are determined.
On the other hand, based on the detection of the starting condition from the crank angle signal, a post-starting increase correction coefficient Cs is determined based on the water temperature signal. In addition, the return reduction correction signal Crec is obtained, and the basic injection pulse is corrected using the various correction signals described above, and an invalid injection time Tv based on the battery voltage is calculated, and the injection pulse is similarly corrected to perform the final fuel injection. It calculates pulses and outputs them to the injector 3. Note that the injection timing is set by a separate control system.

The operation of the controller 20 will be explained based on the flowchart of FIG. 4. This flowchart shows only the main part of the routine for calculating the fuel injection pulse.

After the start, the controller 20 moves to step S1.
The system is initialized in step S2, and the output signals of the various sensors are read in order to detect the operating state of the engine 1 in step S2. Then, in step S3, the basic injection time T ₀ =Tp×Ck is calculated based on the intake air amount signal Tp. This basic injection time T ₀ is used to determine the injection amount when controlling at the stoichiometric air-fuel ratio (A/F=14.7), and the coefficient Ck is a matching coefficient between the intake air amount sensor 17 and the injector 3. Further, the intake air amount signal Tp uses a value subjected to intake air temperature correction by the intake air temperature sensor 24.

Next, in step S4, a basic target air-fuel ratio AF is determined according to the operating condition. The basic characteristics of this basic target air-fuel ratio AF are that, as shown in Figure 5, in the relationship between engine speed Ne and load (intake pressure Pb), the high load region is the rich region, and the low and medium load region is the rich region. is set in the lean region. Near the boundary line a between the rich region and the lean region, the air-fuel ratio changes rapidly due to a slight change in load, but in order to transition between the two regions accurately and without shock, it is necessary to In order to precisely control the air-fuel ratio in response to changes in operating conditions, a basic target air-fuel ratio AF is determined using the first map _M1 and the second map _M2 .

An example of the first map _M1 is shown in FIG. 6, where the first air-fuel ratio AF1 is set according to the engine speed Ne and the intake air amount signal Tp, and the numbers in each area are the values of the air-fuel ratio. It shows. On the other hand, as shown in Fig. 7, the second map _M2 is based on the engine speed Ne.
The second air-fuel ratio AF is set according to the throttle opening Ta and
2 is set, and the numbers in each area indicate the value of the corrected air-fuel ratio. Then, the target air-fuel ratio AF is determined by the first map _M1 determined according to the operating condition.
The second map _M2 is calculated from the value of the air-fuel ratio AF1.
By subtracting the value of air-fuel ratio AF2, i.e., AF=
It is determined by AF1−AF2.

For example, if the engine operating status is the engine speed
In the relationship between Ne and the intake air amount signal Tp, the first
When the value of the air-fuel ratio AF1 is 22, when the engine speed Ne and the throttle opening Ta are 60%, the second air-fuel ratio AF2 is 8, and the basic target air-fuel ratio AF is:
AF=22-8=14. Then, when the throttle opening degree Ta is in the range of 40 to 20%, the second air-fuel ratio
AF2 is finely set from 8 to 2, and the target air-fuel ratio AF
gradually increases to obtain the target air-fuel ratio for transition to the lean region.

Next, in step S5, a water temperature correction coefficient Cw is calculated based on the detection signal of the water temperature sensor 25, and in step S6, the basic target air-fuel ratio obtained in step S4 is calculated using this water temperature correction coefficient Cw.
Correct AF and calculate corrected target air-fuel ratio AFD.
The above water temperature correction coefficient Cw is a value of 1 or less, and the 8th
As shown in the characteristics in the figure, the value is set to be smaller as the water temperature decreases, and the correction target air-fuel ratio AFD is corrected to be richer. When the water temperature rises to about 45° C. or higher, the correction coefficient Cw becomes approximately 1 and becomes approximately the value of the basic target air-fuel ratio AF.

Subsequently, in step S7, it is determined whether the operating state satisfies the feedback condition. This feedback condition is determined based on whether the corrected target air-fuel ratio AFD is 14.7 or higher.
At times, feedback control is performed, and when NO is in the rich region, open control is performed.

When performing feedback control, a reference value Vr, that is, a slice level, for comparison between the output signal Vs of the air-fuel ratio sensor 13 and the corrected target air-fuel ratio AFD is determined in step S8. As shown in FIG. 9, this reference value Vr is determined by determining the voltage value corresponding to the corrected target air-fuel ratio AFD based on a characteristic such that the larger the target air-fuel ratio AFD, the larger the reference voltage value Vr. The reference value Vr and the output signal Vs of the air-fuel ratio sensor 13 are compared, and a feedback correction coefficient Cfb is calculated in step S9, and a learning correction coefficient Cstdy is calculated in step S10.

The feedback correction coefficient Cfb is determined by Cfb=P+∫△Idθ in order to perform PI control. This control compares the air-fuel ratio sensor output Vs with the reference value Vr, and if the sensor output Vs is a large value, the detected air-fuel ratio is leaner than the target air-fuel ratio AFD, so the supplied air-fuel ratio is shifted to the rich side. Conversely, if the sensor output Vs is a small value, the detected air-fuel ratio is richer than the target air-fuel ratio AFD, so the feedback correction coefficient Cfb is calculated to shift the supplied air-fuel ratio to the lean side. . Said P
The value is a value that is uniformly added or subtracted when the magnitude relationship between the output Vs of the air-fuel ratio sensor 13 and the reference value Vr is reversed, and the ΔI value is a value that is added or subtracted at every predetermined crank angle. Above P value and △
The I value is set as follows with respect to the throttle opening so that the feedback correction coefficient Cfb, that is, the supplied air-fuel ratio changes slowly in the idle state. Note that the ΔI value is a value per 360° crank angle.

