JPH0152568B2 - - Google Patents

Description

Detailed Description of the Invention (Industrial Application Field) The present invention provides feedback control to adjust the air-fuel ratio of a mixture supplied to an engine to a set air-fuel ratio according to the output of an air-fuel ratio sensor provided in an exhaust passage. The present invention relates to an improvement of an air-fuel ratio control device for an engine.

(Prior Art) Conventionally, when the air-fuel ratio of the air-fuel mixture supplied to the engine is controlled to the stoichiometric air-fuel ratio for a three-way catalyst as a catalyst device installed in the exhaust passage of an engine, the atmosphere in the catalyst device changes. It is well known that CO, HC, and NOx can be effectively purified at the same time in a ternary atmosphere. In addition, in order to accurately control the air-fuel ratio of the mixture to the set air-fuel ratio (stoichiometric air-fuel ratio), an exhaust gas component concentration sensor (air-fuel ratio sensor) is installed in the exhaust passage upstream of the catalyst device. , an air-fuel ratio control circuit equipped with a comparison circuit, a proportional circuit, an integral circuit, an addition circuit, a duty ratio control circuit, etc. is provided, and the fuel metering device uses the output from the air-fuel ratio control circuit according to the output of the exhaust gas component concentration sensor. There is a known system in which the air-fuel ratio of the air-fuel mixture supplied to the engine is controlled to a set air-fuel ratio by operating the engine.

However, if such feedback control of the air-fuel ratio is performed to control the air-fuel ratio to the stoichiometric air-fuel ratio over the entire operating range of the engine, there is a problem that drivability at high loads that require output deteriorates. A vehicle has been proposed that is equipped with a high load correction device that increases the fuel flow rate from the fuel metering device to enrich the air-fuel ratio when the vehicle is under load, thereby improving drivability. (For example, JP-A-52-
(See Publication No. 129834). This high load correction device detects when the engine is under high load and increases the amount of fuel metered from the fuel metering device based on a high load correction signal unrelated to the output of the air-fuel ratio sensor.

(Problem to be Solved by the Invention) However, in the air-fuel ratio control device having the above-described high-load correction device, when the engine is used at high altitudes, the air-fuel ratio becomes rich due to a decrease in air density. Sometimes, the synergistic effect of the two causes an overbalance of the air-fuel ratio, resulting in problems such as deterioration of drivability and an increase in unburned components in the exhaust gas.

In particular, at high altitudes, in order to obtain the same drivability as on flat land, the fuel metering device must be operated to the high load side, so the above-mentioned high load correction device does not operate on flat land. It will operate even when the device is in operation. Therefore, at high altitudes, the high load correction device operates more frequently, increasing the number of causes of overload, and there is a need to deal with this problem from the standpoint of fuel efficiency.

In view of this, the present invention prevents the air-fuel ratio from becoming overbalanced at high loads at high altitudes by reducing the fuel flow from the fuel metering device, which increases at high loads, in accordance with the drop in atmospheric pressure. This improves driveability and purification of unburned components of exhaust gas.

A further object of the present invention is to configure the above-mentioned air-fuel ratio feedback control, high load correction, and atmospheric pressure correction into a simple system.

(Means for Solving the Problem) In order to achieve the above object, the solving means of the present invention includes an air-fuel ratio sensor that detects the air-fuel ratio of the air-fuel mixture supplied to the engine, and an air-fuel ratio sensor that receives the output of the air-fuel ratio sensor. , an air-fuel ratio control means that outputs an air-fuel ratio control signal to achieve a preset air-fuel ratio; a fuel metering means that receives the output of the air-fuel ratio control means and adjusts the air-fuel ratio of the air-fuel mixture of the engine; a high-load detection means for detecting a high-load operating state of the engine; and a high-load detecting means that operates when the high-load operating state is detected based on the output of the high-load detecting means; a high-load correction means for outputting an increase signal for increasing the fuel flow rate regardless of the air-fuel ratio control signal; and an atmospheric pressure detection means for detecting atmospheric pressure.
The atmospheric pressure correcting means receives the output of the atmospheric pressure detecting means and corrects the increase signal output from the high load correcting means in the direction of decreasing fuel in accordance with a decrease in atmospheric pressure. .

