JPH04347343A - Air-fuel ratio controller - Google Patents

Abstract

PURPOSE:To provide a means which prevents uncomfortable torque fluctuation which is generated when an air-fuel ratio in each cylinder group is controlled separately by an oxygen sensor provided in respective exhaust systems concerning an air-fuel ratio controller of an engine which has two cylinder groups provided with mutually independent exhaust systems such as a V-type engine. CONSTITUTION:Exhaust pipes 6, 7 are provided independently per each of cylinder groups 1a, 1b of respective banks in a V-type engine 1, and exhaust oxygen sensors 8, 9 are provided. Injection quantities of fuel injection valves 12, 13 are varied based on outputs of oxygen sensors 8, 9 by an electronic control unit(ECU) 14, so that an air-fuel ratio may be feedback-controlled. In this case, control which varies a fuel supply quantity in a stepping manner is forbidden to be carried out in both cylinders in a specified time continuously, and then rapid torque variation is prevented.

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 device for an engine, and more particularly to an air-fuel ratio control device for an engine having two independent exhaust passages, such as a V-type engine.

0002

2. Description of the Related Art An air-fuel ratio control device is known in which an O2 sensor or the like is installed in each exhaust passage of an engine having two exhaust passages, and the air-fuel ratio of the cylinders of each exhaust system group is feedback-controlled. For example, as an example of this type of air-fuel ratio control device, Japanese Patent Application Laid-Open No. 56-129730
There is something described in the No. The air-fuel ratio control device disclosed in the same publication provides an exhaust pipe for each bank of a V-type engine, and installs an O2 sensor in each exhaust pipe to detect the oxygen concentration in the exhaust gas to control the air-fuel ratio for each bank. Is going.

Generally, when air-fuel ratio control is performed based on the output of an exhaust O2 sensor, it takes a long time before a change in the air-fuel ratio of the mixture supplied to the combustion chamber is detected as a change in the O2 concentration of the exhaust gas at the location where the O2 sensor is installed. There will be some time delay. Therefore, the actual mixture air-fuel ratio is the target value (for example, the stoichiometric air-fuel ratio).
It will alternately fluctuate between the rich side and the lean side centering on . For this reason, in reality, in order to improve control responsiveness by reducing the fluctuation width and fluctuation period in consideration of the above time delay, when the O2 sensor output changes from the rich side to the lean side, or from the lean side to the rich side. Control is performed to change the air-fuel ratio discontinuously by changing the fuel supply amount stepwise by a predetermined amount.

FIG. 6 shows the air-fuel ratio change when the above control is performed, in which (a) shows the air-fuel ratio of the air-fuel mixture supplied to the combustion chamber, (b) shows the O2 sensor output, and (c) shows the change in the air-fuel ratio of the exhaust gas. O2
Each figure shows a change over time in the air-fuel ratio calculated from the concentration. In the figure, Td is the time delay until a change in the air-fuel mixture air-fuel ratio is detected by the O2 sensor, λo is the target air-fuel ratio, and RSL and RSR are the step shapes when the O2 sensor output changes from lean to rich and from rich to lean, respectively. (hereinafter referred to as skip control value).

[0005]

[Problems to be Solved by the Invention] However, when controlling the air-fuel ratio of two groups of cylinders based on the O2 sensor output of each exhaust system, as in the engine disclosed in Japanese Patent Application Laid-open No. 56-129730, it is difficult to control the air-fuel ratio of each cylinder. The air-fuel ratio of each group will change independently as shown in FIG. Therefore, in normal cases, skip control (
The timing of RSL and RSR is also different for both cylinder groups, and the torque fluctuations associated with skip control are also small. When such a situation occurs, sudden torque fluctuations occur, which may be felt by the driver as a surge or the like.

