JPS5913317Y2 - Air-fuel ratio feedback control device - Google Patents

Description

[Detailed description of the invention] The present invention relates to an air-fuel ratio feedback type fuel injection control device that feedback-corrects the air-fuel ratio of the air-fuel mixture supplied to the engine according to the oxygen concentration in the exhaust gas. be.

Conventionally, when supplying fuel to an engine, an air-fuel ratio characteristic set corresponding to the intake air amount of the engine is programmed, and the amount of fuel is adjusted according to this program.

In this case, even if engine parameters such as intake negative pressure and engine temperature are detected and controlled, operating conditions that change from moment to moment,
It is extremely difficult to operate at the planned air-fuel ratio by correcting machine differences that result from individual engine differences, and this becomes a major obstacle, especially when a catalytic purification device for exhaust purification is installed. It has the disadvantage of being stored away.

An object of the present invention is to provide an air-fuel ratio feedback type fuel injection control device that can eliminate the above-mentioned drawbacks.

In other words, the device of the present invention normally detects the oxygen concentration in the exhaust gas and performs feedback correction on the air-fuel ratio of the air-fuel mixture supplied to the engine according to the integrated output obtained by integrating the output, thereby maintaining a constant air-fuel ratio. Until the engine can be operated and the exhaust gas temperature reaches a permissible temperature at which the oxygen concentration detector can operate normally, the integrating means is set to the initial state and the integrated output is kept within its output fluctuation range. By maintaining the air-fuel ratio at an intermediate value and thereby substantially stopping feedback correction of the air-fuel ratio, it is possible to control the air-fuel ratio in accordance with the state of the feedback control system including the engine, and to eliminate that specific state. Since the integral operation can always be started from an intermediate value within the integral output fluctuation range, there is no restriction on the direction of the integral operation, improving the followability of the engine correction operation of the air-fuel ratio, and moreover, the feedback correction is This allows the amount of feedback correction for the air-fuel ratio to be set to virtually zero at the start of the process, increasing the effectiveness of improvements in terms of exhaust purification and drivability.

An embodiment of the present invention shown in the drawings will be described below.
In this embodiment, air-fuel ratio feedback control is applied to an electronic fuel injection control device, and an engine low temperature state is selected as an example of a specific engine state in which air-fuel ratio feedback control is stopped.

In the block diagram of FIG. 1, 1 is an integral constant converter that detects the engine rotation speed, intake negative pressure, intake air amount, etc., and converts this detected voltage to a reference voltage VB/VB, which is half of the power supply voltage VB.
2 to obtain the integral constant of the negative voltage.

Reference numeral 2 denotes an inverting amplifier, which inverts the integral constant to generate an inverted positive voltage output.

Reference numeral 3 denotes an oxygen concentration detector made of a solid electrolyte such as zircon oxide, which is installed in the exhaust pipe 14 of the engine 13 to detect the oxygen concentration in the exhaust gas.
When the temperature exceeds the permissible temperature range of 50 DEG C. to 600 DEG C., it operates normally in response to the oxygen concentration and generates a concentration detection signal.

Reference numeral 4 denotes a temperature detector consisting of a thermistor, which detects the temperature of the exhaust gas.

Reference numeral 5 denotes an allowable temperature detection circuit which generates a detection output when the exhaust gas temperature reaches an allowable temperature based on the output signal of the temperature detector 4.

Reference numeral 6 denotes a gate circuit, which closes the gate to block the concentration detection signal of the oxygen concentration detector 3 when the permissible temperature detection circuit 5 does not generate a detection output and the temperature is below the permissible temperature, and when the detection output occurs, the gate closes. is opened to allow the concentration detection signal to pass through.

7 is comparative, and normally the concentration detection signal from the oxygen concentration detector 3 is compared with the air-fuel ratio setting value VH, which is preset as the target value of the air-fuel ratio feedback control, and the signal is set to the "0" level or "
It generates a comparison output of 1" level.

