JPS63113146A - Air-fuel ratio control unit for internal combustion engine in idle running - Google Patents

Abstract

PURPOSE:To prevent any air-fuel ratio variations from occurring, by learning a feedback controlled variable to a theoretical air-fuel ratio when an automatic transmission is in a drive range and brake operation is carried out at time of idling, in case of an engine provided with a variable choke carburetor. CONSTITUTION:An oxygen sensor 41, a throttle sensor 42, an engine speed sensor 43, a drive range switch 44 of an automatic transmission and a brake switch 45 are all connected to a control circuit 50 which controls an air-fuel ratio to be fed to an internal combustion engine provided with a variable choke carburetor 10. This control circuit 50 judges it to be in an adle state on the basis of each detected value of the throttle sensor 42 and the engine speed sensor 43, and learns a feedback correction value to the theoretical air-fuel ratio based on the oxygen sensor 14. And, when a deviation within the specified time becomes less than the specified one, the learning is finished, thus open control is carried out on the basis of the learning value.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an air-fuel ratio control device during idling operation of an internal combustion engine that is mounted on a vehicle equipped with an automatic transmission and has a variable venturi carburetor.

[Conventional technology]

In some internal combustion engines having a variable venturi carburetor, feedback control of the air-fuel ratio is performed by controlling the flow rate of bleed air supplied to the fuel passage of the carburetor. This feedback control is performed, for example, in the low-medium load operating range after warm-up, and during idling operation, feedback control is performed to stabilize the operating state, as disclosed in Japanese Patent Application Laid-open No. 124739/1983. Therefore, the supply of bleed air is stopped and open control is performed. That is, the air-fuel ratio during idling operation is slightly rich (about 13 to 14). Further, at this time, secondary air is supplied to the exhaust system, and the purification effect of the exhaust gas by the catalyst is ensured.

By the way, in a vehicle equipped with an automatic transmission, when the automatic transmission is set to the drive range and the brake pedal is depressed while idling, the load on the engine increases and the idle speed increases (decreases). This increases the vibration of the engine.

This vibration causes the main body of the variable venturi carburetor to shake, while the suction piston does not vibrate due to inertia.As a result, the flow area of the fuel passage changes, a large amount of fuel is sucked out, and the air-fuel ratio may become overrich. Under such operating conditions, the idle stability deteriorates, and even if secondary air is supplied to the exhaust system, there arises a problem that the exhaust gas cannot be sufficiently purified.

Therefore, the applicant proposed an air-fuel ratio control device that introduces auxiliary air into the intake system when the automatic transmission is set to the drive range and the brakes are operated during idling operation. There is.

[Problem that the invention seeks to solve]

However, in the above device, auxiliary air is simply introduced into the intake system, and the amount of auxiliary air introduced is not controlled, so the air-fuel ratio may still remain overrich or, conversely, be over-rich. As a result, there were problems in that idle stability was not sufficient and exhaust gas purification efficiency by the catalyst was not sufficiently high.

The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide an air-fuel ratio control device during idling operation of an internal combustion engine, which stabilizes the idling operation state and improves the purification efficiency of exhaust gas by a catalyst. purpose.

[Means for solving problems]

To achieve the above object, the present invention provides an idle air-fuel ratio control device for an internal combustion engine, which is mounted on a vehicle equipped with an automatic transmission and has a variable venturi carburetor, as shown in FIG. an air introduction means A for introducing auxiliary air into the intake system of the engine independently of the carburetor; an air-fuel ratio detection means C provided in the exhaust system of the engine; a driving state detection means for detecting that the transmission is set in the drive range and that a brake operation is being performed on the vehicle; and when the engine is idling, the automatic transmission is set in the drive range. and when a brake operation is being performed on the vehicle, the air introduction means adjusts the air-fuel ratio of the air-fuel mixture supplied to the engine to the stoichiometric air-fuel ratio based on the output of the air-fuel ratio detection means C. A control means B that feedback-controls the air introduction means A, learns the feedback control amount at that time, and after the learning is completed, controls the air introduction means A to open with an open control Ht based on the learned learning control amount. An air-fuel ratio control device during idle operation is provided.

