JPH03189349A - Air-fuel ratio controlling for engine - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a device for controlling the air-fuel ratio of an engine equipped with an electronically controlled fuel injection device.

[Conventional technology]

2. Description of the Related Art Conventionally, some engines whose fuel injection amount is adjusted by electronic control are equipped with an air-fuel ratio control device for automatically controlling the air-fuel ratio.

This device calculates the basic fuel injection amount to obtain a good air-fuel ratio based on the intake flow rate detected by an air flow meter, etc., and calculates the feedback correction amount based on the detected value of a 0° sensor, etc. The final fuel injection amount is set from these values.

Incidentally, the fuel injection amount by the injector and the like is controlled by changing the pulse width of the signal output to the injector. However, as shown in the graph of Fig. 7, the relationship between the pulse width and the actual fuel injection amount is good or close in the region where the pulse width is relatively large (see the solid line), but when the pulse width is In a small region (see broken line), it is very unstable and it is difficult to obtain the desired fuel injection amount. Therefore, in the past, when the calculated final fuel injection amount was less than a preset lower limit value, such as during sudden deceleration, a value larger than this calculated fuel injection amount was set as the actual fuel injection amount. (see Japanese Utility Model Publication No. 58-35633), or by fixing the actual fuel injection amount to the above lower limit value, a stable and reliable fuel injection amount can be obtained.

[Problem to be solved by the invention]

In the above device, when the calculated fuel injection amount is below the lower limit value, the actual fuel injection amount is set to be richer than the calculated ideal fuel injection amount.
The feedback correction amount continues to be calculated based on the detected value of the 02 sensor, so even while the fuel injection amount is fixed at a constant value, the feedback correction amount continues to move in the direction of returning the air-fuel ratio to the phosphorus side. become. Therefore, when the calculated fuel injection amount returns to a value higher than the lower limit value due to idling, the feedback correction amount that had been set to the lean side will not return to the calculated result due to the response delay. This may cause a temporary overlean phenomenon in the engine, leading to problems such as engine stalling.

In view of these circumstances, the present invention adjusts the actual fuel injection amount so that a good air-fuel ratio is always maintained when the calculated fuel injection amount falls below the lower limit value and when it returns to the lower limit value or more. The purpose is to provide a device that can be controlled.

[Means to solve the problem]

The present invention provides a fuel injection amount calculation means for calculating a final fuel injection amount based on a basic fuel injection amount based on an intake flow rate and a feedback correction amount based on an air-fuel ratio detection signal, and a fuel injection amount calculation means for calculating a final fuel injection amount based on the calculation result. In an air-fuel ratio control device for an engine, which is equipped with a control means for controlling a fuel injection amount, when the calculated fuel injection amount is less than or equal to a preset lower limit value, the actual fuel injection amount is adjusted to the lower limit value. The fuel injection control apparatus includes a setting means for setting the amount, and a stopping means for stopping the calculation of the feedback correction amount when the actual fuel injection amount is set to the lower limit value.

[For production]

According to the above configuration, since the calculation of the feedback correction amount is also stopped when the calculated fuel injection amount is fixed at the lower limit value, the feedback correction amount is prevented from progressing toward the lean side while in this fixed state. It will be done. Therefore, when the calculated fuel injection amount later returns to the lower limit value or more, a feedback correction amount suitable for that time is set without causing a response delay.

〔Example〕

FIG. 2 shows the overall configuration of an engine in one embodiment of the present invention. In the figure, 10 is an engine main body, each cylinder of which is provided with a piston 12, and above this piston 12 a combustion chamber 14 is formed. An intake valve 16, an exhaust valve 18, a spark plug 20, etc. are arranged at a position facing the combustion chamber 14, and an intake passage 22 and an exhaust passage 24 are connected to positions communicating with the intake valve 16 and exhaust valve 18, respectively. ing.

In the intake passage 22, an air flow meter 26 for detecting the intake flow rate, a throttle valve 28, and an injector 30 for directly supplying fuel to the engine are arranged in this order, and the upstream and downstream parts of the throttle valve 28 form a bypass passage. 3
1. Further, the exhaust passage 24 is provided with an 02 sensor 32 that detects the oxygen concentration in the exhaust gas, and the engine body 10 is provided with a water temperature sensor 34 that detects the engine water temperature. These 02 sensor 32, water temperature sensor 34, and air flow meter 2
A detection signal such as No. 6 is input to the ECU 40.

