JPH07238848A - Fuel injection control device equipped with NOx catalyst - Google Patents

Abstract

(57) [Abstract] [Purpose] The object of the present invention is to detect and correct variations in the combustion state of an engine, and to set the combustion state to a desired state in a form that matches operating targets such as fuel efficiency priority and exhaust emission priority. It is to be. [Structure] Means for quantitatively detecting the combustion state of the engine, means for calculating the parameters of the combustion state under operating conditions, means for comparing the target value with the parameters for the combustion state under each operating condition, and the comparison results It consists of two or more means for changing the combustion state in the engine. [Effect] According to the present invention, it is possible to detect and correct variations in the combustion state of the engine, and to set the combustion state to a desired state in a form that matches the operation target such as fuel efficiency priority and exhaust emission priority.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel injection system for an internal combustion engine, and more particularly to an internal combustion engine capable of suppressing exhaust emission NOx to a minimum without sacrificing the combustion condition and the drivability in a practical operating range. Fuel injection device.

[0002]

2. Description of the Related Art In the conventional invention, for example, Japanese Patent Laid-Open No. 59-12 is used.
As described in Japanese Patent No. 2763, the engine rotation angular velocity of each cylinder in the explosion stroke is detected, and when this angular velocity is smaller than the angular velocity of other cylinders, correction for combustion improvement is performed. Therefore, no consideration has been given to the minimization of exhaust emission NOx.

[0003]

In the above-mentioned prior art, the parameters of the combustion state are simply compared with those of other cylinders. Therefore, the combustion states of the other cylinders become a disturbance for comparison, an accurate determination cannot be made, and since only the small angular velocity is detected, there is a drawback that it cannot be dealt with when the angular velocity is higher than the others. Further, since there is only one parameter for determining the combustion state, it is impossible to introduce other factors for detecting the limit of drivability, for example.

[0004]

[Means for Solving the Problems] The above-mentioned problems are used in the determination of the limit of drivability at the minimum fuel consumption rate and the determination of the limit of engine stability that minimizes the NOx emission amount by using the parameter for detecting the combustion state. You can solve it by making it possible. That is, it is necessary to pay attention to the fact that these two discriminant values are different on the engine.

[0005]

The two different combustion states are determined by comparing the parameter values of the combustion state with the discriminant value specific to the determination target,
Correct the supplied fuel amount. As a result, the correction value is the discriminant value 1
And the case of the discriminant value 2 are different.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A fuel injection control device for an internal combustion engine according to the present invention will be described in detail below with reference to the illustrated embodiments.

FIG. 1 shows an example of an engine system applied to the present invention. In the figure, the air to be taken in by the engine is taken in from an inlet portion 2 of an air cleaner 1 and a throttle valve for controlling the intake flow rate is housed. Throttle valve body 5
Pass through and enter collector 6. Then, the intake air is distributed to each intake pipe 8 connected to each cylinder of the engine 7 and guided into the cylinder.

On the other hand, fuel such as gasoline is sucked and pressurized by a fuel pump 10 from a fuel tank 9, and then a fuel damper 11, a fuel filter 12, a fuel injection valve (injector) 13, and a fuel pressure regulator 14 are connected to a pipe. Is supplied to the fuel system being operated. Then, this fuel is regulated to a constant pressure by the above fuel pressure regulator 14,
Fuel is injected into the intake pipe 8 from the fuel injection valve 13 provided in the intake pipe 8 of each cylinder.

A signal representing the intake air flow rate is output from the air flow meter 3 and input to the control unit 15.

Further, a throttle sensor 18 for detecting the opening degree of the throttle valve 5 is attached to the throttle valve body 5, and its output is also input to the control unit 15. Next, 16 is a distro (distributor)
A crank angle sensor is built in this distort, and a reference angle signal REF representing the rotational position of the crankshaft and an angle signal POS for detecting the rotational speed (rotation speed) are output. These signals are also output from the control unit. 15 is input.

