JP2015229930A - Engine fuel injection control unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an engine fuel injection control unit capable of achieving both the prevention of breaking of an engine due to overheat in a vehicle running state at full throttle and the improvement in exhaust gas characteristics at high level.SOLUTION: If it is determined that a vehicle reaches a full-throttle running state while an engine 1 is actuated in a high-revolving-speed, high-load range and a cylinder air-fuel ratio is controlled to a rich air-fuel ratio by stopping Ofeedback to a fuel injection quantity and increasing fuel, an increase correction coefficient K for increasing the fuel is gradually reduced to 1.0 so as to maintain the fuel injection quantity corresponding to a stoichiometric air-fuel ratio. As a result, the air-fuel ratio of the engine 1 is kept near the stoichiometric air-fuel ratio over a stoichiometric holding period Tst and the Ofeedback is executed in parallel. By limiting a transition of the air-fuel ratio to a lean air-fuel ratio in the stoichiometric holding period Tst, it is possible to prevent the overheat of the engine 1, and it is also possible to improve a purification function of a three-way catalyst 18 by the transition of the air-fuel ratio to a lean air-fuel ratio.

Description

  The present invention relates to a fuel injection control device for an engine mounted on a vehicle, and more particularly to an engine fuel injection control device that improves exhaust gas characteristics by preventing overheating of the engine when the vehicle is in a fully open running state.

  Conventionally, fuel injection control devices that electronically control the fuel supply to engines for the purpose of improving exhaust gas characteristics and fuel efficiency have become widespread, and not only for four-wheeled vehicles, but also for various motorcycles and tricycles ( This corresponds to the vehicle of the present invention, and the following description extends to the vehicle). In such vehicles, especially motorized bicycles equipped with a small displacement engine, there is not enough engine output, so there are many opportunities to drive the engine in a high rotation and high load range during travel, and more specifically when the throttle is fully opened. In addition, there are many opportunities to enter a traveling state in which the engine speed is balanced (hereinafter, such a traveling state of the vehicle is referred to as a fully opened traveling state).

Since the amount of heat generated by the engine increases in the fully open running state, it is necessary to prevent engine damage due to overheating. Therefore, after stopping the feedback control of the fuel injection amount based on the output of the O ₂ sensor that is executed in the normal running state, the fuel injection amount is increased to enrich the in-cylinder air-fuel ratio of the engine (the latent heat of vaporization). In other words, in the fully open running state, it is unavoidably disadvantageous in terms of exhaust gas characteristics and the like (in terms of fuel consumption) as compared with the normal running state.

  As a countermeasure for such a problem, for example, in the technique of Patent Document 1, execution (rich) and non-execution (lean) of fuel increase are repeated at the cycle of fuel injection timing during high-load operation of the engine. As a result, the exhaust air-fuel ratio of the engine fluctuates between rich and lean in a very short period, and the air-fuel ratio exhaust gas that has been averaged is supplied to the three-way catalyst of the exhaust system. As a result, the three-way catalyst is purified in the exhaust gas on the lean side as compared with the conventional fuel cooling in which the fuel increase is continued, and the exhaust gas characteristics are improved.

Japanese Patent Application Laid-Open No. 7-310569

However, in the technique of Patent Document 1, a trade-off relationship is established between prevention of engine damage due to overheating in high load operation and improvement of exhaust gas characteristics, and it is difficult to satisfy both requirements.
That is, according to the technique of Patent Document 1, enrichment of the in-cylinder air-fuel ratio by executing fuel increase contributes to preventing engine damage, and lean exhaust air-fuel ratio by non-execution of fuel increase improves exhaust gas characteristics. To contribute. And as the vehicle's fully-running state continues, the engine is likely to rise in temperature and breakage, while the vehicle's fully-opening state depends on various factors such as road conditions and driver's driving operation. It may end in a very short time or it may last for a very long time.

  Therefore, in order to prevent overheating of the engine even when the fully open running state continues for a long time, the technique of Patent Document 1 needs to sufficiently enrich the in-cylinder air-fuel ratio by a large fuel increase. However, such an increase in the fuel hinders the leaning of the exhaust air-fuel ratio (the air-fuel ratio after the averaging of rich and lean), and consequently the improvement of exhaust gas characteristics. Naturally, if the increase in fuel is suppressed by giving priority to improving the exhaust gas characteristics, the enrichment of the in-cylinder air-fuel ratio is hindered, and the problem is that overheating of the engine is promoted due to a decrease in latent heat of vaporization.

  The present invention has been made in order to solve such problems. The object of the present invention is to achieve both high-dimensional prevention of engine damage and improvement of exhaust gas characteristics due to overheating of the vehicle when the vehicle is fully opened. An object of the present invention is to provide a fuel injection control device for an engine.

  In order to achieve the above object, an engine fuel injection control device according to the present invention comprises a fully open determining means for determining whether or not a vehicle is in a fully open running state in which the throttle is fully open and the engine rotational speed is balanced, When the fuel injection is controlled and the fully open determining means determines that the vehicle is in the fully open running state, the fuel injection amount of the engine is increased and corrected to increase the air-fuel ratio, and the fully open determining means is used to fully open the traveling state. When it is determined, the increase correction amount by the injection amount control means is gradually decreased to a preset hold value, and the increase correction amount is kept at the hold value and held until the preset hold period elapses after the decrease. And a fully open leaning means for gradually increasing the increase correction amount from the hold value and returning to the value before the decrease when the period has elapsed.