〔Example〕

Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

FIG. 2 is an overall configuration diagram showing an embodiment of the present invention. In the figure, a variable venturi carburetor 10 is connected to an engine main body 32 via an intake manifold 31. A metering needle 13 is provided at the tip of a suction piston 12 disposed upstream of the throttle valve 11.
This metering needle 13 is connected to a pipe 14 forming a fuel passage.
extend within. A metering jet 15 is formed in the pipe 14, and as a result of this metering jet 15 cooperating with the tapered portion 13a of the metering needle 13, an amount of fuel corresponding to the stroke of the piston 12 is sucked. Suction pipe 1
The upper end of the suction pipe 16 is opened within the pipe 14 at a position upstream of the metering jet 15 in the flow direction of the fuel, and the lower end of the suction pipe 16 extends into the float chamber 18 .

The air bleed passage 21 is for supplying bleed air to the metering jet 15, and the lower end thereof is connected to the metering jet 15.
The upper end is connected to an air filter 23 via an air bleed control valve 22. The air bleed control valve 22 is a solenoid valve, which opens and closes in response to an air-fuel ratio signal supplied from a control circuit 50, which will be described later, during air-fuel ratio feedback control, and acts to control the air-fuel ratio to the stoichiometric air-fuel ratio. The air bleed control valve 22 in this embodiment is driven by a pulse signal having a duty ratio as a current equivalent value, and is fully closed when the duty ratio is "0", fully open when the duty ratio is "1", and fully open when the duty ratio is "1". When the value is , it has an intermediate opening degree.

An air-fuel ratio sensor 41 is provided in the exhaust manifold 33. The air-fuel ratio sensor 41 generates a signal according to the air-fuel ratio of exhaust gas. Note that a catalyst 34 for purifying exhaust gas is disposed downstream of the exhaust manifold 33.

In order to introduce auxiliary air into the intake manifold 31 independently of the carburetor 10, an air introduction pipe 34 is connected to the gathering part of the intake manifold 31. The air introduction pipe 34 communicates with the atmosphere via an air filter 35, and an air introduction valve 36 is provided in the middle thereof. The air introduction valve 36 is a solenoid valve having a flow path area capable of introducing an appropriate amount of auxiliary air so that the air-fuel ratio of the air-fuel mixture does not become over-lean or over-rich. The air-fuel ratio is opened and closed depending on the air-fuel ratio, and acts to control the air-fuel ratio to a predetermined air-fuel ratio. The air introduction valve 36 in this embodiment, like the air bleed control valve 22 described above, is driven by a pulse signal having a duty ratio as a current equivalent value. Note that the air introduction pipe 34 and the air introduction valve 36 correspond to the air introduction means A in FIG.

A control circuit 50 corresponding to the control means B in FIG. 1 controls the air bleed control valve 22 and the air introduction valve 36, and is composed of a microcomputer. That is, the control circuit 50 is a microprocessing unit (MPU).
) 51, memory 52, input port 53, output port 54, and bus 55 connecting these. Various engine operating condition signals are input to the input boat 53. The air-fuel ratio sensor 41 detects 1 when the air-fuel ratio is rich beyond the stoichiometric air-fuel ratio.
It generates an "H" level signal and an "L" level signal in lean mode.

The throttle switch 42 is turned on when the throttle valve 11 is opened at a predetermined opening or less, and turned off at other times. The rotation speed sensor 43 generates a signal according to the engine rotation speed. The D range switch 44 outputs a D range signal when the automatic transmission (not shown) is in the drive range (D range), and the brake switch 45 outputs a D range signal when the automatic transmission (not shown) is in the drive range (D range).
(not shown) outputs a brake signal. Output port 54 is connected to air bleed control valve 22 and air introduction valve 36. The MPU 51 is a memory 5
According to the program stored in 2, a signal for driving the air bleed control valve 22 and the air introduction valve 36 is outputted from the output port 54. Note that the throttle switch 42, rotation speed sensor 43, D range switch 44, and brake switch 45 correspond to the operating state detection means in FIG.

