JPS6217341A - Air fuel ratio controller - Google Patents

Abstract

PURPOSE:To reduce the quantity of NOx (nitrogen oxides) emission at the low temperature of an engine, by setting the air fuel ratio thereof at a low-fuel- concentration ratio when the temperature of cooling water is not higher than a preset reference level. CONSTITUTION:When the temperature of cooling water detected by a water temperature sensor 2 is not higher than a reference level, a central controller 10 calculates a basic pulse width to apply a basic calve opening time to an injector 40 to equalize the air fuel ratio of an engine to a low-fuel-concentration ratio. When the detected water temperature has exceeded the reference level due to the completion of warm-up and such a condition as to make it necessary to change the set air fuel ratio to a theoretical ratio exists, the air fuel ratio is gradually changed from the low-fuel-concentration ratio to the theoretical ratio. At such time, the set air fuel ratios for the cylinders of the engine are changed one by one from the low-fuel-concentration ratio to the theoretical ratio at every prescribed number of rotations of the engine. The change in the torque of the engine when the air fuel ratio is charged, is thus reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a device for controlling the air-fuel ratio of a multi-cylinder internal combustion engine.

[Prior Art] Recently, some automobiles are being equipped with internal combustion engines that can operate even at an air-fuel ratio greater than the stoichiometric air-fuel ratio, that is, at a lean air-fuel ratio. This type of air-fuel ratio control for a multi-cylinder internal combustion engine improves acceleration by gradually changing the set air-fuel ratio from the lean air-fuel ratio to the stoichiometric air-fuel ratio as the engine load increases. A proposal aimed at reducing the torque change when changing the set air-fuel ratio at the same time as improving the setting air-fuel ratio?
No. 8-53659.

``Problems to be Solved by the Invention'' By the way, even in a multi-cylinder internal combustion engine that can be operated at a lean air-fuel ratio, it is desirable to promote warm-up when the engine is cold, as in a normal internal combustion engine. As a measure for this in the control device, for example, when the cooling water temperature representing the engine temperature is below a certain reference temperature indicating the presence or absence of a warm-up request, it is possible to set the air-fuel ratio to the stoichiometric air-fuel ratio.

However, when the air-fuel ratio is set to the stoichiometric air-fuel ratio when the engine is cold, the effect of promoting warm-up increases, but on the other hand, the purification ability of the exhaust system catalyst is low when the engine is cold, and a relatively large amount of NOx is emitted. There is a problem of being exposed.

In view of the above, the present invention provides that even after warm-up, when operating at a lean air-fuel ratio of about 18 to 20, NOx emissions are lower than when operating at a stoichiometric air-fuel ratio, as shown in Figure 6. By focusing on this and setting the air-fuel ratio during cold to such a lean air-fuel ratio, the objective is to reduce the amount of NOx emissions compared to when operating at the stoichiometric air-fuel ratio.

Further, in the present invention, after the air-fuel ratio is set to the lean air-fuel ratio during cold conditions, when the warm-up is completed and the conditions for changing the set air-fuel ratio to the stoichiometric air-fuel ratio are satisfied, the air-fuel ratio is set to the lean air-fuel ratio. The purpose is to reduce the torque change when switching from the lean air-fuel ratio to the stoichiometric air-fuel ratio by changing the set air-fuel ratio so that the air-fuel ratio gradually becomes the stoichiometric air-fuel ratio.

[Means for Solving the Problems] In order to achieve this object, the present invention provides an apparatus for controlling the air-fuel ratio of a multi-cylinder internal combustion engine 1 that can be operated at a lean air-fuel ratio, as shown in FIG. A first means 2 that generates a signal according to the cooling water temperature of the engine 1; and according to the signal from the first means 2, the air-fuel ratio is set to lean air when the cooling water temperature is below a predetermined base Q temperature. When the air-fuel ratio is set to the stoichiometric air-fuel ratio and the cooling water temperature exceeds the reference temperature, the conditions for setting the air-fuel ratio to the stoichiometric air-fuel ratio are satisfied, and the air-fuel ratio is set to the stoichiometric air-fuel ratio for each cylinder. The second means 3 switches the fuel ratio from the lean air-fuel ratio to the stoichiometric air-fuel ratio one cylinder at a time every predetermined number of engine revolutions.

[Function] In this way, by setting the set air-fuel ratio during cold conditions to the lean air-fuel ratio, NOx emissions can be reduced, and the switching from the lean air-fuel ratio to the stoichiometric air-fuel ratio is performed gradually. This reduces torque changes.

[Embodiments of the Invention] An embodiment in which the present invention is applied to a four-cylinder internal combustion engine will be described with reference to FIGS. 2 to 5.

