JPS6123633Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to an air-fuel ratio control device for an internal combustion engine, and particularly relates to a feedback control stop function at high temperatures.

Recently, an air-fuel ratio control device has been developed that detects the air-fuel ratio of an air-fuel mixture based on the concentration of exhaust gas components of an engine and performs feedback control so that the air-fuel ratio becomes a constant value.

In the air-fuel ratio control device as described above, when feedback control is performed, the air-fuel ratio is forcibly controlled to a constant value, for example, the stoichiometric air-fuel ratio (14.8). Therefore, some systems are equipped with means for stopping feedback control when the air-fuel ratio is desired to be set to a value other than the stoichiometric air-fuel ratio, for example, when the air-fuel mixture is desired to be enriched at times of high load, sudden acceleration, or low temperatures.

By the way, if the engine temperature becomes higher than the normal operating temperature (for example, 90 degrees Celsius or higher), the temperature of the fuel supplied to the fuel injectors and carburetor will also rise, which may cause the density of the fuel to decrease or parts may evaporate, making engine operation unstable. If feedback control is performed in such a case, the fuel supply may become unstable, which may cause hunting or engine stall.

In conventional equipment, feedback control was stopped at low temperatures as described above, but no consideration was given to abnormalities at high temperatures, resulting in the problem of unstable operating conditions as described above. Ta.

The present invention was made in view of the above problems, and includes a first means for calculating the basic amount of fuel based on signals of engine load and engine rotation, and an output of the first means to be detected by an engine temperature sensor. a second means for calculating the fuel injection amount by correcting it using a correction coefficient that changes according to the signal and an air-fuel ratio feedback coefficient that changes according to the signal from the exhaust sensor; a third means for detecting the temperature of the engine; a fourth means for detecting until a predetermined time has elapsed from the starting point when the engine is started at a high temperature higher than a predetermined value, or until the integrated rotational speed reaches a predetermined value;
A fifth means for fixing the air-fuel ratio feedback coefficient based on the signal of the fourth means, stopping the feedback control, and supplying the fuel injection amount based on the basic amount and the correction coefficient. By having
An object of the present invention is to provide an air-fuel ratio control device that improves drivability and stability after starting an engine at high temperatures.

The present invention will be explained in detail below based on the drawings.

FIG. 1 is a block diagram of an example of an air-fuel ratio control device to which the present invention is applied.

In Fig. 1, 1 is a combustion chamber, 2 is an intake pipe, and 3 is a combustion chamber.
is a throttle valve, 4 is an opening sensor that detects the throttle valve opening, 5 is an intake air amount sensor that detects the amount of intake air, 6
is an exhaust pipe, 7 is an exhaust sensor, 8 is an exhaust purification device such as a three-way catalyst, 9 is a water temperature sensor that detects the temperature of cooling water in the water jacket, 10 is a neutral switch that detects the neutral position of the transmission, Numeral 11 is a vehicle speed sensor that detects the vehicle speed from the rotation of the drive shaft of the transmission, for example, and 12 is a rotation sensor that detects the engine rotational speed, such as a crank angle sensor that outputs a pulse for each unit angle of the crankshaft. Further, 13 is an arithmetic unit, which is composed of, for example, a microcomputer including a central processing circuit (CPU), ROM, RAN, input/output interface, and the like. Further, 14 is a fuel injection valve.

Next, the operation will be explained.

Signals from the various sensors 4, 5, 7, 9, 10, 11, and 12 are provided to the arithmetic unit 13. The arithmetic unit 13 calculates the amount of fuel to be supplied that is suitable for the current operating state based on each of the above-mentioned signals. The fuel injection valve 14 operates according to the calculation result, and injects fuel in an amount corresponding to the calculated fuel supply amount, for example, once per engine rotation.

The injected fuel mixes with air flowing in through the intake pipe 2 to form an air-fuel mixture, which enters the combustion chamber 1 and is combusted.