[0006] As mentioned above, in an engine that performs air-fuel ratio control independently for each of the two cylinder groups, the torque fluctuation due to skip control during normal operation is small, so the torque fluctuation when skip control is performed simultaneously on both cylinder groups. is felt to be very large, and the discomfort given to the driver also increases, resulting in a problem of deterioration of so-called drivability. SUMMARY OF THE INVENTION An object of the present invention is to provide an air-fuel ratio control device that solves the above problems, suppresses unpleasant torque fluctuations caused by skip control, and does not cause deterioration of drivability.

[0007]

[Means for Solving the Problems] According to the present invention, air-fuel ratio detection is provided in each exhaust system of an engine in which a plurality of cylinders are divided into two groups and each cylinder group is provided with an independent exhaust system. The fuel supply amount to each cylinder group is independently feedback-controlled so that the air-fuel ratio becomes a predetermined value based on the output of the means, and when the air-fuel ratio changes from lean to rich, the fuel supply amount is limited to a predetermined amount. In the air-fuel ratio control device, the air-fuel ratio control device is provided with a correction means for increasing the fuel supply amount stepwise by a predetermined amount when the fuel supply amount changes from rich to lean. There is provided an air-fuel ratio control device characterized in that it includes means for prohibiting continuous control between the two cylinder groups within a period.

[0008]

[Operation] The prohibition means constantly monitors the air-fuel ratio skip control timing in each cylinder group, and when the timing is such that skip control is performed in both cylinder groups simultaneously or consecutively within a predetermined time, , one of the skip controls is prohibited to prevent consecutive skip controls from occurring within a predetermined period of time. The prohibited skip control is performed after a predetermined period of time has elapsed, and by dispersing the skip control execution period, torque fluctuations are reduced and drivability is not adversely affected.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a schematic diagram showing the construction of an embodiment of an air-fuel ratio control device according to the present invention. In the figure, 1 is the engine,
In this embodiment, a V-type 6-cylinder engine is used. Three cylinders of the engine 1 are arranged in each of the right bank 1a and the left bank 1b, and each bank 1a, 1b has exhaust pipes 6, 7. The exhaust pipes 6 and 7 merge into one on the downstream side, and a catalytic converter 15 using a three-way catalyst for purifying exhaust gas is provided downstream of this merged portion.

Further, the cylinders of both banks 1a and 1b are connected to a common intake manifold 2 via intake branch pipes 2a and 2b, respectively. In this embodiment, an intake pipe 5 on the upstream side of the intake manifold 2 is provided with a throttle valve 3, a throttle sensor 3a for detecting the throttle valve opening, and an air flow meter 4 for detecting the engine intake air amount. Furthermore, fuel injection valves 12 and 13 are provided at each cylinder inlet portion of the intake branch pipes 2a and 2b.

[0011] Reference numerals 8 and 9 in the figure indicate O2 sensors provided in the exhaust pipes 6 and 7, respectively. In this example, O
2. A sensor using an element made of a zirconia sintered body is used, and is designed to generate a voltage depending on the oxygen concentration of the exhaust gas. In this example, the O2 sensor output voltage VO when the air-fuel mixture is at the stoichiometric air-fuel ratio is used as the reference voltage, and when the air-fuel mixture is on the rich side, the O2 sensor output voltage VO is set as the reference voltage.
2. Since the sensor output is higher than the reference voltage VO and lower than VO when it is on the lean side, it is detected whether the air-fuel mixture is rich or lean.

Further, a cooling water temperature sensor 10 that outputs a voltage signal according to the cooling water temperature is installed in the engine body, and outputs an engine crankshaft rotational speed signal (NE pulse signal) and a reference position signal to a distributor (not shown). NE sensors 11 are respectively provided. Figure 14
The electronic control unit (E) that controls the engine 1 is indicated by
CU). The ECU 14 is a digital computer of a known type, and has a configuration in which a central processing unit (CPU), read-only memory (ROM), random access memory (RAM), and input/output ports are connected via a bidirectional bus.

The ECU 14 performs the air-fuel ratio control of the present invention, and for this purpose, inputs signals from the aforementioned sensors and performs calculations to control the fuel injection amount of the fuel injection valves 12 and 13. 2 to 4 are flowcharts showing a first embodiment of the air-fuel ratio control operation by the ECU 14. FIG. This routine is performed every 120 degrees of rotation of the crankshaft in response to the NE pulse signal from the NE sensor 11, prior to execution of fuel injection.

