Method and apparatus for controlling the warm-up of a three-way catalytic converter

Abstract

To obtain, over the entire cross section of a three-way catalyst, the effect of a perturbation control periodically repeating rich combustion with a large equivalence ratio and lean combustion with a small equivalence for catalyst warming-up.SOLUTION: A three-way catalyst is provided at an outlet part of an exhaust manifold of an internal combustion engine. In order to promote warming-up of the three-way catalyst, M times of rich combustion, which are performed continuously in a plurality of cylinders, and M times of lean combustion, which are performed continuously in the plurality of cylinders, are performed alternately in accordance with a combustion order. The number of times M is larger than or equal to the number N of cylinders included in an internal combustion engine 1. Since rich combustion is performed once in all the cylinders of the plurality of cylinders, and then lean combustion is performed once in all the cylinders of the plurality of cylinders, rich gas and lean gas flow alternately throughout the entire area of the catalyst.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a warm-up control method and apparatus for promoting warm-up of a three-way catalyst by periodically varying the exhaust air-fuel ratio of exhaust gas flowing into the three-way catalyst in an internal combustion engine to rich / lean.

Background Art

[0002] In order to quickly warm up a three-way catalyst provided in an exhaust passage of an internal combustion engine to near its activation temperature, it has been proposed to perform control that periodically repeats rich combustion and lean combustion. For example, Patent Document 1 discloses a catalyst warm-up control called irregular injection dither control, which is a repeating pattern in a straight-four cylinder internal combustion engine where after rich combustion is performed in one cylinder according to the combustion order, lean combustion is continuously performed in a plurality of cylinders. In one embodiment, after rich combustion is performed in one cylinder, lean combustion is performed in two cylinders, then rich combustion is performed in the next one cylinder, and further lean combustion is performed in the next two cylinders, and so on.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Exhaust gas from one cylinder often flows unevenly to a part of the area of the three-way catalyst. Therefore, in the method of Patent Document 1, the gas having a rich exhaust air-fuel ratio due to rich combustion does not reach the entire three-way catalyst, and in some embodiments regarding lean combustion, the gas having a lean exhaust air-fuel ratio also does not reach the entire three-way catalyst. Therefore, the catalytic activity promotion effect due to the periodic variation of rich / lean cannot be maximally obtained over the entire area of the three-way catalyst.

[0005] Furthermore, the method described in Patent Document 1 may result in a lean average air-fuel ratio, potentially leading to NOx emissions. [Means for solving the problem]

[0006] This invention provides a three-way catalytic converter in the exhaust passage of an internal combustion engine, and during the warm-up of this three-way catalytic converter, The exhaust air-fuel ratio of the exhaust gas flowing into the three-way catalytic converter is to vary between rich and lean. A warm-up control method for a three-way catalytic converter that performs perturbation control by periodically repeating a rich combustion period with a high equivalence ratio and a lean combustion period with a low equivalence ratio. and , The rich combustion period and lean combustion period each consist of M rich and lean combustion cycles performed consecutively in multiple cylinders according to the combustion sequence, where the number of these consecutive rich or lean combustion cycles M is equal to or greater than the number of cylinders N in the internal combustion engine, and the rich and lean combustion cycles are equal to each other. Ku , The range of change in the equivalence ratio for rich combustion and lean combustion, with an equivalence ratio of 1 as the baseline, are equal.

[0007] In other words, after rich combustion is performed once in all cylinders of the multi-cylinder engine, lean combustion is performed once in all cylinders of the multi-cylinder engine. [Effects of the Invention]

[0008] According to this invention, rich and lean exhaust gases are distributed throughout the entire region of the three-way catalyst, and the mixture alternates between rich and lean, thus effectively promoting catalytic activity throughout the entire three-way catalyst.

[0009] Also Since the number of consecutive rich combustion cycles M and the number of consecutive lean combustion cycles M are equal for both rich and lean combustion, and the range of change in the equivalent ratio of rich combustion relative to an equivalent ratio of 1 is equal for lean combustion, the average is The air-fuel ratio approaches the stoichiometric air-fuel ratio, suppressing emissions of both HC and NOx. [Brief explanation of the drawing]

[0010] [Figure 1] A diagram illustrating the configuration of an internal combustion engine in one embodiment to which this invention is applied. [Figure 2] A time chart showing several examples of repeating patterns. [Figure 3]An explanatory diagram showing the distribution of exhaust gas from one cylinder in a cross-section of a three-way catalytic converter. [Figure 4] Diagram illustrating the periodic change in rich / lean conditions in a cross-section of a three-way catalyst. [Modes for carrying out the invention]

