JPH0436052A - Air-fuel ratio control device of engine - Google Patents

Abstract

PURPOSE:To prevent torque from being reduced when the operational mode is changed from S-FB to L-FB by performing the control of opening and closing an air control valve for introducing secondary air when the operational mode is changed from S-FB to L-FB. CONSTITUTION:The temperature of cooling water of an engine 14 is above that for starting feedback control and also the operational mode is other than stoichio-feedback, and in addition, a linear air-fuel ratio sensor 7 is activated. Further, secondary air is introduced into the engine 14 under the normal operating condition of the linear air-fuel ratio sensor 7 and a valve means 25 is controlled in such a manner as being opened or closed so that the secondary air is not introduced into the engine 14 under other conditions. Torque is thereby prevented from being reduced when the operational mode is changed from stoichio-feedback S-FB to lean feedback L-FB.

Description

[Detailed description of the invention] [Purpose of the invention] (Industrial application field) The present invention relates to an air-fuel ratio control device for an engine.

(Prior Art) It is known that one method for improving the fuel consumption rate of an engine is to perform combustion with a lean mixture. However, especially when a combustion system using such a lean mixture is introduced into a vehicle engine, sufficient engine output cannot be obtained during acceleration during lean-burn operation where the engine output inevitably decreases, resulting in a poor performance. There is a problem that it is difficult to ensure good vehicle drivability. Therefore, in the past, the operating range of the engine was detected to determine whether to perform lean combustion, and the acceleration state of the engine was also detected to enrich the air-fuel ratio of the air-fuel mixture supplied to the engine combustion chamber at the time of acceleration. In order to secure the engine output by increasing the
This is proposed in Japanese Patent No. 87932.

Furthermore, in a lean burn engine that incorporates a combustion method using a lean mixture as described above, there is a difference between lean feedback (L-F B) control in which the engine is operated by burning a lean mixture and combustion in a rich mixture. Stoichiometric feedback (S
-F B) At the time of control, each air-fuel ratio map is used for switching control.

(Problem to be solved by the invention) However, when switching from stoichiometric feedback (S-FB) to lean feedback (L-FB), the air-fuel ratio of the air-fuel mixture taken into the engine is switched to the lean side, so the torque There was a problem in that the vehicle crashed and the drivability was poor.

The present invention has been made in view of the above-mentioned points, and its purpose is to provide a lean-burn engine that employs stoichiometric feedback (S-
An object of the present invention is to provide an air-fuel ratio control device for an engine that can prevent torque reduction when switching from F B) to lean feedback (L - F B).

[Structure of the Invention (Means for Solving the Problem) Engine operating range determining means for determining a specific operating range of the engine, and an engine operating range determining signal received from the engine operating range determining means and supplied to the engine. A device equipped with a lean air-fuel ratio setting means for setting the air-fuel ratio of the air-fuel mixture to be leaner than the stoichiometric air-fuel ratio, which includes a secondary air supply piping for supplying secondary air to the engine, and a secondary air supply pipe for supplying secondary air to the engine. A valve means provided in the middle of the piping to control the state of introduction of secondary air, the cooling water temperature of the engine is equal to or higher than the phyto-back start water temperature, the mode is other than stoichiometric feedback, and the linear air-fuel ratio sensor is activated, and the linear air-fuel ratio sensor is activated. The air-fuel ratio control device for an engine includes a valve control means that controls the valve means to open when the fuel ratio sensor is normal, and controls the valve means to close under other conditions.

(Function) When the engine cooling water temperature is equal to or higher than the feedback start water temperature, the mode is other than stoichiometric feedback, the linear air-fuel ratio sensor is activated, and the linear air-fuel ratio sensor is normal, secondary air is introduced into the engine. The opening/closing of the valve means is controlled to prevent secondary air from being introduced into the engine under other conditions, thereby preventing a reduction in torque when switching from stoichiometric feedback mode to line feedback mode. ing.

(Embodiment) An engine air-fuel ratio control device according to an embodiment of the present invention will be described below with reference to the drawings.

