JP2000130221A - Fuel injection control device of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the discharge amount of NOx by making the inside of a three way catalyst a reducing atmosphere promptly at the re-start time of a fuel injection after a fuel cut. SOLUTION: When a throttle is fully closed and a rotation speed is high, a speed reduction fuel cut is shifted (S1, S2). When a condition for re-starting a fuel injection from a fuel cut state is established (S3), it is judged whether the re-start of the injection is carried out by a acceleration or not (S4). When the fuel injection is re-started following to the acceleration, the increase amount level is set largely as the fuel cut time is longer (S5) and the fuel injection amount is increased and corrected in response to the increase amount level (S6).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel injection control device for an internal combustion engine, and more particularly to a fuel injection control after a fuel cut.

[0002]

2. Description of the Related Art Conventionally, in a vehicle internal combustion engine, as a measure for improving fuel efficiency, fuel injection into the engine is temporarily performed in a deceleration operation state in which a throttle valve is fully closed and an engine speed is equal to or higher than a predetermined speed. A so-called deceleration fuel cut to stop the engine has been performed.

[0003]

By the way, during the fuel cut, a lot of oxygen is introduced into the three-way catalyst, and the three-way catalyst has an oxygen storage capacity for storing oxygen. Even if fuel injection is restarted, the inside of the three-way catalyst gradually shifts from the oxidizing atmosphere to stoichiometric. Therefore, especially when re-acceleration from the fuel cut state,
While the three-way catalyst is maintained in the oxidizing atmosphere, there is a problem that the conversion rate of NOx decreases and the amount of NOx emission increases.

The present invention has been made in view of the above problems, and has as its object to provide a fuel injection control device for an internal combustion engine that can reduce the amount of NOx emission when fuel injection is restarted after a fuel cut.

[0005]

According to the present invention, there is provided an internal combustion engine having a catalyst in an exhaust system of an engine and configured to temporarily stop fuel injection to the engine under predetermined operating conditions. A fuel injection control device, wherein when fuel injection is resumed from a temporary stop state of the fuel injection, a recovery time increasing means for increasing the fuel injection amount so as to return the inside of the catalyst to a reducing atmosphere is provided. And

According to this configuration, when fuel injection is restarted, the fuel injection amount is increased and corrected to increase the emissions of CO and HC, and the oxygen stored in the catalyst during the fuel cut is reduced to C.
O and HC are consumed for oxidation, so that the oxidizing atmosphere is quickly eliminated.

The fuel injection amount may be increased by so-called interrupt injection in which an additional injection is performed during the normal injection in addition to the normal fuel injection amount increase correction. In the invention described in claim 2, the recovery time increasing means is configured to set the increasing level of the fuel injection amount according to the time during which the fuel supply is stopped.

With this configuration, the longer the fuel cut time, the greater the oxygen storage amount, and the greater the demand for increasing the fuel to return to the reducing atmosphere when fuel injection is resumed. Is variably set so that the amount is increased by an amount corresponding to the oxygen storage amount.

In the invention according to claim 3, the recovery time increasing means is configured to perform the increase correction of the fuel injection amount only at the time of restarting the fuel injection accompanying the shift to the acceleration operation.
According to such a configuration, when the fuel injection is restarted because the rotation speed has fallen below the recovery rotational speed during the deceleration fuel cut, the fuel injection is restarted by depressing the accelerator (opening change of the throttle valve) without performing the increase correction of the fuel injection amount. Sometimes, increase the fuel.

[0010]

According to the first aspect of the present invention, when the fuel injection is restarted after the fuel cut, the inside of the catalyst can be quickly returned to the reducing atmosphere.
This has the effect of reducing x emission.

According to the second aspect of the present invention, the amount of fuel can be increased and corrected by an amount necessary for returning the inside of the catalyst to the reducing atmosphere, and deterioration of fuel efficiency due to the increased correction can be minimized. .

According to the third aspect of the invention, in particular, NOx
By performing the increase correction only at the time of re-acceleration after the fuel cut in which the emission amount increases, there is an effect that the NOx emission amount can be effectively reduced, and deterioration of fuel efficiency due to the increase correction can be suppressed.

[0013]

Embodiments of the present invention will be described below. FIG. 1 is a diagram illustrating a system configuration of an internal combustion engine according to the embodiment.

