JPS6053771B2 - Air fuel ratio control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an air-fuel ratio control device for an engine, such as a V-type multi-cylinder engine, in which at least the exhaust system is independent for each of a plurality of cylinder groups.

For example, V
In the case of an 8-cylinder engine, conventionally the engine consists of two groups of cylinders and the exhaust system is divided into two, as shown in Figure 1.
A configuration in which a three-way catalyst 4a, 4b) and an air-fuel ratio sensor 5a, 5b are provided in each exhaust pipe 3a, 3b of the two cylinder groups, respectively, and a feedback control circuit 6a, 6b for air-fuel ratio control is provided for each cylinder group. It was hot.

Note that 7 is an electronic fuel injection control circuit. The conventional device shown in Fig. 1 requires multiple air-fuel ratio sensors, Ξ main catalysts, and feedback control circuits for air-fuel ratio control even though it is a single engine, so The air-fuel ratio control device is complicated and has the disadvantage of being quite disadvantageous in terms of cost.

In order to avoid this drawback, in the case of such an engine, the individual exhaust gas manifolds are connected to one common main exhaust pipe, and one air-fuel ratio sensor is installed in the middle of this main exhaust pipe, and a catalyst is further installed downstream. However, compared to the case where the air-fuel ratio sensor is installed near the exhaust hole as in an in-line multi-cylinder engine, there is a large difference in the distance from the exhaust hole to the air-fuel ratio sensor. There is a problem in that the response delay of the fuel ratio feedback control system is large and the fluctuation range of the air-fuel ratio becomes large.

It is known that a three-way catalyst can simultaneously purify the three components of exhaust gas, HC, Co) and NOx, at a high purification rate only in a very narrow range around the stoichiometric air-fuel ratio. A large value has the disadvantage of deteriorating the purification rate. By the way, according to the results of the inventors' study, the three-way catalyst has a slightly richer mixture and a slightly leaner mixture than the stoichiometric air-fuel ratio than the exhaust gas purification rate when a mixture with a uniform air-fuel ratio is supplied to the engine. The purification rate is higher when the mixture is supplied alternately and repeatedly.In other words, by alternately supplying rich and lean mixtures in this way, the air-fuel ratio range in which the three-way catalyst can secure the specified purification rate increases. It is known that it will spread.

In order to eliminate the drawbacks of the conventional device, and in view of the above considerations, the present invention provides an air-fuel ratio sensor only in the exhaust system of one cylinder group in an engine consisting of two cylinder groups, and compares the air-fuel ratio of this cylinder group. The other cylinder group outputs a signal in which the average output of the integrating means and a rectangular wave signal output having an opposite phase to the integrated output of the integrating means are superimposed. By adopting a configuration in which the air-fuel ratio is controlled by the air-fuel ratio of the other cylinder group, the air-fuel ratio of the other cylinder group is corrected in the same proportion as that of the one cylinder group by the average output of the integrating means output, and the rectangular wave signal output is Therefore, the exhaust gas purification rate by the three-way catalyst can be improved by repeating the air-fuel ratio between rich and lean, and the exhaust gas purification performance of two cylinder groups can be satisfied with one air-fuel ratio sensor and feedback control means. The purpose is to enable air-fuel ratio control and reduce costs.
゛Also, in the present invention, by controlling the air-fuel ratio of the other cylinder group with a rectangular wave signal having a phase opposite to that of the integrating means output of one cylinder group, the richness and leanness of the air-fuel ratio can be made different between the two cylinder groups. In this way, the engine speed fluctuations between the two cylinder groups are offset, and the engine speed fluctuations are kept to a minimum. The present invention will be described below with reference to an embodiment shown in FIGS. 2 and 3.

Figure 2 is a configuration diagram when applied to a V-type 8-cylinder engine, where 1 is the engine body, 2a and 2b are exhaust manifolds for two cylinder groups of 4 cylinders, and 3a and 3b are downstream of each exhaust manifold. The exhaust pipes 4a and 4b are three-way catalysts provided in each exhaust pipe, and 5 is an air-fuel ratio sensor provided in the exhaust pipe 3a of one cylinder group. 6 is a known feedback control circuit comprising a comparison circuit 61 and an integration circuit 62 as shown in FIG.

Reference numeral 7 designates an electronic fuel injection control circuit, which includes a main calculation circuit 8 that calculates the fuel injection amount per unit engine revolution according to the engine intake air amount, and a main calculation circuit 8 that calculates the fuel injection amount per unit rotation of the engine according to the engine intake air amount. It consists of correction circuits 7a and 7b that perform correction calculations.

The main calculation circuit 8 and the correction circuits 7a and 7b have a known configuration, and in this embodiment, the correction circuits 7a and 7b not only perform correction calculations but also have a function of driving a fuel injection valve (not shown). . Note that one correction circuit 7a
performs correction calculations for one cylinder group, and performs correction calculations for the other cylinder group.
b performs correction calculations for the other cylinder group. 9 is a correction control circuit to which the signal from the feedback control circuit 6 is input; when the integrated output of the integrating circuit 62 increases, it becomes a low level; when it decreases, it becomes a high level; that is, it has a rectangular wave signal that is in opposite phase to the integrated output. A signal obtained by superimposing the output and the average output of the integrating circuit 62 is output to the other correction circuit 7b.