FIG. 2 shows a preparatory stage for starting air-fuel ratio control. In steps 101 to 103, a cylinder group for which air-fuel ratio control is to be performed is determined. This determination is made by setting the value of flag m to either 1 or 2. In this embodiment, when m=1, it represents the cylinder group on the right bank of the engine, and when m=2, it represents the cylinder group on the left bank of the engine, and the value of m is alternately 1 and 2 each time the routine is executed. The control of the right bank and the control of the left bank are performed alternately (step 1).
01-103).

Next, in step 104, the engine speed N, load parameter Q/N,
In addition to the cooling water temperature THW, the current output VOXm of the O2 sensor 8 or 9 of the bank corresponding to the value of the flag m and the O2 sensor output VOXOLDm from the previous execution of the routine are read. Here, the engine speed N is the NE from the NE sensor 11.
By counting pulse signals, Q/N is calculated as the intake air amount per engine revolution, which is obtained by dividing the intake air amount Q obtained from the output of the air flow meter 4 by the engine rotation speed N. ), and E
The one stored in the RAM of the CU 14 is used.

Next, in step 105, it is determined whether conditions for performing air-fuel ratio feedback control (F/B control) are satisfied. Air-fuel ratio feedback control can be used, for example, when starting the engine, increasing the amount of fuel when it is cold (THW<50°C), or cutting the fuel during engine braking.
This is not performed if the O2 sensor has not reached its activation temperature, so if any of these conditions is met (feedback control is not performed), proceed to step 106 and set the feedback correction coefficient FAFm to 1.0. , proceed to step 120 in FIG. 3 and FAFm as described below.
The fuel injection amount (injection time) TAUm is calculated using the value of , and the routine ends.

If the feedback condition is satisfied in step 105, air-fuel ratio feedback control is performed in steps 107 and subsequent steps in FIG. i.e. step
107 is the O2 sensor output VOXm read this time.
is the reference voltage VO (in this example, VO = 0.45V)
Determine whether it is higher. If VOXm≧0.45V, that is, the air-fuel ratio is on the rich side, in step 108, it is determined from the previous O2 sensor output VOXOLDm whether the air-fuel ratio at the time of the previous execution was on the rich side.

If VOXOLDm≧0.45V, that is, the previous time was also rich, the process proceeds to step 110, and the value obtained by subtracting the integral constant KIL from the feedback correction coefficient FAFm-1 of the previous execution is set as the current feedback correction coefficient FAFm. Then step 118
After updating the value of VOXOLDm and storing it in the RAM of the ECU 14 in preparation for the next routine execution, step 1
20, the fuel injection time TAUm is calculated. The fuel injection time TAUm is the time during which the fuel injection valves 12 and 13 are held open, and is a value proportional to the fuel injection amount. Step 12
As shown in 0, TAUm is obtained as a time obtained by multiplying the basic injection time Tp by a value obtained by subtracting 1.0 from the sum of correction coefficients FAFmi and FGmi.

[0019] The basic injection time Tp is the engine load Q/N.
This is a time that is determined separately from the rotation speed N, and FGmi
is a coefficient for correcting variations due to engine operating conditions, engine aging, manufacturing tolerances of fuel injection valves and other parts, etc., and is determined by a routine not shown separately, but will not be explained as it is not directly related to the present invention. Omitted. If the feedback condition is not satisfied in step 105, TAUm is determined only by Tp and FGmi since FAFmi is set to 1.0 in step 106.