The exhaust gas after combustion is discharged via the exhaust pipe 6 and the exhaust purification device 8.

When the exhaust purification device 8 is a three-way catalyst, HC and CO in the exhaust gas are oxidized and NOx is reduced and purified, but the conversion efficiency at this time is determined by the fact that the air-fuel ratio of the mixture is the stoichiometric air-fuel ratio. Maximum when it is hot.

The exhaust sensor 7 detects the concentration of components in the exhaust gas. The characteristics of a zirconia oxygen meter generally used as the exhaust sensor 7 are shown in FIG. In FIG. 2, the point λ=1 indicates the stoichiometric air-fuel ratio.

As can be seen from Fig. 2, when the output voltage Vo of the exhaust sensor 7 is larger than the reference value Vs, the air-fuel ratio is smaller than the stoichiometric air-fuel ratio, and when Vo is smaller than Vs, the air-fuel ratio is larger than the stoichiometric air-fuel ratio. .

Next, the operation of the arithmetic unit 13 will be explained using a microcomputer as an example.

The CPU in the arithmetic unit 13 performs arithmetic operations according to a program stored in the ROM. RAM is also used to temporarily store data and input values during calculations.

Next, the contents of the calculation in the calculation device 13 will be explained using the flowcharts shown in FIGS. 3 and 4.

Figure 3 is a general flowchart for calculating the fuel injection amount.

In FIG. 3, first, in block 21, the intake air amount Q and the rotational speed N are read. Note that Q is a signal from the intake air amount sensor 5, and N is a signal from the rotation sensor 12.

Next, in block 22, the basic quantity Tp is calculated from N and Q.
Calculate. Note that if K is a constant, Tp=KQ/N.

Next, in block 23, a correction coefficient C corresponding to the water temperature and acceleration/deceleration state of the engine is calculated.

Next, in block 24, a feedback coefficient α of the air-fuel ratio is calculated. The details of this block 24 will be described later.

Next, in block 25, each of the above blocks 2
The fuel injection amount Ti=Tp×C×α is calculated based on Tp, C, and α calculated in steps 2, 23, and 24.

Note that the calculation in Fig. 3 is performed for each rotation of the engine, for example.
This is done once at a time, but it may also be done at regular intervals.
Alternatively, only the calculation of block 24 may be performed once per rotation, and the calculations of other blocks may be performed at regular intervals.

Next, the operation of block 24 will be explained in detail.

FIG. 4 is a flowchart showing the contents of block 24 of FIG.

In FIG. 4, first, in block 31, it is determined whether to perform air-fuel ratio feedback control or stop it.

Stopping conditions include, for example, when the water temperature is low, when the exhaust sensor is not activated due to low temperature, when fuel is cut off, when fuel is increased due to high load or sudden acceleration, etc. If these conditions are met, feedback control is activated. stop.

If it is determined in block 31 that the engine will not stop, the process goes to block 32 and reads the output voltage Vo of the exhaust sensor.

Next, in block 33, the output voltage Vo and the reference value are
When Vo≧Vs, that is, when the air-fuel ratio is smaller than the stoichiometric air-fuel ratio, the process goes to block 34, and Vo<
When Vs, that is, when the air-fuel ratio is greater than the stoichiometric air-fuel ratio, the process goes to block 35.

In blocks 34 and 35, a proportional control component P and an integral control component I are calculated.

First, in block 34, since the air-fuel ratio is small, the values of P and I are made small in order to control the air-fuel ratio to be large. That is, as P, give P _R (P _R <0), and as I, I=ι _R ×
Give Tp. Therefore, in this case, P<0, and the value of I decreases by ι _R ×Tp for each rotation.

On the other hand, in block 35, since the air-fuel ratio is large, the values of P and I are increased in order to control the air-fuel ratio to be small. That is, P _L (P _L >0) is given as P, and I+ι _L ×Tp is given as I. Therefore, in this case, P>0, and the value of I is ι _L ×
It will increase by Tp.

