JP2986843B2 - Air-fuel ratio control device for internal combustion engine - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air-fuel ratio control apparatus for an internal combustion engine, and more particularly, to predicting a physical quantity related to an intake air quantity taken into an engine combustion chamber and performing learning control on the air quantity. The present invention relates to an air-fuel ratio control device for an internal combustion engine that controls a fuel ratio.

[Problems to be solved by conventional technology and invention]

As an air-fuel ratio learning control device for an internal combustion engine, Japanese Patent Application Laid-Open
There is an apparatus described in Japanese Patent No. 5239. This device corrects the fuel injection amount at the time of acceleration / deceleration using a fuel injection amount increase / decrease map determined according to the change rate of the intake pressure or the intake air amount and the engine speed. Further, the value of the increase / decrease map is corrected by learning according to the maximum deviation amount of the air-fuel ratio from the reference value during acceleration / deceleration.

In the above-described conventional technology, the fuel injection amount is corrected in accordance with the change rate of the intake pressure or the intake air amount. Complicated correction using the rate of change or the like is required. Therefore, there is a problem that the fuel injection amount cannot be properly corrected with respect to the fuel delay that shows a complicated behavior in the above-described conventional technology. In addition, the correction of the increase / decrease map is performed only using the maximum deviation amount of the air-fuel ratio, and is not corrected using the momentary value of the air-fuel ratio deviation amount.
There is a problem that it is not possible to correct a difference in air-fuel ratio due to a machine-to-machine difference (machine difference) of the internal combustion engine or a change with time. That is, the deviation amount of the air-fuel ratio is caused by a delay in suctioning the amount of intake air into the cylinder due to the intake system volume, a fuel sticking to the inner wall surface of the intake manifold, a fuel delay due to a liquid level flow, and the like. The instantaneous value of the deviation amount of the air-fuel ratio and the waveform pattern of the deviation include information on how various delays contribute. However, if the maximum deviation amount is used as described above, this information is not effectively used, and the air-fuel ratio is not accurately controlled.

The present invention has been made in order to solve the above-described problems, and performs a fuel injection amount correction for a fuel delay showing a complicated behavior by using a dynamic correction element in consideration of a fuel behavior, so that a transient during acceleration or deceleration can be performed. The air-fuel ratio at the time can be maintained at an appropriate value, and the correction factor is corrected using the momentary value of the air-fuel ratio deviation amount, thereby preventing the air-fuel ratio control deviation due to engine difference between the engines and changes over time. It is an object of the present invention to provide an air-fuel ratio control device for an internal combustion engine that can perform the above.

[Means for solving the problem]

In order to achieve the above object, the present invention provides a throttle opening detecting means for detecting an opening of a throttle valve attached to an intake pipe so as to adjust an amount of intake air to be taken into an engine, and a suction valve for detecting the amount of intake air in an engine combustion chamber. Physical quantity detecting means for detecting a physical quantity related to the intake air quantity to be detected, air-fuel ratio detecting means for detecting an exhaust air-fuel ratio from exhaust gas of the engine, and predicting a future physical quantity based on the opening degree of the throttle valve and the physical quantity. Predicting means, a basic injection amount calculating means for calculating a basic fuel injection amount based on a future physical quantity predicted by the predicting means, and a plurality of correction amounts corresponding to a fuel delay for correcting the basic fuel injection amount. A correction amount calculating means for calculating, a correction amount in the past that has affected the exhaust air-fuel ratio at the detected current time (hereinafter, simply referred to as a past correction amount), and the exhaust air-fuel ratio and a target air-fuel ratio. Weighting coefficient learning means for correcting a weight to be applied to each of the plurality of correction amounts in accordance with a difference between the weights, and a weighted average of the plurality of correction amounts based on the plurality of correction amounts and the weights An average value calculating means, and an air-fuel ratio control means for obtaining a fuel injection amount based on the basic fuel injection amount and the weighted average value and controlling an air-fuel ratio based on the fuel injection amount.