Next, the operation of the control circuit 50 will be explained using the flowchart shown in FIG.

FIG. 3 is a flowchart showing the air-fuel ratio control routine, and this routine is interrupted at regular intervals.

First, in step 301, it is determined whether or not the engine 32 is in an idling operating state. If the result of the determination is negative (NO), that is, when the engine 32 is not in an idling operating state, the process proceeds to step 302 and subsequent steps, and air bleed is performed. Feedback control of the air-fuel ratio is performed by driving the control valve 22.

In this embodiment, when the throttle switch 42 is in the on state and the engine speed is below a predetermined value, it is determined that the engine 32 is in the idling state.

In step 302, the air-fuel ratio is equal to the stoichiometric air-fuel ratio (1
4,7) Whether it is richer or not, that is, the air-fuel ratio sensor 41
It is determined whether or not the signal is outputting an "H" level signal.

If the determination result is affirmative (YES), that is, if it is rich, the process proceeds to step 303, and the air bleed control valve 2
The duty ratio of the drive pulse signal supplied to the drive pulse signal 2 is incremented by a predetermined value ΔD. As a result, the opening degree of the air bleed control valve 22 increases, the amount of air bleed increases, and the air-fuel ratio increases toward the stoichiometric air-fuel ratio.

Then, in step 304, a learning end flag F, which will be described later, is set to "0", and the process returns.

On the other hand, if the determination result in step 302 is negative (No), the process proceeds to step 305, where the duty ratio is incremented by the predetermined value ΔDI, and the air-fuel ratio decreases toward the stoichiometric air-fuel ratio. And step 3 above
In step 04, the learning end flag F is set to 0" and the process returns. Through such feedback control in steps 303 and 305, the stoichiometric air-fuel ratio is maintained.

Next, a case where the engine 32 is in an idle operating state will be described. In this case, since the determination result in step 301 is affirmative (YES), the process proceeds to step 306, where the duty ratio of the drive pulse signal supplied to the air bleed control valve 22 is fixed at "0", and the air The bleed control valve 22 is fully closed and air bleed is stopped.

Next, in step 307, it is determined whether the automatic transmission is set to the D range and whether or not a brake operation is being performed. If the determination result is negative (NO), that is, the automatic transmission is If the D range is not set or the brake is not operated, the process advances to step 308.

In step 308, the duty ratio D2 of the drive pulse signal supplied to the air introduction valve 36 is fixed at "0". That is, the air introduction valve 36 is fully closed, and the air-fuel ratio is controlled to be open. And step 3
In step 09, the learning end flag F is set to "0" and the process returns.

On the other hand, the determination result in step 307 is affirmative (YES).
In this case, that is, when the automatic transmission is set to the D range and the brake is being operated, the process proceeds to step 310, where it is determined whether the learning end flag F is set to "1". Ru. If the determination result is negative (NO), that is, if the flag F is not set to "1'", the process proceeds to step 311 and subsequent steps, and feedback control of the air-fuel ratio is performed by driving the air introduction valve 36. , and its control amount, that is, in this embodiment, the duty ratio of the drive pulse signal supplied to the air introduction valve 36 is learned.

That is, in step 311, it is determined whether the air-fuel ratio is richer than the stoichiometric air-fuel ratio, and if it is rich (determination result is affirmative (YES)), the process proceeds to step 312, where the drive pulse signal supplied to the air introduction valve 36 is determined. The duty ratio D of
2 is incremented by a predetermined value ΔD2. As a result, the opening degree of the air introduction valve 36 increases, the amount of auxiliary air introduced into the intake manifold 31 increases, and the air-fuel ratio increases toward the stoichiometric air-fuel ratio. On the other hand, if the determination result in step 311 is negative (No), the process proceeds to step 316, where the duty ratio is incremented by the predetermined value ΔD2, and the air-fuel ratio decreases toward the stoichiometric air-fuel ratio. That is, by such feedback control in steps 312 and 316, the air-fuel ratio rapidly approaches the stoichiometric air-fuel ratio and eventually maintains it.