Reference numeral 20 is an oxygen sensor provided in the exhaust pipe,
In order to detect the actual operating air-fuel ratio,
It detects whether it is a dark state or a thin state, and this output signal is also input to the control unit 15. Further, an NOx reduction catalyst 21 that reduces NOx in the exhaust gas discharged from the engine to render it harmless is attached to the exhaust pipe.

As shown in FIG. 2, the main part of the control unit 15 receives signals from various sensors for detecting the operating state of the MPU, ROM and A / D converter engine as input, and performs a predetermined arithmetic processing. Since various control signals calculated as a result of this calculation are output and a predetermined control signal is supplied to the fuel injection valve 13 and the ignition coil 17, the fuel supply amount control and the ignition timing control are performed. is there.

In such an engine, when the air-fuel ratio of the intake air-fuel mixture is set leaner than the stoichiometric air-fuel ratio, the characteristics shown in FIG. 3 are obtained. If the air-fuel ratio is made lean by keeping the torque and engine speed constant, the pumping loss is reduced because the intake air amount is increased, and the specific heat ratio is improved, so that the fuel consumption rate is improved and the fuel consumption can be improved. on the other hand,
The NOx emission concentration decreases because the combustion temperature decreases when the air-fuel ratio becomes lean, and the combustion stability that can be quantitatively grasped by the torque fluctuation becomes worse because the air-fuel ratio becomes lean and the ignitability of the air-fuel mixture deteriorates. , It gradually deteriorates up to a certain lean, and beyond that, the ignitability deteriorates extremely and the temperature suddenly deteriorates. This torque fluctuation value also has the same meaning as the engine stability shown in the figure. As described above, the combustion stability and the NOx emission concentration in the lean region largely depend on the air-fuel ratio.

Further, there is a limit concentration of NOx which is allowable under the exhaust gas regulation, and this is NO attached to the exhaust pipe.
x The performance of the reduction catalyst will be greatly affected. That is, there are two combustion stability factors, namely, the requirement for drivability and the performance of the NOx reduction catalyst. Therefore, when operating with a lean air-fuel ratio, it is necessary to operate within a range that does not exceed the above two limits, and in order to improve fuel efficiency, it is effective to operate near the limit of combustion stability.
Regarding x, the optimum control value is a little beyond the limit of combustion stability.

Next, the concept of the NOx allowable value when the NOx reduction catalyst is attached, out of these two discriminant values, will be described with reference to FIGS. 4 and 5. FIG. 4 shows the performance of the NOx reduction catalyst. The purification performance depends on the O ₂ concentration, reaches the maximum value at about 4%, and does not change thereafter.
The O ₂ concentration is equivalent to the air-fuel ratio, and 10% has an air-fuel ratio of about 20. Therefore, when the NOx reduction catalyst is used, the degree of freedom in setting the air-fuel ratio can be increased.

Based on this, the setting range of the allowable air-fuel ratio described in FIG. 3 will be described with reference to FIG. First, the allowable NOx value in FIG. 5 is the same value as that in FIG. On the other hand, the exhaust NOx allowable value means the NOx after passing through the NOx reduction catalyst, so that when the same engine is considered, the setting of the air-fuel ratio can be shifted to the lean side by the amount of the purification performance of the NOx reduction catalyst. . As a result, the setting limit of the air-fuel ratio as seen from the NOx emission amount is (A / FL2), which is different from the setting limit (A / FL1) shown in FIG.

Referring to FIG. 6, the relationship with the engine stability at each set limit air-fuel ratio will be described. As shown in the figure (engine stability ΔS) is detected as engine rotation fluctuation. In the figure, the stability that can minimize the exhausted NOx explained in FIG. 5 is ΔS2, and the stability of the torque fluctuation limit shown in FIG. 3 is ΔS2. Since these magnitude relationships do not always show fixed values, they are shown as temporary values in FIG. Next, the intention and embodiment of the present invention will be described with reference to FIG. In the figure, the horizontal axis represents the engine speed and the vertical axis represents the engine load. In this figure, it is (C; NOx region) that has the greatest influence on exhaust emission NOx, and (B; fuel consumption region) and A region have almost no influence. Therefore, it is a very effective means to distinguish the regions in order to achieve the respective performances of the engine and the exhaust purification system efficiently.