  According to the engine fuel injection control apparatus configured as described above, when the vehicle reaches the fully open traveling state, the increase correction amount is decreased based on the determination of the fully open traveling state at an early stage, and the air-fuel ratio of the engine is maintained over the holding period. And lean. During the holding period, even if the air-fuel ratio is made lean, there is no fear of engine damage, and the exhaust gas characteristics are improved by leaning. In addition, since the initial engine in which the fully open running state is started has a relatively thermal margin, the thermal margin can be effectively used for leaning the air-fuel ratio, and the engine is fully opened. It is unpredictable how long the running state will continue, but even if it is completed in a short time, the leaning over the holding period has already been completed, so the effect of leaning will not change at all. It is done.

  In addition, during the holding period, the engine output slightly decreases due to the lean air-fuel ratio, but the increase correction amount is gradually decreasing and increasing, so there is a possibility that the driver in the fully-open running state will notice There is almost no deterioration of the driving feeling.

As another aspect, a catalyst device provided in the exhaust passage of the engine, an O ₂ sensor provided on the upstream side of the catalyst device in the exhaust passage, and an activation determination for determining whether or not the O ₂ sensor is activated. When the activation of the O ₂ sensor is judged by the means and the activation judgment means, the engine fuel injection amount is feedback controlled based on the output of the O ₂ sensor to bring the engine exhaust air-fuel ratio close to the theoretical air-fuel ratio. O ₂ feedback means for maintaining, and the fully open leaning means controls the fuel injection amount of the engine to a value corresponding to the theoretical air-fuel ratio during the holding period, and the O ₂ feedback means controls the O ₂ sensor during the holding period. It is desirable to perform the feedback control based on the output.

When configured in this way, the exhaust air / fuel ratio of the engine can be reliably controlled within the catalyst device window centered on the stoichiometric air / fuel ratio by feedback control based on the output of the O ₂ sensor during the holding period. Function is further improved.

As another aspect, the O ₂ feedback unit is configured to start feedback control based on the output of the O ₂ sensor from that time when the activation determination unit determines activation of the O ₂ sensor during the holding period. It is desirable to do.
In such a configuration, even if the O ₂ sensor is not activated at the beginning of the holding period, feedback control based on the output of the O ₂ sensor is started as soon as the O ₂ sensor is activated. Accurate air-fuel ratio control is realized, and as a result, the purification function of the catalyst device can be maximized.

As another aspect, when the fully open leaning means decreases the increase correction amount to the hold value and the output of the O ₂ sensor reaches a lean determination value set in the vicinity of the theoretical air-fuel ratio in advance, The increase correction amount is regarded as a holding value, and the decrease of the increase correction amount is stopped and kept. The O ₂ feedback means starts from the time when the fully open leaning means stops the decrease of the increase correction amount based on the output of the O ₂ sensor. It is desirable that the feedback control based on the outputs of the _two sensors is started.
In such a configuration, when the output of the O ₂ sensor reaches the lean determination value, it can be estimated that the engine exhaust air-fuel ratio exceeds the theoretical air-fuel ratio and is reversed to the lean side. By maintaining the amount, O ₂ feedback is started after controlling the exhaust air-fuel ratio of the engine to be close to the theoretical air-fuel ratio. For this reason, more accurate air-fuel ratio control is realized, and as a result, the purification function of the catalyst device can be maximized.

As another aspect, when the fully open leaning means returns the increase correction amount from the hold value to the value before the decrease as the hold period elapses, it is set based on the output of the O ₂ sensor when the hold period elapses. It is desirable to configure the value corresponding to the feedback correction amount being the first change of the increase correction amount.
When configured in this way, the torque change of the engine when the increase correction amount is returned to the value before the decrease is suppressed, and the deterioration of the running feeling due to the torque shock is prevented.

As another aspect, when the feedback correction amount at the time when the holding period has elapsed is set to the lean side, the value corresponding to the feedback correction amount is set as the initial decrease of the increase correction amount. It is desirable that the increase correction amount be gradually increased after the first time.
When configured in this way, when returning the increase correction amount to the value before the decrease, by setting the initial change amount of the increase correction amount to the decrease side corresponding to the feedback correction amount on the lean side, Engine torque change is suppressed.

As another aspect, after the increase correction amount is decreased and increased by the fully open leaning means based on the determination of the fully open running state by the fully open determining means, the increase is again increased even if the determination of the fully open running state is continued. It is desirable to further include an increase / decrease prohibiting means for prohibiting the reduction and increase of the correction amount from being made to the fully open leaning means.
When configured in this way, it is possible to prevent the increase correction amount from decreasing and increasing again when the engine has no thermal margin.

As another aspect, during learning operation for learning feedback control by the O ₂ feedback means based on the output of the O ₂ sensor during operation of the engine other than the fully open running state, and during feedback control by the O ₂ feedback means during the holding period It is desirable to further include learning prohibiting means for prohibiting the learning means from executing the learning process.
When configured in this way, the feedback control executed in the fully-open running state is significantly different from the normal feedback control in the engine operating area, and therefore mis-learning is prevented by prohibiting the execution of the learning process. It becomes possible.

  ADVANTAGE OF THE INVENTION According to this invention, the damage prevention of an engine by the overheating in the full open driving | running | working state of a vehicle and the improvement of exhaust gas characteristics can be made compatible in high dimension.

1 is a system configuration diagram showing an engine fuel injection control device of an embodiment. It is a flowchart which shows the full open stoichiometric control routine which ECU performs. It is a flowchart which shows the full open stoichiometric control routine which ECU performs. It is a time chart which shows the execution situation of full-open stoichiometric control when the O ₂ sensor has already been activated before the start of the full-open running state and the O ₂ feedback is completed on the rich side. It is a time chart which shows the execution situation of full-open stoichiometric control when the O ₂ sensor has already been activated before the start of the full-open running state and the O ₂ feedback is finished on the lean side. O ₂ sensor during stoichiometric holding period is a time chart showing the execution status of the fully open stoichiometric control when activated. It is a time chart which shows the execution situation of full-open stoichiometric control when the output of the O ₂ sensor reaches a lean determination value before decreasing to an increase correction coefficient K = 1.0.

