JPS62233440A - Fuel injection control device of internal combustion engine - Google Patents

Abstract

PURPOSE:To reduce discharge of unburnt gas and protect an exhaust catalyst from being deteriorated by stopping feedback control and feedback correction factor at standard value in the case where an output signal of an oxygen concentration detector is continued at set voltage or less for a preset time. CONSTITUTION:A electronic control unit 30 determines if output voltage V of an oxygen concentration detector 20 is less than set voltage V1 when an engine is operated. And a counter is operated when out put voltage V is less than set voltage V1, and it is determined whether a deceleration flag is set or not after a preset time (t) passes. A feed-back correction factor is fixed at a standard value in non-decelerated operation without setting the deceleration flag. On the other hand, the feedback correction factor is made to increase up to the upper limit during any deceleration operation with the deceleration flag is set. Accordingly, a fuel injection time is made to be longer than the minimum injection time, to prevent an air-fuel mixture from excessively being diluted, and discharge of unburnt gas is reduced.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a fuel injection control device for an internal combustion engine.

[Conventional technology]

The fuel injection time is calculated from the intake air amount and engine rotation speed detected by the air flow meter, and the fuel injection time is calculated from the engine rotation speed detected by the air flow meter. Internal combustion engines with cut-off of supply are known. In this internal combustion engine, the fuel supply is stopped only when deceleration operation is started at a rotation speed higher than the fuel cut rotation speed, as described above. Therefore, when deceleration operation is started at a rotation speed lower than the fuel cut rotation speed, fuel continues to be supplied, and in this case, the fuel injection time is calculated from the intake air amount and the engine rotation speed.

However, when the intake air amount is detected by an air flow meter, when deceleration operation starts, the meter plate of the air flow meter rotates too much in the closing direction, so the detected intake air amount does not match the actual intake air amount. It may be considerably lower than that. In this case, the fuel injection time calculated from the intake air amount and engine speed becomes extremely short, resulting in a problem of misfire. In order to solve this problem, an internal combustion engine has a minimum injection time determined in advance, and when the fuel injection time becomes shorter than the minimum injection time during deceleration operation, the fuel injection time is set to the minimum injection time. is publicly known (Japanese Unexamined Patent Publication No. 59-53647)
(see Japanese Patent Publication No. 138245/1983),
However, in these internal combustion engines, even if the fuel injection time is set to the minimum injection time during deceleration operation, the air-fuel mixture becomes lean, resulting in a misfire and the unburned gas is over-oxygenated and discharged into the engine exhaust system. is discharged. When unburned gas is discharged with too much oxygen in this way, the oxidation reaction in the catalyst becomes active, causing the catalyst to overheat, resulting in problems such as catalyst deterioration or cracking. .

On the other hand, fuel injection 11. which achieves the stoichiometric air-fuel ratio by multiplying the basic injection time determined by the engine operating state by a feedback correction coefficient that changes based on the output signal of the oxygen concentration detector. In an internal combustion engine that calculates between % and 100%, by performing feedback control even during deceleration operation, the air-fuel ratio can be brought closer to the stoichiometric air-fuel ratio than when feedback control is not performed. Therefore, performing feedback control during deceleration operation can prevent the air-fuel mixture from becoming extremely lean.1. Since the amount of unburned gas discharged is also reduced, overheating of the catalyst can be prevented.

[Problem that the invention seeks to solve]

However, when performing feedback control based on the output signal of the oxygen concentration detector in this way, for safety reasons, the output signal of the oxygen concentration detector must remain below a predetermined set voltage value for a certain period of time 41P. When this happens, it is necessary to stop the feedback control, reduce the feedback correction coefficient to a reference value (for example, 1.0), and fix it at the reference value. However, when the feedback correction coefficient is lowered to the reference value in this way, the fuel injection time is reduced to the minimum injection time, and as a result, the air-fuel mixture becomes even leaner.

If the air-fuel mixture becomes even leaner, misfires are more likely to occur, and unburnt gas is discharged in an excess of oxygen, causing problems such as overheating and deterioration of the catalyst.