(Function) Accordingly, in the present invention, the fuel metering means is controlled by the air-fuel ratio control means in accordance with the output of the air-fuel ratio sensor, and the air-fuel ratio is controlled to the set air-fuel ratio. When the load is high, the fuel flow rate from the fuel metering means is increased by the output of the increase signal from the high load correction means. At this time, at high altitudes, the atmospheric pressure correction means corrects the fuel increase signal in a direction that decreases the amount of fuel depending on the decrease in atmospheric pressure. That is, at high loads and at high altitudes, the increase in fuel by the high load correction means is suppressed by the atmospheric pressure correction means to a lower level than in the case of flatlands, thereby preventing the air-fuel ratio from becoming overbalanced. On the other hand, when the increase signal is not output, the atmospheric pressure correction means for correcting the increase signal does not operate, and the atmospheric pressure correction means does not reduce the fuel flow rate even at high altitudes.

Furthermore, as mentioned above, the output of the air-fuel ratio control signal is
At high loads, the increase signal is output to the fuel metering means instead of the increase signal, and this increase signal is corrected according to the atmospheric pressure. This can be done using a metering means, which simplifies the fuel system, and because atmospheric pressure correction is automatically canceled in the air-fuel ratio feedback control region, the lean side of the air-fuel ratio in this air-fuel ratio feedback control region Fluctuations will be prevented.

In other words, the above atmospheric pressure correction needs to be performed at a predetermined ratio to the amount of air, so when the load is high, that is, when the amount of air is large, the amount of correction needs to be set to be large. If the atmospheric pressure correction amount is set to a large value in this way, it will be overcorrected at light loads, that is, in the air-fuel ratio feedback control region, and the feedback correction will not be able to follow changes in the operating condition within this feedback control region. Generally, the air-fuel ratio shifts to the lean side, but as mentioned above, atmospheric pressure correction is performed only at high loads, and in the air-fuel ratio feedback control region, by using only feedback control, it is possible to achieve good results in all operating ranges. It is possible to obtain excellent drivability.

(Example) Examples of the present invention will be described below with reference to the drawings. In the overall configuration shown in FIG. 1, 1 is an engine, 2 is a catalyst device consisting of a three-way catalyst installed in an exhaust passage 3 of the engine 1, and 4 is a carburetor installed in an intake passage 5 of the engine 1. , 6 is an air cleaner, and the carburetor 4 is attached with an actuator 7 that adjusts the air-fuel ratio separately from the throttle valve. A fuel metering means 8 is configured to meter the air-fuel ratio of the air-fuel mixture. The actuator 7 of this fuel metering means 8 is composed of a solenoid valve that increases or decreases the amount of bleed air from the carburetor 4 supplied to the intake passage 5, and opens when turned on to make the air-fuel ratio lean. ing.

Reference numeral 9 indicates an exhaust gas component concentration sensor including an oxygen concentration detection sensor as an air-fuel ratio sensor disposed in the exhaust passage 3 on the upstream side of the catalytic converter 2; outputs an air-fuel ratio control signal to the actuator 7 of the fuel metering means 8 to control the air-fuel ratio of the air-fuel mixture supplied to the engine 1 to a preset air-fuel ratio (for example, stoichiometric air-fuel ratio); This is an air-fuel ratio control circuit as an air-fuel ratio control means for adjusting the operation of the air-fuel ratio. Further, the exhaust gas component concentration sensor 9 outputs a signal correlated with the air-fuel ratio of the intake air-fuel mixture by detecting the concentration of the exhaust gas components.

In the air-fuel ratio control circuit 10, 11 is a comparison circuit that outputs a deviation signal between the output of the exhaust gas component concentration sensor 9 and a set value corresponding to the stoichiometric air-fuel ratio, and 12 is a proportional circuit that outputs a proportional signal of this deviation signal. 13 is an integration circuit that outputs an integral signal of the deviation signal; 14 is an addition circuit that outputs an air-fuel ratio control signal obtained by adding the proportional signal and the integral signal; and 15 is a circuit that controls the duty ratio according to the air-fuel ratio control signal. The duty ratio control circuit includes a trigger signal generation circuit 16 that outputs a trigger signal to the duty ratio control circuit 15, and an actuator drive circuit 17 that drives the actuator 7 according to the duty ratio from the duty ratio control circuit 15.