In FIG. 2 showing the overall configuration of this embodiment, the central control device 10 has a crank angle sensor 20 on the input side for detecting the rotation angle of the engine as well as the number of rotations at least every 180'CA. something that generates a pulse,
An air flow meter 30 for detecting the engine load and generating a signal according to the air intake amount, and a water temperature sensor 2 for detecting the engine temperature generating a signal according to the cooling water temperature, respectively. The injector 40 is electrically connected to the output side.

As shown in FIG. 3, the central control device 10 receives the NE low signal from the crank angle sensor 20 and the Q signal from the air flow meter 30, and adjusts the air pressure in response to the engine operating state indicated by these two signals. The calculation means 101 calculates the basic injector opening time, that is, the basic pulse width so that the fuel ratio becomes the stoichiometric air-fuel ratio. The signal S1 corresponding to this calculation result is converted into the input signal S2a from the first correction coefficient setting means 103a by the first multiplication means 102a, that is, the value r1. The signal @S 3 a representing this result is sent to one input terminal of the driving pulse generating means 104, and the signal S1 corresponding to the calculation result is multiplied by the signal representing OJ by the second multiplying means 102b. The input signal S2b from the second correction coefficient setting means 103b, that is, rl, O
A signal S3b representing this result is sent to the other input terminal of the drive pulse generating means 104. Drive pulse generation means 104
As will be described later, both signals S3a and S3b are outputted at the NE low signal according to the signal @S4 from the comparing means 107 and the signal @$8 from the stoichiometric air-fuel ratio setting condition satisfaction determining means 106. Converts to drive pulse and outputs. These output drive pulses S6a, S6b, S6c,
Each S6d is the first cylinder injector 40-
A power transistor 5C)-1 for intermittently energizing the solenoid 4O-1a of No. 1, and another similar power transistor 5C)-1 for the second cylinder.
one transistor 50-2 for the third cylinder, another similar transistor 50-3 for the fourth cylinder, and another similar transistor 50-4 for the fourth cylinder. Transistor 5 by
0 is turned on, and the injector 40 opens the valve by starting energization to the inlet noid 40a due to this switching, and the time is approximately equal to the time width of the drive pulse. An amount of fuel is injected into the engine combustion chamber.

The comparison means 107 receives the signal S5 indicating the reference temperature from the reference temperature setting means 105 and the THW signal, compares the detected water temperature with the reference temperature, and sends the signal S4 indicating the comparison result to the drive pulse generation means 104. Send. This signal S4 is, for example, logic "1" when the detected water temperature is below the base Q temperature, and logic rOJ when it is higher than the reference temperature.

When the drive pulse generation means 104 receives a signal S4 of logic "1" indicating that the detected water temperature is below the reference temperature from the comparison means 107, the drive pulse generation means 104 generates a fuel injection signal for each cylinder determined by the NE multiplication signal. At each timing, the second IJI”3
The signal S3b from the means 102b is converted into a driving pulse having a pulse width corresponding to this signal value, and the signal S3b is converted into a driving pulse having a pulse width corresponding to the signal value, and the signal S3b is converted into a driving pulse having a pulse width corresponding to the signal value. 2nd゜3rd. One pulse is distributed in a predetermined order, such as to the fourth cylinder.

Further, when the driving pulse generating means 104 is sending out the signal $8 indicating that the stoichiometric air-fuel ratio setting condition is satisfied, the signal @S4 indicates that the detected water temperature is the reference temperature. When the input is reversed from the logic "1" indicating that the temperature is below the reference temperature to the logic rOJ indicating that the temperature is higher than the reference temperature, at the injection start timing immediately after this input (referred to as the first timing 7), the 1 Is means 10
The signal S3a from the second multiplication means 102b is converted into a driving pulse, and the signal S3b from the second multiplication means 102b is converted into a driving pulse at the next injection start timing, that is, the second timing, the third timing, and the fourth timing. Convert to driving pulse. Then, at the fifth and sixth timings, the signal S3a is converted into a driving pulse, and at the seventh and eighth timings, the signal S3b is converted into a driving pulse. Then, at the 9th, 10th, and 11th timings, the signal S3a
At the 12th timing, the signal S3b is
Convert to Luz. Then, at the 13th and subsequent timings, the signal S3a continues to be converted into a driving pulse unless the signal S4 from the comparing means 107 is input again as logic "1".

FIG. 4 shows the output signal $ of the comparison means 107 as described above.
4 is a timing chart for explaining changes in the pulse width of the drive pulse S6 before and after the signal S4 is inverted from logic "1" to logic "O".