[Means for solving problems]

In order to solve the above problems, according to the present invention, fuel injection is performed to achieve the stoichiometric air-fuel ratio by multiplying the basic injection time determined by the engine operating state by a feedback correction coefficient that changes based on the output signal of the oxygen concentration detector. calculate the time,
In a fuel injection control device that sets the fuel injection time to the minimum injection time when the calculated fuel injection time is shorter than a predetermined minimum injection time, the output signal of the oxygen concentration detector is set when the vehicle is not decelerating. When the voltage remains below a predetermined set voltage value for a certain period of time, the feedback control is stopped and the feedback correction coefficient is fixed at the reference value. When the voltage is below the set voltage value, feed pack control is continued.

〔Example〕

Referring to Figure 1, 1 is the engine body, 2 is the piston, and 3
is a combustion chamber, 4 is a spark plug, 5 is an intake valve, 6 is an intake boat,
7 indicates an exhaust valve, 8 indicates an exhaust boat, and intake boat 6.
is connected to a surge tank 10 via a branch pipe 9. The surge tank 10 is connected to the air cleaner 1 via the intake duct 11.
2, and a throttle valve 13 connected to an accelerator pedal is disposed within the intake duct ll. A fuel injection valve 14 is installed in each branch pipe 9, and fuel is injected from the fuel injection valve 14 into the corresponding intake boat 6. Each fuel injection valve 14 is connected to an electronic control unit 30, and the fuel injection valve 14 is controlled by an output signal of the electronic control unit 30.

The electronic control unit 30 is composed of a digital computer, which is interconnected by a bidirectional bus 31 and includes ROMs (read only memory) 3 each having a known function.
2. RAM (Random Access Memory) 33. CP
It has a U (microprocessor) 34, an input port 35 and an output port 36. The output port 36 is a drive circuit 37 , 38 , 39 .

It is connected to the corresponding fuel injection valve 14 via 40.

A water temperature sensor 15 that generates an output voltage proportional to the engine cooling water temperature in response to the engine cooling water temperature is attached to the engine body 1, and the water temperature sensor 15 is connected to the human-powered boat 35 via an AD converter 41. Furthermore, a distributor 16 is attached to the engine body 1, and this distributor 16 is equipped with a TDC sensor 17 that detects the intake top dead center of any one cylinder, and a TDC sensor 17 that outputs a reference pulse every time the crankshaft rotates 30 degrees. A crank angle sensor 18 is attached. These TDC sensor 17 and crank angle sensor 18 are connected to input port 35. Further, an exhaust manifold 19 is connected to the exhaust port 8, and an oxygen concentration detector 20 is inserted into the exhaust manifold 19. The output voltage of the oxygen concentration detector 20 changes depending on whether excess oxygen exists in the exhaust gas, that is, whether the air-fuel ratio of the air-fuel mixture supplied into the engine cylinder is greater than the stoichiometric air-fuel ratio. This oxygen concentration detector 20 is an AD converter 4
2 to a human-powered boat 35. Although not shown in the drawings, the exhaust manifold 19 is connected to a catalytic converter. A throttle switch 21 is connected to the valve shaft of the throttle valve 13, and the throttle switch 21 is connected to an input port 35. This throttle switch 2
1 is turned on when the throttle valve 13 is closed to the idling opening. Further, a negative pressure sensor 22 is attached to the surge tank IO, and this negative pressure sensor 22 is connected to the AD
It is connected to input port 35 via converter 43 . Negative pressure sensor 22 generates an output voltage proportional to the negative pressure within surge tank 10 . Furthermore, the vehicle speed sensor 23 is connected to the input port 35 . This vehicle speed sensor 23 generates an output pulse with a frequency proportional to the vehicle speed.