In FIG. 1, a fuel injection valve 2 is provided in an intake passage of an internal combustion engine 1, and a mixture of fuel injected from the fuel injection valve 2 and air measured by a throttle valve 3 is provided. Is sucked into the cylinder via the intake valve 4. The combustion mixture in the cylinder is ignited and burned by spark ignition by the spark plug 5, and the combustion exhaust is discharged to the exhaust passage 7 via the exhaust valve 6.

A three-way catalyst 8 having an oxygen storage capacity is interposed in the exhaust passage 7, and the three-way catalyst 8 purifies CO, HC and NOx in the exhaust gas. The control unit 10 incorporates a microcomputer, determines a fuel injection amount based on detection signals from various sensors, and controls fuel injection by the fuel injection valve 2.

The various sensors include a throttle sensor 11 for detecting the opening TVO of the throttle valve 3, an air flow meter 12 for detecting the intake air flow rate Q of the engine 1,
A crank angle sensor 13 for detecting a crank angle; a water temperature sensor 14 for detecting a cooling water temperature Tw of the engine 1;
An air-fuel ratio sensor 15 that outputs a signal corresponding to the exhaust air-fuel ratio in response to the oxygen concentration in the exhaust gas is provided on the upstream side.

The control unit 10 calculates the engine speed Ne based on the detection signal from the crank angle sensor 13, and calculates the basic fuel injection amount Tp based on the engine speed Ne and the intake air flow rate Q. Further, the basic fuel injection amount Tp is adjusted to a correction coefficient set according to the cooling water temperature Tw or the like, or an air-fuel ratio set so that the air-fuel ratio detected by the air-fuel ratio sensor 15 matches the stoichiometric air-fuel ratio. Correction is made by a feedback correction coefficient or the like to determine the final fuel injection amount Ti. Then, an injection pulse signal having a pulse width corresponding to the fuel injection amount Ti is output to the fuel injection valve 2 at a predetermined injection timing to cause the engine 1 to inject and supply fuel.

Further, in a deceleration operation state in which the throttle valve 3 is fully closed and the engine speed Ne is equal to or higher than a predetermined speed, a shift is made to a so-called deceleration fuel cut in which fuel injection by the fuel injection valve 2 is temporarily stopped. When the valve 3 is opened or the engine rotation speed Ne falls below a predetermined recovery rotation speed, fuel injection is restarted.

Further, when the deceleration fuel cut is restarted, the fuel injection amount is corrected to be increased. The state of the increase correction will be described in detail with reference to the flowchart of FIG. Note that, in the present embodiment, the function as the recovery time increasing means is provided by software in the control unit 10 as shown in the flowchart of FIG.

In the flowchart of FIG. 2, in step S1, it is determined whether or not deceleration fuel is being cut.
In step S1, it is determined whether a deceleration fuel cut condition is satisfied. The deceleration fuel cut condition is, as described above, a deceleration operation state in which the throttle valve 3 is fully closed and the engine speed Ne is equal to or higher than a predetermined speed.

If the deceleration fuel cut condition is not satisfied, the routine proceeds to step S8, in which fuel injection is performed normally. If the deceleration fuel cut condition is satisfied, step S2 is performed.
Then, the fuel cut by which the fuel injection by the fuel injection valve 2 is temporarily stopped is executed.

When the fuel cut is started, step S3
Then, it is determined whether or not the fuel injection restart condition (recovery condition) is satisfied. As described above, when the throttle valve 3 is opened or when the engine rotation speed Ne falls below a predetermined recovery rotation speed, it is determined that the restart condition is satisfied.

When the fuel injection restart condition is satisfied, the process proceeds to step S4, and it is determined whether or not the restart condition is satisfied by opening control of the throttle valve 3, that is, by acceleration.

Here, there is no opening control of the throttle valve 3,
When it is determined that the restart condition is satisfied because the engine rotation speed Ne has fallen below the predetermined recovery rotation speed, the routine jumps to step S8 and immediately resumes normal fuel injection.

On the other hand, when it is determined that the restart condition is satisfied by the opening control of the throttle valve 3, the process proceeds to step S5, and the fuel injection amount increasing level is set based on the time during which the fuel cut has been performed. Specifically, as shown in FIG. 3, as the fuel cut time becomes longer, that is, as the oxygen storage amount in the three-way catalyst 8 increases, the increase level is increased.