In FIG. 1, an air cleaner 13 is installed at the upstream end of an intake passage 11 of an engine 14 mounted on an automobile (not shown), and inside the air cleaner 13, the amount of air passing through the intake passage 11 is detected. An air flow sensor 8 is disposed. Furthermore, this air cleaner 13
is provided with an intake air temperature sensor 9 that detects the temperature of the air passing through the air cleaner 13. Further, the intake passage 11 is provided with a throttle valve 12 connected to an accelerator pedal (not shown) as a human operating member on the downstream side of the air cleaner 13. is provided with a throttle opening sensor 6 that detects the opening over the entire area, and an idle switch 10 that detects whether or not the opening is at the idle position (fully closed position) in an on/off manner. Furthermore, an electromagnetic fuel injection valve (hereinafter referred to as an injector) 2 as a fuel supply device is provided in the intake passage 1 on the downstream side of the throttle valve interposed position. Fuel having a supply pressure controlled so that the differential pressure with the intake pipe internal pressure is constant is introduced into the injector 2, and the fuel is introduced into the injector 2.
The amount of fuel supplied to the injector 4 is set based on the valve opening time of the injector 2. On the other hand, in the exhaust passage 15 of the engine 14, a linear air-fuel ratio sensor 7 whose output changes linearly according to the oxygen concentration in the passage is provided in the upstream exhaust passage where the three-way catalyst 16 is interposed. There is. (In addition, this linear air-fuel ratio sensor 7 can be replaced with an oxygen (02) sensor whose output changes stepwise around the stoichiometric mixture ratio if air-fuel ratio feedback control is not performed during lean combustion.) , the engine 14 includes a water temperature sensor 5 that detects the temperature of its cooling water, and a crank angle sensor 3 that detects its crank angle (a controller that measures the time interval of discrete rank pulse signals generated from the crank angle sensor 3, which will be described later). Engine speed information can be detected by measuring with a timer 1, that is, this crank angle sensor 3 also functions as a rotation speed sensor that detects the engine speed. The detection results of these water temperature sensor 5 and crank angle sensor 3 are combined with the detection results of other sensors (air flow sensor 8, intake air temperature sensor 9, throttle opening sensor 6, idle switch 10, and linear air-fuel ratio sensor 7). Similarly, the data is input to a controller 1 mainly composed of a microcomputer. Furthermore, the detection results of a vehicle speed sensor (not shown) that detects the speed of the vehicle in which the engine 14 is mounted are also input to the controller 1 .

By the way, the controller 1 calculates the air amount A calculated based on the output of the air flow sensor 8 and the crank angle sensor 3.
The operating state of the engine 14 is detected based on the engine rotational speed Ne calculated based on the output of the engine, and a specific operating region based on the lean air-fuel ratio is determined, and these sensors constitute an operating region determining means. There is. Furthermore, the controller 1 is equipped with a first air-fuel ratio map (FIG. 2) in the ROM for operating the engine at a lean air-fuel ratio, and functions as a lean air-fuel ratio setting means.

Further, the controller 1 has a function of determining whether the linear air-fuel ratio sensor 7 has failed and a function of determining whether the linear air-fuel ratio sensor 7 is inactive.

Further, 21 is a surge tank. This surge tank 2
A bypass passage 22 for introducing secondary air is provided between the throttle valve 1 and the upstream side of the throttle valve 12. This bypass passage 22 has a valve 23 that controls the amount of secondary air sent to the engine 14 via this bypass passage 22.
is provided.

Further, one end of a negative pressure intake pipe 24 is connected immediately upstream of the throttle valve 12. This piping 24 is connected to a diaphragm chamber 261 of a negative pressure control valve 26 via an air control valve (ACV) 25. This air control valve 25 is located directly upstream of the throttle valve 12 and the negative pressure control valve 2.
It is controlled to switch between a position where the diaphragm chamber 261 of No. 6 is communicated with the diaphragm chamber 261 and a position where the diaphragm chamber 261 is opened to the atmosphere, and the switching is controlled by a control signal from the controller 1.

7 is connected to the valve body 281 by a link 28. When the atmosphere is introduced into the diaphragm chamber 261, the valve body 281 is in the position shown in the figure, so the valve 23
is considered to be fully closed. On the other hand, when negative pressure is introduced into the diaphragm chamber 261, the amount of movement of the diaphragm 27 against the biasing force of the spring 26+ increases depending on the magnitude of the negative pressure, so the amount of lift of the valve body 281 changes. .

Then, the controller 1 calculates the amount of fuel supplied to the engine 14 based on the input information from each sensor, and sends an output signal based on the calculation result to the injector 2.

At this time, the ROM, which is the storage unit of the controller 1, stores the functional relationship (Tb-Kx
The functional relationship between the proportionality constant (proportional constant) and various operating state information and the correction coefficient is input in advance to A;, and the controller 1 determines the basic injection amount Tb based on the input information from various sensors.
and various correction coefficients are determined, and these are combined to obtain final fuel injection amount data Tinj (valve opening time data of the injector 2), and this fuel injection amount data Tinj is given to the injector 2.