[Action]

The prediction means of the present invention predicts a future physical quantity related to the amount of intake air to be taken into the engine combustion chamber based on the physical quantity related to the opening of the throttle valve and the amount of intake air.
As the physical quantity related to the amount of intake air taken into the engine combustion chamber, the pressure (intake pressure) of intake air in the intake pipe between the throttle valve and the internal combustion engine or the amount of intake air passing upstream of the throttle valve is used. is there. Further, in the case of a multi-cylinder internal combustion engine, there are a case where fuel is injected once or a plurality of times simultaneously for one revolution of the engine in all cylinders and a case where fuel is injected independently for each cylinder. In the case of simultaneous injection of all cylinders, not all of the injected fuel is taken into the specific cylinder, but into other cylinders, so that future time points to be predicted are preferably determined based on experiments. . On the other hand, in the case of multi-cylinder independent injection, the injected fuel is sucked only into the specific cylinder,
The future time point to be predicted is preferably a time point when the amount of intake air drawn into the specific cylinder is determined, that is, a time close to the intake valve closing time during the intake valve opening period of the specific cylinder. The basic injection amount calculation means calculates the basic fuel injection amount based on the future physical quantity predicted by the prediction means. The correction amount calculating means calculates a plurality of correction amounts corresponding to a fuel delay for correcting the basic fuel injection amount. The weight coefficient learning means corrects and determines the weight to be applied to each of the plurality of correction amounts according to the past correction amount and the momentary difference between the exhaust air-fuel ratio and the target air-fuel ratio. The weighted average value calculation means calculates a weighted average value of the plurality of correction amounts by assigning a weight determined by the weight coefficient learning means to each of the plurality of correction amounts. The air-fuel ratio control means determines the fuel injection amount based on the basic fuel injection amount and the weighted average value, and controls the air-fuel ratio based on the fuel injection amount.
As described above, since the basic fuel injection amount is corrected by the weighted average value of the plurality of correction amounts, a compensation component corresponding to the fuel delay of a complicated behavior is added to the basic fuel injection amount, and the basic fuel injection amount is injected into the intake pipe. It is possible to correct a transport delay until the fuel is sucked into the combustion chamber, a delay due to the amount of adhesion to the inner wall of the intake pipe, and the like. In addition, since the weight is corrected according to the past correction amount every moment and the difference between the exhaust air-fuel ratio and the target air-fuel ratio, a plurality of correction amounts having various phase lead components, the exhaust air-fuel ratio, and the target air-fuel ratio are corrected. By taking a temporal correspondence with the difference between the internal combustion engine and the engine, it is possible to form a correction pattern that matches the fuel delay that has changed due to a change in the engine state by correcting the weight coefficient. Correction for changes in the state of the engine can be made. Further, by determining a correction amount for correcting the basic fuel injection amount by a weighted average, the correction amount is determined by an interpolation value of a plurality of correction amounts obtained by the correction means, and how the weight is corrected Even if the correction is performed, the correction amount is always set within a certain range, so that the correction system does not diverge.

〔The invention's effect〕

As described above, according to the present invention, the correction of the fuel injection amount with respect to the fuel delay indicating a complicated behavior is performed by a dynamic correction element in consideration of the behavior of the fuel, and the air-fuel ratio at the time of transition is set to an appropriate value. In addition to being able to hold, it is also corrected using the past correction amount consisting of a plurality of correction elements and the instantaneous value of the deviation amount of the air-fuel ratio. Can be obtained.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In this embodiment, the present invention is applied to a four-cylinder internal combustion engine.
The air-fuel ratio is controlled by injecting fuel independently for each cylinder. In this embodiment, the intake pressure is used as a physical quantity related to the amount of intake air taken into the engine combustion chamber. As shown in FIG. 1, an intake pipe having a throttle body 10 and an intake manifold 20 and an exhaust pipe 34 having an exhaust manifold 32 are connected to the four-cylinder internal combustion engine 26. The throttle body 10 is provided with a throttle valve 12 for adjusting the amount of intake air to be taken into the combustion chamber of the engine 26. This throttle valve
A throttle opening sensor 14 detects the opening of the throttle valve 12 and outputs a signal proportional to the throttle valve opening.
Is installed. Intake manifold 20
A semiconductor-type intake pressure sensor 16 for detecting the absolute pressure (intake pressure) of the intake air in the intake manifold 20 and an intake temperature sensor 18 for detecting the temperature of the intake air are provided. A fuel injection valve 22 is attached to each branch pipe 24 of the intake manifold 20 so as to correspond to each cylinder. At the downstream side of the exhaust manifold of the exhaust pipe 34, an air-fuel ratio sensor 36 composed of an O ₂ sensor or the like for detecting an exhaust air-fuel ratio is attached. Further, the engine 26 is provided with a cooling water temperature sensor 28 for detecting an engine cooling water temperature and a cam position sensor 30 for detecting rotation of a camshaft and outputting an engine rotation speed signal.