The increase of the fuel injection amount is based on the basic fuel injection amount Tp.
And the air-fuel ratio feedback correction coefficient is rich-clamped, and an additional injection (interrupt injection) is performed between normal injections.

In the case of increasing the fuel by rich clamping of the increase correction coefficient or the air-fuel ratio feedback correction coefficient, if the increase correction period is fixed, the increase level corresponds to the increase correction coefficient or the clamp value. If the increase correction coefficient or the clamp value is fixed, the increase level indicates a period during which the increase by the increase correction coefficient or the rich clamping of the air-fuel ratio feedback correction coefficient is performed. Further, a configuration may be adopted in which the longer the fuel cut, the larger the increase rate by the increase correction coefficient or the clamp value, and the longer the increase period. Further, the increase level shown in FIG. 3 may indicate the initial value of the increase correction coefficient or the clamp value, and thereafter, the increase correction coefficient or the clamp value may be reduced at a constant rate.

On the other hand, when increasing fuel by interrupt injection, the increase level indicates the increase level as an interrupt injection amount, the number of interrupt injections, or a combination of the interrupt injection amount and the number of interrupt injections. .

When the increase level is set in step S5,
Proceeding to step S6, the fuel injection is restarted by adding the fuel increase at the fuel increase level. In step S7, it is determined whether or not the increased amount addition condition has been canceled. That is, when the fixed or variable increase period (or the number of interrupt injections for increasing the amount) determined by the setting of the increase level in step S5 has elapsed, it is determined that the increase condition has been canceled, and step S8 is performed. Proceed to. In step S8, the normal fuel injection control is performed, in which the increase in the amount by the increase level in step S5 is not added.

If it is not determined in step S7 that the additional fuel increase condition is canceled, the correction for increasing the fuel when the fuel is restarted is continued. As described above, when the fuel injection is restarted from the fuel cut, by performing the increase correction based on the increase level according to the fuel cut time, the oxidizing atmosphere due to the oxygen stored in the three-way catalyst 8 during the fuel cut is reduced. It is possible to return to the reducing atmosphere promptly after restarting the fuel injection, and it is possible to avoid an increase in the emission amount of NOx when exiting the fuel cut state by acceleration.

Further, by setting the increase level variably in accordance with the fuel cut time, it is possible to perform the minimum increase correction necessary for returning the inside of the three-way catalyst 8 from the oxidizing atmosphere to the reducing atmosphere. Deterioration of fuel efficiency due to the correction can be suppressed.

Further, when the fuel injection is restarted due to the engine rotation speed falling below the recovery rotation, the amount of NOx at the catalyst inlet is sufficiently small. Since the amount does not increase significantly, the increase correction is performed only when fuel injection is restarted by the acceleration at which the NOx amount increases at the catalyst inlet. This also makes it possible to suppress deterioration in fuel efficiency. However, the increase correction may always be performed irrespective of the conditions for restarting the fuel injection.

[Brief description of the drawings]

FIG. 1 is a diagram showing a system configuration of an internal combustion engine according to an embodiment.

FIG. 2 is a flowchart showing the state of injection control at the time of resuming injection after a fuel cut in the embodiment.

FIG. 3 is a diagram showing a correlation between a fuel cut time and an increase level in the embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Internal combustion engine 2 Fuel injection valve 8 Three-way catalyst 10 Control unit 11 Throttle sensor 12 Air flow meter 13 Crank angle sensor

Claims (3)

[Claims] 1. A fuel injection control device for an internal combustion engine, comprising: a catalyst in an exhaust system of the engine, and configured to temporarily stop fuel injection to the engine under predetermined operating conditions. A fuel injection control device for an internal combustion engine, further comprising a recovery time increasing means for increasing and correcting the fuel injection amount to return the inside of the catalyst to a reducing atmosphere when fuel injection is restarted from a temporary stop state. 2. The fuel injection control device for an internal combustion engine according to claim 1, wherein said recovery time increasing means sets an increasing level of the fuel injection amount according to a time during which fuel supply is stopped. 3. The internal combustion engine according to claim 1, wherein the recovery time increasing means performs the increasing correction of the fuel injection amount only when the fuel injection is restarted due to the shift to the acceleration operation. Fuel injection control device.