JP3489441B2 - Air-fuel ratio control device for internal combustion engine - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air-fuel ratio control system for an internal combustion engine equipped with a catalyst having a function of adsorbing HC (hydrocarbon component) contained in exhaust gas of the internal combustion engine.

[0002]

2. Description of the Related Art There is known an internal combustion engine in which an exhaust passage is provided with a three-way catalyst and a catalyst having an HC adsorbing function downstream of the three-way catalyst. 144,144). This is because the three-way catalyst does not reach the activation temperature, HC generated during operation after cold start is temporarily adsorbed on the HC adsorption catalyst, and then the air-fuel ratio is changed when the three-way catalyst reaches the activation temperature. It is diluted to form an oxygen-excess atmosphere, and H
The HC separated from the C adsorption catalyst is oxidized by the catalyst.

By the way, Pt, R applied to a three-way catalyst
The catalytic metal layer such as h and Pd has a storage function of retaining oxygen. Especially, in order to enhance this function, a large amount of oxygen is contained in the catalyst when a cocatalyst with a large amount of oxygen storage such as cerium oxide is used together. Since it is retained in the catalyst, the conversion efficiency of the catalyst is further enhanced by the action of this storage oxygen. This oxygen storage amount has a characteristic that it increases in an atmosphere of lean air-fuel ratio with excess oxygen and decreases in an atmosphere of rich air-fuel ratio with insufficient oxygen.

However, due to the oxygen storage action of such a three-way catalyst, the above-mentioned H
The C adsorption catalyst may not function effectively. If the lean air-fuel ratio is maintained in the idle operation state after the cold start, the oxygen storage amount of the three-way catalyst will be secured, but in the warm-up process before the HC treatment is completed, the driver's idling or starting -If the engine load increases due to acceleration or the like, oxygen is released from the three-way catalyst due to the enrichment of the air-fuel ratio at this time. After that, even if the air-fuel ratio is diluted, the HC on the downstream side remains until oxygen is secured again on the three-way catalyst located on the upstream side.
A time delay occurs until the adsorption catalyst becomes an oxygen excess atmosphere, and it becomes temporarily impossible to supply sufficient oxygen to the HC adsorption catalyst. As a result, the desorbed HC cannot be sufficiently oxidized as the catalyst temperature rises, and the amount of discharged HC increases accordingly. In order to solve this problem, it is considered to maintain the lean air-fuel ratio even when the load is increased, but if this is done, the output cannot be secured and the NOx emission amount also increases.

In order to solve the above problem, in the invention of claim 1, a three-way catalyst is provided in the engine exhaust passage, and H is provided downstream thereof.
In an internal combustion engine in which a processing device including a C adsorbent and a catalyst are respectively interposed, an operating state detecting unit that detects an engine operating state and an oxygen storage amount of a three-way catalyst are set as an air-fuel ratio sensor
The oxygen storage amount calculation means for calculating from the actual air-fuel ratio and the intake air amount actually measured by the engine, and the air-fuel ratio control means for controlling the air-fuel ratio based on the operating state are provided. HC at desorption start before the predetermined high-load operating region, as the oxygen storage amount of the three-way catalyst is to control the air-fuel ratio so that the Oh <br/> et beforehand target value determined on the saturation value near It should be configured.

The invention of claim 2 is the same as the invention of claim 1.
In addition, lowering the target value of the oxygen storage amount,
Air fuel near the rich side or near the stoichiometric air-fuel ratio in the high load operating range
I tried to increase the opportunity to drive at a ratio.

According to a third aspect of the present invention, the air-fuel ratio control means of the first aspect of the invention is configured to control the air-fuel ratio to a lean air-fuel ratio larger than the theoretical air-fuel ratio in a predetermined low load operation range. It is assumed that

According to a fourth aspect of the invention, the three-way catalyst of the third aspect of the invention has a NOx storage material.

According to a fifth aspect of the present invention, the air-fuel ratio control means of the first aspect of the invention is based on the difference between the target value and the calculated value of the oxygen storage amount, and the calculated value is smaller than the target value. It is assumed that the air-fuel ratio is controlled to be large.

[0010]

According to the inventions described in claims 1 and below, H
In the case of a high load operation such as when the driver performs a start operation etc. during warm-up before desorption, the air-fuel ratio is limited to the limit necessary to maintain the target oxygen storage amount of the three-way catalyst. It is controlled on the lean side. As long as the oxygen storage amount is maintained at the target value, it is possible to operate near the stoichiometric air-fuel ratio, so output performance at high load is not impaired, and NOx emissions are suppressed while the subsequent HC treatment is performed. Can be effectively performed.

[0011] it is possible to ensure the oxygen storage amount always sufficient quantity target value of the oxygen storage amount in the three-way catalyst by setting the near saturation value. According to the invention of claim 2,
If the target value is set low as described above, the chances of operating at an air-fuel ratio on the rich side or near the stoichiometric air-fuel ratio at the time of high load increase accordingly, which is advantageous in terms of output performance.