Further, 18 is a high load correction means for increasing the fuel flow rate from the fuel metering means 8 during high loads,
The high load correction means 18 includes a high load switch 20 that closes at high load based on the output of high load detection means 19 that detects high load of the engine 1 by the throttle valve opening, intake negative pressure, etc.; A high load correction signal generation circuit 21 generates an increase signal for high load correction to enrich the air-fuel ratio, and the duty ratio control circuit 15 outputs an increase signal from the high load correction signal generation circuit 21 during high loads. is configured to input.

Reference numeral 22 denotes an atmospheric pressure correcting means interposed between the high load correction signal generation circuit 21 of the high load correcting means 18 and the high load switch 20, and the atmospheric pressure correcting means 22 adjusts the atmospheric pressure. In response to the output from the atmospheric pressure detecting means, an atmospheric pressure correction signal is output that corrects the increase signal so as to reduce the fuel flow rate from the fuel metering means 8, which is increased at high load as the atmospheric pressure decreases. In other words, the increase signal from the high load correction signal generation circuit 21 is corrected to be lowered.

In the air-fuel ratio control circuit 10, when a fluctuation occurs in the air-fuel ratio of the air-fuel mixture supplied to the engine 1 and the output of the exhaust gas component concentration sensor 9 that detects this fluctuation is input to the comparison circuit 11, the comparison circuit 11 performs a comparison. The circuit 11 outputs a high-level signal as a deviation signal when the detection signal exceeds a set value corresponding to the stoichiometric air-fuel ratio, and a low-level signal when it is low. Therefore, the integrated signal of the deviation signal by the integrating circuit 13 gradually increases when the deviation signal is at a high level, but gradually decreases when the deviation signal is at a low level, and the generation of that signal is determined by a predetermined integral constant. This is a signal that fluctuates over time. Correspondingly, the air-fuel ratio control signal outputted from the adding circuit 14 by adding it to the proportional signal of the proportional circuit 12 is set to be lean when the detected air-fuel ratio is richer than the stoichiometric air-fuel ratio; When it is on the side, it becomes a control signal that operates the actuator 7 of the fuel metering means 8 in accordance with the output voltage so as to make the fuel metering device rich.

In response to the air-fuel ratio control signal from the addition circuit 14, the duty ratio control circuit 15 calculates the magnitude (voltage) of the air-fuel ratio control signal when the trigger signal is generated from the trigger signal generation circuit 16, as shown in FIG. 2A. value) determines the duty ratio for driving the actuator 7, and thereby the actuator 7
As shown in Figure B, the opening and closing is controlled by changing the ratio of on time to off time. That is, when the air-fuel ratio control signal corresponding to the air-fuel ratio detected by the exhaust gas component concentration sensor 9 is lower than the set voltage V _b corresponding to the stoichiometric air-fuel ratio, the air-fuel ratio control signal is The lower the voltage value is, the longer the on time of the actuator 7 is, that is, the duty ratio is increased. On the other hand, when the air-fuel ratio control signal corresponding to the air-fuel ratio detected by the exhaust gas component concentration sensor 9 is higher than the set voltage V _b , as shown in FIG. As shown on the right side of A, the higher the voltage value of the air-fuel ratio control signal, the shorter the ON time of the actuator 7, that is, the lower the duty ratio. Furthermore, when the air-fuel ratio control signal is at a voltage V _b corresponding to the stoichiometric air-fuel ratio, the duty ratio of the actuator 7 is set to 50%,
When the voltage Va is lower than that, the duty ratio is set to 100% and the actuator 7 is fully opened, while when the voltage is higher than that, the duty ratio is set to 0.
% so that the actuator 7 is fully closed.

In the air-fuel ratio control circuit 10, when the high load detection means 19 detects that the engine 1 is under high load, the high load switch 20 is closed by the detection signal, and the high load correction signal generation circuit 21 An increase signal for enriching the air-fuel ratio by increasing the output fuel flow rate is superimposed on the air-fuel ratio control signal from the adder circuit 14 and input to the duty ratio control circuit 15. This increase signal makes the level of the air-fuel ratio control signal higher than the voltage Vc at which the duty ratio becomes 0%, sets the duty ratio to 0% regardless of fluctuations in the air-fuel ratio control signal, and sets the actuator 7 in a fully closed state to fuel the fuel. The fuel flow rate from the metering means 8 is increased to enrich the air-fuel ratio.