Hereinafter, an embodiment in which the present invention is embodied in an engine fuel injection control device mounted on a motorcycle (vehicle) will be described.
FIG. 1 is a system configuration diagram showing an engine fuel injection control device of the present embodiment.
The engine 1 of this embodiment is configured as a four-cycle single-cylinder gasoline engine with a displacement of 50 cc, and is mounted on a vehicle as a driving power source. However, the specification of the engine 1 is not limited to this, and can be arbitrarily changed. For example, it may be applied to a large displacement multi-cylinder engine.

  A piston 4 is slidably disposed in a cylinder 3 formed in a cylinder block 2 of the engine 1. The piston 4 is connected to a crankshaft 6 via a connecting rod 5 and interlocked with the reciprocating motion of the piston 4. The crankshaft 6 rotates. A flywheel 7 is attached to the rear end of the crankshaft 6 (on the transmission side (not shown)), and in a predetermined angular region on the outer periphery of the flywheel 7, there is a retractor projection 7a made of a magnetic material for detecting the crank angle. Is formed.

  An intake port 9a and an exhaust port 9b are formed in the cylinder head 9 fixed on the cylinder block 2, and a spark plug 10 is disposed in a posture in which the tip faces the inside of the cylinder. An intake passage 11 connected to the intake port 9a has an air cleaner 12 from the upstream side, a throttle valve 13 that opens and closes in response to the driver's throttle operation, a bypass passage 15 having an ISCV (idle speed control valve) 14, and An injector 16 that injects fuel toward the intake port 9a is provided. The exhaust passage 17 connected to the exhaust port 9b is provided with a three-way catalyst 18 (catalyst device) for purifying exhaust gas and a silencer (not shown).

  An intake valve 20 is disposed in the intake port 9a, and an exhaust valve 21 is disposed in the exhaust port 9b. These intake and exhaust valves 20 and 21 are urged toward the valve closing side by a valve spring 22 and are opened by an intake camshaft 23 and an exhaust camshaft 24 that are driven to rotate in synchronization with the crankshaft 6 on the cylinder head 9. To be spoken. As a result, the intake valve 20 and the exhaust valve 21 are opened and closed at a predetermined timing synchronized with the reciprocation of the piston 4, and the combustion cycle of the engine 1 consisting of four strokes of intake, compression, expansion and exhaust is 720 ° CA in crank angle. Repeated every time.

The fuel (gasoline) stored in the fuel tank 25 is supplied to the injector 16 by a fuel pump 26. The fuel pump 26 is integrated with the injector 16 and connected to the fuel tank 25 via a supply hose 27 and a return hose 28, respectively.
When the fuel pump 26 is operated, the fuel in the fuel tank 25 is introduced into the fuel pump 26 through the supply hose 27 and pressurized to a predetermined pressure, and the pressurized fuel is supplied to the injector 16 and surplus fuel is supplied. Is recovered in the fuel tank 25 via the return hose 28. As a result, fuel of a predetermined pressure is always supplied to the injector 16, and the fuel is injected toward the intake port 9a at a predetermined injection timing and injection amount according to the opening of the injector 16.

  During operation of the engine 1, outside air is sucked into the intake passage 11 through the air cleaner 12 due to the negative pressure generated as the piston 4 descends during the intake stroke, and the intake air is in accordance with the opening of the throttle valve 13. After the flow rate is adjusted, the fuel flows into the cylinder of the engine 1 while the intake valve 20 is opened while being mixed with the fuel injected from the injector 16. After the compression in the subsequent compression stroke, the air-fuel mixture is ignited by the spark plug 10 in the vicinity of the compression top dead center, burns during the expansion stroke, and applies a rotational force to the crankshaft 6 via the piston 4. In the subsequent exhaust stroke, the exhaust gas after combustion is discharged from the cylinder while the exhaust valve 21 is opened, and is discharged outside through the three-way catalyst 18 and the silencer while flowing through the exhaust passage 17.

The combustion cycle of the engine 1 described above is executed based on the control of the ECU 31 (engine control unit). For this purpose, on the input side of the ECU 31, there are an electromagnetic pickup 32 that is arranged opposite to the flywheel 7 and outputs a detection signal synchronized with the reluctator protrusion 7 a, a throttle sensor 33 that detects the opening of the throttle valve 13, and an exhaust passage 17. Various sensors such as an O ₂ sensor 34 that is arranged and varies the output VS in a step-like manner according to a variation in the exhaust air-fuel ratio centered on stoichiometric (theoretical air-fuel ratio), a water temperature sensor 35 that detects the cooling water temperature Tw of the engine 1 Sensors are connected. Various devices such as the igniter 36 for driving the ISCV 14, the injector 16 (control device), the fuel pump 26, and the spark plug 10 (control device) are connected to the output side of the ECU 31.

Based on these sensor information, the ECU 31 operates the engine 1 by executing various controls such as ignition timing control for driving the spark plug 10 and fuel injection control for driving the injector 16.
For example, as the ignition timing control, the ECU 31 determines the target ignition timing based on the engine rotational speed Ne calculated from the detection signal of the electromagnetic pickup 32, the throttle opening θth detected by the throttle sensor 33, and the like. In parallel with this, the ECU 31 shapes the detection signal of the electromagnetic pickup 32 to generate a rectangular wave-shaped crank angle signal synchronized with the reluctator 7a (in other words, the crank angle), and sets the target ignition timing based on the crank angle signal. After specifying the corresponding timing, the igniter 36 is driven to ignite the spark plug 10.