If the previous air-fuel ratio was on the lean side (VOXOLDm<0.45V) in step 108, the routine is executed immediately after the air-fuel ratio changes from lean to rich, so it is necessary to perform the skip control described above. be. Therefore, the process proceeds to step 112, and it is determined whether or not skipping is possible based on the value of the flag XRS. If XRS≠1, the torque fluctuation will not become excessive even if skip control is performed, so in step 114, the current FAFm is set by subtracting the skip value RSL from the previous FAFm value, and step 1
Set XRS to 1 at step 14 and VO at step 117
After updating the XOLDm, the TA is
Determine Um. Since the skip value RSL is larger than the integral constant KIL, when step 114 is executed, TAUm
decreases in a stepwise manner, and the air-fuel ratio changes rapidly (Fig. 6
(see (a)).

Flag XRS is a flag indicating whether or not air-fuel ratio skip control has just been performed, and is set to 1 when skip control is performed (step 116), and thereafter held at XRS=1 for a predetermined period of time. In this embodiment, in order to prevent excessive torque fluctuations from occurring due to continuous skip control, the skip control is performed immediately after the skip control is performed, that is, when XRS=1 in step 112. Step 120 is executed using the same value of FAFm as before without performing step 120. At this time, VO
Since XOLDm is not updated (step 117), skip control is performed when XRS≠
This will be done if it becomes 1. In other words, the current skip control will be delayed until a predetermined period of time has elapsed since the previous execution of the skip control. As a result, torque fluctuations caused by the skip control are dispersed, and drivability does not deteriorate.

FIGS. 4 and 5 each show a routine for resetting the flag XRS to zero, that is, a routine for determining the period for which the state of XRS=1 is maintained. The routine in FIG. 4 is performed as part of the fuel injection execution routine, and
The number of fuel injections CINJ after RS is set to 1 is counted, and in this example, when CINJ becomes 6 or more, that is, after XRS = 1, the crankshaft is
I try to reset the XRS after the rotation is over. Further, FIG. 5 shows a routine for resetting the XRS after a certain period of time has elapsed regardless of the rotation of the crankshaft. In this embodiment, a routine that increments the counter CXRS every 32 milliseconds is executed, and when CXRS≧6, that is, the routine for every 32 milliseconds is repeated six times (after 192 milliseconds have elapsed),
I am trying to reset the RS.

[0023] In normal operation, the interval at which skip control is performed is about 2 to 3 Hz, which is a sufficiently longer period than the time during which the above-mentioned XRS is reset (time during which skip is delayed), so skip control is performed at intervals of approximately 2 to 3 Hz. The delay does not cause any engine control problems. As described above, by controlling the skips in both cylinder groups to be performed at intervals of a certain period of time or more, the air-fuel ratios in both cylinder groups change with a certain phase difference.
Excessive torque fluctuations due to overlapping skips are prevented.

[0024] By the way, conventional control has been used to further shift the phase of the air-fuel ratios of both cylinder groups so that changes in air-fuel ratios of both cylinder groups are in opposite phases, thereby canceling out torque fluctuations of both cylinder groups. Are known. For example, in Japanese Patent Application Laid-open No. 190631/1984, the phase of the air-fuel ratio change in both cylinder groups is changed by 1/2 period so that the air-fuel ratio in both cylinder groups changes symmetrically around the stoichiometric air-fuel ratio. A method of controlling is disclosed. According to the method described in the publication, skip control in the opposite direction is always performed simultaneously in both cylinder groups, and the torque fluctuations in both cylinder groups are in opposite phases and cancel each other out, making it possible to keep torque fluctuations low overall. .

However, the device disclosed in the above publication has a problem in that it is not possible to perform air-fuel ratio feedback control independently for each cylinder group. In addition, as shown in Fig. 1, the exhaust pipes of both cylinder groups are merged, and a three-way catalytic converter is installed on the downstream side of the engine.
Problems may occur if the air-fuel ratio control described in 90631 is performed. In other words, when the air-fuel ratio control described in the above publication is performed, the air-fuel ratio changes of both cylinder groups are always in opposite phases, so the air-fuel ratio changes of both cylinder groups cancel each other out downstream of the exhaust pipe confluence, and the air-fuel ratio changes at the catalyst inlet are reduced to zero. The fuel ratio ends up being a substantially constant value. As is well known, in a three-way catalyst, CO, HC
, NOx vary extremely sensitively to the air-fuel ratio of the exhaust gas, and the conversion efficiency of the three components mentioned above is fully exhibited only within an extremely narrow air-fuel ratio range centered around the stoichiometric air-fuel ratio.