Reference numeral 8 denotes a switching circuit which selects an integral constant of the negative voltage from the integral constant converter 1 and an inverted output of the positive voltage from the inverting amplifier 2 according to the comparison output, and generates the output.

Reference numeral 9 denotes an integrator that integrates the integral constant of the negative voltage or the inverted output of the positive voltage, and uses this integral output to indicate the amount of air-fuel ratio correction.

Reference numeral 10 denotes an output holding feedback circuit serving as a correction stopping means, which inputs the integrated output of the integrator 9 and performs a feedback operation through the gate circuit 6 when no detection output is generated from the allowable temperature detection circuit 5. The integrated output of the integrator 9 is held at the reference voltage VB/2 and correction of the air-fuel ratio according to the oxygen concentration is stopped.

11 is a calculation unit of a generally known electronic fuel injection control device;
The injection pulse is generated according to the air-fuel ratio characteristics by pre-programming an injection pulse with a time width according to engine parameters such as intake negative pressure and engine temperature. The time width of the injection pulse is corrected in accordance with the deviation of the air-fuel ratio.

Reference numeral 12 denotes a solenoid valve which is opened by an injection pulse from the arithmetic unit 11 and injects the requested fuel.

The operation will be explained with the above configuration. When the integrated output of the integrator 9 becomes equal to the reference voltage VB/2, the correction amount of the feedback control system that performs feedback according to the oxygen concentration in the exhaust gas is set to zero. , so that the basic required fuel is injected.

If the temperature of the exhaust gas is below the permissible detection temperature, such as when the engine is started at a low temperature, the oxygen concentration detector 3 will not respond to the oxygen concentration in the exhaust gas and will not generate any output.

Since this state is the same as the detection state when the fuel is thin, the detection signal of the permissible temperature detection circuit 5 which should block the output of the oxygen concentration detector 3 by the gate circuit 6 acts at this time.

That is, the temperature detector 4 and the permissible temperature detection circuit 5 detect that the temperature of the exhaust gas has not reached the permissible temperature, and generate a detection output for operating the gate circuit 6.

As a result, the output holding feedback circuit 10 operates to hold the integrated output of the integrator 9 at the value of the reference voltage VB/2, which indicates that the air-fuel ratio correction amount is zero, and the calculation unit 11 calculates the basic required fuel. The engine 13 generates an injection pulse corresponding to the engine speed, and injects fuel to the engine 13 via the electromagnetic valve 12.

Therefore, the engine is supplied with an air-fuel mixture having an air-fuel ratio that conforms to preset air-fuel ratio characteristics, and it is possible to supply an air-fuel mixture with an air-fuel ratio that is particularly suitable for starting the engine at a low temperature.

Next, when the temperature of the exhaust gas exceeds the allowable temperature, the oxygen concentration detector 3 begins to respond to the oxygen concentration in the exhaust gas, and the gate circuit 6 opens to convert the detection signal of the oxygen concentration detector 3 into a comparator. 7 will pass.

In this state, when the oxygen concentration in the exhaust gas is high and the fuel is thin, the concentration detection signal of the oxygen concentration detector 3 is at a low level, and this low level detection signal is passed through the gate circuit 6 to the comparator. Join 7.

As a result, this comparator 7 compares it with the air-fuel ratio set value VH and generates a "0" level signal, and this "0" level signal selectively activates the switching circuit 8 to output an inverted positive voltage from the inverting amplifier 2. is led to the integrator 9.

Therefore, this integrator 9 integrates the inverted output and generates an integrated output whose voltage gradually decreases.

Based on this integral output, the time width of the injection pulse is gradually lengthened by the calculation unit 11, and the amount of fuel is increased, thereby enriching the supplied fuel.

As this action progresses, the oxygen concentration in the exhaust gas gradually decreases.