In FIG. 7 of the embodiment, ΔS2 in relation to FIG.
It is> ΔS1, but this is not something that sticks out, as explained above.

Next, a method for detecting the engine stability by the rotation fluctuation will be described. Accurate control of the air-fuel ratio supplied to the engine is difficult due to individual variations in the fuel injection valve 13 and the air flow meter 3, deterioration over time, etc., and normally closed loop control is performed. In order to enable the operation in the above operation range, the distorted 16
The crankshaft angle signal or the signal that directly detects the rotation of the crankshaft, such as the rotation detection in the ring gear, measures the rotation of the crankshaft in a sufficiently short time for the intake, compression, explosion, and exhaust strokes. Then, the angular velocity of rotation is measured in minute rotations. The rotational angular velocity in each phase varies depending on the stroke of the engine, and the combustion state of the engine can be known by analyzing this variation. Moreover, the fluctuation of the rotational angular velocity is mainly generated by the explosive force in the explosion stroke of each cylinder, so if the fluctuation of the rotational angular velocity for each explosion stroke of each cylinder is analyzed, the combustion state of the engine for each cylinder will be further detailed. You can also know.

That is, in the case of an actual engine, the combustion state in each combustion often differs depending on the distribution of intake air, the variation of the fuel injection valve 13, the variation of the spark plug, and the like. As a result, the output torque varies, the torque fluctuation increases, and the drivability deteriorates. Moreover, since the operation is performed at a rich air-fuel ratio, the NOx emission concentration is high and the exhaust performance is deteriorated.

Therefore, it is effective to correct the combustion in which the combustion state differs depending on the above-mentioned combustion state parameter in order to prevent the above problems. At this time, in order to quantitatively grasp the combustion with different combustion states and the degree thereof, it is necessary to obtain the difference in the combustion state of each combustion from the average state of the engine, which is the average value of the parameters of the combustion state. ,
It is obtained from the difference from the value of the parameter of the combustion state of each combustion, and the amount of fuel supply is corrected by the magnitude of the difference. That is, when the combustion stability is poor, the correction is performed in the rich direction, and when the combustion stability is good, the correction is performed in the lean direction according to the magnitude of the deviation from the average value. This method absorbs variations in each combustion of the real engine.

FIG. 8 shows an embodiment of the present invention in which the processing of the previous embodiment is represented in a flow chart. At 101, the operating conditions of the engine are taken in, and at 102, the rotational angular velocity required for determining the engine stability is input. In step 103, the target stability parameter ΔS is obtained in advance so that it can be dealt with according to the operating conditions (this step is 108,
It may be the same as 109).

Next, at 104, the operation area is discriminated as described in FIG. 105 if it is determined to be “area A”
And the control ends as it is.

When it is determined that the "region B" of 106 is the fuel consumption priority region, the air-fuel ratio (A / FL1) shown in FIG.
The combustion stability parameter ΔS1 corresponding to is calculated every moment according to the operating conditions of the engine. Next, at 110, the actual combustion stability parameters ΔS and ΔS1 are compared, that is, (Δ
S <ΔS1 + ΔS ′) is calculated, and if this is true, it is determined that the fuel is lean, and at 114,
Enrich the fuel only for a fixed amount. On the other hand, when the determination at 110 is not established, at 112 (ΔS ≧ Δ
S1-ΔS ') is calculated, and if it is not satisfied, the process ends as it is, and if it is satisfied, there is a margin in stability.
At 115, the fuel is also reduced by a fixed amount. In addition, ΔS ′ is a dead zone.

