JPH0788786B2 - Air-fuel ratio controller for engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention is capable of stepwise switching the air-fuel ratio to a leaner than the stoichiometric air-fuel ratio without abrupt torque fluctuation, and further, in the lean region. The present invention relates to an air-fuel ratio control device for an engine, which has improved control accuracy.

[Prior art]

In order to save the fuel consumption of the engine, the air-fuel ratio is switched to leaner than the theoretical air-fuel ratio in idling operation, low rotation and low load, and in operating conditions that do not require much engine output. An air-fuel ratio control method for an engine in which the fuel ratio is substantially equal to or higher than the theoretical air-fuel ratio is already known.

Conventionally, when switching the air-fuel ratio of the engine to a lean region that is leaner than the stoichiometric air-fuel ratio and other regions in accordance with the operating state of the engine, normally, the fuel supply amount is changed without changing the intake air amount. It is configured so that the air-fuel ratio can be controlled by controlling (for example, Japanese Patent Laid-Open No. 57-2101
(See Japanese Patent No. 37).

However, since the output of the engine is proportional to the fuel supply amount, if the fuel is suddenly increased or decreased to switch the air-fuel ratio region between the lean region and other regions, a sudden output change will occur, resulting in torque shock or vibration. There is a problem that occurs.

Therefore, it is conceivable that the air-fuel ratio is gradually changed between the lean region and other regions by gradually changing the fuel supply amount without giving such a sudden change. However, for example, when gradually changing the air-fuel ratio between the lean region of the air-fuel ratio 22 and the region of the theoretical air-fuel ratio (air-fuel ratio 14.7), the region of the air-fuel ratio of about 16 where the production amount of nitrogen oxides is almost maximum is set. It passes through, which is disadvantageous in purifying exhaust gas.

In order to solve such a problem, the present inventors have set a bypass passage bypassing a throttle valve, a valve device provided in the bypass passage for opening and closing the bypass passage, and an air-fuel ratio of the valve device. The valve is equipped with a valve control means that opens when switching from the stoichiometric air-fuel ratio to lean and closes when switching from the lean region to another region.The fuel supply amount is fixed and the intake air amount relative to the fuel supply amount is changed in stages. The invention has invented an air-fuel ratio control device for an engine that increases and decreases mechanically. However, it has been found that when the air-fuel ratio is controlled by controlling the flow of air in this way, the response is slower than when the fuel supply amount is controlled and the air-fuel ratio is controlled.

[Object of the Invention]

The present invention has been made in consideration of the above circumstances, and provides an air-fuel ratio control device for an engine, which is improved so that the output fluctuation due to the switching of the air-fuel ratio is small and the control response is improved. The purpose is.

[Structure of Invention]

In order to achieve the above-mentioned object, the engine air-fuel ratio control device according to the present invention detects the operating state of the engine, and switches the air-fuel ratio to leaner than the stoichiometric air-fuel ratio stepwise in accordance with the operating state. In an engine air-fuel ratio control device including an air-fuel ratio control means, the air-fuel ratio control means is provided in a bypass passage that bypasses a throttle valve, and a bypass passage that adjusts a flow passage cross-sectional area of the bypass passage. A first valve device, a second valve device provided in the bypass passage in series with the first valve device to open and close the bypass passage, and a first valve device that opens and closes the first valve device in conjunction with the throttle valve Valve control means,
The second valve device is provided with a second valve control means that is opened when the air-fuel ratio is switched from the stoichiometric air-fuel ratio to lean and is closed when the air-fuel ratio is switched from lean to another air-fuel ratio, and exhaust gas is provided in the exhaust passage of the engine. Equipped with an exhaust gas sensor that detects gas components and outputs an air-fuel ratio signal corresponding to the actual air-fuel ratio, and at least during lean operation inputs the air-fuel ratio signal to eliminate the deviation between the actual air-fuel ratio and the target air-fuel ratio. Thus, a correction control means for correcting the fuel supply amount is provided.

[Embodiment 1] The following will describe one embodiment of the present invention with reference to FIGS. 1 to 3.