Next, in block 36, a feedback coefficient α=P+I is calculated from P and I.

On the other hand, if it is determined in block 31 that the feedback control should be stopped, the process goes to block 37, where I=1, α
= 1. If the feedback coefficient α is fixed to 1, the feedback control will be stopped.

The present invention relates to the stop condition of block 31 in FIG. 4, and is configured to stop the feedback control immediately after starting when the engine temperature is higher than a predetermined value.

Next, FIG. 5 is a flowchart of one embodiment of the present invention, showing the contents of block 31 in FIG.

In the flowchart of FIG. 5, it is determined in block 51 whether the engine has just started, that is, whether a predetermined period of time has elapsed since the start, or whether the cumulative rotational speed has reached a predetermined constant number. However, the feedback control is configured to stop immediately after startup and when the cooling water temperature is 90°C or higher.

The reason for this configuration is that the fuel condition becomes especially unstable in many cases when restarting at high temperatures (hot restart), and the feedback control stop at high temperatures is only performed immediately after startup. Even if it is limited to , the effect remains almost the same. Furthermore, by limiting the feedback control to only immediately after starting as described above, the period during which the feedback control is stopped can be shortened, thereby making it possible to both prevent deterioration of exhaust gas and improve engine drivability.

As explained above, according to the present invention, the feedback control is stopped immediately after starting at high temperatures, the air-fuel ratio feedback coefficient is clamped, and the fuel injection amount is adjusted to Ti=Tp×
Since it is calculated as C, the fuel injection amount can be corrected according to the engine load, engine speed, and engine temperature, and the fuel can be supplied appropriately according to the operating condition, so it is possible to avoid starting due to a rise in fuel temperature. It is possible to eliminate problems such as immediate hunting and engine stalling, and it is possible to improve engine operability and stability. In addition, by limiting the feedback control to only immediately after startup at high temperatures, the period during which the feedback control is stopped can be shortened, thereby making it possible to prevent deterioration of exhaust gas and improve engine drivability.

[Brief explanation of the drawing]

Fig. 1 is a diagram of an example of an air-fuel ratio control device to which the present invention is applied, Fig. 2 is an output characteristic diagram of an exhaust sensor, and Fig. 3 is a general flowchart for calculating the fuel injection amount.
FIG. 4 is a flowchart of air-fuel ratio control, and FIG. 5 is a flowchart of an embodiment showing the determination of stop conditions according to the present invention. Explanation of symbols, 1... Combustion chamber, 2... Intake pipe, 3
... Throttle valve, 4 ... Opening sensor, 5 ... Intake amount sensor, 6 ... Exhaust pipe, 7 ... Exhaust sensor, 8 ...
Exhaust purification device, 9...Water temperature sensor, 10...Neutral switch, 11...Vehicle speed sensor, 12...
...Rotation sensor, 13...Arithmetic unit, 14...Fuel injection valve.

Claims (1)

[Scope of utility model registration request] In an air-fuel ratio control device that feedback-controls an air-fuel ratio of an air-fuel mixture based on a signal from an exhaust sensor that detects the concentration of exhaust gas components, a first means for calculating a basic amount of fuel based on signals of engine load and engine rotation. and,
a second means for calculating a fuel injection amount by correcting the output of the first means with a correction coefficient that changes according to a signal from an engine temperature sensor and an air-fuel ratio feedback coefficient that changes according to a signal from an exhaust sensor; a third means for detecting the temperature of the engine; and a third means for detecting the temperature of the engine until a predetermined period of time has elapsed from the time of starting when the engine temperature is higher than a predetermined value;
or fourth means for detecting until the cumulative rotational speed reaches a predetermined value, and fixing the air-fuel ratio feedback coefficient based on the signal of the fourth means, stopping the feedback control, and adjusting the fuel injection amount to the desired value. An air-fuel ratio control device comprising: a fifth means configured to supply based on a basic amount and the correction coefficient.