If it is determined to be "area C" of 107, N
This is the Ox priority area, and the air-fuel ratio (A / FL
The combustion stability parameter ΔS2 corresponding to 2) is calculated moment by moment according to the operating conditions of the engine. Next, in 111, the actual combustion stability parameters ΔS and ΔS2 are compared, that is, (ΔS <ΔS2 + ΔS ″) is calculated. If this is true, it is determined that the fuel is lean, and in 114, only a fixed amount is determined. On the other hand, the fuel is enriched.On the other hand, when the determination in 111 is not established, in 113, (ΔS
≧ ΔS21−ΔS ″) is calculated, and if it is not satisfied, the process ends as it is, and if it is satisfied, the fuel is reduced by a fixed amount also at 115, and there is a margin of stability. Note that ΔS ″ is set. It is a dead zone.

The speed of correction of these fuels is determined by the frequency of calculation, but the size is converged if the value is as large as possible within the range where erroneous correction does not occur, depending on the detection time and accuracy of the parameters of combustion stability. Is early.

Further, when the fuel supply amount correction coefficient is stored in a non-volatile memory, a value that absorbs the variation is stored, so that the target air-fuel ratio can be reached quickly.

Further, ΔS ′, S ″ are set in consideration of the case where the combustion stability is erroneously determined.

In the above description, an example in which the parameter of combustion stability is calculated based on the rotational angular velocity is shown. However, it is performed based on other engine parameters such as combustion pressure in the cylinder or vibration of the cylinder block. However, the same effect can be obtained.

Further, in the above description, the correction means is the operation of the fuel supply amount, but a method of operating the intake air amount and the ignition timing may be considered.

Further, when the means for detecting the exhaust air-fuel ratio is provided, the output of the means for detecting the exhaust air-fuel ratio is corrected by the air-fuel ratio in the desired combustion state obtained by the present invention, and the individual variation of the means. The method of absorbing is also effective.

[0032]

According to the present invention, it is possible to detect and correct the variation of each combustion state of the engine, and to set the air-fuel ratio according to the purpose.
It is possible to achieve a combustion state that matches the purpose of the operating area, such as exhaust gas priority.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention.

FIG. 2 is a diagram showing an embodiment of the present invention.

FIG. 3 is a diagram showing a relationship between an air-fuel ratio and engine performance.

FIG. 4 is a diagram showing the performance of a NOx reduction catalyst.

FIG. 5 is a diagram showing an example of use of a NOx reduction catalyst.

FIG. 6 is an explanatory diagram of performance according to an embodiment of the present invention.

FIG. 7 is an example of description according to an embodiment of the present invention.

FIG. 8 is a diagram showing a flowchart for explaining an embodiment of the present invention.

[Explanation of symbols]

3 ... Air flow sensor, 5 ... Throttle valve, 7 ... Engine, 13
… Fuel injection valve.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location F02D 45/00 362 J

Claims (5)

[Claims] 1. A fuel injection control device equipped with a catalyst for reducing NOx in an exhaust system at the same time as performing a correction for quantitatively detecting a combustion state of an engine to improve combustion, and a parameter representing a combustion state of an engine. A fuel injection control device having a correction for improving a combustion state and a function for correcting an exhaust emission NOx component to a minimum. 2. The combustion state is detected when the target supply air-fuel ratio of the internal combustion engine is leaner than the stoichiometric air-fuel ratio, and the combustion state is detected by the rotational stability of the engine. The fuel injection control device is characterized by being operated by operating. 3. A fuel injection control device, characterized in that the allowable limit of the exhaust emission NOx component is detected by the engine rotation stability, and the correction is made by operating the air-fuel ratio. 4. The combustion injection control device according to claim 1, wherein the correction value is integrated for each process, and the fuel supply amount is corrected based on the integrated value. 5. The method according to any one of claims 1 to 4,
A combustion injection control device characterized in that a correction function for improving a combustion state and a correction function for minimizing an exhaust emission NOx component are switched under a predetermined condition to correct the above parameter.