Next, with reference to FIG. 2, the feedback correction coefficient will first be explained. In FIG. 2, ■ indicates the output voltage of the oxygen concentration detector 20, and FAF indicates the feedback correction coefficient. The oxygen concentration detector 20 generates an output voltage of about 0.1 volt when there is excess oxygen in the exhaust gas, that is, when the air-fuel ratio of the air-fuel mixture supplied into the engine cylinder is larger than the stoichiometric air-fuel ratio, When there is almost no oxygen in the exhaust gas, that is, when the air-fuel ratio of the air-fuel mixture supplied into the engine cylinder is smaller than the stoichiometric air-fuel ratio, an output voltage of about 0.9 volts is generated. The output voltage of this oxygen concentration detector 20 is compared with a reference voltage 0, for example 0.45 volts, in an electronically controlled unit 30. As shown in FIG. 2, when the output voltage of the oxygen concentration detector 20 becomes higher than Vo, the feedback correction coefficient F
AF is decreased, and when the output voltage of the oxygen concentration detector 20 becomes lower than Vo, the feedback correction coefficient FAF
is made to increase.

The fuel injection time τ is basically determined by multiplying the basic injection time τp, which is determined from the negative pressure P in the surge tank 10 and the engine speed NE, by the feedback correction coefficient FAF. That is, the basic injection time τp is corrected by the feedback correction coefficient FAF based on the output signal of the oxygen concentration detector 20 so that the air-fuel ratio of the air-fuel mixture supplied into the engine cylinder becomes the stoichiometric air-fuel ratio. The basic injection time τp is preset so that the air-fuel ratio of the air-fuel mixture supplied into the engine cylinder is approximately the stoichiometric air-fuel ratio, so normally FAF is approximately around 1.0 as shown in section a in Figure 2. takes the value of However, when the air-fuel mixture supplied into the engine cylinders becomes linear as during deceleration operation, the output voltage of the oxygen concentration detector 20 decreases as shown in the section of FIG. 2. At this time, if the output voltage of the oxygen concentration detector 20 continues to become lower than Vo, FAF continues to increase. Further, the output voltage of the oxygen concentration detector 20 is set to a set voltage value 1, for example 0.5, which is separate from the reference voltage Vo in the electronic control unit 30.
Compared to 5 volts. This set voltage value (1) is set slightly higher than the reference voltage Vo. When a certain period of time elapses after the output voltage of the oxygen concentration detector 20 falls below the set voltage value V1, the lean flag is set as will be described later. Note that FAF is programmed to continue to be 1.2 when it reaches a predetermined upper limit, for example 1.2, but a description of this program will be omitted.

Next, the control method according to the present invention will be explained with reference to FIG. In Figure 3, NE is the engine speed, τ is the fuel injection time, T is the catalyst temperature of the catalytic converter, and FAF
is the feedback correction coefficient, and the lean flag is the set voltage value v1 when the output signal of the oxygen concentration detector 20 continues for a certain period of time.
This is a flag that is set when the following conditions occur. This lean flag is reset when the ignition switch is turned on.

When deceleration operation is started at time S in FIG. 3, the fuel injection time τ decreases to near the predetermined minimum injection time τmin. The extent to which the fuel injection time τ decreases depends on the engine speed when deceleration starts, and when the engine speed when deceleration starts is relatively high, the minimum injection time τmin is reduced as shown in the third barrier. When the engine speed is relatively low when deceleration is started, the injection time is reduced to the minimum injection time τmin. At this time, the basic injection time τmi determined from the engine speed and the like is shorter than the basic injection time that sets the air-fuel ratio to the stoichiometric air-fuel ratio. Therefore, at this time, the air-fuel mixture is lean, and in this way the air-fuel mixture should be enriched (
F A, F rises. Further, at this time, if unburned gas is discharged to the exhaust manifold 19 due to a misfire, the oxidation reaction becomes active due to excess oxygen, and the catalyst temperature T rises. If the mixture continues to become lean after deceleration operation, FAF
reaches the upper limit value (=1.2) 6 Then, while deceleration operation is being performed, FAF is maintained at the upper limit value, and thus the fuel injection time τ continues to take longer than τsin.