  Further, as fuel injection control, the ECU 31 determines the fuel injection amount (actually, the valve opening time of the injector 16) based on the engine rotational speed Ne, the throttle opening θth, etc., and drives the injector 16 at a predetermined timing of the intake stroke. Fuel injection is executed (injection amount control means). The control state of the fuel injection at this time is switched according to the operation region of the engine 1.

That is, the ECU 31 discriminates the operation region of the engine 1 based on the engine rotational speed Ne, the throttle opening θth, and the like. In the normal rotation and load region, the ECU 31 determines the fuel injection amount from the injector 16 based on the output VS of the O ₂ sensor 34. Feedback control is performed to keep the exhaust air / fuel ratio of the engine 1 in the vicinity of the stoichiometric range (hereinafter, this control is simply referred to as O ₂ feedback), thereby improving the purification function of the three-way catalyst 18 to improve exhaust gas characteristics and reducing fuel consumption. Plan.

On the other hand, in the high rotation and high load region, the ECU 31 stops the O ₂ feedback of the fuel injection amount, and then calculates an increase correction coefficient (≧ 1.0) corresponding to the operation region of the engine 1 from a preset control map, The fuel injection amount from the injector 16 is increased by multiplying the fuel injection amount corresponding to the stoichiometry by the increase correction coefficient. Thus, so-called fuel cooling in which the in-cylinder air-fuel ratio of the engine 1 is enriched is performed, and damage caused by overheating of the engine 1 is prevented by suppressing the combustion temperature in the cylinder.

  And since the fuel cooling in such a high rotation high load area becomes a factor which deteriorates the exhaust gas characteristic of the engine 1, the technique of patent document 1 is proposed as the countermeasure, In the said technique, in the high load area During the operation of the engine 1 in the engine, the execution of the fuel increase (rich) and the non-execution (lean) are only repeated at the fuel injection timing cycle, so that it is impossible to achieve both prevention of engine 1 damage due to overheating and improvement of exhaust gas characteristics. There was a problem.

  In view of the above problems, the present inventor has paid attention to the thermal allowable limit of the engine 1 when the vehicle is in a fully open travel state (a travel state in which the throttle is fully open and the engine rotational speed Ne is balanced). That is, even if the fully open running state is started, the engine temperature does not immediately reach the limit range. Therefore, at the initial stage of the fully opened running state, it can be considered that the engine 1 has a relatively thermal margin, and the fully opened running state As the engine temperature continues, the temperature of the engine 1 rises and the possibility of breakage increases as the margin decreases. Such a tendency means that there is room for leaning the in-cylinder air-fuel ratio at the initial stage of the fully open running state, and there is less room for leaning as the fully opened running state continues.

  As long as the fully open running state is continued, the technology of Patent Document 1 continues the control of the same content (repetition of rich and lean) from start to finish, so even if the fully open running state continues for a long time, the engine 1 In order to prevent overheating of the cylinder, it is necessary to sufficiently enrich the in-cylinder air-fuel ratio by a large increase when the fuel is increased. In addition, when the fully open running state is completed in a short time, the engine temperature does not rise so much, but the cylinder air-fuel ratio can be further leaned, but it is wasted.

  In consideration of such points, the air-fuel ratio is leaned intensively in the initial stage of the fully-open running state where the engine 1 has a relatively thermal margin (control from rich to stoichiometric, If the control is referred to as full-open stoichiometric control), the thermal margin of the engine 1 can be utilized to the maximum for leaning the air-fuel ratio, and the effect is obtained when the fully-open running state is completed in a short time. Even if there is, it can be obtained in the same manner (because the full-open stoichiometric control has already been completed), so that it is possible to prevent damage to the engine 1 due to overheating and improve exhaust gas characteristics at a high level.

Based on the above knowledge, full open stoichiometric control executed when the ECU 31 is in the fully open running state of the vehicle will be described in detail. In the present embodiment, the ECU 31 when executing the fully opened stoichiometric control functions as a fully opened leaning means and an O ₂ feedback means.
2 and 3 are flowcharts showing a fully-open stoichiometric control routine executed by the ECU 31, and the ECU 31 executes the routine every 720 ° CA synchronized with the combustion cycle of the engine 1 while the vehicle is running.

First, in step S2, it is determined whether or not the vehicle has reached a fully open running state. In the present embodiment, when the throttle opening θth = maximum value (throttle fully open) and the running state in which the engine rotational speed Ne is balanced and does not increase any more continues for a predetermined determination time Ts, the vehicle Is determined to have reached the fully open running state. When the vehicle is in a fully open running state, O ₂ feedback of the fuel injection amount is stopped in the fuel injection control, and the in-cylinder air-fuel ratio is controlled to the rich side by the fuel increase, and fuel cooling is performed.
Note that the determination condition for the fully-open running state is not limited to the above-described contents, and can be arbitrarily changed. For example, the vehicle speed V may be applied instead of the engine speed Ne.

In this embodiment, the air-fuel ratio is made lean by the full-open stoichiometric control only when the vehicle is in the full-open running state. This is based on the following two reasons. First, since the engine 1 in the fully open running state is maintained in a high rotation and high load range and the fuel increase for fuel cooling is continued, if the lean period is fully opened by the fully open stoichiometric control, the exhaust gas characteristic of A great improvement in terms of fuel consumption (in terms of fuel consumption). Further, as described below, the fully open stoichiometric control with O ₂ feedback is not very suitable for a sudden change in the operating region (for example, during acceleration immediately before reaching the fully open running state), and the engine 1 in the fully open running state is high. This is because the operation range is suitable for the execution of the full-open stoichiometric control because it is maintained in a steady operation state while being in the rotation high load region.