This ECU 40 has a functional configuration as shown in FIG.

In the figure, the fuel injection amount calculating means 42 calculates a basic pulse width TP according to the basic fuel injection amount based on the detected flow rate Q of the air flow meter 26 and the engine rotation speed N, and also calculates the basic pulse width TP according to the basic fuel injection amount The 02 feedback correction amount CFB is calculated based on the signal, and the pulse width Ti corresponding to the final fuel injection amount is calculated from these values and other correction amounts.

The control means 44 basically controls the fuel injection amount calculation means 4.
Based on the result calculated in step 2, a signal having a corresponding pulse width is output to the injector 30, thereby controlling the actual fuel injection amount.

The setting means 46 sets the pulse width T1 calculated by the fuel injection amount calculation means 42 to a preset lower limit value T1m1n.
If it is below, the pulse width of the signal output by the control means 44 is forcibly set to the lower limit value T1m1n.

Furthermore, the stopping means 48, which is a feature of this device, sets the pulse width Ti to a lower limit value T1 by the setting means 46.
When other conditions (to be described in detail later) are satisfied at the time when iin is fixed, the calculation of the 02 feedback correction amount by the fuel injection amount calculation means 42 is stopped. Further, in this embodiment, the pulse width Ti calculated by the fuel injection amount calculation means 42 is equal to the lower limit value T 1
When the value returns to Illin or higher, the initial value of the 02 feedback correction amount is set to a predetermined setting value.

Next, the details of the actual control of the air-fuel ratio by this device will be explained with reference to the flowcharts of FIGS. 3 and 4.

FIG. 3 shows the process of calculating the actual fuel injection amount. First, various input signals are read in the ECU 40 (step S). Then, the basic pulse width TP corresponding to the basic fuel injection amount is calculated by multiplying the value obtained by dividing the intake flow rate Q by the engine rotation speed N (that is, the intake air amount per engine rotation) by a certain coefficient K. (Step S2). Next, various correction amounts including the o2 feedback correction amount CFB are calculated (step S3), and the final pulse width Ti is calculated based on the total correction amount C1, the basic pulse width T1, and the invalid injection time TV ( Step S4).

Here, if the calculated pulse width Ti exceeds the preset lower limit T1m1n (step S5
(NO), the signal with this pulse width Ti is output as is to the injector 30 (step S7), but if the pulse width Ti is less than or equal to the lower limit T1m1n, then (
YES in step S5), and this lower limit value T1m1n is set as the pulse width Ti to be output (step S6
) is output to the injector 30 (step 37).

That is, the calculated pulse width Ti is the lower limit value T 1m1
If it is less than or equal to n, the pulse width of the output signal is fixed to T1m1n.

On the other hand, the o2 feedback correction amount CFB is set by the process shown in FIG.

First, if the feedback condition is not satisfied (NO in step Sll), the 02 feedback correction amount CFB
is set to 0 (step 502).

For example, if the engine is in a relatively low rotation and low load region,
The above feedback condition also applies when the engine water temperature is in a stable state of 60° C. or higher.

When the feedback condition is satisfied (YES in step S11), the following four conditions (1): The calculated pulse width Ti is less than or equal to the lower limit T 1m1n (that is, the pulse width is fixed at T 1m1n). .

(2) The bypass flow rate is decreasing (that is, the engine is likely to become rich).

(3) 02 feedback correction amount CFB is set value (
Here, it is less than 0%).

(4) A certain amount of time has passed.

If all are satisfied (each step 313 to S16
YES), stop the calculation of the o2 feedback correction amount CFB, and set the correction amount CFB to the set value (+15% here)
(Step S□7), and if the flag is 0 (No in Step 318), the flag is inverted to 1 (Step 519).

It should be noted that to determine whether or not the certain period of time in condition (4) has elapsed, a dedicated timer may be provided, or an 02 sticking timer used for failure determination, etc. may be used. This 02 sticking timer detects whether the elapsed time has reached the set time T when the output of the 02 sensor 32 sticks to the rich side as shown in FIG. 5, and this timer is used. In this case, it is sufficient to check whether the remaining count number M is below a predetermined value.