In the figure, S7a, S7b, S7c, and S7d are information in accordance with the signal S3a, such as a preset value of a down counter or a charging voltage of a capacitor, and any of the same information as described above in accordance with the signal S3b. is selected based on the logic level of signals 34 and 38 and the NE times signal.
~ or the force when discharging represents the Kunt value or the charging voltage, and when the current is not "O" or the charging voltage is not zero volts, a driving pulse is generated.

As shown in this figure, the drive pulse S6 is generated by the signal 34. Either the signal S3a or the signal S3b at S8 is once converted into the signal S7 and then generated, and its pulse width is the first, second, . Third. If all pulses to the 4th cylinder are small and $4 flips to logic "O", only the pulses to the 1st cylinder will be present in the first engine revolution, provided that the signal S8 remains at the logic "1" level. , in the second rotation, the first rotation. The pulse for the second cylinder is the same as that for the first cylinder at the third rotation. The pulses for the second and third cylinders become larger after the fourth rotation, and the pulses for all cylinders become larger.

FIG. 5 shows a flowchart when the microcomputer executes processing similar to the processing described above with reference to FIGS. 3 and 4.

The process shown in this entire figure is started every engine revolution,
First, a reference temperature is set in the same manner as the reference temperature setting means 105 described above (reference numeral 201 in the figure).

Next, similarly to the comparing means 107, the detected water temperature and the set reference temperature are compared (202>).

Thereafter, from the time when the detected water temperature is determined to be below the reference temperature, it is determined that the base Q temperature has been exceeded when it is determined that the conditions for making the set air-fuel ratio the stoichiometric air-fuel ratio are satisfied, An example in which this judgment is maintained will be explained. While the detected water temperature continues to be determined to be below the reference temperature, the first. Second. Third. The correction coefficients Kl, 2, 3, and 4 of the set air-fuel ratio for the fourth cylinder are all set to KL corresponding to the lean air-fuel ratio (203>
.

This K[ corresponds to a correction coefficient smaller than the value "1" described above. When the detected water temperature is determined to be higher than the reference temperature, the conditions for setting the set air-fuel ratio to be the stoichiometric air-fuel ratio have already been established, so immediately after this determination, the correction coefficient is set to 1. 2. to the corresponding KR and other correction coefficients. 3 and 4 are set as K[ (20
4,205.206>. Then, in the next process, that is, the second process after the judgment switch, K1, K2
to KR, K3. 4 is set to KL (207°20
8). Then, in the third process, K1, 2.
Set 3 to KR and K4 to K[ (209, 210
>. In the fourth and subsequent processes, all of Kl, 2, 3, and 4 are set to KRk (21
1>.

As mentioned above, NOx emissions can be reduced by setting the lean air-fuel ratio when the engine is cold, and since the lean air-fuel ratio is gradually switched to the stoichiometric air-fuel ratio, the The change in 10 lux becomes smaller.

[Effects of the Invention] As explained above, according to the present invention, NOx emissions can be reduced by setting the air-fuel ratio during cold conditions to an 8-lean air-fuel ratio, and Since the air-fuel ratio is gradually switched from the lean air-fuel ratio to the stoichiometric air-fuel ratio in conjunction with the setting, torque changes can be kept small.

[Brief explanation of drawings]

Fig. 1 is a block diagram of the present invention, Figs. 2 to 5 show an embodiment of the present invention, Fig. 2 is an overall block diagram, Fig. 3 is a block diagram of the central control unit, and Fig. 4 is a block diagram of the central control unit. FIG. 5 is a timing chart for explaining the processing operation, FIG. 5 is a flowchart substantially equivalent to the block configuration of FIG. 3, and FIG. 6 is an explanatory diagram of NOx emission amount with respect to air-fuel ratio. 1...Multi-cylinder internal combustion engine 2...Water temperature sensor (first means) 10...Central control unit 20...Crank angle sensor 30...Air flow meter 40... injector

Claims (1)

[Scope of Claims] 1. A device for controlling the air-fuel ratio of a multi-cylinder internal combustion engine capable of operating at a lean air-fuel ratio, comprising: a first means for generating a signal according to a cooling water temperature of the engine; According to the signal, when the cooling water temperature is below a predetermined reference temperature, the air-fuel ratio is set to a lean air-fuel ratio, and when the cooling water temperature exceeds the reference temperature,
With the establishment of the conditions for setting the air-fuel ratio to the stoichiometric air-fuel ratio,
and second means for switching the set air-fuel ratio for each cylinder from the lean air-fuel ratio to the stoichiometric air-fuel ratio one cylinder at a time every predetermined number of engine revolutions in order to gradually change the air-fuel ratio to the stoichiometric air-fuel ratio. Characteristic air-fuel ratio control device.