Each of the fuel injection valves 22 is connected to a drive circuit 44.
The drive circuit 44 is connected to a microcomputer 54 that outputs a fuel injection amount signal. The microcomputer 54 is connected to the throttle opening sensor 14, the intake pressure sensor 16, the intake temperature sensor 18, the cooling water temperature sensor 28, the cam position sensor 30, and the air-fuel ratio sensor 36.

The microcomputer 54 calculates a fuel injection amount based on signals input from the throttle opening sensor 14, the intake pressure sensor 16, the intake temperature sensor 18, and the like, and outputs a fuel injection amount signal. , A CPU, and a bus connecting them.

The microcomputer 54 will be described with functional blocks divided by function. The intake pressure predicting means 38 calculates a predicted value of the intake pressure of each cylinder based on the following equation (1) using the engine speed Ne, the intake pressure Ps, and the throttle opening θ. It should be noted that the intake air temperature THA may be further predicted. The basic injection amount calculating means 40 calculates the following value based on the predicted value of the intake pressure calculated by the intake pressure predicting means 38, the engine speed Ne, the intake air temperature THA, the cooling water temperature THW, and the target air-fuel ratio A / F ₀ ( 3) Set the exhaust air-fuel ratio A / F to the target air-fuel ratio A / F according to the formula
A basic fuel injection amount for setting to ₀ is calculated for each cylinder.
The correction amount calculating means 42 calculates a plurality of correction amounts for correcting the basic fuel injection amount for each cylinder based on the basic fuel injection amount. Learning means 48 calculates a weighting based on the difference between the target air-fuel ratio A / F ₀ calculated in the past correction amount and subtracting means 50 and the exhaust air-fuel ratio A / F. The weighted average value calculation means 52 calculates a weighted average value of a plurality of correction amounts from the weight calculated by the learning means 48 and the plurality of correction amounts calculated by the correction amount calculation means 42. The adding means 46 obtains the fuel injection amount by adding the basic fuel injection amount and the weighted average value, and inputs a fuel injection amount signal corresponding to the fuel injection amount to the drive circuit 44. The drive circuit 44 controls the fuel injection valve 22 independently for each cylinder based on the fuel injection amount signal.

Next, a calculation routine for calculating the fuel injection amount by the microcomputer 54 will be described in detail. FIG. 2 shows a fuel injection calculation routine, which is executed every 180 ° CA (crank angle) at the calculation timing shown in FIG. In step 100, the engine speed Ne, intake pressure Ps, throttle opening θ, intake temperature TH
A, the cooling water temperature THW, the exhaust air-fuel ratio A / F, takes in the target air-fuel ratio A / F _0, the engine speed Ne at step 111, determines a region to which the current operating condition is present by the intake pressure Ps. In the next step 102, it is determined whether or not the current operation state belongs to the overlap region (the portion indicated by oblique lines) of the prediction region shown in FIG. The prediction area is the rotation speed Ne and the intake pressure
The region is divided into a plurality of regions by Ps, and the boundary of each region is overlapped to provide an overlap region. If it is determined in step 102 that the current operation state is not the overlap region, the flow proceeds to step 104 at the time (kw + 2) in the region S to which the current operating state belongs, that is, at a time close to the intake valve closing time during the intake valve opening period. Of the intake pressure of the Wth cylinder is calculated according to the following equation (1).

Here, w indicates a cylinder, and when w = 1, the first cylinder # 1,
Third cylinder # 3 when w = 2, fourth cylinder # when w = 3
4, w = 2 indicates the second cylinder # 2. S is the third
This is an integer indicating the number of the area in the figure.

s (kw + 2) = Ps (kw + a 1 (Ps (kw) -Ps (kw-2)) + b 1 (θ (kw) -θ (kw-2)) + b 2 (θ (kw-1) -θ (kw _{-3)) + c 1 (Ne} (kw) -Ne (kw-1)) + c 2 (Ne (kw-1) -Ne (kw-3)) ... (1) Here, (1) the intake air temperature in the formula THA In step 108, the predicted value s (kw + 2) of the region S is set as the predicted value for calculating the basic fuel injection amount qw of the Wth cylinder, and the process proceeds to step 116.