By performing the lean air-fuel ratio operation in the low load range as in the third aspect of the present invention, it becomes possible to secure the maximum oxygen storage amount of the three-way catalyst, which increases the load. Since it is possible to minimize the leaning of the air-fuel ratio at that time, it is advantageous in terms of output and exhaust performance. Note that NOx may be emitted during lean air-fuel ratio operation, but since the amount of emission during idling is very small, it is better to control to lean air-fuel ratio to secure the oxygen storage amount of the three-way catalyst. Is. However, by applying the NOx storage material to the three-way catalyst as in the invention of claim 4, it is possible to reliably prevent the emission of NOx in the lean air-fuel ratio operation state under such a low load.

According to the fifth aspect of the invention, based on the difference between the target value and the calculated value of the oxygen storage amount, the air-fuel ratio is controlled to be larger as the calculated value is smaller than the target value. By controlling the air-fuel ratio to an appropriate level with respect to changes in the oxygen storage amount, it is possible to ensure good engine performance while reliably maintaining the oxygen storage amount.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

In FIG. 1, 1 is a spark ignition type internal combustion engine, 2 is an intake passage thereof, and 3 is an exhaust passage. Reference numeral 4 is an air flow meter provided in the middle of the intake passage 2, and reference numerals 5 and 6 are similarly throttle valves and throttle opening sensors for detecting the opening thereof. Reference numeral 7 is an electromagnetic fuel injection valve for injecting and supplying fuel to the intake port portion, and 8 is a spark plug.

Reference numerals 9 and 10 respectively denote a three-way catalyst and an HC adsorption catalyst as a processing device, which are interposed in the exhaust passage 3. The HC adsorption catalyst 10 comprises a three-way catalyst or an oxidation catalyst in which a coating layer of an HC adsorption material such as zeolite is formed on a catalyst carrier. The three-way catalyst 9 is provided near the outlet of the exhaust manifold 3A so as to reach the activation temperature as soon as possible after starting, and the HC adsorption catalyst 10 is provided near the rear side of the three-way catalyst 9 as shown in the figure. ing. 1
1 is an air-fuel ratio sensor provided on the inlet side of the three-way catalyst, 12
Is a temperature sensor for detecting the catalyst temperature. A controller 13 controls the air-fuel ratio and the ignition timing based on the intake air amount signal from the air flow meter 4 and the rotation signal from a crank angle sensor (not shown).

A feature of the present invention is that in an internal combustion engine equipped with such a three-way catalyst 9 and an HC adsorption catalyst 10, when the load increases in the warm-up process before desorption of HC, the oxygen storage of the three-way catalyst. The point is that the lean air-fuel ratio is controlled to the minimum necessary to maintain the amount. Next, an example of this control will be described with reference to the flow chart shown in FIG.

FIG. 2 shows an air-fuel ratio control routine which is periodically executed by the controller 13. In this air-fuel ratio control, first, after the engine is started, operating state signals such as engine speed, intake air amount, cooling water temperature, catalyst temperature, etc. are detected (step 201), and then the catalyst temperature Tc is obtained by a sensor signal or an estimation calculation. The target equivalent ratio TFBYA is set (steps 202 and 203). The air-fuel ratio is controlled so that the starting air-fuel ratio is slightly higher than the stoichiometric air-fuel ratio in order to improve the ignitability and improve the startability until the engine completes the complete explosion. Is HC adsorption catalyst 1
It is temporarily adsorbed on the HC adsorption layer of 0 and is prevented from being released into the atmosphere. The target equivalence ratio TFBYA is a set value proportional to the reciprocal of the air-fuel ratio, and is a target value for air-fuel ratio control described later.

Next, the catalyst temperature Tc is the HC desorption temperature Tc1.
If Tc ≧ Tc1, it is determined whether HC is being desorbed next, and if it is desorbing, HC is deducted.
The target equivalence ratio TFBYA is set according to the desorption state, and if the desorption is completed, the air-fuel ratio control in the normal state is started (steps 204, 209, 210, 211). Since the desorption amount of HC can be estimated and calculated as a function of, for example, the intake air amount and the catalyst temperature, the target equivalent ratio TF is calculated based on the calculation result.
BYA can be set to a value such that the optimum air-fuel ratio required for desorption of HC can be obtained. Further, since the HC adsorption amount can be estimated as a function of, for example, the fuel injection amount or the intake air amount and a known adsorption efficiency, the desorption amount of HC is compared by comparing this with the desorption amount calculated as described above. It is possible to accurately determine whether or not

In the air-fuel ratio control itself, the basic fuel injection amount (pulse width of the fuel injection valve 7) determined based on the engine speed and the intake air amount is determined based on the air-fuel ratio signal from the air-fuel ratio sensor 11. According to a known method, feedback control is performed so that the target equivalence ratio obtained in step 203 is obtained, or open loop control is performed based on the target equivalence ratio. The normal air-fuel ratio control is, for example, to control the air-fuel ratio to stoichiometric (theoretical air-fuel ratio) in a steady operating state to improve the conversion efficiency of the three-way catalyst, while increasing the rich air when the load demand during acceleration is high. The control is such that a fuel ratio is used to secure an output, and fuel is cut during deceleration where output is unnecessary.