Furthermore, during high loads at high altitudes, the atmospheric pressure correction means 22 that detects a decrease in atmospheric pressure operates and outputs a correction signal for atmospheric pressure, and the increasing level of the air-fuel ratio control signal is adjusted by the increase signal for high load correction. The duty ratio of the actuator 7 is increased in accordance with the decrease in the air pressure, and the fuel metering means 8
This is to suppress the enrichment of the air-fuel ratio by reducing the fuel flow rate from the engine.

FIG. 3 shows a specific configuration of a part of the air-fuel ratio control circuit 10, the high load correction means 18, and the atmospheric pressure correction means 22.

In the duty ratio control circuit 15, 15a is an input terminal to which the air-fuel ratio control signal from the adder circuit 14 is input, and the air-fuel ratio control signal and the trigger signal from the trigger signal generation circuit 16 are input to the oscillation circuit 23.
The output of the duty ratio control circuit 15 is input to the second transistor 25 via the first transistor 24 of the actuator drive circuit 17, and the output of the second transistor 25 is connected to the solenoid 7a of the actuator 7. There is.

Further, in the atmospheric pressure correction means 22, 26 is an atmospheric pressure sensing bellows as an atmospheric pressure detecting means that expands as the atmospheric pressure decreases, 27 is a changeover switch whose contacts are changed by the operation of the atmospheric pressure sensing bellows 26,
Reference numeral 28 designates an atmospheric pressure correction signal generating circuit having a variable resistor R ₃ whose resistance value changes according to the operation of the atmospheric pressure sensing bellows 26 . The changeover switch 27 transmits the increase signal Vd divided by the resistors R ₁ and R ₂ from the high load correction signal generation circuit 21 to the high load detection means 19 via its first contact 27 a (normally closed contact). The signal is connected to the high load correction means 18 so as to be input together with the air-fuel ratio control signal to the oscillation circuit 23 of the duty ratio control circuit 15 when the high load switch 20 is closed. Further, the second contact 27b (normally open contact) of the changeover switch 27, which is closed by the operation of the atmospheric pressure sensing bellows 26, is connected to the variable resistor _R3 of the atmospheric pressure correction signal generation circuit 28,
When the high load switch 20 is closed, a signal from the atmospheric pressure correction signal generation circuit 28 that is divided by the resistors R ₃ , R ₄ and R ₅ is transmitted to the oscillation circuit of the duty ratio control circuit 15 via the second contact 27b. 23 so as to be input together with the air-fuel ratio control signal.

The high load correction means 18 and the atmospheric pressure correction means 2
To explain the operation of 2, when the engine 1 is in a high load operating state, the high load detection means 19 detects the high load state by sensing the fully open state of the throttle valve of the carburetor 4, and switches on the high load switch. 20 is closed.

On flat ground, when the high load switch 20 is closed as described above, the high load correction signal generation circuit 2
A high load correction increase signal having a signal voltage Vd larger than the signal voltage Vc at which the duty ratio becomes 0% is inputted to the duty ratio control circuit 15 via the first contact 27a of the changeover switch 27, and is input from the addition circuit 14. Regardless of the air-fuel ratio control signal of
%). When the output of the duty ratio control circuit 15 is turned off, the first
The transistor 24 and the second transistor 25 are turned off, and the actuator 7 is always fully closed without being excited, reducing the amount of bleed air, increasing the fuel flow rate from the fuel metering means 8, and enriching the air-fuel ratio. , which improves drivability under high loads.

On the other hand, at high altitudes, when the high load switch 20 is closed, the second contact 27b of the changeover switch 27 is closed by the air pressure sensing bellows 26, and the signal from the high load correction signal generation circuit 21 is transferred to the high load switch 20. While the line is cut off, a pressure correction signal that is variable by the operation of the pressure sensing bellows 26 is sent from the pressure correction signal generation circuit 28 to the duty ratio control circuit via the second contact 27b and the high load switch 20. 15 is input. This atmospheric pressure correction signal has a lower voltage than the high load correction increase signal, and increases the duty ratio of the actuator 7 to reduce the fuel flow rate from the fuel metering means 8 and shift the air-fuel ratio to the lean side. It is. In addition, the signal voltage of this atmospheric pressure correction signal decreases as the atmospheric pressure decreases, and operates to further shift to the lean side, thereby suppressing richness.