By the way, the above-mentioned correction coefficients include a warm-up correction coefficient Kv1 that is set according to the engine coolant temperature, an air-fuel ratio correction coefficient that is set for each driving zone, and an intake air temperature that is set according to the t1 intake air temperature. Correction coefficients include 1, acceleration increase coefficient KAC, which is set by detecting sudden acceleration (in addition, correction coefficients at startup based on start detection, invalid time correction coefficients according to changes in battery voltage, etc. are also usually set). ), of which the air-fuel ratio correction coefficient Kml is obtained as the product of the air-fuel ratio oven correction coefficient K O. At this time, the air-fuel ratio oven correction coefficient, , is the engine load condition in order to obtain an air-fuel ratio slightly smaller than the stoichiometric air-fuel ratio in zone In order to obtain the stoichiometric air-fuel ratio or the air-fuel ratio slightly larger than the stoichiometric air-fuel ratio in the zone (i.e., high-speed zone),
The value is set to 1 or slightly smaller than 1 depending on the load condition and rotation speed. In the zone (■), it is set to 1 to obtain the stoichiometric air-fuel ratio. For example, it is set smaller than 1 to obtain 20 to 22).

On the other hand, the feedback coefficient of 0 is always set to 1 in the above-mentioned zones (■) and (2) because feedback correction of the air-fuel ratio is not performed, and in zones (■) and (2), when feedback control of the air-fuel ratio is performed. The setting is performed based on the detection result of the linear air-fuel ratio sensor 7 described above, and is set to 1 when feedback control of the inactive special air-fuel ratio of the linear air-fuel ratio sensor 7 is not performed when the engine is cold. (Note that when using an oxygen sensor (λ sensor) that detects only the vicinity of the stoichiometric air-fuel ratio as an air-fuel ratio sensor, the air-fuel ratio feedback control in the lean air-fuel ratio state is not performed, so it is always set to 1 in zone ) By the way, when the starting state of the vehicle is detected, the air-fuel ratio control in zone (2) is switched to the same control as in zone (2) in order to improve the starting characteristics.

In other words, even when driving is performed in the lean air-fuel ratio control (L-FB) zone (zone marked with ■), the start of the acceleration operation is performed by the driver (depressing the accelerator pedal). From this point until the end of the actual acceleration of the engine, the stoichiometric air-fuel ratio control (S-F B
) zone (thin of ■) is expanded, and the lean air-fuel ratio zone is correspondingly reduced, allowing operation at the stoichiometric air-fuel ratio from a relatively low load range, resulting in natural acceleration that does not go against the driver's wishes. The feeling is achieved. Such expansion of the stoichiometric air-fuel ratio feedback (S-F B) zone is performed by switching the air-fuel ratio map stored in the ROM of the controller 1.

That is, the first air-fuel ratio map shown in FIG. 2 and the second air-fuel ratio map shown in FIG. 3 are switched.

Next, the operation of an embodiment of the present invention configured as described above will be explained. First, in the controller 1, an injector drive interrupt routine (not shown) is executed, and in synchronization with the crank angle signal from the crank angle sensor 3, the time interval between adjacent crank pulses is measured by a clock, and based on the measurement result. The engine rotation speed information Ne is calculated. Then, the amount A of air taken into the engine 14 between adjacent crank pulses, that is, from the time when the previous injection is performed to the time when the current injection is performed, is calculated based on the output of the air flow sensor 8. Then, basic injection amount information Tb is set according to the air amount A, and this basic injection amount information Tb is appropriately corrected to create valve opening time data Tinj of the injector 2. Then, the valve opening time data T1nj is set in an injector driving timer (not shown), and this timer is triggered. Then, the injector 2 is opened for a period of time set by the data Tinj, and fuel is supplied to the engine.

Then, the controller 1 calculates the temporal change rate Δθ of the opening degree θ of the throttle opening degree sensor 6, and if this change rate Δe is determined to be larger than the threshold value, it is determined that acceleration is required. However, the second air-fuel ratio map (FIG. 3) in which the 5-FB zone is expanded is selected.

Further, the controller 1 controls the opening and closing of the ACV 25 through the process shown in the flowchart of FIG. In other words, the engine water temperature detected by the water temperature sensor 5 is equal to or higher than the feedback (F B) starting water temperature (step Sl), and the 5-
mode other than FB (step S2), the linear air-fuel ratio sensor 7 is not malfunctioning (step S3), and
The linear air-fuel ratio sensor 7 is activated (step S
At time 4), the ACV 25 is turned on (opened) by a control signal from the controller 1. Thereby, the position immediately upstream of the throttle valve 12 and the diaphragm chamber 261 of the negative pressure control valve 26 are communicated with each other. For this reason, the diaphragm chamber 26
1 increases in accordance with the engine speed Ne and the throttle opening, and the lift amount of the valve body 281 increases accordingly. Then, the amount of secondary air is increased according to the lift amount of the valve body 281.