Throttle Fully open Other than fully closed P value 0.025 0.047 △I value 0.0021 0.0041 In addition, the calculation of the learning correction coefficient Cstdy is based on the feedback correction coefficient Cfb based on the PI control based on the comparison between the air-fuel ratio sensor output Vs and the reference value Vr. Each feedback correction coefficient when the increase/decrease state of correction coefficient Cfb is reversed
It is obtained by integrating Cfb and calculating the average value when a predetermined number of integrations is reached. However, this calculated latest learning correction coefficient
If Cstdy′ is used as is to correct the basic injection time T ₀ , a large change in the air-fuel ratio will occur if erroneous learning occurs. Therefore, the value actually used as the learning correction coefficient It is calculated by adding and updating the value of 1/4 of the learning correction coefficient Cstdy'.

In step S11, in addition to the feedback correction coefficient Cfb and learning correction coefficient Cstdy, various correction coefficients such as acceleration correction coefficient Cacc, deceleration correction coefficient Cdec, post-start correction coefficient Cs, and return correction coefficient are used.
Ineffective injection time based on Crec and battery voltage
This is to calculate Tv respectively.

Based on the above various correction coefficients, step S12
The final injection pulse width Ti is determined by
When the injection timing is set to a predetermined injection timing based on the final injection pulse width Ti, fuel injection is performed for a period of time equal to the injection pulse width Ti based on the YES determination in step S13.

Final injection pulse width in step S12 above
Ti is calculated by multiplying the basic injection time T ₀ obtained in step S3 by the ratio of the stoichiometric air-fuel ratio (14.7) and the corrected target air-fuel ratio AFD obtained in step S6 to correspond to the corrected target air-fuel ratio AFD. Find the injection time, and then set the feedback correction coefficient Cfb to 1.
The corrected injection time is obtained by adding and subtracting various correction coefficients such as the learning correction coefficient Cstdy and the like and multiplied by the injection time, and the invalid injection time Tv is added to this to obtain the final injection time, that is, the pulse width Ti.

According to the above embodiment, the air-fuel ratio can be accurately feedback-controlled in a region leaner than the stoichiometric air-fuel ratio without causing misfire, and good drivability can be obtained and fuel efficiency can be improved.

In the above embodiment, various corrections are made in addition to feedback correction before and after calculating the final injection pulse, but it is possible to adopt or reject these corrections as appropriate.

[Brief explanation of drawings]

Fig. 1 is a block diagram to clarify the structure of the present invention, Fig. 2 is an overall block diagram of an engine equipped with an air-fuel ratio control device, Fig. 3 is a control block diagram of the controller, and Fig. 4 is the operation of the controller. Fig. 5 is a characteristic diagram showing an example of setting the lean region and rich region according to the operating state, and Fig. 6 is a flowchart diagram for explaining the target air-fuel ratio according to the operating state. A map diagram showing a setting example, FIG. 7 is a map diagram showing a setting example of the second map for determining the target air-fuel ratio according to the operating state, and FIG. 8 is a characteristic diagram showing an example of the characteristics of the water temperature correction coefficient with respect to water temperature. FIG. 9 is a characteristic diagram showing an example of the characteristics of the comparison reference value with respect to the target air-fuel ratio. DESCRIPTION OF SYMBOLS 1...Engine, 2...Intake passage, 3...Injector, 4...Air-fuel ratio adjustment means, 5...Final injection amount calculation means, 6...Basic injection amount calculation means, 7...Target air-fuel ratio calculation means, 8...Feedback coefficient calculation means ,9...
Intake air amount detection means, 10...operating state detection means,
11...Reference value calculation means, 13...Air-fuel ratio sensor, 1
7...Intake air amount sensor, 20...Controller.

Claims (1)

[Claims] 1 An air-fuel ratio control device for an engine that calculates a fuel injection amount according to the operating state of the engine and corrects the fuel injection amount according to a detection signal of an air-fuel ratio sensor, which A basic injection amount calculation means that calculates the basic injection amount corresponding to the air-fuel ratio based on a functional formula, and a target that calculates the target air-fuel ratio corresponding to the operating condition from a map storing a target air-fuel ratio determined in advance according to the operating condition. an air-fuel ratio calculation means; a reference value calculation means for calculating a reference value for comparison of the detection signal of the air-fuel ratio sensor using the target air-fuel ratio;
a feedback coefficient calculation means for comparing the detection signal of the air-fuel ratio sensor with the comparison reference value and calculating a feedback coefficient according to the deviation between the two; and a ratio of the theoretical air-fuel ratio to the target air-fuel ratio calculated by the target air-fuel ratio calculation means. and final injection amount calculation means for correcting the basic injection amount using the feedback coefficient and the feedback coefficient to obtain a final injection amount.