An air cleaner 3 is provided at the start end of the intake passage 2 of the engine 1, and the intake air amount is sequentially detected from there to the end, and an air flow meter 4 that outputs an intake air amount signal corresponding to the intake air amount Q _A , A throttle valve 5, a swirl control valve 6 and a fuel injection device 7 are provided,
The end of the intake passage 2 is connected to the combustion chamber 9 via the intake valve 8. Further, an exhaust valve 11 is arranged at the beginning of the exhaust passage 10 led out of the combustion chamber 9, and an air-fuel ratio signal corresponding to the air-fuel ratio is detected in the middle of the exhaust passage 10 by detecting a gas component in the exhaust gas. Air-fuel ratio sensor 12 and a catalytic exhaust purification device 13
Is provided. Also, a spark plug provided in the combustion chamber 9
14 is connected to an ignition coil 16 via a distributor 15.

The intake passage 2 is further provided with a bypass passage 17 that bypasses the throttle valve 5. The bypass passage 17 is provided with a solenoid valve 18 that opens and closes the bypass passage 17. A sub throttle valve 19 is provided in the bypass passage 17 in series with the solenoid valve 18. This sub-throttle valve 19 has a common valve shaft 20 so that the ratio of the amount of air passing through the bypass passage 17 and the amount of air passing through the throttle valve 5 becomes constant when the solenoid valve 18 is open. The throttle valve 5 is interlocked and connected via the throttle valve 5, and the opening degree is adjusted by an accelerator operating device (not shown). The throttle valve 5 is provided with a throttle sensor 21 for detecting the throttle opening TVθ and outputting a throttle opening signal corresponding to the throttle opening. The throttle sensor 21 is also used as an idling switch that outputs an idling signal when the throttle valve 5 is fully closed. Also, when the fuel injection amount Q _f is fixed and the solenoid valve 18 is opened, the engine can be operated in a stable idling mode.
The diameter of the bypass passage 17 is set to 20% or more of the diameter of the intake passage 2 so that the amount of air that can be secured as described above can be sucked. Furthermore, the mounting opening of the sub-throttle valve 19,
Bypass passage caused by production error of bypass passage 17
The variation in the amount of bypass air passing through 17 has a great effect on the air-fuel ratio when the amount of intake air is very small during idling, etc., but it reduces the influence on the air-fuel ratio due to such variation in the amount of bypass air. Therefore, it is preferable to arrange the upstream opening of the bypass passage 17 as close to the throttle valve 5 as possible.

The engine air-fuel ratio control device is further provided with an electronic control unit (hereinafter referred to as ECU) 22 which controls the operations of the fuel injector device 7 and the solenoid valve 18, and is composed of, for example, a computer. This ECU 22 has a high and low coolant temperature T _W of the engine 1 and a throttle opening TVθ.
The operating state of the engine 1 can be determined based on the magnitude of the input / output signal and the presence / absence of an idling signal.
That is, the ECU 22 includes a water temperature signal input port for inputting a water temperature signal corresponding to the water temperature T _W of the cooling water of the engine 1 from a water temperature sensor (not shown) and a throttle opening for inputting a throttle opening signal and an idling signal from the throttle sensor 21. It also has a temperature signal input port, and determines whether or not the water temperature T _W exceeds a predetermined temperature T ₁ corresponding to the minimum temperature at which stable engine operation can be performed in the lean region, for example, 50 ° C. to 60 ° C. A water temperature discriminating unit and a throttle opening for discriminating whether or not the throttle opening TVθ exceeds a predetermined opening θ opened to obtain a predetermined output when the water temperature T _W exceeds the predetermined temperature T _1. And the water temperature T _W is equal to or lower than the predetermined temperature T ₁ or the water temperature T _W is higher than the predetermined temperature T ₁ and the throttle opening TVθ is the predetermined opening θ. When it exceeds ₁ Further, it has an idling discriminating section for discriminating the presence or absence of an idling signal.

The ECU 22 is also operable when the throttle opening determination unit determines that the throttle opening TVθ is less than or equal to the predetermined opening θ ₁ or when the idle determination unit determines that there is an idling signal. Solenoid valve 18
And a drive unit for closing the solenoid valve 18 when the idling determination unit determines that the idling signal is not input.