  From the above viewpoint, the process of step S2 is set, and when the determination of step S2 is No (No), the ECU 31 ends the routine once because it is not necessary to perform the full-open stoichiometric control. Then, when the vehicle reaches the fully open running state and the determination in step S2 becomes Yes (positive), the process proceeds to step S3, and it is determined whether or not the fully open stoichiometric control has already been executed in the current fully opened running state. When the determination in step S3 is Yes, the routine is terminated, and when the determination is No, the fully open stoichiometric control is executed by the subsequent processing.

When the air-fuel ratio of the engine 1 is temporarily made lean by executing the full-open stoichiometric control, the temperature of the engine 1 rises and the thermal margin greatly decreases. Therefore, as long as the full-open running state is continued, the execution is prohibited from the viewpoint that the second full-open stoichiometric control is impossible (increase / decrease prohibition means). As a result, it is possible to prevent re-execution of the full-open stoichiometric control in a state where the engine 1 has no thermal margin, and more reliably prevent engine damage due to overheating.
However, the present invention is not necessarily limited to this. For example, when a stoichiometric holding period Tst, which will be described later, is set to a very short time, etc., the engine 1 still has a certain degree of thermal margin, so that it is fully opened again after a predetermined time during the fully opened running state. The stoichiometric control may be executed.

In the subsequent step S4, the O ₂ feedback learning process is prohibited (learning prohibiting means). As is well known, feedback control of the fuel injection amount is executed based on the feedback correction coefficient Kfb corresponding to the output VS of the O ₂ sensor 34. In parallel with this, in the learning process, the feedback correction coefficient Kfb is learned as a learning value. (Learning means). As a result, for example, the deviation of the output value caused by, for example, aging deterioration of the O ₂ sensor 34 is immediately reflected in the fuel injection amount as a learned value, and fuel injection control with better responsiveness is possible.
According to the fully open stoichiometric control, the O ₂ feedback is executed even in the fully open running state. However, since the operation region of the engine 1 is greatly different from the normal O ₂ feedback, it causes erroneous learning. Therefore, the learning process of O ₂ feedback is prohibited during the fully open stoichiometric control.

In a succeeding step S6, it is determined whether or not the O ₂ sensor 34 is activated (activation determining means). Since the determination of the activity of the O ₂ sensor 34 is well known, details will not be described. For example, whether or not the output VS of the O ₂ sensor 34 has increased to a predetermined determination value, or the detected temperature of the O ₂ sensor 34 has a predetermined value. It may be determined based on whether or not it has risen to the determination value, or in the case of the O ₂ sensor with heater 34, whether or not the energization time of the heater has reached a predetermined determination value.

When the O ₂ sensor 34 has already been activated before the start of the fully open running state, the determination of Yes is made in step S6 and the process proceeds to step S8, and the increase correction coefficient applied for increasing the fuel as described above. K (increase correction amount) is decreased by a predetermined value set in advance. In the subsequent step S10, it is determined whether or not the output VS of the O ₂ sensor 34 has reached a preset lean determination value VSlean. The lean determination value VSlean is a threshold value that is set slightly leaner than the stoichiometric value. When the condition of step S10 is satisfied, the exhaust air-fuel ratio of the engine 1 that gradually changes from the rich side toward the stoichiometric value by the process of step S8 is determined. It can be inferred that it has reversed to the lean side beyond the stoiki.

If the determination in step S10 is No, it is determined in step S12 whether or not the increase correction coefficient K has decreased to 1.0 (holding value). If the determination is No, the processing in steps S8 to S12 is repeated (lean-opening means when fully open). The increase correction coefficient K gradually decreases (every 720 ° CA interval combustion cycle). If the increase correction coefficient K decreases to 1.0 before the condition of step S10 is satisfied, the determination of Yes is made in step S12 and step S14. Migrate to In step S14, the increase correction coefficient K = 1.0 is maintained (lean-opening means), and in step S16, O ₂ feedback that has been stopped for increasing the fuel amount is started (O ₂ feedback means).

  Thereafter, in step S18, it is determined whether or not a preset stoichiometric holding period Tst (holding period) has elapsed since the start of maintaining the increase correction coefficient K = 1.0. The stoichiometric holding period Tst is a period set in consideration of the thermal margin of the engine 1 in the fully opened running state, and without any fear of damage due to overheating of the engine 1 at the beginning of the fully opened running state. The air-fuel ratio is set as a period near the upper limit at which the air-fuel ratio can be maintained stoichiometrically. While the determination in step S18 is No, the processing in steps S14 and 16 is repeated. When the stoichiometric holding period Tst has elapsed and the determination in step S18 is Yes, the process proceeds to step S20.

FIG. 4 is a time chart showing the execution state of the full-open stoichiometric control when the O ₂ sensor 34 has already been activated before the start of the full-open running state.
For example, when the vehicle reaches a traveling state with the throttle fully opened, the O ₂ feedback is stopped and the fuel increase based on the increase correction coefficient K is started. When the ECU 31 determines that the fully open running state is started based on the passage of the determination time Ts, the increase correction coefficient K for the fuel injection amount is gradually decreased. When the increase correction coefficient K decreases to 1.0 and the fuel injection amount becomes a value equivalent to the stoichiometric value, O ₂ feedback is started. Due to the feedback of the fuel injection amount based on the output VS of the O ₂ sensor 34, the exhaust air-fuel ratio of the engine 1 is maintained in the vicinity of the stoichiometric state, and this operating state is continued for the stoichiometric holding period Tst, and as the stoichiometric holding period Tst elapses. O ₂ feedback is terminated.