Therefore, since the air-fuel mixture does not become extremely lean, misfires are less likely to occur, and the amount of unburned gas discharged is reduced, making it possible to prevent the catalyst from overheating.

Conventionally, as shown by the broken line in FIG. 3, a lean flag is set when the output signal of the oxygen concentration detector 20 continues to be below the set voltage value for a certain period of time t. When the lean flag is set, feedback control is stopped and FAF is fixed at the reference value (=1.O). At this time, the fuel injection time τ decreases to the minimum injection time τmin. As a result, the air-fuel mixture supplied into the engine cylinder becomes even more lean, and the amount of unburned gas discharged into the exhaust manifold 19 increases. In this way, the catalyst temperature T continues to rise as shown by the broken line,
As a result, the catalyst will deteriorate. However, in the present invention, even if the output signal of the oxygen concentration detector 20 continues to be below the set voltage value V1 during engine deceleration operation, the lean flag is not set, and therefore the FAF continues to be maintained at the upper limit value.

As a result, since the fuel injection time τ is set longer than the minimum injection time τmin, it is possible to prevent the catalyst from overheating.

Next, a fuel injection control method according to the present invention will be explained with reference to FIGS. 4 to 7.

FIG. 4 shows the fuel injection processing routine. Referring to FIG. 4, first, in step 50, it is determined whether or not fuel is being cut. When the engine speed at the start of deceleration operation is higher than a predetermined fuel cut speed, the fuel supply is stopped, that is, the fuel is cut. This fuel cut processing is performed in a separate routine. In step 50, it is determined in this separate routine whether fuel cut processing is being performed, and if fuel cut is being performed, the processing cycle is completed. If the fuel is not being cut, the process proceeds to step 51, where it is determined whether the throttle switch 21 is on, that is, whether the throttle valve 13 is in the idling position. Throttle switch 21
is on, the process advances to step 52, and the vehicle speed sensor 23
It is determined from the output signal whether the vehicle speed V is equal to or higher than a predetermined constant speed Vo. If V>Vo, the process proceeds to step 53 where a deceleration flag is set, and then the process proceeds to step 54. Therefore, the process proceeds to step 53 during deceleration operation and when fuel cut is not being performed.

On the other hand, if the throttle switch 21 is not on, or if -≦-Vo, the process proceeds to step 55, where a deceleration flag is set. Next, the process proceeds to step 54, where the feedback correction coefficient FAF is calculated, and then, at step 56, the fuel injection time τ is calculated. Figure 5 shows the lean flag processing routine.
Figure 6 shows the calculation processing routine of FAF.
The figure shows a calculation processing routine for fuel injection time.

Referring to FIG. 5, first, in step 60, it is determined whether the output voltage (2) of the oxygen concentration detector 20 is lower than the set voltage value v1. Next, in step 61, a counting operation is started from when V becomes less than 1. This counting operation is performed, for example, by a counter. Next, in step 62, it is determined from the count value of the counter whether a certain period of time t (FIG. 3) has elapsed since V became below v1. If the predetermined time t has not elapsed, the processing routine is completed. On the other hand, if the predetermined time t has elapsed, the process proceeds to step 63, where it is determined whether or not the deceleration flag is set. If the deceleration flag is not set, that is, if deceleration operation is not being performed, a lean flag is set in step 64, and then the process proceeds to step 65, where FAF is fixed at the reference value (=1.0). On the other hand, when the deceleration flag is set, that is, when deceleration operation is being performed, the processing cycle is completed. Therefore, in this case, the third
As shown in the figure, FAF increases to the upper limit value (=1.2) and is maintained at the upper limit value. On the other hand, ■λ■1
If so, the process proceeds to step 66, where the counter is reset, and then, at step 67, the lean flag is reset.