Further, the ECU 22 has an intake air amount signal input port for inputting an intake air amount signal from the air flow meter 4 in order to control the fuel injection amount corresponding to the intake air amount Q _A and the engine speed N, and the distributor. A rotation speed signal input port for inputting a rotation speed signal corresponding to the engine rotation speed N from 15, the water temperature T _W exceeds the predetermined temperature T ₁ , and the throttle opening TVθ is the predetermined opening θ _{1 A} lean operation map in which a lean target air-fuel ratio read in advance corresponding to the intake air amount Q _A and the engine speed N at the time of the following is stored, and the water temperature T _W is the predetermined temperature T ₁ In the following cases, or when the water temperature T _W exceeds the above-mentioned predetermined temperature T ₁ and the throttle opening TVθ exceeds the above-mentioned predetermined opening θ ₁ , the intake air amount Q _A and the engine speed N are supported. Then the theoretical air-fuel ratio or this The normal operation map stored in advance as the target air-fuel ratio near the air-fuel ratio from the lean operation map or the normal operation map corresponding to the state of the water temperature T _W and the throttle opening TVshita, inhalation detected by the air flow meter 4 Air quantity Q _A and distributor
A target air-fuel ratio determination unit that reads out a target air-fuel ratio corresponding to the engine speed N detected via 15 and determines a target air-fuel ratio TAF, and controls the fuel injection amount of the fuel injection device 7 according to the target air-fuel ratio. It has a fuel injection amount control unit for controlling.

Further, this ECU 22 inputs an air-fuel ratio signal corresponding to the actual air-fuel ratio from the air-fuel ratio sensor 12 in the lean region,
An air-fuel ratio calculator that calculates the actual air-fuel ratio AF, an air-fuel ratio deviation calculator that calculates the deviation between the calculated air-fuel ratio AF and the target air-fuel ratio TAF, and a deviation between the calculated air-fuel ratio AF and the target air-fuel ratio TAF From the lean operation map or the normal operation map, the intake air amount Q _A detected by the air flow meter 4 and the engine speed N obtained via the distributor 15 The reference injection pulse width τ ₁ is calculated from the target air-fuel ratio TAF obtained on the basis of the normal operation map or the lean operation map, and further based on the reference injection pulse width τ ₁ and the air-fuel ratio correction coefficient C. An injection pulse width calculation unit for calculating the injection pulse width τ = τ ₁ (1 + C) is provided. Furthermore, the ECU 22 has an injection control unit for injecting fuel from the fuel injection device 7 over the calculated injection pulse width τ. The ECU 22 has a vehicle speed signal input port for inputting a vehicle speed signal corresponding to the vehicle speed of an automobile (not shown) driven by the engine 1.

In the above configuration, the air-fuel ratio control is executed inside the ECU 22 in accordance with the sequence shown in FIG.