Then, the ECU 31 returns the increase correction coefficient K decreased to 1.0 to the value before the decrease by the processing after step S20 in FIG. 2, but first calculates the initial change amount K0 of the increase correction coefficient K in step S20. To do. As the initial change amount K0 of the increase correction coefficient K, the feedback correction coefficient Kfb at the time when the O ₂ feedback is finished is set with the same magnitude and direction (lean-opening means when fully opened). In the subsequent step S22, the increase correction coefficient K is increased or decreased based on the set initial change amount K0.

Thereafter, in step S24, the increase correction coefficient K is increased by a predetermined value set in advance (lean means when fully opened), and in subsequent step S26, it is determined whether or not the increase correction coefficient K has returned to the value before the decrease. Note that the predetermined value applied to increase the increase correction coefficient K in step S24 may be the same as or different from the predetermined value applied at the time of decrease. While the determination in step S26 is No, the processes in steps S24 and S26 are repeated. If the determination in step S26 is Yes, the process proceeds to step S28, and the routine is terminated after canceling the prohibited O ₂ feedback learning process. To do.

Returning to the time chart of FIG. 4, the description will be continued. The initial increase / decrease when the increase correction coefficient K is restored is executed based on the initial change amount K0 equivalent to the feedback correction coefficient Kfb at the end of the O ₂ feedback. . For this reason, the initial change amount K0 is applied to the correction for the fuel injection amount instead of the feedback correction coefficient Kfb. FIG. 4 shows a case where the rich feedback correction coefficient Kfb is applied at the end of the O ₂ feedback, but the fuel injection amount is based on the initial change K0 on the rich side instead of the feedback correction coefficient Kfb. It is corrected in the increasing direction.

FIG. 5 shows the case where the lean side feedback correction coefficient Kfb is applied at the end of the O ₂ feedback, but the fuel injection amount is based on the lean side initial change amount K0 instead of the feedback correction coefficient Kfb. Is corrected in the decreasing direction. Therefore, in any case, the fuel injection amount does not change substantially, and substantially the same amount of fuel is injected with respect to the previous combustion cycle. Therefore, the torque change of the engine 1 is suppressed, and the fully open stoichiometric control is terminated. Deterioration of running feeling due to torque shock at the time of running is prevented.

When the vehicle reaches the fully open running state as described above, the fully open stoichiometric control is executed in the initial stage, so that the air-fuel ratio of the engine 1 is kept stoichiometric from rich to the stoichiometric holding period Tst. During the stoichiometric holding period Tst, there is no risk of engine damage even if the air-fuel ratio of the engine 1 is held at stoichiometric, and by maintaining the stoichiometric condition, the purification function of the three-way catalyst 18 is enhanced and exhaust gas characteristics are improved (in terms of fuel consumption) )it can.
Since the engine 1 at the initial stage when the fully open running state is started has a comparatively thermal margin, the thermal margin of the engine 1 can be utilized to the maximum to make the air-fuel ratio lean. Also, it is unpredictable how long the fully open running state will continue at this time, but even if it is completed in a short time, the fully open stoichiometric control has already been completed, so what is the effect of leaning? Obtained without change.

In addition, the execution of O ₂ feedback in the high rotation and high load range of the engine 1 is not normally considered, but O ₂ feedback can be executed in the full-open stoichiometric control in which the exhaust air-fuel ratio is stoichiometric. Since the exhaust air / fuel ratio of the engine 1 can be reliably controlled within the window of the three-way catalyst 18 centered on the stoichiometry by this O ₂ feedback, the purification function can be further improved. Therefore, prevention of damage to the engine 1 due to overheating and improvement of exhaust gas characteristics can be achieved at a high level.

  Further, during the stoichiometric hold period Tst, the engine output slightly decreases due to the lean air-fuel ratio, but since the increase correction coefficient K is gradually decreasing and increasing, the driver who is in the fully open traveling state notices. There is almost no possibility. If the engine output decreases even though the throttle is fully open, the driver feels that the driving feeling will deteriorate, but since this situation can be prevented, the above various effects can be obtained while maintaining good drivability. Can do.

The above description is a case where the O ₂ sensor 34 has already been activated before the start of the fully-open running state, but the O ₂ sensor 34 may not have been activated before the start, and the stoichiometric holding period Tst will be described below. A case where the O ₂ sensor 34 is activated and a case where the O ₂ sensor 34 is not activated throughout will be described.

The ECU 31 determines the start of the fully open running state in step S2 of FIG. 2, and after prohibiting the O ₂ feedback learning process in step S4, the ECU 31 determines No in step S6 since the O ₂ sensor 34 has not yet been activated. I will give you. At this time ECU31 reduces the increase correction factor K shifts to step S30 by a predetermined value, determines whether decreased to increase the correction coefficient K is 1.0 Further in step S32, the O ₂ sensor 34 in the subsequent step S6 Determine if activated. When the determinations in steps S32 and S34 are both No, the processes in steps S30 to S34 are repeated. If the increase correction coefficient K decreases to 1.0 before the O ₂ sensor 34 is activated, the determination of Yes is made in step S32. The process proceeds to step S36.

In step S36, the increase correction coefficient K = 1.0 is maintained, and in the subsequent step S38, it is determined whether or not the O ₂ sensor 34 is activated. Since the determination is initially No, the process proceeds to step S40 to determine whether or not the stoichiometric holding period Tst has elapsed. While the determination in step S40 is No, the processes in steps S36 to S40 are repeated.