Next, a routine for calculating the feedback correction coefficient FAF will be explained with reference to FIG. Referring to FIG. 6, first, in step 70, it is determined whether the lean flag is set. If the lean flag is set, the processing routine is completed and therefore FAF is fixed at 1.0 in this case. on the other hand,
If lean flag is not set, step 7
1, it is determined whether the output voltage V of the oxygen concentration detector 20 is smaller than the reference voltage Vo, that is, whether it is lean. In addition, the output voltage of the oxygen concentration detector 20 is as follows.
When is larger than the reference voltage Vo, it is said to be rich. V<
In the case of Vo, that is, when the engine is lean, the process proceeds to step 72, where it is determined whether or not the engine has just changed from rich to lean. If it has just changed from rich to lean, proceed to step 73 and skip the predetermined skip! i1X is added to FAF. As a result, FAF skips IX
only to rise rapidly. On the other hand, if it is lean but not immediately after changing from rich to lean, the process proceeds to step 74 and a constant value A (<X) is added to FAF. As a result, FAF is gradually increased. On the other hand, in step 71 ■-≧-V.

When it is determined that it is rich, step 75
Then, it is determined whether the state has just changed from lean to rich. If it has just changed from lean to rich, the process proceeds to step 76 and a predetermined skip amount yfJ<a is calculated from the FAF.
A constant value B (<Y) is subtracted from .

Next, a routine for calculating the fuel injection time τ will be explained with reference to FIG. Referring to FIG. 7, first, in step 80, the basic fuel injection time τp is determined from the output signal of the negative pressure sensor 22 representing the manifold negative pressure and the output signal of the crank angle sensor 18 representing the engine speed. τp is stored in the ROM 32 as a function of manifold negative pressure and engine speed, for example.

Next, in step 81, the fuel injection time τ is set to τ=τp.
-FAF- is calculated from the formula +τV.

Here, K is a constant determined by water temperature, etc., and τV is an invalid injection time. Next, in step 82, it is determined whether the fuel injection time is shorter than a predetermined minimum injection time τm1n (FIG. 3). If r<τmin, then τ□10 is determined in step 83, and the processing cycle is completed. Therefore, the fuel injection time τ does not become less than τmin. When the calculation of the fuel injection time τ is completed, the process proceeds to step 57 in FIG. 4, where fuel is injected from the fuel injection valve 14.

〔Effect of the invention〕

If feedback control is performed during deceleration operation to prevent misfires during deceleration operation, even if the output signal of the oxygen concentration detector remains below the set voltage value for a certain period of time, the feedback correction coefficient will decrease to the reference value. It is maintained at the upper limit without being forced. the result,
Preventing the catalyst from being overheated and deteriorating because the fuel injection time is longer than the minimum injection time so that the air-fuel mixture does not become extremely lean, thus reducing the amount of unburned gas emissions. I can do it.

[Brief explanation of drawings]

Figure 1 is an overall diagram of the internal combustion engine, Figure 2 is a diagram showing changes in the feedback correction coefficient FAF, Figure 3 is a time chart showing changes in fuel injection time τ, etc., and Figure 4 is a diagram showing execution of fuel injection processing. Fig. 5 is a flowchart for processing the beam flag, Fig. 6 is a flowchart for calculating the feedback correction coefficient FAF, Fig. 7 is a flowchart for calculating the fuel injection time τ. It is 1. lO...Surge tank, 14...Fuel injection valve, 19...Exhaust manifold, 20...Oxygen concentration detector, 21...Slosotros inch, 22...Negative pressure sensor.

Claims (1)

[Claims] The fuel injection time to achieve the stoichiometric air-fuel ratio is calculated by multiplying the basic injection time determined by the engine operating state by a feedback correction coefficient that changes based on the output signal of the oxygen concentration detector, and the calculated fuel injection time is predetermined. In a fuel injection control device that sets the fuel injection time to the minimum injection time when the fuel injection time is shorter than the set minimum injection time, the output signal of the oxygen concentration detector is set to a predetermined set voltage value when the vehicle is not decelerating. When the following conditions continue for a certain period of time, the feedback control is stopped and the feedback correction coefficient is fixed at the reference value, and the output signal of the oxygen concentration detector is below the predetermined set voltage value when the vehicle is decelerating. A fuel injection control device for an internal combustion engine that continues feedback control when the engine is running.