[0011] Hereinafter, an embodiment of this invention will be described in detail with reference to the drawings. Figure 1 is an explanatory diagram showing the schematic configuration of an internal combustion engine 1 in an embodiment to which this invention is applied. The internal combustion engine 1 in this embodiment is a 3-cylinder, 4-stroke, spark-ignition internal combustion engine (a so-called gasoline engine), in which a pair of intake valves 2 and a pair of exhaust valves 3 are provided in the combustion chamber 5 of each cylinder, and a spark plug 4 is positioned in the center of the combustion chamber 5. In the illustrated example, as a direct injection engine, a fuel injection valve 6 that injects fuel into the cylinder is positioned, for example, on the intake valve 2 side. In the present invention, a port injection configuration in which fuel is injected toward the intake port 7 of each cylinder is also possible.

[0012] An electronically controlled throttle valve 10, whose opening degree is controlled by a control signal from the engine controller 9, is interposed upstream of the collector portion 8a of the intake passage 8 connected to the intake port 7 of each cylinder.

[0013] Each cylinder's exhaust port 12 is connected to a branch section of the exhaust manifold 13, and these are combined into a single exhaust passage by the exhaust manifold 13. A three-way catalytic converter 15 for exhaust purification is provided at the outlet of the exhaust manifold 13. The three-way catalytic converter 15 is a so-called monolithic ceramic catalyst, for example, a monolithic ceramic body with fine passages formed therein, coated with a catalytic layer containing a catalytic metal. In addition to the three-way catalytic converter 15 located at the outlet of the exhaust manifold 13, the three-way catalytic converter may also include another three-way catalytic converter (for example, an underfloor catalytic converter) arranged in series downstream.

[0014] An air-fuel ratio sensor 16 for detecting the exhaust air-fuel ratio is positioned upstream of the three-way catalytic converter 15, on the inlet side of the exhaust passage 14. This air-fuel ratio sensor 16 is a so-called wide-range air-fuel ratio sensor that provides an output corresponding to the exhaust air-fuel ratio. Furthermore, a downstream air-fuel ratio sensor, such as an O2 sensor that responds to the composition of the exhaust gas that has passed through the three-way catalytic converter 15, may be additionally provided downstream of the three-way catalytic converter 15 for purposes such as calibrating the air-fuel ratio feedback control system including the air-fuel ratio sensor 16 and diagnosing deterioration of the three-way catalytic converter 15.

[0015] The detection signal from the air-fuel ratio sensor 16 is input to the engine controller 9. Furthermore, the engine controller 9 receives detection signals from numerous sensors, including an air flow meter 20 that detects the intake air volume upstream of the throttle valve 10, a crank angle sensor 21 that detects the engine rotation speed and crank angle position, a water temperature sensor 22 that detects the coolant temperature, and an accelerator opening sensor 23 that detects the amount the accelerator pedal is pressed by the driver. Based on these input signals, the engine controller 9 optimally controls the fuel injection amount and injection timing by the fuel injector 6, the ignition timing by the spark plug 4, the opening degree of the throttle valve 10, and so on.

[0016] As one of the various controls for the internal combustion engine 1, the engine controller 9 performs air-fuel ratio control to optimize the exhaust purification performance of the three-way catalytic converter 15. The air-fuel ratio control estimates the oxygen storage amount of the three-way catalytic converter 15 based on the exhaust air-fuel ratio detected by the air-fuel ratio sensor 16, and feedback-controls the fuel injection amount (injection pulse width) of the fuel injector 5 so that this oxygen storage amount becomes the target oxygen storage amount (usually set to an intermediate value of the oxygen storage capacity (e.g., 50%)). As a result, the exhaust air-fuel ratio is maintained near the stoichiometric air-fuel ratio.

[0017] For such air-fuel ratio feedback control, it is necessary that the three-way catalyst 15 has reached the activation temperature. For example, it is desirable that the three-way catalyst 15 is warmed up to the activation temperature early after the start of the internal combustion engine 1. Therefore, during the warm-up of the three-way catalyst 15, specifically, when the three-way catalyst 15 has warmed up to some extent but has not reached the sufficient activation temperature, the engine controller 9 performs control to periodically repeat rich combustion with a large equivalent ratio and lean combustion with a small equivalent ratio (hereinafter, for convenience, this is referred to as perturbation control). In the perturbation control, the exhaust air-fuel ratio of the exhaust gas flowing into the three-way catalyst 15 fluctuates relatively greatly between rich / lean, so that the reaction between HC etc. during rich combustion and oxygen during lean combustion actively occurs, and the temperature rise of the catalyst is promoted. Further, with respect to the temporary deterioration of the catalyst (a phenomenon in which oxygen, HC, etc. adhere to the catalyst metal surface, the surface area of the catalyst metal decreases, and the catalyst performance deteriorates), by relatively greatly periodically varying the air-fuel ratio of the gas contacting the catalyst as the perturbation control, the poisoning substances covering the catalyst metal surface are peeled off, and the reaction area of the catalyst expands. Thus, the catalyst warm-up is also made rapid by this.