If the O ₂ sensor 34 is activated before the stoichiometric holding period Tst elapses, the determination of Yes is made in step S38, and the O ₂ feedback that has been stopped for fuel increase is started in step S42 (O ₂ feedback means). Thereafter, the processes in steps S36, 38, 42, and 40 are repeated. When the stoichiometric holding period Tst has elapsed and the determination in step S18 is Yes, the same process as described above is executed in and after step S20.
If the O ₂ sensor 34 is not activated during the stoichiometric holding period Tst, the process proceeds to step S20 as the stoichiometric holding period Tst elapses without starting O ₂ feedback.

FIG. 6 is a time chart showing the state of execution of the full-open stoichiometric control when the O ₂ sensor 34 is activated during the stoichiometric holding period Tst.
The increase / decrease of the increase correction coefficient K is the same as in the control situation shown in FIGS. 4 and 5 described above, but at the beginning of the stoichiometric holding period Tst, the O ₂ feedback is not started, and the O ₂ sensor 34 is activated. O ₂ feedback is started after conversion. The same is true in that the increase correction coefficient K is restored based on the initial change amount K0 corresponding to the feedback correction coefficient Kfb at the end of the O ₂ feedback. Therefore, although not redundantly explained, in this case as well, by maintaining the air-fuel ratio of the engine 1 at the stoichiometric period over the stoichiometric holding period Tst, both the prevention of damage to the engine 1 due to overheating and the improvement of exhaust gas characteristics can be achieved at a high level. Can do.

Further, even if the O ₂ sensor 34 is not activated at the beginning of the stoichiometric holding period Tst, when the activation is always determined and activated, O ₂ feedback is immediately started. Therefore, after that, highly accurate air-fuel ratio control can be realized, and as a result, the purification function of the three-way catalyst 18 can be maximized.
Further, when the O ₂ sensor 34 is not activated during the stoichiometric holding period Tst, O ₂ feedback is not executed, but the decrease / increase of the increase correction coefficient K is controlled in the same manner as in FIGS. Therefore, although the accuracy of the air-fuel ratio control is slightly reduced, the damage prevention of the engine 1 and the improvement of the exhaust gas characteristics can be sufficiently achieved as compared with the technique of Patent Document 1.

On the other hand, when the increase correction coefficient K = 1.0, the fuel injection amount equivalent to the stoichiometric value is a value derived from a preset control map, but includes an error that cannot be ignored due to inadequate control map calibration. There is also. For example, when the fuel injection amount is decreased to the increase correction coefficient K = 1.0 (Yes in step S12 or step S32), the actual exhaust air / fuel ratio may already be controlled to the lean side beyond the stoichiometry. A contradiction arises between subsequent O ₂ feedback. In the present embodiment, a countermeasure for such a case is taken, which will be described below.

If the O ₂ sensor 34 has been activated before the start of the fully-open running state, the increase correction coefficient K is decreased in step S8 as described above, and the output VS of the O ₂ sensor 34 becomes the lean determination value VSlean in step S10. It is determined whether or not it has been reached. The process of step S10 is repeated until the increase correction coefficient K decreases to 1.0, and if the condition of step S10 is satisfied before the increase correction coefficient K decreases to 1.0, the process proceeds to step S44.
In step S44, the increase correction coefficient K at that time is maintained, and in step S46, O ₂ feedback is started (lean-opening means, O ₂ feedback means). Thereafter, in step S48, it is determined whether or not the stoichiometric holding period Tst has elapsed. While the determination in step S48 is No, the processes in steps S44 to S48 are repeated, and the process proceeds to step S20 as the stoichiometric holding period Tst elapses.

If the O ₂ sensor 34 has not been activated before the start of the fully-open running state, the increase correction coefficient K is decreased to 1.0 in step S32 after the increase correction coefficient K is decreased in step S30 as described above. In step S6, it is determined whether the O ₂ sensor 34 has been activated. If the O ₂ sensor 34 is activated before the increase correction coefficient K decreases to 1.0, it is determined in step S50 whether the output VS of the O ₂ sensor 34 has reached the lean determination value VSlean. Thereafter, the processing in steps S44 to S48 is repeated until the stoichiometric holding period Tst elapses in the same manner as described above.

FIG. 7 is a time chart showing the execution state of the full-open stoichiometric control when the output VS of the O ₂ sensor 34 reaches the lean determination value VSlean before the increase correction coefficient K decreases to 1.0.
The activation timing of the O ₂ sensor 34 may be the case before the start of the fully-open running state (step S6) or during the decrease of the increase correction coefficient K (step S34). When the condition of VS ≧ VSlean in step 50 is satisfied, the decrease of the increase correction coefficient K is stopped and maintained at that value, and at the same time, O ₂ feedback is started.

Based on the setting of the lean determination value VSlean described above, it can be estimated that the exhaust air-fuel ratio of the engine 1 at this time exceeds the stoichiometry and is reversed to the lean side. Therefore, although the increase correction coefficient K at this point does not decrease to 1.0 in terms of numerical values, the actual fuel injection amount can be regarded as being equivalent to stoichiometry, and by maintaining the increase correction coefficient K at this time, the engine 1 O ₂ feedback can be started after controlling the exhaust air-fuel ratio of the exhaust gas near the stoichiometric range. For this reason, the contradiction between the actual air-fuel ratio and the O ₂ feedback due to the control map calibration insufficiency, etc. can be resolved, and more accurate air-fuel ratio control can be realized, and the purification function of the three-way catalyst 18 can be maximized. Can be demonstrated.