If it is determined in step 102 that the area is an overlap area, in step 110, the time (kw +) of the areas i and j (i and j indicate the area number) belonging to the overlap area.
The predicted values _i (kw + 2) and _j (kw + 2) at the time point 2) are calculated based on the above equation (1). In step 112, weights corresponding to the degree to which the current operating state belongs to the region i and the region j, that is, the fitness levels w _i and w _j are calculated. The weights w _i and w _j are w ₂ and w ₃ when the area 2 and the area 3 overlap as shown in FIG. Then, in step 114, a predicted value for calculating the basic fuel injection amount qw of the Wth cylinder is calculated by the weighted average shown in the following equation (2).

However, w _i and w _j are normalized as 0 ≦ w _i , w _j ≦ 1.

In the next step 116, the predicted value at the time (kw + 2),
Engine speed Ne at current time kw, intake air temperature THA, cooling water temperature TH
W, and calculates the basic fuel injection amount qw of the W cylinder corresponding to the fuel late based on the target air-fuel ratio A / F _0.

qw = f (, Ne, THA, THW, A / F ₀ ) (3) where f represents a function.

 In the next step 118, the basic fuel injection amount qw of the Wth cylinder
Calculate multiple correction amounts corresponding to fuel delay based on
You. That is, as shown in FIG.
Operating state according to the engine speed Ne and the intake pressure Ps
Is determined, and the same as FIG.
Correction amount determined according to intake pressure and engine speed
The current operation state belongs to the overlap area of the calculation area.
Judge whether or not they belong to
In step 132, the duplication of the region r to which the current operating state belongs
Number correction amount Rr₁(Kw), Rr_Two(Kw) ... is calculated. S
In step 135, the correction amount Rr of the region r₁(Kw), Rr_Two(K
w), ... are the correction amount R for the basic fuel injection amount correction₁(K
w), Rr_Two(Kw), ... And the next step
The weight γ of the correction amount at the current time kw at 136_r  (Kw) (
= 1, 2, 3,... M), and in step 137
A weighted average value Rw of a plurality of correction amounts is calculated according to the following equation (4).
Calculate.

On the other hand, when it is determined in step 130 that the area is an overlap area, in step 138, a plurality of correction amounts R _i1 (kw) and R _{i2 of the} areas i and j belonging to the overlap area
_{(Kw), ··· R j1 (} kw), R j2 (kw), calculates the ..., degree belonging to the area i, area j in step 140, i.e., calculates the goodness of fit w _i, w _j .

In the next step 141, the corner area i, j at the current time kw
Γ _i1 (kw), γ _i2 (kw) ...,
Import γ _j1 (kw), γ _j2 (kw) ... and step 14
The weighted average value of a plurality of correction amounts is calculated according to the following equation (5) in 2, Riw = (R _i1 (kw) · γ _i1 (kw) + R _i2 (kw) · γ _i2 (kw) + R _i3 (kw ) ・ Γ _i3 (kw) +…) ÷ (γ _i1 (kw) + γ _i2 (kw) + γ _i3 (kw) + ...) Rjw = (R _j1 (kw) ・ γ _j1 (kw) + R _j2 (kw) ・γ _j2 (kw) + R _j3 (kw) ・ γ _j3 (kw) +…) ÷ (γ _j1 (kw) + γ _j2 (kw) + γ _j3 (kw) + ...) (5) Then, in the next step 144, region i, fitness w _i at j, the correction amount Rw than w _j, is calculated by the following equation.

In the next step 124, the basic fuel injection amount qw of the Wth cylinder
The fuel injection amount of the W-th cylinder is calculated by adding the correction amount Rw to the fuel injection amount, and fuel is injected from the fuel injection valve 22 corresponding to the W-th cylinder at a predetermined fuel injection timing.