That is, first, a water temperature signal corresponding to the water temperature T _{W of the} engine 1 is input from the water temperature sensor to the water temperature determination unit via the water temperature signal input port (F1), and then from the throttle sensor 21 via the throttle opening signal input port. The throttle opening signal is input to the throttle opening determination unit (F2). Next, the water temperature determination unit determines whether the water temperature T _W exceeds the predetermined temperature T ₁ (F3). Here, when the water temperature T _W exceeds the predetermined temperature T ₁ , the throttle opening determination unit determines whether or not the throttle speed TV θ exceeds the predetermined opening θ ₁ (F4 ). If the water temperature determination unit determines that the water temperature T _W is lower than or equal to the predetermined temperature T ₁ , the engine temperature has not risen sufficiently and the air-fuel ratio is set to a lean region that is higher than the theoretical air-fuel ratio. Then, the rotation of the engine becomes unstable during engine operation. If the water temperature T _W exceeds the above-mentioned predetermined temperature T ₁ but the throttle opening TVθ exceeds the above-mentioned predetermined opening θ ₁ , the throttle valve 5 is operated to obtain an output corresponding to the load of the engine. This is when the valve is being opened. Therefore, when the water temperature determination unit determines that the water temperature T _W is the predetermined temperature T ₁ or lower, or
If the water temperature T _W exceeds the predetermined temperature T ₁ but the throttle opening TVθ exceeds the predetermined opening θ ₁ , the idling determination section determines whether or not an idling signal is present (F5). Here, when it is determined that the idling signal is present, when the water temperature T _W is equal to or lower than the predetermined temperature T ₁ , a large amount of air and fuel are added to increase the stability of the idling operation and shorten the warm-up time. When the water temperature T _W exceeds the predetermined temperature T ₁ , it is preferable to supply the intake air amount control in order to prevent an increase in nitrogen oxides due to a fuel control delay at the start of deceleration. It is preferable to give a dashpot effect. Therefore, in this case, the solenoid valve 18 is opened via the drive unit to increase the intake air amount (F6). When the idling determination unit determines that there is no idling signal, it means that the throttle valve is opened to obtain the output corresponding to the load of the engine 1, and the normal air-fuel ratio region is set to secure the desired output. It is necessary to execute the air-fuel ratio control in. Therefore, in this case, in order to execute the air-fuel ratio control by the normal throttle valve 5, the solenoid valve 18 is closed via the drive unit (F7).
The water temperature determination unit determines that the water temperature T _W is equal to or lower than the predetermined temperature T ₁ , but when the idling operation is being executed, the air-fuel ratio is set to the normal air-fuel ratio to ensure the stability of the engine rotation. Even when it is determined that the fuel temperature should be set in the fuel ratio region and the water temperature T _W exceeds the predetermined temperature T ₁ , the throttle opening TVθ exceeds the predetermined opening θ ₁ . The case is a case of operating in the normal air-fuel ratio region in order to obtain the required output. Therefore, in these cases, the opening / closing control of the solenoid valve 18 (F6, or
After performing F7), the intake air amount signal is input from the air flow meter 4 via the intake air amount signal input port, and the rotation corresponding to the engine speed N is input from the distributor 15 via the rotation speed signal input port. A number signal is input (F8), the target air-fuel ratio TAF corresponding to the intake air amount Q _A and the engine speed N is determined by the air-fuel ratio determination unit (F9) based on the normal operation map, and from this target air-fuel ratio TAF The fuel injection pulse width τ is calculated (F10), and the fuel injection amount control unit controls the fuel injection amount injected from the fuel injection device 7 according to the fuel injection pulse width τ (F11).
When the throttle opening determination unit determines that the throttle opening TVθ is less than or equal to the predetermined opening θ ₁ , the engine temperature is sufficiently raised to enable stable lean operation. Moreover, when the engine load is small, it is possible to operate at an air-fuel ratio leaner than the theoretical air-fuel ratio in order to save fuel consumption. Therefore, in this case, the solenoid valve 18 is opened via the drive unit (F12), and a large amount of intake air is drawn into the combustion chamber 9 through the intake passage 2 and the bypass passage 17. Then, the intake air amount signal is input from the air flow meter 4 via the intake air amount signal input port, and the rotation speed signal corresponding to the engine rotation speed N is input from the distributor 15 via the rotation speed signal input port ( F1
3), the target air-fuel ratio TAF corresponding to the intake air amount Q _A and the engine speed N based on the lean operation map is determined by the air-fuel ratio determining section (F14). Then, the output of the air-fuel ratio sensor 12 is read (F15), and the actual air-fuel ratio AF is calculated from the output of this air-fuel ratio sensor 12 (F16). Furthermore, the target air-fuel ratio TAF
Then, the deviation ε of the actual air-fuel ratio AF is calculated (F17), and the air-fuel ratio correction term C is calculated from this deviation ε (F18). Next, the reference injection pulse width τ ₁ is calculated from the target air-fuel ratio TAF (F19), the fuel injection pulse width τ = τ ₁ (1 + C) is calculated (F20), and the fuel injection amount control unit is calculated according to this fuel injection pulse width τ. The fuel injection amount injected from the fuel injection device 7 is controlled by (F11).

In this way, when switching the air-fuel ratio, basically the intake air amount with respect to the fuel injection amount is switched stepwise,
Compared with the conventional one in which the intake air amount is fixed and the fuel injection amount Q _f is switched in stages with _respect to the intake air amount, the change amount of the fuel injection amount can be suppressed to a small amount, and the output change of the engine 1 can be made small. Further, since the deviation between the actual air-fuel ratio and the target air-fuel ratio is calculated and the fuel injection amount is controlled so as to eliminate the deviation, the response is better than when changing only the intake air amount to switch the air-fuel ratio. The control accuracy is high.

In the above embodiment, during warm-up operation of the engine 1, the solenoid valve 18 is opened to increase the intake air amount and correspondingly increase the fuel supply amount to increase the idling speed. Although it is configured to shorten the warm-up time, the opening degree of the throttle valve 5 and the sub-throttle valve 19 is small during the warm-up operation, and the intake air amount tends to be small.
It is preferable to form a notch in the valve to further increase the intake air amount and correspondingly increase the fuel supply amount, further increase the idling speed, and shorten the warm-up time.

Also, during deceleration, an idling signal is input to the ECU 22, and a deceleration determination unit that determines whether or not deceleration is being performed using the idling signal and the rotation speed signal as parameters, and whether or not it is within a predetermined time after the deceleration is started. The ECU 22 is provided with a deceleration time discriminating section for discriminating whether or not the deceleration discriminating section discriminates that the vehicle is decelerating, and the solenoid valve 18 is opened within a predetermined time after the start of the deceleration to exert a dashpot effect. It is advantageous to configure the ECU 22 so that the solenoid valve 18 is closed after a predetermined time has elapsed from the start of the deceleration to prevent the reduction of the braking effect.