Then, the duty ratio Dt set in step 312 or step 316 is learned in step 313, that is, stored in the memory 52 in the control circuit 50, and the process proceeds to step 314.

In step 314, it is determined whether learning of the duty ratio D2 for maintaining the stoichiometric air-fuel ratio has been completed. This determination of completion of learning is made based on, for example, the maximum duty ratio within a predetermined time period including the current routine, which is stored in the memory 52. and the minimum duty ratio DZthin, and when the difference is less than or equal to a predetermined value, it is determined that learning has been completed. Then, if the learning is not completed, that is, if the determination result in step 314 is negative (NO), the process returns, and if the learning is completed, the process proceeds to step 315. Set F to "1" and return.

Next, it is assumed that learning was completed in the previous routine,
In this routine, it is assumed that the engine is in an idling state, the automatic transmission is set to D range, and the brake is being operated. In this case, step 3 of the previous routine
Since flag F is set to "1" in 15,
The determination result in step 310 is affirmative (YES), and the process proceeds to step 317. And step 317
In this case, the duty ratio Dt for maintaining the air-fuel ratio at the stoichiometric air-fuel ratio set in the previous routine is multiplied by an arbitrary constant α as the duty ratio D6 of the drive pulse signal supplied to the air introduction valve 36. Set and return.

The duty ratio D0 set in step 317 above is
The engine is in idle operation and the automatic transmission is in D.
As long as the range is set and the brake operation is performed, the air-fuel ratio is maintained, so the air-fuel ratio is under open control. At this time, by appropriately selecting the constant α, it is possible to set the air-fuel ratio to a desired state. That is, by setting the constant α to, for example, 1.1 to 1.2, the air-fuel ratio can be set to be slightly leaner than the stoichiometric air-fuel ratio, and by setting the constant α to, for example, 0.9 to 1.2.
By setting it to 0.8, the air-fuel ratio can be set to be slightly richer than the stoichiometric air-fuel ratio.

〔Effect of the invention〕

As explained above, according to the present invention, when the automatic transmission is set to the drive range during idling operation and the brake operation is performed, the air-fuel ratio to be open-controlled can be arbitrarily set. By setting the air-fuel ratio appropriately, even in such cases, the air-fuel ratio can be prevented from becoming over-rich or over-lean, stabilizing the idle operating state, and improving the exhaust gas purification efficiency of the catalyst. will improve.

Furthermore, if the air-fuel ratio is set to be slightly leaner than the stoichiometric air-fuel ratio, fuel efficiency can be improved.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of the present invention, FIG. 2 is an overall block diagram showing one embodiment of the present invention, and FIG. 3 is a flowchart showing an air-fuel ratio control routine. 10... Variable venturi carburetor, 32... Engine, 34... Air introduction pipe, 36
... Air introduction valve, 41 ... Air-fuel ratio sensor, 42.
... Throttle sensor, 50... Control circuit.

Claims (1)

[Scope of Claims] 1. An idle air-fuel ratio control device for an internal combustion engine that is installed in a vehicle equipped with an automatic transmission and has a variable venturi carburetor, the device comprising: an auxiliary air-fuel ratio control device for an internal combustion engine having a variable venturi carburetor; an air introduction means for introducing air; an air-fuel ratio detection means provided in the exhaust system of the engine; and an air-fuel ratio detection means that detects that the engine is running at idle, that the automatic transmission is set to a drive range, and that the vehicle a driving state detection means for detecting that a brake operation is being performed on the vehicle; and when the engine is idling, the automatic transmission is set in a drive range, and the vehicle is being braked. Based on the output of the air-fuel ratio detection means, the air introduction means is feedback-controlled so that the air-fuel ratio of the air-fuel mixture supplied to the engine becomes the stoichiometric air-fuel ratio, the feedback control amount at that time is learned, and the learning is completed. an air-fuel ratio control device during idling operation of an internal combustion engine, comprising: control means for controlling the air introduction means to open with an open control amount based on the learned learning control amount;