FIG. 3 shows the comparison circuit 61 and the integration circuit 6 of the feedback control circuit 6.
2 shows a detailed electric circuit of the correction control circuit 9. The comparison circuit 61 consists of resistors 611, 612, 613 and a comparator 614, and the integration circuit 62 consists of resistors 621, 623,
624, 626, 628, and capacitor 6 forming an integrator
25, consists of an operational amplifier 622 and a diode 629. The correction control circuit 9 includes resistors 901, 903, 905, a capacitor 902, and diodes 904, 906. Note that Vcc represents a constant potential from a constant voltage source. Next, the operation of the above-mentioned constituent devices will be explained using the waveform diagram shown in FIG. 4. As shown in FIG.
A signal A whose level changes depending on whether the fuel is thin or lean is output, and this signal A is compared with a comparison level V1 corresponding to a predetermined air-fuel ratio determined by resistors 612 and 613 in a comparison circuit 61 of the feedback control circuit 6. 46F' level shown in Figure 4B,
6601 level signal B.

In other words, this signal B is at the level 1 when the air-fuel ratio is smaller than the predetermined air-fuel ratio (rich), and at the level 1 when it is larger than the predetermined air-fuel ratio (lean)
It becomes ゜0゛ level. This signal B is input to an integrating circuit 62 and integrated, and the integrated output C of this integrating circuit 62 increases as shown in FIG. When the signal B is at the "゜1゛ level, that is, when it is rich, it decreases to make the air-fuel ratio lean.The correction circuit 7a of the electronic fuel injection control circuit 7 Based on this integral output C, the fuel injection amount is corrected so that the air-fuel ratio of one cylinder group becomes a predetermined air-fuel ratio.In addition, the integral output C of the integral circuit 62
is also supplied to the correction control circuit 9, and is connected to a resistor 90 as shown in FIG. 4D.
1. It is converted into an averaged signal D by a capacitor 902. The correction control circuit 9 is further supplied with a signal obtained by dividing the output signal B of the comparator circuit 61 by resistors 626 and 627, and divides this signal and the averaged signal D by resistors 903 and 905,
A signal E shown in FIG. 4E, which is added by diodes 904 and 906, is output. That is, the output signal E of the correction control circuit 9 is at a low level when the integral output C of the integrating circuit 62 increases, and is at a high level when it decreases. , and is supplied to the other correction circuit 7b of the electronic fuel injection control circuit 7. The other correction circuit 7b uses the average output D of the integral output C to correct the air-fuel ratio at the same average rate as the one correction circuit 7a, and uses the rectangular wave signal to correct the air-fuel ratio at a predetermined air-fuel ratio. Since the air-fuel ratio is alternately rich and lean, the purification rate of the three-way catalyst 4b of the other cylinder groups is improved. Furthermore, since this rectangular wave signal is in opposite phase to the integral output C, for example, when the air-fuel ratio of one cylinder group is made richer by increasing the integral output C, the air-fuel ratio of the other cylinder group must be increased. Since both cylinder groups are not repeatedly rich and lean at the same time, engine rotation fluctuation factors can be canceled out and rotation fluctuations can be suppressed. It is possible to stabilize it. In the embodiments described above, the feedback control circuit 6 for air-fuel ratio control has been shown to be composed of a comparator circuit 61 and an integrator circuit 62. A delay circuit may be provided, and furthermore, the comparison level of the comparison circuit 61 may be made variable as is known, and the integration circuit 62 may be provided.
Various methods can be used, such as one in which a known step change is added to the integral output of the integrating circuit 62, or a circuit in which a known circuit is added to hold the integral output of the integrating circuit 62 at a predetermined value during a specific operation of the engine.

As described above, the device of the present invention uses an air-fuel ratio sensor provided in the exhaust system of one cylinder group of an engine consisting of two cylinder groups, and an integral output whose increase/decrease direction is switched based on the signal of this air-fuel ratio sensor. Feedback control means has an integral output and controls the air-fuel ratio of the cylinder group on the saw side to a predetermined air-fuel ratio using this integral output, and the average output of the integral output of this feedback control means and this integral output are in opposite phase. and a correction control means for outputting a signal superimposed with a rectangular wave signal and controlling the air-fuel ratio of the other cylinder group of the two cylinder groups using this signal. In the cylinder group, the air-fuel ratio can be corrected at the same rate as one cylinder group by the average output of the integral output of the integrating means, and the air-fuel ratio can be controlled by alternating rich and lean by rectangular wave signal output. This makes it possible to improve the purification rate of exhaust gas using a three-way catalyst, and the advantage is that it is possible to control the air-fuel ratio to purify the exhaust gas of two cylinder groups with one air-fuel ratio sensor and one feedback control means. It has a certain effect. It is also possible to suppress engine rotational fluctuations by canceling out the engine rotational fluctuation factors between the two cylinder groups at the same time.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a conventional device, Fig. 2 is a block diagram showing an embodiment of the present invention, Fig. 3 is an electric circuit diagram of the main parts shown in Fig. 2, and Fig. 4 is a block diagram of each part shown in Fig. 3. It is an output waveform diagram. 3a... Exhaust pipe of one cylinder group, 5...
・Air-fuel ratio sensor, 6... Feedback control circuit, 62.
...Integrator circuit, 9...Correction control circuit.

Claims (1)

[Claims] 1 An air-fuel ratio sensor provided in the exhaust system of one cylinder group of an engine consisting of two cylinder groups, and an integrating means for outputting an integral output whose increase/decrease direction is switched based on the signal of the air-fuel ratio sensor. Feedback control means for controlling the air-fuel ratio of one cylinder group to a predetermined air-fuel ratio by an output, and a signal obtained by superimposing the average output of the integral output of this feedback control means and a rectangular wave signal having an opposite phase to this integral output. an air-fuel ratio control device comprising: a correction control means for controlling the air-fuel ratio of the other cylinder group of the two cylinder groups based on the output signal;