Even in these cases, the initial increase / decrease when the increase correction coefficient K is restored at the end of the stoichiometric holding period Tst is executed based on the initial change amount K0 corresponding to the feedback correction coefficient Kfb at the end of the O ₂ feedback. The
However, since the increase correction coefficient K is not 1.0 at this time, if the feedback correction coefficient Kfb, which is a correction coefficient for stoichiometry, is set as the initial change amount K0 as it is and applied to increase / decrease in the increase correction coefficient K, the same amount is corrected. It doesn't mean that Such a difference in the degree of influence differs depending on the magnitude of the increase correction coefficient K that is stopped and maintained based on the output VS of the O ₂ sensor 34. Therefore, the feedback correction coefficient Kfb is replaced with the initial change amount K0 while applying the correction according to the magnitude of the increase correction coefficient K at that time so that the same degree of influence is obtained. The increase correction coefficient K is increased or decreased.

This is the end of the description of the embodiment, but the aspect of the present invention is not limited to this embodiment. For example, in the above-described embodiment, the fuel injection control device of the engine 1 mounted on the two-wheeled vehicle is embodied, but the present invention is not limited to this and may be applied to an engine for a three-wheeled vehicle.
In the above embodiment, as the fully open stoichiometric control when the vehicle is in the fully open running state, the air-fuel ratio enriched for the fuel cooling of the engine 1 is kept stoichiometric over the stoichiometric holding period Tst. However, the air-fuel ratio at this time is not limited to stoichiometric, and any air-fuel ratio other than stoichiometric may be maintained as long as the rich air-fuel ratio for the purpose of fuel cooling is made lean.
In the fully open stoichiometric control of the above embodiment, the fuel injection amount is basically decreased to the increase correction coefficient K = 1.0, and the output VS of the O ₂ sensor 34 reaches the lean determination value VSlean during the decrease. In this case, the decrease of the increase correction coefficient K is stopped at that time to prevent an excessive decrease in the fuel injection amount, but the present invention is not limited to this. For example, if the sensor output VS does not reach the lean determination value VSlean even when the increase correction coefficient K is decreased to 1.0, the increase correction coefficient K is further decreased (up to the region of K <1.0), and the sensor output VS is lean. The decrease of the increase correction coefficient K may be stopped when the determination value VSlean is reached.

1 Engine 17 Exhaust passage 18 Three-way catalyst (catalyst device)
31 ECU (injection amount control means, fully open leaning means, O ₂ feedback means,
(Full open determination means, activation determination means, increase / decrease prohibition means, learning means, learning prohibition means)
34 O ₂ sensor

Claims (8)

A fully open determination means for determining whether or not the vehicle is in a fully open running state in which the throttle is fully open and the engine rotational speed is balanced;
An injection amount control means for controlling the fuel injection of the engine and, when the fully open determination means determines that the engine is in a fully open running state, increasing the fuel injection amount of the engine to increase the air-fuel ratio;
When the full-open determination means determines that the vehicle is in the fully-open running state, the increase correction amount by the injection amount control means is gradually reduced to a preset hold value, and after the preset hold period elapses after the decrease. And a fully open leaning means for maintaining the increase correction amount at the hold value and gradually increasing the increase correction amount from the hold value to return to the value before the decrease when the hold period has elapsed. Engine fuel injection control device. A catalyst device provided in an exhaust passage of the engine;
An O ₂ sensor provided upstream of the catalyst device in the exhaust passage;
Activation determination means for determining whether or not the O ₂ sensor is activated;
When the activation determination means determines that the O ₂ sensor is activated, the engine fuel injection amount is feedback-controlled based on the output of the O ₂ sensor, so that the exhaust air-fuel ratio of the engine is the stoichiometric air-fuel ratio. O ₂ feedback means to keep in the vicinity,
The fully opened leaning means controls the fuel injection amount of the engine to a value corresponding to the theoretical air-fuel ratio during the holding period,
The engine fuel injection control device according to claim 1, wherein the O ₂ feedback means executes feedback control based on an output of the O ₂ sensor during the holding period. The O ₂ feedback means starts feedback control based on the output of the O ₂ sensor from that time when activation of the O ₂ sensor is determined by the activation determination means during the holding period. The fuel injection control device for an engine according to claim 2. When the output of the O ₂ sensor reaches a lean determination value set in advance in the vicinity of the theoretical air-fuel ratio in the process of reducing the increase correction amount to the hold value, the fully open time leaning means The increase correction amount is regarded as the holding value, and the decrease of the increase correction amount is stopped and kept,
The O ₂ feedback means, characterized in that it starts outputting the feedback control based of the O ₂ sensor from the time when the O ₂ the fully open time leaning means based on the output of the sensor has stopped decreasing increasing correction amount The engine fuel injection control device according to claim 2. The fully open leaning means is set based on the output of the O ₂ sensor when the holding period has elapsed when the increase correction amount is returned from the holding value to the value before the decrease as the holding period elapses. 5. The fuel injection control device for an engine according to claim 2, wherein a value corresponding to the feedback correction amount being made is the first change amount of the increase correction amount. When the feedback correction amount at the time when the holding period has elapsed is set to the lean side, the fully opened leaning means sets the value corresponding to the feedback correction amount as the initial decrease of the increase correction amount. 6. The fuel injection control device for an engine according to claim 5, wherein after the first time, the increase correction amount is gradually increased. After the full-opening leaning means reduces and increases the increase correction amount based on the determination of the full-open running state by the full-open judging means, the increase correction is performed again even if the judgment of the full-open running state is continued. The engine fuel injection control device according to any one of claims 1 to 6, further comprising an increase / decrease prohibiting means for prohibiting a decrease and an increase in the amount with respect to the fully open leaning means. Learning means for learning feedback control by the O ₂ feedback means based on the output of the O ₂ sensor during operation of the engine in a state other than the full-open running state;
The learning prohibiting means for prohibiting the learning means from executing a learning process during the feedback control by the O ₂ feedback means during the holding period. A fuel injection control device for an engine according to claim 1.

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