Further, when the solenoid valve 18 is locked in the closed state for some reason, this locked state is detected and the fuel supply amount is changed to switch the air-fuel ratio region to the lean region and the other region. It is advantageous to configure the ECU 22 described above. When the solenoid valve 18 is locked in the open state for some reason, the ECU 22 is forced to stop the fuel supply to prevent runaway of the engine.
Is also advantageous.

The present invention is not limited to the fuel injection type engine, but can be applied to an engine having a carburetor, and in the fuel injection type engine, an existing air valve is used to increase the bypass air amount,
It is also possible to change the air-fuel ratio region to the lean region. Further, it is also possible to control the idle rotation by controlling the duty of the solenoid valve 18.

〔The invention's effect〕

As described above, the engine air-fuel ratio control device of the present invention includes a bypass passage bypassing a throttle valve, a valve device provided in this bypass passage, and a lean region in which the air-fuel ratio is leaner than the theoretical air-fuel ratio. A control means is provided to open so that the air-fuel ratio changes from the lean area to the other area when closing, and to change the intake air amount with respect to the fuel supply amount. It is configured to eliminate the deviation between the target air-fuel ratio and the actual air-fuel ratio by adjusting it by adjusting the fuel supply amount, so that the output fluctuation accompanying the change of the air-fuel ratio reduces the intake air amount. It is smaller than the conventional one that is fixed and changes the fuel supply amount with respect to the intake air amount, so that so-called torque shock and vibration can be prevented and the air-fuel ratio can be controlled. It is possible to increase the accuracy. Further, since the intake air amount is changed stepwise when the air-fuel ratio is switched, the air-fuel ratio is switched so as to instantaneously pass through the air-fuel ratio region in which the amount of generated nitrogen oxides is large, and the amount of nitrogen oxides is changed. A small amount is generated, which is advantageous in purifying exhaust gas.

[Brief description of drawings]

FIG. 1 is a block diagram schematically showing an embodiment of the present invention,
FIG. 2 is a longitudinal sectional view of the intake passage and the bypass passage, and FIG. 3 is a flow chart of a control sequence executed in the ECU. In the figure, 1 is an engine, 5 is a throttle valve (throttle valve), 10 is an exhaust passage, 12 is an air-fuel ratio sensor, 17 is a bypass passage, 18 is a second valve device (solenoid valve), 19 is a first valve device ( Sub-slot valve), 22 is correction control means (electronic control unit, which also serves as second valve control means,
ECU).

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁶ Identification number Reference number within the agency FI Technical indication location F02M 69/32 (72) Inventor Akashi Nagao 3-1, Shinchi, Fuchu-cho, Aki-gun, Hiroshima Prefecture Mazda shares In-house (56) Reference JP 60-3440 (JP, A) JP 58-13131 (JP, A) JP 59-70853 (JP, A) JP 58-211543 (JP, A) ) Actual development Sho 60-28259 (JP, U)

Claims (1)

[Claims] 1. An air-fuel ratio control device for an engine, comprising an air-fuel ratio control means for detecting an operating state of the engine and stepwise switching the air-fuel ratio leaner than the stoichiometric air-fuel ratio in accordance with the operating state. The air-fuel ratio control means is provided in a bypass passage that bypasses the throttle valve, and the first passage that is provided in the bypass passage and adjusts the flow passage cross-sectional area of the bypass passage.
A valve device, a second valve device that is provided in the bypass passage in series with the first valve device, and that opens and closes the bypass passage, and a first valve that opens and closes the first valve device in conjunction with the throttle valve. And a second valve control means for controlling the second valve device to open when the air-fuel ratio is switched to a lean region where the air-fuel ratio is leaner than the stoichiometric air-fuel ratio and to close when the air-fuel ratio switches from the lean region to another region, An exhaust gas sensor that detects an exhaust gas component and outputs an air-fuel ratio signal corresponding to the actual air-fuel ratio is provided in the exhaust path of the engine, and the actual air-fuel ratio and the target air-fuel ratio are input by inputting the air-fuel ratio signal in at least the lean region. An air-fuel ratio control device for an engine, comprising a correction control means for correcting a fuel supply amount so as to eliminate a deviation from a fuel ratio.