FIG. 6 shows a learning routine executed every 180 ° CA at the learning timing shown in FIG. Steps
In 150, the difference δ (kw) between the target air-fuel ratio A / F ₀ and the exhaust air-fuel ratio A / F is calculated according to the following equation, and the region r calculated in the previous case without overlap or the region r Weight of region i or region j in the case
_{(R, i, j)} (kw-1) is taken. Where Γ is the weight γ
_{(R, i, j)} (kw) ( _{(r, i, j)} indicates any one of r, i, and j, and = 1, 2,..., M) as a vector representation It is. Where 0 ≦ γ _{(r, i, j)}
(Kw) ≦ 1.0 and normalized. And step 1
In 52, the current time (time kw) according to the following equation (7)
The weight Γ _{(r, i, j)} (kw) is calculated.

Γ _{(r, i, j)} (kw) = Γ _{(r, i, j)} (kw-1) + μ · δ (kw) · Y
_{(R, i, j)} (k′w) (7) Here, δ (kw) = A / F ₀ −A / F.

However, the degree to which the current operating state belongs to each area is 1.0
If it is less than δ, the amount obtained by multiplying the degree of the area to which it belongs by δ (kw) is δ (kw).

Y _{(r, i, j)} (k'w) = [y _{(r, i, j) 1} (k '
w), y _{(r, i, j) 2} (k'w), ... y _{(r, i, j) m}
(K′w)] ^T (T is transposed), and y _{(r, i, j)} (k′w) (= 1, 2, 3,...)
m) is each correction amount at time k′w that affected the air-fuel ratio measured at time kw.

Further, μ is μ = constant, or Or Then, in step 154, the weight of each area Γ
_{(R, i, j)} (kw) is stored.

By using the expression (8) or the expression (9), the convergence of the control can be improved.

FIGS. 8, 9, and 10 functionally express details of steps for calculating a plurality of correction amounts. Figure 8 shows a example of obtaining a plurality of correction amount by multiplying the coefficient α1~α4 defining the first-order difference amount delta and the second difference amount delta ² to the correction amount of the magnitude of the basic fuel injection amount. Incidentally, delta for the first W cylinders, delta ² is given by the following equation.

Figure 9 is a lag filter (q ^-1 represents the time delay operator, beta _1, beta ₂ represents a constant) first-order difference delta of the basic fuel injection amount passed through, the second-order difference delta ^2, coefficient α1 defining the correction amount, [alpha] 2, .alpha.3, in which multiplied by ..., and the first-order difference delta and the value obtained by mixing the second-order difference delta ² which has passed through the delay filter and a plurality of correction amount. FIG. 10 shows a case in which the amount of fuel sucked into the combustion chamber is physically analyzed, and a plurality of correction amounts are calculated based on the analysis. This correction amount includes a cold correction amount, a warm-up correction amount, a low load correction amount, a medium load correction amount,
There is a high load correction amount and the like.

FIG. 11 shows the change in the air-fuel ratio of the above embodiment in comparison with the conventional example.

As described above, according to the present embodiment, the intake pressure in the intake stroke (the intake pressure when the intake valve is closed) is calculated at the time when the fuel injection amount is calculated at the present time and the past intake pressure,
Since the prediction is made based on the rotation speed, the throttle opening, and the like, the conventional intake pressure can be accurately predicted even in a transient state in which the throttle opening and the rotation speed are changing.

Since the prediction region is divided into a plurality of operation regions and prepared, and the regions are overlapped, the prediction value can be obtained in a simple linear form within each region. The predicted value can be obtained by the sum of the linear forms. Therefore, it is not necessary to use another predictive operation expression in the overlap region, whereby the operation can be simplified and the operation expression can be minimized.

Since the correction amount of the basic fuel injection amount correction amount is obtained from the weighted average value of the plurality of correction amounts, the correction can be performed with a correction amount within a predetermined range. Therefore, the correction model corresponding to the engine operating state is obtained by multiplying the analysis model based on the analysis of the fuel behavior (FIG. 10), the first-order difference and the second-order difference of the basic fuel injection amount by a coefficient for determining the magnitude of the correction amount. Model (Fig. 8)
Alternatively, complex behavior can be obtained by multiplying a value obtained by delaying the first-order difference and the second-order difference by a delay filter by a coefficient that determines the magnitude of the correction amount and creating a combined correction model (FIG. 9). The dynamic correction for compensating the dynamics of the fuel delay shown can be performed, and the deviation of the air-fuel ratio due to the fuel suction delay can be corrected.