On the other hand, if at least one of the above four conditions is not satisfied (No in any of steps S L3 to S16), it is determined whether the current flag is 1 or not, that is, the 02 feedback correction It is determined whether or not the calculation of ff1cFB has been stopped, and if the flag is 1 (YES in step S20), that is, if the calculation of CFB has been stopped, the 02 feedback correction amount CFB is set to the set value ( =+15%) (step 521), and the flag is inverted to 0 (step 522).

On the other hand, if the current flag is 0 (step S
20), that is, if the 02 feedback correction amount CFB has not been fixed before, the 02 feedback correction amount CFB is calculated based on the detection signal of the O2 sensor 32 as usual, and the value is used as the actual correction amount. (step 523).

As described above, in this device, the calculated pulse width T1
However, if the pulse width Ti falls to a region where the linearity between the actual fuel injection amount and the actual fuel injection amount decreases, the pulse width Ti is fixed to the lower limit value T 1m1n, thereby improving the stability of the fuel injection amount. can be kept. Moreover, when the pulse width T1 is fixed to T1m1n, the 02 feedback correction amount CF
Since the calculation of B is stopped, the calculated pulse width Ti is lower than the lower limit value T, for example during idling.
Even when it returns to 1m1n or more, by setting the 02 feedback correction amount to an appropriate initial value, it is possible to prevent the overlean phenomenon caused by the delay in response of the feedback correction amount as in the conventional case.

That is, as shown in FIG. 6, in the conventional device,
Even if the fuel injection pulse is fixed at T1m1n (see area A in the diagram), the calculation of the 02 feedback correction amount continues, so even if the fuel injection pulse exceeds Tiin, the response will be delayed and the 0° feedback correction amount will be reduced. remains biased toward the lean side (see dashed line 60 in the figure), and this could lead to occasional overlean conditions.
According to this device, since the 02 feedback correction amount does not fluctuate as the fuel injection pulse is fixed, a good air-fuel ratio can be maintained even after the fixation is released.

In addition, in this example, the calculated pulse width T1 is lower limit value T.
When returning to 1m1n, 02 feedback correction J
iCFB to a preset constant value (in this case +15%)
), but for example, 0 after this return
2. The calculation of the feedback correction amount CFB may be started from the calculated value immediately before the calculation is stopped.

〔Effect of the invention〕

As described above, the present invention sets the actual fuel injection amount to the lower limit value when the calculated fuel injection amount is less than or equal to the preset lower limit value, and also sets the actual fuel injection amount to the lower limit value. Since the calculation of the feedback correction amount is stopped when the pulse width is set to , the calculation of the feedback correction amount is stopped when the pulse width returns to a sufficient value while maintaining the stability of the fuel injection amount in the region where the pulse width is small. Therefore, it is possible to prevent a shift in the feedback correction amount due to a delay in response as in the prior art, and this has the effect of preventing inconveniences such as over-lean.

[Brief explanation of drawings]

FIG. 1 is a functional configuration diagram of an ECU provided in an engine according to an embodiment of the present invention, FIG. 2 is an overall configuration diagram of the engine, and FIGS. 3 and 4 show control operations performed by the ECU. Flowchart, FIG. 5 is a diagram showing the detection signal of the 02 sensor provided in the engine, FIG. 6 is a graph showing the relationship between the engine speed, fuel injection amount, and 02 feedback correction amount in the same engine, and FIG. It is a graph showing the relationship between the pulse width of the signal output to the injector and the actual fuel injection amount. DESCRIPTION OF SYMBOLS 10... Engine body, 26... Air flow meter, 30... Injector, 32... 02 sensor, 4
0...ECU, 42...Fuel injection amount calculation means, 44
. . . control means, 46 . . . setting means, 48 . . . stopping means.

Claims (1)

[Claims] 1. A fuel injection amount calculation means for calculating the final fuel injection amount based on the basic fuel injection amount based on the intake flow rate and a feedback correction amount based on the air-fuel ratio detection signal, and a fuel injection amount calculation means for calculating the final fuel injection amount based on the calculation result. In an air-fuel ratio control device for an engine, the actual fuel injection amount is set to the lower limit value when the calculated fuel injection amount is less than or equal to a preset lower limit value. and stopping means for stopping the calculation of the feedback correction amount when the actual fuel injection amount is set to the lower limit value.