On the other hand, if Tc <Tc1 in step 204, then the oxygen storage amount OS of the three-way catalyst 9 is reached.
Is estimated and calculated from the actual air-fuel ratio actually measured by the air- fuel ratio sensor 11 and the integrated value of the intake air amount (step 205). next,
The load condition of the engine is determined based on the fuel injection amount or the intake air amount, and if the engine is in a predetermined low load operation range including idling, the air-fuel ratio at low load is set (steps 206 and 212). As the air-fuel ratio setting at low load, for example, stoichiometric (theoretical air-fuel ratio) or a slight lean air-fuel ratio is set. Although NOx may be emitted in the lean air-fuel ratio operation, the amount of emission in idling is very small. Therefore, in order to keep the oxygen storage amount of the three-way catalyst 9 near the saturation value, the lean air-fuel ratio is set to the lean air-fuel ratio. It is preferable to control. If necessary, by applying a NOx storage material such as barium oxide to the three-way catalyst 9, NO under such operating conditions can be obtained.
It is possible to reliably prevent x discharge.

On the other hand, when it is determined in step 206 that the engine is in the high load operation range exceeding the predetermined load range,
The equivalent ratio correction value DFBYA is calculated based on the following equation.
However, in the equation, TOS is a target value of the oxygen storage amount of the three-way catalyst 9, OS is the estimated calculated value calculated in step 205, and K is a constant.

DFBYA = K (TOS-OS) Next, this equivalence ratio correction value is set to 1.
The target equivalent ratio TFBYA is obtained by subtracting from 0. At this time, the calculated actual oxygen storage amount OS is the target value T
Since the equivalence ratio correction value DFBYA becomes larger as it is smaller than OS, the target equivalence ratio TFBYA is small accordingly.
In other words, it will be set to the lean side. On the other hand, OS
When exceeds TOS, TFBYA is set to the dark side.

By repeating such control, the oxygen storage amount of the three-way catalyst 9 is maintained at the target value even under high load, and the air-fuel ratio is limited only to the extent necessary to maintain this target oxygen storage amount. Is controlled to the lean side, that is, as long as the oxygen storage amount is secured, it is possible to operate near the stoichiometric air-fuel ratio, so the output performance at high load is not impaired and the NOx emission amount is reduced. It is possible to secure the amount of oxygen necessary for desorbing HC in the three-way catalyst 9 while effectively suppressing the subsequent HC treatment.

[Brief description of drawings]

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

FIG. 2 is a flowchart showing an example of an air-fuel ratio control method of the above embodiment.

[Explanation of symbols] 1 Internal combustion engine 2 Intake passage 3 exhaust passage 4 Air flow meter 5 Throttle valve 6 Throttle opening sensor 7 Fuel injection valve 8 spark plug 9 three-way catalyst 10 HC adsorption catalyst (treatment device) 11 Air-fuel ratio sensor 12 Temperature sensor 13 Controller

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification symbol FI F01N 3/08 B01D 53/34 117A 3/24 129A 53/36 102H (56) Reference JP-A-10-61426 (JP, A) ) JP-A-7-279651 (JP, A) JP-A-7-144119 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) F02D 41/14 310 F01N 3/08 F01N 3 /twenty four

Claims (5)

(57) [Claims] 1. An operating state detecting means for detecting an engine operating state in an internal combustion engine in which a three-way catalyst is provided in an engine exhaust passage and a processing device having an HC adsorbent and a catalyst on the downstream side thereof are respectively interposed. And the oxygen storage amount of the three-way catalyst was measured with an air-fuel ratio sensor.
An oxygen storage amount calculation means for calculating from the actual air-fuel ratio and the intake air amount, and an air-fuel ratio control means for controlling the air-fuel ratio based on the operating state are provided, and the air-fuel ratio control means is provided before starting the HC desorption of the HC adsorbent. the oxygen storage amount of the three-way catalyst at a predetermined high-load operating region is that of the
An air-fuel ratio control device for an internal combustion engine configured to control an air-fuel ratio so as to reach a predetermined target value near a saturation value . 2. The target value of the oxygen storage amount is lowered.
In the high load operating range, on the dark side or near the theoretical air-fuel ratio.
2. The air-fuel ratio control device for an internal combustion engine according to claim 1, wherein the number of opportunities to operate at the air-fuel ratio of is increased . 3. The internal combustion engine according to claim 1, wherein the air-fuel ratio control means is configured to control the air-fuel ratio to a lean air-fuel ratio larger than the stoichiometric air-fuel ratio in a predetermined low load operation range. Air-fuel ratio control system for engines. 4. The air-fuel ratio control device for an internal combustion engine according to claim 3, wherein the three-way catalyst has a NOx storage material. 5. The air-fuel ratio control means is configured to control the air-fuel ratio to be larger as the calculated value is smaller than the target value, based on the difference between the target value and the calculated value of the oxygen storage amount. An air-fuel ratio control system for an internal combustion engine according to claim 1.