However, in reality, it is difficult to control the air-fuel ratio within this narrow range, so by periodically varying the air-fuel ratio as shown in FIG. 6 around the stoichiometric air-fuel ratio, the O2 storage effect of the catalyst can be reduced. Operations are being carried out to increase exhaust gas purification efficiency. In other words, since the catalyst has a function to adsorb excess oxygen that is not used in the reaction (O2 storage function), by periodically changing the air-fuel ratio, excess oxygen can be absorbed when the air-fuel ratio changes to the lean side. can be adsorbed and used in the reaction when the air-fuel ratio changes to the rich side, making it possible to improve the exhaust purification efficiency as a whole.

However, when the air-fuel ratio does not fluctuate as in JP-A-60-190631, good exhaust purification cannot be obtained unless the air-fuel ratio is always maintained within a narrow range around the stoichiometric air-fuel ratio. It disappears. As a practical matter,
Due to problems such as variations in the O2 sensor itself, installation location, injection amount tolerance of the fuel injector, and problems with operating conditions, it is nearly impossible to maintain the exhaust gas at the stoichiometric air-fuel ratio with high accuracy, so the method in the above publication was used. In this case, deterioration of exhaust emissions is unavoidable. On the other hand, in the present invention, as shown in FIG. 7, the air-fuel ratio changes are in opposite phases in both cylinder groups (
), the minimum interval TI for skip control is maintained, so the air-fuel ratio of the exhaust after merging (Figure (c))
A certain level of variation is ensured, and the above-mentioned problems do not occur.

Next, FIGS. 8 and 9 show flowcharts of a second embodiment of air-fuel ratio control of the present invention. In this embodiment as well, the steps in FIG. 2 are executed prior to the control steps in FIGS. 8 and 9, as in the embodiment in FIG. 3. In the embodiment of FIG. 3 described above, if skipping is prohibited (XRS=1) in step 112 or 113, FAF
However, as shown in Figure 6(a), by the time the O2 sensor output has reversed, the air-fuel ratio has already deviated significantly from the stoichiometric air-fuel ratio, and the control From above, it is preferable to correct the FAF as soon as possible. Therefore, in this embodiment, although skipping is not performed in this case, the FAF is corrected by integral control until the XRS is reset (step 250,
Step 251). By controlling in this way, it is possible to prevent the air-fuel ratio from becoming excessively shifted due to skip prohibition. Note that the control steps in FIGS. 8 and 9 are the same control operations as the control steps in FIG. 3 in which the last two digits of the step numbers are common, so the explanation will be omitted.

Next, FIGS. 10 and 11 show flowcharts of a third embodiment of air-fuel ratio control of the present invention. In this embodiment as well, the control shown in FIG. 2 is performed prior to the control shown in FIGS. 10 and 11, and the steps that have the same last two digits of step numbers show the same control operation as shown in FIG. 3. Similar to the example. This embodiment is different from the first and second embodiments in that when skipping is prohibited, a small skip is executed, and the required skip amount is obtained by adding up these skips.

In other words, if skipping is prohibited when the air-fuel ratio changes from lean to rich (if XRS=1 in step 312 in FIG. 10), during the prohibited period, skipping will be 1/3 of the normal size. Repeat (step 351 in FIG. 10). Skip 1/3 3 times until the ban is lifted.
If the total skip amount reaches the required amount after executing the process several times, the process proceeds from step 352 to step 317 in FIG.
OLDm is updated to prevent the skip from being executed again after the prohibition is lifted. In addition, if the skip prohibition is canceled before executing 1/3 skip three times, in step 314A of FIG. 10, the amount of skips that is obtained by subtracting the amount of skips executed so far from the required amount of skips is performed to obtain the total amount of skips required. Make sure it's the same amount. By controlling in this manner, it is possible to further improve controllability than in the second embodiment while preventing torque fluctuations from becoming excessive.