[0018] Here, in the present invention, M times of rich combustion continuously performed in a plurality of cylinders according to the combustion order and M times of lean combustion continuously performed in the same manner are alternately performed. And the number of times M is not less than the number of cylinders N (in one embodiment, 3) included in the internal combustion engine 1. That is, after rich combustion is performed once in all the cylinders of the plurality of cylinders, similarly, lean combustion is performed once in all the cylinders of the plurality of cylinders. As shown in the example described later, stoichiometric combustion with an equivalent ratio of 1 may be performed between rich combustion and lean combustion.

[0019] The time chart of FIG. 2 shows six repetition patterns in a three-cylinder engine as an example. In the three-cylinder engine, as shown in the figure, the combustion order is in the order of #1 cylinder → #3 cylinder → #2 cylinder. "R" in the figure indicates rich combustion, "L" indicates lean combustion, and "S" indicates stoichiometric combustion, respectively.

[0020] Pattern 1 and Pattern 2 are examples in which rich combustion and lean combustion are each continuously performed the same number of times (i.e., in a plurality of cylinders) without intervening stoichiometric combustion. In Pattern 1, rich combustion and lean combustion are each continuously performed 10 times, which is more than the number of cylinders, and both are repeatedly performed alternately. In this Pattern 1, the inversion period of rich combustion / lean combustion becomes relatively long.

[0021] In Pattern 2, rich combustion and lean combustion are each continuously performed 3 times, which is equal to the number of cylinders, and both are repeatedly performed alternately. That is, after rich combustion is performed in all cylinders, lean combustion is performed in all cylinders. <J

[0022] As shown in FIG. 3, in the cross section of the three-way catalyst 15 having a circular or elliptical shape, the exhaust gas of one cylinder flows through a partial region G shown by hatching. That is, the exhaust gas of one cylinder does not spread over the entire cross section of the three-way catalyst 15.

[0023] On the other hand, for example, in Pattern 2, by performing rich combustion in all cylinders, rich exhaust gas spreads over the entire cross section of the three-way catalyst 15. And by performing lean combustion in all cylinders, lean exhaust gas similarly spreads over the entire cross section of the three-way catalyst 15. (a) of FIG. 4 schematically shows a state in which rich exhaust gas (indicated by reference sign GR) is distributed over the entire cross section of the three-way catalyst 15, and (b) shows a state in which lean exhaust gas (indicated by reference sign GL) is distributed over the entire cross section of the three-way catalyst 15. These states (a) and (b) will occur alternately. Therefore, the effects (oxidation effect of HC etc. and recovery effect of primary deterioration) by the perturbation control can be surely obtained over the entire region of the three-way catalyst 15.

[0024] Patterns 3 to 6 in FIG. 2 are examples in which at least one stoichiometric combustion is performed respectively during the transition from the rich combustion period to the lean combustion period and during the transition from the lean combustion period to the rich combustion period. By interposing stoichiometric combustion in this way, the combustion pressure variation and rotational fluctuation based on the difference between the combustion pressure during rich combustion and the combustion pressure during lean combustion are reduced.

[0025] In Pattern 3, rich combustion and lean combustion are performed seven times each consecutively, with one stoichiometric combustion occurring during the transition from rich combustion to lean combustion and one during the transition from lean combustion to rich combustion. In Pattern 4, rich combustion and lean combustion are performed seven times each consecutively, with two stoichiometric combustions occurring during the transition from rich combustion to lean combustion and two during the transition from lean combustion to rich combustion.

[0026] In pattern 5, rich combustion and lean combustion occur three times each in succession, and stoichiometric combustion occurs three times each in succession during the transition from rich combustion to lean combustion and during the transition from lean combustion to rich combustion. In other words, each cylinder performs rich / stoichiometric / lean combustion once in sequence. In pattern 6, rich combustion and lean combustion occur three times each in succession, and stoichiometric combustion occurs once each during the transition from rich combustion to lean combustion and during the transition from lean combustion to rich combustion.