To sequentially correct the weight using the error between the measured exhaust air-fuel ratio and the target air-fuel ratio, the weight coefficient of a correction model that outputs a correction amount that changes over time based on the momentary information of the error is calculated. This corresponds to selection, and an optimal combination of weights according to the current engine operating state is obtained. Therefore,
Fuel correction according to the operating state can be performed, and the air-fuel ratio deviation can be corrected. Further, by dividing the operating region into a plurality of regions and learning the weight of the correction model for each of the divided regions, the correction amount for each of the regions having different characteristics is obtained. In addition, the overlap between the regions is performed, and the correction over the regions is smoothly performed by obtaining the linear sum in the overlap region. In addition, the number of regions is reduced by not providing a model of the overlap region, and the amount of calculation is reduced. can do.

In the above description, the region is divided according to the intake pressure and the engine speed, but may be divided according to acceleration, deceleration, and a steady state. In addition, although the explanation of each cylinder independent injection has been described,
It can be applied to all cylinder simultaneous injection. In this case, the intake pressure at the time determined by an experiment may be predicted. Furthermore, in the present embodiment, an example in which the present invention is applied to an internal combustion engine in which the rotational speed changes rapidly is shown, but the present invention is not limited to this, and may be applied to an internal combustion engine in which the rotational speed is almost constant. . In this case, it is needless to say that the detection of the engine speed becomes unnecessary.

[Brief description of the drawings]

FIG. 1 is a block diagram showing functional blocks of an air-fuel ratio control device according to an embodiment of the present invention, FIG. 2 is a flowchart showing a fuel injection amount calculation routine, FIG. 3 is a diagram for explaining a prediction region, and FIG. FIG. 4 is a diagram for explaining weights for obtaining a predicted value of the overlap area, FIG. 5 is a flowchart showing details of the correction amount calculating step in FIG. 2, and FIG. 6 shows a weight learning routine. FIG. 7 is a timing chart showing a fuel injection amount calculation timing and a learning timing, and FIG.
FIGS. 9 and 10 are block diagrams functionally showing a correction amount calculating step, and FIG. 11 is a diagram showing a comparison between a change in the air-fuel ratio of the present embodiment and a change in the conventional air-fuel ratio. is there. 14 ... throttle opening sensor, 16 ... intake pressure sensor, 18 ... intake temperature sensor, 22 ... fuel injection valve, 28 ... cooling water temperature sensor, 30 ... cam position sensor, 36 ... air-fuel ratio sensor, 54 ... A microcomputer.

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-1-267334 (JP, A) JP-A-3-1644547 (JP, A) JP-A-62-153534 (JP, A) JP-A-1- 315644 (JP, A) JP-A-2-104932 (JP, A) JP-A-63-138127 (JP, A) JP-B-58-54253 (JP, B2) (58) Fields investigated (Int. Cl. ⁶ , DB name) F02D 41/00-41/40

Claims (1)

(57) [Claims] A throttle opening detecting means for detecting an opening of a throttle valve attached to an intake pipe so as to adjust an amount of intake air taken into the engine; A physical quantity detecting means for detecting a related physical quantity; an air-fuel ratio detecting means for detecting an exhaust air-fuel ratio from exhaust gas of the engine; a predicting means for predicting a future physical quantity based on the opening degree of the throttle valve and the physical quantity; Basic fuel amount calculation means for calculating a basic fuel injection amount based on a future physical quantity predicted by the prediction means; and correction amount calculation means for calculating a plurality of correction amounts corresponding to a fuel delay for correcting the basic fuel injection amount To apply to each of the plurality of correction amounts according to the past correction amount that affected the exhaust air-fuel ratio at the detected current time and the difference between the exhaust air-fuel ratio and the target air-fuel ratio. Weight coefficient learning means for correcting the weight, weighted average value calculation means for calculating a weighted average value of the plurality of correction amounts by the plurality of correction amounts and the weight, the basic fuel injection amount and the weighted average value An air-fuel ratio control device for an internal combustion engine, comprising: an air-fuel ratio control unit that determines a fuel injection amount by using the fuel injection amount and controls an air-fuel ratio based on the fuel injection amount.