In the above embodiment, the high load correction increase signal is superimposed on the air-fuel ratio control signal and input to the duty ratio control circuit 15, but the high load switch 20 is closed by the high load detection device 19. In this case, an analog switch 29 may be provided to cut off the air-fuel ratio control signal from the adder circuit 14.

Further, in the above embodiment, an example of the fuel metering means 8 that controls the air-fuel ratio by the carburetor 4 and the actuator 7 that adjusts the amount of bleed air is shown, but other means for changing the air-fuel ratio of the air-fuel mixture are known. techniques can be adopted as appropriate.

(Effects of the Invention) Therefore, according to the present invention as described above, in an air-fuel ratio control device that performs feedback control of the air-fuel ratio of an engine, fuel can be controlled at high loads regardless of the air-fuel ratio control signal for feedback control. By outputting an increase signal for high load correction to increase the amount of fuel to the fuel metering means, and correcting this increase signal for high load correction in the direction of decreasing fuel according to the decrease in atmospheric pressure, a single fuel adjustment can be performed. While simplifying the fuel system by using the quantity means in common for the air-fuel ratio feedback control, high load correction, and atmospheric pressure correction, the increase signal for high load correction is accurately corrected based on the atmospheric pressure, and it is used in high altitudes. It is possible to prevent the air-fuel ratio from becoming overbalanced during high loads, and it is possible to improve driveability and purification of unburned components in exhaust gas.

Furthermore, according to the present invention, the atmospheric pressure correction means does not operate when the fuel flow rate is not increased by the high load correction means, that is, the atmospheric pressure correction is automatically canceled in the air-fuel ratio feedback control region. It is possible to prevent lean side fluctuations in the air-fuel ratio in this air-fuel ratio feedback control region, and it is possible to ensure good drivability in the entire operating region.

[Brief explanation of drawings]

The drawings show an embodiment of the present invention; FIG. 1 is an overall configuration diagram, FIGS. 2A and B are signal waveform diagrams showing the air-fuel ratio control signal and the duty ratio of the actuator, and FIG. 3 is a diagram of an air-fuel ratio control circuit. FIG. 3 is a circuit diagram showing a specific example of a high load correction means and an atmospheric pressure correction means. DESCRIPTION OF SYMBOLS 1... Engine, 2... Catalyst device, 3... Exhaust passage, 4... Carburetor, 5... Intake passage, 6... Air cleaner, 7... Actuator, 8... Fuel metering means, 9... Exhaust gas component concentration sensor (air-fuel ratio sensor), 10... air-fuel ratio control circuit (air-fuel ratio control means), 11... comparison circuit, 12... proportional circuit,
13... Integrating circuit, 14... Adding circuit, 15...
Duty ratio control circuit, 16... Trigger signal generation circuit, 17... Actuator drive circuit, 18...
...High load correction means, 19...High load detection means, 2
0... High load switch, 21... High load correction signal generation circuit, 22... Atmospheric pressure correction means, 23...
Oscillation circuit, 26... Barometric pressure sensing bellows (atmospheric pressure detection means), 27... Changeover switch, 28... Barometric pressure correction signal generation circuit.

Claims (1)

[Claims] 1. An air-fuel ratio sensor that detects the air-fuel ratio of the air-fuel mixture supplied to the engine; and an air-fuel ratio control signal that receives the output of the air-fuel ratio sensor and outputs an air-fuel ratio control signal to achieve a preset air-fuel ratio. an air-fuel ratio control means; a fuel adjustment means that receives the output of the air-fuel ratio control means and adjusts the air-fuel ratio of the air-fuel mixture of the engine; a high-load detection means that detects a high-load operating state of the engine; Activated when a high load operating state is detected based on the output of the load detection means, the fuel metering means is configured to increase the fuel flow rate regardless of the air-fuel ratio control signal from the air-fuel ratio control means. high load correction means for outputting a signal; atmospheric pressure detection means for detecting atmospheric pressure; 1. An air-fuel ratio control device for an engine, comprising: atmospheric pressure correction means for correcting atmospheric pressure in a direction of decreasing the atmospheric pressure.