When this oxygen concentration drops to a predetermined value, the detection signal of the oxygen concentration detector 3 becomes high level, and this high level detection signal is applied to the comparator 7 via the gate circuit 6.
When the air-fuel ratio becomes higher than the set value VH, the switching circuit 8 is selectively activated by the "199 level signal from the comparator 7, and the integral constant output of the negative voltage which becomes the output of the integral constant converter 1 is sent to the integrator 9. lead

Therefore, this integrator 9 integrates the integration constant output and generates an integrated output whose voltage gradually increases.

This integral output shortens the time width of the injection pulse from the calculation unit 11, allowing control to reduce the amount of fuel and approach the optimum air-fuel ratio.

That is, by the feedback control described above, the fuel supplied to the engine 13 when the exhaust gas temperature is equal to or higher than the allowable temperature is corrected according to the oxygen concentration in the exhaust gas, and the air-fuel ratio of the air-fuel mixture is kept at a constant target value. can be controlled.

The main part specific circuit for obtaining the above-mentioned operation is shown in FIG.

This FIG. 2 shows a specific circuit of the parts indicated by numerals 1 to 10 in FIG.
1a2, 1a3゜2a, 5a, 7a, 9a, 10a are operational amplifiers, 6b1, 6b2, 6b3, 8b1, 8b2 are transistors, 9C is an integrating capacitor, 6d1, 6d
2 is a relay, VB is a power supply terminal to which positive voltage VB is applied, and G is a ground terminal.

A is a voltage dividing circuit that divides the power supply voltage VB into λ, and each circuit 2
．． 5. 9.10 to create a reference voltage.

It goes without saying that the feedback control system based on the detection signal of the oxygen concentration detector 3 is not limited to the above-mentioned embodiment and may be of any type.

As mentioned above, the device of the present invention normally detects the oxygen concentration in the exhaust gas and corrects the air-fuel ratio of the mixture supplied to the engine according to the integrated output obtained by integrating the output. Until the engine can be operated at the air-fuel ratio and the exhaust gas temperature reaches the permissible temperature at which the oxygen concentration detector operates normally, the integrating means is set to the initial state, and the integrated output is controlled within its output fluctuation range. Since the feedback correction of the air-fuel ratio is essentially stopped, the air-fuel ratio can be controlled in accordance with the state of the feedback control system including the engine, and the specific state When the problem is resolved, the integral operation can be started in any direction, either increasing or decreasing, based on the intermediate value within the range of variation of the integral output.
There is no restriction on the direction of the integral operation, and the followability of the air-fuel ratio feedback correction operation can be improved.Moreover, the amount of air-fuel ratio feedback correction can be set to substantially zero at the time the feedback correction starts, so the feedback correction Suppresses fluctuations in air-fuel ratio at the start of correction,
It has the excellent effect of greatly improving exhaust purification and drivability.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of an air-fuel ratio feedback type fuel injection control device according to the present invention, and FIG. 2 is an electrical wiring diagram showing an embodiment of a detailed circuit of a main part of the device according to the present invention. 3...Oxygen concentration detector, 4...Temperature detector, 5゜6......Allowable temperature detection circuit forming the main part of the second means, gate circuit, 9 ...Integrator, 1
0... Output holding feedback circuit constituting the first means,
11.12... Arithmetic unit, electromagnetic valve, which forms the main part of fuel injection control means, 13... Engine, 14...
····Exhaust pipe.

Claims (1)

[Scope of utility model registration request] an oxygen concentration detector that detects the oxygen concentration in the exhaust gas of the engine; an integrating means that performs an integral process to form an integral output according to the output signal of the oxygen concentration detector; a first means for setting the integrating means to an initial state and fixing the integral output to an intermediate value within its fluctuation range; , the first means is operated to maintain the integral output at the intermediate value until the exhaust gas temperature of the engine reaches an allowable temperature at which the oxygen concentration detector normally operates; and second means for substantially stopping the feedback correction of the air-fuel ratio feedback type fuel injection control device.