[0027] Furthermore, if the number of consecutive rich and lean combustion cycles M is set to an integer multiple of the number of cylinders in the internal combustion engine 1 (3 in this embodiment), such as "3", "6", or "9", the density variations in the exhaust gas distribution, as illustrated in Figures 3 and 4, are minimized, and the periodic fluctuations of rich / lean in each part of the cross-section of the three-way catalyst 15 are obtained to be substantially equal.

[0028] In all of patterns 1 to 6 in Figure 2, the number of rich combustion cycles is equal to the number of lean combustion cycles. Furthermore, the range of change in the equivalent ratio towards the rich side and the range of change in the equivalent ratio towards the lean side, relative to the stoichiometric pressure, are set to be equal for each cylinder during rich and lean combustion. Therefore, in all of patterns 1 to 6, the average exhaust air-fuel ratio is basically near the stoichiometric air-fuel ratio. As a result, emissions of NOx, along with HC, are suppressed.

[0029] The repeating patterns of rich and lean combustion are not limited to the example in Figure 2. A suitable number of M of rich and lean combustion can be combined, and a suitable number of stoichiometric combustion can also be included. These repeating patterns may be determined in advance by considering various requirements or conditions and used fixedly, or there may be multiple repeating patterns, and the optimal repeating pattern may be selectively executed according to the operating conditions of the internal combustion engine 1 during catalyst warm-up. For example, by selecting a repeating pattern, the reversal period of rich / lean combustion can be made appropriate.

[0030] Although one embodiment of this invention applied to an in-line 3-cylinder internal combustion engine has been described above, this invention is not limited to in-line 3-cylinder internal combustion engines, but can be similarly applied to other types of multi-cylinder internal combustion engines. [Explanation of symbols]

[0031] 1…Internal combustion engine 6…Fuel injector 9…Engine controller 15...Three-way catalyst 16…Air-fuel ratio sensor

Claims

1. A method for warming up a three-way catalytic converter, comprising a three-way catalytic converter in the exhaust passage of an internal combustion engine, wherein during the warm-up of the three-way catalytic converter, perturbation control is performed by periodically repeating a rich combustion period with a large equivalent ratio and a lean combustion period with a small equivalent ratio so that the exhaust air-fuel ratio of the exhaust gas flowing into the three-way catalytic converter fluctuates between rich and lean, The rich combustion period and the lean combustion period each consist of M rich and lean combustion cycles performed consecutively in multiple cylinders according to the combustion sequence, where the number of these consecutive rich or lean combustion cycles M is equal to or greater than the number of cylinders N in the internal combustion engine, and the number of rich and lean combustion cycles are equal to each other. The range of change in the equivalence ratio for rich combustion and the range of change in the equivalence ratio for lean combustion are equal, with an equivalence ratio of 1 as the baseline. A method for controlling the warm-up of a three-way catalytic converter.

2. During the transition from the rich combustion period to the lean combustion period and during the transition from the lean combustion period to the rich combustion period, stoichiometric combustion with an equivalent ratio of 1 is performed in at least one cylinder. A method for controlling the warm-up of a three-way catalytic converter as described in claim 1.

3. It has multiple repeating patterns in which the rich / lean period of perturbation control differs, Select one of the repeating patterns depending on the operating conditions of the internal combustion engine during warm-up. A method for controlling the warm-up of a three-way catalytic converter as described in claim 1.

4. The internal combustion engine is a 3-cylinder internal combustion engine, and the number M mentioned above is 3. A method for controlling the warm-up of a three-way catalytic converter as described in claim 1.

5. A warm-up control device for a three-way catalytic converter, which is equipped with a three-way catalytic converter in the exhaust passage of an internal combustion engine, and which performs perturbation control during the warm-up of the three-way catalytic converter, which periodically repeats a rich combustion period with a large equivalent ratio and a lean combustion period with a small equivalent ratio so that the exhaust air-fuel ratio of the exhaust gas flowing into the three-way catalytic converter fluctuates between rich and lean, The rich combustion period and the lean combustion period each consist of M rich and lean combustion cycles performed consecutively in multiple cylinders according to the combustion sequence, where the number of these consecutive rich or lean combustion cycles M is equal to or greater than the number of cylinders N in the internal combustion engine, and the number of rich and lean combustion cycles are equal to each other. The range of change in the equivalence ratio for rich combustion and the range of change in the equivalence ratio for lean combustion are equal, with an equivalence ratio of 1 as the baseline. A three-way catalytic converter warm-up control system.

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