On the other hand, if the engine water temperature detected by the water temperature sensor 5 is lower than the feedback (FB) start water temperature, or if the 5-FB mode is in effect, or if the linear air-fuel ratio sensor 7 is out of order, or if the linear air-fuel ratio sensor 7
At least one of the cases where is not activated
is satisfied, ACV25
It is turned off (closed control) by a control signal from. Thereby, the atmosphere and the diaphragm chamber 261 of the negative pressure control valve 26 are communicated with each other. Therefore, the bypass passage 22 is blocked by the valve body 281.

Since ACV25 is controlled in this way, when switching from 5-FB mode to L-FB mode, ACV25 is controlled.
By controlling the opening of 25 to increase the amount of secondary air and injecting a fuel injection amount corresponding to the increased amount, 5
- FB mode - Prevents a decrease in torque after switching to FBFB mode, eliminating switching shock.

Further, as in step S1 above, when the engine cooling water temperature is lower than the FB start water temperature, the ACV 25 is closed. This means that ACV25 is opened when the engine coolant temperature is lower than the FB start water temperature, and ACV25 is opened when the engine coolant temperature is higher than the FB start water temperature.
This is because, when closed, a decrease in torque occurs.

Furthermore, the ACV 25 is controlled to be closed when the linear air-fuel ratio sensor 7 is inactive or malfunctions. Since the linear air-fuel ratio sensor 7 cannot be used as a sensor for a certain period of time after starting the engine, the air-fuel ratio is controlled by oven loop control. Then, after a certain period of time has passed after the engine has been started and the linear air-fuel ratio sensor 7 has been activated, the L-
If the ACV 25 has been opened in the previous oven loop control when switching to FB moto, closing the ACV 25 at the time of L-FB switching will result in a reduction in torque. Therefore, when the linear air-fuel ratio sensor 7 is inactive, A
I am trying to close CV25. Also, if the linear air-fuel ratio sensor 7 is out of order, the ACV25
is closed.

In addition, the engine load (A/
N), that is, the amount of intake air per cycle of engine rotation is not used as a determination.

This means that when the engine load (A/N) increases and the air-fuel ratio control switches to oven loop control, the ACV25
is closed, the engine load (A/N) becomes small, the air-fuel ratio control switches to L-FB control, and when the ACV 25 is opened to introduce secondary air, oven loop control and L-FB control are performed. This is because there is a problem that hunting occurs between the oven loop control and the L-FB control near the threshold value for switching between the -FB control and the L-FB control.

[Effects of the Invention] As detailed above, according to the present invention, it is possible to accurately control the opening and closing of the air control valve for introducing secondary air when switching from the 5-FB mode to the L-FB mode. By doing so, it is possible to provide an engine air-fuel ratio control device that can prevent a reduction in torque when changing from 5-FB mode to 2-FBFB mode.

[Brief explanation of the drawing]

FIG. 1 is an overall configuration diagram showing an air-fuel ratio control device for an engine according to an embodiment of the present invention, FIG. 2 is a diagram showing a first air-fuel ratio map, and FIG. 3 is a diagram showing a second air-fuel ratio map. Figure, 4th
The figure is a flowchart for explaining the operation. 1... Controller, 2... Injector, 3...
- Crank angle sensor, 8...Air flow sensor, 14...Enonno, 3...Valve, 6...Negative pressure control valve. 5... Air control valve (A CV)

Claims (1)

[Claims] an engine operating range determining means for determining a specific operating range of the engine, and an air-fuel ratio of the air-fuel mixture supplied to the engine in response to an engine operating range determining signal from the engine operating range determining means, to a side leaner than the stoichiometric air-fuel ratio. In a device equipped with a lean air-fuel ratio setting means for setting a lean air-fuel ratio to a valve means for controlling a state; and when the cooling water temperature of the engine is equal to or higher than the feedback start water temperature and the mode is other than stoichiometric feedback, the linear air-fuel ratio sensor is activated, and the linear air-fuel ratio sensor is normal; An air-fuel ratio control device for an engine, characterized in that the air-fuel ratio control device for an engine is provided with a valve control means for controlling the valve means to open and for controlling the valve means to close under other conditions.