FIGS. 12 and 13 are diagrams illustrating the torque fluctuation suppressing effect when air-fuel ratio control is performed according to the present invention. Figure 12 shows the torque fluctuation (Figure 12(b)) when air-fuel ratio skip control is continuously performed on both cylinder groups during conventional control of a V6 engine (Figure 12(a)).
It shows. One cycle of air-fuel ratio change (a) in the figure is about 500 milliseconds,
The skip amount is approximately 5% of the total amount of fuel injected. Also, the torque fluctuation ((b)) is at engine speed 2000 rpm.
m (i.e. 16 revolutions / 500 milliseconds 48 explosions)
Assuming that, the average value of the torque during the previous six explosions is plotted. Furthermore, Fig. 13 shows the case where the skip of one cylinder group is delayed under the same conditions as above (Fig. 13(a)
)) shows the torque fluctuation (Fig. 13(b)). Figure 12(b)
) compared to rapid fluctuations in torque (I in Fig. 12(b),
It can be seen that the portion indicated by III) is prevented.

[0032]

Effects of the Invention As described above, when the air-fuel ratio of two cylinder groups having separate exhaust systems is feedback-controlled using an air-fuel ratio detector installed in the exhaust pipe, the present invention provides feedback control for both cylinder groups for a predetermined period of time. By providing a means for prohibiting continuous execution of the skip control within the vehicle, excessive torque fluctuations can be prevented and discomfort felt to the driver can be eliminated.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing the configuration of an engine to which an air-fuel ratio control device of the present invention is applied.

FIG. 2 is a flowchart showing a first embodiment of the control operation of the air-fuel ratio control device of the present invention.

FIG. 3 is a flowchart showing a first embodiment of the control operation of the air-fuel ratio control device of the present invention.

FIG. 4 is a flowchart showing a first example of an operation for setting a skip control prohibition period.

FIG. 5 is a flowchart illustrating a second embodiment of the skip control prohibition period setting operation.

FIG. 6 is a diagram illustrating the relationship between the air-fuel mixture and exhaust gas air-fuel ratio and the O2 sensor output.

FIG. 7 is a diagram illustrating air-fuel ratio changes due to control according to the present invention.

FIG. 8 is a flowchart showing a second embodiment of the control operation of the air-fuel ratio control device of the present invention.

FIG. 9 is a flowchart showing a second embodiment of the control operation of the air-fuel ratio control device of the present invention.

FIG. 10 is a flowchart showing a third embodiment of the control operation of the air-fuel ratio control device of the present invention.

FIG. 11 is a flowchart showing a third embodiment of the control operation of the air-fuel ratio control device of the present invention.

FIG. 12 is a diagram showing torque fluctuations caused by a conventional air-fuel ratio control device.

FIG. 13 is a diagram showing torque fluctuations in air-fuel ratio control of the present invention.

[Explanation of symbols]

1...Engine 2...Intake manifold 5...Intake pipe 6, 7...Exhaust pipe 8, 9...O2 sensor 12, 13...Fuel injection valve 14...Electronic control unit (ECU) 15...Three-way catalytic converter

Claims (1)

[Claims] [Claim 1] Dividing a plurality of cylinders into two groups,
The fuel supply amount to each cylinder group is independently controlled so that the air-fuel ratio becomes a predetermined value based on the output of the air-fuel ratio detection means provided in each exhaust system of the engine, which has an independent exhaust system for each cylinder group. When the air-fuel ratio changes from lean to rich, the fuel supply amount is reduced in steps by a predetermined amount, and when the air-fuel ratio changes from rich to lean, the fuel supply amount is reduced in steps by a predetermined amount. The air-fuel ratio control device includes means for performing an increasing correction, further comprising means for prohibiting the stepwise fuel supply amount correction from being performed continuously between the two cylinder groups within a predetermined period. Air-fuel ratio control device.